Geochemical proxy records to reconstruct terrestrial input, redox conditions, and biological production in a tropical paleo-lagoon during the mid-Holocene

Geochemical proxy records to reconstruct terrestrial input, redox conditions, and biological production in a tropical paleo-lagoon during the mid-Holocene | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Geochemical proxy records to reconstruct terrestrial input, redox conditions, and biological production in a tropical paleo-lagoon during the mid-Holocene Caroline Marie B. Jaraula, Chris Carl Agustin V. Toyado This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6897953/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 7 You are reading this latest preprint version Abstract At the forefront of Asian and Pacific climate phenomena, Laguna de Bai in the Philippines could fill knowledge gaps in tropical Western Pacific paleoenvironmental records and help to forecast possible scenarios for semi-enclosed coastal water bodies under the predicted warmer and wetter climate with sea level rise by the end of the 21st century. Using geochemical proxy and grain size records along a sediment core, we describe three major marine phases from 6,510 to 4,590 years ago, when Laguna de Bai's Western Lobe was part of Manila Bay that slowly separated due to the tectonic uplift of the Parañaque Land Strip and interaction with sea level changes during the Holocene. Compared to present-day conditions, the slightly drier Coastal Sub-Tidal Lagoon Phase (6,510 to 6,260 cal BP) had usual marine salinity, oxic bottom waters, and only a partially preserved biological production record, with rainfall similar to that of the early 20th century. The episodic uplift of Parañaque Land Strip and drying climate transformed the Western Lobe into a Shallower Coastal Lagoon (6,260 to 5,310 cal BP) with higher bottom water salinity, suboxic bottom waters, and better preservation of biological production, under an increasingly drier climate. Further uplift of the Parañaque Land Strip restricted Laguna de Bai's Western Lobe even more and commenced the Intertidal Lagoon Phase (5,310 to 4,590 cal BP) with hypersaline, anoxic bottom waters, and well-preserved biological production record, all of which during the mid-Holocene dry period in the Western Pacific. Coastal lagoon Anoxia Hypersalinity Sea level high stillstand Mid-Holocene dry period Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Natural archives, such as lake sediments, provide a continuous record of environmental changes that typically pre-date the instrumental period and written history. Studying records of these changes in a basin ( e.g. salinity, redox conditions, biological production) as well as forcings on the basin ( e.g. climate, sea leve, tectonism) allows us to understand its dynamics and predict its possible future conditions. With this understanding long-term management policies per basin could be better guided, which are key to food, water, and livelihood security in archipelagic nations such as the Philippines. Laguna Lake (alternatively Laguna de Bay or Laguna de Bai) in Southwestern Luzon is a shallow coastal lake (average depth = 2.5 meters; Herrera et al. 2015 ) and is the largest freshwater body in the Philippines (average surface area = 890 km 2 ; Laguna Lake Development Authority 2023 ). It is also the third largest coastal lake in Southeast Asia after Tonle Sap Lake, Cambodia and Songkhla Lake, Thailand (Lehner and Döll 2004 ). Four bays or lobes form the lake (1) Western; (2) Central; (3) Eastern, and (4) Southern (Fig. 1 ). The lake's Western Lobe, on which this study will focus, currently experiences saltwater incursions from January to July annually, corresponding to the dry season. During this time, the lake's level falls below Manila Bay's flood tide level. Along the western shores of the Western Lobe runs the West Marikina Valley Fault. Although this fault is primarily dextral strike-slip, it has a small vertical component (Rimando and Knuepfer 2006 ). This small vertical component is how the Parañaque Land Strip, on which Philippines' capital region stands, has emerged from the sea over the last six millennia. The effect of this rising Parañaque Land Strip, as well as the one to two meters higher than present mean sea level (Maeda et al. 2009 ), and dry climate, on Laguna de Bai Western Lobe salinity has been documented by Jaraula et al. ( 2014 ) using diatom and mollusc bioassemblages, and Ca/Al, Sr/Ba, and Total Organic Carbon (TOC)/S element salinity proxies. The Western Lobe's salinity shifted from marine (6,700 to 5,500 cal BP) to hypersaline (5,500 to 5,100 cal BP), then returned to marine conditions (5,100 to 4,700 cal BP). Subsequently, the salinity continuously decreased from marine-dominated brackish (4,700 to 4,100 cal BP) to freshwater-dominated brackish (4,100 to 3,100 cal BP), then eventually to freshwater (3,100 cal BP to A.D. 1960s). Since then, salinity has increased to brackish (A.D. 1960s to 1998) levels. This study aims to refine the evolution of the lake (Jaraula et al. 2014 ) by also reconstructing rainfall, redox conditions, and biological production in Western Lobe using additional element proxy and grain size records. Methods Collection and sample preparation A 10.5-meter-long sediment core was collected from the Western Lobe of Laguna de Bai in 1998. The collection and subsequent sample preparation and processing are described in Jaraula et al. ( 2014 ). Briefly, the sediment core was collected using a push corer for the top three meters of sediments whereas a suction corer was used for the lower 7.5 meters of sediments. The sediment core sub-samples were first picked for bioclasts ( e.g. shells, twigs) to remove possible (i) shifts in the grain size distribution and (ii) spikes in the concentrations of the elements associated with these clasts. Afterwards, the sediment core was subsampled along its length generally at five-centimeter intervals for the push core and at four-centimeter intervals for the suction core. Due to limitations in size of the push corer and especially the suction corer, subsamples were allocated alternatingly for either grain size or major/trace element analysis so that the entire 10.5-meter length of the sediment core will still have both grain size and major/trace element profiles. Grain sizes were analyzed using a Fritsch Laser Particle Sizer A22 whereas major/trace element concentrations were measured using a Siemens 303AS X-ray fluorescence (XRF) unit. Both analyses were performed at the Geologisches Institut, Universität Bonn, Germany. Major element concentrations are reported as weight percent (wt%) whereas trace element concentrations are reported in parts per million (ppm). Statistical analyses The geochemical proxies which will be used to reconstruct terrestrial input, redox conditions, and primary productivity, as well as to indicate recent pollution were derived from the major and trace element concentrations measured using XRF. A discussion on how each of these proxies operates can be found in the Geochemical proxies section of the Introduction. Geochemical data processing, statistical analyses, and plotting were performed in the R environment (R Core Team, 2022 ). Element/proxy record dis/similarities were determined via Spearman correlation, using the corr.test function of the psych package (Revelle 2022 ), (i) to select for the terrigenous normalizer of the geochemical proxies and (ii) to determine the behavior of a proxy group ( e.g. salinity, biological production). Spearman correlation was chosen over Pearson correlation because not all of the records follow a normal distribution. The distribution of each record was tested for normality with the Shapiro-Wilk test using the shapiro.test function in R's native stats package. The elemental geochemical proxies used in this study were normalized to Ti, unless the proxy, such as Sr/Ba for salinity, is specifically defined. Al, an element associated with clay-sized sediments (Dinelli et al. 2007 ; Liu et al. 2019 ), is usually used as the normalizing element for siliciclastic matrices to correct for apparent enrichments of the other elements in the clay fraction. The sediments in Laguna de Bai's Western Lobe, however, are silt-dominated (Figure S11), and the major terrigenous element associated with silt is Ti (Liu et al. 2019 ), thus, Ti was selected to be the terrigenous normalizer for all proxies used in this study, except those which were specifically defined. Additionally, when the time series of Ti- and Al-normalized proxies were compared against the chemolithostratigraphic boundaries, the Ti-normalized proxies yielded clearer boundaries. Si bio , another specific proxy used to estimate past biological production, was calculated as \(\:{\left(Si\:/\:Ti\right)}_{bio}={Si}_{sample}-{\:Ti}_{sample}{\left(Si\:/\:Ti\right)}_{baseline}\) [1] where the baseline watershed value of Si/Al is 2.96, which is an average of Southern Manila soil Si/Al value of (Tigue et al. 2018 ) and rock Si/Al value of 3.1 from the Western Lobe watershed (SG Catane unpublished data), due to the current scarcity of published element baseline concentrations for the Western Lobe watershed. Chemical Index of Alteration (CIA; Nesbitt and Young, 1982 ), on the other hand, was calculated as: \(\:CIA\:=\:\frac{{Al}_{2}{O}_{3}}{{Al}_{2}{O}_{3}\:+\:CaO*\:+\:{Na}_{2}O\:+\:{K}_{2}O}\times\:100\) [2] where Al 2 O 3 , Na 2 O, and K 2 O are their respective concentrations whereas CaO* is the silicate fraction of total CaO concentration. To our knowledge, there are currently no published data on the major element composition of Laguna de Bai's Western Lobe Watershed to determine CaO*; therefore, CaO* was estimated following McLennan ( 1993 ). Some proxies, e.g. proxy X, were expressed as enrichment factors (EF), which are calculated as \(\:{\left(X\:/\:Ti\right)}_{EF}={\left(X\:/\:Ti\right)}_{sample}{\left(Ti\:/\:X\right)}_{baseline}\) [3] The baseline concentrations of elements for Laguna de Bai's Western Lobe were derived from their concentration medians from 3,100 calendar years before present (cal BP; Jaraula et al. 2014 ) to A.D. 1500, just before Spanish colonizers arrived in the Philippines in A.D. 1521. This time period was chosen because it is the most recent, minimally anthropogenically-impacted phase of the lake. To determine stratigraphic units in the record based on these geochemical proxies, Constrained Incremental Sum of Squares (CONISS; Grimm, 1965 ) hierarchical cluster analysis was performed on the Z-scores of Ti-normalized concentrations of As, Ba, C org , Ca, Ce, Co, Cr, Cs, Cu, Fe, Ga, Gd, Hf, K, La, Mg, Mn, Mo, Na, Nb, Nd, Ni, P, Pb, Rb, S, Si, Sr, Th, U, V, W, Y, Zn, and Zr concentrations and (ii) grain size parameters (mean, median, and 95th percentile grain sizes, and grain size standard deviation). The Z-scores were calculated as \(\:{Z}_{i}=\frac{{X}_{i}-\mu\:}{s.d.\:\left(X\right)}\) [4] where \(\:i\) is a time interval in the geochemical record, \(\:{X}_{i}\) is the value of proxy \(\:X\) during \(\:i\) , \(\:\mu\:\) is the mean value of proxy \(\:X\) , and \(\:s.d.\left(X\right)\) is the standard deviation of proxy \(\:X\) . CONISS was performed using the chclust function of R’s rioja package (Juggins 2022 ). The dissimilarity parameter used between each pair of time intervals in the geochemical record was the Euclidean distance, \(\:d\) , calculated as \(\:{d}_{ij}=\sqrt{{\sum\:}_{k=1}^{l}{\left({Z}_{i}-{Z}_{j}\right)}_{k}^{2}}\) [5] where \(\:i\) and \(\:j\) are two different time intervals in the geochemical record, \(\:l\) is the total number of proxy records used in the CONISS analysis, and \(\:{\left(Z\right)}_{k}\) are the Z-scores of the proxy record \(\:k.\) All available elements were used as parameters to avoid introducing biases by selecting only the proxies discussed in this study. Most, if not all, proxies respond to more than one environmental control, which is why multiple proxies per parameter are employed in reconstructing that parameter. By using all elements, unknown environmental controls could have a better chance of being represented in the CONISS clusters. The grain size parameters (mean, median, and 95th percentile grain size), on the other hand, are hypothesized to document physical process and mechanisms within the paleo-Laguna de Bai Western Lobe basin as the tectonic setting and climate, which translates to the energy available in the environment, would change the distribution of the sediments. The percentages of sand, silt, and clay were not included as they are already represented in the grain size distribution parameters. Results Chemolithostratigraphic units Six chemolithostratigraphic units from 4,590 to 6,510 cal BP were delineated in this study from CONISS hierarchical clustering and generally agree with the three units identified by Jaraula et al. ( 2014 ), Va, Vb, and Vc. Units delineated by Jaraula et al. ( 2014 ) which are based on salinity proxies, diatom and mollusc bioassemblage zones, but with the addition of transitional units Va.b and Vb.c, and Vc subdivided into Vc1 and Vc2 (Fig. 2 ). Additionally, boundaries have shifted a few centuries for this study recalibrated the 14 C ages of Jaraula et al. ( 2014 ) using a more recent radiocarbon calibration dataset ( see the Sediment core chronology section of the Supplementary Material ). These chemolithostratigraphic units are characterized in terms of terrestrial input, redox conditions, and biological production in the following sections. Periods VI and VII were also identified from CONISS. However, because (i) each unit only has two data points for either element proxy or grain size measurements, (ii) both contain anomalous values, and (iii) these units are at the end of the record and not in between other units, little information can be derived out of these four data points. Therefore, they will not be discussed for this study. Trends in proxy and grain size records The descriptive statistics per time period in Fig. 2 for the representative proxy/ies of each reconstructed parameter are presented in Table 1 . Periods VII