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SUMMARY:Mixing and phytoplankton dynamics in Antarctica's coastal seas - F
 ilipa Carvalho\, Rutgers
DTSTART:20161007T100000Z
DTEND:20161007T110000Z
UID:TALK67789@talks.cam.ac.uk
CONTACT:Dr Dave Munday
DESCRIPTION:There is a high spatial and temporal variability in the biophy
 sical processes regulating primary productivity in submarine canyons in An
 tarctic coastal seas\, with Amundsen Sea\, Ross Sea and West Antarctic Pen
 insula canyons being reported as important features for regional primary p
 roduction. Canyon heads in the West Antarctic Peninsula (WAP) are consider
 ed biological “hotspots” by providing predictable food resource and dr
 iving penguin foraging locations\, however the physiology and composition 
 of the phytoplankton blooms and the physical mechanisms driving them aren
 ’t well understood.\n\nUsing autonomous underwater gliders equipped with
  CTD\, chlorophyll and backscatter pucks\, over 30\,000 water column profi
 les in Antarctic coastal seas have been analyzed with the goal of characte
 rizing physically and biologically the upper 100 m of the water column. Th
 e mixed layer depth (MLD)\, determined by the maximum of the buoyancy freq
 uency criteria\, was found to be the MLD definition with the highest ecolo
 gical relevance.\n\nThe strongest signal found was the seasonal cycle. The
  shoaling of the MLD in early January results in increased chlorophyll a c
 oncentrations and as MLD deepens in mid season due to wind forcing\, phyto
 plankton concentrations decrease\, likely due to decreased light availabil
 ity. A consistent secondary peak in chlorophyll matches a shoaling in MLD 
 later in the growth season. A steady warming and increase in salinity of t
 he MLD is seen throughout the season. \n\nTo further evaluate the biologic
 al responses to physical forcing\, the glider was equipped with a PAR sens
 or and integrated with a prototype Fluorescence induction and Relaxation (
 FIRe) sensor. This allowed the continuous and high resolution mapping in d
 epth of the phytoplankton physiological responses to light stress using fl
 uorescence 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 p
 hotosynthetic efficiency) showing reduced values only in the upper 15 mete
 rs at the highest daily irradiance.\nWith decreasing sea ice trends report
 ed 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 efficien
 cy of atmospheric carbon sequestration.
LOCATION:British Antarctic Survey\, Room 307
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