1 Climate Report: Antarctica Liz Suess, Ryan Alliss, Marie Limpahan, Jeff Wilson. Agronomy/Meteorology 406, December 11 , 2009

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Climate Report: Antarctica Liz Suess, Ryan Alliss, Marie Limpahan, Jeff Wilson. Agronomy/Meteorology 406, December 11th, 2009.

Antarctica, the southernmost continent, has a climate drastically different from anywhere on Earth. The land mass is almost entirely covered in ice with sea ice extending out into the ocean being in a constant state of change. The climate of Antarctica is affected by many things, such as its latitude, its topography, and the fact that it is dominated by the Polar Cell. The result is a cold, dry climate, with precipitation being found mostly near the coastlines. This icy habitat is home to one of the best known species in the world, the emperor penguin. The penguin has adapted to living and breeding on or near the coastal ice shelves of Antarctica, however, anthropogenic climate change is putting their habitat, and likewise, their survival in jeopardy. Antarctica is also home to an unusual marine ecosystem due to its frigid history. Antarctica is a climate research hot spot, despite its sub-zero temperatures. Much of the research focuses on global climate change and involves taking ice cores as a means of gathering climate data from over thousands of years. Research is also being done to predict what effect warming might have on Antarctica and the rest of the world.

Introduction

The South Pole’s climate is drastically different than the climate of almost any other continent.

The actual continent of Antarctica is about 1/3 bigger than Australia, but it appears much larger than this due to the large ice sheets that encase it and stretch out over the ocean [Town, 2009]. Not many people realize it, but the climate of Antarctica has a large effect on the climates around the world. For

example, if the ice sheets were to melt in Antarctica, ocean currents would be disturbed because of changes in ocean temperature. Also, low-lying areas may become covered in the millions of tons of water trapped in the Antarctic ice sheets. This information also makes Antarctica a very fun place to study in terms of climate. [Bromwich, 2008]

Temperatures

Antarctica is one place where people are focusing on the effects of climate change. Many computer simulations are attempting to predict how global warming is going to affect the Antarctic ice shelves, which if melted could flood coastal areas

[Bromwich, 2008] However, by comparing the model runs of the last 50 to 100 years to actual records, it is shown that Antarctica has been warming a lot slower than expected. Observed temperatures have only actually risen around 0.2 degrees Celsius, while the models all predicted a

Fig. 1 Temperature trends in Antarctica [Bromwich, much greater change of 0.75 degrees Celsius. This is 2008] believed to be caused by the overestimation of moisture in the atmosphere. Fig. 1 shows that over the last 35 years, the majority of Antarctica has actually been cooling. [Bromwich, 2008]

During summer, only the western peninsula sees temperatures above 0 deg C. The average monthly temperature for the South Pole is -58 deg C in the winter months (April – September). [Town,

2009] The only area that is greatly affected by the warming is the Western Peninsula and that is mostly because it is above that 0 deg C line during the summer months. [Baringer, 2009]

Ice Sheets/Snow

During winter, the sea ice averages around 1 m thick and covers an area roughly 20 million square km. By the end of summer there is roughly 3 million square km of sea ice left [Town, 2009].

The ice sheets over the continent then flows outward, creating ice shelves. The two main shelves are the Ross Ice Shelf and the Filchner-Ronne Ice Shelf [Town, 2009]. What helps to balance the spread of ice over the ocean is waves breaking off large chunks of ice, known as icebergs. These bergs can then travel all around the world depending on where the water temperatures are cool enough for them to stay frozen. [Town, 2009]

Another type of ice common in Antarctica is sea ice. Because the temperatures are so frigid,

every winter the surface of the sea freezes,

which creates large patches of ice. [Town,

2009] This causes other types of ice shelves,

one of which is the Wilkins Ice Shelf. In 2008

there were 3 major breakup events of this

particular ice shelf (see

Fig 2). This was believed to be caused by

either a warming of the water directly

Fig 2. Satellite images of the 2008 Wilkins Ice Shelf break up. [Baringer, 2009] underneath the ice shelf or salt getting onto the ice and causing it to weaken. [Baringer, 2009]

If temperatures were to increase in Antarctica, it is believed that there would be an increase in the amount of snow, since the atmosphere can hold more moisture as it warms. This increase in snow would then cause more ice to form to help balance the melting and break up of ice sheets. [Town, 2009]

General Weather

Snow is another factor that is being studied with the climate of Antarctica. As the temperatures slowly get warmer, the atmosphere can hold more moisture and there is more snow falling to replace the icebergs being pulled into the ocean. One can also look at the albedo of the snow in Antarctica. The best way to look at the albedo of snow cover is to look at the age. In most cases, the albedo of the snow decreases as it gets older due to the snow melting and dirt from the land mixing in with the snow. In

Antarctica, however, the land is so clean that the albedo stays around 0.82 year round. [Genthon, 1997]

El Niño and La Niña tend to have a rather large effect on the weather that happens in Western

Antarctica. In La Niña years, there is a lot of warming that occurs. Precipitation also increases due to the effects of La Niña. El Niño shows a decrease in temperatures and also a decrease in precip.

