Award: OCE-1555726

This project constitutes a contribution to our long-term research on the processes that supply trace elements to the ocean as well as the processes that remove trace elements from seawater. In addition, we exploit radioactive disequilibria within the uranium radioactive decay series to quantify the rates of trace element supply and removal. Trace elements are of interest for several reasons. Most importantly, motivation for our research comes from the processes that supply essential trace element nutrients to marine ecosystems, and the rates of supply by those sources. The enzymes used by organisms to metabolize and utilize the building blocks of life, such as carbon, nitrogen and phosphorous, are nearly all built around a core structure involving a trace element. Not only are these trace elements absolutely essential for life, but in many cases, such as for iron, zinc, cobalt and cadmium, their scarcity limits the growth of organisms and thereby the fertility of much of the ocean, with implications for fisheries and for the efficiency with which the ocean?s "biological pump" extracts carbon dioxide from the atmosphere. Removal of many trace elements from the ocean takes place by adsorption to particles as they settle through the water column, a process referred to as "scavenging." Work at various locations throughout the ocean shows a good correspondence between the rate (intensity) of scavenging and the abundance of particles, both biogenic and lithogenic. This award allowed two graduate students from our group to participate in a research expedition aboard a German cruise across the subtropical South Pacific Ocean. The cruise, RV Sonne, SO245, sailed from Antofagasta, Chile to Wellington, New Zealand (17 December 2015 to 28 January, 2016). This region experiences the lowest biological productivity, the source of biogenic particles, and the lowest aeolian deposition of dust, the principal source of lithogenic particles, of any non-ice-covered region in the ocean. Our specific goals for this project were: 1) to quantify the scavenging intensity in this region and place it in the context of results from a growing database of similar work in other regions, and 2) to quantify the supply of dust to the subtropical South Pacific Ocean. This project was a one-year RAPID grant, which provided funds to cover travel and shipping expenses. Field work was completed only earlier this year, so we have no final results to report at this time. Analytical work on the samples from this cruise is underway, but much more remains to be done. Last Modified: 12/27/2016 Submitted by: Robert F Anderson