Abstract

An Ocean General Circulation Model (OGCM), forced by a simulation of Campanian (80 Ma) climate using the Global ENvironmental and Ecological Simulation of Interactive Systems (GENESIS) Global Climate Model, was compared to proxies for ocean temperature found in the Late Cretaceous geologic record... Show moreAn Ocean General Circulation Model (OGCM), forced by a simulation of Campanian (80 Ma) climate using the Global ENvironmental and Ecological Simulation of Interactive Systems (GENESIS) Global Climate Model, was compared to proxies for ocean temperature found in the Late Cretaceous geologic record. Forty oxygen isotope values were compiled from previously published sources. The isotopic values, derived from the CaC0₃ shells of fossil foraminifera and mollusks in sediment cores, were related to temperature using the equation of Erez and Luz. The temperature estimates from both planktonic (surface dwelling) and benthonic (bottom dwelling) organisms were compared to the OGCM simulation by superimposing the proxy temperature estimates on the OGCM results. The model-data comparison suggests the proxy data derived from planktonic marine organisms may not represent the surface (skin) temperature of the ocean as is often assumed. Even a small range in the depth habitat of planktonic species within the photic zone of the surface mixed layer can bias surface temperature estimates toward colder values. This is especially true in tropical latitudes, where equatorial upwelling brings cold deep water near the surface. Model-data inconsistencies at mid-latitudes are greatest in regions where absolute values of evaporation minus precipitation are the largest, suggesting the vigorous Late Cretaceous hydrologic cycle influences the regional isotopic composition of the ocean surface waters, biasing interpretations of temperature derived from the isotopic composition of planktonic marine organisms. Depth habitat and the latitudinal dependence of the isotopic composition of seawater must be taken into account in any meaningful model-data comparison of sea surface temperature in the geologic past. Show less