Differences in regional responses to climate fluctuations are well documented on short time scales (e.g., El Nino-Southern Oscillation), but with the exception of latitudinal temperature gradients, regional patterns are seldom considered in discussions of ancient greenhouse climates. Contrary to the expectation of global warming or global cooling implicit in most treatments of climate evolution over millions of years, this paper shows that the North Atlantic warmed by as much as 6 °C (1.5%c decrease in 8ls O values of planktic foraminifera) during the Maastrichtian global cooling interval. We suggest that warming was the result of the importation of heat from the South Atlantic. Decreasing North Atlantic 8ls O values are also associated with increasing gradients in planktic 8 13 C values, suggesting increasing surface-water stratification and a correlated strengthening of the North Atlantic Polar Front. If correct, this conclusion predicts arctic cooling during the late Maastrichtian. Beyond implications for the Maastrichtian, these data demonstrate that climate does not behave as if there is a simple global thermostat, even on geologic time scales.

[1] Analysis of 944 single specimens of three species of late Maastrichtian planktonic foraminifera (Racemiguembelina fructicosa, Contusotruncana contusa, and Rugoglobigerina rugosa) from 38 samples spanning the last 3 Myr of the Cretaceous shows consistent isotopic trends through time, consistent isotopic differences among taxa, and high within-sample isotopic variability throughout. Within-sample variability does not change systematically through time for any taxon, but average d 18 O values decrease by $1.5%, and average d 13 C values diverge up section. Comparing taxa, average d 18 O values are similar within most samples, but average d 13 C values generally decrease from R. fructicosa to R. rugosa to C. contusa. In addition, the withinsample variability of individual d 13 C measurements is larger for R. fructicosa than for either C. contusa or R. rugosa, an observation which is consistent with a photosymbiotic habitat for R. fructicosa. In terms of Maastrichtian paleoceanography the negative d 18 O trend of $1.5% corresponds to a temperature increase of $6°C, and the divergence of d 13 C values up section suggests an increasingly stratified water column in the western Atlantic through the late Maastrichtian. We suggest that these trends are best explained by increasing import of South Atlantic waters into the North Atlantic and an intensification of the Northern Hemisphere polar front.

No abstract

No abstract

No abstract