geomagnetic intensity variation during the last 4000 years abstract thellier type determinations of the ancient geomagnetic intensity are reported for a large number of samples from greece comprising ancient pottery and other archaeologically dated forms of baked clay comparison is made with results for other parts of the world of about the same latitude the near east china and the western u s a these data indicate that in the time range studied variation of the geomagnetic dipole moment is unlikely to have been the dominant influence it is suggested that the westward drift of a non dipole disturbance could have been responsible

a comparison of archaeointensity results from chinese ceramics using thellier s and shaw s palaeointensity methods summary a collection of chinese ceramics covering the time period 2700 7500 bp has been investigated using adaptations of both the thellier thellier 1959 and shaw 1974 palaoeintensity techniques several rock magnetic techniques were used to investigate the magnetic properties of the samples and on the basis of these measurements some samples were rejected because of their poor magnetic behaviour anisotropy of magnetic susceptibility ams thermo remanent magnetization trm and anhysteretic remanent magnetization arm were investigated based on the relationship between arm and trm anisotropy modified arms were used for anisotropy correction twenty samples were studied using the shaw method and 34 were studied using the thellier method an acceptable agreement between the results from the two methods was found general features of the secular variation of geomagnetic intensity determined from the present study are consistent with those of the global model of mcelhinny senanayake 1982

two thousand years of archeointensity from west africa this study presents 17 archeointensity estimates from senegal and mali two neighboring countries in west africa for the period 1000 bce to 1000 ce the archeological artifacts used in this study were collected during the course of two separate projects together spanning 22 years and across 8 separate excavations a primary objective of this study was to get accurate dates hence only samples with independent age constraints from pottery style detailed stratigraphy and 14c dates were used a total of 236 specimens from 63 samples were subjected to a double heating paleointensity experiment izzi method from which 95 specimens were selected using a set of very strict selection criteria the paleointensity results were corrected for differential cooling rate effects and remanence anisotropy additionally we demonstrate the equivalence of using tensors derived from anhysteretic and thermal remanences for correcting remanent anisotropy of the specimens and use the former for the anisotropy correction our data show good agreement with the most recent paleosecular variation model but are lower than the pre existing data which are mostly from egypt and morocco the presence of substantial non axial dipolar contributions in the region is evident when virtual axial dipole moments vadms from the published literature are calculated for 20 latitudinal bands and compared with our data the average vadm values show a distinct latitudinal gradient a prominent feature of this dataset is an intensity high observed prior to 700 ce in both senegal and mali comparing this peak with existing records from regions further to the north suggests a small but significant temporal offset and is interpreted to be additional evidence for a geomagnetic field with a significant and rapidly changing non axial dipolar contribution

water induced sliding of rocks on playas alkali flat in big smoky valley nevada summary field evidence climatological data and calculations based on physics prove that tracks on the alkali flat nevada caused by sliding stones playa scrapers result from subaquatic or at least inaquatic sliding driving force usually is the hydraulic energy of surface runoff occasionally wind may contribute additional energy but even then it is mainly propagated through the water this contribution to microgeomorphology and to geomorphodynamics sheds new light on the genesis of sliding tracks and helps to revise the common view of wind as the geomorphic agent on playa surfaces

results of rock magnetic investigations and relative paleointensity determinations on lacustrine sediments from birkat ram golan heights israel i detailed rock magnetic investigations including the analysis of the laboratory installed magnetizations the measurement of hysteresis parameters and the high temperature dependency of the saturation magnetization were carried out on sediments from birkat ram golan heights israel the 550 cm long composite profile composed of three single cores is supposed to span the late holocene i e the last 4400 years at least titanomagnetites in the pseudo single domain range were identified as the main magnetic carrier minerals in the homogenous sediments the variations in concentration and grain size of the magnetic fraction are only partly reflected in the sediment lithology the relative paleointensity was estimated by normalizing the intensity of the natural remanent magnetization nrm after demagnetization at 20 mt j nrm 20 mt by different concentration parameters the median destructive field of the nrm mdf nrm is coherent with the relative paleointensity estimates indicating that a sedimentary effect has not sufficiently been removed by the normalization process the morphologies of these estimates however correspond to the archeomagnetic records from bulgaria and greece therefore a second normalization based on the linear relationship between the paleointensity estimates and the mdf nrm was applied resulting in an improvement of the records

