Limnology in Africa – Hand-Cranked, Deep-Water Research

Last summer, a team of researchers from the University of Wisconsin-Madison’s Center for Limnology and Wright State University in Ohio, were on the shores of Africa’s Lake Tanganyika, the oldest and deepest of the African rift lakes, for the field season. CFL grad student, Ben Kraemer, decided a summer wasn’t long enough and decided to stay for the year. He sent in this dispatch on his experience captaining a ship full of teens from the Maendeleo Youth Home.  BY: Ben Kraemer — One of my major goals for this year is to document changes in water temperature of Lake Tanganyika in response to climate change. Lake Tanganyika, the deepest lake in Africa, has one of the longest records of water temperature for any lake in the world (100+ years), and the data show that the surface is getting warmer by about 0.22 °C per decade. But the impacts of climate change are not only felt at the surface, they are also felt all the way down to the bottom of the lake, 1470 meters below! Because the lake never fully mixes, the deep water tends to stay put for thousands of years, making it a good indicator of long term climate dynamics. So how do we measure a lake’s temperature at 1000+ meters? These days, we use a titanium-encased, pressure-resistant temperature profiler to record the temperature. To determine the warming trend, we compare these data to historical temperature profiles taken over the last century using reversing thermometers, and other methods. While the technology behind the thermometers has changed a lot over the last 100 years, we still use the same kind of hand powered-winches that were used 100 years ago. Sending a titanium thermometer to the bottom of Lake Tanganyika using a hand winch is not an easy task, and I could not do it alone. Luckily, over the past 10 months I have been teaching a group of teens from the Maendeleo Youth Home about the lake and over time, they have become quite interested in all things limnology. This group of limno-savy young people was more than willing to help me deploy the temperature profiler. Last week we all hopped into a wooden boat, and we made our way out over one of the deepest parts of the lake. We let the temperature profiler plunge down to more than 1200 meters depth and then took turns cranking in the wire that suspended the instrument. To help them conceptualize the great depth of the lake, I compared the depth to the distance between Mjini and Mwanga, two main town centers a little more than a kilometer apart. As the wire was reeled in, they imagined passing familiar landmarks enroute between the two town centers. “I just passed that big mango tree,” one of the guys said in Swahili as he was cranking the winch. When the instrument finally reached the surface, I quickly downloaded the data on my field computer and showed them that at 1000 meters, the water was warmer than it was in December 2012, the last time I took a deep temperature profile. And in December 2012, the temperature at 1000 meters was warmer than it was in July 2012. Seeing these data was a very exceptional experience for them because most people who live on Lake Tanganyika’s shores have no access to scientific information about it. Once we were back from the lake, I bought all the kids a soda (which was also an exceptional experience for them!), to thank them for their hard work. They asked to join me the next time I take a deep temperature profile. Even the kids who got seasick asked to go again! They expect that, the next time we go, the deep water will be a little warmer, and, probably that they’ll get another soda!”