Quaternary Science Reviews 29 (2010) 1342–1362

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Quaternary Science Reviews

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100,000 Years of African monsoon variability recorded in sediments of the Nile margin

Marie Revel a,*, E. Ducassou b, F.E. Grousset b, S.M. Bernasconi c, S. Migeon a, S. Revillon d, J. Mascle a, A. Murat e, S. Zaragosi b, D. Bosch f a Geosciences Azur, Observatoire Oce´anologique, La Darse, B.P. 48 06235 Villefranche/Mer, France b Universite´ Bordeaux 1, CNRS, UMR 5805-EPOC, avenue des faculte´s, 33405 Talence cedex, France c ETH Zurich, Geologisches Institut, 8092 Zurich, Switzerland d IFREMER, De´partement Ge´osciences Marines, BP70, 29280, Plouzane´, France e Cnam-Intechmer, BP324, 50103 Cherbourg, France f Laboratoire de Tectonophysique, Universite´ de Montpellier II, 34095 Montpellier, France article info abstract

Article history: Multiproxy analyses were performed on core MS27PT recovered in hemipelagic sediments deposited on Received 20 April 2009 the Nile margin in order to reconstruct Nile River palaeohydrological fluctuations during the last 100,000 Received in revised form years. The strontium and neodymium isotope composition of the terrigenous fraction and the major 17 December 2009 element distribution reveal large and abrupt changes in source, oscillating between a dominant aeolian Accepted 4 February 2010 Saharan contribution during arid periods and a dominant Nile River contribution during pluvial periods. Iron content shows a strong correlation with strontium and neodymium isotopes. This allows the use of a high-resolution continuous Fe record as a proxy of Blue Nile sediment input over the last 100,000 years. The detailed Fe record, with approximately 10 years resolution during pluvial periods, is consistent with subtropical African records of well-dated lake level fluctuations and thus constitutes a first continuous high resolution record of the East African monsoon regime intensity over Ethiopia. The detailed Fe record shows the two main known pluvial periods attributed to strengthening of the African monsoon over Ethiopia, the Nabtian period from 14 to 8 ka cal BP and the Saharan period from 98 to 72 ka BP. For the first time, the last glacial period (Marine Isotope Stage (MIS) 2, 3 and 4) is documented with a continuous record showing large oscillations between high and low East African palaeo-monsoon regimes. The end of the Nabtian period occurred at 8 ka in core MS27PT, i.e. much earlier than on the East Equatorial African region where it ended around 5.5 ka. We interpret this as evidence that the southward shift of the rain belt occurred 3000 years earlier over the Eastern Ethiopian Highland and propose that the gradual southward migration of the rain belt was associated with highly variable intensity and longer rainy seasons from 8 to 5 ka. During the last glacial period, two wet periods are present around 60–50 ka BP and 38–30 ka BP. These two humid periods are in phase with the rise of atmospheric CH4 concen- trations suggesting that wetland tropical African area was one of the sources of the atmospheric CH4 during the MIS 3. During the Last Glacial Maximum and MIS 4, high Saharan aeolian influxes in phase with records of aeolian dust deposited in East Antarctica are documented. This study highlights the importance of reconstructions of monsoon rainfall fluctuation at high temporal resolution to better understand the link between low- and high-latitude climate variability at millennial timescales. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction conveyed and redistributed by atmospheric and oceanic circulation towards high latitudes. The changing strength of this meridional Recently, palaeoclimatic data and climate models have high- heat transfer has strongly contributed to past global climatic lighted the key role of the tropics in global climate (Alpert et al., changes. 2006). At these low latitudes, heat and water vapour are The South-Eastern Mediterranean region experiences particular climatic conditions because of its mid latitude position and its link with the North Atlantic system (Sanchez-Goni et al., 2008) and with * Tel.: þ33 493763744; fax: þ33 493763766. the African subtropical monsoon system (Rohling et al., 2009; E-mail address: [email protected] (M. Revel). Almogi-Labin et al., 2009). The monsoonal system that originates

0277-3791/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2010.02.006 M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362 1343 in the tropical Atlantic and the southern Indian ocean, passes over Atbara River accounts for about 56% of the total annual Nile water N–E Africa and is associated with the low-latitude rainfall system discharge (rising to 68% during maximum summer flow) and for that influence the hydrology of the Levantine Basin through Nile more than 95% of the suspended sediment load (Foucault and River outflow. The seasonal migration of the Inter Tropical Stanley, 1989; Williams et al., 2000). Over a year the Nile River Convergence Zone (ITCZ) – a narrow latitudinal zone of wind has a unimodal discharge curve, with summer floods linked to the convergence and precipitation – determines the onset, duration northward migration of the ITCZ from the equator (20N in August) and termination of the monsoon-rainy season in the tropics and causing heavy monsoon rainfall over the headwaters, and espe- subtropics. The intensity of the summer African/Asian monsoon cially over the Ethiopian Highlands (Fig. 1). During winter, the rainfall is mainly controlled by the amount of solar radiation North African landmass cools relative to the adjacent ocean and the received at low latitudes, modulated by the Earth’s astronomical regional atmospheric circulation reverses. The ITCZ is pushed precessional cycle (Rossignol-Strick, 1985; Fontugne and Calvert, southward and dry conditions and northeast trade winds 1992; Rohling, 1994). predominate. One of the most distinctive features of the Eastern Mediterra- Nile basin hydrology, which represents the main discharge in to nean is the Nile River (Fig. 1). It has a large drainage basin extending the Levantine basin, is closely linked to the intensity of the African/ over more than 30 in latitude, and connecting several different Asian monsoon and large fluctuations in discharge and sediment climatic zones. Its main sources are located in the Ethiopian high- transfer during the Quaternary have been driven by changes in lands (Lake Tana) and the equatorial zone (Lakes Albert and global climate (Woodward et al., 2001; Hassan, 1981; Williams and Victoria). Runoff from the Ethiopian Highlands via the Blue Nile and Adamson, 1980). Periods of higher frequency in Nile river floods

Fig. 1. Map of North East Africa showing the ITCZ position in summer and location of sites (African lakes and altitude) or regions called in text and figures. Shaded areas represent the most productive source of Libyan and Egyptian aeolian dusts (from Prospero et al., 2002). The yellow arrow represents dust storm plumes emitted from Libyan/Egyptian desert and transported over the Mediterranean Sea to Crete/Cyprus by south-easterly winds (from Ganor et al., 1991 and Prospero et al., 2002). Purple arrows show the counter-clockwise Mediterranean Sea surface circulation. Also marked are the Cenozoic Basalt outcrops (dotted red line) adapted from Stein et al. (2007) and the Precambrian crystalline basement. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). 1344 M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362 and related high levels recorded in North-East Africa palaeo-lakes Eastern Libyan Desert into western Egypt. These sources are active have been correlated with the periodic monsoon intensification during much of the year with intensified activity in May–June. called pluvial periods (Said, 1993; Szabo et al., 1995; Gasse, 2000; Quaternary marine sediment records in the Eastern Mediter- Williams et al., 2000; Lamb et al., 2007; Williams, 2009). ranean sea are characterized by the rhythmic deposition of organic Continental records of the Nile fluvial regime have the potential to carbon rich layers, called sapropels which correspond mainly to yield crucial data to reconstruct changes in hydrological regime and pluvial periods over north Africa, and are commonly formed Northeastern African climate (Woodward et al., 2001; Woodward during interglacial periods (Venkatarathnam and Ryan, 1971; et al., 2007; Cohen et al., 2007; Scholz et al., 2007). However, conti- Stanley and Wingerath, 1996; Foucault and Me´lie`res, 2000; nental climate records based on lacustrine sequences, show hiatuses Wehausen and Brumsack, 2000; Calvert and Fontugne, 2001; due to desiccation and subsequent erosion and/or non-deposition of Larrassoano et al., 2003). Many studies have focused on the very sediment and some only provide records with low- temporal reso- late Pleistocene and early Holocene and in particular on sapropel lution (Gasse, 2000; Gasse et al., 2008). In addition, continental S1 (9500–6600 cal ka BP; Emeis et al., 2000). Sapropel S1 is records are often difficult to precisely date by radiocarbon due to the thought to result from increased freshwater supply into the hard water effect and thus make correlation to marine records diffi- Mediterranean Sea by the Nile River. The runoff from the Nile cult (Said, 1981, 1993; Zaki, 2007; Williams, 2009). would have either increased biological production and/or Depositional sequences with high temporal resolution recording increased organic matter preservation in the sediments because of Quaternary climate fluctuations are exceptionally well preserved in inhibited water mass circulation and presence of anoxic deep the Nile margin sediments. The Nile margin is the largest sedi- waters (Rossignol-Strick, 1985; Murat and Got, 2000; Emeis et al., mentary accumulation in the Eastern Mediterranean and was 2000; Ariztegui et al., 2000; Krom et al., 2002; Bard et al., 2002; formed by sediment supplied from the Nile River. Studies conducted Paterne, 2006). In this paper, we evaluate how our records from since 1998 on the Nile margin with seven oceanographic cruises, the Nile margin fit to this general model. have provided a large data set, including detailed bathymetric maps, high-resolution seismic reflection profiles and numerous piston 3. Materials cores (Mascle et al., 2006; Ducassou, 2006; Loncke et al., in press; Migeon et al., in press). One of the most important conclusion of 3.1. Sediment core MS27PT these studies is that although the tectonics and sea-level variations are important influences on Nile margin sedimentation, climate Gravity core MS27PT (N3147090; E2927070; water depth over the Nile catchment is the dominant control for changes 1389 m; 7 m length) was recovered during the 2004 Mediflux- occurring at multi-millennial timescales and that variations in MIMES oceanographic cruise on the western Nile delta, along the sediment supply predominantly reflect monsoonal intensity continental slope approximately 90 km outward of the Rosetta (Ducassou, 2006; Ducassou et al., 2008, 2009). mouth of the Nile (Fig. 2A and B). The seismic record (Fig. 2C) shows This paper presents results from a multi-proxy study performed parallel and continuous reflectors indicating hemipelagic Pleisto- on hemipelagic sediments of core MS27PT recovered on the Nile cene sedimentation not affected by faulting or gravity instabilities. margin in 1389 m water depth (Fig. 2A). It aims to quantify varia- The sedimentological analysis of more than 40 sediment cores from tions in Nile sediment discharge and reconstruct the African the Nile margin (Fig. 2A: white dots) has allowed the different monsoon intensity for the last 100,000 years BP. Using geochemical sedimentary facies (hemipelagites, sapropels, turbidites, slumps methods, we have constrained the different sources of clastic and debrites) and their spatial–temporal distributions over the sediment input and precisely quantify the input of Nile derived entire Nile margin to be defined for the last 200,000 years sediment. (Ducassou et al., 2007; Ducassou et al., 2009; Migeon et al., in press). Core MS27PT (Fig. 2B) was chosen because it is located 2. The East African climate and consequence on the less than 100 km from the Nile River mouth, and thus is ideally Mediterranean sedimentation located to monitor past variation of the Nile flood discharge on the delta. In addition, because it is located outside the Rosetta channel Mediterranean Sea sediments contain a significant terrigenous system it avoids erosion and turbidite deposition. Indeed core component, of both riverine and aeolian origin, due to the relatively MS27PT is characterized by continuous hemipelagic sedimentation small size of the basin. In the Eastern Mediterranean, most terrig- throughout the 7 m. X-ray radiographs and sedimentological enous particles are delivered by the Nile River, with a flux estimated analysis of this core did not reveal any evidence of erosion or at 120.106 t/yr for the present time (Krom et al., 1999; Bout- abnormal contacts and reworked or displaced series. Based on Roumazeilles et al., 2007). Nile River runoff is strongly influenced visual examination, X-ray radiography and thin sections of by seasonal variation in precipitation over tropical Africa in impregnated sediment, we distinguished two different alternating response to the latitudinal migration of the Equatorial- subtropical lithological units (Fig. 3), namely a carbonate-rich facies with rain belt. Generally, aeolian dust is considered to be a minor coarse quartz grains and a clastic mud-rich facies. The mud-rich component of deep-sea sediments, however, the aeolian particle facies is subdivided into three subgroups: sapropels (S1, S3 and flux to the Eastern Mediterranean is unusually high, estimated at S4) deposited under anoxic conditions, a laminated clastic mud, 20–40 g/m2/yr (Herut et al., 2001), and thus is not negligible. The without benthic foraminifera, composed of dark grey clayey-silt Nile margin is located directly on the trajectories of African dust with interbedded dark laminae > 0.3 mm in thickness and a bio- plumes. Dust storms follow a West-South-West trajectory passing turbated clastic mud facies with few benthic foraminifera. mainly over the North African desert and coastline and then swinging northwards over Israel and Turkey (Fig. 1). These storms 3.2. Potential source area of sediments of the Nile margin are usually generated by low-pressure systems, which are trans- ported by the jet stream over the Eastern Mediterranean Basin The source areas of the Nile margin clastic sediment are (Ganor et al., 1991; Moulin et al., 1997). A recent study of major Saharan aeolian dust and Nile-derived fluvial material, which can present-day atmospheric dust sources based on satellite data have two distinct sources: the Blue/Atbara Nile and the White Nile spanning the period 1980–1992 (Prospero et al., 2002) shows that (Krom et al., 1999, 2002; Talbot et al., 2000; Freydier et al., 2001; persistent dust activity in North Africa (Fig. 1) was mainly from the Weldeab et al., 2002; Box et al., 2008). Saharan aeolian and Blue M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362 1345

