fluvial deposits of yellowstone tephras implications for late cenozoic history of the bighorn basin area wyoming and montana abstract several deposits of tephra derived from eruptions in yellowstone national park occur in the northern bighorn basin area of wyoming and montana these tephra deposits are mixed and interbedded with fluvial gravel and sand deposited by several different rivers the fluvial tephra deposits are used to calculate stream incision rates to provide insight into drainage histories and quaternary tectonics to infer the timing of alluvial erosion deposition cycles and to calibrate rates of soil development

altimeter derived variability of surface velocities in the california current system 2 seasonal circulation and eddy statistics abstract satellite surface height and temperature fields are used to examine the seasonal surface circulation in the california current system in spring and summer an equatorward jet develops next to the coast with an initial latitudinal structure that responds to the latitudinal distribution of equatorward alongshore winds this jet moves offshore from spring to fall and develops meanders and closed eddies that contribute eddy kinetic energy and water mass properties to the nearby deep ocean higher eke appears first in spring near the coast and moves offshore with the seasonal jet along altimeter tracks parallel to the coastline 200 and 400 km offshore the greatest eke is found in summer and fall respectively with wavelengths of approximately 300 km these are the wavelengths of the largest meanders and the distance between the largest eddies visible in altimeter snapshots of the jet at 600 800 km offshore the wavelengths are generally smaller 100 150 km similar to eddy sizes reported by others for the quiescent northeast pacific some energy with longer wavelengths arrives at the track 600 km offshore in winter and 800 km offshore in spring which we interpret as the most offshore extension of the eke generated by the jet and eddy system closer to the coast in the previous spring and summer a sequence of snapshots from october 1992 to october 1993 shows details of the evolution of the jet and eddy system over one complete annual cycle

chronology and rates of faulting of ventura river terraces california new evidence concerning the chronology of four late pleistocene terraces of the ventura river near oak view california that are vertically offset and tilted by reverse and reverse flexural slip faults provides a means of estimating rates of fault movement and downcutting by the ventura river radiocarbon ages of charcoal contained within terrace deposits date two of the terraces correlation of soils that have developed on terrace deposits and extrapolation of the rate of vertical displacement of the arroyo parida santa ana fault not a flexural slip fault date the others resulting age estimates for the four main late pleistocene terraces are qt5b 30 000 qt6a 38 000 qt6b 54 000 and qt6c 92 000 yr b p vertical slip rates on flexural slip faults range from 0 3 to 1 1 mm yr and apparently are related to the rate form and mechanics of folding of the north limb of the ayers creek canada larga syncline average rates of downcutting of the ventura river for several intervals during the late pleistocene estimated from the chronology and relative elevation of river terraces north of the arroyo panda santa ana fault upstream from the zone of faulting vary from 0 5 to 1 3 mm yr the range in rates probably reflects variations in local uplift as well as adjustments to changing eustatic sea level climatic conditions and or regional deformation of the western transverse ranges the average rate of downcutting of the ventura river north of the zone of flexural slip faulting is 0 8 mm yr compared with 1 2 to 2 2 mm yr in the deformation zone immediately to the south this apparently indicates that during tectonic deformation there is an approximate balance between the rate of uplift due to faulting and folding and the rate of downcutting by the fluvial system

regional variations in the influence of mesoscale eddies on near surface chlorophyll eddies can influence biogeochemical cycles through a variety of mechanisms including the excitation of vertical velocities and the horizontal advection of nutrients and ecosystems both around the eddy periphery by rotational currents and by the trapping of fluid and subsequent transport by the eddy in this study we present an analysis of the influence of mesoscale ocean eddies on near surface chlorophyll chl estimated from satellite measurements of ocean color the influences of horizontal advection trapping and upwelling downwelling on chl are analyzed in an eddy centric frame of reference by collocating satellite observations to eddy interiors as defined by their sea surface height signatures the influence of mesoscale eddies on chl varies regionally in most boundary current regions cyclonic eddies exhibit positive chl anomalies and anticyclonic eddies contain negative chl anomalies in the interior of the south indian ocean however the opposite occurs the various mechanisms by which eddies can influence phytoplankton communities are summarized and regions where the observed chl response to eddies is consistent with one or more of the mechanisms are discussed this study does not attempt to link the observed regional variability definitively to any particular mechanism but provides a global overview of how eddies influence chl anomalies

a view of the 1993 1994 california current based on surface drifters floats and remotely sensed data near surface drifters were deployed in the california current system during the period 1993 1994 in order to study mean and eddy currents the deployment scheme allowed a 2 year period where data density was high enough to make meaningful estimates of eddy statistics and of seasonal mean currents and variances on a 5 grid eddy variability which tended to be isotropic was higher near the coast standard deviations around 0 2 m s 1 and decreased offshore down to 0 1 m s 1 seasonal mean surface flow west of california was southward during all seasons if a davidson current existed during 1993 1995 it was probably either short lived or only found closer to the coast than our study area i e within 100 150 km of shore in some cases drifter populations within a discrete feature were high enough to allow some detailed resolution of its behavior we note a tendency for individual eddies which can last for up to 3 5 months to drift westward at rates of o 5 km day 1 not all eddies in the region are surface intensified there is clear evidence for at least the occasional presence of a thin meandering southward jet in the region that can be 1000 km or more long this jet can be identified with that found in the coastal transition zone program in association with cool filaments the jet appears to become broader and slower south of point conception we hypothesize on the basis of others results as well as ours that the eddies that are strongest at the surface result primarily from instabilities on a southward alongshore mean current and that eddies that are maximal at depth are spawned by the northward undercurrent

