Iceberg-Induced Collapse of Access Connectivity and a Dramatic Reduction in Chick Survival at the Coulman Island Emperor Penguin Colony

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This study examines a ~ 69% decline in springtime chick counts at Coulman Island in 2025, based on integrated multi-satellite analyses and field surveys. A giant iceberg calved from the Nansen Ice Shelf became grounded in late July along a narrow coastal margin, obstructing the colony's primary access corridor prior to chick rearing. Three-dimensional iceberg reconstruction reveals pronounced morphological asymmetry functioning as a "geometric trap": gentler ocean-facing slopes encouraged adults to ascend, while the colony-facing margin presented a sub-vertical escarpment exceeding 20 m, funneling penguins into impassable culs-de-sac. The semi-enclosed geography of Coulman Island further obscured a residual ~ 1 km passage, preventing effective detours. Very-high-resolution imagery and field observations confirmed near-total absence of guano staining and extensive chick mortality. These findings provide compelling evidence for a "functional collapse of accessibility," wherein iceberg morphology and regional topography synergistically severed the colony's energetic connectivity. As climate change increases ice-shelf instability and iceberg discharge, stochastic physical barriers may increasingly rival gradual sea-ice decline in determining emperor penguin breeding outcomes. Earth and environmental sciences/Environmental sciences/Environmental impact Earth and environmental sciences/Ecology/Ecosystem ecology Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction The Earth system is undergoing rapid change driven by anthropogenic forcing, with mounting evidence that these changes are intensifying environmental pressures on polar ecosystems (Constable et al., 2022 ; Meredith et al., 2019 ; Ranasinghe et al., 2021 ). In Antarctica, recent decades have been marked by documented atmospheric warming (Wang et al., 2025 ), declines in sea-ice extent and thickness (Bocquet et al., 2024 ; Fretwell et al., 2023 ), and an increased frequency of extreme weather events (Siegert et al., 2023 ). Collectively, these environmental shifts are associated with changes in ecosystem structure and have been linked to variation in survival and reproductive performance across Antarctic species (Fretwell et al., 2023 ; Jenouvrier et al., 2021 ; Larsen et al., 2015 ; Trathan et al., 2020 ; Vaughan et al., 2014 ). Among Antarctic marine predators, the emperor penguin ( Aptenodytes forsteri ) has been described as a sentinel species, reflecting broader changes within the Southern Ocean ecosystem (LaRue et al., 2014 ). Its life history is closely linked to the availability of stable sea ice, which supports key stages of its annual cycle, including breeding, incubation, chick rearing, and moulting (Forcada & Trathan, 2009 ; Fretwell et al., 2023 ; Kooyman & Ponganis, 2014 ; Schmidt & Ballard, 2020 ; Trathan et al., 2020 ; Wienecke, 2010 ). Consequently, alterations in sea-ice conditions may increase the risk of reduced breeding performance and could influence long-term population trajectories (Ainley et al., 2010 ; Barbraud & Weimerskirch, 2001 ; Jenouvrier et al., 2009 ; Jenouvrier et al., 2012 ; Jenouvrier et al., 2014 ; Schmidt & Ballard, 2020 ). Given this ecological dependence, emperor penguins have become a focal species for investigating the biological consequences of sea-ice variability and ongoing environmental change in Antarctica (Ainley et al., 2010 ; Jenouvrier et al., 2009 ; LaRue et al., 2014 ). Emperor penguins depend on stable landfast sea ice for breeding, and reproductive success may be compromised when sea ice forms late in the season or breaks up before chicks fledge (Jenouvrier et al., 2021 ; Trathan et al., 2020 ). Because the sea-ice zone supports key foraging activities for this species, reductions in sea ice may influence long-term population viability by constraining access to prey resources (Trathan et al., 2024 ). In addition to recent changes in sea-ice conditions, large iceberg calving events along parts of the Antarctic coastline have been associated with increased cryospheric variability (Liu et al., 2015 ). Such physical disturbances can generate short-term, site-specific ecological impacts by obstructing access to breeding habitats or altering local environmental conditions that support reproductive success, including for apex predators such as emperor penguins. In the context of these cumulative pressures, emperor penguins are currently classified as Near Threatened on the IUCN Red List (Jenouvrier et al., 2021 ; Trathan et al., 2020 ). A reassessment is underway, and recent evaluations have considered the possibility of uplisting the species to Endangered status (C. Brooks, pers. comm., 2026). In response, parties to the Antarctic Treaty System, including those operating under the Protocol on Environmental Protection and the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR), have discussed or implemented management measures intended to reduce additional stressors that may compound the effects of climate change on emperor penguin populations (Berkman et al., 2011 ; Trathan et al., 2020 ). In 2016, the Ross Sea region was designated as a Marine Protected Area (MPA) by CCAMLR under Conservation Measure 91 − 05, partly to conserve key foraging habitats used by emperor penguins within the Ross Sea ecosystem. The MPA encompasses several major emperor penguin breeding sites, including Cape Roget, Coulman Island, Cape Washington, Beaufort Island, Cape Crozier, and Cape Colbeck (Kooyman & Ponganis, 2017 ). Among these sites, Coulman Island (73°28′ S, 169°45′ E), located along the North Victoria Land coast, has been reported as one of the largest emperor penguin colonies globally (Kooyman & Ponganis, 2017 ). Its large colony size has been attributed to favourable regional oceanographic conditions, including high marine productivity and the persistence of stable landfast sea ice between Cape Jones and Coulman Island (Fig. 1 ; Kooyman et al., 2007 ; Kooyman & Kooyman, 1995 ; Kooyman & Ponganis, 2014 ; Kooyman & Ponganis, 2017 ). Owing to its size and geographic setting, the Coulman Island colony represents an important site for ecological research and long-term monitoring, offering insights into population dynamics and linkages with adjacent marine ecosystems, including coastal polynyas and associated food-web processes (Massom et al., 1998 ; Massom et al., 2009 ; Trathan et al., 2020 ). Moreover, Coulman Island functions as a natural laboratory in which the vulnerability and adaptive capacity of a large emperor penguin population can be examined under increasing environmental stochasticity in the Antarctic sea-ice system. Research on emperor penguins has traditionally explained breeding success and population variability primarily using metrics of sea-ice extent, formation timing, and stability (Barbraud & Weimerskirch, 2001 ; Fretwell et al., 2023 ; Jenouvrier et al., 2014 ; Schmidt & Ballard, 2020 ). However, this sea-ice-centred framework does not fully account for documented instances of reduced breeding performance that have occurred under apparently stable sea-ice conditions (Barbraud & Weimerskirch, 2001 ; Kooyman & Ponganis, 2014 ). In recent decades, additional habitat disturbances, either indirectly linked to sea ice or not readily explained by sea-ice variability alone, have occurred episodically. These include ice-shelf calving events and the grounding of large icebergs. The frequency of such cryospheric disturbances has been projected to increase in some regions under continued climate change (Etourneau et al., 2019 ; Joughin & Alley, 2011 ). A well-documented example occurred in 2001 near Cape Crozier in the Ross Sea, where the grounding of giant icebergs (B15A and C16) disrupted a long-established breeding habitat and resulted in the near-total loss of breeding output in the local emperor penguin population (Kooyman et al., 2007 ). In subsequent years, chick production declined to 0–40% of pre-2000 levels, suggesting that iceberg presence caused persistent physical modification of the habitat beyond sea-ice stability alone and affected multiple stages of the breeding cycle (Kooyman et al., 2007 ; Schmidt & Ballard, 2020 ). Notably, impacts of large icebergs on penguin habitats have also been documented outside the immediate breeding period. For example, the collision of a massive iceberg with the Mertz Glacier Tongue removed coastal and fast-ice habitat when breeding birds were absent, leading to delayed ecological consequences for nearby penguin colonies (Ancel et al., 2014 ). Icebergs may impede movement by obstructing access routes between breeding sites, foraging areas, and overwintering habitats. At Beaufort Island, for example, grounded icebergs formed a persistent physical barrier of approximately 150 km between the Ross Sea polynya and the island, constraining access to both feeding and breeding areas (Kooyman et al., 2007 ; Kooyman et al., 2000 ). These conditions were associated with marked declines in breeding pair numbers, elevated chick mortality, and, in some cases, colony abandonment or relocation (Kooyman et al., 2007 ; Kooyman & Ponganis, 2014 ). Collectively, these cases underscore the limitations of sea-ice stability–centred interpretations. They indicate that colony-scale population outcomes can be influenced by the combined effects of multiple, interacting physical and ecological disturbances, rather than solely by sea-ice variability alone. We report on field surveys conducted in mid-November 2025 in the vicinity of Coulman Island, which documented unusually low chick counts relative to recent breeding seasons. When considered alongside contemporaneous satellite imagery, these observations suggest that a primary access corridor linking the marine area between Cape Jones and Coulman Island to the breeding site was obstructed by a large grounded iceberg at the time of the survey. This reduction in accessibility coincided with low chick counts recorded during that season, indicating a temporal association between iceberg-induced obstruction and reduced chick survival. Nevertheless, this study is explicitly framed as an observational case study focused on a single breeding season and does not seek to establish definitive causality between iceberg grounding and reduced chick survival. Instead, our aim is to examine plausible mechanisms through which iceberg-driven disruptions to accessibility may affect emperor penguin breeding processes and to present initial observational evidence of the role that such access constraints may have played in the reduced chick survival observed at Coulman Island. Specifically, we ask whether iceberg grounding can generate short-term accessibility constraints sufficient to affect colony-scale breeding outcomes, even under otherwise stable sea-ice conditions. By integrating field observations with satellite imagery, we assess the spatial configuration and timing of iceberg obstruction relative to observed breeding output. Results Grounded Iceberg Configuration and Observed Breeding Conditions in November 2025. During the annual survey to census emperor penguin chicks at Coulman Island on 12 November 2025 (see Methods), a vertical ice wall estimated to be several tens of metres high was observed approximately 3–5 km north of the colony (Fig. 2 a). Contemporaneous medium-resolution satellite imagery (Landsat) confirmed the presence of a grounded iceberg measuring approximately 15 km in length and 5 km in width (Fig. 2 b). The iceberg was located along a commonly used commuting route between the breeding site and offshore foraging areas, which extend northward and northeastward from the colony (Fig. 1 b). This commuting route was identified through repeated annual field observations of colony movements. Field observations documented adult emperor penguins congregating along the southern margin of the iceberg, where the vertical ice wall extended continuously. During the observation period, no individuals were recorded traversing the cliff or moving southward toward the breeding site. Analysis of Landsat imagery acquired on 1 November 2025 indicated that the iceberg covered an area of approximately 35.86 km². The eastern margin of the iceberg was in direct contact with the edge of long-established landfast ice, forming a continuous ice boundary during the sea-ice season. Repeated satellite observations and in situ surveys showed that the iceberg remained grounded at the same location throughout winter and into early spring. Very-high-resolution Maxar WorldView imagery shows a clear difference in the spatial extent of surface biological indicators (i.e., guano stains) at the breeding site between November 2024 and November 2025, while landfast ice conditions appeared broadly similar during the two periods. In the November 2024 image (Fig. 2 c), extensive and well-defined guano staining was distributed across the landfast ice. In contrast, imagery acquired on 6 November 2025 (Fig. 2 d) shows that guano traces, aggregation patterns, and nesting-related surface features at the same location were largely absent. The contrast in surface biological indicators between the two years occurred under broadly comparable fast-ice conditions, based on visual assessment of satellite imagery. Even when accounting for potential differences in snow cover between the two observation periods, the contrast in surface biological indicators remained evident in both satellite imagery and direct field observations. Calving and Drift–Grounding Chronology of the Nansen Ice Shelf Iceberg. The calving event and subsequent drift–grounding sequence of the iceberg toward the northern margin of Coulman Island were reconstructed through multi-sensor image analysis, integrating MODIS True Color imagery and Sentinel-1 synthetic aperture radar (SAR) time series. Back-tracking analysis shows that the iceberg originated from the Nansen Ice Shelf in Terra Nova Bay. The calving event was identified as occurring on 12 March 2025, with MODIS imagery providing the only direct visual record of the breakup (Fig. 3 ). Imagery acquired on 10 and 11 March 2025 shows a contiguous ice-shelf front with no visible evidence of structural separation (Figs. 3 a, b). In contrast, the image from 12 March (Fig. 3 c) reveals a distinct linear fracture at the ice-shelf front, representing a structural discontinuity consistent with calving. Although extensive cloud cover limited direct delineation of the newly separated iceberg in this scene, in clearer patches areas of thinner cloud display a dark-toned signature at the shelf front. This spectral signature is comparable to surrounding open-ocean surfaces. The subsequent MODIS image from 13 March (Fig. 3 d) clearly shows the iceberg as an independent body, consistent with separation occurring on 12 March 2025. Post-calving movement of the iceberg was tracked stepwise through visual interpretation of a Sentinel-1 SAR time series (Fig. 4 ). Imagery from 7 March shows the pre-calving configuration, with the iceberg still contiguous with the Nansen Ice Shelf front (Fig. 4 a). Following detachment, the iceberg migrated rapidly northeastward, reaching waters near Cape Washington by 19 March (Fig. 4 b). The iceberg then