Award: OCE-1234417

GEOTRACES is an international program that investigates ocean-scale distribution of trace elements and their isotopes (TEIs) in order to improve understanding of biogeochemical cycles in the ocean. Atmospheric input is an important component of TEIs? marine biogeochemical cycling. This project was part of the US GEOTRACES Eastern Pacific Zonal Section, and was carried out in collaboration with Skidaway Institute of Oceanography. The goals of this project were to collect boundary layer atmospheric particles and characterize TEIs along the Eastern Pacific Ocean. This region receives one of the lowest atmospheric deposition input in the global ocean, and provides a contrasting regime for the characterization of aerosol chemistry as compared to the high aerosol deposition regions encountered and sampled during the US GEOTRACES North Atlantic Zonal Section. Through this project, atmospheric deposition samples were made available to other section participants to extend their characterization. Collaborative work with other section participants aimed to quantify atmospheric deposition via chemical tracers, and to determine the solubility and speciation of key TEIs after deposition. Our data showed a strong decrease in the amount of deposited aerosols from near-shore to the open ocean (Figure 1). Elemental ratios showed near-shore aerosols were similar in composition to average crustal material. Given local wind patterns (Figure 2) these atmospheric particles likely originated the arid Bolivian Altiplano and are derived from soil dust. As expected, the soil dust input off Peru was two to three orders of magnitude lower than soil dust input off the west coast of Africa in the North Atlantic (as observed by the US GEOTRACES program). In addition, the prevailing winds prevented this dust input to reach as far into the open ocean as the soil dust plume off of Africa. As a result the atmospheric input of TEIs to surface water in this region is limited, confirming global model output. Quantifying the input of TEIs to the surface ocean is of particular interest for trace elements that are involved in biological processes (e.g. iron), because external inputs of biologically active elements can promote primary production and/or alter the community composition of primary producers in offshore surface waters. Another parameter that is important to the atmospheric input of TEIs is the solubility of the deposited material. Dissolution experiments showed aerosols collected during this project had a similar solubility trend as North Atlantic aerosols. Aerosols derived from soil dust had lower fractional solubility than aerosols collected offshore (with mixed anthropogenic and natural sources, and higher degree of processing in the atmosphere). Last Modified: 03/29/2017 Submitted by: Ana M Aguilar-Islas