the influence of nonlinear mesoscale eddies on near surface oceanic chlorophyll oceanic rossby waves have been widely invoked as a mechanism for large scale variability of chlorophyll chl observed from satellites high resolution satellite altimeter measurements have recently revealed that sea surface height ssh features previously interpreted as linear rossby waves are nonlinear mesoscale coherent structures referred to here as eddies we analyze 10 years of measurements of these ssh fields and concurrent satellite measurements of upper ocean chl to show that these eddies exert a strong influence on the chl field thus requiring reassessment of the mechanism for the observed covariability of ssh and chl on time scales longer than 2 to 3 weeks the dominant mechanism is shown to be eddy induced horizontal advection of chl by the rotational velocities of the eddies

southeast australian late mesozoic and cenozoic denudation rates a test for late tertiary increases in continental denudation throughout the tertiary average rates of erosion of southeast australia have been uniformly low about 10 3 mm yr of surface lowering indicating that this part of the australian continent did not contribute to a rapid increase in ocean basin sedimentation over the past 15 or 20 m y somewhat higher mesozoic rates may be the result of minor tectonism but explanation for the generally low cenozoic and mesozoic erosion rates may be sought in the forest cover and general tectonic stability of southeast australia over this time period australia9s gradually increasing aridity climatic seasonally over the past 20 m y has apparently not resulted in higher average rates of erosion of the continent except perhaps in the very latest tertiary and quaternary

rates of stream incision in the middle part of the arkansas river basin based on late tertiary to mid pleistocene volcanic ash abstract ages and elevations of ash layers correlated with late tertiary and pleistocene eruptions in the western us and present stream elevations are used to calculate net rates of incision by streams in the middle reaches of the arkansas river basin in the south central us the mean of the 23 measurements of rate of stream incision in the study area is 4 2 2 7 cm ky with a range of 0 6 to 9 7 cm ky major influences on rate of stream incision in the study area include the arid to semi arid climate of the region the type of material being incised by streams stream captures and salt dissolution in the bedrock that underlies the region rates of incision exceeded rates of basin filling but significant deposits of unconsolidated late cenozoic sediments occur in the study area basins of streams that have incised the slowest since the late tertiary contain the thickest and most extensive amounts of unconsolidated quaternary sediments rates of incision by streams in the study area are similar to or slower than rates reported for streams elsewhere in the us and the world streams in mountainous regions and areas affected by rapid uplift have incised at rates orders of magnitude faster than streams in the study area

estimates of sea surface height and near surface alongshore coastal currents from combinations of altimeters and tide gauges 1 present methods used to retrieve altimeter data do not provide reliable estimates of sea surface height ssh in the nearshore region resulting in a measurement gap of 25 50 km next to the coast in the present work gridded ssh fields produced by archiving validation and interpretation of satellite oceanographic data aviso in the offshore region are combined with coastal tide gauge time series of ssh to improve estimation in that gap along the west coast of the united states in the northern california current system between 40 and 45n and 123 8 and 126w to assess the increase in skill provided by this procedure the geostrophic alongshore currents calculated from the new ssh fields in the gap region are compared to three in situ nearshore current measurements resulting in correlation coefficients of 0 73 0 83 and standard deviations of the differences of 11 6 12 6 cm s substantially improved from the aviso only results when the ekman current components are estimated and added to the geostrophic currents comparisons to the 10 m deep acoustic doppler current profiler velocities are only slightly improved the ekman components make a more significant contribution when compared to hf radar surface current measurements providing correlations of 0 94 and standard deviations of the differences of 6 4 9 5 cm s these results represent a dramatic improvement in the quality of the ssh fields and estimated alongshore currents when additional realistic ssh data from the coastal region are added here we use coastal tide gauges to provide the additional ssh data but also discuss more general approaches for altimeter ssh retrievals in coastal regions where tide gauge data are not available

quaternary downcutting rate of the new river virginia measured from differential decay of cosmogenic 26al and 10be in cave deposited alluvium the concentrations of the cosmogenic radionuclides sup 26 al and sup 10 be in quartz can be used to date sediment burial here we use sup 26 al and sup 10 be in cave deposited river sediment to infer the time of sediment emplacement sediment burial dates from a vertical sequence of caves along the new river constrain its quaternary downcutting rate to 27 3 4 5 m m y and may provide evidence of regional tectonic tilt 32 refs 3 figs 1 tab

satellite observations of mesoscale eddy induced ekman pumping abstractthree mechanisms for self induced ekman pumping in the interiors of mesoscale ocean eddies are investigated the first arises from the surface stress that occurs because of differences between surface wind and ocean velocities resulting in ekman upwelling and downwelling in the cores of anticyclones and cyclones respectively the second mechanism arises from the interaction of the surface stress with the surface current vorticity gradient resulting in dipoles of ekman upwelling and downwelling the third mechanism arises from eddy induced spatial variability of sea surface temperature sst which generates a curl of the stress and therefore ekman pumping in regions of crosswind sst gradients the spatial structures and relative magnitudes of the three contributions to eddy induced ekman pumping are investigated by collocating satellite based measurements of sst geostrophic velocity and surface winds to the interiors of eddies identified from their sea surface height signatures on average e

