dating loess up to 800 ka by thermoluminescence thermoluminescence tl ages agreeing with expected ages have been obtained for 13 loess samples spanning the age range from 20 to 800 ka our samples are from alaska and north island new zealand and are unusual in tl dating studies of loess older than 80 100 ka by having independent age assignments that are generally well constrained from ages of associated tephra beds with the polymineral fine silt sized 4 11 m grains the partial bleach tl technique yielded expected ages up to about 350 ka whereas the total bleach method gave accurate ages in the range 100 to 800 ka thus the much disputed upper age limit of 100 150 ka for the tl dating of loess now appears to be sample and worker dependent rather than a global property of the tl signals in the tl dominant feldspars

the palisades is a key reference site for the middle pleistocene of eastern beringia new evidence from paleomagnetics and regional tephrostratigraphy abstract the palisades in central alaska is one of the most prominent exposures of quaternary sediments on the yukon river perennially frozen silt and sand at the palisades are presently thought to preserve paleoenvironmental records from the holocene to marine isotope stage mis 8 and beneath a major unconformity the earliest pleistocene 2 ma we present new paleomagnetic and tephrochronologic constraints that substantially revise the age of the sediments at the palisades we describe 15 new tephra beds including five beds below the prominent pal tephra that correlate to known tephra with independent age control from other sites in eastern beringia these five known tephra include chester bluff tephra which is present in east central alaska and the yukon and the newly named alyeska pipeline and taylor highway tephra from central alaska all are constrained to the middle pleistocene paleomagnetic transects from the base of the bluff to the mis 5e forest bed yield normal polarity with the exception of a brief reversal event between old crow tephra 124 10 ka and the mis 5e forest bed that is likely the first documentation of the blake paleomagnetic event in alaskan loess the detailed tephrostratigraphy and paleomagnetic data collectively suggest that most of the sedimentary record at the palisades is middle pleistocene in age the palisades thus preserves a rare record of late to middle pleistocene paleoenvironments with multiple regionally distributed tephra beds

old crow tephra a new late pleistocene stratigraphic marker across north central alaska and western yukon territory old crow tephra is the first extensive pleistocene tephra unit to be documented in the northwestern part of north america it has a calc alkaline dacitic composition with abundant pyroxene plagioclase and fe ti oxides and minor hornblende biotite apatite and zircon thin clear bubble wall fragments are the dominant type of glass shard this tephra can be recognized by its glass and phenocryst compositions as determined by x ray fluorescence microprobe and instrumental neutron activation techniques it has an age between the limits of 60 000 and 120 000 yr set by 14c and fission track measurements respectively old crow tephra has been recognized in the koyukuk basin and fairbanks region of alaska and in the old crow lowlands of the northern yukon territory some 600 km to the east northeast the source vent is unknown but these occurrences considered in relation to the distant locations of potential quaternary volcanic sources demonstrate the widespread distribution of this tephra and underscore its importance as a regional stratigraphic marker

stratigraphic context of old crow tephra holitna lowland interior southwest alaska abstract a thick deposit of old crow tephra was discovered in a bluff exposure along the middle holitna river near the kulukbuk hills 61 20 n latitude 157 10 w longitude in interior southwest alaska this locality is the southwesternmost known deposit of old crow tephra in alaska thickness and grain size data from this site support a source volcano in the eastern aleutian arc pleistocene stratigraphic sequences in the lowland are dominated by upward fining eolian sand sheet deposits and loess separated by organic silt these deposits record at least two episodes of regional glaciation and an intervening nonglacial period marine oxygen isotope stage 3 stage 5 or both old crow tephra crops out near the top of the lower upward fining eolian unit indicating that the ash erupted near the end of an interval of periglacial eolian sedimentation the sequence of eolian deposits that contain old crow tephra probably accumulated during the latter part of marine oxygen isotope stage 6 whereas the overlying eolian sequence formed during the last glaciation stage 2 this stratigraphic position is consistent with other stratigraphic contexts for the tephra and with fission track and thermoluminescence ages of ca 140 000 10 000 yr b p

paleoclimatic forcing of magnetic susceptibility variations in alaskan loess during the late quaternary visual matches and statistical tests suggest correlations between marine isotope curves retrodictive solar insolation at lat 65 n and magnetic susceptibility profiles through late quaternary age alaskan loess sections the susceptibility changes largely appear to reflect variability in magnetite content due to climatically controlled changes in wind intensity and competence magnetic susceptibility profiles through massive loess can provide stratigraphic context for intercalated paleosols and tephras a prominent paleosol correlated with marine isotope stage 5 occurs several metres above the old crow ash in loess sections indicating that this important tephra is older than suggested by thermoluminescence dates and may have been deposited ca 215 25 ka

thermoluminescence dating of periods of loess deposition and soil formation in normandy the least incomplete records of pleistocene climate change come from the study of deep sea sediments in which the stratigraphic record of oxygen isotope variations reflecting terrestrial ice volume is the primary correlation medium on continents the available record is far less complete because many of the characteristics of glaciation are erosional rather than depositional the areas of loess deposition may provide the best deposits in which to develop relatively complete regional stratigraphies that may be compared with the deep sea record1 2 in this study we use thermoluminescence tl dating of loess and of soil developed on loess to test this model we have confined ourselves to the last complete glacial cycle within which the reproducibility of the age determinations is similar to the time resolution of most deep sea core records

