variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

reconstructing the kinematic evolution of curved mountain belts internal strain patterns in the wyoming salient sevier thrust belt u s a analyses of mesoscopic structural and strain patterns in red beds of the triassic ankareh formation and limestones of the jurassic twin creek formation in concert with complementary paleomagnetic studies constrain the three dimensional kinematic evolution of curved fold and thrust systems in the wyoming salient of the sevier thrust belt spaced cleavage fracture and vein networks minor folds and minor faults in limestones and red beds accommodated early layer parallel shortening lps concentrated in front of the growing thrust wedge along with minor strike parallel extension and wrench shear related to the development of orogenic curvature strain estimated using mass balance relations for cleavage seams crinoid ossicles in bioclastic limestone and reduction spots in red beds displays systematic regional patterns principal shortening directions are subperpendicular to structural trend around the salient reflecting a combination of primary curvature and secondary rotation of early lps fabrics lps magnitudes vary from 5 in central parts of the frontal hogsback thrust system where cleavage is absent to 10 30 in the more interior crawford thrust system where cleavage intensity is moderate to strong strain also increases toward the salient ends internal strain is a significant component of total deformation and should be considered when restoring cross sections strain patterns are consistent with a kinematic model involving curved fault slip and differential shortening that produced progressive secondary curvature during thrusting

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

late twentieth century northern hemisphere sea ice record from u s national ice center ice charts 1 arctic sea ice plays a key role in the climate system by acting as the interface between a warm ocean and a cold atmosphere establishing the true pattern of recent behavior of the sea ice in this region is critical to simulating the role of sea ice in future climate recently released operational ice charts from the u s national ice center provide insight into the late twentieth century behavior of northern hemisphere sea ice providing more reliable ice concentrations during summer and freeze up than those available from the passive microwave record the major winter and summer modes of ice concentration variability observed from empirical orthogonal function analysis covering the period 1972 1994 are shown to indicate respectively the 1 year lagged response of the sea ice to the north atlantic oscillation and the winter preconditioning of summer sea ice coverage in the eastern arctic by the north atlantic oscillation feedback to the atmosphere is suggested in each case by zero lag cyclone frequency relationships to these two sea ice modes of variability

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

hydrologically induced slope deformations detected by gps and clinometric surveys in the cansiglio plateau southern alps abstract changes in groundwater or surface water level may cause observable deformation of the drainage basins in different ways we describe an active slope deformation monitored with gps and tiltmeter stations in a karstic limestone plateau in southeastern alps cansiglio plateau the observed transient gps deformation clearly correlates with the rainfall both gps and tiltmeter equipments react instantly to heavy rains displaying abrupt offsets but with different time constants demonstrating the response to different catchment volumes the gps movement is mostly confined in the horizontal plane ssw direction showing a systematic tendency to rebound in the weeks following the rain four gps stations concur to define a coherent deformation pattern of a wide area 12 5 km 2 concerning the whole southeastern slope of the plateau the plateau expands and rebounds radially after rain by an amount up to a few centimeters and causing only small vertical deformation the effect is largest where karstic features are mostly developed at the margin of the plateau where a thick succession of cretaceous peritidal carbonates faces the venetian lowland a couple of tiltmeters installed in a cave at the top of the plateau detect a much faster deformation that has the tendency to rebound in less than 6 h the correlation to rainfall is less straightforward and shows a more complex behavior during rainy weather the different responses demonstrate a fast hydrologic flow in the more permeable epikarst for the tiltmeters drained by open fractures and fissures in the neighborhood of the cave and a rapid tensile dislocation of the bedrock measured at the gps stations that affect the whole slope of the mountain in the days following the rain both tiltmeter and gps data show a tendency to retrieve the displacement which is consistent with the phreatic discharge curve we propose that hydrologically active fractures recharged by rainfall are the most likely features capable to induce the observed strain variations

atmospheric forcing on the barents sea winter ice extent abstract the atmospheric forcing on the barents sea ice extent during winter december february djf has been investigated for the period 1967 2002 the time series for the sea ice extent is updated and includes the winter of 2005 which marks a new record low in the wintertime barents sea ice extent and a linear trend of 3 5 decade 1 in the ice extent was found covariability between the barents sea ice extent and the atmospheric mean seasonal flow and the synoptic cyclones has been discussed separately for the mean flow linear correlations and regression analysis reveal that anomalous northerly southerly winds prevail in the nordic seas during winters with extensive sparse barents sea ice extent some of the variability in the mean flow is captured by the north atlantic oscillation nao however the wintertime link between the barents sea ice extent and the nao is moderate by studying the cyclone activity in the high latitude northern hemisphere using a dataset of individual cyclones two

the transient atmospheric circulation response to north atlantic sst and sea ice anomalies abstract the objective of this study is to investigate the transient evolution of the wintertime atmospheric circulation response to imposed patterns of sst and sea ice extent anomalies in the north atlantic sector using a large ensemble of experiments with the ncar community climate model version 3 ccm3 the initial adjustment of the atmospheric circulation is characterized by an out of phase relationship between geopotential height anomalies in the lower and upper troposphere localized to the vicinity of the forcing this initial baroclinic response reaches a maximum amplitude in 5 10 days and persists for 2 3 weeks diagnostic results with a linear primitive equation model indicate that this initial response is forced by diabatic heating anomalies in the lower troposphere associated with surface heat flux anomalies generated by the imposed thermal forcing following the initial baroclinic stage of adjustment the response becomes progressively more barotropic and increases in both spatial extent an

maintenance of the sea ice edge abstract a coupled global climate model is used to evaluate processes that determine the equilibrium location of the sea ice edge and its climatological annual cycle the extent to which the wintertime ice edge departs from a symmetric ring around either pole depends primarily on coastlines ice motion and the melt rate at the ice ocean interface at any location the principal drivers of the oceanic heat flux that melts sea ice are absorbed solar radiation and the convergence of heat transported by ocean currents the distance between the ice edge and the pole and the magnitude of the ocean heat flux convergence at the ice edge are inversely related the chief exception to this rule is in the east greenland current where the ocean heat flux convergence just east of the ice edge is relatively high but ice survives due to its swift southward motion and the protection of the cold southward flowing surface water in regions where the ice edge extends relatively far equatorward absorbed solar radiation is t

arctic sea ice variability on a timescale of weeks and its relation to atmospheric forcing abstract northern hemisphere sea ice concentration 500 hpa height sea level pressure and 1000 500 hpa thickness at 7 day intervals are examined for the period 1972 1989 with emphasis on the winter season the temporal variability of sea ice concentration is largest along the climatological mean ice edge where its frequency distribution is strongly bimodal with ice free and ice covered conditions being observed much more frequently than partial ice cover these results confirm impressions based on visual inspection of satellite imagery that most of the variability in these regions is associated with the advance and retreat of the ice edge relationships between large scale patterns of atmospheric variability and sea ice variability are investigated making use of singular value decomposition of the temporal covariance matrix the analysis is conducted separately for the atlantic and pacific sectors in agreement with earlier studies based upon monthly mean data on sea ice concentration the strongest

point stability at shallow depths experience from tilt measurements in the lower rhine embayment germany and implications for high resolution gps and gravity recordings summary from 1996 to 1999 we have studied ground tilts at depths of between 2 m and 5 m at three sites in the lower rhine embayment lre western germany the lre is a tectonically active extensional sedimentary basin roughly 50 kmr100 km the purpose of the tilt measurements was a to provide insight into the magnitude nature and variability of background tilts and b to assess possible limitations of high resolution gps campaigns and microgravity surveys due to natural ground deformation the tilt readings sensed by biaxial borehole tiltmeters of baselength 0 85 m cover a frequency range from 10 x8 hz to 10 x2 hz periods from minutes to years assuming that the tilt signals represent ground displacements on a scale typically not larger than several times the tiltmeters baselength and that tilt signals at shallow depth could in a simple geometric way be related to changes in surface elevation and gravity we try to estimate the magnitude level of point movements and corresponding bouguer gravity effects that is generally not surpassed the largest tilt signals observed were some t50 mrad yr x1 i f they were observable over a ground section of extension e g 10 m the converted rates may correspond to about t0 5 mm per 10 m yr x1 in vertical ground displacement and t0 1 mgal yr x1 in bouguer gravity effect respectively large signals are mostly related to seasonal effects probably linked to thermomechanical strain other causes of ground deformation identified include seepage effects after rainfalls order of t10 mrad and diurnal strains due to thermal heating and or fluctuations in the water consumption of nearby trees order of t1 mrad episodic step like tilt anomalies with amplitudes up to 22 mrad at one of the observation sites might reflect creep events associated to a nearby active fault except for short term ground deformation caused by the passage of seismic waves from distant earthquakes amplitudes of non identified tilt signals in the studied frequency range seem not to exceed t2 mrad as the larger tilt signals are close to the precision achieved with modern gps systems and superconducting gravimeters when converted into height and gravity changes further enhancement in resolution of these techniques may require simultaneous recording of local ground deformation at the observation sites

