The history of the Late Weichselian northwestern Barents Shelf, including western Svalbard, has been investigated by provenance/sedimentologist studies of five cores from the continental shelf and slope west of Svalbard. The chronostratigraphy of the cores is based on AMS 14C dates and oxygen isotope analyses. Interpretations of the cores suggest that the ice sheets of western Svalbard and northwestern Barents Sea experienced advances and retreats in two steps. The first significant ice advance beyond the present coastline occurred ca. 22,000 14C yr B.P. and was followed by an ice advance to the shelf edge ca. 18,000 14C yr B.P. Ice recession from the outer shelf and the southwestern Barents Sea began 14,800 14C yr B.P. and was followed by a second ice recession between 13,000 and 12,000 14 C yr B.P. during which ice withdrew from the inner shelf. A minor readvance of the ice sheet on the shelf west of Svalbard occurred close to 12,400 14C yr B.P. The first deglaciation event was associated with release of icebergs containing ice-rafted detritus, while the later episode also included significant amounts of meltwater and fine-grained sediment.

Ice sheet modeling is an essential tool for estimating the effect of climate change on the Greenland ice sheet. The large spatial and long-term temporal scale of ice sheet models limits the amount of data which can be used to test model results. A framework for the analysis of glacial geological data to test ice sheet models is illustrated by a case study in west Greenland. A geological scenario of ice margin positions since the last glacial maximum is based on a review of existing literature and new datings of moraine systems. Ages of moraine systems and associated accuracy ranges are interpolated to a 1 × 1 km grid over an area of about 57,500 km2. Resampling to a 20 × 20 km grid on an ice sheet model coordinates permits a quantitative comparison with modeled ice marginal positions. In view of the uncertainties in the geological scenario, with moraine system ages having an absolute uncertainty of 700 to 3300 cal yr, the Greenland ice sheet model of Huybrechts provides a reasonable simulation of the deglaciation pattern in central west Greenland. Modeled timing of the position of the ice margin generally precedes the geological record by 900 yr. The difference between geology and model is large for areas without proper geological information and small, but still about 500-950 yr, for well-dated moraine systems. Model deficiencies in west Greenland are probably related to the forcing function driving ablation estimates, and especially the forcing function for sea level and the description of calving processes should he reviewed critically. The simplified topography used by the model could also induce errors. Although topography used in models neglects possible important features such as ice streams, we do not find any significant trend between differences and relief amplitude. Missing moraines on the southern part of the shelf and absence of geological information from beneath the present ice sheet affect the character and quality of the geological scenario.

The Markhida Moraine is a broad zone of ice marginal landforms and deposits running E-W across the Pechora lowland in northern Russia. It was formed along the southern margin of an ice sheet advancing onto the coast from the Kara Sea. Previous researchers (Grosswald, 1980, 1983, 1994a: Grosswald et al., 1974) concluded that the moraine was formed during a readvance of the Barents-Kara ice sheet after 9000 14C yr B.P. This conclusion was based on the occurrence of deformed lacustrine sediments dated 9000 to 10,000 14C yr B.P. between two presumed basal tills in the type section at Markhida. A reinvestigation of the section by the authors revealed only one basal till overlain by lacustrine sediments and diamictons, yielding radiocarbon dates between 9000 and 10,000 14C yr B.P. Luminescence dating from the sand underlying the till gave Middle Weichselian ages. Deformation structures and fabric in the sediments overlying the till solely reflect gravity-driven processes, not glaciotectonic deformation as claimed by previous investigators. We conclude that most of these sediments were finally deposited during very slow (retarded) melting of a large body of buried glacier ice and the underlying permafrost. Thus, the Markhida Moraine, as an ice marginal feature, was formed prior to 10,000 14C yr B.P., probably during the Late Weichselian, but possibly as early as the Middle Weichselian.

