Antarctica: Role in Global Climate

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Antarctica: Role in Global Climate

Introduction

The world's climate system is, in some ways, like a complex machine. Heat is moved from place to place by ocean currents and by winds; winds, ocean currents, sea ice, land ice, snow cover, vegetation, and other factors affect climate and are affected by climate. The chemical composition of the atmosphere, which is being changed by humans, is also a factor.

Antarctica is a unique part of the Earth's climate machine. It stores most of the world's freshwater, generates large amounts of sea ice, and is surrounded by pole-circling (circumpolar) currents of air and water. Antarctic conditions influence the pattern of ocean circulation called the thermohaline circulation or Great Conveyor Belt, which transports heat from the tropics toward the poles and increases the ability of the oceans to absorb carbon dioxide from the atmosphere.

Direct observations of Antarctica are difficult to make because of its remoteness and harsh weather. As a result, records of Antarctic climate date back less than 50 years. Satellite observation began in the 1970s and has greatly increased scientists' ability to understand what is happening in Antarctica and its role in global climate. Although uncertainties remain in the understanding of Antarctica's place in the climate system, scientists are beginning to unravel how human-caused climate changes are changing Antarctic weather, and how those changes might affect global climate.

Historical Background and Scientific Foundations

Mapmakers speculated about the existence of a south-polar continent for centuries, but human beings did not glimpse Antarctica until 1820. Although explorations and heroic dashes for the South Pole added to scientific knowledge over the following century, it was not until the International Geophysical Years (IGY) in 1957 to 1958 that modern scientific monitoring of the Antarctic continent began in earnest. In preparation for the IGY, governments established a number of year-round bases in Antarctica, some of which are still in operation. Today, Antarctica is surveyed constantly by ships, permanent bases, free-floating sea buoys, weather balloons, aircraft, and satellites.

In the last 10 to 20 years, understanding of Antarctic climate processes and their connection to the global climate system has advanced. The roles of sea ice, surface ice, melting, reflection of sunlight by ice and clouds, anthropogenic (human-caused) changes to the ozone layer, global warming, and circumpolar circulations of sea water and wind are all better understood now than a few decades ago. A few important aspects of Antarctic climate follow.

Sea Ice and Thermohaline Circulation

The area covered by sea ice in the Antarctic Ocean (also called the South Polar Ocean or Southern Ocean, namely all waters south of 60° south latitude) varies with the season. During the Antarctic summer, sea ice covers 1–1.54 million sq mi (3 or 4 million sq km); in the winter, it covers 6.6–7.73 million sq mi (17–20 million sq km).

Sea ice has several interactions with climate. First, snow and ice are highly reflective. They reflect solar energy to space like a mirror. Open seawater, however, is a comparatively efficient absorber of solar energy. Therefore, the long-term ice shelves and seasonal sea ice of Antarctica, which both consist of floating sheets of frozen sea-water, reduce the amount of energy Earth absorbs. When global warming melts sea ice, Earth becomes a better absorber of heat, which encourages further warming. This is a form of positive feedback: warming causing further warming.

Second, sea ice isolates the water from the air, reducing the transfer of energy between winds and ocean currents.

Third, sea ice affects the global ocean circulations as it freezes and melts. When sea water freezes, its salt cannot be accommodated in the atomic structure of the forming water crystals and is pushed out. Small pockets of saltier (harder to freeze) water form in the ice. These tend to melt their way downward to unfrozen ocean water below. Freezing sea ice is therefore said to reject salt. Salt rejection makes the ocean near new sea ice saltier and, therefore, denser. (When salt dissolves in water it increases its weight without increasing its volume, so salty water is denser than freshwater.) This denser, saltier seawater sinks, pushing deep water aside and causing current to flow. However, when sea ice melts, it adds freshwater to the surrounding ocean, reducing its salinity (saltiness). Both of these processes affect the way in which deep and polar waters trade places with surface and tropical waters over time.

Since saltier water freezes at lower temperatures than less-salty water, the salty water near forming sea ice must be chilled to a lower temperature before it, too, freezes. This enables the wind to remove more heat from the sea near forming sea ice. Colder water, like saltier water, is denser than other water, so cooling also contributes to the sinking of water near the poles. As the area of ocean covered by Antarctic sea ice varies by thousands of square miles from winter to summer, the freezing and melting of sea ice are significant drivers of ocean circulation.

