Most studies of alpine glacial history have concentrated on terminal moraines, but such moraines provide dates only for maximum extents of glaciers. Some lateral moraines have the potential for providing more complete glacial histories, because deposition by distal-flank accretion may result in sequences of stacked tills. Interpretation is aided by (1) the approximation that any continuous surface within the moraine parallel to the moraine's distal flank is isochronous, (2) inset gulley-fill deposits, which provide information on ice-margin history, and (3) incorporated organic material which can be radiocarbon dated. Lateral moraine stratigraphy of Bugaboo Glacier in southeastern British Columbia suggests that the glacier was fairly close to its maximum Neoglacial extent about 2500 14C yr B.P. A slow general expansion punctuated by at least one minor retreat continued from that time and culminated probably in the last century.

Marine molluscan shells from para-type and other localities of the Holsteinian interglaciation were dated by Th/U and the electron spin resonance (ESR) method to more than 350,000 and 370,000 yr B.P., beyond the limit of Th/U dating. The high age estimate is corroborated by a K/Ar age of 420,000 yr B.P. determined from volcanic ash near the base of the Ariendorf paleosol in the Middle Rhine valley believed to be a pedostratigraphic equivalent of the Holsteinian. Shells from the Herzeele marine unit III, an equivalent of the Wacken (Dömnitz) warm stage in northern France and subsequent to the Holsteinian, revealed ages between 300,000 and 350,000 yr B.P. A correlation of these two warm stages with marine oxygen-isotope stages 11 and 9 on the SPECMAP and CARTUNE time scales is suggested. From the benthic oxygen-isotope record one may infer that no exceptionally high global sea-level rise corresponds to the large transgressions of the Holstein Sea in northern Germany. Therefore, a significant proportion of the transgression was probably the result of an unusually large local glacial-isostatic depression caused by the extreme buildup of ice during the preceding Elster glaciation (stage 12). According to the deep-sea record, it lasted approximately 50% longer than the subsequent cold stage 10. The outstanding soil formation with Braunlehm and the well-developed thermal optimum of the Holsteinian are tentatively related to a phase of minimum sea-ice cover in the Norwegian-Greenland Sea, as deduced from long benthic carbon-isotope records from the central Atlantic.

Holocene prograded coastal sequences at Becher/Rockingham, southern Western Australia, contain a detailed record of sea level over the last 6400 yr. Radiocarbon dating and use of a distinct stratigraphic indicator as a sea-level marker permit reconstruction of sea-level history and suggest that the sea was at least 2.5 m above present datum about 6400 yr B.P. before falling to its present level. No evidence was found for eustatic fluctuations of the scale proposed by R. W. Fairbridge [1961, in “Physics and Chemistry of the Earth” (L. H. Ahrens, F. Press, K. Rankema, and S. K. Runcorn, Eds.), Vol. 4, pp. 99–185, Pergamon, Oxford]. The sea-level record preserved on this coast can be explained by hydro-isostasy, tectonism, or eustasy, acting individually or in concert. Without a fixed reference point or analogous data from other locations, a firm conclusion on which mechanism(s) has(have) operated could not be reached. Published sea-level data from this and other coasts are often insufficiently detailed to compare with this study. Application of the techniques of this study to analogous sedimentary sequences elsewhere will provide data of comparable accuracy that would contribute to a more precise understanding of relative sea-level movements in the late Quaternary.

Groundwater from the Ojo Alamo and Nacimiento aquifers in the central San Juan Basin. New Mexico, has yielded 14C ages ranging from modern to 35,000 yr B.P. The Pleistocene-age samples are characterized by a stable isotope content about 25‰ lighter in D and 3‰ lighter in 18O than modern precipitation and groundwater. We attribute this difference to a colder mean annual temperature and perhaps increased winter precipitation. Consideration of various factors controlling the stable isotope composition of the groundwater allows estimation of a 5° to 7°C temperature decrease during the late Wisconsin, accompanied by increased effective precipitation. A similar estimate of the temperature change is obtained from noble-gas paleothermometry. These data support a model of moderately cooler late Pleistocene climate in the American Southwest characterized by summers with less precipitation than today, but wetter winters.

