climatology and interannual variability of north atlantic hurricane tracks the spatial and temporal variability of north atlantic hurricane tracks and its possible association with the annual hurricane landfall frequency along the u s east coast are studied using principal component analysis pca of hurricane track density function htdf the results show that in addition to the well documented effects of the el nino southern oscillation enso and vertical wind shear vws north atlantic htdf is strongly modulated by the dipole mode dm of atlantic sea surface temperature sst as well as the north atlantic oscillation nao and arctic oscillation ao specifically it was found that atlantic sst dm is the only index that is associated with all top three empirical orthogonal function eof modes of the atlantic htdf enso and tropical atlantic vws are significantly correlated with the first and the third eof of the htdf over the north atlantic ocean the second eof of north atlantic htdf which represents the zonal gradient of north atlantic hurricane track density showed no significant correlation with enso or with tropical atlantic vws instead it is associated with the atlantic sst dm and extratropical processes including nao and ao since for a given hurricane season the preferred hurricane track pattern together with the overall basinwide hurricane activity collectively determines the hurricane landfall frequency the results provide a foundation for the construction of a statistical model that projects the annual number of hurricanes striking the eastern seaboard of the united states

the newport fault eocene listric normal faulting mylonitization and crustal extension in northeast washington and northwest idaho the newport fault is a spoon shaped shallowly dipping fault zone across which a proterozoic to tertiary sedimentary suprastructure is juxtaposed above an infrastructure of basement gneiss and granitic batholiths as a result of eocene normal faulting and crustal attenuation chloritic microbreccia occurs at the top of the newport fault zone below which a zone of mylonitization as much as 500 m thick is developed in footwall rocks including the eocene silver point quartz monzonite detailed kinematic analysis of fabric and structures in the mylonite and microbreccia establishes that displacement was normal in sense on both sides of the u shaped fault trace the direction of extension was 74 254 as shown by consistently oriented mylonitic lineation crustal attenuation across the newport and adjacent purcell trench faults may have reached as much as 68 km 120 and in any case it exceeded 35 km 40 during faulting the footwall moved up and out to the east and west relative to the hanging wall forming two flanking footwall culminations or crustal scale boudins tectonic denudation of the footwall infrastructure is shown by eocene k ar cooling ages for granitic rocks within it chrontours that increase in age outward from the newport fault record abrupt cooling of the infrastructure as it was drawn away from the hanging wall the silver point quartz monzonite was emplaced into the dilatant zone between the footwall infrastructural culminations during displacement hanging wall strata were rotated down the listric fault surface the footwall rotated upward and the fault surface flattened probably as a consequence of isostatic adjustment to mass redistribution caused by normal faulting a roll over anticline developed in the hanging wall as it moved into the zone of attenuation between the footwall culminations syntectonic eocene extrusive rocks and coarse clastic deposits accumulated in a growth fault basin on the west flank of the hanging wall anticline crustal extension and normal displacement on the newport fault are compatible with a regional eocene strain regime that crossed northern idaho washington and southern british columbia and produced dextral transcurrent faulting core complex development and clockwise rotation of crustal blocks throughout that area

seismic measurements reveal a saturated porous layer beneath an active antarctic ice stream seismic reflection studies recently conducted on ice stream b part of the marine ice sheet of west antarctica show a metres thick layer immediately beneath the ice in which both compressional p and shear s wave speeds are very low these low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure from this and from arguments presented in an accompanying paper1 to the effect that the layer would be too weak to support the shear stress exerted by the overlying ice we conclude that the layer is deforming and that the ice stream probably moves principally by such deformation

cleavage fold relationships and their implications for transected folds an example from southwest virginia u s a abstract a non coaxial deformation involving pre folding initiation of cleavage perpendicular to bedding is proposed to explain non axial planar cleavage associated with mesoscopic folds in part of the appalachian foreland thrust belt of southwest virginia folds are gently plunging asymmetric upright to slightly inclined sinusoidal forms with non axial fanning cleavage they show extreme local variations in type and degree of transection and the consistency of transection direction these relations are further complicated by hinge migration cleavage fan angles bedding cleavage angles and transection values appear influenced by fold tightness and in part by fold flattening strain fold flattening increments are considered simultaneous with folding axial surface traces and not cleavage traces coincide with the principal extension direction in fold profiles geometric modelling of cleavage fanning and bedding cleavage angle variations for various theoretical folding modes suggest that folding in limestone and sandstone layers was by tangential longitudinal strain significant shape modification and change in bedding cleavage relations occurred after limb dips of 40 and 50 were attained in limestone and sandstone respectively mud rock class 1c folds with convergent cleavage fans show features transitional between buckling and flexural flow initiation of cleavage fabrics during layer parallel shortening prior to significant folding may be important for cleavage evolution in some deformed rocks

