Computer reconstructions of the bathymetry of the lake were used to quantify variations in the size and form of Lake Agassiz during its final two phases (the Nipigon and Ojibway phases), between about 9200 and 7700 14C yr B.P. (ca. 10,300–8400 cal yr B.P.). New bathymetric models for four Nipigon Phase stages (corresponding to the McCauleyville, Hillsboro, Burnside, and The Pas strandlines) indicate that Lake Agassiz ranged between about 19,200 and 4600 km3 in volume and 254,000 and 151,000 km2 in areal extent at those times. A bathymetric model of the last (Ponton) stage of the lake, corresponding to the period in which Lake Agassiz was combined with glacial Lake Ojbway to the east, shows that Lake Agassiz–Ojibway was about 163,000 km3 in volume and 841,000 km2 in areal extent prior to the final release of lake waters into the Tyrrell Sea. During the Nipigon Phase, a number of catastrophic releases of water from Lake Agassiz occurred as more northerly (lower) outlets were made available by the retreating southern margin of the Laurentide Ice Sheet; we estimate that each of the four newly investigated Nipigon Phase releases involved water volumes of between 1600 and 2300 km3. The final release of Lake Agassiz waters into the Tyrrell Sea at about 7700 14C yr B.P. is estimated to have been about 163,000 km3 in volume.

Rapidly accumulating Holocene sediments in estuaries commonly are difficult to sample and date. In Chesapeake Bay, we obtained sediment cores as much as 20 m in length and used numerous radiocarbon ages measured by accelerator mass spectrometry methods to provide the first detailed chronologies of Holocene sediment accumulation in the bay. Carbon in these sediments is a complex mixture of materials from a variety of sources. Analyses of different components of the sediments show that total organic carbon ages are largely unreliable, because much of the carbon (including coal) has been transported to the bay from upstream sources and is older than sediments in which it was deposited. Mollusk shells (clams, oysters) and foraminifera appear to give reliable results, although reworking and burrowing are potential problems. Analyses of museum specimens collected alive before atmospheric nuclear testing suggest that the standard reservoir correction for marine samples is appropriate for middle to lower Chesapeake Bay. The biogenic carbonate radiocarbon ages are compatible with 210Pb and 137Cs data and pollen stratigraphy from the same sites.

Post-settlement changes in sediment transport and accumulation is an important environmental issue in many estuaries, including the Chesapeake. Our data show that large variations in sediment mass accumulation rates occur among sites. At shallow water sites, local factors seem to control changes in accumulation rates with time. Our two relatively deep-water sites in the axial channel of the bay have different long-term average accumulation rates, but the history of sediment accumulation at these sites appears to reflect overall conditions in the bay. Mass accumulation rates at the two deep-water sites rapidly increased by about fourfold coincident with widespread land clearance for agriculture in the Chesapeake watershed.

The chronology of Quaternary paleoenvironment and climate in northeastern Siberia is poorly understood due to a lack of reliable numerical age determinations. The best climatic archives are ice-rich permafrost sequences, which are widely distributed in northeastern Siberia. For this study, 230Th/U-ages were determined by thermal ionization mass spectrometry (TIMS) from frozen peat in a permafrost deposit at the southern cliff of the Bol'shoy Lyakhovsky Island (New Siberian Archipelago), west of the Zimov'e River. These yielded a Pre-Eemian “isochron”-corrected 230Th/U-age of 200,900±3400 yr. This result is reliable because permafrost deposits behave as closed systems with respect to uranium and thorium. Our findings suggest that 230Th/U dating of frozen peat in permafrost deposits is a useful tool for the reconstruction of the Middle Quaternary environment of northern Siberia and of the whole Arctic.

Stratigraphic records from coastal cliff sections near the Marresale Station on the Yamal Peninsula, Russia, yield new insight on ice-sheet dynamics and paleoenvironments for northern Eurasia. Field studies identify nine informal stratigraphic units from oldest to youngest (the Marresale formation, Labsuyakha sand, Kara diamicton, Varjakha peat and silt, Oleny sand, Baidarata sand, Betula horizon, Nenets peat, and Chum sand) that show a single glaciation and a varied terrestrial environment during the late Pleistocene. The Kara diamicton reflects regional glaciation and is associated with glaciotectonic deformation from the southwest of the underlying Labsuyakha sand and Marresale formation. Finite radiocarbon and luminescence ages of ca. 35,000 to 45,000 yr from Varjakha peat and silt that immediately overlies Kara diamicton place the glaciation >40,000 yr ago. Eolian and fluvial deposition ensued with concomitant cryogenesis between ca. 35,000 and 12,000 cal yr B.P. associated with the Oleny and the Baidarata sands. There is no geomorphic or stratigraphic evidence of coverage or proximity of the Yamal Peninsula to a Late Weichselian ice sheet. The Nenets peat accumulated over the Baidarata sand during much of the past 10,000 yr, with local additions of the eolian Chum sand starting ca. 1000 yr ago. A prominent Betula horizon at the base of the Nenets peat contains rooted birch trees ca. 10,000 to 9000 cal yr old and indicates a >200-km shift northward of the treeline from the present limits, corresponding to a 2° to 4°C summer warming across northern Eurasia.

