magnetic fabric in the malanjkhand granite central india implications for regional tectonics and proterozoic suturing of the indian shield abstract in this paper field microstructural and anisotropy of magnetic susceptibility ams data are presented from the 2 48 ga malanjkhand granite and adjacent gneiss with an aim to evaluate the time relationship between fabric development in the granite and regional tectonics the central indian suture cis that demarcates the southern margin of the ne sw to ene wsw trending central indian tectonic zone citz and is a consequence of the accretion between the northern and southern indian shields lies to the north of the granite the northern margin of the granite that has proximity to the cis is mylonitized and shows a dextral top to the ne sense of shear field and magnetic foliation in the gneiss are parallel to each other as well as to the field foliation in the western and northwestern margin of the granite also the field fabrics in the granite and gneiss curve clockwise into the cis the magnetic foliation trajectories curve from a ns orientation in areas remote from the cis to a ne sw orientation in parts that are proximal to the cis in the north the granite shows synmagmatic deformation fabrics such as preferentially oriented zoned feldspar phenocrysts as well as evidence of high t solid state deformation fabric such as chessboard pattern in quartz magnetic anisotropy increases towards the cis which is inferred to support synmagmatic deformation it is concluded that the tectonic evolution of the citz and emplacement fabric development in the malanjkhand granite were synchronous phenomena wnw ese directed convergence led to transpression which is inferred to be responsible for the emplacement of the granite it is concluded that in the malanjkhand granite the development of syndeformational emplacement fabrics to syntectonic cooling was a continuum and the suturing of the northern and southern indian shields along the cis took place during the palaeoproterozoic period thus the study provides an insight into the amalgamation and stabilization of the indian shield during the late archaean palaeoproterozoic time

on the anomalous precipitation enhancement over the himalayan foothills during monsoon breaks an intriguing feature associated with breaks in the indian summer monsoon is the occurrence of intense flood producing precipitation confined to central eastern parts of the himalayan ceh foothills and north eastern parts of india past studies have documented various large scale circulation aspects associated with monsoon breaks however the dynamical mechanisms responsible for anomalous precipitation enhancement over ceh foothills remain unclear this problem is investigated using diagnostic analyses of observed and reanalysis products and high resolution model simulations the present findings show that the anomalous precipitation enhancement over the ceh foothills during monsoon breaks emerges as a consequence of interactions between southward intruding mid latitude westerly troughs and the south asian monsoon circulation in its weak phase these interactions facilitate intensification of mid tropospheric cyclonic vorticity and strong ascending motion over the ceh foothills so as to promote deep convection and concentrated rainfall activity over the region during monsoon breaks mesoscale orographic effects additionally tend to amplify the vertical motions and precipitation over the ceh foothills as evidenced from the high resolution model simulations it is further noted from the model simulations that the coupling between precipitation and circulation during monsoon breaks can produce nearly a threefold increase of total precipitation over the ceh foothills and neighborhood as opposed to active monsoon conditions

potential atmospheric impact of the toba mega eruption 71 000 years ago an approx 6 year long period of volcanic sulfate recorded in the gisp2 ice core about 71 000 5000 years ago may provide detailed information on the atmospheric and climate impact in the toba mega eruption deposition of these aerosols occur beginning of an approx 1000 year long stadial event but not immediately before the longer glacial period beginning approx 67 500 years ago total stratospheric loading estimates over this approx 6 year period range from 2200 to 4400 mt of h sub 2 so sub 4 aerosols the range in values is given to compensate for uncertainties in aerosol transport magnitude and longevity of the atmospheric loading may have led directly to enhanced cooling during the initial two centuries of this approx 1000 year cooling event 25 refs 2 fig 1 tab

the occurrence of lead in antarctic recent snow firn deposited over the last two centuries and prehistoric ice concentrations of lead have been measured by ultraclean isotope dilution mass spectrometry in snow cores covering the last two centuries collected at an inland site in east antarctica using an ultra clean all plastic hand operated auger and in a prehistoric blue ice block collected at an antarctic coastal site lead contamination of 16 to 200 pg pb g existed on the outside of the snow cores but the measured concentrations decreased more or less abruptly along a radius from the outside to the centers of the snow cores establishing interior values in the 1 to 5 pg pb g range some of these interior values are however possibly still slightly affected by lead contamination which could have intruded to the center of the cores because of slight melting of some of the snow cores before laboratory analysis the interior of the blue ice block appears not to have been significantly contaminated and contains about 1 7 pg pb g these new data show that most previously published data on lead in antarctic snow and ice were in high positive error because of contamination during field sampling laboratory analysis or both they show that lead concentrations could not have increased in antarctic snows or ice from prehistoric times to present more than 2 to 3 fold confirming that the remote polar areas of the southern hemisphere are still little affected by industrial lead pollution prehistoric antarctic ice is shown to contain about 1 pg pb g natural excess lead above silicate dust lead this excess cannot be entirely accounted for by volcanoes or sea spray which suggests the possible existence of some other unknown natural source of prehistoric excess lead present day mean eolian fallout flux of lead in antarctica is estimated to be about 0 07 ng pb cm 2 yr 1 which stands in about the same proportion to that in the south pacific westerlies about 1 30 as the flux in greenland is observed to stand to those in the north pacific and north atlantic westerlies

syntectonic anatexis and magmatism in a mid crustal transpressional shear zone an example from the hercynian rocks of the eastern pyrenees abstract hercynian metamorphism and magmatism in the cap de creus peninsula eastern pyrenees occurred contemporaneously with non coaxial deformation in a transpressive regime an example of this has been taken from a migmatite complex in the northern coast the studied area is formed by partially melted sillimanite schists together with two different suites of igneous rocks a calc alkaline magmatic sequence consisting of small granitoid bodies and later peraluminous leucogranites and pegmatites all these rocks occur within a ne sw to e w trending sub vertical high strain zone where a first schistosity is tightly folded and transposed the relations between folds and crenulation cleavage in the metasediments and deformational fabrics in the granitoids and migmatites provide good evidence for the penecontemporaneity of deformational processes magmatism and migmatization furthermore the analysis of cross cutting relationships between different granitoids as well as the observation of their different degrees of deformation verifies that magmatism in this area took place as synkinematic consecutive intrusions from the more basic magmas to the peraluminous acid dykes

granite ascent in convergent orogenic belts testing a model the common spatial relationship in convergent orogenic belts between a crustal scale shear zone system high grade metamorphic rocks and granites suggests a feedback relation between crustal anatexis and contractional deformation that helps granite extraction and focuses granite ascent such a feedback relation has been proposed for ascent of early devonian granites in west central maine this interpretation requires that deformation metamorphism and plutonism were synchronous we have determined precise u pb zircon and monazite ages that we interpret to record time of crystallization of syntectonic granite in metric to decametric sheets and kilometric plutons and of schlieric granite within migmatites ages are in the range ca 408 404 ma within 1 m y at 95 confidence limits these ages are similar to extant u pb monazite ages of ca 405 399 2 ma for syntectonic regional metamorphism in the same area the coincidence between the age of peak metamorphism and crystallization ages of granite shows tectonics metamorphism and magmatism were contemporaneous in support of the feedback model

intrusion level of granitic massifs along the hercynian belt balancing the eroded crust abstract hercynian granitoid intrusions form a long 3200 km belt comparable in size to other batholiths in the world six massifs have been selected which encompass cabeza de araya extremadura spain guitiriz galicia spain pontivy and mortagne brittany france la marche massif central france and fichtelgebirge bavaria germany detailed gravity surveys over these massifs and subsequent inversion provide their shape at depth correlation of the deeper zones with internal structures determine the place of the root zones the shape of the massifs is examined along the strike of the chain the emplacement of individual massifs is controlled by local tectonics most granites are not deeply rooted but one massif cabeza de araya spain shows a root zone presently as deep as 14 km most have about half of their volume in the first 3 km below the present surface estimates of the magma volume transferred result in 1500 km 3 issued from one specific feeder yielding a total of 70 000 km 3 of magma intruded all along the chain the depth of emplacement of the granitic massifs does not show any significant trend along the strike of the chain the shallower massifs in the french massif central correspond to more deeply eroded areas in the center of the chain their root zone as well as the change in the dip of the walls are presently observed at depths ranging between 4 and 6 km in hercynian granites both variations are interpreted as being related to the brittle ductile transition at the time of emplacement gross thermal considerations place the transition at its former place during magma emplacement indicating that the upper crust has not been eroded by more than 6 8 km this estimate severely contrasts with models involving a doubled crust

large scale control of the arabian sea monsoon inversion in august the summer monsoon inversion in the arabian sea is characterized by a large amount of low clouds and august as the peak season atmospheric stratification associated with the monsoon inversion has been considered a local system influenced by the advancement of the india pakistan monsoon empirical and numerical evidence from this study suggests that the arabian sea monsoon inversion is linked to a broader scale monsoon evolution across the african sahel south asia and east asia western north pacific wnp rather than being a mere byproduct of the india pakistan monsoon progression in august the upper tropospheric anticyclone in south asia extends sideways corresponding with the enhanced precipitation in the subtropical wnp equatorial indian ocean and african sahel while the middle part of this anticyclone weakens over the arabian sea the increased heating in the adjacent monsoon systems creates a suppression effect on the arabian sea suggesting an apparent competition among the africa asia wnp monsoon subsystems the peak sahel rainfall in august together with enhanced heating in the equatorial indian ocean produces a critical effect on strengthening the arabian sea thermal inversion by contrast the wnp monsoon onset which signifies the eastward expansion of the subtropical asian monsoon heating might play a secondary or opposite role in the arabian sea monsoon inversion

a northern oscillation relating northern hemispheric pressure anomalies and the indian summer monsoon analysis of the causes of the indian monsoon have concentrated on climatological phenomena in the southern hemisphere such as el nino and the southern oscillation by contrast we have examined meteorological records for the northern hemisphere 0 180 spanning much of this century we find that zonally integrated mean sea level pressure anomalies across eurasia during january to april exhibit a statistically significant negative correlation between values for higher and sub tropical latitudes we further find that there is an association between above normal activity of the indian monsoon and a steep poleward directed pressure anomaly gradient which tends to persist through the summer and may indicate a strong zonal flow in the circumpolar westerlies on the other hand when this pressure anomaly gradient reverses zonality is disturbed and the indian monsoon tends to be drier than usual under these conditions the circumpolar flow becomes persistently meridional as a result of a predisposition to blocking and splitting of the jet

