a continuous 770 year record of volcanic activity from east antarctica a 100 m ice core from site g 15 accumulation rate 0 1 m water yr 1 mean annual temperature 38 c on the mizuho plateau dronning maud land east antarctica has been analysed using the dielectric profiling dep technique the capacitance and conductance of the core were measured at ac frequencies 20 hz 300 khz the high frequency conductivity profile shows variations that are primarily related to the strong acids derived from volcanic activity the tambora 1815 eruption can be identified with the aid of an approximate chronology based on the firn densification rate other historic eruptions can then be recognised beyond about 300 years historical observations are very few however if a constant overall accumulation rate is assumed a well known eruption of 1259 a d can be found near the bottom of the core other peaks in the conductivity profile can then be assigned dates accurate to within a few years using the conductivity profile it is possible to estimate the relative acid deposition fluxes produced by the main eruptions with reasonable accuracy the estimated acid deposisition fluxes realtive to the tambora 1815 eruption of agung 1963 is 27 krakatoa 1883 25 the signal of 1601 28 and that of 1259 53

site information and initial results from deep ice drilling on law dome antarctica the aim of deep ice drilling on law dome antarctica has been to exploit the special characteristics of law dome summit i e low temperature and high accumulation near an ice divide to obtain a high resolution ice core for climatic environmental studies of the holocene and the last glacial maximum lgm drilling was completed in february 1993 when basal ice containing small fragments of rock was reached at a depth of 1196 m accurate ice dating obtained by counting annual layers revealed by fine detail 18 o peroxide and electrical conductivity measurements is continuous down to 399 m corresponding to a date of ad 1304 sulphate concentration measurements made around depths where conductivity tracing indicates volcanic fallout allow confirmation of the dating for agung in 1963 and tambora in 1815 or estimates of the eruption date from the ice dating for the kuwae vanuatu eruption 1457 the lower part of the core is dated by extrapolating the layer counting using a simple model of the ice flow at the lgm ice fabric measurements show a large decrease 250 to 14 mm 2 in crystal size and a narrow maximum in c axis verticality the main zone of strong single pole fabrics however is located higher up in a broad zone around 900 m oxygen isotope 18 o measurements show holocene ice down to 1113 m the lgm at 1133 m and warm 18 o about the same as holocene ice near the base of the ice sheet the lgm holocene 18 o shift of 7 0 only 1 larger than for vostok indicates that law dome remained an independent ice cap and was not overridden by the inland ice sheet in the glacial

comparison of depth dependent fault zone properties in the japan trench and middle america trench spatial variations in mechanical properties of the interplate thrust faults along the japan and middle america subduction zones are examined using teleseismic broadband earthquake recordings moment normalized source duration is used to probe rigidity variations along the interface we invert body waves to estimate source depth and source duration for 40 events in the japan subduction zone and 38 events in the middle america subduction zone for both areas there is a systematic decrease in source duration with increasing depth along the subduction zone interface this is most likely a result of variation in properties of sediments on the plate contact variations in source duration are greatly reduced at depths greater than 18 km in both regions enhanced spatial heterogeneity at shallow depth may reflect variations in plate roughness sediment distribution permeability of the fault zone and stress

antarctic volcanic flux ratios from law dome ice cores 3 climatestudiescenter institutefor quaternarystudies universityofmaine orono me 04469 5717 u s a abstract explosivevolcanic eruptions can inject largequantitiesof sulphur dioxide intothe stratosphere theaerosolsthat result fromoxidationof thesulphur dioxidecanpro duce significant cooling of the troposphere by reflecting or absorbing solar radiation it is possibleto obtainanestimateoftherelativestratosphericsulphuraerosolconcentrationpro duced by different volcanoes by comparing sulphuric acid fluxes determined by analysis of polaricecores here weuseanon sea saltsulphatetimeseriesderivedfromthreewell dated law dome ice cores to investigate sulphuric acid flux ratios for major eruptions over the period ad1301 1995 weuseadditionaldata fromothercorestoinvestigatesystematicspa tial variability in the ratios only for the kuwae eruption law dome ice date ad1459 5 wasthe h2so4 flux largerthanthatdepositedbytambora law domeicedate ad1816 7