and VI (6,640 to 6,590 and 6,590 to 6,510 cal BP) will only be discussed briefly because no trends can be reliably inferred from four data points. Additionally, a description on how each of the proxies in the following sections operates can be found in the Geochemical proxies section of the Introduction. Table 1 Mean, standard deviation, range, and number of data points per chemolithostratigraphic unit of representative proxies for total terrestrial input, weathering/rainfall, salinity, redox, biological production, and grain size percentages %sand, %silt, and %clay Period (cal BP) Total terr. input Weathering / rainfall Salinity Redox 1° Production Grain size Ti (%) Zr/Al (%/%) Sr/Ba (ppm/ppm) Mn/Ti (%/%) bio. Si/Al (%) Sand (%) Silt (%) Clay (%) Vc2 4,910 to 4,590 mean 0.441 13.4 1.31 0.213 6.14 2.49 92.0 5.46 s.d. 0.0207 0.222 0.115 0.00465 0.175 3.05 4.54 1.53 range 0.439 to 0.444 13.1 to 13.7 1.21 to 1.49 0.209 to 0.219 5.87 to 6.35 0.360 to 7.93 83.8 to 95.5 4.14 to 8.28 n 5 5 5 5 5 6 6 6 Vc1 5,310 to 4,910 mean 0.414 14.6 1.89 0.216 7.50 1.32 94.5 4.12 s.d. 0.0144 0.357 0.195 0.00581 2.44 0.465 0.424 0.254 range 0.391 to 0.427 14.0 to 14.9 1.62 to 2.11 0.210 to 0.225 5.32 to 11.6 0.88 to 2.06 93.8 to 94.9 3.70 to 4.36 n 5 5 5 5 5 5 5 5 Vb.c 5,750 to 5,310 mean 0.427 13.9 1.64 0.206 5.11 2.90 88.8 8.29 s.d. 0.0147 0.558 0.531 0.00468 1.56 2.24 4.78 3.07 range 0.413 to 0.452 13.5 to 14.8 0.942 to 2.07 0.203 to 0.214 3.88 to 7.81 0.67 to 6.86 82.8 to 93.3 5.57 to 13.4 n 5 5 5 5 5 6 6 6 Vb 6,070 to 5,750 mean 0.438 15.9 1.44 0.218 9.12 2.23 90.1 7.51 s.d. 0.0102 0.272 0.0456 0.00364 1.01 1.85 2.87 1.96 range 0.427 to 0.451 15.5 to 16.1 1.40 to 1.50 0.213 to 0.222 7.86 to 10.0 0.48 to 4.32 86.1 to 93.0 5.70 to 9.64 n 4 4 4 4 4 5 5 5 Va.b 6,260 to 6,070 mean 0.439 16.2 1.31 0.220 7.48 2.41 89.5 8.13 s.d. 0.0146 0.443 0.0489 0.00311 1.60 0.527 1.24 0.979 range 0.414 to 0.453 15.6 to 16.7 1.22 to 1.36 0.217 to 0.225 5.07 to 9.70 1.67 to 3.06 87.8 to 91.5 6.85 to 9.65 n 6 6 6 6 6 6 6 6 Va 6,510 to 6,260 mean 0.483 16.1 1.06 0.240 4.48 1.65 89.1 9.23 s.d. 0.0211 0.459 0.0926 0.00156 2.10 1.20 1.39 0.851 range 0.451 to 0.507 15.3 to 16.7 0.971 to 1.21 0.237 to 0.242 2.39 to 7.42 0.18 to 3.31 87.3 to 91.4 7.59 to 10.4 n 9 9 9 9 9 10 10 10 VI 6,590 to 6,510 value 1 0.457 19.6 1.24 0.204 19.2 35.7 74.4 5.37 value 2 0.379 18.0 0.450 0.201 11.4 21.6 60.9 2.08 VII 6,640 to 6,590 value 1 0.480 17.9 0.853 0.229 13.1 5.46 85.5 13.9 value 2 0.404 17.0 0.406 0.202 5.06 0.61 84.9 9.61 Terrestrial input Total terrestrial input From Period Va to Va.b, terrigenous elements Ti, and Fe all decreased (Figure S6). Al then increased from late Period Va.b to Period Vb.c, where its concentration plateaued during Period Vc1. Al concentration decreased in Period Vc1 and then increased in Period Vc2. Ti and Fe concentrations, on the other hand, remained relatively constant from late Period Va.b to Period Vc2. Weathering / rainfall During Period Va to early Va.b, Zr/Al was relatively constant, which then generally decreased during Period Vb, to lower values in Periods Vb.c to Vc2, with a brief increase in value but not reaching Va + Va.b levels during Period Vc1 (Figure S7). Salinity From early Period Va, Sr/Ba was constant (Figure S8). It generally began to increase in late Period Va until Vb.c, with a brief drop at around the Vb-Vb.c boundary. Sr/Ba values plateaued from late Vb.c to early Vc1, then decreased starting late Vc1 through Vc2. Redox During Period Va, Mn/Ti was generally constant (Figure S9). Its value then sharply decreased at the Va–Va.b boundary and continued to decrease until Period Vb. Mn/Ti values were lowest during Period Vb.c, which then increased during Periods Vc1 and Vc2 but were still lower then Period Va levels. Biological production Biogenic Si/Al was increasing in a fluctuating manner from a Period Va to early Vb (Figure S10). Its value then decreased at around the Vb-Vb.c boundary, and only increased slightly from late Vb.c. to early Vc1. It then maintained a fairly constant value from late Vc1 to Vc2, with a brief peak around the Vc1-Vc2 boundary. Grain size The percentage of sand during Periods Va was increasing, which then decreased from Va.b to Vb (Figure S11). From Period Vb.c until Vc2, %sand remained constant and at levels lower than those of Periods Va.b and Vb. These periods of relatively low %sand are punctuated by brief increases during early Period Vb.c and the end of Period Vc2. The percentage of silt was relatively constant from Period Va to early Vb.c. However, fluctuations in %silt were more pronounced during Periods Vb and early Vb.c relative to periods Va and Va.b. From early Period Vb.c, %silt increased until late Period Vb.c, and then plateaued from Period Vc1 to most of Vc2. By the end of Period Vc2, %silt dropped to a value lower than Period Va and Va.b means. The percentage of clay was generally decreasing during Period Va until Vb.c. This decreasing trend is punctuated by increases in %clay during Periods Vb and early Vb.c. From Period Vc1 to most of Vc2, %clay remained at their lowest levels in the record, which increased again only by the end of Period Vc2. Discussion Proxy relationships The proxies used in this study were correlated using their entire 6,510 to 4,950 cal BP records rather than per chemolithostratigraphic unit for the data points per unit are often less than 10, and stronger correlations can be derived with more data points per record ( see Figures S3 to S5 for correlation matrices of the element proxies and grain size parameters used in this study ). Terrigenous element proxies Ti, Al, and Fe correlate positively and strongly with each other (p < 95%), which agrees with Lo et al. ( 2017 ) where these elements remain in the residual fraction of rocks or sediments during chemical weathering. In the Southeast Asian region, rainfall is either abundant to provide ample water to support weathering or excessive to limit weathering by transporting clastics faster to depositional environments. Therefore, the Chemical Index of Alteration (CIA) could, for the former case, either increase with more rainfall, or, for the latter case, decrease with more rainfall. Additionally, terrigenous immobile element ( e.g. Al, Ti, Zr, Nb, Hf, Th) ratios may be used to measure the degree of weathering based on their relative immobility: Nb ≈ Th > Zr ≈ Hf > Ti > Al (Babechuk et al. 2015 ; Jiang et al. 2018 ; Lo et al. 2017 ). Based on this order, it is hypothesized that under wetter climate when runoff energy is higher, less mobile terrigenous elements (LMTE) are also deposited in Laguna de Bai's Western Lobe basin along with the relatively more mobile terrigenous elements (MMTE), such that the LMTE/MMTE ratio increases. During drier climatic conditions when energy of runoff is lower, LMTEs are left in the watershed with respect to the MMTEs, and the LMTE/MMTE ratio decreases. Furthermore, K/Rb is another weathering proxy, values of which increase (decrease) with higher (lower) degrees of weathering. This is due to K and Rb able to replace each other in mineral lattices. However, Rb has a slightly ionic radius than K, which makes it easier to desorb from mineral lattices during weathering (Lo et al. 2017 ). Weathering or rainfall proxies, Ti/Al, Zr/Al, Zr/Ti, Th/Al, Th/Ti, Th/Zr, Th/Hf, Nb/Al, Nb/Ti, ( i.e. LMTE/MMTE ratios) and K/Rb, all positively correlate with each other (p < 5%; Figure S3), and these elements negatively correlate with other weathering proxies such as the CIA and Nb/Th (p < 5%). Of these weathering/rainfall proxies, only Zr/Al correlates negatively with the salinity proxy Sr/Ba, which is why Zr/Al will be the representative proxy. The negative correlation between the LMTE/MMTE proxies and CIA suggests a supply-limited weathering regime where the abundance of rainfall in regions, such as that of Laguna de Bai's Western Lobe, limits the weathering time of the sediments because the transport time is decreased (Calabrese and Porporato 2020 ). The coherence of these proxies among their kind, as well as with others such as the salinity proxy Sr/Ba suggests that these proxies are viable weathering/rainfall proxies. The organic-carbon-to-sulfur (C org /S or TOC/S) ratio is used to distinguish marine from freshwater deposits. Sulfate is abundant in marine systems whereas it is limited in freshwater ones. C org /S values of 1.5 to 4 suggest normal marine conditions (Berner and Raisewell 1984 ), whereas 4 to 11 suggest brackish conditions with marine influence (Wei and Algeo 2020 ) compared to 11 to 17 brackish conditions with freshwater influence, and values > 17 suggest freshwater conditions (Woolfe et al. 1995 ). For marine Laguna de Bai (6,640 to 4,700 cal BP). For marine Laguna de Bai (6,640 to 4,700 cal BP), the C org /S proxy cannot resolve the salinity variability, which is why Jaraula et al. ( 2014 ) used additional proxies Ca/Al, Ca/Ti, Sr/Al, Sr/Ti, and Sr/Ba (Nelson 1967 ) to differentiate the salinity phases within the marine period of Laguna de Bai's Western Lobe. Salinity proxies Sr/Ba, Ca/Ti, and Sr/Ti positively correlate with each other (p < 5%; Figure S3). Only Sr/Ba correlates with S/Ti, which is another salinity proxy. This can be expected, however, because S/Ti also carries a redox signal aside from a salinity signal. In fact, S/Ti correlates positively with TOC and TOC/Ti (p < 5%) and negatively with Mn/Ti (p < 5%), supporting its behavior more as a redox proxy rather than a salinity proxy. TOC/S, another salinity proxy, also does not correlate with Sr/Ba, Ca/Ti, nor Sr/Ti. Like S/Ti, TOC/S could vary more with TOC, and hence carry more of a biological production signal rather than a salinity signal. This could also be expected because in marine environments, the TOC/S salinity proxy can no longer resolve salinity variations. This is also why Jaraula et al. ( 2014 ) used Sr/Ba, Ca/Ti, and Sr/Ti alongside TOC/S. Likewise, the coherence of Sr/Ba, Ca/Ti, and Sr/Ti supports their function as salinity proxies. The enrichment of Mn/Ti in the sediments could indicate an oxic water column as dissolved Mn forms particulate Mn oxides which sink to the sediments. A reducing water column, on the other hand, redissolves these Mn oxides and decreases the concentrations of Mn in the sediments (Grybos et al. 2007 ; Johnson et al. 2016 ). Sulfur is abundant in seawater as water-soluble sulfate (SO 4 2− ) and minimally accumulates in the sediments relative to accumulation under reducing water column conditions as sulfide (S 2− ), which accumulates in the sediments (Sharma et al. 2022 ). C org :P also varies inversely with oxygenation (Algeo and Ingall 2007 ) because during oxic conditions, P is deposited and preserved whereas C org is oxidatively depleted. During anoxic conditions, on the other hand, C org is preserved whereas P is released back to the water column (Algeo and Ingall 2007 ; Anderson et al. 2021 ; Parsons et al. 2017 ). Redox proxy Mn/Ti, which increases in value under more oxidizing conditions, correlates negatively with S/Ti, Mo/Ti, and C org :P (p < 5%; Figure S3), which increase in values under more reducing conditions. Additionally, S/Ti correlates positively with Mo/Ti and C org :P (p < 5%). These correlations support the sensitivities of these elements to redox processes. U/Ti, on the other hand, correlates only with Mo/Ti (positively, p < 5%). This is to be expected because U, like Mo, is also enriched in the sediments overlain by reducing water columns. Even though U/Ti does not correlate significantly with Mn/Ti, S/Ti, nor C org :P, its covariation with Mo/Ti would still be coherent with the interpretations from the other redox proxies. It is also important to note that Mn/Ti could also bear a weathering/rainfall signal, as it is also a major and a terrigenous element in Laguna de Bai's Western Lobe sediments, and it correlates positively with the weathering/rainfall signals (p < 5%). Nevertheless, given Mn/Ti's coherence with the other redox proxies, the dominant signal Mn/Ti carries is redox. C org is a paleo-biological production proxy as it represents the remains of plants and organisms that lived or was brought to the Laguna de Bai's Western Lobe basin. C org also participates as a reductant in water column redox reactions. Ba, in the form of barite (BaSO 4 ), is also associated with C org such as organic-rich aggregates and extracellular polymeric surfaces (Dymond et al. 1992 ; Martinez-Ruiz et al. 2019 ), and therefore can likewise be used as a biological production proxy. The C org record of biological production is altered in oxic bottom waters, whereas the Ba record of biological production is destabilized in reducing bottom waters by reducing BaSO 4 into BaS. Nevertheless, BaS, and thus the paleo-biological production record, could still be determined by C org under reducing conditions (Baldi et al. 1996 ). Both C org and Ba are not specific to autochthonous or allochthonous contributions. Si bio , however, derived from total Si and Ti using Eq. 1, is specific to siliceous productivity and is assumed to primarily be from diatom frustules. Biological production proxies TOC, TOC/Ti, Ba/Ti, and bioSi/Al do not correlate to significance with each other (p > 5%; Figure S3), except for Ba/Ti and TOC, which correlate negatively (p < 5%). This suggests that these elements are confounded by environmental controls other than biological production such as redox processes for TOC and Ba, hydrodynamic dispersal for all of the proxies, and taxa specificity for bioSi/Al. Because of this, discussions of biological production in the following sections will also include a discussion on the chemical and/or hydrodynamic preservation of these proxies in the sediment record. For the grain size parameter correlations (Figure S5), %sand correlates positively with the mean grain size, the standard deviation of grain sizes, and the 95th percentile grain size, and negatively with %silt (p < 5%). On the other hand, %silt correlates positively with the median grain size (p < 5%) and negatively with %clay and the 95th percentile grain size (p < 5%). Additionally, %clay correlates negatively