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.

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.

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.

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.

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.

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.

Marine sediment cores from the continental slope off mid-latitude Chile (33°S) were studied with regard to grain-size distributions and clay mineral composition. The data provide a 28,000-yr14C accelerator mass spectrometry-dated record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland. These variations can be interpreted in terms of the paleoclimatic evolution of mid-latitude Chile and are compared to existing terrestrial records. Glacial climates (28,000–18,000 cal yr B.P.) were generally cold–humid with a cold–semiarid interval between 26,000 and 22,000 cal yr B.P. The deglaciation was characterized by a trend toward more arid conditions. During the middle Holocene (8000–4000 cal yr B.P.), comparatively stable climatic conditions prevailed with increased aridity in the Coastal Range. The late Holocene (4000–0 cal yr B.P.) was marked by more variable paleoclimates with generally more humid conditions. Variations of rainfall in mid-latitude Chile are most likely controlled by shifts of the latitudinal position of the Southern Westerlies. Compared to the Holocene, the southern westerly wind belt was located significantly farther north during the last glacial maximum. Less important variations of the latitudinal position of the Southern Westerlies also occurred on shorter time scales.

The magnetobiostratigraphy study of the 130-m-thick Zújar section (Negratı́n clays unit, Guadix-Baza Basin, Spain) provides a remarkable opportunity to improve the correlation of European mammal biostratigraphy to the Geomagnetic Polarity Time Scale. The occurrence of 12 well-defined magnetozones and four paleontological sites with diagnostic faunas ranging from the MN 15 biozone (Ruscinian) to the MN 17 biozone (Villanyian), leads to an unambiguous correlation to chrons spanning from the Gilbert to the Matuyama epochs. This provides two new time constraints: (1) the boundary between MN 15 (Ruscinian) and MN 16 (Villanyian) biozones is recorded between chron C2An.3n and the base of chron C2An.2n and (2) the boundary between the upper and lower MN 16 subzones (Villanyian) is located between chron C2An.2n and the base of chron C2An.1n. The correlation between the Ruscinian–Villanyian boundary and the 3.3-myr-B.P. cooling event seems to be confirmed, while the early/late Villanyian boundary could be tentatively correlated to the glacial event at 2.6 myr B.P. Furthermore, MN 15 faunas are found in the lowermost part of chron C2Ar, which is in agreement with and reinforces the emplacement of the MN 14–MN 15 Ruscinian zones boundary at the reversal from chron 3n.1n to chron C2Ar.