Late Wisconsin Glacial Maximum Research Articles

China Bowl Cave: An Early-Middle Holocene non-analog faunule from Grand Rapids, central Manitoba, Canada

China Bowl, a small vadose cave in the northern Interlake Region of Manitoba, Canada (53+° N, 99+° W), yielded the first recorded cave assemblage from central Manitoba—an Early-Middle Holocene vertebrate faunule dating to 7715 rcy BP (8500 cal y BP). The faunule, comprising mainly small mammals and amphibians, suggests an open taiga punctuated by mixed groves of trees on drier uplands interspersed with low-lying wetlands in an area occupied only a few centuries previously by proglacial Lake Agassiz. Identified elements include 3368 teeth derived from 17 small mammalian species, most of which are today locally sympatric taxa. This late, non-analog fauna, which includes Bison sp. indet., also features collared lemming (Dicrostonyx, perhaps D. richardsoni) which is now disjunct from the China Bowl locality by some 400–500 km to the north. The early postglacial, post-Agassiz occurrence of Dicrostonyx in the northern Interlake supports hypotheses about (Richardson's?) collared lemming still recolonizing northward from a refugium south of the late-Wisconsin Glacial Maximum (LGM) limits as ice and Lake Agassiz shorelines retreated. More than 3800 amphibian bones were also recovered, along with a few snake and fewer avian remains.

Pilot shallow drilling on the continental shelf, Dronning Maud Land, Antarctica

A light, mining drill rig deployed from the stern of a research vessel has been used to carry out shallow drilling in 212 m water depth on the continental shelf in the eastern Weddell Sea. Penetration was 15 m below the seabed with 18% recovery in the 31 hours available for the experiment. The recovered glacigenic sediments are predominantly volcanic material of basaltic and andesitic composition with petrological characteristics and age similar to the continental flood basalts exposed in Vestfjella, about 130 km upstream from the drill site. The sediments include a reworked marine Miocene diatom flora. The material documents oscillations of the East Antarctic Ice Sheet over the past 30 ka. The lowermost diamicton probably represents a deformation till, and the grounding line retreated past the drill site 30 km from the shelf edge about 30 kyr BP. A readvance occurred during the Late Wisconsin Glacial Maximum. Assuming a reservoir correction of 1300 yr, marine conditions existed at the site between 10.1-7 kyr BP, and later at least between 2.8 and 2.5 kyr BP. The stratigraphy at the site has been disturbed by iceberg ploughing and/or contact between the ice shelf and the sea floor during local advances after 2.5 kyr BP.

Shelf progradation on a glaciated continental margin, Queen Maud Land, Antarctica

Abstract A detailed survey of the continental margin in the eastern Weddell Sea demonstrates shelf progradation by material input from discrete glacial wedges that amalgamate to form the present near rectilinear shelf edge. Kvitkuven Ice Rise is located between two trough mouth fans and rests on a thick sediment substratum that predates the shelf sequences north of it. Shelf progradation, west of the ice rise, preceded the progradation east of it. In this way the seaward progression of a shelf edge may reflect the broad scale expansion of the East Antarctic Ice Sheet, but the timing of shelf progradation can be different in adjacent areas. The progradational glacial wedges on the continental shelf mapped by this survey are correlated stratigraphically to be within the post Late Miocene glacial sequence, drilled at ODP Site 693 on the middle continental slope 200 km to the northeast. Two submarine moraine ridge complexes on the shelf parallel the shelf edge. A radiocarbon age of 18.950±280 years BP from the front of the inner complex (water depth 319 m) suggests that grounded ice at most reached the present mid-shelf area in front of the ice rise during the Late Wisconsin Glacial Maximum, or had retreated to this position at that time.

Vegetation and climate change during the Last Interglacial-Glacial cycle in western Tasmania, Australia

Cool temperate Phyllocladus aspleniifolius-Nothofagus cunninghamii rainforest occurred in western Tasmania during Isotope Substage 5e. During most of the Last Glacial Stage (Substage 5d to Stage 2) the vegetation was subalpine woodland and shrubland, or alpine grassland, herbland, and heathland. Montane and subalpine rainforest existed at mid-altitude (516 m) during Substages 5a and 5c. During Stage 2, the Late Wisconsin Glacial Maximum, most of western Tasmania had alpine grassland and herbland vegetation, with areas of sclerophyll woodland and rainforest taxa below 100 m on valley floors near the coast. Cool temperate rainforest developed again during late glacial times (after 14 k 14C yr BP), with maximum development of Nothofagus cunninghamii rainforest in the early Holocene. Estimates of temperature depression, based on depression of the altitudinally zoned vegetation communities, a lapse rate of 0.65 °C/100 m, and comparison with marine core RC 11–120 from the southwestern sub-polar Indian Ocean, indicate that the early stadials (Substages 5b and 5d) were cold, and the early interstadials (Substages 5a and 5c) were cool. Stage 4 was cold and probably fully glacial. Temperature increased early in Stage 3 but then decreased, with some fluctuations, towards Stage 2, the late Wisconsin Glacial Maximum. An abrupt increase in temperature of ca. 6°C occurred after 14 k 14C yr BP.

