[Central and Eastern European Development Studies (CEEDES)] The Baltic Sea Basin || Holocene Evolution of the Southern Baltic Sea Coast and Interplay of Sea-Level Variation, Isostasy,

Chapter 12Holocene Evolution of the Southern Baltic SeaCoast and Interplay of Sea-Level Variation,Isostasy, Accommodation and Sediment Supply

Reinhard Lampe, Michael Naumann, Hinrich Meyer, Wolfgang Janke,and Regine Ziekur

Abstract Coastal barriers and spits develop when the accumulation space avail-able in the coastal sea for sediment deposition decreases and partly fills up. Theaccommodation space increases when sea level rises and decreases when sedimentaccumulates. In addition to the coastal relief prior to the sea-level rise, which deter-mines the potential accommodation, the evolution depends on the volume and rateof sediment supply. The example from the north-eastern German Baltic coast showshow the course of Holocene sea-level rise (Littorina transgression) varied due toglacio-isostatic uplift of different coastal sections and thus the growth of accommo-dation space. Further, the role of the sediments which built up the shoreface and thecoastal landforms is discussed. We also examine the influence of the main inclina-tion of pre-transgressional relief on the development, aggradation and progradationof beach ridges, spits and barriers. The determination of the volume of the presentbarriers allows rough estimations regarding the volume of sediment supplied fromeroding cliffs. In a final synopsis, the interplay of all factors is discussed, explainingthe distribution, volume and stability of the barriers along the German Baltic coast.

Keywords Baltic Sea · Germany · Coastal evolution · Sea-leveldevelopment · Isostatic adjustment · Structures and volumes of coastal barriers

12.1 Introduction

Late Quaternary sea-level history from north-western Europe reflects the influ-ence of various eustatic, isostatic, tectonic and, to a minor extent, other factorslike sediment compaction, halokinetics and hydrographic variations. The many

R. Lampe (B)Institut für Geographie und Geologie, Ernst-Moritz-Arndt-Universität Greifswald,D-17487 Greifswald, Germanye-mail: [email protected]

233J. Harff et al. (eds.), The Baltic Sea Basin, Central and Eastern EuropeanDevelopment Studies (CEEDES), DOI 10.1007/978-3-642-17220-5_12,C© Springer-Verlag Berlin Heidelberg 2011

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combinations of these factors in a rather limited area have made north-west European intensively studied natural sea-level laboratory (Mörner 1980).

This study focuses on the southern Baltic coast as an ideal object to study theinterplay of these main natural driving forces of coastal development, the influencesof which are controlled by the sediment supply from both cliffs and sea bottomand the space available for potential sediment accumulation, so-called accommoda-tion space (Posamentier and Allen 1999). Due to the insignificant tidal variationsas a source of uncertainty in sea-level determinations, the eustatic sea-level varia-tions in this area can be identified more precisely than elsewhere. On a millenniumtimescale, neotectonic crustal movements are believed to be insignificant becauseover the last 34 My they have varied from 200 m subsidence in the west to 120m uplift in the north (Ludwig 2001), which is on average equivalent to –0.006 and0.004 mm/year. However, glacio-isostatic movements have to be considered becausethe study area is located in the transition area between the Fennoscandian uplift andthe central European zone where the effects of a decaying glacial forebulge have tobe assumed (Fjeldskaar 1994, Garetsky et al. 2001, Nocquet et al. 2005).

At first, three new relative sea-level curves for the north-east German Baltic coastwill be presented to show the sea-level variation and the tendency and stability ofcrustal behaviour. Results from intense onshore and offshore investigations (drilling,geophysical surveys) will be described to show how the relief prior to the transgres-sion was formed. These data will be used to calculate the sediment volume of thebarriers, which will be related to the sea-level history. Finally, a preliminary modelof coastal evolution along the southern Baltic will be established which considerseustatic and isostatic sea-level variation, sediment supply and accommodation.

12.2 Geographic Setting

Mecklenburg-Vorpommern’s 354-km-long outer (Baltic Sea) coast (Fig. 12.1) con-sists of cliff sections composed of Pleistocene outwash and till, interspersed withlow uplands, barriers, spits and accreting forelands composed of Holocene sandand, to a very minor extent, gravel. The sea coast provides shelter to a longer shore-line within the inner bays or lagoons (boddens). The low-lying coastal segmentsowe their existence to sediment supplied alongshore from eroding bluffs, which areless mobile and are believed to act as headlands (hinge points) that help stabilizeadjacent shores. Approximately 70% of the German Baltic Sea coast erodes at anaverage rate of 0.34 m/year (Ministerium für Bau, Landesentwicklung und Umwelt1994).

