block distributions on itokawa abstract asteroid 25143 itokawa is a small elongated asteroid with two distinct parts the evolution of this two part body has been the source of speculation the scenarios for the formation of this asteroid include two body capture catastrophic disruption and rapid reaccretion yorp spin up and mass shedding and disruption or partial disruption with two body reaccretion in this paper we use the global and regional analyses of block populations and size frequency distributions as evidence of the probable evolutionary history of itokawa the block sample used in this study is believed to be complete for blocks of size 6 m and consists of a sample more than twice as large as previous known studies although block size frequency distributions hint at different evolutionary paths for the head and the body their differences are not statistically significant the distribution of blocks across each body provides clues as to the histories of each body the head is populated in a spherically symmetric fashion while the body has a distinct equatorial peak when considering that the head and the body may have been separate entities for a period of time and estimating a rotational axis using minimum rotational energy considerations the preferential equatorial distribution becomes even more pronounced we interpret this as excellent evidence for the partial disruption of a proto itokawa subsequent planarization of a debris field and reaccretion of the head and the body into its present configuration

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

eolian quartz flux to lake biwa central japan over the past 145 000 years abstract eolian quartz flux eqf g cm 2 103yr 1 to lake biwa central japan provides direct information on variations of the east asian winter monsoon lake biwa sediments spanning the past ca 145 000 yr are characterized by two main periods when eqf values were significantly greater than 5 50 g cm 2 103yr 1 and two main intervals during which eqf values were lower two periods with eqf values 5 50 g cm 2 103yr 1occurred from ca 145 000 to 125 000 and 73 000 to 13 000 yr b p while times of lower eqf values occurred from ca 125 000 to 73 000 yr b p and around ca 5500 yr b p between ca 125 000 and 73 000 yr b p three minimum eqf values and two intervening peaks of slightly higher eqf values are recorded eqf increased markedly from ca 73 000 to 13 000 yr b p whereas between ca 53 000 and 20 000 yr b p the values recorded were relatively lower than those recorded during either the preceding or the subsequent episodes the data imply that the east asian winter monsoon strengthened during the periods when eqf values were high and weakened during the intervals with low eqf values the eqf record of lake biwa can be correlated with the grain size record of the quartz fraction in chinese loess and with the specmap marine 18o record however the eqf record apparently lags ca 5000 yr behind the loess and 18o records during stage 6 5 and 2 1 transitions and ca 10 000 yr during stage 5 4 transition these apparent lags could be due to problems with the chronology alternatively they may imply that the eolian quartz flux depended more on the extent of dust source regions than on wind intensity during these transitions

desert loess versus glacial loess quartz silt formation source areas and sediment pathways in the formation of loess deposits abstract pathways are presented which show the proposed sequence of events involved in the formation of loess deposits both hypothetical deposits and those of central china hungary nigeria and tunisia these pathways illustrate the potential role of and inter relationships between a variety of silt generating mechanisms in the formation of loess using these pathways the existence of desert loess is discussed and it is concluded that this depends on how the terms glacial loess and desert loess are applied if desert loess is taken either to signify nonglacial mechanisms of silt production or to characterise the environment from which aeolian entrainment took place then desert loess is a very real and widely distributed deposit however if the term glacial loess is used to refer to the global climatic regime under which the loess deposit has formed rather than the geomorphic mechanisms responsible for silt generation then desert loess would not be an appropriate term for the classification of loess deposits it is suggested that classifying loess deposits with reference to the global climatic regime under which they accumulated would facilitate a greater understanding of the role of environmental conditions at all stages in the formation of loess deposits

rates timing and cyclicity of holocene eolian activity in north central united states evidence from varved lake sediments most of the sediment components that accumulated in elk lake northwestern minnesota during the holocene are autochthonous or biogenic delivered to the sediment water interface on a seasonal schedule preserved in distinct annual laminae varves the main allochthonous component is detrital clastic material as measured by bulk sediment concentrations of aluminum sodium potassium titanium and quartz that enters the lake mostly as eolian dust the eolian clastic influx to elk lake was considerably greater during the mid holocene 8 4 ka than it has been for the past 4000 yr when periods of increased eolian activity correspond to the time of the little ice age and the dust bowl geochemical records of eolian activity exhibit distinct cyclicities with dominant periodicities of 400 and 84 yr

slip distribution fault geometry and fault segmentation of the 1944 bolu gerede earthquake rupture north anatolian fault turkey the 1944 bolu gerede earthquake m s 7 3 occurred along the north anatolian fault in northern turkey and ruptured for about 180 km of the fault the surface slip distribution and fault geometry which provide fundamental data on detailed fault segmentation and recurrence of faulting during a multisegment rupture are poorly known for this event we conducted geomorphological and geological investigations and eyewitness interviews to determine cumulative offsets through several earthquake cycles the 1944 rupture comprised five fault segments based on slip distribution and fault step overs and bends from west to east they are called the bolu yenicaga gerede ismetpasa and bayramoren segments the segments were 21 to 46 km long and the average slip was 1 9 4 3 m similar to well examined segments of the 1999 izmit rupture in contrast the fault jogs were relatively small suggesting that the 1944 earthquake rupture process was relatively smooth and of short duration proposed fault segmentation is consistent with the extent of surface ruptures and damage intensity associated with historical earthquakes in 967 1035 and 1050 a d historical records indicate that the bolu and yenicaga segments ruptured in 967 a d and the gerede ismetpasa and possibly bayramoren segments ruptured in 1035 a d therefore the 1944 rupture occurred as a consequence of multisegment rupture which consists of at least two distinct earthquake segments along the gerede segment which slipped 3 to 6 m in 1944 cumulative offsets of 6 to 25 m were observed these offsets are double triple and quadruple multiples of the 1944 slip implying a similar slip distribution during the four most recent large earthquakes along this segment and supporting the concept of characteristic slip even though the rupture length varied greatly during the last four earthquake cycles

the full glacial environment of the northern seward peninsula alaska reconstructed from the 21 500 year old kitluk paleosol abstract paleoenvironmental conditions are reconstructed from soils buried under volcanic ash ca 21 500 years ago on the seward peninsula soil development was minimal reflecting the continuous regional deposition of loess which originated from river floodplains and the exposed chukchi shelf cryoturbated soil horizons ice wedges and ice lens formation indicate a permafrost environment and mean annual temperatures below 6 to 8 c shallow active layers average 45 cm minimal evidence for chemical leaching of soils and the presence of earthen hummocks indicate a cold and seasonally dry climate neither steppe nor polar desert soils are appropriate analogues for these zonal soils of loess covered central beringia no exact analogues are known however soils underlying dry tundra near the arctic coast of northern yakutia russia and under moist nonacidic tundra of the alaskan north slope have properties in common with the buried soils

