Evidence for double diffusion in temperate meromictic lakes
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Cites background from "Evidence for double diffusion in te..."
...Previously only reported in tropical lakes, this phenomenon has been observed in meromictic lakes of the temperate climate zone as well (Sánchez España et al., 2009; von Rohden et al., 2010)....
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12 citations
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Cites background from "Evidence for double diffusion in te..."
...• Double-diffusion (Brenda: Hamblin et al. 1999; German mining lakes: von Rohden et al. 2010)....
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References
2,722 citations
"Evidence for double diffusion in te..." refers background in this paper
...The phenomenon of double diffusive convection has been discussed in detail in numerous observational, laboratory, and theoretical studies (e.g. Turner, 1973; Kelley, 2003; Schmitt, 1994)....
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...Von Rohden et al. (2009) discuss this as a result of convective mixing in the mixolimnion. Convective mixing of the upper layer is strongest during summer when nocturnal cooling removes the heat of the preceding daytime through the surface. This drives a convection which reaches the (shallow) chemocline. Therefore the depth of the chemocline gradually increases during summer (chemocline erosion). In the cool season, mixing in the surface layer is weaker (wind speed 2 m above the lake surface∼0.5 m/s on average, virtually not exceeding 2 m/s), and the chemocline gradually moves upwards, presumably due to groundwater inflow. Figure 2b illustrates the situation in the larger Lake Moritzteich. The upper ∼11 m of the water column undergo the “usual” thermal cycle of temperate lakes with a warm epilimnion and a cooler hypolimnion in summer and a homothermal mixolimnion during the cool season. During the warm season starting in April, heat slowly enters the upper monimolimnion (similar to Lake Waldsee). This heating still continues while autumnal cooling already affects the mixolimnion. After the formation of local temperature maxima (e.g., on 19 November at ∼12 m), an inverse temperature profile establishes with gradients of 2–3 C/m between the mixed∼4C mixolimnion and the warmer monimolimnion. Heat diffuses out of the monimolimnion along these gradients. In general, the seasonal temperature signal at the top of the chemocline intrudes to a depth of about 16 m, i.e. at least 4 m into the monimolimnion. The monimolimnion temperatures follow the mixolimnion signal with a depth dependent delay. For example in the profile of 16 December 2008, the temperature has a local maximum at ∼ 14 m while the mixolimnion is cooler, close to 4 C. Towards the bottom, the temperature remains inversely stratified with much less variation, ending at a virtually constant value of ∼7.3C. This indicates a continuous heat flux from the sediments. With respect to electrical conductivity, we find a subdivision of the monimolimnion into two layers: The “upper” monimolimnion extends from the chemocline to ∼14 m depth. It is separated by a density step from the “lower” monimolimnion extending from∼15.8 m to the bottom. This structure as a whole has persisted for several years and has shown only little variation. While the seasonal mixing in the water bodies above the chemoclines is quite different between the lakes, their behaviour regarding the meromixis is similar. Seasonal temperature changes at the top of the chemocline proceed faster and deeper into the monimolimnion than variations of conductivity. This indicates that the effective diffusivities of heat and solutes are different. Hence, vertical transport must to a large extent be at a level close to the molecular diffusion, especially within the chemocline. The vertical density gradients are mainly caused by gradients of dissolved iron and the carbonate system. Ferrous iron (FeII ) which is transported out of the anoxic monimolimnia by diffusion is oxidized in the lower hypolimnion. As particulate ferric iron (Fe III ) it settles back into the monimolimnion, where it eventually redissolves. This chemical cycle results in the conservation of distinct chemoclines and implies an evanescent effective transport of the density regulating iron, sustaining the chemical and therefore the stable density stratification across the chemocline. These geochemical processes are discussed by means of lake Waldsee in Boehrer et al., (2009). The temporal variation of the overall electrical conductivity ( κ25) in the mixolimnion and monimolimnion of Lake Waldsee by about 10% (Fig....
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...Von Rohden et al. (2009) discuss this as a result of convective mixing in the mixolimnion....
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532 citations
"Evidence for double diffusion in te..." refers background or methods in this paper
...where α25 = 1/(25+ n/m), and n, m are the respective regression coefficients (Boehrer and Schultze, 2008)....
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...From the linear regression to the data from 1.5◦C to 30◦C the electrical conductivity for the chosen reference temperature of 25◦C could be evaluated: κ25= C(T ) α25(T −25◦C)+1 , (1) where α25 = 1/(25+ n/m), and n, m are the respective regression coefficients (Boehrer and Schultze, 2008)....
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...Meromixis is a well known phenomenon, also occurring in lakes located in regions in a temperate climate (Boehrer and Schultze, 2008)....
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498 citations
"Evidence for double diffusion in te..." refers background in this paper
...The phenomenon of double diffusive convection has been discussed in detail in numerous observational, laboratory, and theoretical studies (e.g. Turner, 1973; Kelley, 2003; Schmitt, 1994)....
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290 citations
"Evidence for double diffusion in te..." refers methods in this paper
...We therefore developed specific formulas to calculate water density from measured electrical conductivity and temperature, since standard formulas (e.g. Chen and Millero, 1986) did not apply (e.g., Hamblin et al., 1999)....
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174 citations