Paleoindians in beringia: evidence from arctic alaska

Excavations at the Mesa site in arctic Alaska provide evidence for a Paleoindian occupation of Beringia, the region adjacent to the Bering Strait. Eleven carbon-14 dates on hearths associated with Paleoindian projectile points place humans at the site between 9,730 and 11,660 radiocarbon years before present (years B.P.). The presence of Paleoindians in Beringia at these times challenges the notion that Paleoindian cultures arose exclusively in mid-continental North America. The age span of Paleoindians at the Mesa site overlaps with dates from two other cultural complexes in interior Alaska. A hiatus in the record of human occupation occurs between 10,300 and 11,000 years B.P. Late Glacial climatic fluctuations may have made northern Alaska temporarily unfavorable for humans and spurred their southward dispersal.     

The timing of high sea levels over the past 200,000 years

The (230)Th ages and (234)U/(238)U ratios were determined for Barbados corals that grew during periods of high sea level within the last 200,000 years. The similarity of the initial (234)U/(238)U ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine (234)U/(238)U ratio 83,000 and 200,000 years ago was within 2 per mil of the modern value. The accuracies of the (230)Th ages are evaluated on the basis of the (234)U/(238)U values and a model of the behavior of uranium and thorium isotopes during diagenesis. For the last three interglacial and two intervening interstadial periods, sea level peaked at or after peaks in summer insolation in the Northern Hemisphere. This overall pattern supports the idea that glacial-interglacial cycles are caused by changes in Earth's orbital geometry. The sea-level drop at the end of the penultimate interglacial, the last interglacial, and a subsequent interstadial period lagged behind the decrease in insolation by 5,000 to 10,000 years.     

Pleistocene brown bears in the mid-continent of North America

Current biogeographic models hypothesize that brown bears migrated from Asia to the New World ~100 to 50 thousand years ago but did not reach areas south of Beringia until ~13 to 12 thousand years ago, after the opening of a mid-continental ice-free corridor. We report a 26-thousand-year-old brown bear fossil from central Alberta, well south of Beringia. Mitochondrial DNA recovered from the specimen shows that it belongs to the same clade of bears inhabiting southern Canada and the northern United States today and that modern brown bears in this region are probably descended from populations that persisted south of the southern glacial margin during the Last Glacial Maximum.     

Instability of glacial climate in a model of the ocean- atmosphere-cryosphere system

In contrast to the relatively stable climate of the past 10,000 years, during glacial times the North Atlantic region experienced large-amplitude transitions between cold (stadial) and warm (interstadial) states. In this modeling study, we demonstrate that hydrological interactions between the Atlantic thermohaline circulation (THC) and adjacent continental ice sheets can trigger abrupt warming events and also limit the lifetime of the interstadial circulation mode. These interactions have the potential to destabilize the THC, which is already more sensitive for glacial conditions than for the present-day climate, thus providing an explanation for the increased variability of glacial climate.     

Finite Radiocarbon Dates of the Port Talbot Interstadial Deposits in Southern Ontario

Three new finite radiocarbon dates Suggest that (i) the thermnal maximum of the Port Talbot interstadial ocurred prior to 47,000 years before the present and (ii) the interstadial deposits were overridden by a glacial advance approximatels 44,000 years before the present. To facilitate correlaltions with other areas, new rock-stratigraphic names are proposed for the Port Talbot type section.     

Molecular analysis of plant migration and refugia in the Arctic

The arctic flora is thought to have originated during the late Tertiary, approximately 3 million years ago. Plant migration routes during colonization of the Arctic are currently unknown, and uncertainty remains over where arctic plants survived Pleistocene glaciations. A phylogenetic analysis of chloroplast DNA variation in the purple saxifrage (Saxifraga oppositifolia) indicates that this plant first occurred in the Arctic in western Beringia before it migrated east and west to achieve a circumpolar distribution. The geographical distribution of chloroplast DNA variation in the species supports the hypothesis that, during Pleistocene glaciations, some plant refugia were located in the Arctic as well as at more southern latitudes.     