Fig. 2. (A) Bathymetric map of the Nile margin (modified from Mascle et al., 2006) with location of cores (white dots) studied by Ducassou et al. (2009) and location of core MS27PT (black dot). (B) Enlargement of the study zone. (C) Seismic profile (location in Fig. 2B).

Nile suspended matter sources display markedly different radio- younger than 30 millions years, located in the Ethiopian Highlands genic isotope compositions because they are derived from (Fig 1: dotted red line). These two major Ethiopian tributaries of different parent rocks. Indeed, the Nile River material comprises the Nile (the Blue Nile and Atbara) provide, respectively, 68% and about 97% riverine-derived sediments produced through erosion 22% of the peak flow in summer and 72% and 25% of the annual of the Atbara and Blue Nile catchment areas (Foucault and Stanley, sediment load (Williams, 2009). In contrast, the White Nile 1989). These terranes are made up of Tertiary basaltic rocks provides 83% of Nile discharge during the month of lowest flow. 1346 M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362

Fig. 3. Synthetic log of the core MS27PT; X-ray images and sediment thin sections of: (1) S1 laminated facies, (2) laminated-bioturbated facies and (3) carbonate-rich facies.

Using Sr isotopes Talbot et al. (2000) showed that overflow of 4. Analytical methods Lakes Victoria and Albert into the Nile drainage network occurred at about 11.5 14C ka before present. 4.1. Stable isotope and AMS 14C measurements The Saharan dusts are derived from older (Precambrian gran- itoids) crystalline basement rocks from the North African desert An accurate age model of the core MS27PT was constructed belt (for petrology details, see Stein et al., 2007). Five represen- using 17 Accelerator Mass Spectrometry (AMS) 14C dates and the tative samples of the Saharan dust were collected in Libya (Fig. 1 oxygen isotope record (Tables 1 and 2; respectively; Fig. 4). and Table 4) close to the region of persistent dust activity. In Radiocarbon ages were calibrated to calendar ages by using the addition, two samples were collected along the Nile River, one in CALIB Rev 5.0 program (Stuiver and Reimer, 1993; Hughen et al., the Aswan region along the overbank flood deposit and another 2004; Stuiver et al., 2005). The radiocarbon dates were corrected one from the river sediments deposited around Elephantine Island for marine reservoir age difference (400 years) from Siani et al. (Fig. 1). (2001). M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362 1347

Table 1 Table 2 MS27PT core radiocarbon chronology. The radiocarbon measurements were per- Stable oxygen isotope ratios of planktonic foraminifera species Globigerinoides ruber formed at the Laboratoire de Measure du Carbone 14-Saclay (Paris). var. alba.

Lab. Analytical Depth species Age 14C errors Calibrated MS27PT depth (cm) d13C d18O 14 number of (cm) AMS conv. C age 0.1 0.23 0.80 AMS 14C ages BP (cal. yr BP) 1 LMC SacAOO5001 0_1 G. ruber 1060 35 587 10 1.10 0.88 LMC SacA005002 19-20 G. ruber 1720 40 1227 18 0.83 0.60 LMC SacAOO5003 29-30 G. ruber 6415 50 6830 21 0.26 0.46 LMC SacA 10935 65 G. ruber 7945 30 8407 29 1.24 0.92 LMC SacA 11797 70 G. ruber 8010 30 8465 38 1.13 0.83 LMC SacA 11798 95 G. ruber 8330 30 8915 42 1.15 0.98 LMC SacA 11799 102 G. ruber 8385 30 8987 60 0.47 0.38 LMC SacA 118 120 G. ruber 8520 30 9153 70 0.96 1.07 LMC SacA 10936 205 G. ruber 9185 35 10003 86 0.63 0.89 LMC SacA 10937 293 G. ruber 12795 45 14386 95 1.12 1.08 LMC SacA 10938 315 G. ruber 21920 45 25444 102 0.36 0.85 LMC SacA 11801 333 G. ruber 27760 130 31723 120 0.60 1.29 LMC SacA 11802 342 G. ruber 28450 140 32436 131 0.87 1.04 LMC SacA 11803 350 G. ruber 29940 160 33957 151 0.10 0.27 LMC SacA 11804 358 G. ruber 30470 160 34491 165 0.40 0.80 LMC SacA 11805 380 G. ruber 35270 270 39169 169 0.24 0.29 LMC SacA 11806 390 G. ruber 40710 490 44120 189 0.11 0.52 200 0.42 0.69 200 0.03 0.75 210 0.31 0.45 Stable oxygen isotope ratios of planktonic foraminifera were 220 0.54 0.69 analyzed to establish the stratigraphic framework of the MS27PT 230 0.16 0.24 core. Between 20 and 40 tests of the planktonic foraminifera 240 0.57 0.33 250 0.75 0.27 species Globigerinoides ruber var. alba were picked in each sample 260 0.74 0.59 from the size fraction >125 mm. The tests were gently crushed and 273 0.56 1.21 reacted at 70 C with 100% Phosphoric acid in a ThermoFisher Kiel 280 0.54 2.30 IV preparation device connected to a ThermoFisher Delta V mass 293 0.74 1.84 spectrometer calibrated with the international carbonate standards 303 1.21 3.26 18 18 315 1.43 3.40 NBS19 (d O ¼2.2&) and NBS18 (d O ¼23.01 &) at the 324 1.15 2.67 Geological Institute of the ETH. The data are reported in the 333 0.99 2.62 conventional delta notation with respect to VPDB. The analytical 342 0.70 2.85 reproducibility determined on repeated measurements of an 350 1.24 2.37 358 1.14 2.71 & internal laboratory standard was better than 0.1 . Depth to age 370 0.85 2.08 transformation (Fig. 4) was performed by linear interpolation 380 0.80 1.89 between controls points of AMS 14C dates (for the last 45 ka BP) and 390 0.96 1.99 sapropel events. Additionally, the oxygen isotope record of MS27PT 397 0.63 1.93 is correlated with the isotope record of the SPECMAP reference 410 0.88 1.45 418 0.56 1.27 timescale (Martinson et al., 1987; Paterne et al., 1999; Kallel et al., 430 0.94 2.23 2000; Essalami et al., 2007). 440 0.66 1.36 450 1.19 2.24 4.2. Sedimentological analyses 458 1.25 2.53 470 1.06 1.43 483 0.56 0.78 Grain-size measurements were performed each centimetre, all 490 0.672 0.79 along the core, using a Coulter LS200 laser microgranulometer. 500 0.654 1.70 Grain-size parameters are a mean of 10,000 scans per sample. X-ray 510 0.004 0.79 523 0.652 0.48 radiography was obtained using X-ray Scopix system at the 530 0.285 1.22 University of Bordeaux 1. 540 0.16 0.01 550 0.584 1.43 4.3. Major element analyses by X-Ray Fluorescence (XRF) 560 0.284 0.14 570 0.14 0.36 580 0.914 1.21 4.3.1. XRF Core Scanner on soft sediment 593 1.50 1.24 Core MSPT27 was analyzed using an Avaatech XRF Core 600 1.456 1.74 Scanner at Ifremer, Brest, France. This device allows non- 610 0.84 1.59 destructive extraction of near-continuous records of variations 620 0.646 1.03 630 0.76 0.70 in element concentrations from sediment cores with a minimum 640 0.108 0.72 of analytical effort. Measurements were performed every 1 mm 650 0.31 0.60 with a counting time of 20 sec and a 10 kV, 30 KV and 50 kV 660 0.085 0.57 acceleration intensity. Because the sediment matrix is character- 670 0.46 0.92 ized by variable water content and grain size distributions the 680 0.277 0.66 690 0.30 0.49 XRF scanner only provides a semiquantitative measurement and 700 0.8 1.37 spurious variations can occur due to changes, e.g. in water 710 0.64 0.58 content. Therefore the XRF core scanner results were calibrated 713 0.68 0.16 with quantitative major element concentrations measured by XRF 730 0.55 0.76 1348 M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362