spatial and temporal evolution of coastal depositional systems and regional depositional process regimes campanian western interior seaway u s a abstract this paper provides a critical review and regional synthesis of late cretaceous shallow marine deposits along part of the western margin of the western interior seaway of north america which contains the most extensively documented outcrop based studies of siliciclastic coastal depositional systems in the world the results of this synthesis are presented in the form of paleogeographic maps covering present day new mexico utah colorado and wyoming usa for five timeslices in the campanian these maps are used to evaluate the spatial and temporal evolution of regional depositional process regimes along a large 1000 m stretch of coastline the evolution of regional depositional process regimes is linked to tectonic and paleoceanographic controls on the western interior seaway which enables the results of this synthesis to be applied to prediction of depositional process regimes in other less intensively studied basins six gross depositional environments have been mapped for each timeslice 1 alluvial to coastal plain sandstones 2 coastal plain coals mudstones and sandstones 3 shoreline sandstones 4 marine mudstones 5 gravity flow siltstones and sandstones and 6 marine marls and chalk shoreline sandstones in each timeslice are interpreted in further detail using documented evidence for the three principal classes of depositional process wave tidal and fluvial and published reconstructions of coastal morphology which is widely considered to reflect depositional process regime based on these interpretations shoreline sandstones are assigned to five categories of depositional process regime 1 regressive wave dominated shorefaces and delta fronts 2 regressive river dominated delta fronts 3 regressive mixed tide and wave influenced delta fronts 4 regressive tide dominated delta fronts and 5 transgressive barrier islands back barrier lagoons and estuaries the accuracy of and uncertainty in classification of depositional process regime are critically evaluated additionally stratal thickness and sediment routing pathways have been interpreted in order to assess the impact of tectonic and paleoceanographic controls on spatial and temporal changes in all of the evaluated shallow marine successions thin tide influenced intervals were deposited in back barrier and lagoon systems associated with net transgressive shorefaces and estuaries however it is notable that all preserved tide dominated and tide influenced regressive deltaic systems are located along the northern margin of the utah bight a tectonically related embayment that had a pronounced expression during the middle campanian the southern margin of the embayment and coastlines to the north are conspicuously more wave dominated which supports their exposure to a larger wave fetch in contrast the northern margin of the embayment was relatively wave protected it is concluded that tidal range was amplified due to resonance of the principal semidiurnal tide in the strongly embayed geometry of the middle campanian utah bight

thermochronology of lower cretaceous source rocks in the idaho wyoming thrust belt lower cretaceous organic rich source rocks that are thermally mature to postmature crop out on the absaroka darby and prospect plates in linear belts that run parallel to the trace of the thrusts in the idaho wyoming portion of the idaho wyoming utah thrust belt although the common assumption is that burial by thrust plates and the synorogenic sediments derived from them have been responsible for thermal maturation of the organic rich strata commercial amounts of hydrocarbons have not been found in structural traps in this portion of the thrust belt in a companion paper burtner and nigrini demonstrated that gravity driven fluid flow in the idaho wyoming portion of the thrust belt was responsible for moving large amounts of heat from the depths of the early cretaceous foreland basin eastward toward the stable platform in this paper we demonstrate through the application of organic maturation indicators and a new refinement of the apatite fission track technique that this process heated lower cretaceous organic rich source rocks to temperatures sufficient to generate hydrocarbons hydrocarbon generation and migration occurred prior to the development of the thrusts that are often assumed to have played a major role in the generation and entrapment of hydrocarbons in this portion of the thrust belt

water table effects on the measurement of earth strain abstract forced changes in the water head within a granite penetrating borehole were found to induce anomalously large free surface strains and tilts in the vicinity of the hole this deformation is shown to be due to fluid pressure induced changes in the aperture of a compliant hydraulically conductive fracture at a depth of 100 m and a quantitative analysis of the deformation data is performed to recover fracture characteristics the importance of the effect for secular earth strain measurements is discussed in the light of the ubiquitous nature of both water table fluctuations and fractures in the shallow crust

the development of the odden ice tongue in the greenland sea during winter 1993 from remote sensing and field observations the odden ice tongue in the central greenland sea believed to be associated with midgyre convection developed prominently during the winter of 1993 january april during this period it was studied by a succession of cruises which formed part of the european subpolar ocean programme and which included direct sampling and measurement of the frazil and pancake ice which constituted the material of the ice tongue as well as studies of the ocean structure passive microwave imagery was used to determine the evolution of odden through the winter and when combined with ers 1 synthetic aperture radar studies and the field data yielded estimates of ice extent and thickness through the winter from these studies it was possible to estimate the salt flux into the ocean originating from brine release from sea ice during the growth phases of odden

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part i main features and storm track characteristics of the response observed multidecadal trends in extratropical atmospheric flow such as the positive trend in the north atlantic oscillation nao index may be attributable to a number of causes this study addresses the question of whether the atmospheric trends may be caused by observed trends in oceanic boundary forcing experiments were carried out using the ncar atmospheric general circulation model with specified sea surface temperature sst and sea ice anomalies confined to the north atlantic sector the spatial pattern of the anomalous forcing was chosen to be realistic in that it corresponds to the recent 40 yr trend in sst and sea ice but the anomaly amplitude was exaggerated in order to make the response statistically more robust the wintertime response to both types of forcing resembles the nao to first order even for an exaggerated amplitude the atmospheric response to the sst anomaly is quite weak compared to the observed positive trend in the nao but has the same sign indicative of a weak positive feedback the anomalies in sea ice extent are more efficient than sst anomalies at exciting an atmospheric response comparable in amplitude to the observed nao trend however this atmospheric response has the opposite sign to the observed trend indicative of a significant negative feedback associated with the sea ice forcing additional experiments using sst anomalies with opposite sign to the observed trend indicate that there are significant nonlinearities associated with the atmospheric response the transient eddy response to the observed sst trend is consistent with the positive nao response with the north atlantic storm track amplifying downstream and developing a more pronounced meridional tilt in contrast the storm track response to the observed sea ice trend corresponds to a weaker southward shifted more zonal storm track which is consistent with the negative nao response

estimating the hydrologic induced signal in geodetic measurements with predictive filtering methods the high precision achieved with continuous geodetic instruments makes it necessary to take ambient factors into account among these one of the most disturbing is the hydrologic agent after giving a characterization of the induced signals in the specific case of subsurface tilt and extensometric measurements the techniques of predictive filtering are shown to solve the problem of modeling the induced signals the results obtained here may be applied also to other continuous geodetic and gravity measurements

greenland sea odden sea ice feature intra annual and interannual variability the odden is a large sea ice feature that forms in the east greenland sea that may protrude eastward to 5 e from the main sea ice pack at about 8 w between 73 and 77 n it generally forms at the beginning of the winter season and can cover 300 000 km2 throughout the winter the outer edge of the odden may advance and retreat by several hundred kilometers on timescales of a few days to weeks satellite passive microwave observations from 1978 through 1995 provide a continuous record of the spatial and temporal variations of this extremely dynamic phenomenon aircraft synthetic aperture radar satellite passive microwave and ship observations in the odden show that the odden consists of new ice types rather than older ice types advected eastward from the main pack the 17 year record shows both strong interannual and intra annual variations in odden extent and temporal behavior for example in 1983 the odden was weak in 1984 the odden did not occur and in 1985 the odden returned late in the season an analysis of the ice area and extent time series derived from the satellite passive microwave observations along with meteorological data from the international arctic buoy program iabp determined the meteorological forcing associated with odden growth maintenance and decay the key meteorological parameters that are related to the rapid ice formation and decay associated with the odden are in order of importance air temperature wind speed and wind direction oceanographic parameters must play an important role in controlling odden formation but it is not yet possible to quantify this role because of a lack of long term oceanographic observations

