Late quaternary vegetational change in the Kotzebue sound area, northwestern Alaska

Two sediment cores from Kaiyak and Squirrel lakes in northwestern Alaska yielded pollen records that date to ca. 39,000 and 27,000 yr B.P., respectively. Between 39,000 and 14,000 yr B.P., the vegetation around these lakes was dominated by Gramineae and Cyperaceae with some Salix and possibly Betula nana/glandulosa forming a local, shrub component of the vegetation. Betula pollen percentages increased about 14,000 yr B.P., indicating the presence of a birchdominated shrub tundra. Alnus pollen appeared at both sites between 9000 and 8000yr B.P., and Picea pollen (mostly P. mariana) arrived at Squirrel Lake about 5000 yr B.P. The current foresttundra mosaic around Squirrel Lake was established at this time, whereas shrub tundra existed near Kaiyak Lake throughout the Holocene. When compared to other pollen records from north-western North America, these cores (1) represent a meadow component of lowland. Beringian tundra between 39,000 and 14,000 yr B.P., (2) demonstrate an early Holocene arrival of Alnus in northwestern Alaska that predates most other Alnus horizons in northern Alaska or northwestern Canada, and (3) show an east-to-west migration of Picea across northern Alaska from 9000 to 5000 yr B.P.     

Peopling of the Americas

Study of the prehistory of an Americas has proceeded through successive cycles, in which archaeologists have assumed or postulated hypotheses of migration and development, have searched for evidence with which to test these hypotheses, and have abandoned them when the evidence proved to be contradictory. We are completing the current cycle and must seek new hypotheses that better fit our present evidence.The available data are reviewed to show the inaccuracy of the current hypotheses and to develop new ones. It is suggested that the first Indians arrived during a Lower Lithic age, marked by the manufacture of irregular flakes, trimmed only on their edges. This age may have started as early as 30,000 BP.South of the Laurentide ice sheet, the Lower Lithic age began to give way about 14,000 BP to a Middle Lithic Age. This was marked by a variety of types of bifacially chipped projectile points which seem to have developed locally: Folsomoid points in Anglo-America, Joboid points in the Circum-Caribbean region, and Magelloid points in western and southern South America.North of the ice sheet, the place of the Middle Lithic age was taken by an Upper Lithic age, marked by microblades of Asiatic origin. These appear to have reached the Bering Strait region about 14,000 BP. The dichotomy between the Middle and Upper Lithic ages lasted until the retreat of the ice ca. 8000 BP.     

A lacustrine record of late Pleistocene climatic change in the subtropical Andes

Significant changes in moisture have occurred in the subtropical Andes over the last 20,000 years as evidenced by shorelines of high lake stands and extensive glacial moraines. Lakes with sediment records that reflect these moisture changes are present in some valleys where headwalls are below the snowline elevation reached during the latest Pleistocene glacial culmination (14,000–12,000 BP). One such lake, Laguna Kollpa Kkota, which is located on the western slope of the eastern cordillera in Bolivia, has basal radiocarbon dates of about 20,000 BP. The snowline reconstruction for this site confirms earlier work in the region that suggests late Pleistocene snowline depression was less than 500 m, or half the amount generally considered for low-latitude regions during the last glacial maximum. The sediment stratigraphy from Laguna Kollpa Kkota indicates that sediment accumulation and organic carbon deposition increased significantly from 14,000 to 12,600 BP. This increase in sedimentation may have resulted from greater inwash to the lake and higher productivity In the lake itself as a result of higher lake levels. These changes could reflect the postulated late Pleistocene increase in precipitation that led to the formation of Lago Tauca on the Altiplano and to glacial advances in the surrounding cordillera.     

