Neodymium isotopes in seawater from the Barents Sea and Fram Strait Arctic-Atlantic gateways

摘要

The neodymium concentration, C-Nd, and isotopic composition, epsilon(Nd), in seawater have been determined in the water column at five sites in the Barents Sea-Fram Strait area where most of the water exchange between the Arctic Ocean and the North Atlantic takes place. In the main Arctic Ocean inflow branch across the Barents Sea the concentration and isotopic composition (C-Nd = 15.5 pmol/kg and epsilon(Nd) = -10.8) are similar to those reported for the northeastern Nordic Seas, which is consistent with this region being a source area for the Arctic inflow. Due to the addition of Nd from Svalbard shelf sediments, the C-Nd in the surface waters above 150 m, in the Fram Strait inflow branch is higher by a factor of 2 and the epsilon(Nd) is shifted to lower values (-11.8). In the stratified Nansen Basin, where cold low salinity water overlies warmer Atlantic water the C-Nd and epsilon(Nd) do not vary with the vertical temperature-salinity structure but are essentially constant and similar to those of the Atlantic inflow throughout the entire water column, down to 3700 m depth, which indicates that the Nd is to a large extent of Atlantic origin. Compared to the Atlantic inflow water, the Nd in the major Arctic Ocean outflow, the Fram Strait, show higher C-Nd in the surface waters above 150 m, and a higher epsilon(Nd) (-9.8) throughout the entire water column down to 1300 m depth. Sources for the more radiogenic Nd isotopic composition in deep water of the Fram Strait outflow most likely involve boundary exchange with sediments on the shelf and slope as the water passes along the Canadian archipelago. River water is a possible source in the surface water but it also seems likely that Pacific water Nd, modified by interactions on the shelf, is an important component in the Fram Strait surface outflow. Changes in the relative proportions of inflow of river water and flow of Pacific water through the Arctic Ocean could thus influence the isotopic composition of Nd in the North Atlantic. (c) 2008 Elsevier Ltd. All rights reserved.