preferential dust sources a geomorphological classification designed for use in global dust cycle models received 11 april 2011 revised 28 september 2011 accepted 4 october 2011 published 24 december 2011 1 we present a simple theoretical land surface classification that can be used to determine the location and temporal behavior of preferential sources of terrestrial dust emissions the classification also provides information about the likely nature of the sediments their erodibility and the likelihood that they will generate emissions under given conditions the scheme is based on the dual notions of geomorphic type and connectivity between geomorphic units we demonstrate that the scheme can be used to map potential modern day dust sources in the chihuahuan desert the lake eyre basin and the taklamakan through comparison with observed dust emissions we show that the scheme provides a reasonable prediction of areas of emission in the chihuahuan desert and in the lake eyre basin the classification is also applied to point source data from the western sahara to enable comparison of the relative importance of different land surfaces for dust emissions we indicate how the scheme could be used to provide an improved characterization of preferential dust sources in global dust cycle models

mass and local topography measurements of itokawa by hayabusa the ranging instrument aboard the hayabusa spacecraft measured the surface topography of asteroid 25143 itokawa and its mass a typical rough area is similar in roughness to debris located on the interior wall of a large crater on asteroid 433 eros which suggests a surface structure on itokawa similar to crater ejecta on eros the mass of itokawa was estimated as 3 58 0 18 1010 kilograms implying a bulk density of 1 95 0 14 grams per cubic centimeter for a volume of 1 84 0 09 107 cubic meters and a bulk porosity of 40 which is similar to that of angular sands when assuming an ll low iron chondritic meteorite composition combined with surface observations these data indicate that itokawa is the first subkilometer sized small asteroid showing a rubble pile body rather than a solid monolithic asteroid

late quaternary mis 3 to mis 1 stratigraphic transitions in a highland beringian landscape along the kuskokwim river alaska stratigraphic records extending to marine oxygen isotope stage mis 3 57 000 29 000 cal yr bp or older in beringia are extremely rare three stratigraphic sections in interior western alaska show near continuous sedimentological and environmental progressions extending from at least mis 3 if not older through mis 1 14 000 cal yr bp present the kolmakof sue creek and vabm vertical angle bench mark kuskokwim sections along the central kuskokwim river once a highland landscape at the fringe of central and eastern beringia contain aeolian deposition and soil sequences dating beyond 50 000 14 c yr bp thick peaty soil shallow lacustrine and tephra deposits represent the mis 3 interstade or older sand sheet and loess deposits wedge cast development and very thin soil development mark the later mis 3 period and the transition into the mis 2 stade 29 000 14 000 cal yr bp loess accumulation with thicker soil development occurred between 16 000 13 500 cal yr bp at the mis 2 and mis 1 transition after 13 500 cal yr bp loess accumulation waned and peat development increased throughout mis 1 these stratigraphic sequences represent transitions between a warm and moist period during mis 3 to a cooler and more arid period during mis 2 then a return to warmer and moister climates in mis 1

small scale topography of 25143 itokawa from the hayabusa laser altimeter abstract the surface topography of asteroid 25143 itokawa is explored using the light detection and ranging instrument lidar the data confirm the presence of a rough highland and a smooth lowland the highland is dominated by boulders but also possesses topography associated with surface lineaments and broad surface facets the boulders ensure that the roughness of the highlands over short distances is typically greater relative to most surfaces on 433 eros over larger distances itokawa is always smoother than eros possibly because of its smaller size and weak rubble pile structure the lowlands of itokawa are very smooth and are typically devoid of boulders some transitional regions midway between the highlands and lowlands also exist in these areas craters that retain their regolith fill possess flat floors and resemble ponds seen on 433 eros analyses of surface elevation imagery and a quantitative measure of surface roughness are consistent with regolith flowing downhill from the highlands to fill in the low areas of itokawa probably covering up any pre existing rough terrain using this interpretation we find a minimum 2 3 0 4 m thick layer of regolith in the lowlands which if spread evenly across the entire asteroid corresponds to a 42 1 cm thick layer it is very difficult to generate this amount of regolith with the population of craters seen on itokawa however an itokawa composed of several large masses may have retained this regolith during its formation the presence of such large masses could account for the observed lineaments and what appear to be exposures of bedrock on the largest steep slope observed

stratigraphy and palaeoclimatic significance of late quaternary loess palaeosol sequences of the last interglacial glacial cycle in central alaska abstract loess is one of the most widespread subaerial deposits in alaska and adjacent yukon territory and may have a history that goes back 3 ma based on mineralogy and major and trace element chemistry central alaskan loess has a composition that is distinctive from other loess bodies of the world although it is quartz dominated central alaskan loess was probably derived from a variety of rock types including granites metabasalts and schists detailed stratigraphic data and pedologic criteria indicate that contrary to early studies many palaeosols are present in central alaskan loess sections the buried soils indicate that loess sedimentation was episodic or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input as in china loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess soil formation cycle loess deposition in central alaska took place before and probably during the last interglacial period during stadials of the mid wisconsin period during the last glacial period and during the holocene an unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period our studies lead us to conclude that vegetation plays a key role in loess accumulation in alaska factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods the most important of these is vegetation boreal forest serves as an effective loess trap but sparsely distributed herb tundra does not thus thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central alaska much of the stratigraphic diversity of north american loess including that found in the central lowlands the great plains and alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors

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

coupled climate and sea level changes deduced from huon peninsula coral terraces of the last ice age abstract huon peninsula papua new guinea is a tectonically unstable uplifting shoreline ringed by emergent coral terraces the terraces were formed during episodes of rapid sea level rise when corals constructed large discrete coral platforms that were subsequently uplifted uranium series ages of four prominent huon peninsula last glacial ois 3 coral terraces coincide with the timing of major north atlantic climate reversals at intervals of 6000 7000 yr between 30 000 yr and 60 000 yr ago terrace elevations when combined with uplift indicate 10 15 m high sea level excursions at these times we attribute the growth of the terraces directly to sea level rises arising from ice calving episodes from major north atlantic ice sheets and the antarctic ice sheet that precipitated extremes of cold climate called heinrich events these periods are associated with major discharges of land based ice and enhanced concentrations of ice rafted debris in deep sea cores sea levels at this time were 60 90 m lower than present

geochemical variations in peoria loess of western iowa indicate paleowinds of midcontinental north america during last glaciation peoria loess deposited in western iowa during the last glacial maximum lgm shows distinct geochemical and particle size variations as a function of both depth and distance east of the missouri river geochemical and particle size data indicate that peoria loess in western iowa probably had two sources the missouri river valley and a source that lay to the west of the missouri river both sources indicate that lgm paleowinds in western iowa had a strong westerly component similar to interpretations of previous workers a compilation of loess studies in iowa and elsewhere indicates that westerly winds were dominant during loess transport over much of the midcontinent south of the laurentide ice sheet which is not in agreement with paleowinds simulated by atmospheric general circulation models agcms agcms consistently generate a glacial anticyclone with easterly or northeasterly winds over the laurentide ice sheet and the area to the south of it loess deposition in the midcontinent during the lgm may be a function of infrequent northwesterly winds that were unrelated to the presence of the glacial anticyclone

regolith migration and sorting on asteroid itokawa high resolution images of the surface of asteroid itokawa from the hayabusa mission reveal it to be covered with unconsolidated millimeter sized and larger gravels locations and morphologic characteristics of this gravel indicate that itokawa has experienced considerable vibrations which have triggered global scale granular processes in its dry vacuum microgravity environment these processes likely include granular convection landslide like granular migrations and particle sorting resulting in the segregation of the fine gravels into areas of potential lows granular processes become major resurfacing processes because of itokawa s small size implying that they can occur on other small asteroids should those have regolith