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part ii direct and indirect components of the response the wintertime atmospheric circulation responses to observed patterns of north atlantic sea surface temperature and sea ice cover trends in recent decades are studied by means of experiments with an atmospheric general circulation model here the relationship between the forced responses and the dominant pattern of internally generated atmospheric variability is focused on the total response is partioned into a portion that projects onto the leading mode of internal variability the indirect response and a portion that is the residual from that projection the direct response this empirical decomposition yields physically meaningful patterns whose distinctive horizontal and vertical structures imply different governing mechanisms the indirect response which dominates the total geopotential height response is hemispheric in scale with resemblance to the north atlantic oscillation or northern hemisphere annular mode and equivalent barotropic in the vertical from the surface to the tropopause in contrast the direct response is localized to the vicinity of the surface thermal anomaly sst or sea ice and exhibits a baroclinic structure in the vertical with a surface trough and upper level ridge in the case of a positive heating anomaly consistent with theoretical models of the linear baroclinic response to extratropical thermal forcing both components of the response scale linearly with respect to the amplitude of the forcing but nonlinearly with respect to the polarity of the forcing the deeper vertical penetration of anomalous heating compared to cooling is suggested to play a role in the nonlinearity of the response to sst forcing

tilt and strain deformation induced by hydrologically active natural fractures application to the tiltmeters installed in sainte croix aux mines observatory france we investigate the deformation induced by water pressure variations in hydrologically active natural fractures and recorded by tiltmeters and strainmeters the deformation associated with a single fracture is derived using finite element modelling fem a range in fracture geometries is explored first to highlight the sensitivity of each geometrical parameter to the deformation and secondly to allow transfer to observation sites water level variations in the fracture are then derived from a hydrological model driven by observed rainfall and calibrated on fracture water flow measurements the modelling results are explicitly applied to constrain the local hydrological contribution to observations with the 100 m long hydrostatic tiltmeter installed at sainte croix aux mines france our study shows that well founded physical modelling of local hydrological effect allows a substantial correction of records in observatories

greenland sea sea ice variability over 1979 2007 and its link to the surface atmosphere 1 mean winter arctic sea ice concentration based on passive microwave observations for the period 1979 2007 are analyzed to examine the variability of the western nordic seas marginal ice zone miz a principal component analysis performed on this regional domain shows that the interannual variability is dominated by a mode which captures more than 70 of the total variance and shows only moderate correlation with the leading mode of global northern hemisphere sea ice variability this mode appears to be related to a pattern of sea level pressure slp anomaly centered on the miz with large scale signature resembling the canonical pattern of the north atlantic oscillation nao still this leading mode of sic variability shows a weak temporal correlation with the nao index taking into account the intrinsic spatial asymmetry found between the two phases of the nao based on a weather regimes analysis composite sic fields are constructed which indeed suggest a preferential response of the greenland sea sic variability to negative nao like patterns of slp the slp pattern is consistent with a response of the sea ice margin to the strength of the northerly winds along eastern greenland a weak pattern of surface air temperature anomalies also emerges in the central greenland sea which occurs at least partly as a response of the surface atmosphere to sea ice concentrations changes higher order modes of winter sic variability emerge based on a shorter winter season one mode has much resemblance with the odden nordbukta pattern while another one exhibits a significant signature in the center of the greenland sea convective gyre the odden nordbukta mode shows a more symmetric relation to the nao than the leading sic mode linear regression analysis consistently suggests some link between this mode and the ice area flux through fram strait

tectonic vs shallow origin of geodetically inferred ground movements an ne ardenne belgium case in order to get a better insight into the temporal pattern of height change variations in a moderately seismic intraplate area a 1 km long section has been weekly leveled from april 21 1997 to january 12 1998 in ne ardenne belgium as this section is located very close to a small reservoir of 25u10 6 m 3 it also allowed the influence of lake level variations on the nearby ground motion to be studied the measured height difference variations show a maximum amplitude of 3 45 mm with weekly values not exceeding 1 mm a two dimensional 2d finite element modeling confirms that waterload variations in the lake are the primary cause of movement of the section inducing maximum ground subsidence of about 2 cm and seasonal tilting of 3 4 wrads within a range of 2 3 km we also show that a fault passively alters the spatial distribution of the waterload dependent movements the removal of this component from the observed ground motion leaves oscillating residual displacements characterized by an amplitude of 1 1 5 mm and a period of about 2 months we demonstrate that these displacements are independent of rainfall and probably of groundwater fluctuation too although most of the residual motions take place on the fault straddled by the leveling section no credible mechanism can be found to ascribe these motions to a tectonic process fl 2000 elsevier science b v all rights reserved

timing of deformation in overthrust belt and foreland of idaho wyoming and utah a review of the timing and displacement evidence of the major structures of the western wyoming overthrust belt and foreland shows there is a progression in thrust displacement apparent duration of motion and palinspastic position of thrust traces from west to east those toward the west moved farther for an apparently longer period of time and are more widely spaced in their restored positions than those toward the east however average thrust velocities are all on the order of 0 5 0 5 cm yr 0 2 in yr foreland events are in part synchronous with thrust belt events and had an effect on them although dating precision varies widely on major normal faults present evidence does not contradict the generally held view that all normal faults postdate the youngest thrusting

measurements and interpretations of tilt strain gauges in seismically active areas abstract an overview of different aspects of deformation measurements is given an introduction to the general theory of point crustal deformations with an application to the stress strain relations at the earth surface is made the instrumentation used in crustal deformation measurements is briefly explained emphasizing different constructions of tilt and strainmeters the problems connected with the housing of the instruments i e the cavity and topography effects and with the ambient noise factors as the hydrological and pressure effects are discussed the last part of the paper is concerned with the relation between deformation measurements and seismic events both from a theoretical and observational standpoint a number of examples are shown that report on pre co and post seismic and the secular term deformation in different areas of the world

trend and interannual variability in southeast greenland sea ice impacts on coastal greenland climate variability we describe the recent occurrence of a region of diminished sea ice cover or notch offshore of the kangerdlugssuaq fiord the site of the largest tidewater glacier along greenland s southeast coast the notch s location is consistent with a topographically forced flux of warm water toward the fiord and the decrease of the sea ice cover is shown to be associated with a regional warming of the upper ocean that began in the mid 1990s sea ice in the vicinity of the notch also exhibits interannual variability that is shown to be associated with a seesaw in surface temperature and sea ice between southeast and northeast greenland that is not describable solely in terms of the north atlantic oscillation we therefore argue that other modes of atmospheric variability including the lofoten low are required to fully document the changes to the climate that are occurring along greenland s east coast

influence of oceanic heat variability on sea ice anomalies in the nordic seas 1 a strong control of sea ice area sia in the nordic seas in the period 1982 2006 by oceanic heat variability is reported in particular variability of summer atlantic water temperature in the barents sea opening explains about 75 of the variance of the following winter sia anomalies which opens prospects for seasonal predictability of regional sea ice cover a strong link of winter sia anomalies to variability in the previous spring sea surface temperature on the western greenland sea and eastern barents sea sides of the nordic seas indicates that the oceanic control of sea ice cover in these areas mainly results from postsummer surface reemergence of oceanic heat anomalies generated by earlier atmospheric forcing in particular late winter north atlantic oscillation and anomalous winds across the barents sea ice edge significantly influence next winter sea ice cover on the western and eastern sides of the nordic seas respectively

three dimensional 3 d finite strain at the central andean orocline and implications for grain scale shortening in orogens three dimensional 3 d finite strain analyses from across the central andes are used to document the contribution of grain scale strain in quartzites and sandstones to the total shortening budget the results are compared to thermal stratigraphic and strain data from other fold and thrust belts to determine the influence of lithologic strength and deformation temperature on strain accommodation during orogenic evolution in the central andes 3 d best fit ellipsoids are inconsistently oriented relative to structural trends have short axes at high angles to bedding z mean plunge 78 21 and have bedding parallel long axes x mean plunge 6 24 ellipsoid shapes are dominantly oblate x y z indicate low natural octahedral shear strains e s 0 03 0 19 and have axial ratios that range from 1 02 1 0 81 e s 0 19 to 1 02 1 0 97 e s 0 03 highly variable r f data r f 1 0 5 0 fluctuations exceeding 100 indicate detrital grain shapes may overwhelm any measurable tectonic strain fabric recorded by grain geometry the best fit ellipsoids may reflect either weak compaction strain or they may be related to a depositional fabric at a minimum granular strain was insufficient to reset the detrital grain fabric and therefore grain scale strain in quartzites and sandstones is not a significant factor in deformation we suggest that the nonstrained nature of these stiffer lithologies indicates a lack of regional penetrative strain in the central andes like that quantified in similar lithologies in other orogens the regional lack of strain may be due to deformation temperatures

