a chronology of holocene and little ice age glacier culminations of the steingletscher central alps switzerland based on high sensitivity beryllium 10 moraine dating abstract the amplitude and timing of past glacier culminations are sensitive recorders of key climate events on a regional scale precisely dating young moraines using cosmogenic nuclides to investigate holocene glacier chronologies has proven challenging but progress in the high sensitivity 10 be technique has recently been shown to enable the precise dating of moraines as young as a few hundred years in this study we use 10 be moraine dating to reconstruct culminations of the steingletscher a small mountain glacier in the central swiss alps throughout the holocene the outermost recorded positions of steingletscher most likely occurred in the early holocene and appear nearly synchronous with glacier culminations reported from other regions in the alps a late holocene position corroborates the evidence for a significant glacier advance of similar extent to that of the little ice age lia 3 kyr ago finally fourteen boulders from different moraines yield 10 be ages between 580 and 140 years with analytical precisions mostly 10 dating steingletscher advances during the lia because these lia 10 be ages are in stratigraphic order we tentatively distinguish four lia glacier culminations about 1470 ce 1650 ce 1750 ce and 1820 ce which are in good agreement with existing independent records during the lia in the swiss alps these findings illustrate the high potential of the 10 be moraine dating method to directly link paleo glacier chronologies to historical records and thus present day glacier evolution

recent glacier decline in the kerguelen islands 49 s 69 e derived from modeling field observations and satellite data the retreat of glaciers in the kerguelen islands 49 s 69 e and their associated climatic causes have been analyzed using field data and moderate resolution imaging spectroradiometer modis satellite images to validate a positive degree day pdd model forced by data from local meteorological stations mass balance measurements made during recent field campaigns on the largest glacier of the cook ice cap were compared to data from the early 1970s providing a 40 year view of the differences in the spatial distribution of surface mass balance smb to obtain additional regional data for the validation of our models we analyzed modis images 2000 2012 to determine if our model was capable of reproducing variations in the transient snow line the pdd model correctly simulated the variations in the snow line the spatial variations in the smb and its trend with elevation yet current smb values diverge from their classic linear representation with elevation and stake data at high altitudes now display more negative smb values than expected by analyzing modis albedo we observed that these values are caused by the disappearance of snow and associated feedback on melt rates in addition certain parts of ampere glacier could not be reproduced by the surface energy balance model because of overaccumulation due to wind deposition finally the modis data field data and our models suggest that the acceleration of glacier wastage in kerguelen is due to reduced net accumulation and an associated rise in the snow line since the 1970s

joint inversions of seismic and geodynamic data for models of three dimensional mantle heterogeneity the seismic models of three dimensional 3 d mantle heterogeneity may be interpreted in terms of the density perturbations which drive mantle flow and thus provide important predictions of flow related observables such as the nonhydrostatic geoid the current models of global scale shear velocity heterogeneity provide reasonably good fits to the long wavelength nonhydrostatic geoid data 60 70 variance reductions but rather poor fits to the corresponding free air gravity anomalies 30 40 variance reductions this major difference is due to two factors 1 the very different amplitude spectrum of the gravity anomalies which is nearly flat for degrees l 3 the largest mismatch between the pattern of predicted and observed gravity anomalies is in the southern hemisphere this observation suggests that one reason for the poor overall match between the two fields may be that the global seismic data are not resolving sufficiently well the heterogeneity in the southern hemisphere portion of the deep mantle in contrast the gravity data provide accurate and geographically uniform constraints on the vertically integrated heterogeneity in the mantle we therefore perform a series of experiments in which we simultaneously invert a large set of seismic data which includes long period waveforms ss s and scs s differential travel times and normal mode structure coefficients and the long wavelength gravity anomaly data we thus determine whether it is possible to derive new 3 d heterogeneity models which satisfy both data sets the gravity anomaly data are interpreted in the context of spherically symmetric viscous flow models of the mantle in these inversion experiments we test several radial viscosity and ln ln profiles and thereby assess their plausibility the joint seismic geodynamic inversions reveal that it is indeed possible to greatly improve the fit to the free air gravity anomalies with variance reductions of 80 90 readily accessible while preserving the fit to the seismic data this improvement is achieved with some adjustment to the heterogeneity in the depth range 1500 2500 km where the seismic data constraints appear to be weakest the joint inversions also reveal new structures in the southern hemisphere portion of the lower mantle which apparently are not resolved by the seismic data alone

mantle dynamics influence of the transition zone the question of whether the mantle convects as a single layer or whether the convection is split vertically into two or more layers is perhaps the most fundamental unanswered question concerning the structure and dynamics of the mantle and has ramifications throughout solid earth geosciences the most likely mechanism for enforcing layered convection is the action of the major phase transitions of the transition zone and in particular the strong endothermic phase transition between spinel and perovskite magnesiowiistite that occurs at around 660 km depth because this transition is endothermic it is deflected downwards in cold downwellings and upwards in hot upwellings resulting in a mass anomaly that impedes the penetration of the downwelling or upwelling in the past few years there has been a huge resurgence of interest and modeling activity devoted to studying the influence of the 400 and 660 km phase transitions and the effects identified in these studies may provide the key to reconciling various seemingly contradictory geophysical observations

chaotic subduction like downflows in a spherical model of convection in the earth s mantle numerical models of three dimensional nonlinear thermal convection of very viscous fluids have recently been developed in rectangular1 4 and spherical5 12 geometries as analogues of convection in the earth s mantle here we describe model calculations for a compressible fluid in a three dimensional spherical shell with 80 of the surface heat flow generated within the model mantle in agreement with estimates for the earth s mantle13 the rayleigh number and the numerical resolution for these calculations are greater than those of our previous studies9 10 of internally heated convection in a spherical shell our numerical solutions are strongly chaotic with surface planforms dominated by long curvilinear downflows reminiscent of the descending slabs in the earth s mantle although analogy to the earth s mantle is necessarily imperfect owing to for example the absence of variable viscosity and rheology and hence of lithospheric plates our results suggest that descending slabs play an important part in driving mantle convection and that their chaotic evolution may influence the spatial and temporal behaviour of plates and thus the dispersal and aggregation of continents

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

intermittent layered convection in a model mantle with an endothermic phase change at 670 km it is not yet known whether convection in the earth s mantle occurs in cells that extend throughout the entire depth of the mantle or if the upper and lower mantle convect in independent layers both possibilities seem to be consistent with geochemical and seismologi cal observations1 4 it is generally accepted however that the seismologically observed boundary between the upper and lower mantle at 670 km depth arises from the endothermic phase change spinel perovskite mgo here we investigate the results of including this phase change in a model of mantle convection for realism and to eliminate scaling problems our calculations use commonly accepted values of geophysical parameters for a clapeyron slope y 2 106 a value close to experimental results and theoretical expectations we observe local intermittent mixing between the upper and lower mantle such behaviour may offer a way to reconcile the existence of geophysical evidence for both whole mantle and layered convection

the stability and structure of primordial reservoirs in the lower mantle insights from models of thermochemical convection in three dimensional spherical geometry large scale chemical lateral heterogeneities are inferred in the earth s lowermost mantle by seismological studies we explore the model space of thermochemical convection that can maintain reservoirs of dense material for a long period of time by using similar analysis in 3 d spherical geometry in this study we focus on the parameters thought to be important in controlling the stability and structure of primordial dense reservoirs in the lower mantle including the chemical density contrast between the primordial dense material and the regular mantle material buoyancy ratio thermal and chemical viscosity contrasts volume fraction of primordial dense material and the clapeyron slope of the phase transition at 660 km depth we find that most of the findings from the 3 d cartesian study still apply to 3 d spherical cases after slight modifications varying buoyancy ratio leads to different flow patterns from rapid upwelling to stable layering and large thermal viscosity contrasts are required to generate long wavelength chemical structures in the lower mantle chemical viscosity contrasts in a reasonable range have a second order role in modifying the stability of the dense anomalies the volume fraction of the initial primordial dense material does not effect the results with large thermal viscosity contrasts but has significant effects on calculations with intermediate and small thermal viscosity contrasts the volume fraction of dense material at which the flow pattern changes from unstable to stable depends on buoyancy ratio and thermal viscosity contrast an endothermic phase transition at 660 km depth acts as a filter allowing cold slabs to penetrate while blocking most of the dense material from penetrating to the upper mantle

tertiary tectonic evolution of the external south carpathians and the adjacent moesian platform romania depth interpreted seismic sections of the getic depression foredeep paleostress indicator data and analysis of outcrop to regional scale structures are integrated to derive the tectonic evolution of the south carpathians moesian platform area following late cretaceous and older orogenic phases the south carpathians moesian platform area underwent strike slip deformation with ne sw oriented compression and nw se tension in paleogene to early burdigalian times tensional deformation is recorded which led to the opening of wsw ene to e w trending extensional basins in the late burdigalian ne sw oriented contraction took over causing the oblique inversion of preexisting extensional structures during sarmatian times nw se and slightly younger n s trending compression caused the activation of mainly nw se dextral strike slip faults and in the frontal areas south directed thrusting the nw se direction of extension determined for paleogene to early burdigalian times is hardly compatible with presently accepted models of substantially continuous dextral wrenching between the intra carpathians units to the north of the south carpathians and the moesian platform to the south in contrast we have demonstrated dextral transpressive to transtensional movements within an e w trending corridor from the late burdigalian to late sarmatian which are compatible with available models

long wavelength s wave velocity structure throughout the mantle summary long wavelength s wave velocity anomalies are obtained for the entire mantle by inverting 6ooo long period 40 100s sh body waves and lo00 long period 100 500 s love waves in the shallow mantle the patterns of fast and slow velocity anomalies correlate well with age and tectonics in the depth range of 400 1000 km we find two antipodal fast velocity anomalies one in the western pacific and the other in south america they form a fairly strong i 2 anomaly moreover the 1 2 anomaly is the largest spherical harmonic component throughout the entire mantle except for in the layer of 1000 1300 km depth a fast velocity anomaly near the caribbean previously reported by several other investigators is found between the depths of 1000 and 1300km with diminishing amplitudes it can be traced to canada and the aleutians and may be related to old subducted slabs in the same depth interval similar size anomalies can be found in the middle of the pacific and in the indian ocean these could be checked by more detailed studies to judge the reliability of this study heterogeneity power has a peak at the surface and a secondary peak at the bottom of the mantle d consistent with the existence of chemical and or thermal boundary layers at the base of the mantle we also find a fast velocity anomaly which surrounds the pacific ocean this feature has been found by other researchers previously but its interpretation is difficult due to the trade off between velocity anomaly and core mantle boundary deformation

