cenozoic global ice volume and temperature simulations with 1 d ice sheet models forced by benthic δ18o records variations in global ice volume and temperature over the cenozoic era have been investigated with a set of one dimensional 1 d ice sheet models simulations include three ice sheets representing glaciation in the northern hemisphere i e in eurasia north america and greenland and two separate ice sheets for antarctic glaciation the continental mean northern hemisphere surface air temperature has been derived through an inverse procedure from observed benthic 18o records these data have yielded a mutually consistent and continuous record of temperature global ice volume and benthic 18o over the past 35ma the simple 1 d model shows good agreement with a comprehensive 3 d ice sheet model for the past 3 ma on average differences are only 1 0 c for temperature and 6 2m for sea level most notably over the 35ma period the reconstructed ice volume temperature sensitivity shows a transition from a climate controlled by southern hemisphere ice sheets to one controlled by northern hemisphere ice sheets although the transient behaviour is important equilibrium experiments show that the relationship between temperature and sea level is linear and symmetric providing limited evidence for hysteresis furthermore the results show a good comparison with other simulations of antarctic ice volume and observed sea level

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

the use of multifrequency and polarimetric sir c x sar data in geologic studies of bir safsaf egypt abstract bir safsaf within the hyperarid core of the sahara in the western desert of egypt was recognized following the sir a and sir b missions in the 1980s as one of the key localities in northeast africa where penetration of dry sand by radar signals delineates previously unknown sand buried paleodrainage valleys radar rivers of middle tertiary to quaternary age the bir safsaf area was targeted as a focal point for further research in sand penetration and geologic mapping using the multifrequency and polarimetric sir c x sar sensors analysis of the sir c x sar data from bir safsaf provides important new information on the roles of multiple sar frequency and polarimetry in portraying specific types of geologic units materials and structures mostly hidden from view on the ground and on landsat tm images by a relatively thin but extensive blanket of blow sand basement rock units granitoids and gneisses and the fractures associated with them at bir safsaf are shown here for the first time to be clearly delineated using c and l band sar images the detectability of most geologic features is dependent primarily on radar frequency as shown for wind erosion patterns in bedrock at x band 3 cm wavelength and for geologic units and sand and clay filled fractures in weathered crystalline basement rocks at c band 6 cm and l band 24 cm by contrast quaternary paleodrainage channels are detectable at all three radar frequencies owing among other things to an usually thin cover of blow sand the sir c x sar data investigated to date enable us to make specific recommendations about the utility of certain radar sensor configurations for geologic and paleoenvironmental reconnaissance in desert regions

distribution of high field strength elements y zr ree hf ta th u in adjacent magnetite and chert bands and in reference standards fer 3 and fer 4 from the temagami iron formation canada and the redox level of the neoarchean ocean abstract adjacent magnetite and chert bands and reference standards fer 3 and fer 4 from the neoarchean temagami iron formation if show shale normalized rare earth and yttrium rey patterns with low nd yb ratios and positive eu gd and y anomalies indicating that they formed as marine chemical sediments in contrast to previous claims none of the samples shows any ce anomaly indicating the absence of oxidative ce rey decoupling and arguing against oxic conditions in the wider vicinity of the neoarchean temagami seabasin the distribution of zr hf and ta yields zr hf and hf ta ratios that differ from those of chondrites average upper continental crust and local shales suggesting that the temagami if is the only case observed so far in which a significant fraction of these elements is non detrital but sourced from seawater if neoarchean seawater was characterized by zr hf and hf ta ratios similar to those of modern seawater these ratios point towards preferential scavenging of hf over zr and ta as is typical of the modern ocean similar to the 2 9 ga old mozaan if in the pongola supergroup south africa the temagami if shows low th u ratios that differ from those of the respective local shales and from that of average upper continental crust decoupling of u and th results from u4 oxidation in the earth s surface system and fractionated th u ratios in these marine chemical sediments are therefore at odds with the lack of ce anomalies this suggests a different redox sensitivity of the two paleo redox proxies th u and ce rey and demonstrates that the temagami if and the mozaan if warrant further study of other paleo redox proxies

correcting the cenozoic δ18o deep sea temperature record for antarctic ice volume abstract the oxygen isotope signal in benthic foraminifera from deep sea cores is mainly determined by deep ocean temperature and land ice volume separating the temperature and ice volume signals is a key step in understanding the evolution of cenozoic climate except for the last few million years fluctuations in land ice volume were determined mainly by the size of the antarctic ice sheet here a simplified antarctic ice sheet model and composite deep sea oxygen isotope records are used to derive a deep sea temperature history for the cenozoic the ice sheet model is forced with the oxygen isotope record which is instantaneously corrected for the calculated ice volume therefore the resulting deep sea temperature and antarctic ice volume curves are mutually consistent the temperature record of lear et al science 287 2000 269 derived from the mg ca ratio in benthic calcite is also used to force the ice sheet model the resulting ice volume does not agree well with the ice volume history inferred by lear et al from a comparison of mg ca and 18 o records the most important points emerging from this study are the cenozoic 18 o record from benthic forams is a truly mixed signal ice volume and deep sea temperature contribute equally to the variance for the period of 45 to 30 ma ago 18 o temperatures are significantly lower than mg ca temperatures rapid nonlinear build up of a continental scale ice sheet on the antarctic continent can easily occur for a linear cooling rate it is unlikely that the method of lear et al provides a reliable measure of ice volume the cooling rate at the beginning of the pliocene is much larger in the 18 o temperature curves than in the mg ca temperature curve

the response of a simple antarctic ice flow model to temperature and sea level fluctuations over the cenozoic era an ice flow model is used to simulate the antarctic ice sheet volume and deep sea temperature record during cenozoic times we used a vertically integrated axisymmetric ice sheet model including bedrock adjustment in order to overcome strong numerical hysteresis effects during climate change the model is solved on a stretching grid the cenozoic reconstruction of the antarctic ice sheet is accomplished by splitting the global oxygen isotope record derived from benthic foraminifera into an ice volume and a deep sea temperature component the model is tuned to reconstruct the initiation of a large ice sheet of continental size at 34 ma the resulting ice volume curve shows that small ice caps

a drastic lower miocene regolith evolution triggered by post obduction slab break off and uplift in new caledonia a lower miocene coarse conglomerate that crops out in the nepoui peninsula does not represent the base of the marine transgression that followed obduction in new caledonia instead the conglomeratic alluvial fan that contains peridotite cobbles and reworked weathering products records a short lived episode of terrestrial erosion intercalated between two intervals of subsidence marked by marine carbonate deposition considering the miocene sea level evolution reported in the literature it is concluded that neither lower miocene transgression nor erosion were driven by sea level variation in contrast a southeastward propagating slab tear that initiated at the latitude of the high pressure low temperature metamorphic complex of northern new caledonia likely generated east to west tilting of new caledonia subsidence along the west coast and hence fringing reef development together with moderate erosion of older regolith coincidence between conglomerate deposition and hence prominent erosion that closely followed emplacement of postobduction granitoids influenced by a slab window suggests a genetic link therefore it is concluded that short lived lower miocene erosion was due to slab breakoff and subsequent uplift that occurred at 22 ma lower miocene erosion profoundly dissected the peridotite nappe and in the northern half of new caledonia only left isolated klippes along the west coast

the stability of zincian spinels in sulfide systems and their potential as exploration guides for metamorphosed massive sulfide deposits zincian spinel zn fe mg al 2 o 4 is found in a variety of geologic settings including metamorphosed massive sulfide deposits aluminous metasediments pegmatites and marbles many spinels in and near metamorphosed massive sulfides have formed by desulfidation and oxidation reactions that involve members of the system zn fe al si s o experimental reversals of the simplified reaction zns fes 2al 2 o 3 o 2 znal 2 o sub 4 feal 2 o 4 s 2 using hydrothermal techniques have been obtained at 2 and 5 kb and various temperatures using fe sub 1 x s fes 2 fe 3 o 4 as a buffer calculated positions of the spinel sphalerite equilibria in f sub o 2 f sub s 2 x space for ideal behavior along the znal 2 o 4 feal 2 o 4 join as is suggested by octahedral site preference energies agree with experimental results and theoretical calculations depending on the choice of the free energy of formation of hercynite the compositions of spinels in equilibrium with sphalerite and either pyrite or pyrrhotite become more zn enriched with increasing f sub s 2 and f sub o 2 values and can be used as a measure of f sub o 2 during metamorphism spinel associated with metamorphosed massive sulfide deposits marbles and aluminous metasediments is enriched in the gahnite znal 2 o 4 spinel mgal 2 o 4 and hercynite feal 2 o 4 molecules respectively whereas spinel associated with pegmatites is depleted in the spinel molecule such variability in composition constitutes a potential exploration guide for metamorphosed massive sulfide deposits

processes of buildup and retreat of the greenland ice sheet sensitivity experiments were conducted to study the influence of several physical processes on the evolution of the greenland ice sheet over the last 250 000 years the experiments were carried out by means of a three dimensional thermodynamical model the mass balance is modeled by a surface energy balance model this means that variations in orbital parameters following from the astronomical milankovitch theory can be incorporated in the ablation calculations it is shown that with regard to the greenland ice sheet variations in shortwave radiation are only of minor importance for the changes in volume over time calculations of the various components of the energy balance under glacial and interglacial conditions show that the changes in absorbed shortwave radiation resulting from changes in orbital parameters are considerably smaller than the variations in the sensible heat flux caused by temperature variations thermodynamics are only of importance for the volume changes of the ice sheet if the climate is on average stable over a long period in between 110 kyr b p and 20 kyr b p the ice volume increased slowly due to the cooling of the ice which resulted in a higher effective viscosity and thus a thicker ice sheet the long response time of the thermodynamics means that the thermodynamics cannot play a crucial role during transition from a glacial to a deglacial period which occur typically within several thousands of years the mass balance height feedback has an important function in the buildup of the ice sheet after a warm period like the eemian without isostatic bedrock compensation the ablation will remain very high in some marginal parts yielding a considerably smaller ice sheet volume for the last glacial period