The inner shelf consists primarily of Pleistocene outwash, till and glacial lakesediment (fine sand and silt). The latter forms large flat sediment bodies offshore ofUsedom (Pomeranian Bight), Zingst (Falster–Rügen plane) and Rostocker Heide.Extensions of these sediment bodies can also be found landwards of the presentcoastline below the barriers. The inclination of the glacial lake sediment surface ispredominantly less than 0.1◦ and the depths reach from –8 m below the barriers to

12 Holocene Evolution of the Southern Baltic Sea Coast 235

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Fig. 12.1 Geographic setting along the southern Baltic Sea coast. Pleistocene substrate is shownin grey, Holocene coastal barriers are shown in red. Feeder cliffs are divided into two categoriesregarding altitude (bold line indicates cliff height mainly > 40 m). Note the course of the –10-and –20-m isobaths, which characterize the different offshore relief east and west of the Fischlandbarrier

–15 to –18 m at the edges to the proper basins in the Baltic, where marine mud accu-mulates. In some places, drowned river valleys such as the Oder palaeo-valley canbe traced, incised during the Late Glacial and Early Holocene, when the water tablein the Baltic basin was lowered to about 40 m below mean sea level (msl), i.e. to−40 m. During this period, large areas of the present sea bottom were characterizedby a landscape of wetlands, shallow lakes and even forests.

When the eustatic sea-level rise had risen to the altitude of the thresholds of theGreat Belt system in Denmark, the Baltic basin became connected to the NorthSea. This first intrusion of saltwater into the Baltic basin took place at around9,800–9,200 year cal BP when marine waters could enter through the Great Belt(Winn et al. 1998, Jensen et al. 1997, 2005, Bennike et al. 2004, Björck 2008).The subsequent sea-level rise is called the Littorina transgression in the Baltic Seaduring which the landscapes of today’s coast drowned. During the early transgres-sion phase, the rise was rapid, more than 10 mm/year, but slowed later on. Earlierinvestigations have shown that on Rügen the sea level reached a position of –5m by c. 8,000 year cal BP and a level between –1 and –0.5 m at c. 6,500 yearcal BP (Kliewe and Janke 1982). This period, during which the rate of sea-levelrise largely decreased, is believed to be the time when the main coastal sedimentwedge accumulated between the Pleistocene headlands, thereby isolating lagoonsfrom the Baltic. During the subsequent some thousand years, the sea level varied

236 R. Lampe et al.

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only slightly, and shoreline evolution was characterized mainly by progradation anddune belt development.

The recent relative sea-level change was investigated using repeated precisionlevelling and long-term mareograph records (Montag 1967, Bankwitz 1971, Liebsch1997, Dietrich and Liebsch 2000). The change in pattern, constrained from the latter,is shown in Fig. 12.2. It indicates a shoreline tilt with a relatively slower sea-levelrise on Rügen than is at Wismar. The eustatic rise during the past 100 years isestimated to be 1–1.2 mm/year (Dietrich and Liebsch 2000, Stigge 2003). It cor-responds to the relative rise between the Fischland and the coastal section westof Warnemünde and means that a slight but increasing crustal uplift occurs fromthere towards Rügen and a subsidence towards Wismar and Travemünde. This wasalready concluded by Kolp (1982) and Ekman (1996), who marked the –1 mm/yearisobase as the isoline where the glacio-isostatic emergence fades out.

12.3 Data Acquisition

Sea-level curves deduced from regionally distributed data might be flawed by differ-ential crustal motions. To avoid this source of error, Kíden et al. (2002) recommendsampling areas not larger than 15–30 km in diameter to guarantee that differencesin the crustal movement within the area are small and negligible. For this investiga-tion, data from the three study areas, Wismar Bay (Lampe et al. 2005), Fischland andNorth Rügen/Hiddensee (Lampe et al. 2007), were used which are located along the


gradient of the recent relative sea-level change (Fig. 12.2) and are less than 25 km indiameter. The mareograph records from Wismar, Barth and Saßnitz which representthe relative sea-level rise in these study areas, show a secular rise of 1.4, 1.0 and0.6 mm/year, respectively (Dietrich and Liebsch 2000).

