Areas of southeastern Alaska and the Queen Charlotte Islands of the northwestern Pacific coast of North America were considered to be ice free during the late Wisconsinan glaciation and glacial refugia existed. However, a glacier extended from mainland North America to the shelfbreak in Dixon Entrance separating Alaska and the Queen Charlotte Islands. Glacial retreat to the east began sometime after 15,000 to 16,00014C yr B.P. and ice had completely left Dixon Entrance by 13,500 to 13,00014C yr B.P. A rapid sea-level regression occurred soon after deglaciation began, due to isostatic rebound, with relative sea level falling to approximately 150 m below present in central Dixon Entrance, decreasing the size of the inlet by about 30 percent by 12,40014C yr B.P. The late Quaternary glacial and postglacial stratigraphic sequence is more than 100 m thick overlying older Pleistocene sediments and Tertiary bedrock. A late Wisconsinan diamicton is overlain by glaciomarine muds formed between approximately 14,400 and 13,00014C yr B.P. Contemporaneous with the deposition of the glaciomarine muds an extensive outwash deposit formed off the northern coast of the Queen Charlotte Islands to a present depth of 150 m. During the sea-level lowstand and subsequent transgression, a reworked sand unit was deposited over much of the seafloor to depths greater than 450 m. The unit is exposed at the seafloor over much of the region, suggesting that seabed hydrodynamic energy levels were high after 13,00014C yr B.P. and remain so today.

Sediment cores from three proglacial lakes in northern Banff National Park, Alberta, preserve a record of Holocene glacial activity upvalley which is more continuous and better dated than available surficial records. Dating of the cores is based on tephrochronology and 16 AMS14C ages of terrestrial macrofossils. All cores contain a threefold sequence of lacustrine sediments overlying a late Pleistocene diamicton. Basal lacustrine sediments >10,10014C yr old contain little organic matter. Sediment composition indicates a large glacigenic contribution. A sharp increase in organic content marks the beginning of the Altithermal interval at all three lakes. This transition occurred abruptly at about 10,10014C yr B.P. at Crowfoot Lake and possibly more gradually at the other lakes. Altithermal sediments contain relatively little glacigenic material, and during most of the Altithermal, glaciers may have been absent above Crowfoot and Bow Lakes. Glaciers draining into Hector Lake appear to have persisted through the Altithermal. A subsequent decrease in organic content in each lake, reflecting increased clastic sedimentation, marks the end of the Altithermal and the onset of Neoglacial ice advances. The transition took place between about 5800 and 400014C yr B.P. and may be time-transgressive, beginning earlier in Hector Lake than in Crowfoot Lake. Changing Neoglacial clastic sedimentation rates through the Neoglacial interval indicate two main periods of increased glacier extent, between ca. 3000 and 1800 varve yr ago (ca. 2900–190014C yr B.P.) and during the last several hundred years. During the intervening period glaciers were less extensive, but much more extensive than during the recessions of the Altithermal interval.

Rb, Sr, and magnetic susceptibility have been measured in the last interglacial–glacial loess profiles at Luochuan and Huanxian, central China. A high degree of similarity between the parameters in both profiles suggests that variations of Rb/Sr ratios in the sequence can be regarded as an indicator of East Asian summer monsoon strength. Matching the Rb/Sr record with the SPECMAP δ18O curve suggests that the Rb/Sr ratio responds sensitively to changes of the East Asian monsoon induced by global ice-volume variation.

Geomorphic features inherited from the mid-Holocene glacio-hydro-isostatic sea-level highstand that affected the central Pacific region influence the susceptibility of atoll islets to potentially enhanced wave erosion associated with rise in sea level from global warming. Shoreline morphology on multiple islets of Funafuti atoll in central Tuvalu reflects a relative mid-Holocene sea-level highstand 2.2–2.4 m above modern sea level. Typical islets are composed of unconsolidated post-mid-Holocene sediment resting disconformably on cemented coral rubble formed beneath now-emergent mid-Holocene reef flats. Exposed remnants of the lithified islet foundations serve as resistant buttresses protecting the flanks of atoll islets from wave attack. Islets lacking cemented mid-Holocene deposits as part of their internal structure are migratory sand cays with unstable shorelines. Any future sea-level rise ≥0.75 m, bringing high tide above the elevation of mid-Holocene low tide, might trigger enhanced wave erosion of stable atoll islets by overtopping the indurated mid-Holocene reef platforms. As analogous threshold relations are inferred for other central Pacific atolls, the risk of future inundation of island nations cannot be evaluated solely in terms of expected sea-level rise with respect to gross islet elevations.

