sedimentary characteristics and origin of the late pleistocene ice complex on north east siberian arctic coastal lowlands and islands a review abstract the origin of late pleistocene ice rich fine grained permafrost sequences ice complex deposits in arctic and subarctic siberia has been in dispute for a long time corresponding permafrost sequences are frequently exposed along seacoasts and river banks in yedoma hills which are considered to be erosional remnants of late pleistocene accumulation plains detailed cryolithological sedimentological geochronological and stratigraphical results from 14 study sites along the laptev and east siberian seacoasts were summarized for the first time in order to compare and correlate the local datasets on a large regional scale the sediments of the ice complex are characterized by poorly sorted silt to fine sand buried cryosols toc contents of 1 2 4 8 wt and very high ground ice content 40 60 wt absolute a second large constituent of the ice complex are large syngenetic ice wedges resulting in a total ice content of the ice complex of up to 80 vol ice complex deposits were mostly formed during the middle weichselian interstadial and or during the late weichselian stadial periods a conceptual model of nival lithogenesis of ice complex deposits was developed that integrates various other formation hypotheses a combination of various local and regional paleogeographical geological and paleoclimate conditions controlled the formation of ice complex sequences during the late pleistocene in northern east siberia they are chronologically and stratigraphically but not genetically equivalent to eurasian and alaskan loess deposits

relationship between cyclone tracks anticyclone tracks and baroclinic waveguides abstract this study presents observational results concerning the structure and evolution of high frequency fluctuations with periods shorter than 6 days in the geopotential height field the results are based on a statistical analysis of 1000 500 and 250 mb height fields derived from twice daily nmc final analyses over the northern hemisphere for the 20 winters 1964 65 through 1983 84 the disturbances assume the form of waves elongated in the meridional direction with a mean wavelength of 4000 km a westward tilt with height and a mean eastward phase propagation of 12 1 5 m s 1 these results support an interpretation in terms of finite amplitude baroclinic waves whose structure and evolution varies with geographical location over the continents and especially along the eastern slopes of the rockies and the tibetan plateau the waves show marked departures in structure and evolution from those over the oceans in particular we find evidence of a systematic influence of the terrain in steering the

interannual and decadal modulations recently observed in the pacific storm track activity and east asian winter monsoon abstract interannual variability of the north pacific storm track observed over 17 recent winters is documented the local storm track activity is measured by a meridional flux of sensible heat associated with the lower tropospheric subweekly fluctuations the interannual variability in the heat flux over the northwestern nw pacific is found to be strongest in midwinter the first empirical orthogonal function of the interannual variability in midwinter captures the decadal tendency toward the enhanced storm track activity in midwinter over the nw pacific in association with the decadal weakening of the east asian winter monsoon siberian high and the aleutian low that occurred in the late 1980s the most marked signature of this enhancement is that the midwinter minimum in the storm track activity which had been apparent in the early to mid 1980s almost disappeared afterward as opposed to linear theory of baroclinic instability the enhanced activity occurred despite the weakening of the pacific j

poleward deflection of storm tracks an analysis of 11 years of european centre for medium range weather forecasts data focuses primarily on the vertically averaged high frequency transients the conclusions are discussed in the context of a the winter storm track b monthly variability and c interannual variability a winter storm track results show that the pattern of the forcing by the high frequency eddies along the storm track is highly correlated with the stationary circulation and the forcing itself is primarily responsible for the location of the trough ridge system associated with the stationary flow the results also clarify the role of wind component covariance terms u9y9 and y9 2 2 u9 2 in the column averaged vorticity forcing the simpler term u9y9 has the well known effect of intensifying the anticyclonic cyclonic tendencies on the southern northern side of the jet thereby producing an increase in the barotropic component of the zonal jet the y9 2 2 u9 2 term displays a quadrupole pattern which is also approximately in phase with the trough ridge system associated with the stationary flow b monthly variability eddy activity has been shown to possess a seasonal life cycle increasing during the early fall and reaching a maximum around the month of november then decaying for most of the winter months month to month variations in eddy activity over the pacific ocean show that energy levels increase up through november decreasing thereafter at the same time the trough ridge circulation pattern is intensifying by december baroclinicity in the western pacific has increased substantially and low level eddies are found to break by the middle of the ocean upper level eddies start to break well before reaching the west coast of north america resulting in a displacement of the maximum in y9 2 2 u9 2 westward from its november position and increasing the trough ridge forcing by the high frequency eddies c interannual variability wintertime eddy kinetic energy is seen to extend further eastward through the pacific ocean during the warm phase but displays an abrupt termination during the cold phase anomalies in the eddy transient forcing tend to be quite similar to that of the pacific north american pattern itself the extension of the storm track during the warm phase resembles that of fall conditions and is present in the winter season because the source of low level baroclinicity

inversion of field data in fault tectonics to obtain the regional stress iii a new rapid direct inversion method by analytical means summary a new method for determining the reduced stress tensor with four degrees of freedom the orientations of the three principal stress axes as well as the ratio of principal stress differences using fault slip data or focal mechanisms of earthquakes is presented from a computational point of view the inversion of fault slip data is made in a direct way by purely analytical means as a result the determination process is extremely fast and adaptable on small microcomputers from a physical point of view the method aims at simultaneously i minimizing the angles between theoretical shear stress and actual slip vector and ii having relative magnitudes of shear stress large enough to induce slip despite rock cohesion and friction examples of application to actual fault slip data sets with good or poor variety of fault slip orientations are shown the double significance of the basic criterion adopted results in a more realistic solution of the inverse problem than the single minimization of the shear stria angle

fault kinematics and stress fields in the rwenzori mountains uganda the rwenzori mountains in western uganda form an active rift transfer zone in the western branch of the east african rift system here we quantify local stress fields in high resolution from field observations of fault structures to shed light on the complex polyphase tectonics expected in transfer zones we apply the multiple inverse method which is optimized for heterogeneous fault slip data to the northern and central rwenzori mountains observations from the northern rwenzori mountains show larger heterogeneity than data from the central rwenzori including unexpected compressional features thus the local stress field indicates polyphase transpressional tectonics we suggest that transpression here is linked to rotational and translational movements of the neighboring victoria block relative to the rwenzori block that includes strong overprinting relationships stress inversions of data from the central rwenzori mountains indicate two distinct local stress fields these results suggest that the rwenzori block consists of smaller blocks

convection patterns in the tropical pacific and their influence on theatmospheric circulation at higher latitudes abstract patterns of outgoing longwave radiation olr have been analyzed over the tropical indian and pacific oceans in order to identify the varying influence of their associated convective anomalies on the circulation at higher latitudes particular attention has been given to the changes related to el nino southern oscillation enso events the two leading eofs emperical orthogonal functions of monthly olr anomaly patterns for the region between 20 n 20 s and 70 e 120 w express complementary variations between centers located 1 near 170 w just south of the equator and over the philippines and 2 slightly south of the equator near 145 w and slightly north of the equator near 165 e cluster analysis over a smaller area between 10 s 10 n and 140 e 140 w has highlighted enso related changes with two of the six clusters associated with moderate en and strong en el nino events and a third including most la nina ln events the olr anomaly patterns associated with the 1986 87 and 1991 92 war

north pacific gyre oscillation modulates seasonal timing and ecosystem functioning in the california current upwelling system 1 on interannual and longer time scales dynamical and biogeochemical fluctuations in the north pacific are dominated by two modes of variability namely the pacific decadal oscillation and the north pacific gyre oscillation npgo in this study the regional expression of the npgo in the california current system ccs is detailed the statistical relationship between the npgo index and nearshore wind variability mostly upwelling favorable along the u s west coast is strongest in the wintertime december to march off central california most importantly npgo fluctuations are associated with a seasonal shift of 1 2 months in the onset of the upwelling season regional numerical simulations show that an early late onset of upwelling during the positive negative phase of the npgo leads to a more less productive planktonic ecosystem throughout spring and summer i e several months after the direct npgo effects on the system have ceased these results bring new light on the california ecosystem variability as observed in atypical years such as 2005 and 2007

a new perspective on southern hemisphere storm tracks abstract a detailed view of southern hemisphere storm tracks is obtained based on the application of filtered variance and modern feature tracking techniques to a wide range of 45 yr european centre for medium range weather forecasts ecmwf re analysis era 40 data it has been checked that the conclusions drawn in this study are valid even if data from only the satellite era are used the emphasis of the paper is on the winter season but results for the four seasons are also discussed both upper and lower tropospheric fields are used the tracking analysis focuses on systems that last longer than 2 days and are mobile move more than 1000 km many of the results support previous ideas about the storm tracks but some new insights are also obtained in the summer there is a rather circular strong deep high latitude storm track in winter the high latitude storm track is more asymmetric with a spiral from the atlantic and indian oceans in toward antarctica and a subtropical jet related lower latitu

