JOURNAL OF QUATERNARY SCIENCE (2006) 21(8) 905–919Copyright � 2006 John Wiley & Sons, Ltd.Published online 12 May 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jqs.1011

Storminess variation during the last 6500 yearsas reconstructed from an ombrotrophic peatbog in Halland, southwest SwedenRIXT DE JONG,1* SVANTE BJORCK,1 LEIF BJORKMAN1 and LARS B. CLEMMENSEN2

1 Quaternary Sciences, Lund University, Lund, Sweden2 Geological Institute, University of Copenhagen, Copenhagen, Denmark

de Jong, R., Bjorck, S., Bjorkman, L. and Clemmensen, L. B. 2006. Storminess variation during the last 6500 years as reconstructed froman ombrotrophic peat bog in Halland, southwest Sweden. J. Quaternary Sci., Vol. 21 pp. 905–919. ISSN 0267–8179.

Received 28 September 2005; Revised 9 December 2005; Accepted 18 January 2006

ABSTRACT: Cores taken from an ombrotrophic peat bog in the coastal zone of Halland, southwestSweden, were examined for wind transported mineral grains, pollen and humidity indicators. Thecore covers the period from 6500 cal. yr BP to present. Ombrotrophic conditions existed from ca.4200 cal. yr BP onwards. Bog surface wetness fluctuated strongly until ca. 3700 cal. yr BP, with anapparent dominance of dry summer conditions from 4800–4500 cal. yr BP. Local wet shifts occurredaround 4300, 2800, 2400 and 1500 cal. yr BP, whereas the most recent 600 years of the record showincreasingly dry conditions. Mineral grain content, interpreted as aeolian sand influx (ASI), was usedas a proxy for (winter) storm frequency and intensity until ca. 1500 cal. yr BP, after which increasinghuman impact, as reconstructed by pollen analysis, became a second important potential cause forincreased sand drift. Strongly increased storminess occurred at 4800, 4200, 2800–2200, 1500, 1100and 400–50 cal. yr BP, indicating a dominance of cold and stormy winters during these periods.Many of these storm periods apparently coincide with storm events in other sites in southwesternScandinavia, suggesting that our ASI record reflects a regional scale climatic signal. Furthermorethese stormy periods correlate to well-known cold phases in the North Atlantic region, suggestinga link to large-scale fluctuations in atmospheric circulation patterns. Copyright � 2006 John Wiley& Sons, Ltd.

KEYWORDS: Holocene; sand drift; storminess variation; ombrotrophic bog; atmospheric circulation.

Introduction

The climate of the North Atlantic region has experienced con-siderable variability on a wide range of time scales (Hurrell,1995). Although climate reconstructions exist for many sitesaround the North Atlantic basin, it has proved more difficultto explain the observed climatic variability. To describe betterthe variations in the climatic system, knowledge of past atmo-spheric circulation changes is essential. At present, the domi-nant pattern of atmospheric circulation variability in theNorth Atlantic region is the North Atlantic Oscillation (NAO).The NAO is defined by the pressure gradient between theArctic and subtropical Atlantic in winter (Hurrell et al., 2001)and is expressed most clearly in winter. In general, a strongpressure gradient (positive NAO) is associated with increasedwesterly storms and milder winters in the North Atlantic region(Hurrell and Van Loon, 1997; Dawson et al., 2002, 2003),whereas in a negative NAO phase cyclone tracks arepositioned further south and are generally weaker. However,

Dawson et al. (2002) have shown that in recent times increasedstorm activity in northwest Europe has occurred during bothpositive and negative NAO situations. Dawson et al. (2002)argued that the increased storminess during the latter climaticscenario was linked to the formation of high pressure overIceland and the build up of sea ice in the Iceland/GreenlandSea causing a southward deflection of storm tracks. Therefore,knowledge about past NAO variations cannot be used directlyto determine past storminess variations and vice versa.However, if detailed information on storminess is combinedwith temperature and humidity records for example, it maybe possible to reconstruct likely atmospheric circulationpatterns that are associated with these stormy periods.Until recently, little was known about past storm frequency

and intensity in the period prior to instrumental measuring (ca.AD 1750) (Lamb, 1991; Jonsson, 1994). However, studiesof coastal dunefield development in many parts of northwestEurope have added to our knowledge of past storminess varia-tions (Pye and Neal, 1994; Wilson et al., 2001; Clemmensenet al., 2001c; Clarke et al., 2002; Wilson, 2002; Wilsonet al., 2004).In a study by Bjorck and Clemmensen (2004) the amount

of aeolian sand influx (ASI) into two raised bogs in Halland,southwest Sweden was used as a proxy for winter storminess.

*Correspondence to: R. de Jong, Quaternary Sciences, Lund University,Solvegatan 12, Lund 22362, Sweden. E-mail: rixt.de_jong@geol.lu.se

Sand influx is, however, also influenced by sediment availabil-ity, which is controlled mainly by the degree of vegetationcover and the moisture content of the sediment (Li et al.,2004; Wiggs et al., 2004). Intense cultivation, overgrazingand forest disturbance make soils more prone to erosion, whichcan lead to increased sand transport even under less windyconditions. Therefore knowledge of the extent of humanimpact is necessary to interpret increased sand drift correctly.To discern between human and climatic impact on sand

transport, this study combines detailed pollen analysis withaeolian sand influx (ASI) reconstructions on a peat sequenceaccumulated in an ombrotrophic bog. The Undarsmosse bogis situated on the coastal plain of the province of Halland,southwest Sweden (Fig. 1). This area is particularly sensitiveto changing storm frequencies since it is positioned in the pathof cyclones (Lamb, 1977). The bog site is open to winds from alldirections, ensuring that the ASI index records all past sand driftevents in the area. The use of raised bogs as an archive has theadvantage of continuous sedimentation and relatively easy dat-ing procedures. Therefore, as compared to dune developmentstudies, this study provides a well dated and continuous record

of past sand drift events in the region. We present a detailedreconstruction of aeolian sand influx (ASI) variation, vege-tation change and human impact in the study area from6500 cal. yr BP to present. These data are combined with otherstudies from southwestern Scandinavia to allow for a regionalscale reconstruction of past storm frequency and intensity.

