The Impact of Climate Changes in the Glaciers and Ice Shelves of the Antarctic Peninsula
A report by Engineer Pedro Skvarca in the
auditorium of Malba. Buenos Aires, July 2005
I assume most of the people have seen the movie “The Day After Tomorrow” The film starts with the disintegration of a giant part of an ice shelf –the so called Larsen shelf B– and though the story is a bit fictitious since time scale cannot actually be reproduced in a movie, this has served to show the worldwide repercussion the event had. The Larsen B shelf collapse made a first page news in The New York Times.
At present there are two regions in Antarctica which cause much concern to scientists. One of them is in the Antarctic Peninsula where, as I have just mentioned, a huge mass of ice shelves was disintegrated; the other is the west area of Antarctica. What is critical in the latter is the fact that the ice mass which has a surface of millions of square kilometers leans on rock over 1,500 meters under sea level; a collapse of this huge “ice sheet” would be catastrophic for all mankind.
I will particularly focus on the consequences climate change in the Antarctic Peninsula has over the ice masses in the region. Most of you are familiar with the name of our bases in Antarctica –namely Orcadas, Esperanza, Marambio and Matienzo. In the temperature records from those stations we’ll see how the regional atmospheric warming affected the glaciers and the ice shelves in the area. I’ll deal in particular with the NE of the Antarctic Peninsula and the impact produced by the climatic variation in the Glaciers of the islands Vega, James Ross and the NE part of the Larsen Ice Shelf.
The meteorological station in Orcadas has been operating since 1904. Thus, they have been able to show a record produced by their instruments for over a hundred years. This record has detected a gradual warming of the atmosphere as of the 1930s. Ever since then and up to the present, temperature in this region rose 0.026°C per year. On the other hand, from a reading of the temperature records coming from Faraday station (today called Vernadsky), we know that the average annual temperature of the air in the Antarctic Peninsula grew over 2.5°C in the last 50 years, with a projection of 4.4°C per century. The tendency to a warming up of temperature can also be observed in those records from Esperanza station (a fifty year record) and Marambio (a thirty year record). The record of Orcadas also indicates that the two past decades were the ones with the higher temperatures during the twentieth century. On the other hand, from tests on sample ice pieces taken from the Antarctic plateau, we can tell these two decades were the warmest in the last 500 years.
It’s really important for the study of glaciers to learn about the tendencies in the average annual temperatures. The weather records in Orcadas, Esperanza, and Marambio show a positive tendency which is quite evident. For Orcadas is +0.036°c a year, for Esperanza is a bit higher, and in the case of Marambio, even higher, with +0.07°C per year. These trends are higher as we move southwards. The average summer temperatures (AST) are primordial for the Glaciers since they cause the loss of Glacier mass through surface fusion of the ice.
An overwhelming evidence of the changes caused by the atmospheric and oceanic warming in the Antarctic Peninsula is the recession and the final disintegration of the northern area of the Larsen ice shelf. The two most manifest events in the past ten years are concerned with the disintegration of sectors A and B of the Larsen shelf, which coincided with the maximum summer temperatures recorded up to then in the region. The average summer temperatures (AST) are the result of the average of those recorded during December, January and February.
The collapse of the area known as Larsen A (to the North of the 65°S) took place at the beginning of 1995, during summer, when the AST grew, for the first time, to 0°C. As regards the area Larsen B. which collapsed in February-March 2002, the AST was even higher. During summer 2001-2, Esperanza base recorded an AST of +2.4°C, in Marambio was of +0.7°C and in Matienzo –which is the station in the Nunatak Larsen, very near the Larsen B shelf, was of 1.3°C (over zero). From 1975 to the beginning of 2005 the Larsen Ice Shelf lost over 13,000 km2 to the North of the 66°C, mainly due to climate change.