storm tracks in the southern hemisphere abstract from 1979 to 1989 global european centre for medium range weather forecasts ecmwf analyses of many meteorological variables important in baroclinic storms have been bandpass filtered to highlight fluctuations on 2 to 8 day time scales in order to illuminate the relationships among the variables in baroclinic storm track regions because of the greater zonal symmetry in the southern hemisphere sh versus the northern hemisphere nh it is possible to examine these relationships over a zonal sector without being dominated by local effects associated with jet stream entrance and exit regions of the storm tracks the bandpassed variance of geopotential height is used to define the storm track and its meridional profile has a pronounced midlatitude maximum in the sh the locations of the jet stream and the variance maxima of meridional and zonal velocity components vorticity vertical motion specific humidity and temperature all bear a distinctive relationship to the storm track but the lat

new insights into the weichselian environment and climate of the east siberian arctic derived from fossil insects plants and mammals multidisciplinary study of a key section on the laptev sea coast bykovsky peninsula east lena delta in 1998 2001 provides the most complete record of middle and late weichselian environments in the east siberian arctic the 40 m high mamontovy khayata cliff is a typical ice complex section built of icy silts with a network of large syngenetic polygonal ice wedges and is richly fossiliferous in combination with pollen plant macrofossil and mammal fossils a sequence of ca 70 insect samples provides a new interpretation of the environment and climate of the area between ca 50 and 12 ka the large number of radiocarbon dates from the section together with an extensive 14c database on mammal bones allows chronological correlation of the various proxies the bykovsky record shows how climate change and the last glacial maximum in particular affected terrestrial organisms such as insects and large grazing mammals both during the presumed karginsky interstadial mis 3 and the sartanian glacial mis 2 the vegetation remained a mosaic arctic grassland with relatively high diversity of grasses and herbs and dominance of xeric habitats the tundra steppe type this biome was supported by a constantly very continental climate caused by low sea level and enormous extension of shelf land variations within the broad pattern were caused mainly by fluctuations in summer temperature related to global trends but overprinted by the effect of continentality no major changes in humidity were observed nor were advances of modern type forest or forest tundra recorded suggesting a major revision of the karginsky interstadial paradigm the changing subtypes of the tundra steppe environment were persistently favourable for mammalian grazers which inhabited the shelf lowlands throughout the studied period mammal population numbers were lowered during the lgm especially toward its end and then flourished in a short but impressive peak in the latest weichselian just before the collapse of the tundra steppe biome throughout mis 3 and mis 2 the climate remained very favourable for the aggradation of permafrost no events of regional permafrost degradation were observed in the continuous bykovsky sequence until the very end of the pleistocene

testate amoebae record from the laptev sea coast and its implication for the reconstruction of late pleistocene and holocene environments in the arctic siberia abstract our study aims to look for testate amobae ta in the surface and fossil sediments from the cape mamontov klyk 73 60 73 63 n 116 88 117 18 e southern coast of the laptev sea ca 150 km west of the lena delta and to discuss the potential of ta analysis for glacial interglacial environmental reconstructions in arctic siberia the radiocarbon age determination suggests that the studied sediments accumulated between ca 45 000 14c yr bp and present a total of 98 ta taxa were identified in the 10 recent surface and 59 fossil samples results of taxonomical identification and ecological analysis of ta in the modern and fossil samples suggest that major changes in the soil moisture conditions took place our results show that soil living taxa dominated the ta assemblages at the study sites during the past 45 000 years the environmental conditions of the study area were most favourable relatively warm and humid during the kargin interstadial ca 45 000 25 000 14c yr bp an opposite situation is reconstructed for the sartan stadial ca 25 000 15 000 14c yr bp during the kargin interstadial optimum conditions occurred between ca 44 000 and 40 000 14c yr bp characterised by highest ta abundances and taxa diversity this initial optimal phase was followed by the interval with drier and colder conditions about 40 000 30 000 14c yr bp the sediments dated between ca 24 000 and 18 000 14c yr bp show low ta abundances and diversity in agreement with the much colder and drier environments during the maximum phase of the last glacial the onset of the holocene is indicated by a broad representation of obligate hydrophilic taxa especially from genus difflugia suggesting wet and relatively warm conditions by comparison with other environmental proxies used in the studied sections as well as from the neighbouring arctic regions our results suggest that ta analysis can provide valuable information contributing to the better understanding of the late quaternary climate and environments in arctic siberia

an objective cyclone climatology for the southern hemisphere abstract an objective method is developed and used to derive a climatology of centers of cyclonic vorticity for the southern hemisphere based on twice daily european centre for medium range weather forecasts ecmwf 1000 hpa analyses during 1980 86 these centers were computed as local minima of geostrophic relative vorticity g extending previous studies based on pressure minima this use of g avoids a bias favoring slower and or deeper cyclones that occurs when pressure is used and includes a large number of additional mobile vorticity centers in the 45 55 s band that are missed where a local pressure minimum cannot be found an automated tracking algorithm similar to that of murray and simmonds is used to match predicted location pressure and g from previous track history with available centers large numbers of g centers were found south of 60 s and near the midlatitude continents as in previous studies these were a mixture of migratory centers and other fixed topographic features the maxi

seasonal variations in the southern hemisphere storm tracks and jet streams as revealed in a reanalysis dataset abstract regional characteristics of the climatological seasonal variations in southern hemisphere sh storm tracks are examined based on a reanalysis dataset when differences in vertical structure between the subpolar and subtropical jet streams spj and stj respectively are considered the regional characteristics can be interpreted reasonably well from a potential vorticity perspective of baroclinic eddy growth and downstream development of a baroclinic wave packet eddy activity in the upper and lower tropospheres is strongest in the core region of the spj over the eastern south atlantic and indian ocean throughout the year even in austral winter when the intense stj forms over the indian ocean and south pacific showing its eddy driven nature the spj accompanies the strong surface westerlies along a well defined baroclinic zone above an intense oceanic frontal zone in this core region of the storm track low level eddy activity is strongly correlated with the local near surface baroclinicity

tracing the exhumation history of the rwenzori mountains albertine rift uganda using low temperature thermochronology the rwenzori mtns form a striking feature within the albertine rift of the east african rift system they are made up of a dissected precambrian metamorphic basement block reaching heights of more

geometry of propagating continental rifts reconstruction of past plate configurations through palinspastic restoration of continental margins1 4 requires a detailed knowledge of the geometries of horizontal continental extension extension is often restricted to discrete linear zones termed rifts5 6 and rift models that invoke propagating vertical dykes and cracks7 10 are useful for assessing the relative significance and timing of uplift subsidence and extension in the tectonic evolution of rift basins however many models do not adequately account for the observed asymmetry of rifts i describe here the general three dimensional character of young and aborted continental rifts which can be used to derive a structural model for the propagation of rifts in continental lithosphere the rifts become asymmetric as a consequence of the role played by low angle normal faults in the overall rift geometry

the angular velocity of nubia relative to somalia and the location of the nubia somalia antarctica triple junction summary an ew analysis of geologically current plate motion across the southwest indian ridge swir and of the current location of the nubia antarctica somalia triple junction is presented spreading rates averaged over the past 3 2 myr are estimated from 103 well distributed nearly ridge perpendicular profiles that cross the swir all available bathymetric data are evaluated to estimate the azimuths and uncertainties of transform faults six are estimated from multibeam data and 12 from precision depth recorder pdr data if both the nubian and somalian component plates are internally rigid near the swir and if the nubia somalia boundary is narrow where it intersects the swir that intersection lies between 26 e and 32 e thus the boundary is either along the spreading ridge segment just west of the andrew bain transform fault complex abtfc or along some of the transform fault complex itself these limits are narrower than and contained within limits of 24 et o 33 e previously found by lemaux et al from an analysis of the locations of magnetic anomaly 5 the data are consistent with a narrow boundary but also consistent with a diffuse boundary as wide as 700 km the new nubia somalia pole of rotation lies 10 north of the bouvet triple junction which places it far to the southwest of southern africa the new angular velocity determined only from data along the swir indicates displacement rates of somalia relative to nubia of 3 6 0 5 mm yr 1 95 per cent confidence limits towards 176 s04 e between somalia and nubia near the swir and of 8 3 1 9 mm yr 1 95 per cent confidence limits towards 121 s59 e near afar the new nubia somalia angular velocity differs significantly from the nubia somalia angular velocity estimated from gulf of aden and red sea data this significant difference has three main alternative explanations i that the plate motion data have substantial unmodelled systematic errors ii that the nubian component plate is not a single rigid plate or iii that the somalian component plate is not a single rigid plate we tentatively prefer the third explanation given the geographical distribution of earthquakes within the african composite plate relative to the inferred location of the nubia somalia boundary along the swir