Fig. 4. Age/depth relation along the oxygen isotope curves of Globigerinoides ruber var. alba of core MS27PT. Linear interpolation was used between the seventeen 14C calendar ages (orange dots) and the sapropels (white dots) S3 (78–81 kyr) and the double S4 (95 and 98 kyr). The chronology of the MIS 5/4 transition and the MIS 5 are based on sapropels ages defined by Kallel et al. (2000). Inferred sedimentation rates are given in cm/ka (right axis). The clastic mud (sapropel, laminated, bioturbated) and carbonate-rich facies are indicated along depth (x axis) with the isotopic stages (numbers), sapropel layers (S1–S4 dotted patterns), pluvial periods (grey patterns) and arid periods (black grey patterns). LH, Late Holocene; EMH, Early Middle Holocene; YD, Younger Dryas. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). on discrete sediment aliquots sampled at 20 cm resolution (red re-weighed to determine loss on ignition (LOI). Thereafter, 1 g of diamonds in Figs 5 and 6, Table 3). For the elements plotted in ignited material was mixed with 5 g of Johnson Matthey flux 100B Figs 5 and 6 (Ca, Ti, Fe and sulfur), we obtained a very good (80% lithium metaborate and 20% dilithium tetraborate) and fused correlation between the two methods. To correct the drift of the to glass disc. When the weight of ignited material was less than 1 g XRF Core Scanner, the element counts were normalized to the the mass of flux was weighted accordingly to the 1:5 ratios. Major total count numbers. elements were determined by XRF (X-Ray Fluorescence) at the University Claude Bernard of Lyon (UMR 5570 – Laboratoire des 4.3.2. XRF geochemical analyses on discrete sediment samples Sciences de la Terre). Accuracy and precision were checked by Major element analyses (Table 3) were performed on 1.2 g of international standard reference material and replicates of analyses powdered and homogenized sample. After 70 min combustion at of selected samples. The analytical accuracy was within 1% of 1000 C the samples were cooled to room temperature and certified values and the precision was better than 3%. Fig. 5. Oxygen isotope curves (Globigerinoides ruber var. alba), total organic carbon (TOC) and geochemical records of the MS27PT sediment on the depth scale (cm). Relative element contents (line): sulfur (S), barium (Ba), calcium oxide (CaO) and manganese oxide (MnO). Absolute S, CaO and MnO contents (red diamonds). Isotopic stages (numbers), synthetic log, sapropel layers (S1 to S4 dotted patterns) and arid periods (grey patterns) are also indicated. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). 1350 M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362

Fig. 6. Oxygen isotope curves, median parameter and geochemical records vs. age of core MS27PT. Relative element contents (line): iron (Fe), titanium (Ti), calcium oxide (CaO). Relative Fe, Ti CaO contents (line) and absolute S, CaO and Si/Al ratio contents (red diamonds). Isotopic stages (numbers), sapropel layers (S1 to S4 dotted patterns), arid periods (grey patterns) are indicated. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362 1351

Table 3 Major element data measured by X-Ray Fluorescence in Lyon.

MS27PT SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O TiO2 P2O5 Ba L.O.I. H2O- Total depth (cm) wt (%) wt (%) wt (%) wt (%) wt (%) wt (%) wt (%) wt (%) wt (%) wt (%) (ppm) 0.1 24.64 7.46 4.04 0.11 3.38 27.39 0.36 0.46 0.54 0.12 146 27 2 97.87 1 23.89 7.60 4.12 0.11 3.28 27.60 0.37 0.58 0.53 0.12 137 28 3 98.66 10 19.08 5.95 2.94 0.10 3.34 33.18 0.35 0.46 0.38 0.11 162 31.33 2.05 99.27 18 26.10 9.18 4.91 0.36 3.04 23.51 0.92 0.49 0.60 0.12 131 25 4 98.87 21 28.26 10.33 5.63 0.46 2.86 21.06 0.58 0.68 0.66 0.12 210 23 5 98.33 29 34.15 12.68 7.99 0.04 2.62 12.00 0.83 0.98 0.79 0.13 420 18 9 99.15 38 32.49 12.29 6.37 0.04 2.87 15.56 0.59 0.92 0.77 0.14 273 20 6 98.20 42 30.78 11.7 6.08 0.04 2.9775 14.94 1.96 0.86 0.74 0.14 20 6 96.28 42a 30.38 11.39 6.07 0.04 2.98 14.89 1.84 0.79 0.74 0.14 251 21 6 96.13 50 31.86 12.14 6.33 0.04 2.75 12.33 0.79 0.97 0.77 0.14 216 17 13 98.35 55 41.53 15.6 9.12 0.08 2.9475 5.76 0.9775 1.45 1.1825 0.17 12 8 99.34 60 40.86 16.37 9.08 0.05 2.86 5.95 0.85 1.26 1.04 0.15 283 14 7 99.16 65 37.76 14.94 8.50 0.05 2.98 4.94 3.32 1.52 0.97 0.14 346 16 7 97.93 69 42.32 15.38 9.4 0.11 2.91 2.81 2.82 1.515 1.37 0.17 12 8 99.00 70 39.76 15.81 9.21 0.06 2.86 3.91 1.64 1.34 1.08 0.14 330 13 7 96.00 73.5 37.52 14.91 8.49 0.05 2.9625 4.765 2.9975 1.47 0.9775 0.1325 16 9 99.34 76 38.34 15.21 8.65 0.06 2.98 5.26 2.85 1.51 0.99 0.14 374 15 7 98.07 80 37.09 12.80 8.05 0.07 2.93 4.92 2.51 1.32 1.27 0.14 162 14 10 95.85 95 38.46 15.10 8.54 0.05 3.18 4.35 3.59 1.66 1.03 0.14 248 15 7 97.99 100 36.75 14.33 8.33 0.04 3.08 4.79 2.50 1.49 0.99 0.15 253 15 8 95.66 103 42.47 14.73 8.9825 0.09 3.0575 3.8 2.655 1.58 1.46 0.17 12 7 98.48 110 40.92 15.83 9.00 0.05 3.14 3.74 2.72 1.50 1.11 0.16 274 13 7 98.19 120 38.75 15.02 8.41 0.05 3.075 3.545 3.405 1.635 1.0675 0.155 14 10 99.23 141 39.16 14.93 7.99 0.07 3.20 5.83 2.08 1.52 1.02 0.18 176 14 8 97.98 151 41.70 15.69 8.65 0.06 3.14 4.29 2.32 1.71 1.18 0.17 235 12.84 7.61 99.36 161 39.32 14.98 8.55 0.09 3.05 4.09 2.27 1.42 1.10 0.16 166 12 11 98.30 177 42.79 16.72 8.76 0.07 3.25 4.36 0.725 1.5175 1.1025 0.18 12 8 98.64 180 40.39 14.90 8.39 0.10 3.07 4.63 2.47 1.49 1.20 0.17 190 13 10 99.05 189 43.61 16.35 9.54 0.08 2.95 3.74 1.11 1.44 1.26 0.17 196 11 8 99.01 200 40.75 15.21 9.15 0.07 2.99 5.12 1.43 1.44 1.06 0.17 194 12 10 99.10 205 43.62 15.59 9.70 0.09 3.16 3.86 1.76 1.79 1.23 0.17 204 11 7 98.79 210 42.85 15.77 9.33 0.11 3.10 4.10 2.24 1.80 1.24 0.18 214 12.01 7.12 99.85 221 38.38 14.20 8.45 0.08 2.69 4.12 1.09 1.29 1.11 0.16 162 10 11 92.03 230 43.14 16.00 9.78 0.10 3.06 4.35 1.51 1.64 1.24 0.19 226 10.69 7.87 99.57 250 41.02 14.98 9.13 0.20 3.16 5.14 2.69 1.65 1.18 0.19 185 12 8 99.29 260 42.16 15.30 9.24 0.18 3.09 5.03 2.11 1.77 1.21 0.19 230 11.55 7.88 99.71 280 40.30 14.24 9.14 0.14 3.19 7.71 1.52 1.70 1.10 0.21 235 12.67 7.43 99.35 303 24.27 6.63 3.23 0.25 4.22 27.67 0.64 0.55 0.45 0.12 133 28 2 98.64 315 23.56 6.02 3.07 0.33 3.64 26.40 0.53 0.44 0.43 0.10 207 27 6 98.18 333 39.37 13.78 8.29 0.20 3.38 10.23 0.91 1.51 1.00 0.16 239 14.48 6.30 99.61 342 39.39 13.29 10.00 0.21 3.33 7.87 1.56 1.88 0.99 0.22 231 13.39 7.13 99.26 358 34.51 11.64 6.20 0.20 3.36 13.02 1.76 1.17 0.83 0.14 211 18 7 98.21 380 38.34 12.97 7.00 0.15 3.56 11.81 1.19 1.60 0.94 0.16 241 15.84 5.49 99.05 397 38.05 11.76 7.23 0.18 3.78 13.58 1.06 1.57 0.84 0.18 217 18 3 98.92 418 39.92 14.45 8.73 0.12 3.31 6.92 2.83 1.73 1.14 0.18 281 15 5 99.01 440 41.98 14.99 8.89 0.13 3.25 6.97 0.97 1.74 1.18 0.19 255 12.00 6.95 99.24 460 25.52 6.78 3.15 0.30 3.77 27.23 0.65 0.64 0.46 0.13 119 27 3 98.92 470 42.38 15.69 9.15 0.07 2.92 6.84 0.88 1.66 1.04 0.14 197 11.94 7.12 99.83 483 44.05 16.63 9.58 0.06 2.89 4.92 1.38 1.65 1.11 0.13 268 12 5 99.01 503 39.12 15.69 9.31 0.08 2.64 3.30 2.38 1.58 1.06 0.14 270 17 6 98.30 523 40.57 16.11 9.16 0.08 2.78 3.47 2.01 1.60 1.07 0.13 281 13 9 99.21 550 42.42 16.77 9.30 0.07 2.79 3.82 0.93 1.61 1.09 0.14 369 12.47 8.00 99.41 573 43.81 16.72 9.46 0.08 3.01 4.59 1.31 1.66 1.16 0.16 273 12 5 99.03 593 41.40 13.71 7.21 0.12 3.47 10.06 1.37 1.80 0.97 0.14 237 15 4 98.97 610 20.94 6.22 3.05 0.43 3.84 31.02 0.28 0.46 0.41 0.28 134 31 1 98.64 620 38.34 13.09 7.02 0.14 3.18 12.81 0.51 1.52 0.84 0.13 195 15.56 6.07 99.21 640 42.26 16.86 8.42 0.07 2.77 5.61 0.83 1.52 1.05 0.14 306 12.07 7.69 99.29 660 41.40 16.71 9.22 0.06 2.67 3.61 1.90 1.71 1.06 0.14 343 12.44 8.45 99.37 680 45.09 17.58 9.37 0.12 2.87 2.94 0.84 1.76 1.13 0.15 278 9.73 8.22 99.80 700 44.81 16.97 9.13 0.06 2.91 3.36 0.95 1.72 1.16 0.15 206 9.76 8.58 99.56 730 44.25 17.26 9.83 0.06 2.79 2.91 0.73 1.63 1.17 0.16 330 10.70 8.14 99.63

