In the northeastern St. Elias Mountains in southern Yukon Territory and Alaska, C14-dated fluctuations of 14 glacier termini show two major intervals of Holocene glacier expansion, the older dating from 3300-2400 calendar yr BP and the younger corresponding to the Little Ice Age of the last several centuries. Both were about equivalent in magnitude. In addition, a less-extensive and short-lived advance occurred about 1250-1050 calendar yr BP (A.D. 700–900). Conversely, glacier recession, commonly accompanied by rise in altitude of spruce tree line, occurred 5975–6175, 4030-3300, 2400-1250, and 1050-460 calendar yr BP, and from A.D. 1920 to the present. Examination of worldwide Holocene glacier fluctuations reinforces this scheme and points to a third major interval of glacier advances about 5800-4900 calendar yrs BP; this interval generally was less intense than the two younger major intervals. Finally, detailed mapping and dating of Holocene moraines fronting 40 glaciers in the Kebnekaise and Sarek Mountains in Swedish Lapland reveals again that the Holocene was punctuated by repeated intervals of glacier expansion that correspond to those found in the St. Elias Mountains and elsewhere. The two youngest intervals, which occurred during the Little Ice Age and again about 2300–3000 calendar yrs BP, were approximately equal in intensity. Advances of the two older intervals, which occurred approximately 5000 and 8000 calendar yr BP, were generally less extensive. Minor glacier fluctuations were superimposed on all four broad expansion intervals; those of the Little Ice Age culminated about A.D. 1500–1640, 1710, 1780, 1850, 1890, and 1916. In the mountains of Swedish Lapland, Holocene mean summer temperature rarely, if ever, was lower than 1°C below the 1931–1960 summer mean and varied by less than 3.5°C over the last two broad intervals of Holocene glacial expansion and contraction.

Viewed as a whole, therefore, the Holocene experienced alternating intervals of glacier expansion and contraction that probably were superimposed on the broad climatic trends recognized in pollen profiles and deep-sea cores. Expansion intervals lasted up to 900 yr and contraction intervals up to 1750 yr. Dates of glacial maxima indicate that the major Holocene intervals of expansion peaked at about 200–330, 2800, and 5300 calendar yr BP, suggesting a recurrence of major glacier activity about each 2500 yr. If projected further into the past, this Holocene pattern predicts that alternating glacier expansion-contraction intervals should have been superimposed on the Late-Wisconsin glaciation, with glacier readvances peaking about 7800, 10,300, 12,800, and 15,300 calendar yr BP. These major readvances should have been separated by intervals of general recession, some of which might have been punctuated by short-lived advances. Furthermore, the time scales of Holocene events and their Late-Wisconsin analogues should be comparable. Considering possible errors in C14 dating, this extended Holocene scheme agrees reasonably well with the chronology and magnitude of such Late-Wisconsin events as the Cochrane-Cockburn readvance (8000–8200 C14 yr BP), the Pre-Boreal interstadial, the Fennoscandian readvances during the Younger Dryas stadial (10,850-10,050 varve yr BP), the Alleröd interstadial (11,800-10,900 C14 yr BP), the Port Huron readvance (12,700–13,000 C14 yr BP), the Cary/Port Huron interstadial (centered about 13,300 C14 yr BP), and the Cary stadial (14,000–15,000 C14 yr BP). Moreover, comparison of presumed analogues such as the Little Ice Age and the Younger Dryas, or the Alleröd and the Roman Empire-Middle Ages warm interval, show marked similarities. These results suggest that a recurring pattern of minor climatic variations, with a dominant overprint of cold intervals peaking about each 2500 yr, was superimposed on long-term Holocene and Late-Wisconsin climatic trends. Should this pattern continue to repeat itself, the Little Ice Age will be succeeded within the next few centuries by a long interval of milder climates similar to those of the Roman Empire and Middle Ages.