Terrigenous sediments from Ceara Rise in the western tropical Atlantic Ocean record Pleistocene Amazon Basin climate variability. Iron oxides and oxyhydroxides in this region originate mainly from chemically leached Amazon lowland soils. Concentrations of goethite and hematite in the terrigenous fraction consistently peak during transitions from glacial to interglacial periods, suggesting an increased proportion of erosive products derived from the Amazon lowlands compared to the physically weathered highlands. Lowland Amazon Basin precipitation changes, monitored by the percentage of goethite relative to total iron oxides, lead ice age extremes with maximum aridity during ice growth and maximum precipitation during ice melt. Rapid climate changes over the Amazon Basin may reflect shifts in the position of the Intertropical Convergence Zone forced by northern hemisphere insolation at precessional (1/23,000 yr−1) and obliquity (1/41,000 yr−1) frequencies. Variance in the orbital eccentricity bands (1/100,000 and 1/413,000 yr−1) may be explained by nonlinear amplification of insolation forcing at precessional frequencies. The early response of Amazon precipitation to insolation, ahead of high-latitude ice volume (δ18O) at all orbital frequencies, suggests that tropical aridity is part of the chain of events leading to ice ages, rather than a response to glacier oscillations.

A history and conception of glacial events for the central Karakoram Himalaya, proposed some 80 years ago by Giotto Dainelli, are largely accepted today. However, certain deposits identified as terminal moraine complexes marking glacial episodes were actually emplaced by rock avalanches. In the Skardu and Shigar intermontane basins of Baltistan, at least 15 rock avalanche events were previously mapped as moraine or till. Criteria used for distinguishing these catastrophic landslide deposits emphasize homogeneous lithology of rubble and matrix, clast shape, facies characteristics, the large scale unity of emplacement, and morphological relations to valley topography. The deposits of three events, at Katzarah, Satpura, and the north end of Shigar Valley, have been reconstructed in detail. Thick supraglacial debris does not result in similar deposits. Extensive valley fills, river terraces, large sediment fans, and lacustrine sediments formerly attributed to late-glacial conditions are reinterpreted as postglacial events involving rock avalanches that interrupted fluvial development. Existing reconstructions of glaciations are left in doubt, especially late-glacial events in the central Karakoram, as are the roles assigned to Karakoram, main Indus Valley, and western Himalayan ice.

A late-glacial to early Holocene record of pollen, plant macrofossils, and charcoal has been obtained from two cores from Browns Pond in the central Appalachians of Virginia. An AMS radiocarbon chronology defines the timing of moist and cold excursions, superimposed on the overall warming trend from 14,200 to 750014C yr B.P. This site had cold, moist conditions from ca. 14,200 to 12,70014C yr B.P., with warming at 12,730, 11,280, and 10,05014C yr B.P. A decrease in deciduous broad-leaved tree taxa andPinus strobus(haploxylon) pollen, simultaneous with a reexpansion ofAbies,denotes a brief, cold reversal from 12,260 to 12,20014C yr B.P. A second cold reversal, inferred from increases in montane conifers, is centered at 750014C yr B.P. The cold reversals at Browns Pond may be synchronous with climate change in Greenland and northwestern Europe. Warming at 11,28014C yr B.P. shows the complexity of regional climate responses during the Younger Dryas chronozone.

In the southern Argentine Andes, ten advances of valley glaciers were used to reconstruct the late-glacial and Holocene glacier history. The accumulation areas of these glaciers lie in the Precordillera and are thus independent of fluctuations of the South Patagonian Icefield. Like the Viedma outlet glacier, the valley glaciers advanced three times during late-glacial time (14,000–10,000 yr B.P.). The youngest advance correlates with the Younger Dryas Stade, based on two minimum AMS14C dates of 9588 and 9482 yr B.P. The second oldest advance occurred before 11,800 yr B.P. During the first half of the Holocene, (ca. 10,000–5000 yr B.P.), advances culminated about 8500, 8000–7500, and 5800–5500 yr B.P. During the second half of the Holocene, advances occurred between ca. 4500 and 4200 yr B.P., as well as between 3600 and 3300 yr B.P. In the Rı́o Cóndor valley three subsequent advances have been identified.

