variations of the effective elastic thickness reveal tectonic fragmentation of the antarctic lithosphere abstract to this day little is known about thermal and rheological properties of the antarctic lithosphere we derive the effective elastic thickness t e as a proxy for these parameters by using ice thickness bedrock topography and a combination of new satellite and high resolution terrestrial gravity data cross spectral analysis based on the fan wavelet technique was employed to calculate t e variations by means of admittance and coherence techniques our results confirm a clear tectonic division of antarctica with predominantly high values in east antarctica eant t e 60 80 km and low values in west antarctica want t e 5 20 km for the transantarctic mountains separating these provinces we found t e to be around 10 km along the whole chain which is comparable to want apart from this general division we found fragmentation of the lithosphere within these provinces especially eant doesn t represent a single lithospheric block but shows strong variations of t e the highest values are found around the aurora subglacial basin t e 90 km and in dronning maud land t e 80 km the minimum value of t e within eant 15 km is found in the lambert graben such a low value can be associated with active rifting in the permian triassic strong localized erosion or possibly the effect of a cenozoic mantle plume according to the coherence calculations the weak zone extends to the gamburtsev subglacial mountains gsm showing a distinct decrease of t e to 25 30 km thus this weak channel divides the previously mentioned strong blocks however the admittance analysis gives relatively high values t e 70 km for the gsm based on the analysis of the wavelength dependent admittance and coherence results and misfits for several principal locations we give some preference to the coherence based values

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

coordinated hydrological regimes in the indo pacific region during the past two millennia instrumental data suggest that major shifts in tropical pacific atmospheric dynamics and hydrology have occurred within the past century potentially in response to anthropogenic warming to better understand these trends we use the hydrogen isotopic ratios of terrestrial higher plant leaf waxes delta d wax in marine sediments from southwest sulawesi indonesia to compile a detailed reconstruction of central indo pacific warm pool ipwp hydrologic variability spanning most of the last two millennia our paleodata are highly correlated with a monsoon reconstruction from southeast asia indicating that intervals of strong east asian summer monsoon easm activity are associated with a weaker indonesian monsoon im furthermore the centennial scale oscillations in our data follow known changes in northern hemisphere climate e g the little ice age and medieval warm period implying a dynamic link between northern hemisphere temperatures and ipwp hydrology the inverse relationship between the easm and im suggests that migrations of the intertropical convergence zone and associated changes in monsoon strength caused synoptic hydrologic shifts in the ipwp throughout most of the past two millennia

erosion driven uplift in the gamburtsev subglacial mountains of east antarctica the relative roles of climate and tectonics in mountain building have been widely debated central to this debate is the process of flexural uplift in response to valley incision here we quantify this process in the gamburtsev subglacial mountains a paradoxical tectonic feature in cratonic east antarctica previous studies indicate that rifting and strike slip tectonics may have provided a key trigger for the initial uplift of the gamburtsevs but the contribution of more recent valley incision remains to be quantified inverse spectral free air admittance and bouguer coherence methods indicate that unusually for continents the coherence between free air gravity anomalies and bedrock topography is high 0 5 and that the elastic thickness of the lithosphere is anomalously low 15 km in contrast to previously reported values of up to 70 km the isostatic effects of two different styles of erosion are quantified dendritic fluvial incision overprinted by alpine style glacial erosion in the gamburtsevs and outlet glacier type selective linear erosion in the lambert rift part of the east antarctic rift system 3d flexural models indicate that valley incision has contributed ca 500 m of peak uplift in the gamburtsevs and up to 1 2 km in the lambert rift which is consistent with the present day elevation of oligocene miocene glaciomarine sediments overall we find that 17 25 of gamburtsev peak uplift can be explained by erosional unloading these relatively low values are typical of temperate mountain ranges suggesting that most of the valley incision in the gamburtsevs occurred prior to widespread glaciation at 34 ma the pre incision topography of the gamburtsevs lies at 2 2 5 km above sea level confirming that they were a key inception point for the development of the east antarctic ice sheet tectonic and or dynamic processes were therefore responsible for ca 80 of the elevation of the modern gamburtsev subglacial mountains

rapidly intensifying hurricane guillermo 1997 part i low wavenumber structure and evolution abstract the structure and evolution of rapidly intensifying hurricane guillermo 1997 is examined using airborne doppler radar observations in this first part the low azimuthal wavenumber component of the vortex is presented guillermo s intensification occurred in an environmental flow with 7 8 m s 1 of deep layer vertical shear as a consequence of the persistent vertical shear forcing of the vortex convection was observed primarily in the downshear left quadrant of the storm the greatest intensification during the 6 h doppler observation period coincided with the formation and cyclonic rotation of several particularly strong convective bursts through the left of shear semicircle of the eyewall some of the strongest convective bursts were triggered by azimuthally propagating low wavenumber vorticity asymmetries mesoscale budget analyses of axisymmetric angular momentum and relative vorticity within the eyewall are presented to elucidate the mechanisms contributing to guillermo s structural evol

seismic stratigraphy and sediment distribution on the wilkes land and terre adelie margins east antarctica abstract seismic reflection data show the existence of two major sedimentary basins along the continental margin of wilkes land and terre adelie east antarctica that contain more than 5 s twt 9 km of sediments four seismic megasequences are identified ms4 to ms1 that are bounded by basement unconformities of interpreted turonian maastrichtian and early middle eocene age and the seafloor the 4 5 km thick rift and pre rift sediments are concentrated in a margin parallel basin sabrina basin on the basis of seismic correlation with the australian margin this basin is interpreted to be of late jurassic to mid cretaceous age the post rift sediments are generally thick along the margin and in the adjacent deep ocean basin but are particularly thick in a major depocentre off west wilkes land named here the budd coast basin bcb the bcb contains a maximum observed thickness of 5 s twt 9 km of post rift sediments and its location suggests that the sediments were largely derived from a sub glacial basin currently occupied by the totten glacier within the post rift sediments a major regional unconformity is identified that is interpreted to be of early middle eocene age 45 ma while some previous interpretations have suggested that this unconformity marks the onset of the glaciation of east antarctica the unconformity is interpreted here to be the product of the major global plate reorganisation in the middle eocene and the coincident sharp increase in the sea floor spreading rate between australia and antarctica a seismic unconformity that can be correlated with the onset of glaciation is not identified and the position of glacial onset within the sedimentary section can only be estimated through the extrapolation of sedimentation rates from the underlying section and from deep sea drilling project site 269 the post middle eocene section is much thicker than the underlying post rift section and this is interpreted to be largely due to the very high sediment fluxes associated with the period of polythermal glaciation from 34 9 ma sediment isochron and isopach maps derived from a regional seismic grid show that the depocentre of the bcb trends approximately north south beneath the continental slope but is deflected to the east beneath the deep ocean basin this distribution indicates that deep marine processes were important in lateral along margin sediment transport a west to east direction of movement is inferred by the sediment distribution this direction is opposite to the present day marginal currents along the continental slope and rise

a stalagmite record of holocene indonesian australian summer monsoon variability from the australian tropics oxygen isotopic data from a suite of calcite and aragonite stalagmites from cave kni 51 located in the eastern kimberley region of tropical western australia represent the first absolute dated high resolution speleothem record of the holocene indonesianeaustralian summer monsoon iasm from the australian tropics stalagmite oxygen isotopic values track monsoon intensity via amount effects in precipitation and reveal a dynamic holocene iasm which strengthened in the early holocene decreased in strength by 4 ka with a further decrease from w2 to 1 ka before strengthening again at 1 ka to years to levels similar to those between 4 and 2 ka the relationships between the kni 51 iasm reconstruction and those from published speleothem time series from flores and borneo in combination with other data sets appear largely inconsistent with changes in the position and or organization of the intertropical convergence zone itcz instead we argue that the el nino southern oscillation enso may have played a dominant role in driving iasm variability since at least the middle holocene given the muted modern monsoon rainfall responses to most el nino events in the kimberley an impact of enso on regional monsoon precipitation over northwestern australia would suggest non stationarity in the long term relationship between enso forcing and iasm rainfall possibly due to changes in the mean state of the tropical pacific over the holocene

glacial to holocene swings of the australian indonesian monsoon the australian indonesian monsoon is an important component of the climate system in the tropical indo pacific region 1 however its past variability relation with northern and southern high latitude climate and connection to the other asian monsoon systems are poorly understood here we present high resolution records of monsoon controlled austral winter upwelling during the past 22 000 years based on planktic foraminiferal oxygen isotopes and faunal composition in a sedimentary archive collected offshore southern java we show that glacial interglacial variations in the australian indonesian winter monsoon were in phase with the indian summer monsoon system consistent with their modern linkage through cross equatorial surface winds likewise millennial scale variability of upwelling shares similar sign and timing with upwelling variability in the arabian sea on the basis of element composition and grain size distribution as precipitation sensitive proxies in the same archive we infer that austral summer monsoon rainfall was highest during the bolling allerod period and the past 2 500 years our results indicate drier conditions during heinrich stadial 1 due to a southward shift of summer rainfall and a relatively weak hadley cell south of the equator we suggest that the australian indonesian summer and winter monsoon variability were closely linked to summer insolation and abrupt climate changes in the northern hemisphere the seasonality of the global monsoon is of central importance to the global hydrologic cycle and its environmental influence on human societies palaeoclimate reconstructions generally agree that the strengths of the east asian monsoon and the indian monsoon are tightly coupled to the northern hemisphere climate through zonal migrations of the monsoon convection centres also interpreted as intertropical convergence zone itcz migration 26 the mechanism of the australianindone

