identifying global seismic anisotropy patterns by correlating shear wave splitting and surface wave data we compare a global compilation of shear wave splitting measurements with azimuthal seismic anisotropy parameters inferred from surface wave tomography the currently available splitting dataset is taken from a novel comprehensive collection of available publications that is updated interactively online the comparison between the two types of data is made by calculating predicted splitting parameters from the anisotropic tomography model comparing these predicted splitting parameters with the observed ones we find a considerable correlation between the two datasets at global scale this result is noteworthy since such correlation did not seem to exist in previous studies the spatial resolution associated with the two types of methods is rather different while surface waves have good vertical resolution and poor lateral resolution of several hundreds of kilometers sks splitting measurements have good lateral but poor vertical resolution the correlation can be understood in light of recent propositions that anisotropy seen by sks splitting constrains mostly the upper mantle and therefore a similar depth region as surface waves the correlation also confirms the generally good quality of the shear wave measurements as well as that of the anisotropic tomography model

global mantle heterogeneity and its influence on teleseismic regional tomography abstract a new global p wave tomography model is determined using a flexible grid parameterization this new model better reveals the mantle structure under the polar regions than the previous tomographic models the subducting slabs are generally imaged clearly as high velocity high v zones the young slabs are still subducting in the upper mantle and the mantle transition zone mtz whereas the old and ancient slabs are either stagnant in the mtz or have subducted down to the lower mantle even reaching the core mantle boundary low velocity low v anomalies are generally revealed in the mantle under the hotspot regions it seems that a variety of mantle upwelling plumes exist some strong plumes are visible in the whole mantle under the long living hotspots such as those in south central pacific africa hawaii and iceland whereas weak plumes are visible in only some depth range under the minor hotspots under the intraplate volcanoes in east eurasia bering sea and west alaska significant low v anomalies are revealed in the upper mantle which may reflect hot and wet upwelling associated with corner flows in the big mantle wedge bmw above the stagnant pacific slab in the mtz and perhaps deep slab dehydration as well the subduction triggered magmatism in the bmw may be a new class of mantle plumes we also used the new global model to investigate the influence of whole mantle heterogeneity on the determination of upper mantle tomography under japan with a teleseismic inversion method the results show that the mantle heterogeneities outside the target volume of regional tomography can cause significant changes 0 2 0 4 s to the observed relative travel time residuals of a distant earthquake the pattern of regional tomography remains the same even after correcting for the whole mantle heterogeneity but there are some changes in the amplitude of velocity anomalies in the regional tomography hence it is necessary to correct for the mantle heterogeneities outside the target volume so as to obtain a better regional tomography

on recent seismic tomography for the western united states 1 in recent years a number of relatively high resolution seismic tomography models for the uppermost mantle underneath the western united states have been published and vigorous debate has ensued about their tectonic interpretation i present a straightforward yet quantitative comparison between models in order to help establish a framework for geodynamic interpretation and to help judge the role of tomographic theory vs data selection mapped s and p wave anomalies are found to be remarkably consistent between models which implies that seismologists are beginning to narrow down the structure underneath active continental margins to scales of 200 km large discrepancies between published anomaly amplitudes exist however and the models on the high end of the spectrum raise questions as to how they are to be interpreted in terms of temperature composition and melting

including anisotropy in 3 d velocity inversion and application to marlborough new zealand summary two types of seismic velocity heterogeneity are often observed in a given region pronounced patterns of anisotropy shown by local earthquake shear wave splitting and seismic velocity structure imaged by local earthquake traveltimes we seek to combine these types of observations by including anisotropy in 3 d velocity inversion the fast polarization directions from local earthquake shear wave splitting are used to define an initial anisotropy model the ray paths are estimated for each of the shear wave splitting observations and the 3 d initial model is determined via an averaging process and a coherence analysis the initial magnitude of anisotropy at a node is dependent on the number of adjacent ray paths and the consistency of the shear wave splitting anisotropy measurements the traveltime inversion is parametrized with an isotropic component and two azimuthal anisotropy parameters for each node the ray paths are defined with approximate 3 d ray tracing and for each point along a ray path the velocity is defined as a function of the ray path azimuth at that point a blended approach is used to damp the perturbations to the magnitude of anisotropy and or perturbations to the fast direction tests with synthetic traveltime data show that the anisotropic velocity inversion method is reliable application to the marlborough region shows variations in anisotropy in the brittle crust ductile lower crust mantle and subducted slab the patterns are consistent with the shear wave splitting observations but show some additional features the maximum anisotropy is approximately 12 per cent oriented northeast between the awatere and wairau faults this high anisotropy may reflect deformation and extensive fracturing in a region of high total shear strain in the region of interaction of the ductile lower crust with the shallow subducting slab moderate anisotropy with east west orientation is imaged this is consistent with ductile deformation roughly parallel to the plate velocity

mesozoic plate motion history below the northeast pacific ocean from seismic images of the subducted farallon slab the high resolution seismic imaging of subducted oceanic slabs1 2 has become a powerful tool for reconstructing palaeogeography3 the images can now be interpreted quantitatively by comparison with models of the general circulation of the earth s mantle4 here we use a three dimensional spherical computer model of mantle convection5 6 to show that seismic images of the subducted farallon plate provide strong evidence for a mesozoic period of low angle subduction under north america such a period of low angle subduction has been invoked independently to explain rocky mountain uplift far inland from the plate boundary during the laramide orogeny7 the computer simulations also allow us to locate the largely unknown kula farallon spreading plate boundary the location of which is important for inferring the trajectories of suspect terrain across the pacific basin8

effects of low temperature alteration on the rbsr age of andesitic igneous rocks park volcanics group southland new zealand abstract low temperature alteration of glassy andesites of the park volcanics group of southern new zealand has involved the addition of relatively radiogenic sr the loss of rb and k and the degassing of ar these combine to increase the measured rb sr age and lower the k ar age holocrystalline and least altered glassy samples from the glenham area southland give broadly similar rb sr mineral whole rock and k ar total rock ages close to 207 ma this date is 15 ma older than that suggested in earlier stratigraphic studies but is not incompatible with current field observations barnicoat andesites from nelson and gowan andesites from western southland may be broadly coeval although subtle geochemical and petrographic differences rule out cogenesis

archaea mediate anaerobic oxidation of methane in deep euxinic waters of the black sea we evaluate anaerobic oxidation of methane aom in the black sea water column by determining distributions of archaea specific glyceryl dialkyl glyceryl tetraethers gdgts and 13c isotopic compositions of their constituent biphytanes in suspended particulate matter spm sinking particulate matter collected in sediment traps and surface sediments we also determined isotopic compositions of fatty acids specific to sulfate reducing bacteria to test for biomarker and isotopic evidence of a syntrophic relationship between archaea and sulfate reducing bacteria in carrying out aom bicyclic and tricyclic gdgts and their constituent 13c depleted monocyclic and bicyclic biphytanes down to 67 indicative of archaea involved in aom were present in spm in the anoxic zone below 700 m depth in contrast gdgt 0 and crenarchaeol derived from planktonic crenarchaeota dominated the gdgt distributions in the oxic surface and shallow anoxic waters fatty acids indicative of sulfate reducing bacteria i e iso and anteiso c15 were not strongly isotopically depleted e g 32 to 25 although anteiso c15 was 5 more depleted in 13c than iso c15 our results suggest that either aom is carried out by archaea independent of sulfate reducing bacteria or those sulfate reducing bacteria involved in a syntrophy with methane oxidizing archaea constitute a small enough fraction of the total sulfate reducing bacterial community that an isotope depletion in their fatty acids is not readily detected sinking particulate material collected in sediment traps and the underlying sediments in the anoxic zone contained the biomarker and isotope signature of upper water column archaea aom specific gdgts and 13c depleted biphytanes characteristic of the spm in the deep anoxic zone are not incorporated into sinking particles and are not efficiently transported to the sediments this observation suggests that sediments may not always record aom in overlying euxinic water columns and helps explain the absence of aom derived biomarkers in sediments deposited during past periods of elevated levels of methane in the ocean

global marine gravity from retracked geosat and ers 1 altimetry ridge segmentation versus spreading rate 1 three approaches are used to reduce the error in the satellite derived marine gravity anomalies first we have retracked the raw waveforms from the ers 1 and geosat gm missions resulting in improvements in range precision of 40 and 27 respectively second we have used the recently published egm2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean third we have used a biharmonic spline interpolation method to construct residual vertical deflection grids comparisons between shipboard gravity and the global gravity grid show errors ranging from 2 0 mgal in the gulf of mexico to 4 0 mgal in areas with rugged seafloor topography the largest errors of up to 20 mgal occur on the crests of narrow large seamounts the global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate for rates less than about 60 mm a the typical ridge segment is 50 80 km long while it increases dramatically at higher rates 100 1000 km this transition spreading rate of 60 mm a also marks the transition from axial valley to axial high we speculate that a single mechanism controls both transitions candidates include both lithospheric and asthenospheric processes

constraints on mantle anisotropy beneath precambrian north america from a transportable teleseismic experiment data from the apt89 transportable teleseismic experiment was examined to characterize the variations in shear wave splitting along a 1500 km traverse in north america see silver et al 1993 this issue three geologic terranes were sampled the western superior province of the canadian shield the trans hudson orogen and the wyoming craton the primary goal was to determine the extent to which the anisotropy was controlled by archean and proterozoic tectonic episodes of the large suite of teleseismic events recorded 5 were suitable for determining the fast polarization direction and delay time t from the phases sks and skks the resulting observations reveal two important features first the values of display good geologic coherence stations along the northern part of the array in the exposed shield reveal a consistent ene direction for that is generally parallel to exposed geologic structures within the part of the superior province buried beneath phanerozoic cover rotates to a ne sw azimuth as do geophysical indicators of geologic fabric moving onto the trans hudson changes abruptly to a more ew azimuth the stations within the wyoming craton suggest values with a more northerly direction although the waveforms from these stations are more complex second t which ranges between 0 40s and 1 75s shows systematic variations across the traverse the largest delay times approaching 2 s are found in a 250 km wide band from red lake ontario to the u s canada border t is reduced to about 1 s or less both north and south of this region for the stations with detectable splitting we find an inverse relationship between s isotropic station delays derived from the portable data set and t which is most easily explained by the anisotropy being primarily localized in the fast presumably lithospheric mantle the splitting observations overall suggest that mantle anisotropy along this traverse is dominated by precambrian fossil anisotropy that is preserved in the subcontinental lithosphere