a comparison of the strain of crinoid columnals with that of their enclosing silty and shaly matrix on the appalachian plateau new york abstract a pole figure goniometer was used to measure the preferred orientation of the basal planes of chlorite in 87 samples from the upper devonian clastic rocks of the appalachian plateau new york interpretation of the preferred orientation according to the theory of march yields an estimate of how much an element of the sediment has changed shape since deposition this deformation can be interpreted according to three distinct models for the strain history all begin with compaction followed by one of three types of tectonic strain 1 a plane strain that conserves bedding plane area by compensating for horizontal shortening with horizontal elongation at right angles 2 one that uniaxially shortens a horizontal line normal to the fold axes without compensating elongation and 3 a plane strain again which conserves the area in the vertical plane containing a shortened horizontal direction by stretching it vertically for lack of suitable names we will simply call the three total strains type b u and v from the initials of the distinguishing features of their tectonic increment the horizontal strain components estimated from preferred orientation are compared at a number of localities with those implicit in the principal horizontal diameters of the elliptical outlines of deformed crinoid columnals found on bedding planes expressed for constant bedding plane area or type b total strain the strain in the direction of greatest elongation measured by preferred orientation was found to range from no recorded strain to 0 19 with a median of 0 04 as a rule however the more intensive strains were recorded in shales with a fine grained phyllosilicate content exceeding 85 by volume in which the mean was 0 07 deformed crinoid columnals in the same set of samples have elongations parallel to their long axes that range from 0 04 to 0 10 with a median and average of 0 07 the discrepancy between the two sets of strain measures at least in the coarser and more permeable rock types may either be real and caused by easier flushing of dissolved ions or may be caused by imperfect strain recording in coarse matrix materials

age and regional tectonic implications of late cretaceous thrusting and eocene extension cabinet mountains northwest montana and northern idaho understanding the kinematic and temporal relationships between the cordilleran magmatic belt and the foreland fold and thrust belt can provide insights into the development of thrust systems in retro arc settings combining data from field mapping and 40 ar 39 ar geochronometry and thermochronometry we show that late cretaceous thrusting in the cabinet mountains of the northwest montana thrust belt coincided both spatially and temporally with hinterland magmatism thrusting and magmatism in the hinterland of the northwest and southwest montana thrust belt were coeval with development of the foreland fold and thrust belt during the late cretaceous movement on the moyie thrust a principal thrust in the western part of the purcell anticlinorium occurred between ca 71 and 69 ma in the cabinet mountains the anticlinorium developed by systems of east and west directed trusts with a southward decrease in slip on the moyie thrust that the heloped contribute to less overall shortening in the anticlinorium in montana than in british columbia the lithosphere underlying the anticlinorium may have been thermally weakened by magmatic heating promoting the development of both the late cretaceous thrusts and early to middle eocene normal faults

out of phase relationship between tropical cyclones generated locally in the south china sea and non locally from the northwest pacific ocean tropical cyclones tcs in the south china sea scs are either generated locally or formed non locally in the northwest pacific ocean nwp and entered into the scs here it is found that local tcs vary out of phase with non local tcs in summer that is if fewer more tcs enter into the scs from the nwp more fewer tcs are generated over the scs further analyses show that variability of the western pacific subtropical high wpsh is responsible for the out of phase relationship as the wpsh shifts eastward westward fewer more non local tcs formed in the nwp can enter into the scs because tcs are recurved northward moved westward due to the eastward westward movement of the wpsh positive negative low level vorticity anomalies weak strong vertical wind shear between the upper and lower troposphere and anomalous upward downward motion in the middle troposphere are induced in the northern scs the changes in the relative vorticity vertical wind shear and vertical velocity are favorable unfavorable for the local tc genesis in the scs these variations of non local and local tcs result in an out of phase relationship between tcs formed locally in the scs and non locally in the nwp

west antarctic ice streams draining into the ross ice shelf configuration and mass balance extensive airborne radar soundings closely tied to accurately located ground stations made over a portion of the west antarctic inland ice sheet and the ross ice shelf have enabled us to map the boundaries of the ice streams and their flow bands on the ross ice shelf the surfaces of the active ice streams a and b are heavily crevassed but there are no visible crevasses on ice stream c however the existence of numerous crevasses at a depth of about 35 m implies that ice stream c ceased to be active about 250 years ago there is a complex zone at the head of ice stream b that suggests that ice stream b is currently widening and advancing toward the interior of the ice sheet the grounding lines between the inland ice and the ice shelf were mapped from the surface elevations using the requirement of hydrostatic balance and the character of the radar echoes the inland ice is more extensive than previously mapped and includes a large weakly grounded area downstream of ice streams a and b where the surface elevations are barely above hydrostatic equilibrium crary ice rise extends 70 km upstream of the previously mapped position to relate surface elevation data from satellite observations to sea level three geoidal models were tested we conclude that the gem 10c model is the best of the three for this section of antarctica a new map of surface elevation shows deep marginal troughs and longitudinal ridges along ice streams a and b but not on ice stream c whose surface contours show signs of stagnation ice stream c shows a strongly positive and ice stream b a significantly negative net balance rate ice streams a and d also show a significantly negative net flux whereas ice streams e and f do not the overall net balance of this part of the west antarctic inland ice is suggestively negative 23 15 km3 yr 1 from the measured flux into the ross ice shelf and previous measurements we calculate an average basal melt rate from beneath the ice shelf of 0 12 0 03 m yr 1

