Cenozoic and Late Mesozoic paleoceanographic and paleoglacial history recorded in circum-Antarctic deep-sea sediments

Abstract Sedimentological and isotopic studies of cores collected by the DV “Glomar Challenger” and the USNS “Eltanin” from the circum-Antarctic region have revealed a chronology of paleoceanographic changes in the Southern Ocean and the paleoglacial history of Antarctica for the past 80 m.y. Oxygen and carbon isotopic compositions of planktonic and benthonic foraminifera and calcareous nannofossils contained in deep-sea sediment cores record paleoceanographic changes in oceanic surface and bottom waters. These data can be interpreted in terms of paleotemperatures, growth of the polar ice-caps and changes in oceanic circulation. Composite high- and low-latitude time-series plots of both oxygen and carbon isotopic data obtained from Cenozoic and Late Mesozoic calcareous micro- and nannofossils are considered in the light of existing knowledge of Antarctic glacial chronology. A slight decline in both surface- and bottom-water temperatures is recorded during the Middle to Late Maastrichtian, at the end of the Cretaceous. Circum-Antarctic oceanic surface-water isotopic temperatures recorded by calcareous nannofossils are similar to bottom-water values recorded by deep-sea benthonic foraminifera elsewhere in the world's oceans, indicating that a thermohaline circulation system driven by sinking of dense water in high latitudes was active throughout the Late Cretaceous. Temperatures during the Paleocene and Early Eocene were warmer than those during the Late Cretaceous minimum. A long-term Cenozoic cooling began during middle Early Eocene time. It was marked by periods of more stable temperatures followed by times of rapid temperature decrease. The late Middle Eocene—Late Eocene was a time of stable temperatures. A significant 5°C decrease in bottom- and surface-water temperatures occurred near the Eocene/Oligocene boundary, marking the production of Antarctic bottom waters at near-freezing temperatures from this time onward (Kennett and Shackleton, 1976). This drop was followed by a moderate Early Miocene—Early mid-Miocene warming and then a period of stable temperatures, until the Middle Miocene at which time a worldwide increase in δ 18O of both planktonic and benthonic carbonate tests occurred. This has been interpreted as either an indication of a major build-up in the Antarctic ice-sheet, or a combination of temperature drop and ice-volume increase. Small quantities of ice-rafted sediment in the circum-Antarctic region are first recorded in Early Eocene—Oligocene sediment cores from the southeastern Pacific sector of the Southern Ocean. The southeastern Indian Ocean sector north of Wilkes Land and the Ross Sea contains evidence of possible ice-rafting during the Early Oligocene, and more definitive evidence of ice-rafting during the Late Oligocene. Early Miocene deep-sea sediments also contain small amounts of ice-rafted debris. There is strong evidence for a significant intensification of ice-rafting during Middle Miocene time, confirming that the increase in O18 in carbonates at that time must in part be related to build-up of the Antarctic ice-sheet.