dynamical response of the tropical pacific ocean to solar forcing during the early holocene we present a high resolution magnesium calcium proxy record of holocene sea surface temperature sst from off the west coast of baja california sur mexico a region where interannual sst variability is dominated today by the influence of the el nino southern oscillation enso temperatures were lowest during the early to middle holocene consistent with documented eastern equatorial pacific cooling and numerical model simulations of orbital forcing into a la nina like state at that time the early holocene ssts were also characterized by millennial scale fluctuations that correlate with cosmogenic nuclide proxies of solar variability with inferred solar minima corresponding to el nino like warm conditions in apparent agreement with the theoretical ocean dynamical thermostat response of enso to exogenous radiative forcing

development and application of a simplified coplane wind retrieval algorithm using dual beam airborne doppler radar observations for tropical cyclone prediction abstractbased on established coplane methodology a simplified three dimensional wind retrieval algorithm is proposed to derive two dimensional wind vectors from radial velocity observations by the tail doppler radars on board the noaa p3 hurricane reconnaissance aircraft validated against independent in situ flight level and dropsonde observations before and after genesis of hurricane karl 2010 each component of the retrieved wind vectors near the aircraft track has an average error of approximately 1 5 m s 1 which increases with the scanning angle and distance away from the aircraft track simulated radial velocities derived from a convection permitting simulation of karl are further used to systematically quantify errors of the simplified coplane algorithm the accuracy of the algorithm is strongly dependent on the time between forward and backward radar scans and to a lesser extent the zero vertical velocity assumption at large angles relative to a plane parallel with the aircraft wings a proof

isostatic model and isostatic gravity anomalies of the arabian plate and surroundings the isostatic modeling represents one of the most useful geological reduction methods of the gravity field with the isostatic correction it is possible to remove a significant part of the effect of deep density heterogeneity which dominates in the bouguer gravity anomalies although there exist several isostatic compensation schemes it is usually supposed that a choice of the model is not an important factor to first order since the total weight of compensating masses remains the same we compare two alternative models for the arabian plate and surrounding area the airy model gives very significant regional isostatic anomalies which cannot be explained by the upper crust structure or disturbances of the isostatic equilibrium also the predicted isostatic moho is very different from existing seismic observations the second isostatic model includes the moho which is based on seismic determinations additional compensation is provided by density variations within the lithosphere chiefly in the upper mantle according to this model the upper mantle under the arabian shield is less dense than under the platform in the arabian platform the maximum density coincides with the rub al khali one of the richest oil basin in the world this finding agrees with previous studies showing that such basins are often underlain by dense mantle possibly related to an eclogite layer that has caused their subsidence the mantle density variations might be also a result of variations of the lithosphere thickness with the combined isostatic model it is possible to minimize regional anomalies over the arabian plate the residual local anomalies correspond well to tectonic structure of the plate still very significant anomalies showing isostatic disturbances of the lithosphere are associated with the zagros fold belt the collision zone of the arabian and eurasian plates

tectonic significance of the lambert graben east antarctica reconstructing the gondwanan rift antarctica s lambert graben australia s north west shelf and the eastern indian peninsula all host thick fault bounded permian triassic successions these terranes were adjacent to each other in gondwana the lambert graben intersects the modern coastline strikes oblique to shelf architecture and has a geophysical signature that can be traced 1000 km inland vitrinite reflectance data from the graben margins record permian triassic infill australia s north west shelf is the relict of an intracontinental carboniferous permian rift that was infilled during the permian triassic then driven to oceanic completion during jurassic cretaceous gondwana breakup this rift was compartmentalized over length scales of 650 km corresponding to accommodation zones margin normal geophysical lineaments and long lived crustal weaknesses in eastern india similar compartmentalization is marked by extensive coal bearing graben systems gondwana reconstructions indicate that the lambert graben corresponds to the orientation and length scale of carboniferous permian rift compartmentalization the lambert graben represents an accommodation zone of a wide intracontinental rift that extended from australia s north west shelf between india and antarctica to southern africa this rift collected gondwana s thick permian triassic sedimentary blanket and rich alluvial coal deposits

brittle deformation relating to the carboniferous cretaceous evolution of the lambert graben east antarctica a precursor for cenozoic relief development in an intraplate and glaciated region abstract stress inversions of kinematic data measured from brittle deformation structures exposed in the southern prince charles mountains have been carried out to elucidate the drivers of intracontinental deformation responsible for the development of the lambert graben east antarctica four palaeostress fields d 1 d 4 were identified from these data which when coupled with pre existing geochronological and sedimentological evidence provide a clear deformation framework the architecture of the lambert graben is dominantly defined by north south trending d 2 and northeast southwest trending d 3 faults that formed respectively during 1 carboniferous permian intracontinental extrusion and 2 cretaceous transtensional tectonics related to the dispersion of east gondwana interestingly sub ice topography in the southern prince charles mountains and further south towards the gamburtsev mountains is defined by bedrock lineaments that parallel the orientations of the main fault arrays previous work shows that the development of relief in the southern prince charles mountains is tertiary in age and probably not associated with carboniferous permian or cretaceous tectonic events based on a clear spatial link between the orientations of faults and bedrock lineaments we suggest that inherited fault zones were integral in accommodating uplift driven by plate flexure as a response to crustal unloading during glacial incision

inner core structure of hurricane alicia from airborne doppler radar observations abstract airborne doppler radar measurements are used to determine the horizontal winds vertical air motions radar reflectivity and hydrometer fallspeeds over much of the inner core region within 40 km of the eye of hurricane alicia 1983 the reconstructed flow field is more complete and detailed than any obtained previously the data show both the primary azimuthal and secondary radial height circulations the primary circulation was characterized by an outward sloping maximum of tangential wind the secondary circulation was characterized by a deep layer of radial inflow in the lower troposphere and a layer of intense outflow above 10 km altitude the rising branch of the secondary circulation was located in the eyewall and sloped radially outward discrete convective scale bubbles of more intense upward motion were superimposed on this mean rising current and convective scale downdrafts were located throughout and below the core of maximum precipitation in the eyewall precipitation particle

denudational and thermal history along a transect across the lambert graben northern prince charles mountains antarctica derived from apatite fission track thermochronology 1 the denudational history along a transect across the western margin of the lambert graben northern prince charles mountains east antarctica is quantified on the basis of thermal history modeling of apatite fission track data from four vertical profiles early cretaceous paleogeothermal gradients estimated from the fission track data increase from 19 c km 1 50 km west of the rift margin to 29 c km 1 within the immediate vicinity of the western master fault two discrete phases of enhanced denudation during the phanerozoic are inferred for the western rift margin the first occurred during the early paleozoic with minimum denudation of between 1 6 and 5 0 km which is broadly coeval with initial rifting and the major period of permo triassic sedimentation within the lambert graben the formation of the graben was related to the formation of the ancestral gamburtsev mountains due to variscan compression and substantial crustal thickening of the east antarctic craton the second phase of denudation commenced in the early cretaceous with estimated amounts ranging between 1 0 and 4 5 km generally increasing toward the rift margin with the maximum total denudation occurring 20 km west of the western master fault of the graben the early cretaceous phase of denudation was probably related to tectonic reactivation of the earlier permo triassic rift during the initial separation of the indian and antarctic sector of gondwana

estimates of te for continental regions using goce gravity satellite only gravity fields and surface gravity obtained from altimetric measurements now agree well at wavelengths greater than 180 km satellite gravity fields can therefore be used to estimate the elastic thickness tete in regions where surface observations are sparse they are used for this purpose in a number of continental regions of india africa and antarctica where the topography is sufficiently rough and also in regions of the usa china australia and siberia where there are surface measurements estimates of tete for antarctica depend on measurements of ice thickness which are now available for much of the continent values of tete are obtained using two methods from the admittance between the free air gravity and the topography and from the coherence between bouguer gravity anomalies and the topography the first but not the second gives values of tete that are everywhere less than the seismogenic thickness where there is sufficient topography estimates of tete from precambrian shields are all greater than 10 km and do not correlate with the lithospheric thickness they are probably are governed by variations in crustal heat generation rates values for regions strongly affected by phanerozoic tectonics are all less than 7 km and all such regions are underlain by thin lithosphere

multi scale variability of the asian monsoon recorded in an annually banded stalagmite during the neoglacial from qixing cave southwestern china abstract solar forcing of the asian summer monsoon asm and the embedded feedback mechanism remain highly controversial in this study interannual scale asm variability from 3 58 to 2 28 ka bp is reconstructed based on the 18 o record of an annually laminated stalagmite from qixing cave in southwestern china the cave 18 o record agrees well with a record of solar activity on the centennial scale during the whole time series furthermore statistical analysis of singular spectrum and wavelet spectrum shows a significant cycle of 60 years one of the solar activity cycles the two lines of evidence have consolidated the solar impact on a centennial decadal time scale of asm variability timing and structure of the 2 8 ka event detected in various archives at a global scale have been well determined in our 18 o record with a high precision time scale established by absolute 230 th dating and annual layer counting we observed an asymmetrical pattern of the event i e a gradual transition at the onset with a rapid end which can be interpreted as a far field effect of changing thermohaline circulations in the north atlantic we further demonstrate a striking inverse correlation between the asm and the indonesian australian summer monsoon iasm on the centennial scale including three dominant asm depression events that are related to periods of weak solar activity the evidence we present here supports that ocean atmosphere interactions amplified the solar signal and caused abrupt cooling events in widespread areas during the holocene

