bouguer gravity map of indonesia abstract a bouguer gravity map of indonesia on mercator projection at a scale of 1 5 000 000 and with a contour interval 20 mgal has been prepared over the past few years as part of a joint research program of the geological survey of indonesia and the university of new england armidale a new base station network was set up throughout indonesia and tied to the igsn stations at sydney and singapore a discussion of the gravity features and the tectonic implications are given the map is obtainable in folded form only from the publications department university of new england armidale n s w australia 2351 for a 5 plus postage

lead pb in old antarctic ice some from dust some from other sources 1 recently published data on amounts and isotopic compositions of lead pb and on amounts of mineral dust in pre industrial antarctic ice can be further interpreted by means of simple calculations these show that two distinct types of pb were provided by the atmosphere to the continent in varying proportions during pleistocene and holocene time one type of pb is that contained in the mineral lattices of dust it has non radiogenic isotopic proportions the other type of pb is not associated with dust minerals is more radiogenic and is consistent with an origin in emissions from ocean island volcanoes worldwide or from some antarctic volcanoes

glacial to holocene implications of the new 27000 year dust record from the epica dome c east antarctica ice core insoluble dust concentrations and volume size distributions have been measured for the new 581 m deep dome c epica ice core antarctica over the 27000 years spanned by the record microparticle measurements from 169 levels to date confirm evidence of the drastic decrease in bulk concentration from the last glacial maximum lgm to the holocene interglacial by a factor of more than 50 in absolute value and of about 26 in flux unique new features revealed by the epica profile include a higher dust concentration during the antarctic cold reversal phase acr by a factor of 2 with respect to the holocene average this event is followed by a well marked minimum that appears to be concomitant with the methane peak that marks the end of the younger dryas in the northern hemisphere particle volume size distributions show a mode close to 2 m in diameter with a slight increase from the lgm to the holocene the lgm holocene concentration ratio appears to be dependent on particle size and for diameters from 2 to 5 m it changes from 50 to 6 glacial samples are characterised by well sorted particles and very uniform distributions while the interglacial samples display a high degree of variability and dispersion this suggests that different modes of transport prevailed during the two climatic periods with easier penetration of air masses into antarctica in the holocene than during glacial times assuming that southern south america remained the main dust source for east antarctica over the time period studied the higher dust content recorded during the acr which preceded the younger dryas period represents evidence of a change in south america environmental conditions at this time a wet period and likely mild climate in south america is suggested at circa 11 5 11 7 kyr bp corresponding to the end of the younger dryas the holocene part of the profile also shows a slight general decrease in concentration but with increasingly large particles that may reflect gradual changes at the source

flux and size fractionation of 3he in interplanetary dust from antarctic ice core samples article i nfo accretion of extraterrestrial material to earth is of interest for a variety of reasons including as a possible driver of long or short term climate change and as a record of solar system events preserved in the geological record 3 he is highly enriched in extraterrestrial material and provides a useful tracer of its input into sedimentary archives previous work showed that polar ice could be a suitable archive for studying variations in extraterrestrial input additional measurements reported here confirm that the late quaternary 3 he flux derived from antarctic ice samples is similar to 3 he fluxes determined from marine sediments the mean flux from nine replicate 1 kg ice samples from the vostok ice core site 112 115 m depth age of 3800 years is 1 25 0 37 10 12 cm 3 stp cm 2 ka 1 mean 2se the large range for the 9 replicates is probably due to the small number of interplanetary dust particles idps present and illustrates that large ice samples are required for precise constraints on temporal variations in the 3 he flux size fraction experiments show that the majority of the 3 he flux is delivered by particles in the 5 10 m size range consistent with the hypothesis

volcanic layers in antarctic vostok ice cores source identification and atmospheric implications fifteen visible volcanic ash layers tephra from vostok ice cores have been analyzed for major elements trace elements and sr and nd isotope composition comparison of their geochemical signatures to lava composition from the inventory of antarctic and subantarctic volcanoes which have been active over the last 0 5 million years indicates that nine layers originate from activity of the south sandwich volcanic arc three from southern south america one from the antarctic peninsula bransfield strait and one from west antarctica marie byrd land province the large size of the tephra up to 50 m requires rapid atmospheric transfer from the volcanic centers to east antarctica rapid tropospheric transport from the southwestern atlantic penetrating east antarctica therefore predominates during the period studied whether in glacial or interglacial climatic mode in spite of the low frequency of occurrence of visible tephra layers in vostok core one event every 20 kyr the overall atmospheric pathway of these ash events appears consistent with the almost continuous advection of continental dust from south america