secular variation from mexican stalagmites their potential and problems abstract as part of a feasibility study to see whether stalagmites could provide useful records of secular variation nine oriented stalagmites were collected from the states of chiapas and san luis potosi mexico of these six have yielded measurable natural remanent magnetizations nrms throughout their length the cleaned magnetizations of one of these samples were shown unequivocally to have recorded the ambient field and there is no reason to believe that this is not true of the primary magnetizations of other samples the sequences of palaeofield directions up the samples length have varying degrees of resolution and serial correlation depending on the rate of field change as averaged by the stalagmite growth rate and the thickness of the measured specimens ages and growth rates were estimated by the u th method the main problem in stalagmite palaeomagnetic analysis is a weak nrm although this may be avoided by judicious choice of the sample samples which possess significant viscous components may be cleaned by alternating field or thermally if there is sufficient magnetic material unlike many sediments stalagmites do not appear to suffer from depositional error problems dating problems may include low initial u content yielding ages with large errors and the presence of allogenic 230 th in detritus which causes older apparent ages the dating limit is 350 ka it is usually not possible to obtain long records comparable with those of most lake sediments and there are aesthetic reasons for not spoiling caves adorned with stalagmites the method is seen to be complementary to the use of sedimentary sequences to study palaeosecular variation studies of the rock magnetism of stalagmites are presented to suggest the mineral carriers of the magnetization and the origins of the natural remanence

archeointensities in greece during the neolithic period new insights into material selection and secular variation curve numerous archeomagnetic studies have provided high quality data for both the direction and the intensity of the geomagnetic field essentially in europe for the last 10 millennia in particular greece supplies a lot of archeological materials due to its impressive cultural heritage and volcanic activity so that numerous data have been obtained from burnt clays or historical lava flows the most recent greek secular variation curves are available for the last 8 millennia for the intensity and the last 6 millennia for the direction nevertheless the coverage still presents several gaps for periods older than 2500 bc in an effort to complete the greek curve and extend it to older times we present the archeointensity results from three neolithic settlements in northern greece the samples are of two different natures burnt structures from avgi 5250 150 bc and vasili 4800 200 bc as well as ceramics from dikili tash 4830 80 bc and vasili 4750 250 bc the samples have been subjected to standard rock magnetic analyses in order to estimate the thermal stability and the domain state of the magnetic carriers before archeointensity measurements surprisingly very few ceramic samples provided reliable archeointensities whereas samples from burnt structures presented a very good success rate complementary studies showed that a detailed examination of the matrix color following archeological information and classification standards can be a decisive test for pre selection of sherds in spite of these unsuccessful measurements from ceramics we obtained an intensity value of 73 5 1 1 t for dikili tash a higher value than the other data obtained in the same area during the same period however we do not have evidences for a technical artefact during the experiment the burnt structures yielded two reliable archeointensities of 36 1 1 8 t and 46 6 3 4 t for avgi and vasili respectively finally we achieved a new archeomagnetic dating for these sites by comparing these new archeointensity values combined to the directional measurements already published with the bulgarian secular variation curve these new results contribute to extend the greek secular variation reference curve towards older periods

secular variation of the earth s magnetic field in the balkan region during the last eight millennia based on archaeomagnetic data summary the first archaeomagnetic secular variation sv curves for the whole southern balkan peninsula are presented these are based on all data within a 700 km circle centred at thessaloniki 40 60on 23 00oe this data set consists of 325 directional and 625 intensity data mainly from greece bulgaria serbia and southern hungary some data from southern italy are also included the sliding moving window technique was used to calculate a continuous sv curve for intensity while the directional sv curves were calculated using the bivariate extension of the fisher statistics these curves are well constrained and clearly show the main features of the geomagnetic field variation in this region during the last eight millennia comparisons with the predictions of the scha dif 3k and scha dif 8k regional and the cals7k 2 and arch3k 1 global geomagnetic field models show a good agreement for the last 3000 years but differences for older times the balkan sv curves identify several rapid changes of the geomagnetic field in eastern europe and can be used as reference curves for archaeomagnetic dating in the balkan peninsula

