Late Holocene effective precipitation variations in the maritime regions of south-west Scandinavia

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Quaternary Science Reviews 28 (2009) 54ndash64

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Quaternary Science Reviews

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Late Holocene effective precipitation variations in the maritimeregions of south-west Scandinavia

R De Jong a1 D Hammarlund a A Nesje bc

a GeoBiosphere Science Centre Department of Geology Quaternary Sciences Lund University Solvegatan 12 SE-223 62 Lund Swedenb Department of Earth Science University of Bergen Allegaten 41 N-5007 Bergen Norwayc Bjerknes Centre for Climate Research Allegaten 55 N-5007 Bergen Norway

a r t i c l e i n f o

Article historyReceived 11 April 2008Received in revised form 29 August 2008Accepted 22 September 2008

Corresponding author Tel thorn41 31 6315092 faxE-mail address dejonggiubunibech (R De Jong

1 Present address Department of Geography UnivCenter for Climate Change Research Erlachstrasse 9a

0277-3791$ ndash see front matter 2008 Elsevier Ltddoi101016jquascirev200809014

a b s t r a c t

At present the climate in south-west Scandinavia is predominantly controlled by westerlies carryingmoist Atlantic air which forms a main source of precipitation in all seasons Past variations in the ratiobetween precipitation and evaporation (effective precipitation) from terrestrial sites however mayindicate changes in the degree of maritime influence Palaeoclimatic archives in this region are thusideally situated to study past changes in atmospheric circulation patterns In this study multi-proxycomparisons of records from three peat bogs and two lakes are used to reconstruct regional-scalevariations of effective precipitation in south-west Sweden during the Late Holocene The total aeoliansediment influx into two peat bogs is used as a proxy for storm activity The frequency of storm phasesincreases strongly after ca 2500 cal yrs BP Dry conditions occur on a regional scale around 4800ndash44002000ndash1700 1300ndash1000 700ndash500 and 300ndash100 cal yrs BP In addition a comparison to winter precipi-tation reconstructed from four Norwegian glaciers shows similar variations during the past ca 2000years This indicates that the climate in both regions was controlled by large-scale atmospheric circu-lation dynamics of the North Atlantic region The strong variability of effective precipitation and stormactivity after ca 2500 cal yrs BP indicates a highly variable climate

2008 Elsevier Ltd All rights reserved

1 Introduction

The climate of northern Europe is strongly affected by ocean andatmosphere processes through changes in northward heat andmoisture transport to the North Atlantic (Moros et al 2004)Currently the western coastlines of southern Scandinavia experi-ence a maritime climate with predominantly westerly air flow(Jonsson and Barring 1994 Bjune et al 2005) Moist Atlantic air isa main source of precipitation in this region and exerts a strongcontrol on temperatures in all seasons In addition atmosphericblocking ie the occurrence of a high pressure zone over Scandi-navia resulting in the divergence of westerly air flow northward andsouthward has a profound effect on regional climates (Jonsson andFortuniak 1995 Barry and Chorley 1998) Blocking in wintertime isassociated with cold and dry conditions whereas blocking insummer leads to prolonged high temperatures and dry conditions(Jonsson and Fortuniak 1995) As a result peat bogs lakes and

thorn41 31 6315144)ersity of Bern and Oeschger

3012 Bern Switzerland

All rights reserved

glaciers that are dependent on precipitation are likely to record long-term variations in the degree of maritime influence and atmosphericblocking in the area Such records can be used for studies of thecharacter and timing of climatic changes in south-western Scandi-navia in particular changes in the degree of maritime influence inthe region These terrestrial records may therefore provideimportant information on past changes in oceanic and atmosphericcirculation patterns

Classical stratigraphical studies of Swedish peat bogs (egGranlund 1932) showed that humidity varied throughout theHolocene with the occurrence of so-called lsquorecurrence surfacesrsquolayers of low-humified peat on top of dark brown peat which wereassumed to have developed synchronously in peat bogs acrossa wide region Although later studies showed that this assumptionwas not entirely correct this early work illustrated the potential ofpeat bogs as archives for past climatic fluctuations Later detailedstratigraphical and vegetational studies were performed to recon-struct humidity variations from lake-sediment records bypinpointing lake-level high stands and low stands (eg Digerfeldt1988 Almquist-Jacobson 1995) whereas detailed analyses of peatremains in north-west Europe showed clear variations in bogsurface wetness during the mid- to late Holocene (eg Blackfordand Chambers 1993 Mauquoy and Barber 2002 Langdon and

R De Jong et al Quaternary Science Reviews 28 (2009) 54ndash64 55

Barber 2005) More recently variations in effective precipitation insouthern Sweden were based on oxygen and carbon isotopicrecords from carbonate-rich sediments at Lake Igelsjon south-central Sweden (Hammarlund et al 2003 Fig 1) The isotopicvariations were interpreted as reflections of changing effectiveprecipitation ie changes in the evaporationinflow ratio of thebasin This implies that changes in effective precipitation reflectvariations in summer temperature as well as annual precipitation

In order to reliably reconstruct large-scale climatic patternsmultiple study sites are needed to separate local effects from theimpact of regional- or global-scale climatic changes In this studyproxy data from five sites in south-west Sweden are used forreconstruction of regional-scale variations in effective precipitation(Fig 1) We use organic bulk density (OBD) measurements from theStore Mosse Bog and two other peat bogs to reconstruct bog surfacewetness (BSW) variations since ca 6500 cal yrs BP OBD valuesreflect the degree of peat decomposition since this affects theaverage particle size of the peat and thereby the water contentlow-decomposed peat contains large Sphagnum remains and hasa high water content (Bjorck and Clemmensen 2004) HoweverOBD values should be interpreted carefully since they are alsosensitive to non-climatic factors such as local bog developmentlocal bog vegetation changes and drainage These problems will bediscussed in Section 51 In addition proxy-based reconstructions ofstorm activity are used as a source of information on past atmo-spheric conditions in the region These reconstructions are basedon the total aeolian sediment deposition in two peat bogs in south-west Sweden Undarsmosse Bog (De Jong et al 2006) and StoreMosse Bog (De Jong 2007)

Fig 1 Map showing the location of the Store Mosse Bog situated at the transition between tand coring location are also indicated to the right The positions of Lake Igelsjon (Hammarluand Hyltemossen Bog (Bjorck and Clemmensen 2004) in south-west Sweden are indicated awas derived (Bjune et al 2005)

To enable a regional-scale reconstruction of effective precipita-tion changes in southern Sweden OBD records from the StoreMosse Bog (this study Fig 1) the Undarsmosse Bog (De Jong et al2006) and the Hyltemossen Bog (Bjorck and Clemmensen 2004)are compared to the palaeohydrological records from Lake Igelsjon(Hammarlund et al 2003) and Lake Bysjon (Digerfeldt 1988) Wethen compare this regional pattern of effective humidity variationsin southern Sweden to a reconstruction of winter precipitationderived from glaciers in south-west Norway (Nesje et al 2001Bjune et al 2005) Since these glaciers are also situated ina strongly oceanic climate (Nesje et al 2008) this comparisonprovides insight into large-scale patterns of atmospheric circula-tion Thus the aims of this study are (1) to assess the reliability ofOBD as a proxy for BSW variability (2) to construct a regionalscheme of effective precipitation fluctuations in south-west Swe-den and (3) to assess the wider implications of the reconstructedvariations in effective precipitation and storm activity

2 Study area

Store Mosse Bog is situated on the coastal plain of the provinceof Halland south-west Sweden (Fig 1) The coastal plain is ca 10ndash20 km wide and the elevation is 10ndash25 m above sea level Lundqvistand Wohlfarth (2001) dated the deglaciation of the coastal plain to16000 cal yrs BP After the initial deglaciation the ice marginfluctuated strongly resulting in the formation of a successive seriesof moraine ridges and thick glaciofluvial and glaciomarine depositswest of the ice margin (Berglund 1995) Because of substantialfluctuations of relative sea level after the deglaciation sediments

he coastal plain and the upland areas of south-central Sweden (inset) The local settingnd et al 2003) Lake Bysjon (Digerfeldt 1988) Undarsmosse Bog (De Jong et al 2006)s well as the glaciers in south-west Norway from which the winter precipitation record

