modeling of deep water renewal through cold convective plumes abstract in only a few regions in the world ocean surface water is transformed into deep water by open ocean convection in this paper small areas of vertical flow or plumes are studied using a steady state model integrated in streamline coordinates we use an entrainment hypothesis based on knowledge about in mixing of water across the shear zone from an area of low turbulence into an area of high turbulence this results in a model using conservation equations for momentum heat and salt and a nonlinear equation of state effects of earth rotation are included the depth reached by surface water when moving through stationary plumes is predicted and found strongly dependent on the properties in the surface layer this layer has to be colder but only slightly denser than the water just below it to be a source for steady state plumes the thermobaric effect the dependency of compressibility on the temperature plays a major role for the plume penetration depth in weakly stratified cold water like in the greenland sea deep convection is found to be possible and efficient through steady state plumes initial excess density of less than 5 10 3 kg m 3 caused by low temperature can give convection deeper than 1500 m through plumes with horizontal scales of a few hundred meters and vertical velocities of order a few tens of centimeters per second

arctic ocean deep water masses in the western iceland sea the icelandic danish contribution to the international greenland sea project was devoted to a study of the distribution and transport of water masses in the western iceland sea each year in september from 1987 to 1991 temperature and salinity were observed on a station net in the area off east greenland from the denmark strait in the south to 72 30 n the data reveal that the deep water column of the western iceland sea is occupied by a number of slightly different water masses which all can be traced back to a formation in the arctic ocean it is especially noticeable that in some years almost undiluted eurasian basin deep water can be observed as far south as the denmark strait

impact processes permafrost dynamics and climate and environmental variability in the terrestrial arctic as inferred from the unique 3 6 myr record of lake el gygytgyn far east russia a review lake el gygytgyn in far east russia is a 3 6 myr old impact crater lake located in an area that has never been affected by cenozoic glaciations nor desiccation the unique sediment record of the l

variability in deep exchange between the eurasian and greenland basins evidence from tritium and helium 3 observations of decay corrected tritium in the deep eurasian basin and northern fram strait since 1979 indicate a significant decrease in 1993 whereas a box model predicts a steady decline with time the model simulates the greenland sea and eurasian basin deep water observations reasonably closely up to the early 1990s when it is retuned to simulate the 1993 decrease in the deep eurasian basin water tritium the deep exchange between the greenland sea and eurasian basin occurs over a shorter time scale this is likely in response to the reduced deep water formation in the greenland sea in the early 1980s modeled tritium in the deep eurasian basin shows the same trends as in the greenland sea and deep norwegian sea but with time lags of 8 2 y and 17 2 y respectively these lags are in close agreement with values indicated by tritium helium3 dating

paleomagnetic results from ch ijee s bluff porcupine river yukon territory abstract paleomagnetic vectors and magnetic susceptibility data are reported from a section at ch ijee s bluff on the banks of the porcupine river yukon territory the site is an important natural archive for the study of the last interglaciation in north america isotope stage 5 and has been intensively investigated the particular section covered by this report contains the old crow tephra oct which is an important chronostratigraphic marker in yukon and alaska the most significant finding is the identification of the biwa i jamaica subchron 2 3 m below the oct smaller scale geomagnetic secular variation features are also found and these have potential for lateral correlation as well as being of interest to geomagnetists due to the high latitude of the site a zone of distinctly shallower inclinations occurs near the oct and can be matched to a similar zone found at a site along the old crow river more than 40 km away magnetic susceptibility profiles also appear to correlate over distances of tens of kilometres and may thus provide useful confirmation of interpretations based on other data

biostratigraphy of the last glacial period in europe the european early weichselian early wurmian is characterized by two long and relatively warm interstadials brorup and odderade which can be traced and correlated with certainty across large parts of europe the amersfoort interstadial described earlier from the netherlands has been included in the brorup and represents the older part of it both great interstadials were forested in north west central and southern europe in the north conifer forests prevailed giving way towards the south to deciduous forests the climatic gradient was distinctly steeper mainly due to southward displacement of the gulf stream the two great interstadials are synchronous with the isotopic stages 5a and 5c in the deep sea cores subsequent to eemian brorup and odderade and from within the context of a continuous series two additional and clearly delimited interstadials have been recorded in a new standard profile from oerel nw germany these are now described as the oerel and glinde interstadials they were not forested and belong to the early pleni weichselian the lower one oerel can probably be correlated with the 3rd weichselian wurmian interstadial in southern central europe ognon ii durnten samerberg 3 while the upper one glinde has so far no known counterpart for the younger pleni glacial it is assumed that there was a long phase during which it was not too cold the formation of humic layers during this phase took place at different times partly due to local edaphic factors so that the relevant 14c dates show a wide scatter the hengelo and denekamp interstadials represent only slight ameliorations which facilitated the formation of shrub tundra and can be recorded in certain regions only

late quaternary sedimentary processes and ocean circulation changes at the southeast greenland margin a study has been made of late quaternary depositional processes and bottom current activity on the southeast greenland margin using seismic sub bottom profiling and deep tow side scan sonar data as well as sediment core information the seabed data demonstrate the occurrence of strong southerly bottom currents prevailing on the slope and rise well defined longitudinal bedforms indicate maximum mean near bottom current velocities of up to at least 1 0 m s at the depth stratum of labrador sea water 800 1500 m similarly strong currents occur in denmark strait overflow water dsow at the base of the slope whereas more basinward the maximum dsow flow speed is lower iceberg plow marks were found down to about 700 m water depth both at the shelf edge and on the lower slope and rise the seafloor morphology is indicative of downslope sediment transport and mass flow deposition which is concluded to be a typically glacial feature after generally more sluggish deep water circulation during the last glacial maximum dsow basin ventilation was re established shortly before 13 3 ka on the shelf in front of the retreating greenland ice margin permanent or semi permanent sea ice conditions prevailed until about 12 5 ka at that time increased irminger current activity had resulted in warming and east greenland current egc controlled iceberg drift increased no evidence was found for a return to extreme glacial conditions or a ceasing of dsow flow during the younger dryas abundant coarse ird collected at greater water depth from shallow sub seabed strata has a provenance mainly in the northern part of east greenland 68 73 n which demonstrates the existence of a pre holocene egc system initially extending to beyond the shelf edge

formal ratification of the quaternary system period and the pleistocene series epoch with a base at 2 58 ma in june 2009 the executive committee of the international union of geological sciences iugs formally ratified a proposal by the international commission on stratigraphy to lower the base of the quaternary system period to the global stratotype section and point gssp of the gelasian stage age at monte san nicola sicily italy the gelasian until then had been the uppermost stage of the pliocene series epoch the base of the gelasian corresponds to marine isotope stage 103 and has an astronomically tuned age of 2 58 ma a proposal that the base of the pleistocene series epoch be lowered to coincide with that of the quaternary the gelasian gssp was also accepted by the iugs executive committee the gssp at vrica calabria italy which had hitherto defined the basal boundary of both the quaternary and the pleistocene remains available as the base of the calabrian stage age now the second stage of the revised pleistocene in ratifying these proposals the iugs has acknowledged the distinctive qualities of the quaternary by reaffirming it as a full system period correctly complied with the hierarchical requirements of the geological timescale by lowering the base of the pleistocene to that of the quaternary and fully respected the historical and widespread current usage of both the terms quaternary and pleistocene copyright 2009 john wiley sons ltd

tephrochronology magnetostratigraphy and mammalian faunas of middle and early pleistocene sediments at two sites on the old crow river northern yukon territory canada abstract alluvial and lacustrine sediments exposed beneath late pleistocene glaciolacustrine silt and clay at two sites along the old crow river northern yukon territory are rich in fossils and contain tephra beds surprise creek tephra szt occurs in the lower part of the alluvial sequence at crh47 and little timber tephra ltt is present near the base of the exposure at crh94 surprise creek tephra has a glass fission track age of 0 17 0 07 ma and little timber tephra is 1 37 0 12 ma all sediments at crh47 have a normal remanent magnetic polarity and those near ltt at crh94 have a reversed polarity in agreement with the geomagnetic time scale small mammal remains from sediments near ltt support an early pleistocene age but the chronology is not so clear at crh47 because of the large error associated with the szt age determination tephrochronological and paleomagnetic considerations point to an mis 7 age for the interglacial beds just below szt at crh47 and at chester bluffs in east central alaska but mammalian fossils recovered from sediments close to szt suggest a late irvingtonian age therefore older than mis 7 further studies are needed to resolve this problem

