Dissolved trace elements in the tropical Northwest Pacific Ocean

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This project involves a collaboration with Chinese scientists in the analysis of seawater samples collected during mid-2019 in the Northwest Pacific Ocean. The cruise (designated GP09) is part of an international collaborative research effort known as GEOTRACES, which is examining the distributions of trace elements and isotopes throughout the oceans. Some trace elements are micro-nutrients in the ocean, others are potentially toxic in small quantities, and still others can be tracers or indictors of the extent of various ocean processes such as hydrothermal inputs or productivity. The GP09 cruise affords an opportunity to obtain trace element clean water samples from a region that is geologically complex as well as being a meeting place for various ocean currents and water masses. It will sample the southwest corner of the North Pacific subtropical gyre, one of the largest oligotrophic (i.e., low nutrient) ocean regions and arguably the largest continuous ecosystem on Earth. This region is likely impacted by dust input (including anthropogenic aerosols), nitrogen fixation, hydrothermal inputs, and island effects associated with weathering of the Philippines and margin cycling. Determining material sources, sinks, and cycling in this region is ultimately important for understanding controls on the region's productivity. Many of the trace elements to be determined are also of relevance for paleo-proxy applications (i.e., for understanding what the sediment records of these elements tell us about past ocean processes). However, successful paleo-proxy applications generally require further insight into the processes that affect the cycling of the proxy elements. Because of the wide range of parameters to be determined by GP09 participants, the cruise affords substantial opportunities for collaboration with Chinese colleagues. The knowledge and experience gained from this project will be incorporated into the principle investigator's courses in oceanography. For outreach activities, in collaboration with the University of Southern Mississippi Marine Education Center, high school students will be invited to attend lectures given by scientists about their research. A postdoctoral scholar will also be trained as part of the projectA researcher from the University of Southern Mississippi will obtain clean, filtered trace element samples from a mid-2019 oceanographic research cruise in the Northwest Pacific Ocean. The cruise (GP09) is part of the GEOTRACES program and was led by researchers from Xiamen University, China, with additional participants from other major Chinese oceanographic institutions. The geological and hydrographic complexity, along with the oligotrophic nature of the GP09 cruise track, make this an especially interesting region for study. Trace element distributions are likely to provide insight into various source, sink, and cycling processes of broad interest. For example, a number of the elements we will study have been used (or proposed to be used) as paleoredox and paleoproductivity proxies [e.g., barium (Ba), rare earth elements (REEs), vanadium (V), cadmium (Cd)], but a better understanding of their oceanic cycling is needed to more fully understand their proxy signals. The studies proposed here are also pertinent to important issues including delivery of mineral dust and nutrient iron to the surface ocean [gallium (Ga), REEs and possibly Cd and V], removal and internal cycling of trace elements [Ba, REEs], tracing sources of material including margin sources [Ba, manganese (Mn), REEs, V] and hydrothermal influences [Mn, Ba, REEs], as well as understanding of conservative versus non-conservative changes in tracer distributions [Ba, REEs, V]. The cruise also allows extensive collaboration with other, mainly Chinese, investigators. Thus, the dissolved Ga data will be compared with data obtained by colleagues on distributions of other lithogenic, rapidly-scavenged elements like aluminum (Al) and thorium-232; the dissolved Ba data will be shared with those determining radium and Ba isotopes; and, the REE data will be made available to those examining neodymium isotopes, as well as compared with other scavenging tracers such as Ga, Al, and Th.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.