potential analogues for paleoclimatic variations in eastern interior alaska during the past 14 000 yr atmospheric circulation controls of regional temperature and moisture responses the paleoclimatic history of a region can be viewed as a series of surface temperature and moisture anomalies through time the effects of changes in large scale climatic controls e g insolation major circulation controls can be mediated by the influence of smaller scale controls e g topographic barriers coastlines this may result in heterogenous surface climatic responses at the regional and sub regional scale divergent paleoclimatic trajectories between regions may be explainable in terms of such meso scale patterns using modern analogues for paleoclimate we examine how the sequence of climatic variations in eastern interior alaska during the interval 12 000 0 14c yr bp could have been generated by specific atmospheric circulation patterns fossil pollen and lake level records document the long term trends in temperature and effective moisture for the region water balance modelling provides additional estimates of paleoprecipitation synoptic climatological patterns are described using the modern instrumental record of upper level and sea level pressure surface temperature and precipitation at 12 000 14c yr bp eastern interior alaska was cooler and drier than present a situation generated today by a southward displacement of the jet stream conditions warmer and drier than present at 9000 14c yr bp may have been generated by increased ridging north of alaska and a weakened westerly circulation warmer wetter conditions than present possibly prevailed in the late middle holocene these might reflect ridging over alaska and troughing further west cool wet conditions feature enhanced westerly flow into alaska through an eastward shift in the east asian trough and positive pressure anomalies in the north pacific they may be analogous to cold periods of the little ice age the analogues demonstrate how surface conditions in other parts of beringia may sometimes be similar to while at other times different from those in the eastern interior these broader spatial patterns provide hypotheses about past climates that can be tested with paleoclimatological data for example the widespread positive temperature anomalies associated with the warm dry 9000 14c yr bp analogue fit with the expansion northward of the eastern siberian treeline the anomalously cool conditions in northeast siberia associated with the warm wet analogue may explain the continued late middle holocene treeline advance in alaska while there was retreat in siberia

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

late glacial and holocene sedimentation vegetation and climate history from easternmost beringia northern yukon territory canada abstract beringian climate and environmental history are poorly characterized at its easternmost edge lake sediments from the northern yukon territory have recorded sedimentation vegetation summer temperature and precipitation changes since 16 cal ka bp herb dominated tundra persisted until 14 7 cal ka bp with mean july air temperatures 5 c colder and annual precipitation 50 to 120 mm lower than today temperatures rapidly increased during the bolling allerod interstadial towards modern conditions favoring establishment of betula salix shrub tundra pollen inferred temperature reconstructions recorded a pronounced younger dryas stadial in east beringia with a temperature drop of 1 5 c 2 5 to 3 0 c below modern conditions and low net precipitation 90 to 170 mm but show little evidence of an early holocene thermal maximum in the pollen record sustained low net precipitation and increased evaporation during early holocene warming suggest a moisture limited spread of vegetation and an obscured summer temperature maximum northern yukon holocene moisture availability increased in response to a retreating laurentide ice sheet postglacial sea level rise and decreasing summer insolation that in turn led to establishment of alnus betula shrub tundra from 5 cal ka bp until present and conversion of a continental climate into a coastal maritime climate near the beaufort sea

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

late wisconsin environments of the bering land bridge abstract late wisconsin paleobotanical and fossil insect data from the central and northern sectors of the bering land bridge indicate widespread mesic shrub tundra environments even during the last glacial maximum vegetation before the last glacial maximum was a birch heath graminoid tundra with few or no steppe elements shrubs were not an important element of the vegetation but were present in small numbers during the interval 20 000 14 000 yr bp land bridge vegetation was dominated by birch graminoid tundra with small ponds containing aquatic plants heaths were relatively unimportant insects from this interval were indicative of arctic climate with drier tundra than during the late glacial during the late glacial interval 14 000 11 000 yr bp land bridge vegetation was dominated by birch heath graminoid tundra with small ponds choked with aquatic plants the insect record indicates open ground habitats dominated by mesic tundra by 11 000 yr bp insect data suggest that summer temperatures on the emergent bering shelf were warmer than present day upland regions in western alaska summer temperatures on the chukchi shelf were warmer than the present day north slope of alaska contrary to previous hypotheses we found no evidence of steppe tundra on the land bridge new accelerator mass spectrometer ams 14c dates show that much of the land bridge was above sea level and thus available for human and animal migration until as late as 11 000 yr bp

postglacial vegetation history of the mackenzie river basin abstract three radiocarbon dated cores from small lakes provide pollen records of postglacial vegetation change in the central mackenzie river basin these data are combined with previously published records to reconstruct vegetation development from central alberta to the mackenzie delta the paleoecological data demonstrate that a continuous corridor of herb and shrub dominated vegetation extended between beringia and the great plains of north america from deglaciaiton until about 10 000 yr b p the initial vegetation was replaced by spruce forests between 10 000 and 8500 yr b p significant vegetation change continued until approximately 500 yr b p when the muskeg dominated landscape typical of the present subarctic was established the initial herb and shrub vegetation was likely a reprise of conditions which existed during earlier pleistocene deglaciations these conditions may have provided a favorable environment for animals adapted to nonforested vegetation and promoted migration southward from beringia and northward from the great plains during the last deglaciation and earlier pleistocene deglaciations the sequence of postglacial vegetation change in the mackenzie basin likely reflects a combination of climatic change edaphic change and plant migration patterns and interactions

triaxial rheological property of sandstone under low confining pressure abstract the creep behavior of the rock mass in an anchoring section affects the control effect of the piles and the long term stability of the landslide and stabilizing slide structure the confining pressure of the anchoring section in the majiagou landslide in the three gorges reservoir is low to study the creep behavior of sandstone at low confining pressures the triaxial compression test and triaxial creep test are performed on the jurassic sandstone in the three gorges reservoir at three low confining pressures i e 3 0 mpa 5 0 mpa and 7 0 mpa the test results show three typical stages initial creep steady state creep and accelerated creep when the deviatoric stress is greater than the yield stress with the test results in this study an improved burgers model is developed to describe the initial creep and steady state creep furthermore a nonlinear newton component is added to the accelerated creep model the test data at all stages are well fitted by the developed creep models in this paper we take the critical stress that causes the steady state creep as the long term strength with the developed creep models the long term strength of the sandstone can be derived in comparison to the short term strength the internal friction angle and cohesion of the long term strength decrease by 15 and 13 respectively and the compression strength could be decreased by more than 50 thus in the design of stabilizing piles of the majiagou landslide the effect of rock creep on the strength should be considered

late quaternary vegetation history of the fishhook bend area porcupine river alaska ped pond is a lake lying in a pleistocene scour channel of the porcupine valley the valley is considered to be a possible path of late quaternary species migrations between interior alaska and northwest canada pollen in the oldest lake sediments ca 13 000 years old indicates that shrub birch and willow probably occurred locally in a sparsely vegetated herb dominated landscape populus juniperus and typha latifolia increased about 10 000 years ago suggesting particularly warm temperatures during the early holocene picea glauca which is presently common in the surrounding forests first arrived near ped pond about 8500 years ago this arrival date together with existing evidence from other sites indicates that spruce expanded rapidly across far eastern beringia 8000 9000 years ago other boreal forest taxa picea mariana betula papyrifera and alnus spp became established locally between 7000 and 8000 years bp a date of ca 7500 years bp at ped pond suggests that the alnus rise in northeast

paleoenvironmental analyses of an organic deposit from an erosional landscape remnant arctic coastal plain of alaska abstract the dominant landscape process on the arctic coastal plain of northern alaska is the formation and drainage of thaw lakes lakes and drained thaw lake basins account for approximately 75 of the modern surface expression of the barrow peninsula the thaw lake cycle usually obliterates lacustrine or peat sediments from previous cycles which could otherwise be used for paleoecological reconstruction of long term landscape and vegetation changes several possible erosional remnants of a former topographic surface that predates the formation of the thaw lakes have been tentatively identified these remnants are characterized by a higher elevation a thick organic layer with very high ground ice content in the upper permafrost and a plant community somewhat atypical of the region ten soil cores were collected from one site and one core was intensively sampled for soil organic carbon content pollen analysis and 14c dating the lowest level of the organic sediments represents the earliest phase of plant growth and dates to ca 9000 cal bp palynological evidence indicates the presence of mesic shrub tundra including sedge birch willow and heath vegetation and microfossil indicators point to wetter eutrophic conditions during this period carbon accumulation was rapid due to high net primary productivity in a relatively nutrient rich environment these results are interpreted as the local response to ameliorating climate during the early holocene the middle holocene portion of the record contains an unconformity indicating that between 8200 and 4200 cal bp sediments were eroded from the site presumably in response to wind activity during a drier period centered around 4500 cal bp the modern vegetation community of the erosional remnant was established after 4200 cal bp and peat growth resumed during the late holocene carbon accumulation rates cars were greatly reduced in response to the combined effects of declining productivity associated with climatic cooling and increased nutrient stress as paludification and permafrost aggradation sequestered mineral nutrients

late quaternary vegetation and climate history of the central bering land bridge from st michael island western alaska pollen analysis of a sediment core from zagoskin lake on st michael island northeast bering sea provides a history of vegetation and climate for the central bering land bridge and adjacent western alaska for the past 30 000 14 c yr b p during the late middle wisconsin interstadial 30 000 26 000 14 c yr b p vegetation was dominated by graminoid herb tundra with willows salix and minor dwarf birch betula nana and ericales during the late wisconsin glacial interval 26 000 15 000 14 c yr b p vegetation was graminoid herb tundra with willows but with fewer dwarf birch and ericales and more herb types associated with dry habitats and disturbed soils grasses poaceae dominated during the peak of this glacial interval graminoid herb tundra suggests that central beringia had a cold arid climate from 30 000 to 15 000 14 c yr b p between 15 000 and 13 000 14 c yr b p birch shrub ericales sedge moss tundra began to spread rapidly across the land bridge and alaska this major vegetation change suggests moister warmer summer climates and deeper winter snows a brief invasion of populus poplar aspen occurred ca 11 000 9500 14 c yr b p overlapping with the younger dryas interval of dry cooler climate during the latest wisconsin to middle holocene the bering land bridge was flooded by rising seas alder shrubs alnus crispa colonized the st michael island area ca 8000 14 c yr b p boreal forests dominated by spruce picea spread from interior

