Arctic vs. North Atlantic water mass exchanges in Fram Strait from Pb isotopes in sedimentsThis article is one of a series of papers published in this Special Issue on the theme Polar Climate Stability Network.

Abstract

Surface sediment samples (n = 10), collected between Spitzbergen and Greenland, and two cores raised east (C04) and west (C16) from Fram Strait were analyzed for their chemical and isotopic (Pb) compositions to trace the source of sediments and water masses exchanging between the Arctic and the North Atlantic oceans. In surface sediments, variable major and trace element concentrations suggest variations in both the mineralogy (carbonate and quartz dilution of other silicate minerals) and source regions of detrital supplies, based on Th/Zr and, to a lesser extent, on Th/U ratios. Each core site shows specific but nearly constant Th/Zr ratios, indicating homogeneous source supplies. At both core sites, Pb concentrations and isotopic compositions display similar patterns: homogeneous low Pb and radiogenic crustal signals below 5–10 cm, contrasting with high Pb and less radiogenic anthropogenic inputs at core-tops. However, the differing pre-anthropogenic Pb isotopic ratios in C04 and C16 confirm the involvement of distinct source supplies east and west of Fram Strait. We suggest that this isotopic specificity is mainly owing to inputs of material carried from northwestern Europe by the North Atlantic water mass and from the Laptev Sea by the Transpolar Drift, respectively. Some material from the Greenland margin and possibly from the North Atlantic Ocean may reach this zone as well. Sediments from the western Arctic are not significantly transported into the Fram Strait area, suggesting that the Canadian and the Eurasian basins remained decoupled, at least during the time span of the cored sediments (∼2000 years).