formation of denmark strait overflow water by mixing in the east greenland current abstract hydrographic data and current meter records from the east greenland current collected during theperiod 1987 to 1989 around the latitude of the central greenland sea reveal the formation of a watermass having the characteristics of denmark strait overflow water dsow the downstream southwestward transport of this newly formed water mass can be substantial amounting to roughly halfof the outflow of dsow through denmark strait as reported in the literature the formation of dsow inthe east greenland current results from isopycnic mixing of recirculated atlantic water and upper arcticintermediate water substantial formation occurs when the neccessary conditions for baroclinic instabilityare satisfied and the current variability due to mesoscale eddies is high this is subject to significantchanges from year to year

gis based landslide susceptibility assessment a case study in kelemen valley yenice karabuk nw turkey this study focuses on revealing the landslide susceptibility of mainly the kelemen valley and adjacent valleys in the western black sea region of turkey by investigating the parameters causing landslide occurrences in the region in a gis environment and applying the frequency rate method on landslide prone areas many buildings and houses in the study area 382 houses to be exact had to be evacuated by the general directorate of disaster affairs of turkey based on the findings from landslide studies conducted in the region since 1950 and were declared unsuitable for construction and residence due to disaster therefore it is of a vital significance to disclose the factors of landslide occurrences in the kelemen valley and consequently to prepare landslide susceptibility maps for this purpose 82 landslide exposed areas are determined by field surveys and checked against satellite imagery all 82 landslides are found to have occurred in the cretaceous ulus formation with the same climate and same vegetation which are not considered distinctive parameters for the region these findings have given rise to exclude these parameters from analyses on the basis that they are proclaimed as common parameters instead the parameters such as slope aspect and distance to river are taken into consideration and assessed in arcgis software finally the landslide susceptibility of the region has been obtained furthermore a comparison is conducted between the existing landslides and the outcome map and it is deduced that the map produced has a correlation ratio of 86 with the existing occurrences for high risk areas this finding clearly dictates that landslide prone areas need to be accounted for when planning for new settlement areas

hemispheric asymmetry of deep water transport modes in the western atlantic subtropical studies of the atlantic meridional cold water flow show a hemispheric contrast in the dominant southward transport mode below 2000 m in the north atlantic lower deep water ldw 1 8 2 4 c dominates with small transport of middle deep water mdw 2 4 3 2 c while in the south atlantic the opposite is observed we use numerous observations in the western basins of the tropics to show that the transition occurs rapidly near the equator in the western atlantic a meridional section in the central brazil basin suggests zonal flows are responsible for the transition ldw transport from the guiana basin north of the equator flows eastward in the northern brazil basin and is inferred to continue on through the romanche fracture zone into the eastern atlantic an opposing flow of mdw from the eastern tropical atlantic flows toward the western boundary where it bifurcates to supply mdw to the deep western boundary current dwbc of the brazil basin as well as to feed the northward flow of mdw in the guiana basin offshore of the dwbc the magnitude of each of these oppositely directed flows is roughly 7 sv we furthermore speculate that they are connected predominantly by upwelling from ldw to mdw within the low latitude eastern basin the overall deep water transport system below 2000 m in the western basins of the mid and low latitude atlantic is thus found to comprise the following three distinct components 1 a strong dwbc transport of ldw with associated recirculation dominates the guiana basin north of the equator 2 in the northern brazil basin just south of the equator a narrow eastward flow absorbs the ldw and carries it eastward while a somewhat broader westward flow imports mdw into the western basin 3 this mdw flow then bifurcates with the southward branch causing the mdw dominance in the brazil basin where the mdw dominated dwbc and associated recirculations are the third component of the deepwater transport system

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

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

intensification of the atlantic deep circulation by the canadian archipelago throughflow abstract low salinity water export through the canadian archipelago is one of the main components of the freshwater budget in the arctic ocean nevertheless the canadian archipelago is closed in most global ocean models how it is that deep water formation at high latitudes of the northern hemisphere depends on the opening and closing of the canadian archipelago is investigated an ice ocean coupled model whose horizontal resolution is 1 is used without restoring surface salinity to observed data when the canadian archipelago is open the atlantic deep circulation strengthens by 21 this enhancement is caused by intensification of deep water formation in the northern north atlantic ocean surface salinity in these regions is affected by the east greenland current which flows from the fram strait and increases its salinity when the canadian archipelago is opened the low salinity flow through the canadian archipelago affects surface salinity only in the western part of the labrador sea a cyclonic c

last interglacial climates the last interglacial commonly understood as an interval with climate as warm or warmer than today is represented by marine isotope stage mis 5e which is a proxy record of low global ice volume and high sea level it is arbitrarily dated to begin at approximately 130 000 yr b p and end at 116 000 yr b p with the onset of the early glacial unit mis 5d the age of the stage is determined by correlation to uranium thorium dates of raised coral reefs the most detailed proxy record of interglacial climate is found in the vostok ice core where the temperature reached current levels 132 000 yr ago and continued rising for another two millennia approximately 127 000 yr ago the eemian mixed forests were established in europe they developed through a characteristic succession of tree species probably surviving well into the early glacial stage in southern parts of europe after ca 115 000 yr ago open vegetation replaced forests in northwestern europe and the proportion of conifers increased significantly farther south air temperature at vostok dropped sharply pulses of cold water affected the northern north atlantic already in late mis 5e but the central north atlantic remained warm throughout most of mis 5d model results show that the sea surface in the eastern tropical pacific warmed when the ice grew and sea level dropped the essentially interglacial conditions in southwestern europe remained unaffected by ice buildup until late mis 5d when the forests disappeared abruptly and cold water invaded the central north atlantic ca 107 000 yr ago

late quaternary iceberg rafted detritus events on the denmark strait southeast greenland continental slope 65 n related to north atlantic heinrich events hu93030 007 lcf 65o01 39 0 n and 30o14 81 0 w is a 4 5 m long giant 11 cm diameter piston core from 1800 m water depth on the continental slope south of the denmark strait sill the core sampled acoustically stratified sediments at a site below the kangerlussuaq trough nine ams 14 c dates on planktic foraminifera indicate that the core spans 14 to 28 14 c ka the sediments consists of two principal lithofacies lithofacies i li comprises tan ochre intervals with abundant ice rafted sandstone siltstone clasts larger than 2 mm and with an average thickness of 47 cm it is also associated with peaks in carbonate content and toc lithofacies ii lii consists of fine grained dark gray hemipelagic sediment there are three distinct intervals of li dated between 14 3 and 15 5 lic 20 1 and 21 9 lib 24 7 and 25 8 lia ka the ages suggest that deposition of li is approximately coeval with heinrich events 1 and 2 in the north atlantic whereas lia appears younger than h 3 lithofacies i is derived from far travelled ice bergs from an unknown source but not from the northeastern laurentide ice sheet stable isotope studies on neogloboquadrina pachydermasinistral show little evidence for significant meltwater events associated with li but surprisingly light oxygen isotopic events are present in the benthic foraminiferal analyses cibicidoides wuellerstorfiand melonis zaandamae the ages of the hu93030 007 iceberg rafted detritus ird events are similar to ird peaks in cores north of denmark strait on the east greenland slope hu87033 009 lcf se baffin slope 62o30 99 0 n and 59o26 82 0 w 1437 m wd is situated in a similar position to hu93030 007 but with respect to the laurentide ice sheet its d 18 o record on planktic foraminifera is virtually identical to that of hu93030 007 the timing of ird events is similar in both these cores between 14 and 30 ka h 3 may be present in hu87033 009 as an ird event but in contrast to h 1 and h 2 it is not evident as a discernible detrital carbonate event 1998 elsevier science b v all rights reserved

an 18 million year record of vegetation and climate change in northwestern canada and alaska tectonic and global climatic correlates abstract we reconstruct long term vegetation paleoclimatic trends spanning the last 18 million years in alaska yukon and far western northwest territories twenty one average percentage spectra for pollen and spores are assembled from eight surface subsurface sections the sections are dated independently or by correlation pollen and spore ratios indicate the direction of change in vegetation and climatic parameters growing season temperature test tree canopy density cest and paludification at study sites pest a global warm peak ca 15 ma is shown by the abundance of thermophilous taxa including fagus and quercus a temperature decline immediately following 15 ma parallels climatic reconstructions based on marine oxygen isotopes subsequent declines correlate to the messinian event and the onset of late pliocene pleistocene glaciation after 7 ma herbs and shrubs become more important elements of the palynological assemblages suggesting a more continental colder drier climate however a late pliocene warm interval is evident vegetation climatic changes during the early to late miocene show synchrony with and are most economically attributable to global events after 7 ma vegetation climate change is attributed primarily to latest miocene to pleistocene uplift of the alaska range and st elias mts the continuing influence of global climatic patterns is shown in the late pliocene warm interval despite uplift to the south the opening of the bering strait ca 3 ma may have moderated the climate in the study area

