Were shallow carbonate geochemistry and production different during the last interglacial period?

Abstract

The facies, mineralogy, and isotope geochemistry of shallow water carbonates serve as proxies for paleoclimate parameters such as the global carbon cycle and relative sea level. To accurately reconstruct past climates from the rock record, we must understand how shallow carbonate geochemistry responds to both global carbon cycle perturbations and local environmental change. Shallow carbonate stratigraphies from the most recent Pleistocene glacial cycles present an opportunity to begin untangling signals for the d13C of global seawater DIC and local banktop processes. However, while shallow carbonates often are the only surviving archive of pre-Cenozoic climate, the geochemistry of Recent shallow carbonate stratigraphies largely was overprinted by karst and meteoric diagenesis during the last glacial sea level lowstand. To understand how shallow carbonate geochemistry has changed during the Pleistocene, we instead must look to the periplatformal slope and proximal basins. These deep environments serve as a refuge for carbonate produced on the shelf, and contain a record of shallow carbonate geochemistry that persists across ice ages. We study 21 short piston cores from around Bahamian platforms to explore differences in banktop production and geochemistry between the Holocene interglacial and the last interglacial (LIG) periods. We find that LIG surface conditions produced banktop carbonate with elevated mean d18O compared to the Holocene, and that higher LIG sea level likely increased export of banktop carbonate to the periplatform. We show that in spite of differences in sea level and local surface conditions, the d13C of banktop carbonate remained constant between the LIG and the Holocene.