{"paper_id":"1dce3e23-87ae-482d-b1a4-bacb26a9e62f","body_text":"In situ imaging of large colonial Phaeocystis quantifies inefficient carbon export | 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 In situ imaging of large colonial Phaeocystis quantifies inefficient carbon export Manon Laget, Andreas Rogge, Matthias Wietz, Lillian Musselman, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7773706/v2 This work is licensed under a CC BY 4.0 License Status: Posted Version 2 posted You are reading this latest preprint version Show more versions Abstract Phaeocystis is a cosmopolitan phytoplankter found across diverse marine environments, often forming extensive colonial blooms. Despite their global ecological significance, quantifying the distribution of large colonies and their contribution to carbon export remains challenging due to their fragile structure, limiting the understanding of the biological carbon pump. Here, we show the first in situ quantification of Phaeocystis colonies >600 µm in high spatiotemporal resolution using the Underwater Vision Profiler 6, a quantitative and non-destructive camera system, allowing a mechanistic understanding of flux attenuation. We document a massive colonial Phaeocystis bloom in the subarctic Labrador Sea, and a sedimentation event in the Antarctic Weddell Sea. The resulting carbon inventories indicate that large Phaeocystis colonies contribute little to vertical carbon fluxes below the productive mixed layer. Despite comprising an important fraction of large particle biovolume, they contributed at most 15% to vertical carbon fluxes in the surface Labrador Sea and 0.25% in the Weddell Sea upper mesopelagic. Their slow sinking velocity likely promoted grazing and remineralization in the upper water column, therefore reducing export efficiency into mesopelagic waters. As Phaeocystis blooms are expected to increase worldwide, integrating in situ high-resolution spatiotemporal data is essential to understand ecological dynamics and biogeochemical impacts of this cosmopolitan phytoplankton taxon. Earth and environmental sciences/Ocean sciences/Marine biology Earth and environmental sciences/Biogeochemistry/Carbon cycle Earth and environmental sciences/Ecology/Biogeochemistry/Carbon cycle Full Text Additional Declarations The authors declare no competing interests. Supplementary Files SuppInfo.pdf Cite Share Download PDF Status: Posted Version 2 posted You are reading this latest preprint version Show more versions 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-7773706\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":true,\"archivedVersions\":[],\"articleType\":\"Article\",\"associatedPublications\":[],\"authors\":[{\"id\":525698710,\"identity\":\"ec5443a2-14d5-4293-b5e3-0614c1aedb6d\",\"order_by\":0,\"name\":\"Manon 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