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

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

arctic marginal ice zone trending wider in summer and narrower in winter 1 declines in arctic sea ice extent and thickness suggest scientifically important changes in the spatial pattern of the marginal ice zone miz a dynamic and biologically active band of sea ice cover close to open ocean arctic miz widths were measured in satellite era sea ice concentrations over the years 1979 2011 using a recently published miz width analysis method over the record the warm season july september miz width increased by 13 km decade 1 amounting to a 39 widening this widening trend resulted from a marked poleward advancement of the miz poleward edge into regions where sea ice was increasingly younger and thinner at the beginning of annual melt while the miz s equatorward edge moved comparatively little the warm season miz widening contrasted in sign and strength with a cold season february april miz narrowing trend 4 km decade 1 amounting to a 15 narrowing

nontidal tilt and water table variations in a seismically active region in quebec canada abstract an array of three borehole tiltmeters was installed in 1981 in the charlevoix region of quebec canada an area of high intraplate seismic activity a magnitude 7 0 earthquake struck the area in 1925 and the last major event was a magnitude 5 0 event which occurred in 1979 the nontidal tilt from two 47 m deep boreholes correlates strongly with transient and seasonal water table fluctuations this suggests a dominant influence of pore pressure effects on that part of the tilt signal the episodic nature of such effects makes it difficult to separate them from potential earthquake precursors during the build up of tectonic stress we present both an empirical and a deterministic approach to tackle this problem the former consists of removing pore pressure effects from the tilt signal by using simple empirical relations the latter is an attempt to model the physical process through finite element calculations based on biot s consolidation theory for elastic porous media although in our case some boundary conditions are poorly known it is believed that biot s theory is adequate to describe the observed phenomena

quantifying vertical axis rotation in curved orogens correlating multiple data sets with a refined weighted least squares strike test 1 map scale curvature is a fundamental feature of most contractional orogenic belts and is central to understanding the kinematic and dynamic evolution of mountain systems paleomagnetic analysis combined with detailed structural studies is the most robust means of quantifying vertical axis rotations that produce curvature over a range of temporal and spatial scales this paper explores how vertical axis rotations can best be evaluated for multiple data sets by applying a weighted least squares method to the classic strike test this refined method provides measures of best fit slope confidence interval and goodness of fit between map scale structural trend paleomagnetic rotations and deformation fabric orientations structural trend is estimated by averaging fold axial trace formation contact and bed strike data over kilometer scale areas paleomagnetic and deformation fabric site mean orientations and measurement uncertainties are estimated using vector and bootstrap statistics weighting factors are estimated from combined measurement uncertainty structural noise related to small scale block rotation and stress strain refraction and variations in restoration paths the number of sites needed to obtain a significant confidence interval in strike test slope is a function of combined uncertainty in paleomagnetic or deformation fabric directions and the total range in structural trend around a curved orogen improved estimates of strike test slope and rotation thus require systematic sampling with a wide distribution of sites evaluation of appropriate weighting factors and statistical analysis a case study is presented that highlights application of this refined method to paleomagnetic and deformation fabric data sets from the wyoming salient of the sevier thrust belt paleomagnetic data yield a strike test slope of 0 76 0 11 indicating that the wyoming salient is a progressive arc with 3 4 secondary curvature related to vertical axis rotation synchronous with large scale thrusting and 1 4 initial curvature finite strain anisotropy of magnetic susceptibility and mesoscopic structural orientations which are related to early layer parallel shortening all yield strike test slopes of 0 9 0 1 comparing these slopes with paleomagnetic results indicates that deformation fabrics had initial curvature and thus cannot be used alone to accurately estimate rotations by integrating systematic paleomagnetic and structural data using statistical analysis curvature models for the wyoming salient are closely constrained

arctic ice ocean prediction system evaluating sea ice forecasts during xuelong s first trans arctic passage in summer 2017 in an effort to improve the reliability of arctic sea ice predictions an ensemble based arctic ice ocean prediction system arciops has been developed to meet operational demands the system is based on a regional arctic configuration of the massachusetts institute of technology general circulation model a localized error subspace transform ensemble kalman filter is used to assimilate the weekly merged cryosat 2 and soil moisture and ocean salinity sea ice thickness data together with the daily advanced microwave scanning radiometer 2 amsr2 sea ice concentration data the weather forecasts from the global forecast system of the national centers for environmental prediction drive the sea ice ocean coupled model the ensemble mean sea ice forecasts were used to facilitate the chinese national arctic research expedition in summer 2017 the forecasted sea ice concentration is evaluated against amsr2 and special sensor microwave imager sounder sea ice concentration data the forecasted sea ice thickness is compared to the in situ observations and the pan arctic ice ocean modeling and assimilation system these comparisons show the promising potential of arciops for operational arctic sea ice forecasts nevertheless the forecast bias in the beaufort sea calls for a delicate parameter calibration and a better design of the assimilation system

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

conditions during syntectonic vein formation in the footwall of the absaroka thrust fault idaho wyoming utah fold and thrust belt abstract the twin creek limestone in the footwall of the absaroka thrust sheet contains three sets of bed normal syntectonic calcite veins vein formation occurred during cretaceous motion along the absaroka thrust fault as indicated by 1 crosscutting relationships among these vein sets 2 a previously dated solution cleavage and 3 calcite twin analysis fluid inclusions in the veins and overburden estimates constrain inclusion entrapment temperatures to be between 175 c and 328 c results from stable oxygen isotopes indicate that the host and vein fluid compositions were in near isotopic equilibrium applying both reasonable geothermal gradients and constraints on overburden temperature yields fluid pressures during vein precipitation that are near hydrostatic all data taken together suggest both that vein formation within the twin creek formation occurred in a relatively closed system and that the veins filled near hydrostatic fluid pressure because the veins fill precursory cracks vein filling might not reflect the maximum fluid pressure that existed during the complete vein forming process

velocity field of the western entrance to the barents sea 1 by the use of 4 year long records from moored current meters between 71 30 n and 73 30 n of the western entrance to the barents sea the velocity field of the atlantic inflow is examined the mean velocity field shows the atlantic inflow as a wide core that occupies most of this section but the general picture is a velocity field that is dominated by large and frequent fluctuations the key parameter that to a large degree determines the spatial distribution of the velocity field is sea level changes within the section that are induced by the local wind field the main process is the ekman transport through its ability to accumulate water thereby creating strong gradients of barotropic pressure and associated currents southwesterly winds along the norwegian coast and southeasterly winds farther north will in general create wide inflows while northerly winds will result in wide outflows these flow regimes may be persistent for up to 2 3 weeks and are related to the relative strength and lateral extension of the icelandic low and the arctic high although the alignment of the local isobars must be considered in order to be able to describe the details of the flow

