US GEOTRACES GP17-OCE and GP17-ANT: Particulate and biogenic trace elements in the South Pacific and Southern Ocean

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The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. Many trace metals, such as iron, manganese and zinc, are essential for life and serve as nutrients for phytoplankton. However, regions of the Pacific and Southern Oceans have very low concentrations of iron and manganese, in particular, limiting the growth of phytoplankton at times. This project will improve understanding of the uptake and removal of micronutrient metals by phytoplankton in these regions. This project will accomplish three main objectives: 1) measure the concentrations of phosphorus and eleven trace metals in particles collected from the upper region of the South Pacific and Southern Oceans during a cruise from Tahiti to Chile; 2) measure a subset of these elements, along with carbon, sulfur and silicon, directly in phytoplankton cells collected from these waters; and 3) measure the same elements in phytoplankton collected from coastal Antarctic waters on a subsequent, companion cruise into the Amundsen Sea. Two undergraduate student interns will be involved in the project, along with a postdoctoral scholar. The scientific results and research experience will be shared with additional undergraduates through two classes, and the project will be brought to the broader public through a virtual reality game and associated activities produced during the project and introduced through libraries and institutional outreach events.The U.S. GEOTRACES GP17-OCE expedition, planned for late 2022, aims to determine the distribution of trace elements and isotopes along a transect spanning regions of global importance to nutrient and carbon cycling, crossing the South Pacific Gyre, the iron-limited waters of the Antarctic Circumpolar Current, Pacific Deep Waters with hydrothermal inputs, and waters near the Chilean margin. The South Pacific Gyre and Pacific sector of the Southern Ocean are climate-critical regions for the transfer of heat, carbon, and nutrients within the global ocean, and they are a region where phytoplankton growth is typically limited by low concentrations of iron (Fe) in the surface ocean. The researchers will use inductively-coupled plasma mass spectrometry and synchrotron x-ray fluorescence microscopy to address three primary research questions focused on the internal biogeochemical cycling of trace elements in this region: 1) How do trace element contents of dominant phytoplankton taxa respond to environmental macronutrient and trace element gradients? 2) How does the trace element composition of the various particulate matter fractions (lithogenic, authigenic, biogenic) vary across the section? 3) How does the composition and stoichiometry of particulate material influence trace element cycling and trace element:nutrient stoichiometry of the surrounding water masses?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.