identification of cyclone track regimes in the north atlantic a langrangian type climatology of north atlantic cyclones is established based on the high resolution european centre for medium range weather forecasts data set of the 1000 hpa height field first an algorithm is introduced to identify mid latitude cyclones and cyclone paths with as few constraints as possible cluster analysis of relative cyclone displacements yields three types of cyclone tracks characterizing stationary north eastward and zonally travelling storms the internal lagrangian statistics of these cyclone track types reveal representative life cycles for central pressure and geopotential height gradients and a power law scaling behaviour of cyclone displacements finally a basic climatology of north atlantic cyclone track regimes is deduced in terms of a time series and circulation statistics

searching for eustasy in deglacial sea level histories abstract perturbations to the earth s gravity field and solid surface associated with glacial isostatic adjustment gia cause the total observable sea level change to depart from the eustatic curve which is defined as a spatially uniform height shift of the ocean surface to accommodate any mass gained lost from grounded ice in this study we apply a state of the art model of gia induced sea level change to quantify the magnitude and spatial form of this departure at the global scale for a range of model parameters with an aim to identify regions that are well suited to obtain accurate and precise estimates of eustatic sea level and therefore past grounded ice volume in general our results indicate that eustatic sea level is not a directly measurable quantity and so must be estimated by subtracting a model derived estimate of non eustatic contributions from observations in this regard we use our results to isolate regions where this procedure can be applied with optimal accuracy and precision that is where 1 the gia predictions are relatively insensitive to plausible ranges in input parameters and 2 where the non eustatic contribution is small i e the predicted sea level closely approximates the eustatic value we present maps that can be employed by the field community to identify areas where sea level reconstructions would be well suited to arrive at robust estimates of eustatic sea level note that sea level changes associated with tectonic motion and changes in ocean water temperature salinity which also lead to departures from eustasy are not considered in this analysis

causes of reduced north atlantic storm activity in a cam3 simulation of the last glacial maximum abstract the aim of this paper is to determine how an atmosphere with enhanced mean state baroclinity can support weaker baroclinic wave activity than an atmosphere with weak mean state baroclinity as a case study a last glacial maximum lgm model simulation previously documented to have reduced baroclinic storm activity relative to the modern day climate simulated by the same model despite having an enhanced midlatitude temperature gradient is considered several candidate mechanisms are evaluated to explain this apparent paradox a linear stability analysis is first performed on the jet in the modern day and the lgm simulation the latter has relatively strong barotropic velocity shear it was found that the lgm mean state is more unstable to baroclinic disturbances than the modern day mean state although the three dimensional jet structure does stabilize the lgm jet relative to the eady growth rate next feature tracking was used to assess the storm track seeding and temporal growth of distur

relationship between cyclone tracks anticyclone tracks and baroclinic waveguides abstract this study presents observational results concerning the structure and evolution of high frequency fluctuations with periods shorter than 6 days in the geopotential height field the results are based on a statistical analysis of 1000 500 and 250 mb height fields derived from twice daily nmc final analyses over the northern hemisphere for the 20 winters 1964 65 through 1983 84 the disturbances assume the form of waves elongated in the meridional direction with a mean wavelength of 4000 km a westward tilt with height and a mean eastward phase propagation of 12 1 5 m s 1 these results support an interpretation in terms of finite amplitude baroclinic waves whose structure and evolution varies with geographical location over the continents and especially along the eastern slopes of the rockies and the tibetan plateau the waves show marked departures in structure and evolution from those over the oceans in particular we find evidence of a systematic influence of the terrain in steering the

variations of northern hemisphere storm track and extratropical cyclone activity associated with the madden julian oscillation abstractthis study investigates the intraseasonal variations of the northern hemispheric storm track associated with the madden julian oscillation mjo during the extended boreal winter november april using 36 yr 1979 2014 of reanalysis data from era interim two methods have been used to diagnose storm track variations in the first method the storm track is quantified by the temporal filtered variance of 250 hpa meridional wind vv250 or mean sea level pressure pp the intraseasonal anomalies of vv250 composited for eight mjo phases are characterized by a zonal band of strong positive or negative anomalies meandering from the pacific all the way across north america and the atlantic into northern europe with weaker anomalies of opposite sign at one or both flanks the results based on pp are consistent with those based on vv250 except for larger zonal variations which may be induced by surface topography in the second method an objective cyclone tracking scheme has been used to track the

a complete formalism for the inversion of post glacial rebound data resolving power analysis summary a formal inverse theory for mantle viscosity based upon the data of glacial isostatic adjustment is here formulated and applied to synthetic data in this theory full account has been taken of the normal mode nature of the forward problem for realistic viscoelastic maxwell models of the planet since it is impossible to accurately infer the excitation and decay constants of the individual normal modes from the observations the formalism is cast in terms of the observed gross earth data in the time domain in this analysis expressions are required for the first order perturbations in both the modal amplitudes and relaxation times that are induced by an arbitrary radial perturbation to the starting viscosity profile a numerical technique is developed which enables us to accurately determine differential kernels for the modal amplitudes the analogous kernels for the modal decay times are derived analytically peltier 1976 and the complete set of kernels is shown to satisfy the physical constraint imposed by the uniqueness of the state of isostatic equilibrium for the viscously incompressible maxwell models that we employ when the problem is parametrized in terms of the logarithm of viscosity the kernels are capable of accurately predicting shifts in the normal mode characteristics for at least an order of magnitude variation in mantle viscosity using bayesian statistics a formal inversion is applied to a set of synthetically generated data these data chosen to reproduce the space time coverage of the actual observables include a subset related to the global gravity field and a large sequence of idealized relative sea level rsl curves it is found that even very weak a priori constraints can provide a stable and accurate inversion a resolving power analysis indicates a spatial resolution of approximately 1200km near the core mantle boundary cmb with a gradual improvement to better than 350km in the middle of the upper mantle subsets of the synthetic data are inverted in order to examine conditions on stability and accuracy and to determine their relative contributions to the spatial resolution data from progressively older beaches are shown to contribute most to the spatial resolution at all depths though the improvement in lower mantle resolution converges for data obtained from beaches formed within the last 5000 yr furthermore the rsl curves in the vicinity of the peripheral bulge of the ancient laurentide ice sheet are significant contributors to lower mantle resolution as demonstrated in previous analyses of the forward problem the inversion of this subset of the data also appears to be encouragingly stable

