direct comparison of marine and terrestrial climate variability during marine isotope stages 6 and 5 results from santa barbara basin odp hole 893a 1 planktonic foraminiferal 1 8 o pollen and opal records from santa barbara basin are used to evaluate climate changes in the northeast pacific during marine isotope stages mis 6 and 5 while the oak and foraminifera record the major glacial interglacial changes opal is not correlated with these large scale transitions surface water warming in the basin was synchronous with terrestrial warming but earlier than ice sheet melting and increasing northern hemisphere insolation at termination ii during and immediately after deglaciation our marine proxies indicate the presence of an isothermal upper water column later in substage 5e the water column became thermally stratified surface productivity increased and laminated sediments began accumulating sediment trap and hydrographic data suggest these changes were due to the onset of a strong seasonal cycle similar to that seen today in the basin a series of rapid coolings within mis 5 appears to be synchronous with north atlantic ice rafting events and greenland stadials

pollen taphonomy in a canyon stream abstract surface soil samples from the forested chuska mountains to the arid steppe of the chinle valley northeastern arizona show close correlation between modern pollen rain and vegetation in contrast modern alluvium is dominated by pinus pollen throughout the canyon it reflects neither the surrounding floodplain nor plateau vegetation pollen in surface soils is deposited by wind pollen grains in alluvium are deposited by a stream as sedimentary particles clay size particles correlate significantly with pinus quercus and populus pollen these pollen types settle as clay does in slack water chenopodiaceae amaranthus artemisia other tubuliflorae and indeterminate pollen types correlate with sand size particles and are deposited by more turbulent water fluctuating pollen frequencies in alluvial deposits are related to sedimentology and do not reflect the local or regional vegetation where the sediments were deposited alluvial pollen is unreliable for reconstruction of paleoenvironments

quaternary pollen taphonomy examples of differential redeposition and differential preservation pollen assemblages are affected by a variety of processes between dehiscence and recovery here two examples from western canada illustrate two of the most important biases affecting pollen assemblages after production and initial dispersal a site in canada s yukon territory provides evidence of selective redeposition of penecontemporaneous pollen grains which is detectable only through paired coring a deposit on the floor of a kettle depression shows trends in the ratios of extra local pollen types which are opposed to the trends shown in a core taken from the slope of the same depression this is explained as a trend to reduced mobility of saccate grains with time due to increased permeability of the substrate on the kettle slope a study of the differential degradation of populus pollen illustrates the complexities of pollen preservation populus pollen is generally recognized as more susceptible to corrosion than are most other pollen types the poor preservation of this pollen type is attributed largely to its lack of harmomegathic adaptation and low sporopollenin content this real susceptibility is compounded by the pollen grain s lack of distinctive surface ornamentation inhibiting recognition of damaged grains at least part of the general impression of poor preservation of populus pollen may be due to a recent increase in the abundance of populus on the landscape in western canada early studies in this region may have sampled sediments from before the increase in populus and compared their pollen spectra with post populus increase vegetation

seismic anisotropy of the pacific ocean inferred from long period surface waves dispersion abstract the dispersion of surface rayleigh and love waves in the period range 40 300 s along a large number of paths allows the estimation of both the azimuthal anisotropy and the shear wave polarization anisotropy the regional dispersion is determined taking into account simultaneously its dependence with age and an azimuthal factor the pacific ocean has been divided into 5 regions for rayleigh waves and into 3 regions for love waves this partition discriminates the regions of extreme age which show a fast variation of dispersion with age from the regions of intermediate age where the variation is weak a variation of 2 of rayleigh wave group velocity with the azimuth of the path measured with respect to the direction of spreading is displayed up to very long period on the contrary the azimuthal anisotropy for love waves is difficult to resolve for rayleigh waves the present day direction of plate motion seems to agree best with the direction of maximum velocity on the other hand the isotropic inversion of the regional dispersion curves indicates except for young regions a discrepancy between rayleigh wave and love wave models with this hypothesis sh velocities are higher than sv velocities for the regions older than 23 ma down to a depth of 300 km which is indicative of the presence of polarization anisotropy the latter very weak for the young part of the ocean increases with age and reaches 7 for the oldest region

millennial scale climate variability of the northeast pacific ocean and northwest north america based on radiolaria and pollen abstract radiolaria and pollen abundances in marine sediment cores from the northeast pacific are used to reconstruct oceanographic and continental climate change during the past glacial cycle 0 150 kyr these data allow direct comparison of the climate response of continental and oceanic systems detailed 18 o and ams 14 c measurements provide a link into global stratigraphic frameworks canonical correlation analysis extracts two modes of variation common to both the radiolaria and pollen records the first mode of variation correlates an assemblage of radiolaria associated with coastal upwelling with increased redwood western hemlock and alder pollen this association is consistent with the modern relationship between coastal upwelling coastal fog and redwood forests a second canonical mode relates an oceanic fauna now found in highest abundance in the far north pacific with reduced pine and western hemlock pollen abundance comparison of these records to an ice core 18 o record suggests that at wavelengths 3000 years warm events in greenland are correlated to intervals of increased coastal upwelling off oregon decreases in importance of very cold north pacific fauna suggesting warming and increases in pollen associated with wetter coastal environments radiolarian based sea surface temperature estimates suggest that the variability of the northeast pacific on this time scale is about 2 c warming in the coastal regions reflects reduced advection of the california current but is moderated by increases in cool coastal upwelling we infer that the response of the northeast pacific to millennial scale climate changes is related to changes in atmospheric circulation at mid to high latitudes preliminary analysis suggests that oceanic variability off oregon at wavelengths 18 o records this variability is associated with changes in subtropical faunal elements without similar changes in other faunal elements this finding suggests that unlike longer period millennial scale events the propagation of the shorter wavelength events to the northeast pacific is through subtropical or tropical teleconnections

dispersion and attenuation of mantle waves through waveform inversion summary we propose a new approach to the determination of elastic and anelastic parameters of the earth s structure from seismic data instead of measuring such functionals of the medium response as the phase delay or spectral ratios we perturb parameters of the model to satisfy the observed waveforms the advantage of our waveform inversion technique wit is that it uses the properties of the earth as a smoothing filter also because the earth s structure is the common denominator the method allows simultaneous interpretation of different functionals of this structure for example the waveforms of rayleigh and love waves for the same source receiver pair following extensive testing of the method on synthetic and actual data we subject results of our analysis of 37 recordings for various sources and stations to pure path decomposition the period range of analysis extends from 160 to 630s we distinguish four types of regions stable continents areas tectonically active within the last 400myr ocean floors younger than 38 myr and old ocean floors older than 38 myr the results indicate significantly different responses of the oceanic and continental areas at long periods stable continental and tectonic regions have nearly the same dispersion for periods greater than 300 35os and then diverge rapidly with stable continents showing higher velocities the young and old oceans on the other hand become distinct at periods as long as 500 s the old oceans are faster in terms of shear velocity models the data are consistent with a difference of about 4 per cent between the young and old oceans in a depth range from 400 to 670 km while the continental regions are similar and close to the global average at shallower depths our structures are conceptually similar to those inferred from previous pure path analyses and short period surface wave studies while we cannot yet establish statistically significant differences in q for the four regions such differences are obtained if one distinguishes only between continents and oceans the q for the latter is 10 20 per cent lower in the period range of the analysis

pollen based evidence of extreme drought during the last glacial 32 6 9 0 ka in coastal southern california abstract high resolution pollen analyses of sediment core ledc10 1 from lake elsinore yield the first well dated terrestrial record of sub centennial scale ecologic change in coastal southern california between 32 and 9 ka in the lake elsinore watershed the initial mesic montane conifer forests dominated by pinus and cupressaceae with trace amounts of abies and picea were replaced by a sequence of multiple extended severe mega droughts between 27 5 and 25 5 ka in which halophytic and xerophytic herbs and shrubs occupied an ephemeral lake this prolonged and extended dry interval which corresponds with warm waters offshore imply strengthening of the north pacific high and persistent below average winter precipitation the subsequent contrasting monotonic occurrence of montane conifers reflects little variation in cold mesic climate until 15 ka postglacial development of quercus woodland and chaparral mark the return to more xeric warmer conditions at this time a brief reversal at 13 1 12 1 ka as reflected by an expansion of pinus is correlative with the younger dryas and interrupts development of warm postglacial climate subsequent gradual expansion of xeric vegetation post younger dryas denotes the establishment of a winter hydroclimate regime in coastal southern california that is more similar to modern conditions pollen based reconstructions of temperature and precipitation at lake elsinore are generally correlative with pollen based paleoclimatic reconstructions and foraminifera based sea surface temperatures from santa barbara basin in marine core odp 893 the conspicuous absence of the 27 5 25 5 ka glacial mega drought in the santa barbara basin pollen record highlights the sensitivity of lake elsinore to hydroclimate change and thus the importance of this new record that indicates that mega drought can occur during the full glacial when climatic boundary conditions and forcings differed substantially from the present

anisotropy beneath hawaii from surface wave particle motion observations observed polarization ellipses for fundamental mode surface waves observed at a digital station in hawaii deviate from those expected for isotropic models of crust and mantle structure for that region the anomalous motion occurs as rotations of the ellipse about all three axes in a cartesian corrdinate system the largest and most consistent deviations occur as anomalous slopes of the ellipse about the horizontal axis transverse to the direction of propagation

upper mantle flow beneath french polynesia from shear wave splitting summary upper mantle flow beneath the south pacific is investigated by analysing shear wave splitting parameters at eight permanent long period and broad band seismic stations and 10 broad band stations deployed in french polynesia from 2001 to 2005 in the framework of the polynesian lithosphere and upper mantle experiment plume despite the small number of events and the rather poor backazimuthal coverage due to the geographical distribution of the natural seismicity upper mantle seismic anisotropy has been detected at all stations except at tahiti where two permanent stations with 15 yr of data show an apparent isotropy the median value of fast polarization azimuths n67 5 w is parallel to the present pacific absolute plate motion direction in french polynesia apm n67 w this suggests that the observed sks fast polarization directions result mainly from olivine crystal preferred orientations produced by deformation in the sublithospheric mantle due to viscous entrainment by the moving pacific plate and preserved in the lithosphere as the plate cools however analysis of individual measurements highlights variations of splitting parameters with event backazimuth that imply an actual upper mantle structure more complex than a single anisotropic layer with horizontal fast axis a forward approach shows that a two layer structure of anisotropy beneath french polynesia better explains the splitting observations than a single anisotropic layer secondorder variations in the measurements may also indicate the presence of small scale lateral heterogeneities the influence of plumes or fracture zones within the studied area does not appear to dominate the large scale anisotropy pattern but may explain these second order splitting variations across the network