vegetation and paleoclimate of the last interglacial period central alaska the last interglacial period is thought to be the last time global climate was signi cantly warmer than present new stratigraphic studies at eva creek near fairbanks alaska indicate a complex last interglacial record wherein periods of loess deposition alternated with periods of soil formation the eva forest bed appears to have formed about the time of or after deposition of the old crow tephra dated to 160 to 120 ka and is therefore correlated with the last interglacial period pollen macrofossils and soils from the eva forest bed indicate that boreal forest was the dominant vegetation and precipitation may have been greater than present around fairbanks during the peak of the last interglacial period a new compilation of last interglacial localities indicates that boreal forest was extensive over interior alaska and yukon territory boreal forest also extended beyond its present range onto the seward and baldwin peninsulas and probably migrated to higher elevations now occupied by tundra in the interior comparison of last interglacial pollen and macrofossil data with atmospheric general circulation model results shows both agreement and disagreement model results of warmer than present summers are in agreement with fossil data however numerous localities with boreal forest records are in con ict with model reconstructions of an extensive cool steppe in interior alaska and much of yukon territory during the last interglacial 2000 elsevier science ltd all rights reserved

a 14 000yr paleoenvironmental record from windmill lake central alaska lateglacial and holocene vegetation in the alaska range abstract a 14 000 yr high resolution pollen and lake level record from windmill lake in central alaska provides new evidence for the late pleistocene and holocene paleoenvironments of this region at 14 000 14 c yr bp sparse herb tundra and low lake levels indicate a cold arid environment about 11 800 14 c yr bp the vegetation abruptly shifted to a shrub tundra and lake levels increased suggesting warmer and more mesic conditions ca 10 500 10 200 14 c yr bp herbaceous taxa increased at the expense of the shrubs suggesting a transient episode of climatic deterioration nearly contemporaneous with the younger dryas chronozone by 8000 14 c yr bp spruce was present in the watershed and alder grew locally by 6500 14 c yr bp the ams radiocarbon chronology indicates later expansions of betula picea and alnus than at most sites in central alaska which are conventionally dated

two step deglaciation at the oxygen isotope stage 6 5e transition the zeifen kattegat climate oscillation comparison of marine lacustrine and terrestrial records from twenty four sites suggests the existence of a younger dryas type climate oscillation just prior to the oxygen isotope stage 6 5e boundary these records include results from biostratigraphic pedostratigraphic and speleothem studies as well as analyses of stable isotope compositions of marine records and ice cores the climate oscillation is named after the warm zeifen interstadial and the cold kattegat stadial the zeifen interstadial may be related to a major meltwater pulse in the baffin bay labrador sea norwegian sea region the climate oscillation is presumably in part a result of a variation in ocean circulation especially in the strength of the north atlantic drift but changes in the atmospheric circulation also played an important role the geographically widespread distribution of the oscillation suggests that the two step deglaciation influenced both the northern and southern hemispheres c 1996 elsevier science ltd

a late middle pleistocene marine isotope stage 6 vegetated surface buried by old crow tephra at the palisades interior alaska abstract a 40 cm thick primary bed of old crow tephra 131 11 ka an important stratigraphic marker in eastern beringia directly overlies a vegetated surface at palisades west on the yukon river in central alaska analyses of insect bryophyte and vascular plant macrofossils from the buried surface and underlying organic rich silt suggest the local presence of an aquatic environment and mesic shrub tundra at the time of tephra deposition autochthonous plant and insect macrofossils from peat directly overlying old crow tephra suggest similar aquatic habitats and hydric to mesic tundra environments though pollen counts indicate a substantial herbaceous component to the regional tundra vegetation trace amounts of arboreal pollen in sediments associated with the tephra probably reflect reworking from older deposits rather than the local presence of trees the revised glass fission track age for old crow tephra places its deposition closer to the time of the last interglaciation than earlier age determinations but stratigraphy and paleoecology of sites with old crow tephra indicate a late marine isotope stage 6 age regional permafrost degradation and associated thaw slumping are responsible for the close stratigraphic and paleoecological relations between old crow tephra and last interglacial deposits at some sites in eastern beringia

spatiospectral localization of global geopotential fields from the gravity recovery and climate experiment grace reveals the coseismic gravity change owing to the 2004 sumatra andaman earthquake 1 regional mass fluxes owing to transport and adjustment within the earth system that are implicitly contained in the monthly gravity recovery and climate experiment grace global geopotential coefficients are revealed by localizing global spectra using spatiospectrally concentrated window functions we have analyzed 45 monthly global grace harmonic coefficient series in order to find the coseismic signature associated with the 2004 great sumatra andaman earthquake a significant gravity change after the earthquake is found in the time series of the grace coefficients after localization with a single band limited window centered near the north of the island of sumatra this change is undetectable from the original global coefficients or from coefficients localized elsewhere on the globe a step function with its discontinuity at 26 december 2004 usefully models the coseismic gravity change the localized grace coefficients contain the jumps associated with the earthquake up to degree and order 55 although not all of them within this band produce changes that are statistically significant the gravity change calculated from the localized grace coefficients displays 30 gal peak to peak variations that are very well correlated with an independently derived seismic model based on elastic dislocation theory

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

interglacial deposits at birch creek northeast interior alaska abstract a 12 m sequence of lake sediment and peat in a 45 m high exposure on birch creek northeast alaska contains pollen of picea betula alnus and populus and wood of picea and populus this sequence which may represent 10 000 yr of more of accumulation is beyond the limit of radiocarbon dating it lies between two units of loess the underlying loess lies above the old crow tephra recently dated at 149 000 13 000 yr b p the lake sediments probably were deposited during the last interglaciation isotope substage 5e and subsequently buried by wisconsinan loess analogs for the ancient lake may be deep long lived thaw lakes that are present in the modern landscape when birch creek is correlated with other sites across nonglaciated alaska and northwest canada there appears to be a common interglacial signal in sediments overlying the old crow tephra

