Isotopic paleolimnology of Lake Kinneret
Limnol. Oceanogr., 48(1), 2003, 68-78 | DOI: 10.4319/lo.2003.48.1.0068
ABSTRACT: The carbonate, organic C, and N contents and their respective δ13C were measured in four cores from Lake Kinneret, Israel. Using these data and the isotopic difference between coexisting carbonate and organic C, Δδ13C, we attempted to reconstruct the lakes productivity and regional climatic conditions during the late Holocene. The sedimentary record of the last 120 yr (for which climatological data are available) demonstrates that during periods of intense productivity, organic C content and its δ13Corg are high, whereas the Δδ13C values are low. During wet periods, characterized by intense input of particulates and nutrients from external sources, the CaCO3 content, its δ13Ccar and δ18Ocar, and the organic C:N ratios are low. Based on these correlations, the longer sedimentary record of the last ca. 3,300 yr was divided into five stages, which differ in productivity and/or climatic characteristics. This longer sedimentary record indicates that the primary production in Lake Kinneret has varied in the past over a range similar to that observed presently, but the rate of these changes was much slower. The rainiest period recorded in the sediments was from about 200 B.C. to A.D. 200, i.e. during the Roman period, when the region was heavily populated. The recent decrease in δ13C of atmospheric CO2 that accompanies the global anthropogenic CO2 rise seems to be recorded by a commensurate decrease in δ13Ccar of the sediments. The concomitant increase in D δ13C expresses an increase in the isotopic fractionation of the lakes primary producers, which may also be related to the atmospheric CO2 rise.