SOLAR CYCLES IN LATE MIOCENE LAKE SEDIMENTS AND THEIR IMPACT ON LAKE-RELATED ENVIRONMENTS

The global climatic evolution during the Cenozoic Era is well resolved with reference to Milankovitch-scales. Knowledge on climatic variations on smaller time periods, however, remains usually sketchy. Within the Holocene, short-term fluctuations were detected with periodicities ranging around 88, 208, 500, 1000 and 2300 years and could be linked to solar activity. Further back in Earth’s history, such signals are still scarcely recorded, especially due to the lack of an appropriate time resolution.

Our current project on European Late Miocene lake sediments focuses on such short-term-environmental changes. Solar-cycle-related periodicities were already revealed in a continuous 6-m-long core analyzed by 1-cm-sample-resolution. Magnetic susceptibility, natural gamma radiation and the total abundance of ostracods showed repetitive signals corresponding to the Lower and Upper Gleissberg, deVries, 500-year, 1000-year and 2300-year cycles, all imprinted with different intensities and with complex patterns of modulation.

Especially the natural gamma radiation captured oscillations on the smallest scale, indicating that there were re-occurring changes in wind- and/or rainfall pattern at a c.80-year-period. To resolve the impact of solar cycles more precisely, data on vegetation (pollen, dinoflagellates), and geochemistry are now evaluated for a data-set of 150 specimens of the same core. Identical samples as well as the constant 1-cm-sample density were used. Statistical analyzes confirmed the existence of several of the detected solar cycles also within this shorter records. In a next step the observed fluctuations in these proxies will be discussed in terms of paleoecology and paleoclimate. This will help to relate solar forcing with short-term vegetation dynamics and lake evolution during the Late Miocene.

This study is supported by the FWF-project P21414-B16.