Atmospheric and Lateral Inputs of Trace Metals in the Indonesian Through-Flow

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The spawning grounds of the Southern Bluefin Tuna (SBT) lie between the northwestern Australian coast and Indonesia. Waters from the Pacific flow through Island Southeast Asia as the Indonesian Through-Flow (ITF) and into the western Indian Ocean. Nutrient conditions in the ITF are insufficient to support optimum feeding and growth of SBT larvae, and numerous links between the nutrient cycles and food chain remain unknown. There are very few measurements of both major and trace nutrients like nitrogen, phosphorus, and iron made in the region. These nutrients support phytoplankton that form the base of the food chain and affect higher trophic levels, including SBT. This work will investigate the potential sources of major and minor nutrients to the region, including island inputs, Australian dust, monsoon rains, and sedimentary fluxes which will help develop a “nutrient budget” and reveal which sources contribute the greatest to the success of early SBT life stages. This project is a US contribution to the 2nd International Indian Ocean Expedition (IIOE-2) that will advance understanding of biogeochemical and ecological dynamics in the poorly studied eastern Indian Ocean. The project will support an early career postdoctoral researcher and outreach activities will include participation in Open House events and REU summer program at home institution.The ITF can undergo potential changes to the distributions of major and trace nutrients during passage through the straits of southeast island Asia. Coastal currents can resuspend shelf sediments containing nutrients like Si and Fe, while the atmospheric deposition of both natural and anthropogenically derived material from Australia and southeastern Asia can supply N, P, Fe, and other trace metals. Monsoon rains also supply nutrients via wet deposition of aerosols and runoff. These inputs introduce nutrients to the surface ocean of the ITF, where phytoplankton can convert inorganic nutrients to biomass and in turn fuel the entire food chain. In this research aerosols and water column trace metals will be investigated, as a complementary component to another NSF-funded BLOOFINZ project which seeks to understand the N cycling and food-web dynamics of the southern bluefin tuna spawning grounds. The proposed research will address three hypotheses: (H1) The ITF receives inputs of bioactive trace elements from wet and dry atmospheric deposition and resuspended sediments, and (H2) transports these nutrients across the Indian Ocean via the South Equatorial Current (SEC). (H3) Inputs of Fe from atmospheric deposition of mineral and anthropogenic aerosols or continental shelves could help alleviate N limitation in the ITF. To investigate these hypotheses and understand the inputs, removals, and cycles of trace metals in the ITF, the concentrations, elemental ratios, and fluxes of material in aerosols and marine dissolved and particulate phases will be quantified and compared.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.