the annual cycle in equatorial convection and sea surface temperature abstract the coupled atmosphere ocean system in the equatorial eastern pacific and atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes the contrasts are so strong that they dominate the annual march of zonally averaged outgoing longwave radiation for the equatorial belt the march equinox corresponds to the warm season when the equatorial cold tongues in the eastern pacific and atlantic are absent with the onset of summer monsoon convection over colombia central america and west africa in may june northward surface winds strengthen over the eastern pacific and atlantic the equatorial cold tongues reappear and the marine convection shifts from the equatorial belt to the intertropical convergence zones itczs along 8 n as the northern summer program the itczs remain strong and shift northward to new 10 n while sea surface temperature sst continues to drop over the cold tongues and the southern tropics perhaps in response to the

megaflora and palaeoclimate of a late oligocene tropical delta makum coalfield assam evidence for the early development of the south asia monsoon abstract the fossil megaflora from the late oligocene deltaic sediments exposed in the tirap coal mine assam india 27 17 20 n 95 46 15 e laid down at a palaeolatitude of 10 15 n records the composition and climate of tropical vegetation during the last episode of pronounced global warmth before the progressive overall cooling to present day conditions using a new calibration of the climate leaf analysis multivariate program clamp that includes 18 sites from modern vegetation in india the analysis of 80 fossil leaf morphotypes from the tirap mine indicates a mean annual temperature mat of 26 1 2 7 c a warm month mean temperature wmmt of 27 9 3 3 c and a cmmt of 20 1 4 3 c with adjustments for evapotranspirational cooling and underestimation of the wmmt at high temperatures these can be revised upwards to a minimum mat of 28 3 3 7 c a cmmt of 23 5 5 c and a wmmt of 33 6 5 2 c maximum estimates based on evaporative cooling seen in a modern analogue of the tirap environment yield an mat of 32 9 3 8 c a cmmt of 26 8 6 c and a wmmt of 39 7 1 c all uncertainties are 2 sigma precipitation estimates reveal a marked annual variation in rainfall showing a wet season with 20 times the rainfall of the dry season this is a similar regime to that seen in the sunderbans in the modern ganges brahmaputra meghna delta we interpret this to suggest that the south asian monsoon was already established by late oligocene times at an intensity similar to that of today

the influence of sea surface temperature on surface wind in the eastern equatorial pacific weekly to monthly variability abstract temporal correlations between near equatorial surface wind and sea surface temperatures sst at 11 w in the eastern pacific ocean are investigated using data from an array of moored sensors between 5 n and 5 s the signature of tropical instability waves with periods of 20 30 days is apparent in time series of sst and both the meridional and zonal wind components results indicate the existence of a band of pronounced horizontal divergence in the surface wind field associated with the large meridional sst gradient equatorial front normally located just north of the equator perturbations of the equatorial front by the instability waves induce fluctuations in the overlying winds evidence of the air sea coupling is stronger in time series of the meridional gradients of wind and sst than between time series of the variables themselves the meridional differencing serves as a high pass filter in the space domain which removes planetary scale wind fluctuations that are unrelated to the local sst

palynostratigraphy and palynofacies of the early eocene gurha lignite mine rajasthan india abstract a 105 m early eocene section exposed in the gurha mine in the nagaur ganganagar basin rajasthan india archiving remains of equatorial vegetation at a time of extreme global warmth and close to the onset of the india eurasia collision is investigated using palynostratigraphic and palynofacies analyses four palynozones e g palmidites plicatus singh botryococcus braunii kutzing triangulorites bellus kar and ovoidites ligneolus are identified stratigraphically on the basis of abundance of these pollen taxa over others the occurrence of taxonomically highly diverse angiosperm pollen in all the four palynozones attests to an extremely rich near coastal tropical flora subject to frequent wildfires under a strongly seasonal precipitation regime palynotaxa characteristic of these palynozones are widely distributed in other early paleogene sediments of india sedimentary organic matter structured terrestrial biodegraded amorphous grey amorphous resins charcoal black brown debris and algal remains recovered from mire and lacustrine sediments are of terrestrial origin recording fluctuations in burial anoxia and salinity episodes of elevated salinity are due either to seepage of marine waters and or a periodic excess of evaporation over precipitation at times when the depositional system was closed

satellite measurements reveal persistent small scale features in ocean winds four year averages of 25 kilometer resolution measurements of near surface wind speed and direction over the global ocean from the quikscat satellite radar scatterometer reveal the existence of surprisingly persistent small scale features in the dynamically and thermodynamically important curl and divergence of the wind stress air sea interaction over sea surface temperature fronts throughout the world ocean is evident in both the curl and divergence fields as are the influences of islands and coastal mountains ocean currents such as the gulf stream generate distinctive patterns in the curl field these previously unresolved features have important implications for oceanographic and air sea interaction research

consolidation of soil using vertical drains the use of vertical drains is examined critically in view of the fact that in half a century of use there have been a large number of occasions when vertical drains have failed to promote a more rapid consolidation of the soil under load the mode of operation of the drain is discussed and it is shown that an understanding of this has affected the design of the more recent band shaped drains the effects of smear and drain resistance are also discussed reference is made to a three dimensional finite difference computer program modelling the flow of excess pore water in the drain and the surrounding soil which is used to aid in the drain design specific cases which can also be analysed by published techniques have been used to check the validity of the model consideration is also given to the methods of site investigation which should be employed to obtain the appropriate soil parameters for design cases are cited where a lack of data on the soil parameters has restricted the design of the vertical dr

the onset of india asia continental collision early steep subduction required by the timing of uhp metamorphism in the western himalaya ultrahigh pressure uhp rocks in the nw himalaya are some of the youngest on earth and allow testing of critical questions of uhp formation and exhumation and the timing of the india asia collision initial collision of india with asia is widely cited as being at 55f1 ma based on a paleomagnetically determined slowdown of india s plate velocity and as being at ca 51 ma based on the termination of marine carbonate deposition even relatively small changes in this collision age force large changes in tectonic reconstructions because of the rapid india asia convergence rate of 134 mm a at the time of collision new u pb shrimp dating of zircon shows that indian rocks of the tso morari complex reached uhp depths at 53 3f0 7 ma given the high rate of indian subduction this dating implies that indian continental crust arrived at the asian trench no later than 57f1 ma providing a metamorphic age for comparison with previous paleomagnetic and stratigraphic estimates india s collision with asia may be compared to modern processes in the timor region in which initiation of collision precedes both the slowing of the convergence rate and the termination of marine carbonate deposition the indian uhp rocks must have traveled rapidly along a short hence steep path into the mantle early continental subduction was at a steep angle probably vertical comparable to modern continental subduction in the hindu kush despite evidence for modern day low angle subduction of india beneath tibet oceanic slab break off likely coincided with exhumation of uhp terranes in the western himalaya and led to the initiation of low angle subduction and leucogranite generation d 2005 elsevier b v all rights reserved

coupled ocean atmospheric waves on the equatorial front striking 20 30 day sea surface temperature waves observed along the equatorial front in the later half of the year are generally believed to be of an oceanic origin here we report the detection of atmospheric waves that are unambiguously tied to these oceanic waves using new satellite measurements of surface winds a general circulation model simulation reveals that these atmospheric waves have a shallow vertical structure trapped in the planetary boundary layer pbl unlike el nino southern oscillation where changes in deep convection are the cause of anomalous winds vertical wave motion penetrates well above the pbl and is likely to impact the distribution and transport of climatically important gas species such as ozone and dimethyl sulfide

multiproxy paleoaltimetry of the late oligocene pliocene oiyug basin southern tibet the stable isotope compositions of carbonate and organic samples from the oiyug basin in southern tibet allows for model calculations of the oligocene to pliocene paleoelevation of the south central tibetan plateau we measured the oxygen isotope composition of pedogenic and lacustrine calcite dolomite and siderite and the hydrogen isotope composition of n alkanes from plant waxes to reconstruct the 18o and d values of oiyug basin paleometeoric water calculated water isotope values from oiyug basin carbonate and organic samples respectively are in close agreement suggesting the preservation of an unaltered paleometeoric water isotopic signal in these archives late oligocene middle miocene paleoelevation estimates from groundwater pedogenic calcite and lacustrine dolomite indicate basin elevations of 4 1 km 1 2 1 6 km plant wax n alkanes d and lacustrine siderite 18o compositions of middle miocene 15 ma samples indicate paleoelevations of 5 1 km 1 3 1 9 km this estimated elevation is similar to the 5 4 km paleoelevation estimate based on fossil floral physiognomy from the same stratigraphic interval calculated late miocene pliocene paleoelevation estimates derived from the 18o composition of lacustrine marls and carbonate siderite concretions as well as the d from plant wax n alkanes indicate a mean elevation of 5 5 km 1 4 2 0 km at 5 ma although calculated mean paleoelevations for the oiyug basin all fall within the errors associated with the model calculations the close agreement of the different paleoelevation proxies provides an additional degree of confidence in the fidelity of the calculated paleoelevations calculated paleoelevations indicate a possible increase in oiyug basin elevations of 1 4 km between the early and late miocene given the modern oiyug basin elevation of 4 3 km study results allow for a possible 1 km decrease in elevation since the early pliocene these findings in conjunction with other tibetan paleoaltimetry studies are consistent with tectonic models supporting high elevations of the tibetan plateau since the initiation of india asia collision during the eocene and subsequent late cenozoic extensional collapse

stable isotopes reveal southward growth of the himalayan tibetan plateau since the paleocene abstract original stable isotope compositions of carbonates representing conditions in the latest oligocene early miocene kailas and qiabulin areas both in southern tibet record oligocene miocene paleoelevations of the gangdese arc and the himalayan orogen and provide constraints on the formation of the himalayan tibetan plateau oxygen isotope compositions of bivalve shell paleosol and lacustrine carbonates indicate the preservation of unaltered isotopic signals of paleometeoric waters in the kailas and qiabulin areas whereas the oxygen isotopic compositions of liuqu eocene paleosols were likely altered by paleometeoric waters paleoelevation estimates using oxygen isotopes indicate the kailas area was at 4 9 km during 20 19 ma and the qiabulin basin was at 2 0 km during 24 21 ma but rose rapidly to 4 1 km between 21 and 19 ma these results suggest a steep south facing flank on the proto tibetan highland prior to the onset of the india asia collision the himalayan orogen began to be built against the pre existed high 4 5 km gangdese mountains in the early eocene and obtained elevations close to those of the present by the early miocene we propose that the southernmost tibetan plateau and himalayan orogen are the expression of an early eocene to early miocene southward migration of the locus of deformation early stage uplift is linked to the crustal thickening in the early eocene but the dramatic elevation gain in the early miocene may have been caused by indian slab rollback break off and coeval renewed underthrusting behind which late miocene to present east west crustal extension took place

eocene continental climates and latitudinal temperature gradients global climate during the mesozoic and early cenozoic is thought to have been warmer than at present but there is debate about winter temperatures paleontological data indicate mild temperatures even at high latitudes and in mid latitude continental interiors whereas computer simulations of continental paleoclimates produce winter temperatures closer to modern levels foliar physiognomy and floristic composition of 23 eocene floras from the interior of north america and australia indicate cold month means generally 2 c even where the mean annual temperature mat was