Hemipelagic sediments from the Amazon deep-sea fan, ODP Site 932 (5° 12.7′N, 47° 1.8′W), and continental shelf provide a 50,000-yr-long pollen record of Amazon Basin vegetation. The age model for Hole 932A is constrained by eight magnetic remanence intensity features, one paleomagnetic excursion, and three AMS14C dates.Alchornea,Melastomataceae, Myrtaceae, and Moraceae/Urticaceae are dominant taxa in the pollen record between 40,200 and 19,800 cal yr B.P. Andean taxa, such asPodocarpusandHedyosmum,increase in abundance between 19,800 and 11,000 cal yr B.P. and prior to 40,200 cal yr B.P. The Holocene pollen assemblage, derived from Amazon River and continental shelf sediments, is dominated by secondary growth taxa, such asCecropia.Climatic factors influencing the development of glacial and interglacial tropical vegetation are considered by comparing marine with terrestrial records of vegetation change. This comparison shows that the Amazon Basin forests were not extensively replaced by savanna vegetation during the glacial period, contradicting the refugia hypothesis.

The upper Holocene marine section from a kasten core taken from the oxygen minimum zone off Karachi (Pakistan) at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1.2 mm/yr and a unique record of monsoonal climatic variability covering the past 5000 years. Our chronostratigraphy is based on varve counts verified by conventional and AMS14C dating. Individual hemipelagic varve couplets are about 0.8–1.5 mm thick, with light-colored terrigenous laminae (A) deposited mainly during the winter monsoon alternating with dark-colored laminae (B) rich in marine organic matter, coccoliths, and fish debris that reflect deposition during the high-productivity season of the late summer monsoon (August–October). Precipitation and river runoff appear to control varve thickness and turbidite frequency. We infer that precipitation decreased in the river watershed (indicated by thinning varves) after 3500–4000 yr B.P. This is about the time of increasing aridification in the Near East and Middle East, as documented by decreasing Nile River runoff data and lake-level lowstands between Turkey and northwestern India. This precipitation pattern continued until today with precipitation minima about 2200–1900 yr B.P., 1000 yr B.P., and in the late Middle Ages (700–400 yr B.P.), and precipitation maxima in the intervening periods. As documented by spectral analysis, the thickness of varve couplets responds to the average length of a 250-yr cycle, a 125-yr cycle, the Gleissberg cycle of solar activity (95 yr), and a 56-yr cycle of unknown origin. Higher frequency cycles are also present at 45, 39, 29–31, and 14 yr. The sedimentary gray-value also shows strong variability in the 55-yr band plus a 31-yr cycle. Because high-frequency cyclicity in the ENSO band (ca. 3.5 and 5 yr) is only weakly expressed, our data do not support a straightforward interaction of the Pacific ENSO with the monsoon-driven climate system of the Arabian Sea.

Soil chronofunctions are often quasilinear, but those relationships may be only gross, fortuitous generalizations that ignore changes in soils resulting from climatic and other cyclic external influences that govern soil formation or soil degradation. In the Rocky Mountains, soil development has been extensively used to estimate the age of sediments, but the number of soils is usually few, and large ranges in values for soil data may be dismissed as “normal variation.” In a detailed study of soils in the Wind River Range and Wind River Basin, characteristics of near-surface horizons do not follow age trends. However, the underlying carbonate-bearing horizons do have age-related characteristics. This “soil paradox” may be related to glacial–interglacial cycles in which (1) wind erodes near-surface horizons and then provides new parent material and (2) cryoturbation disrupts carbonate horizons, remobilizing carbonate and changing carbonate morphology but with only minimal loss of carbonate from the soil.

δ18O values of sulfate minerals from a 186-m core (past 200,000 years) in Death Valley varied from +9 to +23‰ (V-SMOW). Sulfates that accumulated in the past ephemeral saline lake, salt pans, and mud flats have relatively low δ18O values similar to those of present-day local inflows. Sulfates that accumulated during two perennial lake intervals, however, have higher δ18O values, reflecting changes in temperature, lake water levels, and/or sulfur redox reactions. Over the same time interval, the δ18O record for sulfate had excursions that bear similarities to those found for carbonate in the Death Valley core, marine carbonate (SPECMAP), and polar ice in the Summit ice core, Greenland. The δ18O record differed considerably from the records reported for carbonate at Owens Lake and Devils Hole, which probably relates to different water sources. Death Valley, Owens Lake, and Devils Hole are responding to the same climatic changes but manifesting them differently. In Death Valley sediments, the isotopic composition of sulfate may have potential as an indicator of paleoenvironmental changes.