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

jurassic arthropod tracks from northern iran abstract in 2010 a siltstone slab containing three arthropod trackways was discovered in the middle jurassic dansirit formation in the ruyan region central alborz mountains northern iran quality of preservation is varied but the best preserved track sequences consist of a chevron shaped pair of outer tracks surrounding two pairs of inner tracks these trace fossils are named herein as a new ichnogenus and ichnospecies porpaichnus dansiritensis the depositional environment of the track bearing stratum is enigmatic if the sediment is of littoral origin the footprints were likely made by a decapod crustacean for a terrestrial deposit the imprint morphology is possible evidence of an arachnid that used its pedipalps to supplement four pairs of walking legs these morphological characteristics suggest the track maker is may have been an early member of the infraorder mygalomorpha if so the 170 ma trackways are the earliest known evidence of a tarantula like spider although the oldest known tarantula fossils date to the miocene fossil evidence of mygalomorph spiders dates to the cretaceous and molecular clock evidence suggests that divergence of spider families occurred in the late paleozoic

identification of last interglacial deposits in eastern beringia a cautionary note from the palisades interior alaska last interglacial sediments in unglaciated alaska and yukon eastern beringia are commonly identified by palaeoe cological indicators and stratigraphic position 2 5 m above the regionally prominent old crow tephra 124 10 ka we demonstrate that this approach can yield erroneous age assignments using data from a new exposure at the palisades a site in interior alaska with numerous exposures of last interglacial sediments tephrochronology stratigraphy plant macrofossils pollen and fossil insects from a prominent wood rich organic silt unit are all consistent with a last interglacial age assignment however six 14 c dates on plant and insect macrofossils from the organic silt range from non finite to 4 0 14 c ka bp indicating that the organic silt instead represents a holocene deposit with a mixed age assemblage of organic material in contrast wood samples from presumed last interglacial organic rich sediments elsewhere at the palisades in a similar stratigraphic position with respect to old crow tephra yield non finite 14 c ages given that local permafrost thaw since the last interglaciation may facilitate reworking of older sediments into new stratigraphic positions minimum constraining ages based on 14 c dating or other methods should supplement age assignments for last interglacial sediments in eastern beringia that are based on palaeoecology and stratigraphic association with old crow tephra copyright 2011 john wiley sons ltd

a mascon approach to assess ice sheet and glacier mass balances and their uncertainties from grace data the purpose of this paper is to assess the mass changes of the greenland ice sheet gris ice sheets over antarctica and land glaciers and ice caps with a global mascon method that yields monthly mass variations at 10 242 mascons input for this method are level 2 data from the gravity recovery and climate experiment grace system collected between february 2003 and june 2013 to which a number of corrections are made with glacial isostatic adjustment gia corrections from an ensemble of models based on different ice histories and rheologic earth model parameters we find for greenland a mass loss of 278 19 gt yr whereas the mass balances for the gris appear to be less sensitive to gia modeling uncertainties this is not the case with the mass balance of antarctica ice history models for antarctica were recently improved and updated historic ice height data sets and gps time series have been used to generate new gia models we investigated the effect of two new gia models for antarctica and found 92 26 gt yr which is half of what is obtained with ice 5g based gia models where the largest gia model differences occur on east antarctica the mass balance of land glaciers and ice caps currently stands at 162 10 gt yr with the help of new gia models for antarctica we assess the mass contribution to the mean sea level at 1 47 0 09 mm yr or 532 34gt yr which is roughly half of the global sea level rise signal obtained from tide gauges and satellite altimetry

permafrost response to last interglacial warming field evidence from non glaciated yukon and alaska abstract we present stratigraphic observations from three sites in eastern beringia ch ijee s bluff in northern yukon and nearby exposures on the old crow river the palisades on the yukon river in alaska and placer mining exposures at thistle creek in west central yukon which provide insight into the response of permafrost to regional warming during the last interglaciation chronology is based on the presence of old crow tephra an important regional stratigraphic marker that dates to late marine isotope stage 6 supplemented by paleoecology and non finite 14c ages on wood rich organic silts old crow tephra overlies several relict ice wedges at the palisades and thistle creek indicating that permafrost at these sites did not thaw completely during the last interglaciation prominent deposits of last interglacial wood rich organic silt are present at multiple sites in eastern beringia and probably represent accumulations of reworked forest vegetation due to thaw slumping or deposition into thermokarst ponds or depressions consistent stratigraphic relations between these deposits old crow tephra and ice wedge pseudomorphs at our three study sites and at least six other sites in eastern beringia suggest that thaw of shallow permafrost was widespread during the last interglaciation limited stratigraphic evidence suggests that thaw was probably on the order of meters rather than 10s of meters the ubiquity of shallow permafrost degradation during the last interglaciation suggests that current ground warming may foreshadow widespread near surface thaw under even modest future warming scenarios however the persistence of relict pre last interglacial ice wedges highlights the potential for the regional antiquity of discontinuous permafrost and provides compelling field evidence for the long term resilience of deep permafrost during sustained periods of warmer than present climate

vegetation history of pleasant island southeastern alaska since 13 000 yr b p abstract a 13 000 year history of late quaternary vegetational and climatic change has been derived from lacustrine sediments from pleasant island in the glacier bay region of southeastern alaska early arrival of lodgepole pine and mountain hemlock indicated by the presence of pollen and conifer stomata suggests expansion from refugia in the alexander archipelago a short term climatic reversal possibly correlated with the european younger dryas is inferred from the expansion of tundra elements and deposition of inorganic sediments between 10 600 and 9900 14 c yr b p two peat cores from the lake catchment verify holocene vegetation changes and aid in the separation of biogenic from climatic forces affecting vegetation history differences in pollen representation among the three cores illustrate the variation among pollen collecting substrates as well as the spatial heterogeneity of peatland development and its dependence on local hydrology initial peat accumulation and soil paludification occasioned by increases in temperature and precipitation in the early holocene allowed western and mountain hemlock to replace sitka spruce 8500 8000 yr b p open muskeg became widespread about 7000 yr b p and allowed lodgepole pine to reinvade the region after a 2000 yr absence the extensive replacement of fen elements by bog taxa at 3400 yr b p suggests increased paludification due to changing hydrologic conditions its correlation with the upland expansion of tsuga heterophylla suggests the onset of a cooler wetter neoglacial climate in southeastern alaska

