Early Holocene Times Research Articles

Volcanic geology and eruption frequency, S�o Miguel, Azores

Six volcanic zones comprise Sao Miguel, the largest island in the Azores. All are Quaternary in age except the last, which is partly Pliocene. From west to east the zones are (1) the trachyte stratovolcano of Sete Cidades, (2) a field of alkali-basalt cinder cones and lava flows with minor trachyte, (3) the trachyte stratovolcano of Agua de Pau, (4) a field of alkali-basalt cinder cones and lava flows with minor trachyte and tristanite, (5) the trachyte stratovolcano of Furnas, and (6) the Nordeste shield, which includes the Povoacao caldera and consists of alkali basalt, tristanite, and trachyte. New radiocarbon and K-Ar ages augment stratigraphic data obtained during recent geologic mapping of the entire island and provide improved data to interpret eruption frequency. Average dormant intervals for the past approximately 3000 years in the areas active during that time are about 400 years for Sete Cidades, 145 for zone 2, 1150 for Agua de Pau, and 370 for Furnas. However, the average dormant interval at Sete Cidades increased from 400 to about 680 years before each of the past two eruptions, and the interval at Furnas decreased from 370 to about 195 years before each of the past four eruptions. Eruptions in zone 4 occurred about once every 1000 years during latest Pleistocene and early Holocene time; none has occurred for about 3000 years. The Povoacao caldera truncates part of the Nordeste shield and probably formed during the middle to late Pleistocene. Calderas formed during latest Pleistocene time at the three younger stratovolcanoes in the sequence: outer Agua de Pau (between 46 and 26.5 ka), Sete Cidades (about 22 ka), inner Agua de Pau (15.2 ka), and Furnas (about 12 ka). Normal faults are common, but many are buried by Holocene trachyte pumice. Most faults trend northwest or west-northwest and are related to the Terceira rift, whose most active segment on Sao Miguel passes through Sete Cidades and zone 2. A major normal fault displaces Nordeste lavas 150–250 m and may mark the location of an ancestral Terceira rift. Recent seismicity (e.g., in the 1980s) generally has been scattered, but some small earthquake swarms have occurred beneath the north-eastern flank of Agua de Pau.

Dissimilarity coefficients for fossil pollen spectra from Iowa and western illinois during the last 30,000 years

Abstract Fossil pollen counts from Iowa and western Illinois ranging in age from 30,000 yr B.P. to the present were compared with the modern pollen rain of eastern North America using dissimilarity coefficients (squared chord distances). The fossil samples came from several sites to give a general representation to the major vegetational changes in the region. The best analogs were for the period from 28,000 to 25,000 yr B.P., when Picea‐Pinus forests existed that were apparently comparable to the modern boreal forest. Some acceptable analogs also exist for samples dating from full‐glacial time (about 25,000 to about 15,000 yr B.P.), when open spruce forests and parklands similar to the northern edge of the present boreal forest were present, and from late Holocene time (the last 6000 yrs), when the modern prairie and oak savanna were developing. Many samples from late‐glacial (about 15,000 to 10,000 yr B.P.) and early Holocene (10,000 to 6,000 yr B.P.) time have no acceptable analogs. Reconstructions fro...

Geology and paleoecology of early Holocene lacustrine deposits in the Columbia River valley near Fauquier, southern British Columbia

Early Holocene lake sediments are exposed near Fauquier, on the east side of the Arrow lakes in the Columbia River valley of British Columbia. A glacial lake occupied the valley at the time of deglaciation, but by 10 ka BP this had been replaced by a nonglacial lake that was at least 250 km long and as much as 5 km wide.Comparison of pollen and macroscopic plant remains in these nearshore and littoral deposits with modern vegetation indicates that many of the plants present between 9 and 10 ka BP are found in the area today, either along the valley floor or at higher elevations in the subalpine zone nearby. Some of the organic material may be allochthonous; this complicates paleoecological and paleoclimatological interpretations. It appears that the climate in the Columbia River valley between 9 and 10 ka BP was as wet or wetter than at present. The presence of many of these species in the southern Columbia River valley of British Columbia during early Holocene time suggests that elements of the modern vegetation had migrated rapidly northward from southern refugia, probably within 1500 years of the end of the last glacial episode.