cool equatorial terrestrial temperatures and the south asian monsoon in the early eocene evidence from the gurha mine rajasthan india abstract early eocene 55 52 ma laminated lacustrine sediments overlying lignites in the gurha mine 27 87398 n 72 86709 e rajasthan india yield a diversity of fossil leaves flowers fruits seeds and insects clamp multivariate foliar physiognomic analysis of two horizons separated by an estimated several tens of thousands of years of deposition indicates cool equatorial 10 n temperatures and a pronounced monsoon signature a lower assemblage consisting of 54 leaf morphotypes and an upper assemblage of 57 leaf forms yielded mean annual temperatures mat of 24 7 and 23 9 c respectively the uncertainty 2 82 c means these temperature regimes are identical despite few similarities in the morphotypes between the two assemblages the mean annual range of temperature mart was approximately 9 7 c for both assemblages when corrected for evapotranspirational cooling these temperature regimes are similar to those experienced today at 10 n on the west coast of india and surprisingly cool for the tropics at a time of extreme global warmth growth was year round the tropical to paratropical fossil floras also suggest a moist regime 80 annual relative humidity and high mean annual precipitation of 1800 mm for both assemblages but with a pronounced wet dry seasonality indicative of a pronounced monsoonal regime the lower assemblage has a stronger monsoon index 11 8 than the upper assemblage 8 8 the two assemblages seem to have been deposited less than 100 ka apart this suggests that not only a pronounced south asian monsoon existed when india and asia first made contact but also a variation in monsoon strength existed that cannot be ascribed to tectonic drivers

provenance analysis of upper cretaceous strata in the tethys himalaya southern tibet implications for timing of india asia collision abstract the provenance of upper cretaceous strata in the tethys himalaya provides critical constraints on the closure time of the neo tethys ocean and the initial india asia collision this paper reports detailed petrographic studies in situ detrital zircon u pb ages and lu hf isotopic analyses whole rock nd isotopes and cr spinel electronic microprobe data from upper cretaceous clastic sedimentary rocks of the tethys himalaya near gyangze southern tibet the berriasian coniacian jiabula formation consists of black mudstone chert and minor quartz arenite and is dominated by detrital zircons with archean cambrian u pb ages which were most likely derived from the indian continent overlying conformably is the santonian maastrichtian chuangde formation which consists of red shale limestone and chert the chuangde formation is in turn overlain by the late maastrichtian late paleocene zongzhuo formation which is composed of black mudstone and lithic sandstone enclosing various olistoliths of sandstone limestone and chert the rilang conglomerate is a lens which is located within the upper part of the zongzhuo formation and consists of an upward thinning and fining succession of volcanic conglomerate sandstone and black mudstone the zongzhuo formation and the rilang conglomerate record an abrupt influx of cretaceous zircon grains with juvenile hf isotopic compositions arc related cr spinels and positive end 0 sediments suggesting an arc and suture zone provenance the change in provenance of upper cretaceous strata from the southern indian continent to a northern arc and suture zone is attributed to either 1 initial collision between the indian plate and lhasa terrane or 2 initial collision between the indian plate and an intra oceanic arc we prefer option 1 that the initiation of india asia collision occurred during maastrichtian 70 65 ma

refining clamp investigations towards improving the climate leaf analysis multivariate program clamp climate leaf analysis multivariate program has been used for the past 17 years to estimate palaeoclimatic conditions the reliability and applicability of this method based on leaf physiognomic characters of fossil woody dicots has been widely discussed over the same period the present study focuses on some technical aspects of clamp mainly on its robustness in the context of the theoretical unimodal requirements of canonical correspondence analysis and introduces correction coefficients for these aspects of the statistical approach as a new way of interpreting and improving on clamp estimates this tool was tested on datasets derived from 17 european fossil floras ranging in age from the late oligocene to the pliocene additionally an objective statistical method for the selection of the best suited modern vegetation dataset from 144 site physg3br or 173 physg3ar extant biotopes is proposed

air sea fluxes and surface layer turbulence around a sea surface temperature front the observed effects of sharp changes in sea surface temperature sst on the air sea fluxes surface roughness and the turbulence structure in the surface layer and the marine atmospheric boundary layer are discussed in situ flux and turbulence observations were carried out from three aircraft and two ships within the fasinex framework three other aircraft used remote sensors to measure waves microwave backscatter and lidar signatures of cloud tops descriptions of the techniques intercomparison of aircraft and ship flux data and use of different methods for analyzing the fluxes from the aircraft data are described changing synoptic weather on three successive days yielded cases of wind direction both approximately parallel and perpendicular to a surface temperature front for the wind perpendicular to the front wind over both cold to warm and warm to cold surface temperatures occurred model results consistent with the observations suggest that an internal boundary layer forms at the sst

paleocene eocene record of ophiolite obduction and initial india asia collision south central tibet 1 uppermost cretaceous to eocene marine sedimentary sequences occur both to the south and north of the yarlung zangbo suture in south central tibet they consist of indian margin strata of the northern tethyan himalaya and asian margin strata of the gangdese forearc both assemblages are characterized by major changes in depositional environment and sedimentary provenance at 65 ma and an appearance of detrital chromium rich spinel of ophiolite affinity tio2 generally 0 1 wt during the paleocene ophiolitic melange exposed along the suture could have provided a source for detrital spinel the melange occurs in the hanging wall of a north dipping south directed mylonitic shear zone which includes a tectonic sliver of mafic schist amphibole from the schist yields 40ar 39ar ages of 63 ma which we attribute to cooling during slip along the shear zone and southward obduction of the melange melange obduction was coeval with the development of an angular unconformity within the gangdese forearc basin to the north between late maastrichtian time and 62 ma upper paleocene to middle eocene sandstones in the northern tethyan himalaya yield 200 120 ma u pb detrital zircon ages and 190 170 ma 40ar 39ar detrital mica ages these detrital grains were most likely sourced from regions north of the yarlung zangbo suture suggesting that onset of india asia collision in south central tibet is middle eocene or older in age collectively our results support previous suggestions that oceanic rocks were obducted onto the northern margin of india during latest cretaceous earliest tertiary time coeval changes in gangdese forearc sedimentation raise the possibility that this obduction event marks onset of tectonic interaction between india and asia at 65 ma alternatively in concert with the conventional view of eocene collision initiation the obducted oceanic rocks may be of intraoceanic origin while coeval changes in gangdese forearc sedimentation may be a consequence of an increase in the rate of ocean continent convergence following the demise of the intraoceanic subduction zone

east central asian climate evolved with the northward migration of the high proto tibetan plateau the evolution of cenozoic climate patterns in asia has been linked to uplift of the tibetan plateau tp retreat of the paratethys sea and global cooling however less attention has been placed on the latitudinal change of the tp here we report new climate modeling to explore how modern climate changes as a function of topographic growth and spatial migration of the tp our results show that the northward displacement of the uplifted proto tp within the subtropics can significantly affect the wind and precipitation pattern over east central asia by compiling proxy based climatic records paleolatitudinal and paleoelevational evolution models of the proto tp and in comparison with previous modeling under a global paleogeography we suggest that the northward migration of the proto tp in the paleogene could have intensified the aridity in central asia but its influence on east asian precipitation and monsoonal circulation could be dependent on the paleogeography and other boundary conditions plain language summary the evolution of the asian monsoons and aridification of asia s interior are thought to be driven by tibetan himalayan uplift recent geological observations suggest that the uplifted proto tibetan plateau proto tp migrated northward in the subtropics since the early eocene and reached its present position by the latest oligocene we therefore simulated the effects of this process on east central asian climate our climate modeling shows the northward migration of the high proto tp from 21 29 degrees n to 29 37 degrees n can significantly change the present day wind and precipitation patterns over east central asia especially central asia become drier because of the displacement of the anomalous dry belt caused by large scale atmospheric subsidence we further suggest that forcing by the paleolatitudinal migration of the high proto tp within the subtropics from the eocene to the earliest miocene could have drove the central asian paleoclimate to dryer conditions but migration might not be the sole parameter that governed the east asian monsoon during the paleogene

dating the indian continental subduction and collisional thickening in the northwest himalaya multichronology of the tso morari eclogites multichronometric studies of the low temperature eclogitic tso morari unit ladakh india place timing constraints on the early evolution of the northwest himalayan belt several isotopic systems have been used to date the eclogitization and the exhumation of the tso morari unit lu hf sm nd rb sr and ar ar a ca 55 ma age for the eclogitization has been obtained by lu hf on garnet omphacite and whole rock from mafic eclogite and by sm nd on garnet glaucophane and whole rock from high pressure metapelites these results agree with a previously reported u pb age on allanite and together these ages constrain the subduction of the indian continental margin at the paleocene eocene boundary during exhumation the tso morari rocks underwent thermal relaxation at about 9 3 kbar characterized by partial recrystallization under amphibolite facies conditions ca 47 ma as dated by sm nd on garnet calcic amphibole and whole rock from metabasalt rb sr on phengite apatite and whole rock and ar ar on medium si phengite from metapelites ar ar analyses of biotite and low si muscovite from metapelites which recrystallized at 5 kbar toward the end of the exhumation show that the tso morari unit was at upper crustal levels ca 30 ma these results indicate variable exhumation rates for the tso morari unit beginning with rapid exhumation while the indian margin subduction was still active and later proceeding at a slower pace during the crustal thickening associated with the himalayan collision

oceanic and atmospheric anomalies of tropical instability waves tropical instability waves tiws are detected in remotely sensed sea surface height ssh temperature sst and wind records of the eastern equatorial pacific analyses of tiw anomaly relationships reveal strong dynamical influence of tiws within approximately 5 of the equator the first influence is advective heat flux the primary forcing of tiw sst anomalies is advection of the meridional temperature gradient by tiw currents the second influence is modification of the wind stress and ekman pumping fields by tiw surface ocean currents by affecting surface stress and hence roughness tiw currents in this low wind region introduce a significant bias in scatterometer vector wind measurement this bias is evident in both nscat and quikscat winds the difference between wind measurements from tao moorings and scatterometers is phase locked with tiw sst oscillations these results have important implications for scatterometry and for understanding tropical dynamics thermodynamics and biogeochemistry

observations of coupling between surface wind stress and sea surface temperature in the eastern tropical pacific satellite measurements of surface wind stress from the quikscat scatterometer and sea surface temperature sst from the tropical rainfall measuring mission microwave imager are analyzed for the three month period 21 july 20 october 1999 to investigate ocean atmosphere coupling in the eastern tropical pacific oceanic tropical instability waves tiws with periods of 20 40 days and wavelengths of 1000 2000 km perturb the sst fronts that bracket both sides of the equatorial cold tongue which is centered near 1 8s to the east of 1308w these perturbations are characterized by cusp shaped features that propagate systematically westward on both sides of the equator the space time structures of these sst perturbations are reproduced with remarkable detail in the surface wind stress field the wind stress divergence is shown to be linearly related to the downwind component of the sst gradient with a response on the south side of the cold tongue that is about twice that on the north side the wind stress curl is linearly related to the crosswind component of the sst gradient with a response that is approximately half that of the wind stress divergence response to the downwind sst gradient the perturbed sst and wind stress fields propagate synchronously westward with the tiws this close coupling between sst and wind stress supports the wallace et al hypothesis that surface winds vary in response to sst modification of atmospheric boundary layer stability

