Beschreibung: The Eocene-Oligocene transition (EOT) marked the initiation of large-scale Antarctic glaciation. This fundamental change in Cenozoic climate state is recorded in deep-sea sediments by a rapid benthic foraminiferal δ18O increase and appearance of ice-rafted debris in the Southern Ocean. However, we know little about the magnitude of cooling associated with the EOT in shallow water environments, particularly at mid- to high-latitudes. Here we present new paleomagnetic and stratigraphic records of the C13r/C13n magnetochron boundary and the EOT in the clay-rich Blanche Point Formation (BPF), South Australia. The BPF was deposited in a shallow shelf setting (water depths of 〈100 m) at a paleolatitude of ~51 °S. We present high-resolution δ18O, δ13C, and Mg/Ca records of environmental change from well-preserved benthic foraminifera of latest Eocene age at this site. A marked, negative δ13C excursion occurs immediately before a δ18O increase, which may be a globally representative signal. A ~2 °C cooling of shallow shelf seawater is evident from benthic foraminiferal Mg/Ca across EOT Step 1, the first step in the two-step benthic foraminiferal δ18O increase across the EOT. This cooling signal is both sufficient to account fully for the δ18O increase in our data and is of similar amplitude to that documented in published records for shallow shelf and the upper water column in open ocean settings, which suggests no obvious polar amplification of this cooling signal. Our results strengthen the evidence base for attributing EOT Step 1 to global cooling with little contribution from ice volume growth and contradict the mechanism suggested to explain the inferred northward migration of the intertropical convergence zone in the contemporaneous equatorial Pacific Ocean.

Beschreibung: Glassy Turonian foraminifera preserved in clay-rich sediments from the western tropical Atlantic yield the warmest equivalent d18O sea-surface temperatures (SSTs) yet reported for the entire Cretaceous-Cenozoic. We estimate Turonian SSTs that were at least as warm as (conservative mean ~30 °C) to significantly warmer (warm mean ~33 °C) than those in the region today. However, if independent evidence for high middle Cretaceous pCO2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea-surface pH, our conservative and warm SST estimates would be even higher (32 and 36°C, respectively). Our new tropical SSTs help reconcile geologic data with the predictions of general circulation models that incorporate high Cretaceous pCO2 and lend support to the hypothesis of a Cretaceous greenhouse. Our data also strengthen the case for a Turonian age for the Cretaceous thermal maximum and highlight a 20-40 m.y. mismatch between peak Cretaceous-Cenozoic global warmth and peak inferred tectonic CO2 production. We infer that this mismatch is either an artifact of a hidden Turonian pulse in global ocean-crust cycling or real evidence of the influence of some other factor on atmospheric CO2 and/or SSTs. A hidden pulse in crust cycling would explain the timing of peak Cretaceous-Cenozoic sea level (also Turonian), but other factors are needed to explain high-frequency (~10-100 k.y.) instability in middle Cretaceous SSTs reported elsewhere.

Beschreibung: The dataset compiles reconstructed changes in bottom water temperature and global ice volume from 0 to 17 Ma using δ18O in conjunction with Mg/Ca records of the infaunal benthic foraminifer, O. umbonatus from Ocean Drilling Program (ODP) Site 130-806 (equatorial Pacific; ~2500 m). This dataset covers the middle Miocene to present (17-0 Ma) and has an average temporal resolution of ~0.2 Ma. Application of the new equations to the Site 130-806 record leads to the suggestion that global ice volume was greater than today after the Middle Miocene Climate Transition (~14 Ma). ODP Site 130-806 bottom waters cooled and freshened as the Pacific zonal sea surface temperature gradient increased, and climate cooled through the Pliocene, prior to the Plio‐Pleistocene glaciation of the Northern Hemisphere.