Seasonal variations in the carbon isotope composition of components of the pelagic food web in Lake Kinneret were recorded and compared with those recorded for bulk plankton from the lake in the early 1970s. Individual planktonic components as well as bulk plankton were isotopically lightest shortly after overturn in January and heaviest in May, after the peak of the annual bloom of the dinoflagellate Peridinium gatunense. The range of VC values observed over an annual cycle and the annual and seasonal means varied considerably between taxa. Within the primary producers, P. gatunense (range, -23.2 to -17.97~) was significantly "C-enriched relative to concurrent nanoplankton (-27.4 to -19.0%$. Zooplankton 6°C showed indistinct taxon-specific differences but greater seasonal variation (-33.8 to -19.8%0) than any phytoplankton component examined. Adult fish exhibited smaller 6i3C variability than the planktonic components. End-member isotope compositions confirmed the linkages nanoplankton + zooplankton + Kinneret sardines, and Peridinium + Sarotherodon galilaeus. Likely grazing of zooplankton on isotopically heavy Peridiniopsis spp. in spring and on a yet undetected light component in winter were implicated. The data demonstrate that the 613C of bulk particulate organic matter samples provides only a simplified view of a complex picture of 613C dynamics within the pelagic food web of a freshwater system.

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Throttling of freshwater inputs into the meromictic Dead Sea weakened the long-term stability of the water column. Between 1975 and 1978 successive deepenings of the pycnocline from 70 meters to beyond 200 meters were recorded. Complete overturn finally took place during the winter of 1978-1979. This unique process was accompanied by changes in the geochemistry of several components.

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