Millennial multi-proxy reconstruction of oasis dynamics in Jordan, by the Dead Sea

Abstract

Vegetation reconstructions in the Dead Sea region based on sediment records are potentially biased, because the vast majority of them derive from the western side of the sea, and only focus on large areas and time spans, while little is known about extra-local (< 1,000 m radius) to local (< 20 m radius) changes. To fill this gap, we compared a vegetation survey with modern pollen assemblages from the “Palm Terrace” oasis ca. 300 m b.s.l. (below sea level), at the eastern edge of the Dead Sea. This revealed how the oasis vegetation is reflected in pollen assemblages. In addition, two sediment cores were collected from the centre and the edge of a mire at the oasis to reconstruct past vegetation dynamics. We analysed sedimentary pollen and microscopic charcoal, as well as the sediment chemistry by X-ray fluorescence (XRF) and conductivity, focusing on the past ~ 1,000 years. Pollen results suggest that mesophilous Phoenix dactylifera (date palm) stands and wetland vegetation expanded there around ad 1300–1500 and 1700–1900. During the past ca. 100 years, drought-adapted Chenopodiaceae gained ground, partly replacing the palms. Results from elemental analysis, especially of elements such as chlorine, provide evidence of enhanced evaporative salinization. Increasing desertification and the associated decline of mesophilous date palm stands during the past ca. 50 years is probably related to a decrease in annual precipitation and also corresponds to decreasing water levels in the Dead Sea. These have mainly been caused by increasing extraction of fresh water from tributaries and wells, mainly for local agriculture and industry. In the future, with hotter and drier conditions as well as increased use of water, oasis vegetation along the Dead Sea might be at further risk of contraction or even extinction.