Petrology of the zoned calcalkaline magma chamber of Mount Mazama, Crater Lake, Oregon

Evolution of the magma chamber at Mount Mazama involved repeated recharge by two types of andesite (high-Sr and low-Sr), crystal fractionation, crystal accumulation, assimilation, and magma mixing (Bacon and Druitt 1988). This paper addresses the modal compositions, textures, mineral chemistry and magmatic temperatures of (i) products of the 6845±50 BP climactic eruption, (ii) blocks of partially fused granitoid wallrock found in the ejecta, and (iii) preclimactic rhyodacitic lavas leaked from the chamber in late Pleistocene and early Holocene time. Immediately prior to the climactic eruption the chamber contained ≳ 40 km3 of rhyodacite (10 vol% plag + opx + aug + hb + mt + ilm, ∼880° C) overlying high-Sr andesite and cumulus-crystal mush (28–51 vol% plag + hb ± opx ± aug + mt ± ilm, 880° to ≥950° C), which in turn overlay low-Sr crystal mush (50–66 vol% plag + opx + aug ± hb ± ol + mt + ilm, 890° to ≥950† C). Despite the well known compositional gap in the ejecta, no thermal discontinuity existed in the chamber. Pre-eruptive water contents of pore liquids in most high-Sr and low-Sr mushes were 4–6 wt%, but on average the high-Sr mushes were slightly richer in water. Although parental magmas of the crystal mushes were andesitic, xenocrysts of bytownite and Ni-rich magnesian olivine in some scoriae record the one-time injection of basalt into the chamber. Textures in ol-bearing scoriae preserve evidence for the reactions ol + liq = opx and ol + aug + liq(+ plag?) = hb, which occurred in andesitic liquids at Mount Mazama. Strontium abundances in plagioclase phenocrysts constrain the petrogenesis of preclimactic and climactic rhyodacites. Phenocryst cores derived from high-Sr and low-Sr magmas have different Sr contents which can be resolved by microprobe. Partition coefficients for plagioclase in andesitic to rhyolitic glasses range from 2 to 7, and increase as glass %SiO2 increases. Evolved Pleistocene rhyodacites (∼30–25,000 BP) and rhyodacites of the Holocene Llao Rock center (7015±45 BP) contain Sr-poor plagioclase and are derivatives from low-Sr magma. Rhyodacites of the Pleistocene Sharp Peak domes, Holocene Cleetwood flow (∼6850 BP), and climactic ejecta contain discrete Sr-rich and Sr-poor plagioclase phenocryst populations and are hybrids produced by mixing low-Sr rhyodacite (containing Sr-poor plag + opx + aug) with a more mafic high-Sr magma (with Sr-rich plag [ + hb?]). The data reinforce the conclusions of crystal-liquid mixing calculations (Bacon and Druitt 1988), and suggest some important refinements to the magma chamber model.

Late Weichselian‐Holocene foraminiferal stratigraphy and palaeohydrogrphic changes in the Gothenburg area, southwestern Sweden

Marine clay from two cores (50 and 36m deep) from Gothenburg, southwestern Sweden, have been analysed using different stratigraphic methods. Foraminiferal stratigraphy complemented withe lithostratigraphy, pollen and mollusc analyses show an environmental succession from arctic conditions with water depths up to 100m during Late Welchselian time, to a boreal shallow water environment in early Holocene time. A comparison of the foraminiferal faunas with those from corresponding investigations from southern Bohuslän, NW of Gothenburg, shows a similar development in the two areas. The sudden environmental change around the Pleistocene/Holocene boundary (10,000 years B.P.) along the Swadish west coast is attributed to changes of the hydrographic patterns; a general shift of the circulation pattern of the Skagerrak/ Kattegat at that time and or a large supply of fresh water flowing into the area from the Lake Vanern basin.