[Baringer, 2009]

There are also many other strange weather phenomena that can occur mostly due to the very cold temperatures found in the Polar regions. One of the most interesting is clouds that form in the stratosphere and mesosphere. Clouds in the mesosphere are called noctilucent clouds and they form by the oxidation of methane. They reside about 80 km off of the surface and can be seen when the sun is approximately 10 deg below the horizon. Stratospheric clouds (or nacreous clouds), however, are much harder to see. Surface temperatures below -83 deg C allow the stratosphere to be at a temperature where clouds can form. Normally there is so little moisture that the stratosphere cannot be cooled enough to form clouds. These clouds are about 20 km off the ground and can be seen when the sun is 5 deg below the horizon. These nacreous clouds also play a major role in the breakup of ozone. [Town,

2009]

Ozone Hole

One of the biggest factors in climate change around the planet is the ozone hole, which resides in the atmosphere above Antarctica. Increasing levels of bromine and chlorine are causing the hole to get larger every year. Another factor in ozone depletion is the forming of nacreous clouds mentioned above. When these clouds form, chlorine particles in the atmosphere become reactive, which causes ozone deterioration. The record largest ozone hole area was 27.7 million square kilometers in 2006.

[Baringer, 2009] This decrease in ozone when paired with an increase in greenhouse gasses is causing the winds in the southern hemisphere to be more persistent, which is warming the Western Peninsula but causing the rest of Antarctica to become even more isolated. [Town, 2009]

The ozone hole also causes many problems when it comes to temperatures. As the hole gets bigger, the atmosphere is unable to absorb as much radiation. This allows temperatures to be a lot cooler because the high albedo of the snow causes almost all of the radiation to be reflected back into space [Baringer, 2009].

Causes of Climate

Overview

The Antarctic climate is dominated by cold temperatures, high winds, and lack of precipitation.

You can attribute almost of these traits by the location of this continent, at the South Pole. The lack of direct solar radiation severely limits how warm Antarctica can be. The polar cell is located over this continent, limiting the amount of precipitation that falls. Most of the precipitation is found over the

lower latitudes around the coasts of Antarctica where transient cyclones can penetrate the landmass.

Elevation effects also create a downward sloping wind, known as the katabatic wind, which is caused by not only the pressure gradient force but by gravity as well (Warren and Town, 2009).

Geography

Antarctica is centered right over the South Pole with the landmass stretching out to latitude of

70 degrees south. A peninsula, located at 60 degrees west reaches to the lowest altitude of nearly 60 degrees south. This peninsula, known as the Antarctica Peninsula, has the warmest temperatures due to its location and interesting climatic changes over the past one hundred years. Antarctica contains a total area of 14 million square miles (1) with a coastline stretching a total distance of 17,986 kilometers. The

continent averages between 2,000 and 4,000 meters

in height, with the highest point being at Vinson

Massif at 4,897 meters which is roughly 50 percent

the height of Mount Everest in Asia. In general, the

elevation of the continent increases with the

average maximum being near the South Pole. The

continent is covered with ice sheets. Nearly 98

percent of the entire continent is made up of ice,

which lowers the amount of friction between the wind and the ground which will create higher wind speeds across Antarctica. Fig. 3. shows Antarctica in terms of latitude, longitude, and elevation. (CIA, 2009)

Energy Balance

Since Antarctica is located at such a high latitude the amount of direct solar radiation is very little during the entire year. The irradiance, which is the rate at which energy passes through a unit area on a plane surface, is defined by the following formula.

F=2πIcos(θ)δw [Wallace and Hobbs, 2006]

Where F is the irradiance, I is the solar intensity, θ is the zenith angle, and δw is the arc of the solid angle. Taking the limit as theta approaches 90 degrees, the amount of incoming radiation over an area goes to zero. Because of the Earth’s tilt Antarctica will still receive some energy however another factor also limits the energy being absorbed. The albedo ranges from .60 near the coasts up to nearly .96 across the continent. This means that of that small amount of incoming solar radiation, at least three- fifths of it is reflected, yielding a tiny amount of absorbed energy into the continent. Heat fluxes come from descending air that warms adiabatically and from latent heat fluxes such as deposition of water vapor to the solid state. In the end, the net energy budget yields very little energy explaining why temperatures reach so low [Laine, NA].

