A study of oxygen isotopic fractionation during bio-induced calcite precipitation in eutrophic Baldeggersee, Switzerland

Citation:
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.

Date Published:

Jul

Keywords:

bicarbonate, carbonic-acid, co2, disequilibrium, equilibrium, high-resolution varve, lake-ontario, patterns, sediments, water

Abstract:

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.

Notes:

n/a

Website

DOI:

10.1016/s0016-7037(99)00049-6