Progress in Oceanography 44 (1999) 369–386

Palaeo-environmental variations in easternMediterranean sediments: a multidisciplinary

approach in a prehistoric setting

Gert J. De Langea,*, P.J.M. Van Santvoorta, C. Langereisa, J.Thomsonb, C. Corsellic, A. Michard d, M. Rossignol-Stricke,

M. Paternef, G. Anastasakisg

a Department of Geochemistry, Institute Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CDUtrecht, The Netherlands

b Southampton Oceanography Centre, Southampton, UKc Department Scienze della Terra, University of Milan, Italyd GJosciences de l’Environnement, Aix-en-Provence, France

e University P. & M. Curie, Paris VI, Francef CNRS, Gif-sur-Yvette, France

g National and Capodistrian University of Athens, Greece

Abstract

Not only the occurrence of distinct organic-rich intervals (sapropels), but also the relativecontents of key major and minor elements and isotopes in the sediments of the eastern Mediter-ranean, appear to be cyclic and to be astronomically associated. Interpretations of the environ-mental conditions leading to sapropel formation are based on results from sedimentological,micropalaeontological and geochemical studies of the dark-coloured layers and thecream/brownish sediments that occur above and below them. Part of the signal may beremoved by early diagenetic processes. The extent and direction of these processes are ulti-mately controled by the amount and reactivity of organic matter.

The interval of dark colour associated with a sapropel is often somewhat thicker than thatdefined by the.2% Corg definition and usually has a sharp colour change at upper and lowerboundaries. A grey so-called ‘proto-sapropel’ layer of variable thickness underlies most sapro-pel layers. A few centimeters above the most recent sapropel S1, is usually found a clear dark-brown layer 2–3 cm thickness is usually found, which has a diffuse, often mottled, upperboundary and a relatively abrupt colour transition at its lower boundary. The colour is charac-

* Corresponding author. Tel.:+30-535034.E-mail address:gdelange@geo.uu.nl (G.J. De Lange)

0079-6611/99/$ - see front matter 1999 Elsevier Science Ltd. All rights reserved.PII: S0079 -6611(99 )00037-3

370 G.J. De Lange et al. / Progress in Oceanography 44 (1999) 369–386

teristic of Mn oxyhydroxide enrichments. In the interval from the dark-brown layer to thevisible upper S1 boundary, there is usually an increasingly red-brownish colour.

The distinct upper manganese Marker-Bed has been related to the Santorini (Minoan) erup-tion in 3356±18 BP (Bruins, H. J., & Van Der Plicht, J. (1996). The Exodus enigma.Nature,London, 382, 213–214), but is more likely to be associated with a Basin-wide re-ventilationevent induced by changing climatic (humidity) conditions.

Using barite-Ba as a paleo-productivity indicator, enhanced fluxes, and hence increases inaccumulation rates of organic carbon to the seafloor, must have occurred from approximately9 to 5 ky BP. The perfect correlations between observed Corg and calculated Corg from theCorg/Ba relation in the visible S1 interval, and the total lack of such correlation in the intervalbetween the darkbrown layer and the visible S1 layer are remarkable. It seems, therefore, thatS1 deposition lasted from 9 to 5 ky BP but the organic carbon for the upper part has beenremoved. The double barium peak visible in a number of sediments studied in high-resolution,may be related to the ‘Flooding’ of the Black Sea that occurred around 7150 BP (Ryan, W.B. F., Pittman, W. C., Major, C. O., Shimkus, K., Moskalenko, V., Jones, G. A., Dimitrov,P., Gorur, N., Sakinc, M., & Yuce, H. (1997). An abrupt drowning of the Black Sea shelf.Marine Geology, 138, 119–126).

Using various ‘proxies’, the (initial) occurrence of eastern Mediterranean sapropels appearscyclic and to be strongly related to the Monsoonal/Insolation Index. However, the relativevalue of an insolation maximum and initial Corg content of the corresponding sapropel are notalways related in a simple way. This again points to additional (possibly hydrographic) factorsdetermining (the intensity of) sapropel formation.

Understanding the mechanisms of sapropel formation and their subsequent preservation isnot only necessary if our reconstructions of palaeoenvironmental conditions in the EasternMediterranean are to be improved, but may also assist in understanding the present-day situ-ation and in forecasting possible future developments.

The observed paleoenvironmental variations are discussed in a geochemical and environ-mental context, and are illustrated using typical examples from the eastern Mediteranean.1999 Elsevier Science Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371

2. Material and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

3. Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3743.1. Manganese marker bed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3763.1.1. Steady-state diagenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3763.1.2. Major hydrothermal eruption . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3763.1.3. Major re-ventilation event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378

3.2. Double barium peak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379

4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383

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References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383

1. Introduction

In the deep marine environment, the organic carbon content (Corg) preserved in asediment is primarily a balance between the initial input flux of organic matter andits subsequent oxidation by bottom water oxygen. Most marine sediments have Corg

contents in the range 0.2–2%. The Eastern Mediterranean sedimentary record, there-fore, comprises an intercalation of unusually Corg-rich sediments (the sapropels)within Corg-poor sediments, caused by repeated fluctuations through time in either(or both) the Corg flux from surface ocean export production or in dissolved bottomwater O2 concentrations.

This intercalation is reflected by alternating layers of (light) brown hemipelagicorganic-poor and dark olive-green organic-rich sediments. The occurrence of saprop-els appears to have been associated with climatic changes. Cycles in the obliquityof the Earth’s axis and the precession of the equinoxes are the underlying controlingvariables that influence the global climate through their effects on planetary inso-lation (Berger & Loutre, 1992). The timing of sapropel formation coincides with thetimes of maximum summer insolation, and seems to be related to the (African-Indian)Monsoon intensity (e.g. Rossignol-Strick, 1983; Hilgen, 1991; Lourens, Hilgen,Zachariasse, Van Hoof, Antonarakou, & Vergnaud-Grazzini, 1996; Langereis,Dekkers, De Lange, Paterne, & Van Santvoort, 1997; Rossignol-Strick, Paterne, Bas-sinot, Emeis, & De Lange, 1998).

