global upper mantle structure from finite frequency surface wave tomography 1 we report global shear wave velocity structure and radial anisotropy in the upper mantle obtained using finite frequency surface wave tomography based upon complete three dimensional born sensitivity kernels because wavefront healing effects are properly taken into account finite frequency surface wave tomography improves the resolution of small scale mantle heterogeneities especially for deep anomalies that are constrained by the longest period surface waves in our finite frequency model ffsw1 the globally averaged radial anisotropy shows a transition from positive sh sv to negative anisotropy sv sh at about 220 km consistent with a change in the dominant mantle circulation pattern from predominantly horizontal flow at shallow depths to vertical flow at greater depths the radial anisotropy beneath cratons and the old pacific plate agrees well with previous studies however our model exhibits a strong negative radial anisotropy at depths greater than 120 km beneath mid ocean ridges a feature that is not present in previous upper mantle models more interestingly the depth extent of the ridge anomalies is distinctly different beneath fast and slow spreading centers anomalies beneath fast spreading centers are stronger but the strength decreases rapidly below 250 km in contrast beneath slow spreading centers such as the northern mid atlantic ridge and the red sea anomalies extend down at least to the top of the transition zone the different depth extent of the ridge anomalies suggests that the primary driving force of slow spreading seafloor may be different from that of fast spreading seafloor and that active upwelling beneath slow spreading ridges may play a major role in the opening of the seafloor

pressure transient analysis for two phase geothermal wells some numerical results a numerical geothermal reservoir simulator is used in a series of calculations to help devise interpretation techniques for analyzing pressure transient data from two phase geothermal reservoirs the investigations include 1 the drawdown buildup behavior of initially two phase liquid water steam reservoirs 2 the drawdown buildup response of initially single phase reservoirs which undergo flashing as a result of fluid production and 3 the effects of cold water injection into hot two phase reservoirs production drawdown buildup data from two phase either initially or due to production induced boiling reservoirs may be analyzed in the usual manner to yield kinematic mobility buildup data from reservoirs which undergo flashing on production also offer the possibility of determining absolute formation permeability injection data can be interpreted in a straightforward manner to yield absolute formation permeability the corresponding falloff data appear however to be of little value

interpretation of downhole data and development of a conceptual model for the redondo creek area of the baca geothermal field available drilling records downhole surveys and surface discharge measurements from the wells drilled in the redondo creek area through 1981 were examined to determine the depths at which the wells penetrate permeable zones and thereby define those locations at which the pressure temperature measurements actually correspond to the reservoir conditions the results of these individual well analyses are used to estimate the initial pressure and temperature distributions of the reservoir system in the redondo creek area this information together with the well stratigraphy and the zones of fracture permeability penetrated by the wells is presented on vertical sections across the area the extent of a two phase region at the top of the reservoir system is also estimated using the pressure temperature distributions and the measured carbon dioxide content of the surface discharge from the baca wells the conceptual model presented provides the framework needed for detailed reservoir engineering studies 34 references 26 figures

validity domain of the born approximation for seismic waveform modelling in realistic 3 d earth structure while the first order born approximation is increasingly being used in many seismic tomography efforts its domain of validity to forward model seismic waveforms has not been quantified in the context of current 3 d earth models yet we here address this issue by comparing teleseismic synthetic surface waveforms calculated using the born approximation with spectral element method solutions for a variety of realistic global 3 d earth models we find that the born approximation has a very limited domain of validity when applied to seismic waveforms specifically it can only accurately model the phase amplitude of surface waveforms for source receiver paths leading to time shifts smaller than about 15 per cent 5 per cent of the wave period considered these conditions usually occur in earth models as s20rts or s40rts combined with a homogeneous crust for periods longer than t 80 90 s for models with stronger heterogeneity and or realistic 3 d crustal structure only the phase of waveforms with periods longer than 120 130 s can be accurately modelled with the born approximation

