Award: OCE-1736321

The international GEOTRACES program aims to identify processes and quantify fluxes that control the distribution of trace elements and isotopes (TEIs) in the ocean. Some TEIs are important micronutrients, which may control biological productivity. Others may become concentrated as they pass up the food web and reach potentially harmful levels in some seafood. But measurements of these TEIs are not adequate to determine controlling processes or quantify their fluxes in the marine environment. Radionuclide tracers provide a means to link TEI measurements with fluxes and processes. Our project measured226Ra (half-life = 1600 years) and228Ra on a GEOTRACES north to south transect in the Pacific Ocean (152W). Twenty-three profiles from the surface to seabed were measured to develop a complete section of the radium distributions. We compared the radium distributions to distributions of other TEIs and found, as others had before, strong correlations of 226Ra and barium, indicating similar behaviors.Some stations had deep excesses of226Ra,reflecting benthic inputs, which are more significant for 226Ra than for barium. Mass balance calculations suggested that while regional barium fluxes nearly balance, the Pacific is likely a significant source of226Rato the global ocean. We used the measurements of228Radium to trace water movements and current speeds in the upper Pacific and to determine regions near the seabed where sediment‐water interactions are most intense. The upper ocean measurements confirmed a broad circulation pattern that brought water from the Asian margin to the northeast Pacific at speeds of 28 cm/sec, in agreement with other estimates of these current speeds. Near the seabed we discovered a region of enhanced228Ra activity indicating intense sediment‐water interactions. These regions were also enriched in 226Ra. Such regions may control the release of TEIs from the seabed to the water column. We anticipate others will utilize these data to elucidate aspects of other TEI distributions. Last Modified: 04/11/2024 Submitted by: WillardSMoore