231Pa/230Th records of Arctic/Atlantic interchange in Fram Strait

Abstract:

Fram Strait, the Arctic Ocean's only deep passage for exchange with lower latitude oceans, today serves as a conduit for waters flowing north into the Arctic Ocean and south into the Atlantic. Reconstruction of circulation patterns and strength at depth in the strait can help to clarify the history of Arctic/Atlantic deep water exchange and Arctic contributions to global meridional overturning circulation. We will present new sedimentary measurements of radioisotopes ²³¹Pa and ²³⁰Th to provide information on this exchange in the past and its relationship to sedimentation and climatic events. Coretop and downcore ²³¹Pa/²³⁰Th ratios from Arctic sediments indicate that ²³¹Pa has been exported from the central Arctic basin throughout the Holocene and deglaciation. Fram Strait represents a possible sink for this “missing” ²³¹Pa. Preliminary results from ODP Holes 908A and 909A, at 1274 m and 2519 m water depths respectively in the central strait, suggest that ratios in this region during the Holocene have varied between ~0.106 (above the ²³¹Pa/²³⁰Th production ratio of 0.093 in seawater, indicating net import of ²³¹Pa)and ~0.055 (well below the production ratio, indicating net export of ²³¹Pa). Further measurements in cores from the Greenland and Svalbard continental slopes will give a fuller regional picture of ²³¹Pa deposition and transport across the strait.