Summary of Abstract Submission

Abstract Submission No. IO50-04-0028PresentationOral

BIOGEOCHEMICAL AND ECOLOGICAL IMPACTS OF BOUNDARY CURRENTS IN THE INDIAN OCEAN

Raleigh R. Hood*1, Lynnath E. Beckley2, Jerry D. Wiggert3

1 University of Maryland, USA
2 Murdoch University, Australia
3 University of Southern Mississippi, USA

ABSTRACT :

Boundary currents mediate the fluxes of biogeochemical properties and planktonic ecosystems between major oceanic biomes and, in so doing, they also impact higher trophic level productivity, behavior and recruitment. In the northern Indian Ocean, several boundary current systems are seasonally reversing. These reversing surface currents are unique to monsoon-driven systems and although their transports are relatively small, they have profound biogeochemical and ecological impacts. For example, the nutrient stoichiometry of water upwelled along the coast of Oman during the Southwest Monsoon induces iron limitation and influences the species composition of the resulting blooms, and higher trophic level planktonic species have evolved behavioral responses (vertical migration) to the seasonally changing conditions. The southern currents (Agulhas and Leeuwin) both flow poleward throughout the year. The transport of the Leeuwin Current is also relatively small, but the poleward direction is unique among eastern boundary currents and it has many unusual biogeochemical and ecological impacts. For example, it sheds anomalous high chlorophyll, warm-core, downwelling eddies that transport productive diatom communities westward into open ocean waters and it impacts rock lobster larvae recruitment and fate. In contrast, the transport of the Agulhas Current is huge, but it does not generate large seaward propagating eddies along the South African coast. Rather, meanders and eddies in the current propagate alongshore and interact with seasonal changes in the winds and topographic features. This gives rise to seasonally variable localized upwelling and downwelling circulations with commensurate changes in primary production and higher trophic level responses.