Analyses of Quaternary landscape evolution tend to focus on events associated with culminations of glacial and interglacial ages, but for most of Quaternary time, environments were intermediate in character. Average Quaternary glacial conditions, based on assessment of the marine isotope record, approximated those near the stage 2/stage 1 transition and during substages 5b and 5d; isotope stages 3 and 4 and substages 5a-d lie within one standard deviation of the mean value. Under average glacial conditions, ice sheets lying over northern North America and Europe were much more contracted than their full-glacial counterparts, and the distribution of mountain glaciers reflected a snowline depression of some 500 m. Geomorphic processes operating under average Quaternary conditions contributed importantly to landscape evolution. Examples of landscapes that may represent such average conditions include cirques and fluvial deposits of the Pacific Northwest, the fjords and strandflat of western Norway, and atolls of the tropical oceans. By examining the geologic record from the perspective of average conditions, rather than those of climatic extremes, added insight can be gained regarding the evolution of Quaternary landscapes.

Direct information on the isotopic composition and timing of the now-vanished Laurentide glacier can be found in subglacial calcite or in early diagenetic concretions from glaciolacustrine deposits. Th/U isotopic measurements on early diagenetic concretions frome Lake Deschaillons varves (St. Lawrence Lowland, Québec) date the early Wisconsinan major ice advance at ca. 80,000 yr (isotopic stage 5a/4 transition). Significant retreat occurred at ca. 46,000 yr (isotopic stage 3) as indicated by Th/U isochrones on early diagenetic concretions from Lake Gayhurst varves in the Appalachian foothills of Québec. During the maximum extension of the ice, which is dated at ca. 22,000 yr by Th/U measurements on subglacial calcite at Cantley (northern margin of the St. Lawrence Lowland), δ18O values (vs PDB) ranging from −16/−19‰ (surficial ice) to ca. −30‰ (basal ice) are inferred for the Laurentide ice isotopic composition. Superimposition of two phases of carbonate precipitation does not prevent the establishment of their respective age and isotopic composition through correlation of independent parameters and calculation of mixing lines.

During the latest Quaternary, freshwater pluvial lakes intermittently formed in the topographically closed Willcox basin, Arizona. A lacustrine sequence of six separate high stands of Lake Cochise is documented by stratigraphic studies, 19 radiocarbon ages, and supplementary evidence. Two stands of pluvial Lake Cochise, older than 14,000 yr B.P., reached elevations above 1290 m. The prominent 1274-m shoreline of Lake Cochise, which circumscribes the basin, was largely created during a high stand between 13,750 and 13,400 yr B.P. During the Holocene, water filled the Willcox basin three times to an elevation slightly below the crest of the 1274-m shoreline. This occurred once during the early Holocene around or before 8900 yr B.P. and twice during the later part of the middle Holocene. Since the middle Holocene, only shallow ephemeral lakes have occupied the deflated central portion of ancient Lake Cochise, a depression known as the Willcox Playa. The lacustrine sequence of Lake Cochise provides an independent evaluation of late Quaternary paleoclimatic reconstructions for southern Arizona and the American Southwest.

Twenty samples of artifactual ostrich eggshell and hearth charcoal, firmly to loosely associated with basinal lacustrine, playa, and sand sheet sediments in the Dakhleh Oasis region of south-central Egypt, yield radiocarbon ages between ca. 8800 and ca. 4700 yr B.P. The sediments record variable sedimentary responses to an early Holocene pluvial interval in this virtually rainless region. Differences of hydrogeology and morphometry among and within basin types complicate paleoclimatic interpretation.

Variation in the size of lakes in the Lahontan basin is topographically constrained. River diversion also has played a major role in regulating lake size in Lahontan subbasins. The proper gage of lake response to change in the hydrologic balance is neither lake depth (level) nor lake volume but instead lake-surface area. Normalization of surface area is necessary when comparing surface areas of lakes in basins having different topographies. To a first approximation, normalization can be accomplished by dividing the paleosurface area of a lake by its mean-historical, reconstructed surface area.

