ICY EDGE: The retreat of Antarctic sea ice led to the warming of deep ocean waters—and thus the end of the last Ice Age—according to new research.
Image: NASA
Earth's climate can be sensitive, changing after a variety of events. A volcanic eruption or meteorite impact, for instance, can send enough particles into the air to block the sun and cool the climate. A thickening blanket of greenhouse gases can trap heat. And, more commonly, according to some scientists, slight changes in Earth's orientation toward the sun can cause it to cool or warm in so-called Milankovitch cycles (named after the Serbian engineer who first described them). Now, new evidence from a marine sediment core from the deep Pacific points to warmer ocean waters around Antarctica (in sync with the Milankovitch cycle)—not greenhouse gases—as the culprit behind the thawing of the last ice age.
Ice cores drawn from Antarctica and Greenland have shown that carbon dioxide (CO2) levels in the atmosphere began to rise at roughly the same time as the vast ice sheets began to melt. But it remained unclear exactly which came first: melting ice and warming seas released more CO2 or more CO2 led to melting ice and warming seas.
By studying sediment cores from the deep Pacific near the Philippines, paleoclimatologist Lowell Stott of the University of Southern California in Los Angeles and his colleagues revealed that the temperatures of the deepest seas rose by around 2 degrees Celsius (3.6 degrees Fahrenheit) at least 1,000 years before sea-surface temperatures. "Even accounting for the uncertainties of the age of CO2, the deep sea warmed substantially before the CO2 began to rise," Stott says. "The deep Pacific is such an enormously large volume of water that [this warming] reflects the input of a tremendous amount of energy into the global system."
Stott and his colleagues used the isotopes of oxygen contained within the remnants of microscopic surface and deep-sea creatures to establish temperatures; they then used a radioactive isotope of carbon to date their age. Combining the two techniques showed that deep-sea creatures dealt with a warmer climate long before their surface brethren did, they report in the online edition of Science.
Because such deep seawater circulates from the coast of Antarctica, this deep-water warming implies that the Southern Ocean drove the last major climate change. Stott notes that the periodic wobble in the Earth's rotational axis described by the Milankovitch cycles led to more sunshine falling on the Antarctic at the same time—a likely cause of the warming waters. "The amount of solar energy increased at the same time as this deep-sea warming," he says. "Sea ice around the Southern Ocean was withdrawing."
According to the marine core sample, a full millennium passed—enough time for both the deep and surface waters to entirely switch places—before sea-surface temperatures and global atmospheric levels of CO2 began to rise. The greenhouse gas then further warmed the changing climate, Stott says.
This year, the sea ice around Antarctica grew to its largest extent since satellite observation began in 1979—whereas the Arctic arrived at record minimum—meaning present climate change is a far different scenario. In fact, the Milankovitch cycles would predict gradual global cooling. Man-made greenhouse gases, primarily CO2, are unequivocally driving present-day warming, according to the Intergovernmental Panel on Climate Change. "This kind of study discusses the natural cycle and could help define the likely positive feedbacks we can expect in the long-term future, [for example] as temperatures warm, the ocean will want to give up more CO2, or rather absorb less," says climatologist Gavin Schmidt of NASA's Goddard Institute of Space Studies. "But it has no direct impact on attribution of 20th century warming."*
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Add CommentNow the question should be asked,"Why is the Artic Ocean warming?" You almost touched on it by describing Milankovitch cycles. The warble is caused by an increase in magma in the northern or southern latitudes. As proof of this has not the magnetic north deviated 33 feet towards Canada in recent years? A recent expedition to the Arctic discovered thousands of volcanic vents along the Kobienski and Gakkel ridges. In the case of the Gakkel Ridge they expected to see nothing because of the way the plates converged. But they found thousands of vents. Could this be the true reason for oceanic warming? The extreme increase of underwater volcanic activity is well documented.
Reply | Report Abuse | Link to this1999. "Ice Core records of Atmospheric CO2 Around the
Reply | Report Abuse | Link to thisLast Three Glacial Terminations"
(Fischer & al., Science 283, 12. marts 1999, p.1712ff)
also told us (9 years ago and desperately challenged by IPCC) that temperature lagged CO2 by about 800 years.
The resultats are based on deltaD in the Vostok ice core
(delta Deuterium = variations in the proportion of 2/1H (heavy hydrogen) to the common 1/1H isotope in the water before it froze) - a standard indicator of water temperature.
Correction: In English "12. marts" is "March 12" - sorry about that :-)
Reply | Report Abuse | Link to thisThose volcanic vents probably have as little heating effect as do car exhausts, or central heating flues, compared to the effects of CO2.
Reply | Report Abuse | Link to thisDeep Magma is solid due to the intense pressure at depth and migrates laterally at but a few millimeters per year. All over the world the earth's core is evacuating heat constantly. What causes deep 'Hot Spots' is not yet clear. Mauna Loa is a hot-spot, having little effect on ocean temperatures....
Mr. Schmidt seems a bit jumpy, as if every new scientific report is a challenge on global warming: "says climatologist Gavin Schmidt of NASA's Goddard Institute of Space Studies. 'But it has no direct impact on attribution of 20th century warming.' "
Reply | Report Abuse | Link to thisNo doubt. It is about the end of the last ice age and it probably bears upon anticipation of the next one. Schmidt's opinion ought not to have been invited or published here as if it were some sort of public peer review.
However, he is right to think that a great many people are going to admit the possibility that this mysterious heat source still exists and is still driving, in part, climate variability. He ought to have said, "That's fascinating; let's discover the heat source." We may need it to stave off the next ice age.