upwelling filaments off cap blanc interaction of the nw african upwelling current and the cape verde frontal zone eddy field 1 the hydrographical and dynamical properties of the upwelling filaments forming off cap blanc mauritania are investigated using remotely sensed and in situ data collected in april may 2009 during the strongest upwelling season the area is situated at the southern edge of the nw african upwelling system where the cape verde frontal zone cvfz separates warmer saltier north atlantic central water nacw and cooler fresher south atlantic central water sacw sea surface temperature images indicated the presence of an upwelling filament extending 280 km offshore rooted over the cap blanc promontory and entrained around a warm core anticyclonic eddy after this filament started to decay a new cold filament developed at the approximate same location high resolution moving vessel profiler mvp and acoustic doppler current profiler adcp surveys of these mesoscale structures revealed that both filaments were carrying south atlantic central water sacw offshore through an intense jet like flow similarity of the relative vorticity structure across the filament with that of the tangent eddy suggested that the latter was responsible for the offshore current tracking of this eddy in altimetric data demonstrated that it originated from the cvfz as implied by its hydrographic structure altimetric data also revealed that another anticyclonic structure centered over the cap blanc promontory was responsible for the northwestward advection of sacw into the base of the filament the results support the idea that some upwelling filaments can be produced by the interaction of an external eddy field including topographic eddies with the upwelled water

differentiating pleistocene tectonically driven and climate related fluvial incision the sanggan river datong basin north china the sanggan river is an alluvial river flowing through a graben basin system of the northern shanxi rift zone north china during pleistocene times the river reach in the datong basin was affected successively by various external variables such as invasion by basaltic flow along valley faulting and climatic change therefore it provides excellent constraints for differentiating tectonically driven and climate related fluvial incision in the context of tectonic subsidence based on equilibrium profile analysis k ar dating of basalts 0 74 0 41 ma studies of the river terrace and of stream action history we present a conceptual model for differentiating fault driven and climate related fluvial incision by the river the results show that fluvial incision induced by tectonic lowering of the base level due to along valley movement on the sanggan river fault is equal to fault displacement the amount of post basalt fluvial incision of the reach upstream from the lava dam is 23 to 25 m of which the fault driven and climate related incisions are 15 m and 8 to 10 m respectively the former predominating over the latter the total amount of incision in the lava dam reach is 40 to 47 m of which the fault driven and climate related incisions are 10 m and 30 37 m respectively here the latter is predominant over the former since 0 41 0 10 ma the rate of fluvial incision of the lava dam reach of the river has reached 98 115 m ma which is 1 5 2 times as great as those of the reaches upstream and downstream from the lava dam the higher rate of fluvial incision can be attributed to high water levels supplied by the onset and maintenance of backwater conditions in the reach upstream from the lava dam due to the long period of warm and humid climate in this region plucking abrasion and knickpoint migration appear to be the primary erosional processes in the lava dam reach

the pearlette family ash beds in the great plains finding their identities and their roots in the yellowstone country abstract for many years the numerous deposits of so called pearlette volcanic ash in the great plains region of the united states were considered to be the remnants of the same volcanic event and were used as a time stratigraphic marker of probable middle pleistocene age although a few early workers had suggested that more than one air fall event might be represented among the pearlette occurrences it was not until the latter half of the present century after identification of volcanic ash beds by detailed chemical and mineralogical methods had been developed that it could be established that the pearlette family of volcanic ashes included three ash beds of subtly differing characteristics development of isotopic methods of age determination has established that the ages of the three are significantly different 2 09 1 29 and 0 60 ma the area of distribution of the pearlette family ash beds was found to include not only the great plains but also to extend across the rocky mountain and the basin and range provinces to the pacific ocean the search for the sources of these three similar appearing ash beds facilitated greatly by information gained from concurrent mapping projects underway in areas of major late cenozoic volcanic activity in western united states ultimately led to the sites of the caldera forming eruptions in the yellowstone national park region

volcanic ash beds recorders of upper cenozoic silicic pyroclastic volcanism in the western united states stratigraphic relationships and tephrochronologic information for volcanic ash beds 4 0 0 1 m y of the western interior allow the recognition of at least 68 different ash falls the average reoccurrence rate based on the succession of the isotopically dated ash beds is near one eruption every 57 000 years the ash beds were grouped into two chemical types rhyolitic and dacitic the main property that distinguishes dacitic from rhyolitic ashes is the larger ca and mg and smaller k content in dacitic ashes dacitic volcanic ashes were defined to have more than 0 55 wt ca rhyolitic ashes were subdivided further into two types w and g type based on the presence of biotite in the w type and its absence in g type w type rhyolitic ashes are chalky white have less than 0 55 wt fe have colorless glass shards of pumiceous habit g type rhyolitic ashes are light to medium gray have from 0 55 to 2 0 wt fe in the glass shards lack biotite have colorless platy bubble wall and bubble junction glass shards dacitic ashes are light gray to grayish brown have more than 0 55 wt fe and ca and have a complex mixture of colorless to light brown shards including pumiceous fibrous chunky and bubble wall and bubble junction types w type rhyolitic ashes possibly formed from magmas that were cooler 695 to 830 c and thus more viscous than the hotter 870 to 1000 c magma progenitors of g type ashes based on fe ti oxide mineral compositions primary microphenocrysts in the ash beds comprise assemblages of the following quartz sanidine plagioclase biotite amphibole clinopyroxene orthopyroxene fayalite zircon apatite allanite chevkinite sphene magnetite and ilmentite fayalite and chevkinite only have been found in g type biotite and sphene only have been found in w type rhyolitic ashes are highly evolved and contain 74 79 wt sio2 dacitic ashes vary from 67 77 wt sio2 al ranges from 10 5 to 14 5 wt al2o3 mg ranges from 0 06 to 1 0 wt mgo and fe as fe3o4 ranges from 0 50 to 4 1 wt dacitic ash beds have the most 0 80 3 8 wt as fe3o4 and rhyolitic ashes have the least 0 50 1 9 wt as fe3o4 ca varies from an unusually low amount 0 25 wt cao in a few rhyolitic ashes to as much as 2 2 in some dacitic ashes rhyolitic glasses show larger eu deficiencies compared to dacitic glasses on rare earth element diagrams w type rhyolitic glasses have moderately large la to sm ratios and have la contents from about 30 to 100 times chondrite values g type rhyolitic glasses also have moderately large la to sm ratios and contain somewhat more la than do the w type rhyolitic ashes generally from 100 to 300 times chondrites amounts