role of off shelf to on shelf transitions for east antarctic sea ice dynamics during spring 2003 1 during austral spring 2003 mesoscale sea ice drift and deformation off east antarctica were investigated using in situ data from a nine buoy array upon deployment the array comprised an area of about 4000 km2 with a mean ice concentration of 96 half hourly sea ice velocities were coherent across all buoys at zonal meridional separations of less than 160 km 70 km regional cross spectral correlation was high at synoptic scales and also at semidiurnal periods off the continental shelf atmospheric synoptic scale forcing explained in excess of 85 of the ice drift variability this is significantly more than found in the weddell sea where significant ice drift variability is derived from oceanic forcing peak frequencies of semidiurnal contributions covaried with latitude and are largely associated with the inertial response over the continental shelf coincident diurnal and semidiurnal variances in ice motion arose from tidal forcing net divergence over 37 days resulted in an expansion to 270 of the initial area although regional ice concentration reduced only slightly high frequency processes namely inertial response and to a lesser degree tidal forcing dominated the variability of all deformation parameters in contrast to ice motion low frequency processes played a secondary role in sea ice deformation this high frequency dominance is similar to what has been found in the weddell sea although many observations there were limited to the continental shelf where tidal processes dominate sea ice motion and deformation were not affected by a seasonal transition nor did the regional ice characteristics show any signal of seasonal change instead local ice dynamics were strongly influenced by bathymetrically dependent processes

the effective elastic thickness of the continental lithosphere comparison between rheological and inverse approaches 1 following the release of global continental effective elastic thickness te maps obtained using different approaches we now have the opportunity to provide better constraints on te we improve previous estimates of te derived from thermo rheological models of lithospheric strength or ter using new equations that consider variations of the young s modulus in the lithosphere these new values are quantitatively compared with those obtained from an inverse approach or tei based on a comparison of the spectral coherence between topography and gravity anomalies with the flexural response of an equivalent elastic plate to loading the two models show in general a good agreement having equal means at the 95 significance level in about half of the continental areas in other regions tei exceeds ter in about 65 of the data points showing that tei provides an upper bound on te the two data sets have a similar range but demonstrate different distributions ter has a bimodal distribution with the two peaks representative of the cratons and of the areas outside of them in contrast tei has more uniform distribution without predominant peaks our models show higher similarities in the meso cenozoic orogens than in the archaean and proterozoic shields and platforms due to the methods employed for the regions with the most robust determinations of ter and tei the relationship between them is close to linear the results of this work can be used for further studies on the mechanical properties of the lithosphere

elastic thickness of the himalayan tibetan orogen estimated from the fan wavelet coherence method and its implications for lithospheric structure abstract this paper is concerned with the spatial variation of the elastic thickness t e in the himalayan tibetan orogen and its implications for the understanding of lithospheric structure and deformation new t e maps of the himalayan tibetan orogen are generated from the new combined satellite terrestrial gravity eigen6c3stat and topography etopo1 models using the fan wavelet coherence technique the high t e values 60 km are observed in the indian shield and the tarim basin while the low t e values 40 km are prevailing over most of the tibetan plateau we also find that the t e distributions estimated using the high and low central wavenumber i e k 0 wavelets are different in southern tibet by combining constraints from the current seismic and thermo rheological modeling this difference may reflect that the strength of the lithosphere in southern tibet mainly resides in the lithospheric mantle within most parts of central and northern tibet the t e values are relatively low 30 km indicating that the entire lithosphere is weak our analysis finds that the t e variations are probably associated with changes in lithosphere structure we interpret the abrupt changes in t e between southern and northern tibet to indicate the location of the underthrusting strong indian lithosphere beneath tibet our results suggest that the northern limit of the underthrusting indian plate reaches as far north as the hindu kush and the southwestern margin of the tarim basin near 70 80 e and extends along the bangong nujiang suture in the central 80 87 e eastward between 87 e 93 e it may move to the indus tsangpo suture indicating a delamination of indian mantle lithosphere there further to the east it may underthrust northward beneath the eastern qiangtang block

dynamics of the intertropical convergence zone over the western pacific during the little ice age precipitation patterns in the western pacific changed at the onset of the little ice age a synthesis of precipitation reconstructions suggests that this change resulted from a contraction of the intertropical convergence zone

flexural rigidity of the basin and range colorado plateau rocky mountain transition from coherence analysis of gravity and topography stochastic inversion for flexural loads and flexural rigidity of the continental elastic layer can be accomplished most effectively by using the coherence of gravity and topography however the spatial resolution of coherence analysis has been limited by use of two dimensional periodogram spectra from very large 105 km 2 windows that generally include multiple tectonic features using a two dimensional spectral estimator based on the maximum entropy method the spatial resolution of flexural properties can be enhanced by a factor of 4 or more enabling more detailed analysis at the scale of individual tectonic features this new approach is used to map the spatial variation of flexural rigidity along the basin and range transition to the colorado plateau and middle rocky mountains physiographic provinces large variations in flexural isostatic re sponse are found with rigidities ranging from as low as 8 7x102o n m elastic thickness t 4 6 km in the basin and range to as high as 4 1x1024 n m t 77 km in the middle rocky mountains these results compare favorably with independent determinations of flexural rigidity in the region areas of low flexural rigidity correlate strongly with areas of high surface heat flow as is expected from the contingence of flexural rigidity on a temperature dependent flow law also late cenozoic normal faults with large displacements are found primarily in areas of low flexural rigidity while deformation fronts of mesozoic tertiary overthrusts occur 0 to 100 km east of the low rigidity region the highest flexural rigidity is found within the archean wyoming craton where evidence suggests that deeply rooted cratonic lithosphere may play a role in deter mining the distribution of tectonism at the surface

holocene surface hydroclimate changes in the indo pacific warm pool abstract the indo pacific warm pool ipwp is an area hosting key tropical climate processes such as the el nino southern oscillation enso and indian ocean dipole iod the tropical climate processes via various feedback mechanisms control the surface ocean climate in the indian ocean and its surrounding continents on annual to inter annual timescales however little has been known about how the tropical processes are effective forcing climate mechanism over longer timescales here we presented a reconstruction of the spatiotemporal pattern of sea surface temperature sst with inferred hydroclimate changes since the early holocene 11ka using proxies of planktonic foraminifer shell mg ca organic biomarker tex86 foraminifer oxygen isotopes and a terrigenous bit index measured from a 220 cm long core bs24 2 724041 n 97 010943 e 1015 m water depth which was taken offshore of northwest sumatra in the eastern indian ocean with an age model of 13 ams 14c dating by the uses of planktonic foraminiferal shells from the core the tex86h temperatures of bs24 show as summer weighted and reflect integrated thermal effects from the surface to thermocline water while the mg ca temperature of bs24 better reflects mean annual sst our results along with a regional synthesis of published sst records from the ipwp suggest that the ipwp has migrated eastwardly since the mid holocene 5ka in phase with this eastward migration the ipwp ssts have decreased but the upwelling in the eastern indian ocean appears to have been a persistent feature since the mid holocene our empirical orthogonal function eof analysis on the compiled ipwp sst records indicates two dominant modes of spatio temporal variability of surface hydrographes in the ipwp that are attributed to a combined effect of orbital and solar forcing with expressions analogous to the indian ocean basin wide mode iobm and the indian ocean dipole model iod

forcing of wet phases in southeast africa over the past 17 000 years a continuous record of hydrologic variability for the past 17 000 years at the mouth of the zambezi river shows that hydrologic conditions in southeast africa were controlled by variations in local insolation and migrations of the intertropical convergence zone rather than by indian ocean temperature records of hydroclimatological variability in southern africa since the last glacial maximum have produced a conflicting picture of the relative influences of events in the remote northern hemisphere and the more local indian ocean this paper presents a continuous record of hydrological variability for the past 17 000 years from marine sediment core drilled off the mouth of the zambezi river the record shows that hydrological conditions in the region were influenced by variations in local insolation and migrations of the intertropical convergence zone which were probably driven by events in the northern hemisphere rather than the indian ocean intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast africa since the last glacial maximum about 20 000 years ago in particular the relative importance of atmospheric and oceanic processes is not firmly established1 2 3 4 5 southward shifts of the intertropical convergence zone itcz driven by high latitude climate changes have been suggested as a primary forcing2 3 whereas other studies infer a predominant influence of indian ocean sea surface temperatures on regional rainfall changes4 5 to address this question a continuous record representing an integrated signal of regional climate variability is required but has until now been missing here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro climatology in southeast africa during rapid climate changes over the past 17 000 years our results are based on a reconstruction of precipitation and river discharge changes as recorded in a marine sediment core off the mouth of the zambezi river near the southern boundary of the modern seasonal itcz migration indian ocean sea surface temperatures did not exert a primary control over southeast african hydrologic variability instead phases of high precipitation and terrestrial discharge occurred when the itcz was forced southwards during northern hemisphere cold events such as heinrich stadial 1 around 16 000 years ago and the younger dryas around 12 000 years ago or when local summer insolation was high in the late holocene that is during the past 4 000 years

