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

We present pore fluid geochemistry, including major ion and trace metal concentrations the isotopic composition of calcium sulfate, from uppermost meter sediments Gulf Aqaba (Northeast Red Sea) Iberian Margin (North Atlantic Ocean). In both locations, we observe strong correlations among calcium, magnesium, strontium, sulfate as well sulfur alkalinity, suggestive active changes in redox state pH that should lead to carbonate mineral precipitation dissolution. The isotope (δ 44 Ca) is, however, relatively invariant our measured profiles, suggesting is not occurring within boundary layer at these sites. explore several reasons why δ Ca might be changing studied despite other ions their composition, mixing between surface deep minerals below layer, possibility iron manganese cycling inhibits precipitation, may slow enough preclude fractionation during precipitation. Our results suggest dissolution particularly diffusive elicit a more complex response than previously thought.