development of vegetation in the central mojave desert of california during the late quaternary vegetation analysis of 47 neotoma packrat middens from the core of the central mojave desert of california reveal changes in desert plant community composition over the last ca 24 000 years bp one of the lowest and most arid locations in north america habitat currently dominated by mojave desert larrea tridentata creosote bush was occupied prior to ca 11 500 years bp by pinus monophylla pinon juniperus osteosperma utah juniper purshia mexicana bitterbush cercocarpus ledifolius mountain mahogany and prunus fasciculata desert almond woodland above 1000 m p monophylla juniperus woodland was widespread over the southern and central mojave desert however less than 150 km north of the central mojave j osteosperma steppe dominated the landscape paleoecologic records spanning latitude 358n ca 378n document a biogeographic boundary between milder moister environments to the south and the colder drier environments to the north at elevations b1000 m desert scrub species of lycium cooperi wolfberry salvia mojavensis mojave sage and the mesophytic prosopis juliflora mesquite occurred near the shore of pluvial lake mojave from ca 8810 to 8430 years bp larrea is not recorded on the xeric carbonate substrates 605 m until ca 6990 years bp then took over 2000 years to dominate the regional landscape modern vegetation associates such as thamnosma montana desert rue and atriplex confertifolia shadscale were established by ca 4500 years bp late holocene vegetation changes document neoglacial cooling and wetter conditions than today between ca 3490 and 2640 years bp paralleling the regional pluvial lake highstands and marsh deposit records decreases of mesophytic mojave desert associates in the granite mountains suggest climates similar to today s aridity between ca 1970 and 1440 years bp mesophytic species increase in middens

climate change and the episodicity of sediment flux of small california rivers abstract we studied the streamflow and sediment flux characteristics of the 20 largest streams entering the pacific ocean along the central and southern california coast extending for 750 km from monterey bay to just south of the u s mexico border drainage basins ranged in area from 120 to 10 800 km2 with headwater elevations ranging from 460 to 3770 m annual streamflow ranged from 0 to a maximum of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 1 times 10 9 end document m3 yr for the santa clara river in 1969 with a

surface wave propagation in an ocean basin with an anisotropic upper mantle numerical modelling summary the characteristics of surface wave propagation in ocean basins are examined numerically for models with two types of anisotropic alignment in the upper mantle one resulting from glide plane slip in olivine with horizontal or vertical slip planes and the other from syntectonic recrystallization of olivine in a zone of horizontal shear glide plane slip can cause highly anomalous inclined rayleigh particle motion in the third generalized mode corresponding to the isotropic second rayleigh mode the amplitude of this anomaly is rather insensitive to details of the structure syntectonic recrystallization can cause an anomalous combination of inclined and tilted rayleigh motion in all modes the variation with period of the amplitude of the anomaly in the fundamental mode can indicate the approximate depth to the anisotropic layer in both types of alignment the sense of tilt and the inclination varies with direction of propagation in a manner characteristic of the structural symmetry

vegetation response to southern california drought during the medieval climate anomaly and early little ice age ad 800 1600 abstract high resolution studies of pollen in laminated sediments deposited in santa barbara basin sbb core spr0901 02kc reflect decadal scale fluctuations in precipitation spanning the interval from ad 800 1600 from ad 800 1090 during the medieval climate anomaly mca sbb sediments were dominated by xeric vegetation types drought resistant coastal sagebrush and chaparral implying reduced precipitation in the southern california region drought adapted vegetation abruptly decreased at ad 1090 and was rapidly replaced by mesic oak quercus woodlands associated with an increased pollen flux into the basin after a mesic interval lasting 100 years pollen flux and the relative abundance of quercus pollen dropped abruptly at ad 1200 when the rapid rise of chaparral suggests a significant drought similar to that of the mca ad 800 1090 this brief resurgence of drought adapted vegetation between ad 1200 1270 marked the end of the mca droughts a gradual increase in mesic vegetation followed characterizing cool hydroclimates of the little ice age lia in coastal southern california the presence of xeric vegetation in sbb coincides with major drought events recorded in tree rings and low lake levels elsewhere in california except for the brief drought between ad 1130 1160 correlative diatom and terrigenous sediment input proxy records from sbb are largely supportive of the pollen record predominantly linking the mca with drought and la nina like conditions and the lia with wetter more el nino like conditions differences between paleoclimate proxies pollen diatoms and terrigenous sediment in sbb exist however possibly reflecting the temporal and spatial differences in the generation of each proxy record as well as their individual sensitivity to climate change

high resolution climatic evolution of coastal northern california during the past 16 000 years holocene and latest pleistocene oceanographic conditions and the coastal climate of northern california have varied greatly based upon high resolution studies ca every 100 years of diatoms alkenones pollen caco 3 and total organic carbon at ocean drilling program odp site 1019 41 682 n 124 930 w 980 m water depth marine climate proxies alkenone sea surface temperatures ssts and caco 3 behaved remarkably like the greenland ice sheet project gisp 2 oxygen isotope record during the balling allerod younger dryas yd and early part of the holocene during the yd alkenone ssts decreased by 3 c below mean bolling allerod and holocene ssts the early holocene ca 11 6 to 8 2 ka was a time of generally warm conditions and moderate caco 3 content generally 4 the middle part of the holocene ca 8 2 to 3 2 ka was marked by alkenone ssts that were consistently 1 2 c cooler than either the earlier or later parts of the holocene by greatly reduced numbers of the gyre diatom pseudoeunotia doliolus 10 and by a permanent drop in caco 3 to 3 starting at ca 5 2 ka coastal redwood and alder began a steady rise arguing for increasing effective moisture and the development of the north coast temperate rain forest at ca 3 2 ka a permanent ca 1 c increase in alkenone sst and a threefold increase in p doliolus signaled a warming of fall and winter ssts intensified higher amplitude and more frequent cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature enhanced el nino southern oscillation enso cycles have characterized the site 1019 record since about 3 5 ka

pleistocene water cycle and eastern boundary current processes along the california continental margin 1 coastal marine sediments contain mixtures of terrestrial and marine paleoclimate proxies that record how the coastal water cycle has behaved over long time frames we explore a 600 kyr marine record from odp site 1018 located due west of santa cruz california to identify coastal wet and dry periods and to associate them with oceanographic processes wet periods in central california identified by increased tree pollen relative to pollen from grasslands and scrublands are found on every major deglaciation in the last 600 kyr sea surface temperature sst data were collected for the last two deglaciations wet periods are associated with a rapid rise in sst off central california sst gradients along the california margin and changes in biogenic deposition show that wet periods in central california are associated with a weakening of the california current and weakened coastal upwelling high carbonate production suggests that there was significant curl of wind stress upwelling offshore we propose that wet periods in central california are associated with a meteorological connection to the tropical pacific and weakened southward flow in the california current that shunted temperate pacific water northward into the alaska gyre we do not observe evidence for a south shifted westerly storm track at the last glacial maximum but find that wet periods are diachronous along the california margin the wettest period around the santa barbara basin peaked at 16 ka preceding the wet peak in central and northern california by 4 kyr

pollen analysis of a late glacial and holocene sediment core from mono lake mono county california pollen analysis of a 752 cm core from mono lake mono county california indicates generally high lake levels 11 600 7000 14c yr b p moderate lake levels until ca 4000 14c yr b p and fluctuating levels to the present drying events with lake levels near or below the historic minimum are dated ca 8800 4000 2400 and 1100 14c yr b p chronologic control is provided by six radiocarbon dates and six volcanic ashes the rate of upland vegetation change is greatest 11 000 4000 and 1130 14c yr b p juniperus and sequoaidendron pollen declines 11 000 yr b p marking the transition from late glacial juniper woodland to holocene steppe high values 5 20 of sequoaidendron pollen are unique to this study and may indicate the presence of these trees east of the sierra crest the pollen based reconstructions of climate are generally cooler and wetter than today with relatively dry but cool climate during the early holocene the contrast between higher lake levels and more arid vegetation during the early holocene can be explained by insolation driven seasonality greater summer insolation produced summer drought but lower winter insolation led to greater snowpack greater spring runoff and higher lake levels increased artemisia and other compositae pollen percentages mark the establishment of modern vegetation ca 2000 14c yr b p during the late holocene the pollen based reconstructions of climate generally match the mono lake fluctuations proposed by stine 1990 but fewer fluctuations are recorded

latest pleistocene to holocene hydroclimates from lake elsinore california abstract the hydroclimate of the southwestern united states us region changed abruptly during the latest pleistocene as the continental ice sheets over north america retreated from their most southerly extent to investigate the nature of this change we present a new record from lake elsinore located 36 km inland from the pacific ocean in southern california and evaluate it in the context of records across the coastal and interior southwest united states including northwest mexico the sediment core recovered from lake elsinore provides a continuous sequence with multi decadal resolution spanning 19 9 ka bp sedimentological and geochemical analyses reveal hydrologic variability in particular sand and carbonate components indicate abrupt changes at the oldest dryas od bolling allerod ba and younger dryas yd transitions consistent with the timing in greenland hydrogen isotope analyses of the c28 n alkanoic acids from plant leaf waxes dwax reveal a long term trend toward less negative values across 19 9 ka bp dwax values during the od suggest a north pacific moisture source for precipitation consistent with the dipping westerlies hypothesis we find no isotopic evidence for the north american monsoon reaching as far west as lake elsinore therefore we infer that wet dry changes in the coastal southwest were expressed through winter season precipitation consistent with modern climatology comparing lake elsinore to other southwest records notably cave of bells and fort stanton we find coincident timing of the major transitions od to ba ba to yd and hydrologic responses during the od and ba the hydrologic response however varied during the yd consistent with a dipole between the coastal and interior southwest the coherent pattern of hydrologic responses across the interior southwest us and northwest mexico during the od wet the ba drier and yd wet follows changes in the atlantic meridional overturning circulation presumably via its combined influence on north pacific winter storm tracks and the extent magnitude of the north american monsoon in contrast lake elsinore and the coastal southwest experiences a deglacial drying trend punctuated by abrupt change at the od to ba and ba to yd transitions this trend tracks rising greenhouse gases through the deglacial with an apparent southward shift in westerly moisture sources adjusting to the retreating ice sheet