Associated to this increase in the air temperature, a very revealing thinning and negative mass balances have been detected in the glaciers of the NE of the Antarctic Peninsula. The Bahía del Diablo, in Vega island, whose front ends in solid ground, is a glacier we’ve been studying for over 20 years now. At present, it’s the only glacier in Antarctica where a mass balance has been continually monitored for the past six years. The mass balance of a glacier is the difference between what is annually added to a glacier (through snowfalls) and what is taken away from it (due to fusion in summer). In the lower area of Bahía del Diablo Glacier we have measured a manifest decrease of the surface level. This glacier has lost thickness with an average rate of 0.9m per year between 1984 and 2005. The mass balances measured between 1999-2000 and 2004-5 were always negative, with an average loss of 270mm in terms of water. It’s usual in glaciology to express the accumulation and the ablation parameters out of which the mass balances result in “water equivalents” i.e. the equivalent of snow thickness or ice in water mm.
To show that this process not only occurs in a glacier, we also present those changes seen in the Lamb Cape Glacier. This is a rebuilt glacier in the SW of the same island. Twenty years ago this glacier ended in the sea but since then it has overtly receded (24 meters) in the past 20 years, at an annual average rate of 1,20 m / per year. In the neighboring island we have also analyzed the behavior of most of the discharge glaciers and we realized that the area decreased between 1975 and 1988 at a rate of 1,8 km2 / per year. Very recent studies extended until the year 2002 indicate that the recess rate of these glaciers, compared with the previous period, grew over twice, that is 3.8 km2 per year. In 27 years, those between 1975 and 2002, the glaciers in the island became 78, 8 km2 smaller which implies a decrease of 3.9% in the glacial area. These data are full samples of how the atmospheric warming in the region affects the glaciers, and serve to show clearly what is happening in the NE area of the Antarctic Peninsula.
It must also be said that the data of mass balance regarding Bahía del Diablo Glacier are the only contribution of Antarctica to the World Glacier Monitoring Service (WGMS), sponsored by UNESCO, which collects mass balance data coming from many glaciers all over the planet –something essential to evaluate the impact caused by climate changes in all the Earth. This monitoring task is quite important since the glaciers are excellent indicators of climate change.
ice shelves
We are especially interested in showing and analyzing the major changes produced in the Antarctic Peninsula due to climate improvement, I mean the disintegration of the ice shelves.
The ice shelves are also glaciers which have the peculiarity of flowing in the sea without friction. They are extensions of the glaciers or earthly “ice sheets” in the sea. The shelves flow due to their own weight, that is to say, gravity. As their surface is almost flat with smooth undulations, the breaking off in their front parts give rise to the so called tabular icebergs. The tides create rising and falling movements in the ice shelves, and these cause the latter to rise and fall even though they have such large extensions and thickness. In the case of Larsen this is about some 200 meters near its front and 350, 400 meters in the contact with the inner ice. The great ice shelves such as those called Ross and Filchner-Ronne can have a thickness which goes up to 1,500 meters in the union with the headline making continent. In the case of the Larsen Ice Shelf the vertical oscillation caused by the tides is one of about 3 meters.
The shelves continue to exist due to the accumulation of snow on their surface and the water that freezes at their foundations, whereas they lose mass volume mainly because of the break off of the icebergs or “calving” in their front parts and also due to basal fusion. The Larsen Shelf alone frees into the oceans some 20 gigatons per year due to basal ice fusion. Even if the fusion or disintegration of the floating ice shelves do not contribute to the global rise in the sea level, the redistribution of water which was originally frozen may have wide implications in the patterns of oceanic circulation and modify also the salinity of the “Antarctic Deep Ocean Water” from the Weddell Sea, one rich in nutritious elements, which comes to surface at the “Antarctic Convergence”.
significance of the ice shelves
The ice shelves border on a 44% of the Atlantic coast and stand for an 11% of the Antarctic ice surface. The larger ones are those called Ross, Filchner-Ronne, and Ammery and then comes that of Larsen –the one we are going to deal with.
