Global Glacial Maximum Research Articles

Paléoenvironnements des îles japonaises lors de la dernière période glaciaire

The paper summarizes the paleoenvironments of the last glacial time from a viewpoint of glaciation, permafrost and vegetation. Sea level changes played a critical role on glaciation and human migration to Japanese Islands. Glaciation was limited to the high mountains, and its expansion was much larger in the former stage (MIS 3/4) than in the global glacial maximum (MIS 2). A land bridge between Sakhalin and Hokkaido was important for the migration of paleolithic people from Northern Asia to Japan. Discontinuous permafrost environment with forest tundra and Taiga type conifer forest vegetation in Hokkaido supported the paleolithic hunter-gatherers of big games, developing a microblade culture. Termination of last glacial time caused a drastic environmental change such as a decay of glaciers, permafrost and land bridge. Rapid vegetation change decreased big games and the humans changed their food strategy from a big game hunting to a fishing and a gathering plant resources such as acorns and walnuts. This change created a pottery (Jômon) culture which seems to be brought in Hokkaido from the south between 15,000 ∼ 14,000cal BP. The encounter of paleolithic and southern Jômon peoples in Hokkaido generated a new human group, the northern Jômon people, which might be a origin of the Aïnu, the indigenous people in Japan, especially in Hokkaido.

The Late Quaternary Evolution of the Upper Reaches of Fluvial Systems in the Southern East European Plain

Networks of dry valleys (or balkas) and hollows in the upper reaches of fluvial basins in extraglacial areas in the Penultimate Glaciation (Marine Isotope Stage 6—MIS 6) regions of the East European Plain demonstrate clear incision/aggradation rhythms corresponding to global glacial/interglacial climate cycles. The first phase of each incision/aggradation rhythm began after the global glacial maximum and was characterized by a cool and humid climate, permafrost and sparse vegetation, when high surface runoff and active linear erosion formed a dense network of gullies. The second phase occurred at the glacial–interglacial transition and the subsequent interglacial period with its warm and humid climate and dense vegetation. This phase was distinguished by the partial filling of fluvial forms with slopewash deposits, the transformation of gullies into dry valleys (balkas) and the subsequent stabilization of fluvial forms marked by the formation of mature soils on the sides and bottoms of balkas. The third phase of the rapid accumulation of balkas developed during the cold and dry part of the next glacial epoch, resulting in the balkas becoming shallow hollows filled in with sediments. The last full incision/aggradation rhythm occurred in the late MIS 6 to mid-MIS 2. The erosion network formed during the late MIS 6 was almost completely filled by mid-MIS 2, and its manifestation in the modern topography is limited to a network of shallow hollows in the upper parts of the fluvial systems. The modern (incomplete) incision/aggradation rhythm began in the late MIS 2 and caused the formation of the modern erosion landscape in the upper reaches of fluvial systems. This rhythm is now in the stabilization phase, and the main accumulation phase of this rhythm is still far in the future.

Timing of past glaciation at the Sierra de Aconquija, northwestern Argentina, and throughout the Central Andes

