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

ekman modulation of the sea surface temperature on the eastern south pacific abstract nine years of data 1992 2000 were used to study the evolution of the sea surface temperature sst over the eastern south pacific our analysis shows that the variability in the sst on the interannual scale is attributed mainly to the equatorial el nino la nina events while cooling associated with the wind ekman drift is an important component of the annual cycle the anomalies at the interannual scale show up as a front that parallels the coast at the seasonal scale anomalous warming and cooling of coastal waters is strongly altered by the local effect of the wind driven ekman transport this latter effect is especially significant along the peruvian and northern chilean coast where wind induced upwelling and cooling is out of phase with other important annual forcings i e radiation and annual kelvin waves these local wind effects show up in the time latitude plots as a thinning of the warm water bands along the peruvian coast 10 s y 17 s and a thickening of the bands further south 18 s y 22 s three anomalous events that stand out clearly at the interannual scale are el nino 92 93 la nina 96 and el nino 97 98 their individual evolutions over time and along the coast are very different though the least intense of the three the 92 93 event had the longest duration the 96 event was the shortest in duration and its strongest anomaly occurred around the peruvian coast similar to the warm event of 92 93 the strongest event for the period occurred in 97 98 its warm anomaly showing strongly along the whole latitudinal extent of the study area contrary to what occurs at the seasonal scale the increase on east west ekman transport on the interannual scale seems to be in phase with other relevant cooling and warming mechanisms the interannual ekman anomalous transports are at their maximum near the peruvian northern chilean coast however they do not seem to alter the sst in a significant way a similar situation has been described for sea level data in the california current system i e interannual variability being associated mostly with variability of equatorial origin while seasonal variability is associated to both wind forced local variability and remotely forced variability j geophys res 94 1989 3159

circulation and low frequency variability near the chilean coast remotely forced fluctuations during the 1991 92 el nino results are reported from the first long recording current meter observations over the slope off chile these observations at 308s during the 1991 92 el nino event are analyzed together with observations of currents at a local deep sea site local wind and sea level sea level from the peru and chile coasts and wind temperature and currents from the equatorial pacific mean poleward flow of 12 cm s21 was observed within the peru chile undercurrent over the slope mean flow in the depth range of antarctic intermediate water was not distinguishable from zero in the presence of strong low frequency lf variability which dominated slope currents at all depths the strongest lf fluctuations had periods of about 50 days but periods of 10 and about 5 days were also observed significant local wind forcing of slope currents was only found in the period band 6 10 days and may be related to coastal trapped waves in the atmosphere our analysis shows that free coastal trapped waves in the ocean arriving from the north dominated the lf variability over the shelf and slope off northern and central chile during the 1991 92 el nino event strong 50 day period fluctuations there started their journey about two months earlier and 15 000 km farther up the coastal equatorial waveguide near the date line in the equatorial pacific as equatorial kelvin waves forced by westerly wind events of similar period upon reaching the south american coast these waves forced coastal trapped waves which propagated along the peru coast into the study region likewise a scenario of equatorial trapped waves forcing coastal trapped waves may explain 10 day as well as 6 day and 4 5 day period coastal trapped waves off chile stemming from mixed rossby gravity and inertia gravity waves trapped at the equator since the large 50 day period coastal trapped waves may strongly modify coastal upwelling source water such remotely forced waves may have a significant influence on the pelagic ecosystem off chile at least during el nino events

a 40 50 day oscillation in sea surface temperature along the central california coast abstract previous studies of the tropical troposphere indicate the presence of a 40 50 day quasi periodic oscillation in zonal winds spectral analysis of extensive daily sea surface temperatures ssts reveals a significant increase in variance i e a quasi periodic oscillation between 40 and 50 days along the california coast as far south as santa barbara 34 3 n and at least as far north as port arena 39 n increases in the amplitude of this oscillation at granite canyon 36 n in some cases coincide with local el nino warming episodes the local surface winds which also contain a quasi periodic oscillation between 40 and 50 days are coherent with and lead sea surface temperature by approximately 10 days consistent with local wind forcing it is suggested that the 40 50 day oscillation in sea surface temperature off central california may be related to the 40 50 day oscillation in the tropical troposphere through atmospheric teleconnections between the tropics and mid latitudes

a numerical study of the upwelling circulation off central chile effects of remote oceanic forcing 1 a numerical ocean model is used to study the upwelling circulation off central chile in response to local winds and remote forcing in an idealized study of equatorial forced intraseasonal variability period of 50 days a first mode coastal trapped wave ctw paddle is applied to the northern boundary with coastal sea level amplitude of 12 cm without this ctw forcing the steady seasonal winds upwell undercurrent water from depths of 250 320 m to depths of 180 250 m the subsequent formation of mesoscale and headland eddies drive this water into the gulf of arauco and to depths of 50 120 m with the ctw paddle the circulation is strongly modified the mesoscale and headland eddies reform during the ctw upwelling phase during the ctw upwelling phase the upwelling over winds and eddies is enhanced by up to 40 m on the shelf model simulations are undertaken using realistic winds and a ctw paddle modulated by observed sea level without ctw forcing included in the model the agreement with data is poor in the gulf of arauco area the variability of alongshore currents below 130 m is dominated by ctw activity above 130 m wind driven current variability dominates in agreement with the idealized ctw analysis water is found to be upwelled from depths of 320 m to 100 m or less and 10 c undercurrent water is found at the surface and within the gulf