mean earth ellipsoid determined from seasat 1 altimetric observations the radius and the origin of a mean earth ellipsoid have been determined using geoid heights derived from seasat 1 radar altimetric observations of the ocean surface and potential coefficients while assuming that the altimetric geoid is the best available adjustments are made to the geoid derived from potential coefficients so that the geoid differences are minimized this adjustment is then applied to the ellipsoid which best fits the geoid derived from potential coefficients solutions using two different sets of altimetric geoid heights and geoid heights based on the dod wgs 72 and geml0b potential coefficients gave a mean ellipsoid with radius a 6378134 9 m and origin shifts less than l m in the x and y components and approximately 2 5 m in the z component a description of the geoid height data used in the solutions for the ellipsoid parameters results of the solutions and a summary are presented

annually resolved southern hemisphere volcanic history from two antarctic ice cores the continuous sulfate analysis of two antarctic ice cores one from the antarctic peninsula region and one from west antarctica provides an annually resolved proxy history of southern semisphere volcanism since early in the 15th century the dating is accurate within 3 years due to the high rate of snow accumulation at both core sites and the small sample sizes used for analysis the two sulfate records are consistent with each other a systematic and objective method of separating outstanding sulfate events from the background sulfate flux is proposed and used to identify all volcanic signals the resulting volcanic chronology covering 1417 1989 a d resolves temporal ambiguities about several recently discovered events a number of previously unknown moderate eruptions during late 1600s are uncovered in this chronology the eruption of tambora 1815 and the recently discovered eruption of kuwae 1453 in the tropical south pacific injected the greatest amount of sulfur dioxide into the southern hemisphere stratosphere during the last half millennium a technique for comparing the magnitude of volcanic events preserved within different ice cores is developed using normalized sulfate flux for the same eruptions the variability of the volcanic sulfate flux between the cores is within 20 of the sulfate flux from the tambora eruption

high precision dating of volcanic events a d 1301 1995 using ice cores from law dome antarctica a record of volcanic activity over the period a d 1301 1995 has been extracted from three law dome ice cores east antarctica the record dating is unambiguous at the annual level from a d 1807 to 1995 and has an uncertainty of 1 year at a d 1301 signals from 20 eruptions are preserved in the record including those of two unknown eruptions with acid deposition beginning in a d 1810 8 and a d 1685 8 the beginning of the ice core signal from the a d 1815 tambora eruption is observed in the austral summer of a d 1816 1817 the mean observed stratospheric transport and deposition time to law dome from the eruption site is 1 5 years 0 6 years from 11 well dated eruptions the largest eruption observed in the law dome record has its maximum in a d 1460 with volcanic sulfate deposition beginning in the austral winter of a d 1459 this event is also observed in other ice core records and is attributed to the volcano kuwae with an eruption date in the range a d 1455 9 1459 9 if all sources of error are considered this is at least three years later than the date previously ascribed by dendrochronological and historical studies

a comparison between lageos laser ranging and very long baseline interferometry determined baseline lengths the nasa crustal dynamics project uses satellite laser ranging slr and very long baseline interferometry vlbi data collected and analyzed by the goddard space flight center and the jet propulsion laboratory for the measurement of geodynamic and geodetic parameters an important parameter is the determination of the baseline length or intersite distance since october 1979 baselines determined from slr data and vlbi data have been compared to help assess the accuracy of the baseline measurements from these independent techniques eight locations in the continental united states participated in the comparison westford massachusetts fort davis texas platteville colorado and quincy owens valley goldstone pasadena and monument peak california twenty two baseline lengths between these locations as determined by slr were differenced from the corresponding vlbi determinations the rms scatter about zero for the length differences is 5 2 cm with a mean of 1 0 1 1 cm and there is no apparent scale factor between these two distance determinations for this result the monument peak quincy baseline has been adjusted for tectonic plate motion by using the slr determined baseline rate for the eight other baselines crossing a plate boundary tectonic motion was not modeled if a model for this motion based upon baseline changes derived from strain rates is applied the rms scatter about zero for the 22 differences becomes 7 2 cm with a mean of 1 0 1 1 cm the above results are within the combined error budgets of the slr and vlbi baseline length determinations