a changing arctic seasonal ice zone observations from 1870 2003 and possible oceanographic consequences 1 changes in the extent of seasonal ice were investigated using historical and satellite observations for the period 1870 2003 the seasonal ice zone siz has been gradually expanding since 1870 with a marked acceleration over the past three decades and has migrated north to encompass all peripheral arctic seas the expansion of the siz may be increasing the salinity of the upper arctic ocean consistent with recent observations the migration of the siz over continental shelves may also be enhancing the formation rate and salinity of arctic deep waters which are subsequently advected to the convective region of the greenland iceland norwegian sea thereby influencing the formation of north atlantic deep waters and related global thermohaline circulation

increasing amount of arctic ocean deep waters in the greenland sea 1 in the last three decades deep convection has come to a halt in the greenland sea hydrographic data reveal that during this period temperature and salinity in the deep greenland sea have increased at mean rates without precedent in the last 100 years and these trends are among the highest in the global deep ocean the origin of these changes is identified as the advection of arctic ocean deep waters and the necessary transports to explain them are calculated 0 44 0 09 sv despite the fact that the deep greenland sea hardly covers 0 05 of the global surface the resulting trends constitute 0 3 of the world ocean heat content increase per unit area of earth s surface and 0 1 of the global sea level rise these results suggest that changes of the deep arctic mediterranean and their contribution to the global budgets need to be addressed

some dynamical constraints on upstream pathways of the denmark strait overflow abstractthe east greenland current egc had long been considered the main pathway for the denmark strait overflow dso recent observations however indicate that the north icelandic jet nij which flows westward along the north coast of iceland is a major separate pathway for the dso in this study a two layer numerical model and complementary integral constraints are used to examine various pathways that lead to the dso and to explore plausible mechanisms for the nij s existence in these simulations a westward and nij like current emerges as a robust feature and a main pathway for the denmark strait overflow its existence can be explained through circulation integrals around advantageous contours one such constraint spells out the consequences of overflow water as a source of low potential vorticity a stronger constraint can be added when the outflow occurs through two outlets it takes the form of a circulation integral around the iceland faroe ridge in either case the direction of overall

the contribution of the greenland and barents seas to the deep water of the arctic ocean the deep waters of the arctic ocean are traditionally held to be fed by an influx of norwegian sea deep water nsdw via the northward flowing west spitsbergen current discrete sample and ctd observations obtained from the greenland spitsbergen passage in august 1981 during the transient tracers in the ocean tto north atlantic expedition showed a 100 m thick layer of modified greenland sea deep water gsdw colder and fresher than nsdw at 2500 m spreading northward along the bottom of a deep unimpeded channel underneath the nsdw since the available data indicate that arctic ocean deep water aodw has a higher salinity than nsdw mixing of nsdw and gsdw can not produce aodw therefore other sources such as the peripheral arctic shelf seas must contribute dense saline water to the arctic ocean concentrations of 137cs and 90sr observed in aodw are greater than those observed in gsdw and nsdw the concentrations of these radionuclides on the barents sea shelf are sufficiently high and in the correct relative proportions to support this proposition

middle to late pleistocene ice extents tephrochronology and paleoenvironments of the white river area southwest yukon abstract sedimentary deposits from two middle to late pleistocene glaciations and intervening non glacial intervals exposed along the white river in southwest yukon canada provide a record of environmental change for much of the past 200 000 years the study sites are beyond the marine isotope stage mis 2 glacial limit near the maximum regional extent of pleistocene glaciation non glacial deposits include up to 25 m of loess peat and gravel with paleosols pollen plant and insect macrofossils large mammal fossils and tephra beds finite and non finite radiocarbon dates and twelve different tephra beds constrain the chronology of these deposits tills correlated to mis 4 and 6 represent the penultimate and maximum pleistocene glacial limits respectively the proximity of these glacial limits to each other compared to limits in central yukon suggests precipitation conditions were more consistent in southwest yukon than in central yukon during the pleistocene conditions in mis 5e and 5a are recorded by two boreal forest beds separated by a shrub birch tundra that indicate environments as warm or warmer than present a dry treeless steppe tundra dominated by artemisia frigida upland grasses and forbs existed during the transition from late mis 3 to early mis 2 these glacial and non glacial deposits constrain the glacial limits and paleoenvironments during the middle to late pleistocene in southwest yukon

a primitive equation ocean circulation model using a general vertical coordinate transformation 2 application to an overflow problem the version of the ocean general circulation model of the geophysical fluid dynamics laboratory with a generalized vertical coordinate transformation introduced in part 1 is used to study the overflow of a zonal ridge in a coarse resolution grid typical for climate applications the configuration roughly resembles the greenland scotland ridge with respect to scale latitude and height of the ridge reasonable qualitative agreement with observed conditions over the iceland faroe section has been achieved especially when a deeper passage was included at the eastern end of the idealized model ridge upwelling of deep water occurs at the eastern boundary where friction and more importantly diapycnal diffusion accomplish the necessary changes in potential vorticity the overflow consists of intermediate water when the renewal time for the deep water is made much larger than that for intermediate water the meridional mass transport is most sensitive to geometric factors like the height of the ridge frictional and diapycnal processes are crucial for the potential vorticity conversion at the ridge and have a strong effect on the water mass distribution bottom friction increases the near bottom flow across f h lines resulting in a large amount of northern basin deep water south of the ridge this effect can be represented only when the frictional bottom boundary layer is adequately resolved by the numerical grid

middle pleistocene mis 7 to holocene fossil insect assemblages from the old crow basin northern yukon canada abstract the old crow basin northern yukon provides a key record of environmental change in northwestern north america from the late middle pleistocene through the early holocene site chronologies are based on the presence of the old crow tephra oct 124 10 ka at three sites and provide a stratigraphic framework for observations ecological affinities of fossil insects indicate that pleistocene environments were dominated by dry tundra and steppe tundra forest insect species are relatively rare even during the last interglaciation mis 5e and it is only by considering the total insect assemblages that interglacial beds can be recognized last interglacial insects from these sites indicate a relatively wet and warm tundra environment with evidence for sparse forest vegetation rare taxa with strong affinities to warmer temperatures are present and could suggest a warmer than modern climate early holocene deposits yield a greater abundance of forest insects relative to mis 5 or 7 interglacial deposits fossil insect assemblages reflect the position of the sites above the arctic circle and in contrast to central yukon sites steppe insects are less common during cold stages and forest insects are less common during warm stages these data suggest overall that the contrast between cold and warm stages was less pronounced than in other regions of yukon and alaska and may indicate influence of persistent large regional lakes during the pleistocene

pre glacial and interglacial pollen records over the last 3 ma from northwest canada why do holocene forests differ from those of previous interglaciations we synthesize pollen spectra from eleven dated stratigraphic sections from central and northern yukon palaeomagnetic and tephra dating indicates the earliest assemblages representing closed canopy pinus and picea forest are middle late pliocene age more open forest conditions indicated by increased poaceae and with evidence of permafrost are dated at ca 3 ma while pinus pollen is abundant at 3 ma it is reduced in records after 2 6 ma and subsequent pleistocene interglacial forest records are repeatedly dominated by picea along with alnus and small but significant amounts of abies surface sample comparisons indicate that abies was more widespread and abundant in past interglaciations than at present and that middle pleistocene piceaeabies forest grew in the northern yukon porcupine basin 500 km beyond modern abies limits in contrast pinus which occurs today in southern and central yukon was not a significant component of these pleistocene interglacial forests late holocene pollen assemblages with rare abies and high pinus are the most distinct in the past 2 6 ma possible factors driving holocene difference are paleoclimate paludification changes in megafaunal herbivory and an unusual fire regime anthropogenic burning is a factor unique to the holocene and if it is shown to be important in this case it would challenge our notion of what constitutes boreal wilderness

