At the heart of the paper, Solar Forcing of the Polar Atmosphere, are calcium, nitrate and sodium data from ice cores collected in four Antarctic locations and comparisons of those data to South Pole ice core isotope data for beryllium-10, an indicator of solar activity. The authors also point to data from Greenland and the Canadian Yukon that suggest similar relationships between solar activity and the atmosphere in the northern hemisphere. They focus on years since 1400 when the Earth entered a roughly 500-year period known as the Little Ice Age.
The researchers' goal is to understand what drives the Earth's climate system without taking increases in greenhouse gases into account, says Mayewski. "There are good reasons to be concerned about greenhouse gases, but we should be looking at the climate system with our eyes open," he adds. Understanding how the system operates in the absence of human impacts is important for responding to climate changes that might occur in the future.
Mayewski founded the International Transantarctic Scientific Expedition (ITASE) and is the co-author of The Ice Chronicles: The Quest to Understand Global Climate Change, published in 2002 with Frank White. The United States' ITASE office is located at UMaine. Antarctic locations used in the paper include: Law Dome, a 4,576-foot high ice mound located about 68 miles from the coast facing the Indian Ocean and the site of an Australian research station; Siple Dome, a 2,000-foot high ice covered mound located between two ice streams that flow out of the Transantarctic Mountains into the Ross ice shelf, and the site of a U.S. research station; and two ITASE field sites west of Siple Dome where ice cores were collected during field surveys in 2000 and 2001.
The authors are Mayewski, Kirk A. Maasch, Eric Meyerson, Sharon Sneed, Susan Kaspari, Daniel Dixon, and Erich Osterberg, all from UMaine; Yping Yan of the China Meterological Association; Shichang Kang of UMaine and the Chinese Academy of Sciences; and Vin Morgan, Tas van Ommen and Mark Curran of the Antarctic Climate and Ecosystems CRC in Tasmania.
Since at least the 1840s when sunspot cycles were discovered, scientists have proposed that solar variability could affect the climate, but direct evidence of that relationship and understanding of a mechanism have been lacking.
The ice core data show, the authors write, that when solar radiation increases, more calcium is deposited at Siple Dome and at one of the ITASE field sites. The additional calcium may reflect an increase in wind strength in mid-latitude regions around Antarctica, they add, especially over the Indian and Pacific Oceans. Calcium in West Antarctic ice cores is thought to derive mainly from dust in Australia, Africa and South America and from sea salt in the southern ocean.
That finding, they note, is consistent with other research suggesting that the sun may affect the strength of those mid-latitude winds through changes in stratospheric ozone over Antarctica.
The authors also refer to sodium data from Siple Dome ice cores that have been reported by Karl Kreutz, director of UMaine's stable isotope laboratory. Changes in sodium appear to be associated with air pressure changes over the South Pacific.
Ice core data from Law Dome focus on changes in nitrate and may reflect changing wind patterns over Antarctica. The wind currents that bring nitrate to the continent, however, are less well known than those that carry sodium and calcium.
Researchers in the UMaine Climate Change Institute (http://www.climatechange.umaine.edu/) have focused on the relationship between solar variability and climate, particularly the use of isotopes in tree rings and ice cores to provide an indication of the sun's strength. The ice core data reported in the paper demonstrates a direct atmospheric consequence associated with changing solar radiation.
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