Jiggling the tropical thermostat in the Cretaceous hothouse.
Richard D. Norris et al. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543-1541, USA. Pages 299-302.
Computer simulations of modern climate have been used to suggest that Earth's surface temperature is set by a thermostat produced by feedback systems between incoming radiation from the sun, cloud formation, and radiated heat from Earth's surface. In theory, average tropical surface temperatures should not climb much above 30 C (86 F). Paleoclimate studies have previously shown that some subtropical locations on Earth regularly experienced sea surface temperatures of ~30 C or even a few degrees higher during warm periods in Earth history. These results raise the possibility that tropical temperatures (which should be warmer than the subtropics) exceeded the thermostat value predicted by climate models. The authors present the first solid evidence that Earth's thermostat was, as of 90 Ma, set ~5 C warmer than it is today. Their data come from analysis of exceptionally well preserved planktic foraminifera (a kind of marine microfossil) from a deep-sea drill site in the tropical Atlantic. The authors analysis of the light stable isotope geochemistry of the foraminifer shells suggest that tropical sea surface temperatures were ~35 C (95 F) during the Cenomanian-Turonian hothouse. The authors conclude that Earth's thermostat may not be so reliable after all.
Climatic conditions during marine oxygen isotope stage 6 in the eastern Mediterranean region from the isotopic composition of speleothems of Soreq Cave, Israel.
Contact: Ann Cairns
Geological Society of America