Sapropels have not been formed during every maximum in the insolation curve.This lack of formation may have resulted from variations in climatic conditionsduring the maxima such that sapropels did not always form. Alternatively, sapropelsinitially deposited may subsequently have disappeared as a result of ongoing oxi-dation reactions (e.g. De Lange, Middelburg, & Pruysers, 1989; Pruysers, DeLange, & Middelburg, 1991; Pruysers, De Lange, Middelburg, & Hydes, 1993;Thomson, Higgs, Wilson, Croudace, De Lange, & Van Santvoort, 1995; VanSantvoort et al., 1996).

Enhanced levels of barite-barium, a proxy which is thought to be related to primaryproductivity in the surface waters of the ocean (e.g. Dymond, Suess, & Lyle, 1992;Francois, Honjo, Manganini, & Ravizza, 1995) are usually found at the mostemphatic maxima in the insolation curve (e.g. Van Santvoort, De Lange, Langereis,Dekkers, & Paterne, 1997). However, the origin of the ‘bio-barite’ proxy is not yetfully understood, and seems to reflect an association between photic zone primaryproductivity and the quantities of barium in settling organic debris.

Highly reducing conditions may lead to the incomplete preservation of barite-Bain the reduced sedimentary interval (e.g. Church, 1979; Brumsack, 1986; Van Os,Middelburg, & De Lange, 1991; Torres, Brumsack, Bohrmann, & Emeis, 1996).Because of the rapid alternation of distinct reduced sediment intervals with (sub)oxicintervals for some sapropels, the barite-barium has been redistributed over rathershort distances, whereas for others it appears to have remained in place. As a conse-

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quence, the enhanced productivity ‘event’ can still be detected, or in the case ofimmobility can be used to detect the initial limits of the interval of enhanced pro-ductivity even when the Corg signal has been totally or partially removed. (e.g. VanSantvoort et al., 1996, 1997).

The origin and mode of sapropel formation has been disputed ever since their firstrecovery in bottom sediments from the eastern Mediterranean (e.g. Kullenberg, 1952;Olausson, 1961; Cita, Vergnaud-Grazzini, Robert, Chamley, Ciaranfi, & D’Onofrio,1977; Rossignol-Strick, Nesteroff, Olive, & Vergnaud-Grazzini, 1982; Rossignol-Strick, 1983; Calvert, 1983; Anastasakis & Stanley, 1986; Howell, Thunnell, Tappa,Rio, & Sprovieri, 1988; Rohling & Gieskes, 1989; Troelstra, Ganssen, Van DerBorg, & De Jong, 1991; Fontugne & Calvert, 1992; Calvert, Nielsen, & Fontugne,1992; Van Os, Lourens, Hilgen, & De Lange, 1994; Thomson, Higgs, Wilson, Croud-ace, De Lange, & Van Santvoort, 1995; Van Santvoort et al., 1996; Strohle &Krom, 1997).

Two processes enhanced primary productivity leading to enhanced organic matterfluxes to the seafloor, and stagnation leading to enhanced preservation of organicmatter fluxes at the seafloor, have most frequently been cited as resulting in theirformation acting either separately or in combination. Using barite-barium as a pro-ductivity proxy, it is beyond doubt that productivity has been enhanced during per-iods of sapropel formation, although the exact magnitude of the increase can yet notbe determined with certainty, because of the lack of calibrating parameters for suchalternate environmental conditions as those occuring in sapropel periods in the east-ern Mediterranean (Dymond et al., 1992; Francois et al., 1995; Dymond & Collier,1996). There are some convincing indications that anoxic bottom water, and possiblyeven (lower) photic zone anoxic conditions coincided with deposition of at least someof the sapropel intervals (Passier, Bosch, Nijenhuis, Lourens, Boettcher, Leenders etal., 1998).

Paleoclimatic humidity variations and the related fluctuations in the density andtemperature of outflowing Mediterranean deep water has lead to speculations as tothe possible effect of these variations on the Global Conveyer Belt, in particular onthe Gulfstream in the North Atlantic (Reid, 1979). Similarly dramatic changes intemperature and salinity (density) of deep Mediterranean waters seem to be forcedat present, largely by anthropogenic influences, such as the great reductions ininflows of water from rivers reaching the Mediterranean as a result of the AswanHigh Dam in the Nile, and the enhanced use of water for irrigation. This has leadto a renewed speculation on the possible imminent consequences for the global, butin particular the European, climate. Johnson (1997), for example, has suggested thebuilding of a dam to control the in- and outflow of water through the Straits ofGibraltar so as to prevent a shift in the climates of Canada and Europe in the nearfuture. If such a dam were to be constructed, it might perhaps conserve global cli-mate, but it would have dramatic environmental consequences for what would thenbe a poorly flushed Mediterranean. Clearly, it is of vital importance to know and tounderstand the paleoceanography in connection to paleo-environmental conditionsof the (eastern) Mediterranean. In the present paper some aspects will be discussedin relation to observations on eastern Mediterranean sediments deposited during the

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last 10 000 years, which may be linked to some prehistoric events. Understandingthe mechanisms of sapropel formation and their preservation is not only a basicnecessity for improved reconstructions of palaeoenvironmental conditions in theEastern Mediterranean, but may also assist in understanding the present-day situationand possible future developments (e.g. Bethoux, Gentili, Raunet, & Tailleze, 1990;Bethoux & Gentili, 1996; Roether et al., 1996).

2. Material and methods

Core material discussed here was collected during cruises of: R/VMarion Duf-resne in 1991 (MARFLUX-1) and R/VUrania in 1994 (PALAEOFLUX-3). Thesample locations are shown in Fig. 1.

Oxygen concentrations and redox potentials were measured onboard as soon aspossible after core recovery. Pore waters were obtained by squeezing. The shipboardroutine has been described in detail elsewhere (De Lange, 1992). Box cores wereextruded at 1 cm resolution and squeezed in a glovebox with a high-quality nitrogen

Fig. 1. Eastern Mediteranean sample locations discussed in the text: boxcore UM26, and Long Pis-toncore KC01B.

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atmosphere. Sampling and pore water extraction took place at in situ temperatures(13°C).

Profiling of dissolved oxygen in sediments was carried out using a new robustoxygen electrode (Cussen, Braithwaite, & Wilson, 1994). The stiffness of the sedi-ment and the relative size of the core tubes to the oxygen probe presented problemswhen forcing the probe to depths.15 cm. Hence the profiles were measured in twoor three 15 cm sections, each time removing the upper 10 cm of the sediment thathad already profiled.