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

geological noise in near surface electromagnetic induction data 1 controlled source electromagnetic induction is a geophysical technique used to identify anthropogenic and natural features such as unexploded ordnance or fluid pathways in the shallow subsurface however electromagnetic responses are difficult to interpret owing to the complexity of the underlying electrical conductivity structure we show here that electromagnetic responses are fractal signals reflecting a very rough distribution of electrical conductivity apparent conductivity profiles across a floodplain and a fractured sandstone aquifer both show that the fractal properties of the surface response depend on the complexity of the causative geological structure small scale fluctuations in the response due to geological noise are inherently reproducible and are not caused by random instrumental or atmospheric effects as often assumed new approaches to modeling are required to take full advantage of the rich information content of near surface electromagnetic data

a magnetotelluric profile across central java indonesia along a n30 e striking profile in central java indonesia we recorded broadband magnetotelluric data at 8 sites in the period range 0 01 s 10000s a preliminary analysis of apparent resistivity phase and magnetic transfer function data favours a one dimensional interpretation of most sites for the upper 3 5 km of the crust and a two or three dimensional structure for the lower crust several conductive features can be distinguished i a strong ocean effect at the southern most site ii a zone of very high conductivity in the central part of the profile and iii a conductor in the north that cannot be caused by the shallow java sea we discuss tentatively causes for these anomalies the conductor in the central part of the profile is probably connected with volcanic or geothermal activity while the anomaly in the north could be an expression of processes associated with an active fault zone

interpretation of long offset transient electromagnetic data from mount merapi indonesia using a three dimensional optimization approach in the years 1998 2000 and 2001 long offset transientelectromagnetic lotem surveys were carried out at the active volcanomerapi in central java the measurements investigated the conductivitystructure of the volcanic edifice our area of interest which is belowthe summit and the upper flanks was investigated using horizontal andvertical magnetic field time derivative data from seventransmitter receiver setups because of topography and athree dimensional 3 d underground structure a 3 d interpretation isused the method optimizes few parameters of a 3 d model by a stableleast squares joint inversion of the data providing sufficientresolution capability reasonable data fits are achieved with anonhorizontally layered model featuring a very conductive basement belowdepths of 1 5 km while hydrothermal alteration is also considered wetentatively explain the high conductivities by aqueous solutions withrelatively high salt contents a large magma body or a small superficialreservoir below merapi s central volcanic complex as discussed by otherauthors cannot be resolved by the lotem data

meteoric smoke fallout over the holocene epoch revealed by iridium and platinum in greenland ice an iridium anomaly at the cretaceous tertiary boundary layer has been attributed to an extraterrestrial body that struck the earth some 65 million years ago1 it has been suggested that during this event the carrier of iridium was probably a micrometre sized silicate enclosed aggregate2 or the nanophase material of the vaporized impactor3 but the fate of platinum group elements such as iridium that regularly enter the atmosphere via ablating meteoroids remains largely unknown here we report a record of iridium and platinum fluxes on a climatic cycle timescale back to 128 000 years ago from a greenland ice core4 we find that unexpectedly constant fallout of extraterrestrial matter to greenland occurred during the holocene whereas a greatly enhanced input of terrestrial iridium and platinum masked the cosmic flux in the dust laden atmosphere of the last glacial age we suggest that nanometre sized meteoric smoke particles5 6 formed from the recondensation of ablated meteoroids in the atmosphere at altitudes 70 kilometres are transported into the winter polar vortices by the mesospheric meridional circulation7 and are preferentially deposited in the polar ice caps this implies an average global fallout of 14 5 kilotons per year of meteoric smoke during the holocene

gravity changes and internal processes some results obtained from observations at three volcanoes temporal gravity changes provide information about mass and or density variations within and below the volcano edifice three active volcanoes have been under investigation each of them related to a plate boundary mayon luzon philippines merapi java indonesia and galeras colombia the observed gravity changes are smaller than previously expected but significant for the three volcanoes under investigation and within the observation period mainly the increase of gravity is observed ranging from 1 000 nm 2 to 1 600 nms 2 unexpectedly the gravity increase is confined to a rather small area with radii of 5 to 8 km around the summit at mayon and merapi the parallel gps measurements yield no significant elevation changes this is crucial for the interpretation as the internal pressure variations do not lead to significant deformation at the surface thus the classical mogi model for a shallow extending magma reservoir cannot apply to confine the possible models the attraction due to changes of groundwater level or soil moisture is estimated along the slope of merapi exemplarily by 2 d modelling mass redistribution or density changes were evaluated within the vent as well as deeper fluid processes to explain the gravity variations the results are compared to the model incorporating the additional effect of elastic deformation