the multiple inverse method a new technique to separate stresses from heterogeneous fault slip data abstract a new inverse technique is presented here to separate stresses from heterogeneous fault slip data without a priori information on the stresses or on the classification of faults according to the stresses four parameters are determined by the inversion one for the shape of the stress ellipsoid and three for the direction of the stress axes accordingly the inversion is equivalent to the projection of the fault slip data to a point in four dimensional parameter space the data are divided into k element subsets to which the inverse technique is applied where k 4 or 5 is the optimal choice for the stability of solutions and for the reduction of computation significant solutions are identified as clusters in parameter space the technique is demonstrated first by simulated fault slip data as an example field data obtained from miocene fore arc sediments in western japan were processed by the method

an idealized nonlinear model of the northern hemisphere winter storm tracks abstract in this paper a nonlinear dry model forced by fixed radiative forcing alone has been constructed to simulate the northern hemisphere winter storm tracks a procedure has been devised to iterate the radiative equilibrium temperature profile such that at the end of the iterations the model climate closely resembles the desired target climate this iterative approach is applied to simulate the climatological storm tracks in january it is found that when the three dimensional temperature distribution in the model resembles the observed distribution the model storm tracks are much too weak it is hypothesized that this is due to the fact that eddy development is suppressed in a dry atmosphere owing to the lack of latent heat release in the ascending warm air to obtain storm tracks with realistic amplitudes the static stability of the target climate is reduced to simulate the enhancement in baroclinic energy conversion due to latent heat release with this modification the storm tracks in the

significance of a midlatitude sst frontal zone in the formation of a storm track and an eddy driven westerly jet abstract in a set of idealized aquaplanet experiments with an atmospheric general circulation model to which zonally uniform sea surface temperature sst is prescribed globally as the lower boundary condition an assessment is made of the potential influence of the frontal sst gradient upon the formation of a storm track and an eddy driven midlatitude polar front jet pfj and on its robustness against changes in the intensity of a subtropical jet stj in experiments with the frontal midlatitude sst gradient as that observed in the southwestern indian ocean transient eddy activity in each of the winter and summer hemispheres is organized into a deep storm track along the sst front with an enhanced low level baroclinic growth of eddies in the winter hemisphere another storm track forms just below the intense stj core but it is confined to the upper troposphere with no significant baroclinic eddy growth underneath the near surface westerlies are strongest near the midlatitude sst front as observe

characteristics of wave packets in the upper troposphere part i northern hemisphere winter abstract gridded data produced by the ecmwf reanalysis project have been analyzed to document the properties of wave packets in the northern hemisphere winter midlatitude upper troposphere based on results from earlier investigations 300 hpa meridional wind variations were chosen for analysis wave packet envelopes were also defined by performing complex demodulation on the wind data the properties of the wave packets are mainly illustrated using time lagged one point correlation maps performed both on and wave packet envelopes the results show that over most regions in the northern hemisphere winter with the exception of the deep tropics and near the aleutian low medium scale waves dominant wavenumber 5 8 exhibit the characteristics of downstream development and occur within wave trains that propagate with eastward group velocities much faster than the phase speeds of individual phases of the waves their group velocity is highly correlated with the local time mean 200 400 hpa wind while the

teleconnections between tropical pacific sst anomalies and extratropical southern hemisphere climate abstractteleconnections from tropical pacific sea surface temperature sst anomalies to the high latitude southern hemisphere sh are examined using observations and reanalysis analysis of tropical pacific sst anomalies is conducted separately for the central pacific cp and eastern pacific ep regions during the austral cold season extratropical sh atmospheric rossby wave train patterns are observed in association with both ep and cp sst variability the primary difference between the patterns is the westward displacement of the cp related atmospheric anomalies consistent with the westward elongation of cp related convective sst required for upper level divergence and rossby wave generation consequently cp related patterns of sh sst antarctic sea ice and temperature anomalies also exhibit a westward displacement but otherwise the cold season extratropical sh teleconnections are largely similar during the warm season however extratropical sh teleconnections associated with tropical cp and

post palaeozoic evolution of weathered landsurfaces in uganda by tectonically controlled deep weathering and stripping a model for the evolution of weathered landsurfaces in uganda is developed using available geotectonic climatic sedimentological and chronological data the model demonstrates the pivotal role of tectonic uplift in inducing cycles of stripping and tectonic quiescence for cycles of deep weathering it is able to account for the development of key landforms such as inselbergs and duricrust capped plateaux which previous hypotheses of landscape evolution that are based on climatic or eustatic controls are unable to explain development of the ugandan landscape is traced back to the permian following late palaeozoic glaciation a trend towards warmer and more humid climates through the mesozoic enabled deep weathering of the jurassic mid cretaceous surface in uganda during a period of prolonged tectonic quiescence uplift associated with the opening south atlantic ocean terminated this cycle and instigated a cycle of stripping between the mid cretaceous and early miocene deep weathering on the succeeding miocene to recent african surface has occurred from miocene to present but has been interrupted in the areas adjacent to the western rift where development of a new drainage base level has prompted cycles of stripping in the miocene and pleistocene

paleostress states at the south western margin of the central european basin system application of fault slip analysis to unravel a polyphase deformation pattern abstract we analyse the deformation pattern along the south western margin of the central european basin system cebs where upper carboniferous mesozoic rocks are uplifted due to the late cretaceous basin inversion the geometry of mesoscale faults and associated striae are used to calculate the stress state s responsible for the observed deformation each reduced stress tensor obtained comprises i the directions of the principal stress axes 1 2 and 3 1 2 3 and ii the ratio of principal stress differences r 2 3 1 3 we present a stress inversion technique that allows each stress state inherent in a heterogeneous fault population to be identified by integrating the results of the pbt method turner f j 1953 nature and dynamic interpretation of deformation lamellae in calcite of three marbles american journal of sciences 251 4 276 298 sperner b ratschbacher l and ott r 1993 fault striae analysis a turbo pascal program package for graphical presentation and reduced stress tensor calculation computers geosciences 19 1361 1388 and the multiple inverse method yamaji a 2000 the multiple inverse method a new technique to separate stresses from heterogeneous fault slip data journal of structural geology 22 4 441 452 this comprehensive approach not only facilitates the separation of complex data sets into homogeneous subsets but also guarantees that each stress state derived fulfils both the criteria of low misfit angles wallace bott hypothesis and high shear to normal stress ratios mohr coulomb criterion the reliability of our technique is confirmed by the fact that irrespective of i the number of fault slip data from an outcrop ii the number of subsets they represent and iii the proportion of newly formed and reactivated faults we obtain consistent results from outcrops of variously aged rocks this consistency concerns both calculated stress states as well as locally observed deformation sequences such local chronologies are derived from cross cutting relationships and superimposition of different fault slip data which individually are assigned to a consistent stress state a synthesis of results from different locations of the study area argues for the superposition of two main deformation events most prominently the area was affected by a stress state with a horizontal n s to ne sw directed maximum compression 1 and a low stress ratio which induced reverse and strike slip faulting a pure strike slip regime of e w to nw se directed compression with moderate stress ratios is less prevalent and probably younger the age of the youngest rocks documenting these two phases proves the stress fields to correspond to the polyphase late cretaceous tertiary basin inversion of the cebs during post cenomanian times the youngest tectonic imprints detected in the study area correspond to locally appearing extensional stress states with varying directions of 3 at many sites the youngest derived paleostress state coincides with the present day stress field in terms of the direction of the maximum horizontal stress axis s hmax the only stress state detected which pre dates the basin inversion corresponds to an extensional regime with an wnw ese to nw se directed 3 axis observed only locally in the n s striking leine graben and its prolongation to the north the fact that the majority of variously aged rocks exhibit only the traces of the latest deformation phases indicates a high degree of fault plane reactivation in the study area

