Australia’s contribution to Antarctic climate science

Australia’s Antarctic Science PrograM Edited by D. Michael Stoddart Australian Antarctic Division

April 2008 photographs © Commonwealth of Australia Contents

1 – Introduction 1

2 – The Antarctic Ice Sheet and sea-level 4

3 – Sea Ice 8

4 – The Southern Ocean 12

5 – Reconstruction of past climates 16

6 – Antarctica’s Atmosphere 20

7 – Concluding remarks 22

8 – References 23

1 – Introduction

Australia has had a long and distinguished record of research into Antarctica’s natural phenomena, including early fundamental studies into the nature of the ice sheet, ice shelves and sea ice. As the world’s attention focuses on changing climates in the 21st century that legacy of fundamental work, together with a large suite of interdisciplinary studies embracing the ocean around Antarctica, its biota, and the atmosphere above is of immense value in underpinning to a comprehensive understanding of contemporary change and its environmental consequences.

This paper attempts to summarise the value of the contributions made by Australian scientists to international high-latitude climate science and to indicate the level of international visibility of Australian researchers in Antarctic science. For a country with a population of 20 million Australia’s impact in the international arena is widely felt. Antarctic science was recently identified as one of our international research strengths (PMSEIC 2006). Our natural advantages of proximity to Antarctica make access for scientific research easier than in the case for northern hemisphere nations. The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, 2007) has highlighted the paucity of knowledge about the polar regions of the Earth, regions where climate change is expected to be greatest because of feedback processes involving ice and snow. In particular, the future response of polar ice sheets to global warming is the largest unknown in projecting future sea level rise. The development of more accurate climate predictions requires increased knowledge of the physics Aurora Australis approaching Mawson. Photograph Wayne Papps. and chemistry of the ice on the Antarctic continent and on the Southern Ocean. Antarctica’s vastness and the extent of its organizing committees and activities of the Scientific Committee on winter barrier of sea ice present great challenges to researchers Antarctic Research (e.g. Biological Investigation of Marine Antarctic as well as opportunities for international research leadership. Systems and Stocks, the Global Change and the Antarctic program; Increasingly, new satellites and robotic systems are providing Antarctic Sea Ice Processes and Climate); of the World Climate new eyes on Antarctica and the Southern Ocean and Australian Research Programme (e.g. the World Ocean Circulation Experiment, scientists are at the forefront of research to validate their data. the Climate Variability and Predictability program, the Climate and Cryosphere program, the International Programme for Antarctic Australia’s Antarctic program is highly focused on research of Buoys); of the International Geosphere-Biosphere Programme (e.g. strategic importance to our national future and has produced novel the Joint Global Ocean Flux Experiment, Global Ocean Ecosystem inter-disciplinary approaches to the question of Antarctica’s role – Dynamics); and many more. In this International Polar Year an and that of the high-latitude Southern Ocean – in the global climate Australian is a co-chair of the international planning committee system. Over many years our scientists have taken leadership roles and others are leading significant scientific studies in Antarctica in large-scale international research programs and continue to exert and co-leading or participating in over 40 others. Australians influence in setting research directions for the future. There are few continue to provide scientific leadership in major Antarctic and high-level international programs involving Antarctic and Southern Southern Ocean governance forums, such as the Committee for Ocean science which do not include leadership from Australian Environmental Protection of the Antarctic Treaty, the Scientific scientists. We have played, and continue to play leading roles in the Committees of the Convention for the Conservation of Antarctic

1 Melting sea ice, Tryne Islands. Photograph: Noel Tennant.

Marine Living Resources, the International Whaling Committee, is training 97 Australian higher degree students. Formal and and the Agreement on the Conservation of Albatrosses and informal links with international scientists number in the hundreds. Petrels. International and national recognitions have followed with About 150 peer-reviewed papers are published annually, with several of our scientists receiving accolades for their work, further a similar number of conference and ephemeral papers, making enhancing our national visibility in high southern latitude science. Australia’s program the third most productive in the world, following the USA and the UK (Dastidar and Persson 2005). In a recent review of Australia’s Climate Change Science Program (ACCSP) by Professor Susan Solomon, Chair of This paper summarises the part played by Australian scientists the IPCC Working Group 1, and Professor Will Steffen, and Australian research teams in high-latitude climate science. ANU, noted that Australian science “has been essential to Chapter 2 examines Australian research on ice sheet dynamics furthering the understanding of Southern Ocean physics and the interactions of ice shelves with the ocean underneath and chemistry, and identifying its links to climate change for which are providing crucially important information about how Australia and globally” (Solomon and Steffen, 2007). ice and ocean interact and transfer heat from one to another. The ocean is the greatest heat-pump on the planet and research Interdisciplinary studies involving scientists from the Australian on sea ice, examined in Chapter 3, focuses on how sea ice forms Antarctic Division, CSIRO, the Bureau of Meteorology (principally modifies heat exchange between the ocean and the atmosphere, through the Antarctic Climate and Ecosystems Co-operative and contributes to the circulation of the Earth’s oceans and Research Centre ACE CRC), the universities and colleagues from thus to the transportation of heat around the globe. A major overseas have enabled many significant research projects to be uncertainty for the future is the rate at which global sea level undertaken. Joint experiments with international collaborators have will continue to rise with global warming. The Greenland and brought many millions of dollars-worth of overseas investment Antarctic ice sheets could be the biggest contributors to this. to projects relevant to Australia’s goals in Antarctica and the Southern Ocean. It is the twin philosophies of interdisciplinarity Unlike the Arctic, where large and extensive climate system and partnership which define Australia’s contribution to changes are occurring at present, continent-wide changes in the scientific knowledge of Antarctica and the Southern Ocean. Antarctic have yet to be detected. In part this is because our data base in the Antarctic is less complete and shorter, and in part Because of the logistical challenges posed by the conditions in because some Antarctic changes are regional. The thickness of the Antarctica and the Southern Ocean Australia has had to develop West Antarctic Ice Sheet is decreasing over large areas, and ice a system to tightly integrate its science to maximise the return for shelves along the Antarctic Peninsula are collapsing, but the East every dollar spent. The small size of Australia’s population and Antarctic Ice Sheet is showing little diminution, except in some limited research pool has encouraged it to forge the strongest outlet glacier systems such as the Totten Glacier near Casey. There partnerships with international collaborators. The program has been no statistically significant change in overall Antarctic now has links with 27 research institutions in 29 countries and sea ice extent since the satellite record began in the late 1980s,

2 although a decreasing trend is identified in the Bellingshausen/ Material for this paper has been provided by the Amundsen Sea (west Antarctic Peninsula) sector. Moreover, following people, in consultation with many others: insufficient data are available to determine whether any change has occurred in pack ice thickness over this period. Long-term Neil Adams BoM and ACE CRC studies near Davis Station do, however, reveal a delay in the Ian Allison AAD and ACE CRC time of year at which the annual land-fast ice cover attains its Leanne Armand ACE CRC maximum thickness, and this is linked to recent winter warming. Nathan Bindoff ACE CRC and CSIRO John Church CSIRO and ACE CRC Chapter 4 covers Australian contributions to Southern Ocean Michael Craven AAD and ACE CRC science. Our understanding of the changing biodiversity of organisms Mark Curran AAD and ACE CRC in the upper layers of the ocean is underpinned by knowledge of Marc Duldig AAD physical oceanography, where significant signs of environmental Petra Heil AAD and ACE CRC change are being identified from deep waters. In the deep oceans, Will Howard ACE CRC that part of Earth where some organisms have remained essentially Andrew Klekociuk AAD unchanged for over 500 million years, changes in the chemistry of Rob Massom AAD and ACE CRC the deep layers of the Antarctic Circumpolar Current are occurring Vin Morgan AAD and ACE CRC faster than was previously predicted. At the surface, increasing Damian Murphy AAD uptake of carbon dioxide is changing the acidity of the water Phil O’Brien GA making it harder for the tiny organisms which build shells of calcium Steve Rintoul CSIRO and ACE CRC carbonate to extract that which they need. As these organisms are Bronte Tilbrook CSIRO and ACE CRC at the very base of all marine food webs any impediment to their Tom Trull ACE CRC and CSIRO biology will have escalating ramifications further along the web. Tas van Ommen AAD and ACE CRC Neal Young AAD and ACE CRC In Chapter 5 reconstructions of past climate from analyses of Roland Warner AAD and ACE CRC ice cores and marine sediments are shown to have significantly Tony Worby AAD and ACE CRC advanced our understanding of long-term and short-term climate change. Deep Antarctic ice cores are able to provide Michael Stoddart AAD (Editor) a longer climate record than those from Greenland, and cores from both ice sheets provide a record of different climate forcing and responses in the northern and southern hemispheres. The thickest and oldest ice in Antarctica is very likely to lie within the Australian Antarctic Territory and recovery of an ice core more than one million years old, and analyses of the past climate and atmospheric composition from that will reveal critical processes that have caused major changes to Earth’s climate cycles in the past. To push the record much further back examination of marine sediments has extended our understanding of previous climates back to the start of the Cenozoic era, about 65 million years ago.