The redox potential was measured on split subcores as soon as possible aftercollection by a punch-in Ingoldt Eh electrode with a separate reference electrode. AZobell standard solution (Eh=215 mV at 13°C) was used for calibration.

Sediment samples were freeze dried and finely ground in an agate mortar, thendigested in a mixture of hydrofluoric, nitric and perchloric acids. The final solutionswere analysed by ICP-AES, 1 N HCl on a Perkin Elmer Optima 3000. The qualityof the analyses was monitored by the inclusion of laboratory and international stan-dards. The error in the analyses was,4% for all elements. Organic carbon (Corg) wasdetermined on a Fisons Instruments NCS NA 1500 analyzer using dry combustion at1800°C. Inorganic carbon, as carbonate, was removed before analysis by shakingthe sample for 24 hours in 1 N HCl. This procedure was repeated to ensure that allinorganic carbon had been removed. After drying at 80°C, the sample was groundin an agate mortar. International and in-house standards were used to check theaccuracy of the method. Standard deviations were always,2%.

3. Results and discussion

The usual sequence of colours in alternating intervals of sediments deposited dur-ing the last 10 000 years in the eastern Mediterranean as found in a ‘typical’ coreis as follows:

For sediments from waterdepths shallower than 3 km, the top few mm of sedimentconsists of a pteropod ooze, which overlies a 1–2 cm layer that is slightly morebrownish than the layer of ca. 10 cm below it. About 12–13 cm below the surfaceinterface, a marked dark-brown bed of 3–4 cm thickness is usually found. It has adiffuse, often mottled upper boundary and a relatively abrupt colour transition at itslower boundary (Fig. 2). This dark brown colour is typical of enrichment with Mnoxyhydroxide; this characteristic bed is usually referred to as the (manganese) MarkerBed (e.g. De Capitani & Cita, 1996). At 20–25 cm depth a dark olive-green intervaloccurs which has a sharp colour change at its upper and lower boundary. This isusually referred to as the most recent sapropel S1, but in fact represents only theresidual lower part of what was initially a much thicker sapropel S1 deposit (seeIntroduction and discussion below; e.g. De Lange et al., 1989; Higgs, Thomson,Wilson, & Croudace, 1994; Thomson et al., 1995; Van Santvoort et al., 1996; Thom-son et al., 1999). Between the lower manganese Marker Bed boundary and the upperdark olive-green boundary, there is subtle change in colour from (light) brown to adarker reddish-brown. The S1 sapropel overlies a dark grey interval which is usually

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Fig. 2. Colours for sediments deposited in the last 10 000 years in a core typical for the eastern Mediter-ranean (site UM26). For the same period some reference has been included to (pre)historic events, someof which may be related to features observed in the sediments (see text).

referred to ‘proto-sapropel’, but which is thought to have formed during or slightlyafter sapropel formation (Passier, Middelburg, Van Os, & De Lange, 1996). Belowthe ‘proto-sapropel’ the colour usually changes to light-grey and subsequently tolight-brownish again.

The boundaries of the initial sapropel interval can be detected accurately usingthe barite-barium solid-phase profile (Fig. 3). If sampled in high-resolution, this bar-

Fig. 3. Oxygen, solid-phase Manganese, Org.C, Barium, and redox potential for boxcore UM26. Thegrey interval is the presently visible organic-rich S1 sapropel interval; dashed line indicates level ofmanganese-rich Marker Bed and the inferred initial ending of the S1 interval (figure after Van Santvoortet al., 1997). For colours, see Fig. 2.

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ium depth profile usually shows a double-peak. Accumulation of the organic richsapropel is thought to have occurred during the relatively wet climatic interval from9 to 5 kyrs BP. The ending of sapropel accumulation appears to have coincided withthe formation of the manganese Marker Bed. Subsequent oxidation by oxygen diffus-ing down from the sediment interface has resulted in the partial or even completeremoval of the initial sapropel organic matter and its pyrite contents (e.g. De Langeet al., 1989; Higgs et al., 1994; Thomson et al., 1995; Van Santvoort et al., 1996).It has also resulted in the slight increase in reddish (Fe-oxyhydroxides) and brownish(Mn-oxyhydroxides) colours going from the lower boundary of the Marker Bed tothe upper boundary of the dark olive-green interval.

In the next sections the possible origins of the manganese Marker Bed and of thedouble nature of the barite peak will be discussed.

3.1. Manganese marker bed

The distinct dark-brown interval, commonly refered to as (manganese Marker Bed)appears to occur in sediments throughout the eastern Mediterranean.14C-dated orextrapolated datings of this interval all come out around 5 kyr BP (e.g. Van Santvoortet al., 1996; De Lange et al., personal communication). This clear layer, therefore,indicates an important basin-wide process during which large amounts of Mn-oxyhy-droxides have been deposited on the seafloor. Only three general geochemical pro-cesses can account for such deposition: 1) steady-state diagenesis; 2) a major hydro-thermal eruption; and 3) a major re-ventilation event.

3.1.1. Steady-state diagenesisDuring steady-state diagenesis in hemipelagic suboxic sediments a distinct peak

of Mn-oxyhydroxides may develop at the boundary of upward diffusing dissolvedMn and of downward diffusing dissolved oxygen (e.g. Froelich et al., 1979; Bur-dige & Gieskes, 1983). In the 3 cores studied thus far at high resolution, the oxidationfront, i.e. the boundary where upward moving dissolved Mn and downward movingdissolved oxygen meet, appears to be located at the upper boundary of the darkolive-green interval (see Van Santvoort et al., 1996). Consequently, the oxidationfront occurs well (ca. 7 cm) below the upper manganese Marker Bed. Therefore, theMarker Bed in the cores is unlikely to be associated with the diagenetic steady stateformation of a Mn-peak at an oxidation-front moving upward in pace with the sedi-mentation rate.