The overturning or circulation of the world's oceans driven by heat and saltiness is called the thermohaline circulation (thermo for heat, haline for salt). The thermohaline circulation transports heat from the equator to the polar regions, which has many effects on climate, including making Europe's climate milder. By bringing water from the bottom of the ocean to the top, it increases the ocean's ability to absorb carbon dioxide from the atmosphere.

Ice shelves in Western Antarctica, particularly along the shores of the Antarctic Peninsula, have been destabilized by anthropogenic global warming and are melting

at a faster rate. In a 35-day period in 2002, an area of floating ice called the Larsen B ice shelf, undermined by warm water currents, disintegrated completely into thousands of icebergs that floated away and melted. The shelf had been the size of the state of Rhode Island, 1,253 sq mi in extent (3,250 sq km) and 720 ft (220 m) thick. In 2006, scientists with the British Antarctic Survey announced that they had shown a definite climatic connection between this event and human-caused global warming. Warm westerly winds blowing across the peninsula, which climate models attribute to anthropogenic warming, were clearly responsible for the breakup of Larsen B.

The Antarctic Ice Sheet

Antarctica's ice sheet, which covers most of the continent, has an average thickness of 1.5 mi (2.5 km) and holds about 7 million cubic mi (29 million cubic km) of ice, about 90% of the world's freshwater. This is enough water to raise sea level worldwide by about 200 ft (61 m) if the entire ice sheet were to melt. Snowfall adds mass to the ice sheet while glaciers flowing to the sea and chunks of ice breaking off the edges of ice shelves remove it.

Ice that is floating in water does not deepen that water when it melts, so the melting Antarctic sea ice does not raise sea levels directly. However, melting of ice that rests on land does raise sea levels. Both of Earth's two great overland ice sheets, in Greenland and Antarctica, are now known to be melting. Further, ice shelves act as dams or barriers holding back (or at least slowing down) glaciers and ice rivers transporting ice from inland to the coast; therefore, when ice shelves shrink or disappear, melting of the Antarctic ice sheet can be accelerated.

Speedup of ice movement from this and other causes has been observed for several hundred glaciers in Western Antarctica, where most of Antarctica's recent warming has happened. This area has warmed by about
4.5°F (2.5°C) over the last 50 years, as much as anywhere on the planet. Eastern Antarctica is higher in altitude, and, therefore, colder than Western Antarctica. It also tends to be better isolated from the rest of the climate system by the ring-shaped circumpolar circulations of westerly winds and ocean currents. As a result, Eastern Antarctica has undergone slight cooling over the last several decades even as the rest of the world, including Western Antarctica, has seen significant warming.

WORDS TO KNOW

ANTARCTIC CIRCUMPOLAR CURRENT: An ocean current that circles Antarctica from west to east (clockwise, looking down on the continent), enabling mixing of the waters of the world's oceans. Also termed the West Wind Drift.

ANTHROPOGENIC: Made by people or resulting from human activities. Usually used in the context of emissions that are produced as a result of human activities.

BIPOLAR SEESAW: The tendency of climate to warm at the North Pole while it cools at the South Pole and vice versa. Paleoclimatic data show that this seesaw effect has occurred many times in the geological past and is related to changes in ocean circulation, but scientists do not yet completely understand the mechanism of the seesaw.

BUOYS: Tethered or free-floating devices that bear navigational aids, instruments, and in some cases radio equipment for automatically collecting and reporting data on oceanic and atmospheric conditions. Buoys may float on or beneath the surface, depending on their purpose.

ICE SHEET: Glacial ice that covers at least 19,500 square mi (50,000 square km) of land and that flows in all directions, covering and obscuring the landscape below it.

ICE SHELF: Section of an ice sheet that extends into the sea a considerable distance and that may be partially afloat.

OZONE LAYER: The layer of ozone that begins approximately 9.3 mi (15 km) above Earth and thins to an almost negligible amount at about 31 mi (50 km) and shields Earth from harmful ultraviolet radiation from the sun. The highest natural concentration of ozone (approximately 10 parts per million by volume) occurs in the stratosphere at approximately 15.5 mi (25 km) above Earth. The stratospheric ozone concentration changes throughout the year as stratospheric circulation changes with the seasons. Natural events such as volcanoes and solar flares can produce changes in ozone concentration, but man-made changes are of the greatest concern.