iridium enrichment in volcanic dust from blue ice fields antarctica and possible relevance to the k t boundary event abstract blue ice fields in antarctica well known as stranding zones of antarctic meteorites contain ice that is several tens to hundreds of thousand years old which records numerous events that have taken place since its formation among the most important structures on the ice fields are dust bands which are mostly of volcanic origin and consist of small volcanic glass shards and lithic fragments petrographic and chemical studies of a number of dust bands during earlier investigations have shown that significant ash layers are deposited at distances of up to several thousand kilometers from the source volcanoes samples of dust layers taken in the lewis cliff beardmore glacier area in antarctica analyzed in the course of this work for major and trace elements were identified as consisting of volcanic ash probably originating from the pleiades melbourne volcanic province northern victoria land some of these dust samples were found to contain iridium in concentrations of up to 7 5 ppb a positive correlation between ir and se as well as enrichments in as sb and other volcanogenic elements has been observed the dust samples investigated here have very small grain size consistent with the distance from the source volcanoes the small grain size of the dust suggests that the ir enrichment is a surface effect and was probably caused by condensation from a vapor phase this is the first time that significant ir enrichments have been found in volcanic dust which demonstrates that ir and possibly also other platinum group metals may be present in some volcanic ash deposits although this has been doubted by the proponents of the pure impact theory for the k t boundary event the results of this study suggest that the ir in the k t boundary clays is not necessarily of cosmic origin but alternatively may have originated from mantle reservoirs that were tapped during extensive volcanic eruptions which may been triggered by impact events

magnetization of polar ice a measurement of terrestrial dust and extraterrestrial fallout abstract laboratory induced remanent magnetization of polar ice constitutes a measurement of the magnetization carried by the ferromagnetic dust particles in the ice this non destructive technique provides a novel kind of information on the dust deposited on the surface of polar ice sheets measurements made on ice samples from greenland north grip ice core and antarctica vostok and epica dome c ice cores allowed the recognition of a fraction of magnetic minerals in ice whose concentration and magnetic properties are directly related to that of insoluble dust the source of this fraction of magnetic minerals thus appears closely related to terrestrial dust transport and deposition and its magnetic properties are informative of the dust provenance areas the rock magnetic properties of the dust may reflect distinct changes of dust source areas from glacial to interglacial periods in agreement with and adding further information to the isotopic 87 sr 86 sr and 143 nd 144 nd analyses a second magnetic fraction consists of particles of nanometric size which are superparamagnetic at freezer temperature and whose concentration is independent of the mass of aerosol dust found in the ice the source of these nanometric sized magnetic particles is ascribed to fallout of meteoric smoke and their concentration in ice was found to be compatible with the extraterrestrial fallout inferred from ir concentrations the diameter of the smoke particles as inferred from magnetic measurements is in the range of about 7 20 nm

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

climate related variations in atmospheric sb and tl in the epica dome c ice east antarctica during the past 800 000 years 1 a record of antimony sb and thallium tl from the european project for ice coring in antarctica epica dome c antarctic ice core provides the characteristics of climate related natural changes in concentrations and fluxes of these toxic elements over the time period back to marine isotope stage 20 2 800 kyr b p a strong variability in concentrations and fluxes are observed for both elements with considerably higher values during glacial maxima and lower values during intermediate and warm periods rock and soil dust accounts for on average 58 of sb and 76 of tl in ice during glacial maxima this contribution remains significant during warm periods accounting for 21 for sb and 27 for tl the contribution from volcanoes appears to be very important particularly for tl when climatic conditions become warmer with an estimated volcanic contribution of 72 for tl during interglacials the sea salt contribution is significant for sb particularly during intermediate climatic periods with an average contribution of 17 this sea salt contribution is most likely caused by greater production of sea salt from highly saline frost flowers and relatively more efficient transport of sb enriched sea ice salt from source areas on the east antarctic plateau our ice core data along with snow data recently reported from the antarctic snow layers at dome fuji shows that the present day sb flux 6 6 ng m2 yr is approximately double the highest natural level 2 8 ng m2 yr during glacial maxima throughout the last successive eight glacial interglacial cycles this result indicates that human activity has induced the greatest perturbation of the atmospheric cycle of sb ever experienced over a period of 800 kyr in the most remote area on earth

3 d modeling of the deep electrical conductivity of merapi volcano central java integrating magnetotellurics induction vectors and the effects of steep topography we derive a 3 d model of the electrical conductivity structure of merapi volcano in central java from magnetotelluric mt sounding curves and geomagnetic induction vectors topography has been considered explicitly in the model the overall magnitude of the conductivities is constrained by mt measurements while lateral variations are mainly derived from geomagnetic induction vectors the resulting model is consistent with both the mt transfer functions apparent resistivities and phases and the magnetic transfer functions induction vectors the final model consists of two 3 d structures i e a central conductor and a second conductor lying to the southwest of the summit the high conductivity material is probably hot saline water as suggested by position and lateral extent of the high conductivity material

