dynamic landscapes and human dispersal patterns tectonics coastlines and the reconstruction of human habitats studies of the impact of physical environment on human evolution usually focus on climate as the main external forcing agent of evolutionary and cultural change in this paper we focus on changes in the physical character of the landscape driven by geophysical processes as an equally potent factor most of the landscapes where finds of early human fossils and artefacts are concentrated are ones that have been subjected to high levels of geological instability either because of especially active tectonic processes associated with faulting and volcanic activity or because of proximity to coastlines subject to dramatic changes of geographical position and physical character by changes of relative sea level these processes can have both beneficial effects creating ecologically attractive conditions for human settlement and deleterious or disruptive ones creating barriers to movement disruption of ecological conditions or hazards to survival both positive and negative factors can have powerful selective effects on human behaviour and patterns of settlement and dispersal we consider both these aspects of the interaction develop a framework for the reconstruction and comparison of landscapes and landscape change at a variety of scales and illustrate this with selected examples drawn from africa and arabia

on the hemispheric origins of meltwater pulse 1a abstract during the glacial interglacial transition that began subsequent to the last glacial maximum approximately 21 000 calendar years ago globally averaged eustatic sea level rose by approximately 120 m as climate warmed to its current holocene state this rise of relative sea level rsl did not occur smoothly however but was characterized by the occurrence of one or more episodes of extremely rapid increase the most extreme of these events has come to be referred to as meltwater pulse 1a and was initially identified in the coral based record of rsl history from the island of barbados in the caribbean sea although it has usually been assumed that this episode of rapid rsl rise was derivative of a partial collapse of the northern hemisphere ice sheets it has recently been suggested that this pulse could have originated in a dramatic melt back of the antarctic ice sheet in this paper the arguments presented in favour of the southern hemisphere source are revisited in order to assess the plausibility of this alternative scenario based upon the analyses presented it is concluded that the evidence previously provided in support of the southern hemisphere scenario is in fact unable to rule out an entirely northern hemisphere source for the meltwater pulse 1a since explicit evidence does exist that both the laurentide and fennoscandian ice sheets contributed to this event and that antarctic ice sheet melting occurred significantly later the southern hemisphere appears not to have been a prime mover of northern hemisphere events

population wide garnet growth zoning revealed by la icp ms mapping implications for trace element equilibration and syn kinematic deformation during crystallisation the strong partitioning of many trace elements into garnet and their slow diffusivities in both garnet and the rock matrix means that their distribution may record valuable petrogenetic information not documented by major elements in metamorphic rocks complex trace element growth zoning in garnet porphyroblasts from a garnet grade metapelite from the barrovian sequence of the sikkim himalaya is assessed using quantified la icp ms raster mapping coupled with x ray micro computed tomography the data document systematic changes in the zoning patterns from early to late nucleated crystals and also suggest that the ree y chemistry incorporated into garnet is dependent on persistent disequilibrium in the rock volume there is evidence for hree y diffusion haloes surrounding growing garnets and a heterogeneous hree y distribution in the rock matrix annuli superimposed on oscillatory zoning are not consistent with formation during some rock wide event but are dependent on the spatial disposition of the garnet annuli are interpreted to reflect an integrated history of varying growth rates and the incorporation of pre existing heterogeneities due to relatively slow matrix diffusivities conversely smooth zoning of many transition metals indicate that their distribution in garnet may be controlled by equilibrium partitioning between garnet and the rock matrix significant rotation of garnet porphyroblasts during growth is revealed due to immobility of cr over the duration of the crystallisation interval and overprinting of the heterogenous precursor cr distribution strain rate estimates derived from this zoning are on the order of 10 11 10 12 hbox s 1

post processing removal of correlated errors in grace data 1 gravity fields produced by the gravity recovery and climate experiment grace satellite mission require smoothing to reduce the effects of errors present in short wavelength components as the smoothing radius decreases these errors manifest themselves in maps of surface mass variability as long linear features generally oriented north to south i e stripes the presence of stripes implies correlations in the gravity field coefficients here we examine the spectral signature of these correlated errors and present a method to remove them finally we apply the filter to a model of surface mass variability to show that the filter has relatively little degradation of the underlying geophysical signals we seek to recover

itrf2008 contribution to glacial isostatic adjustment and recent ice melting assessment 1 we investigate what information station vertical velocities of the itrf2008 provide on global geodetic parameters and by extension on glacial isostatic adjustment gia and recent ice melting rim processes we infer degree 2 spherical harmonic coefficients shc of the earth figure change and thej2 gravity rate j 2 which we compare with five gia models we find j 2 to be 0 0 2 4 10 11 yr 1 which is consistent with recent studies that propose a j 2 change in the 1990s due to rim whose contribution to the j 2 would be today around 3 5 4 0 2 4 10 11 yr 1 such results favor peltier 2004 vm2 or paulson et al 2007 gia models the itrf2008 shc that are directly impacted by the gia rotational feedback confirm with a good precision recent results from grace mission that initiated a debate on gia rotational feedback and about peltier gia model quality we find a coefficient consistent with paulson s and other model and more than 7 times smaller than coefficients in peltier s models two explanations are possible 1 if the model of peltier 2004 vm2 were to be correct then the strong rotational feedback in the model must be counteracted by a strong rotational feedback in the opposite direction generated by current ice loss 2 if the model of paulson et al 2007 were to be correct therefore gia and rim separately induce negligible rotational feedbacks both answers are quite extreme and call for more investigation on gia modeling and rotational feedback

space geodetic and water level gauge constraints on continental uplift and tilting over north america regional convergence of the ice 6g_c vm5a vm6 models

the rotational stability of an ice age earth summary predictions of glaciation induced changes in the earth s rotation vector exhibit sensitivities to earth structure that are unique within the suite of long wavelength observables associated with glacial isostatic adjustment henceforth gia and despite nearly a quarter of a century of research these sensitivities remain enigmatic previous predictions of present day true polar wander tpw speed driven by gia have indicated for example a strong sensitivity to variations in the thickness of the elastic lithosphere and the treatment phase or chemical of the density discontinuity at 670 km depth nakada recently presented results that suggest that the predictions are also sensitive to the adopted rheology of the lithosphere however his results have introduced an intriguing paradox in particular predictions generated using a model with an extremely high viscosity lithospheric lid do not converge to results for a purely elastic lithosphere of the same thickness mitrovica as cited by nakada has suggested that the paradox originates from an inaccuracy in the traditional rotation theory e g wu peltier associated with the treatment of the background equilibrium rotating form upon which any load and rotation induced perturbations are superimposed we revisit these issues using a new treatment of the linearized euler equations governing load induced rotation perturbations on viscoelastic earth models we demonstrate that our revised theory in which the background form of the planet combines a hydrostatic component and an observationally inferred excess ellipticity resolves the apparent paradox calculations using the revised theory indicate that earlier predictions based on earth models with purely elastic lithospheric lids are subject to large errors indeed previously noted sensitivities of tpw speed predictions to the thickness and rheology elastic versus viscous of the lithosphere largely disappear in the application of the new theory significant errors are also incurred by neglecting the stabilizing influence of the earth s excess ellipticity finally we demonstrate that the contribution from rotational feedback on predictions of present day rates of change of the geoid sea surface and crustal velocities are overestimated by the traditional rotation theory and this has implications for analyses of ongoing satellite e g grace missions and geodetic gps surveys