ventilation of the arctic ocean estimated by a plume entrainment model constrained by cfcs intermediate and deep water formation rates in the arctic ocean are estimated using a plume entrainment model based on shelf slope processes and constrained by tracer distributions within the deep basin each plume is initiated by a fraction rj leaving the shelf break at 200 m followed by an entrainment of rj for every 150 m depth the plume descends the model is tuned by varying rj to achieve the transient tracer cfc 12 and carbon tetrachloride distribution as measured in the nansen amundsen and makarov basins during the oden 1991 expedition and the concentrations in the source waters are calculated assuming a water in 100 equilibrium with the atmosphere the formation of water entering below 500 m is computed to be 1 5 and 1 9 sv when constrained by cfc 12 and ccl4 respectively with a total uncertainty of 0 45 sv sensitivities of the model settings to the entrainment rate degree of saturation of the transient tracer in the source waters and age of the atlantic layer water are investigated processes in the arctic ocean contribute around 1 3 of the approximately 5 6 sv that flows over the scotland greenland ridge with the rest likely attributed processes in the greenland and iceland seas we thus conclude that the arctic ocean has to be included in the discussion of the sensitivity of the greenland scotland overflow to a climate change

branching of atlantic water within the greenland spitsbergen passage an estimate of recirculation atlantic water aw supplies the largest source of heat mass and salt to the arctic ocean via fram strait greenland spitsbergen passage yet it represents only a fraction of the atlantic water that resides in the greenland iceland norwegian and barents seas this is a result of both the branching of the central core of aw along its northward flow and the modification of its t s signature through air sea ice interactions and internal mixing this paper addresses the quantitative analysis of the three dominant atlantic water cores within fram strait and north of 76 n using an 11 year 1977 to 1987 hydrographic database spatial variations of heat volume and salt along its flow path of some 600 km showed that the major core of atlantic water that directly enters the arctic ocean svalbard branch did not extend past 20 e of the 9719 km3 of atlantic water existing within the region one third resided within the svalbard branch the remainder 22 and 45 were held within the return atlantic current and the yermak branches respectively restricting the analysis to a southern limit of 79 n effectively removed the return atlantic current and showed a nearly equal split between the two remaining branches work completed by bourke et al 1988 indicated that the yermak branch is largely recirculated to the south if true this analysis supports rudels 1987 model estimate of a 50 recirculation of aw within this region

age of some pleistocene interglacial beds and associated fossils in eastern beringia defined by fission tracks in glass shards of chester bluff tephra

a short circuit in thermohaline circulation a cause for northern hemisphere glaciation the cause of northern hemisphere glaciation about 3 million years ago remains uncertain closing the panamanian isthmus increased thermohaline circulation and enhanced moisture supply to high latitudes but the accompanying heat would have inhibited ice growth one possible solution is that enhanced moisture transported to eurasia also enhanced freshwater delivery to the arctic via siberian rivers freshwater input to the arctic would facilitate sea ice formation increase the albedo and isolate the high heat capacity of the ocean from the atmosphere it would also act as a negative feedback on the efficiency of the conveyor belt heat pump

saline outflow from the arctic ocean its contribution to the deep waters of the greenland norwegian and iceland seas abstractsince 1985 various investigators have proposed that norwegian sea deep water nsdw is formed by mixing of warm and saline deep water from the arctic ocean with the much colder and fresher deep water formed by convection in the greenland sea gsdw we here report on new observations which suggest significant modification and expansion of this conceptual model we find that saline outflows from the arctic ocean result in several distinct intermediate and deep salinity maxima within the greenland sea the southward transport of the two most saline modes is probably near 2 sv mixing of gsdw and the main outflow core found over the greenland slope derived from about 1700 m in the arctic ocean cannot by itself account for the properties of nsdw instead the formation of nsdw must at least in part involve a source which in the arctic ocean is found below 2000 m the mixing of various saline outflows is diapycnal while significant nsdw production appears to occur in northern fram strait large amounts of saline arctic ocean outflow also traverse the western greenland sea without mixing and enter the iceland sea during the past decade deep convection in the greenland sea has been greatly reduced while deep outflow from the arctic ocean appears to have continued resulting in a markedly warmer slightly more saline and less dense deep regime in the greenland sea american geophysical union 1991

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

neoglacial change in deep water exchange and increase of sea ice transport through eastern fram strait evidence from radiogenic isotopes sediment core msm5 5 712 from the west spitsbergen continental margin has been investigated at high resolution for its seawater derived neodymium nd and lead pb isotope compositions stored in ferromanganese oxyhydroxide coatings of the sediment particles to reconstruct holocene changes in the sources and mixing of bottom waters passing the site the radiogenic isotope data are used in combination with a multitude of proxy indicators for the climatic and oceanographic development of the eastern fram strait during the past 8500 years to calibrate the downcore data seawater and core top samples from the area were analysed for their radiogenic isotope compositions core top leachates reveal relatively high more radiogenic nd isotope compositions between end 9 7 and 9 1 which are higher than present day seawater end in eastern fram strait 12 6 to 10 5 and indicate that the seawater values have only been established very recently the core top data agree well with the downcore signatures within the uppermost 40 cm of the sediment core end 9 1 to 8 8 indicating a reduced inflow of waters from the nordic seas concurrent with cool conditions and a south eastward shift of the marginal ice zone after ca 2 8 cal ka bp late holocene high sea ice abundances in eastern fram strait are coeval with the well known neoglacial trend in the northern north atlantic region in contrast warmer conditions of the late early to mid holocene were accompanied by lower less radiogenic end signatures of the bottom waters indicating an increased admixture from the nordic seas 10 6 to 10 1 a shift to significantly more radiogenic end signatures of the detrital material also occurred at 3 cal ka bp and was accompanied by a marked increase in supply of fine grained ice rafted material irf from the arctic ocean to the core site the most likely source areas for this radiogenic material are the shallow arctic shelves in particular the kara sea shelf the evolution of the pb isotope compositions of past seawater was dominated by local signatures characterized by high 208 207 206pb 204pb values during the warm early and mid holocene periods related to enhanced chemical weathering on svalbard and high glacial and riverine input derived from young granitic more radiogenic material to the west spitsbergen margin at 3 cal ka bp both detrital and seawater pb isotope data changed towards more kara sea like signatures

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

evidence for early glaciation of southeastern beringia between the klondike plateau and yukon tanana highlands of yukon and alaska respectively current maps explain glaciated alpine locales and periglacial areas in terms of localized pliocene pleisto

microfaunal evidence for elevated pliocene temperatures in the arctic ocean the migration of thermophilic marine ostracoda into the arctic ocean during the pliocene indicates that winter and summer ocean temperatures around arctic margins were 0 c and 3 c respectively and that ice free conditions existed for most or all of the arctic by at least 3 5 3 0 ma probably earlier the opening of the bering strait allowed marine organisms to migrate through the arctic ocean mostly from the pacific ocean migrant taxa such as cythere hemicythere and neomonoceratina are known from pliocene deposits of alaska and canada as well as neogene deposits of the north pacific and atlantic oceans on the basis of ecological and zoogeographic information on ostracode species from more than 800 modern core top samples for the north atlantic north pacific and arctic oceans we determined winter and summer temperature tolerances for migrant taxa to be at or above about 0 c and 3 c this suggests ice free summers and probably a perennially ice free arctic ocean in some regions elevated water temperatures in the arctic ocean between 3 5 and 2 0 ma is supported by evidence for late pliocene increased meridional heat transport in the north atlantic ocean

a mid holocene shift in arctic sea ice variability on the east greenland shelf records of iceberg rafting and palaeohydrography from two east greenland shelf cores jm96 1206 1 gc and jm96 1207 1 gc are reported benthic foraminifera stable isotopes and ird e uxes indicate a shift toward colder lower salinity polar conditions c 5 cal ka a new proxy of iceberg rafting on the east greenland shelf is the e ux of calcium carbonate tic thought to be derived from glacial erosion of cretaceous calcareous mudstones a change in the regularity and spacing of carbonate e ux peaks at c 4 7 cal ka in jm96 1207 coincides with the onset of neoglacial cooling in the renland ice core d 18 o record we propose that the carbonate e ux peaks between 4 7 and 0 4 cal ka are related to sea surface coolings associated with increased e ux of polar water and sea ice in the east greenland current these peaks are synchronous with sea surface coolings interpreted from north atlantic deep sea cores but additional peaks centred around 2 4 and 3 8 cal ka in jm96 1207 suggest that the shelf site captures higher frequency events the data indicate that severe arctic sea ice events began in the neoglacial interval and that earlier holocene cool events in deep sea records are associated with other processes such as release of meltwater from residual glacier ice and glacial lakes

