the relationships between large scale variations in shear velocity density and compressional velocity in the earth s mantle a large data set of surface wave phase anomalies body wave travel times normal mode splitting functions and long period waveforms is used to investigate the scaling between shear velocity density and compressional velocity in the earth s mantle we introduce a methodology that allows construction of joint models with various levels of scaling complexity d ln d lnvs d lnvs d lnvp in order to detect seismological signatures of chemical heterogeneity we demonstrate that the data sets considered cannot be fit concurrently with a uniform or a positive and uniform throughout the mantle the variance reductions to p wave travel times and vp sensitive modes are up to 40 higher with our preferred model of anisotropic shear and compressional velocity than the recent anisotropic shear velocity model s362ani m which was constructed assuming a uniform throughout the mantle several features reported in earlier tomographic studies persist after the inclusion of new and larger data sets anticorrelation between bulk sound and shear velocities in the lowermost mantle as well as an increase in with depth in the lower mantle are largely independent of the regularization scheme when correlations between density and shear velocity variations are imposed in the lowermost mantle variance reductions of several spheroidal and toroidal modes deteriorate by as much as 40 recent measurements of the splitting of 0s2 in particular are largely incompatible with perfectly correlated shear velocity and density heterogeneity throughout the mantle a way to significantly improve the fits to various data sets is by allowing independent density perturbations in the lowermost mantle our preferred joint model consists of denser than average anomalies 1 peak to peak at the base of the mantle roughly coincident with the low velocity superplumes the relative variation of shear velocity density and compressional velocity in our study disfavors a purely thermal contribution to heterogeneity in the lowermost mantle with implications for the long term stability and evolution of superplumes

establishing soil and surficial geologic habitat criteria for presumed gypsophiles the example of eriogonum corymbosum var nilesii mojave desert u s a abstract detailed soil and surficial geologic data are needed for ecological interpretations yet are often absent or incomplete in published studies of arid land ecology or biogeography clear edaphic habitat definitions are needed for gypsophilic plants including the las vegas buckwheat e corymbosum var nilesii lvb a rare shrub endemic to the mojave desert as a case study we use soil profile data and high resolution 1 3000 scale surficial geologic maps to identify likely edaphic controls of lvb habitat potential habitat and non habitat distributions we confirm gypsiferous substrates lacking hard physical surface crusts as a boundary condition in most but not all population clusters but find that fine grained carbonate rich soil lacking gypsum is also viable habitat as is shallow 1 m coarse grained alluvium and or surfaces with tightly interlocking desert pavement exclude lvb our results challenge the view of this target species as a true gypsophile however it remains unclear whether carbonate rich habitats represent ideal conditions or refugia this study underscores the important merits of surficial geologic mapping and soil morphological description for ecological research conservation restoration and land management in arid environments especially gypsum soils worldwide

drizzle in stratiform boundary layer clouds part ii microphysical aspects abstract this is the second of two observational papers examining drizzle in stratiform boundary layer clouds part i details the vertical and horizontal structure of cloud and drizzle parameters including some bulk microphysical variables in this paper the focus is on the in situ size resolved microphysical measurements particularly of drizzle drops r 20 m layer averaged size distributions of drizzle drops within cloud are shown to be well represented using either a truncated exponential or a truncated lognormal size distribution the size resolved microphysical measurements are used to estimate autoconversion and accretion rates by integration of the stochastic collection equation sce these rates are compared with a number of commonly used bulk parameterizations of warm rain formation while parameterized accretion rates agree well with those derived from the sce initialized with observed spectra the autoconversion rates seriously disagree in some cases these disagreements need to be addr

cloud radar doppler spectra in drizzling stratiform clouds 1 forward modeling and remote sensing applications 1 several aspects of spectral broadening and drizzle growth in shallow liquid clouds remain not well understood detailed cloud scale observations of microphysics and dynamics are essential to guide and evaluate corresponding modeling efforts profiling millimeter wavelength cloud radars can provide such observations in particular the first three moments of the recorded cloud radar doppler spectra the radar reflectivity mean doppler velocity and spectrum width are often used to retrieve cloud microphysical and dynamical properties such retrievals are subject to errors introduced by the assumptions made in the inversion process here we introduce two additional morphological parameters of the radar doppler spectrum the skewness and kurtosis in an effort to reduce the retrieval uncertainties a forward model that emulates observed radar doppler spectra is constructed and used to investigate these relationships general analytical relationships that relate the five radar observables to cloud and drizzle microphysical parameters and cloud turbulence are presented the relationships are valid for cloud only cloud mixed with drizzle and drizzle only particles in the radar sampling volume and provide a seamless link between observations and cloud microphysics and dynamics the sensitivity of the five observed parameters to the radar operational parameters such as signal to noise ratio and doppler spectra velocity resolution are presented the predicted values of the five observed radar parameters agree well with the output of the forward model the novel use of the skewness of the radar doppler spectrum as an early qualitative predictor of drizzle onset in clouds is introduced it is found that skewness is a parameter very sensitive to early drizzle generation in addition the significance of the five parameters of the cloud radar doppler spectrum for constraining drizzle microphysical retrievals is discussed

soil water flux in the southern great basin united states temporal and spatial variations over the last 120 000 years the disposal of hazardous and radioactive waste in arid regions requires a thorough understanding of the occurrence of soil water flux and recharge soil water chemistry and isotopic data are presented from three deep vadose zone boreholes 230 m at the nevada test site located in the great basin geographic province of the southwestern united states to quantify soil water flux and its relation to climate the low water contents found in the soils significantly reduce the mixing of tracers in the subsurface and provide a unique opportunity to examine the role of climate variation on recharge in arid climates tracing techniques and core data are examined in this work to reconstruct the paleohydrologic conditions existing in the vadose zone well beyond the timescales typically investigated stable chloride and chlorine 36 profiles indicate that the soil waters deep in the vadose zone range in age from approximately 20 000 to 120 000 years secondary chloride bulges that are present in two of the three profiles support the concept of recharge occurring at or near the last two glacial maxima when the climate of the area was considerably wetter and cooler the stable isotopic composition of the soil water in the profiles is significantly more depleted in heavy isotopes than is modern precipitation suggesting that recharge under the current climate is not occurring at this arid site past and present recharge appears to have been strongly controlled by surface topography with increased incidence of recharge where runoff from the surrounding mountains may have been concentrated the data obtained from this detailed drilling and sampling program shed new light on the behavior of water in thick vadose zones and in particular show the sensitivity of arid regions to the extreme variations in climate experienced by the region over the last two glacial maxima

high temperature elasticity of iron bearing olivines the first high temperature data on the nine adiabatic elastic moduli for iron bearing olivine are reported these measurements are on two single crystal specimens of natural olivine at ambient pressure and from room temperature to a maximum of 1500 k the two specimens contain 8 and 9 modal percent fayalite which required the oxygen fugacity be controlled at high temperature to preserve their chemical stability the rectangular parallelepiped resonance apparatus was adapted to buffer the specimens from the atmosphere with a mixture of co and co2 gas a small increase 1 2 gpa in the adiabatic bulk modulus of each specimen over that of end member forsterite was found the data are high quality to extreme temperatures with good agreement found when comparing the temperature derivatives of the elastic moduli of the two specimens neither specimen exhibits measurable nonlinear temperature dependence in the computed isotropic bulk and shear moduli which is in contrast to published forsterite data the temperature derivatives of the isotropic bulk modulus ks are 1 69 1 80 10 2 gpa k 1 for the two olivine specimens and the shear modulus g derivatives are 1 38 1 36 10 2 gpa k 1 these derivatives are only slightly larger in magnitude than ks t p 1 56 10 2 and g t p 1 30 10 2 gpa k 1 found previously for iron bearing olivine over a very small temperature range there are also no significant differences between the temperature derivatives found here and the average derivatives of end member forsterite from data retrieved over a slightly larger temperature range several dimensionless parameters have been calculated from these results and are discussed in view of systematics which bear on high pressure phases in earth s transition zone one result from these systematics related to the seismic velocities in the earth and especially the shear wave velocities is that an olivine content of less than 50 is implied at the 400 km discontinuity if earth s upper mantle is isochemical furthermore the substitution of almost 10 iron for magnesium at the forsterite end of the olivine solid solution series has little effect on the dimensionless parameters or on the temperature derivatives of the elastic moduli at high temperature

