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

estimating groundwater exchange with lakes 1 the stable isotope mass balance method groundwater inflow and outflow contributions to the hydrologic budget of lakes can be determined using a stable isotope 18o 16o mass balance method the stable isotope method provides a way of integrating the spatial and temporal complexities of the flow field around a lake thereby offering an appealing alternative to the traditional time and labor intensive methods using seepage meters and an extensive piezometer network in this paper the method is applied to a lake in northern wisconsin demonstrating that it can be successfully applied to lakes in the upper midwest where thousands of similar lakes exist inflow and outflow rates calculated for the wisconsin lake using the isotope mass balance method are 29 and 54 cm yr respectively which compare well to estimates derived independently using a three dimensional groundwater flow and solute transport model of 20 and 50 cm yr such a favorable comparison lends confidence to the use of the stable isotope method to estimate groundwater exchange with lakes in addition utilization of stable isotopes in studies of groundwater lake systems lends insight into mixing processes occurring in the unsaturated zone and in the aquifer surrounding the lake and verifies assumed flow paths based on head measurements in piezometers

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

holocene glacier advances in the headwaters of sredniaya avacha kamchatka russia abstract holocene glacial deposits in sredniya avacha headwaters are subdivided into three age groups events a b and c based upon geomorphic features tephrochronology and lichenometry tephras of opala volcano 1400 1500 yr b p ksudach volcano 1700 1800 and 6000 yr b p and zavaritskiy volcano 2800 yr b p are used as stratigraphic markers rhizocarpon geographicum l dc and rhizocarpon section alpicola growth curves are established using tephrochronologically dated and historical surfaces the age of event a pre hypsitermal moraines is constrained by an age of 6000 yr b p for overlying ksudach 2 tephra and an age of 7200 lichenometric l yr b p event b neoglaciation had a multiple nature with the most prominent advances at 4300 3500 3300 2800 2600 2100 1800 1400 and 1300 1100 l yr b p the culmination occurred before 2800 yr b p as suggested by a date for zavaritskiy volcano tephra found on the glacial and outwash deposits less extensive glacier advances of event c little ice age occurred at 800 600 500 200 180 110 and 90 40 l yr b p the ela depression was 200 250 100 150 30 70 m during the culmination of events a b and c respectively

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

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

a laboratory experiment on the dynamics of the land and sea breeze abstract the land and sea breeze lsb circulation was simulated in a laboratory using a temperature controlled water tank flow visualization by tellurium and phenolphthalein and velocity measurement by laser doppler velocimeter were carried out in addition to temperature measurements from similarity considerations the simulated flow pattern was shown to have good correspondence with that in the atmosphere it was shown that the overall features of the lsb flow pattern consist of a closed circulating motion caused by the periodically changing horizontal temperature difference between the land and the sea and several kinds of small scale motions induced by the periodic variation of the land surface temperature itself the most important small scale motion is the cellular convection which occurs all over the land surface due to unsteady heating from below in the morning calm other small scale motions such as longitudinal vortex rows which are formed inland throughout the sea breeze layer and gravity c

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 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

petrogenesis of a basalt rhyolite tephra from the west central afar ethiopia the cindery tuff is an unusual tephra fall deposit that contains evidence for the mixing of basaltic and rhyolitic liquids prior to eruption it contains clear rhyolitic glass shards together with brown basaltic glass spheres and a broadly bimodal phenocryst assemblage brown glasses are ferrobasaltic in composition and are similar to the voluminous pliocene tholeiites of the surrounding west central afar volcanic field both are enriched in the light rare earth and incompatible elements and possess higher 87sr 86sr and lower 143nd 144nd than morb rhyolitic glasses are subalkaline and compared to the basaltic glasses are strongly depleted in the compatible elements and enriched in the incompatible elements both glass types have similar incompatible element and isotopic ratios and with the rhyolite glass showing a 2 fold parallel enrichment in rare earth element abundances over the basaltic glass these observations suggest that the two glasses are genetically related

fission track ages of late cenozoic distal tephra beds in the yukon territory and alaska six distal tephra beds from the yukon territory and alaska have been dated by the fission track method zircon and glass ages were determined for the fort selkirk and lost chicken tephra beds but only glass ages for the others assuming that no track fading has occurred in the glass old crow and dawson tephra beds are younger than 120 000 and 52 000 years bp respectively mosquito gulch tephra is 1 22 ma old fort selkirk tephra is about 1 ma old the ester ash bed is 0 45 ma old and the best estimate of the age of lost chicken tephra is the range 1 7 2 6 ma it is evident from these results and from the known abundance of tephra beds within late cenozoic deposits of the yukon territory and alaska that application of the fission track method to distal tephra in conjunction with detailed characterization studies offers great potential for elucidation of the late cenozoic geologic history of alaska and the yukon territory

