Late Quaternary vegetation of Chukotka (Northeast Russia), implications for Glacial and Holocene environments of Beringia

lable at ScienceDirect

Quaternary Science Reviews 107 (2015) 112e128

Contents lists avai

Quaternary Science Reviews

journal homepage: www.elsevier .com/locate/quascirev

Late Quaternary vegetation of Chukotka (Northeast Russia),implications for Glacial and Holocene environments of Beringia

Patricia M. Anderson a, *, Anatoly V. Lozhkin b

a Earth & Space Sciences, Quaternary Research Center, University of Washington, Seattle, WA 98195-1310, USAb Northeast Interdisciplinary Science Research Institute, Far East Branch Russian Academy of Sciences, 16 Portovaya Street, Magadan 685000, Russia

a r t i c l e i n f o

Article history:Received 11 July 2014Received in revised form16 October 2014Accepted 16 October 2014Available online

Keywords:BeringiaChukotkaPostglacial thermal maximumVegetation historyPollenPlant macrofossils

* Corresponding author.E-mail address: [email protected] (P.M. And

http://dx.doi.org/10.1016/j.quascirev.2014.10.0160277-3791/© 2014 Elsevier Ltd. All rights reserved.

a b s t r a c t

Two lake records from the Kankaren region of southern Chukotka, when combined with other palyno-logical and macrofossil data, document spatial and temporal variations in the regional vegetation historysince ~21,000 14C/25,400 cal yr BP. Full-glacial environments were severely cold and arid in central andnorthern Chukotka, whereas southern sites experienced conditions that were relatively moist, althoughstill drier than present. Southern Chukotka may represent a western extension of environments of theland bridge proper, including a possible “moisture” barrier to intercontinental migration. Shrub Betulatundra established earliest in southern Chukotka (~15,800e14,000 14C/19,000e16,700 cal yr BP;~13,000 14C/15,300 cal yr BP central and north), Pinus pumila earliest in the north (~9600 14C/11,100 cal yr BP; ~7600 14C/8400 cal yr BP south), and shrub Alnus earliest in both the south and north(~12,000e11,000 14C/13,800e12,900 cal yr BP). These patterns support the presence of cryptic refugia forBetula and Alnus in Chukotka during the full glaciation. In contrast, P. pumila probably migrated intoChukotka from populations located in the northern coastal lowlands and from mountainous regions ofsouthwestern Beringia. Evidence for a thermal optimum (~11,000e8000 14C/12,900e9000 cal yr BP) isstrong in northern Chukotka but is absent in central and southern areas.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

During the most recent glacialeinterglacial cycle the greatestdivergence of modern and ancient environments of Beringiaoccurred during the Last Glacial Maximum (LGM; peaking at~18,000 14C BP/~21,000 cal yr BP; in Western Beringia dated to~12,500e25,000 14C BP/~14,700e30,000 cal yr BP). Arctic coastswere located ~600e900 km to the north of modern, and ChukchiPeninsula, the Siberian lowlands, and coastal Alaska were land-locked (Fig. 1). Only the shores of southwestern Chukotka, Kam-chatka Peninsula, and the Okhotsk Sea were little changed fromtoday. Although glaciers were more common than present, theygenerally were limited tomountain valleys, the exception being theextensive ice build-up in southern Alaska (Hamilton,1994; Barr andClark, 2012). The full-glacial biota also varied markedly from pre-sent. The LGM fauna included a variety of extinct and extant largemammals, the iconic figure being the woolly mammoth (Mammu-thus primigenius), and insect assemblages from Eastern and West-ern Beringia were more closely associated with steppe rather than

erson).

arctic tundra (Guthrie, 1982, 1990; Elias, 2000; Elias et al., 2000).The region-wide vegetation of Beringia was initially viewed asrather monolithic (although with a patchwork of habitats found atthe landscape level) with disagreement on whether the plantcommunities had greater affinity to arctic tundra or steppe-tundra(Hopkins et al., 1982). The nature of the LGM vegetation has beencontentious, particularly in the pioneering stages of research whenrecords were limited in number and geographic distribution (e.g.,Ritchie and Cwynar, 1982 vs. Guthrie, 1982). However, as additionalsites were investigated and more sophisticated analytical tech-niques, such as linked climate-vegetation models (Bigelow et al.,2003; Kaplan et al., 2003; Allen et al., 2010), became available,ideas about the nature of the LGM vegetation and regional envi-ronmental variability have been refined. For example, the pre-dominance of cool, moist habitats in Central Beringia have beenproposed as a “barrier” or “filter” that prevented biotic exchangesbetween Asia and North America, particularly of insects and somelarger animals (e.g., woolly rhinos, short-faced bears, camels;Guthrie, 2001; Yurtsev, 2001; Elias and Crocker, 2008).

Unlike the relative stability of the LGM, the late glaciation intothe early Holocene (~12,500e8000 14C/~14,700e9000 cal yr BP) is atime of great global change, and nowhere is this more evident thanin Beringia. With increasing summer insolation, glacial melting,

Delta:1_given name

Delta:1_surname

mailto:[email protected]

http://crossmark.crossref.org/dialog/?doi=10.1016/j.quascirev.2014.10.016&domain=pdf

www.sciencedirect.com/science/journal/02773791

http://www.elsevier.com/locate/quascirev

http://dx.doi.org/10.1016/j.quascirev.2014.10.016



Fig. 1. Map of Beringia showing locations of the: a) approximate location of the 18,000 14C/21,000 cal yr BP shoreline (following Lozhkin, 2002), b) approximate location of the12,000 14C/13,800 cal yr BP shoreline, c) study area, and d) sites mentioned in the text. The 18,000 14C shoreline corresponds to �100 m depth; the 12,000 14C line to �37 m depth.The lighter dashed line on the mainland depicts the western boundary of Chukotka. The map key is: 1) Wrangel Island (Mamontovaya River (WR-12) and Tundrovaya River ex-posures, 2) Lake El'gygytgyn, 3) Kresta Gulf, 4) Anadyr Lowland sites (Sunset, Malyi Kretchet and Melkoye lakes), 5) Ledovyi Obryv, 6) Smorodinovoye Lake, 7) Glukhoye Lake, and 8)Zagoskin Lake. See Fig. 2 for details of the study area.

P.M. Anderson, A.V. Lozhkin / Quaternary Science Reviews 107 (2015) 112e128 113

warming seas, rising sea-levels, and changes in extent and durationof sea ice, the biotic environments of Beringia were being impactedfrom a variety of atmospheric andmarine influences (Bartlein et al.,1991, 1998). Vegetation responses to these forcing factors weremarked initially by the spread of shrub Betula tundra, followed bythe development of a unique deciduous forest/high shrub biome,and finally the establishment of evergreen conifers (Picea glaucaand Picea mariana in Eastern Beringia and Pinus pumila in WesternBeringia; Edwards et al., 2005; Brubaker et al., 2005). Sites dating tothis interval are more abundant than for the LGM, but in-terpretations are still dominated by data from Alaska and theKolyma and northern Okhotsk drainages.

The paucity of paleovegetational information from Chukotka,despite it forming a key link between far Western and CentralBeringia, has been the result of the limited numbers of sites and/orthe weak chronological control in many records from this region(Anderson et al., 2002). For example, 6 palynological records

encompass part or all of the full glaciation. Yet studies thatemployed systematic age-evaluations for inclusion/exclusion ofrecords in regional analyses incorporated only 1 Chukotkan site inEdwards et al. (2000) and Bigelow et al. (2003), 2 sites in Edwardset al. (2005), and 3 sites in Brubaker et al. (2005). Data coverage forthe Lateglacialeearly Holocene is no better with only 1 of 15palynological sites from Chukotka having a complete record for theinterval (Brubaker et al., 2005; Edwards et al., 2005). Unlike theLGM, vegetation patterns in this more recent interval can be sup-plemented by radiocarbon-dated macrofossils from peats andpaleosols, but here too the data are limited to 8 sites and provideonly brief temporal “snapshots” (Binney et al., 2009).

The paleovegetation reconstructions offered for other regions ofBeringia largely have been presumed to hold true for Chukotka. Yetthis brief overview underscores the limitation of the Chukotkandata for tracing the spatial and temporal variations in the lateQuaternary landscapes. The recent addition of continuous records

P.M. Anderson, A.V. Lozhkin / Quaternary Science Reviews 107 (2015) 112e128114

from Lake El'gygytgyn in the Chukchi Uplands (Lozhkin et al., 2007;Fig. 1), 3 lake sites from the Anadyr Lowland (Lozhkin andAnderson, 2013), and 2 lake sites from the Kankaren region ofsouthern Chukotka (described in this paper) help to clarify patternsof change in the late Quaternary vegetation. These sites form auseful north-south transect through eastern Chukotka that can beextended further northward with the inclusion of paleobotanicalrecords from Wrangel Island (Lozhkin et al., 2001). Although thistransect does not represent all areas of Chukotka, it is sufficient toprovide a provisional vegetation history that can be used to better

Fig. 2. Map of study area showing the locations of Gytgykai and Patricia lakes. The

evaluate the previously proposed paleoenvironmental patterns.Gytgykai and Patricia lakes (Figs. 1 and 2) are 2 of the few Chu-kotkan sites that provide complete records from the LGM to pre-sent, and they form the southern anchor of the paleovegetationaltransect. Although both sites have been used in previous publica-tions about herb zone assemblages (Lozhkin et al., 1998) and inregional summaries (Anderson et al., 2002; Ager, 2003; Bigelowet al., 2003; Kaufman et al., 2004; Brubaker et al., 2005; Edwardset al., 2005), this article is the first detailed presentation and dis-cussion of the data.

map key is 1) Anadyr Lowland; 2) lake; and 3) elevation (m above sea level).

Fig. 3. Vegetation map of Chukotka and adjacent regions adapted from Kolosova(1980). The map key is: 1) discontinuous herb-dominated tundra; 2) wet to mesicarctic tundra dominated by Cyperaceae spp. and shrubs of low growth form; 3) borealforest with Larix gmelinii; 4) upland and mesic tundra; 5) high shrub tundra of Pinuspumila and Duschekia fruticosa; and 6) mesic tundra often with mid-sized shrubs.


2. Geographic setting

Chukotka occupies the far northeast edge of Asia extendingwestward from the Bering Sea to the eastern Kolyma drainage andfrom the Chukchi and East Siberian seas southward to the KoryakUpland (Fig. 1). The topography is dominated by 3 uplands: Annui,(maximum elevation 1700 m), Chukchi (maximum elevations1200e1500 m), and Koryak (maximum elevations 1600e1800 m).A series of lowlands characterize the northern coasts, with a moreextensive and interior lowland associatedwith the Anadyr drainagein central Chukotka. The Anadyr River, which generally flows fromwest to east, is the major Chukotkan waterway with other smallerrivers emptying to the East Siberian, Chukchi, or Bering seas.Thermokarst processes are active through much of the region,especially in low-lying terrain. Permafrost thickness can be up to400e500 m.

The northern coastal plain of Chukotka is dominated by gra-minoid tundrawith prostrate shrubs of Salix and Betula exilis (Shilo,1970; Fig. 3). The Chukchi Upland, Chukchi Peninsula, and theAnadyr Lowland support a mosaic of shrub tundra communities.The most common shrubs include B. exilis, Betula divaricata (syn.Betula middendorffii), Salix spp., Ericales, and Duschekia fruticosa(shrub Alnus). P. pumila is absent on the Chukchi Peninsula but ispresent in the other two regions on sites with sufficient summerwarmth and snow cover (Andreev, 1980). P. pumila and D. fruticosabecome more common at lower latitudes and ultimately form aunique high shrub tundra (heights of up to 2 m) or “prostrate”forest (Sochava, 1956) in southern Chukotka. The highest elevationsthroughout the region support relatively small areas of herb-

dominated tundra (not shown in Fig. 3). Larix gmelinii is found inwestern Chukotka, extending eastward to the upper Anadyrdrainage. The trees tend to form openwoodland or forest-tundra atlower elevations. Other trees include Populus tremula, Populussuaveolens, Betula platyphylla, and Chosenia arbutifolia. However,these species are not common and tend to be restricted to southernand central Chukotka, sometimes extending as far eastward as theupper Anadyr drainage.

The paleogeography of Chukotka has changed dramaticallysince the LGM; (Fig. 1). At the height of the last glaciation(~18,000 14C/~21,000 cal yr BP), the exposed Bering Land Bridgewas ~1000 km wide at its maximum. The present-day coastal andnear-coastal locations of northern and central Chukotka becamepart of the interior of the vast Beringian subcontinent. However,shoreline configuration changed little for southeastern Chukotka,neighboring Kamchatka, and the northern Okhotsk coast. Varioustimes have been offered for the initial opening of Bering Strait withmost falling between 12,000e10,000 14C/13,800e11,400 cal yr BP(Elias et al., 1992, 1996, 1997; Lozhkin, 2002; Brigham-Grette et al.,2003; England and Furze, 2008; Keigwin et al., 2013). By the lateglaciation, the near-modern Chukotkan coastline was in place andWrangel Island, although larger than present, was detached fromthe mainland. However, to the west of the island a large coastalplain extended ~500 km to the north of the contemporary conti-nental shoreline. Near modern sea-levels were obtained by~5000 14C/~5700 cal yr BP throughout Beringia.