control of granite emplacement by regional deformation abstract a combination of structural measurements and gravity data is used to investigate the mode of granite emplacement in various tectonic settings the deepest zones revealed by gravity data provided those zones also show vertical lineations in outcrop are interpreted as magma feeder channels these structures or root zones reflect the flow pattern of the upwelling magma while being emplaced they can be interpreted within the regional stress field active during that time granites intruded during transcurrent shearing have only a few feeder channels these roots are not connected to the main shear zone all of them lie within locally extensional areas of the regional stress field this situation is also observed in granites emplaced during a compressional phase of deformation when emplaced during a regionally extensional phase the granitic plutons are very thin with many small deeper zones in which variously evolved granite types may be intrusive these regions vertically differentiated are also interpreted as feeder channels the different morphology at depth as well as the difference in the number of root zones suggest that deformation controls the emplacement of granitic plutons the root zones are oriented at a high angle to the direction of maximum compression when magma is emplaced in a plastic crust if the pluton is emplaced higher in a brittle crust then the roots are aligned with the maximum compression according to the andersonian theory of fracture the orientation of the root zone along the direction of extension in a plastic crust may be explained by shearing which acts as a valve mechanism for segregating magma in all the examples the geometry of the root zone relative to the major fault plane implies that the shear zone does not induce magma generation and that it does not serve as a guide for magma emplacement

progressive development of structures in a ductile shear zone in the singhbhum shear zone of eastern india successive generations of folds grew in response to a progressive ductile shearing during this deformation a mylonitic foliation was initiated and was repeatedly transposed the majority of fold hinges were formed in an arcuate manner at low angles to the y axis in an e w trending subhorizontal position and major segments of the fold hinges were then rotated towards the down dip northerly plunging x axis the striping and intersection lineations were rotated in the same manner the down dip mylonitic lineation is a composite structure represented by rotated early lineations and newly superimposed stretching lineations the consistent asymmetry of the folds the angular relations between c and s surfaces and the evidence of two dimensional boudinage indicate that the deformation was non coaxial but with a flattening type of strain with 1 2 the degree of non coaxiality varied both in space and time from the progressive development of mesoscopic structures it is concluded that the 2 3 km wide belt of ductile shear gave rise to successive anastomosing shear zones of mesoscopic scale when a new set of shear lenses was superimposed on already sheared rocks the preexisting foliation generally lay at a low angle to the lenses no new folds developed where the acute angle was sympathetic to the sense of shear displacements where the acute angle was counter to the sense of shear the pre existing foliation lying in the instantaneous shortening field was deformed into a set of asymmetric folds

isotopic evidence of contaminant lead in the south atlantic troposphere and surface waters abstract the third intergovernmental oceanographic commission ioc baseline contaminant cruise may june 1996 has established the first lead isotopic compositions in the surface water and the atmosphere of the equatorial and south atlantic ocean these ratios have evidenced both anthropogenic and natural origins of lead along the cruise transect from 33 s to 10 n the isotopic gradients tentatively have been attributed to aeolian as well as surface water advective inputs from a suite of rather local and remote sources to the southern hemisphere relatively low 206pb 207pb ratios x sd were encountered within the south equatorial current between 17 s and 5 s 1 156 0 003 those were bracketed by more radiogenic ratios at higher latitudes in the southern hemisphere 33 s to 23 s within the brazil current and the subtropical gyre 1 163 0 003 and in the northern hemisphere 0 to 10 n 1 165 0 005 the latter were comparable to ratios of surface water in the north atlantic equatorial ocean 1 169 0 006 under a combined contaminant influence of both north american westerlies 1 19 1 20 and european easterlies 1 155 1 165 that predominance of contaminant lead contrasts with the measurable presence of natural lead in surface waters of the equatorial ocean which are attributed to aeolian inputs of saharan dust the ratios of lead in surface waters at higher latitudes in the south atlantic are characteristic of anthropogenic lead aerosols also detected in antarctic ice and could substantiate as well the hypothesized aerosol recycling of lead by sea spray emission in the far southern hemisphere the atmospheric lead isotopic compositions 206pb 207pb in bulk depositions 1 171 0 006 precipitation 1 171 0 006 and aerosols 1 168 0 011 were generally more radiogenic than the surface waters 1 162 0 005 beside a poor representation of a short term atmospheric sampling this difference could reflect a recent evolution in atmospheric lead emissions which have not yet been reflected in oceanic surface waters it may also be due in part to advective lead inputs from surface oceanic circulation of the south equatorial current

emplacement mechanism of the main granite pluton of the lavras do sul intrusive complex south brazil determined by magnetic anisotropies abstract magnetic fabric and rock magnetism studies were performed on apparently isotropic granite facies from the main intrusion of the lavras do sul intrusive complex pluton lsic rio grande do sul south brazil this intrusion is roughly circular 12 13 5 km composed of alkali calcic and alkaline granitoids with the latter occupying the margin of the pluton magnetic fabrics were determined by applying both anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization aarm the two fabrics are coaxial the parallelism between ams and aarm tensors excludes the presence of a single domain sd effect on the ams fabric of the granites several rock magnetism experiments performed in one specimen from each sampled site show that for all sites the magnetic susceptibility is dominantly carried by ferromagnetic minerals while mainly magnetite carries the magnetic fabrics lineations and foliations in the granite facies were successful determined by applying magnetic methods magnetic lineations are gently plunging and roughly parallel to the boundaries of the pluton facies except at the few sites in the central facies which have a radial orientation pattern in contrast the magnetic foliations tend to follow the contacts between the different granite facies they are gently outerward dipping inside the pluton and become either steeply southwesterly dipping or vertical towards its margin the lack of solid state and subsolidus deformations at outcrop scale and in thin sections precludes deformation after full crystallization of the pluton this evidence allows us to interpret the observed magnetic fabrics as primary in origin magmatic acquired when the rocks were solidified as a result of processes reflecting magma flow the foliation pattern displays a dome shaped form for the main lsic pluton however the alkaline granites which outcrop in the southern part of the studied area have an inward dipping foliation and the steeply plunging magnetic lineation suggests that this area could be part of a feeder zone the magma ascent probably occurred due to ring diking

teleconnections between the subtropical monsoons and high latitude climates during the last deglaciation the major deglacial intensification of the southwest monsoon occurred at 11 450 150 calendar years before present synchronous with a major climate transition as recorded in greenland ice an earlier event of monsoon intensification at 16 000 150 calendar years before present occurred at the end of heinrich layer 1 in the atlantic and parallels the initial rise in global atmospheric methane concentrations and the first abrupt climate changes in the antarctic thus the evolution of the monsoonal and high latitude climates show teleconnections but hemispheric asymmetries superimposed on abrupt events the monsoonal climate shows high frequency variability of 1785 1450 and 1150 year oscillations and abrupt climate change seems to occur when at least two of these oscillations are in phase

flow in natural shear zones the consequences of spinning flow regimes abstract the ancient flow regime in natural shear zones is often considered to have followed a deformation path comparable to that in theoretical shear zones i e progressive simple shear between rigid wall rocks with a persistent flow plane orientation parallel to the edges of the zone this is often based on the presence of monoclinic fabric elements in the zones which indicate a dominantly non coaxial flow regime though not necessarily persistent simple shear the deformation fabric of a shear zone from the pyrenees illustrates that even at a kinematic vorticity number of w 1 simple shear along the entire deformation path obliqueness of the flow planes with the edges of the zone is possible for some time if incremental stretching axes were rotating with respect to zone edges this implies that ductile deformation must have taken place in the wall rock of the zone such a flow regime may be difficult to recognize with the fabric criteria used at present but leads to an unusual kinematic significance of the shear zone involved in extreme cases the zone may have acted as a passive marker in a ductilely deforming medium it also means that not only w must be known to reconstruct the ancient flow regime in natural shear zones but at least also the time dependence of the orientation of the incremental stretching axes

strain partitioning during partial melting and crystallizing felsic magmas abstract the rheology of partly molten felsic systems changes dramatically during the onset of melting and through crystallization solid to liquid and liquid to solid transitions are not rheologically identical contradicting the concept of a unique rheological critical melt percentage we use four thresholds separating the successive stages according to the melt fraction for the melting transition 1 the liquid percolation threshold connects the melt pockets at about 8 of melt thus allowing local magma displacement at the metric scale and 2 for greater melt percentages 20 25 a melt escape threshold corresponds to the onset of transport over large distances of the melt and part of the residual solid phase leading ultimately to granitic bodies for the solidification transition 3 the first formation of a rigid framework of crystals which can accumulate stress although the melt can still flow corresponds to the rigid percolation threshold 55 solids and 4 the system becomes totally locked at about 72 75 solid which corresponds to the particle locking threshold the present paper focuses on strain partitioning induced by the coexistence of two contrasting rheological phases between these thresholds on a variety of scales non coaxial deformation is preferentially accommodated by the lower viscosity melt which increases the vorticity in the melt phase and reinforces asymmetries in the flow pattern strain partitioning also increases the scale length of the weakest phase during melting and magma ascent whereas strain partitioning decreases the scale length during crystallizing strain partitioning also affects the migration of melt by raising the particle locking threshold and lowering the melt escape threshold for three dimensional deformations such as transpression the direction of melt segregation e g horizontal may differ from the direction of melt migration e g vertical

midlatitude rossby wave modulation of the indian summer monsoon the dominant mode of july august seasonal variability of indian summer monsoon rainfall obtained by performing an empirical orthogonal function analysis over india excluding north east india for the period 1979 2014 is highly correlated to the quasi stationary mid latitude eurasian rossby wave train known as the silk road pattern a new hypothesis has been proposed and tested using observed indian rainfall and era interim dataset by which the positive feedback between the mid latitude rossby wave and the indian summer monsoon circulation has been established a rossby wave train features successive upper tropospheric negative and positive geopotential height anomalies over the north east of the mediterranean and north west of india respectively the negative height anomaly decreases the sum of the vertical integral of potential and internal energy while this increases in the region of positive geopotential height anomalies this is associated with middle to lower tropospheric mid latitude descent and ascent anomalies at 40 e and 50 e which cause negative surface temperature anomalies over syria iraq jordan and saudi arabia and a positive surface temperature anomaly over iran respectively the negative and positive surface temperature anomalies are associated with positive and negative surface pressure anomalies over saudi arabia and iran respectively which generate anomalous northwesterly winds over eastern saudi arabia and persian gulf further downstream this anomalous northwesterly wind combines with the climatological background cross equatorial southwesterly flow in the arabian sea the flow further converges towards central and north west india the flow also acts as a source of moisture supply from the warm arabian sea and persian gulf for the deep convection over western ghats north west and central india and hence reinforces active indian summer monsoon conditions

