OS019-02
A Recirculating, Subsurface Eddy Increases Deep Residence Times in an Antarctic Biological Hotspot

Wednesday, 9 December 2020: 10:33
Virtual
Katherine Hudson1, Matthew J Oliver1, Josh T Kohut2, Michael S Dinniman3, John Michael Klinck II3, Hank Statscewich4, Kim Sarah Bernard5 and William Fraser6, (1)University of Delaware, Newark, DE, United States, (2)Rutgers University, Marine and Coastal Sciences, New Brunswick, NJ, United States, (3)Old Dominion University, Center for Coastal Physical Oceanography, Norfolk, VA, United States, (4)University of Alaska Fairbanks, College of Fisheries and Ocean Sciences, Fairbanks, AK, United States, (5)Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States, (6)Polar Oceans Research Group, Sheridan, MT, United States
Abstract:
Palmer Deep Canyon is a persistent biological hotspot along the Western Antarctic Peninsula. This has led to the ‘canyon hypothesis’ which relates local geological and physical oceanographic features to the hotspots. Historically, the upwelling of nutrient-rich deep water to the surface mixed layer in the submarine canyon was thought to drive biological productivity, attracting krill, penguins, and other marine top predators to the region. However, recent observations of low surface residence times, lack of deep water upwelling, and abundant surface nutrient concentrations at Palmer Deep Canyon have called the upwelling mechanism into question.

Sloped isopycnals and a subsurface particle layer observed over the canyon by three Slocum gliders in 2015 suggested the presence of a deep subsurface eddy. Regional Ocean Modeling System (ROMS) simulations, in conjunction with the deployment of three gliders in 2020 and the previous 2015 deployments, suggest that a recirculating cyclonic eddy is present in Palmer Deep Canyon and is most coherent during the austral summer. Neutrally buoyant particle simulations using the ROMS with 1.5 km horizontal resolution were used to test the hypothesis that residence times increase with depth within the canyon. Particles were seeded on a 4 km horizontal grid, every 2 days, at several depths over two separate 6-month simulation periods that included different austral summers. These simulations suggest that the deep eddy increases residence times. In-situ images and water samples from the subsurface particle layer observed in 2015 and 2020 suggest that small detritus particles are retained within the canyon. These seasonal, retentive features of Palmer Deep Canyon could be critical to the establishment of the biological hotspot by increasing residence times for the Antarctic krill, a local keystone species and important food source for nearby penguin colonies.

Previous Abstract | Next Abstract >>