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Ice Locks Lake Secrets: Dye Study Reveals Slow Mix
9 Sep
Summary
- Dye released in 1984 under lake ice showed slow dispersion.
- Wind creates seiche currents that move ice and drag water.
- Water's density anomaly at 4°C keeps columns layered below ice.
In 1984, a study involving dye injected under the ice of Swedish lakes demonstrated that water mixing below the ice was significantly slower than previously assumed. Findings indicated that about 95 percent of the dye remained in the uppermost seven meters, a detail from Lars Bengtsson's research published in 1986. This research investigated dispersion in ice-covered lakes, including Lake Erken near Stockholm.
Bengtsson's work revealed that wind influences water movement indirectly by tilting the ice sheet, creating seiche currents. These currents drag the water beneath through friction, though their speed is quite slow. Later research in 1996 compared various mixing processes, finding seiche-driven currents were much more significant than convection from the lakebed, but still confined to thin horizontal layers.
This layering phenomenon is primarily due to water's unique density property, reaching maximum density at 4°C. This anomaly prevents vertical mixing beneath the ice. Bengtsson's studies collectively suggest that ice cover redirects rather than halts water currents, confining them to horizontal layers, a principle now established within physical limnology.