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

x sar interferometry first results repeat pass interferometry data were acquired during the first and second sir c x sar missions in april and october 1994 this paper presents the first results from x sar interferometry at four different sites the temporal separations were one day and six months at two sites the coherence requirements were met resulting in high quality interferograms a digital elevation model in ground range geometry has been derived the limitations of the x sar interferometry are discussed

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

modeling the oxygen isotopic composition of the north american ice sheet and its effect on the isotopic composition of the ocean during the last glacial cycle contribution to the change of seawater d 18 o dw between the last glacial maximum lgm and the holocene and to evaluate the effect of nonequilibrium isotopic composition of the nais on the relationship between ice volume variations and the ocean isotopic enrichment the enrichment due to the nais at the lgm was 0 63 corresponding to 60 of the lgm sea level lowstand and to a mean d 18 o of the nais of approximately 31 the modeled nais volume variations and the induced dw changes over the past 120 000 years indicated no significant time lag the inaccuracy associated with linearly inferring ice volume variations from dw changes was generally less than 10 citation sima a a paul m schulz and j oerlemans 2006 modeling the oxygen isotopic composition of the north american ice sheet and its effect on the isotopic composition of the ocean during the last glacial cycle geophys res lett 33 l15706 doi 10 1029 2006gl026923

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

local and regional trends in plio pleistocene δ18o records from benthic foraminifera we present new orbital resolution pliocene pleistocene benthic stable oxygen isotope 18ob records from ocean drilling program sites 1264 and 1267 from walvis ridge in the southeast atlantic we compare long term 250 kyr interbasin 18ob gradients between pacific and north atlantic regional stacks as well as intra and interbasin gradients from the perspective of walvis ridge the 18ob values from sites 1264 and 1267 are almost always higher than deep north atlantic and pacific sites with large gradients 0 5 emerging abruptly at 2 4 ma and persisting until 1 3 ma from this we infer the presence of a new water mass which resulted from the influence of dense 18o enriched nordic sea overflow waters via the abyssal east atlantic meanwhile long term average 18ob values in the north atlantic appear to have remained within 0 0 25 lower than in the pacific however the magnitude of this difference is sensitive to the inclusion of records from the equatorial west atlantic these results together with constraints based on temperature salinity and density suggest an influence of the seawater 18o 18osw versus salinity relationship of source waters on 18ob values within the atlantic in particular the abrupt emergence at 2 4 ma of higher 18ob values at sites 1264 and 1267 relative to north atlantic records appears to require a low latitude surface water 18osw signal this implies a connection between northward heat transport and deep water export into the abyssal east atlantic hence our results have implications for the interpretation of 18ob records and highlight the potential for 18ob to constrain deep atlantic water mass sources and pathways during the plio pleistocene

global ice volume variations through the last glacial cycle simulated by a 3 d ice dynamical model abstract a coupled ice sheet ice shelf bedrock model was run at 20 km resolution to simulate the evolution of global ice cover during the last glacial cycle the mass balance model uses monthly mean temperature and precipitation as input and incorporates the albedo mass balance feedback the model is forced by the grip and vostok derived temperature records and by sea level and solar radiation variations which are distributed spatially and seasonally model simulations show that at the last glacial maximum lgm a volume of ice representing about 65 m of sea level equivalent is stored on the eurasian continent whereas north america stores 42 m the other regions greenland tibet south america and antarctica contribute about 17 m to global sea level lowering at the lgm compared to present day sensitivity experiments show that the ice volumes of the eurasian and north american ice sheets are particularly sensitive to summer temperature changes finally the timing and mechanism of grounded ice formation and expansion for the last glacial were studied for the eurasian and north american continents ice sheet formation begins at 118 kyr bp in the barents and kara sea region over baffin island and in the high cordilleran range following a 4 c cooling alternating regions of ice sheet expansion by direct snowfall ice flow and grounding of ice shelves can be identified these relate to specific geomorphological traces and may as such help in model validation

areal distribution of the oxygen isotope ratio in greenland mean values of the oxygen isotope ratio relative to standard mean ocean water 8 180 in 0 reported for 46 sites on the greenland ice sheet are compiled together with data on mean annual surface temperature latitude 8180 elevation and mean annual shor test distance to the open ocean denoted by the 10 sea ice concentration boundary stepwise regression analyses with 8180 as the dependent variable define two robust models in the forward mode at the 99 9 confidence level only temperature enters the model in the backward mode at the 95 con fidence level only temperature latitude and distance to the open ocean remain in the model inversions of the models on the basis of 160 gridpoint locations 100 km apart in the area delimited by the surface equilibrium line produce four contoured distributions of b iho two distributions are based on the bivariate model and two on the multivariate modcl the sccond distribution for each model is obtained substituting mean annual surfa ce tempe ratu re values obtained from the nim bus 7 temperature humidity infrared radiometer thir database all four distribu tions are considered valid and differences between them are evaluated using contoured anomaly maps it is suggested that the inversion o the multivariate model using thir data pro ides the more reliable pattern for stu dies of atmospheric advection or for the derivation of ice flow adjustments for 81ho series obt ained from deep core or ablation zone sites

hydrothermally altered volcanic rocks metamorphosed at granulite facies conditions an example from the grenville province a 1 2 ga association of aluminous gneisses garnetites and white felsic gneisses of andesitic composition in the southern manicouagan area central grenville province provides evidence consistent with protolith formation and hydrothermal alteration in a submarine volcanic environment in addition to field relations potential relics of quartz phenocrysts in the aluminous gneisses revealed by sem mla scanning electron microscope with a mineral liberation analysis software imaging are consistent with a volcanic precursor moreover in these rocks aluminous nodules and seams of sillimanite are considered to represent metamorphosed hydrothermal mineral assemblages and to reflect former pathways of hydrothermal fluid these features are preserved despite the grenvillian granulite facies metamorphic overprint and evidence of partial melting in addition the garnetites are inferred to represent hydrothermally altered products of the white gneisses based on the gradational contacts between the two rock t

transient nature of the earth s climate and the implications for the interpretation of benthic δ18 o records abstract from the marine benthic 18 o records it is known that the earth s climate has experienced significant variability over the past 40 million years in general a number of assumptions are often needed to disentangle the benthic 18 o data into its temperature and ice volume contributions in this study a transient 1 d ice sheet model is used which overcomes these shortcomings by relating temperature to the benthic 18 o data leading to a self consistent and continuous record of 18 o temperature and sea level the contribution of land ice to benthic 18 o is examined with a set of sensitivity experiments varying the mean 18 o of the ice for different ice sheets it is shown that the scaling factor of sea water 18 o w to sea level is not constant over the long time scales however our sensitivity experiments do show that over the long time scale the general assumed 1 0 1 1 per 100 m of sea level is in reasonable agreement with our model results moreover the sea level ice volume response to temperature s t is shown to vary through time with the largest response found when variations in antarctic ice volume dominates the sea level variations during the oligocene to early miocene furthermore this response is quite large compared to the individual response of ice sheets during the plio pleistocene whereas the combined s t in this period is comparable to that during the oligocene accordingly the transient behaviour is very important for the interpretation of data records with respect to climate sensitivity and climate change during the past 40 million years

mercury and silver rich ferromanganese oxides southern california borderland deposit model and environmental implications mercury and silver enriched ferromanganese oxide crusts were recovered at water depths of 1 750 to1 300 m from la victoria knoll located about 72 km off the coast of northern baja california no other ferromanganese precipitate found so far in the modern ocean basins is similarly enriched in hg and ag the precipitates consist of submetallic gray brecciated mn oxide layers overlain by brown earthy laminated fe mn oxide crusts both oxide types are rich in hg to 10 ppm and ag to 5 5 ppm the mn rich layers are composed of mno 2 with lesser amounts of 10a and 7a manganates whereas the mn phase in the fe mn crusts is solely mno 2 the fe phase in both layers is x ray amorphous established criteria for distinguishing hydrothermal versus hydrogenetic crusts indicate that the mn rich layers are predominantly of low temperature hydrothermal origin whereas the fe mn crusts are hydrogenetic although there is some overlap in the source of chemical components in both types la victoria knoll is uplifted continental basement rock with basalt andesite and schist cropping out at the surface the knoll may have an intrusive core the hg and ag were derived from leaching by hydrothermal fluids of organic matter rich sediments in basins adjacent to la victoria knoll and to a lesser extent from continental basement rocks underlying the knoll and adjacent basins both rock types are notably enriched in ag and hg faults were the main fluid transport pathway and hydrothermal circulation was driven by high heat flow associated with thinned crust other elements derived from the hydrothermal fluids include tl cd cr and li the main host for hg and ag is feooh although mno 2 likely hosts some of the ag minor sulfide and barite also may contain small amounts of these metals possible analogs in the geologic record for this deposit type are found in the basin and range province of the western united states and mexico the discovery highlights the fact that fluids circulating along faults in the offshore california borderland are transporting potentially toxic metals hg ag tl as cd cr pb and ni and depositing them on and just below the ocean floor

