sedimentary characteristics and origin of the late pleistocene ice complex on north east siberian arctic coastal lowlands and islands a review abstract the origin of late pleistocene ice rich fine grained permafrost sequences ice complex deposits in arctic and subarctic siberia has been in dispute for a long time corresponding permafrost sequences are frequently exposed along seacoasts and river banks in yedoma hills which are considered to be erosional remnants of late pleistocene accumulation plains detailed cryolithological sedimentological geochronological and stratigraphical results from 14 study sites along the laptev and east siberian seacoasts were summarized for the first time in order to compare and correlate the local datasets on a large regional scale the sediments of the ice complex are characterized by poorly sorted silt to fine sand buried cryosols toc contents of 1 2 4 8 wt and very high ground ice content 40 60 wt absolute a second large constituent of the ice complex are large syngenetic ice wedges resulting in a total ice content of the ice complex of up to 80 vol ice complex deposits were mostly formed during the middle weichselian interstadial and or during the late weichselian stadial periods a conceptual model of nival lithogenesis of ice complex deposits was developed that integrates various other formation hypotheses a combination of various local and regional paleogeographical geological and paleoclimate conditions controlled the formation of ice complex sequences during the late pleistocene in northern east siberia they are chronologically and stratigraphically but not genetically equivalent to eurasian and alaskan loess deposits

preliminary paleoenvironmental analysis of permafrost deposits at batagaika megaslump yana uplands northeast siberia a megaslump at batagaika in northern yakutia exposes a remarkable stratigraphic sequence of permafrost deposits 50 80 m thick to determine their potential for answering key questions about quaternary environmental and climatic change in northeast siberia we carried out a reconnaissance study of their cryostratigraphy and paleoecology supported by four rangefinder 14c ages the sequence includes two ice complexes separated by a unit of fine sand containing narrow syngenetic ice wedges and multiple palaeosols overall the sequence developed as permafrost grew syngenetically through an eolian sand sheet aggrading on a hillslope wood remains occur in two forest beds each associated with a reddened weathering horizon the lower bed contains high amounts of larix pollen 20 plus small amounts of picea and pinus pumila and is attributed to interglacial conditions pollen from the overlying sequence is dominated by herbaceous taxa 70 80 attributed to an open tundra landscape during interstadial climatic conditions of three hypothetical age schemes considered we tentatively attribute much of the batagaika sequence to marine isotope stage mis 3 the upper and lower forest beds may represent a mid mis 3 optimum and mis 5 respectively although we cannot discount alternative attributions to mis 5 and 7

in situ x ray observations of phase assemblages in peridotite and basalt compositions at lower mantle conditions implications for density of subducted oceanic plate 1 phase relationships in klb 1 peridotite normal type mid oceanic ridge basalt nmorb and k rich basalt compositions were investigated experimentally from 28 to 143 gpa and 2050 to 3000 k a laser heated diamond anvil cell with the synchrotron x ray diffraction was developed to perform in situ observations of samples at simultaneous high pressures and temperatures we confirmed that the peridotite composition crystallized into an assemblage of mg perovskite ca perovskite magnesiowustite at pressures below 97 gpa and that nmorb and k rich basalt compositions both crystallized as mg perovskite ca perovskite stishovite an aluminous phase with a cafe2o4 type structure at pressures below 68 gpa the orthorhombic mg perovskite is stable in natural rock compositions at pressures less than 97 gpa corresponding to about 2200 km depth phase transition of silica phase from stishovite to cacl2 type phase was observed at 78 gpa in nmorb composition moreover we observed that nmorb crystallized in to an assemblage of cairo3 type mg fe sio3 ca perovskite pbo2 type silica an aluminous phase with a calcium cati2o4 type structure at 143 gpa corresponding to the core mantle boundary depth we measured the unit cell volumes of minerals in the nmorb composition at high p t and thereby estimated the density of subducted morb to a depth of 1800 km in the lower mantle in this depth regime morb is denser than model mantle densities e g prem and ak135 the estimated density of morb may contribute to an understanding of dynamics of the subducted slab in the deep lower mantle

the sedimentary record and neoglacial history of tide lake northwestern british columbia tide lake was the largest glacier dammed lake in british columbia before its demise in the early twentieth century situated in the northern coast mountains the lake was impounded by frank mackie glacier and its neoglacial end moraine a study of tide lake has provided information on styles of glaciolacustrine sedimentation and the chronology of the neoglacial interval much of the sediment underlying the floor of tide lake was transported by subglacial and proglacial meltwater streams flowing from nearby glaciers during the last phase of the lake large subaqueous fans were built in front of berendon and frank mackie glaciers and deltas formed on the east side of the basin rhythmically bedded fine sediments which cover much of the lake floor but are almost completely lacking on the slopes above were deposited from underflows originating on deltas and subaqueous fans and by fallout from interflows and overflows three major and one minor lake phases are recognized from stratigraphic geomorphic radio

late holocene activity of sherman and sheridan glaciers prince william sound alaska abstract two adjacent glaciers in the chugach mountains of south central alaska have markedly different histories on decadal to perhaps centennial timescales sheridan glacier has advanced and retreated hundreds of metres during the latest holocene its recent fluctuations have markedly altered local base level of sherman river which drains sherman glacier and flows into sheridan lake sheridan glacier advanced to its greatest extent during the little ice age raising base level of sherman river and inducing aggradation there of up to 17 m of sediment retreat of sheridan glacier formed a series of lakes that have coalesced as lower lake outlets have become available base level of sherman river has dropped resulting in the evacuation of substantial volumes of sediment from sherman river valley in about 2000 the terminus of sheridan glacier began to disintegrate retreat accelerated dramatically in 2010 by 2016 the glacier had retreated an average of 600 m from its 2010 terminus although some areas retreated up to 1 9 km and others did not retreat at all meanwhile sherman glacier continued a slow advance initiated by a rock avalanche that blanketed much of its ablation area in the 1964 alaska earthquake

constraints on lower mantle composition from molecular dynamics simulations of mgsio3 perovskite abstract we have carried out molecular dynamics simulations of mgsio 3 perovskite pv in order to determine its equation of state and elastic parameters under pressure and temperature conditions of the earth s lower mantle combining this information with density and elastic constants for mg fe o magnesiowustite mw and including the effects of iron on the density of perovskite we investigated possible compositional models for the lower mantle by calculating seismic velocities and densities as functions of depth and comparing them to the globally averaged seismological models ak135 f and prem the calculations were done along several possible geothermal gradients both adiabatic and non adiabatic and for a range of mg fe partitioning coeffcients k fe mg pv mw 0 10 0 35 our results indicate that the most probable compositional models for the lower mantle are pyrolitic with x mg 0 87 and x pv 0 54 for increasing temperatures at the top of the lower mantle the best fitting models increase slightly in both iron and silica content

spin state of ferric iron in mgsio3 perovskite and its effect on elastic properties abstract recent studies have indicated that a significant amount of iron in mgsio 3 perovskite pv is fe 3 fe 3 fe 10 60 due to crystal chemistry effects at high pressure p and that fe 3 is more likely than fe 2 to undergo a high spin hs to low spin ls transition in pv in the mantle we have measured synchrotron mossbauer spectroscopy sms x ray emission spectroscopy xes and x ray diffraction xrd of pv with all iron in fe 3 in the laser heated diamond anvil cell to over 100 gpa fe 3 increases the anisotropy of the pv unit cell whereas fe 2 decreases it in pv synthesized above 50 gpa fe 3 enters into both the dodecahedral a and octahedral b sites approximately equally suggesting charge coupled substitution combining sms and xes we found that the ls population in the b site gradually increases with pressure up to 50 60 gpa where all fe 3 in the b site becomes ls while fe 3 in the a site remains hs to at least 136 gpa fe 3 makes pv more compressible than mg endmember below 50 gpa because of the gradual spin transition in the b site together with lattice compression the completion of the spin transition at 50 60 gpa increases bulk modulus with no associated change in density this elasticity change can be a useful seismic probe for investigating compositional heterogeneities associated with fe 3

thermoelastic properties of post perovskite phase mgsio3 determined experimentally at core mantle boundary p t conditions we have performed in situ x ray diffraction measurements on mgsio3 up to 144 5 gpa and 2535 k to obtain a precise experimental determination of the elastic properties of the post perovskite polymorph of mgsio3 at high pressure and temperature the complete dataset is comprised of 24 data points at ambient temperature and an equal number at high temperature fitted physical properties are the room temperature bulk modulus the gruneisen parameter with its volume dependency the thermal expansion with its temperature dependency and the linear incompressibilities as well as thermal expansions and their temperature dependency on each axis elastic anisotropy is observed the structure being much more compressible along the b axis and less compressible along the c axis in agreement with theoretical calculations we also demonstrate with the present study that experiments can provide precise information on the elasticity of complex materials at extreme pressure and temperature conditions

eemian and late glacial holocene palaeoenvironmental records from permafrost sequences at the dmitry laptev strait ne siberia russia abstract terrestrial permafrost sections from the southern and northern coasts of dmitry laptev strait have preserved records of landscape transition from glacial to interglacial periods they allow geomorphologic and environmental changes to be traced from pre eemian time to the eemian and from the late glacial to the holocene the transition from one period to another induced extensive thawing of permafrost thermokarst evolving thermokarst depressions transformed formerly frozen ground into taberal unfrozen deposits with accumulating overlying lacustrine deposits lacustrine horizons rich in palaeontological remains retain evidence of changes in environmental conditions the pollen records reflect changes from grass sedge dominated vegetation during the early eemian to shrub dominated spectra during the middle eemian thermal optimum followed by late eemian grass sedge dominated tundra vegetation abundant larix pollen have been found in middle eemian deposits from the south coast of the dmitry laptev strait oyogos yar but are absent in similar deposits from the north coast bol shoy lyakhovsky island likely indicating that the northern tree line was located near the oyogos yar region during the eemian thermal optimum grass sedge dominated tundra vegetation occurred during the late glacial holocene transition which was replaced by shrub tundra during the early holocene rich fossil ostracod records from eemian and late glacial holocene lacustrine deposits could be correlated with the eemian thermal optimum and the late glacial allerod warm period for both periods the stable oxygen isotope data from the fossil ostracods suggest an approximate mean summer water temperature range between about 10 and 19 c in the palaeo lakes