a Replicate.

4.4. Organic matter analyses 4.5. Sr and Nd radiogenic isotope analyses

Samples were freeze-dried and aliquots of 50 mg were decal- Chemical extractions for Sr and Nd isotopes were carried out at the cified with 1 M H3PO4 and dried on a hot plate at 50 C. The organic Laboratory of Tectonophysics of Montpellier (France). Sufficient carbon concentration was determined by combustion in a LECO CS sample was weighed to yield about 100 mg of alumino-silicate 300 carbon sulphur analyser. Reproducibility of Total Organic material after dissolution of the carbonates, and crushed in Carbon (TOC) measurements was 0.02%. a grinder. After leaching for 30 min. at room temperature with acetic 1352 M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362

Table 4 Sr and Nd isotopic data measured on the carbonate-free fraction of core MS27PT sediments.

Samples Location Type or Age [Sr]ppm 87Sr/86Sr (2sig*106) [Nd] ppm 143Nd/144Nd (2sig*106) 3Nd(0) Sourcesa (Latitude Longitude) (cal yr BP) MS27PT core (depth cm) Age, cal yrs BP Surface sediment (0-0.5) (3147’ 90 N, 2927’ 70 E) 614 0.711896 10 0.512141 7 9.7 1 18 (3147’ 90 N, 2927’ 70 E) 1135 0.711257 11 0.512232 9 7.9 1 21 (3147’ 90 N, 2927’ 70 E) 1227 0.710637 10 0.512255 22 7.5 1 42 (3147’ 90 N, 2927’ 70 E) 7399 0.709501 13 0.512269 7 7.2 1 50 (3147’ 90 N, 2927’ 70 E) 7750 0.710485 11 1 60 (3147’ 90 N, 2927’ 70 E) 8188 0.709238 17 1 69 (3147’ 90 N, 2927’ 70 E) 8453.4 0.706974 11 0.512326 10.0 6.1 1 80 (3147’ 90 N, 2927’ 70 E) 8645 0.708409 9 0.512400 10 4.6 1 84 (3147’ 90 N, 2927’ 70 E) 8719 0.708506 8 0.512234 11 7.9 1 86 (3147’ 90 N, 2927’ 70 E) 8753 0.708439 11 1 89 (3147’ 90 N, 2927’ 70 E) 8807 0.70802 10 0.512407 9 4.5 1 103 (3147’ 90 N, 2927’ 70 E) 8994 0.707311 7 0.512409 8 4.5 1 103 replicate (3147’ 90 N, 2927’ 70 E) 8994 0.7079 8 1 112 (3147’ 90 N, 2927’ 70 E) 9081 0.706716 8 0.512414 10 4.4 1 166 (3147’ 90 N, 2927’ 70 E) 9726 0.707843 8 1 177 (3147’ 90 N, 2927’ 70 E) 9897.3 0.708732 8 0.512403 8 4.6 1 200 (3147’ 90 N, 2927’ 70 E) 9953 0.708449 10 0.512392 11 4.8 1 205 (3147’ 90 N, 2927’ 70 E) 10003 0.707896 10 0.512400 10 4.6 1 221 (3147’ 90 N, 2927’ 70 E) 10590.4 0.708571 10 1 250 (3147’ 90 N, 2927’ 70 E) 11501.2 0.707994 9 0.512401 6 4.6 1 270 (3147’ 90 N, 2927’ 70 E) 12176.4 0.709076 17 0.512354 8 5.5 1 290 (3147’ 90 N, 2927’ 70 E) 13950 0.708477 11 0.512385 8 4.9 1 296 (3147’ 90 N, 2927’ 70 E) 15893 0.712517 10 0.512103 10 10.4 1 303 (3147’ 90 N, 2927’ 70 E) 19412 0.71372 8 0.512182 10 8.9 1 315 (3147’ 90 N, 2927’ 70 E) 25444 0.712243 10 0.512187 9.0 8.8 1 374.5 (3147’ 90 N, 2927’ 70 E) 37999.5 0.709046 9 0.512410 7 4.4 1 397 (3147’ 90 N, 2927’ 70 E) 46491.6 0.71144 11 0.512213 18 8.3 1 418 (3147’ 90 N, 2927’ 70 E) 53606.4 0.708386 10 0.512396 9 4.7 1 458 (3147’ 90 N, 2927’ 70 E) 67158.4 0.714991 13 0.512107 27 10.4 1 483 (3147’ 90 N, 2927’ 70 E) 75628.4 0.709108 11 0.512196 62 8.6 1 523 (3147’ 90 N, 2927’ 70 E) 79237.5 0.708521 16 0.512386 5 4.9 1 550 (3147’ 90 N, 2927’ 70 E) 80250 0.708729 10 0.512380 6 5.0 1 593 (3147’ 90 N, 2927’ 70 E) 88628 0.709863 11 0.512238 10 7.8 1 610 (3147’ 90 N, 2927’ 70 E) 91760 0.712793 8 0.512103 10 10.4 1 732 (3147’ 90 N, 2927’ 70 E) 98810 0.709325 9 1 Potential Source Areas type of sediments PSA LIBYE (<30mm) N05 2620’N, 1006’E Sand dunes 113.9 0.718597 35.5 0.511849 15.4 1 (<30mm) N19 2458’N, 1143’E Sand dunes 73.8 0.718587 35.1 0.511988 12.6 1 (<30mm) N26 2535’N 1634’E Sand dunes 183.5 0.706511 50.3 0.512470 3.8 1 (<30mm) N35 2830’N, 1324’E Sand dunes 124.1 0.716029 56.5 0.512002 13.0 1 (<30mm) N36 3056’N, 1433’E Sand dunes 85.5 0.718235 49.2 0.511880 15.3 1 (<30mm) Lybia Lybia 0.715206 15 0.512088 10 10.7 2 Lybian turbidite 3217’N, 2637’E LC24 Lybian- 0.715 10.5 3 Egyptian shelf Nile sediment (<30mm) Assouan overbank 0.705944 0.512464 3.4 1 floods deposit Assouan Elephantine 265.0 0.705801 36.5 0.512812 +3,4 1 sediment North Soudan PM <20mm 204.8 0.70567 4 North Soudan PM <20mm 208.5 0.70661 4 Nile delta H21/6 PM <20mm 140.3 0.70647 4 Nile delta J21/4 PM <20mm 123.2 0.70713 4 Nile delta xxix PM <20mm 116.6 0.70753 4 Alexandria sediments Site I 900 cm ¼ 1800 BP 0.709234 0.512263 7.3 5 1400 cm ¼ 2200 BP 0.710863 0.512246 7.6 5 Site II 600 cm ¼ 4200BP 0.709793 0.512216 8.2 5 900 cm ¼ 5400 BP 0.512327 6.1 5 Aerosols Israel Soreq Cave aerosols 54.6 0.719666 7.1 0.512084 10.8 1 Aerosols Red Sea Red Sea residue residue 114.0 0.715874 34.7 0.512098 10.5 6

