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

Mid-Cretaceous delta(18)O paleotemperatures are compared with temperatures predicted by an ocean general circulation model. The delta(18)O paleotemper atures, calculated assuming a delta(w) of -1.0 parts per thousand (SMOW), a re 5.6 degrees C lower at low latitudes and 2.4 degrees C higher at middle and high latitudes than the model-predicted, mixed-layer temperatures. The model-data comparison is improved after accounting for the spatial variabil ity of delta(w) and after considering the paleohabitats of the marine organ isms from which delta(18)O values were measured. Paleotemperatures adjusted using the Broecker [1989] delta(w)-S relationship and the model-predicted salinity are 3.4 degrees C higher at low-latitude sites and 1.9 degrees C l ower at higher-latitude sites. Moreover, seven of nine low-latitude paleote mperatures intersect the model-predicted temperature within the upper 100 m of the water column, a depth consistent with the interpreted paleohabitats of the analyzed organisms. However, adjusted paleotemperatures for three o f five Southern Hemisphere high-latitude locations are at least 9 degrees C higher than the model-predicted temperatures for these locations. The mode l-data comparison suggests that mid-Cretaceous delta(18)O values are compat ible with sea surface temperatures as high or higher than those simulated b y an ocean general circulation model of the mid-Cretaceous with 4 x present -day atmospheric pCO(2).