large scale ice flow over a viscous basal sediment theory and application to ice stream b antarctica recent seismic studies of ice stream b antarctica and field analysis of mid latitude glacial deposits suggest that deformable basal sediments e g water saturated till are important in determining ice sheet flow if the ratio of till viscosity to effective ice viscosity is small vertical shear associated with horizontal flow is confined to the deforming bed alone ice flow over a deformable bed is thus akin to that of floating ice shelves because ice shelves flow over inviscid seawater for some antarctic ice streams and possibly for portions of the late wisconsin ice sheets in north america and eurasia basal drag associated with deforming basal sediment does not induce significant vertical gradients of horizontal velocity instead basal drag affects the flow as if it were a horizontal body force balanced by longitudinal and transverse deviatoric stress gradients comparison of the observed flow of ice stream b to finite element simulations incorporating a viscous basal till suggest that a simple till theology is sufficient to explain the current velocity profile these simulations also highlight the importance of horizontal deviatoric stress in regions where driving stress and basal stress do not locally balance while bed deformation is critical to ice stream existence sensitivity tests suggest that ice shelf back pressure is still a crucial control affecting ice stream response to atmospheric and oceanic climate

a microstructural and microchemical study of cleavage lamellae in a slate abstract the results of a detailed microstructural and microchemical study of a slate from the chewton area victoria australia are reported in which it was found that cleavage developed from microcrenulations phyllosilicates in p domains differed in their chemistry from those in q domains and were concentrated in the p domains by localized metamorphic reactions which were aided by mechanical rotation and solution processes wide dark cleavage lamellae often taken as evidence for the passive concentration of insoluble minerals appear to have had a similar origin the p domains exhibited two types of microstructure one which was consistent with annealing and the other with deformation within the domain cataclasites had formed along some p domains suggesting that they had become preferential sites for late phase brittle deformation

leading tropical modes associated with interannual and multidecadal fluctuations in north atlantic hurricane activity abstract interannual and multidecadal extremes in atlantic hurricane activity are shown to result from a coherent and interrelated set of atmospheric and oceanic conditions associated with three leading modes of climate variability in the tropics all three modes are related to fluctuations in tropical convection with two representing the leading multidecadal modes of convective rainfall variability and one representing the leading interannual mode enso the tropical multidecadal modes are shown to link known fluctuations in atlantic hurricane activity west african monsoon rainfall and atlantic sea surface temperatures to the tropics wide climate variability these modes also capture an east west seesaw in anomalous convection between the west african monsoon region and the amazon basin which helps to account for the interhemispheric symmetry of the 200 hpa streamfunction anomalies across the atlantic ocean and africa the 200 hpa divergent wind anomalies and both the structure and spatial scale

atlantic ocean modulated hydroclimate of the subtropical northeastern mexico since the last glacial maximum and comparison with the southern us abstract proxy records generated from chemical composition and radiocarbon dating of a sediment sequence collected from the el potosi basin provide information about variable hydroclimate of the subtropical northeastern mexico since the last glacial maximum lgm minimal amounts of runoff and more carbonate deposition during 19 ka represent the lgm the deglaciation was wetter compared to the lgm and enhanced runoff during 19 12 ka transported more ti bearing clastics from a relatively humid watershed over the deglaciation the basin received more runoff during the bolling allerod compared to the heinrich stadial 1 and younger dryas reduction in the amount of runoff during 10 1 ka and deposition of unweathered si bearing clastics during 4 1 ka suggest that the holocene was drier compared to the deglaciation hydroclimates of the northeastern mexico and southern us were synchronous during the lgm as well as deglaciation change from the drier lgm to wetter bolling allerod occurred as the gulf of mexico became warmer and the region received more summer precipitation however the dissimilarities observed in regional hydroclimates of the holocene need further evaluation

recent increase in south pole snow accumulation this paper summarizes the 37 year history of net accumulation measurements at the geographic south pole obtained by numerous investigators using a variety of techniques these data lead to the conclusion that annual net snow accumulation has increased in the vicinity of south pole station sps since 1955 the records were examined for evidence of a station effect and it is concluded that not all of the observed increase can be attributed to snow drift associated with the presence of the station furthermore the accumulation increase at the south pole appears consistent with increases observed at other locations on the east antarctic plateau and in the peninsula region as well these data suggest that the recent accumulation increase at sps may be regionally extensive over the east antarctic plateau

strain analysis of the ninemile fault zone western montana insights into multiply deformed regions abstract by means of detailed field mapping and a systematic strain analysis we investigated the development of the ninemile fault in western montana the fault has been considered to be either a mesozoic or mid tertiary strike slip fault or a late eocene early oligocene normal fault the rock of the study area experienced a mesozoic to early tertiary ne sw shortening expressed by thrusts folds and pervasive cleavage we estimated total strain by measuring preferred orientation of chlorite grains in samples from within and near the ninemile fault zone and by calculating the strain according to the march theory our goal was to explain how strain accumulated by successive superposition of strains during the two deformation events onto an early compaction strain in all samples the minimum elongation direction maximum shortening is nearly vertical the maximum elongation directions of all the samples outside the ninemile shear zone are subperpendicular to the strike of the shear zone whereas in the shear zone they are either parallel to the strike of the shear zone or form an angle of about 45 the systematic variation in the principal strain directions is the result of two deformational events expressed by local structures created by early ne sw shortening and later ne sw extension the observed strain requires that the ninemile fault a normal fault during the tertiary had earlier been either a thrust or a zone of contractional shear deformation along which there was fault perpendicular shortening and fault parallel extension although the average value of maximum elongation is greater within the ninemile shear zone than outside it varies significantly inside the fault zone suggesting a highly inhomogeneous strain distribution created by a complex deformation history