tide gauge based sea level variations since 1950 along the norwegian and russian coasts of the arctic ocean contribution of the steric and mass components 1 we investigate sea level change and variability in some areas of the arctic region over the 1950 2009 period analysis of 62 long tide gauge records available during the studied period along the norwegian and russian coastlines shows that coastal mean sea level corrected for glacial isostatic adjustment and inverted barometer effects in these two areas was almost stable until about 1980 but since then displayed a clear increasing trend until the mid 1990s the mean coastal sea level closely follows the fluctuations of the arctic oscillation ao index but after the mid to late 1990s the co fluctuation with the ao disappears since 1995 the coastal mean sea level average of the norwegian and russian tide gauge data presents an increasing trend of 4 mm yr using in situ ocean temperature and salinity data down to 700 m from three different databases we estimated the thermosteric halosteric and steric sum of thermosteric and halosteric sea level since 1970 in the north atlantic and nordic seas region incomplete data coverage prevented us from analyzing steric data along the russian coast we note a strong anti correlation between the thermosteric and halosteric components both in terms of spatial trends and regionally averaged time series the latter show a strong change as of 1995 that indicates simultaneous increase in temperature and salinity a result confirmed by the empirical orthogonal function decomposition over the studied region regionally distributed steric data are compared to altimetry based sea level over 1993 2009 spatial trend patterns of observed altimetry based sea level over 1993 2009 are largely explained by steric patterns but residual spatial trends suggest that other factors contribute in particular regional ocean mass changes focusing again on norwegian tide gauges we then compare observed coastal mean sea level with the steric sea level and the ocean mass component estimated with grace space gravimetry data and conclude that the mass component has been increasing since 2003 possibly because of the recent acceleration in land ice melt

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

grace measurements of mass variability in the earth system monthly gravity field estimates made by the twin gravity recovery and climate experiment grace satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers the annual cycle in the geoid variations up to 10 millimeters in some regions peaked predominantly in the spring and fall seasons geoid variations observed over south america that can be largely attributed to surface water and groundwater changes show a clear separation between the large amazon watershed and the smaller watersheds to the north such observations will help hydrologists to connect processes at traditional length scales tens of kilometers or less to those at regional and global scales

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

deepest mantle viscosity constraints from earth rotation anomalies 1 the radial variation of viscosity from earth s surface to the core mantle boundary is most accurately determined on the basis of observations related to the glacial isostatic adjustment gia process beneath a depth of approximately 1250 km the primary constraints available pertain to the anomalies in earth s rotational state that have previously been shown to be intimately linked to the same gia process responsible for postglacial sea level variability it is demonstrated that these anomalies are capable of resolving a difference between d viscosity and that of the overlying region which extends upwards to the 1250 km depth horizon a trade off is shown to exist between the viscosities in these deepest mantle layers that may be resolved by the observed direction of true polar wander

rates of li diffusion in garnet coupled transport of li and y rees numerical simulation of stranded diffusion profiles in partially resorbed garnet crystals from the aureole of the makhavinekh lake pluton labrador canada yields quantitative rates of intracrystalline diffusion for li in garnet diffusion coefficients for li at 700 900 c and 0 53 gpa are 0 5 1 5 log10 units lower than those for divalent cations in the same samples and match those for y and yb this correspondence likely stems from coupled substitution of li and y or ree ions in the garnet structure the requirement of local electroneutrality limits li mobility to be no faster than that of y rees because of this coupling li zoning in garnet is retained to comparatively high temperatures making garnet a valuable monitor of the behavior of li in deep crustal systems

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

precipitation of rutile and ilmenite needles in garnet implications for extreme metamorphic conditions in the acadian orogen u s a we report the discovery of oriented needles of rutile and ilmenite in garnet crystals from granulite facies metapelitic rocks of the merrimack synclinorium connecticut and present a precipitation model for their origin the rocks were strongly metamorphosed and deformed during the devonian acadian orogeny the needles are primarily elongated parallel to in garnet rutile has anomalous extinction angles as great as 35 cf griffin et al 1971 rutile and ilmenite needles are typically a few hundred nanometers to several micrometers in diameter and are several tens of micrometers to nearly a millimeter long other oxide inclusions that may be present include submicrometer to micrometer scale twinned rutile bicrystals as well as srilankite and a crichtonite group mineral some garnet cores have unusual box shaped quartz inclusions which coexist with ti fe oxide needles and commonly contain micrometer scale rods of f oh cl apatite negative garnet crystal pores are also widespread ti fe oxide needles are restricted to garnet core regions rims have a distinctly different inclusion population dominated by granulite facies minerals including sillimanite spinel cordierite and k feldspar consequently the garnet core regions represent an earlier distinct period of growth relative to the rims garnet cores contain 25 35 pyrope and a host of minor and trace constituents including tio2 0 07 0 6 wt cr2o3 0 01 0 10 wt na2o 0 01 0 03 wt p2o5 0 01 0 09 wt and zro2 up to 150 ppm na2o and zro2 correlate positively with tio2 titanium zoning is preserved in some garnets zoning profiles and two dimensional chemical mapping show that ti and to a lesser degree cr are depleted around ti fe oxide inclusions therefore we conclude that the needles are precipitates that formed from ti bearing garnet during exhumation and cooling garnet contained sufficient ti to form precipitates no ti source external to garnet was necessary titanium bearing garnets that contain oriented ti fe oxide needles are known primarily from ultrahigh pressure metamorphic rocks mantle peridotites and pyroxenites and high pressure granulites thus the presence of needle bearing garnets in connecticut strongly suggests that a previously unrecognized domain of extreme pressure and or temperature metamorphism exists in the acadian orogen

inference of mantle viscosity from grace and relative sea level data summary gravity recovery and climate experiment grace satellite observations of secular changes in gravity near hudson bay and geological measurements of relative sea level rsl changes over the last 10 000 yr in the same region are used in a monte carlo inversion to infer mantle viscosity structure the grace secular change in gravity shows a significant positive anomaly over a broad region 3000 km near hudson bay with a maximum of 2 5 gal yr 1 slightly west of hudson bay the pattern of this anomaly is remarkably consistent with that predicted for postglacial rebound using the ice 5g deglaciation history strongly suggesting a postglacial rebound origin for the gravity change we find that the grace and rsl data are insensitive to mantle viscosity below 1800 km depth a conclusion similar to that from previous studies that used only rsl data for a mantle with homogeneous viscosity the grace and rsl data require a viscosity between 1 4 1021 and 2 3 1021 pa s an inversion for two mantle viscosity layers separated at a depth of 670 km shows an ensemble of viscosity structures compatible with the data while the lowest misfit occurs for upper and lower mantle viscosities of 5 3 1020 and 2 3 1021 pa s respectively a weaker upper mantle may be compensated by a stronger lower mantle such that there exist other models that also provide a reasonable fit to the data we find that the grace and rsl data used in this study cannot resolve more than two layers in the upper 1800 km of the mantle

rates of hydrothermal cooling of new oceanic upper crust derived from lithium geospeedometry episodic emplacement and cooling of lavas and dikes at mid ocean ridges leads to large fluctuations in hydrothermal fluxes and biological activity however the processes operating beneath the seafloor during these transient events such as permeability creation and dike cooling are poorly understood we have developed a new approach to determine the cooling rate of the sheeted dike complex based on the extent of diffusion of lithium from plagioclase into clinopyroxene during cooling we have calibrated this li geospeedometer using new high temperature experiments to determine both the temperature dependence of the partitioning of li between plagioclase and clinopyroxene and the diffusion coefficient for li in clinopyroxene application of this method to lavas and dikes from odp hole 504b shows that cooling rates vary dramatically with depth in the upper oceanic crust extremely rapid cooling rates 450 c hr 1 in the upper part of the sheeted dike complex are sufficient to power hydrothermal megaplume formation within the overlying water column

