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

Abstract

The continental shelf of the West Antarctic Peninsula (WAP) is characterized by strong along‐shore 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 × 105 m3/s) of cold water toward the central WAP (cWAP) in winter, which reverses in summer with a net flow (5.2 × 105 m3/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°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.

Subsurface Eddy Facilitates Retention of Simulated Diel Vertical Migrators in a Biological Hotspot

“…However, because the MLD plays a role in determining residence time, differences between ROMS modeled MLD and actual MLD could play an important role in interpreting these results. If summer MLDs are shallower than the model predicts (Hudson et al, 2021;Wang et al, 2022), real migrating zooplankton over PDC may spend less time in the low residence time surface layer compared to our simulations. Therefore, the observed migrations to 50 m may still result in increased residence times, however, MLD predictions by ROMS need to be improved to test this hypothesis.…”

“…Residence times were greatest in the presence of shallower MLD, supporting our hypothesis that a thinner surface layer, indicated by a shallower MLD, increases migrating zooplankton residence times. Importantly, ROMS predicts deeper MLD and less stratification during the summer in PDC (Hudson et al., 2021; Wang et al., 2022). A shallower, more stratified surface ocean means that it is more isolated from deeper water masses.…”

A subsurface eddy associated with a submarine canyon increases availability and delivery of simulated Antarctic krill to penguin foraging regions

“…Comparisons of in situ observations from the 2019−2020 austral summer and ROMS simulations from the same austral summer simulated here illustrate that the subsurface eddy over PDC is more baroclinic than simulations predict (Hudson et al 2021). The model also predicts deeper mixed layers than observed by autonomous underwater gliders deployed within the region, suggesting that stratification is under-predicted in the model over PDC (Hudson et al 2021, Wang et al 2022. This has led to the hypothesis that surface waters are more isolated from the effects of the canyon than the model suggests and would explain why the eddy is often visible in the surface in the model (Hudson et al 2021, this study) but is only observed in surface currents when stratification and winds are low (Hudson et al 2021).…”

Spatiotemporal Overlap of Baleen Whales and Krill Fisheries in the Western Antarctic Peninsula Region

“…Sea surface temperature has been found to be an important covariate influencing the habitat selection of humpback whales in the Southern Ocean (e.g., Andrews-Goff et al, 2018;Bestley et al, 2019;Riekkola et al, 2019;Reisinger et al, 2021). Johannessen et al (2022) observed a positive correlation between humpback whale presence and sea surface temperature in the Bransfield Strait region, and interpret this as a preference for the warm, nutrient-rich Circumpolar Deep Water that is delivered onto the continental shelf (Martinson & McKee, 2012;Wang et al, 2022), driving marine productivity (e.g., Ducklow et al, 2012).…”