Beringian Paleoecology: Results from the 1997 Workshop Scott A

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 Our joint "eld of Beringian research has bene"tted greatly from the cessation of that undeclared war. Many The "rst book on Beringian paleoenvironments was scientists now travel back and forth between the US and The Bering Land Bridge, published in 1967 (Hopkins, Russia to visit "eld sites, collaborate on joint research 1967). The volume entitled Paleoecology of Beringia, pub- projects, and attend meetings. Attendees at the 1997 lished in 1982 broke considerable new ground in this "eld workshop presented new contributions on paleoenviron- Hopkins et al. (1982). Since then, scientists from North ments from prior to the Last Interglacial to the Holo- America and Russia have worked steadily on this topic, cene, as well as contributions on the archaeology of the and the 1997 Beringian Paleoenvironments workshop region (another of David Hopkins' scienti"c passions). provided a vehicle for the presentation of the next iter- East met west in a way that was scarcely possible until ation of Beringian research. Of course David Hopkins is a few years ago. The 1997 workshop was a scienti"c the common link between these two publications. David success, and the convenors (Julie Brigham-Grette and edited the "rst book, co-edited the second book, and has myself) took that opportunity to launch this volume on generally been a driving force in Beringian research for Beringian paleoenvironments. more than 50 years. The 1997 workshop brought to- The paleoecological and archaeological papers pre- gether a large group of people who came to honor David sented at the 1997 workshop gave rise to 20 papers and the accomplishments of his career in Beringian re- spanning many research themes, ranging from lake levels search. Especially noteworthy in this most recent work- and paleosols to the botanical composition of shop was the presence of many Russian scientists, who steppe}tundra and proposed routes of human migration acknowledge David as the one who began the di$cult from the Old World to the New. Some of the featured process of breaking down the barriers between scientists topics are as follows: on both sides of the Cold War who share an interest in Beringia. (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 * Corresponding author. Tel.: #1-303-492-5158; fax: #1-303-492- glaciation in Beringia 6388. (4) Full glacial environments in Beringia E-mail address: [email protected] (S.A. Elias). (5) Lateglacial environments in Beringia

(6) Early Holocene environments in Beringia search of Elias et al. (2001) suggests that the OCt fell (7) The Late Pleistocene archaeology of Siberia during a cool period late in isotope stage 6. Forest (8) The timing, adaptations, and possible migration beds in the Noatak sequence lie well above the tephra routes of people entering the New World in riverbank deposits. McDowell and Edwards (2001) described a stratigraphic sequence from Birch Creek, In this paper, I will summarize the major new "ndings near Circle, Alaska. At this site, OCt was deposited relating to these topics, and synthesize regional recon- at least 6 m below sediments indicative of interglacial structions of paleoenvironments estimated for the vari- environments (i.e., sediments containing abundant ous time intervals. spruce pollen and macrofossils). Pollen spectra from loess deposits between the OCt and the interglacial 1.1. Timing and environments associated with the Old forest bed are indicative of cold climatic conditions. Crow tephra in Eastern Beringia The authors o!er three alternative explanations for this stratigraphic sequence, (1) the OCt was deposited The Old Crow tephra (OCt) is an ash that probably during the isotope stage 6/5 transition, and a strongly came from an eruption (or series of eruptions) from an developed glacial interval occurred early in stage 5; as-yet unidenti"ed volcano in the Alaska Peninsula (2) the OCt was deposited during a `non-Milankovitcha region. Estimates of the age of this tephra, based warm interval late in stage 6; and (3) the OCt was on "ssion-track and uranium-series ages, average deposited far earlier, perhaps as far back as isotope 140,000$20,000 years. However, the stratigraphic data stage 7, and the overlying `colda loess was deposited in from sites across Alaska and the Yukon con#ict as stage 6, followed by the forest bed, indicative of stage to the timing and environmental conditions associated 5 interglacial environments. Alternative 1 is essentially with the deposition of the OCt (Hamilton and Brigham- the same as the scenario reconstructed by Elias et al. Grette, 1991). Unfortunately, the data presented at the (2001) from the Nk-26 site on the Noatak River. Both 1997 workshop by PeH weH et al. (1997) and by Muhs the Birch Creek and the Noatak River fossil records et al. (2001) did nothing to change this situation. may contradict the results of the Eva Creek study, in The timing