fabric analysis of quartzites with negative magnetic susceptibility does ams provide information of spo or cpo of quartz abstract we ask the question whether petrofabric data from anisotropy of magnetic susceptibility ams analysis of deformed quartzites gives information about shape preferred orientation spo or crystallographic preferred orientation cpo of quartz since quartz is diamagnetic and has a negative magnetic susceptibility 11 samples of nearly pure quartzites with a negative magnetic susceptibility were chosen for this study after performing ams analysis electron backscatter diffraction ebsd analysis was done in thin sections prepared parallel to the k1k3 plane of the ams ellipsoid results show that in all the samples quartz spo is sub parallel to the orientation of the magnetic foliation however in most samples no clear correspondance is observed between quartz cpo and k1 magnetic lineation direction this is contrary to the parallelism observed between k1 direction and orientation of quartz c axis in the case of undeformed single quartz crystal pole figures of quartz indicate that quartz c axis tends to be parallel to k1 direction only in the case where intracrystalline deformation of quartz is accommodated by prism slip it is therefore established that ams investigation of quartz from deformed rocks gives information of spo thus it is concluded that petrofabric information of quartzite obtained from ams is a manifestation of its shape anisotropy and not crystallographic preferred orientation

evolution of fabric in chitradurga granite south india a study based on microstructure anisotropy of magnetic susceptibility ams and vorticity analysis abstract in this paper the fabric in massive granite 2 6 ga from the chitradurga region western dharwar craton south india is analyzed using microstructure anisotropy of magnetic susceptibility ams study and kinematic vorticity analysis the microstructural investigation on the granite shows a progressive textural overprint from magmatic through high t to low t solid state deformation textures the mean magnetic foliation in the rocks of the region is dominantly nw se striking which have developed during regional d1 d2 deformation on account of ne sw shortening the plunge of the magnetic lineation varies from nw to vertical to se and interpreted to be a consequence of regional d3 deformation on account of nw se to e w shortening the vorticity analysis from magnetic fabric in the region reveals that the nw se oriented fabric formed under pure shear condition during d1 d2 regional deformation however some parts of the region particularly close to the adjacent chitradurga shear zone show that the magnetic fabrics are oblique to the foliation as well as shear zone orientation and inferred to be controlled by simple shearing during d3 regional deformation the shape preferred orientation spo analysis from oriented thin sections suggest that the shape of the recrystallized quartz grains define the magnetic fabric in chitradurga granite and the degree of the spo reduces away from the chitradurga shear zone it is interpreted that the change in magnetic fabrics in some parts of the granite in the region are dominantly controlled by the late stage sinistral shearing which occurred during the development of chitradurga shear zone

role of equatorial central pacific and northwest of north atlantic 2 metre surface temperatures in modulating indian summer monsoon variability the interannual variability of indian summer monsoon rainfall ismr have been examined in association with the variability of 2 metre surface temperature 2mst and lower and upper tropospheric pressure and wind patterns over the globe using era 40 reanalysis dataset the analysis of 44 years 1958 2001 data reveals a recurrent negative phase of enso la nina pattern the increase in 2mst over tropical southwest pacific and intensification of subtropical westerly jet stream over indian ocean due to the consequence of thermal wind balance the intensification of jet forms anticyclonic anomaly which intensifies mascarene high as the atmospheric response is equivalent barotropic over there the mascarene high intensifies the cross equatorial flow and hence indian summer monsoon ism circulation while during non enso years data reveals a recurrent positive relationship of ismr with 2mst anomaly over northwest of north atlantic and intensification and shift of north atlantic westerly jet stream to higher latitudes the jet stream intensifies the meridional vorticity dipole formed due to azores high and the entrance of asian subtropical westerly jet stream over north atlantic and west mediterranean sea a wave activity flux for stationary rossby waves diverges out of the vorticity dipole toward downstream along the asian jet stream over the eurasian region the jet stream acts as a wave guide and the successive troughs and ridges of the rossby waves travel along the jet and influence upper tropospheric tibetan high and hence ism circulation

magnetic fabric shape preferred orientation and regional strain in granitic rocks since granites do not preserve easily mappable foliations lineations and strain markers determining the degree of shape preferred orientation spo in them is challenging the aim of this paper is to present a methodology for determining variation in the degree of spo in granites and to test the feasibility of correlating the same with regional strain the case of the godhra granite located in the southern parts of aravalli mountain belt india is taken as an example degree of spo is determined using two different techniques a anisotropy of magnetic susceptibility ams and b strength of mineral lineation determined by calculating the concentration parameter k of von mises distribution by digital image analysis of biotite kbi and feldspar kf in thin sections prepared parallel to the magnetic foliation plane spo data obtained using the above two techniques from 20 samples distributed across the entire granite are analysed samples with a higher k also have a stronger magnetic fabric magnetic lineation l and degree of magnetic anisotropy p 0 also the degree of spo is greater for granites from the southern parts as compared to the northern parts it is argued that this variation in degree of spo cannot be attributed to rheological differences or strain resulting from difference in aspect ratios regional strain is inferred as the dominant factor since the emplacement of the godhra granite is synchronous with the tectonic rejuvenation along the central indian tectonic zone citz that lies to its south the higher degree of spo in the southern parts is attributed to its proximity to the citz whilst caution needs to be exercised to directly apply magnetic data as a measure of strain intensity on a regional scale it can be a useful guide to select samples for detailed spo analysis using some alternative technique especially for granites and other magmatic rocks that are devoid of mesoscopic strain markers 2006 elsevier ltd all rights reserved

kinematic evolution of the mbakop pan african granitoids western cameroon domain an integrated ams and ebsd approach abstract this study integrates anisotropy of magnetic susceptibility microstructural and crystallographic preferred orientation cpo data from the mbakop granitic pluton mgp pan african age in order to decipher its kinematic evolution the mgp lies close to ne sw branch of central cameroon shear zone ccsz and is emplaced in gneissic basement high mean magnetic susceptibility and presence of multi domain magnetite are recorded quartz cpo measured using electron backscatter diffraction reveals dominance of rhomb prism and prism slip in different samples which is consistent with microstructures developed under upper greenschist amphibolite facies conditions quartz cpo along with other kinematic indicators feldspar porphyroclasts mineral fish indicate non coaxial deformation was important during tectonic evolution of the mgp contrasting sense of shear is recorded implying multi stage mylonitization in the western cameroon domain top towards south sense of shear is related to regional d 2 deformation 613 585 ma while top towards north is related to d 3 585 540 ma the magnetic fabric in mgp records d 3 the obliquity between mean orientation of magnetic foliation n12 e and the ne sw ccsz branch n48 e gives kinematic vorticity number of 0 95 this indicates dominantly simple shear with a minor pure shear component it is concluded that regional transpression was important during mgp emplacement

extratropical influences on the inter annual variability of south asian monsoon the effects of extratropical dynamics on the interannual variations in south asian monsoon sam are examined based on ncep ncar reanalysis and cru precipitation data a conditional maximum covariance analysis is performed on sea level pressure 200 hpa geopotential heights and the sam rainfall by removing the linear effects of el nino southern oscillation from the fields it is found that two modes provide a strong connection between the upper level circulation in the atlantic european region and sam rainfall the circumglobal teleconnection cgt and the summer north atlantic oscillation snao the structures in the 200 hpa heights of both modes in the atlantic region are similar in the atlantic region and their southeastward extension to south asia sa also corresponds to upper level ridges in their positive phases in slightly different positions nevertheless the influence of both modes on sam rainfall is distinct whereas a positive cgt is related to a widespread increase of rainfall in sam a positive snao is related to a precipitation dipole with its positive phase over pakistan and the negative phase over northern india the physical mechanisms for the influence of cgt and snao on sam are related to the upper level geopotential anomaly which affects the amplitude and position of the low level convergence the small displacements of the centers of these responses and the low level cold advection from the north east of sa in case of snao explain the differences in the corresponding sam rainfall distributions these findings are confirmed with the relatively high resolution coupled climate model ec earth which gives confidence in the physical basis and robustness of these extratropical variability modes and their influence on the south asian monsoon rainfall

blocking highs over asia and monsoon droughts over india severe summer droughts of the indian subcontinent have been found to accompany prolonged breaks in the south west monsoon data from the years of severe drought suggest that the associated breaks were due to upper tropospheric blocking ridges over east asia we present here a model for the evolution of two such blocking ridges the east asia eabr and the west asia wabr apparently an intense wabr the initiator of the monsoon break precedes the formation of the eabr this cycle could be a way of predicting years of intense drought or monsoon activity

methods and applications of magnetic anisotropy a special issue in recognition of the career of graham j borradaile methods and applications of magnetic anisotropy a special issue in recognition of the career of graham j borradaile

understanding the revival of the indian summer monsoon after breaks abstractin this paper the authors suggest a dynamical mechanism involved in the revival of the summer monsoon after breaks in this context the authors carry out a diagnostic analysis using the datasets from national centers for environmental prediction reanalysis 2 for the period 1979 2007 to identify a robust mechanism that typifies breaks and subsequent revival of monsoon the authors find during the peak of significant breaks an anomalous southward shift of the subtropical westerly jet stream which is invariably accompanied by an anomalous northward shift of a stronger than normal easterly jet these major changes during a break facilitate an instability mechanism which apparently leads to formation of a synoptic disturbance formation of such a disturbance is critical to the subsequent revival of the summer monsoon in 61 of the observed break to active revivals computations of energetics and correlation analysis carried out suggest an increase in the eddy kinetic energy at the expense of the mea

