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

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<ul><li><p>lable at ScienceDirect</p><p>Quaternary Science Reviews 107 (2015) 112e128Contents lists avaiQuaternary Science Reviews</p><p>journal homepage: www.elsevier .com/locate/quascirevLate Quaternary vegetation of Chukotka (Northeast Russia),implications for Glacial and Holocene environments of Beringia</p><p>Patricia M. Anderson a, *, Anatoly V. Lozhkin b</p><p>a Earth &amp; 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, Russiaa r t i c l e i n f o</p><p>Article history:Received 11 July 2014Received in revised form16 October 2014Accepted 16 October 2014Available online</p><p>Keywords:BeringiaChukotkaPostglacial thermal maximumVegetation historyPollenPlant macrofossils* Corresponding author.E-mail address: (P.M. And</p><p> 2014 Elsevier Ltd. All rights reserved.a b s t r a c t</p><p>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.</p><p> 2014 Elsevier Ltd. All rights reserved.1. Introduction</p><p>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 thanerson).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).</p><p>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,</p><p>Delta:1_given nameDelta:1_surnamemailto:pata@u.washington.edu;</p></li><li><p>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><p>P.M. Anderson, A.V. Lozhkin / Quaternary Science Reviews 107 (2015) 112e128 113warming 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.</p><p>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 recordsencompass 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).</p><p>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></li><li><p>P.M. Anderson, A.V. Lozhkin / Quaternary Science Reviews 107 (2015) 112e128114from 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 betterFig. 2. Map of study area showing the locations of Gytgykai and Patricia lakes. Theevaluate 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 key is 1) Anadyr Lowland; 2) lake; and 3) elevation (m above sea level).</p></li><li><p>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.</p><p>P.M. Anderson, A.V. Lozhkin / Quaternary Science Reviews 107 (2015) 112e128 1152. Geographic setting</p><p>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.</p><p>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 prostrateforest (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.</p><p>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.</p><p>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.</p><p>3. Study sites</p><p>Patricia (PA; informal name; 63 190 3000 N,176 300 E; 121 m asl)and Gyt...</p></li></ul>