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Catastrophes and Prehistory

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Author Topic: Catastrophes and Prehistory  (Read 6405 times)
Troy Exeter
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Posts: 2113

« on: March 18, 2007, 09:05:42 pm »

Antarctic ice sheet key to sudden sea level rise
Researchers show Antarctic ice sheets may not be as stable as previously thought. by Janet Wong

March 28, 2002 -- Physicists from Canada, the United States and Britain have concluded that a massive and unusually abrupt rise in sea level about 14,000 years ago was caused by the partial collapse of ice sheets in Antarctica, solving a mystery scientists have been heatedly debating for more than a decade.
Near the end of the last Ice Age, the Earth's sea level abruptly rose over 20 metres - four times faster than usual for that time period and at least 20 times faster than sea levels are rising now, report geophysicists Jerry Mitrovica of the University of Toronto, Peter Clark of Oregon State University , Glenn Milne of the University of Durham in the U.K. and Mark Tamisiea, a post-doctoral fellow at U of T, in the March 29 issue of Science .
The cause of this event - called the global meltwater pulse 1A, first identified in 1989 - has been unknown until now. The scientists say their research not only pinpoints the source of the meltwater pulse as coming from West Antarctica. It also makes the case that significant climatic events can occur very rapidly and unpredictably.

Ancient Mangrove Forests Found Under Reef

North Queensland marine researchers have opened a window into the past by exposing ancient mangrove forests entombed beneath the Great Barrier Reef.
Dr Dan Alongi from the Australian Institute of Marine Science says they have unearthed 9,000-year-old mangroves in old river channels that were swamped when sea levels rose after the last ice age.
He says the relic mangroves show an abrupt rise in the sea level, 20 times faster than previously thought.
"Material was very much intact, it didn't even have time to fully decompose when it was buried, so it does tell us that when climate change happened at least when it happened in the past it was comparatively quick," he said.

A cold event 8,200 years ago

Nature 22 July 1999

A cold event occurred between 8,400 and 8,000 years ago which affected Europe, North Africa and North America causing significant climate changes. It is believed to have been triggered by global warming which caused a catastrophic drainage of the Laurentide lakes in Canada.
This cooling event was forced by a massive outflow of fresh water from the Hudson Strait. The glacial lakes Agassiz and Ojibway were originally dammed by a remnant of the Laurentide ice sheet and drained catastrophically 8,470 calendar years ago. The sudden increase in freshwater, reduced sea surface salinity and altered ocean circulation, thereby initiating the most abrupt and widespread cold event to have occurred in the past 10,000 years.

Antarctic mud reveals ancient evidence of global climate change

By Mark Shwartz

In 1998, ODP scientists extracted a 150-foot-long sediment core from the muddy bottom of the Palmer Deep - a submerged section of the continental shelf along the west Antarctic Peninsula about 3,000 feet below sea level. The sediment sample was loaded with the shells of microscopic creatures called diatoms dating back some 10,000 years to the beginning of the Holocene - the most recent geologic epoch.
"The Antarctic Peninsula is an ideal region to investigate climate change at decadal to millennial time scales due to its location in one of the Earth's most dynamic climate systems," noted Dunbar. "The ODP sample gives us the first continuous, high-resolution Holocene sediment record from the Antarctic continental margin."
The sediment sample revealed higher concentrations of diatom shells during the mid-Holocene, roughly 5,500 to 7,000 years ago, which indicates that the waters surrounding the Antarctic Peninsula were more biologically productive then. According to Dunbar, higher productivity suggests that sea ice was less abundant during the mid-Holocene - a further indication that temperatures were higher. 
"We think it was quite a bit warmer then," he observed, noting that geochemical analysis of the sediment also revealed higher levels of nitrogen during the mid-Holocene. "Warmer temperatures appear to have produced freshwater streams that fed nitrogen and other nutrients into coastal waters," he explained.
During this warm period, sea levels rose from approximately 10m below the present sea level to approximately 1.7m higher than present day levels.
Legends around the Caribbean tell of a heavy rain falling for many days and many were drowned. It was this deluge that separated their islands from the mainland.
Little by little subsequent tempests submerged the lands of the Bahamas, separating the people from one another by arms of the sea.

Future studies of archaeological remains on the Bahama Banks will most likely prove that this strategically placed large island at the end of the Northern Equatorial current and at the beginning of the Gulf Stream was not only the homeland of Many American tribes, but was also the homeland of many European tribes such as the Basques and Celts.
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