the last interglaciation in alaska stratigraphy and paleoecology of potential sites at least 20 localities in alaska contain deposits that may provide information on the last interglaciation oxygen isotope substage 5e these widely dispersed localities include river bluffs coastal bluffs and terraces elevated marine shorelines lake basins and artificial excavations most of the inferred interglacial deposits contain macrofossils or pollen that are older than the range of radiocarbon dating and commonly indicate climate as warm as or warmer than the present at a few localities evidence for deep thaw of permafrost also indicates a warm paleoclimate at eight localities the old crow tephra occurs at or below organic deposits that may represent substage 5e the tephra occurs beneath conspicuous organic deposits at fairbanks the yukon palisades and holitna lowland and directly above a peat bed at hogatza mine at birch creek halfway house ky 11 and imuruk lake the tephra occurs within a paleosol or organic deposit but other organic horizons that more likely indicate interglacial conditions occur at higher stratigraphic levels the varied stratigraphic relations of the old crow tephra suggest that it may have been deposited close to the boundary between isotope substages 6 and 5 which is dated at about 130 ka in the marine record and between 132 and 140 ka on land these age relations suggests that the tephra may have been deposited about 135 5 ka validating the recent fission track age determination of 140 10 ka for this deposit six coastal localities contain deposits of probable interglacial age and these commonly are associated with evidence for eustatic sea levels higher than those of the present beach and sublittoral sediments of the pelukian transgression occur up to 12 m asl along the northwest coast of alaska and are correlative with barrier island and lagoonal sediments on the alaskan arctic coastal plain both sets of deposits commonly contain extralimital mollusks and microfauna that indicate marine water slightly warmer than present and suggest that seasonal sea ice did not extend south of bering strait during the last interglacial as it does today farther south elevated marine terrace deposits on amchitka island contain marine invertebrates that indicate a climate warmer than at present peat horizons in coastal exposure at goose bay and coastal terraces at lituya bay contain pollen spectra that suggest forests like those of the present day and spruce macrofossils exposed on baldwin peninsula indicate boreal forest more extensive than at present sediments from several lakes in northwestern alaska may contain continuous records of the last interglaciation a major warm interval possibly isotope substage 5e has been identified in a core from squirrel lake by a peak in picea pollen that indicates forest extension beyond present limits similar pollen records are potentially available from two maars which formed in the cape espenberg area more than 125 ka terrestrial organic deposits thought to record the last interglaciation occur interstratified with marine and glaciogenic sediments in the nushagak lowland of southwest alaska and on baldwin peninsula in kotzebue sound extensive exposures along the copper and nenana rivers may also contain organic deposits that record the last interglaciation

variability of sea ice cover in the chukchi sea western arctic ocean during the holocene 1 dinocysts from cores collected in the chukchi sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques holocene sequences have been recovered in a down slope core b15 2135 m 75 44 n sedimentation rate of 1 cm kyr 1 and in a shelf core p1 201 m 73 41 n sedimentation rate of 22 cm kyr 1 the shelf record spanning about 8000 years suggests high frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar cal years b p the condensed offshore record b15 reveals an early postglacial optimum with minimum sea ice cover prior to 12 000 cal years b p which corresponds to a terrestrial climate optimum in bering sea area dinocyst data indicate extensive sea ice cover 10 months yr 1 from 12 000 to 6000 cal years b p followed by a general trend of decreasing sea ice and increasing sea surface salinity conditions superimposed on large amplitude millennial scale oscillations in contrast 18o data in mesopelagic foraminifers neogloboquadrina pachyderma and benthic foraminifers cibicides wuellerstorfi reveal maximum subsurface temperature and thus maximum inflow of the north atlantic water around 8000 cal years b p followed by a trend toward cooling of the subsurface to bottom water masses sea surface to subsurface conditions estimated from dinocysts and 18o data in foraminifers thus suggest a decoupling between the surface water layer and the intermediate north atlantic water mass with the existence of a sharp halocline and a reverse thermocline especially before 6000 years b p the overall data and sea ice reconstructions from core b15 are consistent with strong sea ice convergence in the western arctic during the early holocene as suggested on the basis of climate model experiments including sea ice dynamics matching a higher inflow rate of north atlantic water

time dependent brittle creep in darley dale sandstone 1 the characterization of time dependent brittle rock deformation is fundamental to understanding the long term evolution and dynamics of the earth s crust the chemical influence of pore water promotes time dependent deformation through stress corrosion cracking that allows rocks to deform at stresses far below their short term failure strength here we report results from a study of time dependent brittle creep in water saturated samples of darley dale sandstone initial porosity 13 under triaxial stress conditions results from conventional creep experiments show that axial strain rate is heavily dependent on the applied differential stress a reduction of only 10 in differential stress results in a decrease in strain rate of more than two orders of magnitude however natural sample variability means that multiple experiments must be performed to yield consistent results hence we also demonstrate that the use of stress stepping creep experiments can successfully overcome this issue we have used the stress stepping technique to investigate the influence of confining pressure at effective confining pressures of 10 30 and 50 mpa while maintaining a constant 20 mpa pore fluid pressure our results demonstrate that the stress corrosion process appears to be significantly inhibited at higher effective pressures with the creep strain rate reduced by multiple orders of magnitude the influence of doubling the pore fluid pressure however while maintaining a constant effective confining pressure is shown to influence the rate of stress corrosion within the range expected from sample variability we discuss these results in the context of microstructural analysis acoustic emission hypocenter locations and fits to proposed macroscopic creep laws

transgressions rethinking beringian glaciation abstract the purpose of this investigation is to encourage a fresh look at pleistocene beringia heretofore flooding of bering strait has been cited as the only barrier to migration with marine sea transgressions being a sea gate that closed off migration during glacial interstadials and interglaciations however the possibility exists that glacial advances were also barriers with marine ice transgressions being an ice gate that closed off migration during glacial stadials and glacial maxima this possibility proceeds from the marine ice transgression hypothesis mith which states that marine ice sheets form on the broad arctic continental shelf of northern hemisphere continents when sea ice thickens grounds and domes in shallow water and then transgresses landward as continental ice sheets and seaward as floating ice shelves hughes 1987 landward transgression is onto coastal lowlands during pleistocene glaciations a marine ice sheeet extending from spitsbergen to greenland may have transgressed the circumpolar continental landmass at its lowest and narrowest gap central beringia and calved into the pacific ocean four models of beringian glaciation are presented based on the distinction between marine glaciation and highland glaciation central beringia was glaciated only in highlands in the traditional model hopkins et al 1982 was also glaciated by a self sustaining ice shelf floating over the deep ocean basins of the bering sea in the model by grosswald and vozovik 1984 was glaciated by a marine ice sheet that covered highlands the continental shelf and supplied the ice shelf in a model for maximum pleistocene glaciation and was glaciated by a marine ice sheet in the chukchi sea that merged with highland glaciers transgressed the continental shelf of the western bering sea and calved into the southern bering sea along the edge of the continental shelf in a model for the last glaciation field tests are suggested to assess the viability of these four models the first model is already established for highland glaciation in alaska but less established in siberia the last model should be the easiest to evaluate for marine glaciation the last model limits human migration across the beringian land bridge to brief intervals between stadials and interstadials of the last glaciation cycle when both the ice gate and the sea gate were opened to human migration this model can influence the sea change now underway among quaternary scientists studying peopling of the americas based on the archaeological linguistic and ethnic diversity among native american populations

dynamics diffusion and geomorphological significance of tidal residual eddies many shallow tidal areas show the occurrence of ebb and flood surplusses organized in cell like structures or tidal residual eddies they seem to arise from a nonlinear transfer of vorticity from the oscillating tidal field to the mean field the irregular structure of the bottom topography or the coastline acting as a catalyst to produce the necessary vorticity gradients the dynamical characteristics of the eddies assist our understanding of the geomorphology of the sea bed

impact of weathering on the geomechanical properties of rocks along thermal metamorphic contact belts and morpho evolutionary processes the deep seated gravitational slope deformations of mt granieri salincriti calabria italy abstract numerous deep seated gravitational slope deformations dsgsds occur throughout italy that originate from particular tectono stratigraphic settings relief seismicity deglaciation as well as from intense and deep processes of chemico physical weathering of crystalline metamorphic rocks these dsgsds are particularly widespread in the calabrian mountains this study is focused on the mt granieri salincriti slope on the ionian side of the serre massif where granites and granodiorites stilo unit palaeozoic are in contact with metamorphites through a thermal metamorphic aureole this setting generates deep geochemical processes inducing intense chemical weathering these processes are mainly due to the interaction between groundwater and the sulphides that are contained in the local pegmatitic hydrothermal intrusions especially along the thermal metamorphic contact belt the mt granieri salincriti slope has an important dsgsd which is associated with many active and or quiescent landslides among these landslides the salincriti rock avalanche debris flow about 2 m m3 represents the paroxysmal and terminal stage of the deep creep deformations of mt granieri typifying a geological setting that is common in the calabrian arc this multi disciplinary study assessed the weathering susceptibility of the local crystalline metamorphic rocks especially those lying along thermal metamorphic contact belts by characterising the weathering horizons and the spatial distribution of weathering in the rock mass the study was also aimed at identifying the relations between weathering above all deep geochemical processes effects on rocks and slope morphodynamics the methodology was based on detailed geological data geological engineering surveys geomorphology and surface hydrogeology analyses as well as physico mechanical laboratory tests these investigations supported by a monitoring program led to the development of an engineering geological model of the slope geological character attributed to a thermal metamorphic contact belt geomorphological evidence and geomechanical elements elucidated the interactions between deep geochemical processes and weak belts in the investigated rocks as well as the critical role that these interactions play in the evolution of deep seated creep deformations and associated shallow landslides

middle to late wisconsinan climate and ecological changes in northern alaska evidences from the itkillik river yedoma abstract continuous paleoenvironmental records covering the period prior to the last glacial maximum in northeastern beringia are sparse this study presents a multi proxy analysis of a 35 m high yedoma exposure located on the right bank of the itkillik river in alaska the exposure accumulated over 39 thousand years kyr during the middle wisconsinan interstadial and the late wisconsinan glacial advance we identified five stratigraphic units based on pollen carbon and ice content and isotopic composition 18o of the sediments middle wisconsinan climate in northern alaska promoted peat accumulation prior to 33 6 cal kyr bp calibrated kyr before present reconstructed july air temperatures were 1 2 c lower than current at 34 8 cal kyr bp consistent with the timing of the interstadial climatic optimum in interior alaska and yukon colder by up to 4 c and drier conditions characterize the transition from interstadial to glacial conditions between 33 6 and 29 8 cal kyr bp late wisconsinan 29 8 17 9 cal kyr bp july air temperatures were 2 3 c lower than today with grassland vegetation dominated by poaceae artemisia and forbs in contrast to the modern cyperaceae dominance moister and warmer environmental conditions after 17 9 cal kyr bp correspond to the late glacial to early holocene interval

a 130 0 year history of vegetation and environmental change at jan lake east central alaska pollen stomates and macrofossils were analysed from a 3 63 m sediment core at jan lake eastcentral alaska in order to improve spatial resolution of patterns of vegetation history in this region the chronology was based on 19 ams 14c dates on plant macrofossils and concentrated pollen zone jan i 12400 11 600 yr bp records a unique herb tundra pollen assemblage particularly high in chenopodia ceae adding supporting evidence for a spatial mosaic of lateglacial vegetation in east central alaska unexpected pollen of picea betula and alnus in lateglacial sediments appears to arise from reworking of older pollen bearing deposits according to a radiocarbon date of 22180yr bp on a pollen sample shrub betula tundra dominates zone jan il 11 600 10000 yr bp with indications of climatic amelioration tree species populus picea glauca betula papyrifera began to arrive in zone jan illa 9200 6600 yr bp and the modern boreal forest including alnus and picea mariana became established during zone j

