Wind‐driven ocean dynamics impact on the contrasting sea‐ice trends around West Antarctica

Abstract

Since late 1978, Antarctic sea‐ice extent in the East Pacific has retreated persistently over the Amundsen and Bellingshausen Seas in warm seasons, but expanded over the Ross and Amundsen Seas in cold seasons, while almost opposite seasonal trends have occurred in the Atlantic over the Weddell Sea. By using a surface‐forced ocean and sea‐ice coupled model, we show that regional wind‐driven ocean dynamics played a key role in driving these trends. In the East Pacific, the strengthening Southern Hemisphere (SH) westerlies in the region enhanced the Ekman upwelling of warm upper Circumpolar Deep Water and increased the northward Ekman transport of cold Antarctic surface water. The associated surface ocean warming south of 68°S and the cooling north of 68°S directly contributed to the retreat of sea‐ice in warm seasons and the expansion in cold seasons, respectively. In the Atlantic, the poleward shifting SH westerlies in the region strengthened the northern branch of the Weddell Gyre, which in turn increased the meridional thermal gradient across it as constrained by the thermal wind balance. Ocean heat budget analysis further suggests that the strengthened northern branch of the Weddell Gyre acted as a barrier against the poleward ocean heat transport, and thus produced anomalous heat divergence within the Weddell Gyre and anomalous heat convergence north of the gyre. The associated cooling within the Weddell Gyre and the warming north of the gyre contributed to the expansion of sea‐ice in warm seasons and the retreat in cold seasons, respectively.

Sex‐specific effects of fisheries and climate on the demography of sexually dimorphic seabirds

“…This sex‐specific response supports our predictions about more pelagic females and is consistent with Weimerskirch et al () who found that shifts in meridional winds primarily affected foraging performance of female wandering albatross Diomedea exulans . However, the inverse relationship between zonal winds and male NGP survival is contrary to our predictions and may therefore indicate other indirect effects, such as wind‐driven changes in oceanographic conditions (Holland & Kwok, ; Lee et al, ).…”

Vertical ocean heat redistribution sustaining sea-ice concentration trends in the Ross Sea

“…4 ), leading to strong annual mean trends and a clear feedback signature. In other sectors, the trends over 1979–2013 vary between seasons, leading to smaller trends in annual average, and suggesting that other processes with out-of-phase impacts across seasons are dominant 29 . Furthermore, the insignificant positive correlations from 0 to 50 m in the Bellingshausen–Amundsen sector in observations (Supplementary Fig.…”

Antarctic sea-ice expansion and Southern Ocean cooling linked to tropical variability

“…In addition, a strengthening of westerlies at ~60S and related enhanced northward Ekman transport (Fig. 5f) are likely to facilitate sea ice expansion during cold seasons 54 .…”