impact of a coastal trapped wave on the near coastal circulation of the peru upwelling system from glider data alongshore velocity data from a glider repetitive section off the coast of peru 14 s are used to study the cross shore structure and temporal variability of the peru current system during a 5 week period in april may 2010 besides providing substantial information on the surface frontal jet associated with the peru coastal current and the surfacing peru chile undercurrent that flows poleward trapped on the continental shelf and slope the glider data reveal the presence of an intense deep equatorward current which transports up to 2 5 sv the dynamics of this current are investigated using an eddy resolving regional model the variability of the vertically sheared alongshore flow is shown to be related to the passage of a poleward propagating coastal trapped wave likely of equatorial origin solutions from a two dimensional linear coastal wave model suggest that the alongshore current observed vertical structure is associated with the second and third baroclinic modes of the coastal trapped wave

propagation and forcing of high frequency sea level variability along the west coast of south america tide and wind data from coastal and island stations from buenaventura colombia 4 n to callao peru 12 s have been analyzed for the 1979 1984 time period to determine the propagation and forcing characteristics of coastal sea level variability at periods of days to weeks as well as how they vary either with season or between the 1982 1983 el nino southern oscillation enso period and non enso years during four non enso years the ensemble averaged cross spectra between coastal sea level height slh and local winds show weak evidence of local forcing during the whole year without significant differences between the austral summer and winter seasons other than a greater energy in the wind fluctuations at talara during summer cross spectra between slh series from neighboring stations show evidence of poleward phase propagation during winter seasons at speeds of about 2 0 m s 1 between la libertad and talara at periods of a week or more and about 2 7 m s 1 between talara and callao at periods of 5 11 days but no propagation is found during summers during the 1982 1983 enso there is a large increase in slh energy at most frequencies at all coastal stations but especially in the 8 to 11 day band where energies are enhanced by as much as an order of magnitude above non enso levels the cross spectra between adjacent slh stations indicate a nondispersive poleward propagation of events during the 1982 1983 enso with phase speeds of 2 2 3 5 m s 1 from la libertad to talara periods of a week or more and 3 4 3 6 m s 1 from talara to callao 3 5 days or more as with the slh energy the coherence and phase propagation were much stronger along the peru coast in 1982 1983 than during non enso periods especially in the 8 to 11 day band the one third increase in phase speeds during the enso over the non enso speeds is found to be consistent with the anomalous depression of the density structure during el nino comparisons between coastal slh and the local alongshore wind suggest that locally forced slh variability was obscured during the 1982 1983 enso by the noncoastally forced but energetic propagating fluctuations which probably originated in the equatorial waveguide

analysis of sediment from steps in a small catchment in the polish carpathians in relation to the transition zone between the hillslope and fluvial system abstract an investigation to determine the transition zone between the hillslope system and the fluvial system in connection with the degree of differentiation of sediment located upstream and downstream of log steps ls and boulder steps bs was undertaken in the channel of a stream located in a small mountain catchment area in the silesian beskidy mts polish carpathians a stream channel into which large wood was introduced artificially several years ago granulometric analyses of 41 samples taken from upstream 21 and downstream 20 of steps were performed to analyze the effectiveness of log steps and boulder steps in the differentiation of mineral sediment it was demonstrated that log steps have a significant impact on the functioning of the channel by shaping its longitudinal profile and affecting the transport of mineral material whereas boulder steps retain less sediment showing the beneficial effects of artificial creation of log steps in mountain stream channels results of granulometric analyses suggested the location of the theoretical transition zone between the hillslope system and the fluvial system suggesting the location and range of this zone in small mountain catchment areas can change depending on the intensity and range of slope processes in the longitudinal profile of the channel

further evidence for coastal trapped waves along the peru coast abstract time series of coastal sea level during 1976 77 from 2 12 s to 17 s along the west coast of south america show that low frequency 0 25 cycles per day cpd fluctuations propagate poleward with the phase speed of baroclinic kelvin waves 2 3 m s 1 the alongshore coherence is highest in the frequency band 0 1 0 2 cpd computing the frequency domain empirical orthogonal functions eof for alongshore current from an army of current meters extending from 5 s to 15 s during march may 1977 gives 70 of the variance in the 0 1 0 2 cpd frequency band to an eof mode with poleward phase propagation at 2 75 m s 1 the vertical structure of the alongshore current fluctuations 0 1 0 2 cpd over the continental slope at 5 s and 15 s is consistent with a first mode baroclinic kelvin wave the current and sea level fluctuations are coherent and propagate poleward through latitudes where their frequency equals the local inertial frequency the fluctuations are not significantly coherent with coastal

intraseasonal oscillations in sea level along the west coast of the americas abstract hourly observations of coastal sea level at stations from peru to british columbia are analyzed for low frequency content a space time contour plot of sea level from four years of data during the 1971 75 period shows the meridional structure of the seasonal cycle and interannual variability associated with the 1972 73 el nino oscillations with intraseasonal periods of 36 73 days are also evident coherent over alongshore distances of several thousand kilometers further investigation using spectral methods and empirical orthogonal function analysis in the frequency domain reveals in particular that intraseasonal sea level variability has a peak in spectral density along the coasts of south america central america and mexico with high coherence from near the equator tumaco 2 n north to central california 34 n and south to at least callao 12 s phase propagation north of the equator is poleward at 150 200 kilometers day atmospheric pressure alongshore wind stress and wind stress cu