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

stratigraphy fossils and age of sediments at the upper pit of the lost chicken gold mine new information on the late pliocene environment of east central alaska abstract the upper pit at the lost chicken placer gold mine in east central alaska contains fossils that provide information on the flora and insect fauna of interior alaska just before the onset of global cooling at 2 5 myr fossils come from sediments interbedded with the lost chicken tephra dated at 2 9 0 4 myr early late pliocene and portray the floodplain and valley of a small creek within a region dominated by a coniferous forest richer in genera and species than the present one climate was wetter and less continental and there was probably little or no permafrost at least one other pliocene tephra the fortymile tephra occurs at the site and is also associated with plant and insect fossils among these fossils are extinct plants and insects like those found at other tertiary sites in northern canada and alaska the lost chicken sequence is the same age as the beaufort formation on meighen island more than 1000 km to the north like lost chicken meighen island sediments contain fossils representing a diverse boreal environment this shows that the latitudinal climate gradient during early late pliocene time was shallower than at present and the boreal forest had a far greater latitudinal span than now

numerical simulation of the interaction between the sea breeze front and horizontal convective rolls part i offshore ambient flow abstract a three dimensional cloud resolving model is used to investigate the interaction between the sea breeze circulation and boundary layer roll convection horizontal convective rolls hcrs develop over land in response to strong daytime surface heating and tend to become aligned parallel to the vertical wind shear vector whereas the land sea heating contrast causes the formation of the sea breeze front sbf along the coastline the ability of hcrs to modulate the along frontal structure of the sbf is examined complementing and extending previous observational and numerical studies three simulations are discussed the first two demonstrating that the model can produce both phenomena independently the third is initialized with offshore mean flow and vertical shear perpendicular to the coastline and results in a sharply defined inland propagating sbf that encounters hcrs aligned perpendicular to it before the interaction takes place the sbf is nearly two dimensional and devoid of along front

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

magnetic reversal history of pleistocene sediments at old crow northwestern yukon territory the banks of the porcupine river near old crow in the unglaciated part of the northern yukon consist of about 55 m of interbedded fluvial and lacustrine gravels sands silts and clays this sequence was sampled closely for palaeomagnetic analysis and the sediments were found to possess a natural remanent magnetization nrm that is stable in direction with mean destructive fields of 200 300 oe 16 24 ka m therefore good palaeomagnetic data can be obtained from sediments that have been subjected to permafrost conditions although some samples show disturbance of nrm directions by cryoturbation magnetic polarity transitions are centred at 17 and 26 m above river level and the 15 samples between them define an interval of reversed polarity of considerable duration the behaviour of nrm during the transition periods is complex with declination switching abruptly by 180 but with the inclination displaying very erratic variation over a considerable time this may be caused by mixing in single samples of c

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

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

the formation of new england coastal fronts abstract coastal fronts are a frequent late fall and early winter feature of eastern new england weather data from a mesoscale observing network is used to describe the process of coastal frontogenesis and to determine the causes of formation three distinct types of coastal frontogenesis are found to occur in new england and examples of each are presented using mesoscale surface maps and time series type a coastal fronts form during cold air outbreaks as winds veer from offshore to onshore type b coastal fronts form in the evening as air temperatures over land fall below air temperatures over water both types of fronts represent thermally direct circulations which are created by heating from the warm sea surface often in combination with radiational cooling over land type c coastal fronts are caused by upstream blocking when a stable region of warm advection such as warm front approaches the appalachian mountains from the south type a and type b fronts are described in terms of land and sea bre