Late Quaternary sediment facies in Prydz Bay, East Antarctica and their relationship to glacial advance onto the continental shelf

A marine survey in Prydz Bay, provides an unparalleled view of glacigenic and marine sedimentation across Prydz Channel and Amery Depression during the Late Quaternary. Gravity cores and a suite of eight radiocarbon dates indicate that the Late Wisconsin Glacial Maximum (LGM) was associated with grounding of a palaeo-ice shelf along the periphery of Prydz Channel. Deposition in front of the grounding line was dominated by ice-rafting. A granulated facies, containing angular clay and diamicton clasts, was producd by a combination of regelation freezing, near to the grounding line, and remelting of this basal debris in the sub-ice shelf setting. Beneath these LGM marine deposits lie two key beds of diatom ooze that are distinct in size sorting and Pliocene diatoms. These “interstadial” units can be traced across most of the Prydz Channel, and are underlain by additional glacial marine units. Debris related to the Lambert Deep is distinct from detritus from eastern Prydz Bay and deposition of these two sources within the channel oscillated during the LGM. We suggest that coastal drainage systems contributed to a limited glaciation of the shelf during the LGM, rather than direct outflow via the Lambert/Amery system. It is proposed that shelf-wide glaciation is related to the duration of glacial sea level lowstands rather than the absolute magnitude of eustatic fall during such episodes.

Additional radiocarbon date from Dante outwash fan, King Valley, and dating of the late Wisconsin glacial maximum in western Tasmania

A radiocarbon date of 19 I 00 ± I 00 yr BP (SUA 2856) closely dates the maximum extent of glacier ice at Lake Beatrice in the upper Dante Rivulet during the Late Wisconsin in western Tasmania. Study of the Dante Glacier outwash fan deposits shows that they overlie a palaeosol and an older outwash gravel formation, and are interstratified with fluvial silts containing transported organic detritus deposited by flooding of the King River. Examination of available radiocarbon dates obtained from the palaeosol and interstratified silts shows that the palaeosol, Dante ourwash and fluvial silt sequence was formed during a relatively short period preceding and around the peak of the Late Wisconsin glacial stade (18-20 kyr BP). The data suggest that the Dante Glacier extended to its end moraine limits for only a short time.

Thermoluminescence chronology of Toronto-area Quaternary sediments and implications for the extent of the midcontinent ice sheet(s)

We report direct dating, by thermoluminescence (TL) methods, of key Quaternary stratigraphic horizons in the Toronto area. TL ages indicate that (1) most of the exposed sediments of the Don Formation at the sampled site were probably deposited during the closing phase of the Sangamon Interglacial (∼80 ka; oxygen isotope stage 5a), not the climatic optimum substage 5e (∼120∼130 ka),as generally supposed; (2) overlying deltaic strata of the Scarborough Formation, which accumulated in an ice-dammed ancestral Lake Ontario, were deposited between 60 and 50 ka (early Wisconsin, oxygen isotope stage 4); (3) the Sunnybrook diamict, overlying the Scarborough Formation, was deposited in the middle Wisconsin at ∼40-45 ka (oxygen isotope stage 3), likely by glaciolacustrine processes, rather than before 65 ka, as previously supposed; (4) sediments of the Upper Thorncliffe Formation lying stratigraphically just beneath the last-glacial-maximum Hallton Till were deposited at ∼23 ka, consistent with reliable 14 C dating. Thus, the earliest Wisconsin incursion of the (proto) Laurentide Ice Sheet into the Lake Ontario basin, as recorded by the Scarborough Formation, probably did not take place until at least 60 ka, and did not extend south and southwest of the Toronto area until after ∼25 ka. Ice-free conditions probably persisted over large areas of midcontinent North America from the end of the Illinoian glaciation at ∼130 ka to the late Wisconsin glacial maximum at ∼20 ka.

