Dissolved And Particulate 226Ra Along GEOTRACES Pacific Meridional Transect

Emilie Le Roy1, Matthew A Charette1, Tristan J Horner2, Paul Henderson1, Pieter van Beek3 and Marc Souhaut3, (1)Woods Hole Oceanographic Institution, Marine Chemistry & Geochemistry, Woods Hole, MA, United States, (2)Woods Hole Oceanographic Institution, Marine Chemistry & Geochemistry, Woods Hole, United States, (3)LEGOS Laboratoire d'Etudes en Geophysique et Oceanographie Spatiale, Toulouse, France
We report the basin-scale distribution of dissolved and particulate 226Ra along GEOTRACES Pacific Meridional Transect (GP15; Alaska to Tahiti; September–November 2018). We find that the dissolved 226Ra distribution is strongly influenced by the water masses encountered along the section. We observe high 226Ra activities in deep waters (Circumpolar Deep Water and Pacific Deep Water) reflecting deep circulation, mixing and a pronounced regional source in the North-East Pacific. In contrast, activities of 226Ra are low in surface and intermediate depth due the presence of intermediate and mode waters, from the south (Antarctic Intermediate Water, Subantarctic Mode Water) and the north (North Pacific Intermediate Water). These waters display low 226Ra, likely due to the uptake within planktonic tests and/or co-precipitation with barite (BaSO4) followed by export with settling or sinking particles. Particulate 226Ra concentrations are used to quantify non-conservative dissolved–particulate transformations. Despite the extremely low 226Ra activities encountered in particles, significant variations are observed. We will discuss these variations in the context of known biogeochemical, terrestrial, hydrothermal, and benthic processes and assess the importance of these processes in mediating basin-scale 226Ra distributions.