surface climate variations over the north atlantic ocean during winter 1900 1989 abstract the low frequency variability of the surface climate over the north atlantic during winter is described using 90 years of weather observations from the comprehensive ocean atmosphere data set results are based on empirical orthogonal function analysis of four components of the climate system sea surface temperature sst air temperature wind and sea level pressure an important mode of variability of the wintertime surface climate over the north atlantic during this century is characterized by a dipole pattern in ssts and surface air temperatures with anomalies of one sign cast of newfoundland and anomalies of the opposite polarity off the southeast coast of the united states wind fluctuations occur locally over the regions of large surface temperature anomalies with stronger than normal winds overlying cooler than normal ssts this mode exhibits variability on quasi decadal and biennial time scales the decadal fluctuations are irregular in length averaging 9 years before 1945 and 1

arctic sea ice variability in the context of recent atmospheric circulation trends abstract forty years 1958 97 of reanalysis products and corresponding sea ice concentration data are used to document arctic sea ice variability and its association with surface air temperature sat and sea level pressure slp throughout the northern hemisphere extratropics the dominant mode of winter january march sea ice variability exhibits out of phase fluctuations between the western and eastern north atlantic together with a weaker dipole in the north pacific the time series of this mode has a high winter to winter autocorrelation 0 69 and is dominated by decadal scale variations and a longer term trend of diminishing ice cover east of greenland and increasing ice cover west of greenland associated with the dominant pattern of winter sea ice variability are large scale changes in sat and slp that closely resemble the north atlantic oscillation the associated sat and surface sensible and latent heat flux anomalies are largest over the portions of the marginal sea ice zone in which the tr

focused ion beam fib combined with sem and tem advanced analytical tools for studies of chemical composition microstructure and crystal structure in geomaterials on a nanometre scale abstract in order to make meaningful interpretations of trace element and isotopic information from geomaterials prior characterization of the material of interest with respect to structural and chemical homogeneity radiation damage and microstructure is often required transmission electron microscopy tem is a powerful analytical tool that may be used to fully characterise a wide range of synthetic and natural materials the focused ion beam technique fib is an ideal tool for tem sample preparation that allows for the fabrication of electron transparent foils with typical dimensions of 15 10 0 150 m from any region of interest i e site specific and in virtually any material fib sample preparation consumes only a small volume of material approximately 2300 m 3 for a standard foil with the dimensions 15 10 0 150 m leaving most of the material essentially unaffected by the sampling process modern tem facilitates the measurement of chemical composition with unsurpassed spatial resolution e g nanometer scale high resolution imaging and electron diffraction provide important complimentary structural information it is the combination of crystal structure information and chemical composition that allows for the complete characterization of the volume of interest high resolution elemental mapping or line scans may be used to acquire complete energy dispersive x ray analysis edx spectra of a material pixel by pixel subsequent evaluation of the data allows for the correlation of the edx spectrum with the respective elemental map or line scan with an image thus illustrating spatially resolved chemical composition variations at the 0 5 1 0 wt level frequently minerals enclose sub micrometer or even nanometre sized inclusions of minerals fluids or silicate melt which are of great interest to geoscientists nanoinclusions e g in diamond or olivine are of particular interest because they may have preserved their original crystal structure thus providing a geobarometer recording the pressure conditions at the time of formation of the inclusion fib tem are appropriate techniques to sample and subsequently define the chemical composition and the structural state of mineral inclusion on the nanometre scale the combination of fib with an sem allows for 3d information to be obtained from samples including 3d imaging e g phase distribution and volume of the individual phases in symplectites 3d distribution of elements in a specific volume 3d elemental maps and three dimensional texture analysis using electron backscatter diffraction ebsd

evidence of nonlinear dynamics in the eastward shift of the nao 1 hilmer and jung 2000 have identified an eastward shift in the sea level pressure slp pattern associated with interannual variability of the north atlantic oscillation nao that took place around 1980 we investigate the nature of the eastward shift using a primitive equation dry atmospheric model driven by diabatic forcing diagnosed from observations the model results reveal the nonlinear dependence of the spatial pattern of the nao on the nao index the pattern being shifted to the east west for high low nao index general agreement is found between the model and observations we suggest that the eastward shift noted by hilmer and jung 2000 is a consequence of the trend towards higher nao index during the last several decades of the 20th century

the link between the north atlantic oscillation and arctic sea ice export through fram strait abstract recently hilmer and jung have shown that the wintertime link between the north atlantic oscillation nao and the sea ice export through fram strait changed from zero correlation 1958 77 to about 0 7 1978 97 during the last four decades in the current study the authors focus on the question of how the two phenomena are linked in a long term context during wintertime december march this is done on a statistical basis using data from a century scale control integration of the coupled general circulation model echam4 opyc3 along with historical sea level pressure data for the period 1908 97 from the results of this study there is less indication that a significant link on interannual and decadal timescales between the nao and the sea ice export through fram strait is a characteristic property of the climate system at least under present day climate conditions this missing link can be explained by a vanishing net impact of the nao on sea ice thickness as well as sea ice drift near fram st

grain scale pressure variations and chemical equilibrium in high grade metamorphic rocks in the classical view of metamorphic microstructures fast viscous relaxation and so constant pres sure is assumed with diffusion being the limiting factor in equilibration this contribution is focused on the only other possible scenario fast diffusion and slow viscous relaxation and brings an alter native interpretation of microstructures typical of high grade metamorphic rocks in contrast to the pressure vessel mechanical model applied to pressure variation associated with coesite inclusions in various host minerals a multi anvil mechanical model is proposed in which strong single crystals and weak grain boundaries can maintain pressure variation at geological time scales in a polycrystalline material in such a mechanical context exsolution lamellae in feldspar are used to show that feldspar can sustain large differential stresses 10 kbar at geological time scales furthermore it is argued that the existence of grain scale pressure gradients combined with diffusional equilibrium may explain chemical zoning preserved in reaction rims assuming zero net flux across the microstructure an equilibrium thermodynamic method is introduced for inferring pressure variation corresponding to the chemical zoning this new barometric method is applied to plagioclase rims around kyanite in fel sic granulite bohemian massif czech republic yielding a grain scale pressure variation of 8 kbar in this approach kinetic factors are not invoked to account for mineral composition zoning preserved in rocks metamorphosed at high grade

