EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2025-3149 Drivers of Phytoplankton Bloom Interannual Variability in the Amundsen and Pine Island Polynyas Liniger Guillaume https://orcid.org/0000-0001-5380-5425 1 2 3 Lannuzel Delphine 1 4 5 Moreau Sébastien 6 7 Dinniman Michael S. https://orcid.org/0000-0001-7519-9278 8 Strutton Peter G. https://orcid.org/0000-0002-2395-9471 1 2 4 Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia Australian Research Council Centre of Excellence for Climate Extremes, University of Tasmania, Hobart, Australia Monterey Bay Aquarium Research Institute, Moss Landing, CA, USA Australian Centre for Excellence in Antarctic Science, University of Tasmania, Hobart, Australia Australian Antarctic Program Partnership, University of Tasmania, Hobart, Australia Norwegian Polar Institute, Tromsø, Norway iC3: Centre for ice, Cryosphere, Carbon and Climate, Department of Geosciences, UiT The Arctic University of Norway, 9037 Tromsø, Norway Center for Coastal Physical Oceanography, Old Dominion University, Norfolk, VA, USA 25 07 2025 2025 1 34 Copyright: © 2025 Guillaume Liniger et al. 2025 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3149/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3149/egusphere-2025-3149.pdf

The Amundsen Sea Embayment experiences both the highest ice shelf melt rates and the highest biological productivity in West Antarctica. Using 19 years of satellite data and modelling output, we investigated the long-term influence of environmental factors on the phytoplankton bloom in the Amundsen sea (ASP) and Pine Island polynyas (PIP). We tested the prevailing hypothesis that changes in ice shelf melt rate could drive interannual variability in the polynyas&rsquo; surface chlorophyll-<em>a</em> (chl<em>a</em>) and Net Primary Productivity (NPP). We found that the interannual variability and long-term change in glacial meltwater may play an important role in chl<em>a</em> variance in the ASP, but not for NPP. Glacial meltwater does not explain the variability in both chl<em>a</em> and NPP in the PIP, where light and temperature are the main drivers<em>.</em> We attribute this to potentially greater amount of iron-enriched meltwater brought to the surface by the meltwater pump downstream of the PIP, and the coastal ocean circulation accumulating and transporting iron towards the ASP.