Late quaternary land snails from the north coast of Jamaica: Local extinctions and climatic change

Analysis of the land snail faunas and chronology ( 14C and amino acid epimer ratios) of six late Quaternary deposits from a site on the north coast of Jamaica provides a basis for reconstruction of local extinction events and their relation to paleoclimate. Paleotemperature estimates are derived from epimerization rates at an interior site and indicate an average Holocene-late last glacial temperature difference of c.4–5°C. Size variation in land snails indicates relatively dry conditions during the late last glacial and moist conditions in the late Holocene, followed by drier conditions beginning sometime during the last millennium. The rich faunas of the latter half of the last glacial are represented today at the same site by only a relatively few remnant species. Two major periods of extinction are identified. During latest last glacial to early Holocene time, a number of species became locally extinct, probably due to increased temperatures; many survive today in the cooler interior of the island. Extensive extinctions occurred again during the last millennium. These apparently resulted largely from habitat disturbance by man. A similar pattern of late Holocene extinctions has also been documented for vertebrates on other tropical islands and is also thought to result from human disturbance.

River piracy at Kakariki, north-western Wairarapa, New Zealand

Abstract The part of Mangahao River that traverses the Tararua Range, upstream from Kakariki, was captured at some time in the Holocene Epoch (about 5,000-10,000 years B.P.) from the Hukanui Stream, which was formerly a major tributary ofthe Mangatainoka River. The captured segment now delivers high floods more than an order of magnitude greater than the mean annual flow of the Mangahao, and its diversion from the Hukanui Stream was a large drainage change. The capture site is on the line of the active Wellington Fault. The main factors that caused the capture were: (1) dextral displacement of the captured segment relative to the former Mangahao River; (2) in sequent erosion along the crush zone of the fault by a tributary of the former Mangahao; (3) aggradation of the floodplain of the captured segment during the Last Stadial of the Last Glaciation; and (4) easy lateral erosion of the fault crush zone by the captured segment during early Holocene time. The Mangahao provided a shorter route than the Mangatainoka to the local base-level (head of Manawatu Gorge) and the newly diverted water quickly excavated a deep ravine that now has a flood-plain 45 m lower than the early Holocene flood-plain of the Hukanui Stream at Kakariki.

Late Holocene Sea-Level Record in a Core from the Puget Lowland, Washington

AbstractDiatoms and lithological facies of an 8.45-m core collected from Shine swamp (47°52′20″N lat, 122°41′45″W long; about 2 m above the mean tide level) in the northern Puget Lowland reveal a rise in relative sea level during the past 6000 yr. A layer of fresh-water peat at a depth of 6.6-6.3 m (ca. 7000-5000 yr B.P.) indicates a low stand of the sea in early and middle Holocene time. About 5000 yr ago the rise in relative sea level resulted in accumulation of subtidal or lower intertidal clayey gyttja and gyttja which contain mainly marine and brackish-water diatoms (80–95%). By about 3500 yr B.P., the basin had shoaled to upper intertidal levels, and peat began to accumulate again while the sea continued its relative rise. During the period of this continuous peat growth, several alterations in fresh-water and marine/brackish-water diatom assemblages took place, indicating slight differences in the contemporaneous sea-level rise and vertical peat growth.

Time/Depth Distribution of Late Quaternary Uvigerina peregrina, North American Continental Margin: Morphological and Paleoceanographic Implications

