Quaternary Research 77 (2012) 245–250

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Stable isotope composition of subfossil Cerastoderma glaucum shells from theSzczecin Bay brackish deposits and its palaeogeographical implications (South BalticCoast, Poland)

Ryszard K. Borówka a, Wacław Strobel b, Stanisław Hałas c,⁎a Institute of Marine and Coastal Sciences, Faculty of Geosciences, University of Szczecin, Mickiewicza 18, 70-383 Szczecin, Polandb Institute of Agrophysics, Polish Academy of Science, Doświadczalna 4, 20-290 Lublin, Polandc Institute of Physics, Maria Curie-Skłodowska University, pl. Marii Curie-Skłodowskiej 1, 20-031 Lublin, Poland

⁎ Corresponding author.E-mail addresses: ryszard@univ.szczecin.pl (R.K. Bor

w.strobel@ipan.lublin.pl (W. Strobel), stanislaw.halas@p

0033-5894/$ – see front matter © 2012 University of Wdoi:10.1016/j.yqres.2012.01.001

a b s t r a c t

a r t i c l e i n f o

Article history:Received 28 December 2010Available online 27 January 2012

Keywords:Stable isotopesCerastoderma glaucum shellsPalaeotemperatureSzczecin Lagoon

The environmental conditions of the Szczecin Bay, which existed prior to Szczecin Lagoon, have beenreconstructed on the basis of the stable carbon and oxygen isotope (18O and 13C) analysis and radiocarbondates obtained for subfossil shells of Cerastoderma (Cardium) glaucum. The shells in the collected core werewell preserved in their life positions, representing a geochemical record of past temperature variation overthe middle Holocene. Three major periods with different thermal conditions have been distinguished inthe interval ~6000–4300 cal yr BP, when the important Littorina regional transgression took place. Duringthe first period, 6000–5250 cal yr BP, water temperature decreased by 1.4°C, and then remained constantover the second period (5250–4750 cal yr BP). In contrast, during the third period (4750–4300 cal yr BP)both δ-values were highly variable and the mean summer temperature (March–November) increased byabout 3.5°C. During first two periods, δ18O and δ13C were significantly correlated, indicating stability of theenvironmental conditions.

© 2012 University of Washington. Published by Elsevier Inc. All rights reserved.

Introduction

The reconstruction of environmental conditions in the Baltic Seahas been attempted utilizing various paleoecological and paleogeo-graphical methods by a number of researchers listed below. The lateglacial and Holocene development of the Baltic Sea was controlledby varying temporally and spatially postglacial eustatic sea level andisostatic rebound of the areas previously covered by permanent ice(Björck, 1995; Harff and Meyer, 2011). In consequence, significantvariations of the area and local sea level occurred, leading to seriouschanges of the whole marine ecosystem resulting from changes inwater salinity, temperature and concentration of dissolved oxygenin deep water.

These changes, which were essentially induced by the amounts ofwater inflowing from the North Sea and climatic changes in the BalticSea basin, can be reconstructed utilizing cores of preserved sedimentsfrom deep basins (Sohlenius et al., 2001; Harff et al., 2011) alike thosefrom the Baltic littoral zones (Borówka et al., 2005; Lampe, 2005;Uścinowicz, 2006; Miettinen et al., 2007; Kabailiene et al., 2009;Rotnicki, 2009).

ówka),oczta.umcs.lublin.pl (S. Hałas).

ashington. Published by Elsevier In

For paleoecological reconstructions of salinity, temperature, andbottom-water oxygen content, various approaches have been usedincluding paleobotanical (Witak, 2002; Witkowski et al., 2004;Brenner, 2005; Jankowska et al., 2005; Witak and Dunder, 2007;Leśniewska andWitak, 2008; Miotk-Szpiganowicz et al., 2008) paleo-zoological (Damušyte, 2009) and isotopic methods (Punning et al.,1988; Emeis et al., 2003; Widerlund and Andersson, 2006, 2011).Paleoclimatic studies based on the records from adjacent continentalareas, particularly those used for modeling of temperature and pre-cipitation during the late glacial period and the Holocene, were alsoimportant for understanding the environmental changes of the BalticSea. These studies used mainly palynological and isotopic methods(e.g. Seppä and Poska, 2004; Antonsson and Seppä, 2007; Skrzypeket al., 2009; Heikkilä and Seppä, 2010). Palynological studies per-formed in the areas of the South Scandinavia, Finland, Latvia andEstonia lead to conclusion that the Holocene Thermal Maximumoccurred there ca. 8000–4000 cal yr BP, with the highest temperaturesat the beginning of this period (Heikkilä and Seppä, 2010), while in theSW Poland the highest temperatures occurred ca. 5000 cal yr BP(Skrzypek et al., 2009).

One of the most accurate methods used for the reconstruction ofphysical-chemical properties of marine water is the analysis of stablecarbon and oxygen isotope compositions of carbonates from recentand fossilized mollusk shells. This approach was successfully appliedfor paleotemperature studies of many basins (Epstein et al., 1953;

c. All rights reserved.

Figure 1. The study area map showing location of sediment core.

Table 1The lithology of the core 35/99 from the Szczecin Lagoon.

Depth bellowbed surface (m)

Altitude(m a. s. l.)

Lithology

0.00–0.16 −5.01 to−5.17

Shell layer (Dreissena polymorpha)

0.16–0.29 −5.17 to−5.30

Shell layer (Dreissena polymorpha) with admixtureof dark organic mud

0.29–0.43 −5.30 to−5.44

Fine-grained dark-gray sand with admixture offreshwater mollusks shell (Bithynia tentaculata,Valvata piscinalis, Unio sp., Pisidium sp.)