of this volcanic eruption (or series of erup- which the OCt may associated with full interglacial envi- tions) is critical to Eastern Beringian paleoenviron- ronments. mental research, because the OCt is a prominent It is possible that the solution to this problem lies in stratigraphic marker, tying together the chronologies multiple episodes of OCt ash deposition, emanating from of many sites in Alaska and the Yukon Territory. a series of eruptions of the same volcano over a period of New ages on this tephra will soon be forthcoming, perhaps several thousand years. Detailed trace-element but for the time being, we can only say with certainty analysis of OCt samples may resolve this issue. Until that the OCt was deposited sometime between late these are done, we are left with more questions than isotope stage 6 and the last interglaciation (isotope answers. stage 5e). Ideally, paleoecological reconstructions based on fossil beds intimately associated with the OCt 1.2. Last Interglacial environments of Eastern Beringia could be used to help clarify the age of the ash, but there has never been a general consensus about these recon- Related to the OCt topic is the issue of isotope stage 5e structions, and the 1997 workshop only added to the environments in Beringia. Given that the main forest bed controversy. from Eva Creek represents the last interglaciation, the Muhs et al. (2001) reported on paleoenvironments and fossil record from the Eva Forest Bed is consistent with vegetation associated with OCt deposits at the Eva regional reconstructions of warmer-than-present condi- Creek site, near Fairbanks. In their reconstruction, the tions across Eastern Beringia. Both Elias (2001) and OCt may have fallen during a time of warmer-than- Muhs et al. (2001) agree that summer temperatures must modern climate, when spruce forest dominated interior have been warmer than modern during stage 5e. Elias' Alaska. Their paleoenvironmental reconstruction, which mutual climatic range (MCR) studies from fossil beetle included greater-than-modern annual precipitation, sug- assemblages estimate that mean July temperatures gests that the OCt could have been deposited at or near (TMAX) were about 53C warmer than modern, although the height of the last interglacial period. In contrast to estimates from individual sites ranged from 2.3 to 8.33C. this, Elias (2001) reported that OCt-associated deposits There is a general trend in the MCR data from stage 5e from the Noatak River drainage of northwestern Alaska in Eastern Beringia: greatest level of summer temper- are indicative of arctic tundra environments, and that the atures in the east (Yukon Territory), and least level of OCt underlies isotope stage 5e deposits in the Noatak summer warming in the west (near the Bering Land stratigraphy. Mean July temperatures inferred from Bridge and the Paci"c Ocean). However, this recon- OCt-associated fossil beetle assemblages from the struction appears to be at odds with the climatic recon- Noatak were 23C colder than present. The Noatak re- struction of Brigham-Grette and Hopkins (1995), that S.A. Elias / Quaternary Science Reviews 20 (2001) 7}13 9 suggested warmer-than-modern climates in western levels. Al"mov and Berman (2001) suggest that TMAX in Alaska during stage 5e, based on shifts in sea-ice limits, northeastern Siberia was 12}133C during the LGM. the lack of permafrost in some coastal regions, and These temperatures are essentially the same as modern warmer-than-modern ocean currents in the Bering Sea TMAX in their study region. The authors concluded o! Nome. that the most important di!erence between LGM and recent climates in this region was increased continen- 1.3. Interstadial environments from the middle of the last tality. Other lines of evidence, such as periglacial glaciation in Beringia features that developed during the LGM, indicate that mean annual temperatures dropped signi"cantly The interstadial interval during the middle of the last during the LGM (Hopkins, 1982). Most paleoclimatol- glaciation is generally thought to have lasted from 60,000 ogists would agree that on a very broad-scale, Beringia to about 26,000 yr BP (all ages in this paper are given was relatively dry and cold with cooler summers during in radiocarbon years before present), although it was the LGM. More mesoscale patterns indicate east to far from a homogeneous interval in terms of paleo- west trends in temperature and moisture gradients environments. According to the MCR estimates based on with colder and drier conditions dominant over eastern fossil beetle data (Elias, 2001), the maximum TMAX Beringia (Carter, 1981; Lozhkin et al., 1993; Anderson levels of the interstadial occurred toward the end of and Brubaker, 1994; Hamilton, 1994; Anderson et al., this interval, centering around 30,000 yr BP. Anderson 1997; Brigham-Grette et al., 2001). On the "nest spatial and Lozhkin (2001) compared the paleobotanical scales, Beringia during the LGM likely existed as a