Observations on the atmosphere above Antarctica is the subject of Chapter 6. Research into the Antarctic atmosphere is contributing to routine global weather forecasting, and to improvements in the numerical weather prediction models that provide these. Research into changes in the stratosphere and above is showing this part of Antarctica’s environment is also changing. As the climate research community turns its attention to the region of the atmosphere between 10 and 100 km Australian data are contributing to new models of what future climates may be like.

3 2 – The Antarctic Ice Sheet and sea-level

The intense cold of the Antarctic ice sheet is a major component of the global climate system through its influence on surface energy and moisture fluxes, clouds, precipitation, and atmospheric and oceanic circulation, and the ice sheet contains enough water mass to raise global sea level by nearly 60 m. The ice sheet is nourished by snowfall and loses mass by iceberg discharge and melt from the base of floating ice shelves around the coast. Any imbalance between these input and output mass terms affects global sea level.

Australian scientists have studied this ice sheet mass Balance Loss Ice Sheet Gain Flux km3/km/yr budget since the International Geophysical Year (1957/58), collecting detailed data on ice flow, ice thickness and other ice sheet characteristics on over- Total snow traverses. These have penetrated deep into the LGB imbalance +22% interior of Antarctica, and along more than 5000 km is 38 km3/yr of the coastal perimeter (Figure 1). These observations [~15% of alone are insufficient to accurately estimate the state the total of balance of the ice sheet, but they do provide the snow input] essential information to calibrate and validate new Wilkes L +21% satellite measurements of the ice sheet and assist in developing numerical models of the ice sheet.

Australians also played pioneering roles in km understanding the physics of ice flow, and in the Fig 1. The mass balance of the interior of the East Antarctic ice sheet. The development of computer model simulations of ice map (left) shows the balance flux, which is the volume of ice that must sheets. We have continued those modelling efforts, be discharged to balance the annual snow fall onto the ice sheet. This is with projections of Antarctica’s response to climate derived by a computer model (Budd and Warner, 1996) for a given snow change scenarios (Budd and others 1994, O’Farrell and fall distribution: the blue areas are low ice discharge rates and the red are others 1997, Warner and Budd 1998). As indicated high rates, on a logarithmic scale. The plot (right) compares the modelled by the IPCC AR4, the role of the great ice sheets is mass flux across the 200 surface elevation contour with the discharge the largest unknown in estimating future sea level derived from ice velocity and ice thicknesses measured by Australian over rise, and this remains a major focus of our research. snow traverses between 40°E and 130°E (black dots). Where the balance The complexity of ice flow processes revealed by flux is greater than the measured flux the interior ice sheet is growing, and modern observations, including sub-glacial lakes vice versa. Much of this part of Antarctica is nearly in balance, although and rivers, and accelerations in ice stream flows, gains in the Lambert Glacier Basin (LGB, top) and Wilkes Land (bottom) calls for a reappraisal of the dynamic character of ice lead to an overall gain for this part of the ice sheet that is equivalent to sheets in the global climate system, and is driving a drop in sea level of 0.1 mm per year. Different balance conditions in international efforts to endow the next generation other parts of Antarctica, and between the 2000 m elevation contour of computer models with sufficient physical realism and the coastline, also impact sea level, and overall Antarctica is probably to address the sea level question. Models can contributing to a net sea level rise. integrate diverse insights into the ice sheet system, bringing theory and observations into a constructive confrontation. They also enable us to extrapolate from limited observations to parts of the ice sheet where data In addition to the complexity observed at the geographical scale, are sparse or non-existent (Warner and Budd, 2000) on the the ice flow is nonlinear at the microscale. Australian studies of basis of physical insights rather than statistical analyses. crystallography and ice deformation showed that the development

4 + 0.02 of patterns of crystal orientations can increase m/yr + 0.08

2500m aal m/yr ice flow rates by more than a factor of four LGB Traverse 1600 m aal (e.g. Russell-Head and Budd 1979, Jacka Survey section - 0.01 and Budd 1989). We have maintained a Floating 320 m aal focus on ice flow properties (Li and others Grounding line AM04 AM01 70 m aal 60 m aal 1996,Wang and Warner 1998, Warner Sea Borehole Borehole and others 1999, Wang, Warner and Budd level Grounded - 2.0 m/yr 2002) as an essential ingredient for realistic - 1.2 m/yr computer models of ice sheet evolution. - 4.1 m/yr

1000 750 500 250 0 Distance from front of ice shelf (km) A major focus of Australian ice sheet studies has been in the Lambert Glacier basin, the Fig 2. A schematic section through the Lambert Glacier drainage basin: from the largest drainage basin in east Antarctica. centre of the ice sheet and along 550 km of floating Amery Ice Shelf to the coast. Using results from ground surveys, satellites, The ice mass flowing across sections at different elevations (dotted vertical lines) and numerical models it has been estimated has been derived from Australian field observations, enabling the state of balance that this part of the east Antarctic ice sheet, of different parts of the system to be estimated. Inland, the grounded ice sheet unlike West Antarctica, is close to balance has a slight mass gain (blue arrows), although there are large error limits to these at present (Fricker et al., 2000; Testut et al., estimates. Once floating, the ice shelf sustains large losses from melt at the ice 2003). A major problem in mass budget ocean boundary (red arrows). There is a net loss from this basal melting but there studies such as these is that the output are also areas in the north-west of the shelf where refreezing onto the base occurs. term (ice outflow) varies on time-scales of Four boreholes have been made through the ice shelf into the underlying water centuries to millennia, whereas the input cavity (e.g. black lines at AM01 and AM04) to sample this ice and to investigate (snowfall) varies annually. Ice core studies melting and freezing processes beneath the shelf. can provide information on the variability and past rates of snowfall (e.g. Goodwin et al., 2003; Monaghan et al., 2006) and meteorological studies porous and infiltrated with sea water, making it highly vulnerable provide understanding of the processes controlling precipitation to rapid melting (Craven et al., 2004; Craven et al., submitted). The in Antarctica (Massom et al., 2004; Xiao et al., 2004). processes of melt and ice shelf collapse have been investigated using computer models of the ice shelf and the ocean circulation The interior of Antarctica is mainly drained by large ice streams beneath it (Williams et al., 2001, 2002), and studies have also and outlet glaciers, typically feeding into floating ice tongues or ice been made of the rate of iceberg calving from the Amery (Fricker shelves. Ice is lost from these by calving of icebergs and by melting et al., 2002) and of processes causing the rifting that forms the from the base due to contact with sea water. These floating ice icebergs (Fricker et al., 2005). A schematic of the mass balance of bodies are the most vulnerable part of the ice sheet system to the Lambert Glacier-Amery Ice Shelf system is shown in Fig 2. change, although their collapse would not itself contribute to sea level rise. However significantly increased discharge of grounded The combined contribution from Antarctica and Greenland ice occurred along the Antarctic Peninsula after ice shelves, which to current sea level rise is only about 0.4 mm/yr, a small formerly buttressed the glaciers, collapsed. For over four decades part of the total current sea level rise (Lemke et al., 2007). Australian scientists have been studying the dynamics, mass budget However, dynamic instability in ice sheet response to global and ice shelf-ocean interaction of the Amery Ice Shelf, which is warming is potentially the largest unknown in projecting fed from the Lambert Glacier basin, linking our pioneering field future sea level over centennial to millennial timescales. surveys (Allison, 1979; Budd et al., 1982) to the most contemporary satellite measurements (Young and Hyland 2002; King et al., Australian research combined satellite altimetry (Watson et al., 2007). Satellite and airborne measurements have shown that there 2003, 2004) and in situ data (Church et al., 2004) to show that is very active melting and refreezing occurring beneath the ice from 1870 to the present sea level has risen by just under 20 cm, shelf, and that layers of ice refrozen from the ocean underlie some at an average of 1.7 mm yr-1 during the 20th century (Church and parts of the shelf in bands up to 200 m thick (Fricker et al., 2001). White 2006) Fig 3. However for the 20 year periods centred on Scientists in Australia’s Antarctic program have drilled a number 1992 and later, the rate of sea-level rise was 3 mm yr-1, almost of holes up to 720 m depth through the Amery Ice Shelf into the twice the average for the 20th century and 25% greater than the ocean beneath and found that the lowest 100 m of refrozen ice is next largest period of high rates of sea-level rise during the 1940s.

