According to a large multinational team of researchers, West Antarctica began emerging from the last Ice Age about 20,000 to 22,000 years ago, well before other regions of Antarctica and the rest of the world, and up to four millennia earlier than previously thought.
For more than a century scientists have known that Earth’s Ice Ages are caused by the wobbling of the planet’s orbit, which changes its orientation to the Sun and affects the amount of sunlight reaching higher latitudes.
The Northern Hemisphere’s last Ice Age ended about 20,000 years ago, and most evidence has indicated that the Ice Age in the Southern Hemisphere ended about 2,000 years later, suggesting that the south was responding to warming in the north.
But a new study, published online in the journal Nature, shows that Antarctic warming began 2,000 – 4,000 years earlier than previously thought. The study is significant because it adds to the growing body of scientific understanding about how the Earth emerges from an Ice Age.
The key to the discovery about West Antarctica resulted from analysis of the 3,405-m ice core, one of the deepest ever drilled in Antarctica.
“This ice core is special because it came from a place in West Antarctica where the snowfall is very high and left an average of 20 inches of ice or more per year to study. Not only did it allow us to provide more accurate dating because we can count the layers, it gave us a ton more data – and those data clearly show an earlier warming of the region than was previously thought,” explained study co-author Prof Edward Brook from the Oregon State University.
Prof Brook and his colleagues hypothesize that changes in the total amount of sunlight in Antarctica and melt-back of sea ice caused early warming at this coastal site – warming that is not recorded by ice cores in the interior of the continent.
“The site of the core is near the coast and it conceivably feels the coastal influence much more so than the inland sites where most of the high-elevation East Antarctic cores have been drilled. As the sunlight increased, it reduced the amount of sea ice in the Southern Ocean and warmed West Antarctica. The subsequent rise of CO2 then escalated the process on a global scale,” Prof Brook said.
“What is new here is our observation that West Antarctica did not wait for a cue from the Northern Hemisphere before it began warming. What hasn’t changed is that the initial warming and melting of the ice sheets triggered the release of CO2 from the oceans, which accelerated the demise of the Ice Age.”
“The recent increase in CO2 via human causes is also warming the planet, but much more rapidly,” the scientist concluded.
Bibliographic information: Fudge TJ et al. Onset of deglacial warming in West Antarctica driven by local orbital forcing. Nature, published online August 14, 2013; doi: 10.1038/nature12376