Description: The water masses passing the Fram Strait are mainly responsible for the exchange of heat and freshwater between the Nordic Seas and the Arctic Ocean (the Arctic Mediterranean, AM). Disentangling their exact sources, distribution and mixing, however, is complex. This work provides new insights based on a detailed geochemical tracer inventory including dissolved Nd isotope (e-Nd), rare earth element (REE) and stable oxygen isotope (d18O) data along a full water depth section across Fram Strait. We find that Nd isotope and REE distributions in the open AM primarily reflect lateral advection of water masses and their mixing. Seawater-particle interactions exert important control only above the shelf regions, as observed above the NE Greenland Shelf. Advection of northward flowing warm Atlantic Water (AW) is clearly reflected by an e-Nd signature of -11.7 and a Nd concentration ([Nd]) of 16 pmol/kg in the upper ~500 m of the eastern and central Fram Strait. Freshening and cooling of the AW on its way trough the AM are accompanied by a continuous change towards more radiogenic e-Nd signatures (e.g. -10.4 of dense Arctic Atlantic Water). This mainly reflects mixing with intermediate waters but also admixture of dense Kara Sea waters and Pacific-derived waters. The more radiogenic e-Nd signatures of the intermediate and deep waters (reaching -9.5) are mainly acquired in the SW Nordic Seas through exchange with basaltic formations of Iceland and CE Greenland. Inputs of Nd from Svalbard are not observed and surface waters and Nd on the Svalbard shelf originate from the Barents Sea. Shallow southward flowing Arctic-derived waters (〈200 m) form the core of the East Greenland Current above the Greenland slope and can be traced by their relatively radiogenic e-Nd (reaching -8.8) and elevated [Nd] (21-29 pmol/kg). These properties are used together with d18O and standard hydrographic tracers to define the proportions of Pacific-derived (〈~30% based on Nd isotopes) and Atlantic-derived waters, as well as of river waters (〈~8%). Shallow waters (〈150 m) on the NE Greenland Shelf share some characteristics of Arctic-derived waters, but exhibit less radiogenic epsilon-Nd values (reaching -12.4) and higher [Nd] (up to 38 pmol/kg) in the upper ~100 m. This suggests local addition of Greenland freshwater of up to ~6%. In addition to these observations, this study shows that the pronounced gradients in epsilon-Nd signatures and REE characteristics in the upper water column provide a reliable basis for assessments of shallow hydrological changes within the AM.

Description: To better understand the inputs of riverine REEs and Hf to the ocean and their impact on the open ocean we collected filtered seawater samples from 16 full water column profiles along the Congo River plume at the coast of Congo and Gabon and along an offshore section at 3°S, complemented by three freshwater samples collected directly from the Congo River. The water samples from the Congo River plume were collected during GEOTRACES cruise GA08 with German RV Meteor (M121) in November and December 2015 with a stainless steel CTD rosette and a towed fish for surface waters. River water end-member samples from the Congo River at zero salinity were taken upstream by boat in May, July and October 2017 near the center of the river at ~6°S and ~12.5°E (stations 12.1–12.3). We determine for the first time REE and Hf concentrations and isotope compositions within the Congo River plume and quantify Nd and Hf fluxes. Based on these data we evaluate how far the Congo River plume is traceable by these geochemical parameters, how it contributes to their budgets in the South East Atlantic Ocean, and to which degree the Nd and Hf isotope and REE distributions can be used as water mass tracers in areas of high continental inputs.