secular variation of the geomagnetic field intensity during the past 2000 years in japan abstract we report the results of paleointensity determination with volcanic rocks of izu oshima and fuji volcano japan samples used for the present study were basaltic rocks from nine lava flow units of oshima volcano which erupted between ad 590 and 1950 and aokigahara lava flow derived from fuji volcano in ad 864 demagnetization and several rock magnetic experiments show that the samples have stable single component remanences which are carried by magnetite or titanomagnetite with the psd magnetic domain state thellier s method was used for the paleointensity experiments and reliable determinations for 10 eruptive units were obtained from 58 samples in total the unit mean values generally show good consistency with the previous archaeointensity and paleointensity results allowing us to construct a reference curve of the field intensity variation for the past 2000 yr in japan the reference curve has a general trend of decreasing intensity since ad 500 showing two peaks of the field strength around ad 500 and 1400 and two troughs around ad 1200 and 1700 since around ad 800 the field intensity predictions for japan by the inversion spherical harmonic models show good consistency with the reference curve suggesting that the peak and the troughs in this period have probably been produced mainly by non dipole sources the geocentric axial dipole variation extracted from the reference curve with the inversion model shows good agreement with the global averages of the virtual axial dipole moment except that our reference curve yields a significant peak around ad 500 this suggests that a temporal strengthening of the dipole moment might have occurred over a few hundred years around ad 500

a regression model for the mass balance distribution of the vatnajokull ice cap iceland a non linear regression model describing the mass balance distribution of the whole vatnajokull ice cap iceland for the years 1992 2000 is presented all available data from some 40 locations over this 9 year period were used to determine the parameters of the model the regression model uses six adjustable parameters which all have a clear physical interpretation they are the slope direction and the height of the equilibrium line altitude ela plane two altitude mass balance gradients and a maximum value of the surface mass balance it is found that the temporal variation of the observed mass balance distribution can be accurately described through annual shifts of the ela annual shifts in ela are on the order of 100 m which is of the same magnitude as the change expected to be caused by the climate variation predicted during the next decades a slight trend towards a more negative mass balance is detected during this 9 year period

on the characterization of glacier response by a single time scale glacier response to climate can be characterized by a single time scale when the glacier changes sufficiently slowly then the derivative of volume with respect to area defines a thickness scale similar to that of johannesson and others and the time scale follows from it our version of the time scale is different from theirs because it explicitly includes the effect of surface elevation on mass balance rate which can cause a major increase in the time scale or even lead to unstable response the time constant has a dual role controlling both the rate and magnitude of response to a given climate change data from south cascade glacier washington u s a illustrate the ideas some of the difficulty in obtaining accurate values for the thickness and time scales and the susceptibility of all response models to potentially large errors

glacier changes in southeast alaska and northwest british columbia and contribution to sea level rise 1 the digital elevation model dem from the 2000 shuttle radar topography mission srtm was differenced from a composite dem based on air photos dating from 1948 to 1987 to determine glacier volume changes in southeast alaska and adjoining canada srtm accuracy was assessed at 5 m through comparison with airborne laser altimetry and control locations measured with gps glacier surface elevations lowered over 95 of the 14 580 km2 glacier covered area analyzed with some glaciers thinning as much as 640 m a combination of factors have contributed to this wastage including calving retreats of tidewater and lacustrine glaciers and climate change many glaciers in this region are particularly sensitive to climate change as they have large areas at low elevations however several tidewater glaciers that had historically undergone calving retreats are now expanding and appear to be in the advancing stage of the tidewater glacier cycle the net average rate of ice loss is estimated at 16 7 4 4 km3 yr equivalent to a global sea level rise contribution of 0 04 0 01 mm yr

tectonic controls on rates and spatial patterns of glacial erosion through geothermal heat flux abstract glacial erosion has shaped many mountain belts during the cold periods of the late cenozoic the rate of glacial erosion is sensitive to the subglacial environment including both the subglacial hydrology and the basal thermal regime geothermal heat from underlying bedrock is a major contributor to glacier energy budgets controlling ice dynamics at the ice bed interface by changing the basal temperature and the supply of meltwater despite the known influence of geothermal heat on the subglacial environment its impact on glacial erosion has received little study the geothermal heat flux in glaciated mountain ranges varies widely as a function of the tectonic setting therefore if glacial erosion is sensitive to geothermal heat flux the evolution of glaciated landscapes may depend upon tectonically controlled geothermal gradients we explore the impact of geothermal heat flux on the rates and spatial patterns of glacial erosion in mountain ranges using numerical models we couple a sliding dependent glacial erosion model with the parallel ice sheet model pism to simulate the evolution of a synthetic glacial landscape we find a robust tendency for increasing glacial erosion with increasing geothermal heat flux the spatial pattern of erosion also varies with the magnitude of geothermal heat flux at low geothermal heat flux glacial erosion is consistently focused in major valleys as geothermal heat flux increases the area of significant glacial erosion expands into higher elevations and the rate of erosion increases the location of maximum erosion migrates up valley as geothermal heat flux increases suggesting that glacial erosion tends to produce distinct landscapes as a function of geothermal heat flux our finding suggests that active mountain belts with high geothermal heat flux will express the glacial buzzsaw effect in which high elevation topography is preferentially removed by glacial erosion glaciers at passive margins with low geothermal heat flux in contrast will tend to incise deep valleys at relatively low elevations previous work on the interaction between tectonics and landscape evolution has focused on relief generation and fracturing of rocks our results introduce a novel potential linkage between tectonics and erosion based on the sensitivity of glacial erosion to geothermal heat

the development of antarctic glaciation and the neogene paleoenvironment of the maurice ewing bank abstract a micropaleontologic magnetostratigraphic and sedimentologic analysis of 56 piston cores provides the basis of a geologic study of the late miocene to holocene depositional and erosional history of the intermediate depth maurice ewing bank meb located at the eastern extremity of the falkland malvinas plateau southwest atlantic ocean sedimentation on the meb is controlled presently by the position of the polar front and strong bottom currents beneath the axis of the antarctic circumpolar current acc fluctuations in the position of the polar front and in the intensity of the acc are inferred to have largely controlled deposition on the meb since the initiation of acc flow over the bank in the miocene the sedimentary record of the meb is used to infer the late miocene to holocene oceanographic and climatic conditions in the south atlantic sector of the southern ocean the meb suffered major erosion by intense acc flow during late miocene time which exposed cretaceous miocene sediment near the surface and shaped the present configuration of the bank this erosional event is inferred to have occurred during late miocene to early pliocene time 7 2 4 7 m y b p with the major phase of erosion occurring between middle magnetostratigraphic chron 7 and late chron 6 7 2 6 2 m y b p we suggest that the miocene sedimentary record of the meb and other paleoenvironmental evidence from the circum antarctic region precludes the existence of a west antarctic ice sheet or extensive ice shelves along the antarctic margin prior to the late miocene during the late miocene a west antarctic ice shelf formed in the former west antarctic sea and rapidly thickened until it grounded below sea level to form the west antarctic ice sheet formation of this ice sheet with floating and partially grounded extensions ice shelves in the ross and weddell embayments led to the first major production of true antarctic bottom water formed in a manner similar to today which permanently altered global abyssal circulation late miocene changes in oceanic ccd levels and a permanent shift in the oceanic 13 c 12 c composition may be attributed to this major change in abyssal circulation a decrease in acc velocity during an early pliocene amelioration of climate led to resumption of deposition on the bank from 4 7 to 3 9 m y b p intensification of the acc during the late gilbert and early gauss chrons again resulted in limited deposition and widespread erosion and or non deposition over most of the meb from 4 0 to 3 2 m y b p acc velocity apparently began to wane during the middle of the gauss chron and allowed widespread deposition on the bank during late gauss time 2 9 2 48 m y b p and over more limited areas during earliest matuyama time 2 48 to about 2 2 m y b p during middle to late matuyama time bottom current intensity reached its greatest post miocene level forming a regional disconformity between sediments of about 2 0 and 1 0 m y in age this increased circumpolar circulation and associated erosion is inferred to have peaked during the late matuyama chron 1 2 1 0 m y b p and is approximately the same age as the tentatively dated greatest patagonian glaciation in nearby southern argentina between 1 0 and 0 7 m y b p the bank was blanketed with a coarse erosion resistant layer of ice rafted detritus which armored the older sediment thereby protecting it from major subsequent erosion sedimentation on the meb during the bruhnes chron 720 000 yr b p present was intermittent and finally culminated with the deposition of a veneer of carbonate ooze during or since latest pleistocene time