sedimentary processes in the great lakes sediments in the great lakes are subject to four general categories of processes input transport deposition and postdepositional alteration sedimentary input is from coastal erosion 64 riverine input 26 atmospheric transport 3 and several lesser sources 7 once in the lake sediments are transported to their place of deposition along the bottom and or in suspension depending upon grain size and density the rate of deposition in the great lakes is variable and ranges from zero in some areas to over 6000 g m sup 2 yr sup 1 in the eastern basin of lake erie after deposition sediments undergo bioturbation dissolution of carbonate and opal remobilization of many metals followed by reprecipitation within the surficial oxidized layer and degradation of organic compounds

joints microfractures and the formation of solution cleavage in limestone the geometry of solution cleavage surfaces in limestones indicates a close connection between cleavage formation and joint and microfracture surfaces these relations suggest that networks of microfractures and joints act both as conduits for transport of dissolved phases and as surfaces on which the cleavage nucleates material transport is by darcyian type bulk flow and is thus not a rate limiting process this contrasts with metamorphic terranes where the transport mechanism diffusion has been identified as a rate limiting step cleavage surfaces of weak to moderate intensities or spacing may form parallel to nonprincipal planes of finite strain

the problem of shearing along axial plane foliations abstract the structural significance of axial plane foliations cannot be understood unless we make a distinction between rotation of the material plane foliation and rotation of the geometrically defined x y plane of the strain ellipsoid if the foliation rotates as a material plane at any stage of deformation then its final orientation will be different from that of the x y plane it is suggested that reorientation of foliation takes place by some combination of the formation of foliation e g recrystallization along the x y plane and passive rotation of the material plane foliation in the same continuous deformation the deviation between the foliation and the x y plane is then much less than 5 degrees however because of this deviation a considerable amount of shear strain may develop along the foliation the analysis thus explains how a foliation can be approximately parallel to the x y plane and yet be a plane of shearing

partial interlayers in phyllosilicates studied by transmission electron microscopy interstratification of complete layers has long been recognized in phyllosilicates interlayering on a fine scale with a host containing partial layers of a second phase has only recently been recognized by using tem considering similarities in structural units of phyllosilicates this type of interlayering should be expected alteration samples from butte montana show extensive development of partial interlayers in kaolinite sericite and pyrophyllite kaolinite found in plagioclase sites always grows from smectite and in the growth process incorporates unit cell thick lenses of the smectite the interlayers show up as increased spacing in 001 fringes and cause considerable strain in the surrounding kaolinite structure pyrophyllite studied was found to have abundant interlayers and inclusions of muscovite this muscovite was identified from diffuse 10 a reflections and microanalysis the muscovite inclusions are usually less than 5 layers thick and extend from 50 a to 1 000 a in the ab plane in sericite fine interlayering is subtle for the interlayers vary only slightly in unit cell size and composition from the host however structural changes are significant enough to cause imagable strain contrast in the host zones of fine interlayers are thought to mark healed subgrain boundaries which originally were zones of compositional heterogeneity

climate modulation of north atlantic hurricane tracks the variability of north atlantic tropical storm and hurricane tracks and its relationship to climate variability is explored tracks from the north atlantic hurricane database for the period 1950 2007 are objectively separated into four groups using a cluster technique that has been previously applied to tropical cyclones in other ocean basins the four clusters form zonal and meridional separations of the tracks the meridional separation largely captures the separation between tropical and more baroclinic systems while the zonal separation segregates gulf of mexico and cape verde storms general climatologies of the seasonality intensity landfall probability and historical destructiveness of each cluster are documented and relationships between cluster membership and climate variability across a broad spectrum of time scales are identified composites with respect to cluster membership of sea surface temperature and other environmental fields show that regional and remote modes of climate variability modulate the cluster members in substantially

a simple atmospheric model of the local and teleconnection responses to tropical heating anomalies abstract a minimal complexity model of both the local and remote stationary responses of the atmosphere to tropical heating anomalies is described and demonstrated two levels are recast as baroclinic and barotropic components with thermal advection in the tropics neglected the model is linearized about some idealized and realistic background wind fields and forced with a localized heating for illustration in the tropics the baroclinic responses are familiar from the matsuno gill model these excite barotropic responses by advective interactions with vertical background wind shear the barotropic signals are in turn transmitted to high latitudes only in the presence of barotropic background westerly winds for an el nino like equatorial heating the barotropic response has anticyclones to the north and south of the heating reinforcing opposing the anticyclonic cyclonic baroclinic gyres in the upper lower troposphere with realistic background flows the model reproduces the hemispheric asymmetry

the concept of steady state foliation abstract a steady state foliation is thought of as a foliation with constant orientation and intensity in a rock undergoing steady state flow the problem discussed is whether such straininsensitive foliations exist in rocks and how they might be distinguished from the more familiar strain sensitive foliations steady state foliations would be useful indicators of stress or of strain rate yet misleading if used as indicators of finite strain one requirement for maintenance of steady state foliations is operation of processes that locally weaken grain shape preferred orientation or reduce grain aspect ratios or destroy lithological layering during flow these are the inverses of the processes normally discussed in connection with foliation development many such processes are known though the details of how and when they operate efficiently enough to stabilize a foliation are unknown there is however a tendency for some of them to operate more efficiently at high strains high temperatures and in flow regimes with high vorticity natural and experimental high temperature shear zones are accordingly one environment in which steadystate foliations may be encountered an experiment is described in which a thin specimen of para dichlorobenzene was given a large shearing deformation at 90 of its absolute melting point a steady state foliation was not produced but the technique is a promising one for further microstructural studies where in situ observation of material undergoing large deformations is desirable