eddy properties in the california current system 1 eddy detection and tracking algorithms are applied to both satellite altimetry and a high resolution dx 5 km climatological model solution of the u s west coast to study the properties of surface and undercurrent eddies in the california current system eddy properties show remarkable similarity in space and time and even somewhat in polarity summer and fall are the most active seasons for undercurrent eddy generation while there is less seasonal variation at surface most of the eddies have radii in the range of 25 100 km sea level anomaly amplitudes of 1 4 cm and vorticity normalized by f amplitudes of 0 025 0 2 many of the eddies formed near the coast travel considerable distance westward with speeds about 2 km day consistent with the effect anticyclones and cyclones show equatorward and poleward displacements respectively long lived surface eddies show a cyclonic dominance the subsurface california undercurrent generates more long lived anticyclones than cyclones through instabilities and topographic coastline effects in contrast surface eddies and subsurface cyclones have much more widely distributed birth sites the majority of the identified eddies have lifetimes less than a season eddies extend to 800 1500 m depth and have distinctive vertical structures for cyclones and anticyclones eddies show high nonlinearity rotation speed higher than propagation speed and hence can be efficient in transporting materials offshore

sea surface temperature fronts in the california current system from geostationary satellite observations 1 sea surface temperature sst fronts are determined for the 2001 2004 time period from geostationary operational environmental satellites goes data in the california current system ccs the probability of detecting a sst front at an individual pixel location in the ccs is presented as a bi monthly climatology fronts clearly indicate the seasonal evolution of coastal upwelling as well as meanders and filaments that are often linked with irregularities in coastline geometry winter is characterized by low frontal activity along the entire coast fronts first appear close to the coast during spring particularly south of cape blanco where upwelling favorable winds are already persistent the area of high frontal activity continues to increase during summer especially between monterey bay and cape blanco extending more than 300 km from the coast the region with high frontal activity widens at 2 6 km day 1 off northern baja california a band with persistent fronts is found close to the coast year round but there is no evidence of a seasonal widening of the area of higher activity during fall the weakening of upwelling favorable winds leads to a gradual decrease in frontal activity an empirical orthogonal function eof decomposition reveals the development of sst fronts associated with seasonal upwelling for locations north of monterey bay with less summer intensification to the south the first appearance of fronts close to the coast during spring and the occurrence of the fronts offshore later in the season are represented by additional statistically significant eof modes

eddy induced sea surface temperature gradients in eastern boundary current systems many processes are known to influence the distribution of sea surface temperature sst fronts in eastern boundary current systems ebcs including wind forcing mesoscale activity flow instabilities and flow topography interactions here we used satellite observations to quantify the relative importance of one of these processes mesoscale eddy activity on the distribution of sst gradients in ebcs eddies are characterized by large sst and sst gradient anomalies in all ebcs at the end of the upwelling season eddy induced sst gradients are dominant components of the full sst gradient offshore of 300 km from the coast especially in regions of high eddy activity comparisons between eddy induced and full sst gradients in the california current system indicate that the offshore migration of mesoscale eddies plays a significant role on the seasonal widening of the region of high frontal activity sst gradients associated with anticyclonic eddies are largest within 400 km from shore while the signature of cyclones can extend for up to 700 km from the coast

coastal upwelling in the california current system abstract coastal upwelling in the california current system has been the subject of large scale studies off california and baja california and of small scale studies off oregon recent studies of the winds along the entire coast from 25 n to 50 n indicate that there are significant along shore variations in the strength of coastal upwelling which are reflected in the observed temperature distribution active upwelling appears to be restricted to a narrow coastal band about 10 25 km wide along the entire coast but the region influenced by coastal upwelling may be much wider intensive observations of the upwelling zone during summer off oregon show the presence of a southward coastal jet at the surface a mean vertical shear a poleward undercurrent along the bottom and persistently sloping isopycnals over the continental shelf most of the upwelling there occurs during relatively short periods several days long of upwelling favorable winds during the upwelling season off oregon the offshore ekman transport is carried by the surface ekman layer and the onshore return flow occurs through a quasi geostrophic interior it is not known whether the structure and dynamics observed off oregon are typical of the upwelling zone along the entire coast though some of the same features have been observed off baja california current and future research will eventually show whether the oregon results are also applicable in the region of persistently strong upwelling favorable winds off northern california and in the region of complex bathymetry off central and southern california

