Biogeochemical implications from dissolved rare earth element and Nd isotope distributions in the Gulf of Alaska.

Haley, Brian A., Frank, Martin, Hathorne, Ed C. and Pisias, Nick (2014) Biogeochemical implications from dissolved rare earth element and Nd isotope distributions in the Gulf of Alaska. Geochimica et Cosmochimica Acta, 126 . pp. 455-474. DOI 10.1016/j.gca.2013.11.012.

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Abstract

Dissolved rare earth element (REE) concentrations and Nd isotope compositions were measured for surface waters and full water column profiles of the Gulf of Alaska (GoA), and compared to water mass properties and circulation in order to better understand the mechanisms controlling the input and transport of REEs in the ocean. The REEs display a typical open-ocean range of concentrations (i.e., La: 12-66 pM; Lu: 0.2-2.5 pM) and depth distributions (i.e., surface ocean depletion and enrichment with water depth). Nd isotope signatures are highly radiogenic, as expected for the North Pacific margin (ranging from -3.8 to +0.2 epsilon Nd). The most radiogenic values were found in the coastal waters but also in the cores of eddies, indicating efficient export of REEs from the margins and across the mixed layer. This is the first time that distinct Nd isotope distributions in near surface waters can be directly assigned to offshore eddy transport. A distinct mid-depth (similar to 2200 m) Nd isotope signal was found that most likely reflects advection of a water mass that formed through past down-welling in the Northern Pacific. Subsurface Nd isotope compositions appear to behave conservatively and can be explained through a REE distribution model proposed here. This model is based on multivariate analysis of the REEs and invokes two distinct "pools" of dissolved REEs: a "passive pool" complexed by carbonate ions, and a "bio-reactive pool" that is microbially manipulated. The latter "pool" is only significant in the upper water column and most likely reflects the indirect effects of microbial cycling of iron. Our model of the open ocean REE distribution contributes to explaining the conservative nature of Nd isotopes and provides a mechanism linking surface ocean and pore water REE dynamics

Document Type: Article
Keywords: dissolved rare earth elements, Nd isotopes, Gulf of Alaska
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Kiel University
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.gca.2013.11.012
ISSN: 0016-7037
Projects: Transdrift, Laptev Sea System
Date Deposited: 06 Feb 2014 09:53
Last Modified: 19 Jun 2017 10:25
URI: http://oceanrep.geomar.de/id/eprint/23314

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