Study area

The Undarsmosse bog is situated 2.5 km inland on the coastalplain of Halland (Fig. 1). The coastal plain is 10–20 km wideand the elevation generally lies between 10 and 25ma.s.l.However, bedrock hills reaching up to 140ma.s.l. are foundclose to the present coastline in central and northern Halland.These hills, as well as the bedrock underlying the coastal plain,predominantly consist of gneisses and gabbros (Caldeniuset al., 1956). East of the coastal plain the terrain rises up to200ma.s.l. The coastline is characterised by a mix of beach

Figure 1 Location map showing the location of Undarsmosse bog in Halland, southwest Sweden, as well as the position of other studies mentionedin the text; B, Boarps mosse (Bjorck and Clemmensen, 2004); H, Hyltemossen (Bjorck and Clemmensen, 2004); K, Karingsjon (Bjorkman and Persson,2005); S, Sandsjon (Thelaus, 1989); and V, Vejers dunefield (Clemmensen et al., 2001a, in press)

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ridges and extensive dune areas, (marine) reworked tills, mor-aine ridges and bedrock outcrops (Caldenius et al., 1956;Caldenius, 1966).The deglaciation of the Halland coastal plain is dated to

16000 cal. yr BP (Lundqvist and Wohlfarth, 2001). However,after initial deglaciation the ice margin fluctuated consider-ably, resulting in thick glaciofluvial and glaciomarine depositswest of the ice margin (Berglund, 1995). The relative sea-levelchanges of the region have been substantial; the marine limit issituated 50–80ma.s.l (von Post, 1947; Berglund, 1995).Around 10000 to 10 500 cal. yr BP a regression maximumto 20m below present sea level took place, followed bya transgression to 8m above present sea level around7000–6000 cal. yr BP (Bjorck, 1987). This maximum wasfollowed by an oscillating, but gradually falling sea level(Morner, 1969). This implies substantial reworking of the gla-cial sediments on the low-lying coastal plain, whereas the bed-rock hills must have been islands during the time of maximumsea level.

Site description

The study site (Fig. 1) is an ombrotrophic bog situated at20ma.s.l. The areal extent of the original peat bog is ca.3.15 km2. The modern bog surface is, however, approximatelyonly half that size owing to extensive peat cutting. The bogis situated in a basin with a threshold in the northern part at16–17ma.s.l. (Caldenius et al., 1956; Caldenius, 1966). Thebasin is flanked by low bedrock hills to the east and west,which are partially covered by silty tills. Cores were taken inthe northern part of the basin at approximately 100m fromthe western edge of the modern bog surface, where the flankinghills are lowest. The terrain to the north and south is flat.The Undarsmosse basin was isolated from the sea at ca.12 000 cal. yr BP (Berglund, 1995).The vegetation on the hills is dominated by pine plantations.

The hill in the west is part of a nature reserve and has morediverse vegetation with beech forest, alder fen and grazingareas. The bog is surrounded by a narrow rim of birch and pinetrees, growing on the relatively dry areas where extensive drai-nage and peat cutting has taken place. Outside this area inten-sive land use is carried out on the peaty soils. The modern bogvegetation is dominated by Calluna vulgaris and several otherEricaceae species in the field layer, whereas the bottom layer isdominated by Sphagnum spp. Low pine and birch trees occurin small groups. The bog is still growing today.Sandy sediments are found immediately west and east on the

northern flanks of the basin at a minimum distance of 600m tothe coring location (Passe, 1988). Northwest and west of thesite, small active dune areas are present, whereas in 1819Brandberg (in von Post, 1933) mapped an additional activesand drift area immediately south of the bog.

Climatological setting

The province of Halland lies in the path of westerlies, produ-cing a mild coastal climate with cool summers (16 �C July aver-age temperature) and relatively mild winters (�4 �C Januaryaverage temperature). At present annual precipitation is around900mmyr�1 and the mean number of days with snow covervaries between 75 and 100 days (Raab and Vedin, 1995).The weather is, however, extremely variable being controlledby the frequency, intensity and position of the passing

low-pressure systems and associated cyclones. At present,wind patterns in southwestern Scandinavia show a clear E–Wbimodality, with the highest wind speeds associated with wes-terly directions. Westerly stormwinds are caused by cyclonespassing north of Halland towards the east (Jonsson, 1994). East-erly winds of storm force may occur when cyclones pass southof Halland, which is often associated with a high-pressure fieldsituated over northern Scandinavia. The easterly winter windscan bring snow, although westerly stormwinds can also carrysnow.

Methods

Corings were carried out in the central part of the bog using aRussian peat sampler (7.5 cm diameter). The corings were car-ried out in two parallel holes with considerable overlapping,thus ensuring full stratigraphic recovery. The depth of theorganic-rich deposits was 339 cm. Cores were described indetail in the field, then wrapped in plastic foil and stored in adeep freezer. Next, the frozen cores were cut into 2 cm seg-ments in the upper metre of the core, and 1-cm slices in thelower part. Each segment was sampled for pollen analysis,ash-free organic bulk density (OBD), ignition residue (IR) andmineral grain analysis, leaving a sufficient amount of materialfor 14C dating and other future analysis. Pollen analysis wascarried out on 47 samples, whereas OBD, IR and ASI valueswere measured at all 276 levels.The (frozen) samples for OBD, IR and mineral grain analysis

were weighed and the wet volume was estimated by water dis-placement (giving wet weight cm�3). The samples were thendried at 105 �C overnight and weighed to estimate water con-tent and dry weight cm�3. Subsequently the samples wereburnt at 550 �C for 4.5 h and weighed, providing the organiccarbon and ash content (IR). Since the water content, volumeand IR for each sample were measured, it was possible to cal-culate ash-free organic bulk density (OBD), i.e. dry weight oforganic matter cm�3 wet material. OBD is related to howfine-grained the peat is, i.e. decomposition rate. Therefore, itcan also be used as a proxy for the degree of humification. Ahigh OBD value is interpreted as representing a high degreeof humification (Bjorck and Clemmensen, 2004).The ignition residue was dissolved with 10% HCl and ana-

lysed using a 50� zoom stereomicroscope. The mineral parti-cles were divided into quartz and non-quartz grains andcounted. The quartz particles were divided further into threegrain-size classes; fine sand (125–200 mm), medium sand(200–350mm) and coarse sand (>350mm). For each samplethe maximum grain-size was measured. Since the volume ofeach sample was known and an age–depth model was avail-able, the concentration (grains cm�3) as well as the influx rateof each grain-size class, i.e. number of grains cm�2 yr�1, wascalculated.To avoid contamination, 2 cm3 samples for pollen analysis

were taken from the central part of each segment with a care-fully cleaned knife. Lycopodium tablets were added prior tofurther treatment to allow for pollen concentration and influxcalculations (Stockmarr, 1971). The samples were preparedfor pollen analysis following standard methods (Berglund andRalska-Jasiewiczowa, 1986; Moore et al., 1991) with an over-night cold HF treatment to ensure that all quartz particles weredissolved. The samples were sieved with a 125mm mesh.Microscope slides were prepared from the residue and pollen,Sphagnum spores and charcoal particles >25mm werecounted. The pollen keys in Moore et al. (1991) were used

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for determination of critical pollen types, as well as illustrationsby Reille (1992). The reference collection at the QuaternarySciences pollen laboratory at Lund University was used tocheck some determinations. The program Tilia (Grimm,1992) was used for the calculation of percentages and concen-trations and for the construction of the pollen diagram. Morethan 500 arboreal pollen grains were counted at all levelsexcept at two levels with very low pollen concentrations.At 14 levels samples were taken for AMS 14C dating, of which

13 were bulk peat samples and one sample (LUS-5959) wasdone on macrofossils of birch twigs, to check the reliabilityof the bulk samples (Table 1). All samples were taken fromthe inner part of a segment. The macrofossil sample was sievedand birch twigs with bark were picked out. The samples were

processed at the Radiocarbon Dating Laboratory in Lund andthe Poznan Radiocarbon Laboratory. The radiocarbon dateswere calibrated using the IntCal04 calibration curve (Reimeret al., 2004) using the OxCal 3.10 program (Bronk Ramsey,1995, 2001). All ages mentioned in this text refer to calendaryears before 1950 (cal. yr BP), unless stated otherwise.