with the mean and median grain sizes, as well as the standard deviation (p < 5%). These correlations suggest that sand, or the lack of it, is the main driver of grain size variability in Laguna de Bai Western Lobe's 6,510 to 4,950 cal BP sediment record. Sand variability is apparent during the Coastal Lagoon Period of Laguna de Bai's Western Lobe. With increasing restriction imposed on Laguna de Bai's Western Lobe basin by the rising Parañaque Land Strip since Period Vb.c silt became even more dominant in the sediment record, with variability introduced since then by clay. Periods VII, VI, and coastal sub-tidal lagoon period Va Period Va is considered a coastal lagoon by Jaraula et al. ( 2014 ; Fig. 3 ) based on the assemblage of molluscs Anomalocardia sp., Leptaxinus sp., and Tellina sp.; and the C org /S value of < 4 (Berner and Raisewell 1984 ). Based on Zr/Al, rainfall during this period was similar or slightly drier than historic times. At the start of Period Va, when Laguna de Bai's Western Lobe basin was around eleven meters deep based on the basin's sedimentation rates (Figure S2) and a paleo-sea level of one meter apmsl (Maeda et al. 2009 ), the paleo-lagoon waters were generally oxic as indicated by the mean C org :P value of 44.6 (Algeo and Ingall 2007 ; Figure S9; Table S1 ). The C org :P then increased to a mean of 87.9, a level considered suboxic ( i.e. 50 ≤ C org :P ≤ 100; Algeo and Ingall 2007 ; Table S1 ) during transition Period Va.b. These C org :P values are consistent with the deoxygenation of the bottom waters identified from increasing Mo/Ti, which attained mean values of 26.8, higher than those of Va (mean = 16.6; Table S1 ). Sedimentary Mo enrichment/depletion is a fairly reliable proxy for this period as it responds more specifically to redox in non-sulfidic, reducing environments (Paul et al. 2023 ). Furthermore, Mo-U covariation follows the enrichment/depletion pathway (Fig. 5 ) of unrestricted, vertically well-mixed water columns (Algeo and Tribovillard 2009 ) where sedimentary U concentration varies inversely with oxygenation as U exists as soluble species in oxic water columns, but forms organic matter-U(VI) complexes (Trenfield et al. 2011 ) or precipitates as U(IV) in reducing water columns. Both processes operate mostly at the Fe(II)-Fe(III) redox boundary and sequester U in the sediments (Behrends and Van Cappellen 2005 ; Duan et al. 2023 ; Liger et al. 1999 ; Tsarev et al. 2016 ). Likewise, Mo, as molybdates, is soluble in oxic water columns. Mo only begins to increase from average watershed concentrations when the water column become sulfidic where molybdates are converted into thiomolybdates in the presence of H 2 S (Hlohowskyj et al. 2021 ). The thiomolybdates are then scavenged by organic matter (Dahl et al. 2016 ) or Fe-S phases and are deposited to the sediments (Vorlicek et al. 2018 ). The decreasing oxygenation of Laguna de Bai's Western Lobe bottom waters during Periods Va.b and Vb may have resulted from an increase in siliceous and non-siliceous biological production and/or the increased trapping of organic matter from the watershed and from biological production in the water column due to the continual uplift of the Parañaque Land Strip. This is seen in the concurrent increases in bioSi/Al and C org /Ti (or TOC/Ti; Figure S10). The concurrent increases in both bioSi/Al and %sand, however, could suggest that the apparent increase in siliceous organisms could be due to the addition of sand, to which Si is associated (Dinelli et al. 2007 ; Liu et al. 2019 ). Still, diatoms range from clay- to sand-sized particles, which would imply a lessened effect of sand addition from the watershed to the apparent increase in bioSi/Al. Furthermore, bioSi/Al, to some degree, takes into account the variability of terrestrial input ( see Eq. 1 ), which could further dampen the effect of sand addition from the watershed to the biogenic silica record. In addition, the watershed of Laguna de Bai's Western Lobe is more mafic (Defant et al. 1991 ) relative to some silicic areas in Laguna de Bai's Southern Lobe watershed (Vogel et al. 2006 ). Therefore, it is less likely that the concurrent increases in bioSi/Al and %sand is due to terrigenous sand adding to the biogenic silica record. The proportions of siliceous and non-siliceous contributions to the TOC, also, could not be determined with the current dataset due to the oxic to suboxic conditions of Laguna de Bai's Western Lobe during this time which limits C org preservation. The increasing %sand relative to the succeeding periods is also consistent with the relatively less restricted Western Lobe basin during this time, as well as the natural shallowing of the lagoon due to sediment filling the basin. Transition periods Va.b, Vb, and Vb The assemblage of molluscs during these periods (6,260 to 5,750 cal BP), Peronidia venulosa , Anomalocardia squamosa , A. scabra , Ostrea sp., Rissoina sp., Tellina sp., Leptomya sp., and Turrid sp., suggests that Laguna de Bai's Western Lobe was shallowing (Jaraula et al. 2014 ). The increasing Western Lobe salinity from late Period Va towards hypersaline conditions in the late Period Vb.c and early Vc1 could be due to the increasing water column stratification from increasing basin restriction imposed by the continually uplifting Parañaque Land Strip from late Period Va to early Period Va.b. This is supported by the abrupt decrease in Mn/Ti at the start of Period Va.b, suggesting that bottom water oxygen exchange with the atmosphere is increasingly limited. Since the late Period Va.b, the decreasing rainfall strengthened this water column stratification. Considering that biological production proxies C org , C org /Ti, and bioSi/Al all increased during this period of higher-than-usual-marine salinity ( i.e. hypersaline), the following are hypothesized: (i) planktonic primary producers, including the siliceous majority, could tolerate this salinity regime; (ii) the rising Parañaque Land Strip prevents the particulate C org and biogenic Si particles from being dispersed out of the Laguna de Bai's Western Lobe basin and the increasingly reducing conditions during this period preserved the C org rain in the sediments; and (iii) increasing salinity also increases the flocculation of dissolved and suspended matter to the sediments, consequently increasing light penetration into the water column. The first hypothesis is possible due to the occurrence of bivalves and gastropods even during the hypersaline periods Vc1 and Vc2 (Jaraula et al. 2014 ). However, as a hypersaline watermass develops on the surface, its density also increases which would cause it to sink and join the bottom water. Unless the hypersaline watermass had already become pervasive in Laguna de Bai's Western Lobe basin, they are likely confined to the bottom water, and it is likely that the salinity proxies used in this study reflect bottom water salinities and leave the surface waters still less saline than the bottom waters. In the second hypothesis, Parañaque Land Strip could indeed play a role in the preservation of particulate C org and biogenic Si, but it would not be able to explain the drop in biological production in the early Vb.c period, when sea level briefly overtopped the rising Parañaque Land Strip. The third hypothesis could be the case in Period Vb.c, as this was also observed by Santiago (1991), but in the brackish salinity regime of Laguna de Bai's Western Lobe in the A.D. 1980s. The decreasing %sand and increasing %silt suggests a decrease in the hydrodrynamic energy in the Western Lobe as the rising Parañaque Land Strip limits the fetch distance for surface waves coming from Manila Bay, which is longer than the fetch distance from Laguna de Bai's Southern Lobe. The decreasing %clay, on the other hand, could be due to the shallowing of the Western Lobe. These grain size characters also persisted over Periods Vb.c until Vc2. Hypersaline intertidal lagoon periods Vb.c, Vc1, and Vc2 This period was interpreted by Jaraula et al. ( 2014 ) as an intertidal lagoon (Fig. 4 ) based on mollusc assemblages of Thiara granifera , Cycladicama tsuchii , Atactodea striata , Turrid sp., and Cassis sp. The continual tectonic uplift of the Parañaque Land Strip should have allowed fresh water from the watershed to accumulate in the basin. However, the drier climate in the Western Tropical Pacific from 5,500 to 2,600 cal BP relative to the previous periods from 6,510 to 5,500 cal BP, as documented by the chemical weathering proxies, with higher CIA, lower LMTE/MMTE and K/Rb ratios relative to Period Va, could be due to the millennial-scale migrations of the mean ITCZ position (Sachs et al., 2018 ; Yokoyama et al., 2011 ) as well as lower El Niño/Southern Oscillation activity (Chen et al. 2016 ; McGregor and Gagan 2004 ; Stevenson et al. 2010 ). This drier climate coupled with saltwater incursions due to the two-meter sea level stillstand apmsl, provided the conditions to raise Laguna de Bai's Western Lobe basin salinity eventually to peak hypersaline levels by late Period Vb.c which was sustained until early Vc1. The invariant behavior of Mo relative to U from Period late Vb.c to Vc2 (Fig. 5 ) suggests a stratified water column with reducing and possibly sulfidic bottom waters where the O 2 -H 2 S chemocline is above the sediment-water interface and there are inadequate phases delivering and resupplying the bottom waters with Mo. The remaining bottom water Mo is scavenged at the sediment-water interface to depletion whereas U is reduced a-/biotically in ferruginous (Behrends and Van Cappellen 2005 ; Duan et al. 2023 ) and sulfidic (Hyun et al. 2014 ) zones. Likewise, S/Ti maintained levels higher than those of Period Va. This could be expected because late Periods late Vb.c to early Vc1 are the periods of peak hypersalinity. Additionally, the C org :P molar ratio could be affected during this time by the hypersaline conditions, which concentrate P in the sediments (Figures S9 and S10). This would then lead to apparent oxygenation trends in C org :P since C org is fairly constant. This is why for the hypersaline period late Vb.c to early Vc1, the C org :P redox proxy could be ineffective. C org could be the most reliable biological production proxy for these periods due to its ideal preservation in the sediments deposited under reducing conditions, possibly even sulfidic because of the stable stratification during the hypersaline phase. This could explain the higher mean C org concentrations in the sediments deposited during Periods Vc1 and Vc2 than those deposited during Period Va. On the other hand, the preservation of the Ba record could have been destabilized due to reducing bottom waters converting barite (BaSO 4 ) into unstable BaS (Baldi et al. 1996 ), consequently resulting into lower mean Ba concentrations during Periods Vc1 and Vc2 relative to Period Va (Figure S10). The slight increase in Zr/Al in Period Vc1 and the further emergence of the Parañaque Land Strip could have increased the freshwater budget and decreased the saltwater incursions into the Western Lobe, respectively (Fig. 6 ). Since then, the hypersaline bottom waters of Laguna de Bai's Western Lobe waned in pulses from late Vc1 to Vc2 (Figure S8). S/Ti maintained elevated values until Period Vc2, which was when hypersalinity was already declining. This could suggest that, during Period Vc2, S/Ti carried a redox signal, and from the covariation of Mo and U, bottom waters had reducing conditions even when hypersalinity was already waning (Figure S9). Considering that the Philippines is at the center of Asian and Pacific climate phenomena, this study is one of only a handful of paleoclimate reconstructions from Philippine natural archives. Furthermore, this study, to our knowledge, would be the first to integrate the dynamics of climate, tectonics, sea level, with basin salinity, redox conditions, and primary production at centennial time scales over 1,900 years in the mid-Holocene. This reconstructed dynamics could be applied to predict the possible conditions of embayments and coastal lakes in the future, where wetter climate (Mandapaka and Lo 2018 ) and higher sea levels (Kahana et al. 2016 ) forecasted by the end of the 21st century. Additionally, organic geochemical proxies in future studies in tandem with the current element geochemical proxies could further validate and refine the current reconstruction. Declarations Funding We would like to thank the following for funding this study: Office of the Vice-Chancellor for Research and Development, University of the Philippines Diliman [grant number 00007NSET]. This study was also an offshoot of a project, under the supervision of Dr. Fernando Siringan, funded by the Laguna Lake Development Authority. Acknowledgements We are grateful for Dr. Kasuo Maeda who provided the sediment corer; Mr. Zenon Mateo and Mr. Neil John Macalalad who helped in collecting the sediment core; Dr. Jean Thein of the Geologisches Institut, Universität Bonn, who generously arranged for the use of their geochemical and sedimentological laboratories; Dr. Ralf Klingel, Erika Ochterbek, and Waltraud Strauss for providing technical support during the sample processing. References Algeo TJ, Ingall E (2007) Sedimentary C org :P ratios, paleocean ventilation, and Phanerozoic atmospheric pO 2 . In: Pope MC, Algeo T, Saltzman MR, Bartley JK (eds) Neoproterozoic to Paleozoic Ocean Chemistry. Paleogeogr Paleoclim Paleoecol 256: 130–155 Algeo TJ, Tribovillard N (2009) Environmental analysis of paleoceanographic systems based on molybdenum-uranium covariation. 