DISCUSSION

Discussion: a critique of Possible waterwaysbetween the Marmara Sea and the Black Sea in the lateQuaternary: evidence from ostracod and foraminiferassemblages in lakes İznik and Sapanca, Turkey,Geo-Marine Letters, 2011

Cenk Yaltırak & Umut B. Ülgen & Cengiz Zabcı &Sven Oliver Franz & Sena Akçer Ön & Mehmet Sakınç &

M. Namık Çağatay & Bedri Alpar & Kurultay Öztürk &

Cemal Tunoğlu & Selma Ünlü

Received: 1 September 2011 /Accepted: 9 December 2011 /Published online: 23 December 2011# Springer-Verlag 2011

Abstract The identification of past connection routes be-tween the Black Sea and the Sea of Marmara, other than thetraditional one through to the Bosphorus Strait, would be ofconsiderable interest to the international scientific community.Nazik et al. (Geo-Mar Lett 31:75–86 (2011) doi:10.1007/s00367-010-0216-9) suggest the possibility of two alternative

waterway connections via lakes Sapanca and İznik. TheirBlack Sea to Sea of Marmara multi-connection hypothesis,which is based on undated marine fossils collected in bothlakes from surficial grab samples, conflicts with many earlierstudies. In this contribution, the hypothesis and the underlyingdata are discussed in the light of previous tectonic, sedimen-tological and limnological findings showing that it is impos-sible to have had marine connections through lakes Sapancaand İznik during the last 11.5 ka. Global sea-level trends andtectonic uplift rates would accommodate a connection be-tween the Sea of Marmara and Lake İznik in the middlePleistocene. Uplift rates for the northern block of the NorthAnatolian Fault, when compared with the global sea-levelcurve, clearly indicate that there cannot have been a connec-tion through the İzmit Gulf–Lake Sapanca–Sakarya Valley forat least the past 500 ka. Moreover, borehole sediments alongthe western shores of Lake Sapanca, which reach down to thebedrock, do not contain any marine fossils.

Introduction

The Black Sea, one of the largest marine basins worldwide,has a modern connection with the Mediterranean Seathrough the Sea of Marmara, with linkages provided bythe Bosphorus and the Çanakkale straits. However, numer-ous scientific studies have revealed time periods when theBlack Sea lost its connection with the Sea of Marmara andturned into an isolated basin (e.g., Aksu et al. 1999, 2002;Çağatay et al. 2003; Eriş et al. 2007; Hiscott et al. 2007).

C. Yaltırak (*) :C. ZabcıFaculty of Mines, Department of Geological Engineering,İstanbul Technical University,34469 Maslak, İstanbul, Turkeye-mail: yaltirak@itu.edu.tr

U. B. Ülgen : S. A. Ön :M. N. ÇağatayEastern Mediterranean Centre for Oceanography and Limnology,İstanbul Technical University,34469 Maslak, İstanbul, Turkey

S. O. FranzSteinmann Institute for Geology, Mineralogy and Paleontology,Section Geology, University of Bonn,Nußallee 8,53115 Bonn, Germany

M. SakınçEurasia Institute of Earth Sciences, İstanbul Technical University,34469 Maslak, İstanbul, Turkey

B. Alpar :K. Öztürk : S. ÜnlüInstitute of Marine Sciences & Management, İstanbul University,34116 Vefa, İstanbul, Turkey

C. TunoğluFaculty of Engineering, Department of Geological Engineering,Hacettepe University,06532 Beytepe, Ankara, Turkey

Geo-Mar Lett (2012) 32:267–274DOI 10.1007/s00367-011-0270-y

Furthermore, a connection between the Sea of Marmara andthe Black Sea via the İzmit Gulf, Lake Sapanca and theSakarya Valley has previously been suggested as an alter-native route by, among others, Pfannenstiel (1944) andYanko-Hombach et al. (2007). Nazik et al. (2011) considerboth this alternative connection and an additional possiblewaterway, starting from Gemlik Bay, crossing Lakeİznik, and finally reaching the Black Sea through theSakarya Valley. They suggest that both of these routesmay have been active in the late Quaternary. Nazik etal. (2011) base their hypothesis on the following con-siderations (we quote):

1. “The presence of at least ten marine ostracod and 23foraminifer species in the sediments of Lake İznik, andat least one marine ostracod and two foraminifer speciesin the sediments of Lake Sapanca confirm that theselakes must have been connected to the world oceansometime during the late Quaternary” (p. 75);

2. “Whatever the case, the findings of this study clearlydemonstrate that vertical tectonic movements need to betaken into account when reconstructing the late Quater-nary sea-level history of this region” (p. 75);

3. “ … the latest flooding event must have occurred in theHolocene, given that marine microfossils were found inthe youngest surface sediments of both lakes” (p. 85).

