Several temporal and event classifications are used for the Quaternary glacial and interglacial record in the Great Lakes region of North America. Although based on contrasting principles, the classifications, as practiced, are similar to one another in most respects and they differ little from the classification proposed by Chamberlin a century ago. All are based on stratigraphic units having time-transgressive boundaries; thus the associated time spans and events are diachronous. Where application of geochronologic classification based on isochronous boundaries is not practical or useful, we advocate the use of diachronic principles to establish local and regional temporal and event classifications. Diachronic and event classifications based on such principles are proposed herein for the Great Lakes region. Well-established names, including Wisconsin, Sangamon, and Illinois, are used at the episode (or glaciation/interglaciation) rank without significant redefinition. The Hudson Episode (Interglaciation) is introduced for postglacial time, the current interglacial interval. The Wisconsin Episode is divided into the Ontario, Elgin, and Michigan Subepisodes in the eastern and northern parts of the Great Lakes region and into the Athens and Michigan Subepisodes in the southern and western parts of the Great Lakes region.

Morphologic and stratigraphic evidence shows that a late-glacial ice cap existed on part of the Eastern Cordillera of Ecuador (Lat. 0° 20′ S) on ground with a mean elevation of 4200 m where none exists now. An outlet glacier from an ca. 800 km2ice cap terminated at 3850 m altitude in the Papallacta valley on the eastern side of the plateau. Radiocarbon dates show that moraines formed by this advance were ice-free by 13,20014C yr B.P. Tephras and the age of organic deposits at the plateau edge indicate ice-free conditions before 11,80014C yr B.P. This interval was followed by the expansion of an ca. 140 km2ice cap that discharged glaciers into adjacent valleys where terminal moraines were built at 3950 m altitude. AMS and conventional radiocarbon dates from macrofossils, peat, and gyttja above and below till of the readvance indicate that the ice cap formed between ca. 11,000 and 10,00014C yr B.P. and was thus coeval with the European Younger Dryas event. The ice cap developed in response to a surface temperature cooling of at least 3°C in the tropical Andes, a finding that is consistent with a coupled equatorial/high latitude North Atlantic climate system operating at the late-glacial/Holocene transition. These results are further evidence that Younger Dryas cooling may have been a global event.

Mountain glaciers in Scandinavia are currently advancing while most of the monitored mountain glaciers of the world are retreating. We examine atmospheric circulation variability and compare changes in air pressure indices to changes in the mass balance of glaciers in the northeastern part of the Atlantic Ocean. The glacier mass balance correlates well with the strength of maritime flow in both winter and summer, the presence of high pressure over the Barents Sea being a critical factor in summer. The advance of Scandinavian glaciers is due partly to persistently strong westerlies over the northeastern Atlantic during post-1980 winters and partly to cold summertime flow, which together have helped maintain positive glacier net balance by decreasing ablation since 1980.

Calibration of radiocarbon dates of postglacial geomorphic events in southeastern Alberta, Canada, reveals a strong association between type of geomorphic event and seasonality of insolation. The late glacial and postglacial periods can be divided into four major episodes: glaciation, ca. >20,000 cal yr B.P.; deglaciation, ca. 20,000–12,000 cal yr B.P.; landscape stability, ca. 12,000–10,000 cal yr B.P.; and landscape instability, ca. 10,000–0 cal yr B.P. This indicates that there was significantly more time than previously thought (12,000–13,000 yr) for postglacial processes. Glaciation, deglaciation, maximum landscape stability (indicating maximum aridity), and landscape instability did not lag behind minimum, increasing, maximum, and decreasing seasonality of insolation, respectively.

A comparison of paleomagnetic secular variation in sediment of Pleistocene Lake Lahontan in the northwestern Great Basin with secular variation in lake sediment in the Mono Basin, California, indicates that Lake Lahontan was in the valley of the Truckee River between Pyramid Lake and Wadsworth, Nevada, from about 19,000 to 13,000 yr B.P. The secular variation in older Lake Lahontan sediment in the Truckee River valley has the general features of secular variation in middle Pleistocene lacustrine sediments near Rye Patch Dam, Nevada, 125 km to the east. On the basis of field mapping and tephrochronology, the sections of older lacustrine sediments are not coeval. The apparent, but erroneous, correlation of those sediments emphasizes the need for multiple dating methods when paleomagnetic secular variation is used to date stratigraphy.

Lunettes—isolated dunes on the lee side of playa basins—are common landforms on the Southern High Plains of northwest Texas and eastern New Mexico. The dunes contain calcareous (15–40% CaCO3) sandy loam or loamy sand, with minor amounts of sepiolite, deposited 25,000–800014C yr B.P. and derived by deflation of lacustrine carbonate in the basins. The dunes also contain low carbonate (0–15% CaCO3) sand or loamy sand that was deposited 25,000–15,000 yr B.P. and 8000–5000 yr B.P. and was derived by deflation that created the basins or deflated from sand deposited in the basins. Buried soils are common in the lunettes: A-Bk profiles characterize soils formed in the calcareous sandy loam; the sandy low-carbonate sediments contain A-Bt profiles in the oldest sand of some dunes, and A-Bw, A-Bt, or A-Btk in the early and middle Holocene sand. The dune stratigraphy, combined with carbon isotope data (derived from dated A-horizons in lunettes), suggests the following scenario for the Southern High Plains. The lunettes began forming as low-carbonate sand dunes in the late Pleistocene as playa basins were formed or deepened by wind erosion. The erosion repeatedly alternated with stability. The environment probably was cool and dry, but one or more cool and wet intervals 25,000–15,000 yr B.P. resulted in a rise in the water table and deposition of lacustrine carbonate in the deepest basins. There may have been short departures toward warmer (and probably toward drier) conditions throughout this time. Episodically dry conditions 15,000–8,000 yr B.P. resulted in deflation of the carbonate and further dune construction by repeated accretion of calcareous sandy loam or loamy sand. The low carbonate sand was deposited during widespread drought and deflation 8000–5000 yr B.P. The dunes have been largely stable in the late Holocene.

