The dissolved Beryllium isotope composition of the Arctic Ocean

摘要

We present the first comprehensive set of dissolved 10Be and 9Be concentrations in surface waters and vertical profiles of allmajor sub-basins of the Arctic Ocean, which are complemented by data from the major Arctic rivers Mackenzie, Lena, Yeni-sey and Ob. The results show that 10Be and 9Be concentrations in waters below 150 m depth are low and only vary within afactor of 2 throughout the Arctic Basin (350-750 atoms/g and 9-15 pmol/kg, respectively). In marked contrast, Be isotopecompositions in the upper 150 m are highly variable and show systematic variations. Cosmogenic 10Be concentrations rangefrom 150 to 1000 atoms/g and concentrations of terrigenous 9Be range from 7 to 65 pmol/kg, resulting in 10Be/9Be ratios (atom/atom) between 0.5 and 14 × 10~(-8).Inflowing Atlantic water masses in the Eurasian Basin are characterized by a10Be/9Be signature of 7 × 10~(-8).The inflow of Pacific water masses across the Bering Strait is characterized by lower ratios of 2-3 × 10~(-8),which can be traced into the central Arctic Ocean, possibly as far the Fram Strait. A comparison of thehigh dissolved surface 10Be and 9Be concentrations (corresponding to low 10Be/9Be signatures of 2 × 10~(-8))in the EurasianBasin with hydrographic parameters and river data documents efficient and rapid transport of Be with Siberian river watersacross the Siberian Arctic shelves into the central Arctic Basin, although significant loss and exchange of Be on the shelvesoccurs. In contrast, fresh surface waters from the Canada Basin also show high cosmogenic 10Be contents, but are notenriched in terrigenous 9Be (resulting in high 10Be/9Be signatures of up to 14 x 10-8). This is explained by a combinationof efficient scavenging of Be in the Mackenzie River estuary and the shelves and additional supply of cosmogenic 10Be viaatmospheric fallout and melting of old sea ice. The residence time of Be in the deep Arctic Ocean estimated from our datais 800 years and thus similar to the average Be residence time in the global ocean.