holocene coastal glaciation of alaska holocene uctuations of the three cirque glaciers on the seward peninsula and ve groups of tidewater and land terminating glaciers along the northernmost gulf of alaska provide a proxy record of late holocene climatic change furthermore the movements of the coastal glaciers were relevant to late holocene native american migration the earliest expansion was recorded about 6850 yr bp by hubbard glacier at the head of yakutat bay in the gulf of alaska however its down fjord advance to the bay mouth was delayed until 2700 bp similarly expansions of the icy bay bering and mccarty glaciers occurred near their present termini by 3600 3000 bp compatible with marked cooling and precipitation increases suggested by the alaskan pollen record decrease in glacier activity 2000 bp was succeeded by advances of gulf coastal glaciers between 1500 and 1300 bp correlative with early medieval expansions across the northern hemisphere a medieval optimum encompassing at least a few centuries prior to ad 1200 is recognized by general retreat of land terminating glaciers but not of all tidewater glaciers little ice age advances of land based glaciers many dated with the precision of tree ring cross dating were centered on the middle 13th or early 15th centuries the middle 17th and the last half of the 19th century a d strong synchrony of these events across coastal alaska is evident 2000 elsevier science ltd all rights reserved

late pleistocene and holocene paleoenvironments of the north pacific coast abstract unlike the north atlantic the north pacific ocean probably remained free of sea ice during the last glacial maximum lgm 22 000 to 17 000 bp following a eustatic low in sea level of ca 120 m at 19 000 bp a marine transgression had flooded the bering and chukchi shelves by 10 000 bp post glacial sea level history varied widely in other parts of the north pacific coastline according to the magnitude and timing of local tectonism and glacio isostatic rebound glaciers covered much of the continental shelf between the alaska peninsula and british columbia during the lgm maximum glacier extent during the lgm was out of phase between southern alaska and southern british columbia with northern glaciers reaching their outer limits earlier between 23 000 and 16 000 bp compared to 15 000 14 000 bp in the south glacier retreat was also time transgressive with glaciers retreating from the continental shelf of southern alaska before 16 000 bp but not until 14 000 13 000 bp in southwestern british columbia major climatic transitions occurred in the north pacific at 24 000 22 000 15 000 13 000 and 11 000 9000 bp rapid climate changes occurred within these intervals including a possible younger dryas episode an interval of climate warmer and drier than today occurred in the early holocene cooler and wetter conditions accompanied widespread neoglaciation beginning in some mountain ranges as early as the middle holocene but reaching full development after 3000 bp

tide gauge records of uplift along the northern pacific north american plate boundary 1937 to 2001 1 vertical crustal motions at 15 sites along the northern pacific north america plate boundary are determined using relative sea level changes from tide gauge records our analysis is based on monthly mean sea levels from which barometric pressure and seasonal effects are removed the records are corrected for common mode oceanographic variations these records are statistically examined for non linear behavior related to glacial isostatic tectonic and postseismic effects to estimate land uplift rates the local effect of global sea level rise is removed from the relative sea level rates slow rates of vertical motion are observed along the southern strike slip plate boundary the extremely rapid uplift of the northern strike slip boundary can be attributed entirely to viscoelastic postglacial rebound associated with tidewater glacier retreat in glacier bay and regional post little ice age deglaciation isostatic modeling indicates a mantle viscosity of 2 1019 5 1019 pa s similar to that found elsewhere along the pacific north america plate margin at yakutat near the transition of plate motion from strike slip to subduction complex non linear behavior is evident with a significant change in uplift rate following the 1979 st elias earthquake non linear uplift rates are predominant within the 1964 great alaskan earthquake near field rapid uplift at kodiak during a 3 5 year period starting mid 1964 totaled 47 8 cm anchorage seward and seldovia exhibited oscillatory uplift in the period immediately following the earthquake until mid 1972 since mid 1972 uplift rates have increased steadily at anchorage seward cordova and valdez during this period nikiski and kodiak show decreasing uplift rates

late holocene high resolution glacial chronologies and climate kenai mountains alaska recent retreat of outlet glaciers from the harding and grewingk yalik icefields has revealed a vast array of deposits on the eastern and western flanks of the kenai mountains that records multiple glacier advances into coastal forests during late holocene time treering dating together with radiocarbon and lichenometric analyses allows for the reconstruction of these glacial fluctuations to decadal precision over the past two thousand years the records of fluctuations are derived from 16 land terminating and seven tidewater glaciers in three fjord systems as well as two cirque glaciers three major intervals of holocene glacier expansions are evident they occurred about 3600 yr b p 600 a d and during the little ice age from 1300 to 1850 a d the earliest expansion beyond present ice margins is known only from the mccarty tidewater glacier the 600 a d event involved the simultaneous advance of land terminating and tidewater glaciers during the little ice age however tidewater glaciers were advancing several centuries prior to their land terminating neighbors those land terminating glaciers on the western mountain flank retreated from their little ice age maxima as much as two centuries before those on the eastern mountain flank land terminating tongues on the eastern more maritime mountain flank have shown more sensitivity to variations in winter precipitation during the little ice age and within recent decades than the more continental glaciers on the western flank that are affected more by summer temperatures the glacial and climatic records suggest that advances of the ice tongues from about 1420 to 1460 a d between 1640 and 1670 a d at about 1750 a d and from 1880 to 1910 a d reflected times of increased winter precipitation advances between 1440 to 1460 a d from 1650 to 1710 a d and from 1830 to 1860 a d followed intervals of lower summer temperatures

stratigraphic evidence for multiple holocene advances of lillooet glacier southern coast mountains british columbia holocene lateral moraines in the coast mountains of british columbia are commonly composed of multiple drift units related to several glacier advances in this paper we document lateral moraine stratigraphy at lillooet glacier in the southern coast mountains five tills separated by laterally extensive paleosols and layers of large woody debris were found in three cross sectional exposures through the northeast lateral moraine and two shallow gullies incised into its steep proximal face eighteen new radiocarbon ages constrain the timing of five separate advances of lillooet glacier 1 prior to 3000 14 c years bp 2 3000 14 c years bp 3 2500 14 c years bp 4 1700 to 1400 14 c years bp and 5 during the little ice age lia after 470 14 c years bp the lillooet glacier chronology is broadly synchronous with other glacier records from the coast mountains these records collectively demonstrate climate variability at higher frequencies during the late holocene than is apparent from many paleoecological reconstructions reconstructions of glacier fluctuations are often hampered by poor preservation of landforms that predate the extensive lia advances of the latest holocene our results highlight the potential of lateral moraine stratigraphy for reconstructing these earlier events

