3. 1 Introduction 2 Deep Time 1 The greenhouse world: from Gondwana breakup to 34 million years




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MASTER COPY 27 March 2009


Chapter 3


Antarctic climate and environment history in the pre-instrumental period


Chapter Editor

Dominic A. Hodgson


Authors:

Hodgson DA, Abram N, Anderson J, Bargelloni L, Barrett P, Bentley MJ, Bertler NAN, Chown S, Clarke A, Convey P, Crame A, Crosta X, Curran M, di Prisco G, Francis, J.E., Goodwin I, Gutt J, Massé G, Masson-Delmotte V, Mayewski PA, Mulvaney R, Peck L, Pörtner H-O, Röthlisberger R, Stevens MI, Summerhayes CP, van Ommen T, Verde C, Verleyen E, Vyverman W, Wiencke C, Zane, L.


This chapter should be cited as:

Hodgson DA, Abram N, Anderson J, Bargelloni L, Barrett P, Bentley MJ, Bertler NAN, Chown S, Clarke A, Convey P, Crame A, Crosta X, Curran M, di Prisco G, Francis, J.E., Goodwin I, Gutt J, Massé G, Masson-Delmotte V, Mayewski PA, Mulvaney R, Peck L, Pörtner H-O, Röthlisberger R, Stevens MI, Summerhayes CP, van Ommen T, Verde C, Verleyen E, Vyverman W, Wiencke C, Zane, L (2009) Antarctic climate and environment history in the pre-instrumental period. In: Turner J, Convey P, di Prisco G, Mayewski PA, Hodgson DA, Fahrbach E, Bindschadler R, Gutt J (eds) Antarctic Climate Change and the Environment. Scientific Committee for Antarctic Research, Cambridge


Chapter contents

3.1 Introduction

3.2 Deep Time

3.2.1 The greenhouse world: from Gondwana breakup to 34 million years

3.2.2 Into the Icehouse world: the last 34 million years

3.3 The last Million years

3.3.1 Glacial interglacial cycles

3.3.2 The transition to Holocene interglacial conditions: the ice core record

3.3.3 Deglaciation of the continental shelf, coastal margin and continental interior

3.3.4 Antarctic deglaciation and its impact on global sea level

3.3.5 Sea ice and its influence on climate




3.4 The Holocene

3.4.1 Holocene climate changes: the ice core record

3.4.2 Changes in sea ice extent through the Holocene

3.4.3 Regional patterns of Holocene climate change in Antarctica

3.5 Biological responses to climate change

3.5.1 The terrestrial environment

3.5.2 The marine environment

3.6 Concluding remarks




3.1 Introduction



This chapter reviews Antarctic climate and environmental history from deep time through to the present. First, the large scale changes that have shaped the climate and environments of Antarctica and its surrounding ocean are described; from its early origins as the centrepiece of the Gondwana supercontinent, though its subsequent breakup and isolation by the circumpolar Southern Ocean c. 180 Ma (million years) ago. This is followed by a description of the formation of the first ice sheets on the continent c. 34 Ma, and later, the development of the 100 ka (thousand years) glacial cycles that have characterised the last 0.9 Ma. The climate at the end of the last major glaciation, retreat of the ice sheet and its effects on global sea level, and the changing distribution of sea ice and its effect on climate are then described. Our present interglacial, the Holocene is described in detail from a combination of ice cores, marine sediments, lake sediments and terrestrial records with a focus on both regional and continent-wide climate and environmental variability, against which the climate changes in the instrumental period (Chapter 4) and the predicted climate changes of the future (Chapter 5) can be compared. In order to facilitate such comparison, towards the end of the chapter we examine the evolutionary and biogeographical factors that have shaped the contemporary biota of the continent, including some of the physiological adaptations in the marine realm that have led to the distinctive marine fauna seen today. This section also highlights some of the reorganisations in species distributions that have occurred during the relatively minor natural climate changes of the Holocene that are being used to inform our understanding of the climate and biological changes that might be anticipated in the near future (Chapter 5).


The modern climate over Antarctica and the Southern Ocean results from the interactions within the ice sheet – ocean – sea ice – atmosphere system. Knowledge of how this system responds to past and present climate forcing and the phasing of climate events on regional to hemispheric scales is essential for understanding the behaviour of the Earth’s past, present, and future climate. Studying the history of Antarctic climate and environment is also important as it provides the context for understanding present day climate and environmental changes both on the continent and elsewhere. Together, the climate and environmental studies allow researchers to determine the processes that led to the development of our present interglacial state, and to define the ranges of natural climate and environmental variability on timescales from decades to millennia that have prevailed over past millions of years in the past. Once this natural variability is known we can more confidently determine when changes have exceeded the natural state. We can also study, for example, past warm periods to determine the processes in the oceans, atmosphere, cryosphere and biosphere that might have caused them and the effects that they had on the environment at those times.


In Antarctica, past climates and environments can be reconstructed from a range of palaeoenvironmental records, each of which provides different, yet often complementary, information on the patterns, processes and mechanisms of change. These span a range of different, and sometimes overlapping, timescales. Instrumental data from satellites, ground-based instruments and oceanographic surveys provide detailed information about past climates for much of the last four decades. However, for records that pre-date this ‘instrumental period’ it is necessary to use the stratigraphic records contained in lake sediments, marine sediments and ice cores, and for the longest time periods, geological records on land and in deep ocean sediments.


Geological records are used to study the distant past, or ‘deep time’. A particular value of studying climate in the distant past is that we need to go back more than 30 million years to find atmospheric CO2 concentrations at more than twice pre-industrial levels, which we are projected to encounter by the end of this century. Geologists have termed this the “greenhouse” world, and both the biota and geothermometers indicate it was indeed several degrees warmer, in contrast to the “icehouse” world that was initiated with the first ice sheets on Antarctica 34 million years ago. In the pages that follow we will briefly outline the main features of this world and chart the changes that have taken place as CO2 levels declined and persistent ice sheets grew in the Antarctic.


Geological records of past climate on land in Antarctica are generally accessible only in mountains around the margin or in the Transantarctic Mountains due to the thick continental ice cover (Fig. 3.1). These records either largely predate Gondwana breakup, which began around 180 million years ago, or in the case of sediments deposited since glaciation began they are mostly are patchy and difficult to date (Barrett 1996). However a few places, like the Antarctic Peninsula, have well-exposed post-breakup sedimentary strata that predate the first ice sheets. James Ross Island and Seymour Island in particular have yielded a great variety of plant and animal fossils from Late Cretaceous and early Cenozoic times (100-34 Ma ago); (Francis et al. 2008a)). In addition, deep drilling into marine sediments on the continental margin of Antarctica (Fig. 3.1) has provided records of Antarctica’s climate during the tens of millions of years that it has been ice-covered (Barrett 2008).

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