Table 1AMS 14C dating results from the Store Mosse Bog and calibrated ages

Depth (cm) 14C age (2s) Cal age BP (2s) Lab No

4ndash5 990 50 882 101 LuS 640926ndash27 985 40 878 83 LuS 641035ndash36 140 40 105 50

or 225 60LuS 6619

45ndash46 470 40 507 46 LuS 644970ndash71 850 40 743 60 LuS 6411105ndash106 1145 40 1070 100 LuS 6412142ndash143 1540 50 1435 100 LuS 6413181ndash182 1905 40 1830 100 LuS 6414200ndash201 2095 50 2045 115 LuS 6620223ndash224 2670 40 2800 50 LuS 6450272ndash273 3850 50 4280 135 LuS 6451339ndash340 5920 50 6760 120 LuS 6452

R De Jong et al Quaternary Science Reviews 28 (2009) 54ndash6456

below the marine limit (ca 65ndash75 m Berglund 1995) experiencedconsiderable reworking The coastal plain is characterised by siltyand sandy wave-reworked glacial sediments overlain by dune fieldsand peat deposits Granitic bedrock outcrops in the area reacha maximum elevation of 140 m asl

The current regional climate in the province of Halland isstrongly controlled by westerly air flow resulting in mild maritimeconditions with cool summers (July average temperature 16 C) andmild winters (January average temperature 2 C) Precipitation inHalland is relatively low in the narrow coastal zone on average700ndash800 mm per year whereas values up to 1200 mm per year arerecorded in the upland region (SMHI 2008) The number of dayswith snow cover per year varies in the range of 25ndash75 The weatherin all seasons is variable being controlled by the strength positionand frequency of passing cyclones Analyses of geostrophic windspeeds in southern Sweden from AD 1881 to 1997 show that windsfrom a westerly direction dominate the wind spectrum andmaximum wind speeds occur between October and March (Alex-andersson et al 1998 Nilsson et al 2004) Easterly winds withstorm force are associated with atmospheric blocking when high-pressure cells are situated over northern Scandinavia

Store Mosse Bog is situated at the eastern limit of the coastalplain at the transition to the upland region It receives 1000ndash1200 mm of precipitation per year The peat deposit has developedin an elongated bedrock basin of ca 240 ha (Paringsse 1989) The bogsurface is located at 23 m asl with drainage towards the north-east The bedrock slope on the eastern side of the basin rises steeplyto 140 m asl To the south the basin is dammed by the Spannarpterminal moraine system The Store Mosse Bog has been subjectedto severe peat cutting resulting in a system of ditches and ridgesacross the entire bog surface Drainage channels were dug aroundAD 1930 after which industrial-scale peat cutting commencedCores were taken from a remaining ridge in the north-central partof the peat deposit where disturbance of the peat sequence wasexpected to be minimal

3 Materials and methods

Below the methods applied to the Store Mosse Bog peatsequence are described These are identical to the methods appliedat Undarsmosse Bog as described in De Jong et al (2006) andhighly similar to the methodology applied by Bjorck and Clem-mensen (2004) at the Hyltemossen Bog site

31 Organic bulk density and aeolian sediment influx

Cores were taken from the central part of the Store Mosse Bogusing a Russian peat sampler (75 cm diameter) The cores werewrapped in plastic cling-film and stored frozen to prevent waterloss Next the frozen cores were cut into 1-cm slices Each slice wassampled for organic bulk density (OBD) and aeolian sedimentinflux (ASI) Samples from each frozen peat slice were weighed andthe wet volume was estimated by water displacement The sampleswere then dried overnight at 105 C and weighed again to deter-mine water loss giving the water content From these values boththe wet weight and dry weight could be calculated Subsequentlyeach sample was ignited at 550 C for 45 h The ignition residue(IR) was weighed providing the percentage of non-organic matterand the ash weight To calculate the ash-free OBD the weight of theminerogenic matter (IR) was subtracted from the weight of the dryorganic matter and then divided by the initial volume of thesample IR samples were subsequently rinsed with 10 HCl and theremaining mineral grains were used for ASI analysis The mineralgrains were analysed under a 50 zoom stereomicroscopeSamples with a very high fine particle content were sieved at 63 mmbefore further analysis All quartz grains gt125 mm were counted in

each sample Furthermore the maximum grain size in each samplewas determined

32 Radiocarbon dating and chronologies

The age model for the Store Mosse peat record is based on 10AMS radiocarbon dates of bulk peat samples (Table 1) Wherepossible plant remains other than Sphagnum were removed fromthe samples The radiocarbon dates were calibrated using theIntCal04 calibration data set (Reimer et al 2004) as implementedin the OxCal 310 program (Bronk Ramsey 1995 2001) The age-depth model (Fig 2) is a combination of two linear segmentsconnected by a short third-degree polynomial function anda second-degree polynomial function for the uppermost partAccording to this model the average peat accumulation rate is03 mmyr in the lower part and 11 mmyr in the upper part of therecord The two uppermost dates shown in Fig 2 were excludedfrom the age-depth model This uppermost layer of peat (unit VI) isthought to be an artefact of peat excavation as peat was left to dryon the sampled ridge This is confirmed by a pollen spectrum of thisunit which is similar to that from around 900 cal yrs BP (unpub-lished data) The age of the lsquooriginalrsquo surface at 33 cm depth istherefore unknown but is estimated to date to around 20 cal yrs BPwhich corresponds to the onset of industrial scale peat cutting atthis site All dates mentioned in this text refer to calibrated yearsbefore AD 1950 unless stated otherwise

4 Results

41 Store Mosse peat stratigraphy and OBD

The stratigraphy of the Store Mosse peat record is shown in Fig 3together with OBD values and Sphagnum spore influx values Theoldest part of the sequence consists of gyttja (not investigated) UnitI (332ndash307 cm) is a 25 cm thick layer of highly humified fen peatwith Carex remains and some woody particles Several charcoallayers were observed in the bottom part of this unit From unit II andupwards Sphagnum remains are present in increasing abundanceUnit II is composed of a lower part of highly decomposed fen peatwith bands of Eriophorum and some Sphagnum remains a middlepart of light brown medium-decomposed fen peat and an upperpart of highly decomposed fen peat with relatively more Sphagnumremains The transition to unit III is gradual Unit III (193ndash122 cm)consists of medium-humified Sphagnum peat and is characterisedby frequent occurrences of 1ndash2 cm thick bands of light brown low-humified peat alternating with thin less frequent bands of darkerbrown Eriophorum The transition to Sphagnum peat between unitsII and III is also characterised by a steep increase in Sphagnum sporeinflux values (see Fig 3) as well as Sphagnum spore concentrations(not shown) Unit IV is characterised by light brown low-humified

Dep

th

(cm

)

Age (cal yr BP)

0 1000 2000 3000 4000 5000 6000

350

300

250

200

150

100

50

0

Fig 2 Agendashdepth relationship and positions of radiocarbon-dated samples for theStore Mosse peat core


Sphagnum peat and high Sphagnum spore influx values andconcentrations Although Sphagnum spore values are not a directmeasure of the amount of Sphagnum occurring locally due todifferent rates of sporulations between species and depending ongrowth conditions (Chambers et al 1997) the strong increasesupports the interpretation that the transition to raised bog

OBD(grcm3)

Sphagnum (sporescm

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

Cal yrs BPStratigraphic unitsa b c

Fig 3 Data from the Store Mosse Bog showing (a) stratigraphy and the descriptions of the fimatch the age-scale) OBD values are shown in (b) where high values are interpreted as dryThe ignition residue (IR) aeolian sediment influx values (ASI) and maximum grain sizeombrotrophic conditions reflected in the stratigraphy OBD values and Sphagnum influx va

conditions occurred around this time Unit V consists of medium-high humified Sphagnum peat On top of unit V there is a highlyhumified dark brown reworked peat as noted above As a result theyoungest part of the record is the top of unit V

Relatively stable and high OBD values were recorded throughoutunits I and II (ca 6500ndash2000 cal yrs BP) whereas generally lowervalues characterise unit III and the lower part of unit IV (ca 1700ndash700 cal yrs BP) Peak OBD values occur at ca 4800ndash4300 2500ndash20001300ndash1100 700ndash500 and 350ndash50 cal yrs BP In general there isa good correspondence between the OBD record and the degree ofpeat humification as noted in the stratigraphical description

