cenozoic global ice volume and temperature simulations with 1 d ice sheet models forced by benthic δ18o records variations in global ice volume and temperature over the cenozoic era have been investigated with a set of one dimensional 1 d ice sheet models simulations include three ice sheets representing glaciation in the northern hemisphere i e in eurasia north america and greenland and two separate ice sheets for antarctic glaciation the continental mean northern hemisphere surface air temperature has been derived through an inverse procedure from observed benthic 18o records these data have yielded a mutually consistent and continuous record of temperature global ice volume and benthic 18o over the past 35ma the simple 1 d model shows good agreement with a comprehensive 3 d ice sheet model for the past 3 ma on average differences are only 1 0 c for temperature and 6 2m for sea level most notably over the 35ma period the reconstructed ice volume temperature sensitivity shows a transition from a climate controlled by southern hemisphere ice sheets to one controlled by northern hemisphere ice sheets although the transient behaviour is important equilibrium experiments show that the relationship between temperature and sea level is linear and symmetric providing limited evidence for hysteresis furthermore the results show a good comparison with other simulations of antarctic ice volume and observed sea level

eemian cooling in the norwegian sea and north atlantic ocean preceding continental ice sheet growth changing conditions in the north atlantic region may drive global climate changes1 2 according to previous reconstructions of the last interglacial the eemian north atlantic sea surface tempera tures ssts were similar to present day values3 in the norwegian sea even warmer conditions appeared as a single pulse of short duration4 5 whereas the greenland ice record suggests that the warm interglacial air temperatures were interrupted by several cold periods6 here we use faunal and stable isotope analyses of foraminifera in two sediment cores from the north atlantic ocean and norwegian sea to reconstruct high resolution records of sst and sea surface salinity sss during the eemian interglacial our results which differ significantly from the greenland record6 show a sharp decrease in sst and sss of the norwegian sea associated with a more moderate cooling and freshening of the north atlantic at the middle of isotope substage 5e several millennia before the beginning of continental ice sheet growth changes in the norweg ian sea surface conditions appear to have represented an important climate change affecting global atmospheric and thermohaline circulations

analysis of teleseismic body waves radiated from the loma prieta earthquake broad band data from iris and orfeus data centers the arcess array and scp station are analyzed to infer fault plane geometry and the character of rupture during the october 17 1989 loma prieta earthquake interference of p and sp seen in the p wave forms is consistent with the 18 km source depth inferred from local observations a minimum source depth of 14 km is inferred from interpretation of the s wave arrival time relative to instrument trigger using horizontal strong motion accelerations observed at corralitos california p sp s and ss polarities and relative amplitudes are used in a comprehensive grid search to infer that oblique right lateral faulting occurred on a steeply dipping 56 60 section of the san andreas fault with an equal amount of thrust component consistent with aftershock locations a suite of point moment tensor inversions for source depths spanning the observed depth of aftershock hypocenters yields similar mechanisms the best moment tensor in terms of wave form fit and minimum non double couple component occurs for a source depth of 8 km substantially shallower than the locally inferred hypocenter seismic moment for this model is 2 3 1026 dyn cm the slow growth of the p displacement pulse with time and impulsive sp suggests a working model for fault rapture where rupture initiates at 18 km and propagates upwards and outwards along the fault the p wave forms show the effects of variations in rupture along the plane through observation of a cascade of successively larger subevents

source finiteness of large earthquakes measured from long period rayleigh waves the source finiteness parameters of 11 large shallow earthquakes were determined from long period rayleigh waves recorded by the global digital seismograph network and international deployment of accelerometers networks the basic data sets are the seismic spectra of periods from 150 to 300 s in the determination of source process times we used furumoto s phase method and a linear inversion method in which we simultaneously inverted the spectra and determined the source process time that minimizes the error in the inversion these two methods yielded consistent results the source process times of the sumbawa indonesia colombia ecuador valparaiso chile and michoacan mexico earthquakes were estimated to be 79 118 69 and 77 s respectively from the linear inversion method the source process times determined from long period surface waves were in general longer than those obtained from body waves source finiteness of large shallow earthquakes with rupture on a fault plane with a large aspect ratio was modeled with the source finiteness function introduced by ben menahem the spectra were inverted to find the extent and direction of the rupture of the earthquake that minimize the error in the inversion for a rupture velocity of 2 5 km s 1 the estimated rupture was unilateral 100 km long and along the strike n26 w for the may 26 1983 akita oki japan earthquake 165 km and s57 e for the september 19 1985 michoacan mexico earthquake 256 km and n31 e for the december 12 1979 colombia ecuador earthquake and 149 km and s15 w for the march 3 1985 valparaiso chile earthquake the results for the august 19 1977 sumbawa indonesia earthquake showed that the rupture was bilateral and in the direction n60 e these results are in general consistent with the rupture extent inferred from the aftershock area of these earthquakes

changing influence of antarctic and greenlandic temperature records on sea level over the last glacial cycle we use a simple model to analyse the relationship between ice core temperature proxy data and global ice volume eustatic sea level data over the last glacial cycle lgc by allowing the temperature forcing to be a mix of greenlandic and antarctic signals we optimise the proportion of this mixing to fit sea level data we find that sea level forcing is best represented by a mix of antarctic and greenlandic temperature signals through the whole glacial cycle we suggest that a distinct bipolar switch occurs which links eustatic sea level more closely with the antarctic like variability during the glacial period mis 4 3 and 2 and more closely to the greenland like variability during the last termination ti and the interglacial periods holocene and mis 5 this switch may be caused by the spatio temporal distribution of ice sheet collapse perhaps linked to glacial to interglacial changes in deep water distribution in the ocean which in turn drive changes in pole ward heat and moisture transport

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

effects of spatial discretization in ice sheet modelling using the shallow ice approximation this paper assesses a two dimensional vertically integrated ice model for its numerical properties in the calculation of ice sheet evolution on a sloping bed using the shallow ice approxi mation we discuss the influence of initial conditions and individual model parameters on the model s numerical behaviour with emphasis on varying spatial discretizations the modelling results suffer badly from numerical problems they show a strong dependence on gridcell size and we conclude that the widely used gridcell spacing of 20 km is too coarse the numerical errors are small in each single time step but increase non linearly over time and with volume change as a result of feedback of the mass balance with height we propose a new method for the calculation of the surface gradient near the margin which improves the results significantly furthermore we show that we may use dimension analysis as a tool to explain in which situations numerical problems are to be expected

simulations of the northern hemisphere through the last glacial interglacial cycle with a vertically integrated and a three dimensional thermomechanical ice sheet model coupled to a climate model

deglaciation of the northern hemisphere at the onset of the eemian and holocene high resolution tims u series dating of sea level events obtained from coral reef complexes suggests that global deglaciation from the saale penultimate glacial to the eem interglacial marine 18o stages 6 5 may have occurred earlier in relation to milankovitch insolation forcing than that from the wisconsinan glacial to the holocene interglacial marine 18o stages 2 1 however the interpretation of these data has been problematic because of the possibility of isotope exchange in order to investigate whether these different lead lag relations between milankovitch forcing and ice volume are feasible from the point of view of large scale ice sheet dynamics and thermodynamics the three dimensional polythermal ice sheet model sicopolis simulation code for polythermal ice sheets is applied to the entire northern hemisphere which gives the major contribution to global ice volume changes due to the relative stability of the antarctic ice sheet and simulations through the last two climatic cycles are conducted the simulations cover the interval from 250 kyr bp until today and are driven by surface temperature reconstructions of deep ice cores grip vostok and simple parameterizations for the change of precipitation with time discussion of the results is focused on the saale eem and the wisconsinan holocene transitions the amount and rate of deglaciation are in good agreement with the specmap record for both cases and the evidence of the data for an early start of the eem interglacial is supported

