t phase spectra seismic moments and tsunamigenesis t phase spectrograms and spectra derived from deep ocean hydrophones for tsunamigenic and non tsunamigenic earthquakes in the pacific reveal the following 1 substantial amounts of t phase energy at high frequencies i e 1 hz to at least 35 hz 2 strong correlations of spectral strengths in the 10 hz to 35 hz frequency range to seismic moments and 3 large spectral strengths at high frequencies for tsunamigenic earthquakes these findings are consistent with the low attenuation of the so und fixing and ranging sofar channel which permits efficient propagation of high frequencies to great distances and with the perception that large earthquakes may generate high frequency signals at the water sediment interface which can best be observed by hydroacoustic sensors in the low noise environment of the deep oceans in addition these studies confirm that 1 source bathymetry can strongly influence the character of t phases 2 islands or seamounts near the source area can act as secondary radiators of energy which add to the complexity and duration of the coda 3 there appears to be no significant dependence of t phase strength on earthquake source mechanism and 4 the strength of the t phase is dependent on the purity of its oceanic travel path the strong correlation of t phase spectral strengths to seismic moments suggests that substantial improvements in the reliability of tsunami warnings may be possible by using t phases as an additional independent single station method for estimating seismic moments finally the high frequencies observed in the t phase may be associated with important alternate mechanisms for tsunamigenesis other than faulting i e slumpage compaction or liquefaction

significant unreported earthquakes in aseismic regions of the western pacific with data recorded by a deep ocean hydrophone array centrally located in the northwestern pacific basin near wake island significantly large earthquakes were found to have their epicenters within the interior of the pacific plate the signal noise ratio of the largest is about 40 1 at a distance of 2268 km although all of these earthquakes were unreported in national earthquake information service neis listings comparisons with the po so phases of other earthquakes reported by neis indicate that these earthquakes could have body wave magnitudes in excess of 5 0

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

calibration of the calcite water oxygen isotope geothermometer at devils hole nevada a natural laboratory abstract the 18 o of ground water 13 54 0 05 and inorganically precipitated holocene vein calcite 14 56 0 03 from devils hole cave 2 in southcentral nevada yield an oxygen isotopic fractionation factor between calcite and water at 33 7 c of 1 02849 0 00013 1000 ln calcite water 28 09 0 13 using the commonly accepted value of calcite water t of 0 00020 k 1 this corresponds to a 1000 ln calcite water value at 25 c of 29 80 which differs substantially from the current accepted value of 28 3 use of previously published oxygen isotopic fractionation factors would yield a calcite precipitation temperature in devils hole that is 8 c lower than the measured ground water temperature alternatively previously published fractionation factors would yield a 18 o of water from which the calcite precipitated that is too negative by 1 5 using a temperature of 33 7 c several lines of evidence indicate that the geochemical environment of devils hole has been remarkably constant for at least 10 ka accordingly a re evaluation of calcite water oxygen isotopic fractionation factor may be in order assuming the devils hole oxygen isotopic value of calcite water represents thermodynamic equilibrium many marine carbonates are precipitated with a 18 o value that is too low apparently due to a kinetic isotopic fractionation that preferentially enriches 16 o in the solid carbonate over 18 o feigning oxygen isotopic equilibrium

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

younger dryas style cooling events at glacial terminations i vi at odp site 658 associated benthic δ13c anomalies constrain meltwater hypothesis high resolution planktonic and epibenthic stable isotope records from ocean drilling program site 658 off northwest africa provide a basis for a detailed study of glacial terminations i vi during the last 650 000 years the duration of the terminations was about one half to one quarter of an orbital precession cycle 5800 10 700 years when its amplitude was high at low amplitudes the terminations lasted longer than half an obliquity cycle 29 000 years marked climatic rebounds similar to the younger dryas each with a duration of 1000 2500 years subdivided all six terminations into distinct steps a b and c important parts of the deglacial steps were as brief as 700 1000 years the speed of climatic change suggests that special associations existed between orbital forcing and inherent instability of the ice sheets in harmony with published models the more rapid pulses of glacial meltwater incursions to the northern north atlantic led to one or more brief short term shut downs of north atlantic deep water formation this process is reflected by pronounced benthic 13c minima that precisely coincide in most cases with the end of the 18o deglaciation steps and immediately terminate with succeeding younger dryas style cooling events thus we conclude that the rebounds resulted from a short term antecedent estuarine circulation regime in the north atlantic except for the younger dryas itself which succeeded the allerod with its well ventilated atlantic deepwater circulation and hence continues to be an enigma

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

stable isotope record and its palaeoenvironmental interpretation for a late middle pleistocene speleothem from victoria fossil cave naracoorte south australia abstract a speleothem from victoria fossil cave south australia provides a continuous stable isotope record from 185 to 157 ka oxygen isotope analysis indicates that at commencement of deposition mean annual temperatures were much lower than at present and that between 178 and 162 ka regional surface temperatures were similar to today such high temperatures during an interstadial are surprising but may be attributable to increased continentality due to low sealevels carbon isotope analysis indicates the presence of an active vegetation cover dominated by c3 plants during the interstadial while a sparse vegetation dominated by c4 grasses appears to have been dominant during full glacial conditions variations in moisture availability and vegetation productivity are probably closely related to stages in the precessional cycle