The Antarctic Ice Sheet and sea-level 5 Pacific and Indian Ocean islands (Church et al., 2006a) and an increase in sea-level rise and in the frequency of extreme sea-level events of a given height around Australia (Hunter 2004, Church et al., 2006c). These results have been used in Fig 3 Observations and modeled values for tidal height at ten Australian ports, a number of papers relevant to local planning from 1920 to the present (Walsh et al., 2004) and outreach documents (Church et al., 2006b, 2007c; Pyper et al., 2007).

These results were a key finding of the IPCC Fourth Assessment Another important contributor to sea level rise is the melting Report 2007 (Figure SPM-3 of the Report). Although the rate of of temperate glaciers, estimated to be contributing about coastal sea-level rise was larger during the 1990s, this was not the 0.8 mm/a (Lemke et al., 2007). Glaciers on sub-Antarctic case over longer periods (White et al., 2005). Since 1990 sea level Heard Island are retreating rapidly and overall are estimated to has been rising at the very upper limit of the IPCC 2001 and 2007 have lost more than 10% of their volume since 1947 (Ruddell, projections (Rahmstorf et al., 2007), raising concern that the IPCC 2006). One Heard Island glacier being monitored by the projections may have underestimated the rate of future sea-level rise. Australian Antarctic program, Brown Glacier, has lost up to 25% of its volume over this period and has shown considerably From 1963 to 1991 a series of violent volcanic eruptions resulted in accelerated retreat since 2000 (Thost and Truffer, in press). cooling (and, hence, contraction) of the upper ocean and presumably offsetting some of the increase in sea-level rise that would otherwise This fundamental work has also enabled a series of detailed have occurred (Church et al., 2005; Church and White 2006). studies examining the impact of sea-level rise and changes in storm intensity on vulnerable areas around the Australian coastline A combination of satellite and in situ data (including those collected (Church et al in press), and providing key input for Tasmania’s as part of the Australian Base Line Sea-level Array and the coastal vulnerability study (Sharples 2006). This latter report has Australian-funded South Pacific Sea-level and Climate Monitoring laid the basis for an Australian coastal vulnerability study now Project) has provided convincing evidence for sea-level rise at underway and supported by the Australian Greenhouse Office.

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3 – Sea Ice

Each autumn the surface ocean around Antarctica freezes forming a veneer of sea ice. At its maximum in September, Antarctic sea ice extends over about 20 million square kilometres (nearly three times the area of Australia). However, Antarctic sea ice is highly seasonal, and at its minimum in February it has an extent of only 3-4 million square kilometres. Sea ice cover contributes strongly to the global weather and climate system. It restricts heat exchange between the ocean and the atmosphere, and salt rejected from seawater during freezing changes the density structure of the ocean, and is a major driver of global ocean circulation. The sea ice is highly vulnerable to climate change, as is now clearly seen in the Arctic. The decrease in sea ice extent has an important feedback effect on the climate that accelerates warming, and much of the enhanced warming predicted for polar regions is a result of this feedback. Sea ice is also extremely important as a substratum, refugium and food source for polar marine ecosystems (Nicol et al., 2006), which can be predicted to be impacted upon as the extent of sea ice declines.

It has long been recognized that proper representation of Polynyas around the coast of Antarctica are small areas of a few sea ice in coupled ocean-atmosphere models is essential for 1000s of square kilometres that have anomalously low amounts of numerical weather prediction and for future climate projection. sea ice because the ice that forms there is continuously scoured off In the southern hemisphere, however, knowledge of sea ice by strong winds (Massom et al., 1998; Bindoff et al., 2000). New characteristics, and of the processes that determine these and ice immediately forms, and this formation/removal cycle leads to the interaction of it with the atmosphere and ocean are not a very high total ice production. The water left below contains far well known. Key characteristics of Antarctic sea ice that effect more salt than normal and becomes very dense, contributing to climate are its extent, thickness, concentration, drift, and the the formation of Antarctic bottom water (AABW) that sinks to the thickness of the accumulated snow cover. Changes in these abyssal depths of the ocean and is a major driver of overturning attributes significantly alter ocean-atmosphere interaction, ocean circulation in the global ocean. Each of these experiments has circulation, and ecological variables such as primary production, made an important contribution to our understanding of the role food web dynamics and ocean sustainability. Australia’s sea of sea ice in the climate system. The HIHO experiment confirmed ice research over the last two decades has greatly improved that the thickness of sea ice, one of the most important variables in understanding of Antarctic sea ice processes, particularly through determining heat exchange between the ocean and atmosphere, sophisticated, multi-disciplinary in situ measurement campaigns is controlled as much by mechanical deformation of the ice as it is from research ice breakers operating within the ice at most times by simple melt/freeze processes (Worby et al., 1998). In the MGP of the year. Australia is one of a handful of nations that has been experiment, we made the first winter measurements of the very able to conduct this important research, and has made a major high rate of sea ice production in a coastal polynya, of as much as contribution to international climate science in this field. It is set 15 m per year (Lytle et al., 2001; Roberts et al., 2001), enabling the to contribute strongly to the next IPCC Assessment Report. effect of this on the formation of AABW to be quantified (Bindoff et al., 2001). A bi-polar comparison of the physical mechanisms Over the past decade, Australia has conducted a number of major responsible for polynya formation and maintenance, and their sea ice field campaigns, including the “Heat In, Halide Out (HIHO)” variability to climate change has been conducted by Barber experiment in the winter of 1995 – the first multidisciplinary winter and Massom (2007). Of particular interest are the deep-water sea ice experiment in the east Antarctic sea ice zone – and the polynyas, in which the heat stored in the deeper ocean layers is “Mertz Glacier Polynya (MGP)” experiment in 1999, also in winter. readily transferred to the surface by convection and mixing.

8 Australia has made an extremely valuable contribution to our current knowledge of the thickness of Antarctic sea ice through the compilation of more than two decades of ship-based data into a circumpolar climatology (Worby and Ackley, 2000; Worby, in press), providing the first-ever description of the regional and seasonal variability in the distribution of Antarctic sea ice thickness. The work not only establishes a baseline against which to measure future change, but also provides a data set against which climate models can be assessed or initialized (Fig 4).

Recovering sea ice sample Photograph Sandra Zicus.

A great deal of international research focuses on the use of satellite-based instruments to monitor sea ice variables for change. Fig 4 Winter sea ice thickness (m). Parameters such as sea ice cover and extent are monitored routinely on a daily basis (Lubin and Massom 2007; Worby and Comiso, A similar climatology of Antarctic sea ice drift (Heil and Allison 2004), but other parameters such as sea ice and snow cover 1999) provided a comprehensive assessment of the dynamics thickness and ice drift are not well resolved with satellite data. of the East Antarctic sea ice zone. Australian scientists have New satellite instruments and techniques are being designed and led programs developing such data compilations which built to make these measurements (Lubin and Massom 2007), but can be used to derive important climate related properties, these must be developed and validated against measurements such as how much solar radiation is reflected from sea made within the sea ice zone. Observations from the Australian sea ice, for the whole sea ice zone (Brandt et al., 2005). ice research campaign “Antarctic Remote Ice Sensing Experiment (ARISE)” in 2003 are being directly applied to the validation and A number of Australian studies using proxy data for sea ice extent development of NASA and European Space Agency (ESA) satellite suggest there was a significant decline in Antarctic sea ice extent algorithms. The future development of satellite instruments for between 1950 and 1970, before satellite observations commenced. monitoring the Antarctic relies heavily on high quality field data They have been based on historical whaling data (de la Mare, 1997) for ground-truthing the data from prototype sensors deployed and the concentration of methanesulphonic acid (a by-product in the field and satellites. Australia plays a leading role in this of sea ice algae respiration) in a coastal ice core at Law Dome work, having strong links with European, US and Japanese space (Curran et al., 2003). These studies are major contributions to the program researchers. The results of satellite-validation studies from international climate debate in that they point to the possibility of Australia’s ARISE program has made a significant contribution to abrupt recent changes in sea ice extent, and raise questions about improving satellite-derived estimates of sea ice concentration and the processes involved and the impacts on other climate variables. temperature (Massom et al., 2006a), surface albedo and skin- surface temperature (Scambos et al., 2006), snow thickness (Worby The thickness and distribution of sea ice which is permanently et al., in press) and the distribution of thin ice (Tamura et al., 2006). attached to land and grounded icebergs around the coast of