SOUTHERN ANNULAR MODE: Pattern of oscillation (regular back-and-forth change) in atmospheric pressure and windspeeds that occurs in the extratropical Southern Hemisphere; the southern counterpart of the North Atlantic Oscillation. Also termed Antarctic Oscillation or High Latitude Mode. Scientists have attributed the increasing magnitude of the southern annular mode to stratospheric ozone depletion and greenhouse gas increases.

THERMOHALINE CIRCULATION: Large-scale circulation of the world ocean that exchanges warm, low-density surface waters with cooler, higher-density deep waters. Driven by differences in temperature and saltiness (halinity) as well as, to a lesser degree, winds and tides. Also termed meridional overturning circulation.

Circumpolar Flows

Both air and water circle Antarctica from west to east like cars driving around a racetrack. These winds, like the general westward drift of weather all over the planet, are driven by the Earth's axial rotation and temperature

differences between the poles and equator. Ocean currents flow in a similar pattern around Antarctica. Circumpolar winds also blow around the North Pole, but masses block the formation of a circum-Arctic ocean current. The westerly circling of water around Antarctica is called the Antarctic Circumpolar Current (ACC). The ACC plays an important role in the thermohaline circulation, acting as a blender for the waters of the world's oceans.

Short-term Climate Oscillations

Long-term climate cycles include ice ages lasting 100,000 years, caused by regularly recurring changes in Earth's orbit. Climate also shows much more rapid cycles of climate variability. The most important of these in the Antarctic region is the Southern Annular Mode or SAM, also called the Antarctic Oscillation. “Annular” means ring-shaped, and an oscillation occurs when a physical system switches repeatedly between two conditions. The SAM is an oscillation involving weather conditions over the South Pole and in the ring of eastward-moving air around Antarctica. In one state of the oscillation, pressure is low over the South Pole (central Antarctica) and high in the circumpolar wind ring; in this state, the westerly winds blow more strongly. At the other end of the oscillation, conditions are reversed. Pressure is high over the pole and low in the wind ring (also called a circumpolar vortex), which blows less strongly. The SAM shifts from one state to another over weeks, months, or years in an irregular way, but pressure always goes up over the center of the continent when it decreases in the circumpolar vortex and vice versa.

Changes in the SAM have been linked to climate changes in the Southern Hemisphere. Analysis of weather-balloon data measurements from 1969 to 1998 shows that the SAM has been spending more time at the positive or strong-wind end of its cycle. This, in turn, may be a result of human-caused changes in the atmosphere. Specifically, certain industrial chemicals (mostly chlorofluorocarbons) have caused a hole to appear in the ozone layer over Antarctica for part of every year since the 1980s. The hole reached a record size in 2000. Normally, the ozone layer absorbs solar energy and heats the stratosphere (upper atmosphere). Loss of ozone over central Antarctica, which occurs every year from September to December, therefore cools the stratosphere. September–December stratospheric temperatures dropped about 18°F (10°C) from 1985 to 2002.

In 2002, David W. J. Thompson and Susan Solomon, climate scientists working at the U.S. National Oceanic and Atmospheric Administration (NOAA), proposed a two-part theory concerning the SAM: 1) Changes in the SAM could, they said, account for about half of the observed warming of the Antarctic Peninsula and the southern tip of South America and about 90% of the slight cooling seen over central Antarctica. 2) Changes in the SAM could in turn be traced to ozone destruction caused by human activity. The second part of this theory was more controversial than the first.

How changes in the SAM might affect the rest of the global climate system and be affected in turn by it is still uncertain. However, scientists have increasingly been modifying their older view that the Antarctic climate is more or less irrelevant to global climate, isolated by the circumpolar vortex. A surprisingly strong connection between Antarctic and global climate has recently been discovered in the bipolar seesaw.

Bipolar seesaw

A connection between Antarctic climate and the climate of the north-polar region was first proposed in 1998. Comparison of climate information from ice cores from Antarctica and from Greenland, near the North Pole, showed that in case after case, over tens of thousands of years, while Greenland was undergoing a warming trend Antarctica was cooling, and while Antarctica was warming, Greenland was cooling. This back-and-forth pattern was dubbed the bipolar seesaw. (“Bipolar” means two poles, in this case the North and South Poles.)

