Resolving seasonal rainfall changes in the Middle East during the last interglacial period

Bibliographic Collection: 
Publication Type: Journal Article
Authors: Orland, Ian J.; He, Feng; Bar-Matthews, Miryam; Chen, Guangshan; Ayalon, Avner; Kutzbach, John E.
Year of Publication: 2019
Journal: Proceedings of the National Academy of Sciences
Volume: 116
Issue: 50
Pagination: 24985
Date Published: 2019/12/10
Publication Language: eng

The Middle East was a gateway for early human migration out of Africa, and it is likely that the region’s climate played an important role in this anthropogenic transition. This study is motivated by conflicting interpretations of rainfall seasonality from regional paleoenvironmental records. Specifically, we address whether summer monsoon rainfall may have expanded northward into the Middle East in the past. Today, the region has dry summers and relatively wet winters; the northern limit of the modern monsoon is far to the south. Here, we combine climate modeling with seasonal-resolution geochemical analysis of cave carbonates from Israel and find evidence for summer monsoon rainfall during recurrent intervals of the last interglacial period, which overlaps with archeological indicators of human migration.Paleorainfall proxy records from the Middle East have revealed remarkable patterns of variability since the penultimate glacial period (140 ka), but the seasonality of this signal has been unresolvable. Here, seasonal-resolution oxygen isotope data from Soreq Cave speleothems suggest that summer monsoon rainfall periodically reaches as far north as Israel—well removed from the modern monsoon—at times (∼125, 105 ka) that overlap with evidence for some of the earliest modern human migrations out of Africa. These seasonal proxy data are corroborated by seasonal-resolution model output of the amount and oxygen-isotope ratio of rainfall from an isotope-enabled climate model. In contrast to the modern regional climate where rainfall is delivered predominantly in winter months along westerly storm tracks, the model suggests that during extreme peaks of summer insolation—as occurs during the last interglacial (e.g., 125, 105 ka)—regional rainfall increases due to both wetter winters and the incursion of summer monsoons. This interpretation brings clarity to regional paleoproxy records and provides important environmental context along one potential pathway of early modern human migration.

Short Title: Proc Natl Acad Sci USA