Timing and pattern of the last deglaciation in the Kattegat region, southwest Scandinavia

This paper presents evidence on the timing and pattern of the Late Weichselian deglaciation in SW Scandinavia, particularly in the Öresund–Kattegat region before the Allerød interstadial. New radiocarbon ages and evaluated older dates demonstrate that active glacier ice had left eastern Denmark, southern Halland and western Skåne before 14,000 BP. The deglaciation in the Öresund region took place mainly under glacioestuarine conditions in a narrow fjord or inlet with some marine influence, as indicated by radiocarbon-dated finds of Polar Cod ( Boreogadus saida ) and the vertebra of a Ringed Seal ( Phoca hispida ). The Swedish west coast experienced glaciomarine and deltaic ice proximal conditions, where Vendsyssel was at the same time under full marine conditions with little evidence of ice rafting. A paleogeographic interpretation illustrates land, sea and ice configurations around 14,000 BP. We suggest that a subsequent lateglacial transgression reached the entire region almost simultaneously and peaked around 13,300 BP. This led to deposition of an ice-rafted diamicton ( the Öresund diamicton ) in Skåne and Sjælland, and of glaciolacustrine mud in Halland. We propose that the complex transgression and regression events recorded in the region were governed by interaction of the eustatic sea level rise, isostatic reponse to glacier unloading and possibly also by damming by an ice stream in the Skagerrak and northern Kattegat.     

A 40,000-yr record of environmental change from Burial Lake in Northwest Alaska

Burial Lake in northwest Alaska records changes in water level and regional vegetation since ∼ 39,000 cal yr BP based on terrestrial macrofossil AMS radiocarbon dates. A sedimentary unconformity is dated between 34,800 and 23,200 cal yr BP. During all or some of this period there was a hiatus in deposition indicating a major drop in lake level and deflation of lacustrine sediments. MIS 3 vegetation was herb-shrub tundra; more xeric graminoid-herb tundra developed after 23,200 cal yr BP. The tundra gradually became more mesic after 17,000 cal yr BP. Expansions of Salix then Betula, at 15,000 and 14,000 cal yr BP, respectively, are coincident with a major rise in lake level marked by increasing fine-grained sediment and higher organic matter content. Several sites in the region display disrupted sedimentation and probable hiatuses during the last glacial maximum (LGM); together regional data indicate an arid interval prior to and during the LGM and continued low moisture levels until ∼ 15,000 cal yr BP. AMS ¹⁴C dates from Burial Lake are approximately synchronous with AMS ¹⁴C dates reported for the Betula expansion at nearby sites and sites across northern Alaska, but 1000-2000 yr younger than bulk-sediment dates.     

Late quaternary pollen records from the Kobuk and Noatak river drainages, northwestern Alaska

Pollen diagrams from Joe and Niliq Lakes date to ca. 28,000 and 14,000 yr B.P., respectively. Mesic shurb tundra grew near Joe Lake ca. 28,000 to 26,000 yr B.P. with local Populus populations prior to ca. 27,000 yr B.P. Shrub communities decreased as climate changed with the onset of Itkillik II glaciation (25,000 to 11,500 yr B.P.), and graminoid-dominated tundra characterized vegetation ca. 18,500 to 13,500 yr B.P. Herb tundra was replaced by shrub Betula tundra near both sites ca. 13,500 yr B.P. with local expansion of Populus ca. 11,000 to 10,000 yr B.P. and Alnus ca. 9000 yr B.P. Mixed Picea glauca/P. mariana woodland was established near Joe Lake ca. 6000 yr B.P. These pollen records when combined with others from northern Alaska and northwestern Canada indicate (1) mesic tundra was more common in northwestern Alaska than in northeastern Alaska or northwestern Canada during the Duvanny Yar glacial interval (25,000 to 14,000 yr B.P.); (2) with deglaciation, shrub Betula expanded rapidly in northwestern Alaska but slowly in areas farther east; (3) an early postglacial thermal maximum occurred in northwestern Alaska but had only limited effect on vegetation; and (4) pollen patterns in northern Alaska and northwestern Canada suggest regional differences in late Quaternary climates.     