the 13c suess effect in scleractinian corals mirror changes in the anthropogenic co2 inventory of the surface oceans 1 new 13 c data are presented from 10 coral skeletons collected from florida and elsewhere in the caribbean dominica dominican republic puerto rico and belize these corals range from 96 to 200 years in age and were collected between 1976 and 2002 the change in the 13 c of the skeletons from these corals between 1900 and 1990 has been compared with 27 other published coral records from the atlantic pacific and indian oceans the new data presented here make possible for the first time a global comparison of rates of change in the 13 c value of coral skeletons of these records 64 show a statistically significant p 0 05 decrease in 13 c towards the modem day 23 out of 37 this decrease is attributable to the addition of anthropogenically derived co 2 13 c suess effect to the atmosphere between 1900 and 1990 the average rate of change of the 13 c in all the coral skeletons living under open oceanic conditions is approximately 0 01 o yr 1 in the atlantic ocean the magnitude of the decrease since 1960 0 019 yr 1 0 015 is essentially the same as the decrease in the 13 c of atmospheric co 2 and the 13 c of the oceanic dissolved inorganic carbon 0 023 to 0 029 yr 1 while in the pacific and indian oceans the rate is more variable and significantly reduced 0 007 yr 1 0 013 these data strongly support the notion that i the 13 c of the atmosphere controls ambient 13 c of the dissolved inorganic carbon which in turn is reflected in the coral skeletons ii the rate of decline in the coral skeletons is higher in oceans with a greater anthropogenic co 2 inventory in the surface oceans iii the rate of 13 c decline is accelerating superimposed on these secular variations are controls on the 13 c in the skeleton governed by growth rate insolation and local water masses

global anisotropy in the upper mantle inferred from the regionalization of phase velocities a data set of 2600 paths for rayleigh waves and 2170 paths for love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70 250 s the epicenters were chosen so that the paths provide uniform spatial and azimuthal coverage of earth a synthetic seismogram is computed for each path and compared to the observed seismogram in order to infer the phase velocity along each path to process such a large data set a new tomographic technique is designed a good correlation is found with surface tectonics in the whole period range for love waves and at shorter periods for rayleigh waves the directions of maximum velocities are also well correlated with plate tectonics motions for the 2 azimuthal term of rayleigh waves when the power spectrum of heterogeneities is computed it is found that for love waves the even orders are usually larger than the odd orders for rayleigh waves the degrees 2 and 6 dominate only at long periods suggesting a deep origin for these components

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

toroidal mantle flow through the western u s slab window the circular pattern of anisotropic fast axis orientations of split sks arrivals observed in the western u s cannot be attributed reasonably to either preexisting lithospheric fabric or to asthenospheric strain related to global scale plate motion a plume origin for this pattern accounts more successfully for the anisotropy field but little evidence exists for an active plume beneath central nevada we suggest that mantle flow around the edge of the sinking gorda juan de fuca slab is responsible for creating the observed anisotropy seismic images and kinematic reconstructions of gorda juan de fuca plate subduction have the southern edge of this plate extending from the mendocino triple junction to beneath central nevada and flow models of narrow subducted slabs produce a strong toroidal flow field around the edge of the slab consistent with the observed pattern of anisotropy this flow may enhance uplift extension and magmatism of the northern basin and range while inhibiting extension of the southern basin and range

p wave anisotropic tomography of the nankai subduction zone in southwest japan 1 the active subduction of the young philippine sea phs plate and the old pacific plate has resulted in significant seismic heterogeneity and anisotropy in southwest sw japan in this work we determined a detailed 3 d p wave anisotropic tomography of the crust and upper mantle beneath sw japan using 540 000 p wave arrival times from 5 249 local earthquakes recorded by 1095 stations the phs slab is imaged clearly as a high velocity high v anomaly which exhibits considerable lateral variations significant low velocity low v anomalies are revealed above and below the phs slab the low v anomalies above the phs slab may reflect the upwelling flow in the mantle wedge and the phs slab dehydration and they form the source zone of the arc volcanoes in sw japan the low v zones under the phs slab may reflect the upwelling flow in the big mantle wedge above the pacific slab the anisotropy in the crust and upper mantle is complex in kyushu the p wave fast velocity direction fvd is generally trench normal in the mantle wedge under the back arc which is consistent with the corner flow driven by the phs slab subduction the fvd is trench parallel in the subducting phs slab under kyushu we think that the intraslab seismicity is a potential indicator to the slab anisotropy that is the phs slab with seismicity has kept its original fossil anisotropy formed at the mid ocean ridge while the aseismic phs slab has reproduced the anisotropy according to its current deformation

shear wave splitting and the pattern of mantle flow beneath eastern oregon a r t i c l e i n f o article history the tectonic and geologic setting of eastern oregon includes the volcanically active high lava plains hlp province and the accreted terrains of the blue and wallowa mountains and is bounded by the columbia river ood basalts to the north basin and range extension to the south the cascade arc to the west and stable north america to the east several models have been proposed to explain the tectonic evolution of eastern oregon and in particular the voluminous volcanic activity in the hlp but a consensus on which model fully describes the complex range of processes remains elusive measurements of the seismic anisotropy that results from active mantle ow beneath the region can provide a crucial test of such models to constrain this anisotropy here we present new sks splitting results obtained at approximately 200 broadband seismic stations in eastern oregon and the surrounding region data come from the usarray transportable array ta and two temporary experiments carried out in the hlp and in the wallowa mountains our splitting data set includes 2900 individual splitting measurements from sks phases recorded between 2006 and 2008 stations in eastern oregon exhibit signi cant shear wave splitting with average delay times at individual stations between 0 8 s and 2 7 s in the hlp nearly all observed fast directions are approximately e w while to the north in the blue and wallowa mountains there is more variability in the splitting patterns the average delay time observed at stations located in the heart of the hlp province is 2 s well above the global average of 1 s for continental regions we infer from the large split times and homogeneous fast directions that there must be signi cant active ow in a roughly e w direction in the asthenosphere beneath the hlp this inferred ow eld places a strong constraint on models that seek to explain the young tectonomagmatic activity in the region in the wallowa region the anisotropic signature is more complicated and there may be a signi cant contribution from fossil fabrics in the crust or mantle lithosphere

origin and distribution of terrestrial organic matter in the nw mediterranean gulf of lions exploring the newly developed bit index the branched and isoprenoid tetraether bit index is based on the relative abundance of nonisoprenoidal glycerol dialkyl glycerol tetraethers gdgts derived from organisms living in terrestrial environments versus a structurally related isoprenoid gdgt crenarchaeol produced by marine crenarchaeota the bit index varies between 0 and 1 representing marine and terrestrial organic matter om end members respectively hopmans et al earth planet sci lett 224 107 116 2004 in this study the applicability of the bit index to trace terrestrial om is tested in combination with other organic parameters toc c n ratio 13corg total lipid and n alkane in the gulf of lions a river dominated continental margin of the western mediterranean we analyzed a variety of soils and riverbed sediments from the continent as well as surface sediments from the shelf and canyons the bit index in soils and riverbed sediments shows high values 0 9 while it varies between 0 02 and 0 83 in marine sediments decreasing seaward from the inner shelf to the slope for marine surface sediments high bit values are associated with lower 13corg values as well as higher toc contents and higher n alkane concentrations our results confirm that the bit index can be applied in coastal marine environments in order to characterize terrestrial om as proposed by hopmans et al 2004 therefore the bit index is a useful addition to the proxies presently available for studying the origin and distribution of om in continental margins and especially valuable in multiproxy studies

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

multiscale seismic tomography and mantle dynamics abstract in this article we first introduce the methodology of multiscale seismic tomography and the way to interpret the obtained tomographic images and then review the significant recent results of multiscale seismic tomography with emphasis on mantle plumes and subducting slabs global and regional tomography shows that most of the slab materials under western pacific and east asia are stagnant in the mantle transition zone before finally collapsing down to the core mantle boundary as a result of large gravitational instability from phase transitions local and teleseismic tomography studies have imaged clearly the subducting slabs and arc magma chambers in the upper mantle wedge indicating that geodynamic systems associated with arc magmatism and back arc spreading are related to deep processes such as convective circulation in the mantle wedge and dehydration reactions of the subducting slab because most hotspots are located in poorly instrumented continental and oceanic regions 3 d crust and upper mantle structure is determined for only a few hotspots such as iceland yellowstone and eifel which are covered by seismic networks and plume like slow anomalies are revealed under those hotspots global tomography has revealed deep mantle plumes under the major hotspots such as hawaii iceland kerguelen south pacific and africa strong lateral heterogeneities are revealed at the bottom of the mantle which are associated with the deeply subducted slabs and the birth of mantle plumes a thorough understanding of the deep earth structure will only be achieved by a combination of more effective seismic imaging techniques and dense coverage of global seismic networks particularly in the oceans

vertical mantle flow associated with a lithospheric drip beneath the great basin rapid surface uplift or subsidence and voluminous magmatic activity have often been ascribed to regional scale downwelling of lithospheric mantle however because lithospheric drips sinking plumes of cold and dense lithosphere are relatively small and transient features direct evidence of their existence has been difficult to obtain moreover the significant vertical mantle flow that should be associated with such structures has not been detected here we integrate seismic anisotropy data with tomographic images to identify and describe a lithospheric drip beneath the great basin region of the western united states the feature is characterized by a localized cylindrical core of cooler material with fast seismic velocities and mantle flow that rapidly shifts from horizontal to vertical our numerical experiments suggest that the drip can be generated by gravitational instability resulting from a density anomaly of as little as 1 and a localized temperature increase of 10 the drip tilts to the northeast opposite to the motion of the north american plate in the hotspot reference frame and thereby indicates northeast directed regional mantle flow seismic anisotropy data for the great basin region of the western united states coupled with tomographic images help delineate a northeast dipping lithospheric drip numerical experiments suggest that the drip could have formed owing to gravitational instability triggered by a density increase of about 1 and a temperature increase of about 10

p wave anisotropic tomography of the crust and upper mantle under hokkaido japan abstract we determined a 3 d anisotropic velocity structure beneath hokkaido in northern japan using a large number of first p wave arrival times the travel time inversion is parameterized with an isotropic component and two anisotropic parameters for each grid node by assuming p wave azimuthal anisotropy with hexagonal symmetry axis distributed horizontally the geometries of the conrad and moho discontinuities and the upper boundary of the subducting pacific plate are taken into account in the model our results show that low velocity zones exist beneath active arc volcanoes in the crust and in the central portion of mantle wedge above the high velocity pacific slab which are similar to the previous tomographic images p wave anisotropy is revealed in the crust mantle wedge and the subducting pacific slab in the upper crust the anisotropy is possibly caused by microcracks and cracks in the lower crust the anisotropic structure is different from that in the upper crust and it may be affected considerably by the plastic flow deformation in the mantle wedge the fast velocity direction fvd is generally trench normal in most of the study area while it becomes trench parallel in the pacific coast areas close to the trench which agrees with the shear wave splitting results beneath the volcanic front the fvd is also trench parallel which may suggest the existence of complex 3 d mantle flow in the mantle wedge the fvd in the subducting pacific slab is nearly north south which likely keeps the original fossil anisotropy of the pacific plate formed at the mid ocean ridge or is affected by the olivine fabric transition from a type to b type fabric due to the changes in water content stress and temperature

