September 5, 2013
West Antarctica’s Ice Sheet 20 Million Years Older Than Previosuly Estimated
April Flowers for redOrbit.com - Your Universe Online
A research team led by professors at the University of California Santa Barbara (UCSB) has revealed that, contrary to popular belief, an ice sheet on West Antarctica existed 20 million years earlier than previously thought. These results, published in Geophysical Research Letters, mark a paradigm shift for our understanding of the Earth’s great global ice sheets.
Ice sheets first grew on the West Antarctic subcontinent around 34 million years ago at the start of a global transition from warm greenhouse conditions to a cool icehouse climate. Computer simulations from prior studies were unable to produce the amount of ice that geological records indicate existed at that time because neighboring East Antarctica could not support it.
Understanding that more ice grew than could be hosted on only East Antarctica, some scientists theorize that the missing ice formed in the northern hemisphere millions of years before the documented ice growth, which started about 3 million years ago. The current research, however, reveals that is it not necessary to have ice hosted in the northern polar regions at the start of greenhouse-icehouse transition.
The same research team published studies in 2009 and 2012 showing that West Antarctica bedrock was much higher in elevation at the time of the global climate transition than it is today, with much of its land above sea level. The belief of the scientific community that West Antarctic elevations had always been low lying (as they are today) led researchers to ignore it in previous studies. Despite a warmer ocean in the past , the current study presents compelling evidence that this higher land mass enabled a large ice sheet to be hosted earlier than previously realized.
"Our new model identifies West Antarctica as the site needed for the accumulation of the extra ice on Earth at that time," said Douglas S. Wilson, a research geophysicist in UCSB's Department of Earth Science and Marine Science Institute. "We find that the West Antarctic Ice Sheet first appeared earlier than the previously accepted timing of its initiation sometime in the Miocene, about 14 million years ago. In fact, our model shows it appeared at the same time as the massive East Antarctic Ice Sheet some 20 million years earlier."
A sophisticated numerical ice sheet model was used to support this view. The research team used their new bedrock elevation map for the Antarctic continent to create a computer simulation of the initiation of the Antarctic ice sheets. In contrast to previous computer simulations of Antarctic glaciations, the new study found the nascent Antarctic ice sheet included substantial ice on the subcontinent of West Antarctica. About 10 percent of the total ice on Antarctica is contained in the West Antarctica Ice Sheet, which is similar in scale to the Greenland Ice Sheet.
In scenarios of sea-level rise due to global warming, West Antarctica and Greenland are both major players because of the sensitivity of the ice sheets on these subcontinents. Should the West Antarctic Ice Sheet melt, recent estimates conclude that global sea level would rise an average of 11 feet – adding to the sea-level rise from the melting of the Greenland Ice Sheet (about 24 feet).
A range of ice sheets were computed that consider the uncertainty in the topographic reconstructions, all of which show ice growth on East and West Antarctica 34 million years ago. The scientists were surprised to find that the total volume of ice on East and West Antarctica at that time could be more than 1.4 times greater than previously realized and was likely larger than the ice sheet on Antarctica today.
"We feel it is important for the public to know that the origins of the West Antarctic Ice Sheet are under increased scrutiny and that scientists are paying close attention to its role in Earth's climate now and in the past," concluded Bruce Luyendyk, UCSB professor emeritus in the Department of Earth Science and research professor at the campus's Earth Research Institute.