global ice sheet system interlocked by sea level abstract denton and hughes 1983 quaternary research 20 125 144 postulated that sea level linked a global ice sheet system with both terrestrial and grounded marine components during late quaternary ice ages summer temperature changes near northern hemisphere melting margins initiated sea level fluctuations that controlled marine components in both polar hemispheres it was further proposed that variations of this ice sheet system amplified and transmitted milankovitch summer half year insolation changes between 45 and 75 n into global climatic changes new tests of this hypothesis implicate sea level as a major control of the areal extent of grounded portions of the antarctic ice sheet thus fitting the concept of a globally interlocked ice sheet system but recent atmospheric modeling results manabe and broccoli 1985 journal of geophysical research 90 2167 2190 suggest that factors other than areal changes of the grounded antarctic ice sheet strongly influenced southern hemisphere climate and terminated the last ice age simultaneously in both polar hemispheres atmospheric carbon dioxide linked to high latitude oceans is the most likely candidate shackleton and pisias 1985 atmospheric carbon dioxide orbital forcing and climate in the carbon cycle and atmospheric co2 natural variations archean to present e t sundquest and w s broecker eds pp 303 318 geophysical monograph 32 american geophysical union washington d c but another potential influence was high frequency climatic oscillations 2500 yr it is postulated that variations in atmospheric carbon dioxide acted through an antarctic ice shelf linked to the grounded ice sheet to produce and terminate southern hemisphere ice age climate it is further postulated that milankovitch summer insolation combined with a warm high frequency oscillation caused marked recession of northern hemisphere ice sheet melting margins and the north atlantic polar front about 14 000 14c yr b p this permitted renewed formation of north atlantic deep water which could well have controlled atmospheric carbon dioxide w s broecker d m peteet and d rind 1985 nature london 315 21 26 combined melting and consequent sea level rise from the three warming factors initiated irreversible collapse of the interlocked global ice sheet system which was at its largest but most vulnerable configuration

lake devlin and pinedale glacial history front range colorado abstract glacial lake devlin was an ice margin lake that formed during pinedale time when the north boulder creek valley glacier blocked the mouth of a tributary near the downvalley limit of glaciation the lake was about 2 km long and as much as 60 m deep and was fed by meltwater from small valley glaciers it accumulated sediment apparently without interruption for about 10 000 yr the inception of lake devlin between 23 500 and 21 000 yr b p provides a limiting date for the maximum expansion of pinedale ice because the lake could not form until the north boulder creek glacier had advanced to within 2 km of its downvalley limit the maximum lowering of timberline which occurred about 19 000 yr b p is assumed to coincide with the pinedale glacial maximum apparent timberline elevations determined from picea pinus pollen ratios suggest that ice front positions during the time between 23 000 and 19 000 yr b p may have been only slightly less extensive than at the pinedale maximum lake devlin drained catastrophically about 13 000 yr b p which was after ice had receded from the outlet area pinedale glaciation in the front range began about or after 30 000 yr b p and final deglaciation occurred between 15 000 and 12 000 yr b p

ree th hf ta in bamble gabbros southern norway and their amphibolitized equivalents implications for gabbro tectonic setting abstract the bamble gabbros hyperites are a group of partly metamorphosed proterozoic basic intrusions in the bamble sector of southern norway they are discordant to structures formed during the kongsbergian 1 54 ga high grade metamorphism yet are themselves partially amphibolitized in some localities transitions from gabbro to amphibolite occur over only a few metres a previous study of closely spaced gabbro amphibolite sample pairs revealed that amphibolitization was accompanied by increases in k fe3 p h2o rb cl zr and decreases in ca fe2 s zn si co new data for ree th hf ta in the same samples indicate that the only possible metamorphic modification of these elements is a barely significant increase in la in one locality eu eu ratios are preserved this adds confidence to the use of ree as petrogenetic indicators in amphibolitized basic rocks the resistance of sm nd and lu hf ratios to the amphibolitization may indicate that these isotopic systems could be used to gain geochronological and petrogenetic information from the gabbros and their amphibolitized equivalents the combined chemical data fingerprint the gabbros as similar to present day destructive plate margin related basic rocks this is surprising as it has previously been widely supposed that they are an expression of the tensional alkaline magmatism that was widespread in the north atlantic province at 1 25 ga it thus seems more likely that the bamble gabbros are related to renewed subduction after the 1 25 ga anorogenic period the geochemistry of these widespread gabbros must be accounted for in future proterozoic scandinavian tectonic reconstructions

superposed neoglacial and late pinedale wisconsinan tills titcomb basin wind river mountians western wyoming abstract late pinedale wisconsinan and neoglacial deposits mantle most valley floors above the timberlane in the wind river mountains although these tills are generally assigned ages by radiocarbon relative topographic position weathering characteristics and soil morphology they are rarely superposed this paper describes a sequence of moraines in titcomb basin where early neoglacial till now called indian basin till is superposed on a moraine of late pinedale age providing important information on relative ages for the two tills late pinedale deposits radiocarbon date at ca 8000 yr b p from bog bottom organic materials time of onset of neoglaciation is unknown while the termination of the indian basin advance is placed at ca 3000 yr b p differences in soil profile morphology particle size mineralogy and chemistry are described and discussed with respect to relative age assignment while profile morphology and particle size differences appear important in differentiating the two soils differences in clay mineral composition appear to have greater utility in discriminating post indian basin soils from post late pinedale soils

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

laurentide ice sheet instability during the last deglaciation the factors leading to the full retreat of ice sheets during deglaciation are debated numerical modelling suggests that the laurentide ice sheet retreated only after a threshold for warming and radiative forcing was passed in the holocene

tephrochronology of late wisconsin deglaciation and holocene glacier fluctuations near glacier peak north cascade range washington abstract tephra layers near glacier peak in the north cascade range provide limiting dates for four periods of alpine glacier advance field relations suggest that late wisconsin alpine glaciers last advanced prior to the eruption of tephra layers from glacier peak about 11 250 yr b p late wisconsin deglaciation in the central north cascades was complete prior to the glacier peak tephra eruptions glaciers again expanded in the early holocene about 8400 8300 yr b p soil formed in alpine meadows during an episode of mild climate in the middle holocene prior to at least two intervals of glacier expansion an older episode between 5100 and 3400 yr b p and a younger episode within the last 1000 yr