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Supplementary Files TableS1ToyadoJaraulaPaleolimnol.pdf SupplementaryInformation.odt Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 04 Nov, 2025 Reviews received at journal 17 Jul, 2025 Reviewers agreed at journal 25 Jun, 2025 Reviewers invited by journal 25 Jun, 2025 Editor assigned by journal 24 Jun, 2025 Submission checks completed at journal 24 Jun, 2025 First submitted to journal 15 Jun, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6897953","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":477944832,"identity":"35820184-d044-4bb8-84cb-2faa687ccd37","order_by":0,"name":"Caroline Marie B. Jaraula","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABCUlEQVRIiWNgGAWjYLCCBwYMDIwNIFYBgxyIOvCAkJYEuBYDBmOwlgSCWuAsA4bEBlQRTMDffvbhg4SCO3LMQMZnHgO79Plhhx8CbbGT023ArkXiTLqxQYLBM2PGnnRjaR6D5NyNt9MMgFqSjc0OYNdiwJDGJpFgcDixsSGNAaiFOXfj7ASQlgOJ23Bp4X8G1lLf2P+M+TePQX264ez0D/i1SEBsSWCckcYGtOVwgrx0Dn5bJG48Ywb65bBh44xnbJZzDI4bbpDOKTiQYIDbL/z9aYwPPvw5LG/Yn8Z8401Ftbz87PTNHz5U2Mnh0gIHhg0wpx6ABAthIA9nNOBRNQpGwSgYBSMSAAA2Yl3eKzkvegAAAABJRU5ErkJggg==","orcid":"","institution":"University of the Philippines Diliman","correspondingAuthor":true,"prefix":"","firstName":"Caroline","middleName":"Marie B.","lastName":"Jaraula","suffix":""},{"id":477944833,"identity":"bb25de22-81b8-47f7-bd6e-e7c2fbe391d4","order_by":1,"name":"Chris Carl Agustin V. Toyado","email":"","orcid":"","institution":"University of the Philippines Diliman","correspondingAuthor":false,"prefix":"","firstName":"Chris","middleName":"Carl Agustin V.","lastName":"Toyado","suffix":""}],"badges":[],"createdAt":"2025-06-15 11:08:13","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6897953/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6897953/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85647319,"identity":"2c5f9e7b-3e7f-4401-a44e-a6456da574f0","added_by":"auto","created_at":"2025-06-30 08:46:30","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":202662,"visible":true,"origin":"","legend":"\u003cp\u003eClimatic, hydrodynamic, and tectonic setting of Laguna de Bai, with focus on the lake's Western Lobe for this study.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6897953/v1/f955b4a5b4d52a7706a3f068.png"},{"id":85647312,"identity":"73cda1d1-38c4-4e14-b305-a1903844956c","added_by":"auto","created_at":"2025-06-30 08:46:30","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":110545,"visible":true,"origin":"","legend":"\u003cp\u003eChemolithostratigraphic units derived from Constrained Incremental Sum of Squares (CONISS) hierarchical cluster analysis on (i) Ti-normalized elemental concentration records and (ii) grain size parameter records (\u003cem\u003ei.e.\u003c/em\u003e, mean, median, standard deviation, and 95\u003csup\u003eth\u003c/sup\u003e percentile). Numbers at the leaves of the cluster trees indicate the depth of the sediment. The ages of the boundaries were determined from the age model of this study (Figure S2).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6897953/v1/12cc1f0f43470ba346eb8765.png"},{"id":85647318,"identity":"380134fc-b2df-4dff-86fc-9a78515667d3","added_by":"auto","created_at":"2025-06-30 08:46:30","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":73789,"visible":true,"origin":"","legend":"\u003cp\u003eReconstruction of Laguna de Bai's Western Lobe, Parañaque Land Strip, and Manila Bay during Periods Va to Vb with usual to higher-than-usual seawater salinity. The view is looking southeast with sea level 1 m above present-day. Parañaque Land Strip is still mostly submerged with the paleo-Laguna de Bai Lagoon connected to Manila Bay.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6897953/v1/26a4fd80b6d6c402ee6f6d49.png"},{"id":85648958,"identity":"10aed482-90fb-49e6-bea2-30b1416d9a46","added_by":"auto","created_at":"2025-06-30 08:54:30","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":84762,"visible":true,"origin":"","legend":"\u003cp\u003eReconstruction of Laguna de Bai's Western Lobe, Parañaque Land Strip, and Manila Bay during Periods Vc1 to early Vc2–waxing to peak hypersalinity. The view is looking southeast with sea level 1.5 to 3 m above present-day. Parañaque Land Strip has partially emerged, restricting water exchange between paleo-Laguna de Bai Lagoon and Manila Bay.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6897953/v1/f2755a04bac1be644813d5c4.png"},{"id":85648959,"identity":"3c5d7ca3-ca33-4c7d-8838-687e14bd4de0","added_by":"auto","created_at":"2025-06-30 08:54:30","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":32863,"visible":true,"origin":"","legend":"\u003cp\u003eMo-U covariation in Laguna de Bai's Western Lobe during the marine phase (6,640 to 4,700 cal BP). The increasing diameters indicate the forward direction of time. Black circles represent the hypersaline period (5,500 to 5,100 cal BP). Diagonal lines labeled with Mo/U\u003csub\u003esw\u003c/sub\u003e indicate the concentration ratios in the sediments relative to that of seawater. The gray arrows serve as guides to the general patterns of Mo-U covariation: particulate shuttle, redox variation, and evolving watermass chemistry.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6897953/v1/676108fc493c39759e80616c.png"},{"id":85647343,"identity":"89655613-7f17-4a66-8b58-fe129f24d7bd","added_by":"auto","created_at":"2025-06-30 08:46:31","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":81939,"visible":true,"origin":"","legend":"\u003cp\u003eReconstruction of Laguna de Bai's Western Lobe, Parañaque Land Strip, and Manila Bay during Periods Vc3–waning hypersaline. The view is looking southeast with sea level 1.5 to 3 m above present-day. Parañaque Land Strip continually emerged from Period Vc1 (Figures 3 and 4), further restricting water exchange between paleo-Laguna de Bai Lagoon and Manila Bay.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6897953/v1/3b1b22d02fbbae4657cdc404.png"},{"id":85649674,"identity":"2c117353-e486-413a-bf98-f2b5febcfe82","added_by":"auto","created_at":"2025-06-30 09:02:37","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1306763,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6897953/v1/beffff7e-dfdb-4cac-9621-d2edd9aaa108.pdf"},{"id":85648972,"identity":"2932f6f3-1a00-4c41-9379-a9901d5c4cdb","added_by":"auto","created_at":"2025-06-30 08:54:31","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":67052,"visible":true,"origin":"","legend":"","description":"","filename":"TableS1ToyadoJaraulaPaleolimnol.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6897953/v1/7ed3c83cecb9deccfe29cebe.pdf"},{"id":85649673,"identity":"bb116a79-a66f-4d09-a26d-d11b08cdcd7f","added_by":"auto","created_at":"2025-06-30 09:02:31","extension":"odt","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":3128283,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.odt","url":"https://assets-eu.researchsquare.com/files/rs-6897953/v1/3a3f96c9adad0a48b635544b.odt"}],"financialInterests":"No competing interests reported.","formattedTitle":"Geochemical proxy records to reconstruct terrestrial input, redox conditions, and biological production in a tropical paleo-lagoon during the mid-Holocene","fulltext":[{"header":"Introduction","content":"\u003cp\u003eNatural archives, such as lake sediments, provide a continuous record of environmental changes that typically pre-date the instrumental period and written history. Studying records of these changes in a basin (\u003cem\u003ee.g.\u003c/em\u003e salinity, redox conditions, biological production) as well as forcings on the basin (\u003cem\u003ee.g.\u003c/em\u003e climate, sea leve, tectonism) allows us to understand its dynamics and predict its possible future conditions. With this understanding long-term management policies per basin could be better guided, which are key to food, water, and livelihood security in archipelagic nations such as the Philippines.\u003c/p\u003e \u003cp\u003eLaguna Lake (alternatively Laguna de Bay or Laguna de Bai) in Southwestern Luzon is a shallow coastal lake (average depth\u0026thinsp;=\u0026thinsp;2.5 meters; Herrera et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) and is the largest freshwater body in the Philippines (average surface area\u0026thinsp;=\u0026thinsp;890 km\u003csup\u003e2\u003c/sup\u003e; Laguna Lake Development Authority \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). It is also the third largest coastal lake in Southeast Asia after Tonle Sap Lake, Cambodia and Songkhla Lake, Thailand (Lehner and D\u0026ouml;ll \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Four bays or lobes form the lake (1) Western; (2) Central; (3) Eastern, and (4) Southern (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The lake's Western Lobe, on which this study will focus, currently experiences saltwater incursions from January to July annually, corresponding to the dry season. During this time, the lake's level falls below Manila Bay's flood tide level. Along the western shores of the Western Lobe runs the West Marikina Valley Fault. Although this fault is primarily dextral strike-slip, it has a small vertical component (Rimando and Knuepfer \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). This small vertical component is how the Para\u0026ntilde;aque Land Strip, on which Philippines' capital region stands, has emerged from the sea over the last six millennia.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe effect of this rising Para\u0026ntilde;aque Land Strip, as well as the one to two meters higher than present mean sea level (Maeda et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), and dry climate, on Laguna de Bai Western Lobe salinity has been documented by Jaraula et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) using diatom and mollusc bioassemblages, and Ca/Al, Sr/Ba, and Total Organic Carbon (TOC)/S element salinity proxies. The Western Lobe's salinity shifted from marine (6,700 to 5,500 cal BP) to hypersaline (5,500 to 5,100 cal BP), then returned to marine conditions (5,100 to 4,700 cal BP). Subsequently, the salinity continuously decreased from marine-dominated brackish (4,700 to 4,100 cal BP) to freshwater-dominated brackish (4,100 to 3,100 cal BP), then eventually to freshwater (3,100 cal BP to A.D. 1960s). Since then, salinity has increased to brackish (A.D. 1960s to 1998) levels. This study aims to refine the evolution of the lake (Jaraula et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) by also reconstructing rainfall, redox conditions, and biological production in Western Lobe using additional element proxy and grain size records.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eCollection and sample preparation\u003c/p\u003e\n\u003cp\u003eA 10.5-meter-long sediment core was collected from the Western Lobe of Laguna de Bai in 1998. The collection and subsequent sample preparation and processing are described in Jaraula et al. (\u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). Briefly, the sediment core was collected using a push corer for the top three meters of sediments whereas a suction corer was used for the lower 7.5 meters of sediments. The sediment core sub-samples were first picked for bioclasts (\u003cem\u003ee.g.\u003c/em\u003e shells, twigs) to remove possible (i) shifts in the grain size distribution and (ii) spikes in the concentrations of the elements associated with these clasts. Afterwards, the sediment core was subsampled along its length generally at five-centimeter intervals for the push core and at four-centimeter intervals for the suction core. Due to limitations in size of the push corer and especially the suction corer, subsamples were allocated alternatingly for either grain size or major/trace element analysis so that the entire 10.5-meter length of the sediment core will still have both grain size and major/trace element profiles. Grain sizes were analyzed using a Fritsch Laser Particle Sizer A22 whereas major/trace element concentrations were measured using a Siemens 303AS X-ray fluorescence (XRF) unit. Both analyses were performed at the Geologisches Institut, Universit\u0026auml;t Bonn, Germany. Major element concentrations are reported as weight percent (wt%) whereas trace element concentrations are reported in parts per million (ppm).\u003c/p\u003e\n\u003cp\u003eStatistical analyses\u003c/p\u003e\n\u003cp\u003eThe geochemical proxies which will be used to reconstruct terrestrial input, redox conditions, and primary productivity, as well as to indicate recent pollution were derived from the major and trace element concentrations measured using XRF. A discussion on how each of these proxies operates can be found in the Geochemical proxies section of the Introduction.\u003c/p\u003e\n\u003cp\u003eGeochemical data processing, statistical analyses, and plotting were performed in the R environment (R Core Team, \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). Element/proxy record dis/similarities were determined \u003cem\u003evia\u003c/em\u003e Spearman correlation, using the corr.test function of the psych package (Revelle \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e), (i) to select for the terrigenous normalizer of the geochemical proxies and (ii) to determine the behavior of a proxy group (\u003cem\u003ee.g.\u003c/em\u003e salinity, biological production). Spearman correlation was chosen over Pearson correlation because not all of the records follow a normal distribution. The distribution of each record was tested for normality with the Shapiro-Wilk test using the shapiro.test function in R's native stats package.