calcrete in quaternary coastal dunes in southwestern australia a capillary rise phenomenon associated with plants abstract non pedogenic calcrete is forming as a thin sheet 10 50 cm thick just above the water table in the subsurface of a barrier dune terrain in south western australia the calcrete is forming in response to the regional evapo transpirative regime the annual rainfall is high but of short duration and it infiltrates rapidly into the sandy substrates relatively high air temperatures and evaporation coupled with wind stress combine to produce a water vapor deficit across the dune terrain the vegetation responds by drawing upon phreatic water and pellicular water of the vadose zone thereby precipitating caco3 where plants are not drawing phreatic water calcrete is developing by evaporation of water at the top of the zone of capillary rise various structure types of calcrete are developed in the study area namely rhizoconcretionary mottled massive and laminar forms these occur in a definite stratigraphic sequence related to maturity of profile vegetation cover and thickness of the vadose zone rhizoconcretionary calcrete forms in the vadose zone mottled and massive calcrete frequently capped by laminar calcrete develop in the zone of capillary rise these latter calcrete types form a sheet that is ubiquitous and parallel to the water table since it is a feature of the water table the calcrete sheet may potentially transect regional stratigraphic boundaries and unconformities at the local level the various structural types of calcrete may he used as paleowater table indicators

mantle discontinuities and temperature under the north american continental keel a ubiquitous feature of upper mantle seismic velocity models has been the presence of high velocity keels beneath stable continental interiors1 2 3 4 5 uncertainty remains however regarding the maximum depth to which continental keels extend the degree to which they have cooled the mantle that surrounds them and their role in mantle flow here we investigate thermal anomalies across the eastern margin of the north american continental keel by imaging the seismic discontinuities at depths of 410 and 660 km with compressional to shear converted waves recorded by a 1 500 km long seismometer deployment in the eastern united states the thickness of the transition zone the region nominally between depths of 410 and 660 km and the depth to the 410 km discontinuity indicate that cold keel material and sub keel downwellings must be largely confined to the upper mantle and may impinge on the transition zone only in localized regions and with thermal anomalies of less than 150 k a 20 km depression of the 660 km discontinuity to the south of the westernmost stations coincides with a region of fast velocity in the deep transition zone2 and may be associated with the remnants of the subducted farallon plate1 2 4

large scale atmospheric forcing by southeast pacific boundary layer clouds a regional model study abstract a regional model is used to study the radiative effect of boundary layer clouds over the southeast pacific on large scale atmosphere circulation during august october 1999 with the standard settings the model simulates reasonably well the large scale circulation over the eastern pacific precipitation in the intertropical convergence zone itcz north of the equator and marine boundary layer stratocumulus clouds to the south in a sensitivity experiment with the radiative effect of liquid clouds south of the equator over the eastern pacific artificially removed boundary layer clouds south of the equator almost disappear and precipitation in the itcz is reduced by 15 20 indicating that the stratocumulus clouds over the southeast pacific have both local and cross equatorial effects examination of the differences between the control and sensitivity experiments indicates that clouds exert a net diabatic cooling in the inversion layer in response to this cloud induced cooling an in situ anom

boundary layer cloud and drizzle variability in the southeast pacific stratocumulus regime abstract the southeast pacific stratocumulus regime is an important component of the earth s climate system because of its substantial impact on albedo observational studies of this cloud regime have been limited but during the past 5 yr a series of cruises with research vessels equipped with in situ and remote sensing systems have provided unprecedented observations of boundary layer cloud and drizzle structures these cruises started with the east pacific investigation of climate epic 2001 field experiment followed by cruises in a similar area in 2003 and 2004 pan american climate studies pacs stratus cruises the sampling from these three cruises provides a sufficient dataset to study the variability occurring over this region this study compares observations from the 2004 cruise with those obtained during the previous two cruises observations from the ship provide information about boundary layer structure fractional cloudiness cloud depth and drizzle characteristics this study indicat

δs at high pressure and dlnvs dlnvp in the lower mantle s a measure of the sensitivity of the adiabatic bulk modulus to isobaric density changes controls lateral variations of p wave velocities to estimate the effect of pressure on s we have performed lattice dynamic calculations of the cubic alkaline earth oxides we used a many body parametric hamiltonian that reproduces the available laboratory data on thermoelastic properties the calculations were carried out for p t conditions that correspond to those of the lower mantle we find that s decreases from 4 1 at standard conditions to 2 at lower mantle conditions the latter value is consistent with d l anderson s estimates based on geophysical data with s 2 and a corresponding parameter for shear modulus not decreasing with compression no partial melting is required to account for the observation that lnvs lnvp 2 in the lower mantle although more data and calculations on additional minerals are needed to draw any firm conclusions our results indicate that the relatively small lateral variations of lnvp when compared to lnvs are due entirely to compressional effects

the relationship between shear and compressional velocities at high pressures reconciliation of seismic tomography and mineral physics the value of the parameter from low pressure laboratory measurements disagrees with the value from seismic observations the parameter relates the isobaric change in shear velocity vs to the change in compressional velocity vp seismic evidence indicates exceeds 2 0 in the lower mantle whereas data on a variety of minerals at high temperature t and ambient pressure p result in lower values we reconcile these differences our ab initio model calculations on mgo show that increases with p and is 2 0 2 5 at lower mantle pressures there is no need to assume partial melting to explain the seismic data these calculations also provide insight into the p and t dependence of the dimensionless parameter 1 g g t p where g is the isotropic shear modulus and is the volume thermal expansivity using measured values of thermoelastic parameters coupled with thermodynamic identities we seek constraints on s 1 ks ks t p where ks is the adiabatic bulk modulus and confirm that p causes s to decrease we find poisson s ratio increases with p and t altogether these results show that for mgo increases from 1 3 at ambient conditions to over 2 at lower mantle conditions we expect other mantle minerals to behave similarly therefore we find that reconciliation of the mineral physics approach with that of seismic tomography concerning does not require special assumptions about the state of the lower mantle

stable isotopic evidence for a pedogenic origin of carbonates in trench 14 near yucca mountain nevada layered carbonate and silica encrust fault fractures exposed in trench 14 near yucca mountain site of the proposed high level nuclear waste repository in southern nevada comparison of the stable carbon and oxygen isotopic compositions of the fracture carbonates with those of modern soil carbonates in the area shows that the fracture carbonates are pedogenic in origin and that they likely formed in the presence of vegetation and rainfall typical of a glacial climate their isotopic composition differs markedly from that of carbonate associated with nearby springs the regional water table therefore remained below the level of trench 14 during the time that the carbonates and silica precipitated a period probably covering parts of at least the last 300 000 years

thermal expansion measurements at very high pressure systematics and a case for a chemically homogeneous mantle new data on thermal expansivity of iron to over 400 kbar in laser and electrically heated diamond anvil cells and on mgo and forsterite from spectroscopic data to over 200 kbar and previously measured adiabats boehler 1982 imply that at high pressure may be described by a constant value of 1n 1nv t 5 5 0 5 this behavior is supported by previous measurements at lower pressures on a large variety of materials densities of magnesio wustite and silicate perovskite in a pyrolitic ratio calculated at lower mantle conditions using a finite strain equation and at high pressures using the above systematics match those in prem through the entire lower mantle making a strong case for a uniform mantle

a calcrete based u th chronology for landform evolution in the sorbas basin southeast spain nodular and massive calcretes from alluvial terraces in the sorbas area of southeast spain have been dated by the u th isochron method to between 8 350 ka alternative approaches have been used to generate the multiple samples for the isochron method for several of the calcretes dates agreed closely when obtained by total dissolution of a number of nodules or by the sequential dissolution in different acids of a single nodule however fractional dissolution of a single nodule in the same acid revealed two stages of precipitation of different age it is considered that the calcretes may not be strictly pedogenic in origin and that groundwater processes linked to the alluvial environment may have been involved also nevertheless their dates provide minimum ages for a chronostratigraphic framework for terrace evolution

constraints on lower mantle physical properties from seismology and mineral physics the ratio of relative shear s to compressional p lateral seismic velocity variations is potentially an important constraint on the mineral physics of the earth s lower mantle recent seismic results show that there is an increase in this ratio from 1 7 to 2 6 in the lower mantle to 2000 km depth which is significantly greater than published values in the mineral physics literature we calculate in terms of s ln ks ln and a ln ln s and show that the seismic variation of within the depth range that p and s models appear proportional is consistent with scalings computed using recent results from geodynamics and mineral physics studies furthermore we find that s 1 at 1900 300 km depth irrespective of a

