magnetic parameter variations in the chaona loess paleosol sequences in the central chinese loess plateau and their significance for the middle pleistocene climate transition abstract a high resolution rock magnetic investigation was performed on the chaona quaternary loess paleosol sequences in the central chinese loess plateau based on a newly developed independent unturned time scale and magnetic records we reconstructed the history of the east asia monsoons during the last 3 ma and explored the middle pleistocene climate transition mpt rock magnetic results show that the loess layers are characterized by relatively high coercivity and remanent coercivity lower magnetic susceptibility ms and that the paleosol layers are characterized by relatively high ms saturation magnetization and remanent saturation magnetization spectrum analyses indicate that there are various periods in addition to orbital periodicities according to the onset and stable appearance of 100 kyr period we consider that the mpt recorded in this section began at 1 26 ma and was completed by 0 53 ma which differs from previous investigations based on orbitally tuned time scales the forcing mechanism for the mpt was more complicated than just the orbital forcing we conclude that the rapid uplift of the tibetan plateau may have played an important role in the shift of periodicities during the middle pleistocene

long term fluvial archives in the fen wei graben central china and their bearing on the tectonic history of the india asia collision system during the quaternary abstract staircases of large scale river terraces are striking features of the landscape in the fen wei graben adjacent to the qinling orogenic belts central china field investigations indicate that all five river terraces are composed of a basal channel gravel and an overlying thick loess palaeosol succession as chinese loess stratigraphy has been well studied it favours age determination of these terraces and their correlation with the marine oxygen isotope stages our research indicates that the ages of the five terraces are approximately 2 6 1 2 0 9 0 65 and 0 15 ma respectively the formation of these river terraces within the fen wei graben has been attributed to nw se crustal extension associated with left lateral displacement between the north and south china blocks in response to the northward movement of india towards asia since cenozoic time thus the stepped terraces in the fen wei graben reflects elements of the india asia collision systems in which terraces define episodes of accelerated northward movement of india towards asia during the quaternary

ekman transport along the galician coast northwest spain calculated from forecasted winds 1 ekman transport is studied close to the galician coast by means of forecasted winds provided by meteogalicia from november 2001 to october 2004 three different coastal zones are identified western coast from mino river to cape finisterre middle coast from cape finisterre to cape ortegal and northern coast from cape ortegal to cape penas in addition to existence of long term variations the periodicity of the transport signal is characterized by an annual component 365 days a seasonal fluctuation 50 to 80 days and a timescale related to passing storms 15 20 days although the periodicity of the signal is similar at the three zones owing to external meteorological forcing the ekman transport is modulated by the presence of the coast in such a way that seasonal patterns vary in intensity and direction along the coast thus the autumn winter pattern is characterized by high transport at the northern and middle coast pointing landward perpendicular to the shoreline and moderate values at the western coast pointing landward and oblique to the shoreline on the other hand the spring summer pattern is characterized by high transport at the western coast pointing seaward perpendicular to the shoreline the same orientation is observed at the middle coast although with a lower magnitude finally ekman transport at the northern coast points landward and oblique to the shoreline the different transport orientations are shown to be responsible for the upwelling probability variation along the coast

effects of wind stress and wind stress curl variability on coastal upwelling abstract aircraft measurements during the winter 1989 shelf mixed layer experiment smile and summer 1982 coastal ocean dynamics experiment code were used to characterize the spatial variation of the low level wind and wind stress over the northern california shelf the curl of the wind stress was calculated from directly measured turbulent stress components the accuracy of the computed curl was estimated to be adequate to map the spatial structure wintertime measurements showed a concentration of large positive curl over 1 pa 100 km 1 west of point arena regardless of wind direction due to the effects of the coastal topography on the wind fields results from summertime measurements showed a similar local maximum of positive curl west of point arena larger curl values over 3 5 pa 100 km 1 however were observed across a hydraulic jump propagating from stewarts point for highly supercritical marine boundary layer flow a two layer vertically integrated numerical model of coastal upwellin

observed dynamics of coastal flow at cape mendocino during coastal waves 1996 abstract airborne in situ and remote meteorological measurements from around cape mendocino california sampled during the coastal waves 1996 field program are analyzed for three different days 7 12 and 26 june 1996 two days conformed to typical summertime conditions with a strong northerly downcoast flow while the wind on the third day was weaker on the first 2 days the flow was supercritical in the sense that the froude number was larger than unity and these 2 days feature expansion fans in the lee of the cape on the third day no such phenomenon was observed all 3 days had a strong thermal wind caused by the marine inversion sloping down toward the coast on the first 2 days the flow aloft was westerly or northerly so that the thermal wind added to the background flow results in a strong jet on the third day the flow aloft was southerly and consequently even with the added thermal wind the northerly flow in the marine layer was too weak to be supercritical the main difference between t

observations of large wind shear above the marine boundary layer near point buchon california abstractparticularly strong winds along the coast of southern california on 24 may 2012 were measured by the wyoming king air research aircraft during the precision atmospheric marine boundary layer experiment preamble the fast flow is bounded laterally by the coastal topography and vertically by a pronounced temperature inversion separating the cool moist air in the marine boundary layer mbl from the warm dry air aloft many studies have investigated the response of this two layer flow to changes in the coastline by invoking hydraulic theory which explains the essential characteristics including changes in mbl depth and the attendant wind processes occurring just above the mbl are important to the low level thermodynamic and kinematic structure observations on this day demonstrate how the large shear above the mbl can impact the lower atmosphere a typical two layer system was observed north of point buchon which was supercritical around point buchon the depth of the mbl decreased and wind i

physical modeling of an outflow event in howe sound british columbia outflow winds occur when differing air masses are separated by a coastal mountain barrier in extreme cases the cross barrier pressure gradient and the high degree of stratification often approaching a distinct layered structure result in channel winds which exhibit hydraulic features we present a study of outflow winds in howe sound british columbia a field investigation aimed specifically at locating and quantifying hydraulic effects was undertaken during the winter months of 1992 1993 microbarographs positioned in the region recorded pressure changes at discrete locations in the streamwise direction the pressures obtained during a severe outflow wind event which occurred from december 27 1992 to january 1 1993 show a highly variable lower layer depth suggestive of hydraulic control experiments were conducted with a three dimensional physical model that is geometrically and kinematically similar to howe sound synoptic conditions recorded during the outflow wind event in howe sound in december 1992 were used to determine appropriate model flow forcing the expanse of supercritical flow area was observed to be relatively sensitive to changes in along channel pressure gradient and downstream depth when compared to changes in discharge channel sinuosity and local topography appeared to force critical conditions at specific locations for example a channel bend combined with headlands was observed to force a situation where subcritical and supercritical streams flow side by side flow separation resulting in lateral shear discontinuities produced similar conditions these effects are discussed and put into context with field observations field and model results show good agreement

formation of the yellow river inferred from loess palaeosol sequence in mangshan and lacustrine sediments in sanmen gorge china abstract the formation of the yellow river was a significant geological and hydrological event in the history of landscape evolution in northern china resulting from interactions between various earth system processes earlier concepts about the ages of the river s formation are quite controversial this paper investigates the age of the samen gorge the last gorge along the course of yellow river before it reaches the sea the main research materials presented here are a 172 1 m thick loess palaeosol sequence in mangshan located in the south side of the yellow river b lacustrine sediments of the former sanmen lake the chronology is based on the stratigraphical correlations with the well dated loess palaeosol sequence in luochuan of central loess plateau palaeomagnetism and optically stimulated luminescence osl and thermoluminescence tl datings an abrupt increase in the rate of sedimentation is recognized in the stratigraphical layers l 2 and above of the mangshan sequence the loess unit l 1 and palaeosol unit s 1 of mangshan are much thicker than those of other sections in loess plateau as well indicating a new and unique source only for the mangshan region the aeolian deposition of the loess is found to have started at ca 150 ka in the bottom of the former large lake west of the sanmen gorge and suggests desiccation of the former sanmen lake at this point in time the yellow river could bring large amount of fluvial sediment east of the sanmen gorge after the gorge was downcut the fluvial sediment is suggested to be the new source of loess identified in the mangshan sequence therefore it is concluded that the downcutting of the sanmen gorge started at ca 150 ka and indicates the full development of the yellow river

the horizontal momentum balance in the marine atmospheric boundary layer during code 2 abstract the horizontal momentum balance in the marine atmospheric boundary layer during the coastal ocean dynamics experiment code is analyzed using meteorological data from an array of surface moorings previous studies have indicated the presence of orographically generated mesoscale features that are induced by strong southward flow around point arena the present analysis demonstrates that during periods of strong southward flow the cross shore momentum equation is dominated by a balance between the ageostrophic acceleration associated with the flow curvature around point arena and the cross shore pressure gradient while the along shore momentum equation is dominated by a balance between vertical stress divergence and alongshore pressure gradient these balances are consistent with results from a shallow water model of the marine layer the calculations provide evidence for orographic modification of the horizontal structure of the boundary layer under a broader range of southward flow conditio