radar glacier zones in southeast alaska u s a field and satellite observations the ability of synthetic aperture radar sar to record change in glaciers and icefields on seasonal to interannual time scales is useful in maritime mountain regions where visible data are often obscured by clouds a time series of radarsat and second european remote sensing satellite ers 2 sar images shows dramatic changes related to the onset and progression of glacier melting on the juneau icefield southeast alaska u s a four radar glacier zones are interpreted from sar images as snow that is dry during winter an early snowmelt m a second phase of snowmelt m2 and bare ice these zones develop every year on the juneau icefield and other mid latitude glaciers summer field observations on the juneau icefield during 1997 and 1998 constrain interpretations of the c band radar glacier zones of the two zones that occur in melting snow m m2 m has low radar backscatter coefficients 12 of the subsequent m2 zone snow moisture and surface roughness at the scale of the radar wavelength 5 6 cm were measured to characterize the melt zones correlation length wetness and grain size in the two zones are not distinguishable in the late ablation season mean surface roughness due to the presence of suncups is higher in the m2 zone than in the m zone and probably causes the higher backscatter due to greater scattering

a new rock magnetic approach to selecting sediments for geomagnetic paleointensity studies application to paleointensity for the last 4000 years the hypothesis that the ratio of detrital remanent magnetization to anhysteretic remanent magnetization drm arm for sediment samples is a measure of relative geomagnetic paleointensity is critically evaluated by two distinct approaches one approach is a detailed rock magnetic examination of the implicit assumptions of the drm arm method and the construction of a selection process by which to identify sediments that conform to requirements satisfying these assumptions sediments are uniform with respect to drm arm ratio if they contain magnetite in the 1 15 ym particle size range as the predominant magnetic mineral and have variations in magnetite content of less than 20 30 times the minimum concentration the drm arm ratios of these sediments should provide estimates of relative geomagnetic paleointensity relative particle size variations in magnetite are detected with a plot of anhysteretic susceptibility xarm versus low field susceptibility x and the size range 1 15 m is approximately identified by high field hysteresis parameters a rock magnetic evaluation of leboeuf lake sediments with these techniques indicates that these sediments are suitable for a relative plaeointensity study the second approach to evaluating the drm arm ratio as a measure of relative paleointensity is direct comparison with absolute paleointensity data a comparison between the leboeuf lake estimates and thellier thellier results from the western united states supports the conclusion that suitable sediments can record geomagnetic paleointensity fluctuations

consistent treatment of errors in archaeointensity implies rapid decay of the dipole prior to 1840 we present a meta analysis of 223 archaeo and palaeointensities spanning the period 1840 1990 and compare these data with the geomagnetic field model gufm1 jackson et al 2000 philos trans r soc lond a 358 957 990 we find that the principal source of uncertainty in all the data regardless of experimental method or number of samples is due to systematic error this error is quantified and it is shown that the data is capable of estimating the magnitude of the geomagnetic field for the period with reasonable accuracy but only if errors are estimated on the basis of the field strength rather than the measured intensity the findings are then applied to archaeointensity data from the period 1590 1840 and it is shown that the most likely behaviour of the field was a decay of the axial dipole at a similar rate to that observed since 1840 we show that underestimation of the field s magnitude can be an artefact of inconsistent error estimation

atmospheric sciences in antarctica the antarctic is an interesting land that has become the focus of much attention in the last decade its undisturbed geological record dating back to the last interglacial period a locale with seas and lakes populated with interesting organisms a land with beautiful twilights and lovely cirrus and stratospheric cloud formations a whole continent dedicated by international treaty to scientific research these factors provide good reasons for the renewed interest a recent review by weller et al 1987 explores in more detail the many scientific ideas that make antarctica an attractive laboratory studies relating to sundry aspects of the earth s geosphere biosphere system draw scientists from the whole spectrum of scientific disciplines

modelling a paleo valley glacier network using a hybrid model an assessment with a stokes ice flow model modelling paleo glacier networks in mountain ranges on the millennial timescales requires ice flow approximations hybrid models calculating ice flow by combining vertical shearing shallow ice approximation and longitudinal stretching shallow shelf approximation have been applied to model paleo glacier networks on steep terrain yet their validity has not yet been assessed quantitatively moreover hybrid models consistently yield higher ice thicknesses than last glacial maximum geomorphological reconstructions in the european alps here we compare results based on the hybrid parallel ice sheet model pism and the stokes model elmer ice on the rhine glacier a catchment of the former european alpine icefield for pism we also test two magnitudes of flux limitation in a scheme that reduces shearing velocities we find that the flux limitation typically used in pism yields significantly reduced shearing speeds and increases ice thicknesses by up to 500 m partly explaining previous overestimations however reducing the ice flux limitation allows the hybrid model to minimize this mismatch and captures sliding speeds ice thicknesses ice extent and basal temperatures in close agreement with those obtained with the stokes model

shallow shelf approximation as a sliding law in a thermomechanically coupled ice sheet model 1 the shallow shelf approximation a balance of membrane stresses for ice flow is an effective sliding law for ice sheet modeling our use of it as a sliding law becomes a standard model for ice stream flow when the sliding velocity is large 100 m a 1 and faster following schoof 2006a we describe the basal resistance as plastic till for which the yield stress is given by a mohr coulomb formula pore water pressure is related to basal melt rate the velocity field used in the mass continuity and conservation of energy equations is an average of velocities from the shallow shelf approximation and the nonsliding shallow ice approximation using this scheme our model has realistic time dependent ice streams which exhibit the range of surface velocities seen in actual ice streams we demonstrate the model at high spatial resolution 5 km grid over multiple millenia using its implementation in the parallel ice sheet model numerical experiments show that the entire scheme is stable with respect to many parameter changes some experiments reveal significant ice stream variability in a hypothetical steady climate with characteristic cycles on the order of 1000 years we believe this is the first practical whole ice sheet model with a unified treatment of vertical shear stresses and membrane stresses it is capable of high resolution thermomechanically coupled multimillenia simulations of ice sheets containing ice streams

satellite derived volume loss rates and glacier speeds for the juneau icefield alaska we provide a high resolution map of elevation change rates dh dt at the juneau icefield jif southeastern alaska in order to quantify its contribution to sea level rise between 2000 and 2009 2013 we also produce the first high resolution map of ice speeds at the jif which we use to constrain flux and look for acceleration we calculate dh dt using stacked digital elevation models dems from the advanced spaceborne thermal emission and reflection radiometer aster instrument and the shuttle radar topography mission srtm taking into account srtm c band penetration via comparison with srtm x band elevations overall the jif is losing mass less rapidly 0 13 0 12mw e a than other alaskan icefields 0 79mw e a we determine glacier speeds using pixel tracking on optical image pairs acquired from 2001 to 2010 by aster from radar image pairs acquired between 2007 and 2011 and from radar interferometry in 1995 we detect seasonal speed variations but no interannual acceleration ruling out dynamics as the cause of the observed thinning thinning must therefore be due to the documented warming in the region flux measurements confirm this for mendenhall glacier showing that calving constitutes only 2 5 5 of mass loss there