prograde peak and retrograde p t paths from aluminium in orthopyroxene high temperature contact metamorphism in the aureole of the makhavinekh lake pluton nain plutonic suite labrador static heating during intrusion of the makhavinekh lake pluton mlp caused replacement of garnet in the adjacent country rocks tasiuyak gneiss by coronal assemblages of orthopyroxene cordierite thermometry based on al solubility in orthopyroxene applied to relict garnet and neighbouring orthopyroxene preserves a temperature gradient from 700 to 900 c at distances between 5750 and 20 m from the intrusion reaffirming the robustness of this thermometry technique intracrystalline and intergranular variations of al zoning in orthopyroxene are well preserved suggesting that little diffusional modification of al growth zoning occurred maximum al2o3 in orthopyroxene ranges from c 2 0 wt at 5750 m from the intrusion to a maximum of 4 3 wt at the contact individual orthopyroxene grains show decreasing al from core to rim in samples 500 m from the intrusion while those at greater distances show an increase from core to rim these features are interpreted with the aid of numerical models for conductive heat flow in the aureole coronas in samples close to the intrusion grew at high temperatures and along t t paths dominated by cooling so maximum al content in orthopyroxene in these samples occurs in the cores of grains that grew during the earliest stages of garnet consumption in contrast the corona forming reactions in rocks further from the contact proceeded along prograde heating paths so maximum al content in orthopyroxene occurs in the rims of grains that grew during the final stages of garnet consumption these results document the ability of al in orthopyroxene thermometry to preserve a detailed record of thermal histories in contact metamorphic granulites they suggest that similar intracrystalline and intergranular variations of al zoning in orthopyroxene in regional granulites may also preserve portions of both the prograde and peak t evolution

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

pleistocene deglaciation and the earth s rotation implications for mantle viscosity summary recent results from the analysis of postglacial rebound data suggest that the viscosity of the earth s mantle increases through the transition region models which fit both relative sea level and free air gravity data have viscosities which increase from a value near 1022 poise in the upper mantle beneath the lithosphere to a value of about 1023 poise in the lower mantle in this paper we analyse the effect of deglaciation upon the earth s rotation and thereby show that the observed secular trend polar wander evident in the ils ipms pole path and measurements of the non tidal acceleration of the length of day are both consistent with the viscosity profile deduced from postglacial rebound the two analyses are therefore mutually reinforcing

monazite and xenotime petrogenesis in the contact aureole of the makhavinekh lake pluton northern labrador high temperature 700 900 c metamorphism in the contact aureole of the makhavinekh lake pluton mlp northern labrador led to the growth of monazite and xenotime during progressive replacement of regional garnet bearing assemblages m1 by lower pressure symplectitic coronas of orthopyroxene cordierite m2 in the inner aureole 500 m from the contact where m1 garnet is strongly resorbed high y hree monazite xy hree 0 14 0 18 occurs as small isolated grains and as discontinuous rims on partially resorbed pre m2 monazites that were liberated from garnet xenotime also occurs as small isolated grains within m2 coronas ion microprobe dating of thin high y rims indicates that new monazite growth occurred during m2 monazite xenotime miscibility gap temperatures are consistent with al solubility in orthopyroxene thermometry estimates indicating that peak temperatures in the inner aureole are accurately recorded and preserved by monazite m2 monazite records therefore the temperature and timing of m2 metamorphism two net transfer reactions modelled using singular value decomposition in the system p y hree lree are proposed to account for the growth of m2 phosphates 1 38 grt1 1 mnz1 1 13 mnz2 and 2 737 grt1 1 ap 1 mnz2 3 4 xno2 reaction 1 conserves p and gave rise to locally coronitic high y overgrowths on partially resorbed pre m2 monazite whereas reaction 2 accounts for the growth of small new monazite and xenotime grains both reactions were highly localized within individual m2 coronas due to slow intergranular diffusion accompanying fluid undersaturated metamorphism in the mlp aureole similar monazite forming reactions are expected in other polymetamorphosed granulites

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

closing the sea level rise budget with altimetry argo and grace 1 an analysis of the steric and ocean mass components of sea level shows that the sea level rise budget for the period january 2004 to december 2007 can be closed using corrected and verified jason 1 and envisat altimetry observations of total sea level upper ocean steric sea level from the argo array and ocean mass variations inferred from grace gravity mission observations we find that the sum of steric sea level and the ocean mass component has a trend of 1 5 1 0 mm a over the period in agreement with the total sea level rise observed by either jason 1 2 4 1 1 mm a or envisat 2 7 1 5 mm a within a 95 confidence interval

glaciers dominate eustatic sea level rise in the 21st century ice loss to the sea currently accounts for virtually all of the sea level rise that is not attributable to ocean warming and about 60 of the ice loss is from glaciers and ice caps rather than from the two ice sheets the contribution of these smaller glaciers has accelerated over the past decade in part due to marked thinning and retreat of marine terminating glaciers associated with a dynamic instability that is generally not considered in mass balance and climate modeling this acceleration of glacier melt may cause 0 1 to 0 25 meter of additional sea level rise by 2100

li as a barometer for bimineralic eclogites experiments in natural systems abstract experiments performed in eclogitic systems show that the partitioning of li between garnet and clinopyroxene is pressure dependent in natural eclogitic bulk compositions this supports experimentally the hypothesis based on the analysis of li in eclogitic xenoliths and inclusions in diamond that the partitioning of this particular element between clinopyroxene and garnet is very sensitive to changes in pressure and could be calibrated as a barometer for bimineralic eclogites in order to calibrate this pressure dependence into a barometer 16 multianvil experiments were performed from 4 to 13 gpa and 1100 1500 c using starting materials sourced from a well preserved mg rich eclogitic xenolith from the roberts victor kimberlite pipe south africa our findings reinforce the general trend we observed in the cmas system that d li cpx grt for li decreases with increasing p and that at p 12 gpa garnet is able to incorporate more li than clinopyroxene multiple linear regression was applied to our experimental results to create the barometer p 0 000963 t ln d li cpx grt 1 581 0 252 where p is pressure in gpa t is temperature in c and d li cpx grt is defined as the partitioning coefficient of li obtained by dividing the concentration of li in cpx by the concentration of li in garnet this barometer reproduces the experimental conditions to 0 2 gpa it is applicable to mg rich eclogitic xenoliths and to peridotitic and eclogitic inclusions in diamond application of the barometer to diamond bearing xenoliths results in pressures in the diamond stability field clinopyroxene is easily corrupted in xenoliths and also preferentially takes in li during short lived metasomatic processes care must be taken therefore to analyse primary unaltered clinopyroxene our preliminary application to natural samples shows that the barometer can be applied beyond the experimental range to pressures down to 3 5 gpa this is higher than the pressures encountered in crustal eclogites and thus the barometer is not applicable to these eclogites

parameters of subsurface brines and hydrothermal processes 12 15 months after the 1999 magmatic event at the main endeavor field as inferred from in situ time series measurements of chloride and temperature 1 phase separation at mid ocean ridge hydrothermal systems is a widely distributed frequently occurring process it is highly sensitive to dynamic subsurface pressure and temperature conditions and has a significant impact on chloride concentrations of hydrothermal fluid although vapor phases produced by phase separation are observed in a variety of hydrothermal settings observation of conjugate brines that must be produced concurrently are more rare and the fate of subsurface brines is still not well understood here we use an array of in situ chloride sensors deployed at the main endeavor field on the juan de fuca ridge in the wake of a magmatic event to monitor the behavior of hydrothermal vent effluent with high temporal resolution our results provide evidence of near critical chloride depleted fluids within the crust up to 486 m beneath the seafloor we estimate that a brine reservoir stored beneath the main endeavor field is constrained to temperatures between 131 c and 326 c for chloride concentrations ranging from 6 to 25 wt nacl respectively our data suggest that subsurface fluids and circulation pathways vary widely over spatial scales on the order of meters under these circumstances simultaneous measurements of multiple fluid parameters at a high temporal resolution are essential to understanding subsurface hydrothermal processes associated with magmatic events

