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| Titel |
Evidence for double diffusion in temperate meromictic lakes |
| VerfasserIn |
C. Rohden, B. Boehrer, J. Ilmberger |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 14, no. 4 ; Nr. 14, no. 4 (2010-04-13), S.667-674 |
| Datensatznummer |
250012268
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| Publikation (Nr.) |
 copernicus.org/hess-14-667-2010.pdf |
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| Zusammenfassung |
| We present CTD-measurements from two shallow meromictic mining lakes. The
lakes, which differ in size and depth, show completely different seasonal mixing
patterns in their mixolimnia. However, the measurements document the occurrence
of similar seasonal convective mixing in discrete layers within their monimolimnia.
This mixing is induced by double diffusion and can be identified by the characteristic
step-like structure of the temperature and electrical conductivity profiles. The steps
develop in the upper part of the monimolimnion, when in autumn cooling mixolimnion
temperatures have dropped below temperatures of the underlying monimolimnion.
The density gradient across the chemocline due to solutes overcompensates the
destabilizing temperature gradient, and moreover, keeps the vertical transport close
to molecular level. In conclusion, preconditions for double diffusive effects are given
on a seasonal basis.
At in general high local stabilities N2 in the monimolimnia of 10−4–10−2s−2, the
stability ratio Rρ was in the range of 1–20. This quantitatively indicates that double
diffusion can become visible. Between 1 and 6 sequent steps, with sizes between 1 dm and 1 m, were visually identified in the CTD-profiles. In the lower
monimolimnion of the deeper lake, the steps systematically emerge at a time delay of
more than half a year, which matches with the progression of the mixolimnetic
temperature changes into the monimolimnion.
In none of the lakes, the chemocline interface is degraded by these processes.
However, double diffusive convection is essential for the redistribution of solutes in
the inner parts of the monimolimnion at longer time scales, which is crucial for the
assessment of the ecologic development of such lakes. |
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