late paleozoic closure of the ob zaisan ocean along the irtysh shear zone nw china implications for arc amalgamation and oroclinal bending in the central asian orogenic belt the largest accretionary orogen in the world the central asian orogenic belt has evolved through the assembly of various oceanic and continental blocks understanding the processes associated with the development of this orogenic belt relies on precise recognition of the boundaries between various terranes one such major suture zone which records the collisional history of the siberian marginal arc system chinese altai with intra oceanic arc systems east west junggar is the irtysh shear zone in nw china the spatial continuity and the tectonic nature of this shear zone are still poorly understood but its development has supposedly made a significant impact on the architecture of the western central asian orogenic belt and the formation of the kazakhstan orocline here we provide new insight into the evolution of this shear zone based on detrital zircon ages hf isotope composition structural data and ar ar age constraints on the timing of deformation our results show a major discrepancy in detrital zircon populations and hf model ages across the southern chinese altai and the northern east west junggar thus allowing us to map the exact location of the tectonic boundary detrital zircon data constrain the initial closure of the ob zaisan ocean to the late carboniferous 323 ma and new structural and ar ar geochronological data shed light on the subsequent collisional processes we propose that the collisional zone between the chinese altai and the east west junggar was initially subjected to crustal thickening at ca 323 295 ma followed by orogen parallel extension ca 295 ma and transpressional deformation ca 286 253 ma the closure of the ob zaisan ocean in nw china postdates the initial phase of oroclinal bending in the western central asian orogenic belt thus indicating that oroclinal bending initiated during subduction based on our new constraints and other available geological data we suggest that the early stage of oroclinal bending was likely driven by slab rollback

polarimetric signatures of sea ice 1 theoretical model physical structural and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice physical properties of sea ice constituents such as ice brine air and salt are presented in terms of their effects on electromagnetic wave interactions sea ice structure and geometry of scatterers are related to wave propagation attenuation and scattering temperature and salinity which are determining factors for the thermodynamic phase distribution in sea ice are consistently used to derive both effective permittivities and polarimetric scattering coefficients polarimetric signatures of sea ice depend on crystal sizes and brine volumes which are affected by ice growth rates desalination by brine expulsion drainage or other mechanisms modifies wave penetration and scattering sea ice signatures are further complicated by surface conditions such as rough interfaces hummocks snow cover brine skim or slush layer based on the same set of geophysical parameters characterizing sea ice a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies for interpretation of sea ice polarimetric signatures

first early permian paleomagnetic pole for the yili block and its implications for late paleozoic postorogenic kinematic evolution of the sw central asian orogenic belt we conducted a paleomagnetic study on the early permian volcanic and sedimentary rocks and the neoproterozoic mafic dikes in the yili block nw china magnetite and hematite were proven to be the principal magnetic remanence carriers demagnetizations revealed stable characteristic remanence magnetizations with a sole reversed magnetic polarity the magnetic remanence of only the early permian strata turned out to be primary based on positive fold tests meanwhile the magnetic remanence age of the mafic dikes is ambiguous accordingly the first early permian paleomagnetic pole for the yili block is calculated at 81 5 n 256 5 e n 11 and a95 10 9 comparisons of this new pole with published ones from the yili tarim and south junggar blocks provide new quantitative constraints on late paleozoic kinematic evolution of the sw central asian orogenic belt 1 between the yili and tarim blocks significant relative movement took place along major strike slip faults during the late carboniferous to early permian 580 290 km and the early to late permian 585 340 km and the displacement rate increased from the late carboniferous to early permian 19 3 9 7 mm yr to the early to late permian 29 3 17 0 mm yr 2 a significant relative rotation of 28 3 18 3 in the late permian and a lateral displacement of 630 295 km after the late permian occurred between the yili and south junggar blocks the significant strike slip movements played an important role in the formation of the central asian orogenic belt and should be considered with great attention in tectonic and paleogeographic reconstructions

tectonic entities connection between west junggar nw china and east kazakhstan abstract west junggar nw china and east kazakhstan are situated in the southwest of the central asian orogenic belt caob tectonic entities in the two areas share the same tectonic evolution history and make up the famous horseshoe shaped orocline in central asia this paper presents a newly compiled cross border tectonic sketch map of west junggar and east kazakhstan and proposes the extension of the chingiz tarbagatai belt and the north balkhash west junggar belt the chingiz tarbagatai belt in east kazakhstan consists mainly of middle late ordovician differentiated volcanic rocks pyroclastic sediments and flysch while in the tarbagatai mountain in china tarbagatai kujibai ophiolite is newly found with zircon gabbro age of 478 3 ma and the ordovician flysch metamorphosed to a greenschist facies is distinguished from devonian carboniferous rock associations therefore the early paleozoic chingiz tarbagatai belt of east kazakhstan evidently extends to the northern part of west junggar along the tarbagatai orogenic belt the north balkhash west junggar belt lying south to the chingiz tarbagatai belt is separated by the ew trending baiyanghe heshituoluogai depression in west junggar early ordovician early silurian ophiolitic fragments and related pyroclastic sediments are widely exposed in tekturmas north balkhash and agadyr of east kazashtan similarly early paleozoic ophiolites have also been verified in tangbale mayile baerluke darbut and karamay of west junggar in recent years therefore nearly all ophiolites in west junggar and east kazakhstan are proved to have formed in early paleozoic which suggests that the evolution of the paleo ocean in the two areas reached its peak in the early paleozoic based on the ages of the tangbale karamay and hongguleleng ophiolites an early paleozoic continental accretionary belt extending from tangbale to hongguleleng is determined at the nw margin of the junggar basin for the first time according to spatiotemporal comparison ophiolites exposed in west junggar and east kazakhstan might originate from the same paleo ocean tectonic region and then the north balkhash in east kazakhstan and the west junggar were offset for a long distance with respect to each other by the major junggar dextral fault because of the large scale accretion of continental crust before silurian the late paleozoic ocean in west junggar and east kazakhstan became smaller with residual nature and extensive arc basin trench systems might be absent during the closure of this residual ocean

heat flux through sea ice in the western weddell sea convective and conductive transfer processes the heat flux through the snow and sea ice cover and at the ice ocean interface were calculated at five sites in the western weddell sea during autumn and early winter 1992 the ocean heat flux averaged 7 2 w m2 from late february to early june and average ice air heat flux in the second year floes depended on the depth of the snow cover and ranged from 9 to 17 0 8 w m2 in late february three of the five sites had an ice surface which was depressed below sea level resulting at two of the sites in a partially flooded snow cover and a slush layer at the snow ice interface as this slush layer froze to form snow ice the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower salinity nutrient rich seawater from the ocean upper layer we estimate that about half of the second year ice in the region was covered with this slush layer early in the winter as the slush layer froze over a 2 to 3 week period the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover on an area wide basis approximately 10 cm of snow ice growth occurred within second year pack ice primarily during a 2 to 3 week period in february and march this ice growth near the surface of the ice provides a salt flux to the upper ocean equivalent to 5 cm of ice growth despite the thick about 1 m ice cover in addition to the ice growth in the small area less than 5 open water regions

paleomagnetic constraints on the paleogeography and oroclinal bending of the devonian volcanic arc in kazakhstan abstract a prominent feature of the central part of the ural mongol orogenic belt is a series of concentric horse shoe shaped volcanic arcs with the youngest arc on the inside this structure was long suspected to be an orocline but unequivocal evidence for this was lacking mainly because paleomagnetic results of suitable age from this area remained sparse but also because their interpretation was not straightforward due to a long history of deformations associated with the protracted late paleozoic assembly of asia our paleomagnetic study of middle devonian basaltic and andesitic flows in southeastern kazakhstan revealed two main components of magnetization the primary nature of a high temperature magnetization tilt corrected dec 286 5 inc 46 4 95 7 8 k 29 2 n 13 sites is supported by the presence of antipodal directions and a baked contact test we also isolated a post folding overprint with an in situ mean direction dec 134 9 inc 43 0 95 4 9 k 71 6 n 13 sites the age of this overprint can be estimated as early permian with a high degree of confidence the declination of the overprint is seen to be deflected counter clockwise by 100 6 relative to the 290 ma reference direction indicating that the studied locality similar to many other localities in the region was affected by late orogenic rotations we use the overprint s deflection to correct the declination of the primary devonian magnetization for these late orogenic block rotations declinations from other silurian and devonian paleomagnetic results in the subduction related devonian volcanic arc of kazakhstan have been corrected for such rotations wherever the latter are reasonably well documented using corrected declinations as passive markers we restored the trend of the volcanic belt to its devonian configuration our analysis indicates that the presently curved belt was nearly straight and nw se trending this 1500 km long volcanic belt characterized the northeastern margin of a landmass in today s central kazakhstan where subduction occurred towards the southwest oroclinal bending of this arc took place in the interval between the middle devonian and the late permian

isentropic analysis of polar cold airmass streams in the northern hemispheric winter abstractan analysis method is proposed for polar cold airmass streams from generation to disappearance it designates a threshold potential temperature t at around the turning point of the extratropical direct etd meridional circulation from downward to equatorward in the mass weighted isentropic zonal mean mim and clarifies the geographical distributions of the cold air mass the negative heat content nhc their horizontal fluxes and their diabatic change rates on the basis of conservation relations of the air mass and thermodynamic energy in the northern hemispheric winter the polar cold air mass below t 280 k has two main streams the east asian stream and the north american stream the former grows over the northern part of the eurasian continent flows eastward turns down southeastward toward east asia via siberia and disappears over the western north pacific ocean the latter grows over the arctic ocean flows toward the eastern coast of north america via hudson bay and disappears ov

multifrequency polarimetric synthetic aperture radar observations of sea ice the first known fully polarimetric airborne synthetic aperture radar sar data set of sea ice is introduced images were acquired in the beaufort bering and chukchi seas in march 1988 during a campaign for validation of defense meteorological satellite program special sensor microwave imager radiometer ice products statistics of the magnitude phase and polarization of complex backscattered signals recorded by the jet propulsion laboratory three frequency sar are examined in detail for various scenes with different ice characteristics the full stokes matrix information generated from c l and p band data characterize the scattering behavior of different ice types polarization ratios and phase differences between linear copolarized returns are used for discrimination between particular image features and mechanisms are suggested for the observed polarimetric characteristics results indicate that combinations of frequency and polarization enhance current capability to distinguish ice of different properties using single frequency fixed polarization micro wave radar a specific example is the polarimetric identification of new ice formation which may not be easily distinguished in ers 1 5 3ghz vv polarization sar data such findings are consistent with theoretical model simulations of scattering characteristics of sea ice overall these preliminary results demonstrate that radar polarimetry will likely add a new dimension to our current capability for extracting geophysically important ice variables using radar remote sensing methods