Eolian and subaqueous landforms composed of gypsum sand provide geomorphic evidence for a wet episode at the termination of glacial climate in southwestern North America. Drying of pluvial Lake Estancia, central New Mexico, occurred after ca. 12,000 14C yr B.P. Thereafter, eolian landforms on the old lake floor, constructed of gypsum sand, were overridden by rising lake water, modified by subaqueous processes, and organized into beach ridges along the lake's eastern shore. Preservation of preexisting eolian landforms in the shallow lake suggests abupt changes in lake level and climate. Available radiocarbon ages suggest that the final highstand recorded by beach ridges may have developed during the Younger Dryas (YD) stade. The beach ridges provide information about lake surface area, which was 45% of the lake area reached during the maximum highstands of the late Pleistocene. A similar proportional response has been reported for YD climate changes outside the North Atlantic region.

Large heat storage capacity in the western equatorial Pacific has played an important role in modulating global climate. The fluctuation in pollen and spore abundances, together with organic matter (OM) and lithogenics sedimentation, was investigated to reconstruct terrestrial and marine environmental change around New Guinea during the Late Pleistocene. Although appreciable contribution from Indonesian Maritime Continent was expected, the majority of the pollen and spore grains found in core C4402 was transported from New Guinea. Fern spores accounted for 70% (46–90%) of the total pollens and spores. Positive correlation between lithogenic content and the relative abundance of fern spores suggests that lithogenics could be derived from coastal lowland.

The mass accumulation rate (MAR) of pollen and spores varied from 44 to 7,031×10−3 grains cm−2 yr−1 with maxima in oxygen isotope stages (OIS) 2, 3, 4, and around the OIS 4/5 boundary. Less rainfall during glacial times generally enhanced transport of pollen by wind to Site C4402. Their scavenging from the water column was promoted by high activity of the biological pump. Pollen record from core C4402 suggests that lower montane group vegetation was dominant relative to lowland vegetation and upper and mid-montane group during glacial times. Although appreciable contribution by terrestrial OM is expected from high correlation of MAR between organic carbon (OC) and pollen and spores, fairly low COrganic/N ratios and δ13C values (around −20‰) of OM demonstrate that OM in core C4402 is mainly of marine origin.

The woodland-steppe ecotone of the southeastern Inner Mongolian Plateau in northern China is located at the northwestern limit of the Pacific monsoon influence, where the landscape may have been a sensitive recorder of past climatic changes. Physical, chemical, and biological analyses of AMS 14C-dated sediment sequences from two lakes of this region were used to reconstruct the Holocene vegetation and desertification history and distinguish four periods: (1) a cold and humid period from 10000 to 8000 14C yr B.P., (2) a warm and humid period from 8000 to 5900 14C yr B.P., (3) a warm and dry period from 5900 to 2900 14C yr B.P., and (4) a cool and dry period from 2900 14C yr B.P. to the present. The increased aridity during the middle Holocene was likely caused by increased winter temperatures and enhanced winter evaporation. The transition from a humid to an arid climate after ∼5900 14C yr B.P. coincided with enhanced aeolian activity, and deciduous woodlands were replaced by pine woodlands and then by steppes in response to the climatic deterioration. These transitions led to the present desertification. The records suggest that a simple association of thermal and moisture conditions, such as warm/wet or cold/dry, may be misleading.

A newly identified tephra in stratified deposits in southwestern Utah, dated ∼14,000 14C yr B.P., may aid in correlating late Pleistocene deposits across parts of the southern Great Basin and west-central Colorado Plateau. Geochemical analyses of the ash suggest the tephra originated from Mono Craters, California, and most probably correlates with Wilson Creek ash #3. Because the ash is 2 mm thick ∼550 km from its source, the event may have been larger than others correlated to Mono Craters eruptions.

