the influence of climate on the tectonic evolution of mountain belts simple physical arguments analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate however obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging spatial correlations between intense precipitation or glaciation and zones of rapid rock uplift have indeed been documented in numerous mountain ranges and are consistent with model predictions more compelling evidence such as tectonic changes in response to rather than just coincident with climate change has however rarely been documented triggered by a climate driven increase in erosion rate friction dominated mountain ranges are expected to show a number of simultaneous responses a decrease in the width of the range a temporary increase in sediment yield a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins the most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the european alps and the st elias range of alaska field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view

shredding of environmental signals by sediment transport 1 landscapes respond to climate tectonic motions and sea level but this response is mediated by sediment transport understanding transmission of environmental signals is crucial for predicting landscape response to climate change and interpreting paleo climate and tectonics from stratigraphy here we propose that sediment transport can act as a nonlinear filter that completely destroys shreds environmental signals this results from ubiquitous thresholds in sediment transport systems e g landsliding bed load transport and river avulsion this morphodynamic turbulence is analogous to turbulence in fluid flows where energy injected at one frequency is smeared across a range of scales we show with a numerical model that external signals are shredded when their time and amplitude scales fall within the ranges of morphodynamic turbulence as signal frequency increases signal preservation becomes the exception rather than the rule suggesting a critical re examination of purported sedimentary signals of external forcing citation jerolmack d j and c paola 2010 shredding of environmental signals by sediment transport geophys res lett 37 l19401 doi 10 1029 2010gl044638

importance of a stochastic distribution of floods and erosion thresholds in the bedrock river incision problem 1 fluvial erosion of bedrock occurs during occasional flood events when boundary shear stress exceeds a critical threshold to initiate incision therefore efforts to model the evolution of topography over long timescales should include an erosion threshold and should be driven by a stochastic distribution of erosive events however most bedrock incision models ignore the threshold as a second order detail in addition climate is poorly represented in most landscape evolution models so the quantitative relationship between erosion rate and measurable climatic variables has been elusive here we show that the presence of an erosion threshold when combined with a well constrained probabilistic model of storm and flood occurrence has first order implications for the dynamics of river incision in tectonically active areas first we make a direct calculation of the critical shear stress required to pluck bedrock blocks for a field site in new york second we apply a recently proposed stochastic threshold bedrock incision model to a series of streams in california with known tectonic and climatic forcing previous work in the area has identified a weak relationship between channel gradient or relief and rock uplift rate that is not easily explained by simpler detachment limited models the results with the stochastic threshold model show that even low erosion thresholds which are exceeded in steep channels during high frequency flood events fundamentally affect the predicted relationship between gradient and uplift rate in steady state rivers in a manner consistent with the observed topography this correspondence between theory and data is however nonunique models in which a thin alluvial cover may act to inhibit channel incision in the low uplift rate zone also provide plausible explanations for the observed topography third we explore the broader implications of the stochastic threshold model to the development of fluvial topography in active tectonic settings we suggest that continued field applications of geomorphic models including physically meaningful thresholds and stochastic climate distributions are required to advance our knowledge of interactions among surficial climatic and crustal processes

reconciling tectonic shortening sedimentation and spatial patterns of erosion from 10 be paleo erosion rates in the argentine precordillera abstract the temporal evolution of erosion over million year timescales is key to understand the development of mountain ranges and adjacent fold and thrust belts while models of orogenic wedge dynamics predict an instantaneous response of erosion to pulses of rock uplift stream power based models predict that catchment wide erosion maxima significantly lag behind a pulse of rock uplift here we explore the relationships between rock uplift erosion and sediment deposition in the argentine precordillera fold and thrust belt at 30 s using a combination of 10be derived paleo erosion rates constraints on re exposure using 26al 10be ratios geomorphic observations and detrital zircon provenance we demonstrate that the attainment of maximum upland erosion rates lags the maximum rate of deformation over million year timescales the magnitudes and causes of the erosional delays shed new light on the catchment erosional response to tectonic deformation and rock uplift in orogenic wedges

