enhanced terrestrial weathering runoff and surface ocean carbonate production during the recovery stages of the paleocene eocene thermal maximum 1 the carbonate saturation profile of the oceans shoaled markedly during a transient global warming event known as the paleocene eocene thermal maximum petm circa 55 ma the rapid release of large quantities of carbon into the ocean atmosphere system is believed to have triggered this intense episode of dissolution along with a negative carbon isotope excursion cie the brevity 120 220 kyr of the petm reflects the rapid enhancement of negative feedback mechanisms within earth s exogenic carbon cycle that served the dual function of buffering ocean ph and reducing atmospheric greenhouse gas levels detailed study of the petm stratigraphy from ocean drilling program site 690 weddell sea reveals that the cie recovery period which postdates the cie onset by 80 kyr is represented by an expanded 2 5 m thick interval containing a unique planktic foraminiferal assemblage strongly diluted by coccolithophore carbonate collectively the micropaleontological and sedimentological changes preserved within the cie recovery interval reflect a transient state when ocean atmosphere chemistry fostered prolific coccolithophore blooms that suppressed the local lysocline to relatively deeper depths a prominent peak in the abundance of the clay mineral kaolinite is associated with the cie recovery interval indicating that continental weathering runoff intensified at this time as well robert and kennett 1994 such parallel stratigraphic changes are generally consonant with the hypothesis that enhanced continental weathering runoff and carbonate precipitation helped sequester carbon during the petm recovery period e g dickens et al 1997 zachos et al 2005

earthquakes beneath the himalayas and tibet evidence for strong lithospheric mantle eleven intracontinental earthquakes with magnitudes ranging from 4 9 to 6 occurred in the mantle beneath the western himalayan syntaxis the western kunlun mountains and southern tibet near xigaze between 1963 and 1999 high resolution seismic waveforms show that some focal depths exceeded 100 kilometers indicating that these earthquakes occurred in the mantle portion of the lithosphere even though the crust has been thickened there the occurrence of earthquakes in the mantle beneath continental regions where the subduction of oceanic lithosphere ceased tens of millions years ago indicates that the mantle lithosphere is sufficiently strong to accumulate elastic strain

gravity and gps measurements reveal mass loss beneath the tibetan plateau geodetic evidence of increasing crustal thickness 1 today some tens of million years after its creation by the collision between india and asia the tibetan plateau is the highest and largest plateau on earth results of geological and tectonic studies indicate that the plateau is extending however almost no quantitative evidence shows whether the plateau is still uplifting or thickening nowadays herein we present geodetic evidence of mass loss beneath the tibetan plateau and increasing crust thickness combined absolute gravity and global positional system gps measurements at three stations in southern and southeastern tibet during two decades reveal uplifting of the tibetan plateau at a millimeter per year level but its underlying mass is diminishing indicating that the crustal thickness is increasing at an annual millimeter to decimeter level

organic carbon burial following the middle eocene climatic optimum in the central western tethys we present trace metal geochemistry and stable isotope records for the middle eocene alano di piave section ne italy deposited during magnetochron c18n in the marginal tethys ocean we identify a sim 500 kyr long carbon isotope perturbation event we infer to be the middle eocene climatic optimum meco confirming the northern hemisphere expression and global occurrence of meco interpreted peak climatic conditions are followed by the rapid deposition of two organic rich intervals le 3 toc and contemporaneous positive delta 13 c excursions these two intervals are associated with increases in the concentration of sulphur and redox sensitive trace metals and low concentrations of mn as well as coupled with the occurrence of pyrite together these changes imply low possibly dysoxic bottom water o 2 conditions promoting increased organic carbon burial we hypothesize that this rapid burial of organic carbon lowered global it p co 2 following the peak warming and returned the climate system to the general eocene cooling trend

paleogene calcite compensation depth in the eastern subtropical pacific answers and questions 1 ocean drilling program leg 199 drilled a north south transect across the eocene paleoequator in the eastern pacific permitting reconstruction the calcite compensation depth ccd since earliest eocene time the ccd was relatively shallow near the early eocene pacific equator 3200 m and unlike modern latitudinal ccd gradients deepened to the north to 3600 m paleolatitude 10 n at 41 ma the ccd underwent a brief sharp transient deepening of 700 m then remained shallow until the eocene oligocene boundary at the e o boundary the ccd deepened by 1200 m in less than 300 kyr this rapid deepening served to more than double the area of seafloor subject to caco3 deposition sea level fall associated with ice volume buildup and ensuing shelf basin fractionation is unlikely to be the sole cause of the increased deep ocean caco3 burial rather a sudden rapid increase in the amount of ca entering the ocean appears necessary to explain the observations