evaluation of the rhenium osmium geochronometer in the phosphoria petroleum system bighorn basin of wyoming and montana usa rhenium osmium re os geochronometry is applied to crude oils derived from the permian phosphoria formation of the bighorn basin in wyoming and montana to determine whether the radiogenic age reflects the timing of petroleum generation timing of migration age of the source rock or the timing of thermochemical sulfate reduction tsr the oils selected for this study are interpreted to be derived from the meade peak phosphatic shale and retort phosphatic shale members of the phosphoria formation based on oil oil and oil source rock correlations utilizing bulk properties elemental composition 13c and 34s values and biomarker distributions the 34s values of the oils range from 6 2 to 5 7 with oils heavier than 2 interpreted to be indicative of tsr the re and os isotope data of the phosphoria oils plot in two general trends 1 the main trend n 15 oils yielding a triassic age 239 43 ma with an initial 187os 188os value of 0 85 0 42 and a mean square weighted deviation mswd of 1596 and 2 the torchlight trend n 4 oils yielding a miocene age 9 24 0 39 ma with an initial 187os 188os value of 1 88 0 01 and a mswd of 0 05 the scatter high mswd in the main trend regression is due in part to tsr in reservoirs along the eastern margin of the basin excluding oils that have experienced tsr the regression is significantly improved yielding an age of 211 21 ma with a mswd of 148 this revised age is consistent with some studies that have proposed late triassic as the beginning of phosphoria oil generation and migration and does not seem to reflect the source rock age permian or the timing of re migration late cretaceous to eocene associated with the laramide orogeny the low precision of the revised regression 21 ma is not unexpected for this oil family given the long duration of generation from a large geographic area of mature phosphoria source rock and the possible range in the initial 187os 188os values of the meade peak and retort source units effects of re migration may have contributed to the scatter but thermal cracking and biodegradation likely have had minimal or no effect on the main trend regression the four phosphoria sourced oils from torchlight and lamb fields yield a precise miocene age re os isochron that may reflect the end of tsr in the reservoir due to cooling below a threshold temperature in the last 10 m y from uplift and erosion of overlying rocks the mechanism for the formation of a re os isotopic relationship in a family of crude oils may involve multiple steps in the petroleum generation process bitumen generation from the source rock kerogen may provide a reset of the isotopic chronometer and incremental expulsion of oil over the duration of the oil window may provide some of the variation seen in 187re 188os values from an oil family

tidal and secular tilt from an earthquake zone thresholds for detection of regional anomalies abstract tiltmeter data from an array of three boreholes at the charlevoix observatory in the charlevoix seismic region of que bec have been analysed for evidence of tectonically related signals the secular tilt is dominated by water table induced effects which can be substantially removed by linear regression of the water level on the tilt short term days to months anomalies are shown to be detectable at the 0 3 rad to 1 rad level depending on the depth of the measurement long term changes in the linear drift as small as 0 1 rad yr would be detectable in all of the boreholes large spatial anomalies in the mean tidal admittance among boreholes preclude its use in refining either models of the regional crustal structure or the adjacent marine tide distribution strongly coherent time variations in the tidal admittance among the observations of all the major tidal constituents are shown to be generated by corresponding variations in marine tidal loading in the st lawrence estuary diurnal band variations are closely correlated with the tide gauge data the semi diurnal constituents show a weaker correlation because of the complex spatial pattern within the estuary of time variations in this band inspection of the residual admittance variations for the m2 and o1 constituents demonstrates that the thresholds for detecting tectonic tidal tilt anomalies are 2 and 5 8 respectively the level of earthquake activity in the charlevoix seismic zone throughout the period of the borehole tiltmeter experiment was sufficiently low that no significant tilt anomalies were expected or were undeniably detected

naturally weathered feldspar surfaces in the navajo sandstone aquifer black mesa arizona electron microscopic characterization abstract naturally weathered feldspar surfaces in the jurassic navajo sandstone at black mesa arizona was characterized with high resolution transmission and analytical electron microscope hrtem aem and field emission gun scanning electron microscope feg sem here we report the first hrtem observation of a 10 nm thick amorphous layer on naturally weathered k feldspar in currently slightly alkaline groundwater the amorphous layer is probably deficient in k and enriched in si in addition to the amorphous layer the feldspar surfaces are also partially coated with tightly adhered kaolin platelets outside of the kaolin coatings feldspar grains are covered with a continuous 3 5 m thick layer of authigenic smectite which also coats quartz and other sediment grains authigenic k feldspar overgrowth and etch pits were also found on feldspar grains these characteristics of the aged feldspar surfaces accentuate the differences in reactivity between the freshly ground feldspar powders used in laboratory experiments and feldspar grains in natural systems and may partially contribute to the commonly observed apparent laboratory field dissolution rate discrepancy at black mesa feldspars in the navajo sandstone are dissolving at 10 5 times slower than laboratory rate at comparable temperature and ph under far from equilibrium condition the tightly adhered kaolin platelets reduce the feldspar reactive surface area and the authigenic k feldspar overgrowth reduces the feldspar reactivity however the continuous smectite coating layer does not appear to constitute a diffusion barrier the exact role of the amorphous layer on feldspar dissolution kinetics depends on the origin of the layer leached layer versus re precipitated silica which is uncertain at present however the nanometer thin layer can be detected only with hrtem and thus our study raises the possibility of its wide occurrence in geological systems rate laws and proposed mechanisms should consider the possibility of this amorphous layer on feldspar surface

modeling subsurface flow in sedimentary basins groundwater flows that arise in sedimentary basins from the effects of topographic relief buoyant convection sediment compaction erosional unloading and combinations of these driving forces can be described using quantitative modeling techniques models can be constructed to consider the effects of heat and solute transport petroleum migration and the chemical interaction of water and rocks the accuracy of model predictions however is limited by the difficulty of predicting hydrologic properties of sediments on regional dimensions estimating past conditions such as topographic relief and knowledge of how physical and chemical processes interact over gelogic time scales progress in basin modeling will accelerate as hydrologic research efforts are better integrated with those of other specialities such as sedimentology rock mechanics and geochemistry

geographic muting of changes in the arctic sea ice cover the seasonal cycle in arctic sea ice extent is asymmetric its amplitude has grown in recent decades as the ice has retreated more rapidly in summer than in winter these seasonal disparities have typically been attributed to different physical factors operating during different seasons here we show instead that the seasonal asymmetries in arctic sea ice extent are a geometric consequence of the distribution of continents coastlines block southward ice extension during winter thereby muting changes in ice extent but they have relatively little effect at the time of summer minimum extent we suggest that the latitude of the arctic sea ice edge averaged zonally over locations where it is free to migrate is the most readily interpretable quantity to describe the northern hemisphere sea ice cover we find that the zonal mean sea ice edge latitude during the 1978 present era of satellite measurements has been following an approximately sinusoidal seasonal cycle that has been migrating northward at an approximately annually constant rate of 8 km year these results suggest a change in perspective of the most critical quantities for understanding changes in arctic sea ice

drivers of declining sea ice in the arctic winter a tale of two seas 1 while the summer perennial arctic sea ice has declined markedly in recent decades the maximum extent of the winter ice cover had decreased only slightly until the past few years when it also receded dramatically this investigation reveals that the timing of maximum extent varies greatly and the drivers of ice edge location differ strikingly between two of the areas where it varies most the bering and barents seas between 1979 and 2005 in the bering sea the ice edge is influenced mainly by anomalies in easterly winds associated with the aleutian low which was particularly strong during the 1980s the barents sea ice edge in contrast is driven primarily by two factors anomalies in sea surface temperature particularly close in time to the maximum extent and by southerly wind from the south anomalies integrated back to mid and early winter the hemispheric mean decline in winter ice extent is due in large part to increasing sea surface temperatures in the barents sea and adjoining waters which are consistent with increased concentrations of greenhouse gases

recent crustal movements of tectonic or human originborehole tilt measurements aperiodic crustal tilt in an aseismic area nine months of tilt measurements at tidal sensitivity with an askania tiltmeter at a depth of 12m show aperiodic tilts with time scales of two days and upwards statistically significant correlations are found with meteorological variables and in particular with variations in the local groundwater table typically a variation in the tilt of 1 microradian is associated with a variation in the groundwater table of about 1 m the seasonal variation over the last two years in groundwater has a range of 3 m about a mean level approximately 2 5 m below the ground surface these variations have been continuously measured by a neyrpic tide gauge in a 50 m uncased borehole in addition to this seasonal variation are episodic events some in excess of 1m associated with heavy rainfall 2 3 cm these events have a rapid onset lasting 1 day followed by a decay lasting 10 days or more tilt events associated with similar groundwater variation could in a seismic region be easily mistaken for precursory tilt and this work emphasises the necessity of taking a complete account of meteorology in seismic zones where strain and tilt measurements are in progress further work is in progress with the askania tiltmeter which is now installed in an adjacent borehole at a depth of 30 m and a hughes tm 3 bubble tiltmeter installed at 12m with the aim of investigating mechanisms by which meteorology including groundwater level affects tilt most similar measurements of tilt e g in north america new zealand and germany using various techniques at different depths in different geological conditions indicate meteorological perturbations of the tilt signal and it is suggested that continuous monitoring of water table level will enable these perturbations to be better understood