The mechanism proposed for the bipolar seesaw is as follows. The thermohaline circulation of the oceans moves large amounts of heat northward in the Atlantic Ocean. This circulation is partly driven by the sinking of cooled waters near Antarctica. When the thermohaline circulation slows or stops, less heat travels northward through the Atlantic, while less cold water is removed from the vicinity of Antarctica. Thus, Greenland cools while Antarctica warms. When the thermohaline circulation starts up again, the pattern is reversed. Greenland warms as heat is transported northward and Antarctica is cooled.

IN CONTEXT: ICE SHELVES

A Rhode Island-sized piece of one of Antarctica's floating ice shelves broke up into a fleet of thousands of icebergs over a few weeks in early 2002. Ice shelves are the floating edges of continental glaciers that form where a glacier flows out over the sea. The shelves that cover most of Antarctica's coastal inlets (narrow strips of water running into the land or between islands) and bays are the outlets of faster-moving currents called ice streams that drain ice from the interior of ice sheets.

In 2002, Thomas Stocker, a physicist at the University of Bern, Switzerland, suggested a challenge to the seesaw theory. Ice-core data showed that as Antarctica was warming steadily from about 19,000 years ago to

10,000 years ago, a sudden, relatively brief (1,800-year) Antarctic cooling event, named the Antarctic Cold Reversal, occurred. According to the seesaw hypothesis, Stocker said, this should have occurred at the same time as the sudden warming seen in Greenland 14,500 years ago. However, it actually occurred about 500 years too soon, while the climate was still warm in Greenland. This, Stocker said, was a serious challenge to the bipolar seesaw. Relatively rapid changes in Antarctic climate, he argued, on the scale of decades or centuries, were probably isolated from the rest of the world's climate by the circumpolar vortex and the Antarctic Circumpolar Current.

However, in 2006, a team of scientists from ten European countries, also using ice-core data, validated the bipolar seesaw for the period from 55,000 to 10,000 years ago. During this interval, even short, weak temperature changes in Antarctica are matched quickly by changes in Greenland and thus, presumably, in the thermohaline circulation. The apparent time-mismatch between Greenland and Antarctic temperatures during the Antarctic Cold Reversal that Stocker had noted was probably due to imprecise matching of the layers in Greenland and Antarctica ice cores. The 2006 seesaw conclusion was reached using a new ice core from Dronning Maud Land in Antarctica. This allowed for higher-resolution climate reconstruction than earlier ice cores because more snow falls each year in Dronning Maud Land, laying down thicker annual ice layers that are easier to count.

These results show that the Antarctic climate is in fact tightly linked with global climate. Given the circumpolar wind and ocean currents, which should have an isolating or decoupling effect between Antarctica and the rest of the world, this result is surprising. A group of Danish scientists from the Ice and Climate group at the Niels Bohr Institute, University of Copenhagen, that were involved in the 2006 confirmation of the bipolar seesaw released a statement that said it was “really astounding how systematically heat is moved between the north and south hemisphere with the Seesaw, causing really dramatic climate changes during the glacial period.”

Impacts and Issues

Antarctic climate, like global climate change, is nothing new. Cylinders of ice up to 2 mi (3.2 km) long, drilled from thick deposits in Antarctica and Greenland, have supplied an 800,000-year archive of air samples that shows that Earth's climate has always varied, often quickly and dramatically. Changes in Earth's orbit around the sun and other factors have caused many periods of global cooling and warming.

However, the situation today is different. In the last few years, scientific evidence has indicated that the recent rapid warming of global climate is caused mostly by human activity. Changes in Antarctic climate, including the breakup of ice shelves, accelerated glacial movement, increased snowfall in some areas, and intensified climate oscillations have all been linked to anthropogenic climate changes, including ozone depletion and warming.

The consequences of large amounts of Antarctic melting could be catastrophic. Melting of the West Antarctic ice sheet alone (where most warming is seen to date, and where most future warming is expected to happen) would raise sea levels by 20 ft (6 m). About 100 million people live within about 3 ft (1 m) of today's sea level, and about 600 million live within about 20 ft (6 m) of sea level. Recent work has shown that although ice is accumulating in some parts of Antarctica, it is being lost in others, with loss outpacing gain. Overall, Antarctica is losing about 36 cubic mi (152 cubic km) of ice per year, causing about 0.016 in (0.4 mm) of sea level rise per year.

