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Optical sensing of plankton communities and dynamics
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Possible explanations for the unexpected lack of phytoplankton biomass in naturally iron fertilized waters near Heard and McDonald islands in the Southern Ocean
Tuesday 8th @ 1130-1150, Conference Room 7
Bozena Wojtasiewicz, CSIRO Oceans and Atmosphere
Thomas W. Trull* , CSIRO Oceans and Atmosphere
Diana M. Davies, Antarctic Climate and Ecosystems CRC
Christina Schallenberg, Antarctic Climate and Ecosystems CRC
Lesley Clementson, CSIRO Oceans and Atmosphere
Nick. J. Hardman-Mountford, CSIRO Oceans and Atmosphere
Presenter Email: Tom.Trull@csiro.au |
| Satellite remote sensing of ocean color reveals high chlorophyll biomass extending more than 1000 km downstream in the Antarctic Circumpolar Current from the Kerguelen Plateau. Oceanographic voyages have verified this to be increased phytoplankton biomass stimulated by natural inputs of iron, the limiting nutrient in the Southern Ocean. Putative iron supply mechanisms include resuspension of sediments on the plateau and terrestrial inputs from the the islands at each end of the central plateau of the Kerguelen islands in the north and Heard and McDonald islands (H&M) in the south. H&M are volcanically active, and H also has glaciers that reach from the top of its Big Ben central volcanic peak to terminate in the sea. Surprisingly, close to H&M, satellite images indicate a halo of low biomass. During 2016, the Heard Earth Ocean Biosphere Investigation studied this region in detail - high iron levels were confirmed and fast repetition fluorometry indicated high photosynthetic competence in the diatom dominated phytoplankton community. So, why is the halo present? This presentation will combine sensor observations of radiation, fluorescence, backscatter, and absorption with physiochemical data to address several possibilities: i) satellite imaging does not see the biomass because of other light absorbing materials in the water ii) deep mixing near the islands dilutes the biomass iii) horizontal advection moves waters away from the islands faster than biomass can accumulate and iv) phytoplankton are rapidly removed by grazing or other mechanisms. |
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