0.43–0.58 −5.44 to−5.59

Fine-grained light-gray sand with admixture ofmarine and brackish mollusks shell (Cerastodermaglaucum, Hydrobia ventrosa, H. ulvae, Macomabalthica)

0.58–0.86 −5.59 to−5.87

Fine-grained dark-gray sand with admixture ofmarine and brackish mollusks shell (C. glaucum,H. ventrosa, H. ulvae, M. balthica)

0.86–1.02 −5.87 to−6.03

Fine-grained light-gray sand with admixture ofmarine and brackish mollusks shell (C. glaucum,H. ventrosa, H. ulvae, M. balthica)

1.02–1.92 −6.03 to−6.93

Fine-grained gray sand with admixture of marineand brackish mollusks shell (C. glaucum, H. ventrosa,H. ulvae, M. balthica)

1.92–2.20 −6.93 to−7.21

Dark-brown peat

2.20–2.52 −7.21 to−7.53

Dark-brown detritus gyttja

2.52–3.00 −7.53 to−8.01

Fine-grained light-brown sand with a root traces

3.00–3.50 −8.01 to−8.51

Fine-grained light-gray sand, horizontally laminated

246 R.K. Borówka et al. / Quaternary Research 77 (2012) 245–250

Mook and Vogel, 1968; Mook, 1971; Schöne et al., 2005) and fortracing of their salinity (Keith and Parker, 1965; Punning et al.,1988; Emeis et al., 2003; Mueller-Lupp et al., 2003; Simstisch et al.,2005).

The reconstruction of water temperature in a basin may be used toinfer atmospheric circulation in the past. Alheit and Hagen (1997)demonstrated that thermal conditions of littoral water in the SouthBaltic, including Szczecin Lagoon, are related in a significant degreeto the atmospheric circulation in Europe. Winter temperatures of air(Marsz, 1999) and of water in the littoral zones of the South Baltic(Gierjatowicz, 2003, 2007, 2011) are significantly correlated withthe fluctuations of North Atlantic Oscillation Index (NAO). The high-est winter temperatures are related to the maxima of western circu-lation, i.e. with the inflow of warm air masses from Atlantic. Insummer, the water temperatures are positively correlated with thefrequency of air masses inflowing from the east, whereas they arenegatively correlated with air masses inflows from the northwestand north (Girjatowicz et al., 2002). It is highly probable that recentlyobserved regularities might be referred to the whole Holocene, there-fore they might be useful in the interpretation of dominant types ofair circulation in the littoral zone of the South Baltic. The purpose ofthe present study was to determine temperature variations in theformerly existed open-sea Szczecin Bay, which was replaced by thecurrent Szczecin Lagoon. The open-sea Szczecin Bay existed betweenthe Middle Atlantic and the Middle Subboreal periods (Borówka et al.,2002, 2005, 2009; Borówka and Osadczuk, 2003). During this periodthe sedimentation of sand with significant addition of mollusk shellswas dominant in prevailing brackish conditions (Borówka et al.,2002, 2005; Woziński et al., 2003). Among numerous fossilizedmollusk species, the dominant was Cerastoderma (Cardium) glaucum,however, other species, includingMacoma balthica, Hydrobia ventrosaand Hydrobia ulvae were also common. The biometric analysis ofCerastoderma glaucum shells confirmed that the autochthonic popula-tion was very well developed, and displayed a typical age and sizestructure (Woziński et al., 2003). Many of C. glaucum shells havebeen observed in their typical living position, what proves in situlocation at the bottom of the bay and prove that sediments have notbeen redeposited later on. Therefore, these unique well-preservedmollusk shells have been chosen for assessment of paleohabitat con-ditions based on the collected sediment core no. 35/99.

Study area

The core no. 35/99 selected for laboratory analyses of extractedshells was collected from central-western part of the Szczecin Lagoon(location: 53° 45′ 29″ N, 14° 19′ 26″ E, see Fig. 1). In the lowermostpart of the core at −7.53 to −8.51 m with respect to the currentsea level (a.s.l.) dominate fluvial sands deposited from the old Odrariver valley at time of the late glacial (Borówka et al., 2002, 2005).Above these sands limnic formations such as gyttja and highlydecomposed peats have been deposited (Table 1). The total thicknessof the lacustrine–swampy formations is 60 cm. At the level of−6.93 m there appears a distinct erosional unconformity betweenpeat and the cover of fine and very fine grained sands with marineand brackish mollusks. These sediments have total thickness of147 cm and extend up to −5.44 m a.s.l. Those sediments are coveredby 14 cm layer of fine-grained sands with admixture of fresh watermollusk shell, and also 29 cm layer of recently deposited shells ofDreissena polymorpha. The top of the bottom deposits reaches altitudeof −5.01 m a.s.l. (Table 1).

According to the recent studies (Borówka et al., 2009) the radio-carbon dates of 66 shells of C. glaucum preserved in their livingposition, extracted from 14th profiles of sandy sediments, showsthat the studied shellswere accumulated at the bottomof the SzczecinBay during the period between 6460±40 and 3040±35 cal yr BP(7378±41 to 3269±53 cal yr BP). About 4800 cal yr BP began the

formation of the Uznam sandbar, which gradually isolated theSzczecin Bay from the direct influence of the Baltic Sea (Prusinkiewiczand Noryśkiewicz, 1966; Borówka et al., 1986; Osadczuk, 2002;Reimann et al., 2009). This process was completed about 3600 to3300 cal yr BP, when a retrograde delta of the Świna river wasdeveloped between these sandbars (Borówka et al., 2009).

Figure 2. The relationship between depth position in the core and age of Cerastodermaglaucum shells. A third degree polynomial was fitted to the experimental data. On thebasis of the obtained polynomial the interpolated age was calculated for all theanalyzed sells.