Sea Ice 9 SIPEX. Aurora Australis in the pack ice. Photograph: Sandra Zicus

Antarctica (fast ice) is also sensitive to climate change/variability. with other factors to create a major phytoplankton bloom, Fast ice is trapped close to the coast and its thickness is determined but had a negative impact on the growth of Antarctic krill – by local conditions, in particular air temperature, wind speed a key component of the Southern Ocean food chain. Adélie and direction. Observations of fast ice thickness at the Australian penguins experienced the largest recorded between-season stations of Mawson and Davis have been made since the 1950s breeding population decrease and lowest reproductive (one of the longest Antarctic sea ice data sets). From these Heil success in a 30-year time series, highlighting the relationship (2006) has shown for Davis a delay in the time of year at which between changes in the physical environment and the the annual fast ice cover attains its maximum thickness which is breeding success of top level predators. At Béchervaise linked to recent winter warming. A satellite-derived “snapshot” Island, near Mawson, where Australian researchers have of fast ice extent around east Antarctica by Giles et al. (in press) been closely monitoring a breeding population of Adélie is another important example of valuable baseline data against penguins for the past 17 years a build-up of coastal ice five which future changes can be monitored. Links between grounded years ago shows no sign of dispersing, with an associated icebergs, fast ice distribution and polynya processes have been dramatic downward change in the annual breeding success reported by Massom (2003) and Massom et.al. (2001). of the birds. Large-scale effects of sustained patterns of anomalous atmospheric circulation on sea ice distribution, International collaborative studies have been carried out in similar to those shown to occur in west Antarctica have also the Antarctic Peninsula region to further our understanding been shown to occur in the Australian sector (Massom et al., of the complex interactions between the physical and 2003). The Australian sea ice research team also recently biological environment in the sea ice zone (Massom et al., participated in a German-led international, multi-disciplinary 2006b; in press). This part of Antarctica has experienced a Ice Station Polarstern (ISPOL) study in the Weddell Sea. steady decline in Antarctic sea ice extent over the past few This study focused on improving the understanding of decades, coupled with one of the largest warming trends on sea ice dynamics in this region (Heil et al., in press), and Earth. The new research highlights the strong links between the thermodynamic evolution of the sea ice cover during hemispheric patterns of atmospheric circulation, sea ice and the summer melt period (Tison et al., in press). These are ecological processes. In the late winter through the summer important processes that must be properly understood and of 2001/2 for example, extreme ice compaction driven by integrated into more accurate climate prediction models. unusually sustained periods of northerly winds combined

10 Sea Ice 11 4 – The Southern Ocean

The Southern Ocean plays several key roles in the Earth’s climate system (Rintoul et al., 2001). The strong eastward flow of the Antarctic Circumpolar Current (Fig 5) connects the great ocean basins and allows the existence of a global-scale pattern of ocean currents known as the ‘thermohaline’ (based on heat and salinity) or ‘overturning’ circulation (Fig 6).

Fig 6 A schematic view of the Southern Ocean overturning circulation. (SAMW – Sub-Antarctic mode Water; AAIW – Antarctic Intermediate Water; UCDW – Upper Circumpolar Deep Water; LCDW – Lower Circumpolar Deep Water; NADW – North Atlantic Deep Water; AABW – Antarctic Bottom Water; STF – Sub-Tropical Front; SAF – Sub-Antarctic Front; PF – Polar Fig 5. The Antarctic Circumpolar Current is the world’s largest Front.) current flowing from west to east around Antarctica. It moves a mass of water equivalent to 20 times the volume of water in Australian-led research has resulted in a much deeper Sydney Harbour every minute. understanding of the dynamics, structure, and variability of the Antarctic Circumpolar Current. This has included the first direct The overturning circulation, in turn, influences climate by measurements of absolute transport of the current (Phillips and transporting vast amounts of heat around the earth and by Rintoul, 2002; Yaremchuk et al., 2001), determining the role sequestering carbon dioxide into its deeps. Dimethyl sulphide of eddy fluxes in the dynamical and thermodynamical balance released by micro-organisms living in the sunlit zone forms of the current (Phillips and Rintoul, 2000; Meijers and Bindoff, a base nuclei for cloud formation and thus has a feedback 2007), and developing innovative analysis techniques allowing effect on further insolation (Gabric A. et al.,2001) seasonal to inter-annual variability of the current to be assessed for the first time (Rintoul and Sokolov, 2001; Rintoulet al., 2002; Australian researchers have provided a new view of the major Sokolov et al., 2004). Recent work has revealed the current pathways involved in the global overturning circulation (Sloyan consists of multiple jets or filaments, reconciling an apparent and Rintoul, 2001a; Speer et al., 2000). They have demonstrated discrepancy between views of the current based on ship-data that water mass transformations in the Southern Ocean connect and theoretical studies (Sokolov and Rintoul, 2002; 2007). the upper and lower limbs of the overturning, in contrast to the long-standing view that the overturning was closed through wide- The rate at which water is transferred from the sea surface to spread interior mixing. This work has provided the observational the deep ocean determines how much heat and carbon dioxide support for a new conceptual model of the dynamics of the the ocean can store, and thus influences the rate and magnitude Southern Ocean, in which the three-dimensional ocean circulation, of climate change. The physical processes responsible for this eddy fluxes, water mass conversion, wind forcing and topographic transfer are difficult to observe and have until recently been poorly interactions are intimately linked (Rintoul et al., 2001). understood. Our researchers have made significant advances

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Fig 7 A summary of observed changes in the ocean in recent decades. Overall, the changes observed to date are consistent with the patterns of ocean changes expected from model projections of climate change resulting from enhanced greenhouse warming. (IPCC) by identifying and quantifying the key processes responsible for surface ocean. This helped motivate and guide the development water mass formation in the Southern Ocean. They have shown of a new representation of ocean eddies (Gent et al., 1995). This that the Adélie Land coast of Antarctica is a primary source of parameterisation has led to the greatest single improvement in AABW, in contrast to the prevailing view that the Weddell and the performance of ocean climate models in the last decade. Ross Seas were the only significant sources of this water mass (Rintoul, 1998). The MGP study (Chapter 3) provided direct Other investigations have focused on changes in specific regions evidence of rapid sea ice formation and the production of AABW of the ocean. A number of studies from Australia and overseas (Williams and Bindoff, 2003; Marsland et al., 2004; Williams et al., have shown that the Southern Ocean is warming at a rate greater 2007). By combining observations and simple dynamical models than the global average (Aoki et al. 2005a), and that the warmer the first quantitative estimates of the circumpolar formation rate ocean is in turn driving more rapid melting of floating glacial ice of Subantarctic Mode Water and Antarctic Intermediate Water around the margin of Antarctica. The additional glacial ice melt – the water masses that form the upper limb of the overturning has caused significant freshening of the dense water formed near circulation (Sloyan and Rintoul, 2001b) – were made. Antarctica, illustrating the tight link between high-latitude climate processes and the global ocean circulation (Aoki et al., 2005b; Oceans in the polar regions are changing more rapidly than those Rintoul, 2007). The melting and, in some cases, catastrophic elsewhere. Through repeated samples taken along standard ocean break-up of floating ice shelves along west Antarctica and the transects Australian researchers carried out some of the first Antarctic Peninsula, has been linked to more rapid outflow of ice studies to document changes in the ocean and have continued from glaciers on land; these results suggest present estimates to lead in this area, documenting global-scale changes in ocean of sea-level rise, which neglect this source of water, may be too properties that are consistent with the pattern of global warming conservative (Rahmstorf et al., 2007). Water masses involved in in climate model projections (Bindoff and Church, 1992; Wong the upper limb of the overturning circulation have also changed et al., 2001; Dickson et al., 2001; Hegerl et al., 2007). This work has in recent decades and Australian research has revealed both included new analytical approaches that help guide the physical the nature and causes of these changes (Murray et al., 2007; interpretation of changes in the ocean, approaches that have Rintoul and England, 2002; Banks and Bindoff, 2003). Overall, been widely adopted by other researchers in the field (Bindoff and the pattern of change observed in the ocean is consistent with McDougall, 1994). Australian research in the Southern Ocean has the expected pattern from climate models (Helm et al., 2007). made a direct contribution to improving projections of future climate The “fingerprint” of climate change in the ocean provides some change. A comparison of measurements with the outputs of models of the strongest evidence yet to support the conclusion that showed that the models were mixing too deeply in the Southern human activities are already changing Earth’s climate (Fig 7). Ocean, and therefore underestimating the rate of warming in the

