dynamics of wind forced coherent anticyclones in the open ocean we numerically study the dynamics of coherent anticyclonic eddies in the ocean interior for the hydrostatic rotating stably stratified turbulence we use a high resolution primitive equation model forced by small scale winds in an idealized configuration many properties of the horizontal motions are found to be similar to those of two dimensional and quasi geostrophic turbulence major differences are a strong cyclone anticyclone asymmetry linked to the straining field exerted by vortex rossby waves which is also found in shallow water flows and the complex structure of the vertical velocity field which we analyze in detail locally the motion can become strongly ageostrophic and vertical velocities associated with vortices can reach magnitudes and levels of spatial complexity akin to those reported for frontal regions transport and mixing properties of the flow field are further investigated by analyzing lagrangian trajectories particles released in the pycnocline undergo large vertical excursions because of the vertical velocities associated to the vortices with potentially important consequences for marine ecosystem dynamics

geomagnetic field for 0 3 ka 2 a new series of time varying global models 1 steadily increasing numbers of archeomagnetic and paleomagnetic data for the holocene have allowed development of temporally continuous global spherical harmonic models of the geomagnetic field extending present and historical global descriptions of magnetic field evolution the current work uses various subsets of improved data compilations details of which are given in a companion paper by donadini et al 2009 and minor modifications of standard modeling strategies using temporally and spatially regularized inversion of the data and cubic spline parameterizations for temporal variations to produce five models with enhanced spatial and temporal resolution for 0 3 ka spurious end effects present in earlier models are eliminated by enforcing large scale agreement with the gufm1 historical model for 1650 1990 a d and by extending the model range to accommodate data older than 3 ka age errors are not considered as a contribution to data uncertainties but are included along with data uncertainties in an investigation of statistical uncertainty estimates for the models using parametric bootstrap resampling techniques we find common features but also significant differences among the various models indicating intrinsic uncertainties in global models based on the currently available holocene data model cals3k 3 based on all available archeomagnetic and sediment data without a priori quality selection currently constitutes the best global representation of the past field the new models have slightly higher dipole moments than our previous models virtual axial dipole moments vadms calculated directly from the data are in good agreement with all corresponding model predictions of vadms these are always higher than the spherical harmonic dipole moment indicating the limitations of using vadms as a measure of geomagnetic dipole moments

a bayesian iterative geomagnetic model with universal data input self consistent spherical harmonic evolution for the geomagnetic field over the last 4000 years abstract changes of the earth s magnetic field have been observed with varying spatial and temporal resolution since the middle ages by means of compasses and later by refined mechanical inclination and intensity instruments until the modern use of quantum mechanical devices and satellite observations ancient records on the other hand rely on the natural magnetization of archaeological artifacts and other materials such as rocks and sediments being therefore indirect less accurate and sparser the combination of such heterogeneous records into a single self consistent global model of the geomagnetic field is very challenging the highly uneven data coverage both in space and time requires a careful handling of data uncertainties and error correlations previous models dealt with this problem using separated treatments of instrumental data and indirect records respectively as well as a different handling of the dipole field component with respect to non dipole terms here we present a global geomagnetic field model based for the first time on the simultaneous inversion of historical archaeomagnetic and volcanic records using a bayesian approach with minimal committing time regularization that minimizes the energy of secular variation a detailed assessment of data uncertainty and error correlation is used to minimize artifacts generated by the appearance of an overwhelming number of incomplete mostly declination only records associated with shipboard measurements in the early colonial period our model yields lower dipole energies which better match modern values as well as higher non dipole energies and a stronger secular variation of the dipole moment some model artifacts associated with extremely heterogeneous distributions of records in time and space are not completely eliminable and might be caused by incorrect a priori uncertainty assessments alternatively they might represent an intrinsic limit that can be overcome only by adding new records at critical locations and times

dispersion of sea ice in the bering sea the dispersion of sea ice in the bering sea is analyzed in terms of the changes in separation between pairs of ice floes the statistics of these changes depend on the separation itself and on the time interval over which the changes are measured rather than being constant as in the case of molecular or fickian diffusion the diffusivity increases according to the 1 8 power of the separation for short times the diffusivity is proportional to time for times greater than 3 days the diffusivity appears to approach a constant value for any particular separation comparison with other data shows that the ice floe diffusivity is about an order of magnitude smaller than the diffusivity at the surface of the temperate ocean and about an order greater than the diffusivity of sea ice in the beaufort sea

high fidelity archeointensity results for the late neolithic period from central china author s cai s tauxe l wang w deng c pan y yang l qin h abstract 2020 american geophysical union all rights reserved archeomagnetism focuses on exploring high resolution variations of the geomagnetic field over hundreds to thousands of years in this study we carried out a comprehensive study of chronology absolute and relative paleointensity on a late neolithic site in central china ages of the samples are constrained to be 3 500 3 000 bce a period when available paleointensity data are sparse we present a total of 64 high fidelity absolute paleointensities demonstrating the field varied quickly from 55 to 90 zam2 between 3 500 3 000 bce our results record a new archeomagnetic jerk around 3 300 bce which is probably non dipolar origin the new results provide robust constraints on global geomagnetic models we calculated a revised chinese archeointensity reference curve for future application the variations of absolute and relative paleointensity versus depth show good consistency reinforcing the reliability of our results this new attempt of combining absolute and relative paleointenstiy provides a useful tool for future archeomagnetic research

reconstructing holocene geomagnetic field variation new methods models and implications reconstructions of the holocene geomagnetic field and how it varies on millennial timescales are important for understanding processes in the core but may also be used to study long term solar terrestrial relationships and as relative dating tools for geological and archaeological archives here we present a new family of spherical harmonic geomagnetic field models spanning the past 9000 yr based on magnetic field directions and intensity stored in archaeological artefacts igneous rocks and sediment records a new modelling strategy introduces alternative data treatments with a focus on extracting more information from sedimentary data to reduce the influence of a few individual records all sedimentary data are resampled in 50 yr bins which also means that more weight is given to archaeomagnetic data during the inversion the sedimentary declination data are treated as relative values and adjusted iteratively based on prior information finally an alternative way of treating the sediment data chronologies has enabled us to both assess the likely range of age uncertainties often up to and possibly exceeding 500 yr and adjust the timescale of each record based on comparisons with predictions from a preliminary model as a result of the data adjustments power has been shifted from quadrupole and octupole to higher degrees compared with previous holocene geomagnetic field models we find evidence for dominantly westward drift of northern high latitude high intensity flux patches at the core mantle boundary for the last 4000 yr the new models also show intermittent occurrence of reversed flux at the edge of or inside the inner core tangent cylinder possibly originating from the equator less

holocene palaeomagnetic secular variation at lake biwa central japan summary we have conducted a palaeomagnetic study on three sediment cores obtained from a single site in lake biwa central japan a total of 1430 discrete samples from three cores show strong and stable remanence which is carried by pseudo single domain magnetite palaeomagnetic records from individual cores show little scatter of directions and there is excellent correlation among the records from the site a composite palaeomagnetic secular variation psv record for the holocene was constructed after fine scale adjustment and stacking of the three records the age model is based on two wide spread tephra layers kawagodaira 3150 yr bp calendar years and kikaiakahoya 7250 yr bp our results show that the declinations and inclinations are strikingly similar to archaeomagnetic data from southwest japan for the last 2000 years the psv record from lake biwa shows good correlation in directions with that of beppu bay located about 500 km west of lake biwa although the beppu bay record shows relatively smaller amplitudes of both inclination and declination probably due to heavy smoothing of the initial results when the lake biwa record is compared with the proposed type curve for southwest japan there is considerable disagreement throughout the holocene a re analysis of the data sets and other information used to construct the type curve revealed that the discrepancy in the results was due to inadequate age determination for the cores used in previous studies we conclude that the stacked psv record from lake biwa meets the criteria required for a reliable curve moreover our results resolve the complications found in the correlation of psv records in southwest japan and thereby contribute to a better understanding of holocene psv

paleosecular variations since 9000 yr bp as recorded by sediments from maar lake shuangchiling hainan south china abstract high resolution paleosecular variation psv can play an important role in sediment dating and for understanding the temporal characteristics of the geodynamo of the earth s magnetic field in this article based on magnetic susceptibility correlation a composite sediment profile has been compiled from a 16 m long core hn 2 and a 8 m deep well hn 3 in shuangchiling maar lake a crater basin located on hainan island southern china fine and homogeneous silty clay corroborates with a stable continuous and undisturbed deposition a u channel based paleomagnetic study constrained by ams14c chronology derived from leaves plant debris and woods and supported by rock magnetic data indicates that the lake sediments document a reliable paleosecular variation psv record since 9000 cal year bp comparison of our psv features with other records from lakes biwa japan erhai china baikal russia as well as archaeomagnetic records demonstrate that the inclination pattern is generally synchronous within chronological uncertainties suggesting further psv dating may be valuable for stratigraphic correlation on a regional scale

