Study by research team, published in the Jan. 26 issue of Science magazine, proves that climate changes in the Northern Hemisphere affect the climate south of the equator

Study by research team, published in the Jan. 26 issue of Science magazine, proves that climate changes in the Northern Hemisphere affect the climate south of the equatorJanuary 26, 2001Judy Holmesjlholmes@syr.edu

A team of scientists from Syracuse University, Duke Universityand the University of Nebraska proved what many suspected all along–changes inclimate in the Northern Hemisphere have a direct effect on climate conditionssouth of the equator.

In a study published in the Jan. 26 issue of Science, theresearchers documented the first record of climate change in tropical SouthAmerica over the past 25,000 years. Contrary to previous conclusions, theresearchers found that when the Northern Hemisphere was buried under layers ofglacial ice, unusually wet conditions dominated South American tropical areas.It was previously believed that during the last glacial maximum (LGM), theclimate in tropical South America was characterized by arid conditions.

“We have a unique record of climate change in tropicalSouth America that shows when global climate conditions cooled and the glaciersadvanced, wetter climates prevailed in the Andes, and when things warmed up andglaciers receded, conditions in Amazonia got drier,” says Geoffrey Seltzer,associate professor of earth sciences at Syracuse University.

Seltzer, Paul A. Baker of Duke University and Sherilyn C.Fritz of the University of Nebraska are the lead researchers on a series ofprojects to study long-term climate changes in the South American tropics. Thegroup has done extensive studies of sediment cores they obtained from LakeTiticaca, which straddles the border of Peru and Bolivia high in the AndesMountains, and from the Altiplano of Bolivia. The Bolivian Altiplano includesone of the world’s largest salt flats. Their work has been providingscientists with a better understanding of how long-term climate variationsoccur.

“If we understand climate variations that occur fromnatural forces, we will be in a better position to predict what could happen asa result of the things humans do that affect the environment,” Seltzersays.

As the only large and deep freshwater lake in South America,Lake Titicaca holds an important climatic record in the layers of sedimenthidden beneath the water. Sediment has been building in the lake for more than25,000 years, says Seltzer, who, with Baker and Fritz, has returned to LakeTiticaca to prepare to drill the sediments beneath the lake in an effort touncover a longer record of tropical wet and dry phases.

“Unlike the Northern Hemisphere, where weather patternsoriginate in the west, the dominant source of moisture in the low latitudescomes from the east,” Seltzer says. “Therefore, major changes inclimate that occur over the Amazon will be similar to what we see in the Andesand which is recorded in the lake sediments.”

At least two forces drive global climate changes–periodicfluctuations in the Earth’s orbit around the sun, which affects the amount ofsolar radiation various regions of the Earth receive, and changes in sea surfacetemperatures, Seltzer says.

According to the study in Science, an analysis of the sedimentcores revealed periods of time during the past 25,000 years when the water levelin Lake Titicaca dropped some 80 to 100 meters, indicating dry climateconditions, and times when the lake overflowed continuously to the south,indicating wet climate conditions. The wet conditions corresponded to existingrecords of unusually cold sea surface temperatures in the northern AtlanticOcean, which occurred about 21,000 years ago. The cold sea surface temperaturesoccurred during the last glacial maximum and were strong enough to alter climateconditions in the South American tropics. When the glaciers receded and the seasurface temperatures warmed, drier conditions predominated in the Andes, Seltzersays.

During the past 2,000 years, Lake Titicaca has developed anoverflow outlet, Seltzer says. “We believe these latest changes are due toorbital variations where the Earth’s position changes in relationship to thesun. Things are getting a bit wetter and a little colder, which is an indicationof a move toward another period of glaciation in the Andes.”