paleohydrologic record from lake brine on the southern high plains texas the timing of changes in the stage and salinity of double lakes of lynn county texas was estimated using dissolved chloride profiles across an underlying shale layer lake conditions over the past 30 to 50 ka can be inferred from the chloride profiles by using the advective velocity of the pore water through the shale and an appropriate coefficient of molecular diffusion the profiles suggest that net evaporative conditions existed over the southern high plains for the past 50 ka a period of increasing salinity in the lake began at 20 ka and reached current levels at 5 ka in addition deflationary conditions were present for at least 4 ka and likely began or were accelerated during the most recent altithermal period at 5 ka this type of lake brine record may also exist in many other saline lake environments throughout the great plains of north america

influence of matrix diffusion and exchange reactions on radiocarbon ages in fissured carbonate aquifers the parallel fissure model coupled with the equation of diffusion into the matrix and with exchange reaction equations has been used to derive a simple formula for estimating the influence of matrix porosity and reaction parameters on the determination of radiocarbon ages in fissured carbonate rocks examples of evidently too great radiocarbon ages in carbonate formations which are not explainable by models for the initial sup 14 c corrections can easily be explained by this formula parameters obtained for a chalk formation from a known multitracer experiment combined with a pumping test suggest a possibility of sup 14 c ages more than three orders of magnitude greater than the ages which would be observed if the radiocarbon transport took place only in the mobile water in the fissures it is shown that contrary to the solute movement on a small scale and with a variable input the large scale movement characteristic for the sup 14 c dating does not necessarily require the knowledge of kinetic parameters because they may be replaced by the distribution coefficient discordant tritium and sup 14 c concentrations are commonly interpreted as a proof of mixing either in the aquifer or at the discharge site for fissured carbonate formations however anmore alternative explanation is given by the derived model showing a considerable delay of sup 14 c with respect to nonsorbable tracers less

pleistocene deposits in pierre saint martin cave french pyrenees abstract pleistocene deposits in alpine pierre saint martin cave are preserved in an abandoned river gallery the deposits 300 m long and 25 m high are composed of a lower unit of fallen blocks overlain by debris flows a main unit of laminated clay and a series of river terraces inset into these units the lower and main units are each overlain by speleothems the lower unit represents a cold period probably isotope stage 10 corroded speleothems above it have given u th ages greater than 300 000 330 000 yr b p the main unit with carbonate rich varves devoid of pollen represents a glaciation that occurred before 225 000 yr b p and probably correlates with stage 8 even though such a glaciation has not been previously recognized in the pyrenees the river terraces covered by many noncorroded speleothems probably formed during stage 7 u th ages between 194 000 and 211 000 225 000 yr b p subsequent sinking of an underground river protected the deposits from erosion

assessing the strength of the monsoon during the late pleistocene in southwestern united states abstract improved predictions of drought require an understanding of natural and human induced climate variability long term records across glacial interglacial cycles provide the natural component of variability however few such records exist for the southwestern united states us and quantitative or semi quantitative records of precipitation are absent here we use the hydrogen isotope d value of c28 n alkanoic acid in lacustrine sediments of pleistocene age to reconstruct d values of precipitation in northern new mexico over two glacial interglacial cycles 550 000 360 000 years before present and obtain a record of monsoon strength overall reconstructed d values range from 53 8 to 94 4 with a mean value of 77 5 8 remarkably this variation falls within the measured present day summer monsoonal and winter weighted means 50 3 3 and 106 4 20 respectively suggesting that processes similar to those of present time also controlled precipitation during marine isotope stage mis 13 to 10 using the d summer monsoonal and winter mean values as end members we interpret our reconstructed d record of precipitation as a direct and semi quantitative indicator of monsoon strength during mis 13 to 10 interglacial periods were characterized by greater monsoon strength but also greater variability compared to glacial periods pronounced cycles in the strength of the monsoon occurred during interglacial periods and in general were positively correlated with maximum mean annual temperatures our estimates of monsoon strength are supported by independent proxies of ecosystem productivity namely toc 13c of toc and si ti ratio and warm pollen taxa juniperus and quercus interglacial variability in the strength of the monsoon resembles a response to the land sea surface temperature contrast lstc except for the early part of mis 11 during this period lstc would have remained relatively strong while monsoonal strength decreased to a minimum this minimum occurred following the warmest interval of mis 11 suggesting a more complex driving of monsoon strength during warm periods in addition this period of monsoon minimum coincided with a core section of mud cracked sediments that suggest low monsoonal precipitation was an important factor in the onset of drought our estimates of monsoon strength represent a record of natural variability in the region that is relevant to present time in particular the variability during interglacial mis 11 which is considered an analog for the current interglacial our results suggest that natural variability can cause significant reductions in monsoonal precipitation with the implication of a potentially adverse effect from sustained warming

the identification of precipitation amount effect with a water isotope enabled threshold model in vadose zone a case study in ordos plateau accurate estimation of precipitation amount recharged to the groundwater is essential to the water balance calculation of a groundwater system in regional scale in the torrid zones the proportion of heavier water isotopes in precipitation presents a negative correlation with the precipitation amount the physical processes explicating this so called amount effect have not been well understood this paper focuses on the d relationships of local precipitation and groundwater to explain the isotopic variability in ordos plateau china in order to better understand the physical process interpreting the amount effect a numerical threshold model in the vadose zone to relate the ineffective precipitation amount and isotopic abundance of precipitation and groundwater was supposed by comparing the modelled d with that in groundwater ineffective precipitation a value of 6 12 mm was obtained in ordos plateau thus the potential groundwater recharge from the precipitation in the region can be deduced the methodology proposed in this study will provide useful insights into the estimation of precipitation contribution to groundwater in other similar areas in the world