a revised late quaternary vegetation history of the unglaciated southwestern yukon territory canada from antifreeze and eikland ponds antifreeze pond was thought to contain the oldest record of continuous environmental change in the southwestern yukon we have revised the original interpretation of the vegetation history of antifreeze pond and this region based on new pollen stomate and macrofossil analysis along with 38 new accelerator mass spectrometry ams 14c dates from antifreeze pond and nearby eikland pond although the overall pattern of vegetation change is similar to the previously published antifreeze pond record our new analysis indicates that the timing of the major vegetation shifts is substantially different particularly during the late glacial and early holocene periods from 17 000 9000 cal years bp the original antifreeze pond record was thought to span a mid wisconsinan interstadial 30 000 cal years bp and the full glacial period our results however indicate that the material of mid wisconsinan age was likely deposited by slumping around the pond making interpretation of the paleoenvironment difficult

characterisation and palaeoclimate of a loess like permafrost palaeosol sequence in ne siberia abstract we studied a 15 m high loess like permafrost palaeosol sequence the tumara palaeosol sequence tps which developed on a middle pleistocene fluvio glacial terrace of the tumara river various analytical methods were applied to characterise the tps similar to typical loess palaeosol sequences e g in china europe etc pedogenetic clay formation mineral weathering and smaller grain sizes are interpreted as representing warmer and more favourable climatic conditions interglacials or interstadials soil organic matter som however reveals an unfamiliar inverse pattern high organic carbon contents c org 1 characterise the dark grey glacial palaeosols whereas lower contents c org 0 5 are found in the brown interglacial stadial palaeosols this can be explained with permafrost and water logging having inhibited som mineralisation during cold periods d l ratios of aspartic acid and lysine proved to be useful proxies for both som aging and palaeotemperature with amino acid racemization being enhanced in interglacial stadial palaeosols on the basis of the geochemical and grain size results further palaeoclimatically relevant proxies describing the palaoewind strength u ratio the mineral weathering chemical index of alteration rb k and the changing mineral input signal ba ti zr ti al were applied to the tps in combination with numeric dating results radiocarbon and luminescence and in the context of other northern hemispheric records the simple warm cold stratigraphy as derived from the palaeoenvironment climate proxies suggests that the tps represents the last 240 000 years

boulder size and shape distributions on asteroid ryugu abstract in 2018 the japanese spacecraft hayabusa2 arrived at the small asteroid ryugu the surface of this c type asteroid is covered with numerous boulders whose size and shape distributions are investigated in this study using a few hundred optical navigation camera onc images with a pixel scale of approximately 0 65 m we focus on boulders greater than 5 m in diameter smaller boulders are also considered using five arbitrarily chosen onc close up images with pixel scales ranging from 0 7 to 6 cm across the entire surface area 2 7 km2 of ryugu nearly 4400 boulders larger than 5 m were identified boulders appear to be uniformly distributed across the entire surface with some slight differences in latitude and longitude at 50 km 2 the number density of boulders larger than 20 m is twice as large as on asteroid itokawa or bennu the apparent shapes of ryugu s boulders resemble laboratory impact fragments with larger boulders being more elongated the ratio of the total volume of boulders larger than 5 m to the total excavated volume of craters larger than 20 m on ryugu can be estimated to be 94 which is comparatively high these observations strongly support the hypothesis that most boulders found on ryugu resulted from the catastrophic disruption of ryugu s larger parent body as described in previous papers watanabe et al 2019 sugita et al 2019 the cumulative size distribution of boulders larger than 5 m has a power index of 2 65 0 05 which is comparatively shallow compared with other asteroids visited by spacecraft for boulders smaller than 4 m the power index is even shallower and ranges from 1 65 0 05 to 2 01 0 06 this particularly shallow power index implies that some boulders are buried in ryugu s regolith based on our observations we suggest that boulders near the equator might have been buried by the migration of finer material and as a result the number density of boulders larger than 5 m in the equatorial region is lower than at higher latitudes

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

dust records from varved lacustrine sediments of two neighboring lakes in northeastern china over the last 1400 years dust storms are natural phenomena described in chinese historical documents as early as 1150 bc these documents provide a way to evaluate proxy data from different natural records the minerogenic clastic content and grain size from two closed maar lakes located a short distance apart in northeastern china were analyzed the area is located in the path of dust storms the minerogenic clastics in the studied maar lakes originate mainly from dust deposition general variations of the minerogenic clastic content in these two neighboring lakes show a good coincidence with dust concentration in a tibet ice core and dust events as recorded in historical documents the minerogenic clastic content in the lake sediments is linked with the climate conditions in the dust source regions and wind strength three periods of intensive dust events ad 1050 1330 ad 1590 1690 and the last 200 years have been identified during the past 1500 years the recent increasing pattern of clastic content could be linked to human activity in the dust source regions significantly most of the medieval warm period mwp was marked by a high frequency of dust storms

origin and paleoclimatic significance of late quaternary loess in nebraska evidence from stratigraphy chronology sedimentology and geochemistry muhs d r bettis iii e a aleinikoff j n mcgeehin j p beann j skipp g marshall b d roberts h m johnson w c benton r 2008 origin and paleoclimatic significance of late quaternary loess in nebraska evidence from stratigraphy chronology sedimentology and geochemistry gsa bulletin 120 11 12 1378 1407

small scale topography of 433 eros from laser altimetry and imaging abstract the near laser rangefinder nlr obtained more than 16 million range returns from asteroid 433 eros we present the first results from analyses of topographic profiles interpreted with the aid of simultaneous boresighted images obtained by the near multispectral imager msi the location of the nlr boresight relative to that of msi is determined by detailed correlations of ranging data and simultaneous images including cases where the laser boresight slewed off and on the limb of the asteroid and cases where the laser illuminated a boulder close to the time of an image in the data presented the precision of the range measurements is about 1 m with the minimum spot diameter under 5 m and successive spots are contiguous or overlapping elevation on the irregular object eros is given with respect to the gravitational and centrifugal potential landslides in craters are characterized possible crater benches are identified examples of infilled craters are presented these observations suggest a depth of unconsolidated regolith which is subject to sliding of typically a few tens of meters an example of structurally controlled cratering is presented examples of tectonic features are described surface roughness on eros is approximately self affine from scales of a few meters to hundreds of meters a comparison of fractal statistics shows that eros is extremely rough on observed scales when compared to terrestrial a a lava on submeter scales and undisturbed lunar regolith on subcentimeter scales