evolution of the elastic moduli of seismogenic triassic evaporites subjected to cyclic stressing seismic cycles lead to variations in rock physical properties quantifying these changes is of key importance in building reliable crustal deformation models here we report laboratory measurements of the uniaxial compressive strength ucs young s modulus and poisson s ratio both static es s and dynamic ed d of the seismogenic triassic evaporites of the northern apennines triassic evaporites are composed of dolostones anhydrites and gypsum gypsum was the weakest lithology with ucs values ranging from 10 to 26 mpa anhydrite exhibited intermediate values from 52 to 144 mpa and dolostones were the strongest with a maximum ucs of 228 mpa during uniaxial cyclic stressing experiments we observed complex variations in es and s with large increases are observed in the early cycles stage 1 followed by essentially constant values stage 2 before es decreases and s increases approaching failure stage 3 complementary microseismicity acoustic emission ae data show no significant ae during stage 1 then the stress needed to induce ae remained essentially constant stages 2 and 3 integration of mechanical data with microstructural observations suggests a first stage dominated by compaction and strengthening a second stage characterised by quasi elastic behaviour associated with the development of randomly oriented microfractures and a third stage of weakening due to the growth of macrofractures parallel to the direction of the load laboratory dynamic elastic moduli are on average in agreement with dynamic elastic moduli used in crustal modelling however static values of young s modulus are about 50 lower than dynamic ones and static values of poisson s ratio are about 40 higher with respect to dynamic values these observations suggest that the frequency effect on the difference between laboratory and crustal scale dynamic moduli values is rather small and that static values of modulus are more appropriate for crustal deformation modelling than seismically derived values

lake morphometry sediment mixing and the selection of sites for fine resolution palaeoecological studies abstract palaeoecologists are increasingly using close interval or continuous sampling of lake sediments to construct fine resolution records of environmental change the degree of temporal resolution sought in these studies is typically decades or years the use of lake sediments for such fine resolution reconstructions assumes that temporal mixing of the sediments is negligible in this paper we examine the physical and biological processes that cause sediment mixing in small lakes we use physical models and empirical data to develop a set of heuristics relating lake depth and area to sediment mixing by slumping waves currents and bioturbation we also develop a heuristic that allows information on lake depth and area to be used to determine if the sediments of a lake will likely be massive or annually laminated in general the degree of sediment mixing likely to occur in a small lake is directly related to the depth and surface area of the lake however each of the agents of mixing has a different critical relationship with lake depth and surface area we present a series of equations and a summarizing figure that based on lake surface area and maximum depth allows the type of thermal stratification polymictic dimictic or meromictic and the degree of sediment mixing present in the lake to be inferred

comparison between predicted and observed physical features of sandbanks a linear stability analysis has been carried out to investigate the influence of parameters like tidal current depth and coriolis force on sand bank formation the applied analytical model allowed the computation of the horizontal wave number corresponding to the fastest initial growth rate of seabed form perturbations sandbank wavelength and the angle between the crest of the sandbank and tidal current direction were also obtained the experiments show an exponential decay of this angle for increasing values of tidal currents at a particular depth the sand bank wavelength grows almost linearly with the velocity we compared these theoretical results with observations of sandbank features in several geographic areas persian gulf the gulf of korea gulf of california and the north sea the results show that all observed sand bank wavelengths and angles are in very close agreement with the calculated theoretical curves

latest pleistocene increase in wind intensity recorded in eolian sediments from central alaska abstract a brief increase in wind intensity between ca 11 100 and 10 700 yr b p is recorded by a sharp increase in sediment grain size at eolian sections along the nenana river in central alaska this occurred at the same time as the younger dryas climatic reversal in northern europe and an increase in the vigor of atmospheric circulation recorded by greenland ice cores climatic fluctuations in high latitude areas during younger dryas time may reflect variations in the co2 content of the atmosphere

chronology and glass chemistry of tephra and cryptotephra horizons from lake sediments in northern alaska usa holocene tephrostratigraphy in alaska provides independent chronology and stratigraphic correlation in a region where reworked old holocene organic carbon can significantly distort radiocarbon chronologies here we present new glass chemistry and chronology for holocene tephras preserved in three alaskan lakes one in the eastern interior and two in the southern brooks range tephra beds in the eastern interior lake sediment core are correlated with the white river ash and the hayes tephra set h 4200 3700 cal yr bp while an additional discrete tephra bed is likely from the aleutian arc alaska peninsula cryptotephras non visible tephras found in the brooks range include the informally named ruppert tephra 2700 2300 cal yr bp and the aniakchak caldera forming event ii tephra cfe ii 3600 cal yr bp a third underlying brooks range cryptotephra is chemically indistinguishable from the aniakchak cfe ii tephra 4070 3760 cal yr bp and is likely to be from an earlier eruption of the aniakchak volcano

tidal hydrodynamics and fine grained sediment transport on the radial sand ridge system in the southern yellow sea abstract the large radial sand ridge rsr system located in the southern yellow sea off the jiangsu coast is characterized by a radial current field and high suspended sediment concentrations sscs significant rectilinear currents are present over the northern sand ridge area whereas rotary currents prevail over the southern area the transition between the two being dominated by a locally generated trapped wave observations undertaken in 2006 and 2007 indicate a seasonal pattern in the ssc and associated dynamic characteristics the results of a calibrated hydrodynamic model show that the m2 tide dominates the rsr area the maximum tidal amplitude in the core region close to land being approximately 2 m an amphidromic point is located some distance north of the rsr off the abandoned yellow river mouth 121 686 e 34 6 n specifically the eulerian and lagrangian residual currents flow southward in both summer and winter whereas the stokes drift is directed southward in the north and northward in the south moreover in deep water the lagrangian residual current is mainly determined by the eulerian residual current whereas it is strongly influenced by the stokes drift in shallow water the seasonal variation in the residual current in the southern yellow sea is a good indicator for the location of the yellow sea warm current yswc in both summer and winter measurements show that a ssc peak appears off the abandoned yellow river delta in response to the strong currents and plentiful supply of fine grained sediment from coastal erosion another ssc peak lying close to the north branch of the changjiang river mouth is related to the abundant suspended sediment supplied by the river seasonal variations in ssc are observed in the study area maximum average values and widest diffusion from land occurring in winter this being contrasted by minimum mean values in summer sensitivity experiments demonstrate that the main factor influencing the distribution of ssc is the tide while river discharge wind and wave effects are small and very localized to explain the seasonal variation in ssc the role of hydrodynamics initial conditions and temperature are tested in the model the results show that the hydrodynamics play a significant role whereas the initial conditions only have a minor regional influence temperature on the other hand is also shown to greatly influence the seasonal variation in ssc because of substantial changes in the viscosity of the water and the erosion shear stress the modeled results are used to calculate sediment fluxes which are shown to be consistent with the lagrangian residual current pattern while wind waves can significantly change the fluxes in winter bed elevations change substantially on a monthly time scale in general the deep channels are undergoing erosion while the shallow ridges and coastal tidal flats are accreting the net sediment transport being directed towards the coastal tidal flat and the changjiang yangtze river subaqueous delta

a late wisconsin and holocene vegetation history from the central brooks range implications for alaskan palaeoecology abstract five pollen diagrams reveal late wisconsin and holocene vegetation changes in the walker lake alatna valley region of the central brooks range approximately 100 km west of the area studied by d a livingstone 1955 ecology 36 587 600 new insights into the vegetation history of this region are provided by calculations of pollen influx and by the use of linear discriminant analysis to separate picea glauca and p mariana pollen three major pollen zones are identified 1 a basal herb zone characterized by high percentages of cyperaceae gramineae salix and artemisia and low total pollen influx 2 a shrub betula zone with increased total pollen influx and very high percentages of betula pollen predominantly in the size range of b nana and b glandulosa and 3 and alnus zone dominated by alnus pollen lakes currently within the boreal forest or near tree line show relatively high percentages of picea pollen in the alnus zone several striking vegetation changes occurred between ca 10 000 and 7000 yr b p between ca 11 000 and 10 000 yr b p populus balsamifera pollen percentages as great as 30 indicate that this species was present at low elevation sites near walker lake these populations declined abruptly ca 10 000 yr ago and have never regained prominence about 8500 yr b p picea glauca pollen reached 10 15 indicating the arrival of p glauca in or near the study area p glauca populations evidently decreased ca 8000 yr ago when picea pollen percentages and influx fell to low values about 7000 yr b p alnus pollen percentages and influx rose sharply as alder shrubs became established widely picea once more expanded ca 5000 yr ago but these populations were dominated by p mariana rather than p glauca which increased slowly at this time and may still be advancing northward some vegetation changes have been remarkably synchronous over wide areas of interior alaska and probably reflect responses of in situ vegetation to environmental changes but others may reflect the lagged responses of species migrating into new areas

cryostratigraphy paleogeography and climate change during the early holocene warm interval western arctic coast canada botanical and cryostratigraphic records from northwest canada indicate that the climate of the early holocene was considerably warmer than today tree line was over 100 km farther north and a thaw unconformity dating from 8000 14c years bp formed at the base of an active layer 2 5 times thicker than at present numerous thermokarst lake basins formed in the preceding millennia both the botanical and cryostratigraphic indices described are products of summer conditions previous reconstructions of early holocene climate have not assessed the significance of paleocoastal location on the seasonality and extent of apparent climate warming at present there is a steep gradient in growing season conditions between cooler sites on the beaufort sea coast and warmer inland locations winter conditions are more uniform because both sea and land are snow covered coastal retreat in the region has been rapid due to sea level rising over a gently sloping shelf containing readily erodible sediments the coastlin

comment on latest pleistocene increase in wind intensity recorded in eolian sediments from central alaska by n bigelow j e beget and w r powers

uniaxial strength testing of non welded calico hills tuff yucca mountain nevada abstract a detailed investigation of the strength properties of calico hills tuff was undertaken to further characterize the behavior of this unit uniaxial compression tests on 43 specimens of massive and reworked tuff show a dependence of peak strength and young s modulus on the total porosity and thereby on the geologic history of the calico hills tuff the average young s modulus poisson s ratio and compressive peak strength of dry specimens of massive and reworked tuff are 5 43 0 96 gpa 9 80 0 89 gpa 0 194 0 052 0 244 0 067 and 26 34 5 13 mpa 38 64 4 96 mpa wet specimens of massive tuff have compressive strengths of 15 34 0 70 mpa lower than those of dry specimens the post peak region for this brittle tuff is characterized by rapid load drops and well defined residual strengths associated with growth of macrocracks and small faults in the specimens

late quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern seward peninsula alaska a terrestrial sediment sequence exposed in an eroding pingo provides insights into the late quaternary environmental history of the northern seward peninsula alaska we have obtained the first radiocarbondated evidence for a mid wisconsin thermokarst lake demonstrating that complex landscape dynamics involving cyclic permafrost aggradation and thermokarst lake formation occurred over stadiale interstadial as well as glacialeinterglacial time periods high values of picea pollen and the presence of larix pollen in sediments dated to 50e40 ka bp strongly suggest the presence of forest or woodland early in mis 3 the trees grew within a vegetation matrix dominated by grass and sedge and there is indirect evidence of grazing animals thus the interstadial ecosystem was different in structure and composition from the holocene or from the preceding last interglacial period an early holocene warm period is indicated by renewed thermokarst lake formation and a range of fossil taxa multiple extralimital plant taxa suggest mean july temperatures above modern values the local presence of spruce during the early holocene warm interval is evident from a radiocarbon dated spruce macrofossil remain and indicates significant range extension far beyond the modern tree line the first direct evidence of spruce in northwest alaska during the early holocene has implications for the presence of forest refugia in central beringia and previously assumed routes and timing of post glacial forest expansion in alaska

moduli stress dependency in anisotropic rock masses abstract joint effects on rock mass anisotropy are examined by considering granodiorite and metasediment rock masses that were encountered in two different tunnelling projects composite moduli are determined using two simple models representing the constraints of equilibrium and compatibility the equilibrium constraint gives a lower value modulus where there is no stress redistribution as the rock mass deforms the compatibility constrained modulus characterises the stress distribution and redistribution as deformation occurs rock mass moduli and their dependance on joint orientation and imposed stress ratio environments are examined by considering rock masses encountered in two tunnelling projects it is shown that rock mass anisotropy is not only very sensitive to joint characteristics and orientation but also to in situ stresses in a very poor class 5 metasedimentary rock mass it is shown that in situ stresses induce significant anisotropies whereas initially pseudo isotropic elasticity was assumed because of the multiple jointing

a multi proxy reconstruction of environmental change spanning the last 37 000 years from burial lake arctic alaska abstract sediment cores from burial lake located in the western brooks range in arctic alaska record paleoenvironmental changes that span the last 37 000 calendar years before present cal yr bp we identified four distinct lithologic subunits based on physical properties dry bulk density magnetic susceptibility sediment composition and geochemical proxies organic matter biogenic silica c n organic matter 13c and 15n and elemental data from scanning x ray fluorescence the multi proxy approach and relatively high temporal resolution at multi decadal to centennial time scales of our proxy analysis compared with previous studies of intermediate water depth cores from burial lake provide new insights into the paleoenvironmental history of the region spanning the period prior to the last glacial maximum relatively high lake levels and gradually decreasing in lake and terrestrial productivity occur during the mid wisconsin interstadial from 37 200 to 29 600 cal yr bp the subsequent period is defined by falling and lower lake levels with decreasing effective moisture windier conditions and sustained low aquatic productivity throughout the lgm between 29 600 and 19 600 cal yr bp the last deglaciation that commenced by 19 600 cal yr bp is characterized by gradual changes in several sediment physical and geochemical proxies including increasing c n ratios and terrestrial productivity decreasing magnetic susceptibility and clastic sediment flux along with rising and relatively higher lake levels a decrease in aeolian activity after 16 500 cal yr bp is inferred from the appearance of fine very fine sandy silt sediment compared to coarse sediments through the lgm and last deglaciation the highest levels of terrestrial inputs along with increasing and variable aquatic productivity occur during the lateglacial to early holocene interval between 16 500 and 8800 cal yr bp the absence of multi proxy evidence for a strong climatic reversal during the younger dryas from burial lake sediments contrasts with some paleorecords showing cooler temperatures and or dry conditions in northern alaska at this time peak levels of sediment organic content and terrestrial productivity at burial lake between 10 500 and 9900 cal yr bp coincide with the early holocene summer insolation maxima which likely represents summertime warming and an enhanced flux of watershed derived organic matter from permafrost degradation the remainder of the holocene since 8800 cal yr bp at burial lake is characterized by relatively high and stable lake levels landscape stabilization and relatively high and variable levels of aquatic productivity

a 16 000 yr long sedimentary sequence from lakes peters and schrader neruokpuk lakes northeastern brooks range alaska sediments that accumulate in high latitude lakes serve as valuable environmental archives of changing conditions in a region currently undergoing rapid change a previously unexplored sedimentary sequence reaching back 16 000 years from lakes peters and schrader neruokpuk lakes in the northeastern brooks range 69 n alaska shows distinct changes in accumulation rates and biophysical properties including bulk density bd organic matter om content and grain size distribution at five widely distributed core sites the oldest sediments contain little om and accumulated rapidly as glaciers retreated around 15 ka om peaked between 12 and 10 ka along with northern hemisphere summer insolation bd increased and om decreased until around 5 ka possibly reflecting a decrease in river transported terrestrial om from 5 2 ka om consistently increased suggesting a rise in river discharge or a rise in summer temperatures which led to higher productivity or both after 2 ka sediments increased in bd and decreased in om suggesting glacier growth evidence for glacier expansion late during the little ice age is weak but increased sedimentation rates may reflect glacier retreat during the last century this study provides a framework for future paleoenvironmental research of a rare archive in a relatively pristine arctic setting

holocene development of boreal forests and fire regimes on the kenai lowlands of alaska several studies have noted a relationship between vegetation type and fire frequency yet despite the importance of ecosystem processes such as fire the long term relationships between disturbance climate and vegetation type are incompletely understood we analysed pollen plant macrofossils and sedimentary charcoal from three lakes within the kenai lowlands to determine postglacial relationships between disturbance climate and vegetation for the boreal forest of southwest alaska an herb tundra was established in the lowlands following deglaciation by 13 000 cal bp salix alnus and probably betula kenaica expanded in the area after 10 700 cal bp followed by picea glauca by 8500 cal bp picea mariana became established by 4600 cal bp the early holocene was probably the driest time during the postglacial as determined by aquatic plant macrofossils and climate models lake levels reached near modern conditions by at least 8000 cal bp mean fire intervals mfi were longest during the shrubherb tundra phase 1389 65 yr decreased after expansion of b kenaica salix and populus 779 49 yr and picea glauca 819 41 yr and increased again with the arrival of p mariana 1309 66 yr unlike previous studies our data demonstrate the highest fire frequencies during the early to mid holocene and less frequent fire during the late holocene when p mariana forests dominated the lowlands early holocene forests of p glauca and b kenaica existed in summers that were longer and drier than today while the increasingly wetter and cooler climates of the late holocene probably hindered forest fire around paradox lake perhaps because of less frequent summer drought

lagrangian trajectories residual currents and rectification process in the northern gulf of california abstract considering a semi implicit approximation of the coriolis terms a numerical solution of the vertically integrated equations of motion is proposed to test the two dimensional numerical model several experiments for the calculation of euler stokes and lagrange residual currents in the gulf of california were carried out to estimate the lagrangian residual current trajectories of particles were also simulated the applied tidal constituents were m2 s2 k2 n2 k1 p1 and o1 at spring tides strong tidal velocities occur in the northern half of the gulf in this region of complex geometry depths change from a few meter in the northern shelf zone to more than 3000 m in the southern part in the archipelago region the presence of islands alters amplitude and direction of tidal currents producing a rectification process which is reflected in a clockwise circulation around tiburon island in the lagrangian residual current the rectification process is explained by the superposition of the euler and stokes residual currents residual current patterns show several cyclonic and anticyclonic gyres in the northern gulf of california numerical experiments for individual and combinations of several tidal constituents revealed a large variability of lagrangian trajectories

responses of an arctic landscape to lateglacial and early holocene climatic changes the importance of moisture many of the physical and biological processes that characterize arctic ecosystems are unique to high latitudes and their sensitivities to climate change are poorly understood stratigraphic records of land surface processes and vegetation change in the arctic foothills of northern alaska reveal how tundra landscapes responded to climatic changes between 13 000 and 8000 14 c yr bp peat deposition began and shrub vegetation became widespread ca 12 500 14 c yr bp probably in response to the advent of warmer and wetter climate increased slope erosion caused rapid alluviation in valleys and populus trees spread northward along braided floodplains before 11 000 14 c yr bp lake levels fell and streams incised their floodplains during the younger dryas yd 11 000 10 000 14 c yr bp a hiatus in records of populus suggest that its geographic range contracted and pollen records of other species suggest a cooler and drier climate during this interval basal peats dating to the yd are rare suggesting that rates of paludification slowed immediately after 10 000 14 c yr bp lake levels rose streams aggraded rapidly again intense solifluction occurred and populus re invaded the area moist acidic tundra vegetation was widespread by 8500 14 c yr bp along with wet organic rich soils most of these landscape scale effects of climatic change involved changes in moisture although low temperature is the most conspicuous feature of arctic climate shifts in effective moisture may be the proximate cause for many of the impacts that climate change has in arctic regions r 2002 elsevier science ltd all rights reserved

coseismic damage and softening of fault rocks at seismogenic depths abstract elastic stiffness a critical property for stress orientation propagation of earthquake ruptures and associated seismic waves and the capability of crustal rocks to store strain energy is expected to be highly variable throughout the seismic cycle due to complex sequences of damage and healing post seismic healing and exhumation related alteration render it impossible to assess how well rock stiffness as measured in the laboratory on samples collected from fault zones represents in situ coseismic rock stiffness at seismogenic depths here we estimate the in situ coseismic stiffness of fault rocks from the pseudotachylyte bearing gole larghe fault zone italian southern alps using aspect ratio measurements of pseudotachylyte injection veins and numerical simulations aspect ratios of injection veins cutting across tonalite and cataclasite exhibit a maximum vein aperture positively correlating with vein length to model vein opening fault and injection veins are assumed to be filled with pressurized melt consistent with recent results from studies of melt lubrication we assume that the magnitude of the melt pressure is in equilibrium with the fault normal stress and the fault vein approximately maintains constant thickness during slip the numerical simulations of injection vein opening due to pressurized frictional melt indicate that the average in situ coseismic stiffness of the wall rocks is 5 50 times smaller than the stiffness obtained from laboratory measurements on the same rocks in their present day state the disagreement between laboratory measurements and simulations brings into question the appropriateness of using laboratory derived values for rock stiffness to model coseismic processes at depth

ostracode geochemical record of holocene climatic change and implications for vegetational response in the northwestern alaska range abstract trace element analysis of the calcareous shells of ostracodes in a sediment core from farewell lake provides the first limno geochemical record for climatic reconstructions in alaska when compared with pollen data from the same site this record offers new insights into climatic controls over vegetation dynamics during the holocene the low mg ca ratios and high sr ca ratios suggest that a relatively cold dry climate prevailed in this region between 11 000 and 9000 yr b p uncalibrated14c ages are used throughout the paper this result contrasts with previous interpretations of a thermal maximum at this time corresponding to the widespread establishment ofpopuluswoodland forest the trace element record suggests instead that the warmest period of the early holocene at farewell lake was between 8500 and 8000 yr b p during the decline ofpopulus marked decreases in sr ca and mg ca suggest a major increase in effective moisture around 6500 yr b p which coincided with the establishment ofpiceaboreal forests in the farewell lake region this climatic change was probably widespread throughout much of alaska and adjacent canada and might have induced the rapid spread ofalnusand the shift frompicea glaucatop marianadominance across that region our geochemical record also suggests that the late holocene climate history was more complex than previously thought on the basis of palynological studies according to this record growing season temperatures increased 6000 4500 yr b p decreased 4500 1500 yr b p and increased with fluctuations afterward after 6000 yr b p stratigraphic changes in pollen percentages ofpiceaappear to be positively related with those of mg ca this relationship implies that once the threshold of effective moisture was crossed for the establishment ofpiceaforests temperature was the primary control ofpiceapopulation density