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

combination of various observation techniques for regional modeling of the gravity field modeling a very broad spectrum of the earth s gravity field needs observations from various measurement techniques with different spectral sensitivities typically high resolution regional gravity data are combined with low resolution global observations to exploit the gravitational information as optimally as possible we set up a regional modeling approach using radial spherical basis functions emphasizing the strengths of various data sets by the flexible combination of high and middle resolution terrestrial airborne shipborne and altimetry measurements the basis functions are defined and located in the region of interest in such a manner which the highest measure of information of the input data is captured any functional of the earth s gravity field can be derived as e g quasi geoid heights or gravity anomalies here we present results of a study area in northern germany a comprehensive cross validation to external observation data delivers standard deviations less than 5 cm differences to an existing regional quasi geoid model count on average 6 cm and proof the plausibility of our solution the comparison with existing global models reaches higher standard deviations for the more sensitive gravity anomalies as for quasi geoid heights showing the additional value of our solution in the high frequency domain covering a broad frequency spectrum our regional models can be used as basis for various applications such as refinement of global models national geoid determination and detection of mass anomalies in the earth s interior

150 000 years of loess accumulation in central alaska abstract the halfway house site in interior alaska is arguably the most studied loess deposit in northwestern north america the site contains a complex paleomagnetic and paleoenvironmental record but has lacked the robust chronologic control that would allow its full potential to be exploited detailed reexamination of stratigraphy paleomagnetics and tephrostratigraphy reveals a relatively complete marine isotope stage mis 6 to holocene record constrained by the old crow 124 10 ka vt 106 10 ka sheep creek klondike ca 80 ka dominion creek 77 8 ka and dawson ca 30 2 cal ka bp tephras we show two well developed paleosols formed during marine isotope stages mis 5e and 5a while mis 5c and 5b are either poorly represented or absent the new tephrostratigraphy presented here is the most complete one to date for the late pleistocene and indicates mis 5 sediments are more common than previously recognized a magnetic excursion within the sediments is identified as the post blake excursion 94 1 7 8 ka providing independent age control and adding to the increasing body of evidence that alaskan loess is a detailed recorder of variations of the earth s magnetic field over time a high resolution magnetic susceptibility profile placed into this new chronostratigraphic framework supports the hypothesis that wind intensity is the main variable controlling fluctuations in susceptibility correlation of the susceptibility record to global marine 18o records is complicated by highly variable accumulation rates we find the lowest rates of accumulation during peak warm and cold stages while abrupt increases are associated with periods of transition between marine isotope sub stages building on previous accumulation models for alaska surface roughness is likely a leading variable controlling loess accumulation rates during transitions and peak cold periods but the negligible accumulation during mis 5e and 5a suggests that loess production was exceedingly low negating the role of surface roughness this interplay of variables leads to optimal conditions for loess accumulation during transitions between isotope stages and to a somewhat lesser extent stadials and interstadials

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

paleoecology of two marine oxygen isotope stage 7 sites correlated by the sheep creek tephra northwestern north america abstract pollen analysis at two sites correlated by the presence of the 190 000 yr old sheep creek tephra documents fluctuations in vegetation and climate consistent with this date and indicates that the records span marine oxygen isotope stage 7 and the stage 6 7 transition dawson cut near fairbanks alaska provides a 5 2 m long pollen record of interglacial boreal forest succeeded by shrub tundra and then forest tundra ash bend stewart river central yukon provides a 9 5 m long record of interglacial boreal forest succeeded by forest tundra shrub tundra and herbaceous tundra the replacement of forest at both sites by more open or tundra vegetation indicates warm interglacial conditions giving way to cold and arid climate it is not clear whether stage 7 was warmer than the present the warm cool warm climate oscillation evident at both sites may correlate to lake baikal substages 7a 7b and 7c sheep creek tephra fell on forest tundra vegetation

tephrochronology of late cenozoic loess at fairbanks central alaska nineteen distinctive distal tephra beds from the gold hill loess in the fairbanks region central alaska are divided into two groups based on their color mineralogy glass shard morphology and the major and trace element composition of their glass shards this dichotomy in tephra composition is believed to reflect the two source regions namely the eastern aleutian arc alaska peninsula region and the wrangell volcanic field despite the fragmentary nature of the preserved loess record which contains many local unconformities these tephra beds can be used to link the numerous loess exposures in the fairbanks region in their proper time sequence establishing thereby a comprehensive reliable time stratigraphic framework because these distal tephra beds are related to large magnitude volcanic eruptions given the long distance to the nearest possible source vent they will also enable correlation of the late cenozoic sedimentary sequence at fairbanks to those of adjacent regions of alaska and the yukon tephra beds with bubble wall or chunky glass shards have been dated by the isothermal plateau fission track method results demonstrate that the gold hill loess spans a long interval of time from late pliocene time to the last interglacial about 125 ka however the age of the basal part of this formation is not well constrained due to the apparent absence of tephra beds paleomagnetic studies suggest that loess deposition in the fairbanks region began about 3 ma

