Because sediment is deposited in the lake in annual layers, the cores provide a detailed record of Lake Tanganyika's past temperatures and productivity and of the regional wildfires.
The instrument record of lake temperatures from the 20th century agrees with the temperature analyses from the cores, Cohen said.
The cores were extracted as part of the UA's Nyanza Project, a research training program that brought together U.S. and African scientists and students to study tropical lakes. The National Science Foundation funded the project.
"A big part of our mandate for the Nyanza Project was looking at the interconnectivity between climate, human activity, resources and biodiversity," said Cohen, who directed the multi-year project.
Lake Tanganyika and similar tropical lakes are divided into two general levels. Most of the fish and other organisms live in the upper 300 feet (about 100 meters). At depths below that, the lake waters contain less and less oxygen. Below approximately 600 feet, the lake water, although nutrient-rich, has no oxygen and fish cannot live there.
During the region's windy season, the winds make the lake's surface waters slosh back and forth, mixing some of the deep water with the upper layers. This annual mixing resupplies the lake's food web with nutrients and drives the lake's productivity cycle, Cohen said.
However, as Lake Tanganyika warms, the upper waters of the lake become less dense. Therefore, stronger winds are required to churn the lake waters enough to mix the deeper waters with the upper layer. As a result, the upper layers of the lake are becoming increasingly nutrient-poor, reducing the lake's productivity.
In addition, warmer water contains less d
|Contact: Mari N. Jensen|
University of Arizona