The timing of deglaciation in the Lake Agassiz basin is critical in establishing the routing of meltwater and precipitation runoff from a 2,000,000-km2 region of central North America and in evaluating the influence this water had on rivers and oceans into which it drained. Dates of 12,400 ± 420 and 12,100 ± 160 yr B.P. for moss at the Rossendale site in Manitoba have long been a key for those advocating an “early” deglacial chronology in this region. However, new dates for wood from this site and paleoecological interpretations of ostracods, molluscs, and the dated moss all support a “young” deglacial scenario. Of particular significance is the fact that the dated moss, Scorpidium scorpioides, is a subaquatic type subject to contamination by old carbon dissolved from bedrock. In fact, most subaquatic moss may be unreliable for radiocarbon dating. For these reasons, the 12,400 and 12,100 yr B.P. dates are rejected. New dates of 9600 ± 70 and 9510 ± 90 yr B.P. for wood from the same organic-rich unit containing the dated moss, ostracods, and molluscs fit well with the “young” deglacial chronology of the southwestern Laurentide ice margin advocated by many. In short, the ice margin appears to have retreated into the southern Lake Agassiz basin after 12,000 yr B.P. and north of the Rossendale site by 11,000 yr B.P. About 10,000 yr B.P., following the Moorhead low-water phase, Lake Agassiz rose to the Campbell level. The dated organic matter at Rossendale was deposited in a lagoon behind the Campbell beach.

Numerical and calibrated age determinations of the late Quaternary alluvial fan deposits of the Soda Mountains piedmont in the Mojave Desert provide an opportunity to study the utility of the multiparameter relative-age (RA) method for distinguishing and mapping geomorphic surfaces on a desert piedmont. Most RA parameters could not discriminate between deposits of Holocene age, although pavements have formed over locally significant parts of surfaces as young as middle Holocene. Several parameters, including lithologic composition, particle size, soil development, and varnish cover, permit distinguishing between Holocene surfaces and late Pleistocene surfaces. Statistically significant differences in initial particle size and lithology of the deposits, inferred to be the result of complex interaction among hillslope, alluvial fan, and eolian processes and climatic change, create conditions unfavorable for use of most RA techniques. In contrast, soil-profile development and varnish cover data are successful in discrimination among deposits of Holocene and Pleistocene age. This is attributed to the development of pedogenic features and varnish that are strongly dependent on dust influx and to the relatively minor dependence of these features on differences in the depositional character of the fan.

When considering the formation of tunnel valleys, most researchers have appealed to basal melting as the primary source of water. Erosion of the tunnel valleys can then be accomplished by steady-state drainage over a long period or by storage and subsequent catastrophic release. However, field relationships in a large system of tunnel valleys formed by the Superior lobe in central Minnesota indicate that another source of water must be considered. The Minnesota tunnel valleys are composed of individual segments 10–20 km long, and the segments commonly terminate in subaerial outwash fans at recessional ice margin positions. Eskers, associated with the tunnel valleys, are also composed of short segments, frequently beginning at moulin kames and terminating at the head of outwash fans. The dominant source of the water responsible for tunnel-valley formation was seasonal meltwater from the glacier surface that reached the bed through moulins and crevasses. The apparent continuity of the valleys resulted from the headward development of the englacial drainage system during ice retreat.

Discovery in 1980 of Camp 18 of the 1930 Bagnold expedition in northwestern Sudan has resulted in an exceptionally long record of barchan movement from which an average rate of 7.5 m/yr has been calculated. Measurements of the rate of dune advance since 1980 have not varied significantly, indicating a state of quasiequilibrium exists. The dune field is moving over an undulating sand sheet exhibiting various stages of Holocene pedogenesis and containing Neolithic sites. The sand sheet overlies Pleistocene alluvium with stronger stages of pedogenesis. All of these deposits may be a significant source of dune sand. Wind-blown grass fragments trapped by advancing slipfaces mark former slipface positions and indicate late Holocene rainfall events, which can be radiocarbon dated. Parabolic forms (revealed by SPOT images) at the windward ends of the dune fields are transitional to barchans, suggesting sand accumulation in vegetation germinated during a Holocene wet period. In addition, sand streaks from sand-sheet undulations suggest that active eolian erosion of sand sheets contributes to the sand supply of dune fields. Pedogenesis during pluvial periods contributes to silt and clay fractions of bimodal sand sheet sediments. From wind streaks on LANDSAT images and an estimated average rate of dune advance, positions of dune fields during past hyperarid periods can be estimated.

The rates of CaCO3 formation in desert soils of the American Southwest are highly variable and potentially useful in estimating the age of soil profiles. The objective of this study was to examine the correlation between the long-term rate of CaCO3 formation (LTR) and modern mean annual precipitation (MAP) and temperature (MAT). LTR is not significantly related to temperature but is linearly related to MAP [LTR = 0.0150(MAP − 37), r 2 = 0.924]. The slope of the regression is significantly different from 0.0 and is equivalent to a calcium concentration of 6.0 mg liter−1 in rainfall. However, the intercept term, which suggests a lower limit of precipitation for CaCO3 formation of 37 mm, is not significantly different from 0.0. The LTR-MAP relationship may be useful in estimating the age of soil profiles by the CaCO3 method in the desert Southwest.

