Award: OCE-1458936

The Arctic Ocean represents only 3% of the total area of global ocean. About 50% of the seafloor of the Arctic Ocean is shallow continental shelf (less than 130 m deep), and so only accounts for 1% of the volume of the global ocean. Despite it's relatively small size and volume, the Arctic receives 10% of the global freshwater runoff and is influenced by seasonal formation of sea ice. Due to the unique processes operating in the Arctic Ocean it is an ideal location to examine how trace metals are introduced to seawater, how they are removed from seawater, and how they behave in between. This project used samples of seawater collected during the 2015 Arctic Ocean voyage of the Coast Guard Research Icebreaker USS Healy to examine the cycling of the rare earth element neodymium (Nd). Nd is a valuable tracer of seawater mixing and processes involving land-seawater interactions, however the sources of Nd to the oceans are not fully understood. While it is clear that almost all of the Nd in the ocean is delivered by rivers, deep waters have much higher Nd concentrations suggesting delivery of excess Nd to deep waters, however the processes responsible for this delivery are unknown. The Arctic Ocean provides the possibility to unravel this mystery. In addition to its intrinsic scientific value, the Arctic is experiencing antropogenically-driven warming that will alter freshwater delivery, permafrost, degassing, and sea-ice formation. Our results reveal that Nd in the surface ocean have isotopic fingerprints that faithfully reflect the source of freshwater and mixing between different water masses from the Atlantic and Pacific. Deep water is enriched with Nd, and these enrichments appear to be accompanied by 1) artifacts of the chemical process of aerobic respiration, and 2) elevated suspended particle levels. These results strongly indicate that Nd is transferred to the deep ocean on sinking particles, but that Nd is also released from resuspended sediments from bottom currents. One unexpected result is that the isotopic fingerprint of deep waters shifted closer to Pacific values compared to samples collected in the early 2000?s. While this result must be confirmed with repeated measurements and future sampling, our observations suggest that the deep Arctic Ocean may be more dynamic than previously believed. In addition to supporting research that produced these insights, this project also contributed to the scientific education of 1 PhD student and 3 undergraduate students. This award also allowed the PhD student was able to take advantage of an opportunity to participate in a research cruise to collect seawater samples in a polar region, which was a unique and important training opportunity. Students also interacted collaboratively with scientists and other students from the two collaborative institutions, Oregon State University and Lamont Doherty Earth Observatory. The PhD student traveled to both institutions as part of this project to exchange data and ideas. Last Modified: 03/17/2019 Submitted by: Howard Scher