Beringian paleoecology: results from the 1997 workshop

Quaternary Science Reviews 20 (2001) 7}13

Beringian paleoecology: results from the 1997 workshop Scott A. Elias* Institute of Arctic and Alpine Research, University of Colorado 1560, 30th Street, Campus Box 450, Boulder, CO, 80309-0450, USA

Abstract Much progress has been made in the various "elds concerned with Beringian studies since the publication of Paleoecology of Beringia in 1982. The 1997 Beringian Paleoenvironments workshop brought together Russian, Canadian, and American scientists, and the paleoecological and archaeological presentations gave rise to 20 papers. The main points of most of these papers are summarized here, in the context of speci"c research topics, including (1) timing and environments associated with the Old Crow tephra in Eastern Beringia; (2) Last Interglacial environments of Eastern Beringia; (3) interstadial environments from the middle of the Last Glaciation in Beringia; (4) full glacial environments in Beringia; (5) Lateglacial environments in Beringia; (6) early Holocene environments in Beringia; (7) Late Pleistocene archaeology of Siberia; and 8) the timing, adaptations, and possible migration routes of people entering the New World.  2000 Elsevier Science Ltd. All rights reserved.

1. Introduction The "rst book on Beringian paleoenvironments was The Bering Land Bridge, published in 1967 (Hopkins, 1967). The volume entitled Paleoecology of Beringia, published in 1982 broke considerable new ground in this "eld Hopkins et al. (1982). Since then, scientists from North America and Russia have worked steadily on this topic, and the 1997 Beringian Paleoenvironments workshop provided a vehicle for the presentation of the next iteration of Beringian research. Of course David Hopkins is the common link between these two publications. David edited the "rst book, co-edited the second book, and has generally been a driving force in Beringian research for more than 50 years. The 1997 workshop brought together a large group of people who came to honor David and the accomplishments of his career in Beringian research. Especially noteworthy in this most recent workshop was the presence of many Russian scientists, who acknowledge David as the one who began the di$cult process of breaking down the barriers between scientists on both sides of the Cold War who share an interest in Beringia.

* Corresponding author. Tel.: #1-303-492-5158; fax: #1-303-4926388. E-mail address: [email protected] (S.A. Elias).

Our joint "eld of Beringian research has bene"tted greatly from the cessation of that undeclared war. Many scientists now travel back and forth between the US and Russia to visit "eld sites, collaborate on joint research projects, and attend meetings. Attendees at the 1997 workshop presented new contributions on paleoenvironments from prior to the Last Interglacial to the Holocene, as well as contributions on the archaeology of the region (another of David Hopkins' scienti"c passions). East met west in a way that was scarcely possible until a few years ago. The 1997 workshop was a scienti"c success, and the convenors (Julie Brigham-Grette and myself) took that opportunity to launch this volume on Beringian paleoenvironments. The paleoecological and archaeological papers presented at the 1997 workshop gave rise to 20 papers spanning many research themes, ranging from lake levels and paleosols to the botanical composition of steppe}tundra and proposed routes of human migration from the Old World to the New. Some of the featured topics are as follows: (1) Timing and environments associated with the Old Crow tephra in Eastern Beringia (2) Last Interglacial environments of Eastern Beringia (3) Interstadial environments from the middle of the last glaciation in Beringia (4) Full glacial environments in Beringia (5) Lateglacial environments in Beringia