42 Minerogenic content

The ignition residue (IR) is shown in Fig 3 together with the totalaeolian sediment influx (ASI) of grains gt125 mm and the maximumgrain size observed in each sample IR values show a long-term trendof decreasing values from ca 5500 to 2500 cal yrs BP followed bya period with strong fluctuations The long-term decrease is mostlikely related to changes in the peat type as well as compaction of thematerial The strong fluctuations in IR after ca 2500 cal yrs BPcorrelate with ASI peaks and are interpreted as a climatic signalHowever ASI depends on sediment availability as well as a trans-porting agent in this case strong winds that can carry sand grains tothe centre of a raised bog This process would be greatly facilitated bythe presence of a snow cover on the generally irregular bog surfaceTo explain the presence of many relatively large (up to 1500 mm)sand grains in peat cores Bjorck and Clemmensen (2004) thereforeinferred niveo-aeolian conditions In addition in this region mostwinds with storm force occur during autumnndashwinter Thus the ASIpeaks are interpreted mainly as periods of increased winter stormactivity but the possibility of occasional sand transport to the bogsduring severe spring and summer storms is not ruled out As will bediscussed in Section 43 changes in sediment availability throughland use and vegetation disturbances have a minor effect on the ASIsignal

influx2yr)

IR ()

ASI (gt125microm)(grainscm2yr)

Maximum grain size(microm)

yrs ADBC

2000

1500

1000

500

0

-500

-1000

-1500

-2000

-2500

-3000

-3500

-4000

-4500

d e f

ve stratigraphic units recognised in the peat core (the stratigraphy has been adjusted toconditions and low values indicate high BSW Sphagnum influx values are shown in (c)values are plotted in graphs (d) (e) and (f) respectively The gradual transition tolues is indicated by the solid horizontal line


The Store Mosse record shows a clear increase in ASI influx valuesafter ca 2500 cal yrs BP In addition peak values are recorded morefrequently after this time ASI peaks are recorded before 5000 andaround 4700 2500ndash2000 1800 1700 1600ndash1400 1200ndash1050 800ndash500 and 350ndash100 cal yrs BP Maximum grain size values fluctuatestrongly in the period before ca 2500 cal yrs BP and the largest grainswere deposited during this period However these peak values arebased on single samples with very few large grains and are thereforenot reliable as climatic indicators After 2500 cal yrs BP the averagesize of the largest grains is smaller but peaks are based on multiplesamples and have a longer duration These peaks also show a goodcorrelation to the ASI values ASI peaks are therefore interpreted asa proxy for increased storm activity with more frequent andor moreintense storms causing an increase in the sediment transport intothe bog and a relative increase in the size of grains that aretransported

Most interestingly comparison to the record from UndarsmosseBog (Fig 4) shows that the timing of ASI peak events is remarkablysimilar in the two records despite chronological uncertaintiesa distance between the sites of ca 60 km and the different charac-teristics of the surrounding areas Undarsmosse Bog is situated inclose proximity to sandy beaches and dune areas whereas StoreMosse Bog lies more inland in a siltyndashsandy agricultural area Theattribution of individual peaks and the climatic interpretation ofthese peaks as periods of increased winter storm frequency andorintensity have been discussed in De Jong et al (2006 2007) and DeJong (2007) and will not receive further attention here Howeverthe shift from relatively low ASI before ca 2800ndash2600 cal yrs BP tohigh ASI values frequent ASI peaks and a higher level of lsquoASIbackground noisersquo after this time are of interest here and will bediscussed in Section 53 Comparison of the Store Mosse ASI data

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

0

0 44

(grainscm2yr)

0 1 20020406081

cultivated ( pollen)

cal yrs B

P

ASIa b

Fig 4 Comparison between the records from Store Mosse Bog (left side of each axis) and Uncumulative pollen percentage for types indicative of cultivation (Secale Cerealia) (b) ASI valrespectively) and (c) cumulative pollen percentage for types indicative of grazing (PoaceaRumex acetosaacetosella)

with the OBD and water-table records from the Hyltemossen andUndarsmosse Bogs and the humidity proxies from Lakes Igelsjonand Bysjon will provide the basis for evaluation of atmosphericcirculation dynamics in south-west Sweden

43 Land use and sediment availability in the Store MosseBog region

For a correct interpretation of ASI as a climatic proxy it isimportant to assess the possible influence of changes in sedimentavailability through land use and vegetation disturbance on ASIFig 4 shows the total ASI values for the Undarsmosse and StoreMosse Bogs Furthermore the total percentages of pollen typesindicating agriculture and grazing are shown separately for eachsite Only pasture on grasslands and woodlands is taken intoaccount here It was not possible to reconstruct grazing on heathlands due to the abundance of heath in the local bog vegetation Thecomplete pollen records and interpretation of vegetation devel-opment are provided in De Jong et al (2006) for Undarsmosse Bogand De Jong (2007) for Store Mosse Bog The comparison of the ASIrecords and land use indicators shows that as agricultural areasexpanded after ca 3000 cal yrs BP the amplitude of ASI peaksincreased The long-term patterns of the ASI records are thus tosome extent influenced by local- to regional-scale increases inhuman impact

The direct comparison of individual ASI peaks with land use atthe same time shows a different relation though ASI peaks occurwhen pollen types indicating cultivated fields are scarce This canbe seen at both sites for all individual ASI peaks except one The ASIpeak at Undarsmosse Bog occurring at ca 800 cal yrs BP coincideswith a generally high value for cultivated fields Thus with one

0 4 8 12

2000

1500

1000

500

0

-500

-1000

-1500

-2000

-2500

-3000

-3500

-4000

-4500

4812

3 4

grazing indicators ( pollen)

years A

DB

C

c

darsmosse Bog (right side of each axis modified from De Jong (2007)) showing (a) theues of sand grains gt125 mm (note that the values are clipped at 1 and 4 grainscm2yrelt 40 mm Asteraceae (Taraxacum) Plantago lanceolata Potentilla Rubiaceae (Galium)


exception ASI peaks occur when crop cultivation is limited Forpasture the pattern is less clear but there is no consistent pattern ofa causal link between (over)grazing and ASI peaks either Highgrassland values frequently occur after ASI peaks (for examplearound 2000 1350 and 500 cal yrs BP at Store Mosse Bog andaround 1100 800 and 500 cal yrs BP at Undarsmosse Bog) or duringperiods of generally very low ASI values (eg around 3500 cal yrs BPat Store Mosse Bog and around 2800 cal yrs BP at UndarsmosseBog) These findings thus imply that although the overall increasein the amplitude of ASI peaks may be related to increased land usethe timing of ASI peaks is not The timing of ASI peaks is thereforeinterpreted as a climatic signal of increased storm activity

5 Discussion

51 OBD as a proxy for effective humidity changes

In Fig 5 the OBD record from Store Mosse Bog is shown incomparison to proxy data reflecting effective precipitation andBSW from other sites in south-west Sweden The chronologies ofHyltemossen Bog and Undarsmosse Bog are based on eight and 14AMS 14C dates respectively with details provided in Bjorck andClemmensen (2004) and De Jong et al (2006) In addition testateamoebae analysis was carried out on samples from UndarsmosseBog covering approximately the last 1700 years (De Jong et al2007) From these the variations in the depth of the water tablewere reconstructed using the transfer function developed byCharman and Blundell (2007) At Hyltemossen Bog humificationvalues were also measured for the period 2500 cal yrs BP topresent (Bjorck and Clemmensen 2004) This record is generallyin good agreement with the OBD record from the same site with

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

gcm3

permil V-SMOW

Cal yrs B

P

a b c

Fig 5 Humidity fluctuations in south-west Sweden as reflected by (a) d18O data obtained froOrganic Bulk Density (OBD) variations at Undarsmosse Bog (De Jong et al 2006) (c) a test2007) (d) OBD variations at Hyltemossen Bog (Bjorck and Clemmensen 2004) (e) OBD variacentral Sweden (Rundgren 2008) and (g) lake-level fluctuations reconstructed from sedimthe reconstructed low lake level around 1500 cal yrs BP that is most likely an artefact of humof records reflect relatively dry conditions Solid horizontal lines indicate the onset of omb

high absorbance values ca 1900ndash1700 1300ndash1000 and after800 cal yrs BP Fig 5 shows that the different peat bog records allinterpreted as proxies for BSW show many similarities but alsosome clear differences Below we discuss the main differencesbetween these records to assess the reliability of OBD records asproxies for BSW