ice 5g and ice 6g models of postglacial relative sea level history applied to the holocene coral reef record of northeastern st croix u s v i investigating the influence of rotational feedback on gia processes at tropical latitudes abstract fossil coral reefs along the northeastern coast of st croix in the caribbean sea provide an 8000 year record of dated and interpreted holocene sea level change we herein compare this record with the predictions of models of glacio hydro isostatic adjustment for st croix and for additional sites at similar latitudes in the greater and lesser antilles region rsl predictions are based upon the model ice 5g vm2 and with a modified model ice 6g vm5a both including and excluding the influence of rotational feedback misfits between the modeled sea levels and the local geologic data are most apparent for models without rotational feedback particularly in the prediction of a 2 to 4 m unsupported mid holocene misfit at 4 ka as well as a small amplitude highstand that extends from 2 5 to 1 5 ka incorporation of the influence of rotational feedback provides the best fit to the data largely eliminating the unsupported mid holocene misfit between the data field and the sea level histories predicted by the models without rotational feedback and fitting data older than 5 kyr more closely than a previously published latitudinally averaged sea level curve for the western atlantic the st croix data therefore demonstrate that rotational influence extends at least 27 further south from its 45 n mid latitude extremum along the us east coast and identifies tropical latitudes as influenced by proglacial forebulge collapse implications for reef based sea level reconstruction include the ability to accurately model sea levels at specific tropical sites with partial holocene chronologies using the ice 6g vm5a model with rotational feedback latitudinally averaged sea level curves are therefore of limited use in understanding the relative importance of contributing physical influences on postglacial sea level history

the dynamical equations of polar wander and the global characteristics of the lithosphere as extracted from rotational data abstract the initial value problem describing the linear responses of the spin axis of a layered viscoelastic planet from surface loading is studied by means of laplace transform techniques a complete solution of polar motion requires the usage of two classes of eigenspectra one arising from viscoelastic relaxation of the mantle due to surface forcing the other involving the gradual readjustment of the spin axis as a consequence of mantle viscoelasticity our analytical 4 layer model comprising an elastic lithosphere a two layer adiabatically stratified viscoelastic mantle and an inviscid core has been incorporated into this formalism in which rotational deformation and isostatic relaxation are taken into account for all times from employing both sets of rotational data polar variations from the 70 years of data from the international latitude service i l s and the non tidal deceleration of the length of the day l o d an estimate of the globally averaged lithosphere of between 130 and 200 km is obtained from the long wavelength flexural mode due to the degree two harmonic this range of values may have strong implications on the mode of continental evolution

lateral variations in mantle rheology implications for convection related surface observables and inferred viscosity models summary over the past decade numerous analyses of convection related observables such as horizontal surface divergence geoid or gravity anomalies and dynamic surface topography have been carried out in the context of tomography based mantle flow models one of the major objectives of this modelling has been the inference of the rheological structure of the mantle with few exceptions these studies have been conducted in the framework of a viscous flow theory which assumes that the mantle rheology may be represented in terms of an effective viscosity which varies with depth only here we present a detailed assessment of the impact of lateral variations in viscosity on global convection related observables using forward modelling of buoyancy induced flow in a 3 d spherical shell we find that the resulting dynamic topography at the surface and the core mantle boundary as well as the gravitational response of the earth are affected relatively little by the inclusion of lateral viscosity variations lvv when compared with results for a purely 1 d radial viscosity model in particular we found that the effect of lvv on the global observables is significantly smaller than the variability due to uncertainties in the current seismic tomography models we also quantify the effect of lvv in the context of the viscosity inverse problem using two synthetic data sets generated with a 1 d viscosity profile and with a fully 3 d viscosity model in which the lvv span across three orders of magnitude we compared the 1 d viscosity profiles recovered from the inversions and found that lvv have virtually no effect on our inversion results the synthetic viscosity inversion further revealed that the effect of lvv is small in comparison to the uncertainties arising from the seismic tomography models the inversions also suggest that the 1 d viscosity profiles derived from actual surface data represent the depth variation of the horizontally averaged logarithm of the 3 d viscosity distribution in the mantle intr o duction constraining the rheological properties of the mantle using surface geophysical data has traditionally involved separate treatments of short seismic intermediate solid earth tides long postglacial rebound and very long mantle convection timescale processes in each case the initial focus historically speaking has been on the inversion of the data to determine a one dimensional 1 d purely radial variation of the relevant rheological parameter e g elastic moduli intrinsic attenuation and viscosity which provides the best fit to the data it has long been recognized particularly in the context of the seismic inverse problem that the search for a 1 d earth model is subject to possible bias due to the presence of lateral variations in structure which may be as significant as the radial variations especially at shallow depths this paper is concerned with the mantle viscosity field the earliest inferences of the radial i e horizontally averaged profile of viscosity based on glacial isostatic adjustment gia data e g mcconnell 1968 parsons 1972 were characterized by a pronounced increase of viscosity with depth in the top half of the mantle however these were followed by two decades of gia research that argued for an essentially isoviscous

a new perspective on southern hemisphere storm tracks abstract a detailed view of southern hemisphere storm tracks is obtained based on the application of filtered variance and modern feature tracking techniques to a wide range of 45 yr european centre for medium range weather forecasts ecmwf re analysis era 40 data it has been checked that the conclusions drawn in this study are valid even if data from only the satellite era are used the emphasis of the paper is on the winter season but results for the four seasons are also discussed both upper and lower tropospheric fields are used the tracking analysis focuses on systems that last longer than 2 days and are mobile move more than 1000 km many of the results support previous ideas about the storm tracks but some new insights are also obtained in the summer there is a rather circular strong deep high latitude storm track in winter the high latitude storm track is more asymmetric with a spiral from the atlantic and indian oceans in toward antarctica and a subtropical jet related lower latitu

thermal history of the earth a corollary concerning non linear mantle rheology abstract mantle rheology and the convective cooling process exert a close mutual control on one another so that the cooling rate can be calculated with only a rudimentary idea of the material properties of the mantle however the distinction between linear i e newtonian viscous behaviour and non linear or power law rheology in which the creep rate depends upon stress as n with n 1 it isportant we find that the present rate of loss of residual heat is almost twice as great with n 3 as it si tn the linear case n 1 since this net heat loss is simply the difference between the observed total mantle heat flux and the radiogenic heat input the radioactive content of the mantle is predicted to be substantially less in the non linear case an examination of the plausible ranges of the u th and k contents of the mantle shows that the requirement for radiogenic heat by the linear model us unreasonably high this observation strengthens an earlier very tentative conclusion based on temperatures of komatiite lavas that convective mantle rheology is non linear the alternative conclusion would be that the earth contains 30 ppb of u compared with carbonaceous chondrites 20 ppb or ordinary chondrites 15 ppb

investigations of fennoscandian glacial isostatic adjustment using modern sea level records we present a new method for determining the rates from a network of regional tide gauge data the method involves using a model for the sea level observations annual averages of relative sea level that explicitly includes a term for the interannual sealevel variations which are assumed to be constant for all sites in the network the resulting simultaneous analysis of all the sea level observations yields sea level rates which are biased by the unknown temporal slope of the interannual variations by differencing sea level rate estimates with respect to one site site referenced sea level rates are calculated which are free from this bias the differencing procedure also removes any signal due to a common sea level rate such as might be associated with eustatic sea level rise the resulting site referenced sea level rates therefore in principle reflect only the relative vertical crustal motions of the tide gauge sites with respect to the geoid these site referenced sea level rates represent a potentially more accurate data set than have previously been used for sea level studies we have used these rates to investigate glacial isostatic adjustment gia in fennoscandia specifically we have used the site referenced sea level rates within the baltic sea to estimate adjustments to the ice history and earth model which are used to calculate vertical rates of adjustment due to gia a method never before used for fennoscandia the parameters selected were lithospheric thickness the viscosities of assumed isoviscous upper and lower mantles and a fennoscandian ice thickness scaling parameter we present the results of this estimation procedure for a specific test ice model we also find evidence that the sea level record for the site nearest the center of uplift furuogrund may be contaminated by systematic errors of unknown origin data from this site have previously been used to determine a rate for the maximum uplift that we find is perhaps 1 mm yr 1 or 10 too large

