With NSF Grant, ODU's Burdige Will Be Looking for Missing Neodymium Flux

Old Dominion University oceanographer David Burdige will do some scientific sleuthing in what might be called "The Case of the Missing Neodymium Flux" as an investigator on a $264,000 project funded by the National Science Foundation (NSF).

Isotopes of the rare earth element neodymium are present in varying forms in the oceans. Scientists use the slight atomic differences between these isotopes to trace them back to the land mass where they originated, and because of this, the isotopes serve as tracers of circulation in today's oceans. Also, in the layers of sediments at the ocean's bottom, neodymium isotopic signatures form a record of ocean circulation going back millions of years.

But while more and more scientists are looking to neodymium isotopes for answers about the oceans and global climate, there remain unanswered questions about the oceanic neodymium budget. There seems to be more of the element getting into the oceans than anyone has accounted for. This has been dubbed the "neodymium paradox."

Some researchers have speculated that particles deposited in the oceans by winds or rivers release more neodymium upon contact with seawater than has been measured so far. Burdige and his partner in the NSF study, Karen H. Johannesson, a geochemist at Tulane University, believe, on the other hand, that groundwater discharges that happen under the surface of the oceans contain precisely the concentrations and forms of isotopes needed to balance the neodymium budget.

The three-year NSF grant was funded through a program at NSF called Emerging Topics in Biogeochemical Sciences and is titled "Collaborative Research: Evaluating the Role of Submarine Groundwater Discharge in the Oceanic Neodymium Budget."

Burdige, who is professor and eminent scholar of ocean, earth and atmospheric sciences, said the questions about the neodymium budget limit the ability of researchers to "confidently interpret the geochemistry of neodymium in the modern oceans and, perhaps more importantly, to read the paleoceanographic neodymium isotope record."

Preliminary analysis by Burdige and Johannesson, which was reported in an article they wrote for the journal Earth and Planetary Science Letter, suggests that submarine groundwater discharge (SGD) to the oceans is a major component of the missing neodymium flux.

"A primary goal of this project is to assemble a data base of neodymium concentrations and isotope ratios for groundwaters from a range of locations that discharge to the coastal oceans," the researchers wrote in their project proposal. "These data will subsequently be used to develop a global mass balance model to test whether the measured neodymium concentrations and isotope ratios of SGD are sufficient to balance the oceanic neodymium budget. The model will also be used to evaluate the impact of varying groundwater neodymium fluxes, and their associated isotopic composition, on the paleoceanographic neodymium isotope record preserved in hydrogenous sediments."

Burdige said he believes the proposal also hits on other important issues beyond neodymium, "namely the ability to begin to quantify groundwater discharge to the oceans, in general." This has become a hot topic in recent years, and he thinks that this aspect of the project caught the attention of geochemists, hydrogeologists and oceanographers more broadly interested in better understanding land-ocean couplings. The NSF grant runs from Oct. 1 of this year thru September 2011.