University of Massachusetts, United States

The Cenomanian/Turonian boundary interval (CTBI) at ODP Site 1050 (30 degrees 6'N, 76 degrees 14'W) yields an unusually well-preserved oxygen and carbon isotope profile for sediments of this age. Our study reveals that extinction of the deep-dwelling planktic foraminifer genus Rotalipora and Globigerinelloides bentonensis occurs at a level where middle bathyal waters increased from 15 to 19 degrees C, which is warmer than any other time during the Cretaceous and Cenozoic. The intermediate water warming may have caused a breakdown in the vertical structure of the water column, and could explain the extinction of the deeper dwelling planktic taxa. This warming event has also been identified from oxygen isotopic records of deep-sea planktic foraminifera in the southern high latitudes and is consistent with paleontological evidence for extreme warmth in the Arctic. On the other hand, sea surface temperature estimates based on planktic foraminiferal d18O values from Site 1050 (corrected for the modern day salinity gradient) remain steady throughout the CTBI, varying between 23 to 26 degrees C, which is within the range of subtropical SSTs today. Co-occurrence at Site 1050 of volcaniclastic sediments with the warmest benthic foraminiferal paleotemperatures supports previous speculation that there was a substantial increase in global volcanism and atmospheric pCO2 outgassing across the CTBI. If increased pCO2 was the primary mechanism driving the middle Cretaceous supergreenhouse then we must explain how heat was transported from the tropics to the poles with enough efficiency to maintain a latitudinal thermal gradient profile that was nearly flat.