Saturday, November 28, 2009

Hints of a Catastrophic Paleoclimatic Event from Manny the Mammoth

In an effort to gain insight into the challenges posed by climate change, I just spent the last couple of hours watching the animated feature film “Ice Age 2 – The Meltdown.” The plot of the cartoon centers on a group of anthropomorphized prehistoric mammals (a mammoth, saber-toothed tiger, sloth and a halfwit saber-toothed squirrel) as they flee an impending flood and their certain extinction. Interestingly enough, the floodwaters in the movie purportedly result from a period of global warming and the associated thawing of their fictional ice-aged world. Initially, the characters in the film celebrate the rising temperatures with lakeside antics, but their clowning around comes to an abrupt end when they realize that their short-term fun-in-the-sun will inevitably end with substantial losses in lakeside real-estate, an ecosystem on which they’ve come to depend.

All considered I enjoyed the cartoon; mostly because of its paleoclimatological accuracy. Well, maybe it wasn’t all that accurate, but the underlying theme wasn’t too far-off…

Parallels between the feature and the real paleontological past can be glimpsed when consideration is given to the thermal fluctuations and water linked extinctions portrayed in the film. To explain, the impending floodwaters in the movie were precariously dammed by a mile-high glacial wall. It was the gradual disintegration of this frozen barrier that established the dramatic timeline for the lead mammals escape from danger. The waters bound by the glacial front had accumulated through the receding of the glacier itself, and should the wall be breached the waters would be freed to reap havoc. Although such a physical setting may seem a bit far fetched, it just so happens that between 12,900–11,500 years ago similar lakeside conditions may have contributed to the extinctions of numerous North American mammal species.

Characters from the ‘Ice Age 2’ ; glacier and glacial lake (Lake Agassiz?) in background.

During the Wisconsin glaciations about 12,000 years before the present, a massive continental ice sheet covered most of what is today the United States and Canada. As the Wisconsin came to a close, rising temperatures instigated its receding glaciers to form a colossal lake; roughly centered on modern day Manitoba. The lake was uniquely positioned in such a way that a combination of topography and its inclusive glacial blockades trapped the discharge of meltwater. The glacial melt, being unable to drain, resultantly accumulated in a water body that covered nearly half of a million square kilometers – Lake Agassiz. As in the animated movie, once sufficient hydrology was achieved to overcome its restricting geography and ice, the water was released in a catastrophic flooding event of incomprehensible immensity. However, unlike the cartoon’s scripted drama, the direst impact to fauna 12,000 years ago wasn’t the risk of drowning; the biggest consequence of the flood was its affects to global climate.

The enormous quantity of water released from the rupture of Lake Agassiz’s glacial banks, as opposed to flowing directly southward, chose to exit by way of the Saint Lawrence River. Following the St. Lawrence, the freshwaters moved eastward and into the North Atlantic. Once in the North Atlantic, the vast icy water cooled the warmer North Atlantic Current, and rapidly diluted the saline gradients that help drive its heat-conveying waters. Known as thermohaline circulation, variations in ocean water density create flow patterns that convey heat from regions proximal to the equator to those areas located more pole-ward; the constituent variations in density are brought about by surficial heat and saline content. The rupture of Lake Agassiz impacted the thermohaline circulation of the North Atlantic Current, altered heat transfer to the northern hemisphere, and drastically changed the Pleistocene climate of the North American Continent. The rapid climate change associated with the Lake Agassiz event is known as the Younger Dryas stadial (a ‘stadial’ is the name assigned to a period of cooling temperatures).

During the Younger Dryas stadial, mean annual temperatures throughout large portions of the Northern Hemisphere plummeted by as much as five-degrees Celsius. The drop in temperature caused some regions to re-glaciate, despite what had until recently been a warming trend. Climate change forced ecosystems into flux, and likely contributed to the extinction of several genera of mammals – The End Pleistocene Extinction Event.

The End Pleistocene Extinction Event marked the end of the road for some of the characters portrayed in the Ice Age movie, saber-toothed cats, giant sloths, mastodons and similar mammals. As a matter of fact, a recent article in Science collaborated the extinction chronology for more than 30 genera of Pleistocene fauna; the study used data from FAUNMAP to determine that the extinctions occurred nearly simultaneously.

Although much is known about the Younger Dryas stadial, its exact contribution to the End Pleistocene Extinction is still largely a matter for debate. Complicating the issue is the immigration of Clovis people into North America at about the same time that the Younger Dryas was putting a strangle-hold on the climate. The Clovis may have participated in the mammals’ disappearance through hunting – the Overkill Hypothesis.

Faith, J., & Surovell, T. (2009). Synchronous extinction of North America's Pleistocene mammals Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0908153106


  1. I wonder if we could push the cartoon at the republican national committee as a documentary, maybe its at a level they could understand.

    On second thought, no. Theyd probably see the residing glaciers as providing greater areas for oil exploration.

  2. Your obviously a conspirator in ‘climategate.’