New Constraints on the Physical and Biological Controls on the Silicon Isotopic Composition of the Arctic Ocean

• Published in: Frontiers in Marine Science
• Main Authors: Brzezinski, Mark A., Closset, Ivia, Jones, Janice L., de Souza, Gregory F., Maden, Colin
• Other Authors: National Science Foundation
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Frontiers Media SA 2021
• Subjects: Arctic Ocean; Bering Strait; canada basin; Chukchi; Chukchi Sea; North Pole
• Online Access: http://dx.doi.org/10.3389/fmars.2021.699762; https://www.frontiersin.org/articles/10.3389/fmars.2021.699762/full

The silicon isotope composition of silicic acid, δ 30 Si(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, δ 30 Si(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 δ 30 Si(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 δ 30 Si(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. δ 30 Si(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 δ 30 Si(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.