Variability and Dynamics of Along‐Shore Exchange on the West Antarctic Peninsula (WAP) Continental Shelf

The continental shelf of the West Antarctic Peninsula (WAP) is characterized by strong alongshore hydrographic gradients resulting from the distinct influences of the warm Bellingshausen Sea to the south and the cold Weddell Sea water flooding Bransfield Strait to the north. These gradients modulate the spatial structure of glacier retreat and are correlated with other physical and biochemical variability along the shelf, but their structure and dynamics remain poorly understood. Here, the magnitude, spatial structure, seasonal-to-interannual variability, and driving mechanisms of along-shore exchange are investigated using the output of a high-resolution numerical model and with hydrographic data collected in Palmer Deep. The analyses reveal a pronounced seasonal cycle of along-shore transport, with a net flux (7.0 x 10(5) m(3)/s) of cold water toward the central WAP (cWAP) in winter, which reverses in summer with a net flow (5.2 x 10(5) m(3)/s) of Circumpolar Deep Water (CDW) and modified CDW (mCDW) toward Bransfield Strait. Significant interannual variability is found as the pathway of a coastal current transporting Weddell-sourced water along the WAP shelf is modulated by wind forcing. When the Southern Annual Mode (SAM) is positive during winter, stronger upwelling-favorable winds dominate in Bransfield Strait, leading to offshore advection of the Weddell-sourced water. Negative SAM leads to weaker upwelling- or downwelling-favorable winds and enhanced flooding of the cWAP with cold water from Bransfield Strait. This process can result in significant (0.5 degrees C below 200 m) cooling of the continental shelf around Palmer Station, highlighting that along-shore exchange is critical in modulating the hydrographic properties along the WAP. Plain Language Summary The melting of glaciers and the structure of ecosystems along the West Antarctic Peninsula have been influenced by the local temperature and salinity patterns. Our understanding of what controls the spatial structure and temporal variability of these gradients is limited. In this study, we analyze output from a state-of-the-art numerical model and find that there is strongly seasonal and interannual variability in the along-shore exchange processes that control those gradients. The interannual variability of the along-shore exchange is related to the local winds. As the wind conditions vary in response to hemispheric-scale climate processes, the amount of cold water flowing into the central West Antarctic Peninsula from Bransfield Strait varies interannually. We show this is a key process in the evolution of ocean properties in the West Antarctic Peninsula continental shelf.