General Circulation

The circulation abides by the current understanding of the general circulation as described by the modified three cell model. Antarctica is in the polar cell region where a large area of subsidence dominates. Because this air is descending over the continent very small amounts of precipitation are accumulated. Downward motion will increase the temperature of the air parcel via adiabatic compression thus raising the relative humidity.

This leads to clear skies and a lack of a saturated environment suitable for precipitation. If

precipitation does occur it mainly will fall

in the form of snowfall because the

temperature rarely exceeds 0 degrees

Celsius. The polar cell describes air being

blown out from the poles towards the

equator until being caught into Rosby

waves which are the synoptic cyclones

that cause weather in the mid-latitudes.

These transient eddies can make it to the

Antarctic coast, but rarely plunge pole Fig. 4. A typical synoptic pattern [Antarctica] Isobars are in blue with satellite imagery. ward into the continent. These cyclones

give an increased chance of precipitation to the coasts due to their dynamics. Fig 4 shows an image of a

typical synoptic view of Antarctica. Clearly a large area of high pressure is centered over the continent

with cyclones circling just off the coast. On average about only two inches of precipitation fall inland,

while twenty to forty inches may fall on the

coastlines because of these transient eddies

[Warren and Town, 2009].

Katabatic Winds

This polar circulation, along with

Fig. 5. Force diagram of the katabatic winds. the gradual elevation increase towards the [Katabatic]

poles, yields a unique event to Antarctica known as the katabatic wind. This is caused by the cold, dense air from the poles being blown down the ice sheet and out into the ocean. Wind speed is normally calculated based solely on the pressure gradient force; however the sloping elevation adds the gravitational force into the mix. The components of both the pressure gradient force and gravitational force have the same sign yielding a much stronger wind. This lowers the amount of friction yielding a much higher wind. These winds can be in excess of hurricane force yielding dangerous wind chills and blizzard conditions. The direction of these winds are not directly south to north, but rather curved by the Coriolis force. This force deflects motion to the left in the southern hemisphere due to the Earth’s rotation. This creates a general circulation of easterly winds near the coastline of Antarctica [Ball,

1956].

Antarctica is dominated by extreme radiative cooling that yields descending air at the poles and movement towards the equator. This downward motion limits the amount of precipitation that falls on the inner areas of the continent. Winds across the region are mainly easterlies caused by the katabatic wind and coriolis force.

Biology of Antarctica

Antarctica’s climate is incredibly harsh due to its latitude. The Antarctic Circle lies at 66.5 degrees South. The continent of Antarctica lies south of this point. Here, temperatures average -45 deg

C. The land is covered mostly in ice and sea ice, extending from the actual land mass. The ice and snow cover severely limit terrestrial biology. Because of this, the majority of species found in Antarctica are marine or migratory. Following, is a discussion of an unusual quality of the shallow ocean waters found in the Antarctic region, and a description a threat to one of Antarctica’s most well known species. 9

Marine Ecology

Diving in the shallow waters off of the coast of Antarctica, one would find a preponderance of sea stars, urchins, brittle stars, and various other invertebrates, while sharks and other large predatory fish would be absent.

Richard B. Aronson and Daniel B. Blake [2001] explain why a unique predator/prey relationship has evolved in the benthic zone of shallow water habitats of Antarctica. Typically, one finds higher predation levels in shallow water, but in Antarctica, the benthic zone is an area of lower predation. Slow-moving, shell drilling invertebrates make up most of the predators. Larger, skeleton breaking predators such as sharks and crabs are absent. This is not to say that there were never sharks or crabs in the Antarctic waters. They disappeared during the late Eocene period, part of a global cooling period that happened 55.8 to 33.9 million years ago. The loss of the faster skeleton breaking predators is what allowed slower shell drilling predators to take hold in the region. The result is a

Paleozoic-like ecosystem more commonly found in the deeper regions of oceans [Aronson and Blake,

2001] .

Today, an abundance of echinoids (sea urchins) keeps the Antarctic shallow benthic zone from seeming entirely Paleozoic-like. Echinoids feed on microalgae and diatoms, suggesting higher levels of herbivory than one would expect in a Paleozoic-like environment [Aronson and Blake, 2001].