discontinuous ephemeral streams abstract many ephemeral streams in western north america flowed over smooth valley floors before transformation from shallow discontinuous channels into deep arroyos these inherently unstable streams of semiarid regions are sensitive to short term climatic changes and to human impacts because hillslopes supply abundant sediment to infrequent large streamflow events discontinuous ephemeral streams appear to be constantly changing as they alternate between two primary modes of operation either aggradation or degradation may become dominant attainment of equilibrium conditions is brief disequilibrium is promoted by channel entrenchment that causes the fall of local base level and by deposition of channel fans that causes the rise of local base level these opposing base level processes in adjacent reaches are maintained by self enhancing feedback mechanisms the threshold between erosion and deposition is crossed when aggradational or degradational reaches shift upstream or downstream extension of entrenched reaches into channel fans tends to create continuous arroyos upvalley migration of fan apexes tends to create depositional valley floors with few stream channels less than 100 years is required for arroyo cutting but more than 500 years is required for complete aggradation of entrenched stream channels and valley floors discontinuous ephemeral streams have a repetitive sequence of streamflow characteristics that is as distinctive as sequences of meander bends or braided gravel bars in perennial rivers the sequence changes from degradation to aggradation headcuts concentrate sheetflow a single trunk channel conveys flow to the apex of a channel fan braided distributary channels end in an area of diverging sheetflow and converging sheetflow drains to headcuts the sequence is repeated at intervals ranging from 15 m for small streams to more than 10 km for large streams lithologic controls on the response of discontinuous ephemeral streams include 1 amount and size of sediment yielded from hillslopes 2 infiltration capacity of valley floor alluvium that influences both the unit stream power available for upstream headcut migration and the attenuation of flashy streamflow events by riparian vegetation in sheetflow reaches and 3 cohesiveness of alluvium which affects headcut and streambank morphology and rates of arroyo extension downcutting and widening initiation of arroyo cutting may be too complex to be attributed to a single cause such as change in mean annual precipitation or grazing by livestock but is most likely associated with a decrease in density of protective plant cover on hillsides and along valley floors relatively larger unit stream power makes downstream reaches more susceptible to initial entrenchment during floods than headwaters reaches and favors persistent arroyos entrenchment continues until an equilibrium longitudinal profile is briefly attained then channel widening occurs streambanks are undercut and aggradation begins

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

interaction between mingling mafic and felsic magmas its roles in differentiation of a quartz monzonite and mmes from eastern south china abstract compositional profiles and mapping of selected mafic microgranular enclaves mmes in muchen quartz monzonite in eastern south china give constraints on the interaction between mingling mafic and felsic magmas the intrusion is a typical i type mme bearing magnetite series granitoid in western pacific the mmes and host quartz monzonite are not deformed and have similar magnetic fabrics which does not support the mmes are restites or earlier solidified mafic rocks but implies mafic magma globules flowed with felsic magma the two mmes represent mafic magma interacting with felsic magma at early and late stage respectively the late stage mme has a hbl bt kfs pl mag assemblage the early stage mme has a cpx bt kfs pl mag assemblage with a rim similar to the late stage mme acicular apatite implies rapid cooling of the mafic magmas however the similar isotopic ratios and mafic silicate compositions of the mme and quartz monzonite indicate partial equilibrium during magma interactions al in hornblende estimates the pluton emplacement at 3 1 3 6 km and therefore the magma mingling mixing still worked at shallow levels most trace element harker diagrams do not produce linear variation trends and magma mixing cannot solo explain such a pattern enrichments of na2o ree y nb ta ga fe3 and depletions of k2o rb ba sr in the mmes through diffusion caused noticeable chemical differentiation of both mafic and felsic magmas therefore mass transfer during magma mingling is an important mechanism influencing petrography and chemical compositions of i type granitoids such processes may also extensively occur in the deep hot zones of the continental arc environments

downstream patterns of bed material grain size in a large lowland alluvial river subject to low sediment supply 1 a new data set of bimodal subaqueous channel bed sediments was analyzed for longitudinal patterns in grain size it yielded two interesting observations 1 separate fining trends in d50 exist for gravel and fines that overlap for 175 river kilometers and 2 this overlap in fining trends results in a protracted nonabrupt gravel to sand transition these suggest bed patchiness that is interpreted in the context of inherent grain size bimodality localized hydraulic sorting due to spatially heterogeneous and low sediment supply and local deviations in channel gradient the data also show that tributaries have a minor impact on main stem downstream fining due to basin shape and tectonic history in addition subaqueous channel sediments were observed to be finer than nearby sediments collected from exposed bars which may indicate a narrow active zone of transport where bars are disconnected from sediment movement this research has implications for bed material collection and theories of downstream fining