paleomagnetism of mid paleozoic subduction related volcanics from the chingiz range in ne kazakhstan the evolving paleogeography of the amalgamating eurasian composite continent the tectonic and paleogeographic evolution of the ural mongol belt between the cratons of baltica siberia and tarim is key to the formation of the eurasian composite continent during paleozoic time but the views on this complicated process remain disparate and sometimes controversial a study of three volcanic formations of mid silurian lower to middle devonian and middle devonian age from the southwestern boundary of the chingiz range ne kazakhstan yields what are interpreted as primary paleomagnetic directions that help clarify the evolution of the belt a single polarity characteristic component in mid silurian andesites yields a positive intraformational conglomerate test whereas dual polarity prefolding components are isolated from the two devonian collections post folding reversed polarity overprint directions have also been isolated and are likely of permo triassic age these new data can be evaluated together with previously published paleomagnetic results from paleozoic rocks in the chingiz range and allow us to establish with confi dence the polarity of each result and hence to determine the hemisphere in which the area was located at a given time we conclude that ne kazakhstan was steadily moving northward albeit with variable velocity crossing the equator in silurian time these new paleomagnetic data from the chingiz range also agree with and reinforce the hypothesis that the strongly curved volcanic belts of kazakhstan underwent oroclinal bending between middle devonian and middle permian time a comparison of the chingiz paleolatitudes with those of siberia shows insofar as the sparse data allow similarities between the northward motion of the chingiz unit and that of siberia which imposes important constraints on the evolving paleogeography of the ural mongol belt

the percolation phase transition in sea ice sea ice exhibits a marked transition in its fluid transport properties at a critical brine volume fraction p c of about 5 percent or temperature t c of about 5 c for salinity of 5 parts per thousand for temperatures warmer than t c brine carrying heat and nutrients can move through the ice whereas for colder temperatures the ice is impermeable this transition plays a key role in the geophysics biology and remote sensing of sea ice percolation theory can be used to understand this critical behavior of transport in sea ice the similarity of sea ice microstructure to compressed powders is used to theoretically predict p c of about 5 percent

large scale inverse ku band backscatter modeling of sea ice polar sea ice characteristics provide important inputs to models of several geophysical processes microwave scatterometers are ideal for monitoring these regions due to their sensitivity to ice properties and insensitivity to atmospheric distortions many forward electromagnetic scattering models have been proposed to predict the normalized radar cross section spl sigma spl deg from sea ice characteristics these models are based on very small scale ice features and generally assume that the region of interest is spatially homogeneous unfortunately spaceborne scatterometer footprints are very large 5 50 km and usually contain very heterogeneous mixtures of sea ice surface parameters in this paper we use scatterometer data in a large scale inverse modeling experiment given the limited data resolution we adopt a simple geometric optics forward scattering model to analyze surface and volume scattering contributions to observed ku band signatures a model inversion technique based on recursive optimization of an objective function is developed the result is a least squares estimate of three surface parameters the power reflection coefficient at nadir the rms surface slope and the volume scattering albedo simulations demonstrate the performance of the method in the presence of noise the inverse model is implemented using ku band image reconstructed data collected by the national aeronautics and space administration scatterometer the results are used to analyze and interpret spl sigma spl deg phenomena occurring in the antarctic and the arctic

syncollisional gabbro in the irtysh shear zone eastern kazakhstan compositions geochronology and geodynamic implications abstract new data of petrography mineralogy and geochemistry from the irtysh shear zone in eastern kazakhstan reveal three types of gabbro 1 dolerite and gabbrodolerite 2 biotite bearing gabbronorite and gabbrodiorite and 3 layered peridotite gabbro intrusions rocks of types 1 and 2 occur mainly as small bodies and share similarity in major and trace element compositions layered gabbro type 3 forms the largest intrusion in the area and has a different composition higher cao and al2o3 but lower k2o tio2 p2o5 zr nb ree correspondingly the gabbro of two first types may result from differentiation of the same tholeiite magma whereas the layered gabbro rather derived from a magma intermediate between tholeiite and calc alkaline series according to geochemical and isotopic signatures both types of primary magma originated from the same sublithospheric depleted mantle by low and high degree partial melting of spinel lherzolite the obtained 317 313 ma u pb and ar ar ages of the gabbro fall within the time of collisional events in the area the suggested model explains the origin of syncollisional gabbro as intrusion of ascending mafic melts from a mantle wedge at the transform boundary of colliding plates along the irtysh shear zone where strike slip faulting produced slab windows open to inputs of hot asthenospheric material

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

palaeomagnetism and geochronology of mafic dykes in south siberia russia the first precisely dated early permian palaeomagnetic pole from the siberian craton summary new palaeomagnetic and geochronological data from mafic dykes emplaced into the basement of the siberian craton on the southwestern coast of the baikal lake are present the concordant zircon u pb shrimp age of these dykes is 275 4 ma palaeomagnetic study of the dykes isolated a stable primary remanence with steep upward direction supported by a positive baked contact test the palaeomagnetic pole 50 5 n 121 4 e a95 16 7 is the first precisely dated siberian pole between 360 and 260 ma it falls near the interpolated siberian apwp and suggests that siberia had not joined eurasia by 275 ma the studied dykes are the first reported evidence of permian magmatic activity in the cratonic part of southern siberia they are probably related to the prominent 300 260 ma magmatic event recognized in trans baikalia the comparison of our new result with recently published palaeomagnetic data from transbaikalia suggests that differential movements between the siberian craton and blocks of transbaikalia around 275 ma are unlikely this confirms tectonic models considering trans baikalia as an andean type active margin of the siberian continent in permian times

paleomagnetism of paleozoic and mesozoic sediments from the southern margin of mongol okhotsk ocean far eastern russia 1 this paper presents new data from paleomagnetic investigations of middle paleozoic early middle late devonian early carboniferous and middle jurassic geological units from the amuria block south of the mongol okhotsk suture zone with fold tests for all localities and two polarities for the devonian our new results constrain the evolution of the mongol okhotsk ocean from the devonian to the middle jurassic the corresponding paleopoles lie at 21 6 n 6 3 e dp dm 5 3 10 6 for early devonian 26 3 n 345 3 e dp dm 6 4 12 8 for early middle devonian 24 6 n 12 9 e dp dm 8 7 16 9 for middle late devonian 40 5 n 352 4 e dp dm 9 16 7 for late devonian 39 8 n 31 6 e dp dm 10 15 5 for early carboniferous and 46 n 37 9 e dp dm 9 4 13 4 for middle jurassic the poles confirm that the large paleozoic mongol okhotsk ocean closed during the jurassic ending up in the late jurassic or early cretaceous at the eastern end of the suture zone as originally proposed on geological grounds the new paleomagnetic results exhibit large tectonic rotations about local vertical axes which we interpret as probably arising from both the collision process and left lateral shear movement along the suture zone related to incipient extrusion of amuria due to indentation of india into asia

stratosphere troposphere coupling during spring onset abstract the authors perform an observational study of the relation between stratospheric final warmings sfws and the boreal extratropical circulation sfw events are found to provide a strong organizing influence upon the large scale circulation of the stratosphere and troposphere during the period of spring onset in contrast to the climatological seasonal cycle sfw events noticeably sharpen the annual weakening of high latitude circumpolar westerlies in both the stratosphere and troposphere a coherent pattern of significant westerly easterly zonal wind anomalies is observed to extend from the stratosphere to the earth s surface at high latitudes prior to after sfw events coinciding with the polar vortex breakdown this evolution is associated with a bidirectional dynamical coupling of the stratosphere troposphere system in which tropospheric low frequency waves induce annular stratospheric circulation anomalies which in turn are followed by annular tropospheric circulation anomalies the reg

a broad spectral interdisciplinary investigation of the electromagnetic properties of sea ice this paper highlights the interrelationship of research completed by a team of investigators and presented in the several individual papers comprising this special section on the office of naval research onr arlington va sponsored sea ice electromagnetics accelerated research initiative ari the objectives of the initiative were the following 1 understand the mechanisms and processes that link the morphological and physical properties of sea ice to its electromagnetic em characteristics 2 develop and verify predictive models for the interaction of visible infrared and microwave radiation with sea ice 3 develop and verify inverse scattering techniques applicable to problems involving the interaction of em radiation with sea ice guiding principles for the program were that all em data be taken with concurrent physical property data salinity density roughness etc and that broad spectral data be acquired in as nearly a simultaneous fashion as possible over 30 investigators participated in laboratory field and modeling studies that spanned the em spectrum from radio to ultraviolet wavelengths an interdisciplinary approach that brought together sea ice physicists remote sensing experts in fill measurements and forward and inverse modelers primarily mathematicians and em theorists was a hallmark of the program along with describing results from experiments and modeling efforts possible paradigms for using broad spectral data in developing algorithms for analyzing remote sensing data in terms of ice concentration age type and possibly thickness are briefly discussed

thin saline ice thickness retrieval using time series c band polarimetric radar measurements the application of time series radar measurements to accurately invert the thickness of saline ice is presented in this study the authors describe briefly some experimental observations from the united states army cold regions research and engineering laboratory hanover nh 1993 crrelex 93 campaign of microwave scattering from sea ice they demonstrate that volume scattering from brine inclusions is an important contribution to the backscatter response of saline ice in this case from the experimental findings and the thermophysics of ice growth they develop an inversion algorithm for the ice thickness based on a dynamic electromagnetic scattering model of saline ice this inversion algorithm uses a parametric estimation approach in which the radiative transfer equation is used as the direct scattering model to calculate the backscattering signatures from ice medium and the levenberg marquardt method is employed to retrieve ice thickness iteratively additional information provided by the saline ice thermodynamics is applied to constrain the electromagnetic inverse problem to achieve a reasonably accurate reconstruction the inversion results using this algorithm and the data from crrelex 93 experiment are compared the accurate thickness retrieval suggests the potential use of this algorithm for retrieving geophysical parameters from satellite remote sensing data

paleomagnetism of the siberian traps new data and a new overall 250 ma pole for siberia the flood basalt province in siberia is one of the largest in the world but the number of reliable paleomagnetic data on these volcanics is still limited we studied lava flows and trap related intrusions from two areas in the north and west of the siberian platform a dual polarity characteristic component was isolated from most samples with the aid of stepwise thermal and alternating field demagnetization we then compiled all published paleomagnetic data on the siberian traps that have been obtained according to modern standards also included are presumably trap related overprint directions in paleozoic rocks although these overprints and trap results may locally differ the corresponding mean poles based on remagnetized sediments and volcanics show excellent overall agreement and justify pooling of both data types several ways of data grouping were attempted the trap mean pole proved to be rather insensitive to statistical treatment irrespective of the averaging procedure used the overall mean poles for the siberian traps nsp2 55 1 n 147 0 e n 8 k 123 a95 5 0 or nsp4 57 2 n 151 1 e n 8 k 192 a95 4 0 differ slightly but significantly from the coeval mean poles of baltica torsvik 2001 van der voo r and torsvik t h the quality of the european permo triassic paleopoles and its impact on pangea reconstructions in timescales of the paleomagnetic field j e t channell d v kent w lowrie and j g meert eds agu geophys monogr 2004 135 29 42 we consider possible causes for this difference and conclude that it could be explained either by persistent non dipole terms in the permo triassic geomagnetic field or widespread inclination shallowing in the european data