time of initial thrusting in the sevier orogenic belt idaho wyoming and utah reexamination of the distribution of fossils found in the earliest preserved synorogenic conglomerates within the sevier thrust belt suggests that initial thrust movement may be no older than aptian age this interpretation is corroborated by subsidence analyses of sedimentary sequences lying within and east of the idaho wyoming and utah thrust belts a major episode of middle cretaceous aptian cenomanian subsidence is interpreted as recording the initiation of thrust loading deformation in the adjacent sevier orogenic belt an earlier subsidence event took place during middle jurassic time more than 30 m y prior to the cretaceous event and may be the result of tectonic events to the west that are unrelated to thrust deformation in the idaho wyoming and utah thrust belts we find no verifiable evidence to support previous interpretations that sevier belt deformation and uplift began in late jurassic time

timing of exhumation wheeler pass thrust sheet southern nevada and california late jurassic to middle cretaceous evolution of the southern sevier fold and thrust belt zircon u th he zhe thermochronologic data for 46 samples from the wheeler pass thrust sheet which carries thick passive margin strata and is discontinuously exposed across the southern part of the sevier fold and thrust belt record late jurassic cooling related to exhumation during early thrust slip and local middle cretaceous cooling related to footwall basement imbrication within the frontal part of the wheeler pass sheet exposed in the northwest spring mountains zhe ages decrease from ca 160 to 140 ma over a paleodepth interval of 6 to 9 km in devonian to lower cambrian strata interpreted to record exhumation and enhanced cooling above a frontal ramp followed by slow cooling a similar pattern of zhe ages occurs over a more limited paleodepth range exposed within the resting spring range to the south in the nopah range zhe ages of ca 140 ma in lower cambrian strata record early cooling followed by slow cooling until ca 100 ma zhe ages in underlying paleoproterozoic basement rocks decrease from ca 100 to 85 ma over a paleodepth interval of 9 to 12 km interpreted to record uplift exhumation and cooling during footwall basement imbrication as slip was transferred eastward onto the keystone thrust system late jurassic slip on the wheeler pass thrust overlapped with deformation along the nw trending east sierran thrust system early hinterland crustal thickening and growth of the sierra magmatic arc and may have been correlative with early deformation in the central nevada thrust belt slip on the wheeler pass thrust preceded major slip on other thrust sheets that carried thick passive margin strata in more northern parts of the sevier belt probably reflecting the influence of different initial widths and tapers of the passive margin sedimentary wedge

transient deformation of karst aquifers due to seasonal and multiyear groundwater variations observed by gps in southern apennines italy we present gps hydrological and grace gravity recovery and climate experiment observations in southern apennines italy pointing to a previously unnoticed response of the solid earth to hydrological processes transient patterns in gps horizontal time series near to large karst aquifers are controlled by seasonal and interannual phases of groundwater recharge discharge of karst aquifers modulating the extensional 3 mm yr strain within the tectonically active apennines we suggest that transient signals are produced below the saturation level of the aquifers and above a poorly constrained depth in the shallow crust by time dependent opening of sub vertical fluid filled conductive fractures we ascribe this process to the immature karstification and intense tectonic fracturing favouring slow groundwater circulation and to multi year variations of the water table elevation influenced by variable seasonal recharge the vertical component displays seasonal and multi year signals more homogeneously distributed in space and closely correlated with estimates of total water storage from grace reflecting the elastic response of the lithosphere to variations of surface water loads the different sensitivities of vertical and horizontal components to the hydrologically induced deformation processes allow us to spatially and temporally resolve the different phases of the water cycle from maximum hydrological loading at the surface to maximum hydrostatic pressure beneath karst aquifers finally we suggest that transient deformation signals in the geodetic series of the apennines are correlated to large scale climatic patterns northern atlantic oscillation through their influence on precipitation variability and trends at the regional scale

apatite fission track results from ireland and the porcupine basin and their significance for the evolution of the north atlantic abstract apatite fission track analysis was applied to samples from the irish mainland and exploration boreholes 13 3 1 26 26 1 and 26 28 1 in the northern porcupine and donegal basins to study the regional thermal and tectonic history of the irish continental margin samples from the irish mainland have apatite ages ranging from 301 25 to 56 5 ma with mean track lengths in the range 13 89 0 25 to 11 19 0 22 m and indicate higher temperatures during the middle jurassic about 160 180 ma and during the late cretaceous to early tertiary about 50 80 ma these two periods of increased palaeotemperatures correlate with major reorganizations in plate movements and suggest that uplift and erosion after the maximum palaeotemperatures was achieved as a consequence of a variation in the regional pattern of crustal stress the results from borehole 26 28 1 indicate that within the resolution of the data all samples are presently at their maximum post depositional burial temperatures to produce the mean track length results in the range 11 24 0 49 to 11 81 0 20 m from borehole 26 26 1 it is necessary to invoke post palaeocene geothermal gradients in excess of 50 c km increased relative to the present day gradient 28 c km similar increased geothermal gradients are recognized during the early tertiary in adjacent sedimentary basins and may be explained as a result of heat advection by gravity driven fluid flow established in response to tectonic uplift of the basin margins

strainmeters and tiltmeters despite steady effort over the last century continuously recording tiltmeters and strainmeters have not yet been successful except for earth tide measurements this article reviews the techniques and instrument designs that have been developed in this field the continuous measurement of true tectonic motions which have rates of 10 14 s 1 requires extremely high instrument stability but more rapid motions tides and seismic waves apart are even smaller and not much more easily detectable much past effort has been spent improving the transducers used in these instruments which usually measure small displacements the commonest choices are optical the most accurate capacitive the most sensitive and inductive the most rugged nowadays building a transducer is the easiest part a much harder task equally important to a good design is attaching the instrument to the ground so that it can detect the signal wanted this part of the design includes choosing a location a large underground opening is thermally stable but distorting a surface installation is easy to build but noisy because of soil weathering and a borehole is inaccessible to weather but also to the operator all such installations and indeed the whole field of strain and tilt measurement of course rely on the assumption that the deformations of interest can be measured over baselengths of a few hundred meters or less this is true for tides and seismic waves but unproven for tectonic motions appropriate attachment techniques differ for each location and many mundane details such as cementing techniques for borehole instruments remain to be worked out the goal of measuring tectonic and tidal tilt has created many tiltmeter designs most are relatively small instruments that use some form of pendulum or bubble level a few use a liquid surface to measure tilts over a long baseline repeated experience has shown the latter type when well built to be superior to the former proving end monument motions to be a dominant source of noise the same appears to hold true for strainmeters the best results coming from long base laser instruments though strainmeters using rigid or flexible material length standards are useful for special purposes and borehole instruments show promise because achieving a good design has been so difficult it is important to select the goals an instrument must meet and be prepared to compromise on others the difficulty of validating results from this type of instrument makes comparison tests essential such tests as have been made so far show that good results cannot be gotten at low cost or without careful attention to details

atmospheric influence on arctic marginal ice zone position and width in the atlantic sector february april 1979 2010 arctic marginal ice zone miz widths in the atlantic sector were measured during the months of maximum sea ice extent february april for years 1979 2010 using a novel method based on objective curves through idealized sea ice concentration fields that satisfied laplace s equation over the record the labrador sea miz mizl had an average width of 122 km and narrowed by 28 while moving 254 km poleward the greenland sea miz mizg had an average width of 98 km and narrowed by 43 while moving 158 km west toward the greenland coast and the barents sea miz mizb had an average width of 136 km and moved 259 km east toward the eurasian coast without a trend in width trends in miz position and width were consistent with a warming arctic and decreasing sea ice concentrations over the record beyond the trends nao like atmospheric patterns influenced interannual variability in miz position and width mizl widened and moved southeast under anomalously strong northerly flow conducive to advection of sea ice into the labrador sea mizg widened and moved northeast under anomalously weak northerly flow conducive to diminishing the westward component of sea ice drift and mizb widened and moved poleward at the expense of pack ice under anomalously strong southwesterly flow conducive to enhancing oceanic heat flux into the barents sea in addition meridional flow anomalies associated with the nao per se moved mizb east and west by modulating sea ice concentration over the barents sea

