Pathways and retention times in a biologically productive canyon system on the West Antarctic Peninsula

Palmer Deep is a highly productive coastal canyon on the continental shelf of the West Antarctic Peninsula (WAP). Primary productivity in the canyon is hypothesized to be fueled by nutrients provided by the Upper Circumpolar Deep Water (UCDW), a water mass originating off the shelf. To evaluate the influence of UCDW on the canyon, we use the Regional Ocean Modeling System (ROMS) model to investigate the common pathways the UCDW takes to reach Palmer Deep canyon, near the United States Palmer Station. We also investigate the circulation of the water mass within the canyon itself. Virtual drifters were advected in the velocity field of a six-year model run on the WAP. At sub-pycnocline depths, three primary pathways from the northern shelf edge to Palmer Deep were identified, each of which involved cyclonic circulation within a shelf-incising trough. Temperature and salinity of water moving along these pathways was most significantly modified when it reached the latitude of Boyd Strait, which is likely to be influenced by cold Antarctic Coastal Current Water from the Weddell Sea. Most of the flow into the canyon occurred on the northwest side and most of the outflow was through the south. Retention times in the canyon increased with depth, with particles being retained for 50-100 days at depths where UCDW commonly intrudes, supporting the idea that canyons promote productivity by providing a reservoir for nutrient-rich water masses.