Geochemical Changes in the Caspian Salt Marshes Due to the Sea Level Fluctuations

The Caspian Sea is subject to alternating transgressions and regressions that exert a strong impact on the topography, sediments, vegetation, and soils in coastal zones. The last transgression of the Caspian Sea (1978-1995) caused the development of a marsh-lagoon system along the accumulative seashore of the Central Dagestan. Salt marshes are complex and dynamic systems highly vulnerable to sea level fluctuations; therefore, they may be considered as a regional model of rapid environmental changes. Hazards in coastal zones may critically change the soil geochemistry affecting agricultural potential of large areas. Assessments of risks of the natural hazards in coastal zones are extremely difficult unless the end-to-end understanding of all natural factors. The research in the Caspian region shows the impact of extreme events in the coastal zones. Detailed landscape-geochemical investigations of the Caspian salt marshes were carried out in 1995-1996 (during the final stage of the transgression period) and in 2001-2003 (during the period of the sea level stabilization). These coastal areas are influenced by different landscape-geochemical processes, such as sulfidization, gleyzation, ferrugination, humus accumulation, halogenesis, and changes of alkali-acidic conditions. The development of the processes characterizes different stages of the Caspian Sea level fluctuations. This paper presents a discussion on stages and rates of landscape-geochemical processes, formation of geochemical barriers, and trace elements distribution in soils of the salt marshes.Geoscience & EngineeringCivil Engineering and Geoscience

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

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