A sequential method for quantitative identification of sediment source components, based on magnetic measurements, has been developed and tested for sediments from the Rhode River, Maryland. Simulated mixing tests and multiple regression were employed to establish numerical relationships between source component proportions and the magnetic measurements of mixtures. On the basis of these multivariate mixing models, source components of three estuarine sediment cores were estimated by linear programming. The results strongly support the previous studies on this catchment which indicated a dramatic change in sediment source some 150 to 200 yr ago. Quantitative calculations are more useful and informative than purely qualitative descriptions.

A dense network of 3.5 kHz and Uniboom seismic profiles revealed the geological evolution of the Ierissos-Alexandroupolis Shelf area of the northern Aegean during the latest sea-level rise. Near the end of the Pleistocene, ca. 14,000 yr B.P., the sea was at about − 120 m, and almost 5300 km2 of shelf was exposed to subaerial erosion. Two permanet lakes existed in the Ierissos and Kavalla Gulfs, as well as a number of ephemeral lakes scattered throughout the rest of the area. Kavalla Gulf was drained by the Nestos River which joined the Strymon River at the outer Strymonikos Plateau. On the flat Samothraki Plateau were dune fields, marshes, and a number of minor seasonal rivers, while the Evros River flowed east of the plateau. By ca. 13,000 yr B.P. the sea had risen to − 70 m and covered 30% of the previously exposed shelf. The lakes at Ierissos and Strymonikos Gulfs were shallower and the sea approached to within about 5 km of them. Kavalla Gulf and the adjacent eastern Strymonikos Plateau lay 10 m above sea level, while the sea intruded along river mouths at the Samothraki Plateau. During this transgression of the sea river-bed gravels and sands were covered by silts and clays. At the Pleistocene-Holocene transition, ca. 10,500 yr B.P., the sea lay at about − 50 m and in areas of steep slope the coast was close to its present position. At Kavalla Gulf, the sea advanced along the paleochannel of the Nestos River, and the island of Samothraki was separated from the mainland. By ca. 7500 yr B.P. the sea was only 15 m below its present level and the northeastern Aegean shelf assumed nearly its present morphology. The Nestos River changed course to the east and Thassos Island was separated from the mainland. Coarse sediment formed wedges nearshore, whereas fine-grained sediments were distributed widely by current action. In many areas, relict sediments are present.

The Pilliga Sandstone region of the northwest slope of New South Wales has a natural vegetation cover of sclerophyllous relatively closed to open forests with a largely heathy understorey, and a warm, subhumid and continental climate. Pollen analysis of spring-fed deposits gives a vegetation history extending from at least 30,000 yr B.P. to the late Holocene. Tree pollen became scarce after about 25,000 yr B.P. and an assemblage dominated by Chenopodiaceae, Liguliflorae, Tubuliflorae, and probably Poaceae developed. No similar assemblage is known from present pollen rain studies carried out in Australia. However, it clearly represents a treeless open shrub-steppe formation and therefore an arid or semiarid environment. The site thus provides evidence of an eastward late Pleistocene extension of the arid zone in Australia, and is the first full-glacial vegetation record between 20° and 35° latitude in Australia. The present vegetation cover did not become reestablished until the beginning of the Holocene, which raises questions about the form in which Pilliga Sandstone vegetation survived full-glacial conditions.

Eight marine transgressions have been recognized from more than 30 deep drill holes (ca. 300 m deep) through Quaternary sequences in the Yangtze River delta region. These are, in ascending order, the Rugao and Zhoupe transgressions (early Pleistocene); the Shanghai, Jiading, and Wangdian transgressions in the middle Pleistocene; the Jiangyin and Gehu transgressions in the late Pleistocene; and the Zhenjiang transgression in the Holocene. The transgressions correspond to warm periods and regressions to cold periods. The younger transgressions were not only of shorter duartion, but also of larger magnitude. The findings verify that there were five moderately warm periods during the early to middle Pleistocene and two very warm periods during the late Pleistocene in the Yangtze River delta region.

Many proxy indicators of past climate integrate the effects of temperature and precipitation, and not all indicators integrate these effects in the same way. This poses a problem in the reconstruction of past climate. A study of the response of tree growth around Lake Superior and the water supplies to that lake to summer climate shows differences and similarities in response. Tree growth is positively correlated with precipitation—although the response is reduced when conditions are very wet—and negatively correlated with temperature. In contrast, the water supplied to the lake are positively correlated with both precipitation and temperature; the correlation with temperature is, however, not very strong. Multiple regression models developed to assess the relative magnitudes of the similarities and differences show that the similarity in response to precipitation accounts for about 30% of the variance in water supplies, the nonlinear response of trees—represented by a log transformation—accounts for an additional 15%, and the difference in response to temperature is equivalent to about 30% of the variance in water supplies.

