Centennial- to Decadal-Scale Environmental Shifts in and around Lake Pannon Related to a Major Late Miocene Lake-Level Rise

A detailed ultra-high-resolution sampling of a 37-cm-long core of Upper Miocene lake sediments of the long-lived Lake Pannon has been performed. Despite a general stable climate at c. 11-9 Ma, several high-frequency oscillations of paleoenvironmental parameters are revealed by the analysis over a short time span of less than 1000 yr. Shifts of the lake level, associated with one major 3rd order flooding are reflected by all organisms through a cascade of environmental changes on a decadal scale. Within few decades, the pollen record documents shifting vegetation zones due to the landward migration of the coast; the dinoflagellate assemblages switch towards “offshore-type” due to the increasing distance to the shore; the benthos is affected by low oxygen conditions due to the deepening. These simple interactions are accentuated by smaller scale cycles, which lack this tight interconnection. Especially, the pollen data document a clear cyclicity that is expressed by iterative low pollen-concentration events coupled with low taxonomic diversities. These “negative” cycles are partly reflected by dinoflagellate blooms suggesting a common trigger-mechanism and a connection between terrestrial environments and surface waters of Lake Pannon. The benthic fauna of the core, however, does not reflect these surface water cycles. This forcing mechanism is not understood yet but periodic climatic fluctuations are favoured as hypothesis instead of further lake level changes. E.g. short phases of low precipitation, reducing pollen production and suppressing effective transport by local streams might be a plausible mechanism. This study is the first hint towards solar activity related high frequency climate changes during the Vallesian (Late Miocene) around Lake Pannon and should encourage further ultra-high-resolution analyses in the area.