8000 year old wood from the athabasca glacier alberta several wood fragments of pinus sp dated at 8230 80 and 8000 90 years bp and abies sp were recovered from the snout of the athabasca glacier this wood derived from an unknown source up valley indicates that the glacier was less extensive than at present during the hypsithermal and that an area up valley of the present snout was tree covered ca 8000 8300 years bp

response of interior north america to abrupt climate oscillations in the north atlantic region during the last deglaciation several broad scale climatic oscillations during the last deglaciation are well documented in regions around the north atlantic ocean this paper reviews empirical evidence for these deglacial climatic oscillations from non coastal north america and discusses implications for testing climatic simulations and for understanding the cause and transmittal mechanisms paleoclimatic interpretation of oxygen isotope records from several small sites in the eastern great lakes region indicates a classic deglacial climatic sequence that is comparable with records from europe and greenland the climatic events as interpreted from crawford lake oxygen isotopes include the bolling allerod boa warming at 12 700 14c bp a warm boa at 12 500 10 920 14c bp an intra allerod cold period shortly before 11 000 14c bp a cold younger dryas yd climate reversal at 10 920 10 000 14c bp the holocene warming at 10 000 14c bp a brief preboreal oscillation pb at 9650 14c bp and an early holocene cold event at 7500 14c bp 8200 cal bp some of these events were also evident from changes in upland and aquatic vegetation and sediment lithology the pronounced yd climatic reversal has been documented from pollen records along the ecotones at this time and from glacier readvances in the great lakes region along the rocky mountains from alberta to colorado the yd event is indicated by alpine glacier advance and or shift in timberline vegetation in minnesota and upper new york early holocene climatic instability is also suggested by oxygen isotope records and or varve thickness the regional variations in evidence for the yd and other events in north america suggest that climatic oscillations may have different expressions in paleo records depending on geographic location and characteristics of a particular site the extent and magnitude of these climatic oscillations across north america suggest that these oscillations are an expression of climatic change that was probably widespread rather than locally induced by a nearby glacier the location of these sites implies that climatic signals were likely carried over the northern hemisphere through the atmosphere as indicated by general circulation models we hypothesize that the lack of evidence for a cold yd in interior north america west of the great lakes region and east of the rocky mountains was caused by the trapping of cold arctic air mass north of the laurentide ice sheet and by uninterrupted northward expansion of warm caribbean air this strongly contrasted climate also produced non analogous biological assemblages

holocene tephrostratigraphy and glacial fluctuations in waterton lakes and glacier national parks alberta and montana waterton lakes national park in alberta and glacier national park in montana lie along adjacent sections of the continental divide in the rocky mountains in cirques or near divides there is evidence for two ages of glacial deposits younger deposits are generally well preserved poorly vegetated and bear no tephra and no or very small lichens older deposits are more poorly preserved better vegetated bear rhizocarpon sp lichens at least up to 92 mm in diameter and bear tephra the tephra often occurs in two different coloured horizons but both are compositionally equivalent to mazama tephra the older advance has a minimum age of about 6800 14c years bp and a probable maximum age of about 12 000 14c years bp it is correlated with the pre mazama crowfoot advance of the canadian rockies deposits of the younger advance are probably not too much older than mid 19th century because some glaciers began retreating from the deposits about then the younger advance is correlated to the cavell advance of t

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

response of the columbia river fluvial system to holocene climatic change abstract an understanding of the response of a fluvial system to past climatic changes is useful for predicting its response to future shifts in temperature and precipitation to determine the response of the columbia river system to previous climatic conditions and transitions a well dated sequence of floodplain development in the wells reservoir region was compared with the paleoenvironmental history of the columbia river basin results of this comparison indicate that aggradation episodes occurring approximately 9000 8000 7000 6500 4400 3900 and 2400 1800 yr b p coincided with climatic transitions that share certain characteristics the inferred climates associated with aggradation had at least moderate rates of precipitation that occurred mainly in winter coupled with moderate winter temperatures such conditions would have resulted in the buildup of snowpacks and a high frequency of rain on snow events the warming and precipitation increases predicted for the pacific northwest under most co2 doubling scenarios are likely to repeat these conditions which could increase the frequency of severe sediment laden floods in the columbia river basin

new pollen and beetle analyses at the mary jane site colorado evidence for late glacial tundra conditions analyses of fossil pollen and beetles from a late pinedale peat deposit from the upper fraser river colorado allow a reassessment of previously published paleoenvironmental evidence from the site between 13 800 and at least 12 600 yr b p the environment was an open tundra indicative of a cold dry climate scattered spruce trees were probably present at the site by the end of the record ca 12 300 yr b p

neoglaciation in the southern coast mountains of british columbia chronology prior to the late neoglacial maximum moraine stratigraphy and morphology radiocarbon dates from klinaklini franklin tiedemann gilbert and bridge glaciers and related information from elsewhere in the coast mountains are used to construct a chronology for glacier fluctuations the garibaldi phase of glacier expansion 6000 5000 14c years bp at the end of the early holocene xerothermic interval is indicated by overridden tree stumps the mid neoglacial tiedemann advance 3300 1900 14c years bp is represented by moraines till and meltwater sediments at three glaciers but only tiedemann glacier attained its greatest holocene extent at this time late neoglacial expansion commenced before 900 14c years bp and continued without notable interruption until glaciers achieved their maximum post pleistocene expansion during the eighteenth and nineteenth centuries evidence for the garibaldi and tiedemann events is scarce within the coast mountains because of the more extensive late neoglacial advance however correlative advances have been

paleoenvironmental interpretations of holocene insect fossil assemblages from the la poudre pass site northern colorado front range abstract a sequence of peats from the la poudre pass site northern front range colorado rockies yielded abundant insect fossil assemblages studied intervals ranged in age from nearly 10 000 yr b p to about 5400 yr b p seventy named insect taxa were extracted from the peat among these are a mixture of aquatic and terrestrial species several taxa from the lowest 10 cm are indicative of climatic conditions found today in montane forest regions although conifers were probably not present at the site until several centuries after the initiation of peat deposition later insect assemblages contain a mixture of both tundra and forest faunal elements suggesting the close proximity of altitudinal tree limit to the site from about 9500 yr b p through the uppermost level studied 5400 yr b p

glacial chronology of the ruby mountains east humboldt range nevada abstract the ruby mountains east humboldt range one of the interior mountain groups of the basin and range province lies about midway between the wasatch mountains and the sierra nevada after blackwelder s description in his review of glaciation in the western mountains sharp mapped and named the deposits of the lamoille and angel lake glaciations and correlated them with early and late wisconsin deposits of the great lakes area the refinement of relative dating rd methods the availability of airphotos and modern topographic maps and new road cuts have aided the restudy of these alpine glacial deposits and the basis for their correlation lamoille moraines are smooth ridges and show little detail of constructional topography valleys glaciated only by lamoille ice still show the characteristics of a glaciated trough but they have been greatly modified by weathering and erosion granite boulders on lamoille moraines are pitted and pegmatites have grotesque shapes with 30 cm deep pits cuts through lamoille end moraines and alluvial talus cones expose a thick soil profile with a well developed blocky structure in a reddish brown argillic b horizon subsurface granitic boulders in the b horizon of lamoille tills show much greater weathering than do those in angel lake tills in contrast angel lake moraines are irregular and rugged contain closed depressions and have been little altered since deposition surfaces scoured by angel lake ice are fresh and unweathered granites of angel lake moraines have weathered surfaces but show little pitting pegmatites have pits up to 10 cm deep the thin soil profiles on angel lake tills and alluvial talus cones display brown colors minor clay accumulation and no b horizon structure these weathering and morphological differences suggest that the lamoille deposits have been exposed to weathering and erosion for a period of time as much as an order of magnitude longer than the angel lake deposits thus only the angel lake is wisconsinan in age and the lamoille drift is more reasonably correlated with the illinoian stage of the great lakes region