magnetic reversal frequency and apparent polar wander of the siberian platform in the earliest palaeozoic inferred from the khorbusuonka river section northeastern siberia summary marly limestones that crop out along the khorbusuonka river northeastern siberian platform define a well dated lower and middle cambrian sequence which was sampled for magnetostratigraphy in the upper part of the section from the uppermost lower cambrian toyonian stage to the middle cambrian amgan and mayan stages thermal demagnetization isolates two magnetic components carried either by magnetite haematite or both the first is parallel to the recent geomagnetic field at the site and is removed in the low to middle temperature range the second component is isolated at higher temperatures and has dual magnetic polarities this component yields a positive but partial since we consider only two sites fold test with other middle cambrian data previously obtained from the distant kulumbe river section and was probably acquired during sedimentation or at an early stage of diagenesis it records a very high magnetic reversal frequency of at least six to eight reversals per myr during the entire middle cambrian assuming a 10 myr duration for this epoch a much more complex palaeomagnetic behaviour is observed within the upper tommotian lower atdabanian lower cambrian part of the khorbusuonka section demagnetization diagrams show large overlaps between magnetic components which prevents the isolation of a clear magnetic component at high temperatures analysis of these overlaps is however consistent with the existence of an ill determined primary magnetic direction for the lower cambrian which is very different from that isolated in the middle cambrian although still in need of further confirmation the possibility that a large drift in siberian apparent polar wander occurred over a rather short time during the lower cambrian appears to be supported by our data

the classification of arctic sea ice types and the determination of surface temperature using advanced very high resolution radiometer data the accurate quantification of new ice and open water areas and surface temperatures within the sea ice packs is a key to the realistic parameterization of heat moisture and turbulence fluxes between ocean and atmosphere in the polar regions multispectral noaa advanced very high resolution radiometer 2 avhrr 2 satellite images are analyzed to evaluate how effectively the data can be used to characterize sea ice in the bering and greenland seas both in terms of surface type and physical temperature the basis of the classification algorithm which is developed using a late wintertime bering sea ice cover data is that frequency distributions of 10 8 m radiances provide four distinct peaks representing open water new ice young ice and thick ice with a snow cover the results are found to be spatially and temporally consistent possible sources of ambiguity especially associated with wider temporal and spatial application of the technique are discussed an ice surface temperature algorithm is developed for the same study area by regressing thermal infrared data from 10 8 and 12 0 m channels against station air temperatures which are assumed to approximate the skin temperatures of adjacent snow and ice the standard deviations of the results when compared with in situ data are about 0 5 k over leads and polynyas to about 0 5 1 5 k over thick ice this study is based upon a set of in situ data limited in scope and coverage cloud masks are applied using a thresholding technique that utilizes 3 74 and 10 8 m channel data the temperature maps produced show coherence with surface features like new ice and leads and consistency with corresponding surface type maps further studies are needed to better understand the effects of both the spatial and temporal variability in emissivity aerosol and precipitable atmospheric ice particle distribution and atmospheric temperature inversions

paleomagnetism of the early triassic semeitau igneous series eastern kazakstan 1 paleomagnetic results obtained from the early triassic semeitau igneous series sis yield a high quality pole for eastern kazakstan that is concordant with reference poles for siberia and europe strongly supporting the hypothesis that kazakstan was already joined with eurasia at this time of the 25 sites that were measured data were straightforward for 20 sites 2 of which recorded normal polarity and 18 of which recorded reverse 5 sites were discarded because of severe overprinting unstable demagnetizations or extremely scattered within site directions combining sites judged to be the same cooling unit and taking the average of 15 cooling units of equal weight we calculated a pole located at 56 n 139 e n 15 k 24 6 95 7 9 for the sis we consider this pole to be reliable the sampling of temporally spaced extrusives and more slowly cooled intrusives and the presence of both polarities strongly suggest that this pole averages secular variation the 40ar 39ar determinations on sanidine crystals from two extrusive units yielded highly consistent ages of 248 2 0 5 and 248 8 0 5 ma comparison of our pole for the sis with the siberian reference pole shows relative translation 8 10 and rotation 1 16 that are indistinguishable from zero at 95 confidence this result fails to confirm hypothesized post permian rotation of the siberian craton relative to its margins and provides no evidence for left lateral motion on the east west shear zones in which the semeitau is located the similarity of ages between the sis and the siberian traps supports speculation of a genetic relationship between the two

collision of the tacheng block with the mayile barleik tangbale accretionary complex in western junggar nw china implication for early middle paleozoic architecture of the western altaids abstract western junggar in nw china located to the southeast of the boshchekul chingiz bc range and to the north of the chu balkhash yili microcontinent cby played a key role in the architectural development of the western altaids however the mutual tectonic relationships have been poorly constrained in this paper we present detailed mapping field structural geology and geochemical data from the barleik mayile tangbale complex bmtc in western junggar the complex is divisible into zones i ii and iii which are mainly composed of cambrian silurian rocks zone i contains pillow lava siliceous shale chert coral bearing limestone sandstone and purple mudstone zone ii consists of basaltic lava siliceous shale chert sandstone and mudstone zone iii is characterized by basalt chert sandstone and mudstone these rocks represent imbricated ocean plate stratigraphy which have been either tectonically juxtaposed by thrusting or form a melange with a block in matrix structure all these relationships suggest that the bmtc is an early middle paleozoic accretionary complex in the eastern extension of the bc range these early paleozoic oceanic rocks were thrust onto silurian sediments forming imbricate thrust stacks that are unconformably overlain by devonian limestone conglomerate and sandstone containing fossils of brachiopoda crinoidea bryozoa and plant stems and leaves the tectonic vergence of overturned folds in cherts drag related curved cleavages and type structures on the main thrust surface suggests top to the nw transport moreover the positive end t values of volcanic rocks from the tacan 1 drill core and the positive ehf t values and post cambrian ages of detrital zircons from silurian and devonian strata to the south of the tacheng block indicate that its basement is a depleted and juvenile lithosphere and there was a radial outward transition from coral bearing shallow marine shelf to deep ocean pelagic environments and from oib e morb to n morb lava geochemistry away from the tacheng block comparisons with published data suggest that these positive isotopic values stratigraphic structural and geochemical relationships can be best understood as an analogue of the relationships between the ontong java oceanic plateau and the pacific oceanic crust therefore we propose that the basement of the tacheng block was an early paleozoic oceanic plateau the southern part of the tacheng block was an accretionary complex and the northern part was an oceanic basin in the early paleozoic the configuration of which is similar to that of the present ontong java oceanic plateau situated on the pacific oceanic crust and its accretion into the solomon accretionary complex the presence of ordovician ssz type ophiolites early paleozoic blueschist and silurian ssz type intrusions in the bmtc and early middle paleozoic continental arc related intrusive rocks in the northern margin of the cby provide further corroboration of a former subduction zone between the southern west junggar and the northern margin of the cby furthermore consideration of the fact that the kokchetav north tianshan range was collaged to the southern margin of the cby in the ordovician devonian indicates that both ranges were amalgamated synchronously with the cby constructing the early middle paleozoic architecture of western altaids

ordovician carboniferous tectono sedimentary evolution of the north nuratau region uzbekistan westernmost tien shan abstract the tien shan is a c 2500 km long orogenic belt of which the nuratau region of eastern uzbekistan forms the western part petrographical and field analysis of the ordovician carboniferous succession in the north nuratau region provided the basis for a reconstruction of the depositional settings along part of the northern margin of the alai continent and their evolution during the period of closure of the turkestan ocean which separated the alai and the kazakh kyrgyz continents initial sedimentation ordovician was broadly carbonate dominated although by mid late ordovician times siliciclastic input predominated in some areas these variations between clastic and carbonate dominated regions may have been related to tectonic activity within the alai continent carbonate sedimentation was reestablished in the wenlock with broad shelf systems forming along the continental margin volcanic activity in the early devonian records a period of tectonic instability and this was followed by the reestablishment of the carbonate mosaic albeit with a greater degree of instability as indicated by stratigraphic gaps than in the silurian this pattern extended up into the carboniferous culminating in backarc related magmatic activity final closure of the turkestan ocean involved significant folding and thrusting as well as a major change from compressional to strike slip movement

paleomagnetism and dating of a thick lava pile in the permian bakaly formation of eastern kazakhstan regularities and singularities of the paleomagnetic record in thick lava series abstract paleomagnetic results on thick lava series are among the most important sources of information on the characteristics of ancient geomagnetic fields most paleo secular variation data from lavas psvl are of late cenozoic age there are far fewer results from lavas older than 5 ma the central asia orogenic belt that occupies several million square kilometers in asia is probably the world s largest area of paleozoic volcanism and is thus an attractive target for psvl studies we studied a ca 1700 m thick lava pile in eastern kazakhstan of early permian age magmatic zircons successfully separated from an acid flow in this predominantly basaltic sequence yielded an early permian age of 286 3 3 5 ma oriented samples were collected from 125 flows resulting in 88 acceptable quality flow means n 4 samples radius of confidence circle 95 15 of the high temperature magnetization component the uniformly reversed component is pre tilting and arguably of a primary origin the overall mean direction has a declination 242 0 and an inclination 56 2 k 71 5 95 1 8 n 88 sites pole at 44 1 n 160 6 e a95 2 2 our pole agrees well with the early permian reference data for baltica in accord with the radiometric age of the lava pile and geological views on evolution of the western part of the central asia orogenic belt the new early permian result indicates a comparatively low level of secular variation especially when compared to psvl data from intervals with frequent reversals still the overall scatter of dispersion estimates that are used as proxies for sv magnitudes elongation values and elongation orientations for psvl data is high and cannot be fitted into any particular field model with fixed parameters both observed values and numerical simulations indicate that the main cause for the scatter of form parameters elongation values and elongation orientations is the too small size of collections dispersion estimates concentration parameter and standard angular deviation are more robust and their scatter stems from other sources which may include non stochastic features of datasets like clusters loops etc or non stationary behavior of secular variation magnitude over time intervals of many million years

identification of sea ice types in spaceborne synthetic aperture radar data an approach for identification of sea ice types in spaceborne synthetic aperture radar sar image data is presented the unsupervised classification approach involves cluster analysis for segmentation of the image data followed by cluster labeling based on previously defined look up tables containing the expected backscatter signatures of different ice types measured by land based scatterometer the particular look up table used for labeling a segmented image is selected based on the seasonal and meteorological conditions at the time of data acquisition the extensive scatterometer observations and experience accumulated in field campaigns during the last 10 years were used to construct these look up tables these tables are expected to evolve as sea ice observations from the european ers 1 sar become available this paper presents the classification approach its expected performance the dependence of this performance on radar system performance and expected ice scattering characteristics results using both aircraft and simulated ers 1 sar data are presented the results are compared to limited field ice property measurements and coincident passive microwave imagery an algorithm based on this experimental approach has been implemented in the geophysical processor system at the alaska sar facility for classification of sea ice data in ers 1 c band sar data the importance of an integrated postlaunch program for validation and improvement of this approach is discussed