a comparison of mineral grain fabrics and finite strain in amphibolites from eastern finland fabrics in amphibolite rocks from the kuopio area eastern finland are described and compared with results of finite strain analysis the area consists of mantled gneiss domes which are deep seated diapiric structures results concern the cover rocks of the domes strain ellipsoids range in shape from prolate to oblate 0 67 v 0 52 strain intensities vary strongly preferred orientations of hornblende have been measured by x ray texture goniometry and corresponding fabric ellipsoids calculated using an eigenvalue method the same has been done for biotite where present fabric ellipsoids obtained for biotite are all oblate 0 04 vf 0 76 those obtained for hornblende range from prolate to oblate 0 60 vf 0 73 intensities of hornblende fabric are weaker than those of biotite fabric local variations of results are induced by grain scale factors such as grain size or original fabrics no simple correlation is found between intensities of fabric and strain in general increasing stra

spatial variations in major u s hurricane activity statistics and a physical mechanism abstract the authors provide a statistical and physical basis for understanding regional variations in major hurricane activity along the u s coastline on long timescales current statistical models of hurricane activity are focused on the frequency of events over the entire north atlantic basin the exception is the lead author s previous work which models the occurrence of hurricanes over the caribbean sea gulf of mexico and the southeast u s coast separately here the authors use statistics to analyze data from historical and paleoclimatic records to expand this work in particular an inverse correlation in major hurricane activity across latitudes at various timescales is articulated when activity is above normal at high latitudes it tends to be below normal at low latitudes and vice versa past research paleoclimatic records and historical data hint at the potential of using the north atlantic oscillation nao as an indicator of where storms will likely track over long timescales an excite

the relationship of strain and preferred orientation of phyllosilicate grains in rocks a review abstract the calculation of strain from the preferred orientation of platy phyllosilicate grains taking strain to be homogeneous is surprisingly often successful from a pragmatic point of view although numerous theoretical objections to this procedure can be and have been raised for the calculation to succeed the original distribution of mica or clay mineral grains must be known or assumed the usual assumption that the starting distribution was random and therefore nearly uniform implies that the strain history of pelitic sediments is taken to start when the watery sediment was last stirred by waves or bioturbation or if it was laid down in still anoxic waters from the moment of first deposition it therefore includes compaction as part of the strain history which is usually neglected by structural geologists originally random distribution of clay flake orientations has been observed in recently deposited sediments in many instances and has been theoretically explained in various ways exceptions probably exist but their frequency has not been estimated biologically disturbed sediments may be brought nearer to a state of random orientation of clay flakes than they were at deposition with the exception of whole beds or concretions in which pores are early filled with cement mudrocks are almost always compacted by the weight of later deposits the strain so induced is axially symmetric about the vertical and thus about the pole of the bedding planes compaction acts on soft unconsolidated rocks but may continue with increasing overburden on rocks strengthened by cementation and by increasing interlocking of grains tectonic deformation may start early before the rock is fully compacted or it may begin only much later and the mechanisms of deformation increase in complexity with the increasing temperature and hydrostatic stress of deeper burial up to a certain level of mild metamorphism however phyllosilicate grains seem to be rather permanent if not as mineral species then at least by preservation of their constituent sheets of silica tetrahedra given this permanence the mechanisms of rock deformation whether intergranular slip cataclasis or dissolution and reprecipitation and various intragranular processes in the non phyllosilicate matrix hardly matter as far as the recording of strain is concerned even a certain amount of stress solution at especially heavily loaded points of the phyllosilicate grains themselves does not destroy their value as strain markers as long as the dissolved material is disposed of mainly by crystallographically continuous overgrowth on existing grains the same holds for local dissolution of phyllosilicates in portions of old grains that have become thermodynamically unstable by bending widespread irregular or random nucleation and growth of newly nucleated phyllosilicate grains at intermediate or high grades of metamorphism can reduce the reliability of the strain record and so can domainal structure of the deformed rock if both the volume fraction of phyllosilicate grains and the intensity of total strain differ sharply from one domain to another if distinct domains are not equant and have themselves a strong preferred orientation of shape nevertheless rocks containing an anastomosing network of zones rich in phyllosilicate grains as slates and other deformed mudrocks commonly do have in many cases been found to have average preferred orientations of mica or chlorite which if used to estimate the strain give results similar to those obtained from independent strain markers in the same rocks thus the most significant verification of the usefulness of strain estimates by measurement of preferred orientation is the mutual confirmation with independently determined strain the limit to such verification is the rarity of strain markers so that the coexistence of two independent ones is exceptionally rare for this reason however it is important to make full use of the orientation of phyllosilicate grains where they are available the alternative to have no strain measurements at all causes structural geologists to miss potential information