simulations of supercritical flow around points and capes in a coastal atmosphere fully 3d nonlinear model simulations for supercritical flow along locations at the california coast at cape mendocino and point sur are presented the model results are objectively and subjectively verified against measurements from the coastal waves 1996 experiment with good results they are then analyzed in terms of the flow structure the impact of the local terrain the atmospheric forcing on the ocean surface and the momentum budgets it is verified that the flow is supercritical fr 1 within a rossby radius of deformation from the coast and that it can be treated as a reduced gravity shallow water flow bounded by a sidewall the coastal mountain barrier as the supercritical flow impinges on irregularities in the coastline orientation expansion fans and hydraulic jumps appear the modeled froude number summarizes well the current understanding of the dynamics of these events in contrast to inviscid irrotational hydraulic flow the expansion fans appear as curved lines of equal pbl depth and lens shaped maxima in wind speed residing at the pbl slope this is a consequence of the realistic treatment of turbulent friction modeled mean pbl vertical winds in the hydraulic features range 6 1 2 cm s21 while larger vertical winds 6 5 10 cm s21 are due to the flow impinging directly on the mountain barrier local terrain features at points or capes perturb the local flow significantly from the idealized case by emitting buoyancy waves the momentum budget along straight portions of the coast reveals a semigeostrophic balance modified by surface friction while being geostrophic in the across coast direction the along coast momentum shows a balance between the pressure gradient force and the turbulent friction in the expansion fans the flow is ageostrophic and the imbalance is distributed between turbulent friction and ageostrophic acceleration according to the magnitude of the former there is also a good correspondence between the magnitude of the local curl of the surface stress vector and the measured depression in sea surface temperature sst in areas where the latter is large and the along coast flow is relatively weak implying that a substantial portion of the upwelling is driven locally supplying the measured sst in the numerical simulations with a considerable depression along the coast had only marginal feedback effects on the character of the flow

control of barrier island shape by inlet sediment bypassing east frisian islands west germany abstract a study of the east frisian islands has shown that the plan form of these islands can be explained by processes of inlet sediment bypassing this island chain is located on a high wave energy high tide range shoreline where the average deep water significant wave height exceeds 1 0 m and the spring tidal range varies from 2 7 m at juist to 2 9 m at wangerooge an abundant sediment supply and a strong eastward component of wave power 4 4 103 w m 1 have caused a persistent eastward growth of the barrier islands the eastward extension of the barriers has been accommodated more by inlet narrowing than by inlet migration it is estimated from morphological evidence that a minimum of 2 7 105 m3 of sand is delivered to the inlets each year via the easterly longshore transport system much of this sand ultimately bypasses the inlets in the form of large migrating swash bars the location where the swash bars attach to the beach is controlled by the amount of overlap of the ebb tidal delta along the downdrift inlet shoreline the configuration of the ebbtidal delta in turn is a function of inlet size and position of the main ebb channel the swash bar welding process has caused preferential beach nourishment and historical shoreline progradation along the east frisian islands this process has produced barrier islands with humpbacked bulbous updrift and bulbous downdrift shapes the model of barrier island development presented in this paper not only explains well the configuration of the german barriers but also the morphology of barriers along many other mixed energy coasts

stacked 2 6 ma grain size record from the chinese loess based on five sections and correlation with the deep sea δ18o record 1 this study aims to establish a stacked climate record of the quaternary period from the chinese loess sequence and to address the forcing mechanisms for the regional climate history of the loess plateau by correlating the stacked record with a composite 18o record in deep sea sediments a total of 18 352 samples were obtained from five loess sections located at baoji lingtai jingchuan puxian and pingliang in the southern and middle loess plateau these yielded high resolution grain size records between section correlation of these shows that although small depositional hiatuses are present in places within a single section most parts of the sections display near continuous dust deposition throughout the quaternary the grain size records were tuned simultaneously to the theoretical variations in obliquity and precession of the earth s orbit the grain size records plotted on their orbital timescales were then averaged to form a stacked loess grain size time series termed the chiloparts record this resolves most of the orbital timescale paleoclimate events buried in the loess soil sequences of the southern and middle loess plateau and can be used as a regional archive of the pleistocene climate history in the loess plateau comparison of the chiloparts record with a composite marine 18o record shows that for the past 1 8 ma the loess paleosol record can be correlated almost cycle by cycle with the marine record several discrepancies in the climatic events between the two records have also been identified implying that regional forcing mechanisms may have played a part in the climatic evolution of the chinese loess plateau

post glacial landscape response to climate variability in the southeastern san juan mountains of colorado usa abstract geomorphic mapping in the upper conejos river valley of the san juan mountains has shown that three distinct periods of aggradation have occurred since the end of the last glacial maximum lgm the first occurred during the pleistocene holocene transition 12 5 9 5 ka and is interpreted as paraglacial landscape response to deglaciation after the lgm evidence of the second period of aggradation is limited but indicates a small pulse of sedimentation at 5 5 ka a third more broadly identifiable period of sedimentation occurred in the late holocene 2 2 1 ka the latest two periods of aggradation are concurrent with increases in the frequency of climate change in the region suggesting that holocene alpine and sub alpine landscapes respond more to rapid changes in climate than to large singular climatic swings soil development and radiocarbon dating indicate that hillslopes were stable during the holocene even while aggradation was occurring in valley bottoms thus we can conclude that erosion does not occur equally throughout the landscape but is focused upslope of headwater streams along tributary channels or on ridge tops this is in contrast to some models which assume equal erosion in headwater basins

geochemical evidence for the use of magnetic susceptibility as a paleorainfall proxy in the tropics abstract several workers have estimated paleomonsoonal rainfall using proxies that are related to wind strength upwelling productivity chemical weathering and pedogenesis in an earlier work on sediments of thimmannanayakanakere tk a lake in southern india shankar r prabhu c n warrier a k vijaya kumar g t sekar b 2006 a multidecadal rock magnetic record of monsoonal variations during the past 3700 years from a tropical indian tank journal of the geological society of india 68 447 459 we suggested that magnetic susceptibility lf may be used as a proxy to estimate the paleomonsoonal rainfall in tropical regions this was based on the positive correlation between magnetic susceptibility of tk sediments and instrumental rainfall data and backed up by historical records and paleoclimate proxy data from widely separated regions of india in this paper we provide geochemical data results of cbd extraction and elemental analysis and their statistical analysis pca to support our earlier proposition that lf may be used as a proxy for paleomonsoonal rainfall in the tropical regime the cbd treatment of sediment samples reduced the average lf from 132 to 64 10 8 m3 kg 1 average fd from 12 91 to 2 01 10 8 m3 kg 1 and average fd from 8 9 to 3 showing that the samples do contain pedogenic magnetite further samples of high low rainfall periods showed a higher lower reduction in the magnetic parameters suggesting a higher lower content of pedogenic magnetite metal al ratios fe al ti al na al mn al pb al zn al cu al k al ca al mg al and sr al are positively correlated most of them at the 1 level with lf suggesting that the tk sediments are derived mainly from the catchment in particular ti al k al and k na ratios that are good indicators of chemical weathering intensity cwi start increasing from 2 cal ka b p onwards corresponding to increasing lf increasing rainfall from this time as chemical weathering is principally driven by rainfall temperature being constant in tropical regions data on cwi indicators provide support to the hypothesis that lf estimates paleomonsoonal rainfall principal component analysis of geochemical and magnetic data shows that three important factors explain the variance in the data set terrigenous pedogenic rainfall and carbonate low rainfall or drought thus our data strengthen shankar et al s shankar r prabhu c n warrier a k vijaya kumar g t sekar b 2006 a multidecadal rock magnetic record of monsoonal variations during the past 3700 years from a tropical indian tank journal of the geological society of india 68 447 459 hypothesis that magnetic susceptibility may be used as a proxy for monsoonal rainfall in the tropical milieu we have proposed a model to explain pedogenesis chemical weathering intensity and carbonate precipitation which are all related to rainfall in the tk catchment

