Award: OCE-1434085

The mission of the GEOTRACES Program is "to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes (TEIs) in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions." This is highly relevant to the Arctic, where rapid climate change and accompanying biogeochemical responses are occurring. For this reason there was an international GEOTRACES effort in the Arctic in summer-fall 2015, comprising icebreaker programs from Germany, Canada, and the United States. These chemical species play important roles in the ocean as nutrients, tracers of oceanographic processes, and as contaminants from human activity. Their biogeochemical cycling has direct implications for research in such diverse areas as the carbon cycle, climate change and ocean ecosystems. The need for a comprehensive, coordinated study of these TEIs motivated the creation of GEOTRACES, an international research program focused on understanding the cycling of TEIs in the ocean. The research funded from this grant directly addresses one of the critical objectives in the GEOTRACES Science Plan: "Develop and refine chemical tracers in the surface ocean for quantification of atmospheric deposition". This grant supported analysis of the isotope 7Be (half-life 53.3 days) in the water column, aerosols, snow, ice, and melt ponds along the US Arctic GEOTRACES transect in 2015. Many processes in the ocean cannot be directly observed and as such, tracers are used to provide important constraints on their rates and pathways. Be-7 is a tracer that, because of its mode of input from the atmosphere, allows evaluation of mixing processes applicable to TEIs in the upper ocean, evaluation of the partitioning of atmospherically-derived TEIs between the different Arctic catchments, and can provide estimates of the flux of TEIs into the Arctic water-ice system. This work addressed key tasks formulated within the GEOTRACES Science and Arctic Implementation Plans: 1) Provide realistic estimates of the underlying transport processes influencing measured TEI distributions. Water column measurements of 7Be were used as a tracer of physical mixing processes, which redistribute biologically active species in the upper water column. Given 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. 2)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 are critical. The inventory of 7Be within these catchments were used to trace the partitioning of atmospherically deposited elements within the Arctic ocean/ice system. 3) Improve methods for quantifying the atmospheric deposition of TEIs: The PI used measurements of 7Be in the surface waters and in the lower atmosphere to develop estimates of the atmospheric input of relevant TEIs. In the Arctic, aerosol deposition is an important pathway for delivering trace element species, including contaminants from man-made sources. Assessment of this input has heretofore proven to be difficult given the harsh environmernt and limited research opportunities in the Arctic. Last Modified: 10/04/2018 Submitted by: David C Kadko