predicting extreme phases of the indian summer monsoon abstract extreme active and break phases of the indian summer monsoon ism often bring about devastating floods and severe draughts here it is shown that these extreme phases exhibit distinctive precursory circulation conditions in both the tropics and extratropics over a range of antecedent periods the extremely active monsoon over northern india is preceded by a strengthening of the upper tropospheric central asian high and enhancement of the tropical convection over the equatorial indian ocean and the south china sea the concurrent buildup of the anomalous high over central asia and the arrival of tropical convection over northern india increase the likelihood of occurrence of a heavy rainy period there similarly the concurrent anomalous low over central asia and the arrival of suppressed convection originating from the equatorial indian ocean and the south china sea precede extremely strong monsoon breaks over northern india two predictors can be used to predict the extreme active break phases

process of magnetite fabric development during granite deformation this study evaluates the fabric defined by magnetite grains in a syntectonically deformed granite and deciphers the processes that led to magnetite fabric development anisotropy of anhysteretic re

temporal variability in the northern arabian sea oxygen minimum zone omz during the last 225 000 years the northern arabian sea is one of the few regions in the open ocean where thermocline water is severely depleted in oxygen the intensity of this oxygen minimum zone omz has been reconstructed over the past 225 000 years using proxies for surface water productivity water column denitrification winter mixing and the aragonite compensation depth acd changes in omz intensity occurred on orbital and suborbital timescales lowest o2 levels correlate with productivity maxima and shallow winter mixing precession related productivity maxima lag early summer insolation maxima by 6 kyr which we attribute to a prolonged summer monsoon season related to higher insolation at the end of the summer periods with a weakened or even non existent omz are characterized by low productivity conditions and deep winter mixing attributed to strong and cold winter monsoonal winds the timing of deep winter mixing events corresponds with that of periods of climatic cooling in the north atlantic region

summer monsoon rainfall variability over north east regions of india and its association with eurasian snow atlantic sea surface temperature and arctic oscillation this observational study during the 29 year period from 1979 to 2007 evaluates the potential role of eurasian snow in modulating the north east indian summer monsoon rainfall with a lead time of almost 6 months this link is manifested by the changes in high latitude atmospheric winter snow variability over eurasia associated with arctic oscillation ao excessive wintertime eurasian snow leads to an anomalous cooling of the overlying atmosphere and is associated with the negative mode of ao inducing a meridional wave train descending over the tropical north atlantic and is associated with cooling of this region once the cold anomalies are established over the tropical atlantic it persists up to the following summer leading to an anomalous zonal wave train further inducing a descending branch over ne india resulting in weak summer monsoon rainfall

the indian summer monsoon drought of 2002 and its linkage with tropical convective activity over northwest pacific the indian subcontinent witnessed a severe monsoon drought in 2002 which largely resulted from a major rainfall deficiency in the month of july while moderate el nino conditions prevailed during this period the atmospheric convective activity was anomalously enhanced over northwest and north central pacific in the 10 20 n latitude belt and heavy rainfall occurred over this region in association with a series of northward moving tropical cyclones similar out of phase rainfall variations over the indian region and the northwest nw pacific have been observed during other instances of el nino southern oscillation enso the dynamical linkage corresponding to this out of phase rainfall variability is explored in this study by conducting a set of numerical experiments using an atmospheric general circulation model the results from the model simulations lend credence to the role of the tropical pacific sea surface temperature anomalies in forcing the out of phase precipitation variability over the nw pacific and the indian monsoon region it is seen that the enso induced circulation response reveals an anomalous pattern comprising of alternating highs and lows which extend meridionally from the equatorial region into the sub tropic and mid latitude regions of west central pacific this meridional pattern is associated with an anomalous cyclonic circulation over nw pacific which is found to favor enhanced tropical cyclonic activity and intensified convection over the region in turn the intensified convection over nw pacific induces subsidence and rainfall deficiency over the indian landmass through anomalous east west circulation in the 10 20 n latitude belt based on the present findings it is suggested that the convective activity over nw pacific is an important component in mediating the enso monsoon teleconnection dynamics

circumglobal wave train and the summer monsoon over northwestern india and pakistan the explicit role of the surface heat low this study examines the influence of the mid latitude circulation on the surface heat low hl and associated monsoon rainfall over northwestern india and pakistan using the era40 data and high resolution t106l31 climate model echam5 simulation special emphasis is given to the surface hl which forms over pakistan and adjoining areas of india iran and afghanistan during the summer season a heat low index hli is defined to depict the surface hl the hli displays significant correlations with the upper level mid latitude circulation over western central asia and low level monsoon circulation over arabian sea and acts as a bridge connecting the mid latitude wave train to the indian summer monsoon a time lagged singular value decomposition analysis reveals that the eastward propagation of the mid latitude circumglobal wave train cgt influences the surface pressure anomalies over the indian domain the largest low negative pressure anomalies over the western parts of the hl region i e iran and afghanistan occur in conjunction with the upper level anomalous high that develops over western central asia during the positive phase of the cgt the composite analysis also reveals a significant increase in the low pressure anomalies over iran and afghanistan during the positive phase of cgt the westward increasing low pressure anomalies with its north south orientation provokes enormous north south pressure gradient lower pressure over land than over sea this in turn enables the moist southerly flow from the arabian sea to penetrate farther northward over northwestern india and pakistan a monsoon trough like conditions develops over northwestern india and pakistan where the moist southwesterly flow from the arabian sea and the persian gulf converge the convergence in association with the orographic uplifting expedites convection and associated precipitation over northwestern india and pakistan the high resolution climate model echam5 simulation also underlines the proposed findings and mechanism

the role of stress in ductile deformation abstract the concept of progressive ductile deformation has previously been discussed mainly in kinematic terms little attention has been paid to the principal stresses that control the formation of ductile deformation patterns many deformation patterns of rocks may have been created in a stress field of stable orientation an equation derived here directly links the orientation of the major axis of deviatoric stress to the stretch and rotation components of plane isochoric deformation in isotropic rocks estimations of rotation and stretch of finite strain ellipsoids may therefore aid the recovery of palaeostress axes using a nomogram introduced here the inclination of the major principal deviatoric stress axis with respect to a reference plane controls both the particle movement paths and mode of progressive deformation the deformation tensor obtained by integrating the rate of displacement or velocity gradient equations is first expressed in time dependent terms comprising only the normal and shear components of the strain rate tensor mohr s equations of stress can then be used to link strain rates to the major principal stress responsible for them the rate of progressive deformation is determined by the rheology of the deforming rocks and the magnitude of the deviatoric stress this derivation yields a time dependent deformation tensor which is expressed in terms of the dynamic viscosity and the magnitude and orientation of the major deviatoric stress with respect to a reference plane the significance of this deformation tensor is illustrated by forward modelling using computer graphics these allow the progressive deformation of a unit volume of rock in response to deviatoric stresses of various stable orientations to be visualized

characteristics and mechanisms of the subseasonal eastward extension of the south asian high abstractthis study investigates the features of eastward extension of the south asian high sah and its connection with diabatic heating and rainfall over eastern asia on subseasonal time scales the causes of sah s eastward extension are examined by potential vorticity pv diagnosis with emphasis on the joint role of diabatic heating feedback and midlatitude wave train the sah s eastward extension features eastward propagation of a wave train across eurasia among the wave train the migration of weak high from the western flank of the tibetan plateau tp to the east of tp contributes to the sah s eastward extension at the early stage when the sah approaches its easternmost position a strong negative pv positive geopotential height center prevails to the east of the tp at 200 hpa the associated anomalies in diabatic heating and rainfall include the anomalous heating and above normal rainfall over the south china sea scs and subtropical western pacific occurring 12 days before the sah s eastern

modification of fabric in pre himalayan granitic rocks by post emplacement ductile deformation insights from microstructures ams and u pb geochronology of the paleozoic kinnaur kailash granite and associated cenozoic leucogranites of the south tibetan detachment zone himachal high himalaya the present day south tibetan detachment std of higher himalaya is a system of low angle normal faults in the himachal high himalaya the std hanging wall is characterized by the presence of s type per aluminous paleozoic 475 ma granite called the kinnaur kailash granite kkg this granite is later intruded by cenozoic leucogranites 18 ma in vicinity of the std zone in this work microstructures anisotropy of magnetic susceptibility ams and u pb geochronology were carried out on the kkg and the leucogranites with an aim to a understand the conditions of fabric development and b decipher the tectonic relationship between deformation along the std and the evolution of these granites microstructural features and magnetic anisotropy indicate that the granites are intensely deformed in vicinity of the std and preserve their emplacement related fabric in the interior parts it is inferred that close to the std zone fabrics of both the kkg and the leucogranite are tectonic and are modified by the cenozoic 20 ma right lateral slip and extensional tectonics magnetic fabric in the interior parts of the kkg is related to its emplacement indicating that original fabric was preserved u pb geochronology of zircons from two samples of the kkg yields crystallization age of 477 6 3 4 and 472 4 ma the leucogranite gives a crystallization age of 18 5 0 6 ma zircons from the kkg also reveal signatures of a deformation event 20 6 2 3 ma at its rim it is inferred that deformation of the external rim of the kkg and crystallization of the leucogranites are synchronous and triggered by ductile deformation along the std

seismic and magnetic susceptibility anisotropy of middle lower continental crust insights for their potential relationship from a study of intrusive rocks from the serre massif calabria southern italy abstract we investigated the relationships between fabric seismic and magnetic anisotropy on lithotypes representative of a continental crust exposed in the serre massif southern italy in particular from five granitoids and one metagabbro cubes were cut according to the fabric elements and seismic properties up to 400 mpa confining pressure were measured with a triaxial multi anvil apparatus we also calculated the elastic properties based on the mineral content and composition in granitoids measured average compressional wave velocity vp of the fracture free aggregate at 400 mpa is 6 2 km s whereas average shear wave velocity vs is 3 6 km s with poisson s ratio ranging from 0 240 to 0 257 related to the modal proportions of quartz in metagabbro average vp and vs at 400 mpa are 6 9 km s and 3 7 km s respectively results showed that intrinsic velocity distribution after microcracks closure depends on progressive alignment of anisotropic minerals such as biotite amphibole and pyroxene with maxima velocities localized within the foliation plane mean magnetic susceptibility k m of the granitic rocks is 6 si units indicating that paramagnetic minerals such as biotite and amphibole control the intensity of magnetic anisotropy comparison of seismic and magnetic anisotropies highlighted the different role of constituting minerals over the petrophysical properties moreover a positive correlation between seismic and magnetic anisotropy has been recognized indicating that biotite and amphibole contribute to the petrophysical and textural anisotropy in the middle crust conversely in metagabbro the anisotropy of magnetic susceptibility ams is controlled by magnetite and pyrrhotite although these form

