Causes and consequences of natural and anthropogenically induced late Holocene hydrological variations on the largest freshwater system in the Lesser Caucasus (Lake Sevan, Armenia)

Abstract

Although Lake Sevan is the largest freshwater reservoir in the Caucasus, no paleohydrological or paleoenvironmental investigations have been carried out on profundal sediments so far. Here we present high-resolution sedimentological results from a 141 cm-long sediment core covering the past 4870⁺¹⁹⁰/_-245 cal a BP. The chronology is based on a combination of ¹³⁷Cs/²¹⁰Pb and radiocarbon dating supported by paleomagnetic secular variation stratigraphy, providing new inclination and declination data for the Caucasus. The time frame covered by this sequence is characterized by a long-term lake level rising trend superimposed by smaller-scale hydrological variations which is in agreement with the rest of the Lake Sevan basin. In the presented sedimentary sequence, the superimposed hydrological variations seem to be coherent with the Hallstatt and Eddy cycles.

A distinct shift towards wetter conditions is observed between 2500 and 2000 cal a BP resulting in a very high lake level. An artificial lake level drop of about 20 m in the 20th century led to anoxic conditions similar to the ones during a low lake level at 4870⁺¹⁹⁰/_-245 cal a BP. This study shows that under natural conditions Lake Sevan was able to recover from this oxygen deficit when the lake level increased, implying that this would also happen to the artificially lowered lake today if the lake level were raised.