effect of anisotropy and groundwater system geometry on seepage through lakebeds 2 numerical simulation analysis abstract the interaction of lakes and groundwater is controlled partly by the geologic framework through which the water flows two interrelated geometric factors of the groundwater system that affect flow are overall geometry of the system and anisotropy of the porous media within the system numerical simulation analysis was made for variations in the coefficient of anisotropy for each of several lake and groundwater settings having different geometric configurations these analyses indicate that for a given geometric setting as the anisotropy of geologic materials decreases seepage from a lake decreases and depth of the local groundwater flow system associated with the lake increases transformation of scale of groundwater systems that have anisotropic media to isotropic equivalents results in a change in the overall geometry because of the different slopes of the water table and lakebed resulting from the scale transformations a series of numerical experiments were made for various geometric configurations for a given anisotropy these analyses indicate that as thickness of the groundwater system decreases relative depth of the local flow system increases and seepage from the lake decreases

tectonic controls on tholeiitic and calc alkaline magmatism in the aleutian arc the tectonic position of aleutian arc volcanic centers and their magmatic differentiation trends calc alkaline or tholeiitic appear to correlate from 160 w to 175 e the volcanoes form four major arc segments that coincide with earthquake aftershock zones and major geographic features on both the upper and lower plates the tholeiitic volcanoes are large primarily basaltic centers that occur between or at the end of segments where magmas can more easily reach the surface and undergo shallow closed system differentiation the calc alkaline volcanoes are smaller more andesitic centers that occur in the middle of segments where transit through the upper plate is apparently more difficult differentiation is deeper and the intrusive to extrusive ratios are higher than in the tholeiitic centers the chemistry of the least differentiated basalts at both types of centers is similar and suggests a common parent magma probably derived from mantle peridotite conditions for the derivation of the two trends through crystal fractionation support the proposed model the tholeiitic magmas show characteristics i e no hydrous phenocrysts fe enrichment trend parallel ree patterns vitrophyric and esites and dacites consistent with low pressure high temperature crystallization in large shallow magma chambers the calc alkaline magmas show characteristics i e some hydrous phenocrysts no fe enrichment trend nonparallel rare earth patterns porphyritic lavas consistent with higher pressure and lower temperature of crystallization than the tholeiitic series tertiary plutons also show both calc alkaline and tholeiitic trends and appear to be chemically similar to the quaternary volcanoes the larger plutons are calc alkaline and probably represent the extensive 1002 km magma chambers of the small calc alkaline volcanoes the small shallow tholeiitic plutons complement the large tholeiitic volcanoes and reflect the greater percent of extrusive rocks in the tholeiitic series

interaction between turbulent flow and sea breeze front over urban like coast in large eddy simulation turbulent flow and its interaction with a sea breeze front sbf over an urban like coast with a regular block array were investigated using a building resolving computational fluid dynamics model it was found that during daytime with an offshore ambient flow streaky turbulent structures tended to grow within the convective boundary layer cbl over a warm urban surface ahead of the sbf the structures were organized as streamwise streaks at an interval of a few hundred meters which initiated at the rooftop level with strong wind shear and strengthens in the cbl with moderate buoyancy the streaks then interacted with the onshore propagating sbf as it made landfall the sbf which was initially characterized as a shallow and quasi linear feature over the sea developed three dimensional structures with intensified updrafts at an elevated frontal head after landfall frontal updrafts were locally enhanced at intersections where the streaks merged with the sbf which greatly increased turbulent fluxes at the front the frontal line was irregular because of merging tilting and transformation effects of vorticity associated with streaky structures inland penetration of the sbf was slowed by the frictional effect of urban like surfaces and turbulent flow on land the overall sbf intensity weakened after the interaction with turbulent flow these findings aid understanding of local weather over coastal cities during typical sea breeze conditions

characterization identity distribution and source of late cenozoic tephra beds in the klondike district of the yukon canada a large number of distal silicic tephra beds have been preserved in the late cenozoic deposits of the klondike region yukon territory forty one tephra samples representing twelve distinctive beds are detailed in this study they range in composition from basaltic andesite to high silica rhyolite and were deposited during the late pliocene to late wisconsinan time interval seven tephra beds are derived from volcanoes in the wrangell volcanic field and four come from the more distant eastern aleutian arc alaska peninsula region but the source of the single andesitic tephra is unknown the widespread and well known old crow and sheep creek tephra beds have been identified in the klondike district but all the other tephra units are characterized in detail for the first time the ages of most tephra beds are poorly constrained but will undoubtedly become better known with the application of recently developed glass fission track methods hence prospects are favourable for the eventual development