routine characterization and interpretation of complex alkali feldspar intergrowths almost all alkali feldspar crystals contain a rich inventory of exsolution twin and domain microtextures that form subsequent to crystal growth and provide a record of the thermal history of the crystal and often of its involvement in replacement reactions sometimes multiple microtextures strongly influence the subsequent behavior of feldspars at low temperatures during diagenesis and weathering they are central to the retention or exchange of trace elements and of radiogenic and stable isotopes this review is aimed at petrologists and geochemists who wish to use alkali feldspar microtextures to solve geological problems or who need to understand how microtextures influence a particular process we suggest a systematic approach that employs methods available in most well founded laboratories the crystallographic relationships of complex feldspar intergrowths were established by the 1970s mainly using single crystal x ray diffraction but such methods give limited information on the spatial relationships of the different elements of the microtexture or of the mode and chronology of their formation which require the use of microscopy we suggest a combination of techniques with a range of spatial resolution and strongly recommend the use of orientated sections sections cut parallel to the perfect 001 and 010 cleavages are the easiest to locate and most informative techniques described are light microscopy scanning electron microscopy using both backscattered and secondary electrons including the use of surfaces etched in the laboratory electron probe microanalysis and analysis by energy dispersive spectrometry in a scanning electron microscope transmission electron microscopy we discuss the use of cathodoluminescence as an auxiliary technique but do not recommend electron backscattered diffraction for feldspar work we review recent publications that provide examples of the need for great care and attention to pre existing work in microtextural studies and suggest several topics for future work

catastrophic ice shelf breakup as the source of heinrich event icebergs 1 heinrich layers of the glacial north atlantic record abrupt widespread iceberg rafting of detrital carbonate and other lithic material at the extreme cold culminations of bond climate cycles both internal glaciologic and external climate forcings have been proposed here we suggest an explanation for the iceberg release that encompasses external climate forcing on the basis of a new glaciological process recently witnessed along the antarctic peninsula rapid disintegrations of fringing ice shelves induced by climate controlled meltwater infilling of surface crevasses we postulate that peripheral ice shelves formed along the eastern canadian seaboard during extreme cold conditions would be vulnerable to sudden climate driven disintegration during any climate amelioration ice shelf disintegration then would be the source of heinrich event icebergs

spatial pattern and zonal shift of the north atlantic oscillation part ii numerical experiments abstract in this part the spatial evolution of an initial dipole anomaly in a prescribed jet is at first investigated by numerically solving linear and nonlinear models without forcing in order to examine how the spatial pattern of a dipole anomaly depends on the meridional distribution of a specified jet it is shown that in a linear experiment an initial symmetric dipole anomaly in the meridional direction can evolve into a northeast southwest ne sw or northwest southeast nw se tilted dipole structure if the core of this jet is in higher latitudes the north or in lower latitudes the south this is in agreement with the result predicted by the linear rossby wave theory in slowly varying media the conclusion also holds for the nonlinear and unforced experiment north atlantic oscillation nao events are then reproduced in a fully nonlinear barotropic model with a wavemaker that mimics the atlantic storm track eddy activity in the absence of topography the spatial tilting of the eddy driven nao

vertical extrusion and horizontal channel flow of orogenic lower crust key exhumation mechanisms in large hot orogens a large database of structural geochronological and petrological data combined with a bouguer anomaly map is used to develop a two stage exhumation model of deep seated rocks in the eastern sector of the variscan belt an early sub vertical fabric developed in the orogenic lower and middle crust during intracrustal folding followed by the vertical extrusion of the lower crustal rocks these events were responsible for exhumation of the orogenic lower crust from depths equivalent to 18 20 kbar to depths equivalent to 8 10 kbar and for coeval burial of upper crustal rocks to depths equivalent to 8 9 kbar following the folding and vertical extrusion event sub horizontal fabrics developed at medium to low pressure in the orogenic lower and middle crust during vertical shortening fabrics that record the early vertical extrusion originated between 350 and 340 ma during building of an orogenic root in response to se directed saxothuringian continental subduction fabrics that record the later sub horizontal exhumation event relate to an eastern promontory of the brunia continent indenting into the rheologically weaker rocks of the orogenic root indentation initiated thrusting or flow of the orogenic crust over the brunia continent in a north directed sub horizontal channel this sub horizontal flow operated between 330 and 325 ma and was responsible for a heterogeneous mixing of blocks and boudins of lower and middle crustal rocks and for their progressive thermal re equilibration the erosion depth as well as the degree of reworking decreases from south to north pointing to an outflow of lower crustal material to the surface which was subsequently eroded and deposited in a foreland basin indentation by the brunia continental promontory was highly noncoaxial with respect to the se oriented saxothuringian continental subduction in the early visean suggesting a major switch of plate configuration during the middle to late visean