processes of buildup and retreat of the greenland ice sheet sensitivity experiments were conducted to study the influence of several physical processes on the evolution of the greenland ice sheet over the last 250 000 years the experiments were carried out by means of a three dimensional thermodynamical model the mass balance is modeled by a surface energy balance model this means that variations in orbital parameters following from the astronomical milankovitch theory can be incorporated in the ablation calculations it is shown that with regard to the greenland ice sheet variations in shortwave radiation are only of minor importance for the changes in volume over time calculations of the various components of the energy balance under glacial and interglacial conditions show that the changes in absorbed shortwave radiation resulting from changes in orbital parameters are considerably smaller than the variations in the sensible heat flux caused by temperature variations thermodynamics are only of importance for the volume changes of the ice sheet if the climate is on average stable over a long period in between 110 kyr b p and 20 kyr b p the ice volume increased slowly due to the cooling of the ice which resulted in a higher effective viscosity and thus a thicker ice sheet the long response time of the thermodynamics means that the thermodynamics cannot play a crucial role during transition from a glacial to a deglacial period which occur typically within several thousands of years the mass balance height feedback has an important function in the buildup of the ice sheet after a warm period like the eemian without isostatic bedrock compensation the ablation will remain very high in some marginal parts yielding a considerably smaller ice sheet volume for the last glacial period

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

sst and ice sheet impacts on the mis 13 climate as a first qualitative assessment tool loveclim has been used to investigate the interactions between insolation ice sheets and the east asian monsoon at the marine isotopic stage 13 mis 13 in work by yin et al clim past 4 79 90 2008 clim past 5 229 243 2009 the results are in need of validation with a more sophisticated model which is done in this work with the arpege atmospheric general circulation model as in the earth system model of intermediate complexity loveclim arpege shows that the northern hemispheric high insolation in summer leads to strong mis 13 monsoon precipitation data from the chinese loess plateau indicate that mis 13 was locally a warm and humid period guo et al in clim past 5 21 31 2009 yin and guo in chin sci bull 51 2 213 220 2006 this is confirmed by these general circulation model gcm results where the mis 13 climate is found to be hotter and more humid both in the presence and absence of any added ice sheets loveclim found that the combined effects of the ice sheets and their accompanying ssts contribute to more precipitation in eastern china whilst in arpege the impact is significant in northeastern china nonetheless the results of arpege confirm the counter intuitive results of loveclim where ice sheets contribute to enhance monsoon precipitation this happens through a topography induced wave propagating through eurasia with an ascending branch over northeastern china a feature which is also seen in loveclim the sst forcing in arpege results in a strong zonal temperature gradient between the north atlantic and east eurasia which in turn triggers an atmospheric gravity wave this wave induces a blocking okhotskian high preventing the northwards penetration of the meiyu monsoon front the synergism between the ice sheets and sst is found through the factor separation method yielding an increase in the meiyu precipitation though a reduction of the changma precipitation the synergism between the ice sheets and sst play a non negligible role and should be taken into consideration in gcm studies preliminary fully coupled aogcm results presented here further substantiate the finding of stronger mis 13 monsoons and a reinforcement from ice sheets this work increases our understanding of the signals found in the paleo observations and the dynamics of the complex east asian summer monsoon

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

sensitivity studies of northern hemisphere glaciation using an atmospheric general circulation model abstract the u k university global atmospheric modeling programme gcm is used to investigate whether the growth of northern hemisphere ice sheets could have been initiated by changes of orbital parameters and sea surface temperature two different orbital configurations corresponding to the present day and 115 kyr bp are used the reduced summer solar insulation in the northern hemisphere results in a decrease of the surface temperature by 4 to 10 c in the northern continents and to perennial snow in some high latitude regions therefore the model results support the hypothesis that a deficit of summer insulation can create conditions favorable for initiation of ice sheet growth in the northern hemisphere a decreased sea surface temperature northward of 65 n during the northern hemisphere summer may contribute to the maintenance of ice sheets a simple mixed layer ocean model coupled to the gcm indicates that the changes of sea surface temperature and extension of sea ice due to insulation changes pl

aftershock slip behavior of the 1989 loma prieta california earthquake an analysis of 745 aftershocks of the m7 1 loma prieta earthquake of 17 october 1989 reveals a wide variety of focal mechanisms at the northwestern end of the aftershock zone earthquakes that apparently occurred off the main rupture plane exhibit mechanisms with predominantly reverse slip on planes nearly parallel to the san andreas fault at the southeastern end the mechanisms exhibit right lateral motion on near vertical planes suggesting that these aftershocks involve slip on the san andreas fault few of the aftershock mechanisms in the central zone resemble the main shock mechanism strike n130 degree e dip 70 degree sw rake 104 degree but instead exhibit reverse right lateral left lateral and normal motion on planes subparallel to the main shock rupture plane the dip of the aftershock zone is parallel to the main shock slip plane and includes the main shock hypocenter however the lack of agreement between the main shock and the aftershock mechanisms suggests that few of the aftershocks occurred on the main shock slip plane this behavior is consistent with observations of aftershock sequences for other dip slip events and also with studies indicating that main shock rupture zones are at all other times mostly aseismic if the stress drop for the main shock relievedmore most of the tectonic stress the mechanisms could reflect the heterogeneity of the near field stress redistribution alternatively the variety of the aftershock mechanisms may reflect deformation by block motion within a narrow zone adjacent to the main shock rupture plane less

global ice volume variations through the last glacial cycle simulated by a 3 d ice dynamical model abstract a coupled ice sheet ice shelf bedrock model was run at 20 km resolution to simulate the evolution of global ice cover during the last glacial cycle the mass balance model uses monthly mean temperature and precipitation as input and incorporates the albedo mass balance feedback the model is forced by the grip and vostok derived temperature records and by sea level and solar radiation variations which are distributed spatially and seasonally model simulations show that at the last glacial maximum lgm a volume of ice representing about 65 m of sea level equivalent is stored on the eurasian continent whereas north america stores 42 m the other regions greenland tibet south america and antarctica contribute about 17 m to global sea level lowering at the lgm compared to present day sensitivity experiments show that the ice volumes of the eurasian and north american ice sheets are particularly sensitive to summer temperature changes finally the timing and mechanism of grounded ice formation and expansion for the last glacial were studied for the eurasian and north american continents ice sheet formation begins at 118 kyr bp in the barents and kara sea region over baffin island and in the high cordilleran range following a 4 c cooling alternating regions of ice sheet expansion by direct snowfall ice flow and grounding of ice shelves can be identified these relate to specific geomorphological traces and may as such help in model validation