geodetic radio interferometric surveying applications and results very long baseline interferometry vlbi observations collected primarily under projects polaris polar motion analysis by radio interferometric surveying and iris international radio interferometric surveying since 1980 have been used to derive polar motion and ut1 time series the typical 24 hour observing sessions using the multistation north america europe network yield estimates of the x and y components of the pole with uncertainties of 1 2 milliseconds of arc mas and ut1 with uncertainties of 0 05 0 1 ms of time preliminary experimental results indicate that ut1 can be tracked by a single vlbi interferometer to the 0 1 ms level in observing periods of about 1 hour the same observations have been used to estimate the relative rates of motion of the north american and european tectonic plates and investigate possible regional deformations of the north american plate with uncertainties of a few millimeters per year check the accuracy of the adopted nutation series to the millisecond of arc level estimate earth tide love numbers for each observatory site with uncertainties of about 1 in h and 25 in l and determine the coordinates of 20 radio sources to a few milliseconds of arc temporal variations in the apparent positions of the radio sources caused by relativistic deflections of the radio signals in the solar gravitational field have been used to estimate the relativistic deflection parameter yielding a value of 1 000 0 003

upper plate rigidity determines depth varying rupture behaviour of megathrust earthquakes seismological data provide evidence of a depth dependent rupture behaviour of earthquakes occurring at the megathrust fault of subduction zones also known as megathrust earthquakes1 relative to deeper events of similar magnitude shallow earthquake ruptures have larger slip and longer duration radiate energy that is depleted in high frequencies and have a larger discrepancy between their surface wave and moment magnitudes1 3 these source properties make them prone to generating devastating tsunamis without clear warning signs the depth dependent rupture behaviour is usually attributed to variations in fault mechanics4 7 conceptual models however have so far failed to identify the fundamental physical causes of the contrasting observations and do not provide a quantitative framework with which to predict and link them here we demonstrate that the observed differences do not require changes in fault mechanics we use compressional wave velocity models from worldwide subduction zones to show that their common underlying cause is a systematic depth variation of the rigidity at the lower part of the upper plate the rock body overriding the megathrust fault which deforms by dynamic stress transfer during co seismic slip combining realistic elastic properties with accurate estimates of earthquake focal depth enables us to predict the amount of co seismic slip the fault motion at the instant of the earthquake provides unambiguous estimations of magnitude and offers the potential for early tsunami warnings models compiled from subduction zones worldwide show that the elastic properties of the rock overlying shallow subduction megathrusts can be used to estimate potential slip possibly enabling early tsunami warnings

on differential scale changes and the satellite doppler system z shift an often neglected but important role is played by differential scale changes in transforming geodetic datums a rigorous account of scale variations in any transformation involving reference ellipsoids and its effects on geodetic heights is essential this role provides a plausible explanation for the reported z shift between the doppler defined terrestrial systems and the satellite laser ranging frames

station coordinates baselines and earth rotation from lageos laser ranging 1976 1984 satellite laser range slr measurements to lageos from may 1976 to january 1984 have been used to compute earth rotation parameters and the geocentric positions of 57 laser tracking station sites occupied during this interval the station position determinations were part of a simultaneous solution which includes lageos orbit elements in 15 day arcs and earth rotation parameters in 3 day subarcs using residuals from a 7 7 year lageos long arc lla 8402 systematic differences between the terrestrial reference frames implied by the university of texas station coordinate solution lsc 8402 and by previous solutions computed at the university of texas ut and at goddard space flight center gsfc are reviewed the new solution resolves a 0 72 m z axis difference between the terrestrial reference system origins inferred from the gsfc solution sl5 and the previous ut solution lsc 8112 the implied origins of the lsc 8402 solution and the sl5 solution are consistent to less than 60 mm in all components and after removing orientation and scale differences the coordinates for 26 common tracking stations have an rms difference of less than 80 mm the rms difference in baseline length for 22 station pairs used in the recent crustal dynamics project very long baseline interferometry vlbi slr intercomparison experiment is 50 mm between the gsfc and ut laser solutions and 40 mm between the ut laser solution and the vlbi solution the earth rotation parameters computed in 3 day intervals have an internal precision of 2 marc sec 62 mm at the earth s surface for xp and yp and 0 15 ms 70 mm at the equator for ut1 the estimated accuracy of the series based on dual baseline vlbi intercomparisons is approximately 2 marc sec for xp and yp and 0 2 ms for ut1 the effects of plate motion on the determination of the secular drift in polar motion using the 7 7 year series is shown to be at the level of 1 marc sec yr finally baseline changes have been investigated by repeated station coordinate determinations using 60 day subsets of the 7 7 year interval of the lageos data set in each 60 day solution interval orbit elements were estimated at 15 day intervals and earth rotation parameters were determined at 5 day intervals for the 4 year period beginning in january 1980 baseline length changes inferred by the successive 60 day solutions were found to be in general agreement with the motions predicted by the am1 2 plate motion model of minster and jordan