The Store Mosse and Undarsmosse peat records show clearlydecreasing OBD trends around 2100 and 1700 cal yrs BP respec-tively from values well above 01 gcm3 to values around 008 gcm3 At Hyltemossen Bog a transition from values of 010ndash012 to008 gcm3 can be seen around 3200 cal yrs BP These shifts to lowerOBD values are interpreted as local transitions from fen peat toombrotrophic bog conditions characterised by an increase ofSphagnum growth andor a decrease of peat humification resultingin increased peat accumulation (Fig 5) The transition occurred firstat the most upland site (Hyltemossen Bog) followed by Store MosseBog which receives 300ndash400 mm more precipitation annually thanUndarsmosse Bog Undarsmosse Bog was the last site to developinto a raised peat bog Here this transition was also observed in thetestate amoebae data which indicate minerotrophic conditionsprior to 1700 cal yrs BP (unpublished data) Therefore the generaltransition to lower OBD values should not only be interpreted asa climatic signal but also as a result of local bog development

Furthermore due to the transition from fen peat to ombro-trophic peat at the three sites the sensitivity of the peat bogs toclimatic variability changes with time Whereas raised bogs dependon precipitation and evaporation from the bog surface and aresensitive to changes in both directions during the fen stage of thepeat records (thus during the period before ca 2000 cal yrs BP forStore Mosse Bog) it seems that OBD is sensitive to prolonged dryconditions but relatively less to increases in wetness Prolonged dry

gcm3

DRY

LOWHIGH

d e f g

gcm3

m the Lake Igelsjon sediment record (Hammarlund et al 2003 Jessen et al 2005) (b)ate amoebae-based water table reconstruction from Undarsmosse Bog (De Jong et altions at Store Mosse Bog (this study) (f) wet-shifts recorded in peat bogs in Varmland

ent stratigraphic studies at Lake Bysjon (Digerfeldt 1988) The question mark indicatesan impact around the lake Grey shading indicates the time periods when the majority

rotrophic conditions at the three bog sites


conditions led to a lowering of the groundwater table (and thus fenwater table) causing a strong increase of peat humification Thiscan be seen clearly eg around 4800ndash4400 cal yrs BP In generalhowever fens are much less sensitive archives of climatic changesthan ombrotrophic bogs The timing of the transition to raised bogconditions at the three bog sites (indicated in Fig 5) shouldtherefore be kept in mind

Another important feature of the OBD records is the nearabsence of variability in the Undarsmosse record at 1500ndash300 cal yrs BP In contrast the OBD records from the Store Mosseand Hyltemossen Bogs as well as the water-table reconstructionfrom Undarsmosse Bog show large variability during this time Thereason for the absence of variability in the OBD record fromUndarsmosse is not well understood but it may be related to therelatively dry conditions at this site in comparison to the othermore inland sites Due to the relatively low precipitation Undars-mosse Bog may have a thicker acrotelm Due to the longer residencetime of the peat-forming vegetation in this aerated zone post-depositional decomposition possibly took place during a longerperiod here than at the other two sites This would smooth outinitial OBD variations but it would not affect the testate amoebaerecord since secondary decomposition does not affect the speciescomposition in the peat

The interpretation of OBD records as well as the morefrequently used peat humification records (eg Chambers et al1997 Borgmark 2005) as proxies for BSW is hampered by theinfluence of local vegetation changes which are often related tochanges in micro-topography of the bog surface As discussed byeg Chambers et al (1997) and Yeloff and Mauquoy (2006)different species and parts of peat-forming plants decay atdifferent rates Thus the decomposition of plant types thatgenerally occur in eg hollow microforms may result in differen-tial OBD as well as humification values whereas macrofossilanalysis would show that these all reflect relatively high BSW Onthe other hand eg Sillasoo et al (2007) noted that discrepanciesbetween humification records and BSW reconstructions based onmacrofossils may be due to the long response time of plants toaltered hydrological conditions For all reasons mentioned abovea multi-proxy approach to BSW reconstructions is highly recom-mended (eg Yeloff and Mauquoy 2006)

The differences between the records considered in this studyindicate that single OBD records may not reliably reflect regional-scale BSW variations However the apparent correlation betweenthe different datasets shown in Fig 5 indicates that when OBDdata are used in combination with records from other localitiesand with other proxies such records may provide importantinformation on regional-scale variations in BSW and effectiveprecipitation

52 Humidity variations in south-west Sweden

To assess regional-scale variations in humidity the peat OBDrecords are compared to two lake-sediment records (Fig 5) Thelake-level reconstruction of Digerfeldt (1988) gives millennial-scaleevidence of high-stands and low-stands at Lake Bysjon in south-ernmost Sweden The curve in between these high- and low-standsis based on linear interpolation Although the dating of the LakeBysjon record (Digerfeldt 1988) is problematic since the chro-nology is based on bulk radiocarbon dates and pollen-basedcorrelation these data indicate a general lake-level rise and thus anincrease in wetness around 3000 cal yrs BP This is seeminglyinterrupted by a lake-level low-stand indicating drier conditionsaround 1500 cal yrs BP However later work has indicated thatlowering of the sedimentation limit at this time is most likely anartefact of human-induced vegetation changes ie increasedopenness around the lake causing a stronger wind fetch which

resulted in wave erosion at the lake shores (G Digerfeldt personalcommunication)

A detailed palaeohydrological study based on stable isotopeanalyses of the Lake Igelsjon sediment record was presented byHammarlund et al (2003) and provided with a revised chro-nology by Jessen et al (2005) The d18O record was obtained onbulk carbonates precipitated mainly by Chara algae and inter-preted as a proxy for effective precipitation (Hammarlund et al2003) Periods of elevated evaporationinflow ratios of the basin(high summer temperature andor low annual precipitation) arereflected in the d18O record as less negative values whereasintervals of strongly negative d18O values are indicative of theopposite (coldwet conditions) Comparison to a pollen-basedtemperature reconstruction from nearby Lake Flarken (Seppaet al 2005 Fig 6) has shown that the long-term (millennial-scale) trends in the isotope-based record of effective precipitationappear to be driven mainly by temperature with superimposedeffects of short-term variations in precipitation The Lake Igelsjonrecord is based on a highly detailed chronology before ca3000 cal yrs BP (Hammarlund et al 2003 Jessen et al 2005)whereas the dating control and sample resolution are lower inthe subsequent part

Together these six records are used to construct a regionalscheme of effective precipitation fluctuations in south-west Swe-den during the past ca 6500 years Dry periods identified in themajority of the six records are shaded in Fig 5 and summarised inTable 2 After 3000 cal yrs BP the dating of these dry periods ismainly based on the OBD record from Store Mosse Bog since boththe chronological control and sampling density are highest herePrior to this the timing of the shaded intervals is based on the LakeIgelsjon record where five radiocarbon dates obtained on plantmacrofossils are available between 3500 and 4500 cal yrs BP (Jes-sen et al 2005) Despite inherent differences in sensitivitytemporal resolution and spatial representation there is a strongagreement between the different proxy records The comparisonshows that predominantly dry periods occurred at a regional scaleat approximately 4800ndash4400 2000ndash1700 1300ndash1000 700ndash500and 300ndash100 cal yrs BP (see Fig 5 and Table 2) Taking into accountthe chronological uncertainties at the Store Mosse and Undars-mosse Bogs during the dry period at 4800ndash4400 cal yrs BP it ispossible that the maximum OBD values recorded at this stagerepresent the same episode of maximum dryness as recorded atLake Igelsjon around 4500 cal yrs BP

Wetter conditions most likely prevailed in between these dryperiods for example around 3500 1500 and 1000 cal yrs BP Thelatter period is characterised by a decrease in d18O at Lake Igelsjonbut does not appear in the OBD records from the Store Mosse andUndarsmosse sites However wet-shifts are recorded in nearly allrecords in Fig 4 around 4400 1500 and 1000 cal yrs BP These wet-shifts are in good agreement with wet-shifts recorded at egSvanemose Bog Denmark (Barber et al 2004) and many other sitesin north-west Europe as summarised by Hughes et al (2000) andBarber et al (2003)

