A Mechanism for the Formation of the Weddell Polynya in 1974

Tatsuo Motoi Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan

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No Buo Ono Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan

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Masaaki Wakatsuchi Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan

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Abstract

The formation of the Weddell Polynya is investigated with a one-dimensional, convective mixed-layer model, using in situ data from late summer 1974 as initial conditions. We propose that a high-salinity mixed layer in summer resulted in the formation of the Weddell Polynya in 1974. The model results show that the high salinity allows deep convection driven by surface cooling alone, and the resulting upward transfer of heat and salt prohibits sea-ice formation throughout the winter, subject to the freshwater input less than 0.4 m yr−1. Because of the uncertainty of amount of the actual freshwater input in 1974, whether sea ice formed is ambiguous. However, the occurrence of the deep convection during the 1974 polynya formation is confirmed by summer data from 1975, showing the modification of deep water to be colder, fresher and richer in oxygen than in 1974. The upward heat flux through the deep convection resulted in the formation of the Weddell Polynya in 1974.

Abstract

The formation of the Weddell Polynya is investigated with a one-dimensional, convective mixed-layer model, using in situ data from late summer 1974 as initial conditions. We propose that a high-salinity mixed layer in summer resulted in the formation of the Weddell Polynya in 1974. The model results show that the high salinity allows deep convection driven by surface cooling alone, and the resulting upward transfer of heat and salt prohibits sea-ice formation throughout the winter, subject to the freshwater input less than 0.4 m yr−1. Because of the uncertainty of amount of the actual freshwater input in 1974, whether sea ice formed is ambiguous. However, the occurrence of the deep convection during the 1974 polynya formation is confirmed by summer data from 1975, showing the modification of deep water to be colder, fresher and richer in oxygen than in 1974. The upward heat flux through the deep convection resulted in the formation of the Weddell Polynya in 1974.

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