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!”