slip rate and mode of the feldbiss normal fault roer valley graben after removal of groundwater effects abstract the feldbiss fault is the main active fault bounding to the southwest the roer valley graben of nw europe in order to investigate the reasons of the discrepancy between its short and long term slip rate estimates we have repeatedly surveyed a 2 3 km long line by levelling at sittard the netherlands from april 2001 to december 2004 simultaneously three superposed aquifers were monitored on both sides of the fault the across fault differential groundwater variations are shown to be responsible for a seasonal 0 87 mm m vertical motion of the fault mainly through the effect of pore pressure changes in confined aquifers after removal of this effect i get a residual trend of 0 60 0 11 mm yr for the relative motion of the hangingwall this trend was disturbed in the summer of 2002 by transient millimetre level up and down motions temporally associated with the small eschweiler earthquake that occurred on july 22 2002 on the feldbiss fault at a distance of 35 km from sittard i explain this as a creep event triggered by the passage of trapped seismic waves the subsisting discrepancy between the long term slip rate of 0 06 mm yr and short term rates of 1 5 mm yr from 1962 to 2001 and 0 6 mm yr from 2001 to 2004 is tentatively interpreted as resulting from the current occurrence of a decade long episode of aseismic slip involving a large part of the fault plane occasionally associated with minor seismicity this aseismic slip event could betray a thickening of the transitional region located below the upper crustal zone of stable sliding it causes a total fault slip of 5 10 cm in a few tens of years releasing smoothly all or a great part of the strain accumulated during the previous 1 2 ky of fault quiescence

kinematic history of the meade thrust based on provenance of the bechler conglomerate at red mountain idaho sevier thrust belt with up to 45 km of slip the meade thrust fault in southeastern idaho is one of the major thrusts in the sevier thrust belt yet its age of displacement has remained enigmatic because of the lack of a derivative synorogenic deposit we propose that the synorogenic conglomerate produced by initial meade thrusting crops out on red mountain in southeastern idaho 1 5 km east of the present trace of the meade thrust this conglomerate historically has been considered part of the ephraim formation of the lower cretaceous gannett group but we suggest that it is a conglomeratic facies of the bechler formation localized to the area of red mountain regional stratigraphic considerations and paleontological dates from underlying and overlying strata indicate that the bechler conglomerate facies bcf is aptian in age the bcf is 850 m thick and consists of pebble to boulder conglomerate sandstone and mudrock deposited by fluvial and mass flow processes on medial to distal parts of an alluvial fan paleocurrent data indicate an eastward fan shaped dispersal pattern the bcf contains clasts of micritic limestone chert pebble conglomerate and cherty litharenite that were derived from the ephraim formation in addition the conglomerate contains abundant clasts of ordovician carboniferous and lower mesozoic rocks that crop out on both the meade thrust sheet and the paris thrust sheet 25 30 km to the west the base of the bcf is marked by a local 27 angular unconformity on top of the ephraim formation the bcf contains intraformational progressively rotated angular unconformities internal growth folds and minor dip discontinuities that were produced by simultaneous folding and sediment accumulation on the proximal footwall of the meade thrust provenance modeling indicates that the bcf was derived from mesozoic strata that were exposed along the frontal part of the meade thrust sheet and from paleozoic strata that were coevally exposed in the hindward located paris thrust sheet topography on the paris sheet was rejuvenated as it was carried passively over a major ramp in the meade thrust provenance and structural data are combined to produce an incremental bulk rock retrodeformation of initial meade displacement clasts of jurassic twin creek limestone with pressure solution cleavage in the lower part of the bcf indicate that an episode of layer parallel shortening occurred in the meade hanging wall prior to meade displacement this may have been related to emplacement of the paris thrust sheet the bcf recorded 6 km of initial meade related shortening by thrust slip and fault propagation folding during aptian time illite crystallinity systematic fracture sets in the ephraim formation and bcf finite strain in meade footwall and hanging wall rocks and thermal models by previous workers indicate that the meade thrust sheet ultimately overrode the bcf and other footwall rocks probably during albian cenomanian time the bcf and the meade thrust were folded during slip on thrust faults related to the northern crawford thrust during coniacian time a revised interpretation of gannett group provenance throughout the thrust belt suggests that the ephraim formation was derived from both the paris thrust sheet and an older hindward located thrust sheet the bechler was derived from the meade and paris sheets

thermochronology of the idaho wyoming thrust belt during the sevier orogeny a new calibrated multiprocess thermal model in the idaho wyoming portion of the idaho wyoming utah thrust belt gravity driven fluid flow was responsible for moving large amounts of heat from the depths of the early cretaceous foreland basin eastward toward the stable platform in the process isotherms were depressed in the vicinity of the paris willard thrust 100 to 140 m y a and geothermal gradients became abnormally high along the eastern flank of the foredeep the abnormally high heat flow along the eastern flank of the foredeep caused early and relatively shallow generation of hydrocarbons from the permian phosphoria formation in that area movement on the crawford and meade thrusts 80 to 100 m y a disrupted this major hydrodynamic system moving the locus of meteoric recharge eastward and causing sudden c oling of strata along the western margin of the foreland although this hydrodynamic system continued to shift eastward as thrusting moved progressively eastward its thermal impact decreased as the remaining foreland basin became shallower and narrower the new thermal model calibrated with apatite fission track and organic maturation data has significant implications for hydrocarbon exploration in thrust belts it suggests that the effect of fluid flow on temperature should not be ignored when reconstructing the thermal histories of these complex areas areas of above normal surface heat flow can within relatively short periods of time become regions of abnormally low surface heat flow depending on the positions of source rocks in the hydrodynamic system this variability in heat flow can result in either earlier or later generation of hydrocarbons than would normally be expected when other process models are applied

a wave based model for the marginal ice zone including a floe breaking parameterization 1 the marginal ice zone miz is the boundary between the open ocean and ice covered seas where sea ice is significantly affected by the onslaught of ocean waves waves are responsible for the breakup of ice floes and determine the extent of the miz and floe size distribution when the ice cover is highly fragmented its behavior is qualitatively different from that of pack ice with large floes therefore it is important to incorporate wave ice interactions into sea ice ocean models in order to achieve this goal two effects are considered the role of sea ice as a dampener of wave energy and the wave induced breakup of ice floes these two processes act in concert to modify the incident wave spectrum and determine the main properties of the miz a simple but novel parameterization for floe breaking is derived by considering alternatively ice as a flexible and rigid material and by using current estimates of ice critical flexural strain and strength this parameterization is combined with a wave scattering model in a one dimensional numerical framework to evaluate the floe size distribution and the extent of the miz the model predicts a sharp transition between fragmented sea ice and the central pack thus providing a natural definition for the miz reasonable values are found for the extent of the miz given realistic initial and boundary conditions the numerical setting is commensurate with typical ice ocean models with the future implementation into two dimensional sea ice models in mind

thermal models of thrust faulting constraints from fluid inclusion observations willard thrust sheet idaho utah wyoming thrust belt the thermal effects associated with emplacement of the willard thrust sheet within the idaho utah wyoming thrust belt have been numerically modeled fluid inclusion studies and mineralogy including illite crystallinity narrowly limit choice of permissible thermal models permissible models have initial thermal gradients between about 30 c km and 35 c km and fluid pressures less than lithostatic pressure fluid inclusions were trapped in syntectonic veins within the basal part of the willard thrust sheet and in cataclastically deformed basement within the footwall homogenization temperatures have a bimodal distribution in the willard sheet with maxima at 180 c and 260 c and a unimodal distribution in the footwall with a maximum at 200 c these temperatures along with fluid composition determine fluid density and define isochores along which the fluids were trapped illite crystallinity and mineralogy record maximum temperatures in the range of 300 c to 500 c with somewhat lower maximum temperatures in the footwall thermal models for emplacement of the willard sheet indicate that the hanging wall undergoes initial rapid cooling but the footwall undergoes initial warming due to tectonic burial later both areas undergo approximately isothermal decompression as erosion proceeds p t paths for reasonable parameter values intersect the modal isochores and are consistent with mineralogy as required for a permissible model the thermal model provides a reasonable framework for understanding the thermal history of the willard sheet the models are sensitive to thrust sheet thickness initial heat flow and thermal conductivity the thermal models are relatively insensitive to erosion history for reasonable erosion rates and to redistribution of heat producing elements for the low values typical of sedimentary rocks