continued northward, approaching to within approximately 40 km south of Coulman Island (Fig. 4 c), and by 16 June was observed in close proximity to the island’s southern coastline (Fig. 4 d). Thereafter, the iceberg progressed northward along the island’s eastern flank (Fig. 4 e), following a trajectory consistent with the spatial distribution of surrounding consolidated pack ice. Imagery from 16 July shows that the western terminus of the iceberg became increasingly constrained by surrounding sea ice near Coulman Island (Fig. 4 f). During this period, the iceberg exhibited the onset of counter-clockwise rotation. Subsequent scenes show continued rotation accompanied by a reduction in translational motion (Fig. 4 g). By 28 July, the iceberg appears to have become topographically anchored or grounded at its observed position adjacent to Coulman Island (Fig. 4 h). The most recent SAR image acquired on 13 November 2025 (Fig. 4 i) shows no discernible change in iceberg position or orientation relative to late July. This observation is consistent with the iceberg remaining stationary for several months following grounding in late July 2025. Long-term Chick Census at the Coulman Island Colony. Figure 5 presents a long-term census of emperor penguin chicks at Coulman Island spanning 1983 to 2025. The time series comprises data from 21 breeding seasons, integrating historical records reported by Barber-Meyer et al. ( 2008 ) and Kooyman and Ponganis ( 2017 ) with standardised aerial survey monitoring conducted since 2017 by the Korea Polar Research Institute (KOPRI) (see Methods). Across the full observation period, chick abundance at the Coulman Island colony shows substantial interannual variability over multiple decades. Among observations prior to 2000, the highest recorded chick count was 34,735 individuals in 1992, followed by 27,920 in 1990 and 21,708 in 1983. The mean chick abundance between 1983 and 2000 was 24,667 ± 6,622 individuals. Literature-based records from the period after 2000 and prior to the initiation of KOPRI surveys also show substantial interannual variability. During this interval, chick counts of 25,244 individuals were reported in 2012 and 22,511 individuals in 2008. The mean for the post-2000 pre-KOPRI period was 18,305 ± 5,651 individuals, lower than the 1983–2000 mean. This period included several years with low chick counts, including 9,305 individuals in 2010 and 12,382 individuals in 2011 (Kooyman & Ponganis, 2017 ). Since 2017, aerial photograph–based surveys conducted by the Korea Polar Research Institute (KOPRI) have provided a standardised time series of chick counts at Coulman Island. During this period, recorded chick numbers were 16,571 in 2017, 21,286 in 2018, 24,464 in 2019, 23,223 in 2021, 22,903 in 2022, 18,723 in 2023, and 21,242 in 2024, yielding a mean of 21,202 ± 2,745 individuals. In contrast, the 2025 chick count represents the lowest value recorded since 1983 and falls below the range documented during the KOPRI monitoring period. During the November survey, 6,081 chicks were counted. A subsequent December survey identified additional small breeding sub-groups, increasing the final total to 6,658 individuals (see Methods). The 2025 total corresponds to an approximate 69% reduction relative to both the KOPRI-era mean (21,202 individuals) and the 2024 count (21,242 individuals). The proportional decline in 2025 exceeds that reported for 2010, when chick production was estimated at 56% of the 2006 minimum and 41% of the 2008 estimate (Kooyman & Ponganis, 2014 ). The total number of adults counted in 2025 was 15,242, yielding a chick-to-adult ratio of approximately 0.44, which is slightly below the lower bound of the previously reported range (0.46–0.99) for the Coulman Island colony (Kooyman & Ponganis, 2017 ). Discussion Accessibility Collapse and Its Potential Role in Reduced Chick Survival. We describe this phenomenon as an accessibility collapse, in which breeding and foraging habitats remain physically present, but functional connectivity between them is disrupted by transient physical barriers. The 2025 event at Coulman Island is consistent with the possibility that, even under relatively stable landfast sea-ice conditions, the grounding of a single large iceberg may substantially constrain functional access between breeding and foraging habitats and be associated with reduced chick survival. Notably the timing of iceberg immobilisation coincided with the transition from incubation to early chick rearing, a period recognised as particularly sensitive to changes in habitat accessibility and environmental conditions (e.g., Fretwell et al., 2023 ; Jenouvrier et al., 2009 ; Trathan et al., 2020 ). During this phase, successful parental coordination and food provisioning depend on reliable access between the breeding site and adjacent marine habitat (Sara Labrousse et al., 2021 ; Winterl et al., 2024 ). Disruption during this stage may represent a plausible mechanistic pathway linking altered habitat accessibility to reduced chick survival. Field observations in November 2025 documented an approximately 20 m high vertical ice wall immediately north of the Coulman Island colony, forming a continuous physical barrier between the breeding site and offshore foraging areas (Fig. 1 ). Very-high-resolution optical imagery further showed a marked reduction in guano staining and aggregation signatures at the breeding site in 2025 compared with 2024 (Figs. 2 c, d). Guano accumulation detected in satellite imagery has been widely used as a proxy for colony presence and breeding activity in emperor penguins (Fretwell et al., 2012; LaRue et al., 2014 ). Although surface appearance may also be influenced by snowfall or local snow redistribution, the near absence of staining patterns, together with direct field observations at the colony, is consistent with substantially reduced breeding output during the 2025 season. These remote-sensing indicators coincide temporally with an approximately 69% reduction in chick numbers, recorded during two spring surveys in 2025 using the same census protocols applied in previous years (Fig. 5 ), supporting the interpretation of a marked reduction in breeding output relative to recent observations. The scale of reproductive loss observed in 2025 is consistent with the close temporal alignment between iceberg grounding and the phase of the emperor penguin breeding cycle when energetic provisioning demands are highest. Following egg laying in May–June, males incubate eggs through June–July while females undertake extended foraging trips at sea (Supplementary Fig. S1 ). Given the timing of iceberg grounding in late July, incubation and hatching likely proceeded largely as normal. However, when females returned to relieve incubating males, iceberg-induced access constraints may have delayed or disrupted parental exchange. Likewise, males completing incubation may have experienced difficulty accessing viable routes to the sea, potentially compounding delays in coordinated foraging and return exchanges. Disruption of these tightly synchronised parental roles during early chick rearing could substantially reduce food delivery to newly hatched chicks, making starvation a plausible outcome (Jenouvrier et al., 2012 ; Massom et al., 2009 ; Zimmer et al., 2007 ). The initial field survey documented multiple chick carcasses within the colony area (Supplementary Fig. S2), a pattern compatible with elevated early-stage mortality. While some level of chick mortality occurs annually in emperor penguin colonies (Barber-Meyer et al., 2008 ; Barbraud & Weimerskirch, 2001 ), chick carcasses appeared to be encountered more frequently during site visits in 2025 than in previous years; however, these impressions were not based on systematic counts. The observed reduction in chick numbers occurred despite relatively stable landfast sea-ice conditions similar to those in the previous year (refer to Figs. 2 c, d). This pattern is consistent with the 2025 event differing from declines primarily associated with sea-ice loss or local habitat collapse (Kooyman & Ponganis, 2014 ; Kooyman & Ponganis, 2017 ). Instead, the combined observations are consistent with a disruption of functional connectivity between breeding and foraging habitats. This configuration corresponds to what we term an accessibility collapse, in which breeding and foraging habitats remain physically present while the movement corridors linking them are obstructed. Under such conditions, normal parental exchange and chick provisioning may become constrained, even in the absence of substantial changes in sea-ice extent or stability. The evidence linking iceberg-induced access blockage to reduced breeding output is inferential rather than directly demonstrative of causality. This interpretation is based on the close spatio-temporal alignment between iceberg grounding, the disappearance of surface indicators of colony occupation, and the substantial reduction in chick numbers, rather than on direct observations of failed parental exchange. Although adults were also counted during the survey (15,242 individuals), alternative explanations, including partial redistribution to neighbouring colonies, cannot be fully excluded (Cristofari et al., 2016 ; Fretwell & Trathan, 2019 ; LaRue et al., 2024 ). Nevertheless, collectively, the 2025 event is consistent with the possibility that a short-lived but substantial physical barrier to movement between the ocean and the breeding site was present during a sensitive phase of the emperor penguin life cycle, and that such a barrier may have contributed to reduced chick survival. Iceberg Morphology as a Geometric Trap. Beyond the mere presence of a grounded iceberg, its detailed morphology appears to have influenced the degree to which access to the Coulman Island breeding site was constrained. Photogrammetry-based elevation analysis (see Methods) reveals marked asymmetry in iceberg geometry along its grounding axis (Fig. 6 ). In the western sector (transects T1–T2), the ocean-facing side forms a relatively gentle slope, whereas the colony-facing southern margin rises abruptly as a sub-vertical escarpment exceeding 20 m in height, effectively limiting direct access to the breeding site. In the eastern sector (transects T3–T4), steep ice faces are present on both the colony-facing southern side and the ocean-facing northern side, forming a more topographically confined configuration. Notably, a narrow passage of approximately 1 km intermittently persisted along the eastern margin between the iceberg and Coulman Island (see Fig. 2 b). This corridor was not fully obstructed and may have allowed limited movement between the colony and offshore waters. This asymmetric structure may have functioned as a geometric trap, defined here as a topographic arrangement in which asymmetric slopes and limited openings increase movement costs and delay access to the breeding site. Although the eastern corridor remained partially open, accessing this passage likely required substantial lateral movement along the iceberg margin, increasing travel distance and time. Given the asymmetric slope configuration, individuals approaching along the gently sloping western face may have been preferentially channelled toward the impassable southern escarpment, thereby increasing travel time before locating the narrow eastern opening. Field observations documenting adult penguins remaining in prolonged stasis along the southern ice walls (Supplementary Fig. S3) are compatible with restricted and spatially heterogeneous access pathways at the time of observation. While rerouting through the eastern corridor cannot be excluded, the observed spatial concentration of individuals suggests that access constraints were non-uniform and likely imposed differential movement costs, particularly in terms of increased travel time and energetic expenditure, across the iceberg perimeter (Jenouvrier et al., 2021 ; Kooyman et al., 2007 ). Consequently, delays associated with locating or navigating limited access corridors during early chick rearing could substantially reduce provisioning frequency to newly hatched chicks (Barbraud et al., 2015 ; S. Labrousse et al., 2021 ). Such topographically induced delays are particularly consequential during the early chick-rearing period, when provisioning schedules are tightly constrained and energetic margins are narrow. Following hatching, emperor penguin chicks can survive only for a limited period on esophageal secretions (penguin milk) provided by the incubating male (Prévost, 1961 ; Wienecke & Robertson, 1997 ). Even modest increases in travel time under these conditions may therefore translate into disproportionate increase in chick mortality risk (Jenouvrier et al., 2021 ; Trathan et al., 2020 ). Distinctiveness from Historical and Regional Analogues. The 2025 reduction in breeding output at Coulman Island differs in several respects from previously documented declines at this colony and elsewhere (Barber-Meyer et al., 2008 ; Kooyman & Ponganis, 2014 ; Kooyman & Ponganis, 2017 ). Long-term monitoring has documented substantial interannual variability in chick numbers at Coulman Island, including an approximately 46% decline in 1993 and a reduction exceeding 50% in 2010 (Fig. 5 ). The 2010 decline was accompanied by reduced adult attendance and was interpreted as reflecting physiological or behavioural decisions by adults to forego breeding, potentially associated with reproductive senescence or insufficient energetic reserves (Kooyman & Ponganis, 2014 ). The rapid recovery of adult numbers by 2011 supports the interpretation that this event primarily reflected a temporary suspension of breeding rather than large-scale loss following breeding initiation. In contrast, observations from 2025 suggest that many adults initiated breeding but experienced early-stage reproductive loss, as evidenced by the continued presence of adults at the colony, a reduced chick-to-adult ratio, and minimal late-season surface evidence of active breeding. This inference is supported by the continued presence of adults at the colony alongside a relatively low chick-to-adult ratio (0.44). While such ratios are known to vary among colonies and years (Kooyman & Ponganis, 2014 ; Kooyman & Ponganis, 2017 ), this pattern is more consistent with reduced breeding output during chick rearing than solely with pre-breeding abstention (Kooyman & Ponganis, 2014 ). Accordingly, the 2025 event appears distinct from previously documented mechanisms and is more consistent with an extrinsic physical disruption than with intrinsic life-history trade-offs. Comparisons with other iceberg-related reproductive declines further clarify this distinction. The well-documented impacts of the B15A–C16 iceberg complex at Cape Crozier and Beaufort Island illustrate two contrasting mechanisms (Kooyman et al., 2007 ). At Cape Crozier, reduced breeding output was associated primarily with the destruction or destabilisation of fast-ice breeding habitat. At Beaufort Island, by contrast, breeding habitat remained intact, but access routes were obstructed, necessitating extended detours that disrupted provisioning. The Coulman Island event more closely resembles the Beaufort Island mechanism, although important differences remain. Unlike Beaufort Island, the semi-enclosed coastal