Advances in cosmogenic nuclide exposure dating have made moraines valuable terrestrial recorders of palaeoclimate. A growing number of moraine chronologies reported from the Central Andes show that tropical glaciers responded sensitively to past changes in precipitation and temperature over timescales ranging from 103 to 105 years. However, the causes of past glaciation in the Central Andes remain uncertain. Explanations have invoked insolation-modulated variability in the strength of the South American Summer Monsoon, teleconnections with the North Atlantic Ocean, and/or cooling in the Southern Hemisphere. The driver for these past climate changes is difficult to identify, partly due to a lack of dated moraine records, especially in climatically sensitive areas of the southern Central Andes. Moreover, new constraints are needed on precisely where and when glaciers advanced. We use cosmogenic 10Be produced in situ to determine exposure ages for three generations of moraines at the Sierra de Aconquija, situated at 27°S on the eastern flank of the southern Central Andes. These moraines record glacier advances at approximately 22 ka and 40 ka, coincident with summer insolation maxima in the sub-tropics of the Southern Hemisphere, as well as at 12.5 ka and 13.5 ka during the Younger Dryas and the Antarctic Cold Reversal, respectively. We also identify minor glaciation during Bond Event 5, also known as the 8.2 ka event. These moraines register past climate changes with high fidelity, and currently constitute the southernmost dated record of glaciation on the eastern flank of the Central Andes. To contextualise these results, we compile 10Be data reported from 144 moraines in the eastern Central Andes that represent past glacier advances. We re-calculate exposure ages from these data using an updated reference production rate, and we re-interpret the moraine ages by taking the oldest clustered boulder age (after the exclusion of outliers attributed to nuclide inheritance) as closest to the timing of glacier advance—an approach for which we provide empirical justification. This compilation reveals that Central Andean glaciers have responded to changes in temperature and precipitation. We identify cross-latitude advances in phase with insolation cycles, the last global glacial maximum, and episodes of strengthened monsoonal moisture transport including the Younger Dryas and Heinrich Stadials 1 and 2. Our results from the Sierra de Aconquija allow us to constrain the southerly limit of enhanced precipitation associated with Heinrich Stadials at ∼25°S. More broadly, our findings demonstrate at both local and regional scales that moraines record past climate variability with a fine spatial and temporal resolution.

The Campo Felice late Pleistocene Glaciation (Apennines, central Italy)

AbstractStudy of the glacial deposits and lacustrine sediments of Campo Felice (Apennines, central Italy) has enabled the glacial phases of the last 40 ka to be dated more precisely, and has demonstrated that the maximum glacial advance did not occur in correspondence with the last global glacial maximum and with the coldest and most arid phase suggested by the pollen, but in a period dated between about 33 and 27 ka, characterized by a less extreme climate. Furthermore, a glacial expansion took place also in the period prior to 35 ka. Correlation with the Alpine glacial variations has shown that the Apennine last glacial maximum occurred before that of the southern slope of the Alps. Copyright © 2012 John Wiley & Sons, Ltd.

Late Quaternary glaciation history of Isla de los Estados, southeasternmost South America

Isla de los Estados is a mountainous island southeast of Tierra del Fuego, in southernmost South America. Its central and eastern parts have an alpine topography, transected by U-shaped valleys, small, partly over-deepened fjords, and a multitude of abandoned cirques, all associated with extensive former local glaciations. Traces of glacial erosion generally reach 400–450 m a.s.l., and above that trimline a distinct sharp-edged nunatak derived landscape is present. The westernmost part of the island has a lower, more subdued topography, reflecting its “softer” geology but possibly also over-running and erosion by mainland-derived ice streams. The present study concentrated on glacigenic sediment sequences exposed along coastal erosional cliffs. A combination of OSL and 14C datings show that these sediments mostly date from the latest (Wisconsinan/Weichselian) glacial cycle, i.e. from the last ca. 100 ka with the oldest (glaciolacustrine) deposits possibly as old as 90–80 ka. The upper parts of overlying tills, with associated lateral and terminal moraines from glaciers that expanded onto an eustatically exposed dry shelf north of the island, date from the last global glacial maximum (LGM). Radiocarbon ages of peat and lake sediments indicate that deglaciation began 17–16 cal ka BP.

Late Pleistocene mountain glaciation in Alaska: key chronologies

AbstractMoraine sequences of mountain glaciers can be used to infer spatial and temporal patterns of climate change across the globe. Alaska is an accessible high‐latitude location in the Northern Hemisphere and contains a rich record of alpine glaciation. Here, we highlight the key chronologies from three mountain ranges in Alaska that reveal the timing and spatial extent of Late Pleistocene glaciation, and pay particular attention to age of the penultimate glaciation. The most extensive glacier advance of the last glaciation occurred prior to the last global glacial maximum. Cosmogenic exposure ages from moraine boulders in three sites spanning 800 km indicate that this penultimate advance most likely culminated during marine isotope stage (MIS) 4 or early MIS 3. During MIS 2, more limited glacier expansion generated multiple moraines that span from prior to the global Last Glacial Maximum (LGM) through the Lateglacial period. Glaciers retreated from their terminal positions ca. 27–25 ka in arctic Alaska and ca. 22–19 ka in southern Alaska. Moraines in at least two ranges date to 12–11 ka, indicating a glacial advance during the Younger Dryas period. Reconstructed equilibrium‐line altitudes of both penultimate and MIS 2 glaciers were lowered only 300–600 m – much less than elsewhere in the Americas. Alaska is documented to have been more arid during MIS 2, perhaps due in large part to the exposure of the Bering–Chukchi platform during eustatic sea‐level lowering. The restricted ice extent is also consistent with the output of climate models that simulate a lack of significant summer cooling. Copyright © 2008 John Wiley & Sons, Ltd.