Nazik et al. (2011) acknowledge that 14C dating of car-bonate microfossils would be required for a more preciseaging of the waterway connections. In their study, 47 surfi-cial samples (uppermost 10 to 20 cm of the lake deposits)were recovered from the two lakes on irregular grids atvarious water depths using a grab sampler.

We argue that a hypothesis advocating the existence of“possible waterway connections between the Black Sea andthe Marmara Sea in the Holocene” cannot be based solelyon the presence of marine fossils. The incorporation ofconstraints from multidisciplinary aspects such as tectonics,sedimentology, stratigraphy and paleoclimate must, in addi-tion, be applied to make a valid paleogeographical recon-struction. Furthermore, their suggested timing of theconnections stands in acute contradiction to the results ofother investigations in both lakes. We begin by synthesizingthe results of previous work focusing on regional tectonics,limnological assessments in both lakes, and global sea-levelchange.

Lake İznik

Morphotectonic aspects

The suggested southern possible waterway starts in GemlikBay, and crosses the Karsak and Pamukova sills at the

western and eastern ends of Lake İznik before reaching theBlack Sea through the Sakarya Valley (Fig. 5 of Nazik et al.2011). Indeed, SRTM-derived digital elevation models(DEMs) and topographic profiles along the valleys clearlyshow that the proposed connection would have to crossthe Karsak Sill (+85 m) at the western end of the lake,and the Pamukova Sill (+380 m) at the eastern end(Fig. 1). The average elevation of the shoreline of Lakeİznik is currently ~85 m.

Global sea-level change and regional tectonic uplift

Previous studies have identified numerous marine terraces atmany localities on the Gelibolu and Armutlu peninsulas in theMarmara region. Absolute dating of these late Pleistoceneterraces gives an average tectonic uplift rate of 0.3±0.05 mm/year for the last 200 ka for the block south of thenorthern branch of the North Anatolian Fault (NAF; Paluskaet al. 1989; Yaltirak et al. 2000, 2002). Considering thistectonic uplift rate and the global sea-level curve (Chappelland Shackleton 1986) precludes any possible connection be-tween Gemlik Bay and Lake İznik across the Karsak Sill(+85 m) during the late Pleistocene–Holocene (Fig. 2). How-ever, an extrapolation backward in time using the same upliftrate shows that, in the period 200–600 ka, at first sight theremay have been up to four marine linkages: (1) 322–332 ka BP,(2) 365–370 ka BP, (3) 380–420 ka BP, and (4) 475–575 kaBP. During these time intervals, spillpoints at sills should haveled to the formation of marine terraces at elevations of +85 to+125 m in Gemlik Bay, at the Karsak Strait or at the peripheryof Lake İznik. The existence of middle Pleistocene terracescontaining Caspian and Azov-Black Sea bivalve species, butno Mediterranean ones, has been identified in a study byİslamoğlu (2009). Based on these faunal data, the existenceof a marine waterway is incompatible with the paleoceanog-raphy of the Marmara Sea for the period 322–370 ka BP,when the area of the modern Gelibolu Peninsula was occupiedby scattered islands (Fig. 11 in Yaltırak et al. 2002) that wouldnot have allowed unimpeded Mediterranean faunal migration.However, a connection between Lake İznik and the Sea ofMarmara may have been possible in the periods 380–420 and475–575 ka BP.

Applying the same extrapolated tectonic uplift rate, aconnection between Lake İznik and the Black Sea acrossthe Pamukova Sill (+380 m) can be excluded for the last520 ka (Fig. 2). For this topographic high to have been lowenough to allow a connection, tectonic uplift rates wouldneed to have been 38.5 mm/year for a connection at the baseof the Holocene, 3.1 mm/year for a connection at 120 ka,2 mm/year for a connection at 190 ka, 1.2 mm/year for aconnection at 325 ka, 0.9 mm/year for a connection at410 ka, and 0.8 mm/year for a connection at 490 ka. Thesevertical movement rates are all well above the calculated

268 Geo-Mar Lett (2012) 32:267–274

rates of uplift of late Pleistocene marine terraces in theMarmara region. For comparison, slip-rate studies of theHimalayan frontal thrust give values such as 19 mm/yearin western Nepal (Jouanne et al. 2004) and ~13 mm/year inNW India (Wesnousky et al. 1999), both being significantlylower than those required for marine waters to have crossedthe Pamukova Sill en route to the Black Sea at any timeduring the Holocene. Moreover, a tectonic study shows thatLake İznik is a transtensional basin that is subsiding actively(Öztürk et al. 2009). This local tectonic deformationrepresents another argument against the Nazik et al.(2011) hypothesis in terms of relative elevation differencebetween the Sea of Marmara and Lake İznik.