on the recovery of effective elastic thickness using spectral methods examples from synthetic data and from the fennoscandian shield there is considerable controversy regarding the long term strength of continents te while some authors obtain both low and high te estimates from the bouguer coherence and suggest that both crust and mantle contribute to lithospheric strength others obtain estimates of only 25 km using the free air admittance and suggest that the mantle is weak at the root of this controversy is how accurately te can be recovered from coherence and admittance we investigate this question by using synthetic topography and gravity anomaly data for which te is known we show that the discrepancies stem from comparison of theoretical curves to multitaper power spectral estimates of free air admittance we reformulate the admittance method and show that it can recover synthetic te estimates similar to those recovered using coherence in light of these results we estimate te in fennoscandia and obtain similar results using both techniques te is 20 40 km in the caledonides 40 60 km in the swedish svecofennides 40 60 km in the kola peninsula and 70 100 km in southern karelia and svecofennian central finland independent rheological modeling using a xenolith controlled geotherm predicts similar high te in central finland because te exceeds crustal thickness in this area the mantle must contribute significantly to the total strength te in fennoscandia increases with tectonic age seismic lithosphere thickness and decreasing heat flow and low te correlates with frequent seismicity however in proterozoic and archean lithosphere the relationship of te to age is ambiguous suggesting that compositional variations may influence the strength of continents copyright 2004 by the american geophysical union

enso driven carbon see saw in the indo pacific 1 the sediment trap experiments have been carried out during the 2001 2002 el nino la nina transition in the monsoon driven and freshwater influenced upwelling system off south java the results indicate that enhanced precipitation rates and associated river discharges increase the co2 uptake of the biological pump by increasing the organic carbon export and reducing the carbonate precipitation the freshwater furthermore forms a buoyant low salinity surface layer that caps off the nutrient and co2 rich subsurface waters which shortens the upwelling season during wet la nina conditions a reduced capping effect during dryer el nino conditions strengthens the upwelling and as shown by our model results increase co2 emission into the atmosphere along the freshwater influenced continental margins in se asia by contrast el nino weakens upwelling and reduces the co2 emission in the equatorial pacific ocean

upwelling variability off southern indonesia over the past two millennia modern variability in upwelling off southern indonesia is strongly controlled by the australian indonesian monsoon and the el nino southern oscillation but multidecadal to centennial scale variations are less clear we present high resolution records of upper water column temperature thermal gradient and relative abundances of mixed layer and thermocline dwelling planktonic foraminiferal species off southern indonesia for the past two millennia that we use as proxies for upwelling variability we find that upwelling was generally strong during the little ice age lia and weak during the medieval warm period mwp and the roman warm period rwp upwelling is significantly anticorrelated to east asian summer monsoonal rainfall and the zonal equatorial pacific temperature gradient we suggest that changes in the background state of the tropical pacific may have substantially contributed to the centennial scale upwelling trends observed in our records our results implicate the prevalence of an el nino like mean state during the lia and a la nina like mean state during the mwp and the rwp

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

a reassessment of spectral te estimation in continental interiors the case of north america 1 conventional spectral te studies use the real part of the admittance between gravity anomalies and topography or alternatively the square of the magnitude of the coherency i e coherence here we show the utility of treating both the admittance and coherency as complex quantities inverting the real parts to estimate te we use the imaginary parts to tell if the inversion is biased by noise one method inverts the square of the real coherency with the internal to total load ratio f derived as a function of wave number directly from the gravity and topography the other method inverts the real part of the admittance assuming that f is wave number independent we test the methods using synthetic elastic plate models loaded at the surface and moho in such a way that the final relief is the actual north american topography in some of the models we add gravity noise generated by a model having both surface and internal loads such that the final topography is zero and find that both methods are susceptible to noise application of the two methods to north america gives te maps showing substantial agreement except in regions affected by noise but these are not a dominant part of the total area given the suggested mechanisms by which noise might arise it is not surprising that it is not a more widespread feature of the north american craton importantly both methods show that large parts of the canadian shield are characterized by te 100 km

new antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in antarctica gravity surveying is challenging in antarctica because of its hostile environment and inaccessibility nevertheless many ground based airborne and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s we present the first modern antarctic wide gravity data compilation derived from 13 million data points covering an area of 10 million km2 which corresponds to 73 coverage of the continent the remove compute restore technique was applied for gridding which facilitated levelling of the different gravity datasets with respect to an earth gravity model derived from satellite data alone the resulting free air and bouguer gravity anomaly grids of 10 km resolution are publicly available these grids will enable new high resolution combined earth gravity models to be derived and represent a major step forward towards solving the geodetic polar data gap problem they provide a new tool to investigate continental scale lithospheric structure and geological evolution of antarctica

mapping the mechanical anisotropy of the lithosphere using a 2d wavelet coherence and its application to australia abstract we develop a new method for imaging the spatial variations of the anisotropy of the flexural response of the lithosphere and apply it to recent topographic and gravity data sets over australia the method uses two dimensional morlet wavelet transforms superposed in a strictly controlled geometry to estimate the auto and cross spectra of the two data sets in a number of different directions the resulting wavelet coherence is a function of scale or wavelength as well as orientation and is inverted at each spatial location for the three parameters of an anisotropic thin elastic plate model i e maximum and minimum flexural rigidities and the orientation of the maximum extensive tests of the method on synthetic anisotropic but uniform data sets show that it retrieves the amplitude and orientation of the anisotropy with useful accuracy the results for australia west of 143 e show a strong correlation with the shallower layers 75 175 km of a recent model of seismic sv wave azimuthal anisotropy the weak axes i e of minimum flexural rigidity in most cases are approximately at right angles to the fast axes of the seismic anisotropy implying that for precambrian australia they arise from the same source this is most likely deformation resulting from the most recent episode of orogeny

fossil dripwater in stalagmites reveals holocene temperature and rainfall variation in amazonia abstract most proxy records used for reconstruction of holocene climate of amazonia are unable to quantitatively distinguish between the effect of temperature and rainfall amounts we present a new isotope technique applied to a 13 500 yr stalagmite archive from peruvian amazonia by analysing the coupled isotope composition of fossil dripwater trapped in stalagmite fluid inclusions and that of the calcite hosting the fluid inclusions we were able to calculate independent paleotemperatures and rainfall amounts this stalagmite record shows that holocene climate variation was controlled by orbitally forced southward migration of the inter tropical convergence zone while temperature remained constant isotope variation of rainwater reflected in fluid inclusion water 18o composition suggests a 15 30 increase in convective rainfall through the holocene a comparison of the low land peruvian fluid inclusion record with the high andean huascaran ice core record shows a constant 12 offset of 18o curves for the holocene suggesting that andean vertical temperature gradients lapse rates did not vary much over the last 9000 years during the younger dryas interval however the offset of 18o values was much higher than in the holocene this may be attributed to a relative drop in air temperatures in the highlands higher lapse rate caused by long distance teleconnections to climate perturbations in the north atlantic in a wider perspective fluid inclusion isotope analysis drastically improves paleotemperature reconstructions based on speleothem calcite 18o data because it provides the 18o value of drip water through time which is usually the most important unknown in paleotemperature equations

mid to late holocene australian indonesian summer monsoon variability abstract the australian indonesian monsoon has a governing influence on the agricultural practices and livelihood in the highly populated islands of indonesia however little is known about the factors that have influenced past monsoon activity in southern indonesia here we present a 6000 years high resolution record of australian indonesian summer monsoon aism rainfall variations based on bulk sediment element analysis in a sediment archive retrieved offshore northwest sumba island indonesia the record suggests lower riverine detrital supply and hence weaker aism rainfall between 6000 yr bp and 3000 yr bp compared to the late holocene we find a distinct shift in terrigenous sediment supply at around 2800 yr bp indicating a reorganization of the aism from a drier mid holocene to a wetter late holocene in southern indonesia the abrupt increase in rainfall at around 2800 yr bp coincides with a grand solar minimum an increase in southern indonesian rainfall in response to a solar minimum is consistent with climate model simulations that provide a possible explanation of the underlying mechanism responsible for the monsoonal shift we conclude that variations in solar activity play a significant role in monsoonal rainfall variability at multi decadal and longer timescales the combined effect of orbital and solar forcing explains important details in the temporal evolution of aism rainfall during the last 6000 years by contrast we find neither evidence for volcanic forcing of aism variability nor for a control by long term variations in the el nino southern oscillation enso

continuous 150 k y monsoon record from lake eyre australia insolation forcing implications and unexpected holocene failure our reconstructed history of lake eyre provides the first continuous continental proxy record of australian monsoon intensity over the past 150 k y this continental record s broad correspondence to the marine isotope record demonstrates that this very large catchment with its hydrology dependent on a planetary scale climate element responds to milankovitch scale climate forcing abrupt transitions from dry phases to wet phases ca 125 and 12 ka coincide with northern hemisphere winter insolation minima rather than southern hemisphere summer insolation maxima indicating that northern hemi sphere insolation exerts a dominant control over the intensity of the australian monsoon stratigraphic and dating uncertainties of other wet phases preclude conclusive correlation to specific insolation signals but within the uncertainties are consistent with northern hemisphere forcing regardless of the hemispheric forcing the low intensity of the early holocene australian monsoon by comparison with the last interglacial and particularly the last high level lacustrine event at 65 60 ka when all forcing elements were modest is an enigma that can be explained by a change in boundary conditions within australia