the pangaea megamonsoon records evidence from the triassic mungaroo formation northwest shelf of australia abstract an integrated analysis in this study of paleogeographic paleontologic seismic and sedimentologic data has been used to explain the effect of the pangaean megamonsoon on the whole triassic especially the middle late triassic mungaroo formation in the north carnarvon basin northwest shelf of australia our results show that the three triassic formations from bottom to top locker shale mungaroo formation and brigadier formation comprise a complete depositional cycle and correspond to an undeveloped strong and weak monsoon periods respectively during the strong monsoon period of the mungaroo formation the palynological evidences exhibited mixture spore pollen characteristics of the hygrophytic assemblage spore pollen from the pteridophyte spores seed ferns and cycads pollen in humid environment of lowlands and coastal plain and the xerophytic assemblage pollen from the drought tolerant plants of the interior mountainous areas the sedimentary evidences of the mungaroo formation show low angle shingled progradational seismic reflection configuration the highly seasonal variations in precipitation during deposition of the mungaroo formation exhibited typical sandwiched depositional characteristics of coarse channels sandstone fining upward fluvial aggradational cycles facs with poor to moderately sorting and angular to subangular roundness organic mudstone and coal seam interbedded finally in contrast to today s typical examples of poyang lake delta a shallow water braided delta conceptual depositional model of the mungaroo formation is formed with a large proximal and distal delta plain and small delta front the model results serve mainly to indicate the importance of various climate forming factors climate topography eustatic whereas tectonic activity unlikely played any significant role in this process

quasi lagrangian large eddy simulations of cross equatorial flow in the east pacific atmospheric boundary layer using a large eddy simulation les the atmospheric boundary layer abl is numerically modeled along 958w from 88 st o 48n during boreal autumn and compared to observations from the east pacific investigation of climate processes in the coupled ocean atmosphere system epic 2001 since the local abl winds are predominantly southerly in this season a quasi lagrangian forcing is used in which the abl air column is forced as if it were advecting northward with the mean september october 2001 meridional wind across the equatorial cold tongue and the rapidly warming ssts to the north pressure gradients and large scale zonal advective tendencies are prescribed as a function of latitude where possible observations from the epic 2001 experiment are used for forcing and for comparison with model results the abl s modeled vertical structure accords with the conceptual model of wallace et al and agrees well with observations surface stability accounts for the minimum in surface wind over the equatorial cold tongue and the maximum over the warm water to the north stability of the lower abl over the cold tongue allows a jet to accelerate at about 500 m height relatively uncoupled to the frictional surface layer vertical mixing over the warm water to the north distributes this momentum to the surface additional simulations were performed to explore the modeled abl s sensitivity to pressure gradients zonal advection free tropospheric humidity and initial conditions the model abl was robust changing the forcings resulted in little change in the modeled structure the strongest sensitivity was of stratocumulus clouds over the cold tongue to cloud top radiative cooling once formed at the southern edge of the cold tongue modeled stratocumulus clouds demonstrate a remarkable ability to maintain themselves over the cold tongue in the absence of surface fluxes by radiative cooling at their tops the persistence of thin stratocumulus clouds in this lagrangian model suggests that horizontal advection of condensate might be an important process in determining cloudiness over the cold tongue

asian summer monsoon changes the pollen flow on the tibetan plateau abstract abundant evidence has revealed that the tibetan plateau s uplift influenced the evolution of the asian summer monsoon system pollen as fine powdery substance which can be easily transmitted by wind currents has great potential to be used as an indicator of the monsoon s intensity and flow direction and used for the detection and evaluation of the ancient monsoon on the tibetan plateau hence it is extremely important and necessary to achieve a better understanding of the modern pollen deposition model on the plateau however most of the previous studies mainly focused on the coupling of surface pollen deposition and regional vegetation and the establishment of the transfer function between pollen vegetation climate on the tibetan plateau but largely neglected the direct correlation of the modern surface pollen deposition and the monsoon s intensity and its current direction we have comprehensively analysed a dataset of the surface pollen on the tibetan plateau and discovered that 1 the surface pollen assemblage can reflect the alpine meadows steppe and desert vegetation which means that surface pollen data can be used to assess the deep time vegetation 2 most of the exotic pollen are from trees the spatial distribution trend of these tree pollen s relative abundance is highly coupled with the path of the asian summer monsoon and the extent to which it encroached on the tibetan plateau these results unambiguously demonstrate that tree pollen deposition on the tibetan plateau is dominated by the asian summer monsoon i e the upslope movement of the modern asian summer monsoon drives the spread of pollen rain from low altitude vegetation to high altitude areas if a similar scenario happened at different stages of the asian summer monsoon evolution and the tibetan plateau uplift the pollen buried in the sediments have the potential to reflect the current direction and intensity of the asian summer monsoon at that time moreover it would provide a simple and potentially practical proxy for the study of the evolutionary history of the asian summer monsoon e g wind direction and intensity under the influence of the plateau s uplift

why the itcz is mostly north of the equator abstract although the distribution of sunshine is symmetrical about the equator the earth s climate is not climatic asymmetries are prominent in the eastern tropical pacific and atlantic oceans where the regions of maximum sea surface temperature convective cloud cover and rainfall are north of the equator this is the result of two sets of factors interactions between the ocean and atmosphere that are capable of converting symmetry into asymmetry and the geometries of the continents that determine in which longitudes the interactions are effective and in which hemisphere the warmest waters and the intertropical convergence zone are located the ocean atmosphere interactions are most effective where the thermocline is shallow because the winds can readily affect sea surface temperatures in such regions the thermocline happens to shoal in the eastern equatorial pacific and atlantic but not in the eastern indian ocean because easterly trade winds prevail over the tropical atlantic and pacific wher

paleogene monsoons across india and south china drivers of biotic change monsoonal climates at low latitudes 32 n are an inevitable consequence of seasonal migrations of the inter tropical convergence zone itcz but the character of these monsoons depends on continental configuration orographic expression and the strength of hadley circulation to explore the evolution of monsoon systems across southern asia we compare climate signatures archived in ten paleogene floras from northern india tibet and southern china occupying low palaeolatitudes at a time of extreme global warmth and elevated co2 fossil leaf form reveals that under such hothouse conditions megathermal early eocene to earliest miocene forests were exposed to strong monsoonal climates typical of those experienced today arising from annual migrations of the itcz possibly enhanced by a lower equator to pole temperature gradient throughout the paleogene an elevated tibetan highland produced no discernable modification of this itcz monsoon although rainfall seasonality similar to that of the modern south asia monsoon sam is observed in northern india as early as the beginning of the eocene despite its near equatorial palaeoposition in south china rainfall seasonality increased progressively achieving modern monsoon like wet season dry season precipitation ratios by the early oligocene despite evidencing weak rainfall seasonality overall fossil leaves from south china have exhibited monsoon adapted morphologies comparable to those seen in today s indonesia australia monsoon for at least 45 million years together the indian and south china fossil leaf assemblages show that the evolution of megathermal ecosystems across southern asia has been influenced profoundly by monsoonal climates for at least the last 56 million years the paleogene itcz driven monsoon system strongly impacted india as it transited the equator likely eliminating gondwanan taxa not able to adapt to seasonal precipitation extremes furthermore powerful seasonally reversing winds and associated surface ocean currents are likely to have facilitated two way biotic transfer between india and eurasia long before closure of the tethys ocean

central asian moisture modulated by proto paratethys sea incursions since the early eocene abstract the establishment and evolution of the asian monsoons and arid interior have been linked to uplift of the tibetan plateau retreat of the inland proto paratethys sea and global cooling during the cenozoic however the respective role of these driving mechanisms remains poorly constrained this is partly due to a lack of continental records covering the key eocene epoch marked by the onset of tibetan plateau uplift proto paratethys sea incursions and long term global cooling in this study we reconstruct paleoenvironments in the xining basin ne tibet to show a long term drying of the asian continental interior from the early eocene to the oligocene superimposed on this trend are three alternations between arid mudflat and wetter saline lake intervals which are interpreted to reflect atmospheric moisture fluctuations in the basin we date these fluctuations using magnetostratigraphy and the radiometric age of an intercalated tuff layer the first saline lake interval is tentatively constrained to the late paleocene early eocene the other two are firmly dated between 46 ma top magnetochron c21n and 41 ma base c18r and between 40 ma base c18n and 37 ma top c17n remarkably these phases correlate in time with highstands of the proto paratethys sea this strongly suggests that these sea incursions enhanced westerly moisture supply as far inland as the xining basin we conclude that the proto paratethys sea constituted a key driver of asian climate and should be considered in model and proxy interpretations

cool tropics in the middle eocene evidence from the changchang flora hainan island china abstract the middle eocene lutetian bartonian 48 6 37 2 ma near equatorial megafossil flora from swamp and lacustrine facies of the lower changchang formation hainan island south china 19 631463 n 110 445049 e is highly diverse 200 taxa dominated by an unusual mixture of angiosperms typical of modern temperate subtropical and tropical evergreen and deciduous forms it is also rich in palms multivariate analysis of the architecture of minimally transported woody dicot leaves reveals a mean annual air temperature mat of 22 4 7 c with a marked thermal seasonality range of 21 c the year round humid climate lacked any monsoonal signature the overall climate signal is compatible with the growth characteristics exhibited by fossil wood but is warmer than the climate signal derived from pollen and spores using co existence analysis corrections for possible palaeoelevation of the basin bring the megafossil derived mat estimate in line with 54 52 ma sea surface and soil temperatures obtained from the gulf coast usa palaeolatitude 30 n using multiple geochemical proxies and supports the claim that the low latitude eocene climate was not uniformly warm this challenges previous conclusions based on 18 o analysis of unaltered calcareous microfossils our air temperature data also adds to the challenge of understanding heat transport away from the equator to higher latitudes during hothouse climate regimes

numerical assessment of equivalent diameter equations for prefabricated vertical drains the design approaches to prefabricated vertical drains pvds for different geotechnical and geoenvironmental engineering applications involve converting the pvd s rectangular band shape to an equivalent circular shape to simplify the analytical analysis several equivalent diameter equations for pvds are available in the literature however these equations produce different equivalent diameters and no definitive recommendation is available regarding their validity the aim of this study is to assess numerically the validity of these equations and identify the most appropriate one for use in design

the evolution of yarlung tsangpo river constraints from the age and provenance of the gangdese conglomerates southern tibet abstract cenozoic conglomerates are exposed discontinuously along the length of the yarlung tsangpo suture zone on the southern margin of the gangdese arc these conglomerates the gangdese conglomerates herein record a crucial stage in the uplift and erosion histories of the southern tibet after the initial india asia collision in the mt kailas area the gangdese conglomerates strata consist of multiple sedimentary cycles and each cycle is a fining upward sequence that was deposited by alluvial fan braided river and delta systems whereas in the xigaze area the gangdese conglomerates strata comprise a coarsening upward sequence that was deposited by delta braided river and alluvial fan systems based on the detrital and igneous zircon u pb ages the depositional ages of the gangdese conglomerates are late oligocene to early pliocene ca 26 5 ma in the mt kailas area late oligocene to middle miocene ca 26 15 ma in the xigaze area and late oligocene to early miocene ca 26 19 ma in the zedong area paleocurrent measurements and provenance data i e conglomerate clast composition sandstone petrology and detrital zircon age indicate that the initial detritus of the gangdese conglomerates were entirely derived from the north mainly from the gangdese arc sediment resulting from denudation to the south the xigaze forearc basin the yarlung tsangpo suture zone and the northern margin of the indian plate first appeared by the early miocene ca 19 ma and subsequently increased in abundance gradually our new results together with previous data from the xigaze area reveal 3 major stages in the evolution of the yarlung tsangpo river system 1 the southward flowing stage ca 26 19 ma featured southward draining transverse rivers that transported materials from the gangdese arc southward southward paleocurrents in the gangdese conglomerates indicate a northern source 2 the westward flowing stage ca 19 15 ma developed due to the uplift of the suture zone and tethys himalaya to the south northward draining rivers began to develop and lakes resembling a string of beads formed and finally connected together initiating the westward flowing paleo yarlung tsangpo river westward paleoflows were recorded in the gangdese conglomerates 3 the eastward flowing stage ca 15 ma present resulted from differential uplift and denudation of the southern tibet which reversed the direction of the young yarlung tsangpo river by ca 15 ma the deposition of the gangdese conglomerates was controlled by eastward paleoflows at this point the modern eastward flowing yarlung tsangpo river system was established