mechanisms for linear sandbank formation and maintenance in relation to dynamical oceanographic observations abstract theories associated with flow in the vicinity of headlands and sandbanks together with proposed mechanisms for sandbank formation and maintenance are reviewed to exemplify water and sand movement around a sandbank on a tidally dominated shelf tidal currents in the vicinity of a headland associated linear sandbank are described these data are integrated with sedimentological information on bedforms and grain size distributions the sandbank under detailed investigation the scarweather sands is located along the northern coastline of the bristol channel uk which is an area susceptible to high energy inputs the maximum spring tidal range here is around 10m and a 6000km fetch is available for storm wave approach from the atlantic ocean but the area is 460km from the shelf break detailed observations are presented from 11 long term current meter stations located within 10km of the sandbank currents are described in terms of residual water circulation shallow water harmonics and tidal ellipse characteristics bedload transport paths are inferred from the distribution of bedforms grain size and m2 m4 tidal current interactions transport vectors are predicted from near bed current meter observations combined with empirically derived formulae it is demonstrated that water circulation and sand transport paths form part of a clockwise eddy system around the sandbank mechanisms controlling the location and the characteristics of this particular sandbank are shown to be explicable in terms of a combination of models for sandbank formation and maintenance the results of the present study are thought to be applicable directly to headland associated sandbanks elsewhere it is shown on the basis of theoretical considerations that the pattern of residual water movement and possibly sand transport around this sandbank could be extended to continental shelves on a global basis

dated wood from alaska and the yukon implications for forest refugia in beringia abstract postulations on the existence of forest refugia in parts of beringia during the last glacial have been in large part based on ambiguous evidence existing data on radiocarbon dated and identified fossil wood and macrofossils from alaska and northwest canada are synthesized here and are augmented by results of palynological studies in an effort to show the persistence of some and total extinction of other tree and large shrub species possible dispersal routes taken by species that reinvaded beringia in postglacial times are also reconstructed from the fossil record macrofossil and pollen evidence when combined with climatic factors makes cottonwood a good candidate for survival during the last glacial larch and aspen are also candidates though the evidence for them is less positive pollen and macrofossils of alder are very scarce in deposits of the last glacial age and if it survived at all it was probably in very isolated vegetatively reproducing clones shrub birch may have been present in beringia but tree birch probably was reintroduced during the holocene spruce also appears to have been absent in alaska from about 30 000 to 11 500 yr ago and probably reinvaded beringia from a refugium south of the laurentide ice sheet

anisotropy in jointed rock mass breakage abstract cracks in a rock material are generally closed and have no volume effect on the rock material s deformational characteristics these closed cracks however markedly effect the rock materials strength joints on the other hand do have a volume effect on the rock mass s deformational behaviour as well as its strength or stability in order to define the rock mass s deformational characteristics the deformational moduli are expressed in terms of equilibrium and or compatibility models for complete definition of the rock mass s deformational moduli both models are required these models describe the deforming rock mass when there is no stress redistribution equilibrium model or when there is stress redistribution compatibility model for joints it is shown that both the equilibrium and compatibility models are required to define the rock mass s deformational characteristics while for cracks only the equilibrium model is required it is shown that shear moduli have major affects on the rock mass s deformational behaviour by incorporating joint shear strength and griffith crack energy initiation criteria griffith strength loci for hard and soft rock masses are obtained these strength loci are produced for both shear and pseudo young s rock mass moduli for the hard rock the strength loci are significantly different indicating that the rock mass s failure mode possesses different energy balances for the soft rock mass the two strength loci are similar indicating that in the rock mass s failure from either shear or direct deformation the energy balances are nearly equal this suggests that the soft rock mass has minimal size effects

interfacial friction induced pressure and implications for the formation and preservation of intergranular coesite in metamorphic rocks abstract the finding of intergranular coesite and coesite pseudomorphs has been taken as critical evidence to support that the formation of coesite was related to regional ultrahigh pressure uhp metamorphism rather than the pressure vessel effect previous laboratory deformation experiments found that coesite occurs in practically undeformed strain forbidden zones immediately adjacent to the piston sample interfaces while the mean stress applied to the specimen is remarkably lower than the quartz coesite equilibrium boundary the formation and preservation of intergranular coesite in eclogites from uhp metamorphic terranes and the occurrence of coesite in strain forbidden zones within experimentally deformed rocks can be more satisfactorily explained by the theory of interfacial friction induced pressure which is a well known in metal forging during certain episodes of fast tectonic deformation under high transient differential stresses the interfacial friction can induce very significant deformation pressures in thin layers of weak materials e g sio2 between large garnet crystals that are refractory and mechanically strong thus act as excellent anvils the local deformation pressure which deviates from the lithostatic value is likely an intrinsic property of highly constrained flows of weak materials between strong walls at least on a microstructural scale

holocene history of the great kobuk sand dunes northwestern alaska abstract located just north of the arctic circle the great kobuk sand dunes gksd are an inland dune field that is closely surrounded by boreal forest the history of the gksd tells us about changes in aridity a climatic parameter whose history is poorly understood at high latitudes vegetated dunes in several states of geomorphic preservation surround the active dune field today evidencing a complex history of holocene activity small lakes in the forest bordering the dunes accumulate wind blown sand we use 14 c dated lake sediment cores to reconstruct a continuous history of sand influx over the last 8000 yr the validity of this record is supported by limiting ages obtained from stratigraphic sections within the dune field the extent of the gksd underwent a fluctuating shrinkage coincident with neoglaciation this downsizing trend was interrupted by periods of increased sand deposition into lakes occurring 4800 4200 3300 2600 1300 700 and 300 100 calendar years ago aridity in the kobuk valley during the holocene probably was controlled by the frequency of north pacific storms entering the region in late summer our results describe the first continuous history of changing moisture balance for central beringia during the holocene and comprise a baseline against which future records of climatic and ecological change in this region can be compared

lateglacial and holocene isotopic and environmental history of northern coastal alaska results from a buried ice wedge system at barrow barrow the northernmost point in alaska is one of the most intensively studied areas in the arctic however paleoenvironmental evidence is limited for northern alaska for the lateglacial holocene transition for a regional paleoenvironmental reconstruction we investigated a permafrost ice wedge tunnel near barrow alaska the studied site was first excavated in the early 1960s and intercepts a buried ice wedge system at 3e6 m depth below the surface a multi methodological approach was applied to this buried ice wedge system and the enclosing sediments which in their combination give new insight into the late quaternary environmental and climate history results of geochronological sedimentological cryolithological paleoecological isotope geochemical and microbiological studies reflect different stages of mid to late wisconsin mw to lw allerod ad younger dryas yd preboreal pb and late holocene paleoenvironmental evolution the lwage of the site is indicated by ams dates in the surrounding sediments of 21 7 kyr bp at the lateral contact of the ice wedge system as well as 39 5 kyr bp below the ice wedge system it is only recently that in this region stable isotope techniques have been employed i e to characterize different types of ground ice the stable isotope record oxygen 18o hydrogen d of two intersecting ice wedges suggests different phases of the northern alaskan climate history from ad to pb with radiocarbon dates from 12 4 to 9 9 kyr bp ranging from 14 8 to 10 6 kyr cal bp stable isotope geochemistry of ice wedges reveals winter temperature variations of the lateglacial holocene transition including a prominent yd cold period clearly separated from the warmer ad and pb phases yd is only weakly developed in summer temperature indicators such as pollen for the northern alaska area and by consequence the yd cold stadial was here especially related to the winter season this highlights that the combination of winter and summer indicators comprehensively describes the seasonality of climate relevant processes in discrete time intervals the stable isotope record for the barrow buried ice wedge system documents for the first time winter climate change at the lateglacial holocene transition continuously and at relatively high likely centennial resolution

paleoecology of late glacial peats from the bering land bridge chukchi sea shelf region northwestern alaska insect fossils and pollen from late pleistocene nonmarine peat layers were recovered from cores from the shelf region of the chukchi sea at depths of about 50 m below sea level the peats date to 11 300 11 000 yr b p and provide a limiting age for the regional pleistocene holocene marine transgression the insect fossils are indicative of arctic coastal habitats like those of the mackenzie delta region mean july temperatures 10 6 14 c suggesting that 11 000 yr ago the exposed chukchi sea shelf had a climate substantially warmer than modern coastal regions of the alaskan north slope the pollen spectra are consistent with the age assignment to the birch interval 14 000 9000 yr b p the data suggest a meadow like graminoid tundra with birch shrubs and some willow shrubs growing in sheltered areas

the evolution of elastic moduli with increasing crack damage during cyclic stressing of a basalt from mt etna volcano article i nfo volcanic edifices such as mt etna italy are commonly subject to repeated cycles of stress over time due to the combination of magma emplacement from deep reservoirs to shallow depths and superimposed tectonic stresses such repeated stress cycles lead to anisotropic deformation and an increase in the level of crack damage within the rocks of the edifice and hence changes to their elastic moduli which are a key parameter for reliable modelling of deformation sources we therefore report results of changes in elastic moduli measured during increasing amplitude cyclic stressing experiments on dry and water saturated samples of etna basalt in all experiments the young s modulus decreased by approximately 30 over the total sequence of loading cycles and the poisson s ratio increased by a factor of approximately 3 0 5 microseismicity in terms of acoustic emission ae output was also recorded throughout each experiment our results demonstrate that ae output only re commences during any loading cycle when the level of stress where ae ceased during the unloading portion of the previous cycle is exceeded a manifestation of the kaiser stress memory effect in cycles where no ae output was generated we also observed no change in elastic moduli this result holds for both mechanical and thermal stressing our results are interpreted in relation to measurements of volcano tectonic seismicity and deformation at mt etna volcano

structural response and rock bolting of a rock mass abstract stability of a discontinuous rock mass represented as a blocky rock mass is examined and defined in terms of stress redistribution and formation of hinges the anisotropic compliance of the rock mass controls the initial stress distribution and as small deformational rotations occur finite deformations with the anisotropic compliances control the stress redistributions these stress redistributions induce and intensify stress gradients which in turn encourage further rotations and stress redistributions mechanistic deformations such as slip and rotation cause the blocky mass to act as a structure with the formation of hinges these hinges localise the resultant force at a hinge the force can change its magnitude and line of action but it cannot change its point of application stability of the blocky rock mass is considered in terms of redundancy and as each hinge is formed the redundancy is reduced beaming and arching as a means of load and stress redistribution are examined control of beaming and arching by using rock bolts is considered in relation to stress redistribution and inhibiting the formation of hinges