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

holocene diatom records of wetland development near weipa cape york australia abstract to better understand the response of tropical wetlands to holocene environmental changes two lacustrine diatom records from weipa cape york have been investigated the record from big willum bw01 commenced approx 7 9 calibrated thousand years before present k cal a bp and details stages of initial swamp development a phase of ephemeral conditions between approximately 5 7 and 2 2 k cal a bp and relative wetland stability after 2 2 k cal a bp lithological and to a lesser extent diatom assemblage changes in bw01 appear to be linked to broad scale changes in effective precipitation the record from little willum lw01 commenced around 0 9 k cal a bp and documents initial phases of swamp development until approximately 0 8 k cal a bp with subsequent relative wetland stability the uppermost 10 cm of this record approximately spanning the last 40 years coincide with mining activity in the region only minor changes in the diatom assemblage are recorded for this period implying that the overall character of the swamp probably remained unchanged both sites offer new insights into wetland dynamics in australia s dry tropics and demonstrate that changes in these lacustrine systems were probably driven by shifts in effective precipitation in particular during the late holocene

high and low latitude forcing of the east african climate since the lgm inferred from the elemental composition of marine sediments off tanzania abstract we present x ray fluorescence xrf scanner measurements from a 6 m long sediment core geob12624 1 on the upper slope of tanzania to reconstruct the climatic evolution in east africa since the last glacial maximum lgm log ratios of fe ca and ti ca are indicative for sediment discharge of the rufiji river which is controlled by climatic conditions in the rufiji catchment area the most significant changes in major elemental composition occurred at 15 1 and 7 4 ka highlighted by the regime shift index values the data set records distinct precipitation peaks during the early holocene this corresponds a maximum in the northern hemisphere nh summer insolation and results in a transition from the arid lgm to the humid early holocene our geochemical record also indicates that this climatic transition was interrupted by two severe droughts that occurred during nh cold intervals the heinrich stadial 1 hs1 and the younger dryas yd through a comparison with other nearby paleoclimatic records we suggest that arid climatic conditions only occurred in east africa north of 8 10 s whereas in southern east africa around 15 20 s increased humidity during the hs1 and yd prevailed we thus conclude that these two drought events were caused by a southward migration of the intertropical convergence zone itcz which was fostered by the nh cooling during the hs1 and yd hence our new geochemical record clearly documents that the east african climate not only responded to low latitude insolation forcing on sub orbital time scales but also was strongly influenced by high latitude cooling during the hs1 and yd periods

basic mechanism for abrupt monsoon transitions abstract monsoon systems influence the livelihood of hundreds of millions of people during the holocene and last glacial period rainfall in india and china has undergone strong and abrupt changes though details of monsoon circulations are complicated observations reveal a defining moisture advection feedback that dominates the seasonal heat balance and might act as an internal amplifier leading to abrupt changes in response to relatively weak external perturbations here we present a minimal conceptual model capturing this positive feedback the basic equations motivated by observed relations yield a threshold behavior robust with respect to addition of other physical processes below this threshold in net radiative influx r c no conventional monsoon can develop above r c two stable regimes exist we identify a nondimensional parameter l that defines the threshold and makes monsoon systems comparable with respect to the character of their abrupt transition this dynamic similitude may be helpful in understanding past and future variations in monsoon circulation within the restrictions of the model we compute r c for current monsoon systems in india china the bay of bengal west africa north america and australia where moisture advection is the main driver of the circulation

global gravity bathymetry and the distribution of submarine volcanism through space and time 1 the seafloor is characterized by numerous seamounts and oceanic islands which are mainly volcanic in origin relatively few of these features 0 1 however have been dated and so little is known about their tectonic setting one parameter that is sensitive to whether a seamount formed on near or far from a mid ocean ridge is the elastic thickness te which is a proxy for the long term strength of the lithosphere most previous studies are based on using the bathymetry to calculate the gravity anomaly for different values of te and then comparing the calculated and observed gravity anomaly the problem with such an approach is that bathymetry data are usually limited to single beam echo sounder data acquired along a ship track and these data are too sparse to define seamount shape we therefore use the satellite derived gravity anomaly to predict the bathymetry for different values of te by comparing the predicted bathymetry to actual shipboard soundings in the vicinity of each locality in the wessel global seamount database we have obtained 9758 te estimates from a wide range of submarine volcanic features in the pacific indian and atlantic oceans comparisons where there are previous estimates show that bathymetric prediction is a robust way to estimate te and its upper and lower bounds te at sites where there is both a sample and crustal age show considerable scatter however and there is no simple relationship between te and age nevertheless we are able to tentatively assign a tectonic setting to each te estimate the most striking results are in the pacific ocean where a broad swath of on ridge volcanism extends from the foundation seamounts and ducie island easter island ridge in the southeast across the equator to the shatsky and hess rises in the northwest interspersed among the on ridge volcanism are flank ridge and off ridge features the indian and atlantic oceans also show a mix of tectonic settings off ridge volcanism dominates in the eastern north atlantic and northeast indian oceans while flank ridge volcanism dominates the northeastern indian and western south atlantic oceans we have been unable to assign the flank ridge and off ridge estimates an age but the on ridge estimates generally reflect we believe the age of the underlying oceanic crust we estimate the volume of on ridge volcanism to be 1 1 106 km3 which implies a mean seamount addition rate of 0 007 km3 yr 1 rates appear to have varied through geological time reaching their peak during the late early cretaceous and then declining to the present day

extensive retreat and re advance of the west antarctic ice sheet during the holocene to predict the future contributions of the antarctic ice sheets to sea level rise numerical models use reconstructions of past ice sheet retreat after the last glacial maximum to tune model parameters 1 reconstructions of the west antarctic ice sheet have assumed that it retreated progressively throughout the holocene epoch the past 11 500 years or so 2 4 here we show however that over this period the grounding line of the west antarctic ice sheet which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf retreated several hundred kilometres inland of today s grounding line before isostatic rebound caused it to re advance to its present position our evidence includes first radiocarbon dating of sediment cores recovered from beneath the ice streams of the ross sea sector indicating widespread holocene marine exposure and second ice penetrating radar observations of englacial structure in the weddell sea sector indicating ice shelf grounding we explore the implications of these findings with an ice sheet model modelled re advance of the grounding line in the holocene requires ice shelf grounding caused by isostatic rebound our findings overturn the assumption of progressive retreat of the grounding line during the holocene in west antarctica and corroborate previous suggestions of ice sheet re advance 5 rebound driven stabilizing processes were apparently able to halt and reverse climate initiated ice loss whether these processes can reverse present day ice loss 6 on millennial timescales will depend on bedrock topography and mantle viscosity parameters that are difficult to measure and to incorporate into ice sheet models

calcification depths and temperatures of planktonic foraminifera off southwest hainan island and their paleoceanographic implications abstract the east asian monsoon system influences the local oceanographic and climatic conditions of south china sea scs making the habitat depths of planktonic foraminifera pf specific for this region the previous paleo ocean reconstructions of scs have been based on calcification habitat depths derived from other oceans which may have affected the accuracy of interpretations in this study the calcification depths of globigerinoides ruber globigerinoides sacculifer and neogloboquadrina dutertrei from sediment traps deployed at 1000 m depth off southwest hainan island from july 2012 to april 2013 were analyzed with regard to the stable isotopes of oxygen 18o and carbon 13c to calculate their regional apparent calcification depths acds with the overall aim to improve the reconstruction of the upper ocean thermal structure acds and temperature estimated from foraminifera 18o ranged from 0 to 42 m and 25 c for g ruber 30 65 m and 23 3 c for g sacculifer and 75 100 m and 20 3 c for n dutertrei respectively the difference between the thermocline species n dutertrei and mixed layer species g ruber and g sacculifer 18o 18oth ml and the temperature t shows water column stratification the periods of lower and higher t and 18o were in phase with the changes in regional overlying wind speed additionally this study reveals that n dutertrei lives and calcifies its shells within the base of the mixed layer depth mld and upper thermocline depth in scs overall the results from this study provide a new insight to understand the mixed layer and thermocline depth in the northern scs