main eddy vertical structures observed in the four major eastern boundary upwelling systems in the four major eastern boundary upwelling systems ebus mesoscale eddies are known to modulate the biological productivity and transport near coastal seawater properties toward the offshore ocean however little is known about their main characteristics and vertical structure this study combines 10 years of satellite altimetry data and argo float profiles of temperature and salinity and our main goals are i to describe the main surface characteristics of long lived eddies formed in each ebus and their evolution and ii to depict the main vertical structure of the eddy types that coexist in these regions a clustering analysis of the argo profiles surfacing within the long lived eddies of each ebus allows us to determine the proportion of surface and subsurface intensified eddies in each region and to describe their vertical structure in terms of temperature salinity and dynamic height anomalies in the peru chile upwelling system 55 of the sampled anticyclonic eddies aes have subsurface intensified maximum temperature and salinity anomalies below the seasonal pycnocline whereas 88 of the cyclonic eddies ces are surface intensified in the california upwelling system only 30 of the aes are subsurface intensified and all of the ces show maximum anomalies above the pycnocline in the canary upwelling system 40 of the aes and 60 of the ces are subsurface intensified with maximum anomalies extending down to 800 m depth finally the benguela upwelling system tends to generate 40 50 of weak surface intensified eddies and 50 60 of much stronger subsurface intensified eddies with a clear geographical distribution the mechanisms involved in the observed eddy vertical shapes are discussed

eddy activity in the four major upwelling systems from satellite altimetry 1992 2007 eddy activity in the four major eastern boundary upwelling systems ebus is investigated using 15 years of satellite altimetry data based on the analysis of more than 4000 long lived eddy trajectories in every ebus we show that mesoscale structures are mainly generated along the continental coasts and south of the main archipelagos and propagate westward with velocities increasing toward the equator these mesoscale eddies having radii of 70 160 km are then frequently observed along the coastal transition zones and frontal regions and some large oceanic areas are preferentially populated by cyclonic or anticyclonic eddies temporal variations of the number of newly formed eddies and the associated eddy activity index defined as the mean eddy energy density are finally examined at seasonal and interannual scales the strongest seasonal interannual respectively variations are observed in the california benguela upwelling systems the proposed indices also exhibit contrasted long term trends in each ebus which suggests that eddy activity might be sensitive to a warming climate

the tempo of geomorphological change evidence from southeastern australia a revised denudational chronology based on k ar dating of basalts for much of southeastern australia shows that many major topographic features are far older than was previously realized some upland surfaces originated in the mesozoic and others in the early tertiary in some areas the last major uplift and onset of canyon cutting occurred prior to the mid oligocene apart from the slow headward extension of canyons and localized high level stripping much of the region had taken on approximately its present day form by the mid miocene paradoxically however none of the mechanisms that have been proposed to explain the survival of paleoforms hold here these instances may well be typical of large parts of the interior of tectonic plates and a revision of widely held estimates of modal rates of denudation seems required

seasonal cycles of currents temperatures winds and sea level over the northeast pacific continental shelf 35 n to 48 n seasonal cycles of coastal wind stress adjusted sea level asl shelf currents and water temperatures off the west coast of north america 35 n to 48 n are estimated by fitting annual and semiannual harmonics to data from 1981 1983 longer records 9 34 years of monthly asl indicate that these two harmonics adequately represent the long term monthly average seasonal cycle and that the current measurement period is long enough to estimate the seasonal cycles we characterize the differences between fall winter and spring summer as follows for fall winter monthly mean winds north of 35 n are northward for 3 6 months longer in the north than in the south south of 35 n the mean winds are near zero or weakly southward monthly mean alongshore currents are northward over midshelf and shelf break at all locations sampled at depths of 35 m and deeper and are associated with high coastal sea levels and relatively warm water temperatures for spring summer monthly mean wind stresses are southward at all latitudes for 3 6 months longer in the south than in the north sea levels are low and water temperatures are relatively cool monthly mean currents at 35 m depth over the shelf are southward for 1 6 months longer at the shelf break than over midshelf and longer in the north than in the south while the deeper currents are less southward or northward the magnitudes of the seasonal cycles of all variables are maximum between approximately 38 n and 43 n generally decreasing slightly to the north and greatly to the south at each location the seasonal cycle of the alongshore current from 35 m depth at midshelf leads the sea level slightly and both lead the wind stress and temperatures by 1 2 months the seasonal cycles of all variables show a south to north progression south leads north by 1 2 months at 48 n annual mean currents at 50 m depth over the shelf break oppose the annual mean wind northward wind and southward current similarly at 35 n annual mean currents at 35 m depth over both midshelf and shelf break are opposed to the annual mean wind southward wind and northward current from 35 n to 43 n both summer and winter regimes are dominated by strongly fluctuating currents