Results and interpretation

Stratigraphy and OBD

The 339 cm thick sequence from the Undarsmosse bog consistsof gyttja and peat resting on a sandy silt with FeS laminations,which according to Berglund (1995) is of marine origin (Fig. 2).These lowermost minerogenic units are outside the scope ofthis study. Caldenius (1966), however, provides a stratigraphicdescription and pollen diagram of a few selected tree types forthe entire Holocene sequence.Units I and II are composed of clayey gyttja and carr

peat respectively, whereas all other units are composed ofSphagnum peat (Fig. 2(a)). OBD values fluctuate stronglyin the lowest part of the core, with high values from290–300 cm and 320–330 cm. A clear maximum is reachedat 298 cm depth (ca. 4850 cal. yr BP; Fig. 2(c)), indicating veryhigh humification of the peat and thus dry bog surface condi-tions. From 170 to 270 cm depth OBD values fluctuate arounda mean value of 0.18 g cm�3. At the transition from unit IIIto unit IV at 170 cm OBD values decrease strongly, reachinga minimum of 0.05 g cm�3 in unit V (ca. 1400 cal. yr BP).After this minimum OBD values increase slowly, reachingtwo peak values of 0.25 g cm�3 in the strongly humified sandypeat at 9 cm depth and at 19 cm depth (70 and 230 cal. yr BPrespectively).

Table 1 Radiocarbon dates from Undarsmosse bog and calibratedages, calibrated with the IntCal04 calibration curve (Reimer et al.,2004)

Depth (m) Radiocarbon age Calibrated age Laboratory no.(14C yr BP) (2� interval)

0.20–0.22 175� 50 310– �11 LuS-58390.30–0.31 490� 35 560–490 Poz-35930.66–0.68 1055�50 1080–900 LuS-58401.00–1.01 1250�40 1280–1070 Poz-35941.50–1.51 1605�60 1630–1350 LuS-58412.00–2.01 2150�40 2310–2220 2210–2000 Poz-35952.33–2.34 2565�60 2790–2450 LuS-58422.54–2.56 3200�50 3560–3340 LuS-59572.74–2.75 3425�50 3840–3560 LuS-59582.91–2.92 4275�60 4980–4780 4770–4610 LuS-59593.03–3.04 4580�60 5470–5040 LuS-58433.14–3.15 4575�80 5500–4950 LuS-58443.20–3.21 5285� 110 6300–5750 LuS-58453.29–3.30 5560�60 6480–6270 Poz-3596

Figure 2 (a) Stratigraphical units from the Undarsmosse core, showing the transition from marine clay to dark brown highly humified carr peat at5800cal. yr. BP, to light brown colours and lower degrees of humification after the formation of Sphagnum peat at ca. 4200 cal. yr. BP. (b) OrganicBulk Density values (OBD). (c) Age–depth model for the studied core, based on 14 calibrated radiocarbon dates. Sedimentation rates are lowest in thecarr peat and highest in the low humified Sphagnum sequence of stratigraphical unit IV–VI

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The gradual change from gyttja to carr peat to Sphagnumpeat in units I–III reflects the transition from an open laketo a fen with trees to a raised bog. The alternation of dark brownand light brown layers in units III–VIII is interpreted as reflect-ing different degrees of humification. Comparison betweenlithostratigraphy and the measured OBD values shows thatunits with an observed low degree of humification (light col-ours, units IV–VI and VIII) generally have lowOBD values. Thiscan be interpreted as an indication of wet (summer) conditionsand a long growing season during the formation of these units,resulting in increased primary production. It has to be kept inmind though that peat humification can take place a long timeafter deposition. The degree of humification does therefore notnecessarily reflect the conditions during deposition and anyshort-term variation may be obscured.

Chronology

The age–depth model (Fig. 2) is based on 14 radiocarbon dates(Table 1). From these dates the most likely age–depth modelwas constructed using a combination of a 7th and 10th degreepolynomial fit. The model shows a gradually changing accu-mulation rate ranging from 0.02 cmyr�1 in units 1 and 2 to0.14 cmyr�1 in units 4, 5 and 6. The uppermost sections showa return to lower accumulation rates (0.07cmyr�1). The vary-ing accumulation rate means that the sampled intervals (1 or2 cm) usually correspond to 10–30 yr, but below 270 cm depth1 cm of sediment represents 50 yr, and the measured values arethus a mean of that time slice. However, it is not knownwhether ASI peaks are formed during one single event or duringa series of events covering several years. Therefore it is likelythat the amplitudes of the ASI peaks occurring below ca.270 cm depth (ca. 3500 cal. yr BP) are underestimated as com-pared to younger peaks, since the influx values are divided overa longer time interval. Furthermore, since the 2� error is usedfor the age model it implies that the model should be seen as anenvelope around the curve (Fig. 2). These error margins shouldbe considered when peak events reconstructed here are com-pared to data from other sites.

Pollen stratigraphy and vegetation development

The simplified pollen percentage diagram in Fig. 3 shows themain features of the vegetation development from 6500cal. yr BPto present. Pollen types that occur sporadically or at very lowfrequencies have been omitted in the diagram, but are in-cluded in the pollen sum. Owing to the setting of the site in asemi-enclosed basin, the pollen diagram mainly reflects localvegetation changes, especially during the early part of thesequence. The regional component of the diagram becomesstronger as the landscape becomes more open. The pollen dia-gram was divided into six local pollen assemblage zones basedon visual inspection and cluster analysis of the data (Johnson andWichern, 1998).

Pollen zone UmA (6500–5400 cal. yr BP)

The complete dominance of Alnus pollen (70%), the very hightotal pollen concentrations (exceeding 1� 106 grains cm�3)and the lithostratigraphy of this interval indicate that during thistime the area was covered by an alder fen. The near absence of

pollen of light-demanding plants such as herbs and grasses(mainly below 2%), suggests a closed vegetation and a verylocal pollen signal. The low values for Ulmus and Tilia(<2%) indicate a restricted presence of these trees in thesurroundings, whereas the slightly higher values of Quercus(5–10%) indicate that oak was growing on drier ground inthe area.