\u003c/p\u003e\n\u003cp\u003eThe elemental geochemical proxies used in this study were normalized to Ti, unless the proxy, such as Sr/Ba for salinity, is specifically defined. Al, an element associated with clay-sized sediments (Dinelli et al. \u003cspan class=\"CitationRef\"\u003e2007\u003c/span\u003e; Liu et al. \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e), is usually used as the normalizing element for siliciclastic matrices to correct for apparent enrichments of the other elements in the clay fraction. The sediments in Laguna de Bai's Western Lobe, however, are silt-dominated (Figure S11), and the major terrigenous element associated with silt is Ti (Liu et al. \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e), thus, Ti was selected to be the terrigenous normalizer for all proxies used in this study, except those which were specifically defined. Additionally, when the time series of Ti- and Al-normalized proxies were compared against the chemolithostratigraphic boundaries, the Ti-normalized proxies yielded clearer boundaries. Si\u003csub\u003ebio\u003c/sub\u003e, another specific proxy used to estimate past biological production, was calculated as\u003c/p\u003e\n\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\left(Si\\:/\\:Ti\\right)}_{bio}={Si}_{sample}-{\\:Ti}_{sample}{\\left(Si\\:/\\:Ti\\right)}_{baseline}\\)\u003c/span\u003e\u003c/span\u003e [1]\u003c/p\u003e\n\u003cp\u003ewhere the baseline watershed value of Si/Al is 2.96, which is an average of Southern Manila soil Si/Al value of (Tigue et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e) and rock Si/Al value of 3.1 from the Western Lobe watershed (SG Catane unpublished data), due to the current scarcity of published element baseline concentrations for the Western Lobe watershed. Chemical Index of Alteration (CIA; Nesbitt and Young, \u003cspan class=\"CitationRef\"\u003e1982\u003c/span\u003e), on the other hand, was calculated as:\u003c/p\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:CIA\\:=\\:\\frac{{Al}_{2}{O}_{3}}{{Al}_{2}{O}_{3}\\:+\\:CaO*\\:+\\:{Na}_{2}O\\:+\\:{K}_{2}O}\\times\\:100\\)\u003c/span\u003e \u003c/span\u003e [2]\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003ewhere Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Na\u003csub\u003e2\u003c/sub\u003eO, and K\u003csub\u003e2\u003c/sub\u003eO are their respective concentrations whereas CaO* is the silicate fraction of total CaO concentration. To our knowledge, there are currently no published data on the major element composition of Laguna de Bai's Western Lobe Watershed to determine CaO*; therefore, CaO* was estimated following McLennan (\u003cspan class=\"CitationRef\"\u003e1993\u003c/span\u003e). Some proxies, \u003cem\u003ee.g.\u003c/em\u003e proxy X, were expressed as enrichment factors (EF), which are calculated as\u003c/p\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{\\left(X\\:/\\:Ti\\right)}_{EF}={\\left(X\\:/\\:Ti\\right)}_{sample}{\\left(Ti\\:/\\:X\\right)}_{baseline}\\)\u003c/span\u003e \u003c/span\u003e [3]\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eThe baseline concentrations of elements for Laguna de Bai's Western Lobe were derived from their concentration medians from 3,100 calendar years before present (cal BP; Jaraula et al. \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e) to A.D. 1500, just before Spanish colonizers arrived in the Philippines in A.D. 1521. This time period was chosen because it is the most recent, minimally anthropogenically-impacted phase of the lake.\u003c/p\u003e\n\u003cp\u003eTo determine stratigraphic units in the record based on these geochemical proxies, Constrained Incremental Sum of Squares (CONISS; Grimm, \u003cspan class=\"CitationRef\"\u003e1965\u003c/span\u003e) hierarchical cluster analysis was performed on the Z-scores of Ti-normalized concentrations of As, Ba, C\u003csub\u003eorg\u003c/sub\u003e, Ca, Ce, Co, Cr, Cs, Cu, Fe, Ga, Gd, Hf, K, La, Mg, Mn, Mo, Na, Nb, Nd, Ni, P, Pb, Rb, S, Si, Sr, Th, U, V, W, Y, Zn, and Zr concentrations and (ii) grain size parameters (mean, median, and 95th percentile grain sizes, and grain size standard deviation). The Z-scores were calculated as\u003c/p\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{Z}_{i}=\\frac{{X}_{i}-\\mu\\:}{s.d.\\:\\left(X\\right)}\\)\u003c/span\u003e \u003c/span\u003e [4]\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:i\\)\u003c/span\u003e\u003c/span\u003e is a time interval in the geochemical record, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{X}_{i}\\)\u003c/span\u003e\u003c/span\u003e is the value of proxy \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:X\\)\u003c/span\u003e\u003c/span\u003e during \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:i\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mu\\:\\)\u003c/span\u003e\u003c/span\u003e is the mean value of proxy \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:X\\)\u003c/span\u003e\u003c/span\u003e, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:s.d.\\left(X\\right)\\)\u003c/span\u003e\u003c/span\u003e is the standard deviation of proxy \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:X\\)\u003c/span\u003e\u003c/span\u003e. CONISS was performed using the chclust function of R\u0026rsquo;s rioja package (Juggins \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). The dissimilarity parameter used between each pair of time intervals in the geochemical record was the Euclidean distance, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:d\\)\u003c/span\u003e\u003c/span\u003e, calculated as\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{d}_{ij}=\\sqrt{{\\sum\\:}_{k=1}^{l}{\\left({Z}_{i}-{Z}_{j}\\right)}_{k}^{2}}\\)\u003c/span\u003e\u003c/span\u003e [5]\u003c/p\u003e\n\u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:i\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:j\\)\u003c/span\u003e\u003c/span\u003e are two different time intervals in the geochemical record, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:l\\)\u003c/span\u003e\u003c/span\u003e is the total number of proxy records used in the CONISS analysis, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\left(Z\\right)}_{k}\\)\u003c/span\u003e\u003c/span\u003e are the Z-scores of the proxy record \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:k.\\)\u003c/span\u003e\u003c/span\u003e All available elements were used as parameters to avoid introducing biases by selecting only the proxies discussed in this study. Most, if not all, proxies respond to more than one environmental control, which is why multiple proxies per parameter are employed in reconstructing that parameter. By using all elements, unknown environmental controls could have a better chance of being represented in the CONISS clusters. The grain size parameters (mean, median, and 95th percentile grain size), on the other hand, are hypothesized to document physical process and mechanisms within the paleo-Laguna de Bai Western Lobe basin as the tectonic setting and climate, which translates to the energy available in the environment, would change the distribution of the sediments. The percentages of sand, silt, and clay were not included as they are already represented in the grain size distribution parameters.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eChemolithostratigraphic units\u003c/p\u003e \u003cp\u003eSix chemolithostratigraphic units from 4,590 to 6,510 cal BP were delineated in this study from CONISS hierarchical clustering and generally agree with the three units identified by Jaraula et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), Va, Vb, and Vc. Units delineated by Jaraula et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) which are based on salinity proxies, diatom and mollusc bioassemblage zones, but with the addition of transitional units Va.b and Vb.c, and Vc subdivided into Vc1 and Vc2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Additionally, boundaries have shifted a few centuries for this study recalibrated the \u003csup\u003e14\u003c/sup\u003eC ages of Jaraula et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) using a more recent radiocarbon calibration dataset (\u003cem\u003esee the Sediment core chronology section of the Supplementary Material\u003c/em\u003e). These chemolithostratigraphic units are characterized in terms of terrestrial input, redox conditions, and biological production in the following sections.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePeriods VI and VII were also identified from CONISS. However, because (i) each unit only has two data points for either element proxy or grain size measurements, (ii) both contain anomalous values, and (iii) these units are at the end of the record and not in between other units, little information can be derived out of these four data points. Therefore, they will not be discussed for this study.\u003c/p\u003e \u003cp\u003eTrends in proxy and grain size records\u003c/p\u003e \u003cp\u003eThe descriptive statistics per time period in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e2\u003c/span\u003e for the representative proxy/ies of each reconstructed parameter are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Periods VII and VI (6,640 to 6,590 and 6,590 to 6,510 cal BP) will only be discussed briefly because no trends can be reliably inferred from four data points. Additionally, a description on how each of the proxies in the following sections operates can be found in the Geochemical proxies section of the Introduction.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMean, standard deviation, range, and number of data points per chemolithostratigraphic unit of representative proxies for total terrestrial input, weathering/rainfall, salinity, redox, biological production, and grain size percentages %sand, %silt, and %clay\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePeriod\u003c/p\u003e \u003cp\u003e(cal BP)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTotal terr. input\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eWeathering / rainfall\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSalinity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRedox\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u0026deg; Production\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c10\" namest=\"c8\"\u003e \u003cp\u003eGrain size\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTi\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eZr/Al\u003c/p\u003e \u003cp\u003e(%/%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSr/Ba (ppm/ppm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMn/Ti\u003c/p\u003e \u003cp\u003e(%/%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003ebio. Si/Al\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eSand\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSilt\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eClay\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e\u003cb\u003eVc2\u003c/b\u003e\u003c/p\u003e \u003cp\u003e4,910 to 4,590\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003emean\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.441\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.213\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e6.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e92.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e5.46\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003es.d.\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0207\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.222\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.115\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.00465\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.175\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e4.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e1.53\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003erange\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.439 to 0.444\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.1 to 13.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.21 to 1.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.209 to 0.219\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5.87 to 6.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.360 to 7.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e83.8 to 95.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e4.14 to 8.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e\u003cb\u003eVc1\u003c/b\u003e\u003c/p\u003e \u003cp\u003e5,310 to 4,910\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003emean\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.414\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.216\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e7.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e94.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e4.12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003es.d.\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0144\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.357\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.195\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.00581\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.465\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.424\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.254\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003erange\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.391 to 0.427\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.0 to 14.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.62 to 2.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.210 to 0.225\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5.32 to 11.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.88 to 2.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e93.8 to 94.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e3.70 to 4.36\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e\u003cb\u003eVb.c\u003c/b\u003e\u003c/p\u003e \u003cp\u003e5,750 to 5,310\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003emean\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.427\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.206\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e88.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e8.29\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003es.d.\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0147\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.558\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.531\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.00468\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e4.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e3.07\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003erange\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.413 to 0.452\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.5 to 14.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.942 to 2.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.203 to 0.214\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3.88 to 7.