Dissolved And Particulate 226Ra Along GEOTRACES Pacific Meridional Transect

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.