Late Pleistocene glaciations also helped shape the Chukotkanlandscape, but in a more limited way as compared to shorelinereconfigurations. Recent studies suggest the occurrence of twoglaciations following the last interglaciation (Oxygen Isotope Stage(OIS) 5), one equivalent to OIS2 age and a second of OIS3 or OIS4 age(Gualtieri et al., 2000; Heiser and Roush, 2001; Brigham-Gretteet al., 2003; Barr and Clark, 2012). The OIS2 or Sartan glaciationwas limited throughout Western Beringia, with maximum glacialextent of ~20e40 km in Chukotka (Barr and Clark, 2012). Based onfield evidence and 36Cl dating from the Mainitz Lake area (Fig. 2),OIS2 glaciers did not extend beyond ~20 km, with glacial advancesfrom the east, west and/or south (Gualtieri et al., 2000). Datessuggest that ice may have occupied the southern Mainitz basinfrom at least ~19,500 to ~10,000 14C/~23,300e11,400 cal yr BP.However, the latter datemay bemisleading, coming from a youngerrock that possibly had been redeposited onto the 13.8 m laketerrace through frost-heaving. Patricia Lake, which is adjacent toMainitz Lake, is lower in elevation than the 13.8 m terrace, sug-gesting that it would have been ice covered (or perhaps nonexis-tent) during the LGM. However, both 14C dates and pollenstratigraphy from the lake core indicate a full-glacial age for initiallake formation.

3. Study sites

Patricia (PA; informal name; 63� 190 3000 N,176� 300 E; 121 m asl)and Gytgykai (GY; 63� 250 N; 176� 320 3000 E; 102.5 m asl) lakes arelocated ~10 km apart in rolling terrain that borders the Anadyrdepression and the Kankaren Range to the north and east,respectively (Fig. 2). The lakes are within the Mainitz-Pekulneiitectonic zone, which trends north-south from the PekulneiiRange through Mainitz Lake to Pekulneiskoye Lake (Chekov, 1998).The regional bedrock is Late JurassiceEarly Cretaceous sandstone,conglomerate, siltstone, and argillite. PA lies within a region ofterraces, moraine belts, and drift associated with OIS2 glaciation,whereas GY is ~3 km beyond these limits (Gualtieri et al., 2000). Wenoted apparent 20e40-m-high moraines around GY that are likelypre-OIS2 age. Mean annual, July, and January temperaturesare �10.1 �C, 12.6 �C and �26.7 �C, respectively; annual and

Table 2Radiocarbon and calibrated ages from Gytgykai and Patricia lakes.

Depth (cm) CAMS Labnumber

14C date Calibrated age(mean and2s range)

Material dated

Gytgykai Lake40e43 19,047 6180 ± 60a 7095

6940e7250Humic acid

166e169 19,036 2750 ± 60 28652750e2980

Humic acid

212e215 19,044 8130 ± 60a 91308980e9280

Humic acid

322e325 19,048 12,300 ± 50a 14,29013,970e14,610

Humic acid

352e355 19,043 14,230 ± 60a 17,30516,990e17,620

Humic acid

427e430 19,045 13,830 ± 1060 16,28513,640e18,930

Humic acid

602e605 19,494 30,670 ± 310 35,15034,650e35,650

Humins

813e816 19,046 24,030 ± 470a 28,83027,840e29,820

Humic acid

918e920 14,599 18,900 ± 100 22,60022,230e22,970

Terrestrialplant material

Patricia Lake


seasonal precipitation values are 314 mm, 48 mm, and 20 mm,respectively (Berezovo meteorological station; Klyukina, 1960).Average number of days with snow cover is 238 with a date of 17October for the first established snow-cover and a date of 26 Mayfor the first snow melt.

PA is 800 m long and 500 m wide. The lake is comprised of asingle basin with maximum water depth of 11 m. GY, also a singlebasin, is 1350 m long with a maximumwidth of 1000 m and waterdepth of 5.15 m. Like PA, the bottom of GY is flat and broad (~400 mwidth). Both lakes are closed basins and of glacial origin (e.g., kettleor morainally dammed). The study sites are within the high shrubtundra zone of P. pumila and D. fruticosa or the stlanik phytogeo-graphic subzone (Razzhivin, 1994). The slope and flat tops of themoraines near the lakes are covered by P. pumila. P. pumila alsoforms thickets in association with D. fruticosa, B. divaricata, andSalix spp. on the nearby mountain slopes and along lake and rivershorelines. Other woody to semi-woody taxa include a variety ofericads (e.g., Ledum palustre, Empetrum nigrum, Vaccinium vitis-ideae, V. uliginosum). Graminoids dominate the herbaceous com-munities. A small, well-developed population of P. suaveolens hasestablished in the valley between PA and GY.

40e45 31,635 1380 ± 60 12181215e1220

Bulk sediment

73e76 55,361 1740 ± 190 17001290e2110

Charcoal;moss fragments

130e131 64,804 2920 ± 50 30752930e3220

Bulk sediment

215 29,858 4390 ± 60 49604850e5070

Bulk sediment

280e285 49,693 5600 ± 120 64256180e6670

Charcoal

295e300 31627 6010 ± 60 68606720e7000

Bulk sediment

335e336 64,805 6760 ± 60 76057510e7700

Bulk sediment

404e407 58,291 7770 ± 280 86608020e9300

Insects; Betula seed

415 30,161 10,450 ± 70 12,33512,100e12,570

Bulk sediment

432e433 64,806 12,140 ± 50 13,99013,830e14,150

Bulk sediment

459e460 64,807 15,810 ± 110 19,05018,730e19,370

Bulk sediment

a Radiocarbon dates used in the Gytgykai age model.

4. Methods and chronology

GY and PA were cored using a modified Livingstone pistonsampler (Wright et al., 1984) from an open-water platform insummer of 1992. The uppermost, flocculent sediments werecollected with a plexiglass tube and the two records merged usingpollen percentages. Core sediments were described qualitatively(Table 1), and 1 cm3 samples were processed for palynologicalanalysis following procedures developed for arctic sediments(PALE, 1993). Pollen sums are a minimum of 300 identified pollengrains. Percentages of individual taxa are calculated using a sum ofidentified pollen grains, whereas the subsum percentages (Treesand shrubs, Herbs, Spores) are based on a sum of all pollen andspores. Zone boundaries were based on changes in percentages ofmajor taxa. By convention, pollen from the shrub D. fruticosa(formerly Alnus or Alnaster fruticosa) is referred to as Alnus in thepollen diagrams and shrub Alnus in the text. Other botanicalnomenclature follows Czerepanov (1995). Loss-on-ignition (LOI)was calculated following standard methods (PALE, 1993).

Radiocarbon dates from PA (Table 2) indicate two differentsedimentation rates above and below ~410 cm (Fig. 4). The shiftfrom relatively slow (~0.008 cm yr�1) to relatively rapid(~0.052 cm yr�1) sedimentation does not correspond to any changein sediment type or the placement of radiocarbon samples. PercentLOI (Fig. 5) is comparable in the upper ~400 cm of the core

Table 1Sediment description, Gytgykai and Patricia lakes.

Site Depth (cm) Description

Patricia Lake 0e14 Watery silt14e352 Silt with thin layers of

fine-grained organics352e428 Silt with thin layers (nonorganic)428e512 Silt with 1e5 cm thick

layers of medium-grained sandGytgykai Lake 0e8 Watery silt

8e744 Silt with organics, either scattered orin small layers (maximumthickness of 2 mm)

744e765 Sand, fine-grained, well sorted765e942 Silt942e1000 Sand

(generally between ~20 and 30%), conceivably indicating a simi-larity in sediment source and basin stabilization that perhaps wasinfluenced by lake-level and ice-extent changes associated with theformation of the 13.8 m terrace at Mainitz Lake (Gualtieri et al.,2000). In consideration of the core sedimentology and thedateedepth relationships, simple linear interpolation was used asan age model for PA. Because the calculated ages for vegetationchanges at PA differ from shifts documented in other areas ofWestern Beringia, we also developed a tentative age model for GYto compare to the PA chronology. In this model, we selected asubset of 4 dates (noted in Table 2) that seemed most reasonable inlight of previously established timing of vegetation shifts inWestern Beringia (Anderson and Lozhkin, 2002). IntCal09 (Reimeret al., 2009) was used to calibrate the radiocarbon dates.

5. Results

The pollen stratigraphy in the PA and GY diagrams (Figs. 6 and 7;Table 3) parallels the sequences from other regions of WesternBeringia with assemblages dominated by herbs (zones PA1 andGY1), Betula (zones PA2 and lower GY2), AlnuseBetula (zones PA3,

Fig. 4. Ageedepth relationship at Patricia Lake.


PA4, and upper GY2), and PinuseAlnuseBetula (zones PA5 and GY4)pollen.

The herb zones at both sites are characterized by high per-centages of Cyperaceae, Poaceae, and Artemisia pollen, taxa thattypify LGM assemblages across Beringia. Although radiocarbon

Fig. 5. Percent loss-on-ignition, pollen zones, radiocarbon dates, and sediment typesfrom Patricia Lake. The figure key is: 1) water-rich silt; 2) silt with organics; 3) finelylaminated silt; and 4) silt with layers of sand.

reversals at GY prevent a determinative chronology, the nearly600 cm of sediments (much of which is fine-grained), the range ofradiocarbon dates in zone GY1 (extrapolated basal age of27,400 14C/~32,000 cal yr BP), and limited extent of regionalglaciation probably indicate the existence of the lake throughmuch or all of the latest Pleistocene. The PA basin appears to beyounger, consistent with the glacial reconstruction for the MainitzLake area, and has an extrapolated basal age of ~21,300 14C/~25,600 cal yr BP.

Zones GY1A and GY1B have consistent albeit low (generally<10%) pollen percentages of Betula, Alnus, and Salix with relativelyhigh percentages of Polygonaceae, Saxifragaceae, and Asteraceae.Selaginella rupestris spores display their greatest values for thecore. These subzones are separated by the slightly higher per-centages of woody species in zone GY1B. Zone GY1C displays noneof these modest increases in the mentioned forbs and showssomewhat lesser values of woody taxa. This subzone differs fromzones GY1A and GY1B in that palynomorphs were too sparse toobtain adequate counts in the majority of levels between ~585 and360 cm. Unlike a second gap in counts (~780e740 cm; zone GY1B),this upper interval is not associated with sedimentary changesthat might account for a reduction in pollen concentration. Such adrop could reflect a decrease in vegetation cover, but the change isnot associated with an increase in taxa associated with disturbedor stony habitats (e.g., S. rupestris, Artemisia and otherCompositae).

Zone PA1, unlike zone GY1, has no samples that were too barrenfor counting. The PA record shares with GY modest percentages ofwoody taxa and a similarity in the minor herb pollen flora. How-ever, zone PA1 displays much greater percentages of S. rupestrisspores and lesser values of Polygonaceae, Saxifragaceae, andAsteraceae pollen. Caryophyllaceae pollen percentages are thehighest in the core as are values of Hepaticae and Bryales spores.Minor herb taxa are similar between the 2 diagrams except for theoccasional appearance of Fabaceae, Lamiaceae, Epilobium, Polyg-onum aviculare, Polygonum aconogonon, Claytonia, and Chamaene-rion types in zone GY1. Total pollen accumulation rates (PAR) are<100 grains cm�2 yr�1 in zone PA1 and generally between 100 and200 grains cm�2 yr�1 in zone GY1.

The herb-dominated spectra are replaced by those with highpercentages of Betula (zone PA2; zone GY2,1 sample only). The maintaxa and the numbers of minor herb types decrease from the pre-vious zone. Sphagnum spores increase in both records, associatedwith a decline in S. rupestris spores. Percentages of Polypodiaceaespores also increase at GY. If the ~12,300/~14,200 cal and

Fig. 6. Percentage diagrams from Patricia Lake showing: a) main taxa and 2) minor taxa. The lithology key is: 1) water-rich silt; 2) silt with organics; 3) finely laminated silt; and 4)silt with layers of sand (see Table 1).