late quaternary history of tundra vegetation in northwestern alaska pollen analysis of a new core from joe lake indicates that the late quaternary vegetation of northwestern alaska was characterized by four tundra and two forest tundra types these vegetation types were differentiated by combining quantitative comparisons of fossil and modern pollen assemblages with traditional qualitative approaches for inferring past vegetation such as the use of indicator species although imprecisely dated the core probably spans at least the past 40 000 yr a graminoid salix tundra dominated during the later and early portions of the glacial record the middle glacial interval and the transition from glacial to interglacial conditions are characterized by a graminoid betula salix tundra a populus forest betula shrub tundra existed during the middle potion of this transition being replaced in the early holocene by a betula alnus shrub tundra the modern picea forest shrub tundra was established by the middle holocene these results suggest that the composition of modem tundra communities in northwestern alaska developed relatively recently and that throughout much of the late quaternary tundra communities were unlike the predominant types found today in northern north america although descriptions of vegetation variations within the tundra will always be restricted by the innate taxonomic limitations of their herb dominated pollen spectra the application of multiple interpretive approaches improves the ability to reconstruct the historical development of this vegetation type

experimental investigation of the mechanical properties of synthetic magnesium sulfate hydrates implications for the strength of hydrated deposits on mars 1 we have carried out uniaxial compression experiments to determine the mechanical properties of three crystalline magnesium sulfate hydrates that may be present in the near surface environment of mars our synthetic samples of kieserite mgso4 h 2o epsomite mgso4 7 h2o and meridianiite mgso4 11h2o have mean values of unconfined compressive strength of 6 3 0 7 12 9 1 8 and 30 1 4 5 mpa respectively young s modulus of 0 8 0 1 2 9 0 4 and 5 9 0 8 gpa respectively and mean porosity values of 47 8 0 5 11 1 0 6 and 2 9 0 2 respectively although our tests cannot quantify a systematic relationship between hydration state and mechanical properties the different porosities produced by consistent sample preparation methods suggest that the addition of non cation coordinated water molecules likely reduces the strength of individual sulfate hydrate phases however the bulk mechanical properties of our synthetic specimens are instead controlled predominantly by the sample porosity generally the strength increases as the porosity decreases we expect the mechanical properties of sulfate hydrate deposits on mars to be governed by the bulk porosity rather than the strength of the pure solid phase we have performed cyclic stressing tests replicating possible periodic depositional and erosional periods on mars resulting from obliquity changes a gradual compaction and reduction in sample porosity rather than an increase in crack damage is observed with each loading cycle suggesting that the evolution of mechanical properties will depend on local factors such as bulk density in addition to the overall stress history

full glacial upland tundra vegetation preserved under tephra in the beringia national park seward peninsula alaska the nature of the full glacial vegetation of beringia has been the subject of a great deal of investigation and debate here we present a reconstruction of an intact example of the full glacial upland vegetation of part of the northern seward peninsula at one point in time the area was blanketed by more than 1 m of tephra ca 18 000 14c bp ca 21 500 cal bp and the former land surface was preserved in the permafrost the discovery of the land surface provides a unique opportunity to study a fossil ecosystem preserved in situ macrofossils were used to reconstruct the vegetation growing at several sites on the buried land surface the macrofossil assemblages indicate a vegetation characterized by graminoids and forbs with the occasional occurrence of salix arctica the vegetation was dominated by kobresia myosuroides other sedges carex and grasses with a ne scale mosaic related to snow accumulation and moisture availability overall the vegetation was a closed dry herb rich tundra grassland with a continuous moss layer growing on calcareous soil that was continuously supplied with loess nutrient renewal by loess deposition was probably responsible for the relatively fertile vegetation and the occurrence of a continuous mat of acrocarpous mosses good physiognomic analogues can be suggested but no exact modern vegetational analogues have been found probably because the full glacial environment and climate with loess deposition do not occur today 2000 elsevier science ltd all rights reserved

thermoluminescence dating of an arctic lake core from alaska abstract eight samples were selected from a 14 m core record from squirrel lake in the alaskan arctic for fine grain partial bleach thermoluminescence tl dating nine radiocarbon 14 c ages were available for comparison three tl ages of 8 8 to 11 6 ka in the upper 2 5 m do not exceed calendar corrected 14 c ages suggesting that zeroing of light sensitive tl in the detrital feldspars has been effective enough in this depositional environment to allow accurate dating of deeper core samples of similar sedimentology tl ages of 60 65 ka for two samples in the 4 9 7 m depth range are consistent with an infinite 14 c age of 38 6 ka at 5 8 m tl ages from 83 11 to 125 31 for three samples in the depth range 11 13 5 m suggest that this core record encompasses the last interglacial period 80 130 ka these first tl ages for sediments from an arctic lake core demonstrate the potential of the method for providing a directly measured chronology beyond the radiocarbon dating range in the climatically sensitive arctic regions

climate change and arctic ecosystems 1 vegetation changes north of 55 n between the last glacial maximum mid holocene and present a unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55 n at the last glacial maximum lgm and mid holocene 6000 years b p the pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups five tundra types cushion forb tundra graminoid and forb tundra prostrate dwarf shrub tundra erect dwarf shrub tundra and low and high shrub tundra were distinguished and mapped on the basis of modern pollen surface samples the tundra forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed during the mid holocene the tundra forest boundary was north of its present position in some regions but the pattern of this shift was strongly asymmetrical around the pole with the largest northward shift in central siberia 200 km little change in beringia and a southward shift in keewatin and labrador 200 km low and high shrub tundra extended farther north than today at the lgm forests were absent from high latitudes graminoid and forb tundra abutted on temperate steppe in northwestern eurasia while prostrate dwarf shrub erect dwarf shrub and graminoid and forb tundra formed a mosaic in beringia graminoid and forb tundra is restricted today and does not form a large continuous biome but the pollen data show that it was far more extensive at the lgm while low and high shrub tundra were greatly reduced illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types

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

eastern beringia and beyond late wisconsinan and holocene landscape dynamics along the yukon coastal plain canada terrestrial permafrost archives along the yukon coastal plain northwest canada have recorded landscape development and environmental change since the late wisconsinan at the interface of unglaciated beringia i e komakuk beach and the northwestern limit of the laurentide ice sheet i e herschel island the objective of this paper is to compare the late glacial and holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice analyses at these sites involved a multi proxy approach including sedimentology cryostratigraphy palaeoecology of ostracods stable water isotopes in ground ice hydrochemistry and ams radiocarbon and infrared stimulated luminescence irsl dating ams and irsl age determinations yielded full glacial ages at komakuk beach that is the northeastern limit of ice free beringia herschel island to the east marks the late wisconsinan limit of the northwest laurentide ice sheet and is composed of ice thrust sediments containing plant detritus as young as 16 2 cal ka bp that might provide a maximum age on ice arrival late wisconsinan ice wedges with sediment rich fillings on herschel island are depleted in heavy oxygen isotopes mean delta o 18 of 29 1 parts per thousand this together with low d excess values indicates colder than modern winter temperatures and probably reduced snow depths grain size distribution and fossil ostracod assemblages indicate that deglaciation of the herschel island ice thrust moraine was accompanied by alluvial proluvial and eolian sedimentation on the adjacent unglaciated yukon coastal plain until similar to 11 cal ka bp during a period of low glacio eustatic sea level the late glacial holocene transition was marked by higher than modern summer temperatures leading to permafrost degradation that began no later than 11 2 cal ka bp and caused a regional thaw unconformity cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone thermokarst activity led to the formation of ice wedge casts and deposition of thermokarst lake sediments these were subsequently covered by rapidly accumulating peat during the early holocene thermal maximum a rising permafrost table reduced peat accumulation and extensive ice wedge growth resulted from climate cooling starting in the middle holocene until the late 20th century the reconstruction of palaeolandscape dynamics on the yukon coastal plain and the eastern beringian edge contributes to unraveling the linkages between ice sheet ocean and permafrost that have existed since the late wisconsinan

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

stratigraphy of the colorado creek mammoth locality alaska abstract the colorado creek mammoth locality in west central alaska contains the remains of two mammoths that were scavenged by carnivores sedimentologic interpretations of the reworked eolian deposits surrounding the bones supplemented by 10 radiocarbon dates indicate that the lower and upper mammoths died and were buried within separate but superimposed thaw gullies about 23 000 and 16 000 yr ago respectively from our results we propose a polycyclic taphonomic model for thaw gullies governed largely by slope aspect rather than regional climate and in which mixing between faunal horizons is more likely than not variations in the rate of silt influx and the position of the permafrost table provide a paleoclimatic proxy record that can be correlated to other records in eastern beringia

lateglacial and holocene paleoenvironmental changes recorded in lake sediments brock plateau melville hills northwest territories canada sediments from south lake brock plateau melville hills northwest territories provide one of the longest postglacial records from the mainland western canadian arctic outside of eastern beringia sedimentation commenced at least 13 900 cal yr bp and possibly as early as 16 000 cal yr bp in response to early deglaciation of the site pollen is present throughout the record with an initial artemisia salix assemblage indicative of very cold conditions consistent with a locally severe younger dryas stade or simply continued proximity of the laurentide ice sheet margin c 12 700 to 11 500 cal yr bp at c 11 000 cal yr bp abiotic proxies signal a transition to warmer conditions corroborated by a pollen assemblage dominated by betula and cyperaceae although south lake was biologically productive during the early holocene c 11 000 to 7000 cal yr bp diatoms and other siliceous organisms are notably absent from the record suggesting severe silica limitation rises in alnus crispa and picea mariana pollen at c 7000 cal yr bp suggest cooling and or an increase in effective moisture wetter conditions and increased hydrological inputs and silica supply likely led to the establishment of a pioneering diatom community at c 6500 cal yr bp decreased organic sedimentation after c 2000 cal yr bp suggests cooler conditions additionally changing niveo eolian deposition of sand on lake ice varied with a c 3000 year periodicity through the entire record the south lake multiproxy record supports the hypothesis that the brock plateau was one of the earliest deglaciated regions during the late wisconsinan

a re evaluation and spatial analysis of evidence for a younger dryas climatic reversal in beringia abstract an objective classification of paleoclimatic proxies from 75 lake and peat records is used to re evaluate data quality and inferred climatic patterns in beringia during the younger dryas mapped data reveal coherent but spatially complex regional patterns suggesting the younger dryas was characterized by 1 cooling in southern alaska eastern siberia and portions of northeastern siberia and 2 uniform to warmer than present conditions through most of central alaska northeastern siberia and possibly the russian far east and northern alaska the beringian patterns correspond to distinctive large scale climatic forcings although in some locations further modified by more local influences such as topography general circulation models and modern synoptic climatology provide a conceptual framework for exploring possible mechanisms responsible for the observed changes forcings and associated climatic responses consistent with the proxy data include 1 lowered sea surface temperatures in the north atlantic and pacific reducing temperature and precipitation in eastern siberia 2 intensified aleutian low and lowered sea surface temperatures causing cooler summers and higher winter precipitation in southern alaska 3 stronger pacific subtropical high and an eastward shift of the east asian trough reducing summer temperatures in southern alaska and causing relative warmth in northeastern siberia and 4 strong high pressure system producing warm dry conditions in interior alaska