oxygen and carbon isotopes of detrital carbonate in north atlantic heinrich events abstract we report oxygen and carbon isotope results of detrital carbonate grains from heinrich layers at three sites in the north atlantic located along a transect from the labrador sea to the eastern north atlantic oxygen isotopic values of individual detrital carbonate grains from six heinrich layers at all sites average 5 6 1 5 1 n 166 reflecting values of dolomitic limestone derived from source areas in northeastern canada the 18o of bulk carbonate at integrated ocean drilling program iodp site u1308 re occupation of deep sea drilling project dsdp site 609 in the eastern north atlantic records the proportion of detrital to biogenic carbonate and 18o decreases to 5 during heinrich h events 1 2 4 and 5 relative to a background value of 1 to 2 for biogenic carbonate bulk 18o also decreases during h3 and h6 but only attains values of 1 indicating either a greater proportion of biogenic to detrital carbonate or a different source because the 18o of detrital carbonate is 9 lower than foraminifer carbonate any fine grained detrital carbonate not removed from the inner test chambers will lower foraminifer 18o we conclude bulk carbonate 18o is a sensitive proxy for detrital carbonate and may be useful for identifying heinrich layers in cores within and near the margins of the north atlantic ice rafted detritus ird belt

the southern ocean surface between marine isotope stages 6 and 5d shape and timing of climate changes summer sea surface temperature ssst and sea ice extent obtained at millennial to centennial resolution are presented for seven cores recovered in the atlantic and western indian antarctic zone from termination ii and the last interglacial s s i e marine isotope substage mis 5e the diatom based ssst estimates show that during the late mis 6 intensified export of cold waters from the weddell sea resulted in sssts close to 0 c in the central and eastern atlantic sector due to northward expansion of the winter sea ice edge by 3 5 latitude the sea ice seasonality was reduced such conditions have great potential for efficient year round reduction in air sea gas exchange and glacial co2 draw down the warming at termination ii started at 132 131 ka marked by rapid retreat of the sea ice edge the ssst increased within a few thousands of years to reach maximum interglacial summer temperatures ranging between 2 5 and 3 5 c in the earliest mis 5e 128 125 ka besides a distinct cold reversal around 129 5 ka the warming was punctuated by short lived temperature rebounds with amplitudes of 1 1 5 c occurring at 200 300 yr frequency thus in the range of the periodicity of solar input increased chaetoceros spp abundance suggests meltwater events as the primary cause of the coolings the ssst optimum characterised by strongly enhanced biogenic sedimentation rates ended at ca 125 ka with the full re establishment of the global conveyor belt and beginning of the northern hemisphere climatic optimum at this time sssts decreased stepwise and stabilised on values slightly warmer than today showing in the following period of mis 5e only low amplitude oscillations during mis 5d a northward expansion of the sea ice field took place but sssts only slightly colder than modern ones and a weakened meridional temperature gradient indicate that the southern ocean did not fall in a true glacial mode the tight correlation between southern ocean ssst and winter sea ice records and vostok atmospheric temperature and co2 records support the idea that the antarctic winter sea ice and southern ocean temperature exert a primary control on the atmospheric ocean co2 exchanges and hence on global climate reduction of the antarctic sea ice field and increase of ssst at the onset of termination ii could have been triggered by precessional changes influencing southern high latitude summer insolation positive feedback mechanisms reduction of surface albedo and release of co2 into the atmosphere and changes in global ocean circulation affected by a collapse or strong reduction in north atlantic deep water nadw production could have induced further reinforcement of the southern ocean warming