uppermantle anisotropy and the oceanic lithosphere rayleigh wave and love wave dispersion data for oceanic paths cannot be satisfied by an isotropic uppermantle and it is incorrect to invert these two datasets independently for separate isotropic structures available phase and group velocity data are inverted for oceanic structure as a function of age taking into account anelastic dispersion sphericity and anisotropy the resulting models are quite different from previous results which ignore the above effects and the extra parameters involved in proper anisotropic inversion the models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age and an anisotropic low velocity zone with an age dependent anisotropy the lid or seismic lithosphere reaches a maximum thickness of 50 km which is about one half the thickness obtained in previous isotropic or pseudo isotropic inversions the seismic lithosphere therefore may be comparable in thickness to the elastic or flexural lithosphere raising the possibility that both are controlled by effects other than temperature stress and time such as mineralogy crystal orientation or partial melting the velocities in the low velocity zone are higher than inferred by previous surface wave studies

anisotropy and shear velocity heterogeneities in the upper mantle long period surface waves are used to map lateral heterogeneities of velocity and anisotropy in the upper mantle the dispersion curves are expanded in spherical harmonics up to degree 6 and inverted to find the depth structure the data are corrected for the effect of surface layers and both love and rayleigh waves are used shear wave velocity and shear polarization anisotropy can be resolved down to a depth of about 450 km the shear wave velocity distribution to 200 km depth correlates with surface tectonics except in a few anomalous regions below that depth the correlation vanishes cold subducted material shows up weakly at 350 km as fast s wave anomalies in the transition region a large scale pattern appears with fast mantle in the south atlantic s anisotropy at 200 km can resolve uprising or downwelling currents under some ridges and subduction zones the pacific shows a nw se fabric

a fan dam for tulare lake california and implications for the wisconsin glacial history of the sierra nevada historic fluctuations and late quaternary deposits of tulare lake in the southern san joaquin valley indicate that maximum lake size has depended chiefly on the height of a frequently overtopped spillway this dependence gives tulare lake a double record of paleoclimate climate in the tulare lake region has influenced the degree to which the lake fills its basin during dry seasons and dry years during the past 100 000 130 000 yr incidence of desiccation of tulare lake inferred from stiffness mud cracks and other hand specimen properties has been broadly consistent with the lake9s salinity and depth inferred from diatoms and ostracodes and with regional vegetation inferred from pollen climate however also appears to control basin capacity itself tulare lake becomes large as a consequence of glacial outwash aggradation of its alluvial fan dam late wisconsin enlargement of tulare lake probably resulted from the last major glaciation of the sierra nevada the lake9s spillway coincides with the axis of the glacial outwash fan of a major sierra nevada stream moreover sediment deposited in the transgressive lake resembles glacial rock flour from the sierra nevada differential tectonic subsidence and deposition by a coast range creek facilitated the building of tulare lake9s fan dam during the late wisconsin but were less important than deposition of sierra nevada outwash four stratigraphically consistent 14 c dates on peat and wood give an age of 26 000 yr b p for the start of tulare lake9s late wisconsin transgression the last major sierra nevada glaciation tioga glaciation thus may have begun about 26 000 yr b p provided that vigorous glacial outwash deposition began early in the glaciation onset of the tioga glaciation about 26 000 yr b p is consistent with new stratigraphic and radiocarbon data from the northeastern san joaquin valley these data suggest that the principal episode of glacial outwash deposition of wisconsin age began in the san joaquin valley after 32 000 yr b p rather than at least 40 000 yr b p as previously believed an earlier enlargement of tulare lake probably resulted from a fan dam produced by the penultimate major tahoe glaciation of the sierra nevada average sedimentation rates inferred from depths to a 600 000 yr old clay and from radiocarbon dates indicate that this earlier lake originated no later than 100 000 yr b p the tahoe glaciation therefore is probably pre wisconsin

oriented olivine crystals in the upper mantle a test from the inversion of multimode surface wave data abstract a large love rayleigh wave discrepancy of phase velocity has been observed for mantle overtones in the pacific ocean to test if preferred orientation of olivine crystals can be the cause for such an anisotropic behaviour we have considered that upper mantle material might be represented by a medium with hexagonal symmetry and a horizontal symmetry axis oriented in the direction of preferred orientation of the olivine crystal a axis a set of love and rayleigh wave data that are related to paths crossing the whole pacific plate have been inverted within this framework considering three parameters varying with depth s velocity density and the proportion of oriented crystals crystals are found to be preferentially oriented to 400 km depth different orientations of the symmetry axis have been tested a good fit to the data is obtained for an axis trending e w to se nw in qualitative agreement with the average trend of the absolute plate motion along the investigated paths the model presented in this study predicts azimuthal variations of fundamental mode rayleigh wave velocities in good agreement with estimates published in the literature

measurement of mantle wave velocities and inversion for lateral heterogeneity and anisotropy 1 analysis of great circle phase velocities long period 100 330 s fundamental mode love and rayleigh waves have been processed to measure the great circle phase velocities for about 200 and 250 paths respectively the observations are inverted for regionalized phase velocities and for an even order harmonic expansion of the lateral velocity heterogeneity the regionalized inversions achieve a maximum variance reduction of about 65 and 85 for the love and the rayleigh wave data respectively the l max 2 inversions give a maximum variance reduction of about 60 and 90 for love and rayleigh waves respectively the l max 8 inversion does not make a large improvement in the fit the love wave phase velocities have more power in l 4 and 6 relative to l 2 than the rayleigh waves for both love and rayleigh wave data the sectoral component dominates the l 2 harmonics and this component is stable if we increase l max from 2 to 6 heat flow also has strong sectoral components lm 22 which are approximately in phase with those of the phase velocities the l 2 harmonics of the nonhydrostatic geoid are dominated by large zonal lm 20 and moderate sectoral components the sectoral components are in phase with those of the phase velocities the sectoral pattern of heat flow and phase velocity is controlled by high heat flow low velocity of the east pacific rise and western north america which is reinforced by low velocities in the antipodal region red sea gulf of aden east african rift by contrast the geoid l 2 pattern is dominated by geoid highs over the western pacific subduction zones a spherical harmonic expansion of regionalized phase velocities shows that they have l 2 variations similar to those of the l max 2 nonregionalized inversions this means that the regionalization approach is appropriate as a first step for studying lateral heterogeneity of the earth however the great circle phase velocities are not sufficient by themselves to uniquely locate the lateral heterogeneity the same is true for free oscillation data regions of convergence have the interesting property of being slow for short period waves and fast faster than shields for long period waves

response of california current forcing to mid holocene insolation and sea surface temperatures 1 we find that mid holocene insolation causes systematic changes in wind forcing of the california current system suppressing wind stress in the spring and enhancing wind stress in the summer and autumn both large and regional scale processes play an important role in the insolation enhancement of wind stress with elevated summer insolation magnifying both large scale sea level pressure gradients and regional scale land sea thermal contrast we find that prescribed changes in large scale sea surface temperatures ssts amplify the response of nearshore wind stress to mid holocene insolation with sst magnification of changes in large scale sea level pressure gradients overcoming sst muting of changes in regional scale land sea thermal contrast the climate model simulations are supported by proxy inferred cooler than present sea surface temperatures in the northern california current system as well as by high nitrogen isotope values in the southern california current system our results highlight the importance of multiscale dynamical interactions in regulating the response of regional environments to global scale changes in radiative forcing

apparent synchroneity of submillennial scale climate events between greenland and santa barbara basin california from 30 10 ka abstract evidence is presented from odp hole 893a santa barbara basin for possible synchroneity between greenland and california margin submillennial climate change records during termination 1 and the last glacial maximum lgm planktonic foraminiferal isotope and faunal records are compared to the gisp2 18o records greenland for the interval between 30 and 10 ka using a new chronology based on 38 planktonic 14c dates apparent synchronous climatic events include interstadial is events 2 3 and 4 a broad warming trend between 21 and 19 ka and a broad cooling trend between 19 and 17 ka bolling and allerod warm episodes separated by the cooler older dryas event younger dryas cool episode and the preboreal the resulting tight correlation supports an intimate teleconnection between santa barbara basin surface waters and greenland air temperatures differences between greenland and santa barbara basin suggest that some regional variations were superimposed on the global pattern of climate change e g the pre bolling warming

stable isotope evidence for a foggy climate on santa cruz island california at 16 600 cal yr b p abstract in this study we use stable isotope analysis to investigate the climate in southern coastal california during the last 10 000 years of the pleistocene by comparing the carbon and oxygen stable isotope ratios of preserved douglas fir pseudotsuga menziesii wood from santa cruz island to modern douglas fir wood from northern california ams age determination indicates that the preserved trees grew at about 16 600 270 cal yr b p after isolating cellulose from both the modern and pleistocene wood to remove any potential bias due to differential decomposition rates of wood components loader n j robertson i mccarroll d 2003 comparison of stable carbon isotope ratios in whole wood cellulose and lignin of oak tree rings palaeogeography palaeoclimatology palaeoecology 196 395 407 we find that the pleistocene douglas fir wood has significantly greater carbon isotope discrimination and significantly more enriched 18 o than the modern douglas fir wood which suggests that the douglas fir trees growing on santa cruz island at 16 600 cal yr b p experienced less moisture stress and used more enriched water from fog than douglas fir trees at point reyes today

variation with age of anisotropy under oceans from great circle surface waves global great circle measurements of regionalized mantle love wave phase velocities are interpreted in terms of regional models the same study had been made by j j leveque 1980 for rayleigh waves and the resulting models for the two oceanic regions of different ages are used as a basis for comparison the observed love wave dispersion cannot be explained with these models if isotropic the models obtained by inversion of love wave data are compared with the models mentioned the discrepancy appearing in the 250km depth range between the velocities h and v of respectively sh and sv waves is indicative of polarization anisotropy moreover we put forward a significant variation from young to old oceans the difference between h and v is of the order of 1 for the former compared to 3 for the latter this variation can bring information about the behaviour of upper mantle materials in connection with the motion of oceanic plates

