Project: US GEOTRACES ARCTIC: Measuring stable isotopes of carbon in dissolved inorganic carbon and oxygen/argon gas ratios to show impact of organic matter export on nutrient distributions

NSF Award Abstract:
A scientist from the University of Washington will participate in the 2015 U.S. GEOTRACES Arctic Ocean cruise and measure the vertical distribution of the stable isotopes of carbon found in dissolved inorganic carbon (del13C), a tracer of biogeochemical cycling. In addition, he will determine the spatial variation in the ratio of oxygen gas to argon gas (O2/Ar) in surface water samples because this ratio can be used as a proxy for organic matter export. In common with other multinational initiatives in the International GEOTRACES Program, the goals of the U.S. Arctic expedition are to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions. Some trace elements are essential to life, others are known biological toxins, and still others are important because they can be used as tracers of a variety of physical, chemical, and biological processes in the sea. Results from this study will further our understanding of the processes that control observed trace elements, nutrients, and the stable carbon isotopes in dissolved inorganic carbon in the present day ocean and use this information to gain information on past changes in ocean circulation on carbon cycling. This project will also provide training opportunities for undergraduate students, and results will be integrated into public outreach activities and material for class lectures.

A better understanding of the impact of physical and biological processes on the distribution of nutrient and trace elements in the modern ocean is critical to our interpretation of future changes in their distributions in the Arctic and their utility as proxies of circulation and biological pump conditions in the historic ocean. One key parameter needed to understand these processes is del13C of dissolved inorganic carbon, for which little to no data currently exists in the Arctic Ocean. This study will aim to measure the depth distribution of the del13C of dissolved inorganic carbon and the dissolved O2/Ar ratio in the surface layer of the ocean. These measurements will help to quantify the contributions of chemical processes and the biological pump on the spatial distribution of nutrients, trace elements, and del13C, as well as estimate organic matter export rates from the surface ocean.