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

transcritical flows in the coastal marine atmospheric boundary layer abstract numerical solutions of shallow water flow in a variable width channel are computed to model the summertime marine atmospheric boundary layer off the u s west coast using an idealization of the coastline in the vicinity of point arena california as an example several steady state base flows are presented that are hydraulically transcritical these flows are strongly nonlinear weakly rotational and are forced by constant pressure gradients and damped by nonlinear bottom drag at the sea surface the transcritical base flows are supercritical in the vicinity of bends in the coastline but are subcritical to the north upstream and to the south downstream where the coastline is straight within the supercritical region orographic bends in the coastline produce expansion fans and compression jumps the same structures found in globally supercritical flows when the imposed pressure gradient forcing is increased the resulting base flow has a supercritical to subcritical transitional jump that

lithology and the evolution of bedrock rivers in post orogenic settings constraints from the high elevation passive continental margin of se australia understanding the role of lithological variation in the evolution of topography remains a fundamental issue especially in the neglected post orogenic terrains such settings represent the major part of the earth s surface and recent modelling suggests that a range of interactions can account for the presence of residual topography for hundreds of millions of years thereby explaining the great antiquity of landscapes in such settings field data from the inland flank of the se australian high elevation continental margin suggest that resistant lithologies act to retard or even preclude the headward transmission of base level fall driven by the isostatic response to regional denudation rejuvenation be it episodic or continuous is caught up on these resistant lithologies meaning in effect that the bedrock channels and hillslopes upstream of these stalled knickpoints have become detached from the base level changes downstream of the knickpoints until these knickpoints are breached therefore catchment relief must increase over time a landscape evolution scenario that has been most notably suggested by crickmay and twidale the role of resistant lithologies indicates that detachment limited conditions are a key to the longevity of some post orogenic landscapes whereas the general importance of transport limited conditions in the evolution of post orogenic landscapes remains to be evaluated in field settings non steady state landscapes may lie at the heart of widespread slowly evolving post orogenic settings such as high elevation passive continental margins meaning that non steady state landscapes with increasing relief through time are the rule rather than the exception

the late miocene and pliocene climate in east asia as recorded by grain size and magnetic susceptibility of the red clay deposits chinese loess plateau abstract grain size characteristics of the aeolian red clay sediment series in china demonstrate the existence of warm cool alternations during the late miocene and pliocene from the dissimilarity between the temporal patterns of grain size and magnetic susceptibility it is inferred that the finest grain size fraction in the red clay clay and very fine silt is transported by the wind as is the case of the coarser silty component relatively cool climatic conditions are indicated by increased loess supply represented by the silty component from the nw caused by a stronger winter monsoon as in the overlying quaternary system it is striking that at the same time the amounts of clay also increased probably due to transportation by intensified westerly circulation relatively warm periods are characterized by opposite grain size properties these warm cool alternations on the asian continent dated by palaeomagnetic analyses correlate well with already established changes in sea level and ice sheet volumes up to 6 ma in addition time series analysis of the grain size signal points to an orbitally forced climatic cyclicity precession eccentricity and weak obliquity

post glacial entrenchment and knickpoint migration of the yarlung tsangpo gorge southeastern tibetan plateau abstract the formation of the yarlung tsangpo river system is commonly thought to be controlled by tectonic processes initiated several million years ago however climate change may also play an important role in guiding drainage evolution here we reconstruct the drainage history of the yarlung tsangpo gorge using field observations age constraints from optically stimulated luminescence and radiocarbon dating paleosalinity reconstruction and grain size analysis of lacustrine deposits and river valley characteristics field observations clay boron derived paleosalinity reconstruction and grain size analysis of lacustrine deposits demonstrate that a closed inland saline lake existed upstream of the yarlung tsangpo gorge implying that cutting of the gorge postdated this paleolake optically stimulated luminescence and radiocarbon dating suggest that the paleolake formed at least 51 ka and terminated after 13 ka with a shift in global climate following the last glacial maximum the paleolake drained by river capture and the gorge entrenchment commenced at the village of jiala northwest of the namche barwa peak approximately 13 10 ka ago the evolution of the yarlung tsangpo occurred on a remarkably short timescale of just tens of thousands of years in response to drainage system reorganization the yarlung tsangpo incised at an average rate of at least 26 mm yr the rapid fluvial incision initiated at jiala 13 ka ago propagated rapidly upstream at 2 12 m yr the yarlung tsangpo knickpoint has not stabilized but will likely continue to migrate upstream

diurnal cycle of supercritical along coast flows abstract in this study a three dimensional hydrostatic mesoscale model is used to address the transient behavior of supercritical along coast flow a control experiment and several sensitivity tests are performed in order to investigate the diurnal cycle of flow characteristics an idealized representation of the northern california terrain is used and the model results are interpreted within the reduced gravity shallow water concept in two preceding studies by the authors this theory appeared to be violated since the flow accelerated along the coastline upstream of the change in coastline orientation even though the flow was supercritical here it is shown that the criticality of the flow for typical summertime conditions along the california coast actually varies diurnally the gradual acceleration of the flow along the upstream coastline is established during a subcritical phase of the simulation thus the shallow water concept is not violated because the along coast jet is primarily driven by

evidence of a geological event and environmental change in the catchment area of the yellow river at 0 15 ma abstract yellow river erosion through longyang gorge and sanmen gorge at 0 15 ma corresponds with a rapid uplifting of the qinghai xizang tibet plateau and strong incision in the middle and upper reaches of the yellow river evidence from the upper reaches middle reaches and lower reaches suggests that this event was controlled by intensive tectonic movement and climatic change evidence suggests that the onset of the last interglacial in the upper reaches began a little earlier than 0 15 ma and coincides with lake sedimentary records and oxygen isotope records from the guliya ice core in the tibet plateau

reconstructing the interacting effects of base level climate and tectonic uplift in the lower mino river terrace record a gradient modelling evaluation the origin of the lower mino river terraces in the nw iberian peninsula has been a topic of debate since the 1940s various hypotheses about their main controlling factors have been put forward but general consensus is still lacking field studies of terrace distribution and the weathering of quartzite pebbles in the terrace deposits demonstrated that terrace longitudinal correlation is not parallel to the current river bed in addition the longitudinal profile model fluver2 was used to simulate the profile evolution of the mino river over the past 450 ka a reconstructed longitudinal profile and an offshore climate record were used as inputs several scenarios with variable uplift rates were investigated and evaluated against properties of four selected reaches along the river for a match with the number of terraces their relative altitude timing and sediment thickness an uplift scenario with a net constant vertical uplift rate of 0 08 m ka 1 yielded the best results the best fit scenarios indicate that base level changes from glacioeustatic changes in combination with tectonic uplift are the main driving forces of the observed terrace formation and valley incision contrary to most nw european fluvial systems the timing of upstream controlled sediment supply has a less dominant effect on terrace formation this can be explained by the close proximity to the narrow passive atlantic margin

long term morphodynamic evolution of texel inlet and its ebb tidal delta the netherlands abstract a series of regular bathymetric surveys of texel inlet and its ebb tidal delta spanning a period of over 400 years forms a unique long term morphodynamic dataset of this largest inlet of the wadden sea the substantial changes in ebb tidal delta evolution provide a clear example of the response of the inlet system to the cumulative effects of human intervention analysis of the evolution of the ebb tidal delta morphology shows different stages each characterized by specific orientations of the main channels and shoals prior to construction of extensive coastal defense works on the southern shore of the inlet in 1750 a d the ebb tidal delta showed a downdrift asymmetry periodic shoal breaching and downdrift channel relocation were the dominant mechanisms for sediment by passing major shoal bypassing after construction of the coastal defence works a stable ebb tidal delta with a westward stretching main ebb channel developed over a period of ca 60 years damming of the zuiderzee the major part of the back barrier basin in 1932 a d distorted this stable state and over a period of about 40 years the main channel switched to a southward course remaining stable ever since during the pre and post damming stable states the sediment bypassing took place as minor shoal by passing the main channel remained in position and smaller parts of the swash platform periodically migrated landward over the ebb tidal delta the well monitored large scale changes on the ebb tidal delta which were initiated by the construction of the coastal defence works and closure of the zuiderzee show that incorporation of inlet modifications and back barrier processes is vital for a correct description of the ebb tidal delta dynamics and processes of texel inlet a conceptual model is introduced to describe the process response relation between intervention and ebb tidal delta change

mesoscale simulation of supercritical subcritical and transcritical flow along coastal topography abstract a mesoscale atmospheric model is used to address the characteristics of stratified flow bounded by a side wall along a varying coastline initial froude number values are varied through alteration of marine inversion strength permitting examination of supercritical subcritical and transcritical flow regimes encountering several coastal configurations consistent with shallow water models sharp drops in boundary layer depth and flow acceleration occur in flow rounding convex bends however significant flow response occurs in the stratified layer aloft which is unexplained by conventional shallow water theory the strongest flow acceleration occurs in the transcritical case while regardless of inversion strength the deformation of the isentropes aloft shows general structural similarity advection of horizontal momentum is an important component of the horizontal force balance a simulation having several coastline bends exhibits a detached oblique hydraulic jump upwind of a concave bend t