implications for measuring seasonality in the marine bivalve saxidomus gigantea abstract sclerochronological and sclerochemical analysis of shellfish remains from archaeological sites afford the opportunity to understand environmental change and its impacts on human populations through time during the late holocene in the gulf of alaska goa the paleoenvironmental record reflects fluctuating marine conditions throughout the region in the kodiak archipelago in the gulf of alaska changing environmental conditions population growth technological transitions and contact with other communities likely promoted the transition from needs based maritime hunting and gathering to surplus based semi permanent villages the precise role of climate in this transition is understudied few paleoclimate reconstructions are available for the kodiak archipelago and climate reconstructions for the goa are often insufficient for archaeological research because they lack sub annual resolution and cannot produce a detailed understanding of seasonal behaviors in human populations analysis of shellfish remains from archaeological sites in the archipelago may provide additional paleoenvironmental information for the gulf of alaska measuring and comparing the length of seasonal shell growth in select species of bivalves may complement stable oxygen isotope analysis together providing a more precise paleoclimate reconstruction this research utilizes the growth of saxidomus gigantea also known as s giganteus abundant both on modern and ancient coastlines to provide information about the length of its growing seasons to measure seasonality a total of 25 modern samples were collected from alaska and british columbia and the number of lunar daily growth increments ldgi was counted between annual winter growth bands confirmed by 18o maxima measured in sinusoidal time series clams collected from alaska grew a total of 143 34 days while british columbian clams grew 273 14 days 18o values and the number of ldgi per year were then compared to previous studies along the pacific northwest coast 18o values were more positive from annual winter growth bands from alaskan samples average value of 1 0 than british columbian samples average value of 0 2 maximum 18o values from winter growth generally increased with latitude r2 0 67 as did the number of ldgi per year r2 0 74 minimum 18o values did not appear to be significantly related to latitude r2 0 42 this method was then applied to three archaeological samples collected from the rice ridge site kod 363 the uyak site kod 145 and the settlement point site afg 105 from the kodiak archipelago alaska which grew an average of 166 22 days to confirm that these methods can be applied to archaeological samples through time to detect spatial and temporal changes in seasonality these results suggest that changes in sea surface conditions and seasonality are detectable both spatially and temporally through detailed sclerochronological and sclerochemical analysis of shellfish remains from archaeological sites and offer the potential to reconstruct marine environmental conditions throughout the holocene

dendrochronology and late holocene history of bering piedmont glacier alaska fluctuations of the piedmont lobe of bering glacier and its sublobe steller glacier over the past two millennia are reconstructed using 34 radiocarbon dates and tree ring data from 16 sites across the glaciers forelands the general sequence of glacial activity is consistent with well dated fluctuations of tidewater and land terminating glaciers elsewhere along the gulf of alaska extensive forested areas along 25 km of the bering ice margin were inundated by glacio lacustrine and glacio fluvial sediments during a probable ice advance shortly before 500 cal yr a d regrowth of forests followed the retreating ice as early as the 7th century a d with frequent interruptions of tree growth due to outwash aggradation forests overrun by ice and buried in outwash indicate readvance about 1080 cal yr a d retreat followed with ice free conditions maintained along the distal portions of the forefield until the early 17th century after which the ice advanced to within a few kilometers of its outer neoglacial moraine ice reached this position after the mid 17th century and prior to 200 yr ago since the early 20th century glacial retreat has been punctuated by periodic surges the record from forests overrun by the nonsurging steller lobe shows that this western ice margin was advancing by 1250 a d reaching near its outer moraine after 1420 cal yr a d since the late 19th century the lobe has dominantly retreated

geomorphic processes influence human settlement on two islands in the islands of four mountains alaska the islands of four mountains island group of the aleutian island arc is remote and difficult to access consequently little fieldwork has focused on geomorphic processes and their relationship to island morphology climatic change and human settlement we investigated glacial fluvial and slope processes on the morphologically different carlisle cleveland and tana volcanoes the islands were extensively glaciated at the last glacial maximum lgm and there is evidence for a neoglacial advance on the highly dissected tana volcano a large basin is likely the result of a pre lgm sector collapse and subsequent glacial erosion into weak hydrothermally altered rock valley and moraine morphology is also influenced by hydrothermal alteration on both tana and carlisle there are sediment fans composed dominantly of thick debris flow deposits mantled by 3 m of layered tephras fine grained alluvium and anthropogenic deposits debris flow deposition was favored during the unstable paraglacial landscape of the early holocene latest pleistocene the earliest direct archaeological evidence for settlement is 3 8 cal ka bp but soil geochemical evidence suggests that the islands were inhabited by 7 3 cal ka bp this discrepancy in the archaeological record may be explained by geomorphic processes including coastal erosion and unstable geomorphic surfaces

ultra rapid landscape response and sediment yield following glacier retreat icy bay southern alaska abstract glacial retreat and opening of taan fjord an arm of icy bay alaska in the last two decades drove a base level fall of 400 m at the outlets of four tributary valleys in the region of the current tyndall glacier terminus response in the tributary valleys to this base level fall includes evacuation of stored sediment incision of slot gorges into bedrock and landsliding on valley walls fluvial transfer of eroded bedrock glacial deposits and stored nonglacial fluvial deposits after 1983 resulted in progradation of fan deltas toward the fjord centerline at the outlet of each of the four catchments in the largest nonglacial tributary valley 0 08 km 3 8 of the 0 59 km 3 of 500 m thick stored fluvial and colluvial deposits has been transferred to the adjacent fjord a percentage of the fjord sedimentation in the last two decades thus includes material eroded from bedrock and stored in the landscape during the previous glacial expansions distal deltaic deposits extend across the fjord floor and likely interfinger with distal proglacial deltaic deposits sourced from the tyndall glacier a paraglacial landscape response such as the one exhibited in upper taan fjord where sediment delivery to fjords from tributary sources in synchrony with sediment produced by primary bedrock erosion by glaciers helps to explain the order of magnitude discrepancy between sediment yields from alaskan tidewater glaciers on 10 0 to 10 2 year timescales and sediment yields and exhumation rates on 10 4 to 10 6 year timescales

ice front variation and tidewater behavior on helheim and kangerdlugssuaq glaciers greenland we used satellite images to examine the calving behavior of helheim and kangerdlugssuaq glaciers greenland from 2001 to 2006 a period in which they retreated and sped up these data show that many large iceberg calving episodes coincided with teleseismically detected glacial earthquakes suggesting that calving related processes are the source of the seismicity for each of several events for which we have observations the ice front calved back to a large pre existing rift these rifts form where the ice has thinned to near flotation as the ice front retreats down the back side of a bathymetric high which agrees well with earlier theoretical predictions in addition to the recent retreat in a period of higher temperatures analysis of several images shows that helheim retreated in the 20th century during a warmer period and then re advanced during a subsequent cooler period this apparent sensitivity to warming suggests that higher temperatures may promote an initial retreat off a bathymetric high that is then sustained by tidewater dynamics as the ice front retreats into deeper water the cycle of frontal advance and retreat in less than a century indicates that tidewater glaciers in greenland can advance rapidly greenland s larger reservoir of inland ice and conditions that favor the formation of ice shelves likely contribute to the rapid rates of advance

a 1119 year tree ring width chronology from western prince william sound southern alaska living and subfossil trees from glacier forefields are used to develop a 1119 year long tree ringwidth chronology strong cross dating among ring width series from sites up to 60 km apart and an analysis of sample homogeneity support combination of all samples into a single regional composite chronology comparison with instrumental climate data indicates may through july temperatures of the growth year are the primary control on ring widths multidecadal length warm periods in western prince william sound during the past 800 years were centred on ad 1300 1440 and possibly 1820 multidecadal length cool periods were centred on ad 1400 1660 and 1870 this is the first tree ring chronology from the gulf of alaska region to extend into the first millennium ad

