Collaborative Research: US GEOTRACES GP17-OCE and GP17-ANT: Properties and processes impacting other trace element and isotope cycles using noble gas and stable isotope tracers

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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. This project will undertake measurements of noble gas concentrations, helium and oxygen isotope abundances, and tritium on two upcoming U.S. GEOTRACES expeditions to the South Pacific, Southern Ocean, and Amundsen Sea. The noble gas and isotope tracers will be used to determine the contributions of hydrothermal venting, glacial meltwater, and sea ice formation to the water masses of the region. Glacial melt and sea ice production are considered important drivers of trace element cycling on the Antarctic continental shelf. These processes also help establish the properties of Southern Ocean-sourced deep water. Upwelling of deep-sourced hydrothermal water could deliver limiting micronutrients such as iron to the surface waters of the Southern Ocean, driving enhanced primary productivity. Deeper-lying hydrothermal plumes may export fluxes of hydrothermal trace elements and isotopes (TEIs) through the Drake Passage. The project will support a graduate student, teacher professional development, and public outreach.During the GEOTRACES GP17-OCE expedition, the team will measure helium-3, helium concentration, and neon concentration. On the GP17-ANT expedition, they will measure the concentrations of all five noble gases, helium-3, the stable isotope composition of water, and tritium. Specific aims include (1) to study pathways for hydrothermal inputs throughout the South Pacific, (2) to quantify other hydrothermally-sourced TEI fluxes and scavenging rates, (3) to quantify the inputs of snow and sea ice melt in relation to iron and other TEIs in the Amundsen Sea, (4) trace the ice shelf pump mechanism in the Amundsen Sea, and examine the spread of northward spread of meltwater and TEIs from the ice-covered marginal seas to the open Southern Ocean. In addition, since there is evidence that not all the hydrothermal inputs to the Southern Ocean have been discovered, the expeditions have the potential to expand knowledge of where additional hydrothermal systems, important to the biogeochemistry of the water column, are located.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.