Pollen analysis of a 15.5-m sediment core from Lake Naivasha, central Rift Valley of Kenya, reveals that the vegetation from before 20,290 to nearly 12,000 yr B.P. was dominated by open grassland, indicating arid conditions. Within this period a moderately wetter climate existed between 17,000 and 15,000 yr B.P., shown by relatively slight increase in both the montane and lowland forest vegetation. From approximately 12,000 to 6500 yr B.P., a change toward more trees and forests started at lower altitudes around the basin of Lake Naivasha, and later in the higher montane regions. After 6000 yr B.P. a decline in forest and lowland trees opened the vegetation into more grasslands and by 4000 yr B.P. a vegetation similar to the present was attained and has persisted to the present. During this period shallow-water aquatic plants became abundant in Lake Naivasha.

Thermoluminescence (TL) age estimates have been obtained on coarse-grained detrital feldspar from Eemian beach sand (substage 5e), early Weichselian dune sands (substages 5d and 5b), and pre-Eemian beach sand. The past radiation dose is obtained using the additive dose method. Even for the oldest samples, which date to 300,000 yr B.P. by other methods, the TL signal is not in saturation and can be doubled by the addition of laboratory radiation doses without saturation being achieved. This is contrasted with the behavior of polymineral, silt-sized grains from loess in the adjacent area. The TL age estimates are systematically underestimated by about 40% when compared with the expected geological ages. However, they are in correct stratigraphic order and demonstrate that stage 5 beach deposits can be distinguished from those resulting from earlier high sea levels using TL signals from potassium feldspars.

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.

The Makatea Islands in the southern Cook Islands consist of a degraded volcanic core surrounded by emergent “makatea” limestones. While much of this reefal limestone is of Tertiary age, the seawardmost reefs are late Pleistocene. Last-interglacial reefs (oxygen isotope substage 5e) identified by U-series dating reach 12.2 m on Atiu (mean age of three samples 126,000 ± 5000 yr B.P.), 9.8 m on Mitiaro (mean age of five samples 119,000 ± 3000 yr B.P.), 10.0–12.7 m on Mauke (mean age of four samples 128,000 + 5000, −4,000 yr B.P.), and 14.5–20.0 m on Mangaia (mean age of four samples 115,000 ± 7000 yr B.P.). On Atiu, Mauke, and Mitiaro a lower reef unit has been identified, and is separated from the overlying substage 5e reef by a sharp discontinuity, often with a crust of coralline algae. U-series dating from Atiu and Mauke indicates that this is a stage 7 reef formed in the penultimate interglaciation. The Makatea Islands have emerged as a result of flexure of the lithosphere in response to loading by the Pleistocene volcanic island of Rarotonga. Isolated outcrops of makatea limestone on Rarotonga reach 3.5 m and are probably of substage 5e age. Elastic and viscoelastic models of lithospheric flexure predict that much of the compensatory movement should occur shortly after the emplacement of the load. However, the age and elevation of late Quaternary reefs on the southern Cook Islands, where a Pleistocene volcanic island has loaded relatively old ocean floor (>80 myr), indicate that differential uplift has been continuing over the last 250,000 yr.

Detailed morpho- and lithostratigraphic investigations, allied with radiometric dating, in the Voidomatis basin, Epirus, northwest Greece, have identified four Quaternary terraced alluvial fills that range from middle Pleistocene to historic in age. Major-periods of alluviation during the late Quaternary were associated with valley glaciation (ca. 26,000–20,000 yr B.P.) and subsequent deglaciation (ca. 20,000–15,000 yr B.P.) in the Pindus Mountains during Late Würmian times, and more recently linked to overgrazing sometime before the 11th century AD. The late Quaternary alluvial stratigraphy of the Voidomatis River is more complex than the “Older Fill” and “Younger Fill” model outlined previously, and it is suggested that these terms should no longer form the basis for defining alluvial stratigraphic units in the Mediterranean Basin.

Corals from raised reef terraces on two islands (Zabargad and Northern Brother), considered to have been tectonically uplifted in connection with the Red Sea rifting, were dated with the U-series method. At Zabargad, there are at least three systems of raised coral reefs. The oldest terrace (>290,000–300,000 yr B.P.) is found at +10 to +15 m. A 200,000 yr B.P. high-sea stand is recorded by a terrace relict at +17 m on peridotite bedrock; the youngest system (125,000–138,000 yr B.P.) is very well represented around the island, with terraces at about +6 to +8 m. Corals from Northern Brother yield ages of 132,000–135,000 and 204,000 yr B.P. suggesting the existence of two systems of interglacial raised reefs. Both islands appear to have been tectonically quite stable since at least 125,000 yr B.P.