The importance of the ice shelves is to be found in their stabilizing function over the “sheets of ice” and the glaciers that feed them. This has been a topic of many scientific debates during the past decades. It’s interesting to learn a bit of the history of the Larsen Ice Shelf. The name it bears is after Carl Larsen, captain of the Jason. He discovered the spot and sailed around it in the summer of 1892-3, having reached on that occasion the 68° 10’ south latitude due to the exceptional conditions of sea ice. In that voyage he also discovered the nunataks Foca and the Jason peninsula. It was then in October 1902 that an Argentinean, Lieutenant José María Sobral, from the Argentine Navy, together with the famous expeditionary Dr. Otto Nordenskjold and Jonassen from the Swedish expedition, journeyed into it as well as studied for the first time the area of the Larsen Shelf B –a spot which has raised so much talk. In their journey, using dogs, they reached the nunatak Borchgrevink, at the 66° 03’ S; 62° 30 W. Nordenskjold was the one who, as early as then, proposed the term “Shelfeis” (in Spanish “hielo de barrera”) for these platforms of floating ice. Almost a century after, in October 2001, I was part of a group of Argentineans (scientists from the Instituto Antártico) who traveled and researched into that ice shelf for the last time -since it no longer exists today.
The disintegration of some areas of the Larsen shelf is especially important since it is the first time that man is able to observe, in a direct way, phenomena of such extent that took place with unexpected celerity. They can serve as laboratory tests which might help to prevent what could happen in the future with the great ice shelves of Ross or Filchner-Ronne. As we can see, those two shelves are the ones that contain the greater part of the Antarctic “ice sheets”. At the beginnings of the year 2003 we showed the first evidences of the consequences caused by the removal of the ice shelves from the glaciers that fed them.
features of the larsen shelf as observed before the collapse
During the spring of 1994 we made a field campaign into the Larsen A sector and we could hardly believe what we saw. This shelf, whose surface some years before was almost entirely flat, plain and even, and with very few morphological features, was furrowed by a large amount of cracks, crevices or “rifts” and collapsed depressions. In an image from the meteorological satellite NOAA-AVHRR taken in February 1995 a vast tail of ice debris and a gigantic iceberg, called A-32 were observed. The area of debris corresponded to the Larsen A sector which had just been disintegrated. An area of over 800 km2 was, literally speaking, broken to smithereens in only a few weeks; the original mass turned into thousands of small icebergs and ice debris. These fragments almost reached the isle of Marambio, some 150 km away. After that, since the year 1963, we’ve monitoring, with the aid of all the satellite images available and some measuring of the terrain, the succeeding positions of the Larsen A front so as to see how the ice shelf has been receding with time until its final collapse.
Larsen B was the other sector of the ice shelf which extended south of Larsen A (between the 65 and the 66° south latitude) where we could see for the first time, as early as 1994, vast clefts over 100 meters wide and out of which, some years later, great portions of the shelf broke off and produced many tabular icebergs. On one occasion we even landed in one of them to produce glaciological observations.
In the spring of 2001 we carried out the last field campaign into the Larsen B sector. On that opportunity we made a great deal of measuring and also recorded data which we are still analyzing and processing. With the aid of the satellite positioners and the signals installed in the shelf during September-October 1996 we were able to learn the speed of the ice flow in this sector of the shelf. Between 1997- 99 the shelf flowed a meter per day but in the period 1999-2001, that is only some months before the collapse, the shelf speed raised in a 26%. This is a very important piece of information for now we know that any similar rise of speed in any other ice shelf would be an alarm signal prior to its disintegration. Before these studies, nothing was known as to the behavior of the ice shelves before their collapse.
On February 17th, 2002 we were in Marambio Base. On that occasion, we flew over Larsen shelf B and made a terrain mapping of its front using a Twin Otter from our Air Force. With the same plane we made a second mapping and that was on March 13th, only a few days after the collapse. The two plotting charts we were able to produce between one date and the next enabled us to measure accurately the disintegrated area. Our GPS flights and the MODIS images taken by the NASA satellite TERRA made it possible for us to determine that as of January 31st, that is to say in a period of 41 days, 3,200 km2 of the Larsen B shelf had disappeared. As additional information we may say that the analysis of marine sediment samples taken out by American scientists in front of Larsen B some months before the event led to the conclusion that this kind of phenomenon had not taken place for at least the past 9,000 years.
what happened during the 2001-2002 summer?
As a result of the positive temperatures recorded during the 2001-2002 summer, there were great amounts of fusion water on the ice shelf surface. The presence of an abundant volume of fusion water is very important since this triggers the disintegration of the ice shelves. Water, a product from the surface fusion, gets into the fissures and crevices of the shelf and enlarges them through expansion when it gets frozen; thus, the process of fragmentation continues until the collapse occurs.
