oxygenation episodes on the continental shelf of central peru remote forcing and benthic ecosystem response abstract the interplay between the oxygen minimum zone and remotely forced oxygenation episodes determines the fate of the benthic subsystem off the central peruvian coast we analyzed a 12 year monthly time series of oceanographic and benthic parameters at 94 m depth off callao central peru 12 s to analyze i near bottom oxygen level on the continental shelf in relation to dynamic height on the equator 095 w and ii benthic ecosystem responses to oxygen change macrobiotic infauna meiofauna and sulphide oxidizing bacteria thioploca spp shelf oxygenation episodes occurred after equatorial dynamic height increases one month before consistent with the propagation of coastal trapped waves several but not all of these episodes occurred during el ninos the benthic biota responded to oxygenation episodes by undergoing succession through three major ecological states under strong oxygen deficiency or anoxia the sediments were nearly defaunated of macro invertebrates and thioploca was scarce such that nematode biomass dominated the macro and meiobiotas when frequency of oxygenation events reduced the periods of anoxia but the prevailing oxygen range was 10 20 mol l 1 mats of thioploca formed and dominated the biomass finally with frequent and intense 40 mol l 1 oxygenation the sediments were colonized by macrofauna which then dominated biomass the thioploca state evolved during the 2002 2003 weak en while the macrofauna state was developed during the onset of the strong1997 1998 en repeated episodes of strong oxygen deficiency during the summer of 2004 in parallel with the occurrence of red tides in surface waters resulted in the collapse of thioploca mats and development of the nematode state ecological interactions may affect persistence or the transition between benthic ecosystem states

long term talus flatirons formation in the hyperarid northeastern negev israel abstract colluvial sediments of talus relicts talus flatirons around mesas preserve a record that sheds light on slope forming processes at temporal scales 103 yr the sedimentology and soil stratigraphy of two groups of talus flatirons in the northeastern hyperarid negev desert reveal four deposition events in the younger talus and at least two in the older one numerical modeling of high resolution 10be depth profiles suggests that these taluses were deposited during the middle pleistocene the younger talus group first depositional event occurred at 551 142 80 ka and its abandonment occurred at 270 38 17 ka the abandonment of the older talus group and stabilization of its surface occurred at 497 114 176 ka these ages indicate that the development of the studied talus sequence is not specifically associated with pleistocene glacial interglacial cycles the 10be modeled concentrations indicate significant differences in the average inheritance of talus flatirons of different groups these differences can be attributed to variability in the transport distance and duration of gravel exposure during transport but could also reflect some temporal variability in cliff retreat our results also demonstrate that talus slopes in hyperarid areas despite their steepness can store sediment for long periods 500 ka and thus constitute a valuable archive

rectification of the madden julian oscillation into the enso cycle an ocean general circulation model forced with idealized purely oscillating wind stresses over the western equatorial pacific similar to those observed during the madden julian oscillation mjo developed rectified low frequency anomalies in sst and zonal currents compared to a run in which the forcing was climatological the rectification in sst resulted from increased evaporation under stronger than normal winds of either sign from correlated intraseasonal oscillations in both vertical temperature gradient and upwelling speed forced by the winds and from zonal advection due to nonlinearly generated equatorial currents the net rectified signature produced by the mjo like wind stresses was sst cooling about 0 48c in the west pacific and warming about 0 18c in the central pacific tending to flatten the background zonal sst gradient it is hypothesized that in a coupled system such a pattern of sst anomalies would spawn additional westerly wind anomalies as a result of sst induced changes in the low level zonal pressure gradient this was tested in an intermediate coupled

sediment yield exceeds sediment production in arid region drainage basins we use 10 be and 26 al to determine long term sediment generation rates identify significant sediment sources and test for landscape steady state in nahal yael an extensively studied hyperarid drainage basin in southern israel comparing a 33 yr sediment budget with 33 paired 10 be and 26 al analyses indicates that short term sediment yield 113 138 t km 2 yr 1 exceeds long term sediment production 74 16 t km 2 yr 1 by 53 86 the difference suggests that the basin is not in steady state but is currently evacuating sediment accumulated during periods of more rapid sediment generation and lower sediment yield nuclide data indicate that 1 sediment leaving the basin is derived primarily from hillslope colluvium 2 bedrock weathers more rapidly beneath a cover of colluvium than when exposed and 3 long term erosion rates of granite schist and amphibolite are similar

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

crustal structure off norway 62 to 70 north abstract extensive geophysical surveys have been undertaken on the volcanic passive continental margin offshore norway between 62 and 70 n during the last 25 years three main margin segments have been identified the lofoten vesteralen margin the voring margin and the more margin the main features of the margins are prominent marginal highs including seaward dipping reflector sequences and an up to 22 km thick volcanic and transitional crust prominent escarpments the voring plateau escarpment and the faeroe shetland escarpment and up to 12 km deep post jurassic sedimentary basins east of the escarpments velocity depth solutions from about 250 sonobuoys expanding spread profiles and refraction profiles have been compiled and contoured isovelocity horizon contour maps and velocity transects outline a crust which broadly thickens from an oceanic crust with a normal oceanic type velocity structure to a ca 35 km thick continental crust with a continental velocity structure beneath the norwegian coast anomalous features include local crustal thickening below the more and vering marginal highs and high velocity bodies in the lower crust in the extension of the precambrian lofoten vesteralen archipelago the free air seasat derived gravity anomalies show a good correlation with the high velocity bodies and show prominent ne trending highs from the rockall plateau porcupine plateau region over the more voring and lofoten vesteralen margins to the southwestern barents sea

vp vs ratio along the voring margin ne atlantic derived from obs data implications on lithology and stress field a total of 13 regional ocean bottom seismograph obs profiles with an accumulated length of 2207 km acquired on the voring margin ne atlantic have been travel time modelled with regards to s waves the vp vs ratios are found to decrease with depth through the tertiary layers which is attributed to increased compaction and consolidation of the rocks the vp vs ratio in the intra campanian to mid campanian layer 1 75 1 8 in the central voring basin is significantly lower than for the layers above and beneath suggesting higher sand shale ratio this layer was confirmed by drilling to represent a layer of sandstone this mid cretaceous anomaly is also present in the northern voring basin as well as on the southern lofoten margin further north the vp vs ratio in the extrusive rocks on the voring plateau is estimated to be 1 85 conformable with mafic basaltic rocks landward of the continent ocean transition cot the vp vs ratio in the layer beneath the volcanics is estimated to be 1 67 1 75 these low values suggest that this layer represents sedimentary rocks and that the sand shale ratio might be relatively high here the vp vs ratio in the crystalline basement is estimated to be 1 67 1 75 in the basin and on the landward part of the voring plateau indicating the presence of granitic granodioritic continental crust in the lower crust the vp vs ratio in the basin decreases uniformly from southwest to northeast from 1 85 1 9 to 1 68 1 73 suggesting a gradual change from mafic gabbroic to felsic granodioritic lower crust significant 3 5 azimuthal s wave anisotropy is observed for several sedimentary layers as well as in the lower crust all these observations can be explained by invoking the presence of liquid filled microcracks aligned vertically along the direction of the present day maximum compressive stress nw se

rectification of enso variability by interdecadal changes in the equatorial background mean state in a cgcm simulation the link between the changes in equatorial background stratification and el nino southern oscillation enso modulation is investigated using a simulation from a 260 yr long coupled general circulation model cgcm the work focuses on the role of nonlinearities associated with equatorial wave dynamics as a first step the low frequency change in mean stratification is diagnosed and documented from the shallow water parameters derived from a vertical mode decomposition of the cgcm the parameters vary differently according to the baroclinic mode order which may explain why a flattening thermocline does not necessarily lead to reduced enso activity estimations of baroclinic mode contributions to zonal current anomalies indicate that the decadal variability projects differently for the baroclinic modes as compared to the interannual variability in particular the high order modes associated with decadal variability have a more pronounced signature in the western pacific whereas that associated with interannual variability i e enso shows more energy in the eastern pacific in the light of the results of the cgcm vertical mode decomposition an intermediate coupled model icm is used to test whether the nonlinearities associated with the changes in the baroclinic mode energy distribution can lead to coherent enso modulation the results indicate that rectification of the interannual variability enso time scales by the interdecadal variability associated with changes in the oceanic mean states takes place in the icm the rectified effect results mostly in an increased variability and skewness of the zonal advection which tends to produce a zonal seesaw of the sea surface temperature anomaly a tropical mechanism for producing enso modulation is then proposed that reconciles both the rectified effect resulting from nonlinearities associated with equatorial wave dynamics and the tropical decadal mode of thermocline depth arising from ekman pumping anomalies located in the central south pacific