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

the erosion response to quaternary climate change quantified using uranium isotopes and in situ produced cosmogenic nuclides abstract studying how catchment erosion has responded to past climate change can help us better understand not only how landscape evolution operates but also predict the consequences of future climate change on soil resource availability recent years have seen the development of tools that allow a quantitative assessment of past changes in catchment erosion this work reviews the principles of the application of in situ produced cosmogenic nuclides and uranium isotopes to quantifying past erosion rates results highlight the role of periglacial processes and mass wasting in dictating how catchment erosion responds to climatic variability at the 10 kyr scale at the million year scale it is more difficult to untangle the role of climate and tectonics a strong coupling exists at the 10 kyr to 100 kyr scales between climatic cycles and the transfer time of regolith from source to sink this coupling reflects changes in sediment source that are either set by changes in vegetation cover at the catchment scale or by the storage of sediments on continental shelves at a larger scale although further analytical developments are required for these tools to reach their full potential existing works suggest that in the near future they will provide unprecedented quantitative insights on how soil and fluvial systems adapt to external perturbations climatic tectonic and or anthropic

controls on the erosion of cenozoic asia and the flux of clastic sediment to the ocean rates of continental erosion may be reconstructed from variations in the rate of accumulation of clastic sediment most of which lies offshore global rates of marine sedimentation are usually considered to have reached a maximum after 3 4 ma driven by enhanced erosion in a variable glacial interglacial climate however a new compilation of seismic data from the marginal seas of asia now shows that only the red river reached its historic peak after 4 ma sediment flux from asia first peaked in the early middle miocene 24 11 ma well before the initiation of a glacial climate indicating that rock uplift and especially precipitation are the key controls on erosion at least over long periods of geologic time reconstructions of weathering in east asia show that faster erosion correlates with more humid warm climates in the early middle miocene changing to less erosive drier climates after 14 ma when antarctic glaciation begins average rates of sedimentation on most east asian continental margins since 1 8 ma are 5 6 times less than the modern fluvial flux implying that the flux to the oceans varies sharply on short timescales and is not always buffered over timescales of 10 4 yr by storage in flood plains

geological aspects of decomposition of corpses in mass graves from ww1 and 2 located in se poland the investigations were carried out to identify processes and mineral products in the diversified subsoil sediments of mass graves from ww1 four graves and 2 five graves and their surroundings as well as the relations between the development of sediments within the mass graves and the scale of migration of the products of corpse decomposition the author studied the role of iron compounds and clay minerals in the decomposition of human corpses buried in mass graves followed by the migration of selected elements in particular he concentrated on the list of elements found in the diversified sediments of nine mass graves from se poland and to their relationship with phosphorus compounds the methods applied included scanning electron microscopy sem and optical polarizing microscopy samples were collected from various depths in trenches and holes dug in the vicinity of the graves the sediments from the burial horizon and when possible the sediments underlying the grave studied downslope detected phosphorus occurs as a weakly crystalline compound in silt rich sediments with relatively stable water conditions in silt rich sediments with relatively stable moisture content phosphorus occurs as a weakly crystalline compound more stable aggregates of decomposition products have been found on quartz grains covered with clay ferruginous rims fragments of human soft tissue were found only in those graves from ww2 there is no link between the spectrum of elements in the sediments of the graves and the period of burials the decomposition products that form depend primarily on the type of sediments in which the mass graves were dug and secondarily although related on the moisture content of the sediments it has been found that stabilization of decomposition products in situ is related to the presence of iron compounds and clay minerals particularly in finer grained aleuritic pelitic sediments

role of climate changes for wind gap formation in a young actively growing mountain range wind gaps in actively growing mountain ranges are unique geomorphological features testifying to the competition between tectonics and fluvial incision although it is clear that these landforms reflect the defeat of rivers during sustained rock uplift the role of climate changes in their formation has never been explored here we use a coupled tectonics landscape evolution model to show that temporal changes in precipitation rate exert an important control on wind gap formation in models with a constant precipitation rate rivers flowing across a growing range are either defeated at an early stage or they abandon their valleys very late if at all if precipitation varies wind gaps form mostly 100 200 ka after a transition to drier conditions because of sediment aggradation upstream of the range our results suggest that the pliocene quaternary aridification of central asia contributed to wind gap formation in active mountain ranges in the foreland of northeastern tibet this article is protected by copyright all rights reserved

environmental signal propagation in sedimentary systems across timescales abstract earth surface processes operate across erosionally dominated landscapes and deliver sediment to depositional systems that can be preserved over a range of timescales the geomorphic and stratigraphic products of this source to sink sediment transfer record signals of external environmental forcings as well as internal or autogenic dynamics of the sedimentary system here we evaluate environmental signal propagation across sediment routing systems with emphasis on sediment supply qs as the carrier of up system forcings we review experimental numerical and natural examples of source to sink sediment routing and signal propagation during three timescales 1 historic which includes measurement and monitoring of events and processes of landscape change and deposition during decades to centuries 2 centuries to several millions of years referred to as intermediate timescale and 3 deep time we discuss issues related to autogenic dynamics of sediment transport transient storage and release that can introduce noise lags and or completely mask signals of external environmental forcings we provide a set of conceptual and practical tools for evaluating sediment supply within a source to sink context which can inform interpretations of signals from the sedimentary record these tools include stratigraphic and sediment routing system characterization sediment budgets geochronology detrital mineral analysis e g thermochronology comparative analog approaches and modeling techniques to measure calculate or estimate the magnitude and frequency of external forcings compared to the characteristic response time of the sediment routing systems