The Southern Ocean 13 One of the most important ways in which the Southern Ocean influences global climate is by absorbing and storing carbon dioxide. About half of the carbon dioxide released by human activities is now found in the ocean; about 34% of the so-called anthropogenic carbon has been taken up in the Southern Ocean with the overturning circulation transporting much of this carbon north and storing it in the sub-Antarctic region (McNeil et al., 2001; Sabine et al., 2002, 2004; McNeil et al. 2003; Takahashi et al., 2002). Australian measurements have made such estimates in the Southern Ocean possible. Australia has obtained the only multi-year record of the amount of carbon sinking as particles in the Southern Ocean Fig 8 The yellow band shows the extent of a phytoplankton bloom following the first (Trull et al., 2001;), and determined that this international iron fertilization experiment in water south east of Australia. carbon export occurs more effectively in the Sub-Antarctic than Antarctic waters (Lourey and Trull, 2001; While the fact that the Southern Ocean is very effective at Trull et al., 2001; Wang et al., 2001, 003; Cardinal et al., 2004; removing carbon dioxide from the atmosphere, and can be Difioreet al., 2006). Studies of this modern sedimentation has viewed as beneficial in that by so doing it slows the rate of led to improved understanding of past variations of climate and global warming, the additional carbon dioxide is changing the associated ecosystem responses (Lourey et al., 2003; 2004; King chemistry of the ocean in important ways. As additional amounts and Howard, 2003, 2004, 2005; Cardinal et al., 2005, 2006). of carbon dioxide dissolve in the ocean the sea water becomes Australian scientists have also provided important new insights more acidic and less saturated in calcium carbonate. The effect of into the biological processes that help transfer carbon into the these changes is to make it more difficult for the most abundant deep ocean throughout the global ocean (Buesseler et al., 2007). organisms on the planet – the phytoplankton – to obtain the calcium carbonate from the water they need for their tiny shells. Australian scientists played key roles in the first international Because the saturation state of carbon in seawater is lower iron fertilization experiment to prove that the addition of small in colder water the damaging effects of acidification will first amounts of iron can stimulate a phytoplankton bloom in the become evident in the Southern Ocean (Orr et al., 2005). (Fig 9) nutrient-rich waters of the Southern Ocean, helping to confirm the hypothesis that biological production was iron-limited (Boyd et al. Export Flux of Organic Carbon: Northern and Southern Hemispheres 2000; Trull et al, 2001; Bowie et al, 2001; Nodder et al., 2001; Trull and Armand, 2001; Karsh et al., 2003). The experiment was carried out south of Australia because the detailed knowledge of the ocean circulation developed by our team meant we could identify a suitable site for the iron addition. The phytoplankton bloom fuelled by the iron supply was visible from space six weeks after the iron was added (Abraham et al., 2000; Fig 8). 142°E 170°W Subsequent work in collaboration with French researchers revealed similar responses to natural iron inputs over the Fig 9 Carbon dioxide absorbed by the surface ocean can be Kerguelen Plateau, including more efficient transfer of carbon transferred to the deeps either by physical processes (Fig 5) or by to deep waters in sinking particles than had been observed in biological processes. This figure shows the rate at which carbon artificial iron fertilizations (Blainet al., 2007). A recent study is transported to the deep ocean by sinking particles produced demonstrated the importance of iron input from the atmosphere by biological activity, as measured by moored sediment traps. in driving Southern Ocean productivity (Cassar et al., 2007). Values south of Australia are from Trull et al 2001; global compilation updated from Honjo 1997.

14 Photograph: Wayne Papps.

Water and drought are increasingly critical issues for Australia. between oceanographic properties of the upper layers of the Recent studies have implicated high-latitude processes in the recent Southern Ocean with its biota and how oceanographic change in decline in rainfall experienced in southern Australia (Cai and Cowan, reflected in biotic change (Smetacek and Nicol 2005; Nicol et al., 2006). The band of westerly winds over the Southern Ocean has 2004). Australian studies on sea ice extent have explored the use of shifted southward in recent decades. The storm systems that bring a proxy, methanesulphonic acid (MSA), as an indicator of the extent most rain to southern Australia are steered by these winds and have of sea ice over time periods of a few to several decades (Curran also shifted south, so they no longer cross the continent (Frederiksen et al., 2003). It is known that dimethosulphoniopropionate – a and Frederiksen, 2007). Most of the changes in the storm tracks precursor of methanesulphonic acid – is positively correlated with observed to date are believed to be ultimately related to ozone phytoplankton ingestion by krill. Australian research (Kawaguchi loss over Antarctica which perturbs temperature profiles in the et al., 2005) has modeled the contribution made by feeding krill to tropopause region (8-12 km above the Earth) interfering with the the total flux of these compounds, opening up new thoughts about development of weather cells in the troposphere, while greenhouse how best to reconstruct past sea ice extents from study of MSA gas-induced warming is expected to result in similar trends in the in ice. Other Australian studies have shown how ocean currents future (Cai and Cowan, 2007). The shifting wind patterns have also influence the distribution of organisms from plankton to whales been shown to drive important changes in the ocean, including (Trull et al., 2001; Sokolov et al., 2006; Sokolov and Rintoul 2007b; changes in upwelling of deep water (Oke and England, 2004; Sen Biuw et al., 2007), producing information which is guiding the Gupta and England, 2006). Since the deep water is rich in carbon, development of management strategies for marine resources and which is released to the atmosphere when it reaches the surface, to investigate the likely impact of climate change and variability on the net effect is that the Southern Ocean has become less effective marine life and ecosystems (Grant et al., 2006). Studies which link at absorbing carbon dioxide, and hence at slowing the pace of the physical and the biotic environments such as these have helped global warming, in recent decades (Lenton and Matear, 2007). established Australia’s high visibility in the scientific committees of the Convention for the Conservation of Antarctic Marine For many years Australia has been at the forefront of research into Living Resources and the International Whaling Commission. the composition of the planktonic fauna of the surface waters of the Southern Ocean. Through its international leadership of the Much of the progress made in recent years has depended on the Southern Ocean Continuous Plankton Recorder program Australia establishment of innovative, long-term observational programs. is drawing attention to the rapid changes observable in this A dedicated effort over the last 15 years has turned the Australian important element of the marine biota, similar to those previously sector of the Southern Ocean from one of the least to one of observed in the north Atlantic and which have led to ecological the best observed parts. An observing system based on ships, and economic impacts. Five countries are currently involved in the satellites, robotic sub-surface floats, moorings and recently, program, which the Scientific Committee on Antarctic Research has sensors incorporated into marine mammal tracking devices, has recognized as of high priority. Australia’s comprehensive marine been implemented and continues to evolve as new technology surveys conducted in recent years have focused on the relationship and new ideas open up new opportunities (Rintoul et al., 2001).

The Southern Ocean 15 5 – Reconstruction of past climates

The Antarctic ice sheet contains within its layers a rich archive of information on past climatic and environmental changes. As snow is successively buried it is compressed to form glacial ice. This ice carries traces of dissolved impurities, variations in water isotopes, and bubbles of air, sealed within as the snow is compacted, which can be analysed to study past atmospheric and climatic variations.