local and remote forcing of sea surface temperature in the coastal upwelling system off chile an analysis is presented of records of sea surface temperature sst sea level and winds collected during the period 1991 1995 along the coast of northern and central chile sea level also from the peru coast in 1991 1994 and of sst from remote sensing during the austral summers of 1991 and 1992 off northern chile large interannual fluctuations of sst and sea level off northern chile are linked to vertical displacements of the equatorial thermocline during el nino la nina events in the intraseasonal 50 day band sst and sea level are intimately related all along the coast whereby sst anomalies lag sea level perturbations by about 12 days such sea level fluctuations are due to free coastal trapped waves ultimately forced via equatorial kelvin waves by 50 day wind events in the western and central tropical pacific these results and those of the remote sensing analysis suggest significant remote forcing of sst fluctuations in the coastal zone off chile by the action of the coastal trapped waves off central chile sst is also related to local wind stress in the intraseasonal band simulations with a simple local wind driven upwelling entrainment model capture rather well observed synoptic and intraseasonal oscillations of sst there off northern chile however this simple model is not successful in simulating observed sst an attempt to include effects of coastal trapped waves into this simple one dimensional model did not improve model fit to data at either location an explanation for the apparent strong influence of these waves on sst along this coast should therefore be sought in other effects not considered by this model such as cross shelf and alongshore advection

the equatorial source of propagating variability along the peru coast during the 1982 1983 el nino using data obtained from tide gages in south america current meters along the equator and the peru coast and an array of pressure gages and inverted echo sounders within and around the galapagos archipelago we have analyzed the equatorial origin of coastal trapped waves observed by cornejo rodriquez and enfield this issue along the peru coast during the intense 1982 1983 el nino the propagating fluctuations along the coast were much stronger at that time than either before or after the el nino and the variability was not locally forced by coastal winds we find that the coastal variability was also more energetic during previous el nino occurrences at periods of 1 2 weeks the meridional component of currents on the equator is up to an order of magnitude more energetic than the zonal fluctuations and is consistently associated with sea level that fluctuates antisymmetrically between hemispheres at periods longer than 2 weeks the zonal velocity component is more energetic and the cross equatorial sea level variability is symmetric the meridional and zonal phase structures of cross spectra involving the currents and sea level establish the 1 to 2 week equatorial fluctuations as mixed rossby gravity yanai waves of low wave number with infinite phase speed standing oscillations in the middle of the band 10 days the corresponding structures for longer periods are consistent with nondispersive kelvin waves frequency domain eof modes of the sea level and current data establish the mixed rossby gravity waves as the principal source of the strong trapped wave variability in the 1 to 2 week band along the ecuador peru coast during the 1982 1983 el nino episode

the intraseasonal oscillation in eastern pacific sea levels how is it forced abstract daily sea level and surface winds at eastern pacific shore locations and equatorial islands together with gridded five day averages of 850 mb winds have been analyzed for the 1979 84 period to determine how the 40 60 day intraseasonal oscillation of eastern pacific sea levels is forced as described by spillane et al for 1971 75 the oscillation was also present in 1980 84 from callao peru to san francisco with maximum energy near 52 57 days and band limits of 43 and 65 days during 1980 84 there was no evidence for forcing of the large scale oscillation in the eastern pacific although a local contribution of forcing was superimposed on the remote signal at the california stations interannual fluctuations in amplitude were evident in the sea level time series consistent with those of the corresponding wind oscillation in the western equatorial pacific the oscillation was best developed in both variables in 1980 82 and became weak or nonexistent during the recovery phase of the 1982 83 e

sediment grain size characteristics and its source implication in the ningxia inner mongolia sections on the upper reaches of the yellow river abstract the ningxia inner mongolia nim reaches of the yellow river are characterized by a high sediment load severe siltation large channel migration and frequent dike breaching resulting in substantial social economic and environmental problems for residents along the river therefore studies on the grain size characteristics of sediments in the nim reaches of the yellow river and locating the primary sediment source areas are important for the prevention and mitigation of silt accumulation and the construction of water conservation facilities in this study 361 samples from the yellow river and 178 samples from potential source areas were analyzed large grain sizes in the riverbed and floodplain materials were found in the desert sections and in sections containing 10 tributaries respectively the size of the riverbed and floodplain materials fluctuates relatively frequently in the tributary sections and is coarser at confluences of the tributaries with the yellow river the floodplain material is better sorted than the riverbed material and the sorting coefficients especially the former fluctuate most widely in the tributaries sections two main fractions of the floodplain and most of the riverbed materials in the major river reaches are observed 3 9 63 m and 63 250 m the first fraction component of the riverbed material 63 250 m is found in the desert sections and part of the tributary sections whereas the second fraction component 250 500 m is found in some parts of the desert sections the variations in the size characteristics of the riverbed and floodplain materials demonstrate that both materials are derived from lateral sources the main sources of the riverbed materials are the ulan buh desert and the kubuqi desert in the wuhai zhonghexi reaches and the main sources of the riverbed and floodplain materials are the 10 tributaries in the zhonghexi lama bay reaches the riverbed and floodplain materials in the desert sections are deposited near the source and far from the source respectively both types of sediments in the tributary sections are mainly deposited near their sources through wind and hydraulic sorting the size of the riverbed material in the tributaries sections becomes finer in contrast to that in the desert sections which suggests that coarse sediments have not been effectively carried downstream

log step and clast interactions in mountain streams in the central cascade range of washington state usa article i nfo field surveys of log steps in high gradient streams investigate the interactions between log steps and clasts to assesswhethersecond growthwoodcanformlogstepscapableof diverting flowandactingassignificant rough ness elements similar to those formed by old growth wood we measure the functional log diameter and step height as well as visually estimate the clast size in the step of 102 log steps in 15 high gradient streams in the centralcascaderangeofwashington usa wecomparestepheightdatatomeasurementsofmaximumbankfull depthtomeasurethe capability of log steps to divert flowrelativeto theirclastsizeand log diameter stepheight positively correlates with functional log diameter p b 0 001 and clast size additionally a threshold clast size exists above which functional log diameter more strongly correlates with step height indicating that clast size can limit step height we find that steps with cobble or larger n64 mm clasts in the step are 3 7 times more likely to reach or exceed bankfull depth than steps with smaller than cobble clasts in the step we conclude that it is necessary for steps formed by small logs to have large clasts in the step in order to reach bankfull depth act as significant roughness elements and create flow diversions implying that the potential for second growth forests to maintain log steps similar to those formed by old growth logs depends on the size of bed material