the time dependence of intense archeomagnetic flux patches 1 the long term temporal behavior of intense geomagnetic flux patches at the core mantle boundary and the relation with lower mantle lateral heterogeneity are under debate we apply an algorithm to detect centers of intense flux patches and track their time evolution in a recent archeomagnetic field model in order to study the kinematics of such intense magnetic flux patches on millennial timescale we find that most intense flux patches appear near the edge of the tangent cylinder quasi stationary periods with small oscillations of patches occur more than drifts detailed comparison of the archeomagnetic patches behavior with that seen in numerical dynamos with tomographic heat flux boundary conditions suggests that core mantle thermal coupling could be the cause of a statistical preference for some longitudes on the long term which does not exclude significant time spent away from the preferred longitudes this could explain the roughly coincident locations of high latitude patches in the historical geomagnetic field with that of the time average paleomagnetic field together with the much weaker patches intensity in the latter alternating eastward and westward drifts are also observed the drifts are more westward than eastward especially in the southern hemisphere indicating that the time average zonal core flow may also be driven by core mantle thermal coupling an average patch lifetime of 300 years is found which we hypothesize may indicate the vortex lifetime in the outer core

contrasts in sea ice deformation and production in the arctic seasonal and perennial ice zones 1 four years 1997 2000 of radarsat geophysical processor system rgps data are used to contrast the sea ice deformation and production regionally and in the seasonal siz and perennial piz ice zones ice production is of seasonal ice in openings during the winter three day estimates of these quantities are provided within lagrangian elements initially 10 km on a side a distinct seasonal cycle is seen in both zones with these estimates highest in the late fall and with seasonal minimums in the midwinter regional divergence over the winter could be up to 30 spatially the highest deformation is seen in the siz north of coastal alaska both ice deformation and production are higher in the siz deformation related ice production in the siz 0 5 m is 1 5 2 3 times that of the piz 0 3 m this is connected to ice strength and thickness atmospheric forcing and boundary layer structure contribute to only the seasonal and interannual variability seasonal ice growth in ice fractures accounts for 25 40 of the total ice production of the arctic ocean uncertainties in these estimates are discussed by itself this deformation ice production relationship could be considered a negative feedback when thickness is perturbed however the overall effect on ice production in the face of increasing seasonal and thinner weaker ice coverage could be modified by local destabilization of the water column promoting overturning of warmer water due to increased brine rejection and the upwelling of the pynocline associated with increased occurrence of large shear motion in sea ice divergence is shown to be negligibly correlated to cyclonic motion in summer and winter in both ice zones

paleosecular variations of the geomagnetic field during the holocene from eastern asia abstract high resolution paleomagnetic secular variation psv records bear great information of dynamics processes of the earth s geomagnetic field and can be further used for inter profile correlation and for dating sediments however effects of changes in the depositional environment on psv records have not been fully determined this study constructed holocene psv records for the gravity piston core zsqd34 obtained from the northern south china sea rock magnetic and transmission electron microscope tem results indicate that single sd and psd domain magnetites are the main carrier of the natural remanent magnetization comparable to the records derived from the freshwater lakes and the modeling results we observed that direction curves from these two environments of contrasting salinity content are rather consistent the direction curves are independent of the constructed salinity however the gradual increasing trend of relative intensity since about 5 kyr might be related to the decreasing sea surface salinity furthermore on the centennial and millennial time scale the relative intensity and salinity show some positive relation suggesting a potential contribution of salinity to the paleomagnetic relative intensity recording processes

estimating suppression of eddy mixing by mean flows particle and tracer based estimates of lateral diffusivities are used to estimate the suppression of eddy mixingacrossstrongcurrents particlesandtracersare advectedusingavelocityfieldderivedfromseasurface height measurements from the south pacific in a region west of drake passage this velocity field has been used in a companion paper to show that both particle and tracer based estimates of eddy diffusivities are equivalent despite recent claims to the contrary these estimates of eddy diffusivities are here analyzed to show 1 that the degree of suppression of mixing across the strong antarctic circumpolar current is correctly predicted by mixing length theory modified to include eddy propagation along the mean flow and 2 that the suppressioncan beinferredfromparticletrajectoriesby studyingthestructureofthe autocorrelationfunction of the particle velocities beyond the first zero crossing these results are then used to discuss how to compute lateral and vertical variations in eddy diffusivities using floats and drifters in the real ocean

full vector archaeomagnetic records from anatolia between 2400 and 1350 bce implications for geomagnetic field models and the dating of fires in antiquity abstract anatolia as one of the busiest crossroads of ancient civilizations provides an ideal platform for archaeomagnetic studies previous results from the middle east have suggested the occurrence of a strong peak in geomagnetic intensity at 1000 bce associated with dramatic field strength variations that could require a radical rethinking of geodynamo theory the behavior of the field in the centuries preceding this peak remains poorly constrained however here we present the results of full vector archaeomagnetic experiments performed on 18 sets of samples from three archaeological sites belonging to assyrian trade colony and hittite periods associated rock magnetic analyses showed that the major magnetic carrier is magnetite chemically stable up to 700 c and the magnetic mineral assemblage is composed mostly of non interacting psd grains the directional results are compared with existing data and with the most recent global geomagnetic field models pfm9k 1b and sha dif 14k the directions are in remarkably good agreement with sha dif 14k which is based on archaeomagnetic and lava flow data together with our earlier results from anatolia we triple the existing database of directions for the 700 year long period 2200 1500 bce over a large region from greece to azerbaijan and from moldavia ukraine to egypt three archaeointensity methods thermal izzi thellier microwave thellier and the multi specimen protocol msp produced virtual axial dipole moment estimates 9 0 10 9 10 22 am 2 that are somewhat higher than contemporaneous regional and global data and model predictions suggesting that the field was already substantially stronger than today more than 800 years prior to the reported peak in addition to constraining geomagnetic variability our data also allow us to assign relative dates to inferred fire events in the assyrian trade colony period sites this allows us to conclude that the fire events at the largest site kultepe were not all contemporaneous with one another and with the abandonment of the site as has been previously hypothesized

bottom up control of geomagnetic secular variation by the earth s inner core temporal changes in the earth s magnetic field known as geomagnetic secular variation occur most prominently at low latitudes in the atlantic hemisphere that is from 90 degrees east to 90 degrees east whereas in the pacific hemisphere there is comparatively little activity this is a consequence of the geographical localization of intense westward drifting equatorial magnetic flux patches at the core surface despite successes in explaining the morphology of the geomagnetic field numerical models of the geodynamo have so far failed to account systematically for this striking pattern of geomagnetic secular variation here we show that it can be reproduced provided that two mechanisms relying on the inner core are jointly considered first gravitational coupling aligns the inner core with the mantle forcing the flow of liquid metal in the outer core into a giant westward drifting sheet like gyre the resulting shear concentrates azimuthal magnetic flux at low latitudes close to the core mantle boundary where it is expelled by core convection and subsequently transported westward second differential inner core growth fastest below indonesia causes an asymmetric buoyancy release in the outer core which in turn distorts the gyre forcing it to become eccentric in agreement with recent core flow inversions this bottom up heterogeneous driving of core convection dominates top down driving from mantle thermal heterogeneities and localizes magnetic variations in a longitudinal sector centred beneath the atlantic where the eccentric gyre reaches the core surface to match the observed pattern of geomagnetic secular variation the solid material forming the inner core must now be in a state of differential growth rather than one of growth and melting induced by convective translation

observation of cyclone induced inertial sea ice oscillation in fram strait 1 in march 2007 the field campaign framzy took place in the region between spitsbergen and greenland one goal of the experiment was the observation of cyclone impact on ice drift by means of autonomous meteorological buoys deployed on sea ice on 23 march an intense cyclone of about 500 km diameter passed with about 20 m s from south to north over the ice covered part of the fram strait and induced strong inertial oscillations of the sea ice ice drift velocity fluctuations abruptly increased by a factor of three to values of more than 1 m s this was caused by a resonant wind forcing for almost three quarters of the inertial oscillation depending on the local ice conditions the oscillations lasted over a two to five days period the inertial oscillations caused ice drift divergence fluctuations of 6 10 6s 1 and a reduction of ice concentration by up to 11

a late holocene geomagnetic secular variation record from erhai lake southwest china a secular variation record of the geomagnetic field direction for the last 6 5 kyr has been obtained from the magnetization of sediment cores from erhai lake southwest china in order to make a comparison with this record secular variation in east central china was investigated by combining available magnetic field data from historical records and archaeomagnetic measurements since about 350 be the secular variation in erhai lake shows features consistent with the combined record except for the oldest three observed declination swings in sian from 720 to 900 ad many features of declination and inclination in china also occur in japan from 500 to 1000 ad declination was westerly ranging from about 20 degrees to 5 degrees in erhai lake east central china and japan

velocity probability density functions for oceanic floats probability density functions pdfs of daily velocities from subsurface floats deployed in the north atlantic and equatorial atlantic oceans are examined in general the pdfs are approximately gaussian for small velocities but with significant exponential tails for large velocities correspondingly the kurtoses of the distributions are greater than three similar pdfs are found in both western and eastern regions above and below 1000 m depth with more significant non gaussianity in the north atlantic than at the equator analogously lagrangian statistics in decaying two dimensional turbulence also display non gaussian velocity pdfs with approximately exponential tails in the limit of large reynolds number