A Late Quaternary sea-level curve for South Africa is presented on the basis of new and published data from a range of sea level indicators and a variety of locations. Available evidence suggests that sea level in South Africa broadly follows that described from the Caribbean but that deviations occur during sea-level highstands. During the last interglaciation (oxygen isotope stage 5) and the late Holocene, coastal emergence produced higher sea levels in South Africa than those identified in the Caribbean during the same time intervals. This is tentatively ascribed to predicted lithospheric deformation in continental margin settings.

Lateral variations in whole-rock and clay geochemistry of basal Bed II claystones in Olduvai Gorge, Tanzania, reflect water quality differences across the Eastern Lacustrine Plain ∼1.75 myr ago. Bulk Ba/Sr and (Na2O+K2O+MgO)/Al2O3 range from 1.4 to 4.2 and from 0.7 to 1.4, respectively, and indicate leaching of lacustrine claystones beneath freshwater wetlands at times following lake retreat. Bulk MgO/Al2O3 (0.3–1.0) and molar Mg/Al (0.5–3.9) ratios of <0.2-μm clays reflect alteration of Mg-rich lacustrine clays. These indicators point to freshest conditions near Locality 43 of Hay (1976; HWK-East; Leakey, 1971), moderate conditions to the east (Locality 40-MCK), and high salinity and alkalinity to the west (Localities 85-VEK, 45-FLK).

Clay geochemistry and artifact abundances are well correlated (r=−0.67, p<0.005), suggesting a relationship between paleo-water quality and hominid paleoecology. This pattern is consistent with predictions of greatest artifact discard/loss around freshwater sources where scavanging opportunities were greatest for hominids. This quantifies a relationship between artifact density distribution and a paleoecological proxy over landscape scales for the first time in Early Stone Age archaeology. In contrast, fossil bone abundance is uncorrelated (r=0.14, p=0.6), reflecting more complex taphonomic processes. Quantitative tests of landscape-scale land-use models are important for understanding early hominid behavior and its evolution.

A 467-cm core (B94/3) from the Alta Babicora basin in the Chihuahuan Desert, northern Mexico (29°N, 108°W), documents lake-level and climate changes over the past ca. 65,000 yr. Chronological control is provided by four accelerator mass spectrometry 14C dates and five U-series dates on diatom silica. The core has been analyzed for magnetic susceptibility, loss-on-ignition, carbonate content, sediment chemistry and mineralogy, and pollen and diatom composition. The basin was occupied by a deep freshwater lake throughout the late Pleistocene which, based on shoreline evidence, was at least 19 m deeper than today. The lake shallowed after ca. 57,000 yr B.P. High variability typified the period between 54,600 and 38,000 yr B.P., probably with periodic desiccation and deflation. A deep-water lake was reestablished after 38,000 yr B.P. and persisted until ca. 29,000 yr B.P. Shallowing occurred through the last glacial maximum, although the lake was still deeper than at present. The Pleistocene–Holocene transition was marked by a distinctive change in the diatom flora. There is no diatom record for much of the Holocene, but other proxies indicate generally dry, stable catchment conditions. The Babicora record is more akin to those from the southwest United States than it is to Central America and northern South America. Wet conditions in the late Pleistocene are attributed to winter rainfall from midlatitudes in contrast to the modern, tropical, summer rainfall regime.

Abundant mammal (45 localities) and plant (52 sections) fossil data collected from the Russian Plain deposits of the Middle Valdai Briansk Interstade indicate a period of noticeable warming. These materials were jointly analyzed. The data were organized in the database software PARADOX and then moved to the GIS program ARC/INFO. Mathematical methods as well as traditional research methods were used for the analysis. The reconstructed biogeographical provinces illustrate the specific environmental and climatic conditions of the Briansk Interstade. Analogues of modern natural zones did not exist at this time on the Russian Plain. The Briansk landscapes reflect the moderate-cool climate of this period, when the majority of northern subarctic plant and mammal species extended their ranges considerably to the south to the Central Russian Plain. At the same time, steppe species penetrated farther north and west. This combination shows that the continuous forest zone was destroyed during the Briansk Inter-stade. Five biogeographical provinces have been reconstructed from the north to the south for the Russian Plain during the Briansk warming on the basis of joint analysis of mammalian and botanical data.