Measured 18O/16O ratios from the Greenland Ice Sheet Project 2 (GISP2) ice core extending back to 16,500 cal yr B.P. provide a continuous record of climate change since the last glaciation. High-resolution annual 18O/16O results were obtained for most of the current millennium (A.D. 818-1985) and record the Medieval Warm Period, the Little Ice Age, and a distinct 11-yr 18O/16O cycle. Volcanic aerosols depress central Greenland annual temperature (∼1.5°C maximally) and annual 18O/16O for about 4 yr after each major eruptive event. On a bidecadal to millennial time scale, the contribution of solar variability to Holocene Greenlandic temperature change is ∼0.4°C. The role of thermohaline circulation change on climate, problematic during the Holocene, is more distinct for the 16,500-10,000 cal yr B.P. interval. (Analogous to 14C age calibration terminology, we express time in calibrated (cal) yr B.P. (A.D. 1950 = 0 cal yr B.P.)). The Oldest Dryas/Bølling/Older Dryas/Allerød/Younger Dryas sequence appears in great detail. Bidecadal variance in 18O/16O, but not necessarily in temperature, is enhanced during the last phase of lateglacial time and the Younger Dryas interval, suggesting switches of air mass transport between jet stream branches. The branched system is nearly instantaneously replaced at the beginning of the Bølling and Holocene (at ∼14,670 and ∼11,650 cal yr B.P., respectively) by an atmospheric circulation system in which 18O/16O and annual accumulation initially track each other closely. Thermodynamic considerations of the accumulation rate-temperature relationship can be used to evaluate the 18 O/16O-temperature relationship. The GISP2 ice-layer-count years of major GISP2 climate transitions also support the use of coral 14C ages for age calibration.

Variations in the amount and composition of sedimentary organic matter in glacial and interglacial deposits of the last 2.7 myr correlate with late Cenozoic climatic and oceanographic changes in the Norwegian-Greenland Sea. These variations are predominantly caused by the changing supply of terrestrial and reworked organic matter. The highest amounts of terrestrial organic particles (macerals) and of reworked coal clasts in glacial and early deglacial diamictons are closely related to glacial erosion of Mesozoic strata that crop out along the Scandinavian Shelf. The first occurrence of coal clasts at 2.53 myr demonstrates an initial advance of continental ice margins to these source areas. The establishment of anoxic conditions at the sea floor during diamicton deposition probably reflects an increased vertical flux of labile organic matter due to lithogenic adsorbtion followed by an almost complete mineralization at the water/sediment interface. The content of marine organic matter was continuously low over the past 2.7 myr except for past interglacial highstands (i.e., isotopic event 5.5.1), suggesting persistent diagenetic degradation of the labile organic fraction. The marine organic matter exclusively consists of residual dinoflagellate cysts and fragments of them.

New radiocarbon ages for Sierra Nevada deglaciation, the first 10 Be measurements from the Laurentide terminal moraine, and calculations based on paleomagnetic field strength have the potential to substantially improve the accuracy of cosmogenic age estimates. Specifically, three new constraints apply to the interpretation of measured abundances of in situ produced cosmogenic 10Be and 26Al: (1) A suite of minimum-limiting radiocarbon dates indicates that the Sierra Nevada was deglaciated at least several thousand years earlier than assumed when Nishiizumi et al. (1989) first calibrated 10Be and 26 Al production rates based on polished bedrock surfaces in the range, with retreat beginning by 18,000 cal yr B.P. and completed by 13,000 cal yr B.P. (2) Concentrations of 10Be in moraine boulders and glacier-polished bedrock in New Jersey show little variance (10%, 1σ) and can be used to calculate a preliminary 10Be production rate (integrated over the past 21,000-22,000 cal yr B.P. at 41°, 200-300 m altitude) that is about 20% lower than currently accepted. (3) Calculations of the effect of past geomagnetic field-strength variations on production rates suggest that the use of temporally averaged production rates may generate age errors of >20%; however, cosmogenic exposure ages can be corrected for this effect, although the corrections currently are imprecise. Many previously reported late-Pleistocene 10Be and 26Al exposure ages are probably too young and are less accurate and less precise than implied by reported uncertainties. The discrepancy between accepted production rates and those calculated from Laurentide exposures, when considered together with the Sierran deglacial chronology and the model results, suggest that correlations between cosmogenic and other numerical ages, especially for brief events like the Younger Dryas and Heinrich events, will not be robust until temporal variations and the altitude/latitude scaling of production rates are fully understood and quantified at levels comparable to current analytic uncertainties (∼3%).

