Paleotemperature History of the Cenozoic and the Initiation of Antarctic Glaciation: Oxygen and Carbon Isotope Analyses in DSDP Sites 277, 279 and 281

Abstract

An oxygen and carbon isotopic history based on analyses of benthonic and planktonic foraminifera in three overlapping subantarctic sections is presented for the last 55 m.y. with a sampling interval ofless than 1 m.y. Surface temperature at Site 277, on the Campbell Plateau, was about 19°C in the early Eocene, about 13°C in the middle Eocene, about 11°C in the late Eocene, and about 7°C in the Oligocene. Declines in temperature appear to have been rather rapid and are separated by episodes of relative temperature stability. Bottom temperature at Site 277 was about 1°C below surface temperature in the Paleocene and about 2°C below surface temperature in the Oligocene.Site 279, on the Macquarie Ridge, records an early Miocene warming of over 2°C followed by a cooling and a second similar temperature rise in the middle Miocene. Bottom temperature at this somewhat deeper site was about 3°C below surface temperature and was probably as low as 4°C during part of the early Miocene. Comparisons between Sites 277 and 279 suggest that from the early Oligocene temperatures of deep water were low like the present day, implying that the mean annual temperature in high southern latitudes was near freezing by the beginning of the Oligocene (but certainly no earlier). From this time glaciers would have descended to sea level, and there would have been sea-ice production. If an ice sheet were present, it could not have been more than a small fraction of its present-day size.Site 281, on the South Tasman Rise, extends the record into the middle and late Miocene during which time the major East Antarctic ice sheet accumulated. A significant rise in surface temperature during the late Miocene did not cause the melting of this ice sheet, demonstrating that by this time it had already achieved its present invulnerability to climatic change. Since temperatures during much of the Miocene were significantly above any Pleistocene values, it is extremely unlikely that any climatic change in the geologically near future will significantly affect the stability of the East Antarctic ice sheet.

Structure of the integument of southern right whales, Eubalaena australis

“…The establishment of the CAC meant that, from mid-Oligocene times onward, areas such as the Campbell Plateau (which border the Sub-Antarctic region) were affected by these climatic changes. Shackleton and Kennett (1975) stated that temperatures on the Campbell Plateau dropped from 198C in the Early Eocene to 118C in the Late Eocene and to 78C in the Oligocene. The Balaenidae are thought to be the oldest of the modern mysticete fami- lies, evident in the fossil record during the Mid-Oligocene (Fordyce, 1980).…”

Late Eocene to middle Miocene (33 to 13 million years ago) vegetation and climate development on the North American Atlantic Coastal Plain (IODP Expedition 313, Site M0027)

“…Lycopodium spore tablets were added in order to calculate pollen concentrations (Stockmarr, 1971). Palynomorphs were identified at 400×/500×/1000× magnification using a Zeiss Axio Scope.…”

Warm ocean processes and carbon cycling in the Eocene

“…the presence of cold-blooded animals and frost-intolerant plant species at high latitudes [7][8][9]) and analysis of leaf morphology [10]. The oxygen stable isotope ratio (δ 18 O) of deep-sea benthic foraminifera [11][12][13][14] shows that bottom waters probably exceeded 10-12 • C in the Early Eocene, cooling to 5 • C by the end of the epoch [13,14]. This trend was interrupted by intervals of relative stability or transient warming events, such as at the Middle Eocene Climatic Optimum [15,16].…”