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

late holocene glacial activity at bromley glacier cambria icefield northern british columbia coast mountains canada retreating and downwasting glaciers in the british columbia coast mountains are exposing the remains of forests buried during holocene age glacial advances despite recent progress in discerning th

recent progress in studies of the elastic properties of earth materials abstract technological advances now allow the elastic moduli and acoustic wave velocities of minerals to be measured or calculated under extreme conditions of pressure and temperature p and t that closely mimic the p t conditions throughout much of earth s interior in this special issue the papers on the elasticity of earth materials report new results that provide excellent examples of these advances here we briefly discuss the scientific context for the elasticity papers in this special issue and some of the future challenges that are critical for advancing our understanding of the compositional state of the deep earth through studies of the elastic properties of materials

effect of fe enrichment on seismic properties of perovskite and post perovskite in the deep lower mantle recent experimental measurements of the equation of state of perovskites and post perovskites in the mg fe sio3 and mg fe al fe al si o 3 systems over a wide range of iron contents are used to constrain the effects of fe and al on density and bulk modulus of these phases at deep mantle pressures the density of fe bearing perovskite follows a linear relationship with fe content at a representative mid mantle depth of 1850 km 80 gpa 80 g cm 3 5 054 1 1 270 3 x fe the bulk modulus of silicate perovskite is not sensitive to fe content and follows the relationship k 80 gpa 546 2 12 25 x fe the velocity heterogeneity parameter partial derivative ln v b partial derivative x fe determined by experimental values for the bulk sound speed is 0 10 1 in agreement with theory and the behaviour of other fe bearing silicates near the core mantle boundary fe rich post perovskite is observed to be more compressible than the mg end member in contrast to theoretical predictions from experimental data the densities of perovskite and post perovskite at 125 gpa 2700 km depth are 125 pv g cm 3 5 426 11 1 38 4 x fe and 125 ppv g cm 3 5 548 1 1 41 3 x fe the density contrast across the post perovskite transition is similar to 2 per cent irrespective of fe content but the contrast in bulk sound speed increases with fe content al rich silicates exhibit no significant differences in density or compressibility relative to al free silicates but may be responsible for seismic heterogeneities due to differences in the depth and width of the post perovskite transition observations of increased densities in large low shear velocity provinces and ultra low velocity zones may be consistent with local iron enrichment from mg 90 to mg 78 88 and mg 50 respectively

neoglacial history of robson glacier british columbia as glaciers in the canadian rockies recede glacier forefields continue to yield subfossil wood from sites overridden by these glaciers during the holocene robson glacier in british columbia forme

mid holocene glacier expansion between 7500 and 4000 cal yr bp in the british columbia coast mountains canada the mid holocene behaviour of five glaciers in the british columbia coast mountains was reconstructed from radiocarbon ages and stratigraphic analysis subfossil wood evidence at canoe fyles jaco

ice complex permafrost of mis5 age in the dmitry laptev strait coastal region east siberian arctic ice complex deposits locally known as the buchchagy ice complex are exposed at both coasts of the east siberian dmitry laptev strait and preserved below the yedoma ice complex that formed during mis3 and mis2 marine isotope stage and lateglacial holocene thermokarst deposits mis1 radioisotope disequilibria 230th u of peaty horizons date the buchchagy ice complex deposition to 126 16 13 kyr and 117 19 14 kyr until 98 5 kyr and 89 5 kyr the deposit is characterised by poorlysorted medium to coarse silts with cryogenic structures of horizontal ice bands lens like and lenslike reticulated segregation ice two peaty horizons within the buchchagy ice complex and syngenetic ice wedges 2e4 m wide up to 10 m high are striking the isotopic composition d18o dd of buchchagy ice wedge ice indicates winter conditions colder than during the mis3 interstadial and warmer than during mis2 stadial and similar atmospheric winter moisture sources as during the mis2 stadial buchchagy ice complex pollen spectra reveal tundra steppe vegetation and harsher summer conditions than during the mis3 interstadial and rather similar vegetation as during the mis2 stadial short term climatic variability during mis5 is reflected in the record even though the regional chronostratigraphic relationship of the buchchagy ice complex to the last interglacial remains unclear because numerical dating is widely lacking the present study indicates permafrost ice complex formation during mis5 sensu lato and its preservation afterwards palaeoenvironmental insights into past climate and the periglacial landscape dynamics of arctic lowlands in eastern siberia are deduced from the record

pressure and temperature dependence of elastic wave velocity of mgsio3 perovskite and the composition of the lower mantle abstract simultaneous measurements of compressional p and shear s wave velocities and unit cell volume density have been conducted on mgsio 3 perovskite to 9 2 gpa and 873 k using ultrasonic interferometry in conjunction with x ray diffraction finite strain analysis of current data allowed us to determine the elastic moduli and their pressure derivatives independent of the pressure measurement the results are k s 253 2 gpa g 173 1 gpa k s p 4 4 1 and g p 2 0 1 the temperature derivatives of the bulk and shear moduli were tightly constrained from acoustic velocity measurements yielding k s t 0 021 2 gpa k and g t 0 028 2 gpa k p and s wave velocities and density profiles for a pyrolite compositional model consisting of magnesium silicate perovskite and magnesiowustite are calculated at lower mantle depths along a 1600 k adiabatic geotherm the results agree with those of seismic model prem within 0 5 0 5 and 0 3 respectively from 800 to 2600 km the effect of fe and mg partitioning between magnesium silicate perovskite and magnesiowustite on the calculated velocities and density is negligibly small compared to the effects of composition and temperature simultaneous constraints from p and s wave velocities and density support for a homogeneous lower mantle with pyrolitic composition

the role of al defects on the equation of state of al mg fe sio3 perovskite abstract we performed compression curves of aluminous silicate perovskite al pv synthesized under various conditions of pressure temperature and mgo or sio 2 activities using laser heated diamond anvil cell at the esrf grenoble we refined bulk moduli k 0 from 235 to 270 gpa in agreement with the wide range of values reported in the literature we observe that al pv phase synthesized at high temperature in the sio 2 rich system is more compressible than al pv phase synthesized at high pressure in the mgo rich system as suggested by various authors the resolution of this controversy rests on a better understanding of the crystal chemistry of al in perovskite which involves at least two competitive mechanisms substitution of si in the octahedral site only or a coupled substitution on both mg and si sites the vacancy mechanism is expected to reduce the k 0 significantly due to the presence of oxygen vacancies all compression curves performed in this study can be explained by considering that the vacancy mechanism is favored at high temperatures and that the coupled mechanism is favored at high pressures these trends agree well with previous reports for mg fe si al o 3 perovskite compositions relevant to the lower mantle the two previous reports and our new data set for a morb type perovskite phase agree well with each other with higher k 0 values between 260 and 270 gpa compared with k 0 253 gpa for the pure mgsio 3 phase suggested from previous studies in these compounds coupled substitution of al 3 and fe 3 cations leads to a well constrained crystal chemistry therefore the low k 0 value observed in some of the previous studies for fe free al pv is likely to be irrelevant for mantle perovskite some questions may remain only for the mantle region just below the 670 km discontinuity where pressures remain moderate thus potentially allowing for at most 2 of oxygen vacancies however it is clear that using low k 0 values to extrapolate to greater depths is unjustified