Mountain-derived versus shelf-based glaciations on the western Taymyr Peninsula, Siberia

The early Russian researchers working in central Siberia seem to have preferred scenarios in which glaciations, in accordance with the classical glaciological concept, originated in the mountains. However, during the last 30 years or so the interest in the glacial history of the region has concentrated on ice sheets spreading from the Kara Sea shelf. There, they could have originated from ice caps formed on areas that, for eustatic reasons, became dry land during global glacial maximum periods, or from grounded ice shelves. Such ice sheets have been shown to repeatedly inundate much of the Taymyr Peninsula from the north-west. However, work on westernmost Taymyr has now also documented glaciations coming from inland. On at least two occasions, with the latest one dated to the Saale glaciation (marine isotope stage 6 [MIS 6]), warm-based, bedrock-sculpturing glaciers originating in the Byrranga Mountains, and in the hills west of the range, expanded westwards, and at least once did such glaciers, after moving 50–60 km or more over the present land areas, cross today’s Kara Sea coastline. The last major glaciation affecting southwestern Taymyr did, however, come from the Kara Sea shelf. According to optically stimulated luminescence dates, this was during the Early or Middle Weichselian (MIS 5 or 4), and was most probably not later than 70 Kya. South-western Taymyr was not extensively glaciated during the last global glacial maximum ca. 20 Kya, although local cold-based ice caps may have existed.

Glaciers in the Polar Urals, Russia, were not much larger during the Last Global Glacial Maximum than today

10Be exposure dates from boulders indicate that the Chernov Moraines located only 1 km beyond the Chernov Glacier in the Polar Urals, Russia, were formed during the time of the Last Global Glacial Maximum (LGM). Six samples from large boulders on the moraine yielded a mean age of 21.5±2.3 (std. error) kyr. The distinct semicircular Usa Moraine is located beyond the western flank of the Urals. Boulders in the valley between the Chernov and Usa moraines yielded some spread in 10Be -ages, but four out of seven yielded ages 50–60 kyr. We conclude that the Usa and Chernov Moraines represent the maximum glacier extent during Marine Isotope Stages (MIS) 4 and 2, respectively. The exceptionally small extent of the LGM glacier is explained with a dry LGM climate, but also with the fact that present day cirque glaciers in the Polar Urals are extremely favoured by topographical factors such as leeward accumulation and shadowing mountain walls, advantages which decrease when the glaciers grow.

Mountain-derived versus shelf-based glaciations on the western Taymyr Peninsula, Siberia

The early Russian researchers working in central Siberia seem to have preferred scenarios in which glaciations, in accordance with the classical glaciological concept, originated in the mountains. However, during the last 30 years or so the interest in the glacial history of the region has concentrated on ice sheets spreading from the Kara Sea shelf. There, they could have originated from ice caps formed on areas that, for eustatic reasons, became dry land during global glacial maximum periods, or from grounded ice shelves. Such ice sheets have been shown to repeatedly inundate much of the Taymyr Peninsula from the north-west. However, work on westernmost Taymyr has now also documented glaciations coming from inland. On at least two occasions, with the latest one dated to the Saale glaciation (marine isotope stage 6 [MIS 6]), warm-based, bedrock-sculpturing glaciers originating in the Byrranga Mountains, and in the hills west of the range, expanded westwards, and at least once did such glaciers, after moving 50–60 km or more over the present land areas, cross today’s Kara Sea coastline. The last major glaciation affecting southwestern Taymyr did, however, come from the Kara Sea shelf. According to optically stimulated luminescence dates, this was during the Early or Middle Weichselian (MIS 5 or 4), and was most probably not later than 70 Kya. South-western Taymyr was not extensively glaciated during the last global glacial maximum ca. 20 Kya, although local cold-based ice caps may have existed.

