Photos by Joshua Brown
Covering approximately 660,000 square miles, the Greenland ice sheet serves as a bellwether of climate conditions such as the Earth鈥檚 temperature and projected sea-level rise.
Scientists trying to learn more from the largest ice sheet outside of Antarctica have had only a historically limited view into its past 鈥� just the last 125,000 years. But a in the December 8 edition of the journal Nature offers a first detailed climatological history, dating back 7.5 million years, of the Greenland ice sheet.
听
The team鈥檚 study of sandy deposits swept out to sea by rivers of glacial run-off across eastern Greenland suggests the ice sheet has been a 鈥減ersistent and dynamic鈥� presence that has melted and re-formed periodically in response to temperature fluctuations of just a few degrees, confirming that the ice sheet is a sensitive responder to global climate change.
鈥淲e wanted to develop a better understanding about how the Greenland ice sheet has survived prior eras of warming and periods of deglaciation,鈥� co-author and Boston College Assistant Professor of Earth and Environmental Sciences Jeremy Shakun said. 鈥淟ooking back millions of years contributes to our understanding of how much the Earth needs to warm before the ice sheet deteriorates.鈥�
The findings appear along with a report by another team of researchers, who reached a different conclusion studying a bedrock sample taken from beneath today鈥檚 ice sheet. Their findings point to a 280,000-year span about 1.1 million years ago when Greenland was ice-free, which runs counter to scenarios used in current computer models.
鈥淭hese results appear to be contradictory鈥攂ut they may not be,鈥� said University of Vermont geologist Paul Bierman, one of Shakun鈥檚 co-authors. He noted that both studies have 鈥渟ome blurriness鈥� in what they are able to resolve about short-term changes and the size of the ancient ice sheet. 鈥淭heir study is a bit like one needle in a haystack,鈥� he says, 鈥渁nd ours is like having the whole haystack, but not being sure how big it is.鈥�
Additional co-authors of the report听听included UVM post-doctoral researcher Lee B. Corbett, Susan R. Zimmerman of Lawrence Livermore National Laboratory, and Dylan H. Rood of Imperial College London.