Australian ice core research dates from the late 1960s, however the early work was primarily aimed at understanding the dynamics of the ice sheet by measuring properties such as temperature and crystal size and orientation. Through the 1980s, an increased interest in palaeo-climate prompted by the realisation of recent climate change, led to accelerated international interest in retrieval of ice cores for climate studies. A number of deep drilling projects including one at Vostok in the Australian Antarctic Territory together with the development of new techniques led Antarctic ice core climate record from the Law Dome, inland from Casey to ice core records spanning hundreds of thousands of years. Station Photograph Vin Morgan

Australian contributions have focussed on ice cores from the 2006). This is the longest such record and shows overall warming relatively high snowfall areas in the coastal region of east Antarctica, in phase with that of the Southern Hemisphere, but interrupted mainly at Law Dome. In 1993 a major project there culminated in in the late 20th century, likely by strengthening of high-latitude the recovery of a 1200 m long surface-to-bedrock ice core from westerly winds: a manifestation of increasing strength of the near the Dome’s summit. This core provides a record extending back atmospheric Southern Annular Mode (SAM), itself a product some 90,000 years, with higher time-resolution for recent millennia of changes in the concentration of atmospheric ozone. than any other Antarctic ice core. It also provides information on the response of the active coastal zone of the ice sheet to the sea A 50 year continent-wide snowfall reconstruction which made level and climate changes associated with the transition from the significant use of the LD record (Monaghan et al., 2006) last Ice Age. The scientific output from this ice core research has showed, contrary to model expectations for a warming climate, made a significant contribution and improved our knowledge in that there has not been any significant change in Antarctic a range of areas from climate forcing (with studies of relevance snowfall over 50 years, although it also reveals large spatial to volcanic, greenhouse gas and solar forcing), natural climate and temporal variability. The Law Dome climate record has also variability and recent change, with connections to Australian climate, been used in hemispheric and global climate reconstructions of and are included in the 3rd and 4th IPCC Assessment Reports. the last 2000 years (Mann and Jones, 2003; Jones and Mann, 2004). The Law Dome record was the only source of proxy The emphasis on detailed time resolution enabled by the Law data for Antarctica over this period in the reconstruction. Dome ice core has been the principal contribution of the Australian programme. The high resolution allows annual layers to be counted In addition to climate reconstructions, the Law Dome ice core accurately, which gives very well dated records (Palmer et al., data provide proxies for climate forcing. In particular, the record of 2001) that can be compared, through the period of overlap, with volcanic eruptions (Palmer et al., 2001a, 2002) provides a reference instrumental meteorological data to calibrate ice core ‘proxy’ climate forcing series for modelling climate changes over recent centuries. signals (van Ommen and Morgan, 1997; McMorrow et al., 2004). Solar variability is also an important factor in understanding and modelling past climate variations. Ice core beryllium-10 data are Very few annually resolved records are available from Antarctica, used to infer past variations, and studies at Law Dome are providing and the Law Dome record has provided a fundamental resource calibration constraints that will lead to better understanding of in reconstructions of climate. This includes a recent two hundred this proxy (Pedro et al., 2006). Solar variations are also playing year reconstruction of Antarctic temperatures (Schneider et al., a role in atmospheric chemistry and climate. Studies on the Law

16 Dome chemistry and particularly on nitrate have been used to place been used to ‘hind-cast’ earlier sea ice extent, revealing a decrease limits on the size of the solar influence (Palmer et al., 2001b). of around 20% with large decadal changes superimposed.

An area of pre-eminent international impact of the Law Dome ice core program has been in the reconstruction of past atmospheric composition. This work, a collaboration between CSIRO and AAD, has provided the best records of pre-industrial and anthropogenic changes for a range of atmospheric gases

(Fig 10), including the radiatively important species CO2, CH4 and N2O (Etheridge et al., 1996, 1998; MacFarling-Meure et al., 2006). This work has been extended by wider international collaboration and isotopic studies, with recent work showing major underlying changes in methane sources over centuries prior to the increase from industrialization (Ferretti et al., 2005). Fig 11: Law Dome concentrations of methanesulphonic acid (MSA, red) and sea-ice extent (blue) from satellite measurements graphed as 3 year running means. The pale red curve shows the long-term trend (20 year running mean) (Adapted from Curran et al., 2003).

The strong maritime climate at Law Dome provides not only high resolution, but also climate information that links with mid- latitudes. Winter sea-salt levels in the ice core are connected with mid-latitude atmospheric pressure (Goodwin et al., 2004; Souney et al., 2002) and have been used as a proxy for the winter SAM strength. Recent analyses showing strong correlation between precipitation changes in south-western Australia and those in Antarctica are providing a context for the current drought in that part of Australia (van Ommen and Morgan, 2007).

Fig 10: Reconstruction of atmospheric composition of major The Law Dome ice core allows longer-term changes to be probed greenhouse gases from Law Dome ice core measurements. with particular emphasis on changes during the emergence from (MacFarling Meure et al., 2006). the last ice age. A persistent question in understanding of ice age cycles is understanding cause and effect, and hence the sequence Looking at more recent climate history, the detailed ice core of events. The high resolution of the Law Dome record allows for records are being used to understand variability during the era of much tighter dating ties to Northern Hemisphere ice cores because anthropogenic influence. Changes are seen in a range of proxies, uncertainties surrounding the air-trapping process are relatively and these can be compared with the longer term record. smaller at Law Dome. This tighter synchronization was used to tie the Antarctic changes from Law Dome with rapid climate change One parameter of particular interest in the high latitude climate in the northern hemisphere around 15 thousand years ago. The system is the extent of winter sea ice, which is potentially an results showed for the first time that Antarctic changes did not early indicator of climate change. While satellite observations follow the rapid northern hemisphere changes as had been thought, are inconclusive, showing no significant trends over the available and if anything the sequence placed the Antarctic change ahead of observing period since the late 1970s, ice core data (Fig 11) rapid northern changes by a few centuries (Morgan et al., 2002). suggest there has been a considerable decline since the mid 1900s (Curran et al., 2003). Chemical measurements from ice cores at Changes are evident in atmospheric circulation through Law Dome, and more recently from Wilhelm II Land (Foster et al., the termination of the last ice age. Comparison of chemical 2006), show a significant correlation between sulphur compounds concentrations with inland ice cores shows that the present emitted by sea ice algae and the winter sea ice extent. This maritime coastal climate at Law Dome only developed in the late correlation, established by comparison with the satellite data, has stages of the deglaciation (Curran et al., 2007) and indeed the

Reconstruction of past climates 17 full modern-day high precipitation régime developed only well into the present interglacial period (van Ommen et al., 2004).

The high resolution of the Law Dome ice core allows for detection of relatively rapid climate events that are difficult to detect in other Antarctic records. One such event – the final in a series that punctuated the last ice age – occurred around 8200 years ago and is well known from Greenland ice cores. The event almost certainly has its origins in the northern hemisphere during an outburst from a lake system created during the demise of the Northern Hemisphere ice sheets of the last ice age. The changes left a large signature in global atmospheric methane, but it is not clear if it also triggered climate Recovering a 100 m Antarctic ice core for study of climate variations responses in the southern hemisphere. The Law Dome record shows over the last few centuries. Photographer Tas van Ommen the clearest and best-timed Antarctic signature of the methane marker and reveals that there is little evidence for an accompanying which the background climate variability can be measured, and climate response in Antarctica (van Ommen et al., 2007). against which the human climate impact can be detected.

As the mechanisms underlying the climate links and the proxies For example, the change from 41,000 year cycles to 100,000 year measured in the ice are better understood, there is considerable climate cycles occurred during the Plio-Pleistocene time period – a potential to shed light on observed climate changes in Australia period which has attracted considerable interest from Australian as well as Antarctica and the southern hemisphere generally. palaeoceanographers. Cores taken from the sea bed contain Such work will be most fruitful as it draws together multiple proxy records of past flora and fauna whose shells and skeletons and multiple ice core records. With current international concern contain a record of sea temperature and water characteristics. on climate change and in the context of increasing international From these ‘proxies’ Australian scientists have materially assisted collaboration directed toward ice core research, plans are in train our understanding of the evolution of the climate, from the start to extend this work (Brook and Wolff, 2006). Under the banner of the Cenozoic to historical times during which analyses of air of the International Partnership in Ice Core Sciences, plans are trapped in ice cores can provide accurate data on climates. being developed to establish a denser network of Antarctic ice cores and also to recover an ice core extending back over The circumpolar Southern Ocean formed when Australia broke 1 million years when the Earth’s glacial-interglacial climate cycle away from Antarctica and began drifting north about 83 million changed from 41,000 years to its present 100,000 years. An ice years ago, according to seismic reflection, magnetic data and core spanning this period will allow the relationship between drilling of the Antarctic and Australian margins. Drilling by the atmospheric composition and environmental temperature to be Ocean Drilling Program1 led by Australian scientists showed determined. As it is predicted that some of Antarctica’s oldest ice that a deep seaway opened between Australia and Antarctica is to be found in Australia’s Antarctic Territory it behoves Australia about 35-33.5 million years ago (Exon et al. 2002; Stickley to take international leadership in such a fundamental study. et al. 2004), concurrent with glacial ice first reaching sea level on the Antarctica coast (Barrett 1999; Cooper and O’Brien The keys to understanding some processes controlling climate 2004). Oxygen isotope measurements on marine microfossils and ice-sheet dynamics, and atmospheric CO2 lie in oceanic indicate a major increase in global ice volumes and cooling of records. Palaeoceanography has contributed to the understanding the ocean at ~33.9 million years ago (Zachos et al. 2001). of these climate dynamics on three main time scales: 1) the Cenozoic time frame (65.5 million years ago to present) Australian scientists developed a model for the inception of Antarctic over which the ice sheets, the ocean basins, and continental glaciation based on the thermal isolation of Antarctica resulting positions have reached their current arrangements; 2) the from the development of the Antarctic Circumpolar Current. This Plio-Pleistocene time frame (5.3 million years-11,000 years allowed the East Antarctic Ice Sheet (EAIS) to develop (Kennett ago) during which the 100,000 year cycle of orbital forcing 1977; Kennett and Exon 2004). An alternative view from climate has dominated climate variability and in which the Southern modeling suggests falling global atmospheric CO2 levels were the Ocean has played a controlling role in determining atmospheric cause of Antarctic cooling (DeConto and Pollard 2003; Huber et al.