geometry surrounding the Coulman Island colony (Fig. 1 ) appears to have restricted the availability of alternative navigation routes. Whereas penguins at Beaufort Island undertook extended detours, the Coulman Island iceberg exhibited an asymmetric configuration, with a gently sloping ocean-facing surface that may have channelled returning adults toward an impassable southern escarpment, thereby increasing movement costs before alternative routes were located (Supplementary Fig. S4). Alternative explanations, particularly large-scale redistribution of breeders to neighbouring colonies, are not strongly supported by available evidence. Coulman Island is classified as a suburbanite colony, with late-season dispersal typically limited to approximately 10–15 km (Kooyman & Ponganis, 2017 ). Moreover, chick counts at the two nearest colonies, Cape Washington and Cape Roget, in 2025 were comparable to their respective five-year means, with only modest increases relative to 2024 (unpublished data). Even when combined, these increases account for approximately 5.5% of the deficit observed at Coulman Island, suggesting that redistribution alone is unlikely to fully explain the magnitude of decline. To evaluate whether surviving chicks experienced compromised condition, flipper length and body mass were measured in 37 individuals during a December 2025 visit. No significant differences were detected relative to chicks measured at Cape Washington. This pattern suggests that chicks surviving beyond the early post-hatching period were able to receive adequate provisioning later in the season. In addition, during ground visits, no adult carcasses were observed. Although access was severely constrained, it was not entirely blocked, suggesting that delayed but ultimately successful parental exchange may have occurred. Available observations therefore indicate that the primary demographic effect of the 2025 event was expressed through reduced chick survival rather than detectable adult mortality. Future Perspectives: Stochastic Risks in a Changing Ross Sea. The 2025 Coulman Island event is more appropriately interpreted as a localised, event-driven disturbance rather than as evidence of chronic risk to emperor penguins across the Ross Sea. The Ross Sea region has historically exhibited relatively high sea-ice stability and has been identified as a potential climate refuge for emperor penguins under future warming scenarios (Jenouvrier et al., 2009 ; Jenouvrier et al., 2014 ). Nevertheless, this event highlights a class of stochastic risks that may be insufficiently represented in demographic models primarily focused on large-scale mean-state variables, such as regional sea-ice extent. The drift and grounding pathway of the 2025 iceberg underscores the importance of both timing and spatial configuration in shaping ecological outcomes. Unlike iceberg C-33, which transited the Coulman Island sector in October 2016 during fast-ice breakup and did not ground (Dziak et al., 2019 ), the 2025 iceberg arrived in late July, coinciding with peak seasonal consolidation of landfast ice (Fig. 7 ). This timing likely enhanced coupling with the consolidated ice matrix, likely increased rotational pivoting, grounding, and prolonged immobilisation near the coast. Increasing instability of Antarctic ice shelves over recent decades has been identified as a contributing factor to the frequency of large iceberg calving events (Greene et al., 2022 ; Scambos et al., 2017 ; Wille et al., 2022 ), a trend closely linked to climate-change signals, including ocean warming (Etourneau et al., 2019 ; Joughin & Alley, 2011 ). Large icebergs that remain grounded near the coast for extended periods pose a direct threat to the geomorphological integrity of emperor penguin breeding sites or disrupt access routes to key foraging areas, leading to substantial ecological disturbance. As climate change progresses, the combined effects of increased sea-ice instability, landfast-ice breakup, and earlier seasonal sea-ice loss are expected to amplify the stochastic risks associated with such large iceberg events (Schmidt & Ballard, 2020 ). Emperor penguin responses to environmental change are likely nonlinear, emerging from interactions among sea ice, prey availability, episodic disturbance, and movement processes such as dispersal and emigration (Ainley et al., 2010 ; LaRue et al., 2024 ). Although inter-colony connectivity and behavioural flexibility may buffer populations at the metapopulation scale (Briëd et al., 1999 ; Fretwell & Trathan, 2019 ; LaRue et al., 2014 ), this flexibility does not preclude severe local reproductive collapse when accessibility abruptly declines at critical stages of the breeding cycle. Future assessments of emperor penguin breeding prospects would benefit from explicitly incorporating stochastic iceberg–sea-ice interactions, including the timing of calving, drift pathways, grounding probability, and residence time near breeding sites (Fretwell & Trathan, 2019 ; Jenouvrier et al., 2021 ). Calving timing, drift pathway, grounding probability, and coastal residence time define a suite of low-frequency but high-impact stochastic risks that can generate severe local reproductive failure even under otherwise favourable regional sea-ice conditions. Addressing these risks will require long-term, cross-disciplinary monitoring frameworks that integrate ocean circulation, sea-ice dynamics, landfast-ice development, and ice-shelf stability. Such integrated approaches are essential for identifying emerging ecological chokepoints and for developing early-warning indicators of vulnerability in an increasingly dynamic Antarctic system. Methods Study Area and Colony Context. The study was conducted at the emperor penguin colony located on the fast ice along the northern margin of Coulman Island (73°28′ S, 169°45′ E), North Victoria Land, Ross Sea, Antarctica (Fig. 1 ). This colony is situated within a semi-enclosed coastal embayment bounded by Cape Jones to the south and open waters extending northward toward the Ross Sea polynya system. The northwestern sector of Coulman Island, together with Cape Washington and Cape Roget, is recognised as one of the most important emperor penguin breeding regions in the Ross Sea and has historically supported one of the most productive mega-colonies globally (Kooyman & Ponganis, 2014 ). The colony is established on seasonally forming annual fast ice along the island's northern coast and is characterised by unconstrained topographic relief, permitting extensive lateral expansion of the breeding aggregation. On this basis, the Coulman Island colony is classified as a suburban colony (Kooyman & Ponganis, 2017 ). During the breeding season, the colony typically occupies an area of approximately 5 km × 2 km and, between late October and early December, frequently undergoes spatial fragmentation into 10–30 discrete sub-colonies. These subunits have been reported to shift up to 10 ~ 15 km from the original breeding location in response to local fast-ice conditions and access to foraging areas. Emperor Penguin Census Surveys. This study comprised two field surveys conducted on 13 November 2025 and 5 December 2025 at the Coulman Island emperor penguin colony. The November survey was conducted under the auspices of the Korea Polar Research Institute (KOPRI) annual monitoring programme and primarily aimed to estimate chick and adult abundance at Coulman Island and other colonies in northern Victoria Land. The December survey was designed to complement the initial observations and focused on (i) verification of habitat conditions, (ii) limited morphometric assessment of chick body condition, and (iii) high-resolution documentation of iceberg topography (elevation and morphology). Both surveys utilised a helicopter-mounted platform for systematic aerial photogrammetry. During standard census operations, flight altitude was maintained at approximately 600 m above ground level, ensuring a consistent ground sampling distance comparable to that used in KOPRI monitoring surveys since 2017. This consistency in flight altitude, image resolution, and survey extent ensured methodological comparability across years. Image interpretation and counting were performed through a systematic manual visual census conducted independently by four experienced observers. Counts from each observer were compared to assess inter-observer variability. The coefficient of variation (CV) among observers was 2.04%, indicating high consistency. This level of agreement is comparable to, or lower than, inter-observer variability previously reported for penguin counts derived from high-resolution imagery (typically ≤ 2.5%; Fretwell, 2024 ). Adult emperor penguins were distinguished by their characteristic black-and-white plumage, whereas chicks exhibited predominantly grey coloration, facilitating reliable classification under the image resolution achieved. At the time of the November survey, the breeding aggregation had transitioned from a consolidated incubation cluster to multiple smaller subgroups, consistent with patterns described for the early chick-rearing phase (Kooyman & Ponganis, 2014 ). Each subgroup was visually delineated, imaged separately, and counted independently prior to aggregation of totals (Supplementary Fig. S6). Survey coverage included the full spatial extent of the breeding area and adjacent fast-ice margins to minimise omission of peripheral groups. The November survey recorded 6,081 chicks. During the December visit, additional small subgroups located near the colony periphery were identified, resulting in a revised total of 6,658 chicks. Both surveys applied identical counting criteria to maintain interannual comparability with previous KOPRI datasets (2017–2024). Adult counts were conducted concurrently in November using the same imagery-based approach, yielding a total of 15,242 individuals. During the December survey, limited ground landings were conducted at selected locations to obtain morphometric measurements of 37 chicks. Body mass was measured using a portable digital scale, and flipper length was measured using a standard calliper. Individuals selected for comparison were within a flipper-length range comparable to chicks measured at Cape Washington during the same season. Since 2017, KOPRI has conducted annual aerial surveys to monitor chick abundance at Coulman Island. Surveys were not conducted in 2020 due to restrictions associated with the COVID-19 pandemic. The resulting time series provides a consistent baseline for evaluating interannual variability in breeding output and for comparison with satellite-derived colony estimates. Satellite Data and Iceberg Tracking. To reconstruct the calving, drift, grounding, and final configuration of the iceberg, and to assess its association with reduced chick survival at Coulman Island, we integrated multi-sensor satellite datasets with complementary spatial and temporal characteristics. These included MODIS Terra True Color imagery, Sentinel-1 synthetic aperture radar (SAR), Landsat-8/9 Operational Land Imager (OLI), and very-high-resolution WorldView imagery. The timing of calving from the Nansen Ice Shelf was determined using MODIS Terra imagery at 500 m spatial resolution. High-resolution optical imagery from WorldView, Landsat, and Sentinel-2 was examined but did not provide suitable coverage for the critical period, either due to data gaps or insufficient visibility of the detachment event. Despite partial cloud cover, MODIS imagery acquired on 12 March 2025 revealed a distinct structural discontinuity at the ice-shelf front, and subsequent imagery confirmed the presence of an independent iceberg body. These observations enabled identification of 12 March 2025 as the calving date. Post-calving drift was tracked using Sentinel-1 SAR imagery, which provides all-weather, day-and-night observational capability. Sentinel-1 scenes were obtained from the Alaska Satellite Facility Data Search Portal and all available acquisitions between 11 March and 28 July 2025, during which the iceberg was clearly detectable within the sensor swath, were included in the analysis. A total of 27 SAR scenes were analysed. The iceberg outline was manually digitised in each scene, and centroid positions derived from these polygons were linked sequentially to reconstruct the drift trajectory. Grounding was inferred from a marked reduction in translational displacement, the onset of rotational pivoting, and subsequent positional stability adjacent to the southern margin of Coulman Island after 28 July 2025. Landsat-8/9 OLI imagery (30 m spatial resolution), obtained from the United States Geological Survey EarthExplorer archive, was used to delineate the final horizontal footprint of the grounded iceberg and to quantify its spatial relationship with the northern access corridor to the colony. The scene acquired on 11 November 2025, temporally closest to the field survey, was used to estimate iceberg surface area and assess occlusion of the primary access pathway. Very-high-resolution Maxar WorldView imagery was used to evaluate surface biological indicators at the breeding site. WorldView-3 imagery acquired on 20 November 2024 and WorldView-2 imagery acquired on 6 November 2025 provided sub-meter spatial resolution necessary for reliable visual discrimination of guano staining patterns. Together, these satellite datasets enabled a systematic reconstruction of iceberg dynamics and their spatial configuration relative to the breeding site, forming the basis for interpretation of potential access constraints during the 2025 breeding season. Identification of the Primary Commuting Pathway. The primary commuting pathway between the Coulman Island colony and adjacent marine foraging areas was identified based on repeated field observations conducted during annual surveys since 2017, supplemented by aerial imagery. Across multiple breeding seasons, adult emperor penguins were consistently observed moving predominantly along the northern and northeastern margin of the colony toward the sea-ice edge between Cape Jones and Coulman Island. These directional patterns were documented qualitatively during helicopter-based surveys and were supported by aggregation trails and surface disturbance patterns visible in high-resolution imagery (Supplementary Fig. S6). Iceberg Morphology and Elevation Analysis . To evaluate whether the grounded iceberg may have functioned as a geometric constraint on movement between the colony and offshore waters, we constructed and analysed a high-resolution Digital Surface Model (DSM) of the iceberg using aerial photogrammetry. For contextual assessment of relative position and elevation, we referenced the 2 m-resolution Reference Elevation Model of Antarctica (REMA) v2.0 mosaic (Howat et al., 2019 ). Horizontal coordinates were defined in WGS84 / Antarctic Polar Stereographic (EPSG:3031), and elevations were initially referenced to the WGS84 ellipsoid (EPSG:4979). The aerial DSM was generated from 1,071 photographs acquired from a helicopter platform circling the iceberg. Most images were captured at approximately 1,200 m above ground level to document the overall geometry of the iceberg, while additional lower-altitude flights at approximately 600 m were conducted along steep cliff sections to obtain higher-detail coverage of vertical and near-vertical surfaces. Imagery was acquired using a Canon EOS R5 camera equipped with a 100 mm lens. Three-dimensional reconstruction was performed in Agisoft Metashape Professional v2.2.2 using structure-from-motion workflows, and the resulting model was processed in Global Mapper to produce elevation products at an effective spatial resolution of ~ 1.2 m. Because the aerial DSM and REMA employ different vertical reference systems, the EGM2008 geoid was applied to convert ellipsoidal elevations to orthometric heights for consistency. Given the remote Antarctic setting, ground control points were not available. However, the objective of this analysis was to quantify relative morphological contrasts, on the order of tens of metres, between the colony-facing and ocean-facing flanks of the iceberg. Such large-scale geometric asymmetries are robust to metre-scale vertical uncertainty and provide a basis for evaluating whether iceberg morphology may have increased travel distance, constrained access corridors, or redirected movement pathways. Declarations Competing interests The authors declare no competing interests. Funding This work was supported by Korea Institute of Marine Science & Technology Promotion(KIMST) grant funded by the Ministry of Oceans and Fisheries(KIMST RS-2022-KS221661) Jinku Park 1 , Jong-U Kim 2 , Youmin Kim 2,3 , Yongsik Jeong 1 , Younggen Oh 2,4 , Jungyuem Kim 2 , Jeong-Hoon Kim 2* Author contributions J.P. conceived this study and led the manuscript writing. J.