pleistocene epigenetic and syngenetic frost fissures belchatow poland pseudomorphs of cryogenic fissures in stratified medium to fine silty sand and sand at belchatow poland indicate both epigenetic and syngenetic freezing of sediments at various times during the pleistocene syngenetic fissures are more frequent they are typically 0 5 2 0 m in vertical dimension range in width from 5 to 20 cm exhibit both upwarps and downwarps of enclosing sediments and are offset from each other in the stratigraphic sequence epigenetic fissures are larger generally increase in width upwards and are related to an inferred ground surface it is difficult to distinguish between syngenetic fissures that penetrate permafrost and soil ground veins or wedges that require only deep seasonal frost for their formation cold continental environments characterized by rapid sedimentation and permafrost aggradation appear most conducive for formation of syngenetic fissures today both large and small syngenetic fissures are known to exist in the permafrost regions of siberia but are rarely

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

early and late holocene glacial fluctuations and tephrostratigraphy cabin lake alaska marked changes in sediment types deposited in cabin lake near cordova alaska represent environmental shifts during the early and late holocene including fluctuations in the terminal position of sheridan glacier cabin lake is situated to receive meltwater during periods when the outwash plain of the advancing sheridan glacier had aggraded a brief early holocene advance from 11 2 to 11 0 cal ka is represented by glacial rock flour near the base of the sediment core non glacial lake conditions were restored for about 1000 years before the water level in cabin lake lowered and the core site became a fen the fen indicates drier than present conditions leading up to the holocene thermal maximum an unconformity spanning 5400 years during the mid holocene is overlain by peat until 1110 ce when meltwater from sheridan glacier returned to the basin three intervals of an advanced sheridan glacier are recorded in the cabin lake sediments during the late holocene 1110 1180 1260 1540 and 1610 1780 ce the sedimentary sequence also contains the first five reported tephra deposits from the copper river delta region and their geochemical signatures suggest that the sources are the cook inlet volcanoes redoubt augustine and crater peak and possibly mt churchill in the wrangell volcanic field copyright 2013 john wiley sons ltd

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

effects of water table configuration on seepage through lakebeds the interaction of lakes and groundwater is controlled in part by the configuration of the water table near a lake seepage from lakes does not occur if the water table mound between the lake and a regional groundwater discharge arca is sufficiently high and the water table gradient between the mound and the discharge area sufficiently small water table configurations associated with two grountlwatcr systems of different geometry were examined by digital simulation for the first setting there is no seepage from the lake if the water table gradient from the mound to the regional discharge area is 0 011 for the second the critical gradient is about 0 009 seepage from the lake occurs if water table gradients are greater than these two values for various glacial terrains in which most natural lakes occur water table gradients of 0 010 or greater are most common in the more rugged end moraines consisting of silty till and gradients of 40 010 are common in arcas of ground moraine outwash plains

differences between the last two glacial maxima and implications for ice sheet δ18o and sea level reconstructions studies of past glacial cycles yield critical information about climate and sea level ice volume variability including the sensitivity of climate to radiative change and impacts of crustal rebound on sea level reconstructions for past interglacials here we identify significant differences between the last and penultimate glacial maxima lgm and pgm in terms of global volume and distribution of land ice despite similar temperatures and radiative forcing our analysis challenges conventional views of relationships between global ice volume sea level seawater oxygen isotope values and deep sea temperature and supports the potential presence of large floating arctic ice shelves during the pgm the existence of different glacial modes calls for focussed research on the complex processes behind ice age development we present a glacioisostatic assessment to demonstrate how a different pgm ice sheet configuration might affect sea level estimates for the last interglacial results suggest that this may alter existing last interglacial sea level estimates which often use an lgm like ice configuration by several metres likely upward

late quaternary caldera forming eruptions in the eastern aleutian arc alaska late quaternary calderas have been identified at 12 of 40 volcanic centers in the eastern aleutian arc and sufficient radiocarbon dates and geologic information have now been obtained to either date or constrain the timing of the climactic caldera forming eruptions at least eight major caldera forming events each characterized by estimated eruption volumes of more than 10 km 3 occurred at seven different volcanic centers in the holocene and as many as six of these had estimated eruption volumes of more than 50 km 3 eruptions of similar magnitude formed two other calderas in wisconsin time the dating of these hitherto little known events adds significantly to the previously existing chronology of large prehistoric eruptions this refined chronology is important in understanding eruption induced climate changes in assessing volcanic hazards and in developing a tephrochronology for northwestern north america