extratropical anticyclonic rossby wave breaking and indian summer monsoon failure interactions between midlatitude disturbances and the monsoonal circulation are significant for the indian summer monsoon ism rainfall this paper presents examples of monsoon midlatitude linkage through anticyclonic rossby wave breaking rwb over west asia during june july and august of the years 1998 2010 rwb events over west asia are identified by the inversion of the potential vorticity air mass at three different isentropic levels 340 350 and 360 k using daily ncep ncar reanalysis it is observed that rwb took place over west asia before during breaks in the ism further these events occur on the anticyclonic shear side of the subtropical jet where the gradient of the zonal wind is found to be high rwb is responsible for the southward movement of high potential vorticity air from the westerly jet leading to the formation of a blocking high over the arabian region in turn this blocking high advects and causes the descent of upper tropospheric cold and dry air towards central india such an air mass with low moist static energy inhibits deep monsoonal convection and thereby leads to a dry spell in fact we find that rwb induced blocking over west asia to be one of the major causes of dry spell break episodes in ism additionally the presence of cold air over central india reduces the north south thermal contrast over the monsoon region thereby modifying the local hadley circulation over the region

circumglobal teleconnection in the northern hemisphere summer analysis of the 56 yr ncep ncar reanalysis data reveals a recurrent circumglobal teleconnection cgt pattern in the summertime midlatitude circulation of the northern hemisphere this pattern represents the second leading empirical orthogonal function of interannual variability of the uppertropospheric circulation the cgt having a zonal wavenumber 5 structure is primarily positioned within a waveguide that is associated with the westerly jet stream the spatial phases of cgt tend to lock to preferred longitudes the geographically phase locked patterns bear close similarity during june august and september but the pattern in july shows shorter wavelengths in the north pacific north america sector the cgt is accompanied by significant rainfall and surface air temperature anomalies in the continental regions of western europe european russia india east asia and north america this implies that the cgt may be a source of climate variability and predictability in the above mentioned midlatitude regions the cgt has significant correlations with the indian summer monsoon ism and el nino southern oscillation enso however in normal ism years the cgt enso correlation disappears on the other hand in the absence of el nino or la nina the cgt ism correlation remains significant it is suggested that the ism acts as a conductor connecting the cgt and enso when the interaction between the ism and enso is active enso may influence northern china via the ism and the cgt additionally the variability of the cgt has no significant association with the arctic oscillation and the variability of the western north pacific summer monsoon the circulation of the wave train shows a barotropic structure everywhere except the cell located to the northwest of india where a baroclinic circulation structure dominates two possible scenarios are proposed the abnormal ism may excite an anomalous west central asian high and downstream rossby wave train extending to the north pacific and north america on the other hand a wave train that is excited in the jet exit region of the north atlantic may affect the westcentral asian high and thus the intensity of the ism it is hypothesized that the interaction between the global wave train and the ism heat source may be instrumental in maintaining the boreal summer cgt

on the relationship between east equatorial atlantic sst and ism through eurasian wave the dominant mode of july august ja seasonal variability of indian summer monsoon rainfall ismr are obtained by performing empirical orthogonal function eof analysis the first dominant mode of ismr and its relationships with the sea surface temperature sst pressure level wind and geopotential height gph fields are examined using gridded datasets for the period 1979 2014 the principal component of the first leading mode pc1 obtained in the eof analysis of ja rainfall over indian landmass is highly correlated with north west and central india rainfall and anti correlated with east equatorial atlantic sst eeasst the positive eeasst anomaly intensifies the inter tropical convergence zone over atlantic and west equatorial africa which generates stationary wave meridionally as meridional transfer of energy is strong as the influence of background jet streams are minimal over north africa and europe the anomalous positive and negative gph are generated over sub tropics and extra tropics respectively due to the stationary wave this increases the climatological background steep pressure gradient between sub tropics and extra tropics consisting of anomalous negative gph field over north west nw europe and vice versa for negative eeasst anomaly the anomalous positive gph over nw europe acts as center of action for the propagation of a rossby wave train to nw india via europe consisting of anomalous high over nw of india this intensifies the tibetan high westward which reinforces the outbreak of monsoon activities over central and nw india

the low latitude monsoon climate during dansgaard oeschger cycles and heinrich events during the last 100 000 years dansgaard oeschger cycles d o cycles and heinrich events have been the dominant signal of past climate variability over greenland and the north atlantic the succession of stadials cold and interstadials warm associated with these cycles has been documented in records from the entire northern hemisphere south america new zealand antarctica the south atlantic and the southern ocean evidently climate forcing in the d o band affects both hemispheres the origin and cause of these teleconnected patterns is still unknown even if a large proportion of the cooling in europe and northern asia during heinrich events is a meteorological response to cold surface water in the north atlantic resulting from the surge of the laurentian and scandinavian ice sheets but this does not imply that the d o cycles are a priori caused by the collapse of these large icesheets a severe challenge to a primary origin from the northern ice sheet and north atlantic comes from the observation that warming in antarctica and the circumpolar current leads the north atlantic changes by some 1500 years charles et al 1996 blunier et al 1998 in the second part of the paper we investigate new deep sea records from the low latitude monsoon system mainly corroborating the result of schulz et al 1998 that the indian monsoon showed d o variability the abundance of eolian dust indicating continental humidity aridity in core 70kl from the arabian sea shows humid intervals which seem to correlate with temperature maxima in the antarctic vostok ice core apparently the low frequency sub milankovitch variability of the monsoon is associated with the southern hemisphere the d o scale component in the monsoonal climate on the other hand shows a succession of short humid intervals the sequence is most closely comparable to the greenland temperature record and to the stadial interstadial succession in the pacific santa barbara basin odp 893 in order to understand the global forcing of climate change in the d o band it appears necessary to quantify the phase relationships not only between d o cycles in the polar ice cores bender et al 1994 blunier et al 1998 steig et al 1998 but also between the low latitude pacific indian ocean and the high latitude records

eastward propagating mjo during boreal summer and indian monsoon droughts improved understanding of underlying mechanism responsible for indian summer monsoon ism droughts is important due to their profound socio economic impact over the region while some droughts are associated with external forcing such as the el nino and southern oscillation enso many ism droughts are not related to any known external forcing here we unravel a fundamental dynamic process responsible for droughts arising not only from external forcing but also those associated with internal dynamics we show that most ism droughts are associated with at least one very long break vlb breaks with duration of more than 10 days and that the processes responsible for vlbs may also be the mechanism responsible for ism droughts our analysis also reveals that all extended monsoon breaks whether co occurred with el nino or not are associated with an eastward propagating madden julian oscillation mjo in the equatorial indian ocean and western pacific extending to the dateline and westward propagating rossby waves between 10 and 25 n the divergent rossby wave associated with the dry phase of equatorial convection propagates westward towards indian land couple with the northward propagating dry phase and leads to the sustenance of breaks thus the propensity of eastward propagating mjo during boreal summer is largely the cause of monsoon droughts while short breaks are not accompanied by westerly wind events wwe over equatorial western pacific favorable for initiating air sea interaction all vlbs are accompanied by sustained wwe the wwes associated with all vlb during 1975 2005 initiate air sea interaction on intraseasonal time scale extend the warm pool eastward allowing the convectively coupled mjo to propagate further eastward and thereby sustaining the divergent circulation over india and the monsoon break the ocean atmosphere coupling on interannual time scale such as el nino can also produce vlb but not necessary

magnetic fabric as a vorticity gauge in syntectonically deformed granitic rocks a concept is presented to quantify vorticity using magnetic fabric data determined from anisotropy of magnetic susceptibility ams analysis in syntectonic granites whose emplacement is synchronous with tectonics of adjacent shear zones the latter is considered to define the direction of extensional flow apophysis ae it is suggested that the magnetic foliation traces the direction of maximum instantaneous stretching axis during the final stage of ductile deformation hence the angle between mean orientation of magnetic foliation and ae gives the kinematic vorticity number wn this concept is tested in two granites from india godhra granite western india and chakradharpur granitoid eastern india the analysis explains the kinematics of fabric development within the granites and also the evolution of structural elements in the surrounding rocks it is also suggested that in cases where granite margins get mylonitized synchronously with tectonic activity along adjacent shear zones the angle between mean magnetic foliation of the granite margin samples and the shear zone can help calculate wn the example of malanjkhand granite central india is discussed to highlight this using magnetic fabric a value of wn 0 98 is recorded for granite margin samples implying their deformation by dominantly simple shear oblique quartz foliation recorded on the microscale in the granite margin samples yields wn 0 94 which is similar to the value obtained using ams it is thus concluded that magnetic fabric provides a possibility to quantify vorticity in syntectonic granites in 2 dimension

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

has modulation of indian summer monsoon rainfall by sea surface temperature of the equatorial pacific ocean weakened in recent years in this paper the east west tropical walker circulation and its linear association with sea surface temperature sst of the nino 3 region and indian summer monsoon rainfall ismr have been investigated walker circulation reverse walker circulation is primarily forced by ssts of the equatorial pacific ocean in this study velocity potential field of 0 21 sigma level over the tropics was considered as proxy of the zonal tropical circulation walker circulation reverse walker circulation principal component analysis of the monsoon season tropical velocity potential data of 0 21 sigma level for the two periods 1951 1980 and 1981 2010 was done separately we find that earlier two different patterns of the velocity potential field forced by probably two distinct modes of el nino episodes were associated with the ismr these two el nino episodes respectively correspond to the strong el nino events where in warming was extended up to the date line primarily zonal and the moderate el nino events in which warming having north south extension was limited to the eastern pacific ocean only however in recent years only the first pattern of the velocity potential field induced by the strong el nino events warming extending up to the date line was correlated with the ismr further in the later period 1981 2010 velocity potential field at 0 21 sigma level over the tropical pacific and indian oceans which appeared to be primarily driven by sst anomalies of the equatorial pacific ocean in the first period was found to be significantly correlated with the extra tropical circulation anomalies also therefore modulation of the ismr through velocity potential field over the tropical indian and pacific oceans in the later period may have additional significant impact of the extra tropical circulation anomalies this might have led weak correlation between the ismr and ssts of the nino 3 region which is actually being observed in recent years

iron in east antarctic snow implications for atmospheric iron deposition and algal production in antarctic waters to evaluate the deposition and solubility of aerosol iron in the antarctic seasonal sea ice zone ssiz iron was measured in snow samples collected from three areas in the ssiz prydz bay dumont d urville sea and ross sea and one continental area princess elizabeth land of east antarctica concentrations of total dissolvable iron that soluble at ph 2 ranged from 20 2950 pg g 1 with the lowest concentrations measured in snow from the dumont d urville sea using estimates of snow accumulation rates we calculate atmospheric iron deposition fluxes of 0 017 0 11 mg m 2 yr 1 0 30 2 0 mol m 2 yr 1 which are generally lower than previously published estimates measurements of iron in filtered meltwaters of snow samples from prydz bay and princess elizabeth land suggest that 10 90 of the total atmospheric iron is readily soluble assuming our results to be broadly representative of atmospheric deposition over seasonally ice covered high nutrient antarctic waters we use our mean estimates of atmospheric iron deposition 1 1 mol m 2 yr 1 and solubility 32 to calculate that atmospheric iron potentially supports annual phytoplankton production of 1 1 1012 mole c in the antarctic ssiz which is less than 5 of the estimated total annual primary production in this ocean region

