Baffin Island and The Big Chill
After four mild centuries, Greenland's climate turned grim in 1280 -- too cold for Norsemen to venture out to to farm, let alone rape, pillage, loot, or burn. Had Viking vices included climate modeling, King Magnus Law-Mender might have sent a long ship south to ask the Sultan of Solo throw some extra virgins in volcanoes, for evidence from the ice caps of Baffin Island, Geophysical Research Letters reports, focuses blame for the end of the Medieval Warm period on tropical eruptions.
The paper by Professor Gifford Miller of the University of Colorado Institute of Arctic and Alpine Research uses radiocarbon dating of plant remains emerging from beneath the receding ice to show it has shrunk 50 % since 1950 due to warming temperatures, and may vanish by midcentury. The Baffin Island ice caps are now smaller in area than at any time in the last 1,600 years,
"Even with no additional warming, our study indicates these ice caps will be gone in 50 years or less," he said.
The study also showed two distinct ice cap growth bursts around 1280 A.D. and 1450 A.D., matching ice core records of stratospheric aerosols. Miller take this to imply that major tropical volcanic eruptions caused the Little Ice Age that wiped out the Viking colonies in Greenland.
Most of Baffin's 196,000 square miles lie above the Arctic Circle.The research incorporates a half century of satellite data and aerial photos to document the shrinkage of the more than 20 ice caps on the island's northern plateau. Up to four miles long and generally less than 100 yards thick, and frozen to their beds,Miller says their "ice is so cold and thin that it doesn't flow, so the ancient landscape on which they formed is preserved pretty much intact"
In addition to carbon-dating plant material from the ice edges, the researchers extracted and analyzed carbon 14 that formed inside the Baffin Island rocks as a result of ongoing cosmic radiation bombardment, revealing the amount of time the rocks have been exposed,. Carbon 14 in quartz indicates that several thousand years ago the island had more extensive ice cover, which
Miller thinks was caused by decreasing summer sun as a result of precession of the Earth's axis. "This makes the recent ice cap reduction on Baffin Island even more striking."
Funded by the NSF, the study is remarkable for its novel use of radiocarbon samples from rocks for dating ice advance and retreat. Carbon 14 is formed by cosmic ray neutrons interacting with nitrogen, which comprises most of the atmosphere. There are traces of nitrogen in quartz as well, and recent advances in accelerator mass spectroscopy enable the traces of 14C formed in quartz to be counted in some cases literally one atom at a time, to date how long it has been exposed to the sky or shielded by ice-- 10 meters of water, liquid or solid, roughly approximates the shielding effect of the atmosphere.
your carbon dating article is most insightful. great job.
Posted by: Thomas P. Elderville | April 18, 2009 at 05:29 AM