Stichel, Torben and Pahnke, Katharina and Duggan, Brian and Goldstein, Steven L. and Hartman, Alison E. and Paffrath, Ronja and Scher, Howie D. (2018) TAG plume: revisiting the hydrothermal neodymium contribution to seawater. Frontiers in Marine Science, 5. p. 96. ISSN 2296-7745

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Official URL: http://dx.doi.org/10.3389/fmars.2018.00096

Abstract

We present results on the distribution of +Nd and [Nd] from the TAG hydrothermal vent field and adjacent locations collected during the GEOTRACES GA03 cruise in October 2011. Our results show that Nd isotopes directly below and above the plume do not significantly deviate fromaverage NADW(+Nd =−12.3±0.2).Within the plume, however, isotope values are shifted slightly toward more radiogenic values up to +Nd = −11.4. Interestingly at the same time a significant decrease in [Nd] along with rare earth element (REE) fractionation is observed, indicating enhanced scavenging within the plume despite the change in Nd isotopes. Elemental concentrations of Nd are reduced by 19.6– 18.5 pmol/kg, coinciding with the maximum increase of mantle derived helium (xs3He) from 0.203 to 0.675 fmol/kg, resulting in an average 1.8 pmol/kg decrease in [Nd] relative to an expected linear increase with depth. The inventory loss of Nd within the plume sums up to 614 nmoles/m2, or 6%, if a continuous increase of [Nd] with depth is assumed. Compared to BATS and the western adjacent station USGT11-14, the local inventory loss is even higher at 10%. The tight relationship of xs3He increase and [Nd] decrease allows us to estimate scavenging rates at TAG suggesting 40 mol/year are removed within the TAG plume. A global estimate using power output along ocean ridges yields an annual Nd removal of 3.44 × 106 mol/year, which is about 71% of riverine and dust flux combined or 6–8% of the estimated global flux of Nd into the ocean. The change in Nd isotopic composition of up to 0.7 more radiogenic +Nd values suggests an exchange process between hydrothermally derived particles and seawater in which during the removal process an estimated 1.1 mol/year of hydrothermal Nd is contributed to the seawater at the TAG site. This estimate is only 0.1% of the global Nd signal added to the ocean by boundary exchange processes at ocean margins, limiting the ability of changing the Nd isotopic composition on a global scale in contrast to the more significant estimated sink of elemental Nd in hydrothermal plumes from this study.

Item Type: Article
Additional Information: Publiziert mit Hilfe des DFG-geförderten Open Access-Publikationsfonds der Carl von Ossietzky Universität Oldenburg.
Uncontrolled Keywords: neodymium isotopic compositions, GEOTRACES, hydrothermal plume, rare earth elements, seawater, TAG
Subjects: Science and mathematics > Chemistry
Science and mathematics > Earth sciences and geology
Science and mathematics > Life sciences, biology
Divisions: Faculty of Mathematics and Science > Institute for Chemistry and Biology of the Marine Environment (ICBM)
Date Deposited: 11 Sep 2019 10:14
Last Modified: 26 Sep 2019 11:06
URI: https://oops.uni-oldenburg.de/id/eprint/4140
URN: urn:nbn:de:gbv:715-oops-42215
DOI: doi:10.3389/fmars.2018.00096
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