the anatomy of a gondwanan terrane the neoproterozoic ordovician basement of the pre alpine sebes lotru composite terrane south carpathians romania abstract the sebes lotru terrane in the south carpathians mountain range comprises a lower neoproterozoic metamorphic unit lotru and an upper ordovician metamorphic unit cump na that were juxtaposed during the variscan orogeny two orthogneisses from the lotru metamorphic unit yield u pb la icp ms zircon crystallization ages of 549 3 3 8 ma and 587 5 3 ma respectively two orthogneisses from the cump na metamorphic unit yield zircon crystallization ages of 458 9 3 5 ma and 466 0 4 2 ma respectively high u zircons from two other orthogneisses from the cump na metamorphic unit have ages ranging from 400 ma to 320 ma which are interpreted to reflect protracted zircon recrystallization during the regionally significant variscan collisional event detrital zircons from a metasedimentary gneiss in the cump na metamorphic unit have ages ranging from 0 5 ga to 2 8 ga the 0 5 ga age constrains the maximum sediment deposition age to be late cambrian the source most compatible with the range of precambrian detrital ages in the sebes lotru terrane is northeastern gondwana the sebes lotru terrane was part of a continental subduction collision system as a lower plate after about 400 ma and reached peak metamorphic conditions between 350 and 320 ma e g medaris et al 2003 a cross cutting granite vein has a zircon u pb crystallization age of 321 5 3 1 ma which constrains minimum age of ductile deformation during the variscan collision in this region the trace of the rheic suture within the south carpathians is located between the ordovician upper part of the sebes lotru terrane and the dr gsan pre alpine terrane of the danubian domain

subducted slabs and the geoid 1 numerical experiments with temperature dependent viscosity one of the most powerful constraints on mantle viscosity comes from the correlation of the long wavelength degree 4 9 geoid with that predicted by a density model for subducted slabs the effect of lateral variations of viscosity should be most pronounced at subduction zones due to the strong effect of temperature on viscosity an idealized slab model with temperature dependent viscosity is considered with various lateral and vertical viscosity structures using a two dimensional finite element formulation the viscosity parameterization affects the amplitude of the long wavelength geoid anomaly but not the sign of the correlation between the geoid and density anomalies depth dependent viscosity models with a high viscosity lithospheric layer do not completely match the temperature dependent laterally varying results suggesting that the rheology of the slab does have an effect on the long wavelength surface topography and geoid however this affect is minor suggesting that the radial models of mantle viscosity inferred from surface observables are correct to first order in contrast the short wavelength features are dramatically affected by the rheology of the region surrounding the downwelling further study of the shorter wavelength geoid over subduction zones may provide better insight into subduction zone processes

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

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

global mapping of topography on the 660 km discontinuity long period precursors to the ss seismic phase are used to produce global maps of topography for the discontinuity at 660 km depth in the upper mantle these maps indicate discontinuity depth variations of up to 30 km and suggest a correlation between regional depressions in the 660 km discontinuity and subduction zones a result more consistent with models in which the subducting slabs are deflected horizontally at the discontinuity than with models of unhindered slab penetration into the lower mantle

silica precipitates in omphacite from eclogite at alpe arami switzerland evidence of deep subduction observations of oriented sio2 precipitates in omphacite from eclogite with tholeiitic basalt protolith bordering the alpe arami garnet peridotite massif ticino switzerland and petrological studies of the eclogitic mineral assemblages suggest that this rock was subjected to higher pressure metamorphism than previously realized we employed various calibrations of the fe2 mg exchange thermometer and calculations of equilibria with thermodynamic data considering the calcium tschermak s component caal2sio6 of garnet pyroxene pairs from these calculations it is concluded that the eclogitic lenses have recorded at least four stages of mineral growth corresponding to the following stage i prograde c 2 4 gpa 700 c stage iia maximum recorded grade c 7 0 gpa 1100 c stage iib retrograde c 3 7 gpa 900 c stage iii retrograde c 2 1 gpa 750 c because of the preservation of stage i a relatively rapid subduction and exhumation of alpe arami eclogite is suggested the exhumation path of the eclogitic rock is in good agreement with most exhumation paths inferred for the alpe arami garnet lherzolite proposed previously by several authors based upon a variety of different observations although the eclogite and peridotite exhumation paths may diverge at depths greater than 120 km

anisotropy of heterogeneity scale lengths in the lower mantle from pkikp precursors summary the anisotropy of heterogeneity scale lengths in the lower mantle is investigated by modelling its evect on the high frequency precursors of pkikp scattered by the heterogeneities although models having either an isotropic or an anisotropic distribution of scale lengths can fit the observed coda shapes of short period precursors the frequency content of broad band pkikp precursors favours a dominantly isotropic distribution of scale lengths precursor coda shapes are consistent with 1 per cent fluctuations in p velocity in the wavenumber band 0 05 0 5 km 1 extending to 1000 km above the core mantle boundary and with a d region open to circulation throughout the lower mantle the level of excitation of pkikp precursors observed in the frequency band 0 02 2 hz requires a power spectrum of heterogeneity that is nearly white or slowly increasing with wavenumber anisotropy of scale lengths may exist in a d layer having larger horizontal than vertical scale lengths and produce little or no detectable evects on pkikp precursors for p velocity perturbations as high as 3 per cent when averaged over a vertical scale of several kilometres and much higher when averaged over scales of hundreds of metres or less

dynamics of former ice lobes of the southernmost patagonian ice sheet based on a glacial landsystems approach reconstructions of former ice masses from glacial geomorphology help to constrain the nature and timing of glaciation in relation to climatic forcing this paper presents a new reconstruction of the glacial history of five ice lobes in southernmost south america the bahia inutil san sebastian magellan otway skyring and rio gallegos ice lobes we use previous geomorphological mapping of glacial landforms to reconstruct former glacial limits and proglacial lakes demarcate flow sets from the distribution of glacial lineations and evaluate glacial landsystem signatures and their palaeoglaciological implications evidence suggests that the ice lobes predominantly reflect active temperate glacial landsystems which may have switched to polythermal systems when periods of cold based ice developed ephemerally this complex landsystem signature implies that the ice lobes were sensitive to regional climate variability with active re advances during overall retreat of the ice margins there is also evidence for periods of fast ice flow and possible surge like activity in the region followed by the rapid retreat or even collapse of some of the ice lobes in association with proglacial lakes constraining our new reconstruction with published chronological information suggests that at least some of the ice lobes advanced before the global last glacial maximum glgm ca 26 5 19 ka during the last glacial cycle our new reconstruction demonstrates a more complex picture of ice dynamics than has previously been portrayed and one in which the advance and retreat of the ice lobes was likely to have been primarily driven by changes in climate as such ice advances before the glgm in the southernmost part of the patagonian ice sheet are likely to indicate a wider climatic forcing at this time

calibration of cosmogenic 36cl production rates from ca and k spallation in lava flows from mt etna 38 n italy and payun matru 36 s argentina abstract published cosmogenic 36cl production rates from ca and k spallation differ by almost a factor of 2 in this paper we determine production rates of 36cl from ca and k in samples of known age containing little cl ca rich plagioclases and k feldspars were separated from a total of 13 samples collected on the surfaces of four basaltic lava flows at mt etna 38 n italy and from a trachyte lava flow at payun matru volcano 36 s argentina eruption ages determined by independent methods range between 0 4 and 32 ka sample site elevations range between 500 and 2500 m corresponding scaling factors were calculated using five different published scaling models four of which consider paleo geomagnetic field variations integrated over the exposure durations the resulting five data sets were then analyzed using a bayesian statistical model that incorporates the major inherent uncertainties in a consistent way spallation production rates from ca and k considering all major uncertainties are 42 2 4 8 atoms 36cl g ca 1 a 1 and 124 9 8 1 atoms 36cl g k 1 a 1 normalized to sea level and high latitude using the scaling method of stone 2000 scaling models that account for paleo geomagnetic intensity changes yield very similar mean values at most 4 if the uncertainties in the independent ages are neglected in the bayesian model the calculated element specific production rates would be about 12 higher our results are in agreement with previous production rate estimations both for ca and k if only low cl i e 20 ppm samples are considered

in situ cosmogenic 10be production rate at lago argentino patagonia implications for late glacial climate chronology abstract when calculated with the commonly accepted average northern hemisphere production rate 10 be dates of surface boulders on moraines in the lago argentino area of patagonia are younger than minimum limiting 14 c ages for the same landforms this disagreement could result from the lack of a regional 10 be production rate calibration site to assess this possibility we here present high precision measurements of 10 be in samples collected from surface boulders on the herminita and puerto bandera moraine complexes deposited alongside lago argentino on the eastern flank of the andes at 50 s in patagonia together with maximum and minimum limiting 14 c ages for the two moraine systems these measurements confine the local 10 be production rate to between 3 60 and 3 82 atoms g yr midpoint 3 71 0 11 atoms g yr when using a time dependent scaling method that incorporates a high resolution geomagnetic model this range includes upper and lower error bounds of acceptable production rates derived from both the herminita and the puerto bandera sites the upper limit of this range is more than 12 below the average northern hemisphere production rate as calculated using the same scaling method given in balco et al quat geochron 3 2008 174 195 other scaling models yield production rates with similarly large offsets from the balco et al 2008 rate on the other hand the range of acceptable production rate values determined from patagonia overlaps at 1 with and encompasses the production rate recently derived in macaulay valley in the southern alps of new zealand a putnam et al quat geochron 5 2010a 392 409 within uncertainties i e overlap at 1 sigma this patagonian production rate range also agrees with a recently determined production rate from low elevation sites in northeastern north america and northern norway when the macaulay production rate is used to calculate patagonian exposure dates 14 c and 10 be chronologies are mutually compatible for late glacial moraine systems both chronologies then indicate that outlet glaciers of the southern patagonian icefield achieved a late glacial maximum in the western reaches of lago argentino at 13 000 cal yr bp at the end of the antarctic cold reversal 14 500 12 900 cal yr bp outlet glaciers subsequently receded to near present day ice margins during the younger dryas stadial 12 900 11 700 cal yr bp this general retreat was interrupted about 12 200 cal yr bp when upsala glacier constructed an interlobate complex of moraine ridges on herminita peninsula mountain glaciers in patagonia and new zealand on both sides of the south pacific ocean exhibited a coherent pattern of late glacial ice margin fluctuations

detailed seismic stratigraphy of lago puyehue implications for the mode and timing of glacier retreat in the chilean lake district lago puyehue is a glacigenic lake in the chilean lake district 40 s with a complex deglaciation history a detailed seismic stratigraphic study of its sedimentary infill indicates a much earlier retreat of the glacier from the lago puyehue basin than the neighbouring glacier from the lago rupanco basin because of their close proximity rupanco meltwater streams played an important part in the depositional processes of lago puyehue a timing discrepancy between the in lake ages of a sediment core and the outer lake ages of moraine deposits re opens the discussion on the timing of deglaciation in the southern hemisphere copyright 2011 john wiley sons ltd