-H.K. conceived and supervised the study. J.U.K. and Y.K. contributed to the acquisition of field observation data and participated in writing and editing the manuscript. Y.J. contributed to data processing and analysis. Y.O. reviewed and provided feedback on the manuscript. J.K. assisted in the acquisition of field observation data. Acknowledgement We would like to express our sincere gratitude to Myeongho Seo, safety instructor, for his valuable assistance with the aerial photography campaign and the iceberg surface modeling. His support greatly improved the quality and completeness of this study. We also extend our sincere appreciation to Gerald Kooyman, Michelle LaRue, and Cassandra Brooks for their careful review of the manuscript and their constructive comments. Their insights and expertise substantially strengthened the scientific interpretation and clarity of this work. Data availability Landsat-8 and Landsat-9 Operational Land Imager (OLI) surface reflectance images used to assess regional sea-ice conditions and the presence of grounded icebergs around Coulman Island were obtained from the U.S. Geological Survey EarthExplorer portal ( https://earthexplorer.usgs.gov ). Very high-resolution optical satellite imagery used for visual confirmation of emperor penguin breeding status and guano presence, including WorldView-3 (20 November 2024) and WorldView-2 (6 November 2025), was provided by Maxar Technologies and analysed under a research license; these data are not publicly redistributable but can be accessed from the data provider subject to licensing conditions. MODIS Terra true-color imagery used to constrain the timing of iceberg calving from the Nansen Ice Shelf was accessed via NASA Worldview ( https://worldview.earthdata.nasa.gov ). Sentinel-1 C-band SAR data employed to reconstruct the iceberg drift and grounding trajectory were obtained from the Alaska Satellite Facility (ASF) Distributed Active Archive Center ( https://search.asf.alaska.edu ). The Reference Elevation Model of Antarctica (REMA) v2.0 mosaic, used as ancillary elevation data for iceberg surface analysis, is publicly available from the Polar Geospatial Center (PGC) at the University of Minnesota ( https://www.pgc.umn.edu/data/rema ). Helicopter-based aerial photographs acquired during the November and December 2025 field surveys using a Canon EOS R5 camera were collected by the authors and are not publicly archived due to logistical and operational constraints, but may be made available upon reasonable request to the corresponding author. References Ainley, D. G., Russell, J., Jenouvrier, S., Woehler, E., Lyver, P. O. B., Fraser, W. R., & Kooyman, G. L. (2010). 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P., Gilbert, C., Beaulieu, M., Ancel, A., & Plötz, J. (2007). Foraging movements of emperor penguins at Pointe Géologie, Antarctica. Polar Biology , 31 (2), 229–243. https://doi.org/10.1007/s00300-007-0352-5 Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryJKPARKCEE.docx Iceberg-Induced Collapse of Access Connectivity and a Dramatic Reduction in Chick Survival at the Coulman Island Emperor Penguin Colony Cite Share Download PDF Status: Under Review Version 1 posted 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. 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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-9024637","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":600502137,"identity":"f94844f8-1878-4ca9-b69f-eadc1fb371bc","order_by":0,"name":"Jeong-Hoon Kim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3UlEQVRIiWNgGAWjYBACxhlsDAcYKtjkJEC8BBDBQ5SWM3zGxGthkGAD6muTS5wBFyGkhXl2W+Khm21m6TPbe499eMBwT46B5+wD/A6bc+zA4Zxzabmzec4lz0hgKDZm4G03IOCX9IbDOWXHcudJ5BgD/ZKQ2MDPht9hEC1s/9PloFrqidCSBnRYG1uCNFRLAgNvG0EtCYdzzrAZzuw5l8yQYJBg2MZzDL8Wwxlpxp9zKtjkJY73Hmb8UZEgz8+TRkBLA5wJig9gWBHwCQODPIJJMNZHwSgYBaNgpAIAijRBokG4zZAAAAAASUVORK5CYII=","orcid":"","institution":"Korea Polar Research Institute","correspondingAuthor":true,"prefix":"","firstName":"Jeong-Hoon","middleName":"","lastName":"Kim","suffix":""},{"id":600502138,"identity":"e6c6392e-0d95-460c-af7c-7430ff700c38","order_by":1,"name":"Jinku Park","email":"","orcid":"https://orcid.org/0000-0002-9598-2101","institution":"Korea Polar Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Jinku","middleName":"","lastName":"Park","suffix":""},{"id":600502139,"identity":"64ee5bfc-d638-42f0-a7d8-62af302d7a7e","order_by":2,"name":"Jong-U Kim","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Jong-U","middleName":"","lastName":"Kim","suffix":""},{"id":600502140,"identity":"a5e92fc6-46ca-49b8-810b-218c9740ee8b","order_by":3,"name":"Youmin Kim","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Youmin","middleName":"","lastName":"Kim","suffix":""},{"id":600502141,"identity":"e4d86446-1bdd-47b3-ba6c-1aae374ab926","order_by":4,"name":"Yongsik Jeong","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Yongsik","middleName":"","lastName":"Jeong","suffix":""},{"id":600502142,"identity":"43310f1a-72dc-4c87-b6b1-d8bf8bb87fe8","order_by":5,"name":"Younggen Oh","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Younggen","middleName":"","lastName":"Oh","suffix":""},{"id":600502143,"identity":"0bf1de75-c461-47a6-b64a-3f9305fdef91","order_by":6,"name":"Jungyuem Kim","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Jungyuem","middleName":"","lastName":"Kim","suffix":""}],"badges":[],"createdAt":"2026-03-04 01:41:04","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9024637/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9024637/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104780218,"identity":"ee885ccf-4898-4b50-bb07-921d7218fdf1","added_by":"auto","created_at":"2026-03-17 07:51:29","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":584632,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMaps of the Ross Sea and the Coulman Island emperor penguin colony. a \u003c/strong\u003eBathymetry and geographic setting of the western Ross Sea derived from the General Bathymetric Chart of the Oceans (GEBCO) global bathymetric grid (https://www.gebco.net).\u003cstrong\u003eb \u003c/strong\u003eWorldView-2 optical imagery showing the fast-ice platform adjacent to Coulman Island and the location of the emperor penguin breeding colony (red shading). The yellow arrows denote the access corridors commonly used by emperor penguins to move between the breeding site and adjacent foraging habitats.\u003c/p\u003e","description":"","filename":"Fig01.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9024637/v1/104646d0b574db03cf820103.jpg"},{"id":104441640,"identity":"63e890e2-e7ee-4e93-bf03-4c0ed183d419","added_by":"auto","created_at":"2026-03-11 18:37:18","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1305047,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGrounded iceberg near Coulman Island and remotely sensed evidence of reduced breeding output. a \u003c/strong\u003ePhotograph showing the grounded iceberg located immediately north of Coulman Island in the 12 November 2025 field survey. \u003cstrong\u003eb \u003c/strong\u003eLandsat image (1 November 2025) indicating the grounded iceberg (outlined in red), with an estimated area of 35.86 km², resting against the fast ice that extends from Coulman Island.\u003cstrong\u003e c \u003c/strong\u003eWorldView-3 image from 20 November 2024 showing guano stains at the colony site.\u003cstrong\u003e d \u003c/strong\u003eWorldView-2 image from 6 November 2025 showing the site with guano largely absent. On this image, due to cloud cover, the boundary of the iceberg is not clearly discernible. The actual iceberg position should therefore be referenced from\u003cstrong\u003e \u003c/strong\u003e(b)\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Fig02.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9024637/v1/feba9d7f06e43fdedbf8496d.jpg"},{"id":104441639,"identity":"ddcd2440-d833-4f5e-b4fc-6b5de59cd21d","added_by":"auto","created_at":"2026-03-11 18:37:18","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":835583,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMODIS True Color images capturing the calving event of the Nansen Ice Shelf. a-d \u003c/strong\u003eSequential MODIS True Color images acquired between 10 and 13 March 2025 showing the progression of the calving event at the Nansen Ice Shelf. The coastline (grey line) is derived from the SCAR Antarctic Digital Database (2010), orange arrows indicate the location of the calving point, and the yellow circle highlights the newly detached iceberg visible on 13 March 2025.\u003c/p\u003e","description":"","filename":"Fig03.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9024637/v1/4a93c6c211361cac8857b7c7.jpg"},{"id":104441641,"identity":"9091a065-19c6-4f4e-b37b-3fa96b4cf9a6","added_by":"auto","created_at":"2026-03-11 18:37:18","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":928300,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSAR time series showing the drift and grounding of the iceberg north of Coulman Island. \u003c/strong\u003eSentinel-1 SAR images acquired on \u003cstrong\u003ea \u003c/strong\u003e7 March,\u003cstrong\u003e b \u003c/strong\u003e19 March, \u003cstrong\u003ec \u003c/strong\u003e4 June ,\u003cstrong\u003ed \u003c/strong\u003e16 June,\u003cstrong\u003e e \u003c/strong\u003e4 July,\u003cstrong\u003e f \u003c/strong\u003e16 July,\u003cstrong\u003e g \u003c/strong\u003e22 July, and\u003cstrong\u003e h \u003c/strong\u003e28 July show the sequential movement of the iceberg from its initial position near the Drygalski Ice Tongue to its final grounding location north of Coulman Island.\u003cstrong\u003e i \u003c/strong\u003eThe most recent image acquired on 13 November shows that the iceberg has remained in the same grounded position since 28 July.\u003c/p\u003e","description":"","filename":"Fig04.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9024637/v1/9635ad32de35b46740b1c497.jpg"},{"id":104441645,"identity":"2a213542-7893-4756-b9a5-48ee9f72444f","added_by":"auto","created_at":"2026-03-11 18:37:18","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":222991,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLong-term chick counts at the Coulman Island emperor penguin colony. Chick count records from 1983 to 2025 were compiled from three sources. \u003c/strong\u003eThe counts from Barber-Meyer et al. (2008) cover the period from 1983 to 2005, followed by the counts reported by Kooyman and Ponganis (2017) for 2005-2012, and recent observations conducted by the Korea Polar Research Institute (KOPRI) spanning 2017-25. Bars represent the total number of chicks counted in each surveyed year.\u003c/p\u003e","description":"","filename":"Fig05.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9024637/v1/3d211a343759d81b8799fea7.jpg"},{"id":104780237,"identity":"c4f9a693-6e1d-40a8-9e9b-45aec84605a3","added_by":"auto","created_at":"2026-03-17 07:51:38","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":575273,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThree-dimensional morphology and elevation profiles of the grounded iceberg at Coulman Island. a \u003c/strong\u003eRegional topography derived from the Reference Elevation Model of Antarctica (REMA), overlaid with a high-resolution photogrammetric surface model of the grounded iceberg generated from aerial imagery (see Methods). The inset shows the iceberg surface coloured by elevation and the locations of four transects (T1–T4) used for profile extraction. \u003cstrong\u003eb \u003c/strong\u003eElevation profiles along transects T1–T4, illustrating the strong morphological asymmetry of the iceberg. Elevations were calculated using the same geoid reference as REMA; therefore, the values do not represent absolute elevations and should be interpreted only in a relative sense.\u003c/p\u003e","description":"","filename":"Fig06.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9024637/v1/d535f42aa0ff0f2a63fb469f.jpg"},{"id":104441643,"identity":"fd0a0758-31c7-4d02-99c8-a9862e2ad425","added_by":"auto","created_at":"2026-03-11 18:37:18","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":491736,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of iceberg drift pathways in 2025 and 2016 and the influence of fast-ice boundaries on iceberg movement.\u003c/strong\u003eReconstructed drift trajectories of the 2025 iceberg (magenta) and the C-33 iceberg in 2016 (brown) from the Nansen Ice Shelf toward the western Ross Sea, showing broadly similar pathways guided by regional bathymetric structure (background color). Dates indicate sequential positions identified from SAR imagery. The yellow circles indicate the well-known emperor penguin breeding colonies (Cape Washington and Coulman Island) located along the drift pathway of these icebergs, and the orange solid lines delineate the outer boundary of landfast sea ice in Wood Bay and Lady Newnes Bay. The configuration of the landfast sea ice was derived from satellite imagery (Supplementary Fig. S5).\u003c/p\u003e","description":"","filename":"Fig07.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9024637/v1/afa9af26a7733e62d0d4d572.jpg"},{"id":104784224,"identity":"81f6077c-226b-44a2-b357-5defa876b55e","added_by":"auto","created_at":"2026-03-17 08:05:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6071521,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9024637/v1/f9850995-63cb-4063-8021-8cc8d2847d5e.pdf"},{"id":104780251,"identity":"dfc94b3f-427c-4f2a-8c6d-db7e9734f01c","added_by":"auto","created_at":"2026-03-17 07:51:43","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":4564961,"visible":true,"origin":"","legend":"Iceberg-Induced Collapse of Access Connectivity and a Dramatic Reduction in Chick Survival at the Coulman Island Emperor Penguin Colony","description":"","filename":"SupplementaryJKPARKCEE.docx","url":"https://assets-eu.researchsquare.com/files/rs-9024637/v1/7ff8dfcf6e5692a25c5ae5f0.