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.67 to 6.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e82.8 to 93.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e5.57 to 13.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e\u003cb\u003eVb\u003c/b\u003e\u003c/p\u003e \u003cp\u003e6,070 to 5,750\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003emean\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.438\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.218\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e9.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e90.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e7.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003es.d.\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0102\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.272\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.0456\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.00364\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e1.96\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003erange\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.427 to 0.451\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15.5 to 16.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.40 to 1.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.213 to 0.222\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e7.86 to 10.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.48 to 4.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e86.1 to 93.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e5.70 to 9.64\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e\u003cb\u003eVa.b\u003c/b\u003e\u003c/p\u003e \u003cp\u003e6,260 to 6,070\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003emean\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.439\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.220\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e7.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e89.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e8.13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003es.d.\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0146\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.443\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.0489\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.00311\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.527\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.979\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003erange\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.414 to 0.453\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15.6 to 16.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.22 to 1.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.217 to 0.225\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5.07 to 9.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.67 to 3.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e87.8 to 91.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e6.85 to 9.65\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e\u003cb\u003eVa\u003c/b\u003e\u003c/p\u003e \u003cp\u003e6,510 to 6,260\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003emean\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.483\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.240\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e89.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e9.23\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003es.d.\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0211\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.459\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.0926\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.00156\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.851\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003erange\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.451 to 0.507\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15.3 to 16.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.971 to 1.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.237 to 0.242\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2.39 to 7.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.18 to 3.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e87.3 to 91.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e7.59 to 10.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eVI\u003c/b\u003e\u003c/p\u003e \u003cp\u003e6,590 to 6,510\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003evalue 1\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.457\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.204\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e19.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e35.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e74.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e5.37\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003evalue 2\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.379\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.450\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.201\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e11.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e21.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e60.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e2.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eVII\u003c/b\u003e\u003c/p\u003e \u003cp\u003e6,640 to 6,590\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003evalue 1\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.480\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e17.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.853\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.229\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e13.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e5.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e85.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e13.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003evalue 2\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.404\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e17.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.406\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.202\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e84.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e9.61\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTerrestrial input\u003c/p\u003e\n\u003ch3\u003eTotal terrestrial input\u003c/h3\u003e\n\u003cp\u003eFrom Period Va to Va.b, terrigenous elements Ti, and Fe all decreased (Figure S6). Al then increased from late Period Va.b to Period Vb.c, where its concentration plateaued during Period Vc1. Al concentration decreased in Period Vc1 and then increased in Period Vc2. Ti and Fe concentrations, on the other hand, remained relatively constant from late Period Va.b to Period Vc2.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eWeathering / rainfall\u003c/h3\u003e\n\u003cp\u003eDuring Period Va to early Va.b, Zr/Al was relatively constant, which then generally decreased during Period Vb, to lower values in Periods Vb.c to Vc2, with a brief increase in value but not reaching Va\u0026thinsp;+\u0026thinsp;Va.b levels during Period Vc1 (Figure S7).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSalinity\u003c/p\u003e \u003cp\u003eFrom early Period Va, Sr/Ba was constant (Figure S8). It generally began to increase in late Period Va until Vb.c, with a brief drop at around the Vb-Vb.c boundary. Sr/Ba values plateaued from late Vb.c to early Vc1, then decreased starting late Vc1 through Vc2.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eRedox\u003c/p\u003e \u003cp\u003eDuring Period Va, Mn/Ti was generally constant (Figure S9). Its value then sharply decreased at the Va\u0026ndash;Va.b boundary and continued to decrease until Period Vb. Mn/Ti values were lowest during Period Vb.c, which then increased during Periods Vc1 and Vc2 but were still lower then Period Va levels.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBiological production\u003c/p\u003e \u003cp\u003eBiogenic Si/Al was increasing in a fluctuating manner from a Period Va to early Vb (Figure S10). Its value then decreased at around the Vb-Vb.c boundary, and only increased slightly from late Vb.c. to early Vc1. It then maintained a fairly constant value from late Vc1 to Vc2, with a brief peak around the Vc1-Vc2 boundary.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eGrain size\u003c/p\u003e \u003cp\u003eThe percentage of sand during Periods Va was increasing, which then decreased from Va.b to Vb (Figure S11). From Period Vb.c until Vc2, %sand remained constant and at levels lower than those of Periods Va.b and Vb. These periods of relatively low %sand are punctuated by brief increases during early Period Vb.c and the end of Period Vc2.\u003c/p\u003e \u003cp\u003eThe percentage of silt was relatively constant from Period Va to early Vb.c. However, fluctuations in %silt were more pronounced during Periods Vb and early Vb.c relative to periods Va and Va.b. From early Period Vb.c, %silt increased until late Period Vb.c, and then plateaued from Period Vc1 to most of Vc2. By the end of Period Vc2, %silt dropped to a value lower than Period Va and Va.b means.\u003c/p\u003e \u003cp\u003eThe percentage of clay was generally decreasing during Period Va until Vb.c. This decreasing trend is punctuated by increases in %clay during Periods Vb and early Vb.c. From Period Vc1 to most of Vc2, %clay remained at their lowest levels in the record, which increased again only by the end of Period Vc2.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eProxy relationships\u003c/p\u003e \u003cp\u003eThe proxies used in this study were correlated using their entire 6,510 to 4,950 cal BP records rather than per chemolithostratigraphic unit for the data points per unit are often less than 10, and stronger correlations can be derived with more data points per record (\u003cem\u003esee Figures S3 to S5 for correlation matrices of the element proxies and grain size parameters used in this study\u003c/em\u003e). Terrigenous element proxies Ti, Al, and Fe correlate positively and strongly with each other (p\u0026thinsp;\u0026lt;\u0026thinsp;95%), which agrees with Lo et al. (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) where these elements remain in the residual fraction of rocks or sediments during chemical weathering.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the Southeast Asian region, rainfall is either abundant to provide ample water to support weathering or excessive to limit weathering by transporting clastics faster to depositional environments. Therefore, the Chemical Index of Alteration (CIA) could, for the former case, either increase with more rainfall, or, for the latter case, decrease with more rainfall. Additionally, terrigenous immobile element (\u003cem\u003ee.g.\u003c/em\u003e Al, Ti, Zr, Nb, Hf, Th) ratios may be used to measure the degree of weathering based on their relative immobility: Nb\u0026thinsp;\u0026asymp;\u0026thinsp;Th\u0026thinsp;\u0026gt;\u0026thinsp;Zr\u0026thinsp;\u0026asymp;\u0026thinsp;Hf\u0026thinsp;\u0026gt;\u0026thinsp;Ti\u0026thinsp;\u0026gt;\u0026thinsp;Al (Babechuk et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Jiang et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Lo et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Based on this order, it is hypothesized that under wetter climate when runoff energy is higher, less mobile terrigenous elements (LMTE) are also deposited in Laguna de Bai's Western Lobe basin along with the relatively more mobile terrigenous elements (MMTE), such that the LMTE/MMTE ratio increases. During drier climatic conditions when energy of runoff is lower, LMTEs are left in the watershed with respect to the MMTEs, and the LMTE/MMTE ratio decreases. Furthermore, K/Rb is another weathering proxy, values of which increase (decrease) with higher (lower) degrees of weathering. This is due to K and Rb able to replace each other in mineral lattices. However, Rb has a slightly ionic radius than K, which makes it easier to desorb from mineral lattices during weathering (Lo et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWeathering or rainfall proxies, Ti/Al, Zr/Al, Zr/Ti, Th/Al, Th/Ti, Th/Zr, Th/Hf, Nb/Al, Nb/Ti, (\u003cem\u003ei.e.\u003c/em\u003e LMTE/MMTE ratios) and K/Rb, all positively correlate with each other (p\u0026thinsp;\u0026lt;\u0026thinsp;5%; Figure S3), and these elements negatively correlate with other weathering proxies such as the CIA and Nb/Th (p\u0026thinsp;\u0026lt;\u0026thinsp;5%). Of these weathering/rainfall proxies, only Zr/Al correlates negatively with the salinity proxy Sr/Ba, which is why Zr/Al will be the representative proxy. The negative correlation between the LMTE/MMTE proxies and CIA suggests a supply-limited weathering regime where the abundance of rainfall in regions, such as that of Laguna de Bai's Western Lobe, limits the weathering time of the sediments because the transport time is decreased (Calabrese and Porporato \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The coherence of these proxies among their kind, as well as with others such as the salinity proxy Sr/Ba suggests that these proxies are viable weathering/rainfall proxies.\u003c/p\u003e \u003cp\u003eThe organic-carbon-to-sulfur (C\u003csub\u003eorg\u003c/sub\u003e/S or TOC/S) ratio is used to distinguish marine from freshwater deposits. Sulfate is abundant in marine systems whereas it is limited in freshwater ones. C\u003csub\u003eorg\u003c/sub\u003e/S values of 1.5 to 4 suggest normal marine conditions (Berner and Raisewell \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1984\u003c/span\u003e), whereas 4 to 11 suggest brackish conditions with marine influence (Wei and Algeo \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) compared to 11 to 17 brackish conditions with freshwater influence, and values\u0026thinsp;\u0026gt;\u0026thinsp;17 suggest freshwater conditions (Woolfe et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). For marine Laguna de Bai (6,640 to 4,700 cal BP). For marine Laguna de Bai (6,640 to 4,700 cal BP), the C\u003csub\u003eorg\u003c/sub\u003e/S proxy cannot resolve the salinity variability, which is why Jaraula et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) used additional proxies Ca/Al, Ca/Ti, Sr/Al, Sr/Ti, and Sr/Ba (Nelson \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1967\u003c/span\u003e) to differentiate the salinity phases within the marine period of Laguna de Bai's Western Lobe.