A 12.5-kyr history of vegetation dynamics and mire development with evidence of Younger Dryas larch presence in the Verkhoyansk Mountains, East Siberia, Russia

A 12.5-kyr history of vegetation dynamics and mire development withevidence of Younger Dryas larch presence in the VerkhoyanskMountains, East Siberia, Russia

KIRSTINWERNER, PAVEL E. TARASOV, ANDREI A. ANDREEV, STEFANIE MULLER, FRANKKIENAST, MICHAEL ZECH,WOLFGANG ZECH AND BERNHARDDIEKMANN

BOREAS Werner, K., Tarasov, P. E., Andreev, A. A., Muller, S., Kienast, F., Zech, M., Zech, W. & Diekmann, B. 2010(January): A 12.5-kyr history of vegetation dynamics and mire development with evidence of Younger Dryas larchpresence in the Verkhoyansk Mountains, East Siberia, Russia. Boreas, Vol. 39, pp. 56–68. 10.1111/j.1502-3885.2009.00116.x. ISSN 0300-9483.

A 415 cm thick permafrost peat section from the Verkhoyansk Mountains was radiocarbon-dated and studiedusing palaeobotanical and sedimentological approaches. Accumulation of organic-rich sediment commenced in aformer oxbow lake, detached from a Dyanushka River meander during the Younger Dryas stadial, at �12.5 kyrBP. Pollen data indicate that larch trees, shrub alder and dwarf birch were abundant in the vegetation at that time.Local presence of larch during the Younger Dryas is documented by well-preserved and radiocarbon-dated needlesand cones. The early Holocene pollen assemblages reveal high percentages of Artemisia pollen, suggesting thepresence of steppe-like communities around the site, possibly in response to a relatively warm and dry climate�11.4–11.2 kyr BP. Both pollen and plant macrofossil data demonstrate that larch woods were common in theriver valley. Remains of charcoal and pollen of Epilobium indicate fire events and mark a hiatus �11.0–8.7 kyr BP.Changes in peat properties, C31/C27 alkane ratios and radiocarbon dates suggest that two other hiatuses occurred�8.2–6.9 and�6.7–0.6 kyr BP. Prior to 0.6 kyr BP, a major fire destroyed the mire surface. The upper 60 cm of thestudied section is composed of aeolian sands modified in the uppermost part by the modern soil formation. For thefirst time, local growth of larch during the Younger Dryas has been verified in the western foreland of the Ver-khoyansk Mountains (�170 km south of the Arctic Circle), thus increasing our understanding of the quick refor-estation of northern Eurasia by the early Holocene.

Kirstin Werner (e-mail: [email protected]), Leibniz Institute of Marine Sciences Kiel (IFM-GEOMAR),Wischhofstr. 1-3, D-24148 Kiel, Germany; Pavel E. Tarasov (e-mail: [email protected]) and StefanieMuller(e-mail: [email protected]), Institute for Geological Sciences/Palaeontology, Free University Berlin, Mal-teserstr. 74-100, D-12249 Berlin, Germany; Andrei A. Andreev (e-mail: [email protected]) and Bernhard Diek-mann (e-mail: [email protected]), Alfred Wegener Institute for Polar and Marine Research, Research UnitPotsdam, Telegrafenberg A43, D-14473 Potsdam, Germany; Frank Kienast (e-mail: [email protected]),Senckenberg Research Institute and Natural History Museum, Research Station for Quaternary Palaeontology, AmJakobskirchhof 4, D-99423Weimar, Germany;Michael Zech (e-mail: [email protected]), University of Bayreuth,Chair of Geomorphology and Department of Soil Physics, Universitatsstraße 30, D-95440 Bayreuth, Germany; Wolf-gang Zech (e-mail: [email protected]), University of Bayreuth, Institute of Soil Science and Soil Geography,Universitatsstraße 30, D-95440 Bayreuth, Germany; received 9th April 2009, accepted 2nd July 2009.

Late Quaternary pollen and plant macrofossil recordsare crucial for the reconstruction of past vegetation andclimate dynamics (e.g. Fægri & Iversen 1989) and fordata-model comparison and validation of climate andvegetation modelling results (e.g. Kageyama et al.2001). The latter are extremely useful for reliable pre-dictions of future environmental changes under variousscenarios. Environmental records from vast areas ofSiberia, rich in resources yet sparsely populated, areparticularly important in the discussion of past changesin plant and animal communities (e.g. Kienast et al.2005), human habitation (e.g. Dolukhanov et al. 2002)and future environmental sustainability of this uniqueregion with temperature anomalies greatest in theNorthern Hemisphere, extremely cold winters and anextensive layer of continuous permafrost (ACIA 2004).

East Siberia occupies a large area in northeasternAsia approximately between 901 and 1301E. Its borderto West Siberia follows the Yenissei River, while theVerkhoyansk Mountains separate the region fromnortheastern Siberia and from the Russian Far East

(Alpat’ev et al. 1976). The western slopes of the Ver-khoyansk Mountains (maximum altitude 2389m a.s.l.)mark the easternmost periphery of Atlantic climaticinfluence in continental Siberia. The area is known forits low winter temperatures and extensive spread of colddeciduous larch-dominated boreal forests (Alpat’evet al. 1976; Prentice et al. 1992). During the past 20years, Lateglacial and Holocene environments havebeen studied in East Siberia, including its central (e.g.Andreev & Klimanov 1989, 2005; Andreev et al. 1989,1997; Katamura et al. 2006), northern (e.g. Jasinskiet al. 1998; Andreev et al. 2001, 2002, 2004, 2009; Pi-saric et al. 2001; Schirrmeister et al. 2008) and southern(e.g. Andreev & Klimanov 1991; Andreev et al. 1997)parts (Fig. 1A). Nonetheless, there is an obvious lack ofpalaeoecological data on the eastern part of the region.Multidisciplinary German–Russian research carriedout in the Verkhoyansk Mountains since 2002 has pro-vided new information on the reconstruction of the lateQuaternary mountain glaciation (Stauch 2006), peri-glacial landscape development (Popp et al. 2006, 2007;

DOI 10.1111/j.1502-3885.2009.00116.x r 2009 The Authors, Journal compilation r 2009 The Boreas Collegium

Zech et al. 2008) and vegetation and climate dynamics(Diekmann et al. 2007; Muller et al. 2009). This last-mentioned publication reports uninterrupted growth oflarch trees in the study area during the past 15 kyr,based on the pollen record from Lake Billyakh. How-ever, larch macrofossils were not found in the studiedlacustrine sediments.

