Cosmic Dust in Ice Cores Sheds Light on Earth's Past Climate
Each year, nearly 40,000 tons of cosmic dust fall to Earth from outer space. Now, the first successful chronological study of extraterrestrial dust in Antarctic ice has shown that this amount has remained largely constant over the past 30,000 years, a finding that could help refine efforts to understand the timing and effects of changes in the Earth's past climate. The same study also used an improved analytical technique to show that dust carried to Antarctica from continental sources changed, depending on climate.
The study, which appears a recent issue of the journal Science, involved researchers from the Lamont-Doherty Earth Observatory, a part of The Earth Institute at Columbia University, and the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany. The depth of the core they examined corresponded to the period between 6,800 years and 29,000 years before the present day - a span that includes the height of the last glacial period, and the transition to warm conditions similar to today.
The scientists collected particulate matter from the European Project for Ice Coring in Antarctica (EPICA) ice core and measured the concentration of helium-3 (3He), a rare isotope that is plentiful in the sun's solar wind, and is carried to Earth imbedded in cosmic dust particles measuring just a few thousandths of a millimeter in diameter. These dust particles carry their exotic helium load to the Earth's surface where they are preserved in the snow and ice of the polar ice caps, among other places.
Because ice cores from the polar caps provide a high-resolution temporal record of the past, the researchers were able to measure fine variations in the rate of cosmic dust accumulation between glacial and interglacial periods, as well as the helium isotope characteristics of these rare particles. They found that the accumulation of cosmic dust did not change appreciably as the Earth emerged from the last great Ice Age and entered the current warm period.
In addition, this was the first study to examine both cosmic and terrestrial dust using the same helium-isotope technique. As a result, they also found that the composition of mineral dust particles carried by wind from the southern continents to Antarctica changed considerably as the Earth's climate changed.
"The terrestrial dust coming down on Antarctica during the Ice Age obviously is not the same as that during warm periods," says Gisela Winckler, a Doherty associate research scientist at Lamont-Doherty and lead author on the study. "This may be due to the mineral dust originating from different regional sources or to changes in the process responsible for producing the dust."