the evolution of the shiwanghe river valley in response to the yellow river incision in the hukou area shaanxi china abstract tributary response to mainstream incision is an important landscape evolution process the objective of this study is to examine tributary valley evolution in response to mainstream incision the shiwanghe river a tributary of the yellow river in the hukou area was chosen for a case study the terraces and knickpoints of the shiwanghe river were investigated and correlated to those of the mainstream optically stimulated luminescence osl was applied to date fluvial terraces longitudinal profiles of river and terraces were used to analyze valley evolution the terrace sequence of the shiwanghe river near their confluence is almost identical to the yellow river terraces at the hukou area this suggests that terrace formations of the tributary and the mainstream are synchronous and influenced by similar factors but the formation age of the same tributary terrace varies from downstream to the upper reaches of the river valley for such terraces their formation should be controlled by knickpoint migration a sudden drop in base level caused by the yellow river incision would trigger the formation of a knickpoint in the tributary a new terrace would be formed as the knickpoint propagated upstream throughout the tributary valley due to the different erodibility of bedrock a set of interbedded sandstone and shale the major knickpoint would disassemble into a cluster of small ones during its propagation the age of terrace formation with various valley segments depends on knickpoint migration rate and distance from the confluence vertical incision of the yellow river results in knickpoint recession of its tributaries the migration rate of knickpoints was affected by climate lithologic variation and to some extent structural control

evolution of the late cenozoic tectonic stress regime in the shanxi rift central north china plate inferred from new fault kinematic analysis abstract the shanxi rift an intracontinental belt along the eastern margin of the ordos block north china plate has undergone multi stage extensional deformation during the late cenozoic in this study new fault kinematic analysis of boundary faults in the shanxi rift constrained by geochronological data defines a three stage tectonic stress regime since the late miocene providing new structural evidence for deciphering the northeastward growth of the tibetan plateau the earliest stage involved a transtensional stress regime of nw se extension and ne sw compression in the late miocene early pleistocene ca 10 1 8 ma and characterized by mean principal stress axes of 1 at 344 7 87 2 2 at 217 6 01 1 and 3 at 128 1 01 0 the early transtensional stress regime was responsible for the opening of the shanxi rift and was very likely associated with intensive right lateral pull apart activity in the eastern ordos block due to the northeastward growth of the tibetan plateau during the second stage the stress regime changed to less intense ne sw extension with mean stress orientations of 323 3 85 2 for 1 127 5 02 9 for 2 and 214 9 02 6 for 3 in the early late pleistocene ca 1 8 0 11 ma this stage is marked by a distinct shift from fluvio lacustrine to fluvio piedmont sedimentary facies at the end of the early pleistocene and the widespread eruption of basalt in the datong basin north of the shanxi rift this short lived extension appears to be the result of relaxation in the midst of crustal shortening during growth of the tibetan plateau the third stage was transtensional characterized by nnw sse extension and wnw ese compression 1 at 060 88 9 2 at 074 9 03 9 and 3 at 164 00 since the late pleistocene ca 0 11 ma causing dextral shear deformation in the shanxi rift and the disappearance of its paleo lake this stage resulted from regional ene wsw shortening due to northeastward growth of the tibetan plateau

the approximate age of the planation surface and the incision of the yellow river abstract the yellow river huang he downstream of the jinshaan canyon displays well preserved fluvial terrace sequences below an extensive planation surface at the northeastern ordos plateau despite a series of well developed geomorphic surfaces the landscape evolution of the plateau is largely unconstrained the jinshaan canyon formed by the deeply incising yellow river through the ordos plateau provides keys to understanding the landscape evolution of this plateau with respect to the nearby northeastern margin of the tibetan plateau this paper presents two sets of magnetostratigraphic results derived from the aeolian deposits red clay and loess on the planation surface and the uppermost yellow river terrace in the middle part of the jinshaan canyon magnetostratigraphic analysis reveals that the planation surface and the uppermost yellow river terrace formed respectively at circa 3 7 ma and circa 1 2 ma ago the ordos plateau is the product of a period of planation culminating just before circa 3 7 ma and then was interrupted by an episode of uplift which may be correlated with the accelerated growth of the tibetan plateau in the miocene pliocene the drainage system in the jinshaan canyon was re organized around 3 7 ma no correlation seems to exist between an older drainage existing prior to circa 3 7 ma and the present yellow river network in the jinshaan canyon even though sedimentary and tectonic evidence suggests that the drainage in the middle reach of the yellow river formed in the late miocene early pliocene the yellow river has developed its rectangular course around the ordos plateau only since circa 3 7 ma

adjustment of the marine atmospheric boundary layer to a coastal cape abstract during summer significant changes in marine atmospheric boundary layer mabl speed and depth occur over small spatial scales 100 km downstream from topographic features along the california coast in june and july 1996 the coastal waves 96 project collected observations of such changes at capes with an instrumented aircraft this paper presents observations from the 7 june flight when the layer averaged speed increased 9 m s 1 and depth decreased by 500 m over a 75 km downwind from cape mendocino accompanied by enhanced surface fluxes and local cloud clearing the acceleration and thinning are reproduced when the flow is modeled as a shallow transcritical layer of fluid impinging the bends of a coastal wall leading to the interpretation that they are produced by an expansion fan model runs were produced with different coastlines and imposed pressure gradients with the best match provided by a coastline in which the cape protruded into the flow and forced a response in the subcritical r

the evolution of a terrace sequence along the yellow river huanghe in hequ shanxi china as inferred from optical dating abstract investigations of river terraces are often seriously hindered by difficulties in dating the formation of terraces using conventional and well established methods such as 14c dating in this paper recently developed optical dating techniques were applied to a yellow river terrace sequence in the hequ area shanxi province china based on field investigations four terraces were identified systematic sampling for optical dating was carried out on these terrace deposits the single aliquot regenerative dose method was used to determine equivalent dose by analyzing the degree of bleaching of fluvial samples maximum and minimum optical ages were obtained for these samples the minimum optical dates obtained are geomorphologically and stratigraphically consistent with each other suggesting that the dates are reliable the formation ages of the four terraces are 3 4 10 20 25 30 and 90 ka respectively on the basis of these optical dates the geomorphological evolution of the terrace sequence was established and the factors affecting the terrace development discussed

coastal jet adjustment near point conception california with opposing wind in the bight abstracttypical spring and summer conditions offshore of california consist of strong northerly low level wind contained within the cool well mixed marine boundary layer mbl that is separated from the warm and dry free troposphere by a sharp temperature inversion this system is often represented by two layers constrained by a lateral boundary aircraft measurements near point conception california on 3 june 2012 during the precision atmospheric mbl experiment preamble captured small scale features associated with northerly flow approaching the point with the added complexity of encountering opposing wind in the santa barbara channel an extremely sharp cloud edge extends south southwest of point conception and the flight strategy consisted of a spoke pattern to map the features across the cloud edge lidar and in situ measurements reveal a nearly vertical jump in the mbl from 500 to 100 m close to the coast and a sharp edge at least 70 km away from the coast in this case it is hypothesized that

the marine atmospheric boundary layer jet in the coastal ocean dynamics experiment the vertical and horizontal structure of the atmospheric boundary layer near the northern california coast was investigated during spring upwelling conditions as part of the 1981 coastal ocean dynamics experiment two daytime aircraft flights were devised to measure mean and turbulent quantities for 25 km tracks along and across the continental shelf from 30 to 1200 m altitude the pacific high offshore and an inland thermal low characterized the synoptic situations and equatorward winds resulted which produced intense ocean upwelling the wind profile was found to be jet shaped maximum wind speeds were 25 m s 1 and 16 m s 1 at 400 and 100 m respectively in the two flights above and below the heights of the jet speed maxima the wind speed decreased rapidly sharp density inversions existed at the levels of the peak wind speeds in one flight the inversion also sloped down toward the coast turbulence was effectively confined below the inversions strong zonal temperature gradients above the inversion between the hot land and cool marine air caused a thermal wind for which the wind speed decreased with height below the inversion turbulent stress divergence was large and effective in transferring the horizontal momentum of the wind to the sea slowing the wind there was also a small thermal wind below the inversion but opposite to the one above owing to the well mixed air temperature following the sea surface temperature which was cold at the coast and relatively warmer offshore owing to the upwelling these effects explain the jet shaped wind profile the mean momentum equations show that an acceleration toward the coast can balance the pressure gradient coriolis and turbulent stress divergence forces and there were some observations to support this complete balance was not obtained for the turbulent kinetic energy budget inferred dissipation rates were too large

orographic shaping of us west coast wind profiles during the upwelling season spatial and temporal variability of nearshore winds in eastern boundary current systems is affected by orography coastline shape and air sea interaction these lead to a weakening of the wind close to the coast the so called wind drop off in this study regional atmospheric simulations over the us west coast are used to demonstrate monthly characteristics of the wind drop off and assess the mechanisms controlling it using a long term simulation we show the wind drop off has spatial and seasonal variability in both its offshore extent and intensity the offshore extent varies from around 10 to 80 km from the coast and the wind reduction from 10 to 80 we show that when the mountain orography is combined with the coastline shape of a cape it has the biggest influence on wind drop off the primary associated processes are the orographically induced vortex stretching and the surface drag related to turbulent momentum flux divergence that has an enhanced drag coefficient over land orographically induced tilting twisting can also be locally significant in the vicinity of capes the land sea drag difference acts as a barrier to encroachment of the wind onto the land through turbulent momentum flux divergence it turns the wind parallel to the shore and slightly reduces it close to the coast another minor factor is the sharp coastal sea surface temperature front associated with upwelling this can weaken the surface wind in the coastal strip by shallowing the marine boundary layer and decoupling it from the overlying troposphere