evidence from Siberia, Alaska, and the Yukon Terri- `habitat mosaica controlled by local factors such tory. They found that during the relatively warm inter- as topography and drainage (Anderson and Brubaker, vals of the interstadial, Western Beringia (northeast 1994; Elias et al., 1997; Schweger, 1997). The discre- Siberia) was more extensively forested than was Eastern pancies between geomorphological, palynological, Beringia. Spruce forests were limited to lowlands of and entomological reconstructions indicate that further interior Alaska and the Yukon Territory, while larch research is needed to clarify LGM environments in reached almost modern forest distribution in parts of Beringia. Siberia. The period of maximum tree-cover occurred The insect evidence thus points to relatively mild cli- between about 35,000 and 33,000 yr BP, but forests were matic conditions in Beringia during the LGM, com- also present in Western Beringia and the Yukon Terri- pared with far more dramatic cooling of summer tory between about 39,000 and 33,000 yr BP. The and winter temperatures in regions south of the conti- paleobotanical evidence suggests that the period of max- nental ice sheets. What vegetation cover developed imum warmth occurred throughout Beringia between in Beringia during the LGM? Most previous paleo- 35,000 and 33,000 yr BP. botanical studies from this interval have focused on pollen extracted from cores. As Anderson et al. (1994) 1.4. Full glacial environments in Beringia point out, the interpretation of ancient tundra vegetation based on fossil pollen spectra is inherently di$cult, be- Climatic conditions in Beringia during the Last Gla- cause of low taxonomic resolution, poor dispersal of cial Maximum (LGM) are generally believed to have minor pollen types, and the wide ecological tolerances been cold and dry. Glaciers grew in regional mountain of genera or species that dominated the pollen ranges, but only succeeded in covering lowlands south of rain. However, Goetcheus and Birks (2001) have been the Alaska Range. For the most part, lowland regions of able to describe the LGM vegetation of the northern Beringia remained ice-free during the LGM, probably Seward Peninsula, based on a di!erent approach. because aridity deprived mountain glaciers of the moist- They studied ancient land surface macrofossils pre- ure necessary to expand their margins signi"cantly. The served beneath volcanic ash. Overall, they found that only paleotemperature estimates for the LGM that came the vegetation was a closed, dry, herb-rich tundra out of the recent workshop were the MCR estimates for with a continuous moss layer, growing on calcareous fossil beetle assemblages in Alaska (Elias, 2001) and esti- soil that was continuously supplied with loess. They mates based on beetle assemblage data from north- interpreted the soils of the Seward Peninsula during the eastern Siberia (Al"mov and Berman, 2001). The Alaskan LGM as relatively fertile, being sustained by nutrient fossil beetle assemblages from this interval renewal from loess deposition and the occurrence (20,000}18,000 yr BP) yielded a series of TMAX ranging of a continuous mat of acrocarpous mosses. There from 5.53C colder than modern at 20,000 yr BP (Blue"sh are no exact modern analogues for this vegetation, prob- Caves, Yukon) to 0.93C warmer than modern at ably because the full-glacial environment and climate 18,000 yr BP (Bering Land Bridge Park, Seward Penin- with loess deposition do not occur today. It also remains sula). The Eastern Beringian data also suggest that to be demonstrated that the vegetation preserved in TMIN levels were also within a few degrees of modern Goetcheus and Birks' site represents the steppe}tundra 10 S.A. Elias / Quaternary Science Reviews 20 (2001) 7}13 vegetation envisioned by paleobotanists as having dom- throughout Beringia, however. It began in northwestern inated many regions of Beringia in the late Pleistocene. Alaska by 14,000 yr BP, and took place from 13,000 to The mystery of the nature and ecology of steppe}tundra 12,500 yr BP in Western Beringia. There is evidence of remains unsolved. a climatic oscillation during the Younger Dryas chrono- Walker et al. (2001) take a di!erent tack in the debate zone (10,800 to 10,000 yr BP) in Eastern Beringia on ancient steppe}tundra, suggesting that moist (Brubaker et al., 2001). Elias (2001) found evidence of nonacidic tundra (MNT) growing today on the Alaskan a decline in TMAX values during this interval, especially North Slope may have some important similarities in arctic beetle assemblages. Bigelow and Edwards (2001) with the ancient Beringian steppe}tundra. MNT noted that there was a reduction in shrub tundra and an grows on calcium-rich, "ne-grained soils with rela- increase in herb tundra in central Alaska from 10,500 to tively high pH. Compared to tussock tundra, MNT 10,200 yr BP. However, Lozhkin et al. (2001) noted that soils have 10 times the extractable Ca in the active layer, evidence for a