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

eustatic variations during the paleocene eocene greenhouse world we reconstruct eustatic variations during the latest paleocene and earliest eocene 58 52 ma dinoflagellate cysts grain size fractions and organic biomarkers in marine sections at four sites from three continents indicate an increased distance to the coast during the paleocene eocene thermal maximum petm the same trend is recognized in published records from other sites around the world together the data indicate a eustatic rise during the petm beginning 20 to 200 ka before the globally recorded negative carbon isotope excursion cie at 55 5 ma although correlations are tentative we recognize other global transgressions during chrons c25n and c24n the latter may be associated with eocene thermal maximum 2 53 5 ma or the x event 52 ma these results suggest a link between global sea level and hyperthermal intervals potentially because of the melting of small alpine ice sheets on antarctica thermal expansion of seawater or both however the early onset of sea level rise relative to the cie of the petm suggests contributions from other mechanisms perhaps decreasing ocean basin volume on sea level rise copyright 2008 by the american geophysical union

dynamics of fossil fuel co2 neutralization by marine caco3 a detailed model of the ocean circulation and carbon cycle was coupled to a mechanistic model of caco3 diagenesis in deep sea sediments to simulate the millennium scale response of the oceans to future fossil fuel co2 emissions to the atmosphere and deep sea simulations of deep sea injection of co2 show that caco3 dissolution is sensitive to passage of high co2 waters through the atlantic ocean but caco3 dissolution has a negligible impact on atmospheric pco2 or the atmospheric stabilization co2 emission in the coming centuries the ultimate fate of the fossil fuel co2 will be to react with caco3 on the seafloor and on land an initial caco3 dissolution spike reverses the net sedimentation rate in the ocean until it is attenuated by an enhanced vertical gradient of alkalinity after about 1000 years the magnitude of the initial spike is sensitive to assumptions about the kinetics for caco3 dissolution but subsequent behavior appears to be less model dependent neutralization by seafloor caco3 occurs on a timescale of 5 6 kyr and is limited to at most 60 70 of the fossil fuel release even if the fossil fuel release is smaller than the seafloor erodible inventory of caco3 additional neutralization by terrestrial caco3 restores a balance between caco3 weathering and seafloor accumulation on a timescale of 8 5 kyr while the deficit of seafloor caco3 the lysocline is replenished with an e folding timescale of approximately 18 kyr the final equilibrium with caco3 leaves 7 8 of the fossil fuel co2 remaining in the atmosphere to be neutralized by the silicate rock cycle on a time frame of hundreds of thousands of years

time variable ice loss in asian high mountains from satellite gravimetry abstract substantial amount of glacial ice is considered to be melting in the asian high mountains gravimetry by grace satellite during 2003 2009 suggests the average ice loss rate in this region of 47 12 gigaton gt yr 1 equivalent to 0 13 0 04 mm yr 1 sea level rise this is twice as fast as the average rate over 40 years before the studied period and agrees with the global tendency of accelerating glacial loss such ice loss rate varies both in time and space mass loss in himalaya is slightly decelerating while those in northwestern glaciers show clear acceleration uncertainty still remains in the groundwater decline in northern india and proportion of almost isostatic e g tectonic uplift and non isostatic e g glacial isostatic adjustment portions in the current uplift rate of the tibetan plateau if gravity increase associated with ongoing glacial isostatic adjustment partially canceled the negative gravity trend the corrected ice loss rate could reach 61 gt yr 1

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

vertical crustal movement around the southeastern tibetan plateau constrained by gps and grace data abstract using measurements of continuous gps stations and grace across the southeastern tibetan plateau we found that the grace derived vertical displacements are highly correlated with gps modeled vertical annual and semiannual displacements which demonstrates that the vertical seasonal variations on ground surface are mainly caused by hydrological mass loading after removing grace modeled seasonal variations from the gps time series we used a stacking technique to filter out the common mode errors then we estimated the best noise model for the filtered time series which can be best characterized by power law noise model finally we determined the rates of vertical crustal movement of southeastern tibetan plateau our results suggest that the southeastern tibetan plateau is undergoing uplift whereas the southern sichuan yunnan fragment is subsiding with respect to the region to the north the assumption of uniform extension throughout the crust does not explain the subsidence of southern sichuan yunnan fragment