life cycles of persistent anomalies ii the development of persistent negative height anomalies over the north pacific ocean abstract the present study extends our previous work on the life cycles of persistent anomalies by providing more comprehensive analyses of the synoptic and dynamical characteristics associated with the developments of the anomalies we focus here on the developments of major cases of persistent negative height anomalies over the extratropical central north pacific pac region during wintertime these ewes are generally manifested at the surface by an anomalously intense and eastward displaced aleutian low and at upper levels by an abnormally strong zonal jet that extends across most of the western and central pacific at midlatitudes the associated flow anomalies usually resemble particularly strong realizations of the pacific north american pna teleconnection pattern the large scale flow anomalies are typically preceded by a buildup of anomalously cold air over asia and an intensification of the upper level jet over southeastern asia and the fox western pacific a few days prior to the larger scal

modelling changes in the dielectric and scattering properties of young snow covered sea ice at ghz frequencies observations of the physical properties of the snow cover and underlying young fast ice in resolute passage canada were made during the winter of 1982 detailed measurements of snow density and ice and snow temperatures salinities and brine volumes were made over a period of 46 d beginning when the ice was 0 4 m thick and about 9 d old the recorded values are used in a theoretical mixture model to predict the dielectric properties of the snow cover over the microwave frequency range the results of this analysis are then used to investigate the effects of the snow properties on the radar backscatter signatures of young sea ice the results show that backscatter is a function of the incidence angle and can change significantly over short periods of time during the early evolutionary phase of ice and snow cover development this has important consequences for the identification of young ice forms from sar or slar images

late orogenic large scale rotations in the tien shan and adjacent mobile belts in kyrgyzstan and kazakhstan abstract most of kazakhstan belongs to the central part of the eurasian paleozoic mobile belts for which previously proposed tectonic scenarios have been rather disparate of particular interest is the origin of strongly curved middle and late paleozoic volcanic belts of island arc and andean arc affinities that dominate the structure of kazakhstan we undertook a paleomagnetic study of carboniferous to upper permian volcanics and sediments from several localities in the ili river basin between the tien shan and the junggar alatau ranges in southeast kazakhstan our main goal was to investigate the permian kinematic evolution of these belts particularly in terms of rotations about vertical axes in the hope of deciphering the dynamics that played a role during the latest paleozoic deformation in this area this deformation in turn can then be related to the amalgamation of this area with baltica siberia and tarim in the expanding eurasian supercontinent thermal demagnetization revealed that most permian rocks retained a pretilting and likely primary component which is of reversed polarity at three localities and normal at the fourth in contrast most carboniferous rocks are dominated by postfolding reversed overprints of probably mid permian age whereas presumably primary components are isolated from a few sites at two localities mean inclinations of primary components generally agree with coeval reference values extrapolated from baltica whereas declinations from primary as well as secondary components are deflected counterclockwise ccw by up to 90 such ccw rotated directions have previously also been observed in other tien shan sampling areas and in the adjacent tarim block to the south however two other areas in kazakhstan show clockwise cw rotations of permian magnetization directions one area is located in the kendyktas block about 300 km to the west of the ili river valley and the other is found in the chingiz range to the north of lake balkhash and about 400 km to the north of the ili river valley the timing of the ccw as well as cw rotations is clearly later than the disappearance of any marine basins from northern tarim the tien shan and eastern kazakhstan so that the rotations cannot be attributed to island arc or andean margin plate settings instead we attribute the rotations to large scale east west present day coordinates sinistral wrenching in an intracontinental setting related to convergence between siberia and baltica as recently proposed by natal in and engor natal in b a and engor a m c 2005 late palaeozoic to triassic evolution of the turan and scythian platforms the pre history of the palaeo tethyan closure tectonophysics 404 175 202 our previous work in the chingiz and north tien shan areas on ordovician and silurian rocks suggested relative rotations of 180 whereas the permian declination differences are of the order of 90 between the two areas thus we assume that about 50 of the total post ordovician rotations are of pre late permian age with the other half of late permian earliest mesozoic age the pre late permian rotations are likely related to oroclinal bending during plate boundary evolution in a supra subduction setting given the calc alkaline character of nearly all of the pre late permian volcanics in the strongly curved belts

the western central asian orogenic belt a window to accretionary orogenesis and continental growth abstract the architecture of accretionary orogens is a key to understand continental growth here we present an overview of the orogenic components and their amalgamation in the western central asian orogenic belt caob the caob records the convergence and interactions among various types of orogenic components including the japan type mariana type and alaska aleutian type arc systems as well as the active marginal sequences of the siberia craton which incorporated wide accretionary complexes and accreted arcs and terranes during construction of the caob the kazakhstan arc chain was characterized by multiple subduction whereas the northern fringe of the tarim craton remained mostly as a passive margin the multiple convergence and accretions among these various orogenic components generated huge orogenic collages in the late paleozoic and even in the early triassic involving parallel amalgamation circum microcontinent amalgamation and oroclinal bending the preservation of trapped basins played a significant role in orogenesis with some parts of the oceanic plate being subducted and others behaving as rigid units the orogenesis in the caob was long lived lasting for more than 800 m y involving multiple subduction and long continuous accretion and featuring the complexity of accretionary orogenesis and continent growth

evolution of electromagnetic signatures of sea ice from initial formation to the establishment of thick first year ice the spatial and temporal distribution of new and young sea ice types are of particular interest because of the influence this can exert on the heat and mass balance of the polar sea ice the objective of the present work is to characterize the temporal evolution of the electromagnetic em signatures of sea ice from initial formation through the development of first year fy ice on the basis of the temporal variations in the physical properties of the ice the time series of young sea ice signatures including microwave emissivity radar backscatter and visible and infrared spectral albedo has been measured at successive stages in the growth and development of sea ice both under laboratory and field conditions these observations have been accompanied by studies of the physical properties that influence the interaction between radiation and the ice this has resulted in a consistent data set of concurrent multispectral observations that covers essentially all phases of the development of the different types of sea ice from initial formation to thick fy ice mutually consistent theoretical models covering the entire wavelength range of the observations are applied to selected cases and successfully match the observations principal component analysis pca of the data set suggests combinations of the set of frequencies to effectively distinguish among different stages in the temporal evolution of the sea ice

on the secular change of spring onset at stockholm 1 a newly developed method the ensemble empirical mode decomposition was applied to adaptively determine the timing of climatic spring onset from the daily temperature records at stockholm during 1756 2000 secular variations of spring onset and its relationships to the north atlantic oscillation nao and to the temperature variability were analyzed a clear turning point of secular trend in spring onset around 1884 1885 from delaying to advancing was found the delaying trend of spring onset 6 9 days century during 1757 1884 and the advancing one 7 days century during 1885 1999 were both significant the winter nao indices were found to be correlated with the spring onset at stockholm at an inter annual timescale only for some decades but unable to explain the change of the long term trends the secular change from cooling to warming around the 1880s especially in terms of spring temperature might have led to the secular change of spring onset

permian palaeomagnetism of east kazakhstan and the amalgamation of eurasia summary most of kazakhstan belongs to the ural mongol belt the tectonic evolution of which is poorly understood as demonstrated by disparate tectonic models suggested thus far we undertook a palaeomagnetic study of upper permian basalts and andesites from two localities in east kazakhstan in order to evaluate the final stages of the evolution of this belt and eurasian amalgamation thermal demagnetization revealed a single pre tilting characteristic component of ubiquitously reversed polarity from all samples the mean declination of this remanence from one locality agrees rather well with the permian european palaeomeridian whereas that from the other is clockwise rotated by 28 8 the overall mean inclination of 49 4 differs by 9 7 4 2 from the reference inclination calculated for our localities from the eurasian mean pole for the 245 260 ma interval and is in agreement with 260 275 ma data we account for the observed pattern by either a slightly erroneous rock age lithologies are somewhat older than indicated by geological data or non dipole octopole components of the geomagnetic field because significant relative motion of the study area with respect to eurasia is not demonstrated we conclude that welding of kazakhstan europe and siberia was essentially completed by mid permian time

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

observed changes in baroclinic wave activity during the life cycles of low frequency circulation anomalies abstract anomalous baroclinic wave activity during the onset and decay of blocking patterns in the northern hemisphere winter is investigated based upon a 30 year record of 500 mb height and sea level pressure a slowly varying envelope function is defined at each gridpoint in order to represent the modulation of the amplitude of baroclinic wave activity by the low frequency circulation anomalies related to blocking the envelope function fields and the low frequency circulation fields are composited relative to the onset and decay times of four persistent dipole patterns in low frequency circulation anomalies located downstream of the climatological mean stormtracks one polarity of the anomaly patterns corresponds to dipole or modon like blocking patterns over the eastern oceans and the other to strong zonal flow patterns each of the eight composites is comprised of more than 50 persistent blocking or zonal flow episodes the most striking common feature observed during the onset of blocking over th

siluro devonian paleomagnetic results from the tuva terrane southern siberia russia implications for the paleogeography of siberia new paleomagnetic data from seven sections of siluro devonian age sedimentary sequences in the tuva terrane south siberia russia reveal the presence of up to three different components of magnetization component a is of recent or late mesozoic cenozoic origin and component b identified unambiguously in 25 samples from one section yields a sample mean direction declination inclination of 300 6 54 7 k 42 2 95 4 5 in geographic and 283 9 63 5 k 45 4 95 4 3 in stratigraphic coordinates however since the results of the fold test are inconclusive no further attempt has been made to assign an age to this magnetization component c with unblocking temperatures of 500 680 c is identified in all seven sections and with dual polarity after bedding correction the section mean directions all plot along a common small circle in stereographic projection with a mean inclination of 42 1 n 7 sites k 184 2 95 2 9 it passes the inclination only fold test the within site fold test both on the 95 significance level and the reversal test and is thus interpreted as being primary in origin and siluro devonian in age adopting the normal polarity option for component c yields a paleolatitude of 24 n 2 for the tuva terrane on the basis of geological evidence the tuva terrane was clearly accreted to siberia by early silurian times the results obtained in this study therefore indicate lower paleolatitudes for siberia than those predicted from previously published apparent polar wander paths for the siberian platform and demonstrate that siberia was positioned between the equator and 30 n during latest silurian earliest devonian times these new results are also supported by paleoecological and paleoclimatological evidence the dispersion of declinations along a small circle is indicative of clockwise block rotations within the tuva terrane of up to 72 with respect to siberia