Age and significance of the Late Pleistocene Dawson tephra in eastern Beringia

Dawson tephra, recently recognized in the Klondike area of Yukon Territory, records one of the largest Quaternary volcanic eruptions in Beringia. Its composition is similar to that of Old Crow tephra, indicating a source in the Aleutian arc-Alaska Peninsula region of southwestern Alaska. Its primary thickness in central Yukon is nearly twice that of Old Crow tephra, which has an estimated eruption volume of >50 km³. The distribution of Dawson tephra is still poorly known, but based on its source area and occurrence in central Yukon, it should be widespread across southern Alaska, Yukon and the Gulf of Alaska. New radiocarbon ages indicate the eruption occurred at about 24,000 ¹⁴C yr BP (ca 27,000 cal yr BP). The Dawson tephra is a valuable marker bed for correlating late Pleistocene records across large areas of eastern Beringia and adjacent marine records.     

Late Glacial environmental changes indicated by a coleopteran succession from North Wales

This investigation was designed to compare the environmental inferences that can be made from fossil Coleoptera with those that can be made from palynological data. In the Glanllynnau kettle hole, sedimentation began at 14,000 BP and continued until about 10,000 BP. The Coleoptera from these deposits show that during this period there was only one climatic oscillation and that this differed in both timing and intensity from oscillations inferred from palynological evidence. Thus, at about 13,000 BP, an intensely cold continental climate suddenly gave place to a period with summer temperatures at least as warm as those at the present day, but during this episode the landscape was entirely without trees. From 12,000 BP to about 10,000 BP there was a progressive deterioration in the temperature, and the period of Betula forest, broadly equivalent to the Allerød, is shown to have a less thermophilous fauna than that of the previous pollen Zone I. An attempt is made to explain this anomaly in terms of the differential rate of response of the plants and animals to rapid climatic changes.     

Late Pleistocene and Holocene glacial history of James Ross Island, Antarctic Peninsula

Studies of Quaternary glacial stratigraphy and morphology around the Antarctic Peninsula have shown that James Ross Island in the western Weddell Sea probably has the best occurrences of stratigraphic sections with dateable material in the region. The stratigraphy includes sections with indefinite radiocarbon age, and three separate aminozones can be recognized. Except for indications of an early deglaciation around c . 10,000 BP, the field evidence from northern James Ross Island suggests a glacial readvance around 7000 BP. It is concluded that the readvance reflects the combined effects of eustatic sea level rise and Holocene warming, leading to increased precipitation and a positive mass balance. The most recent large-scale deglaciation in the area took place around 6000–5000 BP. This confirms the evidence from lake sediments and moss banks in other parts of the Antarctic Peninsula region, which shows that, in most cases, the initiation of organic deposition took place after c . 6000 BP. The literature on the Holocene glacial and environmental history of the region is reviewed in light of the new field evidence.     

Archaeology of the Pleistocene-Holocene boundary in Brazil

After a short history of Brazilian research about Pleistocene peopling, the Late Pleistocene/Early Holocene changes of climate and resources are discussed. Claims for a very ancient presence of Man before 13,000 BP (Itaboraí, Toca da Esperança, Pedra Furada and Lapa Vermelha sites) are polemic, because putative structures and artifacts could have been made by natural processes. In central and northeastern Brazil some sites dated between 14,000 and 10,000 BP provide clear evidence of human activities and coexistence with huge Pleistocene mammals.In a synthesis of our present knowledge about the 12,000/8000 BP period, biological aspects of the Lagoa Santa people and their subsistence are discussed. The main regional traditions are Umbu with bifacial projectile points, and Humaitá with heavy implements in the southern part of Brazil. In the central and northeastern regions, the Itaparica tradition is characterized by typical retouched flakes and limaces. Although projectile points are generally thought to be absent in the earliest levels of this tradition, some have been found in Boquete Cave. In Amazonia, some cultural aspects seem to have been the same as in central Brazil.     

