Collaborative Research: US GEOTRACES GP17-OCE: Shipboard Measurements of Dissolved Aluminum, Iron, and Manganese – Tracing Inputs to the South Pacific Gyre and Southern Ocean

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The goal of the international research program GEOTRACES is to understand the distributions of trace chemical elements and their isotopes in the oceans. The importance of trace elements in the ocean lies in their roles as essential micronutrients for marine phytoplankton (e.g., iron), as toxicants (e.g., lead), and as tracers of past and present oceanic processes (e.g., thorium). In this project, the dissolved concentrations of two micronutrient trace elements (iron and manganese) and a tracer of atmospheric dust deposition (aluminum) will be measured in seawater samples collected during a research cruise in the southeastern Pacific Ocean and adjacent Southern Ocean, in order to better understand the inputs of these micronutrients and their impact on biological processes in these regions. Chemical analyses will be performed at sea in near real-time, thus providing a first glimpse of data that will inform the cruise sampling strategy and the analyses performed by other investigators. The project involves two US laboratories, and will support the research of a graduate and undergraduate student. The U.S. GEOTRACES GP17-OCE expedition will focus on the distribution of trace elements and isotopes along a transect crossing the South Pacific Gyre and the Pacific sector of the Southern Ocean, where the supply of dissolved iron (DFe) and manganese (DMn) to the surface ocean is thought to regulate primary production and associated cycling of carbon and nutrient elements. The investigators will undertake shipboard and post-cruise measurements of dissolved aluminum (DAl), DFe and DMn in order to constrain (1) the magnitude of dust deposition to this ocean region and the fidelity of DAl and DMn as tracers of aeolian iron inputs; (2) the origin of deep-ocean DAl and DFe anomalies, and their implications for deep sources of these elements; and (3) the source and fate of hydrothermal DFe emissions from the deep ocean and their role in supporting Southern Ocean primary production. Project results, complemented by measurements of other trace chemical species made by collaborators on GP17-OCE, will advance the understanding of the processes that control the oceanic inventories and distributions of DAl, DFe and DMn, and their trajectories of future change.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.