Uvigerina peregrina from the continental slope of the eastern United States exhibits morphological and distributional evidence for distinct populations at water depths from about 700 to 5000 m since 25, 000 years before present (YBP). During the glacial maximum (18, 000 YBP) this species occupied water depths from 2400 to 4350 meters. Beginning 16, 000 YBP, U. peregrina diverged into two populations. The main population rangedfrom 3000 to 4350 m water depth, contracted during late glacial and early Holocene time, and finally vanished from a depth of 3600 m at 8000 YBP. An isolated portion of the glacial age population survived between 2100 and 2300 m and connected the late glacial and late Holocene populations of U. peregrina. The modern population of U. peregrina first appeared about 4000 YBP and is confined to water depths of 900 to 3000 m with its acme between 1600 and 2500 meters. Fourier shape analysis shows that the modern and glacial age populations of U. peregrina are morphologically distinct. The observed morphological and distributional differences indicate that the modern and glacial-age specimens represent discrete populations rather than an upslope migration of a single population. Water masses of the western North Atlantic have significant control on the spatial and temporal distribution of this species. Paleobathymetric and paleoceanographic reconstructions using U. peregrina should consider the population affinity, especially in the western North Atlantic.

Holocene evolution of the northeastern corner of the Nile Delta

The constructive phase of the modern Nile Delta, as manifested in a 48-m section drilled east of the Suez Canal, commenced in very early Holocene times. Sands rich in marine fauna were deposited in the littoral zone and the shoreline was more than 20 km landward of its present-day position. Subsequently, clays and silts were dumped from the Nile distributaries and the marine faunal spectrum became very limited and brackish. Later in early and middle Holocene times the sediments deposited were rich in freshwater, delta-plain diatoms and pollen and in allochthonous fern spores from the tropics, indicating proximity of a distributary mouth. The middle part of the section (22.5-17.5 m) is very poor in faunal and floral remains; pollen grains from sabkha vegetation are abundant. The environment, which seems lagoonal and slightly hypersaline, is related to the sea regression in middle Holocene times. Euryhaline pelecypods, dating from about 3000 yr B.P., are abundant around the 8-m depth. Upward, there is an increase in pollen grains from sabkhas; the section is poor in diatoms and those present are mostly euryhaline and lagoonal. Allochthonous spores derived from the nearby Pelusiac Branch are abundant. Between 3000 and 2000 yr B.P. the constructive phase of the modern delta terminated and winnowed sands began accreting in front of the delta plain.

Systematics and Biogeography of Onychomys leucogaster in Western North America

Systematic and biogeographic relationships of Onychomys leucogaster in western North America were assessed using morphometric, karyotypic, and fossil data. The names O. l. utahensis and O. l. fuscogriseus are relegated to synonymy with O. l. brevicaudus . Populations in northeastern Oregon and eastern Washington are named and described as a new subspecies. Populations in the Wyoming Basin are referred to the Northern Plains subspecies, O. l. missou-riensis . We hypothesize that O. leucogaster inhabited a “cold” desert refugium in the location of the present Mohave “hot” desert during the last glacial episode. The species colonized the Great Basin during late glacial time and the Wyoming Basin and northern Columbia Plateau during early Holocene time. Populations of O. leucogaster on the Colorado Plateau phenetically are more like those on the Central Great Plains than those in the Great Basin or Wyoming Basin.

A Study of the Distribution of Freshwater Mussels (Mollusca: Pelecypoda: Unionoida) of the Lake Champlain Drainage in Northwestern New England