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

geochemistry of hydrothermal sediments from odp sites 834 and 835 in the lau basin southwest pacific abstract geochemical investigations have been carried out on hydrothermally enriched metalliferous sediments collected at odp sites 834 and 835 in the lau basin enhanced hydrothermal inputs of both mn and fe occur in an acidreducible oxide phase unlike mid ocean ridge sediments where fe is mainly present in more resistant hcl soluble phases barium v co ni cu zn pb and rees mainly follow mn and fe in their behaviour and associations and are thought to be largely scavenged from seawater by mn and fe rich plume particulates although there is a significant hcl soluble non hydrothermal component of ba present compositional differences between eastern lau spreading centre and central lau spreading centre hydrothermal sediments and between them and hydrothermal sediments on mid ocean ridges are thought to be due to a combination of factors including temporal and areal variation in the composition of hydrothermal solutions variation in hydrothermal flux to the sediments related to their proximity to propagator or spreading centre and variable containment of the lau basin hydrothermal plume consequent on changing basin morphology through time our results are consistent with published models for the evolution of the lau basin and confirm that a time lag occurs between propagator passage and maximum hydrothermal flux to associated sediments

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

proterozoic copper deposits in nw queensland australia sulfur isotopic data sulfur isotopic disequilibrium is commonly observed between associated pyrite and copper sulfides in nw queensland a sulfur isotopic study of copper mineralization in dolomites at paradise valley and arenites at mammoth has allowed the significance of such disequilibrium to be evaluated copper mineralization at paradise valley is characterized by a greater enrichment in 34s with 34s values often greater than 30 for both copper sulfides and associated syngenetic diagneetic pyrite at mammoth copper sulfides have isotopic compositions 34s 15 9 to 0 3 transitional between disseminated syngenetic diagenetic pyrite 34s 5 7 to 1 7 and epigenetic vein pyrite 34s 17 9 to 7 1 suggesting progressive reaction and replacement of syngenetic diagenetic pyrite by a copper bearing mineralizing fluid under oxidizing conditions the isotopic data within the constraints imposed by geological and geochemical factors support a model of reaction between copper bearing mineralizing fluids and pre existing syngenetic diagenetic pyrite for both the carbonate and arenite hosted deposits

deep sea temperature and ice volume changes across the pliocene pleistocene climate transitions earth has undergone profound changes since the late pliocene which led to the development 2 7 million years ago ma and intensification 0 9 ma of large scale northern hemisphere ice sheets recorded as transitions in the benthic foraminiferal oxygen isotope 18ob record here we present an orbitally resolved record of deep ocean temperature derived from benthic foraminiferal magnesium calcium ratios from the north atlantic which shows that temperature variations are a substantial portion of the global 18ob signal the record shows two distinct cooling events associated with the late pliocene lpt 2 5 to 3 ma and mid pleistocene mpt 1 2 to 0 85 ma climate transitions whereas the lpt increase in ice volume is attributed directly to global cooling the shift to 100 000 year cycles at the mpt is more likely to be a response to an additional change in ice sheet dynamics

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

tracer transport in the greenland ice sheet three dimensional isotopic stratigraphy abstract polar ice cores can provide both a record of climate history and a sharp test of the performance of numerical ice dynamics models the stratigraphic structure of an ice sheet is an expression of its full depositional and dynamic history and thus presents a greater challenge to computer models than merely matching the contemporary ice thickness and areal extent we describe a coupled model of ice and tracer dynamics that is realized by adding a semi lagrangian tracer transport scheme to a conventional thermomechanical ice dynamics model model skill is demonstrated by using ice core data from the grip site near summit greenland to successfully predict the isotopic stratigraphy of ice cores at other deep drilling sites the success of this effort indicates that when compensated for the effects of ice flow and elevation all the deep cores relate a coherent glacial history over the past 120 000 years according to the simulation results the oldest greenland ice lies beneath the grip gisp2 and northgrip sites although comparably old ice may also be found in north greenland and east central greenland

overview of the spaceborne imaging radar c x band synthetic aperture radar sir c x sar missions abstract the spaceborne imaging radar c x band synthetic aperture radar sir c x sar the most advanced imaging radar system to have flown in earth orbit was carried in the cargo bay of the space shuttle endeavour in april and october 1994 sir c x sar simultaneously recorded data at three wavelengths l c and x bands 23 5 cm 5 8 cm and 3 1 cm respectively in addition the full polarimetric scattering matrix was obtained at l and c band over a variety of terrain and vegetation types scientists are using multifrequency polarimetric sir c x sar data in studies of geology hydrology ecology oceanography and radar remote sensing techniques the october sir c x sar flight also included acquisition of experimental repeat pass interferometry data which have been used to generate digital elevation models and to detect surface motions in volcanic tectonic and glacial terrains results from sir c x sar clearly show the increased value of using multiparameter and interferometric capabilities to characterize earth s surface and vegetation cover and to generate geophysical products compared with optical sensors or single channel radars alone

eocene circulation of the southern ocean was antarctica kept warm by subtropical waters 1 near the eocene s close 34 million years ago the climate system underwent one of the largest shifts in earth s history antarctic terrestrial ice sheets suddenly grew and ocean productivity patterns changed previous studies conjectured that poleward penetration of warm subtropical currents the east australian current eac in particular caused eocene antarctic warmth late eocene opening of an ocean gateway between australia and antarctica was conjectured to have disrupted the eac cooled antarctica and allowed ice sheets to develop here we reconstruct eocene paleoceanographic circulation in the tasmanian region using 1 biogeographical distributions of phytoplankton including data from recently drilled ocean drilling program leg 189 sites and 2 fully coupled climate model simulations we find that the eac did not penetrate to high latitudes and ocean heat transport in the region was not greater than modern our results do not support changes in thermal isolation as the primary driver of the eocene oligocene climatic transition

middle proterozoic ocean chemistry evidence from the mcarthur basin northern australia we report on the iron sulfur systematics and s isotopic compositions of upper paleoproterozoic carbonaceous shales from the wollogorang and lower reward formations mcarthur basin northern australia iron speciation in these rocks is similar to that of modern euxinic black sea sediments and distinct from sediments depositing from oxygenated water providing persuasive evidence of euxinic depositional environments in a mid proterozoic marine basin high values of degree of pyritization dop also indicate anoxic bottom water conditions at the time of shale deposition as does the relatively uniform isotopic composition of sedimentary sulfides the isotopic composition of the sulfides is however quite enriched in 3 4 s and for the lower reward formation similar to contemporaneous seawater sulfate these 3 4 s enriched sulfides are consistent with extensive or even complete sulfate depletion within the euxinic basins in which the sediments were deposited based on analogy with modern euxinic environments and further constrained by model results middle proterozoic seawater sulfate concentrations were probably within the range of 0 5 to 2 4 mm taken together our results indicate a relatively low sulfate late paleoproterozoic ocean and sulfidic deep waters in the mcarthur seaway a condition that could have encompassed much larger regions of the ocean

cooling and ice growth across the eocene oligocene transition the eocene oligocene e o climate transition ca 34 ma marks a period of antarctic ice growth and a major step from early cenozoic greenhouse conditions toward today s glaciated climate state the transition is represented by an increase in deep sea benthic foraminiferal oxygen isotope 18o values occurring in two main steps that reflect the temperature and 18o of seawater existing benthic mg ca paleotemperature records do not display a cooling across the transition possibly reflecting a saturation state effect on benthic foraminiferal mg ca ratios at deep water sites here we present data from exceptionally well preserved foraminifera deposited well above the calcite compensation depth that provide the first proxy evidence for an 2 5 c ocean cooling associated with the ice growth this permits interpretation of e o 18o records without invoking northern hemisphere continental scale ice

constraints on the ocean oxygen isotopic enrichment between the last glacial maximum and the holocene paleoceanographic implications abstract we review the various methods which have been applied to estimate the change of seawater 18 o w between the last glacial maximum lgm and the holocene the most accurate constraints on these estimates are provided by the measurement of pore waters 18 o and by high resolution records of benthic foraminifer 18 o in the high latitude oceans of both hemispheres they show that the 18 o of seawater in the deep ocean during the lgm was 1 05 0 20 heavier than today with significant regional variations constraints resulting from ice sheet models are less accurate because both the volume and isotopic composition of each ice sheet are still poorly known the amplitude of the benthic 18 o change between the lgm and the holocene together with the 18 o and 13 c values of the benthic foraminifera genus cibicides during the lgm show that the southern ocean deep waters were extremely cold close to the freezing point during this time deep waters of the south atlantic and the pacific oceans were at least 1 3 c warmer than those of the southern ocean overall the glacial deep ocean below 2500 m was characterized by extremely cold temperatures everywhere lower than 0 c 18 o values of benthic foraminifer from the north atlantic are highly variable this variability suggests that deep atlantic waters were not homogeneous probably because they resulted from the sinking of different surface water masses at various locations during winter the deep waters in the north atlantic were at most 2 c warmer than in southern ocean alternatively they could have been nearer the freezing point with a 18 o value lighter than the mean ocean water brine formation during winter would preserve such light 18 o values of the northern north atlantic surface water