Independent evidence of increased effective precipitation insouth-west Scandinavia during recent millennia is provided bya compilation of peat-stratigraphic data from central and northernSweden (Rundgren 2008) Based on well-dated records from morethan 10 sites in the province of Varmland (situated between theSwedish and Norwegian sites included in the present study)average peat accumulation rates reach a distinct peak at 2500ndash2000 cal yrs BP indicative of elevated BSW Moreover the recordfrom Varmland shows a good correlation with the BSW variationsinferred from this study Wet-shifts reconstructed from Varmlandpredominantly occur at or shortly after the end of the dry phasesrecorded in south-west Sweden around 3800 2500 1700 and900 cal yrs BP (Fig 5)

ordmC

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

Pw western Norway

Cal yrs B

P

mm

DRY

Glacier fluctuations Annual mean Tlake Flarken

140 120 100 80 60 43210-1-2 5 6 7 8 9

EXPANSION

Fig 6 Comparison between the regional-scale fluctuations in effective precipitation inferred for south-west Sweden (relatively dry periods represented by grey shading same as inFig 5) winter precipitation changes based on four glacier records from western Norway glacier extent variations of the Jostedalsbreen Glacier (Nesje et al 2001) and the pollen-based reconstruction of annual mean temperature from Lake Flarken (Seppa et al 2005) The comparison between the Norwegian winter precipitation record and the regionalreconstruction of effective precipitation from south-west Sweden indicates apparently synchronous variations in effective precipitation in these areas after ca 2000 cal yrs BP Theasterisk indicates a period of very high d18O-inferred effective precipitation at Lake Igelsjon (see Fig 5)


53 Synchronous variations in effective precipitation in themaritime regions of southern Norway and Sweden

Currently the coastal areas of southern Sweden and south-westNorway experience a maritime climate mainly controlled by thefrequency and intensity of passing cyclones Therefore reconstruc-tions of effective precipitation in both regions are expected to showsimilar long-term trends Fig 6 shows a comparison between thereconstructed effective precipitation changes (dry phases) insouthern Sweden and a reconstruction of changes in winter precip-itation (Pw) based on four glacier records from south-west NorwayJostedalsbreen Hardangerjoslashkulen Bjoslashrnbreen and SposlashrteggbreenThese four glaciers are situated in western and central southernNorway (Fig 1) and are controlled mainly by winter precipitation(Bjune et al 2005 Nesje et al 2008) The reconstruction of winter

Table 2Dry time periods in south-west Sweden as recorded in one lake study and three peatbog records Dry time periods are indicated with an x whereas questionmarksindicate that no increase in dry conditions was recorded for a specific site For theUndarsmosse Bog site both the OBD record and the water table reconstruction basedon testate amoebae (TA from 1700 cal yrs BP) were used

Cal yrsBP

LakeIgelsjon

UndarsmosseBog OBD

UndarsmosseBog TA

HyltemossenBog

StoreMosseBog

4800ndash4400

x x No data x x

2000ndash1700

x No data x

1300ndash1000

x x x x

700ndash500 x x x300ndash100 x x x x

precipitation is based on the exponential relationship between meansolid winter precipitation and the equilibrium line altitude (ELA) andablation season (springndashsummer) temperature (Dahl and Nesje1996 Nordli et al 2005) Summer temperatures were reconstructedfrom pollen-climate transfer functions from nearby lake sediments(Bjune et al 2005) The resulting average Pw is shown in Fig 6 Forcomparison the record of retreat and expansion of the Joste-dalsbreen glacier is also shown as well as the pollen-basedtemperature reconstruction from Lake Flarken close to Lake Igelsjon(Seppa et al 2005) Together with the records shown in Fig 5 thesedata indicate progressive millennial-scale trends towards lowertemperature expansion of the Jostedalsbreen glacier and higher lakelevels since ca 4400 cal yrs BP

Important to note is that the effective precipitation recon-structions from southern Sweden are interpreted mainly assummer signals although changes in winter precipitation may alsohave affected the records Dry conditions indicate a relative waterdeficit during the summer months which may be related to highsummer evaporation andor generally low annual precipitationThe Norwegian Pw record is however a proxy for (solid) winterprecipitation whereas the record of glacier fluctuations is affectedby winter precipitation as well as by summer temperature In moredetail the comparison to the south Swedish reconstruction of dryand wet periods shows that after ca 2000 cal yrs BP the effectiveprecipitation record and the Pw record appear to show similar long-term trends despite the differences between the seasons that theproxy data mainly represent and their chronological uncertaintiesThe correspondence between the datasets after this time suggeststhat subsequent changes in climate along the south-west coasts ofScandinavia were controlled by the same long-term variations inatmospheric circulation patterns The climatic variability in the LateHolocene will be discussed in Section 55


Before ca 2000 cal yrs BP the effective humidity and Pw recon-structions show no apparent correlation or at times even oppositesignals for example at 4800ndash4200 cal yrs BP and around3500 cal yrs BP A possible explanation for these discrepancies isthat climatic forcing was more local and seasonal differences werelarger as compared to recent millennia (Kutzbach et al 1993)However specific factors controlling each record could also causedifferent signals in the two regions First as discussed in Section 51the Swedish sites had not yet developed into raised bogs at thistime and the climatic interpretation of OBD values prior to this isproblematic Second the development of glaciers that are nowmaritime may not always have been primarily dependant onwinter precipitation as summer ablation may have been animportant factor This explains why the continuous decrease in Pw

between ca 5000 and 3500 cal yrs BP corresponds to an expansionof the Jostedalsbreen glacier (Fig 6) whereas a retraction wouldhave been expected if the glaciers were controlled mainly by winterprecipitation around this time The Lake Flarken record showsdecreasing mean annual temperatures during this period Thus itappears that the currently maritime glaciers of south-westernNorway were more sensitive to summer temperature prior to ca2000ndash2500 cal yrs BP

54 Past storm activity in south-west Sweden

The increase in total ASI and the more frequent occurrence ofASI peaks after ca 2500 cal yrs BP (Figs 3 4) can be explained bythree factors (1) increased sample resolution after ca2000 cal yrs BP (Fig 2) which makes individual ASI peaks appearhigher as compared to before 2000 cal yrs BP (2) increased sedi-ment availability due to generally intensified land use and (3) anincreased frequency and intensity of winter storms Although (1)and (2) certainly affect peak amplitudes and the total ASI influxthese factors alone cannot explain the more frequent occurrence ofASI peaks after ca 2500 cal yrs BP The duration of ASI peaksrecorded after this time is so long (ca 50ndash200 years) that thesewould also have been visible in the older part of the record witha lower sample resolution albeit with a lower amplitude At StoreMosse Bog ASI values are close to zero between 4600 and2500 cal yrs BP though and at the Undarsmosse site this is the casebetween 4000 and 2800 cal yrs BP (De Jong et al 2006) These lowvalues cannot be attributed entirely to low sediment availabilityaround this time since the pollen data (Fig 4) show that agricul-tural activities commenced already around 4200 cal yrs BP

An alternative explanation for the increase in ASI influx around2500 cal yrs BP could be a change in the vegetation structure on andaround the bog as dense vegetation could filter out sand grains andthus lead to reduced ASI However although this mechanismcannot be ruled out entirely it is not supported by pollen analysisPollen analysis shows that total tree percentages are constant andhigh during the period 6500 cal yrs BP ndash present whereas trees thatat present typically grow on bogs in south-west Sweden such asPinus and Betula occur at high values from 3500 cal yrs BP onwardsand 2500ndash700 cal yrs BP respectively (unpublished data) Alnusa tree that typically grows in the wet areas surrounding the StoreMosse and Undarsmosse Bogs at present shows high pollenpercentages from ca 5000 to 1200 cal yrs BP Thus trees and shrubsappear to have been present on and around the bog already prior tothe ASI increase and a filtering effect is thus likely to have takenplace throughout the reconstructed period Therefore the shiftfrom low to high ASI peak frequencies around 2500 cal yrs BP isinterpreted primarily as an increase in the frequency of extremestorm events

The ASI records do not resolve whether more frequent ASI peaksare related to an increase in the number of winter storms duringspecific periods or to an increase in the intensity of storms It is

thus possible that ASI peaks reflect a low number of very severestorms or that they reflect a period of prolonged stormy conditionsA modelling study of cyclone activity during the so-called Maundersolar Minimum (MM AD 1645ndash1715) shows that the stormfrequency was low in northern Europe during the MM whereasstorm intensity was significantly higher in winter as compared tomodern time (Raible et al 2007) ASI values are extremely higharound this time (300ndash220 cal yrs BP) in both records This suggeststhat at least for this time period the ASI records are stronglysensitive to extreme events rather than the total number of winterstorms (Raible et al 2008)