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

barometric pressure variations associated with eastern pacific tropical instability waves abstract barometric pressure surface temperature and wind time series in the eastern equatorial pacific are analyzed to determine if oceanic tropical instability wave tiw sea surface temperature variations cause barometric pressure gradients large enough to influence the atmospheric boundary layer during the study period from april 2001 to september 2002 11 tiws propagated westward past 110 w causing a spectral peak at 20 30 days in the sea surface temperature sst meridional difference between 2 n 110 w and 0 110 w likewise the meridional pressure difference also had a spectral peak in the 20 30 day tiw band cross spectral analysis shows that within the tiw band sst induced pressure variations were roughly 0 1 hpa c 1 in magnitude the resulting pressure gradient force is comparable in magnitude to other terms in the meridional momentum balance implications about the role of the boundary layer capping in the adjustment to sst forcing are discussed

observations of sst induced perturbations of the wind stress field over the southern ocean on seasonal timescales the surface wind stress response to sea surface temperature sst over the latitude range 308 608 si n the southern ocean is described from the national aeronautics and space administration s quikscat scatterometer observations of wind stress and reynolds analyses of sst during the 2 yr period august 1999 to july 2001 while ocean atmosphere coupling at midlatitudes has previously been documented from several case studies this is the first study to quantify this relation over the entire southern ocean the spatial structures of the surface wind perturbations with wavelengths shorter than 108 latitude by 308 longitude are closely related to persistent spatial variations of the sst field on the same scales the wind stress curl and divergence are shown to be linearly related respectively to the crosswind and downwind components of the sst gradient the curl response has a magnitude only about half that of the divergence response this observed coupling is consistent with the hypothesis that sst modification of marine atmospheric boundary layer mabl stability affects vertical turbulent mixing of momentum inducing perturbations in the surface winds the nonequivalence between the responses of the curl and divergence to the crosswind and downwind sst gradients suggests that secondary circulations in the mabl may also play an important role by producing significant perturbations in the surface wind field near sst fronts that are distinct from the vertical turbulent transfer of momentum the importance of the wind stress curl in driving ekman vertical velocity in the open ocean implies that the coupling between winds and sst may have important feedback effects on upper ocean processes near sst fronts

gondwana to asia plate tectonics paleogeography and the biological connectivity of the indian sub continent from the middle jurassic through latest eocene 166 35 ma abstract using the most up to the date information available we present a considerably revised plate tectonic and paleogeographic model for the indian ocean bordering continents from gondwana s middle jurassic break up through to india s collision with asia in the middle cenozoic the landmass framework is then used to explore the sometimes complex and occasionally counter intuitive patterns that have been observed in the fossil and extant biological records of india madagascar africa and eastern eurasia as well those of the more distal continents although the paleogeographic model confirms the traditional view that india became progressively more isolated from the major landmasses during the cretaceous and paleocene it is likely that at various times minor physiographic features principally ocean islands provided causeways and or stepping stone trails along which land animals could have migrated to from the sub continent aside from a likely link albeit broken by several marine gaps to africa for much of this time it is notable that the present day recent biota of madagascar indicates that the ancestors of five land mammal orders plus bats crossed the 400 km wide mozambique channel at different times in the cenozoic it is possible that the kerguelen plateau connected india and australia antarctica in the mid cretaceous approximately 115 90 ma later the seychelles mascarene plateau and nearby elevated sea floor areas could have allowed faunas to pass between southern india and madagascar in the late cretaceous from around 85 65 ma with an early cenozoic extension to this path forming as a result of the reunion hot spot trace islands growing on the ocean floor to the ssw of india the modelling also suggests that india s northward passage towards asia with eventual collision at 35 ma involved the ne corner of the sub continent making a glancing contact with sumatra followed by burma from 57 ma late paleocene onwards a scenario which is compatible with the fossil record indicating that india asia faunal exchanges began occurring at about this time finally we contend that a number of biologically based direct terrestrial migration routes that have been proposed for last 15 m y of the cretaceous asia to india antarctica to madagascar and or india can probably be dismissed because the marine barriers likely varying from 1000 up to 2500 km were simply too wide

dynamical analyses of marine atmospheric boundary layer structure near the gulf stream oceanic front the effects of the sea surface temperature s s t front at the edge of the gulf stream on the marine atmospheric boundary layer mabl are investigated using a numerical model to study the modification effects of an oceanic front on the mabl structure the situation simulated is flow from over cold shelf water to over the warm water of the gulf stream the initial temperature and humidity profiles of the air are specified to be near neutral over the cold water and are therefore typical of undisturbed conditions the differential in s s t across the oceanic front creates a horizontal variation in the surface perturbation pressure and the stability the surface perturbation pressure and turbulent fluxes modulate the flow and produce horizontal variations in horizontal wind components with associated vertical motions a thermally direct cell is produced as a result of the s s t difference across the front the isotherms slope upward towards the warm water entrainment of inversion layer air and upward vertical motion over the warm water cause the mabl to be deeper there a layer of cloud forms over warm water and is associated with mixed layer deepening rather than lowering of the condensation level turbulent fluxes in the mabl show considerable spatial variation surface stress is much larger over the front and over the warm water than over the cold water this is mostly caused by wind speed changes associated with the front changes in the drag coefficient due to changes in surface roughness and stability are much less important mean budgets for temperature and total water indicate that there is a balance between horizontal advection and turbulent flux divergence the u momentum budget shows that once the geostrophic balance terms are subtracted the balance is mainly between the pressure gradient force associated with the induced temperature field and turbulent friction with horizontal advection and the coriolis force acting on the geostrophic departure playing minor roles the v momentum budget shows a balance between horizontal advection coriolis force and friction although there are few data for comparison the results are in qualitative agreement with observations in the area this study shows that the s s t front at the gulf stream edge produces marked local changes in the nearby atmospheric surface layer

asian eocene monsoons as revealed by leaf architectural signatures abstract the onset and development of the asian monsoon systems is a topic that has attracted considerable research effort but proxy data limitations coupled with a diversity of definitions and metrics characterizing monsoon phenomena have generated much debate failure of geological proxies to yield metrics capable of distinguishing between rainfall seasonality induced by migrations of the inter tropical convergence zone itcz from that attributable to topographically modified seasonal pressure reversals has frustrated attempts to understand mechanisms underpinning monsoon development and dynamics here we circumvent the use of such single climate parameter metrics in favor of detecting directly the distinctive attributes of different monsoon regimes encoded in leaf fossils leaf form adapts to the prevailing climate particularly under the extreme seasonal stresses imposed by monsoons so it is likely that fossil leaves carry a unique signature of past monsoon regimes leaf form trait spectra obtained from fossils from eocene basins in southern china were compared with those seen in modern leaves growing under known climate regimes the fossil leaf trait spectra including those derived from previously published fossil floras from northwestern india were most similar to those found in vegetation exposed to the modern indonesia australia monsoon i am which is largely a product of seasonal migrations of the itcz the presence of this distinctive leaf physiognomic signature suggests that although a monsoon climate existed in eocene time across southern asia the characteristics of the modern topographically enhanced south asia monsoon had yet to develop by the eocene leaves in south asia had become well adapted to an i am type regime across many taxa and points to the existence of a pervasive monsoon climate prior to the eocene no fossil trait spectra typical of exposure to the modern east asia monsoon were seen suggesting the effects of this system in southern china were a much later development

greater india basin hypothesis and a two stage cenozoic collision between india and asia cenozoic convergence between the indian and asian plates pro duced the archetypical continental collision zone comprising the himalaya mountain belt and the tibetan plateau how and where india asia convergence was accommodated after collision at or be fore 52 ma remains a long standing controversy since 52 ma the two plates have converged up to 3 600 35 km yet the upper crustal shortening documented from the geological record of asia and the himalaya is up to approximately 2 350 km less here we show that the discrepancy between the convergence and the shortening can be explained by subduction of highly extended continental and oceanic indian lithosphere within the himalaya be tween approximately 50 and 25 ma paleomagnetic data show that this extended continental and oceanic greater india promontory resulted from 2 675 700 km of north south extension between 120 and 70 ma accommodated between the tibetan himalaya and cratonic india we suggest that the approximately 50 ma india asia collision was a collision of a tibetan himalayan microconti nent with asia followed by subduction of the largely oceanic greater india basin along a subduction zone at the location of the greater himalaya the hard india asia collision with thicker and contiguous indian continental lithosphere occurred around 25 20 ma this hard collision is coincident with far field deforma tion in central asia and rapid exhumation of greater himalaya crys talline rocks and may be linked to intensification of the asian monsoon system this two stage collision between india and asia is also reflected in the deep mantle remnants of subduction imaged with seismic tomography

equal strain consolidation by vertical drains this paper shows the development of a series of closed form solutions of equal strain consolidation in the presence of a vertical drain with smear and well resistance using an approach that considers the effects of both the radial and vertical drainage in a fully coupled fashion solutions are obtained for the excess pore pressure and the degree of consolidation in the compressible soil subjected to a step or ramp loading situation the closed form solutions in the present paper may be evaluated in an electronic spreadsheet on a standard personal computer

india asia collision and the cenozoic slowdown of the indian plate implications for the forces driving plate motions the plate motion of india changed dramatically between 50 and 35 ma with the rate of convergence between india and asia dropping from 15 to 4 cm yr this change is coincident with the onset of the india asia collision and with a rearrangement of plate boundaries in the indian ocean on the basis of a simple model for the forces exerted upon the edges of the plate and the tractions on the base of the plate we perform force balance calculations for the precollision and postcollision configurations we show that the observed euler poles for the indian plate are well explained in terms of their locations and magnitudes if 1 the resistive force induced by mountain building in the himalaya tibet area is 5 6 10 12 n m 2 the net force exerted upon the indian plate by subduction zones is similar in magnitude to the ridge push force 2 5 10 12 n m and 3 basal tractions exert a resisting force that is linearly proportional to the plate velocity in the hot spot reference frame the third point implies an asthenospheric viscosity of 2 5 10 19 pa s assuming a thickness of 100 150 km synthetic euler poles show that crustal thickening in the tibetan plateau was the dominant cause of the cenozoic slowdown of the indian plate