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(6) Early Holocene environments in Beringia (7) The Late Pleistocene archaeology of Siberia (8) The timing, adaptations, and possible migration routes of people entering the New World In this paper, I will summarize the major new "ndings relating to these topics, and synthesize regional reconstructions of paleoenvironments estimated for the various time intervals. 1.1. Timing and environments associated with the Old Crow tephra in Eastern Beringia The Old Crow tephra (OCt) is an ash that probably came from an eruption (or series of eruptions) from an as-yet unidenti"ed volcano in the Alaska Peninsula region. Estimates of the age of this tephra, based on "ssion-track and uranium-series ages, average 140,000$20,000 years. However, the stratigraphic data from sites across Alaska and the Yukon con#ict as to the timing and environmental conditions associated with the deposition of the OCt (Hamilton and BrighamGrette, 1991). Unfortunately, the data presented at the 1997 workshop by PeH weH et al. (1997) and by Muhs et al. (2001) did nothing to change this situation. The timing of this volcanic eruption (or series of eruptions) is critical to Eastern Beringian paleoenvironmental research, because the OCt is a prominent stratigraphic marker, tying together the chronologies of many sites in Alaska and the Yukon Territory. New ages on this tephra will soon be forthcoming, but for the time being, we can only say with certainty that the OCt was deposited sometime between late isotope stage 6 and the last interglaciation (isotope stage 5e). Ideally, paleoecological reconstructions based on fossil beds intimately associated with the OCt could be used to help clarify the age of the ash, but there has never been a general consensus about these reconstructions, and the 1997 workshop only added to the controversy. Muhs et al. (2001) reported on paleoenvironments and vegetation associated with OCt deposits at the Eva Creek site, near Fairbanks. In their reconstruction, the OCt may have fallen during a time of warmer-thanmodern climate, when spruce forest dominated interior Alaska. Their paleoenvironmental reconstruction, which included greater-than-modern annual precipitation, suggests that the OCt could have been deposited at or near the height of the last interglacial period. In contrast to this, Elias (2001) reported that OCt-associated deposits from the Noatak River drainage of northwestern Alaska are indicative of arctic tundra environments, and that the OCt underlies isotope stage 5e deposits in the Noatak stratigraphy. Mean July temperatures inferred from OCt-associated fossil beetle assemblages from the Noatak were 23C colder than present. The Noatak re-

search of Elias et al. (2001) suggests that the OCt fell during a cool period late in isotope stage 6. Forest beds in the Noatak sequence lie well above the tephra in riverbank deposits. McDowell and Edwards (2001) described a stratigraphic sequence from Birch Creek, near Circle, Alaska. At this site, OCt was deposited at least 6 m below sediments indicative of interglacial environments (i.e., sediments containing abundant spruce pollen and macrofossils). Pollen spectra from loess deposits between the OCt and the interglacial forest bed are indicative of cold climatic conditions. The authors o!er three alternative explanations for this stratigraphic sequence, (1) the OCt was deposited during the isotope stage 6/5 transition, and a strongly developed glacial interval occurred early in stage 5; (2) the OCt was deposited during a `non-Milankovitcha warm interval late in stage 6; and (3) the OCt was deposited far earlier, perhaps as far back as isotope stage 7, and the overlying `colda loess was deposited in stage 6, followed by the forest bed, indicative of stage 5 interglacial environments. Alternative 1 is essentially the same as the scenario reconstructed by Elias et al. (2001) from the Nk-26 site on the Noatak River. Both the Birch Creek and the Noatak River fossil records may contradict the results of the Eva Creek study, in which the OCt may associated with full interglacial environments. It is possible that the solution to this problem lies in multiple episodes of OCt ash deposition, emanating from a series of eruptions of the same volcano over a period of perhaps several thousand years. Detailed trace-element analysis of OCt samples may resolve this issue. Until these are done, we are left with more questions than answers. 1.2. Last Interglacial environments of Eastern Beringia Related to the OCt topic is the issue of isotope stage 5e environments in Beringia. Given that the main forest bed from Eva Creek represents the last interglaciation, the fossil record from the Eva Forest Bed is consistent with regional reconstructions of warmer-than-present conditions across Eastern Beringia. Both Elias (2001) and Muhs et al. (2001) agree that summer temperatures must have been warmer than modern during stage 5e. Elias' mutual climatic range (MCR) studies from fossil beetle assemblages estimate that mean July temperatures (TMAX) were about 53C warmer than modern, although estimates from individual sites ranged from 2.3 to 8.33C. There is a general trend in the MCR data from stage 5e in Eastern Beringia: greatest level of summer temperatures in the east (Yukon Territory), and least level of summer warming in the west (near the Bering Land Bridge and the Paci"c Ocean). However, this reconstruction appears to be at odds with the climatic reconstruction of Brigham-Grette and Hopkins (1995), that

