Observational evidence for a poleward migration of warm Circumpolar Deep Water towards Antarctica

Observational evidence for a poleward migration of warm Circumpolar Deep Water towards Antarctica | 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 Observational evidence for a poleward migration of warm Circumpolar Deep Water towards Antarctica Joshua Lanham, Sarah Purkey, Kaushik Srinivasan, Matthew Mazloff, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7021596/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Apr, 2026 Read the published version in Communications Earth & Environment → Version 1 posted You are reading this latest preprint version Abstract The formation and downwelling of cold Antarctic Bottom Water (AABW) and the concurrent upwelling of warm Circumpolar Deep Water (CDW) around the Antarctic margin are key processes in the global climate system, driving the renewal of cold dense water to the deep ocean, while transporting heat, nutrients, and carbon upwards and poleward towards Antarctic ice shelves. Observational and modelling studies have documented that AABW has warmed, freshened, and contracted in recent decades. However, the response of CDW to anthropogenic forcing is less clear, with some model-based studies projecting a poleward migration of its southern boundary. In this study, we utilise the physical and chemical seawater properties measured from relatively sparse ship-based observations to robustly classify Southern Ocean water masses. We then train a random forest machine learning model to accurately apply the water mass classification to the abundant Argo temperature and salinity data spanning the Southern Ocean over the past two decades, allowing for local assessment of variability on monthly-to-decadal timescales. Our analysis reveals an increase (decrease) in CDW thickness near (away from) the continent, indicating a poleward migration of CDW upwelling. This trend is accompanied by a contraction in AABW layer thickness along the Antarctic margin. This spatial redistribution suggests an enhanced heat flux toward the Antarctic continental shelf, with potential implications for basal ice shelf melting and sea-level projections. Earth and environmental sciences/Climate sciences/Ocean sciences/Physical oceanography Earth and environmental sciences/Ocean sciences/Physical oceanography Full Text Additional Declarations There is NO Competing Interest. Supplementary Files SI.pdf Supplementary Information Cite Share Download PDF Status: Published Journal Publication published 28 Apr, 2026 Read the published version in Communications Earth & Environment → 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. 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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-7021596","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":508900034,"identity":"309813df-d13b-4075-b57a-0fb3a51f141e","order_by":0,"name":"Joshua 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