texture mineralogy and rock strength in horizontal stress related coal mine roof falls abstract geologic structures can represent planes of preferential weakness that by dismembering the roof beam may contribute to the failure of roof spans however beam deflection and roof failure also occur in rocks where no visible geologic discontinuities are present this suggests that roof failure may depend on rock strength which in turn depends on intrinsic textural properties inherent to the rock in this study rock samples were collected from horizontal stress related roof fall material in coal mines for petrographic characterization and compressive strength testing brittle stress failure prone rock types include thinly interlaminated siltstone and shale and black shale that had been lightly recrystallized samples exhibit a narrow range of density values between approximately 2 5 3 0 g cm3 but exhibit a wide range of unconfined compressive strength values between approximately 20 70 mpa results of laboratory observations suggest that for samples of coal mine immediate roof shale compressive strength is not well correlated with density grain size sutured grain boundaries or quartz content these results for shale are generally at odds with the results of similar studies for sandstone the great variability of strength texture and mineralogy documented in these samples may be an indication of their complexity and the need for specialized methodology in the study of shale strength

postglacial vegetation and climate change in the northern bristol bay region southwestern alaska pollen analysis of sediment cores from grandfather and ongivinuk lakes reveals a record of postglacial vegetation and climate change in the northern bristol bay region the chronology is based on six conventional 14c dates of bulk organic matter from the grandfather core a mesic herb tundra dominated the landscape 13 000 9800 yr b p betula shrubs probably first appeared in the region 11 300 yr b p but were restricted to favorable microhabitats until 9800 yr b p the later establishment of betula shrubs and relatively low betula pollen abundance in these records compared to other areas of eastern beringia suggest that postglacial warming in southwestern alaska was dampened by regional climatic controls possibly low sea surface temperatures of the north pacific ocean between 10 800 and 9800 yr b p diminished betula shrub cover along with decreased aquatic productivity as recorded by pediastrum cell nets and biogenic silica suggest a brief reversion to colder and drier climatic conditions possibly associated with the younger dryas event around 9800 yr b p betula shrub tundra and meadow communities expanded probably in response to increased temperature and precipitation alnus arrived and formed extensive thickets within the region ca 7400 yr b p the establishment of the modern boreal forest tundra ecotone is marked by the arrival of picea glauca at grandfather lake ca 4000 yr b p and the subsequent increase to present population densities ca 2000 yr b p the unique features of these pollen records emphasize the spatial complexity of late quaternary vegetation and climate history in eastern beringia

late pleistocene vertebrates and other fossils from epiguruk northwestern alaska abstract sediments exposed at epiguruk a large cutbank on the kobuk river about 170 km inland from kotzebue sound record multiple episodes of glacial age alluviation followed by interstadial downcutting and formation of paleosols vertebrate remains from epiguruk include mammoth bison caribou an equid a canid arctic ground squirrel lemmings and voles radiocarbon ages of bone validated by concordant ages of peat and wood span the interval between about 37 000 and 14 000 yr b p the late pleistocene pollen record is dominated by cyperaceae with artemisia salix betula and gramineae also generally abundant the fossil record from epiguruk indicates that the kobuk river valley supported tundra vegetation with abundant riparian willows during middle and late wisconsin time large herbivores were present during the height of late wisconsin glaciation as well as during its waning stage and the preceding interstadial interval the kobuk river valley would have been a favorable refugium for plants animals and possibly humans throughout the last glaciation

late quaternary vegetational change in the kotzebue sound area northwestern alaska abstract two sediment cores from kaiyak and squirrel lakes in northwestern alaska yielded pollen records that date to ca 39 000 and 27 000 yr b p respectively between 39 000 and 14 000 yr b p the vegetation around these lakes was dominated by gramineae and cyperaceae with some salix and possibly betula nana glandulosa forming a local shrub component of the vegetation betula pollen percentages increased about 14 000 yr b p indicating the presence of a birchdominated shrub tundra alnus pollen appeared at both sites between 9000 and 8000yr b p and picea pollen mostly p mariana arrived at squirrel lake about 5000 yr b p the current foresttundra mosaic around squirrel lake was established at this time whereas shrub tundra existed near kaiyak lake throughout the holocene when compared to other pollen records from north western north america these cores 1 represent a meadow component of lowland beringian tundra between 39 000 and 14 000 yr b p 2 demonstrate an early holocene arrival of alnus in northwestern alaska that predates most other alnus horizons in northern alaska or northwestern canada and 3 show an east to west migration of picea across northern alaska from 9000 to 5000 yr b p

late quaternary pollen records from the kobuk and noatak river drainages northwestern alaska abstract pollen diagrams from joe and niliq lakes date to ca 28 000 and 14 000 yr b p respectively mesic shurb tundra grew near joe lake ca 28 000 to 26 000 yr b p with local populus populations prior to ca 27 000 yr b p shrub communities decreased as climate changed with the onset of itkillik ii glaciation 25 000 to 11 500 yr b p and graminoid dominated tundra characterized vegetation ca 18 500 to 13 500 yr b p herb tundra was replaced by shrub betula tundra near both sites ca 13 500 yr b p with local expansion of populus ca 11 000 to 10 000 yr b p and alnus ca 9000 yr b p mixed picea glauca p mariana woodland was established near joe lake ca 6000 yr b p these pollen records when combined with others from northern alaska and northwestern canada indicate 1 mesic tundra was more common in northwestern alaska than in northeastern alaska or northwestern canada during the duvanny yar glacial interval 25 000 to 14 000 yr b p 2 with deglaciation shrub betula expanded rapidly in northwestern alaska but slowly in areas farther east 3 an early postglacial thermal maximum occurred in northwestern alaska but had only limited effect on vegetation and 4 pollen patterns in northern alaska and northwestern canada suggest regional differences in late quaternary climates

late quaternary vegetational history of the black river region in northeastern alaska two pollen diagrams describe the previously unknown vegetational history of the black river and little black river drain ages of northeastern alaska tundra grew throughout much of the region between ca 19 800 and 15 000 years bp prior to 18 000 years bp the vegetation was dominated perhaps by xeric cyperaceae communities but apparently between ca 18 000 and 15 000 years bp a more diverse herb tundra characterized the vegetation herbaceous species continued to be important in the vegetation until ca 9700 years bp although betula nana glandulosa and salix species became more common after 15 000 years bp at ca 9700 years bp a major change in the vegetation occurred with the spread of populus probably p balsamifera b nana glandulosa and salix possibly resulting in a mosaic of shrub tundra and populus gallery forest picea glauca migrated into the black river region ca 7500 years bp followed by alnus ca 7200 years bp and picea mariana ca 6000 years bp herb zone records from the black rive

the lateglacial and postglacial vegetation history of the northwestern limits of beringia based on pollen stomate and tree stump evidence abstract in order to reconstruct the late and postglacial vegetation history of the northwestern edge of beringia a sediment core was collected from a lake north of the present treeline along the lower lena river of northeastern siberia and analysed for fossil pollen and stomates in addition fossil tree stumps were collected in the vicinity of the lake eight radiocarbon dates indicate that the lake sediment record spans at least the past 12 300 yr bp the early vegetation at this site was dominated by herb and shrub tundra possible evidence of younger dryas cooling consisting of a decrease in shrub birch and increases in grass and herbaceous plants occurs between 11 000 and 10 000 yr bp forests dominated by larix dahurica and including picea obovata extended northward to the site between 8500 and 3500 yr bp there is an agreement between the pollen stomate and tree stump evidence for this advance the modern vegetation of shrub tundra was established after 3500 yr bp

the rheological transition in plagioclase bearing magmas 1 volcanological processes such as melt segregation ascent and eruption are directly dependent on the rheological behavior of magmatic suspensions an increase of the crystal fraction of the suspension leads to the formation of a solid particle network which abruptly increases magma viscosity the crystal fraction at which this rheological transition occurs depends on parameters such as the strain rate and the size shape and sorting of particles to determine the influence of the crystal shape on the rheological transition suspensions of plagioclase a representative anisometric crystal have been investigated at high temperatures and pressures synthetic suspensions with crystal fractions s ranging from 0 38 to 0 75 were deformed both in compression and torsion in a paterson apparatus at 300 mpa 900 c and 800 c and for strain rates between 1 0 10 5 and 1 0 10 3 s 1 all suspensions exhibit a non newtonian shear thinning rheological behavior the experimental results coupled with existing data and models at low crystal fractions s 0 3 allow several rheological domains to be identified from steady state flow to strain weakening each characterized by a specific microstructure in particular a progressive evolution from a pervasive to a strain partitioning fabric is found when increasing the crystal fraction our results highlight the influence of both the strain rate and the shape of crystals on the rheological behavior of magmas during crystallization magmatic suspensions of anisometric minerals such as plagioclase would develop a solid particle network earlier s 0 3 than suspensions of isometric minerals s 0 5 our study shows that localization of strain early in the crystallization history of mushy zones in the magma chamber near the conduit margins and at the base of lava flows would facilitate the mobilization the transfer and the final emplacement at the surface of highly viscous feldspar rich magmas

late quaternary lacustrine pollen records from southwestern beringia sediment cores from three lakes in the upper kolyma region northeast russia provide the first well dated continuous record of late quaternary vegetation change from far southwestern beringia the oldest pollen zone tentatively assigned to the karginsk mid wisconsinan interstade indicates an artemisia shrub tundra with pinus pumila betula and alnus at mid to low elevations with the onset of the sartan late wisconsinan stade pinus disappeared probably indicating severely cold dry winters and cool summers as conditions deteriorated further an artemisia gramineae tundra developed selaginella rupestris and minor herb taxa indicate the presence of poor soils and disturbed ground this herb tundra was replaced by a short lived 1000 yr betula alnus shrub tundra followed by the rapid establishment of a larix dahurica forest with a betula exilis ericales lichen understory populus suaveolens and chosenia may have formed limited hardwood gallery forests at this time modern vegetation associations probably developed during the early holocene with the arrival of pinus pumila ca 9000 yr b p this shrub became important in the forest understory and with b exilis formed a belt of shrub tundra beyond altitudinal treeline comparison of the upper kolyma and alaskan pollen records indicates that important differences in vegetation types and timing of vegetation change occurred across beringia during the late quaternary

rock creep and the development of the niagara cuesta this work addresses the post glacial development of the niagara escarpment speci cally the east facing scarp slopes between hamilton and collingwood the escarpment is one of a series of scarps that shape the great lakes basin one interpretation suggests that the escarpment has evolved through homoclinal recession to the west it is therefore viewed as an erosional feature brought about due to uvial action on the weaker shale formations that underlie the cap rock however the deposition of large amounts of drift during the pleistocene glaciation has resulted in the disruption of the preglacial drainage pattern within the great lakes basin therefore the current drainage is typically orthogonal to the scarp face with an absence of uvial action along the base consequently the cuesta is experiencing an extremely slow rate of retreat conventional thinking on the evolution of the present morphology suggests that it developed rapidly following deglaciation due to periglacial processes the concept of the escarpment as a relict feature during the holocene therefore pervades the modern literature however the cambering of the cap rock towards the scarp face and the apparent motion of individual joint bounded blocks indicates that in the absence of exogenetic processes a slow development due to endogenetic processes has dominated the modern development of the escarpment it has been proposed that the present morphology of the cliffed sections may be due to deformation within the shale layers in order to test this hypothesis the rheology of the rocks that form the escarpment was tested and compared to the gravitational stresses that would be expected within the rock mass the results indicate that the compressive strength of the shale layers of the cabot head formation is lower than the expected effective stresses it is therefore concluded that in the absence of high con ning stresses as would be expected near the cliff face slow plastic deformation within this formation is occurring the morphological expression of this deformation is seen in the cambering of the escarpment the dilation of pre existing joints and the rotation of joint bounded blocks

