Universität zu Köln

Janssen, David J., Abouchami, Wafa, Galer, Stephen J. G., Purdon, Kathryn B. and Cullen, Jay T. ORCID: 0000-0002-6484-2421 (2019). Particulate cadmium stable isotopes in the subarctic northeast Pacific reveal dynamic Cd cycling and a new isotopically light Cd sink. Earth Planet. Sci. Lett., 515. S. 67 - 79. AMSTERDAM: ELSEVIER SCIENCE BV. ISSN 1385-013X

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Abstract

The nutrient-type distribution of dissolved cadmium concentrations (dCd) reflects a biological control in the global ocean, with uptake of dissolved Cd into biogenic particles in surface waters and regeneration of particulate Cd at depth. Depth profiles of dissolved Cd stable isotope composition ((d delta Cd-114/110), while sparse in coverage, exist for most of the major ocean basins, with spatial coverage improving through the efforts of the GEOTRACES program. However, a dearth of similarly resolved particulate delta Cd-114/110 (delta Cd-114/110) distributions limits our ability to use stable Cd isotopes to better understand Cd cycling in the global ocean. Here we present two p delta Cd-114/110 depth profiles from the subarctic northeast Pacific which demonstrate more complex delta Cd-114/110 cycling than dissolved profiles would suggest. Surface p delta Cd-114/110, while lighter than surface d delta Cd-114/110, is heavy relative to Pacific deepwater and crustal p delta Cd-114/110 components. Surface particulate and dissolved delta Cd-114/110 distributions are not well explained by closed-system Rayleigh fractionation following a single fractionation factor, in agreement with other recent studies in the Atlantic and Pacific Oceans. These variable fractionation trends in surface waters complicate the potential utility of delta Cd-114/110 as a paleoproductivity proxy. Particulate delta Cd-114/110 becomes lighter as particulate Cd is remineralized in the nutricline, reaching a minimum p delta Cd-114/110 of around -0.5 parts per thousand, among the lightest values reported in natural telluric samples. This p delta Cd-114/110 trend within the nutricline might be explained by (1) multiple pools of particulate Cd with different isotopic compositions and labilities, or (2) by fractionation during particulate Cd remineralization. The observed shallow loss of heavy p delta Cd-114/110 above the winter mixed layer, rather than the formation of especially light surface p delta Cd-114/110, may help to maintain the observed surface-to-deep d delta Cd-114/110 gradient. Below the mid-depth p delta Cd-114/110 minimum, p delta Cd-114/110 increases with depth toward the deepwater d delta Cd-114/110 value, possibly reflecting an isotopic equilibration between the particulate and dissolved phases. Dissolved delta Cd-114/110 profiles show uniform isotope composition at intermediate depths, while calculated remineralized p delta Cd-114/110 is isotopically variable and distinct from the bulk dissolved pool. This suggests that one-dimensional particle export and regeneration is not the primary control on d delta Cd-114/110 in the Pacific Ocean, but rather that regenerated delta Cd-114/110 is spatially or temporally variable and an advected d delta Cd-114/110 signal from subsurface Southern Ocean waters controls deep North Pacific d delta Cd-114/110. Our results imply that export of isotopically light p delta Cd-114/110 to shelf sediments may act as an important oceanic sink, helping to balance the known sources and sinks of Cd with the global deepwater d delta Cd-114/110. (C) 2019 Elsevier B.V. All rights reserved.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Janssen, David J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Abouchami, Wafa UNSPECIFIED UNSPECIFIED UNSPECIFIED Galer, Stephen J. G. UNSPECIFIED UNSPECIFIED UNSPECIFIED Purdon, Kathryn B. UNSPECIFIED UNSPECIFIED UNSPECIFIED Cullen, Jay T. UNSPECIFIED orcid.org/0000-0002-6484-2421 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-147162
DOI:	10.1016/j.epsl.2019.03.006
Journal or Publication Title:	Earth Planet. Sci. Lett.
Volume:	515
Page Range:	S. 67 - 79
Date:	2019
Publisher:	ELSEVIER SCIENCE BV
Place of Publication:	AMSTERDAM
ISSN:	1385-013X
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language WATER COLUMN; SOUTHERN-OCEAN; LINE-P; PARTICLES; PHYTOPLANKTON; FRACTIONATION; CARBON; ZINC; INSIGHTS; SEAWATER Multiple languages Geochemistry & Geophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/14716