Pollen zone UmB (5400–4600 cal. yr BP)

The clear decrease of Alnus (<15%) and increasing Quercusand Betula pollen grains (to 20% and 60%, respectively) indi-cate drier conditions at the study site. The fen was probably notas extensive as before and at the edges Sphagnum firstappeared. The strong increase of oak and birch pollen indicatesthat the vegetation around the coring site became more openand dry. The near absence of herb and grass pollen (<2%),however, indicates that the landscape was still characterisedby a closed vegetation and the pollen signal is almost entirelylocal, i.e. restricted to the basin and immediate surroundings.

Pollen zone UmC (4600–2600 cal. yr BP)

The appearance and continuous presence of Sphagnum sporesindicate that the fen was gradually overgrown by Sphagnumand a raised bog started to form at ca. 4400 cal. yr BP(Figs. 2 and 3). As a result, accumulation rates increased, whichis indicated by a dramatic decrease of the total pollen concen-tration from values exceeding 1� 106 grains cm�3 to valuesaround 0.2� 106 gr cm�3. Sphagnum values remain ratherlow (ca. 5%) until ca. 2900 cal. yr BP and the presence of Cal-luna indicates that conditions were relatively dry. However,bog surface wetness was sufficiently high to support the forma-tion of Sphagnum peat throughout this time period. The peakvalue of Sphagnum (>15%) around 2700 cal. yr BP indicatesa temporary shift to locally wet conditions, since Sphagnumrequires a high groundwater level.The high values of Pinus pollen (15–20%) indicate that pine

trees were locally present. The local vegetation was thus domi-nated by pine growing on the raised bog, with heath vegetationoccupying lighter patches. The increase of heather indicatesthat the local vegetation was opening up. Furthermore Corylus,grasses and herb pollen increase slowly whereas the tree pollensum decreases. This shows that the general landscape was alsoopening up. The opening of the landscape may have beenenhanced by forest fire(s), as indicated by distinct charcoalpeaks shortly before 4000 cal. yr BP.Pollen grains of Plantago lanceolata, an indicator of human

impact, particularly for grazed vegetation (Behre, 1981), occursporadically and at low values (1%). The same is true for theArtemisia and Cannabis pollen types. Both Artemisia andP. lanceolata can be interpreted as indicators for meadow land,although some Artemisia pollen grains can derive from A.maritima, which grows at coastal sites (Behre, 1981). However,as these human-indicator pollen types occur as single grainsand are not continuously present, they cannot be used as con-clusive evidence for human presence near the coring site. It istherefore most likely that the forest fires in the early part of thiszone were natural and that human impact was insignificantclose to the study site. However, around 2800 cal. yr BP simul-taneous small peaks of the grazing indicators Artemisia andP. lanceolata are observed, as well as a small peak in Cannabisvalues. This indicates that at this time grazing may haveoccurred in the vicinity of the bog.

STORMINESS VARIATION DURING THE LAST 6500 YEARS IN SW SWEDEN 909

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Pollen zone UmD (2600–1400 cal. yr BP)

The onset of this zone is characterised by a sudden and verystrong increase of Calluna up to values greater than 50% at2600 cal. yr BP. This could be interpreted as a result of forestclearance to enable grazing in the area. However, charcoalvalues as well as human-indicator pollen types remainlow throughout the zone. Therefore a natural cause for theCalluna increase is more likely. If conditions temporarilybecame wetter, as indicated by the Sphagnum peaks at3000–2600 cal. yr BP and 2400 cal. yr BP, this may explainthe decline in pine values from 40% to ca. 10%. Subsequentlylight-demanding species, such as Calluna, increased locally.The low values of Sphagnum after 2400 cal. yr BP, however,indicate a fast return to drier conditions (Barber et al., 2003).A temporary rise of the local water table has thus resulted in

open and low heath vegetation on the bog. The continuous pre-sence of non-local herbs indicates that the landscape surround-ing the bog was also more open. The low presence of humanimpact indicator species Plantago lanceolata and Cannabisshow that local land use was limited, but it became moreimportant towards the end of this zone. Around 1500 cal. yr BPsmall peaks in Cannabis and P. lanceolata indicate that limitedcultivation of hemp as well as grazing took place in or near thestudy area.

Pollen zone UmE (1400–400 cal. yr BP)

The strong increase of Sphagnum spores and Cyperaceaepollen (to ca. 40%) at the onset of the zone indicates a risingwater table. The bog was locally dominated by Cyperaceaeinstead of Calluna, which decreases to values around 25%.However, Calluna was still an important constituent of thebog vegetation. Increasing grass and juniper values indicatemeadowland in the vicinity of the bog (Behre, 1981), whereasthe first occurrence of Secale grains shows that cereal farmingtook place. The simultaneous increase of Cannabis, Plantagolanceolata and Rumex acetosa/R. acetosella pollen types upto values around 3% shows that land use in general wasincreasing. The establishment of the light-demanding Fagus(>5%) at the expense of broad-leaved trees such as elm andlime shows that the woodlands around the site became moreopen, probably as a result of human disturbance (Bjorkmanand Bradshaw, 1996).

Pollen zone UmF (400 cal. yr BP–present)

The strongly increased values of Calluna (>50%) and thedecreasing frequencies of both Sphagnum and Cyperaceaeindicate drier conditions at the coring site (Barber et al.,2003) and most likely the presence of heath vegetation outsidethe bog. This is confirmed by the Juniperus pollen peak at300 cal. yr BP, which indicates grazing areas at dry sites sur-rounding the bog, most likely on heaths with stands of juniper(Behre, 1981). The near absence of charcoal, however, indi-cates that burning of the heaths was rare. The tree pollen sumreaches a minimum around 100 cal. yr BP, indicating a strongdecrease of forested areas, which is in agreement with histori-cal records from this time (Malmstrom, 1939). The Secale peakshows that cereal cultivation was also important. Humanimpact on the landscape thus appears to have been severe,as is also shown by high values for Plantago lanceolata, Secaleand Rumex acetosa/R. acetosella around 300 cal. yr BP.

The most recent part of the profile is characterised by pollenassemblages showing a return to more closed vegetation, witha retreat of grazed vegetation and an increase of forested areas.Pine and alder probably increased both on the bog and in thesurrounding area, whereas the increase of oak, hornbeam,beech and spruce was limited to the dry areas on the surround-ing hills. The general increase of forested areas is alsodescribed in historical records and is mainly attributed to moreconcentrated land use and forest plantation (Malmstrom,1940).