reinterpretation of the exposed record of the last two cycles of lake bonneville western united states a substantially modified history of the last two cycles of lake bonneville is proposed the bonneville lake cycle began prior to 26 000 yr b p the lake reached the bonneville shoreline about 16 000 yr b p poor dating control limits our knowledge of the timing of subsequent events lake level was maintained at the bonneville shoreline until about 15 000 yr b p or somewhat later when catastrophic downcutting of the outlet caused a rapid drop of 100 m the provo shoreline was formed as rates of isostatic uplift due to this unloading slowed by 13 000 yr b p the lake had fallen below the provo level and reached one close to that of great salt lake by 11 000 yr b p deposits of the little valley lake cycle are identified by their position below a marked unconformity and by amino acid ratios of their fossil gastropods the maximum level of the little valley lake was well below the bonneville shoreline based on degree of soil development and other evidence the little valley lake cycle may be equivalent in age to marine oxygenisotope stage 6 the proposed lake history has climatic implications for the region first because the fluctuations of lake bonneville and lake lahontan during the last cycle of each were apparently out of phase there may have been significant local differences in the timing and character of late pleistocene climate changes in the great basin second although the bonneville and little valley lake cycles were broadly synchronous with maximum episodes of glaciation environmental conditions necessary to generate large lakes did not exist during early wisconsin time

facies model of a semiarid freshwater wetland olduvai gorge tanzania the sedimentology and stratigraphy of a freshwater wet land in early pleistocene 1 75 ma volcaniclastic deposits olduvai gorge tanzania are characterized using texture mineralogy micro fossils and stratigraphic description to create a depositional facies model the freshwater wetland was located on the margin of a semi arid closed basin containing a playa lake the lake margin deposits are dominated by two distinct lithologies waxy claystones and earthy sediments waxy sediments are olive green dense claystones that con tain authigenic minerals such as trona and represent a fluctuating saline alkaline lake hay 1976 earthy sediments are beige friable siltstones that contain siliceous microfossils bone fragments and minor pebbles they represent the freshwater wetland microfossils from the earthy sediments and diatomites indicate freshwater marsh biota with some rare salt tolerant species associated lithofacies are diatomite carbonate and sandstone interpretation of vertical and lateral lithofacies variations in the 2 km 2 wetland based on 50 excavations identified seven distinct sub environments spring deposits perennial marsh pool ephemeral wet land fringing wetland wetland channel and ephemeral stream the stratigraphic sequence estimated to represent an 40 50 kyr long interval indicates that persistent 10 3 yr wet periods prevailed dur ing the deposition of thick waxy clays when the lake expanded and flooded the wetlands and equally long intervening dry periods caused the lake to contract allowing the flourishing of wetlands and accretion of earthy sediment the lithofacies associations in the olduvai paleo wetland provides an important first step in the development of a de positional environmental model for freshwater wetlands that can be tested elsewhere particularly in arid and semiarid settings

multiple scale simulations of stratocumulus clouds 1 this study introduces a flexible multiple nested modeling framework developed from the weather research and forecasting wrf model for boundary layer cloud research it features a nested large eddy simulation in a hindcasting mode that allows a direct comparison between simulations and observations using this approach we simulated two stratocumulus cases observed at the southern great plains observing site the simulation observation comparisons demonstrate that the multiple nested wrf well reproduces the cloud properties and vertical velocity fields detected by cloud radar and other remote sensing instruments the simulations show that 1 the cloud fields can be strongly modulated by mesoscale organizations 2 the vertical velocity variance and skewness in the boundary layer have well defined diurnal variations and are strongly dependent on external forcings but the in cloud turbulent statistics appears to be more controlled by the internal turbulent processes 3 the organized structures of stratocumulus are only slightly skewed which is consistent with the cloud radar observations that the updraft fraction is close to 50 and 4 the vertical distribution of cloud water and the associated high order moments of continental stratocumulus can be substantially different from its marine counterpart due to different ambient thermodynamic structures this study suggests that the multiple scale wrf modeling system provides a great numerical framework that can be used to address various issues regarding the parameterization of boundary layer clouds

late quaternary zonation of vegetation in the eastern grand canyon fossil assemblages from 53 packrat middens indicate which plant species were dominant during the last 24 000 years in the eastern grand canyon past vegetational patterns show associations that cannot be attributed to simple elevational displacement of the modern zones a model emphasizing a latitudinal shift of climatic values is proposed

late quaternary environmental changes in the upper las vegas valley nevada abstract five stratigraphic units and five soils of late pleistocene to holocene age crop out in dissected badlands on corn creek flat 30 km northwest of las vegas nevada and at tule springs nearer to las vegas the record is dominantly fluvial but contains evidence of several moister marsh forming periods the oldest unit b dates perhaps to the middle wisconsin and the more widespread unit d falls between 30 000 and 15 000 yr b p unit d therefore correlates with pluvial maximum lacustrine deposits elsewhere in the great basin standing water was not of sufficient depth or extent during either period to form lake strandlines between 14 000 and 7200 yr b p unit e standing surface water gradually decreased a trend also apparent in great basin pluvial lake chronologies during the same period groundwater carbonate cementation and burrowing by cicadas cicadae accompany the moist phase units after 7200 yr b p increased wind action decreased biotic activity and at least 25 m of water table lowering accompanied widespread erosion of older fine grained deposits based on pack rat midden and pollen evidence this coincides with major vegetation changes in the valley from sagebrush dominated steppe to lower mohave desertscrub

regional model simulations of marine boundary layer clouds over the southeast pacific off south america part ii sensitivity experiments abstract the sensitivity of a regional climate model to physical parameterizations and model resolution is investigated in terms of its simulation of boundary layer stratocumulus scu clouds over the southeast pacific specifically the physical schemes being tested include shallow cumulus convection subgrid vertical mixing cloud droplet number concentration cdnc and drizzle as described in part i the model with standard settings captures the major features of the boundary layer in the region including a well mixed marine boundary layer a capping temperature inversion scu clouds and the boundary layer regime transition from the well mixed layer near the coast of south america to a decoupled cloud layer over warmer water to the west turning off the shallow cumulus parameterization results in a dramatic increase in the simulated scu clouds while the boundary layer structure becomes unrealistic losing the decoupled regime over warm water with reduced penetrative mixing at the top of shallow cu

validation and sensitivities of frontal clouds simulated by the ecmwf model abstract clouds simulated by the european centre for medium range weather forecasts ecmwf model are composited to derive the typical organization of clouds surrounding a midlatitude baroclinic system comparison of this composite of about 200 cyclones with that based on satellite data reveals that the ecmwf model quite accurately simulates the general positioning of clouds relative to a low pressure center however the optical depths of the model s high low clouds are too small large relative to the satellite observations and the model lacks the midlevel topped clouds observed to the west of the surface cold front sensitivity studies with the ecmwf model reveal that the error in high cloud optical depths is more sensitive to the assumptions applied to the ice microphysics than to the inclusion of cloud advection or a change of horizontal resolution from 0 5625 to 1 69 lat this reflects the fact that in the ecmwf model gravitational settling is the most rapid process controlling the abundance of ic

late pleistocene c4plant dominance and summer rainfall in the southwestern united states from isotopic study of herbivore teeth abstract patterns of climate and c4plant abundance in the southwestern united states during the last glaciation were evaluated from isotopic study of herbivore tooth enamel enamel 13c values revealed a substantial eastward increase in c4plant consumption formammuthusspp bisonspp equusspp andcamelopsspp the 13c values were greatest inbisonspp 6 9 to 1 7 andmammuthusspp 9 0 to 0 3 and in some locales indicated c4 dominated grazing the 13c values of antilocaprids were lowest among taxa 12 5 to 7 9 and indicated c3feeding at all sites on the basis of modern correlations between climate and c4grass abundance the enamel data imply significant summer rain in parts of southern arizona and new mexico throughout the last glaciation enamel 18o values range from 19 0 to 31 0 and generally increase to the east this pattern could point to a tropical or subtropical source of summer rainfall at a synoptic scale the isotope data indicate that interactions of seasonal moisture temperature and lowered atmospheric pco2determined glacial age c4abundance patterns