Lake Champlain occupies a large shallow basin in northeastern North America and drains to the St. Lawrence River. The freshwater mussel fauna of the lake's drainage system includes both Northern Atlantic and Interior Basin species. An analysis of the distribution of the mussel species in the eastern and southern drainage streams of Lake Champlain reveals that fall lines have controlled upstream migration at various stages during the lake's postglacial history. Species composition differs above and below fall lines within drainage streams and varies geographically between drainage streams. Such distribution patterns may be explained by proposed periodic invasions of Lake Champlain by species during specific postglacial lake stages. simple species lists, with little emphasis being placed on details of distribution of species and how the geography and geology of the region have controlled the dispersal of spe- cies recolonizing Lake Champlain during late Pleistocene and early Holocene times. The present study provides a detailed account of the distribution of the freshwater mussels in the eastern Lake Champlain watershed in northwestern New England. Us- ing extant museum records and data gathered during my own field investigations, and available information on the structural and surface geology of the Champlain lowland and western New England, a history of late and postglacial dispersal of mussels into Lake Champlain is developed. The previous literature on Lake Champlain unionoids is very limited. Concerning the New England sector, Adams (1841, 1853) presented brief lists which provided enough information to firmly document the extension of ranges of several Interior Ba- sin species into Lake Champlain. Adams' observations were repeated in subsequent fau- nal lists (e.g., Stimpson, 1851; Johnson, 1915; Johnson, 1980). Gray (1883) gave Lake Champlain drainages in Vermont as the eastern range limit of Lasmigona compressa. Re- cently, Clarke (1981) listed a few records of Alasmidonta undulata from the Lake Cham- plain drainage in Vermont. Similarly, the portion of Lake Champlain in New York has been little studied with respect to unionoid mussels. Lea (1834) first described Symphynota benedictensis ( =Ano- donta grandis) from near Ticonderoga on Lake Champlain. Dekay (1943) later listed a few Lake Champlain records for unionoids, and some time after, Marshall (1895) listed the known distribution of unionoids in Lake Champlain based on New York State Mu- seum records. Finally, Letson (1905) presented a list of New York unionoid mussels that included all known Lake Champlain records. More recently Clarke and Berg (1959) cited the first record of Anodontoides ferussacianus from Lake Champlain, and Smith (1982) provided records for A. ferussacianus and other species in a few of the uppermost Lake Champlain drainage streams. No reports exist of the mussel fauna in the small portion of the Lake Champlain drainage in Canada.

Quaternary sedimentation in Shelikof Strait, Alaska

Shelikof Strait, a nearly parallel-sided marine channel between the Kodiak island group and the Alaska Penninsula, has experienced a succession of distinct sedimentary environments during Quaternary time. Pleistocene glaciers carved a deep basin into bedrock in the southwest part of the strait and a shallower platform surface with incised channels in the northeast. The basin and channels were filled with glacial and glacialmarine sediment before and during the time that ice retreated and oceanic conditions returned. Restricted marine conditions prevailed in early Holocene time and sediment prograded transversely into the strait from the adjacent landmasses, with some localized dispersal to the deep, central strait. Onset of modern open-marine conditions commenced when regional currents breached the sill across Kennedy and Stevenson Entrances to combine with sediment-laden outflow from Cook Inlet and deposit a blanket of well-stratified sediment throughout the strait.

Foraminiferal distribution on the continental margin off Nova Scotia

Q-mode factor analysis of total foraminiferal abundance data (living plus dead) from 250 grab samples taken from the continental margin off Nova Scotia allows the determination of eight factor assemblages. On the northeastern shelf, an exclusively agglutinated assemblage dominated by Adercotryma glomerata occupies both banks and basins. Central shelf basins contain a predominantly calcareous assemblage dominated by Globobulimina auriculata and Nonionellina labradorica. Transitional between these two factor assemblages is an agglutinated assemblage dominated by Saccammina atlantica. Consistently present along the shelf edge is a Trifarina angulosa assemblage. In northeastern bays and a few samples near Sable Island, an agglutinated Eggerella advena assemblage is found. A relict and transport affected assemblage dominated by Elphidium excavatum occurs in the southwestern approaches to Emerald Basin. Sandy/gravelly areas of the inner shelf and outer bank regions are characterized by a Cibicides lobatulus assemblage. The statistical relationships of these defined assemblages to various aspects of the marine environment (depth, temperature, salinity, percent gravel, sand and mud) were investigated through multiple regression techniques. Results indicate that the present foraminiferal distribution patterns off Nova Scotia are influenced by the prevailing watermass characters and substrate. The Adercotryma glomerata assemblage is influenced by the presence of cold, (0–4°C) low salinity waters (32–33‰) of arctic, Labrador Current origin. The central basin assemblage ( G. auriculata) is related to warmer (8–12°C) more saline waters (35‰) of slope origin. The transition between these two bottom waters is marked by the opportunistic Saccammina atlantica assemblage. Preferred substrate character possibly determines the occurrence of the Cibicides lobatulus, Islandiella islandica and Eggerella advena assemblages. Trifarina angulosa shows a significant relationship to salinity and depth. Although the surficial sediments on the Nova Scotian Shelf are largely the product of reworking of glacial deposits during late glacial and early Holocene times, all but the E. excavatum factor assemblage appear to be in equilibrium with the modern oceanographic regime.