A 16 000‐year record of vegetational change in south‐western Alaska as inferred from plant macrofossils and pollen

Pollen and macrofossil analyses of a sediment core from Beaver Pond (60° 37′ 14″ N, 154° 19′ W, 579 m a.s.l.) reveal a record of regional and local postglacial vegetation change in south‐western Alaska. The chronology is based on five AMS (accelerator mass spectrometry) ¹⁴C ages obtained from terrestrial plant macrofossils. Pollen and macrofossil records suggest that open herb and shrub tundra with e.g. Poaceae, Cyperaceae, Artemisia, Vaccinium and Salix prevailed on the landscape before ca. 14 000 cal a BP. The shift from herb‐ to shrub‐dominated tundra (Salix, subsequent Betula expansion) possibly reflects climatic warming at the beginning of the Bølling period at ca. 14 700–14 500 and around 13 500 cal a BP. Vegetation (Betula shrub tundra) remained relatively stable until the early Holocene. Macrofossil influx estimates provide evidence for greater biomass in Betula shrub tundra during the early postglacial period than today. Charcoal accumulation rates suggest tundra fire activity was probably greater from ca. 12 500 to 10 500 cal a BP, similar to results from elsewhere in Alaska. The pollen and macrofossil records of Beaver Pond suggest the prevalence of low shrub tundra (shrub Betula, Betula nana, Vaccinium, Ledum palustre, Ericaceae) and tall shrub tundra (Alnus viridis ssp. crispa, Salix) between 10 000 and 4000 cal a BP. This Holocene vegetation type is comparable with that of the modern treeless wet and moist tundra in south‐western Alaska. The expansion of Picea glauca occurred ～4000 cal a BP, much later than that of A. viridis (ssp. crispa), whereas in central and eastern Alaska Picea glauca expanded prior to or coincident with Alnus (viridis). At sites located only 200–400 km north‐east of Beaver Pond (Farewell and Wien lakes), Picea glauca and Betula forests expanded 8000–6000 cal a BP. Unfavourable climatic conditions and soil properties may have inhibited the expansion and establishment of Picea across south‐west Alaska during the mid and late Holocene. Copyright © 2011 John Wiley & Sons, Ltd.     

Late Quaternary sea-level changes and palaeoseismology of the Bering Glacier region,Alaska

Glacial isostatic adjustment and multiple earthquake deformation cycles produce temporal and spatial variability in the records of relative sea-level change across south-central Alaska. Bering Glacier had retreated inland of the present coast by 16 ka BP and north of its present terminus by ～14 ka BP. Reconnaissance investigations in remote terrain provide new but limited insights of post-glacial relative sea-level change and the palaeoseismology of the region. Relative sea-level was above present ～9.2 ka BP to at least 5 ka BP before falling to below present. It was above present by the early 20th century, before land uplift in the 1964 M 9.2 earthquake. The pattern of relative sea-level change differs what may be expected in comparison with model predictions for other seismic and non-seismic locations. Buried mud–peat couplets show a great earthquake ～900 cal BP, including evidence of a tsunami. Correlation with other sites suggest simultaneous rupture of adjacent segments of the Aleutian megathrust and the Yakutat microplate.     

Ground ice and slope sediments archiving late Quaternary paleoenvironment and paleoclimate signals at the margins of El'gygytgyn Impact Crater, NE Siberia

An accumulation terrace close to the El'gygytgyn Impact Crater in northeastern Siberia contains stratigraphic and periglacial evidence of the paleoenvironmental and paleoclimatic history and permafrost dynamics during late Quaternary time. A succession of paleo active-layer deposits that mirror environmental changes records periods favorable for the establishment and growth of ice-wedge polygonal networks and sediment variations. These two elements of the periglacial landscape serve as complementary paleoenvironmental archives that can be traced back to ∼ 14,000 cal yr BP. The slope sediments and the ground ice contained therein have prominent relative maxima and minima in properties (grain size, total organic content, oxygen isotopes). They document a regional early Holocene thermal maximum at about 9000 cal yr BP, followed by a transition to slightly cooler conditions, and a subsequent transition to slightly warmer conditions after about 4000 cal yr BP. Results from sedimentary analysis resemble morphological and geochemical (oxygen and hydrogen isotopes) results from ice wedge studies, in which successive generations of ice-wedge polygonal networks record warmer winters in late Holocene time. Moreover, peaks of light soluble cation contents and quartz-grain surface textures reveal distinct traces of cryogenic weathering. We propose a conclusive sedimentation model illustrating terrace formation in a permafrost terrain.     