origin of last glacial loess in the western yukon tanana upland central alaska usa loess is widespread over alaska and its accumulation has traditionally been associated with glacial periods surprisingly loess deposits securely dated to the last glacial period are rare in alaska and paleowind reconstructions for this time period are limited to inferences from dune orientations we report a rare occurrence of loess deposits dating to the last glacial period 19 ka to 12 ka in the yukon tanana upland loess in this area is very coarse grained abundant coarse silt with decreases in particle size moving south of the yukon river implying that the drainage basin of this river was the main source geochemical data show however that the tanana river valley to the south is also a likely distal source the occurrence of last glacial loess with sources to both the south and north is explained by both regional synoptic scale winds from the northeast and opposing katabatic winds that could have developed from expanded glaciers in both the brooks range to the north and the alaska range to the south based on a comparison with recent climate modeling for the last glacial period seasonality of dust transport may also have played a role in bringing about contributions from both northern and southern sources

arctic ground squirrels of the mammoth steppe paleoecology of late pleistocene middens 24000 29450 14c yr bp yukon territory canada abstract this paper presents paleoecological analyses of 48 fossil arctic ground squirrel spermophilus parryii middens nests and caches recovered from ice rich loess sediments in the klondike region of west central yukon territory ams radiocarbon dates and stratigraphic association of middens with dawson tephra 25 300 14 c yr bp indicate these paleoecological data reflect the onset of glacial conditions of early marine isotope stage mis 2 and terminal mis 3 24 000 29 450 14 c yr bp plant macrofossils include at least 60 plant taxa including diverse graminoids poa elymus trachycaulus kobresia myosuroides steppe forbs penstemon gormanii anemone patens var multifida plantago cf canescens tundra forbs draba spp bistorta vivipara dwarf shrubs salix cf arctica s cf polaris sage artemisia frigida and rare trees picea mariana many of these taxa identified in the middens represent the first recorded fossils for these plants in eastern beringia and add to our knowledge of the floristic composition of pleistocene vegetation and biogeography in this region fossil beetles include typical members of the eastern beringian steppe tundra fauna lepidophorus lineaticollis and connatichela artemisiae and others suggesting predominantly dry open habitats cache forage selection is suggested by some plant taxa which were particularly frequent and abundant in the middens bistorta vivipara kobresia myosuroides ranunculus spp potentilla erysimum cf cheiranthoides poa carex and draba factors such as proximity of vegetation to burrows and abundance of fruits and seeds per plant were probably important in cache selection glacial conditions enabled arctic ground squirrels to form widespread and dense populations in regions such as the klondike in which they are rare or absent at present this fossil midden record supports previous hypotheses that suggest arctic ground squirrels evolved in and are well adapted to the open steppe tundra vegetation loessal soils and glacial climates of the mammoth steppe biome

vegetation buried under dawson tephra 25 300 14c years bp and locally diverse late pleistocene paleoenvironments of goldbottom creek yukon canada paleoecological research at goldbottom creek in the klondike region of yukon territory nw canada documents an in situ riparian grassy meadow that was buried during the winter or early spring by dawson tephra near the onset of marine isotope stage mis 2 ca 25 300 14 c years bp analyses of vascular plant macrofossils bryophytes pollen insects and paleosols from the riparian meadow contrast with evidence for well drained upland steppe tundra habitats obtained from fossil arctic ground squirrel middens within the same valley the mesic valley bottom vegetation consisted of grasses deschampsia caespitosa alopecurus sedges carex horsetail equisetum cf palustre diverse bryophytes and few forbs upland habitats with dry loessal soils along the valley slopes contained graminoids elymus festuca kobresia myosuroides sage artemisia frigida and diverse steppe and tundra forbs phlox hoodii plantago cf canescens anemone patens var multifida bistorta vivipara draba these paleoecological data highlight the effect of topographic position and moisture on substrates and their control on local scale habitat variability this study represents the first recorded in situ riparian surface from the unglaciated pleistocene refugium of beringia and provides well documented evidence for local habitat heterogeneity and ecosystem structure within the mammoth steppe biome other radiocarbon dated paleoecological data from our study sites indicate that full glacial steppe tundra habitats in west central yukon territory were established during the later stages of the mis 3 interstadial by 29 000 14 c years bp the diverse data obtained through integration of multiple paleoecological methods

a late quaternary record of eolian silt deposition in a maar lake st michael island western alaska abstract recent stratigraphic studies in central alaska have yielded the unexpected finding that there is little evidence for full glacial late wisconsin loess deposition because the loess record of western alaska is poorly exposed and not well known we analyzed a core from zagoskin lake a maar lake on st michael island to determine if a full glacial eolian record could be found in that region particle size and geochemical data indicate that the mineral fraction of the lake sediments is not derived from the local basalt and is probably eolian silt deposition took place from at least the latter part of the mid wisconsin interstadial period through the holocene based on radiocarbon dating based on the locations of likely loess sources eolian silt in western alaska was probably deflated by northeasterly winds from glaciofluvial sediments if last glacial winds that deposited loess were indeed from the northeast this reconstruction is in conflict with a model derived reconstruction of paleowinds in alaska mass accumulation rates in zagoskin lake were higher during the pleistocene than during the holocene in addition more eolian sediment is recorded in the lake sediments than as loess on the adjacent landscape the thinner loess record on land may be due to the sparse herb tundra vegetation that dominated the landscape in full glacial time herb tundra would have been an inefficient loess trap compared to forest or even shrub tundra due to its low roughness height the lack of abundant full glacial eolian silt deposition in the loess stratigraphic record of central alaska may be due therefore to a mimimal ability of the landscape to trap loess rather than a lack of available eolian sediment

late pleistocene eolian sand sheets in alaska abstract nonglaciated lowlands in central and southwestern alaska contain extensive deposits of upper quaternary eolian sand derived largely from major outwash rivers although surface dunes are common deep exposures consistently reveal that subhorizontally stratified sand and silt deposits dominate over dune cross strata we hypothesize that 1 many of the subhorizontally stratified deposits represent full glacial eolian sand sheets formed when sand supply was limited by seasonally variable combinations of ice cementation snow cover high groundwater tables and vegetation and 2 many surface dunes reflect late glacial and postglacial reworking under conditions of increased short term availability of loose sand the morphology of some surface dunes may therefore reflect mainly the intensity of reworking since the last glacial maximum rather than full glacial paleowind vectors or the age of the bulk of the underlying deposits

deposition and pedogenesis of periglacial sediments and buried soils at the serpentine hot springs archaeological site seward peninsula ak abstract soil micromorphology is an excellent tool for relating quantitative laboratory data to soil development in complex pedogenic settings this study utilizes micromorphology scanning electron microscopy bulk soil geochemistry clay mineralogy and particle size analysis to reconstruct the depositional and pedogenic history of the serpentine hot springs fluted point site on the seward peninsula alaska sediment deposition occurred via colluviation which dominated during the late glacial period and early to middle holocene and aeolian processes which dominated during the younger dryas yd and late holocene two buried soils are present one dating to the holocene thermal maximum htm and the other dating just before the neoglacial period pedofeatures fall into four categories 1 cryogenic features 2 clay illuviation features 3 podzolization redox features and 4 anthropogenic features the spatial relationships among these features provides insight into the pedogenic history of the soil the htm soil is characterized by clay illuviation suggesting warm mildly acidic well drained soil conditions the pre neoglacial soil is characterized by incipient placic horizon development and podzolization indicative of moist acidic variably drained conditions cryogenic features associated with late holocene neoglaciation dominate the modern soil despite cryogenic activity and the presence of permafrost the cultural stratigraphy of the site remains intact