cenozoic plate reconstruction of southeast asia abstract the india eurasia collision alone set up a series of chain reactions and caused the formation and destruction of sedimentary basins within the domain of the collision belt changes in the rate and angle of convergence between the india and eurasia plates reflect different stages of tectonic development in southeast asia for example extrusion of the indochina block induced the consumption of the pre existing proto south china sea along northeastern kalimantan and led to the eventual opening of the south china sea along the south china margin subsequent motions of the sino burma thailand malay peninsula sumatra and kalimantan blocks have produced a succession of basins stretching from north sumatra to central thailand and on to the natuna area we present reconstructions of the southeast asia region at 60 ma 50 ma 40 ma 30 ma 20 ma 15 ma 10 ma and 5 ma it is clear from the reconstructions that the impact between greater india and southeast asia took place in the northwestern part of southeast asia the duration for the impact was probably from the middle eocene to early miocene this timing is in good agreement with the dating of the main red river fault motion wu et al 1989 scharer et al 1990 since the impact between greater india and southeast asia was basically west of the burma block there is no reason to assume that the sumatra malay peninsula and kalimantan should extrude to the southeast first along the left laterally displaced mae ping and three pagodas fault zones as suggested by peltzer and tapponnier 1988 if the opening of the central thailand basins the gulf of thailand and the malay basin are taken into consideration a dextral megashear zone is required to compensate the relative motion between indochina and the malay peninsula this dextral megashear zone might even extend into western kalimantan and serve as a boundary between the indochina block and kalimantan

new results on the resistivity structure of merapi volcano indonesia derived from three dimensional restricted inversion of long offset transient electromagnetic data three long offset transient electromagnetic lotem surveys werecarried out at the active volcano merapi in central java indonesia during the years 1998 2000 and 2001 the measurements focused on the general resistivity structure of the volcanic edifice at depths of 0 5 2 km and the further investigation of a southside anomaly the measurements were insufficient for a full 3d inversion scheme which could enable the imaging of finely discretized resistivity distributions therefore a stable damped least squares joint inversion approach is used to optimize 3d models with a limited number of parameters the mode ls feature the realistic simulation of topography a layered background structure and additional coarse 3d blocks representing conductivity anomalies twenty eight lotem transients comprising both horizontal and vertical components of the magnetic induction time derivative were analyzed in view of the few unknowns we were able to achieve reasonable data fits the inversion results indicate an upwelling conductor below the summit suggesting hydrothermal activity in the central volcanic complex a shallow conductor due to a magma filled chamber at depths down to 1 km below the summit suggested by earlier seismic studies is not indicated by the inversion results in conjunction with an anomalous density model derived from arecent gravity study our inversion results provide information about the southern geological structure resulting from a major sector collapse during the middle merapi period the density model allows to assess a porosity range andthus an estimated vertical salinity profile to explain the high conductivities on a larger scale extending beyond the foothills of merapi

southern ocean sea ice extent productivity and iron flux over the past eight glacial cycles sea ice and dust flux increased greatly in the southern ocean during the last glacial period palaeorecords provide contradictory evidence about marine productivity in this region but beyond one glacial cycle data were sparse here we present continuous chemical proxy data spanning the last eight glacial cycles 740 000 years from the dome c antarctic ice core these data constrain winter sea ice extent in the indian ocean southern ocean biogenic productivity and patagonian climatic conditions we found that maximum sea ice extent is closely tied to antarctic temperature on multi millennial timescales but less so on shorter timescales biological dimethylsulphide emissions south of the polar front seem to have changed little with climate suggesting that sulphur compounds were not active in climate regulation we observe large glacial interglacial contrasts in iron deposition which we infer reflects strongly changing patagonian conditions during glacial terminations changes in patagonia apparently preceded sea ice reduction indicating that multiple mechanisms may be responsible for different phases of co2 increase during glacial terminations we observe no changes in internal climatic feedbacks that could have caused the change in amplitude of antarctic temperature variations observed 440 000 years ago

deglaciated areas of kilimanjaro as a source of volcanic trace elements deposited on the ice cap during the late holocene abstract ice fields on kilimanjaro 5895 m a s l tanzania are retreating and 85 of the ice cover has been lost since 1912 the degree to which this recession is exceptional during the holocene is uncertain as age control of the entire ice stratigraphy exists only for the very shallow and very bottom ice of the northern ice field this empirical evidence suggests that the kilimanjaro ice cover may be a persistent holocene feature while a model based on maximum possible extent and a constant shrinkage rate of the summit glaciers suggests a cyclic decay time on the order of one to two centuries today the mass balance of these ice fields is negative and no persistent ice accumulation zones are observed over multiannual scales the expanding deglaciated area within the kilimanjaro caldera should act as an increasingly larger and productive source of volcanic origin aeolian dust that is quickly deposited onto the surface of the adjacent ice fields particularly in the seasonal absence of caldera snow cover variations in the local dust influx may directly influence albedo and the energy balance of these ice fields investigating the characteristics of insoluble material entrapped in the ice remnants of kilimanjaro can thus provide insights into the extent of ice and or continuity of the summit snow cover through time here we report the trace element composition linked to the insoluble particles entrapped in holocene kilimanjaro ice in the context of the current understanding of the past ice accumulation processes including solid precipitations and ablation contributing to build the horizontal caldera ice fields for this purpose we analysed an ice core drilled to bedrock from the northern ice field thought to span the late holocene 2200 bc 1950 ad the ultra low trace element concentrations recorded in this kilimanjaro core are consistent with a generally low volcanic dust source availability i e limited exposure of the deglaciated area in the caldera and fairly continuous ice accumulation during the late holocene in contrast the maximum concentrations for most of the trace elements recorded in the surface ice section suggest that the current lack of ice accumulation on the kilimanjaro ice fields is unusual over the last 4 ka