black mats spring fed streams and late glacial age recharge in the southern great basin black mats are prominent features of the late pleistocene and holocene stratigraphic record in the southern great basin faunal geochemical and sedimentological evidence shows that the black mats formed in several microenvironments related to spring discharge ranging from wet meadows to shallow ponds small land snails such asgastrocopta tappanianaandvertigo berryiare the most common mollusk taxa present semiaquatic and aquatic taxa are less abundant and include catinellids fossaria parva gyraulus parvus and others living today in and around perennial seeps and ponds the ostracodescypridopsis okeechobiandscottia tumida typical of seeps and low discharge springs today as well as other taxa typical of springs and wetlands are common in the black mats several new species that lived in the saturated subsurface also are present but lacustrine ostracodes are absent the 13c values of organic matter in the black mats range from 12 to 26 reflecting contributions of tissue from both c3 sedges most shrubs and trees and c4 saltbush saltgrass plants carbon 14 dates on the humate fraction of 55 black mats fall between 11 800 to 6300 and 230014c yr b p to modern the total absence of mats in our sample between 6300 and 230014c yr b p likely reflects increased aridity associated with the mid holocene altithermal the oldest black mats date to 11 800 11 60014c yr b p and the peak in the14c black mat distribution falls at 10 00014c yr b p as the formation of black mats is spring related their abundance reflects refilling of valley aquifers starting no later than 11 800 and peaking after 11 00014c yr b p reactivation of spring fed channels shortly before 11 20014c yr b p is also apparent in the stratigraphic records from the las vegas and pahrump valleys this age distribution suggests that black mats and related spring fed channels in part may have formed in response to younger dryas yd age recharge in the region however the inception of black mat formation precedes that of the yd by at least 40014c yr and hydrological change is gradual not rapid

the micromorphology of younger dryas aged black mats from nevada arizona texas and new mexico abstract black mats are organic rich sediments and soils that form in wet environments associated with spring discharge micromorphological and geochemical analyses of 25 black mats dating to the younger dryas chronozone 12 9 11 7 ka and early holocene were conducted to determine their composition and depositional environment samples were collected from arizona new mexico texas and nevada micromorphological analyses were conducted on thin sections using polarized and blue fluorescent light these analyses determined that black mats contain humic acids fine 5 20 m plant fragments diatoms phytoliths and gastropods the dominant type of organic matter in black mats is derived from herbaceous plants contradicting previous studies that supported algal or charcoal sources differences in the micromorphological characteristics of the samples revealed that black mats formed as three different types organic horizons moist soils and ponded sediments depending on their topographic position in relation to the water table the microscopic evidence found in black mats supports the presence of widespread wet environments in nevada and arizona during the younger dryas chronozone clearly indicating a sustained period of greater effective moisture optimal for spring discharge and black mat formation

finescale structure and microphysics of coastal stratus observations were made of unbroken marine stratus off the coast of oregon using the combined capabilities of in situ probes and a 95 ghz radar mounted on an aircraft reflectivity and doppler velocity measurements were obtained in vertical and horizontal planes that extend from the flight lines data from three consecutive days were used to examine echo structure and microphysics characteristics the clouds appeared horizontally homogeneous and light drizzle reached the surface in all three cases radar reflectivity is dominated by drizzle drops over the lower two thirds to four fifths of the clouds and by cloud droplets above that cells with above average drizzle concentrations exist in all cases and exhibit a large range of sizes the cells have irregular horizontal cross sections but occur with a dominant spacing that is roughly 1 2 1 5 times the depth of the cloud layer doppler velocities in the vertical are downward in all but a very small fraction of the cloud volumes the cross correlation between reflectivity and vertical doppler velocity changes sign at or below the midpoint of the cloud indicating that in the upper parts of the clouds above average reflectivities are associated with smaller downward velocities this correlation and related observations are interpreted as the combined results of upward transport of drizzle drops and of downward motion of regions diluted by entrainment the in situ measurements support these conclusions

fossil packrat middens and the tandem accelerator mass spectrometer analyses of well preserved plant remains from ancient packrat neotoma middens have yielded much information on the history of vegetation fauna and climate from the more arid portions of north america over the past 40 000 years1 2 in most of the modern deserts woodland or forest communities were present during the last glacial age the wisconsin radiocarbon dating of packrat midden assemblages from a single cave or from several nearby sites in a homogeneous local area can yield a detailed local vegetation chronology for many thousands of years from within 30 50 m on the rocky slopes in front of the dry rock shelters3 4 the development of radiocarbon dating using the tandem accelerator mass spectrometer tams allows direct dating of very small samples here we present 20 examples of tams radiocarbon dates on packrat midden materials to illustrate their usefulness in testing anomalous mixtures of species in ice age communities understanding the details of plant migrations and refining wisconsin and holocene time boundaries based on range changes of important plant species table 1 fig 1

relationship between climate and vegetation and the stable carbon isotope chemistry of soils in the eastern mojave desert nevada abstract the relationship between the stable c isotope composition of the soil environment and modern climate and vegetation was determined empirically along a present day climatic transect in the eastern mojave desert the 13c of the soil co2 and carbonates decreased with increasing elevation and plant density even though plant assemblages at all elevations were isotopically similar several factors including differences in the ratios of pedogenic of limestone calcite and differences in past vegetation were considered as explanations of this trend however it appears that in the sparsely vegetated mojave desert the 13c of pedogenic carbonate is controlled by differences in plant density and biological activity this relationship may provide a tool for assessing past vegetational densities as long as the vegetation is isotopically homogeneous

radar observations of updrafts downdrafts and turbulence in fair weather cumuli abstract observations from a 94 ghz radar are used to define the vertical structure of marine fair weather cumuli doppler spectra obtained from the radar provide mean vertical velocities as well as detailed spectral shapes that can be used to infer small scale vertical velocity shear illuminate cloud microphysical processes and provide estimates of turbulence dissipation rates these new observations facilitate the analysis and understanding of in cloud circulations and the physical processes involved since the cloud boundaries and dimensions are mapped along with the internal structure of the clouds coincident observations from a 915 mhz radar wind profiler were used to further define the turbulence structure in and around the clouds the observations document the detailed vertical and horizontal dimensions of updraft and downdraft circulations in the clouds observed the two cumuli studied in detail have similar circulation patterns an updraft core surrounded by downdrafts although the clouds ha

stasis and change in holocene small mammal diversity during a period of aridification in southeastern utah biological conservation depends on understanding and disentangling the effects of decadal to centennial scale dynamics from the millennial scale dynamics documented in the fossil record the american southwest is expected to become increasingly arid over the next few decades and will continue to experience large scale human land use in various forms a primary question is whether the ecological fluctuations recorded over the past few decades fall outside the range of variation expected in the absence of recent land use and management i excavated and quantified mammal diversity change in two fossil bearing alcoves east canyon rims 2 and rone bailey alcove located in san juan county utah ams radiocarbon dates on 33 bone samples from these sites span 4 4 0 5 kyr and shed light on pre industrial faunal dynamics in the region over the course of environmental change localities with comparable small mammal diversity have not been reported from this region previously so these deposits provide novel insig

morphology and genesis of carbonate soils on the kyle canyon fan nevada u s a the physical and chemical properties of soils formed in an arid climate on calcareous alluvium of the kyle canyon alluvial fan southern nevada were studied in order to infer the rates and relative importance of various soil forming processes these studies included field and microscopic observations and analyses of thin sections major oxides extractable iron and clay minerals the results are interpreted to reflect five major pedogenic processes 1 the calcic horizons and calcretes of kyle canyon soils form by precipitation of caco3 derived from eolian dust and alluvium as clast coats matrix cement and massive layers 2 the a and uppermost b horizons are essentially dust derived for they contain large amounts of detrital material not present in the alluvial parent material and their major oxide content is similar to that of modern dust 3 clay particles are translocated from a into b horizons 4 iron bearing minerals in the near surface b horizons are slowly oxidized 5 carbonate and aluminosilicate grains are both displaced and replaced by pedogenic caco3 the silica released by replacement of aluminosilicates may be locally precipitated as amorphous or opaline silica and or incorporated into newly formed palygorskite and sepiolite rates of soil development at kyle canyon are approximate due to uncertainties in age estimates some soil field properties change at rates that are similar to rates for soils formed in rhyolitic parent material near mercury nevada the rate of accumulation of caco3 3 5 g m 2 yr 1 at kyle canyon is an order of magnitude faster than that near mercury but is comparable to rates calculated for soils in southern new mexico and utah

late quaternary environments in ruby valley nevada abstract palynological data from sediment cores from the ruby marshes provide a record of environmental and climatic changes over the last 40 000 yr the modern marsh waters are fresh but no deeper than 3 m a shallow saline lake occupied this basin during the middle wisconsin followed by fresh and perhaps deep waters by 18 000 to 15 000 yr b p no sediments were recovered for the period between 15 000 and 11 000 yr b p possibly due to lake desiccation by 10 800 yr b p a fresh water lake was again present and deeper than modern conditions lasted until 6800 yr b p the middle holocene was characterized by very shallow water and perhaps complete desiccation the marsh system deepened after 4700 yr b p and fresh water conditions persisted until modern times vegetation changes in ruby valley were more gradual than those seen in the paleolimno logical record sagebrush steppe was more widespread than at present through the late pleistocene and early holocene giving way somewhat to expanded shadscale vegetation between 8500 and 6800 yr b p shadscale steppe contracted by 4000 yr b p but had greater than modern coverage until 1000 to 500 yr ago pinyon juniper woodland was established in the southern ruby mountains by 4700 yr b p