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

a framework for interpreting paleoclimatic variations in eastern beringia abstract paleoclimatic variations in a particular region can be viewed as the outcome of the superimposition of the effects of a number of large scale controls a framework for understanding paleoclimatic variations in a region can be established by considering the long term history of those controls jointly with climatic modeling results that illustrate how regional climates respond to changes of individual controls the relevant controls of late quaternary paleoclimatic variations in eastern beringia include 1 the size of the ice sheet which influences both atmospheric circulation and temperature 2 insolation which influences mainly temperature and seasonality 3 carbon dioxide concentration in the atmosphere which influences temperature and 4 feedbacks involving sea ice sea surface temperatures and snow cover which reinforce the insolation effects we review the results of a number of paleoclimatic experiments with general circulation models to illustrate the potential response of eastern beringia to the variations of these controls we then present a framework for understanding paleoclimatic variations in eastern beringia by describing the likely responses of the climate of this region to the known variations in the controls in addition we discuss key times during the quaternary when particular combinations of the controls give rise to natural experiments which lend themselves to the testing of particular hypotheses our understanding of the nature of climatic variations at high latitudes should increase through examination of paleoclimatic evidence that documents the response of the region at those key times

late pleistocene environments of the western noatak basin northwestern alaska glacial lake noatak formed repeatedly during middle and late pleistocene time as expanding glaciers from the delong mountains blocked the noatak river valley downcutting by the noatak river has exposed thick sediment successions in bluffs up to 86 m high two river bluffs nk 26 and nk 29a contain correlative organic rich flood plain deposits that were formed during and after deposition of the old crow tephra at about the transition between oxygen isotope stage 6 and oxygen isotope stage 5 at the beginning of the last interglaciation both bluffs also contain older interglacial or interstadial flood plain deposits of uncertain age pollen and beetle remains were recovered from the older and younger flood plain deposits at each bluff pollen from the younger flood plain deposits suggests tundra vegetation with local dominance of sedge juniperus abundances were locally high especially around the time of old crow tephra deposition mutual climatic range mcr estimates from the insect fossil assemblages suggest that mean summer temperatures tmax near the time of old crow tephra deposition were about 2 c colder than modern mean winter temperatures were very similar to those of today a younger sample from the same interglacial deposit yielded a tmax estimate of 2 c warmer than modern signaling interglacial warming pollen from the older interglacial deposit at nk 29a suggests mesic tundra with boreal forest more distant than it is today mcr analysis of a possibly correlative older interglacial deposit at nk 26 suggests a tmax about 2 c below present

age of sheep creek tephra pleistocene in central alaska from thermoluminescence dating of bracketing loess the age of the sheep creek tephra sct a widespread marker ash bed in eastern alaska and western yukon territory has been ambiguous and controversial we have obtained three reliable thermoluminescence age estimates from bracketing loess near fairbanks that imply a deposition age of about 190 000 20 000 yr for sct three of six loess samples near and closely bracketing the sct beds near fairbanks yielded younger age estimates 117 000 and 135 000 yr most likely based on field aspects because of reworking and contamination by translocated grains the new reliable age assignment of 190 000 yr confirms independent stratigraphic evidence of a pre last interglaciation age and stratigraphic evidence from one site upper eva creek that sct is older than the more widespread 140 000 yr old old crow tephra the sct age also has implications for regional correlations of glacial and nonglacial deposits in particular it supports the stratigraphic and geomorphic interpretation that the delta glaciation in the east central alaska range and the reid glaciation in western yukon territory are older than the last interglaciation isotope substage 5e

an extensive middle to late pleistocene tephrochronologic record from east central alaska abstract chester bluff cb in yukon charley rivers national preserve ycnp alaska contains an extensive middle to late pleistocene tephra record within thick loess deposited on a terrace the regionally prominent old crow oc tephra 140 10 ka gi tephra 560 80 ka of fairbanks the preido hill prh tephra of the klondike and vt tephra 77 8 4 1 ka of both the klondike and fairbanks were found at cb the presence of these tephra beds will aid in correlating disparate paleoenvironmental records across eastern beringia there are 15 new tephra beds 11 from the wrangell volcanic field wvf and or hayes volcano one from the aleutian arc alaska peninsula aaap and three unclassified beds cb is normally magnetized indicating the entire sequence is of bruhnes age

regional high resolution spatiotemporal gravity modeling from grace data using spherical wavelets we determine a regional spatiotemporal gravity field over northern south america including the amazon region using grace inter satellite range rate measurements by application of a wavelet based multiresolution technique a major advantage of this method is that we are able to represent the amazon hydrological signals in form of time series of detail signals with level dependent temporal resolution the coarser structures generally require only ten days whereas the medium and finer details are computable from one month of data to this end we employ the basic property of multiresolution representations which is to split a signal into detail signals each related to a specific resolution level and computable from data covering a specific part of the spectrum our results which for the first time fully exploit the spatial and temporal resolutions of grace data in modeling amazon hydrological fluxes are in good agreement with hydrological models and gps derived height variations

evidence of quaternary climatic variations in a sequence of loess and related deposits at birch creek alaska implications for the stage 5 climatic chronology abstract a 45 m outcrop of quaternary sediments on birch creek near circle alaska reveals a record of fluctuating environmental conditions that probably spans several glacial interglacial cycles from base to top the deposits are forested floodplain warm colluvium with ice wedges cold forest soil warm loess cold paleosol containing old crow tephra oct cool to warm loess cold lacustrine very warm loess cold and modern forest soil warm resolution of the paleoclimatic history associated with the oct event is critical to understanding the nature of stage 5 in the western north american arctic application of recent age estimates for the oct tephra ca 140 000 yr bp to the birch creek section would indicate that either i the tephra paleosol dates from the 6 5 5 transition a strongly developed glacial interval occurred within stage 5 and the overlying very warm interval occurred in 5 3 or 5 1 or ii the tephra was deposited during a non milankovitch warming event late in stage 6 a paleoclimate chronology provides an alternative interpretation iii in which the tephra paleosol corresponds to stage 6 or even stage 7 the overlying loess to stage 6 and the lake sediments to all or part of stage 5 but the oct is older than 140 000 yr bp chronologies ii and iii imply a very warm beginning to stage 5 consistent with paleoclimate model simulations and data from other regions