comment on ocean mass from grace and glacial isostatic adjustment by d p chambers et al 1 the modern global theory of the glacial isostatic adjustment gia process is a theory that directly addresses the extent to which the geoid of classical geodesy is impacted by this phenomenon because the geoid is by conventional definition the surface of constant potential that overlaps the surface of the sea in the absence of currents and tides we may determine the impact of the gia process upon it only by explicit analysis of the manner in which mass is redistributed among the ocean basins and the level of the sea is thereby influenced although the dominant contribution to gia is that associated with the transfer of mass between the oceans and the continents there is an additional influence due to the variations in earth s rotational state this influence feeds back onto the geoid in the recent paper by chambers et al 2010 several arguments were presented that question earlier attempts to discuss the consequences of this feedback these arguments are interesting and we address them in what follows

an estimate of motion between the spin axis and the hotspots over the past century 1 estimates of the motion of the spin axis over the past century either neglect plate motion or are relative to the mean lithosphere to understand the response of the spin axis to mass changes it is more useful to estimate spin axis motion relative to the hotspots because the hotspots well represent the solid earth the hotspots originate in the lower mantle which comprises 2 3 of the earth s volume relative to the lower mantle the plates and the upper mantle move in opposite directions to a large extent canceling each other out the mean lithosphere moves quickly relative to the hotspots and poorly represents the solid earth the spin axis has moved relative to the hotspots over the past century along the 68 4 w meridian at 4 03 milliarcsecond yr this motion is 11 counterclockwise of 0 5 milliarcsecond yr faster than and 25 different than spin axis motion relative to the mean lithosphere

on the origins of earth rotation anomalies new insights on the basis of both paleogeodetic data and gravity recovery and climate experiment grace data 1 the theory previously developed to predict the impact on earth s rotational state of the late pleistocene glaciation cycle is extended in particular we examine the extent to which a departure of the infinite time asymptote of the viscoelastic tidal love number of degree 2 k2t from the observed fluid love number kf impacts the theory a number of tests of the influence of the difference in these love numbers on theoretical predictions of the model of the glacial isostatic adjustment gia process are explored relative sea level history predictions are shown not to be sensitive to the difference even though they are highly sensitive to the influence of the changing rotational state itself we also explore in detail the accuracy with which the gravity recovery and climate experiment grace satellite system is able to observe the global gia process including the time dependent amplitude of the degree 2 and order 1 spherical harmonic components of the gravitational field the only components that are significantly influenced by rotational effects it is explicitly shown that the grace observation of these properties of the time varying gravitational field is sufficiently accurate to rule out the values predicted by the ice 5g vm2 model of peltier 2004 however we also note that this model is constrained only by data from an epoch during which modern greenhouse gas induced melting of both the great polar ice sheets and small ice sheets and glaciers was not occurring such modern loss of grounded continental ice strongly influences the evolving rotational state of the planet and thus the values of the degree 2 and order 1 stokes coefficients as they are currently being measured by the grace satellite system a series of sensitivity tests are employed to demonstrate this fact we suggest that the accuracy of scenarios for modern land ice melting may be tested by ensuring that such scenarios conform to the grace observations of these crucial time dependent stokes coefficients

lithium and its isotopes as tracers of subduction zone fluids and metasomatic processes evidence from the catalina schist california usa abstract the catalina schist well studied for its tectonometamorphic history and geochemical evolution provides a field area in which to evaluate the extent of li mobility in subduction zone fluids and the degree to which li isotopes can trace metamorphic fluid rock interactions a suite of 63 samples of the catalina schist that represent a range of metamorphic grades and diverse lithologies was analyzed for li concentration and isotope composition metasedimentary rocks show no evidence for significant loss of li with increasing metamorphic grade despite the wide range of prograde p t histories represented by the five tectonometamorphic units with the highest grade rocks having experienced peak temperatures near 750 c metamafic rocks similarly show no change in li concentration as a function of grade that can be directly related to varying degrees of devolatilization the li concentrations and 7 li of metasedimentary rocks appear to best correlate with a chemical alteration index that likely reflects differential extents of weathering in the sediment sources the 7 li of most metamafic rocks including gabbroic metaconglomerate cobbles veins and melange matrix reflects overprinting of the li isotope compositions derived through transfer of li in fluids from sedimentary lithologies in the same tectonometamorphic units thus it appears that li was mobilized in fluids released from metasedimentary rocks but that the loss was insufficient to affect the bulk 7 li and li content of the metasedimentary rocks veins and melange matrix have the highest li concentrations of all samples analyzed ranging up to 70 ppm some veins and amphibolite grade mafic rocks have low 7 li suggestive of li diffusion through an intergranular fluid taken together these observations suggest mobilization of li during high pressure temperature p t fluid rock interactions that also resulted in enrichments in b n and some large ion lithophile elements k rb cs ba in the veins melange matrix and cobbles this study demonstrates that although li is mobile in high p t metamorphic fluids it does not partition into fluids to the extent demonstrated for n b and cs the latter elements showing large depletions in the higher grade catalina schist metasedimentary rocks thus even in relatively warm subduction zones deeply subducted metasedimentary rocks are expected to largely retain their li inventory to depths of at least 40 km the maximum depth at which units of the catalina schist experienced peak metamorphism

greenland mass balance from grace 1 we use 22 monthly grace gravity recovery and climate experiment gravity fields to estimate the linear trend in greenland ice mass during 2002 2004 we recover a decrease in total ice mass of 82 28 km3 of ice per year consistent with estimates from other techniques our uncertainty estimate is dominated by the effects of grace measurement errors and errors in our post glacial rebound pg correction the main advantages of grace are that it is sensitive to the entire ice sheet and that it provides mass estimates with only minimal use of supporting physical assumptions or ancillary data

did glacially induced tpw end the ice age a reanalysis previous studies of earth rotation perturbations due to ice age loading have predicted a slow secular drift of the rotation axis relative to the surface geography i e true polar wander tpw of order of several degrees over the plio pleistocene it has been argued that this drift and the change in the geographic distribution of solar insolation that it implies may have been responsible for important transitions in ice age climate including the termination of ice age cycles we use a revised rotational stability theory that incorporates a more accurate treatment of the earth s background ellipticity to reconsider this issue and demonstrate that the net displacement of the pole predicted in earlier studies disappears this more muted polar motion is due to two factors first the revised theory no longer predicts the permanent shift in the rotation axis or the so called unidirectional tpw that appears in the traditional stability theory and second the increased background ellipticity incorporated in the revised predictions acts to reduce the normal mode amplitudes governing the motion of the pole we conclude that ice age induced tpw was not responsible for the termination of the ice age this does not preclude the possibility that tpw induced by mantle convective flow may have played a role in major plio pleistocene climate transitions including the onset of northern hemisphere glaciation

