Diel Vertical Migration of Krill in a Subsurface Eddy may Promote Retention within Palmer Deep Canyon
Katherine Gallagher1, Matthew J Oliver1, Josh T Kohut2, Dr. John Michael Klinck II, PhD3 and Michael S Dinniman3, (1)University of Delaware, Newark, DE, United States, (2)Rutgers University, Marine and Coastal Sciences, New Brunswick, United States, (3)Old Dominion University, Center for Coastal Physical Oceanography, Norfolk, VA, United States
Abstract:
Palmer Deep Canyon is a biological hotspot along the Western Antarctic Peninsula. The observation of persistent hotspots in association with submarine canyons along the peninsula has led to the ‘canyon hypothesis’ which relates local geological and physical oceanographic features to the hotspots. Historically, the upwelling of nutrient-rich Upper Circumpolar Deep Water to the surface mixed layer in the submarine canyon was thought to drive biological productivity, attracting krill and penguins to the region. However, recent observations of low surface residence times, lack of Upper Circumpolar Deep Water in the surface layer, and abundant surface nutrient concentrations at Palmer Deep Canyon, along with experimental results that suggest that surface plankton communities are not nutrient-limited, have called the upwelling mechanism into question.
Sloped isopycnals and an observed subsurface particle layer over the canyon suggest the presence of a deep subsurface eddy. Neutrally buoyant particle simulations using the Regional Ocean Modeling System with 1.5 km horizontal resolution suggest that this deep eddy may increase residence times in the biological hotspot and may serve as a mechanism to retain krill. To test the hypothesis that vertical migrating krill could be retained by this deep eddy, particles with realistic vertical migration behavior were seeded on a 4 km horizontal grid, every 2 days, at 20 and 120 m depth over a 6-month simulation period during the austral summer of 2008. Diel vertical migrations between 20 m at night and 120 m during the day were simulated at three migrating speeds and were driven by sun angle. Early results indicate that both deep and vertically migrating particles may be retained within a closed eddy over Palmer Deep Canyon.