tectonic and climatic forcing on the panj river system during the quaternary surface processes involve complex feedback effects between tectonic and climatic influences in the high mountains of pamir the ongoing india asia collision provokes the development of east west trending mountain ranges that impose structural control on flow directions of the pamir rivers the evolving relief is further controlled by strong moisture gradients the decreasing precipitations from the southern and western margins of the pamir plateau to its center in their turn control the emplacement of glaciers chronologies of glacial records from the pamir plateau attest for strong climatic variability during the quaternary corresponding remnants of glacial advances suggest glacial morphodynamic restricted to 4 000 m a s l since marine isotope stage 4 the panj the trunk river of pamir deflects from the predominant westward drainage connecting its main tributaries at the western margin of the drainage basin the geometry of the river network and the pattern of incision characterize the panj as a composite river river reaches of indicated low incision coincide with west trending valleys parallel to domes and their bounding faults valley shape ratios reflect increased incision in north trending sections but do not match with changes in the catchment geometry or erodibility of rock types modelled riverbed profiles distinguish three panj reaches the upstream increase in convexity suggests successive river captures in response to local base level changes the northward deflected river reaches link the local base levels which coincide with the southern boundaries of the shakhdara and yazgulom dome and darvaz range we argue that tectonics plays a large role controlling the drainage system of the panj and hence surface processes in the pamir mountains

bedrock river incision response to basin connection along the jinshan gorge yellow river north china abstract the jinshan gorge of the yellow river connecting the hetao and the fenwei basins is a key area for understanding the formation and evolution of the drainage system in response to bedrock river incision we have measured fluvial terraces along the gorge in the field in detail the longitudinal profile and published dating of terraces indicate that rapid river incision occurred in the late pleistocene the deactivated boundary faults and uniform lithology of the gorge have no measurable influence the incision changes in precipitation are consistent with incision rate in late pleistocene rapid in mis5 and low in mis3 whereas appearing inconsistent in mis7 when high rainfall was associated with low incision rates we infer the variation of discharge to large paleolakes drainage in response to connection of the hetao and fenwei basins revealed by lacustrine platform in these two basins fast paleolake regressions took place approximately at 0 22 ma in the fenwei basins leading to base level fall and then 0 10 ma in the hetao basins causing an abrupt increase in discharge these two events made major contributions to the rapid bedrock river incision

response of the summer marine layer flow to an extreme california coastal bend abstract a summer wind speed maximum extending more than 200 km occurs over water around point conception california the most extreme bend along the u s west coast the following several causes were investigated for this wind speed maximum 1 synoptic conditions 2 marine layer hydraulic flow effects 3 diurnal variations 4 mountain leeside downslope flow 5 sea surface temperature structure and 6 island influence synoptic conditions set the general wind speed around point conception and these winds are classified as strong moderate or weak the strong wind condition extends about point conception reaching well offshore toward the southwest and the highest speeds are within 20 km to the south moderate wind cases do not extend as far offshore and they have a moderate maximum wind speed that occurs over a smaller area in the western mouth of the santa barbara channel the weak wind speed case consists of light and variable winds about point conception each category occurs about one third

large scale structure of the june july 1996 marine boundary layer along california and oregon abstract data from surface stations profilers long range aircraft surveys and satellites were used to characterize the large scale structure of the marine boundary layer off of california and oregon during june and july 1996 to supplement these observations june july 1996 averages of meteorological fields from the u s navy s operational coupled ocean atmospheric mesoscale prediction system coamps model were generated for the region model calculations show a broad band of fast northerly surface winds exceeding 7 m s 1 extending along the california oregon coast buoy measured peaks of 7 1 m s 1 off bodega bay 7 2 m s 1 off point piedras blancas and 8 8 m s 1 near point conception were reported mean winds at the buoys located 15 25 km offshore are generally faster than those at coastal stations and all station winds are faster in the afternoon the aircraft and station observations confirm that an air temperature inversion typically marks the top of the marine boundary layer which deepens offs

astronomical calibration of loess paleosol deposits at luochuan central chinese loess plateau abstract the 140 m loess paleosol profile at luochuan in the central chinese loess plateau was sampled at 5 cm intervals in loess units and at 3 cm in paleosol units in order to obtain a high resolution climatic record covering the past 2 5 million years all samples were measured for magnetic susceptibility which is regarded as a good proxy index of the east asian summer monsoon strength on the basis of the astronomical theory of pleistocene climatic change an age model of the luochuan loess paleosol sequence was developed by tuning the magnetic susceptibility record to time series of insolation changes the results show that the ages of the boundaries between the malan and lishi and lishi and wucheng loess formations are 71 and 1320 kyr bp respectively the onset of loess accumulation is at 2470 kyr bp our age model was tested by comparing the orbitally derived ages with absolute age determinations of magnetic reversals and cross spectrum analyzing with solar radiation variations for summer at 65 n these indicate that the calibration provides a reliable time scale for the luochuan loess paleosol deposit

the summertime low level jet and marine boundary layer structure along the california coast abstract this paper examines the strong summertime northerly low level jet llj that frequently exists along the california coast the persistent synoptic scale pressure distribution north pacific high to the west thermal low to the east and baroclinity created by the juxtaposition of the heated continent and the cool marine layer produce the mean structure of this llj strong diurnal thermal forcing coupled with topographic influences on the flow modulate the jet structure position and intensity a mesoscale model is used to examine many of the complex facets of the llj flow dynamics several sensitivity studies in addition to a control experiment aid in this investigation principal findings of this study include the following the pronounced east west slope of the marine planetary boundary layer mpbl is not due primarily to colder sst values along the coast dynamically forced low level coastal divergence coupled with synoptic scale divergence appears to be dominant in determining mpbl i

regional analysis of bedrock stream long profiles evaluation of hack s sl form and formulation and assessment of an alternative the ds form the equilibrium form of the fluvial long profile has been used to elucidate a wide range of aspects of landscape history including tectonic activity in tectonic collision zones and in continental margin and other intraplate settings as well as other base level changes such as due to sealevel fluctuations the hack sl form of the long profile which describes a straight line on a log normal plot of elevation normal versus distance logarithmic is the equilibrium long profile form that has been most widely used in such studies slope area analysis has also been used in recent years we show that the sl form is a special case of a more general form of the equilibrium long profile here called the ds form that can be derived from the power relationship between stream discharge and downstream distance and the dependence of stream incision on stream power the ds form provides a better fit than the sl form to river long profiles in an intraplate setting in southeastern australia experiencing low rates of denudation and mild surface uplift we conclude that if an a priori form of the long profile is to be used for investigations of regional landscape history the ds form is preferable in particular the ds form in principle enables equilibrium steepening due to an increase in channel substrate lithological resistance parallel shift in the ds plot to be distinguished from disequilibrium steepening due to long profile rejuvenation disordered outliers on the ds plot slope area analysis and the slope distance ds approach outlined here are complementary approaches reflecting the close relationship between downstream distance and downstream catchment area copyright 2006 john wiley sons ltd

numerical modeling of glacial sediment production and transport during deglaciation abstract we aim to improve the understanding of sediment fluxes originating from ice sheet outlet glaciers in order to explain the evolution of sedimentary fjord fills a numerical glacial erosion and sediment flux process model has been developed to quantify sediment generation and subglacial transport dynamic ice sheet cover is generated from topography and climate parameters affecting the glacial net mass balance pressure temperature and velocity characteristics of the ice sheet force erosion at the glacier bed bed erodability depends on bedrock hardness and potential shielding by sediment after erosion sediment is either stored at the bed or transported either by meltwater or englacially within basal ice model experiments show ice retreat is driven by valley topography rapid retreat occurs in the flatter valley stretches and slower retreat in the steeper parts of a glacial valley distinct depocenters of exposed sediment develop during retreat predicted erosion rates in the glaciated valley range from 37 to 56 mm yr for different climate scenarios which is well within the range of reported field reconstructions erosion is significantly accelerated beneath warm based ice and the effect of an enlarged warm based footprint during warming compensates for decreasing ice mass topographic shielding of bedrock by previously eroded material in large areas constrains erosion by a factor 4 simulated glacier retreat and melt water flux initially occur at a high rate and subsequently decelerate while sediment delivery exhibits a distinct lagging of several thousands of years behind the meltwater flux upon the transition from glaciation to deglaciation the subglacial system is in a sediment starved state late deglacial erosion and sub and englacial sediment storage cause a lagging sediment delivery to downstream periglacial fluvial and lacustrine domains