A packrat midden located in the Sierra San Francisco, Baja California Sur, Mexico, dating to ca. 10,200 14C yr B.P., contains remains of California juniper (Juniperus californica) and other taxa now associated with southern California chaparral. California juniper does not occur in the Sierra San Francisco today, although “relict” populations of a few chaparral taxa still occur at higher elevations. This midden record documents the early Holocene occurrence of Baja California coniferous woodland and chaparral vegetation far south of its present distribution or its previously known extent from other fossil records. Based on modern climatic tolerances of California juniper and other taxa, central Baja California experienced a mild Mediterranean-type climate at least 5°–6°C cooler than the climate of today, with at least twice the winter precipitation the region now receives.

More than 30 fossil coleopteran (beetle) assemblages have been recorded from oxygen isotope stage 3 in northern Europe, comprising several hundred identified species. Using the mutual climatic range method for quantifying palaeotemperatures, these assemblages show that the climates of the times can be divided into two distinct interstadial types. One, a short phase of temperate/oceanic climate occurred between 43,000 and 42,000 14C yr B.P. when conditions were not much different from those of the present day. In spite of the temperate climate, trees did not colonize northwestern Europe at this time. Two, both before and after this temperate interlude there were phases of cold/continental climate during which summers were too cold for trees to grow and winters were of Siberian intensity. It is possible that periods of even colder conditions intervened from time to time between the interstadial but, because of the intensity of the cold, biological systems were so inhibited that no fossil evidence for them can be found in northern Europe. Evidence for them must be sought in the fossil records from the warmer parts of southern Europe or in the physical evidence in the Greenland ice cores.

Pleistocene fluvial landforms and riparian ecosystems in central California responded to climate changes in the Sierra Nevada, yet the glacial history of the western Sierra remains largely unknown. Three glacial stages in the northwestern Sierra Nevada are documented by field mapping and cosmogenic radionuclide surface-exposure (CRSE) ages. Two CRSE ages of erratic boulders on an isolated till above Bear Valley provide a limiting minimum age of 76,400±3800 10Be yr. Another boulder age provides a limiting minimum age of 48,800±3200 10Be yr for a broad-crested moraine ridge within Bear Valley. Three CRSE ages producing an average age of 18,600±1180 yr were drawn from two boulders near a sharp-crested bouldery lateral moraine that represents an extensive Tioga glaciation in Bear Valley. Nine CRSE ages from striated bedrock along a steep valley transect average 14,100±1500 yr and suggest rapid late-glacial ice retreat from lower Fordyce Canyon with no subsequent extensive glaciations. These ages are generally consistent with glacial and pluvial records in east-central California and Nevada.

Four data sets yield information about Holocene climatic change in China at different scales of space and time: (a) 120-yr ground temperature and precipitation measurements covering eastern China; (b) two NOAA 10-yr 850 hPa wind records that highlight features of data set a; (c) an 1100-year record of annual calcite accumulation on a stalagmite near Beijing, and (d) Lamb-type average wetness and temperature data from Chinese historical records back to A.D. 1470 and 1450, respectively. Dry–wet fluctuations and cold–warm oscillations are inferred using the long-term stalagmite thickness series. Quasi-70, 140, 450, and 750-yr oscillations have been detected using a wavelet transform technique. A phase relationship between temperature and precipitation oscillations has been identified based on modern observations and historical records. In northern China, relatively lower temperatures correlate with periods when precipitation shifted from above to below normal. Three colder periods during the Little Ice Age (LIA) in China are inferred, centered in the late 14th century (750-yr oscillation), the early 17th century (450-yr), and the 19th century (140-yr). The latest cool period (1950s–1970s) is found at the 70-yr oscillation. Interdecadal drought–flood and cold–warm differences are explained using modern circulation patterns. LIA climate in China was likely controlled by East Asian monsoon circulation anomalies that were affected by variations in continent–ocean thermal contrast.

The dating of the Campanian Ignimbrite (CI) eruption to ∼37,000 cal yr B.P. draws attention to the coincidence of this volcanic catastrophe and the suite of coeval, Late Pleistocene biocultural changes that occurred within and outside the Mediterranean region. These included the Middle to Upper Paleolithic cultural transition and the supposed change from Neanderthal to “modern” Homo sapiens anatomy, a subject of sustained debate. No less than 150 km3 of magma were extruded in the CI eruption, the signal of which can be detected in Greenland ice cores. As widespread discontinuities in archaeological sequences are observed at or following the CI event, a significant interference with ongoing human processes in Mediterranean Europe is hypothesized.