a 1 ¼ this work; 2 ¼ Grousset et Biscaye (2006); 3 ¼ Reeder et al, (1998); 4 ¼ Krom et al, (1999); 5 ¼ Freydier et al., (2001); 6 ¼ Grousset et al, (1988). M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362 1353 acid buffered to pH 5 to remove carbonates, the samples were cannot be visually determined because post-depositional re- centrifuged and the supernatant discarded. The remaining sediment oxidation processes following the cessation of anoxic conditions was further washed three times with ultra-pure water, discarding the often changes the colour of their upper part from black to grey. supernatant each time. A 50 mg aliquot, was taken for analysis of Sr Therefore, in our core we define sapropel thicknesses (dotted and Nd isotope ratios. Samples were dissolved into Savillex beakers in patterns in Fig. 5) using peaks in S and Ba concentrations and TOC aHFþ HClO4 þ HNO3 mixture. Chemical extractions of Sr and Nd contents 1.2%. Ba has been proven to be the best proxy of the were carried out following the analytical procedures of Pin et al. original organic carbon contents (Freydier et al., 2001; Weldeab (1994) and Richard et al. (1976). The isotopic measurements (Table et al., 2003). S1, S3 and S4 are characterized by Ba con- 4) were made at the University Paul Sabatier in Toulouse (France), tent > 240 ppm compared to w150 ppm for the surface sediment using a multi-collector mass spectrometer Finnigan MAT 261. (Table 3). The transition from the bioturbated to the laminated The measured 87Sr/86Sr and 143Nd/144Nd ratios were corrected for facies (e.g. 205 cm in Fig. 3 and 5; corresponding to 10 ka cal. BP in mass fractionation by normalizing to 86Sr/88Sr ¼ 0.1194 and Fig. 6) shows a progressive increase of sulphur and organic carbon 146Nd/144Nd ¼ 0.7219, respectively. Strontium standard NBS 987 was contents and a decrease in Mn contents. measured with an average 87Sr/86Sr ¼ 0.710262 (n ¼ 4) versus the The evolution of major element concentrations and median certified value of 0.710250. Neodymium ratio of standard (LA JOLLA grain-size of core MS27PT are presented in Fig. 6 as a function of n ¼ 4) was analyzed with an average of 143Nd/144Nd ¼ 0.511843 age. These data systematically document abrupt and large- (n ¼ 4) versus the certificate value of 0.511850. For convenience, Nd amplitude changes in sediment composition between carbonate- 143 144 isotopic ratios results are expressed as: 3Nd(o) ¼ [[ Nd/ Nd rich arid periods (grey patterns) and Fe/Ti-rich pluvial periods. (meas.)/143Nd/144Nd (CHUR)] 1] 104. The CHUR (Chondritic The carbonate-rich facies is characterized by high CaO contents Uniform Reservoir) value is 0.512638 (Jacobsen and Wasserburg, (30 wt %) and Si/Al ratios (values > 3.3); low Fe (3 wt %) and TiO2 1980). Blanks averaged 0.1 ng and were negligible in all cases. (<0.5 wt %) contents and a median grain size around 6 mm. The grain size frequency curve (not shown) indicates a modal grain size 5. Results centered around 40 mm, corresponding to coarse quartz grains, which can be also observed in thin section (Fig. 3). The dispersed 5.1. Chronology and sedimentation rate occurrence of these quartz grains in the matrix, indicate an aeolian mode of transport. The d18O of G. ruber in core MS27PT (Fig. 4) display large varia- Pluvial periods are characterized by the deposition of sapropels tions ranging from 3.4 & to 1.3 & as expected in the Levantine 4, 3 and 1, (with TOC 1.2%; Fig. 5), systematically preceded by the basin (e.g. Almogi-Labin et al., 2009). The correlation with the d18O laminated clastic mud facies, which itself is preceded by the bio- SPECMAP curve of (Martinson et al., 1987), and with Kallel et al. turbated clastic mud facies. (2000) and AMS 14C indicates that the core extends from historical The laminated and bioturbated facies reveal the same marked times (587 cal years BP) back to MIS 5c dated at 99 ka BP. This time decreases in CaO (<4%) balanced by an increase in Fe (>9%) and Ti period includes three sapropels (S4, S3 and S1), the last glacial cycle contents (>1%) and a constant grain-size mode around 3.5 mm, (MIS 2, 3 and 4) and the Holocene. The d18OofG.ruber in sapropel S1 except for the individual flood laminae. The individual flood is very low (d18O ¼1.29) because of increased freshwater input laminae (Fig. 3) display discrete increases in grain size and Ti from the Nile (Vergnaud-Grazzini et al., 1986). Similar low d18O (Table 3) indicating the presence of higher current speeds able to values associated with MIS 1 and 5 are recorded in the Levantine transport larger particles such as Ti-rich heavy minerals. The grain- Basin by Essalami et al. (2007) from core MD84-632 that covered the size distribution frequency curve of these mud facies reveals last 25 ka, and by Almogi-Labin et al. (2009) from core 9509 which a drastic decrease of the 40 mm mode and the thin section obser- covered the last 90 ka. The agreement of these three records, shows vations indicate a concentration of small (w20–30 mm) quartz that our sedimentary record is continuous and without major gaps. (þbiotite, plagioclase, pyroxene and amphibole) grains at the The linear sedimentation rate (LSR) is highly variable between bottom of each lamina, suggesting a long transport and a fluvial 1.4 and 108 cm/ka (Fig. 4). The highest LSR values of 108 cm/ka and origin (Ducassou et al., 2008). 26 cm/ka for the early Holocene and MIS 5, respectively, are observed during interglacial periods. Drastic decreases in LSR to 5.3. Sr and Nd isotopic composition of the carbonate-free fraction w3 cm/ka are documented during glacial periods. Another signif- icant feature is the abrupt change in sedimentation rate between The Sr and Nd isotopic compositions of the carbonate free the early–middle Holocene (10–8 ka BP: w100 cm/ka; 8–6.8 ka: <63 mm sediment fraction of core MS27PT and of the potential w25 cm) and the late Holocene 6.8–1.2 ka BP: w2 cm). This marked source area samples are listed in Table 4, and plotted in Fig. 7. decrease is associated with a change in facies from a clastic-rich 87Sr/86Sr ratios range from 0.707 to 0.715 and 3Nd(0) between 4 mud to a carbonate-rich facies (Fig. 3). and 10. All Sr and Nd isotopic values of core MS27PT sediments lie This shows that throughout the last 100 ka the sedimentation along a hyperbolic mixing curve linking a depleted mantle-derived rate at the coring location is strongly influenced by the Nile river end-member (Blue Nile River material provided by erosion of contribution. The climate of tropical Africa is dominated by vari- Ethiopian Basalts) and a continental crust end-member (Saharan/ ability in effective moisture, rather than temperature as at higher Libyan dusts derived from the erosion of crystalline rocks). The latitudes. In consequence, in the following, we will name the late relatively tight distribution of all values along the mixing hyperbola Holocene (LH), Younger Dryas (YD), MIS 2, 4 and 5b periods (grey clearly demonstrates that the isotopic compositions of the sedi- patterns in Figs. 4–6) as arid periods (instead of glacial periods) and ments for the last 100 ka can be explained by a simple mixing early–middle Holocene (EMH), MIS 5a and 5c as pluvial periods model between a Libyan/Egyptian dust-member and a Blue Nile (instead of interglacial). end-member. The 3Nd(0) values are unlikely to be significantly modified 5.2. Major element characteristics of Nile margin sediments during chemical weathering on land; in contrast, Sr isotopes are influenced by grain size effects and the degree of weathering As shown by previous studies, (Coolen et al., 2002; Weldeab (Dasch, 1969; Tutken et al., 2002). In the studied core, the Sr et al., 2003; Paterne, 2006) the thickness of sapropel layers isotopic compositions exhibit similar large shifts to the Nd isotopic 1354 M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362 composition along the last 100,000 years. This suggests that the same Nile River sediment source but different processes of trans- 87Sr/86Sr ratio shifts can be interpreted as a shift in the source and port and depositional conditions. not as change in the degree of chemical weathering of the same The sediments of the arid intervals of MIS 2, 4 and 5b, associated source region. to the carbonate-rich facies, display higher 87Sr/86Sr ratio val- In comparison to cores BC07 and BC19 from Freydier et al. ues > 0.713 and lower 3Nd(0) of about 10 which are consistent (2001), the MS27PT sediments have a more radiogenic Sr isotope with a drastic change in source, mainly an increase of Libyan and composition, indicating higher Blue Nile contribution. This is Egyptian dust contributions and a decrease in Blue Nile suspended consistent with the closer proximity of our core (w90 km) to the particulate matter. The sediment deposited during the late Holo- Rosetta Nile mouth. In comparison to core KL83 from Weldeab et al. cene arid period displays intermediate values between those of the (2002), we observe similar patterns, which is consistent with the sapropel and of the carbonate-rich facies. surface current patterns of the Levantine basin. The Levantine In Fig. 7, the mixing hyperbola constructed on the basis of both surface current (Fig. 1) flows from east to west and induces a strong Sr and Nd isotopic composition and concentration (Faure, 1986) influence of the Nile plume on the Israel coast (Almogi-Labin et al., allows us to quantify a Blue Nile River contribution ranging from 2009). Sr and Nd isotopic ratios of the individual flood laminae 40 to 70% during pluvial periods (Pluvial EMH and MIS 5), (Fig. 3) in the laminated facies display 87Sr/86Sr of w0.707 and whereas during the arid periods, the Nile River contribution falls 3Nd(0) around 4. Such extreme values suggest a ‘‘pure’’ Blue Nile to z15% and the Saharan dust contribution reaches z85%. flood input, not contaminated by dust deflated from the surrounding deserts, demonstrating a direct and intense flood 6. Discussion input from remote Ethiopian sources. The laminated EMH sedi- ment, MIS 3 and MIS 5 samples display 3Nd(0) values around 7 6.1. Arid/Pluvial Ca–Fe cycles in the Nile margin sediments and 87Sr/86Sr ratios around 0.709. Similar Sr and Nd isotopic ratio values are obtained for sapropel S1, S3 and S4 ranging from 0.7085 The main feature of our multi-proxy study of MS27PT sedi- to 0.711 and 3Nd(0) 7to9. The laminated and bioturbated ments (Figs. 4–7) is the large amplitude of change in Ca and Fe sediments reveal exactly the same isotopic values suggesting the contents between pluvial and arid periods associated with drastic