time dependent deformation and stress relaxation after strike slip earthquakes the quasi static time dependent behavior after strike slip earthquakes is studied using three dimensional finite element models the effects of lateral heterogeneities finite fault and nonuniform fault slip are included models of a great earthquake and a medium size earthquake are constructed using a set of possible viscosity structures deformation change after an earthquake is found to be sensitive to the viscosity structure located beneath the fault zone the presence of low viscosity beneath the fault concentrates the horizontal displacement near the fault zone and completely changes the character of vertical deformation thus leveling in addition to horizontal geodetic measurements after a strike slip event is important in determining the viscosity structure near fault zones the shear stress in front of the fault tip increases significantly within several decades after the event for models with a shallow low viscosity zone beneath the fault this accelerated stress accumulation is consistent with the observed phenomenon of earthquake migration along the north anatolian fault zone

global glacial isostatic adjustment palaeogeodetic and space geodetic tests of the ice 4g vm2 model analyses of the global process of glacial isostatic adjustment and post glacial relative sea level change continue to deliver important insights into earth system form and process one successful model of the related phenomenology is based upon a spherically symmetric internal viscoelastic structure for the solid earth which has been denoted vm2 and a model of the most recent deglaciation event of the current ice age denoted ice 4g the primary purpose of this paper is to describe several new a posteriori tests that have recently been performed to further investigate the quality of this global solution to the inverse problem for both mantle viscosity and deglaciation history that is posed by the observables associated with this large scale geodynamic phenomenon i focus especially upon the misfits of observations to the theoretical predictions of this model which i am currently using to further refine its properties and upon predictions made using it of geophysical signals that should soon become visible in the context of the gravity recovery and climate experiment grace satellite mission among the required refinements to ice 4g one that is necessary to eliminate a recently revealed misfit to space geodetic constraints on the present day rate of radial motion at the yellowknife location well to the west of hudson bay and a similar misfit to absolute gravity measurements to the southwest of the bay is the insertion of a keewatin dome of thick ice centred over yellowknife with a ridge of ice extending to the south east in the geomorphological literature the existence of such a keewatin dome previously has been hypothesised but chronological control was lacking on the surface features that suggested its former existence an important additional constraint that requires the late glacial existence of this important feature consists of new inferences of the last glacial maximum lowstand of the sea from sites in the far field of the main concentrations of land ice copyright 2002 john wiley sons ltd

the melting history of the late pleistocene antarctic ice sheet spatial and temporal variations in the sea levels of the past 20 000 years around the globe place constraints on the melting history of the major late pleistocene ice sheets the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9 000 6 000 years ago when it may have lagged behind minor melting of the antarctic ice sheet continued throughout the holocene

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

a simple kinematic source of skewness in atmospheric flow fields abstractgeopotential height fields exhibit a well known pattern of skewness with distributions that are positively skewed on the poleward side of the midlatitude jets storm tracks and negatively skewed on the equatorward side this pattern has often been interpreted as a signature of nonlinear dynamical features such as blocking highs and cutoff lows and there is renewed interest in the higher moments of flow variables as indicators of the nature of the underlying dynamics however this paper suggests that skewness can arise as a simple kinematic consequence of the presence of jet streams and so may not be a reliable indicator of nonlinear dynamical behavior in support of this reanalysis data are analyzed to demonstrate a close link between the jet streams and the skewness patterns further evidence is provided by a simple stochastic kinematic model of a jet stream as a gaussian wind profile the parameters of this model are fitted to data from the reanalysis and also from an aquaplanet general circ

late pleistocene and holocene sea level change along the australian coast abstract tectonically the australian continent is relatively stable and as such it provides a good platform for studying late pleistocene and holocene sea level change the observations indicate that present sea level was reached at about 6000 years ago and that since then level has remained constant to within a few metres considerable spatial variability in the amplitude of the emergence and in the time at which sea levels first reached their present values have been observed spatial variability has also been observed in the sea level during the last glacial maximum and during the late phase of the holocene transgression much of this variaiblity is the result of the earth s adjustment to the glacial melting in the late pleistocene early holocene time and the concomitant distribution of this meltwater into the oceans conclusions that are drawn from matching observations with this glacio hydro isostatic model include the following 1 the mantle viscosity increases with depth the average upper mantle viscosity is about 2 3 10 20 pa s and the average lower mantle defined as below 670 km depth viscosity is about 10 22 pa s the average lithospheric thickness for the coastal and offshore region is about 70 80 km lateral variations in these mantle parameters are indicated 2 the addition of melwater into the oceans did not cease 6000 years ago but continued at a reduced rate up to more recent times adding an amount of water equivalent to a 3 m sea level rise in this interval 3 the amplitude of the holocene emergence is a function inter alia of coastal geometry and significant variations occur over distances of a few hundred kilometres and more holocene highstands of 1 2 m are generally well developed at the continental margins but are less well developed or do not developed at all at offshore islands and reefs 4 variations in the time of maximum emergence also occur being earlier at upstream tidal river sites than at coastal sites at offshore reefs or islands the sea level curve lags the coastal curves by 1000 years or more 5 considerable spatial variability occurs in the sea levels at the time of the last glacial maximum with variations of up to 30 m occurring across the continental shelves 6 there is generally no need to invoke tectonic movements to explain the sea level data along the australian coast but possible exceptions occur for the perth region and for tasmania

the impact of variability in the rheological activation parameters on lower mantle viscosity stratification and its dynamics the recently discovered spin state crossover in iron in major mantle minerals at high pressures should exert dramatic influences on transport properties such as the activation creep parameters in the deep mantle wentzcovitch et al 2009 have computed the elastic parameter of ferropericlase that is affected by this crossover the bulk modulus at high realistic conditions using first principles density functional theory plus hubbard u as a consequence of the spin crossover there is a significant softening of the bulk modulus and an attendant reduction of the activation energy in the creep law using a parameterized model capturing the basic physics we have studied the dynamical consequences within the framework of a 2 d cartesian convection model our models reveal a series of asthenospheres and are characterized first by a low viscosity channel below the 670 km boundary second asthenosphere caused by an increase of temperature and decrease in grain size reduction superplascity with the post spinel transition which results in partially layered convection further the variability of the rheological parameters leads to the prevalent formation of viscosity minimum at a depth of about 1600 km third asthenosphere caused by spin crossovers followed by a viscosity hill in the bottom half of the lower mantle the latter due to the increase of the activation energy in some low spin irons at the bottom of the mantle our numerical simulations reveal a tendency to the formation of small scale convection below the 670 km boundary and bigger stabilized plumes and or plume clustering in the deep lower mantle other material properties at the bottom of the mantle decrease of thermal expansivity radiative thermal conductivity also exert significant influence on the multi scale lower mantle plume dynamics