In these areas, peat samples from both basal peat layers (sensu Lange and Menke1967) and coastal mire profiles (Lampe et al. 2007) were taken, retrieved duringonshore and ship-based offshore surveys. To evaluate the sea-level control, the sam-ples were checked for the intensity of marine influences using pollen, diatoms andfloral macro remains (Endtmann 2005, Lampe 2004, Lampe et al. 2005, Mandelkowet al. 2005). Floral macro remains from these samples or bulk subsamples were14C-AMS dated. The data set was extended by datings from both underwater in situfinds of tree stumps and archaeological finds (bones and woods). In a few cases,previous 14C dates from basal peat layers were considered, which were convention-ally analysed. All age data were calibrated to calendar years before present (yearcal BP) using CalPal software (Danzeglocke et al. 2007). The 2σ confidence inter-val in the calendar age ranges was used in the construction of the sea-level curves.To estimate the altitude error, all sample depths were related to recent mean sealevel. Considering the many errors possible when relating the position of the sam-ples to the former sea level, its altitude can be determined with an accuracy of –0.1to –0.5 m for precisely levelled sampling sites and +0.2 to –0.8 m for all othersites. These age–depth ranges were used for the construction of the relative sea-levelcurves and their error envelopes (Lampe et al. 2007).

To determine the pre-transgressional relief, the distribution of the coastal sed-iments, their thickness and facies were surveyed extensively by means of motorhammer-driven drilling equipment. Ground penetration radar (GPR) surveys werecarried out for layer tracing between the auger holes and for recognizing internalstructures (van Heteren et al. 1999; Jol et al. 2003; Neal 2004) except in artificiallydrained areas where introduced saltwater prevented useful measurements (Lampeet al. 2004). For ship-based offshore investigations, a 4-m vibrocorer was used.Sediment echosounding (SES) surveys were made off Zingst, Rügen and Usedom,using an INNOMAR SES-96 set. Signal recording was restricted to 10 or 15 mbelow the sediment surface.

To estimate the volumes of the barriers, all information from geological maps,drilling results and GPR surveys regarding the depth of the transgression contactwere gathered and checked against each other. Based on these data the pre-transgressional land surface was modelled using an ordinary kriging algorithm fromstandard geostatistical software (Keckler 1997). For the present land surface a digitalelevation model from the State Survey Office was used and for consistency rea-sons was recalculated to the same resolution as the surfaces modelled. On averagethe modelled surface deviates less than 10% from measured depths. The differencebetween the pre-transgressional land surface and the recent land surface representsthe volume of the sediments accumulated under marine–brackish or aeolian condi-tions. This volume was recalculated to match a volume assumed to have been erodedfrom neighbouring Pleistocene feeder cliffs.

238 R. Lampe et al.

12.4 Investigation Results

12.4.1 Sea-Level Development

In all study areas the sea-level development shows the same tendency (Fig. 12.3). Inall of them, the rapid rise ended at about 7,500 year cal BP as also found by otherinvestigators (Fig. 12.4). The subsequent development was characterized by a veryslow rise or even stagnation with minor variations. Neither desiccation horizons incoastal mire profiles nor intercalated peat horizons in the sandy barriers have beendetected. This finding supports the statement that sea-level variations with ampli-tudes wider than the estimated error band of sea-level determination did not occur.Short-term fluctuations of more than 1 m as described by Behre (2003) or Yu (2003)and Yu et al. (2007) from neighbouring areas (Fig. 12.4) were not found and cannotbe confirmed. During the last c. 1,000 years the rise became more important again(Late Subatlantic transgression; Lampe and Janke 2004) but was interrupted dur-ing the Little Ice Age. During this period a prominent black pitchy soil layer wasformed in the coastal mires, possibly caused by peat desiccation and degradation.Comparable layers were described from many sites along the German and DanishNorth Sea coast (Freund and Streif 1999, Gehrels et al. 2006) and indicate that LittleIce Age sea-level changes were a widespread phenomenon. At the southern Balticcoast, it was probably the only significant oscillation throughout the last 5,000 years.For other minor fluctuations, as during the Bronze Age, vague but not convincingevidence exists.