magnetotelluric and geomagnetic modelling reveals zones of very high electrical conductivity in the upper crust of central java abstract we present results of two and three dimensional modelling of magnetotelluric and geomagnetic data from central java indonesia we adopt a hypothesis testing approach where we examine the influence of individual structural elements of competing models on the total model responses the models show that ocean anomalies do not overwhelm the signal due to strong electrical conductivity anomalies within java these highly conducting regions with resistivities of below 1 m are located in the central and northern parts of the island fitting of the geomagnetic data requires that the innermost parts of both regions consist of material with extremely low resistivity 0 2 m young sediments tephra and their alteration products can be responsible for some of the low resistivity regions at shallow depths the two zones of extremely high conductivity however are best explained as consequences of geothermal activity in the vicinity of active volcanism mt merapi in central java and by fluid or graphite enrichment along shear zones in northern java subduction zone related processes in a depth range of 70 400 km cannot be resolved because the highly conductive regions at shallow depths effectively screen deeper structures

persistent ice cloud in the midsummer upper mesosphere at high latitudes three dimensional modeling and cloud interactions with ambient water vapor 1 we infer from the observed occurrence frequency of polar mesosphere summer echoes and from the three dimensional 3 d modeling of conditions in the high latitude mesopause region that a persistent layer of icy particles exists in midsummer at all latitudes poleward of about 60 n at and a few kilometers below the mesopause all of these icy particles are transported equatorward by the climatological mean winds at the same time many of the larger icy particles possess a high enough sedimentation velocity to induce a net downward transport of water vapor both types of particle motions cause the mesopause region to become substantially dryer than without these transports of icy particles we follow the interactions between water vapor and icy particles by means of a 3 d dynamical and chemical model which includes a module for the formation growth and sublimation of icy particles for midsummer conditions and poleward of 67 n latitude the model predicts 1 a strongly dehydrated region typically above 84 km in which the water vapor mixing ratio can fall below 0 2 ppmv and 2 atmospheric regions with enhanced water vapor abundance near both the lower and the equatorward borders of the icy particle layer

structure and evolution of lithospheric slab beneath the sunda arc indonesia tomographic imaging reveals seismic anomalies beneath the sunda island arc indonesia that suggest that the lithospheric slab penetrates to a depth of at least 1500 kilometers the sunda slab forms the eastern end of a deep anomaly associated with the past subduction of the plate underlying the mesozoic tethys ocean in accord with previous studies the lithospheric slab was imaged as a continuous feature from the surface to the lower mantle below java with a local deflection where the slab continues into the lower mantle the deep slab seems to be detached from the upper mantle slab beneath sumatra this complex slab structure is related to the tertiary evolution of southeastern asia and the indian ocean region

large pt anomaly in the greenland ice core points to a cataclysm at the onset of younger dryas one explanation of the abrupt cooling episode known as the younger dryas yd is a cosmic impact or airburst at the yd boundary ydb that triggered cooling and resulted in other calamities including the disappearance of the clovis culture and the extinction of many large mammal species we tested the ydb impact hypothesis by analyzing ice samples from the greenland ice sheet project 2 gisp2 ice core across the bolling allerod yd boundary for major and trace elements we found a large pt anomaly at the ydb not accompanied by a prominent ir anomaly with the pt ir ratios at the pt peak exceeding those in known terrestrial and extraterrestrial materials whereas the highly fractionated pt ir ratio rules out mantle or chondritic sources of the pt anomaly it does not allow positive identification of the source circumstantial evidence such as very high superchondritic pt al ratios associated with the pt anomaly and its timing different from other major events recorded on the gisp2 ice core such as well understood sulfate spikes caused by volcanic activity and the ammonium and nitrate spike due to the biomass destruction hints for an extraterrestrial source of pt such a source could have been a highly differentiated object like an ir poor iron meteorite that is unlikely to result in an airburst or trigger wide wildfires proposed by the ydb impact hypothesis

does interplanetary dust control 100 kyr glacial cycles the cause of the 100 kyr glacial interglacial cycles during the past 800 kyr is one of the fundamental puzzles in paleoclimatology the widely accepted milankovitch theory relating earth s climate cycles to variations in insolation caused by periodic changes in orbital parameters has difficulties to explain the predominant 100 kyr rhythm although earth s eccentricity varies with a period of 100 kyr the resulting change in insolation is too small to produce the corresponding climate cycle by direct forcing imbrie et al paleoceanography 8 1993 699 in order to solve the 100 kyr problem muller and macdonald nature 377 1995 107 science 277 1997a 215 proc nat acad sci usa 94 1997b 8329 proposed an alternative orbital but non milankovitch mechanism attributing the glacial cycles to regular variations in the accretion of interplanetary dust particles idp caused by 100 kyr cycles in the orbital inclination of the earth to test this controversial hypothesis we study the idp accumulation in deep sea sediments from a period in the early pleistocene we find apparent 41 kyr cycles but no 100 kyr periodicity in the idp accumulation rate as there is no known mechanism to produce 41 kyr cycles in idp supply from space we conclude that the 41 kyr cycles are caused by the dynamics of sediment accumulation and that changes in the idp flux do not drive the pleistocene glacial cycles r 2004 elsevier ltd all rights reserved