problem of secondary porosity frio formation oligocene texas gulf coast secondary porosity formed by the dissolution of both carbonate and silicate minerals especially k feldspars is widely developed in sandstones of the frio formation oligocene in the texas gulf coast co 2 produced by decarboxylation of organic matter is commonly suggested as the acid required for dissolution material balance calculations indicate that co 2 produced by decarboxylation of organic matter in frio formation shales can account for a regional average of only 1 or 2 secondary porosity in frio formation sandstones yet point count data indicate an average of 10 secondary porosity long distance fluid transport many kilometres and or other mechanisms of acid generation should therefore be considered carbon isotopic data on dissolved inorganic carbon in formation water co 2 in produced natural gas and carbonate cements indicate that co 2 produced by decarboxylation had a minor impact on these carbon reservoirs the reaction kerogen water methane carbon dioxide can explain the isotopic data but alone it is insufficient to account for all the secondary porosity unless long distance material transport is involved

mesoscale sea ice deformation in the east greenland marginal ice zone in this paper mesoscale 10 km ice kinematics data obtained during the drift phase of the 1983 marginal ice zone experiment are analyzed the measurements were made with a microwave transponder system accurate to better than 1 m from the point of view of granular media theory the ice pack was close to ideal over the scale of the array the pack was quite regular with floes of relatively uniform size closely packed together the main external driving force for the ice was the ocean current simultaneous current measurements were made at three of the strain array sites the ice behaved in a relatively rigid manner with more shear than dilatation occurring least squares fits of the strain rate tensor showed the deformation field to be quite homogeneous superimposed on the rigid motion were smaller fluctuations with a spectrum falling off proportional to frequency to the power of 3 2 to 2 close examination of individual strain lines showed rather discontinuous distance changes more representative of plastic slip rather than floe bumping although a substantial signal at the inertial period was present in the absolute drift no clear peaks at this period occurred in the spectra of the strain rate tensor invariants analysis of the spatial variation of the underlying ocean currents revealed quite a different picture from that of the ice kinematics in particular the current field exhibited a much greater spatial variability than the ice motion with considerable variance at the inertial period coherence between the ice and ocean differential velocity was small for all frequencies overall the rigid interactive character of the compact ice cover prevented most of the differential ocean currents from being transferred to the differential ice motion

mesoscale eddies in the fram strait marginal ice zone during the 1983 and 1984 marginal ice zone experiments during the summer marginal ice zone experiment in fram strait in 1983 and 1984 fourteen mesoscale eddies in both deep and shallow water were studied between 78 o and 81on sampling combined satellite and aircraft remote sensing observations conductivity temperature depth observations drift of surface and subsurface floats and current meter measurements typical scales of these eddies were 20 40 km rotation was mainly cyclonic with a maximum speed in several cases subsurface of up to 40 cm s observations further suggest that the eddy lifetime was at least 20 to 30 days five generation sources are suggested for these eddies several of the eddies were topographically trapped while others primarily formed by combined baroclinic and barotropic instability moved as much as 10 15 km d with the mean current the vorticity balance in the nontrapped eddies is dominated by the stretching of isopycnals accompanied by a change in the radial shear in the most completely observed eddy south of 79on the available potential energy exceeded the kinetic energy by a factor of 2 quantitative estimates suggest that the abundance of these eddies enhances the ice edge melt up to 1 2 km d

atmospheric forcing of fram strait sea ice export a closer look fram strait is the primary region of sea ice export from the arctic and therefore plays an important role in regulating the amount of sea ice and freshwater within the arctic we investigate the variability of fram strait sea ice motion and the role of atmospheric circulation forcing using daily data during the period 1979 2006 the most prominent atmospheric driver of anomalous sea ice motion across fram strait is an east west dipole pattern of sea level pressure slp anomalies with centers of action located over the barents sea and greenland this pattern also observed in synoptic studies is associated with anomalous meridional winds across fram strait and is thus physically consistent with forcing changes in sea ice motion the association between the slp dipole pattern and fram strait ice motion is maximized at 0 lag persists year round and is strongest on time scales of 10 60 days the slp dipole pattern is the second empirical orthogonal function eof of daily slp anomalies in both winter and summer when the analysis is repeated with monthly data only the barents center of the slp dipole remains significantly correlated with fram strait sea ice motion however after removing the leading eof of monthly slp variability e g the north atlantic oscillation the full east west dipole pattern is recovered no significant slp forcing of fram strait ice motion is found in summer using monthly data even when the leading eof is removed our results highlight the importance of high frequency atmospheric variability in forcing fram strait sea ice motion

weathering rinds and rock coatings from an arctic alpine environment northern scandinavia coarse rock debris exposed in the subaerial environment of northern sweden displays the development of a wide variety of surface coatings these include weathering rinds as well as a great diversity of geochemical coatings including those dominated by ca fe si and al each of these types of rock coatings displays a high degree of geochemical complexity the weathering rinds exhibit both geochemical and morphologic changes to the parent rock cores including extensive dissolution oxidation and hydration as well as disaggregation fracturing and cementation by secondary geochemical coatings chemical breakdown of the rock to form weathering rinds includes loss of k si mg and ca and buildup of fe weathering rinds are fundamentally the result of dissolution as no clay minerals were identified in the rinds rock coatings are distinguished from rinds by their clear accretionary nature despite the distinction made between weathering rinds and rock coatings it is important to note that often the two are intimately related the presence of rock coatings as well as weathering rinds on rock surfaces amplifies the important role played by geochemical processes in the arctic alpine climate of northern sweden in particular as well as its significance in landscape evolution in such environments in general

ferro and antiferromagnetism of ultrafine grained hematite aluminum substituted hematite here referred to as al hm is an important magnetic mineral for paleo and environmental magnetism however the magnetic properties of nanosized al hm are poorly known in this study a series of al hm samples fourteen samples and their nonsubstituted counterparts referred to as pure hm seven samples were synthesized with particle sizes ranging from 14 to 124 nm with decreasing particle size coercive force bc magnetic remanence mr acquired in a 5 t field at room temperature and the maximum blocking temperature tb of al hm descend gradually tb drops abruptly from 800 to 200 k at 17 2 3 7 nm this size defines the superparamagnetic sp single domain sd threshold of al hm which is significantly lower than that of pure hm 27 5 1 5 nm the antiferromagnetic high field susceptibility anti and the saturation magnetization ms for the weak ferromagnetic component in hematite are both correlated negatively with temperature between 20 and 300 k and grain size in the vicinity of the sp threshold for very small grains below 16 17 nm tb increases with increasing particle size however beyond this size it descends with increasing particle size up to 19 nm before increasing with grain size again these trends are attributed to the competition of surface anisotropy and bulk anisotropy elastic anisotropy this new study substantially improves our understanding of the complex magnetic properties of fine grained al hm and pure hm in natural sample which is significant for the paleoenvironmental and climatic studies of natural samples e g red beds soils

sea ice motion as a drunkard s walk observations of sea ice displacement over short periods of time are used to deduce some statistics of the ice motion over long periods of time the objective is to follow the trajectory of a piece of ice starting at a randomly selected time and location and ending when the ice either melts or leaves the arctic basin trajectories are also followed backward in time to the time and location where the piece of ice was formed statistical properties considered are the age and remaining lifetime of ice in various locations and the probability that ice presently occupying a particular location was originally created or will ultimately melt in certain regions possible applications are to the distribution of pollutants by sea ice and to the design of experiments involving drifting measurement platforms

anomalous dispersion of sea ice in the fram strait region the single particle dispersion of sea ice in the fram strait region is investigated using ice drift buoys deployed from 2002 to 2009 within the fram strait cyclones and the arctic climate system study campaigns a new method to estimate the direction of the mean flow based on a satellite drift product is introduced as a result the bias in the dispersion introduced by the mean flow is eliminated considering only the displacements of the buoys in the cross stream direction results show an absolute dispersion growing quadratically in time for the first 3 days and an anomalous dispersion regime exhibiting a strongly self similar scaling following a 5 4 power law for time scales larger than 6 days persisting over the whole time series of length 32 days the non gaussian distribution of the velocity fluctuations with a skewness of 0 15 and a kurtosis of 7 33 as well as the slope of the lagrangian frequency spectrum between 2 and 1 are in agreement with the anomalous diffusion regime comparison with data from the international arctic buoy program yields similar results with an anomalous dispersion starting after 10 days and persisting over the whole time series of length 50 days the results suggest the presence of deformation and shear acting on the sea ice dispersion the high correlation between the cross stream displacements and the cross stream wind velocities shows the important role of the wind as a source for the anomalous dispersion

archeomagnetic secular variation from korea implication for the occurrence of global archeomagnetic jerks abstract an archeomagnetic paleosecular variation psv was first defined in korea using baked materials collected from 26 kilns or hearths with ages ranging from 1100 bc to ad 1790 variations of geomagnetic declination and inclination from the korean peninsula are distinctively different from the prediction of a global model cals3k 3 or cals7k 2 for the past 3500 yr in particular a distinctive offset in magnitude and phase is noticeable between the observations and predictions at 745 bc ad 300 and ad 1400 1700 a bi plot of magnetic declination versus inclination displays three cusps at the corresponding time intervals these time intervals are nearly identical to or at least overlap with three of the four potential archeomagnetic jerks suggested by gallet et al 2003 from the european archeomagnetic data a comparison of the psv curves for neighboring countries regions revealed that european archeomagnetic jerks at 800 bc ad 200 ad 800 and ad 1400 were all preserved in east asia suggesting that the archeomagnetic jerks were global or at least northern hemispheric features

