The Sahara-East Mediterranean dust and climate connection revealed by strontium and uranium isotopes in a Jerusalem speleothem

摘要

This paper explores the potential of Sr and U isotope systems in speleothems as tracers of eolian dust transport and hydrological conditions. The study focuses on a speleothem from Jerusalem spanning the past 220 kyr. This speleothem provides a precisely dated record of dust flux from the Sahara to the East Mediterranean. Enhanced dust flux and Terra Rossa soil development are reflected by elevated ~(87)Sr/~(86)Sr ratios in the speleothem (0.7082–0.7086), while lower ~(87)Sr/~(86)Sr ratios (～0.7078) indicate higher contribution of the local bedrock due to low dust flux and low soil accumulation. The strontium isotope system in the speleothem is a robust monitor of the Sahara monsoon-modulated climate, since dust uptake is related to development or reduction in vegetation cover of Sahara soil. The [~(234)U/~(238)U] activity ratios in the speleothem range between 1.12 and 1.0. The high activity values may indicate selective removal of ~(234)U from the soil while the low values converge to the bedrock. The migration of 234U to the cave reflects mainly the regional hydrological conditions that are modulated by the North Atlantic–Mediterranean climate system. Thus, the speleothem provides a combined record of the monsoon–North Atlantic climatic systems. Long-term stability in glacial ~(87)Sr/~(86)Sr ratios (0.7083±0.0001 over the past 220 kyr) suggests an overall similarity in eolian dust sources, and uniformity in the synoptic conditions that dominate the dust storm tracks during glacial periods.