Shoreface translation and the Holocene stratigraphic record: Examples from Nova Scotia, the Mississippi Delta and eastern Australia

Classic descriptive models of barrier sedimentation have been developed with data from the Atlantic and Gulf coasts of the United States. These models are dominated by low to moderate rates of relative sea level (RSL) rise and wave energy. Barriers respond by landward recycling of sediment through the mechanism of shoreface retreat. Sedimentation processes on the central coast of New South Wales (N.S.W.), Australia, consist of rapid RSL rise in early Holocene times followed by a stillstand since 6500 B.P. Wave energy is relatively high year-round and sand sources for barrier formation are only found on the inner shelf. Barrier sedimentation on the central coast of N.S.W. exhibits a thick, composite sequence composed of a basal marine transgressive sand overlain by regressive beach and dune facies. The Louisiana coast surrounding the Mississippi delta is underlain by compacting deltaic muds which generate very rapid rates of RSL rise. The Louisiana coast experiences low wave energy punctuated by high-energy tropical and extra-tropical storm events. Barrier sediments accumulate from the erosion of deltaic headlands and undergo a transformation from subaerial barrier island systems to subaqueous shoals located on the inner shelf. Drumlins experience coastal erosion on the Eastern Shore of Nova Scotia and provide a sediment source for compartmented estuary mouth barriers. An ongoing, moderate rise of RSL results from the passage of a glacial forebulge. Wave energy is intermediate between Louisiana and N.S.W. and displays a seasonal pattern dominated by frequent winter storms. Coastal barrier sedimentation is episodic, consisting of a period of beach ridge progradation followed by barrier destruction and re-establishment further landward. The three contrasting sedimentary sequences found in examples from Louisiana, N.S.W. and Nova Scotia indicate that presently available sedimentation models from locations such as the middle Atlantic or Texas coasts of the United States may only represent well-documented regional case studies. A true generalised coastal sedimentation model is required which can identify the parameters controlling vertical and horizontal translation of the depositional surface and provide relationships between these parameters which quantitatively predict the genesis, distribution and geometry of coastal sedimentary facies.

Late Pleistocene and early Holocene environmental history of southwestern Washington State, U.S.A.

A comparison of pollen records and associated plant remains from sites along a major precipitation gradient in southwestern Washington enables reconstruction of the late Quaternary environment during glacial and early Holocene time. During the Evans Creek Stade (25 000 – 17 000 years BP) little moisture reached lowlands east of the Olympic Mountains and as a result both the Puget Trough and the Columbia Basin featured a cold dry climate and parkland–tundra vegetation In glacial time, greatest aridity seems to have occurred between 19 000 and 17 000 years BP. After 17 000 years BP the development of mesophytic subalpine parkland suggests that maritime conditions extended farther east into the Puget Trough, and the Cascade Range became an important precipitation divide. Conditions warmer and (or) drier than today developed throughout western Washington between 10 000 and 8000–6000 years BP. Vegetation on opposite sides of the Cascade Range became dissimilar as early as 17 000 years BP, but this trend was accentuated in late glacial and early Holocene time.

Signification dynamique et climatique des formations et terrasses fluviatiles en Afrique du Nord et au Proche-Orient. Rapport

In the bibliography concerning North Africa or Near East, there are a few significant informations on the sequence of alluvial deposits since the last interglacial time. The reconstruction of the environment in this area is based on limited evidences, but the similar succession of same faciès seems to have a climatic origin. After the end of the Ouljian transgression (the last Interglacial), the most complete sequences are characterized by a vertical cutting through former alluvial deposits and after, by a important aggradation of great size boulders during the Mousterian period. The large quantities of coarse material are interpreted as indications of probably colder climate and of stronger flood waters. Between 40 000 and 15 000 y B.P., fluvial dynamics is very different as two or three successive episods of silt deposition are observed in many sections at that time. The climatic interpretation of these sediments is still questionable because silts have two possible origins : eolian dust or pedogenesis. At last, during Tardiglacial and Early Holocene times, wadis were cutting down, then again depositing some gravels and boulders (or eolian sands redeposited by fluvial processes) which nevertheless seem indicate a drier period, at least in North Africa. After the neolithic settlement, fluvial deposits are too much modified to state a precise evaluation of environment and climatic conditions.