CO2; and 3) the Holocene (11,000 years ago to the present), in 1 Predecessor to the Integrated Ocean Drilling Program, which Australia will join in 2008.

18 2004). Integrated Ocean Drilling Program sediment cores show The EAIS fluctuated mainly in a 41,000 year cycle associated cooling of the Arctic Ocean at the same time the EAIS developed with orbital tilt (Grützner et al. 2003; Naish et al. 2001), until supporting the role of CO2 in polar cooling and ice sheet formation, ~900,000 years ago when global and Antarctic climate cycles rather than the instigation of the Antarctic Circumpolar Current. changed to be dominated by 100,000 year cycles (Tziperman and Carbon dioxide levels, inferred from geochemical proxies, were Gildor 2003). Australian led ODP drilling off Prydz Bay, suggests 1000 to 2000 ppm, during the warm, ice-free “Greenhouse” that the highest ice volumes ever recorded were reached prior world of the early Cenozoic (Pagani et al. 2005; Pearson and to 1.1 million years ago (Cooper and O’Brien, 2004), and the

Palmer 2000). CO2 levels have been below 500 ppm since present Antarctic ice sheet state developed between 500,000 and “Icehouse” climates began ~33 Ma (Pearson and Palmer 2000) 900,000 years ago (Fink et al. 2006; Whitehead et al. 2006). during which time the Antarctic Ice Sheet has oscillated between ~50%-125% of its current size )Cooper and O’Brien 2004; Donda Finally, marine sediments indicate warmer-than-present conditions et al. 2007; Pekar and DeConto 2006; Wade and Palike 2004). during the progressive cooling of the Plio-Pleistocene age (McKelvey et al. 2001; Whitehead et al. 2006). The role of Antarctic ice- The Southern Ocean has played a key role in modulating volume variations in Pleistocene sea-level cycles is still a matter

Southern Hemisphere climate and atmospheric CO2 over the Plio- of debate (Rohling et al. 2004) because the indicators of sea Pleistocene and Australian scientists have been closely involved level (for example oxygen isotope ratios in marine microfossils in field and theoretical studies. Geochemical models suggest or coral terraces) do not uniquely identify the locations of ice that Southern Ocean sea-ice, circulation and productivity could sheets responsible for the sea-level changes. Thus there is a all play a role in controlling atmospheric CO2 (Howard and Prell need for direct observations on the maximum extent of the EAIS 1994; Sigman and Boyle 2000), but insufficient data constrains at glacial maxima; i.e. we need to know where the edge of the our full understanding of the past behavior of these physical and ice sheet has been (O’Brien et al. 1999). Since the EAIS edge at biogeochemical records. Nevertheless, Southern Ocean cycles of the glacial maxima is today located under water, obtaining well- temperature (Brathauer and Abelmann 1999; Howard and Prell dated records of ice-sheet grounding requires the recovery and 1992), sea ice, (Armand and Leventer 2003; Crosta et al. 2004) analysis of further marine sediment samples from shelf basins. carbon isotopic variability (Moy et al. 2006) and other variables are all nearly “in-phase” with global climate cycles. The possible The global view of Holocene climate variability, which spans the mechanisms maintaining this near-synchronicity include the level of period from 11,000 years ago to the present, is one of relative atmospheric CO2 , thus suggesting Southern Ocean processes are stability and low variability, yet little is known of Southern Ocean in themselves important global climate feedback mechanisms. Holocene variability. Some core records from the South Atlantic suggest mid-Holocene cooling (Hodell et al. 2001). However, there Additionally, Southern Ocean palaeoceanographic data have given are few marine records of sufficient resolution in the Australian us access to a range of environmental variability unattainable Antarctic sector to detect Holocene events such as the 8,200 year in the historical record and subsequently provides limits on the ago (cooling) event, an anomaly observed in Northern Hemisphere dynamic range of key physical and ecological components of records (Morrill and Jacobsen 2005). Australian research reveals the Southern Ocean. Microfossil data has shown that biome records capable of resolving Holocene variability do not show boundaries like the Antarctic Polar Front Zone (APFZ), one of the significant Holocene climate anomalies in sea ice extent or sea- most extensive biological gradients on the planet (Tynan 1998), surface temperature, suggesting that palaeoclimate variations have moved as much as 5 degrees of latitude during the glacial- are not uniform around the Antarctic and that records from the interglacial cycles of the past ~500,000 years (CLIMAP 1981; Australian Sector may have unique characteristics not seen in the Morley 1989; Howard and Prell 1992; King and Howard 2000; South Atlantic or other basins (Howard et al. 2007). Sediment Armand and Leventer 2003; Gersonde et al. 2005). The ecological, cores from continental shelf basins do, however, suggest variability physical oceanographic, and biogeochemical implications of such in bottom-water production and these records may put modern large-scale movements of the APFZ are dramatic. These datasets changes in deep-water circulation into perspective (Harris et al. carry lasting messages about the structure and biodiversity of 2001). Some high-accumulation-rate deposits in continental shelf Southern Ocean ecosystems: their persistence, ability to re- basins can resolve interannual-to-interdecadal-scale variability arising organise, and resilience in the face of climate perturbations. from such modes of variability as El Niño, the Southern Annular Mode, and solar variability (Crosta et al. 2005; Leventer et al. 1996; Marine records equally provide evidence, unattainable by ice cores, Stickley et al. 2005). Such records are important in being directly on the behavior of the ice-sheet itself in the face of large-scale comparable to ice-core records like those recovered at Law Dome. climate forcing by changes in the Earth’s orbit, CO2, and sea-level.

Reconstruction of past climates 19 6 – Antarctica’s Atmosphere

The Bureau of Meteorology (BoM) has been involved in collecting weather data in Antarctica since the first Australian National Antarctic Research Expedition of 1947/48 and continues to collect surface and upper air observations from the three continental stations at Casey (1969-present), Davis (1957-present) and Mawson (1954-present). Casey and Davis maintain a twice daily upper air observational program using radiosondes with Mawson maintaining a single daily radiosonde flight. All three stations are part of the World Meteorological Organisation (WMO) Global Upper Air Network. Observations from the three continental stations not only provide a basic dataset for study of the Antarctic and global climate but they provide data for assimilation by global and regional Numerical Weather Prediction (NWP) systems used by both regional and global forecasting offices. The upper air program contributes valuable data for studies of climate processes in the lower stratosphere.

