Tracing climate-driven water level fluctuations of Lake Prespa (Greece) to lacustrine beach ridge sediments: a modern case study to facilitate past lake level reconstruction

Abstract

The Prespa Lake Basin (southwestern Balkans) contains a unique Holocene beach ridge record, which offers the opportunity to reliably reconstruct past water-level fluctuations based on absolute geomorphic stage index points. Such lake-level records are of great value for generating robust (quantified) hydro-climatic interpretations. These are urgently required for the Balkans, located at the juncture of contrasting Mediterranean climate and hydrological domains, as the few regional lake-proxy records covering the past millennium lack chronological resolution and appear to show different timing of wet-dry episodes. In order to use lake stage records for past climate change reconstructions, it is vital to understand modern lake-level sensitivity to specific hydro-climatic events and to track this signal to the landform-sediment archive. Accordingly, this paper analyses the impact of recent hydro-climate variability on the level of Lake Megali Prespa and traces this water-level signal to modern beach ridge sediments to facilitate future lake-level reconstructions. Annual lake fluctuations are strongly related to cumulative wet season precipitation which is highly correlated to the North Atlantic Oscillation. Lake Prespa reacts to sustained water balance changes by adjusting its lake surface area and thus surface evaporation. Historical water levels fluctuated between 853 and 842 m. Within this height range, lake surface areas change abruptly at 853–852, 847–846 and < 842 m. At stage levels in between these thresholds, set by the bathymetry, lake surface area only changes marginally and hydro-climatic conditions are approximately stable. This study finds that lake-level fluctuations are reliably registered by lacustrine beach sediment facies. Major lake level movements, which cross bathymetric thresholds, are clearly registered in the sediment-stratigraphic record by characteristic truncation surfaces and deposits. The chronological resolution of this lake-level record, and therefore the hydro-climatic signal it contains, is up to decadal timescales. Establishing quantified hydrological change estimates from the Prespa beach-ridge record requires knowledge of lake surface areas at specific lake stage index points. Modern analogues will give the difference in annually evaporated lake water volume between key stages. These differences are approximately equivalent to the change in water input (precipitation and discharge) and/or water loss (evaporation).