Despite the similarity of the three sea-level curves, they differ regularly in thedepth–age relationship, indicating a persistent movement of the Earth’s crust andthus signifying isostatic movements, with most isostasy on Rügen and least in theWismar Bay. More information about this process can be gained only by using geo-physical models or by comparing the relative curves with a curve from a nearby areabelieved to be tectonically stable. As the German North Sea coast (sea-level curvefrom Behre (2003) in Fig. 12.4) was recently identified as a subsiding region (Vinket al. 2007) and most of the Baltic coasts are influenced by uplift (sea-level curvefor S-Sweden in Fig. 12.4 from Yu (2003)), the nearest curve suitable for compari-son is located at the Belgian North Sea coast (Fig. 12.4; Denys and Baeteman 1995;Kíden et al. 2002). A sea-level development comparable to what was observed atthe German Baltic coast can be expected for the Polish coast (Fig. 12.4, Uscinowicz2003) as the tectonic and isostatic conditions are similar (Garetsky et al. 2001).Due to the data available from the south Baltic coastal area, the comparison wasrestricted to the period since 8,000 year cal BP (Fig. 12.4).

From the correctness of all curves provided, three conclusions can be drawn: (i)the intense sea-level fluctuations found by Yu (2003) and Behre (2003) are not con-firmed by other investigators, although minor variations are definitely not excludedwhen sea-level error bands are considered. (ii) The curve from the German NorthSea coast is related to mean high water level and all other curves to mean sea level,i.e. the altitude of the German North Sea curve is usually lower than all others. (iii)The assumption of a tectonically stable Belgian coast allows inferences onto the


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Fig. 12.3 Relative sea level (RSL) curves for the Wismar Bay (a), Fischland (b) and northRügen/Hiddensee (c). Red triangles designate data from terrestrial deposits, green diamonds desig-nate telmatic deposits and blue circles designate archaeological finds in marine nearshore deposits.Horizontal bars represent double standard deviation (2σ ), vertical bars indicate estimated altitudeerror of sea-level position. The sea-level curves are depicted as error envelopes within which thesea-level position most probably was located

240 R. Lampe et al.

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Fig. 12.4 Error bands of the RSL curves for Wismar Bay, Fischland and N-Rügen/Hiddensee. Forcomparison the RSL error band of the Belgian coast (Kíden et al. 2002) and the RSL curves ofS-Sweden (Yu 2003), the Polish Baltic coast (Uscinowicz 2003) and the German North Sea coast(Behre 2003) are shown

isostatic movement of the other coastal areas. Higher sea-level curves are influencedby uplift, while the lower ones are influenced by subsidence. The north-easternGerman coast, therefore, belongs to the outermost edge of the Scandinavian uplift,where the isostatic upheaval, or unloading effect, fades out. In the areas aroundWismar and Fischland, the isostatic emergence already ceased more or less but itprobably continues on Rügen. More recently, for the Wismar area, even a slightsubsidence seems possible. These conclusions are in line with the results of thegauge investigations. Also the Polish coast seems to be stable. However, this curveand the German North Sea curve were constructed from regionally wider distributeddata and, therefore, differences in movement between single coastal sections werepossibly not detected.

12.4.2 Relief Prior to Transgression

From Fig. 12.1, differences regarding the extent of the barriers along the north-eastern German Baltic coast can be deduced. Obviously, more barriers occureastwards of the Fischland than westwards and are wider, longer and probably more


voluminous. To investigate the causes of this barrier size distribution, numerousdrillings and GPR surveys on the barriers, vibrocoring and SES surveys offshoreand in the lagoons were carried out. The extensive fieldwork resulted in an in-depthknowledge regarding the internal structure and facies distribution of the sedimentsfrom which the relief prior to the transgression can be deduced (Fig. 12.5 showsexamples). In the coastal area from Usedom Island in the east to the Fischland in thewest, the Pleistocene uplands consist predominantly of glacio-fluvial/lacustrine sandwith some till beds and are characterized by a highly undulating relief with eleva-tions up to +60 m and interjacent depressions down to –20 m. Up to a level of c. –12to –8 m the depressions are filled with slightly carbonate-bearing fine-to-mediumsand, containing diatoms and molluscs, indicating cold freshwater environments(Fig. 12.5a). The AMS radiocarbon dates imply that they are of Late Glacial Age,i.e. older than 11,700 year cal BP (cf. Walker et al. 2009). The surface of the LateGlacial sand dips very slightly to –15 to –18 m northwards towards the proper Balticbasin where a steeper decline occurs (Fig. 12.1). In the surface, numerous dead icedepressions are indented and completely filled with interbedded fine sand and silt(Fig. 12.5b). Also, some palaeo-channels intersect the surface. The most prominentone is the wide Oder palaeo-valley, located east of Rügen (Fig. 12.1). The surface