tidal modulation of nonvolcanic tremor episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of japan and cascadia in cascadia such episodes typically last a few weeks and differ from normal earthquakes in their source location and moment duration scaling the three most recent episodes in the puget sound southern vancouver island portion of the cascadia subduction zone were exceptionally well recorded in each episode we saw clear pulsing of tremor activity with periods of 12 4 and 24 to 25 hours the same as the principal lunar and lunisolar tides this indicates that the small stresses associated with the solid earth and ocean tides influence the genesis of tremor much more effectively than they do the genesis of normal earthquakes because the lithostatic stresses are 10 5 times larger than those associated with the tides we argue that tremor occurs on very weak faults

horizontal structure of 500 mb height fluctuations with long intermediate and short time scales abstract maps of standard deviations and one point correlation maps based on twice daily data subjected to a variety of temporal filters are presented in order to document the horizontal structure of 500 mb height fluctuations with different time scales the filters have been chosen to isolate fluctuations with long time scales periods much longer than 30 days intermediate time scales 10 30 day periods and short time scales 2 5 6 day periods the one point correlation maps for long time scales resemble the teleconnection patterns described by wallace and cutzler these patterns are strongly regionally dependent with meridionally oriented dipole structures in the jet exit regions over the oceans indicative of strong fluctuations in the zonal wind for intermediate time scales the dominant patterns consist of more zonally oriented wave trains which originate in the jet entrance regions and cross the jet streams as they curve southeastward into the tropics another important distinction between th

surface cyclones in the era 40 dataset 1958 2001 part i novel identification method and global climatology abstract a novel method is introduced to generate climatological frequency distributions of meteorological features from gridded datasets the method is used here to derive a climatology of extratropical cyclones from sea level pressure slp fields a simple and classical conception of cyclones is adopted where a cyclone is identified as the finite area that surrounds a local slp minimum and is enclosed by the outermost closed slp contour this cyclone identification procedure can be applied to individual time instants and climatologies of cyclone frequency fc are obtained by simple time averaging therefore unlike most other climatologies the method is not based on the application of a tracking algorithm and considers the size of cyclones in combination with a conventional cyclone center tracking algorithm that allows the determination of cyclone life times and the location of cyclogenesis and cyclolysis additional frequency fields can be obtained for special categories of cyclones that are gener

last glacial maximum and holocene climate in ccsm3 abstract the climate sensitivity of the community climate system model version 3 ccsm3 is studied for two past climate forcings the last glacial maximum lgm and the mid holocene the lgm approximately 21 000 yr ago is a glacial period with large changes in the greenhouse gases sea level and ice sheets the mid holocene approximately 6000 yr ago occurred during the current interglacial with primary changes in the seasonal solar irradiance the lgm ccsm3 simulation has a global cooling of 4 5 c compared to preindustrial pi conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at lgm tropical sea surface temperature sst cools by 1 7 c and tropical land temperature cools by 2 6 c on average simulations with the ccsm3 slab ocean model suggest that about half of the global cooling is explained by the reduced lgm concentration of atmospheric co2 50 of present day concentrations there is an increase in the antarctic circumpolar current an

constraints on the greenland ice sheet since the last glacial maximum from sea level observations and glacial rebound models abstract geomorphological descriptions of changes in the extent of the greenland ice sheet gis have been combined with glacial isostatic adjustment models to reproduce the sea level history of greenland since the last glacial maximum lgm the contribution to past sea level change around greenland due to ice load changes outside of that region has been considerable 10 s of meters while still contributing a rise of several mm yr 1 today the isostatic contribution to relative sea level around greenland from changes in the gis is found by iteratively perturbing preliminary ice models with different lgm extents and deglaciation starting times the resulting first order model that provides the best agreement between observed and predicted sea level contributes 3 1 and 1 9 m water equivalent of additional ice relative to present day ice volumes at the lgm and younger dryas respectively the gis in most areas does not appear to have extended far onto the continental shelf the exceptions being southern most southwest greenland and northern east greenland as well as at the coalescence of the northwest greenland and innuitian ice sheets changes in ice thickness since the lgm were 500 m along the present day outer coast and 1500 m along some parts of the present day ice margin the observed mid to late holocene fall in sea level to below the present day level and the subsequent transgression seen in some areas implies that the gis retreated behind the present day margin by distances of the order of 40 km before readvancing

on postglacial sea level iii incorporating sediment redistribution we derive a generalized theory for gravitationally self consistent static sea level variations on earth models of arbitrary complexity that takes into account the redistribution of sediments the theory is an extension of previous work that incorporated into the governing equations shoreline migration due to local sea level variations and changes in the geometry of grounded marine based ice in addition we use viscoelastic love number theory to present a version of the new theory valid for spherically symmetric earth models the love number theory accounts for the gravitational deformational and rotational effects of the sediment redistribution as a first illustrative application of the new theory we compute the perturbation in sea level driven by an idealized pulse of sediment transport into the gulf of mexico we demonstrate that incorporating a gravitationally self consistent water load in this case significantly improves the accuracy of sea level predictions relative to previous simplified treatments of the sediment redistribution

glacio seismotectonics ice sheets crustal deformation and seismicity abstract the last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity this growth has been driven largely by the emergence of postglacial rebound models pgm constrained by new field observations that incorporate increasingly realistic rheological mechanical and glacial parameters in this paper we highlight some of these recent field based investigations and new pgms and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation the emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern canada and fennoscandia however many of these models neglect important parameters such as topography lateral variations in lithospheric strength and tectonic strain built up during glaciation in glaciated mountainous terrains glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields in general the short term response to ice fluctuations is similar to the earth s response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre existing stress state when the ice fluctuations occur on the spatial scale and magnitude of the late pleistocene glaciation and deglaciation however the viscoelastic response of the earth especially the mantle causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex the regions of greatest ice thickness and the regions marginal to the late pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting the mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused and continues to cause measureable crustal deformation at hundreds of kilometres from the ice margins for both tectonically active and cratonic regions palaeoseismic investigations of late pleistocene and holocene faults are an important tool in evaluating earthquake hazard the predicted response of the earth over this time however is very dependent on the model assumed for most regions far more carefully designed field observations are needed to constrain the existing rheological and ice models

deformation of the viscoelastic earth due to the secular change in the earth s axis of rotation summary the cause of the secular change in the earth s rotation axis relative to the surface geography is regarded as the viscoelastic response of the earth to the mass displacement generated by late pleistocene deglaciation and the sea level changes related to it on the other hand the secular drift of the pole will also bring about viscoelastic change in the earth s shape because the earth is not a sphere but a spheroid with an equatorial bulge in the case of polar drift we estimated the deformation of the earth s surface and the earth s core as well as the change in the earth s gravity field we used a compressible radially stratified maxwell viscoelastic earth model for the inverse calculations and also investigated if the viscous flow in the mantle can compensate for the mass redistribution caused by polar drift as a result of these calculations the viscous flow in the mantle seems not to be able to compensate for the mass redistribution caused by polar drift if the mantle viscosity is higher than 10 poise the agreement or disagreement between the rotation axis of the earth and the principal axis of inertia determined by satellites can add a new constraint to the viscosity of the earth s mantle