cenozoic and late mesozoic stratigraphy and subsidence history of the norwegian margin the stratigraphy of the passive continental margin off norway is mapped utilizing both deep sea drilling project dsdp data at five sites on the outer margin and multichannel seismic mcs data collected by lamont doherty geological observatory distinct units in the acoustic stratigraphy are tied to biostratigraphic and lithostratigraphic units in the drill data and mapped throughout most of the margin stratigraphy of the pre lower eocene section not encountered in drilling is inferred from depositional patterns and correlation with the continental shelf sequences the stratigraphy of which has been developed independently from detailed surveys the margin can be divided into three physiographic provinces two broad shelf and slope regions separated by the jan mayen fracture zone and the steep narrow shelf and slope off the lofoten islands each experienced a separate cenozoic subsidence history the voring plateau is partly underlain by oceanic crust it subsided nearly 1 000 m less than expected from thermal contraction but it did so following the development of a relatively deep water environment in the paleocene north of the voring plateau the margin may have subsided a few hundred metres more than thermal studies had predicted there is no evidence for a phase of extensional deformation associated with the inception of spreading the youngest faulted level occurs at the late jurassic level preceding sea floor spreading by nearly 100 ma and deformation in the cretaceous section is characterized by large uplift structures that may be of halokinetic origin the physiographic provinces as well as the cenozoic subsidence patterns along the margin appear to be related to the style and extent of mesozoic basin development and tectonics along the margin

upwelling response to atmospheric coastal jets off central chile a modeling study of the october 2000 event the spatial and temporal variability of nearshore winds in eastern boundary current systems affect the oceanic heat balance that drives sea surface temperature changes in this study regional atmospheric and oceanic simulations are used to document such processes during an atmospheric coastal jet event off central chile the event is well reproduced by the atmospheric model and is associated with the migration of an anomalous anticyclone in the southeastern pacific region during october 2000 a robust feature of the simulation is a sharp coastal wind dropoff which is insensitive to model resolution as expected the simulated oceanic response is a significant sea surface cooling a surface heat budget analysis shows that vertical mixing is a major contributor to the cooling tendency both in the jet core area and in the nearshore zone where the magnitude of this term is comparable to the magnitude of vertical advection sensitivity experiments show that the oceanic response in the coastal area is sensitive to wind dropoff representation this is because total upwelling i e the sum of coastal upwelling and ekman pumping depends on the scale of wind dropoff because the latter is much larger than the upwelling scale coastal wind dropoff has only a weak positive effect on vertical velocities driven by ekman pumping but has a strong negative effect on coastal upwelling interestingly though the weakening of coastal winds in the dropoff zone has a larger effect on vertical mixing than on vertical advection with both effects contributing to a reduction of cooling

improving in situ cosmogenic chronometers new radiocarbon ages for sierra nevada deglaciation the first 10 be measurements from the laurentide terminal moraine and calculations based on paleomagnetic field strength have the potential to substantially improve the accuracy of cosmogenic age estimates specifically three new constraints apply to the interpretation of measured abundances of in situ produced cosmogenic 10be and 26al 1 a suite of minimum limiting radiocarbon dates indicates that the sierra nevada was deglaciated at least several thousand years earlier than assumed when nishiizumi et al 1989 first calibrated 10be and 26 al production rates based on polished bedrock surfaces in the range with retreat beginning by 18 000 cal yr b p and completed by 13 000 cal yr b p 2 concentrations of 10be in moraine boulders and glacier polished bedrock in new jersey show little variance 10 1 and can be used to calculate a preliminary 10be production rate integrated over the past 21 000 22 000 cal yr b p at 41 200 300 m altitude that is about 20 lower than currently accepted 3 calculations of the effect of past geomagnetic field strength variations on production rates suggest that the use of temporally averaged production rates may generate age errors of 20 however cosmogenic exposure ages can be corrected for this effect although the corrections currently are imprecise many previously reported late pleistocene 10be and 26al exposure ages are probably too young and are less accurate and less precise than implied by reported uncertainties the discrepancy between accepted production rates and those calculated from laurentide exposures when considered together with the sierran deglacial chronology and the model results suggest that correlations between cosmogenic and other numerical ages especially for brief events like the younger dryas and heinrich events will not be robust until temporal variations and the altitude latitude scaling of production rates are fully understood and quantified at levels comparable to current analytic uncertainties 3

estimates of the rate of regolith production using and from an alpine hillslope abstract the production of regolith is a fundamental geomorphic process because most surface processes transport only unconsolidated material we use concentrations of the cosmogenic radionuclides crns 10 be and 26 al in regolith and bedrock to deduce the rate of production of regolith on an alpine hillslope in the wind river range wy these calculations are based on a theoretical model which we develop here this model shows that it is important to consider dissolution of regolith in regolith production and in basin averaged erosion rate studies rates of production of regolith are uniform along the hillslope and the mean rates for the entire hillslope deduced from 10 be and 26 al are 14 3 4 0 and 13 0 4 0 m ma 1 respectively rates of production of regolith deduced from 10 be concentrations in regolith mantled bedrock support the rates deduced from regolith concentrations in the alpine environment examined here the rate of production of regolith beneath 90 cm of regolith is nearly twice as fast as the average rate of production of regolith on bare rock surfaces which small et al small e e anderson r s repka j l finkel r 1997 erosion rates of alpine bedrock summit surfaces deduced from in situ 10 be and 26 al earth and planetary science letters 150 413 425 previously documented rock mantled with regolith probably weathers more rapidly than bare rock because the water required for frost weathering is limited on bare rock surfaces because the hillslope examined here is convex with constant curvature and regolith production and thickness are uniform down the slope the regolith volume flux must be proportional to the local slope of the hillside therefore our results are consistent with gilbert s gilbert g k 1909 the convexity of hilltops journal of geology 17 344 350 steady state hillslope hypothesis if tor height and the difference between rates of weathering on bare and regolith mantled rock provide a fair estimate of the age of summit flats steady state hillslope conditions have been attained in less than several million years

tropical pacific baroclinic mode contribution and associated long waves for the 1994 1999 period from an assimilation experiment with altimetric data an ocean general circulation model ogcm of the tropical pacific in which combined topex poseidon and ers sea level anomalies are assimilated over january 1994 through july 1999 is used to investigate equatorial wave characteristics during the intense 1997 1999 el nino la nina event near the equator the linear vertical modes are estimated at each grid point of the ogcm simulation with and without assimilation consistently with an increase of the vertical gradient within the thermocline and a rise of the thermocline depth in the eastern basin the assimilation results in an increased contribution of the higher order baroclinic modes in the eastern basin and a decreased contribution of the first baroclinic mode in the western pacific for the zonal current variability for pressure the first baroclinic mode contribution is reduced whereas the higher order modes contribution is weakly impacted kelvin and first meridional rossby waves are then derived for the first two more energetic baroclinic modes in the simulation with assimilation kelvin waves of both modes constructively contribute to the strong warming observed in 1997 with the first second baroclinic mode being more energetic than the second first baroclinic mode in the early mature stage of the warming kelvin waves of both modes reflect as first meridional rossby waves at the eastern boundary reflection efficiency of 95 and contribute to push back the warm pool westward the reversal of the warming is apparently initiated by the second baroclinic mode contribution which controls the position of the 28 c isotherm in the surface layer in the far eastern pacific from january 1998 at the western boundary reflections of rossby waves take place for both modes with an estimated total efficiency of 50 at 165 e this suggests that in our model the delayed oscillator theory is not applicable for explaining the reversal from warm to cold conditions in 1998 while the zonal advective feedback was at work more generally the study suggests that it is necessary to take into account the vertical structure of the ocean when interpreting altimetric data which can be done through an assimilation experiment

low frequency modulation of intraseasonal equatorial kelvin wave activity in the pacific from soda 1958 2001 intraseasonal equatorial kelvin wave activity iekw at a low frequency in the pacific is investigated using the simple ocean data assimilation soda oceanic reanalyses a vertical and horizontal mode decomposition of soda variability allows estimation of the kelvin wave amplitude according to the most energetic baroclinic modes a wavenumber frequency analysis is then performed on the time series to derive indices of modulation of the iekw at various frequency bands the results indicate that the iekw activity undergoes a significant modulation that projects onto baroclinic modes and is not related in a straightforward manner to the low frequency climate variability in the pacific linear model experiments corroborate that part of the modulation of the iekw is tightly linked to change in oceanic mean state rather than to the low frequency change of atmospheric equatorial variability

second and first baroclinic kelvin modes in the equatorial pacific at intraseasonal timescales 1 topex poseidon sea level and time series from the tao tropical atmosphere ocean array of moorings over 1992 1999 are used to investigate the spatiotemporal characteristics of equatorial kelvin waves in the pacific at period shorter than 180 days spectral analyses show high oceanic energy in two separate bands of period around 70 days and 120 days signals are coherent in both bands all along the equator ocean general circulation model ogcm simulations forced by different wind stress fields are also analyzed and exhibit the same features observed and modeled sea level dynamic height and 20 c isotherm depth band pass filtered around 70 days show an eastward propagation at phase speed of 2 4 2 9 m s 1 typical of the first baroclinic kelvin mode the meridional and vertical structures of the equatorial waves at the onset of the 1997 el nino are also those expected for a first kelvin mode at 120 day period phase speeds meridional and vertical structures are closer to those expected for a second baroclinic mode both modes are nevertheless present in the two frequency bands a simple kelvin wave model shows that the wind at 120 day period seems to force the kelvin waves at the same period however the predominance of second baroclinic mode at 120 day period cannot be explained solely by the characteristics of the wind ogcm simulations rather suggest the importance of internal oceanic processes such as vertical redistribution of energy from first to second baroclinic mode as the waves propagate eastward model outputs over 1984 1999 indicate that these equatorial kelvin waves at 70 and 120 day period may have an effect on el nino since they seem to be stronger at its onset