~14,230 14C/~17,000 cal yr BP dates reflect an accurate chronology,then the establishment of Betula shrub tundra near GY occurred~13,000 14C/15,300 cal yr BP based on shifts in the pollen percent-ages. Two alternate age schemes at PA indicate an older timing ofthis transition: ~16,000 14C/~19,000 cal yr BP (using the15,810 14C BP date) or ~14,900 14C/~18,100 cal yr BP (eliminating the15,810 14C BP date). Both of the PA ages are significantly earlier thanthe ~12,500 14C BP (14,700 cal yr BP) age seen in other pollen recordsfrom Western Beringia (Anderson and Lozhkin, 2002). PARs forBetula at both PA (<10 grains cm�2 yr�1 in zone PA1;

30e100 grains cm�2 yr�1 in zone PA2) and GY (<10 grains cm�2 yr�1

in zone GY1; 30e120 grains cm�2 yr�1 in zone GY2) parallel thepercentages.

The third major change in pollen assemblages is marked by theincrease in Alnus percentages (zone PA3; zone GY2). Woody orsemi-woody taxa (Alnus, Betula, Salix, Ericales) dominate thespectra. Percentages of Polypodiaceae spores increase in the GYrecord, remaining relatively high to the top of the core. This tran-sition is dated to ~12,100 14C/~14,000 cal yr BP at PA and calculatedas ~11,800 14C/~13,700 cal yr BP at GY. Following the initial rise in

Fig. 7. Percentage diagrams from Gytgykai Lake showing: a) main taxa and b) minor taxa. The lithology key is: 1) water-rich silt; 2) silt with organics; 3) sand; and 4) silt (seeTable 1).


Alnus percentages, there is an interval where Alnus remains high orincreases slightly, Betula decreases, and Pinus pollen appearsconsistently (zone PA4, zone GY3). The BetulaeAlnus record showstwo hiatuses at GY (~330e310 cm; 220e190 cm), where pollen/spore concentrations were insufficient to get adequate counts. As inzone GY1C, there is no correspondence with sedimentary changes.

The final vegetation change is indicated by the rise in Pinus subg.Haploxylon pollen (in this region associated with P. pumila). The

increase is estimated to be ~5700 14C/~6500 cal yr BP at PA. Twoalternate age schemes at GY indicate this change occurred~7600 14C/~8400 cal yr BP (if the 6180 14C BP is deemed correct) or~6500 14C/~7400 cal yr BP (if the 6180 14C BP is deemed incorrect).Percentages of Alnus pollen decline in both records and Betulapollen percentages showa general albeit slight decrease. Other taxaremain similar to the previous zone. A fourth interval of uncount-able samples occurs between ~180 and 130 cm at GY.

Table 3Ages of pollen zones, Gytgykai and Patricia lakes.

Regional and localpollen zones

Patricia lake Gytgykai lake

14C and calibrated ages 14C and calibrated ages

Pinus (PA5; GY4) 5700e0 14C6500e0 cal

6500 or 7600ae0 14C~7400 or 8400e0 cal

Alnus (PA3 & PA4;upper GY2 & GY3)-

12,100e570014C~14,000e6500 cal

11,800e6500/7600 14C~13,700e7400/8400 cal

Betula (PA2; lower GY2) 15,800e12,10014C~19,000e14,000 cal

13,100e11,80014C~15,500e13,700 cal

Herb (PA1, GY1) 15,800e21,300~19,000e25,600 cal

27,400e13,10014C~32,000e15,500 cal1C 18,100e13,10014C21,400e15,500 cal1B 24,700e18,10014C~29,800e21,400 cal1A 27,400e24,70014C~32,000e29,800 cal

a See text for explanation of alternate age schemes.


6. Vegetation history of the Kankaren region

6.1. The Last Glacial Maximum

Discussions of Beringian environments during the LGM oftenstress whether the vegetation was primarily arctic tundra orcroyoxerophytic steppe and to a lesser degree whether the plantcover was mostly discontinuous or continuous (e.g., Hopkins et al.,1982). A major limitation in determining the paleovegetation re-lates to pollen and spore morphology that often restricts thetaxonomic level to which palynomorphs can be assigned, therebyalso limiting the reconstruction of past habitats. In the GY and PArecords (zones PA1 and GY1), the main pollen taxa (Cyperaceae,Poaceae, Artemisia), the range of minor herb taxa, and low PAR areall typical of arctic tundra settings (Hult�en, 1968; Cwynar, 1982).Loss-on-ignition values of <10% at Patricia Lake (Fig. 5) suggest amoderate vegetation cover with minimal organic input fromoverland drainage. While disturbed-ground taxa and low PAR(<200 grains cm�2 yr�1) in the Kankaren records perhaps reflectdiscontinuous vegetation, PAR of ~300 grains cm�2 yr�1 have beenreported from lake basins similar in size to GY and PA in modernprostrate shrub tundra in the foothills of northern Alaska, wherevegetation cover is 80e100% (Oswald et al., 2003a). While theKankaren vegetation here is not inferred to be prostrate shrubtundra, the modern study shows that relatively low PAR do notnecessarily reflect a limited vegetation cover.

Although the broad scale vegetation of the Kankaren region canbe classified as graminoid-ArtemisiaeSalix tundra, minor pollentaxa provide more vegetational detail. They attest to a variety ofhabitats that characterized the landscape and are consistent withthe topographic complexity of the region. For example, dry ordisturbed sites are suggested by pollen from Compositae, Cheno-podiaceae, Brassicaceae, Caryophyllaceae, Apiaceae, Fabaceae, P.aconogonon, Dryas, and Plantago. The location of such habitatsprobably encompassed lake beaches, streamsides, frost-disturbedlowland soils, and well-drained sunny slopes. The high percent-age of S. rupestris spores indicates poorly vegetated stony slopes.Moister sites are suggested by Polygonaceae, Ranunculaceae, Tha-lictrum (although some Thalictrum species are associated withrocky slopes), Claytonia, and Astragalus. Such associations likelyreflect the presence of moister soils. Sphagnum spores also suggestthe existence of stabilized, mesic surfaces.

Snow beds, usually found in protected sites in valleys and hillyterrain, are often cited as examples of mesic settings during theLGM. A study of modern plant associations and soil conditions in

Chukotka has shown the importance of Salix, Artemisia, and Carexspecies (e.g., Salix polaris, Salix chamissonis, Artemisia tilesii,Artemisia arctica, Carex nesophila, Carex scirpoidea) in snow bedcommunities (Razzhivin, 1994). Razzhivin concluded that areaswith moderate snow depths were especially favorable for plantgrowth because: 1) the snow cover provides protection during thecold season; 2) permafrost processes are minimal, thus lesseningthe extent of disturbed sites and allowing a more continuousvegetation cover; and 3) such locales have a relatively greateraccumulation of organic matter. This modern study, of course, cannot definitively specify the details of the full-glacial environ-ments, but it does suggest that taxa that are common in LGMspectra (i.e., Cyperaceae, Artemisia) may be equally indicative ofmesic as xeric conditions. The presence of mesic habitats (basedon insect data) has been noted at the nearby Ledovyi Obryv site(Fig. 1). If relatively moist LGM conditions in the Main valley werenot restricted to disparate sites with atypical microclimates, theunusually high percentages of Cyperaceae pollen in the Kankarenrecords might reflect the general importance of snow bed com-munities on the landscape. These data may also indicate thatsouthern Chukotka experienced more moderate climates ascompared to other areas of Western Beringia (see Section 7 forfurther discussion).

Woody species, although likely not abundant, were present inthe Kankaren region, suggesting sufficient effective moisture andprotective snow cover to permit survival in the severe LGM climate.Shrubs may have been more common before ~18,100 14C/~21,400 cal yr BP, perhaps indicating an increase in snow cover,effective moisture, and/or growing season temperatures. Thispattern is consistent with a division of the LGM into an early cry-ohygrotic (cold, moist) and a later cryoxerotic (cold, dry) stagenoted in sites from Siberia and Western Beringia (Kind, 1974;Grichuk, 1984). Salix was almost certainly the most commonshrub throughout the LGM, probably growing in prostrate form(e.g., Salix arctica) in more exposed sites and scattered on lowerslopes and in wetter fluvial areas and snow beds (e.g., S. lanata,S. polaris). Although Ericales pollen appears less regularly than doesSalix, these woody to semi-woody plants probably occurred in low-growth forms.

The fossil pollen percentages of Betula and Alnus are below themodern pollen threshold for establishing shrub presence (Lozhkinet al., 2001). However, the rapid increase in Betula percentages inzones PA2 and GY2 is consistent with patterns associated with theprobable presence of small refugia in sheltered valleys (Brubakeret al., 2005). Although presenting a different stratigraphicpattern than Betula (see section 7 for further discussion), shrubAlnus also probably survived in southern Chukotka during theLGM. In addition to the mapped patterns presented by Brubakeret al. (2005), paired pollen-macrofossil studies indicate a taxonmay be present even when percentages are below modern pollenthresholds (e.g., Hu et al., 1993; Binney et al., 2009). An investi-gation of modern pollen rain in Alaskan lakes noted a modestrange of 600e800 m as a pollen source area (Oswald et al., 2003b).Granted, this modern work was done in prostrate and dwarf shrubtundra, and the LGM vegetation at PA and GY probably had a lessershrub component. However, the study is a reminder that sourceareas for the major taxa need not be overly influenced by long-distance sources (note: the same would be true for Cyperaceaeand Artemisia and their possible association with local snow bedcommunities).

6.2. The Late Glaciation

The rapid rise in Betula pollen percentages (zone PA2 and lowerzone GY2) is a biostratigraphic pattern consistent with the regional


replacement of full-glacial tundra by shrub Betula tundra that hasbeen documented across Beringia (Brubaker et al., 2005; Edwardset al., 2005). This change typically is associated with the beginningof postglacial climatic amelioration and dates to~12,000e12,500 14C/~13,800e14,700 cal yr BP in most WesternBeringian sites (Anderson and Lozhkin, 2002). While the~13,000 14C/~15,300 cal yr BP date at GY for the percent increase inBetula pollen generally is consistent with the regional pattern, the~15,800 14C/~19,000 cal yr BP (or ~14,900 14C/~18,100 cal yr BP ifthe 15,800 14C BP is discarded) at PA is surprisingly early. Given theproximity of the 2 sites, ages for this vegetation change would beexpected to be similar. This discrepancy possibly relates to theradiocarbon samples themselves (i.e., relying on age schemes usinghumic acid (GY) vs. AMS bulk sediment (PA) dates; Table 2).Because of the potentially lengthy storage of carbon on the land-scape prior to its deposition in lake basins, humic acid dates arecharacteristically “too old” (Atkin et al., 1985). In the case of GY, thispotential offset seems to be minimal, with the Betula rise fallingwithin the age range defined by Brubaker et al. (2005). AMS bulk-sediment dates also can provide “too old” ages, as studies inEastern Beringia have shown (e.g., Bigelow and Edwards, 2001).However, an examination of sites from Northeast Siberia(Anderson and Lozhkin, 2002) where macrofossil and bulk sampleshave been analyzed from the same or nearby levels suggests thatthere is not a systematic offset related to either sample (macro-fossil vs. bulk peat/lake sediment) or site (peat section vs. lake)type. Although possible that the ~15,800 14C/~19,000 cal yr BP datefrom PA does not accurately reflect the expansion of shrub Betula inthe Kankaren area, the age is consistent with sites from CentralBeringia (Ager, 2003; Elias et al., 1996; Table 4). We believe that thedifference of ~2800/1800 14C yr in the zone-boundary ages be-tween GY and PA most probably relates to the difficulty inobtaining counts in this portion of the GY core. That is, the lack ofsamples from 325 to 360 cm prevents an accurate age assignmentfor the herb-Betula zone transition and additional counts, if theywere possible, likely would result in an age more consistent withthe PA record.

The Kankaren records suggest that shrub Betula had anincreased importance on the landscape possibly starting as early as~15,800 14C/~19,000 cal yr BP. However, the persistence of pollenfrom graminoids, Artemisia, and Salix and the variety of minor taxaindicate that the landscape heterogeneity characteristic of the LGMcontinued into the Late Glaciation. Nonetheless, the nature of thatmosaic probably differed between the 2 intervals, a reflection ofameliorating conditions. For example, the decrease in S. rupestrisspores (particularly at PA) associated with the Betula rise suggests amore extensive vegetation cover on nearby stony slopes and/or inpreviously disturbed sites in the valley lowlands as compared to theLGM. Modest increases in percentages of Sphagnum spores implylocal landscape stabilization and greater effective moisture oneither local or regional scales. LOI of ~12% (Fig. 4) in zone PA2 may

Table 4Approximate 14C and calibrated ages for initial spread of shrub species.

