Hydrological variability in northern Levant

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May 10, 2011 - rising up to 3083 m a.s.l. in Mount Lebanon at only 20–25 km from the sea .... From the seashore upward, the western slopes of Mount Lebanon ...
Climate of the Past Discussions

Discussion Paper

Clim. Past Discuss., 7, 1511–1566, 2011 www.clim-past-discuss.net/7/1511/2011/ doi:10.5194/cpd-7-1511-2011 © Author(s) 2011. CC Attribution 3.0 License.

This discussion paper is/has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP if available.

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Hydrological variability in northern Levant over the past 250 ka

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1,**

1

1,*

2

, L. Vidal , A.-L. Develle , and E. Van Campo

´ CEREGE, UMR6635, CNRS – (Aix-Marseille Universite-CNRS-IRD-CdeF), BP 80, 13545 Aix-en-Provence cedex 04, France 2 ECOLAB, UMR5245, (CNRS-Universite´ de Toulouse-INPT), BP 24349, 31062 Toulouse cedex 9, France * now at: Laboratoire Chrono-Environnement, UMR6249, CNRS – Universite´ de ´ 16 Route de Gray, 25030, Besanc¸on cedex, France Franche-Comte,

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7, 1511–1566, 2011

Hydrological variability in northern Levant F. Gasse et al.

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F. Gasse

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Correspondence to: F. Gasse ([email protected]) Published by Copernicus Publications on behalf of the European Geosciences Union.

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Received: 13 April 2011 – Accepted: 14 April 2011 – Published: 10 May 2011

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Invited contribution by F. Gasse, recipient of the EGU Hans Oeschger Medal 2010.

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Hydrological variability in northern Levant F. Gasse et al.

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The Levant features sharp climatic gradients from North to South and from West to East resulting in a large environmental diversity. The lack of long-term record from the northern Levant limits our understanding of the regional response to glacial-interglacial boundary conditions in this key area. The 250 ka paleoenvironmental reconstruction presented here is a first step to fill this geographical gap. The record comes from a 36 m lacustrine-palustrine sequence cored in the small ˆ intra-mountainous karstic basin of Yammouneh (northern Lebanon). The paper combines times series of sediment properties, paleovegetation, and carbonate oxygen isotopes, to yield a comprehensive view of paleohydrologic-paleoclimatic fluctuations in the basin over the two last glacial-interglacial cycles. Efficient moisture was higher than today during interglacial peaks around 240, 215–220, ∼130–120 ka and 11–9 ka (although under different Precipitation minus Evaporation balance). Moderate wetting events took place around 170, 150, 105–100, 85–75, 60–55 and 35 ka. The penultimate glacial period was generally wetter than the last glacial stage. Local aridity culminated from the LGM to 15 ka, possibly linked to water storage as ice in the surrounding highlands. An overall decrease in local water availability is observed from the profile base to top. Fluctuations in available water seem to be primarily governed by changes in local summer insolation controlled by the orbital eccentricity modulated by the precession cycle, and by changes in precipitation and temperature seasonality. Our record is roughly consistent with long-term climatic fluctuations in northeastern Mediterranean lands, except during the penultimate glacial phase. It shares some features with speleothem records of western Israel. Conversely, after 130 ka, it is clearly out of phase with hydrological changes in the Dead Sea basin. Potential causes of these spatial heterogeneities, e.g., changes in atmospheric circulation, regional topographic patterns, site-specific climatic and hydrological factors, are discussed.

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Hydrological variability in northern Levant F. Gasse et al.