reconstruction of prehistoric landfall frequencies of catastrophic hurricanes in northwestern florida from lake sediment records abstract sediment cores from western lake provide a 7000 yr record of coastal environmental changes and catastrophic hurricane landfalls along the gulf coast of the florida panhandle using hurricane opal as a modern analog we infer that overwash sand layers occurring near the center of the lake were caused by catastrophic hurricanes of category 4 or 5 intensity few catastrophic hurricanes struck the western lake area during two quiescent periods 3400 5000 and 0 1000 14 c yr b p the landfall probabilities increased dramatically to ca 0 5 per yr during an hyperactive period from 1000 3400 14 c yr b p especially in the first millennium a d the millennial scale variability in catastrophic hurricane landfalls along the gulf coast is probably controlled by shifts in the position of the jet stream and the bermuda high

atlantic warm pool acting as a link between atlantic multidecadal oscillation and atlantic tropical cyclone activity 1 multidecadal variability of atlantic tropical cyclone activity is observed to relate to the atlantic multidecadal oscillation amo a mode manifesting primarily in sea surface temperature sst in the high latitudes of the north atlantic in the low latitudes of the north atlantic a large body of warm water called the atlantic warm pool awp comprises the gulf of mexico the caribbean sea and the western tropical north atlantic awp variability occurs on both interannual and multidecadal timescales as well as with a secular variation the awp multidecadal variability coincides with the signal of the amo that is the warm cool phases of the amo are characterized by repeated large small awps since the climate response to the north atlantic sst anomalies is primarily forced at the low latitudes and the awp is in the path of or a birthplace for atlantic tropical cyclones the influence of the amo on atlantic tropical cyclone activity may operate through the mechanism of the awp induced atmospheric changes the awp induced changes related to tropical cyclones that we emphasize here include a dynamical parameter of tropospheric vertical wind shear and a thermodynamical parameter of convective instability more specifically an anomalously large small awp reduces enhances the vertical wind shear in the hurricane main development region and increases decreases the moist static instability of the troposphere both of which favor disfavor atlantic tropical cyclone activity this is the most plausible way in which the amo relationship with atlantic tropical cyclones can be understood

potential role of atlantic warm pool induced freshwater forcing in the atlantic meridional overturning circulation ocean sea ice model simulations recent studies have indicated that the multidecadal variations of the atlantic warm pool awp can induce a significant freshwater change in the tropical north atlantic ocean in this paper the potential effect of the awp induced freshwater flux on the atlantic meridional overturning circulation amoc is studied by performing a series of ocean sea ice model experiments our model experiments demonstrate that ocean response to the anomalous awp induced freshwater flux is primarily dominated by the basin scale gyre circulation adjustments with a time scale of about two decades the positive negative freshwater anomaly leads to an anticyclonic cyclonic circulation overlapping the subtropical gyre this strengthens weakens the gulf stream and the recirculation in the interior ocean thus increases warm cold water advection to the north and decreases cold warm water advection to the south producing an upper ocean temperature dipole in the midlatitude as the freshwater salty water is advected to the north atlantic deep convection region the amoc and its associated northward heat transport gradually decreases increases which in turn lead to an inter hemispheric sst seesaw in the equilibrium state a comma shaped sst anomaly pattern develops in the extratropical region with the largest amplitude over the subpolar region and an extension along the east side of the basin and into the subtropical north atlantic based on our model experiments we argue that the multidecadal awp induced freshwater flux can affect the amoc which plays a negative feedback role that acts to recover the amoc after it is weakened or strengthened the sensitivity of amoc response to the awp induced freshwater forcing amplitude is also examined and discussed

relative magnitudes of shear and longitudinal strain rates in the inland antarctic ice sheet and response to increasing accumulation an approximation common to vertically integrated and three dimen sional models used to simulate growth and retreat of ice sheets in response to changes in climate and sea level is that the component of the mean column velocity attr ibutable to longitudinal strain rates is small relative to the component attributable to shear strain rates parallel to the geoid and can be neglected we investigate the internal consistency of this shallow ice approximation by using a three dimensiona l model of the antarctic ice sheet to calculate the ratio of the horizontal shear strain rates averaged through the low est 10 of the ice depth to the horizontal longitudinal strain rates averaged through the total ice depth this ratio is plotted for the regions of the ice sheet characterized by inland ice sheet flow i e where the surface elevations are above 1500 m in east antarctica and above 950 m in west antarctica these areas are generally inland of the ice streams the areas where this ratio exceeds 10 50 and 100 are delineated for the cases of i no basal motion and ii moderate basal motion the results generally support the validity of the shallow ice approximation throughout most areas of the inland antarctic ice sheet although it breaks down as expected near flow divides and mountain ranges the model is also employed to simulate the response of the ice sheet to linearly increasing accumula tion rates such that the present accumulation is doubled after 100 years and then held constant using the surface kinematic equation the results suggest that the accum ulation increase in east antarctica during recen t decades observed in widely spaced ice cores may be sufficient to account for a positive change in the time rate of change of the surface heights of up to 0 1 m a i during this time period throughout the areas north of 72 s if the accumulation increase has been widespread

