Early diagenesis of calcium carbonate in Long Island Sound sediments: Benthic fluxes of Ca<SUP>2+</SUP> and minor elements during seasonal periods of net dissolution

Abstract

The present study confirms the quantitative significance of carbonate dissolution for associated major and minor element solute fluxes in shelf deposits of temperate regions. Multiple measurement techniques all demonstrate that net dissolution of CaCO 3 dominates during winter in Long Island Sound sediments and results in large fluxes of Ca 2+ , Sr 2+ , and F - out of the seafloor. Ca 2+ fluxes averaged from 4 independent methods range from ∼5 to ∼13 mmol m -2 d -1 with highest flux occurring when surface deposits are most undersaturated with respect to common biogenic carbonates. A significant proportion of dissolution, 40-100%, results from oxidation of reduced metabolites such as FeS, NH + 4 , and Mn 2+ . Results suggest that 90% of the CaCO 3 precipitated each year is dissolved, equivalent to a loss of ∼90-190 g CaCO 3 m -2 yr -1 . Given the general similarity between Long Island Sound and other muddy coastal estuaries along the eastern coast of North America and elsewhere (e.g. Chesapeake Bay, Delaware Bay, Narragansett Bay, Buzzards Bay, Casco Bay), these relative flux measurements are likely to be indicative of much larger temperate regions.