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The Levant (Fig. 1), which extends from Southeast Turkey to northern Egypt and Arabia, is a key area to study climatic changes at the transition between the temperate Mediterranean domain and the subtropical belt of the Saharan-Arabian desert. Moisture in the region primarily comes from the eastern Mediterranean Sea (EMS). Rainfall decreases with latitude, and more sharply from W to E with distance from the seashore and because mountain ranges running parallel to the coastline intercept a large part of the precipitation coming from the West. Altitudes range from ∼425 m below sea level (b.s.l.) along the Dead Sea shore to more than 3000 m above sea level (a.s.l.) in Lebanon. This unique physiogeographic pattern results in a large diversity of environmental conditions which vary dramatically over short distances. Numerous geological and archeological data show that the Levant has experienced huge climatic fluctuations and a long history of human evolution during the Late Quaternary. Changes in water availability may have played a major role in the early modern humans migration out of Africa and in the Pleistocene-Holocene cultural dynamics of Eurasia (Bar-Yosef, 1998; Vaks et al., 2007; Shea, 2008; Carto et al., 2009; Waldmann et al., 2010; Frumkin et al., 2011). However, a North-South disparity in data coverage limits our understanding of the response of the whole Levantine region to global climatic changes and of the relationships between societal evolution and climates. In central and southern Levant (Israel mainly), intensive paleoenvironmental studies have provided well-dated, long-term, high resolution records. In the rain-shadow of the Judean mountains, lake level fluctuations and periods of speleothem growth/non deposition in the Dead Sea basin demonstrate generally high effective moisture attributed to enhanced rainfall during glacial phases, and dry conditions during Interglacials (see the recent reviews by Enzel et al., 2008; Waldmann et al., 2010; Frumkin et al., 2011). 18 Long-term δ O fluctuations in continental carbonates in the Levant are primarily driven by the glacial/interglacial variations in the isotopic composition of the moisture source (the EMS surface water) (Frumkin et al., 1999; Bar-Matthews et al., 2003; Kolodny et

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al., 2005). However, rainfall amount is probably the second order factor that modulates 18 δ O changes, and has likely increased in western Israel during Interglacials (BarMatthews et al., 2003; Almogi-Labin et al., 2009; Frumkin et al., 2011). In the southern Negev desert, only sporadic wet pulses have occurred and were possibly associated with intrusions of humidity from southern sources during interglacial periods (Vaks et al., 2010; Waldmann et al., 2010). In northern Levant (Lebanon, northern Syria and SE Turkey), no record spans the last climatic cycles. The few available records (≤21 ka) show a large early Holocene wetting followed by a desiccation trend after 7–6 ka (Yasuda et al., 2000; Verheyden et al., 2008; Hajar et al., 2008, 2010; Develle et al., 2010). Northward, long-term pollen, lake and speleothem records from northeastern Mediterranean regions to western Iran ´ (Lezine et al., 2010; Tzedakis et al., 1994, 2009; Djamali et al., 2008; Badertscher et al., 2011) reflect generally warm-wetter interglacial and cold-drier glacial environments related to temperature and ice sheet waxing/waning in higher latitudes of the Northern Hemisphere (NH), but hydrologically out of phase with the Dead Sea basin evolution. New data are needed to decipher whether climatic changes well recorded in the southern Levant have also affected the northern Levant, and understand how the whole region has responded to the North Atlantic-Mediterranean system and to southern influences. The present paper provides a long multiproxy paleoenvironmental record for the northern Levant. It derives from a lacustrine sediment sequence collected in the ˆ small karstic basin of Lebanon (Yammouneh, Fig. 1), and spans approximately the past 250 ka. The sequence has already been analyzed for chronological purposes and sedimentary processes (Develle, 2010; Develle et al., 2011), carbonate oxygen isotopes (only the past 21 ka; Develle et al., 2010), and paleovegetation (Van Campo et al., unpublished). Major results are briefly summarized below. In addition, we present 18 new δ O data spanning the last 250 ka. Our aim here is to combine time series from individual indicators to yield a comprehensive view of environmental fluctuations in the basin over the two last glacial-interglacial cycles. An attempt is made to disentangle

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the role of local versus regional and global climate factors by comparison with other environmental records from surrounding regions. We discuss the potential causes that might explain spatial similarities and disparities in the hydrological evolution of the Levant. 2 Modern setting

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Hydrological variability in northern Levant F. Gasse et al.