nanotunnels and pull aparts defects of exsolution lamellae in alkali feldspars we have studied defects associated with flat lens shaped perthitic albite lamellae in alkali feldspars using sem and tem in orthoclase phenocrysts from the shap granite cumbria nw england bulk composition or 70 20 ab 29 05 an 0 85 no dislocations were found even in optically fresh parts of grains instead dissolution inferred to be localized on edge dislocation loops has created tiny nanotunnels typically t effect of the 1 an in the feldspars is taken into account for commencement of coherent exsolution the orientation of the pericline twins was fixed shortly after coherent exsolution began previous work has indicated that edge dislocations would start to form during cooling at 400 c so that nanotunnels form at still lower t dry heating experiments were carried out to establish the stability of the defects and the homogenization behavior of the exsolution lamellae na k exchange is rapid on heating above the coherent solvus and chemical homogenization of lamellae is complete after 24 h at 700 c in contrast nanotunnels persist for 148 h at 1000 c and 5748 h at 700 c below the coherent solvus exsolution lamellae thin on heating leaving nanotunnels stranded in the orthoclase matrix microtextures related to si al ordering patterns in the framework such as albite twins are not eliminated forming ghost like lamellar strain patterns in chemically homogeneous feldspar the presence of nanotunnels in optically fresh alkali feldspars shows that not only granites but also granulite facies rocks have been pervasively affected by fluids at low t both nanotunnels and pull aparts have important implications for feldspar reactivity in the upper crust for 18 o exchange and for transport of 40 ar both in nature and in laboratory step heating

robustness of low frequency circulation patterns derived from eof and rotated eof analyses abstract the robustness of low frequency circulation patterns defined by unrotated and rotated empirical orthogonal functions e0fs are compared based on the northern hemisphere 10 day low pass filtered wintertime 500 hpa height field the pacific north american pattern and the north atlantic oscillation are the most prominent modes of low frequency variability in the data the reproducibility of the spatial patterns derived from eof and rotated eof analysis is assessed by repeating the analysis on 50 subsets of the data each comprised of the maps belonging to 22 randomly selected winters from the 44 winters in the total record the results indicate that rotated spatial patterns are less sensitive to sampling fluctuations than their unrotated counterparts

interdecadal variations in the relationship between the winter north atlantic oscillation and temperature in south central china abstractinterdecadal variations in the relationship between the winter north atlantic oscillation nao and surface air temperature in china are investigated using observational and reanalysis data focus is on south central china in which temperature variability is strongly related to the nao it is revealed that the relationship shows clear interdecadal variations in midwinter during 1951 2015 a relatively weak in phase relationship occurs before the early 1970s p1 but a significant out of phase relationship dominates in the last two decades of the twentieth century p2 though it is clearly weaker from the late 1990s onward observational evidence shows that such interdecadal variations are related mainly to variations in the spatial pattern and amplitude of the nao the northern center of the nao shifted eastward over the second half of the twentieth century in addition the amplitude of the center strengthened from p1 to p2 resulting in a perturbation in the atmospheric circulation response p

dislocation formation and albitization in alkali feldspars from the shap granite orthoclase rich alkali feldspars in the lower devonian shap granite northwest england contain two generations of albite rich feldspar these have partially replaced earlier exsolution microtextures consisting of albite lamellae coarse semicoherent albite films and fine coherent albite platelets in tweed orthoclase the earlier generation of replacive albiterich feldspar ab90an9ori occurs together with orthoclase rich feldspar ab10or90 i n veins that crosscut exsolution microtextures throughout grain interiors this episode of recrystallization was mediated by magmatic fluids at 410 8c estimated from two feldspar geothermometry and was driven by stored elastic strain energy which was relatively homogeneously distributed throughout the microtextures the later generation of replacive albite rich feldspar which is restricted to grain margins and is compositionally pure ab 99 was produced by magmatic hydrothermal fluids at 370 8c this generation of albite rich feldspar does not crosscut exsolution microtextures and has selectively replaced volumes of highly elastically strained feldspar surrounding edge dislocations along semicoherent albite films marked differences in controls of the localization of the two generations of replacive albite rich feldspar by pre existing exsolution microtextures indicate that significant numbers of edge dislocations developed along albite films after the first phase of fluid feldspar interaction and associated albitization but before the second phase this relation indicates that edge dislocations formed between 410 and 370 8c these observations have important implications for understanding the factors that control the interaction of alkali feldspars with fluids both in cooling igneous rocks and in clastic sedimentary rocks during diagenesis

northern hemisphere winter circulation associated with the north atlantic oscillation and stratospheric polar night jet the interannual variability of the atmospheric winter circulation as characterized by the geopotential height at 500 hpa and temperature at 850 hpa associated with the north atlantic oscillation nao and stratospheric polar night jet pnj is examined it is suggested that the wintertime atmospheric circulation related to the nao index can be separated into two different modes of variability one is a regional mode characterized by a meridional dipole type pattern in the 500 hpa geopotential height anomaly field over the atlantic region the other having more zonal structure extends over wider region of the northern hemisphere this is also related to the lower stratospheric polar night jet air temperature near the surface over the eastern part of the eurasian continent is more closely correlated with the above mentioned hemispheric mode of variability than the regional nao

the nature of potassium feldspar exsolution microtextures and development of dislocations as a function of composition in perthitic alkali feldspars transmission electron microscope data on the morphology of exsolution lamellae the nature of the potassium feldspar and the development of dislocations at lamellar interfaces in coherent cryptoperthites and fine microperthites are reviewed dislocations have been reported previously in only two crystals and periodic dislocations noted in only one an or rich microperthite periodic dislocations spacing 100 150 nm are here described from a ternary mesoperthite or26 ab52 an22 small crystallites 30 nm of other phases have sometimes nucleated on the dislocations the 020 lattice fringes of the feldspar phases have been imaged the difference in 020 spacings can be almost entirely accommodated by the regular dislocations so that the boundaries may be termed nearlyperfectly semicoherent

