Earth's land-sea distribution modifies the temperature response to orbitally induced perturbations of the seasonal insolation. We examine this modification in the frequency domain by generating 800,000-yr time series of maximum summer temperature in selected regions with a linear, two-dimensional, seasonal energy balance climate model. Previous studies have demonstrated that this model has a sensitivity comparable to general circulation models for the seasonal temperature response to orbital forcing on land. Although the observed response in the geologic record is sometimes significantly different than modeled here (differences attributable to model limitations and feedbacks involving the ocean-atmosphere-cryosphere system), there are several results of significance: (1) in mid-latitude land areas the orbital signal is translated linearly into a large (>10°C) seasonal temperature response; (2) although the modeled seasonal response to orbital forcing on Antarctica is 6°C, the annual mean temperature effect (<2°C) is only about one-fifth that inferred from the Vostok ice core, and primarily restricted to periods near 41,000 yr; (3) equatorial regions have the richest spectrum of temperature response, with a 3000-yr phase shift in the precession response, plus some power near periods of 10,000–12,000 yr, 41,000 yr, 100,000 yr, and 400,000 yr. Peaks at 10,000–12,000 yr and 100,000 and 400,000 yr result from the twice-yearly passage of the sun across the equator. The complex model response in equatorial regions has some resemblance to geologic time series from this region. The amplification of model response over equatorial land masses at the 100,000-yr period may explain some of the observed large variance in this band in geologic records, especially in pre-Pleistocene records from times of little or no global ice volume.

The geochemistry, petrography, and distribution of the Jarvis Creek Ash (Péwé, 1965, 1975a) indicate that this tephra from the lower Delta River area of central Alaska is correlative with vol volcanic ash from sites in south-central Alaska near Tangle Lakes (upper Delta River area) and the Cantwell ash from Hayes volcano found in the upper Nenana River area (Riehle et al., 1990). Volcanic glass compositions of distal Jarvis Creek and Tangle Lakes tephra samples are compositionally restricted, while several discrete glass populations are present in some samples are compositionally collected nearer Hayes volcano. These correlations extend the known distribution of Hayes volcano tephras across the Alaska Range and into central Alaska, a distance of more than 650 km. New geochronologic data for the Jarvis Creek Ash suggest it was deposited ca. 3660 ± 125 yr B.P., consistent with previous age estimates of tephra eruptions at the Hayes volcano. The name “Jarvis Creek Ash” has well-established priority with respect to “Cantwell ash” or other local names for this tephra layer from the Hayes volcano.

Temporal change in the growth of speleothems in the United Kingdom during the past 150,000 years is shown to be related to the insolation variation by the Milankovitch theory. The speleothem data compiled by Gordon et al. (1989. Quarternary Research 31, 14–26) have two Milanokovitch frequencies: the ca. 40,000-yr period related to change in the earth's obliquity and the ca. 20,000-yr period related to the precession of the equinoxes. The abundance of speleothem growth was, in general, large during the last interglaciation and small during the last glaciation. In both periods, however, speleothem abundance was greater during periods of strong insolation and less during weak insolation.

Recent explanations of widespread rhythmically layered sediments in eastern Washington as the result of repeated great floods from glacial Lake Missoula implicitly suggest a paleomagnetic test for validity. If each conjectural flood layer is separated by years or decades, as hypothesized, a sequence of several such flood beds should record measurable secular variation in geomagnetic field direction. In the Sanpoil River valley where the rhythmite sequences are thought to have been deposited in glacial Lake Columbia, the paleomagnetic test consists of measuring remanent magnetization (RM) directions for thick, upwardly fining beds inferred to be sediments deposited by the influx of flood waters from glacial Lake Missoula into glacial Lake Columbia. Laboratory measurements of samples from three widely spaced sections along the Sanpoil River yield RM vectors with erratic inclinations, apparently affected by varying contributions of inclination error and (or) compaction shallowing, but with declinations that generally differ statistically from one flood to the next and that show the same west-to-east trend at all three locations. The rates of declination change inferred from these data are consistent with modern rates, thus providing the first geophysical evidence supporting the timing in the tens-of-floods theory.

Magnetic and chemical analyses of 1-m piston cores from Loch Ba, Scotland illuminated the presence of a ferrimagnetic mineral which is sensitive to atmospheric oxidation and is soluble in H2O2. This phase, plausibly only an authigenic sulfide, is probably spinel Fe3S4 (greigite). Authigenesis of Fe3S4 requires reactive FeS and elemental S, the latter likely being derived from in situ oxidation of bisulfide near the sediment redoxycline. This is consistent with the observation of maximum “oxidation-sensitive” magnetic fractions around the oxic/anoxic sediment boundary at ca. 4–16 cm depth. Progressive pyritization of Fe3S4 during burial provides the most viable explanation for the loss of “oxidation-sensitive” phases at greater depth. The results extend the range of environments known to be subject to postdepositional magnetic enhancement to include oligotrophic lakes with relatively low productivity. This may have ramifications for magnetically based sediment-source linkage, core correlation, and pollution studies which fail to demonstrate that magnetostratigraphic profiles are solely reflectively of allogenic mineral presence.

The 13C/12C ratios of occluded carbon within opal phytoliths from the northern Great Plains show potential as a basis for paleoclimatic reconstruction. A significant correlation exists between the carbon isotopic composition of a host plant and that of the organic matter in its phytoliths. The 13C/12C ratios for phytoliths from surface layers of soils along climatic gradients reflect the current proportions of C3 and C4 plants. Variations in the δ13C values of phytoliths with soil depth are caused by a variety of processes: burial of soil surface by dust, bioturbation, and possible illuviation by percolating water. Also, contributions of phytoliths by dust and roots have unknown isotopic effects. The δ13C values of phytoliths from soils increase with decreasing 14C age, suggesting that the proportion of C4 plants in this region has increased during the Holocene. Phytoliths of apparent mid-Holocene age suggest exclusive dominance by C4 plants which agrees with paleoclimatic interpretations of an arid middle Holocene climate.