247R.K. Borówka et al. / Quaternary Research 77 (2012) 245–250

Material and methods

For stable isotope analyses, 25 shells of C. glaucum shells preservedin their living position (right and left shell from each individual) wereextracted from the core in 5 cm intervals from sections between 0.45and 1.85 m below the bed surface (Table 1). A small radial piece wasbroken off from each shell and then pulverized in an agate mortar.The second shell was preserved for other analyses like 14C. Carbondioxide from the shell carbonate was extracted with 100% of ortho-phosphoric acid in a vacuum line at 25°C (McCrea, 1950). The isotopeanalysis (both δ13C and δ18O)was performed in theMass SpectrometryLaboratory at M. Curie-Sklodowska University, Lublin, using dual inletand triple collector mass spectrometer with standard uncertainty0.06‰.

Among the 25 shells of C. glaucum designed for stable isotopeanalyses, radiocarbon ages were determined for eight of the Poznań14C Laboratory (Table 2). The selection criteria were: (1) marginalposition of their occurrence; and (2) depth in core at which a changein δ18O trend was recorded. The reservoir effect correction was deter-mined using the ChronoMarine Reservoir Database (http://intcal.qub.ac.uk/marine/) to be −300 yr. The calibrated ages (Table 2) werecalculated using the program CalPal-online (Jöris and Weninger, 1998;http://www.calpal-online.de) provided by Isotope Laboratory at theCologne University. Moreover, in the Poznań 14C Laboratory a series ofpeat and gyttja samples from layers below the marine series were alsodated.

The relationship between the depth and radiocarbon age ofC. glaucum shells has been determined based on the experimentaldata (Fig. 2). It was found that a third-degree polynomial fits thedata well (R2 attained the value of 0.996). From this polynomial fitthe dateswere calculated for all undated 25 shell samples (interpolatedages in Table 3).

Additionally, two modern shells of C. glaucum from the littoralzone of Pomeranian Bay near Międzyzdroje and Świnoujście(Table 3) were isotopically analyzed for direct comparison of thereconstructed average temperature with the instrumentally recordedon-site water temperature (see discussion section).

Results

The investigated series of marine sediments accumulated overalmost 1700 yr, between 6018±72 and 4324±63 cal yr BP (5530±40 and 4180±35 14C yr BP). The sedimentation rate was not constant(Fig. 2), initially it was ~0.4 mm/yr, whereas at its final stage it exceeded1.7 mm/yr.

During the period of accumulation of marine sediments, thecarbonates in C. glaucum shells show a significant spread of δ18Ovalues (−6.47 to −4.84‰ vs. VPDB), with an average value of−5.64‰. The δ13C values varied in the range from −4.04‰ to−2.19‰ (average −3.11‰). The temporal plots of both δ-valuesare shown in Figure 3. Three major periods can be distinguished on

Table 2The results of radiocarbon dating of Cerastoderma glaucum shells from the Szczecin Lagoon

Depth (m) Sample name Material Altitude (m a.s.l.) 14C age (

0.52–0.56 ZS 35/12 C. glaucum −5.57 4180±30.60–0.65 ZS 35/14 C. glaucum −5.66 4415±30.80–0.85 ZS 35/18 C. glaucum −5.86 4320±31.10–1.15 ZS 35/25 C. glaucum −6.16 4515±31.35–1.40 ZS 35/30 C. glaucum −6.41 4685±31.45–1.50 ZS 35/32 C. glaucum −6.51 4750±31.55–1.60 ZS 35/34 C. glaucum −6.61 4950±31.80–1.85 ZS 35/39 C. glaucum −6.86 5530±41.92–2.00 ZS 35/42 Peat −7.01 7030±92.15–2.20 ZS 35/46 Peat −7.21 8810±12.35–2.40 ZS 35/50 gyttja −7.41 1020±1

a Reservoir corrected age.

the basis of the δ18O value variations. During the first period (I),from ca. 6000 to 5250 cal yr BP, δ18O values initially increased, thenduring the second period (II), from 5250 to 4750 cal yr BP they attainedthe maximum value in this core (sectional thin layer of sediments wasaccumulated at depths from 155 to 120 cm). In contrast, during thethird period (III) from ca. 4750 to 4200 cal yr BP, δ18O gradually de-creased to values lower than those observed during the first period(the maximum accumulation rate was recorded in this section).

Minimum δ13C values of ca. −4‰, are recorded at 5310, 4904 and4266 cal yr BP, whereas maximum values, ca. −2.2‰, occurred at5120, 4560 and 4415 cal yr BP. These maximum δ13C values areclose to those observed for shells of live mollusks collected from theopen Baltic Sea (−1.13‰ for modern shells: Table 3). In general,δ13C does not show a distinct long-term correlation with δ18O.However, in contrast to the whole time span (r=0.14), a statisticallysignificant correlation between δ13C and δ18O is observed for thebottom part of the core, older than 5000 cal yr BP (r=0.61, n=10,significance level α=0.05).

Interpretation of isotope data

In the case of studied shells mineralogical analyses weren't made.However, according to Eisma et al. (1976) modern shells of C. glaucumare composed of aragonite. In fossils, as the result of diageneticprocesses, a gradual replacement of aragonite by calcite takes place.For example Molodkov (1996) claimed 10% loss of aragonite in favorof calcite within 6500–5500 yr old shells of C. glaucum.

It is commonly acknowledged that the δ18O values of molluskshells depend on the environmental conditions in the studied basin.In the case of marine and oceanic basins, which are characterized byrelatively constant salinity, δ18O values predominantly reflect watertemperature (Epstein et al., 1953; Mook and Vogel, 1968; Mook,

— core 35/99.