Short-term atmospheric C14 variations measured from tree rings correlate closely with Holocene glacier and tree-line fluctuations during the last 7000 yr. Such a correspondence, firstly, suggests that the record of short-term C14 variations may be an empirical indicator of paleoclimates and, secondly, points to a possible cause of Holocene climatic variations. The most prominent explanation of short-term C14 variations involves modulation of the galactic cosmic-ray flux by varying solar corpuscular activity. If this explanation proves valid and if the solar constant can be shown to vary with corpuscular output, it would suggest that Holocene glacier and climatic fluctuations, because of their close correlation with short-term C14 variations, were caused by varying solar activity. By extension, this would imply a similar cause for Late-Wisconsin climatic fluctuations such as the Alleröd and Younger Dryas.

This paper attempts to relate current knowledge of sea-level history in Beringia to the Broecker-van Donk “Termination” concept of climatic and sea-level history. The Einahnuhtan transgression is thought to represent Termination III, which according to Broecker and van Donk, took place about 225,000 y.a. The Kotzebuan transgression is thought to represent a positive fluctuation that modulated the generally falling sea level during the ensuing 100,000 yr. Sea level probably fell to about −135 m in the Bering Sea area during the maximum phase of the penultimate glaciation. The two Pelukian shorelines probably represent Termination II (about 125,000 yr BP in the Broecker-van Donk chronology) and one of the two positive fluctuations that modulated the generally falling sea level of early Wisconsinan time, about 105,000 and 80,000 y.a. according to Broecker and van Donk. Another positive modulation brought sea level to at least −20 m, about 30,000 y.a. Sea level evidently fell to between −90 and −100 m during the late Wisconsinan regression, but a substantial part of the outer Bering shelf remained submerged. Submerged shoreline features at −38m, −30 m, −24 to −20 m, and −12 to −10 m represent stillstands or slight regressions that modulated Termination I, the late Wisconsinan, and early Holocene recovery of sea level.

European geologists, in general, have tended to favor a “short” chronology for the glacial Pleistocene, with four major glacial cycles in the past 500,000 or 600,000 yr. Interpretation of ocean floor sediments by Emiliani and others has accorded with this view, in contrast to the “long” chronology of Ericson and Wollin and their followers, who spread the four North American glacial episodes over a 2-m.y. period. An examination of the available radiometric dates and age estimates from paleomagnetic polarity zones serves to confirm Richmond's view that the four major European glacials do not equate with the four North American glacials in a simple one-to-one manner, but that the Illinoian matches the Elster (Mindel) rather than the Saale (Riss). The Alpine Günz is then equated broadly with the Kansan and overlaps in time with the Jaramillo normal polarity event at about 900,000 y.a. The Nebraskan is older than 1.2 m.y. and is thus coeval with the European Upper Villafranchian, within which the Donau and Biber glacial events may be traced. Montane glaciation certainly extended back into the Tertiary but cold pulses of sufficient duration to produce continental glaciation were more marked through the past 1.5 m.y. More critical studies of the terrestrial record are needed before firm correlations can be made.

Spectral analysis of deep-sea sediments indicates that the fluctuations in compositional parameters are not random fluctuations with time. Spectra show significant peaks representing periodicities in the data of 380, 1300, and 2600 years. Two of these periods are similar to periods reported in 14C fluctuations. Analysis of a paleotemperature curve from the North Atlantic shows that the characteristics of the fluctuations within interglacial and glacial stages of the climate are similar, and that the spectrum has a significant peak at 2600 years.

Fire largely determined the composition and structure of the presettlement vegetation of the Boundary Waters Canoe Area as well as the vegetation mosaic on the landscape and the habitat patterns for wildlife. It also influenced nutrient cycles, and energy pathways, and helped maintain the diversity, productivity, and long-term stability of the ecosystem. Thus the whole ecosystem was fire-dependent.