Ignition residue and aeolian sand influx (ASI)

The ignition residue (IR) shows large fluctuations with highvalues at the top and bottom of the core (>10%mineral matter)and low values (<2%) from 1400 to 600 cal yr BP (Fig. 4). IRreflects the amount of clastic matter in a sample, i.e. the sumof mineral particles and biogenic silica formed by plants grow-ing in situ (phytoliths). During analysis of the ignition residue itwas observed that the amount of biogenic silica was low.Since the coring site is situated in a bedrock basin with one

outlet to the north and no inlets, the only mode of transport ofnon-biogenic large particles into the central part of the bog isby wind. This is certainly the case during the raised bog stage(4400 cal. yr BP–present), but most likely also during the fenstage (5800–4400 cal. yr BP) and earlier. This is supported bythe fact that throughout the core, the majority of large sandgrains are well rounded and frosted, indicating aeolian rework-ing. Both ASI values and maximum grain-size are interpreted asa proxy for winter storminess (Bjorck and Clemmensen, 2004),although especially ASI values are affected by source areacharacteristics and sample resolution variations. Therefore, toavoid over-interpretation of the data, only peaks that are pre-sent in both the ASI and the grainsize records are discussedhere.For the last 6500 cal. yr BP eight periods (peak groups 1–8;

Fig. 4) with clearly increased maximum grain-size and ASIvalues have been reconstructed. Concentration values are notshown since these reflect a nearly identical trend to influxvalues. Maximum grain-size values vary strongly between150 and 1600mm (Fig. 4(c)). Peak groups are characterisedby a general increase in grain-size to>400mm, whereas groups3–5 show exceptionally high values up to 1600 mm. Peakgroups also show high but fluctuating ASI values, reachingmaxima of >2 grains cm�2 yr�1. ASI is low between 6200and 5300, 3800 and 2900, and 2200 and 1200 cal. yr BP. Aclear increase in the number of ASI peaks and their amplitudeoccurs after ca. 3000 cal. yr BP. This is mainly due to a higherresolution of the dataset after ca. 3500 cal. yr BP (Fig. 2), whichautomatically generates higher amplitudes of the ASI record.

Regional climate and landscape development

To examine the validity of aeolian sand influx into raised bogsas a proxy for past storminess, the results from Undarsmossebog (Fig. 5) are compared to other sites in southwestern Scan-dinavia (Fig. 6). To study further the cause for the sand influxpeaks, a comparison to vegetation development and humanimpact is provided. Potential climate proxies from this study,mainly sand influx and local wetness, are used to define the‘climate zones’ used here (Fig. 5). These climate zones differonly slightly from the pollen zones.

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Climate zone Um1 (6500–4400 cal. yr BP)

This time period is characterised by a densely vegetated fen atthe site. The vegetation in the surrounding area was closed andthere is no evidence for human impact in the area. At other sitesin Halland human impact is also limited during this time(Thelaus, 1989; Bjorkman and Persson, 2005), although inDenmark and southern Sweden strong deforestation andexpansion of agriculture took place (the so-called ‘Landnam’phase) (Iversen, 1941; Berglund, 1969; Berglund et al.,1991). Despite the closed character of the vegetation, threeASI events with a maximum grain size >600mm are recordedaround 5200 and 4900–4700 cal. yr BP, which implies locallysevere storm conditions. At Hyltemossen bog (Fig. 1), ASIvalues also show increased values at these times (Bjorck andClemmensen, 2004) (Fig. 6), whereas at the Vejers dunefieldin western Denmark (Fig. 1) intense aeolian sand drift startedaround 5000 cal. yr BP (Clemmensen et al., in press). Thismay suggest that increased storminess occurred at a regionalscale around 5200 and 4800 cal. yr BP.At our site, ASI peak 7 coincides with strongly increased

OBD values (increased humification), especially around4800 cal. yr BP (Fig. 7). Furthermore pine pollen influx values(Fig. 7) show an increasing trend and total pollen concentra-tions are high, which most likely indicates dry summer condi-tions during ASI peak 7. This is in agreement with lake-levelstudies done by, for example, Digerfeldt (1988) showing lowlake levels in southern Sweden during this period. This might

indicate a dominance of continental conditions around4800 cal. yr BP, with dry warm summers and cold winters, pos-sibly with strong easterly winds. However, more detailed infor-mation on temperature fluctuations and wind directions isneeded to verify this.

Climate zone Um2 (4400–2800cal. yr BP)

During this time interval the vegetation on the bog was dense,but the landscape outside the bog opened up slowly. Thiscoincides with a period of expanding pasture land anddeforestation all over northwest Europe (Berglund, 2003).At Undarsmosse, however, indications for human impactare few and late in comparison with other sites in the region(Bjorkman and Persson, 2005).The slow increase of the relative importance of Sphagnum

after 4500 cal. yr BP and the subsequent development of araised bog broadly coincides with Sphagnum increase at othersites in the region, e.g. in Karringsjon at ca. 4100 cal. yr BP(Bjorkman and Persson, 2005) and in Sandsjon around 4400–4150 cal. yr BP (Thelaus, 1989). Furthermore OBD valuesdecrease between 4300 and 3700 cal. yr BP (Fig. 7). Lake-levelstudies show similar results, with lake-level rise starting around4500–4400 cal. yr BP as shown by Almquist-Jacobson (1995)and Hammarlund et al. (2003) (with revised age model inJessen et al., 2005). Since these are regionally synchronous

(%)

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Figure 4 (a) Variation of the ignition residue in time. The variations in ash content are mainly related to the type of sediment, showing highest valuesin the bottom during the clay–gyttja stage of stratigraphical unit I (Fig. 2) and lowest values shortly after 1400 cal. yr. BP, when Sphagnum growth onthe bog was at a maximum. The exceptionally high values in the top are interpreted as a result of strongly increased human impact around the studysite. (b) ASI variation of sand grains>200mm. (c) Maximum grain-size variation, showing a clear correlation with sand influx values. Sand drift peaks 1to 8 are based on high influx values and grain-size maxima together

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changes, they can be interpreted as a climatic signal (Harrisonand Digerfeldt, 1993), indicating a shift to wetter and/or coolerconditions (Hammarlund et al., 2003). This wet-shift has beenrecorded in many sites in northwestern Europe, see, for exam-ple, Barber et al. (2003). After 3700 cal. yr BP, OBD and pineinflux values increase at our site, which is interpreted as ashift to drier summer conditions. This may imply an increasingdominance of continental conditions with cool winter condi-tions and dry summers. These conditions may have prevaileduntil ca. 2800 cal. yr BP, when a strong peak of Sphagnuminflux (Fig. 7) indicates a local rise of the groundwater tableand thus a temporary shift to wetter conditions.Sand influx is generally low during this period, except for a

clear increase in grain size and ASI values around 4300, 4100and 3900 cal. yr BP (peak group 6). The occurrence of thesepeaks before the opening of the landscape indicates that localstorm conditions must have been severe in order to transportparticles up to 600mm to the centre of the bog. The coincidentincrease of sand influx into Hyltemossen bog (Bjorck andClemmensen, 2004) and the increase of inland sand transportand dune development at Vejers and Lodbjerg dune fields inDenmark (Clemmensen et al., 2001a,c, in press) show thatthese storm events were regionally significant (Fig. 6). Thedeposition of peak group 6 (4300–3800 cal. yr BP) coincideswith a shift to wetter conditions, which might indicate predo-minantly maritime conditions at this time, with increased pre-cipitation, cooler summers and increased cyclone activityespecially in winter.After these peaks ASI values at Undarsmosse remain low for

ca. 1000 yr. Low values are also seen at Hyltemossen bog untilca. 3400 cal. yr BP, which suggests that the low influx is a cli-

matic signal, i.e. indicating low storm frequency and intensitybetween at least 3900 and 3400 cal. yr BP.