14C yr BP) R corra (14C yr BP) Age (cal yr BP) Laboratory number

5 3880 4324±63 Poz-123915 4115 4678±102 Poz-123925 4020 4489±39 Poz-123945 4215 4761±73 Poz-123955 4385 4957±62 Poz-123965 4450 5117±121 Poz-123975 4650 5393±55 Poz-123980 5230 6018±72 Poz-123990 7030 7851±88 Gd-1222310 8810 9892±197 Gd-1222480 10420 12237±316 Gd-15090

Table 3Results of carbon and oxygen stable isotope analysis of carbonate shell material relatedto the depth and age of shell sample.

Sample no. Depth of shellsample (cm)

δ18OVPDB

(‰)δ13CVPDB

(‰)

14C Age(cal yr BP)

Interpolatedage (cal yr BP)

1 48.0 −5.99 −4.08 42662 54.0 −5.98 −3.49 4324 43183 62.5 −6.47 −2.70 43814 67.5 −5.82 −2.20 44155 72.5 −5.98 −2.90 44466 82.5 −6.17 −3.62 4489 45057 88.0 −5.70 −2.34 45378 92.5 −5.77 −2.19 45649 97.5 −5.98 −3.15 459510 104.5 −5.92 −2.95 464211 108.0 −5.40 −2.75 466712 112.5 −6.07 −3.33 4761 470213 117.5 −5.96 −3.73 474514 122.5 −5.29 −3.80 479215 132.5 −5.23 −4.01 490416 137.5 −5.62 −3.00 4957 496917 142.5 −5.00 −2.90 504218 147.5 −4.84 −2.24 5117 512219 152.5 −5.00 −2.73 521220 157.5 −5.63 −3.90 5393 531021 162.5 −5.19 −3.27 541922 167.5 −5.68 −3.52 553923 172.5 −5.42 −3.63 566924 177.5 −5.38 −2.51 581225 182.5 −5.53 −2.71 6018 5968

Modern shells (2 yr old specimens)Międzyzdroje Bottom −5.55 −1.13 2008–2009 –

Świnoujście Bottom −5.55 −1.13 2008–2009 –

248 R.K. Borówka et al. / Quaternary Research 77 (2012) 245–250

1971; Schöne et al., 2005). In this case an increase of 1‰ in δ18Ocorresponds to a temperature decrease of 4.5°C. Therefore, watertemperatures in which shells grew can be determined from theirδ18O values using a calibration curve, e.g. as elaborated by Epsteinet al. (1953) (see Fig. 2 in Friedman and O'Neil, 1977). However, thecalculated temperatures depend on the value of δ18O for waterwhere the analyzed shells grew. In paleoclimate studies this valueusually is not known, therefore it needs to be estimated as accuratelyas possible. For a rough estimation of isotope temperatures, we haveassumed that the current δ18O of water in the Pomeranian Bay(−6.4‰ vs. VSMOW, Fröhlich et al., 1988) fairly accurately reflectsthe environmental conditions where the studied cockles lived.

In order to verify our calculations and cross-check the validity ofour approach, we also analyzed δ18O of modern shells of C. glaucum(Table 3). The isotope temperature calculations were comparedwith multiple years of water temperature measurements in thePomeranian Bay near Międzyzdroje (Majewski, 1974) and also

Figure 3. δ18O and δ13C values of Cerastoderma glaucum shells as a function of age.

considered on biology and life conditions of the Baltic population ofC. glaucum (Wołowicz, 1991). It is well-known from the literature(Boyden, 1972; Wołowicz, 1991) that C. glaucum build their shellsfrom March to November. In winter months (December–March),their shell growth stops, and concentric annual rings (tidal growth)form. Cockles predominantly prefer shallow and near-bottom waterbelow the depth of wave activity in a place characterized by limitedsediment movement. However, there are places, e.g., covered bays,where we can find cockles at depths lower than 1 m. The maximumdepth that these species occur in the Baltic Sea is 25 m.

In the Szczecin Bay, the maximum depth for the studied period(6000–4300 cal yr BP) was 5–6 m, and the minimum probably notlower than 2 m, since the sea level in the past was ~4 m lower thanit is the at present (Borówka et al., 2009). In this situation, a thermo-cline could not be formed. In conclusion, it can be stated that thebottom water temperature, if diurnal variations are averaged, wassimilar to the average temperature of the vegetation season.

Multi-yearmeasurements of thewater temperature inMiędzyzdrojeprove that the average temperature for period frombeginning of April toend of November is 13.3°C. Knowing the δ18O value for present shellsfrom this location (−5.5‰ vs. VPDB) and selecting a reasonable valuefor water (−6.9‰ vs. VSMOW, see discussion below) it was possibleto calculate water temperature using different empirical formulas(Table 4).

Inasmuch as the shell carbonate is aragonite, in the formulas forcalcite–water fractionation a correction of +0.7‰ for aragonite–calcite fractionation was applied. Unfortunately this correction isanother source of uncertainty in calculated temperatures. Böhmet al. (2000) reviewed eleven values from different studies foraragonite–calcite fractionation and found these values to range from+0.6 to +1.1‰. On the basis of calculated temperatures presented inTable 4, we tested which equation is most appropriate for our applica-tion. The best agreementwith recentmeanwater temperature recordedfrom April to November (13.3°C) was obtained using Craig's formula,but the two other formulas for calcite–water fractionation yield closeresults considering mentioned above uncertainty of aragonite–calcitefractionation and inherent uncertainties of empirical equations. Notethat the value of δ18O=−6.9‰ assumed for water gives the bestmatch for the recorded temperature (13.3°C). This value appears to bereasonable, because it must be slightly lower than that determined forthe Pomeranian Bay (−6.4‰ vs. VSMOW, Fröhlich et al., 1988) due tostronger influence of the Odra River. The calculation of water tempera-tures in the Szczecin Bay over whole period 6000–4300 cal yr BP hasbeen made with the Craig's formula. The reconstructed temperaturesmay be biased by uncertainty of water δ18O and its variation overtime. Nevertheless, the temperature-change trends are independentof δ18O variations and allowed distinguishing three periods of distincttemperature changes (Table 5).

