How do shallow carbonates record sea level and seawater chemistry?

Abstract

Much of our understanding of Earth history comes from shallow-water carbonates because deep-ocean archives tend to get metamorphosed or subducted. However, little work has been done to calibrate how ocean chemistry and early marine diagenesis are recorded in modern shallow carbonates. As a result, interpretations of climate from ancient stratigraphy have large and unquantified uncertainties. We use a combination of satellite remote sensing and field geology to explore the relationship between water depth and facies. In the context of these new bathymetric and facies maps, we present 6,000 new measurements of the carbon isotopic composition of benthic forams, solitary corals, calcifying green algae, ooids, coated grains, and lime mud from the modern Bahamas. We integrate these carbonate d13C measurements with water depth, facies, trace element, and seawater geochemistry data in order to isolate and quantify the levers driving d13C of banktop carbonate away from contemporaneous open-ocean values.