2035Traces Of Immense Prehistoric Arctic Ice Sheets During The Pleistocene
- Oct 2, 2013Patterson and his colleagues have created the highest resolution record of the 'Big Freeze' event to date, from a mud core taken from an ancient lake, Lough Monreach, in Ireland. Using a scalpel layers were sliced from the core, just 0.5mm thick, representing a time period of one to three months excerpt from http://www.sciencedaily.com/releases/2009/11/091130112421.htm.Traces Of Immense Prehistoric Arctic Ice Sheets During The PleistoceneBy News Staff | September 30th 2013
Geologists and geophysicists have discovered traces of large ice sheets from the Pleistocene on a seamount off the north-eastern coast of Russia, confirming for the first time that within the past 800,000 years in the course of ice ages, ice sheets more than a kilometer thick also formed in the Arctic Ocean.
This makes it possible to write an accurate climate history for this part of the Arctic. They had discovered the first signs of conspicuous scour marks and sediment deposits on the ocean floor north of Wrangle Island (Russia) on a Polar stern expedition in 2008 but they were unable to gather extensive proof until last year, during an Arctic expedition on the South Korean research vessel Araon. "After we had analysed the bathymetric and seismic data from our first voyage, we knew exactly where we needed to search and survey the ocean floor with the swath sonar of the Araon on the second expedition," said Frank Niessen of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), first author of the study.
The result of this research is a topographic map of the Arlis Plateau, a seamount on which deep, parallel-running furrows can be discerned on the upper plateau and the sides – and over an area of 2500 square kilometers and to an ocean depth of 1200 meters. "We knew of such scour marks from places like the Antarctic and Greenland. They arise when large ice sheets become grounded on the ocean floor and then scrape over the ground like a plane with dozens of blades as they flow.
"The remarkable feature of our new map is that it indicates very accurately right off that there were four or more generations of ice masses, which in the past 800,000 years moved from the East Siberian Sea in a north-easterly direction far into the deep Artic Ocean," says Niessen.
These new findings overturn the traditional textbook view of the history of Arctic glaciations."Previously, many scientists were convinced that mega-glaciations always took place on the continents – a fact that has also been proven for Greenland, North America, and Scandinavia. However, it was assumed that the continental shelf region of North-eastern Siberia became exposed in these ice ages and turned into a vast polar desert in which there was not enough snow to enable a thick ice shield to form over the years. Our work now shows that the opposite was true. With the exception of the last ice age 21,000 years ago, ice sheets formed repeatedly in the shallow areas of the Arctic Ocean. These sheets were at least 1200 meters thick and presumably covered an area as large as Scandinavia," says Niessen.
The AWI scientists still cannot say for certain, however, under what climate conditions these ice sheets formed and when exactly they left their marks on the bottom of the Arctic Ocean. "We theorize that the East Siberian ice sheets arose during various ice ages when the average global temperature was around five to eight degrees Celsius cooler than what it is today. But evidently this relatively minor temperature difference was often sufficient to allow initially thin ocean ice to grow into an immense ice cap..." says the geologist.
Published in Nature Geoscience.
excerpts from: http://www.science20.com/news_articles/traces_immense_prehistoric_arctic_ice_sheets_during_pleistocene-121411
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