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

temperature profile for glacial ice at the south pole implications for life in a nearby subglacial lake airborne radar has detected 100 lakes under the antarctic ice cap the largest of which is lake vostok international planning is underway to search in lake vostok for microbial life that may have evolved in isolation from surface life for millions of years it is thought however that the lakes may be hydraulically interconnected if so unsterile drilling would contaminate not just one but many of them here we report measurements of temperature vs depth down to 2 345 m in ice at the south pole within 10 km from a subglacial lake seen by airborne radar profiling we infer a temperature at the 2 810 m deep base of the south pole ice and at the lake of 9 c which is 7 c below the pressure induced melting temperature of freshwater ice to produce the strong radar signal the frozen lake must consist of a mix of sediment and ice in a flat bed formed before permanent antarctic glaciation it may like siberian and antarctic permafrost be rich in microbial life because of its hydraulic isolation proximity to south pole station infrastructure and analog to a martian polar cap it is an ideal place to test a sterile drill before risking contamination of lake vostok from the semiempirical expression for strain rate vs shear stress we estimate shear vs depth and show that the icecube neutrino observatory will be able to map the three dimensional ice flow field within a larger volume 0 5 km3 and at lower temperatures 20 c to 35 c than has heretofore been possible

volcanic aerosol records and tephrochronology of the summit greenland ice cores the recently collected greenland ice sheet project 2 gisp2 and greenland ice core project ice cores from summit greenland provide lengthy and highly resolved records of the deposition of both the aerosol h2so4 and silicate tephra components of past volcanism both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism climate system the continuous time series of volcanic so42 for the last 110 000 years show a strong relationship between periods of increased volcanism and periods of climatic change the greatest number of volcanic so42 signals many of very high magnitude occur during and after the final stages of deglaciation 6000 17 000 years ago possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins sea level change the increase in the number of volcanic so42 signals at 27 000 36 000 and 79 000 85 000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation respectively a comparison of the electrical conductivity of the gisp2 core with that of the volcanic so42 record for the holocene indicates that only about half of the larger volcanic signals are coincident in the two records other volcanic acids besides h2so4 and other so42 sources can complicate the comparisons although the threshold level picked to make such comparisons is especially critical tephra has been found in both cores with a composition similar to that originating from the vatnaoldur eruption that produced the settlement layer in iceland mid a d 870s from the icelandic eruption that produced the saksunarvatn ash 10 300 years ago and from the icelandic eruption s that produced the z2 ash zone in north atlantic marine cores 52 700 years ago the presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras the presence of both rhyolitic and basaltic shards in the z2 ash in thegisp2 core and the composition of the basaltic grains lend support to multiple icelandic sources torfajokull area and katla for the z2 layer deposition of the z2 layer occurs at the beginning of a stadial event further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions

plate tectonics and net lithosphere rotation over the past 150 my we have developed an improved model of global digital palaeo plate boundaries and plate motion to describe the distribution and history of plates since the late jurassic from this history we computed net lithospheric rotation nr through time confirming the so called westward drift but only for the past 30 myr the nr has significantly smaller magnitudes 0 13 my past 5 my than for some other plate models it averages to 0 11 0 03 my for the past 50 my with a small but systematic increase toward the present the westward drift seen only for the past 30 my is attributed to the increased dominance of a steadily growing and accelerating pacific plate nr shows peaks with time but only an early tertiary peak of 0 33 my when the indian plate was undergoing the largest known acceleration deceleration can be interpreted with some confidence we find a linear decreasing trend in net rotation over the past 150 my but attribute this trend to increasing reconstruction uncertainties back in time as subduction consumed more than half of the oceanic crust since the jurassic after removing a linear time trend we find a nr average of about 0 12 my for the past 150 my

evidence for holocene changes in australian indonesian monsoon rainfall from stalagmite trace element and stable isotope ratios abstract trace element and stable isotope ratios from an active stalagmite lr06 b1 recovered from liang luar cave on the island of flores eastern indonesia are used to reconstruct the position of the austral summer inter tropical convergence zone and australian indonesian summer monsoon variability during the holocene uranium series dating of the stalagmite shows that it commenced growth 12 640 years ago with hiatuses spanning 8 560 to 6 420 and 3 670 to 2 780 years ago stalagmite mg ca and sr ca ratios correlate significantly with one another and with 18 o and 13 c throughout the record this suggests that the mg ca and sr ca ratios are dominated by prior calcite precipitation a process whereby degassing in the vadose zone during periods of low recharge causes deposition of calcite and disproportionate loss of ca 2 ions relative to mg 2 and sr 2 upstream of the stalagmite the degree of initial 234 u 238 u disequilibrium also appears to have been controlled by recharge to the overlying aquifer together with the mg ca sr ca and 18 o values the initial uranium isotope activity ratios 234 u 238 u i imply a generally drier early holocene coincident with a lower sea level and lower southern hemisphere summer insolation comparison of speleothem 18 o time series from flores and borneo shows that they vary in unison for much of the holocene however there is a significant decrease in the borneo 18 o record 6 000 to 4 000 years ago that does not occur in the flores record this anomaly may be related to a change in the australian indonesian summer monsoon circulation in response to a protracted positive phase of the indian ocean dipole under this scenario stronger upwelling off of western indonesia would based on present day effects result in reduced summer convective activity over flores and a subsequent northward shift of the intertropical convergence zone

tropical rainforest dynamics and palaeoclimate implications since the late pleistocene nilgiris india a multiproxy study involving sedimentology palynology radiocarbon dating stable isotopes and geochemistry was carried out on the parsons valley lake deposit nilgiris india to determine palaeoclimatic fluctuations and their possible impact on vegetation since the late pleistocene the 72 cm deep sediment core that was retrieved reveals five distinct palaeoclimatic phases 1 warm and humid conditions with a high lake stand before the last glacial maximum lgm 29 800 cal yr bp subsequently changing to a relatively cool and dry phase during the lgm 2 considerable dry conditions and lower precipitation occurred between 16 300 and 9500 cal yr bp during this period the vegetation shrank and perhaps was confined to moister pockets or was a riparian forest cover 3 an outbreak in the shift of monsoonal precipitation was witnessed in the beginning of the mid holocene around 8400 cal yr bp implying alteration in the shift toward warm and humid conditions resulting in relatively high pollen abundance for evergreen taxa 4 this phase exhibits a shift to heavier 13 c values around 1850 cal yr bp with an emergence of moist deciduous plants pointing to drier conditions 5 human activities contributed to the exceedingly high percentage of acacia and pinus pollen during the little ice age

isostatic response of the australian lithosphere estimation of effective elastic thickness and anisotropy using multitaper spectral analysis gravity and topography provide important insights regarding the degree and mechanisms of isostatic compensation the azimuthally isotropic coherence function be tween the bouguer gravity anomaly and topography evolves from high to low for increasing wavenumber a diagnostic that can be predicted for a variety of lithospheric loading models and used in inversions for flexural rigidity thereof in this study we investigate the isostatic response of continental australia we consider the effects of directionally anisotropic plate strength on the coherelce the anisotropic coherence function is calculated for regions of australia that have distinctive geological and geophysical properties the coherence estimation is performed by the thomson multiple slepian taper spectral analysis method extended to two dimensional fields our analysis reveals the existence of flexural anisotropy in central australia indicative of a weaker n s direction of lower te this observation is consistent with the suggestion that the parallel faults in that area act to make the lithosphere weaker in the direction perpendicular to them it can also be related to the n s direction of maximum stress and possibly the presence of e w running zones weakened due to differential sediment burial rates we also demonstrate that the multitaper method has distinct advantages for computing the isotropic coherence function the ability to make many independent estimates of the isostatic response that are minimally affected by spectral leakage results in a coherence that is more robust than with modified periodogram methods particularly at low wavenumbers our analysis elucidates the reasons for discrepancies in previous estimates of effective elastic thickness te of the australian lithosphere in isotropic inversions for te we obtain values that are as much as a factor of 2 less than those obtained in standard inversions of the periodogram coherence using bouguer gravity and topography but greater than those obtained by inversions that utilize free air rather than bouguer gravity and ignore the presence of subsurface loads however owing to the low spectral power of the australian topography the uncertainty on any estimate of te is substantial

inconsistent sea surface temperature and salinity changing trend in the northern south china sea since 7 0 ka bp abstract the south china sea scs is an important moisture and heat source in the asian monsoon system and its environmental changes influence economic and social stability in southeast asia and east asian previous records on sea surface temperature sst and salinity sss were mostly from one sediment core and or only showed fragmentary information it is hard to provide insights into the mechanisms of the overall paleoceanographical environmental variability in the northern scs in this study paired 18o and mg ca records of planktonic foraminifer globigerinoides ruber from core s0204b nearby the luzon strait 21 13 818 n 118 3 077 water depth 1822 m and core ghe 27l 19 85 n 115 34 e water depth of 1533 m in the central northern scs were analyzed so as to better understand the physical process of the sst and sss changes in the northern scs and its relationship with the tropical pacific the results demonstrate that the sst is relatively stable and seawater 18o 18osw values a salinity proxy shows a decrease trend since 7 0 ka bp in core s0204b by contrast sst and 18osw in core ghe 27l exhibit an overall increasing trend at the same time indicating apparent regional discrepancy on the changing trend of the sst and sss in the northern scs we suggest that the thermal and hydrographic conditions in core s0204b were primarily influenced by the outer western pacific water however the thermal and hydrographic conditions in core ghe 27l may be predominantly controlled by the weakened asian monsoon during the mid late holocene which was induced by the southern migration of intertropical convergence zone itcz and stronger ei nino southern oscillation

wavelet analysis of the coherence between bouguer gravity and topography application to the elastic thickness anisotropy in the canadian shield summary we use a wavelet transform to compute the local and azimuthal variations of the coherence between bouguer gravity and topography in eastern canada the isotropic coherence is calculated by averaging the wavelet spectra from optimally overlapping 2 d morlet wavelets having an isotropic spectral envelope in adjacent directions within 180 defining the so called fan wavelet the isotropic wavelet coherence spectrum is inverted to obtain local estimates of the elastic thickness te of the lithosphere we calculate the anisotropic coherence by restricting the fan wavelet over an azimuthal range of 90 the direction of maximum coherence is diagnostic of the direction of preferred isostatic compensation or the direction where the lithosphere is weakest the coherence is inverted using the theoretical response of a thin anisotropic plate model we have carried out extensive tests on synthetic topography and bouguer gravity data sets to verify that 1 the wavelet method can recover te for simple models with either homogeneous or spatially variable rigidity patterns and that 2 the method can determine azimuthal variations in the 2 d coherence for homogeneous models with anisotropic te we have used data from the eastern canadian shield to infer the variations in te and the anisotropy of the coherence the relative variations in te show trends similar to those obtained in previous studies that used different spectral methods the wavelet transform gives te values between 30 and 120 km te is generally high 80 km throughout eastern canada lower values 30 60 km are found in the eastern grenville province in the northern appalachians and in the superior province in the great lakes region the high values found in hudson bay are consistent with previous studies of elastic thickness and models of basin subsidence the direction of maximum coherence obtained from the wavelet method is also consistent with our previous results obtained with the multitaper method and shows that the weak mechanical axis is perpendicular to the fast seismic axis where seismic anisotropy has been detected