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Iceberg-Induced Collapse of Access Connectivity and a Dramatic Reduction in Chick Survival at the Coulman Island Emperor Penguin Colony","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe Earth system is undergoing rapid change driven by anthropogenic forcing, with mounting evidence that these changes are intensifying environmental pressures on polar ecosystems (Constable et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Meredith et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Ranasinghe et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In Antarctica, recent decades have been marked by documented atmospheric warming (Wang et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2025\u003c/span\u003e), declines in sea-ice extent and thickness (Bocquet et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Fretwell et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), and an increased frequency of extreme weather events (Siegert et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Collectively, these environmental shifts are associated with changes in ecosystem structure and have been linked to variation in survival and reproductive performance across Antarctic species (Fretwell et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Jenouvrier et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Larsen et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Trathan et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Vaughan et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Among Antarctic marine predators, the emperor penguin (\u003cem\u003eAptenodytes forsteri\u003c/em\u003e) has been described as a sentinel species, reflecting broader changes within the Southern Ocean ecosystem (LaRue et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Its life history is closely linked to the availability of stable sea ice, which supports key stages of its annual cycle, including breeding, incubation, chick rearing, and moulting (Forcada \u0026amp; Trathan, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Fretwell et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Schmidt \u0026amp; Ballard, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Trathan et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Wienecke, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Consequently, alterations in sea-ice conditions may increase the risk of reduced breeding performance and could influence long-term population trajectories (Ainley et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Barbraud \u0026amp; Weimerskirch, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Jenouvrier et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Jenouvrier et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Jenouvrier et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Schmidt \u0026amp; Ballard, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Given this ecological dependence, emperor penguins have become a focal species for investigating the biological consequences of sea-ice variability and ongoing environmental change in Antarctica (Ainley et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Jenouvrier et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; LaRue et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eEmperor penguins depend on stable landfast sea ice for breeding, and reproductive success may be compromised when sea ice forms late in the season or breaks up before chicks fledge (Jenouvrier et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Trathan et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Because the sea-ice zone supports key foraging activities for this species, reductions in sea ice may influence long-term population viability by constraining access to prey resources (Trathan et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In addition to recent changes in sea-ice conditions, large iceberg calving events along parts of the Antarctic coastline have been associated with increased cryospheric variability (Liu et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Such physical disturbances can generate short-term, site-specific ecological impacts by obstructing access to breeding habitats or altering local environmental conditions that support reproductive success, including for apex predators such as emperor penguins. In the context of these cumulative pressures, emperor penguins are currently classified as Near Threatened on the IUCN Red List (Jenouvrier et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Trathan et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). A reassessment is underway, and recent evaluations have considered the possibility of uplisting the species to Endangered status (C. Brooks, pers. comm., 2026). In response, parties to the Antarctic Treaty System, including those operating under the Protocol on Environmental Protection and the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR), have discussed or implemented management measures intended to reduce additional stressors that may compound the effects of climate change on emperor penguin populations (Berkman et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Trathan et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn 2016, the Ross Sea region was designated as a Marine Protected Area (MPA) by CCAMLR under Conservation Measure 91\u0026thinsp;\u0026minus;\u0026thinsp;05, partly to conserve key foraging habitats used by emperor penguins within the Ross Sea ecosystem. The MPA encompasses several major emperor penguin breeding sites, including Cape Roget, Coulman Island, Cape Washington, Beaufort Island, Cape Crozier, and Cape Colbeck (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Among these sites, Coulman Island (73\u0026deg;28\u0026prime; S, 169\u0026deg;45\u0026prime; E), located along the North Victoria Land coast, has been reported as one of the largest emperor penguin colonies globally (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Its large colony size has been attributed to favourable regional oceanographic conditions, including high marine productivity and the persistence of stable landfast sea ice between Cape Jones and Coulman Island (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e; Kooyman et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Kooyman \u0026amp; Kooyman, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Owing to its size and geographic setting, the Coulman Island colony represents an important site for ecological research and long-term monitoring, offering insights into population dynamics and linkages with adjacent marine ecosystems, including coastal polynyas and associated food-web processes (Massom et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Massom et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Trathan et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Moreover, Coulman Island functions as a natural laboratory in which the vulnerability and adaptive capacity of a large emperor penguin population can be examined under increasing environmental stochasticity in the Antarctic sea-ice system.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eResearch on emperor penguins has traditionally explained breeding success and population variability primarily using metrics of sea-ice extent, formation timing, and stability (Barbraud \u0026amp; Weimerskirch, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Fretwell et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Jenouvrier et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Schmidt \u0026amp; Ballard, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). However, this sea-ice-centred framework does not fully account for documented instances of reduced breeding performance that have occurred under apparently stable sea-ice conditions (Barbraud \u0026amp; Weimerskirch, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In recent decades, additional habitat disturbances, either indirectly linked to sea ice or not readily explained by sea-ice variability alone, have occurred episodically. These include ice-shelf calving events and the grounding of large icebergs. The frequency of such cryospheric disturbances has been projected to increase in some regions under continued climate change (Etourneau et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Joughin \u0026amp; Alley, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). A well-documented example occurred in 2001 near Cape Crozier in the Ross Sea, where the grounding of giant icebergs (B15A and C16) disrupted a long-established breeding habitat and resulted in the near-total loss of breeding output in the local emperor penguin population (Kooyman et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). In subsequent years, chick production declined to 0\u0026ndash;40% of pre-2000 levels, suggesting that iceberg presence caused persistent physical modification of the habitat beyond sea-ice stability alone and affected multiple stages of the breeding cycle (Kooyman et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Schmidt \u0026amp; Ballard, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Notably, impacts of large icebergs on penguin habitats have also been documented outside the immediate breeding period. For example, the collision of a massive iceberg with the Mertz Glacier Tongue removed coastal and fast-ice habitat when breeding birds were absent, leading to delayed ecological consequences for nearby penguin colonies (Ancel et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIcebergs may impede movement by obstructing access routes between breeding sites, foraging areas, and overwintering habitats. At Beaufort Island, for example, grounded icebergs formed a persistent physical barrier of approximately 150 km between the Ross Sea polynya and the island, constraining access to both feeding and breeding areas (Kooyman et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Kooyman et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). These conditions were associated with marked declines in breeding pair numbers, elevated chick mortality, and, in some cases, colony abandonment or relocation (Kooyman et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Collectively, these cases underscore the limitations of sea-ice stability\u0026ndash;centred interpretations. They indicate that colony-scale population outcomes can be influenced by the combined effects of multiple, interacting physical and ecological disturbances, rather than solely by sea-ice variability alone.\u003c/p\u003e \u003cp\u003eWe report on field surveys conducted in mid-November 2025 in the vicinity of Coulman Island, which documented unusually low chick counts relative to recent breeding seasons. When considered alongside contemporaneous satellite imagery, these observations suggest that a primary access corridor linking the marine area between Cape Jones and Coulman Island to the breeding site was obstructed by a large grounded iceberg at the time of the survey. This reduction in accessibility coincided with low chick counts recorded during that season, indicating a temporal association between iceberg-induced obstruction and reduced chick survival. Nevertheless, this study is explicitly framed as an observational case study focused on a single breeding season and does not seek to establish definitive causality between iceberg grounding and reduced chick survival. Instead, our aim is to examine plausible mechanisms through which iceberg-driven disruptions to accessibility may affect emperor penguin breeding processes and to present initial observational evidence of the role that such access constraints may have played in the reduced chick survival observed at Coulman Island. Specifically, we ask whether iceberg grounding can generate short-term accessibility constraints sufficient to affect colony-scale breeding outcomes, even under otherwise stable sea-ice conditions. By integrating field observations with satellite imagery, we assess the spatial configuration and timing of iceberg obstruction relative to observed breeding output.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e \u003cb\u003eGrounded Iceberg Configuration and Observed Breeding Conditions in November 2025.\u003c/b\u003e During the annual survey to census emperor penguin chicks at Coulman Island on 12 November 2025 (see Methods), a vertical ice wall estimated to be several tens of metres high was observed approximately 3\u0026ndash;5 km north of the colony (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Contemporaneous medium-resolution satellite imagery (Landsat) confirmed the presence of a grounded iceberg measuring approximately 15 km in length and 5 km in width (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). The iceberg was located along a commonly used commuting route between the breeding site and offshore foraging areas, which extend northward and northeastward from the colony (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). This commuting route was identified through repeated annual field observations of colony movements. Field observations documented adult emperor penguins congregating along the southern margin of the iceberg, where the vertical ice wall extended continuously. During the observation period, no individuals were recorded traversing the cliff or moving southward toward the breeding site. Analysis of Landsat imagery acquired on 1 November 2025 indicated that the iceberg covered an area of approximately 35.86 km\u0026sup2;. The eastern margin of the iceberg was in direct contact with the edge of long-established landfast ice, forming a continuous ice boundary during the sea-ice season. Repeated satellite observations and in situ surveys showed that the iceberg remained grounded at the same location throughout winter and into early spring.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eVery-high-resolution Maxar WorldView imagery shows a clear difference in the spatial extent of surface biological indicators (i.e., guano stains) at the breeding site between November 2024 and November 2025, while landfast ice conditions appeared broadly similar during the two periods. In the November 2024 image (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec), extensive and well-defined guano staining was distributed across the landfast ice. In contrast, imagery acquired on 6 November 2025 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed) shows that guano traces, aggregation patterns, and nesting-related surface features at the same location were largely absent. The contrast in surface biological indicators between the two years occurred under broadly comparable fast-ice conditions, based on visual assessment of satellite imagery. Even when accounting for potential differences in snow cover between the two observation periods, the contrast in surface biological indicators remained evident in both satellite imagery and direct field observations.\u003c/p\u003e \u003cp\u003e \u003cb\u003eCalving and Drift\u0026ndash;Grounding Chronology of the Nansen Ice Shelf Iceberg.