ocean atmosphere in situ observations at the brazil malvinas confluence region 1 this paper presents a description of marine atmospheric boundary layer mabl and oceanic boundary layer obl interactions at the brazil malvinas confluence although this region is known as one of the most energetic zones of the world ocean very few studies have addressed the mechanisms of oa interaction there based upon novel direct in situ simultaneous oa observations our results show that the obl mabl exchanges are closely correlated with the sea surface temperature sst field the heat fluxes range from 110 w m 2 over warm waters down to 18 w m 2 over cold waters higher heat fluxes and air sea temperature differences are associated with stronger near surface winds this suggests that the mabl is modulated at the synoptic temporal and spatial scale by the strong surface thermal gradients between the warm brazil and the cold malvinas falklands currents

tectonic implications of felsic tuffs within the lower miocene gangrinboche conglomerates southern tibet felsic tuffs are interbedded with the gangrinboche conglomerates adjacent to the yarlung tsangpo suture zone in southern tibet laser ar ar dating of mineral separates indicates they are of early miocene age such tuffs are most likely an eruptive manifestation of geochemically indistinguishable coeval felsic adakitic intrusions that are widely reported across southern tibet the considerable lateral e w extent of the gangrinboche conglomerates and their depositional setting indicates sediment accumulation in an overall n s compressional regime and thereby places important constraints on the tectonic setting in which magmatism initiated the conglomerates were folded and truncated during back thrusting associated with development of the north directed great counter thrust as n s trending rifts associated with e w extension of the tibetan plateau cut both the conglomerates and this thrust system it can be inferred that post collisional volcanism is unlikely to have been genetically linked to later e w extension early miocene slab break off beneath tibet provides a model that appears to be consistent with petrogenesis of the associated magmatic suite which requires a lowermost crust or lithospheric mantle generation molasse accumulation and uplift and emplacement of north himalayan gneiss domes

an empirical model for surface wind stress response to sst forcing induced by tropical instability waves tiws in the eastern equatorial pacific abstract high resolution space based observations reveal significant two way air sea interactions associated with tropical instability waves tiws their roles in budgets of heat salt momentum and biogeochemical fields in the tropical oceans have been recently demonstrated however dynamical model based simulations of the atmospheric response to tiw induced sea surface temperature ssttiw perturbations remain a great challenge because of the limitation in spatial resolution and realistic representations of the related processes in the atmospheric planetary boundary layer pbl and their interactions with the overlying free troposphere using microwave remote sensing data an empirical model is derived to depict wind stress perturbations induced by tiw related sst forcing in the eastern tropical pacific ocean wind data are based on space time blending of quick scatterometer quikscat direction interval retrieval with thresholded nudging dirth satellite observations and ncep analysis fields sst d

stratigraphic evidence for an early collision between northwest india and asia the collision of india with asia1 had a profound influence on late cretaceous and cenozoic oceanography2 climate3 fauna extinctions4 and the motion of at least some of the earth s litho spheric plates5 as the collision ended a period of rapid indo asian convergence6 a precise knowledge of its timing when the crust of the neo tethys ocean was completely subducted7 at some point along the plate boundary is important for understanding its wider consequences but current estimates of the collision age range from 65 to 38 myr before present6 8 11 here we report the results of extensive biostratigraphic analyses from waziristan and kurram in northwest pakistan which show that accretionary prism and trench strata were first thrust onto the northwest indian passive margin after 66 myr but before 55 5 myr after this time volcanic arc fragments the accretionary prism trench material and imbricates of the north indian slope were raised to shallow water depths and overlapped by upper palaeocene shallow water carbonates and shales12 14 indicative of post collision thrusting in this region finally both the suture and the indian craton were overlapped by continuous unconformable upper lower eocene shallow marine strata demonstrating that suturing was complete by 49 myr

insights on the kinematics of the india eurasia collision from global geodynamic models the eocene india eurasia collision is a first order tectonic event whose nature and chronology remains controversial we test two end member collision scenarios using coupled global plate motion subduction models the first conventional model invokes a continental collision soon after 60 ma between a maximum extent greater india and an andean style eurasian margin the alternative scenario involves a collision between a minimum extent greater india and a neotethyan back arc at 60 ma that is subsequently subducted along southern lhasa at an andean style margin culminating with continent continent contact at 40 ma our numerical models suggest the conventional scenario does not adequately reproduce mantle structure related to tethyan convergence the alternative scenario better reproduces the discrete slab volumes and their lateral and vertical distribution in the mantle and is also supported by the distribution of ophiolites indicative of tethyan intraoceanic subduction magmatic gaps along southern lhasa and a two stage slowdown of india our models show a strong component of southward mantle return flow for the tethyan region suggesting that the common assumption of near vertical slab sinking is an oversimplification with significant consequences for interpretations of seismic tomography in the context of subduction reference frames

ocean currents evident in satellite wind data satellite mounted radar scatterometers designed to quantify surface winds over the ocean actually measure the relative motion between the air and the ocean surface estimates of the wind stress from conventional surface wind measurements are usually derived neglecting ocean currents however when the relative motion is used the differences in the estimated stress can be as large as 50 near the equator and may even reverse sign during an el nino this assertion is supported by the strong relationship between the surface currents measured by the tropical atmosphere ocean tao array in the pacific ocean and the differences between the winds estimated from scatterometer data and those measured by tao anemometers the fact that the scatterometer measures relative motion and not wind alone makes scatterometer derived stress a more accurate representation of the boundary condition needed for both atmospheric and oceanic models than stress fields derived neglecting ocean currents

a preliminary assessment of plant biotic interactions in the eocene of south china evidence from liquidambar l saxifragales altingiaceae abstract the study of fossil plant biotic mainly arthropod interactions offers an opportunity to understand the evolutionary process in palaeoecosystems and their response to climate fluctuation despite the importance of such investigations not much is known about plant arthropod associations from the cenozoic floras of asia exceptionally diverse eocene floras from adjacent maoming and changchang sedimentary basins of southern china provide valuable insights into low latitude palaeoecosystems these floras indicate different intensities of plant arthropod interactions and probably viral bacterial or fungal infection two upper eocene floras from the maoming basin are markedly distinct from two approximately contemporaneous middle eocene floras of the changchang and maoming basins in exhibiting much more abundant and diverse plant damage types dts for equivalent comparisons we focus on well sampled fossil leaves of liquidambar l altingiaceae present and relatively abundant in both basins l maomingensis and liquidambar sp 1 from both upper eocene maoming floras exhibit mainly external foliage feeding in contrast almost only galling occurs on liquidambar sp 2 leaves from the middle eocene changchang flora the differences in the diversity and frequency of dts in the studied palaeofloras could have been affected by a progressive warming and increase in climate seasonality over the middle late eocene interval as well as by habitat conditions and plant successional status we hypothesize that l maomingensis and liquidambar sp 1 from the maoming basin inhabited the early successional riparian forests on an alluvial plain whereas liquidambar sp 2 from the changchang basin was a component of more mature plant communities

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

coastal ecosystem responses to late stage deccan trap volcanism the post k t boundary danian palynofacies of mumbai bombay west india abstract the deccan trap continental flood basalt eruptions of india occurred c 67 63 ma thus spanning the cretaceous tertiary boundary 65 ma deccan eruptions were coeval with an interval of profound global environmental and climatic changes and widespread extinctions and this timing has sparked controversy regarding the relative influence of deccan volcanism upon end cretaceous catastrophic events if deccan trap activity was capable of affecting global ecosystems evidence should be present in proximal indian sedimentary facies and their palaeontological contents the impact of late stage deccan volcanism upon biota inhabiting mumbai bombay island s post k t boundary lagoonal systems is documented here sediments or intertrappeans which accumulated within these lagoons are preserved between trap lavas that characterise the closing stages of this flood basalt episode mumbai island formation intertrappean faunal and floral communities are conspicuously distinct from those common to many pre k t boundary late maastrichtian intertrappeans across the deccan province the latter sedimentary intercalations mostly developed in cognate semiarid palustrine ecosystems by contrast those around mumbai evolved in sheltered peripheral marine settings within subsiding continental margin basins unique to this late deccan stage and under an increasingly humid danian climate geochemical analyses reveal that mumbai sedimentation and diagenesis were intimately related to local explosive volcanic and regional intrusive activity at c 65 63 ma although tectonic and igneous events imprinted their signatures throughout these sedimentary formations organisms usually sensitive to environmental perturbations including frogs and turtles thrived critically palynofacies data demonstrate that whilst plant material deposition was responsive to environmental shifts there were no palpable declines in floral productivity following mumbai pyroclastic discharges therefore it is implausible that this late stage explosive volcanism influenced major ecosystem collapses globally

the influence of sea surface temperature on surface wind in the eastern equatorial pacific seasonal and interannual variability abstract the climate of the eastern pacific exhibits a pronounced equatorial asymmetry boundary layer air originating in the southern hemisphere trades crosses the equator and flows into the intertropical convergence zone itcz whose southern limit is nearly always located at least 4 to the north of the equator the sea surface temperature sst distribution is characterized by a prominent cold tongue centered 1 s a strong frontal zone centered 2 n and a warm eastward current centered near 5 n the surface wind field exhibits a pronounced horizontal divergence as the air flows northward across the oceanic frontal zone these features vary in strength in response to the annual cycle and the el nino southern oscillation phenomenon the northward cross equatorial surface winds the cold tongue and the frontal zone all tend to be strongest during the cold season july through november during the cold season of the coldest years when the cold tongue is most prominent the cross equatorial flow t

early eocene leaves of northwestern india and their response to climate change abstract today the existence of tropical rainforests in the indian subcontinent is restricted to the fringes of the western ghats greater assam region and some small places in odisha however the palaeovegetation reconstruction in this study illustrates the existence of equatorial tropical forest in northwestern india bikaner rajasthan during the early eocene fossil leaves described here were collected from the gurha lignite mine of bikaner and showed affinities with holigarna grahamii anacardiaceae pterygota alata malvaceae syzygium spp s fruticosum and s cumini myrtaceae and gardenia spp g lucida and g gummiefra rubiaceae contrary to the present day dry and desertic conditions the fossil records provide strong evidence of humid tropical and paratropical evergreen forest with monsoon seasonality existing in and around the study area during the depositional period any shift in climatic conditions has drastic effects on the vegetation cover of a region in time and space this drastic change in climate has led to the extinction of tropical rain forest from this region this might be due to the northward movement of the indian subcontinent away from the equator formation of the himalayas and monsoon or changes in monsoon pattern

boundary layer depth entrainment and decoupling in the cloud capped subtropical and tropical marine boundary layer abstract estimates of marine boundary layer mbl depth and degree of decoupling for two regions of the subtropical and tropical east pacific are presented using satellite observations from the moderate resolution imaging spectroradiometer modis and the tropical rainfall measuring mission trmm microwave imager tmi these data are combined in a novel way with ncep reanalysis data and a mixing line parameterization to estimate the mean entrainment rate we over the two regions mean entrainment rates vary geographically and have maxima just downwind of the californian coast we 4 5 mm s 1 and also in the core of the equatorial east pacific cold tongue where mean we exceeds 6 mm s 1 entrainment exceeds subsidence by 30 or less in the subtropical stratocumulus regions north of the equatorial cold tongue entrainment greatly exceeds subsidence producing a rapid deepening of the mbl as air flows over a marked sst gradient shallow mbls zi 500 700 m are found to be well mixed in general the deco