late pliocene dawson cut forest bed and new tephrochronological findings in the gold hill loess east central alaska thick loess deposits in the fairbanks region of interior alaska are a rich source of information on past climates and environments during the late cenozoic and the numerous distal silicic tephra beds preserved within them offer the potential for good chronological control the dawson cut forest bed lies in the lower part of this loess cover plant macrofossils consist of picea glauca picea mariana betula papyrifera and populus balsamifera but no pinus these fossils together with the abundance and size of spruce remains pollen tree ring characteristics and 13 c values of spruce wood demonstrate that the boreal forest represented by the dawson cut forest bed was similar to the modern boreal forest of central alaska warming conditions during the early part of the dawson cut interglaciation initiated thawing of permafrost and melting of ground ice as evidenced in the presence of ice wedge casts and major erosion of the lower gold hill loess tephrochronological magnetostratigraphic and glass fission track dating studies in the fairbanks area and at the palisades site on the yukon river in central alaska suggest an age for the dawson cut forest bed of ca 2 ma hence the northern boreal forest of northwestern north america as we know it today has a long history that probably extends back to at least 2 ma

isotope stage 5 130 74 ka in greenland a review abstract marine and glacigene deposits dated with varying degrees of certainty to isotope stage 5 130 74 ka are exposed in coastal cliffs in 18 areas and localities in northern and eastern greenland dating methods include thermoluminescence tl u th methods and correlation with the deep sea record amino acid parameters are used for correlation between localities deposits from the last interglaciation isotope substage 5e are rare and have been found only at three localities in both west and east greenland their mollusc and foraminifer faunas indicate more vigorous sea surface circulation and sea surface temperatures some degrees higher than known from the holocene during this warm period ice sheet growth began in northwest greenland the ice sheet reached its maximum for the last ice age during the succeeding phase provisionally correlated with isotope substage 5d this was followed by a new warm period with increased influx of warm subarctic water and high summer temperatures on land provisionally correlated with isotope substage 5a in east greenland the observations indicate a more complex ice sheet history the record from greenland is very similar to that obtained in adjacent coastal areas of the high arctic implying that the rapid shifts from warm to cold during isotope stage 5 were especially conducive to the formation of the embryonic north american and scandinavian ice sheets at high northern latitudes probably because the pulses of warm water were required to advect sufficient moisture into these areas to allow the growth of continental ice sheets

the fox permafrost tunnel a late quaternary geologic record in central alaska the fox permafrost tunnel which penetrates 110 m into frozen sediments of gold stream valley provides a continuous exposure of fossiliferous silt and alluvium above schistose bedrock deposition of fluvial gravel was followed by a long interval of loess accretion and permafrost aggradation that was punctuated by episodes of thaw and of gullying and redeposition of silt imbricated sandy gravel above the bedrock contains lenses of finer alluvium that contain wood fragments and some rooted stumps radiocarbon dates indicate that the gravel is older than 40 ka but absence of mature soil and weathering profiles at its upper contact indicates that fluvial activity must have continued until shortly before loess accretion began at the tunnel site silt is the most widespread depositional unit in the tunnel this deposit is of eolian origin loess but some has been redeposited by slope processes the silt units contain abundant ground ice as pore filings lenses wedges and buried pond ice loess accretion was interrupted by a period when little loess accumulated and when large ice wedges formed in the lower loess unit and subsequently were truncated by thaw loess began forming sometime before 40 ka and was rapidly accreting by 39 ka under xeric conditions with open vegetation a sharply decreased rate of loess accretion associated with local erosion and thaw between about 36 and 30 ka is marked by anomalous cation concentration values lenses of buried sod fossils indicative of moist to wet substrates and truncated ice wedges beneath small frozen ponds or streamlets that occupied ice wedge troughs a later episode of rapid loess influx under drier conditions began after 30 ka and coincided with glacial advances of late wisconsin age in the adjoining alaska range large ice wedges also formed in the upper loess unit but only their bases are exposed in the tunnel and their history of development is uncertain fanlike deposits of poorly sorted debris near the tunnel portal formed between about 12 5 and 11 ka during deep erosion of loess slopes under moister conditions the deposits locally form two subunits the younger over whelmed a stand of tall willows on the floor of goldstream valley between about 11 3 and 11 1 ka the older may have formed about 1 000 yr earlier stratigraphic records elsewhere in central alaska indicate variable middle wisconsin environments followed by colder and drier conditions that began between 30 and 25 ka and persisted until perhaps 12 5 ka widespread loess erosion and redeposition subsequently occurred under moister and probably warmer conditions renewed early holocene loess deposition may have been widespread but its exact environmental controls are uncertain our data challenge three generally accepted concepts of late quaternary periglacial processes in central alaska we contend that 1 many ice wedge systems may have formed under interstadial conditions rather than full glacial conditions 2 episodes of rapid loess influx may have been partly out of phase with episodes of glacier expansion and 3 redeposition of loess by solifluction sheetwash and gully formation may have been episodic and required conditions moister than those under which the loess initially accreted

accelerated west antarctic ice mass loss continues to outpace east antarctic gains a b s t r a c t article history while multiple data sources have confirmed that antarctica is losing ice at an accelerating rate different measurement techniques estimate the details of its geographically highly variable mass balance with different levels of accuracy spatio temporal resolution and coverage some scope remains for methodological improvements using a single data type in this study we report our progress in increasing the accuracy and spatial resolution of time variable gravimetry from the gravity recovery and climate experiment grace we determine the geographic pattern of ice mass change in antarctica between january 2003 and june 2014 accounting for glacio isostatic adjustment gia using the ij05 r2 model expressing the unknown signal in a sparse slepian basis constructed by optimization to prevent leakage out of the regions of interest we use robust signal processing and statistical estimation methods applying those to the latest time series of monthly grace solutions we map antarctica s mass loss in space and time as well as can be recovered from satellite gravity alone ignoring gia model uncertainty over the period 2003 2014 west antarctica has been losing ice mass at a rate of 121 8g t yr and has experienced large acceleration of ice mass losses along the amundsen sea coast of 18 5g t yr 2 doubling the mass loss rate in the past six years the antarctic peninsula shows slightly accelerating ice mass loss with larger accelerated losses in the southern half of the peninsula ice mass gains due to snowfall in dronning maud land have continued to add about half the amount of west antarctica s loss back onto the continent over the last decade we estimate the overall mass losses from antarctica since january 2003 at 92 10 gt yr