internal structure of mount merapi indonesia derived from long offset transient electromagnetic data 1 a long offset transient electromagnetic lotem survey was carried out on merapi volcano indonesia in 1998 lotem data have been recorded at 41 receiver locations which cover a 10 km w e and a 15 km s n profile the signals were transmitted at four locations on the south west and north sides of merapi the data were interpreted with one dimensional 1 d inversions in addition two particular features were investigated with 3 d modeling on the south flank the magnetic field data show strong 3 d distortions consistently over the profile which can only be explained by a conductive near surface structure like a fracture filled with conductive fluids the simulation of topographic effects shows that the interpretation is not significantly affected on both profiles the most striking feature is a conductive layer of 20 m at depths of 500 1000 m below the surface and a thickness of 1 2 km the cause of the increased conductivity may be different for the summit area the intermediate zone and at the flanks below the summit in vicinity of the conduit the decrease in resistivity is produced either by hydrothermal fluids by partial melts or rocks altered by the hydrothermal system or by a combination in the intermediate zone between the conduit and the flanks either alteration or hydrothermal fluids may be the source of the conductivity increase fluids seem to be the most likely cause for the conductive layer at the flanks and the west east striking anomaly from the resistivity of the conductive layer and the typical porosity of volcanic rock we estimate fluid resistivities of 0 2 1 m

characteristics and sources of tephra layers in the epica dome c ice record east antarctica implications for past atmospheric circulation and ice core stratigraphic correlations thirteen discrete air fall tephra layers were identified in the last 200 000 yr section of the epica dome c ice record drilled in the east antarctic plateau 75 06 s 123 21 e quantitative grain size glass particle morphology and the grain discrete major element composition of the glass fraction of these layers were investigated through comparison with literature data on the rock composition of quaternary volcanic centres located within and around antarctica five tephra layers were attributed to south sandwich volcanoes in the south atlantic ocean two to south shetland volcanoes northern antarctic peninsula two to andean volcanoes and four to antarctic marie byrd land and melbourne provinces the abundance of layers originating in the southern part of the atlantic confirms that westerly atmospheric circulation spiralling towards east antarctica prevailed over the last 200 ka moreover the record of events from antarctic centres suggests that atmospheric trajectories from west to east antarctica can also be significant a few ash layers are geochemically distinct and appear equivalent to levels from vostok and dome fuji deep ice records located ca 600 km and ca 2000 km respectively from dome c on the antarctic plateau these layers provide unambiguous markers for future correlation with other antarctic ice cores and circumpolar marine climatic records they also provide reliable constraints to get a common timescale by glaciological modelling and represent a first step towards absolute ice core dating

trace metal suites in antarctic pre industrial ice are consistent with emissions from quiescent degassing of volcanoes worldwide abstract trace metals are more abundant in atmospheric load and deposition material than can be due to rock and soil dusts and ocean salt in pre industrial ice from coastal west antarctica dust and salt account for only a few percent of the lead cadmium and indium that is present in most samples less than half in any sample for these trace metals the deposition rate to the pre industrial ice is approximately matched by the output rate to the atmosphere by quiescent non explosive degassing of volcanoes worldwide according to a new estimate the basis of the match is the masses and proportions of the metals and the proportions of pb isotopes in ice and in volcano emissions the isotopic compositions of pb in ice are similar to those of a suite of ocean island volcanoes mostly in the southern hemisphere the natural baseline values for pre industrial atmospheric deposition fluxes of trace metal suites at taylor dome and the worldwide quiescent volcano emissions fluxes to which they are linked constitute a reasonably well constrained baseline component for deposition fluxes of metals in modern times

dust transport to dome c antarctica at the last glacial maximum and present day the antarctic polar ice core records show large changes in the concentration of dust over glacial interglacial timescales this paper explores how much of this variation is due to changes in the transport of dust from arid regions to the ice cores back trajectories initialised from the site of dome c ice core antarctica are calculated using an offline trajectory code forced by modelled winds output from the ukmo unified model running under present day and lgm boundary conditions as well as comparing the present day and lgm back trajectories their seasonal and interannual variability is also explored the results suggest that the patagonian provenance of the dome c dust can be understood in terms of the atmospheric transport whereas the total change in dust concentration requires changes to the sources or sinks