mass accumulation rates in asia during the cenozoic summary this work establishes estimates of mass accumulation rates in 18 mostly offshore sedimentary basins in asia since the beginning of the cenozoic 66 ma the estimates were derived from isopach maps cross sections and drill holes or stratigraphic columns assuming regional similarity of the strata average solid phase volumes and accumulation rates were calculated for nine epochs approximately corresponding to geological periods palaeocene 66 58 ma eocene 58 37 ma oligocene 37 30 and 30 24 ma miocene 24 17 17 11 and 11 5 ma pliocene 5 2 ma and quaternary 2 0 ma these rates shed new light on the geological history of asia since the onset of the collision of india with asia 50 ma the overall average accumulation rates curve for asian sedimentary basins since the beginning of the tertiary shows an exponential form with slow accumulation rates less than 0 5 106 km3 myr 1 until the beginning of the oligocene more than 15 myr after the onset of the collision from the oligocene onwards rates increase quickly in an exponential manner reaching their maximum values in the quaternary more than 1 5 106 km3 myr 1 from these observations we suggest that extrusion and crustal shortening are complementary processes that have been successively dominant throughout the india eurasia collision history at smaller scales one may distinguish between independent histories at the subcontinental and basin scales this permits a comparison of the relative importance of tectonic and climatic erosion processes affecting the different mountain belts of asia during the cenozoic

steady 10be derived paleoerosion rates across the plio pleistocene climate transition fish creek vallecito basin california rates of erosion over time provide a valuable tool for gauging tectonic and climatic drivers of landscape evolution here we measure 10be archived in quartz sediment from the fish creek vallecito basin to resolve a time series of catchment averaged erosion rates and to test the hypothesis that aridity and increased climate variation after ca 3 ma led to an increase in erosion rates in this semi arid ice free setting the fish creek vallecito basin located east of the peninsular ranges in southern california is an ideal setting to derive a plio pleistocene paleo erosion rate record the basin has a rapid sediment accumulation rate a detailed magnetostratigraphic age record and its stratigraphy has been exposed through recent rapid uplift and erosion a well defined source region of uniform lithology and low erosion rate provides a high reproducible 10be signal we find that paleo erosion rates were remarkably consistent between 1 and 4 ma averaging 38 24 m myr 2 modern catchment averaged erosion rates are similar to the paleo erosion rates the uniformity of erosion over the past 4 myr indicates the landscape was not significantly affected by late pliocene global climate change nor was it affected by a local long term increase in aridity

post collisional sediment budget history of the alps tectonic versus climatic control based on the sediment budget of the eastern swiss and western alps since the oligocene the regional tectonic evolution has been identified as the dominant factor it is superimposed on the influence of both regional and global climate change and global sea level change during late pliocene and pleistocene times climate became the dominant factor because of cyclic glaciations the early post collisional history of the alps is characterized by a doubling of sediment discharge rates around the rupelian chattian boundary this increase is attributed to isostatic re adjustment either after large scale thermal reorganization of the lithosphere related to slab break off or to crustal thickening as continental crust became subducted from middle oligocene to late miocene times the overall trend of sediment discharge rates in the entire alps was modified only during relatively short lived phases these are characterized by an increase in aquitanian ca 23 21 ma and late burdigalian times ca 18 16 4 ma and a decrease in early to middle burdigalian 21 19 ma and langhian to serravalian times 16 4 12 ma an important still ongoing period of uplift reflected by rapidly increasing sediment discharge rates started in latest miocene times in the swiss and western alps and affected the eastern alps some 2 million years later the reason for this uplift is not clear but deep seated lithospheric processes appear to be likely

immediate propagation of deglacial environmental change to deep marine turbidite systems along the chile convergent margin abstract understanding how earth surface processes respond to past climatic perturbations is crucial for making informed predictions about future impacts of climate change on sediment fluxes sedimentary records provide the archives for inferring these processes but their interpretation is compromised by our incomplete understanding of how sediment routing systems respond to millennial scale climate cycles we analyzed seven sediment cores recovered from marine turbidite depositional sites along the chile continental margin the sites span a pronounced arid to humid gradient with variable relief and related sediment connectivity of terrestrial and marine environments these sites allowed us to study event related depositional processes in different climatic and geomorphic settings from the last glacial maximum to the present day the three sites reveal a steep decline of turbidite deposition during deglaciation high rates of sea level rise postdate the decline in turbidite deposition comparison with paleoclimate proxies documents that the spatio temporal sedimentary pattern rather mirrors the deglacial humidity decrease and concomitant warming with no resolvable lag times our results let us infer that declining deglacial humidity decreased fluvial sediment supply this signal propagated rapidly through the highly connected systems into the marine sink in north central chile in contrast in south central chile connectivity between the andean erosional zone and the fluvial transfer zone probably decreased abruptly by sediment trapping in piedmont lakes related to deglaciation resulting in a sudden decrease of sediment supply to the ocean additionally reduced moisture supply may have contributed to the rapid decline of turbidite deposition these different causes result in similar depositional patterns in the marine sinks we conclude that turbiditic strata may constitute reliable recorders of climate change across a wide range of climatic zones and geomorphic conditions however the underlying causes for similar signal manifestations in the sinks may differ ranging from maintained high system connectivity to abrupt connectivity loss