the mescal cave fauna san bernardino county california and testing assumptions of habitat fidelity in the quaternary fossil record abstract the late pleistocene and holocene vertebrate fossil record for the northern mojave desert southwestern usa is known primarily from five sites until now only two of these have been radiometrically dated and temporal placement of the others has been based on stratigraphic or biostratigraphic correlation leading to circular interpretations of mammal extirpations in the mojave here i report a revised and complete faunal list for mescal cave along with 22 ams radiocarbon dates from 5 vertebrate taxa recovered from its deposits the results reported here demonstrate time averaging in mescal cave encompassing around 34 ka a maximum age 14 ka older and minimum age 10 ka younger than previously thought furthermore radiocarbon analyses suggest local extirpation of marmota flaviventris around 3 6 cal ka bp considerably younger than expected based on regional patterns of warming and aridification in the mojave conversely radiocarbon dates from another presumably boreal species neotoma cinerea are considerably older than expected suggesting either that climate change at this site did not directly mirror regional patterns that habitat requirements for these two species are not strictly boreal or cool mesic as has often been assumed or that local edaphic conditions and or competitive interactions overrode the regional climatic controls on theses species distribution

thermodynamic and radiative structure of stratocumulus topped boundary layers abstractstratocumulus topped boundary layers stbls observed in three different regions are described in the context of their thermodynamic and radiative properties the primary dataset consists of 131 soundings from the southeastern pacific sep 90 soundings from the island of graciosa grw in the north atlantic and 83 soundings from the u s southern great plains sgp a new technique that makes an attempt to preserve the depths of the sublayers within an stbl is proposed for averaging the profiles of thermodynamic and radiative variables a one dimensional radiative transfer model known as the rapid radiative transfer model was used to compute the radiative fluxes within the stbl the sep stbls were characterized by a stronger and deeper inversion together with thicker clouds lower free tropospheric moisture and higher radiative flux divergence across the cloud layer as compared to the grw stbls compared to the stbls over the marine locations the stbls over sgp had higher wind shear and a n

level of lake lahontan during deposition of the trego hot springs tephra about 23 400 years ago abstract the trego hot springs tephra bed is a silicic tephra about 23 400 yr old found at several localities in pluvial lake sediments in northern nevada southern oregon and northeastern california it has been characterized petrographically by the major and minor element chemistry of its glass and by its stratigraphic position with respect to other tephra layers at a newly described locality on squaw creek northwest of gerlach nevada at the north end of the smoke creek desert trego hot springs tephra has been found in sediments of the sehoo and indian lakes formations the depositional environments of these sediments show that when the tephra fell pluvial lake lahontan stood between 1256 and 1260 m and that immediately thereafter the lake rose to at least 1275 m these data corroborate earlier findings by benson quaternary research 9 300 318 from radiometric dating of calcareous tufa however the lake lahontan area has been affected by isostatic subsidence and rebound in response to changing water loads so that caution is required in the use of lakeshore elevations in correlation

chronology sedimentology and microfauna of groundwater discharge deposits in the central mojave desert valley wells california during the late pleistocene emergent groundwater supported persistent and long lived desert wetlands in many broad valleys and basins in the american southwest when active these systems provided important food and water sources for local fauna supported hydrophilic and phreatophytic vegetation and acted as catchments for eolian and alluvial sediments desert wetlands are represented in the geologic record by groundwater discharge deposits which are also called spring or wetland deposits groundwater discharge deposits contain information on the timing and magnitude of past changes in water table levels and thus are a source of paleohydrologic and paleoclimatic information here we present the results of an investigation of extensive groundwater discharge deposits in the central mojave desert at valley wells california we used geologic mapping and stratigraphic relations to identify two distinct wetland sequences at valley wells which we dated using radiocarbon luminescence and uranium series techniques we also analyzed the sediments and microfauna ostracodes and gastropods to reconstruct the specifi c environments in which they formed our results suggest that the earliest episode of high water table conditions at valley wells began ca 60 ka thousands of calendar yr b p and culminated in peak discharge between ca 40 and 35 ka during this time cold 4 12 c emergent groundwater supported extensive wetlands that likely were composed of a wet sedge rush tussock meadow mixed with mesic riparian forest after ca 35 ka the water table dropped below the ground surface but was still shallow enough to support dense stands of phreatophytes through the last glacial maximum lgm the water table dropped further after the lgm and xeric conditions prevailed until modest wetlands returned briefl y during the younger dryas cold event 13 0 11 6 ka we did not observe any evidence of wet conditions during the holocene at valley wells the timing of these fl uctuations is consistent with changes in other paleowetland systems in the mojave desert the nearby great basin desert and in southeastern arizona near the border of the sonoran and chihuahuan deserts the similarities in hydrologic conditions between these disparate locations suggest that changes in groundwater levels during the late pleistocene in desert wetlands scattered throughout the american southwest were likely driven by synopticscale climate processes

pluvial climatic episodes in north america and north africa types and correlation with global climate abstract differences in late quaternary pluvial chronologies among the world s deserts can be related to fundamental differences in the climatology of those pluvial episodes paleoenvironmental records and climate model simulations for two northern hemisphere desert regions are used to illustrate two types of pluvial climatic regime in the higher latitude deserts of the american southwest pluvial conditions during the last glacial maximum were caused by the southward displacement of the westerly jet stream in turn caused by the blocking effect of laurentide ice sheet and a steepened arctic equator pressure gradient winter seasonality of precipitation and substantially lower mean annual temperatures are reflected in the paleoenvironmental record and simulated by models of 18 000 yr b p climate a second pluvial climate type which strongly influences the lower latitude deserts of north africa is characterized by enhanced summer monsoons and occurs during interglacials and perhaps interstadials the primary forcing mechanism of the last pluvial episode in the sahara and libyan deserts appears to have been increased solar radiation milankovitch forcing causing thermally enhanced ocean land pressure gradients and increased flow of maritime tropical air into the interior of the continent poleward displacement of the summer monsoon is consistent with floristic evidence for summer seasonality of precipitation and replicated by model simulations of 9000 and 6000 yr b p climate chronologies from some deserts such as the southern portion of the american southwest suggest the consecutive occurrence of both types of pluvial climatic regime pluvial conditions during the last glacial maximum were brought about by the equatorward displacement of the prevailing westerlies a subsequent more subdued pluvial period occurred later between 12 500 and 8000 yr b p caused by the poleward displacement of summer monsoons characterization of the climatology of pluvial episodes generates explanations for their temporal distribution and therefore this approach may be useful in assessing the quaternary chronology of pluvial episodes in other desert regions

cloud radar doppler spectra in drizzling stratiform clouds 2 observations and microphysical modeling of drizzle evolution sites is presented the evolution of the doppler spectra moments is consistent with the onset and growth of drizzle particles and can be used to assist modeling studies of drizzle onset and growth time height radar observations are used to exhibit the coherency of the doppler spectra shape parameters and demonstrate their potential to improve the interpretation and use of radar observations in addition a simplified microphysical approach to modeling the vertical evolution of the drizzle particle size distribution in warm stratiform clouds is described and used to analyze the observations the formation rate of embryonic drizzle droplets due to the autoconversion process is not calculated explicitly however accretion and evaporation processes are explicitly modeled the microphysical model is used as input to a radar doppler spectrum forward model and synthetic radar doppler spectra moments are generated three areas of interest are studied in detail early drizzle growth near the cloud top growth by accretion of the well developed drizzle and drizzle depletion below the cloud base due to evaporation the modeling results are in good agreement with the continental and maritime observations this demonstrates that steady state one dimensional explicit microphysical models coupled with a forward model and comprehensive radar doppler spectra observations offer a powerful method to explore the vertical evolution of the drizzle particle size distribution

soil evolution along an altitudinal transect in the eastern mojave desert of nevada u s a amundson r g chadwick o a sowers j m and doner h e 1989 soil evolution along an altitudinal transect in the eastern mojave desert of nevada u s a geoderma 43 349 371 six soil profiles were examined along an altitudinal transect from 840 to 2170 m in the eastern mojave desert of southern nevada the soils formed on gravelly limestone alluvium which varied in age from holocene to mid pleistocene climate and vegetation varied from an arid desert scrub community at the low elevation to a sub humid coniferous forest at the highest elevation silicate clay mineralogy was similar to that of the parent material in all the holocene soils but differed with elevation in the mid pleistocene soils these being dominated by palygorskite at 1400 m and smectite at 2150 m pedogenic carbonate content of the bk horizons and morphologic stage of carbonate accumulation increased with soil age with the exception of the 2150 m site where excess moisture leaches carbonate out of the profile dcb extractable iron increased with both age and elevation whereas soil organic c and c02 increased primarily with elevation reflecting the gradient in moisture regime and biologic productivity aeolian dust may have a strong role in the formation of the vesicular platey surface horizons at many of the sites

