Climate of the Late Cretaceous North American Gulf and Atlantic Coasts

Understanding the response of temperature to elevated atmospheric CO2 during past greenhouse intervals such as the Late Cretaceous can constrain hypotheses of expected future warming tied to the rise of modern atmospheric CO2 levels. Here we present new reconstructions of Gulf and Atlantic Coast coastal marine temperatures through the late Campanian (∼76-72 Ma) and Maastrichtian (72 Ma-66 Ma), as determined by carbonate clumped isotope analysis of marine bivalves and gastropods. We find temperatures in the range of ∼7-25 °C across multiple sites located between 31°N and 36°N paleolatitude, and cooler temperatures of ∼3-14 °C at sites around 39°N paleolatitude. Temperatures agree across a variety of taxa, indicating no appreciable organism-specific vital effects. The calculated paleotemperatures are very similar to modern marine temperatures at the same locations, despite the Late Cretaceous generally being considered a warmer interval. Clumped isotope temperatures are cooler than published temperatures from a nearby site measured using the TEX86 paleotemperature proxy, revealing a potential warm bias in TEX86 temperature estimates. The best agreement between clumped isotope and TEX86 temperatures is achieved when using the TEX86L calibration over TEX86H or BAYSPAR calibrations.