polyphase rift evolution of the voring margin mid norway constraints from forward tectonostratigraphic modeling the mid norwegian voring margin bounding the northern atlantic underwent several rift episodes after the caledonian orogeny permo triassic extension concentrated at the eastern inner margin followed by jurassic cretaceous extension at the center of the margin finally more westward the last rift episode led to continental breakup in the earliest eocene although the general architecture of the margin may be clear the timing and distribution of particularly the oldest rift structures are poorly constrained we use two dimensional forward tectonostratigraphic modeling for better quantitative understanding of the tectonic evolution of the margin two regional profiles crossing the margin have been analyzed modeling of the two profiles integrates the basin shape and fill as well as the underlying crustal structure of the margin the modeling allows us 1 to quantify the distribution and timing of extension of subsequent rift episodes 2 to predict the basin and crustal architecture at deep levels and 3 to test different interpretations of the seismic data the level of lithospheric necking during basin formation is constrained by basement topography and moho depth and lies within the middle crust 20 km furthermore we investigate the migration of the rift axes and the elastic lithospheric strength during the different rift episodes locations of previous extension are not reactivated during renewed rifting instead renewed rifting occurs preferentially in regions where the lithosphere has experienced less extension

southern hemisphere origins of the 1976 climate shift 1 observations from the tropical pacific ocean identify an abrupt climate shift in 1976 with surface temperatures changing from cooler than normal to warmer than normal in the span of about 1 year model results show that this climate shift originates with subsurface temperature anomalies in the south tropical pacific ocean which propagate first to the western boundary then northward to the equator and finally eastward along the equator to 140 w where they rise to the surface the results suggest that changes in the north pacific respond to changes in the tropical pacific

change in el nino flavours over 1958 2008 implications for the long term trend of the upwelling off peru abstract the tropical pacific variability has experienced changes in its characteristics over the last decades in particular there is some evidence of an increased occurrence of el nino events in the central pacific a k a central pacific el nino cp el nino or el nino modoki in contrast with the cold tongue or eastern pacific ep el nino which develops in the eastern pacific here we show that the different flavours of el nino imply a contrasted equatorial kelvin wave ekw characteristic and that their rectification on the mean upwelling condition off peru through oceanic teleconnection is changed when the cp el nino frequency of occurrence increases the simple ocean data assimilation soda reanalysis product is first used to document the seasonal evolution of the ekw during cp and ep el nino it is shown that the strong positive asymmetry of enso el nino southern oscillation is mostly reflected into the ekw activity of the ep el nino whereas during cp el nino the ekw is negatively skewed in the eastern pacific along with slightly cooler conditions off peru shallow thermocline during cp el nino this is favourable for the accumulation of cooler sst anomalies along the coast by the remotely forced coastal kelvin wave such a process is observed in a high resolution regional model of the humboldt current system using the soda outputs as boundary conditions in particular the model simulates a cooling trend of the sst off peru although the wind stress forcing has no trend the model is further used to document the vertical structure along the coast during the two types of el nino it is suggested that the increased occurrence of the cp el nino may also lead to a reduction of mesoscale activity off peru

basin structure on the norwegian margin from analysis of digitally recorded sonobuoys during r v robert d conrad cruise 21 a large number of sonobuoys were recorded in the voring more and adjacent basins at the margin off norway the digital sonobuoy data have been transformed into the domain of intercept time tau and ray parameter p and inverted by the tau sum method to obtain better definition of the near seafloor velocities using also the precritical energy a move out correction has been applied to the tau p data conventional analyses of the x t data were also performed in general the various types of analyses complement each other and should be used interactively together with forward modeling to obtain the optimal velocity depth function the sonobuoy results have outlined in a regional sense the pre cenozoic sedimentary basin at the margin this basin attains a maximum sediment thickness of 8 10 km of which only the upper half is defined by seismic reflection profiling at the outer margin the marginal escarpments form major discontinuities in the lateral velocity distribution the survey has proven that sonobuoy profiles recorded during standard seismic reflection profiling in major marginal basins may provide important new information particularly about the deeper parts of the basins that is not directly available from the reflection profiles

modes of covariability between sea surface temperature and wind stress intraseasonal anomalies along the coast of peru from satellite observations 2000 2008 1 the tropical rainfall measuring mission microwave imager sea surface temperature sst and quikscat wind stress satellite data are used to investigate the intraseasonal upwelling variability along the coat of peru over the period 2000 2008 two regions of peak variance correspond to the central peru region pisco region 15 s and the northern peru region piura region 5 s a covariance analysis reveals a significant coherency between winds and sst anomalies off pisco consistent with ekman pumping and transport dynamics the upwelling cell consists in a meridionally extended fringe of colder warmer water extending as far as 250 km from the coast at 15 s in the piura region the intraseasonal covariability pattern is represented by two modes one relevant to the direct ekman dynamics and the other one associated with the remote forcing of intraseasonal oceanic kelvin wave two regimes of variability are evidenced a low period regime 10 25 days is the signature of ekman transport pumping dynamics and is remotely forced by the migratory atmospheric disturbances across the southeastern pacific anticyclone a high period regime 35 60 day band is associated with the combined forcing of oceanic equatorial kelvin waves and migratory atmospheric disturbances in the midlatitudes in particular the modes of covariability exhibit a prominent 50 day period energy peak it is shown that this period arises from the impact of the first two baroclinic modes kelvin wave with the second baroclinic mode kelvin wave being more influential on the piura region

the non layering of gravel streambeds under ephemeral flood regimes abstract the two layer format common to perennial streambeds in which a relatively coarse armour overlies a finer subarmour develops as a function of both the ingress and subsequent near surface winnowing of interstitial material and the selective non entrainment or slower transport velocity of coarse clasts ephemeral streams appear to lack such vertical layering or are characterized by weak layer development some of this may be due to the degree of mixing associated with the scour and fill process however continuous monitoring of bedload discharge in the nahal yatir in the northern negev desert reveals that sediment transport rates are extremely high so that the chance of armour layer development through selective non entrainment is much reduced indeed a comparison of the bedload and bed material size distributions confirms a high degree of similarity and hints at equal mobility regardless of clast size the monitoring programme also indicates that the bed becomes highly mobile at comparatively modest fluid shear so that practically all floods are associated with high transport rates consequently the winnowing that might be brought about by low transport rate events does not occur even within a single event winnowing is precluded by the rapid nature of flow recession that is so characteristic of flash floods the high degree of bed material mobility is attributable in part to the lack of strength that would otherwise be a corollary of armour development however it also highlights the divergent nature of the feedback loops that govern the relationship between flow and channel deposit in ephemeral and perennial systems

modelling shear waves in obs data from the voring basin northern norway by 2 d ray tracing three component recordings from an array of five ocean bottom seismographs in the northwestern part of the voring basin have been used to obtain a 2 d shear wave s wave velocity depth model the shear waves are identified by means of travel time differences compared to the compressional p waves and by analyzing their particle motions the model has been obtained by kinematic travel time ray tracing modelling of the obs horizontal components

timing of surficial process changes down a mojave desert piedmont abstract we measured 10 be and 26 al in 29 sediment samples to infer the history and millennial scale rates of change down a low gradient piedmont a common but enigmatic landform that dominates the mojave desert nuclide data suggest that a large volume of sediment was deposited on the proximal east range road piedmont in fort irwin california 75 500 yr ago since then this material has been stable or eroding slowly in contrast on the distal piedmont 3 5 km from the upland source basins soil stratigraphy suggests that there have been alternating periods of surface stability erosion and deposition over the last 70 000 yr nuclide data from samples amalgamated along cross piedmont transects suggest that long term average down gradient sediment speeds range from 9 cm yr 1 near the uplands to 22 cm yr 1 6 km down piedmont these speeds are similar to 10 be estimated sediment speeds down three other piedmonts in the mojave desert suggesting that piedmont surface morphologies dominated by shallow migrating channels have similar sediment transport rates the timing of surface process change down the east range road piedmont is determined by a combination of sediment available in the source basins sediment transport rates and the size of the piedmont

rock lithology and porosity determination from shear and compressional wave velocity data examined in this study are previously published laboratory shear s and compressional p wave velocity measurements on water saturated sandstone calcareous sandstone dolomite and limestone cores as well as laboratory porosity measurements on the sandstone and limestone cores sandstone and limestone porosities range from 092 to 299 and from 006 to 229 respectively differential pressure was varied from 500 to 6000 psi corresponding to approximate burial depths from 290 to 3460 m respectively sandstone limestone and dolomite are effectively separated by poisson s ratio or equivalently by the ratio of p to s wave velocity separation of sandstone and limestone appears to result from the difference in of the matrix material namely quartz 056 and calcite 316 respectively an empirical function 1 v a b was fit by regression analysis to sandstone and limestone velocity vs and vp versus porosity values at each differential pressure in this equation a and b are const