present day crustal deformation in china constrained by global positioning system measurements global positioning system gps measurements in china indicate that crustal shortening accommodates most of india s penetration into eurasia deformation within the tibetan plateau and its margins the himalaya the altyn tagh and the qilian shan absorbs more than 90 of the relative motion between the indian and eurasian plates internal shortening of the tibetan plateau itself accounts for more than one third of the total convergence however the tibetan plateau south of the kunlun and ganzi mani faults is moving eastward relative to both india and eurasia this movement is accommodated through rotation of material around the eastern syntaxis the north china and south china blocks east of the tibetan plateau move coherently east southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year respectively with respect to the stable eurasia

mass accumulation rates in asia during the cenozoic summary this work establishes estimates of mass accumulation rates in 18 mostly offshore sedimentary basins in asia since the beginning of the cenozoic 66 ma the estimates were derived from isopach maps cross sections and drill holes or stratigraphic columns assuming regional similarity of the strata average solid phase volumes and accumulation rates were calculated for nine epochs approximately corresponding to geological periods palaeocene 66 58 ma eocene 58 37 ma oligocene 37 30 and 30 24 ma miocene 24 17 17 11 and 11 5 ma pliocene 5 2 ma and quaternary 2 0 ma these rates shed new light on the geological history of asia since the onset of the collision of india with asia 50 ma the overall average accumulation rates curve for asian sedimentary basins since the beginning of the tertiary shows an exponential form with slow accumulation rates less than 0 5 106 km3 myr 1 until the beginning of the oligocene more than 15 myr after the onset of the collision from the oligocene onwards rates increase quickly in an exponential manner reaching their maximum values in the quaternary more than 1 5 106 km3 myr 1 from these observations we suggest that extrusion and crustal shortening are complementary processes that have been successively dominant throughout the india eurasia collision history at smaller scales one may distinguish between independent histories at the subcontinental and basin scales this permits a comparison of the relative importance of tectonic and climatic erosion processes affecting the different mountain belts of asia during the cenozoic

erosion history of the tibetan plateau since the last interglacial constraints from the first studies of cosmogenic 10be from tibetan bedrock abstract the cosmogenic 10be exposure histories of in situ bedrock surfaces from the tibetan plateau indicate low erosion rates of

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

investigating possible gravity change rates expected from long term deep crustal processes in taiwan we propose to test if gravimetry can prove useful in discriminating different models of long term deep crustal processes in the case of the taiwan mountain belt we discuss two existing tectonic models that differ in the deep processes proposed to sustain the long term growth of the orogen one model assumes underplating of the uppermost eurasian crust with subduction of the deeper part of the crust into the mantle the other one suggests the accretion of the whole eurasian crust above crustal scale ramps the lower crust being accreted into the collisional orogen we compute the temporal gravity changes caused only by long term rock mass transfers at depth for each of them we show that the underplating model implies a rate of gravity change of 6 10 2 gal yr 1 a value that increases to 2 10 2 gal yr 1 if crustal subduction is neglected if the accretion of the whole eurasian crust occurs a rate of 7 10 2 gal yr 1 is obtained the two models tested differ both in signal amplitude and spatial distribution the yearly gravity changes expected by long term deep crustal mass processes in taiwan are two orders of magnitude below the present day uncertainty of land based gravity measurements assuming that these annually averaged long term gravity changes will linearly accumulate with ongoing mountain building multidecadal time series are needed to identify comparable rates of gravity change however as gravity is sensitive to any mass redistribution effects of short term processes such as seismicity and surface mass transfers erosion sedimentation groundwater may prevent from detecting any long term deep signal this study indicates that temporal gravity is not appropriate for deciphering the long term deep crustal processes involved in the taiwan mountain belt

north american continental margin records of the paleocene eocene thermal maximum implications for global carbon and hydrological cycling the impacts of the paleocene eocene thermal maximum petm 55 ma one of the most rapid and extreme warming events in earth history are well characterized in open marine and terrestrial environments but are less so on continental margins a major carbon sink here we present stable isotope carbonate content organic matter content and c n ratio records through the petm from new outcrop sections in california and from cores previously drilled on the new jersey margin foraminifer 18o data suggest that midlatitude shelves warmed by a similar magnitude as the open ocean 5 c 8 c while the carbon isotope excursion cie recorded both in carbonate and organic matter 13c records is slightly larger 3 3 4 5 than documented in open ocean records sediment accumulation rates increase dramatically during the cie in marked contrast to the open ocean sites in parallel mass accumulation rates of both organic and inorganic carbon also increased by an order of magnitude the estimated total mass of accumulated carbon in excess of pre cie rates suggests that continental margins at least along north america became carbon sinks during the cie mainly because of weathering feedbacks and rising sea level this result is significant because it implies that the negative feedback role of carbon burial on continental margins was greater than previously recognized