analysis of a grace global mascon solution for gulf of alaska glaciers we present a high resolution gravity recovery and climate experiment grace mascon solution for gulf of alaska goa glaciers and compare this with in situ glaciological climate and other remote sensing observations our grace solution yields a goa glacier mass balance of 65 11 gt a 1 for the period december 2003 to december 2010 with summer balances driving the interannual variability between october november 2003 and october 2009 we obtain a mass balance of 61 11 gt a 1 from grace which compares well with 65 12 gt a 1 from icesat based on hypsometric extrapolation of glacier elevation changes we find that mean summer june august air temperatures derived from both ground and lower troposphere temperature records were good predictors of grace derived summer mass balances capturing 59 and 72 of the summer balance variability respectively large mass losses during 2009 were likely due to low early melt season surface albedos measured by the moderate resolution imaging spectroradiometer modis and likely associated with the 31 march 2009 eruption of mount redoubt southwestern alaska grace data compared well with in situ measurements at wolverine glacier maritime alaska but poorly with those at gulkana glacier interior alaska we conclude that although goa mass estimates from grace are robust over the entire domain further constraints on subregional and seasonal estimates are necessary to improve fidelity to ground observations

estimate of the magnetic anisotropy effect on the archaeomagnetic inclination of ancient bricks abstract the magnetic fabric of 59 bricks coming from 5 ancient kilns has been studied by measuring the anisotropy of magnetic susceptibility ams and the anisotropy of isothermal airm anhysteretic aarm and thermal atrm remanent magnetization the bricks are characterized by a well developed magnetic fabric that matches their flat shape the shape of the anisotropy ellipsoids is in almost all cases oblate with the maximum and intermediate axes lying parallel to the large face of the brick and the minimum axis perpendicular to it the directions of the principal axes are almost the same irrespectively of the type of anisotropy measured whereas the degree of anisotropy of the airm aarm and atrm is much higher than the ams as the bricks lie horizontally within the kiln the planar magnetic fabric results in an inclination shallowing of the archaeomagnetic direction with respect to that of the earth s magnetic field at the time of their last cooling estimation of this effect on the grounds of atrm measurements yields a shallowing that varies from 4 to 10 for individual samples such inclination difference may significantly bias archeomagnetic dating for the case of the canosa late roman kiln it leads to a dating error of more than two centuries

antarctic aerosols a review the vast ice sheet of antarctica is isolated geographically but not meteorologically from the rest of the planet tropospheric aerosols in or near the accumulation mode size around a half micron diameter reside in the atmosphere for tens of days and teleconnect antarctica with other regions by transport that reaches planetary scales of distances the aerosol on the ice sheet therefore at any time and place represents memory modules of events that took place at regions separated from antarctica by tens of thousands of kilometers scientific attention to this collective aerosol system provides insight into long range atmospheric transport investigations of particles in the ultraclean air over antarctica were slow to get going mainly because of a failure to recognize the possibility of semiglobal transport of dust as a result this field is very young having gone through its romantic period of exploratory studies in the late 1960s and entered into a time of synthesis and paradigm building only in the mid 1970s an important recent discovery is that the aerosol number concentration the condensation nuclei cn over this distant ice sheet undergoes a regular methodical and predictable seasonal variation nearly disappearing around winter solstice but being relatively robust i e comparable to what one finds over mid oceans in summer a weakened seasonal modulation of cn is found at coastal sites circumstantial evidence indicates that the cn over the ice are produced from gas photolytically thus the tiniest particles over antarctica are products of a slow chemical conversion within the atmosphere itself a major discovery with numerous possible deep geobiological ramifications is that the aerosol over the ice sheet is by mass 70 90 sulfate in the molecular form of hydrated droplets of sulfuric acid except during transient events of a few days duration when atmospheric transport forces warm moist air from the oceans into the interior continental regions these events are most frequent in late winter early spring accompanying the breakdown of the circumpolar vortex these sodium storms transport large quantities of sea salt to the central ice sheet sporadically chemical studies of the submicron ice cap aerosols indicate that there is a uniquely winter and uniquely summer crustal insoluble aerosol that represents 5 of aerosol mass but which has provided an interesting long term permanent record of itself going back 2 105 years in the ice in terms of aerosol mass the aerosol is composed of crustal products 5 transported sea salt residues highly variable but averaging 10 ni rich meteoric material and anomalously enriched material with an unknown origin most of the antarctic aerosol however is the natural acid sulfate aerosol apparently deriving from biological processes taking place in the surrounding oceans

on estimating length fluctuations of glaciers caused by changes in climatic forcing the reaction of alpine glaciers to shifts in the equilibrium line altitude ela is calculated by using a two dimensional numerical model to solve the full equations for the velocity and stress fields full system model in the absence of basal motion rates of advance and retreat of the snout of typically sized alpine glaciers are found to be insensitive to the details of the flow at the snout even when the glaciers are far from steady state a comparison of results obtained with a full system model and a shallow ice approximation sia model yields no significant differences in advance or retreat rates this assumption has been implicitly made in numerous previous climatic studies and is here shown to be well justified using a realistic mass balance altitude feedback only slight model dependent changes in steady state lengths are found the relative importance of mass balance and glacier dynamics for the transient response of alpine glaciers to changes in the ela is given a precise meaning by determining the model dependent additional shifts in ela needed for the sia and the full system models to produce identical changes in length for alpine glaciers these additional shifts in ela are on the order of 10 m which is within the error range of ela estimates it follows that at least in the absence of significant basal motion there is no need to include the effects of horizontal stresses when calculating the reaction of alpine glaciers to climatic changes attention should focus on accurate determination of the mass balance distribution and model tuning to give realistic ice thickness distributions

archeomagnetism of potsherds from grand banks ontario a test of low paleointensities in ontario around a d 1000 an archeomagnetic study was carried out on 24 pottery fragments from grand banks southern ontario 14 c dating on maize found in the same pit as the potsherds gives an age in the range a d 990 1160 modal age a d 1030 hysteresis measurements indicate that the natural remanent magnetization is carried by pseudosingle domain magnetite grains paleointensity experiments were done on 63 samples using a thellier type double heating method half of the samples were heated in helium and the other half in air hysteresis measurements on samples after heating to various temperatures reveal only slight mineralogical changes during heating steps thirty reliable results give a paleofield intensity of 42 0 7 4 wt and a virtual axial dipole moment of 7 0 1 3u10 22 am 2 this result is in agreement with the low virtual axial dipole moment values given by studies on material from ontario compared to the values from the southwestern usa in the interval a d 900 1400 fl 2001 elsevier science b v all rights reserved

determination of geomagnetic palaeointensities in vacuum summary specimens with low and intermediate curie points from six hawaiian historic basalt flows were used for the determination of the intensity of the historic geomagnetic field by the thelliers method the specimens were heated either in air or in a vacuum of lo torr the regional intensity of the earth s magnetic field at the time of extrusion of these rocks is known from direct observations the palaeointensities determined in vacuum from four low and intermediate curie point flows are correct within the uncertainty caused by the local field anomalies whereas those determined in air from the same four flows are of lesser quality and accuracy unaltered submarine basalts have similarly low curie points and thus may also be amenable to palaeointensity determination in vacuum the behaviour of the remaining two flows which had higher curie points was more erratic and they yielded less accurate palaeointensities regardless of whether they were determined in air or vacuum the thelliers technique thellier thellier 1959 is one of the most widely used methods for the determination of palaeointensities of the earth s magnetic field from rocks it consists of comparing the thermal spectrum of the natural remanent magnetization nrm of an igneous rock with that of an artifically induced thermoremanent magnetization trm in the same specimen it is assumed that the nrm is a trm acquired during the initial cooling of the rock and that its original thermal spectrum remained unchanged throughout the history of the rock in practice these conditions are not easily met because of two reasons first the nrm acquired by the rock at the time of its formation may be different from that measured in the laboratory because of viscous decay or the superimposition on the nrm of secondary components of magnetization in some cases however this problem may be overcome by thermal cleaning which is an integral part of this technique second when rocks are heated they undergo alterations which affect the chemical composition size and shape of their magnetic mineral grains the effect of these changes may be such that the nrm and trm are produced in two magnetically different materials thus rendering the determination of palaeointensity unreliable because oxidation is the change most likely to occur when heating is carried out in air many authors have recommended the use of high curie temperature rocks which

