Water mass transformation in the Barents Sea inferred from radiogenic neodymium isotopes, rare earth elements and stable oxygen isotopes.

Laukert, Georgi , Makhotin, Mikhail, Petrova, Mariia V., Frank, Martin, Hathorne, Ed C. , Bauch, Dorothea , Böning, Philipp and Kassens, Heidemarie (2018) Water mass transformation in the Barents Sea inferred from radiogenic neodymium isotopes, rare earth elements and stable oxygen isotopes. Chemical Geology . DOI 10.1016/j.chemgeo.2018.10.002.

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Abstract

Highlights

• First comprehensive seawater Nd isotope and REE data set for the Barents Sea
• Water masses traced with Nd isotopes, salinity and stable oxygen isotopes
• No release of particulate REEs to the dissolved load except for cerium
• Transformation of Atlantic Water accompanied by pronounced REE removal from the dissolved phase

Abstract

Nearly half the inflow of warm and saline Atlantic Water (AW) to the Arctic Ocean is substantially cooled and freshened in the Barents Sea, which is therefore considered a key region for water mass transformation in the Arctic Mediterranean. Numerous studies have focused on this transformation and the increasing influence of AW on Arctic climate and biodiversity, yet geochemical investigations of these processes have been scarce. Using the first comprehensive data set of the distributions of dissolved radiogenic neodymium (Nd) isotopes (expressed as ɛNd), rare earth elements (REE) and stable oxygen isotope (δ18O) compositions from this region we are able to constrain the transport and transformation of AW in the Barents Sea and to investigate which processes change the chemical composition of the water masses beyond what is expected from circulation and mixing.

Inflowing AW and Norwegian Coastal Water (NCW) both exhibit distinctly unradiogenic ɛNd signatures of −12.4 and −14.5, respectively, whereas cold and dense Polar Water (PW) has considerably more radiogenic ɛNd signatures reaching up to −8.1. Locally formed Barents Sea Atlantic Water (BSAW) and Barents Sea Arctic Atlantic Water (BSAAW) are encountered in the northeastern Barents Sea and have intermediate ɛNd values resulting from admixture of PW containing small amounts of riverine freshwater from the Ob (<~1.1%) to AW and NCW. Similar to the Laptev Sea, the dissolved Nd isotope composition in the Barents Sea seems to be mainly controlled by water mass advection and mixing despite its shallow water depth. Strikingly, the BSAW and BSAAW are marked by the lowest REE concentrations reaching 11 pmol/kg for Nd ([Nd]), which in contrast to the Nd isotopes, cannot be attributed to the admixture of REE-rich Ob freshwater to AW or NCW ([Nd] = 16.7, and 22 pmol/kg, respectively) and instead reflects REE removal from the dissolved phase with preferential removal of the light over the heavy REEs. The REE removal is, however, not explainable by estuarine REE behavior alone, suggesting that scavenging by (re)suspended (biogenic) particles occurs locally in the Barents Sea. Regardless of the exact cause of REE depletion, we show that AW transformation is accompanied by geochemical changes independent of water mass mixing.

This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.

Document Type: Article
Keywords: Arctic Ocean, Barents Sea, Neodymium isotopes, Rare earth elements, Water masses, Scavenging
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.chemgeo.2018.10.002
ISSN: 0009-2541
Projects: POMOR
Date Deposited: 16 Oct 2018 07:22
Last Modified: 16 Oct 2018 07:22
URI: http://oceanrep.geomar.de/id/eprint/44494

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