Late Glacial and Holocene Paleoliminology of two temperate lakes inferred from sediment organic 𝛿13C chronology

[摘要] The stable carbon isotope (𝛿13C) and elemental C/N ratios in Total Organic Carbon (TOC) extracted from radiometrically dated cores from two Midwestern USA lakes were determined to investigate the factors that control these values in temperate lakes. The range of 𝛿13C values ( -26 to -32%) and C/N ratios (mean value ∼ 10.8) are typical of values reported for other temperate lake organic matter in this region. In the core from Lake Winnebago, Wisconsin, a negative correlation was seen between the TOC and 𝛿13C, which can be interpreted in terms of a re-mixing and consumption of sedimented organic carbon along with rapid equilibration throughout the water column. No correlation was seen between the TOC and 𝛿13C in the record from Ladd Lake, Ohio, implying that in this latter lake productivity alone was not a singular process controlling the isotope ratio. Here, it is suggested that equilibrium conditions are maintained such that the DIC of the water is never depleted of aqueous CO2 during high organic production and the resulting 𝛿13C of the organic carbon lacks correlation with the TOC. Further, in this lake a fine resolution analysis was carried out which indicated a possible anthropogenic influence on the isotope ratio around times when human settlement (∼ 300 yrs ago) and enhanced agricultural practices ( ∼ 80 yrs ago) were significant. The study shows that carbon isotope studies are useful in paleolimnologic investigations.

[学科分类] 天文学(综合)

[关键词] Organic carbon;lake sediments;carbon isotope ratios;lake productivity.