The role of mixed layer depth in regulating primary production at Palmer Deep Canyon (West Antarctic Peninsula)

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Palmer Deep Canyon in the West Antarctic Peninsula (WAP) is considered a biological “hotspot” by providing predictable food resource and driving penguin foraging locations. However, the physiology and composition of the phytoplankton blooms as well as the physical mechanisms driving them aren’t well understood. The aim of this study is to characterize the dynamics of the spring phytoplankton bloom over Palmer Deep Canyon.

Here, a 5-year record of slocum glider deployments is analyzed. The depth of the mixed layer (MLD) was determined (using the maximum of the buoyancy frequency as the criteria), and its biological implications evaluated. In most glider profiles, the lower boundary of the chlorophyll concentration profile appears to be well correlated with the depth of the ML. The shoaling of the MLD in early January results in increased production, as evaluated by increased chlorophyll a concentrations. MLD deepens in early February, where a decreased in phytoplankton concentration is seen, likely due to decreased light availability. Throughout the season, the MLD gets, in average, warmer and saltier.