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

a new method to estimate ice age temperatures on glacial time scales the waxing and waning of the eurasian and north american ice sheets depend largely on variations in atmospheric temperature as global sea level is primarily determined by the volume of these ice sheets there is a direct yet complex relation between global sea level and the northern hemispheric nh temperature this relation is essentially represented by a model of the nh ice sheets we use a thermomechanical ice sheet ice shelf bedrock model in conjunction with an inverse method to deduce a time series of nh temperature from 120 kyr bp until present that is consistent with the observed global sea level record the advantage of this method is that it provides the annual mean surface air temperature averaged over the nh continents north of 40 n the results reveal that ice age temperatures were 4 10 c lower than today which agrees with other temperature reconstructions however reconstructed temperatures are comparitively low during the early stages of the glacial a feature that is consistent with the rapid growth of the ice sheets the sensitivity of the results for uncertainties in precipitation rate in observed sea level and in some other model parameters is examined to quantify the error in reconstructed temperature during the glacial period 120 15 kyr bp surface air temperatures in the nh north of 40 n were 7 2 1 5 c lower than today s interglacial temperatures

radar interferometry and its application to changes in the earth s surface geophysical applications of radar interferometry to measure changes in the earth s surface have exploded in the early 1990s this new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times the resulting interferogram is a contour map of the change in distance between the ground and the radar instrument these maps provide an unsurpassed spatial sampling density 100 pixels km 2 a competitive precision 1 cm and a useful observation cadence 1 pass month 1 they record movements in the crust perturbations in the atmosphere dielectric modifications in the soil and relief in the topography they are also sensitive to technical effects such as relative variations in the radar s trajectory or variations in its frequency standard we describe how all these phenomena contribute to an interferogram then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments including the four satellites currently in orbit ers 1 ers 2 jers 1 and radarsat the next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement respecting the limits of the technique assessing its uncertainty recognizing artifacts and discriminating different types of signal we then review the geophysical applications published to date most of which study deformation related to earthquakes volcanoes and glaciers using ers 1 data we also show examples of monitoring natural hazards and environmental alterations related to landslides subsidence and agriculture in addition we consider subtler geophysical signals such as postseismic relaxation tidal loading of coastal areas and interseismic strain accumulation we conclude with our perspectives on the future of radar interferometry the objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it

metamorphosed proterozoic zn pb ag mineralization in the foster river area northern saskatchewan canada metamorphosed zn pb occurrences fable lake george sito south sito southwest sito west sito east robyn lake and mackie lake with high zn pb ratios occur in the foster river area northern saskatchewan on the southeast margin of the paleoproterozoic wollaston domain the sito east prospect the largest of these occurrences contains 50 000 tonnes of 4 5 zn with one drill intercept containing 11 m of 4 2 zn and 0 6 pb most prospects are hosted in a thin areally extensive metaquartzite within a thick sequence of metasiltstones and metaquartzites in the middle of the paleoproterozoic wollaston group occurrences in metaquartzites and metaarkoses which locally contain gahnite spessartine and or graphite are spatially associated with metaexhalites iron formation and quartz garnetite and strata bound metamorphosed hydrothermal alteration zones nodular sillimanite rock post archean australian shale normalized rare earth element ree patterns of all three rock types are characterized by light ree enrichment positive ce anomalies neutral to strongly negative eu anomalies and heavy ree depletion consistent with an environment of deposition distinguished by a high 30 wt continental detrital component and formation from or interaction with low temperature 250 c near neutral ph and high fo2 fluids sulfur isotope compositions of sulfides at foster river are highly enriched in 34s 34s 26 2 38 1 n 20 and resulted from microbial reduction of partially reduced seawater sulfate in a restricted basin the spatial association of spessartine and gahnite bearing lithologies and silicate facies iron formation with paleoproterozoic base metal sulfides in a psammopelitic host sequence implies similarities between sulfide mineralization in the foster river area and broken hill type pb zn ag deposits however the markedly enriched 34ssulfide compositions low pb pb zn and ag pb zn ag ratios low ag contents and apparent absence of metavolcanic and metavolcaniclastic rocks in the dominantly clastic rock sequence hosting the sulfides in the foster river area suggest that these occurrences are part of a metamorphosed sedimentary exhalative system with broken hill type affinities similar to that associated with the formation of the gamsberg zn south africa kanmantoo group pb zn south australia and sullivan pb zn canada deposits

some geochemical indicators for discrimination between diagenetic and hydrothermal metalliferous sediments abstract two types of metalliferous sediments are known hydrothermal associated with tectonic faults and diagenetic enriched in precipitates from seawater they are similar in their appearance and chemical composition only the first type is an indicator for hydrothermal discharge therefore in exploration criteria for differentiating between the two are needed four possible indicators have been investigated and are discussed a differences in p y correlation b differences in cr zr correlation c different distribution patterns of ree and d different as contents the as content is easy to determine and seems to be at the present time the most suitable criterion for determining the genesis of the metalliferous sediments

a continuous simulation of global ice volume over the past 1 million years with 3 d ice sheet models sea level records show large glacial interglacial changes over the past million years which on these time scales are related to changes of ice volume on land during the pleistocene sea level changes induced by ice volume are largely caused by the waxing and waning of the large ice sheets in the northern hemisphere however the individual contributions of ice in the northern and southern hemisphere are poorly constrained in this study for the first time a fully coupled system of four 3 d ice sheet models is used simulating glaciations on eurasia north america greenland and antarctica the ice sheet models use a combination of the shallow ice and shelf approximations to determine sheet shelf and sliding velocities the framework consists of an inverse forward modelling approach to derive a self consistent record of temperature and ice volume from deep sea benthic 18o data over the past 1 million years a proxy for ice volume and temperature it is shown that for both eustatic sea level and sea water 18o changes the eurasian and north american ice sheets are responsible for the largest part of the variability the combined contribution of the antarctic and greenland ice sheets is about 10 for sea level and about 20 for sea water 18o during glacial maxima however changes in interglacials are mainly caused by melt of the greenland and antarctic ice sheets with an average time lag of 4 kyr between melt and temperature furthermore we have tested the separate response to changes in temperature and sea level for each ice sheet indicating that ice volume can be significantly influenced by changes in eustatic sea level alone hence showing the importance of a simultaneous simulation of all four ice sheets this paper describes the first complete simulation of global ice volume variations over the late pleistocene with the possibility to model changes above and below present day ice volume constrained by observations of benthic 18o proxy data

geodetically accurate insar data processor we present a new interferometric synthetic aperture radar insar processing approach that capitalizes on the precise orbit tracking that is available with modern radar satellites our method uses an accurate orbit information along with motion compensation techniques to propagate the radar echoes to positions along a noninertial virtual orbit frame in which the location and focusing equations are particularly simple so that images are focused without requiring autofocus techniques and are computed efficiently motion compensation requires two additional focus correction phase terms that are implemented in the frequency domain if the images from an interferometric pair or stack are all computed along the same reference orbit flat earth topographic correction is not needed and image coregistration is simplified obviating many difficulties that are often encountered in insar processing we process several data sets collected by the alos palsar instrument and find that the geodetic accuracy of the radar images is 10 20 m with up to 20 m of additional image distortion needed to align 100 km 100 km scenes with reference digital elevation models we validated the accuracy by using both known radar corner reflector locations and by the registration of the interferograms with digital maps the topography corrected interferograms are free from all geometric phase terms and they clearly show the geophysical observables of crustal deformation atmospheric phase and ionospheric phase

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

thermochronology of the needle falls shear zone a post collisional high strain zone of the trans hudson orogen the needle falls shear zone is a major paleoproterozoic discontinuity separating an archean craton from accreted paleoproterozoic terranes in the western trans hudson orogen it is a 1 km wide subvertical mylonite zone forming the southwestern sector of a northeast trending shear system extending for more than 400 km kinematic data indicate oblique east side up dextral strike slip displacement throughout its evolution from ductile through late brittle deformation for most of its exposed length it marks the northwestern margin of the wathaman batholith the oldest pb evaporation ages of zircons from mylonite average 1857 ma consistent with published zircon ages of the wathaman batholith confirming the batholith is protolith for much of the shear zone the synkinematic metamorphic assemblage of amphibole biotite quartz feldspar signifies deformation under amphibolite facies conditions 500 630 c oxygen isotope fractionations between quartz hornblende and quartz biotite pairs in textural equilibrium

mineralogy bulk and rare earth element geochemistry of massive sulphide associated hydrothermal sediments of the brunswick horizon bathurst mining camp new brunswick massive sulphides are spatially and temporally associated with iron formation if and other hydrothermal sedimentary rocks in the vicinity of the brunswick no 12 brunswick no 6 and austin brook deposits bathurst mining camp sulphide carbonate oxide and silicate predominant if is present carbonate predominant if is best developed in and around the brunswick no 12 deposit whereas hematite bearing if is absent here but prominent in the austin brook brunswick no 6 area the if is composed dominantly of si co2 fe mn and ca minor constituents include mg p ti al and s statistically significant interelement correlations between eu fe mn pb zn cd au ca sr ba p co2 and s indicate that these elements were precipitated from hydrothermal fluids vented onto the seafloor positive interelement correlations between si ti al mg k zr rare earth elements ree s except eu se v y yb co ni and cr reflect the presence of detrital clastic mafic and aluminosilicate minerals and

accuracy of topographic maps derived from ers 1 interferometric radar an interferometric radar technique for topographic mapping of surfaces promises a high resolution approach to the generation of digital elevation models the authors present analyses of data collected by the synthetic aperture radar instrument on board the ers 1 satellite on successive orbits use of a single satellite in a nearly repeating orbit is attractive for reducing cost and spaceborne hardware complexity also it permits inference of changes in the surface from the correlation properties of the radar echoes the data have been reduced to correlation maps and digital elevation models the correlation maps show that temporal correlation decreases significantly with time but not necessarily at a constant well defined rate likely depending on environmental factors when correlation among passes remains high however it is possible to form digital elevation models analyses of noise expected in ers 1 interferometric data collected over alaska and the southwestern united states indicate that maps with relative errors less than 5 m rms are possible in some regions however orbit uncertainties imply that tie points are required in order to reduce absolute height errors to a similar magnitude the authors find that about 6 tie points per 40 spl times 40 km scene with 5 m rms or better height accuracy are needed to keep systematic map height errors below 5 m rms the performance of the ers 1 radar system for topographic applications though useful for a variety of regional and local discipline studies may be improved with respect to temporal decorrelation errors and absolute height acuity by modifying the orbit repeat period and incorporating precise orbit determination techniques the resulting implementation will meet many but not all objectives of a global mapping mission