arctic late paleocene early eocene paleoenvironments with special emphasis on the paleocene eocene thermal maximum lomonosov ridge integrated ocean drilling program expedition 302 we reconstruct the latest paleocene and early eocene 57 50 ma environmental trends in the arctic ocean and focus on the paleocene eocene thermal maximum petm 55 ma using strata recovered from the lomonosov ridge by the integrated ocean drilling program expedition 302 the lomonosov ridge was still partially subaerial during the latest paleocene and earliest eocene and gradually subsided during the early eocene organic dinoflagellate cyst dinocyst assemblages point to brackish and productive surface waters throughout the latest paleocene and early eocene dinocyst assemblages are cosmopolitan during this time interval suggesting warm conditions which is corroborated by tex86 reconstructed temperatures of 15 18 c inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower eocene spectral analysis reveals that the cyclicity recorded in x ray fluorescence scanning fe data from close to eocene thermal maximum 2 53 ma presence confirmed by dinocyst stratigraphy is related to precession within the lower part of the petm proxy records indicate enhanced weathering runoff anoxia and productivity along with sea level rise on the basis of total organic carbon content and variations in sediment accumulation rates excess organic carbon burial in the arctic ocean appears to have contributed significantly to the sequestration of injected carbon during the petm

bouguer gravity anomaly and isostasy at western sichuan basin revealed by new gravity surveys a dense relative gravity and global positioning system observation network with 302 stations was measured in the western sichuan basin sb to study gravity and isostasy bouguer gravity anomalies are negative in the study area and change gradually from about 110 mgal 10 5m s 2 in the southeast to 220 mgal in the northwest the new data reveal that the moho beneath the western sb changes gradually from 39 5 km in the southeast to 43 7 km in the northwest and is inclined slightly to the northwest beneath the chengdu plain the isostatic crustal thickness calculated by airy isostatic theory varies between 39 5 and 42 0 km the longquan shan lqs marks a clear boundary in the state of isostastic compensation in the study area the moho depth is almost identical to the airy isostatic crustal thickness east of the lqs where the crust is in isostatic balance however on the chengdu plain west of the lqs differences between the moho depth and airy isostatic crustal thickness became larger from east to west where the crust is out of isostatic balance this indicates that the load of the longmen shan lms on the west part of the crust of sb is mainly borne by the crust beneath the chengdu plain and does little influence the crust east of the lqs as a result we deduce that the lqs fault zone is a deeply rooted high angle fault zone that was broken by the load of the lms

geodetic changes associated with crustal deformation on the andean backarc of san juan argentina in this work we have analyzed the results of temporal geodetic variations associated with tectonic deformation on the andean backarc in southern san juan province argentina this area is affected by the subduction of the juan fernandez ridge and has the greatest seismic hazard in argentina since 2000 we have monitored the variations of gravity annually with high precision g4d in the active deformation belt around the city of san juan 31 s to 32 s 68 w to 69 w temporal gradients of g4d have been associated with active structures and interpreted as subsurface mass redistributions as a result of accumulation and release of stress these data in addition to the topographic deformations measured by the global positioning system gps and the identification of structures in the crystalline basement from the geophysical models allow us interpret mechanisms of deformation in the contact between the precordillera and pampean ranges in the foreland of san juan in this area after more than a decade of low activity in 2012 the tulum fault system tfs was reactivated generating crustal events of moderate magnitude including an earthquake of mw 5 0 january 18 2012 according to our interpretation the fault system accumulated elastic deformation for more than 10 years expressed as height increases at gravity stations decrease of g4d until the year 2011 the january 18 2012 earthquake released part of the energy at the same time as a coseismic increase of g4d this should be reflected in regional tectonic subsidence from the point of view of conventional gravimetric models however gps reoccupation of the benchmarks located in this fault system indicates a generalized increase in altitude of the fault system in the last 15 years tfs behavior could be assumed as topographic flexural displacements induced by a system of blind faults we analyzed the time series of a permanent global navigation satellite system gnss station located to the north of the tfs the grls station 31 61os 68 32ow presents slow variation in the vertical and north components the variation began on december 20 2011 reaching its maximum amplitude on january 18 2012 the geodetic variations coincide with the period of seismic reactivation