constraints on the origin of slab and mantle wedge anomalies in tonga from the ratio of s to p velocities we examine two prominent upper mantle velocity anomalies in the southwest pacific the tonga slab anomaly and the corresponding overlying mantle wedge anomaly using data collected during a combined land sea deployment of temporary seismometers the linear geometry and small interstation spacing of the instruments yield high resolution data along a cross section of the tonga subduction zone including the actively spreading lau back arc basin we estimate the relative variation of p and s velocity often described as lnvs lnvp for the slab and mantle wedge anomalies using two distinct methods a linear regression of the p and s travel time residuals and detailed modeling of the velocity structure using a three dimensional finite difference travel time algorithm the two methods yield similar results with of the slab being 1 1 1 5 and of the mantle wedge being 1 2 1 3 these values are consistent with experimental data concerning the effect of temperature on p and s wave velocities in the upper mantle and are lower than what is expected for velocity anomalies generated by the presence of partial melt these observations imply that either the theoretical estimates of for partial melt are too large or very little partial melt is present beneath the lau basin in the latter case melt must be quickly removed from the rock matrix such that the velocity anomalies are due to increased temperature and not melt the bulk of the velocity anomaly in the mantle wedge can be explained by temperature anomalies of 400 600 c because of the amplification of temperature derivatives of seismic velocity by anelastic effects such large thermal anomalies generated by decreased lithospheric thickness and mantle upwelling beneath the fast spreading lau back arc basin can still leave the mantle near the solidus even after accounting for the effect of increased volatile content in the mantle wedge the lower amplitude velocity reductions in the deeper wedge are likely related to an increased concentration of volatiles from the subducting slab

scales of heterogeneity near the core mantle boundary we have mapped shear velocity variations near the base of the mantle with scs s differential travel times beneath the north atlantic there is a systematic variation in velocity over a distance of 1500 km or more with a pronounced low velocity anomaly centered roughly beneath madeira island beneath the northern indian ocean there is no similar long wavelength anomaly the average scs s residual beneath the indian ocean is 3 6 0 7 s more negative than the atlantic residual indicating faster average velocities near the base of the mantle

origin of desert loess from some experimental observations a longstanding problem of quaternary geology has been the origin of the silty deposit known as loess of the many explanations for its formation and distribution1 2 the most commonly accepted is that the silt is produced by subglacial grinding processes1 3 4 followed by redistribution and deposition by the wind the large expanses of loess in central europe are therefore considered to be the consequence of quaternary glaciation5 there is however a view6 7 that loessic silt may also originate as the product of processes in hot deserts some proponents of the desert loess hypothesis consider that silt size material is the product of weathering processes7 which may include salt weathering8 or weathering down incipient cracks9 an alternative mechanism is aeolian attrition of sand grains although probably as a result of the experimental work of kuenen10 smalley and krinsley11 consider that only fine silt 2 6 m is produced in large quantities by the abrasion of quartz grains we have simulated aeolian attrition of angular quartz grains previously produced by weathering in deserts the products of abrasion show that both coarse and fine silt sizes are produced these findings suggest that desert aeolian processes can produce loess we also suggest that much of this material from many deserts has been deposited in the sea but that the chinese loess could have been produced in the gobi desert the finest particles produced by such attrition may be a source of silica for silcrete formation

a revised chronology for the last pleistocene lake cycle in the central lahontan basin radiocarbon dates of plant materials from packrat middens in caves below the elevation of the last high stand of pleistocene lake lahontan in conjunction with radiocarbon dates of ancient archaeological materials provide evidence that the last high stand terminated before 12 070 yr b p this new information suggests that the last major fluctuation in the level of lake lahontan was approximately synchronous with those of lakes bonneville and russell and that these three lakes probably responded contemporaneously to the same regional paleoclimatic changes

global mantle tomography progress status in the past 10 years abstract we review the present status of global mantle tomography and discuss two main classes of models that have been developed in the past 10 years p velocity models based on large datasets of travel times from the international seismological centre bulletins often referred to as high resolution models and s velocity models based on a combination of surface wave and hand picked body wave travel times or waveforms referred to as long wavelength models we discuss their respective strengths and weaknesses as well as progress in the resolution of other physical parameters such as anisotropy anelasticity density and bulk sound velocity using tomographic approaches we present the view that future improvements in global seismic tomography require the utilization of the rich information contained in complete broadband seismic waveforms this is presently within our reach owing to theoretical progress as well as the increase in computational power in recent years

short scale heterogeneity in the lowermost mantle insights from pcp p and scs s data we compare lateral variations at the base of the mantle as inferred from a global dataset of pcp p travel time residuals measured on broadband records and existing p and s tomographic velocity models as well as scs s travel time data in some selected regions in many regions the pcp p dataset implies short scale lateral variations that are not resolved by global tomographic models except under eastern eurasia where data and models describe a broad region of fast velocity anomalies across which variations appear to be of thermal origin in other regions such as central america and southeastern africa correlated short scale lateral variations several hundred kilometers are observed in pcp and scs implying large but not excessive values for the ratio r d ln vs d ln vp v2 5 on the other hand in at least two instances in the heart of the african plume and on the edge of the pacific plume variations in p and s velocities appear to be incompatible implying strong lateral gradients across compositionally different domains possibly also involving topography on the core mantle boundary one should be cautious in estimating r at the base of the mantle from global datasets as different smoothing and sampling of p and s datasets may result in strong biases and meaningless results 7 2002 elsevier science b v all rights reserved

the turbulence structure in a continental stratocumulus cloud from millimeter wavelength radar observations abstract the turbulent scale vertical velocity structure in a continental stratocumulus cloud is studied using a 3 mm wavelength doppler radar operating in a vertically pointing mode the radar observations provided 30 m sampling in the vertical with 2 s averages of 10 000 samples vertical velocity measurements were made continuously for an 8 h period and were further supported by measurements of cloud base height from a laser ceilometer and liquid water path from a microwave radiometer during the beginning of the observational period the cloud layer extended between 200 and 800 m the vertical velocity variance profiles evolved systematically over the period from a well defined peak in the upper part of the cloud layer of 0 7 m2 s 2 to a peak in the lower part of the cloud layer of 0 2 m2 s 2 as the layer became decoupled later in the observing period the vertical velocity skewness during the well coupled conditions was negative through most of the cloud consistent with the presence of relatively n

late glacial and early holocene vegetation and climate change near owens lake eastern california abstract pollen and algae from owens lake in eastern california provide evidence for a series of climatic oscillations late in the last glaciation juniper woodland which dominated the owens valley from 16 200 to 15 500 cal yr b p suggests much wetter conditions than today although still wetter and cooler than today the area then became fairly warm and dry with woodland being replaced by shrubs mainly sagebrush from 15 500 to 13 100 cal yr b p next chenopodiaceae shadscale increased woody species declined and lake levels fell all evidence for a brief ca 100 200 yr drought about 13 000 cal yr b p the climate continued to oscillate between wet and dry from 13 000 to 11 000 cal yr b p after 11 000 cal yr b p low lake levels and the increased dominance of desert shrubs indicate the beginning of warm dry holocene conditions the region s climate was unstable during the younger dryas but uncertainities in dating prevent identification of the younger dryas interval in the owens lake record comparison of the owens lake record with studies in the sierra nevada and great basin suggest that the climate was generally wetter between 13 000 and 11 000 cal yr b p with warmer summers although no consistent pattern of climate change emerges

late quaternary environments and biogeography in the great basin abstract plant and animal remains found in packrat neotoma spp middens and cave fill from the eastern and southern great basin region reveal the presence of subalpine conifers and boreal mammals at relatively low elevations during the late wisconsin limber pine pinus flexilis and bristlecone pine p longaeva were important in the late pleistocene plant communities throughout this region spruce picea cf engelmannii and common juniper juniperus communis were present in some of the more northerly localities and douglas fir pseudotsuga menziesii and white fir abies concolor were present in southern and eastern localities single needle pinyon pine pinus monophylla common across this region today was apparently not present north of the sheep range of southern nevada during the late wisconsin pikas ochotona cf princeps small boreal mammals present in only a few great basin mountain ranges today were common throughout the region heather voles phenacomys cf intermedius have been found in two cave fill deposits in nevada though they are unknown in the great basin today limber and bristlecone pines are generally restricted to rocky substrates in modern subalpine habitats in the great basin and this may also have been the case when these plants grew at lower elevations during the late wisconsin subalpine conifers were present on the rock outcrops sampled by the packrat middens but shrub communities perhaps dominated by sagebrush artemisia spp may have been present on alluvial valley bottom substrates forested habitats would thus have been isolated habitat islands as they are today boreal small mammals including pikas and heather voles were able to colonize the great basin mountain ranges during the late pleistocene we suggest that these mammals were able to survive in the intervening valley bottoms under a cool summer climatic regime and that continuous forest or woodland corridors were not necessary for migration