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The steep topography of the Levant is related to the active Levant Fault System (Le Pichon and Gaulier, 1988) that runs from the NW tip of the Red Sea to SE Turkey. East of narrow coastal plains, SSW-NNE mountain ranges create an orographic barrier, rising up to 3083 m a.s.l. in Mount Lebanon at only 20–25 km from the sea shore. Just eastward, a chain of deep tectonic basins stretches along the Levant Fault (from south to North, the Arava valley, the Dead Sea and Tiberias lake basins along the Jordan Valley, and the Ghab Valley in Syria; Fig. 1). Regional climate is primarily controlled by the Mediterranean cyclonic systems related to the North Atlantic system, but distance from the seashore and the complex orography strongly modulate the regional and local rainfall pattern. The Levant experiences a Mediterranean climate with wet cool winter and warm dry summer. Winter precipitation is generated by the cyclonic activity over the Sea (Sharon and Kutiel, 1986), when the Siberian anticyclone is reinforced over SW Asia and the Azores High extends over North Africa and Spain (Fig. 2a, b). The Mediterranean cyclogenesis is influenced by the surrounding regions and possibly by long distance teleconnections, e.g., the North Atlantic Oscillation (NAO) (Ziv et al., 2006, 2010; Dayan et al., 2008; Raible et al., 2010). Cyclones, either generated in the Mediterranean basin or penetrating from the North Atlantic, are steered by the mid-latidude westerlies and tend to propagate eastward along the northern coast of the Mediterranean until reaching the Levant region. When propagating over the relatively warm seawater, air

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2.1 Main physiogeographic features of the Levant region

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ˆ The Yammouneh basin (34.06◦ N–34.09◦ N, 36.0◦ E–36.03◦ E, 1360 m a.s.l.), 6 km long, 2 km wide, lies at approximately 37 km from the sea shore on the eastern flank of Mount Lebanon (Fig. 3). The basin is today entirely cultivated. It was occupied in its southern part by a seasonal lake from at least Roman times to the 1930’s when it was drained for irrigation of the Bakka plain. No paleo-shoreline was observed, 1516

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ˆ 2.2 The Yammouneh basin in Lebanon

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Hydrological variability in northern Levant F. Gasse et al.

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masses become saturated by moisture. In the EMS, polar intrusions create a deep upper-level trough accompanied by low-level cyclogenesis. The strength and position of cyclones formed or reactivated in the EMS (the Cyprus Lows, Fig. 2a) largely control the winter rainfall temporal and spatial variability in the Levant (Enzel et al., 2003; Ziv et al., 2006). In summer (Fig. 2c, d), when the Siberian anticyclone is attenuated and the Azores anticyclone and the mid-latitude westerly belt are shifted northward, the Levantine region is warm and dry. The summer low-pressure systems developed southward and eastward (the Red Sea Trough and the Persian Trough) are generally hot and dry (Kahana et al., 2002). Several mechanisms indirectly relate the Levant to subtropical and tropical climates. Very dry summer conditions over the eastern Mediterranean region and northeastern Sahara are partly due to the subsidence of easterly airflows linked to the Indian monsoon activity (Rodwell and Hopkins, 1996; Ziv et al., 2004). Most of the occasional rainfalls occurring in the Negev desert during spring and autumn are in conjunction with an active Red Sea Trough extending from East Africa through the Red Sea (Kahana et al., 2002). Heavy dust storms of North African origin are frequent from December to April. Saharan dust influx to the region has often been attributed to the thermal lows of the Sharav cyclones formed over Libya and Egypt (Alpert and Ziv, 1989) and the Red Sea through, but the cold Cyprus Lows also play a major role in attracting Saharan dust plumes (Dayan et al., 2008). The Nile River discharge, which depends on tropical rainfall in Ethiopian highlands and equatorial East Africa, affects the EMS hydrothermal dynamics (Rossignol-Strick and Paterne, 1999) and thus sea-land interactions.

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suggesting that the paleolake never reached high levels during a period long enough to leave geomorphic evidence. The basin is a SSW-NNE depression of tectonic origin ˆ along the Yammouneh Fault, a segment of the Levant Fault System. It was downfaulted through thick sub-tabular sequence of intensively karstified Cenomanian dolomitic limeˆ stones (Dubertret, 1975; Hakim, 1985). The strike-slip Yammouneh Fault is active −1 (slip rate: 3.8–6.4 mm yr ) but vertical movements likely remained negligible during ¨ the Late Quaternary (Daeron et al., 2004, 2005, 2007; Elias, personal communicaˆ tion, 2009). Westward, the Yammouneh basin is limited by the high Mna¨ıtra plateau that abruptly rises to 2100 m a.s.l. To the East, gently sloping hills (Jabal el-Qalaa, ˆ 1500 m a.s.l.) separates the Yammouneh basin and the large Bakka plain synclinal. ´ ´ In Lebanon (Service Meteorologique du Liban, 1977; Karam, 2002), mean Annual Precipitation (MAP) ranges from 700–1000 mm along the coast, >1400 mm in Mount Lebanon, to 400 mm in the Bakka plain and 2000