ultra low rare earth element content in accreted ice from sub glacial lake vostok antarctica this paper reports the first rare earth element ree concentrations in accreted ice refrozen from sub glacial lake vostok east antarctica ree were determined in various sections of the vostok ice core in order to geochemically characterize its impurities samples were obtained from accreted ice and for comparison from the upper glacier ice of atmospheric origin undisturbed disturbed and glacial flour ice ree concentrations ranged between 0 8 56 pg g 1 for ce and 0 0035 0 24 pg g 1 for lu in glacier ice and between 0 1 24 pg g 1 for ce and 0 0004 0 02 pg g 1 for lu in accreted ice interestingly the ree concentrations in the upper accreted ice ac1 characterized by visible aggregates containing a mixture of very fine terrigenous particles and in the deeper accreted ice ac2 characterized by transparent ice are lower than those in fresh water and seawater respectively we suggest that such ultra low concentrations are unlikely to be representative of the real ree content in lake vostok but instead may reflect phase exclusion processes occurring at the ice water interface during refreezing in particular the uneven spatial distribution on the order of a few cm and the large range of ree concentrations observed in ac1 are consistent with the occurrence absence of the aggregates in adjacent ice and point to the presence of solid phase concentration exclusion processes occurring within separate pockets of frazil ice during ac1 formation interestingly if the lree enrichment found in ac1 was not produced by chemical fractionation occurring in lake vostok water this may reflect a contribution of bedrock material possibly in combination with aeolian dust released into the lake by melting of the glacier ice collectively this valuable information provides new insight into the accreted ice formation processes the bedrock geology of east antarctica as well as the water chemistry and circulation of lake vostok

electromagnetic evidence for an ancient avalanche caldera rim on the south flank of mount merapi indonesia abstract long offset transient electromagnetic lotem data and vibrotem data from the south flank of mount merapi on java island indonesia are interpreted with one dimensional 1d inversions as well as two dimensional 2d forward modelling one dimensional joint inversions of several components of the electromagnetic field with occam s method reduce the number of equivalent models which were derived from inversions of single components and fit the data to a similar misfit the 1d results together with results from other geophysical measurements serve as the basic model for further 2d forward modelling the final model depicts a layering that follows the topography of the strato volcano in the depth range of 500 m to 1000 m the resistivity of the layers decreases rapidly downwards into a good conductor with resistivities below 10 m the deepest layer has a resistivity of 0 4 m which is quantitatively explained with a combination of saline fluids and hydrothermally altered minerals furthermore the final model supports a hypothesis from the interpretation of central loop tem transient electromagnetic data that there is a fault structure below the southern flank approximately 7 3 km south of the summit to the north of the fault the top of the good conductor is lowered from a depth of 500 m to 1000 m we propose that the fault structure coincides with an ancient avalanche caldera rim

interpretation of recent crustal movementsbouguer gravity map of indonesia a bouguer gravity map of indonesia on mercator projection at a scale of 1 5 000 000 and with a contour interval 20 mgal has been prepared over the past few years as part of a joint research program of the geological survey of indonesia and the university of new england armidale a new base station network was set up throughout indonesia and tied to the igsn stations at sydney and singapore a discussion of the gravity features and the tectonic implications are given the map is obtainable in folded form only from the publications department university of new england armidale n s w australia 2351 for a 5 plus postage

a 220 kyr record of pb isotopes at dome c antarctica from analyses of the epica ice core pb isotopic compositions and pb and ba concentrations are reported in epica dome c ice core samples dating to 220 kyr bp indicating that pb isotopic compositions in antarctic ice vary with changing climate 206pb 207pb ratios decrease during glacial periods with the lowest values occurring during colder climatic periods stages 2 4 and 6 and the holocene low pb concentrations 10 pg g were found during cold climatic periods ba a proxy for mineral dust was used to determine that dust usually accounts for 70 of pb in dome c ice while the remaining 30 was attributed to volcanic emissions pb isotopic compositions at dome c differ from those reported in pre industrial ice from other antarctic locations due to greater proportions of dust pb at dome c

a climatic control on the accretion of meteoric and super chondritic iridium platinum to the antarctic ice cap meteoric smoke particles msps form through the vaporization of meteoroids and the subsequent re condensation of metallic species in the mesosphere recently iridium and platinum enrichments have been identified in greenland ice layers and attributed to the fallout of msps supplying polar latitudes with cosmic matter during the holocene however the msp fallout to antarctica during the earth s climatic history remains essentially unknown we have determined iridium and platinum in deep antarctic ice from dome c and vostok dated back to 240 kyrs bp we find high super chondritic fluxes during warm periods and low meteoric accretion during glacial times a pattern that is opposite to any known climatic variation in dust fallout to polar regions the proposed explanation of this accretion regime is a weaker polar vortex during warm periods allowing peripheral air masses enriched in volcanic iridium and platinum to penetrate inland to antarctica the msp signal emerges only during cold phases and is four times lower than in the greenland ice cap where more snow accumulates this suggests that wet deposition is an important route of cosmic material to the earth s surface