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

the elastic solid solution model for minerals at high pressures and temperatures non ideality in mineral solid solutions affects their elastic and thermodynamic properties their thermobaric stability and the equilibrium phase relations in multiphase assemblages at a given composition and state of order non ideality in minerals is typically modelled via excesses in gibbs free energy which are either constant or linear with respect to pressure and temperature this approach has been extremely successful when modelling near ideal solutions however when the lattice parameters of the solution endmembers differ significantly extrapolations of thermodynamic properties to high pressures using these models may result in significant errors in this paper i investigate the effect of parameterising solution models in terms of the helmholtz free energy treating volume or lattice parameters rather than pressure as an independent variable this approach has been previously applied to models of order disorder but the implications for the thermodynamics and elasticity of solid solutions have not been fully explored solid solution models based on the helmholtz free energy are intuitive at a microscopic level as they automatically include the energetic contribution from elastic deformation of the endmember lattices a chemical contribution must also be included in such models which arises from atomic exchange within the solution derivations are provided for the thermodynamic properties of n endmember solutions examples of the use of the elastic model are presented for the alkali halides pyroxene garnet and bridgmanite solid solutions elastic theory provides insights into the microscopic origins of non ideality in a range of solutions and can make accurate predictions of excess enthalpies entropies and volumes as a function of volume and temperature in solutions where experimental data are sparse or contradictory the helmholtz free energy approach can be used to assess the magnitude of excess properties and their variation as a function of pressure and temperature the formulation is expected to be useful for geochemical and geophysical studies of the earth and other planetary bodies

interglacials of the last 800 000 years interglacials including the present holocene period are warm low land ice extent high sea level end members of glacial cycles based on a sea level definition we identify eleven interglacials in the last 800 000 years a result that is robust to alternative definitions data compilations suggest that despite spatial heterogeneity marine isotope stages mis 5e last interglacial and 11c 400 ka ago were globally strong warm while mis 13a 500 ka ago was cool at many locations a step change in strength of interglacials at 450 ka is apparent only in atmospheric co2 and in antarctic and deep ocean temperature the onset of an interglacial glacial termination seems to require a reducing precession parameter increasing northern hemisphere summer insolation but this condition alone is insufficient terminations involve rapid nonlinear reactions of ice volume co2 and temperature to external astronomical forcing the precise timing of events may be modulated by millennial scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere a variety of temporal trends is observed such that maxima in the main records are observed either early or late in different interglacials the end of an interglacial glacial inception is a slower process involving a global sequence of changes interglacials have been typically 10 30 ka long the combination of minimal reduction in northern summer insolation over the next few orbital cycles owing to low eccentricity and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future

neoglaciation in the southern coast mountains of british columbia chronology prior to the late neoglacial maximum moraine stratigraphy and morphology radiocarbon dates from klinaklini franklin tiedemann gilbert and bridge glaciers and related information from elsewhere in the coast mountains are used to construct a chronology for glacier fluctuations the garibaldi phase of glacier expansion 6000 5000 14c years bp at the end of the early holocene xerothermic interval is indicated by overridden tree stumps the mid neoglacial tiedemann advance 3300 1900 14c years bp is represented by moraines till and meltwater sediments at three glaciers but only tiedemann glacier attained its greatest holocene extent at this time late neoglacial expansion commenced before 900 14c years bp and continued without notable interruption until glaciers achieved their maximum post pleistocene expansion during the eighteenth and nineteenth centuries evidence for the garibaldi and tiedemann events is scarce within the coast mountains because of the more extensive late neoglacial advance however correlative advances have been

a mineralogical model for density and elasticity of the earth s mantle 1 we present a thermodynamic model of high pressure mineralogy that allows the evaluation of phase stability and physical properties for the earth s mantle the thermodynamic model is built from previous assessments and experiments in the five component cfmas system cao feo mgo al2o3 sio2 including mineral phases that occur close to typical chemical models of the mantle and reasonable mantle temperatures in this system we have performed a system gibbs free energy minimization including pure end member phases and a nonideal formulation for solid solutions solid solutions were subdivided into discrete pseudocompounds and treated as stoichiometric phases during computation of chemical equilibrium by the simplex method we have complemented the thermodynamic model with a model of shear wave properties to obtain a full description of aggregate elastic properties density bulk and shear moduli that provide a useful basis for the consideration of seismic and geodynamic models of the earth s mantle the thermodynamic model described here is made available for research and training purposes through a web interface http www earthmodel org we examine its validity in light of experiments from mineral physics and briefly discuss inferences for mantle structure

the deep permafrost carbon pool of the yedoma region in siberia and alaska estimates for circumpolar permafrost organic carbon oc storage suggest that this pool contains twice the amount of current atmospheric carbon the yedoma region sequestered substantial quantities of oc and is unique because its deep oc was incorporated into permafrost during ice age conditions rapid inclusion of labile organic matter into permafrost halted decomposition and resulted in a deep long term sink we show that the deep frozen oc in the yedoma region consists of two distinct major sub reservoirs yedoma deposits late pleistocene ice and organic rich silty sediments and deposits formed in thaw lake basins generalized as thermokarst deposits we quantified the oc pool based on field data and extrapolation using geospatial datasets to 83 61 57 gt for yedoma deposits and to 128 99 96 gt for thermokarst deposits the total yedoma region 211 160 153 gt is a substantial amount of thaw vulnerable oc that must be accounted for in global models

late holocene fluctuations of the bear river glacier northern coast ranges of british columbia canada during holocene advances of the bear river glacier in northwestern british columbia ice pushed against a bedrock slope on the north side of bear river pass as it was being diverted eastward and westward along the pass the result is a series of till sheets plastered against the rock slope and separated by wood mats this sequence of tills provides an unusually detailed record of early neoglacial history and shows that neoglacial expansion in the northern coast mountains began earlier than previously known moraines show the extent of little ice age expansion and documents related to the long mining history of the area provide records of post lia recession the oldest deposits in the area are a small lateral moraine outside of a prominent lia moraine and a till in the pass older than c 3500 14c yr bp the small moraine is undated it may be equivalent to the latest pleistocene crowfoot advance which produced similar moraines in the southern coast mountains and eastern cordillera wood mats in the pa

230th u dating of frozen peat bol shoy lyakhovsky island northern siberia abstract the chronology of quaternary paleoenvironment and climate in northeastern siberia is poorly understood due to a lack of reliable numerical age determinations the best climatic archives are ice rich permafrost sequences which are widely distributed in northeastern siberia for this study 230 th u ages were determined by thermal ionization mass spectrometry tims from frozen peat in a permafrost deposit at the southern cliff of the bol shoy lyakhovsky island new siberian archipelago west of the zimov e river these yielded a pre eemian isochron corrected 230 th u age of 200 900 3400 yr this result is reliable because permafrost deposits behave as closed systems with respect to uranium and thorium our findings suggest that 230 th u dating of frozen peat in permafrost deposits is a useful tool for the reconstruction of the middle quaternary environment of northern siberia and of the whole arctic

dendroglaciological evidence for holocene glacial advances in the todd icefield area northern british columbia coast mountains accelerated glacial recession and downwasting in pacific north america is exposing land surfaces and fea tures buried by glacial advances that in many locations predate the recent little ice age lia dendrochronologic analyses of increment core samples from living trees abies lasiocarpa tsuga mertensiana and samples of subfossil wood collected in the todd icefield area boundary ranges british columbia coast mountains provide the basis for a dendroglaciological and radiocarbon based reconstruction of late holocene glacier activity five intervals of glacier ex pansion were recorded by trees killed or buried by advancing glaciers 1 an advance prior to 3000 14 c years bp 2 an advance at 3000 14 c years bp that coincides with the regional tiedemann advance 3 an unattributed advance at 2300 14 c years bp 4 a two phase advance at 1700 and 1450 14 c years bp that corresponds with the regional first millennium advance 5 an advance with three phases of expansion that began prior to 750 14 c bp and is con sistent with the regional early lia interval and a two phase interval of late lia expansion culminating after 240 and 100 years bp this chronology of late holocene glaciation matches that emerging from similar investigations in the coastal cordillera of pacific north america and provides additional support for the regional significance of both the tiedemann and the first millennium advances resume une recession et une fonte glaciaire accelerees dans l ocean pacifique en amerique du nord exposent des sur faces de terrain et des traits caracteristiques enfouis sous des avancees glaciaires lesquelles dans bien des cas datent d avant le recent petit ge glaciaire des analyses dendrochronologiques d echantillons proportionnels de carottes pris

vegetation and climate history in the laptev sea region arctic siberia during late quaternary inferred from pollen records abstract paleoenvironmental records from a number of permafrost sections and lacustrine cores from the laptev sea region dated by several methods 14 c ams tl irsl osl and 230 th u were analyzed for pollen and palynomorphs the records reveal the environmental history for the last ca 200 kyr for interglacial pollen spectra quantitative temperature values were estimated using the best modern analogue method sparse grass sedge vegetation indicating arctic desert environmental conditions existed prior to 200 kyr ago dense wet grass sedge tundra habitats dominated during an interstadial ca 200 190 kyr ago reflecting warmer and wetter summers than before sparser vegetation communities point to much more severe stadial conditions ca 190 130 kyr ago open grass and artemisia communities with shrub stands alnus fruticosa salix betula nana in more protected and moister places characterized the beginning of the last interglacial indicate climate conditions similar to present shrub tundra alnus fruticosa and betula nana dominated during the middle eemian climatic optimum when summer temperatures were 4 5 c higher than today early weichselian sparse grass sedge dominated vegetation indicates climate conditions colder and dryer than in the previous interval middle weichselian interstadial records indicate moister and warmer climate conditions for example in the interval 40 32 kyr bp salix was present within dense grass sedge dominated vegetation sedge grass artemisia communities indicate that climate became cooler and drier after 30 kyr bp and cold dry conditions characterized the late weichselian ca 26 16 kyr bp when grass dominated communities with caryophyllaceae asteraceae cichoriaceae selaginella rupestris were present from 16 to 12 kyr bp grass sedge communities with caryophyllaceae asteraceae and cichoriaceae indicate climate was significantly warmer and moister than during the previous interval the presence of salix and betula reflect temperatures about 4 c higher than present at about 12 11 kyr bp during the allerod interval but shrubs were absent in the younger dryas interval pointing to a deterioration of climate conditions alnus fruticosa betula nana poaceae and cyperaceae dominate early holocene spectra reconstructed absolute temperature values were substantially warmer than present up to 12 c shrubs gradually disappeared from coastal areas after 7 6 kyr bp when vegetation cover became similar to modern a comparison of proxy based paleoenvironmental reconstructions with the simulations performed by an earth system model of intermediate complexity climber 2 show good accordance between the regional paleodata and model simulations especially for the warmer intervals