Extinction chronology of the cave lion Panthera spelaea

The cave lion, Panthera spelaea, was widespread across northern Eurasia and Alaska/Yukon during the Late Pleistocene. Both morphology and DNA indicate an animal distinct from modern lions (probably at the species level) so that its disappearance in the Late Pleistocene should be treated as a true extinction. New AMS radiocarbon dates directly on cave lion from across its range, together with published dates from other studies – totalling 111 dates – indicate extinction across Eurasia in the interval ca. 14–14.5 cal ka BP, and in Alaska/Yukon about a thousand years later. It is likely that its extinction occurred directly or indirectly in response to the climatic warming that occurred ca. 14.7 cal ka BP at the onset of Greenland Interstadial 1, accompanied by a spread of shrubs and trees and reduction in open habitats. Possibly there was also a concomitant reduction in abundance of available prey, although most of its probable prey species survived substantially later. At present it is unclear whether human expansion in the Lateglacial might have played a role in cave lion extinction. Gaps in the temporal pattern of dates suggest earlier temporary contractions of range, ca. 40–35 cal ka BP in Siberia (during MIS 3) and ca. 25–20 cal ka BP in Europe (during the ‘Last Glacial Maximum’), but further dates are required to corroborate these. The Holocene expansion of modern lion (Panthera leo) into south-west Asia and south-east Europe re-occupied part of the former range of P. spelaea, but the Late Pleistocene temporal and geographical relationships of the two species are unknown.     

Pleistocene vertebrates of the Yukon Territory

Unglaciated parts of the Yukon constitute one of the most important areas in North America for yielding Pleistocene vertebrate fossils. Nearly 30 vertebrate faunal localities are reviewed spanning a period of about 1.6 Ma (million years ago) to the close of the Pleistocene some 10 000 BP (radiocarbon years before present, taken as 1950). The vertebrate fossils represent at least 8 species of fishes, 1 amphibian, 41 species of birds and 83 species of mammals. Dominant among the large mammals are: steppe bison (Bison priscus), horse (Equus sp.), woolly mammoth (Mammuthus primigenius), and caribou (Rangifer tarandus) – signature species of the Mammoth Steppe fauna (Fig. 1), which was widespread from the British Isles, through northern Europe, and Siberia to Alaska, Yukon and adjacent Northwest Territories. The Yukon faunas extend from Herschel Island in the north to Revenue Creek in the south and from the Alaskan border in the west to Ketza River in the east. The Yukon holds evidence of the earliest-known people in North America. Artifacts made from bison, mammoth and caribou bones from Bluefish Caves, Old Crow Basin and Dawson City areas show that people had a substantial knowledge of making and using bone tools at least by 25 000 BP, and possibly as early as 40 000 BP. A suggested chronological sequence of Yukon Pleistocene vertebrates (Table 1) facilitates comparison of selected faunas and indicates the known duration of various taxa.     

The Pleistocene/Holocene transition and human occupation in the Central Andes of Argentina: Agua de la Cueva locality

In the Central Andes of Argentina, evidences of early human occupations come from the Precordillera, a low mountain system which was under periglacial conditions prior to 14,000 ¹⁴C yr BP, when the Cordillera Principal and Cordillera Frontal were glaciated. The corridors for human migration across the Andes may have opened before 13,000 ¹⁴C yr BP. The Pleistocene/Holocene transition gave rise to a substantial variability of environments and consequently of natural resources for early people, who found in the Precordillera new ecosystems with suitable conditions for living. The first human groups arrived ca. 11,000 ¹⁴C yr BP at Agua de la Cueva rockshelter, located at 2900 m above sea level in the western flank of the Precordillera. The occurrence of raw material outcrops close to the site and the archaeofaunistic record indicate a local and likely seasonal exploitation of mountain resources. These early people lived in a shrub steppe environment under cooler and probably wetter conditions in which camelids were the most important food resource. Since 9000 ¹⁴C yr BP, warmer and drier conditions were dominant. Except for a lower intensity of human occupations, the site function of Agua de la Cueva seems to have remained the same.     