Denton and Hughes (1983, Quaternary Research 20, 125–144) postulated that sea level linked a global ice-sheet system with both terrestrial and grounded marine components during late Quaternary ice ages. Summer temperature changes near Northern Hemisphere melting margins initiated sea-level fluctuations that controlled marine components in both polar hemispheres. It was further proposed that variations of this ice-sheet system amplified and transmitted Milankovitch summer half-year insolation changes between 45 and 75°N into global climatic changes. New tests of this hypothesis implicate sea level as a major control of the areal extent of grounded portions of the Antarctic Ice Sheet, thus fitting the concept of a globally interlocked ice-sheet system. But recent atmospheric modeling results (Manabe and Broccoli, 1985, Journal of Geophysical Research 90, 2167–2190) suggest that factors other than areal changes of the grounded Antarctic Ice Sheet strongly influenced Southern Hemisphere climate and terminated the last ice age simultaneously in both polar hemispheres. Atmospheric carbon dioxide linked to high-latitude oceans is the most likely candidate (Shackleton and Pisias, 1985, Atmospheric carbon dioxide, orbital forcing, and climate. In “The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to Present” (E. T. Sundquest and W. S. Broecker, Eds.), pp. 303–318. Geophysical Monograph 32, American Geophysical Union, Washington, D.C.), but another potential influence was high-frequency climatic oscillations (2500 yr). It is postulated that variations in atmospheric carbon dioxide acted through an Antarctic ice shelf linked to the grounded ice sheet to produce and terminate Southern Hemisphere ice-age climate. It is further postulated that Milankovitch summer insolation combined with a warm high-frequency oscillation caused marked recession of Northern Hemisphere ice-sheet melting margins and the North Atlantic polar front about 14,000 14C yr B.P. This permitted renewed formation of North Atlantic Deep Water, which could well have controlled atmospheric carbon dioxide (W. S. Broecker, D. M. Peteet, and D. Rind, 1985, Nature (London) 315, 21–26). Combined melting and consequent sea-level rise from the three warming factors initiated irreversible collapse of the interlocked global ice-sheet system, which was at its largest but most vulnerable configuration.

The constructive phase of the modern Nile Delta, as manifested in a 48-m section drilled east of the Suez Canal, commenced in very early Holocene times. Sands rich in marine fauna were deposited in the littoral zone and the shoreline was more than 20 km landward of its present-day position. Subsequently, clays and silts were dumped from the Nile distributaries and the marine faunal spectrum became very limited and brackish. Later in early and middle Holocene times the sediments deposited were rich in freshwater, delta-plain diatoms and pollen and in allochthonous fern spores from the tropics, indicating proximity of a distributary mouth. The middle part of the section (22.5-17.5 m) is very poor in faunal and floral remains; pollen grains from sabkha vegetation are abundant. The environment, which seems lagoonal and slightly hypersaline, is related to the sea regression in middle Holocene times. Euryhaline pelecypods, dating from about 3000 yr B.P., are abundant around the 8-m depth. Upward, there is an increase in pollen grains from sabkhas; the section is poor in diatoms and those present are mostly euryhaline and lagoonal. Allochthonous spores derived from the nearby Pelusiac Branch are abundant. Between 3000 and 2000 yr B.P. the constructive phase of the modern delta terminated and winnowed sands began accreting in front of the delta plain.

Time series depicting mountain glacier fluctuations in the Alps display generally similar patterns over the last two centuries, as do chronologies of glacier variations for the same interval from elsewhere in the Northern Hemisphere. Episodes of glacier advance consistently are associated with intervals of high average volcanic aerosol production, as inferred from acidity variations in a Greenland ice core. Advances occur whenever acidity levels rise sharply from background values to reach concentrations ≥1.2 μequiv H+/kg above background. A phase lag of about 10–15 yr, equivalent to reported response lags of Alpine glacier termini, separates the beginning of acidity increases from the beginning of subsequent ice advances. A similar relationship, but based on limited and less-reliable historical data and on lichenometric ages, is found for the preceding 2 centuries. Calibrated radiocarbon dates related to advances of non-calving and non-surging glaciers during the earlier part of the Little Ice Age display a comparable consistent pattern. An interval of reduced acidity values between about 1090 and 1230 A.D. correlates with a time of inferred glacier contraction during the Medieval Optimum. The observed close relation between Noothern Hemisphere glacier fluctuations and variations in Greenland ice-core acidity suggests that sulfur-rich aerosols generated by volcanic eruptions are a primary forcing mechanism of glacier fluctuations, and therefore of climate, on a decadal scale. The amount of surface cooling attributable to individual large eruptions or to episodes of eruptions is simlar to the probable average temperature reduction during culminations of Little Ice Age alacier advances (ca. 0.5°–1.2°C), as inferred from depression of equilibrium-line altitudes.