Evidence of a two-fold glacial advance during the last glacial maximum in the Tagliamento end moraine system (eastern Alps)

The glacial history of the Tagliamento morainic amphitheater (southeastern Alpine foreland, Italy) during the last glacial maximum (LGM) has been reconstructed by means of a geological survey and drillings, radiocarbon dating and pollen analysis in the amphitheater and in the sandur. Two phases of glacial culmination, separated by a distinct recession, are responsible for glacial landforms and related sediments in the outer part of the amphitheater. The age of the younger advance fits the chronology of the culmination of the last glaciation in the Alps, well established between 24 and 21 cal ka BP (20 to 17.5 14C ka BP), whereas the first pulse between 26.5 and 23 cal ka BP (22 to 21 14C ka BP), previously undated, was usually related to older (pre-LGM) glaciations by previous authors. Here, the first pulse is the most extensive LGM culmination, but is often buried by the subsequent pulse. The onset and final recession of the late Würm Alpine glaciation in the Tagliamento amphitheater are synchronous with the established global glacial maximum between 30 and 19 cal ka BP. The two-fold LGM glacial oscillation is interpreted as a millennial-scale modulation within the late Würm glaciation, caused by oscillations in inputs of southerly atmospheric airflows related to Dansgaard–Oeschger cycles. Phases of enhanced southerly circulation promoted increased rainfall and ice accumulation in the southern Alps.

Cosmogenic exposure dating of late Pleistocene moraine stabilization in Alaska

Seventy-three new 1 0 Be/ 2 6 Al ages from 57 moraine boulders and 2 tors, together with 43 previously published cosmogenic exposure ages from 41 moraine boulders, allow us to critique the use of cosmogenic exposure (CE) dating of moraine boulders in Alaska. Boulder exhumation during moraine degradation likely gives rise to the largest uncertainty in constraining the timing of initial moraine stabilization following ice retreat. Isotopic inheritance appears to be most important for moraines deposited close to their cirque headwalls. Boulder-surface (bedrock) erosion rate can be roughly constrained and leads to a range in moraine stabilization ages. Snow-cover history is difficult to constrain, but its effect is thought to be minor for the tall boulders sampled. Despite these complications, the CE ages provide important new information regarding the timing of the last and penultimate glaciations in Alaska. Three penultimate moraines yielded CE ages that overlap with marine isotope stage (MIS) 4/early MIS 3 (45-65 ka) rather than MIS 6 (ca. 140 ka). Based on a combination of our new CE chronologies and existing 1 4 C ages from six study areas, glaciers retreated from their local late Wisconsin maxima: ca. 24-27 ka, Kokrines Hills (west-interior Alaska); ca. 24-26 ka, northeastern Brooks Range (NE Alaska); ca. 21-23 ka, Yukon Tanana Upland (east-interior Alaska); ca. 22 ka, Ahklun Mountains (SW Alaska); ca. 20 ka, western Alaska Range (central Alaska); ca. 16-18 ka, Chuilnuk Mountains (SW Alaska). Overall, glacier retreat was concurrent with the peak of the last global glacial maximum, probably in response to limited moisture availability.

The North Taymyr ice-marginal zone, Arctic Siberia—a preliminary overview and dating