late quaternary paleoceanography of the eurasian basin arctic ocean we reconstructed late quaternary deep 3000 4100 m and intermediate depth 1000 2500 m paleoceanographic history of the eurasian basin arctic ocean from ostracode assemblages in cores from the lomonosov ridge gakkel ridge yermak plateau morris jesup rise and amundsen and makarov basins obtained during the 1991 polarstern cruise modern assemblages on ridges and plateaus between 1000 and 1500 m are characterized by abundant relatively species rich benthic ostracode assemblages in part reflecting the influence of high organic productivity and inflowing atlantic water in contrast deep arctic eurasian basin assemblages have low abundance and low diversity and are dominated by krithe and cytheropteron reflecting faunal exchange with the greenland sea via the fram strait major faunal changes occurred in the arctic during the last glacial interglacial transition and the holocene low abundance low diversity assemblages from the lomonosov and gakkel ridges in the eurasian basin from the last glacial period have modern analogs in cold low salinity low nutrient greenland sea deep water glacial assemblages from the deep nansen and amundsen basins have modern analogs in the deep canada basin during termination 1 at intermediate depths diversity and abundance increased coincident with increased biogenic sediment reflecting increased organic productivity reduced sea ice and enhanced inflowing north atlantic water during deglaciation deep nansen basin assemblages were similar to those living today in the deep greenland sea perhaps reflecting deepwater exchange via the fram strait in the central arctic early holocene faunas indicate weaker north atlantic water inflow at middepths immediately following termination 1 about 8500 7000 year b p followed by a period of strong canada basin water overflow across the lomonosov ridge into the morris jesup rise area and central arctic ocean modern perennial sea ice cover evolved over the last 4000 5000 years late quaternary faunal changes reflect benthic habitat changes most likely caused by changes in the import of cold deepwater of greenland sea origin and warmer and middepth atlantic water to the eurasian basin through the fram strait and export of arctic ocean deepwater

an inverse modeling study in fram strait part ii water mass distribution and transports abstract a water mass analysis is carried out in fram strait between 77 15 and 81 15 n based on three dimensional large scale potential temperature and salinity distributions reconstructed from the mizex 84 hydrographic data collected in summer 1984 combining these distributions with the geostrophic flow field derived from the same data in a companion paper schlichtholz and houssais 1999 the heat fresh water and volume transports are estimated for each of the water masses identified in the strait twelve water masses are selected based on their different origins among them the polar water pw enters fram strait from the arctic ocean both over the greenland slope and over the western slope of the yermak plateau in the atlantic water aw range four modes with distinct geographical distributions are indentified in the deep water range the eurasian basin deep water ebdw is confined to the lena trough and to the molloy deep area where it is involved in a cyclonic circulation the warm and shallower mode of the norwegian sea deep water nsdw concentrated to the west is mainly seen as an outflow from the arctic ocean while the cold and deeper mode essentially observed to the east enters the strait from the greenland sea apart from the ebdw there is a tendency for all water masses of polar origin to flow along the greenland slope the two most abundant water masses the aw and the nsdw occupy as much as 67 of the total water volume the southward net transport of pw through fram strait is about 1 sv at 78 9 n at the same latitude the net transport of aw is southward and equal to about 1 7 sv only the transport of the warm mode aww is northward amounting to 0 2 sv the overall net outflow of the deep waters to the greenland sea is about 2 6 sv two upper water masses the fresh aw f and the cold awc mode of the aw and one deep water mass the nsdw appear to be produced in the strait with production rates between 77 6 and 79 9 n of about 0 2 1 0 and 1 7 sv respectively a southward net fresh water transport through the strait of about 2000 km 3 yr 1 relative to a salinity of 34 93 is mainly due to the pw the net heat transport relative to 0 1 c is northward but undergoes a rapid northward decrease suggesting an area averaged surface heat loss of 50 100 w m 2 in the strait

pleistocene stratigraphy paleopedology and paleoecology of a multiple till sequence exposed on the little bear river western district of mackenzie n w t canada the little bear river section lies in a transition zone between mackenzie lowland and canyon ranges of mackenzie mountains within the transition zone the maximum extent of the laurentide ice sheet overlaps the former extent of montane glaciers that emanated from the higher parts of canyon ranges or from the still higher backbone ranges to the southwest five montane tills each with a paleosol developed in its upper part indicate five separate glaciations during each of which a valley glacier emanating from the headwaters of little bear river extended eastward into the transition zone the uppermost of the montane tills is overlain by boulder gravel containing rocks of canadian shield origin deposited by the laurentide ice sheet solum and b horizon depths red colours and lack of leaching and cryoturbation indicate that although each successive interglacial interval was cooler than the preceding one even the last of the intervals was warmer than the holocene climatic conditions during one of the int

paleomagnetic evidence for multiple late pliocene early pleistocene glaciations in the klondike area yukon territory the late pliocene early pleistocene terraces of the klondike area provide a conformal record of sedimentation which marks the transition from preglacial to glacial conditions and is one of the most complete records of glaciation and interglaciation in the northern cordillera preglacial sedimentation is recorded in the lower white channel gravel that contains a reverse normal polarity sequence a re aggradation of the nonglaciated valleys of the goldfields in response to late pliocene cooling is recorded by the upper white channel gravel which is characterized by a dominant normal polarity with a lower reversal likely associated with the first ice wedge casts klondike gravel interfingers with upper white channel and is normally magnetized indicating an equivalent magnetostratigraphic unit this glaciofluvial gravel provides evidence of extra basinal clasts marking a major reorganization of drainage associated with the first advance of the cordilleran ice sheet in western yukon territory correlated

the last koy yukon interglaciation in the yukon comparisons with holocene and interstadial pollen records paleoclimatic reconstructions for the last interglacial lig isotope substage 5e have achieved new importance for testing climate model simulations and predicting the outcome of global warming lig deposits at ch ijee s bluff northern yukon display high fossil spruce pollen frequencies extralimital species and a lack of interglacial permafrost all evidence of a warmer than present climate at the site comparisons between the ch ijee s bluff lig pollen record and late glacial holocene pollen stratigraphy demonstrates a high degree of similarity that implies similar patterns and rates of species migration and regugia compared to mid and early wisconsinan pollen stratigraphy the climate of the wisconsinan interstades was not as warm as that of the lig or today s lig warmth was insufficient for the spread of pine into northern yukon alder so important in the northern forests now appears to have had a less important role during the lig perhaps indicating less widespread permafrost and paludification fossiliferous deposits beneath hungry creek till hughes et al 1981 are reassigned to the lig

buoyancy and eddy driven circulation in the atlantic layer of the canada basin 1 the circulation driven by buoyancy and mesoscale eddy effects in the atlantic layer of the canada basin is obtained diagnostically from a climatological density field the buoyancy forcing is caused by the divergence of diapycnal flow the diapycnal flow is estimated from a density balance between the diapycnal advection and diffusion based on the density field on the other hand the eddy forcing is formulated as the curl of vertical friction the vertical friction is estimated from geostrophic shear which is obtained from the density field both the flow fields caused by the buoyancy forcing and by the eddy forcing similarly suggest a new flow structure characterized by a transbasin westward flow which appears from the eastern central basin to the southwestern basin the transbasin westward flow is also shown in geostrophic circulation at 500 m relative to reference levels in a wide range 1000 3000 m the significant part of the flow is consistent with a temperature distribution at 500 m

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

orbital forcing of bottom current enhanced sedimentation on feni drift ne atlantic during the mid pleistocene feni ridge is a plastered sediment drift deposited along the northwestern flank of rockall trough ne atlantic under the influence of deep geostrophic currents formed by intermittent overflows of arctic intermediate water from the norwegian sea across the iceland scotland ridge nsow lower deep water ldw a derivative of antarctic bottom water from the south atlantic mixed with old north atlantic deep water nadw also bathes the lower flanks of the drift below 2500 m deep sea drilling project site 610 was drilled in a sediment wave field on the surface of feni drift 2417 m though the sediments recovered proved to be typically pelagic preserving a high resolution 5 cm kyr 1 quaternary record of orbitally modulated ice rafting and biogenic productivity cycles but showing little evidence of current affected deposition from particle size and compositional analyses of the biogenic and lithogenic 10 m silt which we then compared with records of the percentage and flux of ice rafted detrital ird sand foraminifera and coccoliths for the same interval cross spectral comparisons were then made between these records and variations in a model of northern hemisphere ice volume ice sheet growth and decay in response to orbitally forced insolation changes at 65 n variations in the relative proportions and fluxes of ird sand foraminifera and coccoliths all covary closely with orbitally forced ice volume fluctuations but with differing amplitude coherency and phase relationships at each milankovitch frequency however there is a significant component of variance in pelagic and ice rafted sedimentation which is controlled by bottom currents and this shows excellent phase and coherency agreement with the ice volume model at all orbital frequencies the relative enrichment coarseness and flux of the contourite silt fraction of feni drift sediments all increase during glacial or cold stages of the mid pleistocene relative to warm stages suggesting that currents were stronger during these periods possible explanations for such changes in current activity include 1 an increased flux of nsow via the wyville thompson ridge into the rockall trough during glacials but not due to increased production of nsow 2 ldw presently lying below 2500 m rises during glacials by at least 50 60 m thereby flooding over the surface of feni ridge at site 610 3 the path of a major recirculation gyre in the lower nadw ldw system presently situated marginally south of site 610 encroaches upon the southern tip of feni ridge during glacials and 4 the rockall trough itself is a site of deep water formation during glacials analogous to labrador sea deep water formation today