The characteristics of a new type of rock varnish from the hyperarid coastal deserts of northern Peru, combined with laboratory experiments on associated soil materials, provide new insights into the formation of rock varnish. The Peruvian varnish consists of an Fe-rich, Mn-poor component covering up to 95% of a varnished surface and a Fe-rich, Mn-rich component found only in pits and along cracks and ridges. The alkaline soils plus the catalytic Fe oxyhydroxides that coat much of the varnish surfaces make the Peruvian situation ideal for physicochemical precipitation of Mn. However, the low Mn content of the dominant Fe-rich, Mn-poor component suggests that such precipitation is minor. This, plus the presence of abundant bacteria in the Mn-rich varnish and the recorded presence of Mn-precipitating bacteria in varnish elsewhere, suggests that bacteria are almost solely responsible for Mn-precipitation in rock varnish. A set of experiments involving Peruvian soil samples in contact with water-CO2 solutions indicates that natural fogs or dews release Mn but not Fe when they come in contact with eolian materials on rock surfaces. This mechanism may efficiently provide Mn to bacteria on varnishing surfaces. The lack of Fe in solution suggests that a large but unknown proportion of Fe in varnish may be in the form of insoluble Fe oxyhydroxides sorbed onto the clay minerals that form the bulk of rock varnish. The results of this study do not substantively change R. I. Dorn's paleoenvironmental interpretations of varnish Mn:Fe ratios, but they do suggest areas for further inquiry.

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.

Multiple stratigraphies of subtropical South Atlantic cores reveal significant stratigraphic discrepancies between the nannofossil and the foraminiferal carbonates. Variations in the stratigraphic signals carried in the nannofossil-dominated <38 μm fraction and foraminifera-dominated >38 μm fraction were measured with detailed stratigraphies of δ18O, δ13C, 14C, grain size, percentage carbonate, percentage aragonite, and taxonomic composition across the last deglaciation in INMD box core 111 No. 9. Three other cores (INMD box cores 113 and 115, and V 22–174), also from the shallow flanks of the mid-Atlantic ridge in the South Atlantic (10°–17° S), contain similar stratigraphies indicating that these cores represent regional patterns. The onset of the deglacial δ18O shift in foraminiferal carbonate occurs 6 to 20 cm deeper than the δ18O shift in the nannofossil fraction. Nineteen accelerator mass spectrometer 14C dates of various fractions (<38 μm, 38–62 μm, 62–150 μm, 150–250 μm, >355 μm, and G. ruber) from INMD Box 111 show that the components within an individual core slice may differ by up to 4900 14C years. Twelve traditional 14C dates (determined by beta counting) of the >38 and <38 μm fractions from six levels in INMD Box 111 No. 6 confirm the large offsets. The observed isotopic offsets are not explained by an individual process, and suggest that multiple causes have left a lumpy stratigraphic record. However, the variability in the data illustrates the difficulty in accurately measuring the chronology of deglaciation, reopens the question of which components of pelagic sediment best monitor surface water conditions, and complicates the direct interpretation of benthic-planktonic age differences in terms of ocean ventilation changes.

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.

January Cave, in the Rocky Mountains of southwestern Alberta, has yielded vertebrate remains from a coprocenosis of mid-Wisconsinan-age. Taphonomic analysis indicates accumulation by raptors, mostly owls, and mammalian carnivores. The vertebrate record, together with pollen analysis, indicates that cool, dry conditions prevailed in an extensive tundra-like environment, with prairie elements in the valleys below. Thirty-four mammalian taxa have been recovered from January Cave. Today, some of these species (e.g., Lemmus sibiricus and Dicrostonyx torquatus) do not coexist with others (e.g., Cynomys sp., Mustela nigripes, Vulpes velox, and Lagurus curtatus). Therefore, the January Cave local fauna represents a “nonanalog” mammalian community characteristic of the late Pleistocene. It suggests that the region enjoyed an equable climate, with reduced climatic extremes but still cool, further supporting a mid-Wisconsinan age estimate for the fauna. It is the first major, small vertebrate fauna of its age to be reported from Alberta.

Distributions of freshwater and brackish-water diatoms from dust samples and modern sediments of the equatorial Atlantic demonstrate different transport mechanisms and source areas. Both Melosira spp. and Stephanodiscus spp. are transported via winds from the southern Sahara and Sahel in Northern Hemisphere winter. The core-top distribution of Cyclotella striata delineates the extent of the low-salinity plume formed by runoff from the Zaire River into the extreme eastern Atlantic. The transport mechanism and source areas for Melosira spp. during arid phases have not changed appreciably in the last 130,000 yr. There is no evidence for long-distance transport of freshwater diatoms by the southeast trade winds. This study confirms the validity of paleoclimatic research which inferred eolian transport of Melosira spp. in the winter dust plume from source regions north of the equator, although fluviatile input of Melosira valves into nearshore sediments cannot be ruled out.

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.

A 20-cm-thick volcanic ash layer at the Palisades along the Yukon River is geochemically correlated with the Old Crow tephra. A buried organic and wood-rich layer above the Old Crow tephra probably records the last interglaciation. The recognition of the Old Crow tephra provides the first chronologic information on the age of the thick sequence of Pleistocene sediments at the Palisades, an important ice-age mammal site in central Alaska and a key locality for the reconstruction of the history of the Yukon River and the last interglaciation in central Alaska.

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.