orographic precipitation and the relief of mountain ranges 1 the influence of climate on the relief of mountain ranges has long been supposed but has received little quantitative investigation the simplified system of a longitudinal river profile in a bedrock channel coupled to a physically based model of orographic precipitation is used to explore how orographically influenced patterns of precipitation affect the relief of fluvially sculpted mountain ranges it is shown that the impact on the orography depends on the nature of the precipitation regime significant changes in relief also occur for imposed temperature changes of realistic magnitude although the ability of the relief to respond to any given change depends sensitively on its response time and the timescale of the forcing

flotation and retreat of a lake calving terminus mendenhall glacier southeast alaska usa mendenhall glacier is a lake calving glacier in southeastern alaska usa that is experiencing substantial thinning and increasingly rapid recession long term mass wastage linked to climatic trends is responsible for thinning of the lower glacier and leaving the terminus vulnerable to buoyancy driven calving and accelerated retreat bedrock topography has played a major role in stabilizing the terminus between periods of rapid calving and retreat lake terminating glaciers form a population distinct from both tidewater glaciers and polar ice tongues with some similarities to both groups lacustrine termini experience fewer perturbations e g tidal flexure high subaqueous melt rates and are therefore inherently more stable than tidewater termini at mendenhall rapid thinning and simultaneous retreat into a deeper basin led to flotation conditions along approximately 50 of the calving front this unstable terminus geometry lasted for approximately 2 years and culminated in large scale calving and terminus collapse during summer 2004 buoyancy driven calving events and terminus break up can result from small rapidly applied perturbations in lake level

laboratory antarctica research contributions to global problems research in antarctica is becoming increasingly important in the large interdisciplinary studies of connections within the earth9s geosphere biosphere system four examples of broad research areas are discussed upper atmosphere research explores the sun earth interactions which are most intense in the polar regions the mass balance and dynamics of the large antarctic ice sheet and its paleoclimatic records recovered from deep ice cores are important indicators of past and present global changes antarctica and sediment cores from the southern ocean contain the history of inception and growth of the ice masses and their subsequent fluctuations and the long term history of paleoclimate the remarkable adaptations of antarctic biota to extreme cold and drought may allow through biotic monitoring the detection of changes in the ocean and climate of antarctica

terminus dynamics at an advancing glacier taku glacier alaska taku glacier alaska usa is currently in the advance stage of the tidewater glacier cycle we investigated the near terminus dynamics by measuring surface velocities surface elevation changes ice thickness and ablation velocities vary on sub daily diurnal seasonal and interannual timescales flowline modeling shows that the modeled surface velocities are sensitive to changes in till yield strength and thus effective basal pressures the glacier bed deepens in the up glacier direction and this imposes a minimum subglacial water pressure necessary for water to drain along the bed in a simple model we impose water pressure gradients based on phreatic surfaces of constant slopes to simulate the winter summer transitions this proves sufficient to explain an observed early season switch from compressional to block flow velocities also vary between years changing basal conditions can result in lower horizontal velocities which decrease the ice supply to the terminus and result in temporary surface lowering but a decrease in ice flux to the terminus must lead to ice storage further upstream and that ice mass will eventually reach the terminus this can explain the observed episodic nature of terminus advance

runaway thinning of the low elevation yakutat glacier alaska and its sensitivity to climate change lake calving yakutat glacier in southeast alaska usa is undergoing rapid thinning and terminus retreat we use a simplified glacier model to evaluate its future mass loss in a first step we compute glacier wide mass change with a surface mass balance model and add a mass loss component due to ice flux through the calving front we then use an empirical elevation change curve to adjust for surface elevation change of the glacier and finally use a flotation criterion to account for terminus retreat due to frontal ablation surface mass balance is computed on a daily timescale elevation change and retreat is adjusted on a decadal scale we use two scenarios to simulate future mass change 1 keeping the current 2000 10 climate and 2 forcing the model with a projected warming climate we find that the glacier will disappear in the decade before 2110 or 2070 under constant or warming climates respectively for the first few decades the glacier can maintain its current thinning rates by retreating and associated loss of high ablating low elevation areas however once higher elevations have thinned substantially the glacier can no longer counteract accelerated thinning by retreat and mass loss accelerates even under constant climate conditions we find that it would take a substantial cooling of 1 5 degrees c to reverse the ongoing retreat it is therefore likely that yakutat glacier will continue its retreat at an accelerating rate and disappear entirely

derivation and analysis of a complete modern date glacier inventory for alaska and northwest canada we present a detailed complete glacier inventory for alaska and neighboring canada using multi sensor satellite data from 2000 to 2011 for each glacier we derive outlines and 51 variables including center line lengths outline types and debris cover we find 86 723 km 2 of glacier area 27 109 glaciers 0 025 km 2 similar to 12 of the global glacierized area outside ice sheets of this area 12 0 is drained by 39 marine terminating glaciers 74 km of tidewater margin and 19 3 by 148 lake and river terminating glaciers 420 km of lake river margin the overall debris cover is 11 with considerable differences among regions ranging from 1 4 in the kenai mountains to 28 in the central alaska range comparison of outlines from different sources on 2500 km 2 of glacierized area yields a total area difference of similar to 10 emphasizing the difficulties in accurately delineating debris covered glaciers assuming fully correlated systematic errors uncertainties in area reach 6 for all alaska glaciers but further analysis is needed to explore adequate error correlation scales preliminary analysis of the glacier database yields a new set of well constrained area length scaling parameters and shows good agreement between our area altitude distributions and previously established synthetic hypsometries the new glacier database will be valuable to further explore relations between glacier variables and glacier behavior

contribution of alaskan glaciers to sea level rise derived from satellite imagery over the last 50 years retreating glaciers and ice caps gic contributed 0 5 mm yr to sea level rises slr and one third is believed to originate from ice masses bordering the gulf of alaska however these estimates of ice wastage in alaska are based on methods that measure a limited number of glaciers and extrapolate the results to estimate ice loss for the many thousands of others how these methods capture the complex pattern of decadal elevation changes at the scale of individual glacier and mountain range is unclear here combining a comprehensive glacier inventory with elevation changes derived from sequential digital elevation models dems we found that between 1962 and 2006 alaskan glaciers lost 41 9 8 6 km 3 yr water equivalent w e and contributed 0 12 0 02 mm yr to slr our ice loss is 34 lower than previous estimates reasons for our lower values include the higher spatial resolution of our glacier inventory and the reduction of ice thinning under debris and at the glacier margins which were not resolved in earlier work estimates of mass loss from gic in other mountain regions could be subject to similar revisions

some evidence for sharp changes in the archaeomagnetic intensity variation during the last 2000 years abstract an assessment of archaeomagnetic intensities from greek and bulgarian data sets during the last 2000 years indicates sharp changes in their variation particular emphasis is given to the reliability of these data and the results are discussed in terms of a latitude effect