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

flux of anthropogenic carbon into the deep greenland sea measurements of the carbonate system and the transient tracers cfc 11 and carbon tetrachloride ccl4 in the greenland sea and western eurasian basin are used to deduce the sources and magnitude of excess dissolved inorganic carbon in the deep greenland sea the salinity in the deep greenland sea has increased during the past 20 years as a result of arctic ocean water advecting into the area from salinity and temperature data the relative amount of advective water below 1500 m is estimated to 2 yr 1 between 1982 and 1994 data from the western eurasian basin collected during the oden 91 cruise are used as the advective source waters a mixing box model is applied to estimate the evolution of cfcs and anthropogenic total dissolved inorganic carbon in the deep waters of the greenland sea since preindustrial times the source functions are the surface water concentrations of cfc 11 ccl4 and total dissolved inorganic carbon ct which are the result of anthropogenic emission in order to explain the measured cfc data in the greenland sea an annual percent renewal by deep water formation of between 0 5 and 1 2 is needed below 1500 m corresponding to a mean ventilation of 0 17 0 05 sv considering realistic uncertainties in the calculations this ventilation gives a sequestering of anthropogenic carbon dioxide which in 1994 equaled 2 4 0 7 1012 g c yr 1

changes in the properties and distribution of the intermediate and deep waters in the fram strait abstract the fram strait is the only deep connection between the arctic ocean and the nordic seas greenland iceland and norwegian seas with a sill depth of approximately 2600 m consequently observations from this area reflect changes in the deep waters of the arctic mediterranean possible changes in the properties and distribution of the intermediate and deep water masses passing through the fram strait have been studied for the period from 1982 to 2008 at a zonal section at 79 n with special emphasis on the period from 1997 to 2008 the temperature of the arctic intermediate water shows large interannual variability where the period from 2002 to 2004 was especially cold indicating a strong winter convection in the nordic seas prior to those years the deep water originating from the norwegian sea has become warmer by about 0 10 c during the study period the changes in the properties of the norwegian sea deep water are caused by changes in its composition i e an increasing fraction of the eurasian basin deep water and a decreasing fraction of the greenland sea deep water each year if this trend continues the norwegian sea deep water will have similar characteristics as the eurasian basin deep water in about 15 years a prominent feature seen in the s diagrams from the deep fram strait is the disappearance of water with the characteristics of greenland sea deep water this very cold water temperature below 1 1 c was not observed after 1997 and the minimum temperature in the strait increased by 0 24 c between 1982 and 2008 in the fram strait the fraction of intermediate waters has increased while the fraction of deep waters from the nordic seas has decreased the fraction of deep waters originating from the arctic ocean shows no trend

mixing and convection in the greenland sea from a tracer release experiment convective vertical mixing in restricted areas of the subpolar oceans such as the greenland sea is thought to be the process responsible for forming much of the dense water of the ocean interior1 2 deep water formation varies substantially on annual and decadal timescales3 4 5 and responds to regional climate signals such as the north atlantic oscillation6 7 its variations may therefore give early warning of changes in the thermohaline circulation that may accompany climate change8 here we report direct measurements of vertical mixing by convection and by turbulence from a sulphur hexafluoride tracer release experiment in the central greenland sea gyre in summer we found rapid turbulent vertical mixing of about 1 1 cm2 s 1 in the following late winter part of the water column was mixed more vigorously by convection indicated by the rising and vertical redistribution of the tracer patch in the centre of the gyre at the same time mixing outside the gyre centre was only slightly greater than in summer the results suggest that about 10 of the water in the gyre centre was vertically transported in convective plumes which reached from the surface to at their deepest 1 200 1 400 m convection was limited to a very restricted area however and smaller volumes of water were transported to depth than previously estimated9 our results imply that it may be the rapid year round turbulent mixing rather than convection that dominates vertical mixing in the region as a whole

central arctic paleoceanography for the last 50 kyr based on ostracode faunal assemblages abstract the paleoceanography of the central arctic ocean was reconstructed for the last 50 kyr marine isotope stages mis 1 3 based on ostracode assemblages from 21 14c dated sediment cores from the mendeleev lomonosov and gakkel ridges arctic sediments deposited during the holocene interglacial period mis 1 the bolling allerod and larger interstadial dansgaard oeschger do events 3 4 8 and 12 contain abundant cytheropteron spp henryhowella asperrima and krithe spp at intermediate deep depths 1000 to 3000 m these assemblages suggest a ventilated deep arctic ocean water mass similar to the modern arctic ocean deep water aodw during these time periods in contrast sediment deposited during stadial events corresponding to heinrich events 1 2 3 and 4 also possibly the younger dryas yd contain abundant polycope spp 60 80 suggesting a greater influence of the atlantic layer al on the arctic intermediate water aiw and aodw reduced sea ice during the early holocene the last deglacial and mis 3 interstadials is indicated by the reoccurrence of acetabulastoma arcticum an epipelagic species that is parasitic on sea ice dwelling amphipods one hypothesis to explain these oceanographic changes during longer stadial events particularly within the last glacial period mis 2 involves sluggish ocean circulation thicker sea ice cover and a deeper halocline with ocean exchange between greenland sea and arctic ocean deep water through the fram strait

a latest pliocene age for the earliest and most extensive cordilleran ice sheet in northwestern canada abstract the klondike gravel is a widespread glaciofluvial gravel marking the earliest and most extensive cordilleran ice sheet cis in nw north america new terrestrial cosmogenic nuclide tcn burial ages indicate this gravel was emplaced 2 64 0 20 0 18 ma 1 coupled with previously interpreted paleomagnetic stratigraphy this numerical age constrains the timing of the earliest cis to the late gauss chron and provides a minimum age for the upper white channel gravel a significant placer gold source in the yukon this implies the first cis glacial maximum pre dates the maximum extent of the laurentide ice sheet indicating that during the initial stages of northern hemisphere glaciation the most extensive glaciers were present in the relatively cold and high elevation northern cordillera our results verify the cis as a likely source of persistent coeval ice rafted debris in the northern pacific and suggest that the first cis formed as a response to the establishment of the northern pacific halocline and emergence of the 41 ka obliquity cycle during the plio pliocene transition

the origin of norwegian sea deep water a nearly homogeneous water mass the norwegian sea deep water is found below 2000 m depth in the norwegian and lofoten basins of the norwegian sea recent observations indicate that this water is a mixture of relatively cold and fresh greenland sea deep water with warmer saltier eurasian basin deep water from the arctic ocean we have found this mixture along the western and southern periphery of the greenland sea near the level where the pressure compensated densities of the parent water masses are equal the along isopycnal mixing produces a remarkably uniform water mass which can be traced only a short distance away from its entry into the norwegian sea through gaps in the mid ocean ridge north of jan mayen island direct measurements of flow through these gaps confirm motion in the proper sense to accomplish this connection

