Investigation of the Rate of Shelf-Basin Interaction in the Western Arctic Using Radium Isotopes: SBI Phase II

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The largely landlocked Arctic Ocean receives input from the Pacific and Atlantic Ocean and from rivers draining the surrounding continents. These inflows are important sources of salt, heat, nutrients, sediment and organisms for the central basin. With the exception of a portion of the Atlantic Ocean contribution, these inputs must cross continental shelves where they are modified significantly by benthic, water column, and air-ice-ocean interactions. As a consequence of the cross-shelf transports, there are significant biogeochemical exchanges between the shelves and the central basin. However, we currently lack the information to quantify these exchanges. In order to address this lack, this project proposes as part of the western Arctic Shelf-Basin Interaction (SBI) Phase II program to apply an isotopic water mass tracer technique to assess the pathways and rates of exchange between the western Arctic shelves and the interior Arctic Ocean basin. The proposed technique uses the measured concentrations in the water column of the two naturally occurring radioisotopes 228Ra and 226Ra. Because 228Ra, which has a half life of 5.77 years, is derived solely from shelf sediments, it provides unambiguous evidence of the presence of shelf water. Its relative concentration in shelf and basin waters can therefore provide quantitative information on shelf-basin water transports. This technique is mature and has been used in shelf-basin exchange investigations in other regions. Results of a pilot research project carried out during the SBI Phase I program have demonstrated utility of this tracer technique in the western Arctic Ocean. For the proposed research, tracer data collected from vessels along transects through the study region will be analyzed within the context of nearshore and offshore field and modeling studies that focus on understanding cross-shelf transport. An emphasis will be placed on the role of mesoscale eddies in this transport. Where appropriate, the shorter-lived 224Ra with its 3.64-day half life will be measured at sea to supplement the dataset. Radium tracer data will also be collected whenever possible from other platforms such as moored arrays provided by other SBI investigators.