multi proxy record of holocene glacial history of the spearhead and fitzsimmons ranges southern coast mountains british columbia abstract evidence from glacier forefields and lakes is used to reconstruct holocene glacier fluctuations in the spearhead and fitzsimmons ranges in southwest british columbia radiocarbon ages on detrital wood and trees killed by advancing ice and changes in sediment delivery to downstream proglacial lakes indicate that glaciers expanded from minimum extents in the early holocene to their maximum extents about two to three centuries ago during the little ice age the data indicate that glaciers advanced 8630 8020 6950 6750 3580 2990 and probably 4530 4090 cal yr bp and repeatedly during the past millennium little ice age moraines dated using dendrochronology and lichenometry date to early in the 18th century and in the 1830s and 1890s limitations inherent in lacustrine and terrestrial based methods of documenting holocene glacier fluctuations are minimized by using the two records together

stratigraphy and chronology of quaternary deposits of the puget lowland and olympic mountains of washington and the cascade mountains of washington and oregon in the southern puget lowland probably are correlative with salmon springs drift but farther north drift directly beneath vashon till is most likely correlative with much younger drifts such as the double bluff or possession drifts thus virtually all previouslymapped salmon springs drift needs to be re examined to determine if it is indeed correlative with salmon springs drift or is younger

an absolute paleotemperature record from 10 to 6 ka inferred from fluid inclusion d h ratios of a stalagmite from vancouver island british columbia canada abstract by using continuous helium flow during the crushing of calcite speleothem samples we are able to recover liberated inclusion waters without isotopic fractionation a paleotemperature record for the jacklah jill cave locality vancouver island bc was obtained from a 30 cm tall stalagmite that grew 10 3 6 3 ka ago using 18 o values of the crushed calcite and of the inclusion water as inferred from its d it is found that the locality experienced mean annual temperature variations up to 11 c over a 4 ka period in the early holocene at the beginning of the period local temperature quickly increased from a minimum of 1 c to around 10 c but this early climate optimum about 3 c warmer than today only lasted for 1200 years about 8 6 ka ago temperature had declined to 7 c approximately the same as the modern cave temperature since then the study area has experienced only minor temperature fluctuations but there was a brief fall to 4 c at around 7 ka ago which might be caused by a short lived expansion of local alpine glaciers the long term t dependence of d was 1 47 c identical to the value in modern precipitation

regional significance of an early holocene moraine in enchantment lakes basin north cascade range washington abstract the upper enchantment lakes basin in the north cascade range of washington displays two moraine belts each recording an episode of glacier advance after the end of the last glaciation the inner belt the brynhild 0 1 to 0 5 km beyond existing glaciers postdates mount st helens wn tephra 450 yr old which lies only beyond the moraines the morainal surface is only slightly weathered is almost barren of lichens and is devoid of soil evidence suggesting that the brynhild moraines are no more than a century old the outer moraine the brisingamen 0 3 to 0 7 km beyond existing glaciers is weathered and is covered with large lichens on and behind the brisingamen moraine the mazama ash 6900 yr old is present beneath the mount st helens yn and wn tephras despite more than 7 millennia of weathering the rock surface behind the brisingamen moraine is measurably less weathered than the surface beyond which was last glaciated during the rat creek advance about 13 000 yr ago the age of the brisingamen moraine therefore is probably early holocene the brisingamen moraine evidently correlates with moraines near glacier peak near mount rainier in northeastern and central oregon in the southern canadian rockies and in the northern u s rocky mountains these regional effects suggest that a climatic episode of cooling or increased snowfall affected the entire region some time during the early holocene

surface exposure ages of front range moraines that may have formed during the younger dryas 8 2 cal ka and little ice age events abstract surface exposure 10 be ages have been obtained on boulders from three post pinedale end moraine complexes in the front range colorado boulder rounding appears related to the cirque to moraine transport distance at each site with subrounded boulders being typical of the 2 km long chicago lakes glacier subangular boulders being typical of the 1 km long butler gulch glacier and angular boulders being typical of the few hundred m long isabelle glacier surface exposure ages of angular boulders from the isabelle glacier moraine which formed during the little ice age lia according to previous lichenometric dating indicate cosmogenic inheritance values ranging from 0 to 3 0 10 be ka 1 subangular boulders from the butler gulch end moraine yielded surface exposure ages ranging from 5 to 10 2 10 be ka we suggest that this moraine was deposited during the 8 2 cal ka event which has been associated with outburst floods from lake agassiz and lake ojibway and that the large age range associated with the butler gulch end moraine is caused by cosmogenic shielding of and or spalling from boulders that have ages in the younger part of the range and by cosmogenic inheritance in boulders that have ages in the older part of the range the surface exposure ages of eight of nine subrounded boulders from the chicago lakes area fall within the 13 0 11 7 10 be ka age range and appear to have been deposited during the younger dryas interval the general lack of inheritance in the eight samples probably stems from the fact that only a few thousand years intervened between the retreat of the pinedale glacier and the advance of the chicago lakes glacier in addition bedrock in the chicago lakes cirque area may have remained covered with snow and ice during that interval thus partially shielding the bedrock from cosmogenic radiation

dendroglaciological evidence for holocene glacial advances in the todd icefield area northern british columbia coast mountains accelerated glacial recession and downwasting in pacific north america is exposing land surfaces and fea tures buried by glacial advances that in many locations predate the recent little ice age lia dendrochronologic analyses of increment core samples from living trees abies lasiocarpa tsuga mertensiana and samples of subfossil wood collected in the todd icefield area boundary ranges british columbia coast mountains provide the basis for a dendroglaciological and radiocarbon based reconstruction of late holocene glacier activity five intervals of glacier ex pansion were recorded by trees killed or buried by advancing glaciers 1 an advance prior to 3000 14 c years bp 2 an advance at 3000 14 c years bp that coincides with the regional tiedemann advance 3 an unattributed advance at 2300 14 c years bp 4 a two phase advance at 1700 and 1450 14 c years bp that corresponds with the regional first millennium advance 5 an advance with three phases of expansion that began prior to 750 14 c bp and is con sistent with the regional early lia interval and a two phase interval of late lia expansion culminating after 240 and 100 years bp this chronology of late holocene glaciation matches that emerging from similar investigations in the coastal cordillera of pacific north america and provides additional support for the regional significance of both the tiedemann and the first millennium advances resume une recession et une fonte glaciaire accelerees dans l ocean pacifique en amerique du nord exposent des sur faces de terrain et des traits caracteristiques enfouis sous des avancees glaciaires lesquelles dans bien des cas datent d avant le recent petit ge glaciaire des analyses dendrochronologiques d echantillons proportionnels de carottes pris