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

intracrystalline deformation and nanotectonic processes in magnetite from a naturally deformed rock abstract although experimental studies have shown dislocation creep to be an important deformation mechanism in magnetite at medium to high temperature evidence of intracrystalline deformation in magnetite remains to be established in natural tectonically deformed rocks in this study we investigate intracrystalline deformation features and nanostructures in elongated magnetite from a naturally deformed rock mylonitized mica schist deformed in a large scale shear zone of the seve nappe swedish caledonides the magnetite grains have very high aspect ratios up to 10 40 that result in very high degree of magnetic anisotropy in the rock we show low and high angle grain boundaries lagb and hagb in magnetite using a combination of electron backscatter diffraction and high resolution transmission electron microscopy hrtem analysis hrtem studies on lamellae excavated perpendicular to the lagb and hagb reveal translational and rotational moire fringes respectively dislocations slip bands stacking faults twins and recrystallized domains are observed in the vicinity of the grain boundaries thus providing unequivocal evidence of intracrystalline deformation of magnetite our study also reveals the presence of biotite inclusions intergrown epitaxially with magnetite that show no evidence of lattice defects thus suggesting that the intracrystalline deformation of magnetite took place under wet conditions the movement at the grain boundaries is interpreted as a response to regional tectonics with a top to nw transport direction it is established that at the nanoscale the lagb and hagb were favourably oriented to accommodate strain dominantly by translation and rotation respectively thus the nanotectonic processes are consistent with the regional tectonic reference frame the importance of evaluating ductile behaviour of magnetite from deformed polymineralic rocks in petrofabric analysis and modeling the relation between strain and rock magnetic anisotropy is discussed

rapid climate transitions in a coupled ocean atmosphere model recent geochemical data1 2 have challenged the view that rapid climate fluctuations in the north atlantic at the end of the last glacial were caused by the thermohaline circulation of the ocean being switched on or off instead these data suggest that the circulation pattern must have switched between a warm deep mode and a cold shallow mode probably associated with different sites of deep convection3 here i present simulations with a three dimensional ocean model coupled to an idealized atmosphere which show this kind of transition the mechanism for the transition is a rearrangement of convection in the north atlantic triggered by a brief freshwater pulse this results in a drop in sea surface temperature in the north atlantic by up to 5 c within less than 10 years the rate of north atlantic deep water nadw forma tion is the same in the cold climate as in the warm climate but nadw sinks to intermediate depths only while antarctic bottom water pushes north to fill the entire abyssal atlantic

kinematic analysis using ams data from a deformed granitoid abstract this study highlights the usefulness of anisotropy of magnetic susceptibility data from a deformed granitoid in deciphering its kinematic evolution vis a vis shear zone data are presented from the chakradharpur granitoid ckpg that lies to the north of the northerly dipping ene wsw striking singhbhum shear zone ssz eastern india whilst the foliation recorded in the field in some parts of the granitoid is parallel to the ssz the magnetic foliation is n54 e 90 mean orientation it is suggested that the magnetic fabric provides a window into an evolutionary stage prior to the final shearing thrusting event the evidence of which is preserved on the mesoscopic scale it is envisaged that during the initial stages of deformation there was simple shear along the evolving ssz that resulted in sinistral strike slip movement the vorticity axis at this stage was steeply plunging and sense of rotation was anticlockwise space was generated in a direction n25 e perpendicular to maximum instantaneous stretching axis into which ckpg emplaced synchronously with regional deformation and evolving ssz with continued deformation there was thrusting along the ssz the vorticity axis flipped to a sub horizontal orientation thus leading to the development of down dip stretching lineations and sheath folds within the ssz however at the same time the vorticity axis responsible for fabric evolution within the syntectonically crystallizing cooling ckpg was steeply plunging with clockwise rotation the magnetic foliation mean orientation n54 e 90 developed during the final stage of syntectonic crystallization however deformation in the region and thrusting along the ssz continued even after the ckpg had fully crystallized and solidified which led to the development of the ene wsw striking mesoscopic foliation that is parallel with the ssz we propose that the angle between the magnetic foliation and the ssz foliation recorded in the field enables to decipher the kinematic vorticity number of flow responsible for fabric evolution of the ckpg it is concluded that transpression was an important mechanism and during regional deformation whilst the ssz developed structures by dominantly simple shear the ckpg underwent dominantly pure shear

reconstruction of deformation and flow parameters from deformed vein sets abstract in any homogeneously deformed material sets of material lines with a similar stretch history occupy sectors with a scale and orientation that depend on finite strain area change rate and vorticity of the parent flow if the size and shape of these material line sectors are known they can be used to determine the sense of shear and to calculate deformation and flow parameters even if actual stretches along material lines are unknown in rocks which have undergone near homogeneous deformation on a large scale the orientation of sets of boudinaged folded and folded boudinaged or boudinaged folded veins can be used for such calculations a general theoretical background to the problem is presented and a mohr circle construction to carry out the deformation and flow analysis is introduced among other statements the theory predicts that shortened or folded boudins must develop in non coaxial monophase deformation with considerable area change in the plane of observation or in polyphase deformation

a 2 200 years periodicity in the asian monsoon system we have carried out a high resolution study of fluctuations in upwelling intensity along the oman margin western arabian sea through the last 19 130 years based on several marine microfossil indices of upwelling we document a periodicity of 2 200 years in the upwelling indices which would be governed by the south west sw monsoon with such a periodicity our data further demonstrate greater amplitude in the variability of the sw monsoon during the holocene than during the last glacial period our reported 2 200 years periodicity has two implications 1 oceanic circulation changes partly influence monsoon strength at sub milankovitch cycles 2 previously documented 2 300 years periodicity in atmospheric 14c might be induced by oceanic circulation changes

heavy metals in the near surface aerosol over the atlantic ocean from 60 south to 54 north the participate heavy metal concentrations of cr fe ni cu zn cd tl and pb were determined in the atmosphere over the atlantic ocean from 60 s to 54 n with the definitive method of isotope dilution mass spectrometry the samples were collected during an expedition with the german polar research ship polarstern the sampling and the sample treatment were carried out under strict contamination control fe was used as a reference element for the influence of crustal material calculating the corresponding enrichment factors ef fe for the other metal traces the heavy metal concentrations varied up to more than 3 orders of magnitude which represents the different natural and anthropogenic sources and influences on the composition of the marine aerosol tl showed the lowest abundance of all heavy metals with concentrations of less than 20 pg m 3 for all samples except those from the area around the english channel the concentration ranges for the other elements were cr 0 08 9 ng m 3 fe 2 6 7500 ng m 3 ni 0 05 10 ng m 3 cu 0 02 20 ng m 3 zn 0 09 450 ng m 3 cd 0 003 3 5 ng m 3 and pb 0 05 200 ng m 3 the lowest element concentrations were usually measured in the remote areas of the south atlantic whereas the highest ones were detected around the english channel however at some sampling sites over the north atlantic very low cd and pb values in the range of 6 20 pg m 3 and 0 5 ng m 3 respectively were determined which could be attributed to arctic air masses by their corresponding backward trajectories due to high fe concentrations a substantial influence of crustal material was observed in the atmosphere southeast of the south american continent in the south atlantic area of the southeast trades and over the north atlantic west of north africa ef fe values for the most part less than 10 for cr and ni and less than 50 for cu indicate that the influence of crustal material for these metals is much higher than for zn cd and pb where ef fe values between 500 and 5000 had often been determined this is due to anthropogenic and biological influences the anthropogenic influence was clearly identified e g over the south atlantic near the la plata area in the english channel and over the north sea whereas a substantial biological influence could be observed over the south atlantic in the area of the southeast trades

a high resolution record of late quaternary upwelling along the oman margin arabian sea based on planktonic foraminifera planktonic foraminiferal abundances fluxes test sizes and coiling properties are influenced in various ways by the southwest monsoon winds and associated upwelling in the western arabian sea to determine the short term changes in the southwest monsoon we have carried out a high resolution time series analysis of three upwelling indices total flux of planktonic foraminiferal tests and flux and relative abundance of the planktonic foraminiferal species globigerina bulloides from ocean drilling program odp site 723a oman margin western arabian sea spanning the last 19 kyr in addition we have determined the relationships between upwelling intensity and the relative abundance fluxes and shell concentrations of various planktonic foraminiferal species upwelling indices suggest that from 19 to 16 ka 22 to 18 2 cal kyr b p the sw monsoon was relatively strong compared to the period 15 8 to 12 5 ka 17 8 to 13 8 cal kyr b p the intensification of the sw monsoon took place at 12 ka 13 1 cal kyr b p and reached a peak between 10 and 5 ka 10 6 and 4 8 cal kyr b p the high resolution data further demonstrate that the sw monsoon has started weakening from 5 ka 4 8 cal kyr b p and the weakest phase was in place at 3 5 ka 3 cal kyr b p which coincides with evidence of an arid climate in western tibet fluxes and shell concentrations of many of the planktonic foraminiferal species increased between 12 and 5 ka in response to the intensification of the sw monsoon winds after the last glacial period globigerina bulloides shows a fivefold to tenfold increase in flux during this period of intense upwelling the other species whose fluxes are influenced by this upwelling change are in order from strongest to weakest response globigerinita glutinata globigerinoides ruber neogloboquadrina dutertrei globigerinella aequilateralis globigerina falconensis and globigerinoides sacculifer the relative abundances of g bulloides and g ruber increased during intense upwelling whereas the relative abundances of g glutinata n dutertrei g falconensis and g sacculifer did not increase during this period which might be due to differences in the productivity of various species in relation to upwelling change therefore the fluxes and shell concentrations provide better and more reliable information about the changes in the monsoon system in the arabian sea than relative abundance data