> 600 800–1000 > 900 − 1000 > 1000 > 1200

20 16–18 15–16 10–15 0–5

Pistacia, Myrtus. . . . Evergreen Quercus, Pinus Deciduous Quercus Cedrus, Abies Juniperus

900–1800 > 1800

600–800 > 800

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Evergreen Quercus Juniperus

Western flank of Mt Lebanon Lower Mediterranean belt Middle Mediterranean belt Upper Mediterranean belt Montane belt Subalpine belt Western flank of Mt Lebanon

Bekaa plain

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Steppe elements

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MAP (mm yr )

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Altitude (m a.s.l.)

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ˆ Table 1. Distribution of the modern vegetation belts in the Yammouneh area as a function of location, altitude, mean annual precipitation (MAP) and mean annual temperature (MAT). After Abi-Saleh and Safi (1988).

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Observations and Analyses

Variables included in PCA

Variable

Nb of analyzed samples

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Table 2. Performed analyses on the upper 36 m of core YAM04-C’. Variables included in the PCA are numbered in column 2.

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Sediment composition

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Whitish powdery, sandy carbonate Pale gray to pale brown marl Yellowish brown to reddish brown silt Olive gray silty clay Brownish gray silty clay Dark brown, peaty or paleosoil-like levels

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XRD mineralgy (% weight dry sediment)

Calcite (+ Aragonite: 0–3 %) Quartz K-Feldspaths + Plagioclases Dolomite Clay minerals

TOM (% weight dry sediment)

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Total magnetic susceptibility (10

160 160 160 160 160 160

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Hydrological variability in northern Levant F. Gasse et al.

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2 3 4 5 6 7

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Main lithofacies types

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Ca Si Al Fe Ti K

2109 2109 2109 2109 2109 2109

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Steppic-desertic landscape Middle Mediterranean zone Upper Mediterranean zone Montane belt Subalpine zone Aquatic + Hydrophilous (% total pollen)

Artemisia + Chenopodiaceae + Cichoroideae Pinus + evergreen Quercus Deciduous Quercus Cedrus + Abies Juniperus Myrioplyllus, Potamogeton, Typha, Cyperaceae, Ranunculus

225 225 225 225 225 225

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δc derived from ostracod δ 18 O values

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Microscopic observations Grain size analysis

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SI)

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Quartz

0.791 −0.756 −0.620

−0.970 −0.674

0.509

−0.551 −0.607 −0.484 −0.760 −0.754 −0.806 −0.836 −0.786

−0.807 −0.640 −0.411 −0.728 −0.794 −0.784 −0.812 −0.732

0.570 0.663 0.330 0.687 0.787 0.744 0.882 0.689

0.361 0.335 −0.495

0.361 0.428 −0.572

−0.338 −0.496 0.616

Kaolinite+ smectite+ chlorite

K-Fedspaths + Plagio.

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TOM

Al (rel. cont)

Si (rel. cont)

K (rel. cont)

Ti (rel. cont)

Fe (rel. cont)

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0.460 0.678 0.625 0.641 0.520 0.640 0.509 0.866

0.602 0.545 0.602 0.587 0.528

−0.410 −0.708

0.526 0.624 0.661 0.624 0.657 0.697

0.648

0.411 0.456 0.592 0.584 0.628

0.426 0.976 0.927 0.868

0.961 0.955 0.794

0.943 0.851

0.828

−0.342

−0.406

−0.407

−0.392

−0.316

0.387

0.553

0.470

0.578

0.408

−0.674

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Calcite (+ aragonite)

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Calcite (+ aragonite) (%) Quartz (%) Kaolinite+smectite +chlorite (%) K-Fedspaths + Plagio. (%) Magnetic Susceptibility (SI) TOM (%wt) Al (rel. cont) Si (rel. cont) K (rel. cont) Ti (rel. cont) Fe (rel. cont) Juniperus (%) Abies + Cedrus (%) Deciduous Quercus (%) Everg. Quercus + Pinus (%) Steppic (%) Aquatic + subaquatic (%) 18 δ O carbonate (PDB ‰) AP %

Ca (rel. cont)

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Table 3. Significant simple linear correlation coefficients (p < 0.001) between environmental ˆ variables from Yammouneh.