potential glacial evidence for the younger dryas event in the cordillera of north and south america there is debate as to whether or not the younger dryas yd climatic event affected areas outside of the north atlantic region the potential of alpine glacial deposits to record the yd is of interest because alpine glaciers would be likely to leave a morainal record even during minor short lived advances caused by a period of deteriorating climate in the cordilleran ranges of north and south america there are several candidate moraines many bracketed between radiocarbon ages of ca 12 and 10 ka which may be yd in age the best examples are in the canadian and american rockies the ecuadorian peruvian and bolivian andes and around the patagonian ice cap in most cases temporal brackets are not narrow enough and some radiocarbon ages may not be accurate enough to allow correlation at the present time there are two cases of lateglacial readvance whose ages are interpreted to match or fall within the yd interval an advance of the crowfoot glacier in canada is interpreted to have occurred within the period ca 11 3 and 10 14c ka bp and an advance of the reschreiter glacier in ecuador is interpreted to have culminated in the period ca 11 to 10 6 14c ka bp the latter interpretation depends on an assumption that lake level variations were caused by glacier advances and retreats

assessing ams 14c ages of detrital organics from holocene and late pleistocene moraines east central sierra nevada california usa obtaining age estimates of moraines which have insufficient carbon for conventional 14 c dating may be possible by ams 14 c dating of detrital organic material in the till matrix sufficient detrital carbon was available in the till matrix of holocene and late pleistocene moraines of upper laurel creek canyon east central sierra nevada california for ams 14 c measurements radiocarbon analysis of till matrix organics from the moraine closest to the headwall ml reveals an age of 2875 60 bp eth 13550 the next oldest moraine m2 yields 4450 60 bp eth 12810 m3 the oldest moraine in the bloody mountain cirque yielded organics with a radiocarbon age of 13 600 120 bp eth 12812 while results are preliminary these ages are among the first on till matrix in the sierra nevada and are consistent with geomorphic context other palaeoecologic records in the sierra nevada and palaeolake records in the western united states

glacier change in western north america influences on hydrology geomorphic hazards and water quality the glaciers of western canada and the conterminous united states have dominantly retreated since the end of the little ice age lia in the nineteenth century although average rates of retreat varied from strong in the first half of the twentieth century with glaciers stabilizing or even advancing until 1980 and then resuming consistent recession this retreat has been accompanied by statistically detectable declines in late summer streamflow from glacier fed catchments over much of the study area although there is some geographical variation over recent decades glaciers in northwest bc and southwest yukon have lost mass dominantly by thinning with relatively low rates of terminal retreat and glacier fed streams in that region have experienced increasing flows in many valleys glacier retreat has produced geomorphic hazards including outburst floods from moraine dammed lakes mass failures from oversteepened valley walls and debris flows generated on moraines in addition to these hydrologic and geomorphic changes evidence is presented that glacier retreat will result in higher stream temperatures possibly transient increases in suspended sediment fluxes and concentrations and changes in water chemistry with climate projected to continue warming over the twenty first century current trends in hydrology geomorphology and water quality should continue with a range of implications for water resources availability and management and hydroecology particularly for cool and cold water species such as salmonids copyright 2008 john wiley sons ltd

latest pleistocene and holocene glacier fluctuations in southernmost tierra del fuego argentina abstract some researchers propose that summer insolation controls long term changes in glacier extent during the holocene if this hypothesis is correct the record of glacier fluctuations at high latitudes in the southern hemisphere should differ from that in the northern hemisphere although the chronology of holocene glacier fluctuations in the northern hemisphere is well established much uncertainty remains in the ages of holocene glacier fluctuations in the southern hemisphere especially south america here we report on latest pleistocene and holocene glacier fluctuations at the southern end of the andes north and west of ushuaia argentina surface exposure ages 10 be from glaciated bedrock beyond cirque moraines indicate that alpine areas were free of ice by ca 16 9 ka one and in some cases two closely spaced moraines extend up to 2 km beyond little ice age moraines within many of the cirques in the region the mean age of five 10 be ages from two pre little ice age moraines is 14 27 12 67 ka whereas a minimum limiting radiocarbon age for a smaller recessional moraine in one cirque is 12 38 12 01 ka our ages imply that following glacier retreat beginning about 18 52 17 17 ka cirque glaciers first advanced during the antarctic cold reversal 14 5 12 9 ka and may have later advanced or stabilized in the younger dryas chronozone 12 9 11 7 ka based on the distribution of thick geochemically distinct and well dated hudson tephra no holocene moraines appear to be older than 7 96 7 34 ka at some sites there is evidence for one or more advances of glaciers sometime between 7 96 7 34 ka and 5 29 5 05 ka to limits only tens of meters beyond little ice age maximum positions taken together the data 1 do not support the summer insolation hypothesis to explain holocene glacier fluctuations in southernmost patagonia 2 confirm paleobotanical evidence for a warm dry early holocene and 3 suggest that some glaciers in the region reached extents comparable to those of the little ice age shortly before 5 29 5 05 ka

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

holocene glacier fluctuations in the canadian cordillera alberta and british columbia abstract although the record of holocene glacier fluctuations in british columbia and alberta is still very fragmentary much recent progress has been made in their study dating of end moraines has been supplemented by studies of lateral moraine stratigraphy and dating of glacially overridden organic matter upstream of end moraines dates from sites close to contemporary glaciers indicate that ice had retreated to about its present limits before 10 ka bp prior to deposition of mazama tephra a minor pre hypsithermal readvance the crowfoot advance left deposits in the rockies and the interior of british columbia the earliest known neoglacial advances occurred 5 6 ka bp in the coast mountains and shortly after 4 ka bp in the rockies an advance culminating ca 4 3 ka bp has been reported from bugaboo glacier while evidence of another advance culminating in the period ca 2 5 1 8 ka bp the tiedemann advance is reported from more than one site following a recession the little ice age expansion the cavell advance began shortly after 900 bp this advance culminated in most cases in the 18th or 19th centuries the crowfoot tiedemann and little ice age advances were apparently of roughly the same magnitude the latter was most extensive in most cases but at several sites crowfoot moraines lie slightly farther downvalley than little ice age moraines during the present century ice fronts have generally retreated particularly rapidly in the period 1920 1950 a d although rates of retreat have decreased in the last three decades and some glaciers have readvanced slightly

modeling past and future alpine permafrost distribution in the colorado front range rock glaciers a feature associated with at least discontinuous permafrost provide important topoclimatic information active and inactive rock glaciers can be used to model current permafrost distribution relict rock glacier locations provide paleoclimatic information to infer past conditions future warmer climates could cause permafrost zones to shrink and initiate slope instability hazards such as debris flows or rockslides thus modeling change remains imperative this research examines potential past and future permafrost distribution in the colorado front range by calibrating an existing permafrost model using a standard adiabatic rate for mountains 0 5 c per 100 m for a 4 c range of cooler and warmer temperatures according to the model permafrost currently covers about 12 per cent 326 1 km2 of the entire study area 2721 5 km2 in a 4 c cooler climate 73 7 per cent 2004 4 km2 of the study area could be covered by permafrost whereas in a 4 c warmer climate almost no permafrost would be found permafrost would be reduced severely by 93 9 per cent a loss of 306 2 km2 in a 2 0 c warmer climate however permafrost will likely respond slowly to change relict rock glacier distribution indicates that mean annual air temperature maat was once at least some 3 0 to 4 0 c cooler during the pleistocene with permafrost extending some 600 700 m lower than today the model is effective at identifying temperature sensitive areas for future monitoring however other feedback mechanisms such as precipitation are neglected copyright 2005 john wiley sons ltd