paleointensity of the earth s magnetic field recorded by two late quaternary volcanic sequences at the island of la reunion indian ocean a paleomagnetic study has been undertaken on two late quaternary volcanic sequences from the piton de la fournaise volcano island of la reunion in order to provide absolute paleointensities of the earth s magnetic field from a site in the southern hemisphere the pattern of secular variation recorded by both sequences clearly indicates that the extrusion rate of the lava flows was not constant with time a detailed investigation of the magnetic properties of the samples was carried out in parallel with paleointensity experiments which were performed with the thellier method samples with minimum overprint composed by single domain or pseudo single domain magnetite showing good thermal stability and a narrow blocking temperature spectrum were the most successful during thellier s experiments values of the paleofield strength from 19 to 55 mt have been obtained on 23 flows among the 30 which were sampled few variations 7 5 9 9 1022 a m2 are observed in the virtual dipole moments vdms determined on the youngest sequence 5 12 ka those values are within the range of fluctuations of the worldwide variations of vdms for this period on the other hand data from the oldest sequence 82 98 ka are the first paleointensity values obtained in that time period and the observed vdms extend from 4 1 to 8 8 1022 a m2 these results suggest that for this time interval the field did not depart from its average behavior

sedimentary record of two geomagnetic excursions within the last 15 000 years in beijing china a fresh water sedimentary sequence from haidian in the beijing basin has been sampled in three parallel trenches up to 300 m apart for paleomagnetic study age control is provided by nine radiocarbon dates indicating an average accumulation rate of 45 cm ka a total of 683 specimens were measured for paleomagnetic directions two short excursions of field direction are recorded at closely comparable depths in all three cores occurring between 5 060 and 4 860 90a b p and 14 230 and 13 690 130 a b p interpolated ages the paleomagnetic records for the individual trenches were adjusted to a common depth scale using stratigraphic markers and then merged the record correlates quite well with a paleomagnetic record in beijing basin sediments 55 km to the southwest changgou section with regard to both the large excursions and also some of the smaller variations in direction the excursions appear to reflect real geomagnetic phenomena not artifacts of recording but the spatial extent regional or global of the anomalous geomagnetic signals is not known

archaeomagnetic paleointensity in the american southwest during the past 2000 years abstract an archaeomagnetic paleointensity study was carried out on pottery samples from the hohokam anasazi and mogollon cultures of the american southwest the thellier thellier paleointensity experiment was used on 187 specimens from 77 different sherds derived from 23 archaeological sites interpretations were made for 127 specimens from 54 sherds about a two thirds success rate the median value for the quality factor was 12 the results were corrected for magnetic anisotropy owing to a fabric in the pottery using an easy plane model of magnetization the anisotropy of the hard axis relative to the easy plane of magnetization averaged 31 the correction factor for the paleointensity was typically 5 4 and systematically increased the paleointensities because the laboratory heatings were applied within the easy plane the sample average paleointensities were compiled along with other data from north america the hohokam data were kept as a separate set because of uncertainties concerning the hohokam chronology curves of the virtual axial dipole moment vadm variation for the hohokam and non hohokam data sets were derived using a moving window smoothing technique the hohokam and non hohokam curves show good agreement regardless of which hohokam chronology is used relative paleointensity records from north american lake sediments are also congruent with the archaeointensity results despite the scatter in the archaeomagnetic data the correlation of these records suggests that the secular variation pattern is being recovered the field strength at 300 bc is 30 40 higher than at present a low from 250 to 1250 ad is 10 15 weaker than at present and a peak at 1500 ad is about 30 higher than at present the low from 250 to 1250 ad in comparison with global paleointensity compilations suggests a substantial non dipole field in north america at that time the rate of change of the archaeomagnetic vadm is similar to rates observed today

a reconciled estimate of glacier contributions to sea level rise 2003 to 2009 glaciers distinct from the greenland and antarctic ice sheets are losing large amounts of water to the world s oceans however estimates of their contribution to sea level rise disagree we provide a consensus estimate by standardizing existing and creating new mass budget estimates from satellite gravimetry and altimetry and from local glaciological records in many regions local measurements are more negative than satellite based estimates all regions lost mass during 2003 2009 with the largest losses from arctic canada alaska coastal greenland the southern andes and high mountain asia but there was little loss from glaciers in antarctica over this period the global mass budget was 259 28 gigatons per year equivalent to the combined loss from both ice sheets and accounting for 29 13 of the observed sea level rise

microwave palaeointensities from a recent mexican lava flow baked sediments and reheated pottery microwave palaeointensity pi estimates have been produced from samples from the 1670 yr old xitle lava flow mexico seventeen out of 19 experiments were successful producing high quality estimates and a mean pi of 58 3 7 9 5 wt within errors of that expected from global data for the time period the dispersion is high but could be reduced to 5 5 wt by using stricter selection criteria previous data obtained by the thellier coe method using samples from the same lava flow were less successful and of much lower quality producing a higher mean of 67 9 7 9 8 wt 25 out of 65 samples this difference is most probably caused by the presence of multi domain particles producing concave up arai plots combined with alteration processes affecting the thellier coe experiments at higher temperatures pi calculations restricted to the initial part of an arai plot therefore tend to overestimate the correct values in addition to lava samples microwave pis were also determined from pottery fragments recovered from the contact zone between the lava flow and the underlying baked sediments which were also studied these materials also provided good quality results with a higher mean pi of 66 8 7 7 1 wt which is still statistically indistinct from that produced by the microwave analysis of the lava samples nevertheless these samples seem to be less suitable for pi determinations because they are characterised by larger magnetic grains and apparently more prone to thermally induced alteration than the lava samples we conclude that in the case of the xitle lava the microwave pi method is superior to the conventional thellier coe method in many respects and that the results produced by the latter method even when satisfying strict acceptance criteria may be unreliable however we also draw attention to the fact that microwave produced pi determinations though of high technical quality may still be prone to inaccuracy when rock magnetic parameters indicate that the material is likely to be a poor pi recorder as for the pottery sediment and some of the lava samples described here 2003 elsevier b v all rights reserved

an enthalpy formulation for glaciers and ice sheets polythermal conditions are ubiquitous among glaciers from small valley glaciers to ice sheets conventional temperature based cold ice models of such ice masses cannot account for that portion of the internal energy which is latent heat of liquid water within temperate ice so such schemes are not energy conserving when temperate ice is present temperature and liquid water fraction are however functions of a single enthalpy variable a small enthalpy change in cold ice is a change in temperature while a small enthalpy change in temperate ice is a change in liquid water fraction the unified enthalpy formulation described here models the mass and energy balance for the three dimensional ice fluid for the surface runoff layer and for the subglacial hydrology layer together in a single energy conserving theoretical framework it is implemented in the parallel ice sheet model results for the greenland ice sheet are compared with those from a cold ice scheme this paper is intended to be an accessible foundation for enthalpy formulations in glaciology

variations in the geomagnetic dipole moment over the last 12 000 years summary an analysis has been made of archaeointensity data for the past 12 000 years there are 3243 results from diverent areas of the world covering the past 12 000 years of these 2203 are from the european region and 1040 are from the rest of the world the archaeointensity data set analysed in the present study is almost three times larger than that used by mcelhinny senanayake 1982 although there is no major diverence between our global data and the earlier data the data for the non european region have been improved and we now have a data set for asia

modeling the evolution of the juneau icefield between 1971 and 2100 using the parallel ice sheet model pism we study the evolution of the juneau icefield one of the largest icefields in north america 3700 km 2 using the parallel ice sheet model pism we test two climate datasets 20 km weather research and forecasting model wrf output and data from the scenarios network for alaska planning snap derived from spatial interpolation of observations good agreement between simulated and observed surface mass balance was achieved only after substantially adjusting wrf precipitation to account for unresolved orographic effects while snap s climate pattern is incompatible with observations of surface mass balance using the wrf data forced with the rcp6 0 emission scenario the model projects a decrease in ice volume by 58 68 and a 57 63 area loss by 2099 compared with 2010 if the modeled 2070 99 climate is held constant beyond 2099 the icefield is eliminated by 2200 with constant 1971 2010 climate the icefield stabilizes at 86 of its present day volume experiments started from an ice free state indicate that steady state volumes are largely independent of the initial ice volume when forced by identical scenarios of climate stabilization despite large projected volume losses the complex high mountain topography makes the juneau icefield less susceptible to climate warming than low lying alaskan icefields