crustal structure and evolution of the southern voring basin and voring transform margin ne atlantic abstract the dominantly passive volcanic voring and more margins ne atlantic are separated by the 200 km long voring transform margin vtm the southern voring basin and the vtm have been studied by use of four regional ocean bottom seismograph obs profiles combined by gravity modelling the models demonstrate a complex pattern of magmatism along the transform margin the distribution of magmatism seems to be related to the existence and trend of a lower crustal 8 km s body interpreted as eclogitized rocks present in the southern voring basin early tertiary breakup related magmatic leakage across the continent ocean transition cot appears to be facilitated where this layer is absent these results support earlier workers who have concluded that the jan mayen fracture zone originated from a caledonian zone of weakness we propose that partly eclogitized rocks were uplifted into the lower crust close to this zone during the caledonian orogeny and that this body acted as a barrier to magma emplacement during the late cretaceous early eocene phase of rifting breakup the eclogitized terrain also appears to have caused northeastward channeling of the late cretaceous early tertiary intrusions within the voring basin an up to 10 km thick pre cretaceous sedimentary basin in the southern voring basin may be genetically related to the ns trending late paleozoic and mesozoic rift basins in north east greenland

influence of oceanic intraseasonal kelvin waves on eastern pacific hurricane activity abstractrecent studies have highlighted the role of subsurface ocean dynamics in modulating eastern pacific epac hurricane activity on interannual time scales in particular the well known el nino southern oscillation enso recharge discharge mechanism has been suggested to provide a good understanding of the year to year variability of hurricane activity in this region this paper investigates the influence of equatorial subsurface subannual and intraseasonal oceanic variability on tropical cyclone tc activity in the epac that is to say it examines previously unexplored time scales shorter than interannual in an attempt to explain the variability not related to enso using ocean reanalysis products and tc best track archive the role of subannual and intraseasonal equatorial kelvin waves ekw in modulating hurricane intensity in the epac is examined it is shown first that these planetary waves have a clear control on the subannual and intraseasonal variability of thermocline depth in the epac

crustal structure and transform margin development south of svalbard based on ocean bottom seismometer data abstract the barents sea is located in the northwestern corner of the eurasian continent where the crustal terrain was assembled in the caledonian orogeny during late ordovician and silurian times the western barents sea margin developed primarily as a transform margin during the early tertiary in the northwestern part south of svalbard multichannel reflection seismic lines have poor resolution below the permian sequence and the early post orogenic development is not well known here in 1998 an ocean bottom seismometer obs survey was collected southwest to southeast of the svalbard archipelago one profile was shot across the continental transform margin south of svalbard which is presented here p wave modeling of the obs profile indicates a caledonian suture in the continental basement south of svalbard also proposed previously based on a deep seismic reflection line coincident with the obs profile the suture zone is associated with a small crustal root and westward dipping mantle reflectivity and it marks a boundary between two different crystalline basement terrains the western terrain has low 6 2 6 45 km s 1 p wave velocities while the eastern has higher 6 3 6 9 km s 1 velocities gravity modeling agrees with this as an increased density is needed in the eastern block the s wave data predict a quartz rich lithology compatible with felsic gneiss to granite within and west of the suture zone and an intermediate lithological composition to the east a geological model assuming westward dipping caledonian subduction and collision can explain the missing lower crust in the western block by subduction erosion of the lower crust as well as the observed structuring due to the transform margin setting the tectonic thinning of the continental block during opening of the norwegian greenland sea is restricted to the outer 35 km of the continental block and the continent ocean boundary cob can be located to within 5 km in our data distinct from the outer high commonly observed on transform margins the upper part of the continental crust at the margin is dominated by two large rotated down faulted blocks with throws of 2 3 km on each fault apparently formed during the transform margin development analysis of the gravity field shows that these faults probably merge to one single fault to the south of our profile and that the downfaulting dominates the whole margin segment from spitsbergen to bjornoya south of bjornoya the faulting leaves the continental margin to terminate as a graben 75 km south of the island adjacent to the continental margin there is no clear oceanic layer 2 seismic signature however the top basement velocity of 6 55 km s 1 is significantly lower than the high 7 km s 1 velocity reported earlier from expanding spread profiles esps and we interpret the velocity structure of the oceanic crust to be a result of a development induced by the 7 8 km thick sedimentary overburden

late quaternary history of the chemehuevi mountain piedmont mojave desert deciphered using 10be and 26al we used the cosmogenic nuclides 10 be and 26 al as cosmic ray dosim eters to track sediment movement across the incised chemehuevi mountain piedmont surface the piedmont extends 12 km from highland source basins to an ephemeral wash at the toe of the piedmont nuclide activity in sediment from steep source basins and from the bedrock pediment allows us to estimate rates of sediment generation and thus the rate at which sediment is supplied to the piedmont from weathering rock analysis of amalgamated sediment samples collected along 4 km long transects spaced at 1 km intervals from the mountain front provide context for understanding nuclide activity in sediment samples collected from two soil pits and demonstrate that sediment steadily moves down the channel network samples from the two soil pits allow for estimates of sediment deposition rates and thus further illuminate piedmont history model results suggest that the chemehuevi mountains are eroding about 40 mm ky 1 whereas the mountain proximal bedrock pediment and the interpiedmont saw tooth range are eroding more slowly 10 to 21 mm ky 1 and 9 5 mm ky 1 respectively cosmogenic nuclide profiles in two soil pits suggest a complex history of deposition at rates between 19 to 39 mm ky 1 and stability over the past 60 ky a change in process from sediment deposition to sediment transport occurred distally on the piedmont approximately 8 ky ago while the mid piedmont piedmont surface has been stable since the mid holocene the incised chemehuevi mountain piedmont is changing at rates similar to planar and uniformly active piedmonts such as those adjacent to the iron and granite mountains all three piedmonts have average sediment grain velocities of decimeters per year long term source basin erosion rates between 35 to 40 mm ky depositional hiatuses around the pleistocene holocene climatic transition from moister to drier conditions and pleistocene deposition rates of 18 to 39 mm ky such similarity in piedmont behavior despite clear differences in morphology and appearance might suggest large scale geologic and climatic controls on the generation transport and deposition of sediment in the mojave desert

stone movement on hillslopes in the mojave desert california a 16 year record previous research has shown that either hydraulic action or creep may be the dominant process transporting coarse debris down hillslopes in the american southwest this study analyses the movement over 16 years of painted stones on two hillslopes in the central mojave desert to ascertain which of these two processes dominate in this region the distance moved m is found to be directly related to length of overland flow x and hillslope gradient s and inversely related to particle size d the fact that m is more highly correlated with x than with s suggests that hydraulic action rather than creep is the dominant process it is concluded that this is probably the case over most of the mojave and sonoran deserts on slopes up to at least 24 and that it is only at higher elevations where winters are more severe that creep may become dominant

mechanisms of tropical pacific interannual to decadal variability in the arpege orca global coupled model spatial and temporal structures of interannual to decadal variability in the tropical pacific ocean are investigated using results from a global atmosphere ocean coupled general circulation model the model produces quite realistic mean state characteristics despite a sea surface temperature cold bias and a thermocline that is shallower than observations in the western pacific the periodicity and spatial patterns of the modelled el nino southern oscillations enso compare well with those observed over the last 100 years although the quasi biennial timescale is dominant lag regression analysis between the mean zonal wind stress and the 20 c isotherm depth suggests that the recently proposed recharge oscillator paradigm is operating in the model decadal thermocline variability is characterized by enhanced variance over the western tropical south pacific 7 s the associated subsurface temperature variability is primarily due to adiabatic displacements of the thermocline as a whole arising from ekman pumping anomalies located in the central pacific south of the equator related wind anomalies appear to be caused by sst anomalies in the eastern equatorial pacific this quasi decadal variability has a timescale between 8 years and 20 years the relationship between this decadal tropical mode and the low frequency modulation of enso variance is also discussed results question the commonly accepted hypothesis that the low frequency modulation of enso is due to decadal changes of the mean state characteristics

using 10be and 26al to determine sediment generation rates and identify sediment source areas in an arid region drainage basin we measured 10 be and 26 al in 64 sediment and bedrock samples collected throughout the arid 187 km 2 yuma wash drainage basin southwestern arizona from the measurements we determine long term time integrated rates of upland sediment generation 81f 5gm 2 year 1 and bedrock equivalent lowering 30f 2mm a 1 consistent with other estimates for regions of similar climate lithology and topography in a small f 8k m 2 upland sub basin differences in nuclide concentrations between bedrock outcrops and hillslope colluvium suggest weathering of bedrock beneath a colluvial cover is a more significant source of sediment 4010 4 kg year 1 than weathering of exposed bedrock surfaces 1010 4 kg year 1 mixing models constructed from nuclide concentrations of sediment reservoirs identify important sediment source areas hillslope colluvium is the dominant sediment source to the upper reaches of the sub basin channel channel cutting of alluvial terraces is the dominant source in the lower reaches similarities in nuclide concentrations of various sediment reservoirs indicate short sediment storage times 10 3 years nuclide concentrations measured in channel sediment from tributaries of yuma wash and in samples collected along the length of the wash were used to construct mixing models and determine sediment sources to the main stem channel we find an exponential decrease in the channel nuclide concentrations with distance downstream suggesting that as much as 40 of sediment discharged from yuma wash has been recycled from storage within basin fill alluvium sediment generation and denudation rates determined from the main stem are greater 25 than rates determined from upland sub basins suggesting that currently sediment may be exported from the basin more quickly than it is being generated in the uplands independence of nuclide concentration and sediment grain size indicates that channels transport sediment in discrete pulses before rapidly depositing poorly sorted material suggesting that differences in transport times for different size materials are minimal d 2002 elsevier science b v all rights reserved

