A microparticle concentration peak in a GISP2 ice core contains volcanic glass shards of rhyolitic composition that correspond in age to the 1479-1480 A.D. Mt. St. Helens Wn eruption. These glass shards are compositionally similar to the Wn tephra and constitute 83% of the total particle population. The shards are very coarse-grained (up to 40 μm diameter), suggesting rapid transport from their source to Greenland. A major sulfate peak in the ice occurs approximately 4 months after deposition of the glass shards. This difference in depositional timing suggests primarily tropospheric transport of the ash and stratospheric transport of the sulfate aerosol. Large-scale climatic perturbations following this eruption were evidently negligible. Glaciochemical seasonal indicators suggest a late-fall to early-winter 1479 A.D. eruption.

Optical dating of late Quaternary quartz dune sands from the Clear Creek portion of Ferris dune field, Wyoming, demonstrates the considerable potential of the technique as a chronostratigraphic tool. A sequence of radiocarbon-dated Holocene interdune strata permit optical dating of the intercalated dune sand to be tested; the concordance is good. The optical dates for the aeolian deposits not datable by radiocarbon suggest that aeolian sedimentation at Clear Creek peaked during two relatively short phases at ca. 8500 and 4000 yr B.P. The dates indicate that aeolian accumulation maxima (at least in the Clear Creek area) may not be synchronous with previously defined phases of marked aridity.

Accelerator mass spectrometer radiocarbon ages of the Roxana Silt (loess) along the Upper Mississippi Valley of Wisconsin and Minnesota indicate that loess sedimentation of the Roxana Silt occurred between about 55,000 and 27,000 14 C yr B.P. However, due to local environmental controls, the basal age at any given site may range from 55,000 to 35,000 14C yr B.P. The radiocarbon ages presented here are in agreement with previous radiocarbon ages for the Roxana Silt in its type area of west-central Illinois, but indicate that long-term sedimentation rates along the bluffline of the Upper Mississippi Valley were very slow (4-8 cm/1000 yr) compared to long-term sedimentation rates along the bluffline of the type area (40-70 cm/1000 yr). Comparison of radiocarbon ages for midcontinent middle Wisconsinan loess deposits indicates that sedimentation along the Mississippi River valley may have preceded loess sedimentation along the Missouri River valley by as much as 20,000 yr or that basal ages for middle Wisconsinan loess along the Missouri Valley are erroneously young. The bracketing ages for the Upper Mississippi Valley Roxana Silt indicate that the Mississippi River valley was receiving outwash sedimentation between 55,000 and 27,000 14C yr B.P.

Streamflow since 1560 A.D. for four rivers within the Sacramento River Basin, California, has been reconstructed dendroclimatically. Both the highest and the lowest reconstructed streamflows occurred during the historical period, with high flows from 1854 to 1916 and low flows from 1917 to 1950. Prolonged (decade-scale) excursions from the mean have been the norm throughout the reconstructed period. The periods of high and low streamflow in the Sacramento Basin are generally synchronous with wet and dry periods reconstructed by dendroclimatic studies in the western United States. The record indicates a number of asynchronous droughts or wet years. The strongest contrasts are developed between northern (western Washington and Oregon or the Columbia Basin) and southern (the Sacramento Basin or central California) climate regions. These asynchronous events may be due to variation in the latitude of the subtropical high and in the latitudinal position of winter storms coming off the Pacific. No association was found with El Niño-Southern Oscillation events.

Although the Tibetan Plateau greatly influences the atmospheric circulation of the Nortbern Hemisphere, few continuous paleoclimatic records are available from the plateau. A 13,000-yr pollen and diatom record from the Sumxi-Longmu Co basin in western Tibet gives information on major changes both in regional vegetation and in local hydrology. After the basin first filled ca. 13,000 yr B.P., a dry spell occurred about 10,500 yr B.P. within the interval spanned by the European Younger Dryas chronozone. A major environmental change occurred suddenly at ≈10,000 yr B.P., with the establishment of wet conditions, and was followed by a long-term trend toward maximum aridity, which lasted approximately 6000 yr. Short-term oscillations are superimposed on this general climatic change with a major reversal event about 8000 yr B.P. and a second wet pulse leading to a maximum lake volume ca. 7500-6000 yr B.P. Maximum aridity occurred 4300 yr B.P. The major environmental fluctuations recorded at Sumxi-Longmu Co appear in phase with climatic changes recognized in north tropical Africa, suggesting that the 8000 to 7000-yr-B.P. event was caused by an abrupt disequilibrium in the climatic system, as was the Younger Dryas and possibly the 4300-yr-B.P. event.

