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A Recirculating Eddy Promotes Subsurface Particle Retention in an Antarctic Biological Hotspot
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  • Katherine L Hudson,
  • Matthew John Oliver,
  • Josh Kohut,
  • Michael S. Dinniman,
  • John Klinck,
  • Carlos Moffat,
  • Hank Statscewich,
  • Kim S. Bernard,
  • William Fraser
Katherine L Hudson
University of Delaware

Corresponding Author:khudson@udel.edu

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Matthew John Oliver
University of Delaware
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Josh Kohut
Rutgers State University of New Jersey
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Michael S. Dinniman
Old Dominion University
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John Klinck
Center for Coastal Physical Oceanography
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Carlos Moffat
University of Delaware
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Hank Statscewich
University of Alaska Fairbanks
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Kim S. Bernard
Oregon State University
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William Fraser
Polar Oceans Research Group
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Palmer Deep Canyon is one of the biological hotspots associated with deep bathymetric features along the Western Antarctic Peninsula. The upwelling of nutrient-rich Upper Circumpolar Deep Water to the surface mixed layer in the submarine canyon has been hypothesized to drive increased phytoplankton biomass productivity, attracting krill, penguins and other top predators to the region. However, observations in Palmer Deep Canyon lack a clear in-situ upwelling signal, lack a physiological response by phytoplankton to Upper Circumpolar Deep Water in laboratory experiments, and surface residence times that are too short for phytoplankton populations to reasonably respond to any locally upwelled nutrients. This suggests that enhanced local upwelling may not be the mechanism that links canyons to increased biological activity. Previous observations of isopycnal doming within the canyon suggested that a subsurface recirculating feature may be present. Here, using in-situ measurements and a circulation model, we demonstrate that the presence of a recirculating eddy may contribute to maintaining the biological hotspot by increasing the residence time at depth and retaining a distinct layer of biological particles. Neutrally buoyant particle simulations showed that residence times increase to upwards of 175 days with depth within the canyon during the austral summer. In-situ particle scattering, flow cytometry, and water samples from within the subsurface eddy suggest that retained particles are detrital in nature. Our results suggest that these seasonal, retentive features of Palmer Deep Canyon are important to the establishment of the biological hotspot.
Nov 2021Published in Journal of Geophysical Research: Oceans volume 126 issue 11. 10.1029/2021JC017304