Award: OCE-2124317

We developed a new global model to simulate the distributions of the naturally-occurring radioactive isotopes232Th,230Th, and231Pa in the global ocean. Over the past 15 years, globally distributed measurements of these isotopes have been made as part of the GEOTRACES program. Our modeling efforts were aimed at synthesizing our understanding of these isotopes and using them to improve the ways the biogeochemical processes were previously being modeled. We began simulating these isotopes using the existing dissolved iron model in the Community Earth System Model (CESM). We quickly realized that improvements needed to be made to the model. Namely, we needed to add enhanced removal of elements from the surface ocean by sinking particles to the model to accurately simulate the surface distributions of230Th and231Pa. Second, we needed to add enhanced removal of elements at depth by resuspension of bottom sediments to accurately simulate the deep distributions of230Th and231Pa. Our newly developed model accurately simulates the global distributions of thorium and protactinium isotopes. In regions where inaccuracies persisted, we have been able to identify regional improvements that must be made to the broader CESM model (e.g. changes in particle flux) necessary for accurate simulations. By applying our230Th model to the dust-borne isotope232Th, we have identified regions where atmospheric dust deposition, something notoriously difficult to measure in the open ocean, is underestimated in current atmospheric dust models. We are able to use our coupled230Th-232Thsimulations to create optimized, data-constrained atmospheric dust deposition fields that can be used widely for studies of marine biogeochemical cycling and its response to past and future climate change. Last Modified: 02/07/2025 Submitted by: JessFAdkins