outward growth of the tibetan plateau during the cenozoic a review abstract the surface uplift history of the tibetan plateau tp offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the asian monsoon various models have been proposed to reveal the surface uplift history of the tp but controversies remain we evaluate these models using data from sedimentology and stratigraphy structural geology magmatism exhumation and paleoaltimetry studies structural analyses indicate that thrust belts which spread from the central tp outward toward its surrounding margins accommodated most of the india asia convergence and facilitated crustal shortening and thickening in the central tp eocene adakitic rocks located in the qiangtang and the lhasa blocks likely were generated by partial melting of an eclogitic source paleogene 50 30 ma potassic rocks only occur in the qiangtang block whereas late oligocene late miocene 26 8 ma potassic rocks occur both in the qiangtang and lhasa blocks low temperature thermochronologic ages in the central tp are older than 40 35 ma whereas those in the margins are younger than 20 ma mostly late miocene and pliocene pleistocene in age independent paleoaltimetry estimates suggest that the lhasa and qiangtang terranes attained their current elevations during the eocene most likely due to the initial collision between india and lhasa whereas the hoh xil basin area to the north and himalayas to the south were still low even below sea level in the latter case we argue for an inside out growth pattern for the tibetan plateau the tp grew southward and northward from a nucleus of high topography and is likely to continue expanding along the mazar tagh fault to the northwest the kuantai shan hei shan longshou shan to the northeast the longquan shan to the east and the shillong plateau to the south if the northward force of india would not diminished

initial india asia continental collision and foreland basin evolution in the tethyan himalaya of tibet evidence from stratigraphy and paleontology abstractthe onset of the india asia continent continent collision in tibet was accompanied by the elimination of oceanic crust and the development of a peripheral foreland basin on the subducting continental crust however owing to the progressively southward migration of this foreland basin the appearance of flexural uplift forebulge predated flexural subsidence foredeep at the distal location such as at gamba and tingri in the southern tethyan himalaya consequently to trace and date this forebulge may provide a better constraint on the india asia collision at gamba and tingri our studies on the stratigraphy paleontology and paleoenvironment show that depositional cessation of the limestones occurred at shallow benthic zone 7 sbz 7 54 55 ma in the gamba area and at the base of sbz 10 52 8 ma in the tingri area at gamba a conglomerate layer within the upper zongpu formation is suggested to represent the formation of the forebulge at the onset of the foreland basin and the coincidenc

tropical instability wave kinematics observations from the tropical instability wave experiment the kinematics of planetary waves originating from instability of the nearsurface equatorial currents are reported on using velocity measurements from an array of acoustic doppler current profilers deployed in the equatorial pacific during the tropical instability wave experiment a distinctive wave season was observed from august to december 1990 with wave energy confined primarily above the core of the equatorial undercurrent particle motions in the horizontal plane are described by eccentric ellipses oriented toward the north but tilting into the cyclonic shear of the south equatorial current the tilt is maximum near the surface just north of the equator and decreases to the south and with depth the distribution of wave variance is narrowband in both frequency and zonal wavenumber with central period zonal wavelength and westward directed phase propagation estimated to be 500 hours 1060 km and 59 cm s 1 respectively neither the meridional nor the vertical wavenumber component is statistically different from zero these results generally agree with previous findings on tropical instability waves from the atlantic and pacific oceans and in the undersampled arena of geophysical measurements they provide an example where statistical inference is supported by an ensemble of independent measurements

provenance of the upper cretaceous eocene deep water sandstones in sangdanlin southern tibet constraints on the timing of initial india asia collision abstractthe first arrival of sedimentary material from asia onto the indian continental margin provides a minimum constraint on the timing of initial india asia collision a combination of petrology detrital cr spinel geochemistry and zircon u pb dating of the upper cretaceous to eocene deep water succession at the sangdanlin section southern tibet provides evidence for major provenance change within the strata the upper cretaceous paleocene denggang formation quartzarenites contain zircons with dominant proterozoic ordovician u pb ages with an additional age peak of early cretaceous which we interpret to be derived from the northern indian margin by contrast the lithic sandstones of the early to middle eocene sangdanlin and zheya formations are dominated by zircons younger than 200 ma showing one major peak at 80 125 ma and two subdominant peaks at 54 70 and 180 196 ma comparable to those from the gangdese magmatic arc cr spinels in the sangdanlin and zheya formations are abundant and char

the influence of cross equatorial pressure gradients on the location of near equatorial convection tomas and webster note that in regions where there is a substantial cross equator surface pressure gradient there is locally anticyclonic absolute vorticity on the low pressure side of the equator and thus the flow in this region meets the parcel criterion for inertial instability they hypothesize that the atmospheric response to this absolute vorticity distribution is a convergence divergence doublet in the boundary layer the convergence centre results in strong convection and thus is very important in determining the strength and location of convection i e the intertropical convergence zones whereas the divergence centre results in suppressed convection in this work a zonally symmetric model of the boundary layer is developed to investigate this hypothesis further an analysis of a linearized version of the model indicates that although the observed flow in these regions meets the parcel criterion for instability it does not satisfy the linear stability criteria because of the stabilizing influence of dissipation and the finite vertical scale much greater shear than that observed is required for linear instability it is noted however that when the parcel criterion is met one of the nonlinear terms which was neglected in the linear analysis may have an important influence on the flow several experiments are performed integrating the full nonlinear model relaxing back to a pressure distribution having a cross equatorial gradient to test whether the observed vorticity wind and convergence distributions can be well simulated it is found that the simulations reach a steady state in which there is a region of locally anticyclonic absolute vorticity on the low pressure side of the equator this absolute vorticity distribution results in an anomalous acceleration of the meridional wind and a convergence divergence doublet similar to that observed by tomas and webster this response is explained as resulting from accelerations that act to bring the zonal flow out of geostrophic balance as it passes through the region of locally anticyclonic absolute vorticity the response of the meridional wind to the strength of the pressure gradient is quasi linear for small and somewhat larger values of forcing but between these values there is a range where the response is highly nonlinear i e large increases in the strength of the meridional wind result from small changes in the pressure gradient it is suggested that this nonlinear response may play a role in the observed sudden onset of the monsoon circulations the nonlinear model is also forced using pressure distributions taken from observations the resulting steady state simulated vorticity wind and convergence distributions closely match the observations for the cases of pressure distributions taken from the east pacific and east atlantic during july when forced using the pressure distribution from the indian ocean region during july the model produces an unrealistically strong meridional wind response some improvement is obtained by including the latitudinally dependent zonal pressure gradient force which is moderately strong in this region finally the model is forced using a pressure distribution taken from observations in the central pacific ocean during july in this case the cross equator pressure gradient is near zero

atmospheric manifestation of tropical instability wave observed by quikscat and tropical rain measuring mission observations from two new spaceborne microwave instruments in 1999 clearly reveal the atmospheric manifestation of tropical instability waves north of the pacific equatorial cold tongue a unique zonal temporal band pass filter enables the isolation of the propagating signals and the determination of their phase differences the phase differences between the propagation of wind and sea surface temperature sst signals observed from space and the vertical wind profiles measured from a research ship are consistent with the hypothesis that the coupling between wind and sst is caused by buoyancy instability and mixing which reduces the wind shear in the atmospheric boundary layer the coupling causes higher evaporative cooling over the warm phase and infers a negative thermal feedback

observations of planetary boundary layer structure in the eastern equatorial pacific abstract atmospheric soundings were collected from a research ship in the eastern equatorial pacific to determine the kinematic and thermodynamic structure of the planetary boundary layer pbl in the vicinity of a strong front in sea surface temperature sst these observations have been used to test the hypothesis proposed by wallace et al and hayes et al that the low level wind shear was enhanced on the cold side of the front because of greater static stability the pbl structure was analyzed from a transect along 110 w from 10 n to 5 s with a focus on the 500 m deep atmospheric mixed layer as defined with respect to virtual potential temperature v significant mixed layer variability was found due to diurnal and other effects but there were systematic differences in mean structure as a function of latitude the mixed layer was neutrally stratified over warm water between 6 5 n and 1 5 n and was slightly stably stratified over the cooler water between 1 n and 2 s the mean total vertical wind

tethyan and indian subduction viewed from the himalayan high to ultrahigh pressure metamorphic rocks abstract the himalayan range is one of the best documented continent collisional belts and provides a natural laboratory for studying subduction processes high pressure and ultrahigh pressure rocks with origins in a variety of protoliths occur in various settings accretionary wedge oceanic subduction zone subducted continental margin and continental collisional zone ages and locations of these high pressure and ultrahigh pressure rocks along the himalayan belt allow us to evaluate the evolution of this major convergent zone 1 cretaceous 80 100 ma blueschists and possibly amphibolites in the indus tsangpo suture zone represent an accretionary wedge developed during the northward subduction of the tethys ocean beneath the asian margin their exhumation occurred during the subduction of the tethys prior to the collision between the indian and asian continents 2 eclogitic rocks with unknown age are reported at one location in the indus tsangpo suture zone east of the nanga parbat syntaxis they may represent subducted tethyan oceanic lithosphere 3 ultrahigh pressure rocks on both sides of the western syntaxis kaghan and tso morari massifs formed during the early stage of subduction exhumation of the indian northern margin at the time of the paleocene eocene boundary 4 granulitized eclogites in the lesser himalaya sequence in southern tibet formed during the paleogene underthrusting of the indian margin beneath southern tibet and were exhumed in the miocene these metamorphic rocks provide important constraints on the geometry and evolution of the india asia convergent zone during the closure of the tethys ocean the timing of the ultrahigh pressure metamorphism in the tso morari massif indicates that the initial contact between the indian and asian continents likely occurred in the western syntaxis at 57 1 ma west of the western syntaxis the higher himalayan crystallines were thinned rocks equivalent to the lesser himalayan sequence are present north of the main central thrust moreover the pressure metamorphism in the kaghan massif in the western part of the syntaxis took place later 7 m y after the metamorphism in the eastern part suggesting that the geometry of the initial contact between the indian and asian continents was not linear the northern edge of the indian continent in the western part was 300 to 350 km farther south than the area east of the nanga parbat syntaxis such en baionnette geometry is probably produced by north trending transform faults that initially formed during the late paleozoic to cretaceous gondwana rifting farther east in the southern tibet the collision occurred before 50 6 0 2 ma finally high pressure to ultrahigh pressure rocks in the western himalaya formed and exhumed in steep subduction compared to what is now shown in tomographic images and seismologic data

age of initiation of the india asia collision in the east central himalaya abstract we document the stratigraphy and provenance of the lower tertiary terrigenous sections in the zhepure shan region of the tethyan himalaya southern tibet using petrographic and geochemical whole rock and single grain techniques the cretaceous early tertiary shelf deposits of shallow marine carbonates and siliciclastics of the former indian passive margin near the western end of the zhepure shan are conformably overlain by lower tertiary clastic rocks sandstones in the jidula formation paleocene mostly contain monocrystalline quartz grains of cratonic origin in contrast significant amounts of immature framework grains with a distinct ophiolitic and volcanic arc influence are present in the youxia early eocene and shenkeza post early eocene formations major trace and rare earth element concentrations in both sandstones and shales complement the petrographic data and indicate that the source of the jidula formation consisted primarily of quartzose basement rocks probably of indian con