interdecadal variations in north atlantic sea surface temperature and associated atmospheric conditions abstract evidence is presented for a distinct pattern of ocean atmosphere relationship associated with interdecadal variability in the north atlantic region using a century of surface marine observations it is shown that middle and high latitude sea surface temperature sst display a long term fluctuation with negative anomalies before 1920 and during the 1970s and 1980s positive sst conditions prevailed from about 1930 to 1960 the pattern of interdecadal sst variability is constructed by subtracting the average field during 15 cold years from that during a similar interval of warm years the early century warming and the more recent cooling display a similar spatial pattern in both cases the pattern is basin scale and largely of one polarity with maxima in the vicinity of iceland in the labrador sea and northeast of bermuda the corresponding differences in surface atmospheric conditions are determined by averaging and subtracting in the same manner fields of sea level pressure slp and surf

comment on catastrophic ice shelf breakup as the source of heinrich event icebergs by c l hulbe et al hulbe et al 2004 argue that the original binge purge model of their coauthor macayeal 1993a 1993b is not appropriate for heinrich events but that a new ice shelf collapse mechanism may work we believe that thenew collapse mechanism disagrees with important dataand that macayeal s original model remains viable afterappropriate modifications we have enjoyed a fascinatingdiscussion with hulbe et al on this topic which isstimulating our thinking and research and we presentsome of the arguments here for a wider audience

intracrystalline microstructures in alkali feldspars from fluid deficient felsic granulites a mineral chemical and tem study samples of essentially dry high pressure felsic granulites from the bohemian massif variscan belt of central europe contain up to 2 mm large perthitic alkali feldspars with several generations of plagioclase precipitates in an orthoclase rich host the first generation takes the form of lenses homogeneous in size whereas the size of a second generation of very thin albite rich precipitates is more variable with comparatively high aspect ratios in the vicinity of large kyanite garnet or quartz inclusions the first generation of plagioclase precipitates is significantly less abundant the microstructure is coarser than in the remainder of the perthitic grain and the host is a tweed orthoclase the first generation of precipitates formed at around 850 c during the high pressure stage 16 18 kbar of metamorphism primary exsolution was followed by primary coarsening of the plagioclase precipitates which still took place at high temperatures 850 700 c the coarsening was pronounced due to the access of fluids in the outer portions of the perthitic alkali feldspar and in more internal regions around large inclusions the second generation of albite rich precipitates was formed at around 570 c tem investigations revealed that the interfaces between the second generation plagioclase lamellae and the orthoclase rich host are coherent or semi coherent during late evolutionary stages of the perthite albite linings were formed at phase boundaries and the perthitic microstructure was partially replaced by irregularly shaped precipitates of pure albite with incoherent interfaces the albitization occurred below 400 c and was linked to fluid infiltration in the course of deuteric alteration based on size distribution analysis it is inferred that the precipitates of the first generation were most probably formed by spinodal decomposition whereas the precipitates of the second generation rather were formed by nucleation and growth

semi brittle flow of granitoid fault rocks in experiments field studies and seismic data show that semi brittle flow of fault rocks probably is the dominant deformation mechanism at the base of the seismogenic zone at the so called frictional viscous transition to understand the physical and chemical processes accommodating semi brittle flow we have performed an experimental study on synthetic granitoid fault rocks exploring a broad parameter space temperature t 300 400 500 and 600 c confining pressure pc 300 500 1000 and 1500 mpa shear strain rate 10 3 10 4 10 5 and 10 6 s 1 to finite shear strains 0 5 the experiments have been carried out using a granular material with grain size smaller than 200 m with a little h2o added 0 2wt only two experiments performed at the fastest strain rates and lowest temperatures have failed abruptly right after reaching peak strength 1400 mpa all other samples reach high shear stresses 570 1600 mpa then weaken slightly by 10 190 mpa and continue to deform at a more or less steady state stress level clear temperature dependence and a weak strain rate dependence of the peak as well as steady state stress levels is observed in order to express this relationship the strain rate stress sensitivity has been fit with a stress exponent assuming n and yields high stress exponents n 10 140 which decrease with increasing temperature the microstructures show widespread comminution strain partitioning and localization into slip zones containing at first nanocrystalline and partly amorphous material later during continued deformation fully amorphous material in slip zones despite the mechanical steady state conditions the fabrics in the slip zones and outside continue to evolve and do not reach a steady state microstructure below 5 within the slip zones the fault rock material progressively transforms from a crystalline solid to an amorphous material we present and interpret the experimental results both in terms of sliding friction and viscous flow and we discuss the possible effect that the formation of nanocrystalline and amorphous layers may have on earthquake nucleation

low temperature coherent exsolution in alkali feldspars from high grade metamorphic rocks of sri lanka in the alkali feldspars of the amphibolite and granulite facies rocks of sri lanka a late stage final exsolution event is observed which produced film lamellae and fine scale spindles these were investigated by optical microprobe single crystal transmission electron microscopy and atomic resolution microscopy techniques the lamellae and spindles exsolved below the coherent solvus at temperatures as low as 300 to 350 c precession photographs and arm micrographs show that the intergrowth is perfectly coherent in sections 010 the rhombic section of the pericline twins corresponds to analbite or high albite the albite lamellae and spindles nucleated and grew at low temperatures in a metastable disordered structural state within a tweed orthoclase matrix and became periodically twinned analbite or high albite which subsequently developed only a slight increase in al si order the relationship between twin periodicity and lamellar width predicted for coherent intergrowths by willaime and gandais 1972 is obeyed in or rich grains in which coherent exsolution is the only exsolution event the film lamellae tend to be restricted to the rim the fine scale spindles to the centre of the grains the films nucleated heterogeneously at grain boundaries and grew towards the grain centres fine scale spindles probably nucleated homogeneously in the interior part of grains heterogeneous nucleation and coherent growth are not mutually exclusive