\u003c/p\u003e \u003cp\u003eSalinity proxies Sr/Ba, Ca/Ti, and Sr/Ti positively correlate with each other (p\u0026thinsp;\u0026lt;\u0026thinsp;5%; Figure S3). Only Sr/Ba correlates with S/Ti, which is another salinity proxy. This can be expected, however, because S/Ti also carries a redox signal aside from a salinity signal. In fact, S/Ti correlates positively with TOC and TOC/Ti (p\u0026thinsp;\u0026lt;\u0026thinsp;5%) and negatively with Mn/Ti (p\u0026thinsp;\u0026lt;\u0026thinsp;5%), supporting its behavior more as a redox proxy rather than a salinity proxy. TOC/S, another salinity proxy, also does not correlate with Sr/Ba, Ca/Ti, nor Sr/Ti. Like S/Ti, TOC/S could vary more with TOC, and hence carry more of a biological production signal rather than a salinity signal. This could also be expected because in marine environments, the TOC/S salinity proxy can no longer resolve salinity variations. This is also why Jaraula et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) used Sr/Ba, Ca/Ti, and Sr/Ti alongside TOC/S. Likewise, the coherence of Sr/Ba, Ca/Ti, and Sr/Ti supports their function as salinity proxies.\u003c/p\u003e \u003cp\u003eThe enrichment of Mn/Ti in the sediments could indicate an oxic water column as dissolved Mn forms particulate Mn oxides which sink to the sediments. A reducing water column, on the other hand, redissolves these Mn oxides and decreases the concentrations of Mn in the sediments (Grybos et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Johnson et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Sulfur is abundant in seawater as water-soluble sulfate (SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e) and minimally accumulates in the sediments relative to accumulation under reducing water column conditions as sulfide (S\u003csup\u003e2\u0026minus;\u003c/sup\u003e), which accumulates in the sediments (Sharma et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). C\u003csub\u003eorg\u003c/sub\u003e:P also varies inversely with oxygenation (Algeo and Ingall \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) because during oxic conditions, P is deposited and preserved whereas C\u003csub\u003eorg\u003c/sub\u003e is oxidatively depleted. During anoxic conditions, on the other hand, C\u003csub\u003eorg\u003c/sub\u003e is preserved whereas P is released back to the water column (Algeo and Ingall \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Anderson et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Parsons et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRedox proxy Mn/Ti, which increases in value under more oxidizing conditions, correlates negatively with S/Ti, Mo/Ti, and C\u003csub\u003eorg\u003c/sub\u003e:P (p\u0026thinsp;\u0026lt;\u0026thinsp;5%; Figure S3), which increase in values under more reducing conditions. Additionally, S/Ti correlates positively with Mo/Ti and C\u003csub\u003eorg\u003c/sub\u003e:P (p\u0026thinsp;\u0026lt;\u0026thinsp;5%). These correlations support the sensitivities of these elements to redox processes. U/Ti, on the other hand, correlates only with Mo/Ti (positively, p\u0026thinsp;\u0026lt;\u0026thinsp;5%). This is to be expected because U, like Mo, is also enriched in the sediments overlain by reducing water columns. Even though U/Ti does not correlate significantly with Mn/Ti, S/Ti, nor C\u003csub\u003eorg\u003c/sub\u003e:P, its covariation with Mo/Ti would still be coherent with the interpretations from the other redox proxies. It is also important to note that Mn/Ti could also bear a weathering/rainfall signal, as it is also a major and a terrigenous element in Laguna de Bai's Western Lobe sediments, and it correlates positively with the weathering/rainfall signals (p\u0026thinsp;\u0026lt;\u0026thinsp;5%). Nevertheless, given Mn/Ti's coherence with the other redox proxies, the dominant signal Mn/Ti carries is redox.\u003c/p\u003e \u003cp\u003eC\u003csub\u003eorg\u003c/sub\u003e is a paleo-biological production proxy as it represents the remains of plants and organisms that lived or was brought to the Laguna de Bai's Western Lobe basin. C\u003csub\u003eorg\u003c/sub\u003e also participates as a reductant in water column redox reactions. Ba, in the form of barite (BaSO\u003csub\u003e4\u003c/sub\u003e), is also associated with C\u003csub\u003eorg\u003c/sub\u003e such as organic-rich aggregates and extracellular polymeric surfaces (Dymond et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1992\u003c/span\u003e; Martinez-Ruiz et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), and therefore can likewise be used as a biological production proxy. The C\u003csub\u003eorg\u003c/sub\u003e record of biological production is altered in oxic bottom waters, whereas the Ba record of biological production is destabilized in reducing bottom waters by reducing BaSO\u003csub\u003e4\u003c/sub\u003e into BaS. Nevertheless, BaS, and thus the paleo-biological production record, could still be determined by C\u003csub\u003eorg\u003c/sub\u003e under reducing conditions (Baldi et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). Both C\u003csub\u003eorg\u003c/sub\u003e and Ba are not specific to autochthonous or allochthonous contributions. Si\u003csub\u003ebio\u003c/sub\u003e, however, derived from total Si and Ti using Eq.\u0026nbsp;1, is specific to siliceous productivity and is assumed to primarily be from diatom frustules.\u003c/p\u003e \u003cp\u003eBiological production proxies TOC, TOC/Ti, Ba/Ti, and bioSi/Al do not correlate to significance with each other (p\u0026thinsp;\u0026gt;\u0026thinsp;5%; Figure S3), except for Ba/Ti and TOC, which correlate negatively (p\u0026thinsp;\u0026lt;\u0026thinsp;5%). This suggests that these elements are confounded by environmental controls other than biological production such as redox processes for TOC and Ba, hydrodynamic dispersal for all of the proxies, and taxa specificity for bioSi/Al. Because of this, discussions of biological production in the following sections will also include a discussion on the chemical and/or hydrodynamic preservation of these proxies in the sediment record.\u003c/p\u003e \u003cp\u003eFor the grain size parameter correlations (Figure S5), %sand correlates positively with the mean grain size, the standard deviation of grain sizes, and the 95th percentile grain size, and negatively with %silt (p\u0026thinsp;\u0026lt;\u0026thinsp;5%). On the other hand, %silt correlates positively with the median grain size (p\u0026thinsp;\u0026lt;\u0026thinsp;5%) and negatively with %clay and the 95th percentile grain size (p\u0026thinsp;\u0026lt;\u0026thinsp;5%). Additionally, %clay correlates negatively with the mean and median grain sizes, as well as the standard deviation (p\u0026thinsp;\u0026lt;\u0026thinsp;5%). These correlations suggest that sand, or the lack of it, is the main driver of grain size variability in Laguna de Bai Western Lobe's 6,510 to 4,950 cal BP sediment record. Sand variability is apparent during the Coastal Lagoon Period of Laguna de Bai's Western Lobe. With increasing restriction imposed on Laguna de Bai's Western Lobe basin by the rising Para\u0026ntilde;aque Land Strip since Period Vb.c silt became even more dominant in the sediment record, with variability introduced since then by clay.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePeriods VII, VI, and coastal sub-tidal lagoon period Va\u003c/p\u003e \u003cp\u003ePeriod Va is considered a coastal lagoon by Jaraula et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e3\u003c/span\u003e) based on the assemblage of molluscs \u003cem\u003eAnomalocardia\u003c/em\u003e sp., \u003cem\u003eLeptaxinus\u003c/em\u003e sp., and \u003cem\u003eTellina\u003c/em\u003e sp.; and the C\u003csub\u003eorg\u003c/sub\u003e/S value of \u0026lt;\u0026thinsp;4 (Berner and Raisewell \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1984\u003c/span\u003e). Based on Zr/Al, rainfall during this period was similar or slightly drier than historic times. At the start of Period Va, when Laguna de Bai's Western Lobe basin was around eleven meters deep based on the basin's sedimentation rates (Figure S2) and a paleo-sea level of one meter apmsl (Maeda et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), the paleo-lagoon waters were generally oxic as indicated by the mean C\u003csub\u003eorg\u003c/sub\u003e:P value of 44.6 (Algeo and Ingall \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Figure S9; Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). The C\u003csub\u003eorg\u003c/sub\u003e:P then increased to a mean of 87.9, a level considered suboxic (\u003cem\u003ei.e.\u003c/em\u003e 50\u0026thinsp;\u0026le;\u0026thinsp;C\u003csub\u003eorg\u003c/sub\u003e:P\u0026thinsp;\u0026le;\u0026thinsp;100; Algeo and Ingall \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e) during transition Period Va.b. These C\u003csub\u003eorg\u003c/sub\u003e:P values are consistent with the deoxygenation of the bottom waters identified from increasing Mo/Ti, which attained mean values of 26.8, higher than those of Va (mean\u0026thinsp;=\u0026thinsp;16.6; Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Sedimentary Mo enrichment/depletion is a fairly reliable proxy for this period as it responds more specifically to redox in non-sulfidic, reducing environments (Paul et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Furthermore, Mo-U covariation follows the enrichment/depletion pathway (Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e5\u003c/span\u003e) of unrestricted, vertically well-mixed water columns (Algeo and Tribovillard \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) where sedimentary U concentration varies inversely with oxygenation as U exists as soluble species in oxic water columns, but forms organic matter-U(VI) complexes (Trenfield et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) or precipitates as U(IV) in reducing water columns. Both processes operate mostly at the Fe(II)-Fe(III) redox boundary and sequester U in the sediments (Behrends and Van Cappellen \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Duan et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Liger et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Tsarev et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Likewise, Mo, as molybdates, is soluble in oxic water columns. Mo only begins to increase from average watershed concentrations when the water column become sulfidic where molybdates are converted into thiomolybdates in the presence of H\u003csub\u003e2\u003c/sub\u003eS (Hlohowskyj et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The thiomolybdates are then scavenged by organic matter (Dahl et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) or Fe-S phases and are deposited to the sediments (Vorlicek et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe decreasing oxygenation of Laguna de Bai's Western Lobe bottom waters during Periods Va.b and Vb may have resulted from an increase in siliceous and non-siliceous biological production and/or the increased trapping of organic matter from the watershed and from biological production in the water column due to the continual uplift of the Para\u0026ntilde;aque Land Strip. This is seen in the concurrent increases in bioSi/Al and C\u003csub\u003eorg\u003c/sub\u003e/Ti (or TOC/Ti; Figure S10). The concurrent increases in both bioSi/Al and %sand, however, could suggest that the apparent increase in siliceous organisms could be due to the addition of sand, to which Si is associated (Dinelli et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Liu et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Still, diatoms range from clay- to sand-sized particles, which would imply a lessened effect of sand addition from the watershed to the apparent increase in bioSi/Al. Furthermore, bioSi/Al, to some degree, takes into account the variability of terrestrial input (\u003cem\u003esee Eq.\u0026nbsp;1\u003c/em\u003e), which could further dampen the effect of sand addition from the watershed to the biogenic silica record. In addition, the watershed of Laguna de Bai's Western Lobe is more mafic (Defant et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1991\u003c/span\u003e) relative to some silicic areas in Laguna de Bai's Southern Lobe watershed (Vogel et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Therefore, it is less likely that the concurrent increases in bioSi/Al and %sand is due to terrigenous sand adding to the biogenic silica record. The proportions of siliceous and non-siliceous contributions to the TOC, also, could not be determined with the current dataset due to the oxic to suboxic conditions of Laguna de Bai's Western Lobe during this time which limits C\u003csub\u003eorg\u003c/sub\u003e preservation. The increasing %sand relative to the succeeding periods is also consistent with the relatively less restricted Western Lobe basin during this time, as well as the natural shallowing of the lagoon due to sediment filling the basin.