Facies control on carbonate δC on the Great Bahama Bank

The carbon isotopic (δC) composition of shallow-water carbonates often is interpreted to reflect the δC of the global ocean and is used as a proxy for changes in the global carbon cycle. However, local platform processes, in addition to meteoric and marine diagenesis, may decouple carbonate δC from that of the global ocean. We present new δC measurements of benthic foraminifera, solitary corals, calcifying green algae, ooids, coated grains, and lime mud from the modern Great Bahama Bank. We find that vital effects, cross-shelf seawater chemistry gradients, and meteoric diagenesis produce carbonate with δC variability rivaling that of the past two billion years of Earth history. Leveraging Walther’s Law, we illustrate how these local δC signals can find their way into the stratigraphic record of bulk carbonate.