A reinterpretation of mid-Cretaceous hallow marine temperatures through model-data comparison

Abstract. Mid-Cretaceous •5180 paleotemperatures are compared with temperatures predicted by an ocean general circulation model. The •5180 paleotemperatures, calculated assuming a •5,,. of-1.0%o (SMOW), are 5.6øC lower at low latitudes and 2.4øC higher at middle and high latitudes than the model-predicted, mixed-layer temperatures. The model-data comparison is improved after accounting for the spatial variability of •5,, and after considering the paleohabitats of the marine organisms from which •5180 values were measured. Paleotemperatures adjusted using the Broecker [1989] •5,.-S relationship and the model-predicted salinity are 3.4øC higher at low-latitude sites and 1.9øC lower at higher-latitude sites. Moreover, seven of nine low-latitude paleotemperatures intersect the model-predicted temperature within the upper 100 m of the water column, a depth consistent with the interpreted paleohabitat of the analyzed organisms. However, adjusted paleotemperatures for three of five Southern Hemisphere high-latitude locations are at least 9øC higher than the model-predicted temperatures for these locations. The model-data comparison suggests that mid-Cretaceous •5180 values are compatible with sea surface temperatures a high or higher than those simulated by an ocean general circulation model of the mid-Cretaceous with 4 x present-day atmospheric pCO2. 1