Shifting runoff from the Negev to the Mediterranean during sapropel S5 in the Dead Sea watershed

Abstract:

Nd-Sr isotopes were analyzed in the fine detritus material (FDM), sampled from the ICDP-funded Dead Sea Deep Drilling Project at Marine Isotope Stage MIS5e interval. Stage 5e, extending from ~134 to 116 ka BP, was overall an arid period in the Levant region, as reflected by deposition of thick sequences of halite along with FDM of flood origin in the Dead Sea. While the early (~134-129 ka BP) and late (~122-116 ka BP) intervals of MIS5e were dominated by halite deposition, a long sequence of FDM with no halite was deposited during the MIS5e peak at ~128-122 ka BP, indicating wetness in the watershed coeval with sapropel S5 in the Mediterranean, the result of enhanced Nile discharge, in turn reflecting enhanced African monsoon rains at the River Nile headwaters. Towards the end of S5 (~124-122 ka BP) primary aragonite precipitated in the Dead Sea within the FDM sequences, indicating bicarbonate supply to the lake. The Nd-Sr isotope ratios in the MIS5e FDM reflect changes in flood sources in the watershed. The floods are dictated by rain patterns, which depend on the prevailing synoptic conditions (e.g. Mediterranean versus southern sources). Overall the Nd-Sr signal of the MIS5 FDM lie between the fields of Saharan Shield, Arabian-Nubian Shield (ANS), and Nile sediment sources. The data show clear shifts between the pre-S5 interval and early S5, which shows the strongest ANS component, then the late S5 interval, which shows the strongest Saharan component. Early S5 is dominated by FDM from loess-like sources, in the northern Negev desert while the late S5 sediments reflect bicarbonate and FDM from Sahara dust settled on the Judean Mountains. These shifts indicate early S5 flooding from mainly southern sources during the peak of the precession-driven S5 monsoon interval, and resumption of Mediterranean-derived rains in the Dead Sea watershed as the monsoon weakened.