Dating pleistocene archeological sites by protein diagenesis in ostrich eggshell

Eggshells of the African ostrich (Struthio camelus), ubiquitous in archeological sites in Africa, have been shown by laboratory simulation experiments to retain their indigenous organic matrix residues during diagenesis far better than any other calcified tissue yet studied. The rate of L-isoleucine epimerization to D-alloisoleucine follows reversible first-order kinetics and has been calibrated for local temperature effects and used to estimate the age range of stratified archeological sites. Age estimates are consistent with radiocarbon dates from several stratified archeological sites. With adequate calibration, this technique can provide accurate ages to within 10 to 15 percent for strata deposited within the last 200,000 years in the tropics and the last 1,000,000 years in colder regions such as China.     

Congruent paleomagnetic and archeomagnetic records from the Western United States: a.d. 750 to 1450

Two independently dated, high-resolution paleomagnetic records, one lacustrine and one archeological, record the passage across western North America of the same nondipole feature of the geomagnetic field during the time interval from A.D. 750 to 1450. Although these sequences indicate that correlation between paleomagnetic and archeomagnetic records is feasible under certain conditions, differences between the records underscore the difficulty of dating accurately an archeological site by correlation of a single archeomagnetic direction with a secular variation curve.     

Rapid Variations in Atmospheric Methane Concentration During the Past 110,000 Years

A methane record from the GISP2 ice core reveals that millennial-scale variations in atmospheric methane concentration characterized much of the past 110,00 years. As previously observed in a shorter record from central Greenland, abrupt concentration shifts of about 50 to 300 parts per billion by volume were coeval with most of the interstadial warming events (better known as Dansgaard-Oeschger events) recorded in the GISP2 ice core throughout the last glacial period. The magnitude of the rapid concentration shifts varied on a longer time scale in a manner consistent with variations in Northern Hemisphere summer insolation, which suggests that insolation may have modulated the effects of interstadial climate change on the terrestrial biosphere.     

Asynchronous climate changes in the North Atlantic and Japan during the last termination

Pollen records from the annually laminated sediment sequence in Lake Suigetsu, Japan, suggest a sequence of climate changes during the Last Termination that resembles that of the North Atlantic region but with noticeable differences in timing. An interstadial interval commenced a few centuries earlier [approximately 15,000 years before the present (yr B.P.)] than the North Atlantic GI-1 (B?lling) event. Conversely, the onset of a Younger Dryas (YD)-like cold reversal (12,300 to 11,250 yr B.P.) postdated the North Atlantic GS-1 (YD) event by a few centuries. Climate in the Far East during the Last Termination reflected solar insolation changes as much as Atlantic influences.     

Rise and fall of the Beringian steppe bison

The widespread extinctions of large mammals at the end of the Pleistocene epoch have often been attributed to the depredations of humans; here we present genetic evidence that questions this assumption. We used ancient DNA and Bayesian techniques to reconstruct a detailed genetic history of bison throughout the late Pleistocene and Holocene epochs. Our analyses depict a large diverse population living throughout Beringia until around 37,000 years before the present, when the population's genetic diversity began to decline dramatically. The timing of this decline correlates with environmental changes associated with the onset of the last glacial cycle, whereas archaeological evidence does not support the presence of large populations of humans in Eastern Beringia until more than 15,000 years later.     

A Fluted Point from the Uptar Site, Northeastern Siberia

Lanceolate bifacial points, including one fluted specimen, have been collected from beneath an early Holocene tephra at the Uptar site, northeastern Siberia. Thus, the technology associated with the well-known Paleoindian tradition was not confined to the Americas. The Uptar collection does not compare readily with other Beringian complexes and demonstrates that there is greater diversity in the archaeological record of northeastern Siberia than traditional colonization models imply.     