At least some overstory elements in virtually all forest stands still date from regeneration that followed one or more fires since 1595 A.D. The average interval between significant fire years was about 4 yr in presettlement times, but shortened to 2 yr from 1868 to 1910 during settlement. However, 83% of the area burned before the beginning of suppression programs resulted from just nine fire periods: 1894, 1875, 1863–1964, 1824, 1801, 1755–1959, 1727, 1692, 1681. The average interval between these major fire years was 26 yr. Most present virgin forests date from regeneration that followed fires in these years. Significant areas were also regenerated by fires in 1903, 1910, 1936, and 1971. Most major fire years occurred during prolonged summer droughts of subcontinental extent, such as those of 1864, 1910, and 1936. Many fires were man-caused, but lightning ignitions were also common. Lightning alone is probably a sufficient source of ignitions to guarantee that older stands burned before attaining climax. Dry matter accumulations, spruce budworm outbreaks, blowdowns, and other interactions related to time since fire increase the probability that old stands will burn. Vegetation patterns on the landscape were influenced by such natural firebreaks as lakes, streams, wetlands, and moist slopes. Red and white pine are most common on islands, and to the east, northeast, or southeast of such firebreaks. Jack pine, aspen-birch, and sprout hardwood forests are most common on large uplands distant from or west of such firebreaks.

A Natural Fire Rotation of about 100 yr prevailed in presettlement times, but many red and white pine stands remained largely intact for 150–350 yr, and some jack pine and aspen-birch forests probably burned at intervals of 50 yr or less. There is paleoecological evidence that fire was an ecosystem factor before European man arrived, and even before early man migrated to North America. Probably few areas ever attained the postulated fir-spruce-cedar-birch climax in postglacial times. To understand the dynamics of fire-dependent ecosystems fire must be studied as an integral part of the system. The search for stable communities that might develop without fire is futile and avoids the real challenge of understanding nature on her own terms.

To restore the natural ecosystem of the Canoe Area fire should soon be reintroduced through a program of prescribed fires and monitored lightning fires. Failing this, major unnatural, perhaps unpredictable, changes in the ecosystem will occur.

A simplified and more accurate version of the quantitative paleoenvironmental method proposed by Imbrie and Kipp (1971) is described, which is based on untransformed rather than transformed species per cent data. The method yields faunal indices (Ts, Tw, S), useful both as objective measures of paleontological properties and as estimates of Pleistocene sea-surface summer and winter temperatures (Ts, Tw) and salinity (S). Similarly, the oxygen-isotope method yields objective measurements of δ O18, useful stratigraphically and as indications of past changes in isotopic water composition and temperature.

Laboratory errors of the two methods have about the same magnitude relative to ranges observed in V12-122. Accuracy of faunal indices as estimates of oceanic conditions is evaluated by study of modern oceanographic data and sea-bed samples. Under favorable conditions, accuracy is apparently limited primarily by the degree of ecological control exercised by the estimated parameter. Accuracy of the isotopic paleotemperature estimates is limited primarily by uncertainty as to the magnitude of the water-correction term in the isotope equation, a value which combines global ice-volume and local evaporation-precipitation effects.

Curves of δ O13 and S in V12-122 record all or part of seven major climatic cycles, and display a fundamental periodicity of about 85,000 years. Ts and Tw curves show small but significant differences: two phase shifts in estimated temperature minima, and a long-term increasing trend.

Amplitude-frequency histograms of Tw and δ O18 indicate that only two percent of the time during the past 450,000 years have Caribbean temperatures been as warm and isotopic ratios as low as they are today.

A comparison of the magnitude of δ O18 change (2.2%.) during the shift from late-glacial to post-glacial times, with that of the faunally estimated change in average temperature (2.2°C), provides a basis for estimating the associated change in isotopic water composition (1.8%.) by back-calculation in the isotope equation. At least 0.4%. of this change in A is attributed to an evaporation-precipitation effect, and the balance (≤1.4%.) to an icevolume effect.

