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. The isotopes of the rare earth element neodymium (Nd), and for that matter the rare earth element concentrations (REE), are recognized as important tracers of ocean water mass sources and transport, as a result they are considered as a ‘key trace element and isotope (TEI)’ to be measured on GEOTRACES cruises.

The Eastern Pacific Zonal Transect (EPZT) was an excellent place to utilize Nd isotopes and REE. The transect crosses many environments, including open-ocean and near continent environments, an intense oxygen minimum zone, and the Earth’s most active ocean ridge, thus offering the unique opportunity to greatly improve our understanding of these tracers. Moreover before this project, this is a region that was virtually devoid of such data. In addition, the Pacific is where data and ocean circulation models of the REE and Nd isotopes show the greatest global discrepancy.

With the data we acquired, we are in the process of evaluating how well these tracers reflect ocean circulation as well as the impacts of such processes as particulate exchange near the ocean surface, in areas of high biological productivity, where there are high concentrations of particulates near the ocean floor, or near hot water vents associated from oceanic volcanism.

Among our findings is that along the South American margin, there are large inputs of REE from volcanic ash into the water, extending to a few thousand meters. Farther afield this effect remains strong in shallow waters (up to several hundred meters of depth) and is associated with volcanic ash blown into the Pacific from Andean volcanoes. In fact, in the shallow water this effect can be traced all the way to Tahiti. REE from volcanics can also be seen deep in the water column near the volcanic East Pacific Rise in the middle of the transect. In the deep water away from land masses the REE in the water reflect the mix of water masses.

Broader Impacts:

This project addresses dynamic processes involved in present and past climate changes, which make it appealing both for the scientific community and the broad general audience. The project makes important contributions to the understanding of biogeochemical cycles in the ocean, and reinforcement of the application of Nd isotopes and REE as oceanographic tracers. The results will be of high interest to a wide range of ocean and climate scientists as well as policy makers, who need to understand global warming and its impact on the ocean. The project contributes to human resources, and  has helped to advance the careers of early career researchers who were working to achieve tenure when the project started (Brian A. Haley of Oregon State University), or 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 California State University at Bakersfield), and a female Ph.D. student (Yingzhe Wu, now a postdoc at Columbia).

Last Modified: 05/12/2019
Modified by: Steven L Goldstein