sensitivity of late glacial and holocene climates to the combined effects of orbital parameter changes and lower boundary condition changes snapshot simulations with a general circulation model for 18 9 and 6 ka bp

holocene glacier fluctuations in the american cordillera abstract in many areas of the american rocky mountains colorado wyoming utah idaho montana cascade range washington oregon and the sierra nevada california radiocarbon ages suggest that ice receded to near present limits before 10 ka bp a pre altithermal readvance or stillstand left moraines ca 1 3 km beyond and ca 50 300 m below present glacier margins at one locality on glacier peak in washington these deposits are perhaps dated to the early holocene but in general these deposits are probably at least 10 ka old glacial advances during the altithermal ca 8 to 5 ka bp elsewhere are rare radiocarbon evidence for altithermal glacial advances in the colorado front range is questionable the earliest radiocarbon dated neoglacial advances occurred about 5 ka bp in the washington cascades moraines and related deposits believed to be of early neoglacial age i e 5 to 3 ka bp elsewhere are poorly dated for example moraines believed to date to the early neoglacial in colorado triple lakes and wyoming temple lake are actually late pleistocene age based on radiocarbon ages derived from lake sediments at the type localities although relative age data i e lichens rock weathering soils from many areas suggest a three fold neoglacial sequence little supporting radiocarbon evidence is available however tephrochronology distinguishes three neoglacial advances near mount rainier in washington in most mountain ranges of the western united states fresh unweathered sharp crested moraines usually adjacent to present ice margins or near headwalls in empty cirques date to the little ice age of the last several centuries however detailed photographic or other historical records of glacial fluctuations during the last century are rare and detailed mass balance studies rarer still whether or not pre little ice age glacial fluctuations in the american cordillera are synchronous must await better radiometric dating of local moraine sequences

varve studies at hector lake alberta canada and the relationship between glacial activity and sedimentation glacial lake sedimentary records from hector lake in banff national park alberta are examined with the aim of clarifying the relationship between glacial activity and outwash sedimentation rhythmic couplets in lake bottom sediments provide a method for accurate documentation and dating of recent sedimentation chronology as analysis of 137cs content indicates that the couplets are of annual periodicity i e varves a comparison of sedimentation rate records with recent regional glacial history indicates that high sedimentation rates of one to a few decades duration occur either during and immediately following periods of moraine deposition ie maximum ice stands or during periods of rapid ice recession comparison of sedimentary records with somewhat longer term glacial and vegetation records indicates that sedimentation rate variations of several centuries duration closely parallel changes in upvalley ice extent over this time scale high sedimentation rates occur during periods of relatively increased ice extent low rates during periods of reduced ice extent within this general pattern however sedimentation rates may remain very high for nearly a century following maximum ice stands due to the exposure of unstable glaciogenic deposits to fluvial reworking during ice recession

early holocene glacier advance in the north cascade range washington moraines and glacial drift of the white chuck advance were deposited in early holocene time in cirques near glacier peak washington these sediments overlie glacier peak tephra including layers g n f c m t and b which were erupted between about 12 500 and 11 250 yr b p white chuck drift is overlain by mazama tephra layer o deposited about 6 700 yr b p charcoal collected from till deposited during the white chuck advance is about 8 300 to 8 400 radiocarbon years old indicating that the glacial advance that deposited the till occurred about this time and that a previously unrecognized period of cooling and or increased precipitation of sufficient intensity to produce glacial advances comparable to or greater than those of the recent little ice age occurred in early holocene time in the north cascade range other pre altithermal moraines from the cascades the rocky mountains laurentide canada and baffin island may have been produced during this cool period

thermochronologic data from tobago west indies constraints on the cooling and accretion history of mesozoic oceanic arc rocks in the southern caribbean fission track thermochronologic studies on mid cretaceous dioritic and tonalitic rocks from tobago west indies provide important temporal constraints on post magmatic mesozoic cooling as well as the final phase of accretion of these oceanic arc plutonic rocks onto the continental margin of northern south america zircon fission track data indicate that the plutonic rocks of tobago cooled through the zircon closure isotherm 250 200 c at about 103 ma apatite ages and track length analysis suggest rapid cooling through the apatite annealing zone 120 60 c at about 45 ma furthermore the track lengths in apatites from these plutonic rocks are all greater than 14 microns which implies that these rocks have not been above 50 c since 45 ma if a geothermal gradient of 25 c km is inferred the analyzed samples have been at depths of less than 2 km since 45 ma tobago has occupied an upper crustal structural position since the mid cretaceous and significant final uplift of these mesozoic oceanic arc rocks occurred in the mid eocene the tectonothermal history of tobago since the mid eocene has not involved deep burial or a high temperature thermal flux this history apparently has chiefly involved translation of the tobago terrane along the caribbean south america plate boundary zone at upper crustal levels

evidence for cirque glaciation in the colorado front range during the younger dryas chronozone abstract late pleistocene glacial chronologies developed for the front range mountains of colorado include two or more cirque glacier advances locally known as the satanta peak advances sediment cores were recovered from sky pond an alpine lake 3320 m located less than 100 m downvalley from a moraine that exhibits late pleistocene to early holocene relative age features and appears to correlate to the satanta peak deposits one of the cores penetrated 0 5 m of basal diamict and recovered 3 3 m of overlying sediments that are predominantly gyttja an accelerator mass spectrometry ams age of 12 040 60 yr14c b p was obtained from directly above the basal diamict and is similar to other reported ages for cirque deglaciation in the front range mountains the lower portion of the gyttja contains an interval of clastic sediments that show characteristics consistent with glacial activity in alpine catchments radiocarbon ages obtained from below and near the upper contact of this clastic interval are 11 070 50 and 9970 8014c yr b p respectively an additional ams age of 10 410 9014c yr b p was obtained from within the clastic interval in a second core the most likely source for this interval of clastic sediments is a moraine situated directly upvalley from sky pond and consequently it appears that the deposition of this moraine was coeval with the european younger dryas event 11 000 10 00014c yr b p similarities in soil development weathering features and altitude between this moraine and the type satanta peak moraines suggest that the moraines are correlative these findings are in agreement with a growing body of evidence that suggests a relatively minor advance of alpine glaciers occurred in the north american rockies during the younger dryas chron

a late pleistocene to holocene record of precipitation reflected in margaritifera falcata shell δ18o from three archaeological sites in the lower salmon river canyon idaho oxygen 18 18o concentrations in margaritifera falcata shells preserved in three archaeological sites in the lower salmon river canyon of idaho are compared with modern mussel shells shell 18o records show that late pleistocene and early holocene climates were drier with occasional periods of increased precipitation after c 4000 years bp precipitation is higher in the salmon river basin than at present and trends toward modern conditions after c 1800 years bp the climatic conditions reflected by fluctuations in shell 18o are matched by regional palaeoenvironmental records including pollen glacial and palaeohydraulic proxy sources and are compared with major changes in plateau prehistoric cultural patterns studies of late quaternary records of freshwater bivalve shell 18o are useful for reconstructing climatic conditions and complement geoarchaeological studies in riparian contexts