temperatures at the last interglacial simulated by a coupled ocean atmosphere climate model the last interglacial eemian 125 000 years ago has generally been considered the warmest time period in the last 200 000 years and thus sometimes been used as a reference for greenhouse projections herein we report results from a coupled ocean atmosphere climate model of the surface temperature response to changes in the radiative forcing at the last interglacial although the model generates the expected summer warming in the northern hemisphere winter cooling of a comparable magnitude occurs over north africa and tropical asia the global annual mean temperature for the eemian run is 0 3 degrees c cooler than the control run validation of simulated sea surface temperatures ssts against reconstructed ssts supports this conclusion and also the assumption that the flux correction fitted for the present state operates satisfactorily for modest perturbations our results imply that contrary to conventional expectations eemian global temperatures may already have been reached by the mid 20th century

old crow tephra across eastern beringia a single cataclysmic eruption at the close of marine isotope stage 6 abstract old crow tephra is the largest and most widespread quaternary eruption presently known in eastern beringia its major and trace element geochemistry fe ti oxides and stratigraphic and paleoecological context indicate that it is the result of a single cataclysmic eruption the proximal region may well have experienced tephra fallout from small eruptions just prior to or after the old crow event but there is no evidence to indicate that the distal area was affected we recalculate the glass fission track age at 124 10 ka which coupled with stratigraphic and paleoenvironmental reconstructions indicates that deposition occurred prior to development of the last interglacial boreal forest which suggests a latest marine isotope stage mis 6 age the bulk tephra volume erupted is estimated by three different approaches that are in broad agreement at 200 km 3 but this result must be considered as tentative given the poor controls on definition of isopachs over such a large area the source caldera although presently unrecognized is located in the eastern aleutian arc possibly at or near the emmons lake volcanic center

paleoenvironments of the last interglacial in northwest north atlantic region and adjacent mainland canada abstract the paleoenvironmental conditions that prevailed in the northwest north atlantic regions and adjacent mainland canada during the last interglacial are documented through lithostratigraphical and paleontological data in terrestrial sections and marine cores with special reference to the deep sea records that allow global correlations based on their isotopic stratigraphy the onshore paleovegetational data and the offshore planktonic faunal and algal records demonstrate much warmer than present terrestrial and marine environments during the climate optimum of the last interglacial sensu stricto isotopic substage 5e optimal conditions persisted in surface water of the labrador sea during the early glacial inception isotopic substage 5e 5d transition when extensive ice masses developed over arctic canada a deterioration of sea surface temperature in labrador sea followed the maximum 18 o peak of isotopic substage 5d during the later part of stage 5 climatic conditions similar to the present prevailed over southeastern canada and a recurrent warming is recorded in south central labrador sea fluctuating ice volumes in the canadian arctic led to episodic dilution of surface water masses in baffin bay and the eastern labrador sea and subarctic conditions apparently prevailed in nearshore environments of baffin island despite an ice marginal context

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

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

old crow tephra found at the palisades of the yukon alaska abstract a 20 cm thick volcanic ash layer at the palisades along the yukon river is geochemically correlated with the old crow tephra a buried organic and wood rich layer above the old crow tephra probably records the last interglaciation the recognition of the old crow tephra provides the first chronologic information on the age of the thick sequence of pleistocene sediments at the palisades an important ice age mammal site in central alaska and a key locakity for the reconstruction of the history of the yukon river and the last interglaciation in central alaska

the last interglacial as recorded in the greenland ice sheet and canadian arctic ice caps abstract the greenland ice sheet and canadian arctic ice cap record of the last interglacial undertood broadly as marine isotopic stage 5 is critically reviewed lack of age control on the deep ice core records leaves open two largely different interpretations of the climate in marine isotopic stage 5 either most of stage 5 with the exception of substage 5e experienced a cold climate and the main change from interglacial to glacial conditions took place at the boundary between substages 5e and 5d or during much of stage 5 the climate was integracial type i e as warm as or warmer than at present with substage 5d as the only period with a glacial type climate it is concluded that most of the hard evidence is in favour of the latter scenario ice sheet dynamic model studies using the warm marine isotopic stage 5 scenario indicate that the greenland ice sheet in the warmest periods of stage 5 had split up into a main ice sheet covering central and northern greenland and a much smaller ice cap over the southeastern highlands the greenland record of marine isotopic stage 5 is then discussed in relation to other paleoclimatic and paleoenvironmental records the possibility of major inter hemispheric differences of the climate in mid and late marine isotopic stage 5 is discussed it is concluded that it is important to study the entire marine isotopic stage 5 not only substage 5e in order to understand possible differences in the global climatic responses to nearly indentical peaks in orbitally driven summer insolation changes in the northern hemisphere