separating climate induced mass transfers and instrumental effects from tectonic signal in repeated absolute gravity measurements we estimate the signature of the climate induced mass transfers in repeated absolute gravity measurements based on satellite gravimetric measurements from the gravity recovery and climate experiment grace mission we show results at the globe scale and compare them with repeated absolute gravity ag time behavior in three zones where ag surveys have been published northwestern europe canada and tibet for 10 yearly campaigns the uncertainties affecting the determination of a linear gravity rate of change range 3 4 nm s 2 a in most cases in the absence of instrumental artifacts the results are consistent with what is observed for long term repeated campaigns we also discuss the possible artifact that can result from using short ag survey to determine the tectonic effects in a zone of high hydrological variability we call into question the tectonic interpretation of several gravity changes reported from stations in tibet in particular the variation observed prior to the 2015 gorkha earthquake

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

regulation of atmospheric co2 by deep sea sediments in an earth system model 1 we have extended the genie 1 earth system model to include a representation of sedimentary stratigraphy and the preservation of biogenic carbonates delivered to the ocean floor this has enabled us to take a novel approach in diagnosing modern marine carbon cycling assimilating observation of the calcium carbonate caco3 content of deep sea sediments with an ensemble kalman filter the resulting calibrated model predicts a mean surface sediment content 32 5 wt close to the observed value 34 8 wt and a global burial rate of caco3 in deep sea sediments of 0 121 pgc yr 1 in line with recent budget estimates of 0 10 0 14 pgc yr 1 we employ the genie 1 model in quantifying the multimillennial scale fate of fossil fuel co2 emitted to the atmosphere in the absence of any interaction between ocean and sediments an equilibrium partitioning of co2 is reached within 1000 years of emissions ceasing with 34 645 ppm remaining in the atmosphere out of a total fossil fuel burn of 4173 pgc an additional 12 of co2 emissions 223 ppm are sequestered as bicarbonate ions hco3 by reaction with deep sea carbonates seafloor caco3 neutralization on a timescale of 1 7 ka excess of carbonate weathering on land over deep sea burial results in a further net transformation of 14 of co2 emissions 261 ppm into hco3 terrestrial caco3 neutralization on a timescale of 8 3 ka we have also assessed the importance of a changing climate in modulating the stabilization of atmospheric co2 through ocean sediment interaction increased ocean stratification suppresses particulate organic carbon export which in turn enhances seafloor caco3 preservation the resulting reduction in the sequestration of fossil fuel co2 represents a new positive feedback on millennial scale climate change

evaluation of glacier changes in high mountain asia based on 10 year grace rl05 models in this paper 10 years of time variable gravity data from the gravity recovery and climate experiment release 05 have been used to evaluate the glacier melting rate in high mountain asia hma using a new computing scheme i e the space domain inverse method we find that in hma area there are three different kinds of signal sources that should be treated together the two generally accepted sources glacier melting and india underground water depletion are estimated to change at the rate of 35 0 5 8 gt yr 0 09 mm yr sea level rising and 30 6 5 0 gt yr respectively the third source is the remarkable positive signal 30 gt yr in the inner tibetan plateau which is challenging to explain further we have found that there is a 5 year undulation in pamir and karakoram which can explain the controversies of the previous studies on the glacier melting rate here this 5 year signal can be explained by the influence of arctic oscillation and el nino southern oscillation

co seismic surface ruptures in qiangtang terrane insight into late cenozoic deformation of central tibet abstract recently large earthquakes mostly occurred at the plateau margins along major lithospheric faults however a co seismic rupture has been discovered in central tibet along the burgar co fault bgcf a 150 km long northwest trending right lateral strike slip fault within the hinterland of the qiangtang terrane central tibet the activity of the bgcf is marked by a 50 km long fresh surface rupture from 83 38 57 e 33 58 54 n to 84 09 50 e 33 47 42 n restrained by a bend with a 17 counter clockwise angle geomorphic offsets measured in the field and from high resolution satellite images indicate the lateral displacements cluster at 1 4 0 1 m 2 7 0 4 m 5 4 0 6 m 9 2 0 8 m and 12 5 1 m the smallest value average 1 4 0 1 m maximum 1 8 m is defined as the most recent co seismic offset of a magnitude mw 7 earthquake other clusters are interpreted as the cumulative events which demonstrate that earthquakes frequently took place along the bgcf the seismic behavior of the bgcf together with widespread sinuous north trending grabens and ne nw strike slip faults around western and central qiangtang indicates that the most recent active structures have deformed scattered in the internal part of this terrane additionally the conjugate strike slip fault systems along the bangong nujiang suture define an intangible southern boundary altogether implying that the qiangtang terrane has undergone significant deformation thus can no longer be treated as an integral block finally compared with the continental slip in eastern qiangtang an alternative geodynamic model for qiangtang is inferred a weak channel flow decoupling the upper and middle lower crust which facilitates the southeastwards extrusion as an entire block in the east and continuous deformation as scattered small crustal wedges without expansive upper and middle lower crust decoupling underground in the western and central areas the qiangtang terrane serves as the dominant place for extensive material to migrate eastward accommodating simultaneous e w extension and n s compression