\u003c/p\u003e \u003cp\u003eTransition periods Va.b, Vb, and Vb\u003c/p\u003e \u003cp\u003eThe assemblage of molluscs during these periods (6,260 to 5,750 cal BP), \u003cem\u003ePeronidia venulosa\u003c/em\u003e, \u003cem\u003eAnomalocardia squamosa\u003c/em\u003e, \u003cem\u003eA. scabra\u003c/em\u003e, \u003cem\u003eOstrea\u003c/em\u003e sp., \u003cem\u003eRissoina\u003c/em\u003e sp., \u003cem\u003eTellina\u003c/em\u003e sp., \u003cem\u003eLeptomya\u003c/em\u003e sp., and \u003cem\u003eTurrid\u003c/em\u003e sp., suggests that Laguna de Bai's Western Lobe was shallowing (Jaraula et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The increasing Western Lobe salinity from late Period Va towards hypersaline conditions in the late Period Vb.c and early Vc1 could be due to the increasing water column stratification from increasing basin restriction imposed by the continually uplifting Para\u0026ntilde;aque Land Strip from late Period Va to early Period Va.b. This is supported by the abrupt decrease in Mn/Ti at the start of Period Va.b, suggesting that bottom water oxygen exchange with the atmosphere is increasingly limited. Since the late Period Va.b, the decreasing rainfall strengthened this water column stratification.\u003c/p\u003e \u003cp\u003eConsidering that biological production proxies C\u003csub\u003eorg\u003c/sub\u003e, C\u003csub\u003eorg\u003c/sub\u003e/Ti, and bioSi/Al all increased during this period of higher-than-usual-marine salinity (\u003cem\u003ei.e.\u003c/em\u003e hypersaline), the following are hypothesized: (i) planktonic primary producers, including the siliceous majority, could tolerate this salinity regime; (ii) the rising Para\u0026ntilde;aque Land Strip prevents the particulate C\u003csub\u003eorg\u003c/sub\u003e and biogenic Si particles from being dispersed out of the Laguna de Bai's Western Lobe basin and the increasingly reducing conditions during this period preserved the C\u003csub\u003eorg\u003c/sub\u003e rain in the sediments; and (iii) increasing salinity also increases the flocculation of dissolved and suspended matter to the sediments, consequently increasing light penetration into the water column. The first hypothesis is possible due to the occurrence of bivalves and gastropods even during the hypersaline periods Vc1 and Vc2 (Jaraula et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). However, as a hypersaline watermass develops on the surface, its density also increases which would cause it to sink and join the bottom water. Unless the hypersaline watermass had already become pervasive in Laguna de Bai's Western Lobe basin, they are likely confined to the bottom water, and it is likely that the salinity proxies used in this study reflect bottom water salinities and leave the surface waters still less saline than the bottom waters. In the second hypothesis, Para\u0026ntilde;aque Land Strip could indeed play a role in the preservation of particulate C\u003csub\u003eorg\u003c/sub\u003e and biogenic Si, but it would not be able to explain the drop in biological production in the early Vb.c period, when sea level briefly overtopped the rising Para\u0026ntilde;aque Land Strip. The third hypothesis could be the case in Period Vb.c, as this was also observed by Santiago (1991), but in the brackish salinity regime of Laguna de Bai's Western Lobe in the A.D. 1980s. The decreasing %sand and increasing %silt suggests a decrease in the hydrodrynamic energy in the Western Lobe as the rising Para\u0026ntilde;aque Land Strip limits the fetch distance for surface waves coming from Manila Bay, which is longer than the fetch distance from Laguna de Bai's Southern Lobe. The decreasing %clay, on the other hand, could be due to the shallowing of the Western Lobe. These grain size characters also persisted over Periods Vb.c until Vc2.\u003c/p\u003e \u003cp\u003eHypersaline intertidal lagoon periods Vb.c, Vc1, and Vc2\u003c/p\u003e \u003cp\u003eThis period was interpreted by Jaraula et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) as an intertidal lagoon (Fig.\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e4\u003c/span\u003e) based on mollusc assemblages of \u003cem\u003eThiara granifera\u003c/em\u003e, \u003cem\u003eCycladicama tsuchii\u003c/em\u003e, \u003cem\u003eAtactodea striata\u003c/em\u003e, \u003cem\u003eTurrid\u003c/em\u003e sp., and \u003cem\u003eCassis\u003c/em\u003e sp. The continual tectonic uplift of the Para\u0026ntilde;aque Land Strip should have allowed fresh water from the watershed to accumulate in the basin. However, the drier climate in the Western Tropical Pacific from 5,500 to 2,600 cal BP relative to the previous periods from 6,510 to 5,500 cal BP, as documented by the chemical weathering proxies, with higher CIA, lower LMTE/MMTE and K/Rb ratios relative to Period Va, could be due to the millennial-scale migrations of the mean ITCZ position (Sachs et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Yokoyama et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) as well as lower El Ni\u0026ntilde;o/Southern Oscillation activity (Chen et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; McGregor and Gagan \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Stevenson et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). This drier climate coupled with saltwater incursions due to the two-meter sea level stillstand apmsl, provided the conditions to raise Laguna de Bai's Western Lobe basin salinity eventually to peak hypersaline levels by late Period Vb.c which was sustained until early Vc1.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe invariant behavior of Mo relative to U from Period late Vb.c to Vc2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e5\u003c/span\u003e) suggests a stratified water column with reducing and possibly sulfidic bottom waters where the O\u003csub\u003e2\u003c/sub\u003e-H\u003csub\u003e2\u003c/sub\u003eS chemocline is above the sediment-water interface and there are inadequate phases delivering and resupplying the bottom waters with Mo. The remaining bottom water Mo is scavenged at the sediment-water interface to depletion whereas U is reduced a-/biotically in ferruginous (Behrends and Van Cappellen \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Duan et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) and sulfidic (Hyun et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) zones. Likewise, S/Ti maintained levels higher than those of Period Va. This could be expected because late Periods late Vb.c to early Vc1 are the periods of peak hypersalinity. Additionally, the C\u003csub\u003eorg\u003c/sub\u003e:P molar ratio could be affected during this time by the hypersaline conditions, which concentrate P in the sediments (Figures S9 and S10). This would then lead to apparent oxygenation trends in C\u003csub\u003eorg\u003c/sub\u003e:P since C\u003csub\u003eorg\u003c/sub\u003e is fairly constant. This is why for the hypersaline period late Vb.c to early Vc1, the C\u003csub\u003eorg\u003c/sub\u003e:P redox proxy could be ineffective.\u003c/p\u003e \u003cp\u003eC\u003csub\u003eorg\u003c/sub\u003e could be the most reliable biological production proxy for these periods due to its ideal preservation in the sediments deposited under reducing conditions, possibly even sulfidic because of the stable stratification during the hypersaline phase. This could explain the higher mean C\u003csub\u003eorg\u003c/sub\u003e concentrations in the sediments deposited during Periods Vc1 and Vc2 than those deposited during Period Va. On the other hand, the preservation of the Ba record could have been destabilized due to reducing bottom waters converting barite (BaSO\u003csub\u003e4\u003c/sub\u003e) into unstable BaS (Baldi et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1996\u003c/span\u003e), consequently resulting into lower mean Ba concentrations during Periods Vc1 and Vc2 relative to Period Va (Figure S10).\u003c/p\u003e \u003cp\u003eThe slight increase in Zr/Al in Period Vc1 and the further emergence of the Para\u0026ntilde;aque Land Strip could have increased the freshwater budget and decreased the saltwater incursions into the Western Lobe, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Since then, the hypersaline bottom waters of Laguna de Bai's Western Lobe waned in pulses from late Vc1 to Vc2 (Figure S8). S/Ti maintained elevated values until Period Vc2, which was when hypersalinity was already declining. This could suggest that, during Period Vc2, S/Ti carried a redox signal, and from the covariation of Mo and U, bottom waters had reducing conditions even when hypersalinity was already waning (Figure S9).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eConsidering that the Philippines is at the center of Asian and Pacific climate phenomena, this study is one of only a handful of paleoclimate reconstructions from Philippine natural archives. Furthermore, this study, to our knowledge, would be the first to integrate the dynamics of climate, tectonics, sea level, with basin salinity, redox conditions, and primary production at centennial time scales over 1,900 years in the mid-Holocene. This reconstructed dynamics could be applied to predict the possible conditions of embayments and coastal lakes in the future, where wetter climate (Mandapaka and Lo \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and higher sea levels (Kahana et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) forecasted by the end of the 21st century. Additionally, organic geochemical proxies in future studies in tandem with the current element geochemical proxies could further validate and refine the current reconstruction.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe would like to thank the following for funding this study: Office of the Vice-Chancellor for Research and Development, University of the Philippines Diliman [grant number 00007NSET]. This study was also an offshoot of a project, under the supervision of Dr. Fernando Siringan, funded by the Laguna Lake Development Authority.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe are grateful for Dr. Kasuo Maeda who provided the sediment corer; Mr. Zenon Mateo and Mr. Neil John Macalalad who helped in collecting the sediment core; Dr. Jean Thein of the Geologisches Institut, Universität Bonn, who generously arranged for the use of their geochemical and sedimentological laboratories; Dr. Ralf Klingel, Erika Ochterbek, and Waltraud Strauss for providing technical support during the sample processing.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAlgeo TJ, Ingall E (2007) Sedimentary C\u003csub\u003eorg\u003c/sub\u003e:P ratios, paleocean ventilation, and Phanerozoic atmospheric pO\u003csub\u003e2\u003c/sub\u003e. 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Geophys Res Lett 38: L00F03\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-paleolimnology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jopl","sideBox":"Learn more about [Journal of Paleolimnology](http://link.springer.com/journal/10933)","snPcode":"10933","submissionUrl":"https://submission.nature.com/new-submission/10933/3","title":"Journal of Paleolimnology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Coastal lagoon, Anoxia, Hypersalinity, Sea level high stillstand, Mid-Holocene dry period","lastPublishedDoi":"10.21203/rs.3.rs-6897953/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6897953/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAt the forefront of Asian and Pacific climate phenomena, Laguna de Bai in the Philippines could fill knowledge gaps in tropical Western Pacific paleoenvironmental records and help to forecast possible scenarios for semi-enclosed coastal water bodies under the predicted warmer and wetter climate with sea level rise by the end of the 21st century. Using geochemical proxy and grain size records along a sediment core, we describe three major marine phases from 6,510 to 4,590 years ago, when Laguna de Bai's Western Lobe was part of Manila Bay that slowly separated due to the tectonic uplift of the Parañaque Land Strip and interaction with sea level changes during the Holocene. Compared to present-day conditions, the slightly drier Coastal Sub-Tidal Lagoon Phase (6,510 to 6,260 cal BP) had usual marine salinity, oxic bottom waters, and only a partially preserved biological production record, with rainfall similar to that of the early 20th century. The episodic uplift of Parañaque Land Strip and drying climate transformed the Western Lobe into a Shallower Coastal Lagoon (6,260 to 5,310 cal BP) with higher bottom water salinity, suboxic bottom waters, and better preservation of biological production, under an increasingly drier climate. Further uplift of the Parañaque Land Strip restricted Laguna de Bai's Western Lobe even more and commenced the Intertidal Lagoon Phase (5,310 to 4,590 cal BP) with hypersaline, anoxic bottom waters, and well-preserved biological production record, all of which during the mid-Holocene dry period in the Western Pacific.\u003c/p\u003e","manuscriptTitle":"Geochemical proxy records to reconstruct terrestrial input, redox conditions, and biological production in a tropical paleo-lagoon during the mid-Holocene","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-30 08:46:24","doi":"10.21203/rs.3.rs-6897953/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-11-04T16:14:09+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-17T14:14:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"319289995829211532316841127855843860360","date":"2025-06-26T01:06:27+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-25T14:37:15+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-24T05:00:02+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-24T04:59:16+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Paleolimnology","date":"2025-06-15T11:00:00+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-paleolimnology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jopl","sideBox":"Learn more about [Journal of Paleolimnology](http://link.springer.com/journal/10933)","snPcode":"10933","submissionUrl":"https://submission.nature.com/new-submission/10933/3","title":"Journal of Paleolimnology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"32138486-01cd-4590-83ef-5a37382a670a","owner":[],"postedDate":"June 30th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2026-01-14T14:24:27+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-30 08:46:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6897953","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6897953","identity":"rs-6897953","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}