non gaussian velocity probability density functions an altimetric perspective of the mediterranean sea abstract velocity probability density functions pdfs are a key tool to study complex flows and are of great importance to model particle dispersion the pdfs of geostrophic velocities derived from sea level anomalies maps for the mediterranean sea have been computed and analyzed guided by recent results found in studies of two dimensional and geostrophic turbulence at the basin scale results show that the geostrophic velocity pdf derived from sla maps is non gaussian to understand the origin of this non gaussianity a topological partition of the flow based on the okubo weiss parameter is applied to separate the contribution of coherent vortices from the background field after such separation the non gaussian part of the pdf appears mostly associated with the presence of such structures only about 20 of the vortices identified in the dataset are mainly responsible for this deviation these vortices called intense vortices in previous works are those vortices with values of the amplitude larger t

float derived isopycnal diffusivities in the dimes experiment as part of the diapycnal and isopycnal mixing experiment in the southern ocean dimes 210 subsurface floats were deployed west of the drake passage on two targeted density surfaces absolute single particle diffusivities are calculated for the floats the focus is on the meridional component which is less affectedby the meanshear the diffusivitiesare estimatedin severalways including a novelmethodbased on the probability density function of the meridional displacements this allows the determination of the range of possible lateral diffusivities as well as the period over which the spreading can be said to be diffusive the method is applied to the float data and to synthetic trajectories generated with the massachusetts institute of technologygeneral circulationmodel mitgcm becauseof ballastingproblems manyofthefloatsdid not remain on their targeted density surface however the float temperature records suggest that most occupied asmallrangeofdensities sothefloatsweregroupedtogetherfortheanalysis thelatterfocuseson asubsetof 109 of the floats launched near 1058w the different methods yield a consistent estimate for the diffusivity of 800 6 200m 2 s 21 the same calculations were made with model particles deployed on 20 different density surfaces and the result for the particles deployed on the neutral density surface g 5 27 7 surface was the same within the errors the model was then used to map the variation of the diffusivity in the vertical near the core of the antarctic circumpolar current acc the results suggest mixing is intensified at middepths between 1500 and 2000m consistent with several previous studies

arctic sea ice velocity field general circulation and turbulent like fluctuations 1 using buoy trajectories of the iabp data set we analyze the arctic sea ice velocity field as the superposition of a mean field and fluctuations we study how the mean field can be objectively defined using appropriate spatial and temporal averaging scales depending on the season considered 400 km and 5 months for winter i e approximately all the polar winter duration and 200 km and 2 months for summer i e approximately all the polar summer duration the mean velocity field shows a strong intra annual between winter and the following summer as well as interannual variability the fluctuations i e the remaining part of the velocity field after subtracting the mean field are analyzed in terms of diffusion properties although the arctic sea ice cover is a solid we show that the fluctuations follow the same diffusion regimes as the ones predicted for turbulent flows as observed in geophysical fluids like the ocean or the atmosphere we found that the integral time and the diffusivity of sea ice are in the same ranges as those estimated for the ocean i e 1 5 days in winter and 1 3 days in summer and 0 44 103 m2 s for winter and 0 45 103 m2 s in summer respectively however the statistics of the sea ice fluctuating velocity deviate from classical turbulence theory as they show exponential instead of gaussian distributions sea ice velocity and acceleration are intermittent and both are characterized by a multifractal scaling the oceanic and atmospheric dynamic forcing cannot explain solely the statistical properties of sea ice kinematics and dynamics we argue that sea ice dynamic is significantly influenced by the interplay of multiple fractures that are activated intermittently within the ice pack

an estimate of the mean field of arctic sea ice motion the observational basis for our understanding of sea ice motion comes from the trajectories of particular ice floes these ice floes may have been marked by a manned research station or more recently by an automatic data buoy since 1893 almost 100 station years of drift data have been recorded using the principles of optimal linear estimation these data are used to obtain a quantitative estimate of the field of mean motion

emergence and evolution of the south atlantic anomaly revealed by the new paleomagnetic reconstruction shawq2k abstract the south atlantic anomaly saa is one of the most outstanding features of the present geomagnetic field thus a good knowledge of the saa is clue for a better understanding of the dynamical behavior of the geomagnetic field to achieve this goal paleomagnetic data are crucial since they provide the unique way to investigate past changes in the earth s magnetic field here we present a new global geomagnetic field reconstruction the shawq2k model which is based on a critical revision of the global archeomagnetic and volcanic dataset the new model provides an improved description of the geomagnetic field during the last 2 millennia and yields surprising outcomes about the emergence and development of the saa it shows that the reversed flux patch observed at the core mantle boundary and linked to the saa emerged in the southern hemisphere from at least 950 ad this patch moved westward from the equator to southern latitudes being clearly isolated after 1400 ad in addition since 1550 ad a second reversed flux patch moving northeastward is observed in the north atlantic the new data now available for the southern hemisphere coming from africa and south america together with the use of an appropriated weighting scheme in the modeling process have improved our understanding of past geomagnetic field behavior and showed new evolutionary aspects of the saa

arctic sea ice circulation and drift speed decadal trends and ocean currents 1 we examine the basinwide trends in sea ice circulation and drift speed and highlight the changes between 1982 and 2009 in connection to regional winds multiyear sea ice coverage ice export and the thinning of the ice cover the polarity of the arctic oscillation ao is used as a backdrop for summarizing the variance and shifts in decadal drift patterns the 28 year circulation fields show a net strengthening of the beaufort gyre and the transpolar drift especially during the last decade the imprint of the arctic dipole anomaly on the mean summer circulation is evident 2001 2009 and enhances summer ice area export at the fram strait between 2001 and 2009 the large spatially averaged trends in drift speeds winter 23 6 decade summer 17 7 decade are not explained by the much smaller trends in wind speeds winter 1 46 decade summer 3 42 decade notably positive trends in drift speed are found in regions with reduced multiyear sea ice coverage over 90 of the arctic ocean has positive trends in drift speed and negative trends in multiyear sea ice coverage the increased responsiveness of ice drift to geostrophic wind is consistent with a thinner and weaker seasonal ice cover and suggests large scale changes in the air ice ocean momentum balance the retrieved mean ocean current field from decadal scale average ice motion captures a steady drift from siberia to the fram strait an inflow north of the bering strait and a westward drift along coastal alaska this mean current is comparable to geostrophic currents from satellite derived dynamic topography

holocene paleomagnetic secular variation from east china sea and a psv stack of east asia abstract paleomagnetic secular variation psv provides information on the mechanisms of the geodynamo and can also be used for stratigraphic correlation on a regional scale in this study we constructed psv curves of relative rapidly deposited holocene marine sequence from east china sea results show that the dominant magnetic carriers are pseudo single domain psd to multidomain md magnetites paleomagnetic directions are preserved by coarse grained magnetite even affected by post depositional diagenetic alteration the psv record of core md06 3040 exhibits six major inclination peaks and five declination swings during the holocene the periodicities for inclination are about 2000 and 550 years and for declination are about 1400 and 500 years the psv of md06 3040 is comparable to archeomagnetic and historic results for the last 2500 years and to psv results from lake sediments in southern china and japan during the holocene a psv stack of east asia is constructed by sedimentary and archeological psv results which can be used as an important reference curve for a large region and the psv correlation between sites can be applied for relative dating of east asia

an updated global review of solutional weathering processes and forms in quartz sandstones and quartzites abstract quartz is considered one of the less soluble minerals of the earth s crust and thus hardly affected by chemical weathering despite this for more than forty years it is clear that the formation of caves and peculiar solutional weathering dominated landforms in quartz rich lithologies is common and shares several similarities to the well known karstic ones in carbonate rocks in the last thirty years great strides have been made in furthering our knowledge of the distribution of these forms around the world and the geochemical processes involved these studies have clearly shown that solutional weathering is a fundamental process acting through intergranular dissolution of quartz increasing the rock porosity and decreasing the rock strength to erosion this process has been described in the concepts of arenization and phantomization and the widespread evidences of the fundamental role of quartz solution in landform genesis has even developed to the extent of several geomorphologists reassessing the definition of the term karst and its application to these peculiar lithologies nonetheless the process is complicated by several factors related both to environmental conditions water chemistry and availability as well as to the compositional and textural characters of the lithology presence of clays iron hydroxides carbonate cement etc all these aspects have to be taken carefully in consideration in order to understand if solution is a dominant or accessory process in the landscape evolution in this review the state of knowledge on the relevant chemical processes weathering mechanisms and speleogenesisk involved in the surface and underground karstification and clear examples of quartz solution and solutional landforms from different world locations are outlined and discussed

reconstructing the holocene geomagnetic field abstract knowledge of the holocene evolution of earth s magnetic field is important for understanding geodynamo processes in the core is necessary for studying long term solar terrestrial relationships and can provide useful age constraints for archeologicaland stratigraphic applications continuous time varying global field models based on archeo and paleomagnetic data are useful tools in this regard we use a comprehensive data compilation and recently refined modelling strategies to produce cals10k 1b the first time varying spherical harmonic geomagnetic field model spanning 10 ky the model is an average obtained from bootstrap sampling to take account of uncertainties in magnetic components and ages in the data and hence has version number 1b instead of 1 this model shows less spatial and temporal resolution than earlier versions for 0 3 ka and particularly aims to provide a robust representation of the large scale field at the core mantle boundary cmb we discuss the geomagnetic dipole evolution and changes in holocene magnetic field morphology at the cmb as shown by the new reconstruction the results are compatible with earlier models cals3k 3 and cals3k 4 for 0 3 ka but reveal some clear deficiencies in the 0 7 ka cals7k 2 model prior to 3 ka cals10k 1b is able to resolve mobile and structurally evolving high latitude radial field flux lobes at the cmb in both hemispheres as well as persistent non zonal structure in the 10 ky average contributions to the average field from time varying structures in the equatorial indonesian australian region are particularly striking