Climate zone Um3 (2800–2200cal. yr BP)

This period includes the Sub-Boreal to Sub-Atlantic transitionand is characterised by distinct changes in vegetation andASI. The landscape became more open, initially only slightly,as shown by a small increase of non-local herb pollen at ca.2800 cal. yr BP. This is followed by a dramatic local openingof the vegetation around 2600 cal. yr BP. This coincides withlandscape opening all over northwest Europe (Berglund,2003) and is also seen locally at, for example, Sandsjon,although landscape opening was not very distinct here(Thelaus, 1989).Sphagnum and pine influx values vary strongly during this

time period, which is interpreted as reflecting alternating wetand dry conditions at the study site (Fig. 7). Wet conditionsprobably prevailed around 2900–2800 cal. yr BP, whichcoincides with a lake-level highstand in southern Sweden(Digerfeldt, 1988; Thelaus, 1989) and a wet shift recorded atHyltemossen bog (Bjorck and Clemmensen, 2004). A secondslightly wetter period occurred around 2400 cal. yr BP, whichcoincides with a shift to a wetter (and/or colder) climate asreflected by 18O and 13C depletions in Lake Igelsjon in southcentral Sweden (Hammarlund et al., 2003). The increasedwet conditions during this time are also known from otherstudies from northwest Europe, e.g. van Geel et al. (1996)and Barber et al. (2003).

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Figure 5 Summary of data from Undarsmosse bog, showing ASI variations of grains 125–200 mm and 200–350 mm in relation to bog surfacewetness (reconstructed from Sphagnum and Pinus influx values and OBD data), characteristic vegetation types, vegetation openness and thedegree of human impact

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ASI and particle sizes in Undarsmosse bog increase stronglyduring this time period, reaching peak values at 2800, 2600and 2400–2200 cal. yr BP (peak group 5). Increased storminessas recorded by peaks 5c and 5d is also found in many dune sitesalong the Danish west coast (Clemmensen et al., 2001b,c,in press). Peak group 5 closely coincides with influx peaksrecorded in Hyltemossen and Boarps mosse bog sites (Fig. 1)(Bjorck and Clemmensen, 2004), which are dated to ca.2800–2300 cal. yr BP. It is probable that several of these peaksreflect the same climatic event as peak group 5 from our studysite, since the dates fall within a radiocarbon plateau (Reimeret al., 2004). Furthermore, due to the error margins that areinherent in age models, a direct correlation between peakevents recorded at different sites cannot be established withcertainty. However, the shift to increased storminess asrecorded by all records considered here (Fig. 6) does suggestan intensified storm climate at a regional scale between ca.2800 and 2200 cal. yr BP.The comparison between sand influx data and pollen

data (Fig. 7) shows that the onset of peak 5 coincides withincreased wetness on the bog (peak Sphagnum influx values),whereas peaks 5a and 5c occur during relatively dry bog sur-face conditions, as reflected by increased pine influx values,decreased Sphagnum influx and a peak OBD value around2300 cal. yr BP. Lake levels are at a maximum shortly after3000 cal. yr BP but decrease after that (Digerfeldt, 1988). It thusappears that the Sub-Boreal to Sub-Atlantic transition in south-western Scandinavia was characterised by a strong increase

in storm activity and strongly fluctuating bog surface wetness.Increased storminess occurred during wet as well as dryintervals.

Climate zone Um4 (2200–1500cal. yr BP)

During this time the vegetation on the bog was dominatedentirely by Calluna heath, which indicates open and relativelydry conditions. The surrounding landscape opened up andboth grazing and pasture indicators increase. This is alsoobserved at Karingsjon (Fig. 1), where a clear increase in theimportance of pasture coincides with the temporary disappear-ance of broad-leaved trees such as elm and lime and anincrease of beach (Bjorkman and Persson, 2005). Fagus isfavoured by disturbances (Bjorkman, 1999) and increasedbeech pollen values thus indicate forest opening, possibly bygrazing. By the end of this period only small forests remainedin the Karingsjon area (Bjorkman and Persson, 2005). Althoughthis strong forest opening is not seen around Undarsmosse bog,the slight increase of human impact indicators and non-localherbs does indicate a more open landscape.Relatively dry conditions are reconstructed for the time per-

iod 2200–1500 cal. yr BP; Sphagnum influx values show thelowest values since the establishment of a raised bog at this siteand the bog vegetation is dominated by Calluna heath. Thisperiod coincides with lowered lake levels in south and central

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ldFigure 6 Regional comparison of ASI data from this study site (a) with ASI data from Boarps Mosse (b) and Hyltemossen (c) (Bjorck and Clemmensen,2004); grain-size maxima as recorded in the Skagerrak by Hass (1996), who interpreted these as reflecting stormy winter-like conditions (d); the onsetof aeolian activity at Vejers dune field (Clemmensen et al., 2001a, in press)

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Sweden (Digerfeldt, 1988; Almquist-Jacobson, 1995). Maxi-mum grain sizes are small and ASI values are low. After ca.1500 cal. yr BP. a regional shift to wetter conditions (Digerfeldt,1988; Gedda, 2001) and possibly longer growing seasonscaused a strong increase of Sphagnum growth on the bog,resulting in low peat humification as reflected by the stronglydecreased OBD values (Fig. 7). This shift coincides withincreased wetness recorded in many sites in northwesternEurope (Barber et al., 2003).