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

the periglacial climate and environment in northern eurasia during the last glaciation this paper summarizes the results of studies of the late weichselian periglacial environments carried out in key areas of northern eurasia by several queen teams european science foundation esf programme quaternary environment of the eurasian north the palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the eu funded project eurasian ice sheets these data prove beyond any doubt that with the exception of the northwestern fringe of the taymyr peninsula the rest of the eurasian mainland and severnaya zemlya were not affected by the barents kara sea ice sheet during the last glacial maximum lgm inversed modelling based on these results shows that a progressive cooling which started around 30 ka bp caused ice growth in scandinavia and the northwestern areas of the barents kara sea shelf due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets in the rest of the eurasian arctic extremely low precipitation rates less than 50 mm yr 1 did not allow ice sheet growth in spite of the very cold temperatures palaeoclimatic and palaeoenvironmental conditions for the time prior to during and after the lgm have been reconstructed for the non glaciated areas around the lgm ice sheet with the use of faunal and vegetation records permafrost eolian sediments alluvial deposits and other evidences the changing environment from interstadial conditions around 30 ka bp to a much colder and drier environment at the culmination of the lgm at 20 15 ka bp and the beginning of warming around 15 ka bp have been elaborated from the field data which fits well with the modelling results

ferrel circulation variability in the southern hemisphere and its linkages with tropical and subtropical sea surface temperature 1 ferrel circulation variability in the southern hemisphere and its linkages with the tropical and subtropical sea surface temperature sst for the period 1979 2009 are investigated two dominant spatiotemporal patterns of ferrel circulation variability are identified one showing opposing change between the poleward and equatorward portion of 48 s of the ferrel circulation eof1 and the other showing a rather uniform change of the ferrel circulation eof2 an increasing trend is found for the eof1 indicating the strengthening weakening of the poleward equatorward portion of the ferrel circulation for the past three decades although the ferrel circulation strength index suggests an overall weakening of the ferrel circulation distinctly different forms of tropical and subtropical ocean variability are connected to the two dominant modes of ferrel circulation variability statistical analysis suggests that the eof1 has a close association with the warming trend of the tropical and subtropical oceans for the past three decades whereas the eof2 is significantly correlated with sst variability in the pacific that resembles the la nina modoki

the annual cycle of northern hemisphere storm tracks part i seasons abstractin this paper and part ii a comprehensive picture of the annual cycle of the northern hemisphere storm tracks is presented and discussed for the first time it is based on both feature trac

late quaternary ice rich permafrost sequences as a paleoenvironmental archive for the laptev sea region in northern siberia ice rich permafrost sequences with large polygonal ice wedges represent excellent archives for paleoenvironmental reconstruction such deposits contain numerous well preserved records ground ice paleosols peat beds different types of fossils which permit characterization of environmental conditions during a clearly defined period of the past 60 ka based on field investigations carried out within framework of the german russian project laptev sea system 2000 on the bykovsky peninsula se of the lena delta results from cryolithological studies sedimentological analyses as well as new radiocarbon data are presented for the first time it is shown that the ice complex accumulated without significant interruptions from approximately 60 k y b p until the end of the pleistocene geochemical data total organic carbon c n 13corg and the mass specific magnetic susceptibility clearly show changing environmental conditions from stadial to interstadial times in the late pleistocene and during the transition to the holocene these results permit us to reconstruct the development of an arctic periglacial landscape in the coastal lowland during ice complex formation in the late quaternary this evolution coincided generally with the global environmental trend up to marine isotope stage 4

bidimensional diagnostics variability and trends of northern hemisphere blocking abstractin this paper northern hemisphere winter blocking is analyzed through the introduction of a set of new bidimensional diagnostics based on geopotential height that provide information about the occurrence the duration the intensity and the wave breaking associated with the blocking this analysis is performed with different reanalysis datasets in order to evaluate the sensitivity of the index and the diagnostics adopted in this way the authors are able to define a new category of blocking placed at low latitudes that is similar to midlatitude blocking in terms of the introduced diagnostics but is unable to divert or block the flow furthermore over the euro atlantic sector it is shown that it is possible to phenomenologically distinguish between high latitude blocking occurring over greenland north of the jet stream and dominated by cyclonic wave breaking and the traditional midlatitude blocking localized over europe and driven by anticyclonic wave breaking these latter events are uniform

characteristics of the southern hemisphere winter storm track with filtered and unfiltered data abstract the structure and evolution of the fluctuations in synoptic scales in the southern hemisphere sh during winter are discussed using six years of european centre for medium range weather forecasts analyses it is shown that patterns from unfiltered meridional wind series in the sh display all the features needed to represent the synoptic scale waves typical periods and wavelengths are similar to those observed in the northern hemisphere 4 days 4000 km although over the pacific ocean they can be as high as 7 8 days and 4700 km respectively as in the northern hemisphere tilts are not geographically fixed but change with the stage of the evolution of the wave the phase speed of the waves agrees with the low level winds in extensive areas of the middle latitudes and ranges from 12 m s 1 in the indian ocean to 6 m s 1 in the pacific ocean the estimated group velocities achieve maximum values of about 38 m s 1 also in the indian ocean and agree with the upper level maximum winds in accor

re evaluation of the kinematics of victoria block using continuous gnss data the divergent boundary between the somalia and nubia plates is a complex tectonic domain where extensional processes are localized along narrow rift structures isolating small plates imbedded within the east african rift one of these tectonic units is the victoria plate which is the subject of this study here we process space geodetic data for 37 permanent gnss stations distributed along the nubia somalia and victoria plates to 1 compute the motion of the three plates in the itrf2008 reference frame and 2 deduce the relative motion of victoria with respect to its neighboring plates the nubia plate motion is computed from a set of 25 stations the somalia plate motion from a set of 7 stations and the victoria plate motion from a set of 5 stations the instantaneous relative euler poles for the nubia victoria and somalia victoria pairs are now evaluated as 10 6582on 32 9752eo 0 1196o myr and 8 0164os 32 2869oe 0 1589o myr respectively the computation of the relative inter plate velocities along victoria s plate boundary is straightforward in most situations because the western and northeastern boundary segments correspond to well developed rift basins where extension is mostly normal to rift basin flanks and seismicity concentrates along narrow structures this is particular evident on the western branch between victoria and nubia the southeastern limit of the victoria plate is poorly defined and geodetic data indicates that differential motion between somalia and victoria may be accommodated by a complex plate boundary area which roughly encompasses the masai terrain geodetic observations of the victoria somalia boundary along the eastern branch particularly in the manyara rift reveal highly oblique horizontal extension in this region seismicity is sparse which suggests that strain is accommodated by magmatic processes

paleoenvironmental and paleoclimatic records from permafrost deposits in the arctic region of northern siberia ice complexes extremely ice rich permafrost deposits with large ice wedges are widely distributed in the arctic region of northeast siberia they present excellent archives for the reconstruction of late quaternary paleoenvironmental conditions in nonglaciated areas in 1998 1999 and 2000 russian and german scientists worked together on the bykovsky peninsula southeast of the lena delta in order to investigate the ice complex and its associated sediments intensive cryolithological and sedimentological studies radiocarbon age determinations paleobotanical studies micropaleontological investigations studies of mammal and insect fossils and stable isotope analyses of ground ice were performed radiocarbon data have been obtained from the entire exposed sequence coveringapproximately the last 60 000 years the results indicate that compared with modern time the investig ated ice complex sequence was formed duringtwo cooler and more arid stages of the late pleistocene with relatively uniform environmental conditions separated by a stage with environmental variations and more intensive soil formation caused by climate amelioration the late pleistocene environmental changes were not as strong as those occurring during the pleistocene holocene transition where a sharp break is evident r 2002 elsevier science ltd and inqua all rights reserved

el nino flavors and their simulated impacts on atmospheric circulation in the high southern latitudes abstracttwo el nino flavors have been defined based on whether warm sea surface temperature sst anomalies are located in the central or eastern tropical pacific cp or ep this study further characterizes the impacts on atmospheric circulation in the high latitudes of the southern hemisphere associated with these types of el nino events though a series of numerical simulations using the national center for atmospheric research community atmosphere model cam comparing results with the interim ecmwf re analysis era interim cam simulates well the known changes to blocking over australia and a southward shift in the subtropical jet stream across the eastern pacific basin during cp events more importantly for the high southern latitudes cam simulates a westward shift in upper level divergence in the tropical pacific which causes the pacific south american stationary wave pattern to shift toward the west across the entire south pacific these changes to the rossby wave source region impact the south

vegetation and climate history in the laptev sea region arctic siberia during late quaternary inferred from pollen records abstract paleoenvironmental records from a number of permafrost sections and lacustrine cores from the laptev sea region dated by several methods 14 c ams tl irsl osl and 230 th u were analyzed for pollen and palynomorphs the records reveal the environmental history for the last ca 200 kyr for interglacial pollen spectra quantitative temperature values were estimated using the best modern analogue method sparse grass sedge vegetation indicating arctic desert environmental conditions existed prior to 200 kyr ago dense wet grass sedge tundra habitats dominated during an interstadial ca 200 190 kyr ago reflecting warmer and wetter summers than before sparser vegetation communities point to much more severe stadial conditions ca 190 130 kyr ago open grass and artemisia communities with shrub stands alnus fruticosa salix betula nana in more protected and moister places characterized the beginning of the last interglacial indicate climate conditions similar to present shrub tundra alnus fruticosa and betula nana dominated during the middle eemian climatic optimum when summer temperatures were 4 5 c higher than today early weichselian sparse grass sedge dominated vegetation indicates climate conditions colder and dryer than in the previous interval middle weichselian interstadial records indicate moister and warmer climate conditions for example in the interval 40 32 kyr bp salix was present within dense grass sedge dominated vegetation sedge grass artemisia communities indicate that climate became cooler and drier after 30 kyr bp and cold dry conditions characterized the late weichselian ca 26 16 kyr bp when grass dominated communities with caryophyllaceae asteraceae cichoriaceae selaginella rupestris were present from 16 to 12 kyr bp grass sedge communities with caryophyllaceae asteraceae and cichoriaceae indicate climate was significantly warmer and moister than during the previous interval the presence of salix and betula reflect temperatures about 4 c higher than present at about 12 11 kyr bp during the allerod interval but shrubs were absent in the younger dryas interval pointing to a deterioration of climate conditions alnus fruticosa betula nana poaceae and cyperaceae dominate early holocene spectra reconstructed absolute temperature values were substantially warmer than present up to 12 c shrubs gradually disappeared from coastal areas after 7 6 kyr bp when vegetation cover became similar to modern a comparison of proxy based paleoenvironmental reconstructions with the simulations performed by an earth system model of intermediate complexity climber 2 show good accordance between the regional paleodata and model simulations especially for the warmer intervals