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

alkali feldspar microtextures as provenance indicators in siliciclastic rocks and their role in feldspar dissolution during transport and diagenesis abstract alkali feldspars usually exhibit optical or sub optical intergrowths of albite and k feldspar known generically as perthite which have morphologies and crystallographic characteristics that are distinctive of the igneous or metamorphic environment in which they grew and cooled to surface temperatures we review the current terminology and understanding of how the microtextures form and discuss their role in feldspar dissolution during weathering transport and diagenesis we show how microtextures can be used as provenance indicators in arkosic siliciclastic rocks using examples from the fulmar formation a reservoir rock in the upper jurassic humber group in the central north sea in which feldspar dissolution is a major source of secondary porosity we describe the most effective techniques for routine characterization of which the most practical is back scattered electron imaging in a scanning electron microscope often coupled with cathodoluminescence we provide an atlas of the main types of perthitic intergrowth likely to be encountered in igneous and metamorphic rocks worldwide and show how many of the microtextures can be matched in clastic grains in the fulmar formation grains which are preferentially preserved have microtextures that make them relatively unreactive in aqueous fluids at low temperatures and we conclude that provenance has a major impact on reservoir quality detrital grains in the fulmar exhibit authigenic albitization k feldspar overgrowths and replacement and we discuss how diagenetic features can be distinguished from replacive features developed in the protolith

a tem and microprobe study of a two perthite alkali gabbro implications for the ternary feldspar system an unusual magmatic three feldspar syenogabbro occurs 3 m inside the contact of the klokken gabbro syenite stock it contains plagioclase mesoperthite and cryptoperthite together with a low temperature symplectite intergrowth textural relationships have been investigated by cathodoluminescence bulk chemistry by microprobe and exsolution microtextures and intracrystalline boundaries by tem the mesoperthite has a bulk composition around or26ab52an22 well outside accepted limits of ternary feldspar solid solution it is a mainly coherent lamellar intergrowth of sodic andesine and orthoclase with incipient mtwinning the cryptoperthite bulk composition around or61ab33an6 is a coherent lamellar intergrowth of orthoclase and sodic low oligoclase the compositions of the exsolved phases have been estimated the meso and cryptoperthite crystals have sharp boundaries with each other

evidence for a recent change in the link between the north atlantic oscillation and arctic sea ice export evidence for a recent change in the link between the north atlantic oscillation nao and arctic sea ice export through fram strait during wintertime djfm is presented from the analysis of simulated arctic sea ice and observations for the period 1958 1997 whereas no correlation between the two time series is found from 1958 to 1977 r 0 1 the correlation increased significantly thereafter r 0 7 1978 1997 the increased coherency between the nao and arctic sea ice export through fram strait during the last two decades resulted from anomalous meridional wind components near fram strait which were associated with the more easterly position of the nao s centers of interannual variability compared to 1958 1977

barotropic wave propagation and instability and atmospheric teleconnection patterns abstract a global barotropic model linearized about the 300 mb climatological mean january flow is perturbed by applying a series of localized forcings distributed throughout the tropics and subtropics structures which resemble the observed pacific north american and east atlantic teleconnection patterns noted by wallace and gutzler 1981 tend to recur in the responses similar patterns are found to result from the dispersion of isolated initial perturbations placed at a variety of locations in the tropics and midlatitudes it is shown that these structures are related to the most rapidly growing mode associated with barotropic instability of the zonally varying climatological basic state in the absence of damping this mode has an e folding time of about a week and a period close to 50 days in localized regions the instantaneous growth rates can be competitive with those of baroclinic instability these episodes of rapid local barotropic growth are interspersed with intervals in which the local

characteristics of the recent eastward shift of interannual nao variability recent observational studies have shown that the centers of action of interannual variability of the north atlantic oscillation nao were located farther eastward during winters of the period 1978 97 compared to previous decades of the twentieth century in this study which focuses on the winter season december march new diagnostics characterizing this shift are presented further the importance of this shift for nao related interannual climate variability in the north atlantic region is discussed it is shown that an nao related eastward shift in variability can be found for a wide range of different parameters like the number of deep cyclones near surface air temperature and turbulent surface heat flux throughout the north atlantic region by using a near surface air temperature dataset that is homogenous with respect to the kind of observations used it is shown that the eastward shift is not an artifact of changes in observational practices that took place around the late 1970s finally an eof based monte carlo test is developed to quantify the probability of changes in the spatial structure of interannual nao variability for a relatively short 20 yr time series given multivariate white noise it is estimated that the likelihood for differences in the spatial structure of the nao between two independent 20 yr periods which are similar as measured by the angle and pattern correlation between two nao patterns to the observed differences to occur just by chance is about 18 from the above results it is argued that care has to be taken when conclusions about long term properties of nao related climate variability are being drawn from relatively short recent observational data e g 1978 97

reply to comment by alley et al on catastrophic ice shelf breakup as the source of heinrich event icebergs 1 the authors of hulbe et al 2004 are grateful for the opportunity afforded by alley et al s 2005 remarks the original draft of the comment was shared via e mail after which a compelling dialog ensued among the combined group of authors this is we believe exactly what should transpire in the scientific marketplace of ideas and we were pleased to be approached by alley et al 2005 in this way 2 three glaciologic issues do seem to warrant clarification first the notion of ice shelves as debris filters derives mainly from observations at the fronts of antarctica s large ice shelves not from the small fringing ice shelves advocated in the work of hulbe et al 2004 indeed the presence of significant englacial debris in the shattered remains of the larsen b ice shelf was a primary motivation in our revisitation of the original ice shelf hypothesis second it has been observed recently that glaciers in the antarctic peninsula and elsewhere are speeding up in the wake of ice shelf disintegration the details of those speed ups require investigation but this may be a source for additional heinrich layer sediment after the initial ice shelf breakup pulse third the trigger for ice shelf breakup is summertime warmth a signal that may not be apparent in the mean annual temperature revealed by ice core isotopes 3 through all the discussion one fact seems clear neither an ice shelf nor an ice stream surge model adequately addresses all the known demands of theheinrich layer record neither mechanism is completely unique in its sedimentary and geomorphic signature yet hope exists for each has particular attributes that might be exploited in identifying the correct mechanism 4 we believe our original paper addressed the concerns raised by alley et al 2005 thus we decline further comment and eagerly await more news from the geologic record our goal is to improve the understanding of heinrich events not to cling to one explanation or another paleoceanography vol 20 pa1011 doi 10 1029 2004pa001118 2005