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

the chronology of the last glacial maximum and deglacial events in central argentine patagonia this paper evaluates the chronology of the last glacial cycle and deglaciation in the lago pueyrredon valley of central patagonia 47 5 s argentina the valley was a major outlet of the former patagonian ice sheet and the moraines that record its fluctuations are an important proxy record of climate change in southern south america such moraines are well preserved in the lago pueyrredon valley owing in part to the semi arid environment east of the mountain front here we provide the first direct chronology for the age of the rio blanco moraine system by utilizing cosmogenic nuclide surface exposure ages boulders on the moraines give 10be exposure ages that indicate the last glacial maximum lgm maximum extent occurred by 27 25 ka subsequent advances occurred at 23 22 ka 20 18 ka and ca 18 17 ka initial deglaciation began after ca 18 17 ka and was interrupted as evidenced by the lago columna moraines up valley subsequently the outlet glaciers occupying both the lago pueyrredon basin chilean name lago cochrane and the lago buenos aires basin chilean name lago general carrera to the north rapidly retreated more than 80 km at around 16 5 15 ka the timing of the lgm maximum extent and the onset of deglaciation occurred broadly synchronously throughout patagonia deglaciation resulted in a series of interconnected glacier dammed lakes in the region that initially drained toward the atlantic ocean and later drained to the pacific ocean as a consequence of disintegrating ice in the andes

evidence in favour of an extensive ice cover on sub antarctic kerguelen island during the last glacial abstract arguments to date have suggested that during the last glacial wurm wisconsin weichselian sub antarctic kerguelen island did not experience an extensive ice cover and that the fjords and glacial valleys are products of earlier events recent observations of striation orientations travel directions of erratics cirque altitudes and evidence for isostatic uplift suggest that there in fact may have been extensive ice cover the equilibrium line altitude e l a reconstructed for the cirque glacier stage agrees well with that for sub antarctic marion island situated to the west a possible explanation for the lack of glacial deposits and landforms over much of the island is suggested

regionalized comparison of global earth models of seismic velocity geoid and topography implications on the geodynamics of ridges and subductions abstract global earth models of seismic velocity anomalies and geoid heights have been compared using the non parametric spearman rank order correlation test to analyse their spatial coherence at both global and regional scales at the global scale these comparison results are similar to previously published results this confirms that the assumed linear relationship between the tomographic models and the geoid is valid at the global scale the comparison between global earth models was then conducted in two structural provinces a ridge province and a subduction province we observe a positive correlation between tomography and geoid data near the transition zone in the two provinces a significant positive correlation between the geoid and the topography is observed in the subduction province in the l 7 8 and l 9 10 wavebands these positive correlations are consistent with the hypothesis of deep penetration of subducted slabs into the mantle the correlation in these two wavebands also suggests that the mantle heterogeneities under subduction zones are characterized by wavelengths around 4000 km in the ridge province the topography and the tomography are negatively correlated in the upper mantle at shorter wavelengths up to l 15 this result is in favour of a shallow origin of the ridge material

high frequency holocene glacier fluctuations in new zealand differ from the northern signature understanding the timings of interhemispheric climate changes during the holocene along with their causes remains a major problem of climate science here we present a high resolution 10be chronology of glacier fluctuations in new zealand s southern alps over the past 7000 years including at least five events during the last millennium the extents of glacier advances decreased from the middle to the late holocene in contrast with the northern hemisphere pattern several glacier advances occurred in new zealand during classic northern warm periods these findings point to the importance of regional driving and or amplifying mechanisms we suggest that atmospheric circulation changes in the southwest pacific were one important factor in forcing high frequency holocene glacier fluctuations in new zealand

glacial history of sub antarctic south georgia based on the submarine geomorphology of its fjords we present multibeam swath bathymetric surveys of the major fjords surrounding the sub antarctic island of south georgia to characterise the glacial geomorphology and to identify the relative timings and extent of past glacial advance and retreat bathymetry data revealed a range of glacial features including terminal retreat and truncated moraines deep distal outer and shallow proximal inner basins and cross shelf troughs these provide evidence of glacial advance and retreat through several glacial cycles a near consistent pattern of large scale submarine geomorphological features was observed in the different fjords suggesting a similar response of margins of the island ice cap to past climate forcing a relative chronology based on the relationships between the submarine features with their radiocarbon and cosmogenic isotope dated terrestrial counterparts suggests that widely observed inner basin moraines date from the last major glacial advance or last glacial maximum while deep basin moraines may date from an earlier pre lgm more extensive glaciation which we speculate corresponds to mis6 on the sides of the deep basins a series of truncated moraines show ice advance positions from preceding glacial periods the cross shelf troughs and mid trough moraines are interpreted as the product of much more extensive glaciations that predate the fjord geomorphology mapped here thus possibly older than mis6 this hypothesis would suggest that south georgia followed a glacial history similar to that of central patagonia 46 s where a series of pleistocene glaciations of mis 20 and younger extended beyond lgm limits with the most extensive glacial advance occurring at c 1 1 ma

southern patagonian glacial chronology for the last glacial period and implications for southern ocean climate the magellan region of southern south america is in a unique setting at 50 s on the equatorial side of the antarctic frontal zone to record in detail terrestrial glacial to interglacial events a 10be chronology shows growth and millennial fluctuations of a patagonian ice sheet between 25 and 17 6 17 0 cal ka in the strait of magellan the maximum ice margin position is dated to 24 6 0 9 ka and other moraine ages are 18 5 1 8 and 17 6 0 2 ka mean 1 standard deviation in bahia inutil dated moraine ages are 20 4 1 2 and 17 3 0 8 ka the chronology of the local last glacial maximum lgm reveals a record of atmospheric cooling that was broadly in phase with changes in southern ocean conditions such as sea ice fluctuations and surface water characteristics published modeling results indicate that a decline in temperature of 6 c and slight drying over southernmost patagonia could simulate the growth and sustained presence of an ice sheet to the mapped lgm limit the terrestrial record in southern patagonia and marine records in adjacent oceans indicate mean northward movement of the antarctic frontal zone which caused the last southern south american ice age the antarctic frontal zone at present lies only 3 5 to the south some significant changes in the magellan region occurred in step with north atlantic region and the northern hemisphere for example the overall time span of the last glaciation and the timing of maximum ice extent were similar between the hemispheres despite maximum local summer insolation intensity in southern south america other characteristics of the southern patagonian glacial history differ from the north atlantic region specifically an out of phase relationship during deglaciation which is more similar to that of southern ocean and antarctic records

glacier extent in sub antarctic kerguelen archipelago from mis 3 period evidence from 36cl dating documenting sub antarctic glacier variations during the local last glacial maximum is of major interest to better understand their sensitivity to atmospheric and oceanic temperature changes in conjunction with antarctic ice sheet changes however data are sparse because evidence of earlier glacier extents is for most sub antarctic islands located offshore making their observation complex here we present cosmogenic 36cl surface exposure ages obtained from five sites at kerguelen to document the glacial history the 36cl ages from roche moutonnee surfaces erratics and boulders collected on moraines span from 41 9 4 4 ka to 14 3 1 1 ka ice began to retreat on the eastern part of the main island before 41 4 4 4 ka slow deglaciation occurred from 41 to 29 ka there is no evidence of advances between 29 ka and the antarctic cold reversal acr period 14 5 12 9 ka period during the acr however the bontemps and possibly belvedere moraines were formed by the advance of a cook ice cap outlet glacier and a local glacier on the presque ile jeanne d arc respectively this glacier evolution differs partly from that of glaciers in new zealand and in patagonia these asynchronous glacier changes in the sub antarctic region are however in agreement with sea surface temperature changes recorded around antarctica which suggest differences in the climate evolution of the indo pacific and atlantic sectors of antarctica

glacial geomorphology and chronology of deglaciation south georgia sub antarctic we mapped and dated the glacial geomorphology of north east south georgia in the maritime sub antarctic the aim was to examine the timing of deglaciation of the island in the context of inter hemispheric phasing of climate change former glacier limits are restricted to the inner fjords and our detailed mapping of them has demonstrated a consistent geomorphological pattern that is similar across several different glacier types and sizes the pattern comprises three suites of moraines categories a c not all of which are represented at every site because the outer suite is often overridden by younger suites category a is an outer wide low amplitude moraine ridge category b comprises 2 4 sharp crested bouldery moraines that are often located close to or even over riding a and category c is a series of lower amplitude moraines with overprinted streamlined landforms such as flutings analysis of in situ cosmogenic 10be in boulders on these moraines has allowed us to determine a deglacial chronology for the older two moraine groups the age of the inner youngest group has been estimated from soil development the cosmogenic nuclide ages show that the outermost moraine was deposited ca 12 2 1 5 ka bp but that a subsequent readvance in the mid holocene ca 3 6 1 1 ka bp reached and in places over rode this earlier moraine this latter advance coincides with the mid holocene hypsithermal a final late holocene advance reached closely similar limits to the previous two fluctuations and is estimated from soil data to have an age of ca 1 1 ka bp we suggest that the close concordance of late glacial and interglacial limits in this case associated with warming can be explained by a change in dominant forcing during glacials extensive sea ice limits precipitation availability and so glaciers are restricted to the inner fjords during interglacials precipitation is not limited in the same way by sea ice cover and so during warming precipitation increases and tidewater glaciers on the island have responded by advancing this study emphasises the importance of a clear understanding of geomorphology in order to interpret chronological information

