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> Southeastern North America wasn't Very Cold During the Ice Age
MarkGelbart
post Apr 11 2010, 10:33 AM
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In southeastern North America winters weren't particularly cold during the last Ice Age (118,000 BP-11,000 BP), and during some climate cycles winters were even warmer than those of today's. Summers, though, were definitely cooler than today's and would've been much more comfortable. I know most southerners dream of summertime high temperatures of 75 degrees F with low humidity, unlike today's humid 90 degrees F.

There were two main climate cycles during the Wisconsinian Ice Age that also probably prevailed during the previous Ice Ages, and they lasted about 5,000-11,000 years. When the Laurentide Glacier advanced south over Canada and the upper midwestern states, more of the atmosphere's water became locked in ice, thus creating cool, arid climatic conditions across the continent. Sudden warming trends would cause the glacier to recede, creating something scientists call meltwater pulses. During the meltwater pulses, the climate became wamer and there was more precipitation. Eventually, ice dams along the St. Lawrence River would collapse and large volumes of freshwater carrying thousands of icebergs and rocky debris would flood into the North Atlantic. This phenomenon is known as a Heinrich Event. The flood of cold fresh water would shut down the ocean current that keeps temperatures in North America and Europe moderate. Icebergs travelled as far south as off the South Carolina coast where scientists, using side scan sonar, discovered many keel scours from when the rocky bottoms of icebergs scraped furrows on the ocean floor. Temperatures plummetted following these Heinrich events causing climatic conditions to return to the cool arid cycles of before and the Laurentide glacier would once again begin to expand.

South Florida, however, was out of phase with the rest of North America. When the ocean current shut down, this warm water stayed around south Florida, so when the rest of the continent was enduring cold arid climate, south Florida was warm and wet, and vice versa, though during cold stages, south Florida was not subfreezing.

These wild climate swings occurred within less than 50 years, and the climate fluctuations of the Ice Age far surpassed any that have happened during recorded human history, and they surpassed any from the last 11,000 years.

Scientists know all this information from a variety of sources. They know exact average annual temperatures from the chemical compostion of air bubbles trapped in the Greenland glacier, fossil foraminifera in ocean sediment, and fossil groundwater. They can also use analysis of fossil pollen and animal fossils as a proxy for environmental conditions. We know during some Ice Age climate cycles, winters were even warmer in the south than today because of the presence of giant tortoises as far north as north Georgia. But summers were cooler--musk-oxen fossils have been found in Mississippi, Lousiana, and Tennessee; caribou fossils have been discovered in Alabama, Georgia, and S. Carolina; and a stag-moose tooth was found in a phosphate mine in South Carolina. The pollen record shows that northern species of trees mixed with southern species in forests that have no modern analogues. Cypress and magnolia trees grew with a cool weather species of alder in one location for example.

During astonomical cycles when the earth tilts to a lesser degree, temperatures are less seasonal and more uniform.

However, during some climate cycles of the Ice Age, winters were colder than they are today in the southeast. Fossil catfish bones from Georgia show growth rings caused by dormant periods, similar to those found in northern states. Modern southern catfish don't have these growth rings.

Several scientists looked at all the available data and determined that the south Atlantic states provided a "warm thermal enclave" for various species of plants and animals. The farther north and west from this enclave, the colder the temperatures were.

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I don't think I violate the TOS with this little self promotion because my links don't compete with accuweather. My book Georgia Before People: Land of the Saber-tooths, Mastodons, Vampire Bats, and Other Strange Creatures http://stores.lulu.com/GeorgiaBeforePeople and my blog http://markgelbart.wordpress.com/ are about pre-historic ecology, not weather.
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Removed_Member_TNsnowgoose_*
post Apr 11 2010, 06:19 PM
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Nice...Very interesting.......So It didnt get cold enough to kill anything here in the SE?
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Cracker
post Apr 11 2010, 11:47 PM
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yes, very interesting. Nice to see some new information here


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oh smeg
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MarkGelbart
post Apr 12 2010, 07:26 AM
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QUOTE(TNsnowgoose @ Apr 11 2010, 07:19 PM) *
Nice...Very interesting.......So It didnt get cold enough to kill anything here in the SE?


During some climate cycles of the Ice Age, winters throughout the south rarely had frosts. This explains how giant tortoises could expand their range north. I theorize climate cycles that had few frosts occurred when the earth tilted to a lesser degree, so that winters were warmer but summers cooler. It's the earth's tilt that determines the seasons. The degree of earth's tilt varies over time and goes through cycles. When the earth spins, it wobbles like a top.

But there were climate cycles of the Ice Age when southern winters were cooler than those of today. Apparently, however, average winter temperatures were only slightly cooler than averages of the present (maybe 5 degrees F). Scientists theorize that the current off the Atlantic coast kept south Atlantic states relatively warm compared to the rest of the continent.

Scientists used to think that warm weather species of trees retreated to small enclaves in Florida and along the gulf coast, but genetic evidence indicates that during the Ice Age many of these warm weather species of trees (such as southern pines) must have been widespread throughout their current range--more evidence that winter temperatures couldn't have been that much cooler than today, even though the glacier was fairly close. Scientists have even discovered macrofossils of southern pine species in Georgia that date to 30,000 BP.

This post has been edited by MarkGelbart: Apr 12 2010, 07:31 AM
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Cracker
post Apr 18 2010, 11:51 PM
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very nice article; print some more!


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MarkGelbart
post Apr 19 2010, 08:47 AM
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QUOTE(Cracker @ Apr 19 2010, 12:51 AM) *
very nice article; print some more!


Thanks.

My next one will be about the Sangamonian Interglacial Period. I'll write it within the next two weeks.
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