Southern Chukotka Central Chukotka Northern Chuk

Shrub Betula 15,80014C19,000 cal

13,20014C15,600 cal

12,80014C15,100 cal

Shrub Alnus 12,00014C13,800 cal

850014C9500 cal

12,00014C13,800 cal

Pinus pumila 760014C8400 cal

600014C6800 cal

960014C11,100 cal

a Includes areas of the inundated land bridge and bordering coastal areas of Alaska. Sb Trends from Brubaker et al., 2005.

hint at greater vegetation cover near the lake. However, thedeposition of sandy sediments in the basin, whether water- or air-born, suggests the persistence of barren areas in the catchment,consistent with deglaciation in the nearby Kankaren Range andKoryak Upland (Gualtieri et al., 2000). The trace values of Oxytropispollen in zone PA2 is further evidence of the presence of gravelly tosandy soils in the vicinity of the lake. In contrast, sediments(organic silt) and minor pollen taxa suggest that the GY catchmenthad fewer disturbed sites.

Alnus is the last of the deciduous shrubs to expand in the Kan-karen region (zones PA3 and zone GY2). The increase in percentagesat PA and GY indicates that shrub Alnus was widespread beginning~12,000 14C/~13,800 cal yr BP, a chronostratigraphy that is consis-tent with the earlier expansion of Alnus in Western as compared toEastern Beringia (Brubaker et al., 2005). The rise in Polypodiaceaespores suggests the greater occurrence of shrub thickets across thelandscape, but Alnus was probably most common along lake andstream shores andmountain draws. The proliferation of shrub Alnusindicates an increase in soilmoisture and fertility (Moskalyuk, 2008)and generally warmer and wetter conditions as compared to theLGMor earlier in the Late Glaciation. Although the increase in Alnus,the continued importance of Betula, and the decrease in graminoidpollen in the Kankaren records reflect the regional dominance ofdeciduous shrub tundra by ~12,000 14C/~13,800 cal yr BP, the ecol-ogy of the minor taxa in the pollen diagrams points toward thepersistence of a variety of microhabitats near the lakes.

6.3. The Holocene

P. pumila is the final, major addition to the plant communities ofthe Kankaren region. The timing of P. pumila expansion is prob-lematic. Radiocarbon control is better in the PA record, whichsuggests the evergreen shrub was probably present as early as~6700 14C/~7400 cal yr BP but was not widespread until ~5700 14C/~6500 cal yr BP. Two alternative age schemes for GY, dependent onaccepting or rejecting the 6180 14C BP date, suggest P. pumilaexpansion at either ~7600 or 6500 14C/~8400 or 7400 cal yr BP. P.pumila has low shade tolerance and can survive in drier habitats ascompared to shrub Alnus (Moskalyuk, 2008). The ability of theevergreen to colonize more water-stressed sites (e.g., morainalridge-tops and nearby mountain slopes) likely increased theregional vegetation cover, particularly at higher elevationsbordering valleys. P. pumila also requires moderately warm sum-mers (mean July temperatures of 12 �C) and sufficient snow depthsto protect the evergreen branches from winter freezing anddesiccation (Andreev,1980; Kozhevnikov,1981). Such requirementsimply increases in summer warmth and winter snow cover ascompared to the Late Glaciation. The relative uniformity of thepollen assemblages suggests that modern vegetation were estab-lished by the mid-Holocene.

otka Wrangel Island Central Beringiaa Western Beringiab

11,00014C12,9000 cal

15,000e14,00014C18,500e16,700 cal

13,000e12,00014C15,300e13,8000 cal

Absent 800014C9000 cal

800014C9000 cal

Absent Absent Absent

ee text for references.


7. Vegetation history of Chukotka since the LGM and itsimplications for biogeographic patterns in Central andWestern Beringia

The GYand PA records supplement paleobotanical data from ~20radiocarbon-dated exposures and 5 lacustrine records. The conti-nuity of the Kankaren records improves understanding of thevegetation history of Chukotka over the last 21,000þ 14C/25,400þ cal yr (Anderson et al., 2002; Lozhkin et al., 2007; Andreevet al., 2012; Lozhkin and Anderson, 2013; see also; Kuzmina et al.,2011; Berman et al., 2011). Below we consider the regional impli-cations of the GY and PA records, dividing the discussion into full-glacial and postglacial time periods.

7.1. Last Glacial Maximum (~25,000e12,500 14C BP,~30,000e14,700 cal yr BP)

As mentioned in the Introduction, the nature of the LGMvegetation has been an ongoing debate, one that initially focusedon the prevalence of arctic tundra vs. steppe tundra (Hopkins et al.,1982) and then progressed to questions of larger-scale regionalvariability (Guthrie, 2001; Yurtsev, 2001; Elias and Crocker, 2008).Analytical methods for interpreting the palynological data haveprogressed significantly since the 1960se1980s when vegetationreconstructions relied on qualitative comparisons of pollen per-centages and an understanding of the modern ecology of the taxarepresented in the pollen record. The subsequent development ofstatistical comparisons of modern and fossil spectra and the linkingof climate and vegetation models has helped to better determinethe characteristics of the LGM vegetation. Belowwe discuss some ofthese pollen-based methods as applied to Chukotka as aids forclarifying the nature and regional patterns in the vegetation. Wealso examine the importance of insect data for paleovegetationalinterpretations by looking at results from the Ledovyi Obryv site, akey interdisciplinary study from southern Chukotka. Finally, weconsider the evidence for extending the migrational barrier pro-posed for Central Beringia to Chukotka.

7.1.1. The LGM in Chukotka: arctic tundra or steppe? Regionaluniformity or latitudinal gradients?

The biomization method, which uses plant functional types toassign fossil pollen spectra to themost appropriate biome, providesa more systematic approach for assessing the nature of the full-glacial vegetation as compared to interpretations based on quali-tative criteria (Prentice et al., 1992, 1996). When biome modelsinitially were applied in Beringia, the GY record was the onlyChukotkan site that met chronological and sample-interval criteria.In the first biomization experiment, the GY pollen data yielded atundra classification (Edwards et al., 2000). Further model refine-ment incorporated the subdivision of tundra into five types andresulted in an erect dwarf-shrub tundra designation for the site(Bigelow et al., 2003). A third experiment used 4 different atmo-spheric circulation models in conjunction with BIOME4 to simulateLGM vegetation in northern Eurasia (Kaplan et al., 2003). In 3 of thesimulations, low-to-high shrub tundra was indicated for the Kan-karen region, whereas 1 model showed the presence of cushion-forb-moss tundra. All of the above experiments included a steppebiome category, but in each of the biome-based reconstructions theKankaren region was assigned to tundra and not steppe, as alsoheld true for other Beringian sites. While we are reluctant to agreethat shrub tundra was widespread in southern Chukotka, we doconcur with the biomization results that indicate the dominance ofarctic tundra and not steppe during the LGM. The coupled climate-biome models further suggest that conditions in southern

Chukotka were sufficient to support shrub growth and are viableareas for glacial refugia (see also Section 7.2.1).

Regional patterns described in the coupled paleoclimate-BIOME4 simulations are of equal interest as the above vegetationclassifications (Kaplan et al., 2003). In 3 of the 4 model runs, lat-itudinal differences in Chukotkan vegetation were shown; low-shrub tundra dominated in southern Chukotka changing tograminoid-forb and/or cushion forb-lichen-moss tundra in centralto northern areas. In contrast, a single model indicated a ubiquitousoccurrence of cushion forb-lichen-moss tundra. These latter resultsare more in agreement with the presence of a widespread, uniformbiome as advocated by some researchers (see Blinnikov et al., 2011).Nonetheless, even in this model the simulated high arctic vegeta-tion differs greatly from that of a productive mammoth steppe thathas been proposed for full-glacial northern Eurasia. The bestquantitative agreement with the fossil data was found with theLMDH (Laboratoire de Me�ete�eorologie Dynamique) model, therebybolstering conclusions of regional scale variations in the vegetation.While conditions likely were cooler than those represented in themodels (Kageyama et al., 2001), the Kaplan et al. experimentsillustrate that the development of a latitudinal vegetation gradientin Chukotka is consistent with LGM climates.

A qualitative comparison of the major pollen taxa from theKankaren and El'gygytgyn lake records supports the regional vari-ability found in themodel simulations. Although values of Artemisiapollen (~10e20%) are similar, Cyperaceae pollen (~30e60% vs.<20%) is greater in the southern sites, whereas Poaceae pollen isgreater to the north (~50e60% vs. mostly 15e30%). Palynologistshave used the relative relationship of Cyperaceae and Poaceaepercentages to infer changes in moisture. For example, Ager (2003)suggested that higher Cyperaceae percentages at Zagoskin Lake inAlaska (Fig. 1) indicated more mesic conditions during the lateinterstade (OIS 3 equivalent) as compared to the LGM. This rela-tionship would be consistent with the snow bed study of Razzhivin(1994), where Cyperaceae species were important members of themodern plant communities. The El'gygytgyn record shows higherpollen percentages of taxa indicative of dry and/or disturbed sites(e.g., Caryophyllaceae, Brassicaceae, and Papaveraceae), althoughthese taxa may be more characteristic of specific conditions withinthe crater than of the regional vegetation. The Kankaren pollendiagrams also differ from sites farther west in Western Beringia,where Cyperaceae pollen is generally <30% and Poaceae >30%(Lozhkin and Anderson et al., 2002).

Statistical analog analyses provide additional evidence ofregional vegetation variability within Chukotka. Possible analogs(samples with square-chord distances 0.186e0.40; Anderson et al.,1989) for LGM spectra at Lake El'gygytgyn have been found in themodern graminoid-forb tundra on Wrangel Island (Lozhkin et al.,2007). Although 34 steppe and meadow-steppe species are foundon Wrangel Island (Yurtsev, 1982), the regional vegetation isconsidered arctic tundra/polar desert (Kolosova, 1980). The Wran-gel Island analog is shared by other Western Beringian sites. Forexample, Glukhoye Lake (southwest Beringia; Fig. 1) and Smor-odinovoye Lake (northwest Beringia) have good analogs (square-chord distances between 0.96 and 0.185) to the modern Wrangelspectra, suggesting an affinity to the LGM vegetation of northernChukotka. GY and PA spectra also showed possible analogs tocoastal Wrangel Island. Unlike other Western Beringian sites,additional possible analogs were noted for Alaskan coastal sitesbetween ~60� and 70� N, where vegetation is wet to mesic gra-minoid tundra with low shrubs such as Salix ovalifolia and Empe-trum nigrum (Bliss, 1981).

Reconstructed mean July temperatures for Western Beringia,based primarily on insect data, indicate that in many areas sum-mers were as warm as or slightly warmer than present (Berman


et al., 2011). In the case of the Kankaren area, the inferred Julytemperatures were similar to present, although in the Main Rivercatchment summers may have been ~1.5�e1 �C greater than today.Such temperature reconstructions imply that summers were suf-ficiently warm in southern Chukotka for shrub growth, evenincluding P. pumila. The relative paucity of shrubs, as compared tomodern landscapes, possibly reflects the occurrence of loweffective moisture and/or inadequate snow cover. Such conditionswould be consistent with the limited glacial extent noted for thisregion (Brigham-Grette et al., 2003). Reconstructed July temper-atures for the Anadyr Lowland also approximate modern. How-ever, the drying up of lake basins (as indicated by a pollenstratigraphic hiatus and presence of ped-like structures indicativeof subaerial exposure) during the LGM suggests very dry seasonalor annual conditions and sufficiently cool winters to freeze theupper soil layers (Lozhkin and Anderson, 2013). Estimates of LGMclimates from the Lake El'gygytgyn core indicate colder and drierthan present summers (Lozhkin et al., 2007; Melles et al., 2012). Incontrast, the insect-based reconstruction for this area suggestsJuly temperatures of ~2e4 �C warmer than present. An increase insummer warmth might be expected given the greater con-tinentality of northern Chukotka during the LGM, when loweredsea-levels were at a maximum. Such temperatures would allowfor expansion of shrub taxa in northern Chukotka, if effectivemoisture was sufficient. However, an increase in woody taxa isinconsistent with the herb-dominated pollen spectra.

As Elias and Crocker (2008) commented, reconstructingBeringian paleoenvironments is an exercise similar to that of sci-entists trying to describe an elephant when each person is limitedto examining only a small part of the massive animal. Certainlyinterpreting LGM vegetation in Chukotka is limited by the fewnumbers of sites and the differing spatial resolution of the datatypes. For example, modern pollen studies indicate that LakeEl'gygytgyn provides a regional pollen signal and even though asingle site, can be used reliably to infer paleoclimatic trends in theChukchi Upland (Matrosova, 2006; Lozhkin et al., 2007). Insectdata are sensitive to the other end of the spatial spectrum,reflecting local edaphic and microclimatic conditions. Arguablygiven a dense grid of faunal sites a regional paleoclimatic signalcan be inferred for example, through use of Mutual Climatic Rangeanalyses (e.g., Elias, 2001). Nonetheless, paleobotanical and faunaldata, as sparse as they are, and the computer models indicate thepresence of important latitudinal gradients in Chukotkan vegeta-tion and climate during the LGM. Although only to be consideredas a preliminary evaluation of spatial patterning, these data sug-gest that there was not a single uniform biome that characterizedChukotka during the LGM, whether it was mammoth-steppe orarctic tundra.