surface based observations of mesoscale cumulus stratocumulus interaction during astex abstract data obtained from the island of santa maria in the azores during the atlantic stratocumulus transition experiment astex are used to describe cloud and boundary layer structure for a 24 h period on 15 june 1992 over the east central atlantic 37 n 25 10 w the evolution of the mesoscale cloud structure during a 24 h period in the vertical column above the surface site was characterized using a 94 ghz radar a laser ceilometer 3 h radiosonde ascents and surface micrometeorological instrumentation mesoscale circulations and drizzle were found to be key elements of the boundary layer clouds observed in this region during the late night and predawn hours of the study period a single layer of stratocumulus that averaged 200 m in thickness topped a well mixed marine boundary layer mesoscale cellular convection mcc which had ascending regions with horizontal dimensions of 7 km was observed during this period at sunrise decoupling was imposed on this mcc and extreme mesoscale variatio

fidelity of analytic drop size distributions in drizzling stratiform clouds based on large eddy simulations abstract cloud microphysical parameterizations and retrievals rely heavily on knowledge of the shape of drop size distributions dsds many investigations assume that dsds in the entire or partial drop size range may be approximated by known analytical functions the most frequently employed approximations of function are of the type of gamma lognormal khrgian mazin and marshall palmer at present little is known about the accuracy of these approximations the authors employ a dsd dataset generated by the cooperative institute for mesoscale meteorological studies large eddy simulation cimms les explicit microphysics model for stratocumulus cases observed during the atlantic stratocumulus transition experiment astex field project the fidelity of analytic lognormal and gamma type dsd functions is evaluated according to how well they represent the higher order moments of the drop spectra such as precipitation flux and radar reflectivity it is concluded that for boundary layer marine drizzling st

thermodynamically consistent decompression implications for lower mantle composition estimates of the composition of the lower mantle are commonly obtained by a process of adiabatic decompression in which zero pressure mantle parameters are determined with a least squares fit of an equation of state to mantle densities we show that this procedure may lead to biased estimates of the zero pressure density and compressibility of the mantle the bias can be eliminated or minimized by subjecting the equation of state fit to a thermodynamic constraint at zero pressure such inversions provide equations of state that are compatible with the lower mantle as well as the thermal properties of selected mineral models we used this method to evaluate assemblages containing mg fe sio3 perovskite and mg fe o with fe fe mg ratios as high as 0 2 thermodynamic systematics were used to place bounds on the anderson gruneisen parameter s for perovskite we find a fairly large range of acceptable models for the composition of the lower mantle they range from uppermantle like compositions to assemblages that are enriched in both si and fe relative to the upper mantle however a pure perovskite lower mantle whether enriched in fe or not seems improbable small fe enrichments of the order of 1 given density contrasts across the 670 km discontinuity that are probably insufficient to prevent convective mixing of the upper and lower mantles we therefore suggest that unless the mantle is homogeneous in its major oxide components the lower mantle is likely to be enriched in fe by at least several percent

radiocarbon chronology of holocene hydrologic changes in northeastern mali abstract a detailed chronology of hydrological changes that occurred in northeastern mali during the holocene is based on approximately 30 14 c dates of molluscs which were collected from the lacustrine and paludal deposits of the ine sakane sand sea the presence of cemented paleodunes indicates that the end of the pleistocene was and arid period this was followed by an early holocene lacustrine episode ca 9500 6500 yr b p during which numerous lakes occupied depressions formed in the cretaceous limestones and between the sand ridges these lakes reflect a significant rise in the water table between ca 6500 and 5500 yr b p the lakes dried up although the water table remained close to the ground surface in several areas calcareous concretions formed at the water table fringe during this time thereby fossilizing some of the middle holocene dunes a second lacustrine episode is dated between ca 5500 and 4500 yr b p it corresponds to the establishment of numerous neolithic settlements in the area arid conditions have developed since about 4500 yr b p to attain the conditions of the present day the isotopic composition 18 o and 13 c of the fauna reflects highly variable hydrological conditions groundwaters were recharged by precipitation which was occasionally very depleted in heavy oxygen 18 o 13 evaporation induced an enrichment in 18 o high concentrations characterize some lakes the 13 c content of fossil shells reflect 1 species ecological requirements 2 isotopic composition of the total inorganic dissolved carbon tidc in groundwaters and 3 the lake metabolism

directly dated mis 3 lake level record from lake manix mojave desert california usa abstract an outcrop based lake level curve constrained by 70 calibrated 14 c ages on anodonta shells indicates at least 8 highstands between 45 and 25 cal ka bp within 10 m of the 543 m upper threshold of lake manix in the mojave desert of southern california correlations of manix highstands with ice marine and speleothem records suggest that at least the youngest three highstands coincide with dansgaard oeschger d o stadials and heinrich events 3 and 4 the lake level record is consistent with results from speleothem studies in the southwest that indicate cool wet conditions during d o stadials notably highstands between 43 and 25 ka apparently occurred at times of generally low levels of pluvial lakes farther north as interpreted from core based proxies mojave lakes may have been supported by tropical moisture sources during oxygen isotope stage 3 perhaps controlled by southerly deflection of pacific storm tracks due to weakening of the sea surface temperature gradient in response to north atlantic climate perturbations

j362d28 a new joint model of compressional and shear velocity in the earth s mantle summary the discrimination between chemical and thermal heterogeneity in the earth s mantle remains one of the most important and challenging questions to be answered by observational and theoretical geophysics to answer this question requires a thorough knowledge of the ratio between compressional and shear velocity anomalies we describe results of a joint inversion for compressional and shear velocity in the mantle using a large and diverse data set consisting of traveltimes complete waveforms and surface wave dispersion measurements a horizontal tessellation consisting of 362 spherical splines is used to parametrize the model which is approximately equivalent to a spherical harmonic of degree 18 in resolution the model contains peak variations from prem of up to 7 per cent in s velocity and 2 5 per cent in p velocity in the upper mantle these variations decrease to 1 5 and 0 6 per cent respectively at 1000 km depth and reach 2 5 and 1 0 per cent respectively in the d region the rms ratio of s to p velocity perturbations is fairly constant between 2 0 and 2 5 in the lower mantle but a local minimum in this ratio occurs at a depth of approximately 1700 km resolution tests show that the recovery of p and s velocity is not geographically uniform but also show that this amplitude ratio is well resolved between 670 and 2700 km depth we also observe a persistent negative correlation between bulk sound and shear velocity throughout the same region of the mantle in addition the model contains a minimum correlation between p and s velocity between 670 and 1100 km this feature is supported by both the favourable outcome of resolution experiments and the poor fit provided by the starting model from the inversion in which the p and s velocities are perfectly correlated to our data set of p wave traveltimes the power spectra of both p and s velocity heterogeneity are similar although we note a slightly larger dominance of degree two in the spectra for p velocity in the mid mantle where resolution is highest

on using the relationship between doppler velocity and radar reflectivity to identify microphysical processes in midlatitudinal ice clouds 1 ground based 35 ghz profiling doppler cloud radar observations of ice clouds were used to derive the power law relation between doppler velocity vd and radar reflectivity z vd azb by removing the vertical air motion from vd the power law can be rewritten as vt azb with vt being the reflectivity weighted particle terminal fall velocity profiles of this relation are variable with height an attempt was made to relate this variability to the dominant microphysical processes in different layers of the cloud based on that the possibility of using profiles of the parameters a and b to distinguish different microphysical regimes was explored the methodology was applied to long term measurements january 1997 to december 2010 at the atmospheric radiation measurement site in the southern great plains principal component analysis was used to determine the modes of the profiles that explain most of the observed variance in the observations profile averaged means and standard deviations of parameters a and b amounted to 0 65 0 42 and 0 03 0 19 respectively furthermore three commonly used microphysical relations related to bulk quantities were used to determine values of a and b these results were found to compare reasonably well with the values obtained from the radar observations finally microphysical considerations showed that radar derived values of parameter b can be explained in terms of particle size distribution moment changes