shear wave splitting in the appalachians and the urals a case for multilayered anisotropy observations of shear wave splitting in the northeastern u s appalachians and in the foredeep of the urals vary significantly with the back azimuth and incidence angle of the incoming phase these variations suggest two or more layers within the upper mantle with different anisotropic properties synthetic seismograms for simple multilayered anisotropic structures show that shear wave splitting parameters tend to vary substantially with the direction of approach relying on a subset of back azimuth and incidence angle may strongly bias the model inferred especially if the observations are averaged on the other hand the azimuthal splitting pattern provides additional constraints on vertical or lateral variation of anisotropic properties in the earth using a new error estimation technique for splitting we find that individual measurements from broadband data have errors of the order of 3 7 for the fast direction and 0 1 0 2 s for the delay of split shear waves the azimuthal variation of splitting parameters is broadly consistent throughout the appalachian terranes in the northeast united states especially for two long running stations in the northeast united states hrv harvard massachusetts and pal palisades new york observations can be separated into two distinct populations with mean fast axis azimuths of n60 e 4 and n119 e 2 delay values within each population range from near zero to 1 s azimuthal splitting variation for aru arti russia in the foredeep of uralian mountains is characterized by sharp transitions between different groups of observations using synthetic seismograms in simple structures we develop one dimensional anisotropic models under stations hrv and aru the model for hrv includes two layers of anisotropic material under an isotropic crust with fast axis azimuths n53 e and n115 e for the bottom and the top layers respectively the model for the upper mantle under aru includes a layer with a fast axis at n50 e atop a layer with fast axis azimuth n90 e our modeling confirms the need for a layer of strong anisotropy with a slow axis of symmetry in the lower crust under aru reported by levin and park 1997a our results suggest that both urals and appalachians possess a relict anisotropy in the tectosphere associated with past continental collision and accretion underlain by anisotropy with orientation similar to the local absolute plate motion suggesting an asthenospheric component to the signal

mantle fabric at multiple scales across an archean proterozoic boundary grenville front canada abstract in eastern ontario and southwest quebec canada the proterozoic grenville province abuts against the archean superior province the complex tectonic history of the region is reflected in the pattern of electrical and seismic anisotropy within the lithosphere while asthenospheric anisotropy is expected to reflect current patterns of mantle flow magnetotelluric and teleseismic data from the polaris and fednor experiments and the lithoprobe abitibi grenville transect are examined for sks splitting and geoelectric strike and receiver functions are generated at selected stations in order to characterise both vertical and horizontal variations in anisotropy in the eastern ontario upper mantle the average shear wave split direction coincides with the direction of plate motion split times are found to be strongest in the southern part of the grenville province where asthenospheric flow is enhanced by the presence of a lithospheric divot the ottawa bonnechere graben and the immediate vicinity of the grenville front are regions of altered split direction indicative of a lithospheric component of anisotropy north of the grenville front there is a gradual reorientation of the split direction from ese to ene which is not easily attributable to crustal tectonics and may represent the northern limit of lithospheric deformation produced by the grenville orogen electrical anisotropy is pervasive in the study area the pattern of magnetotelluric strikes is more complex than the sks pattern though after correction for local distortion the geoelectric strikes correlate fairly well with sks measurements at nearby stations obliquity between sks and magnetotelluric results shows no consistent orientation across the study area receiver function analysis at three selected stations is indicative of a subcrustal anisotropic layer with a consistent sse fast direction underlain at station gac by a sequence of anisotropic layers with varying directions this sequence is not observed at station sado combining these results we interpret the strength and direction of anisotropic fabric in the grenville to vary strongly with depth the upper part of the lithosphere contains thin anisotropic layers perhaps related to eclogitization and relict slabs but which are insufficient to explain the observed sks splits the lower lithosphere is likely to be more ductile and uniformly anisotropic and may be an important control on magnetotelluric strike directions as well as a significant contributor to sks splitting the largest contributor to sks splitting in this region is interpreted to be asthenospheric anisotropy related to absolute plate motion

p wave tomography of the western united states insight into the yellowstone hotspot and the juan de fuca slab abstract we used 190 947 high quality p wave arrival times from 8421 local earthquakes and 1 098 022 precise travel time residuals from 6470 teleseismic events recorded by the earthscope usarray transportable array to determine a detailed three dimensional p wave velocity model of the crust and mantle down to 1000 km depth under the western united states us our tomography revealed strong heterogeneities in the crust and upper mantle under the western us prominent high velocity anomalies are imaged beneath idaho batholith central colorado plateau cascadian subduction zone stable north american craton transverse ranges and southern sierra nevada prominent low velocity anomalies are imaged at depths of 0 200 km beneath snake river plain which may represent a small scale convection beneath the western us the low velocity structure deviates variably from a narrow vertical plume conduit extending down to 1000 km depth suggesting that the yellowstone hotspot may have a lower mantle origin the juan de fuca slab is imaged as a dipping high velocity anomaly under the western us the slab geometry and its subducted depth vary in the north south direction in the southern parts the slab may have subducted down to 600 km depth a slab hole is revealed beneath oregon which shows up as a low velocity anomaly at depths of 100 to 300 km the formation of the slab hole may be related to the newberry magmatism the removal of flat subducted farallon slab may have triggered the vigorous magmatism in the basin and range and southern part of rocky mountains and also resulted in the uplift of the colorado plateau and rocky mountains

organic carbon deposition on the north carolina continental slope off cape hatteras usa abstract the continental slope off cape hatteras nc is a region of high sediment accumulation and organic matter deposition sediment accumulation rates range from 3 to 151 cm kyr 1 organic carbon deposition rates are 5 13 moles c m 2 yr 1 the highest reported for the slope off the eastern us burial efficiencies are 3 40 the organic matter deposited is marine in origin and a mix of old and young particles high organic carbon deposition rates support remineralization throughout the upper 2 3 m of sediment deep bioirrigation to depths of 60 100 cm within the seabed affects the biogeochemistry of the sediments by extending the zone of sulfate reduction and by steepening dic porewater gradients through the non local exchange of porewater stable and radiocarbon isotope mixing curves for porewater dissolved inorganic carbon dic indicate that the dominant source of dic accumulating in the upper 2 3 m of the seabed is of nearly uniform 13c 21 10 and 14c 546

fluxes and distribution of tetraether lipids in an equatorial african lake constraints on the application of the tex86 palaeothermometer and bit index in lacustrine settings abstract the distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether gdgt lipids was studied in material from various sources in and around lake challa a crater lake on the southeastern slope of mt kilimanjaro tanzania to examine the provenance of gdgts in lake sediments and their potential application as palaeoenvironmental and palaeoclimatic proxies the study material included samples collected at monthly intervals in a sediment trap over one complete annual cycle particles suspended in the stratified water column profundal surface sediments and soils surrounding the lake the sediment trap time series revealed that crenarchaeol and related isoprenoid gdgts were predominantly produced in january and february following the locally prominent short rain season november december the tex 86 inferred temperature derived from sedimenting particles corresponded well with lake surface water temperature at this time of largest crenarchaeol flux molecular ecological analysis showed that group 1 1a and 1 1b crenarchaeota are the most likely source organisms of these gdgts gdgt 0 in the lake sediments does not only originate from lake surface dwelling crenarchaeota but seems predominantly derived from archaea residing in the deeper anoxic part of the water column the main flux of branched gdgts to the sediment was during the short rain season and is most probably derived from eroded catchment soils in surface run off however a contribution from in situ production of branched gdgts in the lake sediment or water or in groundwater cannot be fully excluded we conclude that palaeoclimatic reconstruction based on branched gdgt distributions in lake sediments should only be performed when the origin of those branched gdgts is well constrained

the fate of the juan de fuca plate implications for a yellowstone plume head beneath the pacific northwest the juan de fuca plate a remnant of the farallon plate continues subducting beneath the north american continent to the east of the cascadia subduction zone lies the yellowstone hotspot track the origins of this track can be traced back to the voluminous basaltic outpourings in the columbia plateau around 17 ma if these basalts are the result of a large melting anomaly rising through the mantle to the base of the north american continent such as a mantle plume head the anomaly would need to punch through the subducting juan de fuca slab here we use teleseismic body wave travel time tomography to investigate the fate of the subducted slab and its possible interaction with a plume head our dataset is derived from the oregon array for teleseismic study oats deployment in oregon and all other available seismic data in this region during the same period in our jdf07 models we image the subducted juan de fuca plate in the mantle east of the cascades beneath oregon where the slab has not been imaged before to a depth of 400 km but no deeper the slab dips similar to 50 degrees e and has a thickness of similar to 75 km immediately beneath the slab we image a low velocity layer with a similar geometry to the slab and extending down to at least similar to 575 km depth in the v model the total length of the high velocity slab is similar to 660 km about 180 km longer than the estimated length of slab subducted since 17 ma assuming similar slab geometry to today this 180 km length of slab would reach similar to 60 km depth comparable to the thickness of continental lithosphere we propose that the absence of the slab below 400 km today is due to the arrival of the yellowstone plume head similar to 17 ma which destroyed the juan de fuca slab at depths greater than the thickness of the continental lithosphere given this scenario the low velocity anomaly beneath the slab is likely the remnant plume head material which has been pulled down by traction with the subducting plate the amplitude of the observed low velocity anomaly is comparable with that expected for plume head material 100 300 degrees c hotter than the surrounding asthenosphere c 2007 elsevier b v all rights reserved

variations in gdgt distributions through the water column in the south east atlantic ocean abstract the tetraether index of 86 carbon atoms tex 86 temperature proxy is widely used in reconstructions of past sea surface temperature most current calibrations are based on surface sediment distributions of the glycerol dialkyl glycerol tetraether lipids gdgts that comprise tex 86 and assume that these gdgts are exported from the upper mixed layer however gdgt export from deeper waters could impact sedimentary gdgt distributions and therefore tex 86 paleothermometry here we examine gdgt distributions in suspended particulate matter spm and underlying sediments collected from the southeast atlantic ocean our results reveal different gdgt distributions specifically the ratio between gdgts bearing 2 vs 3 cyclopentyl moieties 2 3 ratios between surface subsurface 50 200 m and deep water 200 m spm which suggests the occurrence of in situ deep production that is not apparent when considering tex 86 the gdgt distributions in sediments match those of subsurface waters rather than surface waters suggesting that they have not been preferentially derived from the upper mixed layer this is consistent with gdgt abundances being highest in shallow subsurface spm 100 to 200 m it remains unclear what governs the different 2 3 ratios throughout the water column but it is likely related to a combination of temperature and thaumarchaeotal community structure