how fast is the middle lower crust flowing in eastern tibet a constraint from geodetic observations various geophysical observations including seismological and magnetotelluric imaging have implied that the deep crust beneath eastern tibet may be partially melted and flowing faster than the brittle upper crust however it is still unclear how much faster the deep crust is flowing geodetic observations which are more sensitive to dynamic changes provide constraints on the flow rate of the middle and lower crust mlc three dimensional gps velocities show that deformation within the brittle upper crust contributes little 0 02 0 02 mm yr to the overall surface uplift 2 7 0 3 mm yr therefore two plausible models for the surface uplift are discussed which are consistent with the geodetic constraints in the deep crustal flow model crustal thickening requires the horizontal flow rate of the mlc to be 330 710 of the rate of motion of the upper crust and the deepening of the moho is only up to 35 of that required to maintain isostatic balance isostasy may not be maintained over the geodetic timescale in the hybrid model of deep crustal flow and convective lithospheric detachment the moho is uprising and only weak or moderate 130 250 deep crustal flow is required which results in moderate present day crustal thickening beneath eastern tibet this result improves our understanding of the plateau construction and dynamics and also offers advice for numerical simulations

patterns and magnitude of deep sea carbonate dissolution during eocene thermal maximum 2 and h2 walvis ridge southeastern atlantic ocean 1 eocene thermal maximum 2 etm2 or h1 53 7 ma represents a short lived warming episode associated with the injection of a large mass of 13c depleted carbon into the ocean atmosphere system the mass of injected carbon the extent of deep sea dissolution and the amount of warming during etm2 appear to be approximately half of those documented for the paleocene eocene thermal maximum petm 55 5 ma but the pattern of lysocline migration during etm2 has not yet been documented sufficiently to decipher potential differences in carbon sources and sequestration mechanisms we present high resolution carbonate dissolution and bulk stable isotope records across etm2 and the successive h2 event 53 6 ma on a common age model for four sites along the walvis ridge depth transect 1500 to 3600 m paleowater depth to assess lysocline evolution the onset of etm2 is characterized by multiple depth dependent transitions of carbonate dissolution up to 96 of the total flux associated with rapid depletions in bulk carbonate carbon up to 1 1 5 and oxygen up to 0 7 1 5 isotope values h2 shows a 0 7 negative carbon isotope excursion with a coeval decrease in 18o of 0 5 and 80 of carbonate dissolution during etm2 the lysocline recovered within 30 ka we attribute this rapid recovery to terrestrial caco3 neutralization through enhanced chemical weathering of carbonates in soils and rocks according to theory carbonate dissolution was lower after recovery than prior to etm2 indicating carbonate ion oversaturation and a deeper position of the lysocline spectral analysis indicates that the changes in carbonate dissolution and 13c values were precession paced implying that weathering feedbacks and short term perturbations in the carbon cycle were important in determining early eocene background and hyperthermal ocean co32 conditions

hidden sinkholes and karst cavities in the travertine plateau of a highly populated geothermal seismic territory tivoli central italy abstract sinkholes and other karst structures in settled carbonate lands can be a significant source of hazard for humans and human works acque albule the study area of this work is a plio pleistocene basin near rome central italy superficially filled by a large and thick deposit of late pleistocene thermogene travertine human activities blanket large portions of the flat territory covering most evidence from geological surface processes and potentially inducing scientists and public officials to underestimate some natural hazards including those connected with sinkholes to contribute to the proper assessment of these hazards a geomorphologic study of the basin was performed using digital elevation models dems recent aerial photographs and field surveys historical material such as old aerial photographs and past geomorphologic studies both pre dating the most part of quarrying and village building was also used together with memories of the elderly population this preliminary study pointed out the presence of numerous potentially active sinkholes that are at present largely masked by either quarrying or overbuilding where this first study pointed out the apparent absence of sinkholes in areas characterized by high density of buildings a detailed subsurface study was performed using properly calibrated electrical resistivity tomography ert and dynamic penetration measurements dpsh together with some borehole logs made available from the local municipality this second study highlighted the presence of sinkholes and caves that are this time substantially hidden to the resolution of standard methods and materials such as aerial photographs dems and field surveys active sinkhole subsidence in the acque albule basin may explain at least in part the frequent damages that affect numerous buildings in the area the main conclusion from this study is that the mitigation of sinkhole hazard in highly populated areas has to pass through a thorough search of hidden sinkholes that can be masked by the anthropocenic molding and blanketing of the territory for these purposes data from historical pre anthropocene documents as well as where possible subsurface investigations are fundamental

