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

• Main Authors: James, DH, Bradbury, HJ, Antler, G, Steiner, Z, Hutchings, AM, Sun, X, Saar, R, Greaves, M, Turchyn, AV
• Format: Article in Journal/Newspaper
• Language: English
• Published: Frontiers Media SA 2021
• Subjects: carbonate precipitation; calcium isotopes; early diagenesis; microbial sulfate reduction; microbial iron reduction; sedimentary boundary layer; carbonate dissolution; North Atlantic
• Online Access: https://dx.doi.org/10.17863/cam.74106; https://www.repository.cam.ac.uk/handle/1810/326657

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 (δ 44 Ca) 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 δ 44 Ca might not be changing in the studied profiles, despite changes in other major ions and their isotopic composition, including mixing between the ...