\u003c/b\u003e The calving event and subsequent drift\u0026ndash;grounding sequence of the iceberg toward the northern margin of Coulman Island were reconstructed through multi-sensor image analysis, integrating MODIS True Color imagery and Sentinel-1 synthetic aperture radar (SAR) time series. Back-tracking analysis shows that the iceberg originated from the Nansen Ice Shelf in Terra Nova Bay. The calving event was identified as occurring on 12 March 2025, with MODIS imagery providing the only direct visual record of the breakup (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Imagery acquired on 10 and 11 March 2025 shows a contiguous ice-shelf front with no visible evidence of structural separation (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, b). In contrast, the image from 12 March (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec) reveals a distinct linear fracture at the ice-shelf front, representing a structural discontinuity consistent with calving. Although extensive cloud cover limited direct delineation of the newly separated iceberg in this scene, in clearer patches areas of thinner cloud display a dark-toned signature at the shelf front. This spectral signature is comparable to surrounding open-ocean surfaces. The subsequent MODIS image from 13 March (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed) clearly shows the iceberg as an independent body, consistent with separation occurring on 12 March 2025.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePost-calving movement of the iceberg was tracked stepwise through visual interpretation of a Sentinel-1 SAR time series (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Imagery from 7 March shows the pre-calving configuration, with the iceberg still contiguous with the Nansen Ice Shelf front (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). Following detachment, the iceberg migrated rapidly northeastward, reaching waters near Cape Washington by 19 March (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). The iceberg then continued northward, approaching to within approximately 40 km south of Coulman Island (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec), and by 16 June was observed in close proximity to the island\u0026rsquo;s southern coastline (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). Thereafter, the iceberg progressed northward along the island\u0026rsquo;s eastern flank (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee), following a trajectory consistent with the spatial distribution of surrounding consolidated pack ice. Imagery from 16 July shows that the western terminus of the iceberg became increasingly constrained by surrounding sea ice near Coulman Island (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). During this period, the iceberg exhibited the onset of counter-clockwise rotation. Subsequent scenes show continued rotation accompanied by a reduction in translational motion (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg). By 28 July, the iceberg appears to have become topographically anchored or grounded at its observed position adjacent to Coulman Island (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh). The most recent SAR image acquired on 13 November 2025 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ei) shows no discernible change in iceberg position or orientation relative to late July. This observation is consistent with the iceberg remaining stationary for several months following grounding in late July 2025.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eLong-term Chick Census at the Coulman Island Colony.\u003c/b\u003e Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e presents a long-term census of emperor penguin chicks at Coulman Island spanning 1983 to 2025. The time series comprises data from 21 breeding seasons, integrating historical records reported by Barber-Meyer et al. (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) and Kooyman and Ponganis (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) with standardised aerial survey monitoring conducted since 2017 by the Korea Polar Research Institute (KOPRI) (see Methods). Across the full observation period, chick abundance at the Coulman Island colony shows substantial interannual variability over multiple decades.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAmong observations prior to 2000, the highest recorded chick count was 34,735 individuals in 1992, followed by 27,920 in 1990 and 21,708 in 1983. The mean chick abundance between 1983 and 2000 was 24,667\u0026thinsp;\u0026plusmn;\u0026thinsp;6,622 individuals. Literature-based records from the period after 2000 and prior to the initiation of KOPRI surveys also show substantial interannual variability. During this interval, chick counts of 25,244 individuals were reported in 2012 and 22,511 individuals in 2008. The mean for the post-2000 pre-KOPRI period was 18,305\u0026thinsp;\u0026plusmn;\u0026thinsp;5,651 individuals, lower than the 1983\u0026ndash;2000 mean. This period included several years with low chick counts, including 9,305 individuals in 2010 and 12,382 individuals in 2011 (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSince 2017, aerial photograph\u0026ndash;based surveys conducted by the Korea Polar Research Institute (KOPRI) have provided a standardised time series of chick counts at Coulman Island. During this period, recorded chick numbers were 16,571 in 2017, 21,286 in 2018, 24,464 in 2019, 23,223 in 2021, 22,903 in 2022, 18,723 in 2023, and 21,242 in 2024, yielding a mean of 21,202\u0026thinsp;\u0026plusmn;\u0026thinsp;2,745 individuals. In contrast, the 2025 chick count represents the lowest value recorded since 1983 and falls below the range documented during the KOPRI monitoring period. During the November survey, 6,081 chicks were counted. A subsequent December survey identified additional small breeding sub-groups, increasing the final total to 6,658 individuals (see Methods). The 2025 total corresponds to an approximate 69% reduction relative to both the KOPRI-era mean (21,202 individuals) and the 2024 count (21,242 individuals). The proportional decline in 2025 exceeds that reported for 2010, when chick production was estimated at 56% of the 2006 minimum and 41% of the 2008 estimate (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The total number of adults counted in 2025 was 15,242, yielding a chick-to-adult ratio of approximately 0.44, which is slightly below the lower bound of the previously reported range (0.46\u0026ndash;0.99) for the Coulman Island colony (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003e \u003cb\u003eAccessibility Collapse and Its Potential Role in Reduced Chick Survival.\u003c/b\u003e We describe this phenomenon as an accessibility collapse, in which breeding and foraging habitats remain physically present, but functional connectivity between them is disrupted by transient physical barriers. The 2025 event at Coulman Island is consistent with the possibility that, even under relatively stable landfast sea-ice conditions, the grounding of a single large iceberg may substantially constrain functional access between breeding and foraging habitats and be associated with reduced chick survival. Notably the timing of iceberg immobilisation coincided with the transition from incubation to early chick rearing, a period recognised as particularly sensitive to changes in habitat accessibility and environmental conditions (e.g., Fretwell et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Jenouvrier et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Trathan et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). During this phase, successful parental coordination and food provisioning depend on reliable access between the breeding site and adjacent marine habitat (Sara Labrousse et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Winterl et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Disruption during this stage may represent a plausible mechanistic pathway linking altered habitat accessibility to reduced chick survival.\u003c/p\u003e \u003cp\u003eField observations in November 2025 documented an approximately 20 m high vertical ice wall immediately north of the Coulman Island colony, forming a continuous physical barrier between the breeding site and offshore foraging areas (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Very-high-resolution optical imagery further showed a marked reduction in guano staining and aggregation signatures at the breeding site in 2025 compared with 2024 (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, d). Guano accumulation detected in satellite imagery has been widely used as a proxy for colony presence and breeding activity in emperor penguins (Fretwell et al., 2012; LaRue et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Although surface appearance may also be influenced by snowfall or local snow redistribution, the near absence of staining patterns, together with direct field observations at the colony, is consistent with substantially reduced breeding output during the 2025 season. These remote-sensing indicators coincide temporally with an approximately 69% reduction in chick numbers, recorded during two spring surveys in 2025 using the same census protocols applied in previous years (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), supporting the interpretation of a marked reduction in breeding output relative to recent observations.\u003c/p\u003e \u003cp\u003eThe scale of reproductive loss observed in 2025 is consistent with the close temporal alignment between iceberg grounding and the phase of the emperor penguin breeding cycle when energetic provisioning demands are highest. Following egg laying in May\u0026ndash;June, males incubate eggs through June\u0026ndash;July while females undertake extended foraging trips at sea (Supplementary Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Given the timing of iceberg grounding in late July, incubation and hatching likely proceeded largely as normal. However, when females returned to relieve incubating males, iceberg-induced access constraints may have delayed or disrupted parental exchange. Likewise, males completing incubation may have experienced difficulty accessing viable routes to the sea, potentially compounding delays in coordinated foraging and return exchanges. Disruption of these tightly synchronised parental roles during early chick rearing could substantially reduce food delivery to newly hatched chicks, making starvation a plausible outcome (Jenouvrier et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Massom et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Zimmer et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The initial field survey documented multiple chick carcasses within the colony area (Supplementary Fig. S2), a pattern compatible with elevated early-stage mortality. While some level of chick mortality occurs annually in emperor penguin colonies (Barber-Meyer et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Barbraud \u0026amp; Weimerskirch, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2001\u003c/span\u003e), chick carcasses appeared to be encountered more frequently during site visits in 2025 than in previous years; however, these impressions were not based on systematic counts.\u003c/p\u003e \u003cp\u003eThe observed reduction in chick numbers occurred despite relatively stable landfast sea-ice conditions similar to those in the previous year (refer to Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, d). This pattern is consistent with the 2025 event differing from declines primarily associated with sea-ice loss or local habitat collapse (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Instead, the combined observations are consistent with a disruption of functional connectivity between breeding and foraging habitats. This configuration corresponds to what we term an accessibility collapse, in which breeding and foraging habitats remain physically present while the movement corridors linking them are obstructed. Under such conditions, normal parental exchange and chick provisioning may become constrained, even in the absence of substantial changes in sea-ice extent or stability.\u003c/p\u003e \u003cp\u003eThe evidence linking iceberg-induced access blockage to reduced breeding output is inferential rather than directly demonstrative of causality. This interpretation is based on the close spatio-temporal alignment between iceberg grounding, the disappearance of surface indicators of colony occupation, and the substantial reduction in chick numbers, rather than on direct observations of failed parental exchange. Although adults were also counted during the survey (15,242 individuals), alternative explanations, including partial redistribution to neighbouring colonies, cannot be fully excluded (Cristofari et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Fretwell \u0026amp; Trathan, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; LaRue et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Nevertheless, collectively, the 2025 event is consistent with the possibility that a short-lived but substantial physical barrier to movement between the ocean and the breeding site was present during a sensitive phase of the emperor penguin life cycle, and that such a barrier may have contributed to reduced chick survival.\u003c/p\u003e \u003cp\u003e \u003cb\u003eIceberg Morphology as a Geometric Trap.\u003c/b\u003e Beyond the mere presence of a grounded iceberg, its detailed morphology appears to have influenced the degree to which access to the Coulman Island breeding site was constrained. Photogrammetry-based elevation analysis (see Methods) reveals marked asymmetry in iceberg geometry along its grounding axis (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). In the western sector (transects T1\u0026ndash;T2), the ocean-facing side forms a relatively gentle slope, whereas the colony-facing southern margin rises abruptly as a sub-vertical escarpment exceeding 20 m in height, effectively limiting direct access to the breeding site. In the eastern sector (transects T3\u0026ndash;T4), steep ice faces are present on both the colony-facing southern side and the ocean-facing northern side, forming a more topographically confined configuration. Notably, a narrow passage of approximately 1 km intermittently persisted along the eastern margin between the iceberg and Coulman Island (see Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). This corridor was not fully obstructed and may have allowed limited movement between the colony and offshore waters. This asymmetric structure may have functioned as a geometric trap, defined here as a topographic arrangement in which asymmetric slopes and limited openings increase movement costs and delay access to the breeding site. Although the eastern corridor remained partially open, accessing this passage likely required substantial lateral movement along the iceberg margin, increasing travel distance and time. Given the asymmetric slope configuration, individuals approaching along the gently sloping western face may have been preferentially channelled toward the impassable southern escarpment, thereby increasing travel time before locating the narrow eastern opening. Field observations documenting adult penguins remaining in prolonged stasis along the southern ice walls (Supplementary Fig. S3) are compatible with restricted and spatially heterogeneous access pathways at the time of observation. While rerouting through the eastern corridor cannot be excluded, the observed spatial concentration of individuals suggests that access constraints were non-uniform and likely imposed differential movement costs, particularly in terms of increased travel time and energetic expenditure, across the iceberg perimeter (Jenouvrier et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Kooyman et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Consequently, delays associated with locating or navigating limited access corridors during early chick rearing could substantially reduce provisioning frequency to newly hatched chicks (Barbraud et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; S. Labrousse et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Such topographically induced delays are particularly consequential during the early chick-rearing period, when provisioning schedules are tightly constrained and energetic margins are narrow. Following hatching, emperor penguin chicks can survive only for a limited period on esophageal secretions (penguin milk) provided by the incubating male (Pr\u0026eacute;vost, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e1961\u003c/span\u003e; Wienecke \u0026amp; Robertson, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e1997\u003c/span\u003e). Even modest increases in travel time under these conditions may therefore translate into disproportionate increase in chick mortality risk (Jenouvrier et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Trathan et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eDistinctiveness from Historical and Regional Analogues.