adjustments by the charwell river new zealand to uplift and climatic changes major climatic changes and rapid local and regional tectonic movements were common in new zealand during the late quaternary and caused a diversity of adjustments in the drainage basin and piedmont reaches of the charwell river which are separated by the hope fault the onset of semi arid frigid climates during the latest pleistocene probably greatly increased hillslope sediment yields in a periglacial environment and the piedmont reach aggraded as much as 42 m on top of a broad strath with the return of humid mesic climates in the holocene sediment yields decreased as dense forests again mantled the slopes and the piedmont reach degraded as mush as 81 m dating of eleven cut and strath terraces by radiocarbon calibrated weathering rind measurements on greyawake cobbles shows the degradation rates varied greatly during the last 14 ka 1 ka 1000 yr initial degradation rates of 4 m ka 1 increased to 30 m ka 1 by 6 ka ago during a mid holocene climatic optimum since 4 ka ago degradation rates have been only 1 2 m ka 1 comparable to uplift rates in the piedmont reach inferred from marine terrace studies and the river is again cutting a broad strath each broad strath represents equilibrium conditions attained by this powerful stream during interglacial times despite episodes of being overwhelmed by climatically induced sediment yield increases during full glacial climates and having to maintain a long term degradation rate equal to the uplift rate the 75 81 m of degradation since formation of the latest pleistocene fill terrace tread is the sum of the amount of late pleistocene valley floor aggradation and the amount of regional uplift that occurred between the estimated times of major strath formation at about 30 and 0 ka the 39 m of tectonically induced degradation below the pre aggradation strath is sufficiently large that post 30 ka uplift may have doubled holocene degradation rates each of the eleven degradation terraces represents pauses of a few centuries in holocene downcutting brief equilibrium conditions were attained by streambed armoring and concurrent growth of riparian plants both processes progressively increased hydraulic roughness and the shear stresses needed to entrain streambed materials occasional floods possibly from rare cyclones derived from tropical moisture sources destroyed streambed armor and channel downcutting was renewed thus the formation of eleven equilibrium terraces can be accounted for without postulating additional tectonic perturbations or secular climatic changes

an analysis of sst gradients off the peruvian coast the impact of going to higher resolution abstract the peruvian coastal upwelling system pcus is one of the most productive fisheries in the world upwelling events are associated with changes in the magnitude and location of frontal structures sst gradients from four different data sets ncdc remss ostia and mur are compared in two test areas off the pcus paita 5 s and pisco 14 s in both areas gradients derived from the mur data set show greater magnitudes as well as larger seasonal cycles off pisco the magnitude of the seasonal cycle of 2 2 c 100 km in mur is larger than the one derived from the lower resolution data sets all data sets at pisco exhibit a seasonal cycle that peaks in late austral summer and early fall hovmoller diagrams calculated at 5 5 s 10 5 s and 14 5 s show clearly defined offshore maxima in the cross shore gradients for all the data sets upwelling scales determined by the distance to the first maxima vary depending on the data set used at 5 5 s upwelling scales vary from 10 km for mur to 50 km for ncdc at 14 5 s the scales vary from 20 km for mur to 40 km for ostia all four data sets show similar large scale structures associated with the peruvian upwelling however mur shows finer scale structures that are most likely due to submesoscale to mesoscale eddies sub sampled mur 1 km data at the 25 km 9 km and 4 km resolutions compare well in magnitude and phase with the lower resolution products agreement in gradient magnitude between the lower resolution data sets and the mur sub sampled at their respective resolutions implies that the pixel to pixel analysis noise in mur is at a similar level as the other data sets

the blackwater draw formation quaternary a 1 4 plus m y record of eolian sedimentation and soil formation on the southern high plains the southern high plains of northwestern texas and eastern new mexico are mantled by a vast 100 000 km 2 sheet of quaternary eolian sediment locally as much as 27 m thick and termed the blackwater draw formation these sediments generally fine from southwest to northeast exhibiting a linear relationship of decreasing sand content and sand size and increasing silt content with increasing distance indicating the source area to be the pecos river valley as many as six well developed buried soils 2 5yr to 5yr hues bt horizons 1 2 m thick stage ii iii calcic horizons similar to the regional paleustalf and paleustoll surface soils occur in the formation the buried soils indicate episodic sedimentation separated by long periods of landscape stability eolian sedimentation probably occurred during prolonged aridity and stability and pedogenesis likely obtained during subhumid to semiarid conditions similar to those of the late quaternary the presence of the 0 62 m y lava creek b ash and the 1 4 m y guaje ash in the formation shows that the deposit accumulated throughout most of the quaternary data from paleomagnetic thermoluminescence and radiocarbon studies suggest that each cycle of sedimentation stability lasted for several hundred thousand years and that the last depositional event occurred at least several tens of thousands of years ago

seasonal variability of alongshore winds and sea surface temperature fronts in eastern boundary current systems seven years of satellite observations 2003 2009 are used to describe variability in sea surface temperature sst fronts and in the alongshore component of ocean winds and to investigate their relations in four eastern boundary current systems ebcs the general patterns of sst frontal activity are remarkably similar in all ebcs with high frontal probabilities along the coast decreasing with distance from the coastline results from empirical orthogonal function decompositions reveal that the seasonal evolution of sst fronts and wind stress are significantly correlated with intensified upwelling favorable winds associated with an increase in frontal probabilities an offshore migration of the region of high frontal activity is observed during the period of upwelling favorable alongshore wind stress in ebcs in all regions the seasonal variability of frontal activity and wind stress is stronger at mid than at low latitudes the width of the region of high frontal activity is relatively broader in the california and benguela current systems and narrower in the canary and humboldt current systems the width of the band of high frontal activity may be influenced by multiple factors including wind forcing flow topography interactions and mesoscale dynamics while seasonal variability in frontal activity in the california current system acts to reinforce or weaken the average pattern they are substantially different in the canary current system where there is little overlap in the areas characterized by persistent and seasonally varying front activity