impact of the atlantic warm pool on united states landfalling hurricanes 1 the 2010 atlantic hurricane season was extremely active but no hurricanes made landfall in the united states raising a question of what dictated the hurricane track here we use observations from 1970 2010 also extending back to 1950 and numerical model experiments to show that the atlantic warm pool awp a large body of warm water comprised of the gulf of mexico the caribbean sea and the western tropical north atlantic plays an important role in the hurricane track an eastward expansion of the awp shifts the hurricane genesis location eastward decreasing the possibility for a hurricane to make landfall a large awp also induces barotropic stationary wave patterns that weaken the north atlantic subtropical high and produce the eastward steering flow anomalies along the eastern seaboard of the united states due to these two mechanisms hurricanes are steered toward the northeast without making landfall in the united states although the la nina event in the pacific may be associated with the increased number of atlantic hurricanes its relationship with landfalling activity has been offset in 2010 by the effect of the extremely large awp

deformation of till beneath ice stream b west antarctica the behaviour and possible instability of the west antarctic ice sheet depend fundamentally on the dynamics of the large ice streams which drain it model calculations show that most ice stream velocity arises at the bed1 2 and radar sounding has shown the bed to be wet3 but the basal boundary condition is not well understood seismic evidence from the upstream b camp upb on the siple coast of west antarctica4 shows that the ice stream there rests on a layer of unconsolidated sediment averaging 5 or 6 m thick in which the water pressure is only 50 kpa less than the overburden pressure because this thin layer occurs well inland beneath an active ice sheet and rests on a surface showing flutes4 characteristic of glacial erosion5 we presume that it is glacial till we propose here that deformation within the till is the primary mechanism by which the ice stream moves and we discuss implications of this hypothesis

a 3 d model for the antarctic ice sheet a sensitivity study on the glacial interglacial contrast on the longer climatic time scales changes in the elevation and extent of the antarctic ice sheet have an important role in modulating global atmospheric and oceanographic processes and contribute significantly to world wide sea levels in this paper a 3 d time dependent thermomechanical model for the entire ice sheet is presented that is subsequently used to examine the effects of glacial interglacial shifts in environmental boundary conditions on its geometry the model takes into account a coupled ice shelf grounding line dynamics basal sliding and isostatic bed adjustment and considers the fully coupled velocity and temperature fields ice flow is calculated on a fine mesh 40 km horizontal grid size and 10 layers in the vertical for grounded and floating ice and a stress transition zone in between at the grounding line where all stress components contribute in the effective stress in the flow law there is free interaction between ice sheet and ice shelf so that the entire geometry is internally generated a simulation of the present ice sheet reveals that the model is able to yield realistic results a series of sensitivity experiments are then performed in which lower temperatures reduced accumulation rates and lower global sea level stands are imposed either singly or in combination by comparing results of pairs of experiments the effects of each of these environmental changes can be determined in agreement with glacial geological evidence we found that the most pronounced changes show up in the west antarctic ice sheet configuration they appear to be essentially controlled by variations in eustatic sea level whereas typical glacial interglacial changes in temperature and ice deposition rates tend to balance one another these findings support the hypothesis that the antarctic ice sheet basically follows glacial episodes in the northern hemisphere by means of sea level teleconnections grounding occurs more readily in the weddell sea than in the ross sea and long time scales appear to be involved it may take up to 30 40000 years for these continental shelf areas to become completely grounded after an initial stepwise perturbation in boundary conditions according to these reconstructions a steady state antarctic ice sheet may contribute some 16 m to global sea level lowering at maximum glaciation

a theory of finite strain variation through contrasting layers and its bearing on cleavage refraction abstract a theory of finite strain variation in contrasting viscous layers is presented the theory is applicable to layers which are oblique to two principal strains but parallel to the third and is not restricted to plane strain results may be obtained algebraically or by use of the mohr diagram for strain solutions are given for various examples of layering attitude and viscosity ratio measured with respect to a reference layer it is shown that the finite strain ellipsoid changes in shape and orientation across contrasting layers and in some cases the principal axes may be exchanged low strain is indicated in relatively more viscous layers and high strain with extension at a smaller angle to the layering in less viscous layers the latter may approximate simple shear parallel to layering if the strain is sufficiently high the geological implications of the theory are strong strain variations in layered rock sequences it is suggested that in general strain will be inhomogeneous from layer to layer both in orientation and amount the relationship of strain and cleavage are reviewed in the introduction to establish the validity of predicting cleavage patterns from strain data qualitative comparisons between the theoretical results of strain variation and natural cleavage refraction in layered rocks would appear to justify the assumption that cleavages of varied morphologies are sub parallel to the xy planes of strain with this assumption some three dimensional features of planar and linear fabric refraction in contrasting rocks are predicted

classifying el nino modoki i and ii by different impacts on rainfall in southern china and typhoon tracks based on their opposite influences on rainfall in southern china during boreal fall this paper classifies el nino modoki into two groups el nino modoki i and ii which show different origins and patterns of sst anomalies the warm sst anomalies originate in the equatorial central pacific and subtropical northeastern pacific for el nino modoki i and ii respectively thus el nino modoki i shows a symmetric sst anomaly distribution about the equator with the maximum warming in the equatorial central pacific whereas el nino modokiii displays an asymmetric distribution with the warmsstanomaliesextending fromthe northeastern pacifictotheequatorialcentralpacific additionally thewarmsstanomaliesintheequatorialcentralpacific extend farther westward for el nino modoki ii than for el nino modoki i similar to the canonical el nino el nino modoki i is associated with an anomalous anticyclone in the philippine sea that induces south westerly wind anomalies along the south coast of china and carries the moisture for increasing rainfall in southern china for el nino modoki ii an anomalous cyclone resides east of the philippines associated with northerly wind anomalies and a decrease in rainfall in southern china the canonical el nino and el nino modoki i are associated with a westward extension of the western north pacific subtropical high wnpsh whereas el nino modoki ii shifts the wnpsh eastward differing from canonical el nino and el nino modoki i el nino modoki ii corresponds to northwesterly anomalies of the typhoon steeringflow which are unfavorable for typhoons to make landfall in china