\u003c/b\u003e The 2025 reduction in breeding output at Coulman Island differs in several respects from previously documented declines at this colony and elsewhere (Barber-Meyer et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Long-term monitoring has documented substantial interannual variability in chick numbers at Coulman Island, including an approximately 46% decline in 1993 and a reduction exceeding 50% in 2010 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). The 2010 decline was accompanied by reduced adult attendance and was interpreted as reflecting physiological or behavioural decisions by adults to forego breeding, potentially associated with reproductive senescence or insufficient energetic reserves (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The rapid recovery of adult numbers by 2011 supports the interpretation that this event primarily reflected a temporary suspension of breeding rather than large-scale loss following breeding initiation.\u003c/p\u003e \u003cp\u003eIn contrast, observations from 2025 suggest that many adults initiated breeding but experienced early-stage reproductive loss, as evidenced by the continued presence of adults at the colony, a reduced chick-to-adult ratio, and minimal late-season surface evidence of active breeding. This inference is supported by the continued presence of adults at the colony alongside a relatively low chick-to-adult ratio (0.44). While such ratios are known to vary among colonies and years (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), this pattern is more consistent with reduced breeding output during chick rearing than solely with pre-breeding abstention (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Accordingly, the 2025 event appears distinct from previously documented mechanisms and is more consistent with an extrinsic physical disruption than with intrinsic life-history trade-offs.\u003c/p\u003e \u003cp\u003eComparisons with other iceberg-related reproductive declines further clarify this distinction. The well-documented impacts of the B15A\u0026ndash;C16 iceberg complex at Cape Crozier and Beaufort Island illustrate two contrasting mechanisms (Kooyman et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). At Cape Crozier, reduced breeding output was associated primarily with the destruction or destabilisation of fast-ice breeding habitat. At Beaufort Island, by contrast, breeding habitat remained intact, but access routes were obstructed, necessitating extended detours that disrupted provisioning. The Coulman Island event more closely resembles the Beaufort Island mechanism, although important differences remain. Unlike Beaufort Island, the semi-enclosed coastal geometry surrounding the Coulman Island colony (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) appears to have restricted the availability of alternative navigation routes. Whereas penguins at Beaufort Island undertook extended detours, the Coulman Island iceberg exhibited an asymmetric configuration, with a gently sloping ocean-facing surface that may have channelled returning adults toward an impassable southern escarpment, thereby increasing movement costs before alternative routes were located (Supplementary Fig. S4).\u003c/p\u003e \u003cp\u003eAlternative explanations, particularly large-scale redistribution of breeders to neighbouring colonies, are not strongly supported by available evidence. Coulman Island is classified as a suburbanite colony, with late-season dispersal typically limited to approximately 10\u0026ndash;15 km (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Moreover, chick counts at the two nearest colonies, Cape Washington and Cape Roget, in 2025 were comparable to their respective five-year means, with only modest increases relative to 2024 (unpublished data). Even when combined, these increases account for approximately 5.5% of the deficit observed at Coulman Island, suggesting that redistribution alone is unlikely to fully explain the magnitude of decline.\u003c/p\u003e \u003cp\u003eTo evaluate whether surviving chicks experienced compromised condition, flipper length and body mass were measured in 37 individuals during a December 2025 visit. No significant differences were detected relative to chicks measured at Cape Washington. This pattern suggests that chicks surviving beyond the early post-hatching period were able to receive adequate provisioning later in the season. In addition, during ground visits, no adult carcasses were observed. Although access was severely constrained, it was not entirely blocked, suggesting that delayed but ultimately successful parental exchange may have occurred. Available observations therefore indicate that the primary demographic effect of the 2025 event was expressed through reduced chick survival rather than detectable adult mortality.\u003c/p\u003e \u003cp\u003e \u003cb\u003eFuture Perspectives: Stochastic Risks in a Changing Ross Sea.\u003c/b\u003e The 2025 Coulman Island event is more appropriately interpreted as a localised, event-driven disturbance rather than as evidence of chronic risk to emperor penguins across the Ross Sea. The Ross Sea region has historically exhibited relatively high sea-ice stability and has been identified as a potential climate refuge for emperor penguins under future warming scenarios (Jenouvrier et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Jenouvrier et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Nevertheless, this event highlights a class of stochastic risks that may be insufficiently represented in demographic models primarily focused on large-scale mean-state variables, such as regional sea-ice extent. The drift and grounding pathway of the 2025 iceberg underscores the importance of both timing and spatial configuration in shaping ecological outcomes. Unlike iceberg C-33, which transited the Coulman Island sector in October 2016 during fast-ice breakup and did not ground (Dziak et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), the 2025 iceberg arrived in late July, coinciding with peak seasonal consolidation of landfast ice (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). This timing likely enhanced coupling with the consolidated ice matrix, likely increased rotational pivoting, grounding, and prolonged immobilisation near the coast.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIncreasing instability of Antarctic ice shelves over recent decades has been identified as a contributing factor to the frequency of large iceberg calving events (Greene et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Scambos et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Wille et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), a trend closely linked to climate-change signals, including ocean warming (Etourneau et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Joughin \u0026amp; Alley, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Large icebergs that remain grounded near the coast for extended periods pose a direct threat to the geomorphological integrity of emperor penguin breeding sites or disrupt access routes to key foraging areas, leading to substantial ecological disturbance. As climate change progresses, the combined effects of increased sea-ice instability, landfast-ice breakup, and earlier seasonal sea-ice loss are expected to amplify the stochastic risks associated with such large iceberg events (Schmidt \u0026amp; Ballard, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eEmperor penguin responses to environmental change are likely nonlinear, emerging from interactions among sea ice, prey availability, episodic disturbance, and movement processes such as dispersal and emigration (Ainley et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; LaRue et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Although inter-colony connectivity and behavioural flexibility may buffer populations at the metapopulation scale (Bri\u0026euml;d et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Fretwell \u0026amp; Trathan, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; LaRue et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), this flexibility does not preclude severe local reproductive collapse when accessibility abruptly declines at critical stages of the breeding cycle.\u003c/p\u003e \u003cp\u003eFuture assessments of emperor penguin breeding prospects would benefit from explicitly incorporating stochastic iceberg\u0026ndash;sea-ice interactions, including the timing of calving, drift pathways, grounding probability, and residence time near breeding sites (Fretwell \u0026amp; Trathan, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Jenouvrier et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Calving timing, drift pathway, grounding probability, and coastal residence time define a suite of low-frequency but high-impact stochastic risks that can generate severe local reproductive failure even under otherwise favourable regional sea-ice conditions. Addressing these risks will require long-term, cross-disciplinary monitoring frameworks that integrate ocean circulation, sea-ice dynamics, landfast-ice development, and ice-shelf stability. Such integrated approaches are essential for identifying emerging ecological chokepoints and for developing early-warning indicators of vulnerability in an increasingly dynamic Antarctic system.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003cb\u003eStudy Area and Colony Context.\u003c/b\u003e The study was conducted at the emperor penguin colony located on the fast ice along the northern margin of Coulman Island (73\u0026deg;28\u0026prime; S, 169\u0026deg;45\u0026prime; E), North Victoria Land, Ross Sea, Antarctica (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This colony is situated within a semi-enclosed coastal embayment bounded by Cape Jones to the south and open waters extending northward toward the Ross Sea polynya system.\u003c/p\u003e \u003cp\u003eThe northwestern sector of Coulman Island, together with Cape Washington and Cape Roget, is recognised as one of the most important emperor penguin breeding regions in the Ross Sea and has historically supported one of the most productive mega-colonies globally (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The colony is established on seasonally forming annual fast ice along the island's northern coast and is characterised by unconstrained topographic relief, permitting extensive lateral expansion of the breeding aggregation. On this basis, the Coulman Island colony is classified as a \u003cem\u003esuburban colony\u003c/em\u003e (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). During the breeding season, the colony typically occupies an area of approximately 5 km \u0026times; 2 km and, between late October and early December, frequently undergoes spatial fragmentation into 10\u0026ndash;30 discrete sub-colonies. These subunits have been reported to shift up to 10\u0026thinsp;~\u0026thinsp;15 km from the original breeding location in response to local fast-ice conditions and access to foraging areas.\u003c/p\u003e \u003cp\u003e \u003cb\u003eEmperor Penguin Census Surveys.\u003c/b\u003e This study comprised two field surveys conducted on 13 November 2025 and 5 December 2025 at the Coulman Island emperor penguin colony. The November survey was conducted under the auspices of the Korea Polar Research Institute (KOPRI) annual monitoring programme and primarily aimed to estimate chick and adult abundance at Coulman Island and other colonies in northern Victoria Land. The December survey was designed to complement the initial observations and focused on (i) verification of habitat conditions, (ii) limited morphometric assessment of chick body condition, and (iii) high-resolution documentation of iceberg topography (elevation and morphology).\u003c/p\u003e \u003cp\u003eBoth surveys utilised a helicopter-mounted platform for systematic aerial photogrammetry. During standard census operations, flight altitude was maintained at approximately 600 m above ground level, ensuring a consistent ground sampling distance comparable to that used in KOPRI monitoring surveys since 2017. This consistency in flight altitude, image resolution, and survey extent ensured methodological comparability across years.\u003c/p\u003e \u003cp\u003eImage interpretation and counting were performed through a systematic manual visual census conducted independently by four experienced observers. Counts from each observer were compared to assess inter-observer variability. The coefficient of variation (CV) among observers was 2.04%, indicating high consistency. This level of agreement is comparable to, or lower than, inter-observer variability previously reported for penguin counts derived from high-resolution imagery (typically\u0026thinsp;\u0026le;\u0026thinsp;2.5%; Fretwell, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Adult emperor penguins were distinguished by their characteristic black-and-white plumage, whereas chicks exhibited predominantly grey coloration, facilitating reliable classification under the image resolution achieved.\u003c/p\u003e \u003cp\u003eAt the time of the November survey, the breeding aggregation had transitioned from a consolidated incubation cluster to multiple smaller subgroups, consistent with patterns described for the early chick-rearing phase (Kooyman \u0026amp; Ponganis, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Each subgroup was visually delineated, imaged separately, and counted independently prior to aggregation of totals (Supplementary Fig. S6). Survey coverage included the full spatial extent of the breeding area and adjacent fast-ice margins to minimise omission of peripheral groups.