Table 4Water temperature calculated by means of different empirical formulas for modernshells assuming two different δ18O values for water and +0.7‰ correction foraragonite–calcite fractionation.

Implemented formula Calculated water temperature [°C]δ18Oshell=−5.55‰

δw=−6.90‰ δw=−6.40‰

Epstein et al. (1953)a 12.9 10.2Craig (1965)b 13.4 10.7Kim and O'Neil (1997) convertedto °C-scale by Bemis et al. (1998)c

12.2 9.1

Grossman and Ku (1986)d 26.4 23.4

Lower indexes in delta values denote calcite, water and aragonite, respectively. Deltavalues for carbonates are vs. VPDB, whilst vs. VSMOW for water.

a T(°C)=16.5−4.3(δc−δw)+0.14(δc−δw)2.b T(°C)=16.9−4.2(δc−δw)+0.13(δc−δw)2.c T(°C)=16.1−4.64(δc−δw)+0.09(δc−δw)2.d T(°C)=20.6−4.34(δa−δw).

Table 5The calculated range of water temperature variations in the Szczecin Bay (salinity wasassumed to be constant).

Period Depth (cm) Age range(cal yr BP)

Average δ18OVPDB

(and range) (‰)Δ T (°C)

III 120–46 4750–4300 −5.94 (−5.40 to −6.47) +3.5II 155–120 5250–4750 −5.16 (−4.84 to −5.29) ~0I 185–155 6000–5250 −5.47 (−5.19 to −5.68) −1.4

249R.K. Borówka et al. / Quaternary Research 77 (2012) 245–250

During the first period (ca. 6000–5250 cal yr BP), represented bysamples collected from a depth of 185–155 cm, a tendency towardlower temperature with relatively small variations was found. Duringthe second period (ca. 5250–4750 cal yr BP), relating to a thin layer ofsediments at 155–120 cm depth, the temperature was low butrelatively constant. Finally, during the third period (ca.4750–4300 cal yr BP), the temperature gradually increased to ahigher value than that was observed in the first period. In summary,it can be inferred that in the Szczecin Bay, which existed in theplace of the present Szczecin Lagoon ca. 6000–4200 cal yr BP, themean water temperature of growth seasons of C. glaucum (March–November) varied between 10.7 and 17.2°C.

The statistically significant correlation between δ13C and δ18Ovalues of shell carbonate was observed for the periods I and II only(Fig. 3). The most likely reason seems to be varying water tempera-ture during the vegetation period. Both dissolved carbonate species,bicarbonate and carbonate ions, at isotope equilibriumwith dissolvedCO2 have similar sensitivity on temperature variation. According toexperimental laboratory study by Halas et al. (1997) a 1‰ increasein carbonate-CO2 fractionation corresponds to 7.3°C temperaturedecrease. In steady-state conditions, CO2 formed at the bottom ofthe Szczecin Bay had a more or less constant δ13C values, henceδ13C of carbonate shells was only temperature-dependent, unlikeδ18O. Such favorable conditions most likely existed until the Uznamsandbar was formed (after 4800 cal yr BP). This bar significantlyrestricted outflow of the Odra River, what led to variation of salinity,δ18O of water and also δ13C of organic matter deposited at the basin.For this reason both δ18O and δ13C recorded in shell carbonate werenot correlated and were highly variable in the period III (Fig. 3).

Concluding remarks

Taking into account the environmental preferences and biology ofC. glaucum, the determined δ18O values are correlated with meanwater temperature of three seasons (spring, summer, autumn). Itshould be noted that the large variations of δ18O value recorded invertical sediment profile, may also result from the short time ofshell growth, since shells mainly grow during the first two warmseasons of their life (Wołowicz, 1991). Consequently, the obtainedvalues do not represent a multi-year average, but they are informativeof thermal variability through relatively short periods. Nevertheless, asmoothed curve of variation of δ18O may be informative about thethermal properties of water along the considered part of Holocene(ca. 6000–4300 cal yr BP). Considering that the Szczecin Bay was ashallow basin, it can be assumed that in that marine bay only smallsurface-bottom gradients of salinity and summer temperature existed,alike to these observed nowadays in the Szczecin Lagoon. This was theresult of intense water mixing due to wind-forced waves, basincurrents and storm swelling, which prevented a thermocline forma-tion. The fluctuations of water temperature in the Szczecin Bay couldbe induced not only by varying climate, but also by different hydrolog-ical events. In period I there was a temperature drop ~1.5°C, whichwas accompanied by a significant increase of sea level at least about1–2 m (Lampe, 2005; Uścinowicz, 2006; Rotnicki, 2009). The rise insea level caused an increase of water salinity in the bay, and it couldlower the temperature of the bottom water. However, in the period

III the increase of the reconstructed temperature coincides in timewith the progressive isolation from the influences of the Baltic Sea asa result of the development of the Świna Barrier (Borówka et al.,2002, 2005). This isolation not only increased the fraction of watersupplied by the Odra River and decreased water salinity in the Szcze-cin Bay, but also resulted in a higher water temperature.

Similar data were gained in the newest research of air temperaturereconstructions based on palynological (Davis et al., 2003; Seppä andPoska, 2004; Antonsson and Seppä, 2007; Heikkilä and Seppä, 2010)and palaeozoological (Heiri et al., 2004) research from Europe. Similarresults for thermal changes were also observed from Lake Flarken insouthwestern Sweden where water temperature dropped more than1°C from 6000 to 5500 cal yr BP. After a short period of stabilization,the temperature increased by about 2°C during the next thousandyears. Analogous temperature variations for the summer season (July)have been described in the Alps area based on fossil Hironomidae byHeiri et al. (2004).

