Collaborative Research: Constraining Water Mass Age and Particle Flux in the Arctic Ocean Using Pa-231 and Th-230 as Tracers

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Abstract OPP-0002313MoranOPP-0004029EdwardsThis is a collaborative proposal between Principal Investigators at the Universities of Rhode Island and Minnesota-Twin Cities. The Arctic Ocean is much more dynamic than previously believed, characterized by large spatial and seasonal variations in productivity and associated particle flux, significant estuarine input and lateral intrusions of shelf water extending into the interior basins, and topographically-steered boundary currents along the perimeters of basins that result in regional extremes in water mass age. The Principal Investigators hypothesize that "boundary scavenging", controlled by a combination of lateral advection and particle flux, plays a significant role in the removal of particle-reactive chemicals from the water column of the Arctic Ocean. They will evaluate the role of boundary scavenging as it has an important bearing on such key geochemical processes such as the export of carbon to deep waters, the sediment accumulation of reactive chemicals, including contaminants, and the export of these chemicals to the Atlantic. The objective is to constrain these fundamental processes on a basin-wide scale and to develop predictive biogeochemical models for this poorly understood and extreme environment. The Principal Investigators will determine whether that natural radionuclide Protactinium-231 (231Pa) - Thorium -230 (231Th) pair can be used as tracers to provide an integrated picture of water mass age and particle flux on a basin-wide scale in the modem and last glacial Arctic.To provide an increased understanding of the processes that control the redistribution of these tracers in the Arctic Ocean, the Principal Investigators will undertake a comprehensive study that includes paired 231Pa - 231Th analyses in dissolved and particulate samples from the water column, sediment trap material, surface sediments and sediment comes. This should help with a better understanding of the importance of particle composition on 231Pa - 231Th fractionation by quantifying the chemical composition of suspended particulate matter, sediment trap material and surface sediments. Boundary scavenging should be pronounced in the Arctic, due to the combined effects of the high ratio of shelf to open ocean, the regional extremes in water mass age and particle flux, and a dynamic circulation. This environmental setting is markedly different than other ocean regions where Pa and Th tracer studies have been conducted and provides a unique opportunity to investigate boundary scavenging and, in turn, constrain some outstanding questions regarding the paleo-application of 231Pa - 231Th.