mid holocene climates of the americas a dynamical response to changed seasonality simulations of the climatic response to mid holocene 6 ka bp orbital forcing with two coupled ocean atmosphere models foam and csm show enhancement of monsoonal precipitation in parts of the american southwest central america and northernmost south america during northern hemisphere summer the enhanced onshore flow that brings precipitation into central america is caused by a northward displacement of the inter tropical convergence zone driven by cooling of the equatorial and warming of the northern subtropical and mid latitude ocean ocean feedbacks also enhance precipitation over the american southwest although the increase in monsoon precipitation there is largely driven by increases in land surface temperature the northward shift in the equatorial precipitation band that causes enhanced precipitation in central america and the american southwest has a negative feedback effect on monsoonal precipitation in northern south america the simulations demonstrate that mid holocene aridity in the mid continent of north america is dynamically linked to the orbitally induced enhancement of the summer monsoon in the american southwest with a spatial structure wet in the southwest and dry in the mid continent similar to that found in strong monsoon years today changes in winter precipitation along the west coast of north america in central america and along the gulf coast caused by southward displacement of the westerly storm tracks indicate that changes in the northern hemisphere winter monsoon also play a role in regional climate changes during the mid holocene although the simulations with foam and csm differ in detail the general mechanisms and patterns are common to both the model results thus provide a coherent dynamical explanation for regional patterns of increased or decreased aridity shown by vegetation lake status and aeolian data from the americas

out of the tropics the pacific great basin lakes and late pleistocene water cycle in the western united states the water cycle in the western united states changed dramatically over glacial cycles in the past 20 000 years higher precipitation caused desert lakes to form which have since dried out higher glacial precipitation has been hypothesized to result from a southward shift of pacific winter storm tracks we compared pacific ocean data to lake levels from the interior west and found that great basin lake high stands are older than coastal wet periods at the same latitude westerly storms were not the source of high precipitation instead air masses from the tropical pacific were transported northward bringing more precipitation into the great basin when coastal california was still dry the changing climate during the deglaciation altered precipitation source regions and strongly affected the regional water cycle

inversion of multimode surface wave data evidence for sub lithospheric anisotropy summary multiparameter inversions of multimode dispersion data are performed for two large regions the pacific ocean and north america anisotropy is taken into account by considering transversely isotropic structures with a vertical axis of symmetry two fundamental questions are studied in detail 1 how to make the inverted models consistent when using different sets of parameters 2 what is the significance of transversely isotropic inversion for the actual earth s structure it is proved that full consistency of the inverted models can be achieved by properly taking into account some a priori informations on the model and it is shown that the use of transversely isotropic models with vertical axis of symmetry does not cause severe limitations when interpreting the data the models we have obtained are discussed in the light of these investigations considering an olivine rich upper mantle we make a tentative interpretation of these models in terms of preferred orientation of the a axis of the crystals in one fixed horizontal direction

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

wildfire and abrupt ecosystem disruption on california s northern channel islands at the allerod younger dryas boundary 13 0 12 9 ka abstract sedimentary records from california s northern channel islands and the adjacent santa barbara basin sbb indicate intense regional biomass burning wildfire at the allerod younger dryas boundary 13 0 12 9 ka all age ranges in this paper are expressed in thousands of calendar years before present ka radiocarbon ages will be identified and clearly marked 14c years multiproxy records in sbb ocean drilling project odp site 893 indicate that these wildfires coincided with the onset of regional cooling and an abrupt vegetational shift from closed montane forest to more open habitats abrupt ecosystem disruption is evident on the northern channel islands at the allerod younger dryas boundary with the onset of biomass burning and resulting mass sediment wasting of the landscape these wildfires coincide with the extinction of mammuthus exilis pygmy mammoth the earliest evidence for human presence on these islands at 13 1 12 9 ka 11 000 10 900 14c years is followed by an apparent 600 800 year gap in the archaeological record which is followed by indications of a larger scale colonization after 12 2 ka although a number of processes could have contributed to a post 18 ka decline in m exilis populations e g reduction of habitat due to sea level rise and human exploitation of limited insular populations we argue that the ultimate demise of m exilis was more likely a result of continental scale ecosystem disruption that registered across north america at the onset of the younger dryas cooling episode contemporaneous with the extinction of other megafaunal taxa evidence for ecosystem disruption at 13 12 9 ka on these offshore islands is consistent with the younger dryas boundary cosmic impact hypothesis firestone r b west a kennett j p becker l bunch t e revay z s schultz p h belgya t kennett d j erlandson j m dickenson o j goodyear a a harris r s howard g a kloosterman j b lechler p mayewski p a montgomery j poreda r darrah t que hee s s smith a r stich a topping w wittke j h wolbach w s 2007 evidence for an extraterrestrial impact 12 900 years ago that contributed to the megafaunal extinctions and younger dryas cooling proceedings of the national academy of sciences 104 16016 16021

rayleigh wave phase velocities in the pacific with implications for azimuthal anisotropy and lateral heterogeneities summary the lateral distribution of fundamental mode rayleigh wave phase velocities in the pacific has been calculated in order to determine the variation in velocity as a function of the age of the oceanic plate the importance of azimuthal anisotropy and the presence of secondary lateral heterogeneities the data set used in this study consists of phase velocity measurements in the period range 20 125 s for 178 paths traversing the pacific both the pure path and spherical harmonic inversion techniques are used in this investigation with an emphasis placed on determining the effectiveness and resolving power of these methods in calculating the velocity distribution in an oceanic regime the first order velocity age relation which dominantly characterizes surface wave dispersion in an oceanic environment can be adequately modelled by either the pure path or spherical harmonic techniques azimuthal anisotropy is the dominant second order effect and is best developed in regions less than 80 myr in age in this age zone the faster direction of wave propagation is either in the direction of fossil seafloor spreading or in the direction of present day absolute plate motion in the western pacific there is a correlation with paleo relative motion fossil seafloor spreading for periods less than 50 s lateral velocity heterogeneities which are not related to the age of the oceanic plate are found by pure path inversions and are correlated with regions associated with shallow residual depth anomalies this effect slow velocities with respect to the velocity age model monotonically decreases as a function of period and is indicative of a shallow origin age independent anomalies were also modelled by the application of the pure path and spherical harmonic methods in a sequential inversion

geophysical constraints on partial melt in the upper mantle this paper addresses the conditions under which partial melt can exist in the mantle in order to be observed as a geophysical anomaly typical observed anomalies are high electrical conductivity of the order of 0 1 s m or greater velocity decreases of 7 10 seismic q values less than 100 and a frequency band for seismic effects in the region near 1 hz existing theories of electrical conduction in partial melts and of frequency dependent seismic properties together with recent measurements of melt electrical conductivity viscosity and partial melt texture can be used to establish requirements for melt to be observed by geophysical methods from electrical anomalies mainly sensitive to melt volume and its interconnection one can require a minimum melt fraction of several percent at temperatures close to the solidus 1150 1300 c however seismic models demand only a small volume in very flattened shapes aspect ratio 0 001 melt fraction 0 1 further if melt configuration permits seismic dissipation in bulk that is there exist flattened voids intersecting more or less equant voids then it is possible to infer melt fractions for elastic anomalies that are consistent with the several percent required for electrical anomalies observed equilibrium textures of partly melted peridotite together with inferred melt solid surface energies suggest that melt on a grain size scale in a gravitational field segregates into a strongly anisotropic pattern thus if partial melt causes mantle geophysical anomalies it should exist in a variety of void shapes and probably of sizes while the association of electrical and elastic anomalies with indications of reduced density volcanism and high heat flow makes the hypothesis of partial melting an attractive explanation the minimum physical requirement is for existence of relatively high temperature

pressure sensitivity of olivine slip systems and seismic anisotropy of earth s upper mantle the mineral olivine dominates the composition of the earth s upper mantle and hence controls its mechanical behaviour and seismic anisotropy experiments at high temperature and moderate pressure and extensive data on naturally deformed mantle rocks have led to the conclusion that olivine at upper mantle conditions deforms essentially by dislocation creep with dominant 100 slip the resulting crystal preferred orientation has been used extensively to explain the strong seismic anisotropy observed down to 250 km depth the rapid decrease of anisotropy below this depth has been interpreted as marking the transition from dislocation to diffusion creep in the upper mantle but new high pressure experiments suggest that dislocation creep also dominates in the lower part of the upper mantle but with a different slip direction here we show that this high pressure dislocation creep produces crystal preferred orientations resulting in extremely low seismic anisotropy consistent with seismological observations below 250 km depth these results raise new questions about the mechanical state of the lower part of the upper mantle and its coupling with layers both above and below

worldwide distribution of group velocity of mantle rayleigh waves as determined by spherical harmonic inversion we have determined the worldwide distribution of group velocity of mantle rayleigh waves for periods between 100 and 300 sec without assuming any regionalization group slowness 1 u is expressed by spherical harmonics and the coefficients up to angular order 7 have been determined from travel times of rayleigh waves by a least squares method from these u has been synthesized since we cannot obtain information about the odd terms of the expansion from one circuit measurements around the world we have used group velocities of mainly r 2 and r 3 the overall pattern of u for periods between 100 and 200 sec is consistent with results of previous pure path and regional studies group velocities for tectonically active regions are low and those of the shields and the northwestern pacific are high

paleoecology of a middle wisconsin deposit from southern california analysis of a buried deposit in the diamond valley of southern california has revealed well preserved pollen wood and diatom remains accelerator mass spectrometry dates of 41 200 2100 and 41 490 1380 14 c yr b p place this deposit in marine isotope stage 3 diatoms suggest a shallow lacustrine environment pollen data suggest that several plant communities were present near the site with grassland scrub chaparral forest and riparian communities represented comparison with modern pollen suggests similarities with montane forests in the nearby san bernardino and san jacinto ranges indicating vegetation lowering by at least 900 m elevation and temperatures 4 5 c cooler than today an increase in highelevation conifer pollen documents climatic cooling near the profile top early profile diatoms are typical of warm water with high alkalinity and conductivity whereas later diatoms suggest a higher flow regime and input of cooler water into the system we suggest that the sequence is part of the cooling phase of an interstadial dansgaard oeschger cycle records of the middle wisconsin period are rare in southern california but the diamond valley site is similar to records from tulare lake in the san joaquin valley and the odp site 893a record from santa barbara basin it is probable that the diamond valley assemblage is a local expression of a vegetation type widespread in the ranges and basins of southwestern california during the middle wisconsin c 2002 university of washington