7.1.2. Ledovyi Obryv, evidence for moist conditions in southernChukotka

The palynological data from the Kankaren sites suggest thatsouthern Chukotka, while remaining colder and drier than present,experienced relatively mesic conditions during the LGM. However,data from the Anadyr Lowland ~200 km to the north indicate afrigid and arid climate. The most detailed paleoenvironmentalinvestigation from southern Chukotka comes from an area lyingbetween the Anadyr Lowland and the Kankaren Range, and theresults are more inline with the Kankaren material. An interdisci-plinary study of the “Ice Bluff” exposure (IB) at Ledovyi Obryv(Fig. 1; Kuzmina et al., 2011), ~300 km to the northwest of GY andPA, coupled with an earlier palynological and geomorphologicalstudy of the “northern” and “southern” exposures (LON and LOS,respectively; Kotov and Ryabchun, 1986; Lozhkin et al., 2000;Anderson et al., 2002) examined paleobotanical, insect, and

sedimentological data from a 1þ-km-long exposure (varying be-tween 25 and 62 m elevation) along the west bank of the MainRiver (Fig. 1). The Late Pleistocene landscape history of LO is com-plex, indicating the presence of an ancient stream channel andfloodplain some time >42,000 14C BP. With the build up of alluviumand subsequent ice-wedge formation, geomorphological processesduring the LGM were dominated by the creation and drainage ofthermokarst lakes and the development of yedoma relief. Thishistory would suggest that relativelymesic settings were present atleast in this portion of the valley.

Although sediments preserved in exposures represent differentpollen-depositional environments as compared to the stable basinsof PA and GY, the LGM pollen spectra from LON, which contains thebetter-dated LGM record as compared to LOS, are high in Cyper-aceae (>30%) and Poaceae (10e55%), and low in Artemisia (<10%).Bryales spores (up to 80%) are exceptionally high for an LGMassemblage from Western Beringia. Bryales, like graminoids,represent a wide ecological spectrum. Oswald et al. (2003b) notedthat green moss spores (e.g., Tomentypnum nitens, Aulacomniumturgidu, Messia uliginosa) were characteristic of moist graminoid-prostrate shrub tundra found today in the northern Brooks Range.They used Bryales as one group to statistically distinguish prostrateshrub tundra from dwarf shrub tundra in modern pollen samples.Prostrate shrubs on this Alaskan landscape include Salix arctica,S. reticulata, and Arctostyphylos rubra, and Cyperaceae is repre-sented by non-tussock forming species. This vegetation type isassociated with cryoturbated areas, river terraces, recent glacialdeposits, and moderately drained soils. Such a suite of landformswould support a mosaic of dry to relativelymesic surfaces. The low-shrub growth forms associated with this vegetation type isconsistent with the paleovegetation reconstructions in the modelsimulations for southern Chukotka.

Analysis of insect fauna from IB, dated between~24,000e15,000 14C/~29,000e18,500 cal yr BP, indicates a domi-nance of taxa consistent with cold, moist conditions (Kuzminaet al., 2011). Although containing some steppe-tundra species(e.g., Morychus viridis), the assemblage from Ledovyi Obryv dis-plays a clear mesic tundra component. While not abundant, insecttaxa found in shrub tundra appear consistently during the LGM.Shrub pollen (<15% total shrub pollen) is sufficiently low at LON tobe considered as exotic. However, a single Larix grain stronglysuggests environments sufficient to allow limited tree establish-ment sometime between 22,300 ± 200 (MAG-814;~27,000 cal yr BP) and 19,500 ± 500 14C BP (MAG-815;~23,300 cal yr BP), conditions that would also allow for the growthof shrubs. A 14,050 ± 180 14C BP (MAG-1026; ~16,700 cal yr BP)date on unidentified wood provides further support for the pres-ence of woody taxa late in the LGM.

Kuzmina et al. (2011) suggested that the Ledovyi Obryv insectfauna represent a different variant of steppe-tundra assemblages,one having stronger mesic and tundra components, as compared tosites further west and north. They concluded that the vegetation,while having a mosaic character, was likely closer (although notanalogous) to modern mesic tundra than to more xerophyticsteppe-tundra. Berman et al. (2011) also made a distinction be-tween insects indicative of thermophilous steppe dominating as-semblages to the north of the Anadyr Lowlands and those to thesouth that suggest more moderate conditions.

The LO data are in accord with inferences from the Kankarenlakes suggesting relatively mesic conditions in valleys of southernChukotka. In contrast, the Anadyr Lowlands seemed to experienceextremely cold and arid conditions based on the hiatus in thepalynological records. The Chukchi Upland, as represented by LakeEl’gygytgyn, also experienced conditions that were colder and drierthan present. Insect data further suggest a latitudinal and


longitudinal climatic gradient in eastern Chukotka, with the mostmesic conditions likely occurring to the south (Berman et al., 2001;Alfimov and Berman, 2001). Some of this variability can beaccounted for by landscape-level processes and spatial resolutionof the different data types (e.g., river valley vs. upland; insect mi-crohabitats vs. regional pollen signal). However, the regional vari-ability currently documented in Chukotka is particularly strikinggiven the paucity of LGM data. For example, the LGM pollen as-semblages in other areas of Western Beringia represent a moresimilar regional paleovegetation as compared to Chukotka(Anderson and Lozhkin, 2002).

7.1.3. Moisture filter and vegetation gradients, the westwardextension of a Central Beringia migration barrier

Researchers based on various types of biotic data have suggestedthat conditions in Central Beringia differed sufficiently from otherregions of Beringia, resulting in the Bering land bridge acting as a“filter” or “barrier” that limited migration between the continents(Guthrie, 2001; Yurtsev, 2001; Elias and Crocker, 2008). Although anumber of factors might account for regional variability, differencesin effective moisture and the more common presence of mesicsettings are proposed as playing a/the major role in differentiatingCentral Beringia from the remainder of the subcontinent. Elias et al.(1996, 1997) based on pollen, plant macrofossil, and insect datahave provided the most detailed description of areas on the now-submerged Bering land bridge indicating the presence of shrubBetula-graminoid tundra with no evidence of steppe-tundra vege-tation. Kuzmina et al. (2011) and Berman et al. (2011) have pro-posed that the relatively mesic nature postulated for the landbridge also characterized some or all of Chukotka, shifting thismigrational barrier westward.

Chukotka may indeed represent the westward extension of amigrational barrier as proposed by Kuzmina et al. (2011), but wesuggest that this barrier may not relate only to variations inmoisture. As regarding differences in insect fauna between Easternand Western Beringia, Sher (1974) advocated that greater habitatdiversity on the land bridge may have resulted in ecological nichesthat were occupied by indigenous species thereby limiting faunalexchanges between continents. The topographic complexity ofChukotka certainly played a part in the establishment of regionalvegetation gradients and in providing a diversity of local habitats.Chukotka's role as an environmental filter may also relate to vari-ations in annual net primary productivity (aNNP). Model-basedestimates of LGM aNNP for northern Eurasia and Alaska showthat within Western Beringia: 1) the Kolyma drainage has thegreatest aNNP; 2) an area of low aNNP is associated with theKolyma Upland; and 3) eastern Chukotka has variable aNNP withgreater productivity in areas of lower elevations (Allen et al., 2010).Although effective moisture is related to topography and influencesaNNP, the inclusion of eastern Chukotka as an extension of the landbridge “barrier” may relate as much to the spatial variability in itspaleoenvironments, both locally and regionally, as to larger atmo-spheric circulation forcings.

7.2. The Late Glaciation to the middle Holocene (~12,500e8000 14C/~14,700e9000 cal yr BP)

This dynamic interval documents the reorganization of Berin-gian vegetation communities in response to postglacial climaticshifts related to variations in seasonal insolation, rising sea levels,melting glaciers, and warming sea-surface temperatures (Bartleinet al., 1991, 1998). In Western Beringia, the changes in plant com-munities reflect an initial dominance of shrub Betula, replacing theherb-Salix tundra of the LGM, followed by the spread of shrubAlnus and eventually the establishment of conifers through all but

the northernmost regions (Anderson and Lozhkin, 2002). Inaddition to tracing the spatial and temporal patterns of thisvegetation history and the implications for the presence/absenceof full-glacial refugia for woody taxa, we also examine below thenature of Chukotkan vegetation during the postglacial thermalmaximum (PGTM).

7.2.1. Postglacial vegetation of Chukotka, implications for crypticrefugia

As mentioned in Section 6, the vegetation history of Chukotkamust be considered as preliminary because of the paucity of sitesand issues of chronology. However, the available palynologicaldata support previous conclusions about postglacial Beringia; i.e.,that species responded individualistically to climatic change andthat modern plant communities did not survive intact in LGMrefugia to expand with climatic amelioration (Ritchie, 1987;Anderson and Brubaker, 1994). As regards the location andimportance of glacial refugia, scientists, initially working withgenetic markers, began re-evaluating the meaning of such localesin the development of modern plant associations (e.g., Tremblayand Schoen, 1999; Hewitt, 2000). Building on this research, pa-leobotanists suggested the survival of boreal and more temporalplant species in a number of cryptic refugia in Europe (e.g., Williset al., 2000; Stewart and Lister, 2001). Later Brubaker et al. (2005),analyzing mapped pollen data from Beringia, concluded that smallpopulations of woody species also survived the LGM in crypticrefugia. They further concluded that “boreal trees and shrub spe-cies can survive long periods (>10,000 years) of adverse climate assmall populations” and that the paleoenvironmental “heteroge-neity [in Beringia] may have allowed the patchy persistence oftrees and shrubs” (Brubaker et al., 2005, p. 843). Their analysis ofWestern Beringian material relied mostly on sites located to thewest of Chukotka. The more recently available records from Chu-kotka support the conclusions of Brubaker et al., but the new dataalso improve on the understanding of postglacial expansion ofshrub populations (Table 4).

The PA pollen diagram confirms the conclusion based on thepoorer dated GY record, indicating that southern Chukotka wasone of several refugia for Betula. However, the PA data mark theshrub's expansion as early as 15,800 14C/19,000 cal yr BP andcertainly by 14,000 14C/16,700 cal yr BP. Small populations likelyestablished at Ledovyi Obryv by ~14,000 14C/~16,700 cal yr BP(date from woody material) as suggested by low (~10%) butconsistent pollen presence (Anderson et al., 2002). Because of anunconformity in the Anadyr Lowland cores, the timing of shrubBetula establishment is not precise (Lozhkin and Anderson, 2013).However, shrub tundra was certainly present in the Lowland by~11,600 14C/~13,400 cal yr BP (date from charcoal and woodymacrofossil) and possibly as early as ~12,300 14C/~14,200 cal yr BP(humic acid) to 13,200 14C/15,600 cal yr BP (AMS date of bulksediment). Moving northward to Lake El'gygytgyn, Betula pollenpercentages increase ~12,800 14C/~15,100 cal yr BP (based on AMSdates of bulk sediment), but PAR do not rise until ~9900 14C/~11,300 cal yr BP (Lozhkin et al., 2007). Pollen data from perma-frost cores located near El'gygytgyn indicate that Betula estab-lished in the crater prior to 11,800 14C/13,700 cal yr BP, with theshrub decreasing during Younger Dryas times (Andreev et al.,2012). The subsequent pollen percentage increase in the perma-frost cores at ~10,000 14C/~11,400 cal yr BP parallels the increase inPAR in the Lake El'gygytgyn record. Shrub Betula is absent today onWrangel Island, but macrofossils document the presence of Betulasect. Nana in the Academy Tundra ~10,000e9200 14C/~11,400e10,300 cal yr BP and B. exilis in the central mountainvalleys ~11,000e10,000 14C/~12,900e11,400 cal yr BP (Lozhkinet al., 2011a). Palynological data suggest that the shrubs were


restricted to scattered thickets in favorable microhabitats ratherthan forming extensive shrub Betula tundra as inferred for themore southerly sites. Additional records are available fromnortheastern Chukotka (Fig. 1), but the age control is weak. How-ever, these data indicate that Betula-Ericales tundra was presentnear Kresta Gulf (Fig. 1) by at least 8100 14C/9000 cal yr BP and onthe eastern shores of Chukchi Peninsula no later than 8800 14C/9800 cal yr BP (Anderson et al., 2002).

