Peruvian Ice Cores Reveal History Of Earth's Tropical Climate
April 5, 2013

Peruvian Ice Cores Reveal History Of Earth’s Tropical Climate

April Flowers for - Your Universe Online

Earth's tropical climate history has been revealed in unprecedented detail — year by year, for almost 1,800 years — by two annually dated ice cores drawn from the tropical Peruvian Andes.

In 2003, a research team led by Ohio State University retrieved core samples from a Peruvian ice cap. They noticed some startling similarities to ice cores they had gathered from Tibet and the Himalayas. Even though the cores were taken from opposite sides of the planet, patterns in the chemical composition of certain layers matched up.

They describe the find in an online edition of the journal Science Express, calling it the first annually resolved "Rosetta Stone" with which to compare other climate histories from Earth's tropical and subtropical regions over the last two thousand years.

These cores are an important new tool for scientists to study Earth's past climate. In addition, they will help further the understanding of climate changes that are happening today.

"These ice cores provide the longest and highest-resolution tropical ice core record to date," said Lonnie Thompson, distinguished university professor of earth sciences at OSU. "In fact, having drilled ice cores throughout the tropics for more than 30 years, we now know that this is the highest-resolution tropical ice core record that is likely to be retrieved."

Drilled from Peru's Quelccaya Ice Cap, the new cores are especially important because most of their 1,800-year history exists as clearly defined layers of light and dark. The light is a result of accumulated snow of the wet season, while the dark is from dust accumulated over the dry season.

Another reason they are special is the location where they formed, atop the high Andean altiplano in southern Peru. Snowstorms fueled by moist air rising from the Amazon Basin east of the ice cap provide most of the moisture of the region. The west also affects these ice core-derived climate records from the Andes in the form of El Nino, a temporary change in climate, which is driven by sea surface temperatures in the tropical Pacific.

El Nino is recorded in the Quelccaya ice cap as a chemical signature (especially in oxygen isotopes) that indicates sea surface temperatures in the equatorial Pacific Ocean over much of the past 1,800 years.

"We have been able to derive a proxy for sea surface temperatures that reaches back long before humans were able to make such measurements, and long before humans began to affect Earth's climate," Thompson said in a statement.

Ellen Mosley-Thompson is a distinguished university professor of geography at Ohio State and director of the Byrd Polar Research Center. She explained that the 2003 Quelccaya expedition was the culmination of two decades of work.

To gauge Earth's past climate, the Thompsons have retrieved ice cores from some of the most remote areas of the planet, including the Chinese Himalayas, the Tibetan Plateau, Kilimanjaro in Africa, and Papua Indonesia. As the researchers measured the concentrations of key chemicals preserved in thousands of years of accumulated ice, each new core has added a piece to the puzzle.

In 1983, Quelccaya yielded cores that earned the research team their first series of papers in Science. The quality of samples was limited, however, by available technology and the remoteness of the sample site. The nearest road was a two-day walk from the ice cap, forcing them to melt the cores in the field and carry samples back as bottles of water. This rendered some chemical measurements impossible to obtain, and diminished the time resolution available.

"Due to the remoteness of the ice cap, we had to develop new tools such as a light-weight drill powered by solar panels to collect the 1983 cores. However, we knew there was much more information the cores could provide" Mosley-Thompson said. "Now the ice cap is just a six-hour walk from a new access road where a freezer truck can be positioned to preserve the cores. So we can now make better dust measurements along with a suite of chemical analyses that we couldn't make before."

The new cores will provide a permanent record for future use by climatologists. Plants captured by the advancing ice cap 6,000 years ago are now emerging along its retreating margins, for example, revealing the Quelccaya is smaller than it has been in that time period.

"The frozen history from this tropical ice cap–which is melting away as Earth continues to warm–is archived in freezers at -30ºC so that creative people will have access to it 20 years from now, using instruments and techniques that don't even exist today," Thompson said.