Sediment cores from three lakes in the Upper Kolyma region, northeast Russia, provide the first well-dated continuous record of late Quaternary vegetation change from far southwestern Beringia. The oldest pollen zone, tentatively assigned to the Karginsk (mid-Wisconsinan) Interstade, indicates an Artemisia shrub tundra with Pinus pumila, Betula, and Alnus at mid- to low elevations. With the onset of the Sartan (late Wisconsinan) Stade, Pinus disappeared, probably indicating severely cold, dry winters and cool summers. As conditions deteriorated further, an Artemisia -Gramineae tundra developed. Selaginella rupestris and minor herb taxa indicate the presence of poor soils and disturbed ground. This herb tundra was replaced by a short-lived (< 1000 yr) Betula-Alnus shrub tundra followed by the rapid establishment of a Larix dahurica forest with a Betula exilis-ericales-lichen understory. Populus suaveolens and Chosenia may have formed limited hardwood gallery forests at this time. Modern vegetation associations probably developed during the early Holocene with the arrival of Pinus pumila ca. 9000 yr B.P. This shrub became important in the forest understory and, with B. exilis, formed a belt of shrub tundra beyond altitudinal treeline. Comparison of the Upper Kolyma and Alaskan pollen records indicates that important differences in vegetation types and timing of vegetation change occurred across Beringia during the late Quaternary.

Pollen evidence from Lake Shayema, Mianning County, was obtained to examine postglacial vegetation and climatic change in southwestern Sichuan, China. The sclerophyllous character of the region's warm temperate vegetation today is a reflection of extreme drought in spring before the onset of the Asian monsoons. The pollen record displays several changes in the vegetation over the last 11,000 yr. From 11,000 to 9100 yr B.P., cold-tolerant species, such as Abies , Betula, and deciduous oaks, dominated the vegetation. Between 9100 and 7800 yr B.P., the abundance of deciduous oaks decreased and evergreen oaks increased, as did Tsuga and mesic deciduous species. This change suggests a warming climate with increased precipitation. From 7800 to 4000 yr B.P., sclerophyllous species increased at the expense of mesic deciduous species, an indication that precipitation was becoming more seasonal. Except for increased disturbance starting ca. 1000 yr B.P., the predominance of sclerophyllous vegetation continued until today. The pollen results are compatible with proposed global circulation hypotheses of a strengthened monsoon system during the early to mid Holocene.

During strong El Niño events, rainfall anomalies and changes in wind patterns are observed in different regions of South America. Along the central Brazilian coast, during the 1983 El Niño year, the frontal systems were blocked to the south, provoking a reversal of the longshore sand transport. Long-duration reversals of longshore transport were also recorded in Holocene beach-ridge terraces from the Rio Doce coastal plain. This led to the formulation of a model relating these reversals of longshore transport to El Niño-like conditions. El Niño-like conditions are past average climate situations that generate the same perturbations as the strong El Niño events observed during the last decade. They are likely to correspond to the long-duration low phase of the Southern Oscillation. To confirm this hypothesis we compared the Holocene beach-ridge record with other palaeoenvironmental records from regions where strong El Niño events would have a substancial signal as well: (1) water-level fluctuations of Lake Titicaca, (2) a pollen and sediment record in an eastern Amazonian lake, (3) changes of the Rio Xingu discharge in eastern Amazonia, and (4) variations of sand supply at the Rio Piura and Rio Chira outlets in the Sechura Desert. The occurrences of El Niño-like conditions were numerous before 3900-3600 yr B.P., absent between 39003600 and 2800-2500 yr B.P., and infrequent after 2800-2500 yr B.P.

The existing paleoenvironmental data from the Australian arid zone lack sensitivity and come from only a few sites. Macrofossils and pollen from four dated middens of the stick-nest rat (Leporillus spp.) were analyzed from two sites in Western Australia. Animal and plant macrofossil remains were well preserved and provided evidence of change in species distribution within the last 1150 yr. Brush-tail possum and golden bandicoot have contracted their ranges in the recent past, possibly since the introduction of cats into Australia. An undescribed lacewing was also a significant find. Pollen preserved in parts of the same midden and in middens from different sites indicates that records are sensitive to the composition of the local vegetation when the midden was built. Pollen spectra are quite different from playa lakes, which record largely regional vegetation. Pollen preserved in the fecal pellets, desiccated urine, and grass mat nesting material provided similar information but some differences were apparent, suggesting dietary preferences were reflected in the fecal component. The pollen record suggested a trend to less-wooded vegetation cover in central Australia between 900 and 300 yr B.P.

