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T. Sime-Ngando et al. (eds.), Lake Pavin, DOI 10.1007/978-3-319-39961-4_10
Lake Pavin Mixing: New Insights
from High Resolution Continuous
MeasurementsCéline Bonhomme, Didier Jézéquel, Michel Poulin,
Mohamed Saad, Brigitte Vinçon-Leite, and Bruno TassinAbstract
As a meromictic lake, Lake Pavin mixing is very specific. The chemocline located at about
60 m depth separates the mixolimnion (fully or partially mixed according to the year) and
the monimolimnion. Deep layers are geothermally heated and stability is ensured at the
bottom of the lake by the increasing dissolved substance concentration. The monimolim-
nion forms a compartment which has its own specific dynamics but that may interact with
the mixolimnion at large time scales. Understanding of physical mixing processes is crucial
to study further geochemical processes.
Temperature and turbulence were investigated in 2006 and 2007 using continuous mea-
surements, a CTD and a high resolution temperature microstructure profiler (SCAMP).
Continuous measurements give the evidence of a sublacustrine spring discharging intermit-
tently into the mixolimnion around 55 m depth. This cold water input was observed using
thermistor chains at different depths in 2007. Because of its low saline content, the spring
water input rises in the water column by saline convection. The use of a simple conceptual
model, representing turbulent diapycnal diffusivity and convection shows its role in main-
taining the meromixis characteristic of the lake on the intra-annual time scale. The spring
also influences seasonal overturns and thus contributes to establish the depth of the mixo-
limnion–monimolimnion interface on the interannual time scale.
Using SCAMP, vertical dispersion coefficients are estimated by different methods.
Vertical dispersion coefficients show a high space and time variability. The use of these data
in the geochemical model AQUASIM applied to Lake Pavin shows a variability of model
outputs directly depending on mixing inputs and their variability.Keywords
Meromixis • Water mixing • Kz • Turbulence • TemperatureThis chapter is devoted to revisiting the mixing patterns of
Lake Pavin thanks to new insights gained from high-
resolution continuous measurements. In the first section, the
physical regime of Lake Pavin is presented. Then the factors
causing the meromixis are explained, namely the role of a
sublacustrine spring in the mixolimnion and the role of the
winter meteorological conditions. In a third section, high fre-
quency measurements performed in order to assess the verti-
cal diffusivity in the water column are described. The impact
of the intermittency of the diffusion coefficients on the fateC. Bonhomme (*) • M. Saad • B. Vinçon-Leite • B. Tassin
LEESU, UMR MA 102, École des Ponts ParisTech,
Marne-la-Vallée, France
e-mail: [email protected]
D. Jézéquel
IPGP (Institut de Physique du Globe de Paris), Sorbonne Paris
Cité, Univ. Paris Diderot, UMR 7154 CNRS, 1 rue Jussieu, 75005
Paris, France
M. Poulin
Centre de Géosciences, Ecole des Mines ParisTech, Paris, France