Data from prehistoric fluvial deposits can be used to extend the flood history of a river valley beyond historical records, thus increasing our understanding of variability in large, low-frequency flood events and providing a valuable means for paleoenvironmental reconstruction. We have applied this form of analysis to fluvial deposits from an archaeological site on the upper Columbia River in the state of Washington dating from 120 A.D.∗ to 1948 A.D. It was our expectation that, had flood frequencies remained constant, sedimentation event frequency would conform to an exponential function derived from the Wolman and Leopold model of vertical floodplain accretion. Our findings deviate from this model, showing that flood frequencies comparable to those of the twentieth century existed prior to 1020 A.D.∗ and after 1390 A.D.∗ Large floods were three to four times more common during the intervening centuries. On the basis of field evidence, we can rule out changing channel geometry, leaving climatic conditions as the most probable factors controlling this variation in flood frequency.

The Ross Ice Shelf δ18O profile at station J-9 covers at least the last 30,000 yr. It identifies the depth in the core of ice from (i) the last glacial-interglacial transition (266 to 286 m) and (ii) the 1000-m surface elevation (about 140 m). Various processes contribute to the δ18O change observed in the core: (i) climatic warming, mainly caused by a decrease in winter sea ice extent around Antarctica of about 6° latitude early in the glacial-interglacial transition, (ii) decreasing ice sheet thickness later in the glacial-interglacial transition and during the Holocene, and (iii) decreases in elevation and effective distance from the open ocean as the source of the ice in the core shifts along the flow line toward J-9. Average δ18O values of the last 3000 yr imply a fairly stable climate. Yet shorter (102 to 103 yr) δ18O climatic oscillations up to 6‰ are seen in both the Holocene and the glacial portion of the record.

Pleistocene areas of red sediments and carbonized vegetation on the Northern Channel Islands, California, have in the past been interpreted as caused by fires of either natural or human origin. Some are associated with darkened mammoth and bird fossils, and these fossils have been considered as having been burned by early man. Reevaluation of these so-called “fire areas” indicates that the above phenomena are the result of low-temperature (≤100°C), nonheating processes occurring in groundwater. Evidence for this conclusion is derived from field observations on fossil carbonized vegetation, and the geology of the areas. Additional evidence derives from experiments on the red sediments and fossil wood, X-ray diffraction analyses, magnetic analyses, studies on the clay minerals smectite and illite, and the demonstration that fossil mammoth bone contains sufficient Fe and Mn to account for their discoloration. Much of the carbonization of vegetation probably occurred in water rather than in fire. Radiocarbon dates from the islands will probably need to be reevaluated. These data provide evidence contrary to the concept of the occurrence of significant fires, either natural or set by early man, on the Northern Channel Islands.

Ten sites near the Snake River Plain have consistent differences in their climatic histories. Sites at low elevation reflect the “early Holocene xerothermic” of the Pacific Northwest, whereas most climatic chronologies at high elevation indicate maximum warmth or aridity somewhat later, ca. 6000 yr ago. This elevational contrast in climatic histories is duplicated at three sites from the central Snake River Plain. For sites in such close proximity, the different chronologies cannot be explained by changes in atmospheric circulation during the late Quaternary. Rather, the differences are best explained by the autecology of the plants involved and the changing seasonal climate. The seasonal climatic sequence predicted by multiple thermal maxima explains the high- and low-elevation chronologies. During the early Holocene, maximum insolation and intensified summer drought in July forced low-elevation vegetation upward. However, moisture was not a limiting factor at high elevation, where vegetation moved upward in response to increased length of growing season coincident with maximum September insolation 6000 yr ago.