a millennial scale u37k sea surface temperature record from the south china sea 8 n over the last 150 kyr monsoon and sea level influence we report 150 kyr records of u37 sea surface temperature sst and carbonate content with 150 200 year sampling resolution from the southern south china sea scs in the northern margin of the western pacific warm pool wpwp using images core md972151 the glacial interglacial sst change is about 5 c for termination ii 23 5 to 28 5 c and 4 c for termination i 24 to 28 c the simultaneous rise of sea level and u37 sst during termination i suggests that sea level change has played an important role in the scs sst variability by influencing the exchange of tropical ocean warm surface water with the scs through the sunda shelf region sill depth 30 50 m when sea level drop was less than 30 m relative to today s md972151 sst was constantly above 27 c a situation which occurred during mis 5e part of mis5c and 5a and over the last 11 kyr sea level change was also the main control on carbonate content in the scs this was lower during low sea level stands due to the dilution effect of enhanced terrigenous inputs within the limitations of our age model millennial scale sst oscillations 1 5 c over a few hundred years occurred frequently during the entire glacial period correlating reasonably well with the hulu monsoon record from eastern china and the dansgaard oeschger d o cycles recorded for high latitude regions in the northern hemisphere such correlations suggest a possible teleconnection between higher latitude atmospheric forcing and low latitude climate oscillations in the western pacific tropical region via the asian monsoon system carbonate content also reveals millennial scale oscillations during the glacial period with higher content correlated with higher sst millennial scale fluctuations of sst and carbonate contents at this low latitude scs provide additional evidence that high frequency climate changes are global phenomena

mapping the moho with seismic surface waves a review resolution analysis and recommended inversion strategies abstract the strong sensitivity of seismic surface waves to the moho is evident from a mere visual inspection of their dispersion curves or waveforms rayleigh and love waves have been used to study the earth s crust since the early days of modern seismology yet strong trade offs between the moho depth and crustal and mantle structure in surface wave inversions prompted doubts regarding their capacity to resolve the moho here we review surface wave studies of the moho with a focus on early work and then use model space mapping to establish the waves sensitivity to the moho depth and the resolution of their inversion for it if seismic wavespeeds within the crust and upper mantle are known then moho depth variations of a few kilometres produce large 1 perturbations in phase velocities however in inversions of surface wave data with no a priori information wavespeeds not known strong moho depth shear speed trade offs will mask 90 of the moho depth signal with remaining phase velocity perturbations 0 1 only in order to resolve the moho with surface waves alone errors in the data must thus be small up to 0 2 for resolving continental moho with larger errors moho depth resolution is not warranted and depends on error distribution with period an effective strategy for the inversion of surface wave data alone for the moho depth is to first constrain the crustal and upper mantle structure by inversion in a broad period range and then determine the moho depth in inversion in a narrow period range most sensitive to it with the first step results used as reference prior information on crustal and mantle structure reduces the trade offs and thus enables resolving the moho depth with noisier data such information should be used whenever available joint analysis or inversion of surface wave and other data receiver functions topography gravity can reduce uncertainties further and facilitate moho mapping

a north atlantic tephrostratigraphical framework for 130 60 ka b2k new tephra discoveries marine based correlations and future challenges abstract building chronological frameworks for proxy sequences spanning 130 60 ka b2k is plagued by difficulties and uncertainties recent developments in the north atlantic region however affirm the potential offered by tephrochronology and specifically the search for cryptotephra here we review the potential offered by tephrostratigraphy for sequences spanning 130 60 ka b2k we combine newly identified cryptotephra deposits from the ngrip ice core and a marine core from the iceland basin with previously published data from the ice and marine realms to construct the first tephrostratigraphical framework for this time interval forty three tephra or cryptotephra deposits are incorporated into this framework twenty three tephra deposits are found in the greenland ice cores including nine new ngrip tephras and twenty separate deposits are preserved in various north atlantic marine sequences major minor and trace element results are presented for the new ngrip horizons together with age estimates based on their position within the ice core record basaltic tephras of icelandic origin dominate the framework with only eight tephras of rhyolitic composition found new results from marine core md99 2253 also illustrate some of the complexities and challenges of assessing the depositional integrity of marine cryptotephra deposits tephra based correlations in the marine environment provide independent tie points for this time interval and highlight the potential of widening the application of tephrochronology further investigations however are required that combine robust geochemical fingerprinting and a rigorous assessment of tephra depositional processes in order to trace coeval events between the two depositional realms

