A novel proxy approach to constraining atmospheric modes in central and southwestern Iran during Marine Isotope Stage 3

Abstract

Terrestrial paleoclimate records from arid southwestern Asia are relatively sparse. Therefore, the regional impact of abrupt glacial climate variability remains poorly constrained for much of the Western Asia, particularly winter (wet season) dynamics during Marine Isotope Stage 3. Here, we present the first paleoclimate reconstructions of Southwestern and Central Iran, which span the interval ~50-30 ka, based on speleothem δ18O and δ13C. Stable-isotope signals in the two stalagmites are generally uncorrelated and do not exhibit a consistent response to Greenland stadials or interstadials; however, both show a positive δ18O excursion that coincides with Heinrich event 4. This behavior contrasts with that observed in northern Iran, Anatolia, and Levant for the last glacial period. We explore the potential mechanisms for intermittent coupling of speleothem δ18O across Iran through isotope-enabled atmospheric modelling outputs, from which we utilize the spatial δ18O gradient as a proxy for wintertime westerly vs. southerly jet strength. Our results suggest that during Heinrich event 4 and several Greenland stadials, stronger westerly winds enhanced Mediterranean moisture contributions to both sites and reduced aridity in southern Iran. We emphasize the importance of analyzing spatial trends in speleothem δ18O to interpret atmospheric dynamics, rather than relying on time series from single sites.