In this article, we present results of multiproxy studiesof a peat section that accumulated in the lower reachesof the Dyanushka River after �12.5 kyr BP. These re-sults are further used to discuss vegetation, landscapeand climate dynamics in a broader regional context.

Study site and environmental setting

The studied peat section, profile K7/P2 (65102021.600N,125102012.600E, 123m a.s.l.) (Fig. 1C), is located on theright bank of the Dyanushka River (Fig. 1B), whichoriginates in the Verkhoyansk Mountains and is aneastern tributary of the Lena River. It flows westward,crossing a flat plain formed by alluvial deposits of theLena River and partly by glaciofluvial deposits. Themountain glaciations dated to the Late Pleistocene leftat least five end-moraine arcs in the area (Kind 1975;Kolpakov 1986; Stauch 2006). Meandering processesmodified the topography of the generally flat plain (Fig.1), and numerous oxbow lakes – remnants of the for-mer river meanders – are typical features of the modernrelief. Organic accumulation and peat formation pro-

cesses usually start in these lakes after they become de-tached from the river.

The modern climate of the study area is extremelycontinental. Winters are cold with a mean Januarytemperature around �401C, while summers are rela-tively warm with a mean July temperature of about15–191C. Annual precipitation is about 300–400mm,but humidity is high due to low evaporation losses (Al-pat’ev et al. 1976; Climatic Atlas of Asia 1981). Thestudy site is located in the zone of continuous perma-frost, which may be up to 500m thick (Ivanov 1984). Insummer, melting of the active layer provides consider-able amounts of plant-available water in addition to themoderately low atmospheric precipitation.

Today, open cold deciduous forests are widespreadin the study area (Alpat’ev et al. 1976). They are domi-nated by larch (Larix dahurica and L. cajanderi) andbirch (Betula sect. Albae) trees, with abundant shrubsand dwarf shrubs, including Alnus fruticosa, Betula ex-ilis, B. fruticosa and Pinus pumila growing in the un-derstorey (Timofeev 2003). Spruce (Picea obovata) andalder trees (Alnus hirsuta) grow preferentially in theriver and creek valleys with locally moister and warmermicroclimatic conditions (Alpat’ev et al. 1976).

Material and methods

The 415 cm thick section K7/P2 exposed by river ero-sion was sampled in summer 2003. The lens-shaped

Yakutsk

Lena

Riv

er

Vilyui River Aldan River

70°

65°

60°

130°125°

1

2

3

4

5

6

120°115°

7

8

9

10

11

65°

60°

55°

12

300 km

Laptev Sea East Siberian Sea

Verkhoyansky

145°135°125°115° 165°155°

10 km

LakeBillyakhDyanushka River

K7/P2

Range

70°RUSSIA

B

C

A

Lena

Fig. 1. Maps of Eurasia (A) and its north-eastern part (B) showing locations of thepreviously investigated sites mentioned in thetext: 1=Bykovsky Peninsula (Andreev et al.2002; Schirrmeister et al. 2002); 2=NikolayLake (Andreev et al. 2004); 3=Dolgoe Lake(Pisaric et al. 2001); 4=Kurungnakh Island,Buor-Khaya section (Schirrmeister et al. 2003);5=Bolshoy Lyakhovsky Island (Andreev et al.2009); 6=Khomustakh Lake (Andreev et al.1989; Andreev & Klimanov 1989, 2005);7=Ulakhan Chabada Lake (Andreev et al.1997; Andreev &Klimanov 2005); 8=Suollakh(Andreev et al. 1997); 9=Ulu Maaly Alas,Ulakhan Sykkhan Alas, Uinakh Alas, MaralayAlas (Katamura et al. 2006); 10=Smorodino-voye Lake (Anderson et al. 2002); 11=LenaRiver valley (Jasinski et al. 1998); 12=LakeBillyakh (Muller et al. 2009). Map of the studyarea (C). Black star indicates the location of theDyanushka K7/P2 section.

BOREAS 12.5-kyr history of vegetation dynamics, Verkhoyansk Mountains, Russia 57

350 cm peaty unit is underlain by Late Pleistocene flu-vial sands and covered by a 55–60 cm thick layer ofaeolian sand (Fig. 2A). The boundary between thesummer active layer and the frozen sediment was de-tected at 150 cm depth. After cleaning the surface of thesection, a total of 75 samples, each comprising a 5 cmblock, was collected from the 350 cm organic-rich partof the profile. Two samples were collected from the up-permost sand and soil layer.

Plant remains such as larch needles and cones, as wellas unidentified woody remains, were used for ac-celerated-mass spectrometer (AMS) radiocarbon-dating. Altogether 13 radiocarbon dates were obtainedin three laboratories (Table 1). In order to construct the

age–depth model (Fig. 2B), radiocarbon dates wereconverted into calendar ages using the CalPal softwarepackage (http://www.calpal-online.de/) (Danzeglockeet al. 2008). Calendar dates are used consistentlythroughout this study.