dynamics of breaks in the indian summer monsoon abstract in this paper the authors present results of diagnostic analysis of observations and complementary experiments with a simple numerical model that enable them to synthesize the morphology and dynamics of breaks in the indian summer monsoon ism almost one week ahead of the onset of a break spell over india a monotonically decreasing trend in convective activity is found to occur over the bay of bengal in response to a steady eastward spreading of dry convectively stable anomalies from the equatorial indian ocean a major intensification of the convectively stable anomalies over the bay of bengal is seen about 2 3 days prior to commencement of a monsoon break both observations and modeling experiments reveal that rapid northwest propagating rossby waves are triggered in response to such a large strengthening of the convectively stable anomalies it is shown that an abrupt movement of anomalous rossby waves from the bay of bengal into northwest and central india marks the initiation of a break

modulation and amplification of climatic changes in the northern hemisphere by the indian summer monsoon during the past 80 k y high frequency suborbital variations dansgaard oeschger cycles characterize the climatic history of the northern hemisphere as observed in greenland ice cores deep sea sediments of the north atlantic the californian borderland the arabian sea the south china sea and the chinese loess area paleoceanographic data from core kl126 from the bay of bengal in combination with data from the other asian monsoonal areas indicate that the feedback processes involving snow and dust of the tibetan plateau vary the summer monsoon capacity to transport moisture into central south asia and into the atmosphere we postulate that the summer monsoon initiates amplifies and terminates these cycles in the northern hemisphere

inter annual relationship between atlantic sea surface temperature anomalies and indian summer monsoon in this study the simultaneous inter annual relationships between sst anomalies over the northwest atlantic ocean and southwest monsoon rainfall over the monsoon core region have been examined using monthly sst and atmospheric data for the period 1951 2005 statistical analyses reveal significant inter annual simultaneous relationship between the sst anomalies over north atlantic and rainfall over the monsoon core region but with significant epochal variations the relationship has become stronger after mid 1970s when the el nino indian monsoon relationship has weakened positive sst anomalies over the north atlantic ocean shift the north atlantic jet northwards and the associated circulation changes in the upper troposphere influence indian monsoon through the circumglobal teleconnection across central asia the present study thus highlights the important role of north atlantic ocean as an important source of inter annual variability of the indian summer monsoon

natural concentrations of lead in ancient arctic and antarctic ice concentrations of pb and k were determined in a series of veneer layers chiseled in sequence from the outside toward the center of each of the five 1500 5500yr old ice core sections that had been drilled in greenland and antarctic ice they were analogs of very old ice samples analyzed earlier by herronet al 1977 and craginet al 1975 who reported high concentrations of pb in them lead contamination existing at exterior concentrations of about 10 6 ng kg ice had intruded to the centers of the cores establishing interior values of at least 1 4 ng kg ice in three electromechanically drilled camp century core sections taken from fluid filled drill holes corresponding pb concentration changes were 3 10 4 ng kg ice to 1 2 ng kg ice in two thermally drilled new byrd station core sections taken from non fluid filled drill holes contamination made the lowest center concentrations serve only as upper limits to the original concentrations of pb in the ice potassium concentrations decreased from exterior values of about 5 10 5 ng kg ice to an interior value of 2 10 3 ng kg ice in the camp century core sections and from 8 10 4 ng kg ice to 9 10 2 ng kg ice in new byrd station core sections potassium contamination effects were not large within the central portions of the cores these data verify earlier findings by murozumiet al 1969 and extend to a broader geographical significance the general validity of their observation of a 300 fold increase of pb concentrations in the greenland ice sheet during the past 3000 yr our findings refute claims by herronet al 1977 and craguinet al 1975 that 100 fold excesses of natural pb exist in 800 yr old greenland ice above levels contributed by silicate dusts our new data also show that average pb concentrations of 26 ng pb kg ice claimed by boutron and lorius 1979 to be natural and present for 60 yr in snow strata in antarctica did not exist in old antarctic ice and that pb concentrations have increased at least 10 fold in that ice during the past century virtually all of the present day 300 fold excess of pb above natural levels in greenland ice can be shown to be caused by industrial pb emissions to the atmosphere on the basis of the following factors 1 the historic increase of pb in snow strata coincides with the historic increase of industrial pb production and atmospheric emissions 2 mass inventories of industrial emissions can account for the excess pb in polar snow 3 new quantitative measurements of pb emissions from volcanic plumes by buat menard and arnold 1978 pattersonet al 1981 and buat menardet al 1981 and from sea spray by ng and patterson 1981 and settle and patterson 1981 show that these natural sources cannot account for 99 of the excess pb above contributions by silicate dusts observed today in the atmosphere and 4 the historic increase of pb in snow strata is paralleled by analogous increases of excess pb shown by isotopic tracers to be industrial in water laid sediments in a remote continental region shirahataet al 1980 it is now known however that snows display about a 10 fold greater excess of industrial pb above crustal silicate concentrations than exists in the air above the snows

granite emplacement and its relation with regional deformation in the aravalli mountain belt india inferences from magnetic fabric abstract this contribution presents field microstructural and anisotropy of magnetic susceptibility ams data from the godhra granite a ca 1 ga pluton at the southern margin of the aravalli mountain belt western india that lies near the central indian tectonic zone citz the northern and southern margins of the granite are high strain zones with north dipping e w striking foliations and nw plunging stretching lineations the presence of preferentially oriented feldspars suggests that the granite was subjected to magmatic deformation during its emplacement high temperature solid state deformation fabrics are recorded from microstructural studies which imply that the granite is deformed ams data show magnetic foliations and magnetic lineations in the granite with orientations similar to the field data the magnetic foliation in the granite is parallel to the d 3 foliation in the gneissic host rock both the stretching lineations and the magnetic lineations at the granite margin high strain zones are parallel with the axes of d 3 reclined folds in the gneiss therefore the emplacement of the godhra granite is inferred to have taken place syntectonically while the gneiss was undergoing the d 3 phase of deformation the orientation and character of these lineations and the vergence of the d 3 folds imply oblique simple shear which is inferred to have controlled the emplacement of the granite the magnetic fabric data are compared with the regional structural trends of the metasedimentary rocks of the southern aravalli region and the available geochronological data from rocks of the southern aravalli region are summarised based on this information it is suggested that the emplacement of godhra granite deformation of the southern parts of aravalli mountain belt and tectonothermal events along the citz and rodinia supercontinent assembly were related events

winter surface pressure anomalies over eurasia and indian summer monsoon in this study the spatial relationships between the monthly mean sea level pressure mslp anomalies and indian summer monsoon rainfall ismr have been examined using the gridded mslp data gmslp2 for 46 years 1949 1994 winter mslp anomalies over nw europe south europe are negatively positively correlated with ismr during the strong deficient monsoon years there is enhanced weakened poleward pressure gradient over eurasia the europe pressure gradient index which is an indicator of the winter poleward pressure gradient is significantly and positively correlated with ismr this relationship also suggests a link between the north atlantic oscillation and ismr on inter annual time scale the winter pressure gradient over eurasia has physical linkage with indian summer monsoon rainfall through winter snow cover anomalies and springtime mid latitude activities like upper tropospheric blocking highs and stationary wave anomalies

high resolution simulation of the south asian monsoon using a variable resolution global climate model this study examines the feasibility of using a variable resolution global general circulation model gcm with telescopic zooming and enhanced resolution 35 km over south asia to better understand regional aspects of the south asian monsoon rainfall distribution and the interactions between monsoon circulation and precipitation for this purpose two sets of ten member realizations are produced with and without zooming using the lmdz laboratoire meteorologie dynamique and z stands for zoom gcm the simulations without zoom correspond to a uniform 1 1 grid with the same total number of grid points as in the zoom version so the grid of the zoomed simulations is finer inside the region of interest but coarser outside the use of these finer and coarser resolution ensemble members allows us to examine the impact of resolution on the overall quality of the simulated regional monsoon fields it is found that the monsoon simulation with high resolution zooming greatly improves the representation of the southwesterly monsoon flow and the heavy precipitation along the narrow orography of the western ghats the northeastern mountain slopes and northern bay of bengal bob a realistic monsoon trough mt is also noticed in the zoomed simulation together with remarkable improvements in representing the associated precipitation and circulation features as well as the large scale organization of meso scale convective systems over the mt region additionally a more reasonable simulation of the monsoon synoptic disturbances lows and disturbances along the mt is noted in the high resolution zoomed simulation on the other hand the no zoom version has limitations in capturing the depressions and their movement so that the mt zone is relatively dry in this case overall the results from this work demonstrate the usefulness of the high resolution variable resolution lmdz model in realistically capturing the interactions among the monsoon large scale dynamics the synoptic systems and the meso scale convective systems which are essential elements of the south asian monsoon system

isotopic identification of natural vs anthropogenic sources of pb in laramie basin groundwaters wyoming usa water well samples precipitation and leachates of aquifer rock samples from the laramie basin wyoming were analyzed to test the suitability of pb isotopes for tracing hydrologic processes in a basin where sr isotopes had proven effective leachable pb from host rocks to aquifers in this basin have isotopically distinct compositions and isotopic tracing would be effective in differentiating natural sources of pb however in almost all cases this natural signal is apparently swamped by anthropogenic pb sources in drilled water wells the isotopic compositions of these samples cannot be produced by any combination of pb in precipitation and leached pb from the aquifers alone but are consistent with mixtures of anthropogenic pb thorogenic 208pb vs uranogenic 206pb 207pb pb was especially useful for discriminating natural from anthropogenic sources for these samples it is strongly recommended that all four pb isotopes be reported in hydrologic and environmental studies that employ this approach