Stratigraphic analyses of outcrops, shorelines, and diatoms from the southern Bolivian Altiplano (Uyuni-Coipasa basin) reveal two major lacustrine phases during the late-glacial period and the early Holocene, based on a chronology established by radiocarbon and U/Th control. A comparison of14C and230Th/234U ages shows that during times of high lake level, radiocarbon ages are valid. However, during low-water periods,14C ages must be corrected for a reservoir effect. The lacustrine Tauca phase started a little before 16,00014C yr B.P., and the lake level reached its maximum between 13,000 and 12,00014C yr B.P. A dry event (Ticaña) occurred after ca. 12,000 and before 950014C yr B.P. A moderate lacustrine oscillation (Coipasa event) occurred between ca. 9500 and 850014C yr B.P., using a reservoir-corrected conventional14C chronology. Comparisons between the lake-level chronology in the Uyuni-Coipasa basin and data from other southern tropical areas of South America suggest that the lacustrine evolution may reflect large-scale climatic changes.

We estimated minimum mean July temperatures in northwestern and central Europe during the Younger Dryas (10,950–10,15014C yr B.P.) from distributions of climate indicator plant species, which were reconstructed from 140 pollen and plant macrofossil diagrams. Paleobotanical records, mainly from the central and eastern part of the study area, show that the coldest conditions occurred early in the Younger Dryas (before ∼10,55014C yr B.P.). For this phase, mean July temperatures at sea level of around 10°C are suggested for the northern part of the British Isles and for ice-free Scandinavia. We estimated a mean July temperature of 12°C for central England, The Netherlands, and northern Germany. The 13°C mean July isotherm—largely based on the modern distribution ofTypha latifolia—was most probably located in southern England, Belgium, central Germany, and Poland. The reappearance of thermophilous elements in the records after ∼10,55014C yr B.P. suggests a summer warming, at least temporarily, of 1° to 2°C in the study area. The reconstructed temperatures are comparable with temperature estimates based on beetle data. However, they appear rather high when compared with estimates based on glaciological evidence.

Oxygen and hydrogen isotopic compositions of meteoric water are known to correlate with surface air temperature, except in tropical areas. This relationship has been described using a number of terms corresponding to specific observations, such as latitude, altitude and seasonal effects. However, these temperature effects do not seem to apply to precipitation in monsoonal areas of Asia. Questions have been raised as to whether the isotopic composition of meteoric water can be used to reconstruct paleomonsoon intensity. Tree rings of two modern spruce trees (Picea meyeri) and a 10,000-yr-old timber (Picea jezoensis) were analyzed for hydrogen isotopic composition. On average, the older tree is depleted in deuterium by 45‰ compared to the modern trees. We attribute this isotopic depletion to the strength of summer monsoons, which were more intense in the early Holocene than at present. Although this study is not definitive, it suggests that paleomonsoon intensity can be reconstructed by direct or proxy methods that yield the oxygen or hydrogen isotopic composition of meteoric water.

Walpole Island is part of a large freshwater delta located at the St. Clair River mouth in southwestern Ontario. Quaternary deposits on the island consist of Lake Nipissing to Lake St. Clair stage deltaic sediments underlain by a thick sequence of Late Wisconsin glaciolacustrine rhythmites and massive clayey till. These sediments overlie a thin freshwater aquifer resting on Paleozoic bedrock. Porewater δ18O, δD, and δ13CDICprofiles of cores taken from northern and central Walpole Island show that older (>10,000 yr B.P.), deeper glaciogenic porewaters have mixed with, and have been displaced by, younger modern surficial water. In contrast, isotopic profiles from a core taken from southern Walpole Island indicate that modern St. Clair River waters have penetrated the entire 20-m core via fractures, effectively displacing all glaciogenic porewater. Fracturing and faulting are clearly visible throughout the southern core, and their presence may be attributed to its location on the trend of the Electric Fault. These features are interpreted as the product of renewed Holocene fault movement. Porewater Na+, K+, Ca2+, and Mg2+concentration gradients are consistent with the presence of upwardly diffusing deep brine, for which the Electric Fault may serve as a conduit.