A standard technique (Berglund & Ralska-Jasie-wiczowa 1986) was applied to extract pollen, spores andother non-pollen palynomorphs (NPPs) from the sedi-ment matrix. The residues were mounted in glycerineand analysed with a light microscope under 400–1000�magnification. With the exception of two samples from65 cm and 306 cm depth that possessed very low pollenconcentrations, a minimum sum of 250 terrestrial pol-len grains per sample was counted, with spores tallied in

Dep

th (

cm)

0

50

100

150

200

250

300

350

400

Lithology column and description Age (cal. kyr BP)

0 2 4 6 8 10 12

Suggested hiatuses

B

Calibrated AMS dates (kyr BP; 95% range)

Applied age model

Act

ive

laye

r (s

umm

er 2

003)

Per

maf

rost

AModern soil

Grey aeolian sand

Brownish to greyish sandLight violet silt

Fossil soil with charcoal remains

Organic-rich silt, roots in theupper layers and charcoalremains at the basis

Brown peat, fibrous in the upper partand flat in the lower part

Brown fibrous peat with woodand birch bark remains

Brown peat rich in mineral particles,layered, with charcoal remains

Brown fibrous peat, layered, withcharcoal remains in the upper part

Black organic peatReddish to brownish peat, fibrous; withwood remains

Black organic peat, wood remains

Fluvial sand

Brown peat, rich in mineral particles,with Sphagnum and root remains

Grey to black peat, rich in mineralparticles, with root and wood remains

Black to brown peat

Reddish to brownish peat

AMS dates(cal. yr BP;68% range)

607±37

6727±44

6860±64

8277±61

8423±36

12 070±45

12 030±130

12 028±162

12 308±186

8685±42

11 200±25

10 902±143

12 443±186

Plant macrofossils

Roots

Wood remains

Charcoal

Soil

Sand

Silt

Peat

AMS date locations

Fig. 2. Lithology of the K7/P2 section with calibrated radiocarbon ages (A) and age-depth model for the K7/P2 section with suggested sedi-mentary hiatuses (B).

58 Kirstin Werner et al. BOREAS

addition. Published morphological pollen keys (Fægri& Iversen 1989) and pollen atlases (Reille 1992, 1995,1998; Beug 2004) were used for taxonomic determina-tion of the pollen and spores.

In addition to pollen and spores, a number of NPPtypes, including conifer stomata, remains of Chir-onomidae, Neorhabdocoela oocytes, statoblasts offreshwater bryozoans and charcoal particles, were alsoidentified and counted in the pollen slides. The NPPscan also be used for interpretation of past environments(e.g. van Geel 2001). For example, conifer stomata in-dicate the presence of coniferous trees in the close vici-nity of the sampling site (e.g. Parshall 1999; Sweeney2004). Findings of oocytes of the aquatic flatworm (or-der Neorhabdocoela, class Turbellaria) can help in re-constructing water depth and productivity of aquaticcommunities (Haas 1996). Charcoal remains (in-completely burnt plant fragments) are good indicatorsof fire (Clark 1988), in particular fragments larger than100 mm report local fire events within a 100m distance,while smaller particles can be wind-transported overgreat distances (Clark & Royall 1996). However,counting charcoal particles together with pollen is cri-tical because of the possible mix-up with opaque mi-neral material (Clark & Patterson 1984). Taking thisinto account, in the present study the charcoal recordshown in the pollen diagram is comprised solely ofburnt plant remains consisting primarily of conifertracheids.

A total of 11 samples were analysed for plant macro-fossils (Table 2). Each sample (�50ml) was soakedovernight in distilled water and later fractionated usingsieves with mesh sizes of 2000, 1000, 500, 250 and 125mm.The separated fractions were dried at 401C and analysed

under a ZEISS Stemi SV11 stereo microscope. Plant re-mains, including bark, needles and cones of Larix, wereidentified using the reference collection at the AlfredWegener Institute, Research Unit Potsdam.

Altogether 21 samples were analysed for organic par-ticle size distribution. The samples were washed througha 200mm mesh and dried at 401C. Afterwards, fractionsless and greater than 200mm were weighed and theirpercentages were calculated. The organic contentwas determined by the loss-on-ignition (LOI) procedure(Fig. 3). About 2 g of each sample were heated at 5501C

Table 1. AMS radiocarbon dates from the K7/P2 profile. Radiocarbon years before present were converted to calendar years after Danze-glocke et al. (2008).

Depth below the surface(cm)

Dated material 14C age (yr BP; 68%range)

Cal. age (yr BP; 68%range)

Cal. age (yr BP; 95%range)

Laboratorynumber

65–70 Wood charcoal 615�25 607�37 540–700 KIA26851101–106 Unidentified plant

remains5900�40 6727�44 6630–6830 Poz-25423

130–135 Unidentified woodyremains

6011�51 6860�64 6720–7000 Erl6620

170–175 Larch needles 7450�55 8277�61 8160–8400 KIA26017201–206 Unidentified plant

remains7610�50 8423�36 8340–8500 Poz-25395

215–220 Unidentified woodyremains

7875�40 8685�42 8550–8830 KIA29874

230–235 Unidentified plantremains

9540�60 10 902�143 10 600–11 200 Poz-25422

245–250 Larch needles 9760�45 11 200�25 11 110–11 270 KIA26016285–290 Larch needles 10 270�45 12 070�45 11 810–12 250 KIA29875312–317 Unidentified plant

remains10 380�60 12 308�186 11 970–12 650 Poz-25421

340–345 Larch needles 10 260�40 12 028�162 11 800–12 200 KIA26015340–345 Larch cone 10 270�50 12 030�130 11 770–12 290 Poz-28087410–415 Unidentified woody

remains10 521�75 12 443�186 12 150–12 790 Erl6621

Table 2. Macrofossil remains found in the K7/P2 profile.

