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Chlorophyll Production in the Amundsen Sea Boosts Heat Flux to Atmosphere and Weakens Heat Flux to Ice Shelves

The Amundsen Sea in West Antarctica features rapidly thinning ice shelves, large polynyas, and sizable spring phytoplankton blooms. Although considerable effort has gone into characterizing heat fluxes between the Amundsen Sea, its associated ice shelves, and the overlying atmosphere, the effect of...

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Bibliographic Details
Published in:Journal of geophysical research. Oceans 2024-09, Vol.129 (9), p.n/a
Main Authors: Twelves, A. G., Goldberg, D. N., Holland, P. R., Henley, S. F., Mazloff, M. R., Jones, D. C.
Format: Article
Language:English
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Summary:The Amundsen Sea in West Antarctica features rapidly thinning ice shelves, large polynyas, and sizable spring phytoplankton blooms. Although considerable effort has gone into characterizing heat fluxes between the Amundsen Sea, its associated ice shelves, and the overlying atmosphere, the effect of the phytoplankton blooms on the distribution of heat remains poorly understood. In this modeling study, we implement a feedback from biogeochemistry onto physics into MITgcm‐BLING and use it to show that high levels of chlorophyll—concentrated in the Amundsen Sea Polynya and the Pine Island Polynya—have the potential to increase springtime surface warming in polynyas by steepening the attenuation profile of solar radiation with depth. The chlorophyll‐associated warm anomaly (on average between +0.2° ^{\circ}$C and +0.3° ^{\circ}$C) at the surface is quickly dissipated to the atmosphere, by increases in longwave, latent and sensible heat loss from open water areas. Outside of the coastal polynyas, the summertime warm anomaly leads to an average sea ice thinning of 1.7 cm across the region, and stimulates up to 20% additional seasonal melting near the fronts of ice shelves. The accompanying cold anomaly, caused by shading of deeper waters, persists year‐round and affects a decrease in the volume of Circumpolar Deep Water on the continental shelf. This cooling ultimately leads to an average sea ice thickening of 3.5 cm and, together with associated changes to circulation, reduces basal melting of Amundsen Sea ice shelves by approximately 7% relative to the model scenario with no phytoplankton bloom. Plain Language Summary Near the Antarctic coastline the sea ice cover is broken by patches of open water, called polynyas, which often undergo a visible change in color from blue to green as spring progresses. This is due to the chlorophyll produced in blooms of microscopic algae. Here we use computer simulations to investigate the impact of this change in color on the delicate system of ice and ocean in the Amundsen Sea region of west Antarctica. We find that the “greening” of polynyas helps to trap more of the sun's energy close to the sea surface, but that this excess heat is then released back to the atmosphere over the course of the summer. Meanwhile, the deeper waters of the polynya are exposed to less energy from the sun and therefore are cooler than they would be if there were no algae bloom. Ultimately, the cooling of deep waters across the Amundsen Sea weakens
ISSN:2169-9275
2169-9291
DOI:10.1029/2024JC021121