Quaternary sedimentation of the Alaskan Beaufort shelf: Influence of regional tectonics, fluctuating sea levels, and glacial sediment sources

Abstract The offshore stratigraphy of the Quaternary Gubik Formation of Arctic Alaska has been studied on high-resolution seismic profiles with a maximum sub-seafloor penetration of about 100 m. In general, marine transgressive subunits of the Gubik Formation are wedge-shaped on the shelf, thickening slightly seaward to the shelf break, beyond which they are offset by landslides and slumps. Beneath the eastern third of the Alaskan Beaufort shelf, active folding has created two persistent structural depressions, the Eastern and Western Wedge Terranes, in which the wedge morphology is especially well developed. The youngest transgressive marine wedge, which was deposited in such a way as to fill these depressions, leaving a generally flat present-day shelf surface, is inferred to be late Wisconsin or younger in age because it overlies a prominent disconformity interpreted to have been formed during the late Wisconsin glacial sea-level minimum. The thickness of this youngest wedge, Unit A, locally exceeds 40 m on the outer shelf, yet apparently relict gravel deposits collected from its seabed surface indicate that the depositional rate is presently quite low on the middle and outer shelf. Lithologies of the gravels are exotic to Alaska, but similar to suites exposed in the Canadian Arctic Islands. These observations suggest a depositional scenario in which the retreating Laurentide Ice Sheet shed sediment-laden icebergs from the Canadian Arctic Islands into the Arctic Ocean following the late Wisconsin glacial maximum. These bergs were then rafted westward by the Beaufort Gyre and grounded on the Alaskan shelf by northeasterly prevailing winds. Especially large numbers of bergs accumulated in the wedge terrane embayments—created as sea level rose—and melted there, filling the embayments with their sedimentary cargo. As glacial retreat slowed, depositional rates on the shelf dwindled. This mode of deposition in the Alaskan Beaufort wedge terranes may be typical of early post-glacial transgressive phases throughout Quaternary time. It has resulted in the preservation of disconformities that apparently formed during glacioeustatic lowstands, and whose seaward termination depths, appropriately corrected, may yield estimates of lowstand magnitudes. Knowledge of global sea-level fluctuations back through the Sangamon Interglacial (oxygen isotope stage 5e) and possible correlations with dated onshore deposits have facilitated a tentative correlation of major disconformities in the Beaufort Sea record with major 18 O enrichment maxima in the oxygen isotope curve back through stage 8. In this tentative scheme, close similarities between the two data sets occur both in magnitudes and in numbers of fluctuations intervening between major correlation points. Further testing of the Quaternary depositional model suggested here and of the resulting sea level curve awaits the collection and dating of core samples from the Beaufort wedge terranes.

Wisconsin—Holocene paleoenvironment of the Bering Sea: Evidence from diatoms, pollen, oxygen isotopes and clay minerals

A core from the southeastern Bering Sea contains a depositional record of the Wisconsin glacial interval and the Holocene. Four lithologic units show distinctive changes in diatom species, palynomorphs, oxygen isotopes in diatom silica, and clay minerals. Unit 4, the oldest, probably represents the glacial advance of the early Wisconsin and records extensive sea ice cover and a soggy, herbaceous tundra on the exposed continental shelf. Unit 3 represents the stades and interstades of the middle Wisconsin, including an early period of high seasonal variability and a later period with expansion of winter sea ice in the basin and of tundra onshore. Unit 2 represents the late Wisconsin glacial maximum and subsequent deglaciation with a tundra-covered shelf. Sea ice cover increased to a maximum, during which the surface waters were probably covered by sea ice throughout the year. Subsequent to the sea ice maximum the isotope ratios record a major meltwater event. Unit 1 represents the Holocene, with expansion of shrub tundra or scrub forest in the coastal upland and waters of increased temperature and salinity in the Bering Sea.

Ice-Free Conditions on the Queen Charlotte Islands, British Columbia, at the Height of Late Wisconsin Glaciation

New radiocarbon dates and plant macrofossil data establish that parts of the Queen Charlotte Islands, British Columbia, were ice-free during and subsequent to the late Wisconsin glacial maximum on the Pacific coast of Canada. A paleoecological investigation of dated sediments at Cape Ball has indicated that a varied flora consisting of terrestrial and aquatic plants was present there about 16,000 years ago. This finding provides support for the existence of a heretofore questioned biotic refugium on the Queen Charlotte Islands during the last glaciation. These results shed new light on problems of glacial chronology, climatic change, biogeography, and archeology along the western margin of North America.

