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

Abstract

During August–September 1993 the R/V Polarstern expedition ARK IX/4 was made to the Eurasian continental margin of the Arctic Ocean. Sections of oceanographic stations leading from the outer shelf over the continental slopes toward the deep Eurasian Basin were occupied north of the Barents and Laptev Seas. The distributions of the transient tracers CFC‐11, CFC‐12, tritium, and 3 He 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 and salinity data [ Schauer et al. , 1997], clearly showing the inflow of Atlantic water in two branches, the Fram Strait branch and the Barents Sea branch. High CFC and tritium concen‐trations extended down to 1300 m over the Laptev 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 Barents Sea and 6 years at the eastern end of the Nansen Basin, which corresponds 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 Branch 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 Norwegian Sea Deep Water through Fram Strait, but there appeared to be no significant 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 expedition.