S.A. Elias / Quaternary Science Reviews 20 (2001) 7}13

suggested warmer-than-modern climates in western Alaska during stage 5e, based on shifts in sea-ice limits, the lack of permafrost in some coastal regions, and warmer-than-modern ocean currents in the Bering Sea o! Nome. 1.3. Interstadial environments from the middle of the last glaciation in Beringia The interstadial interval during the middle of the last glaciation is generally thought to have lasted from 60,000 to about 26,000 yr BP (all ages in this paper are given in radiocarbon years before present), although it was far from a homogeneous interval in terms of paleoenvironments. According to the MCR estimates based on fossil beetle data (Elias, 2001), the maximum TMAX levels of the interstadial occurred toward the end of this interval, centering around 30,000 yr BP. Anderson and Lozhkin (2001) compared the paleobotanical evidence from Siberia, Alaska, and the Yukon Territory. They found that during the relatively warm intervals of the interstadial, Western Beringia (northeast Siberia) was more extensively forested than was Eastern Beringia. Spruce forests were limited to lowlands of interior Alaska and the Yukon Territory, while larch reached almost modern forest distribution in parts of Siberia. The period of maximum tree-cover occurred between about 35,000 and 33,000 yr BP, but forests were also present in Western Beringia and the Yukon Territory between about 39,000 and 33,000 yr BP. The paleobotanical evidence suggests that the period of maximum warmth occurred throughout Beringia between 35,000 and 33,000 yr BP. 1.4. Full glacial environments in Beringia Climatic conditions in Beringia during the Last Glacial Maximum (LGM) are generally believed to have been cold and dry. Glaciers grew in regional mountain ranges, but only succeeded in covering lowlands south of the Alaska Range. For the most part, lowland regions of Beringia remained ice-free during the LGM, probably because aridity deprived mountain glaciers of the moisture necessary to expand their margins signi"cantly. The only paleotemperature estimates for the LGM that came out of the recent workshop were the MCR estimates for fossil beetle assemblages in Alaska (Elias, 2001) and estimates based on beetle assemblage data from northeastern Siberia (Al"mov and Berman, 2001). The Alaskan fossil beetle assemblages from this interval (20,000}18,000 yr BP) yielded a series of TMAX ranging from 5.53C colder than modern at 20,000 yr BP (Blue"sh Caves, Yukon) to 0.93C warmer than modern at 18,000 yr BP (Bering Land Bridge Park, Seward Peninsula). The Eastern Beringian data also suggest that TMIN levels were also within a few degrees of modern

