Variations of North Atlantic inflow to the central Arctic Ocean over the last 14 million years inferred from hafnium and neodymium isotopes

The warm and saline North Atlantic inflow to the Arctic Ocean is a major component of high northern latitude circulation and the main mechanism of deep water renewal in the Arctic Ocean. Knowledge of its past variability is critical for understanding the high latitude feedback mechanisms of the climate system. Here we present the first combined seawater Hf and Nd isotope compositions of past Arctic Intermediate water extracted from the authigenic Fe-Mn oxyhydroxide fraction of two sediment cores recovered near the North Pole, to reconstruct changes in contributions from glacial brines of the Eurasian shelf and past inflow of Atlantic waters. The Hf and Nd isotopic compositions obtained from leachates of the authigenic fraction show closely coupled and environmentally controlled variations over the past 14 million years. An observed offset of these data from seawater epsilon(Hf) and epsilon(Nd) compositions from other ocean basins (seawater array) is interpreted as the result of continuously prevailing glacial weathering conditions on the high latitude Eurasian continent. In the late Quaternary, large amplitude Hf and Nd isotopic variations of Arctic Intermediate Water (AIW) was characterized by more radiogenic isotope signatures generally prevailing under glacial conditions and less radiogenic values during interglacial periods. On the basis of the close coupling between Nd and Hf isotopes, we suggest that the evolution of Hf isotope compositions of central Arctic AIW has primarily been controlled by changes in ocean circulation and provenance of weathering inputs, rather than changes in weathering regime. (C) 2012 Elsevier B.V. All rights reserved.