IMPLICATIONS OF THE DEAD SEA LEVEL VARIATIONS TO LATE HOLOCENE REGIONAL CLIMATES AND HISTORICAL CULTURES

The late Holocene Dead Sea levels were reconstructed based on direct level indicators, depositional environments, and radiocarbon ages from exposures along the shores of the lake. In these exposures, buried shore ridges, sand, and aragonite crusts recorded absolute elevations of past shores. The lake fluctuated within elevation range of 390 to 415 m below sea level (mbsl). Most of the time the lake was confined to the deeper northern sub-basin and did not rise above the topographic sill (~402 mbsl) separating between the northern and southern sub-basins of the lake. Level rises occurred in the 1st century BC and the 4th century AD (the Roman and early Byzantine periods), in the 11th-12th century AD (the crusader period) and at the end of the 19th century AD. The drastic level drops exposed the sediments to erosion and stream incision. The oldest and probably deepest drop in the lake culminated during the 15th–14th century BC after a retreat from a higher lake stand. Another significant drop occurred after the Byzantine period and continued until the 10th century AD. The Dead Sea is a terminal lake, sensitive to hydrological variations in its catchment and its levels represent the regional climate variability. A quantitative analysis using the modern (last 150 years) instrumental record of natural levels and annual precipitation in Jerusalem enabled us to estimate that rising levels are associated with 648 mm/yr, drops with 445 mm/yr, and stable levels with 553 mm/yr; all with uniform standard deviation of ~120 mm/yr. As Jerusalem rainfall is highly correlated with rain stations in northern Israel these conclusions can be extended to larger areas in the Levant, which are under the same weather systems. These results indicate that level rises mark a significant positive change in the regional annual rainfall that could have contributed to the flourishing in demography and agriculture during the Roman and Byzantine periods, and to the Frankish farm development during the Crusader period. Level drops represent devastating droughts with frequent years with less than 400 mm/yr in Jerusalem. The arid conditions pointed out by the 7th century AD low stands temporally coincide with the Moslem-Arab invasion into the area. Although other historical factors could have been connected, the coincidence with the arid conditions is noteworthy.