three dimensional structure of p wave anisotropy beneath the tohoku district northeast japan 1 we retrieve three dimensional structures of isotropic and anisotropic velocities of p waves of the tohoku district from first p arrival time data assuming azimuthal anisotropy to be caused by hexagonal symmetry axes distributed horizontally in the earth the results show that the high velocity pacific slab is clearly imaged in the isotropic velocity structure even though the azimuthal anisotropy is taken into account in addition small scale low velocity regions and prominent low velocity anomalies are found just below the active volcanoes and in the mantle wedge above the high velocity pacific slab respectively the fast propagation axis of p waves is in mostly e w direction in the upper crust nearly n s and e w directions in the lower crust e w direction in the mantle wedge and n s direction in the descending pacific slab these features of the p wave anisotropy structure are consistent with those of lateral variations of the fast polarization directions measured previously by shear wave splitting observations the plausible factor that causes the crust anisotropy is interpreted as being alignment or preferred orientation of microcracks and crust minerals the mantle wedge anisotropy is attributed to lattice preferred orientation of the mantle minerals arising from present day mantle process such as the mantle wedge convection and the plate motion however the fast propagation axis of p waves in the slab is almost perpendicular to the magnetic lineation of the oceanic plate under the northwest pacific and thus the slab preserves the original anisotropic property that the pacific plate gained when it formed

sources and transport of terrestrial organic matter in vancouver island fjords and the vancouver washington margin a multiproxy approach using d13corg lignin phenols and the ether lipid bit index the branched and isoprenoid tetraether bit index a ratio of marine and terrestrial glycerol dialkyl glycerol tetraether gdgt membrane lipids was recently introduced as a proxy for the fraction of fluvially derived organic carbon oc buried in marine sediments we investigate the source and distribution of terrestrial oc in marine sediments in a large spatial data set that encompasses the washington vancouver island margin vancouver island fjords and puget sound with the goal of comparing the bit index to other traditional measures of terrestrial oc d13 co f oc d13corg and lignin phenols d13corg values and lignin concentrations indicate that the fjords are a significant trap for undegraded wood derived terrestrial material with surface sediments containing up to 76 terrestrial oc these proxies also show significant terrestrial oc contributions to margin sediments up to 54 with most likely an angiosperm source from the columbia river in contrast to d13corg values and lignin concentrations bit index values indicate extremely low terrestrial carbon throughout the study area bit index values range from 0 to 0 28 and are uncorrelated with the other proxies though the bit index did not correlate with other proxies margin gdgt concentrations varied offshore similarly to other terrestrially derived oc and are well correlated with other proxies we suggest that the bit index is best interpreted as a proxy for soil or peat derived oc the majority of terrestrially derived oc delivered to sediment in this area has a lignin rich nonsoil source the disparity between the bit index and other proxies implies that the bit index significantly underestimates terrestrial relative to marine oc input to sediments in areas in which riverine oc input is not soil or peat derived burial of organic carbon oc on continental margins is estimated to account for the majority of the total carbon burial in the ocean and is a significant sink for terrestrial oc hedges and keil 1995 understanding the sources and fate of this terrestrial oc in marine sediments is thus of importance in understanding global biogeochemical cycles in this study we use two traditional proxies for terrestrial oc input to sediments the d 13 c of bulk sedimentary oc d13corg and the concentration of lignin phenols to examine the sources and quantity of terrestrial oc in sediments throughout the washington vancouver island margin vancouver island fjords and puget sound we compare these results to those obtained using a recently introduced proxy for terrestrial oc in marine sediments the branched and isoprenoid tetraether bit index

mapping p wave azimuthal anisotropy in the crust and upper mantle beneath the united states abstract much progress has been made on revealing seismic structure and mantle dynamics beneath the united states us with the earthscope usarray project seismic anisotropy revealed by shear wave splitting studies provides important constraints on constructing geodynamic models with regard to the seismic images but the shear wave splitting observations have poor vertical resolution and so their interpretations are often not unique in this work we used a large number of arrival time data from local and distant earthquakes recorded by the usarray to determine the first p wave azimuthal anisotropy tomography of the crust and upper mantle beneath the us our results show that fast velocity directions fvds in the lithosphere under the tectonically active areas correlate well with the surface tectonic features suggesting that the p wave anisotropy mainly reflects the present deformation a circular pattern of the fvds centered in the great basin is revealed which is well consistent with the specific circular shear wave splitting observations there suggesting that the anisotropy occurs in the crust and uppermost mantle in contrast beneath the stable cratonic region the fvds revealed by this study differ from the shear wave splitting observations but consistent with the features of gravity and magnetic anomalies indicating that the p wave fvds mainly reflect the fossil anisotropy in the lithosphere whereas the s wave splitting observations mainly reflect the significant anisotropy in the asthenosphere the present results shed new light on the seismic anisotropy in the crust and upper mantle and provide new constraints on constructing geodynamic models beneath the us

shear wave splitting beneath the snake river plain suggests a mantle upwelling beneath eastern nevada usa the snake river plain srp a 90 km wide topographic depression in southern idaho is a topographically anomalous feature in the western u s previous seismic studies focused on the northeastern srp to study its relationship with the yellowstone hotspot we present new teleseismic shear wave splitting data from six broadband seismic stations deployed along the axis of the srp from june 2000 to september 2001 we also analyze splitting at hlid a permanent station of the national seismic network located f100 km north of the plain splitting of individual teleseismic phases is consistent at all stations within 2r errors and we favor the interpretation of anisotropy with a single horizontal fast axis although a dipping axis interpretation is statistically permitted at two of the stations our station fast directions as well as shear wave splitting data from numerous other stations throughout the basin and range are best explained by a lattice preferred orientation of olivine due to horizontal shear along the base of the plate associated with the gravitational spreading of buoyant plume like upwelling material beneath eastern nevada into a southwestward flowing asthenosphere with respect to a fixed hotspot reference frame this parabolic asthenospheric flow paf model for the great basin is attractive because it explains the observed high elevations high mantle buoyancy low velocity anomaly beneath eastern nevada high heat flow and depleted geochemistry of some erupted basalts the lack of pliocene recent major volcanism in eastern nevada suggests that a significant amount of the buoyancy flux is due to compositional buoyancy our splitting station delay times vary in a way not predicted by the paf model and can be explained by a zone of aligned magma filled lenses and or partially molten dikes beneath the srp lithosphere a depleted olivine rich residuum underneath the sides of the eastern srp and or the effect of lateral lower crustal flow from beneath the esrp toward its adjacent flanks d 2004 elsevier b v all rights reserved

complex subduction and small scale convection revealed by body wave tomography of the western united states upper mantle abstract new high resolution p and s wave tomography of the united states upper mantle from the pacific coast to the great plains reveals strong multi scale heterogeneity closely correlated with tectonic and magmatic activity we invert teleseismic travel time residuals from the earthscope transportable array and more than 1700 additional temporary and permanent stations for 3 d velocity perturbations to a depth of 1000 km the inversion uses recent advances in western u s crust models to better isolate the mantle component of travel time residuals and frequency dependent 3 d sensitivity kernels to map travel time residuals measured in multiple frequency bands into velocity structure in addition to separate v p and v s models we jointly invert the two datasets for v p v s perturbations by imposing a smoothness constraint on the ln v s ln v p field the joint inversion helps us identify regions where partial melt is probable the amplitude of v p v s and v p v s variations is greatest in the upper 200 km of the mantle and the form of velocity anomalies suggests a provincially heterogeneous lithosphere and the occurrence of widespread small scale convection partially molten mantle is inferred beneath yellowstone and the eastern snake river plain srp the salton trough and the clear lake volcanic field the inferred depth extent of partial melt is consistent with a generally hydrated upper mantle and elevated temperatures beneath the eastern srp and yellowstone despite continuous subduction since the cretaceous the distribution of sub lithospheric high velocity anomalies is dissected similar to other recent studies based on our new tomography models western u s geologic history and plate tectonic reconstructions we infer patchy and incomplete removal of the flat subducting laramide slab and slab tearing associated with eocene accretion in the northwestern u s

complex and variable crustal and uppermost mantle seismic anisotropy in the western united states deformation in the crust and mantle measured using seismic anisotropy is poorly constrained in the western united states because of inconsistencies in the existing data a three dimensional model that reconciles these discrepancies reveals that seismic anisotropy in the crust correlates with different geological provinces but is unrelated to anisotropy in the underlying mantle

stable carbon isotope ratios of intact gdgts indicate heterogeneous sources to marine sediments thaumarchaeota the major sources of marine glycerol dibiphytanyl glycerol tetraether lipids gdgts are believed to fix the majority of their carbon directly from dissolved inorganic carbon dic the 13c values of gdgts 13cgdgt may be powerful tools for reconstructing variations in the ocean carbon cycle including paleoproductivity and water mass circulation if they can be related to values of 13cdic to date isotope measurements primarily are made on the c40 biphytane skeletons of gdgts rather than on complete tetraether structures this approach erases information revealed by the isotopic heterogeneity of gdgts within a sample and may impart an isotopic fractionation associated with the ether cleavage to circumvent these issues we present 13c values for gdgts from twelve recent sediments representing ten continental margin locations samples are purified by orthogonal dimensions of hplc followed by measurement of 13c values by spooling wire microcombustion swim isotope ratio mass spectrometry irms with 1 precision and accuracy of 0 25 using this approach we confirm that gdgts generally around 19 are isotopically heavy compared to other marine lipids however measured 13cgdgt values are inconsistent with predicted values based on the 13c content of dic in the overlying water column and the previously published biosynthetic isotope fractionation for a pure culture of an autotrophic marine thaumarchaeon in some sediments the isotopic composition of individual gdgts differs indicating multiple source inputs the data appear to confirm that crenarchaeol primarily is a biomarker for thaumarchaeota but its 13c values still cannot be explained solely by autotrophic carbon fixation overall the complexity of the results suggests that both organic carbon assimilation ca 25 of total carbon and multiple source s of exogenous gdgts contributing generally 30 of input to sediments are necessary to explain the observed 13cgdgt values the results suggest caution when interpreting the total inputs of gdgts to sedimentary records biogenic or open slope sediments rather than clastic basinal or shallow shelf sediments are preferred locations for generating minimally biased gdgt proxy records