new high precision full vector archaeomagnetic data from a roman kiln in merida spain abstract this study presents new high precision age and full vector archaeomagnetic data from a kiln excavated in the roman archaeological site of mitreo s house merida badajoz spain the age of the kiln was obtained by the stratigraphic method and by the ceramological study of the italic and sigillata pottery found with a very precise age date of 55 15 years ad rock magnetic experiments pointed towards magnetite as the main carrier of remanence and highly reversible thermomagnetic curves suggested that the studied samples were suitable for archaeoeointensity determinations paleomagnetic experiments including thermal and stepwise alternating field demagnetization yielded the following mean direction for the kiln declination d 0 6 inclination i 54 0 k 481 95 2 5 archaeointensityexperiments with the thellier coe protocol on 28 samples yielded successful determinations in 27 cases anisotropy factors between 0 90 and 1 04 were obtained from anisotropy of thermoremanent magnetization atrm experiments a mean anisotropy corrected archaeointensity value f 56 3 5 5 t was obtained the geomagnetic model sha dif 14 k was used for an archaeomagnetic dating yielding a chronological interval between 40 bce and 150 ce this low age resolution when compared with the pottery based age data is related to the behavior of the geomagnetic field in the iberian peninsula during the roman period which does not allow to differentiate well between results corresponding to those centuries however it is also related to the fact that the iberian archaeomagnetic dataset in the analysed time range is highly scattered a high quality full vector data with a very precise age have been obtained which contribute to improve the iberian secular variation curve and geomagnetic databases

are mediterranean mountains entisols weakly developed the case of orthents from sierra nevada southern spain two orthents from sierra nevada national park spain classified as loamy skeletal mesic typic xerorthent and loamyskeletal frigid lithic cryorthent were studied they were situated at 1460 and 2000 m derived from micaschists and quartzites under mediterranean mountain climate conditions with mesic and cryic temperature regimes and xeric moisture regime these orthents are weakly developed as shown by their reduced thickness their lack of diagnostics subsurface horizons sandy loam textures skeletal and lithochromic colors quartz is present in significant amounts particularly in the fine light sand fraction analysis of the quartz grains of the fine light sand by scanning electron microscope sem and backscattered electron images bse revealed the presence of significant physical and chemical alteration features such as fractures corrosion gulfs fields of etch pits and dissolution of intergranular surfaces this process is confirmed by electron microprobe analysis empa since the edges of the quartz grains have a higher proportion of cations other than si compared to their centre further evidence indicates the authigenic nature of the process starting from quartz etching an assessment of soil weathering has been made w index from marcelino et al 1999 the alteration of the quartz together with the development of a ultramicrofabric with several fabric units investigated with sem and other characteristics mineralogical chemical etc are considered indicative of some pedogenic evolution these facts are especially interesting in the case of weakly developed mediterranean mountain soils from sierra nevada where processes of chemical weathering have traditionally not been considered very active d 2003 elsevier b v all rights reserved

negatively skewed aeolian sands from a humid tropical coastal dunefield northern australia abstract this paper describes the nature and environmental significance of variations in textural parameters within a large coastal dunefield in tropical northern australia grain size parameters of modern beaches and foredunes are very similar but are distinct from those of parabolic dune and sandplain environments on average beach and foredune sands have a normal grain size distribution but parabolic dune sands are predominantly negatively skewed negative skewness is interpreted as primarily reflecting sorting of dune sediments by winnowing at dune crests and by avalanching on slip faces a general relationship between mean size and skewness is supported with finer sediments showing increased negative skewness positive skewness can therefore not be used as a diagnostic property of aeolian sediments

secular variation of the intensity of the geomagnetic field in mexico during the first millennium bce in western eurasia the first millennium bce is characterized by the fastest secular variation of the earth magnetic field observed over the last millennia and by a geomagnetic anomaly centered on the middle east on the global scale the variation of the dipolar field during this period remains poorly constrained because of the lack of data in other geographical areas here we presented 23 new mean archaeointensity data on ceramic sherds dated between 1500 bce and 200 ce from chalcatzingo archaeological site in central mexico archaeointensities were determined using the classical thellier thellier protocol with corrections for trm anisotropy and cooling rate effects our work doubles the number of high quality archaeointensity data in mexico during the considered period using a bayesian approach a new secular variation curve was calculated at mexico city between 1500 bce and 200 ce after selection of mexican archaeointensity data after a period of oscillations of the intensity between 20 and 40 t from 1500 to 300 bce the curve shows a large maximum 65 t in the second century bce the corresponding vadm varied between 4 0 and 11 0 1022 am2 which highlights further that the intensity of the geomagnetic field could vary at regional scale over a larger range as previously thought however this amplitude variation may be overestimated as it does not take into account the fast directional variation observed at this time

a simple model for geomagnetic field excursions and inferences for palaeomagnetic observations abstract we explore simple excursion scenarios by imposing changes on the axial dipole component of the holocene geomagnetic field model cals10k 2 and investigate implications for our understanding of palaeomagnetic observations of excursions our findings indicate that globally observed directions of fully opposing polarity are only possible when the axial dipole reverses linearly decaying the axial dipole to zero and then reestablishing it with the same sign produces a global intensity minimum but does not produce fully reversed directions globally reversing the axial dipole term increases the intensity of the geomagnetic field observed at earth s surface across the mid point of the excursion which results in a double dip intensity structure during the excursion only a limited number of palaeomagnetic records of excursions contain such a double dip intensity structure rather the maximum directional change is coeval with a geomagnetic field intensity minimum

improving geomagnetic field reconstructions for 0 3 ka global geomagnetic field reconstructions on millennial time scales can be based on comprehensive paleomagnetic data compilations but especially for older data these still suffer from limitations in data quality and age controls as well as poor temporal and spatial coverage here we present updated global models for the time interval 0 3 ka where additions to the data basis mainly impact the south east asian alaskan and siberian regions we summarize recent progress in millennial scale modelling documenting the cumulative results from incremental modifications to the standard algorithms used to produce regularized time varying spherical harmonic models spanning 1000 bc to 1990 ad from 1590 to 1990 ad gauss coefficients from the historical gufm1 model supplement the paleomagnetic information in addition to absolute paleointensities calibrated relative paleointensity data from sediments are now routinely included iterative data rejection and recalibration of relative intensity records from sediments ensure stable results bootstrap experiments to generate uncertainty estimates for the model take account of uncertainties in both age and magnetic elements and additionally assess the impact of sampling in both time and space based on averaged results from bootstrap experiments taking account of data and age uncertainties we distinguish more conservative model estimates cals3k nb representing robust field structure at the core mantle boundary from relatively high resolution models cals3k n for model versions n 3 and 4 we assess the impact of newly available data and modifications to the modelling method by comparing the previous cals3k 3 the new cals3k 4 and the conservative new model cals3k 4b we conclude that with presently available data it is not feasible to produce a model that is equally suitable for relatively high resolution field predictions at earth s surface and robust reconstruction of field evolution avoiding spurious structure at the core mantle boundary cmb we presently consider cals3k 4 the best high resolution model and recommend the more conservative lower resolution version for studies of field evolution at the cmb

static breakage of granitic detritus by ice and water in comparison with breakage by flowing water temperature cycling between 4 5 1 0 c and 13 0 2 0 c in the presence of added water caused significant breakage of granitic detritus because cycling with only adsorbed water present also caused breakage fragmentation is attributed to both the combined action of ice and adsorbed water and to the latter acting alone breakage evidently resulted from the gradual tensile opening of pre existing cracks weakening then splitting grains surviving unbroken grains show evidence of a fatigue effect quartz split dominantly along pre existing subplanar microfractures whereas feldspar and biotite split along crystal cleavages degree of breakage and product size distribution depend on the crystalline nature of the parent material its previous history and the nature and duration of the breakage process with the first two factors the same size distributions from adsorbed water breakage alone and from that due to adsorbed water plus ice differ slightly both contrast strongly with those of simulated fluviatile breakage whereas the latter preferentially produced 2 20 m particles probably debris of inter particle collisions static breakage split coarser grains wherever major weaknesses occurred producing less selective product size distributions with greater proportions of loess sized material about 20 60 characteristic inflections in the size distribution curves of our experimentally produced debris are also shown by samples from the sola of some frost affected soils partially healed microfractures in plutonic quartz are normally spaced at about 1 10 approaching the downward asymptotic comminution limit for brittle solids about 1 surficial physical processes are capable of reducing only a small proportion of plutonic quartz to this size before its storage in sediments

on the possible occurrence of archaeomagnetic jerks in the geomagnetic field over the past three millennia abstract archaeomagnetism can provide a high resolution full vector description of the earth s magnetic field for the past several thousand years we analyse the bulk of archaeomagnetic data both direction and intensity obtained recently in western europe and the eastern mediterranean covering the past three millennia we demonstrate a remarkable coincidence between sharp cusps in geomagnetic field direction and intensity maxima two clear ones at ad 200 and 1400 two presently less well constrained at 800 bc and ad 800 these sharp changes may constitute a new feature of geomagnetic secular variation archaeomagnetic jerks with time characteristics intermediate between geomagnetic jerks and magnetic excursions

