Distribution of Upper Circumpolar Deep Water on the warming continental shelf of the West Antarctic Peninsula

Sub-pycnocline water on the continental shelf of the West Antarctic Peninsula (WAP) is strongly influenced by intrusions of Upper Circumpolar Deep Water (UCDW), a relatively warm water mass that originates off the shelf within the Antarctic Circumpolar Current. Shipboard measurements over the past two decades indicate that the deep shelf waters are warming, but they are unable to resolve the dimensions and frequency of the UCDW intrusions. Here, we use autonomous underwater vehicles (gliders) to characterize the spatial distribution of UCDW on the WAP continental shelf. We use a ROMS model to study the pathways by which UCDW crosses onto the shelf and travels toward the coast.

We find that in both the traditional shipboard CTD dataset and the recent high-resolution glider dataset, there are consistent spatial patterns with UCDW commonly found in deep bathymetric depressions in the region. UCDW on the shelf is found in features with widths on the order of 10 km, suggesting the importance of mesoscale processes in the transport of heat onto the shelf. The features observed here contribute 10-33% of the heat flux required to balance the heat budget of the WAP and lose heat at a rate of 1.7 ± 0.8 x 10⁶ J/m² between the shelf break and the coast. Drifters released in the ROMS model also follow bathymetric channels toward the coast and showed preference for entering at specific locations along the shelf break.