The ~3000 14C yr difference in the timing of Betula establish-ment between southern and northern Chukotka may partiallyreflect issues with the dating control in the Kankaren sites. How-ever, an early rise in Betula pollen at ~15,000 14C/~18,500 cal yr BPwas also noted at Zagoskin Lake in Alaska (Fig. 1, note: this age isbased on a bulk sediment date which may be in error), and Ager(2003) proposed a rapid spread of shrub Betula tundra across theland bridge between ~15,000e13,000 14C/~18,500e15,300 cal yr BP.Elias et al. (1996) based on plant and insect remains, pollen, andAMS dates on peats proposed that shrub Betula-Ericales-graminoidtundra was common on the land bridge as early as 14,000 14C/16,700 cal yr BP. Thus, an early age for the presence of Betula shrubtundra in southern Chukotka is not unreasonable.

The spatial-temporal trends for Betula in Chukotka suggestsome latitudinal variation with the shrub's early expansion in thesouth and latest to the north (Table 4). We are not suggesting asouth-to-north migrational pattern for Betula. For example, thesimilar ages in central and northern Chukotka would suggest theprevious presence of small populations of Betula in these areas andsupport the proposed patchy distribution of the shrubs during theLGM (Brubaker et al., 2005). While the full-glacial history of theshrub is likely controlled by the landscape heterogeneity, its post-glacial history reflects atmospheric driven changes that resulted inthe establishment of latitudinal climatic gradients in Chukotka.

The earliest expansion of shrub Alnus in Chukotka is docu-mented in the Kankaren region at ~12,000 14C/~13,800 cal yr BP.Although increased numbers of the shrubmay have been present atLedovyi Obryv as early as 14,000 14C/16,700 cal yr BP, Alnus waslikely not common until ~9300 14C/~10,500 cal yr BP. Data from theAnadyr Lowland suggest expansion between 8400e7400 14C/9500e8200 cal yr BP. Alnus pollen percentages in the Lake El'gy-gytgyn record increase ~10,700 14C/~12,800 cal yr BP, but PAR donot rise until ~9900 14C/~11,300 cal yr BP. The permafrost coresindicate the shrub's presence in the El'gygytgyn catchment by~11,800 14C/~13,700 cal yr BP, showing a similar decline as Betuladuring the Younger Dryas. Alnus has been absent onWrangel Islandthroughout the Late Glaciation and Holocene. In contrast to theBetula pattern, shrub Alnus apparently first expanded in northernand southern Chukotka with a relatively late arrival in the AnadyrLowland of central Chukotka.

The mapped pollen data indicate that Alnus expanded earlier inWestern (~12,000 14C/~13,800 cal yr BP) as compared to EasternBeringia (~8000 14C BP; Brubaker et al., 2005). Unlike shrub Betula,which expanded frommultiple locales, the earliest spread of shrubAlnus inWestern Beringiawas restricted to the Kankaren and UpperKolyma/Priokhot'ye (northern coast of Okhotsk Sea) regions. It isunclear why Alnus flourished in these areas and not others,although it may relate to the proximity of modern and LGM sea-levels that perhaps provided more favorable seasonal tempera-tures and precipitation. The relatively late arrival of shrub Alnus inthe Anadyr Lowland (~8400e7400 14C/~9500-8200 cal yr BP) ispuzzling as the shrub is abundant there today, especially along riverbanks. The presence of meadows with shrub Betula thickets, anunusual vegetation type for Late Glacialeearly Holocene WesternBeringia, may have restricted the spread of Alnus into the Lowlandpossibly due to nutrient-poor soils and/or low effective moisture(Moskalyuk, 2008).

In contrast to the deciduous shrubs, the earliest increase in P.pumila appears to occur in northern Chukotka at ~9600 14C/~11,100 cal yr BP, whereas the evergreen does not establish insouthern Chukotka until ~7600e6500 14C/~8400e7400 cal yr BP(Table 4). P. pumila has no postglacial presence on Wrangel Island.

Brubaker et al. (2005) noted that the evergreen shrub probablysurvived inWestern Beringia during the LGM. Subsequent work hasshown a well defined refugium in the mountain valleys of Prio-khot'ye (Pinus percentages up to 40% in contrast to other sites withup to 5%; Anderson et al., 2010). This population decreased duringthe late glaciation, probably due to winter dry conditions. Pollenrecords from Western Beringia indicate a rapid and widespreadpresence of P. pumila ~8000e7600 14C/~9000e8400 cal yr BP(Anderson et al., 2014). This age is similar to that from the Kankarenregion and the Anadyr Lowland. The rapid and nearly synchronouschange of the Western Beringian vegetation is puzzling, because P.pumila colonization, relying on vegetative reproduction and birddispersal of seeds, is thought to be relatively slow. Additionally thepollen records from Priokhot’ye suggest that Lateglacial conditionswere not particularly favorable for P. pumila and likely caused de-clines in refugial populations.

Another curious element in the history of P. pumila is the sur-prisingly early age (~9600 14C/~11,100 cal yr BP) for the shrub'spresence in the Chukchi Upland. Modern pollen samples demon-strate that P. pumila is not as over represented as other Pinus taxa(likely due to its large size; Lozhkin et al., 2001). Furthermore in thecase of the large-diameter Lake El'gygytgyn, the pollen catchmentappears to be from the surrounding Upland, and it is unlikely thecore is overly influenced by long distance pollen rain from suchareas as Eastern Siberia (Matrosova, 2006; Lozhkin et al., 2007).Additionally, there is the question of the source of the Pinus pollen.Evidence exists for the survival of Larix, which shares similarsummer temperature requirements as P. pumila, during the LGM inthe northern coastal lowlands of Western Beringia, but pollen datado not suggest that P. pumila was also present (Anderson et al.,2002). However, plant macrofossils from the lower IndigirkaRiver indicate the presence of P. pumila, L. gmelinii, Picea, and treeBetula by ~10,000 14C/~11,400 cal yr BP (Lozhkin et al., 2011a).Although other data exist supporting treed vegetation in coastalareas of Western Beringia (see Section 7.2.2.), no other sites havebeen found with P. pumila macrofossils. However, the paleobotan-ical data are suggestive of a northern source of P. pumila for theEl'gygytgyn area and a separate southern source for the Kankarenregion.

7.2.2. The postglacial thermal maximumGlobal modeling experiments have focused on 6000 cal yr as

being most representative of a warmer than present climatic sce-nario (e.g., Webb, 1998). However, the PGTM is an asynchronousevent, as evidenced in Beringia where the thermal optimumoccurred ~10,000e8000 14C/~11,400e9000 cal yr BP) with modernvegetation communities in place by the mid-Holocene (Kaufmanet al., 2004; Edwards et al., 2005). The Beringian PGTM, whileincluding some latitudinal range extensions, was primarily char-acterized by the widespread establishment of deciduous forest orwoodland (Edwards et al., 2005). In Western Beringia, this biomeincluded Larix and tree-sized deciduous shrubs (primarily Betulaand Alnus), whereas PopuluseSalix communities occupied much ofEastern Beringia. The discussion of the this unusual biome inEdwards et al. focused on Western Beringia as a whole in partbecause some areas like Chukotka were sparsely represented in thedata set. However, a recent summary of plant macrofossil material(Lozhkin et al., 2011a; see also; Andreev et al., 2012) in combinationwith the lacustrine pollen records indicate differences in thevegetation in northern and southern Chukotka during the PGTM.


Unlike in Eastern Beringia where the PGTM is marked by achange in pollen assemblage, evidence for a thermal optimum inWestern Beringia is inferred primarily by plant macrofossils(although Larix pollen records indicate that this deciduous coniferwas not a major landscape component in Chukotka, in contrast toother areas of Western Beringia). The earliest evidence in Chukotkafor the PGTM dates to ~11,300 14C/~13,200 cal yr BP on southernWrangel Island (Lozhkin et al., 2001). Here macrofossils documentthe establishment of shrub Betula, which currently does not growon the island. By 10,000 14C/11,400 cal yr BP, several sites in thenorthern lowlands to the west of Chukotka (e.g., Kolyma Lowland,Fig. 1) indicate the presence of trees (including Larix, Betula, Picea)and/or tree-sized shrubs (including D. fruticosa, Betula) in areas thattoday are wet to mesic tundra with shrubs of low-growth forms(Fig. 3; Lozhkin, 1993; Lozhkin et al., 2011a). Large-size shrubbranches and Larix pollen dated to ~8400 14C/~9500 cal yr BP alsohave been found in the coastal lowland in northern Chukotka(Anderson et al., 2002).

Evidence for the PGTM is not restricted to lowland settings. Larixseeds and needles dated to ~9800 and ~8100 14C BP (~11,200 and~9000 cal yr BP), respectively, indicate the presence of the trees onthe El'gygytgyn terrace, representing a range extension of ~400 km(Shilo et al., 2008; Andreev et al., 2012). Additional macrofossilsfrom the Upland indicate that the PGTM persisted until ~8100 14C/~9000 cal yr BP (Lozhkin et al., 2011a). Palynological data from theEl'gygytgyn permafrost core document the presence of shrubBetulaeAlnus tundra by ~11,000 14C/~12,900 cal yr BP. Analog-basedpaleoclimatic reconstructions from the Lake El'gygytgyn coreindicate conditions that were warmer than present in the ChukchiUpland between ~10,700e8600 14C/~12,800e9500 cal yr BP(Lozhkin et al., 2007). Basal ages show that peat initiation began~11,000 14C/~12,900 cal yr BP in northern sectors of WesternBeringia with a peak between 10,000e8000 14C/~11,400e9000 cal yr BP, a further suggestion of warm, wet condi-tions during the early Holocene (Lozhkin et al., 2011a). The regionalabsence of P. pumila, which shares similar summer temperaturerequirements as Larix (Andreev, 1980), implies that effectivemoisture in northern Chukotkamay have been a limiting factor. Theabsence of P. pumila likely indicates the depth and/or duration ofsnow fall was insufficient to protect the evergreen shrub fromharsh winter conditions. Lateglacialeearly Holocene precipitationlikely was affected by seasonal insolation patterns and sea-icecoverage and thickness with consequent warming of land sur-faces in autumn and winter (Kutzbach and Gallimore, 1988;deVernal et al., 2005).

In contrast to the north, there is no direct macrofossil proof for aPGTM in southern Chukotka, although it is possible that tree-sizeddeciduous shrubs may have been present in the south. Identifyinggrowth form from pollen can be difficult because there is often amorphological continuum from shrub to tree. In the Kankaren re-cords, the sizes of Betula grains suggest they are from shrub forms(i.e., from sections Costata, Nana, and/or Fruticosa), and Alnusgrains indicate the presence of D. fruticosa and not Alnus trees. Thesame is true for the Anadyr Lowland vegetation (meadows withshrub Betula thickets), which is not indicative of warmer thanpresent conditions. The pollen data, thus, do not indicate thepresence of forest/woodland, but they can not eliminate the pos-sibility of tree-sized shrubs.

Dense stands of Populus currently grow near PA and GY, leadingto speculation at the time we cored the lakes that the modernwoodland may represent a remnant and westward extension of thePopulus forest/woodland noted for Eastern Beringia. However, noPopulus pollen, much less a well defined zone, occurred in theKankaren records. Data from the land bridge itself is limited butwhat is available indicates that Populus was not present (see

Lozhkin et al., 2011b). Thus Populus forest/woodland apparentlywas restricted to the eastern fringes of Central Beringia and areas ofEastern Beringia during the PGTM.

8. Conclusions

The following conclusions are considered as a preliminaryguideline for the vegetation history of Chukotka over the past21,000 14C/25,400 cal yr BP.

1. The Kankaren region of southern Chukotka supported a mosaicof vegetation communities during the LGM, although theabundance of Cyperaceae and certain minor pollen taxa maysuggest the predominance of relatively moist herb-dominatedtundra. Shrub Betula tundra established perhaps as early as15,800 14C/19,000 cal yr BP, followed by the expansion of shrubAlnus (D. fruticosa) at ~12,000 14C/~13,800 cal yr BP and P. pumila~7600 14C/~8400 cal yr BP.

2. Palynological data and computer models indicate that a uniformbiome did not characterize Chukotka during the LGM. Lat-itudinal variations in vegetation were associated with relativelymoist, warm conditions (although still drier and cooler thanpresent) in southern Chukotka with more severe climates incentral and northern regions.

3. Southern Chukotka may represent a geographical extension of amoisture filter, which has been proposed as acting as a migra-tional barrier on the Bering land bridge. The topographiccomplexity of Chukotkan environments and variable annual netproductivity during the LGM probably also played roles inlimiting movement of animal and plant species between Asiaand North America.