formation of secondary porosity in sandstones by quartz framework grain dissolution an understanding of the nature and origin of porosity in sandstones is crucial to the evaluation of their potential as hydrocarbon reservoirs primary porosity is normally destroyed by cementation compaction and pressure solution during burial but it has recently been recognized that significant secondary porosity can develop at depth1 3 this discovery has been called the most significant advance in the study of clastic diagenesis in the past decade 4 several genetic types of secondary porosity have been identified these include porosity formed by 1 fracturing 2 shrinkage 3 dissolution of sedimentary grains and matrix 4 dissolution of authigenic cements and 5 dissolution of authigenic replacive minerals5 formation of secondary porosity by framework grain dissolution has been thought mainly to involve decomposition of feldspars and lithic grains6 7 we demonstrate here that significant secondary porosity can also develop by dissolution of quartz framework grains if the rocks are exposed to alkaline pore fluids during deep burial and or uplift

a matlab tool for archaeomagnetic dating a matlab tool for archaeomagnetic dating has been developed in this work well dated palaeosecular variation curves psvcs can be used to date archaeological artefacts with unknown ages the archaeomagnetic direction declination and or inclination and the archaeointensity obtained from the archaeological artefact are compared with a master psvc in addition historical lava flows with controversial ages can be dated using this methodology the dating process follows the descriptions given by lanos 2004 which is based on the combination of temporal probability density functions of the three geomagnetic field elements here we develop an interactive tool in matlab code to carry out archaeomagnetic dating by comparing the undated archaeomagnetic or lava flow data with a master psvc the master psvcs included with the matlab tool are the different european bayesian curves and those generated using both regional and global geomagnetic field models a case study using all the psvcs available in europe and some undated archaeomagnetic data has been carried out to analyze how the different psvcs affect the dating process in addition the dating uncertainty and the relocation error have been analyzed in the european region results show that some regional bayesian psvcs and the regional scha dif 3k archaeomagnetic model are the best choices to obtain an accurate date in europe moreover when it is available the full geomagnetic field vector must be used for archaeomagnetic dating

a method for correcting geographically separated remanence directions for the purpose of archaeomagnetic dating summary spatial variations in the geomagnetic field must be taken into account if secular variation master curves and directional magnetic dates are to be optimized two methods for relocating remanence vectors have been proposed and in this paper their relative accuracies are compared using a numerical model based on the present day field a method which converts archaeomagnetic directions via a virtual geomagnetic pole is shown to be the more efficient transformation for an archaeomagnetic region the size of the british isles 900 km radius the maximum error in relocating vectors to a central location is predicted to be of the order of 1 2

formation of abnormally high porosity permeability in deltaic sandstones oligocene bozhong depression offshore bohai bay basin china abstract the porosity enhancing capability of secondary porosity in a closed sandstone geochemical system has been suggested to be small in past studies however the mechanisms responsible for the formation of abnormally high porosity permeability remain unclear the oligocene dongying formation in the bozhong depression offshore bohai bay basin preserves abnormally high porosity i e 36 4 average or 42 1 median higher than background values this work selects samples with abnormally high porosity ahp samples with normal porosity np and samples with abnormally low porosity alp and compares their differences in physical properties porosities permeabilities and thin section porosities diagenetic minerals pore structures compaction and cementation detrital compositions and grain texture in an attempt to find the real factors controlling this heterogeneity an effective export of dissolution by products al3 and si4 from ahp to np and alp leads to 2 01 average or 2 11 median newly created porosity in ahp which is still significantly lower than the porosity difference between ahp and np in comparison compaction reduction and mechanisms beneficial for compaction reduction should be the major factors controlling ahp formation the content and distribution pattern of early carbonate cements compared to the sedimentary factors grain size and rigid grains have significant influences on compaction reduction only samples with moderate contents 0 5 3 0 of uniformly point distributed early carbonate cements and with effective export of dissolution by products can form ahp three formation models for alp and two formation models for np are also proposed in summary the evolution of porosity permeability is controlled by early carbonate cements and induced compaction reduction major causes and by feldspar dissolution and redistribution of by products minor causes this work provides new constraints on the formation of ahp and heterogeneity and is therefore important for sandstone reservoir quality prediction

epsilon iron oxide origin of the high coercivity stable low curie temperature magnetic phase found in heated archeological materials the identification of epsilon iron oxide fe2o3 as the low curie temperature high coercivity stable phase hcslt carrying the remanence in heated archeological samples has been achieved in samples from two archeological sites that exhibited the clearest evidence of the presence of the hcslt this uncommon iron oxide has been detected by confocal raman spectroscopy crs and characterized by rock magnetic measurements large numbers of fe2o3 microaggregates in co or isolated clusters in hel could be recognized distributed over the whole sample and embedded within the ceramic matrix along with hematite and pseudobrookite and with minor amounts of anatase rutile and maghemite curie temperature estimates of around 170 c for co and 190 c for hel are lower than for pure synthetic fe2o3 227 c this together with structural differences between the raman spectra of the archeologically derived and synthetic samples is likely due to ti substitution in the fe2o3 crystal lattice the fe2o3 fe2o3 fe2o3 transformation series has been recognized in heated archeological samples which may have implications in terms of their thermal history and in the factors that govern the formation of fe2o3

geomagnetic intensity variations for the past 8 kyr new archaeointensity results from eastern china abstract in this study we have carried out paleointensity experiments on 918 specimens spanning the last 7 kyr including pottery fragments baked clay and slag collected from shandong liaoning zhejiang and hebei provinces in china approximately half of the specimens yielded results that passed strict data selection criteria and give high fidelity paleointensities the virtual axial dipole moments vadms of our sites range from 2 10 22 to 13 10 22 am 2 at 2250 bce our results suggest a paleointensity low of 2 10 22 am 2 which increases to a high of 13 10 22 am 2 by 1300 bce this rapid less than 1000 yrs six fold change in the paleointensity may have important implications for the dynamics of core flow at this time our data from the last 3 kyr are generally in good agreement with the arch3k 1 model but deviate significantly at certain time periods from the cals3k 4 and cals10k 1b model which is likely due to differences in the data used to constrain these models at ages older than 3 ka where only the cals10k 1b model is available for comparison our data deviate significantly from the model combining our new results with the published data from china and japan we provide greatly improved constraints for the regional model of eastern asia when comparing the variations of geomagnetic field in three global representative areas of eastern asia the middle east and southern europe a common general trend of sinusoidal variations since 8 ka is shown likely dominated by the dipole component however significant disparities are revealed as well which we attribute to non dipolar components caused by movement of magnetic flux patches at the core mantle boundary

on the scaling laws derived from ice beacon trajectories in the southern beaufort sea during the international polar year circumpolar flaw lead study 2007 2008 1 sea ice motion is an important element in mass balance calculations ice thermodynamic modeling ice management plans for industry and ecosystems studies in the historical literature sea ice motion in the beaufort sea was characterized by a predominantly anticyclonic motion during winter months with episodic reversals to cyclonic activity during summer however recent studies have shown an increase in cyclonic activity throughout the annual cycle in this paper we examine circulation in the beaufort sea based on the trajectories of 22 ice beacons launched in the franklin bay area during the international polar year circumpolar flaw lead ipy cfl study during an over wintering experiment in 2007 2008 dispersion characteristics of ice motion show that absolute zonal dispersion follows a t2 scaling law characteristic of advection associated with beaufort gyre circulation whereas absolute meridional dispersion follows a scaling law of t5 4 characteristic of floaters and dispersion in 2 d turbulence temporal autocorrelations of ice velocity fluctuations highlight definitive timescales with values of 1 2 0 7 days in the zonal meridional direction near gaussian behavior is reflected in higher order moments for ice velocity fluctuation probability density functions pdfs non gaussian behavior for absolute displacement pdfs indicates spatial heterogeneity in the ice motion fields atmospheric forcing of sea ice is explored through analysis of daily north american regional reanalysis and in situ wind data where it is shown that ice in the cfl study region travels with an average speed of approximately 0 2 and an average angle of 51 5 to the right of the surface winds during the 2007 2008 winter the results from this analysis further demonstrate seasonality in ice drift to wind ratios and angles that corresponds to stress buoy data indicative of increases in internal ice stress and connectivity due to consolidation of the seasonal ice zone to the coast and perennial ice pack during winter in the beaufort sea region

new archaeomagnetic direction results from china and their constraints on palaeosecular variation of the geomagnetic field in eastern asia geophysical journal international new archaeomagnetic direction result from china and its constraints on paleosecular variation of the geomagnetic field in eastern asia journal manuscript id manuscript type date submitted by the author complete list of authors keywords geophysical journal international draft research paper n a cai shuhui institute of geology and geophysics chinese academy of sciences university of california san diego scripps institution of oceanography tauxe lisa scripps oceanographic institution deng chenglong state key laboratory of lithospheric evolution institute of geology and geophysics chinese academy of sciences qin huafeng institute of geology and geophysics state key laboratory of lithospheric evolution pan yongxin institute of geology and geophysics chinese academy of sciences jin guiyun shandong university school of history and culture chen xuexiang shandong university school of history and culture chen wei the sichuan provincial cultural relics and archeology research institute xie fei hebei province institute of cultural relics zhu rixiang institute of geology and geophysics chinese academy of sciences archaeomagnetism geomagnetism and electromagnetism palaeomagnetic secular variation geomagnetism and electromagnetism palaeomagnetism geomagnetism and electromagnetism