the significance of maar volcanoes for palaeoclimatic studies in china abstract the sediments of maar lakes often provide paleoenvironmental records which are highly suitable for palaeoclimatic studies the main advantages of the records from maar lakes compared with other lacustrine records are as follows first the presence of varves annually laminated layers and tephra layers as well as other materials like terrestrial plant macrofossils charcoals organic carbon organic shells suitable for isotopic dating like ams 14c 210pb 137cs 238u 230th 40ar 39ar provides the possibility of developing several independent chronologies enabling the development of robust high resolution chronologies second maars and maar lakes can provide continuous sedimentary records spanning tens of thousands of years tianyang maar in china is hosted the longest known record spanning at least 400 kyr bp that are ideal for the investigation of climate change on different timescales including orbital millennial centennial and annual decadal third recent studies of biomarkers based on long chain alkenones lcas and glycerol dialkyl glycerol tetraethers gdgts have demonstrated the potential of maar lakes for quantitative paleotemperature reconstruction in this study we review some of the more significant achievements of palaeoclimatic research based on maar lake sediment sequences from china with the focus on chronology multiple timescales and quantitative paleoclimatic reconstruction

holocene climate inferred from oxygen isotope ratios in lake sediments central brooks range alaska analyses of sediment cores from two lakes in the central brooks range provide temperature and moisture balance information for the past 8500 cal yr at century scale resolution two methods of oxygen isotope analysis are used to reconstruct past changes in the effective moisture precipitation minus evaporation and temperature effective moisture is inferred from oxygen isotope ratios in sediment cellulose from meli lake area 0 13 km 2 depth 19 4 m the lake has a low watershed to lake area ratio 7 and significant evaporation relative to input summer temperature shifts are based on oxygen isotope analyses of endogenic calcite from tangled up lake area 0 25 km 2 depth 3 5 m this basin has a larger watershed to lake area ratio 91 and less evaporation relative to input sediment oxygen isotope analyses from the two sites indicate generally more arid conditions than present prior to 6000 cal yr b p subsequently the region became increasingly wet temperature variability is recorded minimally at centennial scale resolution with values that are generally cool for the past 6700 cal yr the timing and direction of climate variability indicated by the oxygen isotope time series from meli and tangled up lakes are consistent with previously established late holocene glacier advances at 5000 cal yr b p in the central brooks range and high lake levels at birch lake since 5500 cal yr b p this unique use of oxygen isotopes reveals both moisture balance and temperature histories at previously undetected high resolution temporal scales for northern alaska during the middle to late holocene c 2001 university of washington

last glacial climate instability documented by coarse grained sediments within the loess sequence at fanjiaping lanzhou china optically stimulated luminescence dating grain size analysis and magnetic susceptibility measurements were conducted on the fanjiaping loess section from the western chinese loess plateau the results confirm that last glacial high frequency climatic shifts were documented in mid latitude continental archives the grain size record indicated that coarse grained sediments with horizontal bedding and channel fill structures were only deposited in several short intervals equivalent to the beginning of marine oxygen isotope stage mis 4 and the early to middle mis 3 this probably implies brief rainfall intensification of the asian summer monsoon and its disappearance since the late mis 3 to mis 2 may have been a response to significant glacial cooling in the northern hemisphere previous investigations revealed high sea surface temperatures at high latitudes at the start of mis 4 and the early to middle mis 3 intensification of summer insolation in the northern hemisphere implying evident climate amelioration climate improvement favors boreal forest recovery enhancing both winter and summer air temperatures the resultant smaller equator polar temperature gradient probably helped the moisture laden summer monsoon to penetrate northward this study thus provides new significant information about the response of terrestrial loessic palaeoenvironments to millennial timescale climatic fluctuations during the last glacial period

aeolian stratigraphy describes ice age paleoenvironments in unglaciated arctic alaska abstract terrestrial paleoenvironmental records with high dating resolution extending into the last ice age are rare from the western arctic such records can test the synchronicity and extent of ice age climatic events and define how arctic landscapes respond to rapid climate changes here we describe the stratigraphy and sedimentology of a yedoma deposit in arctic alaska the carter section dating to between 37 000 and 9000 calibrated radiocarbon years bp 37 9 ka and containing detailed records of loess and sand sheet sedimentation soil development carbon storage and permafrost dynamics alternation between sand sheet and loess deposition provides a proxy for the extent and activity of the ikpikpuk sand sea iss a large dune field located immediately upwind warm moist interstadial times ca 37 36 3 32 5 and 15 13 ka triggered floodplain aggradation permafrost thaw reduced loess deposition increased vegetation cover and rapid soil development accompanied by enhanced carbon storage during the last glacial maximum lgm ca 28 18 ka rapid loess deposition took place on a landscape where vegetation was sparse and non woody the most intense aeolian activity occurred after the lgm between ca 18 and 15 ka when sand sheets fringing the iss expanded over the site possibly in response to increasingly droughty conditions as summers warmed and active layers deepened with the exception of this lagged lgm response the record of aeolian activity at the carter section correlates with other paleoenvironmental records from unglaciated siberia and alaska overall rapid shifts in geomorphology soils vegetation and permafrost portray an ice age landscape where in contrast to the holocene environmental change was chronic and dominated by aeolian processes

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

properties and soil development of late pleistocene paleosols from seward peninsula northwest alaska abstract soils on seward peninsula northwest alaska that were buried about 17 500 years ago and froze after burial present a unique opportunity to study soil development under the conditions of the last glacial maximum stratigraphic sections were excavated during the summers of 1993 and 1994 study sites were located on steep banks of thaw lakes we described soil morphology including cryogenic features and sampled for chemical and physical analyses all paleosols are permafrost soils that developed in calcareous loess and have roots present throughout colors are predominantly grayish and either reflect original loess color or periodic saturation of the soils possibly caused by the permafrost environment active layer thicknesses before burial ranged from 32 to 64 cm organic carbon contents average 3 0 carbon nitrogen ratios average 9 cation exchange capacities average 19 1 cmol kg and base saturations generally exceed 100 there is no evidence of leaching in the profile soil formation occurred simultaneously to the deposition of the parent material loess morphological and chemical data suggest that soil development was weak and confined to organic matter accumulation and hydrolysis of iron all studied soils show similar morphological chemical and physical properties which suggests a relatively uniform mode of soil formation in the study area soil forming conditions on northern seward peninsula during the last glacial maximum were severe and combined with fairly continuous loess deposition they resulted in weakly developed nutrient rich soils

change in atmospheric mineral aerosols in response to climate last glacial period preindustrial modern and doubled carbon dioxide climates desert dust simulations generated by the national center for atmospheric research s community climate system model for the current climate are shown to be consistent with present day satellite and deposition data the response of the dust cycle to last glacial maximum preindustrial modern and doubled carbon dioxide climates is analyzed only natural non land use related dust sources are included in this simulation similar to some previous studies dust production mainly responds to changes in the source areas from vegetation changes not from winds or soil moisture changes alone this model simulates a 92 33 and 60 change in dust loading for the last glacial maximum preindustrial and doubled carbon dioxide climate respectively when impacts of carbon dioxide fertilization on vegetation are included in the model terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions probably due to the lack of simulation of glaciogenic dust sources in order to include the glaciogenic dust sources as a first approximation we designate the location of these sources and infer the size of the sources using an inversion method that best matches the available data the inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2 1 to 3 3 times current deposition