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levels. Al"mov and Berman (2001) suggest that TMAX in northeastern Siberia was 12}133C during the LGM. These temperatures are essentially the same as modern TMAX in their study region. The authors concluded that the most important di!erence between LGM and recent climates in this region was increased continentality. Other lines of evidence, such as periglacial features that developed during the LGM, indicate that mean annual temperatures dropped signi"cantly during the LGM (Hopkins, 1982). Most paleoclimatologists would agree that on a very broad-scale, Beringia was relatively dry and cold with cooler summers during the LGM. More mesoscale patterns indicate east to west trends in temperature and moisture gradients with colder and drier conditions dominant over eastern Beringia (Carter, 1981; Lozhkin et al., 1993; Anderson and Brubaker, 1994; Hamilton, 1994; Anderson et al., 1997; Brigham-Grette et al., 2001). On the "nest spatial scales, Beringia during the LGM likely existed as a `habitat mosaica controlled by local factors such as topography and drainage (Anderson and Brubaker, 1994; Elias et al., 1997; Schweger, 1997). The discrepancies between geomorphological, palynological, and entomological reconstructions indicate that further research is needed to clarify LGM environments in Beringia. The insect evidence thus points to relatively mild climatic conditions in Beringia during the LGM, compared with far more dramatic cooling of summer and winter temperatures in regions south of the continental ice sheets. What vegetation cover developed in Beringia during the LGM? Most previous paleobotanical studies from this interval have focused on pollen extracted from cores. As Anderson et al. (1994) point out, the interpretation of ancient tundra vegetation based on fossil pollen spectra is inherently di$cult, because of low taxonomic resolution, poor dispersal of minor pollen types, and the wide ecological tolerances of genera or species that dominated the pollen rain. However, Goetcheus and Birks (2001) have been able to describe the LGM vegetation of the northern Seward Peninsula, based on a di!erent approach. They studied ancient land surface macrofossils preserved beneath volcanic ash. Overall, they found that the vegetation was a closed, dry, herb-rich tundra with a continuous moss layer, growing on calcareous soil that was continuously supplied with loess. They interpreted the soils of the Seward Peninsula during the LGM as relatively fertile, being sustained by nutrient renewal from loess deposition and the occurrence of a continuous mat of acrocarpous mosses. There are no exact modern analogues for this vegetation, probably because the full-glacial environment and climate with loess deposition do not occur today. It also remains to be demonstrated that the vegetation preserved in Goetcheus and Birks' site represents the steppe}tundra

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vegetation envisioned by paleobotanists as having dominated many regions of Beringia in the late Pleistocene. The mystery of the nature and ecology of steppe}tundra remains unsolved. Walker et al. (2001) take a di!erent tack in the debate on ancient steppe}tundra, suggesting that moist nonacidic tundra (MNT) growing today on the Alaskan North Slope may have some important similarities with the ancient Beringian steppe}tundra. MNT grows on calcium-rich, "ne-grained soils with relatively high pH. Compared to tussock tundra, MNT soils have 10 times the extractable Ca in the active layer, half the organic layer thickness, and 30% deeper active layers. Compared with tussock tundra, MNT has twice the vascular-plant species richness, greater habitat diversity, and contains plants with fewer antiherbivory chemicals and more nutrients (particularly calcium). These aspects of the nature of MNT may help us gain a better understanding of the ecology of ancient steppe} tundra. Yurtsev (2001) also emphasizes that Beringia had much greater diversity of herbaceous vegetation (grasses, sedges and forbs) in the mosaic of steppe}tundra landscapes. Based on remnants of steppe vegetation in northeast Asia, Yurtsev described some of the principle types of steppe}tundra vegetation that existed in Beringia, as follows: (1) dry watersheds and slopes had cryophytic (cold-adapted) steppes and cryoxerophytic (cold and dry-adapted) herbaceous and prostrate shrub-herbaceous communities, (2) depressions and valleys were occupied by dry steppe-meadows and brackish-water moist meadows, (3) valley meadows and slope pediments were the most productive as pastures for ungulates due to the redistribution of moisture and nutrients within landscapes, and (4) the lowest parts of the Bering Land Bridge were covered with shrub tundra, which served as a barrier for the dispersal of steppe plants and animals. 1.5. Lateglacial environments in Beringia The Late Glacial period (14,000}10,000 yr BP) was an interval of rapid environmental change throughout Beringia. Climatic #uctuations brought about wholesale changes in the distribution of Beringian plants and animals, and may have played the most important role in the regional extinction of many megafaunal mammal species. According to the fossil beetle data from Eastern Beringia (Elias, 2001), TMAX values began rising by about 12,000 yr BP, reaching warmer-than-modern levels by 11,000 yr BP. The pollen evidence (Bigelow and Edwards, 2001; Brubaker et al., 2001; Edwards et al., 2001) indicates that herbaceous tundra vegetation dominated much of Beringia at the end of the last glaciation, giving way to shrub tundra in most regions between 14,000 and 12,000 yr BP. This transition was not synchronous