The basis of this ecosystem’s evolution is found in a cooling environment. One of the biggest questions concerning global warming is what impacts a warmer planet will have on oceanic ecosystems. The paper suggests that we should see the effects of coastal upwelling become more prominent over the next few decades because of a predicted increase in El Nino events. [Aronson and

Blake, 2001]. Upwelling is a process in which ocean currents take the cold, dense, and nutrient rich water from the deep ocean and bring it up towards the surface. Aronson and Blake [2001] suggest that this trend in increased upwelling will result in a greater future occurrence of ecological patterns like those seen in Antarctica today.

Emperor Penguins

The emperor penguin is arguably one of the most recognizable Antarctic species. It is one of only two species of penguin that remain in Antarctica for their entire lifecycle [Boersma, 2008]. They are famous for their tuxedo-like plumage and their peculiar nesting habits. The species reproduces during the winter, when sea ice is plentiful. Breeding success depends on the sea ice extent because it determines how much food is available and what sort of energy expenditures are involved in hunting.

Too much or too little sea ice both have adverse effects on the penguin population [Jenouvrier et al.,

2008].

Krill serves as a keystone species by supporting the various fish that thrive in the Antarctic waters. Fish are the primary prey of emperor penguins. Colder winters, where sea ice is plentiful, are better for krill populations, resulting in more food for the penguins [Jenouvrier et al., 2008]. Earlier in this paper, we discussed the breaking up of ice shelves along the coast of Antarctica. Reduced sea ice results in lower survival rates or adult emperor penguins [Jenouvrier et al., 2008].

Jenouvrier et. all [2008] examined the results of the most recent IPCC report and suggests that

“increased frequency of warm events associated with projected decreases in SIE (sea ice extent) will reduce the [emperor penguin] population viability. The probability of quasi-extinction (a decline of

95% or more) is at least 36% by 2100.” It is important to note that sea ice reduction is a positive

reinforcement of warming because sea ice provides a reflective surface with a high albedo. As this reflective surface diminishes, more of the Sun’s rays are absorbed at the surface, resulting in warming of the ocean surface [Jenouvrier et al., 2008].

In 2006, a colony of emperor penguins was observed marching from its usual hatching ground to more stable sea ice, where they hatched chicks [Boersma, 2008]. A storm in late September caused the remaining sea ice to break apart, likely killing all of the chicks in the colony [Boersma, 2008]. As warming reduces the amount of stable sea ice, the concern is that events like this one will become more common, resulting in a decimation of the emperor penguin population.

Research in Antarctica

The unique location of Antarctica has given scientists an opportunity to examine past, present, and future climate conditions on earth. The research being done on the continent of Antarctica is performed by scientists of many disciplines and nationalities [Mapstone, 2007].

Polar-ice Core Research

Snow has fallen and compacted into polar-ice on Antarctica for thousands of years. Each layer of snow trapped traces of atmospheric air from the day it fell. These atmospheric traces provide scientists a detailed timeline of climatic changes that have occurred for the past 650,000 years. As a result, much of what science knows about cycles in world climate has been attained by the research performed in the Antarctic [Mapstone, 2007].

Mapstone overviewed the priceless information that is being attained by research in the

Antarctic [Mapstone, 2007]. He pointed out that there are glacial cold and interglacial warm climatic cycles evident in polar-ice core samples taken from Antarctic polar-ice sheets. Small pockets of air that have been trapped inside of the Antarctic polar-ice sheet for thousands of years have revealed changes to the composition of gases in the atmosphere that coincide with these climatic cycles. Ice-core samples show a rise in the level of carbon dioxide contained in the atmosphere precedes an eight to nine degree Celsius cooling of the earth, during which carbon levels drop down to much lower levels.

There has been an unprecedented rise in atmospheric carbon and methane levels since the industrial revolution started, unparalleled by the rise and fall of these gas levels for the past 650,000 years. It is unclear whether this means the rapid rise of carbon and other pollutants in the atmosphere will trigger a similar cold cycle more quickly than it has in the past [Mapstone, 2007].

A British study of a 3270 meter ice core obtained from Antarctica was completed in 2004. This study revealed that greenhouse gases, such as carbon dioxide and methane, have not been near the levels they are today within the past 750,000 years. Dr. Robert Mulvaney of the British study added that ice coring has become a valuable technique because of the detail scientists are able to see in these samples [Allen, 2007].

