Solar-forced 2600 BP and Little Ice Age highstands of the Caspian Sea

Abstract

The level of the Caspian Sea, the largest inland sea in the world, has fluctuated capriciously in history, with amplitudes up to 3 m in the last century, to 25 m in the last millennium, and to over 150 m since the Last Glacial. There is little consensus about the causes, and forecasts are contradictory, mainly due to a lack of solid data about past sea levels before 1837 AD, when instrumental observation started. We studied the Holocene Turali barrier complex along the western Caspian shore in Dagestan, Russia. Barrier dynamics during the last 3 m sea-level cycle in the past century show that only lagoonal deposits overridden by highstand barriers are suitable for dating former highstands. In the Holocene barrier complex, we selected the most suitable sites for dating using ground penetrating radar (GPR) profiles, outcrops and gravel pits. We obtained 14 accelerator mass spectrometry (AMS) 14C data on in situ double-valved molluscs from highstand lagoonal deposits. The results suggest that the last major highstands occurred around 2600 BP and in the Little Ice Age and coincide with global cooling events associated with minima in solar activity. This suggests that millennial precipitation changes in the Volga River drainage basin are also forced by solar activity.