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Abstract. In coastal polynyas, where sea-ice formation and melting occur, it is crucial to have accurate estimates of heat fluxes in order to predict future sea-ice dynamics. The Amundsen Sea Polynya is a coastal polynya in Antarctica that remains poorly observed by in situ observations because of its remoteness. Consequently, we rely on models and reanalysis that are un-validated against observations to study the effect of atmospheric forcing on polynya dynamics. We use austral summer 2022 shipboard data to understand the turbulent heat flux dynamics in the Amundsen Sea Polynya and evaluate our ability to represent these dynamics in ERA5. We show that cold- and dry-air outbreaks from Antarctica enhance air–sea temperature and humidity gradients, triggering episodic heat loss events. The ocean heat loss is larger along the ice-shelf front, and it is also where the ERA5 turbulent heat flux exhibits the largest biases, underestimating the flux by up to 141 W m−2 due to its coarse resolution. By reconstructing a turbulent heat flux product from ERA5 variables using a nearest-neighbor approach to obtain sea surface temperature, we decrease the bias to 107 W m−2. Using a 1D model, we show that the mean co-located ERA5 heat loss underestimation of 28 W m−2 led to an overestimation of the summer evolution of sea surface temperature (heat content) by +0.76 °C (+8.2×107 J) over 35 d. By obtaining the reconstructed flux, the reduced heat loss bias (12 W m−2) reduced the seasonal bias in sea surface temperature (heat content) to −0.17 °C (−3.30 × 107 J) over the 35 d. This study shows that caution should be applied when retrieving ERA5 turbulent flux along the ice shelves and that a reconstructed flux using ERA5 variables shows better accuracy.
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Chlorophyll Production in the Amundsen Sea Boosts Heat Flux to Atmosphere and Weakens Heat Flux to Ice Shelves
Abstract 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 +0.2C and +0.3C) 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.
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- PAR ID:
- 10542456
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 129
- Issue:
- 9
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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