an attempt to determine the absolute geomagnetic field intensity in southwestern iceland during the gauss matuyama reversal abstract we have measured the variation in the intensity of the geomagnetic field during the gauss matuyama n4 r3 polarity reversal by application of the thelliers method to specimens of lava flows from hvalfjordur district in western iceland reynivallahals mts eleven lava flows all show very similar directions corresponding to an equatorial vgp plat 2 9 n plong 81 9 e a95 4 2 k 119 twenty nine specimens from nine of the flows were pre selected for palaeointensity determination on the basis that specimens from the same drill cores showed a single component of magnetisation upon thermal or af demagnetisation and possessed low magnetic viscosity and reversible susceptibility curves upon heating at 600 650 c observation that the directional data obtained in the course of the palaeointensity experiments occasionally showed substantial non linearity indicates that a significant chemical remanent magnetization crm can be acquired in the direction of the laboratory field during heating at t for each double heating step we calculated the ratio of crm t to the magnitude of the natural remanent magnetization nrm t in the direction of characteristic remanence obtained independently from another specimen from the same core when this ratio exceeded 15 the paleointensity data was rejected in addition specimens for which the quality factor was less than 5 were rejected twelve reliable palaeointensity values were obtained from specimens representing five lava flows the results confirm that the palaeointensity was substantially reduced during the n4 r3 reversal the range of mean palaeointensity values obtained for the five flows is 8 8 to 20 5 and the overall mean is 14 8 4 6 t this corresponds to an equivalent vdm of 3 81 1 19 1022 a m2 a comparison of all thellier palaeointensity data from the r3 magnetozone in the rayinivallahals mts area reveals a progressive although irregular increase in the palaeointensity between the gauss matuyama and matuyama reunion reversals this trend is opposite to that expected from the saw tooth model of palaeointensity variations

surface velocities and ice front positions of eight major glaciers in the southern patagonian ice field south america from 2002 to 2011 abstract the patagonian ice fields are known to have undergone rapid retreat of frontal positions and significant thinning of its glaciers over the past decades however surface velocities have been measured at only a few of these glaciers thus it remains uncertain if and to what extent the glacier dynamics has changed over time and contributed to ice loss in these ice fields in this study we examine the temporal evolution of flow velocities and ice front positions at eight major glaciers in the southern patagonian ice field spi hielo patagonico sur by using advanced synthetic aperture radar asar images from the environmental satellite envisat launched in 2002 by the european space agency and advanced land observation satellite phased array type l band synthetic aperture radar alos palsar data recorded from 2002 to 2011 the examined eight glaciers include glaciar jorge montt occidental pio xi or bruggen o higgins viedma upsala perito moreno and grey not all the glaciers revealed significant changes in frontal positions and flow velocities in the study period we detected significant temporal velocity changes at glaciar upsala jorge montt occidental and pio xi among these four glaciers glaciars upsala jorge montt and occidental revealed significant acceleration and terminus retreat and were undergoing dynamic thinning the markedly different absolute velocities but equally large longitudinal near terminus stretching at the three glaciers support a calving model based on crevasse depth criteria which predict a calving position where crevasse depths are equal to ice thickness crevasse depths are controlled by the longitudinal stretching rate meanwhile glaciar pio xi revealed complex spatial and temporal evolution in surface velocities without significant retreat and its dynamics remains enigmatic

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

overview of results of spaceborne imaging radar c x band synthetic aperture radar sir c x sar the spaceborne imaging radar c x band synthetic aperture radar sir c x sar was launched on the space shuttle endeavour for two ten day missions in the spring and fall of 1994 radar data from these missions are being used to better understand the dynamic global environment during each mission radar images of over 300 sites around the earth were obtained returning over a terabit of data sir c x sar science investigations were focused on quantifying radar s ability to estimate surface properties of importance to understanding global change and focused studies in geology ecology hydrology and oceanography as well as radar calibration and electromagnetic theory studies in addition the second flight featured an interferometry experiment where digital elevation maps were obtained by interfering data from the first and second shuttle flight and from successive days on the second flight sir c x sar data have been used to validate algorithms which produce maps of vegetation type and biomass snow soil and vegetation moisture and the distribution of wetlands developed with earlier aircraft data

mass fluxes and dynamics of moreno glacier southern patagonia icefield accumulation ablation calving and flow dynamics of moreno glacier one of the main outlet glaciers of the southern patagonia icefield were studied based on field campaigns and on spaceborne radar imagery acquired by sir c x sar ice velocities and ablation were measured through two summers and one winter the ice depth was sounded seismically at a transect 8 km above the calving front showing a maximum depth of 720 m the velocity field of the terminus was derived from sir c x sar data by means of interferometry and amplitude correlation the average specific annual net accumulation is 5540 500 mm water equivalent the bottom topography of the lake and the high ratio of calving flux to net accumulation explain the remarkable stability of moreno glacier throughout this century which is in contrast to the retreat of other glaciers in this region