Isotopic and faunal methods monitor different responses to global climatic change. Used in conjunction, they provide deeper insights into the past than either could achieve alone.

Bed I in Olduvai Gorge spans the interval from about 1.7 to 2.0 m.y.a., and all evidences of hominid activity at Olduvai are within the latter half of this period. Bed I was deposited in a closed basin approximately 25 km in average diameter, and it can be subdivided into five lithologically different but partly time-equivalent rock assemblages, or lithologic facies, each of which was deposited in the same geographic environment or closely related series of environments. These lithofacies comprise lake deposits, lake-margin deposits, alluvial-fan deposits, alluvial-plain deposits, and lava flows.

Alluvial-plain deposits form the lowermost part of Bed I, and they presumably interfinger northeastward with lake deposits in an area not now exposed. Discharge of the lavas diplaced the lake westward to a position it occupied through the latter half of the deposition of Bed I. The lake fluctuated greatly in salinity, level, and extent, and at times of low level it was highly saline and generally ranged between 7 and 10 km in average diameter. At times of high level it was as much as 15 km in diameter and was relatively fresh, at least along its southeastern margin. The lake-margin deposits accumulated on the zone of relatively flat terrain that was flooded at times of high level. Lake-margin deposits interfinger eastward with deposits of an alluvial fan of pyroclastic materials produced in an explosive phase of the volcano Olmoti. The climate at the time of Bed I was relatively dry although somewhat wetter than the present climate in the same region today.

Quaternary paleotemperatures and sea level records, from both deep sea cores and dated shorelines, provide the basis for testing the Milankovitch hypothesis of climatic change. The longest and most detailed records include (1) oxygen isotope analyses of Caribbean and Atlantic deep sea cores, (2) paleoecological analyses of the same cores, and (3) radiometrically dated raised coral reefs from New Guinea and elsewhere, representing times of relatively high Quaternary sea levels. Time-domain and frequency-domain analysis of these records, shows with a high degree of certainty that Quaternary climatic changes are strongly influenced by the obliquity perturbations and precession of the Earth's orbit. The same analyses also suggest that the time scale adopted by Emiliani for deep sea cores may be more nearly correct than alternative time scales of other workers.

The question of whether insolation changes arising from orbital perturbations can generate ice ages, has been disputed by climatologists. It is shown here that orbital perturbations cannot affect climate indirectly through agencies originating within the Earth, such as vulcanism, and that the primary climatic control is therefore through variation of insolation distribution, as Milankovitch suggested. The conclusion is that climatologic theory must accommodate these facts.

Radiocarbon dates on molluses in marine facies associated with glacial deposits in northern Cumberland Peninsula indicate both main fiord (Laurentide) ice and local glaciers remained at their late Wisconsin maxima until ca. 8000 BP. Essentially continuous deglaciation followed; local corrie glaciers melted out by 7100 BP and by 5500 BP fiord glaciers had receded behind the present margin of the Penny Ice Cap. The Hypsithermal warm interval probably lasted from ca. 8000 to 5000 BP. Lichenometry and radiocarbon dates on peat and buried organic horizons delimit a detailed Neoglacial chronology. Of 46 outlet and corrie glaciers investigated, the oldest Neoglacial moraines are dated lichenometrically at 3200 ± 600 BP. Subsequent advances terminated immediately prior to ca. 1650, 780, 350, and 65 yr BP, the most recent of which marked the most extensive ice coverage during the Neoglacial. The highest occurrence of lateral moraines from late Wisconsin advances of local and Laurentide ice suggest that at the late Wisconsin glacial maximum, depression of snowline varied from 450 m below present at the coast to 350 m below present level in the vicinity of the Penny Ice Cap. Moraines, surrounded by glacial ice and lying above the present steady-state ELA, suggest that during the Hypsithermal snowline was up to ca. 200 m above its present elevation. A radiometrically controlled reconstruction of relative summer paleotemperatures for the postglacial derived independently of lichenometry agrees well with the lichenometric age dating of moraines. The data suggest that between ca. 1650 and 900 BP climatic conditions were unfavorable for glacier growth, whereas the period ca. 800-65 yr BP was one of general glacial activity. During the last decade permanent snow cover has been increasing in the area. Previously reported data on climatic trends in the Canadian Arctic based on palynological analyses are similar to the chronology reported here.