Sample depth belowthe surface (cm)

Identified macrofossil remains

60–65 Unidentified wood pieces and roots, charcoalparticles

65–70 Charcoal particles, mycelium(ectomycorrhiza) of Cenococcum geophilum

120–125 Inflorescence of Eriophorum160–165 Moss (including Sphagnum) remains170–175 Moss (including Sphagnum) remains; seeds of

Carex, Betula,Menyanthes trifoliata, needlesof Larix, seeds of Pinaceae, remains of beetles(Donacia sp. and Saldidae); charcoal particles

214–219 Unidentified wood pieces245–250 Moss (including Sphagnum) remains, needles

of Larix, seeds of Carex, Pinaceae (likelyLarix) and Betula sp., charcoal remains

286–291 Moss (including Sphagnum) remains330–335 Cone of Larix340–345 Needles and cone of Larix, seeds of Pinaceae

(likely Larix) and Carex390.5–395.5 Moss (including Sphagnum) remains

BOREAS 12.5-kyr history of vegetation dynamics, Verkhoyansk Mountains, Russia 59

until weight remained constant (Heiri et al. 2001) andcooled in a desiccator afterwards. The weight loss of eachsample was then measured and expressed as % LOI.

Total organic carbon (TOC) and nitrogen (N) con-tents of 26 samples were determined at the Institute ofSoil Science and Soil Geography, University of Bay-reuth, using dry combustion of finely ground, homo-geneous, 50mg subsamples and thermal conductivitydetection on a Vario EL elemental analyser (Elementar,Hanau, Germany). The detection limits of the machinewere identified by measuring blanks with increasing netweights of wolfram oxide in tin capsules (�0.0002% forTOC and �0.007% for N). Precision was ascertainedby measuring acetanilide as a standard in quad-ruplicate. Mean standard errors were no more than0.02% for TOC and 0.05% for N.

The same samples were analysed for n-alkanes apply-ing the method described by Zech & Glaser (2008). Freelipids were extracted with methanol/toluene (7/3) usingan accelerated solvent extractor (ASE) and subsequentlyconcentrated using rotary evaporation. Lipid extractswere purified on silica-alox columns (2 g of each, 5%deactivated). N-alkanes were eluted with 3�10ml hex-ane/toluene (85/15). Measurements were carried out onan HP 6890 gas chromatograph equipped with a flameionization detector (FID). Alkane biomarkers in sedi-ments and soils can be used to reconstruct changes invegetation cover (e.g. Cranwell 1973; Schwark et al.2002; Zech 2006; Zech et al. 2009). In particular, they are

important constituents of epicuticular plant-leaf waxes(Kolattukudy 1976), with the homologues C27 and C29dominating in most trees and shrubs, and C31 and C33in most grasses and herbs (e.g. Maffei 1996).

Results

Lithostratigraphy and chronology

The section K7/P2 lithology column and a brief descrip-tion of the sedimentary units are provided in Fig. 2A. The415–110 cm depth interval consists of peat layers showingdifferent degrees of decomposition, but with generallygood preservation of organic material. Above 110 cmdepth, the section consists of organic-rich silty and sandyhorizons, charcoal remains and plant roots. The upper-most 5 cm layer represents modern soil formation.

The 13 AMS radiocarbon dates (Table 1) obtainedfrom the section span the time interval between �12.5and 0.6 kyr BP. The dates (Table 1) generally demon-strate a good sequence of ages without major inversions.However, the dates from 285–290 cm (12 308�186 yrBP) and from 312–317 cm (12 070�45 yr BP) seem to bea few hundred years older than suggested by the dateson larch cone (12 030�130 yr BP, Poz-28087) andneedles (12 028�162 yr BP, KIA26015) from 340–345 cm depth in the lower part of the studied section(Fig. 2B). In both cases, the dated material, respectively

10 30 50 7010 30 50 70 90

D

12 443±186

12 028±16212 030±130

11 200±2510 902±143

8685±428423±36

8277±61

6860±64

6727±44

607±37

40

80

120

160

200

240

280

320

360

400

0

Organic matter (%)Depth(cm)

AMS dates(cal. yr BP;68% range) 10 30 50

BAPZ VIII

PZ VII

PZ VI

PZ V

PZ IV

PZ III

PZ II

PZ I

10 30

C

12 070±45

12 308±186

TOC (%) TOC/N Peat particles>200 µm (%)

Pollenzone

Fig. 3. Percentages of organic material (loss on ignition, % LOI) (A), total organic carbon (% of dry weight, TOC) (B), TOC/N ratios (C), andpercentages of peat particles4200mm (D). Dotted lines indicate suggested hiatuses.

60 Kirstin Werner et al. BOREAS

unidentified plant remains and larch needles, does notexclude possible contamination by material reworkedfrom older sediments. Constructing the age–depthmodel we furthermore consider that both the lithologi-cal and geochronological data (Fig. 2) demonstratestepwise accumulation of organic material, suggestingeither dramatic changes in sedimentation rate and/orsedimentary hiatuses around 234–229 cm, 155–150 cmand 75–70 cm depth. Taking into account sharpboundaries between the units and the presence of char-coal, we took the second hypothesis as more realisticand considered hiatuses about 11.0–8.7, 8.2–6.9and 6.7–0.7 kyr BP (Fig. 2B). Additional supportfor the hiatus between 6.7 and 0.7 kyr BP is provided bythe regional pollen stratigraphy, demonstrating thatpollen of Scots pine (Pinus sylvestris type), which is ab-sent in the K7/P2 pollen record, becomes abundant inthe lake and mire sediments after 6.7–6.5 kyr BP (e.g.Muller et al. 2009 and references therein). While theuppermost long hiatus is quite definitive, the lower (andshorter) two are more uncertain.