depositional facies and aqueous solid geochemistry of travertine depositing hot springs angel terrace mammoth hot springs yellowstone national park u s a petrographic and geochemical analyses of travertine de positing hot springs at angel terrace mammoth hot springs yellow stone national park have been used to define five depositional facies along the spring drainage system spring waters are expelled in the vent facies at 71 to 73 8c and precipitate mounded travertine composed of aragonite needle botryoids the apron and channel facies 43 728c is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide oxidizing aquificales bacteria the travertine of the pond facies 30 62 8c varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures calcite ice sheets calcified bubbles and aggregates of aragonite needles fuzzy dumbbells pre cipitate at the air water interface and settle to pond floors the prox imal slope facies 28 54 8c which forms the margins of terracette pools is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face finally the distal slope facies 28 30 8c is composed of calcite spherules and calcite feather crys tals despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization the com positions of spring water and travertine predominantly reflect abiotic physical and chemical processes vigorous co 2 degassing causes a 12 unit increase in spring water ph as well as rayleigh type covariations between the concentration of dissolved inorganic carbon and corre sponding d 13 c travertine d 13 c and d 18 o are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher temperature 50 738c depositional facies conversely

intraplate earthquakes and the state of stress in oceanic lithosphere abstract the sources of stress responsible for oceanic intraplate earthquakes and their usefulness for inferring the tectonic stress field are investigated through a synthesis of the source mechanisms of 58 of the largest such events determined by inversion of long period p and sh waveforms further constraints are provided by the global distribution of oceanic intraplate seismicity and a calculation of the seismic moment release per unit volume of seismogenic lithosphere as a function of lithosphere age although frequently associated with relict tectonic features large oceanic intraplate earthquakes are generally reliable indicators of the state of stress in the source region most oceanic intraplate seismicity occurs in young lithosphere

mass spectrometric 230th 234u 238u dating of the devils hole calcite vein the devils hole calcite vein contains a long term climatic record but requires accurate chronologic control for its interpretation mass spectrometric u series ages for samples from core dh 11 yielded 230 th ages with precisions ranging from less than 1 000 years 2 for samples younger than 140 ka thousands of years ago to less than 50 000 years for the oldest samples 566 ka the 234 u 238 u ages could be determined to a precision of 20 000 years for all ages calcite accumulated continuously from 566 ka until 60 ka at an average rate of 0 7 millimeter per 10 3 years the precise agreement between replicte analyses and the concordance of the 230 th 238 u 234 u 238 u ages for the oldest samples indicate that the dh 11 samples were closed systems and validate the dating technique in general

intraplate seismicity of the pacific basin 1913 1988 we establish here a comprehensive database of intraplate seismicity in the pacific basin relocation and analysis of 894 earthquakes yield 403 reliable intraplate earthquakes during 1913 1988 these numbers do not include earthquake swarms which account for another 838 events most of the remainder 304 events are actually plate boundary earthquakes that have been erroneously located in intraplate regions a significant number occur in recent years when location capabilities should have guarded against this situation relocations involve a careful linear inversion of p and s arrivals accompanied by a monte carlo statistical analysis we have also attentively removed the high number of clerical errors and nuclear tests that exist in epicenter bulletins

high and low latitude orbital forcing of early hominin habitats in south africa abstract reconstructions of african palaeoenvironments are essential for a full understanding of early hominin evolution but they are often hampered by low resolution or discontinuous climatic data here we present high resolution oxygen 18 o and carbon 13 c isotope time series for the pliocene early pleistocene 1 99 to 1 52 ma of south africa derived from the buffalo cave flowstone deposit the 18 o data are dominated by variations at the orbital precession period 18 23 ka as is typical for records of sub tropical monsoon rainfall the 13 c data indicate the proportion of savannah grasses c 4 plants compared to trees and shrubs c 3 plants and this signal is dominated by an obliquity periodicity 40 ka commonly associated with high latitude ice sheet dynamics a rapid increase in savannah grass proportions between 1 78 and 1 69 ma coincides with a pulse in african mammal turnover and lends support to an adaptive link between the appearance of african homo erectus and the increasingly savannah dominated environment

spectral comparisons between explosion p signals from the tuamotu islands nevada and eastern kazakh a comparison is presented between explosion generated teleseismic p signals from single events of comparable magnitude in the tuamotu islands nevada and e kazakh recorded by the wake island hydrophone array spectral analysis of these signals indicates that attenuation presumably under the source is greatest for the tuamotu travel path and least for the e kazakh travel path the high frequencies 3 hz present in e kazakh signals which enhance the detectability of these signals on the ocean bottom near wake where noise levels are low in this range are generally absent in signals from nevada and the tuamotus

