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In their study, the researchers say the major cooling of Earth and continental ice build-up in the Northern Hemisphere 2.7 million years ago coincided with a shift in the circulation of the ocean – which pulls in heat and carbon dioxide in the Atlantic and moves them through the deep ocean from north to south until it’s released in the Pacific.

The ocean conveyor system, Rutgers scientists believe, changed at the same time as a major expansion in the volume of the glaciers in the northern hemisphere as well as a substantial fall in sea levels. It was the Antarctic ice, they argue, that cut off heat exchange at the ocean's surface and forced it into deep water. They believe this caused global climate change at that time, not carbon dioxide in the atmosphere.

drwater wrote:Dissident,

Thanks for the details. It appears that the researchers are hypothesizing that the planet flipped to the current cooler state due to deep ocean circulation changes, which were caused by an increase in Antarctic ice. The real issue this raises is whether the current warming could cause the deep ocean circulation to flip back to the warmer state. That would cause serious problems. So far even though Antarctic ice volume is decreasing, the extent of ocean ice is slightly increasing. Let's hope nothing crops up to change the circulation pattern.

A new study shows that the rise of atmospheric carbon dioxide that contributed to the end of the last ice age more than 10,000 years ago did not occur gradually, but was characterized by three "pulses" in which C02 rose abruptly.

Scientists are not sure what caused these abrupt increases, during which C02 levels rose about 10-15 parts per million – or about 5 percent per episode – over a period of 1-2 centuries. It likely was a combination of factors, they say, including ocean circulation, changing wind patterns, and terrestrial processes.

The finding is important, however, because it casts new light on the mechanisms that take the Earth in and out of ice age regimes. Results of the study, which was funded by the National Science Foundation, appear this week in the journal Nature.


The researchers say that the increase in atmospheric CO2 from the peak of the last ice age to complete deglaciation was about 80 parts per million, taking place over 10,000 years. Thus, the finding that 30-45 ppm of the increase happened in just a few centuries was significant.

The overall rise of atmospheric carbon dioxide during the last deglaciation was thought to have been triggered by the release of CO2 from the deep ocean – especially the Southern Ocean. However, the researchers say that no obvious ocean mechanism is known that would trigger rises of 10-15 ppm over a time span as short as one to two centuries.

"The oceans are simply not thought to respond that fast," Brook said. "Either the cause of these pulses is at least part terrestrial, or there is some mechanism in the ocean system we don't yet know about."
One reason the researchers are reluctant to pin the end of the last ice age solely on CO2 increases is that other processes were taking place, according to Marcott, who recently joined the faculty of the University of Wisconsin-Madison.

"At the same time CO2 was increasing, the rate of methane in the atmosphere was also increasing at the same or a slightly higher rate," Marcott said. "We also know that during at least two of these pulses, the Atlantic Meridional Overturning Circulation changed as well. Changes in the ocean circulation would have affected CO2 – and indirectly methane, by impacting global rainfall patterns."

For many years, Earth scientists have theorized that the remains of Lake Mega-Chad (a huge lake that once existed where Lake Chad now sits in central Africa—on the borders of Nigeria, Chad, Cameroon and Niger) provide the fertilizer for the Amazonian rainforest, thousands of miles away in South America—without a constant infusion of nutrients the lush vegetation would disappear because nutrients are washed away by the constant rainfall. This new study of Lake Mega-Chad now casts some doubt on that theory.
By studying the geography of Lake Chad and the area around it using satellite imagery to make out ancient shorelines, an area that was once covered by water (the Bodélé basin) the researchers found that the region underwent a drying spell some 5,000 years ago, that has lasted to this day. Prior to that, the area had been humid, with a lot of rain, which fed Lake Mega-Chad, the largest lake in the world at that time. But then, something happened and the rains began to slow, which caused the lake to shrink rapidly, just a thousand years ago, much more recently than has been thought. When the lake shrank, it left behind thousands of years of silt deposits (which dried up and formed sand dunes) which has been carried by the wind, perhaps all the way to South America—but only for the last thousand years—which begs the question, where was the Amazon basin getting its fertilizer before that time?

Today all that remains of this enormous lake is Lake Chad. Soon even this whisper of a grander past will vanish – Lake Chad has shrunk by 95% in just the last 50 years. This is highly unfortunate as 30 million people rely on its water for drinking and irrigation.
https://toknowistochange.wordpress.com/tag/lake-chad/

dohboi wrote:Cool idea for a thread!

Isn't that top map a bit off, since 5000 years ago, not only was there a huge lake in what's now the southern Sahara and Sahel, but the Sahara wasn't quite the desert it is now then. Or am I remembering this wrong?

Apneaman wrote:Volcanoes, Not Meteorite, Killed Dinosaurs, Scientist Argues

http://www.livescience.com/25324-volcan ... saurs.html