One of Greenland’s largest glaciers is moving at speeds never before recorded. In the process it’s moving ice from the Greenland ice sheet into the ocean at record rates.
The speed of the Jakobshavn Isbræ — the Jakobshavn Glacier — in western Greenland was measured by researchers from the University of Washington and the German Space Agency (DLR) during 2012 and 2013. The researchers found the glacial flow of Jakobshavn during the summer was up to four times that noted during the 1990s.
Jakobshavn Glacier is one of the few glaciers draining the Greenland Ice Sheet that reaches the sea. It meets the ocean near the Greenlandic town of Ilulissat, formerly known by its Danish name of Jakobshavn, in the Qaasuitsup municipality in western Greenland, about 200 kilometers (120 miles) north of the Arctic Circle.
It’s widely believed the Jakobshavn Glacier was responsible for calving the large iceberg that would ultimately sink the Titanic in 1912.
Jakobshavn Isbræ is significant, not just in relation to Greenland where it drains 6.5% of the Greenland Ice Sheet, and produces around 10 percent of all Greenland's icebergs, but also in global terms. In the late 1990s the speed of the glacier began to increase, following a number of years during which Jakobshavn remained relatively stable.
A 2009 NASA report estimated that Jacobshavn's near-doubling of ice flow from land to ocean was responsible for increasing the rate of sea level rise by about 0.06 millimetres (about 0.002 inches). That may not sound much but it means that one single Greenland glacier accounted for roughly 4 percent of the increase in sea levels recorded during the 20th century.
Commenting on the latest research, published in the geosciences journal, The Cryosphere, lead author Ian Joughin, a researcher at the University of Washington’s Polar Science Center, said, “We are now seeing summer speeds more than 4 times what they were in the 1990s on a glacier which at that time was believed to be one of the fastest, if not the fastest, glacier in Greenland."
During summer 2012, the Jakobshavn glacier reached unprecedented speeds of 46 metres per day, equating to 17 kilometers (about 10.5 miles) per annum. By comparison, in an earlier study to which Joughlin contributed, titled, “Large fluctuations in speed on Greenland's Jakobshavn Isbræ glacier” and published in Nature, a research team noted the flow rates during the period between 1992 and 2003 varied between 5.7 and 12.6 kilometers per year.
According to the research team, the glacial speed recorded during 2012 was the fastest for any glacier or ice stream in Greenland or Antarctica. The increased flow rate of the Jakobshavn glacier means it’s adding more and more ice to the ocean, contributing to sea level rise, at what appears to be an accelerating rate. Even allowing for the slowdown that inevitably occurs during winter, the researchers calculate that the annually averaged speedup over the past couple of years is nearly 3 times what it was in the 1990s.
As Joughlin explained, “We know that from 2000 to 2010 this glacier alone increased sea level by about 1 mm. With the additional speed it likely will contribute a bit more than this over the next decade."
Jakobshavn Isbræ drains the Greenland ice sheet into the Ilulissat Icefjord, a deep ocean fjord on Greenland’s west coast. As can be seen in one of the images, the glacier has been in steady retreat, sometimes halting, since at least 1851.
Between 1851 and 1964, Jakobshavn Isbræ’s calving front, where it meets the fjord, retreated 30 kilometers. After that it hardly moved for almost 35 years. It’s what has happened since the turn of the millennium that’s the real concern. As the image shows, since 2001, Jakobshavn Isbræ has retreated about half the distance it fell back in the century-and-a-half or so between 1851 and 2000. Worse, the fall-back in recent years appears to be accelerating.
Retreat of the Jakobshavn Glacier in Greenland between 1851 and 2006. Since 2000 the speed of retreat has picked up markedly
In 2012 and 2013 the calving front retreated more than a kilometre further inland than in previous summers, say the researchers. Not only that, the depth of ice in the glacier itself is becoming thinner. Also contributing to the accelerated retreat is the depth of the fjord. The scientists say the calving front of the glacier is presently positioned in a deeper area of the Ilulissat Icefjord where the underlying rock bed is about 1300 metres below sea level.
In essence, there’s more space in the fjord to accommodate icebergs breaking off from the glacier and less chance of newly formed icebergs becoming stuck and ‘bunging up’ the glacier’s flow to the sea. As a result the speed of flow of the ice accelerates.
The researchers conclude that the Jakobshavn Isbræ is in an unstable state, with the likelihood of its retreat continuing further inland in the future. By 2100, its calving front could have retreated as far as the head of the Ilulissat Icefjord into which the glacier flows, a distance of roughly 50 kilometers upstream from its present position.
The flow of cold dense freshwater into the North Atlantic looks unlikely to stop any time soon, and could have implications for climate in both North America and Western Europe, although the precise effects remain the subject of debate among climatologists.
But if this winter is anything to go by — a Deep South chilled to the marrow and the ability of Western Europe to absorb any more rainfall at inundation point — the continuing retreat of Jakobshavn Isbræ does not bode well.