Unifying theories on the Southern Ocean bio-optical anomaly

Unifying theories on the Southern Ocean bio-optical anomaly | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Unifying theories on the Southern Ocean bio-optical anomaly Xuerong Sun, Robert Brewin, Giorgio Dall'Olmo, Jaime Pitarch, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7906673/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Phytoplankton in the Southern Ocean play a major role in regulating global biogeochemical cycles, but the region's remoteness makes in-situ monitoring challenging. Satellite ocean colour is among the best tools to monitor phytoplankton dynamics synoptically through retrievals of the chlorophyll-a concentration (Chl-a). However, optical properties in the Southern Ocean deviate from global patterns, causing persistent ocean-colour anomalies and biased Chl-a retrievals. Theories have attributed these anomalies to differences in either phytoplankton composition or non-algal constituents relative to global norms, each capturing important facets but without a unified explanation. Here, using an extensive set of in-situ measurements, we demonstrate that phytoplankton size structure in the Southern Ocean is fundamentally different to other ocean basins. Incorporating this distinct size distribution into an ocean-colour model, with the same set of optical parameters, successfully reproduces the observed bio-optical anomaly. Model simulations further reveal that these size shifts affect bulk optical properties of both phytoplankton and non-algal constituents, providing a unified explanation that reconciles the observed regional anomalies within a global framework. Tracking changes in phytoplankton size structure is key to improving satellite Chl-a trends in the Southern Ocean, with important implications for improved monitoring of the regional biogeochemical cycles that sustain Earth's climate system. Earth and environmental sciences/Ocean sciences/Marine biology Biological sciences/Ecology/Biooceanography/Microbial biooceanography Physical sciences/Optics and photonics/Optical techniques/Imaging and sensing Full Text Additional Declarations There is NO Competing Interest. Supplementary Files Supplementary.pdf Supplementary of Article 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7906673","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":532772392,"identity":"74a617a5-c993-4650-8dad-60963e136d9f","order_by":0,"name":"Xuerong 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Satellite ocean colour is among the best tools to monitor phytoplankton dynamics synoptically through retrievals of the chlorophyll-a concentration (Chl-a). However, optical properties in the Southern Ocean deviate from global patterns, causing persistent ocean-colour anomalies and biased Chl-a retrievals. Theories have attributed these anomalies to differences in either phytoplankton composition or non-algal constituents relative to global norms, each capturing important facets but without a unified explanation. Here, using an extensive set of in-situ measurements, we demonstrate that phytoplankton size structure in the Southern Ocean is fundamentally different to other ocean basins. Incorporating this distinct size distribution into an ocean-colour model, with the same set of optical parameters, successfully reproduces the observed bio-optical anomaly. Model simulations further reveal that these size shifts affect bulk optical properties of both phytoplankton and non-algal constituents, providing a unified explanation that reconciles the observed regional anomalies within a global framework. 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