the impact of wave packets propagating across asia on pacific cyclone development abstract in this paper ecmwf 40 yr reanalysis data have been examined to study the influence of upper level wave packets propagating across asia into the pacific on surface cyclone development over the pacific previous studies have shown that in winter wave packets propagate across asia over two branches a northern branch over siberia and a southern branch along the subtropical jet across southern asia results presented here show that subsequent to the presence of wave packets on either branch the frequency of occurrence of deep cyclones defined as cyclones with central pressure below 960 hpa as well as explosively deepening cyclones those with a deepening rate of 1 bergeron or more are significantly enhanced this enhancement also clearly follows the wave packet eastward as it propagates across the pacific wave packets from the two branches are found to interfere with each other such that if wave packets of the appropriate configuration are present on both the northern and southern branch s

midwinter suppression of baroclinic wave activity in the pacific abstract seasonal variations in baroclinic wave activity and jet stream structure in the northern hemisphere are investigated based upon over 20 years of daily data baroclinic wave activity at each grid point is represented for each day by an envelope function the lowpass filtered time series of the squared highpass filtered geopotential height baroclinic wave activity over the atlantic exhibits a single maximum in january whereas in the pacific it exhibits peaks in late autumn and in early spring and a significant weakening in midwinter which is more evident at the tropopause level than near the surface this suppression occurs despite the fact that the low level baroclinity and the intensity of the jet stream are strongest in midwinter based on the analysis of 31 day running mean fields for individual winters it is shown that over both the oceans baroclinic wave activity is positively correlated with the strength of the upper tropospheric jet for wind speeds up to 45 m s 1 when the strength of t

last glacial interglacial vegetation and environmental dynamics in southern siberia chronology forcing and feedbacks abstract radiocarbon dated pollen and diatom records from lake kotokel in southern siberia help to reconstruct the environmental history of the area since 47 kyr bp pollen spectra composition and reconstructed biome scores suggest predominance of a tundra steppe vegetation and variable woody cover 5 20 between 47 and 30 kyr bp indicating generally a harsh and unstable climate during this interval conventionally regarded as the interstadial within the last glacial the short term climate amelioration episodes in the glacial part of the records are marked by the peaks in taiga and corresponding minima in steppe biome scores and appear synchronously with the hemispheric temperature and precipitation changes recorded in the greenland ice cores and chinese stalagmites transition to full glacial environments occurred between 32 and 30 kyr bp the interval at 30 24 kyr bp was probably the driest and coldest of the whole record as indicated by highest scores for steppe biome woody coverage

el nino related variations in the southern pacific atmospheric circulation model versus observations our objective is two fold 1 to study the influence of tropical pacific sea surface temperature sst anomalies associated with the el nino southern oscillation enso on the southern pacific atmospheric circulation using observations and 2 to assess the ability of a fully comprehensive gcm to reproduce the observed enso related variations the observed circulation features were derived from the national center for environmental prediction ncep reanalyses of observations the gcm used is the atmospheric component of the united kingdom meteorological office ukmo unified model um a detailed study of the impact of the enso on the seasonal mean circulation and on the intraseasonal variability on synoptic time scales has been carried out using both the model and ncep data for austral summer season we have also investigated the relationship between the high frequency hf transients and the quasi stationary mean circulation during selected enso years a regional hadley cell intensity in the tropical pacific has been used as an el nino index to classify the warming and cooling years for our composite analysis during el nino years the regional hadley cell acts as a medium through which the enhanced equatorial convection forces a train of rossby waves to produce the quasi stationary circulation anomalies in extratropics the hadley cell weakens during la nina years and the equatorial convection moves further westwards the rossby wave response to this situation is to reverse the phase of the quasi stationary circulation anomalies by 180 as expected these features are fairly well simulated by the um though the extratropical circulation anomalies in response to the equatorial convection is found about 30 longitude further eastwards than observed during el nino years the model confirms the observational evidence that the storm track variations in the southern subtropical pacific are largely driven by variations in the south pacific convergence zone spcz associated with the el nino and la nina events however the model struggles to reproduce the significant storm track activity present in the ncep data related to the westerly jet stream during la nina years finally the relationship between the hf transients and the quasi stationary anomalies found in both the model and observations supports the role of the hf transients in forcing the time mean circulation as reported by hoerling and ting 1994 for the pacific north american pna region

synoptic behavior of baroclinic eddies during the blocking onset abstract synoptic behavior of individual baroclinic eddies in the course of their interactions with amplifying blocking anticyclones is examined based upon a 30 year record of the tropospheric circulation in the northern hemisphere winter high pass filtered as well as unfiltered fields of geopotential height and potential vorticity were composited relative to the onset of the five different types of blocking patterns before the compositing the entire sequence of the fields was slightly shifted in time and space in such a way that the strongest baroclinic eddy during the onset of each blocking event occupies a prescribed position in the upstream storm track when it reaches its maximum intensity since this shifting considerably reduces the cancellation between the individual high frequency migratory eddies this type of compositing can present a more synoptically oriented view of those interactions than conventional compositing in our composite results one or two pairs of cyclonic and anticyclonic

controls of lithospheric structure and plate kinematics on rift architecture and evolution an experimental modeling of the baikal rift 1 analog models investigate the evolution and architecture of the baikal rift in relation to the rheology of the extending lithosphere and rift kinematics the models focus on the development of the narrow deep and asymmetric basins composing lake baikal and reproduce the extension between the strong siberian craton and the weaker sayan baikal belt model results suggest that the presence of a near vertical weak suture separating the cratonic keel from the mobile belt represents the more convenient rheological configuration leading to a narrow rift characterized by prominent vertical motions and deep depressions these depressions are typically asymmetric and model results suggest that this asymmetry is a consequence of lateral variations in lithospheric rheology which is in turn related to both the variation in thickness of the strong mantle and more importantly the variation in the brittle ductile transition depth between the craton and the belt a significant shallowing of the brittle ductile transition in the crust passing from the craton to the belt is required to fit the asymmetric architecture of the baikal basins with a master fault on the craton side and a monocline with no significant faulting on the belt side analysis of the model deformation pattern suggests that the overall architecture of the basins hosting lake baikal is best fitted for a n140 e directed extension similar to the current gps derived motion and compatible with the stress field inferred on the basis of fault and focal mechanism data this kinematics along with the shape of the siberian craton exerted the major control on the plan view fault architecture and its along axis variations

modoki indian ocean dipole and western north pacific typhoons possible implications for extreme events 1 an interesting feature during el nino modoki summers june august is the occurrence of surplus rainfall anomalies over the south china sea scs and off equatorial tropical northwest pacific based on analyses of observed and reanalyzed data it is noted that anomalous warming in central tropical pacific during an el nino modoki induces a quasi stationary rossby wave response in the form of a low level cyclonic flow over the northern scs this anomalous response favors rainfall enhancement over the scs and also promotes the seasonal typhoon activity we find that this scenario over scs and sub tropical nw pacific is further amplified when an el nino modoki co occurs with a positive indian ocean dipole iod as in 1994 the combination is apparently more conducive for extreme convection events over the region as compared to a pure el nino modoki case the respective impacts of positive iod and el nino on the other hand are opposite to one another the modulation of the typhoon activity by iod events however is prominent only since late 1970s

development and decay processes of dual inversion layers in winter over the northwest coast of the south china sea abstractinversion layers in the lower troposphere appear centered at two heights 1 5 and 4 km over the northwestern coast of the south china sea in late boreal winter the mechanisms of these dua

horst faulting in continental rifts abstract horsts in continental rifts are classified into three types on the basis of their structural characteristics type 1 large horsts bounded by near vertical bifurcating faults at rift termini or structural nodes a subset of this type includes horsts comprising an exceptionally uplifted rift shoulder type 2 generally smaller than type 1 type 2 horsts are commonly associated with graben formed in broad zones of crustal extension and thinning in particular they are a feature of both volcanic and sedimentary basins where they are bounded by listric faults type 3 small horsts occurring close to the margins of rift zones formed in a transtensional regime and bounded by near vertical faults the genesis of type 2 and some type 3 horsts is explained by the vening meinesz isostatic model but type 1 horsts require an additional hydraulic force acting at the base of thick fractured crust small scale convection in the asthenosphere could provide this force