the 3 d structure of mesoscale eddies in the lofoten basin of the norwegian sea a composite analysis from altimetry and in situ data

oceanic variability off the central california coast abstract mesoscale variability off the central california coast is strongly influenced by coastal upwelling and related processes off point sur there is significant space time variability in oceanic properties over periods of days and distances of several tens of km however the internal density field averaged over space ca 120km alongshore and time ca 18 days reveals the expected characteristics of a coastal upwelling regime including an equatorward surface jet 25km to 40km offshore and weaker poleward flow below 150m and within 20km of the coast upper ocean circulation is strongly influenced by the bathymetry offshore to water depths of at least 1000m based on repeated horizontal grids of oceanographic stations horizontal correlation scales for temperature are of the order of 30km in the upper 100m hence a horizontal sampling rate of ca 10km is desirable vertical correlation scales for temperature are of the order of 100m hence a vertical sampling rate of ca 10m is desirable similarly there are indications of a temporal correlation scale of a few weeks hence a temporal sampling rate of ca a few days is desirable empirical orthogonal functions eofs in the cross shore vertical plane suggest the influence of coastally trapped motions within 40km of the coast with an intense alongshore near surface transient coastal jet located ca 20km offshore sudden spring transitions to coastal upwelling conditions are often pronounced in coastal temperature records and they may precede the offshore migration of the major upwelling front by at least a month or more the spring transitions occur over a period of about a week in 1980 the spring transition propagated poleward along the california coast at a speed of ca 64km d 1 during spring and summer movement of a coastal upwelling front often located between 15km and 50km offshore is a major contributor to cross shore variability the upwelling front meanders with an alongshore scale of about 80km a time scale of 30 to 40 days and an amplitude scale of 10km rms based on satellite infrared ir imagery the along shore mean position of the major upwelling front migrates offshore during spring and summer offshore displacement of the front may be caused by ekman transport over periods of days to weeks and by rossby wave dispersion over longer periods during summer a time dependent offshore scale based on rossby wave dynamics was more appropriate than the baroclinic rossby radius every three to four years during 1971 through 1984 el nino episodes produced interannual variability in coastal sea surface temperature sst off central california most of the warming occured during fall and winter el nino episodes were often followed by major spring transitions the recent 1982 1983 episode was 2 to 3 c warmer than the three previous episodes over the past 14 years and its influence lasted almost twice as long

late cenozoic rates of erosion in the western espanola basin new mexico evidence from geologic dating of erosion surfaces erosion surfaces in the espanola basin formed before 350 ka and between 350 and 240 240 and 130 and 130 and 80 ka probably in response to climatic change and regional uplift the surfaces are cut on miocene pliocene and pleistocene deposits and range from about 200 m to 15 m above the present rio chama rio grande system periods when the surfaces formed were dated using varnish cation ratios from exposed clasts the mass of soil carbonate and amino acid ratios in pleistocene gastropods from underlying deposits thorium uranium ages from soil carbonate were used to calibrate a local curve for varnish cation ratios the range in age determined for a given surface although derived from different dating techniques implies that parts of the surface were sites of erosion or aggradation after the surface formed from 1 1 ma to present denudation rates averaged 10 cm 1 000 yr from weakly lithified sandstone less than 7 cm 1 000 yr from indurated tuff and boulder gravel and about 4 cm 1 000 yr from tuff and basalt erosion surfaces were preserved as upland benches and terraces by stream incision during periods of pluvial climate and regional uplift but our data do not permit clear separation of the two causes

experimental study on soil erosion prediction model of loess slope based on rill morphology abstract rill erosion frequently occurs in agriculturally disturbed dry areas despite many research efforts over recent decades the characteristics of rill erosion and its intrinsic mechanisms remain unclear the objectives of this study were to investigate the impacts of rill morphology evolution on rill erosion processes a soil pan 5 m long 1 m wide and 0 6 m deep and with an adjustable slope gradient of 0 30 was subjected to rainfall simulation experiments under three intensities of representative erosive rainfall 66 94 and 127 mm h 1 the rill morphology evolution exhibited significant nonlinear change regulation and the stronger the rainfall intensity the clearer the nonlinear feature the equation between rill morphological characteristics with geomorphological comentropy and bifurcation ratio was generated which indicated that the contribution rate of geomorphological comentropy to sediment yield was 80 and the contribution rate of bifurcation ratio was 20 for the experimental treatments a soil erosion model was constructed with and without rill development and the coefficient to describe the influence of rill development on slope erosion was obtained the rill erosion coefficient was embedded into an existing soil erosion model for steep slopes as a result when rill erosion occurred on the slope the contribution of the rill morphology to the rill erosion was fully realized by the model verification indicated that the accuracy of the model was significantly improved in previous studies the accuracy of slope water erosion prediction model was low because the evolution process of slope topography was not considered our results solve the spatial variability problem in the slope erosion prediction model and improve the simulation accuracy of the soil erosion prediction model on a loess slope

