Robert Anderson; Lamont-Doherty Earth Observatory

"Proxies of Past Changes in Southern Ocean Productivity: Modeling and Experimental Development"

We propose a two part study of the biogeochemical cycling and physical transport of radionuclide tracers in the modern ocean. In the first part, we will examine the scavenging behavior of ²³⁰Th, ²³¹Pa and ¹⁰Be in the Southern Ocean by measuring their concentrations both in the water column and in particulate material collected by sediment traps, in part to test the proposed use of radionuclide ratios (²³¹Pa/²³⁰Th and ¹⁰Be/²³⁰Th) as proxies of export flux. Independently, we will introduce these nuclides into the Hamburg ocean general circulation model to evaluate that component of their transport by ocean circulation that is independent of spatial gradients in particle flux. These combined efforts will better define our ability to use radionuclide ratios to evaluate past changes in ocean productivity, and improve our understanding of the response of ocean productivity to climate variability. Furthermore, the improved understanding of transport and scavenging behavior of ²³⁰Th will, in turn, better enable us to use ²³⁰Th normalization techniques to correct for sediment focusing effects, likely to be a major problem in the APFZ, and thereby relate deepwater rain rates of particulate biogenic phases collected by sediment traps both to rates of production in surface waters, and to rates of accumulation and of regeneration of biogenic material on the sea bed.

We propose to use fractions of sediment trap material collected by the WHOI/OSU consortium. We will collect water and sediment samples during the combined benthic/mooring recovery cruise. We need two berths for people collecting and processing samples and a third for a person to assist with coring operations. We will collaborate with groups collecting sediment trap samples (Honjo/Francois/Dymond/Collier as well as the organic flux group Lee/Wakeham/Hedges); with the benthic flux group (Sayles); and with other groups investigating remineralization of biogenic phases in the deep sea.