The stable isotope archive of Lake Pannon as a mirror of Late Miocene climate change

Lake Pannon was a long-lived Miocene and Pliocene lake system in Central Europe with a famous endemic mollusc fauna. The radiation of melanopsid gastropods and dreissenid bivalves has been explained simply by the opportunity to settle empty ecological niches after the extinction of marine life at the end of the Middle Miocene. This model, however, fails to explain the offset in the timings of evolutionary pulses in different mollusc families. Stable isotope data (oxygen, carbon) indicate a strong climatic forcing on these radiations. Moreover, the investigated time span covers the well-known Vallesian optimum and subsequent crises in European terrestrial ecosystems during the Late Miocene. The new palaeoclimatic data on the strongly changing isotope patterns of mollusc aragonite of Lake Pannon might shed light on the mechanisms acting during this crucial period. ing to the new interpretation, the early lake (∼ 11.6 Ma) was still influenced by the latest Middle Miocene dry spell. This phase coincided with a pronounced radiation of melanopsid gastropods. During the warm early Late Miocene (∼ 10 Ma) humidity increased and culminated in a phase with high summer precipitation. This caused a reorganisation of the coastal–deltaic faunas, suppressing the radiation of melanopsids. On the other hand, high nutrient loads favoured the dispersion of filter-feeding dreissenids. e steadily declining salinity, Lake Pannon remained an alkaline lake with pronounced stratification that was apparently periodically disrupted only during the humid early Late Miocene. A separation of the isotope data into genera and ecological guilds is the prerequisite for discussing overall trends of long-lived lake systems.