Two century-scale time series in northern Bolivia constrain the ages of abrupt changes in the physical, geochemical, and biological characteristics of sediments obtained from lakes that formed during deglaciation from the late Pleistocene glacial maximum. The watersheds of Laguna Viscachani (16°12′S, 68°07′W, 3780 m) and Lago Taypi Chaka Kkota (16°13′S, 68°21′W, 4300 m), located on the eastern and western slopes of the Cordillera Real, respectively, contain small cirque glaciers. A high-resolution chronology of the lake sediments is provided by 23 AMS14C dates of discrete macrofossils. Late Pleistocene glaciers retreated rapidly, exposing the lake basins between 10,700 and 970014C yr B.P. The sedimentary facies suggest that after 890014C yr B.P. glaciers were absent from the watersheds and remained so during the middle Holocene. An increase in the precipitation–evaporation balance is indicated above unconformities dated to ∼230014C yr B.P. in both Lago Taypi Chaka Kkota and Laguna Viscachani. An abrupt increase in sediment accumulation rates after 140014C yr B.P. signals the onset of Neoglaciation. A possible link exists between the observed millennial-scale shifts in the regional precipitation–evaporation balance and seasonal shifts in tropical insolation.

Fine-interval (∼30–45 yr) sampling of a core from Lake Victoria's Damba Channel shows that numerous abrupt changes in the lake's diatom assemblages have occurred in response to climatic fluctuations over the past 11,40014C yr. Four distinct climatic phases bounded by sudden transitions are inferred: (1) variably dry ∼11,400–10,000 yr B.P., (2) humid ∼10,000–7200 yr B.P., (3) more seasonal ∼7200–2200 yr B.P., and (4) more arid ∼2200–0 yr B.P., with a dry “Little Ice Age” event ∼600–200 yr B.P. The diatom-inferred paleoclimatic history for northern Lake Victoria closely resembles that inferred from a well-dated pollen record from Pilkington Bay. Spectral analysis of the diatom record reveals strong periodicities including globally distributed ∼2360–2550, ∼1400, ∼1030–1130, and ∼500 cal-yr cycles. Repeated, rapid shifts betweenAulacoseira- andNitzschia-dominated diatom assemblages suggest that post-1960 changes in the lake's phytoplankton communities have had earlier, climate-driven analogs.

Six cores were collected from a small peatland on the Tuktoyaktuk Peninsula, yielding up to 1.8 m of organic material and 1.2 m of ice-rich material. Stratigraphic relationships, radiocarbon dating, and pollen, plant macrofossil, and isotopic analyses are used to reconstruct the developmental history of the peatland. Organic matter began to accumulate in the basin about 7200 yr B.P., during a period when the climate is thought to have been warmer than present. Initially the permafrost table was probably below the bottom of the basin, and an open-water mineral wetland with emergent and submergent aquatic vegetation occupied the site. Enriched δ18O values from ice samples confirm the existence of an open water body with a water balance strongly affected by evaporation. Transformation to a graminoid fen peatland was underway by 6300 yr B.P. Permafrost and ice began to form in the peatland at this time. Low-centered polygons probably began to develop by 4700 yr B.P. and subsequently evolved into the high-centered polygons which characterise the southwestern part of the peatland today. Peat accumulation in the polygons has been extremely slow for the last 4000 years. The eastern, wetter part of the basin has largely remained unchanged since its inception about 7000 yr B.P. Development of the peatland may be linked to permafrost formation that was controlled by regional climate changes during the Holocene.

AMS14C ages of 10 bones of the caribou (Rangifer tarandus), flat-headed peccary (Platygonus compressus), and giant beaver (Castoroides ohioensis) from the Dutchess Quarry Caves, New York, range from 13,840 ± 80 to 11,670 ± 70 yr B.P. No bones from any of these species are demonstrably associated with Paleoindian artifacts (fluted points) or other cultural materials from the sites because the bones lack unequivocal stratigraphic association with artifacts, as well as physical (taphonomic) evidence for human association (e.g., burning, cut marks, distinctive breakage). Together with the Holocene conventional14C dates of charcoal and the varied stratigraphic proveniences of the fluted points and the dated bones, the new AMS14C dates argue that most strata at the Dutchess Quarry Caves contain a mixture of late Pleistocene and Holocene materials. This mixing probably resulted from post-depositional bioturbation (by humans, rodents, carnivores, and scavengers) and cryoturbation (annual freeze–thaw cycles). Rather than being of cultural origin, the bones of caribou, flat-headed peccary, and giant beaver likely were deposited in the Dutchess Quarry Caves by nonhuman predators or scavengers, such as ursids, canids, felids, condors, or eagles.

Today, precipitation over tropical South America is largely controlled by the seasonal movements of the Inter-Tropical Convergence Zone (ITCZ). During the summer, the ITCZ is shifted southward due to the warming of the continent. Paleoclimate data from southeastern Amazonia and the central Andes indicate that these two areas evolved similarly during the last 30,000 yr. However, between 12,400 and 8800 cal yr B.P., eastern Amazonia received substantial moisture whereas the Bolivian Altiplano was arid. This suggests that the ITCZ during summer was then farther north than it is today.