Ibyuk Pingo, which is 49 m high and 300 m in basal diameter, is one of the largest pingos in the world. Precise surveys carried out for the 1973 to 1983 period indicate that the lower half of the pingo, below a height of 25 m, shows no perceptible growth. From 25 m to the top, the growth steadily increases to a maximum of 2.3 cm/yr at the summit. The source of growth is believed to lie at a depth of about 65 m below the highest peak. Evidence based upon the depth of permafrost near the pingo, radiocarbon dating of wood in the pingo overburden, heat conduction theory, and the measured growth rate suggests an age of about 1300 ± 200 yr. Ibyuk Pingo is in an unstable state and collapse could be initiated by further slumping, a thermal disturbance to the crater, or erosion along a radial dilation crack. A study of the potential collapse pattern of Ibyuk Pingo suggests a number of criteria that might be employed in the environmental reconstruction of large circular features that might be identified as collapsed pingo remnants.

Bottom sediments from three lakes in the Canadian Rocky Mountains were examined with the aim of evaluating the usefulness of downvalley sediment studies in reconstruction of Holocene glacial histories. Analyses of organic carbon and carbonate contents of core sediments provide information on changing sedimentation rate and changing relative importance of glacial and non-glacial sediment sources. Sedimentary histories of the three lakes are similar, suggesting that they record regional glacial/climatic forcing, rather than localized events, and thus that they may be useful in reconstructing Holocene glacial history. Lacustrine sediments indicate a period of high sedimentation rates and relatively large glacial sediment contribution prior to 7500-7000 yr B.P., with much reduced rates and decreased glacial sediment contribution between about 6000 and 4000 yr B.P., possibly interrupted by a brief period of increased glacial sediment output shortly after 5000 yr B.P. Sometime after 4000 yr B.P., sedimentation rates and glacial sediment output began to rise again, reaching approximately present levels by 2750-2650 yr B.P., and have not since returned to low mid-Holocene levels. In detail over the last 3000 yr there is some indication of a slight decrease in sedimentation rate for more than 1000 yr after about 2200 yr B.P. Sedimentation rates and glacial sediment input into all three lakes rose between about 900 and 750 yr B.P. and have remained very high since. If the lake sediments are interpreted as a proxy record of upvalley glacial activity, they allow the development of a glacial chronology which is at once generally consistent with, and more complete and easily datable than, the surficial glacial record.

Five stratigraphic units and five soils of late Pleistocene to Holocene age crop out in dissected badlands on Corn Creek Flat, 30 km northwest of Las Vegas, Nevada, and at Tule Springs, nearer to Las Vegas. The record is dominantly fluvial but contains evidence of several moister, marsh-forming periods: the oldest (Unit B) dates perhaps to the middle Wisconsin, and the more widespread Unit D falls between 30,000 and 15,000 yr B.P. Unit D therefore correlates with pluvial maximum lacustrine deposits elsewhere in the Great Basin. Standing water was not of sufficient depth or extent during either period to form lake strandlines. Between 14,000 and 7200 yr B.P. (Unit E), standing surface water gradually decreased, a trend also apparent in Great Basin pluvial lake chronologies during the same period. Groundwater carbonate cementation and burrowing by cicadas (Cicadae) accompany the moist-phase units. After 7200 yr B.P., increased wind action, decreased biotic activity, and at least 25 m of water-table lowering accompanied widespread erosion of older fine-grained deposits. Based on pack-rat midden and pollen evidence, this coincides with major vegetation changes in the valley, from sagebrush-dominated steppe to lower Mohave desertscrub.

The ubiquitous occurrence of charcoal in the forest soils of the Upper Rio Negro region of Colombia and Venezuela indicates the presence of frequent and widespread fires in the Amazon Basin, possibly associated with extremely dry periods or human disturbances. Charcoal ranged from 3.12 to 24.76 mg/cm3 in the upper 50 cm of soil and was more abundant in Oxisols and Ultisols than in other soil types. Charcoal dates range from 6260 yr B.P. to the present. Several dates coincide with dry phases recorded during the Holocene. Ceramic shards were found at several sites, and thermoluminescence analysis indicates that their ages range from 3750 to 460 yr B.P. The age of charcoal and shards confirms that this region has been subjected to fire and human disturbances during the past 6000 yr.