Younger Dryas-type climatic event is ab- half the organic layer thickness, and 30% deeper active sent from Wrangel Island, and from most northern layers. Compared with tussock tundra, MNT has and eastern regions of Western Beringia. However, twice the vascular-plant species richness, greater habitat Pisaric et al. (2001) reported a possible Younger Dryas diversity, and contains plants with fewer antiherbivory cooling in the lower Lena River basin, based on pollen chemicals and more nutrients (particularly calcium). evidence indicating an increase herbaceous tundra at These aspects of the nature of MNT may help us gain a the expense of shrub tundra. More substantial evidence better understanding of the ecology of ancient steppe} for a Younger Dryas cooling has been interpreted from tundra. pollen records from Kodiak Island (Peteet and Mann, Yurtsev (2001) also emphasizes that Beringia had 1994). much greater diversity of herbaceous vegetation (grasses, In the Mackenzie Mountain region, which lay at the sedges and forbs) in the mosaic of steppe}tundra easternmost edge of Beringia, Szeicz and MacDonald landscapes. Based on remnants of steppe vegetation (2001) found evidence of rapid climatic amelioration in northeast Asia, Yurtsev described some of the prin- by 11,000 yr BP. Populus expanded in these mountains ciple types of steppe}tundra vegetation that existed from 11,000 to 9000 yr BP. During this same interval in Beringia, as follows: (1) dry watersheds and slopes Populus expanded north-central Alaska (Anderson and had cryophytic (cold-adapted) steppes and cryo- Brubaker, 1994). Coniferous forest expansion through xerophytic (cold and dry-adapted) herbaceous and Eastern Beringia came only in the Holocene, possibly prostrate shrub-herbaceous communities, (2) depres- because the only populations of conifers available to sions and valleys were occupied by dry steppe-meadows colonize Alaska were growing in distant regions of the and brackish-water moist meadows, (3) valley meadows Yukon during the Late Wisconsin interval. However, and slope pediments were the most productive as orbital parameters in the Northern high latitudes were pastures for ungulates due to the redistribution of giving extremes of summer insolation and minimal moisture and nutrients within landscapes, and (4) the winter insolation at 11,000 yr BP, so the degree of lowest parts of the Bering Land Bridge were covered with climatic continentality may have played a role in the shrub tundra, which served as a barrier for the dispersal slow migration of conifers. Paleohydrological modeling of steppe plants and animals. by Edwards et al. (2001) suggests that the late glacial period in eastern interior Alaska was a time of relative 1.5. Lateglacial environments in Beringia aridity, so the combination of extremely cold winters and little e!ective moisture may have been impor- The Late Glacial period (14,000}10,000 yr BP) was an tant elements in limiting the expansion of coniferous interval of rapid environmental change throughout Beri- forests in Eastern Beringia. For whatever reason, ngia. Climatic #uctuations brought about wholesale cha- spruce forest did not reach the end of its migration nges in the distribution of Beringian plants and animals, route in southwestern Alaska until as late as 4500 yr BP. and may have played the most important role in the (Brubaker et al., 2001). regional extinction of many megafaunal mammal species. According to the fossil beetle data from Eastern Beringia 1.6. Early Holocene environments in Beringia (Elias, 2001), TMAX values began rising by about 12,000 yr BP, reaching warmer-than-modern levels by The early Holocene was a time of continued climatic 11,000 yr BP. The pollen evidence (Bigelow and Ed- amelioration and overall environmental change. When wards, 2001; Brubaker et al., 2001; Edwards et al., 2001) the continental ice sheets retreated at the end of the last indicates that herbaceous tundra vegetation dominated glaciation and the Bering Land Bridge #ooded with much of Beringia at the end of the last glaciation, giving seawater (11,000 yr BP), Beringia ceased to exist as a co- way to shrub tundra in most regions between 14,000 and herent biological region. Most of the megafaunal mam- 12,000 yr BP. This transition was not synchronous mals that lived in Beringia became extinct between S.A. Elias / Quaternary Science Reviews 20 (2001) 7}13 11