Fig. 7. 87Sr/86Sr versus 3Nd(0) isotopic signature (Table 4) for the carbonate-free, and strictly <63 mm sediment samples of core MS27PT (black diamonds) and potential source area samples (this work and literature). M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362 1355 changes in sedimentation rates ranging from w3 cm/ka during accumulation rate. It is interpreted as an important reduction in arid periods to 26–108 cm/ka during pluvial periods. These results Nile flood intensity. The coarse quartz grains observed in thin indicate two different environmental conditions of sediment sections (Fig. 3) and the Si/Al ratio of up to 3.3, which was inter- transport/deposition, which have been recurrent over the last preted as an increase of quartz/clay ratios by Calvert and Fontugne 100,000 years. (2001), show a systematic change in sources. We interpret this feature as evidence for a higher flux of Saharan aeolian dust, which 6.1.1. Fe- rich pluvial periods (EMH, MIS 5a and 5c) is mainly composed of quartz and clay minerals (Ganor et al., 1991) A significant feature of the pluvial periods is the large increase of during arid periods. Blue Nile suspended particulate matter discharge reflected by high The data presented above, allow for the reconstruction of Fe and Ti contents (Fig. 6). Fe content traces the variability of the a high-resolution record of changes in sediment sources for the last ferromagnesian minerals and should reflect the pyroxene and 100 ka. However, because the XRF scanner analysis is carried out on smectite contents in the Blue Nile River sediment (Foucault and bulk sediment and not on carbonate-free fractions, elemental Stanley, 1989) derived from the weathering of Ethiopian basalts variations appear to be exaggerated as a result of dilution effects. A (Kamel et al., 1994; Sameeh, 2000). Therefore, in this system, we quantitative estimation of the variability of terrigenous sources, is ascribe high Fe content to high Nile flood intensity, which is only possible with the Sr and Nd isotopic composition of carbonate- generally consistent with palaeoclimatic reconstructions of African free samples of the <63-mm fraction of the sediment (Fig. 7). lake levels and of marine sediment from off the coast of Mauritania This isotopic approach, based on the variations of the Rb–Sr and (Gasse, 2000; Tjallingii et al., 2008 and see Section 6.3). This high Sm–Nd isotopic systems in the parent rocks and the natural discharge of Nile-derived suspended particulate matter and related radioactive decay of 87Rb and 147Sm into 87Sr and 143Nd, respec- surface freshwater supply led to a reduction of salinity and density tively, has been previously successfully applied to constrain and of surface waters, enhancing water-column stratification in the quantify different terrigenous source contributions (Revel et al., Mediterranean. Consequently, deep waters became anoxic, leading 1996; Grousset et al., 1998; Grousset and Biscaye, 2005; Revel- to the formation of sapropels. The record of terrigenous Nile sedi- Rolland et al., 2006). ment (Fig. 6) reveals an abrupt MIS2/Holocene transition with an Fe increases from 3% to 10% in less than 3 ka (Fig. 6). In contrast, the 6.2. Pluvial events: quantification establishment of anoxic conditions in the bottom waters is more gradual as it is documented by the textural change from bioturbated In Fig. 8A, the 87Sr/86Sr isotopic ratios, d18O and Fe records to laminated-facies (Figs. 3 and 5). Indeed, this textural change obtained for core MS27PT, are compared with the variations in the cannot be explained by a change in sediment sources because Fe level of Lake Abhe (Gasse, 2000). Quantitative estimations (Fig. 7)of content as well as the Sr and Nd isotope compositions does not the relative contribution of clastic sediments from both Libyan/ change significantly. This clearly reflects a progressive change in Egyptian aeolian and Nile River sources show changes between bottom water ventilation. Increased anoxia in the bottom waters, w15% of Nile contribution and w85% of aeolian dust in arid periods and possibly increased productivity, is reflected in an increase in S to w70% of Nile contribution in pluvial periods. and TOC contents in the sediments. Mn peaks above the sapropel A key question is if these higher relative contributions of aeolian layers are interpreted as a result of the reestablishment of oxic dust during arid periods are due to a drastic decrease in the Nile conditions (Van Santvoort et al., 1996). At the beginning of the River input or are a combination of a Nile decrease with an increase Holocene, these oxic to suboxic conditions have allowed the colo- in aeolian dusts. We propose that the change in 87Sr/86Sr ratios nization by benthic foraminifera, leading to bioturbation of these from 0.706 to 0.713 is explained by an important decrease in the levels (see thin sections in Fig. 3) and destruction of the lamination Nile suspended matter input, which is consistent with the drastic that would have been created by the probable annual Nile flood LSR and Fe content decreases, balanced by an increase of Saharan deposition. In contrast, in the laminated facies, oxygen deficiency aeolian dust, as indicated by the increase in quartz proportion and excluded benthic microfauna and prevented bioturbation. A similar size. During arid periods, the southern ITCZ position induced change in ventilation has been described from the Santa Barbara a more vigorous global atmospheric circulation associated with basin area (Behl and Kennett, 1996; Blanchet et al., 2007). steeper latitudinal thermal gradients and large amounts of dust Another significant consequence of these pluvial periods is the could have been deflated from the surrounding desert to the Nile drastic decrease in CaO contents balanced by a drastic Ti and Fe mouth (Said, 1993; Prospero et al., 2002). This explanation is concentration increases. A strong anti-correlation of CaO with Fe consistent with the elevated 87Sr/86Sr ratios (0.708) observed in (R2 ¼ 0.93) and Ti contents (R2 ¼ 0.86) is observed. a speleothem from the Jerusalem Cave (Frumkin and Stein, 2004), The low Ca contents during the pluvial periods may be some- which was interpreted as an indicator of higher dust fluxes during what surprising. However, because the MS27PT core is located glacial periods and during the late Holocene. Considering their directly under the influence of the Nile River, the strong decrease in timing, the observed increases in Saharan aeolian dusts in the CaO is interpreted as mainly resulting from a dilution of the MS27PT sediment (Fig. 8A) are synchronous with the known global carbonate fraction by the terrigenous input and not as a decrease in enhanced atmospheric dust loads during Quaternary glacial surface productivity. This is consistent with the dramatic increase periods (Rea, 1994; Biscaye et al., 1997; DeMenocal et al., 2000; in accumulation rates (up to 100 cm/kyr) during pluvial periods, Kohfeld and Harrison, 2001; Lambert et al., 2008). Glacial/arid compared to low rates (3 cm/kyr) observed during arid periods. periods are characterised by a widespread African continental Along the whole Nile margin, terrigenous sedimentation rates are aridity in response to decreased boreal summer insolation. This has higher during interglacial periods (MIS 7, 5, 3 and 1), than during led to the weakening of the monsoon and the southward retreat of glacial periods (MIS 8, 6, 4 and 2). This is attributed to the abundant its summer front, which led to the return of hyperarid desert occurrence of Nile floods during interglacial periods (Ducassou conditions over the Sahara (Trauth et al., 2009). This aridity led to et al., 2009). changes in soil moisture, a reduction of savannah-like vegetation and to a decrease of soil cohesiveness throughout the northern 6.1.2. Ca-rich arid periods (LH, MIS 2, 4 and 5b) Sahara, favouring higher dust production. The carbonate-rich facies, which occurs systematically during In contrast, during pluvial periods, our Sr and Nd isotope mixing the glacial/arid periods, is characterized by a drastic decrease in model reveals enhanced Nile contribution oscillating between 40 1356 M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362 M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362 1357 and 70% (Fig. 7). These wet phases are synchronous with the known several important events over the last 100 ka BP: two main Nabtian (14–6 ka BP) and Saharan (w190 to <70 ka BP) African periods of enhanced African monsoon activity corresponding to pluvial periods (Fig. 8A). The change in terrigenous sources recorded the Nabtian and the end of the Saharan pluvials during inter- in the Nile margin sediments are documented by less negative glacial MIS 1 and 5, respectively, and the last glacial period (MIS 3Nd(0) ratios and less radiogenic Sr isotope ratios suggesting 2, 3 and 4) with a continuous record showing large oscillations a higher Ethiopian basaltic input. This, together with the increase in between more intense and less intense East African/West Asian sedimentation rate during pluvial periods, is a strong indication of monsoon activity. enhanced precipitation on land and in particular of high terrestrial runoff from the Ethiopian Highlands. This can be related to a longer 6.3.1. Saharan and Nabtian pluvial periods and/or stronger summer monsoon and to a northward migration of 6.3.1.1. The Saharan period. The enhanced East African/West Asian the rain belt over the Ethiopian Highlands. monsoon activity, recorded in MS27PT sediment, corresponds to In the previous discussion, we have considered the Nile margin the end of the Saharan pluvial period (190–70 ka; Said, 1993) which sediment as a two-component (Saharan dust and Blue Nile input) was defined on the basis African palaeo-lake level reconstructions rather than three-component system (Saharan dust, Blue Nile and (Libya: Petit-Maire, 1982 and Kieniewicz and Smith, 2007; Egyptian White Nile input). Indeed, we consider that the suspended matter and Sudan lakes: Szabo et al., 1995; Sinai Desert: Klein et al., 1990; transported from the White Nile and deposited into the Nile margin Abhe Lake: Gasse, 2000). The oldest pluvial period (MIS 5, Fig. 8A) before 11.5 ka is negligible because Talbot et al. (2000) have suggested displays high flood frequencies from 98 to 92 ka and from 88 to that the main sources of the White Nile, lakes Albert and Victoria, 69 ka, interrupted by an abrupt change to lower flood activity merge into the Nile drainage network only around 11.5 ka. Moreover, periods spanning from 92 to 88 ka. These are in accordance with we consider that the erosion/weathering processes producing fluvial pluvial episodes from 90 to 65 ka determined by uranium-thorium material are more intense in the Blue Nile catchment, compared to the dating of lacustrine deposits of the Eastern Sahara (West Nubian, in granitic White Nile region, mainly because of the basaltic lithology Fig. 1; Szabo et al., 1995). Vermeersch (2005) has shown that, and the higher elevations in the Ethiopian Highlands (Fig. 1). The during the MIS 5 interglacial periods, prehistoric populations Ethiopian Highlands are the first orographic barrier hit by the East- expanded along the Nile valley. After the MIS 5, these populations erlies during the boreal summer. As a consequence, they concentrate seem to progressively decrease and at around 65 ka, aeolian input the precipitation coming from the Indian Ocean leading to a large and dune formation are documented, indicating a return to arid production of sediment, which is transported by the Blue Nile river to conditions (Cohen et al., 2007). the Nile delta (Fig. 1). After 11.5 ka, it is probable that little sediment originating in the upper White Nile made it through the Sudd swamps 6.3.1.2. The Nabtian period. The early–middle Holocene appears to in Sudan (Fig. 1). Some contributions are possible from White Nile have been a very wet phase across much of the Levant and Eastern tributaries further downstream such as the Wadi Howar (Nuba Mediterranean. In Israel, studies of the Soreq Cave speleothems mountains and Jebel Marra weathering), which produce material have revealed Holocene temperatures similar to modern day with with highly radiogenic Sr (>0.722 Talbot et al., 2000)fromthe the late Holocene time around 1ka being slightly cooler and the exposed Proterozoic rocks. Therefore, in spite of a minor potential early Holocene time between 10 and 7 ka slightly warmer (Bar- contribution from White Nile, we conclude that the observed Sr and Matthews et al., 2003; Affek et al., 2008). This is in accordance Nd isotopic composition changes can be used as reliable proxies of with Eastern Mediterranean temperatures deduced from alkenone monsoon intensity variability over Ethiopia. and Sapropel 1 described in the Eastern Mediterranean between To increase the resolution of the Nile discharge reconstruction, w9.5 and 6.6 ka (Emeis et al., 2003). The lowest values of d18Oin we compared the distribution of major elements with the Sr core MS27PT are recorded from 9.5 to 6.8 ka. They are attributed to isotope record. The best correlation of major elements with isotopic a maximum of freshwater flow from the Nile River. The onset of the data (Fig. 9) is obtained for the Fe content with R2 ¼ 0.72 (and for Holocene humid period, documented in MS27PT sediment by Fe/Al ratios with R2 ¼ 0,76). It is also noteworthy that our data show increase of Ethiopian basaltic inputs (Fig. 8A and 8B) and increase in an anticorrelation of Sr ratios and Si/Al ratios, confirming that high sedimentation rate, is dated at 13.95 ka and is followed by an arid Fe contents are a proxy to the Nile suspended particulate matter episode starting at 12.5 ka and then by an intense humid period whereas high Si/Al ratios are a proxy for aeolian Saharan source. from 12 until 8 cal ka. The arid episode is synchronous with the Therefore, we use the Fe/Sr linear correlation to express the Fe Younger Dryas cold episode observed in the Northern Hemisphere content in % of dust and Nile fluvial relative contributions where at ca 12.8–11.6 ka (Bard and Kromer, 1995) and in African lakes a rise in Fe content is interpreted as enhanced East African (Garcin et al., 2007). monsoon activity over the Ethiopian Highlands. The EMH humid period has already been documented in several African lakes from about 12 to 5 ka (Turkana Lake: Johnson, 6.3. Timing of Nile hydrological variability compared with low 1996; Lake Abhe: Gasse, 2000; Lake Abiyata: Chalie´ and Gasse, latitude African climate 2002, Lake Ashenge: Marshall et al., 2009; Lake Mega-Chad: Schuster et al., 2005; Masoko Lake, Tanzania: Garcin et al., 2007), Our high resolution Fe record allows us to reconstruct sub- palaeolakes (Nile catchments: Said, 1993; NW Sudan: Szabo et al., decadal changes in Nile outflow, with 1 mm corresponding to 2 1995). The onset of the humid period in MS27PT sediment dated at years during the pluvial Nabtian period, and therefore to estimate 14 ka is in accordance with the timing of humid Holocene recorded the Ethiopian Highlands precipitation and African/W-Asian in Lake Tana (Fig. 1), which is the source of the Blue Nile in the monsoon intensity. In core MS27PT (Fig. 8A), we identify Ethiopian Highlands (Lamb et al., 2007). These authors

