Premium
Factors controlling δ 13 C values of sedimentary carbon in hypertrophic Baldeggersee, Switzerland, and implications for interpreting isotope excursions in lake sedimentary records
Author(s) -
Teranes Jane L.,
Bernasconi Stefano M.
Publication year - 2005
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2005.50.3.0914
Subject(s) - sedimentary rock , isotopes of carbon , geology , isotope , δ13c , paleontology , stable isotope ratio , oceanography , geochemistry , nuclear physics , physics
We use stable carbon isotope values (δ 13 C) in sedimented organic matter and carbonate as proxy indicators of productivity changes in a highly eutrophic to hypertrophic lake. Stable isotope data from a seasonally sampled sediment core recovered from Baldeggersee, Switzerland were compared with direct and inferred total phosphorus (P) concentrations. Carbon isotope values of sedimentary organic matter (δ 13 C org ) in both seasonal varves and over the past 100 yr are not linearly related to total P concentrations, nor do they mirror observed trends in carbonate isotope values (δ 13 C CaCO3 ). Baldeggersee δ 13 C org values are influenced by both variations in the relative inputs of eukaryotic biomass, which becomes enriched in 13 C with increasing primary productivity, and the contribution of microbial biomass produced in the expanding anoxic bottom waters, which is typically very depleted in 13 C. We also examined the fractionation within the organic matter‐CO 2 –CaCO 3 system, calculated as ε total organic carbon(TOC) = 10 3 {[(δ 13 C CaCO3 + 1,000)/(δ 13 C org + 1,000)] − 1}. Thresholds within the measured ε TOC values represent Baldeggersee CaCO3 trophic status more accurately than δ 13 C org or δ 13 C CaCO3 values alone. In alkaline lakes with endogenic carbonate precipitates, ε TOC values can facilitate accurate interpretation of values and trends in organic carbon isotope data, and can help to better assess trophic history and lake remediation efforts in lake systems that have been heavily affected by cultural eutrophication.