wavelet transform mapping of effective elastic thickness and plate loading validation using synthetic data and application to the study of southern african tectonics 1 we present a new wavelet transform method to map spatial variations in effective elastic thickness te and plate loading ratio f the method assumes a model of thin plate flexural isostasy to describe the mechanical response of the lithosphere to vertical loading in this model the rheological properties of the lithosphere are aggregated into the effective elastic thickness te of an equivalent thin plate overlying an inviscid fluid a number of methods have been developed to map spatial variations in te in an attempt to assess regional patterns of flexural strength our new method first obtains local coherence and local admittance through wavelet cross spectral analysis of surface topography and bouguer gravity anomaly wavelet coherence is used to obtain the local characteristic wavelength which is a function of both te and the degree of relative loading f of the plate by subsurface loads and surface loads loading is the combined effect of erosion sedimentation intrusion faulting and metamorphism wavelet admittance in a normalized form is used to resolve this f te ambiguity and maps are made of the spatial variations in te and f we carry out extensive tests of the wavelet method on simulated topography and bouguer gravity anomaly data that we generate through finite difference simulations of flexural isostasy with spectrally realistic loads and simple spatial variations in te these tests demonstrate that the wavelet inversion method is reasonably robust to uncertainties in loading and in crustal thickness and is able to recover te to within 25 50 of its correct value we apply the wavelet method to southern africa and recover estimates of te principally in the range 25 50 km in good agreement with existing estimates from forward modeling and fourier coherence analyses we find that our te estimates often exceed estimates of crustal thickness pointing to a strong upper mantle in parts of southern africa

decompensative gravity anomalies reveal the structure of the upper crust of antarctica as antarctica is almost entirely covered by thick ice shields impeding in situ measurements information about upper crustal structures and sedimentary basins is still sparse and the analysis of the gravity anomalies offers new insights isostatic gravity anomalies are often used to investigate upper crust structures however compensating masses significantly reduce the gravity effect of unknown sedimentary and upper crustal structures to separate these effects we apply so called decompensative corrections to the isostatic anomalies for the antarctic continent which reach values of up to 70 mgal the obtained decompensative anomalies well correspond to the known sedimentary basins such as in the areas of the filchner ronne ice shelf and lambert graben and also suggest the existence of other large sedimentary deposits both in west and east antarctica which are not or only sparsely mapped by existing seismic surveys e g in coastal dronning maud land and enderby land a dipole like structure exists at the transantarctic mountains and the wilkes subglacial basin suggesting the presence of isostatic disturbances linked to the dynamic uplift of the transantarctic mountains and thick sedimentary accumulations in the east extended positive anomalies in east antarctica are likely related to the old and dense cratonic crust as well as to isostatic disturbances caused by the transition from local to regional compensation around the lambert graben

assimilation of t trec retrieved winds from single doppler radar with an ensemble kalman filter for the forecast of typhoon jangmi 2008 abstracta tropical cyclone tc circulation tracking radar echo by correlation technique t trec developed recently is applied to derive horizontal winds from single doppler radar reflectivity z data combined with radial velocity vr data when available the typically much longer maximum range of z observations compared to vr data allows for much larger spatial coverage of the t trec retrieved winds vtrec when a tc first enters the maximum range of a coastal radar retrieved using data from more than one scan volume the t trec winds also contain valuable cross beam wind information the vtrec or vr data at 30 min intervals are assimilated into the advanced regional prediction system arps model at 3 km grid spacing using an ensemble kalman filter over a 2 h window shortly after typhoon jangmi 2008 entered the vr coverage area of an operational weather radar of taiwan the assimilation of vtrec data produces analyses of the typhoon structure and intensity that more closely match observations than

refined proterozoic evolution of the gawler craton south australia through u pb zircon geochronology abstract through the application of both conventional u pb zircon analyses and small sample u pb isotopic analyses the nature and timing of tectonic events leading to the formation of the gawler craton have been defined more precisely constraints on deposition of early proterozoic iron formation bearing sediments have been narrowed down to the period 1960 1847 ma deformed acid volcanics including the economically important moonta porphyry have zircon ages of 1790 and 1740 ma the voluminous acid gawler range volcanics and correlatives to the east were erupted over a short interval at 1592 2 ma and were intruded by anorogenic granites at 1575 ma small sample zircon analyses proved to be an extremely valuable adjunct to conventional analyses generally yielding more concordant data which forced a curved discordia through an upper intercept slightly younger than from a conventional straight line discordia

the holocene environmental changes in southern indonesia reconstructed from highland caldera lake sediment in bali island diatom pollen geomagnetic and geochemical analyses were carried out on a 3 6 m long sediment core taken from lake buyan a highland caldera lake in central bali island to reconstruct the holocene climate changes in equatorial southern indonesia the core represents 8 thousand years sedimentation of organic diatomaceous lake mud constant inclusion of benthic diatom fossils as main components indicated that suspension and inflow of littoral materials were the main sedimentary process the core contained laminated sediments in two distinct intervals at 6 5 5 0 and 3 6 3 1 cal ky bp and multi proxy records showed generally drier climate in these sections especially at 3 6 3 1 cal ky bp lake bottom waters were more reducing condition in these laminated periods probably due to increased lake productivity by prolonged dry season and wind mixing laminae structures were made up of a layer composed of benthic diatoms and amorphous organic materials and a layer made by only planktonic diatom fossils each of which may represent rainy and dry period deposits although southern indonesia shows clear australian monsoon rainfall seasonality at present counting of layer numbers showed interannual cycles of laminae formation prolonged dry seasons could obscured the rainfall seasonality in these periods but precise depositional patterns were elusive unlaminated sections showed homogeneous sediment mixture of benthic planktonic diatoms and more volume of terrigenous materials indicating wetter climate and seasonality similar to the present time this was supported by the higher share of marsh environment pollens reflecting more stable lake level trends the dry climate from 6 5 cal ky bp was in line with the general perception of stronger enso dynamics from the mid holocene due to weaker than before boreal summer insolation but the sporadic appearances of dry periods imply the influence of regional climate forcings such as temporal migrations of inter tropical convergence zone itcz it was however possible that temporal shifts of large climate mode occurred in equatorial pacific and indian oceans wettest climate was inferred from 3 1 cal ky bp to the present and this might reflect increased importance of austral hemisphere atmospheric convection and subsequent southerly position of itcz in austral summer time

holocene changes in eastern tropical pacific climate inferred from a galapagos lake sediment record abstract paleoclimate records from the tropical pacific suggest the early to mid holocene was a period of reduced el nino southern oscillation enso variability with a transition to modern increased enso frequency occurring some time in the last few thousand years however the nature and timing of this shift remains uncertain due to the discontinuous nature and or coarse resolution of many enso proxies as well as a lack of agreement between previously published records a new continuous climate record from el junco crater lake in the galapagos islands reveals several abrupt changes in lake level and precipitation through the holocene hydroclimatic model simulations suggest that el junco lake level responds sensitively to increases in precipitation associated with el nino events rising during wet el nino events and falling during the intervening dry periods grain size data from el junco sediment cores indicate past lake level variability likely associated with changing seasonal precipitation and enso frequency the grain size data suggest increased precipitation intensity prior to 9000 120 cal years bp and after 4200 130 cal years bp as well as a two step increase in precipitation at 3200 160 and 2000 100 cal years bp maximum holocene precipitation and inferred enso variability occurred between 2000 100 and 1500 70 cal years bp during the same period that six other independent proxy records suggest higher enso frequency and longer stronger el nino events decreasing sediment carbon nitrogen c n ratios in el junco sediments indicate rising lake levels from the early holocene to present corroborating the grain size data the inferred increase in precipitation at 4200 130 cal years bp and at 2000 100 cal years bp coincides with decreasing southwest asian and east asian monsoon intensity suggesting tropical pacific climate and the asian monsoon were interconnected systems at centennial to millennial timescales during the holocene a weakening trend in the asian monsoon and the trend toward wetter conditions at el junco also coincide with a trend toward cooler and drier conditions inferred from cariaco basin sediment proxies from the mid holocene to present suggesting the migration of the intertropical convergence zone itcz likely influenced hydrological changes in both the eastern tropical pacific and the asian monsoon region during the holocene

sensitivity of the australian monsoon to insolation and vegetation implications for human impact on continental moisture balance general circulation model experiments test the geologically based correlation of high monsoon rainfall over interior australia with northern hemisphere insolation and evaluate the sensitivity of the australian monsoon to ecosystem change our results suggest that northern hemisphere insolation control on the intensity of the siberian high rather than summer insolation over the australian continent determines the strength of the australian monsoon on millennial time scales unlike a classic monsoon regime additional simulations show that the penetration of monsoon moisture into the interior is sensitive to biosphere atmosphere feedbacks linked to vegetation type and soil properties this sensitivity offers a resolution to the observed failure of the australian monsoon to penetrate the interior in the holocene postulated regular burning practiced by early humans may have converted a tree shrub grassland mosaic across the semiarid zone to the modern desert scrub thereby weakening biospheric feedbacks and resulting in long term desertification of the continent