glacial rebound and sea level change in the british isles observations of sea levels around the coastline of the british isles for the past 10 000 15 000 years exhibit a major regional variation and provide an important data base for testing models of glacial rebound as well as models of the late devensian ice sheet a high resolution rebound model has been developed which is consistent with both the spatial and temporal patterns of sea level change and which demonstrates that the observations are the result of i the glacio isostatic crustal rebound in response to the unloading of the ice sheet over britain and to a lesser degree of the ice sheet over fennoscandia and ii the rise in sea level from the melting late pleistocene ice sheets including the response of the crust to the water loading the hydro isostatic effect the agreement between model and observations is such that there is no need to invoke vertical crustal movements for great britain and ireland of other than glacio hydro isostatic origin the rebound contributions are important throughout the region and nowhere is it sufficiently small for the sea level change to approximate the eustatic sea level rise the observational data distribution around the periphery as well as from sites near the centre of the former ice sheet is sufficient to permit constraints to be established on both earth model parameters specifying the mantle viscosity and lithospheric thickness and the extent and volume of the ice sheet at the time of the last glaciation preliminary solutions are presented which indicate an upper mantle viscosity of 3 5 1020 pas a lithospheric thickness of about 100 km or less and an ice model that was not confluent with the scandinavian ice sheet during the last glaciation and whose maximum thickness over scotland is unlikely to have exceeded about 1500 m

constraints on mantle viscosity from relative sea level variations in hudson bay a number of previous analyses have suggested that the relative sea level record in hudson bay constrains the viscosity of the lower mantle to be near 1021 pa s these conclusions have been based on a limited number of forward calculations which have assumed an isoviscous lower mantle region we compute frechet kernels for the rsl data in hudson bay to determine the detailed depth dependent sensitivity of the data to variations in a viscosity profile which is consistent with the past inferences we find that the rsl data provide a robust constraint on the average viscosity in the top half of the lower mantle only the average must be near 1021 pa s the data are less sensitive to variations in the viscosity below approximately 1800 km depth and in the upper mantle forward analyses included herein show that the data admit models whose average viscosity in the deep mantle below 1800 km depth and in the upper mantle can differ significantly from the value near 1021 pa s estimated for the top half of the lower mantle the total variation in the viscosity from the surface to the cmb can exceed an order of magnitude or more and still satisfy the constraint provided by the hudson bay rsl data set the necessity of invoking an isoviscous mantle model in previous studies is thus seen to be a consequence of the limited class of viscosity model solutions employed in those studies

the viscosity of the mantle summary creep under low stresses is by diffusion and has a linear relation between stress and strain rate it also obeys the navier stokes equation therefore the viscosity of the mantle may be calculated from solid state theory and also from the slow deformations of the earth the viscosities derived by these methods are in reasonable agreement and both show that the viscosity of the lower mantle is lo5 greater than that of the upper this high viscosity prevents polar wandering and lower mantle convection some suggested modifications of the viscosity depth calculations from post glacial uplift may improve their accuracy considerably 1 the non hydrostatic equatorial bulge all calculations concerned with post glacial uplift haskell 1935 mcconnell 1965 and with convection within the mantle pekeris 1935 have used a linear relation between stress and strain rate creep in the material then obeys stokes equation and therefore may be described by a viscosity which is independent of stress such creep only takes place at stresses below the yield stress p where p is the shear modulus at higher stresses the relation between stress and strain rate is non linear see pratt above at stresses below the yield point diffusion creep alone can operate and it has a linear relation between stress and strain rate the diffusion creep rate also depends exponentially on temperature gordon 1965 and therefore is not sufficiently rapid to be measurable under ordinary laboratory conditions for this reason solids were believed to be unable to deform for stresses below the yield stress a concept called finite strength the stresses caused by the melting of ice caps by the non hydrostatic bulge and by regional temperature differences are probably less than the yield stress thus the viscosity will be stress independent and the equation of a maxwell solid should describe the flow however there are regions where earthquakes occur and where this argument is clearly false the viscosity of the mantle between the crust and a depth of ioookm may be found from the uplift of formerly glaciated areas mcconnell 1965 finds the uplift of fennoscandia can be explained if the viscosity is least at a depth of about 300 km increasing both upwards and downwards fig 2 the viscosity of the lower mantle which is of considerable importance to theories of convection and polar wandering unfortunately cannot be calculated from the uplift for two reasons the first is that the depth to which the flow penetrates in a homogeneous half space is about equal to the radius of the applied load or about 1000 km for fennoscandia this difficulty can be overcome when the uplift of the canadian shield has been measured if however mcconnell is correct and there is a viscosity minimum at a depth of about 300 km a second difficulty arises because the flow in the low viscosity layer will shield the lower mantle from the applied force it is therefore unlikely that any surface load can be used to estimate the viscosity of the lower mantle

the amplitude asymmetry between synoptic cyclones and anticyclones implications for filtering methods in feature tracking abstract the background state is commonly removed from synoptic fields by use of either a spatial or temporal filter prior to the application of feature tracking commonly used spatial and temporal filters applied to sea level pressure data admit substantially different information to be included in the synoptic fields the spatial filter retains a time mean field that has comparable magnitude to a typical synoptic perturbation in contrast the temporal filter removes the entire time mean field the inclusion of the time mean spatially filtered field biases the feature tracking statistics toward large cyclone anticyclone magnitudes in the regions of climatological lows highs the resulting cyclone anticyclone magnitude asymmetries in each region are found to be inconsistent with the unfiltered data fields and merely result from the spurious inclusion of the time mean fields in the spatially filtered data the temporally filtered fields do not suffer from the same problem and produce modest cyclone

late pleistocene and holocene sea level change in the australian region and mantle rheology summary spatial and temporal variations in sea level are produced by the melting of the late pleistocene ice and by the earth s response to the redistribution in surface loads by examining different parts of the sea level curves of the past 20 000 yr from geographically widely distributed regions it becomes possible to constrain models of the melting history of the ice sheets and of the earth s rheology observations from sites away from the former arctic ice sheets such as the australian and south pacific region are particularly important for constraining the total meltwater volumes added into the oceans in the past 20 000 yr and the rates at which this occurred these observations indicate that the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9000 6000 yr ago when it may have lagged behind minor melting of the antarctic ice sheet appears to have continued throughout the late holocene differential observations of the late holocene sea level change recorded at sites in the same region are particularly useful for estimating parameters describing the earth s non elastic response to surface loading the effective parameters used here are a lithospheric thickness an upper mantle viscosity and a lower mantle viscosity describing the response below 670 km depth with the observations used here it is not possible to separate the lithospheric thickness h from the upper mantle viscosity and the viscosity results are based on the assumption that 50 h 100 km neither do these observations provide a resolution of the depth dependence of viscosity in the upper mantle and the resulting estimates are effective parameters only differential sea levels along continental margins and along the shores of large gulfs and bays constrain the effective upper mantle viscosity to be about 1 2 1020 pa s 1 while differential values from islands of different sizes are suggestive of a somewhat lower value the lower mantle taken to be below 670 km depth viscosity is about two orders of magnitude greater than this the estimated ice and rheological models explain many of the holocene sea level observations throughout the australian and southern pacific region the tilting of continental margins as exemplified by observations of variable amplitudes of the holocene high stands and the variable times at which sea levels first reached their present level along the north queensland coast and great barrier reef is well represented by these models differential holocene sea levels observed along the narrow spencers gulf of south australia are also well explained by the models and in neither case is it necessary to invoke tectonic motions predicted late holocene sea levels at small to medium sized islands are characterized by small amplitude high stands that reached their maximum values about 4000 2000 yr ago consistent with observations from the society cook and tuamotu islands