The trends in the reconstructed temperature for the whole ofEurope are not so clear (Davis et al., 2003). Nevertheless, it wasfound that maximum temperature in the west and middle part ofthe continent occurred about 6000 cal yr BP and after this time periodthere was a temperature decrease with many fluctuations.

Taking into account the correlation between water temperature inSzczecin Lagoon and recent atmospheric circulation in the CentralEurope (Girjatowicz et al., 2002), it can be elucidated that the pastperiods with warmer water in the Szczecin Bay correspond to moreoften inflow of warm air masses from east part of the continent.This conclusion is confirmed by excellent corroboration of our recon-structed temperatures in Szczecin Bay with those in Latvia (Heikkiläand Seppä, 2010) and Estonia (Seppä and Poska, 2004).

A general conclusionwhich follows from this study is that C. glaucumshells is an excellent carbonate material for palaeoclimate reconstruc-tions, because this species is very common in shallow basins and theseshells preserve isotopic signatureswell (14C, 13C and 18O). The approachpresented in this study, although its findings refer to the Baltic Searegion only, may be applicable to other regions over the globe in recon-structions of Quaternary climate. Particularly in further studies of theδ13C and δ18O profiles, attention should be paid to sub-periods with astrong correlation between these two values, because a statisticallysignificant positive correlation points to more steady depositionalconditions in these sub-periods relative to other sectors of theanalyzed profile.

Acknowledgments

We thank both anonymous reviewers and Dr. Grzegorz Skrzypekfrom the University of Western Australia for the careful reading ofthe manuscript and for useful comments.

References

Alheit, J., Hagen, E., 1997. Long-term climate forcing of European herring and sardinepopulations. Fisheries Oceanography 6, 130–139.

Antonsson, K., Seppä, H., 2007. Holocene temperatures in Bohuslän, southwestSweden: a quantitative reconstruction from fossil pollen data. Boreas 36, 400–410.

Bemis, B.E., Spero, H.J., Bijma, J., Lea, D.W., 1998. Reevaluation of oxygen isotopic com-position of planctonic foraminifera: experimental results and revised paleotem-perature equations. Paleoceanography 13, 150–160.

Björck, S., 1995. A review of the history of the Baltic Sea, 13.0−8.0 ka BP. QuaternaryInternational 27, 19–40.

Böhm, F., Joachimski, M.M., Dullo, W.C., Eisenhauer, A., Lehnert, H., Reitner, J.,Wörheide, G., 2000. Oxygen isotope fractionation in marine aragonite of corallinesponges. Geochimica et Cosmochimica Acta 64, 1695–1703.

Borówka, R.K., Osadczuk, A., 2003. Zmiany hydrograficzne w obszarze ujściowym Odrypodczas późnego glacjału i holocenu. Prace Komisji Paleogeografii CzwartorzęduPAU 1, 151–155.

Borówka, R.K., Gonera, P., Kostrzewski, A., Nowaczyk, B., Zwoliński, Z., 1986. Stratigra-phy of eolian deposits in Wolin Island and the surrounding area, North-West Po-land. Boreas 15, 301–309.

250 R.K. Borówka et al. / Quaternary Research 77 (2012) 245–250

Borówka, R.K., Latałowa, M., Osadczuk, A., Święta, J., Witkowski, A., 2002. Palaeogeo-graphy and palaeoecology of Szczecin Lagoon. Greifswalder Geographische Arbei-ten 27 (C4), 107–113.

Borówka, R.K., Osadczuk, A., Witkowski, A., Wawrzyniak-Wydrowska, B., Duda, T.,2005. Late Glacial and Holocene depositional history in the eastern part of theSzczecin Lagoon (Great Lagoon) basin — NW Poland. Quaternary International130, 87–96.

Borówka, R.K., Witkowski, A., Latałowa, M., Skowronek, A., Witkowski, A., Harff, J.,Isemer, H.-J., 2009. Sedimentation of a marine deposit in the Szczecin Bay duringthe Littorina transgression. International Conference on Climate Change — TheEnvironmental and Socio-economic Response in the Southern Baltic Region: Con-ference Proceedings, BALTEX, Publication No. 42, 8.

Boyden, R.C., 1972. Behaviour, survival and respiration of the cockles Cerastodermaedule and C. glaucum in air. Journal of the Marine Biological Association of the Unit-ed Kingdom 52, 661–680.

Brenner, W.W., 2005. Holocene environmental history of the Gotland Basin (Baltic Sea)— a micropaleontological model. Palaeogeography, Palaeoclimatology, Palaeoecol-ogy 220, 227–241.

Craig, H., 1965. The measurement of oxygen isotope paleotemperatures. In: Tongiorgi,V.E. (Ed.), Stable Isotopes in Oceanographic Studies and Paleotemperatures. Labor-atorio di Geologia Nucleare, Pisa, pp. 161–182.

Damušyte, A., 2009. Late Glacial and Holocene subfossil mollusk shell on the LithuanianBaltic Sea coast. Baltica 22 (2), 111–122.

Davis, B.A.S., Brewer, S., Stevenson, A.C., Guiot, J., Contributors, Data, 2003. The temper-ature of Europe during the Holocene reconstructed from pollen data. QuaternaryScience Reviews 22, 1701–1716.

Emeis, K.-C.h., Struck, U., Blanz, T., Kohly, A., Vos, M., 2003. Salinity changes in the cen-tral Baltic Sea (NW Europe) over last 10,000 years. The Holocene 13, 411–421.

Epstein, S.R., Buchsbaum, R., Lowenstam, H.A., Urey, H.C., 1953. Revised carbonatewater isotopic temperature scale. Geological Society of America Bulletin 64,1315–1326.