3.1.2. Major hydrothermal eruptionHydrothermal vents are known to produce enormous amounts of dissolved manga-

nese which subsequently oxidize and become distributed over large areas of the ocean(e.g. Klinkhammer, Bender, & Weiss, 1977). Hydrothermal Mn-rich layers or crustshave been described for localities associated with mid-ocean ridges and island arcs(e.g. Hoffert et al., 1978) and in the Eastern Mediterranean (Varnavas, Papapioan-nou, & Catani, 1988; Cita et al., 1989). One of the major catastrophic eruptive eventsthat occurred in the Mediterranean region during the last 5000 years is the Santorini

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‘Minoan’ eruption. This eruption has been held responsible for a major tsunami wavewhich affected the whole of the eastern Mediterranean, and resulted in the depositionof a ‘homogenite’ in the deeper parts of the basin (Cita et al., 1984). The Minoaneruption was likely not only to have caused a tsunami, but also probably generatedan enormous dust cloud that probably extended over the entire eastern Mediterraneanand beyond. It has been suggested (e.g. Vitaliano, 1973; Stanley & Sheng, 1986)that this eruption coincided with the Exodus of the Israelites from Egypt: ‘plagueof darkness’ (EXODUS 10:21), and ‘the retreat and reflooding of the water whilecrossing the sea’ (EXODUS 14: 21–31). The Exodus was followed by 40 years ofroaming through the desert (NUMERI 14:33–34), and the destruction of Jericho(JOSHUA 6: 1–25). The time difference between the averaged14C datings of theSantorini eruption (3356±18 yr BP) and the destruction of Jericho (3311±13 yr BP)is surprisingly close to that 40 years period (Bruins & Van Der Plicht, 1996, andrefs therein).

In view of present-day and inferred past watermasses circulation patterns, a mass-ive emission of dissolved manganese and subsequent Mn-oxyhydroxides related tosuch Minoan eruption, would have spread rapidly throughout the eastern Mediter-ranean. However, there seems to be one problem in linking the formation of themanganese Marker Bed with the Minoan Eruption, namely the timing of the event(s).If one corrects the age found for the Marker Bed for ‘reservoir age’, and if oneassumes that a 3356 BP Mn-event of 15% Mn in a 4 mm thick layer (correspondingto the highest Mn content observed for a ‘marker bed’, found near Crete by DeCapitani & Cita, 1996) was followed by bioturbation of the 3–5 surficial cm of thesediment, then one finds that: 1) the Mn profile versus depth is similar to thoseobserved (e.g. Fig. 4); and 2) the modelled age is similar to the corrected Marker Bedage. Consequently, it is hypothetically possible that the Santorini Minoan eruption islinked to the manganese Marker Bed in eastern Mediterranean sediments. Nonethe-less this option seems less likely, because: 1) up to now all Marker Beds except theone found immediately south of Crete (which has not been dated) demonstrate arather uniform thickness and Mn content (1–1.2%); and 2) several of the older sapro-pels also seem to have been followed by a deposition of Mn-rich interval (markerbed), and for most others similar such initial Mn-rich layer can be suspected (e.g.Van Hoof, Van Os, Rademakers, Langereis, & De Lange, 1993; De Lange et al.,1994; Van Santvoort et al., 1997; Van Santvoort et al., personal communication).Since formation of sapropels has been reported to be closely associated with astro-nomical parameters, it seems unlikely that the Mn-rich intervals that formed sub-sequent to a sapropel, would in general be associated with hydrothermalism. Inaddition, the preserved double-Ba peak (see below) and the Gaussian shaped bariumcurve for the S1 sapropel all indicate that sediment mixing as a result of bioturbationhas been relatively minor.

Consequently, despite being a feasible explanation for the observations of eventsassociated with the formation of the last sapropel S1, and also attractive from aprehistorical perspective, the hydrothermal option is unlikely to provide an adequateexplanation for the occurrence of the upper manganese Marker Bed in most easternMediterranean sediments.

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Fig. 4. Scenario of the hypothesized instantaneous (hydrothermal) deposition of the manganese MarkerBed and its subsequent downward mixing.

3.1.3. Major re-ventilation eventOn the basis of enhanced barite-barium content, enhanced primary productivity

has been reported for the 9 to 5 kyr BP period (e.g. Thomson et al., 1995; VanSantvoort et al., 1996). In addition, there are a number of strong indications thatbottom waters must have been anoxic during formation of sapropel S1, namely: 1)the absence of benthic organisms; 2) enhanced pyrite content with a relative lightδ34S (-40%o) indicating ‘open’ conditions during sulphate reduction, i.e. upper cmsor even bottom water are anoxic; and 3) the presence in some sapropels of isoreniera-tane or its derivatives, which are related to photic zone green algae exclusively livingin an anoxic environment, such as occurs in the present-day Black Sea at 80 mwaterdepth (e.g. Passier et al., 1998, and refs therein). It seems, therefore, well estab-lished that not only the sediments but possibly also the bottom water were anoxicduring deposition of most sapropels.

In the more extreme case, large part of the water column may have been suboxic,with enhanced levels of dissolved Mn2+, which upon a re-ventilation/re-oxidation

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event would suddenly precipitate. This mechanism has been proposed to explain theMn (and Th/Pa) spike observed at the glacial/interglacial transition in some Pacificsediments (Mangini, Eisenhauer, & Walter, 1991; Mangini, Rutsch, Frank, Eisen-hauer, & Eckhardt, 1994). A similar reventilation event, not necessarily invoking asuboxic watercolumn, could explain the basin-wide simultaneous deposition of a Mn-rich layer. The subsequent gradual downward oxidation of the previously anoxicorganic-rich sapropel sediments is in line with this scenario.

In addition, the enhanced freshwater flux into the eastern Mediterranean duringthe ‘wet period’ (e.g. Rossignol-Strick et al., 1982; Rossignol-Strick, 1983, 1997)from 9–5 kyr BP must have resulted not only in enhanced nutrient supplies but mustalso have increased water column stability, i.e. developed stagnant conditions. Thedistinct decrease in such freshwater inputs at the end of the wet period, perhapsaccompanied by different climatic conditions such as wind directions, may havedestabilized the water column. At present the different climatic, and consequentlyhydrographic, conditions result in low productivity, but have not led to the develop-ment of a stagnant and stable water column.

Such variations in climatic conditions have occurred as a result of the cyclic pre-cession-dominated climatic pattern in the Eastern Mediterranean (Fig. 6; e.g. Hilgen,1991; Hilgen, Lourens, Berger, & Loutre, 1993; Lourens et al., 1996; Langereis etal., 1997). At the end of most sapropel periods, there is proof for the (initial) presenceof a Mn-rich layer (e.g. Van Hoof et al., 1993; De Lange et al., 1994; Van Santvoortet al., 1997). Peaks of enhanced Ba (primary productivity), coincide with peaks oflow ARM intensities (relatively low amounts of certain Fe-oxides, i.e. possiblyreduced redox conditions), and peaks of relatively negativeδ18O (enhancedfreshwater). It appears, therefore, that sapropel formation only occurs during rela-tively ‘wet’ periods when ‘low-oxygen’ conditions prevailed, whereas during the‘dry’ periods formation of a sapropel has never occurred.