evidence for a new geomagnetic reversal from lava flows in idaho discussion of short polarity reversals in the brunhes and late matuyama polarity chrons k ar ages and paleomagnetic data for basalt samples from a new core hole site e at the idaho national engineering laboratory inel indicate that the age of the reversed polarity event recorded in snake river plain lavas is older than 465 50 ka 1000 years before present reported previously by champion et al 1981 nine basalt flows eight with normal polarity and one with reversed polarity were recognized in the site e core hole the flows above and below the reversed flow have ages of 491 80 ka and 580 93 ka respectively the inclination of the paleomagnetic field direction of the reversed flow at site e agrees with the inclination of reversed flows elsewhere at inel which have an age of 565 14 ka these reversed flows were previously thought to be correlative with the emperor event we suggest that this polarity event is an older event which we name the big lost reversed polarity subchronozone and subchron a review of data documenting short reversal records from volcanic and sedimentary rocks shows that there is evidence for eight polarity subchrons in the brunhes and two besides the jaramillo in the late matuyama these 10 short subchrons begin to indicate the many short events that cox 1968 hypothesized must exist if polarity interval lengths have a poisson distribution these events are true subchrons not excursions and may or may not have low associated paleointensities although low field strengths might explain why the reversal process aborts the mean sustained polarity interval length since late matuyama chron time is 90 000 years the similarity of this number with the 105 year period of the earth s orbital eccentricity suggests anew that linkage between geomagnetic paleoclimatic and possible underlying earth orbital parameters should be evaluated

mutual climatic range reconstructions of seasonal temperatures based on late pleistocene fossil beetle assemblages in eastern beringia abstract the mutual climatic range mcr method of paleoclimate reconstruction has been employed by paleoentomologists for the last decade a quantitative calibrated method mcr has many advantages over qualitative methods the method has now been developed for arctic faunas climate envelopes for beetle species found in eastern beringia have been compiled using a 25 km gridded north american climate database that pairs climate parameters with modern collection sites linear regressions of predicted on observed values yielded equations used to calibrate the mcr estimates this study presents the initial results from the mcr analysis of 46 fossil beetle assemblages from alaska and the yukon territory the assemblages range in age from about 150 000 9200 yr bp isotope stage six assemblages yielded estimates of mean july temperature tmax 4 5 c colder than at present assemblages associated with the old crow tephra oct dated approximately 140 000 yr bp likewise indicated tmax values well below modern levels isotope stage 5e faunas showed tmax values as much as 3 5 c warmer than modern early wisconsinan assemblages showed climatic cooling with tmax levels dropping as low as 6 c colder than at present a mid wisconsinan interstadial period is marked by warming of mean summer temperatures to near modern levels at some sites last glacial maximum assemblages reflect cooling of tmax to a level about 6 4 c colder than at present although most assemblages from this period yielded mean january temperatures above modern levels warming of summer temperatures began at least by 12 500 yr bp and warmer than modern tmax values were recorded from all assemblages between then and 9200 yr bp

reply to comment on estimating groundwater exchange with lakes 1 the stable isotope mass balance method and estimating groundwater exchange with lakes 2 calibration of a three dimensional solute transport model to a stable isotope plume by david p krabbenhoft et al

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

the use of glass for dating volcanic ash by thermoluminescence the development of a new physical dating method for late pleistocene tephrochronometry is described here tests of laboratory procedures applied to glass from independently dated samples show that the thermoluminescence tl additive dose dating method can yield accurate ages for both proximal and distal tephra from a few hundred years to at least 400 ka the technique involves purification of 4 to 11 m glass by heavy liquid centrifugation pre tl readout heating at 50 75 c for 8 days and careful regression analysis of tl growth curves several unknown age tephra are dated directly by this method for the first time these include five ash beds from summer lake oregon 67 200 ka a sheep creek valley ash from alaska 81 9 ka an ash from nevada 200 50 ka correlated to the wadsworth tephra an unknown ash 210 30 ka from rye patch dam in nevada previously correlated to the 400 to 600 ka dibekulewe tephra and ash 9m from washtucna in eastern washington 250 30 ka