Large lagoons of fusion water gave rise to fresh water cascades like the ones we observed during the glaciological flight. We could see a 30 meter high cascade falling from the front of the shelf into the sea (the shelf is also about 150 long below the sea level). New crevices and the large amount of break-offs we were able to see during the GPS flights indicated that the process was still on course.
The images from different sensors and satellites as well as the GPS mappings made with the use of helicopters and planes enabled us to figure out that only the Larsen shelf lost between 1975 and 2005 over 13,000 km2. As a result of the ice shelves disintegration it can be said that very drastic changes took place on the coast of the Antarctic Peninsula in only a few years and it is this fact which causes the maps of the area to be constantly outdated. As a consequence of the climate change the whole peninsula lost some 18,500 km2 and almost a 70% of this loss corresponds to the Larsen shelf.
A revealing piece of information coming from recent studies indicate that only those glaciers that fed the Larsen B shelf contributed between the years 2002-2003 to the global rise in the sea level with some 27 km3 of water per year. The fact that the disintegration of the shelves and the following ice fusion float in the sea does not imply a rise in the sea level. But the recess of the glaciers beyond the supporting line i.e. that part of them that relies on the rock, does make a significant contribution to the global rise in the sea level.
The glaciers now discharging in Larsen Bay A have also increased their speed notoriously after the disappearance of the ice shelf in that sector. In the case of the Drigalsky Glacier, with a surface of 1000 km2, the speed grew three times in its central part. Besides, it was evident that after the removal of the shelves, the surface of the glaciers grew noticeably smaller i.e. the glaciers have slimmed since ice stretches when it raises its speed.
Studies made on altimeter radar data on board the European satellites ERS-1 and ERS-2 indirectly gave us another important piece of information on the fusion rate that occurs in the foundation of the Larsen Ice Shelf. The shelf not only loses mass in its surface due to atmospheric warming but it undergoes an important loss due to the basal fusion caused by the rise in temperature in the Weddell Sea. This has increased 0.32°C since 1972 and it is known that a rise of 0.1°C implies a basal fusion rate of 1.0 m per year.
Recent scientific studies based on new satellite information has made it possible to assess with keener accuracy how fast the glaciers accelerated and how they slimmed after the removal of the ice shelves. In the case of the Larsen B shelf we know the glaciers
augmented up to eight times their speed since the ice shelf disappeared and that they grew almost 40 meters thinner in less than a year.
We can conclude stating that the past two decades were probably the warmest during the last five centuries. In the preceding twenty years there have been many drastic changes in the glaciers and the ice shelves of the Antarctic Peninsula induced by atmospheric and oceanic warming. The major changes correspond to the disintegration of Sectors A and B of the Larsen Ice Shelf, and their influence in the dynamics of those
glaciers that fed them. We noticed that both events took place and these coincided with the two warmest summers in the region. In areas where the ice shelves no longer exist, the glaciers have started to accelerate and to slim (lose its thickness) significantly, to experiment beats and to recede behind the lines of support all of which contributed to a rise in the sea level.
Much research is still necessary in order to know about the final impact of these changes on the environment but we know that if this increase in the temperature of air and the ocean continues even larger changes can be expected to happen in the Antarctic Peninsula and the rest of Antarctica. It is thought that the Larsen C Shelf, with a surface of 70.000 km2, could disappear in less than a century.
Pedro Skvarca born in Ljubljana in 1944. In 1965 he emigrated to Argentina. He holds a diploma of Ingeniero Geodesta–Geofísico from Universidad de Buenos Aires, and he is devoted to glaciology since he joined the Instituto Antártico Argentino in 1973. He is a member of the International Glaciological Society, of the Grupo Permanente de Ciencia Físicas at the Comité Científico de Investigaciones Antárticas and a regular member of the Academia Nacional de Geografía. He has been on more than 30 campaigns to Antarctica and 20 to the Patagonian glaciers. The product of such intense labor is reflected in the publication of several scientific papers.