scaling properties of sea ice deformation from buoy dispersion analysis 1 a temporal and spatial scaling analysis of arctic sea ice deformation is performed over timescales from 3 h to 3 months and over spatial scales from 300 m to 300 km the deformation is derived from the dispersion of pairs of drifting buoys using the iabp international arctic buoy program buoy data sets this study characterizes the deformation of a very large solid plate the arctic sea ice cover stressed by heterogeneous forcing terms like winds and ocean currents it shows that the sea ice deformation rate depends on the scales of observation following specific space and time scaling laws these scaling properties share similarities with those observed for turbulent fluids especially for the ocean and the atmosphere however in our case the time scaling exponent depends on the spatial scale and the spatial exponent on the temporal scale which implies a time space coupling an analysis of the exponent values shows that arctic sea ice deformation is very heterogeneous and intermittent whatever the scales i e it cannot be considered as viscous like even at very large time and or spatial scales instead it suggests a deformation accommodated by a multiscale fracturing faulting processes

dating of holocene western canadian arctic sediments by matching paleomagnetic secular variation to a geomagnetic field model a recently recovered w6 m long holocene sedimentary sequence piston core 2004 804 650 collected from the beaufort sea western canadian arctic was dated by combining the paleomagnetic secular variation psv and a time varying spherical harmonic model of the geomagnetic field cals7k 2 a u channel based paleomagnetic study reveals the presence of a stable single component of magnetization mad 5 carried by low coercivity ferrimagnetic minerals most likely magnetite in the pseudo single domain grain size range an age depth model spanning the last w6000 calbp was established from nine paleomagnetic tie points obtained by comparing the magnetic declination profiles of core 650 and the cals7k 2 model output in order to verify the robustness of the method both the magnetic inclination and the relative paleointensity rpi records of core 650 were then compared with western north american lacustrine and volcanic holocene psv records as well as with previously published rpi records from the beaufort and chukchi seas several common magnetic inclination features and similar millennial scale fluctuations are detected among the records supporting a common geomagnetic origin of the records and implying consistency of the derived age model these results show the potential of using both the cals7k 2 model output and psv of the geomagnetic field as a practical dating tool

a holocene palaeomagnetic secular variation record from huguangyan maar lake southern china summary a composite holocene sediment profile 5 m in length constrained by both radiocarbon dating and magnetic susceptibility based correlation was obtained from three livingstone piston cores collected in 10 m water depth in the huguangyan hgy maar lake southern china the homogeneous silty clay indicates stable and continuous deposition the dominant magnetic carrier is magnetite in the pseudo single domain grain size range and thus is suitable for recording palaeomagnetic secular variations psv results show that the hgy psv curves can be correlated faithfully to the counterparts at a regional scale therefore the psv data is a potential tool for stratigraphic correlation and for further refining the chronological framework of lake sediment sequences from southern china further comparison of the hgy psv records with the coeval european and north american counterparts confirms the existence of strong permanent magnetic flux lobes at the core mantle boundary the discrepancy in amplitude and out phase pattern among the different regional records may be ascribed to the evolution of the magnetic flux lobes

paleomagnetic secular variation and relative paleointensity during the holocene in south china huguangyan maar lake revisited the scarcity of reliable paleomagnetic secular variation psv records from east asia especially from low latitude regions impedes better understanding of global psv mechanisms here we report on a radiocarbon dated holocene psv record from a composite 6 7 m long core collected from the high sedimentation rate huguangyan maar lake hml in subtropical tropical south china rock magnetic results demonstrate that the natural remanent magnetization resides in single domain magnetite alternating field demagnetization experiments at 1 cm spacing on u channel samples reveal six distinct inclination highs at 7 500 bce 5 100 bce 4 600 bce 3 600 3 400 bce 1 600 1 200 bce and 600 800 ce three inclination lows at 4 800 bce 600 300 bce and 1 000 1 300 ce and three eastward declination trends at 3 600 3 200 bce 2 600 2 400 bce and 400 bce to 200 ce the similarity between the hml psv record and other independently dated records from east asia and geomagnetic field models corroborates the robustness of our age model and holocene psv record strikingly centennial to millennial scale psv features of the hml are comparable within age uncertainties with other holocene records from europe north america and canada suggesting that such directional patterns are likely to be hemispheric in scale although relative paleointensity data of hml are affected by environmental factors e g organic matter diagenesis the record still provides a regionally important new psv reference curve whose conspicuous features may serve as stratigraphic markers for east asian paleorecords

origin of siltstones glacial grinding versus weathering siltstones are unusual rocks they are mainly made up of quartz glacial grinding is considered by some authors to be the main or even the only process generating silt this is supported by 1 the presence of silt in basal tills from present ice caps and above all 2 by the volumetric importance of quaternary loess however ancient glaciogenic sediments contain only a little silt scattered in the matrix of tillites or forming thin intercalations in pro and periglacial deposits these siltstones represent less than 5 of the total volume of upper proterozoic and upper ordovician glaciogenic sequences of west africa on the other hand silt is abundant in weathering profiles of tropical equatorial and mediterranean zones this silt is generated by splitting of minerals mainly quartz inherited from the parent rock quartz grains are partly dissolved in situ and their fragments cemented by iron oxi hydroxides in tropical and equatorial zones and by calcite in mediterranean zones silt is particularly abundant in tropical soils comprising up to 50 75 secondary dissolution of the iron or calcite matrix induces disaggregation of these soils and the release of silt which is later reworked and concentrated by wind or running water weathering processes and especially those operating in tropical zones are the main phenomena generating silt glacial grinding would generate only a little silt a large part of the material of quaternary loess may be derived from glacially reworked weathering profiles

synchronizing holocene lacustrine and marine sediment records using paleomagnetic secular variation high sediment accumulation rates in lacustrine and shallow marine archives around iceland offer the potential to compare high resolution paleoclimatic reconstructions from terrestrial and marine archives however direct comparisons are hampered by difficulties in stratigraphic correlation and in deriving accurate age models for lacustrine archives icelandic paleomagnetic secular variation psv has the potential to synchronize these records here we compare holocene psv from a well dated marine core on the north iceland shelf with psv from two lacustrine archives with comparable sediment accumulation rates hvt03 1a a glacier dominated lake and hak03 1b in a nonglacial catchment geochemically characterized tephra layers combined with unique high amplitude structures in the psv records provide secure tie points every 200 yr once the records are synchronized the chronology from the marine core can be reliably transferred to the two lacustrine records the resultant lacustrine age models reveal large changes in sediment accumulation rate at submillennial scales that escape detection in conventional age models with independent dates every 1 k y sediment accumulation rate changes occur at similar times in both lakes despite very different catchment properties low and regular accumulation rates during the holocene thermal maximum suggest regionally stable vegetated catchments followed by a stepped landscape destabilization during the transition into neoglaciation culminating with maximum sedimentation rates during the little ice age psv allows synchronization between multiple records from nearby marine and lacustrine archives providing improved age models and a means of assessing leads and lags between marine and terrestrial environments

strength of the geomagnetic field in the cretaceous normal superchron new data from submarine basaltic glass of the troodos ophiolite 1 we present here new paleointensity data from 39 sampling sites collected from the quenched margins of pillow lavas and dikes exposed within the troodos ophiolite similar to 92 ma formed during the cretaceous normal superchron cns a period of approximately 40 million years when the geomagnetic field reversed extremely infrequently if at all monte carlo simulations suggest that a minimum of 25 estimates are necessary for a reasonably robust estimate for the average field strength our data suggest a dipole strength equivalent to the present field or nearly twice the post cns average the mean and standard deviation of the dipole moment 81 43 zam 2 z 10 21 from the 57 data points compiled here agree remarkably well with those predicted from the long paleointensity record derived from dsdp site 522 the new data set for the cns suggests a picture of a strong and stable field during the period of time when it stopped reversing moreover the similarity of the cns data with the present geomagnetic field suggests that it is presently in a state of unusual polarity stability

formation of quartz silt during humid tropical weathering of dune sands abstract quartz dune sand grains in northeast australia break down in situ under humid tropical weathering conditions to form substantial amounts of silt fragmentation appears to occur primarily due to silica solution along microfractures and dislocation structures in grains which have experienced tectonic deformation prior to deposition the surface textures of quartz grains viewed with the sem exhibit a close dependency on crystallographic properties in the b and c horizons of some weathered late pleistocene dunes silt forms up to 10 of the bulk sediment local remobilisation of such deposits by wind allows selective removal of the silt which is later deposited as a thin surficial sheet in more sheltered areas downwind these observations provide further evidence that weathering processes provide a major mechanism of silt formation and are an important factor to be considered in relation to the origin of loess and siltstones

secular variation of the direction of the ancient geomagnetic field for loyang region china abstract curves of the variation of the inclination and declination of the geomagnetic field for the loyang region during the last 2400 years are presented an i d diagram of secular variation like that for london has been drawn for loyang