terminating the 100 kyr ice age cycle we report a simulation of the most recent 100 000 year glaciationdeglaciation cycle of the late pleistocene ice age a simulation that delivers an ice sheet chronology that is in close accord with that inferred from the geological record our analyses are performed with a reduced model of the climate system that incorporates significant improvements to the representation of both climate forcing and mass balance response in a previously described theory based upon a coupled one level energy balance model ebm and vertically integrated ice sheet model ism the theory fully incorporates the influences of orbital insolation forcing glacial isostatic adjustment and variations in the atmospheric concentrations of greenhouse gases it correctly predicts the main geographical regions of the northern hemisphere that were glaciated at last glacial maximum 21 000 years ago as well as the abrupt termination of the glacial epoch that occurred subsequently the latter feature of the ice age cycle is obtained without the need to incorporate unconstrained and therefore controversial physical processes into the model a limitation of all previous attempts to understand this global scale climate cycle our analyses suggest that the radiative impact on surface glaciation due to the changing atmospheric concentration of co2 is critical to the ability of the model to deliver a synthetic history of glaciation and deglaciation that is in accord with inferences based upon surface geological and geomorphological evidence with the incorporation of this influence model predicted ice thickness distributions at last glacial maximum lgm are very similar to those of the recently described ice 4g reconstruction that was based upon the inversion of postglacial relative sea level histories

motion on upper plate faults during subduction zone earthquakes case of the atacama fault system northern chile 1 motion on the atacama fault system afs in northern chile is driven by andean subduction zone processes we use two approaches observational and theoretical to evaluate how the afs and other forearc faults responded to coseismic stress induced by one well studied megathrust earthquake the 1995 mw 8 1 antofagasta event we use synthetic aperture radar interferometry insar to search for small scale coseismic and postseismic deformation on individual faults the insar data are ambiguous some images show offset consistent with coseismic faulting on the paposo segment of the afs and others lack such signal the fact that we do not observe the fault like displacement in all coseismic interferograms suggests that atmospheric contamination not tectonic deformation is responsible for the signal to explore the capacity of the earthquake to trigger motion on upper plate faults we use seven published slip maps constrained by geodetic and or seismic data to calculate static and dynamic coulomb stress change csc on faults in the antofagasta region the static csc field varies between models and depends on the distribution of coseismic interplate slip on the basis of the csc distribution predicted by our preferred model constrained by all available data we suggest it was unlikely that the antofagasta earthquake directly triggered normal motion on the afs and the insar data are consistent with this null result field reports of normal faulting related to the earthquake may reflect recent but not coseismic motion or highly localized behavior not representative of the regional coseismic stress field

dynamic topography and long term sea level variations there is no such thing as a stable continental platform abstract globally uniform i e eustatic sea level trends with time scales approaching 100 myr have been inferred from both seismic and backstripping stratigraphic analysis at a small set of geographic sites that are presumed to lie on stable continental platforms and passive continental margins characterized by simple thermal subsidence histories e g the new jersey margin the western african margin we demonstrate using mantle flow simulations based on high resolution seismic tomography that both the new jersey margin and the conjugate western african margin have been subject to orders of 100 m of dynamic i e flow induced topography change over the last 30 myr we also show that the changing pattern of downwelling mantle flow associated with plate subduction is a significant contributor to the background eustatic sea level trend which is also of order 100 m during the 30 myr time window therefore late cenozoic variations of dynamic topography on these passive margin sites are comparable to the eustatic sea level changes and can partially mask the latter furthermore even if the observed trend could be accurately corrected for local dynamic topography variation the residual eustatic signal does not merely reflect changes in mean spreading rates at mid ocean ridges we conclude that the observed long term sea level variations at so called stable sites cannot be interpreted as eustatic moreover previous analyses that have used long term sea level trends as a proxy for spreading rates and geochemical fluxes must be revisited

geology and thermotectonic evolution of the western margin of the trans hudson orogen evidence from the eastern sub athabasca basement saskatchewan in the cree lake zone of northern saskatchewan reworked archean orthogneisses are overlain by a highly deformed supracrustal sequence the paleoproterozoic wollaston group this package of rocks was deformed and metamorphosed during the ca 1 8 ga continent continent collision of the trans hudson orogen tho forming the wollaston fold thrust belt that underlies the eastern athabasca basin the hudsonian structural metamorphic and magmatic evolution of the wollaston fold thrust belt in the eastern athabasca area involved six major stages 1 early collisional stage dp1 at 1860 1835 ma involved burial of wollaston group metasediments from surface to depths equivalent to 3 5vkbar 1 kbar 100 mpa by thrust pile stacking or imbrication tectonics prograde metamorphism with garnet growth and development of early leucosomes and emplacement of ca 1840 ma grey granite suite 2 collisional stage dp2a at 1835 1820 ma involved continued deeper burial of wollaston group metasediments along a prograde

noble gas and halogen evidence for the origin of scandinavian sandstone hosted pb zn deposits abstract fluid origins in the sandstone hosted pb zn class of ore deposit have been investigated in three deposits from scandinavia laisvall vassbo and osen the deposits studied are hosted by autochthonous cambrian sandstones that preserve a near original structural relationship to the underlying precambrian basement enabling the role of basement interaction to be assessed mineral samples have been collected from across the paragenetic sequence sphalerite galena pyrite fluorite and barite of impregnation and related joint hosted mineralization fluid inclusion halogen cl br and i and noble gas isotope 40 ar 36 ar 84 kr compositions were determined simultaneously by noble gas mass spectrometry of irradiated sample splits complementary he isotope analyses are obtained from nonirradiated splits of the same samples 3 he 4 he values at laisvall and osen are highly radiogenic 0 02 ra and the 4 he 40 ar ratio extends to values greater than the crustal production value of 5 characteristic of low temperature crustal fluids at vassbo a slightly elevated 3 he 4 he ratio of 0 1 0 3 ra is compatible with a very minor mantle component 1 4 suggesting a distal source for the basinal brine dominated fluid br cl molar ratios 3 2 8 2 10 3 are greater than the present seawater value of 1 54 10 3 and correspond with i cl molar ratios in the range 64 1600 10 6 the upper limits of both the i cl and br cl values are amongst the highest measured in crustal fluids together the data indicate acquisition of salinity by the evaporation of seawater beyond the point of halite saturation and subsequent fluid interaction with i rich organic matter in the subsurface the data are compatible with the independent transport of sulfate and sulfide and indicate that fluids responsible for joint hosted mineralization were distinct to those responsible for impregnation mineralization all three deposits preserve fluids with 40 ar 36 ar in the range of 6 000 10 000 and fluid inclusion 40 ar concentrations of 0 02 0 05 cm 3 cm 3 fluid inclusion 4 he concentrations are also extremely elevated with maximum values of 0 1 cm 3 cm 3 in laisvall fluorite and sphalerite the high 40 ar 36 ar values together with the high 4 he and 40 ar concentrations result from a very long premineralization crustal residence time on the order of 100 200 ma together the noble gas and halogen data are compatible with a caledonian mineralization event 425 ma caused by mixing of two or more long lived hydrothermal basinal brines and pore fluids at the sites of mineralization the data suggest negligible recharge of the basinal brines by meteoric water and indicate extensive fluid basement interaction before mineralization the similar noble gas composition of each deposit suggests that similar processes operated at all three deposits and favors a single pass fluid flow model for mineralization

differences between the last two glacial maxima and implications for ice sheet δ18o and sea level reconstructions studies of past glacial cycles yield critical information about climate and sea level ice volume variability including the sensitivity of climate to radiative change and impacts of crustal rebound on sea level reconstructions for past interglacials here we identify significant differences between the last and penultimate glacial maxima lgm and pgm in terms of global volume and distribution of land ice despite similar temperatures and radiative forcing our analysis challenges conventional views of relationships between global ice volume sea level seawater oxygen isotope values and deep sea temperature and supports the potential presence of large floating arctic ice shelves during the pgm the existence of different glacial modes calls for focussed research on the complex processes behind ice age development we present a glacioisostatic assessment to demonstrate how a different pgm ice sheet configuration might affect sea level estimates for the last interglacial results suggest that this may alter existing last interglacial sea level estimates which often use an lgm like ice configuration by several metres likely upward

astronomical theory of paleoclimates and the last glacial interglacial cycle in the 19th century croll and pilgrim stressed the importance of severe winters as a cause of quaternary ice ages later on mainly during the first half of the 20th century koppen spitaler and milankovitch regarded high winter and low summer insolation as favoring glaciation after koppen and wegener related the milankovitch new radiation curve to penck and bruckner s subdivision of the quaternary there was a long lasting debate whether or not such changes in the insolation can explain the quaternary glacial interglacial cycles in the 1970s with the improvements of radiometric dating and of acquiring and interpreting the long continuous geological records with the advent of computers and with the development of more sophisticated astronomical and climate models the astronomical theory and in particular its milankovitch version were revived over the last 5 years most geological astronomical and climatological obstacles have been overcome and the causal role of the orbital variations in long term variation of climate is taken almost universally for granted models of different categories of complexity from conceptual ones to 3 d atmospheric general circulation models and 2 d time dependent models of the whole climate system have now been astronomically forced in order to test the physical reality of the astronomical theory for example experiments with both low and high resolution gcms show that the increased seasonality at 9 000 bp leads to intensified summer monsoon circulation of africa and southern asia on the other hand seasonal models for simulating the transient response of the climate system to astronomical forcing are also developed and the output of these most recent modeling efforts compares favorably with data of the past 400 000 years accordingly the model predictions for the next 100 000 years are used as a basis for forecasting how climate would evolve when forced by orbital variations in the absence of anthropogenic disturbances the long term cooling trend which began some 6 000 years ago will continue for the next 5 000 years this first temperature minimum will be followed by an amelioration around 15 000 ap after present by a cold interval centered al 23 000 ap and by a major glaciation at around 60 000 ap