The observations at Australia’s three manned Antarctic stations and supporting Antarctic forecasting. Regional and global NWP are supplemented by data from AAD automatic weather stations systems have developed significantly over the last 10 years, to the (AWS) that have been deployed at more than 20 remote sites in point of not only providing reliable forecasting support but giving the interior of the Australian Antarctic Territory since 1982. These research scientists a valuable tool with which to study the Antarctic measure a range of different meteorological parameters every atmosphere. These tools have allowed Australian meteorologists hour and relay the data to Australia via a satellite link. The data are to better understand the dynamics of significant weather events automatically forwarded to the global meteorological network and affecting Australian Antarctic stations (Adams 2004a, 2004b, used for meteorological forecasting, to support aircraft operations, 2005). International advances in Antarctic meteorology have also to provide climatic information (e.g. Allison, 1998), for studies benefited greatly from modern regional Antarctic NWP systems, of the surface wind processes over the ice sheet, and to support with the Australian work by Parish and Bromwich (1987) on the a variety of other research programs such as the interpretation near surface flow over Antarctica being significantly updated and of proxy climate data in ice cores (e.g. Xiao et al., in press). expanded (Parish and Bromwich 2007) by the analysis of NWP data from the Antarctic Meso-scale Prediction System, AMPS, (Powers The accuracy of Antarctic weather forecasts is based on research et al., 2003). Work is under-way to develop an Antarctic regional and development undertaken within the Antarctic Meteorological version of the newly acquired Unified Model (UM) from the UK Section (AMS) of the Bureau of Meteorology. Research and Meteorological Office. The UM is an advanced NWP system offering development within the AMS includes continued development an improved dynamic and thermodynamic modelling environment of polar NWP systems, developing skills in interpreting remotely which should see improvements to both weather forecasting and sensed data from the Casey and Davis High Resolution our understanding of the high southern latitude atmosphere. Picture Transmission systems, and researching case studies on significant local weather events as aids to developing a better Since 2003 the AAD and the BoM have undertaken balloon-borne understanding of Antarctic weather and improving forecasting ozone measurements at Davis. This work has contributed to two techniques in support of the Australia’s Antarctic program. international projects (Quantitative Understanding of Ozone Losses

by Bipolar Investigations, and the International Polar Year Oracle-O3 The Bureau of Meteorology’s Limited Area Prediction Systems project), and is a component of AAD investigations on the physics (LAPS) (Puri et al. 1998), has been operational in Australia since of ozone depletion and Polar Stratospheric Clouds (Grytsai et al., the late 1990s, and an east Antarctic version of the system (ALAPS) 2007). Ozone resides primarily in the stratosphere (10-50 km was developed in 1999 (Adams 2004), and run in support of the altitude), where it plays a central role in radiative processes of program until 2005. Since early 2005 a polar-stereographic version the upper atmosphere, and acts as a shield protecting life from of ALAPS, called PolarLAPS (Adams 2006), has been in operation harmful ultraviolet radiation. Polar ozone is of particular interest

20 as it should show the first significant signs of a reduction in the man-made ‘ozone-hole’ phenomenon. The Davis measurements are also part of larger ozone program conducted by the BoM which includes in situ and remote sensing measurements of atmospheric ozone at Macquarie Island. A related program of surface ultraviolet measurements undertaken by the Australian Radiation Protection and Nuclear Safety Organisation in the Antarctic and Southern Ocean is providing baseline information on human and biological responses to ultraviolet radiation levels (Gies et al., 2004).

Measurements at Davis by a Light Detection and Ranging (LIDAR) instrument are investigating transport of atmospheric aerosols which may influence the radiative balance of the atmosphere and play a role in cloud formation. Further understanding of cloud formation processes are called for by the IPCC (2007). LIDAR measurements have provided important details on the size distribution of aerosols of meteoritic origin that suggests these aerosols may play a more important role in perturbing climate than previously thought (Klekociuk et al., 2005). Separate studies of the aerosols that comprise Polar Stratospheric Clouds have quantified the importance of planetary scale waves in controlling the specific thermal conditions required for aspects of ozone depletion chemistry to take place.

The LIDAR and the Mesosphere-Stratosphere-Troposphere radar Photo: Frederique Olivier. Davis Lidar at Davis have provided the first southern hemisphere common volume measurements of Polar Mesospheric Clouds and Polar Mesosphere Summer Echoes. These two phenomena are related to poorly characterized region is important to our understanding the formation of extremely small ice particles at high altitudes in the of global climate (Denman et al., 2007; Allen et al., 2006). summer polar atmosphere. The measurements have confirmed that a significant difference exists between the southern and northern The waves that force north-south circulation patterns in our upper polar summer atmospheres at this height, with the temperatures atmosphere vary widely in their time scales and dimensions. above Davis being approximately 3-5ºC warmer than the same The paths of these waves can be diverted by the atmospheric northern latitude (Morris et al., 2007). The Davis observations environments that they pass through which can absorb energy provide support for recent refinements to global circulation and momentum from them. Australian scientists have used radars modelling that includes a more detailed description of the large- for atmospheric wind observations and several optical techniques scale, pole-to-pole flow that occurs in the middle atmosphere. for atmospheric temperature observations at various heights. These measurements, which began at Mawson in the early 1980s The upper reaches of the “middle atmosphere” (10-100 km), have (Macleod and Vincent 1985; Phillips and Vincent 1989) and been a focus of Australian Antarctic research for some time. The continue at Davis to this day, have provided the background to attention of the climate modelling and numerical weather prediction advance our knowledge of dynamics and wave-coupling in this communities has recently turned to the middle atmosphere because region. Recent contributions by Australian scientists and their its inclusion provides better weather forecasting and improved collaborators describe the middle atmosphere in detail including climate change predictions. Large and small-scale waves have a the characterization of planetary scale waves and tides (Burns profound effect on the air motion and thermal environment at these et al., 2003; Innis and Klekociuk 2006; Murphy et al., 2006; 2007); levels. This is most apparent in the polar regions in the presence the variation of smaller scale atmospheric wave activity through of north-south flows driven by the waves. The resulting vertical air normal years and through the anomalous ‘stratospheric warming’ motions act to heat or cool the atmosphere with consequences of 2002 (Dowdy et al., 2007a,b); the identification of wintertime for stratospheric ozone and mesospheric ice crystal growth. It has temperature trends in an atmospheric layer near 87 km (French et al., become clear that an improvement of our understanding of this 2005) which may be a proxy indicator for climate change; and the effect of winds and waves on layered structures in the stratosphere

Antarctica’s Atmosphere 21 7 – Concluding remarks

The preceding pages show that Australia has played a significant role in many aspects of high-latitude climate research over several decades. It is well positioned to continue to contribute to international programs and projects in the future to better understand the role of Antarctica in the global climate system. Australia’s Antarctic program, unlike that of most other nations, is conducted as part of the Government’s stated goals for Antarctica as expressed through its approved Science Strategy. The program strongly encourages interdisciplinary approaches which are now needed to enable us to predict the consequences of changes on the environment as a whole. Working through its four sub- programs, which collectively address the Government’s goals for scientific research, Program Leaders are charged with ensuring that all researchers, whether from within the Antarctic community in Government agencies or from the universities or overseas, integrate their work and focus on agreed objectives. Many international researchers participate in the program; in 2006/07 scientists from 116 institutions in 29 countries conducted about 120 projects. The program is open to researchers from around the world who wish to pursue studies in line with the Government’s approved Science Strategy, available on www.aad.gov.au. The inauguration of Australia’s inter-continental air link is likely to attract more international interset in the program.

Early research in Antarctica was largely disciplinary, in keeping presents. Ozone studies, noctilucent clouds and global with the development of science worldwide. The past decade, circulation models of pole-to-pole flows are contributing or so, has seen strong development of interdisciplinary themes. knowledge about a poorly understood part of the earth’s Thus our marine biological research is very closely integrated atmosphere and the drivers of environmental change. with studies on sea ice dynamics and water chemistry and temperature. In recent years the Antarctic Climate and Ecosystems Australia is faced with considerable opportunities to take world Cooperative Research Centre based at the University of Tasmania leadership in certain aspects of high-latitude climate science. We (a partnership between the CSIRO, the Bureau of Meteorology, have an internationally acclaimed standing in Antarctic science the Australian Antarctic Division and the University of Tasmania particularly in the fields of oceanography, ice studies and marine together with some national and international associates) has ecology. The 4th Assessment of the IPCC drew attention to the embarked on studies to quantify the consequences of ocean paucity of knowledge about the part played by sea ice, glacial variability and change on Southern Ocean ecosystems and is collapse and other polar phenomena in predictive models. We developing models to help explain the relationships between the have the capacity to be a significant interpreter of the causes and

physical forcing of such phenomena as increased CO2 uptake consequences of climate change and variability in Antarctica and and biotic response. Studies are underway to track and monitor the provider of scientific advice through the IPCC to governments how pelagic and benthic ecosystems respond to the decreasing around the world. Since the first Australian expedition to Antarctica

pH of the Southern Ocean due to increased uptake of CO2. in 1911 Australia has invested considerable resources in building a world class program in Antarctic science. Now, more than at Our work in the middle atmosphere is focused on explaining any other over the past century, it is time to put Australia at the atmospheric couplings in climate science, making particular hub of global understanding of the southern polar region. use of the environmental conditions which Antarctica

22

8 – References

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