the influence of a finite glaciation phase on predictions of post glacial isostatic adjustment we predict relative sea level rsl variations present day three dimensional 3d crustal deformation rates and baseline velocities and a set of anomalies in the gravitational field of the planet using a suite of models for the space time geometry of the pleistocene ice sheets these models are distinguished on the basis of the details of the glaciation phase and they include the cases of an infinite glaciation phase i e an assumption of isostatic equilibrium at the time of the last glacial maximum lgm a steady uniform glaciation and a glaciation in which the bulk of the accumulation is limited to the final stages of the growth phase comparison of the observational records of postglacial rsl change with predictions based on the assumption of isostatic equilibrium at lgm have commonly been used to infer both the space time geometry of the final deglaciation event and the mantle viscosity we conclude that both these applications may be influenced significantly by the incorporation of a finite glacial cycle as an example rsl predictions which assume isostatic equilibrium at lgm and those which incorporate a relatively rapid glaciation phase can differ by a factor of 2 or more at some sites within previously glaciated regions when an earth model characterized by a lower mantle viscosity of 1022 pa s is adopted we have also found that differences in the adopted model for the glaciation event are capable of explaining entirely the discrepancies 0 2 mm yr between previously published predictions of present day tangential velocities in north america these discrepancies are characterized by a dominant long wavelength signal and hence they do not necessarily influence strongly predictions of baseline velocities variations in the glaciation model can also have an important effect on predictions of peak gravity anomalies over previously glaciated regions and secular variations in the zonal harmonics of the earth s geoid in both cases the effect may be sufficient to alter significantly the signal from other geophysical processes which may need to be invoked to reconcile the observational constraints

modelling of mantle postglacial relaxation in axisymmetric geometry with a composite rheology and a glacial load interpolated by adjusted spherical harmonics analysis summary although studies on glacial isostatic adjustment usually assume a purely linear rheology we have previously shown that mantle relaxation after the melting of laurentide ice sheet is better described by a composite rheology including a non linear term this modelling is however based on axially symmetric geometry and glacial forcing derived from ice 3g and suffers from a certain amount of arbitrariness in the definition of the ice load in this work we apply adjusted spherical harmonics analysis to interpolate the ice thicknesses of ice 3g and ice 1 glaciological models this filters out the non axisymmetric components of the ice load by considering only the zonal terms in the spherical harmonics expansion the resulting load function is used in finite element simulation of postglacial rebound to compare composite versus purely linear rheology our results confirm that composite rheology can explain relative sea level rsl data in north america significantly better than a purely linear rheology the performance of composite rheology suggests that in future investigations it may be better to use this more physically realistic creep law for modelling mantle deformation induced by glacial forcing

glacial isostatic adjustment and the anomalous tide gauge record of eastern north america sea level variations as recorded by the global network of tide gauges represent a rich data set for studying a wide range of natural and anthropogenic phenomena such as the sea level rise induced by possible global warming for this purpose long term sea level trends must be corrected for the contaminating effects of continuing glacial isostatic adjustment1 5 gia the numerical correction procedure has for sites on the east coast of north america yielded a set of highly anomalous sea level rates characterized by systematic geographical trends2 4 5 we demonstrate that these trends are a consequence of inadequacies in the previous standard numerical prediction for gia in particular we find that the well known trends in the gia corrected tide gauge rates are eliminated if the lower mantle viscosity of the earth model used in the gia prediction is increased this result obviates the need to explain the anomalous trend as a manifestation of gulf stream ocean circulation4 or neotectonic processes2

skewness of low frequency fluctuations in the tropospheric circulation during the northern hemisphere winter abstract departures of lowpass filtered 500 mb height and sea level pressure anomalies from a gaussian distribution have been examined based on northern hemisphere operational analyses for 30 winters at each gridpoint we evaluated several indices that are measures of the differences between the amplitudes and frequencies of the persistent anomalies with positive and negative polarities and differences in the temporal variability observed within extended periods of positive and negative anomalies the spatial patterns for these indices are all quite similar and they resemble the distribution of the moment coefficient of skewness documented by white positive skewness is observed to the north of the stormtrack latitudes and the negative to the south of them the skewness pattern in the sea level pressure field is weaker particularly at high latitudes and it exhibits a bias toward negative skewness anomalies with amplitudes larger than two standard deviations which occur about 5 of the time account

a critical assessment of viscous models of trench topography and corner flow stresses for newtonian viscous flow in a simple geometry e g corner flow bending flow are obtained in order to study the effect of imposed velocity boundary conditions stress for a delta function velocity boundary condition decays as 1 r 2 for a step function velocity stress goes as 1 r for a discontinuity in curvature the stress singularity is logarithmic for corner flow which has a discontinuity of velocity at a certain point the corresponding stress has a 1 r singularity however for a more realistic circular slab model the stress singularity becomes logarithmic thus the stress distribution is very sensitive to the boundary conditions and in evaluating the applicability of viscous models of trench topography it is essential to use realistic geometries topography and seismicity data from northern hoshu japan were used to construct a finite element model with flow assumed tangent to the top of the grid for both newtonian and non newtonian flow power law 3 rheology normal stresses at the top of the grid are compared to the observed trench topography and gravity anomalies there is poor agreement purely viscous models of subducting slables with specified velocity boundary conditions do not predict normal stress patterns compatible with observed topography and gravity elasticity and plasticity appear to be important for the subduction process

