With funding through a Grant for Rapid Response Research (RAPID), a research team at the University of Washington will participate in an originally unplanned oceanographic cruise in autumn 2011, as part of the U.S. GEOTRACES North Atlantic campaign to study carbon and oxygen isotopic signatures in the oceanic water column. The original, incomplete cruise (in autumn 2010) was terminated prematurely because of failure of the ship's propulsion system. The forthcoming follow-up cruise in 2011 will follow a track between Woods Hole, MA and Cape Verde Islands. These RAPID funds are being will cover only the costs of preparing for sample collection during the future cruise and not for laboratory analysis of the seawater samples or synthesis of the data.
This team, originally supported through an ARRA award, will measure the same seawater characteristics on the future cruise as was proposed for the original cruise -- that is, the 13C/12C of dissolved inorganic carbon and the concentration of dissolved O2 and Ar gases. The scientific objectives have not changed; namely, they will quantify the rate of organic matter (OM) export using two separate methods that rely on the measured air-sea disequilibrium for del-13C and for dissolved O2 gas. The team will also determine the impact that OM export and its subsequent remineralization on the relationship between bioactive trace elements (BTE), del-13C-DIC and nutrient relationships in surface waters and at depth.
Broader Impacts: Because these ocean carbon system data will become part of a multi-investigator international study, they will be made available to a worldwide community involved in the study of ocean chemistry and its relationship to global climatic change. Project results will also be incorporated into the principal investigator's teaching curricula, and the project itself will make provision for the participation of idergraduate students in the laboratory analytical work.
Intellectual Merit Goals: The research addressed two of the overriding goals of the GEOTRACES program. First, to improve our understanding of the processes that control trace element distributions in the ocean. Second, to understand the processes that control the concentrations of geochemical species used for proxies of the past ocean environment. Our proposed research has two primary components. First, to measure the 13C/12C of the dissolved inorganic carbon (DIC) during the GEOTRACES cruise in the N. Atlantic Ocean. Second, to quantify the impact that air-sea CO2 gas exchange, OM export, remineralization and circulation have on the modern distributions of bioactive trace elements, 13C/12C-DIC and nutrients in the Atlantic Ocean Field Work: We participated in two GEOTRACES cruises in the N. Atlantic. We collected approximately 500 sea samples for analyzing the 13C/12C of DIC. We measured underway dissolved oxygen and argon gas ratios in the mixed layer during the cruise in 2011. Sample Analysis All 500 samples were analyzed in the laboratory for 13C/12C of DIC. This data has been submitted to the NSF’s BCO-DMO data archive following recommendations of the GEOTRACES program. Data Synthesis The synthesis of the 13C/12C data set collected during the GEOTRACES cruises has finished. The main conclusions are as follows. First, the depth distribution of measured 13C/12C needed to be corrected for anthropogenic change in order to reconstruct steady-state pre-industrial 13C/12C distribution. This correction has an important impact on comparison to nutrient and trace metal distributions. Second, the depth profile of pre-industrial 13C/12C is the mirror image of the depth distributions of nutrients, AOU, and Cadmium. Third, mixing of water masses like Antarctic Intermediate Water, outflow water from the Mediterranean Sea, North Atlantic Deep Water and Antarctic Bottom Water has a major impact on the vertical distributions of δ13C/12C , nutrients, AOU and Cadmium through the thermocline and deep Atlantic Ocean. Fourth, end-member mixing of preformed phosphate and δ13C will complicate attempts to use Cd/Ca and δ13C to reconstruct nutrient levels and biological pump strength in the paleocean. The initial results of this data synthesis were presented at the GEOTRACES workshop in March 2013. The first draft of the paper discussing these results is finished. There will be a special journal issue to publish results of GEOTRACES measurements in N. Atlantic. This paper will be submitted in time to publish in this special issue. Broader Impacts First, the outcome of the research will impact not only the international community involved in the GEOTRACES scientific program but the paleoclimate community as 13C/12C and Cadmium are heavily used proxies for reconstructing ocean conditions during previous climate intervals. Second, the results of the proposed research have been incorporated into the PI’s teaching curricula, specifically, in an undergraduate Oceanography course entitled Climatic Extremes (OCEAN 450) and graduate course entitled Isotope Biogeochemistry (OCEAN 588). Third, there was active undergraduate participation in preparing samples for 13C/12C analyses in the laboratory. Finally, there are clear societal benefits from the outcome of this research has it improves our understanding of the processes that control the uptake of atmospheric CO2 by the ocean and thus will result in improved predictions of future climate change under increasing atmospheric CO2 levels.