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Fig. 12.5 a Example of a GPR record from Hiddensee Island; for location, see line 3 in Fig. 12.6.Depth is calculated as 0.053 m/ns. b and c Examples of SES records from the Falster–Rügen plane;for locations, see lines 1 and 2 in Fig. 12.6. Depth is calculated as 1,500 m/s

242 R. Lampe et al.

of the sandy deposits undulates only slightly and points to a connected Late Glacialfluvio-lacustrine system in the Pomeranian Bight, the Rügen lagoons and the Darss-Zingst area (Lampe 2005). Shallow water-filled depressions, which remained afterthe final drainage of this system, accumulated freshwater mud or lake marl duringthe Early Holocene and mostly silted up in the mid-Holocene.

By contrast, in the area west of the Fischland, the coastal relief is widely char-acterized by higher ground with long till cliff sections. The abrasion platforms infront of the cliffs are covered mostly by lag sediments and show a steeper inclina-tion towards the Baltic basin. Sandy sediments are rare. Only in the Wismar Baya more complex palaeo-valley system determines the relief, incised in the loamyground moraine (Harff et al. 2007). The main differences between the coastal sec-tions located east and west from the Fischland, therefore, are (i) the existence ofdepressions reaching far below the recent sea level, (ii) the availability of sandymaterial from both offshore and onshore sources and (iii) the inclination of thepalaeo-relief towards the proper Baltic basins.

12.4.3 Structure and Volume of Coastal Barriers

The rising Baltic Sea caused groundwater rise in the adjacent coastal mainlandand thus favoured peat accumulation upon the land surface. This ‘basal peat’,mostly some centimetres to two decimetres thick, was later inundated due to thelandward-migrating shoreline. The transgression contact is often marked by a hia-tus of several hundred years due to the erosion of the peat top layer. Usually,a clear nearshore/beach facies cannot be observed or consists only of 1-cm-thick sandy layer. These deposits are overlain by muddy sediments consisting ofsilt with different admixtures of fine sand and up to 25% organic matter. Thelowermost section is strikingly enriched with shells of Hydrobia sp., Cerastodermasp. and Scrobicularia sp., indicating an evolutionary stage where the barriers notyet existed and the present lagoon areas were still bays of the Baltic. The mud grad-ually changes into sand which built the main base of the barrier. At the seasideof the barriers the grain size is coarser, sometimes gravelly, while at the lagoonside, mud–sand interlayerings are observed, which change upwards into fine sand(Fig. 12.6).

Peat is never intercalated in the siliciclastic sequence; only allochthonous flo-ral detritus layers occur. This is an important difference from the coastal sedimentsequence described for the southern North Sea (Behre 2003, Streif 2004) andunderlines the statement that no significant sea-level fluctuation occurred duringits accumulation. At the sea coast the surface of the marine sand package is coveredby progradational beach ridges and dunes, and on the lagoon side the barrier surfaceis flat and covered with fenland peat (‘cover peat’). Radiocarbon datings show thatthe cover peat accretion began at about 800–1,200 year cal BP (Jeschke and Lange1992, Lampe and Janke 2004).

The dense net of boreholes in combination with about 80-km GPR tracks, whichfacilitate interpolation between the drilling profiles, allows for modelling of the base


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and the surface of the coastal sediments and calculation of the volume of the barriers.The sediment volume located at the shoreface was neglected, due to the mostlyuncertain distribution and thickness in the near-coastal zone. The estimated volumesare shown in Table 12.1. Two arguments allow relating the barrier volume with theretreat of the neighbouring cliffs:

(a) In the study areas, no rivers are located, which would deliver significantamounts of sandy material having the potential for nearshore accumulation.

