Researchers studying the effects of ancient climate patterns on Antarctic waters have reached an alarming conclusion: The inhabitants of those seas were able to cling to life by the thinnest of margins during past ice ages, but they might not be able to weather the temperature increases predicted for the next century. In particular danger are the birds and mammals occupying the top of the food chain, such as emperor penguins and sea lions.
Earth's climate may be warming at the moment, but 20 times over the past 2 million years, massive glaciers marching from both poles plunged the planet into a deep freeze. Despite the extreme conditions, the organisms and ecosystems of the poles survived and then sprang forth again during the interglacial periods. But how?
That's what evolutionary ecologist Sven Thatje of the University of Southampton, U.K., and colleagues wanted to find out. They studied detailed fossil evidence in sediment cores from the Southern Ocean floor and data published elsewhere about the physiological characteristics of Antarctic birds and mammals. Based on their findings, the researchers report in the March issue of Ecology, even the coldest periods in the past could not wipe out Antarctica's ecosystems. Mostly the polar creatures migrated to deeper and slightly warmer waters--or, in the case of penguins, traveled along with the expanding sea ice--and then returned to their ancestral habitats when conditions improved.
That's the good news. The bad news is that those ecosystems could be vulnerable to warming. Thatje describes Antarctic organisms as "the champions of cold adaptation." In the past, they endured more severe conditions than anything existing today, he says, but their adaptation came at a price: They cannot tolerate higher temperatures. Even a few degrees of temperature increase in the planet's polar zones could kill off some of the creatures that depend on the cold environment, Thatje says. "Antarctic life has nowhere to go if the warming continues," he says.
It's an important study because it reveals that certain predators, such as sharks and large crabs, are now moving into waters that formerly were too cold to support them, says deep-sea biologist Paul Tyler, who is also at the University of Southampton but was not involved in the research. Over long periods of time, local prey populations could adapt to the predators’ presence and acquire defenses, he says, but the change might be too rapid for adaptation. So "the predators may reduce the prey populations significantly," he says, and further diminish the polar continent's biodiversity.