The North Taymyr ice-marginal zone (NTZ) is a complex of glacial, glaciofluvial and glaciolacustrine deposits, laid down on the northwestern Taymyr Peninsula in northernmost Siberia, along the front of ice sheets primarily originating on the Kara Sea shelf. It was originally recognised from satellite radar images by Russian scientists; however, before the present study, it had not been investigated in any detail. The ice sheets have mainly inundated Taymyr from the northwest, and the NTZ can be followed for 700–750 km between 75°N and 77°N, mostly 80–100 km inland from the present Kara Sea coast. The ice-marginal zone is best developed in its central parts, ca. 100 km on each side of the Lower Taymyr River, and has there been studied by us in four areas. In two of these, the ice sheet ended on land, whereas in the two others, it mainly terminated into ice-dammed lakes. The base of the NTZ is a series of up to 100-m-high and 2-km-wide ridges, usually consisting of redeposited marine silts. These ridges are still to a large extent ice-cored; however, the present active layer rarely penetrates to the ice surface. Upon these main ridges, smaller ridges of till and glaciofluvial material are superimposed. Related to these are deltas corresponding to two generations of ice-dammed lakes, with shore levels at 120–140 m and ca. 80 m a.s.l. These glacial lakes drained southwards, opposite to the present-day pattern, via the Taymyr River valley into the Taymyr Lake basin and, from there, most probably westwards to the southern Kara Sea shelf. The basal parts of the NTZ have not been dated; however, OSL dates of glaciolacustrine deltas indicate an Early–Middle Weichselian age for at least the superimposed ridges. The youngest parts of the NTZ are derived from a thin ice sheet (less than 300 m thick near the present coast) inundating the lowlands adjacent to the lower reaches of the Taymyr River. The glacial ice from this youngest advance is buried under only ca. 0.5 m of melt-out till and is exposed by hundreds of shallow slides. This final glaciation is predated by glacially redeposited marine shells aged ca. 20,000 BP ( 14C) and postdated by terrestrial plant material from ca. 11,775 and 9500 BP ( 14C)–giving it a last global glacial maximum (LGM; Late Weichselian) age.

Geochronology of bonney drift, taylor valley, antarctica: evidence for interglacial expansions of taylor glacier

Taylor Glacier drains into Taylor Valley from Taylor Dome, a peripheral ice rise of the East Antarctic Ice Sheet (EAIS) located near the inland edge of the Transantarctic Mountains. Taylor Glacier and local alpine glaciers have expanded in the present‐day interglaciation, so that they now occupy their maximum positions since the last global glacial maximum. Exposed on the floor and walls of Taylor Valley between Lake Bonney and Canada Glacier, Bonney drift represents the penultimate eastward (downvalley) advance of Taylor Glacier. Lacustrine algal carbonates, which form in shallow proglacial lakes, were found in most excavations into Bonney drift. Both in situ and reworked carbonate samples produced 49 new uranium/thorium (U/Th) dates. U/Th dates of 70 to 130 ka for samples collected from excavations and natural sections, along with geomorphologic evidence reported elsewhere in this issue, confirm that the Bonney advance of Taylor Glacier, along with the concurrent expansion of local alpine glaciers, occurred during the interglaciation corresponding with marine isotope stage (MIS) 5. In addition, δ18 O values (−35 to −43%) of the algal carbonates confirm deposition in a proglacial lake fed by Taylor Glacier meltwater. The detailed distribution of U/Th dates shows that Bonney ice advances occurred in substages 5a, 5c, and 5e. The δ18 O record of the Taylor Dome ice core also indicates ice thickening during these same intervals. The inclusion of older carbonates in Bonney drift affords evidence for proglacial lakes during MIS 7 (160 to 240 ka), MIS 9 (270 to 330 ka), and MIS 11 or older (&370 ka). It is probable that these proglacial lakes were also associated with interglacial expansions of Taylor Glacier. This terrestrial U/Th geochronology affords a regional constraint on the late Quaternary behavior of the peripheral sector of the EAIS drained by Taylor Glacier, consistent with expansion during global interglaciations and recession during global glaciations.

Weichselian geology and palaeoenvironmental history of the central Taymyr Peninsula, Siberia, indicating no glaciation during the last global glacial maximum

Weichselian geology and palaeoenvironmental history of the central Taymyr Peninsula, Siberia, indicating no glaciation during the last global glacial maximum

Weichselian geology and palaeoenvironmental history of the central Taymyr Peninsula, Siberia, indicating no glaciation during the last global glacial maximum

