Summary of Abstract Submission

Abstract Submission No. IO50-04-0048PresentationPoster

BIO-ARGO FLOATS REVEAL SUBSURFACE STRUCTURE OF SOUTHEAST INDIAN OCEAN EDDIES

Helen Phillips*1, Peter Strutton 1, Tom Trull2, Earl Duran1, Sylvia Pump1

1 IMAS, University of Tasmania, Australia
2 CSIRO Oceans and Atmosphere, Australia

ABSTRACT :

There is increasing recognition that eddies modulate open ocean productivity, and that this influence depends on both eddy source and their evolution. Eddies in the southeast Indian Ocean have been recognised, from satellite sea surface height and ocean colour, as important pathways for westward transport of elevated biomass from the eastern boundary Leeuwin Current into the oligotrophic interior. Further it has been hypothesized that, in some eddies, processes at the base of the mixed layer stimulate productivity and sustain phytoplankton biomass for much longer than expected from westward advection alone. Here we present high-frequency profiles of temperature, salinity, chlorophyll, backscatter and oxygen from autonomous floats in anti-cyclonic and cyclonic eddies in the South Indian Ocean. Satellite sea surface height data confirmed that the floats remained trapped in their respective eddies from winter to early summer, sampling the upper 300 m of the water column 6-8 times per day. The total concentration of mixed layer chlorophyll remained relatively constant, although its vertical distribution changed over time. From September to October, it was evenly distributed throughout the mixed layer of both eddies. With the onset of spring warming, the chlorophyll became concentrated at greater depth with less at the surface. Satellite measurement of surface chlorophyll was 3-5 times lower than the float surface measurement throughout the record, partly because of the vertical structure in chlorophyll. There was no significant change in oxygen saturation state coincident with high phytoplankton concentrations at depth, indicating no net community production. The eddies appear to self-sustain their biomass.