(b) Due to the many offshore finds of Preboreal, Boreal and Early Atlantic lakes,mires, forests and archaeological sites, we can exclude any significant erosionand landward sediment transport to build up the barriers.

The above arguments imply that the predominant part of the barrier sand vol-ume must have been provided by cliff abrasion, and maybe also to a minor extentby shoreface abrasion. Considering the height and length of the feeding cliffs, the

244 R. Lampe et al.

Table 12.1 Volume of selected coastal barriers and corresponding retreat of feeder cliffs at thesouthern Baltic coast (Barthel 2002, Hoffmann 2004, Naumann 2006) during the last 8,000 years.For barrier and cliff locations, see Fig. 12.1

Coastal barrier (no.in Fig. 12.1)

Estimated volume(mill m3)

Mean length/heightof feeding cliffs (m)

Calculated cliffretreat (m)

Kieler Ort (2) 11 4,000/4 690Zingst (6) 450 No cliff ?Hiddensee (7) 270 4,500/40 1,500Bug (8) 66 8,000/8 1,030Schaabe (9) 103 17,300/35 170Peenemünde (13) 420

10,500/30 1,810Pudagla (14) 150

above-mentioned volumes correspond to a mean cliff retreat during the last 8,000years as listed in Table 12.1. Similar estimations were published by Uscinowicz(2003, 2006), who assumes that the Polish coast has receded 1,000–1,500 m.

Except for the Zingst study area, all barriers can be explained to be built upmainly from eroded sediment from the nearby cliff sections. For the Zingst penin-sula, the provenance of the sandy material is more difficult to explain; an obviousfeeder cliff does not exist today. The offshore area is widely covered by silty sed-iment of glacio-lacustrine origin (Fig. 12.1) which cannot provide barrier buildingsand. The only possible sources are hypothetical glacio-lacustrine/fluvial sand bod-ies scattered offshore in the vicinity of today’s peninsula. Analogue sediment bodieswere found at the base of the coastal barriers building the backbone of the recentpeninsula (Fig. 12.6). These sediments probably built the glacial lake shore andfringing small deltas and were fluvially intersected after the lake level fell. Theform and extent of these sediment bodies cannot be reconstructed because they arenow completely eroded. The eroded material built spits which became permanentlyreshaped and transgressed with the rising sea level to the recent position of thepeninsula. Behind the slowly moving spits, slack water areas occurred temporarily.Here, small-sized thin lagoonal mud layers accumulated which are located todaysome hundred to thousand meters offshore of Zingst and Hiddensee and are theonly remaining traces of the transgressive proto-barriers.

12.5 Discussion and Conclusions

The internal structure of the barriers shows some critical aspects. The lagoonal mudunderlying the barrier sand was deposited under calm and sheltered conditions, pro-vided by seaward islands, spits or barriers. Further, the occurrence of mud impliesa barrier transgression over the lagoonal sediments and to the limited extent of thebarrier shift (Hurtig 1954, Kliewe and Janke 1982, Lampe 2005). As evident fromship-based offshore investigations (vibrocoring and SES surveys), non-compactedLate Glacial and Early Holocene lake and peat deposits exist seawards of the present


barriers, but relict estuarine mud are not found there, with the exception of the off-shore Zingst and Hiddensee areas. That means that no barriers developed during theearly transgression phase and only narrow, flat, exiguous beach ridges transgressedrapidly over the very gently dipping surface (0.05 . . . 0.15◦, inherited from LateGlacial lakes) driven by the rising sea. Some few overstepped beach ridges occuronly where coarse gravels crop out (Gromoll 1994). Although much sand has beenavailable for sediment transport, the shape and character of the surface left by theLate Glacial drainage system and the modest current and wave energy of the Baltic,further reduced by bottom friction effects, prevented barrier formation. Hence, wecan confirm the results of barrier translation models (Roy et al. 1994, Stolper et al.2005) that on a flat substrate, increasing friction and decreasing wave power led toa reduction in barrier size.

