Study adds new clue to how last ice age ended

Sep 08, 2010
Thick ice once filled New Zealand's Irishman Basin. Credit: Aaron Putnam, University of Maine

As the last ice age was ending, about 13,000 years ago, a final blast of cold hit Europe, and for a thousand years or more, it felt like the ice age had returned. But oddly, despite bitter cold winters in the north, Antarctica was heating up. For the two decades since ice core records revealed that Europe was cooling at the same time Antarctica was warming over this thousand-year period, scientists have looked for an explanation.

A new study in Nature brings them a step closer by establishing that New Zealand was also warming, indicating that the deep freeze up north, called the Younger Dryas for the white flower that grows near glaciers, bypassed much of the southern hemisphere.

"Glaciers in New Zealand receded dramatically at this time, suggesting that much of the southern hemisphere was warming with Antarctica," said study lead author, Michael Kaplan, a at Columbia University's Lamont-Doherty Earth Observatory. "Knowing that the Younger Dryas cooling in the was not a global event brings us closer to understanding how Earth finally came out of the ."

Ice core records show that warming of the , starting 13,000 years ago, coincided with rising levels of the heat-trapping gas, carbon dioxide. The study in Nature is the first to link this spike in CO2 to the impressive shrinking of glaciers in New Zealand. The scientists estimate that glaciers lost more than half of their extent over a thousand years, and that their creep to higher elevations was a response to the local climate warming as much as 1 degree C.

Rock samples were flown out of Irishman Basin by helicopter and shipped to the US for analysis. Credit: Mike Kaplan.

To reconstruct New Zealand's past climate, the study's authors tracked one glacier's retreat on South Island's Irishman Basin. When advance, they drag mounds of rock and dirt with them. When they retreat, bombard these newly exposed ridges of rock and dirt, called moraines. By crushing this material and measuring the build-up of the cosmogenic isotope beryllium 10, scientists can pinpoint when the glacier receded. The beryllium-10 method allowed the researchers to track the glacier's retreat upslope through time and indirectly calculate how much the climate warmed.

The overall trigger for the end of the last ice age came as Earth's orientation toward the sun shifted, about 20,000 years ago, melting the northern hemisphere's large ice sheets. As fresh melt water flooded the North Atlantic Ocean, the Gulf Stream weakened, driving the north back into the ice age. During this time, temperatures in Greenland dropped by about 15 degrees C. For years, scientists have tried to explain how the so-called Younger Dryas cooling fit with the simultaneous warming of Antarctica that eventually spread across the globe.

The Nature paper discusses the two dominant explanations without taking sides. In one, the weakening of the Gulf Stream reconfigures the planet's wind belts, pushing warm air and seawater south, and pulling carbon dioxide from the deep ocean into the air, causing further warming. In the other, the weakened Gulf Stream triggers a global change in ocean currents, allowing warm water to pool in the south, heating up the climate.

Bob Anderson, a geochemist at Lamont-Doherty who argues the winds played the dominant role, says the Nature paper adds another piece to the puzzle. "This is one of the most pressing problems in paleoclimatology because it tells us about the fundamental processes linking climate changes in the northern and southern hemispheres," he said. "Understanding how regional changes influence global climate will allow scientists to more accurately predict regional variations in rain and snowfall."

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User comments : 5

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5 / 5 (2) Sep 08, 2010
I think that if you take this article in conjunction with the following article:


It gives an interesting perspective on two views of the time around the end of the last ice age. It would be interesting to know how close together in time these were.
1 / 5 (1) Sep 09, 2010
So cap-and-trade might have prevented the last ice age from ending? ... This article claims rising C02 levels were responsible for global warming then. How is that possible? C02 is evenly dispersed around the planet. Why would only one hemisphere be affected? It would be more accurate to say that rising C02 levels accompanied warming.
not rated yet Sep 09, 2010
I don't understand the claim that CO2 is "evenly dispersed around the world". The variations may not be great, but I'd like to see some of ref to a study of its distribution because the following facts of physical chemistry and geography seem to me to suggest it should in higher concentrations in the Southern Hemishere: (1) CO2 has a higher molecular weight than N2 and O2; at high concentrations (as near the killer lakes in Africa) CO2 will exclude O2 for days in low lying areas; at atmospheric consentrations, the operations of combinatorial and thermodynamic entropy will permit greater dispersion than higher molecular wt and partial pressure would suggest but not by much. So a much lower percentage of CO2 should be above 10,000 feet than the percentage of O2 and N2. (2) "Consumption" of CO2 should be greater in the North since it has more algae supporting coast line, colder oceans, more plant biomass on land; it should exclude more CO2 as well, having much more land above 10,000 ft.
1 / 5 (6) Sep 09, 2010
New Zealand lost its glaciers for the same reason North America did, the Pole Shift of 10500 BC moved these areas well outside the polar circles, no more complicated then taking an ice cube from the freezer and placing it on a hot sidewalk. The real mystery is why this lie about an Ice Age is not challenged.
5 / 5 (2) Sep 19, 2010
The reason, is because catastrphic tectonic movement related to Pole shift=Balderdash

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