Supercooled water in austral summer in Prydz Bay, Antarctica |
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Authors: | Jiuxin Shi Yaoyao Cheng Yutian Jiao Jiaqiang Hou |
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Institution: | (1) University Bremen, Bremen, Germany;(2) Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany;(3) NASA Goddard Institute for Space Studies, New York, USA;(4) Present address: University of Helsinki, Helsinki, Finland |
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Abstract: | Supercooled water with temperatures below freezing point, was identified from hydrographic data obtained by Chinese and Australian
expeditions to Prydz Bay, Antarctica, during the austral summer. The study shows that most supercooled waters occurred at
depths of 63–271 m in the region north of the Amery Ice Shelf (AIS) front. The maximum supercooling was 0.16°C below the in-situ
freezing point. In temperature and salinity ranges of ?2.14–1.96°C and 34.39–34.46, respectively, the water was colder and
fresher than peripheral shelf water. The supercooled water had less variability in the vertical profiles compared to shelf
water. Based on analysis of their thermohaline features and spatial distribution, as well as the circulation pattern in Prydz
Bay, we conclude that these supercooled waters originated from a cavity beneath the AIS and resulted from upwelling just outside
of the AIS front. Water emerging from the ice shelf cools to an extremely low temperature (about ?2.0°C) by additional cooling
from the ice shelf, and becomes buoyant with the addition of melt water from the ice shelf base. When this water flows out
of the ice shelf front, its upper boundary is removed, and thus it rises abruptly. Once the temperature of this water reaches
below the freezing point, supercooling takes place. In summer, the seasonal pycnocline at ~100 m water depth acts as a barrier
to upwelling and supercooling. The upwelling of ice shelf outflow water illuminates a unique mid-depth convection of the polar
ocean. |
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