ice sheet modelling characteristics in sea level based temperature reconstructions over the last glacial cycle a widely used method for investigating palaeotemperatures is to analyze local proxy records e g ice cores or deep sea sediment cores the interpretation of these records is often not straightforward and global or hemispheric means cannot be deduced from local estimates because of large spatial variability using a different approach temperature changes over the last glacial cycle can be estimated from sea level observations by applying an inverse method to an ice sheet model in order to understand the underlying physical mechanisms we used a 1 d ice sheet model and a 3 d coupled thermodynamic ice sheet ice shelf bedrock model to investigate the importance of several physical processes for the inverse temperature reconstructions results show that i temperature reconstructions are sensitive to the employed formulation of mass balance ii excluding thermodynamics in the ice sheet leads to a smaller temperature amplitude in the reconstruction and iii hysteresis in the non linear relation between sea level and temperature occurs as a consequence of ice redistribution in the process of merging and separation of ice sheets the ice redistribution does not occur if the geometry does not support the formation of a relatively flat dome which tends to be preserved in warming conditions

considering the third dimension in stress triggering of aftershocks 1993 klamath falls oregon earthquake sequence dip slip on a fault of finite dimension produces a static stress change that varies considerably in 3 d the 1993 klamath falls oregon usa earthquake sequence shows a shallow off fault cluster of aftershocks with mixed dip slip and strike slip focal mechanisms modeled static stress change and location of aftershocks show a misleading correspondence when viewed in the customary 2 d presentation full 3 d analysis shows that shallow right lateral slip is consistent with the local stress perturbation following the dip slip main shocks

transient nature of the earth s climate and the implications for the interpretation of benthic δ18 o records abstract from the marine benthic 18 o records it is known that the earth s climate has experienced significant variability over the past 40 million years in general a number of assumptions are often needed to disentangle the benthic 18 o data into its temperature and ice volume contributions in this study a transient 1 d ice sheet model is used which overcomes these shortcomings by relating temperature to the benthic 18 o data leading to a self consistent and continuous record of 18 o temperature and sea level the contribution of land ice to benthic 18 o is examined with a set of sensitivity experiments varying the mean 18 o of the ice for different ice sheets it is shown that the scaling factor of sea water 18 o w to sea level is not constant over the long time scales however our sensitivity experiments do show that over the long time scale the general assumed 1 0 1 1 per 100 m of sea level is in reasonable agreement with our model results moreover the sea level ice volume response to temperature s t is shown to vary through time with the largest response found when variations in antarctic ice volume dominates the sea level variations during the oligocene to early miocene furthermore this response is quite large compared to the individual response of ice sheets during the plio pleistocene whereas the combined s t in this period is comparable to that during the oligocene accordingly the transient behaviour is very important for the interpretation of data records with respect to climate sensitivity and climate change during the past 40 million years

long period and broad band teleseismic body wave modeling of the october 18 1989 loma prieta earthquake inversion of long period teleseismic body waves for the loma prieta earthquake yields a nearly double couple moment tensor corresponding to an oblique mechanism with strike 130 dip 73 and rake 146 the long period centroid depth of the source is 18 km and the seismic moment is 2 8 1019 nm the source time history consists of two pulses with a total duration of 8 9 sec preliminary forward modeling of broad band teleseismic body waves indicates the occurrence of at least two sub sources constraining the fault orientation to the long period inversion result the first source was located at 18 km depth and the second source was located updip at about 14 km depth the second source has a seismic moment 2 7 times that of the first and occurred 2 0 sec after the first the precise location of the second source will require further modeling

quaternary science 2007 a 50 year retrospective this paper reviews 50 years of progress in understanding the recent history of the earth as contained within the stratigraphical record of the quaternary it describes some of the major technological and methodological advances that have occurred in quaternary geochronology examines the impressive range of palaeoenvironmental evidence that has been assembled from terrestrial marine and cryospheric archives assesses the progress that has been made towards an understanding of quaternary climatic variability discusses the development of numerical modelling as a basis for explaining and predicting climatic and environmental change and outlines the present status of the quaternary in relation to the geological time scale the review concludes with a consideration of the global quaternary community and the challenge for the future

the 1993 klamath falls oregon earthquake sequence source mechanisms from regional data we use regional broadband seismograms to obtain seismic moment tensor solutions of the two september 20 1993 mw 6 klamath falls oregon earthquakes their foreshock and largest aftershocks my 3 5 several sub groups with internally consistent solutions indicate activity on several fault segments and faults from the estimated moment tensors and depths of the main shocks and from the aftershock distribution we deduce that both main shocks occurred on an east dipping normal fault pos sibly related to the lake of the woods fault system rotation of t axes between the two main shocks is consistent with the two dominant trends of the aftershocks and mapped faults we pro pose that a change in fault strike acted as temporary barrier sepa rating the rupture of the main shocks empirical green s function analysis shows that the first main event had a longer rupture du ration half duration 1 7 s than the second 1 2 s in december vigorous shallow activity commenced near klamath lake s west ern shore 5 10 km east of the primary aftershock zone it ap pears a mw 5 5 aftershock occurring the day before though within the primary aftershock zone triggered the activity

broadband study of the 1989 loma prieta earthquake we determined the source characteristics of the oct 18 1989 loma prieta california earthquake using teleseismic data the solution from body waves gives a mechanism with dip 70 rake 138 and strike 128 and a seismic moment of 3 10 26 dyne cm m w 6 9 this solution is similar to those obtained from long period rayleigh and love waves p nl waves and first motion data the body wave form suggests a depth of about 15 km the effective duration of the source is 6 sec which suggests a fault length of 30 km and 15 km for bilateral and unilateral faulting respectively considering the extent of the aftershock area we used 35 km as an estimate of the total rupture length the strike slip and the thrust components of the coseismic slip are 177 and 159 cm respectively the large thrust component raises an important question regarding the recurrence pattern if the loma prieta earthquake is a characteristic earthquake with a recurrence interval of about 100 years the 159 cm displacement implies a long term uplift rate of about 1 cm year which appears too large for this region three hypotheses for reconciling this apparent conflict are 1 the geometry of plate motion along the santa cruz mountain segment changes over a time scale of several thousand years so that the coseismic displacement has not accumulated enough to produce high topographic relief 2 the coseismic shp direction varies from event to event 3 the slip plane of the 1989 loma prieta earthquake is different from the major boundary between the pacific and the north american plates if this is the case the loma prieta earthquake is a rather rare non characteristic event the surface slip of about l m for the 1906 san francisco earthquake is one of the key data in long term forecasting no surface slip was observed for the 1989 loma prieta earthquake even if the horizontal slip at depth is as large as 1 8 m this points to a risk of relying too heavily on surface observations for long term seismic risk analysis

stress triggering of conjugate normal faulting late aftershocks of the 1983 ms 7 3 borah peak idaho earthquake the 1984 devil canyon sequence was a late aftershock sequence of the 28 october 1983 ms 7 3 borah peak idaho earthquake the sequence began on 22 august 1984 with the ml 5 8 devil canyon earthquake which nucleated at a depth of 12 8 0 7 km between the surface traces of two normal faults the challis segment of the lost river fault and the lone pine fault two hundred thirty seven aftershocks were recorded by a temporary array during a 3 week period their focal mechanisms and hypocenter distribution define a cross sectional v pattern whose base corresponds to the ml 5 8 event whose tips correspond to the exposed fault traces and whose sides define two planar fault zones oriented n25 w 75 sw challis fault segment and n39 w 58 ne lone pine fault this pattern describes a graben bounded by conjugate normal faults temporal aspects of the devil canyon sequence provide strong evidence that slip on conjugate normal faults occurs sequentially aftershocks occurred primarily along the challis segment until the occurrence of the 8 september 1984 ml 5 0 earthquake along the lone pine fault after which aftershocks primarily occurred along this fault these observations are consistent with worldwide seismologic and geologic observations and with physical andmore numerical models of conjugate normal faulting aftershocks of the devil canyon sequence occurred immediately northwest of the ml 5 8 devils canyon earthquake which itself was immediately northwest of the thousand springs segment of the lost river fault the fault that slipped in association with the ms 7 3 borah peak earthquake coulomb failure stress analysis indicates that stress increases resulting from both the borah peak mainshock and devil canyon ml 5 8 earthquake were sufficient to induce failure on the lone pine fault these space time patterns suggest that conjugate normal faults may transfer stress or accommodate stress changes at the terminations of major normal faults in the basin and range province less