pleistocene paleoenvironmental evolution at continental middle latitude inferred from carbon and oxygen stable isotope analysis of ostracodes from the guadix baza basin granada se spain abstract a representative paleoenvironmental reconstruction of continental middle latitude from ca 2 my to the upper part of middle pleistocene 279 77 ky was obtained from the carbon and oxygen stable isotopes analyzed in ostracode shells cyprideis torosa recovered in the guadix baza basin se spain an intramontaneous closed depression filled by alluvial and lacustrine sediments this study was performed along a 356 m thick composite section dated previously by paleomagnetism and the amino acid racemization method 13c and 18o profiles reflected changes in temperature the evaporation infill ratio in the water bodies and the amount of rain 13c is also affected by changes in plant biomass periods with high 13c and 18o values are associated with warm and dry regimes and with less vegetation which in some cases coincide with the development of displacive gypsum crystals whereas low 13c and 18o values correlate with cold and humid episodes which cause more vegetation biomass and therefore increasing the input of isotopically light carbon intermediate 18o values are linked to temperate dry or humid episodes when they coincide with high or low 13c values respectively 86 paleoclimatic events were distinguished in the pleistocene record from the 13c and 18o profiles from both the statistical analysis of the geochemical data and the geological observations four cold and humid long periods low 18o and four warm and dry long periods high 18o were defined this differs with respect to the paleoclimatological behavior established for the northern hemisphere where during cold periods glacial no water was available while permafrost conditions persisted whereas in warm episodes interglacial higher precipitation rates occurred good correspondences between the guadix baza basin paleoclimatic record and a marine oxygen isotope sequence two continental cores and other long mediterranean paleoenvironmental records pollen sequences from israel were found which suggested that climate changes in the guadix baza basin were in tune with global climatic changes

500 000 year stable carbon isotopic record from devils hole nevada the record of carbon 13 delta 13 c variations in dh 11 vein calcite core from devils hole nevada shows four prominent minima near glacial terminations glacial interglacial transitions v to ii the delta 13 c time series is inversely correlated with the dh 11 oxygen isotope ratio time series and leads it by as much as 7000 years the delta 13 c variations likely record fluctuations in the delta 13 c of dissolved inorganic carbon of water recharging the aquifer how such variations are transported 80 kilometers to devils hole without obliteration by water rock reaction remains an enigma the record may reflect i global variations in the delta 13 c of atmospheric co 2 and hence the delta 13 c of continental biomass or ii variations in extent and density of vegetation in the southern great basin in the latter case delta 13 c minima at 414 334 246 and 133 thousand years ago mark times of maximum vegetation

a 250 000 year climatic record from great basin vein calcite implications for milankovitch theory a continuous record of oxygen 18 18o variations in the continental hydrosphere during the middle to late pleistocene has been obtained from a uranium series dated calcitic vein in the southern great basin the vein was deposited from ground water that moved through devils hole an open fault zone at ash meadows nevada between 50 and 310 ka thousand years ago the configuration of the 18o versus time curve closely resembles the marine and antarctic ice core vostok 18o curves however the u th dates indicate that the last interglacial stage marine oxygen isotope stage 5 began before 147 3 ka at least 17 000 years earlier than indicated by the marine 18o record and 7 000 years earlier than indicated by the less well dated antarctic 18o record this discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine 18o chronology may need revision and that orbital forcing may not be the principal cause of the pleistocene ice ages

structure of the earth oceanic crust and uppermost mantle the past four years have witnessed the introduction of a variety of new instruments and methods for the study of the seismic structure of the oceanic crust and lithosphere the application of these and existing tools has led to the discovery of a number of new phenomena and to a fuller understanding of the genesis and evolution of the oceanic ithosphere borehole seismic instrumentation has become more widely employed ocean bottom seismographs while generally decreasing in number have become significantly more reliable and useful and multichannel seismic systems have been employed in innovative experiments ranging from studies of fracture zones to the regular detection of magma chambers beneath rise axes the techniques available for the analysis of seismic data have become more sophisticated waveforms collected in seismic experiments can now be used directly in constructing and evaluating seismic velocity models and travel time data are regularly inverted directly for structure trial and error modeling has become increasingly unimportant marine seismologists are becoming increasingly involved in understanding the coupling between the ocean and the underlying oceanic lithosphere this has led to a more complete understanding of seafloor noise processes and the partitioning of energy between acoustic and elastic waves

spectral characteristics of p waves from nuclear explosions and yield estimation abstract spectra of teleseismic short period p waves from nuclear explosions show clear path related differences in their high frequency falloff rates p waves from kazakh explosions commonly show significant seismic energy above the frequency of 5 hz when recorded in shield regions peaceful nuclear explosions in the tectonically stable areas of the ussr have similar properties together with the amchitka explosions and salmon nuclear explosions in the western united states algeria and french polynesia show much less high frequency energy in their p wave spectra and signal energy above 5 hz is usually not seen we attribute these variations to lateral changes in the anelastic attenuation properties of the upper mantle for the events in the contiguous united states this interpretation is confirmed by the results of reciprocal measurements of q about 500 p wave spectra not including those utilized in the reciprocal measurements were used to estimate the contribution to t p of the upper mantle q structures under a number of nuclear test sites and observatories

tectonic speleogenesis of devils hole nevada and implications for hydrogeology and the development of long continuous paleoenvironmental records devils hole in southern nevada is a surface collapse into a deep planar steeply dipping fault controlled fissure in cambrian limestone and dolostone the collapse intersects the water table about 15 m below land surface and the fissure extends at least 130 m deeper below water most of the fissure is lined with a 30 cm thick layer of dense maxillary calcite that precipitated continuously from groundwater for 500 000 yr the thick mammillary calcite coat implies a long history of calcite supersaturated groundwaters which combined with the absence of dissolutional morphologies suggests that devils hole was not formed by karst processes devils hole is located in a region of active extension its tectonic origin is shown by evidence of spreading of its planar opening along a fault and by the orientation of its opening and others nearby perpendicular to the northwest southeast minimum principal stress direction of the region most quaternary tectonic activity in the area including seismicity and quaternary faults and fractures occurs on or parallel to northeast striking structures the hydrogeologic implications of this primarily structural origin are that fracture networks and caves opened by extensional tectonism can act as groundwater flowpaths functionally similar to those developed by karst processes and that during active extension transmissivity can be maintained despite infilling by mineral precipitation such extensional environments can provide conditions favorable for accumulation of deposits preserving long continuous paleoenvironmental records the precipitates in devils hole store chronologies of flow system water level fluctuations hydrochemistry a half million yr proxy paleoclimate record evidence of devils hole s tectonic origin and probably atmospheric circulation