coupled greenhouse warming and deep sea acidification in the middle eocene 1 the middle eocene climatic optimum meco is an enigmatic warming event that represents an abrupt reversal in long term cooling through the eocene in order to further assess the timing and nature of this event we have assembled stable isotope and calcium carbonate concentration records from multiple deep sea drilling project and ocean drilling program sites for the time interval between 43 and 38 ma revised stratigraphy at several sites and compilation of 18o records place peak warming during the meco event at 40 0 ma chron c18n 2n the identification of the 18o excursion at sites in different geographic regions indicates that the climatic effects of this event were globally extensive the total duration of the meco event is estimated at 500 ka with peak warming lasting 100 ka assuming minimal glaciation in the late middle eocene 4 6 c total warming of both surface and deep waters is estimated during the meco at the study sites the interval of peak warming at 40 0 ma also coincided with a worldwide decline in carbonate accumulation at sites below 3000 m depth reflecting a temporary shoaling of the calcite compensation depth the synchroneity of deep water acidification and globally extensive warming makes a persuasive argument that the meco event was linked to a transient increase in atmospheric pco2 the results of this study confirm previous reports of significant climatic instability during the middle eocene furthermore the direct link between warming and changes in the carbonate chemistry of the deep ocean provides strong evidence that changes in greenhouse gas concentrations exerted a primary control on short term climate variability during this critical period of eocene climate evolution

seasonal and long term vertical deformation in the nepal himalaya constrained by gps and grace measurements 1 we analyze continuous gps measurements in nepal southern side of the himalaya and compare gps results with grace observations in this area we find both gps and grace show significant seasonal variations further comparison indicates that the observed seasonal gps height variation and grace derived seasonal vertical displacement due to the changing hydrologic load exhibit very consistent results for both amplitude and phase for continuous gps stations whose observation time span are longer than 3 years the average wrms reduction is 45 when we subtract grace derived vertical displacements from gps observed time series the comparison for annual amplitudes between gps observed and grace derived seasonal displacements also shows consistent correlation the good seasonal correlation between gps and grace is due to the improved gps processing strategies and also because of the strong seasonal hydrological variations in nepal besides the seasonal signal grace also indicates a long term mass loss in the himalaya region assuming no gia effect this mass loss therefore will lead to crustal uplift since the earth behaves as an elastic body we model this effect and remove it from gps observed vertical rates with a 2d dislocation model most gps vertical rates especially in the central part of nepal can be interpreted by interseismic strain from the main himalayan thrust and several exceptions may indicate the complexity of vertical motion in this region and some potential local effects

palaeo altimetry of the late eocene to miocene lunpola basin central tibet the elevation history of the tibetan plateau provides direct insight into the tectonic processes associated with continent continent collisions here we present oxygen isotope based estimates of the palaeo altimetry of late eocene and younger deposits of the lunpola basin in the centre of the plateau which indicate that the surface of tibet has been at an elevation of more than 4 kilometres for at least the past 35 million years we conclude that crustal but not mantle thickening models combined with plate kinematic solutions of india asia convergence are compatible with palaeo elevation estimates across the tibetan plateau

varied thermo rheological structure mechanical anisotropy and lithospheric deformation of the southeastern tibetan plateau abstract to investigate the lithospheric structure and deformation of the tibetan plateau we present thermo rheological models for two transects across the southeastern tibetan plateau se tibet showing strong lateral heterogeneity the geodynamic implications are also investigated in relation to gps motions seismic anisotropy seismicity distribution and crustal isostatic state the unmatched pattern between pms and sks splittings which even intersect at right angles to the south of 26 n suggests the crust mantle decoupling constrained by a brittle load bearing layer at the uppermost mantle beneath the indochina block the decoupling may occur below the uppermost mantle the strong crust beneath the south china plate and indochina block implied by the seismicity distribution has two thick brittle load bearing layers indicating a coupled system the crust beneath the emeishan large igneous province elip also has two brittle load bearing layers but the brittle deformation is restricted to the topmost 10 km of the upper and lower crust only one brittle load bearing layer resides in the upper crust in the other part of the chuandian block combining with gps and pms splitting we can infer that the weak crust with seismicity restricted into the depth of