New radiocarbon dates from the inner Continental Shelf off southeastern Massachusetts and a local sea-level–rise curve for the past 12,000 yr

New radiocarbon dates on shells and freshwater peat are used to draw a curve representing local sea-level rise for the past 12,000 yr. The samples were collected near the late Wisconsin glacial maximum where the Continental Shelf suffered the least and most rapid isostatic subsidence and rebound to the advance and retreat of the ice. Because the samples are from quiet-water embayments, they most likely have not been reworked or transported. For these reasons, the curve based on these data is believed to accurately represent sea-level rise in southeastern Massachusetts. Previously published radiocarbon dates from elsewhere on the inner shelf tend to reinforce the curve proposed here and suggest that the curve may be applicable for much of the inner Continental Shelf off the northeastern United States. The proposed sea-level–rise curve indicates that relative sea level was about 70 m below its present level 12,000 yr ago. From that time to about 10,000 yr ago, sea level rose at a rate of 1.7 m/100 yr. Between 10,000 and 6,000 yr ago, the rate of sea-level rise dropped gradually to about 0.3 m/100 yr and remained at that rate until about 2,000 yr ago. From then until now, the rate of sea-level rise has been about 0.01 m/100 yr.

Planktonic foraminiferal diversity in the interglacial and glacial North Atlantic: A test of diversity gradients as a paleoceanographic technique

We calculated diversity indices for planktonic foraminifera in both modern and 18,000 B.P. (late Wisconsin glacial maximum) North Atlantic sediment samples. Modern diversity patterns, especially those based on the Shannon index, reflect present surface circulation. Mapped 18,000 B.P. diversity values reveal a southward migration of the polar front, a shrinking of transitional areas, a southward deflection of the Gulf Stream, and a slight expansion of Sargasso Sea waters. These changes agree with the CLIMAP reconstruction and validate the paleoceanographic utility of diversity maps in epochs prior to the origin of extant species.

Late Quaternary Vegetation History of the Eastern Highland Rim and Adjacent Cumberland Plateau of Tennessee

Vegetation change during the past 25 000 years in and near the present Mixed Mesophytic Forest Region is inferred from pollen and plant macrofossil analyses of sediment cores from two sites on the eastern Highland Rim of Middle Tennessee, USA. Anderson Pond, in White County, dates from 25 000 radiocarbon years BP to present. During the Farmdalian Interstadial, 25 000 yr BP, northern Diploxylon pines, spruce, and deciduous trees were present at Anderson Pond, indicating a cool, moist climate. From 19 000 to 16 300 yr BP, during the Late Wisconsin glacial maximum, boreal taxa of jack pine, spruce, and fir were dominant. Late—glacial climatic amelioration began in Middle Tennessee at about 16 300 yr BP, with replacement of jack pine—spruce—fir forest by deciduous forest. Ash, ironwood, hickory, birch, butternut, willow, and elm increased in importance first, followed by beech and sugar maple. Mixed mesophytic forest taxa were most abundant during the early Holocene, between 12 500 and 8000 yr BP. A warming and drying trend between 8000 and 5000 yr BP is reflected by high influx values for pollen of oak, ash, hickory, swamp alder, and buttonbush, and by diminishing importance of mixed mesophytic forest taxa. Mingo Pond, Franklin County, Tennessee, contains a pollen record estimated to extend back to 14 000 yr BP. Mixed mesophytic forest taxa were abundantly represented at Mingo Pond during the late glacial and early Holocene, along with pollen representing prairie vegetation. Oak and sweetgum dominated the mid— and late Holocene record from Mingo Pond. Stratigraphic sites from the Missouri Ozarks to the Atlantic Coastal Plain date the full glacial in the southeastern United States between 23 000 and 16 500 yr BP. During the glacial maximum, boreal—like coniferous forests of spruce, jack pine, and fir extended southward to 34°N latitude. Mesic deciduous forest persisted through the full glacial at 35°N at Nonconnah Creek near Memphis. Full—glacial refuges for deciduous forest species may have also existed in south—facing gorges of the Cumberland Plateau and southern Appalachian Mountains in addition to bluffs along major streams in the southeastern United States. During the late glacial, beginning about 16 500 yr BP, boreal—like coniferous forest was replaced in midlatitudes (34° to 37°N) by cool—temperate coniferous—deciduous forest. In the early Holocene, between 12 500 and 8000 yr BP, cool—temperate mixed mesophytic forest prevailed between 34° and 37°N. The Mixed Mesophytic Forest Region assumed its present distribution in the mid—Holocene.