Pollen analysis of a 15.5-m sediment core from Lake Naivasha, central Rift Valley of Kenya, reveals that the vegetation from before 20,290 to nearly 12,000 yr B.P. was dominated by open grassland, indicating arid conditions. Within this period a moderately wetter climate existed between 17,000 and 15,000 yr B.P., shown by relatively slight increase in both the montane and lowland forest vegetation. From approximately 12,000 to 6500 yr B.P., a change toward more trees and forests started at lower altitudes around the basin of Lake Naivasha, and later in the higher montane regions. After 6000 yr B.P. a decline in forest and lowland trees opened the vegetation into more grasslands and by 4000 yr B.P. a vegetation similar to the present was attained and has persisted to the present. During this period shallow-water aquatic plants became abundant in Lake Naivasha.

The Makatea Islands in the southern Cook Islands consist of a degraded volcanic core surrounded by emergent “makatea” limestones. While much of this reefal limestone is of Tertiary age, the seawardmost reefs are late Pleistocene. Last-interglacial reefs (oxygen isotope substage 5e) identified by U-series dating reach 12.2 m on Atiu (mean age of three samples 126,000 ± 5000 yr B.P.), 9.8 m on Mitiaro (mean age of five samples 119,000 ± 3000 yr B.P.), 10.0–12.7 m on Mauke (mean age of four samples 128,000 + 5000, −4,000 yr B.P.), and 14.5–20.0 m on Mangaia (mean age of four samples 115,000 ± 7000 yr B.P.). On Atiu, Mauke, and Mitiaro a lower reef unit has been identified, and is separated from the overlying substage 5e reef by a sharp discontinuity, often with a crust of coralline algae. U-series dating from Atiu and Mauke indicates that this is a stage 7 reef formed in the penultimate interglaciation. The Makatea Islands have emerged as a result of flexure of the lithosphere in response to loading by the Pleistocene volcanic island of Rarotonga. Isolated outcrops of makatea limestone on Rarotonga reach 3.5 m and are probably of substage 5e age. Elastic and viscoelastic models of lithospheric flexure predict that much of the compensatory movement should occur shortly after the emplacement of the load. However, the age and elevation of late Quaternary reefs on the southern Cook Islands, where a Pleistocene volcanic island has loaded relatively old ocean floor (>80 myr), indicate that differential uplift has been continuing over the last 250,000 yr.

Corals from raised reef terraces on two islands (Zabargad and Northern Brother), considered to have been tectonically uplifted in connection with the Red Sea rifting, were dated with the U-series method. At Zabargad, there are at least three systems of raised coral reefs. The oldest terrace (>290,000–300,000 yr B.P.) is found at +10 to +15 m. A 200,000 yr B.P. high-sea stand is recorded by a terrace relict at +17 m on peridotite bedrock; the youngest system (125,000–138,000 yr B.P.) is very well represented around the island, with terraces at about +6 to +8 m. Corals from Northern Brother yield ages of 132,000–135,000 and 204,000 yr B.P. suggesting the existence of two systems of interglacial raised reefs. Both islands appear to have been tectonically quite stable since at least 125,000 yr B.P.

Multiple stratigraphies of subtropical South Atlantic cores reveal significant stratigraphic discrepancies between the nannofossil and the foraminiferal carbonates. Variations in the stratigraphic signals carried in the nannofossil-dominated <38 μm fraction and foraminifera-dominated >38 μm fraction were measured with detailed stratigraphies of δ18O, δ13C, 14C, grain size, percentage carbonate, percentage aragonite, and taxonomic composition across the last deglaciation in INMD box core 111 No. 9. Three other cores (INMD box cores 113 and 115, and V 22–174), also from the shallow flanks of the mid-Atlantic ridge in the South Atlantic (10°–17° S), contain similar stratigraphies indicating that these cores represent regional patterns. The onset of the deglacial δ18O shift in foraminiferal carbonate occurs 6 to 20 cm deeper than the δ18O shift in the nannofossil fraction. Nineteen accelerator mass spectrometer 14C dates of various fractions (<38 μm, 38–62 μm, 62–150 μm, 150–250 μm, >355 μm, and G. ruber) from INMD Box 111 show that the components within an individual core slice may differ by up to 4900 14C years. Twelve traditional 14C dates (determined by beta counting) of the >38 and <38 μm fractions from six levels in INMD Box 111 No. 6 confirm the large offsets. The observed isotopic offsets are not explained by an individual process, and suggest that multiple causes have left a lumpy stratigraphic record. However, the variability in the data illustrates the difficulty in accurately measuring the chronology of deglaciation, reopens the question of which components of pelagic sediment best monitor surface water conditions, and complicates the direct interpretation of benthic-planktonic age differences in terms of ocean ventilation changes.

A 20-cm-thick volcanic ash layer at the Palisades along the Yukon River is geochemically correlated with the Old Crow tephra. A buried organic and wood-rich layer above the Old Crow tephra probably records the last interglaciation. The recognition of the Old Crow tephra provides the first chronologic information on the age of the thick sequence of Pleistocene sediments at the Palisades, an important ice-age mammal site in central Alaska and a key locality for the reconstruction of the history of the Yukon River and the last interglaciation in central Alaska.