soil and geomorphic evolution within the rolling red plains using pleistocene volcanic ash deposits abstract pleistocene volcanic ash deposits are found within alluvium from the arkansas river south to the brazos river this drainage area includes tributaries originating in the high plains the raton volcanic field and the rocky mountain front range within the states of colorado new mexico kansas texas and oklahoma thirteen ash deposits are dated from within the high plains of kansas and texas eastward into central oklahoma to understand the geomorphic history and improve soil and geologic mapping within the study area unsolidated tertiary and quaternary sediments deposited in a west to east direction overlie triassic permian and pennsylvanian bedrock volcanic ash deposits are predominantly early to middle pleistocene age volcanic ash deposits were dated by the fission track method on shards the ash deposits are contained within four land resource regions the southern and central high plains the high plains breaks the rolling red plains and the reddish prairies extensive middle pleistocene constructional stream terrace surfaces occur within the rolling red plains multiple stream terrace surfaces were recognized across the study area with the highest level being dated early pleistocene to pliocene and the lowest bordering the holocene floodplains topographic cross sections 100 km long at 1 24 000 scale transecting dated ash deposits and perpendicular to major river systems were used to distinguish terrace levels constructional terrace surfaces dated by ash deposits range from 21 to 100 m above and 1 to 16 km distance from present river channels soil orders formed in quaternary alluvium are entisols inceptisols mollisols alfisols and vertisols ustic and udic soil moisture regimes and a thermic 15 to 22 c mean annual temperature soil temperature regime dominate the study area the same soil series is often mapped on terrace surfaces spanning early to middle pleistocene age because current classification does not recognize differences in deeply weathered soils greater than 2 m and lacks recognition of loess soil great groups found on early and middle pleistocene surfaces were paleustolls and argiustolls

variability of the near surface eddy kinetic energy in the california current based on altimetric drifter and moored current data low pass filtered velocities obtained from world ocean circulation experiment woce surface drifters deployed in the california current off northern california during 1993 1995 have been compared with surface geostrophic velocity estimates made along subtracks of the topex poseidon altimeter and with moored acoustic doppler current profiler adcp data to obtain absolute geostrophic velocities a mean sea surface height ssh field was estimated using the mean drifter velocities and historical hydrographic data and was added to the altimetric ssh anomalies the correlation between collocated drifter and altimetric velocities is 0 73 significant at the 95 level the component of the drifter velocity which was uncorrelated with the altimetric velocity was correlated with the wind in the ekman transport sense monthly averages of eddy kinetic energy eke estimated using all drifter and altimeter data within the domain 124 132 w 33 40 5 n show energy levels for the drifters that are about 13 greater than those for the altimeter drifter altimeter and adcp measurements all exhibit similar seasonal cycles in eke with the altimeter data reaching maximum values of about 0 03 m 2 s 2 in late summer fall wavenumber spectra of the altimeter velocity indicate that the velocity fluctuations were dominated by features with wavelengths of 240 370 km while the adcp data suggest that the temporal scales of these fluctuations are at least several months between 36 and 40 5 n the region of monthly maximum eke migrates westward to about 128 w on a seasonal timescale this region of maximum eke coincides with the maximum zonal ssh gradient with increased eke associated with increased southward flow a simple model shows that much of the seasonal cycle of the ssh anomalies can be produced by linear processes forced by the curl of the wind stress although the model cannot explain the offshore movement of the front

divergent pathways of cyclonic and anti cyclonic ocean eddies satellite altimetry is used to study the propagation pathways of warm and cold ocean eddies in different ocean basins we consider eddies that have a life span longer than 3 months and we present three regional studies in the southeast indian the southeast atlantic and the northeast pacific oceans the case studies show that simple theories for vortex propagation on a plane work in regions where energetic eddies propagate though a weak background flow under these conditions anticyclonic cyclonic eddies propagate westward and equatorward poleward this divergence in the eddy pathways implies a net equatorward eddy heat flux and has implications for the meridional transport of freshwater carbon nutrients etc

a separating coastal upwelling jet at cape blanco oregon and its connection to the california current system the coastal upwelling region near cape blanco oregon 433n o the west coast of the united states was studied using a towed ctd on seasoar a shipboard acoustic doppler current pro ler adcp satellite sea surface temperature maps and surface drifters during august 1995 the equatorward upwelling jet was inshore of the shelfbreak north of cape blanco meandered gently o shore around the cape and then veered sharply o shore just to the south of the cape analysis of vertical sections of density velocity and spicinessa con rmed the separation of an upwelling jet and front the jet was followed from over the shelfbreak north of the cape to 100 km o shore downstream of the cape the separating jet originates from the coastal upwelling jet leaving the shelf but is augmented by an o shore branching of the poleward undercurrent by combining information from adcp streamfunction maps with analysis of hydrographic data including distributions of the tracer like quantity spicinessa a conceptual model of the three dimensional circulation near the cape emerges a mid shelf upwelling jet encounters a coastal promontory then turns o shore stretching and deepening as it crosses the continental margin the jet then turns back shoreward cyclonically where the deepened equatorward ow encounters the top of the poleward undercurrent owing along the continental slope this causes a portion of the undercurrent to turn o shore to join and strengthen the equatorward transport in the separated jet throughout the separation process the coastal upwelling front and jet are continuous robust features separation of a coastal upwelling jet is an important mechanism for cross shelf transport from the coast to the deep ocean cape blanco appears to be the northernmost point where an equatorward jet regularly separates from the coast to become an oceanic jet and thus serves as the northern boundary of the region where an intense meandering current characteristic of the california current system