The Dynamics of Marine Ice Sheets

AbstractMarine ice sheets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes afloat, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates and grounding-line retreat, falling sea-level has the reverse effect. If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a marine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form an ice shelf may take place extremely rapidly. Ice shelves which form in embayments of a marine ice sheet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established; removal of the ice shelf would allow retreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current example is the West Antarctic ice sheet. This is buttressed by the Ross and Ronne Ice Shelves, and if climatic warming were to prohibit the existence of these ice shelves then the ice sheet would collapse. Field observations suggest that, at present, the ice sheet may be advancing into parts of the Ross Ice Shelf. Such advance, however, would not ensure the security of the ice sheet since ice streams that drain to the north appear to flow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sheet retreat.

The Dynamics of Marine Ice Sheets

AbstractMarine ice sheets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes afloat, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates and grounding-line retreat, falling sea-level has the reverse effect. If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a marine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form an ice shelf may take place extremely rapidly. Ice shelves which form in embayments of a marine ice sheet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established; removal of the ice shelf would allow retreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current example is the West Antarctic ice sheet. This is buttressed by the Ross and Ronne Ice Shelves, and if climatic warming were to prohibit the existence of these ice shelves then the ice sheet would collapse. Field observations suggest that, at present, the ice sheet may be advancing into parts of the Ross Ice Shelf. Such advance, however, would not ensure the security of the ice sheet since ice streams that drain to the north appear to flow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sheet retreat.

Karst depressions in a time context

AbstractA study of karst depression enlargement through time on the Western Highland Rim (physiographic province), based on two sets of aerial photography (1937, 1972) and field work, indicates that areal growth rates (dA/dt, m2/a) depend upon the surficial geologic setting. Areal growth rates were calculated from rates of long axis (dL/dt) and mean width (dW/dt) enlargement assuming an elliptical plan shape. Areal growth rates averaged 40, 70, and 100 m2/century for loessial, clayey residual, and silty colluvial surficial material, respectively.Estimates of average apparent age of karst depressions in each of the three surficial materials, based on linear growth rates, varied from 25,000 to 65,000 years B.P. An occurrence of mastodon (Mammut americanum) and ground sloth (Megalonyx jeffersoni) from the Darks Mill depression as well as a pollen record from another depression dating from the Late Wisconsin glacial maximum in the same geomorphic setting yielded dates compatible with estimates of depression age.

Climatic implications of D/H ratios of meteoric water over North America (9500–22,000 B.P.) as inferred from ancient wood cellulose C [sbnd]H hydrogen

δD and δ 13C values have been measured for the unexchangeable hydrogen and the total carbon of cellulose extracted from 40 North American 14C-dated trees that range in age from 9500 to 22,000 years B.P. Meteoric waters which precipitated over ice-free regions of North America in the interval 14,000–22,000 B.P. had more positive δD values than corresponding modern waters by an average of 19‰. Lower ocean temperatures and smaller temperature gradients than exist at present between ocean and ice-free North America are indicated for the late Wisconsin glacial maximum. This is compatible with warmer winters and cooler summers for this glacial period. The δD value of the North American ice sheet during the Late Wisconsin maximum was approximately −100‰ as determined from the inferred δD values of the waters of proglacial lakes Agassiz and Whittlesey. From this figure the increase in δ 18O of the oceans during the glacial maximum can be calculated to have been +0.8‰. At the point where they began to move over the ice, air masses supplying moisture to the North American ice sheet contained a little more than 50% of their original moisture content, which is a much greater percentage than exists in air masses supplying the modern Greenland and Antarctic ice sheets. This relatively vapor-rich air coupled with lower summer temperatures, which reduced ablation, probably contributed to the maintenance and growth of the ice sheet. The transition from glacial to interglacial conditions on North America was rapid and occurred within a 2000–3000-year interval. However, the transition may not have been synchronous over North America. A 40-year δD record in a spruce branch from the Two Creeks (Wisconsin) forest (∼11,800 B.P.) shows large variations which suggest an unusual hydrologic environment in the area of the tree. Cellulose δ 13C values range between −20.8 and −25.9‰, but do not correlate with δD variations for the samples analyzed in this work. Thus, climatic significance of δ 13C variations cannot be resolved from these data.

Late Quaternary glacial and climatic history of northern Cumberland Peninsula, Baffin Island, N.W.T., Canada

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.