last glacial maximum climate in new zealand inferred from a modelled southern alps icefield abstract we present a simulation of the new zealand southern alps icefield at the last glacial maximum lgm c 30 000 20 000 calendar years ago ka in an attempt to constrain the climate of that period we use a 500 m resolution ice sheet model parameterised using empirical glaciological climatological and geological data specific to the model domain to simulate the entire southern alps icefield we find that an lgm cooling of at least 6 6 5 c is necessary to bring about valley glaciers that extend beyond the mountains however climate topography thresholds related to the elevation and hypsometry of individual catchments control the gradient of the rate of glacier expansion in the domain and in order to remain within geologically reconstructed lgm limits we find that the lgm cooling was most likely associated with a precipitation regime up to 25 drier than today wetter than present scenarios give rise to equilibrium line depressions and ice extents that are incompatible with empirical evidence these results perhaps indicate that either the westerly air masses affecting new zealand during the lgm were drier than today or that they were weaker or zonally displaced with respect to present

distribution and provenance of recycled palynomorphs in surficial sediments of the ross sea antarctica abstract quantitative analysis of surficial sediments in the ross sea has shown that the highest densities of recycled palynomorphs occur in a region in the southeast immediately north of the ross ice shelf in the vicinity of roosevelt island there spores and pollen of late cretaceous to early tertiary age predominate eocene dinoflagellates and rare palaeozoic spores are also present in the western half of the ross sea densities of recycled palynomorphs are lower but relative frequencies of palaeozoic types are higher on the continental shelf the palynomorphs have been recovered in equal abundance from sediments identified as basal tills and compound glaci marine sediments comparison of the observed patterns of distribution with patterns of ice flow in the ross ice shelf shows a clear correlation between the high palynomorph densities in the southeastern ross sea and discharge from ice streams d and e geophysical information from aeromagnetic and radio echo sounding surveys in the catchment areas of these ice streams suggests the most likely source for the recycled palynomorphs to be in a region of subdued topography inland of the present grounding line in the marie byrd land sector of the ross ice shelf extending probably not further east than 130 w this region probably represents a continuation of the easternmost ross sea basin the presence of marine eocene sediments there attested to by dinoflagellates in the recycled assemblages accords with suggestions of a late mesozoic cenozoic opening of the ross sea the observed patterns of palynomorph distribution reflect input from ice drainage areas in both east and west antarctica the preservation of sediments of differing provenance in distinct areas on the sea floor probably indicates processes of meltout of debris near the grounding line of the ross ice shelf during past phases of expansion marine bottom currents have not significantly redistributed the recycled microfossils

secular variation in mexico during the last 40 000 years paleomagnetic data are available for mexico from various archives covering irregularly the last 40 000 years data obtained from lake sediments are affected by ambiguous conversion of age to depth and the paleomagnetic data themselves are not of high quality as samples were only demagnetized at one field intensity these lake sediment data are therefore considered as less reliable for construction of a secular variation curve although they may give some qualitative information for the last 25 000 years archeological samples provide data for the period 100 1200 a d their 14 c ages are some times not well constrained with unrecoverable analytical and statistical procedures and often ages were only inferred from the stratigraphic position and the paleomagnetic record the paleomagnetic record of these materials is of high quality with very low internal dispersion although no magnetic cleaning techniques have been applied variations of inclination and declination with time are hampered by large age uncertainties and thus of limited value for the construction of secular variation curves paleomagnetic data from an u th dated stalagmite provide reasonable directions for most of the last 1200 years being of lower quality in those parts with very low remanence intensity the u th age determinations were interpreted in terms of a constant growth rate which might be only valid as a first order approximation recent volcanic rocks from the trans mexican volcanic belt provide 19 paleomagnetic directions of reasonable to high quality and often also absolute paleointensities ages have been determined from 14 c analysis of charcoal or paleosols found below the lavas and extend over the last 40 000 years therefore volcanic rocks provide the most adequate archive for the construction of a secular variation curve but much more volcanic structures need to be dated to obtain a semi continuous secular variation curve comparison of the data from different archives is possible mainly for the last 2500 years and despite the aforementioned problems similar variations of declination and inclination are observed this holds as well when comparing them to data from holocene volcanic rocks from western north america 2002 elsevier science b v all rights reserved

distributed ice thickness and volume of all glaciers around the globe 1 a new physically based approach for calculating glacier ice thickness distribution and volume is presented and applied to all glaciers and ice caps worldwide combining glacier outlines of the globally complete randolph glacier inventory with terrain elevation models shuttle radar topography mission advanced spaceborne thermal emission and reflection radiometer we use a simple dynamic model to obtain spatially distributed thickness of individual glaciers by inverting their surface topography results are validated against a comprehensive set of thickness observations for 300 glaciers from most glacierized regions of the world for all mountain glaciers and ice caps outside of the antarctic and greenland ice sheets we find a total ice volume of 170 103 21 103 km3 or 0 43 0 06 m of potential sea level rise

archaeomagnetic intensity results from california and ecuador evaluation of regional data we present new archaeointensity data for southeastern california v33 n v115 w 50 1500 yr bp and northwestern south america ecuador 2 4 s 80 7 w 4000 5000 yr bp these results represent the only data from california as well as the oldest archaeointensity data now available in northwestern south america in comparing our results to previously published data for the southwestern united states and northwestern south america we note that significant scatter in the existing data makes comparisons and interpretations difficult we undertake an analysis of the sources of data scatter including age uncertainty experimental errors cooling rate differences magnetic anisotropy and field distortion and evaluate the effects of scatter and error on the smoothed archaeointensity record by making corrections where possible and eliminating questionable data scatter is significantly reduced especially in south america but is far from eliminated however we believe the long period fluctuations in intensity can be resolved and differences between the southwestern and south american records can be identified the southwest data are distinguished from the south american data by much higher virtual axial dipole moment values from v0 600 yr bp and by a broad low between v1000 1500 yr bp comparisons to global paleofield models reveal disagreements between the models and the archaeointensity data in these two regions underscoring the need for additional intensity data to constrain the models in much of the world 2002 elsevier science b v all rights reserved

disconformities and paleoceanography in the southeast indian ocean during the past 5 4 million years biostratigraphy and magnetostratigraphy are used to identify deep sea disconformities in the southeast indian ocean the hiatuses are used to define periods of increased bottom water activity and to indicate deep sea circulation patterns during the pliocene and pleistocene seven zones of hiatus are restricted to areas confined by topographic restrictions or by water depth control on bottom water flow an analysis of hiatus frequency reveals that a water depth of about 4 200 m separates disconformities formed by antarctic bottom water 4 200 m and circumpolar deep water 4 200 m hiatus zones in deep basins occur in the tasman emerald balleny and south indian basins and east of the macquarie ridge shallow water hiatus zones 4 200 m occur at the junction of the southeast indian rise the macquarie ridge and the tasman basin and along the antarctic margin changes in the extent of these regional hiatuses are examined by analysis of hiatus occurrence in seven time slices during the past 5 4 m y although the timing of hiatuses produced by deep and shallow water masses are not synchronous the causes of increased bottom water activity may be correlated with paleoclimatic events southern ocean cooling and the proposed re establishment of the west antarctic ice sheet and its fringing ice shelves in the late gilbert chron t 4 2 to 3 6 m y b p were accompanied by increased antarctic bottom water and circumpolar deep water activity as revealed by the frequency of both shallow and deep disconformities the formation of the northern hemisphere barents ice sheet at 3 5 m y b p however led to a decrease in antarctic bottom water production by inhibiting the formation of saline north atlantic deep water which combines with cold antarctic shelf water to form antarctic bottom water cool southern ocean climatic conditions that culminated in the late matuyama chron t 1 66 to 0 72 m y b p resulted in a widespread disconformity produced by increased circumpolar deep water activity and a more restricted disconformity produced by antarctic bottom water the areal extent of both deep and shallow disconformities was reduced after the late matuyama chron t 0 72 m y b p in response to decreased bottom current activity

