Pa-231 and Th-230 in the Western North Atlantic: Disentangling the Effects of Boundary Scavenging and Ocean Circulation

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Boundary scavenging is the increased adsorption of radionuclides such as thorium-230 (Th230) and protactinium-231 (Pa231) onto particles in ocean margin areas; however, this process is not well understood. The sediment record of 231Pa/230Th has played a crucial role in interpreting past ocean circulation and sediment transport, and therefore, it is important to constrain the boundary scavenging component of these radionuclides. A researcher from Woods Hole Oceanographic Institution plans to develop a numerical model of ocean circulation, sediment transport, and particle scavenging to determine the processes that control the distribution of these two radionuclides in the Western North Atlantic. This study is particularly timely, since model observations will be tested using data collected as part of the ongoing GEOTRACES program. The results of this research will be incorporated into coursework taught at the Massachusetts Institute of Technology-Woods Hole Oceanographic Institution Joint Program in Oceanography, and the project will involve a graduate student. The computational codes will be disseminated in such a way that they can be useful to other researcher in the ocean sciences community.Current understanding of boundary scavenging processes on the cycling of particle-reactive elements in the ocean is poor. Simple box models are generally used, which cannot account for the boundary scavenging effects. This research will apply a high spatial resolution, regional model, taking into account ocean circulation, sediment transport, and chemical scavenging. The model will be used to constrain the processes that control oceanic distributions of Th-230 and Pa-231, two radionuclides the ratios of which have been extensively used in studying past ocean circulation. The model will be compared to GEOTRACES data for comparison and to help refine the model, placing the project in line with two of the overriding goals of the GEOTRACES program. The results from this project will be widely applicable to global ocean biogeochemical models that must account for boundary scavenging.