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

Frontiers in Earth Science

Xiaole Sun¹  Harold J. Bradbury²  Alexandra V. Turchyn²  Daniel H. James²  Alec M. Hutchings²  Mervyn Greaves²  Zvi Steiner⁴  Raoul Saar⁵  Gilad Antler⁵ 

[1] Baltic Sea Center, Stockholm University, Stockholm, Sweden;Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom;Department of Earth and Environmental Sciences, Ben-Gurion University of the Negev, Beersheba, Israel;GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany;The Interuniversity Institute for Marine Sciences, Eilat, Israel;

关键词: carbonate precipitation;    calcium isotopes;    early diagenesis;    microbial sulfate reduction;    microbial iron reduction;    sedimentary boundary layer;   

DOI  :  10.3389/feart.2021.601194

来源: DOAJ

【 摘 要 】

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.

【 授权许可】

Unknown