After a summary assessment of certain selected early man sites in various parts of America, the environment of the Venezuelan coastal plain is discussed in order to evaluate the stratigraphy and radiometric dating of the Taima-Taima site, near Coro, Venezuela, where mammals, many now extinct, were killed by people making El Jobo points about 13,000 years ago.

Potentially important areas in Peru, Chile and Brazil are mentioned. Certain problems in the models and interpretation of South American paleoclimates are pointed out.

The presence of at least four different bifacially flaked stone projectile point traditions in widely separated and environmentally diverse parts of America between 11,000 and 13,000 yr ago suggests that the immediate cultural antecedents of these traditions were essentially independent of one another. From this it is argued that several early American flaked-stone point traditions developed indigenously in America from technological bases which were present in the Old World Middle Paleolithic.

The record of charcoal in lake sediments indicates that fire has always been an important ecological factor in the forest history of northeastern Minnesota. The annually laminated sediments of Lake of the Clouds permit precise dating of the charcoal peaks and record the changes in the influx of various pollen types. A detailed record of the past 1000 yr shows that the average frequency of fire is approximately 60–70 yr, with a range of about 20–100 yr. The amount of charcoal in sediments dating between 1000-500 y.a. is consistently higher than that for the last 500 yr, although the fire frequency for the two periods was not appreciably different. Pollen analysis shows no change or only short-term changes in the percentages of major pollen types following charcoal peaks.

Core Vema 28-238 preserves an excellent oxygen isotope and magnetic stratigraphy and is shown to contain undisturbed sediments deposited continuously through the past 870,000 yr. Detailed correlation with sequences described by Emiliani in the Caribbean and Atlantic Ocean is demonstrated. The boundaries of 22 stages representing alternating times of high and low Northern Hemisphere ice volume are recognized and dated. The record is interpreted in terms of Northern Hemisphere ice accumulation, and is used to estimate the range of temperature variation in the Caribbean.

Factor analysis of dissolution-resistant species of planktonic foraminifera in the >250 μm fraction of seabed and core samples from the tropical southeast Pacific yields five mappable varimax assemblages. The distribution of these assemblages in core tops is more related to the subsurface thermal structure than to the surface temperature. A transfer function relating the assemblages in core tops to the temperature at 200 m is applied to five cores. Cycles of estimated temperature in three cores are approximately in phase with climatic cycles in Atlantic cores spanning the past 200,000 yr, and display amplitudes on the order of 5°C. Two zones of increased calcium carbonate dissolution occur in these three cores. These zones occur in the transition from interglacial to glacial intervals. Temperature variations inferred are ascribed to fluctuations of the main thermocline, and the inference is made that during cold intervals the thermocline was displaced upward as the central water mass was areally diminished. A model of circulation dynamics suggests that such areal diminution would be associated with an intensified circulation. No significant fluctuations in the estimated 200 m temperature are inferred for a core in the Galápagos area during the last glacial, but a pronounced peak of high-latitude species Globorotalia inflata does occur. This peak is judged to reflect the removal of a low-oxygen ecological barrier.

During the period between 1650 least 32 fires occurred in Itasca and 1922 at State Park. Twenty-one of these fires were of major consequence. A fire occurred on the average of every 8.8 yr with “major” fires every 10.3 yr. Any specific location in the park was affected by fire about every 22 yr.

Individual burns varied in size from 580 acres to approximately 31,960 acres (99% of the park). Sixteen of the 21 “major” fires resulted in the regeneration of pine forests.