In summary, of the three potential processes that could lead to the formation ofa basin-wide Mn-rich sediment interval, a major reventilation with concomitantchange in redox conditions is the one that best fits most observations.

3.2. Double barium peak

Barium has been reported to be a useful proxy for surface water primary pro-ductivity (e.g. Dymond et al., 1992; Von Breyman, Emeis, & Suess, 1992; De Langeet al., 1994; Francois et al., 1995). Although barite-Ba may be removed during highlyanoxic conditions, the Ba in the sediments studied appears to have remained in-place. Using barite-barium as a productivity proxy it is no doubt that productivityhad been enhanced during periods of sapropel formation. Enhanced levels of Ba areusually found at the most emphatic maxima in the insolation curve (e.g. VanSantvoort et al., 1997), corresponding to periods of enhanced surface water pro-ductivity, and enhanced river discharge and consequently nutrient input. However,the lack of calibrating parameters for the dramatically changing environmental con-ditions during and in between sapropel formation in the eastern Mediterranean, meansthat it is not possible to quantify exactly the prevailing primary productivity

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(Dymond et al., 1992; Francois et al., 1995; Dymond & Collier, 1996). Usuallyenhanced freshwater and nutrient outputs from the Nile, associated with variationsin the Monsoonal index have been reported to have resulted in increases in organicmatter accumulation during the sapropel S1 period (e.g. Rossignol-Strick et al., 1982;Rossignol-Strick, 1983). Recently, in a few high-resolution sediment studies and insome studies in sediments with high-accumulation rates (10–20 cm/kyr) a doublepeak feature in the sedimentary Ba profile and the organic-matter content has beenobserved (Rohling, Jorissen, & De Stigter, 1997; J. Thomson, personal communi-cation; this study).

The calibrated age for the mid-S1 low organic carbon interval in the Adriatic Seais 7470 BP with an estimated.300 yr deviation because of interpolations theseauthors had to use (Rohling et al., 1997).

The saddle between the maxima in the cores of this study (2 subcores from thesame boxcore at site ABC26; and core UM26) is dated at 7000±300; the high erroris mainly caused by interpolation and comparison between14C dated intervals andassumed timing of ‘events’ like age of ‘Marker Bed’ (see above), age of beginningand ending of initial S1 formation (Van Santvoort et al., 1996; De Lange et al.,personal communication.)

These ages are relatively close to the flooding of the Black Sea which is hypothes-ized to have occurred approximately 7150 BP±100 (Ryan et al., 1997). Floodingof the Black Sea is thought to have occurred as a result of the continuous rise insea level at the end of the last Glacial and resulted in the overflow and subsequenterosion of the sill at the Bosporus. The latter authors demonstrated that previouslythe Black Sea was fresh water and nearly 130 m lower than at present and wascatastrophically flooded in a relatively brief time period. They report possible inflowsof 50 km3 of water per day, filling the lake initially at a rate of 10s of cm per day.Any population living on the fertile plains surrounding this freshwater lake, musthave suffered catastrophic flooding possibly as described in the Gilgamesh epic andthe Noah Flood story (GENESIS 7: 11–24). As a consequence, around 7150 BPfarming spread rapidly inland into southeastern Europe (e.g. Hodder, 1990), and lightplough and irrigation techniques appear suddenly in the Transcaucasus (Glumac &Anthony, 1991; ref. in: Ryan et al., 1997).

The flooding of the Black-Sea freshwater lake will have resulted in a major outflowof freshwater enriched in nutrients; consequently, it will have ‘boosted’ the primaryproductivity that had probably been decreasing as a result of the declining waterflowfrom the Nile. This may have generated the double primary peak in productivityrecorded in the sediment as the double Ba peak (Figs. 3 and 5).

Taking an estimate of the time period (500–1500 yrs) that the influence of theBlack Sea freshwater outflow may have persisted in the eastern Mediterranean, it ispossible to compare this flux to that of the hypothesized (10× Present) Nile inputduring sapropel times. Various estimates have been reported for the contemporaryinput of freshwater from the Nile (e.g. from 900 to 2600 m3/s; Frost, O’Nions, &Goldstein, 1986; Emelyanov & Shimkus, 1986). We adopt here the higher value of2600 m3/s, which will, if the input was tenfold greater, flux during sapropel timesand which indicates the flux was 800 km3/yr. The volume of freshwater in the Black

381G.J. De Lange et al. / Progress in Oceanography 44 (1999) 369–386

Fig. 5. Double Barium peak feature and inferred relative impacts on eastern Mediterranean primaryproductivity by ‘Nile’ and ‘Black Sea Flooding’ periods. Barium results from two different boxcorestaken from the UM26 site during two different cruises, 7 years apart. (*) : Ba/Al ratio multiplied withaverage Al content of core; (**): Ba* corrected for non-bio-barite. Lightly shaded area assumed to bethe result from Nile- induced primary productivity, whereas the black area is assumed to be the resultfrom the Black Sea Flooding.

Sea during the ‘preflood’ era is estimated as follows: total present-day volume is537.103 km3 (Emelyanov & Shimkus, 1986), during the Flooding the water levelrose approx. 100 m (Ryan et al., 1997). Correcting for the shelf areas which areshallower than 100 m and for the difference in water-level, results in an estimatedpre-Flood volume of freshwater in the Black Sea to be ca. 500.103 km3. This wouldresult in an estimated freshwater input into the eastern Mediterranean of 1000–333km3/yr throughout the period of 500–1500 years we have assumed the input tohave persisted.

If this hypothesis of subsequent freshwater inputs from Nile and Black Sea iscorrect, then the shape and width of the Ba curve (Figs. 3 and 5) indicates that theeffect of such Black Sea flooding is likely to have influenced the eastern Mediter-ranean rather during a period of 1500 than of 500 years. Similar to the increase inNile input, the pulse of freshwater input from the Black Sea will have resulted inlarge increases in nutrients supply, and concomitantly enhanced primary productivityand hence the rate of barium-accumulation in the sediments (Fig. 6).