Eisma, D., Mook, W.G., Das, H.A., 1976. Shell characteristics, isotopic composition andtrace-element contents of some euryhaline mollusks as indicator of salinity.Palaeogeography, Palaeoclimatology Palaeoecology 19, 39–62.

Friedman, I., O'Neil, J.R., 1977. Compilation of stable isotope fractionation factors ofgeochemical interest. In: Fleischer, M. (Ed.), Data of Geochemistry. US GeologicalSurvey Professional Paper 440-KK, pp. 1–12.

Fröhlich, K., Grabczak, J., Różański, K., 1988. Deuterium and oxygen-18 in the Baltic Sea.Chemical Geology (Isotope Geoscience Section) 72, 77–83.

Gierjatowicz, J.P., 2003. The influence of the North Atlantic Oscillation on water tem-perature at the Polish Balic Coast. Przegląd Geofizyczny 48, 45–60 (in Polish).

Girjatowicz, J.P., 2007. The North Atlantic Oscillation influence on the Odra river estu-ary hydrological conditions. Estuarine, Coastal and Shelf Science 74, 395–402.

Girjatowicz, J.P., 2011. Effect of the North Atlantic Oscillation on water temperature insouthern Baltic coastal lakes. Annales de Limnologie — International. Journal ofLimnology 47, 73–84.

Girjatowicz, J.P., Schmelzer, N., Olechwir, T., 2002. Climatological relationships be-tween atmospheric circulation patterns and hydrological parameters in the Szcze-cin Lagoon. Czasopismo Geograficzne 73, 113–122 (in Polish).

Grossman, E.L., Ku, T.-L., 1986. Oxygen and carbon isotope fractionation in biogenic arago-note: temperature effects. Chemical Geology (Isotope Geoscience Section) 59, 59–74.

Halas, S., Szaran, J., Niezgoda, H., 1997. Experimental determination of carbon isotopeequilibrium fractionation between dissolved carbonate and carbon dioxide. Geo-chimica et Cosmochimica Acta 61, 2691–2695.

Harff, J., Meyer, M., 2011. Coastlines of the Baltic Sea — zones of competition betweengeological processes and a changing climate: examples from the Southern Baltic.In: Harff, J., Björck, S., Hoth, P. (Eds.), The Baltic Sea Basin, Central and Eastern Eu-ropean Development Studies. Springer-Verlag, Berlin Heidelberg, pp. 149–164.

Harff, J., Endler, R., Emelyanov, E., Kotov, S., Leipe, Th., Moros, M., Olea, R., Tomczak, M.,Witkowski, A., 2011. Late Quaternary climate variations reflected in Baltic Sea Sedi-ments. In: Harff, J., Björck, S., Hoth, P. (Eds.), The Baltic Sea Basin, Central and EasternEuropean Development Studies. Springer-Verlag, Berlin Heidelberg, pp. 99–132.

Heikkilä, M., Seppä, H., 2010. Holocene climate dynamics in Latvia, eastern Baltic re-gion: a pollen-based summer temperature reconstruction and regional compari-son. Boreas 39, 705–719.

Heiri, O., Tinner, W., Lotter, A.F., 2004. Evidence for cooler European summers during pe-riods of changingmeltwater flux to the North Atlantic. PNAS 101 (43), 15285–15288.

Jankowska, D., Witak, M., Huszczo, D., 2005. Paleoecological changes of the Vistula La-goon in the last 7000 YBP based on diatom flora. Oceanological and Hydrobiologi-cal Studies 34 (4), 109–129.

Jöris, O., Weninger, B., 1998. Extension of the 14C calibration curve to ca. 40,000 cal BCby synchronizing Greenland 18O/16O ice core records and North Atlantic foraminif-era profiles: a comparison with U/Th coral data. Radiocarbon 40, 495–504.

Kabailiene, M., Vaikutiene, G., Damušyte, A., Rudnickaite, E., 2009. Post-glacial stratig-raphy and paleoenvironment of the northern part of the Curonian Spit, WesternLithuania. Quaternary International 207, 69–79.

Keith, M.L., Parker, R.H., 1965. Local variation of 13C and 18O contents of mollusk shellsand the relatively minor temperature effect in marginal marine environments. Ma-rine Geology 3 (1/2), 115–129.

Kim, S.-T., O'Neil, J.R., 1997. Equilibrium and nonequilibrium oxygen isotope effects insynthetic carbonates. Geochimica et Cosmochimica Acta 61, 3461–3475.

Lampe, R., 2005. Lateglacial and Holocene water-level variations along the NE GermanBalic Sea coast: review and new results. Quaternary International 133–134, 121–136.

Leśniewska, M., Witak, M., 2008. Holocene diatom biostratigraphy of the SW Gulf ofGdańsk, Southern Baltic Sea (part III). Oceanologicaland Hydrobiological Studies37 (4), 35–52.

Majewski, A., 1974. Charakterystyka hydrologiczna Zatoki Pomorskiej. 115 pp.Wydawnictwa Komunikacji i Łączności, Warszawa.

Marsz, A.A., 1999. The North Atlantic Oscillation and the thermal regime in the area ofNorth-West Poland and the Polish Coast of the Baltic Sea. Przegląd Geograficzny71, 225–245 (in Polish).

McCrea, J.M., 1950. On the isotopic chemistry of carbonates and paleotemperaturescale. Journal of Chemical Physics 18, 849–857.

Miettinen, A., Jansson, H., Alenius, T., Haggrén, G., 2007. Late Holocene sea level changesalong the southern coast of Finland, Baltic Sea. Marine Geology 242, 27–38.

Miotk-Szpiganowicz, G., Zachowicz, J., Uścinowicz, S., 2008. Review and reinterpreta-tion of the pollen and diatom data from the deposits of the Southern Baltic lagoons.Polish Geological Institute Special Papers 23, 45–70.