4. Paleobotanical data from Chukotka support an earlier hypoth-esis that shrub Betula, shrub Alnus, and P. pumila survived incryptic glacial refugia in Western Beringia. Shrub Betula mayhave expanded ~2000e3000 14C years earlier in southernChukotka as compared to central and northern regions (~15,800vs. 13,000 14C/~19,000e15,300 cal yr BP). In contrast, shrubAlnus increased at ~12,000e11,000 14C/~13,800e12,900 cal yr BPin southern and northern Chukotka but only ~8500 14C/~9500 cal yr BP in the Anadyr Lowland. Pollen trends for P.pumila indicate earliest expansion in northern Chukotka~9600 14C/~11,100 cal yr BP, but these evergreen shrubs were notwidespread in southern and central Chukotka until~7600e6500 14C/~8400e7400 cal yr BP. Although not definitive,paleobotanical data suggest expansion of shrub Betula and Alnusfrom sites within Chukotka. In contrast, it seemsmore likely thatthere were separate northern and southern source areas outsideof Chukotka for P. pumila.

5. Paleobotanical data indicate that northern Chukotka experi-enced warmer than present conditions between~11,000e8000 14C/~12,900e9000 cal yr BP. Evidence for a PGTMin southern Chukotka is ambiguous. Although not definitive, thecurrent paleobotanical data suggest north-south differences invegetation characteristics related to a latitudinal gradient insummer temperature with warmest conditions occurring innorthern Chukotka and Wrangel Island during the end of theLate Glaciation into the early Holocene.

Acknowledgments

This work was funded by the U.S. National Science Foundation(ATM-9317569) and the Far East Branch, Russian Academy of Sci-ences (12-III-A-09-198, 12-II-CO-08-024) and the Russian Founda-tion for Fundamental Research (12-05-00286). We appreciate the


help of Ju.A. Korzun in figure preparation. We also appreciate thecomments of an unnamed reviewer.

References

Ager, T.A., 2003. Late Quaternary vegetation and climate history of the centralBering land bridge from St. Michael Island, western Alaska. Quat. Res. 60,19e32.

Alfimov, A.V., Berman, D.I., 2001. Beringian climate during the Late Pleistocene andHolocene. Quat. Sci. Rev. 20, 127e134.

Allen, J.R.M., Hickler, T., Singarayer, J.S., Sykes, M.T., Valdes, P.J., Huntley, B., 2010.Last glacial vegetation of northern Eurasia. Quat. Sci. Rev. 29, 2604e2618.

Anderson, P.M., Brubaker, L.B., 1994. Vegetation history of northcentral Alaska: amapped summary of late-Quaternary pollen data. Quat. Sci. Rev. 13, 71e92.

Anderson, P.M., Lozhkin, A.V., 2002. Palynological and radiocarbon data from lateQuaternary deposits of Northeast Siberia. In: Anderson, P.M., Lozhkin, A.V.(Eds.), Late Quaternary Vegetation and Climate of Siberia and the Russian FarEast: a Palynological and Radiocarbon Database. NOAA Paleoclimatology andNorth East Science Center, Magadan, pp. 27e195.

Anderson, P.M., Bartlein, P.J., Brubaker, L.B., Gajewski, K., Ritchie, J.C., 1989. Modernanalogues of late-Quaternary pollen spectra from the western interior of NorthAmerica. J. Biogeogr. 16, 573e596.

Anderson, P.M., Kotov, A.N., Lozhkin, A.V., Trumpe, M.A., 2002. Palynological andradiocarbon data from late Quaternary deposits of Chukotka. In: Anderson, P.M.,Lozhkin, A.V. (Eds.), Late Quaternary Vegetation and Climate of Siberia and theRussian Far East: a Palynological and Radiocarbon Database. NOAA Paleocli-matology and North East Science Center, Magadan, pp. 35e79.

Anderson, P.M., Lozhkin, A.V., Solomatkina, T.B., Brown, T.A., 2010. Paleoclimaticimplications of glacial and postglacial refugia for Pinus pumila in westernBeringia. Quat. Res. 73, 269e276.

Anderson, P.M., Lozhkin, A.V., Minyuk, P.S., Pakhomov, A.Yu, 2014. Environmentalchanges from glacial lake sediments during the Holocene from the Okhotsk-Kolyma drainage divide. Geol. Pac. Ocean 6, 33, 70e80.

Andreev, A.A., Morozova, E., Federov, G., Schirrmeister, L., Bobrov, A.A., Kienast, F.,Schwamborn, 2012. Vegetation history of central Chukotka deduced frompermafrost paleoenvironmental records of the El'gygytgyn impact crater. Clim.Past 8, 1287e1300.

Andreev, V.N. (Ed.), 1980. Vegetation and Soils of Subarctic Tundra. Siberian Branch,Yakutia Subdivision, Biological Institute, USSR Academy of Sciences, Novosibirsk(in Russian).

Atkin, G.R., McKnight, D.M., Wershaw, R.L., MacCarthy, P. (Eds.), 1985. Humic Sub-stances in Soil, Sediment and Water. John Wiley and Sons, New York.

Barr, I.D., Clark, C.D., 2012. Late Quaternary glaciation in far NE Russia; combiningmoraines, topography and chronology to assess regional and global glaciationsynchrony. Quat. Sci. Rev. 53, 72e87.

Bartlein, P.J., Anderson, P.M., Edwards, M.E., McDowell, P.F., 1991. A framework forinterpreting paleoclimatic variations in eastern Beringia. Quat. Int. 10e12,73e83.

Bartlein, P.J., Anderson, K.H., Anderson, P.M., Edwards, M.E., Mock, C.J.,Thompson, R.S., Webb, R.S., Webb III, T., Whitlock, C., 1998. Paleoclimate sim-ulations for North America over the past 21,000 years: features of the simulatedclimate and comparisons with paleoenvironmental data. Quat. Sci. Rev. 17,549e585.

Berman, D., Alfimov, A., Kuzmina, S., 2011. Invertebrates of the relict steppe eco-systems of Beringia, and the reconstruction of Pleistocene landscapes. Quat. Sci.Rev. 30, 2200e2219.

Bigelow, N.H., Edwards, M.E., 2001. A 14,000 yr paleoenvironmental record fromWindmill Lake, central Alaska: Lateglacial and Holocene vegetation in theAlaska Range. Quat. Sci. Rev. 20, 203e213.

Bigelow, N.H., Brubaker, L.B., Edwards, M.E., Harrison, S.P., Prentice, I.C.,Anderson, P.M., Andreev, A.A., Bartlein, P.J., Christiansen, T.R., Cramer, W.,Kaplan, J.O., Lozhkin, A.V., Matveyeva, N.V., Murray, D.F., McGuire, A.D.,Razzhivin, V.Y., Ritchie, J.C., Smith, B., Walker, D.A., Clayden, S.L., Ebel, T.,Gajewski, K., Hahne, J., Holmqvist, B.H., Igarashi, Y., Jordan, J.W.,Kremenetski, K.V., Melles, M., Oswald, W.W., Paus, A., Pisaric, M.F.J.,Shilova, G.N., Seigert, C., Volkova, V.S., Wolf, V.G., 2003. Climate change andArctic ecosystems: 1. Vegetation changes north of 55� N between the last glacialmaximum, mid-Holocene, and present. J. Geophys. Res. 108 (D19), 1870. Alt11-1-Alt11-25.

Binney, H.A., Willis, K.J., Edwards, M.E., Shonil, S.A., Anderson, P.M., Andreev, A.A.,Blaauw, M., Damblon, F., Haesaerts, P., Kienast, F., Kremenetski, K.V.,Krivonogov, S.K., Lozhkin, A.V., MacDonald, G.M., Novenko, E.Yu, Oksanen, P.,Sapelko, T.V., Valiranto, M., Vazhenina, L.N., 2009. The distribution of late-Quaternary woody taxa in northern Eurasia: evidence from a new macro-fossil database. Quat. Sci. Rev. 28 (23e24), 2445e2464.

Blinnikov, M.S., Gaglioti, B.V., Walker, D.A., Wooler, M.J., Zazula, G.D., 2011. Pleis-tocene graminoid-dominated ecosystems in the Arctic. Quat. Sci. Rev. 30,2906e2929.

Bliss, L.C., 1981. North American and Scandinavian tundras and polar deserts. In:Bliss, L.C., Heal, O.W., Moore, J.J. (Eds.), Tundra Ecosystems: a ComparativeAnalysis. Cambridge University Press, Cambridge, pp. 8e24.

Brigham-Grette, J., Gualtieri, L.M., Glushkova, O.Yu, Hamilton, T.D., Mostoller, D.,Kotov, A., 2003. Chlorine-36 and 14C chronology support a limited last glacial

maximum across central Chukotka, northeastern Siberia, and no Beringian icesheet. Quat. Res. 59, 386e398.

Brubaker, L.B., Anderson, P.M., Edwards, M.E., Lozhkin, A.V., 2005. Beringia as aglacial refugium for boreal trees and shrubs: new perspectives from mappedpollen data. J. Biogeogr. 32, 833e848.

Chekov, A.D., 1998. Structure and Development of Cenozoic Formations of NortheastAsia. North East, Interdisciplinary Research Institute, Russian Academy of Sci-ences, Far East Branch, Magadan (in Russian).

Cwynar, L.C., 1982. A late-Quaternary vegetation history from Hanging Lake,northern Yukon. Ecol. Monogr. 52, 1e24.

Czerepanov, S.Z., 1995. Vascular Plants of Russia and Adjacent States (The FormerUSSR). Cambridge University Press, Cambridge.

de Vernal, A., Hillaire-Marcel, C., Darby, D.A., 2005. Variability of sea ice cover in theChukchi Sea (western Arctic Ocean) during the Holocene. Paleoceanography 20,PA4018. http://dx.doi.org/10.1029/2005PA001157.

Edwards, M.E., Anderson, P., Brubaker, L., Ager, T., Andreev, A., Bigelow, N.,Cwynar, L., Eisner, W., Harrison, S., Hu, F., Jolly, D., Lozhkin, A., MacDonald, G.,Mock, C., Ritchie, Sher, A., Spear, R., Williams, J. Yu, 2000. Pollen-based biomesfor Beringia, 18,000, 6000 and 0 14C yr BP. J. Biogeogr. 27, 521e554. Special IssueBIOME 6000: 18,000, 6000 and 0 14C yr BP.

Edwards, M.E., Brubaker, L.B., Anderson, P.M., Lozhkin, A.V., 2005. Functionallynovel biomes: a response to past warming in Beringia, 86 (7), 1696e1703.

Elias, S.A., 2000. Late Pleistocene climates of Beringia, based on fossil beetle anal-ysis. Quat. Res. 53, 229e235.

Elias, S.A., 2001. Mutual climatic range reconstructions of seasonal temperaturesbased on Late Pleistocene fossil beetle assemblages in Eastern Beringia. Quat.Sci. Rev. 20, 77e91.

Elias, S.A., Crocker, B., 2008. The Bering Land Bridge: a moisture barrier to thedispersal of steppe-tundra biota? Quat. Sci. Rev. 27e28, 1e11.

Elias, S.A., Short, S.K., Phillips, R.L., 1992. Paleoecology of late-glacial peats from theBering land bridge, Chukchi Sea shelf region, northwestern Alaska. Quat. Res.38, 371e378.

Elias, S.A., Short, S.K., Nelson, C.H., Birks, H.H., 1996. Life and times of the Beringland bridge. Nature 382, 60e63.

Elias, S.A., Short, S.K., Birks, H.H., 1997. Late Wisconsin environments of the BeringLand Bridge. Palaeogeogr. Palaeoclimatol. Palaeoecol. 136, 293e308.

Elias, S.A., Berman, D., Affimov, A., 2000. Late Pleistocene beetle faunas of Beringia:where East meets West. J. Biogeogr. 27, 1349e1364.

England, J.H., Furze, M.F.A., 2008. New evidence from the western Canadian ArcticArchipelago for the resubmergence of Bering Strait. Quat. Res. 70, 60e67.

Grichuk, V.P., 1984. Late Pleistocene vegetation history. In: Velichko, A.A.,Wright Jr., H.E., Barnosky, C.W. (Eds.), Late Quaternary Environments of theSoviet Union. University of Minnesota Press, Minneapolis, pp. 155e178.

Gualtieri, L., Glushkova, O., Brigham-Grette, J., 2000. Evidence for restricted iceextent during the last glacial maximum in the Koryak Mountains of Chukotkafar eastern Russia. Geol. Soc. Am. Bull. 112, 1106e1118.

Guthrie, R.D., 1982. Mammals of the mammoth steppe as paleoenvironmental in-dicators. In: Hopkins, D.M., Matthews Jr., J.V., Schweger, C.E., Young, S.B. (Eds.),Paleoecology of Beringia. Academic Press, New York, pp. 307e326.

Guthrie, R.D., 1990. Frozen Fauna of the Mammoth Steppe. The University of Chi-cago Press, Chicago.

Guthrie, R.D., 2001. Origin and causes of the mammoth steppe: a story of cloudcover, woolly mammal tooth pits, buckles, and inside-out Beringia. Quat. Sci.Rev. 20, 549e574.

