Glacier beds can get slipperier at higher sliding speeds

As a glacier's sliding speed increases, the bed beneath the glacier can grow slipperier, according to laboratory experiments conducted by Iowa State University glaciologists.

They say including this effect in efforts to calculate future increases in glacier speeds could improve predictions of ice volume lost to the oceans and the rate of sea-level rise.

The glaciologists -- Lucas Zoet, a postdoctoral research associate, and Neal Iverson, a professor of geological and atmospheric sciences -- describe the results of their experiments in the Journal of Glaciology. The paper uses data collected from a newly constructed laboratory tool, the Iowa State University Sliding Simulator, to investigate glacier sliding. The device was used to explore the relationship between drag and sliding speed for comparison with the predictions of theoretical models.

"We really have a unique opportunity to study the base of glaciers with these experiments," said Zoet, the lead author of the paper. "The other tactic you might take is studying these relationships with field observations, but with field data so many different processes are mixed together that it becomes hard to untangle the relevant data from the noise."

Data collected by the researchers show that resistance to glacier sliding -- the drag that the bed exerts on the ice -- can decrease in response to increasing sliding speed. This decrease in drag with increasing speed, although predicted by some theoreticians a long as 45 years ago, is the opposite of what is usually assumed in mathematical models of the flow of ice sheets.

These are the first empirical results demonstrating that as ice slides at an increasing speed -- perhaps in response to changing weather or climate -- the bed can become slipperier, which could promote still faster glacier flow.

The response of glaciers to changing climate is one of the largest potential contributors to sea-level rise. Predicting glacier response to climate change depends on properly characterizing the way a glacier slides over its bed. There has been a half-century debate among theoreticians as to how to do that.

The simulator features a ring of ice about 8 inches thick and about 3 feet across that is rotated over a model glacier bed. Below the ice is a hydraulic press that can simulate the weight of a glacier several hundred yards thick. Above are motors that can rotate the ice ring over the bed at either a constant speed or a constant stress. A circulating, temperature-regulated fluid keeps the ice at its melting temperature -- a necessary condition for significant sliding.

"About six years were required to design, construct, and work the bugs out of the new apparatus," Iverson said, "but it is performing well now and allowing hypothesis tests that were formerly not possible."

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Antarctica's Pine Island Glacier responsive to weather variability

New research released in Science this month indicates the loss of Pine Island Glacier in West Antarctica is a lot more prone to weather and sea variability than in the beginning thought. Findings with a team of researchers at British Antarctic Survey, along with other institutions, show large fluctuations within the sea warmth in Pine Island Bay. They learned that oceanic melting from the ice shelf into that the glacier flows decreased by 50 percent between 2010 and 2012, which might have been because of a La Nin? weather event.

Pine Island Glacier has thinned continuously throughout past decades driven by an acceleration in the flow. The acceleration is regarded as triggered by loss from the floating ice shelf produced because the glacier 35mm slides in to the ocean. Comprehending the processes driving ice shelf loss and also the glacier's fact is answer to assessing just how much it'll lead to rising ocean levels.

It is known much from the loss is because of an in-depth oceanic inflow of Circumpolar Deep Water (CDW) around the continental shelf neighbouring the glacier. This warmer water then gets into a cavity underneath the ice shelf melting it from below.

The passage of the warmer water is made simpler through the unpinning from the ice shelf from an underwater ridge. The ridge had, essentially, behaved like a wall stopping warmer water from dealing with the thickest area of the shelf. This ungrounding event was one of the leading driving forces behind the glacier's rapid change.

In '09, a greater CDW volume and temperature in Pine Island Bay led to a rise in ice shelf melting in comparison towards the before dimensions were drawn in 1994. But findings produced in The month of january 2012, and reported now in Science, reveal that sea melting from the glacier was the cheapest ever recorded. The top thermocline (the layer separating cold surface water and warm deep waters) was discovered to be about 250 metres much deeper in comparison with every other year that dimensions exist.

This decreased thermocline reduces the quantity of warmth flowing within the ridge. High definition simulations from the sea circulation within the ice shelf cavity show the ridge blocks the greatest sea waters from reaching the thickest ice. So its presence improves the ice shelf's sensitivity to climate variability since any alterations in the thermocline can transform the quantity of warmth blocking through.

The fluctuations in temperature recorded through the team might be described by particular weather conditions. In The month of january 2012 the dramatic cooling from the sea round the glacier is thought to become because of a rise in easterly winds triggered with a strong La Nin? event within the tropical Gulf Of Mexico. The winds flow in the west.

The findings suggest there's an intricate interplay between geological, oceanographic and weather processes. The research stresses the significance of both local geology and climate variability in sea melting in this area.

Lead author, Dr Pierre Dutrieux, from British Antarctic Survey (BAS) stated: "We found sea melting from the glacier was the cheapest ever recorded, and under 1 / 2 of that noticed in 2010. This enormous, and unpredicted, variability opposes the common view that the easy and steady sea warming in the area is deteriorating free airline Antarctic Ice Sheet. These results show the ocean-level contribution from the ice sheet is affected by weather variability over an array of time scales."

Co-author, Professor Adrian Jenkins, also from BAS, added: "It's not a lot the sea variability, that is modest in comparison with lots of areas of the sea, however the extreme sensitivity from the ice shelf to such modest alterations in sea qualities that required us unexpectedly. That sensitivity is because of a submarine ridge underneath the ice shelf which was only discovered in '09 when an Autonomous Underwater Vehicle planned the seabed underneath the ice. These new experience claim that the current good reputation for ice shelf melting and loss continues to be a lot more variable than formerly suspected and prone to climate variability driven in the tropics."

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