dendrogeomorphic approaches for identifying the probable occurrence of debris flows and related torrential processes in steep headwater catchments the hrubý jesenik mountains czech republic abstract culminating parts of mid mountain ranges in central europe are interwoven by a network of high gradient streams these parts together with the surrounding slopes form a coupling system in which hazardous geomorphic processes such as landslides debris flows or flash floods can occur in the case of the hrub jesenik mountains eastern sudetes czech republic we present an evaluation of the debris flows and related torrential processes in the high gradient streams of the selected catchment based on dendrogeomorphic methods in addition to the classical dendrogeomorphic approaches we refined the procedure of identifying certain and probable events using new weighted indexes for event reconstruction additionally because of the steep narrow channels without a characteristic accumulation cone a new spatial approach is defined based on the spacing of disturbed trees for each event random distribution or clustering and location of disturbed trees in an individual section of the valley floor using kernel density analysis for each event and calculating the particular grids in arcgis software we are able to describe the spatial reach and probable nature of an event debris flow or hyperconcentrated flow dendrogeomorphic analysis of 397 sampled trees predominantly coniferous trees revealed 24 torrential events 15 certain nine probable since 1928 with peaks in 1991 1997 and 2010 according to index values in addition the spatial distribution of disturbed trees grouped in clusters in these years indicates debris flow events in the upper parts of the catchment it seems that new dendrogeomorphic approaches should be valuable in remote steep headwater catchments where several types of processes affect the valley floors

channel morphology gradient profiles and bed stresses during flood in a step pool channel abstract the stability of a step pool channel is investigated on the basis of measurements during a median annual flood the study reaches range in gradient from 5 to 10 and the flow was 3 m3 s 1 in an 8 m wide channel the estimated shear stress based on the channel gradient was 102 pa which implies that the channel ought to move half meter class boulders calculations of the shear stress using flow resistance equations yield values of about 30 pa these figures imply that the largest boulders in the channel could be moved in fact the channel is stable the effective stress remains well below the threshold to move the large structure forming boulders the steps are stable structures that result from interlocking of the larger stones they are semi randomly located depending on the location of keystones that are deposited in the channel by debris flows or fall out of the banks the high variation in step pool wavelength step height residual pool depth and pool length is indicative of the random nature of step location and structure along a reach there is no convincing evidence that special conditions govern their formation

interdecadal sea surface temperature sea level pressure coupled variability in the south pacific ocean 1 the main coupled sea surface temperature sst sea level pressure slp variability at interdecadal timescale in the south pacific is studied by means of correlation and combined complex empirical orthogonal function cceof analyses the sst slp coupled variability presents a bidecadal cycle from mid 1950s to 1970s and a decadal cycle from 1980s to early 1990s reproducing the enso like interdecadal oscillation particularly the first sst slp cceof mode describes the bidecadal cycle characterized by westward progression of sst and slp anomalies along the tropical pacific while the second sst slp cceof mode shows the decadal cycle with eastward development during both bidecadal and decadal cycles the sst fluctuations in the eastern equatorial pacific and along the western coast of south america are primarily forced by equatorial zonal wind variability specially during the bidecadal cycle the alongshore sst variability south of 30 s is maintained and reinforced by meridional coastal wind fluctuations associated with a stationary slp pattern off southern chile this stationary slp pattern appears connected to sst fluctuations in the central tropical pacific

front eddy influence on water column properties phytoplankton community structure and cross shelf exchange of diatom taxa in the shelf slope area off concepcion 36 37 s in eastern boundary current systems ebcss submesoscale to mesocale variability contributes to cross shore exchanges of water properties nutrients and plankton data from a short term summer survey and satellite time series january february 2014 were used to characterize submesoscale variability in oceanographic conditions and phytoplankton distribution across the coastal upwelling and coastal transition zones north of punta lavapie and to explore cross shelf exchanges of diatom taxa a thermo haline front frn 1 flanked by a mesoscale anticyclonic intrathermocline eddy ite 1 or mode water eddy persisted during the study period and the survey was undertaken during a wind relaxation event at the survey time ite 1 contributed to an onshore intrusion of warm oceanic waters southern section and an offshore advection of cold coastal waters northern section with the latter forming a cold high chlorophyll a filament in situ phytoplankton and diatom biomasses were highest at the surface in frn 1 and at the subsurface in ite 1 whereas values in the coastal zone were lower and dominated by smaller cells diatom species typical of the coastal zone and species dominant in oceanic waters were both found in the frn 1 and ite 1 interaction area suggesting that this mixture was the result of both offshore and onshore advection overall front eddy interactions in ebcss could enhance cross shelf exchanges of coastal and oceanic plankton as well as sustain phytoplankton growth in the slope area through localized upward injections of nutrients in the frontal zone combined with ite induced advection and vertical nutrient inputs to the surface layer