55 Unstable atmospheric conditions in the late Holocene

In the records presented in this study the period after ca2500 cal yrs BP is characterised by frequent fluctuations in effectiveprecipitation Pw and storm activity Studies of current glacierresponses to atmospheric circulation dynamics show that low Pw

values are associated with a high-pressure blocking situation overScandinavia (Nordli et al 2005) The alternation of relatively dryand wet conditions inferred from the present study may thus pointto an alternating dominance of atmospheric blocking and westerlyair flow over southern Scandinavia If this interpretation is correctthe dry periods compiled in Table 2 represent times when atmo-spheric blocking occurred frequently over large parts of southernScandinavia causing low precipitation over glaciers in south-westNorway (eg Nordli et al 2005) and peat bogs and lakes in south-west Sweden in winter Furthermore the relatively dry conditionsin bogs and lakes in south-west Sweden during these times mayindicate that summer evaporation was high as well Periods of highPw low OBD and low d18O values on the other hand indicate strongwesterly flow patterns and frequent passages of cyclones possiblyin all seasons The centennial-scale fluctuations between predom-inantly dry and wet periods (approximately every 200ndash400 years)point to an unstable climate with frequent shifts in the positionand strength of westerlies This is supported by the ASI data whichshow a clear increase in peak frequency after ca 2500 cal yrs BP

Increased climatic variability has been observed in manyrecords from the North Atlantic region in the late Holocene(Snowball et al 2004) On Greenland lake-sediment proxies showthat after 3700 cal yrs BP the climate became relatively drier butsuperimposed on this general trend the millennial- and centennial-scale climatic variations show a clear increase in amplitude(Andresen et al 2004) Marine cores of northern Iceland showindications of increased bottom-current transport and frontalupwelling at 3000ndash1000 cal yrs BP as a result of the proximity tothe marine Polar Front (Andresen et al 2005) South of Icelandmarine records also point to increased climatic instability andperiods of cooling with enhanced cyclone activity after5000 14C yrs BP (Witak et al 2005) These authors interpret thischange as a sign of increased activity of the East Greenland Currentleading to a southward displacement of the Polar Front A partic-ularly rapid transition to more variable climatic conditions around3700 cal yrs BP was described from a varved lake sedimentsequence in northern Sweden where variations in minerogenicinput were interpreted as a record of strongly variable winterprecipitation (Snowball et al 1999) Risebrobakken et al (2003)found that diatom d18O data from the Norwegian Sea reflect highlyvariable conditions after ca 4000 cal yrs BP related to eithera weakening of the westerlies or a stronger variability in theintensity of westerlies Our data support the latter interpretationsince a stronger variability in the intensity as well as the position ofwesterlies would lead to increased fluctuations in effectiveprecipitation and storm activity in our study area

Scottish peat bog studies revealed a pattern of enhancedregionality in BSW during the last 2500 years with an apparent


antiphase behaviour between northerly (low BSW) and southerly(high BSW) bogs from 2500 to 2000 cal yrs BP (Langdon and Barber2005) These regional differences were tentatively interpreted asindications for northward and southward shifts of the Polar FrontRundgren (2008) also described a similar northndashsouth BSWcontrast between south-central and northern Swedish peat bogsafter 2300 cal yrs BP Our data do not show this north-southcontrast during this time period although this could be due to thelimited climatic sensitivity of the peat bog records two of whichwere still minerotrophic at this time (Fig 5) The glacier records doshow very dry conditions during this period however whereas thestrong increase in ASI at this time could also be explained bya closer proximity to the Polar Front Thus the increased climaticinstability in the late Holocene described from our study areas insouth-west Sweden and western Norway is also observed in thewider North Atlantic region and appears to be linked to frequentchanges in the position of the Polar Front

6 Conclusions

The comparison between the south Swedish climate recordsenables a regional reconstruction of variations in effective precip-itation despite differences in the type of sites investigated (lakesand peat bogs) and the proxies used Single OBD records may not beunambiguous proxies for BSW but when several records andproxies are combined OBD can be a helpful tool to reconstructBSW The combination of proxy records evaluated in this studygives evidence of predominantly dry conditions during five timeperiods ca 4800ndash4400 2000ndash1700 1300ndash1000 700ndash500 and300ndash100 cal yrs BP

After ca 2000 cal yrs BP the effective precipitation variations insouth-west Sweden correlate with winter precipitation changesinferred from maritime glaciers in south-west Norway This indi-cates that the climate in both regions was controlled by large-scaleatmospheric circulation dynamics in the North Atlantic region

In the late-Holocene centennial-scale fluctuations in effectiveprecipitation and winter precipitation reflect the alternating domi-nance of atmospheric blocking and westerly flow with frequentpassages of cyclones across southern Scandinavia The strong vari-ability of these records together with the strong increase in winterstorm frequencies after ca 2500 cal yrs BP indicates a highly variableclimate

Acknowledgements

We would like to thank two anonymous reviewers for theirvaluable comments and suggestions to the original manuscript Weare also grateful to Svante Bjorck for discussions and commentsAMS 14C dating was carried out at the Radiocarbon Dating Labo-ratory in Lund Sweden Dating was supported by the Royal Phys-iographic Society (Lund)

References

Alexandersson H Schmith T Iden K Tuomenvirta H 1998 Long-term variationsof the storm climate over NW Europe The Global AtmospherendashOcean System 697ndash120

Almquist-Jacobson H 1995 Lake-level fluctuations at Ljustjarnen central Swedenand their implications for the Holocene climate of Scandinavia PaleogeographyPaleoclimatology Paleoecology 118 269ndash290

Andresen CS Bjorck S Bennike O Bond G 2004 Holocene climate changes insouthern Greenland evidence from lake sediments Journal of QuaternaryScience 19 783ndash795

Andresen CS Bond G Kuijpers A Knutz PC Bjorck S 2005 Holocene climatevariability at multidecadal time scales detected by sedimentological indicatorsin a shelf core NW off Iceland Marine Geology 214 323ndash338

Barber KE Chambers FM Maddy D 2003 Holocene palaeoclimates from peatstratigraphy macrofossil proxy climate records from three oceanic raised bogsin England and Ireland Quaternary Science Reviews 22 521ndash539

Barber KE Chambers FM Maddy D 2004 Late Holocene climatic history ofnorthern Germany and Denmark peat macrofossil investigation at DosenmoorSchleswig-Holstein and Svanemose Jutland Boreas 33 132ndash144

Barry RG Chorley RJ 1998 Atmosphere Weather and Climate seventh edRoutledge London

Berglund M 1995 The late Weichselian deglaciation vegetational developmentand shore displacement in Halland southwestern Sweden Lundqua thesis 35Lund University Lund

Bjune AE Bakke J Nesje A Birks HJB 2005 Holocene mean July temperatureand winter precipitation in western Norway inferred from palynological andglaciological lake-sediment proxies The Holocene 15 177ndash189

Bjorck S Clemmensen LB 2004 Aeolian sediment in raised bog deposits Hal-land SW Sweden a new proxy record for winter storminess variation insouthern Scandinavia The Holocene 14 677ndash688

Blackford JJ Chambers FM 1993 Determining the degree of peat decompositionfor peat-based palaeoclimatic studies International Peat Journal 5 7ndash24

Borgmark A 2005 Holocene climate variability and periodicities in south-centralSweden as interpreted from peat humification analysis The Holocene 15387ndash395

Bronk Ramsey C 1995 Radiocarbon calibration and analysis of stratigraphy theOxCal program Radiocarbon 37 425ndash430

Bronk Ramsey C 2001 Development of the radiocarbon calibration programRadiocarbon 43 355ndash363

Charman DJ Blundell A Accrotelm members 2007 A new European testateamoebae transfer function for palaeohydrological reconstruction on ombro-trophic peatlands Journal of Quaternary Science 22 209ndash221

Chambers FM Barber KE Maddy D Brew J 1997 A 5500-year proxy-climateand vegetation record from blanket mire at Talla Moss Borders Scotland TheHolocene 7 391ndash399

Dahl SO Nesje A 1996 A new approach to calculating Holocene winter precip-itation by combining glacier equilibrium-line altitudes and pine-tree limitsa case study from Hardangerjoslashkulen central southern Norway The Holocene 6381ndash398

De Jong R 2007 Stormy records from peat bogs in south-west Sweden ndash impli-cations for regional climatic variability and vegetation changes during the past6500 years LUNDQUA thesis 58 Lund University Lund