time variations in geomagnetic intensity 1 after many years spent by paleomagnetists studying the directional behavior of the earth s magnetic field at all possible timescales detailed measurements of field intensity are now needed to document the variations of the entire vector and to analyze the time evolution of the field components a significant step has been achieved by combining intensity records derived from archeological materials and from lava flows in order to extract the global field changes over the past 12 kyr a second significant step was due to the emergence of coherent records of relative paleointensity using the remanent magnetization of sediments to retrace the evolution of the dipole field a third step was the juxtaposition of these signals with those derived from cosmogenic isotopes contemporaneous with the acquisition of records new techniques have been developed to constrain the geomagnetic origin of the signals much activity has also been devoted to improving the quality of determinations of absolute paleointensity from volcanic rocks with new materials proper selection of samples and investigations of complex changes in magnetization during laboratory experiments altogether these developments brought us from a situation where the field changes were restricted to the past 40 kyr to the emergence of a coherent picture of the changes in the geomagnetic dipole moment for at least the past 1 myr on longer timescales the field variability and its average behavior is relatively well documented for the past 400 myr section 3 gives a summary of most methods and techniques that are presently used to track the field intensity changes in the past in each case current limits and potential promises are discussed the section 4 describes the field variations measured so far over various timescales covered by the archeomagnetic and the paleomagnetic records preference has always been given to composite records and databases in order to extract and discuss major and global geomagnetic features special attention has been devoted to discussing the degree of confidence to be put in the data by considering the integration of multiple data sets involving different techniques and or materials

paleointensity high at 9000 years ago from volcanic rocks in japan six paleointensities were determined from young lava flows of fuji and oshima volcanoes whose ages are around 8000 to 15000 years b p two lava flows which have well defined ages at 8970 390 years b p and 9260 430 years b p give large paleointensities of 67 12 and 65 6 t respectively another lava flow of less accurate age also gives large paleointensity of 63 6 t the new paleointensity data are consistent with the trend of averaged paleointensity variation in japan for the last 9000 years they form a peak of paleointensity high at around 9000 years b p comparable to the well documented one at 2000 years b p this suggests that there exists a dominant component with a characteristic period of about 7000 years in paleointensity variation large paleointensity at about 8000 10000 years ago is also reported in france and iceland paleointensity variation averaged every 1000 years for the last 14000 years is quite similar in europe and japan the sine curve like variation of paleointensity observed in both europe and japan probably reflects the nature of the dipole moment if we consider much difference of longitude between the two regions

paleointensities for 10 22 ka from volcanic rocks in japan and new zealand abstract eight volcanic rocks from japan and new zealand in the age range 10 50 ka b p were studied using the thellier method paleointensity experiment and yielded five successful results for 10 22 ka samples from the shikotsu kuttara and daisen volcanoes in japan were taken from pyroclastic flows both welded and non welded and a pumice fall deposit one of the two new zealand rocks is a rhyolite lava from the taupo volcanic zone four sites out of seven located on rocks that are not usually subjected to thellier s experiment yielded successful results which indicates that volcanic products such as pyroclastic flows and rhyolite lavas are as good a material as basalt and andesite lavas for application of the paleointensity experiment one paleointensity from new zealand at 9 9 ka is very large at about 100 t and provides support for the paleointensity high found in europe and japan 1 2 the other four paleointensities for 14 22 ka are smaller than the present day value and this agrees with the idea of a broad paleointensity minimum for the period 10 50 ka that was suggested by mcelhinny and senanayake 3 it is also noted that the variation curve of absolute paleointensity from the volcanic rocks is reasonably similar to the relative paleointensity curves from marine and lake sediments which were summarized by tauxe 4

changes in glacier dynamics under the influence of proglacial lake formation in rhonegletscher switzerland to investigate the impact of proglacial lake formation on the dynamics and evolution of glaciers we measured the ice motion of the terminal part of rhonegletscher switzerland where a lake formed in 2005 in 2009 the flow velocity near the terminus was 20 m a 1 one of the survey stakes tripled its velocity between 2006 and 2007 since the lake water pressure was consistently close to the ice overburden pressure it is likely that the high subglacial water pressure enhanced the basal ice motion the estimated flow velocity due to ice shearing was negligibly small almost 100 of the horizontal velocity near the terminus was caused by basal sliding the longitudinal strain rate was large 0 064 a 1 indicating that much of the glacier thinning was due to ice dynamics the region of ice flotation adjacent to the lake expanded between 2008 and 2009 as a result of glacier thinning accordingly a huge uplift of the surface was observed in 2009 it is clear from the vertical ice motion as well as visual observations that the marginal part of the glacier began to float the ice thinning rate in the studied area from 2008 to 2009 was 3 4 m a 1 larger than previous estimates