phase transition of ca perovskite and stability of al bearing mg perovskite in the lower mantle here using in situ x ray diffraction combined with a laser heated diamond anvil cell at high temperatures and high pressures a phase relationship in klb 1 peridotite composition samples was investigated from 38 to 106 gpa and 300 to 2600 k in order to determine the stability of phases in the lower mantle we observed that al bearing mg perovskite and magnesiowustite remained stable up to 106 gpa which corresponds to a lower mantle depth of 2400 km depth by contrast a phase transition in ca perovskite from a cubic to a tetragonal structure was observed the amount of distortion in this material increases as pressure increases at 300 k the temperature of the tetragonal to cubic structure transition therefore appears to increase with increasing pressure there is a possibility that this ca perovskite phase transition contributes to unidentified seismic anomalies in the lower mantle

repeated pleistocene glaciation of the east siberian continental margin during glacial periods ice sheets covered continental margins through much of arctic north america greenland and western eurasia marine structures suggest that an ice sheet up to a kilometre in depth periodically covered the east siberian continental shelf as well

palaeoclimate a fresh look at arctic ice sheets during the last glacial maximum ice sheets in eurasia terminated at the edge of the laptev sea seismic data now suggest that a separate ice sheet was repeatedly centred further east in the east siberian sea during previous glacial periods

the landslide response of alpine basins to post little ice age glacial thinning and retreat in southwestern british columbia abstract the role of post little ice age lia neoglacial retreat on landslide activity is investigated in 19 alpine basins along the upper lillooet river valley british columbia we examine how neoglacial scouring and glacial recession have modified hillslope form and slope stability and construct a decision making flowchart to identify landslide hazards associated with glacial retreat this work is based on field mapping gis analysis statistical associations between landslides and terrain attributes and a comparison between neoglaciated and non neoglaciated terrain within each basin the bedrock landslide response to glacial retreat varies appreciably according to lithology and the extent of glacial scour below the lia trimline valleys carved in weak quaternary volcanics show significant erosional oversteepening and contain deep seated slope movement features active rock fall rock slides and rock avalanches near glacial trimlines basins in stronger granitic rock rarely show increased bedrock instability resulting from post lia retreat except for shallow seated rock slides along some trimlines and failures on previously unstable slopes in surficial materials landslides associated with post lia retreat originate in till or colluvium as debris slides or debris avalanches and are concentrated along lateral moraines or glacial trimlines significant spatial association was also observed between recent catastrophic failures gravitational slope deformation and slopes that were oversteepened then debuttressed by glacial erosion eight out of nine catastrophic rock slope failures occurred just above glacial trimlines and all occurred in areas with a previous history of deep seated gravitational slope movement implying that this type of deformation is a precursor to catastrophic detachment

the compressibility of a natural composition calcium ferrite type aluminous phase to 70 gpa abstract in situ x ray diffraction xrd experiments of a calcium ferrite type aluminous phase that is a sodium host mineral of subducted oceanic crusts into the earth s lower mantle have been carried out using a laser heated diamond anvil cell lhdac up to a pressure of 70 gpa with synchrotron radiation source at the photon factory pf in japan the sample was heated using a nd yag laser at each pressure increment to relax the deviatoric stress in the sample xrd measurements were carried out at 300 k using an angle dispersive technique the pressure was determined from an internal platinum pressure calibrant a birch murnaghan equation of state eos was determined from the experimental unit cell parameters volume v 0 244 07 55 a 3 density 0 4 143 g cm 3 bulk modulus k 0 253 14 gpa and k 0 3 6 0 6 when the first pressure derivative of the bulk modulus k 0 was fixed at 4 the value of k 0 243 2 gpa was obtained the density of the calcium ferrite type aluminous phase is lower than those of co existing mg ca perovskite and hexagonal aluminous phase in subducted oceanic crusts

dry mg fe sio3 perovskite in the earth s lower mantle combined synthesis experiments and first principles calculations show that mgsio3 perovskite with minor al or fe does not incorporate significant oh under lower mantle conditions perovskite stishovite and residual melt were synthesized from natural bamble enstatite samples mg fe mg 0 89 and 0 93 al2o3 0 1 wt with 35 and 2065 ppm weight h2o respectively in the laser heated diamond anvil cell at 1600 2000 k and 25 65 gpa combined fourier transform infrared spectroscopy x ray diffraction and ex situ transmission electron microscopy analysis demonstrates little difference in the resulting perovskite as a function of initial water content four distinct oh vibrational stretching bands are evident upon cooling below 100 k 3576 3378 3274 and 3078 cm 1 suggesting four potential bonding sites for oh in perovskite with a maximum water content of 220 ppm weight h2o and likely no more than 10 ppm weight h2o complementary fe free first principles calculations predict multiple potential bonding sites for hydrogen in perovskite each with significant solution enthalpy 0 2 ev defect we calculate that perovskite can dissolve less than 37 ppm weight h2o 400 ppm h si at the top of the lower mantle decreasing to 31 ppm weight h2o 340 ppm h si at 125 gpa and 3000 k in the absence of a melt or fluid phase we propose that these results resolve a long standing debate of the perovskite melting curve and explain the order of magnitude increase in viscosity from upper to lower mantle

synthesis and equation of state of perovskites in the mg fe 3al2si3o12 system to 177 gpa natural and synthetic pyrope almandine compositions from 38 to 100 mol almandine alm38 alm100 were studied by synchrotron x ray diffraction in the laser heated diamond anvil cell to 177 gpa single phase orthorhombic gdfeo3 type perovskites were synthesized across the entire examined compositional range at deep lower mantle pressures with higher fe contents requiring higher synthesis pressures the formation of perovskite with alm100 fe3al2si3o12 composition at 80 gpa marks the first observation of a silicate perovskite in a fe end member fe enrichment broadens and lowers the pressure range of the post perovskite transition for intermediate compositions such as alm54 but the more fe rich alm100 composition perovskite remains stable to pressures as high as 149 gpa volume compression data for the alm54 and alm100 compositions were fit to the birch murnaghan equation of state the compressibility of perovskites synthesized from compositions along the pyrope almandine join is not strongly sensitive to fe content the compression curves were smooth over the entire measured range and no evidence for a volume anomaly associated with a spin transition was observed c 2012 elsevier b v all rights reserved

effects of fe enrichment on the equation of state and stability of mg fe sio3 perovskite fe rich natural orthopyroxenes with compositions of mg0 61fe0 38ca0 01 sio3 fe 38 and mg0 25fe0 74ca0 01 sio3 fe 74 were studied at pressures up to 155 gpa and temperatures up to 3000 k single phase orthorhombic gdfeo3 type perovskite was synthesized by heating to similar to 2000 k at 63 gpa for the fe 38 composition and at 72 gpa for the fe 74 composition at lower pressures heating both compositions resulted in a mixture of perovskite sio2 and mg fe o these measurements provide new constraints on the dependence of mg fe sio3 perovskite stability on pressure and composition upon further compression and heating at 89 and 99 gpa fe 38 and fe 74 perovskites transformed to two phase mixtures of perovskite and post perovskite consistent with previous findings that increasing fe content lowers the transition pressure the volume of mg fe sio3 perovskites increases linearly with fe content volume data were fit to the birch murnaghan equation of state the bulk modulus at 80 gpa is 550 560 gpa for both fe rich perovskites comparable to or slightly higher than the values measured for mgsio3 perovskite at this pressure indicating that the bulk modulus of perovskite is not strongly sensitive to fe content c 2012 elsevier b v all rights reserved

phase relation and mineral chemistry in pyrolite to 2200 c under the lower mantle pressures and implications for dynamics of mantle plumes 1 phase relations in pyrolite were studied at pressures of 24 and 30 gpa and temperatures up to 2200 c at 24 gpa and 1600 c an assemblage of mg perovskite magnesiowustite ca perovskite and garnet was observed with the proportion of garnet increasing continuously with temperature at 30 gpa only the two perovskites and magnesiowustite were observed and no significant changes in mineral proportions with temperature were observed iron was almost equally partitioned between mg perovskite and magnesiowustite at temperatures below about 1800 c at 24 and 30 gpa with increasing temperature however iron was concentrated more in magnesiowustite at both of these pressures the decrease of al content in mg perovskite with temperature which is caused by an increase in the proportion of garnet is likely to be responsible for the iron partitioning behavior at 24 gpa while the minor elements na al and cr in magnesiowustite may play an important role in fe partitioning at 30 gpa the density difference between ascending hot plumes t 200 and 400 c and the surrounding mantle was calculated using the present experimental data the density difference t 400 c at 30 gpa 806 km depth is 0 06 g cm3 but increases to 0 22 g cm3 at 24 gpa 670 km depth the large increase in the density difference that occurs in a hot plume at the uppermost part of the lower mantle originates from an increase of the proportion of garnet and may be a trigger for the plume s passage through the boundary between the lower mantle and the mantle transition zone

