Water mass mixing versus local weathering inputs along the Bay of Biscay: Evidence from dissolved hafnium and neodymium isotopes.

Dausmann, Veit , Frank, Martin and Zieringer, Moritz (2020) Water mass mixing versus local weathering inputs along the Bay of Biscay: Evidence from dissolved hafnium and neodymium isotopes. Marine Chemistry, 224 (Article number 103844). DOI 10.1016/j.marchem.2020.103844.

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Abstract

Highlights

• Nd isotope data reflect advection and dilution of Mediterranean Outflow Water on its way north in the Bay of Biscay.
• Combined Hf and Nd isotopes are a sensitive indicator of inputs from land as well as long distance advection and mixing.
• Nd isotope results of this and earlier studies demonstrate the temporally variable flow path of Mediterranean Sea Water.

We present dissolved neodymium and hafnium concentrations and isotope compositions of surface and deep-water masses from the Bay of Biscay. Neodymium isotope signatures in surface waters of the Bay of Biscay are mostly dominated by local weathering inputs from the surrounding continental margin. Subsurface Eastern North Atlantic Central Water (ENACW) shows a distinct Nd isotope signature (εNd ≅ −12) at the southwestern-most station and is significantly diluted by mixing with more radiogenic waters or shifted by inputs of relatively radiogenic particulate Nd on its way north along the European margin. Furthermore, the Nd isotope data clearly show a declining fraction of Mediterranean Sea Water (MSW) at intermediate depths on its way north indicating that only 40% to 60% of MSW still present in the mixture at the Galician margin arrive at the stations further north in the Bay of Biscay. An interannual variability of the flow path of MSW is identified when comparing the results of the Nd isotope compositions and salinity data of this study with those of earlier studies from the area.
In agreement with Nd isotope and concentration analyses the Hf isotope composition of MSW is set by large-scale inputs of terrigenous material into the Mediterranean as can be deduced from elevated Hf concentrations still observable at the Galician margin. Hf isotope signatures of all water masses of the Bay of Biscay, moreover, are overprinted by local weathering inputs and do not reflect water mass mixing. However, combined dissolved Nd and Hf isotopes serve as indicators of local weathering influences on signatures expected from long distance water mass mixing.

Document Type: Article
Keywords: Radiogenic isotopes, Mediterranean sea water export, Water mass labeling, Continental inputs, Interannual water mass features, Nd-Hf decoupling
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.marchem.2020.103844
ISSN: 0304-4203
Expeditions/Models/Experiments:
Date Deposited: 24 Jun 2020 09:04
Last Modified: 24 Jun 2020 09:18
URI: http://oceanrep.geomar.de/id/eprint/49956

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