enhanced global continental erosion and exhumation driven by oligo miocene climate change surface erosion is the most significant process responsible for the recycling of continental crust into the upper mantle and controls both exhumation in mountain belts and the long term global climate via chemical weathering earlier studies have highlighted the importance of climate instability since the onset of northern hemispheric glaciation similar to 3 ma as being the primary influence causing high erosion rates since that time here i show that synchronous pulses of erosion and exhumation occurred across eurasia in north america and in africa starting after 33 ma with a prominent peak around 16 ma correlation of these erosional events with changes in global climate suggests that they are controlled by surface processes because these climate events involve both cooling and warming periods the importance of increased seasonality is emphasized as being the key factor in controlling global erosion and exhumation throughout the cenozoic citation clift p d 2010 enhanced global continental erosion and exhumation driven by oligo miocene climate change geophys res lett 37 l09402 doi 10 1029 2010gl043067

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

frequency dependent landscape response to climatic forcing 1 whereas the existence of pronounced orbitally controlled periodicities is a major feature of earth climate its impact on landscape dynamics remains poorly understood we use a landscape evolution model lem to systematically investigate the response of landscapes to a range of periodic oscillations in precipitation the resulting sediment flux evolution displays a pronounced sensitivity to the period of the input precipitation signal such that for a given erodibility a specific periodicity maximizes the amplitude of the response this optimal period of resonance scales as the inverse of the erodibility but is progressively filtered out of the response when the intensity of hillslope diffusion increases this frequency dependent landscape behavior displayed by our model provides a mechanistic perspective on molnar s 2004 proposition that ubiquitous changes in late cenozoic continental denudation could result directly from modifications in the spectral content of the climatic signal

model shows that rivers transmit high frequency climate cycles to the sedimentary record rivers are a major component of sediment routing systems that control the transfer of terrigenous sediments from source to sink although it is widely accepted that rivers are perturbed by millennial scale climatic variability the extent to which these signals are buffered or transferred down river systems to be recorded in sediments at or beyond the river mouth remains debated here we employ a physically based numerical model to address this outstanding issue our model shows that river transport strongly amplifies high frequency sediment flux variations arising from changing water discharge due to positive feedback between discharge and the channel gradient this behavior is distinctly different from short period sediment flux signals with constant water discharge where the output sediment flux is strongly dampened within the river due to negative feedback between the channel gradient and sediment concentration we conclude that marine sedimentary basins may record sediment flux cycles resulting from discharge and ultimately climate variability whereas they may be relatively insensitive to pure sediment flux perturbations such as for example those induced by tectonics

long term stability of global erosion rates and weathering during late cenozoic cooling reports that the geological record of erosion indicates a fourfold increase in global sedimentation rates during the past 5 million years merited a global explanation explanations offered include an increased rate of mountain formation and global cooling now jane willenbring and friedhelm von blanckenburg reanalyse original data sets and use ocean records of beryllium isotope ratios to obtain an indirect measure of past erosion rates and rock weathering they find no clear evidence either for an increase in global erosion or for a pulse of weathered material in the oceans during the past 12 million years they suggest that cenozoic global cooling must have some other cause and the mountain building that did occur had little effect on erosion or weathering flux globally accelerated uplift and global cooling have been suggested as possible causes for a fourfold increase in global sedimentation rates and by inference in erosion rates or weathering fluxes during the past 5 million years here proxy evidence is provided that indicates stable weathering fluxes in the late cenozoic era it is proposed that processes different from an increase in denudation caused cenozoic global cooling over geologic timescales co2 is emitted from the earth s interior and is removed from the atmosphere by silicate rock weathering and organic carbon burial this balance is thought to have stabilized greenhouse conditions within a range that ensured habitable conditions1 changes in this balance have been attributed to changes in topographic relief where varying rates of continental rock weathering and erosion1 2 are superimposed on fluctuations in organic carbon burial3 geological strata provide an indirect yet imperfectly preserved record of this change through changing rates of sedimentation1 2 4 widespread observations of a recent 0 5 myr fourfold increase in global sedimentation rates require a global mechanism to explain them4 5 6 accelerated uplift and global cooling have been given as possible causes2 4 6 7 but because of the links between rates of erosion and the correlated rate of weathering8 9 an increase in the drawdown of co2 that is predicted to follow may be the cause of global climate change instead2 however globally rates of uplift cannot increase everywhere in the way that apparent sedimentation rates do4 10 moreover proxy records of past atmospheric co2 provide no evidence for this large reduction in recent co2 concentrations11 12 here we question whether this increase in global weathering and erosion actually occurred and whether the apparent increase in the sedimentation rate is due to observational biases in the sedimentary record13 as evidence we recast the ocean dissolved 10be 9be isotope system as a weathering proxy spanning the past 12 myr ref 14 this proxy indicates stable weathering fluxes during the late cenozoic era the sum of these observations shows neither clear evidence for increased erosion nor clear evidence for a pulse in weathered material to the ocean we conclude that processes different from an increase in denudation caused cenozoic global cooling and that global cooling had no profound effect on spatially and temporally averaged weathering rates

