Controls on Dissolved Silicon Isotopes Along the U.S. GEOTRACES Eastern Pacific Zonal Transect (GP16)

P. Grasse*, I. Closset, J. L. Jones, S. Geilert, M. A. Brzezinski*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

The distribution of dissolved silicon isotopes (δ30Si) was examined along the U.S. GEOTRACES East Pacific Zonal Transect (GP16) extending from Peru to Tahiti (10°S and 15°S latitude). Surface waters in the subtropical gyre displayed high δ30Si due to strong utilization of silicic acid (DSi). In contrast, surface waters close to the Peruvian coast where upwelling prevailed were less depleted and only moderately fractionated. δ30Si of water masses along the transect was compared with the results of an Optimum Multiparameter Analysis that quantified the fractional contributions of end-member water masses in each sample. Strong admixture of intermediate waters obscured the expected heavy isotopic signatures of Subantarctic Mode Water and Antarctic Intermediate Water. Isotope values were nearly homogenous below 2,000 m (average: +1.3 ± 0.1‰, 1 s.d.) despite the 25 μmol kg−1 range in the DSi content among water masses. This homogeneity confirms prior observations and model results that predict nearly constant δ30Si values of +1.0‰ to +1.2‰ for Pacific deep waters with [DSi] > 100 μmol kg−1. Waters above the East Pacific Rise (EPR) influenced by hydrothermal activity showed a small increase in [DSi] together with dissolved iron, but overall stations close to the EPR were slightly depleted in [DSi] (3 to 6 μmol kg−1) with no significant shift in δ30Si compared to adjacent waters. Hydrothermal [DSi] appears to precipitate within the conduit of the EPR or upon contact with cold seawater resulting in a negligible influence of hydrothermal fluids on δ30Si in deep water.

Original languageEnglish
Article numbere2020GB006538
JournalGlobal Biogeochemical Cycles
Volume34
Issue number9
DOIs
Publication statusPublished - 1 Sept 2020
Externally publishedYes

Bibliographical note

Funding Information:
We greatly thank Captain Russ DeVaney and the crew of the Thomas G. Thompson, as well as the Chief Scientists Jim Moffett and Chris German, for a successful cruise. This work was made possible by funding from the National Science Foundation (NSF) OCE‐1233028 as well as funding from the funding by the Collaborative Research Centre 754 “Climate‐Biogeochemistry Interactions in the Tropical Ocean” (www.sfb754.de), supported by the Deutsche Forschungsgemeinschaft (DFG; SFB 754). R/V

Publisher Copyright:
©2020. The Authors.

Funding

We greatly thank Captain Russ DeVaney and the crew of the Thomas G. Thompson, as well as the Chief Scientists Jim Moffett and Chris German, for a successful cruise. This work was made possible by funding from the National Science Foundation (NSF) OCE‐1233028 as well as funding from the funding by the Collaborative Research Centre 754 “Climate‐Biogeochemistry Interactions in the Tropical Ocean” (www.sfb754.de), supported by the Deutsche Forschungsgemeinschaft (DFG; SFB 754). R/V

Keywords

  • East Pacific Rise
  • GEOTRACES
  • GP16
  • oxygen minimum zone
  • Pacific
  • silicon isotopes

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