effects on bedload transport of experimental removal of woody debris from a forest gravel bed stream experimental removal of woody debris from a small gravel bed stream in a forested area resulted in a four fold increase in bedload transport at bankfull discharge this was caused by increased transportability of sediment previously stored upslope of debris buttresses or in low energy hydraulic environments related to debris bank erosion delivered additional sediment to the channel and transport energy was increased by an inferred increase in the component of total boundary shear stress affecting grains on the bed increased transport following debris removal in may 1987 continued throughout the entire autumn storm season through late november 1987 indicating persistent adjustment of the stream bed and banks despite marked response to earlier flows as large as bankfull stream bed adjustments included development of a semi regular sequence of alternate bars and pools many of which were spaced independently of former pool locations

macrobenthic zonation caused by the oxygen minimum zone on the shelf and slope off central chile abstract the relationship between macrobenthic 300 m zonation and the oxygen minimum zone omz o2

introduction to the special issue on discontinuity of fluvial systems abstract fluvial systems include natural and human created barriers that modify local base level as such these discontinuities alter the longitudinal flux of water and sediment by storing releasing or changing the flow path of those materials even in the absence of distinct barriers fluvial systems are typically discontinuous and patchy the size of fluvial discontinuities ranges across scales from 10 0 m such as riffles to 10 4 m such as lava dams or major landslides the frequency of occurrence appears to be inversely related to size with creation and failure of the small features such as beaver dams occurring on a time scale of 10 0 to 10 1 years and a frequency of occurrence at scales as low as 10 1 m in contrast larger scale discontinuities such as lava dams can last for time scales up to 10 5 years and have a frequency of occurrence of approximately 10 4 m the heterogeneity generated by features is an essential part of river networks and should be considered as part of river management therefore we suggest that natural dams are a useful analog for human dams when evaluating options for river restoration this collection of papers on the studies of natural dams includes bedrock barriers log jams and beaver dams the collection also addresses the discontinuity generated by a floodplain in the absence of an obvious barrier in the channel and tools for evaluation of riverbed heterogeneity it is completed with a study of impact of human dams on floodplain sedimentation these papers will help geomorphologists and river managers understand the factors that control river heterogeneity across scales and around the world

early diagenesis of redox sensitive trace metals in the peru upwelling area response to enso related oxygen fluctuations in the water column pore water and solid phase data for redox sensitive metals mn fe v mo and u were collected on a transect across the peru upwelling area 11 s at water depths between 78 and 2025 m and bottom water oxygen concentrations ranging from 0 to 93 m by comparing authigenic mass accumulation rates and diffusive benthic fluxes we evaluate the respective mechanisms of trace metal accumulation retention and remobilization across the oxygen minimum zone omz and with respect to oxygen fluctuations in the water column related to the el nino southern oscillation enso sediments within the permanent omz are characterized by diffusive uptake and authigenic fixation of u v and mo as well as diffusive loss of mn and fe across the benthic boundary some of the dissolved mn and fe in the water column re precipitate at the oxycline and shuttle particle reactive trace metals to the sediment surface at the lower and upper boundary of the omz at the lower boundary pore waters are not sufficiently sulfidic as to enable an efficient authigenic v and mo fixation as a consequence sediments below the omz are preferentially enriched in u which is delivered via both in situ pre cipitation and lateral supply of u rich phosphorites from further upslope trace metal cycling on the peruvian shelf is strongly affected by enso related oxygen fluctuations in bottom water during periods of shelf oxygenation surface sediments receive particulate v and mo with metal oxyhydr oxides that derive from both terrigenous sources and precipitation at the retreating oxycline after the recurrence of anoxic conditions metal oxyhydr oxides are reductively dissolved and the hereby liberated v and mo are authigenically removed this alternation between supply of particle reactive trace metals during oxic periods and fixation during anoxic periods leads to a preferential accumulation of v and mo compared to u on the peruvian shelf the decoupling of v mo and u accumulation is further accentuated by the varying susceptibility to re oxidation of the different authigenic metal phases while authigenic u and v are readily re oxidized and recycled during periods of shelf oxygenation the sequestration of mo by authigenic pyrite is favored by the transient occurrence of oxidizing conditions our findings reveal that redox sensitive trace metals respond in specific manner to short term oxygen fluctuations in the water column the relative enrichment patterns identified might be useful for the reconstruction of past omz extension and large scale redox oscillations in the geological record

downstream coarsening in headwater channels 1 field data from four mountain drainage basins in western washington document systematic downstream coarsening of median bed surface grain size d50 and a subsequent shift to downstream fining at a drainage area of about 10 km2 analyses of network wide patterns of unit stream power derived from both channel surveys and digital elevation models reveal maximum unit stream power that in all four study areas roughly corresponds with both the grain size maxima and an inflection in the drainage area slope relation thought to represent the transition from debris flow dominated channels to fluvially dominated channels our results support the hypothesis that basin wide trends in d50 are hydraulically controlled by systematic variations in unit stream power in addition to lag deposits forced by mass wasting processes the similar relations found in our four study areas suggest that the tendency for downstream coarsening may be ubiquitous in headwater reaches of mountain drainage basins where debris flow processes set the channel gradient

