US GEOTRACES GP17-OCE and GP17-ANT: Sources and Rates of Trace Element and Isotope Cycling Derived from the Radium Quartet

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The goal of the GEOTRACES program is to “identify processes and quantify fluxes that control the distribution of trace elements and isotopes (TEIs) in the ocean and to establish the sensitivity of these distributions to changing environmental conditions”. This ambitious objective requires coordinated seagoing field work for collection of samples to measure many elements simultaneously across the earth’s major ocean basins. However, these comprehensive global concentration maps for trace elements cannot be properly interpreted without concurrent measurement of radioactive tracers like radium isotopes that can provide time scales of their ocean input. In this project, the investigators will measure the abundance and distribution of radium isotopes in the Southern Ocean between the southern tip of South America and Antarctica, including a detailed characterization of the Antarctic coastal marine environment. The project will support a postdoctoral research associate and involve two undergraduate student researchers in post-cruise analyses.The main motivation of the proposed research is to utilize the quartet of radium (Ra) isotopes (224Ra, 223Ra, 228Ra, 226Ra) to enable source identification and flux quantification of TEIs during the forthcoming US GEOTRACES GP17-OCE and GP17-ANT expeditions. Measurement of Ra isotopes will allow the team to address several key questions related to ocean margin and benthic boundary processes and their role in supplying and transporting TEIs to marine ecosystems including: (1) What are the rates of lateral transport of TEIs from the Antarctic and Patagonian continental margins out to and including the high nutrient low chlorophyll (HNLC) Southern Ocean? (2) What are the TEI fluxes associated with Antarctic glacial meltwater? and (3) What are the time scales of TEI transport associated with Pacific-Antarctic Ridge neutrally buoyant hydrothermal plumes? Boundary inputs are considered to be the dominant source of many key TEIs to the ocean including iron, however, TEI concentrations must be coupled with input and transport rates to determine their effect on marine biogeochemical cycles. The wide range of Ra isotope half-lives (3.66 days to 1600 years) allow for the quantification of TEI transport processes on time scales relevant to ocean mixing processes. The proposed coupled Ra-TEI measurements will allow the full value of the distribution of numerous TEIs as measured by GEOTRACES PIs to be realized.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.