report of 1st discussion group the last interglacial in high latitudes of the northern hemisphere terrestrial and marine evidence abstract the paleoclimatic informations preserved at some selected sites from high northern latitudes correlative with the last interglacial maximum of isotopic substage 5e have been compiled on a hemisphere scale the mapped compilation reveals much warmer climate conditions on average than present in both terrestrial and marine environments and indicates a northward shift of subpolar and boreal bioclimatic zones the data also suggest that temperature and precipitation gradients were significantly different than those of the holocene with particularly efficient latitudinal and eastward transport of warm air masses the paleoenvironmental and paleoclimate trends through the last interglacial sensu lato isotopic stage 5 are more difficult to assess because the chronostratigraphical framework is poorly constrained nevertheless the data suggest important regionalism in the climatostratigraphical trends in particular the large amplitude climatic cyclicity that characterizes the last interglacial of europe is barely observed elsewhere moreover by the end of the last interglacial isotopic substage 5a conditions slightly cooler than present are recorded in western europe while relatively warm conditions similar to today apparently prevailed in circumpolar regions adjacent to the north atlantic despite the onset of ice growth the last interglacial provides paleosynoptic situations unlike those of the present that may contribute to understanding interactions within the environmental system on a hemispheric scale there is however an imperative need for uniformization of data sets and for more accurate chronological control on regional scales

regional gravity field recovery using the goce gravity gradient tensor and heterogeneous gravimetry and altimetry data a regional approach using poisson wavelets is applied for gravity field recovery using the goce gravity field and steady state ocean circulation explorer gravity gradient tensor heterogeneous gravimetry data and altimetry measurements the added value to the regional model introduced by goce data is validated and quantified the performances of the solutions modeled with different diagonal components of goce data and their combinations are investigated numerical experiments in a region in europe show that the effects introduced by goce data demonstrate long wavelength patterns on the centimeter scale in terms of quasi geoid heights which may allow reducing the remaining long wavelength errors in ground based data and improve the regional model the accuracy of the gravimetric quasi geoid computed with a combination of three diagonal components is improved by 0 6 cm 0 5 cm in the netherlands belgium compared to that derived from gravimetry and altimetry data alone when goco05s is used as the reference model moreover the added value from goce data reduces the mean values of the misfit between the gravimetric solution and gps leveling data performances of different components and their combinations are not identical and the solution with vertical gradients is best when a single component is used the incorporation of multiple components shows further improvements and the combination of three components best fits the local gps leveling data further comparison shows our solution is the highest quality and may be substituted for existing models for engineering purposes and geophysical investigations over the target area

the evolution of a thermokarst lake landscape late quaternary permafrost degradation and stabilization in interior alaska thermokarst processes characterize a variety of ice rich permafrost terrains and often lead to lake formation the long term evolution of thermokarst landscapes and the stability and longevity of lakes depend upon climate vegetation and ground conditions including the volume of excess ground ice and its distribution the current lake status of thermokarst lake landscapes and their future trajectories under climatewarming are better understood in the light of their long term development we studied the lake rich southern marginal upland of the yukon flats northern interior alaska using dated lake sediment cores observations of river cut exposures and remotely sensed data the region features thick up to 40 m quaternary deposits mainly loess that contain massive ground ice two of three studied lakes formed 11 000 12 000 cal yr bp through inferred thermokarst processes and fire may have played a role in initiating thermokarst development from 9000 cal yr bp all lakes exhibited steady sedimentation and pollen stratigraphies are consistentwith regional patterns the current lake expansion rates are low 0 to b7 cmyr 1 shoreline retreat compared with other regions 30 cm yr 1 or more this thermokarst lake rich region does not showevidence of extensive landscape lowering by lake drainage nor of multiple lake generations within a basin however lidar images reveal linear corrugations n5 m amplitude deep thermo erosional gullies and features resembling lake drainage channels suggesting that highly dynamic surface processes have previously shaped the landscape evidently widespread early holocene permafrost degradation and thermokarst lake initiation were followed by lake longevity and landscape stabilization the latter possibly related to establishment of dense forest cover partial or complete drainage of three lakes in 2013 reveals that there is some contemporary landscape dynamism holocene landscape evolution in the study area differs from that described from other thermokarst affected regions regional responses to future environmental change may be equally individualistic

on the eruption age and provenance of the old crow tephra abstract tephrochronology is used to correlate and reconstruct geographically disparate sedimentary records of changing environment climate and landscape throughout geologic time single tephra layers represent isochronous markers across broad regions thus accurate and precise radiometric constraints on the timing of eruption are critical to their utility the old crow tephra is found throughout eastern beringia and represents the largest preserved pleistocene ashfall event in the region despite its volume and significance as a stratigraphic marker the provenance of this tephra is debated and the interpreted eruption age of marine isotope stage mis 5 at 125 ka has vacillated to investigate provenance and eruption age we develop a geochemical fingerprint for the old crow tephra via titanomagnetite geochemistry and zircon crystallization cooling age via coupled u pb u th and u th he zircon geochronology our results indicate that old crow oxides are geochemically distinct from the commonly assumed source caldera system at the emmons lake volcanic center elvc zircon crystals from the old crow tephra range in age from proterozoic to pleistocene with concordant zircon u pb u th and u th he dates on the youngest population of grains suggesting crystallization in their parent magma and in turn eruption at 202 9 9 5 ka we discuss strengths and shortcomings of our radiogenic datasets in light of this result and review the far reaching implications of a change in old crow eruption age

tephrochronology and paleoclimatology of the last interglacial glacial cycle recorded in alaskan loess deposits abstract alaskan loess deposits contain long paleoclimatic records analogous to those found in marine and lacustrine sediments and in ice sheets the sedimentology and geophysical properties of alaskan loess were influenced by climatically forced changes in wind intensity storminess temperature and precipitation loess deposits also contain evidence of episodic permafrost and paleosol formation explosive volcanic eruptions paleoecologic changes in high latitude regions quaternary fossils and early human sites and artifacts the old crow tephra ca 140 000 10 000 bp dates the transition between full glacial conditions and the last interglaciation in central alaska climatic amelioration in alaska apparently began prior to astronomically forced increases in insolation a finding consistent with the well dated devil s hole record however time series analysis of loess proxy climate data also demonstrates the effects of orbital precession and obliquity on alaskan climate change numerous short term climate events are recorded in alaskan loess deposits including a climate reversal corresponding to the younger dryas