Chronology of Holocene glaciation, central Brooks Range, Alaska

The central Brooks Range was glacierized in the highest, north-facing cirques during late-middle to late Holocene (Neoglacial) time. This Neoglaciation involved at least 5 major cirque-glacier expansions of similar magnitude, as based on lichenometric mapping of more than 50 glaciers and radiocarbon dates directly associated with 5 moraines. Initial stabilization of debris-covered glaciers took place by early Holocene time, but evidently no moraines formed during this interval. Few morainal ridges are preserved that date from the older expansions, but they have been lichenometrically dated (± 20% age reliability) to 3 separate intervals: 4400, 3500, and 2900 yr B.P. Twelve morainal complexes have ridges indicative of glacial advance that lichenometrically date at 1800 ± 500 yr B.P. Relict lichens that are now emerging undisturbed from beneath a receding glacier toe imply that this time was one of prolonged recession in at least some parts of the Brooks Range, however. Radiocarbon analysis of dead moss at this same site dates a subsequent Neoglacial advance across the cirque floor at 1120 ± 180 yr B.P. Our data suggest that for the past ∼1,100 yr, cirque glaciers have been continuously in more extended positions than they are today. During this glaciologically favorable interval, the last two major advances occurred at 800 ± 150 and 390 ± 90 yr B.P. (A.D. 1410–1600). Glaciers across the central Brooks Range stayed close to their maxima until A.D. 1640–1750. Historical photographs and lichenometry show that retreat was most rapid after A.D. 1870 and decelerated after the mid-1900s. Recession from this most recent Neoglacial maximum has amounted to 150–700 m and continues at present. The cirque glacier advances were accompanied by equilibrium-line altitude (ELA) depressions of 100 to 200 m below levels maintained in the late 1970s. Environmental lapse rate estimates and 1977–1981 glaciologic-meteorologic measurements suggest that summer air temperatures accompanying Neoglacial maxima were, respectively, 1 °C or 3 to 4 °C cooler than those of the late 1970s. Across the central Brooks Range, the Neoglacial maxima ELAs rise northeastward and northward from 2 to 5 m km −1 .

Radiocarbon-dated evidence of worldwide early Holocene climate change

Radiocarbon-dated glacial deposits from several different areas of the world indicate that alpine glaciers and ice caps in parts of both the Northern and Southern Hemispheres expanded in response to climate change in early Holocene time. These data suggest that a worldwide episode of cooler climate similar in scope to the more recent Neoglaciation occurred ca. 8,500−7,500 yr B.P.

Hydrology and climate in the Ross Sea area

Abstract Glacial features in the Ross Sea area are a result of seaward flucuations of outlet glaciers from the ice sheet, alpine glacier variations, and inland advances of a grounded Ross Ice Shelf. Both alpine and outlet glaciers in this area currently may be at their greatest extension since Otiran (Wisconsin) time. Mass balance changes measured on Dry Valley glaciers are very small, indicating conditions close to glacial equilbrium and emphasising a low degree of glacial activity. Accumulation is greatest in summer, suggesting that in this region, a temperature increase may lead to a glacial advance. Hydrological studies include measurement of the Onyx River flow, and early-and late-summer levels of nine enclosed lakes. Annual discharge of water into Lake Vanda by the Onyx River is variable, with pronounced diurnal variation, but there are also several peak flows, each about one week long, each season. Levels of enclosed lakes, lowered from early Holocene times, are currently rising. Beginning-and end-...