Climate zone Um5 (1500–400 cal. yr BP)

Throughout the period 1500–400 cal. yr BP the vegetationon the bog is dominated by Sphagnum, which indicates ahigh local water table. As discussed in the previous section,this coincides with a regional increase in wetness after1500 cal. yr BP. The correlation between OBD values andSphagnum influx is negative after this time, with a correlationcoefficient greater than 0.5 between ca. 1400 and700 cal. yr BP. Grazing and agriculture was intensive near thestudy site as well as in the wider region (Thelaus, 1989;Berglund, 2003).ASI peak 4 (1480–1400 cal. yr BP), which is characterised by

a clear increase in maximum grain size, occurs during this shiftto wetter conditions. Peak 4 also appears to coincide withrenewed aeolian activity at Vejers dunefield (Clemmensenet al., in press) and increased sand influx at Hyltemossen(Bjorck and Clemmensen, 2004). Hass (1996) also recon-structed an increase of sedimentation rates and grain sizes inthe Skagerrak around this time (Fig. 6). He interprets these asa proxy for (winter) storm conditions. Furthermore, an increaseof �18O values is recorded in Skagerrak sediments from ca.1450–1300 cal. yr BP, indicating cooler marine conditions.

Peak 4 may thus represent a regional scale increase in stormi-ness during a temporarily colder climate.ASI peak 3 (1200–1100 cal. yr BP) is characterised by extre-

mely high ASI values and maximum grain sizes greater than1000mm. After deposition of peak 3 influx values remain ratherlow, but the maximum grain size steadily increases andreaches a small maximum just before 700 cal. yr BP (peak2b). At 600 cal. yr BP another peak occurs (peak 2a). Peak 3coincides with a small influx peak at Boarps mosse (Bjorckand Clemmensen, 2004) but just precedes a strong increaseof grain sizes in the Skagerrak at 1100 cal. yr BP (Hass, 1996).Dunefields on the west coast of Jutland were only partly activearound 1100 cal. yr BP, but all dunefields experienced large-scale sand movement around 850 cal. yr BP (Clemmensenet al., 2001a,c; Pedersen and Clemmensen, 2005). So althoughdune formation and increased storm activity is recorded at orjust after the deposition of peak 3 at several sites, the lack ofevidence at other sites makes it difficult to establish a consistentregional picture for storm activity and sand transport during thistime period.Peaks 2a and b indicate increased storminess between ca.

800 and 600 cal. yr BP. Dune formation at the Lodbjerg dunefield commenced around 800 cal. yr BP and continued untilthe present day. At the Vejers dunefield, aeolian activityincreased at 850 cal. yr BP (Clemmensen et al., in press).At ca. 600 cal. yr BP increased sand influx is also recordedat Hyltemossen (Bjorck and Clemmensen, 2004) and in theSkagerrak (Hass, 1996) (Fig. 6), which suggests that the ASI datafrom this study reflect a regional-scale increase in storminess.During this time, conditions were generally still very wet(Fig. 7). The coinciding heavier values of the �18O ratio inthe Skagerrak sediments indicate that this period was markedby cool conditions. These results may suggest that from ca.1500–600 cal. yr BP conditions in southwest Sweden weredominated by an oceanic climate, with high precipitation, cool

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Figure 7 ASI values compared to local bog surface wetness indicators comprising OBD, Pinus influx values and Sphagnum influx values

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and wet summers and increased cyclone activity in winter.After 600 cal. yr BP decreasing Sphagnum influx values andslowly increasing OBD values indicate that local conditionsbecame drier.

Climate zone Um6 (400–present)

Around 400 cal. yr BP a sudden shift to very dry conditions withexpanding Calluna heath is seen around the study site (Fig. 3).This heath extension is recorded at many places alongthe Swedish west coast (Digerfeldt and Hakansson, 1993;Bjorkman, 2001) and has been interpreted as a human-inducedchange; heathlands can develop after deforestation and mainlyform on poor soils. To maintain these heaths, intense grazingand heath burning is required (Behre, 1988). At Undarsmossecharcoal levels are low during this interval, which indicatesthat the heath was probably kept open by intense grazing.The high levels of other anthropogenic indicators show thathuman influence on the vegetation was at a maximum duringthis period. The vegetation was thus very open and land usewas intense, which is confirmed by local historical documentsand land-use maps.The increase of OBD values, pine and Calluna and the

decrease of Sphagnum indicate a local shift to dry conditions(Barber et al., 2003). However, industrial-scale peat cutting ofthe bog started around 1874 (Harplinge hembygd och fornmin-nesforening, 1927) but it is possible that small-scale drainage andpeat cutting started earlier, which could have resulted in an ear-lier lowering of the local water table. It is thus probable that thehumidity record is disturbed after ca. 80cal. yrBP, and possiblyearlier. Furthermore, when comparing our data to other recordsin the period after 400cal. yrBP, it has to be kept in mind that theage uncertainty of our data is relatively high during this period.Therefore comparisons of peak values recorded at Undarsmossewith data from other studies are tentative.Maximum grain sizes and the influx of grains larger than

200mm are high during this period (peak group 1), but theincreased influx of finer particles is much more significant(Fig. 5). The ignition residue and influx of small grainsshow a very strong increase from 400 to 100 cal. yr BP(125–200mm, Figs 4 and 5) with peak values at ca. 230 and100 cal. yr BP (peaks 1a and 1b). This was probably causedby increased land use in the area, creating more open and lessprotected soils, thus allowing for strong erosion of fine particlesand dust. In southern Sweden increased sand drift during the18th century AD is also related to the increased use of marginallands (Barring et al., 2003). The very high amplitude of dust andsand influx is thus interpreted as a result of human impact,whereas the timing of the influx peaks is most likely also relatedto climatic factors.Sand influx into the Undarsmosse bog increased after

400 cal. yr BP and reached peak values around 230 and100 cal. yr BP (peaks 1a and 1b). The high storm activityfrom ca. 400 to 100 cal. yr BP, and possibly earlier from850 cal. yr BP, occurred during the cooling climate of the so-called Little Ice Age, for which evidence is found throughoutthe North Atlantic region (Grove, 2001). The Little Ice Age,however, did not have a stable cold climate, but was charac-terised by large variations on a decadal scale with intermittentwarm intervals.At the Hyltemossen and Boarps mosse sites, influx peaks

are recorded around 300 and 130 cal. yr BP (Bjorck andClemmensen, 2004). Bearing in mind the precision of the agemodels, these peaks may be identical to ASI peaks 1a and 1b(100 and 270–230 cal. yr BP) recorded in this study. In the Ska-