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

pleistocene deglaciation and the global gravity field the present day global geoid and free air gravity anomaly signals induced by pleistocene deglaciation have been computed along with their secular variations a revised green function has been derived for the free air gravity anomaly and we find that an earth model with a lower mantle viscosity moderately larger than the upper mantle value satisfies observations of the anomaly over both hudson s bay and fennoscandia using this preferred earth model the predicted global geoid anomaly map is characterized by peak negative values of 36 7 9 4 and 21 9 m over hudson s bay northern europe and antarctica respectively and by a smooth small amplitude 2 5 m upwarping over the major ocean basins although the field has an order of magnitude less power than the observed there is a significant spatial correlation between the two inferences of mantle viscosity based upon comparisons between the observed geoid and the computed deglaciation induced anomaly are hampered by the large contribution from the convective circulation in the earth s mantle we have subtracted a predicted convection signal based on seismic tomography from the observed field however the residual geoid thus obtained is still too inaccurate to allow a useful comparison in contrast a filtered version of the observed geoid over canada which retains harmonic coefficients in the degree range 10 22 provides a relatively uncontaminated by convection datum that is indeed satisfied by the preferred earth model secular variations in the earth s gravitational field are naturally dominated by the signal from pleistocene deglaciation in this respect we compute zonal harmonics in the expansion of the present day rate of change of the geopotential and in particular we predict amplitudes comparable to that for the previously analysed j2 for j4 j5 j7 and j9 all of which reflect in large part the response due to the melting of the massive laurentide ice sheet this analysis suggests that measurement of these higher order secular variations of the zonal harmonics based upon analysis of long time series of lageos ranging data could provide very useful additional constraints on the radial variation of mantle viscosity these constraints along with all others described in this paper are shown to be relatively insensitive to assumptions concerning the deflection during the glacial isostatic adjustment process of the 400 and 670 km density discontinuities within the mantle

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

lithosphere thickness and mantle viscosity inverted from gps derived deformation rates in fennoscandia summary crustal deformation in fennoscandia is associated with the glacial isostatic adjustment gia process that is caused by ongoing stress release of the mantle after removal of the late pleistocene ice sheet by 10 cal ka bp with an earth model of defined structure and rheology and an ice sheet model of known melting history the gia process can be simulated by geophysical models and the surface deformation rates can be calculated and used to compare with global positioning system gps observations therefore the crustal deformation rates observed by gps in fennoscandia provide constraints on the geophysical models on the basis of two ice sheet models anu ice and ice 5g reconstructed independently by the australian national university anu and university of toronto we use the gps derived deformation rates to invert for lithosphere thickness and mantle viscosity in fennoscandia the results show that only a three layer earth model can be resolved from current gps data providing robust estimates of effective lithosphere thickness upper and lower mantle viscosity the earth models estimated from inversion of gps data with two different ice sheet models define a narrow range of parameter space the lithosphere thickness between 93 and 110 km upper mantle viscosity between 3 4 and 5 0 1020 pa s and lower mantle viscosity between 7 1021 and 13 1021 pa s the estimates are consistent with those inverted from relative sea level indicators

asthenospheric ice load effects in a global dynamical system model of the pleistocene climate in a previous dynamical model the late cenozoic climate variations were simulated taking into account free and forced variations of atmospheric carbon dioxide acting in concert with changes in global ice mass and the deep ocean thermal state all under the influence of the known earth orbital radiative changes this model is now extended by adding another relevant variable bedrock asthenosphere depression including its associated ice calving effects within the context of this extended model we 1 demonstrate the main results of previous bedrock ice sheet models in what we believe is the simplest possible manner 2 show how these previous models can exhibit the mid pleistocene transition with the inclusion of co2 effects 3 discuss the limitations of these previous bedrock models and 4 illustrate the possibility of removing some of these limitations and accounting for further aspects of the paleoclimate record by using the full dynamical system that includes forced and free effects of co2 as well as effects of bedrock depression and milankovitch forcing as one example of a new possibility with bedrock effects included in the full system we can obtain a solution characterized by irregularly spaced intermittent episodes in which the behavior is dominated either by near 40 kyr period oscillations or by near 100 kyr periods such as prevailed over the pleistocene

near field hydro isostasy the implementation of a revised sea level equation summary we describe how the existing sea level equation incorrectly predicts the change in sea level and thus the ocean load in ice covered subgeoidal geographic regions during periods of deglaciation we go on to present a new sea level equation that overcomes this problem and we describe how this equation can be solved in a gravitationally self consistent manner by employing a well known spectral technique application of the new theory to predict relative sea level rsl histories and present day 3 d solid surface deformation rates in northeastern canada based on a single earth model characterized by a lithospheric thickness of 100 km and upper and lower mantle viscosities of 5 1020 and 5 1021 pa s respectively demonstrates that a significant error is introduced when the original theory is employed to predict the oceanic component of the surface load predictions of rsl curves show a discrepancy of 40 per cent at sites where data have been obtained and employed to constrain models of earth viscosity structure and ice sheet histories this error will significantly bias estimates of mantle viscosity structure and ice thicknesses that are based on the original theory in addition predictions of 3 d deformation rates differ by up to 25 per cent in some regions and so future applications that employ these data to constrain models of the glacial isostatic adjustment process should adopt the improved sea level theory in contrast estimates of inverse decay times from the predicted rsl curves are insensitive to within the observational error to the improvement in the surface load introduced by the new theory thus viscosity structure inferences based on this parametrization and the original sea level equation are unaffected by the error in the ocean load finally the new theory predicts a eustatic i e globally uniform rise in sea level over the postglacial period that is 11 m lower than that determined via the original theory therefore estimates of the global ice budget at the last glacial maximum based on far field rsl data and the original sea level theory will be too small by 10 per cent

thermal contraction and flexure of intracratonal basins a three dimensional study of the michigan basin summary cooling of continental lithosphere by thermal conduction to the surface following a heating event imposes a load on the lithosphere and causes subsidence as the basement rocks contract accumulation of sediments in the resulting depression forms a sedimentary basin studies of the geometry of sedimentary basins with horizontal dimensions of a few hundred kilometres suggests the lithosphere responds to loads by regional flexure of a strong elastic or viscoelastic upper lithosphere two and three dimensional models for flexure of the lithosphere owing to thermal contraction are applied to the michigan basin 2 d flexural models are compatible with previously estimated rheological parameters for an elastic lithosphere an effective flexural rigidity of about 5 1029 dyne cm can explain observed gravity anomalies and structural contours across the michigan basin a viscoelastic lithosphere requires an effective flexural rigidity of about 1032 dyne cm for a viscosity of 1025 poise for a 3 d elastic or viscoelastic lithosphere effective flexural rigidity must be approximately an order of magnitude smaller 2 1028 and 1031 dyne cm respectively larger values leave an excessive remaining load at the centre of the basin which is not indicated by observed gravity anomalies the decrease in effective flexural rigidity is attributed to greater difficulty in equi dimensional bending of a 3 d plate the magnitude and spatial distribution of the computed thermal contraction load are consistent with the presumed mechanism as the thermal anomaly of the initial heating event was present mainly at great depths in the lithosphere the lack of geological evidence for an initial heating event prior to subsidence is not a fatal objection to the thermal contraction mechanism of subsidence a driving load presumably from subsurface processes including crustal stretching and emplacement of dense rocks into the crust is necessary to explain the net subsidence of the basin from the time before the heating event until the lithosphere beneath the basin cooled without this driving load the thermal expansion would produce uplift but the surface would subside only back to sea level after the lithosphere cooled theoretical gravity results indicate that the driving load is centred at a depth of approximately 15 km deviations in subsidence curves from exponentials associated with thermal contraction can be explained by changes in sediment supply spatial variations in sediment load caused by regional facies changes produce migration of the centre of maximum deposition water and basement depths are determined for sequential time intervals during basin development the predicted depositional environments are consistent with lithofacies maps of the middle devonian