Analysis of in situ-produced 10Be and 26Al demonstrate that some Australian inselbergs (granitic domes) are among the most stable geomorphic surfaces in the world, eroding at rates as low as 0.6 m/myr. Twenty isotopic analyses of ten samples suggest that the bare bedrock tops of these isolated granitic domes have been exposed to cosmic radiation for at least 0.5 myr and are eroding at a mean model rate less than 0.7 ± 0.1 m/myr (n = 6). Isotopic analyses of samples collected from the top of Mt. Wudinna, Little Wudinna, and Yarwondutta Rock are most consistent with continuous exposure during erosion. On the other hand, samples collected from the flanks of some domes and the tops of other domes have isotopic abundances suggestive of complex exposure histories including burial and reexposure. These unique isotopic data provide the first quantitative information for evaluating longstanding, but previously untested, hypotheses regarding the antiquity and development of these enigmatic landforms and indicate that some Eyre Peninsula inselbergs are probably relict features of pre-Pleistocene landscapes.

The rock magnetic properties of the Chinese loess and paleosols constitute a unique and sensitive record of East Asian paleoclimate through the Quaternary Period. Systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal, which can be easily and rapidly measured at many sites across the Loess Plateau. Variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size, but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages, as well as glaciations and interglaciations. Past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations. The susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the Loess Plateau. Our rainfall reconstructions identify enhanced summer monsoonal activity in the Chinese Loess Plateau region in the early Holocene and the last interglaciation. In the presently semiarid western area of the plateau, annual precipitation in interglacial times was up to 80% higher than at present; in the more humid southern and eastern areas, values were up to 20% higher than today's levels. During the last glaciation, precipitation decreased across the entire plateau, typically by ∼25%. The relationship between pedogenic susceptibility, climate, and weathering age was examined over the Northern Hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate, rather than soil age, is the predominant factor that controls pedogenic susceptibility enhancement in loess soils.

The dynamics of a cliff-top dune system located at the foot of the Mackenzie Mountains was reconstructed by radiocarbon dating and tree ring analysis of forest paleosols in eolian sediments. The first evidence of eolian activity dates to ca. 3000 yr B.P. when the breaching of a bedrock sill initiated the erosion of glaciofluvial deposits that resulted in the exposure of a 75-m-high cliff of erodible sediment. Sandy sediment eroded from the cliff By katabatic winds from the Mackenzie Mountains buried a mature forest growing on alluvial sediments. Despite a minor eolian event between 750 and 860 cal yr A.D., dune development began ca. 1100 cal yr A.D. and has been marked by two major sedimentation periods between ca. 1100 cal yr A.D. and 1460 A.D. and from 1865 to present. Detailed analysis of tree morbidity and mortality indicates that the dune progressed at an average rate of 78 cm/yr for the last century. Dune dynamics are directly related to slope activity that controls the episodic nature of sediment availability and to the katabatic wind regime. Comparison of the dune dynamics and paleoclimatic data suggest a possible influence of warm climate on eolian activity.

Basal sediments of Lake Torfadalsvatn, northern Iceland, record changes in terrestrial and limnic environments in the period 11,300-9000 14C yr B.P. These changes were probably forced by climate and connected with displacements of the marine polar front and sea-ice margin. Pollen, spores, green algae (Pediastrum), saturation isothermal remanent magnetization, and carbon content of the basal sediments provide the first detailed biostratigraphic record of the last glacial-interglacial transition in Iceland. During the first pioneer phase, beginning at ca. 11,300 14C yr B.P., grasses and fell-field herbs became established, and lake productivity was very low. At ca. 10,900 14C yr B.P., climatic and soil conditions became favorable for shrubs and dwarf shrubs. This change, together with increased limnic productivity, clearly indicates long seasons without ice-cover in the sea immediately north of Iceland. A return to a colder climate (Younger Dryas), probably in connection with a southward displacement of the marine polar front, occurred by 10,600 14C yr B.P. Shrub and dwarf-shrub vegetation disappeared, and limnic productivity diminished. A second pioneer vegetation phase, dominated by Oxyria/Rumex and grasses, was initiated by a change to longer seasons without sea ice at ca. 9900 14C yr B.P. This warming is also evident as a contemporaneous increase in lake productivity. After ca. 9400 14C yr B.P. the reestablishment of dwarf-shrub heaths and very high limnic productivity indicate further warming.

