A POSSIBLE RECORD OF BOLLING-ALEROD/YOUNGER DRYAS CLIMATE FLUCTUATIONS FROM THE BLACK SEA
Most samples of Core 379A and all samples of Core 380 exhibit typical lithogenic elemental concentration patterns and Corg:P ratios (15-30) consistent with aerobic bottomwaters. However, core 379A shows two unusual intervals: (1) between 65 and 43 cm, Corg:P ratios repeatedly rise to 50-110 and Cr, Cu, and Ni exhibit modest enrichments (2-3× background) in sub-sapropelic sediment layers, and (2) between 43 and 30 cm, Na and Cl concentrations each rise to ~20-35% (versus <2% Na and ~0% Cl in the rest of the core). We infer that suboxic bottomwater conditions developed in the 65-43-cm interval in an otherwise well-oxygenated lake basin, linked to increased humidity of the Bolling-Allerod warming. The 43-30-cm interval is inferred to represent an evaporative halite layer formed during the Younger Dryas event. The latter is particularly significant given the generally humid conditions that prevailed within the Black Sea watershed. Given an average sedimentation rate for Unit III of ~20±10 cm kyr-1, these two core intervals represent ~0.7-2.2 kyr and 0.4-1.3 kyr, respectively.
These unusual sedimentary signals suggest control by extreme climate fluctuations. Although exact ages are lacking, the existing age constraints suggest the Bolling-Allerod and Younger Dryas events are present in the study cores.