干旱区生态环境知识资源中心

Extremely high sediment accumulation rates in the southeastern (SE) Mediterranean off Israel make this region ideal for high-resolution paleoceanographic reconstructions. Two cores were examined and foraminiferal oxygen and carbon isotope composition as well as physical and geochemical properties of the sediments were used to reconstruct the climatic and environmental changes of the SE Mediterranean Basin during the late Holocene (3.6 ka). The delta(18)O values of Globigerinoides ruber suggest that the freshwater balance changed several times during this time interval. Humid phases took place between 3.5-3.0 ka BP and 1.7-1.0 ka BP. The later was accompanied by enhanced preservation of terrestrial organic matter within the sediment (ORS event). Relatively more and conditions prevailed in this area between 3.0 and 1.7 ka BP. During the last millennia at ca. 0.8 and 0.27 ka two climatic events occurred which are probably correlative to both the Medieval Warm Period and the cooling global event known as the Little Ice Age, respectively. A long-term slight increase in planktonic foraminiferal delta(18)O values occurs together with a gradual decrease in the delta(13)C values of both G. ruber and the benthic foraminifera Uvigerina mediterranea. This trend is associated with an increase in sedimentation rates, Ti/Al ratio, magnetic susceptibility, and color index of the sediments. We suggest that this trend shown by various independent proxies seems to be related to the aridification process that started ca. 7.0 ka in the mid-low latitude desert belt and the SE Mediterranean region and continuous until the present. The long-term delta(13)C decrease shown by surface and bottom water foraminifera reflects a gradual change in the delta(13)C of the dissolved CO2 Of the entire SE Mediterranean water column. This follows the global CO2 rise in the late Holocene as a result of the terrestrial biomass destruction during the aridification process. Moreover the gradual reduction of the vegetation cover in East Africa led to an increased erratic flood-related sediment flux via the Nile River up to the present, This is reflected by the general change in the local sediment composition. At 3,6 ka, the Saharan eolian input reached 65% whereas at about 0.3 ka 70% of the SE Mediterranean sediment was composed of Nile particulate matter. (C) 2001 Elsevier Science B.V. All rights reserved.