measurement of ice sheet topography using satellite radar interferometry detailed digital elevation models dems do not exist for much of the greenland and antarctic ice sheets radar altimetry is at present the primary in many cases the only source of topographic data over the ice sheets but the horizontal resolution of such data is coarse satellite radar interferometry uses the phase difference between pairs of synthetic aperture radar sar images to measure both ice sheet topography and surface displacement we have applied this technique using ers 1 sar data to make detailed i e 80 m horizontal resolution maps of surface topography in a 100 km by 300 km strip in west greenland extending northward from just above jakobshavns isbrae comparison with a 76 km long line of airborne laser altimeter data shows that we have achieved a relative accuracy of 2 5m along the profile these observations provide a detailed view of dynamically supported topography near the margin of an ice sheet in the final section we compare our estimate of topography with phase contours due to motion and confirm our earlier analysis concerning vertical ice sheet motion and complexity in ers 1 sar interferograms

full vector paleomagnetic secular variation records from latest quaternary sediments of lake malawi 10 0 s 34 3 e abstract we have conducted a paleomagnetic study of late quaternary sediments from lake malawi east africa in order to develop a high resolution record of paleomagnetic secular variation psv this study has recovered psv records from two cores 3p 6p in northern lake malawi 10 0 s 34 3 e the psv appears to be recorded in fine grained detrital magnetite titanomagnetite grains detailed af demagnetization of the natural remanence nrm shows that a distinctive characteristic remanence chrm is demagnetized from 20 to 80 mt which decreases simply toward the origin the resulting directional psv records for 3p and 6p are easily correlatable with 29 distinct inclination features and 29 declination features the statistical character of the psv in both cores is consistent with holocene psv noted at other holocene equatorial sites radiocarbon dating of the cores is based on 18 independent radiocarbon dates and four dated stratigraphic horizons that can be correlated into each core the final directional psv time series cover the last 24 000 years with an average sediment accumulation rate of 30 cm kyr we have also developed a relative paleointensity estimate for these psv records based on normalizing the nrm after 20 mt af demagnetization by the sirm after 20 mt af demagnetization changing sedimentation patterns complicate any attempt to develop a single paleointensity record for the entire core lengths we have developed a relative paleointensity record for the last 6000 years that has 14 correlatable features including 5 notable peaks in intensity three of these peaks are synchronous with paleointensity highs farther north in se europe sw asia egypt but two of the peaks are at times of low paleointensity farther north we interpret this to indicate that lake malawi 10 s is at least partly under the influence of a different flux regeneration region of the outer core dynamo a relative paleointensity record was also developed for 11 000 24 000 ybp the general pattern appears to be consistent with other published records but our confidence in the correlations is more limited

spatial distribution of archaeomagnetic vectors within archaeological samples from eisenerz austria summary the archaeological site near eisenerz in upper styria austria called the copper smelting site s1 was used for copper smelting in the middle bronze age 15th 13th century bc the dating of the site is based on pottery finds and has been confirmed by radiocarbon dating samples of several roasting hearths and furnaces have been collected and consolidated in order to investigate the spatial distribution and the stability of the magnetization of these materials around 500 specimens have been obtained for which the natural remanent magnetization nrm and the magnetic susceptibility have been measured with a 2g squid cryogenic magnetometer and a geofyzika kly 2 susceptibility meter respectively variations of the nrm and magnetic susceptibility with depth indicate the layer of heating and give some first evidences about the use of these soils during the smelting procedure higher values of the intensity of the magnetization as well as of the magnetic susceptibility correspond to the more intense heated layer magnetic cleaning thermal and af demagnetization has been performed in pilot samples and revealed the presence of a stable component of the magnetization the examined types of material are suitable for archaeomagnetic investigations the record and the preservation of all the necessary magnetic information provide important knowledge concerning the recent history of the earth s magnetic field

holocene paleointensities thellier experiments on submarine basaltic glass from the east pacific rise a complete description of the geomagnetic field requires both paleodirectional and paleointensity data although the paleointensity data base has grown steadily over the last three decades it remains limited in time and space the majority of data are of holocene age and come from europe furthermore it has been difficult to assess the reliability of the paleointensity determinations here we present paleointensity determinations on precisely dated holocene 0 to 3500 years old submarine basaltic glass from the east pacific rise 15 s to 22 s although hysteresis measurements and low temperature isothermal remanent magnetization irm acquisition experiments document a significant contribution of superparamagnetic grains high blocking temperatures above 400 c and curie temperatures between 490 c and 550 c indicate a single domain low ti magnetite as the carrier of the remanent magnetization this notion is further supported by the fact that saturation of remanence is achieved in moderate fields of about 200 300 mt submarine basaltic glass proves to be nearly ideal for paleointensity determinations in that it produces a high success rate for thellier experiments twenty six out of 30 samples resulted in acceptable paleointenisty determinations multiple experiments on splits from the same sample show good reproducibility the paleointensities for zero age glasses correspond precisely with the present field intensity at the site of recovery the results of the remaining samples range from 16 7 to 53 9 t with corresponding virtual axial dipole moments vadm of 3 61 1022 to 11 9 1022 a m2 the intensities vary rapidly with time excluding a westward drifting nondipole component as the source for these fluctuations basaltic glass is frequently recovered in both dredged and drilled material from the ocean floor the availability of submarine basaltic glass throughout the world oceans therefore holds great potential for a better distribution of paleointensity data through time and space