Limnological aspects

Sediment core studies in Lake İznik go back to 2002, whenFrantz et al. (2006) analyzed three short cores from the deepbasin. Additional work was carried out on 18 short and twolong cores taken from 13 different localities in the lake in2005 (Fig. 3; Ülgen and Franz 2008; Ülgen et al. 2011).210Pb and 137Cs datings show variable sedimentation ratesof 0.2 to 0.4 cm/year on the central shelf (cores IZN05/4E,IZN05/3) and in the northern basin (IZN05/5, IZN05/6), andof 0.4 to 0.8 cm/year in the southern part (IZN05/12, IZN05/13) of the lake (Franz et al. 2006; Ülgen and Franz 2008).The derived sedimentation rates clearly indicate that, unless

Fig. 1 Digital elevation model (white 380, orange 85, yellow 65, red35 m) of the eastern Sea of Marmara showing lakes İznik and Sapanca,and the possible waterways of Nazik et al. (2011) between the BlackSea and the Sea of Marmara: bottom left topographic profile along theproposed waterway from the İzmit Gulf, through Lake Sapanca and the

Sakarya Valley, bottom right topographic profile along the proposedwaterway from the Gemlik Gulf, through Lake İznik, the PamukovaSill, and the Sakarya Valley. Topography and bathymetry are from adigital elevation model using the GeoMapApp database (Ryan et al. 2009)

Geo-Mar Lett (2012) 32:267–274 269

exhumation of deeper layers containing marine fossils tookplace at all these sites, the surficial samples of Nazik et al.(2011) can represent only the last 10 to 40 years of sedi-mentation in Lake İznik. Any evidence for exhumation ofdeeper sediment layers by slumping or similar processes islacking.

Furthermore, 5-m-long cores from Lake İznik haveyielded geochemical proxy data showing climate-sensitivefreshwater inputs that can be expressed in terms of lake-level fluctuations for the last 4,300 years (Ülgen et al. 2011).The oldest calibrated radiocarbon date is 3.8 ka BP at473 cm depth in composite core IZN05-SC4E&LC1(IZN4/05 in Fig. 3), indicating an average sedimentationrate of 0.12 cm/year. Furthermore, no foraminifer or marineostracod fossils were found in any of the cores. Additional-ly, two 14-m-long cores taken in 2009 show a ca.30,000 year paleoclimate record without any marine fossils(P.A. Roeser, personal communication 2011).

A field excursion to Lake İznik was carried out at thebeginning of the summer of 2011 to check the 17 nearshoresampling sites of Nazik et al. (Fig. 3). We observed that, at

seven of these sites (i.e., ca. 40%), surficial samples werecollected at or close to constructions or settlements (D1 andD2 next to the road parallel to the Lake İznik shore, D9 atBoyalıca Beach, D10 near an irrigation canal, D11 at theÇakırca Village shore, D17 very near to a building, and D18in front of an irrigation canal). We did not identify anymarine signal (ostracods and/or foraminifers) in sand sam-ples that we collected at these sites and subsequently exam-ined under the microscope. A marine signal (ostracods and/or foraminifers) was identified in all cases by Nazik et al.(2011). On the other hand, another two of their sites with amarine signal (foraminifers) are remote from constructionactivities.

In this context, it is important to note that the extractionof sand from Lake İznik is legally prohibited and that, forthe last 30 years, sand for construction purposes has there-fore been obtained from both Gemlik Bay and the SakaryaRiver (personal communication from Vehbi Gündüz, co-director of Öztürkler Construction Company). Prior to thistime period, sand taken from Gemlik Bay was the primarysource for construction projects.

Fig. 2 Global sea-level change(modified from Chappell andShackleton 1986) and tectonicuplift rate curves, the latterextrapolated from the uplift rateof Yaltırak et al. (2002)determined from Pleistoceneterraces at the Ganos Fault andthe Armutlu Peninsula

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At their 11 lake sampling sites (Fig. 3), Nazik et al.identified a marine signal (ostracods and/or foraminifers)in six (or seven) cases (cf. their Table 5, which is ambivalentin this respect). Combining this with the nearshore data, therecovery of this signal applies to about 50% of their 28sampling sites in Lake İznik.