on the penetration of the 660 km phase change by mantle downflows we present a simple analytic model of the inter action of cold convective downwelling currents with an dothermic phase change the model describes the ponding and lateral spreading of downflows along the phase transi tion interface a simple comparison of the vertical forces on the ponding material provides a necessary condition for a downflow to penetrate the phase boundary this con dition is fundamentally dependent on the geometry of the downflow for planar downwellings the model predicts a minimum ponding time before the structure can pen etrate the phase boundary for columnar axisymmetric downflows there is no minimum time of spreading required before penetration can proceed the model thus provides an explanation for the observation that in numerical mod els of three dimensional convection with an endothermic phase change cylindrical downflows penetrate the phase interface while planar ones do not since descending slabs in the earth s mantle display a wide spectrum of geome tries between planar and cylindrical given various trench curvatures as well as intersections of two or more subduc tion zones this phenomenon may explain in part why some slabs appear to extend into the lower mantle while others are deflected at the 660 km discontinuity

the last termination in the south indian ocean a unique terrestrial record from kerguelen islands 49 s situated within the southern hemisphere westerly belt the awareness of the significance of the southern ocean in the earth s climate system has become increasingly obvious the deglacial atmospheric co2 rise during warming periods in antarctica has been attributed to co2 ventilation from the deep ocean caused by enhanced upwelling around the antarctic divergence it has been hypothesized that more intense southern hemisphere westerly winds aligned with the antarctic circumpolar current due to a southward shift of the wind belt from its last glacial maximum equator ward position are the main drivers reconstructions of past changes in atmospheric circulation in the southern hemisphere are still scarce and the overall picture is patchy with sometimes contradictory results for obvious reasons most terrestrial records originate from southern south america and new zealand here we present a terrestrial record from the indian sector of the southern ocean from kerguelen islands located at 49 s a peat record is investigated using a multi proxy approach pollen and plant macrofossils magnetic susceptibility xrf analyses biogenic silica content rock eval6 analysis and humification degree peat accumulation starts at about 16 000 cal yr bp with relatively warm and dry conditions the most prominent change in our proxy data occurs at 13 600 cal yr bp when peat ponds were established on the peat surface resulting in lacustrine type deposits as a result of very high humidity and with proxies implying very windy conditions within chronological uncertainties this onset coincides with the onset of the so called oceanic cold reversal based on the deuterium excess data in the epica dome c ice core record kerguelen islands are located in the moisture source area of dome c and a change in atmospheric circulation at that time could explain both records around 12 900 cal yr bp at the end of the antarctic cold reversal pond lake sediments give way to more peaty deposits with proxies suggesting slightly drier less windy and probably warmer conditions kerguelen islands became less influenced by the southern hemisphere westerly winds and these conditions were amplified during the early holocene climate optimum as found in antarctic ice core records

the last glacial maximum at 44 s documented by a 10be moraine chronology at lake ohau southern alps of new zealand abstract determining whether glaciers registered the classic last glacial maximum lgm 26 500 19 000 yrs ago coevally between the hemispheres can help to discriminate among hypothesized drivers of ice age climate here we present a record of glacier behavior from the southern alps of new zealand during the local lgm llgm we used 10 be surface exposure dating methods and detailed glacial geomorphologic mapping to produce a robust chronology of well preserved terminal moraines deposited during the llgm near lake ohau on central south island we then used a glaciological model to estimate a llgm glacier snowline and atmospheric temperature from the ohau glacier record seventy three 10 be surface exposure ages place culminations of terminal moraine construction and hence completions of glacier advances to positions outboard of present day lake ohau at 138 600 10 600 yrs 32 520 970 yrs ago 27 400 1300 yrs ago 22 510 660 yrs ago and 18 220 500 yrs ago recessional moraines document glacier recession into the lake ohau trough by 17 690 350 yrs ago exposure of an ice molded bedrock bench located inboard of the innermost llgm moraines by 17 380 510 yrs ago indicates that the ice tongue had receded about 40 of its overall length by that time comparing our chronology with distances of retreat suggests that the ohau glacier terminus receded at a mean net rate of about 77 m yr 1 and its surface lowered by 200 m between 17 690 and 17 380 yrs ago a long term continuation of ice retreat in the ohau glacier catchment is implied by moraine records at the head of irishman stream valley a tributary of the ohau glacier valley the irishman stream cirque glacier advanced to produce a set of lateglacial moraines at 13 000 500 yrs ago implying that the cirque glacier was less extensive prior to that advance we employed a glaciological model fit to these mapped and dated llgm moraines to derive snowline elevations and temperature parameters from the ohau glacier record the modeling experiments indicate that a snowline lowering of 920 50 m and temperature depression of 6 25 0 5 c below modern values allows for the ohau glacier to grow to an equilibrium position within the lgm moraine belt taken together with a glaciological simulation reported from the irishman stream valley snowlines and temperatures increased by at least 520 m and 3 6 c respectively between 18 000 and 13 000 yrs ago climate parameters derived from the ohau glacier reconstruction are similar to those derived from glacier records from patagonia to air temperature indicators from antarctica as well as to sea surface temperature and stratification signatures of the southern ocean we think that the best explanation for the observed southern llgm is that southern winter duration modulated southern ocean sea ice which in turn influenced southern ocean stratification and made the surface ocean cooler orbitally induced cooling of the southern ocean provides an explanation for the llgm in the southern alps having been coincident with the northern lgm we argue further that the global effect of north atlantic stadials led to disturbance of southern ocean stratification southward shifts of the subtropical front and retreat of southern alps glaciers collapse of southern ocean stratification during heinrich stadial 1 along with attendant sea surface warming triggered the onset of the last glacial termination in the southern alps of new zealand

geoid anomalies from cenozoic subduction in semi dynamical flow models including a phase boundary in order to investigate the relationship between the geoid and plate subduction we develop a 3 d spherical shell model in which the circulation is driven by both buoyancy forces and an imposed surface velocity taken from plate reconstruction for the past 65 ma to avoid numerical resolution problems we use an enhanced value of thermal diffusivity which leads to an overly thick lithosphere the correct amount of buoyancy is re established by using a reduced value of thermal expansion coefficient first we calculate the present temperature field in the mantle due to the cenozoic plate motions for models with and without a phase transition at 660 km depth which is approximated by a locally modified effective thermal expansion coefficient in a second step the geoid anomalies are determined subject to a stress free upper boundary condition when the thermodynamic parameters of the boundary at 660 km allow slab penetration into the lower mantle the medium wavelength l 4 11 geoid agrees well with the observed geoid if there is a moderate increase of viscosity from the upper to the lower mantle when the clapeyron slope is sufficiently negative to prevent slab penetration the agreement is poor

layered convection induced by phase transitions we report a systematic study on the conditions under which an endothermic phase transition can enforce layered convection two dimensional numerical calculations of convection in a domain containing a divariant phase change were performed in the framework of the extended boussinesq approximation i e considering the effects of adiabatic gradient latent heat and frictional heating in the energy equation we find that the critical value of the negative clapeyron slope which must be surpassed in order to induce layered convection decreases in magnitude with increasing rayleigh number ra in the range 104 ra 2 106 near the critical clapeyron slope vacillations between double and single layer convection or strongly leaking double layer convection are possible the breakdown into layers is influenced very little by the latent heat release but depends solely on the phase boundary deflection caused by lateral temperature differences the value of the critical clapeyron slope also seems little affected by the width of the transition zone or by its depth a possible superplastic rheology within the transition zone would tend to favor layered convection scaling the model results to the 670 km discontinuity in the earth s mantle as a possible endothermic phase boundary we estimate the critical clapeyron slope to be in the range of 4 to 8 mpa k 40 to 80 bar k the possibility that the spinel perovskite periclase transition is within this range appears to be remote but certainly cannot be neglected

a possible uhp eclogite in the leaota mts south carpathians and its history from high pressure melting to retrograde inclusion in a subduction melange abstract an unusual eclogite pod containing impure jadeite to omphacite pyroxene with anti phase domain apd visible under the optical microscope is hosted in a medium grade matrix in the leaota massif textural relationships support the hypothesis of garnet formation by peritectic reactions involving high jadeite clinopyroxene while inclusions entrapped in garnet mainly a wide range of amphibole compositions seemingly crystallised from a fluid phase in disequilibrium with the garnet host thermobarometric estimates indicate uhp ht peak conditions 2 8 3 2 gpa 780 840 c inconsistent with those of the associated rocks followed by a complicated exhumation path the p t array of the retrograde path suggests syn subduction exhumation and tectonic inclusion in a melange with a matrix derived from the accretionary wedge partial melting of the subducting slab which induces tectonic weakening may be an effective mechanism in detaching and enclosing small eclogite pods in metamorphic terrains

phase relationships of i type granite with h2o to 35 kilobars the dinkey lakes biotite granite from the sierra nevada batholith the dinkey lakes biotite granite from the sierra nevada batholith was reacted with varying percentages of h 2o in sealed platinum capsules in a piston cylinder apparatus between 10 and 35 kbar the results were combined with the results from previously published experiments to provide comprehensive phase relationships for an i type granite a p t diagram with excess h 2o isobaric t x h 2o diagrams at 25 30 and 35 kbar showing h 2o undersaturated relations the h 2o undersaturated liquidus surface mapped with contours for constant h 2o contents and fields for near liquidus minerals and the solubility of h 2o in granite liquids to 35 kbar results and their implications show 1 the solidus temperature decreases from 680 c at 2 kbar to 620 c at 10 kbar then increases to 700 c at 35 kbar because of changes from less dense to more dense subsolidus mineral assemblages 2 the melting interval with excess h 2o which is only 35 c at 2 kbar increases to 105 c at 10 kbar and 150 c at 35 kbar because the liquidus minimum in the complex rock system departs from granite composition with increasing pressure 3 the solubility of h 2o in granite liquid is 27 2 5 weight percent at 35 kbar and 850 c indicating that a miscibility gap persists between h 2o saturated silicate magmas and aqueous vapor phase at least to pressures corresponding to 120 km depth in the mantle dissolution of alkali feldspar 20 of rock in the subsolidus aqueous vapor phase indicates that deep seated aqueous fluids are concentrated solutions 4 quartz and coesite are the liquidus minerals at mantle pressures for all h 2o contents indicating that granites and rhyolites cannot be primary magmas from mantle peridotite or subducted oceanic gabbroic crust 5 the liquidus surface at crustal pressures with plagioclase and quartz as primary minerals indicates that primary liquids of granite composition with moderate h 2o contents can be generated in the crust at reasonable temperatures these liquids could rise to near surface levels without vesiculation granite liquid together with residual crustal minerals could constitute plutonic magmas of intermediate composition