paleo erosion rates in central asia since 9 ma a transient increase at the onset of quaternary glaciations erosion is a fundamental player of the interactions existing between internal geodynamics and climate in particular through its influence on the carbon dioxide budget however long term 1 ma erosion rates estimated indirectly from sediment budget remain poorly constrained while some studies suggest that worldwide erosion rates increased at the plio pleistocene climatic transition 4 2 ma the validity of this observation and its significance is a matter of debate due to potential biases of the sedimentary record and to the influence of sea level fall on the global sedimentary flux to marginal basins in the present study we estimate erosion rates over the last 9 ma using in situ produced cosmogenic 10be concentrations measured in magnetostratigraphically dated continental sediments we focus on an intracontinental endorheic watershed draining the northern tianshan in central asia a key region regarding the ongoing debate while erosion rates between 0 1 and 1 mm yr 1 are derived from most of our record they reach values as high as 2 5 mm yr 1 from 2 5 to 1 7 ma then after 1 7 ma recent and modern erosion rates fell below 1 mm yr 1 this temporary increase is correlated with the onset of quaternary ice ages and suggests that global climate had a significant and transient impact on erosion

transformation of tectonic and climatic signals from source to sedimentary archive sedimentary rocks reflect past tectonic and climatic events numerical simulations suggest that changes in precipitation and in the rate of tectonic uplift affect the grain size and the distribution of sediments deposited downstream

erosion rates of the bhutanese himalaya determined using in situ produced 10be abstract western bhutan provides an ideal setting to understand the interplay between uplift erosion and fluvial sediment transport in an active mountain environment using in situ produced 10 be 49 samples and 26 al 5 samples in fluvial sediment from nested catchments throughout the puna tsang chhu drainage basin we examine erosion rates in different geomorphic environments including two high relief regions a glacierized zone in the north and a high rainfall zone in the south as well as remnants of an uplifted lower relief paleosurface between them the erosion rates roughly mirror this north south zonation lower rates avg 388 32 m my 1 n 16 prevail in the low relief zone roughly coinciding with lower relief terrain where mean annual precipitation is 1500 mm yr 1 the highest rates avg 956 160 m my 1 n 13 are in the south 27 10 27 35 n where rainfall is 4000 mm yr 1 high rates avg 700 62 m my 1 n 15 also occur in the northern glacierized region 27 70 28 10 n all 49 purified mineral separates used in this study contain measurable amounts of native 9 be up to 900 g violating the assumption of negligible 9 be that is commonly made in the isotope dilution method used to quantify 10 be to correct for this native 9 be we use high precision replicate measurements of 9 be in each sample to calculate 10 be concentrations from measured isotopic ratios neglecting native 9 be would have led to erosion rate overestimates from 400 the pervasive nature of 9 be in these samples underscores the importance of quantifying the native 9 be concentration in mineral separates used for cosmogenic 10 be analysis

a diagnosis of rainfall over south america during the 1997 98 el nino event part ii roles of water vapor transport and stationary waves abstract a diagnosis of rainfall over south america sa during the 1997 98 el nino year is made examining the roles of water vapor transport and stationary waves it is found that the low level jet llj on the eastern side of the central andes is stronger during the el nino event and transports more moisture this seems to be the source for higher rainfall over southeast sa noted during the el nino years a calculation of three dimensional stationary wave activity fs for 1997 and 1998 showed that in the summer of 1996 97 stationary waves propagate poleward and eastward from midlatitudes into the higher latitudes to the west of south sa and then propagate equatorward to the east of sa during the autumn of 1997 the vertical component of fs is consistent with a blocking high over the southeast pacific to the east of this high cold air advection from antarctica occurs and to the west warm air advection occurs this is consistent with negative and positive centers seen in the vertical component of fs t