dendroglaciological reconstruction of late holocene glacier activity at white and south flat glaciers boundary range northern british columbia coast mountains canada holocene glacier activity in the northern british columbia coast mountains canada is described following investigations in the recently deglaciated forefields of white and south flat glaciers spilling from the cambria icefield glacially overridden stumps and detrital wood was radiocarbon and dendrochronologically dated to describe an advance between ad 250 and 650 expansion and thickening of white glacier by ad 765 resulted in creation of an ice dammed lake in south flat valley that persisted until ad 1080 following this the lake drained before refilling in the early little ice age prior to ad 1300 shortly thereafter white and south flat glaciers became confluent and flowed over the valley side toward white lake the characteristics of the site and the preservation of 1500 yr old deposits indicate that the two glaciers remained confluent throughout the remainder of the little ice age only separating following terminal retreat early in the 20th century the late holocene glacial history of whit

numerical 230th u dating and a palynological review of the holsteinian hoxnian interglacial abstract earth scientists increasingly consider the holsteinian interglacial and mis 11 as synonyms despite the limited number of numerical dates and ambiguous stratigraphic and palynological correlation with the numerical marine isotope timescale hence we present new tims 230th u dates from two fen peat layers of the holsteinian reference site at bossel in northern germany and re evaluate published numerical data from two sites with hoxnian deposits in england a new method for the calculation of methodically controlled minimum 230th u ages mcma was developed the synopsis of the 230th u dates allows a correlation of both the holsteinian and hoxnian interglacials to mis 9 this correlation is supported by supplementary 230th u dates of fen peat from several pre eemian but non holsteinian sites in germany there is palynological evidence for a reliable correlation between precisely investigated and numerically dated holsteinian deposits in poland germany england sw ireland and france an apparently contradictory palynological correlation from the french central massif is discussed

latest pleistocene and holocene glacier fluctuations in western canada we summarize evidence of the latest pleistocene and holocene glacier fluctuations in the canadian cordillera our review focuses primarily on studies completed after 1988 when the first comprehensive review of such evidence was published the cordilleran ice sheet reached its maximum extent about 16 ka and then rapidly decayed some lobes of the ice sheet valley glaciers and cirque glaciers advanced one or more times between 15 and 11 ka by 11 ka or soon thereafter glacier cover in the cordillera was no more extensive than at the end of the 20th century glaciers were least extensive between 11 and 7 ka a general expansion of glaciers began as early as 8 4 ka when glaciers overrode forests in the southern coast mountains it culminated with the climactic advances of the little ice age holocene glacier expansion was not continuous but rather was punctuated by advances and retreats on a variety of timescales radiocarbon ages of wood collected from glacier forefields reveal six major periods of glacier advance 8 59 8 18 7 36 6 45 4 40 3 97 3 54 2 77 1 71 1 30 ka and the past millennium tree ring and lichenometric dating shows that glaciers began their little ice age advances as early as the 11th century and reached their maximum holocene positions during the early 18th or mid 19th century our data confirm a previously suggested pattern of episodic but successively greater holocene glacier expansion from the early holocene to the climactic advances of the little ice age presumably driven by decreasing summer insolation throughout the holocene proxy climate records indicate that glaciers advanced during the little ice age in response to cold conditions that coincided with times of sunspot minima priority research required to further advance our understanding of late pleistocene and holocene glaciation in western canada includes constraining the age of late pleistocene moraines in northern british columbia and yukon territory expanding the use of cosmogenic surface exposure dating techniques using multi proxy paleoclimate approaches and directing more of the research effort to the northern canadian cordillera

paleontological records indicate the occurrence of open woodlands in a dry inland climate at the present day arctic coast in western beringia during the last interglacial abstract permafrost records accessible at outcrops along the coast of oyogos yar at the dmitry laptev strait ne siberia provide unique insights into the environmental history of western beringia during the last interglacial the remains of terrestrial and freshwater organisms including plants coleopterans chironomids cladocerans ostracods and molluscs have been preserved in the frozen deposits of a shallow paleo lake and indicate a boreal climate at the present day arctic mainland coast during the last interglacial terrestrial beetle and plant remains suggest the former existence of open forest tundra with larch larix dahurica tree alder alnus incana birch and alder shrubs duschekia fruticosa betula fruticosa betula divaricata betula nana interspersed with patches of steppe and meadows consequently the tree line was shifted to at least 270 km north of its current position aquatic organisms such as chironomids cladocerans ostracods molluscs and hydrophytes indicate the formation of a shallow lake as the result of thermokarst processes steppe plants and beetles suggest low net precipitation littoral pioneer plants and chironomids indicate intense lake level fluctuations due to high evaporation many of the organisms are thermophilous indicating a mean air temperature of the warmest month that was greater than 13 c which is above the minimum requirements for tree growth these temperatures are in contrast to the modern values of less than 4 c in the study area the terrestrial and freshwater organism remains were found at a coastal exposure that was only 3 5 m above sea level and in a position where they should have been under sea during the last interglacial when the global sea level was 6 10 m higher than the current levels the results suggest that during the last warm stage the site was inland and its modern coastal situation is the result of tectonic subsidence

holocene glacier history of frank mackie glacier northern british columbia coast mountains frank mackie glacier repeatedly advanced across the bowser river valley in northwestern british columbia to impound tide lake during the holocene the most recent infilling of tide lake was associa

thermal equation of state of cafe2o4 type mgal2o4 abstract in situ x ray diffraction measurements of cafe 2 o 4 type mgal 2 o 4 have been conducted at pressures up to 42 gpa and temperatures to 2400 k using kawai type multianvil apparatus with sintered diamond anvils additional measurements have also been conducted at pressures to 12 gpa using diamond anvil cell with helium as a pressure medium at room temperature and at temperatures to 836 k at the ambient pressure using a high temperature x ray diffractometer the analysis of room temperature data yielded v 0 240 1 2 a 3 k 0 205 6 gpa and k 0 4 1 3 a fit of the present data to high temperature birch murnaghan equation of state eos yielded k 0 t p 0 030 2 gpa k and 0 a 0 b 0 t with values of a 0 1 96 13 10 5 k 1 and b 0 1 64 24 10 8 k 2 the present data set was also fitted to mie gruneisen debye mgd eos and we obtained 0 1 73 7 q 2 03 37 and 0 1546 104 k density changes of morb have been estimated using the newly obtained thermoelastic parameters assuming that the al rich phase in this composition possesses the cafe 2 o 4 type structure under the lower mantle p t conditions the calculated densities along geotherms for the normal mantle and subducting cold slabs are both significantly higher than those of typical seismological models confirming the conclusion of some recent results on morb by laser heated diamond anvil cell experiments

ferric iron content in mg fe sio3 perovskite and post perovskite at deep lower mantle conditions we have determined the fe 3 fe ratio of al free mg fe sio 3 perovskite post perovskite and mg fe o ferropericlase synthesized at 99 to 187 gpa and 1830 to 3500 k based on the electron energy loss near edge structure elnes spectroscopy the results demonstrate that post perovskite includes minor amounts of ferric iron with fe 3 fe ratios of 0 11 to 0 21 these values are substantially lower than those of al rich post perovskite fe 3 fe 0 59 to 0 69 reported in a previous study suggesting that the fe 3 al 3 coupled substitution is important in post perovskite as in the case of perovskite the al bearing post perovskite in a pyrolitic mantle composition likely contains a considerable amount of ferric iron which affects various physical properties in the lowermost mantle

equations of state of na k al host phases and implications for morb density in the lower mantle abstract we report equations of state eos of two important silicate phases known to store na k and al at pressures and temperatures prevailing in the earth s lower mantle using laser heated diamond anvil cell we produced the ca ferrite type cf and the new aluminum rich nal phases using different synthetic and natural starting materials at pressures ranging from 23 to 65 gpa unit cell volumes were investigated by means of angle dispersive x ray diffraction at the id30 beamline of the esrf synchrotron ring grenoble france cf phases were synthesized in naalsio4 mgal2o4 and naalsio4 mg fe 2sio4 systems and for a natural mid ocean ridge basalt morb the insertion of mgal2o4 in the naalsio4 based lattice has reduced effects on the cf phase eos whereas that of mg fe 2sio4 is mainly to increase the room pressure volume cf phases most relevant to the earth s mantle show compression behavior comparable to the pure naalsio4 cf phase with bulk moduli values close to k0 190 gpa and k0 4 we also synthesized nal phases in naalsio4 mgal2o4 system and using cana and k rich silicate glasses as starting materials all nal compounds investigated show similar compression behavior except for one anomalously naalsio4 rich composition for nal phase with the most natural conditions relevant composition we refine bulk moduli of k0 182 gpa and k0 6 we then model the density profiles expected for the cf and nal phases using our newly determined eos and the most accurate chemical compositions reported in the literature these two phases appear significantly less dense than a pyrolitic type material at all lower mantle pressures and 300 k however the density profiles calculated for mineral assemblages corresponding to typical morb compositions point out to denser morbs compared to the pyrolite this is due to the high fe content in morb yielding a densest fe rich perovskite that counterbalances the lower densities of the cf and nal phases the density gap is calculated between 0 4 and 4 0 depending on the starting morb composition and pressure

ratio of 36cl cl in ground ice of east siberia and its application for chronometry abundance of the cosmogenic nuclide chlorine 36 36cl was measured together with the chloride cl concentration in different horizons of quaternary permafrost samples collected from various types of ground ice in the northeastern part of siberia the 36cl cl in 32 samples ranged in value from 2 4 10 14 to 1 4 10 12 nonetheless after a few extreme values were excluded these 36cl cl ratios provided a local permafrost chronometry the general concordance of the modeled ages with geological expectations and other chronological methods supports the potential power of the proposed dating method however the large observed change in ratios from higher to lower values during the transition from last glacial maximum to holocene climatic conditions remains unexplained an attempt to make use of the corresponding beryllium 10 10be absolute concentrations in the same samples failed because input of 10be attached to particulate matter into permafrost is unknown further 36cl cl serial measurements of modern precipitation and fossil ground ice are needed to refine this dating method into a practical tool with a clear protocol