Despite recent progress in the understanding of Antarctica, its role in global climate change remains uncertain. For example, it is theoretically possible that the bipolar seesaw could be controlled by pushing on either its northern or southern end—that is, by causing climate changes in either the Arctic, the Antarctic, or both. Human-caused changes are indeed happening in both regions today, but it cannot yet be predicted whether these pushes might cause rapid or significant change in thermohaline circulation of the oceans.

Primary Source Connection

Seventy percent of the world's freshwater is contained in the Antarctic cryosphere. The cryosphere is the frozen part of the Earth's surface, which may be ice sheets, ice shelves, glaciers, snow cover, or any other frozen form. This article examines the response of global climate change on the Antarctic cryosphere and how that response contributes to further global climate change.

Ian Allison is a research scientist with the Australian government's Antarctic Division and a contributing writer for Australian Antarctic Magazine.

ANTARCTIC ICE AND THE GLOBAL CLIMATE SYSTEM

Planet Earth is a natural greenhouse. Some naturally occurring atmospheric trace gases, called greenhouse gases, permit incoming solar radiation to reach the Earth's surface but restrict the outward flow of infrared radiation. Carbon dioxide and water vapour absorb this outgoing infrared energy and re-radiate some of it back to ground level. This greenhouse effect is essential to most life on Earth. Without it the average temperature of the surface would be a frigid minus 18°C, rather than about 14°C as it is today.

But the concentration of greenhouse gases in the atmosphere, especially carbon dioxide, has been increased by human combustion of fossil fuels, exacerbated by deforestation. Since the Industrial Revolution began, carbon dioxide levels have risen from 280 parts per million by volume (ppmv) to 370 ppmv, and are reliably predicted to reach double pre-industrial levels in the second half of this century. Humans have also added other greenhouse gases such as methane, CFCs, and nitrous oxide to the atmosphere. The combined effect of these additional gases will be a rise in global temperatures, predicted by climate models to be 1°C to 4°C, by the end of the 21st century.

Global warming will not be uniform over the earth because of the complex interactions within and between oceans, atmosphere, land surface, clouds, biological systems and ice and snow. Some of the largest changes are predicted to occur at high latitudes. Exposed ocean or bare earth caused by the loss of ice and snow cover through melting will result in increased absorption of solar energy, which in turn will further reduce ice and snow cover leading to an amplified effect—a positive feedback. Against this, however, is an increase in heat fluxes from the ocean to the atmosphere—a negative feedback—caused by a decrease in sea ice.

A central objective of Australia's Antarctic program is to understand the role of Antarctica in the global climate system. This requires us to study Antarctic processes contributing to the climate system, determine the response of the Antarctic to climate change and seek evidence of past and present change in the region. Many important Antarctic climate-related processes involve ice. Ice and snow (the ‘cryosphere’) are important components of climate, with snow in particular limiting absorption of solar energy at the surface through its high reflectivity (‘albedo’). Freezing of water and melting of ice involve latent heat exchange, and snow and ice on land or sea inhibit heat transfer. The water volume stored in ice sheets and glaciers is a major factor in considering sea level change. Ice and snow also provide evidence of past change from the ice core climate record and visual evidence of ongoing change due to melt.

All these factors make it important to understand the role of ice and snow in the climate system, a need recognised in the recent establishment of a new international research initiative, Climate and Cryosphere within the World Climate Research Programme. The Australian Antarctic glaciology program contributes to this program with cryosphere studies taking in Antarctic sea ice, the continental ice sheet including ice core climate records, subantarctic glaciers and abrupt change.

Sea ice

The extent of Southern Hemisphere sea ice (frozen sea) varies seasonally by a factor of five, from a minimum of 3– 4 million km² in February to a maximum of 17–20 million km² in September. When the ice forms it ejects salt to the ocean, destabilising the water column and deepening the surface mixed layer. It can also influence formation of the global oceans' deep and bottom water and help drive overturning ocean circulation. Sea ice moved by wind and currents, as it melts, deposits freshwater onto the ocean surface to stabilise the water column. Sea ice has a dramatic effect on the physical characteristics of the ocean surface, modifying surface radiation balance due to its high albedo and influencing the exchange of momentum, heat, and matter between atmosphere and ocean. Through these effects, sea ice plays a key role in the global heat balance. A retreat of sea ice associated with climate warming could have global consequences through various feedback processes.