fluvio pedogenic processes in an ephemeral stream channel nahal yael southern negev israel abstract a detailed stratigraphic survey conducted in the alluvial fill of the channel of nahal yael a small catchment in the southern negev desert indicates the existence of a continuous compacted red colored unit at an average depth of 50 cm beneath the surficial grey non cohesive alluvium granulometric distinction between the grey and the red alluvium is evident only within the fine

equatorially forced intraseasonal propagations along the peru chile coast and their relation with the nearshore eddy activity in 1992 2000 a modeling study 1 a regional eddy resolving oceanic model spanning the 1992 2000 period is used to study the influence of 50 to 80 day intraseasonal equatorial kelvin waves iekw on mesoscale eddy activity off the west coast of peru and northern and central chile the model is shown to realistically simulate nearshore intraseasonal sea level variability poleward propagation of equatorially forced coastal trapped waves along the coastal waveguide and offshore variability related to mesoscale eddies and rossby waves rw in agreement with linear theory rw are confined equatorward of 12 s in the 50 80 days period range south of that critical latitude westward propagation is dominated by energetic mesoscale signals resulting mainly from coastal flow instability sensitivity experiments to the open boundary conditions are then used to estimate to what extent eddy activity is impacted by the remote equatorial forcing a coastal increase in eddy kinetic energy related to the energetic 60 day iekw activity present in the open boundary forcing is evidenced and is largest off northern peru whereas no major changes are observed offshore additional regional simulations with different open boundary conditions corroborate our findings and suggest that this limited effect of iekw on the offshore eddy kinetic energy may be a robust feature citation belmadani a v echevin b dewitte and f colas 2012 equatorially forced intraseasonal propagations along the peru chile coast and their relation with the nearshore eddy activity in 1992 2000 a modeling study j geophys res 117 c04025 doi 10 1029 2011jc007848

rock to sediment slope to sea with 10be rates of landscape change abstract measurements of cosmogenic nuclides predominately 10be allow new insights into the ways in which and the rates at which sediment is generated transported and deposited over timescales ranging from 103 to 106 years samples from rock exposures are used to estimate erosion rates at points on the landscape whereas samples of fluvial sediment provide estimates of basin scale rates of denudation integrated over 104 km2 nuclide data show that hilltop bare rock outcrops erode more slowly than basins as a whole suggesting the potential for relief to increase over time as well drained outcrops grow higher more elaborate experiments and interpretive models provide insight into the distribution of hillslope processes including the bedrock to soil conversion rate which appears to increase under shallow soil cover and then decrease under deeper soils changes in average nuclide activity down slopes can be used to estimate grain speed over millennia suggesting for example that sediment o

sensitivity of the northern humboldt current system nearshore modeled circulation to initial and boundary conditions 1 the influence of the eastern pacific equatorial circulation on the dynamics of the northern humboldt current system is studied using an eddy resolving regional circulation model forced by boundary conditions from three distinct ocean general circulation models the seasonal variability of the modeled nearshore circulation and the mesoscale activity are contrasted in order to evaluate the role of the density forcing the seasonal variability of the surface and subsurface alongshore currents strongly depends on the amplitude and timing of the seasonal eastward propagating equatorial waves the equatorward flow and upwelling intensity are also impacted by nonlinear processes such as the seasonal generation of nearshore mesoscale eddies which create alongshore pressure gradients modulating the surface current boundary conditions affect differently the intensity and phase of the eddy kinetic energy as baroclinic instability is triggered by coastal waves during austral summer and fall whereas it is sustained by the wind driven upwelling during austral winter

habitat of hydrocarbons on the norwegian continental shelf eds a m spenceret al norwegian petroleum society graham and trotman 1986 isbn 0 86010 833 3 price 65 00

interannual long equatorial waves in the tropical atlantic from a high resolution ocean general circulation model experiment in 1981 2000 we investigate the tropical atlantic vertical structure variability 1981 2000 based on the clipper ocean general circulation model ogcm we aim at determining to what extent the observed interannual variability can be explained by the low frequency wave dynamics the linear vertical modes of the ogcm climatological stratification are estimated along the equator the baroclinic mode contributions to surface zonal current and sea level anomalies are calculated and analyzed at interannual timescales the second baroclinic mode is the most energetic the first third mode exhibits a variability peak in the west east the summed up contribution of the high order baroclinic modes 4 6 is as energetic as the gravest modes and is largest in the east wave components are then derived by projection onto the associated meridional structures the effect of longitudinal boundaries near the equator is taken into consideration equatorial kelvin and rossby waves propagations with phases speed close to the theory are identified for the first three baroclinic modes the comparison with a multimode linear simulation corroborates the propagating properties of the ogcm waves coefficients an estimation of the meridional boundary reflection efficiency indicates that wave reflections take place at both boundaries a 65 reflection efficiency is found at the eastern boundary our study suggests that low frequency wave dynamics is to a large extent at work in the tropical atlantic on the basis of what is known on the pacific el nino southern oscillation mode this may provide a guidance for investigating ocean atmosphere mechanisms that can lead to the atlantic zonal equatorial mode

observed relationships between oceanic kelvin waves and atmospheric forcing abstract the madden julian oscillation mjo has been implicated as a major source of the wind stress variability that generates basin scale kelvin waves in the equatorial pacific one source of debate concerning this relationship is the apparent difference in the frequencies of the two processes this work utilizes data from the tropical atmosphere ocean tao array of moored buoys along with outgoing longwave radiation data to show by means of a multiple linear regression model and case studies that the frequency discrepancy is due to a systematic decrease in the phase speeds of the kelvin waves and an increase in the period of the waves toward the east as conditions adjust toward el nino among the potential contributing factors to this phase speed decrease is an apparent air sea interaction that enhances the wind forcing of some of the kelvin waves allowing them to continue to amplify because the propagating wind stress anomaly decelerates to the speed of the developing kelvin wave instead of the sig

sensitivity analysis of pediment development through numerical simulation and selected geospatial query abstract dozens of references recognizing pediment landforms in widely varying lithologic climatic and tectonic settings suggest a ubiquity in pediment forming processes on mountain piedmonts worldwide previous modeling work illustrates the development of a unique range in arid semiarid piedmont slope 3 m y 1 restrict pediment development by fostering piedmont incision and or wholesale removal stripping of regolith mantles prior to footslope pediment development simulations illustrate an insensitivity to alternating layers of sandstone and shale 3 15 m thick oriented in various geometric configurations vertical horizontal and dip slope and generating different regolith hydrologic properties and exhibiting weathering rate variations up to 3 fold higher fluxes and residence times of subsurface groundwater in more humid environments as well as dissolution type weathering lead to a thickening of regolith mantles on erosional piedmonts on the order of 10 1 m and an elimination of pediment morphology an initial test of the model sensitivity analysis in arid semiarid environments for which field reconnaissance and detailed geomorphic mapping indicate the presence of pediments controlled by climatic conditions soil hydrologic properties vegetation characteristics and bedrock weathering style that are known and constant supports our modeling results that pediments are more prevalent in hydrologically open basins

sensitivity of an intermediate ocean atmosphere coupled model of the tropical pacific to its oceanic vertical structure an intermediate ocean atmosphere coupled model icm of the tropical pacific is used to investigate the sensitivity of the coupled system to the oceanic vertical structure the model consists of a three baroclinicmode tropical pacific ocean and a gill tropical atmosphere the mixed layer is similar to the zebiak and cane zc coupled atmosphere ocean model but uses a different parameterization for subsurface temperature derived from xbt data a 100 yr simulation is made and the long term variability of the icm is briefly discussed and compared with the the observations and the zc model the icm reproduces regular enso events with a spectrum peak centered at the period 3 5 yr the presence of higher order vertical modes in the oceanic component of the model allows for reduced off equatorial variability of zonal current and thermocline anomalies and for finer meridional scale for sst anomaly variability in comparison with a simulation with one baroclinic mode only the nature of the processes sustaining the oscillations in the icm is then investigated based on the coupled instabilities and delayed oscillator theories it

