University of Cambridge > Talks.cam > British Antarctic Survey - Polar Oceans seminar series > Mixing and phytoplankton dynamics in Antarctica's coastal seas

Mixing and phytoplankton dynamics in Antarctica's coastal seas

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There is a high spatial and temporal variability in the biophysical processes regulating primary productivity in submarine canyons in Antarctic coastal seas, with Amundsen Sea, Ross Sea and West Antarctic Peninsula canyons being reported as important features for regional primary production. Canyon heads in the West Antarctic Peninsula (WAP) are considered biological “hotspots” by providing predictable food resource and driving penguin foraging locations, however the physiology and composition of the phytoplankton blooms and the physical mechanisms driving them aren’t well understood.

Using autonomous underwater gliders equipped with CTD , chlorophyll and backscatter pucks, over 30,000 water column profiles in Antarctic coastal seas have been analyzed with the goal of characterizing physically and biologically the upper 100 m of the water column. The mixed layer depth (MLD), determined by the maximum of the buoyancy frequency criteria, was found to be the MLD definition with the highest ecological relevance.

The strongest signal found was the seasonal cycle. The shoaling of the MLD in early January results in increased chlorophyll a concentrations and as MLD deepens in mid season due to wind forcing, phytoplankton concentrations decrease, likely due to decreased light availability. A consistent secondary peak in chlorophyll matches a shoaling in MLD later in the growth season. A steady warming and increase in salinity of the MLD is seen throughout the season.

To further evaluate the biological responses to physical forcing, the glider was equipped with a PAR sensor and integrated with a prototype Fluorescence induction and Relaxation (FIRe) sensor. This allowed the continuous and high resolution mapping in depth of the phytoplankton physiological responses to light stress using fluorescence kinetics, as no nutrient limitation was observed. Diel cycles collected show a clear daily cycle dependent on the magnitude of incident radiation, with both Fm (proxy for chlorophyll) and Fv/Fm (indicator of photosynthetic efficiency) showing reduced values only in the upper 15 meters at the highest daily irradiance. With decreasing sea ice trends reported for some Antarctic coastal regions, especially the WAP , the increased phytoplankton exposure to increased irradiance may result in significant ecological and biogeochemical implications, such as the decrease efficiency of atmospheric carbon sequestration.

This talk is part of the British Antarctic Survey - Polar Oceans seminar series series.

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