Fig. 8. (A) The d18O curve, 87Sr/86Sr isotopic ratios and Fe data of the core MS27PT are presented according to time (ka BP). The palaeoclimate reconstruction from African lake Abhe level is reported for comparison (Gasse, 2000). The red dots correspond to 87Sr/86Sr ratios <0.710 interpreted as a dominant Blue Nile suspended matter contribution. The red squares correspond to the maximum of Nile flood periods. The black dots correspond to 87Sr/86Sr ratios > 0.710 interpreted as a dominant crustal contribution (aeolian dusts and/or White Nile input). (B) Focus on the Holocene period. The d18O curve, Fe/Ca ratios, 87Sr/86Sr and 3Nd(0) isotopic signature data of the core MS27PT are presented for the last 20 ka cal BP. The 87Sr/86Sr isotopic compositions recorded in the ODP site 658C offshore western Saharan region is reported for comparison (Cole et al., 2009). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). 1358 M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362

Sr versus Si/Al Sr versus Fe% 12,00 6

y = -1070,5x + 766,99 R2 = 0,768 10,00 5

8,00 4 Fe %

6,00 3 Si/Al

y = 155x - 107,15 4,00 2 R2 = 0,5451

2,00 1

0,00 0 0,720 0,715 0,710 0,705 0,700 87Sr/86Sr

Fig. 9. Correlation curves between Sr isotope compositions and Fe plus Si/Al ratio distribution. demonstrated that the lake began to overflow into the Blue Nile at 6.3.2. The Middle–Late Holocene Pluvial/arid transition 14.75 kyr cal BP, whereas the Blue Nile flood must have been very Our record allows dating the onset of the decrease of Blue Nile much reduced until this time. In contrast, this humid period is water discharge at 8 ka (Fig. 8B). This decrease is documented by documented from the West Nubian palaeolakes from approxi- a decrease in Fe/Ca ratios and in 3Nd(0) and by an increase in the mately 9.5 to 4 ka BP (Hoelzmann et al., 2000) and from 10 to 5 ka 87Sr/86Sr ratios between 8.4 and 8.1 cal BP. This trend is interpreted BP (Szabo et al., 1995). as a reduction of Ethiopian basaltic input suggesting a reduction of The different ages obtained to date the beginning of humid precipitation on the Ethiopian Highlands. Compared to regional EMH period from different archives could be due to (i) to chro- records (Fig. 1) of the continental climatic conditions, our record nological uncertainties due to hard water and reservoir effects shows that: (see discussion in Gasse, 2000), (ii) the fact that our record integrates climate fluctuations across all the Nile River watershed (i) The onset of the decrease in precipitation recorded in the Nile whereas the records of Hoelzmann et al. (2000) and Szabo et al. margin at 8 ka is contemporaneous with the decrease of Lake (1995) document regional climate at a latitude of about 20N. The Tana water-level documented by Lamb et al. (2007). It is also subsequent northward migration of the rain belt between 17 and contemporaneous with Somalian coast aridification. Jung et al. 11 ka cal BP would have caused rainfall first over equatorial lakes (2004) and Ivanochko et al. (2005) showed that the first ari- and then over the Ethiopian Highlands and finally over North dification step occurred at 8.5 ka followed by an unstable Sudan/South Egypt. We also should consider that meltwater from transitional period up to 6 ka. Our record is also contempo- Ethiopian glacier retreat could have caused higher Nile flow as raneous within error with the precipitation decrease recorded soon as 17 cal BP ka (Tiercelin et al., 2008). Sedimentological and in Holocene stalagmites from Qunf and Hoti caves in Oman by geochemical studies conducted on Ethiopian Lake Garda Guracha Fleitmann et al. (2007) who showed that the mean summer sediment document the progressive retreat of a high-altitude ITCZ continuously migrated southwards from 7.8 ka to (w3000 m) glacier in the Bale Mountains since 17 ka cal BP. present. Finally our record is consistent with the aridification Thus, a part of the Fe increases (Fig 8A) dated at 16.8 could be recorded at ODP site 658C offshore the western Saharan region explained by the retreat of Ethiopian glaciers that generates (Cole et al., 2009). These authors hypothesize low siliciclastic discharge of meltwater and glaciogenic sediment transported on flux corresponding to the African Humid Period between 12.3 the Nile margin. and 5.5 cal ka BP on the basis of Sr and Nd radiogenic isotope At the global scale, the MS27PT Fe record is in accordance with tracers. However, as shown on Fig. 8B, their Sr isotope ratios the Epica-Dome C dust record (Antarctica), which reveals that the trend shows more radiogenic ratios already since 8 ka inter- end of the major dust decrease (that characterizes the deglaciation) preted as the onset of the aridification. This trend is followed occurred around 14.6 ka BP (Jouzel et al., 2001; Lambert et al., by a marked increase in radiogenic ratios at 5.5 ka indicating 2008). Afterwards, a transition phase characterized the Antarctic the aridification. Cold Reversal (ACR equivalent but not synchronous with the YD in (ii) In contrast, the decrease in precipitation recorded in the Nile North Hemisphere) and the major lowering of the dust flux started margin occurred earlier than in Equatorial African Lakes. The at about 11.5 ka BP. onset of mid-Holocene aridity is documented at w5.4 cal ka BP M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362 1359