little ice age glacial activity in the mt waddington area british columbia coast mountains canada the establishment of fourteen little ice age lia glacier chronologies in the mt waddington area led to the development of an extended history of glacial activity in this portion of the southern british columbia coast mountains canada the glaciers were located within four different mountain ranges and were of varying size and aspect dendrochronological and lichenometric techniques were used to provide relative age estimates of moraines formed as glacier termini retreated from advanced positions evidence for pre lia glacial events is best preserved at tiedemann glacier where the oldest glacial advances date to a d 620 and 925 933 soil covered and well vegetated moraines built at cathedral pagoda and siva glaciers date to between a d 1203 and 1226 following this event moraines constructed at ragnarok siva and cathedral glaciers in the mid 14th century suggest glaciers in the region underwent a period of downwasting and retreat before readvancing the majority of moraines recorded in the mt waddington area describe late lia glacial events shown to have constructed moraines that date to a d 1443 1458 1506 1524 1562 1575 1597 1621 1657 1660 1767 1784 1821 1837 1871 1900 1915 1928 and 1942 1946 over the last 500 years these moraine building episodes were shown to occur on average every 65 years and suggest there has been prolonged synchronicity in the glaciological response to persistent climate forcing mechanisms nevertheless our analysis suggests that local factors such as aspect and size play an important role in individual glacial response notably ice termini of medium size glaciers facing eastwards showed a quicker response to climatically induced mass balance changes resume l historique de quatorze glaciers de vallee de la region du mont waddington sud de la chaine cotiere de colombie britannique canada durant le petit ge glaciaire pag fut evalue par l utilisation de techniques dendrochronologiques et lichenometriques procurant un ge minimum pour la formation des moraines laterales et frontales multiples les glaciers a l etude d aspect et de taille differents furent selectionnes a partir de quatre chaines de montagnes les evenements qui predatent le pag sont le mieux preserves sur le site du glacier tiedemann ou les plus vieilles avancees glaciaires date de a d 620 et 925 933 des moraines presentant une pedogenese avancee et recouvertes d une dense couverture vegetale furent datees entre a d 1203 et 1226 des moraines construites dans le milieu du 14 e siecle par les glaciers ragnarok siva et cathedral suggerent que les glaciers de la region se sont retires pour par la suite reavancer la majorite des moraines datees le furent vers la fin du pag soit en a d 1443 1458 1506 1524 1562 1575 1597 1621 1657 1660 1767 1784 1821 1837 1871 1900 1915 1928 et 1942 1946 au cours des 500 dernieres annees en moyenne 65 annees separent les differents episodes glaciaires ce qui suggerent un synchronisme des reponses glaciaires aux mecanismes climatiques des donnees preliminaires suggerent que l orientation et la taille des glaciers jouent un role important dans la reponse individualiste des glaciers en fait les terminus glaciaires des moyens glaciers d orientation est semblent repondre plus rapidement a un ajustement de volume interne glaciaire

holocene optimum events inferred from subglacial sediments at tschierva glacier eastern swiss alps abstract this study investigates the subglacial sedimentary archive at tschierva glacier eastern swiss alps subfossil wood remains found at the retreating glacier tongue indicate that their emergence results from recent transport from an upvalley basin a confluence basin like structure was found to exist by georadar measurements underneath the present glacier in combination with high resolution age determinations based on dendrochronology and radiocarbon dating it is implied that a retreated tschierva glacier allowed vegetation growth and sediment accumulation in that basin three periods of glacier recession were detected which occurred around 9200 cal yr bp from 7450 to 6650 cal yr bp and from 6200 to 5650 cal yr bp these periods are called holocene optimum events hoe accordingly an equilibrium line rise 220 m compared to the reference period from 1960 to 1985 was inferred from digital elevation models of former glacier extents since glacier mass balance depends on summer june july august temperature and precipitation an equilibrium line altitude ela rise of 220 m implies a summer temperature increase of about 1 8 c assuming unchanged precipitation during the dated hoe alternative calculations point to probable temperature increase in a broad interval between 1 0 c taking into account a precipitation change of 250 mm a to 2 5 c with 250 mm a precipitation change supporting earlier paleotemperature estimates it is proposed that higher mean summer insolation caused a stronger seasonality during the mid holocene as compared to late holocene conditions

pattern and forcing of northern hemisphere glacier variations during the last millennium time series depicting mountain glacier fluctuations in the alps display generally similar patterns over the last two centuries as do chronologies of glacier variations for the same interval from elsewhere in the northern hemisphere episodes of glacier advance consistently are associated with intervals of high average volcanic aerosol production as inferred from acidity variations in a greenland ice core advances occur whenever acidity levels rise sharply from background values to reach concentrations 1 2 equiv h kg above background a phase lag of about 10 15 yr equivalent to reported response lags of alpine glacier termini separates the beginning of acidity increases from the beginning of subsequent ice advances a similar relationship but based on limited and less reliable historical data and on lichenometric ages is found for the preceding 2 centuries calibrated radiocarbon dates related to advances of non calving and non surging glaciers during the earlier part of the little ice age display a comparable consistent pattern an interval of reduced acidity values between about 1090 and 1230 a d correlates with a time of inferred glacier contraction during the medieval optimum the observed close relation between noothern hemisphere glacier fluctuations and variations in greenland ice core acidity suggests that sulfur rich aerosols generated by volcanic eruptions are a primary forcing mechanism of glacier fluctuations and therefore of climate on a decadal scale the amount of surface cooling attributable to individual large eruptions or to episodes of eruptions is simlar to the probable average temperature reduction during culminations of little ice age alacier advances ca 0 5 1 2 c as inferred from depression of equilibrium line altitudes

a deglacial and holocene record of climate variability in south central alaska from stable oxygen isotopes and plant macrofossils in peat we used stable oxygen isotopes derived from bulk peat d 18 otom in conjunction with plant macrofossils and previously published carbon accumulation records in a w14 500 cal yr bp peat core ht fen from the kenai lowlands in south central alaska to reconstruct the climate history of the area we find that patterns are broadly consistent with those from lacustrine records across the region and agree with the interpretation that major shifts in d 18 otom values indicate changes in strength and position of the aleutian low al a semi permanent low pressure cell that delivers winter moisture to the region we find decreased strength or a more westerly position of the al relatively higher d 18 otom values during the bolling allerod holocene thermal maximum htm and late holocene which also correspond to warmer climate regimes these intervals coincide with greater peat preservation and enhanced carbon c accumulation rates at the ht fen and with peatland expansion across alaska the htm in particular may have experienced greater summer precipitation as a result of an enhanced pacific subtropical high a pattern consistent with modern d 18 o values for summer precipitation the combined warm summer temperatures and greater summer precipitation helped promote the observed rapid peat accumulation a strengthened al relatively lower d 18 otom values is most evident during the younger dryas neoglaciation and the little ice age consistent with lower peat preservation and c accumulation at the ht fen suggesting less precipitation reaches the leeward side of the kenai mountains during periods of enhanced al strength the peatlands on the kenai peninsula thrive when the al is weak and the contribution of summer precipitation is higher highlighting the importance of precipitation seasonality in promoting peat accumulation this study demonstrates that d 18 otom values in peat can be applied