De Jong R Bjorck S Bjorkman L Clemmensen LB 2006 Storminess variationduring the last 6500 years as reconstructed from an ombrotrophic peat bog inHalland southwest Sweden Journal of Quaternary Science 21 905ndash919

De Jong R Schoning K Bjorck S 2007 Increased aeolian activity during humidityshifts as recorded in a raised bog in south-west Sweden during the past 1700years Climate of the Past 3 411ndash422

Digerfeldt G 1988 Reconstruction and regional correlation of Holocene lake-levelfluctuations in lake Bysjon south Sweden Boreas 17 165ndash182

Granlund E 1932 De Svenska hogmossarnas geologi Deras bildningsbetingelserutvecklingshistoria och utbredning jamte sambandet mellan hogmossebildningoch forsumpning Sveriges Geologiska Undersokning C 373

Hammarlund D Bjorck S Buchardt B Israelson C Thomsen CT 2003 Rapidhydrological changes during the Holocene revealed by stable isotope records oflacustrine carbonates from lake Igelsjon southern Sweden Quaternary ScienceReviews 22 353ndash370

Hughes PDM Mauquoy D Barber KE Langdon PG 2000 Mire-developmentpathways and palaeoclimatic records from a full Holocene peat archive atWalton Moss Cumbria England The Holocene 10 467ndash479

Jessen CA Rundgren M Bjorck S Hammarlund D 2005 Abrupt climaticchanges and an unstable transition into a late Holocene thermal declinea multiproxy lacustrine record from southern Sweden Journal of QuaternaryScience 20 349ndash362

Jonsson P Barring L 1994 Zonal index variations 1899ndash1992 links to airtemperature in southern Scandinavia Geografiska Annaler Serie A ndash PhysicalGeography 76 207ndash219

Jonsson P Fortuniak K 1995 Interdecadal variations of surface wind direction inLund southern Sweden 1741-1990 International Journal of Climate 15447ndash461

Kutzbach JE Guetter PJ Behling PJ Selin R 1993 Simulated climatic changesresults of the COHMAP climate-model experiments In InWright Jr HEKutzbach JE Webb III T Ruddiman WF Street-Perrott FA Bartlein PJ(Eds) Global Climates since the Last Glacial Maximum University of MinnesotaPress Minneapolis pp 24ndash93

Langdon PG Barber KE 2005 The climate of Scotland over the last 5000 yearsinferred from multiproxy peatland records inter-site correlations and regionalvariability Journal of Quaternary Science 20 549ndash566

Lundqvist J Wohlfarth B 2001 Timing and east-west correlation of southSwedish ice marginal lines during the Late Weichselian Quaternary ScienceReviews 20 1127ndash1148

Mauquoy D Barber K 2002 Testing the sensitivity of the palaeoclimatic signalfrom ombrotrophic peat bogs in northern England and the Scottish bordersReview of Paleobotany and Palynology 119 219ndash240

Moros M Emeis K Risebrobakken B Snowball I Kuijpers A McManus JJansen E 2004 Sea surface temperatures and ice rafting in the Holocene NorthAtlantic climatic influences on northern Europe and Greenland QuaternaryScience Reviews 23 2113ndash2126

Nesje A Matthews JA Dahl SO Berrisford MS Andersson C 2001 Holoceneglacier fluctuations of Flatebreen and winter-precipitation changes in the Jos-tedalsbreen region western Norway based on glaciolacustrine sedimentrecords The Holocene 11 267ndash280


Nesje A Bakke J Dahl SO LieOslash Matthews JA 2008 Norwegian mountainglaciers in the past present and future Global and Planetary Change 60 10ndash27

Nilsson C Stjernquist I Barring L Schlyter P Jonsson AM Samuelsson H2004 Recorded storm damage in Swedish forests 1901-2000 Forest Ecologyand Management 199 165ndash173

Nordli Oslash Lie Oslash Nesje A Benestad RE 2005 Glacier mass balance in southernNorway modelled by circulation indices and spring-summer temperatures AD1781ndash2000 Geografiska Annaler 87A 431ndash445

Paringsse T 1989 Quaternary Map Varberg NE 1 50000 Swedish Geological SurveySeries Ae 102 Offset Centre AB Uppsala

Raible CC Yoshimori M Stocker TF Casty C 2007 Extreme midlatitudecyclones and their implications for precipitation and wind speed extremes insimulations of the Maunder Minimum versus present day conditions ClimateDynamics 28 409ndash423

Raible CC De Jong R Stocker TF Yoshimori M 2008 Maunder Minimumclimate variability from wind and moisture-sensitive proxies and modelsimulations PAGES News 16 10ndash11

Reimer P Baillie M Bard E Bayliss A Beck J Bertrand C Blackwell P Buck CBurr G Cutler K Damon P Edwards R Fairbanks R Friedrich MGuilderson T Hogg A Hughen K Kromer B McCormac G Manning SRamsey CB Reimer R Remmele S Southon J Stuiver M Talamo STaylor F Van der Plicht J Weyhenmeyer C 2004 IntCal04 TerrestrialRadiocarbon Age Calibration 0-26 cal Kyr BP Radiocarbon 46 1029ndash1058

Risebrobakken B Jansen E Andersson C Kjelde E Hevroslashy K 2003 A high-resolution study of Holocene paleoceanographic changes in the Nordic SeasPaleoceanography 18 1017 doi1010292002PA000764

Rundgren M 2008 Stratigraphy of peatlands in central and northern Swedenevidence of Holocene climatic change and peat accumulation GFF 13095ndash107

Seppa H Hammarlund D Antonsson K 2005 Low-frequency and high-frequency changes in temperature and effective humidity during the Holocenein south-central Sweden implications for atmospheric and oceanic forcings ofclimate Climate Dynamics 25 285ndash297

Sillasoo U Mauquoy D Blundell A Charman D Blaauw M Daniell JGRToms P Newberry J Chambers FM Karofeld E 2007 Peat multi-proxy datafrom Mannikjarve bog as indicators of Late Holocene climate changes in Esto-nia Boreas 36 20ndash37

SMHI (Swedish Meteorological and Hydrological institute) wwwsmhise (accessed27-03-2008)

Snowball IF Sandgren P Petterson G 1999 The mineral magnetic properties ofan annually laminated Holocene lake sediment sequence in Northern SwedenThe Holocene 9 353ndash362

Snowball IF Korhola A Briffa KR Koccedil N 2004 Holocene climate dynamics inFennoscandia and the North Atlantic In In Battarbee RW Gasse FStickley CE (Eds) Past Climate Variability Through Europe and AfricaSpringer Dordrecht The Netherlands pp 465ndash494

Witak M Wachnika A Kuijpers A Troelstra S Prins MA Witkowski A 2005Holocene North Atlantic surface circulation and climatic variability evidencefrom diatom records The Holocene 15 85ndash96

Yeloff D Mauquoy D 2006 The influence of vegetation composition onpeat humification implications for palaeoclimatic studies Boreas 35662ndash673


Barber 2005) More recently variations in effective precipitation insouthern Sweden were based on oxygen and carbon isotopicrecords from carbonate-rich sediments at Lake Igelsjon south-central Sweden (Hammarlund et al 2003 Fig 1) The isotopicvariations were interpreted as reflections of changing effectiveprecipitation ie changes in the evaporationinflow ratio of thebasin This implies that changes in effective precipitation reflectvariations in summer temperature as well as annual precipitation

In order to reliably reconstruct large-scale climatic patternsmultiple study sites are needed to separate local effects from theimpact of regional- or global-scale climatic changes In this studyproxy data from five sites in south-west Sweden are used forreconstruction of regional-scale variations in effective precipitation(Fig 1) We use organic bulk density (OBD) measurements from theStore Mosse Bog and two other peat bogs to reconstruct bog surfacewetness (BSW) variations since ca 6500 cal yrs BP OBD valuesreflect the degree of peat decomposition since this affects theaverage particle size of the peat and thereby the water contentlow-decomposed peat contains large Sphagnum remains and hasa high water content (Bjorck and Clemmensen 2004) HoweverOBD values should be interpreted carefully since they are alsosensitive to non-climatic factors such as local bog developmentlocal bog vegetation changes and drainage These problems will bediscussed in Section 51 In addition proxy-based reconstructions ofstorm activity are used as a source of information on past atmo-spheric conditions in the region These reconstructions are basedon the total aeolian sediment deposition in two peat bogs in south-west Sweden Undarsmosse Bog (De Jong et al 2006) and StoreMosse Bog (De Jong 2007)

