Award: OCE-1459716

Intellectual Merit. An overarching purpose of the International GEOTRACES Program is to characterize the processes that control the distribution of trace elements and isotopes in the world?s oceans. Neodymium (Nd) isotopes are tracers of water mass sources, transport and mixing, and rare earth elements (REEs) show systematic chemical fractionations during environmental processes. Together they provide a powerful tool for analyzing provenances and processes in the oceans that reflect the changing environmental controls on the distribution of trace elements and their isotopes (TEIs). Inherent logistical difficulties make the Arctic Ocean especially scarce in TEI data. The Arctic Ocean has many aspects that make it physically and biologically different than other oceans. It comprises only 3% of the world?s ocean by area. Most oceans are primarily deep ocean, the Arctic is about 50% shallow continental shelf. Therefore its volume is only ~1% of the whole ocean. Yet it receives ~10% of the global freshwater runoff. It has the largest fraction of continental shelves, freshwater input, and sea ice of any major ocean. Moreover, it is isolated from the global ocean, and connected through two shallow gateways. These attributes make the Arctic Ocean likely to show sensitivity to changing inputs of a warming Earth. As a result it holds great potential for improving our understanding of how processes and environments impact TEIs such as Nd isotopes and the REEs. We have found unique aspects of the western Arctic Ocean compared to other ocean basins. In all other oceans, REE concentrations increase with depth below the thermocline, while in the Arctic the REE are high near the surface, decrease through the thermocline, and are nearly constant below. This means that there is no significant flux of REE from the bottom sediments, which has been suggested in the literature as an important REE source. The investigators are discussing why this structure is maintained, and what it means for REE cycling. At the Pacific-Bering Sea location, the water column REE profile is like the other oceans. Along the long shallow Bering Sea continental shelf, we have found where this switch occurs. This project sampled the western Arctic Ocean from the North Pole to the Bering Strait, the shallow Bering Sea continental shelf south of the Strait, and a deep site in the Pacific-Bering Sea. We have found unique aspects of the Arctic Ocean compared to other ocean basins. In contrast to all other ocean basins, REE concentrations in the Arctic are high near the surface, decrease through the thermocline, and are nearly constant below. In all other oceans, REE concentrations increase with depth below the thermocline. The investigators are discussing why this structure is maintained, and what it means for REE cycling. For example, the absence of increased concentrations with depth means there is no significant benthic REE flux. With respect to Nd isotopes, the western Arctic is similar to other oceans in that the shallow zone (mixed layer and thermocline) is isolated from the deep ocean. Within the shallow zone there is a large range of Nd isotope ratios, but the deep western Arctic Ocean shows very small variability throughout. Broader Impacts The Arctic is a place where climate warming and environmental changes are occurring at high rates. Data from this research will provide benchmarks for future trace element and isotope studies to better understand their cycles and how environmental changes will impact this important ocean basin. Research such as this is important for understanding the current state of Arctic Ocean geochemistry and for developing predictive capability as the regional ecosystem continues to warm and influence global oceanic and climatic conditions. The results will be of interest to a wide range of ocean and climate scientists as well as policy makers, who need to understand the processes and impacts associated with our warming planet. The project contributes to human resources, and has helped to advance the careers of early career researchers who were offered junior faculty positions during the grant (Leopoldo Pena, who had been a postdoc at Columbia, now at the University of Barcelona, and Chandranath Basak, also a postdoc at Columbia, now at the University of Delaware), and two female postdocs at Columbia (Yingzhe Wu and Paula Pinedo). Last Modified: 05/27/2021 Submitted by: Robert Anderson