the role of co2 decline for the onset of northern hemisphere glaciation the pliocene pleistocene transition ppt from around 3 2 to 2 5 million years ago ma represented a major shift in the climate system and was characterized by a gradual cooling trend and the appearance of large continental ice sheets over northern eurasia and north america paleo evidence indicates that the ppt was accompanied and possibly caused by a decrease in atmospheric co2 but the temporal resolution of co2 reconstructions is low for this period of time and uncertainties remain large therefore instead of applying existent co2 reconstructions we solved an inverse problem by finding a schematic co2 concentration scenario that allows us to simulate the temporal evolution of key climate characteristics in agreement with paleoclimate records to this end we performed an ensemble of transient simulations with an earth system model of intermediate complexity from which we derived a best guess transient co2 scenario for the interval from 3 2 to 2 4 ma that gives the best fit between the simulated and reconstructed benthic 18o and global sea surface temperature evolution our data constrained co2 scenarios are consistent with recent co2 reconstructions and suggest a gradual co2 decline from 375 425 to 275 300 ppm between 3 2 and 2 4 ma in addition to a gradual decline the best fit to paleoclimate data requires the existence of pronounced co2 variability coherent with the 41 kyr 1 kyr 1000 years obliquity cycle in our simulations the long term co2 decline is accompanied by a relatively abrupt intensification of northern hemisphere glaciation at around 2 7 ma this is the result of a threshold behaviour of the ice sheets response to gradual co2 decrease and orbital forcing the simulated northern hemisphere ice sheets during the early pleistocene glacial cycles reach a maximum volume equivalent to a sea level drop of about 40 m both ice volume and benthic 18o are dominated by 41 kyr cyclicity our simulations suggest that before 2 7 ma greenland was ice free during summer insolation maxima and only partly ice covered during periods of minimum summer insolation a fully glaciated greenland comparable to its present day ice volume is modelled only during glacial maxima after 2 7 ma and more continuously after 2 5 ma

global budget of water isotopes inferred from polar ice sheets 1 water isotope ratios in ice cores and marine sediments are a key indicator of past temperature and global ice volume quantitative interpretation of these ratios requires understanding of the storage capacity and exchanges among the ocean atmosphere and cryosphere we combine numerical models of ice dynamics and tracer transport to predict bulk ice properties by simulating the fine layering of ice sheets locally validated at ice core sites the 18o 16o content of ice sheets is found to vary between the present and 20 kyr ago from 34 to 37 for greenland from 41 to 42 5 for west antarctica and always remained near 56 5 for east antarctica their combined effect on sea water 18o 16o is a 0 08 0 12 increase 20 kyr ago a 1 11 decrease if ice sheets were to vanish we confirm that ice volume changes in antarctica and greenland linearly affect ocean composition though at different rates

sea level changes at the lgm from ice dynamic reconstructions of the greenland and antarctic ice sheets during the glacial cycles abstract new experiments were performed with three dimensional thermomechanical models of the greenland and antarctic ice sheets to simulate their behaviour during the glacial cycles to reconstruct their thickness and extent at the last glacial maximum lgm and to estimate their glacio eustatic contribution to the global sea level stand the calculations used improved ice dynamic and isostatic treatments updated datasets on higher grid resolutions and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations results are discussed from a reference run with standard parameters that is compared with available glacial geological observations and from a series of sensitivity experiments focusing on isostatic adjustment thermomechanical coupling climatic forcing mass balance changes and basal melting rates and viscosity changes of antarctic ice shelves for the antarctic ice sheet we find that volume changes are closely linked with grounding line changes of the west antarctic ice sheet at the lgm the grounding line extended close to the continental shelf break almost everywhere ice over central east antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations for the greenland ice sheet melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the eemian at the lgm the greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas for a plausible range of parameters the experiments indicate that at the time of maximum sea level depression 21 kyr bp the antarctic ice sheet contributed 14 18 m to the sea level lowering and the greenland ice sheet 2 3 m significantly less than the older climap reconstructions whereas both ice sheets were at 21 kyr bp close to their maximum extent the experiments also indicate that their maximum volumes were reached only by 16 5 kyr bp greenland and 10 kyr bp antarctica equal to an additional sea level lowering of respectively 0 4 and 3 7 m holocene retreat was essentially complete by 5 kyr bp in greenland but is found to still continue today in west antarctica before reversing to growth during the next millenium the models were found to reproduce gross features of the ice sheet s history since the lgm in reasonably good agreement with available glacial geological data although observational control on ice thickness changes remains very limited

repeat pass interferometry with airborne synthetic aperture radar it is shown that interference can be observed by coherently combining pairs of either x or c band airborne synthetic aperture radar sar images from separate passes over the same test site coherence between separate images is obtained only if the aircraft is flown and the data are processed in such a way that each resolution cell in the two images is viewed with very nearly the same geometry successful repeat pass interferometric results were obtained from those passes flown by the ccrs convair 580 aircraft with flight line offsets of less than a few tens of meters a summary of the experiment the phase correction of nonrectilinear aircraft motion and the subsequent data processing is provided

sensitivity of the lln climate model to the astronomical and co2 forcings over the last 200 ky the louvain la neuve climate model there referred to as the lln 2 d model has been used extensively to simulate the northern hemisphere ice volume under both the insolation and co2 forcings the period analysed here covers the last 200 ky first sensitivity analyses to constant co2 concentration were performed the model was accordingly forced by insolation changes only the co2 concentration being kept constant to respectively 210 250 and 290 ppmv results show that the simulated ice volume variations are comparable to the geological reconstructions only when the co2 concentration is low 210 ppmv and that the sensitivity of the simulated northern hemisphere ice volume to co2 is not constant through time second three co2 reconstructions were used to force the lln 2 d model in addition to insolation results show 1 a better agreement with the specmap oxygen isotope time series in particular as far as the amplitude of the signal is concerned and 2 that the simulated northern hemisphere ice volume is not very sensitive to the slight differences between these three reconstructions

geology and metamorphism of the montauban north gold zone a metamorphosed polymetallic exhalative deposit grenville province quebec the stratiform gold zones and massive sulfide zn pb cu au ag deposit at montauban quebec occur as part of a series of helikian supracrustal rocks metamorphosed to the upper amphibolite facies the mine sequence at the north gold zone consists of nodular sillimanite gneiss cordierite anthophyllite zincian staurolite kyanite gneiss and manganiferous garnet gahnite quartzitic gneiss porphyroblastic gahnite is present only in the gold bearing unit but finer grained gahnite was observed in the remainder of the sequence for up to 20 m on either side gahnite was formed mainly by desulfurization of sphalerite breakdown of zincian staurolite and breakdown of zn bearing biotite peak metamorphic conditions are estimated at t 650 degrees c p 6 kb f sub o 2 10 super 17 bars and f sub s 2 10 super 2 bars mn ranges up to 25 wt percent in garnet and zn up to 8 wt percent in staurolite zn ratios in staurolite correlate closely with those of gahnite r 0 85 and bulk rock r 0 72 zn cu zn pb bulk ratios increase symmetrically away from the ore zone the mine sequence is interpreted as a metamorphosed exhalative system consisting of a siliceous exhalite containing gold and sulfide mineralization and anomalous mn ba and b the other units were initially chlorite sericite quartz hydrothermal alteration assemblages

topographic mapping from interferometric synthetic aperture radar observations interferometric synthetic aperture radar observations provide a means for obtaining high resolution topographic terrain maps from data acquired simultaneously at two slightly displaced antennas calculation of the three dimensional coordinates of all the points in a radar image can be made from the combination of along track slant range and interferometer fringe measurements thus the result compensates for the layover exhibited by conventional radar maps and removes the false targets generated by multiple signal paths to a given object in the scene we have derived a topographic map of a portion of the san francisco bay area utilizing data that were recorded by a radar system mounted on a nasa cv990 aircraft and processed by a general purpose digital computer this map displays the height above sea level of a region approximately 11 km by 10 km in size sampled on an 11 m pixel grid uncertainties in the estimated height result from imprecise knowledge of the observational geometry radar bandwidth limitations and finite signal to noise ratios for our system each factor contributed approximately 3 4 m to a relative rms error of about 6 m additional global errors of the order of 10 m can result from inaccurate monitoring of aircraft attitude the statistical variation of the height measurements from the ocean portion of the map which we can presume to be quite flat is 2 10 m rms which is consistent with the theoretical estimate comparison of our results with u s geological survey contour maps indicates a high degree of correlation between the two sets of altitude data