the medieval climate anomaly in antarctica abstract the medieval climate anomaly mca is a well recognized climate perturbation in many parts of the world with a core period of 1000 1200 ce here we are mapping the mca across the antarctic region based on the analysis of published palaeotemperature proxy data from 60 sites in addition to the conventionally used ice core data we are integrating temperature proxy records from marine and terrestrial sediment cores as well as radiocarbon ages of glacier moraines and elephant seal colonies a generally warm mca compared to the subsequent little ice age lia was found for the subantarctic islands south of the antarctic convergence the antarctic peninsula victoria land and central west antarctica a somewhat less clear mca warm signal was detected for the majority of east antarctica mca cooling occurred in the ross ice shelf region and probably in the weddell sea and on filchner ronne ice shelf spatial distribution of mca cooling and warming follows modern dipole patterns as reflected by areas of opposing temperature trends main drivers of the multi centennial scale climate variability appear to be the southern annular mode sam and el nino southern oscillation enso which are linked to solar activity changes by nonlinear dynamics

terrestrial and submarine evidence for the extent and timing of the last glacial maximum and the onset of deglaciation on the maritime antarctic and sub antarctic islands this paper is the maritime and sub antarctic contribution to the scientific committee for antarctic research scar past antarctic ice sheet dynamics pais community antarctic ice sheet reconstruction the overarching aim for all sectors of antarctica was to reconstruct the last glacial maximum lgm ice sheet extent and thickness and map the subsequent deglaciation in a series of 5000 year time slices however our review of the literature found surprisingly few high quality chronological constraints on changing glacier extents on these timescales in the maritime and sub antarctic sector therefore in this paper we focus on an assessment of the terrestrial and offshore evidence for the lgm ice extent establishing minimum ages for the onset of deglaciation and separating evidence of deglaciation from lgm limits from those associated with later holocene glacier fluctuations evidence included geomorphological descriptions of glacial landscapes radiocarbon dated basal peat and lake sediment deposits cosmogenic isotope ages of glacial features and molecular biological data we propose a classification of the glacial history of the maritime and sub antarctic islands based on this assembled evidence these include type i islands which accumulated little or no lgm ice type ii islands with a limited lgm ice extent but evidence of extensive earlier continental shelf glaciations type iii seamounts and volcanoes unlikely to have accumulated significant lgm ice cover type iv islands on shallow shelves with both terrestrial and submarine evidence of lgm and or earlier ice expansion type v islands north of the antarctic polar front with terrestrial evidence of lgm ice expansion and type vi islands with no data finally we review the climatological and geomorphological settings that separate the glaciological history of the islands within this classification scheme

predominance of long wavelength heterogeneity in the mantle analysis of travel time anomalies of long period shear waves recorded by the global digital seismographic network indicates that mantle heterogeneities which probably reflect patterns of mantle convection occur most prominently on length scales greater than about 6 000 km when projected onto a two dimensional map at the earth s surface models of mantle convection will need to be able to produce a similar power spectrum

holocene glacier history of the lago argentino basin southern patagonian icefield abstract we present new geomorphic stratigraphic and chronologic data for holocene glacier fluctuations in the lago argentino basin on the eastern side of the southern patagonian andes chronologic control is based on 14c and surface exposure 10be dating after the lateglacial maximum at 13 000 cal yrs bp the large ice lobes that filled the eastern reaches of lago argentino retreated and separated into individual outlet glaciers this recession was interrupted only by a stillstand or minor readvance at 12 200 cal yrs bp the eight largest of these individual outlet glaciers are from north to south upsala agassiz onelli spegazzini mayo ameghino perito moreno and grande formerly frias holocene recession of upsala glacier exposed brazo cristina more than 10 115 100 cal yrs bp and reached inboard of the holocene moraines in agassiz este valley by 9205 85 cal yrs bp ice remained in an inboard position until 7730 50 cal yrs bp several subsequent glacier readvances are well documented for the upsala and frias glaciers the upsala glacier readvanced at least seven times the first being a relatively minor expansion documented only in stratigraphic sections between 7730 50 and 7210 45 cal yrs bp the most extensive holocene advances of upsala glacier resulted in the deposition of the pearson 1 moraines and related landforms which are divided into three systems the pearson 1a advance occurred about 6000 5000 cal yrs bp and was followed by the slightly less extensive pearson 1b and 1c advances dated to 2500 2000 and 1500 1100 cal yrs bp respectively subsequent advances of upsala glacier resulted in deposition of the pearson 2 moraines and corresponding landforms also separated into three systems pearson 2a 2b and 2c constructed respectively at 700 400 and

high resolution seismic stratigraphy of glacial to interglacial fill of a deep glacigenic lake lake le bourget northwestern alps france abstract lake le bourget is a deep peri alpine glacial lake originating from the last glacial the wurm the lake has amassed over 250 m of sediment since the last glacial maximum two seismic sparker surveys on the lake revealed the glacial and post glacial sedimentary infill the depth and the morphology of the wurm erosion surface and penetrated the riss wurm interglacial deposits as deep as the underlying riss erosion surface the density of the seismic grid and the high resolution of the data even at greater depths allowed a detailed study of the sedimentary processes and of their evolution throughout the deglaciation five main seismic facies characterise the basin fill they are interpreted as glacial deposits glacio lacustrine sediments proglacial lacustrine fans alluvial fan deltas and authigenic lacustrine drape these occur as a suite of deposits associated with the major lake tributaries and are the result of major changes in sediment supply and style of discharge into the lake the three dimensional facies associations within the basin fill document the history of the basin and its catchment area since the onset of the deglaciation

mantle phase transitions and layered chaotic convection we report preliminary results from a sequence of very high resolution simulations of the mantle convection process based upon an axisymmetric anelastically compressible spherical model with both olivine spinel and spinel post spinel phase transitions our analyses strongly suggest that at earth like rayleigh numbers near 107 the circulation may be quite strongly layered although a very long timescale transient exists that is characterized by brief excursions into the whole mantle state we suggest the use of a new diagnostic tool that may be employed to determine whether or not the layered state is characteristic of the present day earth

effects of depth dependent thermal expansivity on mantle circulations and lateral thermal anomalies the influences of depth dependent thermal expansivity on the structure of newtonian thermal convection and lateral thermal anomalies are studied in an aspect ratio ten box the effects of the depth dependent expansivity are to produce large aspect ratio cells with a few relatively stationary upwellings the lateral thermal anomalies in the lower mantle are greatly diminished by depth dependent expansivity this together with a decrease in the temperature derivative of seismic velocities in the lower mantle would support the low level of lateral heterogeneities found in recent tomographic studies

melting temperature of the earth s mantle and core earth s thermal structure abstract although the temperature at the top of the lower mantle is well constrained by phase equilibrium data for the transformation of transition zone minerals to the denser perovskite polymorphs the temperature distribution in the lower mantle is poorly known models depend strongly on the assumptions of the amount of internal heating and the viscosity profile new melting data on iron to pressures of the outer core 2 mbar and the observed strong decrease of eutectic melting depression in the fe feo fes system with increasing pressure however tightly constrain the temperature at the inner core boundary to slightly less than 5000 k this estimate can be reconciled with all recent static melting measurements on iron and lays within the uncertainty of shock temperature measurements the resulting temperature at the core mantle boundary of about 4000 k then requires a large temperature gradient at the bottom of the lower mantle of about 1500 k recent findings of the very high melting temperatures o

onset of deglacial warming in west antarctica driven by local orbital forcing an annually resolved ice core record from west antarctica indicates that warming driven by local insolation resulting from sea ice decline began in that region about 2 000 years before warming in east antarctica reconciling two alternative explanations for deglacial warming in the southern hemisphere

a temperature profile of the mantle transition zone the temperature distribution across the transition zone has been determined on the high pressure phase equilibria in the system mg2sio4 fe2sio4 recently determined by katsura and ito 1988 and ito and takahashi 1988 the temperature at the base of the transition zone 655 km depth is estimated to be about 1600 c assuming that the spinel dissociation is responsible for the sharp seismic discontinuity implied by study of reflected waves this estimation would be little modified for the chemically stratified mantle models since the lower mantle is characterized by the stability of perovskite the temperatures in the region from 350 km to 655 km depth are calculated for a peridotitic mantle model assuming an adiabatic temperature gradient the and transformations in mg fe 2sio4 make the temperature profile steep in the depth regions of 390 415 km and 500 530 km respectively the temperature would increase from about 1400 c to 1600 c over the depths interval 350 between 655 km

seismic tomography of the earth s mantle the analysis of information contained in seismograms is the most promis ing tool for retrieving the three dimensional structure of the earth s mantle and thereby improving our understanding of its dynamics the procedure through which three dimensional images of different parts of the earth s interior arc obtained by inversion of a set of observables measured on the surface of the earth is commonly termed tomography by analogy with the medical procedure with which it shares many aspects of methodology but with much less favorable experimental conditions ideally one would like to be able to model entire seismograms over a wide frequency band for a large number of uniformly distributed sources and stations in order to obtain an optimal illumination of the inhomogeneities appropriate for tomographic inversion in practice a number of difficulties and limitations arise onc is the nonuniform distribution of sources and receivers seis micity is concentrated at plate boundaries and the distribution of con tinental and island areas leaves large portions of the oceans unin strumented another difficulty is our limited ability to accurately forward model the effects of wave propagation in a realistic earth which presents departures from a spherically symmetric referencc model of both elastic anc1astic and isotropic anisotropic nature this is why until now the simplest kind of tomography travel time tomography has prevailed relying on simplifying assumptions concerning the interaction of asphericity with propagating seismic waves ray theory and the laws of geometrical optics in their

comparisons of seismic heterogeneity models and convective flow calculations by comparing models of the earth s mantle obtained from seismic tomography with the predictions of convective flow calculations we may interpret the seismic results in terms of mantle flow scenarios the results of such comparisons are consistent with a picture of convective flow in the earth s mantle in which whole mantle style flow is dominant at present but in which phase transition induced localized layering also exists in addition direct examination of the tomographic images show regions where the boundary between upper and lower mantle marks a significant discontinuity in heterogeneity while in other regions heterogeneities appear to be continuous across it