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

seasonal dependence of the mjo enso relationship abstract observations of the development of recent el nino events suggest a pivotal role for the madden julian oscillation mjo previous attempts to uncover a systematic relationship between mjo activity and the el nino southern oscillation enso however have yielded conflicting results in this study the mjo enso relationship is stratified by season and the focus is on mjo activity in the equatorial western pacific the results demonstrate that mjo activity in late boreal spring leads el nino in the subsequent autumn winter for the period 1979 2005 spring is the season when mjo activity is least asymmetric with respect to the equator and displays the most sensitivity to sst variations at the eastern edge of the warm pool enhanced mjo activity in the western pacific in spring is associated with an eastward expanded warm pool and low frequency westerly surface zonal wind anomalies these sustained westerly anomalies in the western pacific are hypothesized to project favorably onto a developing el n

dating soils and alluvium with cosmogenic 21ne depth profiles case studies from the pajarito plateau new mexico usa abstract 21 ne depth profiles measured from amalgamated samples of sand sized quartz from the quaternary bandelier tuff were used to estimate inheritance corrected exposure ages in stream terraces and an alluvial fan on the pajarito plateau stable alluvium and associated soils display a downward decreasing type i nuclide profile pattern bioturbated colluvium with uniform type iii nuclide concentrations has buried these alluvial surfaces another possible profile type with downward increasing nuclide concentrations type ii is described but was not found on the pajarito plateau we present mathematical models for each of the profile patterns relating nuclide concentration to inheritance time averaged bulk density and either exposure time or burial rate curve fits of type i profiles are used to estimate the age of alluvial landforms a burial correction technique for deposits buried by younger colluvium is also presented inheritance and burial corrected 21 ne surface exposure ages of 144 17 ka and 63 8 ka for two pajarito plateau stream terraces agree within error with independent soil profile development index dates of 160 ka and 68 78 ka a soil overlying the 50 60 ka el cajete pumice yields an inheritance corrected 21 ne exposure age of 44 11 ka that also agrees closely with a 14 c age on soil charcoal of 41 ka these results demonstrate that reliable cosmogenic 21 ne exposure ages can be obtained for fine grained alluvial surfaces with the depth profile technique

seismic anisotropy inferred from wide angle reflections off lofoten norway indicative of shear aligned minerals in the upper mantle abstract data from six three component ocean bottom seismographs situated on a 175 km long profile on the continental shelf off lofoten northern norway have been modelled using 2 d seismic ray tracing and p and s wave velocity models for the upper mantle are presented a dipping structure about 10 km below the moho causes strong p and s reflections as well as p to s conversions this upper mantle reflection might be related to a possible seaward dipping master fault and or the presence of partially hydrated peridotite the modelling of these arrivals reveals significant seismic anisotropy in the upper mantle the maximum p wave anisotropy is inferred to be in excess of 15 the maximum s wave anisotropy in the order of 5 10 and the axis of the fast velocity is inferred to be inclined at least 45 from the horizontal the strong anisotropy for p waves indicates that its cause is related to alignment of minerals we postulate that the inferred steep inclination of anisotropic minerals might be a result of shearing along faults and fractures during post caledonian extensional episodes it must be emphasized however that it cannot be excluded that more complicated anisotropic models with other geological implications can also explain the observations satisfactorily the study demonstrates the importance of incorporating s waves in analysis of seismic data because the strong p wave anisotropy would not have been discovered without the constraints given by the s waves

abrupt shift in subsurface temperatures in the tropical pacific associated with changes in el nino radiocarbon 14c content of surface waters inferred from a coral record from the galapagos islands increased abruptly during the upwelling season july through september after the el nino event of 1976 sea surface temperatures ssts associated with the upwelling season also shifted after 1976 the synchroneity of the shift in both 14c and sst implies that the vertical thermal structure of the eastern tropical pacific changed in 1976 this change may be responsible for the increase in frequency and intensity of el nino events since 1976

crustal transect from the north atlantic knipovich ridge to the svalbard margin west of hornsund the crustal structure along a 312 km transect stretching from the axial mountains of the north atlantic knipovich ridge to the continental shelf of svalbard has been obtained using seismic reflection data and wide angle obs data the resulting seismic vp and vs models are further constrained by a 2 d gravity model the principal objective of this study is to describe and resolve the physical and compositional properties of the crust in order to understand the processes and creation of oceanic crust in this extremely slow spreading counterpart of the north atlantic ridge systems vp is estimated to be 3 50 6 05 km s for the upper oceanic crust oceanic layer 2 with a marked increase away from the ridge the measured vp of 6 55 6 95 km s for oceanic layer 3a and 7 10 7 25 km s for layer 3b both with a vp vs ratio of 1 81 except for slightly higher values at the ridge axis does not allow a clear distinction between gabbro and mantle derived peridotite 10 40 serpentized the thickness of the oceanic crust varies a lot along the transect from the minimum of 5 6 km to a maximum of 8 1 km the mean thickness of 6 7 km for the oceanic crust is well above the average thickness for slow spreading ridges 10 mm year half spreading rate the areas of increased thickness could be explained by large magma production rates found in the zones of axial highs at the ridge axis which also have generated the off axial highs adjacent the ridge we suggest that these axial and off axial highs along the ridge control the lithological composition of the oceanic crust this approach suggests normal gabbroic oceanic crust to be found in the areas bound by the active magma segments the axial and off axial highs and mantle derived peridotite outside these zone

vertical structure variability in the equatorial pacific before and after the pacific climate shift of the 1970s 1 oceanic baroclinic modes in the equatorial pacific are estimated using results from the soda system our result suggests that the vertical stratification increases at the upper levels after the late 1970s due to changes in the vertical temperature structure after the late 1970s the variability of the higher order baroclinic mode contributions to current anomalies and surface pressure significantly increases in the central equatorial pacific this is associated with an increase of the dominant period of the enso variability simple coupled model experiments indicate that when atmospheric forcing projects more onto the higher baroclinic modes according to the results of the soda decomposition the amplitude and dominant period of enso increase similarly to what is observed at the pacific decadal shift our results support that the changes in the behavior of enso after the late 1970s are associated with oceanic vertical structural changes in temperature that tend to increase the contribution of higher order baroclinic modes

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

continent ocean transition on the voring plateau ne atlantic derived from densely sampled ocean bottom seismometer data 1 a 180 km long seismic wide angle profile was acquired across the voring plateau ne atlantic using a tuned air gun array and three component ocean bottom seismometers deployed with 5 km spacing the seismic p wave data have been modeled by ray tracing inversion and the model has been constrained by s wave and gravity modeling the data and modeling have allowed us to depict the crustal structure and nature of the continent ocean transition cot in a classical volcanic margin case the p wave velocity near the top of the main crustal layer is estimated to 6 0 km s landward of the 25 km wide cot the seaward increase to 6 5 km s in the cot is conformable with heavily intruded continental crust within this zone farther seaward the velocity increase to 6 9 km s in the same layer suggests the presence of oceanic crust the abundant magmatism landward of and within the cot is primarily observed as extrusives forming wedges of seaward dipping reflectors and mafic lower crustal intrusions underplating the maximum thickness of the oceanic crust is measured to 23 5 km at the seaward termination of the cot

spatially averaged long term erosion rates measured from in situ produced cosmogenic nuclides in alluvial sediment spatially averaged erosion rates of small catchments can be accurately inferred from the concentrations of cosmogenic nuclides in stream sediment here we test this technique at two catchments by comparing erosion rates inferred from cosmogenic nuclides with rates of alluvial fan deposition over the past 16 000 years these two independent estimates agree within one standard error demonstrating that cosmogenic nuclide signatures of stream sediment can be used to measure spatially averaged long term erosion rates using this technique we show that long term erosion rates are an exponential function of average hillslope gradient at these sites

the central pacific el nino intraseasonal kelvin wave in this study we document and interpret the characteristics of the intraseasonal kelvin wave iskw in the pacific over the 1989 2011 period based on observations a linear model and the outputs of an ocean general circulation model ogcm we focus on the wave activity during the central pacific cp el nino events contrasting with the extraordinary el nino of 1997 1998 we find that the iskw activity is enhanced in austral summer spring in the central pacific west of 120 w during cp el nino events the linear model experiment indicates that the austral summer peak is wind forced while the austral spring peak is not and consequently results from nonlinear processes in addition a strong dissipation of the iskws is observed east of 120 w which cannot be accounted for by a linear model using a rayleigh friction a vertical and horizontal mode decomposition of the ogcm simulation further confirms the sharp changes in characteristics of the iskws as well as the reflection of the latter into first meridional rossby wave at the longitude where the maximum zonal gradient of the thermocline is found 120 w our analysis suggests that the confinement of cp el nino warming in the central pacific may result from the reinforcement of the zonal gradient in stratification associated with the la nina like conditions since the late of the 1990s leading to scattering of the energy of the iskws in the eastern pacific

regolith thickness instability and the formation of tors in arid environments 1 we present model results suggesting that a physical erosion bedrock weathering feedback is responsible for the development of isolated bedrock knobs tors inselbergs that often punctuate otherwise smooth pediments of homogeneous basement lithology tors and larger more heavily jointed and morphologically complex exposures inselbergs may arise as a consequence of fluctuations in rainfall and sediment transport conditions combined with a bedrock weathering mechanism that depends on regolith thickness hydrogeochemical considerations and field observations in arid granitic environments suggest that the relationship between weathering rate and regolith thickness exhibits a maximum for a finite thickness of cover we have encapsulated this simple erosion weathering feedback in a numerical model simulating arid semiarid landscape evolution that produces low sloping pediments punctuated by tors tors form during periods of higher effective moisture resulting in local base level incision and regolith thinning on pediments invoking a transition in which mantled surfaces lower at rates exceeding the bare bedrock weathering rate this condition favors the emergence and growth of tors in areas covered by regolith thickness less than a threshold value subsequent shifts in climate or local base level that restore sediment surface lowering rates less than the bare bedrock weathering rate will lead to a progressive decrease in tor height and ultimately their disappearance thus according to this model tors in arid environments represent possibly transient features related to fluctuations in climate or local transport conditions rather than palimpsests of an ancient landscape derived from differential subsurface weathering followed by regolith stripping