pencil structure and strain in weakly deformed mudstone and siltstone abstract weakly deformed mudstone and siltstone middle ordovician knobs formation of the appalachian valley and ridge province south western virginia u s a show strain dependent transitions between bedding fissility pencil structure and cleavage pencil structures are associated with a bulk inhomogeneous shortening deformation where minimum principal strain z ranges between 9 and 26 shortening assuming a plane strain and constant volume where strains are less bedding fissility dominates pencil fragments are defined by intersecting fracture sets subparallel to the pre existing bedding fissility and cleavage their long axes are both parallel to the bedding cleavage intersection and to the inferred y axis of the tectonic strain ellipsoid pencil development is considered to result from fracturing along both fabric anisotropies during weathering and post tectonic stress relaxation pencils show variations in size and shape depending on lithology grain size and composition degree of initial clay preferred orientation degree of cleavage development type of cleavage total bulk strain and degree of strain homogeneity their shape l w however is a direct measure of total y z strain since strain determinations from chlorite pressure fringes on framboidal pyrite within the pencil fragments give y z 0 913 0 019 l w pencil structure is therefore a potential strain marker in weakly deformed rocks

the newport fault eocene listric normal faulting mylonitization and crustal extension in northeastern washington and northwestern idaho discussion and reply

folds and the strain ellipsoid a general model abstract a new general model is proposed to account for non orthogonal relationships of fold axes and axial surfaces to the axes of the finite strain ellipsoid descriptions in the literature of such relationships e g plunge variations and transecting cleavage are reviewed and the development of the model is outlined the model is described in which plane strain k 1 or slight flattening strain k 0 71 or slight constrictional strain k 1 85 are imposed on a suite of layers with oblique orientations to the bulk strain axes x y z folds will initiate perpendicular to the direction of shortening in the layer and develop as non material lines moving through the layer by angular migration at geologically realistic finite strains the folds will be transected by xy cleavage in slight flattening strain folds are likely to be cylindroidal with axes not measurably oblique to xy in slight constrictional strain en echelon periclines are predicted with marked transection by cleavage in some examples the interference of two directions of folding will give rise to severe plunge variations and even downward facing although strain markers frequently indicate finite strains in the flattening field this may result from the superimposition of slightly constrictional tectonic strain on compactional flattening

a model of the antarctic ice sheet numerical modelling of ice sheets and glaciers has become a useful tool in glaciological research a model described here deals with the vertical mean ice velocity is time dependent computes bedrock adjustment and uses an empirical diagnostic relationship to derive the distribution of ice thickness in ice shelves the rate of snowfall and ice snow melt depends on the prescribed sea level temperature surface slope elevation and distance to open water the model is able to reproduce the major features of the antarctic ice sheet when it is run to a steady state for present climatic conditions the main difference with the present ice sheet is that the shallow parts of the weddell sea become covered by grounded ice

pressure solution deformation of the purgatory conglomerate from rhode island pressure solution is the dominant mechanism for the alleghenian age deformation of pennsylvanian quartzite conglomerates from the narragansett basin rhode island this deformation is accompanied by inter cobble rotation and occurred at low metamorphic grades no microscopic evidence for internal penetrative deformation of cobbles in the conglomerate is observed three major pressure solution features are characteristic of this conglomerate adjacent cobbles show indentation relationships with no change in quartz fabrics within the individual cobbles insoluble material is concentrated between cobbles in mutual contact both in the matrix and within the outer margins of the cobbles quartz overgrowths are found at the long axis terminations of the cobbles many other pressure solution features are discussed these features remain recognizable after subsequent metamorphism review of other studies suggests that pressure solution may well be a common conglomerate deformation mechanism during early deformati

late holocene hydroclimate of the western yucatan peninsula mexico chemical composition magnetic susceptibility and texture of sediments in a swamp from the los petenes biosphere reserve provide information about late holocene hydrological variations on the western margin of the yucatan peninsula mexico periods of lower than average amounts of k bearing clastics during 2580 2050 1100 825 and 700 160 cal a bp represent drought intervals magnetic minerals were better preserved during these arid intervals as the swamp was not perennially anoxic hydroclimate was unstable during 2580 2050 cal a bp as several storm surge events occurred within an overall arid interval the drought of 1100 825 cal a bp was contemporary with the terminal classic period and the drought of 700 160 cal a bp was characterized by the lowest erosion as well as highest abundance of authigenic carbonate comparison with other climate proxy records from the region suggests that droughts had different geographic coverage we attribute the different geographic coverage of droughts to variable strengths of polar continental air masses as well as dynamics of the caribbean low level jet and tropical cyclones that brought precipitation into different parts of the peninsula