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

pliocene terrace gravels of the ancestral yukon river near circle alaska palynology paleobotany paleoenvironmental reconstruction and regional correlation abstract gravels deposited by the ancestral yukon river are preserved in terrace remnants on the margins of the yukon river valley near the village of circle in east central alaska plant fossils recovered from sandy silt lenses within these gravels include cones and needles of picea and larix and a variety of seeds seed types include several taxa which no longer grow in alaska such as epipremnum prunus and weigela pollen types recovered from these deposits represent tree and shrub taxa that grow in interior alaska today such as picea larix betula and alnus as well as several taxa that no longer grow in interior alaska today such as pinus tsuga abies and corylus pollen of herb taxa identified include gramineae cyperaceae caryophyllaceae compositae polemonium and epilobium the fossil flora from the gravels near circle are similar and probably age equivalent to the flora recovered from the nenana gravel in the alaska range 250 km to the south palynological and tectonic evidence summarized in this paper now suggests that the nenana gravel was deposited during the early and middle pliocene the presence of plant fossils of tsuga abies pinus weigela and prunus suggests that the mean annual temperature mat of eastern interior alaska during the early and middle pliocene was perhaps 7 9 c warmer and less continental than today s mat of 6 4 c

the eastern beringian vole microtus deceitensis rodentia muridae arvicolinae in late pliocene and early pleistocene faunas of alaska and yukon abstract the fossil vole microtus deceitensis occurs in early pleistocene deposits at fort selkirk yukon territory and late pliocene beds at the type locality cape deceit alaska analyses of simple vs complex morphotypes in the cheek teeth and of differentiation of tooth enamel show that the cape deceit sample of m deceitensis is less derived and thus appears to be older than the fort selkirk sample the fossiliferous deposits at fort selkirk are well constrained by fission track and radiometric dates and are 1 5 to 1 7 myr sediments at cape deceit bear a normal magnetic polarity are correlated with the olduvai subchron and probably are latest pliocene

dating early and middle reid pleistocene glaciations in central yukon by tephrochronology abstract the late cenozoic deposits of central yukon contain numerous distal tephra beds derived from vents in the wrangell mountains and aleutian arc alaska peninsula region we use a few of these tephra beds to gain a better understanding on the timing of extensive pleistocene glaciations that affected this area exposures at fort selkirk show that the cordilleran ice sheet advanced close to the outer limit of glaciation about 1 5 myr ago at the midnight dome terrace near dawson city exposed outwash gravel aeolian sand and loess related to valley glaciers in the adjacent ogilvie mountains are of the same age reid glacial deposits at ash bend on the stewart river are older than oxygen isotope stage ois 6 and likely of ois 8 age that is about 250 000 yr b p supporting evidence for this chronology comes from major peaks in the rates of terrigeneous sediment input into the gulf of alaska at 1 5 and 0 25 myr b p

an eddy parameterization based on maximum entropy production with application to modeling of the arctic ocean circulation abstract an eddy parameterization derived from statistical mechanics of potential vorticity is applied for inviscid shallow water equations the solution of a variational problem based on the maximum entropy production mep principle provides with some physical constraints several viscous terms along with the traditional laplacian operator mep parameterization includes the neptune effect which is similar to that described by holloway the neptune effect describes the interaction of eddies with seafloor topography mep parameterization is then incorporated into a high resolution tidal model of the arctic ocean mep viscosity does not substantially affect the distribution of amplitudes phases and tidal currents however residual tidal circulation is sensitive to employed parameterization in areas of maximum bottom slope the neptune effect is the main contributor among other viscosities the combined effect of the new viscous terms and nonlinear terms results in cyclonic residual tidal circulatio

on the deep and bottom waters of the greenland sea from summer 1989 and 1990 data the deep waters of the central and southern greenland sea are examined using bartlett 1989 and 1990 summer data displayed at very high temperature and salinity resolutions the mixing of arctic ocean deep water aodw with greenland sea deep water gsdw in proportions of about 1 1 to form new norwegian sea deep water nsdw is confirmed however the previously accepted route of this new nsdw through the ridge system into the norwegian sea the jan mayen channel is shown to pass deep water only intermittently a passage through mohn s ridge farther north beginning near 72 06 n 2 w is identified as a more likely route part of the ultimate aodw gsdw mixture is shown to continue on along the greenland continental slope into the iceland sea a peculiar isothermal condition was found in the deeper parts of the gsdw this is postulated to result from upward diffusion of temperature from a layer initially having the adiabatic temperature gradient above the isothermal layer is one of warming and decreasing salinity the result of recent successive deep convections to different depths

pliocene warmth polar amplification and stepped pleistocene cooling recorded in ne arctic russia understanding the evolution of arctic polar climate from the protracted warmth of the middle pliocene into the earliest glacial cycles in the northern hemisphere has been hindered by the lack of co

convection in the greenland sea 1982 1993 convection in the greenland sea is studied using chlorofluorocarbons cfcs components f11 f12 and hydrographic distributions taken in spring 1993 a comparison with cfc data in the greenland sea deep water taken in 1989 shows that the cfc concentrations increased ony slightly that is the deep convection activity below 2200 m depth remained on the very low level of the previous years 1982 1989 a simple convection model shows that in the depth range 550 2250 m the mean annual convection rate ceased significantly in the period from 1989 to 1993 compared to the previous years 1982 1989 for the upper 500 m the modeled tracer concentrations deviate from the observations most likely due to horizontal advection neglected in the model

polycystine radiolarians in surface sediments in the arctic ocean basins and marginal seas abstract the polycystine radiolarian faunas in the arctic ocean including the adjacent arctic seas have been studied in more than 377 surface samples the deep basins in the arctic ocean have revealed 31 polycystine radiolarian species 11 spumellarians and 20 nassellarians the polycystine radiolarian fauna in the southern norwegian sea was introduced from the north atlantic ocean ca 13 400 yr bp the shallow low arctic marginal sea sediments iceland barents and chukchi seas have a strong dominance of cannobotryidae 79 77 and 74 respectively while the deep arctic ocean basins nansen amundsen and makarov basins have a dominance of actinommidae 90 70 and 75 respectively the arctic polycystine radiolarian faunas have a strong affinity with the norwegian sea fauna which supplies the arctic ocean with faunal elements that can live thrive and reproduce there in the chukchi sea the pacific faunal influence is obvious 41 species but none of the pacific species are found in any abundance in the amerasian basin no radiolarian species was found to be endemic to the arctic ocean except for a morphotype of actinomma l leptoderma with a round inner sphere this species is a possible endemic candidate for the arctic ocean eight species are to be found in all of the central arctic basins and can therefore be referred to as circumpolar species actinomma leptoderma leptoderma a l leptoderma with round middle sphere a l longispina a boreale spongotrochus glacialis pseudodictyophimus platycephalus cycladophora davisiana and tholospyris gephyristes while amphimelissa setosa probably is the only true arctic radiolarian species

landslide processes and landslide susceptibility analysis from an upland watershed a case study from st andrew jamaica west indies abstract rainfall induced landslides are common geomorphic events on the steeper slopes of upper st andrew and cause severe environmental engineering social and economic repercussions in the area a geotechnical study was initiated to identify a past present and potential landslide types and sites for landslides b to examine the nature of geological geomorphological and geotechnical conditions under which failures can take place and c the potential landslide hazard in the area 886 failures were mapped more than 80 of which were located in soils a total of 1 55 km2 9 80 of the total area had failed approximately 59 failures per km2 were mapped with the highest density within elastic sedimentary units and weathered granodiorite 789 failure were mapped on slopes between 20 45 with no failure on slope less than 10 481 failures were mapped along twelve major roadways 46 6 km of road with approximately 10 failures km of road analysis of eighteen geotechnical units within nine geological formations revealed that the highest susceptibility for failure was within old landslide deposits with granular nonplastic to low plasticity soils and on slopes between 20 and 30 the lowest susceptibility was found within white limestones and recent alluvium and terrace deposits granular nonplastic to low plasticity soils are generally more susceptible than fine soils especially on slopes between 30 and 45 while granular and expansive clay soils demonstrate similar susceptibilities but on slopes between 30 and 45 and 20 and 45 respectively clastic sedimentary rocks are more susceptible that igneous lithologies an increase in slope angle increases the susceptibility to failures but only on slopes up to 45 an increase in the degree of weathering of soils and bedrock and fracturing of bedrock as well as road construction increases the landslide susceptibility in the area

early wisconsinan mis 4 arctic ground squirrel middens and a squirrel eye view of the mammoth steppe abstract fossil arctic ground squirrel spermophilus parryii middens were recovered from ice rich loess sediments in association with sheep creek klondike and dominion creek tephras ca 80 ka exposed in west central yukon these middens provide plant and insect macrofossil evidence for a steppe tundra ecosystem during the early wisconsinan mis 4 glacial interval midden plant and insect macrofossil data are compared with those previously published for late wisconsinan middens dating to 25 2914c ka bp mis 3 2 from the region although multivariate statistical comparisons suggest differences between the relative abundances of plant macrofossils the co occurrence of steppe tundra plants and insects e g elymus trachycaulus kobresia myosuroides artemisia frigida phlox hoodii connatichela artemisiae provides evidence for successive reestablishment of the zonal steppe tundra habitats during cold stages of the late pleistocene arctic ground squirrels were well adapted to the cold arid climates steppe tundra vegetation and well drained loessal soils that characterize cold stages of late pleistocene beringia these glacial conditions enabled arctic ground squirrel populations to expand their range to the interior regions of alaska and yukon including the klondike where they are absent today arctic ground squirrels have endured numerous quaternary climate oscillations by retracting populations to disjunct interglacial refugia during warm interglacial periods e g south facing steppe slopes well drained arctic and alpine tundra areas and expanding their distribution across the mammoth steppe biome during cold arid glacial intervals