tracking a non dipole geomagnetic anomaly using new archaeointensity results from north east china summary a collection of ceramics and samples collected from north east china with ages ranging from 1000 to 7000 years have been investigated using a modified version of the shaw palaeointensity techniques shaw 1974 rolph shaw 1985 in which only partial nrms and trms pnrms and ptrms with blocking temperatures t above 300 c are used after pre selection of samples by mineral magnetic analysis a secular variation curve obtained from this study is quite consistent with previous results from other areas of china wei et af 1987 tang et af 1991 as well as with the global model of mcelhinny senanayake 1982 comparison of the chinese results with contemporaneous results from greece aitken el af 1989 has allowed us to track the movement of a large non dipole anomaly as it drifts westwards

dynamic behavior of glaciar perito moreno southern patagonia frontal oscillations since the beginning of the 20th century are known at glaciar perito moreno an eastward outlet glacier of hielo patagonico sur southern patagonia ice field in 1900 the calving front was located about 1 km from the opposite bank from 1935 to 1988 ruptures of ice dams occurred at intervals of 1 5 years although this glacier has thus oscillated it can be regarded as having been in a rather stable condition during the last half century ice thickness in the ablation area has also remained unchanged from 1990 to 1996 the near steady behavior of glaciar perito moreno may be attributed to a regulating effect of the calving rate namely a decrease in the ablation amount due to calving with a retreat of the glacier using 12 m long ablation poles ice flow velocities at the ablation area were measured several times in 1993 and 1994 the velocity in the early summer november was found to be slightly larger than the annual mean it is concluded that basal sliding is significant throughout the year at this temperate glacier with large fluctuations within a short period

variations in the geomagnetic dipole moment over the last 12 000 years summary an analysis has been made of archaeointensity data for the past 12 000 years there are 3243 results from diverent areas of the world covering the past 12 000 years of these 2203 are from the european region and 1040 are from the rest of the world the archaeointensity data set analysed in the present study is almost three times larger than that used by mcelhinny senanayake 1982 although there is no major diverence between our global data and the earlier data the data for the non european region have been improved and we now have a data set for asia

recent behaviour of glaciar upsala a fast flowing calving glacier in lago argentino southern patagonia sequential optical images of high spatial resolution were used for the firsttimeto derive surface ice velocitiesof glaciar upsala a fast moving fresh watercalv ing glacier in southern patagonia cross correlation methods applied to four landsat etm images acquired in 2000 01 yielded average velocities of around 1600 ma 1 similar to values measured in the field in november 1993 the derived velocities show almost no seasonalvariation forthe analyzedcalving termini during the periodof satel lite coverage clear readvances were detected in the autumn winter period followed by recessions during summers between 24 april1999 and14 october 2001 the glacier front hasbeen fluctuating seasonally within about 400m in contrast to the previous dramatic recession during the last 2 5years glaciar upsala west terminus had a net advance of around 300m in addition the available satellite images allowed us to determine recent calving speeds and confirm the improved calving rate water depth relationship recently proposed by incorporating new data from patagonian glaciers

high net accumulation rates at campo de hielo patago nico sur south america revealed by analysis of a 45 97 m long ice core a45 97mlongicecorewasrecoveredintheaccumulationareaof glaciar tyndall 50 59 05 s 73 31 12 w 1756ma s l campo de hielo patagonico sur southern patagoniaicefield during december1999 thefirncorewassubjectedtovisualstratigraphic observationandbulkdensitymeasurementsinthefield andlatertoanalysesofwaterisotopes d 18 o dd major dissolved ions and snow algalbiomass the drillhole remained dry down to about 43m depth where a water soaked layer appeared seasonal cycles were found for d 18 o dd and the d excess although the amplitudes of the cycles decreased with depth major dissolved ions na k mg 2 ca 2 cl so4 2 and algal biomass exhibit rapid decreases in the upper 3m probably due to meltwater elution annual increments defined by the d 18 o and d excess peaks suggest that the minimum net accumulation rates at this locationwere17 8ma 1 in1997 98 1998 99 and 411 0ma 1 in1998 99 1999 2000 theseare much higher valuesthanthose previously obtained frompast ice core studies in patagonia but are of the same order of magnitude as those predicted from various observations in ablation areas of patagonian glaciers