paleomagnetic chronology and paleoenvironmental records from drill cores from the hetao basin and their implications for the formation of the hobq desert and the yellow river abstract reconstructing the cenozoic environmental history of hetao basin in the northern part of the ordos plateau in north china is important not only for revealing the evolution of the yellow river but also for understanding the formation of the hobq desert here we present the stratigraphic framework of drill core dr01 with length of 2503 18 m and the results of magnetostratigraphic and esr dating and multi proxy analyses of drill core wedp05 with length of 274 60 m from the hetao basin the magnetostratigraphic and esr results indicate that core wedp05 spans the last 1 68 ma stratigraphic sequence of core dr01 indicates that the hetao area was uplifted and eroded during the early cenozoic before subsiding to form a sedimentary basin subsequently the basin was a fluvio lacustrine environment during the pliocene and then experienced alternating desert and fluvio lacustrine conditions during the quaternary sedimentary facies and multi environmental proxy analyses of core wedp05 indicate that the basin was occupied by a fluvio lacustrine system during the following intervals 1 47 1 30 ma 1 17 1 07 ma 0 68 0 60 ma and from 0 47 ma to the last interglacial and that a desert environment developed during the lake regression phases of 1 30 1 17 ma 1 07 0 68 ma and 0 60 0 47 ma the presence of aeolian sand at the base of core wedp05 suggests that the origin of the hobq desert can be traced back to the early pleistocene and resulted from the erosion and transportation of exposed fluvio lacustrine sediments by near surface winds associated with the asian winter monsoon a large river channel in the hetao basin may have existed as early as the pliocene which was occupied by the yellow river when its upper reaches formed by at least 1 6 ma subsequently at least since 1 2 ma the yellow river formed its drainage system around the hetao basin and controlled the paleoenvironment evolution of the basin

the fluvial cycle at cold warm cold transitions in lowland regions a refinement of theory abstract a previously established non linear theory of river cyclicity as a response to climate change states that short phases of fluvial instability occur both at the transition from relatively warm temperate to cold periglacial and from relatively cold to warm periods such instability typically starts with vertical erosion successively followed by sedimentary fill of the erosive scar in spite of frequent confirmation of this theory by geomorphological reconstructions a few problems arise first there are fewer incision phases than climatic transitions secondly remnants of erosion at cold warm transitions are scarce in contrast to obvious erosion relics at warm cold transitions furthermore it appears that the incision style is strikingly different at both kinds of climatic transitions similarly the long stable phases are also expressed in terms of different floodplain development in cold and warm periods these arguments require a modification of the general non linear theory at the transition from relatively temperate to colder conditions rivers transformed gradually from a regular low energy single channel course to a periodically high energy multi channel type the latter braided type is characterized by intense lateral movement rather than by deep vertical erosion this results in a well expressed morphology of wide extensive floodplains and terraces in contrast the linear and constrained meandering channels incise with small width depth ratio and build floodplains of limited lateral extent consequences are twofold 1 the spatial limitation of the deeply incised meandering valleys at the beginning of warm periods counts against their recognition 2 relatively strong lateral migration of the braided rivers removes most traces of previous meandering systems which contrasts with the limited lateral activity of confined meandering channels it means that in a warm cold warm alternation generally only one phase of vertical erosion is preserved the one that is caused by the high energy braided river at the start of the cold period

adjustment of the marine atmospheric boundary layer to the large scale bend in the california coast 1 observations of the surface wind field off the u s west coast were made from satellite by the sea surface microwave imager ssm i during june 1994 and june 1996 the coast bends inward 28 at 40 n latitude northerly wind speeds are high within a region that extends far south and offshore of this bend bounded on the east by the california coast on average the high speed wind zone extends 250 km from shore and 800 km alongcoast long coast perpendicular aircraft transects show that moving onshore the depth of the mabl decreases the northerly wind speed increases and the froude number increases a network of oceanographic buoys records the surface wind speed direction and pressure from six buoy pressure measurements the geostrophic wind vector was computed to represent the synoptic flow over the oregon northern california coastal waters the satellite surface wind fields were composited by the direction of the buoy geostrophic background wind the predominant direction is 210 180 a high speed region extends south of the bend for directions in the 0 180 range moving counterclockwise which corresponds to a downcoast component of the pressure gradient for directions between 180 and 0 flow splits at the bend and the region of highest winds is found to its north and offshore a high speed region south of the bend was present in 65 of the satellite wind maps as well as in the june averages the flow s response to coastal promontories such as point arena is nested within this broad zone of fast thin likely supercritical flow

a case of rapid rock riverbed incision in a coseismic uplift reach and its implications abstract during the 1999 chi chi earthquake m w 7 6 in taiwan the coseismic displacement induced fault scarps and a pop up structure in the taan river the fault scarps across the river experienced maximum vertical slip of 10 m which disturbed the dynamic equilibrium of the fluvial system as a result rapid incision in the weak bedrock with a maximum depth of 20 m was activated within a decade after its armor layer was removed this case provides an excellent opportunity for closely tracking and recording the progressive evolution of river morphology that is subjected to coseismic uplift based on multistaged orthophotographs and digital elevation model dem data the process of morphology evolution in the uplift reach was divided into four consecutive stages plucking is the dominant mechanism of bedrock erosion associated with channel incision and knickpoint migration the astonishingly high rate of knickpoint retreat kpr as rapid as a few hundred meters per year may be responsible for the rapid incision in the main channel the reasons for the high rate of kpr are discussed in depth the total length of the river affected by the coseismic uplift is 5 km 1 km in the uplift reach and 4 km in the downstream reach the downstream reach was affected by a reduction in sediment supply and increase in stream power the kpr cut through the uplift reach within roughly a decade further significant flooding in the future will mainly cause widening instead of deepening of the channel

differentiating the roles of lithology and uplift in the steepening of bedrock river long profiles an example from southeastern australia hack determined that the equilibrium river long profile on a single lithology is a straight line when plotted semi logarithmically deviation from this straight line may be an equilibrium response to lithological variation or disequilibrium following base level change the amount of deviation d ast at any point downstream of the point of departure from the semi log straight line can be measured by projection of the upstream equilibrium profile and subtraction of the actual stream elevation from the projected elevation comparisons between the values of d ast for a trunk and a tributary at their junction can be used to differentiate steepening as a result of base level change from lithologically induced steepening in the former case d ast represents the incision induced by the base level change and will be equal for the trunk and the tributary it is very unlikely that values of d ast will be equal in the case of lithologically induced steepening because d ast in an

impact of nearshore wind stress curl on coastal circulation and primary productivity in the peru upwelling system 1 coastal upwelling dynamics are strongly affected by alongshore wind stress and nearshore wind stress curl a coupled physical biogeochemical regional model and lagrangian diagnostics are used in the peru current system to determine how the upwelling of nutrients and the primary productivity are impacted by the spatial structure of the nearshore wind stress three wind stress products derived from the ers and quikscat scatterometers and a smoothed quikscat field mainly differing in nearshore wind stress curl patterns were used simulations are found to produce significantly different mean surface chlorophyll distributions and show that strong upwelling favorable nearshore wind stress curl may locally induce a wide coastal productive zone through upwelling of nutrient replete waters brought by a shoaling coastal undercurrent using wind stress products with realistic nearshore patterns is therefore crucial for the modeling of coupled physical biogeochemical coastal processes

the marine layer off northern california an example of supercritical channel flow abstract during the spring and summer northerly winds driven by the north pacific high pressure system are prevalent over the northern california continental shelf only interrupted for periods of a few days when weak or southerly winds occur in the course of the coastal ocean dynamics experiment code fixed station and observations were made to describe the temporal and spatial structure of the lower atmosphere and their relation to the strong upwelling of coastal waters in a region extending up to 40 km offshore and 100 km along the coast these observations suggest that atmospheric conditions during the spring and summer usually fall into one of three categories the surface wind can be everywhere weak pattern 1 it can blow at large speeds in a uniform pattern pattern 2 or finally the structure of the northerly surface wind can be complex with large changes in the wind speed and corresponding changes in the surface pressure over short spatial scales pattern 3 the latter pattern which o

coastal perturbations of marine layer winds wind stress and wind stress curl along california and baja california in june 1999 abstract month long simulations using the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 with a horizontal resolution of 9 km have been used to investigate perturbations of topographically forced wind stress and wind stress curl during upwelling favorable winds along the california and baja california coasts during june 1999 the dominant spatial inhomogeneity of the wind stress and wind stress curl is near the coast wind and wind stress maxima are found in the lees of major capes near the coastline positive wind stress curl occurs in a narrow band near the coast while the region farther offshore is characterized by a broad band of weak negative curl curvature of the coastline such as along the southern california bight forces the northerly flow toward the east and generates positive wind stress curl even if the magnitude of the stress is constant the largest wind stress curl is simulated in the lees of point conception and the santa ba

