By Dr. John J. Hidore
The rapid melting that has taken place in recent decades suggests that with increased temperatures in coming decades there will be rapid melting of the ice shelves and more rapid advance of the glaciers that will cause a rise in sea level.
May 18, 2014—Near Earth’s north and south poles are the coldest areas on the surface of the planet. The area around the North Pole is referred to as the Arctic and that around the South Pole as the Antarctic. The reason these two areas are so cold is that during the course of a year they receive much less solar energy than areas nearer the equator. While they are both very cold regions, the Antarctic and the Arctic are fundamentally very different from each other. The Arctic is largely a sea surrounded by land. On the other hand, the Antarctic is a continent surrounded by sea. While they are basically very different geologically, they have many things in common. One, of course, is that they are very cold environments. Both have large ice sheets and moving glaciers. Another less known feature found in both regions is the ice shelf. Ice shelves are masses of floating ice that are frozen to the seashore. They originated as parts of continental glaciers that slowly flowed off the land and began to float. Though they are floating they are anchored to land.
The Arctic Shelves
Most of the ice making up these shelves is more than 3000 years old. Since their discovery in 1906, these ice shelves have lost 90% of their ice. Some of the ice shelves that existed in 1906 are entirely gone and others are on the verge of melting away. The largest known ice island found in the Arctic Sea is one that broke from the land in 1956. Most of the melting of these ice shelves has taken place in recent decades. In 2005, the Ayles ice shelf was just one of several remaining in the Arctic region of Canada. That year the entire ice shelf broke free from Ellesmere Island. The island is approximately 500 miles south of the North Pole. In fact, using a combination of satellite imagery and seismic data, researchers were able to determine that the shelf actually broke away the afternoon of August 13, 2005. Within a few hours the mass had formed a new ice island, trailing bits of broken ice. The ice island drifted some 30 miles out to sea and then became frozen into the sea ice.
August 2008, the Markham Ice Shelf detached from Ellesmere Island and floated away. Two large pieces of ice also detached from the Serson Ice Shelf, reducing the over-all size of the shelf to less that half what it was the previous winter. It is now largely gone. The Ward Hunt Ice Shelf is also breaking up. It lost 10% of its area in the summer of 2008.
One important aspect worth noting is the breakup of these ice shelves will not have a major effect on sea level since they are already floating in water. Ice floats in water because ice is less dense than water. When water freezes it expands some nine percent, making it less dense than sea water. So when the ice melts its density increases to that of the surrounding sea water. Thus the volume of water does not change. There is actually a slight change due to the difference in density of fresh water and sea water.
Antarctic Ice Shelves
Ice shelves along the West Antarctic Peninsula are either rapidly melting or have broken up altogether. These ice shelves have always shed icebergs. Large pieces of ice occasionally break off the edges of these floating ice masses and drift away from the land mass. In March of 2000, the second largest iceberg ever measured broke free from the Ross Ice Shelf and floated into the Ross Sea. The huge iceberg, B-15, was about 180 miles long and 18 miles wide. Within a week of this iceberg’s formation, three more large pieces broke free from the ice shelf.
Ice Shelves: Melting at an Ever Increasing Rate
Three of the ice shelves disintegrated in the last decade of the 20th century. Many of the ice shelves located on either side of the peninsula have been melting at an ever increasing rate. These ice shelves are the Prince Gustave Channel, Larsen A, Larsen inlet, Muller Ice Shelf, and Wilkins Ice Shelf. Larsen B and Wilkins lost 1180 square miles of ice in just two years from 1998 to 2000. In 2002 a section broke from the Larsen Ice Shelf that was 1200 square miles in size. On February 28, 2008, a large piece of ice broke from the edge of the Wilkins ice shelf. In contrast to the huge pieces breaking off from the Ross Ice Shelf, these shelves are disintegrating in small pieces, which is usually the case with warming temperatures.
Ice shelf Location Year Size ________________________________________________________________________
Ayles Arctic 2005 41mi2
Larsen A Antarctic Peninsula 1995 1620 mi2(4200km2)
Larsen B Antarctic Peninsula 2002 1200 mi2 (3100 km2)
Markham Arctic 2008 19 mi2 (49 km2 )
Ross Antarctic 1987 1834 mi2 (4,750 km)
Ross Antarctic 2000 4,250 mi2-11,000km2
Serson Arctic 2008 lost 50% of area
Ward Hunt Arctic 2003 150 mi2 (384 km2 )
Wilkins Antarctic 2008 160 mi2 (416 km2 )
Collapse of Ice Shelves
What is of most concern is how the breakup of these ice shelves will affect the continental glaciers that are driving the ice shelves seaward. Since ice shelves are anchored to land they hold back the continental glaciers from advancing seaward. It is possible that the removal of these ice shelves will result in more rapid advance and faster melting of the glaciers. The Ross Ice Shelf is an example. It is one of the largest shelves on the West Antarctic ice sheet. The tides lift and lower the shelf twice a day. During high tide the shelf is lifted, there is less friction with the sea floor beneath, and the glacier behind moves forward. At low tide the rate of movement is slowed. Melting of the Ross Ice Shelf would allow the glaciers behind to move forward adding ice to the sea and raising sea level. Winter temperatures in the area have increased some 9 ºF (5º C).
The rapid melting that has taken place in recent decades suggests that with increased temperatures in coming decades there will be rapid melting of the ice shelves and more rapid advance of the glaciers that will cause a rise in sea level. How much sea level will rise depends on many factors which are hard to predict.