HOLOCENE SEA-LEVEL AND CLIMATE CHANGE IN THE BLACK SEA: MULTIPLE MARINE INCURSIONS RELATED TO FRESHWATER DISCHARGE EVENTS

Repeated marine invasions of the Black Sea during the Holocene have been inferred by a number of workers from foraminiferal and other evidence. These sea-level fluctuations have generally been interpreted by eastern scientists as resulting from episodes of marine inflow from the Mediterranean beneath a brackish outflow from the Black Sea. We support this scenario but a fundamental question remains: What caused the repeated marine invasions?

We offer an hypothesis for the repeated marine invasions of the Black Sea based on: 1) the overall similarity of sea-level curves from both passive and active margins of the Black Sea and their similarity to a sequence stratigraphic record from the U.S. mid-Atlantic coast. The similarity of the records from two widely-separated regions suggests their common response to documented Holocene climate ocean-atmosphere reorganizations (coolings); 2) the fact that in the modern Black Sea, freshwater runoff from surrounding rivers dominates over evaporation, so that excess runoff might have temporarily raised Black Sea level (although the Black Sea would have remained brackish).

Following the initial invasion of the Black Sea by marine Mediterranean waters (through the Marmara Sea) in the early Holocene, repeated marine incursions were modulated, or perhaps even caused, by freshwater discharge to the Black Sea. Climatic amelioration (warming) following each documented ocean-atmosphere reorganization during the Holocene likely shifted precipitation patterns in the surrounding region and caused mountain glaciers to retreat, increasing freshwater runoff above modern values and temporarily increasing Black Sea level. Freshwater-to-brackish water discharges initially slowed marine inflow into the Black Sea but upon mixing of runoff with more marine waters beneath them and their eventual exit through the Bosphorus Strait, marine inflow increased again, accounting for the repeated marine invasions. The magnitude of the hydrologic and sea-level fluctuations became increasingly attenuated through the Holocene, in agreement with Black Sea level curves.