Conclusion

Based on the data outlined above we conclude that,regarding the block south of the North Anatolian Faultwhere Lake İznik is located, any possibility for a water-way connection between Gemlik Bay and Lake İznikduring the Holocene or the late Pleistocene is precluded.However, extrapolation of the uplift rate in the context ofthe paleogeographic evolution of the Marmara region,and comparison with the global sea-level curve suggestthat a waterway connection between Gemlik Bay andLake İznik may have existed in the periods 380–420 kaand/or 475–575 ka BP. By the same token, a waterwayconnection across the Pamukova Sill (+380 m) cannothave occurred after the middle Pleistocene.

Contamination originating from construction activitiescould account for the marine signal identified by Nazik etal. (2011) at several nearshore localities. The existence ofthis signal at two probably uncontaminated nearshore sitesand in deeper lake sediments remains unexplained.

Lake Sapanca

Morphotectonic aspects

The northern waterway for a potential connection betweenthe Sea of Marmara and the Black Sea is through the İzmitGulf, Lake Sapanca and the Sakarya Valley (e.g., Nazik etal. 2011). This route has been a continuously popular can-didate for an alternative connection between the Parate-thyean region and the Mediterranean in the Quaternary forsome time (e.g., Ryan and Pitman 1998; Yanko-Hombach etal. 2007). DEMs and topographic profiles show thatSapanca sills separate the İzmit–Sapanca corridor, LakeSapanca and the Sakarya Valley at an elevation of currently+35 m (Fig. 1).

Global sea-level change and the tectonic upliftof the Sapanca region

When we consider the global sea-level curve in combinationwith the average vertical uplift rate calculated by dating oflate Pleistocene marine terraces around the Armutlu andGelibolu peninsulas, it is quite impossible to justify a wa-terway connection during the Holocene between the Sea ofMarmara and the Black Sea via Lake Sapanca and theSakarya Valley. Using an uplift rate of 0.3±0.005 mm/year,the most recent time interval for a possible connection

Fig. 3 Sampling locations of Nazik et al. (2011), as well as Ülgen andFranz (2008) and Ülgen et al. (2011) in Lake İznik: Nazik et al.,sampling 2007: red and blue stars nearshore (D1–D4, D7–D19, n017)and lake sampling locations (Su1–Su11, n011), respectively; Ülgen andFranz, Ülgen et al., sampling 2005: red dots IZN4/05 and IZN13/05 long

cores (~5m), other red dots short cores (~1m, n011). Note that n denotesthe number of locations, not necessarily equivalent to the number of corestaken. Topography and bathymetry are from a digital elevation modelusing the GeoMapApp database (Ryan et al. 2009)

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would have been the penultimate interglacial (Eemian) some120 ka BP (Fig. 2). However, all the marine terraces forwhich this uplift rate is valid are located on the southernblock of the northern branch of the NAF and can, therefore,not be used for the northern side. Marine terraces along thenorth coast of the Sea of Marmara are located at MarmaraEreğlisi (Tekirdağ; 40.982035°N, 27.970995°E) andŞirintepe (İzmit; 40.758471°N, 29.863585°E), where theyare found at elevations of +15 and +20 m, respectively(Altınlı 1968; Sakınç and Yaltırak 1997). The MarmaraEreğlisi terrace has been dated at 116,146±5,353 years BPby optically stimulated luminescence (Y. Altınok, personalcommunication 2011), which yields an uplift rate of ~0.08 mm/year. For comparison, the uplift rate along the nearbysouthwestern Black Sea coast is 0.015–0.032 mm/year (Görüret al. 2001). These rates for the northern block of the northernbranch of the NAF and the nearby Black Sea coast preclude thepossibility of a waterway connection between the İzmit Gulfand Lake Sapanca or between this lake and the Black Seaduring the Holocene.

Limnological and sedimentological aspects

Schwab et al. (2009) give a sedimentation rate of 0.4 to0.8 cm/year for Lake Sapanca, based on 210Pb and 137Csdating of sediment core samples. The 137Cs signature placesthe 1963 peak at 19 and 31 cm depths in cores K6.2 andK7.2, respectively. These results imply that, unless exhuma-tion of deeper sediment layers containing marine fossils hasoccurred at all relevant sites, the surficial samples of Naziket al. (2011) can at best represent the last 12.5 to 25 years,not the entire Holocene.