persistent suborbital climate variability in marine isotope stage 5 and termination ii new surface water records from two high sedimentation rate sites located in the western subtropical north atlantic near the axis of the gulf stream provide clear evidence of suborbital climate variations through marine isotope stage mis 5 persisting even into the warm peak of the interglaciation substage 5e we found that the amplitude of suborbital climate oscillations did not vary significantly for the whole of mis 5 implying that ice volume has little or no influence on the amplitude of suborbital climate variability in this region although some records suggest that longer suborbital variations 4 10 kyr during mis 5 are linked to deepwater changes none of the existing records is of sufficient resolution to assess if a linkage occurred for oscillations shorter than 4 kyr however when examined in conjunction with published data from the norwegian sea new evidence from the subpolar north atlantic suggests that coupled surface deepwater oscillations occurred during the penultimate deglaciation this supports the hypothesis that during glacial and deglacial times ocean ice interactions and deepwater variability amplify suborbital climate change at higher latitudes we suggest that during the penultimate deglaciation the north atlantic deepwater source varied between nordic sea and open north atlantic locations in parallel with surface temperature oscillations

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

apparent splitting of s waves propagating through an isotropic lowermost mantle observations of shear wave anisotropy are key for understanding the mineralogical structure and flow in the mantle several researchers have reported the presence of seismic anisotropy in the lowermost 150 250 km of the mantle i e d urn x wiley jgrb media jgrb52636 jgrb52636 math 0002 layer based on differences in the arrival times of vertically sv and horizontally sh polarized shear waves by computing waveforms at a period 6 s for a wide range of 1 d and 3 d earth structures we illustrate that a time shift i e apparent splitting between sv and sh may appear in purely isotropic simulations this may be misinterpreted as shear wave anisotropy for near surface earthquakes apparent shear wave splitting can result from the interference of s with the surface reflection ss for deep earthquakes apparent splitting can be due to the s wave triplication in d urn x wiley jgrb media jgrb52636 jgrb52636 math 0003 reflections off discontinuities in the upper mantle and 3 d heterogeneity the wave effects due to anomalous isotropic structure may not be easily distinguished from purely anisotropic effects if the analysis does not involve full waveform simulations

transferring radiometric dating of the last interglacial sea level high stand to marine and ice core records in order to derive a radiometric age marker for the end of the penultimate glacial interglacial transition we compiled published u series isotope measurements on corals from the period extending from stage 6 to the middle of the last interglacial and computed the corresponding open system ages using thompson et al model thompson w g spiegelman m w goldstein s l speed r c an open system model for u series age determinations of fossil corals earth planet sci lett 210 2003 365 381 we obtain a global mean age of 126 calendar kyr bp ka 1 7kyr 2 for the beginning of the last interglacial sea level high stand after showing that the phase relationships observed between changes in sea level north atlantic benthic and planktonic foraminifera oxygen isotopic records and atmospheric methane over the last deglaciation were likely also valid over the penultimate deglaciation we derive an age of 131 2ka 2kyr 2 for the abrupt increase in atmospheric ch4 and north atlantic surface temperature marking the end of the penultimate glacial interglacial transition this age is consistent with u th dates of the penultimate glacial interglacial transition recorded in speleothems from sites where speleothems isotopic records are synchronous with north atlantic temperature records over the last deglaciation finally we show that the phase obtained between the climatic response and northern hemisphere summer insolation is not constant from termination ii to termination i implying that northern hemisphere summer insolation alone cannot explain the timing of terminations

the structure of termination ii penultimate deglaciation and eemian in the north atlantic abstract a study of the 140 100 ka interval in core t90 9p from the north atlantic 45 n 25 w based on analysis of oxygen and carbon isotope records from planktonic and benthonic foraminifera and from the bulk sediment fine fraction facilitates a detailed paleoceanographic reconstruction of the penultimate deglaciation termination ii and of the eemian interglacial 18o stage 5e the first step of termination ii was characterised by low productivity and a mixed water column which was a remnant of glacial conditions a 3 ka period of relatively stable conditions with a stratified water column termination ii pause occurred half way through termination ii and preceeded a second and more rapid climatic shift the end of the deglaciation eemian maximum i e isotopic event 5 53 initiated the establishment of strong seasonal water column stratification north atlantic deep water nadw production remained low during the complete glacial interglacial transition after the eemian maximum nadw prodution was restored and bottom waters remained quite stable during the course of the eemian while surface waters gradually cooled in the second half of the stage a short surface water cooling event accompanied by a reduced seasonal water column stratification and nutrient instability occurred at approximately 117 ka bp

