4.7 Article

Mixing and phytoplankton dynamics in a submarine canyon in the West Antarctic Peninsula

Journal

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
Volume 121, Issue 7, Pages 5069-5083

Publisher

AMER GEOPHYSICAL UNION
DOI: 10.1002/2016JC011650

Keywords

phytoplankton; mixed layer depth; Antarctica; glider

Categories

Funding

  1. National Science Foundation [ANT-0823101, ANT-1327248, ANT-1326541, ANT-1142250]
  2. Portuguese doctoral fellowship from Fundacao para a Ciencia e Tecnologia [DFRH-SFRH/BD/72705/2010]
  3. Office of Polar Programs (OPP)
  4. Directorate For Geosciences [1142250, 1331681] Funding Source: National Science Foundation
  5. Office of Polar Programs (OPP)
  6. Directorate For Geosciences [1327248, 1326541] Funding Source: National Science Foundation

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Bathymetric depressions (canyons) exist along the West Antarctic Peninsula shelf and have been linked with increased phytoplankton biomass and sustained penguin colonies. However, the physical mechanisms driving this enhanced biomass are not well understood. Using a Slocum glider data set with over 25,000 water column profiles, we evaluate the relationship between mixed layer depth (MLD, estimated using the depth of maximum buoyancy frequency) and phytoplankton vertical distribution. We use the glider deployments in the Palmer Deep region to examine seasonal and across canyon variability. Throughout the season, the ML becomes warmer and saltier, as a result of vertical mixing and advection. Shallow ML and increased stratification due to sea ice melt are linked to higher chlorophyll concentrations. Deeper mixed layers, resulting from increased wind forcing, show decreased chlorophyll, suggesting the importance of light in regulating phytoplankton productivity. Spatial variations were found in the canyon head region where local physical water column properties were associated with different biological responses, reinforcing the importance of local canyon circulation in regulating phytoplankton distribution in the region. While the mechanism initially hypothesized to produce the observed increases in phytoplankton over the canyons was the intrusion of warm, nutrient enriched modified Upper Circumpolar Deep Water (mUCDW), our analysis suggests that ML dynamics are key to increased primary production over submarine canyons in the WAP.

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