White-tailed deer (Odocoileus virginianus) from central Illinois varied in size during the Holocene. The record, which extends back to 8450 yr B.P., indicates small deer through the mid-Holocene until 3650 yr B.P., after which size increases. Although influences of winter climate, seasonality, anthropogenic effects, and other ecological factors should not be discounted, an intriguing possible cause of the deer size shifts is insolation-driven summer climate and its influence on food resources. In the Holocene, small deer size is correlated with high summer insolation and with low winter insolation. Climatic models indicate that in spite of changes in insolation, Holocene winters did not vary greatly through time, especially in contrast to summers, which were dynamic. Physiological constraints peculiar to O. virginianus make critical the quality of summer forage for determining final adult size. Summer temperature averaged 2°C warmer than present during the middle Holocene, which increased evaporation and probably reduced the period of availability of high-quality forage low in fiber and high in protein. Consequently, less fuel for growth was consumed by mid-Holocene deer and only small body size was achieved. Other possible causes (e.g., Bergmann's rule, seasonality) of clinal variation are considered with reference to central Illinois deer, but at present the most parsimonious explanation appears to be the summer insolation hypothesis.

Late-Quaternary paleoecological and glacial evidence from the higher latitudes of the Southern Hemisphere implies overall uniformity of large-scale glacial and interglacial climatic fluctuations for the past 40,000 yr. Climate of the last glacial maximum, variously dated between 30,000 and 11,000 yr B.P., was relatively cold and dry compared with the warmer, more humid climate of the Holocene and the interstade preceding the last glacial maximum. Conditions were apparently coldest during millennia centered around 20,000 yr B.P. and warmest in the early Holocene. Recorded small-scale fluctuations, frequently variable for any given time interval, are less consistent. A cold late-glacial episode, estimated as occurring between ca. 13,000 and 11,000 yr B.P. in Antarctica, possibly was coeval with the Younger Dryas Stade in northwestern Europe and may be correlative with a climatic episode in southern South America and perhaps in New Zealand and South Georgia; however, there is no evidence for the event in Tasmania. General atmospheric circulation models for the polar latitudes at the time of the last glacial maximum show an intensification of the southern westerlies, apparently a result of the expansion of ice cover in Antarctica and of sea ice in the Southern Ocean.

Pedogenically significant chemical extracts of iron, aluminum, and phosphorus are related mainly to time in chronosequences from Baffin Island (Canadian Arctic), the alpine Sierra Nevada and Wind River Range (western United States), the alpine Khumbu Glacier area (Himalaya, Nepal), and the alpine Southern Alps (New Zealand). Based on the accumulation index for Fe and Al, and the depletion index for P in each region, the following ranking of chemical pedogenic development is obtained: Southern Alps > Khumbu Glacier area ≅ Wind River Range > Sierra Nevada > coastal Baffin Island > inland Baffin Island. The ranking mainly follows regional climate, with the greatest accumulation and depletion to the warmest and wettest environment, and the least accumulation and depletion in the coldest and driest environment.

Three sites on the Point Reyes Peninsula, California, provide evidence of major environmental change during the Pleistocene-Holocene transition. A 12,300-yr-long pollen record from Coast Trail Pond reveals a change from closed canopy Pseudotsuga-Abies forest to coastal scrub and grassland about 10,000 yr B.P. The same change is also evident in pollen records from two sea cliff exposures that contain a series of buried soils interstratified with fluvial and debris-flow deposits. Eight radiocarbon dates from these exposures indicate that aggradation at both sites began ca. 12,000 yr B.P. and that the change from forest to scrub and grassland occurred between 10,300 and 9400 yr B.P. High percentages of alder pollen and bracken fern spores reflect repeated geomorphic disturbance at ca. 10,400 yr B.P. The occurrence of major aggradation accompanied by recurrent debris flows between ca. 12,000 and 10,000 yr B.P. suggests that this was a period of more frequent high-intensity storms.

Radiocarbon dating of bulk sediments has been the standard method for establishing chronologies in the studies of lake sediment cores which have contributed significantly to our knowledge of late Quaternary paleo-environments. These bulk sediment dates are presumed to be direct ageindicators for the speciments (e.g., pollen or macrofossils) which are actually being studied. However, several recent studies have reinforced long-standing apprehensions concerning this presumption. In this study, we demonstrate for the first time the radiocarbon dating of pollen concentrate samples by accelerator mass spectrometry. The dates obtained by this method should provide more reliable radiocarbon chronologies for paleo-environmental studies than have been obtainable by bulk sediment dating.