Topic: Essays

Last updated: April 22, 2019

This study reveals significant sea-ice expansion in the Weddell sea associated with the robust feature of sea surface cooling trend. The strong gushing wind speed i.

e. the westerly winds which are related to SAM and stratospheric ozone depletion over the Antarctica partially explained the variability in the Weddell sea sea-ice extent. We suggested a mechanism which shows significant strengthening of the westerly wind and ACC in austral summer that induces northward transport of the low saline and cool water, accompanied with the upper ocean cooling through an overall loss of net heat flux, conducive for sea-ice expansion.

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When comparing the sea ice anomalies with the local air?sea?ice interaction anomalies in air temperature, sea surface temperature, wind speed and zonal and meridional wind components, it was possible to see that the variation of the Weddell Sea ice influenced the temperature on this sector. Since the Weddell Sea is located south of the entrance of a strong westerly jet positioned between 40 and 50°S, these changes can be explained by the increase (decrease) in the intensity of westerly winds in those seas and the AP and the increase (decrease) in meridional winds in the Henry ice fields. Finally, the increase (decrease) in katabatic winds east of the AP also increases (decreases) the extent of sea ice by pushing the sea ice north and accelerating the freezing of the ocean surface, since these winds are composed of very cold airmasses. Although the great impact of the increased westerly, katabatic, and circumpolar winds was also confirmed in the Weddell sea, some differences with respect to the total trend were identified, especially in the 2010–2015 period. The increase of wind intensity was stronger in the past 5 years, and this could explain the higher increase rate of sea ice in those areas in 2010–2017, compared to 1979–2010. The surface heat flux is not independent of surface winds due to the turbulent heat flux.

The significant drop in the Weddell Sea ice during summer may be related to an increase in the net surface heat flux (shortwave radiation) and north-westerly wind anomalies starting from spring season. This indicates that the north-westerly wind anomalies push the sea ice south-eastward, thus rendering large sea ice-free areas, which marks in depressing the surface albedo and increasing the heat flux due to shortwave radiation. The cyclonic wind anomalies east of the Antarctic Peninsula also tend to reduce the sea ice, probably by generating Ekman upwelling to warm the sea ice from the bottom34.

The oceanic process may contribute to the sea-ice melt, but the sea ice response to this oceanic forcing is slower than that to the atmospheric forcing35. Although the north-westerly wind anomaly contributes to more advection of warm air from the lower latitudes, the sea surface temperature anomaly is spatially limited over the sea-ice reduction area, indicating the dominant role of the ocean in driving the temperature anomaly.


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