Moraines and rock glaciers in Front Range cirques record at least four, and possibly five, intervals of Holocene glacier expansion. The earliest and most extensive was the Satanta Peak advance, which deposited multiple terminal moraines near present timberline shortly before 9915 ± 165 BP. By 9200 ± 135 BP, timberline had risen to at least its modern elevation; by 8460 ± 140 BP, patterned ground on Satanta Peak moraines had become inactive. Although a minor ice advance may have occurred just prior to 7900 ± 130 BP, there is no evidence that glaciers or perennial snowbanks survived in the Front Range during the “Altithermal” maximum (ca. 7500–6000 BP), or during a subsequent interval of alpine soil formation (ca. 6000–5000 BP).

Glaciers were larger during the Triple Lakes advance (5000–3000 BP) than at any other time during Neoglaciation. Minimum ages of 4485 ± 100 BP, 3865 ± 100 BP, and ca. 3150 BP apply to a threefold sequence of Triple Lakes deposits in Arapaho Cirque. After an important interval of soil formation and cavernous weathering, glaciers and rock glaciers of the Audubon advance (1850–950 BP) reoccupied many cirques, and perennial snowbanks blanketed much of the area above present timberline; although the general Audubon snow cover had begun to melt from valley floors by 1505 ± 95 BP, expanded snowbanks lingered on tundra ridge crests until 1050–1150 BP, and glaciers persisted is sheltered cirques until at least 955 ± 95 BP. Following a minor interval of ice retreat, glaciers of the Arapaho Peak advance (300–100 BP) deposited multiple moraines in favorably oriented cirques.

Interpretation of Holocene glacial deposits in the Southern and Central Rocky Mountains has been hampered by (1) a heavy reliance upon relative-dating criteria, many of which are influenced by factors other than age; (2) the assumption that glacial advances in high-altitude cirques can be correlated directly with alluvial deposition in far-distant lowlands; and (3) the assumption that glacial advances have necessarily been synchronous throughout the Rocky Mountain region and the world. Although Holocene glacier fluctuations in the Front Range are believed to reflect changes in regional climate, the Front Range chronology does not have particularly close analogs in other parts of North America. Better-dated local sequences are needed before the hypothesis of global synchroneity can be adequately evaluated; until synchroneity has been proven, long-distance correlations and worldwide cycles of recurring glaciation will remain unconvincing.

At Green Pond, a small permanent sinkhole pond in Bartow County, northwest Georgia, organic silty clays are buried by up to 2 m of colluvium. Pollen from the clays shows that a Pinus-Quercus-herb (pine-oak-herb) flora was present before 29,630 radiocarbon yr ago. It is interpreted as the product of a xeric woodland with prairie-like openings. Between 29,630 and approximately 25,000 BP, pollen of Pinus and herbs was sparse; Quercus and Carya (hickory) predominated in the pollen rain. There were few other deciduous trees. Oak-hickory forest is thought to have been present. From 25,000 to 23,000 BP, more diverse forest with pines and some Picea (spruce) became established. At the same time Taxodium (swamp cypress) was locally abundant, as were shrubs characteristic of Coastal Plain swamps. Some time after 23,000 BP, the pond basin filled with colluvium and no further sedimentation took place, other than thin muck sedimented on the bottom of the present Green Pond.

The sediments were first thought to be of Sangamon age because the pollen sequence has many of the characteristics of an interglacial cycle, but the radiocarbon dates correlate them firmly with the Farmdalian Interstadial. A comparison with known Farmdalian sites is made, but the important sites are in the northern United States and adjacent Canada, too far away to make a useful comparison of the details of pollen diagrams from the two areas. At another Bartow County pond site, Bob Black Pond (Watts, 1970), a flora predominantly of pine with spruce and oak was present immediately before 22,900 BP and a strikingly cold flora with jack-pine, spruce and northern herbs followed immediately after. The radiocarbon dates indicate that the sedimentary sequence at Bob Black Pond immediately follows that at Green Pond.