Fission-track dating of glass is potentially an efficient technique for tephrochronological studies. However, most glasses from Quaternary tephra have very low spontaneous track densities and track counting is laborious. The point-counting technique is a simplified procedure for evaluating fission-track areal densities in a glass shard population that allows the analyst to count larger numbers of tracks in significantly shorter times. A field of view is coded as 1 if its center is on glass and is 0 otherwise, and the total area of glass is estimated by counting the number of 1's. Under simple assumptions, the binomial distribution appears to provide a reasonable evaluation of the additional experimental error in a fission-track density determination by this technique. Glass shard populations have been simulated, assuming that glass areas are random samples from distributions analogous to real ones. The effect of variation in glass area on the relative standard error of the estimated track density is found to be small. The point-counting technique significantly enhances the potential of fission-track dating, especially for very low track densities typical of most Quaternary tephra, as the additional error associated with its use is largely counterbalanced by the greater number of tracks that can be counted.

The Upper Doubs River Valley is a 910-km2watershed feeding into Lake Chaillexon. The lake was formed by a natural rockfall at the end of the Bølling Chronozone (around 14,250 cal yr B.P.) and since then has trapped material eroded from the watershed. The filling process and variations in sediment yield have been investigated by mechanical coring, seismic surveys, and electric soundings. The detrital sediment yield of the upstream watershed can be calculated by quantifying the sedimentary stocks for each climatic stage of the Late-Glacial period and Holocene Epoch and estimating the lake's entrapment capacity. This enables us to determine the intensity of the erosion processes in relation to climate and environmental factors. The Bølling–Allerød Interstade produced the greatest yields with mean values of 19,500 metric tons per calendar year (t/yr). The Younger Dryas Chronozone saw a sharp fall (8900 t/yr) that continued into the Preboreal (2100 t/yr). Clastic supply increased during the Boreal (4500 t/yr) before declining again in the Early Atlantic (2400 t/yr). Since then, yields have risen from 4500 t/yr in the Late Atlantic to 6800 t/yr in the Subboreal and 11,100 t/yr in the Subatlantic. Comparison of quantitative data with the qualitative analysis of the deposits and with the paleohydrologic curve of the watershed based on level fluctuations in lakes around Chaillexon shows that climate was the controlling factor of sediment yield until the Late Atlantic. From the Late Atlantic–Subboreal around 5400 cal yr B.P. (470014C yr B.P.) and especially from the end of the Subboreal Chronozone and during the Subatlantic Chronozone (2770 cal yr B.P./270014C yr B.P.–present) climatic constraints have been compounded by human activity related to forest clearing and land use.

Mussel shells from central California coastal archaeological sites record changes in sea surface temperatures in the past 2000 years. Water temperatures, inferred from oxygen isotopes in the shells, were about 1°C cooler than present and stable between 2000 and 700 yr ago. Between about 700 and 500 yr ago, seasonal variation was greater than present, with extremes above and below historic levels. Water temperatures were 2–3°C cooler than today 500–300 yr ago. The interval of variable sea temperatures 700–500 yr ago partially coincided with an interval of drought throughout central California. A coincident disruption in human settlement along the coast suggests movements of people related to declining water sources. Quantities of fish bone in central coast middens dating to this same period are high relative to other periods, and the remains of northern anchovies, a species sensitive to changing oceanographic conditions, are also abundant. The continued use of local fisheries suggests that changes in settlement and diet were influenced more by drought than by a decrease in marine productivity, as fish provided a staple during an interval of low terrestrial productivity.

The reliability of paleovegetation records inferred from soil phytolith assemblages and SOM (soil organic matter) carbon isotope analysis was examined in light of previous pollen and charcoal reconstructions. The sampled latosol is located in south-central Brazil (Salitre), at a boundary between forest and cerrado. The derived mean age of phytoliths and SOM at each level is the result of a balance between continuous translocation and selective dissolution. It increases with depth in a regular, quantifiable fashion that allows paleoenvironmental interpretation. Phytoliths and SOM tracers first record a savanna phase, associated with the last Holocene long dry period occurring between ca. 5500 and 4500 yr B.P. Two periods of tree community development followed, between ca. 4000 and 3000 and after ca. 970 yr. B.P., leading to the present cerrado/forest association. The dry spell interrupted this trend about 970 ± 60 yr B.P. The second development of woody elements was contemporaneous with an increase in anthropogenic fires. Therefore, climate was more important than fires and human activities in constraining the growth of vegetation during the last nine centuries at Salitre. More generally, despite pedogenic processes, soil phytoliths and δ13C values of the SOM may be accurate tracers of vegetation changes.