late cenozoic climate change paces landscape adjustments to yukon river capture late cenozoic cooling and changes in glacial interglacial cycle tempo are thought to increase global rates of erosion starting 3 million years ago ma bedrock rivers set rates and patterns of erosion in most landscapes but constraints on river response to late cenozoic climate change remain elusive here we determine cosmogenic isotope and luminescence ages of well preserved bedrock terraces along the fortymile river yukon river basin to reconstruct an 5 myr history of fluvial adjustment to late cenozoic climate and yukon river headwater capture at 2 6 ma post capture yukon river downcutting lowered the fortymile river outlet forcing subsequent bedrock incision throughout the fortymile basin in two pulses from 2 4 to 1 8 ma and at 1 ma these pulses of incision disrupted longer intervals of slow river channel sedimentation under near consistent climate forcing from 4 8 to 2 4 ma and from 1 8 to 1 ma the fortymile river delivers sediment to the bering sea where provenance and accumulation rate changes since 4 3 ma match observed variations in incision our results link alluviation and incision to late cenozoic climate steadiness and change respectively and support the hypothesis that climate forced changes in precipitation and runoff fundamentally control the pace of river incision and landscape erosion increased river incision and landscape erosion can be attributed to late cenozoic cooling changes in hydroclimate according to cosmogenic isotope and luminescence ages of a sequence of bedrock terraces in the yukon river basin

the geological significance of cosmogenic nuclides in large lowland river basins abstract measured from a bag of sand taken in large rivers the concentration of cosmogenic nuclides such as in situ produced 10be 26al and 14c can be used to constrain the mean sediment flux of the headwaters and assess the duration of sediment storage from source to sink we revisit these principles with examples from the amazon and ganga basins we identify two end member cases controlling the concentration of cosmogenic nuclides in lowland river sediment 1 if the time scale of floodplain sediment storage is short compared to the half life of the nuclide in situ cosmogenic nuclide concentrations are not significantly altered in lowland basins in this case the concentration of e g in situ produced 10be in the sediment taken in the lowland basin equals in most cases that exported from the sediment source area but the variability in nuclide concentrations between headwater streams is significantly averaged out thus to convert the measured river sediments in situ cosmogenic nuclide concentration into a catchment wide denudation rate production rates are scaled to include those of the sediment producing mountainous areas only rather than the entire catchment area nuclide production in the lowlands where no sediment is being produced is hence excluded this correction is termed floodplain correction 2 if sediment buried for periods of the order of the nuclides half life is episodically re entrained into the active river paired nuclides for example the ratio of 26al 10be through the differential decay of these isotopes constrain the the storage duration and re mixing of floodplain sediment as in situ cosmogenic nuclides measure denudation rates over longer time scales typically integrating between 103 and 105 years their combination with modern estimates of sediment fluxes from river load gauging offers a rich potential of deciphering the controls of earth surface fluxes across large basins from this combination we can assess how river systems react to external perturbations such as climate change or human interference and how such signals are transmitted through the alluvial reaches of lowland basins the most important results in both basins are that i lowland amazon and ganga nuclide concentrations indeed broadly reflect the spatial average of andean and himalayan denudation respectively ii the thus calculated sediment fluxes are within uncertainty of modern fluxes from sediment gauging indicating complete sediment delivery to the sea without net loss into the basin and iii only the amazon basin given its size contains a substantial fraction of sediment buried temporarily in the quaternary finally we provide a short introduction to the use of meteoric cosmogenic nuclide 10be and its ratio to stable 9be released by rock weathering in lowlands in the amazon basin we show that 10be concentrations in fine grained suspended loads depth integrated over the water column using al si ratios provide erosion rates whereas the 10be 9be ratio on be adsorbed to particles provides the denudation rate both are similar to denudation rates from in situ 10be we show that this system responds more sensitively to sediment storage than the in situ system and both accumulation and decay of meteoric concentrations may thus be used to determine sediment residence time

controls on the spacing of first order valleys 1 many landscapes are composed of ridges and valleys that are uniformly spaced even where valley locations are not controlled by bedrock structure models of long term landscape evolution have reproduced this phenomenon yet the process by which uniformly spaced valleys develop is not well understood and there is no quantitative framework for predicting valley spacing here we use a numerical landscape evolution model to investigate the development of uniform valley spacing we find that evenly spaced valleys arise from a competition between adjacent drainage basins for drainage area a proxy for water flux and that the spacing becomes more uniform as the landscape approaches a topographic equilibrium valley spacing is most sensitive to the relative rates of advective erosion processes such as stream incision and diffusion like mass transport such as soil creep and less sensitive to the magnitude of a threshold that limits the spatial extent of stream incision analysis of a large number of numerical solutions reveals that valley spacing scales with a ratio of characteristic diffusion and advection timescales that is analogous to a peclet number we use this result to derive expressions for equilibrium valley spacing and drainage basin relief as a function of the rates of advective and diffusive processes and the spatial extent of the landscape the observed scaling relationships also provide insight into the cause of transitions from rill like drainage networks to branching networks the spatial scale of first order drainage basins the contributing area at which hillslopes transition into valleys and the narrow range of width to length ratios of first order basins