catastrophic overturn of the earth s mantle driven by multiple phase changes and internal heat generation the effects of phase changes and strong internal heat generation may combine to bring about brief but extremely intense episodes of rapid thermal convection in the earth s mantle numerical calculations using realistic thermodynamic properties for the exothermic olivine spinel and endothermic spinel perovskite magnesiowustite phase transitions suggest the transition region of the earth s mantle may act as a capacitor for subducting slabs slab material accumulates in the transition region until a threshold level of thermal buoyancy is reached and is then rapidly discharged into the lower mantle in my calculations this occurs as a catastrophic burst of convection lasting 10 myr with elevated heat transfer rates lasting 100 myr such episodes may be analogs to superplume activity which has been hypothesized to give rise to an intense episode of intra plate volcanism and stabilize the geodynamo against reversals the topography on the two phase change boundaries is found to be negatively correlated with the correlation becoming more negative during periods of rapid convection furthermore the results of this study suggest the transition region of the earth s mantle could be 250 k cooler on average and consequently more viscous than the surrounding mantle

warming and glacier recession in the rakaia valley southern alps of new zealand during heinrich stadial 1 abstract the termination of the last ice age featured a major reconfiguration of earth s climate and cryosphere yet the underlying causes of these massive changes continue to be debated documenting the spatial and temporal variations of atmospheric temperature during deglaciation can help discriminate among potential drivers here we present a 10be surface exposure chronology and glaciological reconstruction of ice recession following the last glacial maximum lgm in the rakaia valley southern alps of new zealand innermost lgm moraines at big ben have an age of 17 840 240 yrs whereas ice marginal moraines or ice molded bedrock surfaces at distances up valley from big ben of 12 5 km lake coleridge 25 km castle hill 28 km double hill 43 km prospect hill and 58 km reischek knob have ages of 17 020 70 yrs 17 100 110 yrs 16 960 370 yrs 16 250 340 yrs and 15 660 160 yrs respectively these results indicate extensive recession of the rakaia glacier which we attribute primarily to the effects of climatic warming in conjunction with geomorphological maps and a glaciological reconstruction for the rakaia valley we use our chronology to infer timing and magnitude of past atmospheric temperature changes compared to an overall temperature rise of 4 65 c between the end of the lgm and the start of the holocene the glacier recession between 17 840 and 15 660 yrs ago is attributable to a net temperature increase of 4 0 c from 6 25 to 2 25 c accounting for 86 of the overall warming approximately 3 75 c 70 of the warming occurred between 17 840 and 16 250 yrs ago with a further 0 75 c 16 increase between 16 250 and 15 660 yrs ago a sustained southward shift of the subtropical front stf south of australia between 17 800 and 16 000 yrs ago coincides with the warming over the rakaia valley and suggests a close link between southern ocean frontal boundary positions and southern mid latitude climate most of the deglacial warming in the southern alps occurred during the early part of heinrich stadial 1 hs1 of the north atlantic region because the stf is associated with the position of the westerly wind belt our findings support the concept that a southward shift of earth s wind belts accompanied the early part of hs1 cooling in the north atlantic leading to warming and deglaciation in southern middle latitudes

the interaction of a subducting lithospheric slab with a chemical or phase boundary we have used a finite element model of time dependent convection to determine the conditions for penetration of the subducted plate into the lower mantle a temperature dependent and non newtonian rheology is applied to achieve platelike behavior of the upper and sinking thermal boundary layer of convection the 650 km discontinuity is taken as either a chemical or phase boundary or as a combination of both it is represented by a marker chain which effects additional buoyancy when distorted out of its equilibrium position when the compositional density contrast is greater than about 5 the descending slab is deflected sidewards at the boundary and two layer convection prevails a resulting depression of the boundary in the range of 50 200 km should be detectable with seismic methods below 5 density difference the slab plunges several hundred kilometers into the lower mantle and below 2 it will probably not stop before reaching the core mantle boundary and extensive mixing would be expected with a pure phase change a negative clapeyron slope of about 6 mpa k 60 bar k is required to establish a type of leaky double layer convection a more moderate slope can aid a small compositional density difference to prevent slab penetration into the lower mantle with the present uncertainties about the physical nature of the 650 km discontinuity a variety of convective styles appears possible on dynamical grounds

long period surface waves and mantle boundary undulations summary we address two questions with synthetic experiments 1 is there sufficient signal in long period surface wave data to provide useful constraints on topography on the internal boundaries in the upper mantle and around the transition zone 2 what is the magnitude and nature of the bias caused by undulations on internal discontinuities on inversions for volumetric structures that do not also include boundary structures the synthetic experiments rest on models of boundary topography on three upper mantle and transition zone discontinuities at 220 400 and 660 km depth the 660 km topographic model is that of shearer masters 1992 we consider the effect of two different 400 km models one is identical to shearer and master s model model a and the other is their model sign flipped model b the 220 km model is ad hoc but has been motivated by the work of revenaugh jordan 1989 1991b who argue that the 220 km discontinuity is not a global feature at all but has a continental affinity for simplicity our 220 km model is global but the jump in material properties across the discontinuity has been reduced relative prem by a factor of two and is based on a continent ocean model which is depressed up to 25 km below continents and ascends 10 km under oceans these resulting boundary models have a significant effect on long period fundamental spheroidal mode structure coefficients with a magnitude on average of 15 30per cent relative to the volumetric models m84a lo2 56 between harmonic degrees 20 l 75 inversion for volumetric structures of the structure coefficients computed with the boundary models alone devoid of volumetric structure shows that simple mantle volumetric structures can be found to fit the boundary structure coefficients nearly perfectly this demonstrates the essential trade off between boundary and volumetric mantle structures using surface wave data alone destructive interference between the effects of the 660km boundary and model b of the 400 km boundary requires a somewhat oscillatory volumetric mantle model to fit the structure coefficients but the resulting volumetric model is no more oscillatory than current models of the upper mantle both boundary models a and b produce on average a 30 per cent volumetric bias relative to m84a lo2 56 from the base of the crust to 1000 km depth the relative nature of the 400 km and 660 km undulations strongly affects the radial distribution of the volumetric bias but has less of an effect on the average size of the bias

alpine polyphase tectono metamorphic evolution of the south carpathians a new overview abstract the main terrains involved in the cretaceous tertiary tectonism in the south carpathians segment of the european alpine orogen are the getic supragetic and danubian continental crust fragments separated by the severin oceanic crust floored basin during the early middle cretaceous times the danubian microplate acted initially as a foreland unit strongly involved in the south carpathians nappe stacking multistage folding thrusting events uplift erosion and extensional stages and the development of associated sedimentary basins characterize the south carpathians during cretaceous to tertiary convergence and collision events the main cretaceous tectogenetic events responsible for contraction and crustal thickening processes in the south carpathians are mid cretaceous austrian phase and latest cretaceous laramide or getic phase in age the architecture of the south carpathians suggests polyphase tectonic evolution and mountain building and includes from top to bottom the getic supragetic basement cover nappes the severin and arjana cover nappes and danubian basement cover nappes all tectonically overriding the moesian platform the severin nappe complex including obarsia and severin nappes with late jurassic early cretaceous ophiolites and turbidites is squeezed between the danubian and getic supragetic basement nappes as a result of successive thrusting of dismembered units during the inferred mid to late cretaceous subduction collision followed by tectonic inversion processes early cretaceous thick skinned tectonics was replaced by thin skinned tectonics in late cretaceous thus the former middle cretaceous austrian nappe stack and its albian lower senonian cover got incorporated in the intra senonian laramide getic stacking of the getic supragetic severin arjana nappes onto the danubian nappe duplex the two contraction events are separated by an extensional tectonic phase in the upper plate recorded by the intrusion of the banatitic magmas 84 73 ma the overthrusting of the entire south carpathian cretaceous nappe stack onto the fold thrust foredeep units and to the moesian platform took place in the late miocene intra sarmatian times and was followed by extensional events and sedimentary basin formation

sub antartic glacier extensions in the kerguelen region 49 s indian ocean over the past 24 000 years constrained by 36cl moraine dating similar to many other regions in the world glaciers in the southern sub polar regions are currently retreating in the kerguelen islands 49 s 69 e the mass balance of the cook ice cap cic the largest ice cap in this region experienced dramatic shrinking between 1960 and 2013 with retreat rates among the highest in the world this observation needs to be evaluated in a long term context however data on the past glacier extents are sparse in the sub antartic regions to investigate the deglaciation pattern since the last glacial maximum lgm period we present the first 13 cosmogenic 36cl surface exposure ages from four sites in the kerguelen islands the 36cl ages from erratic and moraine boulders span form 24 4 2 7 ka to 0 3 0 1 ka we combined these ages with existing glacio marine radiocarbon ages and bathymetric data to document the temporal and spatial changes of the island s glacial history ice began to retreat on the main island before 24 4 2 7 ka until around the time of the antartic cold reversal acr period 14 5 12 9ka during which the bontemps moraine was formed by the advance of a cic outlet glacier deglaciation continued during the holocene probably until 3ka with evidence of minor advances during the last millennium the chronology is in pace with major changes in 18o in a recent west antarctica ice core record showing thet kerguelen islands glciers are particularly sensitive and relevant to document climate change in the southern polar regions

influence of the southern annular mode on the sea ice ocean system 1 the global sea ice ocean model orca2 lim driven by the ncep ncar national centers for environmental prediction national center for atmospheric research reanalysis daily 2 m air temperatures and 10 m winds and by monthly climatologies for precipitation cloud cover and relative humidity is used to investigate the impact of the southern annular mode sam on the antarctic sea ice ocean system our results suggest that the response of the circumpolar southern ocean consists of an annular and a nonannular component for the sea ice cover the non annular component seems to be the most important the annular component strongly affects the overall patterns of the upper ocean circulation when the sam is in its positive phase a northward surface ekman drift a downwelling at about 45 degreess and an upwelling in the vicinity of the antarctic continent are simulated the non annular component has a significant impact at the regional scale especially in the weddell ross amundsen and bellingshausen seas in those regions the pressure pattern associated with the sam induces meridional winds which advect warmer air in the weddell sea and around the antarctic peninsula and colder air in the amundsen and ross seas this implies a dipole response of sea ice to the sam with on average a decrease in ice area in the weddell sea and around the antarctic peninsula and an increase in the ross and amundsen seas during years with a high sam index the long term trend in the observed sea ice area does not appear to be related to the trend in the sam index

response of the antarctic circumpolar current to atmospheric variability abstract historical hydrographic profiles combined with recent argo profiles are used to obtain an estimate of the mean geostrophic circulation in the southern ocean thirteen years of altimetric sea level anomaly data are then added to reconstruct the time variable sea level and this new dataset is analyzed to identify and monitor the position of the two main fronts of the antarctic circumpolar current acc during the period 1993 2005 the authors relate their movements to the two main atmospheric climate modes of the southern hemisphere the southern annular mode sam and the el nino southern oscillation enso the study finds that although the fronts are steered by the bathymetry which sets their mean pathway on first order in flat bottom areas the fronts are subject to large meandering because of mesoscale activity and atmospheric forcing while the dominant mode of atmospheric variability in the southern hemisphere sam is relatively symmetric the oceanic response of the fronts is not show