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

the interaction of lakes with variably saturated porous media numerical simulation of variably saturated porous media indicates that groundwater recharge is variable in time and space depending on the thickness of the unsaturated zone through which infiltrating water must move the resulting complex transient groundwater flow systems have significant impact on contiguous surface water in very permeable media small local closed groundwater flow systems can develop and dissipate within a few weeks to several months after major recharge these have a direct effect on contiguous surface water by alternately causing seepage to and seepage from the surface water the transient nature of these flow systems indicates that reversals of the direction of groundwater flow may be common in less permeable media the same complex flow systems may occur but the time for development and dissipation is much greater for example it is conceivable that small local flow systems may exist for many months or years as a result of major recharge therefore directions of flow in such systems are more stable and the effect on contiguous surface water also is more stable the findings of this study indicate that wells and groundwater quality sampling sites need to be carefully located to define accurately water table configuration groundwater recharge direction of seepage through the beds of surface water bodies and complex geochemical processes related to changing directions of groundwater flow

distribution stratigraphy petrochemistry and palaeomagnetism of the late pleistocene old crow tephra in alaska and the yukon revision accepted january l i 1985 the late quaternary old crow tephra is a two pyroxene calc alkaline dacite whose known areal extent is broadly delimited by a triangle with apices at the seward peninsula the wrangell mountains and the old crow basin in the northern yukon everywhere the tephra is fine grained mdu 5 33 2 0 32 and moderately to poorly sorted 6u 1 33 0 29 samples from the extremities of the fall out zone have similarity coefficients of 0 95 a palaeomagnetic excursion is recorded in sediments just below old crow tephra in the fairbanks area and at imuruk lake on the seward peninsula a short full reversal of the magnetic field has been preserved at the corresponding stratigraphic level near old crow in the northern yukon chronological controls based on i4c and fission track dates and sedimentation rates show that these palaeornagnetic features are almost certainly partial records of the complex geomagnetic blake event which occurred 100 120 ka ago new petrochemical data demonstrate that the source of old crow tephra is in the eastern aleutian arc

age of pre late wisconsin glacial estuarine sedimentation bristol bay alaska pleistocene glacial estuarine sediment deposited in an intertidal environment of northeastern bristol bay southwestern alaska was dated using a variety of approaches including infrared stimulated and thermoluminescence irsl and tl techniques analysis of modern and14c dated holocene tide flat mud demonstrates that the bulk of sediment in this environment is reset by solar radiation thereby lending confidence to ages obtained from similar pleistocene deposits by luminescence techniques irsl seems to be especially well suited for dating with resolution on time scales of 10 000 yr the ages of tide flat mud of the nushagak formation derived from the ahklun mountains to the northwest of bristol bay and of halfmoon bay drift derived from the alaska peninsula to the southeast suggest contemporaneous glacial estuarine deposition related to independent glacial source areas about 75 000 80 000 yr ago this age is consistent with other geochronological data that indicate a pre late wisconsin and post substage 5e age including nonfinite14c ages a lack of interglacial indicators and old crow tephra 140 000 yr atop the drift normal paleomagnetic inclinations and amino acid isoleucine epimerization ratios aile ile aile ile ratios inportlandia arctica 0 052 0 003 from a marine lag horizon at south naknek beach which separates halfmoon bay drift above from older glacial estuarine drift below are only slightly higher than inmya truncata 0 041 0 007 from last interglacial pelukian deposits at nome as laboratory heating experiments show that the two genera epimerize at similar rates these data imply correlation of the marine lag at south naknek beach with pelukian deposits hence glaciers on the alaska peninsula experienced major pre late wisconsin advances both before and after the last interglaciation shells reworked into halfmoon bay drift yield aile ile ratios of 0 028 0 005 forportlandiaat second point and 0 027 0 001 forhiatella arcticaat etolin point together with assumptions about the postdepositional temperature history these ratios indicate that the shells are at least 55 000 yr and probably closer to 90 000 yr although the uncertainty in this age estimate is broad the amino acid and luminescence data converge on an age between about 75 000 and 90 000 yr late during oxygen isotope stage 5 for a major ice advance far beyond late wisconsin limits

large eddy simulation of the onset of the sea breeze this paper describes results from a large eddy simulation les model used in an idealized setting to simulate the onset of the sea breeze as the les is capable of simulating boundary layer scale threedimensional turbulence along with the mesoscale sea breeze circulation a parameterization of the planetary boundary layer was unnecessary the basic experimental design considers a rotating uniformly stratified resting atmosphere that is suddenly heated at the surface over the land half of the domain to focus on the simplest nontrivial problem the diurnal cycle effects of moisture interactions with large scale winds and coastline curvature were all neglected in this study the assumption of a straight coastline allows the use of a rectangular computational domain that extends to 50 km on either side of the coast but only 5 km along the coast with 100 m grid intervals so that the small scale turbulent convective eddies together with the mesoscale sea breeze may be accurately computed through dimensional analysis of the simulation results the length and velocity scales characterizing the simulated sea breeze as functions of the externally specified parameters are identified