experimental investigation of silt formation by static breakage processes the effect of temperature moisture and salt on quartz dune sand and granitic regolith weathering simulations carried out using a climatic cabinet have demonstrated that diurnal temperature and humidity variations typical of those occurring in warm desert environments are ineffective in causing static breakage of quartz dune sand and polymineralic regolith sand grains wetting and drying combined with temperature variations was also found to be a relatively ineffective weathering process these results suggest that crack tip processes are insignificant where mineral grains are not subject to static loading sodium sulphate weathering was found to cause slight damage to quartz dune sand grains and major damage to first cycle regolith grains feldspars and mica in the regolith sands were more susceptible to salt action than quartz salt weathering of the regolith sands produced substantial quantities of silt in the size range typically found in natural loess deposits

genesis of giant sinkholes and caves in the quartz sandstone of sarisarinama tepui venezuela abstract quartz sandstone of the sarisarinama massif in venezuela hosts the world biggest collapse dolines in quartz rich lithologies with volumes up to some millions of cubic meters due to extremely complex logistics required to reach the massif the genesis of these depressions and of the underlying caves has never been studied in detail the lack of field campaigns and extended data has fostered a decade long scientific debate on whether their origin was due to epigenic or hypogenic processes this study integrates petrological structural and hydrochemical observations including analyses of silica concentration ph conductivity of surface and cave waters ec to investigate the speleogenetic processes acting underground petrographic and compositional analyses of the host rock mataui formation show that in the sarisarinama region quartz sandstones are regularly characterized by clay interlayers with significant content of pyrophyllite and kaolinite and minor amount of iron hydroxides compared to surface waters subsurface infiltration along vertical fractures and fault planes show enrichment in silica higher ph and lower ec confirming that chemical weathering is effective underground provoking intergranular silica dissolution along structural discontinuities the weathering of the clay and iron hydroxide interlayers guides the speleogenesis weakening specific stratigraphic levels and causing the collapse and fragmentation of the more resistant quartz sandstone strata the initial void created by piping of the loose sand released by quartz sandstone weathering can migrate upwards by means of roof and wall breakdown this chain of events eventually triggers a collapse at the surface which generates a circular or squared sinkhole the weathering acts mainly along the dominant fracture networks showing a clear guidance by regional tectonics these speleogenetic controls rule out the hypothesis of a hypogenic origin of the simas suggesting a primary role of long term epigenic chemical weathering and mechanical erosion guided by joints weak clay and iron hydroxide interlayers followed by subsequent massive collapses

a new approach for geomagnetic archaeointensity research insights on ancient metallurgy in the southern levant we present results from an archaeointensity investigation based on a relatively unexploited recording medium copper slag deposits together with a recently improved experimental design for the archaeointensity experiment we demonstrate the applicability of this medium as well as other archaeometallurgical artifacts for the study of the ancient geomagnetic field intensity in addition to archaeointensity data from well dated archaeological contexts we obtained reliable archaeointensity results from poorly dated or contentious archaeometallurgical sites in the southern levant these results shed new light on the dating of these sites among them the copper smelting installation of timna 39b a site that has important implications for the beginning of metallurgy during the fifth millennium bce the paper also aims to introduce archaeointensity research to the archaeologist scholar and to encourage further collaboration between the disciplines in future research

new constraints on the variation of the geomagnetic field during the late neolithic period archaeointensity results from sichuan southwestern china we have carried out an archaeomagnetic study on a late neolithic locality liujiazhai in sichuan southwestern china we pull together various dating techniques including radiocarbon analysis optically stimulated luminescence dating stratigraphic information as well as archaeological and archaeomagnetic estimations to constrain the age of the studied samples rock magnetic results indicate thermally stable fine grained magnetite or titanomagnetite as the dominant magnetic carriers more than half of the specimens 141 246 in the paleointensity experiment pass the selection criteria and are considered to record robust intensity values the virtual axial dipole moments range from approximately 2 8 to 7 8 1022 am2 with an average of 5 9 1022 am2 indicating that the geomagnetic intensity around 3000 before the common era b c e is overall lower than the present field intensity 9 8 1022 am2 of this area the new results from liujiazhai are generally consistent with the published data of similar age but deviate from the only available model of cals10k 1b at certain time periods making them important for future improvements of the model those data are significant for constraining the variation of geomagnetic field intensity between 3100 and 2600 b c e and improving the regional model of eastern asia

satellite based estimates of sea ice volume flux through fram strait sea ice volume fluxes through fram strait arctic ocean are estimated for the two icesat measurement periods in february march and october november 2003 by combining sea ice area fluxes determined from space borne microwave observations with estimates of the sea ice thickness distribution inferred from measurements of icesat s geoscience laser altimeter system glas instrument the thickness is derived from icesat data by converting its surface elevation measurements into an ice freeboard estimate combined with prior information about ice density and snow depth and density the freeboard is converted into ice thickness uncertainties in freeboard estimates due to geoid model errors are reduced through the use of the recent geoid from the arctic gravity project missing information about the ocean circulation and ocean tides is approximated locally by interpolating the sea surface height linearly between open leads meridional ice volume fluxes estimated for 798 n using ice drift observed by amsr e quikscat amount to 168 km 3 236 km 3 and 62 km 3 77 km 3 for 30 day periods in february march and october november 2003 respectively these values lie in the range of previous results from similar studies but are considerably smaller than the average ice flux during the 1990s most likely because of a smaller ice drift speed during 2003

palaeomagnetic investigations on lake sediments from ne china a new record of geomagnetic secular variations for the last 37 ka summary detailed palaeomagnetic investigations were carried out on two 23 m long sediment cores from erlongwan maar lake ne china the sediment composition of both cores is nearly identical based on a macroscopical inspection of the cores 410 graded layers intercalated into the laminated sediments were identified measurements of the anisotropy of the magnetic susceptibility revealed that these layers have not disturbed the sediment structure in general but only in intervals where their thicknesses exceeds 50 cm the age model for erlongwan is based on 15 ams 14c datings on bulk sediment showing that the sediment profile spans the last 37 ka cal bp although one of the sediment cores has been slightly deformed during core recovery similar inclination and declination records could be obtained by standard palaeomagnetic methods the stacked inclination and declination records show both variations similar to those known from palaeosecular variation records from eastern china and japan therefore the presented study is a contribution to the ongoing process of compiling a psv mastercurve for east asia

diffusion of sea ice the field of motion of sea ice is such that a lagrangian element will be progressively deformed the deformation can be resolved into a smooth part analogous to the distortion of a highly viscous fluid plus a random and discontinuous part having some similarity to the random motion of a turbulent fluid and the discontinuous motions of plate tectonics the lagrangian element spreads out at a rate determined by the mean field and by the random field but the mean field usually is more important the importance of the random field is that it gradually mixes the lagrangian element with the surrounding ice a mechanism for this mixing is discussed the simplest mode of deformation for sea ice may be a finite shear displacement along a single crack if the ice deforms in this way first along one crack then along another and eventually along a sequence of randomly oriented cracks the result will be a complete reshuffling of the ice pack nearby points disperse compact regions become fragmented this model can be tested against observations of ice motion in terms of the relative diffusion of pairs of points the model predictions have a weak resemblance to actual ice behavior

fram strait sea ice outflow 1 we summarize 24 years 1978 2002 of ice export estimates and examine over a 9 year record the associated variability in the time varying upward looking sonar uls thickness distributions of the fram strait a more thorough assessment of the pmw passive microwave ice motion with 5 years of synthetic aperture radar sar observations shows the uncertainties to be consistent with that found by kwok and rothrock 1999 giving greater confidence to the record of ice flux calculations interesting details of the cross strait motion profiles and ice cover characteristics revealed by high resolution sar imagery are discussed the average annual ice area flux over the period is 866 000 km2 yr between the 1980s and 1990s the decadal difference in the net exported ice area is 400 000 km2 approximately half the annual average except for the years with extreme negative nao correlation of winter ice area export with the nao index remains high r2 0 62 with thickness estimates from uls moorings we estimate the average annual ice volume flux 8 years to be 2218 km3 yr 0 07 sv over the 9 year uls ice thickness data set there is an overall decrease of 0 45 m in the mean ice thickness over the entire time series and a decrease of 0 23 m over the winter months december through march correspondingly the mode of the my ice thickness exhibits an overall decrease of 0 55 m and a winter decrease of 0 42 m these are significant trends whether these trends are indicative of the thickness trends of the arctic ocean is examined as the time varying behavior of the monthly uls thickness distributions can be related not only to the seasonal cycle in the basal growth and melt but also to the magnitude and pattern of ice motion in the arctic ocean and the proximity of the uls moorings to the ice edge

the greenland sea jet a mechanism for wind driven sea ice export through fram strait 1 we present a mechanism for wind driven sea ice export from the arctic ocean through fram strait for the period 1979 2007 using the output of a high resolution regional atmospheric climate model by explicitly calculating the components of the atmospheric momentum budget we show that not large scale synoptic forcing lsc but mainly thermal wind forcing thw causes the persistent northerly jet the greenland sea jet over fram strait the jet results from horizontal temperature gradients in the atmospheric boundary layer abl set up between cold abl air over the sea ice covered western greenland sea and the relatively warmer abl over the ice free eastern greenland sea from 1993 onwards we find a negative trend in thw due to a stronger response to climate warming of the abl over the sea ice covered ocean compared to that over the ice free ocean although on average lsc is smaller than thw year to year variations in lsc explain most of the interannual variability in the sea ice area flux through fram strait r 0 81 a small positive trend is found for lsc partly compensating the decrease in thw in recent years