late holocene vegetation and climate change at moraine bog tiedemann glacier southern coast mountains british columbia moraine bog lies just outside the outermost lateral moraine of tiedemann glacier in the southern coast mountains of british columbia a sediment core taken from the wetland was analyzed for pollen magnetic susceptibility and loss on ignition to reconstruct changes in vegetation and climate during the late holocene vegetation changed little between about 3500 and 2400 14 c years bp a period of local disturbance marked by deposition of a silty clay bed and increases in alnus pollen likely reflecting cooler moister conditions coincides with an extensive holocene advance of tiedemann glacier about 2400 14 c years bp warm dry conditions between about 1900 and 1500 14 c years bp are sug gested by peak values of pseudotsuga pollen and increasing nuphar sclereids the latter suggests lowered water levels this period coincides with a time of drought and increased fire frequency in the southernmost coast mountains about 1300 14 c years bp the forest became more coastal in composition with abundant tsuga heterophylla and abies a n increase in tsuga mertensiana pollen suggests the onset of cool and wet conditions by ca 500 14 c years bp coincident with the little ice age the record of inferred climate change at moraine bog is broadly synchronous with other paleoclimate records from the coast mountains and at the centennial scale with records elsewhere in the world

a 1000 yr record of forest fire activity from eclipse icefield yukon canada a 1000 yr record of forest fire activity has been developed using three annually dated ice cores from eclipse icefield yukon canada forest fire signals were identified as nh4 residuals above a robust spline and corroborated by an empirical orthhogonal function eof analysis that identified a chemical association in the nh4 c 2o4 and k records similar to that observed in forest fire plumes these statistical techniques yielded similar records of forest fire activity although the eof analysis provides more conservative identification of forest fire signals comparison of forest fire signals in the eclipse ice cores with the record of annual area burned in alaska and the yukon demonstrates that 80 of high fire years in alaska and 79 of high fire years in the yukon are identifiable as nh4 concentration residuals in at least one core from eclipse icefield although any individual core records 36 67 of these events the eclipse ice cores record high fire activity in the ad 1760s 1780s 1840s 1860s 1880s 1890s 1920s 1940s and 1980s peak fire activity occurred in the 1890s possibly reflecting anthropogenic ignition sources associated with the large influx of people to the yukon during the klondike gold rush periods of low fire activity are evident during the 1770s 1810s 1830s 1850s 1950s and 1960s extending our proxy of fire activity to ad 1000 using annual nh4 concentrations from our one core that extends back this far provides evidence of high fire activity from 1240 to 1410 during the waning stages of the mediaeval warm period

pacific cod gadus macrocephalus as a paleothermometer otolith oxygen isotope reconstruction stable isotope studies are increasingly important for understanding past environmental and cultural developments along the north pacific rim in this paper we present methods for using pacific cod gadus macrocephalus otoliths as a paleothermometer using a case study from kodiak island alaska the results of this study indicate that pacific cod otoliths record variable paleoenvironmental conditions during the little ice age the broad distribution of pacific cod and success in using the otoliths as a paleothermometer makes this method widely applicable to researchers working throughout the northern pacific rim

tree ring based reconstructions of north american glacier mass balance through the little ice age contemporary warming transition abstract glacier mass balance reconstructions provide a means of placing relatively short observational records into a longer term context in western north america mass balance records span four to five decades and capture a relatively narrow window of glacial behavior over an interval that was dominated by warming and ablation we use temperature and moisture sensitive tree ring series to reconstruct annual mass balance for six glaciers in the pacific northwest and alaska mass balance models rely on the climatic sensitivity of tree ring chronologies and teleconnection patterns in the north pacific the reconstructions extend through the mid to latter portions of the little ice age lia and explore the role of climate variability in forcing mass balance across multiple environmental gradients synchronous positive mass balance intervals coincide with regional moraine building and solar minima whereas differences in lia glacier behavior are related to synoptic climate forcing secular warming in the late 19th century to present corresponds with the only multi decadal intervals of negative mass balance in all glacier reconstructions this suggests that contemporary retreat in western north america is unique with respect to the last several centuries and that regional patterns of glacier variability are now dominated by global climate forcing

expansion of outlet glaciers of the juneau icefield in northwest british columbia during the past two millennia radiocarbon and dendrochronological dating of glacially overridden stumps and detrital wood indicates that two outlet glaciers of the juneau icefield advanced shortly before the little ice age tulsequah glacier advanced to within 2 4 km of its all time holocene limit between ad 865 and ad 940 llewellyn glacier one of the largest glaciers in british columbia advanced sometime between ad 300 and ad 500 and reached to within 400 m of its holocene limit between ad 1035 and ad 1210 well before the climactic classical little ice age advances of the past several centuries our data show that some glaciers in western north america were extensive and expanding at times when alpine glaciers have in the past been assumed to be restricted the evidence raises questions about how to define the time of the beginning of the little ice age and perhaps more importantly about the utility of the term

a 2000 yr long multi proxy lacustrine record from eastern baffin island arctic canada reveals first millennium ad cold period abstract we generate a multi proxy sub centennial scale reconstruction of environmental change during the past two millennia from itilliq lake baffin island arctic canada our reconstruction arises from a finely subsectioned 210pb and 14c dated surface sediment core and includes measures of organic matter e g chlorophyll a carbon nitrogen ratio and insect diptera chironomidae assemblages within the past millennium the least productive and by inference coldest conditions occurred ca ad 1700 1850 late in the little ice age the 2000 yr sediment record also reveals an episode of reduced organic matter deposition during the 6th 7th century ad combined with the few other records comparable in resolution that span this time interval from baffin island we suggest that this cold episode was experienced regionally a comparable cold climatic episode occurred in alaska and western canada at this time suggesting that the first millennium ad cold climate anomaly may have occurred throughout the arctic dramatic increases in aquatic biological productivity at multiple trophic levels are indicated by increased chlorophyll a concentrations since ad 1800 and chironomid concentrations since ad 1900 both of which have risen to levels unprecedented over the past 2000 yr

palaeohydrology of the southwest yukon territory canada based on multiproxy analyses of lake sediment cores from a depth transect lake level variations at marcella lake a small hydrologically closed lake in the southwestern yukon territory document changes in effective moisture since the early holocene former water levels driven by regional palaeohydrology were reconstructed by multiproxy analyses of sediment cores from four sites spanning shallow to deep water marcella lake today is thermally stratified being protected from wind by its position in a depression it is alkaline and undergoes bio induced calcification relative accumulations of calcium carbonate and organic matter at the sediment water interface depend on the location of the depositional site relative to the thermocline we relate lake level fluctuations to down core stratigraphic variations in composition geochemistry sedimentary structures and to the occurrence of unconformities in four cores based on observations of modern limnology and sedimentation processes twenty four ams radiocarbon dates on macrofossils and pollen provide the lake level chronology prior to 10 000 cal bp water levels were low but then they rose to 3 to 4 m below modern levels between 7500 and 5000 cal bp water levels were 5 to 6 m below modern but rose by 4000 cal bp between 4000 and 2000 cal bp they were higher than modern during the last 2000 years water levels were either near or 1 to 2 m below modern levels marcella lake water level fluctuations correspond with previously documented palaeoenvironmental and palaeoclimatic changes and provide new independent effective moisture information the improved geochronology and quantitative water level estimates are a framework for more detailed studies in the southwest yukon