productivity response in the north canary basin to climate changes during the last 250 000 yr a multi proxy approach we present results from the investigation of the primary productivity record over the last 250 kyr in the north canary basin 30 n off northwest africa two distinct productive systems interfere in this area the oligotrophic open ocean and the upwelling filament off cape ghir that occasionally carries offshore cool nutrient rich waters the following geochemical and micropaleontological paleoproductivity proxies have been used in our study calcium carbonate barium excess baexcess total organic carbon toc and diatoms time series analysis of these proxies indicates that paleoproductivity in the north canary basin underwent important changes following precession and eccentricity cycles while the precessional signal appears to be mainly related to trade wind strength superimposed peaks in baexcess toc and diatom records point to large productivity events at terminations i ii and iii lowering of the north atlantic sea surface temperatures by melt water discharges which in turn strengthened the azores high pressure center and increased trade wind velocities is postulated as the mechanism to explain the enhancement of the coastal upwelling and associated filaments at terminations additionally the canary current may play a role in transmitting cold melt waters and nutrients from higher latitudes to the north canary basin

pressure buildup analysis for two phase geothermal wells application to the baca geothermal field the recently published pressure transient analysis methods for two phase geothermal wells are employed to analyze the pressure buildup data for several wells located in the redondo creek area of the baca geothermal field in new mexico the downhole drilling information and pressure temperature surveys are first interpreted to locate zones at which fluid enters the well bore from the formation and to estimate the initial reservoir temperature and pressure in these zones all of the baca wells considered here induced flashing in the formation upon production interpretation of the buildup data for each well considers well bore effects e g phase change in the well bore fluid and location of the pressure sensor with respect to the permeable horizon and the carbon dioxide content of the fluid and its effects on the phase behavior of the reservoir fluids and differentiates between the single and two phase portions of the pressure buildup data different straight line approximations to the two portions i e single and two phase of the data on the homer plot are used to obtain corresponding estimates for the single and two phase mobilities estimates for the formation permeability thickness kh product are also given

imprints of high salinity water plumes originating from the red sea during termination ii abstract the investigation of a core collected in the socotran area western indian ocean provides new insights into water mass exchanges between the red sea and the gulf of aden through the strait of bab el mandeb during the penultimate deglaciation the benthic oxygen isotope record documents the occurrence of stillstands and possibly reversals within the general trend of sea level rise plumes of warm and salty waters are recorded at the surface of the arabian sea and as far as the socotran coast for each increase in sea level these plumes disappeared whenever global sea level stopped rising or showed a brief lowering according to their high salinities these plumes can only originate in the red sea the sill of bab el mandeb becoming deeper and wider during the deglaciation allowed greater exchange between both seas and stronger flow out of the red sea at each episode of sea level rise isotopic and faunal evidence suggest a strengthening of coastal upwelling in the arabian sea during these periods this increase in upwelling activity may explain how plumes of highly saline waters were maintained at the surface moreover the high salinity surface plumes may have facilitated upwelling activity through the destabilisation of density stratification in the upper water column the occurrence of at least high salinity salty water outflows during termination ii confirms the step wise non linear structure of the penultimate deglaciation providing a perfect example of the threshold concept in rapid climate changes