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

sea level measuring the bounding surfaces of the ocean the practical need to understand sea level along the coasts such as for safe navigation given the spatially variable tides has resulted in tide gauge observations having the distinction of being some of the longest instrumental ocean records archives of these records along with geological constraints have allowed us to identify the century scale rise in global sea level additional data sources particularly satellite altimetry missions have helped us to better identify the rates and causes of sea level rise and the mechanisms leading to spatial variability in the observed rates analysis of all of the data reveals the need for long term and stable observation systems to assess accurately the regional changes as well as to improve our ability to estimate future changes in sea level while information from many scientific disciplines is needed to understand sea level change this review focuses on contributions from geodesy and the role of the ocean s bounding surfaces the sea surface and the earth s crust

on eustatic sea level history last glacial maximum to holocene abstract this paper addresses the question of the magnitude and time dependence of the globally averaged eustatic rise of sea level that occurred subsequent to the time of last glacial maximum lgm at approximately 21 000 calendar years before present through the analysis of relative sea level rsl histories predicted by a realistic mass conserving and gravitationally self consistent theory of postglacial sea level change it is demonstrated that there are preferred oceanic locations at which this eustatic function is well approximated by local sea level history one such location is the island of barbados in the caribbean sea a site from which a coral based record exists that extends from mid holocene to lgm because of the sea level ambiguity that is inherent to coral based records however it is important that the global ice equivalent eustatic sea level curve inferred on the basis of the barbados data be tested against observations at other locations from which similarly extensive records are also available but which are derived on the basis of sea level indicators which are not subject to the ambiguities inherent to corals it is shown that when the eustatic function employed in the global theoretical model is tuned so as to enable the model to fit the barbados observations where the maximum relative sea level rsl depression is assumed to be near 120 m then the theory misfits the record from the sunda shelf in the indonesian archipelago as well as the record from j bonaparte gulf in northern australia both of these recently published records appear to constrain the lgm low stand of rsl to a value above 120 m the implications of these results for interpretation of the long coral derived records from the huon peninsula of papua new guinea and the island of tahiti are also discussed

the lageos constraint on deep mantle viscosity results from a new normal mode method for the inversion of viscoelastic relaxation spectra the recently observed acceleration in the node of the orbit of the lageos satellite has previously been shown to provide a good constraint on the viscosity of the earth s mantle beneath the 670 km seismic discontinuity this paper explores the extent to which the previously inferred lower mantle viscosity may be traded off against variations of other properties of the radial viscoelastic structure we show explicitly that the nontidal acceleration of rotation inferred from the lageos data and predicted as a consequence of the earth s response to the last deglaciation event of the current ice age is relatively insensitive both to variations of lithospheric thickness and to the presence or absence of plausible chemical heterogeneity across the 670 km interface it therefore provides a high quality constraint on the viscosity of the deep mantle with the upper mantle viscosity fixed at the nominal value of 1021 pa s the bounds on lower mantle viscosity lm are such that 2 1021 pa s lm 6 1021 pa s even when allowance is made for the presence of a viscous boundary layer at the base of the upper mantle such as would exist if the mantle convective circulation were layered

ice age earth rotation modern predictions of the rotational stability of an ice age earth reflect a convergence of two classic problems in geophysical analysis the modeling of the glacial isostatic adjustment gia process and the rotational stability of terrestrial planets recent theoretical advances in this area have been motivated not by conventional applications such as the inference of earth s deep mantle viscosity but rather by efforts to address vexing problems in global climate change research these advances have demonstrated that traditional calculations of the ongoing motion of the rotation pole relative to the surface geography or true polar wander tpw driven by ice age loading have systematically overestimated this motion by up to a factor of 4 by underestimating by 1 the background flattening of earth s oblate form the physics of this sensitivity is related to concepts that appear in canonical mid twentieth century discussions of earth rotation and avoiding the associated inaccuracy resolves numerous p

glacial isostatic adjustment and earth rotation refined constraints on the viscosity of the deepest mantle we explore the extent to which two properties of earth s present day rotational state may be applied to constrain the viscosity of the lower regions of the lower mantle the analysis builds upon recent advances in understanding the radial resolving power of the relative sea level data of postglacial rebound which have demonstrated anew that no significant increase of viscosity across the 660 km seismic discontinuity appears to be allowed by these data such observations do not constrain the viscosity of the mantle below about 1400 km depth however and here we estimate the average viscosity in this deepest region by invoking observations of the present day rate and direction of polar wander and the present day magnitude of the nontidal acceleration of the rate of planetary rotation since the rotational response to the glaciation cycle depends only upon the degree 2 spherical harmonic components of the induced deformation this response is expected to provide the most specific sampling possible of deep mantle properties our analysis is based upon the use of glacial excitation functions calculated from complete gravitationally self consistent solutions of the sea level equation for the most recent refinement of the history of ice sheet thickness variations across the last glacial interglacial transition namely the ice 4g model this analysis shows that when earth rotation observations are combined with relative sea level constraints the viscosity of the deepest mantle is required to be 1 order of magnitude higher than the viscosity of the upper part of the lower mantle such significant elevation of viscosity in the lowermost region of the lower mantle is also in accord with recent inferences based upon analysis of the nonhydrostatic geoid the analyses presented herein therefore suffice to effect a reconciliation between the requirements of these distinct geophysical observations

constraining models of postglacial rebound using space geodesy a detailed assessment of model ice 5g vm2 and its relatives summary using global positioning system very long baseline interferometry satellite laser ranging and doppler orbitography and radiopositioning integrated by satellite observations including the canadian base network and fennoscandian bifrost array we constrain in models of postglacial rebound the thickness of the ice sheets as a function of position and time and the viscosity of the mantle as a function of depth we test model ice 5g vm2 t90 rot which well fits many hundred holocene relative sea level histories in north america europe and worldwide ice 5g is the deglaciation history having more ice in western canada than ice 4g vm2 is the mantle viscosity profile having a mean upper mantle viscosity of 0 5 1021 pa s and a mean uppermost lower mantle viscosity of 1 6 1021 pa s t90 is an elastic lithosphere thickness of 90 km and rot designates that the model includes rotational feedback earth s response to the wander of the north pole of earth s spin axis towards canada at a speed of 1 myr 1 the vertical observations in north america show that relative to ice 5g the laurentide ice sheet at last glacial maximum lgm at 26 ka was 1 much thinner in southern manitoba 2 thinner near yellowknife northwest territories 3 thicker in eastern and southern quebec and 4 thicker along the northern british columbia alberta border or that ice was unloaded from these areas later thicker or earlier thinner than in ice 5g the data indicate that the western laurentide ice sheet was intermediate in mass between ice 5g and ice 4g the vertical observations and grace gravity data together suggest that the western laurentide ice sheet was nearly as massive as that in ice 5g but distributed more broadly across northwestern canada vm2 poorly fits the horizontal observations in north america predicting places along the margins of the laurentide ice sheet to be moving laterally away from the ice centre at 2 mm yr 1 in ice 4g and 3 mm yr 1 in ice 5g in disagreement with the observation that the interior of the north american plate is deforming more slowly than 1 mm yr 1 substituting vm5a t60 for vm2 t90 that is introducing into the lithosphere at its base a layer with a high viscosity of 10 1021 pa s greatly improves the fit of the horizontal observations in north america ice 4g vm5a t60 rot predicts most of the north american plate to be moving horizontally more slowly than 1 mm yr 1 in agreement with the data ice 5g vm5a t60 rot well fits both the vertical and horizontal observations in europe the space geodetic data cannot distinguish between models with and without rotational feedback in the vertical because the velocity of earth centre is uncertain and in the horizontal because the areas of the plate interiors having geodetic sites is not large enough to detect the small differences in the predictions of rotational feedback going across the plate interiors