chronological constraints on the pre orogenic history burial and exhumation of deep seated rocks along the eastern margin of the variscan orogen bohemian massif czech republic key lithological units of the high grade eastern margin of the bohemian massif were dated using the u pb and pb pb methods on zircons in order to establish a chronological framework for the geodynamic evolution of the variscan orogenic root the protolith ages for metagranitoids orthogneisses and granulites of thickened lower and middle crust reveal the existence of magmatic activity that occurred over a 100 million year time interval from cambro ordovician to early devonian times probably related to discontinuous intracontinental rifting of neoproterozoic crust our geochronological data suggest that the eastern part of the orogenic root represents thermally softened and rifted neoproterozoic crust preserved farther to the east as the brunia microcontinent zircon ages for felsic granulites high grade gneisses of the lower crust and of a syn convergence granodioritic intrusion in the upper crust indicate that thickening and exhumation of the crust occurred during a narrow time interval between 370 and 340 ma exhumation of the lower crust to mid crustal levels was a localized process that occurred at 340 ma and was associated with crustal scale folding in the internal part of the root as well as orogenic channel flow along the eastern collisional margin both types of exhumation mechanisms were driven by deep level wedging indentation of the easterly brunia continent followed by deposition of heavy minerals and pebbles derived from high pressure rocks in the adjacent foreland basin final orogenic development was characterized by ne sw dextral transpressive shearing parallel to the brunia margin as well as dextral trans tension associated with activity along the elbe lithospheric fault these processes affected the marginal parts of the orogenic root and were accompanied by 330 to 325 ma old syntectonic granitoid intrusions along reactivated lithotectonic boundaries rotation of the assembled orogenic belt accompanied by lithospheric faulting driven by westerly subduction roll back may be the most plausible model to explain late deformation of the orogenic root

time temperature evolution of microtextures and contained fluids in a plutonic alkali feldspar during heating microtextural changes brought about by heating alkali feldspar crystals from the shap granite northern england at atmospheric pressure have been studied using transmission and scanning electron microscopy a typical unheated phenocryst from shap is composed of about 70 vol of tweed orthoclase with strain controlled coherent or semicoherent micro and crypto perthitic albite lamellae with maximum lamellar thicknesses 700 c and after 48 h at 700 c all such regions were essentially compositionally homogeneous as indicated by x ray analyses at fine scale in the transmission electron microscope changes in lamellar thickness with time at different t point to an activation energy of 350 kjmol 1 a lamella which homogenised after 6 800 h at 600 c therefore would have required only 0 6 s to do so in the melting interval at 1 100 c subgrains in patch perthite homogenised more slowly than coherent lamellae and chemical gradients in patches persisted for 5 000 h at 700 c homogenisation t is in agreement with experimentally determined solvi for coherent ordered intergrowths when a 50 100 c increase in t for an1 is applied homogenisation of lamellae appears to proceed in an unexpected manner two smooth interfaces microstructurally sharp advance from the original interfaces toward the mid line of each twinned semicoherent lamella in places the homogenisation interfaces have shapes reflecting the local arrangements of nanotunnels or pull aparts analyses confirm that the change in alkali composition is also relatively sharp at these interfaces si al disordering is far slower than alkali homogenisation so that tweed texture in orthoclase tartan twinning in irregular microcline and albite twins in albite lamellae and patches persisted in all our experiments including 5 478 h at 700 c 148 h at 1 000 c and 5 h at 1 100 c even though the ensemble in each case was chemically homogeneous nanotunnels and pull aparts were modified after only 50 min at 500 c following the simulated 40ar 39ar step heating schedule new features called slots developed away from albite lamellae often with planar traces linking slots to the closest lamella slot arrays were often aligned along ghost like regions of diffraction contrast which may mark the original edges of lamellae we suggest that the slot arrays result from healing of pull aparts containing fluid at 700 c and above the dominant defects were subspherical bubbles which evolved from slots or from regions of deuteric coarsening the small degree of partial melting observed after 5 h at 1 100 c was often in the vicinity of bubbles larger micropores which formed at subgrain boundaries in patch perthite during deuteric coarsening retain their shape up to the melting point as do the subgrain boundaries themselves it is clear that modification of defects providing potential fast pathways for diffusion in granitic alkali feldspars begins below 500 c and that defect character progressively changes up to and beyond the onset of melting

exsolution and coarsening mechanisms and kinetics in an ordered cryptoperthite series cryptoperthites from the klokken layered syenite intrusion were examined by tem to determine the role of exsolution ordering and twinning in the development of the coherent microtextures during slow cooling the stratigraphic position of the samples in the layered series giving an independent variable in determining their evolution both periodicity primary and secondary and morphology change with distance from the top of the series most samples contain low microcline in the diagonal association