a new method to estimate ice age temperatures on glacial time scales the waxing and waning of the eurasian and north american ice sheets depend largely on variations in atmospheric temperature as global sea level is primarily determined by the volume of these ice sheets there is a direct yet complex relation between global sea level and the northern hemispheric nh temperature this relation is essentially represented by a model of the nh ice sheets we use a thermomechanical ice sheet ice shelf bedrock model in conjunction with an inverse method to deduce a time series of nh temperature from 120 kyr bp until present that is consistent with the observed global sea level record the advantage of this method is that it provides the annual mean surface air temperature averaged over the nh continents north of 40 n the results reveal that ice age temperatures were 4 10 c lower than today which agrees with other temperature reconstructions however reconstructed temperatures are comparitively low during the early stages of the glacial a feature that is consistent with the rapid growth of the ice sheets the sensitivity of the results for uncertainties in precipitation rate in observed sea level and in some other model parameters is examined to quantify the error in reconstructed temperature during the glacial period 120 15 kyr bp surface air temperatures in the nh north of 40 n were 7 2 1 5 c lower than today s interglacial temperatures

coupled energy balance ice sheet model simulations of the glacial cycle a possible connection between terminations and terrigenous dust we apply a coupled energy balance ice sheet climate model in an investigation of northern hemisphere ice sheet advance and retreat over the last glacial cycle when driven only by orbital insolation variations the model predicts ice sheet advances over the continents of north america and eurasia that are in good agreement with geological reconstructions in terms of the timescale of advance and the spatial positioning of the main ice masses the orbital forcing alone however is unable to induce the observed rapid ice sheet retreat and we conclude that additional climatic feedbacks not explicitly included in the basic model must be acting in the analyses presented here we have parameterized a number of potentially important effects in order to test their relative influence on the process of glacial termination these include marine instability thermohaline circulation effects carbon dioxide variations and snow albedo changes caused by dust loading during periods of high atmospheric aerosol concentration for the purpose of these analyses the temporal changes in the latter two variables were inferred from ice core records of these various influences our analyses suggest that the albedo variations in the ice sheet ablation zone caused by dust loading may represent an extremely important ablation mechanism using our parameterization of dirty snow in the ablation zone we find glacial retreat to be strongly accelerated such that complete collapse of the otherwise stable laurentide ice sheet ensues the last glacial maximum configurations of the laurentide and fennoscandian complexes are also brought into much closer accord with the ice 3g reconstruction of tushingham and peltier 1991 1992 and the ice 4g reconstruction of peltier 1994 when this effect is reasonably introduced

geologically and geomorphologically constrained numerical model of laurentide ice sheet inception and build up abstract the locations shapes and masses of evolving ice sheets during interglacial to glacial transitions remain elusive but need to be clarified for identification of the climatic feedbacks that amplified low amplitude insolation changes to become the major global climatic shift of the last glacial maximum the best way to explore probable spatial patterns of ice sheet inception and build up is through ice sheet modelling and validating model output against geomorphological and geological data we have modelled the 120 55 kyr bp evolution of the laurentide ice sheet focusing on the locations outline flow patterns and basal thermal regimes of its precursor ice centres for this we employed a time dependent mass balance driven finite element model forced with grip ice core oxygen isotope values calibrated to temperature the model achieves a good fit to relict ice flow systems in keewatin the interior plains and the hudson bay lowland thus our model indicates that the first coherent ice centre in north america was situated over baffin island and the melville and boothia peninsulas and expanded onto mainland canada at 90 75 kyr bp a previously unknown 200 km long moraine zone near the thlewiaza river keewatin may demarcate the marginal position of this early central arctic ice sheet cordilleran and keewatin ice merged and the hudson bay lowland was inundated from the east from quebec by 65 kyr bp

modelled nucleation centres of the pleistocene ice sheets from an ice sheet model with subgrid topographic and glaciologic parameterizations abstract ice sheet inception at the onset of the last glacial epoch ca 115 kyr bp is not well understood to cause the northern hemisphere to descend into ice age conditions internal climate system feedbacks must have acted to amplify relatively low amplitude orbital cooling trends while a number of plausible internal mechanisms have been proposed for this internal amplification the dramatic continental ice sheet expansion that is recorded in the marine sediment record is an enduring mystery global sea level lowering of at least 20 m and as much as 75 m over 10 kyr appears typical of the early stages of glacial inception this rate of ice sheet growth has not been freely captured in either glaciologic or climatic models is it because we do not adequately understand the relevant internal feedbacks or fail to capture them in models is it simply related to technical model limitations e g topographic resolution this paper explores the premise that model resolution poses a critical limitation on simulations of ice sheet nucleation i present a series of ice sheet nucleation simulations in north america and eurasia based on an ice sheet model that includes parameterizations of km scale topographic detail snow ice accumulation and melt and glacier dynamics model climate is based on perturbations to modern observational climatology even with this topographic detail and with simulations long enough to allow ice to advect downslope and spread over the terrain it remains difficult to induce a large scale glacierization in both north america and eurasia severe climate perturbations are required cold temperatures need to be accompanied by substantial increases in precipitation in the north atlantic and polar regions in order to accrue continental ice at the rate demanded by sea level reconstructions the simulations presented here are too simple to separate climate perturbations from internal system feedbacks but with modern precipitation rates a combined climate cooling net positive feedback of more than 8 c is required to establish large scale ice sheets in

the loma prieta earthquake of october 18 1989 results of teleseismic mantle and body wave inversion we present the results of an analysis of teleseismic mantle and body wave data observed on digital very broad band stations for the loma prieta earthquake of 10 18 1989 both datasets yield consistent mechanisms with first motion and geodetic measurements an interesting result of the mantle wave analysis is the realization of a special relation of the geographical position of this event its source mechanism and the upper mantle degree 2 heterogeneity bodywave modelling indicates that the mechanism may be a double shock and could correspond to partitioning of the fault into thrust and strike slip motion the available teleseismic data in the appropriate distance range are unfortunately not sufficient to lead to firm conclusions on this point which should be tested by local observations