isotopic characterization of late neogene travertine deposits at barrancas blancas in the eastern atacama desert chile abstract here we explore the potential of spring related surface and subsurface carbonates as an archive of paleoenvironmental change at barrancas blancas located in the broadest and driest sector of the atacama desert at 24 5 s from these deposits we present a new stable isotopic record of paleoenvironmental conditions over portions of the past 11 5 ma u pb dates from the carbonates both surface and subsurface demonstrate that springs have discharged at this location over much of the last 11 5 ma attesting to the exceptional geomorphic stability of the central atacama many of the sampled vein systems line vertical fissures and formed within the aquifer before groundwater discharged at the surface carbonates in such circumstances should not undergo off gassing and kinetic fractionation prior to formation simplifying the interpretation of their isotopic composition oxygen isotopic compositions of carbonates are generally high 5 vpdb and using paleospring water temperatures of 3 13 c reconstructed from clumped isotopes point to strongly up to 50 evaporated water isotope values like those associated with the hyperarid core of the atacama desert today carbon isotopic compositions are also high 3 pdb reflecting a recharge area essentially devoid of plants and dominated by volcanic co 2 as is the case today our isotopic results are very similar to those from the calama basin to the north suggesting that the western face of the andes between 21 and 25 s has been highly evaporative and nearly plantless when these springs discharged over the last 11 5 ma the spring carbonates at barrancas blancas strongly resemble those found at devils hole and furnace creek in death valley usa and as such warrant further exploration as potential archives of climate change

earthquakes in the aseismic regions of the western pacific operators of a deep ocean hydrophone array near wake island in the northwest pacific basin have located several previously unreported earthquakes within 20 of wake island in the aseismic interior of the pacific plate and have suggested high attenuation in the source region to explain why these events have not been reported by seismological agencies the largest such earthquake occurred on 1983 june 29 in the kiribati region readings were submitted to the international seismological centre but the earthquake was excluded from the final analysis because of doubt about its location and interfering arrivals from other earthquakes closer examination now provides a well determined seismological location and a magnitude of 4 7 mb neither amplitudes nor frequency content of australian records of the kiribati earthquake support the existence of a region of abnormally high attenuation beneath the source we suggest that the higher magnitudes reported from the hydrophone measurements result from the efficient coupling of energy from shallow intraplate earthquakes in the pacific basin into the po so waveguide

transmission of δ13c signals and its paleoclimatic implications in liangfeng cave system of guizhou province sw china a series of samples including vegetation soil organic matter soil waters spring bedrock pool water drip waters upper drip waters and ground drip waters and their corresponding speleothems were collected at liangfeng cave lfc system of guizhou province southwest of china respectively from 2003 to 2004 year then their stable carbon isotopes were measured and analyzed results reveal that vegetation is c3 type in lfc system cave overlying 13c signals including values and variations could be transmitted to drip water speleothem speleothem 13c mainly shows a biogenic 13c value character soil co2 from plant respiration and decay and there are remarkable seasonal variations of 13c values for drip water tdic speleothem which are lighter at least 2 0 in the rainy seasons than in the dry ones so it could be feasible to reconstruct high resolution changes of paleoecology and paleoclimate by using speleothem 13c values

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

evidence of younger dryas and neoglacial cooling in a late quaternary palaeotemperature record from a speleothem in eastern victoria australia a calcitic stalagmite collected from a limestone cave in the buchan area of eastern victoria has been dated by three mass spectrometric uranium series analyses two growth phases are represented the older from 13 4 to 10 6 ka and the younger from 3 2 to 2 1 ka oxygen isotope analysis reveals that temperatures were below present day values at all times but particularly cool conditions are indicated between 12 3 and 11 4 ka and neoglacial conditions occurred at about 3 ka the older cold climate event is clearly synchronous with the younger dryas in europe and this is the first time that strong evidence for this event has been found in australia carbon isotope variations are interpreted as indicating changes in plant productivity on the surface and are most likely controlled by variations in summer rainfall they indicate particularly high levels of plant productivity from 11 5 to 11 0 ka 1996 john wiley sons ltd

a diatom record of climate and hydrology for the past 200 ka from owens lake california with comparison to other great basin records abstract diatoms from lake sediments beneath owens lake playa inyo county california document a nearly continuous paleolimnological record of climate and hydrologic change since the penultimate glacial interglacial cycle based on a chronology established by radiocarbon tephrochronology and paleomagnetic control freshwater planktic diatoms especially species of stephanodiscus plagioclase feldspar rich sediments with high magnetic susceptibility and juniperus type pollen characterized the penultimate glaciation at owens lake saline diatoms dominated in the following interglacial period and there are several episodes during which freshwater planktic diatoms became abundant between 100 and 50 ka that may represent interstadial climatic conditions saline diatoms fell to low values after 50 ka but warm season aulacoseira species indicate episodes of significant summer precipitation in the hydrologic balance of owens lake prior to the last glacial maximum by 25 ka glacial environments were again characterized by abundant juniperus plagioclase feldspar and stephanodiscus species generally arid holocene climates were recorded in owens lake by short term fluctuations of saline and freshwater diatoms desiccation and oolitic sediments barren of diatoms comparison to paleoclimate records both north and south of owens lake suggest a southerly displacement of storm tracks originating from the aleutian low during glacial episodes