Dynamics of Pleistocene population extinctions in Beringian brown bears

The climatic and environmental changes associated with the last glaciation (90,000 to 10,000 years before the present; 90 to 10 ka B.P.) are an important example of the effects of global climate change on biological diversity. These effects were particularly marked in Beringia (northeastern Siberia, northwestern North America, and the exposed Bering Strait) during the late Pleistocene. To investigate the evolutionary impact of these events, we studied genetic change in the brown bear, Ursus arctos, in eastern Beringia over the past 60,000 years using DNA preserved in permafrost remains. A marked degree of genetic structure is observed in populations throughout this period despite local extinctions, reinvasions, and potential interspecies competition with the short-faced bear, Arctodus simus. The major phylogeographic changes occurred 35 to 21 ka B.P., before the glacial maximum, and little change is observed after this time. Late Pleistocene histories of mammalian taxa may be more complex than those that might be inferred from the fossil record or contemporary DNA sequences alone.     

Rapid changes in the hydrologic cycle of the tropical Atlantic during the last glacial

Sedimentary time series of color reflectance and major element chemistry from the anoxic Cariaco Basin off the coast of northern Venezuela record large and abrupt shifts in the hydrologic cycle of the tropical Atlantic during the past 90,000 years. Marine productivity maxima and increased precipitation and riverine discharge from northern South America are closely linked to interstadial (warm) climate events of marine isotope stage 3, as recorded in Greenland ice cores. Increased precipitation at this latitude during interstadials suggests the potential for greater moisture export from the Atlantic to Pacific, which could have affected the salinity balance of the Atlantic and increased thermohaline heat transport to high northern latitudes. This supports the notion that tropical feedbacks played an important role in modulating global climate during the last glacial period.     

Holocene sea level changes at the coast of dor, southeast mediterranean

Geological, geomorphological, and archeological data of changes in sea level during the Holocene at the Mediterranean coast of Dor provide a eustatic curve of the region. This curve shows that sea level was approximately 2 meters below the present level 4000 years ago, rose to 1 meter below the present level 3000 years ago, and was 1 meter higher than the present level 1500 years ago. It then dropped to 1 meter below the present level about 800 years ago.     

Batan grande: a prehistoric metallurgical center in peru

Recent archeological fieldwork on the north coast of Peru permits a preliminary reconstruction of a prill-extraction copper and copper alloy smelting process heretofore undocumented in the New World. The process was applied on a large scale during the late pre-Hispanic period. This study provides strong support for the claim that central Andean metallurgy constituted one of the major independent metallurgical traditions of the world.     

Determining the season of death of mammal teeth from archeological sites: a new sectioning technique

Alternating translucent and opaque bands on the roots of mammal teeth are used to determine the age and season of death. These structures are preserved in teeth from archeological sites. However, the standard sectioning technique, which includes decalcification, often destroys archeological specimens. A new, less destructive technique provides analyzable solid sections at costs comparable to decalcification.     

The paredon, Mexico, obsidian source and early formative exchange

In 1975, archeological surface surveys of trade routes located again a pre-Hispanic obsidian source in central Mexico first reported in 1902. Initial trace element studies of the Paredón source through an analysis by neutron activation have been compared with similar studies of the obsidian found at Chalcatzingo 150 kilometers from the source. These comparisons indicate that obsidian from Paredón, rather than Otumba, was of primary importance during the Early Formative in central Mexico.     

Holocene history of cedar and native Indian cultures of the north american pacific coast

A comparison of paleobotanical records with archeological and ethnographic evidence from the Pacific Northwest shows a strong correlation between the expansion of Western red cedar (Thuja plicata) in coastal forests between 5000 and 2500 years ago and the evolution of a massive woodworking technology by native cultures. This suggests that an important component of cultural development was environmentally constrained until large cedar trees, the basic resource for canoe-building and plank-house construction, had become available in late Holocene time.     

A terminal Pleistocene child cremation and residential structure from eastern Beringia

The dearth of human remains and residential sites has constrained inquiry into Beringian lifeways at the transition of the late Pleistocene-early Holocene. We report on human skeletal remains and a residential structure from central Alaska dated to ~11,500 calendar years ago. The remains are from a ~3-year-old child who was cremated in a pit within a semisubterranean house. The burial-cremation and house have exceptional integrity and preservation and exhibit similarities and differences to both Siberian Upper Paleolithic and North American Paleoindian features.