a comparison of the volcanic records over the past 4000 years from the greenland ice core project and dye 3 greenland ice cores since 1980 the electrical conductivity method ecm has been used to infer volcanic acid signals in greenland ice cores the method reveals the great majority of major volcanic eruptions including several known from historic records subsequent ion chromatographic analyses of the acid volcanic layers show the chemical composition i e the concentration of the volcanic acids h2so4 hci and hf plus e g the nonvolcanically derived hno3 while ecm data are available from a large number of shallow depth greenland ice cores covering the past 500 1500 years only the greenland ice core project grip greenland ice sheet project 2 gisp2 and dye 3 deep ice cores exist for a detailed comparative study of volcanic signals in greenland ice cores representing several thousand years comparison of the volcanic signals registered in the grip and gisp2 cores will be presented elsewhere the latter cores were augered 30 km apart and essentially represent the same atmospheric conditions such as temperature snow accumulation and chemical composition of the air here we present a comparison between the major volcanic signals over the past 4000 years in the grip core from central greenland and the dye 3 core from se greenland in order to investigate the depositional differences many of the major signals are detected in both cores but some of the differences in the records can be used to infer the latitudinal band of some eruption sites furthermore the influence of the amount of annual precipitation and glaciological postdepositional processes on the volcanic signals is discussed

f region meridional wind spectral behavior analyses of power spectral density slope and integrated power energy of upper thermospheric meridional wind for eight ionospheric stations in both hemispheres during a full year have been performed the observed spectral slope ranges between 1 2 and 3 depending on station location and epoch of the year presenting levels and variability mostly related with geomagnetic latitude however the associated spectral energy seems to depend on geomagnetic latitude as well as on season at some latitudes but in a different way from the spectral slope both parameters seem to be uncorrelated suggesting that their evolution depends on different physical mechanisms there is not significant correlation between the spectral slope and energy parameters with total meridional wind indicating that they are associated with small scale phenomena rather than with total wind

peroxide concentrations in the dome summit south ice core law dome antarctica measurements of h2o2 concentrations have been made at intervals along the full length of the dome summit south dss ice core from law dome antarctica these results show mean peroxide concentrations of approximately 37 parts per billion by mass over the past 4 kyr and a tendency for concentrations to decrease with age the rate of h2o2 decay in antarctic ice appears slower than in greenland ice and the pattern of measurements suggests an abrupt increase in concentration during the emergence from the last glacial into the holocene there is some evidence for a recent increase in h2o2 but the data so far are not conclusive detailed examination of the timing of the seasonality in h2o2 and 18o shows that peroxide extrema occur very near the solstices these seasonal curves have been used to derive atmospheric seasonal h2o2 curves based on possible air snow partitioning models these show a broad low in atmospheric concentration with a sharp peak which is again very near the summer solstice

precision geodesy using the mark iii very long baseline interferometer system very long baseline interferometry vlbi has been used to make precise measurements of the vector separation between widely separated antennas the system for acquiring and processing vlbi data known as mark iii is described tests of the system show it to have millimeter level accuracy on short baselines measurements of baselines longer than a few hundred kilometers suggest that accuracy is limited by the uncertainty in the calibration of tropospheric path delay to the level of a few centimeters vlbi experiments conducted between 1976 and 1983 have demonstrated the stability of the north american plate by showing that there is no change in the distance between easternl california and massachusetts at the level of a few millimeters per year or greater experiments made from 1980 to 1984 indicate that the distance from massachusetts to sweden is increasing by 1 7 1 cm year where the quoted standard deviation includes the estimated effects of systematic atic errors

