Investigating Droughts and Maya Collapse

March 2, 2011, 4:57 PM By TAKESHI INOMATA

Sunday, Feb. 27

An important component of our research is the study of the past environment and climate changes.

A team of Japanese geologists and plant scientists addresses this by analyzing lake sediments as part of the project financed by the Japanese Ministry of Education, Culture, Sports, Science and Technology and directed by Kazuo Aoyama.

In contrast to archaeologists, who usually specialize in specific geographic regions, those researchers are global travelers. They have been taking lake cores from Japan, China, Cambodia, Bali, Easter Island, Egypt and Peru. The team is known for its uncanny ability to find annual varves and for its innovative analysis. Under specific conditions of seasonal change, lake hydrology and the anoxic water that prevents bottom-dwelling critters from disturbing sediments, thin laminations of deposits may form yearly in lake bottoms. These annual varves are time capsules of environmental data. Through the analysis of geochemistry, isotopes, pollens, diatoms (a group of algae) and other remains in each layer, scholars can trace changes in precipitation, vegetation, agricultural practice, erosion rates, volcanic eruptions, etc., in a yearly resolution.

By collaborating with these natural scientists, we try to examine the effects of environmental changes on social processes, as well as human impact on the environment. A particularly intriguing question is the relation between droughts and drastic social changes. Around the ninth century A.D., many lowland Maya centers were abandoned. This is the phenomenon generally called the Classic Maya collapse. Recent studies of lake cores from the northern Maya lowlands by other scholars have shown possible evidence of droughts during this period.

The drought theory of the Maya collapse has become a point of heated debate among Maya archaeologists and environmental scientists. The unsolved problem is that the northern lowlands are drier areas which appear to be more vulnerable to droughts, yet many centers prospered in this region during the supposed dry spells. The wetter southern lowlands, where Ceibal is located, witnessed the abandonment of many cities, but evidence of droughts in this area remains unclear.

Through high-resolution environmental data, we would like to address this conundrum and other complex relations between humans and the environment. Simply saying droughts caused, or did not cause, the Maya collapse (which refers to significant political changes in certain areas, not to the end of a civilization) is not enough. We want to see how people were affected by climate changes and how they coped with them. Through many changes and crises, including the most severe effects of contact with the Spanish, Maya society and culture have persisted. Today's Maya populations, like our Q'eqchi' friends, make societies as vibrant as their ancestors'.

The leader of the environmental research team is the highly dynamic Hitoshi Yonenobu, a dendrochronologist who specializes in chronological and environmental research through the analysis of tree rings. As both tree rings and lake varves are annual records of the environment and climate, the same basic principles can be applied to their analysis. Kazuyoshi Yamada, a big and powerful natural geographer who earned the nickname of "Japanese Rambo" from our local workers, is a major force behind their hard schedule of coring in one lake after another. Toshiyuki Fujiki is a pollen analyst who looks 15 years younger than his age. Rumor has it that he was treated like a movie star in Cambodia. Yoshitsugu Shinozuka is a gentle geochemist, who carries through his work quietly and steadily. Another main member, Hiroo Nasu, analyzes carbonized remains in lake cores, as well as those from our excavations. Unlike his lake-hopping colleagues, he spends day after day doing flotation in our camp — a process of isolating carbonized remains through the sieving of soils in water. Despite his elementary Spanish, his warm personality and smiles quickly won the friendship of our Guatemalan members.

To find annual varves, they needed to take sediments from water depths of 30 meters or more, which required substantial coring equipment. It took Kazuyoshi two full days to clear the equipment through customs before their pursuit of annual varves was on. Their main targets were Lakes Petexbatun and Las Pozas near Ceibal, and Lake Quexil in the central Guatemalan lowlands.

Hauling the large coring equipment by car and boat, they attacked the lakes one by one. The results appear to have been highly successful. They extracted a series of four-meter-long cores from the deepest parts of those lakes. But annual varves are particularly difficult to find in tropical areas. They will not know if the cores contain annual varves until they open the sample tubes in Japan. Even without annual varves, these long cores promise to provide rich data on environmental changes. Now many days of lab analysis await them.

Source: New York Times