zoned ternary feldspars in the klokken intrusion exsolution microtextures and mechanisms the microtextures developed during relatively slow cooling as a function of bulk composition in zoned ternary feldspars from syenodiorites and syenites in the klokken intrusion described in the preceding paper were determined by tem and their origin and evolution deduced the feldspars normally have a plagioclase core and an alkali feldspar rim cores become smaller and rims larger and the an content of both decrease with distance from the contact of the intrusion the following microtextural sequence was observed the inner plagioclase cores are homogeneous oligoclase andesine with albite growth twins only but are crypto antiperthitic towards the outer core at first small platelets of low sanidine a few nanometres thick and up to 10 nm long occur sporadically only on albite twin composition planes with further increase in bulk or they are homogeneously distributed in the plagioclase thicker through going plates in platelet free areas are found which induce albite twins in the surrounding plagioclase the microtextures in the rims are regular cryptomesoperthitic with 601 lenses or lamellae depending on the bulk or content of low sanidine in albite twinned low oligoclase andesine albite and pericline twins in plagioclase in an m twin relationship together with lenticular low sanidine were found in only one small area the overall diffraction symmetry of the mesoperthites is monoclinic showing that exsolution started in a monoclinic feldspar whereas that of the antiperthites is triclinic the intermediate zone between the core and rim is more complex and microtextures vary over distances of a few micrometres the cryptomesoperthites are very regular where or rich and probably arose by spinodal decomposition the platelets in the outer cores arose by heterogeneous nucleation on twin composition planes and by homogeneous nucleation elsewhere near the intermediate zone they coarsened to give larger plates which induced albite twins in the plagioclase because of the zoning microtextures that were initiated in areas of given composition can propagate laterally into zones of different composition a diagram is given showing the relationship between ternary bulk composition and the microtexture developed in coherent perthitic alkali feldspars and plagioclases from slowly cooled rocks

the relationship of heinrich events and their european precursors over the past 60 ka bp a multi proxy ice rafted debris provenance study in the north east atlantic high resolution multi proxy records of ice rafted debris ird flux and provenance in the ne atlantic detail the development variability and decline of marine margins of the last glacial circum north atlantic ice sheets coupled lithological identification sr and nd isotopic composition and 40ar 39ar ages of individual hornblende grains reduce ambiguity as to ird potential source region allowing clear differentiation between laurentide lis icelandic and british bis ice sheet sources the icelandic and bis are collectively referred to as the nw european ice sheet nweis a step wise increase in the flux of ird to the core site at 26 5 ka bp documents bis advance and glaciation of ireland millennial scale variability of the bis at a 2 ka periodicity is inferred through clusters of pulsed ird fluxes throughout the late glacial 26 5 10 ka bp combination of these european ird events and the 7 ka periodicity of lis instability is thought to account for quasi synchronicity of the nweis and lis ird pulses at heinrich event h 2 and h1 previously suggested to represent the possible involvement of the nweis in the initiation of h events furthermore the lack of extensive nweis marine margin is inferred prior to h3 31 5 ka bp such that no european precursor event is associated with either h5 or h4 this suggests that precursor events were not directly implicated in the collapse of the lis and the persistent instabilities of the bis that are clustered at a 2 ka periodicity are incompatible with the concept that both h events and their precursors are independent responses to a common underlying trigger

microstructural evolution during experimental albitization of k rich alkali feldspar crystals of k feldspar c2 m in contact with highly concentrated aqueous nacl solutions at 500 c and 200 mpa are pseudomorphically replaced by high albite c bar 1 as a result of an interface coupled dissolution reprecipitation process the reaction occurs at an extremely sharp reaction front 10 nm and involves the complete breakdown of the initial framework structure this results in the release of tetrahedrally incorporated elements such as fe3 and ti4 and a significant increase in si al disorder across the reaction interface the evolving microstructure is controlled by crystallographic relations between the phases this leads to highly anisotropic sawtooth shaped intergrowths of albite and initial k feldspar resulting in the least structural misfit between the two framework structures as a result the newly formed interfaces appear to be semicoherent and cracks across the reaction fronts even indicate elastic strain the reaction produces 2 distinctive albite types albite 1 and albite 2 both are polycrystalline with albite 2 showing significantly larger subgrain sizes this indicates a secondary coarsening step driven by the reduction in interfacial energy within the polycrystalline replacement product the reaction also produces a highly porous rim however the porosity is not evenly distributed resulting in a porous albite 1 and a non porous albite 2 that mostly surrounds large euhedral pores despite the substantial volume fraction of porosity in albite 1 no significant 3d interconnectivity could be detected making the presence of a pervasive porosity unlikely however the result of coarsening is the continuous modification of the 3d porosity distribution this could potentially provide a mechanism for fluid transport through the replacement rim until textural and chemical equilibration is achieved

the size distribution of exsolution lamellae in iron free clinopyroxene the size distribution of pigeonite and diopside exsolution lamellae on 001 obtained at temperatures of 1100 1200 and 1300 c and annealing times between 2 and 4320 h was studied by transmission electron microscopy a total of 5192 pigeonite and 5286 diopside lamellae was studied at all three temperatures the size distributions of pigeonite and diopside lamellae are smaller during exsolution compared to the subsequent coarsening process the final size distributions are time invariant indicating that a steady stage distribution is reached the theory of ardell 1972a which assumes volume diffusion as rate limiting process and takes into account the non zero volume fraction of the precipitates describes the experimental size distributions quite well and also leads to the observed exponent of three in the rate law

the microstructures of microcline from some granitic rocks and pegmatites optical microscopy transmission electron microscopy tem and electron diffraction have been used to study the microstructures in a series of microclines from granitic rocks and pegmatites optical microscopy revealed exsolution of albite in all but one specimen and in general the k phase exhibited cross hatched patterns the tem and optical observations confirm earlier ideas that the cross hatching is associated with intersecting sets of albite and pericline twin lamellae which were formed at the transformation from monoclinic to triclinic symmetry however significant changes subsequently occur which produce microstructures involving essentially albite twinning only although the cross hatched morphology is retained and features associated with the original pericline twins are observed in the tem images and in the associated diffraction patterns the four spot diffraction patterns characteristic of m twinning are observed only from volumes of specimen containing discrete domains of albite twinning and domains of pericline twinning streaking of the diffraction spots is associated with the complex structure of the domain boundaries the influence of exsolution of albite on the initiation of the transformation twinning has also been investigated domains of orthoclase within a matrix of twinned microcline were observed in two specimens but the observations do not appear to provide any direct information about the mechanism of the transformation between these two structures