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

effective elastic thickness of the arabian plate weak shield versus strong platform the fan wavelet method has been employed to calculate high resolution maps of variations of the effective elastic thickness eet for the arabian plate and surroundings as the initial data we use high resolution gravity field topography and recent models of sedimentary basins the western part of the plate is generally characterized by low to midvalues of eet 10 30 km while the eastern one by high values 50 km and more in the core this finding confirms that the pronounced asymmetry of the plate is rather associated with fundamental structural differences of the lithosphere than with a forced tilt of the plate due to the rifting in the west southwest and subduction in the northeast therefore the high topography in the western part of the plate is likely supported by relatively hot mantle that is also responsible for the decrease of eet these results are generally in agreement with recent seismic tomography models

global and local isostatic coherence from the wavelet transform 1 a method to compute the variations in lithospheric elastic thickness te has been developed using the wavelet transform the technique which uses a superposition of two dimensional morlet wavelets in a geometry named a fan wavelet is designed to yield isotropic yet complex wavelet coefficients for the co and cross spectra of gravity and topography data these are then used to compute a spatially varying isostatic coherence from which both global and local estimates may be obtained we applied the method to synthetic gravity and topography generated for a thin elastic plate of uniform thickness 20 km yielding an apparent spatially variable te of 24 5 3 5 km the estimated global coherence for this model appears to fit the theoretical prediction as well as fourier transform based estimates and is smoother than these we also computed the wavelet coherence and hence spatially varying te for a plate of non uniform thickness yielding a difference with the model of 2 0 1 7 km

indonesian throughflow drove australian climate from humid pliocene to arid pleistocene late miocene to mid pleistocene sedimentary proxy records reveal that northwest australia underwent an abrupt transition from dry to humid climate conditions at 5 5 million years ma likely receiving year round rainfall but after 3 3 ma climate shifted toward an increasingly seasonal precipitation regime the progressive constriction of the indonesian throughflow likely decreased continental humidity and transferred control of northwest australian climate from the pacific to the indian ocean leading to drier conditions punctuated by monsoonal precipitation the northwest dust pathway and fully established seasonal and orbitally controlled precipitation were in place by 2 4 ma well after the intensification of northern hemisphere glaciation the transition from humid to arid conditions was driven by changes in pacific and indian ocean circulation and regional atmospheric moisture transport influenced by the emerging maritime continent we conclude that the maritime continent is the switchboard modulating teleconnections between tropical and high latitude climate systems

the long term strength of europe and its implications for plate forming processes field based geological studies show that continental deformation preferentially occurs in young tectonic provinces rather than in old cratons this partitioning of deformation suggests that the cratons are stronger than surrounding younger phanerozoic provinces however although archaean and phanerozoic lithosphere differ in their thickness and composition their relative strength is a matter of much debate one proxy of strength is the effective elastic thickness of the lithosphere te unfortunately spatial variations in te are not well understood as different methods yield different results the differences are most apparent in cratons where the bouguer coherence method yields large te values 60 km whereas the free air admittance method yields low values or 1 5 gyr old is much larger mean te 60 km than that of younger lithosphere mean te 30 km we propose that this strength difference reflects changes in lithospheric plate structure thickness geothermal gradient and composition that result from mantle temperature and volatile content decrease through earth s history

increasing australian indonesian monsoon rainfall linked to early holocene sea level rise the australian indonesian summer monsoon affects rainfall variability across the indo pacific region reconstructions of monsoon strength from stalagmites show that precipitation increased from 11 000 to 7 000 years ago as rising global sea level caused the flooding of the indonesian continental shelf the australian indonesian summer monsoon affects rainfall variability and hence terrestrial productivity in the densely populated tropical indo pacific region it has been proposed that the main control of summer monsoon precipitation on millennial timescales is local insolation1 2 3 but unravelling the mechanisms that have influenced monsoon variability and teleconnections has proven difficult owing to the lack of high resolution records of past monsoon behaviour here we present a precisely dated reconstruction of monsoon rainfall over the past 12 000 years based on oxygen isotope measurements from two stalagmites collected in southeast indonesia we show that the summer monsoon precipitation increased during the younger dryas cooling event when atlantic meridional overturning circulation was relatively weak4 monsoon precipitation intensified even more rapidly from 11 000 to 7 000 years ago when the indonesian continental shelf was flooded by global sea level rise5 6 7 we suggest that the intensification during the younger dryas cooling was caused by enhanced winter monsoon outflow from asia and a related southward migration of the intertropical convergence zone8 however the early holocene intensification of monsoon precipitation was driven by sea level rise which increased the supply of moisture to the indonesian archipelago

heat flux variations beneath central greenland s ice due to anomalously thin lithosphere the thermal state of the earth s surface is usually influenced more by climate than by heating from the earth s interior numerical models show that in the oldest and thickest part of the greenland ice sheet geothermal heat flux through an anomalously thin lithosphere leads to strong regional variations in basal melting

global shear speed structure of the upper mantle and transition zone s u m m a r y the rapid expansion of broad band seismic networks over the last decade has paved the way for a new generation of global tomographic models significantly improved resolution of global upper mantle and crustal structure can now be achieved provided that structural information is extracted effectively from both surface and body waves and that the effects of errors in the data are controlled and minimized here we present a new global vertically polarized shear speed model that yields considerable improvements in resolution compared to previous ones for a variety of features in the upper mantle and crust the model sl2013sv is constrained by an unprecedentedly large set of waveform fits 3 4 of a million broad band seismograms computed in seismogram dependent frequency bands up to a maximum period range of 11 450 s automated multimode inversion of surface and s wave forms was used to extract a set of linear equations with uncorrelated uncertainties from each seismogram the equations described perturbations in elastic structure within approximate sensitivity volumes between sources and receivers going beyond ray theory we calculated the phase of every mode at every frequency and its derivative with respect to sand p velocity perturbations by integration over a sensitivity area in a 3 d reference model the normally small perturbations of the 3 d model required to fit the waveforms were then linearized using these accurate derivatives the equations yielded by the waveform inversion of all the seismograms were simultaneously inverted for a 3 d model of shear and compressional speeds and azimuthal anisotropy within the crust and upper mantle elaborate outlier analysis was used to control the propagation of errors in the data source parameters timing at the stations etc the selection of only the most mutually consistent equations exploited the data redundancy provided by our data set and strongly reduced the effect of the errors increasing the resolution of the imaging our new shear speed model is parametrized on a triangular grid with a 280 km spacing in well sampled continental domains lateral resolution approaches or exceeds that of regionalscale studies the close match of known surface expressions of deep structure with the distribution of anomalies in the model provides a useful benchmark in oceanic regions spreading ridges are very well resolved with narrow anomalies in the shallow mantle closely confined near the ridge axis and those deeper down to 100 120 km showing variability in their width and location with respect to the ridge major subduction zones worldwide are well captured extending from shallow depths down to the transition zone the large size of our waveform fit data set also provides a strong statistical foundation to re examine the validity field of the jwkb approximation and surface wave ray theory our analysis shows that the approximations are likely to be valid within certain time frequency portions of most seismograms with high signal to noise ratios and these portions can be identified using a set of consistent criteria that we apply in the course of waveform fitting

variations of the lithospheric strength and elastic thickness in north america we evaluate the effect of temperature variations on strength and effective elastic thickness te of the lithosphere of the north american na continent to this purpose we use two thermal models that are corrected for compositional variations and anelasticity effects in the upper mantle these thermal models are obtained from a joint inversion of gravity data and two recent seismic tomography models na07 and sl2013sv the crustal rheology was defined using nacr14 the most recent na crustal model this model specifies seismic velocities and thickness for a three layer model of the crystalline crust strength in the lithosphere and in the crust has similar distributions indicating that local geotherms play a dominant role in determining strength rather than crustal composition a pronounced contrast is present in strength between cratonic and off cratonic regions lithospheric strength in the off cratonic regions is prevalently localized within the crust and te shows low values 150 km in contrast to previous results our models indicate that phanerozoic regions located close to the edge of the cratons as the appalachians are characterized by low strength we also find that locally weak zones exist within the cratons e g beneath the intracratonic illinois basin and midcontinent rift seismic tomography models na07 and sl2013sv differ mainly in some peripheral parts of the cratons as the proterozoic canadian platform the grenville and the western part of the yavapai mazatzal province where the integrated strength for the model na07 is 10 times larger than in model sl2013sv due to a temperature difference 200 c in the uppermost mantle the differences in te between the two models are less pronounced in both models proterozoic regions reactivated by meso cenozoic tectonics e g rocky mountains and the mississippi embayment are characterized by a weak lithosphere due to the absence of the mechanically strong part of the mantle lithospheric layer intraplate earthquakes are distributed along the edges of the cratons demonstrating that tectonic stress accumulates there while the cores of the cratons remain undeformed in both models intraplate earthquakes occur in weak lithosphere 0 5 1013 pa s te 15 km or near the edges of strong cratonic blocks characterized by pronounced contrasts of strength and te