tectonic evolution of the southern part of aravalli mountain belt and its environs possible causes and time constraints abstract structural studies on proterozoic rocks belonging to the lunavada group southern aravalli mountain belt samb india have shown that they underwent three episodes of deformation which have led to the formation of various regional scale interference patterns whilst the northern parts of the samb underwent brittle ductile deformation the southern portion underwent more ductile deformation on the basis of structural as well as metamorphic studies it has been established earlier that the region was subjected to uplift orogenesis during its evolutionary history in the present paper an attempt is made to visualize the possible causes that led to deformation of the samb the structural geology of which has been established by the authors and to constraint the timing of these events on the basis of already available geochronological data a working hypothesis is proposed according to which it is suggested that deformation of the samb is a result of the accretion of the three protocontinents viz aravalli dharwar and singhbhum during the mesoproterozoic it is envisaged that the accretion of aravalli and singhbhum protocontinents occurred between 1600 and 1400 ma along the ne sw trending son suture and this event led to development of ne sw trending structures in the samb suturing of aravalli and dharwar protocontinents between 1400 and 935 ma along the e w narmada suture was responsible for the e w to nw se trending d 3 structures of the samb it is postulated that the satpura orogeny which resulted in deformation of rocks in satpura mountain range lying to the south of narmada suture was coeval with the accretion of aravalli and dharwar protocontinents

relative levels of natural and anthropogenic lead in recent antarctic snow concentrations of lead have been measured by ultraclean isotope dilution mass spectrometry in large blocks of surface snow collected along a 433 km coast interior axis in east antarctica and near the geographic south pole slight contamination existed on the outside of the blocks but concentration profiles from their exteriors to their interiors indicate that lead concentrations in the innermost parts of the blocks do represent the original concentrations in present day antarctic snow geographical variations of lead concentrations appear to be mainly due to local emissions from dumont d urville and amundsen scott stations the globally significant lead concentration in present day antarctic snow is found to be about 2 pg pb g the corresponding value in antarctic air is estimated to be about 7 pg pb m 3 stp which is approximately fivefold larger than total natural lead contributed by soil dusts volcanoes and sea salts a tentative temporal curve of globally significant lead concentrations in antarctic ice and snow for the last 13 000 years is given it shows concentrations of about 0 4 pg pb g throughout most of the holocene with recent fivefold increases to about 2 pg pb g today the general picture is then that four fifths of total lead in the antarctic troposphere today is anthropogenic

amplitude variations of 1470 year climate oscillations during the last 100 000 years linked to fluctuations of continental ice mass we describe amplitude variations of a 1470 year y signal in the oxygen isotope record from the gisp2 ice core as a function of continental ice mass as recorded in sea level variations the 1470 y signal is closely tied to dansgaard oeschger interstadial events which perturbed the climate system on a global scale large amplitude 1470 y oscillations occur only if continental ice mass exceeds a threshold level equivalent to sea level at approximately 45 m and are tied to times of change in ice mass minima of the 1470 y signal in the greenland ice are associated with short time intervals of relatively stable phases of sea level and with reduced climate variability in the entire periodicity range between approximately 550 5000 y

intraseasonal teleconnection between the summer eurasian wave train and the indian monsoon this study investigated the most recurrent coupled pattern of intraseasonal variability between midlatitude circulation and the indian summer monsoon ism the leading singular vector decomposition svd pattern reveals a significant coupled intraseasonal variation between a rossby wave train across the eurasian continent and the summer monsoon convection in northwestern india and pakistan hereafter referred to as nism the wave train associated with an active phase of nism rainfall displays two high pressure anomalies one located over central asia and the other over northeastern asia they are accompanied by increased rainfall over the western siberia plain and northern china and decreased rainfall over the eastern mediterranean sea and southern japan the circulation of the wave train shows a barotropic structure everywhere except the anomalous central asian high located to the northwest of india where a heat induced baroclinic circulation structure dominates the time lagged svd analysis shows that the midlatitude wave train originates from the northeastern atlantic and traverses europe to central asia the wave train enhances the upper level high pressure and reinforces the convection over the nism region meanwhile it propagates farther toward east asia along the waveguide provided by the westerly jet after an outbreak of nism convection the anomalous central asian high retreats westward composite analysis suggests a coupling between the central asian high and the convective fluctuation in the nism the significance of the midlatitude ism interaction is also revealed by the close resemblance between the individual empirical orthogonal functions and the coupled svd modes of the midlatitude circulation and the ism it is hypothesized that the eastward and southward propagation of the wave train originating from the northeastern atlantic contributes to the intraseasonal variability in the nism by changing the intensity of the monsoonal easterly vertical shear and its associated moist dynamic instability on the other hand the rainfall variations over the nism reinforce the variations of the central asian high through the monsoon desert mechanism thus reenergizing the downstream propagation of the wave train the coupling between the eurasian wave train and nism may be instrumental for understanding their interaction and can provide a way to predict the intraseasonal variations of the indian summer monsoon and east asian summer monsoon

deciphering relative timing of fabric development in granitoids with similar absolute ages based on ams study dharwar craton south india abstract anisotropy of magnetic susceptibility ams data are presented from the koppal granitoid dharwar craton south india that has u pb zircon age of 2528 9 ma the magnetic fabric is oriented in nne ssw direction this is parallel to the planar structures that developed during regional d 3 deformation but oblique to the nnw sse oriented magnetic foliation as well as field foliation d 1 d 2 deformation recorded in the country rock peninsular gneiss variation in the intensity of fabric within the granitoid is mapped it is inferred that the emplacement of koppal granitoid took place by ballooning and fabric development within the pluton was syntectonic with regional d 3 these results are compared with the time relationship between emplacement fabric development and regional deformation reported from the mulgund granite 2555 6 ma u pb zircon which is also located in the dharwar craton and is equivalent to the koppal granitoid in age this granite is known to have emplaced syntectonically with regional d 1 d 2 deformation and is thus not related to the same deformation event as the koppal granitoid despite their similar absolute ages it is argued that in the study area d 3 is 2537 ma while d 1 d 2 is 2549 ma in age thus this study highlights the use of ams in a deciphering the relative timing of regional deformation and emplacement of granitoids of equivalent age and b constraining the timing of regional superposed deformation events

magnetic fabrics and petrofabrics their orientation distributions and anisotropies abstract magnetic fabric and other petrofabric anisotropies may be described by second rank tensors represented by ellipsoids for a homogeneous petrofabric that is adequately sampled a stereoplot of the orientation distribution of the tensors principal axes maximum intermediate and minimum should show three orthogonal concentrations the concentrations form some combination of shapes from circular clusters through partial girdles to full girdles the concentrations elliptical eccentricities are constrained by the symmetry of the sample orientation distribution i e l l s l s etc as well as the individual sample anisotropies the mean orientations of principal axes must be orthogonal just as with individual sample tensors this requires tensor statistics for their calculation jelinek 1978 furthermore elliptical confidence cones for the means should parallel principal planes preserving overall orthorhombic symmetry however in practice sub orthorhombic symmetry may arise from unrepresentative sampling but it may also be a useful indicator of multiple or heterogeneous petrofabrics in the case of magnetic fabrics the wide range in average susceptibility values and variation in magnetic mineralogy permit small numbers of high susceptibility samples to deflect the orientation of the tensor mean away from the majority of samples normalizing the samples by their bulk susceptibility overcomes this but the orientation of high susceptibility outliers may signify an event or subfabric of importance that we should not discard therefore stereoplots of both normalized and non normalized orientation distributions should be compared preferably also identifying the outliers it is important to distinguish the shape of the orientation distribution ellipsoid from the shape of the individual magnetic fabric ellipsoids the qualitative l s nomenclature is best replaced by tj where tj 1 oblate tj 1 prolate jelinek 1981 invariably the orientation distribution is described by an ellipsoid whose shape is more spherical than that of the individual sample anisotropy ellipsoids because the latter have scattered orientations furthermore the shape of the orientation distribution ellipsoid need bear no relation to the shape of individual sample ellipsoid anisotropies the concepts are illustrated with 1119 measurements of anisotropy of magnetic susceptibility ams from seven areas and with 188 measurements of anisotropy of anhysteretic remanence aarm from two areas

noncoaxial k feldspar and ams subfabrics in the land s end granite cornwall evidence of magmatic fabric decoupling during late deformation and matrix crystallization 1 a comparative study of the anisotropy of magnetic susceptibility ams and k feldspar phenocryst fabrics in the land s end granite demonstrates that the ams fabric predominantly reflects late magmatic deformation tensor analysis of the k feldspar fabric shows a complex pattern characterized by meter scale variations in orientation symmetry and intensity mainly related to heterogeneous flow of the phenocryst rich magma during emplacement in contrast the ams fabric is predominantly homogenous subhorizontal and oblate and is stable at the pluton scale quantitative microstructural analysis suggests that the ams fabric is controlled by deformation of the partially crystallized matrix resulting from the combined effects of late internal adjustment within the pluton and regional deformation a general model of fabric development associated with a vertical pure shear overprint on a variable vertical fabric is evaluated by numerical modeling the study demonstrates how the memory of different fabric elements may be dependent upon their grain size crystallization sequence and recorded previous strain

orbital insolation forcing of the indian monsoon a motor for global climate changes abstract both modern and ancient indian summer monsoons are driven by transequatorial pressure differences directly coupled with the insolation difference between the northern and southern subtropical hemispheres a high resolution record of upwelling and dust flux from the western arabian sea resembles an insolation based indian summer monsoon index this index and the observed monsoonal climate variations share major elements on the orbital obliquity and precessional band with the specmap marine oxygen isotope record representing global ice volume the long term evolution of the index mirrors almost exactly the insolation changes at 65 n showing that the forcing of low latitude climate variability has a structure similar to that of the insolation forcing in the high northern latitudes moreover insolation forcing in the low latitudes directly controls atmospheric processes in the african indian and asian monsoon being responsible for a huge amount of transequatorial water vapour and therefore latent heat transport millennial scale variability of the monsoonal climate is concentrated at periodicities near 1100 1450 1750 and 2300 years these cycles are not strictly periodic but occur in bands with specific activity phases and amplitude increases during warm stages and interstadials for the 1100 and 1750 yr cycles whereas the 1450 yr cycle dominates the cold intervals