throughout Beringia, however. It began in northwestern Alaska by 14,000 yr BP, and took place from 13,000 to 12,500 yr BP in Western Beringia. There is evidence of a climatic oscillation during the Younger Dryas chronozone (10,800 to 10,000 yr BP) in Eastern Beringia (Brubaker et al., 2001). Elias (2001) found evidence of a decline in TMAX values during this interval, especially in arctic beetle assemblages. Bigelow and Edwards (2001) noted that there was a reduction in shrub tundra and an increase in herb tundra in central Alaska from 10,500 to 10,200 yr BP. However, Lozhkin et al. (2001) noted that evidence for a Younger Dryas-type climatic event is absent from Wrangel Island, and from most northern and eastern regions of Western Beringia. However, Pisaric et al. (2001) reported a possible Younger Dryas cooling in the lower Lena River basin, based on pollen evidence indicating an increase herbaceous tundra at the expense of shrub tundra. More substantial evidence for a Younger Dryas cooling has been interpreted from pollen records from Kodiak Island (Peteet and Mann, 1994). In the Mackenzie Mountain region, which lay at the easternmost edge of Beringia, Szeicz and MacDonald (2001) found evidence of rapid climatic amelioration by 11,000 yr BP. Populus expanded in these mountains from 11,000 to 9000 yr BP. During this same interval Populus expanded north-central Alaska (Anderson and Brubaker, 1994). Coniferous forest expansion through Eastern Beringia came only in the Holocene, possibly because the only populations of conifers available to colonize Alaska were growing in distant regions of the Yukon during the Late Wisconsin interval. However, orbital parameters in the Northern high latitudes were giving extremes of summer insolation and minimal winter insolation at 11,000 yr BP, so the degree of climatic continentality may have played a role in the slow migration of conifers. Paleohydrological modeling by Edwards et al. (2001) suggests that the late glacial period in eastern interior Alaska was a time of relative aridity, so the combination of extremely cold winters and little e!ective moisture may have been important elements in limiting the expansion of coniferous forests in Eastern Beringia. For whatever reason, spruce forest did not reach the end of its migration route in southwestern Alaska until as late as 4500 yr BP. (Brubaker et al., 2001). 1.6. Early Holocene environments in Beringia The early Holocene was a time of continued climatic amelioration and overall environmental change. When the continental ice sheets retreated at the end of the last glaciation and the Bering Land Bridge #ooded with seawater (11,000 yr BP), Beringia ceased to exist as a coherent biological region. Most of the megafaunal mammals that lived in Beringia became extinct between

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11,000 and 10,000 yr BP. In many parts of the former Beringian region, coniferous forests expanded in the early Holocene. In western Beringia, the "rst major forest expansion began by 11,000 yr BP. This expansion continued throughout much of the early Holocene. For instance, in the lower Lena basin of Siberia, spruce and larch expanded after 8500 yr BP (Pisaric et al., 2001); in the Mackenzie Mountains of Canada, spruce expanded upslope by 8000 yr BP (Szeicz and MacDonald, 2001). Spruce forests were present in central Alaska at the same time (Bigelow and Edwards, 2001). Modeling (Edwards et al., 2001) suggests that climates of interior Alaska were warmer and drier than modern during this interval. 1.7. The late Pleistocene archaeology of Siberia Pitul'ko (2001) summarized the state of archaeological knowledge of the eastern Siberian Arctic. There is a clear distinction between sites in Arctic Siberia and from farther south in Siberia, where numerous sites are located. The ideas on the chronology and the cultural interpretation of northern Siberian sites are based essentially on evidence from southern sites. The number of Arctic sites representing the Late Paleolithic is extremely small and early sites are signi"cantly rare. Thus, there are very few sites associated with the Dyuktai or Sumnagin cultures, and the connection of these sites with the Late Paleolithic is rather questionable. Furthermore, the dating of artifacts relating to the Dyuktai culture is problematic at best. The most reliable evidence suggests that arctic regions of northeastern Siberia were not inhabited by people until the terminal Pleistocene, about 13,000 yr BP. 1.8. The timing, adaptations, and possible migration routes of people entering the New World When and how did people enter the New World? These questions are central to the research of several of the archaeologists contributing to the workshop. New evidence is now coming to light that is forcing a paradigm shift in New World archaeology. The old consensus view of people crossing into the New World via the Bering Land Bridge and then proceeding south along an ice-free corridor in western Canada is being replaced by new ideas. Both Dixon (2001) and Mandryk et al. (2001) argue for a coastal migration pattern in which people traveled by boat from Siberia to Alaska, then farther south. The Paci"c coast route into the New World appears to "t both the geologic and archaeological evidence that has accumulated in recent years. There are two important elements to this argument. First, the Dillehay (1997) discovery of human occupation in southern Chile by