Clearly, future research on sediments from the Aegean Sea should be targeted atclarifying the relative importance of the Black Sea Flooding event to eastern Mediter-ranean paleoceanographic conditions.

382 G.J. De Lange et al. / Progress in Oceanography 44 (1999) 369–386

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383G.J. De Lange et al. / Progress in Oceanography 44 (1999) 369–386

4. Conclusions

O The ‘Monsoonal system’ is closely associated with the humidity of the Mediter-ranean climate;

O Sapropel formation only occurs during humid (pluvial) periods associated withtimes of maximum isolation;

O Sapropel formation is always accompanied by enhanced freshwater input whichleads to enhanced Ba fluxes to the sediments as a result of basin-wide increasesin primary productivity;

O The end of sapropel formation is generally marked by the formation of a manga-nese Marker Bed, in which the enhanced levels of manganese, probably indicatea major change in redox conditions, i.e. a reventilation event;

O The occurence of a double peak in barium is consistent with the catastrophicflooding of the freshwater Black-Sea lake around 7150 BP (Ryan et al., 1997)

O Mediterranean sediments have excellent time control due to the regular presenceof ash-layers and sapropel intervals.

O Mediterranean sediments appear to be excellent recorders of the variations in Glo-bal paleoclimate which result in monsoonal cycles.

Acknowledgements

Captains and crews, and technicians from NIOZ, CNR, and TAAF, are thankedfor their cooperation during cruises with R/VTyro (1991, 1993), R/VUrania (1993,1994) andMarion Dufresne(1991). H.C. de Waard, D. van der Meent, R. Alink,G.N. Nobbe are acknowledged for their analytical assistence. Two anonymous per-sons are acknowledged for their thorough reviews. This research was in part sup-ported by the MAST contracts #MAS1-CT90-00022C (MARFLUX), MAS2-CT93-005 (PALEOFLUX), MAS3-CT95-0043 (CLIVAMP), MAS3-CT96-00137 (SAP),GdL by SOZ/NWO grants and by GOA grant #750.00.620-7290. This is publication# 990606 of the Netherlands School of Sedimentary Geology.

M. Paterne, responsible for the oxygen isotopes, is a participant from the CLIV-AMP Mast-3 project, all the other authors are participants from the SAP Mast-3project. The speculative part in this paper is the responsibility of the first authoralone.

References

Anastasakis, G. C., & Stanley, D. J. (1986). Uppermost sapropel, Eastern Mediterranean: paleoceanogra-phy and stagnation.National Geographical Research, 2, 179–197.

Berger, A., & Loutre, M. F. (1992). Astronomical solutions for paleoclimatic studies over the last 3million years.Earth and Planetary Science Letters, 111, 369–382.

Bethoux, J. P., Gentili, B., Raunet, J., & Tailleze, D. (1990). Warming trend in the Western Mediterraneandeep water.Nature, London, 347, 660–662.

384 G.J. De Lange et al. / Progress in Oceanography 44 (1999) 369–386

Bethoux, J. P., & Gentili, B. (1996). The Mediterranean Sea, coastal and deep-sea signatures of climaticand environmental changes.Journal of Marine Systems, 7, 383–394.

Bruins, H. J., & Van Der Plicht, J. (1996). The Exodus enigma.Nature, London, 382, 213–214.Brumsack, H. J. (1986). The inorganic geochemistry of Cretaceous black shales (DSDP leg 41) in compari-

son to modern upwelling sediments from the Gulf of California, in North Atlantic Paleoceanography.Geological Society of London Special Publication, 21, 447–462.

Burdige, D. J., & Gieskes, J. M. (1983). A pore water/solid phase diagenetic model for manganese inmarine sediments.American Journal of Science, 283, 29–47.

Calvert, S. E. (1983). Geochemistry of Pleistocene sapropels and associated sediments from the EasternMediterranean.Oceanologica Acta, 6, 231–263.

Calvert, S. E., Nielsen, B., & Fontugne, M. R. (1992). Evidence from nitrogen isotope ratios for enhancedproductivity during formation of eastern Mediterranean sapropels.Nature, London, 359, 223–225.

Church, T. M. (1979). Marine barite. In R. G. Burns,Marine Minerals. Short Course Notes, 6(pp. 175–209). Washington, USA: Mineralogical Society of America.

Cita, M. B., Vergnaud-Grazzini, C., Robert, C., Chamley, H., Ciaranfi, N., & D’Onofrio, S. (1977).Paleoclimatic record of a long deep-sea core from the eastern Mediterranean.Quaternary Research,8, 205–235.

Cita, M. B., Beghi, C., Camerlenghi, A., Kastens, K. A., McCoy, F. W., Nosetto, A., Parisi, E., Scolari,F., & Tomadin, L. (1984). Turbidites and megaturbidites from the Herodotus Abyssal Plain (EasternMediterranean) unrelated to seimic events.Marine Geology, 55, 79–101.

Cita, M. B., Aghib, F. S., Arosio, S., Folco, E., Sarto, L., Erba, E., & Rizzi, A. (1989). Bacterial coloniesand manganese micronodules related to fluid escape on the crest of the Mediterranean Ridge.RivistaItaliana di Paleontologia e Stratigraphia, 95, 315–336.

Cussen, H., Braithwaite, A. C., & Wilson, T. R. S. (1994). A robust, pressure-tolerant, low oxygendemand, dissolved oxygen electrode for profiling into deep ocean sediment.Underwater Technology,20, 3–7.

De Capitani, L., & Cita, M. B. (1996). The ‘marker-bed’ of the Mediterranean Ridge diapiric belt: geo-chemical characteristics.Marine Geology, 132, 215–225.

De Lange, G. J. (1992). Shipboard routine and pressure-filtration system for pore water extraction fromsuboxic sediments.Marine Geology, 109, 77–81.

De Lange, G. J., Middelburg, J. J., & Pruysers, P. A. (1989). Discussion: Middle and Late Quaternarydepositional sequences and cycles in the eastern Mediterranean.Sedimentology, 36, 151–158.