late glacial and holocene δ15n and δ13c variation from a kenai peninsula alaska peatland abstract we use stable carbon and nitrogen isotopes from a kenai peninsula alaska fen spanning the late glacial and holocene to enhance our understanding of peatland hydrology and nutrient cycling we find that isotopic values for carbon and nitrogen are lighter in the late glacial and early holocene 28 to 34 and 0 to 4 respectively than the remainder of the record the light 13 c value corresponds with submerged and emergent aquatic vegetation during the late glacial suggesting high respired carbon input similarly light 15 n values imply that nitrogen is derived from sediment and groundwater sources early holocene 13 values ranging from 30 to 34 infer high recycled carbon uptake from methanogenesis related to the warm climate and the wet swale environment a shift to heavier 15 n and 13 c isotopic values 9600 cal yr bp coincides with a change in the lithology to sphagnum dominated peat indicative of peat accumulation above the water table a shift to lighter values from 5500 to 4200 cal yr bp coincides with a period of glacial recession related to warmer conditions whereas a subsequent period of heavier values is correlative with glacial advance culminating at 3000 cal yr bp suggesting that the hydrology of this peatland is closely linked with the glacial meltwater 15 n remains near 0 relatively close to the atmospheric value of 15 n throughout the holocene suggesting that the fen has been supported by n fixation we propose that groundwater on the kenai lowlands was fed by subglacial meltwater and the warm early holocene summers resulted in high glacial ablation and groundwater recharge sustaining a high swanson fen water table cooler temperatures resulted in a decrease of glacial meltwater input at the close of the early holocene

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

late holocene glacial history of scimitar glacier mt waddington area british columbia coast mountains canada scimitar glacier originates below the northeast face of mt waddington in the southern british columbia coast mountains and flows 18 km down valley to calve into a proglacial lake at several locations downwasting of the glacier surface has exposed stacked till units separated by wood bearing horizons in the proximal slopes of lateral moraines flanking the glacier historical moraine collapse and erosional breaching has also revealed the remains of standing trees buried in moraine dammed lake sediments radiocarbon and tree ring dating show that scimitar glacier expanded down valley at least three times in the late holocene the earliest evidence found for ice expansion indicates scimitar glacier was advancing in 3167 2737 cal years bp in association with the regional tiedemann advance following this advance the glacier downwasted prior to expanding in 1568 1412 cal years bp during the first millennial advance a final period phase of moraine construction was initiated during late little ice age glacia

reliability of a fjord glacier s fluctuations for paleoclimatic reconstructions abstract historical observations of fjord glaciers in southern alaska suggest that their fluctuations may be asynchronous with one another and with climate possible causes for anomalous fjord glacier response to climatic changes involve the instabilities inherent in a calving terminus the interaction of fjord geometry with the extent of the calving terminus and the intersection of low lying snow line by a thickening glacier the lituya glacier system in southeast alaska is analyzed with reference to these phenomena to test the reliability of its holocene glacial deposits as paleoclimatic records this fjord glacier is shown to have been probably free of major nonclimatic responses during the holocene except for an insensitive period of up to 1000 yr that followed calving retreats the insensitive period has no functional effect on how the relatively coarse geologic record is interpreted in terms of paleoclimate however it makes impossible any inference of climatic trends from this glacier s behavior in historical times fjord glacier deposits can be dependable records of paleoclimate but each glacier requires careful scrutiny anomalous glacier responses to climate are most likely to occur in fjords of complex geometry in regions of relatively low snow line and where glaciers terminate at fjord mouths bordering the open sea

rapid uplift of southern alaska caused by recent ice loss summary extreme uplift rates and sea level changes in southern alaska have been documented by global positioning system gps surveys tide gauge measurements and studies of raised shorelines the movements detected in a network of 45 gps survey points describe a broad pattern of rapid regional uplift the majority of the study area is uplifting at a rate faster than 10 mm yr 1 with several sites uplifting more rapidly than 25 mm yr 1 new tide gauge data presented here consist of repeat occupations of 18 temporary gauge sites sea level rates at these sites agree with similar measurements in southern alaska taken 50 yr earlier and also with the pattern of uplift derived from the gps data raised shoreline studies at 14 sites document total sea level change with a maximum change in sea level of 5 7 m found in upper lynn canal the start of the ongoing uplift episode that raised these shorelines has been dated with dendrochronology and found to be coincident with the start of the collapse of the glacier bay icefield at ca 1750 ad the pattern of total sea level change is in general agreement with upliftrate measurements with greater sea level change found at the sites closest to the peak uplift rates in upper glacier bay we use a viscoelastic earth model subjected to an ice load history built upon observations of glacial change to predict uplift rates at the tide gauge and gps sites as well as the total uplift at the raised shoreline sites our modelling exercises are limited to an ice load model based on independent studies of the region s glacial history over the past 1 7 kyr to evaluate whether the uplift observations can be explained by simple earth models subjected to this load history two layer earth models consisting of an elastic crust and a low viscosity upper mantle half space can be adjusted to fit either the raised shoreline data or the combined gps and tide gauge uplift rate data but cannot fit all the data with a single set of earth model parameters however all three data sets are consistent with an approximated three layer earth model the combined model is constrained by a total of 77 uplift measurements which at the 95 per cent confidence level require a low viscosity asthenosphere a 1 4 0 3 10 19 pa s and thickness 110 20

timing and climatic controls over neoglacial expansion in the northern coast mountains british columbia canada holocene sedimentary records from two lakes in white pass british columbia show that the onset of neoglacial sedimentation began c 2 ka cal bp prior to this time the lakes accumulated organicrich sediments with properties and sedimentation rates similar to adjacent lakes that have not had glacial influences during the holocene neoglaciation at white pass was coincident with the increased delivery of exotic tsuga heterophylla western hemlock pollen these results together with regional indications for increased delivery of hemlock pollen at 2 ka bp by a deepened low pressure in the northeastern pacific ocean suggest that increased moisture was important for the expansion of glaciers in the region in addition to longer term late holocene cooling

land sea linkage of holocene paleoclimate on the southern bering continental shelf detailed diatom records within surface and core sediments from the southern bering continental shelf sbcs reveal that the holocene evolution of sea ice distribution is associated with low pressure patterns holocene sea ice distribution over the sbcs was mainly controlled by the location of the aleutian low the corresponding paleoceanographic and paleoclimate conditions can be divided into three stages 1 the early holocene before 7000 cal yr bp was characterized by extensive sea ice distribution under two low pressure cells which covered the western bering sea and the gulf of alaska respectively 2 between 3000 and 7000 cal yr bp the low pressure system over the gulf of alaska became weak causing total sea ice mass over the sbcs to retreat 3 in the past 3000 years prevailing southwesterly winds over the sbcs due to the developing aleutian low have reduced further sea ice cover on the sbcs these paleoclimatic changes were probably a response to enso variation the timings of water mass exchanges on the sbcs coincided with sea level change along the alaskan peninsula as a result subsequent morphologic alterations have also influenced the paleoceanographic condition of the sbcs the effect of the surface coastal water and bottom marine water on the sbcs intensified about 6000 cal yr bp when sea level increased

