Collaborative Research: Th-230 as a Sediment Focusing Indicator: constraints from He-3 in Interplanetary Dust Particles

Columbia University, New York NY

Investigators

Abstract

Recently, the 230Th constant-flux proxy (CFP) profiling method of calculating sediment accumulation rates (ARs) has become a topic of significant controversy, especially with respect to the issue of sediment focusing and its quantification. Depending on whether one derives ARs using age models or CFPs leads to vastly different interpretations in paleoceanographic studies. Under this award the PIs will investigate sediment redistribution processes to determine the veracity of the 230Th CFP. They will measure another CFP with an independent source term, namely interplanetary dust particles (IDPs), and the extraterrestrial 3He contained therein. Agreement between 230Th and 3He variations in varied and well-studied depositional environments in the North Atlantic would constitute further support for the use of both CFPs for flux normalization. The data generated on sites with known amounts of sediment focusing and winnowing will help constrain the influence of abyssal currents on IDPs and the sediments carrying adsorbed 230Th, and will provide insights into the extent of hydrodynamic sorting of these particles. When combined with 14C and paired 3He and 230Th measurement on various separated fractions of the fine-grained component of the sediment, the PIs will test the hypotheses that 1) 3He is less sensitive than 230Th to sediment focusing, and 2) the degree to which sediment redistribution processes fractionate 3He-containing IDPs from the 230Th containing portion of the sediment. In the future, the proponents hope to develop a new proxy (3He/230Th ratio) for changes in the strength of deep-sea currents in association with past climatic changes. This project will involve students in their teaching, training and learning.