mgsio3 fesio3 al2o3 in the earth s lower mantle perovskite and garnet at 1200 km depth natural pyroxene and garnet starting materials are used to study the effects of joint fe and al substitution into mgsio3 perovskite at 50 gpa garnet is found to coexist with perovskite in samples containing both fe and al to pressures occurring deep into the lower mantle 1200 km depth the volume of the perovskite unit cell is vo a3 162 59 5 95xfesio3 10 80xal2o3 with aluminum causing a significant increase in the distortion from the ideal cubic cell on the basis of a proposed extension of the mgsio3 al2o3 high pressure phase diagram toward fesio3 fe is shown to partition preferentially into the garnet phase the stability of garnet deep into the lower mantle may hinder the penetration of subducted slabs below the transition zone

the compressibility of hexagonal al rich nal phase similarities and differences with calcium ferrite type cf phase with implications for the lower mantle abstract we have determined the equation of state of a hexagonal al rich type nal phase k0 07na0 81ca0 12 1 01 mg1 62fe0 38 2 00 al4 98fe0 10ti0 05si0 88 6 01o12 an aluminum host mineral that is likely to occur in subducted oceanic crusts mid oceanic ridge basaltic morb in the earth s lower mantle angle dispersive x ray powder diffraction experiments were conducted up to 36 gpa at room temperature at the bl04 b2 at spring 8 fitting a third order birch murnaghan equation of state to the data gives a bulk modulus of k 0 214 2 gpa with k 0 3 0 1 a volume v0 184 55 6 a3 and a zero pressure density of 0 4 g cm3 when k0 is fixed at 4 the value of k 0 202 3 0 9 gpa these values are comparable to those for similar anhydrous hexagonal aluminous phases reported previously by ono et al phys chem minerals 29 2002a 527 the density of nal phase is lower than that of other minerals excluding the cf phase co existing in the subducted oceanic crust such as mg perovskite ca perovskite and stishovite we find that the elastic properties of the hexagonal al rich phase do not change despite substantial variations in si al fe mg na and k content in the nal chemical composition

ice complex formation on bol shoy lyakhovsky island new siberian archipelago east siberian arctic since about 200 ka late quaternary landscapes of unglaciated beringia were largely shaped by ice wedge polygon tundra ice complex ic strata preserve such ancient polygon formations here we report on the yukagir ic from bol shoy lyakhovsky island in northeastern siberia and suggest that new radioisotope disequilibria 230th u dates of the yukagir ic peat confirm its formation during the mis 7a c interglacial the preservation of the ice rich yukagir ic proves its resilience to last interglacial and lateglacial holocene warming this study compares the yukagir ic to ic strata of mis 5 mis 3 and mis 2 ages exposed on bol shoy lyakhovsky island besides high intrasedimental ice content and syngenetic ice wedges intersecting silts sandy silts the yukagir ic is characterized by high organic matter om accumulation and low om decomposition of a distinctive drepanocladus moss peat the yukagir ic pollen data reveals grassshrub moss tundra indicating rather wet summer conditions similar to modern ones the stable isotope composition of yukagir ic wedge ice is similar to those of the mis 5 and mis 3 ics pointing to similar atmospheric moisture generation and transport patterns in winter ice complex data from glacial and interglacial periods provide insights into permafrost and climate dynamics since about 200 ka

the equation of state of orthorhombic perovskite in a peridotitic mantle composition to 80 gpa implications for chemical composition of the lower mantle abstract in situ x ray diffraction of orthorhombic perovskite which is the dominant phase in the earth s lower mantle was carried out on a sample with a klb 1 peridotite composition up to a pressure of 80 gpa using a laser heated diamond anvil cell lhdac with x rays from a synchrotron radiation source at each pressure increment the sample was heated using a yag laser to relax the deviatoric stress in the sample the bulk modulus of the orthorhombic perovskite which contained feo al 2 o 3 tio 2 cao and na 2 o was nearly equal to or slightly larger than that of pure mgsio 3 perovskite the density of the klb 1 peridotite at the top of the lower mantle estimated using thermoelastic parameters is in good agreement with a density profile prem determined from seismic observations the klb 1 peridotite composition is therefore consistent with the bulk composition of the upper part of the lower mantle

holocene glacier activity in the british columbia coast mountains canada abstract the coast mountains flank the pacific ocean in western british columbia canada subdivided into the southern pacific ranges central kitimat ranges and northern boundary ranges the majority of large glaciers and icefields are located in the boundary and pacific ranges prior descriptions of the holocene glacial history of this region indicate the holocene was characterized by repeated episodes of ice expansion and retreat recent site specific investigations augment our understanding of the regional character and duration of these events in this paper previously reported and new radiocarbon evidence is integrated to provide an updated regional assessment the earliest evidence of glacier expansion in the coast mountains comes from the boundary ranges at 8 9 and 7 8 ka and in the pacific ranges at 8 5 8 2 ka with the latter advance corresponding to an interval of rapid global climate deterioration although generally warm and dry climates from 7 3 to 5 3 ka likely limited the size of glaciers in the region there is radiocarbon evidence for advances over the interval from 7 3 to 6 0 and at 5 4 5 3 ka in the pacific ranges following these advances glaciers in the pacific ranges expanded down valley at 4 8 4 6 4 4 4 0 3 5 2 6 1 4 1 2 and 0 8 0 4 ka while glaciers in boundary ranges were advancing at 4 1 4 0 3 7 3 4 3 1 2 8 2 3 1 7 1 1 and 0 8 0 4 ka after 0 4 ka it appears that most glaciers in the coast mountains continued to expand to attain their maximum holocene extents by the early 18th to late 19th centuries this enhanced record of holocene glacier activity highlights the temporal synchrony in the coast mountains individual expansion events in the mid to late holocene broadly correspond to intervals of regional glacier activity reported in the canadian rocky mountains in alaska and on high elevation volcanic peaks in washington state

equation of state of lower mantle al fe mgsio3 perovskite the compression behavior of various al fe bearing mgsio3 perovskites was investigated by powder x ray diffraction up to 70 gpa on the id30 beamline of esrf grenoble france using diamond anvil cell coupled with co2 laser heating we obtained a reliable equation of state up to typical lower mantle pressures in contrast to fe which essentially increases the room pressure unit cell volume v0 the effect of al is to increase the bulk modulus of silicate perovskite this result contrasts with previous determinations performed at pressures below 10 gpa on samples synthesized in the multi anvil press such a difference can be explained by a change in the substitution mechanism of al in mgsio3 with increasing pressure and temperature in agreement with recent ab initio calculations our results confirm that the earth s lower mantle mg fe si ratio is greater than unity because of the high stiffness of silicate perovskite

holocene glacier chronologies are high resolution global and inter hemispheric comparisons possible in the context of reconstruction of holocene glacier chronologies there has been a clear tendency during the past few decades towards imprecise use of the term high resolution furthermore it seems to be increasingly assumed that recently developed terrestrial cosmogenic nuclide dating tcnd is replacing earlier dating methods although recent glaciological knowledge clearly reveals the futility of oversimplified global and inter hemispheric correlation on the basis of few key sites such comparisons are widely attempted stimulated by the example of a recently published article relating to the southern alps of new zealand schaefer et al 2009 science 324 622 625 we highlight some related potential problems with the interpretation of holocene glacier chronologies in particular we consider 1 that the term high resolution should be applied only to decadal scale resolution or better and therefore not to tcnd based chronologies 2 that discontinuous moraine chronologies should not be ter

neoglacial history of the coast mountains near bella coola british columbia the maximum holocene extent of glaciers in the study area is marked by late neoglacial little ice age terminal moraines moraine stratigraphy and 14c dates from a small number of sites suggest that glacier advance almost as extensive as that of the late neoglacial occurred about 2500 14c years bp and that late neoglacial advance began well before 770 14c years bp or the thirteenth century a d glacier termini then stood close to the position of the climax moraines for several centuries dates of stabilization of end moraines at 16 glaciers were determined by dendrochronology with tree ring counts corrected for sampling errors and ecesis most terminal moraines date from 1860 to 1900 many recessional moraines were formed between 1900 and 1940 coincident with a regionally documented phase of cooler and wetter climate the proposed chronology is similar to results from elsewhere in the canadian cordillera

an experimental study of the garnet perovskite transformation in the system mgsio3mg3al2si3o12 phase transformations in the system mgsio3 mg3al2si3o12 have been studied at pressures between 22 and 28 gpa at 1500 c using a multi anvil apparatus majorite garnet with less than about 10 wt al2o3 was found to completely transform into an orthorhombic perovskite structure over a pressure interval between 24 and 27 gpa whereas pyrope garnet disproportionated into sub aluminous perovskite plus corundum solid solutions at pressures greater than 26 5 gpa alumina contents in the perovskite structure are dependent on temperature and increase from 11 wt at 1500 c to 17 wt at 1800 c at a pressure of 27 gpa the alumina content of perovskite also in creases with increasing pressure such that aluminous perovskite with the pyrope composition 25 mol al2o3 should be formed by about 30 40 gpa these observations are consistent with our recent experimental results on a pyrolite composition which demonstrated that no separate aluminous phase exists in the upper part of the lower mantle the entire inventory of al2o3 in pyrolite can be accommodated in solid solution in magnesium silicate perovskite