De Lange, G. J., Van Os, B., Pruysers, P. A., Middelburg, J. J., Castradori, D., Van Santvoort, P., Mu¨ller,P. J., Eggenkamp, H., & Prahl, F. G. (1994). Possible diagenetic alteration of palaeo proxies. In R.Zahn, T. F. Pedersen, M. A. Kaminski, & L. Labeyrie,Carbon cycling in the Glacial Ocean: con-straints on the ocean’s role in global change(NATO ASI Series I. Global Environmental Change.Vol. 17, pp. 225–258). Berlin: Springer Verlag.

Dymond, J., Suess, E., & Lyle, M. (1992). Barium in deep-sea sediment: A geochemical proxy for palaeo-productivity. Paleoceanography, 7, 163–181.

Dymond, J., & Collier, R. (1996). Particulate barium fluxes and their relationships to biological pro-ductivity. Deep-Sea Research II, 43, 1283–1308.

Emelyanov, E. M., & Shimkus, K. M. (1986).Geochemistry and sedimentology of the MediterraneanSea.Dordrecht: Reidel.

Fontugne, M. R., & Calvert, S. E. (1992). Late Pleistocene variability of the carbon isotopic compositionof organic matter in the eastern Mediterranean: Monitor changes in carbon sources and atmosphericCO2 concentrations.Paleoceanography, 7, 1–20.

Francois, R., Honjo, S., Manganini, S. J., & Ravizza, G. E. (1995). Biogenic barium fluxes to the deepsea: implcations for paleoproductivity reconstruction.Global Biogeochemical Cycles, 9, 289–303.

Froelich, P. N., Klinkhammer, G. P., Bender, M. L., Luedtke, N. A., Heath, G. R., Cullen, D., Dauphin,P., Hammond, D., Harman, B., & Maynar, D. V. (1979). Early oxidation of organic matter in pelagicsediments of the Eastern Equatorial Atlantic: Suboxic diagenesis.Geochimica et Cosmochimica Acta,43, 1075–1090.

Frost, C. D., O’Nions, R. K., & Goldstein, S. L. (1986). Mass balance for Nd in the Mediterranean Sea.Chemical Geology, 55, 45–50.

385G.J. De Lange et al. / Progress in Oceanography 44 (1999) 369–386

Glumac, P., & Anthony, D. (1991). The Caucasus. In R. Ehrich,Chronologies in old world archaeology,1 (pp. 275). Chicago: University of Chicago.

Higgs, N. C., Thomson, J., Wilson, T. R. S., & Croudace, I. W. (1994). Modification and completeremoval of eastern Mediterranean sapropels by postdepositional oxidation.Geology, 22, 423–426.

Hilgen, F. J. (1991). Astronomical calibration of Gauss to Matuyama sapropels in the Mediterraneanand implications for the geomagnetic polarity time scale.Earth and Planetary Science Letters, 104,226–244.

Hilgen, F. J., Lourens, L. J., Berger, A., & Loutre, M. F. (1993). Evaluation of the astronomically cali-brated time scale for the late Pliocene and earliest Pleistocene.Paleoceanography, 8, 549–565.

Hodder, I. (1990).The domestication of Europe.Oxford: Blackwell.Hoffert, M., Perseil, A., Hekinian, R., Choukroune, P., Needham, H. D., Francheteau, J., & Le Pichon,

X. (1978). Hydrothermal deposits sampled by diving saucer in Transform Fault ‘A’ near 37°N on theMid-Atlantic Ridge, Famous Area.Oceanologica Acta, 1, 74–86.

Howell, M. W., Thunell, R., Tappa, E., Rio, D., & Sprovieri, R. (1988). Late neogene laminiated andopal-rich facies from the Mediterranean region: Geochemical evidence for mechanisms of formation.Palaeogeography, Palaeoclimatology and Palaeoecologyy, 64, 265–286.

Johnson, R. G. (1997). Climate control requires a Dam at the Strait of Gibraltar.Eos, 78, 277–281.Klinkhammer, G. P., Bender, M., & Weiss, R. F. (1977). Hydrothermal manganese in the Galapagos Rift.

Nature, London, 269, 319–320.Kullenberg, B. (1952). On the salinity of the water contained in marine sediments.Meddel. Fr. Oceanogr.

Instit. Goteborg, 21, 1–38.Langereis, C. G., Dekkers, M. J., De Lange, G. J., Paterne, M., & Van Santvoort, P. J. M. (1997).

Magnetostratigraphy and astronomical calibration of the last 1.1 Myr from an Eastern Mediterraneanpiston core and dating of short events in the Brunhes.Geophysical Journal International, 129, 75–94.

Lourens, L. J., Hilgen, F. J., Zachariasse, W. J., Van Hoof, A. A. M., Antonarakou, A., & Vergnaud-Grazzini, C. (1996). Evaluation of the Plio-Pleistocene astronomical timescale.Paleoceanography, 11,391–414.

Mangini, A., Eisenhauer, A., & Walter, P. (1991). A spike of CO2 in the atmosphere at glacial-interglacialboundaries induced by rapid deposition of manganese in the oceans.Tellus, 43B, 97–105.

Mangini, A., Rutsch, H. J., Frank, M., Eisenhauer, A., & Eckhardt, J. D. (1994). Is there a relationshipbetween atmospheric CO2 and manganese in the ocean. In R. Zahn, T. F. Pedersen, M. A. Kaminski, &L. Labeyrie,Carbon cycling in the Glacial Ocean: constraints on the ocean’s role in global change.NATO ASI Series I. Global Environmental Change. Vol. 17, pp. 87–104. Berlin: Springer Verlag.

Moorby, S. A., Cronan, D. S., & Glasby, G. P. (1984). Geochemistry of hydrothermal Mn-oxide depositsfrom the S.W. Pacific Island Arc.Geochimica et Cosmochimica Acta, 56, 3909–3921.

Olausson, E. (1961). Studies of deep sea cores. Sediment cores from the Mediterranean Sea and the RedSea.Report of the Swedish Deep Sea Expedition 1947-48, 8, 337–391.

Passier, H. F., Middelburg, J. J., Van Os, B. J. H., & De Lange, G. J. (1996). Diagenetic pyritizationunder eastern Mediterranean sapropels caused by downward sulphide diffusion.Geochimica et Cosmo-chimica Acta, 60, 751–763.

Passier, H. F., Bosch, H. J., Nijenhuis, I. A., Lourens, L. J., Boettcher, M. E., Leenders, A., Sinninghe-Damste, J. S., De Lange, G. J., & De Leeuw, J. W. (1998). Eastern Mediterranean euxinia duringPliocene sapropel formation.Nature, London, 397, 146–149.