Ocean Currents/Water Research

Scientists have taken a special interest in the bodies of water that surround the continent of

Antarctica. Temperature changes in the water can disrupt ocean currents and effect climates around the world [Bromwich, 2008]. The waters surrounding the continent are the location of ocean overturning

(upwelling) circulation. A major disruption of this overturning circulation can change the process by which heat and nutrients are transported around the world. This could cause the dramatic cooling of the

climate in northern Europe, and result in the heating of the atmosphere and oceans located at low latitudes. The salinity of Antarctic Bottom Water has dropped in recent years, which implies that a larger amount of polar-ice has been melting. Research is continuing to determine how much the waters surrounding Antarctica are changing with the climate [Mapstone, 2007].

Scientists believe that a significant amount of carbon dioxide is absorbed in the rough, overturning waters surrounding Antarctica [Mapstone, 2007]. A microscopic plant named phytoplankton accounts for a large portion of carbon dioxide absorption in the Southern Ocean. The slowing or changing of the overturning currents could affect the Southern Ocean’s ability to absorb carbon dioxide that otherwise would increase the atmospheric temperature of the earth. Other organisms that live in these waters will be affected as levels of carbon dioxide dissolved in the waters that surround Antarctica increase. Echinoids (sea urchins) and other organisms in the shallow waters around Antarctica rely on an abundant amount of calcite and aragonite to form protective shells

[Aronson and Blake, 2001]. Carbon dioxide dissolved in the waters surrounding Antarctica chemically reacts with calcite and aragonite and has decreased the amount of the minerals available to these organisms. Oversaturation of carbon dioxide dissolved in the Southern Ocean can result in making these waters uninhabitable by the organisms that make up the bottom of the food chain in Antarctic waters. Mapstone and his colleagues believe that the waters surrounding Antarctica will be the first to become saturated with carbon dioxide, and continue to research what happens to the organisms that inhabit this oceanic region [Mapstone, 2007].

The Australian Antarctic Division (AAD) Home Page confirmed Mapstone’s claims and indicates the importance of creating better models to predict the amount of anthropogenic carbon dioxide that can be absorbed by the Southern Ocean [Trull et al, 2002]. AAD expressed their continued dedication to anthropogenic carbon dioxide research in the future.

Polar-ice Melting Research

The introduction mentioned that millions of tons of the earth’s water are stored in the polar-ice sheets on and around Antarctica [Bromwich, 2008]. Studies are showing that an increased amount of polar-ice is melting. Scientists have determined that ice melting from glaciers as well as the Greenland and Antarctic ice sheets has caused the sea level to rise in past years. Nearly 634 million people live less than 30 feet above sea level. If the Antarctic ice sheet melted, the sea level would rise an estimated

60 meters [McGranahan et al, 2007]. As mentioned in section above, Ozone Hole, the decrease of the ozone layer and increases in greenhouse gases has slowed the melting of Antarctica’s polar-ice sheets

[Baringer, 2009].

NASA researchers have been monitoring the amount of ice that surrounds the continent of

Antarctica. As mentioned in the Temperature section above, the western peninsula of Antarctica has been affected the most by warmer temperatures [Baringer, 2009]. This has resulted in scientists concentrating their efforts on this western region of ice that appears to be changing shape the most rapidly. The information collected from satellite imaging and, more recently, aircraft flights by NASA, is an attempt to estimate how much ice is melting around the continent each year. NASA has scheduled

17 flights to observe changes in Antarctic ice formations. The data collected on these flights will help scientists predict the consequences of the changing ice formations on the continent [CNN, 2009].

There are ongoing research projects involving the effects of polar-ice levels on animals such as emperor penguins [Boersma, 2008]. It has been found that seasons with lower amounts of sea-ice are harder on the organisms like krill that penguins feed on [Jenouvrier et al., 2008]. Warmer winters coupled with the waters around Antarctica becoming oversaturated with carbon dioxide will cause

other food sources for penguins to decline (Refer to Emperor Penguin section) [Maptsone, 2007]. The knowledge attained by research in Antarctica has played a pivotal role in today’s understanding of climate, ocean currents, and global warming. The continued research being performed in Antarctica ensures the accrual of knowledge needed to understand, predict and possibly change the future of the

Earth’s climate.

Conclusion

Antarctica, for all its ice, is one of the most important regions of the world when it comes to the issue of anthropogenic climate change. In the public eye, it is one of the key visual representations of the issue. Sea ice extent is seen as a clear indicator that things are not the same as always-- that indeed, the climate is changing. The habitats found on the continent are extremely fragile and susceptible to even small changes in global temperature. For this reason, Antarctica is sure to remain a major point of research and attention as the global climate change issue continues to shape our political, public, and personal decisions in the years to come.

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