quaternary paleoceanography of the deep arctic ocean based on quantitative analysis of ostracoda abstract ostracodes were studied from deep arctic ocean cores obtained during the arctic 91 expedition of the polarstern to the nansen amundsen and makarov basins the lomonosov ridge morris jesup rise and yermak plateau in order to investigate their distribution in arctic ocean deep water aodw and apply these data to paleoceanographic reconstruction of bottom water masses during the quaternary analyses of coretop assemblages from arctic 91 boxcores indicate the following ostracodes are common at all depths between 1000 and 4500 m and species distribution is strongly influenced by water mass characteristics and bathymetry quantitative analyses comparing eurasian and canada basin assemblages indicate that distinct assemblages inhabit regions east and west of the lomonosov ridge a barrier especially important to species living in lower aodw deep eurasian basin assemblages are more similar to those living in greenland sea deep water gsdw than those in canada basin deep water two upper aodw assemblages were recognized throughout the arctic ocean one living between 1000 and 1500 m and the other having high species diversity at 1500 3000 m downcore quantitative analyses of species abundances and the squared chord distance coefficient of similarity reveals a distinct series of abundance peaks in key indicator taxa interpreted to signify the following late quaternary deep water history of the eurasian basin during the last glacial maximum lgm a gsdw aodw assemblage characteristic of cold well oxygenated deep water 3000 m today inhabited the lomonosov ridge to depths as shallow as 1000 m perhaps indicating the influence of gsdw at mid depths in the central arctic ocean during termination 1 a period of high organic productivity associated with a strong inflowing warm north atlantic layer occurred during the mid holocene several key faunal events indicate a period of warming and or enhanced flow between the canada and eurasian basins a long term record of ostracode assemblages from kastenlot core ps2200 5 1073 m water depth from the morris jesup rise indicates a quasi cyclic pattern of water mass changes during the last 300 kyr interglacial ostracode assemblages corresponding to oxygen isotope stages 1 5 and 7 indicate rapid changes in dissolved oxygen and productivity during glacial interglacial transitions

deep water formation and exchange rates in the greenland norwegian seas and the eurasian basin of the arctic ocean derived from tracer balances abstract multi tracer data sets collected in the greenland norwegian seas and the eurasian basin of the arctic ocean in the 1970s and 1980s are used together with temperature and salinity to 1 constrain box model calculations of the deep water formation rates in the greenland sea and the eurasian basin of the arctic ocean and 2 estimate the exchange rates of deep waters depth 1 500m between the greenland norwegian seas and the eurasian basin we obtain deep water formation rates of 0 1sv since 1980 to 0 47sv from at least 1965 to 1980 for the greenland sea and 0 3sv for the eurasian basin of the arctic ocean the southward flux of eurasian basin deep water through fram strait is estimated to be about 1sv about 0 12sv of this flux are transported into the greenland sea about 0 37sv reach the deep norwegian sea through the jan mayen fracture zone and about 0 39sv leave the arctic ocean through a shallower core which more or less directly feeds into the iceland sea and after modification eventually ends up in the overflow waters the outflow of eurasian basin deep water is balanced by deep water formation in the arctic ocean and by inflow of norwegian sea deep water about 0 77sv of deep water formed in the greenland sea and the eurasian basin contribute to the formation of north atlantic deep water uncertainties of the fluxes are estimated to be roughly 20 to 30

glacial interglacial variability in deep sea ostracod assemblage composition at iodp site u1314 in the subpolar north atlantic abstract we present a detailed study of glacial interglacial deep sea benthic ostracod assemblage variability at iodp site u1314 subpolar north atlantic in relation to the history of ice rafting events and changes in deep ocean circulation over the past 170 ky our records of ostracod diversity abundance and dissolution and sediment properties ird and caco 3 show an excellent correspondence to high amplitude orbital and millennial variability observed in the climate records 13 c and 18 o from neighboring deep water sites suggesting that the benthic meiofauna fluctuates synchronously with the prevailing oceanographic conditions surface ocean conditions deep ocean circulation and water temperature and food flux krithe dominant argilloecia and cytheropteron are the most abundant and diverse genera in association with rockallia enigmatica three ostracod assemblages are recognized the genera pennyella argilloecia pelecocythere ambocythere pseudobosquetina bradleya and nannocythere are associated with interglacials and interstadials and possibly reflect increased flux of food to the sediments and more vigorous nadw formation a transitional assemblage composed of species of cytheropteron xestoleberis and eucythere is restricted to climatic transitions and indicate moderate environmental conditions and seasonal productivity a glacial stadial assemblage is characterized by a temporal predominance of either intermediate depth and shallow water arctic subarctic species belonging to cytheropteron polycope pedicythere swainocythere cluthia heterocyprideis elofsonella and finmarchinella or abyssal north atlantic ostracods bythocythere dutoitella bathycythere and bythocypris the influx of high latitude taxa can be partially explained by ice rafting but may also represent a shift of the location of intermediate and deep water convection to the area south of iceland therefore the combination of species characteristic of different watermasses during glacials may reflect shifts in the influence of high nutrient southern source water e g aabw vs low nutrient gnaiw during glacials

vegetation and climate during warmer intervals in the late pleistocene of western and central europe abstract many warmer intervals occurred during the last interglacial glacial cycle 130 10 ka in europe the vegetational record shows several types of such intervals among which the forest periods of the eemian interglacial and the amersfoort brorup interstadials of the early weichselian are of special interest a series of map reconstructions is used to present some of the relevant vegetational and paleoclimatic characterizations they represent two types of temperate intervals occurring in the late pleistocene in europe one with a rather uniform distribution of vegetation types a warmer oceanic climate and a high sea level the other type shows strong vegetation gradients both north south and east west a more continental climate and a relatively low sea level inland ice probably persisted in the far north during this last type of interval it is suggested that these two types of interglacial occurred throughout the pleistocene

the arctic circumpolar boundary current abstract the main water transformations in the arctic mediterranean take place in the boundary current of atlantic water which crosses the greenland scotland ridge from the north atlantic into the eastern norwegian sea it enters and flows around the arctic ocean before it exits the arctic mediterranean as the east greenland current primarily through denmark strait on route it experiences numerous branchings and mergings by examining how the properties of this circumpolar boundary current evolve it is possible to identify and describe the processes causing the water mass transformations in the arctic mediterranean it is also possible to follow the arctic ocean deep waters as they spread into the nordic seas and eventually provide 40 of the overflow water supplying the north atlantic deep water

the intensification of northern component deepwater formation during the mid pleistocene climate transition we reconstruct mid pleistocene marine isotope stages miss 13 18 deepwater hydrography at ocean drilling program site 1063 4583 m water depth subtropical north atlantic using benthic foraminiferal stable isotope records these new records complete an 900 kyr long stratigraphy spanning miss 8 29 250 1030 ka when combined with previously published records from site 1063 the results indicate a change in the circulation regime of the abyssal subtropical north atlantic during mis 17 prior to mis 17 no significant glacial or interglacial 13c gradients are evident between site 1063 and the deep south atlantic after mis 17 interglacial intervals at site 1063 are characterized by 13c values that consistently approach those recorded in the deep north atlantic comparing site 1063 13c values to 26 additional published records throughout the entire atlantic basin supports the idea that this 13c increase is unique to the deep north atlantic after mis 17 the basin wide influence of higher 13c values suggests an increased relative flux of northern sourced bottom waters during interglacial periods the timing of northern sourced water influence at site 1063 is consistent with the timing of a shift in the orientation of the arctic front thus this shift may signify a link between the northward penetration of relatively warm saline surface waters into the norwegian greenland seas stimulating deep convection our findings fit well with the model of imbrie et al 1993 for the importance of the nordic heat pump in establishing strong 100 kyr cyclicity in late pleistocene glacial cycles

old crow tephra 140 10 ka constrains penultimate reid glaciation in central yukon territory abstract old crow tephra 140 10 ka is closely associated with deposits from the penultimate reid glaciation along the pelly river in central yukon territory the elevation of the tephra above present base level and association with deglacial sediments suggests a close minimum age estimate confirming a mis 6 age for the reid glaciation this is in contrast to a mis 4 age for the penultimate gladstone glaciation in southwest yukon this study demonstrates that the assumed synchrony of the penultimate advance of the cordilleran ice sheet has little support and regional controls on the mass balance of source regions of the ice sheet are more important than previously considered