Investigation of subsurface water flow along the continental margin of theEurasian Basin using the transient tracers tritium, He-3, and CFCs

During August-September 1993 the R/V Polarstern expedition ARK IX/4 was mad e to the Eurasian continental margin of the Arctic Ocean. Sections of ocean ographic stations leading fi om the outer shelf over the continental slopes toward the deep Eurasian Basin were occupied north of the Barents and Lapt ev Seas. The distributions of the transient tracers CFC-11, CFC-12, tritium , and He-3 were measured along these sections and are discussed in relation to water mass distribution and circulation along the continental margin of the Eurasian Basin. The tracer data strongly corroborate the temperature a nd salinity data [Schauer ey al., 1997], clearly showing the inflow of Atla ntic water in two branches, the Fram Strait branch and the Barents Sea bran ch. High CFC and tritium concen-trations extended down to 1300 m over the L aptev continental slope, indicating strong inflow of the Barents Sea branch between Franz Josef Land and Severnaya Zemlya. The apparent ages of water in the Fram Strait branch were estimated to be about 2 years north of the B arents Sea and 6 years at the eastern end of the Nansen Basin, which corres ponds to an apparent mean current speed of about 1 cm s(-1). The age of the core of the Barents Sea branch was also estimated to be about 6 years over the Laptev slope region and to increase by 0.5 years as it flowed through this region. A lower limit for the inflow of newly formed Barents Sea Branc h Water was estimated to be 0.5 Sv, and an overall transport for the sum of Fram Strait branch plus Barents Sea branch flow of 4 Sv was estimated from this aging. In the deep water there was clear evidence for the inflow of N orwegian Sea Deep Water through Fram Strait, but there appeared to be no si gnificant input of shelf-derived water from the Santa Anna Trough. If there was any shelf-derived input to Eurasian Basin Bottom Water, it entered at a deeper depth than was sampled on the slope sections in the Laptev Sea or its flow is intermittent and was not occurring during the ARK IX/4 expediti on.