predicted and measured rock mass moduli abstract plate bearing and rock bolt jacking tests are used to measure the in situ deformational response of four jointed rock masses namely sandstone limestone shale and coal samples representing the intact rock and joint material were retrieved from the test sites and examined in the laboratory while performing the joint shear strength tests the joint normal and shear stiffnesses were also measured the predicted values of the rock mass moduli were evaluated using composite theory and the laboratory determined joint stiffnesses and intact rock moduli when evaluating the predicted rock mass moduli lower bound composite formulations were used these predicted rock mass moduli were then compared with the measured in situ deformational moduli joint shear stiffness is an order that is 10 times less than the joint normal stiffness and this has the important effect of disproportionally increasing the deformational response the in situ measured moduli correlate reasonably well with the predicted moduli evaluated from the lower bound deformational formulations however good correlation is obtained when the lower values of joint stiffnesses are used in the lower bound deformational formulations

low and high frequency climate variability in eastern beringia during the past 25 000 yearsthis article is one of a series of papers published in this special issue on the theme polar climate stability network we present new temperature and precipitation reconstructions for the past 25 000 cal years bp from across eastern beringia based on a network of pollen diagrams an updated modern pollen calibration database and an improved methodology using the modern analogue technique mat time series show july temperatures were around 4 c lower during full glacial and january temperatures were about 2 c lower than present annual temperatures rose beginning around 16 000 cal years bp reaching a maximum around 12 000 cal year bp the warming was more rapid in southern beringia annual precipitation varied by 250 mm during the past 25 000 cal years bp maps of reconstructed precipitation patterns show increasingly drier conditions since 12 000 cal years bp that vary regionally suggesting holocene atmospheric circulation changes at multiple time and space scales orbitally forced seasonality changes during the late glacial and early holocene resulted in reversed seasonal temperature reconstructions due to me

holocene landscape development and climatic change in the low arctic northwest territories canada abstract holocene landscape development in the low arctic tundra zone was studied through fossil pollen analysis and sedimentary studies of a radiocarbon dated core of lake sediment the results indicate that holocene landscape development in this area consists of three main stages the first stage occurred between 8500 and 6300 14c yr b p when the local vegetation shifted from a herb and graminoid tundra to betula shrub tundra and finally to spruce forest tundra following the regional deglaciation soil erosion decreased greatly in response to vegetation development the second stage is between 6300 and 3000 14c yr b p during which spruce forest tundra was developed and catchment soil erosion decreased due to increased vegetative cover the chronological difference of several hundred years in the rise of black spruce population among the treeline sites may have been caused by edaphic conditions during the third stage from 3000 14c yr b p to the present vegetation degraded to the modern betula dominated shrub tundra peatlands expanded to its modern extent in the treeline zone from 1300 14c yr b p it seems treeline advanced northerly ca 50 km beyond its present position between 6300 and 3000 14c yr b p reflecting likely a northward retreat of the polar front following the demise of the ice sheet in the middle holocene the retreat of the treeline at ca 3000 14c yr b p may have been responded to an expansion of the north polar vortex or an intensification of the meridional airflow

extending the geochronometry of arctic lake cores beyond the radiocarbon limit by using thermoluminescence reconstructing detailed paleoclimatic paleoenvironmental histories from pleistocene sediments in the arctic is an ongoing challenge because of the difficulty of measuring accurate timescales beyond the range of radiocarbon 14c dating important archives of such histories are arctic lakes that exist outside the known extent of the last major glaciations to develop reliable geochronometry of sediment cores from arctic and other lakes we applied thermoluminescence tl sediment dating methods to 24 samples 8 reported earlier but some reanalyzed here selected from cores from squirrel and joe lakes in northwestern alaska a sequence of 23 14c ages from the upper parts of these cores permitted tests of the zeroing assumption of tl dating that all fine silt grains were exposed to daylight before final burial we performed multiple tl tests on most samples to isolate stable tl signals and measured tl emissions spectra to help characterize samples tl ages generally agree with the 30 kyr age depth trend derived from 14c dating and extend the timescale apparently to 180 ka for squirrel lake and to at least 60 ka for joe lake an anomalously old tl result from squirrel lake is attributed to failure of the tl zeroing assumption within that sediment horizon in the lower joe lake core we assign a timing of 45 ka to 50 ka for the beginning of an apparently climatic warming interval these results identify and quantify the main tl sources of tl age inaccuracy and the preferred tl protocols for accurate tl sediment dating in northern high latitude lake deposits they also provide the first direct chronology beyond the 14c dating range for these lakes

late quaternary paleoclimate of western alaska inferred from fossil chironomids and its relation to vegetation histories abstract fossil chironomidae assemblages with a few chaoboridae and ceratopogonidae from zagoskin and burial lakes in western alaska provide quantitative reconstructions of mean july air temperatures for periods of the late middle wisconsin 39 000 34 000 cal yr b p to the present inferred temperatures are compared with previously analyzed pollen data from each site summarized here by indirect ordination paleotemperature trends reveal substantial differences in the timing of climatic warming following the late wisconsin at each site although chronological uncertainty exists zagoskin lake shows early warming beginning at about 21 000 cal yr b p whereas warming at burial lake begins 4000 years later summer climates during the last glacial maximum lgm were on average 3 5 c below the modern temperatures at each site major shifts in vegetation occurred from 19 000 to 10 000 cal yr b p at zagoskin lake and from 17 000 to 10 000 cal yr b p at burial lake vegetation shifts followed climatic warming when temperatures neared modern values both sites provide evidence of an early postglacial thermal maximum at 12 300 cal yr b p these chironomid records combined with other insect based climatic reconstructions from beringia indicate that during the lgm 1 greater continentality likely influenced regions adjacent to the bering land bridge and 2 summer climates were at times not dominated by severe cold

a 40 000 yr record of environmental change from burial lake in northwest alaska abstract burial lake in northwest alaska records changes in water level and regional vegetation since 39 000 cal yr bp based on terrestrial macrofossil ams radiocarbon dates a sedimentary unconformity is dated between 34 800 and 23 200 cal yr bp during all or some of this period there was a hiatus in deposition indicating a major drop in lake level and deflation of lacustrine sediments mis 3 vegetation was herb shrub tundra more xeric graminoid herb tundra developed after 23 200 cal yr bp the tundra gradually became more mesic after 17 000 cal yr bp expansions of salix then betula at 15 000 and 14 000 cal yr bp respectively are coincident with a major rise in lake level marked by increasing fine grained sediment and higher organic matter content several sites in the region display disrupted sedimentation and probable hiatuses during the last glacial maximum lgm together regional data indicate an arid interval prior to and during the lgm and continued low moisture levels until 15 000 cal yr bp ams 14c dates from burial lake are approximately synchronous with ams 14c dates reported for the betula expansion at nearby sites and sites across northern alaska but 1000 2000 yr younger than bulk sediment dates

a late pleistocene glacial chronology for the southern brooks range stratigraphic record and regional significance radiocarbon dates from 11 measured sections in the koyukuk region provide a chronology of the last pleistocene glaciation glaciers were advancing strongly by 24 000 yr ago they built moraines near the south flank of the brooks range retreated briefly about 22 000 to 20 000 yr b p then readvanced at least one more time into their terminal zones glaciation was accompanied by alluviation of the koyukuk and kobuk drainage systems and by periglacial processes that resemble those taking place today farther north and at higher altitudes moraines near the south flank of the range were being revegetated by 13 500 yr b p a strong final readvance into end moraine belts of some northern valleys occurred about 13 000 to 12 500 yr ago and this event may be synchronous with less extensive glacier readvances in upper valleys of the koyukuk region upper valleys were largely deglaciated by 11 800 yr b p dated stratigraphic sections from the northern alaska range show similar ages for initiation and close of glaciation and also suggest a possible interstadial episode about 20 000 yr ago scanty records of fluctuations during ice wastage probably reflect the general scarcity of datable wood peat and organic soils between about 19 500 and 13 500 yr ago the brooks range and alaska range chronologies closely approximate glacial successions determined else where in eastern beringia and in siberia advance and retreat of glaciers throughout this region evidently were associated with widespread climatic changes that also controlled the late wisconsin history of the laurentide ice sheet the itkillik ii and late itkillik phases of former usage are part of a single glaciation that was entirely separate from the preceding itkillik i ice advance for this reason the local term walker lake glaciation is here extended to the last major glaciation of the entire southern brooks range and use of itkillik phases should be discontinued the term itkillik glaciation is hereby restricted to the next older ice advance in accord with its original definition cold and dry conditions during the last glaciation of eastern beringia are indicated by 1 relatively small mountain glaciers 2 slight 200 m depression of glaciation limits below modern values 3 periglacial features indicating severe frost action on slopes with little protective plant cover 4 widespread accretion of eolian sand 5 low pollen influx rates 6 scarcity of radiocarbon datable organic remains and 7 general absence of carbonaceous paleosols plant growth may have been much more restricted than generally believed with relatively low capacity to support grazing animals and human hunting bands

climate and vegetation in northeastern alaska 18 000 yr b p present changing abundances of taxa in the pollen record of northeastern alaska contain a climate signal and may be compared with gcm simulations of paleoclimates cold dry conditions indicated by full glacial pollen spectra are in broad agreement with model simulations successive expansion of betula and salix and later populus during the deglacial period 14 000 11 000 yr b p are likely correlated with the crossing of temperature thresholds determined largely by the size and position of the laurentide ice a degree of asynchroneity between sites probably reflects differential site responses to regional effects plus inaccuracies of radiocarbon dating the early holocene was probably the warmest period of the present interglacial as summer climate was influenced by a strong positive insolation anomaly picea glauca expanded in majorr river valleys ca 9000 yr ago and slightly later at upland sites in the brooks and alaska ranges at some sites a juniperus subzone which suggests particularly warm and dry conditions occurs between ca 10 000 and 8000 yr b p early mid holocene expansions of alnus 8500 7000 yr b p and picea mariana 7500 5000 yr b p suggest the subsequent development of moister conditions which have continued to the present temporal patterns in picea treeline position during the holocene are different in northern alaska northwestern canada and central canada in alaska the treeline is currently at its furthest holocene extent in northwestern canada the treeline has retreated since the mid holocene and in central canada a mid holocene advance and retreat occurred such differences between regions suggest a complex response of this taxon to climatic controls and underscore the need to interpret vegetation changes in relation to regional scale climate phenomena if the pollen chronology is calibrated with reference to u th dates the relationship of vegetational events to the insolation maximum at ca 10 000 yr b p is significantly altered the changed chronology also affects the interpretation of pollen records in relation to gcm simulations which are partly keyed to calendar years