in Lake Edwards (Russel and Johnson, 2005) and in Lake and interrupted by a drier period dated between 50 and 38 kyr. Abiyata (Chalie´ and Gasse, 2002). A similar timing of humidity is documented from marine sedi- ments from off the coast of Mauritania (Tjallingii et al., 2008). We propose that this offset traces the onset of the southward The pluvial period between 38 and 20 ka BP has already been shift of the rain belt that occurred about 3000 years earlier over observed by Gasse and Street (1978) and Gasse (2000) especially the Ethiopian Highlands (Blue Nile) than over the Equatorial East in Lake Abhe´ (Fig. 8A) and around 26 ka BP by Schuster et al. African region. Our record (Fig. 8B) indicates an increase in (2005) in Lake Chad. This event is well recorded in core 87Sr/86Sr ratios starting at 8 ka interpreted as a decrease of basaltic MS27PT as reflected by an increased Fe content (6%) peaking input from the Ethiopian Highlands, whereas the d18O record around 34–30 ka BP. indicates negative values until 6.8 ka suggesting ongoing fresh- The d18O profile obtained in the Israelian Soreq Cave (Affek et al., water input in the delta. We suggest that this delay (8–6.8) 2008) and in the Levantine basin (Almogi-Labin et al., 2009) for the probably reflect a change in the source of Nile suspended matter last 80 kyr BP reveals pluvial and intermediate temperature around from a predominant Blue Nile source to an increased White Nile 56 kyr BP from the Soreq Cave record and 58–49 ka from the core input. Talbot et al. (2000) suggest that Equatorial Albert and 9509 located in the Levantine basin. This pluvial episode is similar Victoria Lakes merge into the Nile drainage network around to higher humid conditions recorded in MS27PT sediment around 11.5 ka. In this context, we hypothesize that it is the weakening of 63–50 ka. This episode coincides with organic carbon concentra- the Ethiopian input since 8 ka that allows the relative increase in tions >1% in Fig. 5, and high Fe and Ba contents suggesting White Nile input to be observed. The low d18Ovaluesuntil6.8 increases in the Nile contribution. This period could correspond to imply that the Nile margin is probably still fed by the rain belt up the time when the poorly developed sapropel S2 previously to w6 ka through the White Nile. reported in the Mediterranean Sea was formed (Cita et al., 1977; In summary, we propose that since 8 ka, the rain belt started Lourens et al., 1996). This period correlates with the Dansgaard– migrating southward inducing first less precipitation over the Oeschger interstadial 14 (Almogi-Labin et al., 2009) and maximum Ethiopian Highlands. Then, from w8tow6 ka rainfall became more Northern Hemisphere insolation suggesting that the warming in seasonal and highly variable as is suggested from a study of Lake the Northern Hemisphere is expressed in tropical Africa by more Victoria (Stager et al., 2003). Gasse (2000) showed that rapid humid conditions as documented before 70 ka by Scholz et al. climate changes affecting tropical and subtropical Africa occurred (2007). The comparison of our record with the atmospheric CH4 in the interval 8.5–7.8 ka. She proposed that these rapid changes concentrations recorded from the Greenland ice cores (Chappelaz are correlated with the 8.2 Holocene climatic event observed in et al., 1993; Sanchez-Goni et al., 2008) reveals an increase of CH4 Greenland ice cores, and with a significant decrease in methane at in phase with the two increases in Fe (Fig. 8A). Considering that ca. 8.4–8.0 ka (Chappelaz et al., 1993). Then, at about 5 ka, the ari- tropical wetlands could be a source of the atmospheric CH4, we dification dominates over subtropical and tropical Africa. propose that these two humid periods, due to the strength of monsoon, have induced the development of tropical wetlands. 6.3.3. The last glacial period (MIS 2, 3 and 4; 18–73 ka) Thus, the eastern equatorial/tropical Africa must have been among African tropical and subtropical palaeohydrological proxy data these regions contributing to the rise in atmospheric CH4 at around derived from pollen, palaeolakes and groundwater have not 58 and 38 ka cal BP so before the Heinrich events H4 and H6, reached the resolution and continuity necessary to closely compare respectively (H4: 38.2–40.2 kyr cal BP; H6: 65.6 ka cal BP, Jullien them with higher latitudes time series (Gasse, 2000). In particular, et al., 2007; Paterne et al., 1999). the last glacial period is rarely, and not continuously documented. The timing of observed less intense African/Asian palaeo- Here, we present a high temporal resolution and continuous record monsoon periods (such as YD, LGM, MIS 4) and more intense of Nile palaeohydrology intensity for the last glacial period (Fig. 8A). African/Asian monsoon periods (such as the Saharan and Nabtian The Last Glacial Maximum (LGM; ca. 23–18 ka, Gasse, 2000; pluvials) recorded in the MS27PT core coincides quite well with Mix et al., 2001, Hughes and Woodward, 2008) palaeoclimatic climate changes observed in East Africa and in the Levantine basin. records in the Eastern Mediterranean and Levant Sea suggest that Additional studies and more precisely dated cores from the Nile the region was generally cooler (Hayes et al., 2005) and more arid margin, however, are required to improve the time-scales and to with increased wind speeds and dust transport (Calvert and better compare low and high latitude climate variability on Fontugne, 2001) than present. Sea surface temperatures were a millennial scale. However, this study shows the potential of the reconstructed over the last 30.000 years from alkenone paleo- Nile margin location to reconstruct the intensity of the African/ thermometry and planktonic foraminifera assemblages from core Asian monsoon at high resolution and to evaluate phase relations of MD84-632 in the Levantine basin (Essalami et al., 2007). These climate change. data indicate that the LGM was more arid and colder than today by about 6–7 C. Similarly, the Soreq cave speleothem studies 7. Conclusion have revealed that LGM was 6–7 C cooler than the modern day temperature (Bar-Matthews et al., 1999, 2003; Affek et al., 2008) With high-resolution multiproxy analyses of hemipelagic sedi- in agreement with the timing of the last deglaciation recon- ments from the Nile margin we reconstructed Nile River palae- struction recorded at global scale (Genty et al., 2006). Aridity in ohydrological fluctuations for the last 100,000 years. Sr and Nd tropical Africa, at LGM, is primarily attributed to lower tropical isotopes and Fe concentrations document sediment source SSTs, due to increased northward oceanic heat transport out of changes, reflecting alternating aeolian Saharan, and Nile River tropics (Gasse, 2000; Lamb et al., 2007). Global climate models inputs which are related to change in the East African/West Asian simulate a weaker global hydrological cycle than at present and palaeo-monsoon regime intensity over Ethiopia. a decrease in summer precipitation over most of the tropics at For the first time, our geochemical data allow the reconstruc- the LGM. Record from the MS27PT sediment shows a drastic tion of a high-resolution (with decennial resolution during the decrease in the Nile discharge both at the LGM (25–17 cal BP) and pluvial periods) and continuous record of Nile discharge for the during MIS 4 (69–67 ka). Surprisingly, however, MIS 3 is mainly last glacial period (MIS 2–4). Our data show that MIS 2 and 4 were characterized by a more pluvial climate with two periods of arid periods with high Saharan dust input to the Nile margin, in maximum flood events dated to around 38-30 kyr and 60-50 kyr phase with the global increase of atmospheric dust load 1360 M. Revel et al. / Quaternary Science Reviews 29 (2010) 1342–1362 documented in Antarctic ice cores. In contrast, our reconstruction Bar-Matthews, M., Ayalon, A., Gilmour, M., Matthews, A., Hawkesworth, C.J., 2003. shows wetter conditions during MIS 3 compared to MIS 2 and 4, in Sea-land oxygen isotopic relationships from planktonic foraminifera and spe- leothems in the Eastern Mediterranean region and their implication for paleo- agreement with previous well dated records from East Africa and rainfall during interglacials intervals. Geochimica et Cosmochimica Acta 67, speleothem data from Soreq cave in Israel. In particular, two 3181–3199. humid periods around 58 ka and 38 ka cal BP are recorded in Behl, R., Kennett, J.P., 1996. Brief interstadial events in the Santa Barbara basin, NE Pacific during the past 60 kyr. Nature 379, 243–244. phase with the rise of atmospheric CH4 concentrations suggesting Biscaye, P.E., Grousset, F.E., Revel, M., Van der Gaast, S., Hemming, S., Vaars, A., that wetland tropical African area was one of the sources of the Zielinsky, G.A., Sowers, T., 1997. Limits on the origins of last-glacial maximum dust in the GISP2 ice core, Summit, Greenland. Journal of Geophysical Research atmospheric CH4 during the MIS 3. 102, 26,765–26,782. We also document the end of the Saharan pluvial period dated Blanchet, C., Thouveny, N., Vidal, L., Leduc, G., Tachikawa, K., Bard, E., Beaufort, L., from 98 to 69 ka BP, which corresponds to the deposition of sap- 2007. Terrigenous input response to glacial/interglacial climatic variations over ropel 4 and 3 in the Mediterranean Sea. southern Baja California: a rock magnetic approach. Quaternary Science Reviews 26, 3118–3133. Finally, we document the Nabtian pluvial period, dated from 14 to Bout-Roumazeilles, V., Combourieu Nebout, N., Peyron, O., Cortijo, E., Landais, A., 8 cal kyr BP, which corresponds to the deposition of sapropel 1 in the Masson-Delmotte, V., 2007. Connection between South Mediterranean climate Mediterranean Sea. The onset of this pluvial period dated at 14 cal ka and North African atmospheric circulation during the last 50,000 yr BP North BP agrees with several previous studies based on East African lakes. Atlantic cold events. Quaternary Science Reviews 26, 3197–3215. Box, M.R., Krom, M.D., Cliff, R., Almogi-Labin, A., Bar-Matthews, M., Ayalon, A., Surprisingly, the end of the Nabtian period occurred around 8 ka in Schilman, B., Paterne, M., 2008. Changes in the flux of Saharan dust to the East MS27PT sediment, i.e. much earlier than the East African Equatorial Mediterranean Sea since the last glacial maximum as observed through Sr- region where it is at around 5.5 ka. This offset reveals that the isotope geochemistry. Mineralogical Magazine 72, 307–311. Calvert, S.E., Fontugne, M.R., 2001. On the late Pleistocene–Holocene sapropel southward shift of the rain belt occurred 3000 years earlier over the record of climatic and oceanographic variability in the Eastern Mediterranean. Eastern Ethiopian Highlands and traces the gradual southward Paleoceanography 16, 78–94. migration of the rain belt with probably highly variable precipitation Chalie´ and Gasse, 2002. Late Glacial–Holocene diatom record of water chemistry and lake level change from the tropical East African Rift Lake Abiyata (Ethiopia). intensity and/or longer rainy seasons between 8 and 5 ka. Palaeogeography, Palaeoclimatology, Palaeoecology 187, 259–283. Chappelaz, J., Blunier, T., Raynaud, D., Barnola, J., Schwander, J.M., Stauffer, B., 1993. Synchronous changes in atmospheric CH4 and Greenland climate between 40 Acknowledgements and 8 kyr BP. Nature 366, 443–445. Cita, M.B., Vergnaud Grazzini, C., Robert, C., Chamley, H., Ciaranfi, N., d’Onofrio, S., The authors thank the Captain and crew members of the R/V 1977. Paleoclimatic record of a long deep-sea core from the eastern Mediter- ranean. Quaternary Research 8, 205–235. Pelagia and NIOZ for their technical support during the MIMES Cohen, A.S., Stone, J.R., Beuning, K.R.M., Park, L.E., Reinthal, P.N., Dettman, D., cruise. We are grateful to Beatrice Galland for technical assistance Scholz, C.A., Johnson, T.C., King, J.W., Talbot, M.R., Brown, E.T., Ivory, S.J., with the chromatography separations and Pierre Brunet and Claire 2007. Ecological consequences of early Late Pleistocene megadroughts in tropical Africa. Proceedings of National Academy of Sciences 104, 16,422– Boucayrand who helped us for the Sr and Nd analyses in Toulouse. 16,427. We are grateful to Paul Capiez for majo element analyses in Lyon. Cole, J.M., Goldstein, S.L., deMenocal, P.B., Hemming, S.R., Grousset, F.E., 2009. We thank Yann Rolland, Pierrick Rouillard, Catherine Pierre, Cath- Contrasting compositions of Saharan dust in the eastern Atlantic Ocean during the last deglaciation and African Humid Period. Earth and Planetary Science erine Jeandel and Audrey Galve for comments and discussions. We Letters 278, 257–266. thank Elizabeth Michel and Nathalie Nebout for advices on Coolen, M.J.L., Cypionka, H., Sass, A., Sass, H., Overmann, J., 2002. Ongoing modifi- the chronological framework on the core MS27PT. Jamie Woodward cation Mediterranean Pleistocene sapropels mediated by Prokaryotes. Science is thanked for suggestions resulting in a significantly improved 296, 2407–2410. Dasch, E.J., 1969. 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