surface wave propagation in an ocean basin with an anisotropic upper mantle observations of polarization anomalies summary observations of surface waves crossing ocean basins indicate that at least in some cases a better interpretation of what was previously considered to be the simultaneous arrival of fundamental love and second rayleigh modes with similar group velocities is the coupled motion of the second generalized mode surface wave propagating in an anisotropic upper mantle this mode displays the polarization anomalies expected from anisotropic alignments caused by syntectonic recrystallization of olivine in a zone of horizontal shear the polarity of the pattern of anomalies found in waves crossing the pacific basin suggests that the lithosphere is dragging the asthenosphere

radial anisotropy and prior petrological constraints a comparative study click here journal of geophysical research vol 115 b03303 doi 10 1029 2008jb005842 2010 for full article radial anisotropy and prior petrological constraints a comparative study c beghein 1 received 31 may 2008 revised 8 september 2009 accepted 6 october 2009 published 6 march 2010 1 radial seismic anisotropy models are traditionally obtained using empirical constraints based on laboratory experiments and petrological considerations we tested the hypothesis that such petrological constraints affect the uppermost mantle models of s wave anisotropy using a statistical approach in addition we were able to determine which model features are constrained by the data and which are dominated by the prior we focused on large scale models and found that the most likely models obtained in both cases are highly correlated this demonstrates that for the best data fitting solution the geometry of uppermost mantle radial anisotropy is not strongly affected by prior petrological constraints the amplitude of the anomalies however can change significantly the best data fitting model obtained without petrological constraints displays stronger amplitudes than the one obtained with prior this could become an issue when quantitatively interpreting seismic anisotropy models and thus emphasizes the importance of accurately accounting for parameter uncertainties and trade offs and of understanding whether the seismic data or the prior constraints the model we showed that model uncertainties are strongly affected by the prior as the relative rms uncertainties were reduced by a factor of 2 in addition we showed that while the model distributions are not necessarily gaussian a priori imposing petrological constraints can force the distributions to be narrower and more gaussian like as expected from inverse theory finally we demonstrated that the age dependence of seismic wave velocities is robust and independent of prior constraints a similar age signal exists for anisotropy but with larger uncertainties without prior constraints citation beghein c 2010 radial anisotropy and prior petrological constraints a comparative study j geophys res 115 b03303 doi 10 1029 2008jb005842 1 introduction 2 accurately modeling mantle seismic anisotropy that is the dependence of seismic wave velocity with the direction of propagation or polarization can help us under stand mantle deformation karato and toriumi 1989 kendall 2000 becker et al 2003 the coupling between lithosphere and asthenosphere silver and holt 2002 becker et al 2006b mantle composition montagner and anderson 1989 rheology becker et al 2008 and the net rotation of the lithosphere becker 2008 however despite numerous efforts to model mantle seismic anisotropy over the past 20 years uncertainties remain on its exact depth extent and lateral variations in the uppermost mantle on its presence in the transition zone and on its global nature in the d 00 layer fouch and fischer 1996 montagner and kennett 1996 ekstro m and dziewonski 1998 lay et al 1998 trampert and van heijst 2002 wookey et al 2002 gung et al 2003 panning and romanowicz 2006 earth and space sciences department ucla los angeles california usa copyright 2010 by the american geophysical union 0148 0227 10 2008jb005842 09 00 beghein and trampert 2004a 2004b beghein et al 2006 panning and romanowicz 2006 zhou et al 2006 marone et al 2007 nettles and dziewonski 2008 beghein et al 2008 3 discrepancies between models can arise for a variety of reasons to fully describe earth s elastic properties one would ideally want to determine the 21 independent ele ments of the fourth order elastic stiffness tensor at a given time and location inside earth in practice this is challeng ing because seismic data are only sensitive to subsets of those 21 elements tanimoto 1986 chen and tromp 2007 beghein et al 2008 and different types of data depend on different subsets of elastic coefficients see summary tables in chen and tromp 2007 and beghein et al 2008 in addition while some data such as shear wave splitting measurements can provide precise constraints on lateral changes in seismic anisotropy their depth resolution is very poor surface wave and free oscillation data are better suited to constrain depth changes in structure but their lateral resolution is lower than that of body waves this can yield apparent discrepancies and make model comparisons diffi cult moreover three dimensional models of seismic anisot ropy are typically obtained by data inversion which is often an ill posed and ill conditioned problem this means that b03303 1 of 17

interpretation of floodplain pollen in alluvial sediments from an arid region pollen was collected from modern alluvium and from the atmosphere to document the nature and amount of paleoenvironmental information reflected by alluvial pollen chronologies results indicate that pollen in alluvium is a homogeneous mixture derived almost entirely from the floodplain itself the few pollen grains derived from nonfloodplain plant communities and preserved in alluvial sediments are so well mixed that their frequencies no longer reflect the geographic distribution of the specific plant communities in which they originated in contrast the abundance of alluvial pollen grains derived from the major floodplain taxa chenopodiineae ambrosia type varies with summer and winter climate this annual variation is preserved in alluvial pollen assemblages through a combination of processes within sedimentation basins involving discontinuous deposition events and mechanical pollen degradation the high frequency wide amplitude pollen variance in alluvial pollen assemblages contrasts with the low frequency narrow amplitude pollen variance in sediments of lakes and ponds the slight geographic variance in alluvial pollen assemblages in contrast to the large variance in soil pollen allows use of alluvial pollen to infer climate throughout the watershed in which pollen is sampled

rancho la brea stable isotope biogeochemistry and its implications for the palaeoecology of late pleistocene coastal southern california abstract we sampled 143 individuals from rancho la brea rlb large faunal collections for bone collagen stable carbon 13c and nitrogen 15n isotope ratios these collections were recovered from asphalt seeps in the los angeles basin california usa and date from 40 to 12 ka our findings indicate that despite a slight reduction in collagen nitrogen content rlb skeletal remains are relatively well preserved and most yield proteins diagnostic of diet herbivore 13c and 15n values covary with rumination and are consistent with changes in late pleistocene vegetation reconstructed from pollen profiles we find no evidence for reliance on c4 grasses at rlb despite low atmospheric co2 concentrations carnivore 15n values indicate canis dirus smilodon fatalis and panthera leo atrox competed for similar prey sets and were equally reliant on ruminant and nonruminant prey types the 15n values of mammut americanum indicate partial reliance on vegetation with lower 15n values such as nitrogen fixing taxa distinguishing them from the remainder of the study population a comparison of rlb and european faunal 15n values from the late pleistocene suggests that coastal southern california experienced greater aridity

seismic anisotropy and global geodynamics for many years seismic anisotropy was often neglected mostly because of the inherent heavy mathematical and computational tools needed to describe and model its effects on seismic waves the usual basic knowledge about propagation in isotropic media cannot easily apply to anisotropic media where new phenomena come up such as birefringence or shear wave splitting or difference between directions of propagation of phase velocity and of group velocity consequently geophysicists often claimed that it was a second order effect and considered the earth as isotropic this hypothesis was assumed to be a good approximation because of the random orientation of crystals in most parts of the earth and of the random sampling of anisotropic regions by seismic rays this assumption furthermore made easier the description of wave propagation as well as the parameterization of media in inverse problems an isotropic elastic medium can be described by two independent elastic parameters and lame parameters but the simplest anisotropic medium transverse isotropy with a vertical symmetry axis requires 5 independent parameters love 1927 anderson 1961 to date seismic observations have been explained in terms of isotropic and often thermal lateral heterogeneities ignoring manifestations of anisotropy however since the 1960s it was recognized that most parts of the earth are not only laterally heterogeneous but also anisotropic and that seismic anisotropy provides a simple explanation of different observational data seismic anisotropy contrary to isotropy is reflecting some inherent

probability density functions for radial anisotropy implications for the upper 1200 km of the mantle the presence of radial anisotropy in the upper mantle transition zone and top of the lower mantle is investigated by applying a model space search technique to rayleigh and love wave phase velocity models probability density functions are obtained independently for s wave anisotropy p wave anisotropy intermediate parameter r vp vs and density anomalies the likelihoods for p wave and s wave anisotropy beneath continents cannot be explained by a dry olivine rich upper mantle at depths larger than 220 km indeed while shear wave anisotropy tends to disappear below 220 km depth in continental areas p wave anisotropy is still present but its sign changes compared to the uppermost mantle this could be due to an increase with depth of the amount of pyroxene relative to olivine in these regions although the presence of water partial melt or a change in the deformation mechanism cannot be ruled out as yet a similar observation is made for old oceans but not for young ones where vsh s vsv appears likely down to 670 km depth and vph s vpv down to 400 km depth the change of sign in p wave anisotropy seems to be qualitatively correlated with the presence of the lehmann discontinuity generally observed beneath continents and some oceans but not beneath ridges parameter r shows a similar age related depth pattern as shear wave anisotropy in the uppermost mantle and it undergoes the same change of sign as p wave anisotropy at 220 km depth the ratio between dlnvs and dlnvp suggests that a chemical component is needed to explain the anomalies in most places at depths greater than 220 km more tests are needed to infer the robustness of the results for density but they do not affect the results for anisotropy

upper mantle low anisotropy channels below the pacific plate a new 3d anisotropic model has been obtained at a global scale by using a massive dataset of seismic surface waves though seismic heterogeneities are usually interpreted in terms of heterogeneous temperature field a large part of lateral variations are also induced by seismic anisotropy of upper mantle minerals new insight into convection processes can be gained by taking seismic anisotropy into account in the inversion procedure the model is best resolved in the pacific plate the largest and the most active tectonic plate superimposed on the large scale radial parameter and azimuthal anisotropy of vsv velocity within and below the lithosphere correlated with present or past pacific plate motions are smaller scale 1000 km lateral variations of anisotropy not predicted by plate tectonics channels of low anisotropy down to a depth of 200 km hereafter referred to as lac are observed and are the best resolved anomalies one east west channel between easter island and the tonga kermadec subduction zones observed on both radial and azimuthal anisotropies and a second one only observed on azimuthal anisotropy extending from the south west pacific up to south east hawaii and passing through the polynesia hotspot group for plate older than about 40 ma these features provide strong constraints on the decoupling between the plate and asthenosphere they are presumably related to cracking within the pacific plate and or to secondary convection below the rigid lithosphere predicted by numerical and analog experiments the existence and location of these lacs might be related to the current active volcanoes and hotspots possibly plumes in the central pacific lacs which are dividing the pacific plate into smaller units might indicate a future reorganization of plates with ridge migrations in the pacific ocean

measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy 3 inversion lateral heterogeneity in the earth s upper mantle is investigated by inverting dispersion curves of long period surface waves 100 330 s models for seven different tectonic regions are derived by inversion of regionalized great circle phase velocity measurements from our previous studies we also obtain a representation of upper mantle heterogeneities with no a priori regionalization from the inversion of the degree 6 spherical harmonic expansion of phase and group velocities the data are from the observation of about 200 paths for love waves and 250 paths for rayleigh waves for both the regionalized and the spherical harmonic inversions corrections are applied to take into account lateral variations in crustal thickness and other shallow parameters these corrections are found to be important especially at low spherical harmonic order the trench region and fast velocities down to 250 km under shields below 200 km under the oceans both s velocity and s anisotropy support a model of small scale convection in which cold blobs detach from the bottom of the lithosphere when its age is large enough the spherical harmonic models clearly demonstrate a posteriori the relation between surface tectonics and s velocity heterogeneities in the first 250 km all shields are fast most ridges are slow below 300 km a belt of fast mantle follows the pacific subduction zones however at greater depths large scale heterogeneities that seem to bear no relationship to surface tectonics are observed the most prominent feature at 450 km is a fast velocity region under the south atlantic ocean smaller scale heterogeneities that are not related to surface tectonics are also mapped at shallower depths an anomalously slow region centered in the south central pacific is possibly linked to intense hot spot activity a very fast region southeast of south america may be related to subduction of old pacific plate between 200 and 400 km a belt of sv sh anisotropy follows part of the ridge and subduction systems indicating vertical mantle flow in these regions the spherical harmonic results open new horizons for the understanding of convection in the mantle perspectives for the improvement of the models presented are discussed

age independent seismic anisotropy under oceanic plates explained by strain history in the asthenosphere the depth of the oceanic lithosphere asthenosphere boundary lab as inferred from shear wave velocities increases with lithospheric age in agreement with models of cooling oceanic lithosphere on the other hand the distribution of radial anisotropy under oceanic plates is almost age independent in particular radial anisotropy shows a maximum positive gradient at a depth of 70 km which if used as a proxy indicates an age independent lab depth these contrasting observations have fueled a controversy on the seismological signature of the lab to better understand the discrepancy between these observations we model the development of lattice preferred orientation lpo in upper mantle crystal aggregates and predict the seismic anisotropy produced by plate driven mid ocean ridge flows the model accounts for the progressive cooling of the lithosphere with age and can incorporate both diffusion and dislocation creep deformation mechanisms we find that an age independent distribution of radial anisotropy is the natural consequence of these simple flows the depth and strength of anisotropy is further controlled by the deformation regime dislocation or diffusion creep experienced by crystals during their ascent towards and subsequent motion away from the ridge axis comparison to surface wave tomography models yield constraints on rheological parameters such as the activation volume although not excluded additional mechanisms proposed to explain some geophysical signatures of the lab such as the presence of partial melt or changes in water content are not required to explain the radial anisotropy proxy our prediction that the age independent radial anisotropy proxy marks the transition to flow induced asthenospheric anisotropy provides a way to reconcile thermal mechanical and seismological views of the lab

collapse of the california current during glacial maxima linked to climate change on land time series of alkenone unsaturation indices gathered along the california margin reveal large 4 to 8 c glacial interglacial changes in sea surface temperature sst over the past 550 000 years interglacial times with ssts equal to or exceeding that of the holocene contain peak abundances in the pollen of redwood the distinctive component of the temperate rainforest of the northwest coast of california in the region now dominated by the california current ssts warmed 10 000 to 15 000 years in advance of deglaciation at each of the past five glacial maxima ssts did not rise in advance of deglaciation south of the modern california current front glacial warming along the california margin therefore is a regional signal of the weakening of the california current during times when large ice sheets reorganized wind systems over the north pacific both the timing and magnitude of the sst estimates suggest that the devils hole nevada calcite record represents regional but not global paleotemperatures and hence does not pose a fundamental challenge to the orbital milankovitch theory of the ice ages

forward modeling of the development of seismic anisotropy in the upper mantle development of seismic anisotropy in response to upper mantle flow is approached through an integrated numerical model this model allows to predict the splitting parameters for a shear wave propagating across an upper mantle which deformed in response to a given geodynamic process it consists of 1 thermo mechanical modeling of the finite strain field 2 modeling olivine lattice preferred orientation lpo generated by this strain field 3 calculation of the 3 d elastic properties associated with this lpo and 4 estimation of the shear wave splitting parameters the time lag between the fast and slow split shear wave arrivals dt and the polarization azimuth of the fast wave modeled olivine lpo are constrained relative to lpo measured in naturally and experimentally deformed peridotites comparison of predicted shear wave splitting parameters with seismological data allows us to quantify the possible contribution of the modeled upper mantle flow to the measured splitting values and hence to constrain the interpretation of shear wave splitting data in terms of upper mantle flow we use this forward model to investigate the seismic anisotropy generated in ocean basins by a velocity gradient between the plate and the deep mantle fast shear wave polarizations calculated assuming a constant plate motion are in good agreement with both the sks polarization and the fast propagation direction for p and rayleigh waves observed in the pacific and indian oceans suggesting that away from mid ocean ridges seismic anisotropy in oceanic basins primarily results from asthenospheric deformation by resistive drag beneath the plate delay times are however overestimated this may be ascribed to a stronger strain localization in nature or to partial erosion of the anisotropic layer by hotspots indeed hotspot activity may explain the short length scale variations of dt in the southern pacific finally twolayer models that simulate a change in pacific plate motion as suggested by the bend in the hawaii emperor chain fail to reproduce the observed shear wave splitting this is consistent with previous suggestions that the emperor chain track may not faithfully record the pacific plate absolute motion before 43 ma 1998 elsevier science b v all rights reserved

silicic magmas in the izu bonin oceanic arc and implications for crustal evolution abundant rhyolitehaseruptedfromthe izu bonin marianavolca nic arc ibm arc from its earliest stage eocene to the present geochemically three types of quaternary rhyolites exist in the izu bonin arcfront and theyare closely related tovolcanotypeand crus tal structure the dominantly basaltic islands of the volcanic frontproduce small volumes of rhyolites that we call r1 the submarinecalderas of the volcanic front erupt mostly rhyolite that we call r2 seamounts knolls and pillow ridges in thebackarcextensionalzoneare mostly basaltic but also contain rhyolites that we call r3 thethickest total crust and the thickest intermediate compositionmiddle crust occurs below the dominantly basaltic volcanoes whereas the intermediate composition middle crust tends to be thin nerbeneaththesubmarinecalderas r1rhyolitesmaybederivedfromquaternary andesitic sources whereas r2 and r3 rhyolites may bederivedfromoligoceneones thehighercao al

regional and azimuthal dependence of phase velocities of mantle rayleigh waves in the pacific ocean abstract the lateral heterogeneity and azimuthal anisotropy of the upper mantle in the pacific ocean are investigated by analysing rayleigh wave phase velocities in the period range 60 200 s rayleigh waves at periods below 150 s travel fast in the direction parallel to the present day plate motion rayleigh wave velocities at longer periods show a similar azimuthal dependence in most parts of the pacific the average magnitude of the velocity anisotropy in the pacific ocean changes from 1 at 60 s to 0 4 at 200 s the azimuth independent phase velocities increase with the increase in age of the sea floor in the period range 60 120 s but the correlation is weak at longer periods the trade off between the lateral variation and the azimuthal variation is weak except for marginal places of the studied area

late quaternary slip rate of the southern elsinore fault southern california dating offset alluvial fans via 230th u on pedogenic carbonate 1 to understand how strain is accommodated along the pacific north american plate boundary and to assess the associated seismic hazard estimates of long term 103 105 year slip rates for strands of the san andreas fault system are needed the mean slip rate over the past 40 kyr for the southernmost elsinore fault one of the principal strands of the san andreas fault system in southern california was determined using offset alluvial fans dated by u series on pedogenic carbonate two displaced fans correlated with their source drainages using distinctive gravel clast assemblages define offsets of 60 20 and 83 31 m milligram size samples of dense carbonate clast coatings from fan soils provide 230th u based ages of 39 1 5 3 and 46 4 5 3 kyr all errors are 2 respectively for the offset fans our results indicate that the elsinore fault near its southern terminus slipped at a mean rate of 1 6 0 4 mm yr over the past 40 kyr however slip associated with the most recent earthquake on the southern elsinore fault increases northward from the study area and if this pattern has repeated through time the peak slip rate on the southern elsinore fault may significantly exceed our measured rate

where can seismic anisotropy be detected in the earth s mantle in boundary layers during the last 30 years considerable evidence of seismic anisotropy has accumulated demonstrating that it is present at all scales but not in all depth ranges we detail which conditions are necessary to detect large scale seismic anisotropy firstly minerals must display a strong anisotropy at the microscopic scale and or the medium must be finely layered secondly the relative orientations of symmetry axes in the different crystals must not counteract in destroying the intrinsic anisotropy of each mineral and there must be efficient mechanisms of orientation of minerals and aggregates finally the strain field must be coherent at large scale in order to preserve long wavelength anisotropy part of shallow anisotropy can be related to the past strain field frozen in anisotropy however the deep anisotropy is due to the present strain field all these conditions are fulfilled only in boundary layers of convective mantle we review in this paper the seismic data sets which provide insight into the location at depth of large scale anisotropy from the d layer up to the lithosphere in addition to the well documented seismic anisotropy in the lithosphere and asthenosphere there is new evidence of seismic anisotropy in the upper 400 660 km and lower 660 900 km transition zones and in the d layer nonetheless the bulk of the lower mantle seems close to isotropy if we assume the hypothesis that seismic anisotropy is associated with boundary layers in convective systems these observations strongly suggest that the transition zone is a boundary layer which makes the pasage of matter between the upper and the lower mantle difficult however this general statement does not rule out flow circulation between the upper and lower mantles finally the geophysical mineral physics and geological applications are briefly reviewed an intercomparison between surface wave anisotropy and body wave anisotropy data sets is presented we discuss the scientific potential of seismic anisotropy and how it makes it possible to gain more insight into continental root deformation and geodynamics processes

