Caspian sea-level change: a catastrophe and a blessing in disguise
by
Salomon B. Kroonenberg
Delft University of Technology, Department of Applied Earth Sciences, P.O.Box 5028, 2600 GA Delft, the Netherlands

The Caspian Sea, the largest inland water body on earth, shows sea-level fluctuations at much shorter time scales than the world's oceans. It experienced a full sea-level cycle between 1929 and 1995, with an amplitude of 3 metres. Rates of sea-level rate between the 1977 lowstand and the 1995 highstand average a hundred times that of the eustatic rise.

Caspian sea-level change has caused numerous catastrophes and near catastrophes in the recent past. During sea-level fall the northern Caspian sea floor almost desiccated, leaving important ports inaccessible, disrupting spawning grounds for sturgeon, threatening salt extraction in Kara Bogaz Göl, and causing widespread rapid environmental changes along the coasts. Sea level rise threatened towns, infrastructure and agricultural lands along the coasts, caused spreading of oil pollution in the southern Caspian and of polluted Volga sediments in the north, and flooding and salinization in coastal plains.

Coastal management along Caspian shores requires a much greater awareness and reactivity than along most of the other coasts in the world.

However, the Caspian also serves as a natural laboratory for global change and coastal dynamics. In the first place, Caspian sea-level change records discharge changes of the Volga river and hence precipitation in the East-European platform, which in turn is controlled by global circulation patterns.. The recent sea-level cycle shows a good correlation with the North Atlantic Oscillation, so the history of Caspian sea level changes might afford clues for global climatic history.

In the second place, each year of Caspian sea-level change offers an accelerated picture of coastal response to a century of sea-level change along oceanic coasts. Coastal response to sea-level change is strongly dependent upon offshore gradient. The low-gradient Volga delta shows how delta progradation accelerated as a result of sea-level fall. Surprisingly sea-level rise does not immediately lead to delta retrogradation, but only to aggradation, as vegetation keeps the contours of the coast line intact even after 3 metres of sea-level rise. Along the intermediate-gradient Dagestan barrier coast it is seen that larger barrier-lagoon complexes only form during transgressions. Regressions only give low single storm barriers. Ground Penetrating Radar transects of barrier complexes enable a precise correlation between sedimentary architecture and coastal processes. These data have important implications for existing models of coastal lowland development along oceanic shores.

In the third place, the development of recent Caspian deltas (Volga, Terek, Kura) during rapid sea-level fluctuations helps to understand the 3D subsurface architecture of the Pliocene Paleo-Volga delta that hosts most of the oil in the South-Caspian Basin in Azerbaijan. This in turn can lead to a more rational use of natural hydrocarbon resources in in the southern Caspian.

Date received: April 30, 2002