Relative dating of moraines using moraine morphometric and boulder weathering criteria, Kigluaik Mountains, Alaska

Six measurements of surface-boulder weathering and seven measures of moraine morphometrics were taken at 57 sites in the Kigluaik Mountains, Alaska, to test the morphostratigraphic division of five Quaternary glacial units, to test a threefold subdivision of the late Pleistocene glacial unit, and to estimate the timing of glacial advances. Group means from 70% of the relative-age measures exhibit a positive relationship with relative age of the glacial units. The measures most effective at differentiating between moraine groups were: boulder frequency, tall-boulder frequency, boulder height, distal slope, and boulder angularity. Results of dixriminant analysis indicate that moraine-morphometric measures provided slightly better classification results than those of boulder weathering. Discriminant analysis correctly classified 89% of the a priori grouped sites. Multivariate analysis supports the attempted threefold subdivision of the latest Pleistocene Mount Osborn moraines at the 0.056 level of significance. Estimated ages of 60,000 BP for the Salmon Lake and 165,000 BP for the Stewart River glacial units were interpolated by using the relative-age data and ages of 18,000 BP for the Mount Osborn and 810,000 BP for the Nome River units.     

Late- and postglacial environment of the Buzuluk area,middle Volga region,Russia

A 13 m long core from the lake-swamp at Pobochnoye (53°01′30″ N, 51°50′30″ E) in the Buzuluk pine forest in the middle part of the Volga River basin, Russia was studied for pollen, peat stratigraphy, mollusc, δ¹⁸O/δ¹⁶O and δ¹³C/δ¹²C analyses and radiocarbon dating. For the first time the environment history of the east European Russia has been reconstructed for the last 14,000 years; ca 14,000–13,000 BP cold dry steppes spread across the basin of the Samara River. Isotope data indicate that the main climate shift occurred ca 10,000 BP at the Lateglacial–Holocene transition when climate became warmer and forests expanded. Pinus sylvestris L. expanded 10,000 BP. Ca 9,000 BP Ulmus, Quercus and Corylus appeared in the Buzuluk forest followed at ca. 7,000 BP by Alnus, then Tilia and Acer at 6000 BP. Between 6000 and 4500 BP the climatic conditions were optimal for the forest growth in the Samara River basin. 5500–5000 BP the lake became shallower and was transformed into the eutrophic peat swamp. Between 4500–3500 BP climate became drier and hotter and forest less abundant. Between 3500–2400 BP the forest cover again increased. Between 2400–2000 BP the pine forest area has reduced, apparently due to increased dryness, and around 2000 BP the modern environment in the Buzuluk area has been in existence.     

Iceberg discharge to the Chukchi shelf during the Younger Dryas

The extent of glaciation in northwestern Alaska, the source of sediment supply to the Chukchi shelf and slope, and the movement of sea ice and icebergs across the shelf during the last glacial maximum (LGM) remain poorly constrained. Here we present geophysical and geological data from the outer Chukchi margin that reveal a regionally extensive, heavily ice-scoured surface ∼ 5-8 m below the modern seafloor. Radiocarbon dating of this discrete event yields age estimates between 10,600 and 11,900 ¹⁴C yr BP, indicating the discharge event occurred during the Younger Dryas. Based on mineralogy of the ice-rafted debris, the icebergs appear to be sourced from the northwestern Alaskan margin, which places important constraints on the ice extent in northern Alaska during the LGM as well as existing circulation models for the region.