Time Dependent Tracers in Limnology: Sulfur Hexafluoride
(SF6) and Chlorofluorocarbons (CFCs) (update: 8/2003)
We have conducted studies on some of the world's deepest lakes to contribute to a better understanding of the
timescales of mixing and transport in these lakes.
Lake Malawi/Nyasa/Niassa, East Africa
image source: NASA
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In 1997 we participated in an expedition on Lake Malawi/Nyasa/Niassa in
East Africa. This 704 m deep lake is anoxic below a depth of about 220 m.
The main purpose of the expedition was to study
the deep water renewal rates using measurements of the time-dependent
tracer chlorofluorocarbon 12 (CFC-12). We have
also collected samples for nutrients, noble gases, 14C, delta 13C and N2O.
Lake Issyk-Kul, Kyrgyzstan
image source: NASA
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Our expedition to Lake Issyk-Kul, Kyrgyzstan, took place in September 2000.
This lake is the fifth deepest lake in the world
(about 650 m) and it is brakish due to a lack of outlet. Its current salinity
is about 6 g/kg. During this study, time-dependent
(atmospheric) sulfur hexafluoride was sampled for and analyzed for the first time
in a large lake. Our results show that the
deep water is ventilated on a timescale of about one decade. We have also
determined the major ion composition for this lake
and we have collected CTD profiles and samples for the analysis of dissolved oxygen,
nutrients, noble gases and the tracer
tritium. The results are published in two papers (Geophysical Research Letters (GRL),
Geochimica et Cosmochimica Acta (GCA)).
For the paper in GRL, there is an additional table of measurement results available.
See publication list for details.