reconciling the ice 6g_c reconstruction of glacial chronology with ice sheet dynamics the cases of greenland and antarctica we describe a theoretical and numerical framework that has been developed to investigate the compatibility of the ice 6g c reconstruction of the glaciation histories of the greenland and antarctic ice sheets with the latest understanding of ice physics the ice 6g c reconstruction has been produced solely on the basis of the theory of the glacial isostatic adjustment gia process and it has remained an issue as to whether such reconstructions of the time dependent thickness variations of grounded continental ice sheets were compatible with physics based ice mechanical considerations our analyses focus on the evolution over the last glacial cycle of these extent ice sheet complexes and demonstrate that the gia inferred models are entirely consistent with such considerations when uncertainties in net mass balance history are taken fully into account

predictions of secular geoid changes from late pleistocene and holocene antarctic ice ocean mass imbalance summary estimates on ice volume changes in antarctica from both contemporary mass imbalance during the last hundred to thousand years and ice volume changes during the last glacial cycles are difficult to obtain future satellite gravity missions monitoring secular changes in gravity as a proxy of mass changes of the antarctic ice sheet will therefore provide an additional important constraint on the antarctic ice sheet history we assess the contributions from both past ice volume changes during the last glacial cycles and present ice imbalances over antarctica using a variety of published ice models model predictions of secular changes of the geoid anomaly based on plausible mantle viscosity profiles enable us to discuss the importance of past and present ice volume changes and their characteristic signatures while uncertainties arising from the viscosity profile are of secondary importance for model predictions of the secular change of the geoid anomaly we expect significant bias of the observed signal from uncertainties in the timing of the end of deglaciation which is in agreement with previous studies hence the benefit of inferring present day antarctic ice imbalance from satellite gravity missions will depend on improvements to ice models for the last glacial cycle

deformation of the central andes 15 27 s derived from a flow model of subduction zones a simple viscous flow model of a subduction zone is used to calculate the deformation within continental lithosphere above a subducting slab our formulation accounts for two forces that dominate the deformation in the overriding lithosphere tectonic forces and buoyancy forces the tectonic forces arise from the subduction of oceanic lithosphere and produce minor extension in the lithosphere near the trench and compression farther inland buoyancy forces can induce horizontal pressure gradients due to variations in crustal thickness which cause lithospheric extension where the crust is thick numerical solutions obtained by using a finite element technique are compared with observations from the central andes 15 27 s the model predicts the observed deformation pattern of extension in the forearc compression in the western monocline corresponding to magmatic activity extension in the altiplano compression in the eastern monocline and subandes and no deformation in the brazilian shield by comparing the calculated solutions with the large scale tectonic observations we are able to evaluate the forces that govern the deformation in the central andes the approximately constant subduction velocity in the past 26 m y suggests that the rate of crustal shortening in the andes has decreased with time due to the thickening of the crust

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

widespread triggering of nonvolcanic tremor in california we identified seven locations on or near the transform plate boundary in california where nonvolcanic tremor was triggered by the 2002 denali earthquake this result implies that the conditions essential for nonvolcanic tremor exist in a range of tectonic environments models explaining tremor typically require conditions endemic to subduction zones that is high temperatures and fluid pressures because previously tremor was nearly exclusively documented in subduction zones the absence of tremor in geothermal areas is inconsistent with such models additionally we found no correlation between creeping or locked faults and tremor contrary to predictions of frictional models of tremor

toward global inverse solutions for current and past ice mass variations contribution of secular satellite gravity and topography change measurements 1 we investigate the accuracy and resolution of estimating global ice mass variations using secular gravity and ice elevation change observations by the planned gravity recovery and climate experiment grace and icesat missions the gravity and altimetry data combination can determine the total bedrock uplift rate with root mean square rms errors of 0 2 1 3 mm yr when gaussian averaged over a half scale of 250 km moreover covariance analyses indicate that the mean snow compaction error can be constrained to the level of 3 mm yr in equivalent antarctic ice thickness change the mean antarctic present day ice mass change could then be determined to about 4 mm yr for a known viscosity profile such data sets provide a spatial estimate of a linear combination of the late pleistocene deglaciation and a more recent past trend last few thousand years in the greenland and antarctica mass balance for example when the linear rate of the recent past trend is estimated solely for ice history the rms errors of the 450 km gaussian averages range between 1 and 3 cm yr although contaminated by the signature of present day hydrological variations over the deglaciated areas the 450 km gaussian averaged last glacial maximum height of the ancient ice sheets can be determined to a rms level of 300 m the mean recovery errors are less than 100 m however the gravity altimeter data cannot resolve the load history and lower mantle viscosity simultaneously additional data such as relative sea level records must be invoked to overcome this difficulty

eruptions of pavlof volcano and their possible modulation by ocean load and tectonic stresses all nine magmatic eruptions at pavlof volcano in six of the years from 1973 to 1984 have occurred between september 9 and november 20 volumes of erupted material range from 0 1 to 15 9 106 m3 dense rock equivalent at an average rate of 3 106 m3 yr 1 the volumes are estimated from eyewitness reports for two eruptions the others are estimated from a relationship that we derive between eruption volume and harmonic tremor duration and amplitude the volume of lava erupted is approximately time predictable a significant correlation exists between the eruptions and yearly nontidal variations in sea level and may result from ocean loading calculated volume changes beneath the volcano due to ocean loading are from 0 02 to 2 times eruption volumes and we postulate that the volcano acts as a long period several month volume strain meter with lava being preferentially erupted when strain beneath the volcano is compressive the volcano did not erupt during the period 1978 1980 when tilt seismic data and sea level data indicate that deep aseismic slip may have occurred models of this event predict a volume increase beneath the volcano that might have compensated strain from magma injection these observations indicate that pavlof volcano may be responsive to small slow changes in ambient stresses or strains and that these changes may modify or trigger eruptions

observed cyclone anticyclone tropopause vortex asymmetries relatively little is known about coherent vortices near the extratropical tropopause even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues through an objective census of observed tropopause vortices the authors test a hypothesis regarding vortex merger asymmetry where cyclone pairs are repelled and anticyclone pairs are attracted by divergent flow due to frontogenesis emphasis is placed on arctic vortices where jet stream influences are weaker in order to facilitate comparisons with earlier idealized numerical simulations results show that arctic cyclones are more numerous persistent and stronger than arctic anticyclones an average of 15 cyclonic vortices and 11 anticyclonic vortices are observed per month with maximum frequency of occurrence for cyclones anticyclones during winter summer there are are about 47 more cyclones than anticyclones that survive at least 4 days and for longer lifetimes 1 day survival probabilities are nearly constant at 65 for cyclones and 55 for anticyclones mean tropopause potential temperature amplitude is 13 k for cyclones and 11 k for anticyclones with cyclones exhibiting a greater tail toward larger values an analysis of close proximity vortex pairs reveals divergence between cyclones and convergence between anticyclones this result agrees qualitatively with previous idealized numerical simulations although it is unclear to what extent the divergent circulations regulate vortex asymmetries