dendroglaciological reconstruction of late holocene glacier activity at white and south flat glaciers boundary range northern british columbia coast mountains canada holocene glacier activity in the northern british columbia coast mountains canada is described following investigations in the recently deglaciated forefields of white and south flat glaciers spilling from the cambria icefield glacially overridden stumps and detrital wood was radiocarbon and dendrochronologically dated to describe an advance between ad 250 and 650 expansion and thickening of white glacier by ad 765 resulted in creation of an ice dammed lake in south flat valley that persisted until ad 1080 following this the lake drained before refilling in the early little ice age prior to ad 1300 shortly thereafter white and south flat glaciers became confluent and flowed over the valley side toward white lake the characteristics of the site and the preservation of 1500 yr old deposits indicate that the two glaciers remained confluent throughout the remainder of the little ice age only separating following terminal retreat early in the 20th century the late holocene glacial history of whit

tree ring dated little ice age histories of maritime glaciers from western prince william sound alaska tree ring studies at 13 glacier forefields in western prince william sound show little ice age glacial fluctuations were strongly synchronous on decadal timescales cross dated glacially overrun trees at eight sites indicate ice margins advanced in the early late twelfth through thirteenth centuries and middle seventeenth to early eighteenth centuries little ice age tree ring dates of 22 moraines at 13 glaciers show two main periods of stabilization the earlier of these in the first decades of the eighteenth century overlaps with the second period of glaciers overrunning trees and marks culmination of this middle little ice age expansion stabilization of moraines on nine of the study forefields in the latter part of the nineteenth century delineates a third interval of little ice age glacial advance the detailed little ice age record from land terminating glaciers in western prince william sound is consistent on a timescale of decades with four other tree ring dated glacial histories from across the northern gulf of alaska this coastal northeastern pacific glacial record reveals the structure of the little ice age in the region and provides a strong basis for comparison with other proxy climate records spanning the past 1000 years

a 1500 year record of temperature and glacial response inferred from varved iceberg lake southcentral alaska we present a varve thickness chronology from glacier dammed iceberg lake in the southern alaska icefields radiogenic evidence confirms that laminations are annual and record continuous sediment deposition from a d 442 to a d 1998 varve thickness is positively correlated with northern hemisphere temperature trends and more strongly with a local 600 yr long tree ring width chronology varve thickness increases in warm summers because of higher melt runoff and sediment transport as expected but also because shrinkage of the glacier dam allows shoreline regression that concentrates sediment in the smaller lake varve thickness provides a sensitive record of relative changes in warm season temperatures relative to the entire record temperatures implied by this chronology were lowest around a d 600 warm between a d 1000 and a d 1300 cooler between a d 1500 and a d 1850 and have increased dramatically since then combined with stratigraphic evidence that contemporary jokulhlaups which began in 1999 are unprecedented since at least a d 442 this record suggests that 20th century warming is more intense and accompanied by more extensive glacier retreat than the medieval warm period or any other time in the last 1500 yr

alaska tidewater glacier terminus positions 1948 2012 a significant portion of the world s glacier ice drains through tidewater outlets though much remains unknown about the response to recent climate change of tidewater glaciers we present a 64 year record of length change for 50 alaska tidewater glaciers we use u s geological survey topographic maps to provide a base length for glaciers before 1970 using all available cloud free landsat images we manually digitize calving front outlines for each glacier between 1972 and 2012 resulting in a total of more than 10 000 outlines tidewater glacier lengths vary seasonally focusing on the 36 glaciers terminating in tidewater throughout the study period we find a mean standard deviation seasonal variation of 60 85 m a 1 we use these oscillations to determine the significance of interannual changes in glacier length all 36 glaciers underwent at least one period 1 year of significant advance or retreat 28 glaciers underwent at least one period of both significant advance and retreat over the entire period 1948 2012 24 of these glaciers retreated a total uncertainty of 107 95 0 29 km 11 advanced a total of 7 71 0 20 and one chenega glacier did not change significantly retreats and advances are highly variable in time several glaciers underwent rapid short term retreats of a few years duration these retreats occurred after large changes in summer sea surface temperature anomalies further study is needed to determine what triggered these retreats no coherent regional behavior signal is apparent in the length record although two subregions show a coherence similar to recent observations in greenland

paleoceanography of the gulf of alaska during the past 15 000 years results from diatoms silicoflagellates and geochemistry article i nfo abruptly during the bolling allerod bo al warm interval 14 7 12 9 cal ka declined during the younger dryas yd cold interval 12 9 to 11 7 cal kyr bp and rose again during the earliest holocene at this site the record after 11 cal kyr bp is dominated by oceanic diatoms and silicoflagellates with geochemical proxies displaying more subtle variation cores ew0408 66jc in the yakobi sea valley near cross sound and ew0408 11jc in the gulf of esquibel contain an expanded composite record along the southeast alaskan margin core 66jc contains a detailed record of the bo al and yd diatoms and silicoflagellates indicate that coastal upwelling and biosiliceous productivity were strong during the bo al but declined during the yd sea ice related diatoms increased in abundance during the yd indicating cooler but less productive waters

peat accumulation in drained thermokarst lake basins in continuous ice rich permafrost northern seward peninsula alaska thermokarst lakes and peat accumulating drained lake basins cover a substantial portion of arctic lowland landscapes yet the role of thermokarst lake drainage and ensuing peat formation in landscape scale carbon c budgets remains understudied here we use measurements of terrestrial peat thickness bulk density organic matter content and basal radiocarbon age from permafrost cores soil pits and exposures in vegetated drained lake basins to characterize regional lake drainage chronology c accumulation rates and the role of thermokarst lake cycling in carbon dynamics throughout the holocene on the northern seward peninsula alaska most detectable lake drainage events occurred within the last 4 000 years with the highest drainage frequency during the medieval climate anomaly peat accumulation rates were highest in young 50 500 years drained lake basins 35 2 g c m 2 yr 1 and decreased exponentially with time since drainage to 9 g c m 2 yr 1 in the oldest basins spatial analyses of terrestrial peat depth basal peat radiocarbon ages basin geomorphology and satellite derived land surface properties normalized difference vegetation index ndvi minimum noise fraction mnf from landsat satellite data revealed significant relationships between peat thickness and mean basin ndvi or mnf by upscaling observed relationships we infer that drained thermokarst lake basins covering 391 km2 76 of the 515 km2 study region store 6 4 6 6 tg organic c in drained lake basin terrestrial peat peat accumulation in drained lake basins likely serves to offset greenhouse gas release from thermokarst impacted landscapes and should be incorporated in landscape scale c budgets