late cenozoic increase in accumulation rates of terrestrial sediment how might climate change have affected erosion rates abstract accumulation rates of terrestrial sediment have increased in the past few million years both on and adjacent to continents although not everywhere apparently erosion has increased in elevated terrain regardless of when last tectonically active or what the present day climate in many regions sediment coarsened abruptly in late pliocene time sparser data suggest increased sedimentation rates at 15 ma approximately when oxygen isotopes in benthic foraminifera imply high latitude cooling if climate change effected accelerated erosion understanding how it did so remains the challenge some obvious candidates such as lowered sea level leading to erosion of continental shelves or increased glaciation account for increased sedimentation in some but not all areas perhaps stable climates that varied slowly allowed geomorphic processes to maintain a state of equilibrium with little erosion until 3 4 ma when large oscillations in climate with periods of 20 000 40 000 years developed and de

discharge discharge variability and the bedrock channel profile long term bedrock incision is driven by daily discharge events of variable magnitude and frequency with ineffective events below an incision threshold we explore theoretically how this short term stochastic behavior controls long term steady state incision rates and bedrock channel profiles combining a realistic frequency magnitude distribution of discharge with a deterministic detachment limited incision model in which incision rate is a power function of basal shear stress above a critical shear stress our model predicts a power law relationship between steady state slope and drainage area consistent with observations the exponent of this power law is independent of discharge mean and variability while the amplitude factor which controls mountain belt relief is a power law function of mean runoff with an exponent of 0 5 and a complex function of runoff variability in accordance with evidence that incision occurs between 6 and 20 of time in rapidly incising rivers 1 mm yr our model predicts that channel steepness is virtually insensitive to runoff variability runoff variability can only decrease channel steepness for very slow incision rates and or weak lithologies the relationship between channel steepness and incision rate is always a power law whose exponent depends on the channel cross sectional geometry and runoff variability this contradicts models neglecting discharge stochasticity in which the steepness incision scaling is set by the incision law exponent our results suggest that changes in climate variability cannot explain an increase in bedrock incision rates during the late cenozoic within the context of a detachment limited model

modelling geomorphic response to environmental change in an upland catchment in the uk s upland catchments river terraces and alluvial features indicate a history of periodic aggradation and degradation linked to holocene changes in land use primarily deforestation and climate change altering flood frequency and magnitude although both factors are important calculating their individual effects is complicated by the likelihood of their concurrent alteration to investigate the relative impacts of land use and climate change a cellular model is applied to the upland catchments of cam gill beck above starbotton north yorkshire this is divided into 1 million 2 m by 2 m grid cells to which a range of process laws are applied these include approximate expressions for mass movement rates soil creep the influence of vegetation and hillslope hydrology as well as fluvial erosion and deposition in ten grain size fractions this provides a good representation of valley floor geometry while retaining a fully dynamic interaction with the surrounding valley sides previous applications of this model have shown the detailed formation of bars and berms as well as examples of braiding avulsion and channel range running on a silicon graphics origin 2000 computer an ensemble of simulations were completed bracketing a wide range of environmental scenarios involving changes in flood frequency magnitude and vegetation cover over time scales ranging from 10 to 100 years these showed that decreasing tree cover and increasing rainfall magnitude individually produced similar 25 to 100 increases in sediment discharge whereas in combination they generated a 1300 rise furthermore channels formed by the model in response to increased rainfall magnitudes are located where relic channels are found in cam gill beck implying that these are the products of previous periods of high rainfall magnitudes copyright 2000 john wiley sons ltd

