Hydrological variability in the Northern Levant: a 250 ka multi-proxy record from the Yammoûneh (Lebanon) sedimentary sequence
Abstract. The Levant is a key region in terms of both long-term hydroclimate dynamics and human cultural evolution. Our understanding of the regional response to glacial-interglacial boundary conditions is limited by uncertainties in proxy-data interpretation and the lack of long-term records from different geographical settings.
The present paper provides a 250 ka paleoenvironmental reconstruction based on a multi-proxy approach from northern Levant, derived from a 36 m lacustrine-palustrine sequence cored in the small intra-mountainous karstic Yammoûneh basin from northern Lebanon. We combined time series of sediment properties, paleovegetation, and carbonate oxygen isotopes (δc), to yield a comprehensive view of paleohydrologic-paleoclimatic fluctuations in the basin over the two last glacial-interglacial cycles. Integration of all available proxies shows that Interglacial maxima (early-mid MIS 7, MIS 5.5 and early MIS 1) experienced relatively high effective moisture, evidenced by the dominance of forested landscapes (although with different forest types) associated with authigenic carbonate sedimentation in a productive waterbody. Synchronous and steep δc increases can be reconciled with enhanced mean annual moisture when changes in seasonality are taken into account. During Glacials periods (MIS 2 and MIS 6), open vegetation tends to replace the forests, favouring local erosion and detrital sedimentation. However, all proxy data reveal an overall wetting during MIS 6, while a drying trend took place during MIS4-2, leading to extremely harsh LGM conditions possibly linked to water storage as ice in the surrounding highlands. Over the past 250 ka, the Yammoûneh record shows an overall decrease in local effective water, coincident with a weakening of seasonal insolation contrasts linked to the decreasing amplitude of the eccentricity cycle.
The Yammoûneh record is roughly consistent with long-term climatic fluctuations in the northeastern Mediterranean region (except during MIS 6). It suggests that the role of seasonality on effective moisture, already highlighted for MIS 1, also explains older interglacial climate. The Yammoûneh record shares some features with speleothem isotope records of western Israel, while the Dead Sea basin generally evolved in opposite directions. Changes in atmospheric circulation, regional topographic patterns and site-specific hydrological factors are invoked as potential causes of spatial heterogeneities.
Further work is needed to refine the Yammoûneh chronology, better understand its functioning through hydrological and climate modelling, and acquire other long records from northern Levant to disentangle the relative effects of local versus regional factors.