differential response of vegetation to postglacial climate in the lower salmon river canyon idaho late pleistocene to holocene terrestrial climate and vegetation records in the lower salmon river canyon of idaho are interpreted from the stable isotopic composition of soil carbonates and from aeolian sedimentation frequencies carbonate and sediment samples from six sections were processed and analyzed with the resulting isotopic and grainsize data organized in relation to a normalized time series developed from an associated radiocarbon chronology this record is interpreted in regards to changes in aridity temperature and wind speed during the late quaternary and is further compared with regional paleoenvironmental records lowered n 18 o and n 13 c concentrations before 20 000 yr bp are interpreted as reflecting late wisconsinan cold conditions after 18 000 yr bp climatic conditions show warmer periods punctuated by sharp returns to colder temperatures and increased c3 flora by 12 000 yr bp higher resolution data show very unstable climatic conditions across the pleistocene holocene boundary reflected in wide variations in n 18 o and n 13 c and aeolian sand deposition during the period between 12 000 and 9000 yr bp the lower salmon river canyon is thought to have experienced marked seasonality with summers and winters respectively warmer and colder than today this climatic scenario was accompanied by an initial instability in canyon vegetation following the establishment of a low energy floodplain in the canyon after 10 000 yr bp a pattern of c3 dominant riparian flora appears during the middle holocene climatic and vegetative variability is much reduced from the preceding period after 4000 yr bp soil carbonate isotopes reflect a trend toward cooler climate conditions and more mesic vegetation populations 2002 elsevier science b v all rights reserved

probability of moraine survival in a succession of glacial advances emplacement of glacial moraines normally results in obliteration of any older moraines deposited by less extensive glacial advances a process we call obliterative overlap a probability analysis of the likely impact of obliterative overlap on the completeness of the glacial record assumes that moraines were deposited at various distances from their glacial source areas randomly over time assuming randomness and obliterative overlap after 10 glacial episodes the most likely number of surviving moraines is only three the record of the pleistocene is in agreement with the probability analysis the 10 glaciations during the past 0 9 m y inferred from the deep sea record resulted in moraine sequences in which only two or three different aged moraine belts can generally be distinguished

holocene and latest pleistocene glacial chronology glacier national park montana moraines of two different age groups have been identified fronting the present day glaciers and snowfields in glacier national park montana the subdued vegetated moraines of the older group have been found at 25 sites mainly in the central part of the lewis range these older moraines are in places overlain by the mazama ash although the exact age of the moraines has not been determined by radiocarbon dating vegetative evidence and correlation with other pre altithermal age moraines in the rocky mountains suggest that these older moraines date from 10 000 bp or earlier whether these moraines are the product of a separate advance after the end of the wisconsin glaciation or are simply the product of the last advance or stillstand of wisconsin glaciers before final deglaciation is not known moraines of the younger group consisting of fresh bouldery rubble are common throughout glacier park tree ring analyses indicate that some of these younger moraines were deposited by advances that culminated du

strontium 87 strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine subalpine watershed loch vale colorado sr isotopic ratios of atmospheric deposition surface and subsurface water and geologic materials were measured in an alpine subalpine watershed to characterize weathering reactions and identify sources of dissolved ca in stream water previous studies have noted an excess of ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals mixing calculations based on 87 sr 86 sr indicate that on an annual basis 26 67 of ca export in streams is atmospherically derived 23 61 is from weathering of plagioclase and the remainder is from weathering of calcite present in trace amounts in the bedrock a potential source of error when applying sr isotopes in catchment studies is determination of the 87 sr 86 sr of sr released by mineral weathering which is complicated by the wide range of mineral isotopic compositions particularly in older rocks and the variable rates at which the minerals weather in this study base flow stream chemistry was used to represent the 87 sr 86 sr of sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of sr released by weathering in the alpine environment

suggested terminology for quaternary dating methods abstract classification of quaternary dating methods should be based on the level of quantitative information and the degree of confidence contained in the age estimates produced by the dating methods we recommend the use of the terms numerical age calibrated age relative age and correlated age to describe these levels we also classify dating methods by type into sideral isotopic radiogenic chemical and biological geomorphic and correlation methods the use of absolute is inappropriate for most dating methods and should be replaced by numerical the use of date should be minimized in favor of age or age estimate we recommend use of the abbreviations ka and ma for most ages calender dates can be used where appropriate and yr b p can be used for radiocarbon ages

deglaciation and postglacial timberline in the san juan mountains colorado abstract lake emma which no longer exists because of a mining accident was a tarn in a south facing cirque near the headwaters of the animas river in the san juan mountains of southwestern colorado during the pinedale glaciation this area was covered by a large transection glacier centered over the lake emma region three radiocarbon dates on basal organic sediment from lake emma indicate that by ca 15 000 yr b p this glacier one of the largest in the southern rocky mountains no longer existed twenty two radiocarbon dates on picea and abies krummholz fragments in the lake emma deposits indicate that from ca 9600 to 7800 yr b p from 6700 to 5600 yr b p and at 3100 yr b p the krummholz limit was at least 70 m higher than present these data in conjunction with picea pinus pollen ratios from both the lake emma site and the hurricane basin site of j t andrews p e carrara f b king and r struckenrath 1975 quaternary research 5 173 197 suggest than from ca 9600 to 3000 yr b p timberline in the san juan mountains was higher than present cooling apparently began ca 3000 yr b p as indicated by decreases in both the percentage of picea pollen and picea pinus pollen ratios at the hurricane basin site andrews et al 1975 cooling is also suggested by the lack of picea or abies fragments younger than 3000 yr b p at either the lake emma or the hurricane basin site

deglaciation and postglacial environmental changes in the teton mountain range recorded at jenny lake grand teton national park wy abstract sediments contained in lake basins positioned along the eastern front of the teton mountain range preserve a continuous and datable record of deglaciation and postglacial environmental conditions here we develop a multiproxy glacier and paleoenvironmental record using a combination of seismic reflection data and multiple sediment cores recovered from jenny lake and other nearby lakes age control of teton lake sediments is established primarily through radiocarbon dating and supported by the presence of two prominent rhyolitic tephra deposits that are geochemically correlated to the widespread mazama 7 6 ka and glacier peak 13 6 ka tephra layers multiple glacier and climate indicators including sediment accumulation rate bulk density clastic sediment concentration and flux organic matter concentration flux 13c 15n and c n ratios and biogenic silica track changes in environmental conditions and landscape development sediment accumulation at jenny lake began centuries prior to 13 8 ka and cores from three lakes demonstrate that teton glacier extents were greatly reduced by this time persistent ice retreat in cascade canyon was slowed by an interval of small glacier activity between 13 5 and 11 5 ka prior to the end of glacial lacustrine sedimentation 11 5 ka the transition to non glacial sediments marks the onset of holocene conditions at jenny lake and reflects a shift toward warmer summers increased vegetation cover and landscape stability in the tetons we discuss the teton lake sediment records within the context of other regional studies in an effort to construct a comprehensive overview of deglaciation and postglacial environmental conditions at grand teton national park