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

a 37 000 year environmental magnetic record of aeolian dust deposition from burial lake arctic alaska abstract environmental magnetism and radiocarbon dating of burial lake sediments constrain the timing and magnitude of regional aeolian deposition for the noatak region of western arctic alaska for the last 37 000 years burial lake 68 43 n 159 17 w 21 5 m water depth is optimally located to monitor regional dust deposition because it is perched above local drainage and isolated from glacial processes cores collected in the summer of 2010 were studied through the application of magnetizations and progressive alternating field af demagnetization of u channel samples with additional data provided by computed tomography ct derived density hysteresis measurements isothermal remanent magnetization irm acquisition experiments organic carbon content biogenic silica physical grain size radiocarbon dating of wood seeds and plant macrofossils point source magnetic susceptibility and x ray fluorescence xrf with similar magnetic properties to regional alaskan loess deposits low coercivity highly magnetic material deposited during the late pleistocene contrasts with a high coercivity weakly magnetic component found throughout the record consistent with locally derived detritus the relative proportion of low coercivity to high coercivity magnetic material defined by the s ratios is used to reconstruct the regional input of dust to the basin over time a four fold decrease in the low coercivity component through the deglacial transition is interpreted to reflect diminished dust input to the region comparisons with potential sources of dust show that the timing of deposition in burial lake is largely consistent with general aridity lack of vegetative cover and increased windiness rather than glacial advances or retreats the influence from subaerial exposure of continental shelves cannot be ruled out as a significant far field source of dust to interior alaska during the last glacial maximum lgm but is unlikely to have been the sole source or to have contributed to increased dust in both the early and late holocene

regional differences in bone collagen δ13c and δ15n of pleistocene mammoths implications for paleoecology of the mammoth steppe in this study we present bone collagen 13c and 15n values from a large set of pleistocene woolly mammoths mammuthus primigenius from siberia alaska and yukon overall results for mammoth specimens from eastern beringia alaska and yukon significantly differ for both 13c and 15n values from those from western beringia northeastern siberia in agreement with palynological entomological and physiographic data from the same regions these isotopic differences strongly imply that the mammoth steppe the extensive ice free region spanning northern eurasia and northwestern north america was ecologically variable along its east west axis to a significant degree prior to the last glacial maximum lgm the high latitude portions of siberia and the russian far east appear to have been colder and more arid than central alaska and yukon which were ecologically more diverse during the lgm itself however isotopic signatures of mammoths from eastern beringia support the argument that this region also experienced an extremely cold and arid climate in terms of overall temporal trend beringia thus went from a condition prior to the lgm of greater ecological variability in the east to one of uniformly cold and dry conditions during the lgm

continental climate response to orbital forcing from biogenic silica records in lake baikal changes in insolation caused by periodic changes in the earth s orbital parameters provide the primary forcing for global ice ages1 6 but it is not clear to what extent the climates in continental interiors are controlled directly by regional variations in insolation and to what extent they are driven instead by the highly nonlinear response of the oceans and ice sheets here we investigate this question using the record of biogenic silica in lake baikal as a proxy for climate change in this high latitude mid continental region we find a good correlation between this record and that of marine oxygen isotopes4 over the past 250 kyr the baikal record exhibits both a strongly nonlinear component manifested in a 100 kyr periodicity and weaker direct insolation components manifested in the 41 kyr obliquity and 23 and 19 kyr precession orbital cycles these results show that even though extreme continental climates such as this are influenced directly by insolation variations they are dominated by the nonlinear rhythm of the oceans and ice sheets

dirtmap the geological record of dust atmospheric dust is an important feedback in the climate system potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems yet the potential impact of dust on the climate system both in the anthropogenically disturbed future and the naturally varying past remains to be quantified the geologic record of dust provides the opportunity to test earth system models designed to simulate dust records of dust can be obtained from ice cores marine sediments and terrestrial loess deposits although rarely unequivocal these records document a variety of processes source transport and deposition in the dust cycle stored in each archive as changes in clay mineralogy isotopes grain size and concentration of terrigenous materials although the extraction of information from each type of archive is slightly different the basic controls on these dust indicators are the same changes in the dust flux and particle size might be controlled by a combination of a source area extent b dust emission efficiency wind speed and atmospheric transport c atmospheric residence time of dust and or d relative contributions of dry settling and rainout of dust similarly changes in mineralogy reflect a source area mineralogy and weathering and b shifts in atmospheric transport the combination of these geological data with process based forward modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates their controlling mechanisms and how those mechanisms may vary regionally the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150 000 years

a continuous high resolution dust record for the reconstruction of wind systems in central europe eifel western germany over the past 133 ka 1 the last glacial cycle in central europe is dominated by processes of aeolian dust transport and accumulation these dust deposits are preserved in soils and lake sediments and provide detailed information about the climate variability during cold and dry periods especially the transitions from warm into cold periods are characterized by turbulent climate conditions the main problems of terrestrial paleoclimate reconstructions are the completeness of the core material and a sampling resolution to detect single dust storms we use a particle detection method which allows high resolution sub annual analyses of sediment structures in undisturbed samples the elsa eifel laminated sediment archive stack is a compilation of four different lake sediment cores of the eifel region western germany and comprise the period of the last 133 ka the results of our analyses show high frequencies of dust storm events during the first cold events c24 and c23 after the last warm stage in opposition the coldest periods of the last glacial cycle ois 4 70 60 ka bp and ois 2 35 14 ka bp are characterized by stable climate conditions that provide the accumulation of homogenous dust sediments

a 3 m y record of pliocene pleistocene loess in interior alaska many distal tephra beds exist in the thick fossiliferous loess deposits near fairbanks interior alaska isothermal plateau fission track ages determined on glass shards from tephra beds in conjunction with tephrostratigraphic and magnetostratigraphic techniques indicate that loess deposition began in the late pliocene an antiquity previously unsuspected hence there is the opportunity now to reconstruct a detailed well dated record of environmental changes in interior alaska during the past 3 m y

burial and preservation of a 30 000 year old perennial snowbank in red creek valley ogilvie mountains central yukon canada this study describes the origin and age of a body of massive ground ice exposed in the headwall of a thaw slump in the red creek valley central yukon canada the site is located beyond the limits of pleistocene glaciation in central yukon and within the southern limit of the modern continuous permafrost zone the origin of the massive ground ice which is preserved under a fine grained diamicton containing thin layers of tephra was determined through ice petrography stable o h isotope composition of the ice and gas composition of occluded air entrapped in the ice the age of the massive ground ice was established by identifying the overlying tephra and radiocarbon dating of a muck deposit preserved within the ice collectively the results indicate that the massive ground ice formed by snow densification with limited melting refreezing and is interpreted as being a buried perennial snowbank the muck deposit within the ice which yielded an age of 30 720 340 14 c a bp and the dawson tephra 25 300 14 c a bp overlying the perennial snowbank indicates that the snowbank accumulated at roughly the transition between marine isotope stages 3 and 2 dry climatic conditions at this time and possibly high winds enabled the snowbank to accumulate in the absence of extensive local valley glaciation as occurred in the mountains to the south in addition to documenting the persistence of relict permafrost and ground ice to warming climate in regions where they are predicted to disappear by numerical models this study presents evidence of an isotopic biosignature preserved in a body of massive ground ice