a continuous simulation of global ice volume over the past 1 million years with 3 d ice sheet models sea level records show large glacial interglacial changes over the past million years which on these time scales are related to changes of ice volume on land during the pleistocene sea level changes induced by ice volume are largely caused by the waxing and waning of the large ice sheets in the northern hemisphere however the individual contributions of ice in the northern and southern hemisphere are poorly constrained in this study for the first time a fully coupled system of four 3 d ice sheet models is used simulating glaciations on eurasia north america greenland and antarctica the ice sheet models use a combination of the shallow ice and shelf approximations to determine sheet shelf and sliding velocities the framework consists of an inverse forward modelling approach to derive a self consistent record of temperature and ice volume from deep sea benthic 18o data over the past 1 million years a proxy for ice volume and temperature it is shown that for both eustatic sea level and sea water 18o changes the eurasian and north american ice sheets are responsible for the largest part of the variability the combined contribution of the antarctic and greenland ice sheets is about 10 for sea level and about 20 for sea water 18o during glacial maxima however changes in interglacials are mainly caused by melt of the greenland and antarctic ice sheets with an average time lag of 4 kyr between melt and temperature furthermore we have tested the separate response to changes in temperature and sea level for each ice sheet indicating that ice volume can be significantly influenced by changes in eustatic sea level alone hence showing the importance of a simultaneous simulation of all four ice sheets this paper describes the first complete simulation of global ice volume variations over the late pleistocene with the possibility to model changes above and below present day ice volume constrained by observations of benthic 18o proxy data

effect of isostasy on dynamical ice sheet modeling a case study for eurasia 1 isostatic adjustment is an important process when modeling dynamical ice sheet evolution a number of different types of earth model are used to model this process ranging from models with local or elastic lithospheres with a single relaxation time to account for temporal behavior to self gravitating spherically symmetric models of the crust mantle system we performed sensitivity tests to assess the dynamical response of ice sheets to isostatic adjustment the resulting ice sheet geometries depend on the response times of the system including the growth rate of ice sheets versus the relaxation time of the earth differences in lithospheric strength cause large differences in the modeled ice sheets with the largest differences in isostatic adjustment in the vicinity of the ice margins in addition we compared predictions based on an often used flexural model with an elastic plate and a single relaxation time to a spherically symmetric self gravitating viscoelastic approach no flexural model was able to reproduce the viscoelastic response completely due to the fact that the models have an intrinsically different spatial and temporal response when applied to a full transient glacial cycle in eurasia even the best fitting flexural model underestimated the ice volume at the lgm by 30 percent our results indicate that the commonly used value of 3000 years for the relaxation time in flexural models is too short for eurasia by at least 3000 years

frozen bed fennoscandian and laurentide ice sheets during the last glacial maximum the areal extents of the laurentide and fennoscandian ice sheets during the last glacial maximum about 20 000 years ago are well known1 but thickness estimates range widely from high domed2 to thin3 with large implications for our reconstruction of the climate system regarding for example northern hemisphere atmospheric circulation and global sea levels this uncertainty stems from difficulties in determining the basal temperatures of the ice sheets and the shear strength of subglacial materials4 a knowledge of which would better constrain reconstructions of ice sheet thickness here we show that in the absence of direct data the occurrence of ribbed moraines in modern landscapes can be used to determine the former spatial distribution of frozen and thawed bed conditions we argue that ribbed moraines were formed by brittle fracture of subglacial sediments induced by the excessive stress at the boundary between frozen and thawed bed conditions resulting from the across boundary difference in basal ice velocity maps of glacial landforms from aerial photographs of canada and scandinavia reveal a concentration of ribbed moraines around the ice sheet retreat centres of quebec keewatin newfoundland and west central fennoscandia together with the evidence from relict landscapes that mark glacial areas with frozen bed conditions the distribution of ribbed moraines on both continents suggest that a large area of the laurentide and fennoscandian ice sheets was frozen based and therefore high domed and stable during the last glacial maximum

in the shadow of 1857 the effect of the great ft tejon earthquake on subsequent earthquakes in southern california the great 1857 fort tejon earthquake is the largest earthquake to have hit southern california during the historic period we investigated if seismicity patterns following 1857 could be due to static stress changes generated by the 1857 earthquake when post 1857 earthquakes with unknown focal mechanisms were assigned strike slip mechanisms with strike and rake determined by the nearest active fault 13 of the 13 southern california m 5 5 earthquakes between 1857 and 1907 were encouraged by the 1857 rupture when post 1857 earthquakes in the transverse ranges with unknown focal mechanisms were assigned reverse mechanisms and all other events were assumed strike slip 11 of the 13 earthquakes were encouraged by the 1857 earthquake these results show significant correlations between static stress changes and seismicity patterns the correlation disappears around 1907 suggesting that tectonic loading began to overwhelm the effect of the 1857 earthquake early in the 20th century

source characteristics of the loma prieta california earthquake of october 18 1989 from global digital seismic data displacement velocity and acceleration records of p and sh body waves recorded at teleseismic distances are analyzed to determine the static and dynamic source parameters of the loma prieta california earthquake of october 18 1989 m sub b 6 6 m sub s 7 1 three distinct bursts of energy corresponding to three subevents can be recognized in most records the displacement waveforms indicate that the first subevent contributes negligible moment while the largest releases of moment and energy are controlled by the second and third subevents the second and third subevents are located north and south of the initial nucleation a fourth small subevent needed to model later features of the p waveforms suggests that slow slip continued after the major releases of energy occurred the waveforms are fit with a fault plane solution having strike 130 degree dip 65 degree and slip 140 degree for all the subevents the focal depths of the two major subevents are 16 and 12 km and their asperity radii are 4 0 and 6 0 km respectively the seismic moment m sub o is 2 2 times 10 sup 26 dyne cm from spectral analysis of teleseismic velocity the radiated energy e sub s is estimated to be 1 1 times 10 sup 22 dyne cm implying an apparent stress of 15 bars more from the high frequency level of the teleseismic acceleration spectrum and a rupture area of 440 km sup 2 the authors derive a dynamic stress drop of 51 bars less

an estimate of global mean sea level rise inferred from tide gauge measurements using glacial isostatic models consistent with the relative sea level record this study is concerned with the influence of the glacial isostatic adjustment caused by the last pleistocene deglaciation on the present day sea level the viscoelastic deformation caused by the time variable ice and ocean loads is simulated by computing the resulting perturbations for a spherical self gravitating incompressible maxwell viscoelastic earth model the associated variation of the earth rotation is described in terms of the liouville equation which is solved by means of the maccullagh formulae this allows the determination of the vertical displacement and geoid height and thus the solution of the sea level equation we test several viscosity and ice models and evaluate them by comparison of the computed response with the holocene relative sea level record using the optimum combination of viscosity and ice models we then estimate the influence of the last pleistocene deglaciation on the tide gauge measurements a comparison between the observational and residual linear trends for the tide gauge measurements shows a significant reduction of the variance and geographical variability for the latter in particular for the formerly ice covered regions of north america and scandinavia the favoured value determined for the global mean sea level rise is 1 46 0 2 mm a 1

anisotropic models of the upper mantle long period rayleigh wave and love wave dispersion data particularly for oceanic areas have not been simultaneously satisfied by an isotropic structure in this paper available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy anelastic dispersion sphericity and gravity we assume that the surface wave data represents an azimuthal average of actual velocities thus we can treat the mantle as transversely isotropic the resulting models for average earth average ocean and oceanic regions divided according to the age of the ocean floor are quite different from previous results which ignore the above effects the models show a low velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies the correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggestive for most of the earth sh sv in the vicinity of the low velocity zone neat the east pacific rise however sv sh at depth consistent with ascending flow anisotropy is as important as temperature in causing radial and lateral variations in velocity the models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age this layer defines the lid or seismic lithosphere in the pacific the lid thickens with age to a maximum thickness of 50 km this thickness is comparable to the thickness of the elastic lithosphere the lid thickness is thinner than derived using isotropic or pseudo isotropic procedures a new model for average earth is obtained which includes a thin lid this model extends the fit of a prem type model to shorter period surface waves