shear wave anisotropy in the crust mantle wedge and subducting pacific slab under northeast japan to study the anisotropic structure beneath northeast ne japan we made 4366 shear wave splitting measurements using high quality seismograms of many earthquakes occurring in the crust and the subducting pacific slab our results provide important new information on the s wave anisotropy in the upper crust lower crust mantle wedge and subducting pacific slab in the upper crust the anisotropy is mainly caused by the stress aligned fluid saturated microcracks the measured delay times dts increase to 0 10 s at 10 11 km depth the fast velocity directions fvds are parallel to either the tectonic stress or the strike of active faults the maximum dts for the low frequency earthquakes near the moho are 0 15 0 17 s suggesting strong anisotropy at the base of the crust or in the uppermost mantle the measurements for the intermediate depth earthquakes in the pacific slab show dominant e w trench normal fvds in the back arc area and n s trench parallel fvds in the fore arc area the trench normal fvds in the back arc area are caused by the corner flow in the mantle wedge as a result of the subduction of the pacific plate the maximum dts for the slab earthquakes reach 0 30 0 32 s at 100 km depth but only half of the total dts are produced in the mantle wedge the small dts in the mantle wedge may result from an isotropic or weak anisotropic zone in the middle of the mantle wedge in the fore arc the dominant trench parallel fvds for the slab earthquakes are consistent with those for the upper crust earthquakes and 80 of the total dts can be accounted for by the anisotropy in the crust in the subducting pacific slab the trench parallel fvds may reflect either the original fossil anisotropy in the pacific plate when the plate was produced in the mid ocean ridge or the preferred orientations of the crystals and cracks in the upper part of the subducting slab

early paleogene temperature history of the southwest pacific ocean reconciling proxies and models we present a new multiproxy tex86 18o and mg ca marine temperature history for canterbury basin eastern new zealand that extends from middle paleocene to middle eocene including the paleocene eocene thermal maximum petm and early eocene climatic optimum eeco in light of concerns that proxy based sea surface temperature sst estimates are untenably warm for the southwest pacific during the eocene we review the assumptions that underlie the proxies and develop a preliminary paleo calibration for tex86 that is based on four multiproxy eocene records that represent an sst range of 15 34 c for the southwest pacific paleogene we show that tex86l exhibits the best fit with the eocene paleo calibration ssts derived from related proxies tex86h 1 tex86 exhibit a systematic warm bias that increases as tex86 values decrease a warm bias of 4 7 c where tex86 0 7 the tex86l proxy indicates that southwest pacific sst increased by 10 c from middle paleocene to early eocene with sst maxima of 26 28 c tropical during the petm and eeco and an sst minimum of 13 16 c cool warm temperate at the middle late paleocene transition 58 7 ma the base of the eeco is poorly defined in these records but the top is well defined in canterbury basin by a 2 5 c decrease in sst and bottom water temperature bwt in the latest early eocene 49 3 ma bwt falls from a maximum of 18 20 c in the eeco to 12 14 c in the middle eocene overall cooler temperatures are recorded in the mid waipara section which may reflect a deeper 500 m water depth and less neritic depositional setting compared with hampden and odp 1172 200 m water depth the high ssts and bwts inferred for the petm and eeco can be reconciled with eocene coupled climate model results if the proxies are biased towards seasonal maxima and the likely effect of a proto east australian current is taken into account

pre and post industrial environmental changes as revealed by the biogeochemical sedimentary record of drammensfjord norway the biogeochemical sedimentary record of the anoxic drammensfjord norway was investigated on a decadal to centennial time scale over the last millennium in order to reconstruct the pre industrial fjord environment and ecosystem and human induced environmental changes the sediments were dated by a combination of 14c and 210pb analysis and varve counting analysis of the bulk sedimentary parameters and of the biomarker distribution revealed that the sedimentary organic matter of the fjord is primarily of terrigenous origin indicating that the fjord was oligotrophic or mesotrophic the fjord s bottom water has been continuously euxinic since at least 1000 ad but photic zone euxinia occurred only irregularly in the fjord the organic matter flux and composition remained virtually invariable until the 18th century after that time the flux of material derived from coniferous trees started to increase indicated by elevated concentrations of dehydroabietic acid and related compounds but also by raising levels of c24 n alcohols and fatty acids this marked the onset of sawmill activities in the hinterland after the beginning of the industrial revolution around 1850 the flux of organic waste from sawmills and paper mills increased substantially it is suggested that slow bacterial degradation of this relatively nutrient poor organic waste caused a gradual eutrophication trend which is reflected in substantial increased bacterial and moderately increased other aquatic biomarker accumulation rates after the industrial revolution this trend accelerated and was possibly enhanced by a growing population of the area with accompanying agricultural and domestic waste this promoted primary productivity and changed the phytoplankton composition in the fjord

lithosphere asthenosphere interaction beneath the western united states from the joint inversion of body wave traveltimes and surface wave phase velocities summary the relation between the complex geological history of the western margin of the north american plate and the processes in the mantle is still not fully documented and understood several pre usarray local seismic studies showed how the characteristics of key geological features such as the colorado plateau and the yellowstone snake river plains are linked to their deep mantle structure recent body wave models based on the deployment of the high density large aperture usarray have provided far more details on the mantle structure while surface wave tomography ballistic waves and noise correlations informs us on the shallow structure here we combine constraints from these two data sets to image and study the link between the geology of the western united states the shallow structure of the earth and the convective processes in mantle our multiphase dna10 s model provides new constraints on the extent of the archean lithosphere imaged as a large deeply rooted fast body that encompasses the stable great plains and a large portion of the northern and central rocky mountains widespread slow anomalies are found in the lower crust and upper mantle suggesting that low density rocks isostatically sustain part of the high topography of the western united states the yellowstone anomaly is imaged as a large slow body rising from the lower mantle intruding the overlying lithosphere and controlling locally the seismicity and the topography the large e w extent of the usarray used in this study allows imaging the slab graveyard a sequence of farallon fragments aligned with the currently subducting juan de fuca slab north of the mendocino triple junction the lithospheric root of the colorado plateau has apparently been weakened and partly removed through dripping the distribution of the slower regions around the colorado plateau and other rigid blocks follows closely the trend of cenozoic volcanic fields and ancient lithospheric sutures suggesting that the later exert a control on the locus of magmato tectonic activity today the dna velocity models are available for download and slicing at http dna berkeley edu

the origin of n alkanes in santa monica basin surface sediment a model based on compound specific δ14c and δ13c data 14c and 13c values were measured for individual long chain n alkanes c24 33 from santa monica basin sediments the data were then simulated using a three component mixing model designed to represent the contributions of different sources the three selected end members were petroleum modern plant wax and shale derived alkanes the model was optimized to fit the data and to determine the fractional contribution of each component the results indicated that petroleum accounted for 12 of the alkanes in 0 2 5 cm sediment and 5 in 2 5 7 5 cm sediment modern plant waxes contributed 80 0 2 5 cm and 87 2 5 7 5 cm and the remaining 8 of each sample was attributed to the shale source the 14c concentration of the modern terrestrial end member was also determined from the model 14c values of 235 for the 0 2 5 cm post bomb horizon and 0 for the 2 5 7 5 cm pre bomb horizon indicate that plant leaf waxes have a continental residence time of decades in the southern california region

diploptene an indicator of terrigenous organic carbon in washington coastal sediments the pentacyclic triterpene 17 beta h 21 beta h hop 22 29 ene diploptene occurs in sediments throughout the columbia river drainage basin and off the southern coast of washington state in concentrations comparable to long chain plantwax n alkanes the same relationship is evident for diploptene and long chain n alkanes in soils from the willamette valley microorganisms indigenous to soils and soil erosion are indicated as the biological source and physical process respectively for diploptene in coastal sediments similarity between the stable carbon isotopic composition delta 13cpdb of diploptene isolated from soil in the willamette valley 31 2 0 3 and from sediments deposited throughout the washington coastal environment 31 2 0 5 supports this argument values of delta for diploptene in river sediments are variable and 8 17 lighter indicating that an additional biological source such as methane oxidizing bacteria makes a significant contribution to the diploptene record in river sediments selective biodegradation resulting from a difference in the physicochemical association within eroded particles can explain the absence of the more 13c depleted form of diploptene in washington coastal sediments but this mechanism remains unproven

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

the magnitude symmetry and origin of upper mantle anisotropy based on fabric analyses of ultramafic tectonites summary seismic anisotropy within the upper mantle originates from the preferred orientation of highly anisotropic single crystals the symmetry and magnitude of anisotropy depend upon 1 the volume percentages of the minerals constituting the upper mantle 2 the degree and symmetry of preferred orientation of each mineral and 3 the alignment of the minerals crystallographic axes relative to one another the nature of upper mantle anisotropy can be examined by studying mineral orientations within ultramafic rocks which were once part of the mantle petrofabric data for olivine and pyroxene have been used to obtain velocity anisotropy patterns over large regions of ultramafic rocks from the samail ophiolite oman the troodos ophiolite cyprus the bay of islands ophiolife newfoundland the twin sisters ultramafic washington usa the dun mountain ophiolite new zealand the red hills ophiolite new zealand and the red mountain ophiolite new zealand the compressional wave anisotropy calculated for these massifs ranges from 3 to 8 per cent in excellent agreement with observed seismic anisotropy in the upper continental and oceanic mantle the symmetry varies from orthorhombic to axial with the axial symmetry axis corresponding to the olivine a axes maxima and subparallel to spreading directions in oceanic upper mantle pyroxene a b and c axes maxima generally parallel olivine b c and a axes respectively and anisotropy decreases with increasing pyroxene content shear wave splitting is predicted for all propagation directions within the upper mantle symmetry is also orthorhombic or axial with the minimum difference in velocity between the two shear waves parallel to the maximum compressional wave velocity

pn tomography of the western united states using usarray 1 usarray has now provided several years of high quality seismic data and improved ray coverage for much of the western united states which will enable increased resolution for studies of the lithospheric and deeper structure of the north american continent here we analyze pn arrival times from the transportable stations of usarray to resolve crustal thickness and uppermost mantle structure we use 123 008 pn picks from april 2004 to october 2009 as measured by the array network facility at epicentral distances from 180 to 1450 km these picks are derived from 778 stations at 70 km spacing and 7903 earthquakes and quarry blasts applying the classic time term method we use a regularized least squares inversion to estimate crustal thickness variations and image velocity perturbations in the uppermost mantle just below the moho we also consider upper mantle anisotropy and describe the velocity perturbations with a cos 2 azimuthal variation our crustal thickness map generally agrees with receiver function results from other researchers but differs in some details we obtain an average upper mantle velocity of 7 93 km s with higher velocities beneath eastern washington and northern idaho and lower velocities near the california mexico border the sierra nevada the northern coastal california region and the greater yellowstone area we observe large anisotropic anomalies in southern california as well as in the snake river plain area these results should complement other seismic studies e g body and surface wave tomography and shear wave splitting to provide information about composition temperature and tectonic processes in the western united states