europium redox equilibria in aqueous solution thermochemical data and recent advances in theoretical aqueous solution chemistry enable prediction of the relative stabilities of aqueous eu2 and eu3 over a wide range of temperatures and pressures at low temperatures near earth surface conditions the aqueous geochemistry of europium should be dominated by the trivalent state except possibly in the most reducing alkaline pore waters of anoxic marine sediments however at temperatures greater than about 250 c and elevated pressures divalent europium should predominate even with significant amounts of complexing trivalent europium is not stable at elevated temperatures and pressures consequently under most hydrothermal and metamorphic conditions europium in aqueous solution should be divalent at intermediate temperatures around 100 c significant activities of both eu2 and eu3 and related complexes can occur in aqueous solutions depending on the oxidation state and the ph of the solutions and the activities of potential ligands such as sulfate carbonate and chloride the predicted stability of divalent europium in aqueous solution at elevated temperatures is consistent with the large positive europium anomalies in rare earth element patterns of high temperature barites of hydrothermal and metamorphic origin reported by guichard et al 5 and with the observed depletion of europium as a result of high temperature sericitization of feldspar bearing assemblages discovered by alderton et al 1 it is suggested that significant fractionation of europium relative to the other rare earth elements may take place during high temperature hydrothermal alteration processes such as in the mid oceanic ridge systems because of the expected stability of divalent europium during these processes

sir c x sar multifrequency multipass interferometry a new tool for geological interpretation radar remote sensing is a tool of increasing importance in the study of volcanic sites synthetic aperture radar sar is a high resolution imaging tool used to survey areas which are not practical or safe to be directly inspected with the introduction of the across track sar interferometry ifsar technique digital elevation models dem can be produced the usefulness of such interferometric products depends on the ability to extract information that can be used for geological interpretation we analyzed the shuttle imaging radar c sir c x sar multifrequency multipass interferometry mission over mount etna sicily and we performed a supervised geological interpretation of the coherence maps and a fractal based analysis of the ifsar dems the first permits us to recognize different volcanic terrain and to distinguish between vegetated and unvegetated areas while the second allows us to validate the ifsar dems and to detect large scale geological features this latter analysis performed over the photogrammetric dem enabled us to recognize artifacts caused by digitizing and resampling obviously ifsar dems are not affected by these problems as a consequence ifsar products are a valuable aid in geological interpretation

quantifying ice sheet feedbacks during the last glacial inception 1 the last glacial inception 116 ky ago has long been used to test the sensitivity of climate models to insolation from these simulations atmospheric oceanic and vegetation feedbacks have been shown to amplify the initial insolation signal into a rapid growth of ice sheets over the northern hemisphere however due to the lack of comprehensive atmosphere ocean vegetation northern hemisphere ice sheet models the impact of all these feedbacks acting concurrently has not yet been evaluated here we present the results from such a model which simulates significant ice sheet growth over north america but none over eurasia our analyses focus on the different behaviours over these regions and the quantification of the ice sheet feedbacks on climate

modelling west antarctic ice sheet growth and collapse through the past five million years changes in earth s orbit are known to influence climate shifts from cold glacials to warm interglacials how the vast west antarctic ice sheet responds to these fluctuations is uncertain but because its collapse could raise sea levels by about 5 metres of great interest naish et al have analysed the and 1b ocean sediment core extracted from beneath the ross ice shelf as part of the andrill drilling project and find evidence that the ice sheet collapsed periodically during the early pliocene 3 5 million years ago when atmospheric co2 levels were similar to or slightly higher than today s the pattern of collapse suggests an influence of approximately 40 000 year cycles in the tilt of earth s rotational axis obliquity also in this issue of nature in a numerical modelling study focused on the past 5 million years in antarctica david pollard and robert deconto combine ice sheet land supported and ice shelf water supported modelling approaches to simulate the movement of the grounding line the border between land and sea ice their results show that over the past 5 million years the west antarctic ice sheet transitioned between full intermediate and collapsed states in just a few thousand years this means that the ice sheet is likely to disintegrate if ocean temperatures in the area rise by 5 c if the west antarctic ice sheet wais melted sea levels would rise by about 5 m such changes are thought to have occurred in the past but could not be simulated by models pollard and deconto combine ice sheet with ice shelf modelling and show that over the past 5 million years the wais transitioned among full intermediate and collapsed states in only a few thousand years suggesting possible disintegration of the wais if ocean temperatures in the area rise by 5 c the west antarctic ice sheet wais with ice volume equivalent to 5 m of sea level1 has long been considered capable of past and future catastrophic collapse2 3 4 today the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams grounding lines are several hundred metres below sea level and the bed deepens upstream raising the prospect of runaway retreat3 5 projections of future wais behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms6 7 its variation since the last glacial maximum is best known with grounding lines advancing to the continental shelf edges around 15 kyr ago before retreating to near modern locations by 3 kyr ago8 prior collapses during the warmth of the early pliocene epoch9 and some pleistocene interglacials have been suggested indirectly from records of sea level and deep sea core isotopes and by the discovery of open ocean diatoms in subglacial sediments10 until now11 however little direct evidence of such behaviour has been available here we use a combined ice sheet ice shelf model12 capable of high resolution nesting with a new treatment of grounding line dynamics and ice shelf buttressing5 to simulate antarctic ice sheet variations over the past five million years modelled wais variations range from full glacial extents with grounding lines near the continental shelf break intermediate states similar to modern and brief but dramatic retreats leaving only small isolated ice caps on west antarctic islands transitions between glacial intermediate and collapsed states are relatively rapid taking one to several thousand years our simulation is in good agreement with a new sediment record andrill and 1b recovered from the western ross sea11 indicating a long term trend from more frequently collapsed to more glaciated states dominant 40 kyr cyclicity in the pliocene and major retreats at marine isotope stage 31 1 07 myr ago and other super interglacials

continuous simulations over the last 40 million years with a coupled antarctic ice sheet sediment model abstract much of the knowledge of antarctic ice sheet variations since its inception 34 ma derives from marine sediments on the continental shelf deposited in glacimarine or sub ice environments by advancing and retreating grounded ice and observed today by seismic profiling and coring here we apply a 3 d coupled ice sheet and sediment model from 40 ma to the present with the goal of directly linking ice sheet variations with the sediment record the ice sheet model uses vertically averaged ice dynamics and parameterized grounding line flux the sediment model includes quarrying of bedrock sub ice transport and marine deposition atmospheric and oceanic forcing are determined by uniform shifts to modern climatology in proportion to records of atmospheric co2 deep sea core 18o and orbital insolation variations the model is run continuously over the last 40 myr at coarse resolution 80 or 160 km modeling post eocene ice landscape evolution and off shore sediment packages in a single self consistent simulation strata and unconformities are tracked by recording times of deposition within the model sediment stacks which can be compared directly with observed seismic profiles the initial bedrock topography is initialized to 34 ma geologic reconstructions or an iterative procedure is used that yields independent estimates of paleo bedrock topography preliminary results are compared with recognized cenozoic ice sheet variations modern sediment distributions and seismic profiles and modern and paleo bedrock topographies

cenozoic climate changes a review based on time series analysis of marine benthic δ18o records the climate during the cenozoic era changed in several steps from ice free poles and warm conditions to ice covered poles and cold conditions since the 1950s a body of information on ice volume and temperature changes has been built up predominantly on the basis of measurements of the oxygen isotopic composition of shells of benthic foraminifera collected from marine sediment cores the statistical methodology of time series analysis has also evolved allowing more information to be extracted from these records here we provide a comprehensive view of cenozoic climate evolution by means of a coherent and systematic application of time series analytical tools to each record from a compilation spanning the interval from 4 to 61 myr ago we quantitatively describe several prominent features of the oxygen isotope record taking into account the various sources of uncertainty including measurement proxy noise and dating errors the estimated transition times and amplitudes allow us to assess causal climatological tectonic influences on the following known features of the cenozoic oxygen isotopic record paleocene eocene thermal maximum eocene oligocene transition oligocene miocene boundary and the middle miocene climate optimum we further describe and causally interpret the following features paleocene eocene warming trend the two step long term eocene cooling and the changes within the most recent interval miocene pliocene we review the scope and methods of constructing cenozoic stacks of benthic oxygen isotope records and present two new latitudinal stacks which capture besides global ice volume also bottom water temperatures at low less than 30 and high latitudes this review concludes with an identification of future directions for data collection statistical method development and climate modeling

rare earth element study of exhalites within the willyama supergroup broken hill block australia a wide variety of unusual rock types exhalites are commonly associated with or host to exhalative mineralisation within the willyama supergroup chondrite normalised ree patterns of feldspar gahnite calcite magnetite and garnet rich lithologies in the vicinity of stratiform broken hill type pb zn ag mineralisation are lree and eu enriched similar to the ree patterns of pure metalliferous sediments and hydrothermal fluids of the east pacific rise and the red sea in contrast tourmaline garnet amphibole feldspar and gahnite rich exhalites in strike extension of broken hill type orebodies possess lree enrichments and negative eu anomalies and also hree enrichments and negative ce anomalies these ree patterns are the result of decreasing temperatures of the hydrothermal fluids changing oxidation reduction conditions and increasing influence of basic volcanism with increasing distance from the sulphide mineralisation

a coupled climate ice sheet modeling approach to the early cenozoic history of the antarctic ice sheet abstract the sudden widespread glaciation of antarctica and the associated shift toward colder temperatures near the eocene oligocene boundary 34 ma represents one of the most fundamental reorganizations of the global climate system recognized in the geologic record this glacial inception and the subsequent evolution of the early east antarctic ice sheet eais are simulated using a new coupled global climate dynamical ice sheet model accounting for the paleogeography greenhouse gas concentrations changing orbital parameters and varying ocean heat transport suites of long 105 yr climate ice sheet simulations are used to investigate the effects of declining atmospheric co2 compared to those of the tectonic opening of southern ocean gateways and the timing of mountain uplift in the antarctic interior in contrast to the established paradigm for the glaciation of antarctica which centers on the opening of the southern ocean gateways and the thermal isolation of the continent our results show that declining cenozoic pco2 may have played the dominant role first small isolated ice caps formed on the highest antarctic plateaus then as a co2 threshold between 3 and 2 pre industrial level pal was crossed height mass balance feedbacks were initiated during orbital periods with cold austral summers triggering much larger highly dynamic terrestrial ice sheets as co2 continued to decline these isolated ice caps eventually merged into a permanent continental scale eais in our model neither the opening of the southern ocean gateways nor mountain uplift significantly affected the timing of the major ice sheet transition given a scenario of gradually declining co2 from 4 to 2 pal over 10 million years around the eocene oligocene boundary