phase and group velocities and q of mantle love and rayleigh waves of the first two modes and their azimuthal dependences for the 1963 kurile islands earthquake abstract phase and group velocities and q of mantle love and rayleigh waves from the 1963 kurile islands earthquake m w 8 5 were determined over 37 great circle paths by a time variable filtering technique in a period range 100 500 s for the fundamental modes and 100 275 s for the first higher modes the preliminary reference earth model prem explains reasonably well the average dispersion results for the fundamental love and rayleigh waves there exists a small but significant inconsistency between the observation and the model for the first higher love and rayleigh waves the q structure of prem is inconsistent with the observation for the fundamental love waves but explains other observations reasonably well the dispersion of each mode shows a clear azimuthal dependence from which the four azimuthal windows were established the phase and group velocity measurements for each window were in general shown to be mutually consistent the azimuthal variations are largest for the first higher rayleigh waves indicating strong lateral heterogeneity in the structure of the low velocity zone the first of the four windows is characterized by the largest fraction of precambrian shields and the second window by the largest fraction of normal oceans a comparison of these two windows may give some insight into deep lateral heterogeneity between continents and oceans the observed phase and group velocities of the first window are systematically higher than those of the second window for the fundamental love and rayleigh waves at periods up to 400 s and for the first higher love and rayleigh waves up to 175 s their differences are greatest for the first higher rayleigh waves and least for the fundamental rayleigh waves although the fundamental rayleigh waves show the least velocity differences their persistence up to a period of longer than 300 s is in striking contrast with some of the pure path phase velocities derived earlier for continents and oceans a set of models for continents and oceans pem c and pem o are not consistent with our observation the third azimuthal window is characterized by trench marginal seas and the fourth window by mountainous areas typically the asian high plateaus from northern china to the middle east through tibet a comparison of these two windows gives some information about deep structural differences between subduction zones and continental collision zones both belonging to plate convergence zones for the fundamental and the first higher love waves the phase and group velocities for the third window are markedly low whereas those for the fourth window are somewhat comparable to those for the second window slow rayleigh waves are evident for two windows with the fourth window apparently being the slowest for the fundamental rayleigh above 200 s and for the first higher rayleigh for the fundamental rayleigh waves the third window is very slow below 200 s but becomes progressively fast as the period increases and tends to be the fastest window around 400 s suggesting a deep seated high velocity anomaly beneath trench marginal seas the dispersion characteristics of the fourth window indicate a thick high velocity lid with an extensive low velocity zone beneath it the shield like lithosphere coupled with an extensive low velocity zone may be a characteristic feature of continental collision zones the particle motion of the fundamental love waves was found not to be purely transverse to a great circle connecting the epicenter to a station the departure from the purely transverse motion is systematic among different periods different g arrivals g 2 g 3 and different stations which may be interpreted as being due to lateral refraction

long period love wave overtone data in north america and the pacific ocean new evidence for upper mantle anisotropy abstract two tonga trench earthquakes recorded in north america on wwssn long period instruments have been processed by making use of spatial analysis techniques to retrieve the phase velocities of love wave modes dispersion data up to the third overtone at periods longer than 30 s have been obtained for two broad areas the pacific ocean and north america it is found that the observed love wave phase velocities are not in agreement with the values predicted from the previously published models inferred from rayleigh wave data phase velocity discrepancies as large as 3 4 in the pacific ocean and 2 in north america are observed up to the second overtone preliminary direct computations which have been performed in the framework of transversely isotropic models with the axis of symmetry oriented vertically suggest that the cause for this departure from isotropy probably extends to depths 200 km

insights into pollen source area transport and deposition from modern pollen accumulation rates in lake sediments abstract pollen accumulation rates par from late quaternary deposits can provide direct estimates of past plant abundance they are influenced by lake internal processes and therefore rarely used in between site comparisons although few studies from fennoscandia have applied them successfully this study aims to explore how pars from selected lakes from northeast germany reflect differences in plant abundance as a step towards quantitative vegetation reconstructions from pars short sediment cores were collected from 18 lakes of which 16 could be dated by 210pb pars were estimated for the youngest sediment representing approximately two years before sampling in 2009 and samples dated to around 1993 forest inventory data for the two time slices were obtained for 15 km around the sites and standing volume sv was estimated as a measure of above ground biomass pars were compared to the total sv within increasing areas around the lakes as well as to distance weighted sv using the prentice sugita model of pollen dispersal and deposition both assessments of the vegetation data yielded strong linear relationships with pars already over distances of tens of metres to a few kilometres documenting the importance of the local vegetation this indicates the importance of the often neglected trunk space component of pollen transport for small lakes results from the small number of large lakes suggest that these sites receive a larger absolute input of pollen from regional sources these observations indicate that small lakes may be somewhat sheltered from pollen transported above the canopy we demonstrate that pars of the major tree taxa obtained from lake sediments are linear related to the lake surrounding biomass this confirms that par can be used to infer past changes in plant biomass although absolute pollen deposition may also be determined by net primary productivity of the biomass

effects of lateral heterogeneity and source process time on the linear moment tensor inversion of long period rayleigh waves spectra of mantle rayleigh waves recorded on the ida network are inverted to determine the seismic moment tensor of the 9 june 1980 california mexico border earthquake the 29 july 1980 vanuatu islands earthquake and the 9 july 1980 santa cruz islands earthquake examinations are made to correct for phase velocity lateral heterogeneity and source process time a simple regionalization stable continent tectonic region young ocean and old ocean improves results of the linear inversion but the phase correction is not large enough and the discontinuous change of phase velocity across the boundary between regions causes an artificial rapid change in apparent phase velocity as a function of azimuth therefore a more detailed but gradual representation of the lateral heterogeneity is desirable to correct for the propagation effect in the linear inversion a source process time which consists of the nondirectional part of the apparent duration of main faulting and the delay time of the faulting from initial break is estimated by a phase analysis of rayleigh waves the source process time is generally proportional to the seismic moment on the log log scale but some earthquakes deviate considerably from the general relation therefore the measurement of the source process time should be made before the moment tensor inversion the phase errors introduced by the lateral heterogeneity and source process time may cause a bias to low scalar moment

seismic and electrical signatures of the lithosphere asthenosphere system of the normal oceanic mantle although plate tectonics started as a theory of the ocean basins nearly 50 years ago the mechanical details of how it works are still poorly known our understanding of these details has been hampered partly by our inability to characterize the physical nature of the lithosphere asthenosphere system las beneath the ocean we review the existing observational constraints on the seismic and electrical properties of the las particularly for normal oceanic regions away from mid oceanic ridges hot spots and subduction zones where plate tectonics is expected to present its simplest form whereas a growing volume of seismic data on land has provided remarkable advances in large scale pictures seafloor observations have been shedding new light on essential details by combing through these observational constraints researchers are unveiling the nature of the enigmatic las future directions for large scale seafloor observations are also discussed

holocene paleoecology of an estuary on santa rosa island california abstract the middle to late holocene history and early anglo european settlement impacts on santa rosa island california were studied through the analysis of sediments in a small estuarine marsh a 5 4 m long sediment core produced a stratigraphic and pollen record spanning the last 5200 yr three major zones are distinguishable in the core the lowermost zone 5200 to 3250 yr b p represents a time of arid climate with predominantly marine sediment input and high chenopodiaceae and ambrosia pollen values the intermediate zone 3250 yr b p to 1800 a d is characterized by greater fresh water input and high values for asteraceae and cyperaceae pollen and charcoal particles the uppermost zone 1800 a d to present documents the unprecedented erosion sedimentation and vegetation change that resulted from the introduction of large exotic herbivores and exotic plants to the island during anglo european settlement the identification of pollen grains of torrey pine pinus torreyana documents the persistence of this endemic species on the island throughout the middle to late holocene

millennial pulsing of environmental change in southern california from the past 24 k y a record of indo pacific enso events century long variations in coastal california vegetation inferred from polliniferous sediments deposited in the santa barbara basin record a succession of brief 14 c yr b p ka these millennial scale pulses many of which correspond with western great basin hydrological fluctuations are also linked to events of southwest monsoon intensification in southern asia we suggest that these correlative high frequency variations in the asian summer and northeast pacific winter climates may reflect submillennial scale el nino southern oscillation enso type forcing involving water vapor transport over the indian and pacific oceans

fluvial tufa evidence of late pleistocene wet intervals from santa barbara california u s a abstract past pluvials in the western united states provide valuable context for understanding regional hydroclimate variability here we report evidence of conditions substantially wetter than today from fluvial tufa deposits located near zaca lake santa barbara county california that have been dated by radiocarbon 14c and infra red stimulated luminescence irsl two successions of tufa deposition occur within a small catchment that drains miocene monterey formation bedrock 1 a fluvial deposit 0 0 5 m thick 200 m in extent that formed along a narrow valley below a modern spring and 2 a perched deposit 10 m higher 2 m thick 15 m in extent irsl and radiocarbon dating of the perched carbonates suggest at least two episodes of carbonate growth one at 19 4 2 4 1 through 17 8 2 8 1 ka and another at 11 9 1 5 1 ka verified with a charcoal 14c age of 10 95 0 12 2 cal ka bp the relationship between the perched and fluvial spring deposits is inferred to represent a drop in the water table of more than 10 m associated with a transition from a wet climate in the late glacial to a dry holocene today the wet period indicated by the perched tufa deposit between 19 4 and 17 8 ka is relatively consistent with other california climate records both north and south of zaca lake however tufa growth ca 12 to 11 ka demonstrates wet conditions occurred as far south as zaca lake during the younger dryas event in contrast to climate records farther south in lake elsinore that indicate a drying trend through this interval a small shift north in the average position of the winter season storm track could explain wet winters at zaca while at the same time generating dry winters at lake elsinore 275 km southwest of zaca if true these data indicate that rather small latitudinal shifts in the average winter season storm track can produce large changes in regional hydroclimate

