Warm, equable mid-Cretaceous: Stable isotope evidence

Recent studies have proposed widely differing interpretations of mid-Cretaceous oceanic thermal gradients. These disparities result from the combination of stable isotope data from broad stratigraphic intervals characterized by variable paleotemperatures and from different methods used to estimate paleosalinity. We attempt to constrain paleotemperature gradients by focusing on a time slice in the late Albian Atlantic Ocean and by developing a proxy for paleosalinity based on the diversity of nannofossils and planktonic foraminifers. Oxygen isotope analyses of well-preserved planktonic and benthic foraminifers from Deep Sea Drilling Project (DSDP) Site 511 in the high-latitude South Atlantic and DSDP Site 392 in the subtropical North Atlantic are used in paleotemperature estimates. We estimate a mean sea surface temperatures range of 10-13.5°C for Site 511 and 23-29°C for Site 392. These estimates support the existence of warm, equable conditions in the mid-Cretaceous.