Organic and nitrogen contents and organic particle sizedistribution

The content of organic matter LOI reflects high varia-bility within a roughly threefold pattern (Fig. 3A).Highest LOI (80–90%) occur in the fibrous brownishpeat unit between 200 and 110 cm. LOI in the units be-low and above show variations between 20% and 50%,respectively. Particle-size variations (Fig. 3D) arerelated to the distribution of organic matter. Maximumvalues (up to 65%) of coarse organic particles (4200mm)refer to the organic-rich unit at 200–110cm depth, whilefine particles dominate the upper and lower units.

TOC and N contents range from 3.6% to 46.3% andfrom 0.3% to 2.6%, respectively. Distinct maximaare found between 100 and 200 cm depth (Fig. 3B), thusconfirming the organic matter percentages derivedfrom LOI. In contrast, the inorganic mineral materialcontent is significant in the lower part of the section,likely indicating its floodplain oxbow-lake nature,and in the upper aeolian sand layer. TOC/N ratios aregenerally high (415; Fig. 3C), confirming the goodconservation of organic matter as expected in swampyand generally cold arctic environments. TOC/Nminima o15 are only found in the well-aeratedrecent topsoil and at 2.1 to 2.3m depth, the latter coin-ciding with the sedimentary hiatus between 11.0 and8.7 kyr BP.

Pollen and NPP stratigraphy

Main results of the pollen and NPP analyses are shownin Fig. 4 (all raised pollen and NPP data are available inthe PANGAEA data information system, http://doi.

pangaea.de/10.1594/PANGAEA.716835). Relative fre-quencies of terrestrial pollen taxa, including trees,shrubs and herbs, are calculated based on their totalsum taken as 100%. Spore percentages are based onthe sum of pollen and spores. The relative taxa abun-dances for all other microfossil groups shown in Fig. 4are calculated in the same way. For calculation of thetotal pollen concentration (excluding spores and NPP),a tablet with a known number of Lycopodium sporeswas added to every sample. The diagram showingthe pollen, spores and NPP records (Fig. 4) wasvisually subdivided into eight pollen assemblage zones(PZ). Their main features are summarized in thefollowing.

PZ I (415–400 cm) is dominated by pollen of Alnusfruticosa, Larix, Betula nana and Cyperaceae. Remainsof Neorhabdocoela oocytes, Cladocera and chir-onomids are numerous in this zone. Pollen concentra-tion decreases rapidly from 87 800 to 3400 grains/g.

PZ II (400–340 cm) is characterized by pollen ofLarix, with Betula nana, Alnus fruticosa and Cyper-aceae as co-dominants. Neorhabdocoela oocytes, re-mains of Cladocera and chironomids are alsonumerous. Stomata attributed to Larix are found in theupper part of the pollen zone. Pollen concentrationsvary significantly from 7700 to 63 000 grains/g.

PZ III (340–280 cm) demonstrates a slight decrease inLarix pollen percentages. Pollen percentages of Betulanana, Poaceae and, particularly, Artemisia speciesincrease. The presence of mesophytic herbs (Thalic-trum, Sanguisorba officinalis and Ranunculaceae) pol-len is also characteristic of this zone. Larix stomata,Neorhabdocoela oocytes, Cladocera and chironomidremains are detectable, even in high quantities. Pollenconcentrations reach 29 400 grains/g.

PZ IV (280–245 cm) is characterized by a peak inArtemisia pollen. Percentages of Larix pollen increaseas well as pollen percentages of Betula nana. Alnus fru-ticosa pollen decreases slightly in the upper part of thiszone and is displaced by an increase of Alnus hirsutapollen. Neorhabdocoela and Cladocera remains arepresent in high quantities. Maximum pollen concentra-tion attains 47 800 pollen grains/g.

PZ V (245–210 cm) shows a large decrease of Betulanana, Poaceae andArtemisia, accompanied by increases ofCyperaceae, Picea and Pinus pumila pollen percentages.An occurrence of numerous charcoal particles is paralleledby the appearance of Epilobium pollen. Recorded valuesof Larix pollen are still very high. Pollen concentrationsvary greatly between 5300 and 157 900 grains/g.

PZ VI (210–155 cm) demonstrates significantly lowerpercentages of Larix pollen, while the percentages ofPicea, Pinus pumila, Alnus hirsuta and Betula nana pol-len increase. Bryozoan statoblasts, Neorhabdocoelaoocytes, remains of chironomids and Cladocera arepresent in considerable amounts. Pollen concentrationsreach up to 257 700 grains/g.

BOREAS 12.5-kyr history of vegetation dynamics, Verkhoyansk Mountains, Russia 61

Depth (cm)

0 50 100

150

200

250

300

350

400

AM

S d

ates

(cal

. yr

BP

;68

% r

ange

)

607±

37

6727

±44

6860

±64

8277

±61

8423

±36

12 0

70±

45

12 0

30±

130

12 0

28±

162

12 3

08±

186

8685

±42

11 2

00±

25

10 9

02±

143

12 4

43±

186

Lithology

4080

40

IIIVI V IV II IVII

Larix

Picea obovata

Alnus hirsuta

Betula sect. Albae

Pinus pumila

Betula nana

Alnus fruticosa

Salix

Poaceae

Cyperaceae

Artemisia

4040

40

Ericales

RanunculaceaeThalictrumAsteraceaeCaryophyllaceaeChenopodiaceaeSanguisorba officinalis

IndeterminateMyriophyllumMenyanthes trifoliataEquisetumLycopodium sp.PolypodiaceaeSelaginella rupestris

Sphagnum

Bryozoan statoblastsChironomid remains

Neorhabdocoela oocytes

Conifer stomata

Redeposited

40

Charcoal

Pollen concentration (grains/g)

Pollen assemblage zone

Shr

ubs

Tre

esH

erbs

Spo

res

AN

PP

s

VIII

Trees

Shrubs

Herbs

Epilobium

1010

Per

cent

ages

(%

)40

40

Tot

al

Fig.4.Diagram

presentingresultsofpalynologicalan

alysisoftheK7/P2sectionproducedwiththeTilia/TiliaGraphsoftware

(Grimm

1991,2004).Thelogarithmic

scaleisusedforthetotalpollen

concentrations(grains/g).Aquaticpollen

types

aresummarized

under

‘A’.Dotted

lines

indicatesuggestedhiatuses.