lithium isotope behaviour during partial melting of metapelites from the jiangnan orogen south china implications for the origin of ree tetrad effect of f rich granite and associated rare metal mineralization abstract we carried out combined nd and li isotopic studies on the neoproterozoic biotite granites late mesozoic evolved two mica muscovite granites and associated the shuangqiaoshan group metapelites from the jiangnan orogen south china which along with petrological and geochemical data were used to constrain the lithium isotopic behavior during partial melting of metapelites the origin of the ree tetrad effect in evolved granites and implications for related rare metal mineralization the neoproterozoic biotite granites show features typical of s types e g high a cnk ratios and have end 6 9 to 10 and 7li 2 2 4 comparable to the shuangqiaoshan group metapelites with end 6 to 11 and 7li 2 3 7 respectively suggesting that the biotite granites were derived from melting of the metapelites and the li isotopic fractionation during the melting process appears negligible the two late mesozoic shimensi and zengjialong granites occur as small stocks showing high silica peraluminous low cao and sr contents variably enrichment in volatiles f b and are accompanied by w cu and sn mineralization the shimensi granites have end t values of 7 0 8 6 and 7li 2 7 3 9 similar to the shuangqiaoshan group metapelites whereas the zengjialong granites have relatively high end t values 5 1 7 3 and heavy li isotopic features mostly 7li 0 18 1 53 and particularly ree tetrad effect is seen in the latter we argue that the late mesozoic evolved granites formed as a result of re melting of the granulitic residues left in the lower crust after extraction of the neoproterozoic biotite granites from the metapelites such re melting of the residues was triggered by underplating of basaltic magma with more mantle input and f b as well in the source of the zengjialong granites the elevated 7li values of the zengjialong granites were probably caused by intense interaction between melt and external fluids during magma emplacement which in turn resulted in the formation of the ree tetrad effect in the granites isotopic modeling suggests that fluid exsolution from evolved granites is minor and is less likely to have been responsible for the extensive rare metal mineralization as traditionally thought

variations in the earth s oblateness during the past 28 years 1 analysis of satellite laser ranging slr data indicates that the earth s dynamic oblateness j2 has undergone significant variations during the past 28 years the dominant signatures in the observed variations in j2 are 1 a secular decrease with a rate of approximately 2 75 10 11 yr 1 2 seasonal annual variations with a mean amplitude of 2 9 10 10 3 significant interannual variations with timescales of 4 6 years and 4 a variation with period of 21 years and an amplitude of 1 4 10 10 with minimum in december 1988 two large interannual variations are related to the strong el nino southern oscillation events during the periods of 1986 1991 and 1996 2002 and it appears that another interannual cycle may have started in late 2002 the superposition of the decadal variation on the interannual signal makes the j2 fluctuation appear to be anomalously large during the 1996 2002 period contemporary models of the mass redistributions in the atmosphere ocean and surface water can explain a major part of the 4 to 6 year fluctuations however the cause of the decadal variation remains unknown

lithium isotope evidence for light element decoupling in the panama subarc mantle the systematics of fluid mobile trace elements in arc lavas from panama relative to their li isotopic compositions provide unique evidence for the fertilization and subsequent differential extraction of mobile species from the subarc mantle calc alkaline lavas that crystallized between 20 and 5 ma old group that possess 7 li as high as 11 2 have low b be otherwise identical and similarly old calcalkaline lavas with high b be to 23 have mid ocean ridge basalt morb like 7 li 4 7 to 5 6 adakite lavas 3 ma young group possess 7 li from 1 4 to 4 2 and have consistently lower b be than old group lavas consistent with derivation from melting of a devolatilized morb slab if li and b had comparable fluid mobility in the subarc mantle then slab fluids would carry both high b concentrations and elevated 7 li signatures into arc sources and samples with the highest 7 li would also have the highest b be our data suggest that although both li and b are initially derived from the slab older 7 li signatures may be preserved in the mantle beneath arcs as a result regions of the lithospheric mantle will develop li isotope signatures that are heavier than typical morb mantle

detection of a large scale mass redistribution in the terrestrial system since 1998 earth9s dynamic oblateness j2 had been undergoing a decrease according to space geodetic observations over the past 25 years until around 1998 when it switched quite suddenly to an increasing trend that has continued to the present the secular decrease in j2 resulted primarily from the postglacial rebound in the mantle the present increase whose geophysical cause s are uncertain thus signifies a large change in global mass distribution with a j2 effect that considerably overshadows that of mantle rebound

lithium isotope fractionation during incongruent melting constraints from post collisional leucogranite and residual enclaves from bengbu uplift china abstract lithium li elemental and isotopic compositions of the jurassic jingshan leucogranites including garnet rich mafic enclaves and wall rock wuhe gneisses from the southeast margin of north china craton ncc were investigated to understand the behavior of li isotopes during post collisional magmatism the jingshan leucogranites have distinct u shape ree patterns with y and ree concentrations significantly lower yet sr y ratios higher than their presumed source rocks i e the dabie sulu gneisses trace element modeling of ree and sr y suggests these elemental signatures of the jingshan leucogranites can be consistently explained by a fluid present crustal incongruent partial melting bt qz pl h 2 o grt melt leaving mainly grt bt with minor allanite in the residuum the mafic enclaves show identical sr nd isotopic compositions with their host leucogranites contrasting with the wuhe gneiss and the exposed regional lower crust the garnet rich mafic enclaves are thus interpreted as entrained residual phases formed by this incongruent partial melting the jingshan leucogranites show relatively high 7 li values 4 0 to 9 0 and low li concentrations 4 7 11 3 ppm in comparison to published data for worldwide granites in contrast the residual enclaves show low 7 li values as low as 0 6 and high li concentrations as high as 118 ppm garnet separated from residual enclaves is characterized by a narrow range of low 7 li values 1 5 to 0 1 with high li concentrations from 32 9 to 81 7 ppm by contrast coexisting quartz shows relatively high 7 li values 15 0 to 16 6 with very low li concentrations 1 ppm biotite from both leucogranite and residual enclaves shows high li concentrations 195 382 ppm and relatively heavy li isotope compositions 3 2 to 7 5 the li elemental and isotopic signatures of the residual enclaves can be modeled as a grt bt rich residuum mixed with leucogranite melt in various proportions this work indicates that the li isotopic compositions for magmatic rocks that are derived from anatexis of mid to lower crustal gneisses may not be a faithful source indicator as commonly suggested

alkali diffusion in plagioclase feldspar tracer diffusion kinetics at 1 atm pressure under dry conditions using 6li 41k and 87rb in four plagioclase feldspars have been determined diffusion profiles were measured using an ion microprobe sims the arrhenius parameters and 2 uncertainties for li k and rb respectively in albite are pre exponential factor log do 3 8 1 0 3 4 1 4 and 5 8 3 8 in m2 s and activation energies 146 14 296 30 and 283 85 kj mol the diffusion rate of k in albite at 700 c and 100 mpa water pressure equals that at 1 atm dry suggesting that diffusion of k is not dependent on water fugacity between 0 004 and 100 mpa the k diffusion rate depends on plagioclase anorthite content and is approximately 20 times slower in labradorite than albite li diffusion rates in albite and anorthite are identical a linear relation between log d for the alkalis measured and their ionic radius squared permits an estimate of cs diffusion kinetics diffusion rates are isotropic or nearly so in albite