a new high resolution geomagnetic relative paleointensity record for the north american holocene a comparison of sedimentary and absolute intensity data a new high resolution paleointensity record for north america has been constructed using holocene sediments from lake pepin minnesota lake pepin sediments yield the same holocene paleosecular variation curve as nearby lake st croix and satisfy all of the criteria recommended for paleointensity studies absolute paleointensity data for north america recorded by holocene volcanic and archeomagnetic samples provide an independent record of geomagnetic field paleointensity against which the relative intensity records from lake pepin and lake st croix can be compared since the absolute field paleointensity is known a priori the effects of the magnetic recording assemblage can be isolated anhysteretic remanent magnetization arm is the best choice among normalization parameters for the lake pepin sediments as the natural remanent magnetization nrm normalized by arm shows no coherence with magnetic grain size proxies and yields a record of relative paleointensity peaks and troughs whose amplitudes are very similar to those in the archeomagnetic arcmag and lake st croix data sets features with a wavelength of 1000 years are correlative between the three paleointensity records nrm normalized by saturation isothermal remanent magnetization sirm and by susceptibility shows grain size dependences that cause errors in the amplitudes of paleointensity features nrm sirm and nrm are not coherent with their normalizers but are both strongly coherent with independent grain size proxies such as the median destructive field of the nrm and hcr we successfully removed the grain size dependences from nrm sirm by applying a correction function based on the linear relationship between normalized intensity and the median destructive field of the nrm

sensitivity of barnes ice cap baffin island canada to climate state and internal dynamics barnes ice cap is a remnant of the laurentide ice sheet which covered much of northern north america during the last glacial maximum barnes reached a quasi equilibrium state 2000 years ago and has remained similar in size since then with a small increase during the little ice age in this study we combine historical observations 1960 1980 with more recent satellite and airborne data 1995 2010 to drive a mass balance model coupled to a transient thermomechanical model with an adaptive mesh geometry the model is used to characterize the current state of the ice cap and to investigate its stability as a function of climate and its own internal dynamics on millennial time scales we show that ice flow is influenced by adjustment of an unsteady shape by gently sloping bedrock and by contrasting viscosities between the pleistocene and holocene ice on shorter time scales barnes is affected by surge activity sensitivity tests reveal that barnes experienced climate conditions which enabled its stability 2000 to 3000 years ago but will disappear under current climate conditions in the next millennium

magnetic properties and paleointensities as function of depth in a hawaiian lava flow the outcome of paleointensity experiments largely depends on the rock magnetic properties of the samples to assess the relation between volcanic emplacement processes and rock magnetic properties we sampled a vertical transect in a 6 m thick inflated lava flow at hawaii emplaced in 588 ad its rock magnetic properties vary as function of distance from the flow top the observations can be correlated to the typical cooling rate profile for such a flow the top and to a lesser extent the bottom parts of the flow cooled faster and reveal a composition of tm60 in which the magnetic remanence is carried by fine grained titanomagnetites relatively rich in titanium with associated low curie and unblocking temperatures the titanomagnetite in the slower cooled central part of the flow is unmixed into the magnetite and ulvospinel end members as evidenced by scanning electron microscope observation the remanence is carried by coarse grained magnetite lamella tm0 with high curie and unblocking temperatures the calibrated pseudo thellier results that can be accepted yield an average paleointensity of 44 1 2 4 t this is in good agreement with the paleointensity results obtained using the thermal izzi thellier technique 41 6 7 4 t and a recently proposed record for hawaii we therefore suggest that the chance of obtaining a reliable paleointensity from a particular cooling unit can be increased by sampling lavas at multiple levels at different distances from the top of the flow combined with careful preliminary testing of the rock magnetic properties

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

archeomagnetism of ontario potsherds from the last 2000 years an archeomagnetic study was carried out on potsherds samples from sites in ontario with ages ranging from a d 90 to a d 1640 as determined by 14c dating thellier double heating paleointensity experiments were performed in air on 65 specimens of 52 samples from seven sample sets reliable paleointensity estimates were obtained for 49 specimens alternating field and thermal demagnetization temperature dependence of weak field susceptibility and hysteresis measurements indicate that magnetite of pseudo single domain grain size is the carrier of natural remanent magnetization the paleointensity results follow a half cycle sine curve with a steady decrease from 54 0 5 9 t to 37 6 5 7 t between a d 90 and a d 885 and a monotonic increase from 52 0 6 1 t to 59 4 1 7 t between a d 1200 and a d 1900 the paleointensities determined yield virtual axial dipole moments vadms of the earth s magnetic field that agree well with those from other parts of north america except between a d 900 and a d 1400 when they are systematically lower this discrepancy is probably caused by a substantial non dipole field in southwestern north america from the tenth to the fifteenth century since secular variation studies using potsherds from arizona and lake sediments from minnesota show different inclination variations during that period

the challenge of monitoring glaciers with extreme altitudinal range mass balance reconstruction for kahiltna glacier alaska glaciers spanning large altitudinal ranges often experience different climatic regimes with elevation creating challenges in acquiring mass balance and climate observations that represent the entire glacier we use mixed methods to reconstruct the 1991 2014 mass balance of the kahiltna glacier in alaska a large 503 km 2 glacier with one of the greatest elevation ranges globally 264 6108 m a s l we calibrate an enhanced temperature index model to glacier wide mass balances from repeat laser altimetry and point observations finding a mean net mass balance rate of 0 74 mw e a 1 0 04 std dev of the best performing model simulations results are validated against mass changes from nasa s gravity recovery and climate experiment grace satellites a novel approach at the individual glacier scale correlation is strong between the detrended model and grace derived mass change time series r 2 0 58 and p 0 001 and between summer r 2 0 69 and p 0 003 and annual r 2 0 63 and p 0 006 balances lending greater confidence to our modeling results we find poor correlation however between modeled glacier wide balances and recent single stake monitoring finally we make recommendations for monitoring glaciers with extreme altitudinal ranges including characterizing precipitation via snow radar profiling

rapid wastage of alaska glaciers and their contribution to rising sea level we have used airborne laser altimetry to estimate volume changes of 67 glaciers in alaska from the mid 1950s to the mid 1990s the average rate of thickness change of these glaciers was 0 52 m year extrapolation to all glaciers in alaska yields an estimated total annual volume change of 52 15 km 3 year water equivalent equivalent to a rise in sea level sle of 0 14 0 04 mm year repeat measurements of 28 glaciers from the mid 1990s to 2000 2001 suggest an increased average rate of thinning 1 8 m year this leads to an extrapolated annual volume loss from alaska glaciers equal to 96 35 km 3 year or 0 27 0 10 mm year sle during the past decade these recent losses are nearly double the estimated annual loss from the entire greenland ice sheet during the same time period and are much higher than previously published loss estimates for alaska glaciers they form the largest glaciological contribution to rising sea level yet measured

