GEOTRACES Arctic Section: Determining the Pathways, Fate, and Flux of Atmospherically Derived Trace Elements in the ocean/ice system

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In this project, a group of investigators participating in the 2015 U.S. Arctic GEOTRACES expedition will study the areal and depth distribution of Beryllium-7 in the western and central Arctic Ocean. Beryllium-7 (chemical symbol 7Be) is a harmless, naturally-occurring radioisotope (half-life = 53 days) generated worldwide in the upper atmosphere by cosmic ray interaction with certain atmospheric gases. It continuously falls to the Earth's surface, especially during precipitation events, where it can be used as a convenient tracer for a wide variety of environmental processes. It is expected to be very useful in helping to meet the goals of the U.S. Arctic GEOTRACES expedition: namely, 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. Working alongside a multi-institutional team of ocean trace element experts, the work of the 7Be research group should enable the team to determine the importance of atmospheric deposition of aerosols as a pathway for delivering trace elements from the continents to the deep Arctic Ocean and also to study how the presence or absence of surface sea ice influences the behavior of trace elements in the water column. Like many other participants in the expedition, the 7Be researchers plan to train graduate students in their research and to be involved in public educational outreach efforts in coastal communities in Alaska.This project will address three priority tasks formulated within the International GEOTRACES Science and Arctic Implementation Plans. First, it will provide realistic estimates of the underlying transport processes influencing distributions of many trace elements of interest (TEIs). Water column measurements of 7Be will be used as a tracer of physical mixing processes, which redistribute biologically active species in the upper water column. Quantitative knowledge of the circulation, mixing, and ventilation of the water masses within which TEIs reside allows an assessment of the time- and space-integrated in situ biogeochemical behavior of these elements. Secondly, 7Be will be used to trace the partitioning of atmospherically deposited elements within the Arctic catchments. The Arctic is unique to other GEOTRACES basins studied to date. For numerous TEIs, measurement not only in the water column, but also in the additional repositories of ice, snow and melt ponds is critical. The inventory of 7Be within these catchments will be used to trace the partitioning of atmospherically deposited elements within the Arctic ocean/ice system. Thirdly, 7Be data will be used to improve methods for quantifying the atmospheric deposition of TEIs. Measurements of 7Be in the surface waters and in the lower atmosphere will be used to develop estimates of the atmospheric input of relevant TEIs. In the Arctic, aerosol deposition is an important pathway for delivering trace element species, but assessment of this input has heretofore proven to be difficult.