Collaborative Research: A Novel Tracer Approach to Estimate the Atmospheric Input of Trace Elements into the Global Ocean

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The atmospheric input of numerous chemical species into the global ocean equals or exceeds that from river sources and thus constitutes an important budgetary component for these elements. In addition, the atmospheric input of trace elements plays a key role in ocean biogeochemical processes. Assessment of this input is difficult however because measurements of deposition rates to the ocean are rare and susceptible to problems of temporal and spatial variability. Given the dearth of direct measurements, the ocean community must rely on atmospheric transport and deposition models which themselves are poorly constrained as to rainfall amounts and aerosol removal parameterization. Thus indirect methods, such as the use of natural radionuclides delivered to the ocean from the atmosphere are often used to estimate atmospheric inputs. In a novel application developed in this project, researchers at the University of Miami and Florida State University will use measurements of 7Be in the surface waters and in the lower atmosphere, coupled with trace element measurements in aerosols and rain, to provide estimates of the atmospheric input of relevant trace elements into the subtropical North Atlantic. 7Be is a cosmic ray produced radioisotope that becomes associated with particles in the troposphere and subsequently deposited to the surface ocean. Because of its relatively short half-life (53.3 days) it is reasonable to equate the inventory of 7Be decay in the upper ocean to the flux of 7Be from the atmosphere due to wet plus dry deposition. This provides a key linkage between the atmospheric concentration of chemical species and their deposition to the ocean. Such species include many of interest to the GEOTRACES program such as Al, Mn, Fe, Cu, Zn, and Cd. The atmospheric flux of these important trace elements (TEs) can then be estimated from multiplying the 7Be atmospheric flux (determined by its ocean inventory) by the TE/7Be ratios in aerosols and wet deposition. Broader Impacts: This research will directly addresse one of the critical objectives in the International GEOTRACES Science Plan: "Develop and refine chemical tracers in the surface ocean for quantification of atmospheric deposition". The ability to provide estimates of the atmospheric input of relevant trace elements to the ocean will contribute widely to the field of chemical oceanography and elsewhere, including understanding anthropogenic impacts on the oceans and the role atmospheric input of TEs plays in ocean ecology. The results of this project will benefit other international initiatives such as the SOLAS program, and data generated in this work will be available to allow ground-truthing of models of aerosol deposition and atmospheric input. Education and training of graduate students are essential components of this research. The PIs regularly teach undergraduate and graduate classes and incorporate the results of their fieldwork into lecture materials to motivate the next generation of Earth scientists. Undergraduate FSU chemistry and/or biology majors (males, females, minorities) will be involved in the research via annual requests for REU supplements. As they evolve, results will be presented at national/international scientific meetings, and published in peer-reviewed journals. The data will be submitted in a timely manner according to the requirements of NSF/OCE.