Molodkov, A., 1996. ESR dating of Lymnaea baltica and Cerastoderma glaucum from lowAncylus level and transgressive Litorina Sea deposits. Applied Radiation and Iso-topes 47, 1427–1432.

Mook, W.G., 1971. Paleotemperatures and chlorinates from stable carbon and oxygenisotopes in shell carbonate. Palaeogeography, Palaeoclimatology, Palaeoecology 9,245–263.

Mook, W.G., Vogel, J.C., 1968. Isotopic equilibrium between shells and their environ-ment. Science 159, 874–875.

Mueller-Lupp, T., Erlenkeuser, H., Bauch, H.A., 2003. Seasonal and interannual variabil-ity of Siberian river discharge in the Laptev Sea inferred from stable isotopes inmodern bivalves. Boreas 32, 292–303.

Osadczuk, K., 2002. Evolution of the Świna barrier spit. Greifswalder GeographischeArbeiten 27 (C4), 119–125.

Prusinkiewicz, Z., Noryśkiewicz, B., 1966. Problem of age of podzols on brown dunes ofbay bars of river Świna in the light of a palynological analysis and dating by radio-carbon 14C (in Polish, English summary). Zeszyty Naukowe Uniwersytetu MikołajaKopernika w Toruniu. Geografia 5, 75–88.

Punning, J.-M., Martma, T., Kessel, H., Vaikmäe, R., 1988. The isotopic composition ofoxygen and carbon in the subfossil mollusk shells of the Baltic Sea as an indicatorof palaeosalinity. Boreas 17, 27–31.

Reimann, T., Harff, J., Borówka, R., Osadczuk, K., Tsukamoto, S., Frechen, M., 2009. Lumi-nescence dating of coastal sand deposits from the Baltic Sea — examples from theDarss-Zingst and Świna Gates. In: Witkowski, A., Harff, J., Isemer, H.-J. (Eds.), Inter-national Conference on Climate Change – The Environmental and Socio-economicResponse in the Southern Baltic Region: Conference Proceedings, BALTEX, Publica-tion No. 42, 124.

Rotnicki, K., 2009. Identyfikacja, wiek i przyczyny holoceńskich ingresji i regresji Bał-tyku na polskim wybrzeżu środkowym. Wydawnictwo Słowińskiego Parku Naro-dowego, Smołdzino.

Schöne, B.R., Pfeiffer, M., Pohlmann, T., Siegismund, F., 2005. A seasonally resolvedbottom-water temperature record for the period AD 1866–2002 based on shellsof Arctica islandica (Molluska, North Sea). International Journal of Climatology25, 947–962.

Seppä, H., Poska, A., 2004. Holocene annual mean temperature changes in Estonia andtheir relationship to solar insolation and atmospheric circulation patterns. Quater-nary Research 61, 22–31.

Simstisch, J., Erlenkeuser, H., Harms, I., Spielhagen, R.F., Stanovoy, V., 2005. Modern andHolocene hydrographic characteristics of the shallow Kara Sea shelf (Siberia) asreflected by stable isotopes of bivalves and benthic foraminifera. Boreas 34,252–263.

Skrzypek, G., Baranowska-Kącka, A., Keller-Sikora, A., Jędrysek, M.O., 2009. Analogoustrends in pollen percentages and carbon stable isotope composition of Holocenepeat — possible interpretation for palaeoclimatic studies. Review of Palaeobotanyand Palynology 156, 507–518.

Sohlenius, G., Emeis, K.-C.h., Andrén, E., Andrén, T., Kohly, A., 2001. Development of an-oxia during the Holocene fresh–brackish water transition in the Baltic Sea. MarineGeology 177, 221–242.

Uścinowicz, S., 2006. A relative sea level curve for the Polish Southern Baltic Sea. Qua-ternary International 145–146, 86–105.

Widerlund, A., Andersson, P.S., 2006. Strontium isotopic composition of modern andHolocene mollusk shells as a palaeosalinity indicator for the Baltic Sea. ChemicalGeology 232, 54–66.

Widerlund, A., Andersson, P.S., 2011. Late Holocene freshening of the Baltic Sea derivedfrom high-resolution strontium isotope analyses of mollusk shells. Geology 39 (2),187–190.

Witak, M., 2002. Postglacial History of the Development of the Puck Lagoon (the Gulf ofGdańsk, Baltic Sea) Based on the Diatom Flora. Diatom Monographs 2. Koeltz Sci-entific Books, Koenigstein.

Witak, M., Dunder, J., 2007. Holocene diatom biostratigraphy of the SW Gulf of Gdańsk,Southern Baltic Sea (part II). Oceanological and Hydrobiological Studies 36 (3),3–20.

Witkowski, A., Latałowa, M., Borówka, R.K., Gregorowicz, P., Bąk, M., Osadczuk, A.,Święta, J., Lutyńska, M., Wawrzyniak-Wydrowska, B., Woziński, R., 2004. Palaeoen-vironmental changes in the area of the Szczecin Lagoon (the south western BalticSea) as recorded from diatoms. Studia Quaternaria 21, 153–165.

Wołowicz, M., 1991. Geographic Differentiation of the Cardium glaucum PopulationBruguiere (Bivalvia). Hypotheses Concerning the Derivation of the Species and Mi-gration Routes (in Polish, English Summary). Wydawnictwo Uniwersytetu Gdańs-kiego, Gdańsk.

Woziński, R., Wawrzyniak-Wydrowska, B., Borówka, R.K., 2003. The subfossil malako-fauna from the Holocene deposits of the Szczecin Lagoon (in Polish, English sum-mary). In: Borówka, R.K., Witkowski, A. (Eds.), Człowiek i środowiskoprzyrodnicze Pomorza Zachodniego (II Środowisko abiotyczne). Oficyna INPLUS,Szczecin, pp. 113–118.