southern california permanent gps geodetic array error analysis of daily position estimates and site velocities we analyze time series of daily positions estimated from data collected by 10 continuously monitoring global positioning system gps sites in southern california during the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes each time series exhibits a linear tectonic signal and significant colored noise spectral power at frequencies in the range 5 yr 1 to 0 5 d 1 is dominated by white noise or possibly fractal white noise and is several orders of magnitude higher than what would be expected from random walk noise in this short period range attributed by others to geodetic monument motions estimating a single slope for the time series power spectra suggests fractal white noise processes with spectral indices of about 0 4 site velocity uncertainties assuming this fractal white noise model are 2 4 times larger than uncertainties obtained assuming a purely white noise model a combination white noise plus flicker noise spectral index of 1 model also fits the data and suggests that the velocity uncertainties should be 3 6 times larger than for the white noise model we cannot adequately distinguish between these two noise models nor can we rule out the possibility of a random walk signal at the lowest frequencies these questions await the analysis of longer time series in any case reducing the magnitude of low frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments otherwise rate uncertainties estimated from continuous gps measurements may not be improved significantly compared to those estimated from infrequent campaign mode measurements

instantaneous global plate motion model from 12 years of continuous gps observations 1 we estimate a global plate motion model for 17 major and minor tectonic plates solely on the basis of analysis of data from 106 globally distributed continuous gps stations spanning the period from january 1991 to july 2003 site positions estimated from 24 hour segments of data are aligned day by day to the international gps service igs realization of the itrf2000 reference frame using a similarity transformation thereby ensuring that the itrf2000 no net rotation condition is preserved linear velocities of a carefully selected set of stations are estimated from the position time series along with annual and semiannual fluctuations and position offsets due to gps instrument changes a white noise plus flicker noise model is applied to estimate realistic uncertainties for the site velocities which are then propagated into the derived plate motion model parameters we also examine the vertical velocities in the site selection process at the scripps orbit and permanent array center we have implemented a procedure whereby the plate motion model is updated on a regular monthly basis to improve its precision and reliability as new data become available and as a baseline against which anomalous motions can be detected

crustal volume balance during the india eurasia collision and altitude of the tibetan plateau a working hypothesis a working hypothesis is developed for the two stages of evolution of the tibetan plateau during the continental collision between india and eurasia the first phase was dominated by crustal shortening and thickening in what is now tibet while indochina was expelled southeastward away from eurasia at the end of this phase at 17 ma the estimated tibetan crustal thickness was 51 km the second phase has been dominated by thickening of tibet by the influx of crustal material from india with no associated crustal shortening the crustal thickening that is inferred to have occurred by this process is only feasible because leakage of crust from beneath the plateau is restricted by neighboring archean cratons that block lower crustal flow this leakage to the east and south from tibet to beneath yunnan is estimated as 20 30 of the influx at present but was much smaller at the start of this second phase of deformation it is suggested that at 11 ma the force exerted against the tibetan upper crust by this flowing material first exceeded the threshold that this brittle layer could resist and tibet began to extend eastward any satisfactory working hypothesis for the tibetan plateau must explain its dimensions its 17 ma ending of shortening and 11 ma start of extension and volcanism the eastward slip sense on its active normal and strike slip faults and the ratios of their displacements to present day slip rates which imply that their slip rates have gradually increased this working hypothesis accounts for these features and predicts a smooth and continuing increase in altitude

gravity increase before the 2015 mw 7 8 nepal earthquake the 25 april 2015 nepal earthquake mw 7 8 ruptured a segment of the himalayan front fault zone four absolute gravimetric stations in southern tibet surveyed from 2010 2011 to 2013 and corrected for secular variations recorded up to 22 40 1 11 gal yr of gravity increase during this period the gravity increase is distinct from the long wavelength secular trends of gravity decrease over the tibetan plateau and may be related to interseismic mass change around the locked plate interface under the himalayan tibetan plateau we modeled the source region as a disk of 580 km in diameter which is consistent with the notion that much of the southern tibetan crust is involved in storing strain energy that drives the himalayan earthquakes if validated in other regions high precision ground measurements of absolute gravity may provide a useful method for monitoring mass changes in the source regions of potential large earthquakes