the pinatubo eruption in south pole snow and its potential value to ice core paleovolcanic records snow samples collected in the 1996 austral summer at south pole show that sulfate concentrations in snow and by inference sulfur aerosol concentrations in the antarctic atmosphere were elevated from the end of 1991 to mid 1994 over a stable non volcanic background the new data support earlier findings that the june 1991 pinatubo eruption and the hudson eruption in the same year deposited volcanic sulfate and tephra in south pole snow and provide strong evidence of the global distribution of volcanic materials from the pinatubo eruption in this study snow samples were taken in six snow pits spatially distributed around the south pole station in order to evaluate the local spatial variability of volcanic signals due to glaciological variables such as snow accumulation rates and snow redistribution by wind after initial deposition the results indicate that pinatubo sulfate flux varies by as much as 20 throughout a 400 km2 area centered around the south pole station this glaciological variability probably represents the likely range of volcanic signals due to variations in snow deposition and post depositional changes the pinatubo eruption provides an unprecedented opportunity to estimate aerosol mass loadings by explosive volcanic eruptions found in antarctic ice cores via a quantitative relationship between aerosol mass loadings and sulfate flux in antarctic snow here the satellite estimated pinatubo so2 emission and the measured volcanic sulfate flux in snow with an assumed linearly quantitative relationship are used to calculate so2 loadings for several well known volcanic eruptions in the past 300 years covered by a shallow 42 m south pole firn core drilled in 1996 the errors for the calculated mass loadings are estimated by means of the glaciological variability associated with pinatubo volcanic flux

magnetostratigraphy of the late cretaceous to eocene sverdrup basin implications for heterochroneity deformation and rotations in the canadian arctic archipelago the temporal and spatial patterns of sedimentation in the sverdrup basin provide clues to how deformation in the canadian arctic accommodated late cretaceous eocene relative motion between greenland and north america although the sediments contain a rich assemblage of mammal and megafloral fossils dating of the sequence has been controversial some work suggests a dramatic faunal and floral heterochroneity with species appearing in the arctic 2 18 m y prior to their appearance at lower latitudes to obtain a chronostratigraphic framework for these sediments a 2 6 km section of the eureka sound group and kanguk formation on western axel heiberg island was sampled for magnetostratigraphy after removal of a pervasive modern field overprint with thermal and alternating field demagnetization a characteristic remanent magnetization chrm is isolated despite high directional dispersion the chrms form 11 distinct polarity intervals which can be correlated to chrons 34 to 24r this correlation indicates that some of these sediments are 10 m y younger than thought previously reducing the need for large scale heterochroneity sedimentation rates derived from the magnetostratigraphy suggest that an increase in basin subsidence is recorded near the middle of the section sampled a similar pattern has been reported from the eureka sound group exposed on ellesmere island we interpret this increased sedimentation as a response to crustal flexure caused by lithospheric loading during the middle paleocene c26r the loading may be related to a blind thrust system to the west of axel heiberg island that marks compression between north america and greenland driven by rapid seafloor spreading in the labrador sea the new data together with prior results indicate that most of the cretaceous canadian arctic archipelago has undergone a counterclockwise vertical axis rotation the new data are more consistent with this rotation being related to events during chron 26r rather than marking block rotations associated with the terminal eocene phases of eurekan deformation

a 4100 year record of explosive volcanism from an east antarctica ice core extensive archives of volcanic history are available from ice cores recovered from the antarctic and greenland ice sheets that receive and preserve sulfuric acid fallout from explosive volcanic eruptions the continuous detailed average 1 2 samples per year sulfate measurements of a 200 m ice core from a remote east antarctica site plateau remote provide a record of southern hemisphere volcanism over the last 4100 years this extends the volcanic record beyond the last 1000 years covered by previous antarctic ice cores an average of 1 3 eruptions per century is recorded in east antarctic snow during the last 4100 years the record shows that on average eruptions have been more frequent and more explosive during the most recent 2000 years than in the previous 2100 years intervals up to 500 years are observed in which few explosive volcanic signals are detected these periods include 2000 1500 b c no eruptions 500 1 b c two eruptions and 700 1200 a d two eruptions this new plateau remote volcanic record is compared with those from previous antarctic ice cores covering the last 1000 years in terms of dates for volcanic events the new record is in excellent agreement with the earlier records however significant discrepancies are found between these records in relative signal magnitude volcanic flux of several well known events the discrepancies among the records may be explained by the differences in the glaciology at the ice core sites analytical techniques used for sulfate and sulfuric acid measurement and the selection of detection thresholds for volcanic signals comparison with greenland ice core volcanic records indicates that during the last millennium nine large low latitude eruptions contributed significant amounts of volcanic aerosols to the atmosphere of both hemispheres potentially affecting global climate in contrast only one or possibly two such eruptions are found in the first millennium a d