chemical composition of volcanic glasses in visible tephra layers found in a 2503 m deep ice core from dome fuji antarctica twenty six ash layers were found in a 2503 m deep ice core from dome fuji station east antarctica in order to gain information about the sources of ash particles found in the layers major and trace element abundances have been measured the particles found in 21 of the 26 layers were commonly a few tens of m in size suggesting that they originated from volcanoes located in and around the antarctic on the basis of comparison of the major element compositions of these tephras with reference to volcanic rocks and ash the tephras were divided into three types 1 tholeiitic basalt to dacite 2 calc alkaline andesite and 3 trachyandesite to trachyte the source regions appear to be 1 south sandwich islands southern ocean 2 south shetland islands antarctica and or a southern part of the volcanic zone of the andes and 3 marie byrd land and or victoria land antarctica respectively the tephras found in the other five ash layers were significantly smaller 5 m suggesting that they traveled over longer distances abundances of trace elements for the alkaline tephra collected from one layer revealed a possible genetic link to volcanic rocks from marie byrd land in order to correlate between ice cores from dome fuji and vostok antarctica which are widely separated we found coeval ash layers serving as stratigraphic markers of antarctic ice cores a comparison of profiles of 18o 16o 18o and 2h 1h d for the dome fuji and vostok cores indicates that eight ash layers are equivalent in the two cores a clear correlation was found for the chemical compositions of six of these ash layers indicating a high potential for key correlation beds between the deep ice cores from dome fuji and vostok

extraterrestrial accretion from the gisp2 ice core the rate of extraterrestrial accretion for particles in the size range 0 45 m to 20 m was determined from dust concentrates extracted from greenland ice sheet project 2 gisp2 ice core samples using instrumental neutron activation analysis inaa we determined the iridium ir content of the dust following a core specific correction for terrestrial ir and assuming a chondritic ir abundance of 500 ppb we measure an average accretion rate for 0 45 m to 20 m particles over the entire earth of 0 22 0 11 109 g yr kton yr for 317 years of ice through the interval 6 to 20 ka this is consistent with the interplanetary dust accretion rate of 0 17 0 08 x 109 g yr that we derive from published 3he data for the gisp2 core accounting for particles that are larger and smaller than those detected by or experiment our best estimate of the total accretion rate including particle sizes up to about 4 cm in diameter is 2 5 109 g yr the uncertainty in this estimate is dominated by statistical fluctuations in the number of particles expected to end up in the ice core and not by measurement error based on monte carlo simulations we estimate the upper limit for total extraterrestrial accretion to earth of 6 25 109 g yr 95 confidence level this accretion rate is consistent with some estimates from micrometeorite concentrations in polar ice estimates from ground based radar studies and with accretion estimates of 3he bearing interplanetary dust particles assuming that 3he is correlated with particle surface area it is however lower than estimates based on platinum group element studies of marine sediments the conflict may indicate systematic errors with either the marine or the non marine samples departures from the assumed particle spectrum of grun and coauthors or time variable accretion rates with the early holocene period being characterized by low levels of accretion

changes in environment over the last 800 000 years from chemical analysis of the epica dome c ice core the epica ice core from dome c extends 3259 m in depth and encompasses 800 ka of datable and sequential ice numerous chemical species have been measured along the length of the cores here we concentrate on interpreting the main low resolution patterns of major ions we extend the published record for non sea salt calcium sea salt sodium and non sea salt sulfate flux to 800 ka the non sea salt calcium record confirms that terrestrial dust originating from south america closely mirrored antarctic climate both at orbital and millennial timescales a major cause of the main trends is most likely climate in southern south america which could be sensitive to subtle changes in atmospheric circulation sea salt sodium also follows temperature but with a threshold at low temperature we re examine the use of sodium as a sea ice proxy concluding that it is probably reflecting extent with high salt concentrations reflecting larger ice extents with this interpretation the sodium flux record indicates low ice extent operating as an amplifier in warm interglacials non sea salt sulfate flux is almost constant along the core confirming the lack of change in marine productivity for sulfur producing organisms in the areas of the southern ocean contributing to the flux at dome c for the first time we also present long records of reversible species such as nitrate and chloride and show that the pattern of post depositional losses described for shallower ice is maintained in older ice it appears possible to use these concentrations to constrain snow accumulation rates in interglacial ice at this site and the results suggest a possible correction to accumulation rates in one early interglacial taken together the chemistry records offer a number of constraints on the way the earth system combined to give the major climate fluctuations of the late quaternary period

trace elements in vostok antarctic ice during the last four climatic cycles li v cr mn co as rb sr ba bi and u were determined by inductively coupled plasma sector field mass spectrometry icp sfms in various sections of the 3623 m vostok deep antarctic ice core dated from 4600 to 410 000 years bp which corresponds to the last four climatic cycles back to isotopic stage 11 3 concentrations of all elements were found to be highly variable with low values during interglacial periods and warm interstadials and much higher values during the coldest periods of the last four ice ages crustal enrichment factors suggest various sources for the different elements rock and soil dust is the dominant source of v mn rb ba and u whatever the period and of li cr co sr and as during cold periods sea salt aerosol together with aeolian dust also contributes significantly to sr whereas volcanic emissions could provide a significant input for as and bi especially during warm periods