Late Holocene Environmental Changes in a Sediment Core from Al-Kharrar Lagoon, Eastern Red Sea Coast, Saudi Arabia

摘要

This paper aims to reconstruct paleoenvironmental conditions and sea-level changes over the last 5500years. Multi-proxy investigations of sediment types, foraminiferal records, geochemistry parameters and paleotidal elevation changes were conducted on a short sediment core KHAR1 (225cm long) retrieved from the intertidal area of the Al-Kharrar Lagoon. The sediment age was determined using C-14 dating of marine mollusk shells. Results showed that two prominent warming events during AD 750-1500 and 1750-present and a cooling event during AD 1500-1750 were inferred from the variation of benthic foraminiferal composition in core KHAR1. Before 3000 BC interval, the core sediment was deposited under intertidal-subtidal conditions as indicated by the presence of terrestrial sediments (siliciclastic materials), a decrease in subtidal-deep species and a slight drop in the paleotidal elevation about 0.50cm below the present lowest astronomical tide (LAT). From 3000 to 750 BC, deep-lagoonal species such as S. costigera, T. trigonula, T. serrulata and S. communis dominated this interval and co-occurred with a decrease in coarse sand and an increase in muddy substrates, indicating a prevalence of subtidal environmental conditions during the deposition of this interval. With the beginning of the 1st millennium, symbiotic (epiphytic) species started to increase, reaching the highest abundances between AD 800 and 1500. This increase in symbiotic species during the AD 800-1500 interval coincided with a stepwise increase in sea level and may indicate the prevalence of seagrasses associated with the occurrence of warm water due to climate warming prevailed in/around the lagoon during the deposition of this interval that corresponds to the Medieval Warm Period' (MWP). The MWP was followed by cooler (arid) conditions of the Little Ice Age (AD 1500-1750), causing a decrease in the abundance of the epiphytic species S. orbiculus and P. planatus (up to 14%) and a drop in paleotidal elevations. After this, the modern warming conditions prevailed until the present day.