daily scale planetary wave patterns and the modulation of cold season weather in the northern extratropics tropospheric planetary waves often linked to asymmetries in lower boundary forcing significantly modulate atmospheric blocking and storm track structures that are in turn linked to extreme surface weather events day to day variability in the planetary scale circulation taken as wavenumbers 1 to 5 in the daily 500 hpa geopotential heights and the associated impact on storm tracks and regional weather are studied for the period 1950 2005 six boreal cold season distinct planetary wave patterns are identified via hierarchical cluster analysis the first second and sixth patterns feature a prominent zonal wavenumber 1 structure while the fourth and fifth patterns resemble the negative and positive phases of northern annular mode respectively the second pattern represents an amplification of the climatological mean wave structure while the third pattern resembles the zonal wavenumber 3 pattern a multi taper spectral analysis of the daily projection indices indicates that the planetary wave patterns are primarily intraseasonal in nature the first sixth pattern combines the positive negative phase of the pacific north american teleconnection pattern and negative positive phase of the north atlantic oscillation inducing poleward equatorward shifts in the pacific storm track and a weakened strengthened atlantic storm track in contrast the fourth fifth pattern results in a simultaneous equatorward poleward displacement of both storm tracks extreme cold waves over the continental united states us are favored during occurrences of the fourth and sixth patterns during episodes of the first pattern increased rainfall prevails over much of the us while precipitation anomalies induced by the other patterns are more regional in nature

bounds on the complex permittivity of sea ice an analytic method for obtaining bounds on effective properties of composites is applied to the complex permittivity of sea ice the sea ice is assumed to be a two component random medium consisting of pure ice of permittivity 1 and brine of permittivity 2 the method exploits the properties of as an analytic function of the ratio 1 2 two types of bounds on are obtained the first bound r1 is a region in the complex plane which assumes only that the relative volume fractions p1 and p2 1 p1 of the ice and brine are known the region r1 is bounded by circular arcs and for any microgeometry with the given volume fractions must lie inside it in addition to the volume fractions the second bound r2 assumes that the sea ice is statistically isotropic within the horizontal plane the region r2 is again bounded by circular arcs and lies inside r1 built into the method is a systematic way of obtaining tighter bounds on by incorporating information about the correlation functions of the brine inclusions the bounding method developed here which does not assume any specific geometry for the brine inclusions offers an alternative to the classical mixing formula approach adopted previously in the study of sea ice in these mixing formulas specific assumptions are made about the inclusion geometry which are simply not satisfied by the sea ice under many conditions the bounds r1 and r2 are compared with experimental data obtained from artificially grown sea ice at the frequencies 4 8 and 9 5 ghz excellent agreement with the data is achieved

early paleozoic magmatic history of central inner mongolia china implications for the tectonic evolution of the southeast central asian orogenic belt to provide insights into the early paleozoic tectonic evolution of the southern portion of the long lived central asian orogenic belt we have conducted major and trace element analyses and zircon u pb dating of granitoid samples from central inner mongolia our study area covers three pre mesozoic tectonic units from north to south the wenduermiao subduction accretionary complex the bainaimiao magmatic belt and the northern margin of the north china craton our new geochronological and geochemical data show the temporal and genetic relationships between the three tectonic units accordingly we suggest that the wenduermiao subduction accretionary complex developed in the middle cambrian late silurian 509 421 ma comprising of coeval oceanic crust arc magmatism and forearc deposits the bainaimiao continental arc was developed during the late cambrian to early silurian 501 437 ma which superposed on the basement with the affinity of the north china craton the back arc basin opened prior to early silurian and lasted to the late silurian which is slightly younger than bainaimiao island arc the wenduermiao ocean between the wenduermiao subduction accretionary complex and the bainaimiao continental arc existed in early paleozoic

provenance and tectonic setting of late carboniferous clastic rocks in west junggar xinjiang china a case from the hala alat mountains abstract the late carboniferous palaeo tectonic setting of the west junggar region is comprised of arcs alternating with basins geochemical analysis of the sedimentary rocks associated with these arc related basins was conducted to better constrain the provenance and tectonic setting major and trace element geochemistry data of late carboniferous mudstones and sandstones in the hala alat mountains suggest that these sedimentary rocks and their source areas are characterized by the following four features 1 sediments experienced a simple recycling process 2 a low degree weathering conditions in the source areas 3 compositional immature of the sedimentary rocks 4 dominated by intermediate to felsic provenance with a few intermediate to mafic sediments integrated with the palaeo flow data and previous authors works a fore arc basin model is proposed for the tectonic setting of the sedimentary rocks the sawur arc is the primary provenance and supplies the major intermediate to felsic detrital fragments the bozchekul chingiz arc and kexia oceanic island arc are the other two secondary sources

geometry kinematics and tectonic models of the kazakhstan orocline central asian orogenic belt abstract the central asian orogenic belt caob is one of the largest accretionary orogens on earth and is characterized by the occurrence of tight oroclines kazakhstan and tuva mongolian oroclines the origin of these large scale orogenic curvatures is not quite understood but is fundamentally important for understanding crustal growth and tectonic evolution of the caob here we provide an outline of available geological and paleomagnetic data around the kazakhstan orocline with an aim of clarifying the geometry kinematics and geodynamic origin of the orocline the kazakhstan orocline is evident in a total magmatic image and can be traced by the continuation of high magnetic anomalies associated with the devonian volcanic belt and the late devonian to carboniferous balkhash yili arc paleomagnetic data show 112 126 clockwise rotation of the northern limb relative to the southern limb in the late devonian to early carboniferous as well as 15 28 clockwise rotation of the northern limb and 39 40 anticlockwise rotation of the southern limb relative to the hinge of the orocline during the late carboniferous to permian we argue that the kazakhstan orocline experienced two stage bending with the early stage of bending late devonian to early carboniferous 112 126 driven by slab rollback and the later stage late carboniferous to permian 54 68 possibly associated with the amalgamation of the siberian tarim and baltic cratons this new tectonic model is compatible with the occurrence of rift basins the spatial migration of magmatic arc and the development of large scale strike slip fault systems during oroclinal bending

early neoproterozoic gneissic granitoids in the southern yili block nw china constraints on microcontinent provenance and assembly in the sw central asian orogenic belt abstract the central asian orogenic belt caob was built by amalgamation of diverse geologic units including several microcontinents the nature and geodynamic evolution of the precambrian basement of these units are essential to constrain their origin and thus the geodynamic and paleogeographic reconstruction of the accretionary system the yili block located in the west of the chinese tianshan orogen is one of these precambrian based continental constituents field investigations zircon u pb dating and lu hf isotopic analysis whole rock geochemical and sr nd isotopic studies were conducted on the gneissic granitoids from the giergelang area southern yili block these rocks yielded early neoproterozoic zircon u pb ages 962 934 ma containing substantial number of paleo to mesoproterozoic inherited zircons 2403 1268 ma their protoliths belong to peraluminous high k granite series displaying right declining ree patterns and eu negative anomalies together with lile k rb u th enrichment and depletions in ba nb sr p ti they have negative end t values ranging from 2 5 to 4 7 and old nd model ages varying from 1650 ma to 1910 ma they also exhibit highly variable zircon ehf t values 12 1 to 4 4 and hf in zircon model ages 1558 2574 ma integrating all these results it is suggested that the primary magma of gneissic granitoids was generated by partial melting of supracrustal rocks with involvement of old crustal materials a comparison of data from the yili block and its neighboring continental units reveals that the neoproterozoic magmatic event is an important episode of crustal reworking for the major continental blocks within the caob similar neoproterozoic magmatic events and comparable upper neoproterozoic to lower paleozoic stratigraphic sequences of the yili chinese central tianshan and tarim blocks suggest that they had a similar crustal evolution and close tectonic and paleogeographic relation during neoproterozoic and were likely derived from one single continental plate

the structure dynamics and tropospheric signature of the polar annular mode 1 intraseasonal variability in the stratospheric polar vortex is intrinsically linked to concomitant tropospheric variability via the annular modes the primary mode the northern annular mode nam represents variability in the polar vortex strength while the second mode the lesser studied polar annular mode pam represents variability in the latitudinal position of the polar vortex the current study examines the structural evolution zonal mean dynamical forcing and tropospheric impact of discrete pam episodes occurring during boreal winter the analysis identifies large amplitude positive and negative pam events occurring in the absence of nam or sudden stratospheric warming events composite time evolution analyses are performed for both positive and negative pam events the onset of positive negative pam events is preceded by a weak and broad acceleration deceleration within the stratospheric polar vortex at midlatitudes during pam onset the canonical pam structure in zonal mean zonal wind develops over a 5 day period in association with robust stratosphere troposphere coupling zonal wind changes occurring during onset are induced by anomalous wave driving associated with low frequency rossby wave activity after pam onset the zonal wind anomaly features at high latitudes quickly weaken while those in the subtropics and midlatitudes persist for a period of 2 3 weeks during this time pam events provide a statistically significant impact upon the tropospheric circulation with large scale perturbations in a surface air temperature over north america and eurasia and b the structure and amplitude of the primary storm tracks

devonian paleomagnetism of the north tien shan implications for the middle late paleozoic paleogeography of eurasia the ural mongol belt umb between siberia baltica and tarim is widely recognized as the locus of asia s main growth during the paleozoic but its evolution remains highly controversial as illustrated by the disparate paleogeographic models published in the last decade one of the largest tectonic units of the umb is the kokchetav north tien shan domain kntd that stretches from tarim in the south nearly to the west siberian basin the kntd comprises several precambrian microcontinents and numerous remnants of early paleozoic island arcs marginal basins and accretionary complexes in late ordovician time all these structures had amalgamated into a single contiguous domain its paleogeographic position is of crucial importance for elucidating the paleozoic evolution of the umb in general and of the urals in particular the aral formation located in kyrgyzstan in the southern part of the kntd consists of a thick upper devonian frasnian basalt andesite sequence paleomagnetic data show a dual polarity characteristic component dec inc 286 56 95 9 k 21 n 15 sites the primary origin of this magnetization is confirmed by a positive test on intraformational conglomerates we combine this result with other paleozoic data from the kntd and show its latitudinal motion from the late ordovician to the end of the paleozoic the observed paleolatitudes are found to agree well with the values extrapolated from baltica to a common reference point 42 5 n 73 e in our sampling area for the entire interval hence coherent motion of the kntd and baltica is strongly indicated for most of the paleozoic this finding contradicts most published models of the umb evolution where the kntd is separated from baltica by a rather wide ural ocean containing one or more major plate boundaries an exception is the model of engor and natal in a m c engor b a natal in paleotectonics of asia fragments of a synthesis in a yin and m harrison eds the tectonic evolution of asia cambridge university press cambridge 1996 486 640 in which coherent paleolatitudinal motion of baltica and the kntd is hypothesized the latter as part of the kipchak arc we suggest a parallel hypothesis which explains coherent motion of the kntd and baltica in particular we argue that if a basin with oceanic crust ever existed between the kntd and baltica it was a narrow one without significant active spreading in middle to late paleozoic time notably the paleogeographic position of siberia during the middle paleozoic and hence the width of the khanty mansi ocean between siberia on the one hand and baltica kntd on the other hand remains largely unconstrained because of the paucity of high quality silurian devonian and carboniferous paleomagnetic results from siberia