po so synthetics for a variety of oceanic models and their implications for the structure of the oceanic lithosphere summary polso synthetic seismograms were computed for a variety of oceanic structures in order to model data from an t zb 5 7 earthquake recorded during the oss iv seismic experiment satisfactory modelling of polso waveshapes and frequency content was achieved with no lateral heterogeneity but with a small random vertical heterogeneity in the mantle superimposed on a mean velocity structure which is consistent with seismic refraction data the random heterogeneity in the p and s velocities appears to be about 2 per cent with a scale length of 5 km this kind of heterogeneity is easily achieved by varying slightly the major mineral components in either the peridotite or eclogite mantle mineralogy and can be another cause of observed upper mantle anisotropy using a step function source time behaviour our numerical modelling also indicates that in the upper mantle qp is roughly proportional to rising from about 450 at f 1 hz to about 800 at f 15 hz and that q is roughly proportional to rising from about 900 at f 1hz to about 1800 at f 15hz a slight decrease in q from these values in any small zone of the upper mantle reduces so amplitudes drastically and we believe this is why so is sometimes missing from observed seismograms the computed synthetic record sections were also used to examine the relation between intrinsic q and the apparent q inferred from data in earlier studies apparent q was found to be lower than intrinsic q below about 5hz and higher than intrinsic q above 5 hz when these differences are accounted for the mantle q s of this study agree with the mantle q s of butler et al 1987 to within 10 per cent there can no longer be any doubt that oceanic upper mantle q s are very large above 5 hz and that q is about twice as large as qp

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

deglacial paleoclimate in the southwestern united states an abrupt 18 6 ka cold event and evidence for a north atlantic forcing of termination i we present a new u series dated speleothem record pc 1 from the great basin that documents deglacial climate variability between ca 20 1 and 15 6 ka our data show an abrupt 18 6 ka cold event preceding heinrich event 1 that is consistent with expansion of the laurentide ice sheet during the binge phase of ice growth this event coincided with dessication of pluvial lake mojave suggesting cold and dry conditions in the southern great basin at this time pc 1 d 18 o values before and during heinrich event 1 are similar but an increase in stalagmite growth rates suggests wetter conditions that coincided with deposition of spring deposits in southern nevada the time interval of our record is consistent with the timing of pluvial conditions in the great basin as evident from a comparison to regional wetness proxies our new speleothem record recovered from the recharge area for devils hole does not show a d 18 o increase coincident with the abrupt increase in devils hole d 18 o at c 18 ka challenging the view

intraplate deformation in the samoa gilbert ralik area a prelude to a change of plate boundaries in the southwest pacific okal e a woods d f and lay t 1986 intraplate deformation in the samoa gilbert ralik area a prelude to a change of plate boundaries in the southwest pacific in b johnson and a w bally editors intraplate deformation characteristics processes and causes tectonophysics 132 69 71 intense intraplate seismic activity has recently been identified in the west central pacific along a line extending from samoa through the gilbert islands and the ralik fracture zone to the caroline islands over the past 50 years this seismic line has contributed an estimated 15 30 of the entire intraplate seismicity for the pacific plate hawaii excepted focal mechanisms available for ten of the largest events during the 1981 1983 gilbert islands swarm with horizontal compressional stress oriented at right angles to the direction of motion of the plate cannot be reconciled with simple models of intraplate stresses we speculate that they express large scale deformation of that part of the pacific plate related to incipient detachment of a microplate and relocation of the pacific australian subduction zone some 1000 km to the north of its present position

radiation windows as indicators of an astronomical influence on the devil s hole chronology orbitalexplanationsofpaleoclimaticrecordstraditionallyfocusondailyinsolationat 60 n we exemplify how insolation at different latitudes and different times of day can explain the timing of the devil s hole d 18 o record we combine winter tropical noontime insolation associated with the source region for wintertime precipitation and summer extra tropicalnoontimeinsolation producingnoontimeheattowarmterrestrialsurfaces periodsoflowwinterandhighsummerinsolationarecalled radiationwindows andyield drier warmer conditions in the northern hemisphere mid latitudes when radiation windows are compared with the dh 11 record the apparent contradiction with milankovitch winogradetal 1992 mayberesolved themiddle latitudecontinentalclimatesignal as recordedbydh 11 tendstowardacoolingstateuntilinterruptedbyatermination inevery instance where the dh 11 record is warming before a radiation window a termination occurs if radiation windows occur with antecedent cooling then there is a complex response of warming with a variable lag effect yet there are no cases where cooling follows a radiation window