Hamilton, T.D., 1994. Late Cenozoic glaciation in Alaska. In: Plafker, G., Berg, H.C.(Eds.), The Geology of North America, G-1. Geological Society of America,Boulder, pp. 813e844.

Heiser, P., Roush, J.J., 2001. Pleistocene glaciations in Chukotka Russia: morainemapping using satellite synthetic aperture radar (SAR) imagery. Quat. Sci. Rev.20, 393e404.

Hewitt, G., 2000. The genetic legacy of the Quaternary ice ages. Nature 405,907e913.

Hopkins, D.M., Matthews Jr., J.V., Schweger, C.E., Young, S.B. (Eds.), 1982. Paleo-ecology of Beringia. Academic Press, New York.

Hu, F.S., Brubaker, L.B., Anderson, P.M., 1993. A 12,000 year record of vegetationchange and soil development from Wien Lake, central Alaska. Can. J. Bot. 71,1133e1142.

Hult�en, E., 1968. Flora of Alaska and Neighboring Territories. Stanford UniversityPress, Stanford.

Kageyama, M., Peyron, O., Pinot, S., Tarasov, P., Guiot, J., Joussaume, S., Ramstein, G.,2001. The last glacial maximum climate over Europe and western Siberia: aPMIP comparison between models and data. Clim. Dyn. 17, 23e43.

Kaplan, J.O., Bigelow, N.H., Prentice, I.C., Harrison, S.P., Bartlein, P.J., Christensen, T.R.,Cramer, W., Mateyeva, N.V., McGuire, A.D., Murray, D.F., Razzhivin, V.Y.,Smith, B., Walker, D.A., Anderson, P.M., Andreev, A.A., Brubaker, L.B.,Edwards, M.E., Lozhkin, A.V., 2003. Climate change and Arctic ecosystems: 2.Modeling, paleodata-model comparisons, and future projections. J. Geophys.Res. 108 (19), 1871. Alt12-1-Alt12-17.

Kaufman, D.S., Ager, T.A., Anderson, N.J., Anderson, P.M., Andrews, J.T., Bartlein, P.J.,Brubaker, L.B., Coats, L.L., Cwynar, L.C., Duvall, M.L., Dyke, A.S., Edwards, M.E.,Eisner, W.R., Gajewski, K., Geirsd�ottir, A., Hu, F.S., Jennings, A.E., Kaplan, M.R.,Kerwin, M.W., Lozhkin, A.V., MacDonald, G.M., Miller, G.H., Mock, C.J.,Oswald, W.W., Otto-Bleisner, B.L., Porinchu, D.F., Rühland, K., Smol, J.P.,Steig, E.J., Wolfe, B.B., 2004. Holocene thermal maximum in the western Arctic(0e180��o W). Quat. Sci. Rev. 23, 529e560.

http://refhub.elsevier.com/S0277-3791(14)00403-X/sref1



















































































































http://dx.doi.org/10.1029/2005PA001157


































































































Keigwin, L.D., Donnelly, Cook, M.S., Driscoll, N.W., Brigham-Grette, J., 2013. Rapidsea-level rise and Holocene climate in the Chukchi Sea. Geology 34, 861e864.

Kind, N.V., 1974. Geochronology of the Late Anthropogene Based on Isotope Data.Nauka Press, Moscow.

Klyukina, N.K., 1960. Source Book of Applied Climatology of Northeast Siberia. MainAdministration Hydrometeorological Services Ministry USSR Kolyma Hydro-meteorological Services, Magadan Hydrometeorological Observatory, Magadan(in Russian).

Kolosova, L.N. (Ed.), 1980. Geographical Atlas, fourth ed. Head Office of Geodesy andCartography under the Council of Ministers of the U.S.S.R., Moscow (in Russian).

Kotov, A.N., Ryabchun, V.K., 1986. Cryological Complex of Late Pleistocene De-posits of Main River Valley, Part 1, Ledovyi Obryv. Northeast InterdisciplinaryResearch Institute, Far East Branch, USSR Academy of Sciences, Magadan (inRussian).

Kozhevnikov, YuP., 1981. Ecology-floristic changes in the middle part of the AnadyrRiver basin. In: Mazurenko, M.T. (Ed.), Biology of Plants and Flora of the Far East.Institute of Biological Problems of the North, Far East Branch, USSR Academy ofSciences, Vladivostok, pp. 65e78 (in Russian).

Kutzbach, J.E., Gallimore, R.G., 1988. Sensitivity of a coupled atmosphere/mixedlayer ocean model to changes in orbital forcing at 9000 BP. J. Geophys. Res. 93(D1), 803e821.

Kuzmina, S.A., Sher, A.V., Edwards, M.E., Haile, J., Yan, E.V., Kotov, A.N., Willerslev, E.,2011. The late Pleistocene environment of the Eastern West Beringia based onthe principal section of the Main River, Chukotka. Quat. Sci. Rev. 30, 2091e2106.

Lozhkin, A.V., 1993. Geochronology of late Quaternary events in northeasternRussia. Radiocarbon 35, 429e433.

Lozhkin, A.V., 2002. Boundaries of Beringia during the Late Pleistocene and Holo-cene. In: Simakov, K.V. (Ed.), Quaternary Paleogeography of Beringia. NorthEast, Interdisciplinary Research Institute, Russian Academy of Sciences, Far EastBranch, Magadan, pp. 4e12 (in Russian).

Lozhkin, A.V., Anderson, P.M., 2013. Late Quaternary records from the AnadyrLowland, central Chukotka (Russia). Quat. Sci. Rev. 68, 1e16.

Lozhkin, A.V., Anderson, P.M., Brubaker, L.B., Kotov, A.N., Kotova, L.N.,Prokhorova, T.P., 1998. The herb pollen zone from sediments of glacial lakes,Chukotka. In: Simakov, K.V. (Ed.), Environmental Changes in Beringia during theQuaternary. North East, Interdisciplinary Research Institute, Russian Academyof Sciences, Far East Branch, Magadan, pp. 96e111 (in Russian).

Lozhkin, A.V., Kotov, A.N., Ryabchune, V.K., 2000. Palynological and radiocarbondata from the Ledovyi Obryv exposure (southeast Chukotka). In: Simakov, K.V.(Ed.), The Quaternary Period of Beringia. North East, Interdisciplinary ResearchInstitute, Russian Academy of Sciences, Far East Branch, Magadan, pp. 118e131(in Russian).

Lozhkin, A.V., Anderson, P.M., Vartanyan, S.L., Brown, T.A., Belaya, B.V., Kotov, A.N.,2001. Late Quaternary paleoenvironments and modern pollen data fromWrangel Island (northern Chukotka). Quat. Sci. Rev. 20, 217e233.

Lozhkin, A.V., Anderson, P.M., Matrosova, T.V., Minyuk, P.S., 2007. The pollen recordfrom El'gygytgyn Lake: implications for vegetation and climate histories ofnorthern Chukotka since the late middle Pleistocene. J. Paleolimnol. 37,135e153.

Lozhkin, A.V., Anderson, P.M., Vazhenina, L.N., 2011a. Younger Dryas and EarlyHolocene peats from northern Far East Russia. Quat. Int. 237, 54e64.

Lozhkin, A.V., Anderson, P.M., Eisner, W.R., Solomatkina, T.B., 2011b. Late glacial andHolocene landscapes of central Beringia. Quat. Res. 76, 383e392.

Matrosova, T.V., 2006. Modern spore-pollen spectra of the Anadyr Plateau (El'gy-gytgyn Lake). In: Chereshenev, I.A. (Ed.), Geology, Geography, and Biodiversityof North-East Russia, Materials of Far-East Regional Conference in Memory ofA.P. Vas’kovskiy, Vesnik. North East, Interdisciplinary Research Institute,Russian Academy of Sciences, Far East Branch, Magadan, pp. 159e162 (inRussian).

Melles, M., Brigham-Grette, J., Minyuk, P.S., Nowaczyk, N.R., Wennrich, V.,DeConto, R.M., Anderson, P.M., Andreev, A.A., Coletti, A., Cook, T.L., Haltia-Hovi, E., Kukkonen, M., Lozhkin, A.V., Ros�en, P., Tarasov, P., Vogel, H., Wagner, B.,2012. 2.8 million years of arctic climate change from Lake El'gygytgyn, NERussia. Science 337, 315e320.

Moskalyuk, T.A., 2008. On adaptation of trees and shrubs in the north of the RussianFar East. Russ. J. Ecol. 39, 73e82.

Oswald, W.W., Anderson, P.M., Brubaker, L.B., Hu, F.S., Engstron, D.R., 2003a. Rep-resentation of tundra vegetation by pollen in lake sediments of northern Alaska.J. Biogeogr. 30, 521e535.

Oswald, W.W., Brubaker, L.B., Hu, F.S., Gavin, D.G., 2003b. Pollen-vegetation cali-bration for tundra communities in the Arctic Foothills, northern Alaska. J. Ecol.91, 1022e1033.

PALE, 1993. Research Protocols for PALE: Paleoclimates of Arctic Lakes and Estuaries.In: PAGES Workshop Report Series 94-1. Bern.

Prentice, I.C., Cramer, C., Harrison, S.P., Leemans, R., Monserud, R.A., Solomon, A.M.,1992. A global biome model based on plant physiology and dominance, soilproperties and climate. J. Biogeogr. 19, 117e134.

Prentice, I.C., Guiot, J., Huntley, B., Jolly, D., Cheddadi, R., 1996. Reconstructing bi-omes from palaeoecological data: a general method and its application to Eu-ropean pollen data at 0 and 6 ka. Clim. Dyn. 12, 185e196.

Razzhivin, V.Yu, 1994. Snowbed vegetation of far northeastern Asia. J. Veg. Sci. 5,829e842.

Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., BronkRamsey, C., Buck, C.E., Burr, G.S., Edwards, R.L., Friedrich, M., Grootes, P.M.,Guilderson, T.P., Hajdas, I., Heaton, T.J., Hogg, A.G., Hughen, K.A., Kaiser, K.F.,Kromer, B., McCormac, F.G., Manning, S.W., Reimer, R.W., Richards, D.A.,Southon, J.R., Talamo, S., Turney, C.S.M., van der Plicht, J., Weyhenmeyer, C.E.,2009. IntCal09 and marine09 radiocarbon age calibration curves, 0e50,000years cal BP. Radiocarbon 51, 1111e1150.

Ritchie, J.C., 1987. Postglacial Vegetation of Canada. Cambridge University Press,Cambridge.

Ritchie, J.C., Cwynar, L.C., 1982. The late Quaternary vegetation of the north Yukon.In: Hopkins, D.M., Matthews Jr., J.V., Schweger, C.E., Young, S.B. (Eds.), Paleo-ecology of Beringia. Academic Press, New York, pp. 113e126.

Sher, A.V., 1974. Pleistocene mammals and stratigraphy of the Far Northeast USSRand North America. Int. Geol. Rev. 16, 7e10.

Shilo, N.A. (Ed.), 1970. North of the Far East. Nauka, Moscow (in Russian).Shilo, N.A., Lozhkin, A.V., Anderson, P.M., Vazhenina, L.N., Glushkova, O.Yu,

Matrosova, T.V., 2008. New data about the expansion of Larix gmelinii to arcticregions of Beringia during the early Holocene. Dokl. Akad. Nauk. 422, 1e3 (inRussian).

Sochava, V.B., 1956. Dark conifer forests. Plant Cover Soviet Union 1, 132e216 (inRussian).

Stewart, J.R., Lister, A.M., 2001. Cryptic northern refugia and the origins of modernbiota. Trends Ecol. Evol. 16, 608e613.

Tremblay, N.O., Schoen, D.J., 1999. Molecular phytogeography of Dryas integrifolia:glacial refugia and postglacial recolonization. Mol. Ecol. 8, 1187e1198.

Webb III, T. (Ed.), 1998. Late Quaternary Climates: data Synthesis and Model Ex-periments. Quat. Sci. Rev. 17, pp. 6e7.

Willis, K.J., Rudner, E., Sümegi, P., 2000. The full-glacial forests of central andsoutheastern Europe. Quat. Res. 53, 203e213.

Wright Jr., H.E., Mann, D.H., Glaser, P.H., 1984. Piston corers for peat and lake sed-iments. Ecology 65, 657e659.

Yurtsev, B.A., 1982. Relics of xerophyte vegetation of Beringia in northeastern Asia.In: Hopkins, D.M., Matthews Jr., J.V., Schweger, C.E., Young, S.B. (Eds.), Paleo-ecology of Beringia. Academic Press, New York, pp. 157e178.

Yurtsev, B.A., 2001. The Pleistocene “Tundra-Steppe” and the productivity paradox:the landscape approach. Quat. Sci. Rev. 20, 165e174.


























































































































































Documents

Late Quaternary vegetation of Chukotka (Northeast Russia), implications for Glacial and Holocene environments of Beringia