summertime post cold frontal marine stratocumulus transition processes over the eastern north atlantic abstractmarine boundary layer mbl cloud morphology associated with two summertime cold fronts over the eastern north atlantic ena is investigated using high resolution simulations from the weat

investigation of deep slab structure using long period s waves travel times and amplitudes of long period sh scsh ssh and sscsh phases from several deep focus earthquakes in the northwest pacific are analyzed for evidence of lithospheric slab penetration into the lower mantle inclusion of amplitude observations in the analysis provides constraints on lateral velocity gradients present in the deep slabs which are not resolvable using travel times alone travel time and amplitude residual spheres are presented for two deep focus events with good azimuthal coverage but while interesting patterns are present quantitative analysis is precluded by the lack of accurate methods for calculating synthetic long period seismograms for three dimensional slab models therefore we focus our analysis on a two dimensional approximation to the downdip geometry of the kurile and japan slabs which allows comparison of a much larger data set with accurate two dimensional synthetics as well as the use of ss and sscs travel time and amplitude patterns as empirical corrections for deep mantle structure while the limited azimuth range required for this approximation reduces the diagnostic capability of the data it also increases our confidence that the corrected data are most sensitive to the near source region the ss and sscs observations indicate that the downdip shear wave travel time pattern previously attributed to a deep slab extension is primarily caused by broad scale lower mantle heterogeneity once corrected for this structure the s wave observations do not support a simple undeformed slab steepening in dip and penetrating deep into the lower mantle beneath the kurile and japan islands as proposed by jordan 1977 and creager and jordan 1984 1986 rather the observations support shorter and or broader slab models man those previously hypothesized models which can probably be reconciled with p wave data further analysis of the complete three dimensional patterns will be required for more precise resolution of the penetration depths of these slabs if indeed any deep slab heterogeneity is actually seismically detectable

on the anelastic contribution to the temperature dependence of lower mantle seismic velocities abstract there is little agreement regarding the importance of anelastic contributions to the temperature dependence of seismic wave velocities some studies consider the anelastic contribution to be negligible whereas others argue that it may be as important as the purely elastic contribution in order to evaluate these claims we review physically plausible models for mantle relaxation processes and construct a model of activation enthalpy based on solid state physics as well as on recent experimental results we then deduce self consistent 1 d q profiles and evaluate the anelastic contribution to the temperature dependence of v s and v p physically plausible values of activation enthalpies yield anelastic contributions that increase with depth and account for at least 20 of the velocity temperature derivatives at 2600 km we show that anelasticity may significantly moderate temperature variations in hot slow velocity zones this suggests that inferred lateral changes in temperature as well as arguments regarding the presence of chemical heterogeneity and or temperature induced phase transformations are likely to be significantly affected by anelastic effects in the mantle we also compute values of the dimensionless parameters r s p r s and r s we find that anelasticity can either increase or decrease r s p but the magnitude of the correction of the order of 15 is smaller than the uncertainty in the elastic value anelasticity cannot change the sign of r s and r s but it can decrease their values by as much as 50 however given current uncertainties in seismic and mineral data the effects of anelasticity on the dimensionless parameters do not bring any quantitative constraints on lateral variations of temperature chemical composition and or mineral phase

variability of cloud vertical structure during astex observed from a combination of rawinsonde radar ceilometer and satellite the macroscale cloud vertical structure cvs including cloud base and top heights and layer thickness and characteristics of multilayered clouds is studied at porto santo island during the atlantic stratocumulus transition experiment astex by using rawinsonde radar ceilometer and satellite data the comparisons of cvs parameters obtained from four different approaches show that 1 by using the method developed by wang and rossow rawinsonde observations raob s can sample all low clouds and determine their boundaries accurately but oversample low clouds by about 10 mistaking clear moist layers for clouds 2 cloud base heights less than 200 m in the radar data are ambiguous but can be replaced by the values measured by ceilometer and 3 the practical limit on the accuracy of marine boundary layer cloud top heights retrieved from satellites appears to be about 150 300 m mainly due to errors in specifying the atmospheric temperature and humidity in the inversion layer above the cloud the vertical distribution of clouds at porto santo during astex is dominated by low clouds below 3 km a cloud free layer between 3 and 4 km and 20 high clouds with a peak occurrence around 7 8 km low clouds have mean base and top heights of 1 0 km and 1 4 km respectively and occur as single layers 90 of the time for double layered low clouds the tops of the uppermost layers and the bases of the lowermost layers have similar distributions as those of single layered clouds the temporal variations of low clouds during astex are apparently dominated by advecting mesoscale 20 200 km horizontal variations coherent time variations are predominately synoptic timescale 4 5 6 8 days and diurnal variability on the diurnal timescale all cloud properties show maxima in the early morning around 0530 lst decreasing to minima in the late afternoon diurnal variations appear to be altered when high clouds are present above low clouds the general characteristics of cvs in three astex and the first isccp regional experiment fire87 regions derived from a 20 yr rawinsonde dataset are also presented the results suggest that cvs characteristics obtained from data collected at porto santo during astex june 1992 are not representative of other marine stratiform cloud regions

comparing p and s wave heterogeneity in the mantle from the reprocessed data set of engdahl and co workers we have carefully selected matching p and s data for tomographic imaging we assess data and model error and conclude that our s model uncertainty is twice that of the p model we account for this in our comparison of the perturbations in p and s wavespeed in accord with previous studies we find that p and s perturbations are positively correlated at all depths however in the deep mantle systematic differences occur between regions that have undergone subduction in the last 120 million years and those that have not in particular below 1500 km depth ln vs ln vp is significantly larger in mantle regions away from subduction than in mantle beneath convergent margins this inference is substantiated by wavespeed analyses with random realizations of the slab non slab distribution through much of the mantle there is no significant correlation between bulk sound and s wave perturbations but they appear to be negatively correlated between 1700 and 2100 km depth which is also where the largest differences in ln vs ln vp occur this finding supports convection models with compositional heterogeneity in the lowermost mantle

even degree lateral variations in the earth s mantle constrained by free oscillations and the free air gravity anomaly the recent occurrence of several large earthquakes in particular the 1994 june 9 bolivia event has motivated a re examination of the earth s large scale heterogeneity from a normal mode or free oscillation perspective compared to earlier studies the number of normal mode constraints on lateral variations in the mantle has increased five fold and toroidal and cross coupled modes complement the traditional spheroidal mode data set it is demonstrated that this large collection of mode data combined with the free air gravity anomaly can reliably constrain even degree lateral variations in wave velocities as well as density we present the first whole mantle density model constrained by seismology our shear and compressional velocity models are consistent with existing models based upon traveltimes and waveforms and are reasonably well correlated throughout the mantle shear and bulk sound velocity models exhibit a gradual decrease in correlation with depth and are anti correlated near the core mantle boundary we find that lateral variations in density are poorly correlated with wave velocities and are locally anti correlated with shear velocity in the lowermost mantle the correlations between wave velocities and density suggest both a thermal and a compositional origin to lateral heterogeneity in addition to traditional maps of lateral variations in wave velocity we also present maps of lateral variations in shear and bulk moduli the inversion puts weak constraints on even degree topographic variations on the core mantle boundary the 660 km discontinuity and dynamic free surface topography finally we determine both radially and laterally varying scaling relationships including poisson s ratio

mesoscale shallow convection in the atmosphere this paper is a review of the observational experimental theoretical and numerical studies of mesoscale shallow convection msc in the atmosphere typically msc is 1 to 2 km deep has a horizontal length scale of a few to a few tens of kilometers and takes distinctive planforms linear and hexagonal the former is called a cloud street roll or band while the latter is called mesoscale cellular convection mcc comprising three dimensional cells msc is characterized by its shape horizontal extent convective depth and aspect ratio the latter is the ratio of the horizontal extent to that in the vertical for cells the horizontal extent is their diameter whereas for rolls it is their spacing rolls usually align along or at angles of up to 10 from the mean horizontal wind of the convective layer with lengths from 20 to 200 km widths from 2 to 10 km and convective depths from 2 to 3 km the typical value of aspect ratio ranges from 2 to 20 rolls may occur over both water surface and land surfaces mesoscale convective cells may be divided into two types open and closed open cell circulation has downward motion and clear sky in the cell center surrounded by cloud associated with upward motion closed cells have the opposite circulation both types of cell have diameters ranging from 10 to 40 km and aspect ratios of 5 to 50 and both occur in a convective layer with a depth of about 1 to 3 km both the magnitude and direction of horizontal wind in the convective layer change little with height msc results from a complex and incompletely understood mix of processes these processes are outlined and their interplay is examined through a review of theoretical and laboratory analyses and numerical modeling of msc