recognition of paleobiochemicals by a combined molecular sulfur and isotope geochemical approach study of organic matter in immature sediments from a messinian evaporitic basin shows that consideration of structures modes of occurrence and carbon isotopic compositions of free and sulfur bound carbon skeletons allow identification of biochemical precursors detailed information concerning biotic communities present during deposition of sediments can be retrieved in this way moreover unprecedented biochemicals were recognized these extend the horizon of biomarker geochemistry

distribution of intact and core tetraether lipids in water column profiles of suspended particulate matter off cape blanc nw africa in the reconstruction of sea surface temperature sst from sedimentary archives secondary sources lateral transport and selective preservation are considered to be mainly negligible in terms of influencing the primary signal this is also true for the archaeal glycerol dialkyl glycerol tetraethers gdgts that form the basis for the tex86 sst proxy our samples represent four years variability on a transect off cape blanc nw africa we studied the subsurface production vertical and lateral transport of intact polar lipids and core gdgts in the water column at high vertical resolution on the basis of suspended particulate matter spm samples from the photic zone the subsurface oxygen minimum zone omz nepheloid layers nl and the water column between these furthermore we compared the water column spm gdgt composition with that in underlying surface sediments this is the first study that reports tex86 values from the precursor intact polar lipids ipls associated with specific head groups ipl specific tex86 we show a clear deviation from the sea surface gdgt composition in the omz between 300 and 600 m since neither lateral transport nor selective degradation provides a satisfactory explanation for the observed tex derived temperature profiles with a bias towards higher temperatures for both core and ipl specific tex86 values we suggest that subsurface in situ production of archaea with a distinct relationship between lipid biosynthesis and temperature is the responsible mechanism however in the nw african upwelling system the gdgt contribution of the omz to the surface sediments does not seem to affect the sedimentary tex86 as it shows no bias and still reflects the signal of the surface waters between 0 and 60 m

seismic anisotropy and mantle dynamics beneath china abstract we analyzed the shear wave splitting at 138 permanent seismograph stations to study seismic anisotropy and mantle dynamics under mainland china to obtain reliable results we used three different methods to measure the shear wave splitting parameters using core phases sks skks skiks and pks as well as the direct s waves from regional and distant earthquakes our results show that the fast orientations of the anisotropy wnw ese in eastern china are generally consistent with the absolute plate motion apm direction of the eurasian plate suggesting that the anisotropy is mainly located in the asthenosphere resulting from the lattice preferred orientation of olivine due to the shear deformation there the fast axes in western china generally agree with the strikes of the orogens and active faults while they are perpendicular to the direction of the maximum horizontal stress suggesting that the anisotropy in the lithosphere contributes significantly to the observed shear wave splitting the fast axes in western china are also consistent with the apm direction suggesting that the apm driven anisotropy in the asthenosphere is another source of the shear wave splitting there these results suggest that apm driven anisotropy commonly exists under continents similar to that under oceanic regions even though the continental lithosphere has suffered extensive deformation

seismic anisotropy and heterogeneity in the alaska subduction zone summary we determined p and s wave tomography and p wave anisotropic structure of the alaska subduction zone using 259 283 p and 73 817 s wave arrival times from 7268 local shallow and intermediate depth earthquakes recorded by more than 400 seismic stations the results show strong velocity heterogeneities in the crust and upper mantle low velocity anomalies are revealed in the mantle wedge with significant along arc variations under the active volcanoes in the mantle wedge the low velocity zone extends down to 100 150 km depth under the backarc the results indicate that h2o and fluids brought downwards by the subducting pacific slab are released to the mantle wedge by dehydration and they are subsequently transported to the surface by the upwelling flow in the mantle wedge significant p wave anisotropic anomalies are revealed under alaska the predominant fast velocity direction fvd is trench parallel in the shallow part of the mantle wedge 90 km depth and in the subslab mantle whereas the fvd is trench normal within the subducting pacific slab the trench parallel fvds in the mantle wedge and subslab mantle may be caused by 3 d mantle flow that is induced by the complex geometry and strong curvature of the pacific slab under alaska the flat and oblique subduction of the pacific slab may play a key role in forming the trench parallel fvd under the slab the trench normal fvd in the subducting pacific slab may reflect the original fossil anisotropy when the pacific plate was produced at the mid ocean ridge

massive expansion of marine archaea during a mid cretaceous oceanic anoxic event biogeochemical and stable carbon isotopic analysis of black shale sequences deposited during an albian oceanic anoxic event 112 million years ago indicate that up to 80 weight percent of sedimentary organic carbon is derived from marine nonthermophilic archaea the carbon 13 content of archaeal molecular fossils indicates that these archaea were living chemoautotrophically their massive expansion may have been a response to the strong stratification of the ocean during this anoxic event indeed the sedimentary record of archaeal membrane lipids suggests that this anoxic event marks a time in earth history at which certain hyperthermophilic archaea adapted to low temperature environments

stable isotope proxy records in tropical terrestrial environments abstract the tropics refers to an area that is loosely equatorial characterized by relatively high temperatures at low altitude comparatively low seasonal contrast in temperatures and generally high or highly seasonal rainfall the stable isotopes of carbon oxygen and hydrogen are increasingly important tools of relevance to understanding trajectories and mechanisms of past environmental change in the tropics in the case of carbon this is because at the broadest level the carbon isotope composition of organic and carbon containing inorganic proxy materials formed in the tropics can be read as being derived from the balance between c3 tree and c4 grass photosynthesis hence providing a relative measure of vegetation type and indirectly climate likewise changes in the oxygen and hydrogen isotope composition of many proxy materials again at the broadest level can be read as indicative of changes in hydrological conditions and or altitude in the past this review provides an entry point into the literature relating to the use of stable isotopes as terrestrial environmental proxies for past environmental change with a focus on the measurement and interpretation of stable isotope data from the wide range of proxy materials preserved in tropical environments

three dimensional distribution of seismic anisotropy in the hikurangi subduction zone beneath the central north island new zealand 1 we use earthquake arrival time data in the central north island new zealand in inversion for 3 d vp azimuthal anisotropy it is parameterized with an isotropic component and two azimuthal anisotropy parameters for each node and local earthquake shear wave splitting observations define the initial anisotropy model our results suggest that mantle flow either within the mantle wedge or below the subducted slab is not the primary source of anisotropy in the hikurangi subduction zone the largest region of anisotropy that we image is within the subducted slab where anisotropy is consistently trench parallel and 5 9 magnitude from 32 to 185 km depth bending induced yielding in the slab offshore and as it passes through the trench provides an explanation for this slab anisotropy beneath the taupo volcanic zone tvz there is 1 4 trench normal anisotropy within 30 km of the surface of the slab within a region entrained with motion of the slab in contrast only very weak 0 2 anisotropy is imaged in the region of high temperature partial melt arising from active corner flow in the mantle wedge in the crust geologic structure is important with the largest crustal anisotropy 14 related to schist we image significant anisotropy aligned with the margins of the tvz related to extensive fracturing on the margins as the tvz actively extends within the heavily intruded and underplated tvz lower crust the orientation of anisotropy switches to align with the extension direction this orientation is consistent with other geophysical data suggesting the presence of connected melt in this region

origins of archaeal tetraether lipids in sediments insights from radiocarbon analysis abstract understanding the supply and preservation of glycerol dibiphytanyl glycerol tetraethers gdgts in marine sediments helps inform their use in paleoceanography compound specific radiocarbon measurements of sedimentary alkenones from multiple environments have been used to gain insight into processes that affect u 37 k paleotemperature reconstructions similar analyses are warranted to investigate how analogous processes affecting gdgts impact tex 86 paleotemperatures here we present radiocarbon measurements on individual gdgts from bermuda rise and santa monica basin sediments and discuss the results in the context of previous studies of co depositional alkenones and foraminifera the 14 c contents of gdgts and planktonic foraminifera in bermuda rise are very similar suggesting a local source and tex 86 derived temperatures agree more closely with foraminiferal temperatures than do u 37 k temperatures in contrast gdgts in santa monica basin are depleted in 14 c relative to both alkenones and foraminifera and tex 86 temperatures agree poorly with known surface water values we propose three possible factors that could explain these results i gdgts may be labile relative to alkenones during advective transport through oxic waters ii archaeal production deep in the water column may contribute 14 c depleted gdgts to sediments and iii some gdgts also may derive from sedimentary archaeal communities each of these three processes is likely to occur with varying relative importance depending on geographic location the latter two may help to explain why tex 86 temperature reconstructions from santa monica basin do not appear to reflect actual sea surface temperatures terrigenous gdgts are unlikely to be major contributors to bermuda rise or santa monica basin sediments based on values of the bit index the results also indicate that the crenarchaeol regioisomer is governed by processes different from other gdgts individual measurements of the crenarchaeol regioisomer are significantly depleted in 14 c relative to co occurring gdgts indicating an alternative origin for this compound that presently remains unknown re examination of the contribution of crenarchaeol regioisomer to the tex 86 index shows that it is a significant influence on the sensitivity of temperature reconstructions

seismic evidence for widespread western us deep crustal deformation caused by extension morgan moschetti and colleagues use ambient noise tomography data from the western united states to show that strong radial seismic anisotropy exists in the deep crust confined mainly to the geological provinces that have undergone significant extension during the cenozoic era since about 65 million years ago the coincidence of crustal radial anisotropy with these extensional provinces supports the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension here a method of seismic wave imaging known as ambient noise tomography is used to generate high resolution images of seismic wave speeds in the crust and uppermost mantle the observations reveal strong and uniform anisotropy where waves travel through rock at different speeds depending on direction in the deep crust in areas of the western united states that have undergone significant extension during the past 65 million years laboratory experiments have established that many of the materials comprising the earth are strongly anisotropic in terms of seismic wave speeds1 observations of azimuthal2 3 and radial4 5 anisotropy in the upper mantle are attributed to the lattice preferred orientation of olivine caused by the shear strains associated with deformation and provide some of the most direct evidence for deformation and flow within the earth s interior although observations of crustal radial anisotropy would improve our understanding of crustal deformation and flow patterns resulting from tectonic processes large scale observations have been limited to regions of particularly thick crust6 here we show that observations from ambient noise tomography in the western united states reveal strong deep middle to lower crustal radial anisotropy that is confined mainly to the geological provinces that have undergone significant extension during the cenozoic era since 65 myr ago 7 8 the coincidence of crustal radial anisotropy with the extensional provinces of the western united states suggests that the radial anisotropy results from the lattice preferred orientation of anisotropic crustal minerals caused by extensional deformation these observations also provide support for the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension9 10 11