The Taymyr Peninsula constitutes the eastern delimitation of a possible Kara Sea basin ice sheet. The existence of such an ice sheet during the last global glacial maximum (LGM), i.e. during the Late Weichselian/Upper Zyryansk, is favoured by some Russian scientists. However, a growing number of studies point towards a more minimalistic view concerning the areal extent of Late Weichselian/Upper Zyryansk Siberian glaciation. Investigations carried out by us along the central Byrranga Mountains and in the Taymyr Lake basin south thereof, reject the possibility of a Late Weichselian/Upper Zyryansk glaciation of this area. Our conclusion is based on the following: Dating of a continuous lacustrine sediment sequence at Cape Sabler on the Taymyr Lake shows that it spans at least the period 39–17 ka BP. Even younger ages have been reported, suggesting that this lacustrine environment prevailed until shortly before the Holocene. The distribution of these sediments indicates the existence of a paleo‐Taymyr lake reaching c. 60 m above present sea level. A reconnaissance of the central part of the Byrranga Mountains gave no evidence of any more recent glacial coverage. The only evidence of glaciation — an indirect one — is deltaic sequences around 100–120 m a.s.l., suggesting glacio‐isostatic depression and a large input of glacial meltwater from the north. However, 14C and ESR datings of these marine sediments suggest that they are of Early Weichselian/Lower Zyryansk or older age. As they are not covered by till and show no glaciotectonic disturbances, they support our opinion that there was no Late Weichselian/Lower Zyryansk glaciation in this area. We thus suggest that the Taymyr Peninsula was most probably glaciated during the early part of the last glacial cycle (when there was only small‐ to mediumscale glaciation in Scandinavia), but not glaciated during the later part of that cycle (which had the maximum ice‐sheet coverage over north‐western Europe). This fits a climatic scenario suggesting that the Taymyr area, like most of Siberia, would come into precipitation shadow during times with large‐scale ice‐sheet coverage of Scandinavia and the rest of north‐western Europe.

The role of the Indian summer monsoon and the mid-latitude westerlies in Himalayan glaciation: review and speculative discussion

New dates for late Quaternary glaciations in the Himalayas show that, during the last glacial cycle, glaciations were not synchronous throughout the region. Rather, in some areas glaciers reached their maxima at the global glacial maximum of c. 18–20 ka bp , whereas in others glaciers were most extensive at c. 60–30 ka bp . Comparison of these data with palaeoclimatic records from adjacent regions suggest that, on millennial timescales, Himalayan glacier fluctuations are controlled by variations in both the South Asian monsoon and the mid-latitude westerlies.

The Sisters Creek Formation: Pleistocene sediments representing a nonglacial interval in southwestern British Columbia at about 18 ka

Sisters Creek Formation is formally defined, stratotypes are established for it, and the time–space chart is updated for the Fraser Lowland, southwestern British Columbia. The Sisters Creek is a Pleistocene formation comprising in situ and reworked organic-rich sediments, and nonorganic silt, sand, and gravel. The formation was deposited during the Port Moody interstade (within the Late Wisconsinan Fraser Glaciation; δ18O stage 2) between the Coquitlam stade (early Fraser Glaciation) and the main Vashon stadial maximum that occurred about 14.5 ka. The Sisters Creek Formation represents a glacial recession in southwestern British Columbia that generally coincided with the timing of the last global glacial maximum. The new time–space chart implies that, in Fraser Lowland, the Fraser Glaciation represents the rapid advances and retreats of glacial lobes issuing from surrounding mountains, which remained ice-covered during interstades.

Quaternary Climate Change and the Formation of River Terraces across Growing Anticlines on the North Flank of the Tien Shan, China

Nested stream terraces, warped upward over actively growing anticlines along the north flank of the Tien Shan in western China, appear to record alternating phases of valley widening and incision. Differences of relative heights between remnants of four separate strath terraces along one river and between two such terraces along another reach 100 to 120 m over the crests of the anticlines. We infer that this spacing is due to alternating stages of valley widening and rapid incision associated with climate changes with a periodicity of 100 kyr. The crests of the anticlines appear to emerge from the aggrading flanks of the anticlines at an average rate of about 1 mm/a. The maximum heights of 25 and 35 ( ± 10) m for the lowest terraces above their projected initial profiles imply ages of roughly 25 kyr and 35 kyr ( ± 10 kyr). Hence, they suggest that flood plains, which were abandoned to form the terraces, developed adjacent to active stream beds during the last glacial period, when climates were relatively cold and dry. We presume that they were incised during deglacial periods when discharges and stream power increased. Apparent durations of exposure, obtained from $$^{10}Be$$ in quartz cobbles lying on the surface of the lower terrace from one anticline, concur with abandonment and deep (~150 m) incision of the flood plain during the last global deglaciation (ca. 20 to 13 kyr B.P.). A minimum carbon-14 date of 33.9 kyr B.P. from deposits on the lowest terrace sequence from the other anticline, however, implies that such abandonment and incision of this flood plain occurred before the most recent global glacial maximum, about 20 kyr B.P. We infer that incision of this second anticline's floodplain began during an earlier deglacial epoch within the last glacial period (between about 70 and 20 kyr, and perhaps near 35 kyr B.P.).