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

ice wastage on the kerguelen islands 49 s 69 e between 1963 and 2006 1 we observed the wastage of ice masses on the kerguelen islands indian ocean 49 s 69 e using historical information and recent satellite data overall the total ice covered area on the islands declined from 703 to 552 km2 between 1963 and 2001 a reduction of 21 the area of cook ice cap the main ice body decreased asymmetrically from 501 to 403 km2 west flowing glaciers lost 11 of their area while east flowing glaciers lost 28 after 1991 the retreat rate accelerated from 1 9 km2 a 1963 1991 to 3 8 km2 a 1991 2003 between 1963 and 2000 the ice volume loss was 25 30 km3 equivalent to an area average ice thinning rate of 1 4 1 7 m a the glacial retreat took place in the climatic context of a relatively low level of precipitation compared to the 1950s and a 1 c warming that occurred between 1964 and 1982 the acceleration of the ice losses since at least the 1990s indicates that the state of the ice bodies on the kerguelen islands is still far from balanced together with other studies in patagonia south georgia and heard island our analysis is consistent with a pattern of strong and accelerated wastage of ice masses influenced by the southern ocean

the challenging application of cosmogenic dating methods in residual glacial landforms the case of sierra nevada spain abstract an accurate review of the literature on surface exposure dating methods shows evidence of the difficulty in applying cosmogenic dating methods to old moraines because of the intensity of late quaternary erosion processes moreover as in some previous cases we also found special difficulties in applying these methods to lia moraines caused by the intensity of current paraglacial processes the objective of this study is to apply cosmogenic dating methods to very old and very young moraines which in both cases have been or are being affected intensively by erosion with this purpose we collected samples of boulders from moraines corresponding to i the penultimate glaciation and ii the little ice age lia both from sierra nevada in the south of the iberian peninsula the sampling strategy was based on a preliminary accurate analysis of the geomorphological settings of two valley sites that resulted in the collection of only four boulder samples from an old moraine and three more from a very recent moraine using in situ produced cosmogenic 10be to date these boulders the old samples yielded an age of ca 130 135 ka for moraine stabilization the younger samples indicate that the lia moraine accretion probably occurred between the fourteenth and seventeenth centuries with a subsequent stage of accumulation during the nineteenth century as suggested by historical documents dating a glaciation that occurred prior to the last pleistocene glacial cycle and dating lia glacial stages are novel in the context of iberian glaciations and agree with other palaeoenvironmental studies in iberian and in other european mountains the limited number of boulders adequate for cosmic ray exposure dating prevents statistical methods to be applied and therefore highlights the need to improve geomorphological criteria in sample selection

temperature distribution in the crust and mantle in an attempt to understand the temperature distribution in the earth experimental constraints on the geotherm in the crust and mantle are considered the basic form of the geotherm is interpreted on the basis of two dominant mechanisms by which heat is transported in the earth 1 conduction through the rock and 2 advection by thermal flow data reveal that 1 the temperature distributions through continental lithosphere and through oceanic lithosphere more than 60 million years old are practically indistinguishable 2 crustal uplift is instrumental in modifying continental geotherms and 3 the average temperature through the archean crust and mantle was similar to that at present it is noted that current limitations in understanding the constitution of the lower mantle can lead to significant uncertainties in the thermal response time of the planetary interior

glacier retreat in new zealand during the younger dryas stadial the younger dryas a period of sudden cooling in the northern hemisphere about 12 900 years ago is perhaps the best known example of abrupt climate change but the global extent of the younger dryas is a topic of intense debate particularly in the record of glacial behaviour in new zealand a new reconstruction of the growth and retreat patterns of glaciers in the southern alps in new zealand at the time of the younger dryas supports the suggestion that temperature reductions in the north caused warming and glacial retreat in the southern hemisphere through a series of climate feedbacks the younger dryas during which northern hemisphere temperatures cooled drastically in just a few years is perhaps the best known example of abrupt climate change but its global extent is under debate particularly in the record of glacial behaviour in new zealand these authors present evidence for glacial retreat in new zealand during the younger dryas supporting the hypothesis that northern hemisphere climate changes caused southern hemisphere warming through a series of climate feedbacks millennial scale cold reversals in the high latitudes of both hemispheres interrupted the last transition from full glacial to interglacial climate conditions the presence of the younger dryas stadial 12 9 to 11 7 kyr ago is established throughout much of the northern hemisphere but the global timing nature and extent of the event are not well established evidence in mid to low latitudes of the southern hemisphere in particular has remained perplexing1 2 3 4 5 6 the debate has in part focused on the behaviour of mountain glaciers in new zealand where previous research has found equivocal evidence for the precise timing of increased or reduced ice extent1 2 3 the interhemispheric behaviour of the climate system during the younger dryas thus remains an open question fundamentally limiting our ability to formulate realistic models of global climate dynamics for this time period here we show that new zealand s glaciers retreated after 13 kyr bp at the onset of the younger dryas and in general over the subsequent 1 5 kyr period our evidence is based on detailed landform mapping a high precision 10be chronology7 and reconstruction of former ice extents and snow lines from well preserved cirque moraines our late glacial glacier chronology matches climatic trends in antarctica southern ocean behaviour and variations in atmospheric co2 the evidence points to a distinct warming of the southern mid latitude atmosphere during the younger dryas and a close coupling between new zealand s cryosphere and southern high latitude climate these findings support the hypothesis that extensive winter sea ice and curtailed meridional ocean overturning in the north atlantic led to a strong interhemispheric thermal gradient8 during late glacial times in turn leading to increased upwelling and co2 release from the southern ocean9 thereby triggering southern hemisphere warming during the northern younger dryas

a major advance of tropical andean glaciers during the antarctic cold reversal a moraine chronology determined by surface exposure dating shows that glaciers in the northern tropical andes expanded to a larger extent during the antarctic cold reversal 14 500 to 12 900 years ago than during the younger dryas stadial 12 800 to 11 500 years ago contrary to previous studies as a result previous chronologies and climate interpretations from tropical glaciers may need to be revisited the younger dryas was a cold period immediately prior to the present warm interglacial period there is clear evidence that it occurred throughout much of the northern hemisphere but its global extent remains debatable prior work in the tropical andes suggested extensive glacial advances during the younger dryas vincent favier and colleagues present new cosmogenic dating of glacial deposits and a reassessment of existing datasets from other glaciated andean landscapes to show that instead maximal glacial advances took place in the preceding antarctic cold reversal rather than a major advance the younger dryas now appears to have been associated with modest glacial retreat the younger dryas stadial a cold event spanning 12 800 to 11 500 years ago during the last deglaciation is thought to coincide with the last major glacial re advance in the tropical andes1 this interpretation relies mainly on cosmic ray exposure dating of glacial deposits recent studies however have established new production rates2 3 4 for cosmogenic 10be and 3he which make it necessary to update all chronologies in this region1 5 6 7 8 9 10 11 12 13 14 15 and revise our understanding of cryospheric responses to climate variability here we present a new 10be moraine chronology in colombia showing that glaciers in the northern tropical andes expanded to a larger extent during the antarctic cold reversal 14 500 to 12 900 years ago than during the younger dryas on the basis of a homogenized chronology of all 10be and 3he moraine ages across the tropical andes we show that this behaviour was common to the northern and southern tropical andes transient simulations with a coupled global climate model suggest that the common glacier behaviour was the result of atlantic meridional overturning circulation variability superimposed on a deglacial increase in the atmospheric carbon dioxide concentration during the antarctic cold reversal glaciers advanced primarily in response to cold sea surface temperatures over much of the southern hemisphere during the younger dryas however northern tropical andes glaciers retreated owing to abrupt regional warming in response to reduced precipitation and land surface feedbacks triggered by a weakened atlantic meridional overturning circulation conversely glacier retreat during the younger dryas in the southern tropical andes occurred as a result of progressive warming probably influenced by an increase in atmospheric carbon dioxide considered with evidence from mid latitude andean glaciers16 our results argue for a common glacier response to cold conditions in the antarctic cold reversal exceeding that of the younger dryas

multiple phase transitions and the style of mantle convection abstract multiple phase transitions based on experimental and theoretical results have been incorporated into an extended boussinesq model of mantle convection a formulation is used which facilitates the numerical computations of convection with multiple phase transitions and a triple point near the 670 km discontinuity the propensity for layered convection is enhanced by including the additional phase transitions the location of the triple point of the spinel to perovskite phase transitions plays an important role in controlling the fate of the ascending hot plumes a plume with a core temperature above this triple point temperature t c tends to pass easily through the phase boundary at 670 km plumes with a core temperature lower than t c are blocked by the multiple phase transitions both depth dependent thermal expansivity and internal heating increase the tendency of the convective system to layering the dynamical time scales in the transition zone are much shorter than those of the top and bottom boundary layers simulations with increasing rayleigh number ra from 10 6 to 5 10 7 show unambiguously the increased tendency toward layering with larger ra in the early earth when ra was higher and internal heating was several times stronger layered convection might have been the preferred mode of mantle convection with time as both ra and radioactive heating decreased the style of mantle convection would have become less layered

monazite in a variscan mylonitic paragneiss from the munchberg metamorphic complex ne bavaria records cadomian protolith ages small oval shaped unshielded monazite grains found in a variscan garnet muscovite bearing mylonitic paragneiss from the liegendserie unit of the munchberg metamorphic complex mmc in the northwestern bohemian massif central europe yield only pre variscan ages these ages determined with the electron microprobe have maxima at about 545 520 and 495 ma and two side maxima at 455 and 575 ma and are comparable with previously determined ages of detrital zircon reported from paragneisses elsewhere in the nw bohemian massif the pressure p temperature t history of this mylonitic paragneiss determined from contoured p t pseudosections involved an initial stage at 6 kbar 600 c reaching peak p t conditions of 12 5 kbar 670 c with partial melting followed by mylonitization and retrogression to 9 kbar 610 c the monazite representing detrital grains derived from igneous rocks of a cadomian provenance between 575 455 ma has survived these variscan metamorphic deformational events unchanged because this mineral has probably never been outside its p t stability field during metamorphism this article is protected by copyright all rights reserved