Calibration of the radiocarbon timescale of paleoecological records is essential if they are to be explained correctly in terms of their governing ecological or climatological controls. The differences between calendar ages and radiocarbon ages that arise from variations in 14C production through time can distort the chronologies of individual records and the interpretations based on them. Misleading impressions of synchrony or diachrony of events among multiple records can result, and estimates of the apparent duration of episodes and rates of sedimentation and local population changes can be biased. Displays of the temporal patterns of migration or extinction may also be affected. Spurious correlations may arise between records with radiocarbon-controlled chronologies and time series of potential controls that are expressed on a calendar time scale. Support for particular explanations of features in a paleoecological record may vary depending on whether radiocarbon ages are calibrated or not. This situation is illustrated using the eastern Beringian Populus subzone as an example. When the radiocarbon ages that control the timing of the Populus subzone are calibrated, the contemporaneous decrease in ice volume and increase in summer insolation are implicated as the ultimate controls of the occurrence of the subzone.

Paleoclimatic interpretation of proxy data is complicated sometimes by the appearance of heterogeneous patterns of climatic responses across networks of sites. Modern climate analogues for the western United States, similar to those patterns of atmospheric circulation of 18,000 and 9000 yr B.P., were examined in order to explain such patterns of spatial heterogeneity. Modern analogues were defined by comparing modern atmospheric circulation patterns with those simulated by general circulation models. Maps of temperature and precipitation anomalies of the modern analogues reveal patterns of spatial heterogeneity, which resemble the patterns of effective moisture compiled from paleoclimatic data. January 1957 was found to be a reasonable 18,000 yr B.P. analogue, and it features isolated areas of increased wetness in the northern Great Basin and increased dryness in the Northwest interior. Analogues for 9000 yr B.P. from a composite of 11 Augusts display patterns of spatial heterogeneity of effective moisture over most of the mountainous areas. The analogues suggest that spatial heterogeneity of climate is the rule rather than the exception over much of the western United States, with the climatic anomalies at any particular time representing the outcome of the mediation of large-scale atmospheric circulation controls by smaller scale topographic features.

Previously undescribed plant and animal fossils from the Whidbey Formation represent two environments. An upper sand unit contains predominantly terrestrial molluscs (4 taxa), insects, and a vole (cf. Phenacomys), whereas a lower clay unit contains ostracodes (9 taxa), freshwater molluscs (6 taxa), insects (9 taxa), freshwater plant seeds (6 taxa), and fish (cf. Gasterosteus : stickleback). These taxa are compatible with interglacial climatic conditions on a coastal plain environment. The inferred freshwater and terrestrial environments of the Whidbey Formation imply local tectonic subsidence of the regional since the last interglaciation.

Oxygen and hydrogen isotopes were measured in wood cellulose and cellulose-nitrate from trees that grew in different hydrologic settings in southwestern Ontario, Canada. An isotope model that accounts for isotopic fractionations associated with photosynthesis in plants was applied to the stable isotope data to infer past meteoric water isotopic composition and seasonal air moisture variations. The model-inferred climate data was rationalized in terms of the trees' hydrologic environment and weather characteristics of the Great Lakes region. The result is an account of summer and winter conditions in southwestern Ontario for 275 years (1610 to 1885) prior to instrumental climate records. Conditions between 1610 and 1750 are inferred to have been cooler and drier than present. This was followed by a warm-moist climate interval between 1750 and 1885 during which there was an increase in winter precipitation. Cool-dry conditions were recorded instrumentally in this region at the end of the nineteenth century.

Carbon and nitrogen stable isotope analysis of fossil bone collagen reveals that Pleistocene short-faced bears (Arctodus simus) of Beringia were highly carnivorous, while contemporaneous brown bears (Ursus arctos) had highly variable diets that included varying amounts of terrestrial vegetation, salmon, and small amounts of terrestrial meat. A reconsideration of the short-faced bear's highly derived morphology indicates that they foraged as scavengers of widely dispersed large mammal carcasses and were simultaneously designed both for highly efficient locomotion and for intimidating other large carnivores. This allowed Arctodus to forage economically over a large home range and seek out, procure, and defend carcasses from other large carnivores. The isotope data and this reconstruction of Arctodus' foraging behavior refute the hypothesis that competition from brown bears was a significant factor in the extinction of short-faced bears.