The transgressive beach ridges finally stranded at the toes of the Pleistocene ele-vations interspersed mostly seawards between the Late Glacial lake sediments. Dueto the steeper substrate slope, the shoreline recession decelerated and erosion possi-bly started. At that point the ratio between sediment supply and accumulation spacebecame critical and determined whether the volume of the beach ridges grew anddeveloped into spits and barriers or the elevations were finally eroded and drownedand the embryonic spits were eroded. Under this perspective it becomes clear thatsmall elevations may play a special role in the process of beach ridge stranding.They fix the migrating beach ridges/barriers but can maintain them for a longertime only if (i) they will not get drowned by the rising sea and (ii) the sedimentsupply is big enough to fill the still growing accommodation space. Therefore, thepresent barriers are all connected to viable feeder cliffs and in all of them, cores fromPleistocene sediment can be found. All lower elevations located farther seawardsbecame eroded, drowned and today, build shoals and reefs.

After the sea-level rise ceased – and hence the accommodation space started toshrink – the stranded spits grew faster. Where the distance between spit anchors(i.e. the accommodation space) was adequately small in relation to sand supply, spitends grew together and progradation started. This process led to the developmentof bay barriers with wide beach ridge plains and dune fields (Fig. 12.7). Where thedistance between the spit anchors was large compared to the sediment supply, thebays were not completely cut off from the open sea. In fact, these spits are stillgrowing, thereby receding landwards and traversing lagoon sediments (Hiddensee,Zingst, Bug, Rustwerder, Kieler Ort, see Fig. 12.1).

Large areas behind the beach ridges or dune belts on the barriers developed aswind flats, whose surface was levelled due to frequent floodings occurring throughshallow inlets. Vertical sand accumulation in the flats kept pace with the moderatesea-level rise until the inlets became truncated by a beach ridge and peat accumula-tion started (Fig. 12.8; Hoffmann et al. 2005). The preservation of wide flats behindthe beach ridges or dune belts is generally considered to be evidence of shoreline sta-bility or only slight retreat which is in accordance with the finding that the lagoonalsediments usually do not crop out at the sea shoreface.

Where the headlands or islands which provided anchor or hinge points to the bar-riers were not high or voluminous enough to survive, they drowned or were abraded,

246 R. Lampe et al.

A

B

Fig. 12.7 Aerial image of the barrier Schaabe; view is towards east and the Baltic is located on theleft side (for location, see Fig. 12.1, no. 9). Two beach ridge systems are evident: an older system(A), which consists of short, low-lying ridges, bent into the former bay and a second system ofhigher elevated dune ridges (B), which cut off the bay from the sea and show rapid progradation.This system is covered by dense pine forest (Photo: R. Lampe 2007)

A

B

C

Fig. 12.8 Aerial image of the eastern tip of the Zingst peninsula and the offshore sand flats andislands; view is northwards (for location, see Fig. 12.1, no. 6). The inlet is progressively truncatedby a spit (A) growing from west (left) to east (right). Sand flats (B) with incised flooding channelsspread between the islands. In the northern part of the offshore island, progradational beach ridges(C) are visible (Photo: R. Lampe 2007)


thereby opening new sediment transport passages. The former barrier eroded and thesediment was incorporated in a new spit/barrier structure evolving further landwardsat higher elevations. Finally, where the sediment supply exceeded accommodation,the bay was filled and the prograding beach matched the neighbouring coastal cell(Hoffmann and Barnasch 2005). Many permutations are possible between these evo-lutionary types. It can be concluded that the barriers and spits transgressed onlyto a minor extent and only when hinge points were drowned or abraded or whenspace between anchor points was too large. The main processes in shaping of thepresent coast have been stranding, progradation and elongation and are significantlycontrolled by the inherited relief.

The rough volume calculation emphasizes the assumptions that the cliffs pro-vided enough material to build up the barriers and that they receded between 1 and2 km since the Littorina transgression reached the present coastal area. Therefore,the anchor points of the spits experienced approximately the same dislocation. Whenthe sea-level rise decreased at 7,800 year cal BP and, hence, accommodation spacegrew slower, the main phase of barrier building started. In the subsequent 1000 yearsor so, the sediment supply from cliff erosion still continued due to ongoing coastalre-equilibration but exceeded the steadily shrinking accommodation, thus causingfast barrier building. However, this process was different in the three study areas.While on Rügen the spits were rapidly closed to prograding barriers, this processtook much more time in the Darss-Zingst area and occurred in the Wismar Bight toa very limited extent. The difference is caused by both factors: sediment starvationin the Wismar area where cliffs providing sufficient sediment are rare and accom-modation space, which decreased much faster on Rügen than at Wismar due to themore rapid isostatic uplift.