age extent and climatic significance of the c 3400 bp aniakchak tephra western alaska usa tephra deposits at whitefish lake and cape espenberg on the northernmost seward peninsula of western alaska were derived from the aniakchak caldera on the alaska peninsula more than 1500 km to the south radiocarbon dates on the climactic caldera forming aniakchak eruption and on proximal and distal tephra indicate the aniakchak tephra was deposited about 3435 40 bp 3614 3815 cal bp and forms an isochronous marker horizon across much of western alaska the aniakchak tephra eruption and several other targe eruptions during the seventeenth century bc may have had widespread effects on climate

the rubble pile asteroid itokawa as observed by hayabusa during the interval from september through early december 2005 the hayabusa spacecraft was in close proximity to near earth asteroid 25143 itokawa and a variety of data were taken on its shape mass and surface topography as well as its mineralogic and elemental abundances the asteroid9s orthogonal axes are 535 294 and 209 meters the mass is 3 51 1010 kilograms and the estimated bulk density is 1 9 0 13 grams per cubic centimeter the correspondence between the smooth areas on the surface muses sea and sagamihara and the gravitationally low regions suggests mass movement and an effective resurfacing process by impact jolting itokawa is considered to be a rubble pile body because of its low bulk density high porosity boulder rich appearance and shape the existence of very large boulders and pillars suggests an early collisional breakup of a preexisting parent asteroid followed by a re agglomeration into a rubble pile object

characterizing and navigating small bodies with imaging data recent advances in the characterization of small body surfaces with stereophotoclinometry are discussed the principal data output is an ensemble of landmark maps l maps high resolution topography albedo maps of varying resolution that tile the surface of the body because they can have a resolution comparable to the best images and can be located on a global reference frame to high accuracy l maps provide a significant improvement in discriminatory power for studies of small bodies ranging from regolith processes to interior structure these techniques are now being used to map larger bodies such as the moon and mercury l maps are combined to produce a standard global topography model gtm with about 1 57 million vectors and having a wide variety of applications they can also be combined to produce high resolution topography maps that describe local areas with much greater detail than the gtm when combined with nominal predictions from other data sources and available data from other instruments such as lidar or radar solutions for the spacecraft position and camera pointing are the most accurate available examples are drawn from studies of phobos eros and itokawa including surface characterization gravity analysis spacecraft navigation and incorporation of lidar or radar data this work has important implications for potential future missions such as deep interior and the level of navigation and science that can be achieved

holocene loess deposition and soil formation as competing processes matanuska valley southern alaska although loess paleosol sequences are among the most important records of quaternary climate change and past dust deposition cycles few modern examples of such sedimentation systems have been studied stratigraphic studies and 22 new accelerator mass spectrometry radiocarbon ages from the matanuska valley in southern alaska show that loess deposition there began sometime after f6500 14 c yr b p and has continued to the present the silts are produced through grinding by the matanuska and knik glaciers deposited as outwash entrained by strong winds and redeposited as loess over a downwind distance of f40 km loess thickness sand content and sand pluscoarse silt content decrease whereas fine silt content increases loess deposition was episodic as shown by the presence of paleosols at distances 10 km from the outwash plain loess source stratigraphic complexity is at a maximum i e the greatest number of loesses and paleosols at intermediate 10 25 km distances from the loess source surface soils increase in degree of development with distance downwind from the source where sedimentation rates are lower proximal soils are entisols or inceptisols whereas distal soils are spodosols ratios of mobile cao k2o and fe2o3 to immobile tio2 show decreases in surface horizons with distance from the source thus as in china where loess deposition also takes place today eolian sedimentation and soil formation are competing processes study of loess and paleosols in southern alaska shows that particle size can vary over short distances loess deposition can be episodic over limited time intervals and soils developed in stabilized loess can show considerable variability under the same vegetation d 2004 university of washington all rights reserved

late quaternary loess in northeastern colorado part ii pb isotopic evidence for the variability of loess sources a new application of the pb isotopic tracer technique has been used to determine the relative importance of different silt sources for late wisconsin loess in the central great plains of eastern colorado samples of the peoria loess collected throughout the study area contain k feldspar derived from two isotopically and genetically distinct sources 1 glaciogenic material from early and middle proterozoic crystalline rocks of the colorado province and 2 volcaniclastic material from the tertiary white river group exposed on the northern great plains pb isotopic compositions of k feldspar in loess from two dated vertical sections at beecher island and last chance colorado vary systematically implying climatic control of source availability we propose a model whereby relatively cold conditions promoted the advance of front range valley glaciers discharging relatively little glaciogenic silt but strong winds caused eolian erosion of white river group silt due to a decrease in vegetation cover during warmer periods valley glaciers receded and discharged abundant glaciogenic silt while surfaces underlain by the white river group were stabilized by vegetation isotopic data from eastern colorado loess sections record two warm cold warm cycles during late wisconsin time between about 21 000 and 11 000 radiocarbon yr b p similar to results from other studies in the united states and greenland

post eruptive development of the ukinrek east maar since its eruption in 1977 a d in the periglacial area of south west alaska maar eruptions form small initially steep walled basins that contain important archives for the climatic and palaeoenvironmental history in continental areas the two ukinrek maars in south western alaska erupted between 30 march and 9 april 1977 and are the best documented maars that have erupted in historical time this study presents a preliminary analysis of geomorphology hydrology magnetic susceptibility geochemistry and sedimentology data of a field study in august 2004 these results photographs and topographic surveys are combined for reconstructing the post eruptive evolution of ukinrek east maar within less than 30 years the initially polygonal shape of the crater with nearly vertical crater walls has developed into an almost elliptic form with slopes of 35 inclination on debris fans between a few escarpments the water table and the crater floor have risen significantly and the crater diameter depth ratio increased from 3 4 to 5 7 whereas the average height of the crater rim remained almost constant the main sub aerial resedimentation process is formation of rock falls rock slumps and scree resulting in debris flows and turbidites within the lake that is ice covered throughout about half of the year distal lake sediments consist of laminated minerogenic clayey sandy silts that document frequent turbidity currents from the linear sedimentation rate of only ca 5 mm year 1 in 17 cm long cores it may be concluded that the largest portion of the crater sediments formed within the first few months of the maar history however this has to be confirmed by future studies