active transsection faults in rift transfer zones evidence for complex stress fields and implications for crustal fragmentation processes in the western branch of the east african rift new structural and seismologic evidence from the rwenzori mountains uganda indicate that continental rifts can capture and rotate fragments of the lithosphere while rift segments interact in a manner analogous to the interaction of small scale fractures the rwenzori mountains are a basement block within the western branch of the east african rift system that is located at the intersection of two rift segments and is apparently rotating clockwise structural data and new seismological data from earthquake epicentres indicate a large scale 20 km long transsection fault is currently detaching the rwenzori micro plate on its northern margin from the larger victoria plate tanzania craton whereas it is already fully detached in the south we propose that this fault develops due to the rotation of the rwenzori block in a numerical model we show how rift segment interaction block rotation and the development of transsection faults faults that cut through the rwenzori mountains evolve through time the model suggests that uplift of the rwenzori block can only take place after the rift has opened significantly and rotation leads to the development of transsection faults that connect two rift segments so that the block is captured within the rifts our numerical model suggests that the majority of the uplift has taken place within the last 8 ma

seasonal variations in the southern hemisphere storm tracks and associated wave propagation abstract seasonal variations in the southern hemisphere sh storm track characteristics and associated wave propagation are studied using 19 years of ncep ncar gridded data it is found that the sh storm track is strongest in the austral autumn season and weakest in spring the characteristics of wave packets are studied by computing 1 point lag correlation maps with unfiltered meridional wind at 300 hpa it is found that the eastward group velocities of waves are much higher than the phase velocities in the transition seasons this shows that the downstream development occurs throughout the year and is a basic feature of upper tropospheric waves in the midlatitudes of the sh this extends previous studies made for winter and summer seasons based on the indices that show wave coherence and correlation maps it is found that the pathways in the transition seasons split into two branches east of australia in a way similar to what happens in the zonal wind distribution

contrasting the flavors of el nino southern oscillation using sea surface salinity observations 1 the recent detection of a central pacific type of el nino has added a new dimension to the el nino southern oscillation climatic puzzle sea surface salinity sss observations collected during 1977 2008 in the tropical pacific are used to contrast the three eastern pacific ep 1982 1983 1991 1992 1997 1998 and seven central pacific cp 1977 1978 1986 1988 1990 1991 1992 1995 2002 2003 2004 2005 2006 2007 types of el nino events as well as the six ep 1985 1986 1988 1989 1995 1996 1999 2001 2005 2006 2007 2008 and two cp 1983 1984 1998 1999 types of la nina events the ep el nino events result in large 30 longitude eastward displacements of the eastern edge of the low salinity warm pool waters in the equatorial band a resulting well marked sss freshening 1 near the dateline and a sss increase 1 below the mean position of the south pacific convergence zone spcz the cp el nino events are characterized by smaller 50 eastward displacements of the eastern edge a 15 longitude westward shift of the equatorial sss freshening and a comparatively reduced 50 sss increase in the spcz a qualitative analysis indicates that changes in zonal currents and precipitation can account for the observed contrasted signature in sss eastward current anomalies appear over most of the equatorial band during ep el nino events in contrast there is a tendency for zonal current convergence slightly west of the dateline during cp el nino events consistent with the confinement of the warm fresh pool in the western central equatorial basin the related quasi inexistent northeastward migration of the spcz and associated heavy precipitation regime

characterization of stress perturbations near major fault zones insights from 2 d distinct element numerical modelling and field studies jura mountains abstract we consider and discuss the presence of discontinuities in the crust as a major source of stress perturbations based on 2 d distinct element modelling we reconstruct the local stress field around a vertical discontinuity in various geological contexts the resulting stress distribution reveals that major directional stress changes occur near the tips of the discontinuity so that stress deviations can reach values as large as 50 we establish simple relationships controlling stress changes around a pre existing fault zone as a function of 1 the remote differential stress magnitude 1 3 2 the friction coefficient on the discontinuity and 3 the strike of the discontinuity relative to the far field stress as a geological example we present the morez fault zone in the internal jura paleostress reconstruction in forty two sites indicates that the trends of the mio pliocene compression are n110 on average near the fault whereas they are n130 in the surrounding areas a comparison between the results of the tectonic study and those of theoretical modelling suggests that the 20 counterclockwise deviation is directly related to the reactivation of this large weak zone we thus evaluate the role of mechanical decoupling along pre existing zones of weakness especially with consideration to the accommodation of the alpine deformation in the jura belt

dynamics of continental rift propagation the end member modes abstract an important aspect of continental rifting is the progressive variation of deformation style along the rift axis during rift propagation in regions of rift propagation specifically transition zones from continental rifting to seafloor spreading it has been observed that contrasting styles of deformation along the axis of rift propagation are bounded by shear zones the focus of this numerical modeling study is to look at dynamic processes near the tip of a weak zone in continental lithosphere more specifically this study explores how modeled rift behavior depends on the value of rheological parameters of the crust a three dimensional finite element model is used to simulate lithosphere deformation in an extensional regime the chosen approach emphasizes understanding the tectonic forces involved in rift propagation dependent on plate strength two end member modes are distinguished the stalled rift phase is characterized by absence of rift propagation for a certain amount of time extension beyond the edge of the rift tip is no longer localized but occurs over a very wide zone which requires a buildup of shear stresses near the rift tip and significant intra plate deformation this stage represents a situation in which a rift meets a locked zone localized deformation changes to distributed deformation in the locked zone and the two different deformation styles are balanced by a shear zone oriented perpendicular to the trend in the alternative rift propagation mode rift propagation is a continuous process when the initial crust is weak the extension style does not change significantly along the rift axis and lengthening of the rift zone is not accompanied by a buildup of shear stresses model predictions address aspects of previously unexplained rift evolution in the laptev sea and its contrast with the tectonic evolution of for example the gulf of aden and woodlark basin

indo pacific induced wave trains during austral autumn and their effect on australian rainfall abstractduring austral winter and spring the el nino southern oscillation enso and the indian ocean dipole iod individually or in combination induce equivalent barotropic rossby wave trains affecting midlatitude australian rainfall in autumn enso is at its annual minimum and the iod has usually not developed however there is still a strong equivalent barotropic rossby wave train associated with tropical indian ocean sea surface temperature sst variability with a pressure anomaly to the south of australia this wave train is similar in position but opposite in sign to the iod induced wave train in winter and spring and has little effect on australian rainfall this study shows that the sst in the southeastern tropical indian ocean setio displays a high variance during austral autumn with a strong influence on southeast and eastern australian rainfall however this influence is slightly weaker than that associated with sst to the north of australia which shares fluctuations with sst i

trapping of synoptic scale disturbances into the north pacific subtropical jet core in midwinter 1 over the northwestern nw pacific a subtropical jet stream develops at 30 n in midwinter as the east asian winter monsoon intensifies eddies with subweekly periods propagating through the midlatitude tropopause into the nw pacific storm track tend to be trapped into the jet core 1000 km away from a surface baroclinic zone at 40 n while lifted up by 3 km the trapping appears to weaken the interaction of the upper level eddies with the baroclinic zone thus acting against eddy amplification and thereby contributing to the midwinter minimum in the eddy activity as observed before the late 1980s since then under the reduced trapping effect by the weakened jet upper level eddies tended to propagate right above the surface baroclinic zone while strongly interacting it even in midwinter as in fall and spring this midwinter tendency acted to enhance the eddy amplification that led to the recent disappearance of the activity minimum

rift nucleation rift propagation and the creation of basement micro plates within active rifts abstract in this contribution we study the dynamics of rift nucleation and the interaction of propagating rift segments we use the east african rift system ears as a case study with special emphasis on the albertine rift system situated within the western branch of the ears with the 5000 m high rwenzori horst a basement block that was captured by two rift segments fieldwork in the rwenzori mountains shows that the range is not only affected by range parallel faults but that major fault sets cut across the rwenzoris in order to understand these complex fault patterns and the dynamics of the process that leads to the capturing of basement blocks within the extending rift system we developed a two dimensional visco elasto plastic spring model the model shows that propagating rift faults commonly capture micro plates with shapes similar to the rwenzori mountains these micro plates rotate during successive rift opening in a clockwise or anti clockwise sense depending on the direction of the rift segment overstep a left lateral overstep as is the case for the albertine rift system produces a clockwise rotation of the associated micro plate indicating that the rwenzori mountains rotate clockwise during the rotation of the micro plate the local stress field at the rift segment tips is perturbed so that the rifts turn 70 to 90 and propagate towards each other to capture the plates completely this perturbed stress field produces an extensional fault set that is oriented almost parallel to the far field extension direction and explains the range cutting faults that we find in the rwenzori mountains the large scale geometry of the rift system seems to be strongly controlled by rigid cratons in the lithosphere leading to a curvature of the western branch of the ears and a sinistral wrench component in the lake albert rift north of the rwenzori mountains capturing of micro plates of various sizes within the rift system is a common phenomenon and leads to strong perturbations of the local stress field during micro plate rotation the resulting structures are normal and strike slip faults that cut through the micro plates and local reverse faults

