Award: OCE-1737394

The Pacific is the worlds largest body of water, comprising about 1/3 of the Earths surface. Given this, there are proportionately (to other basins) few data regarding many important trace elements and isotopes(TEIs) in this ocean. One of these understudied tracers is neodymium isotopes(eNd), which are widely used as a tracer of both water mass circulation and of the sources and processes that control marine TEI cycling.Use of eNd to better understand the distributions of TEIs in general would help us better interpret these tracers with respect to a myriad of processes, including deep ocean redox cycling, carbon sequestration and ventilation. In turn, these processes further our broader understanding of the environment and climate. The US GEOTRACES Pacific Meridional Transect (GP15, PMT) generated Nd isotope data between Alaska and Tahiti at the 150W meridian in order to help close this knowledge gap. The Pacific plays a critical role in global overturning ocean circulation, as it is the region where deep water is purported to return to the surface and flow back to the Atlantic/Southern Ocean, thus completing the deep ocean water conveyor belt. Neodymium isotopes, as a tracer of ocean circulation, would seem to be critically illustrative of this process. These GEOTRACES eNd data generally agree with this hypothesis, whereby Pacific Deep Water (PDW) has an eNd value of ~-3, compared to the far more non-radiogenic eNd of North Atlantic Deep Water (NADW) of ~-13. PDW in turn is sourced from the Southern Ocean, which has intermediate eNd of ~ -8 to -9. Thus, as nascent PDW flows from the Southern Ocean to the northwest Pacific it interacts with high eNd products of western Pacific volcanism, becoming more positive over its transport path, reaching values of ~-3 to -4 near Japan and Kamchatka. Two critical observations can ben made from the GEOTRACES data: (1) While generally pseudo-conservative, the PDW eNd signature is modified during its flow through the Pacific. (2) This non-conservative behavior is non-uniform, happening only in certain locations of the Pacific (particularly south Pacific). These GEOTRACES data are being developed (with particular reference to the rare earth element concentration data Nd included in the dissolved and particulate phases collected in the GP15 cruise), to better understand the mechanisms of non-conservation of eNd. These data will be used in concert to understand and interpret both the modern and past signals of eNd and thus better constrain Pacific circulation and deep ocean ventilation. Last Modified: 05/13/2024 Submitted by: BrianAHaley