closure of the budget of global sea level rise over the grace era the importance and magnitudes of the required corrections for global glacial isostatic adjustment abstract the budget of global sea level rise includes contributions from several distinct factors including thermosteric effects the wasting of small ice sheets and glaciers and the loss of mass by the great polar ice sheets and by the continents due to desiccation since the former contribution may be estimated on the basis of both hydrographic survey data and more recently using argo float data the second may be estimated on the basis of mass balance measurements on existing ice fields and the latter on the basis of modern grace based time dependent gravity field measurements the inputs to the globally averaged rate of sea level rise may be directly constrained since grace also provides a measurement of the rate at which mass is being added to the oceans we are now in a position to ask whether this rate of mass addition to the oceans matches the rate at which mass is being removed from the continents as demonstrated herein the mass component of the budget of global sea level is closed within the observational errors when the mass derived contribution is added to the thermosteric contribution it is furthermore shown that the inference of the net rate of global sea level rise by the altimetric satellites topex poseidon and jason 1 is also reconcilable over the grace era it is noted those individual terms in the budget especially the contribution from small ice sheets and glaciers remains insufficiently accurate it is demonstrated that the lingering influence of the late quaternary ice age upon sea level is profound and that closure of the budget requires an accurate model of its impact

mantle viscosity and ice age ice sheet topography ice age paleotopography and mantle viscosity can both be inferred from observations of earth s response to the most recent deglaciation event of the current ice age this procedure requires iterative application of a theoretical model of the global process of glacial isostatic adjustment results demonstrate that the iterative inversion procedure converges to a paleotopography that is extremely close to that from the ice 4g model the accompanying mantle viscosity profile is furthermore shown to reconcile the requirements of aspherical geoid anomalies related to the mantle convection process thus resolving a fundamental issue concerning mantle rheology the combined model also explains postglacial sea level histories for the east coast of the united states

astrometric and space geodetic observations of polar wander optical astrometric measurements of star positions taken during the past century have been recently re reduced using the final hipparcos star catalog in order to determine variations in the mean location of the earth s rotation pole with respect to the earth s crust this newly available polar motion series which is the longest homogeneous polar motion series currently available allows the drift in the pole path to be newly estimated during the 1900 0 to 1992 0 span of the smoothed hipparcos polar motion series the earth s rotation pole is observed to drift at a mean linear rate of 3 51 0 01 milliarcseconds year mas yr towards 79 2 0 2 w longitude this new estimate for the observed trend in the pole path which can be considered to be the present day expression of true polar wander is nearly the same as that estimated in previous studies using the homogeneous ils polar motion series

a benchmark study for glacial isostatic adjustment codes the study of glacial isostatic adjustment gia is gaining an increasingly im portant role within the geophysical community understanding the response of the earth to loading is crucial in various contexts ranging from the the interpretation of modern satellite geodetic measurements e g grace and goce to the projections of future sea level trends in response to climate change modern modeling approaches to gia are based on various techniques that range from purely analytical formulations to fully numerical methods despite various teams independently investigating gia we do not have a suitably large set of explicitly validated numerical results through which they may be validated a community benchmark data set would clearly be valuable following the example of the mantle convection community here we present for the first time the results of a benchmark study of codes designed to model gia the approaches benchmarked are based on significantly different codes and different techniques this effort is performed within the working group 4 wg4 of the esf cost action es0701 improved constraints on models of glacial isostatic adjustment our aims are i testing the codes currently in use by the various teams ii establish a sufficiently large set of agreed results iii correct possible systematic errors embedded in the various physical formulations or computer implementations and iv facilitate the dissemination of numerical tools for surface loading studies to the community and to young scientists the test computations are mainly based on models with spherical symmetry and maxwell rheology and include inputs from various different methods and solution techniques viscoelastic normal modes spectral finite elements and finite elements the tests involve the loading and tidal love numbers and their relaxation spectra the deformation and gravity variations driven by surface loads characterized by simple geometry and time history and the rotational fluctuations in response to glacial unloading in spite of the significant differences in the numerical methods employed the test computations show a satisfactory agreement between the results provided by the participants most of the existing misfits have been addressed during the preparation of the manuscript some others are currently the subject of analysis within the wg4 community

deglaciation related features of the earth s gravity field abstract the earth s gravity field is partly a consequence of the delayed rebound of previously glaciated regions and this is most readily seen in the negative anomalies over the hudson bay gulf of bothnia and the central siberian plateau globally the relation between deglaciation and gravity is complicated by the redistribution of the melted ice over the oceans and the deglaciation effects on gravity extend far beyond the boundaries of the former ice loads in this paper we have computed the contribution to the observed potential of the redistribution of mass associated with the late pleistocene deglaciation and found that this is not an insignificant amount in particular this contribution exceeds that arising from the earth s isostatically compensated topography the observed potential has been corrected for both effects but while details in the geoid or gravity anomaly representation change the power spectrum is not significantly modified in particular the decay of the corrected spectrum remains very similar to that observed

quaternary marine terraces sea level changes and uplift history of patagonia argentina comparisons with predictions of the ice 4g vm2 model of the global process of glacial isostatic adjustment abstract quaternary marine terraces have been investigated along a 1000 km stretch of the coast of argentinian patagonia fossil mollusc shells most in living position and collected from raised beaches were dated using the u series esr and 14 c methods our analyses show that holocene sea level in this region culminated 7000 to 8000 bp at 6 7 m amsl this beach slightly increases in altitude southward the last interglacial stage 5e was identified at 16 17 m amsl whereas the highest and morphologically most distinctive radiometrically dated terrace at 250 000 to 330 000 bp exists at an elevation of 33 35 m amsl we estimate a constant rate of tectonic uplift of 0 09 m 1000 yr since the middle pleistocene using this estimate of the local rate of tectonic uplift we correct relative sea level r s l observations for the holocene epoch in turn the inferred holocene sea level histories are compared with those predicted using the ice 4g vm2 model of the global process of glacial isostatic adjustment this model accurately predicts r s l history from all sites along the northern part of the east coast of the south american continent venezuela brazil however along the southern part of the coast of argentinian patagonia there is evidence of an influence that is not accurately represented in this version of the model of the global process of glacial isostatic adjustment we suggest that this influence could be connected to the presence of the broad continental shelf that is located offshore of this region but the influence of significant neotectonic uplift cannot be dismissed

pleistocene deglaciation and the earth s rotation a new analysis summary this paper is concerned with an analysis of the effect of the pleistocene glacial cycle upon the earth s rotation we demonstrate that two important geophysical observables may be explained as aspects of the rotational response to surface mass loading by ice sheets these are the astronomically observed non tidal component of the acceleration of planetary rotation and the secular drift of the rotation pole relative to the surface geography which is evident in the ils pole path the former observation is shown to provide an unambiguous constraint upon the viscosity of the planetary mantle and requires a depth dependence of this parameter which is the same as that which has previously been inferred in studies of the relative sea level variations and free air gravity anomalies associated with post glacial rebound the observed secular drift of the pole cannot provide an independent estimate of the viscosity of the mantle because it depends jointly upon mantle viscosity and lithospheric thickness with the viscosity profile fixed by the rebound data the observed speed of polar wander suggests a continental lithospheric thickness which is in excess of that appropriate for old ocean basins but nevertheless in accord with independent constraints