controls on advance of tidewater glaciers results from numerical modeling applied to columbia glacier 1 a one dimensional numerical ice flow model is used to study the advance of a tidewater glacier into deep water starting with ice free conditions the model simulates glacier growth at higher elevations followed by advance on land to the head of the fjord once the terminus reaches a bed below sea level calving is initiated a series of simulations was carried out with various boundary conditions and parameterizations of the annual mass balance the results suggest that irrespective of the calving criterion and accumulation rate in the catchment area it is impossible for the glacier terminus to advance into deeper water 300 m water depth unless sedimentation at the glacier front is included the advance of columbia glacier alaska is reproduced by the model by including conveyor belt recycling of subglacial sediment and the formation of a sediment bank at the glacier terminus results indicate slow advance through the deep fjord and faster advance in shallow waters approaching the terminal moraine shoal and the mouth of the fjord

signatures of the late holocene neoglacial cold event and their marine terrestrial linkage in the northwestern pacific margin marine microfossil assemblages in core sediments from the northern east china sea ecs were investigated to understand late holocene paleoclimatic changes in the northwestern pacific margin we find a pronounced alternation of ocean condition during the late holocene characterized by an abrupt decrease in dinoflagellate cysts and kuroshio water species of planktonic foraminifera centered at ca 4000 2500 14c yr bp compilation and merger of new and previously published data show that this oceanic event corresponds with terrestrial cooling and dry episodes in the northern china the synchronicity between marine and terrestrial records is considered to be linked to a weakened kuroshio influence that is in coupled with intensified winter monsoon highlighting a significance of oceanic atmospheric dynamics in determining moisture and heat distribution over both oceanic and terrestrial domains superimposed on the late holocene the synchronicity between this particular climatic shift in the northwestern pacific and the neoglacial cold events in the northern high latitude regions is tentatively indicative of a global climate signal possibly associated with dynamics of the north pacific gyre system and the high latitude north atlantic thermohaline circulation and therefore positions of the mean latitude of the kuroshio extension

century scale solar variability and alaskan temperature change over the past millennium 1 correlation of geologic histories from 130 alaskan glaciers with a record of solar variation suggests that multi decadal to century scale temperature variations in the north pacific and arctic sectors have been influenced by solar forcing over the past thousand years mountain glacier fluctuations are primarily a record of summer cooling and the composite glacial history from three climatic regions across alaska shows ice expansions approximately every 200 years compatible with a solar mode of variability the modulating effects of the cold phases of the pacific decadal oscillation and the arctic oscillation may when in phase with decreased solar activity serve to amplify cooling forcing glacier advance

holocene glaciation of alaska and adjoining yukon territory canada abstract holocene glacial fluctuations between arctic central interior and southern maritime alaska are broadly synchronous this synchrony is evident from a review of work in 11 study areas with varying numbers of glaciers 3 100 glacier types subpolar cirque temperate valley tidewater surging and dating methodologies the pattern is temporally and spatially consistent with vegetation data and generally with climatic deteriorations culminating in the little ice age early holocene glacial advances are confirmed for 7 6 5 8 lichen ka bp at 4 of 97 glaciers in the brooks range advances also occurred by 5 85 and 5 7 ka bp at separate glacier tongues in the northern alaska range at least by 6 5 ka bp in lituya bay and possibly also in the malaspina and aleutian islands areas a sharp increase in glacier activity began by 4 4 ka bp in the arctic and glacier bay areas and by about 3 ka bp major glacier advances probably were initiated or well underway throughout alaska during holocene glacial maxima ice filled glacier and lituya bays as well as fjords of prince william sound and massive moraines buried forests in the northeastern st elias mountains area minor recession is recorded directly or implied in most of alaska about 2 ka bp or locally through the following millennium subsequently distinct but locally weak advances occurred by about 1 2 ka bp in most areas again followed by intervals of glacier recession most pervasive and ubiquitous were the little ice age advances initiated about 700 bp these generally culminated in two major advances between about 400 and 50 bp in the arctic those of a d 1600 dominated those of the late 1800s in the gulf of alaska those of the middle 1700s or late 1800s dominated large scale asynchronous advances and retreats of calving tidewater glaciers have been recorded during the twentieth century but most such movements are only indirectly related to climate

timing of the most recent neoglacial advance and retreat in the south shetland islands antarctic peninsula insights from raised beaches and holocene uplift rates abstract the timing of the most recent neoglacial advance in the antarctic peninsula is important for establishing global climate teleconnections and providing important post glacial rebound corrections to gravity based satellite measurements of ice loss however obtaining accurate ages from terrestrial geomorphic and sedimentary indicators of the most recent neoglacial advance in antarctica has been hampered by the lack of historical records and the difficulty of dating materials in antarctica here we use a new approach to dating flights of raised beaches in the south shetland islands of the northern antarctic peninsula to bracket the age of a neoglacial advance that occurred between 1500 and 1700 ad broadly synchronous with compilations for the timing of the little ice age in the northern hemisphere our approach is based on optically stimulated luminescence of the underside of buried cobbles to obtain the age of beaches previously shown to have been deposited immediately inside and outside the moraines of the most recent neoglacial advance in addition these beaches mark the timing of an apparent change in the rate of isostatic rebound thought to be in response to the same glacial advance within the south shetland islands we use a maxwell viscoelastic model of glacial isostatic adjustment gia to determine whether the rates of uplift calculated from the raised beaches are realistic given the limited constraints on the ice advance during this most recent neoglacial advance our rebound model suggests that the subsequent melting of an additional 16 22 increase in the volume of ice within the south shetland islands would result in a subsequent uplift rate of 12 5 mm yr that lasted until 1840 ad resulting in a cumulative uplift of 2 5 m this uplift rate and magnitude are in close agreement with observed rates and magnitudes calculated from the raised beaches since the most recent neoglacial advance along the south shetland islands and falls within the range of uplift rates from similar settings such as alaska

expansion of alpine glaciers in pacific north america in the first millennium a d radiocarbon ages and lichen dated moraines from 17 glaciers in coastal and near coastal british columbia and alaska document a widespread glacier advance during the first millennium a d glaciers at several sites began advancing ca a d 200 300 based on radiocarbon dated overridden forests the advance is centered on a d 400 700 when glaciers along an 2000 km transect of the pacific north american cordillera overrode forests impounded lakes and deposited moraines the synchroneity of this glacier ad vance and inferred cooling over a large area suggest a regional climate forcing and to gether with other proxy evidence for late holocene environmental change during the me dieval warm period and little ice age provide support for millennial scale climate variability in the north pacific region

calendar dated early little ice age glacier advance at robson glacier british columbia canada dendrochronological studies at robson and bennington glaciers have provided the first calendar dating of an early little ice age glacier advance in north america dates derived from in situ stumps indicate that robson glacier began over riding forest between c ad 1142 and 1150 and continued until at least ad 1350 the highest rates of glacier advance c 3 8 m yr 1 occurred between ad 1214 and 1261 based on a series of kill dates from in situ stumps between c ad 1142 1214 and 1261 1350 rates were somewhat lower at c 2 2 5 m yr 1 this glacier advance terminated upvalley of the little ice age maximum position of robson glacier and there is no evidence at this site for glacial events between ad 1350 and 1783 however two smaller glaciers in the robson area and the main tongue of small river glacier have outermost little ice age moraines that date from the first decades of the ad 1700s all glaciers examined in the mount robson area have several well developed moraines dating from the period c

