Introduction

The Antarctic Ice Sheet has existed for approximately 35 million years, but it has fluctuated considerably and has been one of the major driving forces for

Corresponding author. Tel.: +44(0)131 650 7543; Fax: +44(0)131 668 3184; E-mail: [email protected] (M.J. Siegert).

Quat.

Pleistocene

1.81 Ma

LU Z

Pliocene

z

5.33 Ma

Miocene

o

> QC

23.03 Ma

1-QC LU 1-

<

Oligocene

33.9 ± 0.1 Ma

Eocene

55.8 ± 0.2 Ma

Palaeocene

65.5 ± 0.3 Ma

Figure 1.1: Geological time periods during the Cenozoic era. Dates listed on the right hand side are taken from Gradstein et al. (2004).

changes in global sea level and climate throughout the Cenozoic (Fig. 1.1). The rates, size and frequencies of these fluctuations have been the subjects of considerable debate. Determination of the scale and rapidity of the response of large ice masses and associated sea ice to climatic forcing is of vital importance, because ice-volume variations lead to: (1) changing global sea levels on a scale of tens of metres or more, and (2) alteration to the capacity of ice sheets and sea ice as major heat sinks/insulators. It is thus important to assess the stability of the cryosphere under a warming climate (IPCC, 2007), particularly as ice-core records have yielded evidence of a strong correlation between CO2 concentrations in the atmosphere and palaeotemperatures (Fig. 1.2). This concern is justified when CO2 levels are compared with those of the past. Since Antarctica is a major driver of Earth's climate and sea level, much effort has been expended in deriving models of its behaviour. Some of these models have been successfully evaluated against modern conditions. In 2004, modelling the past record of ice-sheet behaviour in response to changes in climate (inferred from ice cores, sedimentary facies and seismic data), palaeoceanographic conditions (inferred from palaeoecology and climate proxies in ocean sediments) and palaeogeography (as recorded in landscape evolution) was seen as a critical next step, and became the focus of the ACE programme.

The ACE programme facilitates research in the broad area of Antarctic climate evolution. The programme links new geophysical surveys and

Figure 1.2: Variation in the Earth's temperature during the last 65 million years, based on reconstructions from deep-marine oxygen isotope records. Future atmospheric temperature scenarios are based on IPCC (2001). Greenhouse trace gas projections are shown at top of diagram. Given the worse-case scenario, planetary temperatures could increase in 100-300 years to a level where, according to our knowledge of previous Antarctic glaciations, ice cover on Antarctica could not be sustained. The representation of palaeo-temperatures is adapted from Crowley and Kim (1995).

Figure 1.2: Variation in the Earth's temperature during the last 65 million years, based on reconstructions from deep-marine oxygen isotope records. Future atmospheric temperature scenarios are based on IPCC (2001). Greenhouse trace gas projections are shown at top of diagram. Given the worse-case scenario, planetary temperatures could increase in 100-300 years to a level where, according to our knowledge of previous Antarctic glaciations, ice cover on Antarctica could not be sustained. The representation of palaeo-temperatures is adapted from Crowley and Kim (1995).

geological studies on and around the Antarctic continent with ice-sheet and climate modelling experiments. The programme determines past climate conditions and changes in both the recent past (i.e. during the Holocene, prior to anthropogenic impacts as well as at the last glacial maximum, when temperatures were cooler than at present) and the more distant past (i.e. in the pre-Quaternary, when global temperature were several degrees warmer than they are today). This cross-disciplinary approach, involving climate and ice-sheet modellers, geologists and geophysicists, has led to a substantial improvement in the knowledge base on past Antarctic climate, and our understanding of the factors that have guided its evolution. This in turn allows us to build hypotheses, examinable through numerical modelling, for how the Antarctic climate is likely to respond to future global change.

0 0

Post a comment