Extreme polar warmth during the Cretaceous greenhouse? Paradox of the late Turonian δ18O record at Deep Sea Drilling Project Site 511

• Main Authors: Karen L. Bice, Brian T. Huber, Richard D. Norris
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2003
• Subjects: Ross Island; James Ross Island; Planktonic foraminifera
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.513.9006; http://www.whoi.edu/science/GG/people/kbice/Bice_etal_2003.pdf

belemnite standard; PDB) coincident with the warmest tropical temperature estimates yet obtained for the open ocean. The lowest planktonic foraminifer d18O values suggest that the upper ocean was as warm as 30–32C. This is an extraordinary temperature for 60S latitude but is consistent with temperatures estimated from apparently coeval mollusc d18O from nearby James Ross Island (65S paleolatitude). Glassy textural preservation, a well-defined depth distribution in Site 511 planktonics, low sediment burial temperature (32C), and lack of evidence of highly depleted pore waters argue against diagenesis (even solid state diffusion) as the cause of the very depleted planktonic values. The lack of change in benthic foraminifer d18O suggests brackish water capping as the mechanism for the low planktonic d18O values. However, mixing ratio calculations show that the amount of freshwater required to produce a 2 % shift in ambient water would drive a 7 psu decrease in salinity. The abundance and diversity of planktonic foraminifera and nannofossils, high planktonic:benthic ratios, and the appearance of keeled foraminifera argue against lower-than-normal marine salinities. Isotope calculations and climate models indicate that we cannot call upon more depleted freshwater d18O to explain this record. Without more late Turonian data, especially from outside the South Atlantic basin, we can currently only speculate on