62 Kirstin Werner et al. BOREAS

PZ VII (155–75 cm) reveals highest pollen con-centrations (up to 2 411 100 grains/g) accompanied byvery high values of Sphagnum spores in the upper partof the zone as well as high percentages of Betula nanaand Ericales pollen. The presence of Epilobium pollen isnoticeable in the upper part of this zone.

PZ VIII (75–0 cm) is characterized by increasedamounts of Epilobium, the highest concentration ofcharcoal remains, a highArtemisia pollen content and thelowest pollen concentrations decreasing to 900 grains/g.In the sample from the modern soil layer, the pollenconcentration increases again to 18 500grains/g.

Plant macrofossils

Details of the plant macrofossil analysis are presentedin Table 2. The most striking feature is the presence ofnumerous macrofossils of Larix, including needles andcones found at different levels. The lower part of theanalysed section (below 175 cm) is also characterized byrelatively high values of stomata and pollen of Larix.Numerous moss remains (mainly Sphagnum) are re-corded between 400 and 160 cm depth. Remains of ashore bug species (family Saldidae) and a leaf beetlespecies of Donacia sp. were found at 175 cm depth. Atthe same level, seeds of Menyanthes trifoliata, a plantcommon to bogs and mires, were also found. Seeds of

Carex, Betula and Pinaceae (likely representing Larix)were abundant in several samples (Table 2) and an in-florescence of cotton-grass (Eriophorum sp.) was foundat 125–120 cm. Numerous particles of charcoal weredetected in macrofossil samples at 250–245, 175–170and 65–60 cm.

Alkane biomarkers

N-alkanes with 25 to 33 carbon atoms clearly dominatein all analysed samples. The alkane patterns thereby re-veal a strong odd over even predominance (OEP) (Fig.5B). This is characteristic of alkanes from plant-leafwaxes and confirms the poor degradation of organicmatter, as already indicated by the high TOC/N ratios.

The alkane ratios C31/C27 range from 0.31 to 1.40(Fig. 5A). Values o1 point to organic matter mainlyderived from trees and shrubs, whereas ratios 41 areevidence of significant input from grasses and herbs.Hence, with the exception of one sample from 347.5 cm,the lowermost part of the section below the sedimen-tary hiatus at around 240 cm depth accumulated in aforested environment with C27 comprising up to 33%of the total alkane amount (Fig. 5B). Distinct C31/C27maxima with ratiosZ1 coincide with the hiatuses at226.5 and 137.5 cm depth and are interpreted in termsof increased input of organic matter derived from

40

80

120

160

200

240

280

320

360

400

0

Depth(cm)

AMS dates(cal. yr BP;68% range)

A

0 1 2

C31/C27Sample 2.5 cm

Sample 347.5 cm

Sample 92.5 cm

Sample 372 cm

Sample 182.5 cm Sample 226.5 cm Sample 283.5 cm

Sample 413 cm

Sample 137.5 cmB

Fig. 5. C31/C27 ratios (A) and percentage changes in n-alkanes composition of selected samples (B). In (A), ratioso1 indicate that the organicmatter was mainly derived from trees and shrubs, whereas ratios 41 point to a significant contribution of grasses and herbs. Dotted linesindicate suggested hiatuses.

BOREAS 12.5-kyr history of vegetation dynamics, Verkhoyansk Mountains, Russia 63

grasses and herbs. From �70 to 170 cm depth, C29,which dominates in heath plants (Ficken et al. 1998),becomes the most abundant alkane with contributionsof up to 41% (Fig. 5B, sample 137.5 cm). This is inagreement with the palynological results showing pol-len of Ericales associated with maxima of Sphagnumspores. The alkane pattern of the recent topsoil (sample2.5 cm) reveals the expected C31 dominance under themodern grass vegetation covering the rim of the scarp.

Reconstruction of vegetation and landscapedevelopment

The Dyanushka K7/P2 section documents Lateglacialto mid-Holocene environmental changes since about12.5 kyr BP. Both peat formation and occurrence of theburnt charcoal horizons point to terrestrial environ-ments. However, aquatic plant and invertebrate re-mains appear throughout the record, suggesting thepresence of shallow water habitats at least seasonally.At present, aquatic environments commonly occurduring early summer, when meltwater and frozenground support the development of shallow ponds intopographic depressions. Desiccation of the upper peatlayers is associated with low precipitation and relativelyhigh temperatures, which are characteristics of the midand late summer season. For example, meteorologicalrecords from Yakutsk demonstrate that in July andAugust day temperatures often exceed 301C and canreach 381C (Alpat’ev et al. 1976). Although peat for-mation in the oxbow-lake setting was repeatedly inter-rupted by fire and/or erosion processes during theLateglacial and Holocene, the palaeobiological and se-dimentary inventory of the section provides valuableinformation on climate-related changes in depositionaldynamics and local to regional vegetation history.