Leroy and Albay (2010) found brackish and marine paly-nomorphs in Lake Sapanca at two periods: the last 30 years,and the period from at least 1,500 to ca. 1,100 years ago.They suggested four mechanisms to explain this: (1) paleo-connections of the lake with the Black Sea and the Sea ofMarmara, (2) fish translocations, which were very commonin Roman times, (3) water bird transport of pollen, phyto-plankton and other small organisms, and (4) dispersal bycatadromous and anadromous fishes, which could havetransported microorganisms to the lake through their sea-sonal contacts with the sea. However, onland borehole stud-ies have recovered no marine species in the Sakarya Valley(Görür et al. 2001, boreholes KCK20 and KCK21 in theirFig. 3) and along the İzmit–Sapanca corridor (Gürbüz andLeroy 2010, borehole C9 in their Fig. 7).

Historical records indicate the existence of a former 17.5-km-long and 60-m-wide connection between the İzmit Gulfand Lake Sapanca. This artificial channel was constructed inthe 5th Century AD during the era of Justinian I (Ulugün2008). During his paleoseismological studies between theİzmit Gulf and Lake Sapanca, Barka (1993) found remnants

of such a canal and interpreted it as part of an unfinishedOttoman structure. The last remnants of the canal werealmost completely destroyed by later earthquakes, but tracesof it can still be identified on satellite images (e.g., GoogleEarth) between the coordinates 40.721628°N/30.044452°E,40.721518°N/30.050917°E, 40.720613°N/30.059604°E,and 40.717661°N/30.081758°E. Moreover, the bathymetryof modern Lake Sapanca (Lettis et al. 2002) shows that thedepth of the basin is sufficiently large to have maintainedsuch a connection around the sea level at the time of canalconstruction. The lake level at that time would have beenabout 20 m above the present-day floor of the basin.

Conclusion

The data presented above preclude any connection betweenthe Sea of Marmara and the Black Sea via the İznik–Sapanca corridor, Lake Sapanca and the Sakarya River forat least the past 500 ka. Furthermore, as the surficial samplesof Nazik et al. (2011) can represent only the last 12.5 to25 years, the evidence for marine organisms in LakeSapanca is interpreted to reflect fish translocations, waterbird transportation, and/or migration of catadromous andanadromous fish. The existence of a historical canal con-necting the İzmit Gulf and Lake Sapanca would have facil-itated such recent faunal migration.

Outlook

Nazik et al. (2011) have presented a hypothesis proposingthe potential existence of waterways between the Black Seaand the Sea of Marmara through lakes Sapanca and İznik inthe late Quaternary (a Holocene age is suggested, because ofthe surficial nature of the samples). Their hypothesis isbased on the presence of foraminifers and marine ostracodsin surficial lake sediments. By implication, they question thereliability of well-established regional tectonic uplift rates.In this discussion, we have demonstrated that the uplift ratesare consistent, and the high uplift rates that would be re-quired to have accommodated Holocene overtopping ofbedrock sills in the area are unreasonable. The main issue,therefore, is the question of how marine fossils have foundtheir way into the surficial sediments of the lakes, and whichcan, at best, represent the last few decades of sedimentation,according to the available limnological data. 137Cs and210Pb measurements clearly show that the informationgleaned from these samples cannot be used in any revisionof Holocene uplift rates.

The present discussion has emphasized that examiningthe potential existence of waterway connections other thanthe link via the Bosphorus Strait between the Black andMarmara seas must be based on multidisciplinary studies

272 Geo-Mar Lett (2012) 32:267–274

involving tectonics, stratigraphy, sedimentology, paleontol-ogy, paleoclimatology and anthropogenic effects (i.e., envi-ronmental modifications due to sediment input to the lakesby human infrastructures; e.g., Gürbüz and Gürer 2008;Anonymous 2011a, 2011b). This requires appropriate sam-pling methods, such as long boreholes not only in the lakesas such but also onland along the routes of such hypotheticalwaterways. Moreover, detailed geomorphological studies oflake terraces would yield invaluable data to test such hy-potheses. Identification of more marine terraces and moredatings are the only valid way to determine and/or reviseexisting uplift rates.

Acknowledgements The 2011 Lake İznik field study was donewithin the C.E.P. Foundation. General funding was by the GermanResearch Foundation (DFG), grant number FR 1199/1-1, 2, the İTUScientific Project Office BAP, grant number 11_04_277, and also byDAAD grant A/04/17884. We wish to thank two anonymous refereesand also Dr. Richard Hiscott for their helpful comments on themanuscript, as well as the journal editors.

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