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

mediterranean vegetation lake levels and palaeoclimate at the last glacial maximum the apparent conflict between pollen evidence for widespread artemisia steppe1 6 implying semi arid conditions and geomorphological evidence for high lake levels4 7 11 has produced controversy about the ice age palaeoclimate of the mediterranean region here we use a water balance model12 to predict catchment runoff and a biome model13 to predict vegetation type to reconstruct the palaeoenvironment around lake loannina a type locality for the northern mediterranean region we show that both sets of evidence are compatible with a summer dry winter wet regime with seasonal temperature anomalies similar to those predicted by atmospheric model simulations of the last glacial maximum14 18 the drying effect of the cold north atlantic ocean may have been counteracted in winter by increased storm frequency under a southward shifted jet stream as shown by several atmospheric models16 18

the gilbert islands republic of kiribati earthquake swarm of 1981 1983 abstract a major swarm of intraplate earthquakes at the southeastern end of the gilbert islands chain 3 5 s 177 5 e commenced in december 1981 and lasted through march 1983 no seismicity had been reported in the historical record in this region prior to 1981 but during the swarm 217 events with mb 4 0 were located by the neis with 86 events having mb 5 0 the source region is quite remote and the uniform detection level for the neis is for mb 4 8 a b value of 1 35 is found for the swarm using the maximum likelihood method four events in the sequence were large enough mb 5 6 5 9 to determine focal mechanisms teleseismically using body and surface wave analysis these events are found to have a range of mechanisms from predominantly thrust with a significant oblique component to purely strike slip the compression axes are consistent for all four events with horizontal orientation trending nne ssw this orientation is perpendicular to the direction of plate motion the events are located at depths between 15 and 20 km placing them deep in the oceanic crust or in the upper mantle no obvious bathymetric feature can be related to the fault plane orientations though there is an offset in the island chain near the epicenters while some characteristics of the swarm suggest a magmatic origin the nature of the focal mechanisms the location of the swarm and the large accumulated moment release of the sequence favor a tectonic origin

regional groundwater flow in structurally complex extended terranes an evaluation of the sources of discharge at ash meadows nevada summary ash meadows nevada usa is a site of major groundwater discharge 38 000 l min in the arid mojave desert and hosts a number of endemic and threatened wetland species in addition to these resources ash meadows may also represent the future discharge location of radionuclide laden waters from nuclear weapons testing at the nevada test site more importantly however ash meadows provides the opportunity to understand the controls on water transfer between basins through fractured bedrock 4000 solute analyses were assembled from the literature into a single database the data were screened for spatial distribution completeness charge balance and elevated temperatures 20 c and within regional flow systems with 246 candidate up gradient water remaining distributed among six potential source areas in addition to and ash meadows itself these potential sources include both carbonate volcanic and perhaps valley fill aquifer systems these waters were characterized by cluster analysis in order to sort similar waters in an objective fashion into potential flow paths and to establish representative endmember waters for inverse geochemical models and other modes of analysis isotopic tracers both conservative and those reflecting water rock interaction all suggest that waters at ash meadows are derived by southward flow from volcanic terranes parallel to the preferred permeability structure induced by active regional east west extension solute balances support this conclusion however this runs counter to the prevailing model that waters at ash meadows are derived from easterly and northeasterly flows from the spring mountains and pahranagat valley areas by interbasin flow through a continuous fractured carbonate aquifer this work suggests that carbonate aquifer systems in extended terranes are more compartmentalized than previously appreciated and that anisotropy in fracture permeability is key to compartmentalization and the control of flow directions

facies system of the eastern barents sea since the last glaciation to present abstract twenty two sediment cores raised from the central and eastern parts of the barents sea have been studied to reconstruct the evolution of the facies system since the late weichselian glaciation multiproxy records reveal four lithostratigraphic units which reflect major development stages of paleoenvironments age control is provided by 23 ams 14 c dates for holocene sections of four cores continental moraine deposits of the last glaciation are overlain by proximal glaciomarine facies of the initial deglaciation phase during this phase the barents sea ice sheet detached from the ground resulting in seawater penetration into troughs iceberg calving deposition of ird and fine grained glacier meltwater load in newly formed marine basins the main deglaciation phase is characterized by pulsed sedimentation from various gravity flows resulting in accumulation of distal glaciomarine facies comprising laminated clay and sand sequences with minor ird redistribution of fine grained suspended matter by bottom currents and brine induced nepheloid flows combined with biogenic processes and minor ice rafting caused facies diversity of the holocene marine sediments the holocene facies of shelf depressions reflect rather high but variable productivity responding to climate changes and variations of atlantic water inflow into the barents sea

devils hole paleotemperatures and implications for oxygen isotope equilibrium fractionation subaqueous calcite in devils hole nevada was growing continuously from slightly super saturated groundwater providing a 570 kyr long o18 paleoclimate record due to its very slow growth it has been assumed to have grown under conditions of isotopic equilibrium however its holocene o18 value is 1 5 higher than predicted by laboratory precipitation based oxygen isotope thermometer calibrations the suggestion that devils hole calcite anchors the isotope thermometer to more 18o enriched values has stirred a debate as to which paleothermometer calibration is relevant for paleoclimate and casts doubt on the validity of o18 based paleotemperatures we used clumped isotopes to test the assumptions of the devils hole alternative 18o thermometer carbonate clumped isotopes are a temperature proxy that measures the abundance of 13c18o bonds in caco3 this proxy is independent of the water composition and therefore gives independent estimates of temperatures when calcite forms at thermodynamic and isotopic equilibrium we find that devils hole water paleotemperatures were constant at 30 6 2 6 c between 27 and 180 ka similarly to the modern groundwater temperature of 32 8 34 3 c the proximity of the devils hole clumped isotope data to values expected based on modern groundwater temperatures supports the notion that devils hole calcite grew under equilibrium conditions therefore the commonly used laboratory based o18 temperature calibrations should be reconsidered the constant water temperature over the glacial interglacial cycles indicates that the long devils hole o18 record reflects only variations in the groundwater o18 values and as such represents a valuable archive of paleoclimate and isotope paleohydrology

