HOW DO CARBONATES RECORD SEAWATER CHEMISTRY? THE BAHAMAS AS A MODERN ANALOGUE FOR CLIMATE RECORDS PRESERVED IN ANCIENT SHALLOW-WATER CARBONATES

Much of our understanding of Earth history comes from shallow-water carbonates because deep ocean archives tend to get metamorphosed or subducted at plate margins. 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 and environmental change from ancient stratigraphy have large and unquantified uncertainties. Modern Bahamian surface sediments vary from 0 to +9 in δ¹³C and -8 to +1 in δ¹⁸O. If we include meteorically altered late Pleistocene sediments in the Bahamas, the δ¹³C range increases to -10 to +9 , the full range of the Neoproterozoic Era. We integrate over 3,000 new measurements of the carbon and oxygen isotopic composition of benthic forams, solitary corals, calcifying green algae, ooids, and lime mud from the modern Bahamas with a simple coupled physical-biogeochemical model to understand how water and sediment chemistry evolve as water moves from the open ocean to the increasingly restricted waters of the Great Bahama Bank. Our study of isotopic variability in the modern Bahamas will help to deconvolve the signals of global seawater, local platform water evolution, and early diagenesis in stratigraphic records of Earth history.