\u003c/p\u003e \u003cp\u003eThe November survey recorded 6,081 chicks. During the December visit, additional small subgroups located near the colony periphery were identified, resulting in a revised total of 6,658 chicks. Both surveys applied identical counting criteria to maintain interannual comparability with previous KOPRI datasets (2017\u0026ndash;2024). Adult counts were conducted concurrently in November using the same imagery-based approach, yielding a total of 15,242 individuals.\u003c/p\u003e \u003cp\u003eDuring the December survey, limited ground landings were conducted at selected locations to obtain morphometric measurements of 37 chicks. Body mass was measured using a portable digital scale, and flipper length was measured using a standard calliper. Individuals selected for comparison were within a flipper-length range comparable to chicks measured at Cape Washington during the same season.\u003c/p\u003e \u003cp\u003eSince 2017, KOPRI has conducted annual aerial surveys to monitor chick abundance at Coulman Island. Surveys were not conducted in 2020 due to restrictions associated with the COVID-19 pandemic. The resulting time series provides a consistent baseline for evaluating interannual variability in breeding output and for comparison with satellite-derived colony estimates.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSatellite Data and Iceberg Tracking.\u003c/b\u003e To reconstruct the calving, drift, grounding, and final configuration of the iceberg, and to assess its association with reduced chick survival at Coulman Island, we integrated multi-sensor satellite datasets with complementary spatial and temporal characteristics. These included MODIS Terra True Color imagery, Sentinel-1 synthetic aperture radar (SAR), Landsat-8/9 Operational Land Imager (OLI), and very-high-resolution WorldView imagery.\u003c/p\u003e \u003cp\u003eThe timing of calving from the Nansen Ice Shelf was determined using MODIS Terra imagery at 500 m spatial resolution. High-resolution optical imagery from WorldView, Landsat, and Sentinel-2 was examined but did not provide suitable coverage for the critical period, either due to data gaps or insufficient visibility of the detachment event. Despite partial cloud cover, MODIS imagery acquired on 12 March 2025 revealed a distinct structural discontinuity at the ice-shelf front, and subsequent imagery confirmed the presence of an independent iceberg body. These observations enabled identification of 12 March 2025 as the calving date.\u003c/p\u003e \u003cp\u003ePost-calving drift was tracked using Sentinel-1 SAR imagery, which provides all-weather, day-and-night observational capability. Sentinel-1 scenes were obtained from the Alaska Satellite Facility Data Search Portal and all available acquisitions between 11 March and 28 July 2025, during which the iceberg was clearly detectable within the sensor swath, were included in the analysis. A total of 27 SAR scenes were analysed. The iceberg outline was manually digitised in each scene, and centroid positions derived from these polygons were linked sequentially to reconstruct the drift trajectory. Grounding was inferred from a marked reduction in translational displacement, the onset of rotational pivoting, and subsequent positional stability adjacent to the southern margin of Coulman Island after 28 July 2025.\u003c/p\u003e \u003cp\u003eLandsat-8/9 OLI imagery (30 m spatial resolution), obtained from the United States Geological Survey EarthExplorer archive, was used to delineate the final horizontal footprint of the grounded iceberg and to quantify its spatial relationship with the northern access corridor to the colony. The scene acquired on 11 November 2025, temporally closest to the field survey, was used to estimate iceberg surface area and assess occlusion of the primary access pathway.\u003c/p\u003e \u003cp\u003eVery-high-resolution Maxar WorldView imagery was used to evaluate surface biological indicators at the breeding site. WorldView-3 imagery acquired on 20 November 2024 and WorldView-2 imagery acquired on 6 November 2025 provided sub-meter spatial resolution necessary for reliable visual discrimination of guano staining patterns.\u003c/p\u003e \u003cp\u003eTogether, these satellite datasets enabled a systematic reconstruction of iceberg dynamics and their spatial configuration relative to the breeding site, forming the basis for interpretation of potential access constraints during the 2025 breeding season.\u003c/p\u003e \u003cp\u003e \u003cb\u003eIdentification of the Primary Commuting Pathway.\u003c/b\u003e The primary commuting pathway between the Coulman Island colony and adjacent marine foraging areas was identified based on repeated field observations conducted during annual surveys since 2017, supplemented by aerial imagery. Across multiple breeding seasons, adult emperor penguins were consistently observed moving predominantly along the northern and northeastern margin of the colony toward the sea-ice edge between Cape Jones and Coulman Island. These directional patterns were documented qualitatively during helicopter-based surveys and were supported by aggregation trails and surface disturbance patterns visible in high-resolution imagery (Supplementary Fig. S6).\u003c/p\u003e \u003cp\u003e \u003cb\u003eIceberg Morphology and Elevation Analysis\u003c/b\u003e. To evaluate whether the grounded iceberg may have functioned as a geometric constraint on movement between the colony and offshore waters, we constructed and analysed a high-resolution Digital Surface Model (DSM) of the iceberg using aerial photogrammetry. For contextual assessment of relative position and elevation, we referenced the 2 m-resolution Reference Elevation Model of Antarctica (REMA) v2.0 mosaic (Howat et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Horizontal coordinates were defined in WGS84 / Antarctic Polar Stereographic (EPSG:3031), and elevations were initially referenced to the WGS84 ellipsoid (EPSG:4979).\u003c/p\u003e \u003cp\u003eThe aerial DSM was generated from 1,071 photographs acquired from a helicopter platform circling the iceberg. Most images were captured at approximately 1,200 m above ground level to document the overall geometry of the iceberg, while additional lower-altitude flights at approximately 600 m were conducted along steep cliff sections to obtain higher-detail coverage of vertical and near-vertical surfaces. Imagery was acquired using a Canon EOS R5 camera equipped with a 100 mm lens. Three-dimensional reconstruction was performed in Agisoft Metashape Professional v2.2.2 using structure-from-motion workflows, and the resulting model was processed in Global Mapper to produce elevation products at an effective spatial resolution of ~\u0026thinsp;1.2 m. Because the aerial DSM and REMA employ different vertical reference systems, the EGM2008 geoid was applied to convert ellipsoidal elevations to orthometric heights for consistency.\u003c/p\u003e \u003cp\u003eGiven the remote Antarctic setting, ground control points were not available. However, the objective of this analysis was to quantify relative morphological contrasts, on the order of tens of metres, between the colony-facing and ocean-facing flanks of the iceberg. Such large-scale geometric asymmetries are robust to metre-scale vertical uncertainty and provide a basis for evaluating whether iceberg morphology may have increased travel distance, constrained access corridors, or redirected movement pathways.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was supported by Korea Institute of Marine Science \u0026amp; Technology Promotion(KIMST) grant funded by the Ministry of Oceans and Fisheries(KIMST RS-2022-KS221661)\u003c/p\u003e \u003cp\u003eJinku Park\u003csup\u003e1\u003c/sup\u003e, Jong-U Kim\u003csup\u003e2\u003c/sup\u003e, Youmin Kim\u003csup\u003e2,3\u003c/sup\u003e, Yongsik Jeong\u003csup\u003e1\u003c/sup\u003e, Younggen Oh\u003csup\u003e2,4\u003c/sup\u003e, Jungyuem Kim\u003csup\u003e2\u003c/sup\u003e, Jeong-Hoon Kim\u003csup\u003e2*\u003c/sup\u003e\u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003eJ.P. conceived this study and led the manuscript writing. J.-H.K. conceived and supervised the study. J.U.K. and Y.K. contributed to the acquisition of field observation data and participated in writing and editing the manuscript. Y.J. contributed to data processing and analysis. Y.O. reviewed and provided feedback on the manuscript. J.K. assisted in the acquisition of field observation data.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e \u003cp\u003eWe would like to express our sincere gratitude to Myeongho Seo, safety instructor, for his valuable assistance with the aerial photography campaign and the iceberg surface modeling. His support greatly improved the quality and completeness of this study. We also extend our sincere appreciation to Gerald Kooyman, Michelle LaRue, and Cassandra Brooks for their careful review of the manuscript and their constructive comments. Their insights and expertise substantially strengthened the scientific interpretation and clarity of this work.\u003c/p\u003e\n\u003ch3\u003eData availability\u003c/h3\u003e\n\u003cp\u003eLandsat-8 and Landsat-9 Operational Land Imager (OLI) surface reflectance images used to assess regional sea-ice conditions and the presence of grounded icebergs around Coulman Island were obtained from the U.S. Geological Survey EarthExplorer portal (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://earthexplorer.usgs.gov\u003c/span\u003e\u003cspan address=\"https://earthexplorer.usgs.gov\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). Very high-resolution optical satellite imagery used for visual confirmation of emperor penguin breeding status and guano presence, including WorldView-3 (20 November 2024) and WorldView-2 (6 November 2025), was provided by Maxar Technologies and analysed under a research license; these data are not publicly redistributable but can be accessed from the data provider subject to licensing conditions. MODIS Terra true-color imagery used to constrain the timing of iceberg calving from the Nansen Ice Shelf was accessed via NASA Worldview (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://worldview.earthdata.nasa.gov\u003c/span\u003e\u003cspan address=\"https://worldview.earthdata.nasa.gov\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). Sentinel-1 C-band SAR data employed to reconstruct the iceberg drift and grounding trajectory were obtained from the Alaska Satellite Facility (ASF) Distributed Active Archive Center (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://search.asf.alaska.edu\u003c/span\u003e\u003cspan address=\"https://search.asf.alaska.edu\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). The Reference Elevation Model of Antarctica (REMA) v2.0 mosaic, used as ancillary elevation data for iceberg surface analysis, is publicly available from the Polar Geospatial Center (PGC) at the University of Minnesota (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.pgc.umn.edu/data/rema\u003c/span\u003e\u003cspan address=\"https://www.pgc.umn.edu/data/rema\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). Helicopter-based aerial photographs acquired during the November and December 2025 field surveys using a Canon EOS R5 camera were collected by the authors and are not publicly archived due to logistical and operational constraints, but may be made available upon reasonable request to the corresponding author.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAinley, D. G., Russell, J., Jenouvrier, S., Woehler, E., Lyver, P. O. B., Fraser, W. R., \u0026amp; Kooyman, G. L. (2010). 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Foraging movements of emperor penguins at Pointe G\u0026eacute;ologie, Antarctica. \u003cem\u003ePolar Biology\u003c/em\u003e, \u003cem\u003e31\u003c/em\u003e(2), 229\u0026ndash;243. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00300-007-0352-5\u003c/span\u003e\u003cspan address=\"10.1007/s00300-007-0352-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\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":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-9024637/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9024637/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRapid environmental change in Antarctica highlights that emperor penguin populations are vulnerable not only to regional sea-ice decline but also to localized physical disturbances that disrupt breeding colony access. This study examines a ~ 69% decline in springtime chick counts at Coulman Island in 2025, based on integrated multi-satellite analyses and field surveys. A giant iceberg calved from the Nansen Ice Shelf became grounded in late July along a narrow coastal margin, obstructing the colony's primary access corridor prior to chick rearing. Three-dimensional iceberg reconstruction reveals pronounced morphological asymmetry functioning as a \"geometric trap\": gentler ocean-facing slopes encouraged adults to ascend, while the colony-facing margin presented a sub-vertical escarpment exceeding 20 m, funneling penguins into impassable culs-de-sac. The semi-enclosed geography of Coulman Island further obscured a residual ~ 1 km passage, preventing effective detours. Very-high-resolution imagery and field observations confirmed near-total absence of guano staining and extensive chick mortality. These findings provide compelling evidence for a \"functional collapse of accessibility,\" wherein iceberg morphology and regional topography synergistically severed the colony's energetic connectivity. As climate change increases ice-shelf instability and iceberg discharge, stochastic physical barriers may increasingly rival gradual sea-ice decline in determining emperor penguin breeding outcomes.\u003c/p\u003e","manuscriptTitle":"Iceberg-Induced Collapse of Access Connectivity and a Dramatic Reduction in Chick Survival at the Coulman Island Emperor Penguin Colony","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-11 18:37:13","doi":"10.21203/rs.3.rs-9024637/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"communications-earth-and-environment","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"commsenv","sideBox":"Learn more about [Communications Earth and Environment](https://www.nature.com/commsenv/)","snPcode":"","submissionUrl":"","title":"Communications Earth \u0026 Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Communications Series","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"73dfeee5-8901-4cea-9b25-beb033f5fd52","owner":[],"postedDate":"March 11th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":63901221,"name":"Earth and environmental sciences/Environmental sciences/Environmental impact"},{"id":63901222,"name":"Earth and environmental sciences/Ecology/Ecosystem ecology"}],"tags":[],"updatedAt":"2026-05-04T08:55:56+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-11 18:37:13","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9024637","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9024637","identity":"rs-9024637","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}