terrestrial organic carbon contributions to sediments on the washington margin elemental and stable carbon isotopic compositions and biomarker concentrations were determined in sediments from the columbia river basin and the washington margin in order to evaluate geochemical approaches for quantifying terrestrial organic matter in marine sediments the biomarkers include an homologous series of long chain n alkanes derived from the surface waxes of higher plants phenolic and hydroxyalkanoic compounds produced by cuo oxidation of two major vascular plant biopolymers lignin and cutin all marine sediments including samples collected from the most remote sites in cascadia basin showed organic geochemical evidence for the presence of terrestrial organic carbon using endmember values for the various biomarkers determined empirically by two independent means we estimate that the terrestrial contribution to the washington margin is 60 for shelf sediments 30 for slope sediments and decreases further to 15 in basin sediments results from the same geochemical measurements made with depth in gravity core 6705 7 from cascadia seachannel suggest that our approach to assess terrestrial organic carbon contributions to contemporary deposits on the washington margin can be applied to the study of sediments depositing in this region since the last glacial period

seismic anisotropy in the eastern united states deep structure of a complex continental plate we have analyzed shear wave splitting recorded by portable and permanent broadband and long period stations located in the eastern united states teleseismic shear waves sks skks and pks were used to retrieve the splitting parameters the orientation of the fast wave polarization plane and the delay time t in total 120 seismic events were processed allowing for more than 600 splitting measurements within the appalachians stations located in the western external part are characterized by t 1s and trending n50 70 e in the south and central regions and n30 40 e in the north closely following the trend of the orogenic belt in these areas the transition region between north and central is characterized by t 1 1 3 s and by e w trending that are at a high angle to the regional geologic trend measurements at two stations located in the eastern internal part of the belt indicate very weak anisotropy the large scale pattern of anisotropy is not consistent with that predicted for simple asthenospheric flow beneath the plate splitting along the southern and eastern margins of the continent is consistent with that expected for grenvillian deformation an alternative model of asthenospheric flow around the cratonic keel cannot be ruled out within the cratonic core the correlation between t and lithospheric thickness suggests a lithospheric anisotropy smaller length scale variations also argue for a significant contribution of lithospheric structures the fabric responsible for shear wave splitting may have formed during tectonic episodes that affected the eastern united states i e the grenville and appalachian orogenies and the subsequent rifting of the north atlantic ocean our observations in the western appalachians suggest that the anisotropy may be preserved since the grenvillian orogeny the absence of detectable splitting in the two stations in the eastern appalachians is attributed to the igneous intrusions related to the atlantic rifting the measurements in the transition between the northern and central southern appalachians constitute an intriguing anomaly whose e w have little obvious relation to the regional surface geology we suggest two possible causes 1 the local dominance of asthenospheric flow motivated by the proximity of a pervasive low velocity anomaly and 2 lithospheric deformation in a transcontinental strike slip fault zone active during the appalachian collision

seismic anisotropy and mantle flow from the great basin to the great plains western united states shear wave splitting and p sks and s travel time residuals are calculated for teleseismic arrivals recorded on the colorado plateau great basin program for array seismic studies of the continental lithosphere passcal portable broadband seismic deployment and for permanent stations in the western united states little shear wave splitting is observed for broadband recordings in the northern colorado plateau the rocky mountains or the central great basin the transition between the colorado plateau and the great basin is marked by moderate shear wave splitting 1 0 s and unusually late teleseismic phase arrivals this suggests material with a higher content of mantle melt or volatiles than regions to either side splitting in the transition between the colorado plateau and great basin is part of a pattern of fast polarizations that align in a semicircle surrounding a central great basin region of null no splitting measurements away from the california plate boundary splitting to the north and south of our study region aligns roughly parallel to the absolute plate motion of the north american plate no simple spatial relation of splitting with geological and geophysical features such as mountain ranges velocity anomalies gravity magnetics or heat flow is evident in most of the western united states however splitting in the great basin is compatible with asthenospheric flow the smallest shear wave splitting delay times coincide with the eureka low in heat flow also having low s velocity at 300 km depth we suggest that the circumferential pattern of fast polarization directions ringing a central region of nulls in the great basin is caused by mantle flow by the interaction of mantle up welling and the absolute motion of the north american plate

deep structure of japan subduction zone as derived from local regional and teleseismic events we have determined a detailed three dimensional p wave velocity structure of the japan subduction zone to 500 km depth by inverting local regional and teleseismic data simultaneously we used 45 318 p wave arrivals from 1241 shallow and deep earthquakes which occurred in and around the japan islands the arrival times are recorded by the japan university seismic network which covers the entire japan islands densely and uniformly we also used 4211 travel time residuals from 100 teleseismic events which are read from seismograms recorded by seismic stations in northeastern japan in comparison with the previous results obtained from only local and regional events the present result for the area around the lower plate boundary and the mantle below the plate is determined more reliably because of the addition of 7035 data from 100 teleseismic events and 41 very deep earthquakes in the crust and uppermost mantle low velocity zones are clearly visible beneath active volcanoes in the mantle wedge the low velocity zones generally parallel with the slab and exist continuously to a depth of about 200 km which is consistent with the petrological geochemical and geodynamic studies we consider that the existence of volcanism related low velocity anomalies in the mantle wedge is a general seismological characteristic of subduction zones in light of all the available tomographic results for many subduction zones in the world the pacific slab beneath japan is imaged more clearly than in previous studies as a high velocity zone with a thickness of 80 90 km and a p wave velocity 4 6 higher than the normal mantle lower velocity anomalies are found in the mantle below the slab

anisotropic pn tomography in the western united states pn travel times are affected not only by lateral variations in crust and mantle velocity but also by significant amounts of laterally varying anisotropy to investigate uppermost mantle anisotropy a tomography algorithm was reformulated to include lateral variations in both velocity and horizontal anisotropy and it was applied to pn travel time data from the western united states results show that anisotropy is as important in explaining the travel time residuals as are the velocity variations a detailed resolution study examined the trade off between the velocity variations and the anisotropy variations and showed that both could be resolved for regions with good ray path coverage pn anisotropy beneath the western united states has maximum amplitudes of 0 3 km s 7 5 when resolved on a length scales of around 3 the orientations of pn anisotropy often correlate well with those inferred from shear wave splitting results this correlation suggests that orientation of mantle anisotropy does not change significantly with depth for many regions the orientation of the pn anisotropy can be correlated with some of the tectonic processes which occur within the western united states for example the fast direction of pn anisotropy parallels the northeast direction of subduction of the juan de fuca plate beneath the northwest pacific coast suggesting that there the anisotropy is related to subduction driven deformation the fast direction of pn anisotropy also parallels the strike of the san andreas fault system in central california indicating that shear strains along the plate boundary may be responsible for the anisotropy there within the great basin the pn anisotropy varies substantially and both partial melting and small scale convection within the uppermost mantle could be responsible for these anisotropy variations

abundance and structural diversity of bacteriohopanepolyols in suspended particulate matter along a river to ocean transect abstract the concentration and structural diversity of a suite of bacteriohopanepolyols bhps was measured in suspended particulate matter spm from six stations along a river ocean transect off the pacific coast of panama riverine spm contained bhps diagnostic of soil input consistent with a terrigenous source the concentration of bhps was 10 times greater in riverine spm than marine spm demonstrating that terrigenous om exported to marine sediments could provide a significant contribution to the marine sedimentary hopanoid inventory given the rich structural diversity of bhps in terrigenous spm interpretations of the sedimentary record of hopanoids in coastal marine settings must resolve inputs from marine pelagic and terrigenous sources

archaeal lipids in neogene dolomites monterey and sisquoc formations california planktic versus benthic archaeal sources abstract the distribution of archaeal lipids including archaeol and glycerol dibiphytanyl glycerol tetraethers gdgts in dolomite concretions and surrounding sediment from the monterey formation miocene and the sisquoc formation miocene pliocene were examined to distinguish planktic from benthic contributions for this purpose dolomites with positive 13 c values 7 to 13 were chosen such highly positive values point to pronounced methanogenesis of benthic archaea in the sedimentary column at first glance distributions and relative abundances of gdgts in both dolomites and background sediment were similar resembling patterns of marine planktic crenarchaea a contribution of benthic euryarchaea to the gdgt pool became evident only from variations in the 13 c values of different biphytanes obtained after ether cleavage of gdgts whereas bi and tricyclic biphytanes had an isotopic signal typical of planktic archaea 13 c 23 6 to 20 5 and 23 4 to 21 2 respectively for both dolomite and background sediment acyclic and monocyclic biphytanes showed lower values for dolomite samples 25 1 to 22 6 and 27 6 to 24 7 respectively indicating a contribution of lipids from benthic archaea the isoprenoid diether archaeol 13 c 23 9 to 22 9 assigned to euryarchaea was only detected in dolomite samples also reflecting additional input from sedimentary archaea probably autotrophic methanogens the occurrence of lipids derived from methanogenic archaea agrees with the strong 13 c enrichment of dolomites and with mineral formation taking place in the zone of archaeal methanogenesis this implies that the lipid biomarker inventory of sedimentary strata needs to be interpreted carefully as it is often not straightforward to discriminate between input from the water column and sedimentary microbial activity