The Younger Dryas

The age–depth model suggests that the lower pollenzones (PZ I to III) represent the Lateglacial, namelywhat is biostratigraphically and chronologically de-fined as the Younger Dryas cooling preceding onset ofthe Holocene interglacial (e.g. Iversen 1954; Rind et al.1986). According to the latest varve-counting of an-nually laminated lake sediments in Germany, this coldepisode chronostratigraphically comprises the time be-tween 12 680 and 11 590 varve yr BP (Brauer et al.2008). Therefore, we may assume that the lower part ofthe analysed section (415–280 cm) accumulated duringmid and late Younger Dryas time. Our data show that,already during this time interval, larch, shrubby birchand alder were abundant around the site. The herb-aceous cover was mainly represented by sedges, withgrasses and Artemisia becoming more abundant in ve-

getation during the later phase of the Younger Dryas(PZ III) after �12 kyr BP, likely indicating increasinglydry conditions. Recorded decreases in percentages oftree and shrub pollen in PZ III corroborate this inter-pretation. However, both pollen and macrofossil re-cords clearly indicate that this environmental changedid not destroy local larch stands. At present, larch al-most reaches the Lena River Delta, �800 km north ofthe Dyanushka site (Kremenetski et al. 1998) and itslatitudinal/altitudinal extension in northern Eurasia islimited mainly by the mean July isotherm of 10–121C(MacDonald et al. 2000). It is plausible that the meanJuly temperature in the study area did not fall belowthis limit during the Younger Dryas.

In East Siberia, the presence of the arboreal vegeta-tion during the coldest phases of the Late Pleistocene,including the Last Glacial Maximum and the YoungerDryas, is difficult to prove on the basis of pollen dataalone. The problem arises from the microscopic size ofpollen grains, the possibility of long-distance transportby wind and/or pollen grains being reworked fromolder interstadial and interglacial sediments. In the caseof the record discussed here, local growth of larch treesduring the Younger Dryas in the Dyanushka Rivervalley is supported by abundant larch pollen, alkanebiomarkers and macrofossils, including needles andcones.

In contrast, Larix pollen is totally missing in the La-teglacial record from northeastern Siberia (Fig. 1, site10), where high percentages of Betula and Alnus (likelyrepresenting shrubby forms of birch and alder), to-gether with Cyperaceae, Poaceae and Artemisia pollenare reported for the end of the Lateglacial, reflecting thedominance of tundra vegetation at locations wherelarch trees grow today (Anderson et al. 2002). Unlikethis area situated in the rain shadow of the Ver-khoyansk Mountains, the Dyanushka site is (and likelywas during the generally drier-than-present Lateglacial)favoured by orographic rainfall and snowfall asso-ciated with the Atlantic air masses (Alpat’ev et al.1976). Younger Dryas pollen records from central andsouthern parts of the study region (Fig. 1, sites 6–8) alsosuggest the dominance of treeless steppe-like and tun-dra-like vegetation, reconstructed on the basis of highpercentages of Poaceae and Artemisia pollen. Larixpollen is known for its short-distance dispersal from thepollen-producing tree and poor preservation (Guninet al. 1999; MacDonald et al. 2000). This fact may ex-plain its low percentages even in the Holocene pollenspectra from lake sediments (Muller et al. 2009). On theother hand, very high contents of Larix pollen in theYounger Dryas sediment from the Dyanushka peatmean that larch was growing absolutely locally on ordirectly beside the site.

In our pollen record, Artemisia and Poaceae aremoderately represented in the pollen spectra prior to�12 kyr BP, while pollen of larch, shrub birch and

64 Kirstin Werner et al. BOREAS

sedge is dominant, suggesting locally moist environ-ments and summer temperatures high enough to sup-port growth of larch trees and boreal shrubs. Pollendata from Lake Khomustakh (Fig. 1, site 6) demon-strate low amounts of larch pollen during the Allerødand the Younger Dryas. The latter study also reportedthe occurrence of an Artemisia pollen maximum duringthe late Younger Dryas and early Holocene interval. Inthe 15 kyr old pollen record from Lake Billyakh (Fig. 1,site 12), located 80 km northeast of section K7/P2, theArtemisia peak is unpronounced during the YoungerDryas (Muller et al. 2009). However, a strengthening ofherbaceous communities compared to shrub tundravegetation and a decrease in both available moistureand possibly winter temperatures were reconstructedfor the Lake Billyakh area between 12.5 and 11.3 kyrBP. The presence of Larix in the Lake Billyakh pollenrecord during the Allerød and Younger Dryas is ingood accord with the current study and suggests thepresence of larch in the Lateglacial vegetation in thewestern Verkhoyansk Mountains. Climate deteriora-tion during the Younger Dryas, following the Allerødinterval with significantly warmer and wetter climate,has been reported at many sites in Siberia (e.g. Velichkoet al. 1997, 2002). However, Velichko et al. (2002)mentioned the possibility of the middle Younger Dryasbeing marked by a short-lived warming event. Con-sistent with our current results, the climate change atthe beginning of the Younger Dryas could be an ex-ternal factor triggering a change in the site hydrology,i.e. isolation of the oxbow lake from the river channeland start of organic sedimentation.

The early Holocene

Onset of the Holocene is represented by pollen zone PZIV of profile K7/P2, dated to �11.5 to 11.1kyr BP. It ischaracterized in the core by highest values of Artemisiapollen (20–40%), suggesting locally drier environmentsand/or disturbed soils favoured by Artemisia. The pre-sence of larch needles and seeds and a gradual increase inits pollen percentages upward suggest further strength-ening of the larch population in the area in response to awarmer early Holocene climate.

This interpretation is in accordance with that of earlyHolocene environments in Siberia on both large (e.g.Velichko et al. 2002) and small regional scales (e.g.Muller et al. 2009). The latter study on Lake Billyakhreconstructed a shift to dominant shrub tundra andmilder climate conditions by �11.3 kyr BP. However,relatively low forest biome scores derived from the earlyHolocene spectra of Lake Billyakh (Fig. 1, site 12) alsosuggest that high summer temperature/evaporation as-sociated with the summer insolation maximum couldbe a limiting factor for the spread of forest vegetationoutside the locally moist river valleys at that time. Theearly Holocene thermal maximum is recorded in var-

ious regions of the Northern Hemisphere, including Si-beria and north Central Asia (Velichko et al. 1997;MacDonald et al. 2000; Kaufmann et al. 2004; Kaplan& Wolfe, 2006; Lozhkin & Anderson 2006; Rudayaet al. 2009). The Rudaya et al. (2009) study also pointsto the early Holocene mid-latitude aridity, whichcaused a delay in the spread of boreal forest vegetationin more southern regions of northern Asia, includingnorthwestern Mongolia, southern Siberia and easternKazakhstan. This aridity could have been a cause of thefires and of a decrease in sediment accumulation re-corded in the K7/P2 peat section.