radiocarbon chronology of the last glacial maximum and its termination in northwestern patagonia abstract we examine the timing and magnitude of the last glacial maximum lgm and the last glacial termination lgt in northwestern patagonia situated in the middle latitudes of south america our data indicate that the main phase of the lgt began with abrupt warm pulses at 17 800 and 17 100 cal yrs bp accompanied by rapid establishment of evergreen temperate rainforests and extensive deglaciation of the andes within 1000 years this response shows that south american middle latitude temperatures had approached average interglacial values by 16 800 cal yrs bp the temperature rise in northwestern patagonia coincides with the beginning of major warming and glacier recession in the southern alps of new zealand at southern mid latitudes on the opposite side of the pacific ocean from this correspondence the warming that began at 17 800 cal yrs bp appears to have been widespread in middle latitudes of the southern hemisphere accounting for at least 75 of the total temperature recovery from the lgm to the holocene moreover this warming pulse is coeval with the first half of the heinrich stadial 1 hs1 in the north atlantic region hs1 featured a decline of north atlantic meridional overturning circulation a southward shift of the westerly wind belt in both hemispheres and of the intertropical convergence zone as well as a weakening of the asian monsoon along with the initiating trigger identifying the mechanisms whereby these opposing climate signals in the two polar hemispheres interacted whether through an oceanic or an atmospheric bipolar seesaw or both lies at the heart of understanding the lgt

development of diapiric structures in the upper mantle due to phase transitions solid state phase transitions in time dependent mantle convection can induce diapiric flows in the upper mantle when a deep mantle plume rises toward phase boundaries in the upper mantle the changes in the local thermal buoyancy local heat capacity and latent heat associated with the phase change at a depth of 670 kilometers tend to pinch off the plume head from the feeding stem and form a diapir this mechanism may explain episodic hot spot volcanism the nature of the multiple phase boundaries at the boundary between the upper and lower mantle may control the fate of deep mantle plumes allowing hot plumes to go through and retarding the tepid ones

geoid pangea and convection abstract we show that the present geoid has a simple low order configuration with an axis of symmetry in the equatorial plane we show further that it is a tennis ball pattern with an equatorial high belt and a polar low one which is clearly controlled by the rotation of the earth finally we show that the outline of pangea between at least 200 ma and 125 ma ago lay along a great circle passing through the paleo poles of rotation thus it also had an axis of symmetry in the equatorial plane this hemispheric super continent configuration ended in middle cretaceous time during a major geologic catastrophe which was accompanied by high rates of spreading hotspot outbreaks and high sea level stands we interpret this evidence in terms of separate steady state lower mantle convection responsible for the present geoid weakly coupled to the upper mantle one this weak coupling leads to the hemispheric continent configuration which ends when excessive heating of the upper mantle due to the insulating continental cap leads to continent dispersal the complete cycle from one supercontinent to the next might be of the order of 400 ma

the dependence of convection planform on mode of heating a fundamental property of a convecting fluid is its planform the distribution in the horizontal plane of hot rising regions and cold sinking regions for the earth s mantle the planform might he visualized as a map of subduction zones hotspots and possibly ocean ridges here i report numerical experiments of convection at high rayleigh number which show a strong dependence of planform on heating mode when heat generation is distributed uniformly through the box the preferred planform consists of an ensemble of time dependent cold axial sinkers distributed in a hot diffuse upward flow when half of the heat is generated within the box and the other half is input through the base the preferred planform consists of an array of hot axial plumes and elongated cold sheets in the former case the mean horizontal wavelength is about equal to the layer depth for the latter it is about twice the layer depth

the specific case of the mid proterozoic rapakivi granites and associated suite within the context of the columbia supercontinent abstract rapakivi granites and the associated suite anorthosite mangerite and charnockite that developed during the mid proterozoic escape the global rules that control usual granitic magma formation about 40 points that characterise the proterozoic magmatism confirm the originality of the magmatism rapakivi granites developed without a global orogenic context within the supercontinent columbia the intrusions extend from the east european shield to the western us through fennoscandia greenland and labrador other occurrences in the amazonian shield australia or south china are less well documented they show no definite trend in age or chemistry that would explain large scale mantle plume effects a mantle upwelling of material is contradictory with the re assembly of a supercontinent because it occurred before this magmatic episode 1 9 1 8 ga at 1 7 ga the supercontinent columbia amalgamated with the collision of the yapavai and mazatzal provinces a model is suggested that takes into account the supercontinent re assembly defining a downwelling flow in the mantle that anchors the continent above it in contrast to a material flow heat is still delivered to the base of the continental lithosphere and is focused toward the juvenile suture zone the base of the crust must reach 1200 1300 c before producing anorthosite magmas under such a high temperature gradient lasting over a long time magmas are transferred toward the upper crust giving the thin 5 km and square shape 100 km that the intrusions presently have heat delivery is essentially conductive leading to long time spans for intrusions the presence of the supercontinent immobile over a descending cell poloidal mode of convection developed a tangential force toroidal mode of convection that partly split the continent through strike slip deformation due to plate rotation it developed progressively between 1 57 and 1 3 ga starting from fennoscandia and then passing to amazonia western us and labrador in a clockwise sense the associated rotation induced sinistral shear manifested by small scale shear zones and the orientation of late magmatic facies topaz bearing granites in each province the proterozoic magmatism appears to be unique because it requires a supercontinent with a zone of juvenile crust surrounded by older cratons the present moho still shows remnants of this process having bumpy undulations that may reach 22 km in amplitude over a distance of 200 km

glacier advance in southern middle latitudes during the antarctic cold reversal the geographic extent of cooling associated with the antarctic cold reversal is unclear dating of glacial moraines in new zealand suggests that the cooling extended into the southern mid latitudes possibly as a result of the northward migration of the southern subtropical front

lateral heterogeneity in the convecting mantle thermally induced lateral heterogeneity in the earth s mantle has been studied in terms of idealized two dimensional constant viscosity numerical models of mantle convection steady model solutions of the temperature and velocity fields were analyzed with respect to both the spatial and spectral signatures of their inherent lateral heterogeneity by examining the changes in spectral signature produced by varying the rayleigh number the degree of internal heating and the depth in the convection cell it has been possible to identify those features of the spectra of lateral heterogeneity which are most indicative of these variations particular attention has been paid to the spectral characteristics of thermal boundary layers within the convecting layer the spectral analysis of known temperature fields represents the forward problem corresponding to the inverse problem of inferring the thermal structure of the mantle from the spectral components of its lateral heterogeneity as determined by seismic tomography the forward problem presented here illustrates a new approach in convection modeling which may ultimately provide important diagnostic criteria for the interpretation of recent tomographic data

convection with internal heat sources and thermal turbulence in the earth s mantle summary the influence of internal heat sources on mantle convection is investigated using numerical calculations of 2 d thermal convection in an infinite prandtl number incompressible fluid the geometry is a cylindrical annulus with inner and outer radii in proportion to the whole mantle time dependent calculations are made starting from random initial conditions with rayleigh numbers rat based on boundary temperature difference and ra based on internal heat production in the range 1dsrats lo7 and osra 524rat at fixed rat increasing ra results in transitions in flow structure from steady cells to a pattern of stationary cells with time variable amplitude and finally to thermally turbulent convection with a non stationary cell count for rat 10 and ra rat approximately the travelling plumes disrupt the large scale circulation producing turbulent convection at ra lo7 the flow is fully developed thermal turbulence and for ra 0 consists of a rapidly fluctuating irregular flow driven by transient rising and sinking sheets of buoyant fluid large fluctuations in total kinetic energy occur in this regime with periodicities ranging from 40 to 1400myr the transition to thermal turbulence occurs in these calculations at rayleigh numbers well below the value estimated for subsolidus convection in the mantle suggesting thermally turbulent convection may occur in the mantle a consequence of internal heat sources thermal turbulence offers an explanation for long term fluctuations in the rate of subduction sea floor spreading and global volcanic activity

short wavelength lower mantle seismic velocity anomalies the lower mantle seismic velocity anomalies display very smooth shapes and low amplitudes in apparent contradiction with the thermal anomalies obtained from chaotic convection models an attempt to reconcile theoretical convection models with tomographic results is presented in this paper along with a coherent approach of lower mantle convection the influences of radial and angular filtering on the shapes and on the amplitudes of anomalies have been monitored a tremendous spreading of the radial anomalies into horizontal structures and a significant loss of amplitude of the anomalies result from this exercice the level of the root mean square of the thermal anomalies falls from several tens of degrees to values in close agreement with tomographic results this study shows that the short wavelength of lower mantle velocity anomalies are dramatically hidden by the truncation level of seismic tomography

regional modeling of surface mass balance on the cook ice cap kerguelen islands 49 circ mathrm s 49 s 69 circ mathrm e 69 e we assess the ability of the regional circulation model mar to represent the recent negative surface mass balance smb observed over the kerguelen islands 49 circ hbox s 69 circ hbox e and evaluate the uncertainties in smb projections until the end of the century the mar model forced by era interim reanalysis shows a good agreement with meteorological observations at kerguelen particularly after slight adjustment of the forcing fields 10 humidity 0 8 circ hbox c all year round to improve precipitation occurrence and intensity the modeled smb and surface energy balance seb are also successfully evaluated with observations and spatial distributions are explained as being largely driven by the elevation gradient and by the strong west to east foehn effect occurring on the ice cap we select five general circulation models gcms from the coupled model intercomparison project phase 5 cmip5 by evaluating their ability to represent temperature and humidity in the southern mid latitudes over 1980 1999 with respect to era interim and use them to force the mar model these simulations fail to replicate smb observations even when outputs from the best cmip5 model access1 3 are used as forcing because all gcms fail in accurately reproducing the circulation changes observed at kerguelen since the mid 1970s global models chosen to represent extreme values of smb drivers also fail in producing extreme values of smb suggesting that more rigorous modeling of present and future circulation changes with gcms is still needed to accurately assess future changes of the cryosphere in this area