enso modoki impact on the southern hemisphere storm track activity during extended austral winter 1 impacts of the recently discovered enso modoki phenomena on extended winter storm track activity in the southern hemisphere are examined using the observed rainfall sea surface temperature and reanalyzed upper air circulation data for the period 1979 2004 the partial correlation technique is utilized to distinguish the impact of enso modoki events from those of the enso and indian ocean dipole iod el nino modoki events introduce an anomalous blocking over central eastern australia which suppresses the storm track activity from southwest till centraleast reducing the storm associated rainfall in southeastern tip and portions of the southeast on the other hand the storm track activity in central argentina is enhanced owing to the strengthened upper air westerlies in this region the impacts from the enso modoki events are apparently stronger than the individual impacts from the enso and iod events

lacustrine thecamoebians mainly arcellaceans as potential tools for palaeolimnological interpretations abstract a number of thecamoebian genera of potential or demonstrated importance for palaeolimnological research mainly arcellacea are discussed what is known about their biology ecology spatial distribution mechanisms of dispersal and characteristic associations is briefly reviewed in the introductory part after a short discussion on the concept of species and the somewhat peculiar way in which it applies to this group of organisms a chapter on systematic taxonomy including an illustrated guide to the identification of the genera is presented the scarce fossil record of the group is then briefly discussed practical instructions on collection preparation and observation of thecamoebians for palaeolimnological research are supplied the paper closes with the presentation of a few studies performed by the authors as examples of how arcellacea can become tools for the solution of palaeolimnological problems

hydrological dynamics and fire history of the last 1300 years in western siberia reconstructed from a high resolution ombrotrophic peat archive siberian peatlands provide records of past changes in the continental climate of eurasia we analyzed a core from mukhrino mire in western siberia to reconstruct environmental change in this region over the last 1300 years the pollen analysis revealed little variation of local pine birch forests a testate amoebae transfer function was used to generate a quantitative water table reconstruction pollen plant macrofossils and charcoal were analyzed to reconstruct changes in vegetation and fire activity the study revealed that mukhrino mire was wet until the little ice age lia when drought was recorded dry conditions during the lia are consistent with other studies from central and eastern europe and with the pattern of carbon accumulation across the northern hemisphere a significant increase in fire activity between ca ad 1975 and 1990 may be associated with the development of the nearby city of khanty mansiysk as well as with the prevailing positive arctic oscillation

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

african stress pattern from formal inversion of focal mechanism data abstract the kinematic models and the associated orientation of extensional stress of the east african rift system have been subjected to much debate since a long time in the past decades the proposed models relied on the interpretation of the overall rift geometry geological fault slip data and the few focal mechanisms available these models generally suffer of a poor time control and an underestimation of the possible changes in the stress field and geodynamic regime with time and space in the recent years there has been a significant increase in the number of focal mechanisms available for the entire rift system and it is now possible to estimate the present day stress field in relative detail based on seismotectonic data alone we compile 347 focal mechanism data from the global harvard cmt catalogue and various other sources and grouped 332 of them in 24 distinct regions boxes on the basis of their geographical proximity kinematic homogeneity and tectonic setting for each box and for the same data set reduced stress tensors have been obtained by formal stress inversion using both the tensor program delvaux sperner 2003 and the slick method michael 1984 1987 both inversion methods show in comparable results in terms of horizontal stress axes orientations and tectonic stress regimes which stem for the robustness of the approach the obtained stress pattern reflects a complex interaction between 1st order effects as different driving forces including plate boundary forces and 2nd and 3rd order effects as gravitational potential of topography intra lithospheric processes and the influence of structural heterogeneities of the rift structures the evidence present in the stress orientations of the 2nd and 3rd order stress pattern as the variations in the horizontal stress axes along the axis of the rift are of particular interest as they were not yet captured or shown in earlier numerical models of the stress field additional sources of tectonic forces in supplement to the gravitational potential energy forces as considered in the earlier models are necessary to explain the observed patterns

testate amoebae protozoa testacealobosea and testaceafilosea as bioindicators in the late quaternary deposits of the bykovsky peninsula laptev sea russia testate amoebae protozoa testacea were studied in the late quaternary permafrost deposits in the siberian arctic bykovsky peninsula of the laptev sea coast 71 40 71 80 n and 129 129 30 e the testacea associations studied reflect specific environmental conditions in paleocryosols which were controlled by the local micro relief as well as by regional climate conditions in total 86 species varieties and forms of testate amoebae were found in 38 pleistocene and holocene samples the rhizopods indicate that soil conditions at ca 53 000 14c years bp were probably rather similar to the modern cold and wet arctic tundra environment more moisture and warmer soil conditions were relatively favorable for rhizopods ca 45 300 43 000 14c years bp but it was significantly drier at about 42 000 14c years bp drier and colder environmental conditions were also present about 39 300 35 000 14c years bp the late pleistocene samples radiocarbon dated to 33 000 12 000 years bp are characterized by a low species diversity and density indicating that this period may have been extremely cold and dry this conjecture is also supported by the polymorphism of some species hydrophilic difflugia species mostly obligate hydrobiotes are broadly represented in the studied holocene samples the species composition and density of rhizopods in the majority of holocene samples suggest wet and relatively warm conditions changes in rhizopod assemblages during the last 53 000 years were not very dramatic mostly consisting of rare species and changes in the dominant species complexes during the pleistocene and holocene however these changes were more drastic during the pleistocene they were probably at least partly responsible for the disappearance of some rare testacean species such as argynnia sp

numerical experiments of the storm track sensitivity to oceanic frontal strength within the kuroshio oyashio extensions the sensitivity of the north pacific storm track to midlatitude oceanic frontal strength within the kuroshio oyashio extensions is investigated by applying artificially changed meridional sea surface temperature sst gradients in the weather research forecasting model version 3 4 the result of sensitivity experiments further confirms the close relationship between the storm track activity and meridional sst gradient i e the storm track activity can be intensified as a response to increases in the oceanic frontal strength in order to better understand the mechanism for the storm track intensification due to increased sst gradient velocity temperature correlation and local energetics are analyzed the result indicates that the enhancement of the meridional sst gradient leads to amplitude magnification of eddy meridional velocity and temperature and their phase consistency suggesting that synoptic scale eddies tend to approach the optimum structure for the baroclinic energy conversion which is mainly responsible for the sst front induced enhancement of storm track activity in order to estimate the impact of the oceanic front on the maintenance of the near surface baroclinicity further investigation is made by the composite analysis with the increase in oceanic frontal strength the near surface baroclinicity experiences a slow but strong restoration the increase in the meridional sst gradient results in the intensification in the cross frontal differential sensible heat flux which can more effectively offset the relaxing effect of the transient eddy poleward heat transport

late pleistocene and holocene vegetation and climate on the taymyr lowland northern siberia abstract pollen records from perennially frozen sequences provide vegetation and climate reconstruction for the last 48 000 14c years in the central part of taymyr peninsula open larch forest with alnus fruticosa and betula nana grew during the kargin middle weichselian interstade ca 48 000 25 000 14c yr b p the climate was generally warmer and wetter than today open steppe like communities with artemisia poaceae asteraceae and herb tundralike communities with dwarf betula and salix dominated during the sartan late weichselian stade ca 24 000 10 300 14c yr b p the statistical information method used for climate reconstruction shows that the coldest climate was ca 20 000 17 000 14c yr b p a warming allerod interstade with mean july temperature ca 1 5 c warmer than today occurred ca 12 000 14c yr b p the following cooling with temperatures about 3 4 c cooler than present and precipitation about 100 mm lower corresponds well with the younger dryas stade tundra steppe vegetation changed to betula nana alnus fruticosa shrub tundra ca 10 000 14c yr b p larch appeared in the area ca 9400 14c yr b p and disappeared after 2900 14c yr b p cooling events ca 10 500 9600 and 8200 14c yr b p characterized the first half of the holocene a significant warming occurred ca 8500 14c yr b p but the holocene temperature maximum was at about 6000 4500 14c yr b p the vegetation cover approximated modern conditions ca 2800 14c yr b p late holocene warming events occurred at ca 3500 2000 and 1000 14c yr b p a cooling little ice age took place between 500 and 200 14c yr ago