increase of the oxygen vacancy component in bridgmanite with temperature abstract the oxygen vacancy ov mgalo2 5 contents in bridgmanite with periclase and or a calcium ferrite type mgal2o4 mg2sio4 phase cf phase were investigated at temperatures of 1700 2000 and 2400 k and a pressure of 27 gpa using an ultrahigh pressure multi anvil press the ov content increases significantly with increasing temperature by consuming coexisting periclase and the charge coupled cc alalo3 component in bridgmanite the increase in ov component at high temperature is promoted by its high entropy the cc components increase largely with temperature compared with the ov content in bridgmanite coexisting with cf phase and periclase because the partition coefficient of mg and al between bridgmanite and cf phase approaches unity because of the mixing entropy the partial molar volumes of ov and cc bridgmanite endmembers at ambient conditions were constrained to be 26 64 and 25 79 cm3 mol respectively with densities of 3 428 and 3 955 g cm3 by assuming linear relationships between wave velocities and density the ov component may therefore cause a velocity reduction by one order of magnitude larger than the cc component at constant al content in bridgmanite the concomitant increase and decrease in ov and cc contents with temperature enhance v p and v s reductions by 0 7 and 2 5 in addition to anharmonic effects the ov component in bridgmanite in subducted slabs is zero because of low temperature and the transport of water and argon trapped by the ov component into the lower mantle by bridgmanite is therefore not expected the storage capacity of these volatiles in subducted slabs will thus be significantly lower than the warm ambient mantle since the ov component is expected to enhance diffusion creep the present results may explain slab stagnation in the mid mantle due to low ov contents at low temperature and vertically straight plumes in the lower mantle due to high ov contents at high temperature

last glacial maximum records in permafrost of the east siberian arctic palaeontological proxy data and cryolithological information from siberian arctic permafrost preserves records of late quaternary climate and environmental conditions in west beringia and their variability which results from interglacial glacial and interstadial stadial dynamics to date the last glacial maximum lgm period has been rather poorly represented in east siberian permafrost records here we present pollen sediment and ground ice stable water isotope data obtained from coastal exposures on bol shoy lyakhovsky island new siberian archipelago arctic ocean that mirror the coldest conditions during the sartan period between about 26 and 22 ka bp using pollen and sediment data for summer conditions and stable water isotope data for winter conditions the pollen record revealed a cold tundra steppe vegetation with characteristic predominance of grass pollen over sedge pollen while the stable isotope ice wedges data indicate extremely cold winter temperatures with mean values of d 18 oo f about 37 dd of about 290 combined with available regional lgm permafrost records that extend from the taymyr peninsula in the west to the yana river lowland in the east the new data set from bol shoy lyakhovsky island indicate that the regional appearance of lgm conditions depended on atmospheric circulation patterns that were influenced by the extent of the northern hemisphere glaciation

expansion of alpine glaciers in pacific north america in the first millennium a d radiocarbon ages and lichen dated moraines from 17 glaciers in coastal and near coastal british columbia and alaska document a widespread glacier advance during the first millennium a d glaciers at several sites began advancing ca a d 200 300 based on radiocarbon dated overridden forests the advance is centered on a d 400 700 when glaciers along an 2000 km transect of the pacific north american cordillera overrode forests impounded lakes and deposited moraines the synchroneity of this glacier ad vance and inferred cooling over a large area suggest a regional climate forcing and to gether with other proxy evidence for late holocene environmental change during the me dieval warm period and little ice age provide support for millennial scale climate variability in the north pacific region

glacier fluctuations during the past 2000 years abstract a global compilation of glacier advances and retreats for the past two millennia grouped by 17 regions excluding antarctica highlights the nature of glacier fluctuations during the late holocene the dataset includes 275 time series of glacier fluctuations based on historical tree ring lake sediment radiocarbon and terrestrial cosmogenic nuclide data the most detailed and reliable series for individual glaciers and regional compilations are compared with summer temperature and when available winter precipitation reconstructions the most important parameters for glacier mass balance in many cases major glacier advances correlate with multi decadal periods of decreased summer temperature in a few cases such as in arctic alaska and western canada some glacier advances occurred during relatively warm wet times the timing and scale of glacier fluctuations over the past two millennia varies greatly from region to region however the number of glacier advances shows a clear pattern for the high mid and low latitudes and hence points to common forcing factors acting at the global scale globally during the first millennium ce glaciers were smaller than between the advances in 13th to early 20th centuries ce the precise extent of glacier retreat in the first millennium is not well defined however the most conservative estimates indicate that during the 1st and 2nd centuries in some regions glaciers were smaller than at the end of 20th early 21st centuries other periods of glacier retreat are identified regionally during the 5th and 8th centuries in the european alps in the 3rd 6th and 9th centuries in norway during the 10th 13th centuries in southern alaska and in the 18th century in spitsbergen however no single period of common global glacier retreat of centennial duration except for the past century has yet been identified in contrast the view that the little ice age was a period of global glacier expansion beginning in the 13th century or earlier and reaching a maximum in 17th 19th centuries is supported by our data the pattern of glacier variations in the past two millennia corresponds with cooling in reconstructed temperature records at the continental and hemispheric scales the number of glacier advances also broadly matches periods showing high volcanic activity and low solar irradiance over the past two millennia although the resolution of most glacier chronologies is not enough for robust statistical correlations glacier retreat in the past 100 150 years corresponds to the anthropogenic global temperature increase many questions concerning the relative strength of forcing factors that drove glacier variations in the past 2 ka still remain

the thermal equation of state of mg fe sio3 bridgmanite perovskite and implications for lower mantle structures the high pressure high temperature equation of state eos of synthetic 13 fe bearing bridgmanite mg silicate perovskite is measured using powder x ray diffraction in a laser heated diamond anvil cell with a quasi hydrostatic neon pressure medium we compare these results which are consistent with previous 300 k sound speed and compression studies with a reanalysis of fe free mg end member data from tange et al 2012 to determine the effect of iron on bridgmanite s thermoelastic properties eos parameters are incorporated into an ideal lattice mixing model to probe the behavior of bridgmanite at deep mantle conditions with this model a nearly pure bridgmanite mantle composition is shown to be inconsistent with density and compressibility profiles of the lower mantle we also explore the buoyant stability of bridgmanite over a range of temperatures and compositions expected for large low shear velocity provinces concluding that bridgmanite dominated thermochemical piles are more likely to be passive dense layers externally supported by convection rather than internally supported metastable domes the metastable dome scenario is estimated to have a relative likelihood of only 4 7 given the narrow range of compositions and temperatures consistent with seismic constraints if buoyantly supported such structures could not have remained stable with greater thermal contrast early in earth s history ruling out formation scenarios involving a large concentration of heat producing elements

palaeobotanical evidence for warm summers in the east siberian arctic during the last cold stage plant macrofossils from the mamontovy khayata permafrost sequence 71 60 n 129 25 e on the bykovsky peninsula reflect climate and plant biodiversity in west beringia during the last cold stage 70 ams and 20 conventional 14c dates suggest sediment accumulation between about 60 000 and 7500 14c yr b p the plant remains prove that during the last cold stage arctic species minuartia arctica draba spp kobresia myosuroides coexisted with aquatic potamogeton vaginatus callitriche hermaphroditica littoral ranunculus reptans rumex maritimus meadow hordeum brevisubulatum puccinellia tenuiflora and steppe taxa alyssum obovatum silene repens koeleria cristata linum perenne the reconstructed vegetation composition is similar to modern vegetation mosaics in central and northeast yakutian relict steppe areas thus productive meadow and steppe communities played an important role in the siberian arctic vegetation during the late pleistocene and could have served as food resource for large populations of herbivores the floristic composition reflects an extremely continental arid climate with winters colder and summers distinctly warmer than at present holocene macrofossil assemblages indicate a successive paludification possibly connected with marine transgression increased oceanic influence and atmospheric humidity although some steppe taxa were still present in the early holocene they disappeared completely before 2900 14c yr b p

the principles of cryostratigraphy abstract cryostratigraphy adopts concepts from both russian geocryology and modern sedimentology structures formed by the amount and distribution of ice within sediment and rock are termed cryostructures typically layered cryostructures are indicative of syngenetic permafrost while reticulate and irregular cryostructures are indicative of epigenetic permafrost cryofacies can be defined according to patterns of sediment characterized by distinct ice lenses and layers volumetric ice content and ice crystal size cryofacies can be subdivided according to cryostructure where a number of cryofacies form a distinctive cryostratigraphic unit these are termed a cryofacies assemblage the recognition if present of i thaw unconformities ii other ice bodies such as vein ice ice wedges aggradational ice and thermokarst cave pool ice and iii ice sand and gravelly pseudomorphs is also important in determining the nature of the freezing process the conditions under which frozen sediment accumulates and the history of permafrost