new perspectives on beringian quaternary paleogeography stratigraphy and glacial history abstract aspects of the paleogeography stratigraphy and glacial history of beringia have been greatly revised over the past 15 20 yr access to north east russia in particular has provided the opportunity to evaluate the beringia landscape as a contiguous subcontinent during the quaternary for the first time new research has made clearer the connection between tectonic forces and the submergence of the bering strait during the middle pliocene revisions in the regional stratigraphy of glacial and interglacial deposits in northwest alaska and northeast russia provide a new foundation for assessing the causes for differences in glacial ice extent through time the consensus of all field workers verifies that glacial ice throughout most of beringia was of very limited extent during the last glacial maximum the onset of regional glaciation during the waning stages of the last interglaciation is clearly out of phase with glaciation at lower latitudes despite the lack of much glacial activity during the early holocene alaska contains a rich record of late holocene glacial response to neoglacial cooling changes in the holocene environment of beringia likely had a profound affect on early inhabitants the curiosity driven vision and spirit of both david hopkins and the late troy pewe have had a profound influence on arctic paleoenvironmental research

late quaternary paleoenvironments of northwestern north america implications for inland versus coastal migration routes abstract although the long held normative view of new world colonization relies on entrance through an interior ice free corridor by terrestrially adapted big game hunters a recently demonstrated human presence in southern chile dating prior to the existence of the corridor route implies different colonization scenarios which must be seriously considered a renewed focus of archaeological and paleoecological research on early post glacial landscapes in northwestern north america has revitalized the ice free vs coastal corridor controversy geological findings from glacial geology and paleo sea levels support the possibility of coastal migration from beringia to the pacific northwest between about 14 000 and 10 000 bp and preliminary paleoecological data suggest that the coastal landscape was in part vegetated and probably able to support a terrestrial fauna including humans the same cannot be said about the ice free corridor

evolving force balance at columbia glacier alaska during its rapid retreat 1 changes in driving and resistive stresses play an essential role in governing the buoyancy forces that are important controls on the speed and irreversibility of tidewater glacier retreats we describe changes in geometry velocity and strain rate and present a top down force balance analysis performed over the lower reach of columbia glacier our analysis uses new measurements and estimates of basal topography and photogrammetric surface velocity measurements made between 1977 and 2001 while assuming depth independent strain sensitivity tests show that the method is robust and insensitive to small changes in the calculation parameters spatial distributions of ice speed show little correspondence with driving stress instead spatial patterns of ice speed exhibit a nonlinear correspondence with basal drag primary resistance to flow comes from basal drag but lateral drag becomes increasingly more important throughout the retreat which may account for observed increases in speed maximum basal drag is always located in a prominent constriction located 12 km upstream from the preretreat terminus once the terminus retreated into deep water off the terminal moraine marking the modern maximum extent the upstream location of this maximum basal drag helped to promote thinning and decrease effective pressure in the lower region by limiting replenishing ice flow from upstream an increase in both ice velocity and calving resulted initiating what appears to be an irreversible retreat

constraints on regional drivers of relative sea level change around cordova alaska abstract new records of paleoenvironmental change from two lakes near cordova south central alaska combined with analysis of previously reported sediment sequences from the adjacent copper river delta provide quantitative constraints on a range of earth system processes through their expression in relative sea level change basal sediment ages from upper whitshed lake indicate ice free conditions by at least 14 140 15 040 cal yr bp while upper and lower whitshed lakes provide only upper limits to relative sea level change interbedded layers of freshwater peat and intertidal silt extending more than 11 m below present sea level in copper river delta indicate net submergence over the last 6000 years and multiple earthquake deformation cycles in contrast lower whitshed lake situated just above present high tide level records only one episode of marine sedimentation commencing ad 1120 1500 that we interpret as the result of isostatic subsidence due to little ice age mass accumulation of the chugach mountain glaciers lower whitshed lake also records isostatic uplift at the end of the little ice age before the end of marine sedimentation caused by 1 5 m coseismic uplift in the great alaska earthquake of ad 1964 we successfully explain the records of relative sea level change from both copper river delta and the whitshed lakes by integrating the effects of eustatic sea level rise glacial isostasy earthquake deformation cycles sediment loading sediment compaction and late holocene changes in glacier mass into a single model this approach provides initial quantitative constraints on the individual contributions of these processes taking reasonable estimates of eustasy post last glacial maximum and neoglacial glacial isostatic adjustment and a simple earthquake deformation cycle we demonstrate that sediment loading and sediment compaction are both contributors to relative sea level rise at copper river delta together producing subsidence averaging approximately 1 2 mm yr 1 over the mid to late holocene further isolation basin studies have the potential to greatly improve our understanding of the individual contributions of these processes in this highly dynamic region

fast tidewater glaciers some iceberg calving outlet glaciers flow continuously at speeds normally associated with surging glaciers arid exhibit dramatic instability scenarios related to those suggested for marine ice sheets no temperate tidewater glaciers are known to have floating termini but many polar and subpolar tidewater glaciers do the fast flow of temperate calving glaciers is almost entirely due to basal sliding and appears to be a function of the effective pressure on the bed which may approach zero and the longitudinal back stress on the terminus the terminus boundary condition the calving relation is imperfectly known yet is vital to the dynamics of these glaciers calving relations for grounded tidewater glaciers have been suggested on empirical grounds but have not been rigorously tested the calving relations for floating termini are virtually unknown this together with the imperfect understanding of basal sliding inhibits confidence in our understanding of the stability of these glaciers columbia glacier alaska is an instructive example because observations have been made on the major changes in its geometry calving rate and dynamics that have occurred in less than 10 years the calving flux has increased more rapidly than the glacier flux causing thinning and retreat as a result the ice velocity has increased markedly the short term velocity changes relate to changes in back pressure ice recession tidal changes and the flux of water injected to the bed these results have relevance to the mechanisms of basal sliding glacier surges and the stability of marine ice streams

organic geochemistry of mid continent middle and late ordovician oils ordovician oils in mohawkian and cincinnatian reservoirs of the united states mid continent retain the biochemical imprint of middle and upper ordovician oceanic life before the evolution of land plants and most vertebrates thus these oils have some geochemical features that distinguish them from younger oils these features include 1 a predominance of n c15 n c17 and n c19 alkanes in the saturated hydrocarbon fraction 2 relatively low amounts of longer chain n alkanes 3 low amounts of chlorophyll derived isoprenoids such as pristane and phytane and 4 abundant c29 sterane relative to c27 with rearranged forms diasteranes predominant over normal steranes ordovician oils also generally contain little sulfur and have a somewhat variable light stable carbon isotopic composition with dgr13csat and dgr13caro values of 28 to 31 pmil pdb but these features are typical of many marine oils the unusual chemistry of these ordovician oils supports the interpretation of reed illich and horsfield 1986 that prokaryotic organisms provided the organic matter for most ordovician oils although their claim for gloeocapsamorpha a problematic unicellular prokaryote possibly a blue green alga or an unusually large bacterium cannot be proven from oil chemistry alone knowing that indigenous mid continent ordovician oils were derived from prokaryotic organisms may aid in future exploration for these reservoirs