influence of overthrusting on maturation of hydrocarbons in phosphoria formation wyoming idaho utah overthrust belt geochemical analyses were performed on 11 phosphoria formation samples collected throughout the wyoming idaho utah overthrust belt maturation models incorporating the thermal effects of thrust faulting with lopatin s techniques were then used to interpret these geochemical data in particular four of the sample sites were selected for detailed thermal modeling these four sites include one sample site in an area unaffected by thrusting two sites located in the hanging walls of major thrusts and one site in the footwall of the darby thrust the detailed thermal modeling shows overthrusting did affect the thermal history of the phosphoria formation the effect of thrusting was to cool the overriding sheet and warm the sediments being overridden thus the hanging wall samples had a different post thrusting thermal history than the footwall sample cooling of the hanging wall slowed post thrusting maturation in the two thrust sheet samples in contrast the footwall sample was exposed to higher temperatures after thrusting and the maturation process was accelerated results of this study indicate that tectonism influences the thermal history of the rocks and should be included in any reliable source rock evaluation program involving overthrust strata a simple evaluation based only on the thickness of the overburden in general will not be sufficient to explain fully the maturation data in the absence of actual geochemical information such as ro tai or cai the models described in this paper appear to be sufficiently accurate to give a reasonable estimate of thermal maturity of a potential source bed

mesozoic evolution hinterland of the sevier orogenic belt west of the mesozoic foreland sevier orogenic belt in northern utah and southern idaho a regional detachment of inferred mid jurassic age occurs in upper mississippian shale and can be traced westward to the margin of the coeval magmatic arc represented by spaced calc alkalic intrusions the detachment may be the oldest and structurally highest intrusions the detachment may be the oldest and structurally highest thrust of the idaho wyoming thrust belt if so it bridges the apparent spatial and temporal gap between magmatism and thrusting thus suggesting a direct genetic link thin skinned deformation is interpreted here to be driven from the heated magmatic arc toward the colder craton by lateral tectonic compression created by lateral volume increase due to intrusion elevated crustal geotherms and possible thickening in the arc the metamorphic complexes occur at the crustal interface between these two thermal tectonic regimes and may themselves be allochthonous

petroleum tectonic comparison of fold and thrust belts the zagros of iraq and iran the pyrenees of spain the sevier of western usa and the beni sub andean of bolivia this work was partially supported by subtetis pie csic 201830e039 and alpimed pie csic 201530e082 projects

layer parallel shortening across the sevier fold thrust belt and laramide foreland of wyoming spatial and temporal evolution of a complex geodynamic system abstract varying patterns of layer parallel shortening lps and vertical axis rotations from the thin skin sevier fold thrust belt to the thick skin laramide foreland of wyoming are quantified from integrated structural anisotropy of magnetic susceptibility ams and paleomagnetic analyses within the sevier belt widespread early lps was accommodated by spaced cleavage fracture sets minor folds and minor faults lps directions are subperpendicular to structural trends of systematically curved thrust sheets of the wyoming salient reflecting a combination of primary dispersion and secondary rotation during thrusting within the laramide foreland limited lps was accommodated mostly by minor faults with conjugate wedge and strike slip geometries lps directions in gentler fold limbs vary from perpendicular to acute with structural trends of variably oriented anastomosing basement cored arches steep forelimbs display more complex relations including younger fault sets that developed during evolving stress states and localized vertical axis rotations although internal strain is limited weak ams lineations defined by kinked and rotated phyllosilicates are widely developed and consistently oriented perpendicular to measured lps directions palinspastically restored lps directions corrected for paleomagnetically determined vertical axis rotations vary on average from w e in the sevier belt to wsw ene in the laramide foreland in detail lps directions display deflections related to primary sedimentary wedge geometry and basement fabrics lps in the sevier belt is interpreted to partly reflect stress transmitted from the hinterland through the growing orogenic wedge and topographic stress along the front of the wedge lps in the laramide foreland is interpreted to partly reflect basal traction during flat slab subduction beneath thick cratonic lithosphere with spatial temporal variations in stress trajectories related to basement heterogeneities and evolving fault systems evidence for significant late n s laramide shortening as proposed by multi stage shortening models is not observed

reconstructing the kinematic evolution of curved mountain belts a paleomagnetic study of triassic red beds from the wyoming salient sevier thrust belt u s a determining the kinematic history and mechanics of curved fold and thrust belts is fundamental to understanding the tectonic evolution of mountain systems to better understand the development of a classic curved fold and thrust belt we completed an integrated paleomagnetic and strain study of the wyoming salient paleomagnetic data are reported here from 154 sites collected from red beds of the triassic ankareh formation in the salient and nine sites collected from the relatively stable foreland red beds display three components with distinctly different magnetic behaviors 1 a near primary triassic magnetization carried by hematite that is stable up to 680 c tr component 91 sites 2 a cretaceous chemical remagnetization carried partly by magnetite k component 32 sites and 3 a recent viscous magnetization that is mostly removed by 350 c site mean vectors for the tr and k components show a high degree of scatter from expected triassic and cretaceous reference directions suggesting significant tilt and rotation subsequent to magnetization acquisition restoration of tilt and folding for individual site means results in well clustered shallow and moderate inclinations for the tr and k components respectively and in variable declinations related to systematic vertical axis rotations statistical analysis of declinations for both components indicates that 75 of present day salient curvature resulted from secondary rotation and 25 of primary curvature was likely related to sedimentary basin architecture analysis of individual thrust systems indicates a slightly greater component of rotation in more internal sheets 80 compared to the frontal thrust sheets 65 suggesting that rotations were concentrated near the leading edge of the propagating fold and thrust wedge with only minor additional rotation of internal sheets transfer zones oblique ramps and more deformed overturned fold limbs display locally more complex patterns which can be understood through careful structural analysis when combined with internal strain data and regional structural relations paleomagnetic data support a kinematic model of a progressive arc with curved thrust slip paths and differential shortening that rotated early layer parallel shortening fabrics and produced minor strike parallel extension this kinematic history likely reflects a combination of processes including greater initial stratigraphic thickness and subsequent shortening and wedge propagation in the central part of the salient presence of a weak basal detachment and fault zone weakening that favored lower taper and buttressing by laramide foreland uplifts that formed along basement promontories at the north and south ends of the salient

remarkable tilt strain anomalies preceding two seismic events in friuli ne italy their interpretation as precursors abstract crustal deformation data collected in the friuli seismic area ne italy through the employment of geodetic instrumentation are analysed to evaluate observed signals considered as preseismic once the disturbing action of atmospherical hydrological factors on local crustal deformation data has been considered in previously published studies two middle term precursors one tilt and one areal strain are presented as being the strongest and more evident signals recorded in the area after the 1976 destructive seismic events an effort is also performed in their interpretation and modelling evaluations on the basis of micro cracking of the source region and aseismic fault creep are done modelling based on trivial rheological models furnishes crustal viscosity values in agreement with the values obtained in the analysis of the silent earthquakes recorded in the same area before the 1976 77 destructive seismic events we put forward the hypothesis that for both the presumably preseismic signals the viscosity plays an important role although in one case slow dislocations could also have occurred the two strong possible preseismic signals here considered support the hypothesis proposed by some authors that evident and reliable precursory signals can be detected only within a distance of 2 3 times the dimensions of the source area

the role of rossby wave breaking in shaping the equilibrium atmospheric circulation response to north atlantic boundary forcing abstract the role of rossby wave breaking rwb is explored in the transient response of an atmospheric general circulation model to boundary forcing by sea ice anomalies related to the north atlantic oscillation nao when the ncar community climate model version 3 was forced by an exaggerated sea ice extent anomaly corresponding to one arising from a positive nao a localized baroclinic response developed and evolved into a larger scale equivalent barotropic pattern resembling the negative polarity of the nao the initial baroclinic response shifted the phase speeds of the dominant eddies away from a critical value equal to the background zonal flow speed resulting in significant changes in the spatial distribution of rwb the forcing of the background zonal flow by the changes in rwb accounts for 88 of the temporal pattern of the response and 80 of the spatial pattern of the zonally averaged response although results here focus on one experiment this rwb critical line mechanism appears to be