Water Mass Distribution and Particle Flux in the Arctic Ocean From Dissolved 10Be and 9Be Concentrations

The Arctic Ocean basin is confined by landmasses similar to the Mediterranean. There is only little deep water formed seasonally on the shelves of the Arctic Ocean despite the low temperatures. This is due to a freshwater lid at the surface which originates from the Arctic rivers. The deeper Arctic Ocean water masses can thus only be renewed at comparatively low rates through the only deep connection to the Atlantic Ocean, the Fram Strait. At the same time the biogenic particulate fluxes in the central Arctic Ocean are very low due to perennial sea ice cover and the organic matter produced in the surface waters is remineralised efficiently. Detrital particle fluxes from either eolian or riverine sources are also very low. We will present the first combined dissolved ¹⁰Be (cosmogenic) and ⁹Be (continental sources) depth profiles from water samples of the major deep basins of the Arctic Ocean collected during the Swedish Arctic Ocean 2001 expedition. Be is 5-10 times less particle-reactive than other previously investigated radionuclides such as Th or Pa and should therefore even at the relatively low Arctic Ocean renewal rates serve as a quasi-conservative tracer for different origins of water masses (Atlantic Ocean/Norwegian Sea, Pacific Ocean, Arctic Shelves). ⁹Be and Nd isotope analyses provide complementary information on the pathways of dissolved material originating from the Arctic continents. Results obtained ten years ago at similar locations as in our study indicated a uniform distribution of ¹⁰Be at low values of 500 +/- 100 atoms/g suggesting restricted input and efficient homogenisation. In contrast, our new results show that in 2001 the inflowing waters from the Atlantic are traced by ¹⁰Be concentrations of up to 1100 atoms/g. In addition, the surface concentrations vary considerably. It will be discussed wether this is a consequence of a seasonal/decadal variability in the distribution of surface water masses, which has been deduced from oceanographic parameters or whether it is related to changes in particulate fluxes.