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

ice thickness of the northern half of the patagonia icefields of south america from high resolution airborne gravity surveys author s gourlet p rignot e rivera a casassa g abstract 2015 american geophysical union all rights reserved we employ high resolution high precision helicopter borne gravity observations of the northern npi and southern patagonia icefields spi south america to infer ice thickness and bed topography using a three dimensional model constrained by fjord and lake bathymetry and a land ice mask the results reveal thicker ice than the reflecting horizon of radar sounders with 1 km deep ice for glaciar san rafael and colonia npi and 1 5 km deep ice for glaciar occidental spi these bedrock troughs channelize fast motion of ice from the plateaus combining ice motion and thickness we calculate balance accumulation levels of 3 6 m yr water equivalent for the plateaus bed elevation remains below sea lake level 15 20 km inland for jorge montt and o higgins which favors retreat and is at sea level for san rafael which halted its retreat the results demonstrate the utility of airborne gravity surveys for providing critical data on ice volume bed elevation and balance accumulation of temperate ice masses

the role of microbial mats in the movement of stones on playa lake surfaces abstract this paper sheds light into the debated mechanisms that move rocks across low gradient surfaces during storm episodes microbial mats are recognised to play a crucial role in sediment destabilisation and the subsequent motion of rocks in a playa lake from central spain widespread countless scars are present on the playa lake sediment surface each terminating at a stone and or a mound of overfolded fragments of microbial mats all available objects including cobble sized stones on the surface were transported for several metres leaving behind furrow like tracks the starting point of the tracks was found underwater on a surface veneered by microbial mats poorly attached to the substrate the flotation and transportation of the microbial upper layer by wind generated water currents are suggested to be a critical element promoting the destabilisation and subsequent transportation of the attached sediment including the rocks the sudden exposure of bubble separated sediment is also envisaged as a source of buoyancy required to lift out the rocks at the starting point of the tracks and to reduce the friction on the base of the rock at the end of the tracks the rocks and the sediment mounds often overlap which reveals that rocks were embedded and transported by sediment rafts across the playa lake surface the combination of the specific sedimentary and weather conditions involved in the transportation of rocks occurs periodically in mudflats the implications are that this is not a local phenomenon but rather is a geographically widespread sedimentary process that may have occurred repeatedly throughout geological time the effects of storm episodes can be inferred in ancient mudflat deposits by the assemblage of variably sized stones and microbial mat related structures

a comparison of archaeointensity results from chinese ceramics using microwave and conventional thellier s and shaw s methods palaeo and archaeointensity determinations of the geomagnetic field are limited by mineralogical alteration that may occur when samples are heated in the laboratory to produce a trm thellier thellier 1959 shaw 1974 by using microwave excitation of the magnetic grains we have been able to create a trm without significantly heating the bulk samples thereby avoiding thermal alteration walton et al 1993 shaw et al 1996 when applied to peruvian ceramics in a manner analogous to the standard thellier method the microwave technique was found to reduce the scatter dramatically in the archaeointensity results shaw et al 1996 in the present study we apply this microwave technique to a collection of chinese ceramics covering the time interval 2700 7500 yr bp these ceramics have already been investigated using adaptations of both thellier s coe 1967 and shaw s rolph shaw 1985 palaeointensity methods yang et al 1993a although an acceptable agreement was found between those two methods the equivalent virtual axial dipole moments vadms were significantly lower than for the global model of mcelhinny senanayake 1982 the present study using the microwave technique with cooling rate correction has provided more consistent vadms and is much closer to the global model

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

archeoint an upgraded compilation of geomagnetic field intensity data for the past ten millennia and its application to the recovery of the past dipole moment 1 this paper presents a compilation of intensity data covering the past 10 millennia archeoint this compilation which upgrades the one of korte et al 2005 contains 3648 data and incorporates additional intensity and directional data sets a large majority of these data 87 were acquired on archeological artifacts and the remaining 13 correspond to data obtained from volcanic products the present compilation also includes important metadata for evaluating the intensity data quality and providing a foundation to guide improved selection criteria we show that 50 of the data set fulfill reasonable reliability standards which take into account the anisotropic nature of most studied objects potsherds the stability of the magnetization and the data dispersion the temporal and geographical distributions of this sub data set are similar to those of the main data set with 72 of the data dated from the past three millennia and 76 obtained from western eurasia approximately half of the selected intensity data are associated with at least an inclination value to constrain the axial and full dipole evolution over the past three millennia requires that we avoid any overrepresentation of the western eurasian data we introduce a first order regional weighting scheme based on the definition of eight widely distributed regions of 30 width within which the selected data are numerous enough the regional curves of virtual axial dipole moments vadm and of mixed vadm virtual dipole moments vdm averaged over sliding windows of 200 years and 500 years testify for strong contributions from either equatorial dipole or nondipole components the computation of global vadm and mixed vadm vdm variation curves assuming an equal weight for each region yields a dipole evolution marked by a distinct minimum around 0 b c a d followed by a maximum around the third fourth century a d a second minimum is present around the eighth century a d this variation pattern is compatible with the one deduced from earlier more

