New Constraints On The Physical And Biological Controls On The Silicon Isotopic Composition Of The Arctic Ocean

The silicon isotope composition of silicic acid, delta Si-30(OH)(4), in the deep Arctic Ocean is anomalously heavy compared to all other deep ocean basins. To further evaluate the mechanisms leading to this condition, delta Si-30(OH)(4) was examined on US GEOTRACES section GN01 from the Bering Strait to the North Pole. Isotope values in the polar mixed layer showed a strong influence of the transpolar drift. Drift waters contained relatively high [Si(OH)(4)] with heavy delta Si-30(OH)(4) consistent with the high silicate of riverine source waters and strong biological Si(OH)(4) consumption on the Eurasian shelves. The maximum in silicic acid concentration, [Si(OH)(4)], within the double halocline of the Canada Basin formed a local minimum in delta Si-30(OH)(4) that extended across the Canada Basin, reflecting the high-[Si(OH)(4)] Pacific source waters and benthic inputs of Si(OH)(4) in the Chukchi Sea. delta Si-30(OH)(4) became lighter with the increase in [Si(OH)(4)] in intermediate and deep waters; however, both Canada Basin deep water and Eurasian Basin deep water were heavier than deep waters from other ocean basins. A preliminary isotope budget incorporating all available Arctic delta Si-30(OH)(4) data confirms the importance of isotopically heavy inflows in creating the anomalous deep Arctic Si isotope signature, but also reveals a surprising similarity in the isotopic composition of the major inflows compared to outflows across the main gateways connecting the Arctic with the Pacific and the Atlantic. This similarity implies a major role of biological productivity and opal burial in removing light isotopes entering the Arctic Ocean from rivers.