Dendroclimatological studies in eastern North America are enhanced by the use of long-time series of maximum latewood densities determined by x-ray densitometry. The densities show higher correlation from tree to tree and site to site than do ring-width measurements from the same trees. Based on the macroclimatic link thus implied, maximum density and width series of Picea rubens Sarg. from high elevations in Maine are used to reconstruct up to 310 yr of past spring temperatures at nearby climate stations. The regression equations explain from 33 to 47% of calibrated variance, and verification testing of the reconstructions produces highly significant correlations and high, positive reduction of error statistics. The climate-wood density relationships are considered in light of tree physiological factors that may explain them. Results from this study are applicable to (1) an increased understanding of the relationship of climate to the formation of wood density and (2) further development of paleoclimatological and paleoenvironmental studies via tree rings in mesic regions such as northeastern North America.

A working hypothesis for the development and maintenance of sorted circles, which are finegrained soil domains delineated by borders of coarser material, involves clast motion relative to soil and intermittent circulatory motion of soil in the active layer. The hypothesis is compatible with the observed size, regularity, sorting, microtopography, surface soil motion, vegetation cover, and subsurface organic carbon content of soil patterns studied in Spitsbergen. Theoretical considerations of buoyancy-driven convection suggest that intermittent convection of thawed soils is plausible, and that the requisite bulk density decrease with depth arises naturally from moisture gradients that develop during the thaw consolidation of ice-rich soils. These considerations also help in understanding the dependence of sorted circles on soil characteristics and on moisture. Moreover, they point to the possible use of sorted patterns as paleoclimatic indicators based on the expected relation between pattern size and active layer depth.

Pedogenic zonation in the soils of the polar regions is a result of gradients in environmental factors and attendant chemical processes. Along a latitudinal transect, it is best manifested at well-drained sites and by soils developed on predominantly silicate rocks. Selected sites in arctic Alaska, in the Canadian arctic, Greenland, and Svalbard adequately fulfill these prerequisites. The processes of podzolization, decarbonization-carbonization, pervection, and salinization as models of arctic pedogenesis demonstrate that processes occurring in the temperate region also operate in the Far North. Brunification, melanization, and oxidation are recognized for the first time as current geochemical and pedogenic mechanisms of the Arctic region. Traditional genetic soil names have been retained because they represent a closer relationship to pedogenic processes than the more modern nomenclature. The identification, the chemical behavior, the strength, abundance, and mobility of the proton donors and conjugate bases are keys to the genesis of soils and the distinction of contrasting soil processes. This new approach to the understanding of arctic pedogenesis can be better fulfilled by collecting, analyzing, and interpreting soil solution obtained in situ.

Pollen, macrofossil (logs and needles), and oxygen-isotope data from tree rings are presented for three alpine bog sites in the Maligne Range of the Canadian Rockies. Organic sedimentation at the Watchtower site began prior to ca. 9500 14C yr B.P. and by 8770 yr B.P. timberlines were at least 100 m above present levels. The two pollen records are dominated by Pinus and subsequent changes in timberlines are inferred from pollen-ratio data (Abies/Pinus) and from macrofossils. The recovered records indicate two periods of high Hypsithermal timberlines ca. 8800-7500 and 7200-5200 yr B.P. separated by a short interval ca. 7300–7400 yr B.P. when timberline approached modern levels. After ca. 4500 yr B.P. timberlines have been similar to or lower than present, reaching minimum values in the last 500 yr. δ18O determinations from the α-cellulose of samples of 5 or 10 annual rings cut from contemporary Picea englemannii at timberline show strong correlations with mean annual temperatures at Jasper. Isotopic determinations from Hypsithermal-age logs recovered from sites above present timberline indicate mean annual temperatures were at least 0.5°C warmer ca. 8060 and 8770 yr B.P. than at present at the Watchtower site. Data from logs at the Maligne Pass site suggest that temperatures were about 1.2° and 1.6°C warmer ca. 6000 and 5300 yr B.P. Estimates of temperature from the pollen-ratio data are more conservative and suggest maximum differences of ca. 1.0°C in July temperatures over the last 8000 yr.