precession phasing offset between indian summer monsoon and arabian sea productivity linked to changes in atlantic overturning circulation results from transient climate modeling experiments indicate an in phase relationship between insolation forcing and indian summer monsoonal precipitation this is in contrast to high resolution radioisotopically dated speleothem oxygen isotope 18o records of china which showed that east asian monsoon maxima lag northern hemisphere peak summer insolation by 2 700 years while an approximately 8 000 year time lag was derived from late pleistocene records of arabian sea sediments here we evaluate the precession phase of the arabian sea signal by comparing a new high resolution productivity and oxygen minimum zone omz intensity record from the arabian sea over the past 450 000 years with the results of a transient climate modeling experiment that includes glacial bound ice volume variations the well established tuning technique between radioisotopically dated north atlantic cold events and the occurrence of deep dwelling planktonic foraminifera in the arabian sea for the last glacial cycle was used to extend the arabian sea chronology independent of orbital tuning cross spectral analysis over the last 224 000 years reveals that arabian sea productivity maxima lag precession minima by 6 900 200 years i e in close agreement with previous reconstructions also our climate modeling simulations are in accord with previous studies indicating an in phase relationship between precession minima and maximum summer monsoon intensity we argue that the summer monsoon is most likely not the main driver of changes in arabian sea biological productivity and omz intensity at the precession frequency band but that changes in the intensity of the atlantic meridional overturning circulation amoc have played the prominent role in controlling the nutrient delivery into the euphotic layer of the northern indian ocean and hence the amount of primary productivity and intensity of the oxygen minimum zone in the arabian sea such a mechanism explains the large precession related time lag between minimum precession and maximum productivity and omz conditions in the arabian sea since intensified amoc occurred during precession maxima

trace sulfate in mid proterozoic carbonates and the sulfur isotope record of biospheric evolution concentrations of oceanic and atmospheric oxygen have varied over geologic time as a function of sulfur and carbon cycling at or near the earth s surface this balance is expressed in the sulfur isotope composition of seawater sulfate given the near absence of gypsum in pre phanerozoic sediments trace amounts of carbonate associated sulfate cas within limestones or dolostones provide the best available constraints on the isotopic composition of sulfate in precambrian seawater although absolute cas concen trations which range from those below detection to 120 ppm sulfate in this study may be compromised by diagenesis the sulfur isotope compositions can be buffered sufficiently to retain primary values stratigraphically controlled 34 s measurements for cas from three mid proterozoic carbonate successions 1 2 ga mescal limestone apache group arizona usa 1 45 1 47 ga helena and newland formations belt supergroup montana usa and 1 65 ga paradise creek formation mcnamara group nw queens land australia show large isotopic variability 9 1 to 18 9 1 1 to 27 3 and 14 1 to 37 3 respectively over stratigraphic intervals of 50 to 450 m this rapid variability ranging from scattered to highly systematic and overall low cas abundances can be linked to sulfate concentrations in the mid proterozoic ocean that were substantially lower than those of the phanerozoic but higher than values inferred for the archean results from the belt supergroup specifically corroborate previous arguments for seawater contributions to the basin limited sulfate availability that tracks the oxygenation history of the early atmosphere is also consistent with the possibility of extensive deep ocean sulfate reduction the scarcity of bedded gypsum and the stratigraphic 34 s trends and 34 s enrichments commonly observed for iron sulfides of mid proterozoic age copyright 2005 elsevier ltd

pliocene pleistocene variability of upwelling activity productivity and nutrient cycling in the benguela region in this study we present combined high resolution records of sea surface temperature sst phytoplankton productivity and nutrient cycling in the benguela upwelling system bus for the past 3 5 ma the sst record provided evidence that upwelling activity off namibia mainly intensified ca 2 4 2 0 ma ago in response to the cooling of the southern ocean and the resultant strengthening of trade winds as revealed by productivity related proxies bus intensification led to a major transition in regional biological productivity when considering the termination of the matuyama diatom maximum a diatom high production event major oceanic reorganization in the benguela was accompanied by nutrient source changes as indicated by a new nitrogen isotopic delta n 15 record that revealed a stepwise increase at ca 2 4 and ca 1 5 ma ago the change in source region likely resulted from significant changes in intermediate water formation tied to the reorganization of oceanic conditions in the southern ocean which may have in turn mainly controlled the global ocean n cycle and therefore the n isotopic composition of nutrients since 3 5 ma ago

tropical ocean temperatures over the past 3 5 million years determining the timing and amplitude of tropical sea surface temperature sst change is an important part of solving the puzzle of the plio pleistocene ice ages alkenone based tropical sst records from the major ocean basins show coherent glacial interglacial temperature changes of 1 to 3 c that align with but slightly lead global changes in ice volume and deep ocean temperature over the past 3 5 million years tropical temperatures became tightly coupled with benthic 18o and orbital forcing after 2 7 million years we interpret the similarity of tropical sst changes in dynamically dissimilar regions to reflect top down forcing through the atmosphere the inception of a strong carbon dioxide greenhouse gas feedback and amplification of orbital forcing at 2 7 million years ago connected the fate of northern hemisphere ice sheets with global ocean temperatures since that time

a new spatial distribution map of δ18o in antarctic surface snow 1 we developed a gridded map of surface antarctic snow isotopic composition using a recently compiled database and the modified bowen and wilkinson 2002 model using latitude and elevation as the primary predictors while also incorporating regional and local deviations based on available isotopic data the map was generated using a 1 km digital elevation model grid data as the model input the average of the absolute deviations between observations and predictions was about 0 8 and the standard deviation is 0 9 the resulting 18o patterns reproduced correctly spatial isotopic gradients with respect to geographical characteristics as well as climatic features

the effect of varying acquisition parameters on the interpretation of sir c radar data the virunga volcanic chain abstract in 1994 the spaceborne imaging radar experiment c sir c acquired five data takes with different acquisition parameters over the virunga volcanic chain zaire changes in incidence angle 20 0 48 1 look direction west and east looking and pulse bandwidth 10 mhz 20 mhz and 40 mhz affect the geologic interpretations drawn from these data we examine differences in spatial distortion of features near the summit of nyiragongo volcano finding that opposite look direction data are helpful in interpreting volcanic features such as the shape of small craters in areas of high relief the relative brightness of lava flows and vegetation change and actually reverse for different wavelengths and polarizations although l band data are best for mapping the outline of the flows c and x band cross polarization data show differences in backscatter intensity between and within flows in addition our ability to discriminate lava flows and vents from surrounding vegetation is strongly influenced by pulse bandwidth resolution and angle of incidence pulse bandwidth is the most important parameter in mapping small topographic features such as volcanic cones and a set of particularly thick flows on the flanks of karisimbi volcano these examples illustrate important considerations of the tradeoffs and priorities in acquisition parameters for future missions such as envisat as well as potential pitfalls for interpretation of existing data

a 5 million year comparison of mg ca and alkenone paleothermometers geochemical sea surface temperature sst proxies such as the magnesium to calcium ratio mg ca in foraminifera and the alkenone unsaturation index uk 37 are becoming widely used in pre pleistocene climate records this study quantitatively compares previously published mg ca and uk 37 data from ocean drilling program odp site 847 in the eastern equatorial pacific to assess the utility of these proxies to reconstruct tropical sst over the last 5 ma foraminiferal mg ca sst calibrations that include a dissolution correction are most appropriate at this location because they provide sst estimates for the youngest sample that are close to modern mean annual sst the long term trends in the two records are remarkably similar and confirm a 3 5 c cooling trend from the early pliocene warm period to the late pleistocene noted in previous work absolute temperature estimates are similar for both proxies when errors in the dissolution correction used to estimate sst from mg ca are taken into account comparing the two sst records at odp site 847 to other records in the region shows that the eastern equatorial pacific was 2 4 c warmer during the early pliocene compared to today

simulating the sea level imprint on marine oxygen isotope records during the middle miocene using an ice sheet climate model 1 oxygen isotopic ratios are implemented in an ice sheet climate model in order to directly compare the modeled isotopic ratio of the seawater to the high resolution isotopic records from deep sea sediment cores in the middle miocene the isotopic depletion resulting from the modeled ice sheet expansion explains the mean oxygen isotope step found in deep sea sedimentary records of 0 5 approximately 85 of the modeled increase in the isotopic composition of seawater is caused by an increase in ice volume the remainder is due to a stronger depletion in oxygen isotopes in the large ice sheet furthermore we also investigated the relation between sea level or global ice volume and the isotopic composition of seawater our experiments confirm the validity of the relation of approximately 1 enrichment per 100 m sea level lowering we further show that this relationship is r estricted by the mean ocean depth and the assumed oxygen isotopic composition of the ice sheet small deviations 10 from this general relationship occur depending on the size and the mean isotopic content of the ice sheet large continental ice sheets are more depleted in heavy oxygen isotopes and therefore reach a slightly higher ratio in contrast small ice sheets have a less depleted isotopic composition and correspondingly have a smaller effect on the isotopic composition of the ocean