initiation and development of the laurentide and cordilleran ice sheets following the last interglaciation abstract fossil records from sites overridden by or adjacent to the laurentide ice sheet indicate that the climate of the last interglaciation oxygen isotope substage 5e ca 130 116 ka was warmer than today following the last interglaciation the laurentide ice sheet first developed during stage 5 over keewatin quebec and baffin island along its northern margin the ice sheet reached its maximum extent of the last glaciation during stage 5 the ice sheet advanced across baffin island onto the continental shelf early during stage 5 5d whereas the advance into the western canadian arctic occurred late during stage 5 5b the ice sheet also may have advanced into the st lawrence lowland during substage 5b although this event may be younger stage 4 the hudson bay lowland became ice free during substage 5a retreat of the ice sheet on baffin island occurred during late stage 5 probably substage 5a the exact timing of retreat from the western canadian arctic is unknown but it occurred before 48 ka the southern sector including the st lawrence lowland was ice free during late stage 5 the hudson bay lowland may have remained ice free through stage 4 and much of stage 3 because of conflicting chronologies however it is more likely that this area was glaciated throughout stage 3 and perhaps stage 4 nevertheless the data demonstrate that the lowland was ice free during part of the last glaciation an independent ice cap developed over the appalachian uplands and advanced across nova scotia during stage 4 perhaps as far as the edge of the continental shelf the ice cap remained active over nova scotia as a setellite to the laurentide ice sheet throughout the remainder of the last glaciation the ice sheet advanced into the st lawrence lowland during stage 4 and subsequently overwhelmed the local ice cap in the appalachian uplands advancing perhaps into northern new england but not farther south the lowland remained covered by the ice sheet until late stage 2 the ice sheet may also have advanced into the lake ontario basin during stage 4 the position of the northern margin of the laurentide ice sheet during stage 4 is not known but it remained an unknown distance behind its maximum position reached during stage 5 cores from baffin bay indicate a substantial decrease in high latitude glaciation during stage 4 following retreat the keewatin sector of the ice sheet may have remained over much of northwestern canada as a quasi stable ice mass until it readvanced during stage 2 similarly the baffin island sector of the ice sheet may have remained largely intact the southern margin of the ice sheet may have advanced into the lake ontario basin and upper mississippi valley during the middle of stage 3 ca 50 ka reaching its maximum extent of the last glaciation during stage 2 ca 18 21 ka advance of the northern margin was younger ca 8 13 ka than that of the southern margin this advance was less extensive than the penultimate advance stage 5 paleoenvironmental records indicate that the last interglaciation in areas covered by and near the cordilleran ice sheet was as warm as or warmer than present the cordilleran ice sheet appears to have developed during stage 5 or 4 at that time it advanced over southern british columbia and into the northern puget lowland there is no record of this event in northern areas that were later covered by the ice sheet the ice sheet disappeared before 59 ka at the beginning of a lengthy nonglacial interval paleoenvironmental records indicate that climate was similar to the present during part of this interval the ice sheet was absent and glaciers probably were confined to mountain areas throughout stage 3 climatic deterioration marking the end of this nonglacial interval may have begun as early as 29 ka by 14 15 ka the ice sheet had achieved its maximum extent of the last glaciation because there are few suitable dating methods capable of resolving events beyond the radiocarbon limit and because sites that preserve a record of events from the last glaciation are spatially restricted we consider this synthesis as tentative and subject to significant revision as dating methods improve nevertheless this perspective of the north american ice sheets through the last glaciation demonstrates their complex and dynamic behavior and attendant rapid fluctuations in ice volume

long period surface wave inversion for source parameters of the 18 october 1989 loma prieta earthquake abstract we performed simultaneous seismic moment tensor inversions of long period 157 288 s fundamental mode rayleigh and love waves from the 1989 loma prieta earthquake to further constrain the source process of the event utilizing a two step spectral inversion technique we explored the model dependence and centroid location sensitivity of the long period surface wave analysis to assess the confidence bounds on the results we found that estimates of the source duration and depth are highly dependent on the choice of propagation attenuation and source velocity structure models including centroid location parameters in the inversion stabilizes moment tensor estimates but yields a biased location away from the epicenter due to model inaccuracies our source duration estimate is 11 5 s using a recent velocity model mpa with the centroid time of 6 s being significantly less than earlier surface wave studies centroids of 10 22 s and hence more compatible with both body wave and strong motion duration estimates an unconstrained moment tensor inversion at the optimum centroid location yields a stable major double couple solution strike 124 6 dip 67 6 rake 126 7 and a seismic moment estimate 3 0 0 2 1019 nm mw 6 9 similar to earlier long period studies and body wave and geodetic results the surface wave centroid depth estimate is 22 11 km which overlaps the body wave estimates 13 5 km thus surface wave source parameters for the loma prieta event allowing for plausible model dependence are fully compatible with body wave determinations and there is no evidence for any anomalous coseismic long period source process

terminating the 100 kyr ice age cycle we report a simulation of the most recent 100 000 year glaciationdeglaciation cycle of the late pleistocene ice age a simulation that delivers an ice sheet chronology that is in close accord with that inferred from the geological record our analyses are performed with a reduced model of the climate system that incorporates significant improvements to the representation of both climate forcing and mass balance response in a previously described theory based upon a coupled one level energy balance model ebm and vertically integrated ice sheet model ism the theory fully incorporates the influences of orbital insolation forcing glacial isostatic adjustment and variations in the atmospheric concentrations of greenhouse gases it correctly predicts the main geographical regions of the northern hemisphere that were glaciated at last glacial maximum 21 000 years ago as well as the abrupt termination of the glacial epoch that occurred subsequently the latter feature of the ice age cycle is obtained without the need to incorporate unconstrained and therefore controversial physical processes into the model a limitation of all previous attempts to understand this global scale climate cycle our analyses suggest that the radiative impact on surface glaciation due to the changing atmospheric concentration of co2 is critical to the ability of the model to deliver a synthetic history of glaciation and deglaciation that is in accord with inferences based upon surface geological and geomorphological evidence with the incorporation of this influence model predicted ice thickness distributions at last glacial maximum lgm are very similar to those of the recently described ice 4g reconstruction that was based upon the inversion of postglacial relative sea level histories

reconstructing the last irish ice sheet 1 changing flow geometries and ice flow dynamics deciphered from the glacial landform record the glacial geomorphological record provides an effective means to reconstruct former ice sheets at ice sheet scale in this paper we document our approach and methods for synthesising and interpre

ice sheet inception subgrid hypsometric parameterization of mass balance in an ice sheet model studies of ice sheet inception and mountain glaciation are limited by model resolution in both atmospheric and glaciologic models the accumulation and ablation of snow and ice are controlled by local climate which is sensitive to topographic features that are subgrid in continent scale investigations climate patterns are complex in areas of high relief but the first order influence of elevation on temperature and atmospheric humidity is quantifiable and is central to glacier mass balance we make substantial improvements to the descriptions of accumulation and ablation in a large scale ice sheet model by incorporating subgrid topographic information the distribution of relief in the large scale model is estimated through a hypsometric parameterization based on the minimum maximum and median topographic elevation this permits accounting of high elevation accumulation and melting in deep valleys we combine this with a parameterization of downslope subgrid ice flux simulating but not explicitly describing the role of alpine glaciers the detailed budgeting of mass balance greatly improves our skill in modelling present day ice distribution in north america we anticipate similar improvements in our ability to model nucleation centres of the quaternary ice sheets this approach may also prove useful in projections of glacier and ice field response to climate change