ice complex formation in arctic east siberia during the mis3 interstadial abstract a continuous 15 m long sequence of ice complex permafrost yedoma exposed in a thermo cirque at the southern coast of bol shoy lyakhovsky island new siberian archipelago dmitry laptev strait was studied to reconstruct past landscape and environmental dynamics the sequence accumulated during the marine isotope stage 3 mis3 interstadial between 49 and 29 ka bp in an ice wedge polygon the frozen deposits were cryolithologically described and sampled on a vertical bluff between two ice wedges according to sedimentological and geochronological data the section is subdivided into three units which correlate with environmental conditions of the early middle and late mis3 period palynological data support this stratification the stable isotope signature of texture ice in the polygon structure reflects fractionation due to local freeze thaw processes while the signature of an approximately 5 m wide and more than 17 m high ice wedge fits very well into the regional stable water isotope record regional climate dynamics during the mis3 interstadial and local landscape conditions of the polygonal patterned ground controlled the ice complex formation the sequence presented here completes previously published mis3 permafrost records in northeast siberia late quaternary stadial interstadial climate variability in arctic west beringia is preserved at millennial resolution in the ice complex a mis3 climate optimum was revealed between 48 and 38 ka bp from the ice complex on bol shoy lyakhovsky island

phase relations of caal4si2o11 at high pressure and high temperature with implications for subducted continental crust into the deep mantle abstract phase relations of the cas phase caal4si2o11 have been investigated at pressures of 10 23 gpa and at temperatures of 1000 1600 c by means of the quench method using the kawai type high pressure apparatus an assemblage of grossular gr corundum cor kyanite ky is stable up to about 10 gpa and at the temperatures examined the assemblage converts into the cas phase at 1600 c and higher pressures below 1450 c however the assemblage first changes to that of gr cor stishovite st corresponding to the dissociation of ky into cor st and then converts to the cas phase with increasing pressure the gr cor st cas boundary has a negative dp dt slope and the gr ky cor cas boundary has a near horizontal slope the triple point at which gr cor ky st and the cas phase coexist is located at around 11 5 gpa and 1450 c stability of the cas phase up to 23 gpa and 1600 c indicates that the cas phase is an important host of al and ca in the continental crust subducted into deep mantle comparison of the densities between the pyrolitic mantle and the subducted continental crust indicates that the continental crust provides a plunging force to the slab subducted into the upper mantle and transition zone whereas the continental crust in turn gives a buoyancy in the lower mantle as the consequence of the substantial changes in mineral assemblage in both the continental crust and pyrolitic mantle through the 660 km discontinuity the formation of the cas phase plays an important role in changing the density of the subducting continental crust

equations of state of the high pressure phases of a natural peridotite and implications for the earth s lower mantle abstract to help determine the chemical composition of the earth s mantle we characterised the high pressure mineral assemblage of an undepleted natural peridotite thought to be representative of the earth s upper mantle to 107 gpa using high resolution x ray diffraction at lower mantle conditions the peridotite transforms to the assemblage 76 2 mg0 88fe0 052 fe0 013 al0 12si0 94 o3 orthorhombic perovskite by volume at zero pressure 17 2 mg0 80fe0 20 o magnesiowustite and 7 1 casio3 perovskite the measured room temperature bulk properties of this high pressure assemblage together with a range of estimates of thermal properties of the constituent minerals appear to be inconsistent with seismological constraints on the density and bulk modulus of the lower mantle our results suggest that the lower mantle differs in bulk composition e g richer in iron mg 0 85 from current estimates for the upper mantle requiring some amount of segregation between the upper and lower mantle over geological history

the record of jokulhlaups from summit lake northwestern british columbia summit lake which is impounded by salmon glacier is the largest self draining ice dammed lake in canada until 1961 it contained few icebergs and was stable overflowing to the north into me bowser river valley the first jokulhlaup occurred in december 1961 after a lengthy period of thinning and retreat of salmon glacier when a subglacial runnel developed in the weakened ice dam allowing the lake to drain suddenly this flood and two others in 1965 and 1967 caused major damage to the road system in the salmon river valley south of the lake since 1965 with three exceptions summit lake has drained annually minor floods along salmon river in 1966 1969 and 1973 may record partial drainings of the lake although other explanations are possible jokulhlaups in recent years have been smaller and have occurred earlier in the year than most of the early floods rapid water level fluctuations associated with the annual emptying and refilling of summit lake have generated large numbers of icebergs der

3d ground penetrating radar imaging of ice complex deposits in northern east siberia abstractice complex deposits are characteristic ice rich formations in northern east siberia and represent an important part in the arctic carbon pool recently these late quaternary deposits are the objective of numerous investigations typically relying on outcrop and borehole data many of these studies can benefit from a 3d structural model of the subsurface for upscaling their observations or for constraining estimations of inventories such as the local carbon stock we have addressed this problem of structural imaging by 3d ground penetrating radar gpr which in permafrost studies has been primarily used for 2d profiling we have used a 3d kinematic gpr surveying strategy at a field site located in the new siberian archipelago on top of an ice complex after applying a 3d gpr processing sequence we were able to trace two horizons at depths below 20 m taking available borehole and outcrop data into account we have interpreted these two features as interfaces of major lithologic units and der

analytical transmission electron microscopy study of a natural morb sample assemblage transformed at high pressure and high temperature natural mid ocean ridge basalt morb samples recovered from diamond anvil cell dac experiments performed between 33 to 89 gpa and 1700 to 2600 k were studied with a transmission electron microscope tem we used the focused ion beam fib lift out technique to prepare the recovered high pressure laser heated samples for tem study observations of tem sections show the presence of five phases for samples transformed at pressures ranging from 33 to 45 gpa al bearing mg perovskite ca silicate perovskite stishovite and two al rich phases the al rich phases were identified by selected area electron diffraction saed patterns and chemical composition analysis and include the new aluminous nal phase with hexagonal structure and the calcium ferrite cf type phase chemical analyses obtained by analytical transmission electron microscopy atem show that mg silicate perovskite is the major host for al with significant amounts also distributed between the cf type and nal phases and less than 1 wt in stishovite beyond pressures of 40 gpa 1100 km depth the al content of mg perovskite and cf type phase increases between 45 and 50 gpa the nal phase disappears this mineralogical change may explain reported seismic anomalies in subduction zones at mid mantle depths

equation of state of al bearing stishovite to 40 gpa at 300 k the compression behavior of al bearing stishovite was investigated by powder x ray diffraction up to 40 gpa with the bl13a beamline at the photon factory kek japan a reliable equation of state for stishovite was obtained using a diamond anvil cell coupled with a yttrium aluminum garnet yag laser heating a sample containing 2 1 wt al 2 o 3 was heated using a yag laser at each pressure increment to relax deviatoric stress x ray diffraction measurements were carried out at 300 k using the angle dispersive technique a least squares refinement of the data yielded equation of state parameters where the bulk modulus k o 282 2 gpa when the first pressure derivative of the bulk modulus k o was fixed at 4 the effect of al is to decrease slightly the bulk modulus of stishovite and increase the density of the subducted oceanic crust the enhanced compressibility of al bearing stishovite certainly has geophysical and geochemical implications for the fate of the subducted slab as this mineral is the main constituent of subducted mid oceanic ridge basalt morb in the earth s mantle

prelude to the extinction revision of the achchagyi allaikha and berelyokh mass accumulations of mammoth abstract the little known achchagyi allaikha mass assemblage of mammoths and the well known berelyokh site lower indigirka river arctic siberia were studied detailed study of the achchagyi allaikha site provided ample data concerning its geology stratigraphy taphonomy and the gender age structure of the taphocoenosis the achchagyi allaikha assemblage included redeposited bones from numerous young not less than 21 and some adult female mammoths with limited quantities of bison equus and rangifer bones collagen from mammoth bones preserved at the achchagyi allaikha site n 6 was radiocarbon dated at 12 490 80 to 12 400 60 bp at the berelyokh site eight mammoth bones were radiocarbon dated at 12 720 100 to 11 900 50 bp one bison bone was dated at 12 380 150 bp and one mammoth bone dated at 36 500 1000 redeposited bone included in younger sediments the mass accumulations are synchronous and are similar in their mode of formation the assemblage of mammoths in the achchagyi allaikha and berelyokh sites resulted from simultaneous deaths of a large number of animals probably herd family groups in one or several seasons it is very probable that the deposits in both cases were not of cultural origin the formation of the burials is a direct consequence of short but strong climatic warming bolling oscillation that resulted in many unfavorable environmental conditions among these the increase of snow cover and stronger spring floods were very notable bolling warming is a model of the large scale holocene event mass death of mammoths during the bolling phase was a prelude to their final extinction

an inventory and morphometric analysis of british columbia glaciers canada we describe an automated method to generate an inventory of glaciers and glacier morphometry from a digital topographic database containing glacier boundaries and a digital elevation model for british columbia canada the inventory contains over 12 000 glaciers with a total cumulative area that exceeds 25 000 km 2 based on mapping from aerial photographs circa the mid 1980s we use the inventory to examine dimensional characteristics among glaciers namely the scaling relations between glacier length width and area glacier length is a good predictor of glacier area and its predictive ability improves when glaciers are stratified by the number of up valley accumulation basins the spatial pattern of glacier mid range altitude parallels glaciation limits previously mapped for british columbia and similarly reflects large scale controls of orographic precipitation and continentality the inventory is also used to refine models that relate glacier mid range and terminus altitudes to regional position aspect and in the case of terminus altitudes an index of glacier shape relations between glacier altitude limits and controlling spatial and topographic factors are used to make further climatic and mass balance inferences from the glacier inventory