Facies control on carbonate δ¹³C on the Great Bahama Bank

The carbon isotopic (δ¹³C) composition of shallow-water carbonates often is interpreted to reflect the δ¹³C 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 δ¹³C from that of the global ocean. We present new δ¹³C 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 δ¹³C variability rivaling that of the past two billion years of Earth history. Leveraging Walther’s Law, we illustrate how these local δ¹³C signals can find their way into the stratigraphic record of bulk carbonate.