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

late twentieth century warming in lake tanganyika unprecedented since ad 500 lake tanganyika has become warmer increasingly stratified and less productive over the past 90 years analyses of lake sediments show that this recent warming is unprecedented within the past 1 500 years

mantle dynamics and seismic anisotropy abstract observations of seismic anisotropy yield some of the most direct constraints available on both past and present day deformation in the earth s mantle insight into the character of mantle flow can also be gained from the geodynamical modeling of mantle processes on both global and regional scales we highlight recent progress toward understanding mantle flow from both observations and modeling and discuss outstanding problems and avenues for progress particularly in the integration of seismological and geodynamical constraints to understand seismic anisotropy and the deformation that produces it to first order the predictions of upper mantle anisotropy made by global mantle circulation models match seismological observations well beneath the ocean basins but the fit is poorer in regions of greater tectonic complexity such as beneath continental interiors and within subduction systems in many regions of the upper mantle models of anisotropy derived from surface waves are seemingly inconsistent with shear wave splitting observations which suggests that our understanding of complex anisotropic regions remains incomplete observations of anisotropy in the d layer hold promise for improving our understanding of dynamic processes in the deep earth but much progress remains to be made in characterizing anisotropic structure and relating it to the geometry of flow geochemical heterogeneity or phase transitions major outstanding problems related to understanding mantle anisotropy remain particularly regarding the deformation and evolution of continents the nature of the asthenosphere subduction zone geodynamics and the thermo chemical state of the lowermost mantle however we expect that new seismological deployments and closer integration of observations with geodynamical models will yield rapid progress in these areas

three dimensional radial anisotropic structure of the north american upper mantle from inversion of surface waveform data summary seismic anisotropy provides insight into palaeo and recent deformation processes and there fore mantle dynamics in a first step towards a model for the north american upper mantle with anisotropy characterized by a symmetry axis of arbitrary orientation aimed at filling the gap between global tomography and sks splitting studies we inverted long period waveform data simultaneously for perturbations in the isotropic s velocity structure and the anisotropic parameter v 2 sh v2 in the framework of normal mode asymptotic coupling theory nact the resulting 2 d broad band sensitivity kernels allow us to exploit the information contained in long period seismograms for fundamental and higher mode surface waves at the same time to ensure high quality of the retrieved regional upper mantle structure accurate crustal cor rections are essential here we follow an approach which goes beyond the linear perturbation approximation and split the correction into a linear and non linear part the inverted data set consists of more than 40 000 high quality three component fundamental and overtone sur face waveforms recorded at broad band seismic stations in north america from teleseismic events and provides a fairly homogeneous path and azimuthal coverage the isotropic part of our tomographic model shares the large scale features of previous regional studies for north america we confirm the pronounced difference in the isotropic velocity structure between the western active tectonic region and the central eastern stable shield as well as the presence of subducted material juan de fuca and farallon plate at transition zone depths the new regional 3 d radial anisotropic model indicates the presence of two distinct anisotropic layers beneath the cratonic part of the north american continent a deep asthenospheric layer con sistent with present day mantle flow and a shallower lithospheric layer possibly a record of ancient tectonic events

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

diagenetic and sedimentological controls on the composition of organic matter preserved in california borderland basin sediments compound specific radiocarbon 14c contents stable carbon isotopes and abundances of phytoplankton and vascular plant derived lipid biomarkers alkenones and fatty acids were obtained from santa barbara basin and santa monica basin sediments along with radiocarbon contents of planktic foraminifera and total organic carbon we investigated core top and prebomb sediment intervals at sites from the flanks and depocenters of the basins deposited under contrasting bottom water oxygen concentrations bulk organic matter generally has the lowest radiocarbon levels of all sediment constituents measured whereas planktic foraminifera tend to be the most radiocarbon enriched alkenones are systematically depleted in radiocarbon with respect to foraminifera short chain c14 c 16 c 18 fatty acids decrease rapidly in absolute abundance and relative to longer chain c24 homologues from core top to prebomb samples the loss of short chain fatty acids with depth is associated with 13c depletion of short chain fatty acids indicating preferential preservation of terrestrially derived fatty acids short chain fatty acids tend to be more 14c enriched relative to alkenones in core top sediments whereas longerchain homologues are generally the most radiocarbon depleted of the lipids studied here less refractory compounds e g short chain fatty acids are thus enriched in radiocarbon with respect to more recalcitrant biomarkers alkenones long chain fatty acids the lower 14c content of more refractory compounds reflects a larger proportion of laterally supplied preaged material greater preservation of labile organic compounds observed at the depocenters than in flank sediments results in the presence of younger biomarkers underlining the important influence of selective degradation of labile compounds on their radiocarbon ages

application of lipid biomarkers to detect sources of organic matter in mud volcano deposits and post eruptional methanotrophic processes in the gulf of cadiz ne atlantic abstract the gulf of cadiz is known as an active mud volcano mv and fluid venting region discovered during the training through research ttr expeditions in 1999 ttr 9 here we report a study of lipid biomarkers in the mud breccia matrix from three mvs in this region the lipid biomarker composition revealed strong compositional resemblance as well as similar thermal maturity properties for the studied mvs this indicates that the primary source of the erupted material for these mvs is located in similar litho stratigraphic units in both areas upward migrated fluid went through the sedimentary series of the allochthonous olistrostrome and through the upper cretaceous horizons the relatively immature characteristics of organic matter from both mud breccia rock clasts and matrix together with the more mature properties of hydrocarbon gases from the same sampling locations indicate that source strata for the initial fluid are located deeper in the subsurface than the source strata for the erupted sedimentary material the presence of microbial lipid biomarkers derived from archaea and sulfate reducing bacteria in the mud breccias revealed anaerobic oxidation of methane aom as a dominant microbial process in these habitats our data suggest that the aom derived lipids are at least in part fossil in origin i e they do not reflect active aom communities and thus reflect aom activity in these mvs integrated over time the low concentrations of aom related biomarkers in these mvs suggest relatively low intensities of aom in the studied mv deposits the distribution of biomarkers suggests an abrupt and brief cold seep activity in the past and the absence of a continuous methane influx in the studied locations

p wave anisotropic tomography beneath northeast japan we determined a 3 d p wave anisotropic tomography beneath northeast japan by using first p arrival times the travel time inversion is parameterized with an isotropic component and two anisotropic parameters for each grid node by assuming p wave azimuthal anisotropy with hexagonal symmetry axis distributed horizontally the geometries of the conrad and moho discontinuities and the upper boundary of the subducting pacific plate are taken into account in the model our extensive synthetic tests show that the anisotropic velocity inversion method is reliable our results show that low velocity zones exist below active volcanoes in the crust in the fore arc mantle wedge and in the central portion of the mantle wedge above the high velocity pacific slab which are similar to the previous tomographic images anisotropic velocity variations are revealed in the crust mantle wedge and the subducting pacific slab the anisotropic patterns are complex and different in the upper and lower crust in the mantle wedge the fast direction of p velocity is generally trench parallel in the fore arc area while it becomes trench normal in the back arc area which agree well with the shear wave splitting results the trench parallel fast direction is revealed beneath the volcanic front which may suggest the existence of complex 3 d mantle flows in the mantle wedge the fast velocity direction in the subducting pacific slab is mostly n s which is likely due to the original fossil anisotropy of the pacific plate formed at the mid ocean ridge our result also suggests that the anisotropy is weak in the upper crust and the average amplitude of the velocity anisotropy in the mantle is no larger than 4

deep structure of southern california abstract we used 214 210 p wave arrival times from 7536 local earthquakes and 16 470 travel time residuals from 332 teleseismic events recorded by the southern california seismic network to determine a detailed three dimensional 3d p wave velocity structure of the crust and mantle down to 600 km depth beneath southern california in this study we have taken into account the moho topography under this region determined by a previous receiver function study we found that the undulations of the moho discontinuity affect considerably the tomographic images of the lower crust and uppermost mantle when the moho topography is taken into account ray paths and travel times can be computed more accurately the tomographic images show a very heterogeneous structure in the crust and upper mantle under southern california the velocity structure in the shallow depth correlates well with the surface geological features three major anomalies in the upper mantle are revealed clearly beneath the southern sierra nevada salton trough and transverse ranges compared with the previous result both the shape and size of the three anomalies show some differences our result revealed two prominent low velocity low v anomalies above the high velocity high v anomalies in the upper mantle under southern sierra nevada and the transverse ranges we consider that the upper mantle anomaly under the transverse ranges was formed through convergence and sinking of the entire subcrustal lithosphere vertical motions and removal of the dense crust root caused the high v anomaly under the southern sierra nevada the prominent low v anomalies above the two high v anomalies were either caused by the crustal materials pulled down to the uppermost mantle or by upwelling of partial melt in asthenosphere when the sinking of lithosphere occurs the salton trough low is the response to the lithospheric extension when the pacific plate was rifted away from the north american plate

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

comparison of organic uk 37 texh86 ldi and faunal proxies foraminiferal assemblages for reconstruction of late quaternary sea surface temperature variability from offshore southeastern australia several proxies have been developed to reconstruct past sea surface temperature sst but different proxies may reflect temperatures of different seasons and each proxy is characterized by certain uncertainties therefore a multiproxy approach is preferred to precisely reconstruct sst here we reconstruct sst of the ocean offshore southeastern australia murray canyons area for the last 135 ka using three independent organic proxies texh86 based on glycerol dialkyl glycerol tetraethers gdgts uk 37 based on alkenones and ldi based on long chain diols in addition to foraminiferal faunal assemblages the organic proxy records show similar trends with the highest temperature 21 c for uk 37 and texh86 and 25 c for ldi during the last interglacial and lowest temperature 8 c for texh86 10 c for uk 37 and 12 c for ldi during the last glacial maximum however the differences in absolute sst estimates obtained by the organic proxies varied over time with differences of up to 9 c between ldi and texh86 the seasonal sst reconstructions based on the modern analogue of foraminiferal assemblages also show similar trends as the organic proxies with highest temperatures during the last interglacial 23 c for the warmest month sst 20 c for mean annual and 18 c for the coolest month and lowest temperature during the last glacial maximum 14 c for the warmest month 11 c for mean annual and 9 c for the coolest month down core comparison between the reconstructed ssts of the organic and inorganic proxies shows that ldi inferred temperatures compare well with the temperature of the warmest month texh86 with the temperature of the coolest month and uk 37 with mean annual temperature an increase in texh86 sst estimates relative to those of other proxies during deglaciations and interglacials suggests that either winter temperatures rapidly warmed possibly due to an invigoration of the leeuwin current over the core site or there was a change in the growth season of the thaumarchaeota the source organism of gdgts our study shows the benefits of a multiproxy approach in the interpretation of sst proxies leading to a more robust knowledge of past ocean temperature changes

global crustal stress pattern based on the world stress map database release 2008 the world stress map wsm project is a global compilation of information on the contemporary crustal stress field from a wide range of stress indicators the wsm database release 2008 contains 21 750 stress data records that are quality ranked using an updated and refined quality ranking scheme almost 17 000 of these data records have a c quality and are considered to record the orientation of maximum horizontal compressional stress sh to within 25 as this is almost a triplication of data records compared with the first wsm database release in 1992 we reinvestigate the spatial wave length of the stress patterns with a statistical analysis on a global 0 5 grid the resulting smoothed global stress map displays both the mean sh orientation that follows from the maximum smoothing radius for which the standard deviation is b25 and a countour map that displays the wave length of the stress pattern this smoothed global map confirms that long wave length stress patterns n2000 km exist for example in north america and ne asia these have been used in earlier analyses to conclude that the global stress pattern is primarily controlled by plate boundary forces that are transmitted into the intraplate region however our analysis reveals that rather short wave length of the stress pattern b200 km are quite frequent too particularly in western europe alaska and the aleutians the southern rocky mountains basin and range province scandinavia caucasus most of the himalayas and indonesia this implies that local stress sources such as density contrasts and active fault systems in some areas have high impact in comparison to plate boundary forces and control the regional stress pattern