In Atlantic Canada, bulk-sediment dates for the onset of a late-glacial cooling, widely regarded as the Younger Dryas event, are highly variable, ranging from 14,300 ± 270 to 10,800 ± 100 yr B.P. We present the first accelerator-mass-spectrometer (AMS) 14C dates from Atlantic Canada, at or close to the boundaries of this event, from six sites in New Brunswick and Nova Scotia. The mean of five dates places the onset of this cooling at ca. 10,770 yr B.P.; the inclusion of a sixth, perhaps anomalously old date, changes the mean to 10,880 yr B.P. The termination averages (three dates) ca. 10,000 yr B.P. These dates place the timing of the Younger Dryas event in Atlantic Canada closer in line with the traditional chronozone boundaries of 11,000 and 10,000 yr B.P. in Northwest Europe.

During the latter part of the last (Otira) glaciation the forest cover of New Zealand was much reduced. It has frequently been postulated, however, that diverse mixed forest communities survived in the far north of North Island. Pollen diagrams and radiocarbon dates from two last glacial and postglacial (Aranuian) sits on the Aupouri Peninsula in the far north of New Zealand are compared with other published palynological and plant macrofossil evidence from the region. Mixed kauri/podocarp/angiosperm forest was present at times during the late Otiran (and Aranuian) and no evidence was found for substantial loss of forest. However, radiocarbon samples from one site, at least, seem to have been contaminated with young carbon; this introduces uncertainty into the chronology established at that site. Possibly nondeposition or erosion has obscured part or all of the late Otiran record at all the sites studied so that very much reduced forest cover at that time cannot be ruled out.

Reevaluation of Quaternary sites of fossil pika (Ochotona) lends no support for the inference that Nearctic pikas were not restricted to rocky habitat. The saxicolous nature of all widespread, isolated populations of extant Nearctic pikas and their closest Palearctic sister taxa support consideration of O. princeps, and perhaps all Nearctic Quaternary Ochotona , as indicators of cool, mesic, rocky situations. As indicators of rocky microhabitat, fossil remains of O. princeps do not require that the entire region was cool and mesic, but only that suitable rocky microhabitat existed in the vicinity. Use of fossil pika dung alone as indicative of pikas in the immediate community is suspect, as the small, round, and buoyant pellets may be transported downslope by hydraulic flushing of talus habitat. Current local elevational lower limits (E) of appropriate habitat for paleoecological reconstruction at extralimital fossil sites are predicted by the equation: E(m) = 14087 - (56.6)°N - (82.9)°W.

Sediments exposed at Epiguruk, a large cutbank on the Kobuk River about 170 km inland from Kotzebue Sound, record multiple episodes of glacial-age alluviation followed by interstadial downcutting and formation of paleosols. Vertebrate remains from Epiguruk include mammoth, bison, caribou, an equid, a canid, arctic ground squirrel, lemmings, and voles. Radiocarbon ages of bone validated by concordant ages of peat and wood span the interval between about 37,000 and 14,000 yr B.P. The late Pleistocene pollen record is dominated by Cyperaceae, with Artemisia, Salix, Betula, and Gramineae also generally abundant. The fossil record from Epiguruk indicates that the Kobuk River valley supported tundra vegetation with abundant riparian willows during middle and late Wisconsin time. Large herbivores were present during the height of late Wisconsin glaciation as well as during its waning stage and the preceding interstadial interval. The Kobuk River valley would have been a favorable refugium for plants, animals, and possibly humans throughout the last glaciation.

The archaeological record from the last millennium in southern California indicates that a period of significant cultural change was associated with a reported marine paleoenvironmental disruption ca. 1150-1250 A.D. A lengthy warm-water anomaly may have in part precipitated more complex sociopolitical and economic responses. We develop independent verification of the perturbation (originally deduced from sediment core data) using archaeological data. Respiratory pore number allometry in the black abalone shell is known to vary clinally in modern populations in response to temperature-induced variation in rate of growth. We use developmental trajectories of abalone from dated, stratified archaeological deposits to reconstruct prehistoric seawater temperatures.