quaternary oceans and climate change lessons for the future there is much interest in ice age studies in recent decades in the context of global warming the relevant findings are these large regular changes in climate occurred within the last million years especially in the northern north atlantic extreme conditions were similar suggesting strong negative feedback at the edges of the range of variation the nature of the periods of climate variation suggests orbital forcing by modulation of internal oscillations involving lagged negative feedback on ice buildup transitions from cold to warm were rapid and they were not readily reversed indicating that ice dynamics underlies abrupt climate change accelerated rates of ice decay upon warming correspond to a sea level rise of one to two m century millennial scale abrupt disturbances known as dansgaard oeschger and heinrich events occur when large ice masses are present in the northern hemisphere they may be considered experiments on the ocean s response to massive meltwater input when using results from ice age studies to project future developments one must be aware that the future will be largely outside of experience with regard to the recent geologic past also there are as yet no generally accepted explanations for striking changes in the past such as the rapid rise of carbon dioxide during deglaciation demonstrating a profound lack of understanding of climate dynamics this is so far the lesson from ice age studies they say much about the deficiencies in our level of understanding and not so much about what is ahead

global shear speed structure of the upper mantle and transition zone s u m m a r y the rapid expansion of broad band seismic networks over the last decade has paved the way for a new generation of global tomographic models significantly improved resolution of global upper mantle and crustal structure can now be achieved provided that structural information is extracted effectively from both surface and body waves and that the effects of errors in the data are controlled and minimized here we present a new global vertically polarized shear speed model that yields considerable improvements in resolution compared to previous ones for a variety of features in the upper mantle and crust the model sl2013sv is constrained by an unprecedentedly large set of waveform fits 3 4 of a million broad band seismograms computed in seismogram dependent frequency bands up to a maximum period range of 11 450 s automated multimode inversion of surface and s wave forms was used to extract a set of linear equations with uncorrelated uncertainties from each seismogram the equations described perturbations in elastic structure within approximate sensitivity volumes between sources and receivers going beyond ray theory we calculated the phase of every mode at every frequency and its derivative with respect to sand p velocity perturbations by integration over a sensitivity area in a 3 d reference model the normally small perturbations of the 3 d model required to fit the waveforms were then linearized using these accurate derivatives the equations yielded by the waveform inversion of all the seismograms were simultaneously inverted for a 3 d model of shear and compressional speeds and azimuthal anisotropy within the crust and upper mantle elaborate outlier analysis was used to control the propagation of errors in the data source parameters timing at the stations etc the selection of only the most mutually consistent equations exploited the data redundancy provided by our data set and strongly reduced the effect of the errors increasing the resolution of the imaging our new shear speed model is parametrized on a triangular grid with a 280 km spacing in well sampled continental domains lateral resolution approaches or exceeds that of regionalscale studies the close match of known surface expressions of deep structure with the distribution of anomalies in the model provides a useful benchmark in oceanic regions spreading ridges are very well resolved with narrow anomalies in the shallow mantle closely confined near the ridge axis and those deeper down to 100 120 km showing variability in their width and location with respect to the ridge major subduction zones worldwide are well captured extending from shallow depths down to the transition zone the large size of our waveform fit data set also provides a strong statistical foundation to re examine the validity field of the jwkb approximation and surface wave ray theory our analysis shows that the approximations are likely to be valid within certain time frequency portions of most seismograms with high signal to noise ratios and these portions can be identified using a set of consistent criteria that we apply in the course of waveform fitting

pressure interference data analysis for two phase water steam geothermal reservoirs a previously published approximate solution by garg 1980 is used to develop a practical procedure for analyzing pressure interference drawdown data from a hot water geothermal reservoir which evolves into a two phase system as a result of fluid production the observation well is assumed to remain in the single phase liquid part of the reservoir a numerical geothermal reservoir simulator is employed in a series of calculations to test the limits of applicability of the interpretation procedure the numerical results suggest that the accuracy of the computed reservoir transmissivity depends somewhat on the size of the induced two phase region even if the two phase zone is extensive the method can still be used to provide a good first approximation for the reservoir transmissivity forward modeling with a numerical reservoir simulator may then be employed to refine this transmissivity estimate numerical results also show that the observation well pressure buildup data will obey the superposition principle after the return of the reservoir to single phase conditions