heat budget analysis of northern hemisphere high latitude spring onset events regional spring onset events are identified within 4 high latitude sectors the primary critical region over north siberia cr greenland north america g na east asia ea and alaska al to identify the primary forcing of the rapid temperature increases observed during spring onset the contributions to the near surface air temperature anomaly tendency are diagnosed within the thermodynamic equation for each of the 4 regional event categories for each region anomalous eddy heat flux convergence is the primary contributor to regional warming prior to and during the early stages of spring onset through day 5 thereafter horizontal advection of the climatological mean temperature by the large scale circulation anomaly field emerges as the leading contributor to regional warming during the later stages of spring onset a parallel diagnostic of storm track strength using the envelope function reveals a systematic weakening of eddy activity within each region leading to a reduction in the northward eddy heat flux out of the domain and an accumulation of heat within the region for cr g na and ea events an east west dipole structure in the sea level pressure anomaly field with lower higher pressure to the west east generates the anomalous southerly flow linked to late period linear warm advection our results indicate that anomalous dynamical processes associated with synoptic eddy activity and stationary wave patterns are the primary contributors to rapid temperature increase during arctic spring onset events with minimal contributions from anomalous diabatic processes

paleomagnetic study of late paleozoic rocks in the tacheng basin of west junggar nw china implications for the tectonic evolution of the western altaids abstract to better understand the tectonic evolution of west junggar in the western altaids we have conducted a combined paleomagnetic and geochronological study on late devonian d3 late carboniferous c2 and early permian p1 successions from the tacheng basin northwest of china both primary and secondary characteristic remanent magnetization components have been successfully isolated and yield three reliable paleomagnetic poles of c2 and late permian p2 ages the c2 and p2 poles reveal a significant clockwise rotation of 35 6 10 4 which is comparable to the rotation deduced in the western part of the chingiz range during the time interval c2 to p2 similar rotation patterns for the two units suggest that the chingiz west junggar has remained as a quasi rigid block by the p2 time and constituted the northeast limb of the kazakhstan orocline the differential rotation of ca 25 to 30 deduced between the northeast and middle limbs of the kazakhstan orocline further suggests that at least a part of the curvature of the balkhash arc was acquired during the c2 to p2 interval and was a continuation of the middle paleozoic oroclinal bending moreover the c2 poles for west junggar and the junggar block are significantly different while the p2 ones almost overlap supporting the view that final closure of the balkhash junggar ocean occurred during the c2 to p2 interval on the other hand a large scale counterclockwise rotation of ca 80 to 90 is observed in west junggar and junggar relative to the western part of the chingiz range since the p2 time and this rotation probably represents an important intra continental deformation within the western part of the altaids a reconstruction of the paleo asian ocean has been proposed in which the kazakhstan orocline was emphasized by using the paleomagnetic results and geological evidence

unraveling the early middle paleozoic paleogeography of kazakhstan on the basis of ordovician and devonian paleomagnetic results abstract it is a common concept that different tectonic units in the western part of the central asian orogenic belt were united into the landmass of the kazakhstania continent in the paleozoic but many important details of its history remain enigmatic and controversial recently published paleomagnetic data from this region demonstrate that the 2000 km long horseshoe shaped devonian volcanic belt was created by oroclinal bending of an originally rectilinear active margin of kazakhstania still the silurian and devonian paleomagnetic results which this interpretation is based upon are limited and unevenly spread along the belt and additional middle paleozoic data are highly desirable accordingly we studied three mid paleozoic objects from different segments of this volcanic belt two of the three new objects yielded paleomagnetic directions that fit perfectly into the oroclinal scenario whereas the third one provided no interpretable data the earlier history of kazakhstania however remains misty we obtained three new ordovician results in north central kazakhstan and found similar inclinations but widely dissimilar declinations previously published data show a large scatter of ordovician declinations in south kazakhstan and kyrgyzstan as well we analyzed all seven middle late ordovician paleolatitudes and came to the conclusion that a nearly e w trending active margin of the kazakhstania landmass had existed at low 10 s latitudes at that time we hypothesize that this margin of the kazakhstania landmass collided with another island arc called baydaulet akbastau and with the aktau junggar microcontinent by the ordovician silurian boundary as a result of this collision subduction ceased and regional deformation magmatism and rotations of crustal fragments took place in most of kazakhstania in silurian time kazakhstania moved northward crossing the equator and rotating clockwise by 45 this changed the orientation of the kazakhstania to nw se and thereby established the rectilinear predecessor of the modern curved devonian volcanic belt

search for proxy indicators of young sea ice thickness the determination of young sea ice thickness from space remains an elusive goal for those interested in the interaction of the oceans and the atmosphere the thermal and chemical state of the ocean and sea ice dynamics recent experiments and models have shown relationships between active and passive microwave signatures of new growing ice and ice thickness the two processes that dominate in determining the microwave signature are changes in dielectric properties and changes in surface roughness in this paper we investigate the competition between these two processes in determining radar backscatter the usefulness of surface roughness as an indicator of young ice thickness and the optimum sensor parameters for observing changes in scattering linked to ice thickness we present simulations that are based on radar observations made on laboratory grown saline ice these observations confirm that surface scattering dominates over volume scattering for 13 9 ghz radar backscatter from young rough ice at most angles and for young smooth ice below 30 although rms roughness and backscatter at 5 3 and 13 9 ghz 23 incidence and vv polarization increase together after about 10 cm of ice growth under quiet conditions it is unlikely that surface roughness and ice thickness are simply connected in real sea ice where surface roughness can change rapidly due to the action of wind waves and snow simulations show however that formation of frost flowers is detectable by spaceborne radar and can serve to classify ice of roughly 5 20 cm thickness since it is a distinct transient event that occurs under physical conditions that constrain the thickness of the ice our experimental data show that future sensors operating near 12 incidence may offer potential for probing the relationship between near surface dielectric properties and ice thickness since the effects of variability in roughness and snowfall are minimized near this angle

middle paleozoic paleomagnetism of east kazakhstan post middle devonian rotations in a large scale orocline in the central ural mongol belt abstract in order to test different hypotheses concerning the paleozoic evolution of the ural mongol belt umb and the amalgamation of eurasia we studied middle devonian basalts from two localities 11 sites and lower silurian volcanics redbeds and intra formational conglomerates from three localities 20 sites in the chingiz range of east kazakhstan the devonian rocks prove to be heavily overprinted in the late paleozoic and a high temperature presumably primary southerly and down component is isolated at only four sites from a homoclinal section most silurian redbeds are found to be remagnetized in the late paleozoic in contrast a bipolar near horizontal remanence isolated from silurian volcanics is most probably primary as indicated by positive tilt and conglomerate tests analysis of paleomagnetic data from the chingiz range shows that southward pointing directions in ordovician silurian and devonian rocks are of normal polarity and hence indicate large scale rotations after the middle devonian the chingiz paleomagnetic directions can be compared with paleozoic data from the north tien shan and with the horseshoe shaped distribution of subduction related volcanic complexes in kazakhstan both paleomagnetic and geological data support the idea that today s strongly curved volcanic belts of kazakhstan are an orocline deformed mostly before mid permian time despite the determination of nearly a dozen new paleozoic paleopoles in this study and other recent publications by our team significant temporal and spatial gaps remain in our knowledge of the paleomagnetic directions during the middle and late paleozoic however the paleomagnetic results from the chingiz range and the north tien shan indicate that these areas show generally coherent motions with siberia and baltica respectively

inverse electromagnetic scattering models for sea ice inverse scattering algorithms for reconstructing the physical properties of sea ice from scattered electromagnetic field data are presented the development of these algorithms has advanced the theory of remote sensing particularly in the microwave region and has the potential to form the basis for a new generation of techniques for recovering sea ice properties such as ice thickness a parameter of geophysical and climatological importance moreover the analysis underlying the algorithms has led to significant advances in the mathematical theory of inverse problems in particular the principal results include the following 1 inverse algorithms for reconstructing the complex permittivity in the helmholtz equation in one and higher dimensions based on layer stripping and nonlinear optimization have been obtained and successfully applied to a lossless laboratory system in one dimension causality has been imposed to obtain stability of the solution and layer thicknesses can be obtained from the recovered dielectric profile or directly from the reflection data through a nonlinear generalization of the paley wiener theorem in fourier analysis 2 when the wavelength is much larger than the microstructural scale the above algorithms reconstruct a profile of the effective complex permittivity of the sea ice a composite of pure ice with random brine and air inclusions a theory of inverse homogenization has been developed which in this quasistatic regime further inverts the reconstructed permittivities for microstructural information beyond the resolution of the wave rigorous bounds on brine volume and inclusion separation for a given value of the effective complex permittivity have been obtained as well as an accurate algorithm for reconstructing the brine volume from a set of values 3 inverse algorithms designed to recover sea ice thickness have been developed a coupled radiative transfer thermodynamic sea ice inverse model has accurately reconstructed the growth of a thin artificial sea ice sheet from time series electromagnetic scattering data

thin ice thickness from satellite thermal imagery sea ice thickness is an important parameter in the surface energy exchange and mass balance of the polar oceans remote sensing offers the opportunity to monitor thin ice routinely we combine measurements of surface temperature from an advanced very high resolution radiometer avhrr with a thermodynamic ice growth model to estimate thin ice and its thickness distribution during the cold season in a beaufort sea area of perennial ice we find that thin ice up to a meter thick had a concentration of 18 in december 1990 and 3 in april 1991 thin ice concentrations near the ice edge in the greenland sea range from 20 to 50 these avhrr derived estimates generally compare well with thickness observations from upward looking sonar given the uncertainties in all the model inputs estimated from avhrr such as radiative and turbulent heat flux components and surface albedo we find that ice thickness is estimated with an uncertainty of roughly 50 the uncertainty in the cumulative thickness distribution is about 3 for ice less than 20 cm thick and about 9 for ice around 1 m thick these magnitudes are significantly smaller than the variations in thin ice observed by satellite in different months and regions we conclude that avhrr is capable of resolving the regional and seasonal variations in thin ice to a level of accuracy useful both for establishing a climatology and for testing ice models