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ˆ Fig. 1. The Levantine region. Location of the Yammouneh basin and of sites cited in the text. For terrestrial records, 1: Jeita Cave; 2: Aammish marsh; 3: Peqiin Cave; 4: Ma’ale Efrayim Cave; 5: Soreq Cave; 6: Jerusalem West Cave; 7: Na‘chal Ami’az Cave.

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Red Sea

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28°N

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Hydrological variability in northern Levant F. Gasse et al.

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32°N

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Ghab basin

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Surface Precipitation Rate (mm/day))

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Sea Level Pressure (mb)

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Hydrological variability in northern Levant F. Gasse et al.

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Fig. 2. Sea level pressure and surface precipitation rate in the Mediterranean region in winter (January–February: a, b) and summer (June–August; c, d) averaged from 1968 to 1996. Source : NCEP /NCAR Reanalysis. NCAA/ESLP Physical Sciences Division (http: //www.cdc.noaa.gov/Composites/Day/). AH: Azores High; SH: Siberian High; CL: Cyprus Low; RST: Red Sea Trough; PT: Persian Trough.

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June to August

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Fig. 3. (a) Satellite view of Lebanon in winter (January 2003), main morphological structures. ˆ (b) The Yammouneh basin with location of the sedimentary profiles. The red dashed line is ˆ the surface trace of the Yammouneh Fault. Arrows schematize the groundwater circulation, from the Mna¨ıtra Plateau which provides the main water inflow to the basin via karstic springs emerging along the western edge of the basin, and infiltration along the eastern edge.

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Discussion Paper | Fig. 4. Major changes in lithofacies along the upper 36 m of core Yam 04 C’. (a) Simplified stratigraphic log. The position of gaps in core recovery and sediment disturbances are plotted on the left, that of chronological markers on the right. (b, g) Pictures of some core sections illustrating the facies diversity. (b) Transition from reddish, oxidized silt of Unit II to olive gray silty clay of Unit III; (c) Pale greenish marl; (d) Typical banded greenish marl; (e) Typical interglacial calcitic powdery deposits; (f) Brownish, coarsely banded silty clay; (g) Peaty marl of Unit X.

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s ed le tim vel a s IS ted ag e MIS 4 - 3 - 2

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Fig. 5. Paleovegetation. Relative frequencies of main pollen taxa or taxa groups vs. depth along the stratigraphical profile. (a) Aquatic and subaquatic plant pollen, expressed in percents of total pollen grains. (b) Tree and steppe pollen groups, expressed in percents of terrestrial taxa. (c) Total percentages of tree pollen (AP %). After Van Campo et al. (2011). (d) Chronological data according to the Develle et al. (2011) age model. Position of the chronological markers (as for Fig. 4), estimated ages of major vegetation changes (in italic, interpolated ages), and Marine oxygen Isotope Stages (MIS; after Martinson et al., 1987). Horizontal dashed lines indicate the major (red) and second order (grey) vegetation changes.

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MIS 7

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75

47±4

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500 III

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nu Ev s er gr e

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Fig. 6. The sedimentary record. Main sedimentological proxies vs. depth along the stratigraphical profile. After Develle et al. (2011). Horizontal dashed lines indicate the major (red) and second order (grey) sedimentation changes. Chronological data as for Fig. 5d.

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Calcite + Aragonite Dolomite Quartz K-Feldspath + Plagio Clay minerals.