unraveling complex exposure burial histories of bedrock surfaces under ice sheets by integrating cosmogenic nuclide concentrations with climate proxy records the production accumulation and decay of cosmogenic radionuclides in rock surfaces subjected to episodes of exposure and burial by ice results in nuclide concentrations in present day rock surfaces that can be used to address a variety of questions in glacial geomorphology and quaternary geology of particular importance is the fact that these nuclide concentrations reflect both the timing of initial exposure of the rock surface and the chronology of subsequent exposure burial and erosion episodes for landscapes where geomorphic evidence indicates that little no erosion occurred constraining the timing of initial exposure and the number of phases of exposure and burial that a rock surface has been subjected to is possible using multiple cosmogenic radionuclide concentrations combined with proxies for the timing and duration of periods of ice cover such as ice core or marine isotope records however interpretations based on this approach require determination of an appropriate cutoff value to separate the proxy record into ice free and ice covered conditions and assessment of the sensitivity of the results to different cutoff values we have developed a numerical model to evaluate variations in total exposure and burial durations as a function of different proxy records and cutoff values this program is available at http www missouri edu liyk climateproxycurve zip initial results for sites in west antarctica and northern sweden show that the method provides a quick and robust way to derive best fit cutoff values and chronologies of burial and exposure and small changes in cutoff values can result in significant shifts in results the method described here provides new insight into the interpretation and reliability of multiple nuclide samples this approach also has the potential to provide improved constraints for ice sheet dynamics and landscape evolution and a means to assess the sensitivity of calculated initial exposure dates to assumptions about ice sheet history

broadband analysis of the 21 september 1993 klamath falls earthquake sequence the source characteristics of the klamath falls earthquake sequence were estimated from broadband seismograms recorded by the berkeley digital seismic network bdsn terrascope and western united states iris stations solutions were obtained for events ranging in size from mw 3 8 to mw 6 0 an empirical green s function inverse approach was used to estimate kinematic source parameters of the two mw 6 0 mainshocks both events were found to have ruptured northwest on adjacent segments of the lake of the woods system of normal faults the two main shocks abut where there is a pronounced 10 to 20 clockwise rotation of strike which may have initially acted as a barrier to a through going mw 6 2 event

dynamics of the north american ice sheet complex during its inception and build up to the last glacial maximum the north american ice sheet complex played a major role in global sea level fluctuations during the late quaternary but our knowledge of its dynamics is based mostly on its demise from the last glacial maximum lgm a period characterised by non linear behaviour in the form of punctuated ice margin recession episodic ice streaming and major shifts in the location of ice divides in comparison knowledge of the pre lgm ice complex is poorly constrained largely because of the fragmentary nature of the evidence relating to ice sheet build up in this paper we explore the inception and growth of ice 120 20 ka using a glacial systems model which has been calibrated against a large and diverse set of data relating to the deglacial interval we make use of calibration data prior to the lgm but its scarcity introduces greater uncertainty which is partly alleviated by our large ensemble analysis results suggest that following the last interglaciation oxygen isotope stage ois 5e the ice complex initiated over the north eastern canadian arctic and in the cordillera within a few thousand years it then underwent rapid growth to an ois 5 maximum at 110 ka 5d and covered 70 of the area occupied by the lgm ice cover although only 30 by volume an ois 5 minimum is modelled at 80 ka 5a before a second phase of rapid growth at the start of ois 4 which culminated in a large ice complex at 65 ka almost as large as at the lgm subsequent deglaciation was rapid maximum modelled sea level contribution of 16 cm per century and resulted in an ois 3 minimum between ca 55 60 ka thereafter the ice complex grew towards its lgm configuration interrupted by several phases of successively less significant mass loss our results support and extend previous inferences based on geological evidence and reinforce the notion of a highly dynamic pre lgm ice complex e g with episodes of 10 s m of eustatic sea level equivalent in 50 but even the thin ois 5 ice sheets exhibit fast flow features several 1000 m a 1 in major topographic troughs notwithstanding the severe limitations imposed by the use of the shallow ice approximation we note that most fast flow features generated prior to the lgm correspond to the location of known ice streams during deglaciation i e in major topographic troughs and over soft sediments at the southern and western margins moreover the modelled flux of these ice streams sensu lato appears to be non linearly scaled to ice sheet volume i e there is no evidence that decay phases were associated with significantly increased ice stream activity this hypothesis requires testing using a model with higher order physics and future modelling would also benefit from additional pre lgm constraints e g dated ice free margin positions to help reduce and quantify uncertainties

a three dimensional climate ice sheet model applied to the last glacial maximum a quasi three dimensional climate model sellers 1983 was used to simulate the climate of the last glacial maximum in order to provide climatic input forthe modelling of the northern hemisphere ice sheets the climate model is basically a coarse gridded gcm with simplified dynamics and was subject toappropriate boundary conditions for ice sheet elevation atmospheric co2 concentration and orbital parameters when compared with the present daysimulation the simulated climate at the last glacial maximum is characterized by a global annual cooling of 3 5deg c and a reduction in global annualprecipitation of 7 5 which agrees well with results from other more complex gcm s also the patterns of temperature change compare fairly with mostother gcm results except for a smaller cooling over the north atlantic and the larger cooling predicted for the summer rather than for the winter overeurasia the climate model is able to simulate changes in northern hemisphere tropospheric circulation yielding enhanced westerlies in the vicinity of thelaurentide and eurasian ice sheets however the simulated precipitation patterns are less convincing and show a distinct mean precipitation increase over thelaurentide ice sheet nevertheless when using the mean monthly fields of lgm minus present day anomalies of temperature and precipitation rate to drive athree dimensional thermomechanical ice sheet model it was demonstrated that within realistic bounds of the ice flow and mass balance parameters veryreasonable reconstructions of the last glacial maximum ice sheets could be obtained

paleoglaciological reconstructions for the tibetan plateau during the last glacial cycle evaluating numerical ice sheet simulations driven by gcm ensembles abstract the tibetan plateau is a topographic feature of extraordinary dimension and has an important impact on regional and global climate however the glacial history of the tibetan plateau is more poorly constrained than that of most other formerly glaciated regions such as in north america and eurasia on the basis of some field evidence it has been hypothesized that the tibetan plateau was covered by an ice sheet during the last glacial maximum lgm abundant field and chronological evidence for a predominance of local valley glaciation during the past 300 000 calendar years that is 300 ka coupled to an absence of glacial landforms and sediments in extensive areas of the plateau now refute this concept this furthermore calls into question previous ice sheet modeling attempts which generally arrive at ice volumes considerably larger than allowed for by field evidence surprisingly the robustness of such numerical ice sheet model results has not been widely queried despite potentially important climate ramifications we simulated the growth and decay of ice on the tibetan plateau during the last 125 ka in response to a large ensemble of climate forcings 90 members derived from global circulation models gcms using a similar 3d thermomechanical ice sheet model as employed in previous studies the numerical results include as extreme end members as an ice free tibetan plateau and a plateau scale ice sheet comparable in volume to the contemporary greenland ice sheet we further demonstrate that numerical simulations that acceptably conform to published reconstructions of quaternary ice extent on the tibetan plateau cannot be achieved with the employed stand alone ice sheet model when merely forced by paleoclimates derived from currently available gcms progress is however expected if future investigations employ ice sheet models with higher resolution bidirectional ice sheet atmosphere feedbacks improved treatment of the surface mass balance and regional climate data and climate reconstructions

