PALEOCEANOGRAPHY, VOL. 6, NO. 1, PAGES 83-98, FEBRUARY 1991 PALEOENVIRONMENTAL EVENTS DURING THE LAST 13,000 YEARS iN THE CENTRAL RED SEA AS RECORDED BY PTEROPODA Ahuva Almogi-Labin, 1Christoph Hemleben, 2 Dieter Meischner, 3 andHelmutErlenkeuser a ABSTRACT. A high-resolution record was obtained by investigating a sedimentary sequence from two cores taken in the central Red Sea (R/V Meteor cruise 5, leg 2). The numerical variations between nonmigratory and migratory pteropods and their stable isotopic record were studied together with variations in the carbonate and total organic carbon content in order to estimate changes in the structure of the water columnduring the last 13 kyr. The results indicate the existence of a highly stratified watercolumn duringdeglaciation and early Holocene (13-8.5 ka). During this period the depthof the mixed layervaried between less than 50-100 m at most, and productivity was markedly reduced in comparison to the recent situation. The inter- mediate and deepwaterwere constantly highly depleted in oxygen. A pronounced Younger Dryas event was recognized at 10.4 ka which coincides with an arid phase on the border land. The oxygenation of the intermediate waterimproved remarkably after 7.5 ka and peaked duringthe period between 4.6 and 2.0 ka. During this period the mixedlayer •Geological Survey of Israel, Jerusalem, Israel. 2Institut und Museum fiir Geologic und Pal•iontologie, Universityof Tfibingen, Tiibingen,Germany. 3Institut fiir Geologie und Pal•iontologie, Abteilung Sedi- ment-Geologic, GSttingen,Germany. 4Institut flit Reine und Angewandte Kernphysik, Univer- sity of Kiel, Germany. Copyright 1991 by the American Geophysical Union. Paper number 90PA01881. 0883-8305/91/90PA-01881 $10.00 reached its present depthand the productivity which was maximalduringmiddle Holocene attained present level during the last 4.6 kyr. INTRODUCTION Quantitative changes through time in pteropod assem- blages havebeen usedfor palcoenvironmental interpretations in earlier studiesof the Red Sea [Herman, 1968; Chen, 1969; Risch, 1976; Yusuf, 1978; Almogi-Labin, 1982; Ivanova, 1985; Almogi-Labin et al., 1986]. It was found that the mostdetailed biostratigraphic record in the Red Sea is that of the pteropods for which a t•w selected abundance peaks and species ratios facilitate precise stratigraphic corre- lations andare indicative of palcoenvironmental conditions. Studies on living pteropods in the Red Seaand elsewhere noted the existence of two groups, the diel migrators andthe nonmigrators [Chenand B6, 1964; van der Spoel, 1967; Frontier, 1973a,b; B6 and Gilmer, 1977; Rottman, 1980; Wormuth, 1981; Almogi-Labinet al., 1988]. The different depth-controlled life strategies may reflect the differences in their adaptation to various water column properties. The oxygen level, decreasing to 0.9-1.3 mL O2/L at intermediate waterdepths in the Red Sea(250-650 m depth),controls the distribution patterns of the mesopelagic pteropods (= diel migratory). The nonmigratory epipelagic species are restricted to the mixedlayer(approximately 0-100 m) in the Red Sea(Table 1). The living assemblage is very similarto the coretop assemblage; hence it is possible to relate the present oceanographic setting to the fossil record[Weikert, 1982, 1987; Almogi-Labin,1984]. We assume that the environmental requirements andphysiological response of the pteropod community have not changed duringthe last 13 kyr. Contrary to the present-day situation wherethe mesopelagic pteropods comprise nearly 75 % of the assem- blage,a succession of epipelagic species dominatedduring