Introduction

Two major scientific breakthroughs occurred in the late twentieth century that revolutionised our understanding of Earth's Quaternary climate system and provided new insight into its pattern of behaviour at both orbital and suborbital time scales.

(1) In the mid-1970s, the first oxygen isotope records, developed from deep-ocean sedimentary archives (e.g. Shackleton and Opdyke, 1976), demonstrated that numerous glaciations of the Northern Hemisphere (NH) continents, and associated fluctuations in global sea level, had occurred in response to variations in Earth's orbital geometry (Hays et al., 1976). Canonical Milankovitch theory (Milankovitch, 1941) had predicted that long-term variations in NH summer insolation influenced by precession (20 kyr cycle) and obliquity (40 kyr cycle) controlled the variability of the NH ice sheets. Subsequent studies indicated that these orbital influences produced globally synchronous responses in: (i) atmospheric circulation (e.g. Petit et al., 1999), (ii) ocean circulation (e.g. Rahmstorf, 2002),

(iii) terrestrial climate (e.g. Leroy and Dupont, 1994; Ding et al., 2002), (iv) sea level (e.g. Chappell and Shackleton, 1986; Naish et al., 1998) and

(iv) Antarctic ice volume (e.g. Denton et al., 1986).

(2) In the late 1980s and early 1990s, the first deep ice core records from Greenland identified a pervasive ~ 1,500 yr long climate cycle manifested as a series of warm phases termed Dansgaard-Oeschger (D-O) interstadials that punctuated the otherwise cold conditions of the glacials (Dansgaard et al., 1993; Hammer et al., 1997). These D-O climate oscillations were also identified in ocean temperature and ice-rafted debris records from NH high-latitude marine sediment cores (e.g. Bond et al., 1997), and indicated a major reorganisation of the NH climate involving switching of the ocean-atmospheric system between two principal modes, warm and cold (e.g. Broecker et al., 1990), over decades to just a few years (Severinghaus et al., 1998).

Millennial-scale climate variability has been associated with far-reaching, but not necessarily globally synchronous influences. These include: (i) abrupt changes in meridional oceanic overturning (e.g. Broecker, 2000; Van Kreveld et al., 2000; Weaver et al, 2003), fluctuating NH ice volumes (Alley & MacAyeal, 1994) associated with metre-scale changes in sea level (Chappell et al., 1996), atmospheric circulation as recorded by Antarctic ice cores (Blunier et al., 1998; EPICA Community Members, 2006) and the response of Southern Hemisphere (SH) glaciers (e.g. Denton and Hendy, 1994).

This burgeoning Quaternary climate dataset, developed largely from NH records, highlighted the dearth of information from Antarctica and the Southern Ocean. A number of important hypotheses and questions began to form concerning the role of Antarctic Ice Sheets and sea ice on ocean circulation and sea level in the Late Pliocene-Pleistocene bipolar glacial world. These included:

1. What is the fundamental response of the Antarctic Ice Sheets to orbital variations?

2. What is the influence of local insolation forcing, and what is the precise phase relationship between NH and SH climatic processes?

3. Did the dramatic millennial-scale, D-O climate cycles of the NH manifest themselves in the SH?

4. If 3 were true, what was the amplitude of the response, and was the SH in-phase or out-of-phase with the D-O cycles? The short duration of these cycles and the inherent uncertainties with age models of the climate proxy records (marine and ice core) being compared is problematic.

5. To what extent did Antarctic ice volume variability at both orbital and suborbital scale modulate or even drive global climate? This question is especially relevant in terms of its influence on seasonal sea-ice distribution, the production of deep water and thermohaline circulation.

6. What has been the contribution of Antarctic ice to global ice volume and sea-level fluctuations through the Quaternary?

7. How have the Antarctic Ice Sheets contributed, and evolved, through major Late Neogene climate thresholds such as: (i) the global cooling ~3.0-2.5 myr associated with the initiation of NH glaciation, and (ii) the onset of the 100 ka climate cycle during the Mid-Pleistocene Transition (MPT).

Owing to Antarctica's remoteness, its extensive sea-ice apron and its extended ice sheet cover for the last 34 million years, such seemingly fundamental questions are only now being addressed, through the recovery of well-dated, deep marine sedimentary and ice core archives that span many glacial-interglacial (G-I) cycles. These records largely stem from three major international drilling initiatives: (1) the European Programme for Ice Coring in Antarctica (EPICA) and its predecessor project at Vostok station, (2) the Integrated Ocean Drilling Programme (IODP) and its predecessor Ocean Drilling Programme (ODP), and (3) continental margin drilling programmes from floating ice platforms such as the Dry Valleys Drilling Project (DVDP), Cenozoic Investigations in Ross Sea programme (CIROS), the Cape Roberts Project and the ANDRILL Program. In this chapter we summarise the present state of knowledge of Late Pliocene-Pleistocene Antarctic-Southern Ocean climate behaviour using data and interpretations from Antarctic ice cores (e.g. Vostok and EPICA), Southern Ocean sediment cores (ODP-IODP) and Antarctic continental margin geological drill cores (CIROS-2, Cape Roberts Project, ANDRILL). We also review the advances provided from numerical ice sheet and global climate models, with special emphasis on the potential of the new datasets to be integrated with a new generation of numerical models.

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