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

a mechanism for na incorporation in garnet an example from garnet in orthogneiss from the su lu terrane eastern china sodian and yttrian na y garnet occurs in orthogneisses of the su lu terrane of eastern china with major quartz microcline and albite and subordinate biotite titanite hematite and zircon acmite rich pyroxene muscovite epidote allanite and hastingsitic amphibole occur in a few of the samples the na y garnet can be divided into almandine spessartinegrossular ai 1 6 per formula unit pfu for 0 12 hereafter denoted as ai garnet and andradite spessartine feh 1 3 pfu hereafter denoted as feh garnet groups average composition of the ai garnet in each sample ranges from alm3ssps13prp grs49adr2 to aim2lsps67prpogrssadr7 the feh garnet contains a calderite component cdr and its composition is alm4 7spslo 2 prp 2adrs9 8 cdr3 12 na y and yb contents of the ai rich garnet reach 0 37 1 46 and 0 42 oxide wt respectively and na y yb 0 99 t 0 16 the feh garnet contains up to 0 11 2 1 and 0 48 wt of na20 y203 and yb203 respectively and its na y yb value 0 17 t 0 1 is lower than that of the ai garnet we conclude that na y and yb are incorporated in the ai rich garnet by the 8jna 8j y yb ca mn 2substitution whereas in the feh garnet y and yb are dominantly incorporated by the 8j y yb l4j ai feh ca mn sl substitution with up to 3 mol y yb for ca mn comparison ofna y yb of garnets in the orthogneisses and in some pegmatites implies that increasing pressure favors incorporation of na with y and yb and that under the albite epidote amphibolite facies or higher pressure conditions y and yb probably substitute into the garnet structure by 8jna 8j y yb ca mn 2 instead of the 8j y yb 4j al feh ca mn sl type substitution effective under lower pressure conditions

multivariate data analysis in palaeoecology and palaeobiogeography a review abstract palaeoecologists and palaeobiogeographers are often confronted with large multivariate data sets from which fossil communities assemblages or associations or faunal provinces are to be recognized the complex multidimensional nature of these data sets the recognition of the enormous variation of communities and environments both in space and time and the difficulties of dealing with these problems by the human mind justify the use of multivariate statistical methods in palaeoecology and palaeobiogeography concepts and basic procedures of several commonly used multivariated statistical methods of palaeoecology and palaeobiogeography are reviewed in the wider context of quantitative community ecology and biogeography basic assumptions about data structure and theoretical and practical limitations are discussed the emphasis is on evaluation of binary similarity coefficients and two multivariate approaches cluster analysis and ordination thirty nine binary similarity coefficients are evaluated against nine criteria jaccard s coefficient of community is found most suitable as a similarity measure between samples under the conditions tested algorithmic procedures of cluster analysis especially the agglomerative hierarchical cluster analysis techniques and indirect ordinations particularly polar ordination principal component analysis principal coordinate analysis correspondence analysis detrended correspondence analysis and nonmetric multidimensional scaling are outlined and their applicability to palaeoecological and palaeobiogeographical data is discussed where the data are appropriate an integration of cluster analysis and ordination is suggested to be applied to the same data

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

rheological stratification of the lithosphere a direct inference based upon the geodetically observed pattern of the glacial isostatic adjustment of the north american continent 1 a sequence of new analyses of the process of glacial isostatic adjustment gia is described the focus is upon the resolution of a recognized flaw in the currently prevalent model of this process that denoted ice 5g vm2 the flaw concerns a previously noted inability of the model to simultaneously reconcile the vlbi and gps measured rates of vertical and horizontal motion in the region of the north american continent that lay outboard and to the south of the laurentide ice sheet lis at last glacial maximum this characteristic misfit of the model to the data has been suggested to be reconcilable only by recourse to models that explicitly incorporate the influence of lateral viscosity heterogeneity it is demonstrated herein that on the contrary this flaw is entirely and unambiguously attributable to the rheological stratification of the lithosphere an influence not previously accounted for in global models of the gia process but which must exist on a priori grounds

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

diffusion obstacles and opportunities in petrochronology many of the approaches in petrochronology are rooted in the assumption of equilibrium diffusion is an expression of disequilibrium the movement of mass in response to chemical potential gradients and isotopes in response to isotopic gradients it is extremely important that we be aware of how the effects of diffusion can place obstacles across our path towards petrochronologic enlightenment conversely the effects of diffusion also provide opportunities for understanding rates processes and conditions experienced by rocks the enormity of the field does not permit us to provide a comprehensive review of either the mathematics of diffusion or quantitative data that have been obtained relevant to the interpretation of diffusive processes in rocks and minerals many resources cover these topics including rimg volume 72 diffusion in minerals and melts zhang and cherniak 2010 and several textbooks crank 1975 glicksman 2000 particularly relevant to the discussion of petrochronology are summaries of the theory and controls on diffusion brady and cherniak 2010 zhang 2010 as well as diffusion rates in feldspar cherniak 2010a accessory minerals cherniak 2010b garnet ganguly 2010 mica pyroxene and amphibole cherniak and dimanov 2010 and melts zhang and ni 2010 zhang et al 2010 rather than duplicate that material our goal is to explore the obstacles and opportunities presented by the effects of diffusion as they inform the rates of petrologic processes to achieve this goal we emphasize key principles and illustrative examples quantitative interpretation of the effects of diffusion assumes predictability of numerous factors that may affect chemical or isotopic transport including temperature initial and boundary conditions water and oxygen fugacities activities of other components multiple mechanisms of diffusion and crystal chemistry coupling of the substitution of elements into different crystallographic sites additionally the extraction of meaningful ages durations of events and temperatures requires

rates of fe mg mn and ca diffusion in garnet extraction of the thermal and chemical histories preserved by modified compositional zoning in garnet is compromised by large uncertainties in experimentally determined diffusion coefficients for principal divalent cations some of this uncertainty derives from long down temperature extrapolations but much of it arises from an inability to account accurately for large variations in diffusivity as a function of garnet composition numerical simulation of stranded diffusion profiles in partially resorbed natural garnets constrains diffusivities at low temperature and reveals a systematic dependence of diffusion rates on host garnet composition a comprehensive model incorporating a simple compositional dependence allows accurate prediction of diffusion rates for fe mg mn and ca for nearly all garnet compositions across the full range of geologically relevant temperatures pressures and oxygen fugacities

dependence of reaction kinetics on h2o activity as inferred from rates of intergranular diffusion of aluminium quantitative constraints on the accelerative effects of h2o on the kinetics of metamorphic reactions arise from a comparison of rates of intergranular diffusion of al in natural systems that are fluid saturated hydrous but fluid undersaturated and nearly anhydrous widths of symplectitic reaction coronas around partially resorbed garnet crystals in the contact aureole of the makhavinekh lake pluton northern labrador combined with time temperature histories from conductive thermal models yield intergranular diffusivities for al from 700 900 c under nearly anhydrous conditions those rates when extrapolated down temperature are approximately three orders of magnitude slower than rates derived from re analysis of garnet resorption coronas formed under hydrous but fluid undersaturated conditions near 575 c in rocks of the llano uplift of central texas which are in turn approximately four orders of magnitude slower than rates at comparable temperatures derived from numerical simulations of prograde garnet growth in fluid saturated conditions in rocks from the picuris range of north central new mexico thus even at constant temperature rates of intergranular diffusion of al and corresponding length scales and timescales of metamorphic reaction and equilibration may vary by as much as seven orders of magnitude across the range of h2o activities found in nature

long term and recent changes in sea level in the falkland islands 1 mean sea level measurements made at port louis in the falkland islands in 1981 1982 1984 and 2009 together with values from the nearby permanent tide gauge at port stanley have been compared to measurements made at port louis in 1842 by james clark ross the long term rate of change of sea level is estimated to have been 0 75 0 35 mm yr between 1842 and the early 1980s after correction for air pressure effects and for vertical land movement due to glacial isostatic adjustment gia the 2009 port louis data set is of particular importance due to the availability of simultaneous information from port stanley the data set has been employed in two ways by providing a short recent estimate of mean sea level itself and by enabling the effective combination of measurements at the two sites the rate of sea level rise observed since 1992 when the modern stanley gauge was installed has been larger at 2 51 0 58 mm yr after correction for air pressure and gia this rate compares to a value of 2 79 0 42 mm yr obtained from satellite altimetry in the region over the same period such a relatively recent acceleration in the rate of sea level rise is consistent with findings from other locations in the southern hemisphere and globally