dating of raised marine and lacustrine deposits in east greenland using beryllium 10 depth profiles and implications for estimates of subglacial erosion here we combine 10be depth profile techniques applied to late glacial ice contact marine and lacustrine deltas as well as boulder exposure dating of associated features in the scoresby sound region east greenland to determine both the surface age and the magnitude of cosmogenic nuclide inheritance boulder ages from an ice contact delta in northern scoresby sund show scatter typical of polar regions and yield an average age of 12 8 0 5 ka about 2 ka older than both our average profile surface age of 10 9 0 7 ka from three depth profiles and a radiocarbon based estimate on the other hand boulder exposure ages from a set of moraines in southern scoresby sund show excellent internal consistency for polar regions and yield an average age of 11 6 0 2 ka the profile surface age from a corresponding ice contact delta is 8 1 0 9 ka while a second delta yields an age of 10 0 0 4 ka measured 10be inheritance concentrations from all depth profiles are internally consistent and are between 10 and 20 of the surface concentrations suggesting a regional cosmogenic inheritance signal for the scoresby sound landscape based on the profile inheritance concentrations we explore the first order catchment averaged bedrock erosion under the greenland ice sheet yielding estimates of total erosion during the last glacial cycle of the order of 2 30 m copyright 2010 john wiley sons ltd

estimating rates of denudation using cosmogenic isotope abundances in sediment we propose as a testable hypothesis a basin scale approach for interpreting the abundance of in situ produced cosmogenic isotopes an approach which considers explicitly both the isotope and sediment flux through a drainage basin unlike most existing models which are appropriate for evaluating in situ produced cosmogenic isotope abundance at discrete points on earth s surface our model is designed for interpreting isotope abundance in sediment because sediment is a mixture of materials in favourable cases derived from throughout a drainage basin we suggest that measured isotope abundances may reflect spatially averaged rates of erosion we investigate the assumptions and behaviour of our model and conclude that it could provide geomorphologists with a relatively simple means by which to constrain the rate of landscape evolution if a basin is in isotopic steady state and if sampled sediments are well mixed

shear wave velocity structure of the shallow sediments in the bohai sea from an ocean bottom seismometer survey abstractto investigate the seismic velocity structure of the shallow sediments in the bohai sea of china we conducted a shear wave velocity inversion of the surface wave dispersion data from a survey of 12 ocean bottom seismometers obss and 377 shots of a 9000 in3 air gun with obs station spacing of approximately 5 km and air gun shot spacing of approximately 190 m high quality scholte wave data were recorded by the obss within 0 4 5 km offset we retrieved the scholte wave phase velocity dispersion for the fundamental mode and first overtone in the frequency band of 0 9 3 0 hz with the phase shift method and inverted for the shear wave velocity structure of the shallow sediments with a damped iterative least squares algorithm pseudo 2d shear wave velocity profiles with a depth of approximately 400 m revealed coherent features of relatively weak lateral velocity variation we also estimated the uncertainty in shear wave velocity structure based on the pseudo 2d profiles from six trial inversions wi

quantifying sediment transport on desert piedmonts using 10be and 26al in situ produced 10 be and 26 al measured in 40 sediment samples collected from the iron and granite mountain piedmonts eastern mojave desert provide a unique view of piedmont modification processes and process rates over the 10 3 to 10 5 year time scale cosmogenic nuclide based models suggest that the iron and granite mountains generate 0 11 0 13 and 0 082 0 097 m 3 of sediment per year per meter of rangefront respectively the sediment moves down the piedmont in an active transport layer atl which is 20 to 30 cm thick based on visual observations measurements of depth to a buried b horizon cosmogenic nuclide data and maximum ephemeral channel depths sediment in this layer is well mixed vertically and horizontally on the 10 2 year time scale indicating that the small ephemeral channels which dominate the piedmont surface migrate quickly interpretive models of increasing nuclide activities at depth in two pits suggest steady sediment deposition on the piedmont at rates between 17 21 and 38 45 m ma 1 until the late pleistocene epoch when a discontinuity to markedly lower nuclide activities in the isotopically well mixed active transport layer suggests that deposition stopped a significant change in piedmont behavior nuclide activities in 10 amalgamated surface samples each collected along a different 4 km long transect increase steadily away from the mountain front thus we infer that sediment is uniformly dosed by cosmic rays as it is transported down the iron and granite mountain piedmonts interpretive models suggest that long term average sediment speeds down the iron and granite mountain piedmonts are a few decimeters to a meter per year d 2002 published by elsevier science b v

westerly wind bursts enso s tail rather than the dog westerly wind bursts wwbs in the equatorial pacific occur during the development of most el nino events and are believed to be a major factor in enso s dynamics because of their short time scale wwbs are normally considered part of a stochastic forcing of enso completely external to the interannual enso variability recent observational studies however suggest that the occurrence and characteristics of wwbs may depend to some extent on the state of enso components implying that wwbs which force enso are modulated by enso itself satellite and in situ observations are used here to show that wwbs are significantly more likely to occur when the warm pool is extended eastward based on these observations wwbs are added to an intermediate complexity coupled ocean atmosphere enso model the representation of wwbs is idealized such that their occurrence is modulated by the warm pool extent the resulting model run is compared with a run in which the wwbs are stochastically applied the modulation of wwbs by enso results in an enhancement of the slow frequency component of the wwbs this causes the amplitude of enso events forced by modulated wwbs to be twice as large as the amplitude of enso events forced by stochastic wwbs with the same amplitude and average frequency based on this result it is suggested that the modulation of wwbs by the equatorial pacific sst is a critical element of enso s dynamics and that wwbs should not be regarded as purely stochastic forcing in the paradigm proposed here wwbs are still an important aspect of enso s dynamics but they are treated as being partially stochastic and partially affected by the large scale enso dynamics rather than being completely external to enso it is further shown that wwb modulation by the large scale equatorial sst field is roughly equivalent to an increase in the ocean atmosphere coupling strength making the coupled equatorial pacific effectively self sustained

crustal composition of the more margin and compilation of a conjugate atlantic margin transect highlights the basement at the mid norwegian more margin is dominantly felsic in composition a lower crustal body is interpreted as a mixture of continental blocks and eclogite the thickness of the outer lower crustal body is twice as thick on the east greenland margin the thinning during this first phase of post caledonian extension was highest for proto norway abstract the inner part of the volcanic passive more margin mid norway expresses an unusual abrupt thinning from high onshore topography with a thick crust to an offshore basin with thin crystalline crust previous p wave modeling of wide angle seismic data revealed the presence of a high velocity 7 7 8 0 km s body in the lower crust in this transitional region these velocities are too high to be readily interpreted as early cenozoic intrusions a model often invoked to explain lower crustal high velocity bodies in the region we present a vp vs model derived from the modeling of wide angle seismic data acquired by use of ocean bottom seismograph horizontal components the modeling suggests dominantly felsic composition of the crust an average vp vs value for the lower crustal body is modeled at 1 77 which is compatible with a mixture of continental blocks and caledonian eclogites the results are compiled with earlier results into a transect extending from onshore norway to onshore greenland back stripping of the transect to early cenozoic indicates asymmetric conjugate magmatism related to the continental break up further back stripping to the time when most of the caledonian mountain range had collapsed indicates that the thinning during the first phase of extension was about 25 higher for proto norway than proto greenland

a regional shear wave velocity model in the central voring basin n norway using three component ocean bottom seismographs abstract a regional ocean bottom seismometer obs dataset was acquired in the central and northern part of the voring basin n norway in 1992 thirty three component obss were deployed along seven regional profiles and the shear waves recorded on the horizontal components have been modelled by use of 2 d ray tracing utilizing an established p wave model in the shallow sediments 1 4 km depth mean vp vs ratios of 2 1 2 2 and 2 3 2 5 are inferred along the nw se and ne sw trending profiles respectively the relatively high mean vp vs ratios in this interval are probably related to unconsolidated sediments in the uppermost layers the azimuthal variation in the vp vs ratios with the fast direction nw se indicates a shear wave anisotropy of 5 10 in this interval consistent with observations further north in the lofoten area in the 5 10 km depth interval high velocity sill intrusions in the sediments are mapped by the p wave modelling these high velocity intrusions act as efficient conversion interfaces confirmed by the shear wave modelling a regional decrease in the vp vs ratios to 1 7 1 8 are observed at 4 6 km depth possibly related to sand rich sediments in the middle cretaceous the upper crust is clearly mapped by the shear waves and the inferred vp vs ratio of 1 75 confirms that the crust in the voring basin is of continental origin an increase of the vp vs ratio 1 8 1 85 in the lower crust indicates a change in its composition possibly explained by a mixing of continental crust and magmatic underplating

