Assessing Sedimentary Boundary Layer Calcium Carbonate Precipitation and Dissolution Using the Calcium Isotopic Composition of Pore Fluids

Daniel H. James, Harold J. Bradbury, Gilad Antler, Zvi Steiner, Alec M. Hutchings, Xiaole Sun, Raoul Saar, Mervyn Greaves, Alexandra V. Turchyn

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

We present pore fluid geochemistry, including major ion and trace metal concentrations and the isotopic composition of pore fluid calcium and sulfate, from the uppermost meter of sediments from the Gulf of Aqaba (Northeast Red Sea) and the Iberian Margin (North Atlantic Ocean). In both the locations, we observe strong correlations among calcium, magnesium, strontium, and sulfate concentrations as well as the sulfur isotopic composition of sulfate and alkalinity, suggestive of active changes in the redox state and pH that should lead to carbonate mineral precipitation and dissolution. The calcium isotope composition of pore fluid calcium (δ44Ca) is, however, relatively invariant in our measured profiles, suggesting that carbonate mineral precipitation is not occurring within the boundary layer at these sites. We explore several reasons why the pore fluid δ44Ca might not be changing in the studied profiles, despite changes in other major ions and their isotopic composition, including mixing between the surface and deep precipitation of carbonate minerals below the boundary layer, the possibility that active iron and manganese cycling inhibits carbonate mineral precipitation, and that mineral precipitation may be slow enough to preclude calcium isotope fractionation during carbonate mineral precipitation. Our results suggest that active carbonate dissolution and precipitation, particularly in the diffusive boundary layer, may elicit a more complex response in the pore fluid δ44Ca than previously thought.

Original languageEnglish
Article number601194
JournalFrontiers in Earth Science
Volume9
DOIs
StatePublished - 5 Aug 2021

Keywords

  • calcium isotopes
  • carbonate dissolution
  • carbonate precipitation
  • early diagenesis
  • microbial iron reduction
  • microbial sulfate reduction
  • sedimentary boundary layer

ASJC Scopus subject areas

  • Earth and Planetary Sciences (all)

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