gerrak coarse sediments are deposited between 600–400 and200–50 cal. yr BP (Hass, 1996). At the Jutland dunefields exten-sive aeolian sand movement took place between 400 and50 cal. yr BP (Clemmensen and Murray, in press). Historicalrecords from Sweden show increased gale frequency in south-ern Scandinavia around 100 cal. yr BP (Franzen, 1991), andDanish data indicate increased storminess around 80 cal. yr BP(Clemmensen et al., 2001c), this being synchronous with peak1a. Danish data on storm surge events along the west coast ofJutland and Schleswig-Holstein record three exceptionallystormy periods at around 320, 230 and 120 cal. yr BP(Clemmensen et al., 2001b). Two of these stormy periodsapparently coincide with peaks 1a and 1b at the Undarsmossebog. Several other studies indicate strong atmospheric circula-tion variations during this time period. Koslowski and Glaser(1999) have shown that the sea-ice extent in the Baltic Seavaried strongly between 450 and 90 cal. yr BP, which theylinked to the varying strength of westerlies in the region. ASIpeak 1a seems to coincide with decreased ice cover, whichKoslowski and Glaser (1999) linked to increased westerlyairflow over the area. Peak 1b (270–230 cal. yr BP), however,apparently coincides with a period of increased sea-ice cover,indicating a frequent occurrence of blocking situations andthus high surface air pressure over northern Europe and wea-kened westerly flow. This is in general agreement with Luterba-cher et al. (2001), who reconstructed sea-level pressures duringthe Late Maunder Minimum (275–235 cal. yr BP) and found amore frequent occurrence of winter pressure patterns with avery strong anticyclone centred over the Baltic. This maysuggest that ASI peak 1b is linked to strong winds from south-easterly directions as described by Bjorck and Clemmensen(2004). However, owing to the age uncertainty in our data aswell as the strongly fluctuating character of the climate duringthis time period, this remains speculative.

Discussion

Aeolian sand influx to bog sites is most likely affected by localland use, which causes differences between the ASI signalsfrom different sites. Furthermore, resolution differences withinand between the cores from the three bog sites in Halland affectthe amplitude of the ASI curves. These factors could explain thelack of similarity in amplitude of individual ASI peaks at thebog sites. Pollen analysis in this study has shown that humanimpact near the Undarsmosse bog was limited until ca.1500 cal. yr BP. Unfortunately no such data are available forthe Boarps mosse and Hyltemossen bog sites, so that it is notpossible to explain the differences between the ASI recordsfrom these sites in more detail. However, the synchroneityof many of the ASI peaks reconstructed here with peak groupsin the previously studied bogs in Halland (Bjorck andClemmensen, 2004) suggests that the ASI signal does haveregional implications. The apparent synchroneity of storminessindicators in Halland and Denmark (dunefield activity) stronglysuggest that the ASI signal can be used as an indicator forregional scale storminess variation.The exact character of these stormy periods is, however, dif-

ficult to establish; it has so far not been possible to determinethe prevailing wind directions from our data. However, sincelarge grains (>200mm) cannot be transported in suspensionover long distances (Tsoar and Pye, 1987), the influx of largegrains into raised bogs is interpreted as niveo-aeolian transport(cf. Dijkmans, 1990; Lewkowicz, 1998), thus transported dur-ing snow storms (Bjorck and Clemmensen, 2004). Bjorck and

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Clemmensen (2004) concluded that niveo-aeolian transportof large sand particles is possible during both easterly and wes-terly winds, during generally cold (winter) conditions. This ideais supported by the results from this study, although we cannotexclude that some sand grains were transported during excep-tionally strong ‘summer’ storms. However, this study alsoshows that all ASI peaks, except peaks 7 and 1b, apparentlywere deposited during periods with wet summer conditions,thus possibly related to a dominance of oceanic conditionsand increased cyclone activity.Interestingly, many stormy episodes recorded at Undars-

mosse bog took place during periods of cooling in the northernNorth Atlantic, especially those events that are recordedaround 4310–4085 (peak 6b and 6c), 2800–2585 (peak 5cand 5d) and 1440 (peak 4) cal. yr BP. These ASI peaks seemto coincide with periods of strong southward deflection ofsea-ice (Bond et al., 1997), which has been linked to solar-induced atmospheric changes (Bond et al., 2001). Two otherASI peaks, at 4800 (peak 7a) and 270–230 (peak 1b) cal. yr BP,also appear to coincide with decreased solar irradiance. It thusseems that increased storm activity in southwest Sweden waslinked to large-scale cooling events in the North Atlanticregion, which are associated with atmospheric and oceanic cir-culation changes as a result of decreased solar irradiance.

Conclusions

The apparent regional synchroneity of the sand influx recordfrom Undarsmosse bog with records from Denmark, theSkagerrak and southern Halland suggest that sand influx intoraised bogs can be used as a proxy for storminess, especiallyin areas or during time periods with weak human impact.Furthermore, the apparently simultaneous occurrence ofincreased sand influx in the study area with cooling in theNorth Atlantic region shows that these large-scale climatic set-backs, tentatively related to solar irradiance fluctuations andfeedbacks through atmospheric and oceanic circulation, areaccompanied by strongly increased storm activity in southwes-tern Scandinavia.Humidity fluctuations, as recorded at Undarsmosse bog, sug-

gest a strong fluctuation of summer humidity in the period6500–3700 cal. yr BP, with a shift to wetter conditions occur-ring at 4300 cal. yr BP. From 3700 to ca. 2800 cal. yr BP localconditions were relatively dry, but around 2800 and2350 cal. yr BP shifts to temporarily wetter conditions tookplace. The last and largest wet shift occurred shortly after1500 cal. yr BP and this wet period lasted until ca.600 cal. yr BP, after which local conditions became drier. Thelast ca. 150 yr of the record are probably influenced by drai-nage and therefore no conclusions can be drawn about humid-ity fluctuations after this time. The broad agreement betweenour humidity data and data from other peat bogs in northwes-tern Europe suggests that the large-scale humidity changesrecorded at our site are related to regional-scale atmosphericcirculation changes.Human impact at this site was generally limited until ca.

1500 cal. yr BP. After this time humans were present in the areaand grazing and cereal cultivation took place. As compared toother sites in southern Sweden, however, human impact wasvery limited at our site. During the last ca. 150 yr landscapeopening and intense land use resulted in soil erosion, as indi-cated by a strongly increased influx of fine material.To establish further the use of aeolian sand influx into raised

bogs as a proxy for (winter) storminess, a similar study will be

conducted in a region where human impact has been moreintense. To study the atmospheric set-up during stormy periodsin more detail, future work should involve, for example, sul-phur analysis to evaluate past sea-salt spray and thus the occur-rence of westerly winds. Furthermore, detailed dating of themost recent part of the cores would allow for a more reliablereconstructions of storminess variation and thus for a bettercomparison with historical and instrumental data.

Acknowledgements This study is part of Rixt de Jong’s PhD thesis(Lund University). We would like to thank Ronnie Liljegren (LU)for valuable comments on the pollen diagram. Our two reviewersAlastair Dawson and Peter Wilson are thanked for comments on themanuscript. Accelerator mass spectronomy (AMS) 14C dating wasdone at the Radiocarbon Dating Laboratory in Lund, Sweden, and atthe Poznan Radiocarbon Laboratory, Poland. Dating was supportedby the Royal Physiographic Society (Lund) and the Swedish ResearchCouncil (VR, grant to SB).

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