The slowing down of sea-level rise between 6,000 and 1,200 year cal BP ledgradually to a decrease in sediment supply and – in sections – to cliff stabiliza-tion, which must have been most pronounced on Rügen. Since c. 1,200 year cal BP,coastal dynamics has increased again as is evident by the occurrence of transgressivedunes. From the younger historical record, fast elongation of spits and impendingbarrier breaching is known. The increased dynamics can be related to the onset ofthe post-Littorina (Late Subatlantic) transgression, the timing of which is evidentfrom the accumulation of the cover peat.

12.6 Summary

To study the interplay between sea-level evolution, crustal movement, accommo-dation and sediment supply, new and detailed investigations of the evolution ofthe southern Baltic coast were conducted based on intensive drilling and geophys-ical surveys both onshore and offshore. An important result of the project wasthe identification of three local relative sea-level curves which clearly show thata fading crustal upheaval occurred which is still in progress on Rügen and – to aminor extent – on the Fischland area, while the movement ceased or changed to aslight subsidence in the Wismar Bay. Because the new RSL curves are well proven

248 R. Lampe et al.

by both archaeological and geological evidence and based on a consistently cali-brated 14C-AMS data set, much clearer conclusions can be drawn about sea-levelfluctuations than before.

Backed by a comprehensive borehole data set, the existing ideas about theHolocene coastal evolution in the southern Baltic were critically evaluated. Itcould be shown that the sediments underlying the barriers belong to a complexfluvio-lacustrine drainage system of Late Glacial Age. Also, the large flat sand/siltdeposits of Usedom and Zingst were primarily built in the Late Glacial period andwere reshaped only slightly during the main Littorina transgression phase. Thisunderlines the importance of the sea-level rise rate for coastal erosion processes.Higher rates cause flatter shoreface profiles which deflect from a Bruun-like equi-librium. When the rise rate decreases, the shoreface profiles tend to rebuild anequilibrium which leads primarily to higher erosion due to deeper profile mould-ing, but to decreasing erosion (and sediment supply) with ongoing approach toequilibrium.

All data from the Fischland in the west to the Usedom Island in the east pointto the existence of an interconnected Late Glacial fluvio-lacustrine system whichcan be related to a level of –8 to –12 m found below all West Pomeranian barriers.During the Littorina transgression the flat surface of these deposits was inundatedvery rapidly and its small inclination is assumed to be the reason that less volu-minous beach ridges/barriers developed and migrated with the transgressing sea.Only at locations of steeper ground could small coastal features like spits grow, butthey were eroded or overstepped when the hinge points drowned. After the sea-level rise became slower at c. 7,800 year cal BP, the sediment supply exceeded thegrowth of the accommodation space. Large beach ridge systems began to accu-mulate at higher elevated islands and promontories and developed into barriers.Progradation started and in bays with closed sedimentary systems, barriers wereshaped to perfectly swash aligned beaches. The sediment volume finally incorpo-rated in the barriers corresponded to a 1–2-km retreat of the feeding cliffs. Shoreprofiles became equilibrated due to the very slow rise rate and the cliff retreat ratesdecreased.

An important alteration in the sediment dynamics occurred with the onset ofthe Late Subatlantic transgression which started at about 1,200 year cal BP. Formerprogradation changed into retrogradation which was connected with sediment mobi-lization and faster shoreline erosion leading to elongation of spits, more frequentinundation and overwash and the development of transgressive dune fields. On theback barriers, peat accumulation started. After an interruption of the rise due to theLittle Ice Age, the higher dynamic mode in coastal behaviour continues after about1850.

Acknowledgements This study was possible due to the financial support provided by theDeutsche Forschungsgemeinschaft, which is gratefully acknowledged (FO 488/1). We thank allmembers of the SINCOS Research Group for valuable data and discussions, and students andstaff from Greifswald University for their help in the field and laboratories. We acknowledgethe recommendations of three anonymous reviewers and the editors which helped to improve thechapter.


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[Central and Eastern European Development Studies (CEEDES)] The Baltic Sea Basin || Holocene Evolution of the Southern Baltic Sea Coast and Interplay of Sea-Level Variation, Isostasy,