the linear response of enso to the madden julian oscillation the possibility that the tropical pacific coupled system linearly amplifies perturbations produced by the madden julian oscillation mjo is explored this requires an estimate of the low frequency tail of the mjo using 23 yr of ncep ncar reanalyses of surface wind and reynolds sst we show that the spatial structure that dominates the intraseasonal band i e the mjo also dominates the low frequency band once the anomalies directly related to enso have been removed this low frequency contribution of the intraseasonal variability is not included in most enso coupled models used to date its effect in a coupled model of intermediate complexity has therefore been studied it is found that this mjo forcing mjo can explain a large fraction of the interannual variability in an asymptotically stable version of the model this interaction is achieved via linear dynamics that is it is the cumulative effect of individual events that maintains ensos in this model the largest coupled wind anomalies are initiated after a sequence of several downwelling kelvin waves of the same sign have been forced by mjo the cumulative effect of the forced kelvin waves is to persist the small sst anomalies in the eastern pacific just enough for the coupled ocean atmosphere dynamics to amplify the anomalies into a mature enso event even though mjo explains just a small fraction of the energy contained in the stress not associated with enso a large fraction of the modeled enso variability is excited by this forcing the characteristics that make mjo an optimal stochastic forcing for the model are discussed the large zonal extent is an important factor that differentiates the mjo from other sources of stochastic forcing

use of multiparameter relative age methods for age estimation and correlation of alluvial fan surfaces on a desert piedmont eastern mojave desert california numerical and calibrated age determinations of the late quaternary alluvial fan deposits of the soda mountains piedmont in the mojave desert provide an opportunity to study the utility of the multiparameter relative age ra method for distinguishing and mapping geomorphic surfaces on a desert piedmont most ra parameters could not discriminate between deposits of holocene age although pavements have formed over locally significant parts of surfaces as young as middle holocene several parameters including lithologic composition particle size soil development and varnish cover permit distinguishing between holocene surfaces and late pleistocene surfaces statistically significant differences in initial particle size and lithology of the deposits inferred to be the result of complex interaction among hillslope alluvial fan and eolian processes and climatic change create conditions unfavorable for use of most ra techniques in contrast soil profile development and varnish cover data are successful in discrimination among deposits of holocene and pleistocene age this is attributed to the development of pedogenic features and varnish that are strongly dependent on dust influx and to the relatively minor dependence of these features on differences in the depositional character of the fan

scaling factors for production rates of in situ produced cosmogenic nuclides a critical reevaluation abstract new scaling factors are presented describing the altitude and latitudinal dependence of production rates for in situ produced cosmogenic nuclides the new factors incorporate the influence of the non dipole contributions to the geomagnetic field on the cosmic ray flux the currently used scaling factors of lal earth planet sci lett 104 1991 424 439 are based on the assumption of a dipole field the overall strategy used in deriving the new scaling factors is however very similar to that of lal and relies on the same and or similar nuclear data in this reevaluation data are only used if the effective geomagnetic parameters inclination horizontal field strength can be reconstructed for the time of measurement the absorption free pathlengths for cosmic rays selected for this study are based on observational data at altitudes relevant for exposure age dating sea level to 7000 m at sea level and latitudes between 20 and 40 the new factors are up to 18 lower and at high altitudes more than 30 higher than those of lal in addition to accounting for the influence of the effective geomagnetic field and providing more applicable estimates of the new factors also allow for correction for the significant deviations from the standard pressure altitude relationship that exist in the atmosphere 10

mapping quaternary alluvial fans in the southwestern united states based on multiparameter surface roughness of lidar topographic data 1 quaternary alluvial fans have diverse surface morphologies related to both depositional and weathering processes numerous studies have demonstrated that the surface expression and morphometry of alluvial fans can be used as an indicator of their relative age of deposition but only recently has there been an effort to utilize high resolution topographic data to differentiate alluvial fans by surface age with automated and quantifiable routines we developed a quantitative model for mapping the relative age of alluvial fan surfaces based on multiparameter surface roughness values computed from 1 m resolution lidar topographic data roughness is defined as a function of observational scale and integration of slope curvature and aspect topographic parameters alluvial fan roughness values were computed across multiple observation scales 3 3 m to 150 150 m based on the standard deviation sd of slope curvature tangential and aspect topographic parameters plots of roughness value versus size of observation scale suggest that the sd of each parameter over a 7 7 m observation window best identified the signature of surface roughness elements roughness maps derived from slope curvature and aspect at this scale were integrated using fuzzy logic the integrated roughness map was then classified into five relative morphostratigraphic surface age categories active wash to 400 ka and statistically compared with a similar fivefold surface age map of alluvial fans developed using traditional field surveys and aerial photographic interpretation the model correctly predicted the distribution and relative surface age of 61 of alluvial fan landforms based on traditional mapping techniques

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

rates of sediment supply to arroyos from upland erosion determined using in situ produced cosmogenic 10be and 26al using 10be and 26al measured in sediment and bedrock we quantify rates of upland erosion and sediment supply to a small basin in northwestern new mexico this and many other similar basins in the southwestern united states have been affected by cycles of arroyo incision and backfilling several times in the past few millennia the sediment generation 275 65 g m 2 yr 1 and bedrock equivalent lowering rates 102 24 m myr 1 we determine are sufficient to support at least three arroyo cycles in the past 3 000 years consistent with rates calculated from a physical sediment budget within the basin and regional rates determined using other techniques nuclide concentrations measured in different sediment sources and reservoirs suggest that the arroyo is a good spatial and temporal integrator of sediment and associated nuclide concentrations from throughout the basin that the basin is in steady state and that nuclide concentration is independent of sediment grain size differences between nuclide concentrations measured in sediment sources and reservoirs reflect sediment residence times and indicate that subcolluvial bedrock weathering on hillslopes supplies more sediment to the basin than erosion of exposed bedrock

evidence of boundary reflection of kelvin and first mode rossby waves from topex poseidon sea level data the topex poseidon sea level data lead to new opportunities to investigate some theoretical mechanisms suggested to be involved in the el nino southern oscillation phenomenon in the tropical pacific ocean in particular we are interested in studying the western boundary reflection a process crucial for the delayed action oscillator theory by using the topex poseidon data from november 1992 to may 1995 we first projected the sea level data onto kelvin and first mode rossby waves then we estimated the contribution of wind forcing to these waves by using a single baroclinic mode simple wave model forced by the ers 1 wind data wave propagation was clearly observed with amplitudes well explained by the wind forcing in the ocean interior evidence of wave reflection was detected at both the western and eastern boundaries of the tropical pacific ocean at the eastern boundary kelvin waves were seen to reflect as first mode rossby waves during the entire period the reflection efficiency in terms of wave amplitude of the south american coasts was estimated to be 80 of that of an infinite meridional wall at the western boundary reflection was observed in april august 1993 in january june 1994 and later in december 1994 to february 1995 although the general roles of these reflection events in the variability observed in the equatorial pacific ocean are not clear the data suggest that the reflections in january june 1994 have played a role in the onset of the warm conditions observed in late 1994 to early 1995 indeed during the january june 1994 period as strong downwelling first mode rossby waves reflected into downwelling kelvin waves easterly wind and cold sea surface temperature anomalies located near the date line weakened and eventually reversed in june july 1994 the presence of the warm anomalies near the date line then favored convection and westerly wind anomalies that triggered strong downwelling kelvin waves propagating throughout the basin simultaneously with the beginning of the 1994 1995 warm conditions

tracking painted pebbles short term rates of sediment movement on four mojave desert piedmont surfaces 1 to quantify short term sediment movement rates across mojave desert piedmonts 1600 painted and numbered pebbles were laid out in paired orthogonal 20 m lines at 4 sites and resurveyed five times over 2 years and revisited 2 years later pebble lines cross shallow 5 15 cm ephemeral channels and adjacent unconsolidated interfluves the latter being the dominant landform at all sites two sites are located on surfaces that have been or are impacted by military training activities including the use of tracked vehicles the two other sites have not been disturbed by human impact three different processes transport pebbles episodic streamflow in ephemeral channels transports a few pebbles long distances decimeters to meters down gradient bioturbation moves many pebbles small distances centimeters in any direction and vehicular disturbance transports pebbles varying distances centimeters to meters in any direction significant down gradient sediment movement occurred dominantly in channels where flowing water was concentrated interfluves were stable surfaces where little transport occurred off road vehicle use is coincident with accelerated pebble movement pebbles moved further and faster down gradient at the disturbed iron mountain and east range road sites mean speeds of 0 18 and 0 34 m yr 1 respectively than at the undisturbed chemehuevi and goldstone sites mean speeds of 0 17 and 0 02 m yr 1 respectively mean pebble movement is highly and negatively correlated with vegetation density short term pebble movement rates are several times lower than long term 103 to 104 year rates suggesting the importance of rare extreme precipitation events for sediment transport such as those of fall and winter 2004