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

isothermal plateau fission track age of the late pleistocene old crow tephra alaska hydrated glass shards of the widespread old crow tephra in alaska have been dated by the isothermal plateau fission track method which corrects for partial track fading if present the weighted mean age of 149 13 ka is older than previous estimates which range from 86 to 109 ka these new data support the view that old crow tephra was deposited during the cold interval that immediately preceded the last interglacial which is dated in the marine record at 125 ka b p it is likely therefore that the buried forest beds and numerous ice wedge pseudomorphs preserved in sediments just above old crow tephra in interior alaska relate to the last interglacial and not a younger warm event of early wisconsin age

vertebrate tracks in pleistocene eolian sand sheet deposits of alaska abstract deformation structures interpreted as vertebrate hoof and foot tracks occur within upper pleistocene eolian sand sheet deposits in the stabilized kantishna sand sea of central alaska and in the nushagak lowland of southwestern alaska exposures of tracks are generally limited to cross sections which reveal concave up deformation structures in which displacement of preexisting strata diminishes downward deposits in both areas contain tracks that are 6 to 16 cm in diameter and are divided by a central ridge reflecting formation by artiodactyl even toed ungulates larger 21 34 cm tracks without a central ridge observed in the nushagak lowland were formed by proboscideans probably woolly mammoth large vertebrate tracks occur within irregularly stratified sand and silty sand that accumulated upon partially vegetated sand sheets and within thin even wind ripple laminae of unvegetated sand sheets the presence of tracks at multiple stratigraphic levels and preservation of roots and rhizocretions within the eolian deposits suggest that vegetated sand sheets may have formed a locally important grazing habitat for large herbivores during at least part of the last glaciation recognition that vertebrate tracks are preserved in eolian sand sheet deposits and in deposits of other environments as well opens a new source of stratigraphic and paleoecological data to aid reconstruction of the vanished ecosystems of beringia

origin of the late quaternary dune fields of northeastern colorado stabilized eolian deposits mostly parabolic dunes and sand sheets cover much of the landscape of northeastern colorado and adjacent parts of southwestern nebraska in four geographically distinct dune fields stratigraphic and soil geomorphic relations and accelerator radiocarbon dating indicate that at least three episodes of eolian sand movement occurred between 27 ka and 11 ka possibly between 11 ka and 4 ka and within the past 1 5 ka thus eolian sand deposition took place under both glacial and interglacial climatic conditions in the youngest episodes of eolian sand movement holocene parabolic dunes partially buried pleistocene sand sheet deposits late holocene sands in the fort morgan and wray dune fields to the south of the south platte river have trace element ratios that are indistinguishable from modern south platte river sands but different from ogallala formation bedrock which has previously been cited as the main source of dune sand on the great plains sands in the greeley dune field to the north of the south platte river have trace element concentrations that indicate a probable laramie formation source measurements of parabolic dunes indicate paleowinds from the northwest in all dune fields in good agreement with resultant drift directions calculated for nearby weather stations thus paleowinds were probably not significantly different from present day winds and are consistent with a south platte river source for the fort morgan and wray dune fields and a laramie formation source for the greeley dune field sand accumulated downwind of the south platte river to form the fort morgan duen field in addition sand was also transported farther downwind over the upland formed by the calcrete caprock of the ogallala formation and deposited in the lee of the upland on the southeast side because of high wind energy the upland itself served as a zone of sand transport but little or no sand accumulation took place on this surface these studies which demonstrate the importance of fluvial source sediments for dune fields in colorado may be applicable to other dune fields in north america because modern drift potentials in northeastern colorado are among the highest in the world the present stability of dunes in the region may be in part a function of the dunes being supply limited rather than solely transport limited extensive 7700 km2 late holocene dunes document that eolian sand in northeastern colorado is very sensitive to small changes in climate or fluvial source conditions

correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods review and evaluation abstract we define tephras and cryptotephras and their components mainly ash sized particles of glass crystals in distal deposits and summarize the basis of tephrochronology as a chronostratigraphic correlational and dating tool for palaeoenvironmental geological and archaeological research we then document and appraise recent advances in analytical methods used to determine the major minor and trace elements of individual glass shards from tephra or cryptotephra deposits to aid their correlation and application protocols developed recently for the electron probe microanalysis of major elements in individual glass shards help to improve data quality and standardize reporting procedures a narrow electron beam diameter 3 5 m can now be used to analyze smaller glass shards than previously attainable reliable analyses of microshards defined here as glass shards in part 2 of the review we describe critically assess and recommend ways in which tephras or cryptotephras can be correlated in conjunction with other information using numerical or statistical analyses of compositional data statistical methods provide a less subjective means of dealing with analytical data pertaining to tephra components usually glass or crystals phenocrysts than heuristic alternatives they enable a better understanding of relationships among the data from multiple viewpoints to be developed and help quantify the degree of uncertainty in establishing correlations in common with other scientific hypothesis testing it is easier to infer using such analysis that two or more tephras are different rather than the same adding stratigraphic chronological spatial or palaeoenvironmental data i e multiple criteria is usually necessary and allows for more robust correlations to be made a two stage approach is useful the first focussed on differences in the mean composition of samples or their range which can be visualised graphically via scatterplot matrices or bivariate plots coupled with the use of statistical tools such as distance measures similarity coefficients hierarchical cluster analysis informed by distance measures or similarity or cophenetic coefficients and principal components analysis pca some statistical methods cluster analysis discriminant analysis are referred to as machine learning in the computing literature the second stage examines sample variance and the degree of compositional similarity so that sample equivalence or otherwise can be established on a statistical basis this stage may involve discriminant function analysis dfa support vector machines svms canonical variates analysis cva and anova or manova or its two sample special case the hotelling two sample t2 test randomization tests can be used where distributional assumptions such as multivariate normality underlying parametric tests are doubtful compositional data may be transformed and scaled before being subjected to multivariate statistical procedures including calculation of distance matrices hierarchical cluster analysis and pca such transformations may make the assumption of multivariate normality more appropriate a sequential procedure using mahalanobis distance and the hotelling two sample t2 test is illustrated using glass major element data from trachytic to phonolitic kenyan tephras all these methods require a broad range of high quality compositional data which can be used to compare unknowns with reference training sets that are sufficiently complete to account for all possible correlatives including tephras with heterogeneous glasses that contain multiple compositional groups currently incomplete databases are tending to limit correlation efficacy the development of an open online global database to facilitate progress towards integrated high quality tephrostratigraphic frameworks for different regions is encouraged

last interglacial age of the eva forest bed central alaska from thermoluminescence dating of bracketing loess abstract the eva forest bed in the yukon tanana upland of east central alaska represents a frozen buried boreal forest this bed consists of well preserved peat lenses sticks roots logs as well as rooted and unrooted stumps of trees where preserved the eva forest bed is overlain by the goldstream formation and underlain by gold hill loess almost all exposures have a prominent unconformity at the top of the gold hill loess even where the forest bed is not preserved attempts have been made over the last 50 yr to determine the age of this bed numerically we report here details of thermoluminescence tl dating of 14 samples of loess from above and below this unconformity in the fairbanks area together with knowledge about the climatic indicators from the eva forest bed these tl age estimates 1 indicate that the most probable age of the eva forest bed is 125 ka the time of the warmest part of oxygen isotope stage 5 and 2 confirm stratigraphic inferences from tephra beds in the upper gold hill loess that erosion has removed variable thicknesses of the original loess complex just prior to the development of the eva forest bed

estimating groundwater exchange with lakes 2 calibration of a three dimensional solute transport model to a stable isotope plume a three dimensional groundwater flow and solute transport model was calibrated to a plume of water described by measurements of 18o and used to calculate groundwater inflow and outflow rates at a lake in northern wisconsin the flow model was calibrated to observed hydraulic gradients and estimated recharge rates calibration of the solute transport submodel to the configuration of a stable isotope 18o plume in the contiguous aquifer on the downgradient side of the lake provides additional data to constrain the model a good match between observed and simulated temporal variations in plume configuration indicates that the model closely simulated the dynamics of the real system the model provides information on natural variations of rates of groundwater inflow lake water outflow and recharge to the water table inflow and outflow estimates compare favorably with estimates derived by the isotope mass balance method krabbenhoft et al this issue model simulations agree with field observations that show groundwater inflow rates are more sensitive to seasonal variations in recharge than outflow

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