The Antarctic icesheet

Antarctica's ice sheet covers 12.4 million km². It comprises 25.7 million km³ of ice or 70 percent of the world's freshwater, which if melted would raise the sea level by nearly 65 m. Mass is continually added to the ice sheet from snowfall, and removed via melt and iceberg calving, particularly from ice shelves. Any change in the ice sheet's ‘mass budget’ caused by imbalance between these mass input and output terms affects sea level. However, with present Antarctic data a 20 percent imbalance, corresponding to about 10 cm of sea-level change per century, cannot be detected with confidence. The ice sheet is not a single dynamic entity, but comprises different drainage systems with both surface mass balance and dynamics responding differently to changing conditions. We need to be able to estimate the sensitivity of the mass budget to climate change before we can estimate Antarctica's future contribution to sea level change.

Most of the ice lost from the ice sheet comes from fast-flowing, wet-based outlet glaciers and ice streams, much of which passes through floating ice shelves. Up to 40 percent of the Antarctic coastline is composed of either large ice shelves in coastal embayments such as Filchner-Ronne, Ross and Amery or fringing shelves on the periphery of the ice sheet such as the West, Shackleton and Larsen shelves. Since ice shelves are floating on ocean waters at the freezing point, even a small change in ocean temperature (induced perhaps by changed ocean currents) can significantly affect the shelves' basal melt rate and cause them to thin much more quickly than rising air temperature. Ice shelves are already floating, which means their disintegration will by itself have no measurable impact on global sea level, but their depletion may lead to increased drainage of grounded ice ‘buttressed’ by the shelves which may cause sea-level rises.

Ice core records of past climate

Antarctica's ice sheet stores the Earth's longest and most representative record of atmospheric composition and temperature in times past. The ice sheet's layers of ice and snow, accumulated over tens or even hundreds of thousands of years, form a natural archive of global environmental information, accessible by drilling into the ice to sample past surface deposits. Analyses of the ice and the material trapped in it allow records to be made of both natural and man-made environmental variations over the time period during which the ice sheet has accumulated. Deep ice cores have yielded evidence of major interrelated climate and cryosphere fluctuations in glacial-interglacial cycles. Accurate information on local, regional and global climate change and potential changes in ice sheet surface elevation are available from ice cores.

Subantarctic glaciers

Like mountain glaciers in most parts of the world, sub-antarctic glaciers have been noticeably retreating over the past 50 years or more. Retreat of non-polar glaciers has contributed to sea level rise over the past century while also providing clear evidence of a changing climate. On Heard Island, for example, the Brown Glacier has decreased in area by 33 percent and in volume by 38 percent over the past 50 years.

Abrupt change

Palaeoclimate records from ice and ocean sediment cores show evidence of abrupt and widespread past climate changes—particularly, it seems, during periods of transition from one climate regime to another over glacial-interglacial cycles. While the causes and mechanisms of such rapid changes are by no means clear, a variety of roles have been suggested for ice sheets, glaciers and sea ice. These include effects of rapid glacial discharge and decomposition with a rise to melting point of basal ice temperature, massive iceberg discharge into the ocean delivering freshwater capable of modifying the overturning circulation of the global ocean, and changing sea ice formation causing change in brine release to the ocean. Greenhouse warming and other human alterations of the climate system may increase the possibility of large and abrupt regional or global climatic events.

A startling illustration of how abrupt some processes are is the recent rapid collapse of the Larsen B Ice Shelf on the eastern side of the Antarctic Peninsula in February and March 2002, when 3250 km² of ice 200 m thick disintegrated over a few weeks…. The break-up of this shelf into thousands of small icebergs is totally different from the normal episodic calving of giant icebergs from the front of ice shelves. Temperatures around the Antarctic Peninsula have risen by 2.5°C over the past 50 years. It is hypothesised that water from large surface melt ponds that formed on the ice shelf as a result of this warming forced open cracks and crevasses to completely fracture the shelf. The ice of the shelf was already floating, so the collapse has no measurable effect on sea level, and direct impacts are believed to be mostly local. However, a similar collapse of some other shelves could bring a significant increase in glacial discharge from the ice sheet.

Ian Allison

allison, ian. “antarctic ice and the global climate system.” australian antarctic magazine (autumn2002): 3–4.