air sea interaction effects in the lower troposphere across the north wall of the gulf stream abstract significant atmospheric and oceanographic differences have often been observed in the regions lying on either side of the north wall of the gulf stream satellite visible range sensors have revealed changes in reflectivity across the gulf stream believed to be due to changes in sea state that are related to these atmospheric and oceanic differences in addition lines of low level cloud paralleling the edge of the gulf stream have been observed to persist in satellite imagery for several days at a time anomalous radar propagation also has been noted to occur in these same regions in an attempt to document the interrelation of these phenomena the lower atmosphere over the north wall of the gulf stream was studied on two separate occasions sea state photography and measurements of sea surface temperature air temperature dew point temperature and atmospheric pressure were made by an instrumented rp 3a aircraft flying at various altitudes from the gulf stream across the north wall and onto

air sea heat exchange along the northern sea surface temperature front in the eastern tropical pacific abstract the atmospheric response to the oceanic forcing in the eastern pacific along the northern equatorial sea surface temperature sst front is investigated in terms of sensible and latent heat flux during the 6 month period from 28 july 1999 to 27 january 2000 and the 7 month period from 28 june 2000 to 27 january 2001 of particular interest is the atmospheric boundary layer abl response to oceanic tropical instability waves tiws that distort the sst front during may january in normal years in previous studies time series of surface heat fluxes clearly show the influence of tiws but the relationship to spatial patterns of sst and wind speed has been inferred only from sparse in situ data in this study satellite observations are used as a basis for compositing in situ data from moorings to compensate for the lack of a spatially dense mooring array the variability in the position of the sst front caused by westward propagating tiws enables fixed mooring locations to measure the abl response

quantifying the rise of the himalaya orogen and implications for the south asian monsoon we reconstruct the rise of a segment of the southern flank of the himalaya tibet orogen to the south of the lhasa terrane using a paleoaltimeter based on paleoenthalpy encoded in fossil leaves from two new assemblages in southern tibet liuqu and qiabulin and four previously known floras from the himalaya foreland basin u pb dating of zircons constrains the liuqu flora to the latest paleocene ca 56 ma and the qiabulin flora to the earliest miocene 21 19 ma the proto himalaya grew slowly against a high similar to 4 km proto tibetan plateau from similar to 1 km in the late paleocene to similar to 2 3 km at the beginning of the miocene and achieved at least similar to 5 5 km by ca 15 ma contrasting precipitation patterns between the himalaya tibet edifice and the himalaya foreland basin for the past similar to 56 m y show progressive drying across southern tibet seemingly linked to the uplift of the himalaya orogen

recognition of tuffs in the middle upper dingqinghu fm lunpola basin central tibetan plateau constraints on stratigraphic age and implications for paleoclimate abstract the lunpola basin plays a key role in determining the elevation history of the central tibetan plateau which is closely related to uplift dynamics and paleoclimatic evolution however accurate age constraints on the basin stratigraphy reflecting tectonic paleo elevation and climate information have long been vigorously debated mostly due to a lack of absolute age controls here we found two altered tuff layers in the middle upper dingqinghu formation fm in the basin stratigraphic sequence detailed lithological mineralogical and geochemical analyses of the tuffs indicate that they came from trachyandesite and identify analcime as the typical alteration mineral suggesting primary deposition la icp ms zircon u pb dating of the tuffs yields concordant ages of 20 6 0 1 ma and 20 7 0 1 ma indicating that the end of the dingqinghu fm i e the lunpola stratigraphic sequence and the uplift of the plateau to its current high elevations occurred much later than previously estimated the contemporaneous thick black oil shales in the lunpola deep lake and biocoenosis together suggest that the climate was humid and warm during this period

the andean type gangdese mountains paleoelevation record from the paleocene eocene linzhou basin abstract paleoelevation reconstruction using oxygen isotopes is making a significant contribution to understanding the cenozoic uplift of the himalayas and the tibetan plateau this paper presents new oxygen and carbon isotopic compositions from well dated tertiary paleosols lacustrine calcareous carbonates and marls from the nianbo 60 54 ma and upper pana formations 51 48 ma of the linzizong group in the linzhou penbo basin the sediments of the nianbo formation which are 180 m thick were deposited in alluvial fans braided rivers fan deltas and on nearshore to offshore lacustrine settings whereas those of the upper pana formation are 100 m thick and are comprised predominantly of proximal alluvial fan and braided river deposits correlations between the lithofacies and stable isotopic compositions suggest that the basin was mainly a hydrologically open environment it is confirmed that the 18 o c and 13 c c values from nianbo and pana formations have not yet been reset by late stage diagenesis based on petrographic examination oxygen isotope of the fossil ostracodes and tectonic deformation of strata the paleoelevations are reconstructed using the corrected most negative paleosurface water 18 o psw values these imply that the linzhou area had attained an elevation of 4500 400 m during the period of the indo asian collision i e achieved a near present elevation and may form an andean type mountain range stretching the gangdese arc before collision the gangdese mountains probably maintained high elevations since at least the paleocene and could play a crucial role in the climate change in the interior of the tibetan plateau during the early cenozoic the paleogeomorphic scenario of the eocene tibet is proposed to exist at two high mountains in excess of 4500 m that sandwiched a low elevation basin

direct observations of atmospheric boundary layer response to sst variations associated with tropical instability waves over the eastern equatorial pacific tropical instability waves tiws with a typical wavelength of 1000 km and period of 30 days cause the equatorial front to meander and result in sst variations on the order of 18 28c vertical soundings of temperature humidity and wind velocity were obtained on board a japanese research vessel which sailed through three fully developed sst waves from 1408 to 1108w along 28n during 21 28 september 1999 a strong temperature inversion is observed throughout the cruise along 28n capping the planetary boundary layer pbl that is 1 1 5 km deep temperature response to tiw induced sst changes penetrates the whole depth of the pbl in response to an sst increase air temperature rises in the lowest kilometer and shows a strong cooling at the mean inversion height as a result this temperature dipole is associated with little tiw signal in the observed sea level pressure slp the cruise mean vertical profiles show a speed maximum at 400 500 m for both zonal and meridional velocities sst based composite profiles of zonal wind velocity show weakened intensified vertical shear within the pbl that is consistent with enhanced reduced vertical mixing causing surface wind to accelerate decelerate over warm cold ssts taken together the temperature and wind soundings indicate the dominance of the vertical mixing over the slp driving mechanism based on the authors measurements a physical interpretation of the widely used pbl model proposed by lindzen and nigam is presented

ocean plate stratigraphy in east and southeast asia abstract ancient accretionary wedges have been recognised by the presence of glaucophane schist radiolarian chert and melange recent techniques for the reconstruction of disrupted fragments of such wedges by means of radiolarian biostratigraphy provide a more comprehensive history of ocean plate subduction and successive accretion of ocean floor materials from the oceanic plate through offscraping and underplating reconstructed ocean floor sequences found in ancient accretionary complexes in japan comprise from oldest to youngest pillow basalt limestone radiolarian chert siliceous shale and shale and sandstone similar lithologies also occur in the melange complexes of the philippines indonesia thailand and other regions this succession is called ocean plate stratigraphy ops and it represents the following sequence of processes birth of the oceanic plate at the oceanic ridge formation of volcanic islands near the ridge covered by calcareous reefs sedimentation of calcilutite on the flanks of the volcanic islands where radiolarian chert is also deposited deposition of radiolarian skeletons on the oceanic plate in a pelagic setting and sedimentary mixing of radiolarian remains and detrital grains to form siliceous shale in a hemipelagic setting and sedimentation of coarse grained sandstone and shale at or near the trench of the convergent margin radiolarian biostratigraphy of detrital sedimentary rocks provides information on the time and duration of ocean plate subduction the ages of detrital sediments becomes younger oceanward as younger packages of ops are scraped off the downgoing plate ops reconstructed from ancient accretionary complexes give us the age of subduction and accretion direction of subduction and ancient tectonic environments and is an important key to understanding the paleoenvironment and history of the paleo oceans now represented only in suture zones and orogenic belts

sedimentology palynostratigraphy and palynofacies of the late oligocene makum coalfield assam india a window on lowland tropical vegetation during the most recent episode of significant global warmth abstract the sedimentology palynofacies and pollen and spore assemblages together with observations on the preserved megaflora from the tirap coal mine assam india 27 17 20 n 95 46 15 e provide important insights into the composition and distribution of plant communities in a late oligocene tropical delta palaeolatitude approximately 18 n these insights take on additional significance because the late oligocene included the last significantly warm interval in earth s history before progressive neogene cooling to the present day icehouse the lower two thirds of a 188 m studied section represents lower delta plain environments with only a small degree of brackish water marine influence raised mires autochthonous swamps and allochthonous organic matter accumulations comprise the vitrinite rich high volatile bituminous b coals the upper third of the section represents upper delta plain environments with high sediment pass through here standing fossil forests attest to frequent inundation and recovery of the arborescent interfluve vegetation throughout the period of deposition of the studied section several 100 kyr sediment supply exceeded increases in accommodation space afforded by basin subsidence relative sea level rise a dominance of spores attributed to cyatheaceous and other fern taxa indicates that tree ferns and other pteridophytes were a major component of the vegetation throughout the environments represented by the section despite the absence of ferns in the megafossil record nypa and mangrove megaremains together with mangrove pollen and acrostichum spores attest to the presence of a mangrove community similar in composition to those of modern southeast asia palms and megathermal tree taxa such as those belonging to the malvaceae meliaceae alangiaceae anacardiaceae and pellicieraceae inhabited the interfluve and swamp forests perennial herbs of the family gunneraceae occur throughout the section palynofacies analysis shows a dominance of anoxic dysoxic environments with a small part of the lower part of the section exhibiting more oxic conditions associated with circumstantial evidence for mild marine possibly tidal influence most palynodebris fluoresce only weakly consistent with the relatively high rank for coals of this age a small number of reworked gondwanic permian grains suggest sediment erosion from the highlands to the north the late oligocene tropical delta vegetation has much in common with modern lowland wet megathermal forests from southeast asia however tree ferns appear more prevalent in the late oligocene

the influence of sea surface temperature gradients on stratiform cloudiness along the equatorial front in the pacific ocean abstract satellite observations of visible cloudiness and sea surface temperature sst are used to test the hypothesis that the configuration of cool low level winds blowing across a sharp sst front in the equatorial eastern pacific gives rise to stratiform clouds on the warm downstream side of the front the results show that there is a maximum in low clouds over the equatorial front during the cold season of 1988 when the front and cross isotherm winds were strong the low cloud maximum was reduced in the warm el nino year of 1987 consistent with the weakening of the front instability waves along the equatorial front were pronounced during the summer and autumn of 1988 the results show a strong association between visible cloud and the sst waves with enhanced reduced cloudiness in the warm troughs cold crests of the waves

