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1999
Teranes, JL, McKenzie JA, Lotter AF.  1999.  Stable isotope response to lake eutrophication: Calibration of a high-resolution lacustrine sequence from Baldeggersee, Switzerland. Limnology and Oceanography. 44:320-333. AbstractWebsite

Stable isotope analyses of discrete seasonal layers from a 108-yr annually laminated freeze-core from Baldeggersee, a small, eutrophic lake in central Switzerland, provide information on the climatological and environmental factors, including lake eutrophication, that control oxygen and carbon isotopic composition of epilimnic biologically induced calcite precipitate. During the last 100 yr, Baldeggersee has undergone major increases in productivity and eutrophication in response to nutrient loading from agriculture and industrialization in the lake's watershed. Calibration of the isotopic signal in Baldeggersec to historical limnological data quantitatively links evidence of isotopic depletion in the sedimented calcite to trophic state of the lake. delta(18)O values from the spring/summer "light" sediment layers steadily diverged to more depleted values in response to historical eutrophication: measured delta(18)O values were up to -1.5 parts per thousand more negative than calculated equilibrium delta(18)O values. Evidence for C-13 depletion in the calcite, relative to equilibrium values, is more difficult to ascertain because of an overall dominance of isotopic enrichment in the dissolved inorganic pool as productivity in Baldeggersee increases. A positive association exists between the degree of oxygen 18 depletion and the calcite crystal size. Thus, large amorphous calcite grains can be used as a proxy for recognizing apparent isotopic nonequilibrium in sediment sequences from highly productive lacustrine environments from all geologic time scales. In contrast to the light layers, the oxygen isotopic composition of the calcite in the late summer/fall "dark" sediment layers is unaffected by the apparent isotope nonequilibrium. Oxygen and carbon isotope values from the dark laminae in the Baldeggersee sediment therefore provide environmental and climatological proxies that can be calibrated with known environmental and regional climate data for the last century.

Teranes, JL, McKenzie JA, Bernasconi SM, Lotter AF, Sturm M.  1999.  A study of oxygen isotopic fractionation during bio-induced calcite precipitation in eutrophic Baldeggersee, Switzerland. Geochimica Et Cosmochimica Acta. 63:1981-1989.   10.1016/s0016-7037(99)00049-6   AbstractWebsite

In order to better understand environmental factors controlling oxygen isotope shifts in autochthonous lacustrine carbonate sequences, we undertook an extensive one year study (March, 1995 to February, 1996) of water-column chemistry and daily sediment trap material from a small lake in Central Switzerland. Comparisons between calculated equilibrium isotope values, using the fractionation equation of Friedman and O'Neil (1977) and measured oxygen isotope ratios of calcite in the sediment-traps reveal that oxygen isotopic values of autochthonous calcite (delta(18)O) are in isotopic equilibrium with ambient water during most of the spring and summer, when the majority of the calcite precipitates. In contrast, small amounts of calcite precipitated in early-spring and again in late-autumn are isotopically depleted in O-18 relative to the calculated equilibrium values, by as much as 0.8 parts per thousand. This seasonally occurring apparent isotopic nonequilibrium is associated with times of high phosphorous concentrations, elevated pH (similar to 8.6) and increased [CO32-] (similar to 50 mu mol/l) in the surface waters. The resulting weighted average delta(18)O Value for the studied period is -9.6 parts per thousand, compared with a calculated equilibrium delta(18)O value of -9.4 parts per thousand. These data convincingly demonstrate that delta(18)O of calcite are, for the most part, a very reliable proxy for temperature and delta(18)O Of the water. Copyright (C) 1999 Elsevier Science Ltd.