do the coarsest bed fractions and stream power record contemporary trends in steep headwater channels abstract three stream channels that were devoid of evidence of past debris flows and one headwater channel that contained debris flow deposits in the flysch western carpathians czech republic were selected to test relationships between in channel processes bed sediments and unit stream power calculated for bankfull and q 20 flows contemporary depositional or erosional trends in the examined headwaters were linked with bed sediments that were represented by the coarsest cobble and boulder fraction with a mean calculated from the five largest particles the downstream trends of the unit stream power were derived for a bankfull discharge and a well documented 20 year flood event in addition the flow competences during the discharges were calculated using indirect bedload transport measurements downstream fining of the cobble and boulder fraction was observed in all of the studied headwaters and unique downstream variations of the unit stream power were calculated for the longitudinal profiles the single thread streams that were devoid of evidence of debris flow events exhibited direct relations between the coarsest sediment size and the unit stream power especially as calculated for the 20 year flood event and for erosional depositional trends of the channel the downstream coarsening of the bed material that was accompanied by an increase in the unit stream power was usually observed in the case of deeply incised 0 5 m above the assumed bankfull depth channel reaches the calculated competence of the 20 year flow was up to twofold higher than that required to entrain the largest bed particle diameters in those channel reaches and even the bankfull flow was potentially capable of transporting the coarsest bed particles in certain of the reaches on the other hand some depositional channel reaches evidently led to the disconnectivity of transport of the coarsest bed material even in the case of the 20 year flood event the longitudinal profile of the channel that had evidence of past debris flows did not clearly show a direct relationship between boulder size and calculated unit stream power and contemporary channel trends this finding reflected the presence of significantly coarser bed material which points to a higher stability of the debris flow influenced channel during ordinary floods when compared to fluvially dominated headwaters that are devoid of debris flows

selective sorting and abrasion of river gravel i theory most gravel rivers show a tendency for characteristic grain size to decrease in the downstream direction over scales of tens or hundreds of kilometers it has been surmised that this downstream fining is due to some combination of selective sorting by which finer grains are preferentially transported downstream and abrasion by which individual particles are reduced in size here a framework for the simultaneous treatment of both phenomena is developed the analysis is restricted to bed load transport of gravel only abrasion due to binary collisions between moving bed load and stationary bed particles is considered the formulation includes the possibility of differential basin uplift and subsidence due to tectonism and mixtures of rock types with differing coefficients of abrasion the formulation of selective sorting is based on the concept of hiding as applied to a surface based bed load transport relation abrasion is first treated in terms of a lagrangian formulation for individual grains and t

seasonal variability of coastal upwelling and the upwelling front off central chile 1 we analyze sea surface temperature sst and chlorophyll a chl a satellite data to study the seasonal variability of the upwelling off central chile data from an oceanographic cruise are used to illustrate the vertical characteristics of the upwelling front and the geostrophic flow the mean offshore extension of the sst front in summer is 110 km there sst changes from 13 5 c near the coast to 14 5 15 c offshore hydrographic data show that the thermocline becomes progressively shallower toward the coast but that at a certain distance it abruptly bends to form a horizontal front that extends until 50 m depth satellite data show that the chl a decays exponentially offshore and a concentration of 1 mg m 3 indicates the offshore limit of the frontal region the sst front observed most of the year is absent in winter when the coastal water is only slightly colder than the oceanic one however relatively higher chl a values remain present near the coast during winter northwest of punta lavapie 37 15 s the frontal region is located progressively farther offshore suggesting that a branch of an equatorward surface jet separates from the coast to form a meander which is associated with a filament of cold water and an anticyclonic eddy observed frequently in this zone during summer hydrographic data show that isotherm and current disturbances related to mesoscale eddies can extend several hundreds of meters below the surface in contrast the coastal jet is quite shallow extending until 150 m depth

the morphologic structure of step pools in mountain streams abstract step pool sequences in streams in the santa monica mountains of southern california impart a characteristic morphologic structure that varies with slope but despite the strong association with slope that suggests a direct process control analysis of 464 step pools in 13 study reaches reveals the relationship to reflect correlation but not necessarily causality the direct control on step height is particle size whereas discharge is the probable causal process determining step wavelength because both particle size and discharge generally change with channel slope downstream a slope variation with step wavelength and height is the apparent indirect geometric result a conceptual model of process form linkages is proposed based on these results whereby the step pool morphology is produced by positive relationships between wavelength and discharge and between height and particle size the model offers new insights for explaining the step pool morphology and it is potentially useful in channeling future efforts toward the appropriate scales and variables

seasonal and interannual variability of currents and temperature off central chile results are reported for continuous 6 year records of current and temperature from a continental slope station at 308s off chile these observations for november 1991 to november 1997 span the moderate weak and strong el nino events of 1991 1992 1994 and 1997 and the la nina event of 1995 1996 results for current and temperature are analyzed together with observations of wind along the south american coast from the ers 1 and 2 satellite scatterometers wind from a local coastal site sea level from northern and central chile sea surface temperature anomalies from the south pacific region and traditional el nino indices mean poleward flow of 12 8 cm s 21 was observed for the 6 year period in the core of the peru chile undercurrent 220 m mean flow in the depth range of antarctic intermediate water 750 m was equatorward at 1 1 cm s 21 intraseasonal scale variability associated with coastal trapped waves was weaker during the austral winter greatest during el nino events and weakest during the la nina event winds adjacent to the coast showed a strong annual cycle with a southward progression of maximum equatorward upwelling favorable winds alongshore flow over the slope exhibited strong semiannual and weaker annual variations poleward flow in the undercurrent was strongest in the austral spring and fall and weakest in the winter near the bottom 750 m seasonal scale variability was less intense but led that higher up in the water column 220 m by 1 month strong interannual variability of alongshore current and temperature was found at all depths over the slope whereby changes at depth led changes higher up a rapid warming event was observed at the end of 1996 beginning of 1997 over the slope this event also seen in sea level and sea surface temperature off chile led el nino indices by several months and may be best explained by local wind anomalies coupled to atmospheric teleconnections from the western tropical pacific at the onset of el nino some aspects of our current and temperature observations are consistent with results from eastern boundary current models our results indicate that both ocean and atmosphere pathways from the equatorial pacific contribute significantly to interannual scale variability of alongshore flow and thermocline depth off chile