the impact of an intense summer cyclone on 2012 arctic sea ice retreat 1 this model study examines the impact of an intense early august cyclone on the 2012 record low arctic sea ice extent the cyclone passed when arctic sea ice was thin and the simulated arctic ice volume had already declined 40 from the 2007 2011 mean the thin sea ice pack and the presence of ocean heat in the near surface temperature maximum layer created conditions that made the ice particularly vulnerable to storms during the storm ice volume decreased about twice as fast as usual owing largely to a quadrupling in bottom melt caused by increased upward ocean heat transport this increased ocean heat flux was due to enhanced mixing in the oceanic boundary layer driven by strong winds and rapid ice movement a comparison with a sensitivity simulation driven by reduced wind speeds during the cyclone indicates that cyclone enhanced bottom melt strongly reduces ice extent for about 2 weeks with a declining effect afterward the simulated arctic sea ice extent minimum in 2012 is reduced by the cyclone but only by 0 15 106 km2 4 4 thus without the storm 2012 would still have produced a record minimum

the response of the pacific storm track and atmospheric circulation to kuroshio extension variability an index of the kuroshio extension front strength is produced using a maximum covariance analysis between sea surface temperature sst and sea surface height ssh gradient observations and composites of the atmospheric state are presented during its positive and negative phases using reanalysis data 1992 2011 it is found that when the kuroshio extension is less more meandering with a stronger weaker sst front the atmospheric heat transport by transient eddies is increased in the western eastern pacific region consistent with an increase decrease in low level baroclinicity analysis of the eddy mean flow interaction shows that this zonal shift in heat transport forces anomalous barotropic flow in the eastern pacific where blocking frequency is strongly influenced the above relationships cannot be reconciled with the known response of the north pacific storm track to remote forcing from the tropical pacific nor can they be explained by the response of the ocean to atmospheric forcing via surface heat fluxes or winds rather the zonal shift in the storm track highlighted here and the associated changes in the large scale circulation are interpreted as a response to the interannual variability of the kuroshio extension front

upper cambrian to middle ordovician magnetostratigraphy from the kulumbe river section northwestern siberia abstract we present the magnetostratigraphy of an upper cambrian to middle ordovician sedimentary section sampled along the kulumbe river in northwestern siberia thermal demagnetization yields the determination of two magnetic components a component of steep inclination is interpreted as a remagnetization acquired during the emplacement of the siberian traps at the permian triassic boundary another component with a moderate inclination essentially carried by hematite and sometimes by magnetite likely represents a syndepositional or nearly syndepositional magnetization of the studied deposits a sequence of 17 magnetic intervals is observed between the upper part of the upper cambrian and the tremadoc three of them being poorly defined by single samples we also find that the llanvirn magnetostratigraphic sequence contains only one reversed polarity interval together with magnetostratigraphic results previously obtained from the moyero river section from siberia our data suggest the occurrence of a 25 30 myr long period during the lower and the middle ordovician characterized by a very low magnetic reversal frequency possibly containing a superchron and dominated by reversed polarity this geomagnetic feature would be compatible with a time constant of about 150 myr in the reversal process through the whole phanerozoic

palaeomagnetism of lower cambrian sediments from the olenek river section northern siberia palaeopoles and the problem of magnetic polarity in the early cambrian summary new palaeomagnetic data from the lower and middle cambrian sedimentary rocks of northern siberia are presented during stepwise thermal demagnetization the stable characteristic remanence chrm directions have been isolated for three cambrian formations both polarities have been observed and mean chrm directions for normal polarity are kessyusa formation lower cambrian d 145 i 4o n 12 ug5 12 8 pole position cd 38 s a 165 e erkeket formation lower cambrian stratigraphically highly d 152 i 47 n 23 ug5 6 8 pole position cd 45 s a 159 e yunkyulyabit yuryakh formation middle cambrian d 166 i 33 n 38 ctg5 4 6 pole position 0 36 s l 140 e these poles are in good agreement with the apparent polar wander path based on the bulk of existing cambrian palaeomagnetic data from the siberian platform in cambrian times the siberian platform probably occupied southerly latitudes stretching from about 35 to o and was oriented reversely with respect to its present position siberia moved northwards during the cambrian by about 10 of latitude this movement was accompanied by anticlockwise rotation of about 30 the magnetostratigraphic results show the predominance of reversed polarity in the early cambrian and an approximately equal occurrence of both polarities in the part of the middle cambrian studied these results are in good agreement with the palaeomagnetic polarity timescale for the cambrian of the siberian platform constructed previously by khramov et al 1987

late palaeozoic to triassic evolution of the turan and scythian platforms the pre history of the palaeo tethyan closure abstract a number of en echelon arranged southwest facing arc fragments of palaeozoic to jurassic ages sandwiched between two fairly straight east northeast trending boundaries constitute the basement of the scythian and the turan platforms located between the laurasian and tethyside units they have until now largely escaped detection owing to extensive jurassic and younger cover and the inaccessibility of the subsurface data to the international geological community these units are separated from one another by linear gently curved faults of great length and steep dip those that are exposed show evidence of strike slip motion the arc units originally constituted parts of a single silk road arc located somewhere south of the present day central asia for much of the palaeozoic although by the late carboniferous they had been united into a continental margin arc south of the tarim basin and equivalent units to the west and east they were stacked into their present places in northern afghanistan turkmenistan caucasus and the northern black sea by large scale right lateral strike slip coastwise transport along arc slicing and arc shaving strike slip faults in the triassic and medial jurassic simultaneously with the subductive elimination of palaeo tethys this gigantic dextral zone the silk road transpression was a trans eurasian structure and was active simultaneously with another similar system the gornostaev keirogen and greatly distorted eurasia the late palaeozoic to jurassic internal deformation of the dniepr donets aulacogen was also a part of the dextral strain in southern europe when the emplacement of the scythian and turan units was completed the elimination of palaeo tethys had also ended and neo tethyan arcs were constructed atop their ruins mostly across their southern parts the western end of the great dextral zone that emplaced the turan and scythian units horsetails just east of north dobrudja and a small component goes along the tornquist teisseyre lineament

inversion of snow parameters from passive microwave remote sensing measurements by a neural network trained with a multiple scattering model the inversion of snow parameters from passive microwave remote sensing measurements is performed with a neural network trained with a dense media multiple scattering model the input output pairs generated by the scattering model are used to train the neural network simultaneous inversion of three parameters mean grain size of ice particles in snow snow density and snow temperature from five brightness temperatures is reported it is shown that the neural network gives good results for simulated data the absolute percentage errors for mean grain size of ice particles and snow density are less than 10 and the absolute error for snow temperature is less than 3 k the neural network with the trained weighting coefficients of the three parameter model is also used to invert ssmi data taken over the antarctic region

palaeomagnetism of the lower ordovician orthoceras limestone st petersburg and a revised drift history for baltica in the early palaeozoic summary palaeomagnetic investigation of lower ordovician limestone in the vicinity of st petersburg yields a pole position at latitude 34 7 n longitude 59 1 e dp dm 5 7 6 4 a probable primary remanence origin is supported by the presence of a field reversal the limestone carries one other remanent magnetization component associated with a mesozoic remagnetization event an apparent polar wander path is compiled for baltica including the new result ranging in age from vendian to cretaceous ages of the published lower to midpalaeozoic palaeomagnetic pole positions are adjusted in accordance with the timescale of tucker mckerrow 1995 the new arenig result is the oldest of a series of ordovician and silurian palaeomagnetic pole positions from limestones in the baltic region there are no data to constrain apparent polar wander for the tremadoc cambrian and latest vendian if the fen complex results previously taken to be vendian in age c 565 ma are reinterpreted as permian remagnetizations an early ordovician cambrian vendian cusp in the polar wander path for baltica is eliminated the apparent polar wander curve might then traverse directly from poles for vendian dykes on the kola peninsula c 580 ma towards our new arenig pole c 480 ma the consequence of this change in terms of the motion of baltica in cambrian times is to reduce significantly a rotational component of movement the new arenig pole extends knowledge of ordovician apparent polar wander an increment back in time and confirms the palaeolatitude and orientation of baltica in some published palaeogeographies exclusion of the fen complex result places baltica in mid to high southerly latitudes at the dawn of the palaeozoic consistent with faunal and sedimentological evidence but at variance with some earlier palaeomagnetic reconstructions

reconstructions of the continents around the north atlantic at about the 60th parallel abstract late carboniferous early tertiary apparent polar wander apw paths 300 40 ma for north america and europe have been tested in various reconstructions these paths demonstrate that the 500 fathom bullard et al fit is excellent from late carboniferous to late triassic times but the continental configuration in northern pangea changed systematically between the late triassic ca 214 ma and the mid jurassic ca 170 ma due to pre drift extension best fit north atlantic reconstructions minimize differences in the late carboniferous early jurassic and late cretaceous tertiary segments of the apw paths but an enigmatic difference exists in the paths for most of the jurassic whereas for the early cretaceous the data from europe are nearly non existent greenland s position is problematic in a bullard et al fit because of a late triassic early jurassic regime of compression 300 km that would be inherently required for the norwegian shelf and the barents sea but which is geologically not defensible we suggest a radically new fit for greenland in between europe and north america in the early mesozoic this fit keeps greenland locked to europe for the late paleozoic early mesozoic and maintains a reconstruction that better complies with the offshore geological history of the norwegian shelf and the barents sea pre drift a24 extension amounted to approximately 450 km on the mid norwegian shelf but with peak extension in the late cretaceous

dramatic interannual changes of perennial arctic sea ice linked to abnormal summer storm activity 1 the perennial september arctic sea ice cover exhibits large interannual variability with changes of over a million square kilometers from one year to the next here we explore the role of changes in arctic cyclone activity and related factors in driving these pronounced year to year changes in perennial sea ice cover strong relationships are revealed between the september sea ice changes and the number of cyclones in the preceding late spring and early summer in particular fewer cyclones over the central arctic ocean during the months of may june and july appear to favor a low sea ice area at the end of the melt season years with large losses of sea ice are characterized by abnormal cyclone distributions and tracks they lack the normal maximum in cyclone activity over the central arctic ocean and cyclones that track from eurasia into the central arctic are largely absent fewer storms are associated with above average mean sea level pressure strengthened anticyclonic winds an intensification of the transpolar drift stream and reduced cloud cover all of which favor ice melt it is also shown that a strengthening of the central arctic cyclone maximum helps preserve the ice cover although the association is weaker than that between low cyclone activity and reduced sea ice the results suggest that changes in cyclone occurrence during late spring and early summer have preconditioning effects on the sea ice cover and exert a strong influence on the amount of sea ice that survives the melt season

