Deep-sea drilling in the Antarctic region (Deep-Sea Drilling Project legs 28, 29, 35, and 36) has provided many new data about the development of circum-Antarctic circulation and the closely related glacial evolution of Antarctica. The Antarctic continent has been in a high-latitude position since the middle to late Mesozoic. Glaciation commenced much later, in the middle Tertiary, demonstrating that near-polar position is not sufficient for glacial development. Instead, continental glaciation developed as the present-day Southern Ocean circulation system became established when obstructing land masses moved aside. During the Paleocene (t = ∼65 to 55 m.y. ago), Australia and Antarctica were joined. In the early Eocene (t = ∼55 m.y. ago), Australia began to drift northward from Antarctica, forming an ocean, although circum-Antarctic flow was blocked by the continental South Tasman Rise and Tasmania. During the Eocene (t = 55 to 38 m.y. ago) the Southern Ocean was relatively warm and the continent largely nonglaciated. Cool temperate vegetation existed in some regions. By the late Eocene (t = ∼39 m.y. ago) a shallow water connection had developed between the southern Indian and Pacific oceans over the South Tasman Rise. The first major climatic-glacial threshold was crossed 38 m.y. ago near the Eocene-Oligocene boundary, when substantial Antarctic sea ice began to form. This resulted in a rapid temperature drop in bottom waters of about 5°C and a major crisis in deep-sea faunas. Thermohaline oceanic circulation was initiated at this time much like that of the present day. The resulting change in climatic regime increased bottom water activity over wide areas of the deep ocean basins, creating much sediment erosion, especially in western parts of oceans. A major (∼2000 m) and apparently rapid deepening also occurred in the calcium carbonate compensation depth (CCD). This climatic threshold was crossed as a result of the gradual isolation of Antarctica from Australia and perhaps the opening of the Drake Passage. During the Oligocene (t = 38 to 22 m.y. ago), widespread glaciation probably occurred throughout Antarctica, although no ice cap existed. By the middle to late Oligocene (t = ∼30 to 25 m.y. ago), deep-seated circum-Antarctic flow had developed south of the South Tasman Rise, as this had separated sufficiently from Victoria Land, Antarctica. Major reorganization resulted in southern hemisphere deep-sea sediment distribution patterns. The next principal climatic threshold was crossed during the middle Miocene (t = 14 to 11 m.y. ago) when the Antarctic ice cap formed. This occurred at about the time of closure of the Australian-Indonesian deep-sea passage. During the early Miocene, calcareous biogenic sediments began to be displaced northward by siliceous biogenic sediments with higher rates of sedimentation reflecting the beginning of circulation related to the development of the Antarctic Convergence. Since the middle Miocene the East Antarctic ice cap has remained a semipermanent feature exhibiting some changes in volume. The most important of these occurred during the latest Miocene (t = ∼5 m.y. ago) when ice volumes increased beyond those of the present day. This event was related to global climatic cooling, a rapid northward movement of about 300 km of the Antarctic Convergence, and a eustatic sea level drop that may have been partly responsible for the isolation of the Mediterranean basin. Northern hemisphere ice sheet development began about 2.5–3 m.y. ago, representing the next major global climatic threshold, and was followed by the well-known major oscillations in northern ice sheets. In the Southern Ocean the Quaternary marks a peak in activity of oceanic circulation as reflected by widespread deep-sea erosion, very high biogenic productivity at the Antarctic Convergence and resulting high rates of biogenic sedimentation, and maximum northward distribution of ice-rafted debris.

Cenozoic evolution of Antarctic glaciation the Circum-Antarctic Ocean and their impact on global paleoceanography

Phanerozoic Paleotemperatures: The Earth’s Changing Climate during the Last 540 million years

Twenty-five years have elapsed since Moreau (1952) completed his outstanding essay, ‘Africa since the Mesozoic: with particular reference to certain biological problems’. This valuable synthesis resulted from his interest in a major problem raised by the avifaunas. They reveal great differences between the four principal habitats of the continent: the arid regions, savanna, lowland evergreen forest, and montane evergreen forest. Since two or more of these ecosystems regularly are contiguous over wide areas, the coexistence of distinct avifaunas in them for a long period of time requires explanation, as does the existence of the different vegetation zones themselves.

Late Cretaceous and Tertiary vegetation history of Africa

The warmest global temperatures of the past 85 million years occurred during a prolonged greenhouse episode known as the Early Eocene Climatic Optimum (52–50 Ma). The Early Eocene Climatic Optimum terminated with a long-term cooling trend that culminated in continental-scale glaciation of Antarctica from 34 Ma onward. Whereas early studies attributed the Eocene transition from greenhouse to icehouse climates to the tectonic opening of Southern Ocean gateways, more recent investigations invoked a dominant role of declining atmospheric greenhouse gas concentrations (e.g., CO2). However, the scarcity of field data has prevented empirical evaluation of these hypotheses. We present marine microfossil and organic geochemical records spanning the early-to-middle Eocene transition from the Wilkes Land Margin, East Antarctica. Dinoflagellate biogeography and sea surface temperature paleothermometry reveal that the earliest throughflow of a westbound Antarctic Counter Current began ∼49–50 Ma through a southern opening of the Tasmanian Gateway. This early opening occurs in conjunction with the simultaneous onset of regional surface water and continental cooling (2–4 °C), evidenced by biomarker- and pollen-based paleothermometry. We interpret that the westbound flowing current flow across the Tasmanian Gateway resulted in cooling of Antarctic surface waters and coasts, which was conveyed to global intermediate waters through invigorated deep convection in southern high latitudes. Although atmospheric CO2 forcing alone would provide a more uniform middle Eocene cooling, the opening of the Tasmanian Gateway better explains Southern Ocean surface water and global deep ocean cooling in the apparent absence of (sub-) equatorial cooling.

https://www.pnas.org/content/pnas/110/24/9645.full.pdf

Eocene cooling linked to early flow across the Tasmanian Gateway

/pdf/origin-signature-and-palaeoclimatic-influence-of-the-59t47dnl5d.pdf

Origin, signature and palaeoclimatic influence of the Antarctic Circumpolar Current

Deep-sea drilling in the Southern Ocean south of Australia and New Zealand shows that the Circum-Antarctic Current developed about 30 million years ago in the middle to late Oligocene when final separation occurred between Antarctica and the continental South Tasman Rise. Australia had commenced drifting northward from Antarctica 20 million years before this.

https://science.sciencemag.org/content/sci/186/4159/144.full.pdf

Development of the circum-antarctic current.

/pdf/introduction-and-explanatory-notes-13mctef1be.pdf

Introduction and Explanatory Notes

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Development of the circum-antarctic current.

Introduction and Explanatory Notes