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

palaeobotanical evidence for warm summers in the east siberian arctic during the last cold stage plant macrofossils from the mamontovy khayata permafrost sequence 71 60 n 129 25 e on the bykovsky peninsula reflect climate and plant biodiversity in west beringia during the last cold stage 70 ams and 20 conventional 14c dates suggest sediment accumulation between about 60 000 and 7500 14c yr b p the plant remains prove that during the last cold stage arctic species minuartia arctica draba spp kobresia myosuroides coexisted with aquatic potamogeton vaginatus callitriche hermaphroditica littoral ranunculus reptans rumex maritimus meadow hordeum brevisubulatum puccinellia tenuiflora and steppe taxa alyssum obovatum silene repens koeleria cristata linum perenne the reconstructed vegetation composition is similar to modern vegetation mosaics in central and northeast yakutian relict steppe areas thus productive meadow and steppe communities played an important role in the siberian arctic vegetation during the late pleistocene and could have served as food resource for large populations of herbivores the floristic composition reflects an extremely continental arid climate with winters colder and summers distinctly warmer than at present holocene macrofossil assemblages indicate a successive paludification possibly connected with marine transgression increased oceanic influence and atmospheric humidity although some steppe taxa were still present in the early holocene they disappeared completely before 2900 14c yr b p

holocene paleoenvironmental records from nikolay lake lena river delta arctic russia radiocarbon dated pollen rhizopod chironomid and total organic carbon toc records from nikolay lake 73 20 n 124 12 e and a pollen record from a nearby peat sequence are used for a detailed environmental reconstruction of the holocene in the lena delta area shrubby alnus fruticosa and betula exilis tundra existed during 10 300 4800 cal yr bp and gradually disappeared after that time climate reconstructions based on the pollen and chironomid records suggest that the climate during ca 10 300 9200 cal yr bp was up to 2 3 c warmer than the present day pollen based reconstructions show that the climate was relatively warm during 9200 6000 cal yr bp and rather unstable between ca 5800 3700 cal yr bp both the qualitative interpretation of pollen data and the results of quantitative reconstruction indicate that climate and vegetation became similar to modern day conditions after ca 3600 cal yr bp the chironomid based temperature reconstruction suggests a relatively warm period between ca 2300 and 1400 cal yr bp which corresponds to the slightly warmer climate conditions reconstructed from the pollen modern chironomid and rhizopod assemblages were established after ca 1400 cal yr bp

thermal and exhumation history of the central rwenzori mountains western rift of the east african rift system uganda the rwenzori mountains mtns in west uganda are the highest rift mountains on earth and rise to more than 5 000 m we apply low temperature thermochronology apatite fission track aft and apatite u th sm he ahe analysis for tracking the cooling history of the rwenzori mtns samples from the central and northern rwenzoris reveal aft ages between 195 0 8 4 ma and 85 3 5 3 ma and ahe ages between 210 0 6 0 ma to 24 9 0 5 ma modelled time temperature paths reflect a protracted cooling history with accelerated cooling in permo triassic and jurassic times followed by a long period of constant and slow cooling than succeeded by a renewed accelerated cooling in the neogene during the last 10 ma differentiated erosion and surface uplift affected the rwenzori mtns with more pronounced uplift along the western flank the final rock uplift of the rwenzori mtns that partly led to the formation of the recent topography must have been fast and in the near past pliocene to pleistocene erosion could not compensate for the latest rock uplift resulting in oligocene to miocene ahe ages

ice complex formation in arctic east siberia during the mis3 interstadial abstract a continuous 15 m long sequence of ice complex permafrost yedoma exposed in a thermo cirque at the southern coast of bol shoy lyakhovsky island new siberian archipelago dmitry laptev strait was studied to reconstruct past landscape and environmental dynamics the sequence accumulated during the marine isotope stage 3 mis3 interstadial between 49 and 29 ka bp in an ice wedge polygon the frozen deposits were cryolithologically described and sampled on a vertical bluff between two ice wedges according to sedimentological and geochronological data the section is subdivided into three units which correlate with environmental conditions of the early middle and late mis3 period palynological data support this stratification the stable isotope signature of texture ice in the polygon structure reflects fractionation due to local freeze thaw processes while the signature of an approximately 5 m wide and more than 17 m high ice wedge fits very well into the regional stable water isotope record regional climate dynamics during the mis3 interstadial and local landscape conditions of the polygonal patterned ground controlled the ice complex formation the sequence presented here completes previously published mis3 permafrost records in northeast siberia late quaternary stadial interstadial climate variability in arctic west beringia is preserved at millennial resolution in the ice complex a mis3 climate optimum was revealed between 48 and 38 ka bp from the ice complex on bol shoy lyakhovsky island

geodynamic significance of the trm segment in the east african rift w tanzania active tectonics and paleostress in the ufipa plateau and rukwa basin abstract the tanganyika rukwa malawi trm rift segment in western tanzania is a key sector for understanding the opening dynamics of the east african rift system ears in an oblique opening model it is considered as a dextral transfer fault zone that accommodates the general opening of the ears in an nw se direction in an orthogonal opening model it accommodates pure dip slip normal faulting with extension orthogonal to the rift segments and a general e w extension for the entire ears the central part of the trm rift segment is well exposed in the ufipa plateau and rukwa basin within the paleoproterozoic ubende belt it is also one of the most seismically active regions of the ears we investigated the active tectonic architecture and paleostress evolution of the ufipa plateau and adjacent rukwa basin and in order to define their geodynamic role in the development of the ears and highlight their pre rift brittle tectonic history the active fault architecture fault kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the trm segment two pre rift brittle events are evidenced an older brittle thrusting is related to the interaction between the bangweulu block and the tanzanian craton during the late pan african early paleozoic it was followed by a transpressional inversion during the early mesozoic this inversion stage is the best expressed in the field and caused dextral strike slip faulting along the fault systems that now control the major rift structures it has been erroneously interpreted as related to the late cenozoic ears which instead is characterized by pure normal faulting our third and last stress stage

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

zonal movement of the mascarene high in austral summer temporal variations in the mascarene high mh defined by the sea level pressure slp maximum within the region of 40 120 e 50 10 s in austral summer november january were investigated using atmospheric reanalysis datasets the mh longitudinal position has a dominant timescale at about 6 years which appears to be independent of the mh intensity variation the mh longitudinal movement is caused by a combination of slp variations in the eastern south indian ocean esio and in the western south indian ocean wsio as follows 1 pressure variations in the esio region are confined to the lower atmosphere up to the mid troposphere and are associated with the el nino southern oscillation events 2 pressure variations in the wsio region characterized by a quasi barotropic structure throughout the troposphere are related to the meridional movement of storm track sea surface temperature anomalies associated with the longitudinal movement of the mh show a southwest northeast dipole structure but this is shifted 10 westward in longitude compared with that associated with the mh intensity

characteristics of wave packets in the upper troposphere part ii seasonal and hemispheric variations abstract gridded 300 hpa meridional wind data produced by the ecmwf reanalysis project were analyzed to document the seasonal and hemispheric variations in the properties of upper tropospheric wave packets the properties of the wave packets are mainly illustrated using time lagged one point correlation maps performed on based on indices that show the coherence of wave propagation as well as examination of correlation maps schematic waveguides were constructed for the summer and winter seasons of both hemispheres along which waves preferentially propagate with greatest coherence in the summers the waveguides basically follow the position of the midlatitude jets in the northern hemisphere winter the primary waveguide follows the subtropical jet over southern asia into the pacific but there is a secondary branch running across russia joining the primary waveguide near the entrance to the pacific storm track over the atlantic the waveguide passes east southeastward toward north africa then bac

the anomalous merging of the african and north atlantic jet streams during the northern hemisphere winter of 2010 the north atlantic jet stream during winter 2010 was unusually zonal so the typically separated atlantic and african jets were merged into one zonal jet moreover the latitude height structure and temporal variabilityofthe northatlanticjet duringthis winterweremore characteristic ofthe northpacific this work examinesthe possibility of aflow regime changefrom an eddy driven to a mixed eddy thermally drivenjet a monthly jet zonality index is defined which shows that a persistent merged jet state has occurred in the past both at the end of the 1960s and during a few sporadic months the anomalously zonal jet is found to be associated with anomalous tropical pacific diabatic heating and eddy anomalies similar to those found during a negative north atlantic oscillation nao state a lagrangian back trajectory diagnosis of eight winters suggests the tropical pacific is a source of momentum to the atlantic and african jets and that this source was stronger during the winter of 2010 the results suggest that the combination of weak eddy variance and fluxes in the north atlantic along with strong tropical heating act to push the jet toward a merged eddy thermally driven state the authors also find significant sst anomalies in the north atlantic which reinforce the anomalous zonal winds particularly in the eastern atlantic