late quaternary loess in northeastern colorado part i age and paleoclimatic significance loess in eastern colorado covers an estimated 14 000 km 2 and is the westernmost part of the north american midcontinent loess province stratigraphic studies indicate there were two periods of loess deposition in eastern colorado during late quaternary time the first period spanned ca 20 000 to 12 000 14 c yr b p ca 20 14 ka and correlates reasonably well with the culmination and retreat of pinedale glaciers in the colorado front range during the last glacial maximum the second period of loess deposition occurred between ca 11000 and 9000 14 c yr b p this interval may be holocene or may correlate with a hypothesized younger dryas glacial advance in the colorado front range sedimentologic mineralogic and geochemical data indicate that as many as three sources could have supplied loess in eastern colorado these sources include glaciogenic silt derived from the colorado front range and two bedrock sources volcaniclastic silt from the white river group and clays from the pierre shale the sediment sources imply a generally westerly paleowind during the last glacial maximum new carbon isotope data combined with published faunal data indicate that the loess was probably deposited on a cool steppe implying a last glacial maximum july temperature depression relative to the present of at least 5 6 c overall loess deposition in eastern colorado occurred mostly toward the end of the last glacial maximum under cooler and drier conditions with generally westerly winds from more than one source

provenance and earthquake signature of the last deglacial xinmocun lacustrine sediments at diexi east tibet abstract well preserved lacustrine sediments are found in some areas in east tibet this region is characterized by a windy and semi arid climate alpine valleys and frequent earthquakes measurements of rare earth elements observations from a scanning electron microscope and a high resolution record of grain size measurements allowed us to compare fine sediments from the xinmocun section in the diexi lake with loess from the chinese loess plateau and south china results indicate that fine grains of the xinmocun lacustrine sediments were transported by wind and trapped in the lake whereas the 16 m fraction was likely from local sources the grain size changes within the section repeatedly show abrupt coarsening and upward fining probably due to palaeoearthquake events large earthquakes in the study area often caused rockfalls and landslides exposing fine sediments that had accumulated on mountains slopes the fine grains were then retransported by wind to the diexi lake optically stimulated luminescence dating of the xinmocun section indicates continuous deposition from 18 65 to 10 63 ka these results indicate that palaeoearthquakes in the study area had a mean recurrence interval of 0 32 ka therefore we propose that lacustrine sediments in a tectonically active region have the potential to record a continuous history of palaeoearthquakes palaeoearthquakes probably produced numerous rockfalls and landslides in alpine valleys and provided significant sources of regional eolian dust

late pleistocene and holocene tephrostratigraphy of interior alaska and yukon key beds and chronologies over the past 30 000 years abstract the aleutian arc alaska peninsula and wrangell volcanic field are the main source areas for tephra deposits found across alaska and northern canada and increasingly tephra from these eruptions have been found further afield in north america greenland and europe however there have been no broad scale reviews of the late pleistocene and holocene tephrostratigraphy for this region since the 1980s and this lack of data is hindering progress in identifying these tephra both locally and regionally to address this gap and the variable quality of associated geochemical and chronological data we undertake a detailed review of the latest pleistocene to holocene tephra found in interior alaska and yukon this paper discusses nineteen tephra that have distributions beyond southwest alaska and that have the potential to become or already are important regional markers this includes three modern events from the 20th century ten with limited data availability but potentially broad distributions and six that are widely reported in interior alaska and yukon each tephra is assessed in terms of chronology geochemistry and distribution with new bayesian age estimates and geochemical data when possible this includes new major element geochemical data for crater peak 1992 redoubt 1989 90 and two andesitic tephra from st michael island tephra d as well as revised age estimates for dawson tephra oshetna hayes set h aniakchak cfe ii and the white river ashes northern and eastern lobes

glacial anticyclone recorded in palouse loess of northwestern united states climate simulations for the last glacial maximum using general circulation models typically show a glacial anticyclone that produced an easterly wind anomaly south of the north american ice sheets evidence of this phenomenon has not been found in eolian sedimentary deposits that record surface wind patterns luminescence ages of loess and accompanying paleoecologic records from opal phytoliths and paleosol units across the columbia plateau washington state united states document a decrease up to fivefold in regional dust production and accumulation from 35 ka to 15 ka this interval corresponds to simulations indicating that a glacial anticyclone weakened prevailing south southwesterly winds that have shaped the eolian landscape of the columbia plateau since at least 75 ka at the same time that the glacial anticyclone suppressed dust production and accumulation enhanced cold and dry conditions resulted in soil formation dominated by intense bioturbation in periglacial steppe accompanied by shallow calcium carbonate precipitation this is the first evidence from eolian deposits in north america verifying that the glacial anticyclone altered surface wind patterns and affected eolian systems during the last glacial maximum

late pleistocene mountain glaciation in alaska key chronologies moraine sequences of mountain glaciers can be used to infer spatial and temporal patterns of climate change across the globe alaska is an accessible high latitude location in the northern hemisphere and contains a rich record of alpine glaciation here we highlight the key chronologies from three mountain ranges in alaska that reveal the timing and spatial extent of late pleistocene glaciation and pay particular attention to age of the penultimate glaciation the most extensive glacier advance of the last glaciation occurred prior to the last global glacial maximum cosmogenic exposure ages from moraine boulders in three sites spanning 800km indicate that this penultimateadvancemostlikelyculminatedduringmarineisotopestage mis 4orearlymis3 during mis 2 more limited glacier expansion generated multiple moraines that span from prior to the global last glacial maximum lgm through the lateglacial period glaciers retreated from their terminal positions ca 27 25ka in arctic alaska and ca 22 19ka in southern alaska moraines in at least two ranges date to 12 11ka indicating a glacial advance during the younger dryas period reconstructed equilibrium line altitudes of both penultimate and mis 2 glaciers were lowered only 300 600m much less than elsewhere in the americas alaska is documented to have been more arid during mis 2 perhaps due in large part to the exposure of the bering chukchi platform during eustatic sea level lowering the restricted ice extent is also consistent with the output of climate models that simulate a lack of significant summer cooling copyright 2008 john wiley sons ltd

distribution of boulders and the gravity potential on asteroid itokawa abstract the small asteroid itokawa was visited in 2005 by the japanese spacecraft hayabusa the images of the surface showed a scenario different to previously visited asteroids itokawa has a small number of large craters and many large boulders randomly distributed on most of the surface we analyse images taken at different surface resolution and configurations corresponding to several regions on the asteroid s surface by overlapping visual images and maps of the total potential and surface gravity we observe a correlation between the distribution of boulders and these parameters the boulders on the surface were identified by visual inspection of several images after fitting ellipses to every boulder we computed their size and the size distribution from decimeters to several meters at different locations in the surface we found that the size distribution is correlated with the total potential and the surface gravity a steeper size distribution shifted towards the small objects is observed in the low negative total potential high surface gravity which corresponds to the muses c region meanwhile in the head and bottom regions of high potential low surface gravity we obtain a shallower size distribution shifted towards the large boulders we confirm there is a size segregation that is correlated with the gravity field which can be explained under the action of the brazil nut effect there is a global relocation of boulders with large ones going into the high potential regions and small ones into the low potential ones a shape segregation is also observed on the location of the boulders more rounded ones are found in the regions of high potential while more elongated ones are frequent in regions of low potential

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