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at least 12,500 yr BP necessitates human migration out of northeast Asia prior to that time (probably 13,000 yr BP or earlier). Second, the opening up of an ice-free corridor between the Laurentide and Cordilleran ice sheets is now believed to have happened only by about 12,400 yr BP (Catto, 1996). The earliest evidence of people living in the proposed ice-free corridor region of Alberta comes from archaeological sites that are younger than 11,000 yr BP (Beaudoin et al., 1996). By that time, people had been established at Monte Verde for more than a millennium. There are other arguments that support water migration over inland migration routes. Even if an ice-free corridor route had been available to early human colonizers in Eastern Beringia, it is highly doubtful that the biological communities in such a recently deglaciated landscape could support hunter}gatherer populations. In contrast to this, the near-shore waters of the North Paci"c were undoubtedly a rich source of food, including marine mammals, "sh, and shell"sh. Marine-adapted peoples could have traveled from the coasts of northeastern Asia to southern South America without having to modify their way of life in any substantial way. Furthermore, geologic evidence o!ered by Mandryk et al. indicates that parts of the British Columbia coast were icefree during the late Wisconsin interval, allowing migrating peoples access to the resources of coastal landscapes. The colonization of interior Eastern Beringia began by 12,000 yr BP, according to evidence from reliably dated sites (Yesner, 2001). Three possibly older cave sites: Blue"sh Caves, Lime Hills Caves, and Trail Creek Caves, have stratigraphic and taphonomic problems that are not easily resolved. As indicated above, the Pleistocene}Holocene transition was a period of rapid environmental change that saw the extinction of many megafaunal mammals in Beringia. These large mammals were the chief prey items of early hunters, so their extinction undoubtedly had an impact on human populations, forcing the development of new hunting strategies and other changes in lifestyle. The climatic changes of the late glacial interval may have forced the extinction of obligate grazers such as mammoth and horse, but it seems to have favored other taxa such as bison and elk, at least until 9,000 yr BP. Faunal data from the Broken Mammoth site in the central Tanana valley demonstrates that people utilized a wide variety of animals for food, including small game, waterfowl, and "sh. We know more about the food habits of the inhabitants of the Broken Mammoth site than we do for most other Beringian sites because Broken Mammoth enjoys exceptional preservation of organic materials. The Broken Mammoth data serves as a reminder of how little we know about these early inhabitants and their lifeways.

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Acknowledgements I thank Pat Anderson, Mary Edwards, and Julie Brigham-Grette for their useful comments on the manuscript, and all of the participants in the Beringian Paleoenvironments Workshop for their excellent contributions and enthusiasm for Beringian research. Financial support for the workshop and for the preparation of this volume was provided by a grant from the US National Science Foundation, OPP-9617429.

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Yesner, D.R., 2001. Human dispersal into interior Alaska: antecedent conditions, mode of colonization, and adaptations. Quaternary Science Reviews 20, 315}327. Yurtsev, B.A., 2001. The Pleistocene `tundra-steppea and the productivity paradox: the landscape approach. Quaternary Science Reviews 20, 165}174.