why do foliar physiognomic climate estimates sometimes differ from those observed insights from taphonomic information loss and a clamp case study from the ganges delta abstract palaeoclimate estimates derived from plant based proxies are potentially subject to uncertainties arising from taphonomic filtering in any given fossil assemblage it is possible to identify the kinds of likely taphonomic influences but virtually impossible to quantify the uncertainties they introduce because filtering removes information because that information is missing it cannot be measured an alternative approach is to measure the maximum uncertainty possible due to specific information loss within recognised analytical protocols in respect of the multivariate foliar physiognomic technique known as clamp climate leaf analysis multivariate program we have attempted to do this by experimentally degrading both the character state scores and the number and composition of taxa as subsets of the full range of character states and taxonomic diversity in the source vegetation in this study a stand of protected vegetation on green island 23 08 58 n 88 26 59 19 e within the ganges delta was sampled following standard clamp protocols the island is subject to annual flooding during the monsoon season and is typical of the kinds of naturally disturbed vegetation likely to be represented in ancient delta floodplain assemblages a total of 56 woody dicot taxa were scored in the living vegetation from this complete sample leaf character states for lobing margin size apex base length to width ratio and shape were removed in turn from all 56 taxa to give 7 analyses simulating worst case taphonomic loss of physiognomic data ten subsets of 20 randomly selected taxa were also analysed to simulate taphonomic diversity loss of almost two thirds of the potentially available taxa in the source vegetation in all cases the completeness statistic remained above the clamp recommended minimum of 0 66 the results show that in all cases the uncertainties arising from taphonomic processes either through taphonomic diversity or character state filtering were not significantly different from the statistical clamp uncertainties associated with the most commonly used calibration dataset physg3brc and gave similar climatic estimates as the source vegetation in its entirety this suggests that stratigraphically well constrained museum collections lacking detailed sedimentary or taphonomic context can still be used with confidence for clamp analyses leaf margin analysis displayed a greater sensitivity to diversity loss the green island estimates suggested a cooler moister climate than that indicated by the observed regional climate as derived from a 0 5 0 5 gridded data set used in climate modelling evaluation the likely cause for this disparity is the prevalence of a sub canopy microclimate signal developed by the vegetation itself and this is strongly dependant on the temperature and humidity characteristics of the regional climate as well as the proximity to water bodies within the sample size limitations of this study this disparity is larger than that introduced by taphonomic processes but potentially can be corrected for

new constraints on the india asia collision the lower miocene gangrinboche conglomerates yarlung tsangpo suture zone se tibet abstract lower miocene conglomerates crop out along the length of the yarlung tsangpo suture zone on the southern margin of the lhasa terrane these conglomerates known by various local names are correlated herein as the gangrinboche conglomerates all units exhibit broadly similar stratigraphic histories and a basal depositional contact upon an eroded surface of rocks of the lhasa terrane is ubiquitous at most localities the tops of sections are either removed by erosion or truncated by north directed thrusts these conglomeratic molasse units developed in response to the india asia collision and record aspects of its development in all units initial clast derivation was from the lhasa terrane on the northern margin of the yarlung tsangpo suture zone up section the first appearance of clasts derived from terranes within the suture zone and the northern margin of india all of which lie to the south of any outcrops of gangrinboche conglomerates is observed although these units were previously thought to be eocene analysis of fossil and structural constraints indicates early miocene deposition as development of the gangrinboche conglomerates records a significant phase in the evolution of the india asia collision understanding of their age and stratigraphic evolution has wider implications for regional tectonic models

the relationship between leaf physiognomy and climate based on a large modern dataset implications for palaeoclimate reconstructions in china abstract in this paper correlation between modern leaf physiognomy and climate in china are examined to optimize the use of leaf characters as a palaeoclimate proxy a large dataset was compiled recording the distribution of leaf physiognomic characters among 3166 native dicot trees species across 732 calibration grids on a county level grids span a range of ecological environments tropical rainforests to alpine shrubs across humid areas thirteen climatic parameters were included for each grid and 22 leaf physiognomic characters were scored for each tree species the correlation between leaf physiognomic characters and climatic parameters were calculated based on single linear regressions slr and multiple linear regressions mlr results indicate clear spatial distribution patterns linked to latitude exist for all leaf characters with temperature coldest month mean temperature cmmt and precipitation growing season precipitation gsp being the main climate controls moreover because leaf characters are more closely correlated with precipitation during the three wettest consecutive months p3wet rather than with precipitation during the three driest consecutive months p3dry seasonal variations in rainfall associated with the asian monsoon might especially influence leaf physiognomic characters closer correlations between leaf physiognomy and climate are seen using mlr compared with slr therefore mean annual temperature mat and mean annual precipitation map based on mlr equations provide the most promising basis for palaeoclimate reconstructions in china

high resolution satellite measurements of the atmospheric boundary layer response to sst variations along the agulhas return current abstract the marine atmospheric boundary layer mabl response to sea surface temperature sst perturbations with wavelengths shorter than 30 longitude by 10 latitude along the agulhas return current arc is described from the first year of sst and cloud liquid water clw measurements from the advanced microwave scanning radiometer amsr on the earth observing system eos aqua satellite and surface wind stress measurements from the quikscat scatterometer amsr measurements of sst at a resolution of 58 km considerably improves upon a previous analysis that used the reynolds sst analyses which underestimate the short scale sst gradient magnitude over the arc region by more than a factor of 5 the amsr sst data thus provide the first quantitatively accurate depiction of the sst induced mabl response along the arc warm cold sst perturbations produce positive negative wind stress magnitude perturbations leading to short scale perturbations in the wind stress curl and divergence fields that are li

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

asian monsoons in a late eocene greenhouse world the strong present day asian monsoons are thought to have originated between 25 and 22 million years myr ago driven by tibetan himalayan uplift however the existence of older asian monsoons and their response to enhanced greenhouse conditions such as those in theeocene period 55 34myrago are unknownbecause of the paucity of well dated records here we show late eocene climate records revealing marked monsoon like patterns in rainfall and wind south and north of the tibetan himalayan orogen this is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from myanmar and by aeolian dust deposition in northwest china our climate simulations support modern like eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhancedgreenhouse conditions counterbalanced the negative effect of lowertibetanrelief onprecipitation these strong monsoons later weakened with the global shift to icehouse conditions 34myr ago

paleontological view of the ages of the deccan traps the cretaceous tertiary boundary and the india asia collision volcanism in the deccan traps of india occurred over at most three magnetic chrons centered on a main reversed chron paleontological data indicate that this reversed chron must coincide with 29r which contains the cretaceous tertiary k t boundary recent 40 ar 39 ar data may therefore provide one of the best estimates of the absolute age of the k t boundary 65 7 2 0 ma moreover the eurasian character of k t boundary terrestrial faunas in india suggests that this was also close to the time of india asia collision this is significantly earlier than generally recognized and implies about 4000 km of continental shortening in the collision zone probably absorbed jointly by crustal thickening and strike slip extrusion

oligocene climate signals and forcings in eurasia revealed by plant macrofossil and modelling results abstract the oligocene represents a transitional time period from a warm climate to a cooler climate that is more representative of the modern day yet a general view of continental climate pattern and forcings are still lacking different proxies and models show striking disparities especially in mid high latitudes requiring validation of oligocene climate reconstruction in order to understand the large scale processes that drive the observed climate changes here we compiled 149 macrofossil floras in the mid high latitudes of eurasia then quantitatively reconstructed the oligocene climate using coexistence approach ca and combined previously published paleoclimate data during the oligocene eurasian mid high latitudes were mainly dominated by a humid subtropical climate mean annual temperature mat ranged between 5 4 c and 25 5 c with mean annual precipitation map ranging from 338 to 2453 mm three regions europe central eurasia and eastern asia indicate different climatic regimes with a generally warmer and wetter climate in europe and a colder and drier climate in central eurasia when compared to eastern asia no significant reorganization of climate was observed between the early and late oligocene the climate anomalies between the oligocene and present indicate that geographic changes e g retreat of the paratethys sea played an important role in shaping the climate pattern of eurasia by comparing the fossil data to a range of different hadcm3l model simulations of the oligocene with differing boundary conditions e g co2 and topography we demonstrate similar large scale climate spatial patterns between models and fossil data however models simulated much higher temperature seasonality lower simulated winter temperatures and higher simulated summer temperatures in eurasia mean annual temperature analysis indicates that simulations with 560 and 1120 ppmv co2 matched better with fossil data when compared to other simulations depending on the topography these results provide some constraints that should be considered for future paleoclimate modelling

position of the lhasa terrane prior to india asia collision derived from palaeomagnetic inclinations of 53 ma old dykes of the linzhou basin constraints on the age of collision and post collisional shortening within the tibetan plateau the lhasa terrane comprises the southern eurasian margin since at least mid cretaceous therefore paleomagnetic data from the lhasa terrane are crucial to reconstruct the pre collisional southern margin of eurasia previous paleomagnetic data from the cretaceous takena formation provide a rough constraint on the pre collisional paleolatitudinal position of the southern eurasian margin however paleogene paleomagnetic data from the lhasa terrane which can provide more direct constraints are very limited in addition reliability of the existing data is ambiguous because of a possible later overprint in our new study 17 sites were drilled from mafic dykes intruded in the t1 unit of the linzizong formation of the linzhou basin near lhasa for paleomagnetic studies figure 1 the dykes were ar 40 ar 39 dated to c 53 ma by yue and ding 2006 from ten sites a higher coercivity component demagnetized between 20 and 100 mt could be isolated detailed rockmagnetic analyses reveal ti rich titanomagnetite as the remanence carrier which suggests that the rock is not much altered and the remanent magnetization is likely of primary origin this is supported by a positive fold test the occurrence of normal and reverse polarity directions within single sites the subvolcanic character of the dykes and the within site scatter as well as the scatter between site mean directions indicate that paleosecular variation is recorded within sites tilt correction was performed using the bedding of overlying fluvial lacustrine sediments and tilt angles of ignimbrite columns postdating the dyke emplacement bedding corrected directions give an overall mean direction of d i 12 3 27 2 95 10 6 k 21 7 n 10 corresponding to a paleolatitude of 13 2 5 8 n at a reference location on the suture zone 20 n 90 e comparison with previous cretaceous data mainly from the takena formation yields a stable position of the lhasa terrane during cretaceous and early eocene this indicates that no large north south crustal shortening occurred along the southern eurasian margin between late cretaceous and early eocene the difference between expected paleolatitudes determined from the apwp of eurasia and observed paleolatitudes reveals relative northward movement of the lhasa block of ca 1847 763 km since early eocene this is attributed to indentation of india into asia and implies a considerable amount of north south crustal shortening two models of greater india were used to determine the extended northern margin of india ali and aitchison 2005 proposed a greater india based on bathymetric features in the eastern indian ocean and patzelt and others 1996 determined the paleolatitude of northern india using paleomagnetic investigations on paleocene sediments of the zongpu formation at gamba and duela intersection of the pre collisional southern eurasian margin and the northern margin of india yields a collision age of the indian and eurasian continents of c 5349 ma an initial collision within this time range is in accordance with previous studies based on paleomagnetic or geologic data e g patriat and achache 1984 klootwijk and others 1992 guillot and others 2003 a significantly later collision age at the eocene oligocene boundary as proposed by aitchison and others 2007 is not in agreement with our new and previous paleomagnetic data from the lhasa block