Fig 1 Map showing the location of the Store Mosse Bog situated at the transition between tand coring location are also indicated to the right The positions of Lake Igelsjon (Hammarluand Hyltemossen Bog (Bjorck and Clemmensen 2004) in south-west Sweden are indicated awas derived (Bjune et al 2005)

To enable a regional-scale reconstruction of effective precipita-tion changes in southern Sweden OBD records from the StoreMosse Bog (this study Fig 1) the Undarsmosse Bog (De Jong et al2006) and the Hyltemossen Bog (Bjorck and Clemmensen 2004)are compared to the palaeohydrological records from Lake Igelsjon(Hammarlund et al 2003) and Lake Bysjon (Digerfeldt 1988) Wethen compare this regional pattern of effective humidity variationsin southern Sweden to a reconstruction of winter precipitationderived from glaciers in south-west Norway (Nesje et al 2001Bjune et al 2005) Since these glaciers are also situated ina strongly oceanic climate (Nesje et al 2008) this comparisonprovides insight into large-scale patterns of atmospheric circula-tion Thus the aims of this study are (1) to assess the reliability ofOBD as a proxy for BSW variability (2) to construct a regionalscheme of effective precipitation fluctuations in south-west Swe-den and (3) to assess the wider implications of the reconstructedvariations in effective precipitation and storm activity

2 Study area

Store Mosse Bog is situated on the coastal plain of the provinceof Halland south-west Sweden (Fig 1) The coastal plain is ca 10ndash20 km wide and the elevation is 10ndash25 m above sea level Lundqvistand Wohlfarth (2001) dated the deglaciation of the coastal plain to16000 cal yrs BP After the initial deglaciation the ice marginfluctuated strongly resulting in the formation of a successive seriesof moraine ridges and thick glaciofluvial and glaciomarine depositswest of the ice margin (Berglund 1995) Because of substantialfluctuations of relative sea level after the deglaciation sediments

he coastal plain and the upland areas of south-central Sweden (inset) The local settingnd et al 2003) Lake Bysjon (Digerfeldt 1988) Undarsmosse Bog (De Jong et al 2006)s well as the glaciers in south-west Norway from which the winter precipitation record




or 225 60LuS 6619













4 Results



Dep

th

(cm

)

Age (cal yr BP)

0 1000 2000 3000 4000 5000 6000

350

300

250

200

150

100

50

0




OBD(grcm3)

Sphagnum (sporescm

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0







influx2yr)

IR ()



yrs ADBC

2000

1500

1000

500

0

-500

-1000

-1500

-2000

-2500

-3000

-3500

-4000

-4500

d e f





500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

0

0 44

(grainscm2yr)

0 1 20020406081


cal yrs B

P

ASIa b






0 4 8 12

2000

1500

1000

500

0

-500

-1000

-1500

-2000

-2500

-3000

-3500

-4000

-4500

4812

3 4


years A

DB

C

c




5 Discussion



6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

gcm3

permil V-SMOW

Cal yrs B

P

a b c





gcm3

DRY

LOWHIGH

d e f g

gcm3
















ordmC

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

Pw western Norway

Cal yrs B

P

mm

DRY


140 120 100 80 60 43210-1-2 5 6 7 8 9

EXPANSION






Cal yrsBP

LakeIgelsjon

UndarsmosseBog OBD

UndarsmosseBog TA

HyltemossenBog

StoreMosseBog

4800ndash4400

x x No data x x

2000ndash1700

x No data x

1300ndash1000

x x x x



















6 Conclusions




Acknowledgements


References






















































or 225 60LuS 6619













4 Results



Dep

th

(cm

)

Age (cal yr BP)

0 1000 2000 3000 4000 5000 6000

350

300

250

200

150

100

50

0




OBD(grcm3)

Sphagnum (sporescm

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0







influx2yr)

IR ()



yrs ADBC

2000

1500

1000

500

0

-500

-1000

-1500

-2000

-2500

-3000

-3500

-4000

-4500

d e f





500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

0

0 44

(grainscm2yr)

0 1 20020406081


cal yrs B

P

ASIa b






0 4 8 12

2000

1500

1000

500

0

-500

-1000

-1500

-2000

-2500

-3000

-3500

-4000

-4500

4812

3 4


years A

DB

C

c




5 Discussion



6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

gcm3

permil V-SMOW

Cal yrs B

P

a b c





gcm3

DRY

LOWHIGH

d e f g

gcm3
















ordmC

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

Pw western Norway

Cal yrs B

P

mm

DRY


140 120 100 80 60 43210-1-2 5 6 7 8 9

EXPANSION






Cal yrsBP

LakeIgelsjon

UndarsmosseBog OBD

UndarsmosseBog TA

HyltemossenBog

StoreMosseBog

4800ndash4400

x x No data x x

2000ndash1700

x No data x

1300ndash1000

x x x x



















6 Conclusions




Acknowledgements


References



















































Dep

th

(cm

)

Age (cal yr BP)

0 1000 2000 3000 4000 5000 6000

350

300

250

200

150

100

50

0




OBD(grcm3)

Sphagnum (sporescm

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0







influx2yr)

IR ()



yrs ADBC

2000

1500

1000

500

0

-500

-1000

-1500

-2000

-2500

-3000

-3500

-4000

-4500

d e f





500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

0

0 44

(grainscm2yr)

0 1 20020406081


cal yrs B

P

ASIa b






0 4 8 12

2000

1500

1000

500

0

-500

-1000

-1500

-2000

-2500

-3000

-3500

-4000

-4500

4812

3 4


years A

DB

C

c




5 Discussion



6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

gcm3

permil V-SMOW

Cal yrs B

P

a b c





gcm3

DRY

LOWHIGH

d e f g

gcm3
















ordmC

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

Pw western Norway

Cal yrs B

P

mm

DRY


140 120 100 80 60 43210-1-2 5 6 7 8 9

EXPANSION






Cal yrsBP

LakeIgelsjon

UndarsmosseBog OBD

UndarsmosseBog TA

HyltemossenBog

StoreMosseBog

4800ndash4400

x x No data x x

2000ndash1700

x No data x

1300ndash1000

x x x x



















6 Conclusions




Acknowledgements


References






















































500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

0

0 44

(grainscm2yr)

0 1 20020406081


cal yrs B

P

ASIa b






0 4 8 12

2000

1500

1000

500

0

-500

-1000

-1500

-2000

-2500

-3000

-3500

-4000

-4500

4812

3 4


years A

DB

C

c




5 Discussion



6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

gcm3

permil V-SMOW

Cal yrs B

P

a b c





gcm3

DRY

LOWHIGH

d e f g

gcm3
















ordmC

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

Pw western Norway

Cal yrs B

P

mm

DRY


140 120 100 80 60 43210-1-2 5 6 7 8 9

EXPANSION






Cal yrsBP

LakeIgelsjon

UndarsmosseBog OBD

UndarsmosseBog TA

HyltemossenBog

StoreMosseBog

4800ndash4400

x x No data x x

2000ndash1700

x No data x

1300ndash1000

x x x x



















6 Conclusions




Acknowledgements


References





















































5 Discussion



6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

gcm3

permil V-SMOW

Cal yrs B

P

a b c





gcm3

DRY

LOWHIGH

d e f g

gcm3
















ordmC

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

Pw western Norway

Cal yrs B

P

mm

DRY


140 120 100 80 60 43210-1-2 5 6 7 8 9

EXPANSION






Cal yrsBP

LakeIgelsjon

UndarsmosseBog OBD

UndarsmosseBog TA

HyltemossenBog

StoreMosseBog

4800ndash4400

x x No data x x

2000ndash1700

x No data x

1300ndash1000

x x x x



















6 Conclusions




Acknowledgements


References































































ordmC

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

Pw western Norway

Cal yrs B

P

mm

DRY


140 120 100 80 60 43210-1-2 5 6 7 8 9

EXPANSION






Cal yrsBP

LakeIgelsjon

UndarsmosseBog OBD

UndarsmosseBog TA

HyltemossenBog

StoreMosseBog

4800ndash4400

x x No data x x

2000ndash1700

x No data x

1300ndash1000

x x x x



















6 Conclusions




Acknowledgements


References


































































6 Conclusions




Acknowledgements


References



















































Late Holocene effective precipitation variations in the maritime regions of south-west Scandinavia

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Transcript of Late Holocene effective precipitation variations in the maritime regions of south-west Scandinavia