sliding stones of racetrack playa death valley usa the roles of rock thermal conductivity and fluctuating water levels abstract on occasion racetrack playa in death valley national park becomes flooded and temperatures then drop appreciably below freezing the thermal conductivity of rock is greater than that of water so heat is conducted from a partially submerged rock faster than from water consequently a collar of thicker ice forms at the water surface a layer of ice forms on more deeply submerged parts of the rock and playa sediment beneath the rock may even become frozen to it while this occurs only a surface layer of ice forms on water away from the rock once the ice becomes thick enough perhaps only 5 10 mm either the buoyancy of the ice or additions of water to the playa by rain snow melt or groundwater seepage then reduce the normal force between the rock and the playa to the point where wind shear can move the ice sheet with its entrained rocks making trails stanley 1955 reid et al 1995 after the ice melts rocks are left at the ends of the trails sometimes atop a pedestal of silt a renewed increase in water level on the playa before the ice melts may lift a rock completely free of the playa surface and whisk it away leaving a rockless trail during a movement event changes in rock orientation or water depth may result in changes in width along the track rock speeds are likely tens to hundreds of millimeters per second

eight thousand years of geomagnetic field intensity variations in the eastern mediterranean 1 twenty new intensity determinations of the ancient geomagnetic field have been obtained from groups of potsherds and brick fragments from syria these artifacts archeologically well dated from 6000 b c to approximately a d 1200 have been analyzed using the thellier and thellier 1959 method as modified by coe 1967 intensity values have been corrected for the effects of anisotropy of thermal remanent magnetization and cooling rate our results indicate that field intensities were moderate in syria from 6000 b c to 3500 b c with values of 30 40 t there was a significant increase in intensity by a factor of 2 from 3500 b c to 700 b c which was interrupted by a moderate decrease between 2550 b c and 1750 b c during more recent periods our results show an intensity minimum approximately a d 200 and a maximum around the tenth century comparison with different data sets from the eastern mediterranean and central asia shows that geomagnetic field intensity variations were consistent at this large regional scale at least over the last 5 millennia

archeomagnetism of ontario potsherds from the last 2000 years an archeomagnetic study was carried out on potsherds samples from sites in ontario with ages ranging from a d 90 to a d 1640 as determined by 14c dating thellier double heating paleointensity experiments were performed in air on 65 specimens of 52 samples from seven sample sets reliable paleointensity estimates were obtained for 49 specimens alternating field and thermal demagnetization temperature dependence of weak field susceptibility and hysteresis measurements indicate that magnetite of pseudo single domain grain size is the carrier of natural remanent magnetization the paleointensity results follow a half cycle sine curve with a steady decrease from 54 0 5 9 t to 37 6 5 7 t between a d 90 and a d 885 and a monotonic increase from 52 0 6 1 t to 59 4 1 7 t between a d 1200 and a d 1900 the paleointensities determined yield virtual axial dipole moments vadms of the earth s magnetic field that agree well with those from other parts of north america except between a d 900 and a d 1400 when they are systematically lower this discrepancy is probably caused by a substantial non dipole field in southwestern north america from the tenth to the fifteenth century since secular variation studies using potsherds from arizona and lake sediments from minnesota show different inclination variations during that period

deformation of the baige landslide tibet china revealed through the integration of cross platform alos palsar 1 and alos palsar 2 sar observations

information on past solar activity and geomagnetism from 10 be in the camp century ice core a nearly continuous record of the concentration of 10be from ice core data is compared with the tree ring derived record for 14c over the same period and it is found that short term trends in these data sets provide a record of solar activity no definitive relationship between the long term trends and the geomagnetic dipole moment is found

rock magnetic and archaeomagnetic investigations on archaeological artefacts from maharashtra india figure s1 irm acquisition curves reveal the presence of soft magnetic mineral saturated between 100 and 300 mt a few samples reveal a dominant high coercivity anti ferromagnetic signal whereas the remaining samples irm curves indicate the occurrence of a low coercivity mineral perhaps magnetite and or titano magnetite