the paleolithic site of longwangchan in the middle yellow river china chronology paleoenvironment and implications the longwangchan paleolithic site situated on the yellow river terraces in the hukou area shaanxi province china was found in 2003e2004 and two areas localities 1 and 2 of the site were excavated in 2005e2008 abundant stone artifacts including microliths a grinding stone fragment and a shovel with some animal bones and shells were recovered from locality 1 in this study the cultural deposits from locality 1 were dated using radiocarbon and optical dating techniques and the sediment properties of the deposits were analyzed the results show that the age of the deposits ranges from 29 to 21 ka and most of them were deposited between 25 ka and 29 ka this indicates that corresponds to late marine isotope stage mis 3 and early mis 2 during the human occupation period the climate in this area became colder and drier sediments from beds where the grinding slab and the shovel were found were dated to w25 ka which is the oldest among the grinding stones found in china the microliths and the grinding stone are important evidence for an incipient socio economic process that eventually led to the regional transition from hunting foraging to farming

adjustment of the summer marine boundary layer around point sur california an instrumented c 130 aircraft flew over water around point sur california on 17 june 1996 under strong northwest wind conditions and a strong marine inversion patterns were flown from 30 to 1200 m elevation and up to 120 km offshore nearshore marine air accelerated past point sur reaching a surface maximum of 17 ms 21 in the lee winds measured over water in and above the marine layer were alongshore with no significant cross shore flow sea level pressure 10 m air temperature and air temperature inversion base generally decreased toward the coast and were an absolute minimum just downcoast of the wind speed maximum the sea surface temperature also decreased toward the coast but was an absolute minimum directly off point sur the nearcoast air temperature inversion base height was 400 m north of point sur decreased to a minimum of 50 m in the lee of point sur then increased farther to the south wind speeds were at a maximum centered along the air temperature inversion base the fastest was 27 m s 21 in the lee of point sur using a froude number calculation that includes the lower half of the capping layer the marine layer in the area is determined to have been supercritical most of the marine layer had froude numbers between 1 0 and 2 0 with the extreme range of 0 8 2 8 temperatures in the air temperature inversion in the lee were substantially greater than elsewhere modifying the surface pressure gradient the overall structure was a hydraulic supercritical expansion fan in the lee of point sur under the influence of rotation and surface friction the naval research laboratory nonhydrostatic coupled ocean atmosphere mesoscale prediction system coamps indicated a broad supercritical marine boundary layer moving to the south along central california and point sur during the aircraft flight the marine boundary layer thinned and accelerated into the lee of point sur which was the site of the fastest sea level wind speed along central california isotherms dip and speeds decreased in the lee of point sur in the capping inversion well above the marine layer coamps forecasted a compression shock wave initiating off the upwind side of the topography behind point sur and other coastal points to the north evidence from the model and the aircraft supports the existence of an oblique hydraulic jump on the north side of point sur

airborne measurements of coastal jet transition around point conception california low level winds along the californian coast during spring and early summer are typically strong and contained within the cool well mixed marine boundary layer mbl a temperature inversion separates the mbl from the warmer free troposphere this setup is often represented by a two layer shallow water system with a lateral boundary near a prominent point such as point conception california the fast moving mbl flow is supercritical and can exhibit distinct features including a compression bulge and an expansion fan measurements from the university of wyoming king air research aircraft on 19 may 2012 during the precision atmospheric mbl experiment preamble captured wind in excess of 14ms 21 off of point conception under clear skies and wind 2ms 21 east of san miguel in the california bight a compression bulge was identified upwind of point conception when the flow rounds the point the mbl undergoes a near collapse and there is a spike in mbl height embedded in the general decrease of mbl height with greater turbulence just downwind that is associated with greater mixing through the inversion layer lidar and in situ measurements reveal that transport of continental aerosol is present near the pronounced mbl height change and that there is a complex vertical structure within the santa barbara channel horizontal pressure gradients are obtained by measuring the slope of an isobaric surface observations of wind and pressure perturbations are able to be linked through a simple bernoulli relationship variation of mbl depth explains most but not all of the variation of the isobaric surface

gap winds in a fjord part ii hydraulic analog abstract a simple shallow water model of gap wind in a channel that is based upon hydraulic theory is presented and compared with observations and output from a 3d mesoscale numerical model the model is found to be successful in simulating gap winds the speed and depth of gap wind flow is strongly controlled by topography horizontal or vertical channel contractions can act to force strong shallow supercritical flow downwind and light deep subcritical flow upwind force balance analysis of the hydraulic model output confirms mesoscale model results and indicates that the prime force balance in gap wind is between external pressure gradient and friction for supercritical flow and between external pressure gradient and height pressure gradient for subcritical flow this force balance changes near channel controls when the balance is between advection and height pressure gradient sensitivity analyses show positive sensitivity of gap wind speed to changes in discharge and external pressure gradient nega

sst wind interaction in coastal upwelling oceanic simulation with empirical coupling observations primarilyfromsatellites haveshownastatisticalrelationshipbetweenthesurfacewindstress and underlying sea surface temperature sst on intermediate space and time scales in many regions inclusive of eastern boundary upwelling current systems in this paper this empirical sst wind stress relationship is utilized to provide a simple representation of mesoscale air sea coupling for an oceanic model forced by surface winds namely the regional oceanic modeling system roms this model formulation is applied to an idealized upwelling problem with prevailing equatorward winds to determine the coupling consequencesonflow sst stratification andwindevolutions theinitiallyuniformwindfieldadjuststhrough coupling to a cross shore profile with weaker nearshore winds similar to realistic ones the modified wind stress weakens the nearshore upwelling circulation and increases sst in the coastal zone the sst induced wind stress curl strengthens offshore upwelling through ekman suction the total curl driven upwelling exceeds the coastal upwelling the sst induced changes in the nearshore wind stress field also strengthen and broaden the poleward undercurrent the coupling also shows significant impact on the developing mesoscale eddies by damaging cyclonic eddies more than anticyclonic eddies which leads to dominance by the latter dynamically this is a consequence of cyclones with stronger sst gradients that induce stronger wind perturbations inthis particularupwellingproblemandthatarethereforegenerally moresusceptibletodisruption than anticyclones at finite rossby number the net effect is a weakening of eddy kinetic energy

supercritical channel flow in the coastal atmospheric boundary layer idealized numerical simulations numerical simulations of supercritical coastal flows were performed with a three dimensional nonlinear hydrostatic meso scale model with a higher order turbulence closure the purpose was to resolve questions from previous studies related to terrain forcing idealized terrain representing northern california was used this facilitated testing of hypotheses in a simple fashion it was found that the angle by which the coast turns away from the flow regulates the acceleration in the expansion fan and determines how far downstream the maximum in the wind speed is located simulations with curved coastlines confirmed that the gradual curvature of the coastal mountains north of cape mendocino is sufficient to excite an expansion fan a decreasing height of the terrain along the coast lead to an increased acceleration of the flow largest when the slope of the terrain was confined to the change in coastline orientation a cape perpendicular to the main coastal mountains significantly blocked the flow even when as low as half the upstream marine atmospheric boundary layer mbl depth moreover a realistic cape caused gravity wave breaking these simulations confirmed that the local terrain at cape mendocino is responsible for the collapse of the mbl in shelter cove one striking feature in this study was that the flow started to accelerate far upstream of the change in coastline orientation even in supercritical conditions this phenomenon was most pronounced in the cases with the highest wind speeds using normalized wind speed and the bernoulli function from calculated back trajectories it was concluded that this feature is not due to deviations from linearity or from the shallow water concept

characteristics and transition mechanism of late cenozoic structural deformation within the niushoushan luoshan fault zone at the northeastern margin of the tibetan plateau abstract the niushoushan luoshan fault zone nlf separates two major tectonic units the ordos block and the northeastern margin of the tibetan plateau the deformational processes within this fault zone recorded the uplift and expansion of the northeastern margin of the plateau however the tectonic transition mechanisms during the end miocene pleistocene and the characteristics of deformation at the end pliocene and their tectonic significances remain unclear in this study a detailed survey of structural deformation within the fault zone was carried out the measurements were combined with regional tectonic analysis and geochronology to determine the effects of changing tectonic stress fields and proposed the following late cenozoic tectonic evolution of the nlf nw se compression and left lateral strike slip deformation in the late miocene pliocene ne sw compression and right lateral strike slip movement in late pliocene middle pleistocene and e w extensional tectonics since the late pleistocene although the late miocene deformation indicates that expansion of the northeastern margin of the tibetan plateau had already reached this fault zone at this time the most intense tectonic deformation did not commence until the end of the pliocene this indicates that the margin of the plateau was expanding at this time the results show that the tectonic evolution of the nlf was closely related to collision between the indian and eurasian plates and to uplift of the tibetan plateau the fault zone also records the expansion of the northeastern margin of the tibetan plateau and the cenozoic tectonic transition of the ordos block from westward extrusion to clockwise rotation