11,000 and 10,000 yr BP. In many parts of the former at least 12,500 yr BP necessitates human migration Beringian region, coniferous forests expanded in the early out of northeast Asia prior to that time (probably Holocene. In western Beringia, the "rst major forest 13,000 yr BP or earlier). Second, the opening up of an expansion began by 11,000 yr BP. This expansion con- ice-free corridor between the Laurentide and Cordilleran tinued throughout much of the early Holocene. For in- ice sheets is now believed to have happened only by stance, in the lower Lena basin of Siberia, spruce and about 12,400 yr BP (Catto, 1996). The earliest evidence of larch expanded after 8500 yr BP (Pisaric et al., 2001); in people living in the proposed ice-free corridor region of the Mackenzie Mountains of Canada, spruce expanded Alberta comes from archaeological sites that are younger upslope by 8000 yr BP (Szeicz and MacDonald, 2001). than 11,000 yr BP (Beaudoin et al., 1996). By that time, Spruce forests were present in central Alaska at the people had been established at Monte Verde for more same time (Bigelow and Edwards, 2001). Modeling (Ed- than a millennium. wards et al., 2001) suggests that climates of interior There are other arguments that support water migra- Alaska were warmer and drier than modern during this tion over inland migration routes. Even if an ice-free interval. corridor route had been available to early human colonizers in Eastern Beringia, it is highly doubtful that the biological communities in such a recently de- 1.7. The late Pleistocene archaeology of Siberia glaciated landscape could support hunter}gatherer populations. In contrast to this, the near-shore waters Pitul'ko (2001) summarized the state of archaeological of the North Paci"c were undoubtedly a rich source knowledge of the eastern Siberian Arctic. There is a clear of food, including marine mammals, "sh, and shell- distinction between sites in Arctic Siberia and from "sh. Marine-adapted peoples could have traveled farther south in Siberia, where numerous sites are from the coasts of northeastern Asia to southern located. The ideas on the chronology and the cultural South America without having to modify their way interpretation of northern Siberian sites are based essen- of life in any substantial way. Furthermore, geo- tially on evidence from southern sites. The number of logic evidence o!ered by Mandryk et al. indicates Arctic sites representing the Late Paleolithic is extremely that parts of the British Columbia coast were ice- small and early sites are signi"cantly rare. Thus, there are free during the late Wisconsin interval, allowing mi- very few sites associated with the Dyuktai or Sumnagin grating peoples access to the resources of coastal land- cultures, and the connection of these sites with the Late scapes. Paleolithic is rather questionable. Furthermore, the dat- The colonization of interior Eastern Beringia began ing of artifacts relating to the Dyuktai culture is proble- by 12,000 yr BP, according to evidence from reliably matic at best. The most reliable evidence suggests that dated sites (Yesner, 2001). Three possibly older cave arctic regions of northeastern Siberia were not in- sites: Blue"sh Caves, Lime Hills Caves, and Trail habited by people until the terminal Pleistocene, about Creek Caves, have stratigraphic and taphonomic prob- 13,000 yr BP. lems that are not easily resolved. As indicated above, the Pleistocene}Holocene transition was a period 1.8. The timing, adaptations, and possible migration routes of rapid environmental change that saw the extinction of people entering the New World of many megafaunal mammals in Beringia. These large mammals were the chief prey items of early hunters, When and how did people enter the New World? so their extinction undoubtedly had an impact on These questions are central to the research of several human populations, forcing the development of new of the archaeologists contributing to the workshop. hunting strategies and other changes in lifestyle. The New evidence is now coming to light that is forcing climatic changes of the late glacial interval may have a paradigm shift in New World archaeology. The forced the extinction of obligate grazers such as mam- old consensus view of people crossing into the New moth and horse, but it seems to have favored other World via the Bering Land Bridge and then proceed- taxa such as bison and elk, at least until 9,000 yr BP. ing south along an ice-free corridor in western Canada Faunal data from the Broken Mammoth site in the is being replaced by new ideas. Both Dixon (2001) central Tanana valley demonstrates that people utilized and Mandryk et al. (2001) argue for a coastal migra- a wide variety of animals for food, including small tion pattern in which people traveled by boat from game, waterfowl, and "sh. We know more about the Siberia to Alaska, then farther south. The Paci"c food habits of the inhabitants of the Broken Mammoth coast route into the New World appears to "t both site than we do for most other Beringian sites because the geologic and archaeological evidence that has Broken Mammoth enjoys exceptional preservation accumulated in recent years. There are two important of organic materials. The Broken Mammoth data elements to this argument. First, the Dillehay (1997) serves as a reminder of how little we know about discovery of human occupation in southern Chile by these early inhabitants and their lifeways. 12 S.A. Elias / Quaternary Science Reviews 20 (2001) 7}13

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