K

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MIS 6

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MIS 7

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MIS 4 - 3 - 2

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Fig. 7. Carbonate Oxygen isotopes. (a) δc profile vs. depth (data points above the core top come from trench TR02 where the mid- and late Holocene is preserved). (b–d) Times series of marine data used to reconstruct δL and ∆δ 18 O versus time. (b) Paleo-temperature data. SSTalk records from cores M40-71 (1) and ODP 967 (2) (Emeis et al., 2003); for comparison, 18 temperature inferred from δ O and δD of fluid inclusions in Soreq Cave speleothems (3, Mc18 Garry et al., 2004). (c) δ O records of planktonic foraminifera (δforam ) from cores MD9501 (1: Almogi-Labin et al., 2009) and ODP 967 (2: Kroon et al., 1998; 3: Emeis et al., 2003). (d) Isotopic composition of sea surface water (δsw ) in the Levantine basin inferred from SSTs in core MD40-71 and δforam from cores MD9501 (1; 0−86 ka) and ODP 967 (2; 78−250 ka). (e) δc (red) and reconstructed δL versus time according to our age model. The blue δL curve is ˆ based on the modern mean annual temperature difference between sea level and Yammouneh, ˆ the green one account for an additional cooling of 2.5 ◦ C at Yammouneh during glacial periods. Vertical dashed lines indicate modern and inferred glacial δP values. (f) Difference between δL 18 and δsw : ∆δ O = δsw− − δL . Colors as for (e). Vertical dashed lines indicate δsw − δP values inferred for modern and glacial times. See text for explanation.

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CPD 7, 1511–1566, 2011

Hydrological variability in northern Levant F. Gasse et al.

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Fig. 8. Principal Component Analysis performed on 21 environmental variables (Table 2) in 157 core levels from core YAM04 C’. (a) Scores of the 2 first components (PC1 and PC2) vs. depth. (b and c) : Projections of environmental variables in the factorial plans F1–F2 and F1–F3, respectively.

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Hydrological variability in northern Levant F. Gasse et al.

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CPD 7, 1511–1566, 2011

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Hydrological variability in northern Levant F. Gasse et al.

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14C ages 260 U/Th age Geomagnetic events

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Fig. 9. Correction of our initial age model assuming that all tree pollen peaks are linked to high ˆ summer insolation at the Yammouneh latitude. Age control points used in the initial age model are plotted on the left. (a) Arboreal pollen percentages (AP %) relative to total terrestrial pollen vs. time according to our initial age model.(b) Summer solar radiation at 34◦ N (Berger, 1978); (c) AP% vs. ages corrected by tuning with summer insolation; (d) Age differences between our initial age model and corrected chronology.

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CPD 7, 1511–1566, 2011

Hydrological variability in northern Levant F. Gasse et al.

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ˆ Fig. 10. Major proxies from Yammouneh versus time (a, f), and potential forcing factors (g, i). Proxy variations according to our initial age model are superimposed in pale gray to those based on corrected ages. (a) Ca relative content and (b) magnetic susceptibility. For clarity, these two variables are plotted as the first component factor of a Singular Spectrum Analysis (performed using the Paillard et al., 1996, software) and representing 84 and 92.3 % of the total variance, respectively. (c) Arboreal pollen percentages relative to total terrestrial pollen (AP %). (d) Tree pollen ratio: cool wet forest/(temperate + Mediterranean forest) elements. (e) δc . (f) ∆δ 18 O (=δsw –dL ; plein curve based on δsw inferred from core MD9501, dashed curve from core ODP 967). (g) Timing of EMS sapropel events (Ziegler et al., 2010). (h) Orbital eccentricity and summer/winter insolation at 34◦ N (Berger, 1978). (i) MIS (Martinson et al., 1987).

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Hydrological variability in northern Levant F. Gasse et al.

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Fig. 11. Some terrestrial regional records from Eastern Mediterranean regions. (a) Lake Ohrid, ´ Albania (Lezine et al., 2010); AP % and calcite in % of the mineral assemblage. (b) AP % ˆ at Tenaghi Philippon, Macedonia (Tzedakis et al., 1994, 2009). (c) AP % at Yammouneh. 18 (d) δ O record from Soreq and Peqiin Caves speleothems, western Israel (Bar-Matthews et al., 2003), and timing of EMS sapropel events (Ziegler et al., 2010). (e) Lake level fluctuations of the Dead Sea and its predecessors (Waldmann et al., 2010). (f) Relative frequency of ages of speleothem deposition in the Dead Sea basin (Lisker et al., 2010): (g) Relative frequency of ages of speleothem deposition in the Negev (Vaks et al., 2010; age frequency is the fraction of speleothems deposited at a certain time with 95 % confidence) and periods of travertine deposition in the Arava valley (Waldmann et al., 2010). (g) Simulated North African runoff (Ziegler et al., 2010). Results from the CLIMBER-2 model using orbital forcing only (black curve), orbital forcing + varying NH ice sheets and greenhouse gas concentrations (red curve); (i) MIS (Martinson et al., 1987).

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