Project: Collaborative Research: US GEOTRACES Pacific Meridional Transect: Sources and Sinks of Neodymium Isotopes and Rare Earth Elements

NSF Award Abstract:
The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. Neodymium (Nd) isotopes and rare earth elements (REE) are widely recognized for their utility as tracers of water transport and as indicators of the sources of trace elements to the oceans. Neodymium isotopes have been designated as "key parameters" to be measured on GEOTRACES expeditions. This project would measure Nd isotopes on a 2018 GEOTRACES expedition in the Pacific Ocean. The North Pacific is a particularly interesting place to measure Nd isotopes because North Pacific and North Atlantic deep waters represent the two end-members of deep ocean composition, and the few data available so far in the North Pacific differ from expectations based on mixing of known water types.

The US GEOTRACES Pacific Meridional Transect (PMT) from Tahiti to Alaska will play an important role in solving the "mystery" of North Pacific neodymium isotope ratios. The PMT is designed to extensively sample the oldest waters in the ocean, along with Alaskan coastal margins, volcanogenic sediments, the meridional dust gradient originating from volcanic arcs and the Asian and North American continents, and large gradients in biological productivity. The primary purpose of this project is to characterize the Nd isotope ratio of seawater along the transect. In order to address fundamental questions on the Nd and REE cycle in the Pacific, the investigators will also quantify boundary exchange effects, atmospheric inputs, provenance of particles, impacts of biological productivity, and fluxes into and out of seawater, in order to assess Nd and REE sources and sinks, and to calibrate Nd isotopes as a paleocirculation proxy in the Pacific. Specific focus areas include: (1) Nd isotopic characterization of the shallow and deep waters, (2) margin processes associated with the Alaska volcanic arc shelf, to study chemical exchanges between particulates, sediments, and seawater Nd isotopes and REE, (3) changing meridional dust sources and its impacts, (4) relationships between bottom sediment types, compositions, nepheloid layers, and their influence on the water column, (5) the effects of pore water flow on the water column; (6) the signal transfer between the deep water and sedimentary archives (e.g., fossil fish teeth, Fe-Mn oxide coatings). The project will advance the career of a postdoctoral research scientist, and support numerous undergraduate students.