This proposal is to investigate the behavior of a range of elements that provide isotopic tracers for particle removal processes in the Canada Basin of the Arctic Ocean. These will include U- and Th-series nuclides, Nd and Pu. The role of partitioning between particulates, colloids, and solution will be emphasized. This region is unique in having exceptionally low particle fluxes compared with other oceans for at least two reasons: (i) It is a fundamental characteristic of the Arctic Ocean that needs to be better understood along with the implications it has for the assimilation of particle-reactive contaminants, and (ii) a careful characterization of the processes in this extreme case will provide an important reference point for other studies. This proposal incorporates current ideas about the role of colloid-size particles in the removal of trace metals by scavenging and this is an important focus of the proposed work. The hypothesis to be tested is as follows: "Due to low particle concentration in the Canada Basin, the colloids play a major role in the cycling of particle-reactive radionuclides." Earlier studies on the dissolved organic carbon and suspended particle concentration (SPM) indicate that the concentration of colloidal material in Canada Basin is likely similar to other major ocean basins while the SPM concentration is about an order of magnitude lower than that of other ocean basins. In order to test the hypothesis, the study will focus along the following lines of investigation: 1. The distribution of the long-lived TH isotopes and short-lived isotopes between particles, colloids, and dissolved species will be measured in the Canada Basin water column in both continental shelf, slope and deep basin. The removal rate by particulate scavenging of Pb and Po will be calculated from their measurement in the water column for comparison with the removal of Th. 2. The distribution of Nd isotopes between particles, colloids and the dissolved species will be m easured. 3. The distribution of dissolved and particulate PU isotopes in the water column will be measured at various sites and their rates of transport and removal will be investigated by comparison with other particle-reactive nuclides. A key aspect of the study is the combining of data for the short-lived isotopes of TH with the long lived Th isotopes and stable Nd isotopes.