Holocene glacier fluctuations in South America and Antarctica

Glacial geologic evidence indicates that glaciers throughout the Andes and Antarctica fluctuated during the Holocene. Radiocarbon dating and other age determinations suggest that glaciers readvanced significantly only during the last 5 ka, reaching positions from several 100 m to a few kilometres beyond their present limits. In South America tenuous evidence from radiocarbon dates, with dendrochronological data and environmental interpretations from pollen analyses indicate four main periods of Neoglacial advance, culminating 5000-4000 BP, 3000-2000 BP, 1300-1000 BP, and 15th-late 19th centuries; smaller advances may have occurred at ca. 8400 BP, ca. 7500 BP, and ca. 6300 BP. The meagre data are consistent in indicating broad synchrony throughout the Andes during the last 5 ka, suggesting response to global climatic changes. Anomalies exist in Patagonia where some tide-water glaciers reached their maximal Holocene limits recently this century. The broad spectrum of differing Antarctic environments produces interesting contrasts. Some local glaciers in the McMurdo Sound area of the East Artarctic continent are more extensive now than during the global glacial maximum ca. 18 ka BP, when they were starved of precipitation. Consistent agreement among 14 radiocarbon dates from the South Shetland Islands indicates two main Holocene glacier advances, the most extensive (2–3 km) peaking in the 12th century, the other culminating in the 18th–19th century. Glaciers in South Georgia reached their most advanced Holocene limits before 2200 BP. Moraine Fjord glacier, which culminated as a 6 km advance between 1460–1700 radiocarbon BP, may have lagged 400–650 years behind the climatic forcing because it could only advance in its deep-water fjord by building a moraine bank. Smaller advances in South Georgia culminated in the 17th–19th centuries and during the 1920s-30s. There is no firm evidence of glacier advances before 3 ka BP in the Southern Ocean-sub-Antarctic domain, but broad synchrony in glacier advances during the last ca. 3000 years appears to have occurred throughout the Andes-Antarctic transect. Caution is required in the interpretation and correlation of moraines associated with calving glaciers and of those with poorly constrained dating.

Lag of the Fraser glacial maximum in the Pacific Northwest: pollen and macrofossil evidence from western Fraser Lowland, British Columbia

Pollen and macrofossil evidence from two sites in northwestern Fraser Lowland reveals that Abies lasiocarpa – Picea cf. engelmannii forest and parkland grew there about 18 000 years ago under cold humid continental conditions. Taxus brevifolia was also a significant constituent of this forest. This plant assemblage resembles the ESSF Biogeoclimatic Zone of subalpine elevations in the northern interior of British Columbia (900–2250 m). Climate was probably cold with low to moderate rainfall and characterized by long, cold, wet winters and very short, probably dry, frost-free summers. Mean annual temperature was depressed about 8 °C and the tree line was probably 1200–1500 m lower than today.Fraser Lowland was probably removed from Pacific oceanic influence because the land–sea interface was located on the continental shelf to the west of Vancouver Island and Washington about the time of the last global glacial maximum, global depression of sea level, and Quadra Sand aggradation in the Pacific Northwest. Lowland glaciation was probably delayed because of insufficient precipitation in the drier macroclimate and the precipitation shadow created behind mountains on Vancouver Island and Olympic Peninsula. We speculate that, as Laurentide ice decayed, there was a northward shift of zonal weather patterns over the eastern Pacific, bringing very wet winters to the Fraser Lowland and providing moisture for rapid, extensive, Vashon glaciation, which culminated about 14 500 BP, lagging at least 3000 years behind the Laurentide glacial maximum.