ice thickness measurements of taku glacier alaska u s a and their relevance to its recent behavior using radio echo soundings and seismic reflections we measured cross sections of taku glacier near juneau alaska to resolve inconsistencies in previous measurements and to understand better the glacier s dynamics the maximum thickness is about 1477 m and the minimum bed elevation is about 600 m below sea level which establishes taku glacier as the thickest and deepest temperate glacier yet measured our data indicate that during the 19th century the terminus of taku glacier may have begun its rapid advance at a position where the ice bed was greater than 300 m below sea level and more than 25 km from the inland end of its submarine trough this behavior is uncharacteristic of temperate tide water glaciers the glacier which no longer calves has eroded a sediment layer 100 m thick since 1890 at an average rate of about 3 m a 1 since 1948 this high erosion rate retards advance by entrenching the glacier into the terminal moraine calculations based on ice deformation theory indicate significant basal ice motion near the terminus and high basal shear stress 140 220 kpa along much of its length estimated differences between ice flux and balance flux are consistent with observed thickening and positive net mass balance these data indicate that ice volume is increasing and that further advance is likely

a linear theory of orographic precipitation a linear theory of orographic precipitation is developed including airflow dynamics condensed water advection and downslope evaporation the formulation extends the widely used upslope model vertically integrated steady state governing equations for condensed water are solved using fourier transform techniques closed form expressions are derived for special cases for more general cases the precipitation field is computed quickly by multiplying the terrain transform by a wavenumber dependent transfer function five length scales are included in the model mountain width a buoyancy wave scale the moist layer depth and two condensed water advection distances the efficiency of precipitation in the model is sensitive to the decay of the forced ascent through the moist layer and to the advection of condensed water downwind into the region of descent the strong influence of horizontal scale on precipitation pattern and amount predicted by the model is discussed the model is illustrated by applying it to the olympic mountains in washington state

fast tidewater glaciers some iceberg calving outlet glaciers flow continuously at speeds normally associated with surging glaciers arid exhibit dramatic instability scenarios related to those suggested for marine ice sheets no temperate tidewater glaciers are known to have floating termini but many polar and subpolar tidewater glaciers do the fast flow of temperate calving glaciers is almost entirely due to basal sliding and appears to be a function of the effective pressure on the bed which may approach zero and the longitudinal back stress on the terminus the terminus boundary condition the calving relation is imperfectly known yet is vital to the dynamics of these glaciers calving relations for grounded tidewater glaciers have been suggested on empirical grounds but have not been rigorously tested the calving relations for floating termini are virtually unknown this together with the imperfect understanding of basal sliding inhibits confidence in our understanding of the stability of these glaciers columbia glacier alaska is an instructive example because observations have been made on the major changes in its geometry calving rate and dynamics that have occurred in less than 10 years the calving flux has increased more rapidly than the glacier flux causing thinning and retreat as a result the ice velocity has increased markedly the short term velocity changes relate to changes in back pressure ice recession tidal changes and the flux of water injected to the bed these results have relevance to the mechanisms of basal sliding glacier surges and the stability of marine ice streams

geomagnetic secular variation we analyse over 175000 magnetic observations from an interval spanning 1695 1980 to produce a sequence of maps of the magnetic field at the core mantle boundary we find that even the earlier data enable us to determine reliable maps we produce these maps at approximately 60 year intervals through the eighteenth and nineteenth centuries and at 10 year intervals in the twentieth century this span of maps is long enough to render straightforward the distinction between static and drifting features in the field we observe that some features show no sign whatsoever of drift over the entire 285 year time interval although others drift westwards in particular we observe that the secular variation is very low beneath the pacific ocean but beneath southern africa and the south atlantic ocean we observe rapid secular variation we interpret the morphology of the static field in terms of a simple model of the dynamo and conjecture that interactions between the core and the mantle are an important element of the process as part of the static field we identify four main concentrations of flux two in each hemisphere at high latitudes these features largely account for the earth s axial dipole moment we find unequivocal evidence that magnetic flux has not remained frozen over the time span of our models much of the diffusive behaviour that we identify is associated with the formation of a pair of flux spots a core spot beneath southern africa early in this century nevertheless we are able to construct maps that satisfy a set of necessary conditions for frozen flux and use these maps to construct maps of the core surface fluid flow based on the steady flow hypothesis although we find no strong evidence against the steady flow hypothesis we do find some grounds on which to doubt the validity of the flow maps

taku glacier alaska u s a on the move again active deformation of proglacial sediments taku glacier is one of the few glaciers in alaska u s a that has advanced over the last century 7 km since 1890 this advance slowed substantially during the past decade but in summer 2001 the glacier terminus began to readvance at a rate of 30 cm d 1 the advance produced dramatic proglacial sediment deformation up to 200 m in from of the terminus two to three large bulges and several secondary bulges developed in the proglacial sediments as a result of glacial compression along a 1 km wide portion of the terminus the bulge nearest the terminus was 10 m high and 65 m wide the middle bulge 7 m high advanced at 15 cm d 1 and the distal bulge 3 m high and 50 m wide at 9 cm d 1 crenulations and prominent fractures developed in the overlying vegetation layer the frontal lobes of the bulges were steep and overlaid a shear zonc where sediments were being thrust up and over the ground surface ice proximal push moraines 1 10 m high formed along much of the 9 km wide terminus although deformation was minimal at some locations

secular variation of archaeomagnetic direction in the american southwest a d 750 1425 oriented archaeomagnetic samples were collected from 158 in situ features at 33 archaeological sites in the southwestern united states seventy three independently dated features were used for analysis of secular variation a moving window technique with outlier rejection was developed to compute a smoothed secular variation curve this technique incorporates weighted fisher statistics to account for imprecision in both the age of remanence acquisition and the direction of magnetization for each feature a mean direction and measure of dispersion is generated for each window of time the secular variation record covers the period a d 750 1425 during which time the virtual geomagnetic pole vgp moves in a generally counterclockwise fashion from 86 n 83 e at a d 750 to the lowest latitude position of 74 n 192 e at a d 1075 and then to 85 n 236 e at a d 1425 the median rate of vgp movement is 0 036 yr 1 similar to present day rates the southwestern record shows close correspondence to other north american archaeomagnetic limnomagnetic and speleomagnetic records the archaeomagnetic record can serve as the master curve for the derivation of archaeomagnetic dates

holocene paleointensities thellier experiments on submarine basaltic glass from the east pacific rise a complete description of the geomagnetic field requires both paleodirectional and paleointensity data although the paleointensity data base has grown steadily over the last three decades it remains limited in time and space the majority of data are of holocene age and come from europe furthermore it has been difficult to assess the reliability of the paleointensity determinations here we present paleointensity determinations on precisely dated holocene 0 to 3500 years old submarine basaltic glass from the east pacific rise 15 s to 22 s although hysteresis measurements and low temperature isothermal remanent magnetization irm acquisition experiments document a significant contribution of superparamagnetic grains high blocking temperatures above 400 c and curie temperatures between 490 c and 550 c indicate a single domain low ti magnetite as the carrier of the remanent magnetization this notion is further supported by the fact that saturation of remanence is achieved in moderate fields of about 200 300 mt submarine basaltic glass proves to be nearly ideal for paleointensity determinations in that it produces a high success rate for thellier experiments twenty six out of 30 samples resulted in acceptable paleointenisty determinations multiple experiments on splits from the same sample show good reproducibility the paleointensities for zero age glasses correspond precisely with the present field intensity at the site of recovery the results of the remaining samples range from 16 7 to 53 9 t with corresponding virtual axial dipole moments vadm of 3 61 1022 to 11 9 1022 a m2 the intensities vary rapidly with time excluding a westward drifting nondipole component as the source for these fluctuations basaltic glass is frequently recovered in both dredged and drilled material from the ocean floor the availability of submarine basaltic glass throughout the world oceans therefore holds great potential for a better distribution of paleointensity data through time and space