carbon isotope records from pacific surface waters and atmospheric carbon dioxide we have stacked planktonic carbon isotope data from three cores in the western equatorial pacific in order to generate a new reconstruction of atmospheric carbon dioxide over the past 450 000 years our new reconstruction resembles that of shackleton et al 1983 based on data from east pacific core v19 30 which successfully predicted features that were subsequently verified by barnola et al 1987 in the record from the vostock ice core in addition the new data confirm the discovery of shackleton and pisias 1985 that changes in atmospheric co2 lead changes in ice volume and hence probably contributed to the glacial interglacial cycles our new reconstruction avoids some of the deficiencies of the previous reconstruction in particular the planktonic species neogloboquadrina dutertrei on which the earlier reconstruction depends does not calcify in truly nutrient free surface water as the model assumes whereas our new reconstruction uses globigerinoides sacculifer which is expected to be more reliable in addition the surface waters in the west pacific are closer to the nutrient free ideal on which the model broecker 1982 depends on the other hand the amplitude of the new reconstruction is significantly smaller than the amplitude observed by barnola et al 1987 it is not clear whether this smaller range is a better estimate of the amplitude of the biological pump effect or whether the true amplitude is reduced by bioturbation in the west pacific cores that we studied

lipid distribution in a subtropical southern china stalagmite as a record of soil ecosystem response to paleoclimate change abstract lipid extracts from a 61 7 cm long subtropical stalagmite in southern china spanning the period of ca 10 000 21 000 yr ago as constrained by u th dating were analyzed using gas chromatography mass spectrometry the higher plants and microorganisms in the overlying soils contribute a proportion of n alkanes identified in the stalagmite the occurrence of lmw lower molecular weight n alkanols and n alkan 2 ones in the stalagmite was mainly related to the soil microorganisms we suggest that hmw higher molecular weight n alkanols and n alkan 2 ones identified in the stalagmite originate from soil organics and reflect input from contemporary vegetation shifts in the ratio of lmw to hmw n alkanols or n alkan 2 ones indicative of the variation of soil ecosystems e g microbial degradation of organic matter and or the relative abundance of soil microorganisms to higher plants are comparable with the subtropical alkenone sst sea surface temperature record of the same period the similar trends seen in the 13c data and the lipid parameters in this stalagmite imply that the overlying soil ecosystem response to climate might be responsible for the variation of 13c values

reconciliation of the devils hole climate record with orbital forcing the driving force behind quaternary glacial interglacial cycles and much associated climate change is widely considered to be orbital forcing however previous versions of the iconic devils hole nevada subaqueous calcite record exhibit shifts to interglacial values 10 000 years before orbitally forced ice age terminations and interglacial durations 10 000 years longer than other estimates our measurements from devils hole 2 replicate virtually all aspects of the past 204 000 years of earlier records except for the timing during terminations and they lower the age of the record near termination ii by 8000 years removing both 10 000 year anomalies the shift to interglacial values now broadly coincides with the rise in boreal summer insolation the marine termination and the rise in atmospheric co2 which is consistent with mechanisms ultimately tied to orbital forcing

uranium series dating of sediments from searles lake differences between continental and marine climate records one of the major unresolved questions in pleistocene paleoclimatology has been whether continental climatic transitions are consistent with the glacial 18 o marine record searles lake in california now a dry salt pan is underlain by sediment layers deposited in a succession of lakes whose levels and salinities have fluctuated in response to changes in climate over the last 3 x 10 6 years uraniumseries dates on the salt beds range from 35 x 10 3 to 231x 10 3 years this range of dates allows identification of lake sediment horizons that are time correlatives of the boundaries of marine isotope stages from the recent 3 4 boundary back to the 8 9 boundary the 5 6 boundary coincided with a deepening of the lake but the analogous 1 2 boundary coincided with desiccation the 3 4 4 5 6 7 7 8 and 8 9 boundaries correspond in age to horizons that record little or no change in sedimentation or climate these hydrologic results demonstrate that the continental paleoclimate record at this mid latitude site does not mimic the marine record

summary of the snowmastodon project special volume a high elevation multi proxy biotic and environmental record of mis 6 4 from the ziegler reservoir fossil site snowmass village colorado usa abstract in north america terrestrial records of biodiversity and climate change that span marine oxygen isotope stage mis 5 are rare where found they provide insight into how the coupling of the ocean atmosphere system is manifested in biotic and environmental records and how the biosphere responds to climate change in 2010 2011 construction at ziegler reservoir near snowmass village colorado usa revealed a nearly continuous lacustrine wetland sedimentary sequence that preserved evidence of past plant communities between 140 and 55 ka including all of mis 5 at an elevation of 2705 m the ziegler reservoir fossil site also contained thousands of well preserved bones of late pleistocene megafauna including mastodons mammoths ground sloths horses camels deer bison black bear coyotes and bighorn sheep in addition the site contained more than 26 000 bones from at least 30 species of small animals including salamanders otters muskrats minks rabbits beavers frogs lizards snakes fish and birds the combination of macro and micro vertebrates invertebrates terrestrial and aquatic plant macrofossils a detailed pollen record and a robust directly dated stratigraphic framework shows that high elevation ecosystems in the rocky mountains of colorado are climatically sensitive and varied dramatically throughout mis 5