glacial stratigraphy of stough creek basin wind river range wyoming abstract multiparameter relative age ra techniques identify four post pinedale morphostratigraphic units in each of three cirque valleys tributary to stough creek basin wind river range wy soil development lichenometry boulder weathering characteristics and the geomorphic relations among morphostratigraphic units indicate glacial deposits here correspond to the sequence previously described in the temple lake valley arct alp res 6 1974 301 cirque deposits in stough creek basin correspond to the temple lake alice lake black joe and gannett peak alloformations gsa abs prog 32 2000 a 16 10 be ages from moraine boulders and polished striated bedrock assoc am geogr annu mtg abs 2000 155 support recent numeric age estimates from temple lake and titcomb basin that indicate the temple lake alloformation corresponds to the younger dryas climate episode geogr phys quat 41 1987 397 geology 23 1995 877 science 268 1995 1329 gsa abs prog 31 1999 a 56 soils described from pinedale recessional deposits here represent the first systematic description of pinedale alpine deposits in the wrr

response of extreme floods in the southwestern united states to climatic variations in the late holocene a regional synthesis of paleoflood chronologies on rivers in arizona and southern utah reveals that the largest floods over the last 5000 years cluster into distinct time periods that are related to regional and global climatic fluctuations the flood chronologies were constructed using fine grained slackwater deposits that accumulate in protected areas along the margins of bedrock canyons and selectively preserve evidence of the largest events high magnitude floods were frequent on rivers throughout the region from 5000 to 360014c yrs bp dendrocalibrated age 3800 2200 bc and increased again after 2200 bp 400 bc with particularly prominent peaks in magnitude and frequency around 1100 900 bp ad 900 1100 and after 500 yrs bp ad 1400 in contrast the periods 3600 2200 bp 2200 400 bc and 800 600 yrs bp 1200 1400 ad are marked by sharp decreases in the occurrence of large floods on these rivers in the modern record storms that generate large floods 10 year in the region fall into three categories 1 winter north pacific frontal storms 2 late summer and fall storms that draw in moisture from recurved pacific tropical cyclones and 3 summer storms mainly convective thunderstorms winter storms and tropical cyclones are associated with the most severe floods on the rivers in this study and are the most probable causes of the paleofloods over the last 5000 years floods from both winter storms and tropical cyclones occur when deep mid latitude troughs steer storm systems into the region composite anomaly maps of daily 700 mbar heights indicate that these floods are associated with a low pressure anomaly off the california coast and a high pressure anomaly over the aleutians or gulf of alaska a strong connection exists between the negative phase of the southern oscillation index often associated with el nin o conditions and the large floods associated with winter storms and tropical cyclones the paleoflood records confirm the existence of centennial scale variations in the conditions conducive to the occurrence of extreme floods and flood generating storms in this region the episodes with an increased frequency of high magnitude floods coincide with periods of cool wet climate in the western u s whereas warm intervals such as the medieval warm period are times of dramatic decreases in the number of large floods a positive relationship between the paleofloods and long term variations in the frequency of el nin o events is evident over the last 1000 years this relationship continues over at least the last 3000 years with warm coastal sea surface temperatures indicative of el nin o like conditions

summary of pre 1980 tephra fall deposits erupted from mount st helens washington state usa mount st helens has been a prolific source of tephra fall deposits for about 40 000 years these tephra deposits 1 record numerous explosive eruptions 2 form important regional time stratigraphic marker beds and 3 record repeated changes in composition within and between eruptive periods

glacier contraction during the middle holocene in the western italian alps evidence and implications radiocarbon dates of peat from the top and base of a bog exposed by recent retreat of rutor glacier show that the glacier front terminated upvalley from the bog from 8400 until at least 6000 b p the evidence is consistent with botanical data that point to a high tree line during the interval and to reconstructed mean july temperatures at least 4 c warmer than present temperatures if the mass balance history of the glacier is typical of other glaciers in this region it is likely that average equilibrium line altitudes during the interval of contraction remained above those of the present and well above those of subsequent neoglacial ice advances

early holocene glaciation on mount baker washington state usa abstract the relation between radiocarbon dated tephras and glacial moraines on the south flank of mount baker washington records evidence of an early holocene glacier advance scoria that erupted from a local cinder cone 8420 70 14 c yr bp 9450 100 cal yr occurs immediately in front of but not on a complex of moraines overlain by mazama ash radiocarbon ages of 7670 130 14 c yr bp 8415 110 cal yr and 7045 65 14 c yr bp 7890 90 cal yr were obtained from charred wood below the mazama ash and above till of the moraines bracketing the age of the glacial advance between 7700 and 8400 14 c yr bp 8400 and 9450 cal yr well preserved little ice age moraines occur proximal to the maximum holocene positions assuming that precipitation regimes were similar depression of former equilibrium line altitudes suggests that climate during the early holocene event was at most 2 c cooler than present and 0 5 c cooler than the little ice age

use of lacustrine sedimentary sequences as indicators of holocene glacial history banff national park alberta canada abstract bottom sediments from three lakes in the canadian rocky mountains were examined with the aim of evaluating the usefulness of downvalley sediment studies in reconstruction of holocene glacial histories analyses of organic carbon and carbonate contents of core sediments provide information on changing sedimentation rate and changing relative importance of glacial and non glacial sediment sources sedimentary histories of the three lakes are similar suggesting that they record regional glacial climatic forcing rather than localized events and thus that they may be useful in reconstructing holocene glacial history lacustrine sediments indicate a period of high sedimentation rates and relatively large glacial sediment contribution prior to 7500 7000 yr b p with much reduced rates and decreased glacial sediment contribution between about 6000 and 4000 yr b p possibly interrupted by a brief period of increased glacial sediment output shortly after 5000 yr b p sometime after 4000 yr b p sedimentation rates and glacial sediment output began to rise again reaching approximately present levels by 2750 2650 yr b p and have not since returned to low mid holocene levels in detail over the last 3000 yr there is some indication of a slight decrease in sedimentation rate for more than 1000 yr after about 2200 yr b p sedimentation rates and glacial sediment input into all three lakes rose between about 900 and 750 yr b p and have remained very high since if the lake sediments are interpreted as a proxy record of upvalley glacial activity they allow the development of a glacial chronology which is at once generally consistent with and more complete and easily datable than the surficial glacial record

holocene alluvial stratigraphy and response to climate change in the roaring river valley front range colorado usa abstract stratigraphic analyses and radiocarbon geochronology of alluvial deposits exposed along the roaring river colorado lead to three principal conclusions 1 the opinion that stream channels in the higher parts of the front range are relics of the pleistocene and nonalluvial under the present climate as argued in a water rights trial usa v colorado is untenable 2 beds of clast supported gravel alternate in vertical succession with beds of fine grained sediment sand mud and peat in response to centennial scale changes in snowmelt driven peak discharges and 3 alluvial strata provide information about holocene climate history that complements the history provided by cirque moraines periglacial deposits and paleontological data most alluvial strata are of late holocene age and record among other things that 1 the largest peak flows since the end of the pleistocene occurred during the late holocene 2 the occurrence of a mid to late holocene interval 2450 1630 cal yr bp of warmer climate which is not clearly identified in palynological records and 3 the little ice age climate seems to have had little impact on stream channels except perhaps for minor 1 m incision

