Antarctic Glacial History

As is discussed in Chapter 7, the East Antarctic plate formed a significant component of the Gondwanaland super-continent during the Jurassic. Since 180 Ma, this continent broke up into what are recognised today as distinct continental landmasses with the repositioning of Antarctica at southern polar latitudes in the Early Cretaceous (ca. 120 Ma). In spite of its polar position, Antarctica is thought to have remained mostly ice-free, vegetated, and with mean annual temperatures above freezing until the latter half of the Cenozoic (around 34 million years ago, Fig. 1.1), whereupon the continent became subject to repeated phases of glaciation at a variety of temporal and spatial scales.

The southern continent and its surrounding ocean basins have been the target of numerous scientific expeditions and several scientific drilling project efforts that have led to significant advances in understanding of Cenozoic climate evolution, oceanography, and biota of the Antarctic continent and the Southern Ocean. The deep-ocean records document clearly the long-term cooling of climates over the past 50 million years and large-scale variability in the last 3-5 million years. They also show events that are either abrupt or brief (e.g. the Paleocene warming event with a duration of less than 1 million years; the Middle-Eocene Climatic Optimum, MECO at ca. 41 Ma), or are marked by a distinct shift in the rate at which long-term changes occur (i.e. middle-Miocene increased cooling trend). The explanation for these events include changes in atmospheric gas concentrations (e.g. carbon dioxide and methane), opening of gateways with enhanced ocean circulation, peaks in orbital forcing resulting from Croll-Milankovitch cyclicities, interactions with northern hemisphere glaciations and others. Scientific drilling on the Antarctic continental shelf and upper slope, to examine the direct record of glaciation, has been sparse and has had significant problems with recovery (<20% in diamict) using current Integrated Ocean Drilling Programme (IODP) techniques. Consequently, the linkages between Antarctic continental shelf and deep-ocean basin records are not well established and the basic problem of ice-sheet history remains unsolved. Proxy measurements (particularly oxygen isotopes) provide general details, but initiation, growth and extent of the ice sheets still are debated.

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