Early and Middle Wisconsin glaciolacustrine sediments exposed at Scarborough Bluffs, Toronto, Canada, contain a low-diversity benthic ostracode fauna dominated by Candona subtringulata and C. caudata. We have studied the oxygen and carbon isotopic compositions of the two ostracode species from the base of the Scarborough section to its top immediately below a Late Wisconsin till. We find an upward decrease in δ18O in both species that is more marked in C. caudata. The shift in δ18O of ostracode calcite from interglacial values of −6 to −8‰, to values of −17‰ immediately below the Late Wisconsin till is the result of (1) lowering of δ18O of the lake as a result of addition of isotopically light meltwater from an advancing and thickening Laurentide Ice Sheet combined with (2) lowering of δ18O of local precipitation entering the lake, due to falling temperatures. In the last stages of the lake, δ18O of the lake water was between −17 and −21‰, corresponding to a lake body composed of between 35 and 55% glacial meltwater. The lake appears to have been isotopically and thermally stratified for part of its history. Differences in δ13C values between C. caudata and C. subtriangulata increase upward in the stratigraphic section. This may record enhanced partitioning of carbon isotopes between surface and bottom waters as a result of increased water depths, photosynthesis by algae, and changes in the input of dissolved organic carbon from the oxidation of organic matter. If the age assessments of these sediments are correct, then these data provide valuable information regarding the isotopic composition of ancestral Lake Ontario and also confirm that the basin was only fully glaciated during the Late Wisconsin.

Results of a high-resolution late-glacial AMS 14C chronology from Rotsee, central Switzerland, have given evidence that the atmospheric radiocarbon concentration was not constant between 13,000 and 9500 yr B.P. This resulted in three marked phases of constant radiocarbon age: at 12,700, at 10,000, and at 9500 yr B.P. New results of a late-glacial varve chronology from Soppensee, central Switzerland, suggest that the younger two phases of constant 14C age each had a duration of ca. 400 calendar years. The length of the late-glacial chronozones has been calculated on the basis of these replicate varve counts and a comparison with their estimated duration in radiocarbon years shows that the estimated duration of the chronozones Bölling (ca. 800 calendar yr vs 1000 14C yr) and Younger Dryas (ca. 900 calendar yr vs 1000 14C yr) agree with the expected time span, whereas the estimated duration of the Alleröd chronozone (ca. 400 calendar yr vs 1000 14C yr) is substantially shorter than expected. Furthermore, a tentative comparison of varve ages and 14C ages suggests that the varve chronology is more than 1000 yr offset toward older ages from the radiocarbon chronology during the late-glacial period.

Holocene marine terraces along 15 km of the northeastern coast of North Island record episodic tectonic uplift. A maximum of seven terraces are arranged in staircase fashion and lie about 20 km above the subduction interface between the Pacific and Australian plates. The highest (T1) corresponds with the maximum of the Holocene marine transgression about 6700 14C yr B.P. Younger terraces are marine abrasion platforms overlain by thin beach deposits. Radiocarbon ages of marine shells from beach deposits indicate that uplift above marine conditions occurred ca. 6700(T1), 5500(T2), 3900(T3), 2500(4), 1600(T5), 1000(T6), and slightly younger than 600(T7) yr B.P. Uplift probably occurred coseismically. The maximum late Holocene uplift rate in the study area is 8 mm/yr. Altitudinal distribution of terraces suggests deformation exists as a ca. 20-km elongate dome, broken at the southern end by the Pakarae fault, which trends across the dome. Rupture on this fault has accompanied the growth of the dome but is not responsible for it. Bathymetric profiling suggests that an active fault, parallel to and about 5 km offshore, is probably responsible for the episodic coastal uplift.

Thermoluminescence (TL) age determinations of alluvial sediments in the tropics are evaluated by comparison with U/Th age determinations of pedogenic accumulations in the alluvium of the lower Gilbert River, a large fan delta in the wet-dry tropics of northern Queensland, Australia. This study extends U/Th dating by applying it not only to calcretes, but also to Fe/Mn oxyhydroxide/oxide accumulations. While a direct correlation cannot be made between U/Th dates from secondary minerals and TL dates from the host sediments, both sets of data show broad consistency. In addition to providing a minima for acceptable TL ages, U/Th dates are useful for determining the chronology of pedogenesis/diagenesis. They show that calcretes and ferricretes have formed under similar climatic conditions in the wet-dry tropics of northern Australia during the late pleistocene. Beneath about 5–12 m the Gilbert fan delta consists of an extensive sand body older than 85,000 yr and probably about 120,000 yr in age, representative of a period of major fluvial activity not repeated since this time. Above are muds and fine sandy muds that extend uninterrupted to the present surface except in the downstream fan where they are bisected by a thin unit of medium sand that TL dates at 40,000–50,000 yr B.P. A system of sandy distributary channels over the fan surface represents an early Holocene fluvial phase probably more active than at present.