a 3 d model for the antarctic ice sheet a sensitivity study on the glacial interglacial contrast on the longer climatic time scales changes in the elevation and extent of the antarctic ice sheet have an important role in modulating global atmospheric and oceanographic processes and contribute significantly to world wide sea levels in this paper a 3 d time dependent thermomechanical model for the entire ice sheet is presented that is subsequently used to examine the effects of glacial interglacial shifts in environmental boundary conditions on its geometry the model takes into account a coupled ice shelf grounding line dynamics basal sliding and isostatic bed adjustment and considers the fully coupled velocity and temperature fields ice flow is calculated on a fine mesh 40 km horizontal grid size and 10 layers in the vertical for grounded and floating ice and a stress transition zone in between at the grounding line where all stress components contribute in the effective stress in the flow law there is free interaction between ice sheet and ice shelf so that the entire geometry is internally generated a simulation of the present ice sheet reveals that the model is able to yield realistic results a series of sensitivity experiments are then performed in which lower temperatures reduced accumulation rates and lower global sea level stands are imposed either singly or in combination by comparing results of pairs of experiments the effects of each of these environmental changes can be determined in agreement with glacial geological evidence we found that the most pronounced changes show up in the west antarctic ice sheet configuration they appear to be essentially controlled by variations in eustatic sea level whereas typical glacial interglacial changes in temperature and ice deposition rates tend to balance one another these findings support the hypothesis that the antarctic ice sheet basically follows glacial episodes in the northern hemisphere by means of sea level teleconnections grounding occurs more readily in the weddell sea than in the ross sea and long time scales appear to be involved it may take up to 30 40000 years for these continental shelf areas to become completely grounded after an initial stepwise perturbation in boundary conditions according to these reconstructions a steady state antarctic ice sheet may contribute some 16 m to global sea level lowering at maximum glaciation

a comparison of different ways of dealing with isostasy examples from modelling the antarctic ice sheet during the last glacial cycle the bedrock isostatic response exerts a strong control on ice sheet dynamics and is therefore always taken into account in ice sheet models this paperreviews the various methods normally used in the ice sheet modeling community to deal with the bedrock response and compares these with a moresophisticated full earth model each of these bedrock treatments five in total are coupled with a three dimensional thermomechanical ice sheet model underthe same forcing conditions to simulate the antarctic ice sheet during the last glacial cycle the outputs of the simulations are compared on the basis of thetime dependent behavior for the total ice volume and the mean bedrock elevation during the cycle and of the present rate of uplift over antarctica thiscomparison confirms the necessity of accounting for the elastic bending of the lithosphere in order to yield realistic bedrock patterns it furthermoredemonstrates the deficiencies inherent to the diffusion equation in modeling the complex deformation within the mantle nevertheless when characteristicparameters are varied within their range of uncertainty differences within one single method are often of the same order as those between the variousmethods this overview finally tries to point out the main advantages and drawbacks of each of these methods and to determine which one is mostappropriate depending on the specific modeling requirements

the importance of thermodynamics for modeling the volume of the greenland ice sheet two different kinds of ice flow models one two dimensional 2 d and the other three dimensional 3 d have been used to test the importance of the thermodynamic response of the greenland ice sheet the basic difference between the two models is that the thermodynamics are neglected in the two dimensional model whereas these are incorporated in the three dimensional model the 2 d and 3 d models are compared in terms of volume response time and total volume of the ice sheet results indicate that the sawtooth character of the ice volume on glacial interglacial timescales is among other possible reasons a result of the thermodynamic coupling the changes in elevation over the last 130 000 years calculated with the three dimensional version are 230 m for the summit drill site and 190 m for the n grip site the standard deviation of the changes in elevation is 55 m for the summit site and 43 m for the n grip site the present day imbalance is merely a result of the rather constant climate over the last 10 kyr and is not determined by the thermodynamics consequently pleistocene temperatures do still exist in the ice sheet but are not important for volume calculations of the present day ice sheet for short term perturbation experiments in the future the pronounced sensitivity of the mass balance will determine the response of the greenland ice sheet whereas thermodynamics will play only a minor role

greenland s contribution to global sea level rise by the end of the 21st century the greenland ice sheet holds enough water to raise the global sea level with 7 m over the last few decades observations manifest a substantial increase of the mass loss of this ice sheet both enhanced melting and increase of the dynamical discharge associated with calving at the outlet glacier fronts are contributing to the mass imbalance using a dynamical and thermodynamical ice sheet model and taking into account speed up of outlet glaciers we estimate greenland s contribution to the 21st century global sea level rise and the uncertainty of this estimate boundary fields of temperature and precipitation extracted from coupled climate model projections used for the ipcc fourth assessment report are applied to the ice sheet model we implement a simple parameterization for increased flow of outlet glaciers which decreases the bias of the modeled present day surface height it also allows for taking into account the observed recent increase in dynamical discharge and it can be used for future projections associated with outlet glacier speed up greenland contributes 0 17 cm to global sea level rise by the end of the 21st century this range includes the uncertainties in climate model projections the uncertainty associated with scenarios of greenhouse gas emissions as well as the uncertainties in future outlet glacier discharge in addition the range takes into account the uncertainty of the ice sheet model and its boundary fields

late quaternary glaciations in far ne russia combining moraines topography and chronology to assess regional and global glaciation synchrony during various periods of late quaternary glaciation small ice sheets caps fields and valley glaciers occupied the mountains and uplands of far ne russia including the verkhoyansk suntar khayata and chersky mountains the kolyma anyuy and koryak highlands and much of the kamchatka and chukchi peninsulas here the margins of former glaciers across this region are constrained through the comprehensive mapping of moraines from remote sensing data landsat 7 etm satellite images aster global digital elevation model gdem2 and viewfinder panorama dem data a total of 8414 moraines are mapped and this record is integrated with a series of published age estimates n 25 considered to chronologically constrain former ice margin positions geomorphological and chronological data are compiled in a geographic information system gis to produce best estimate reconstructions of ice extent during the global last glacial maximum glgm and to a lesser degree during earlier phases of glaciation the data reveal that much of far ne russia 1 092 427 km 2 preserves a glaciated landscape i e is bounded by moraines but there is no evidence of former ice masses having extended more than 270 km beyond mountain centres suggesting that during the late quaternary the region has not been occupied by extensive ice sheets during the glgm specifically glaciers occupied 253 000 km 2 and rarely extended more than 50 km in length during earlier pre glgm periods glaciers were more extensive though the timing of former glaciation and the maximum quaternary extent appears to have been asynchronous across the region and out of phase with ice extent maxima elsewhere in the northern hemisphere this glacial history is partly explained through consideration of climatic forcing particularly moisture availability solar insolation and albedo though topographic controls upon the former extent and dynamics of glaciers are also considered as are topographic controls upon moraine deposition and preservation ultimately our ability to understand the glacial and climatic history of this region is restricted when the geomorphological record alone is considered particularly as directly dated glacial deposits are few and topographic and climatic controls upon the moraine record are difficult to distinguish 2012 elsevier ltd