seismological structure of the upper mantle a regional comparison of seismic layering abstract we investigate seismic layering i e discontinuities regions of anomalous velocity gradients and anisotropy and its lateral variability in the upper mantle by comparing seismic models from three tectonic regions old 100 ma pacific plate younger 40 ma philippine sea plate and precambrian western australia these models were constructed by combining two data sets scs reflectivity profiles which provide travel times and impedance contrasts across mantle discontinuities and observations of frequency dependent travel times of three component turning s ss ss sss sss sa and surface r1 g1 waves which constrain the anisotropic velocity structure between discontinuities the models provide a better fit to observed seismograms from these regions than the current generation of global tomographic models the australian model is characterized by high shear velocities throughout the upper 350 km of the mantle with no low velocity zone lvz in the isotropically averaged shear velocities in contrast the oceanic models are characterized by a thin high velocity seismic lid underlain by a distinct lvz with a sharp boundary the g discontinuity separating them the g is significantly deeper beneath the western philippine sea plate than beneath the older pacific 89 and 68 km respectively implying that thermal cooling alone does not control the thickness of the lid we interpret this discontinuity as a compositional boundary marking the fossilized base of the melt separation zone msz active during sea floor spreading no discontinuity is detected at the base of the lvz in the oceanic models the s velocity gradient between 200 and 410 km depth is much steeper in the oceans than beneath australia this high oceanic gradient is probably controlled by a decrease in the homologous temperature over this depth interval the relative depths of the transition zone tz discontinuities are consistent with clapeyron slopes expected for an olivine dominated mineralogy the 660 km discontinuity displays variability in its amplitude that appears to correlate with its depth shallow and bright beneath the pacific deep and dim beneath australia and the philippine sea such behavior is possibly caused by the juxtaposition of the olivine and garnet components of the phase transition radial anisotropy extends through the upper 250 km of the mantle in the australia model and through the upper 160 km of the two oceanic models the magnitude of anisotropy is consistent with that expected for models of horizontally oriented olivine and the localization of anisotropy in the shallowest upper mantle implies that it reflects strain associated with past or present tectonic events

variation with age of the deep structure of the pacific ocean inferred from very long period rayleigh wave dispersion the propagation of rayleigh waves along 44 direct paths across the pacific ocean is studied and a regionalization of the dispersion according to the age of the sea floor is performed the group velocity dispersion curves characteristic of each one of four age regions considered are obtained for periods up to 300 s these curves show an increase of group velocities with age over the whole period range considered the shear wave velocity models inferred yield a lithosphere thickening with age and show the presence below the lithosphere of two zones where negative velocity anomalies decrease with increasing age the low velocity zone and a zone at a depth of 350 km

investigation of upper mantle structure under young regions of the southeast pacific using long period rayleigh waves abstract long period rayleigh wave group velocity dispersion curves are presented for paths across the east pacific ocean the records are from the ipg site at pamatai tahiti and the ida station at nana for the first time direct path observations of group velocities up to 300 s have been obtained this study shows that for young oceanic regions group velocities are low even at long periods the observations are interpreted in terms of an s wave velocity model by a generalized inversion scheme in the models for young ages the low velocity zone under the asthenosphere lid is well developed with a strong velocity gradient at the bottom of this zone followed at larger depths by a plateau representing a lower velocity zone and a marked gradient at 400 km

extreme southwestern margin of late quaternary glaciation in north america timing and controls well preserved latero frontal moraines in the eastern san bernardino mountains of southern california provide evidence for several glacial advances during the late quaternary and mark the southwesternmost limit of glaciation in the western cordillera using geomorphology and 10be cosmogenic radionuclide dating a succession of moraines from three glaciated valleys is dated to 18 20 ka last glacial maximum 15 16 ka heinrich event 1 12 13 ka younger dryas stade and 5 9 ka early middle holocene these ages substantiate the view that glaciation throughout the american cordilleras was synchronous during the late quaternary furthermore these data show that glacial advances in southern california occur when a significant decrease in summer temperature is coupled with an increase in moisture flux producing high winter snowfall this allows for perennial snow accumulation that may under appropriate conditions persist to form glacial ice

how to relate body wave and surface wave anisotropy seismic anisotropy is one of the most efficient geological and geodynamical tools for understanding the dynamics of the earth upper mantle anisotropy is evident in seismic data sets for the last 30 years primarily from surface wave dispersion curves and body wave sks data we demonstrate in this paper that surface wave and body wave derived anisotropy can be explained by the same anisotropic parameters l gc gs in the simplest case of a horizontal fast symmetry axis one application of this method is to display the sks delay time and the corresponding azimuth which can be derived from surface wave global with a lateral resolution of around 2000 km and regional lateral resolution of 350 km anisotropy tomography a global scale comparison is disappointing since there are only a few areas where both data types are correctly retrieved at the same spatial scale same lateral resolution the anisotropy is well resolved in oceanic basins from surface waves whereas most measurements of sks splitting are available below continents however there is a good agreement between surface wave and body wave anisotropy in regions where large scale processes primarily tectonic are taking place such as the western united states and in central asia in particular we show that at high frequency 1hz the observed sks delay time and azimuth depend on the order in which s waves propagate through the layers a comparison between synthetic and observed sks phases in central asia highlights the varying sensitivity of sks waves at depth we can obtain a good correlation between synthetic and observed sks by considering anisotropy only between 80 and 200 km depth in the tomographic model rather than in the entire upper mantle however it is more difficult to explain the discrepancy between synthetic and observed sks under the eastern united states where a large scale coherent sks anisotropy is present such results call for more sophisticated sks waveform modeling and for enhanced lateral resolution in anisotropic tomographic models

shear velocity and shear attenuation models inverted from the world wide and pure path average data of mantle rayleigh waves 0s25 to 0s80 and fundamental spheroidal modes 0s2 to 0s24 summary global and regional structures of the earth s mantle are studied original phase velocities and q 1 of rayleigh waves are converted to equivalent free oscillation periods and q 1 global average upper mantle shear velocity models are derived from the inversions of the world wide average eigenperiods corrected for attenuative dispersion resolution analysis shows that the thickness and velocity of the lithosphere cannot be determined from our data set inverted models have a well developed low velocity zone in the depth range between 70 and 280 km global average q 1 models for the whole mantle are derived from the world wide average q 1 of mantle rayleigh waves and fundamental spheroidal modes the resolution analysis indicates that q 1 at depths shallower than about 100 km cannot be determined by our data set and that the depth resolution for q 1 of the lower mantle is poor all inverted q 1 models are characterized by a well developed high q 1 zone in the depth range between about 100 and 300 km in the upper mantle q has a minimum value of about 90 at depths around 200 km begins to increase at a depth of about 300 km rapidly increases in the depth range from 300 to 400 km and gradually increases at depths between 400 and 800 km q of the lower mantle is about 330 the boundary between the high q 1 upper mantle and low q 1 lower mantle is sharper than has been suggested in the past inverted q 1 models predict qscs 226 to 250 the earth s surface is divided into mountainous oceanic ridge shield and trench and marginal sea regions and a regionalized shear velocity model of the upper mantle is derived the inversions of the pure path eigenperiods without correction for attenuative dispersion show that strong lateral variations in shear velocity exist at depths shallower than 250 km in the upper mantle a low velocity zone for shear waves exists in the upper mantle beneath all the tectonic regions except perhaps the shield region if the sn velocity of the starting model is equal to or higher than 4 7 km s 1 the shield data require a moderate low velocity zone data from the mountainous region require a much lower shear velocity than the shield region at depths shallower than 250 km the oceanic ridge and trench and marginal sea models have a well developed low velocity zone the shear velocity model for the trench and marginal sea region is characterized by a velocity increase at depths between 250 and 400 km this increase in velocity is interpreted as a consequence of the subducted lithospheric slabs beneath many of our trench and marginal sea regions regional differences in rayleigh wave q 1 are found for modes from 0s25 to 0s45 since the resolving power of this data set is limited we could not locate the depths at which regional variations of q 1 exist since the oceanic q 1 for modes from 0s45 to 0s78 appear to be stable the oceanic q 1 model is derived this model has a well developed high q 1 zone q has a minimum value of about 110 at depths between 200 and 300 km and rapidly increases to a high value of about 250 at a depth of about 400 km

a sedimentary facies model for glacial age sediments in baldwin lake southern california abstract a combined sedimentological and high resolution petrographic analysis was conducted on a glacial age 20 000 65 000 cal yr bp sediment core from baldwin lake southern california the results of this research represent the most complete glacial age terrestrial climate record from southern california to date these results are used to characterize the different sediment types and to investigate the difference in depositional processes and environments between the core s three predominant sediment types massive semi laminated and laminated sediments massive sediments are commonly associated with a blocky texture and or desiccation cracks are organic poor have high magnetic susceptibility values and are coarser grained thin sections from massive sediments reveal a homogenous sediment fabric sub centimeter scale laminated and centimeter scale semi laminated sediments are generally organic rich have low magnetic susceptibility values and are finer grained thin sections from laminated and semi laminated sediments reveal diffuse sub millimeter to millimeter scale laminae this combination of sedimentological and high resolution petrographic data enabled us to characterize four sediment facies each related to specific depositional processes and environments 1 a playa lake 2 a perennial shallow lake 3 an intermediate lake with variable lake level and 4 a perennial deep lake at centennial to millennial timescales lower lake levels are represented by deposition of massive to semi laminated sediments in a playa to a perennial shallow lake environment at similar timescales higher lake levels are recorded by semi laminated to laminated sediments deposited in an intermediate lake to a perennial deep lake environment these results provide an additional sedimentological study for comparison to similar arid environment basins and for comparison to existing regional paleoclimatic reconstructions

the paleoclimatic response of the southern californian margin to the rapid climate change of the last 60 ka a regional overview abstract high resolution planktonic foraminiferal census and stable isotope data from a core transect odp site 1017 893 and 1014 demonstrate remarkable similarities along the southern california margin during the last glacial 60 10 ka bp modern analog technique and 18 o derived sea surface temperatures sst demonstrate sst shifts were regionally expressed supporting the hypothesis that the relative strength of local surface ocean currents affected the advection of subpolar and subtropical water into the region divergent alkenone sst records suggest the flux of planktonic organisms shifted seasonally during the last glacial in response to changing environmental conditions when considered as seasonal sst reconstructions summer oligotrophic surface ocean conditions appear to have a muted response to orbital and millennial scale climate change compared to the surface ocean during high nutrient winter conditions