north atlantic interdecadal variability oceanic response to the north atlantic oscillation 1865 1997 abstract in contrast to the atmosphere knowledge about interdecadal variability of the north atlantic circulation is relatively restricted it is the objective of this study to contribute to understanding how the north atlantic circulation responds to a forcing by the north atlantic oscillation nao on interdecadal timescales for this purpose the authors analyze observed atmospheric and sea surface temperature sst data along with the response of an ocean general circulation model to a realistic monthly surface flux forcing that is solely associated with the nao for the period 1865 1997 in agreement with previous studies it is shown that the relationship between the local forcing by the nao and observed sst anomalies on interdecadal timescales points toward the importance of oceanic dynamics in generating sst anomalies a comparison between observed and modeled sst anomalies reveals that the model results can be used to assess interdecadal variability of the north atlantic circulation the observed

exsolution by spinodal decomposition ii perthite formation during slow cooling of anatexites from ngoronghoro tanzania perthites in slowly cooled granulite facies rocks from the ngoronghoro structure tanzania show complex microstructures reflecting several stages of exsolution and coarsening mesoperthites with an integrated bulk composition of or26 5ab71an2 5 are comprised of lamellar intergrowth of 5 to 10 m wide orthoclase rich and albite rich lamellae spindle perthites with a bulk composition of or67ab31 5an1 5 are comprised of 2 to 10 m wide and several 109s of m long albite rich spindles in an orthoclase rich host in the mesoperthite primary exsolution occurred by spinodal decomposition whereas the spindle perthite formed by a nucleation and growth mechanism the interfaces between the exsolved phases are generally incoherent unmixing and coarsening of the mesoperthite is discussed in the light of non linear uphill diffusion the microstructure evolution and successive chemical separation of the exsolved phases during cooling are modeled based on cahn hilliard theory we find that coarsening primarily occurs during the first 20 c to 30 c of cooling after the homogeneous precursor feldspar has entered the coherent spinodal the extent of coarsening and the characteristic size of the exsolved phases depend on the cooling rate over this temperature interval for geologically relevant cooling rates on the order of 5 c ma to 50 c ma the compositions of the exsolved phases develop along the solvus down to about 480 c to 530 c and are frozen in only at lower temperatures the compositions that are finally preserved in the orthoclase rich and in the albite rich phases depend on cooling rate over this temperature interval both the characteristic lamella width of the mesoperthite as well as the compositions of the exsolved phases indicate slow cooling at 5 c ma during the coarsening stage and down to about 450 c during later stages of the cooling history the albite rich phase of the mesoperthite exsolved about the peristerite gap and the orthoclase rich host of the spindle perthite exsolved a second generation of coherent albite rich spindles the incoherent phase boundaries of the primary perthite microstructures served as passageways for fluids during late stage deuteric alteration which lead to secondary coarsening in the mesoperthite and to alteration of the albite rich precipitates in the spindle perthite finally both types of perthites were replaced by coarse grained patch perthite during deuteric alteration

p t x controlled element transport through granulite facies ternary feldspar from lofoten norway fluid transport on the grain scale controls many rock properties and governs chemical exchange charnockites from lofoten indicate fluid penetration into ternary alkali feldspars controlled by their microtextures in a process of fluid infiltration at granulite facies conditions 600 c and 8 11 kbar tiny pyroxenes enclosed in alkali feldspar reacted to amphiboles which are always spatially connected to perthitic albite investigation of these microtextures by tem imaging of focused ion beam fib prepared foils revealed that pyroxenes in contact with albite lamellae show dissolution features an amorphous fe and cl bearing material interpreted to be a residuum of the percolating fluid was found within albite lamellae textures and mineral compositions indicate that a cl rich aqueous fluid attacked the lamellae which then provided pathways for further fluid flow a correspondence was found between feldspar compositions their microtexture and their degree of alteration as a result of their permeability for fluids at specific temperatures hence in addition to pressure and temperature small variations of feldspar composition can strongly influence the fluid permeability of feldspathic rocks under lower crustal conditions

transient eddy forcing of the rotational flow during northern winter abstract the total direct transient eddy forcing of the vorticity balance in the upper troposphere during northern winter is examined using 11 years of 2 to 8 day bandpassed global analyses most examinations of the importance of high frequency eddy vorticity fluxes to the maintenance of either the climatological standing waves or low frequency anomalous flows have focused on only the horizontal blow or the rotational component of the horizontal transient flow the latter simplification has been shown to be questionable for planetary scales the vorticity flux by the transient divergent flow produces a forcing of the mean streamfunction that is of comparable magnitude with the equivalent rotational term however the streamfunction forcing by the sum of the transient vertical advection and twisting terms largely balances the fearing by the vorticity flux convergence associated with the divergent flow the result is that the convergence of the eddy vorticity flux by the total transient flow is not a good a

plagioclase hosted fe ti oxide micro inclusions in an oceanic gabbro plagiogranite association from the mid atlantic ridge at 13 34 n

strike slip faulting as a trigger mechanism for overpressure release through piercement structures implications for the lusi mud volcano indonesia piercement structures such as hydrothermal vent complexes pockmarks and mud volcanoes are found in various geological settings but are often associated with faults or other fluid focussing features this article aims to investigate and understand the mechanisms responsible for the formation of piercement structures in sedimentary basins and the role of strike slip faulting as a triggering mechanism for fluidization for this purpose four different approaches were combined fieldwork analogue experiments and math