what were the primary forcing mechanisms of high frequency holocene climate and glacier variations a compilation of holocene glacial advances throughout the world is compared with summer solar insolation integrated over the northern hemisphere and the magnitudes of global acid fallout from volcanic eruptions north of 20 s estimated from the acidity signal of annual ice layers in the crete and camp century ice cores in greenland correlation analysis between glacial advances versus volcanic eruptions yielded a correlation coefficient of r 0 71 a climatic forcing curve solar insolation and volcanic eruptions weighted 1 1 versus glacial advances increased the correlation coefficient to r 0 90 this suggests that the combined effect of volcanic aerosols and orbital related northern hemisphere summer insolation may have been the primary forcing mechanism of worldwide climate and glacier fluctuations throughout the holocene

early holocene glacier advance southern coast mountains british columbia canada abstract terrestrial and lake sediment records from several sites in the southern coast mountains british columbia provide evidence for an advance of alpine glaciers during the early holocene silty intervals within organic sediments recovered from two proglacial lakes are bracketed by ams 14 c dated terrestrial macrofossils and mazama tephra to 8780 6730 and 7940 6730 14 c yr bp 10 150 7510 and 8990 7510 cal yr bp radiocarbon ages ranging from 7720 to 7380 14 c yr bp 8630 8020 cal yr bp were obtained from detrital wood in recently deglaciated forefields of sphinx and sentinel glaciers these data together with previously published data from proglacial lakes in the canadian rockies imply that glaciers in western canada advanced during the early holocene the advance coincides with the well documented 8200 yr cold event identified in climate proxy data sets in the north atlantic region and elsewhere

fire and alluvial chronology in yellowstone national park climatic and intrinsic controls on holocene geomorphic processes we employed a systemwide approach a large and robust set of radiocarbon ages and modern process analogs to interpret the holocene history of forest fire related sedimentation and overall alluvial activity in northeastern yellowstone national park debris flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire related sedimentation within valley side alluvial fans of soda butte creek fire related deposits make up approximately 30 of the late holocene fan alluvium fifty 14 c ages on fire related events cluster within the intervals of 3300 2900 2600 2400 2200 1800 and 1400 800 yr b p and suggest earlier episodes of large fires and fan aggradation around 7500 5500 and 4600 4000 yr b p a major pulse of fire related debris flow activity between 950 and 800 yr b p coincided with the height of the widely recognized medieval warm period ca a d 1050 1200 instrumental climate records over the last 100 yr in yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods enhancing the potential for severe short term drought major forest fires and storm generated fan deposition along lower soda butte creek fill cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca 8000 yr b p terrace level t1a 7000 5600 t1b 3100 2600 t2 2000 1300 t3 and post 800 yr b p t4 these periods coincide with overbank sedimentation on slough creek and the lamar river but alternate with intervals of fire related fan deposition implying a strong climatic control local paleoclimatic data suggest cooler effectively wetter conditions during terrace tread formation in warmer drier intervals reduced average runoff in axial streams results in meander belt narrowing concurrent channel incision may be caused by infrequent large floods greater resistance to downcutting however allowed fewer terraces to be formed along slough creek and the lamar river alluvial systems in northeastern yellowstone show a clear response to millennial scale climatic cycles wherein alluvial fans aggrade and prograde over flood plains in drier periods axial streams widen their flood plains and trim back the fans during wetter periods small scale climatic fluctuations of the holocene thus had substantial impact on postglacial landscapes in northeastern yellowstone

a 750 year fire history based on lake sediment records in central yellowstone national park usa a 750 year fire history was reconstructed for the central plateau of yellowstone national park from the deep water sediments of five lakes the charcoal record from a large lake provided a chronology of regional fires data from four small lakes were used to study local and extralocal fires the co occurrence of abundant charcoal and high magnetic susceptibility values at the same stratigraphic level was used as evidence of a local catchment fire and a charcoal peak without high magnetic susceptibility was ascribed to an extralocal fire or a local fire without a related erosion event the fire history was compared with the dendrochronologic fire record for the last 450 years and the close agreement provided the justification to extend the chronology back in time large areas of the region burned in ad 1988 c 1700 c 1560 and c 1440 from c 1220 to 1440 and c 1700 to 1987 intermediate to small areas burned the near absence of fires in the twentieth century prior to the large fires of 1988 is evi

tree ring based streamfiow reconstruction for ashley creek northeastern utah implications for palaeohydrology of the southern uinta mountains two ring width chronologies from douglas fir pseudotsuga menzeisii and one from pinyon pine pinus edulis were used to reconstruct mean annual discharge of ashley creek in the uinta mountains utah for the years ad 1637 1970 a backward elimination multiple linear regression model identified six statistically significant variables including annual lags ranging from 1t o 2 years the final model explains 71 of variability r 2 adjusted for degrees of freedom lost when regressed against the annual discharges recorded for 1915 72 statistical analysis of the model reconstruction using the reduction of error statistic the durbin watson statistic and the hypergeometric distri bution all indicate fidelity of the model for reconstructing discharge the lilliefors test indicates that years of extreme discharge greater than the 90th percentile or less than the 10th percentile are non randomly distributed between 1637 and 1970 persistent years of above median discharge as well as non random clustering of years above the 90th percentile occurred from 1692 1704 and 1898 1945 analysis of the modern gauge data set shows that mean annual discharge on ashley creek explains between 81 and 91 of the variations of mean annual discharge on the other main stream in the southern uinta mountains indicating that reconstructed mean annual discharge on ashley creek is representative of palaeohydrologic conditions across the south flank of the range these data suggest that the southern uinta mountains experienced persistent below median discharge for 1741 1897 through the peak of the little ice age as identified in numerous surrounding mountain ranges in the central rockies this interpretation agrees with lichenometric evidence for extremely limited little ice age glacial activity in the uintas indicating that the range experienced unusually warm dry conditions at this time

lateral moraine stratigraphy and neoglacial history of bugaboo glacier british columbia abstract most studies of alpine glacial history have concentrated on terminal moraines but such moraines provide dates only for maximum extents of glaciers some lateral moraines have the potential for providing more complete glacial histories because deposition by distal flank accretion may result in sequences of stacked tills interpretation is aided by 1 the approximation that any continuous surface within the moraine parallel to the moraine s distal flank is isochronous 2 inset gulley fill deposits which provide information on ice margin history and 3 incorporated organic material which can be radiocarbon dated lateral moraine stratigraphy of bugaboo glacier in southeastern british columbia suggests that the glacier was fairly close to its maximum neoglacial extent about 2500 14c yr b p a slow general expansion punctuated by at least one minor retreat continued from that time and culminated probably in the last century