Pruysers, P. A., De Lange, G. J., & Middelburg, J. J. (1991). Geochemistry of eastern Mediterraneansediments: Primary sediment composition and diagenetic alterations.Marine Geology, 100, 137–154.

Pruysers, P. A., De Lange, G. J., Middelburg, J. J., & Hydes, D. J. (1993). The diagenetic formationof metal-rich layers in sapropel-containing sediments in the eastern Mediterranean.Geochimica etCosmochimica Acta, 57, 527–536.

Reid, J. L. (1979). On the contribution of the Mediterranean Sea outflow to the Norwegian-GreenlandSea.Deep-Sea Research, 26, 1199–1223.

Roether, W., Manca, B., Klein, B., Bregant, D., Geogopoulos, D., Beitzel, V., Kovacevic, V., & Luchetta,A. (1996). Recent changes in Eastern Mediterranean deep waters.Science, 271, 333–335.

Rohling, E. J., & Gieskes, W. W. C. (1989). Late Quaternary changes in Mediterranean IntermediateWater density and formation rate.Paleoceanography, 5, 531–545.

386 G.J. De Lange et al. / Progress in Oceanography 44 (1999) 369–386

Rohling, E. J., Jorissen, F. J., & De Stigter, H. C. (1997). 200 year interruption of Holocene sapropelformation in the Adriatic Sea.Journal of Micropaleoceanography, 16, 97–108.

Rossignol-Strick, M., Nesteroff, W., Olive, P., & Vergnaud-Grazzini, C. (1982). After the deluge: Mediter-ranean stagnation and sapropel formation.Nature, London, 295, 105–110.

Rossignol-Strick, M. (1983). African monsoon, an immediate climate response to orbital insolation.Nat-ure, London, 304, 46–49.

Rossignol-Strick, M. (1997). Sea-Land correlation of pollen records in the Eastern Mediterranean forthe glacial-interglacial transition: biostratigraphy versus radiometric time-scale.Quaternary ScienceReviews, 14, 893–915.

Rossignol-Strick, M., Paterne, M., Bassinot, F. C., Emeis, K. C., & De Lange, G. J. (1998). An unusualmid-Pleistocene monsoon period over Africa and Asia.Nature, London, 392, 269–272.

Ryan, W. B. F., Pittman, W. C., Major, C. O., Shimkus, K., Moskalenko, V., Jones, G. A., Dimitrov, P.,Gorur, N., Sakinc, M., & Yuce, H. (1997). An abrupt drowning of the Black Sea shelf.MarineGeology, 138, 119–126.

Stanley, D. J., & Sheng, H. (1986).Nature, London, 320, 733–735.Strohle, K., & Krom, M. D. (1997). Evidence for the evolution of an oxygen minimum layer at the

beginning of S-1 sapropel deposition in the eastern Mediterranean.Marine Geology, 140, 231–236.Thomson, J., Higgs, N. C., Wilson, T. R. S., Croudace, I. W., De Lange, G. J., & Van Santvoort, P. J.

M. (1995). Redistribution and geochemical behaviour of redox-sensitive elements around S1, the mostrecent Eastern Mediterranean sapropel.Geochimica et Cosmochimica Acta, 59, 3487–3501.

Thomson, J., Mercone, D., De Lange, G. J., & Van Santvoort, P. J. M. (1999). Review of recent advancesin the interpretation of eastern Mediterranean sapropel S1 from geochemical evidence.MarineGeology, 153, 77–89.

Torres, M. E., Brumsack, H. J., Bohrmann, G., & Emeis, K. C. (1996). Barite fronts in continental marginsediments: a new look at barium remobilization in the zone of sulfate reduction and formation ofheavy barites in diagenetic fronts.Chemical Geology, 127, 125–139.

Troelstra, S. R., Ganssen, G. M., Van Der Borg, K., & De Jong, A. F. M. (1991). A Late Quaternarystratigraphic framework for Eastern Mediterranean sapropel S1 based on AMS14C dates and stableoxygen isotopes.Radiocarbon, 33, 15–21.

Van Hoof, A. A. M., Van Os, B. J. H., Rademakers, J. G., Langereis, C. G., & De Lange, G. J. (1993).A paleomagnetic and geochemical record of the upper Cochiti reversal and two subsequent pre-cessional cycles from Southern Sicily (Italy).Earth and Planetary Science Letters, 17, 235–250.

Van Os, B. J. H., Middelburg, J. J., & De Lange, G. J. (1991). Possible diagenetic mobilisation of bariumin sapropelic sediment from the eastern Mediterranean.Marine Geology, 100, 125–136.

Van Os, B. J. H., Lourens, L. J., Hilgen, F. J., & De Lange, G. J. (1994). The formation of Pliocenesapropels and carbonate cycles in the Mediterranean: Diagenesis, dilution, and productivity.Paleoce-anography, 9, 601–617.

Van Santvoort, P. J. M., De Lange, G. J., Thomson, J., Cussen, H., Wilson, T. R. S., Krom, M. D., &Strohle, K. (1996). Active post-depositional oxidation of the most recent sapropel (S1) in sedimentsof the eastern Mediterranean Sea.Geochimica et Cosmochimica Acta, 60, 4007–4024.

Van Santvoort, P. J. M., De Lange, G. J., Langereis, C. G., Dekkers, M. J., & Paterne, M. (1997).Geochemical and paleomagnetic evidence for the occurrence of ‘missing’ sapropels in eastern Mediter-ranean sediments.Paleoceanography, 12, 773–786.

Varnavas, S. P., Papapioannou, J., & Catani, J. (1988). A hydrothermal manganese deposit from theEratosthenes Seamount, Eastern Mediterranean Sea.Marine Geology, 81, 205–214.

Vitaliano, D. B. (1973).Legends of the earth: their geologic origins.Bloomington: Indiana UniversityPress.

Von Breyman, M. T., Emeis, K. C., & Suess, E. (1992). Water depth and diagenetic constraints on theuse of barium as a paleoproductivity indicator. In C. P. Summerhayes, W. L. Prell, & K. C. Emeis,Upwelling systems: evolution since the early miocene. Special Publication of the Geological Societyof London, 64(pp. 273–284). London: The Geological Society.