paleozoic northward drift of the north tien shan central asia as revealed by ordovician and carboniferous paleomagnetism abstract three new middle late ordovician and two new early carboniferous paleomagnetic poles have been obtained from the north tien shan zone ntz of the ural mongol belt in kyrgyzstan and kazakhstan paleolatitudes for the carboniferous are unambiguously northerly and average 15 5 n whereas the ordovician paleolatitudes 6 9 and 9 are inferred to be southerly given that a very large 180 rotation of the ntz would be necessary during the middle paleozoic if the other polarity option was chosen thus the ntz drifted northward during much of the paleozoic east west drift cannot be determined as is well known from paleomagnetic data in addition detailed thermal demagnetization analysis reveals two overprints one of recent age and the other of permian age which is a time of strong deformation in the ntz the paleolatitude of the combined permian overprint is 30 5 2 n the paleolatitudes collectively track those predicted for the area by extrapolation from baltica very well but are different from those of siberia for ordovician times this finding is compatible with sengor and natal in s sengor a m c natal in b a 1996 paleotectonics of asia fragments of a synthesis in yin a harrison m eds the tectonic evolution of asia cambridge univ press cambridge pp 486 640 model of tectonic evolution of the ural mongol belt and disagrees with the models of other researchers declinations of the ordovician and early carboniferous results range from northwesterly to northeasterly and are clearly affected by local relative rotations which seem characteristic for the entire ntz because the permian overprint declinations also show such a spread apparently the important latest paleozoic triassic deformation involved shear zone related rotations as well as folding and significant granitic intrusions

magnetostratigraphy of the moyero river section north western siberia constraints on geomagnetic reversal frequency during the early palaeozoic summary we present the magnetostratigraphy of the early palaeozoic moyero river section in north western siberia the section investigated which consists mainly of reddish limestones marls and greyish limestones extends from the upper cambrian to the lower silurian palaeomagnetic analyses reveal two magnetic components one is interpreted as a remagnetization acquired during siberian trap emplacement the other is believed to be early diagenetic consistent with the established lower palaeozoic apparent polar wander path for siberia reversed polarity dominates from the upper cambrian to the middle ordovician while normal polarity dominates from the upper ordovician to the lower silurian only a few reversals which are poorly defined are observed through the section in particular during the llandeilo these data are in agreement with previous magnetostratigraphic data from the baltic platform and siberia and indicate that magnetic reversal frequency was low during the ordovician because of the time delayed process of acquisition of the magnetization carried by haematite we cannot clearly ascertain if a reversed superchron occurred during the lower to middle ordovician however our results suggest that a 15 myr long reversed interval existed during the arenig

palaeomagnetism of east siberian traps and kimberlites two new poles and palaeogeographic reconstructions at about 360 and 250 ma summary we studied basalt sills and dykes and kimberlite pipes from the eastern part of the siberian platform these are spread out over a few hundred kilometres and are divided into two age groups late permian early triassic mir aikhal and olenyek regions and late devonian early carboniferous viluy and markha basins aikhal region the palaeomagnetic poles determined for each sill or dyke are statistically different from each other but averaging all corresponding directions from these sills and dykes with those from kimberlites of different generations yields results with acceptable statistics this is probably due to the averaging out of secular variation and or changes in magnetic polarity the resulting palaeomagnetic poles allow one to reconstruct the palaeopositions of siberia during the two large flood basalt events at about 360 and 250 ma a significant rotation of the siberian platform during the devonian and carboniferous is suggested the new data are in general agreement with some earlier palaeomagnetic poles for the late permian early triassic traps of the tungusska basin and significantly reduce uncertainties for previous late devonian early carboniferous siberian poles which were very scattered together with geological and absolute age data the palaeomagnetic data support the hypothesis that kimberlite magmatism and trap intrusions were both rapid and relatively close in time the 360 ma event is emerging as a magmatic event with considerable extent over the russian and siberian platforms related to incipient continental break up and triple junction formation possibly at or near the time of the frasnian famennian mass extinction

early paleozoic paleomagnetism of east kazakhstan implications for paleolatitudinal drift of tectonic elements within the ural mongol belt abstract conflicting paleogeographic reconstructions of the ural mongol fold belt have been developed over the past decade very few of them however have been based on paleomagnetic data which still remain scarce the chingiz range in northeastern kazakhstan provides an opportunity to evaluate the tectonic evolution of the central part of this belt through extensive paleomagnetic studies in this paper we report the results from upper cambrian andesites and lower ordovician tuffaceous sandstones within the chingiz range a high temperature component htc decaying to the origin is isolated from upper cambrian rocks at eight sites with an easterly and low intermediate upward direction this component passes the tilt test and is likely primary a htc is also isolated from lower ordovician rocks at 11 sites these site means exhibit a shallow inclination girdle distribution within the southeast quadrant likely due to net rotations within the complex structure studied the inclination only tilt test is positive and the best grouping of data is observed at 100 untilting also included in our paleolatitudinal analyses are new middle and late paleozoic paleolatitudes from nearby parts of the chingiz range as well as published paleomagnetic data from central and east kazakhstan we favor normal polarity of the early paleozoic results of this paper and conclude that the study area moved northward throughout the paleozoic the observed paleolatitudes generally fit the siberian reference data and hence indicate coherent latitudinal motion of the boshekul chingiz tectonic zone and the siberian plate

the role of the kazakhstan orocline in the late paleozoic amalgamation of eurasia article i nfo the kazakhstan orocline a horseshoe shaped belt with volcanic arcs of devonian external and late paleozoic internal age is thought to have formed as a result of convergence between the cratons of siberia baltica and tarim leading to the amalgamation of eurasia paleomagnetic and geologic data indicate that in the middle devonian the arc which is now strongly curved was nearly straight near the northwest southeast trending volcanic margin of a kazakhstania continent to constrain the age of oroclinal bending we conducted a paleomagnetic study of late carboniferous to late permian subduction related volcanics from the middle nw and north eastern ne limbs of the orocline our new results indicate that the rotation of the middle arm of the orocline was essentially completed by the earliest permian while the ne arm probably was still 50 short of its final orientation with respect to baltica the rotation of or rotation within the ne arm was completed by the late permian the paleomagnetic data constraining the timing and rotation patterns lead us to propose the following scenario for the bending of the kazakhstan orocline the orogenic deformation scenario began in the late devonian when an initial collision with tarim pinned kazakhstania s southern corner while a dextral shear motion and a considerable clockwise rotation of siberia dragged its northern end relative convergence between siberia and tarim caused initial buckling of the kazakhstania continental element trapped between them subdividing the belt into three sw nw ne segments continued subduction under the established limbs of the orocline with an estimated outward directed subduction velocity of well less than 1 cm yr gradually led to closure of the intervening junggar balkhash oceanic basin and tightening of the orocline 2008 elsevier b v all rights reserved

dependency of the north pacific winter storm tracks on the zonal distribution of mjo convection 1 we investigate the effects of the tropical madden julian oscillation mjo convection on the zonal location and intensity of storm activity during the boreal cool season nov 1 to feb 28 120 days over the pacific ocean as tropical convection shifts eastward from the eastern indian ocean to the western north pacific mjo induced local hadley circulation leads to an eastward displacement of extratropical rossby wave source rws consequently this influence leads to an eastward shift of the peak area of the storm track the storm track is strongest with the mjo convection over the eastern indian ocean phase 3 and it experiences the suppression when mjo convection is located over the maritime continents phase 4 and it increases again when the mjo propagates to the western pacific phase 5 after which it weakens again phase 6 the intensity of the storm track particularly over the western north pacific 120 e 180 is determined by the integrated effects of three factors the midlatitude convective forcing mcf the jet stream and rws these factors are associated with the locations of mjo convections it is estimated that mjo induced suppression accounts for only 2 5 of the total observed midwinter suppression mws however the pattern generated by the mjo is remarkably similar to the observed meridional displacement of north pacific storm track associated with sub seasonal variation we conclude that the spatial distribution of mjo affects the variation of the pacific storm track but is not a cause of the mws

palaeomagnetism of ordovician and silurian rocks from the chu yili and kendyktas mountains south kazakhstan summary despite significant progress during the last decade the overwhelming majority of the details of the crustal evolution of kazakhstan remain enigmatic the central question of whether kazakhstan amalgamated during the ordovician and has acted as a coherent microplate since or whether kazakhstan is the result of continuous accretion of terranes and arcs along a major subduction system throughout the palaeozoic is still unanswered defining structural units and reconstructing their interaction relative to each other and with respect to siberia and baltica will improve our understanding of continent formation in central asia addressing this problem a detailed palaeomagnetic study of the palaeozoic formations in the chu yili and kendyktas mountains south kazakhstan was undertaken detailed stepwise thermal demagnetization experiments reveal the presence of a post folding component of magnetization with intermediate to high unblocking temperatures component a in almost all samples the in situ mean directions identified in 31 sites range in declination between 150 and 260 and show intermediate and upward pointing inclinations based on the mean inclination a late palaeozoic to early mesozoic age is assumed for this secondary component of magnetization after removal of component a a second component of magnetization component b was identified in red coloured argillites of early arenigian age kendyktas mountains as well as in sediments of early silurian and late silurian to early devonian age chu yili mountains component b passes the fold test enkin 2003 on the 95 per cent confidence level and yields a bedding corrected site mean direction of d 9 2 i 16 9 five sites k 26 9 95 15 0 for the lower ordovician unit and d 346 9 i 23 8 eight sites k 20 8 95 12 4 for the silurian and lower devonian units based on the age of angular unconformities the timing of regional deformation in the agalatas area can be constrained to be late ordovician in age and middle devonian in the chu yili area based on the mean inclination a southerly palaeolatitude of 8 6 8 7 7 6 can be derived for the study area during the early to late ordovician and a northerly palaeolatitude of 12 4 7 7 6 6 for the silurian to early devonian the observed mean declinations for the post folding component a are significantly different from the expected reference directions for the permian based on either the apparent polar wander path for baltica or siberia and suggest counter clockwise rotations of kazakhstan with respect to both during devonian to permian time

late devonian palaeomagnetism of the north tien shan kyrgyzstan can secular variation vary on a short timescale summary we studied more than 80 lava flows from a 600 m thick pile of upper devonian frasnian basalts and andesites of the aral formation in the north tien shan kyrgyzstan central asia with the aid of stepwise thermal demagnetization a high temperature dual polarity component was reliably isolated from most flows the primary origin of the high temperature component is demonstrated by positive reversal conglomerate and fold tests the most prominent and intriguing feature of this late devonian data set involves a clear distinction in angular dispersion between the lower and upper parts of the studied section a rather low concentration parameter k 13 and several directional anomalies characterize the lower section in contrast a much better grouping k 46 and a lack of directional outliers is observed for the dual polarity vectors from the upper flow sequence of the formation we analysed different mechanisms to account for this directional pattern and found that it is possible in just two ways one is to assume that secular variation sv in the upper sequence is strongly underrepresented and it is a coincidence that the mean directions of both polarities are statistically antipodal and the corresponding concentration parameters are statistically equal the other explanation is to hypothesize that the magnitude of sv can vary several fold at the same palaeolatitude and over time intervals estimated as 10 5 10 6 yr this is in sharp contrast with other models of sv where this magnitude has been assumed to be rather time independent for a givenlatitude ourhypothesisaccountsfortheobservedirregularitiesinpalaeomagneticdata but makes attempts to establish a correlation between sv and other parameters geographic latitude reversal frequency age etc more difficult we are aware however that more data are needed to refute or confirm it