the pacific south american modes and tropical convection during the southern hemisphere winter abstract atmospheric circulation features and convection patterns associated with two leading low frequency modes in the southern hemisphere sh are examined in multiyear global reanalyses produced by ncep ncar and nasa dao the two leading modes referred to as the pacific south american psa modes are represented by the first two eof patterns the two patterns are in quadrature with each other and are dominated by wavenumber 3 in midlatitudes with large amplitudes in the pacific south american sector in the pacific anomalies in the subtropics and in the midlatitudes are opposite in phase taken together the two psa modes represent the intraseasonal oscillation in the sh with periods of roughly 40 days the evolution of the psa modes shows a coherent eastward propagation a composite analysis was conducted to study the evolution of tropical convection and the corresponding circulation changes associated with the psa modes outgoing longwave radiation olr anomaly composites during the mature phase

late quaternary variability of sedimentary nitrogen isotopes in the eastern south pacific ocean 1 we present high resolution bulk sedimentary 15n data from the southern edge of the present day oxygen minimum zone of the eastern south pacific the record is interpreted as representing changes in water column nitrogen removal during the last 70 000 years we found significant fluctuations in the isotopic signal that suggest major reorganizations of the oxygen minimum zone at millennial timescales these fluctuations were not related to other millennial scale changes like the northern hemisphere s dansgaard oeschger climate swings or local changes in primary productivity so appear to be dictated by the southern hemisphere s climate rhythm this is preliminarily corroborated by an overall agreement between our 15n data and the sedimentary proxy of ice sheet dynamics in patagonia which is in turn correlated with surface water properties at the midlatitude subduction region of the eastern south pacific intermediate waters finally potential implications on late quaternary changes in atmospheric co2 concentrations are discussed

a comparison of long coastal trapped wave theory with observations off peru abstract the agreement between coastal trapped wave theory and observation is studied for the case of observations made off peru during the 1977 cuea joint ii experiment wave properties are calculated using a numerical model with realistic horizontally uniform stratification and realistic bottom topography these properties are then explored as a function of the ratio of the first internal rossby radius of deformation to the shelf slope width the agreement of observed and calculated first mode free wave phase speeds 230 cm s 1 is excellent while modal structures agree more poorly a forced wave calculation using observed winds and currents as input is used to hindcast alongshore currents and sea level in the frequency band where smith 1978 observed free coastal trapped waves during 1977 the model suggests that most of the observed sea level and alongshore velocity fluctuations in the 5 10 day period band are due to free waves originating equatorward of 5 deg s while winds between 5 deg s and

an exchange window for the injection of antarctic intermediate water into the south pacific antarctic intermediate water aaiw occupies the intermediate horizon of most of the world oceans formed in the southern ocean it is characterized by a relative salinity minimum with a new denser in situ national oceanographic data center dataset the authors have reanalyzed the export characteristics of aaiw from the southern ocean into the south pacific ocean these new data show that part of the aaiw is exported from the subpolar frontal region by the large scale circulation through an exchange window of 10 width situated east of 90 w in the southeast corner of the pacific basin this suggests the origin of this water to be in the antarctic circumpolar current a set of numerical modeling experiments has been used to reproduce these observed features and to demonstrate that the dynamics of the exchange window is controlled by the basin scale meridional pressure gradient the exchange of aaiw between the southern and pacific oceans must therefore be understood in the context of the large basin scale dynamical balance rather than simply local effects

channel reach morphology controls of headwater streams based in flysch geologic structures an example from the outer western carpathians czech republic a detailed measurement of 93 channel reaches that were classified with an adjusted montgomery buffington 1997 reach scale system provided comprehensive information of approximately 9 at a reach parameters the channel gradient the bankfull width the bankfull depth d90 the percentage of resistant rocks in the bed sediment the number of pieces of large woody debris valley confinement direct sediment inputs and the presence of fluvial accumulations in the stream channel in addition the quantified intensity of sediment transport i e ratio between sediment supply and transport capacity in longitudinal stream profiles during flood events has been estimated by the one dimensional bedload transport model tomsed which was validated in two local streams the principal component analysis of the at a reach parameters did not reveal significant groups of channel reach morphologies thus the selected parameters that exclude sediment transport dynamics within stream longitudinal profile cannot reliably distinguish or predict individual channel reach morphologies nevertheless the channel gradient represented the most significant single explanatory variable for stepped bed morphologies the addition of bedload transport parameters demonstrated that limited sediment supply streams and streams with limited transport capacities featured different successions of the channel reach morphologies in terms of the channel gradient and subsequently the fluvial continuity the bedrock cascades and step pools were significant for the first case whereas cascade and step rapid morphology often occurred in higher sediment supply conditions