The early Holocene humid period in NW Saudi Arabia – Sediments, microfossils and palaeo-hydrological modelling

Abstract

An early to mid-Holocene humid period has been inferred from a variety of geo-bio-archives of the Sahara and the Arabian Peninsula including sabkhas, palaeo-lakes, sand dunes, wadis, speleothems or marine sediments. On the Arabian Peninsula, most of these records are located in the southern and southeastern part. Studies from the northern part are rare. This paper presents the first results from palaeo-environmental and hydrological investigations on the sabkha basin of the Tayma oasis, northwestern Saudi Arabia. Sedimentary characteristics, micro- and macrofauna, a digital elevation model based on DGPS measurements, and 14C-AMS data indicate the presence of a perennial lake with a minimum depth of 13 m, a stored water volume of 1.16 × 107 m3 and a surface of 18.45 km2 between 10,000–9000 cal BP. Foraminiferal test malformations and the shape of sieve pores on ostracod valves were used to detect trends in palaeo-salinity and ecological stress conditions. The reconstructed gradual contraction of the lake at least after 8500 cal BP reflects the long-term aridisation trend on the Arabian Peninsula after the early Holocene. Based on the hydrological water balance equation, quantitative data on minimum palaeo-rainfall during the early Holocene humid period were calculated. Input parameters for the equation are the minimum lake level, lake surface, and lake volume during the peak of the early Holocene humid period as well as palaeo-evapotranspiration, groundwater infiltration, and surface runoff. Accordingly, a perennial lake in the endorheic basin of the modern sabkha with a lake level at the same elevation as the uppermost shoreline deposit would have required a minimum annual precipitation of 150 ± 25 mm. This value amounts to c. 300% of recent precipitation rates.