A zircon fission-track age of about 400,000 yr B.P. has been determined for the Rockland tephra, a widespread pyroclastic layer in northern California and western Nevada. New ages of zircon separates from both proximal and distal exposures of this layer range from 370,000 to 460,000 yr; ages of the best material provide a narrower range, from 370,000 yr for unwelded ash-flow tuff to 420,000 yr for distal air-fall ash that appears to be uncontaminated by clastic detritus or xenocrysts. Detrital or xenocrystic grains in the ash-flow tuff may have been annealed during emplacement and cooling of the tuff. Detrital and xenocrystic zircons are identified on the basis of their physical characteristics and distinctly older ages. Independent stratigraphic and magnetostratigraphic data constrain the age of the Rockland tephra between 300,000 and 600,000 yr, a range that is compatible with the fission-track age. Zircon grains containing no spontaneous (fossil) tracks are regarded as part of the normal population of comagmatic grains because maximum ages calculated for these grains form a population that mimics the distribution of ages of individual zircon grains that contain fossil tracks; modal ages of both groups fall between 250,000 and 500,000 yr. Induced fission tracks from grains that lack fossil tracks are included in the age calculations, resulting in significantly younger and more coherent dates than would result if these tracks had been omitted, especially those of the finer-grained distal samples.

Four soil chronosequences in the southern Great Basin were examined in order to study and quantify soil development during the Quaternary. Soils of all four areas are developed in gravelly alluvial fans in semiarid climates with 8 to 40 cm mean annual precipitation. Lithologies of alluvium are granite-gneiss at Silver Lake, granite and basalt at Cima Volcanic Field, limestone at Kyle Canyon, and siliceous volcanic rocks at Fortymile Wash. Ages of the soils are approximated from several radiometric and experimental techniques, and rates are assessed using a conservative mathematical approach. Average rates for Holocene soils at Silver Lake are about 10 times higher than for Pleistocene soils at Kyle Canyon and Fortymile Wash, based on limited age control. Holocene soils in all four areas appear to develop at similar rates, and Pleistocene soils at Kyle Canyon and Fortymile Wash may differ by only a factor of 2 to 4. Over time spans of several millennia, a preferred model for the age curves is not linear but may be exponential or parabolic, in which rates decrease with increasing age. These preliminary results imply that the geographical variation in rates within the southern Great Basin-Mojave region may be much less significant than temporal variation in rates of soil development. The reasons for temporal variation in rates and processes of soil development are complexly linked to climatic change and related changes in water and dust, erosional history, and internally driven chemical and physical processes.

Uranium-series methods were used to date and evaluate pedogenic CaCO3 genesis in the Pinacate volcanic field, northwestern Sonora, Mexico. Soils are developed in eolian deposits on lava flows. 230Th/234U dates of pedogenic carbonate are mininum soil ages because of (1) the time needed to yield clasts from flows and to accrete enough carbonate to sample, (2) subsequent additions of uranium, and (3) continued solution and reprecipitation of carbonate rinds. K-Ar dates of basalt flows are maximum soil ages. Maximum and minimum rates of CaCO3 accumulation are calculated from the Th/U dates and K-Ar dates, respectively. The mean maximum rate is 0.13 g CaCO3/cm2/1000 yr and the mean minimum rate is 0.05 g CaCO3/cm2/1000 yr. Least-squares regressions of pedogenic carbonate and clay content and of Th/U ages against K-Ar ages suggest additions to soils from atmospheric sources throughout the late Quaternary. Morphology of pedogenic carbonate and laboratory data for soluble salts indicate that the climate of the Pinacate has not changed significantly during the past 150,000 yr. Soil variability is influenced by proximity of the eolian source. Near the periphery of the Pinacate, carbonate and clay are evenly distributed throughout soil profiles. Within the volcanic field, carbonate and clay are concentrated in soil horizons, suggesting that additions from atmospheric sources are slow enough to allow translocation.