coastal atmospheric circulation around an idealized cape during wind driven upwelling studied from a coupled ocean atmosphere model abstract the study analyzes atmospheric circulation around an idealized coastal cape during summertime upwelling favorable wind conditions simulated by a mesoscale coupled ocean atmosphere model the domain resembles an eastern ocean boundary with a single cape protruding into the ocean in the center of a coastline the model predicts the formation of an orographic wind intensification area on the lee side of the cape extending a few hundred kilometers downstream and seaward imposed initial conditions do not contain a low level temperature inversion which nevertheless forms on the lee side of the cape during the simulation and which is accompanied by high froude numbers diagnosed in that area suggesting the presence of the supercritical flow formation of such an inversion is likely caused by average easterly winds resulting on the lee side that bring warm air masses originating over land as well as by air warming during adiabatic descent on the lee side of the topographic obstacle mountain leeside

rapid sea level fall and deep ocean temperature change since the last interglacial period we have dated huon peninsula papua new guinea and barbados corals that formed at times since the last interglacial period applying both 230 th and 231 pa dating techniques as a test of age accuracy we show that marine isotope stage mis 5e ended prior to 113 1 8 0 7 kyr when sea level was 319 m during mis 5b sea level was 357 m at 92 6 8 0 5 kyr having dropped about 40 m in approximately 10 kyr during the mis 5c 5b transition sea level then rose more than 40 m during the mis 5b 5a transition also in about 10 kyr mis 5a lasted until at least 76 2 8 0 4 kyr at a level of 324 m at that time combined with earlier data that places mis 4 sea level at 381 m at 70 8 kyr our late mis 5a data indicate that sea level fell almost 60 m in less than 6 kyr 10 6 m kyr during the mis 5 4 transition the magnitude of the drop is half that of the glacial interglacial amplitude and approximatelyequivalent to the volume of the present dayantarctic ice sheet during this interval the minimum average rate of net continental ice accumulation was 18 cm yr likely facilitated by efficient moisture transport from lower latitudes at three specific times 60 6 8 0 3 50 8 8 0 3 and 36 8 0 2 kyr during mis 3 sea level was between 385 and 374 m sea level then dropped to 3107 m at 23 7 8 0 1 kyr early in mis 2 before dropping further to last glacial maximum lgm values and then rising to present values during the last deglaciation times of rapid sea level drop correspond to times of high winter insolation at low northern latitudes and high winter latitudinal gradients in northern hemisphere insolation supporting the idea that these factors mayhave resulted in high water vapor pressure in moisture sources and efficient moisture transport to high latitude glaciers therebycontributing to glacial buildup we combined our sea level results with deep sea n 18 o records as a means of estimating the temperature and ice volume components in the marine n 18 o record this analysis confirms large deep ocean temperature shifts following mis 5e and during termination i deep ocean temperatures changed bymuch smaller amounts between mis 5c and 2 maximum temperature shift in the deep pacific is about 2 whereas the shift at a site in the atlantic is 4 under glacial conditions temperatures at both sites are near the freezing point the shift in the atlantic is likelycaused bya combination of changing proportions of northern and southern source waters as well as changing temperature at the sites where these deep waters form

supercritical marine layer flow along a smoothly varying coastline abstract a model for hydraulically supercritical atmospheric marine layer flow along a smoothly varying coastline is formulated and solved numerically the model is motivated by a recent comparison of code observations to a simple hydraulic theory which suggested the presence of an expansion fan and a compression jump downstream of topographic features the marine layer is modeled as a homogeneous rotating fluid layer decelerated by surface friction and forced by imposed upper level pressure gradients the equations are solved by a characteristic based gridpoint scheme the results indicate that the expansion fan is a robust feature that persists under most conditions in the present more realistic model but is dramatically altered in structure by the presence of friction while the jump may weaken rapidly offshore due mainly to offshore variations of the layer height upstream of the jump the agreement between observations and model predictions is good enough to suggest that a first order description of

climatically controlled river terrace staircases a worldwide quaternary phenomenon a comparison of fluvial terrace sequences from around the world based on data collected as part of international geoscience programme igcp project no 449 has revealed significant patterns river terraces provide important records of uplift which is essential for their formation and of landscape evolution their cyclic formation however almost invariably seems to have been a response to climatic fluctuation sequences in the european core area of igcp 449 which has the longest and most extensive research history have been used as templates for worldwide comparison there is evidence for a global acceleration of uplift at the time of and perhaps in response to the mid pleistocene revolution when climatic fluctuation switched to 100 kyr milankovitch cycles terraces formed prior to this generally consist of wide aggradational sheets that probably each represent formation over several 41 kyr cycles subsequently river valleys became more steeply entrenched and terraces formed in response to the stronger 100 kyr climatic forcing in many cases at approximately one per cycle this paper uses the new data resource to explore differences between records in different climate zones between sequences with variable numbers of middle late pleistocene terraces and between systems in which the all important incision event has occurred in different parts of climatic cycles key records discussed include european examples from the rhine thames somme dniester dnieper don volga and aguas from asia the gediz turkey and orontes syria from north america the south platte and colorado from south africa the vaal and sundays from australia the shoalhaven and from south america the amazon paraguay and tributaries of the colorado and negro

ultra high rates of loess sedimentation at zhengzhou since stage 7 implication for the yellow river erosion of the sanmen gorge abstract the mangshan loess plateau is located 25 km to the west of zhengzhou on the south bank of the yellow river here the river flows out through the sanmen gorge releasing most of its suspended load following a dramatic decrease in gradient the stratigraphy of the mangshan loess deposits consisting of a number of loess and palaeosol sequences was established following magnetostratigraphic studies and measurements of magnetic susceptibility and grain size distribution the bruhnes matuyama boundary was found at the depth of about 130 m indicating that this sequence at mangshan resembles what is observed elsewhere in the loess plateau the upper part of the mangshan loess displays extremely high sedimentation rates 50 m 3 per 1000 years lower susceptibility values and coarser grain size distribution unlike the lower part of the profile and other sections in the loess plateau this striking change indicates that the upper mangshan loess had a different sediment source different from the deserts that act as a common source for most of the loess deposits in central china this sediment source is believed to be the proximal yellow river floodplain and the ancient alluvial fan lying at the eastern end of the sanmen gorge the age estimation of the formation of the alluvial fan based on mangshan loess suggests that the yellow river may have eroded the sanmen gorge at approximately mis 7

evaluating the role of climate and tectonics during non steady incision of the yellow river evidence from a 1 24 ma terrace record near lanzhou china abstract the competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain most of recent studies have attributed terrace formation to climatic changes and held that even in tectonically active settings climate variations control cycles of terrace planation and abandonment based on field investigations of loess paleosol sequences magnetostratigraphy and optically stimulated luminescence osl dating we develop a new chronology for a spectacular flight of terraces along the yellow river near lanzhou china over past 1 24 ma all the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates however the ages of terraces cluster in two relatively short time periods 1 24 0 86 ma and 0 13 ma present during the intervening time between 0 86 ma and 0 13 ma terraces either did not form or were not preserved we suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation preservation thus our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision

climatic control of bedrock river incision bedrock river incision drives the development of much of earth s surface topography and thereby shapes the structure of mountain belts and modulates earth s habitability through its effects on soil erosion nutrient fluxes and global climate although it has long been expected that river incision rates should depend strongly on precipitation rates quantifying the effects of precipitation rates on bedrock river incision rates has proved difficult partly because river incision rates are difficult to measure and partly because non climatic factors can obscure climatic effects at sites where river incision rates have been measured here we present measurements of river incision rates across one of earth s steepest rainfall gradients which show that precipitation rates do indeed influence long term bedrock river incision rates we apply a widely used empirical law for bedrock river incision to a series of rivers on the hawaiian island of kaua i where mean annual precipitation ranges from 0 5 metres to 9 5 metres ref 12 over 70 per cent of the global range and river incision rates averaged over millions of years can be inferred from the depth of river canyons and the age of the volcanic bedrock both a time averaged analysis and numerical modelling of transient river incision reveal that the long term efficiency of bedrock river incision across kaua i is positively correlated with upstream averaged mean annual precipitation rates we provide theoretical context for this result by demonstrating that our measurements are consistent with a linear dependence of river incision rates on stream power the rate of energy expenditure by the flow on the riverbed these observations provide rare empirical evidence for the long proposed coupling between climate and river incision suggesting that previously proposed feedbacks among topography climate and tectonics may occur