Generally warmer than present early Holocene sum-mers in the study area associated with the higher thanpresent summer insolation could have increased therisk of the wild fires which are used to explain the hiatusin the K7/P2 record between 11 and 8.7 kyr BP (PZ V).The occurrence of the fire or several fires, which likelydestroyed the surface of the peat, is documented byhigh amounts of charcoal debris (Fig. 2A).

The middle Holocene

The middle Holocene is represented only fragmentarilyin the K7/P2 section. The respective peat layers are da-ted to �8.7 to 8.2 and �6.9 to 6.7 kyr BP. High organicmatter content and high portions of coarse peat parti-cles point to a low degree of decomposition, possiblysustained by a locally elevated water level supportingthe spread of Sphagnum and Ericales-dominated mirecommunities. Pollen of Myriophyllum, statoblasts offreshwater bryozoans, seeds of Menyanthes trifoliataand remains of cotton-grass (Eriophorum) also point toa locally wetter environment. In turn, the appearance ofcharcoal debris and pollen of Epilobium, which is arapid colonizer of burnt soils, indicates fire eventswhich could have been responsible for the destructionof larger parts of the peat profile, thus causing hiatuses.The warm Holocene climate promoted further changesin local vegetation. The recorded increase in pollenpercentages suggests that spruce (Picea obovata) andtree alder (Alnus hirsuta) reached the area by 8.5 kyrBP, and that the stone pine (Pinus pumila) possibly ap-peared close to the site by 8.3 kyr BP. However, colddeciduous larch forest with a rich shrub understory re-mained a characteristic feature of the valley vegetation,as suggested by both pollen and plant macrofossil data.With the exception of a hiatus dated to �8.2–6.9 kyrBP, there is no evidence of the cooling event culminat-ing in the North Atlantic region at 8.2 kyr BP (Lal et al.2007) in our records or in the pollen record from LakeBillyakh (Muller et al. 2009).

Warmer and wetter than the present middle Holo-cene climate conditions have been reconstructed for thecentral part of the study region (Fig. 1, sites 6–7). In theK7/P2 record, these relatively wet and warm conditions

BOREAS 12.5-kyr history of vegetation dynamics, Verkhoyansk Mountains, Russia 65

are represented by peat formation, locally swampy ve-getation (indicated by an abundance of Sphagnumspores (Fig. 4) and macrofossil remains (Table 2)) andby a high proportion of arboreal tree and shrub pollenin pollen zones PZ V–VII. The peat deposits dated to6.9–6.7 kyr BP are characterized by lower TOC/N ra-tios than in the underlying peat deposits. Taking intoconsideration that these younger deposits form part ofthe recent active permafrost layer, it is likely that thelower TOC/N ratios reflect intensified organic matterdegradation causing loss of carbon.

The last millennium

A charcoal layer in the base of pollen zone PZ VIII isevidence of at least one fire event that destroyed part ofthe underlying peat section. The fire interrupted peataccumulation some time prior to 0.6 kyr BP, as in-dicated by the radiocarbon date on the burnt woodfrom 65–70 cm depth. The top sand layer represents arecent to sub-recent aeolian sand drift.

The late Holocene pollen spectra from Lake Billyakhshow a progressive increase in the amount of herb-aceous pollen after�2 kyr BP (Muller et al. 2009), whichmight be associated with climate deterioration duringthe ‘Neoglacial’ and particularly during the Little IceAge (LIA). The latter interpretation is partly supportedby a cold signal inferred from the isotope compositionof ground ice from the study area dated to the last mil-lennium (Popp et al. 2006). However, the question ofhuman–environmental interactions in the region duringthe past millennium needs further investigation.

Conclusions

For the first time, local growth of larch has been ver-ified in the western foreland of the VerkhoyanskMountains during the Younger Dryas, which is tradi-tionally interpreted in northern Eurasia as the coldestand driest climatic reversal of the Lateglacial. Larchneedles and a cone extracted from the studied sectionwere independently dated in two different radiocarbon-dating laboratories. In both cases, the dates show aYounger Dryas age of about 12 kyr BP. Intensive localforestation during this period is further corroboratedby alkane biomarkers. Literature concerning the La-teglacial and Holocene environments in vast areas ofeast and northeastern Siberia includes a substantialnumber of publications in Russian and internationalreviews. However, abundant larch pollen and macro-fossils have not previously been reported for theYounger Dryas sediments elsewhere in the region.Therefore, our results suggest that arboreal vegetationsuccessfully persisted even during much colder anddrier intervals such as the Younger Dryas in locally fa-vourable environments, and possibly also during the

Last Glacial Maximum. Furthermore, our study clearlydemonstrates the potential of palaeoenvironmental re-search performed on a very local scale.

Acknowledgements. – The work of P. Tarasov, A. Andreev and S.Muller is a contribution to the DFG-sponsored projects RI 809/17and TA 540/1. The work of B. Diekmann, W. Zech and M. Zech wassupported by DFG grants HU 378/12-1 and ZE 154/52-1. We aregrateful to T. Goslar for his generous help with radiocarbon dating ofthe larch cone, to B. van Geel for the unpublished atlas of the NPPs,to J. N. Haas, F. Viehberg, L. Nazarova and S. Kuzmina for theirconsultations and determination of insect remains, to E. Schalk forpolishing the English, and to R. Spielhagen, N. Van Nieuwenhove,P. Jasinski, J. A. Piotrowski and the anonymous reviewer for theirvaluable comments on the manuscript.

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