The δ18O value of the carbonate of land snail shells is related to the 18O content of precipitation, which in turn relates to the source region and trajectory of the rain-bearing air masses. Analyses of 18O of the shell carbonate of 76 radiocarbon-dated Holocene samples of the land snail Trochoidea seetzeni from the northern Negev Desert in southern Israel were carried out and the results were compared to modern snails from the same region. Early Holocene δ18O values are similar to modern but during the period centered around 6500-6000 yr B.P., a depletion of some 2%. below modern is observed. A change in the atmospheric circulation pattern for this period is thus indicated, most likely an increase in the frequency of storm systems reaching the region from north-eastern Africa. By 3500 yr B.P., δ18O values had reached modern levels and indicate a stable pattern of atmospheric circulation since that time.

Packrat middens from the McCullough Range, in the southeastern Mojave Desert of Nevada, record vegetation conditions during the periods 6800 to 5060 yr B.P. and 1250 yr B.P. to present. Their age and location are ideal to test for middle Holocene aridity; the period between 6800 and 5060 yr B.P. does appear to have been more arid than during the late Holocene period of record. This agrees with other evidence for middle Holocene aridity from the Southwest. Arguments for strengthened middle Holocene monsoons in the region are based chiefly on packrat midden samples older than 7500 yr B.P., or on samples that are younger than 5500 yr B.P. Simulations of 6000 yr B.P. climate that fail to show strong subtropical flow into the Southwest are therefore supported by evidence for enhanced aridity in that region.

At the Murray Springs Clovis site in southeastern Arizona, stratigraphic and geomorphic evidence indicates that an abnormally low water table 10,900 yr B.P. was followed soon thereafter by a water-table rise accompanied by the deposition of an algal mat (the “black mat”) that buried mammoth tracks, Clovis artifacts, and a well. This water-table fluctuation correlates with pluvial lake fluctuations in the Great Basin during and immediately following Clovis occupation of that region. Many elements of Pleistocene megafauna in North America became extinct during the dry period. Oxygen isotope records show a marked decrease in δ18O correlated with the Younger Dryas cold-dry event of northern Europe which ended 10,750 yr B.P., essentially the same time as the water table began to rise in southeastern Arizona. Clovis hunters may have found large game animals easier prey when concentrated at water holes and under stress. If so, both climate and human predation contributed to Pleistocene extinction in America.

Cross-sectional topographic profiles of lateral moraines formed during different glaciations were measured at Lee Vining Canyon, California, to determine whether the degree of moraine degradation could be quantified and used for relative dating. Logarithmic plots of the value of a slope parameter against cross-sectional area show distinct linear trends for moraines of different relative ages. The slopes of these trends suggest that the degradation processes are not among those that can be modeled with the linear diffusion equation.

Pollen studies of marine sediments from Atlantic deep-sea core V22-196 (13°50′ N-18°57′ W; 3728-m water depth) are used to reconstruct paleoclimates of north tropical west Africa since 140,000 yr B.P. High concentration of pollen, mainly from Saharan and arid littoral zones suggests a strengthened tradewind circulation since ca. 60,000 yr B.P. that became even stronger after 40,000 yr B.P. and reached a maximum 17,000 yr B.P. Periods of eolian transport of pollen to the Atlantic occurred about 94,000 and 105,000 yr B.P. and during Termination II. Conversely, high relative values of pollen from Sudanian and Guinean zones and from Mangrove and freshwater vegetation, coincident with maxima of dinocyst concentration, are interpreted as reflecting both strong fluvial inputs and the expansion of humid vegetation on the adjacent continent during wet periods dated between 140,000 and 118,000, 105,000 and 96,000, 92,000 and 73,000, 52,000 and 44,000 yr B.P. and 12,000 yr B.P. and the Holocene. The strong correlation of these results from the eastern tropical Atlantic with those from the Arabian Sea corroborates fluctuations of monsoon climate.

A general circulation model (GCM) of the ocean is used to study the effects of changes in the monsoon winds of present day and 9000 yr B.P. on the upwelling in the Arabian Sea. The vertical transport from the ocean GCM is used as a measure of upwelling strength to assess the relative abundance of Globigerina bulloides at present and 9000 yr B.P., during the climatic optimum. The high abundance of G. bulloides at 9000 yr B.P. is probably a result of a doubling of the vertical transport at that time.