stability of creeping soil and implications for hillslope evolution the geomorphic behavior of a soil mantled hillslope undergoing diffusive creep involves a coupling between changes in land surface elevation soil transport rates soil production and soil thickness a linear stability analysis suggests that the coupled response of the soil mantle to small perturbations in soil thickness or surface topography is influenced by two factors the diffusive like behavior of soil creep has a stabilizing effect wherein perturbations in land surface elevation are damped the relation between the soil production rate and soil thickness may be either stabilizing or destabilizing a monotonically decreasing production rate with soil thickness reinforces the stabilizing effect of diffusive land surface smoothing an increasing production rate with soil thickness has a destabilizing effect wherein perturbations in soil thickness or the soil bedrock interface are amplified despite the presence of diffusive land surface smoothing this coupled behavior is insensitive to the transport relation whether the soil flux is proportional to the land surface gradient or to the product of the soil thickness and land surface gradient the latter type of relation nonetheless could lead to a more complex hillslope form than might otherwise be expected for purely diffusive transport moreover the response to periodic sinusoidal variations in the rate of stream downcutting at the lower hillslope boundary involves upslope propagation of coupled damped waveforms in the land surface and the soil bedrock interface the distance of upslope propagation goes with the square root of the product of the transport diffusion like coefficient and the period of the downcutting rate the upper part of the hillslope is therefore insensitive to relatively high frequency variations in stream downcutting so together with a stable behavior of the coupled soil mantle bedrock system this part of the hillslope may exhibit a tendency toward uniform lowering while the lower part behaves transiently conversely in the presence of low frequency variations in stream downcutting hillslope morphology and soil thickness variations are more likely to reflect unsteady conditions over the entirety of the hillslope

landscape reorganization under changing climatic forcing results from an experimental landscape understanding how landscapes respond to climate dynamics in terms of macroscale average topographic features and microscale landform reorganization is of interest both for deciphering past climates from today s landscapes and for predicting future landscapes in view of recent climatic trends although several studies have addressed macro scale response only a few have focused on quantifying smaller scale basin reorganization to that goal a series of controlled laboratory experiments were conducted where a self organized complete drainage network emerged under constant precipitation and uplift dynamics once steady state was achieved the landscape was subjected to a fivefold increase in precipitation transient state throughout the evolution high resolution spatiotemporal topographic data in the form of digital elevation models were collected the steady state landscape was shown to possess three distinct geomorphic regimes unchannelized hillslopes debris dominated channels and fluvially dominated channels during transient state landscape reorganization was observed to be driven by hillslopes via accelerated erosion ridge lowering channel widening and reduction of basin relief as opposed to channel base level reduction quantitative metrics on which these conclusions were based included slope area curve correlation analysis of spatial and temporal elevation increments and wavelet spectral analysis of the evolving landscapes our results highlight that landscape reorganization in response to increased precipitation seems to follow an arrow of scale major elevation change initiates at the hillslope scale driving erosional regime change at intermediate scales and further cascading to geomorphic changes at the channel scale as time evolves

tectonics sedimentation and surface processes from the erosional engine to basin deposition this special issue collects a number of papers mainly reflecting discussions during the tectonics sedimentation and surface processes sessions tssp organized at recent egu conferences 2012 2013 2014 as well as related studies that have appeared in earth surface processes and landforms over the last two years the sedimentary record has long been used to invert for deformation at all scales and in all tectonics settings growth strata sediment provenance sequence stratigraphy and changing depositional environments have all provided first order constraints on quantifying deformation at a range of spatial and temporal scales at the same time these studies have motivated much work on the influence of tectonics on both sedimentation patterns and basin fill successions however relatively few studies have considered the whole integrated system of catchment erosion fluvial transport and sediment deposition together often concentrating on either the basin or the catchment separately recently however methodological progress in quantifying rates of surface processes in the upstream erosion and transfer zones as well as revived interest in the couplings between surface processes tectonics and climate have made it possible to renew our understanding of the interactions between sedimentation and tectonics within the framework of the whole integrated sediment routing system although the studies within this special issue are only a fraction of the work presented over the last five years of the tssp sessions the manuscripts presented here reflect a selection of the broad content and diversity of studies that integrate both sedimentation and surface processes to understand deformation in the context of sedimentary systems they highlight and are organized into three active challenges of the field 1 tectonics and climate into landscapes 2 signal propagation within sediment routing systems and 3 modeling of tectonic and surface processes

modulation of the erosion rate of an uplifting landscape by long term climate change an experimental investigation abstract whether or not climatic variations play a major role in setting the erosion rate of continental landscapes is a key factor in demonstrating the influence of climate on the tectonic evolution of mountain belts and understanding how clastic deposits preserved in sedimentary basins may record climatic variations here we investigate how a change in precipitation influences the erosional dynamics of laboratory scale landscapes that evolved under a combination of uplift and rainfall forcings we consider here the impact of a decrease in the precipitation rate of finite duration on the erosive response of a landscape forced by a constant uplift and initially at a steady state ss1 we performed several experiments with the same amplitude but different durations of precipitation decrease tp we observe that the decrease in precipitation induces a phase of surface uplift of landscapes to a new steady state condition ss2 however the details of the uplift histories timing rate differ between the experiments according to tp we also observe a decrease in the erosion rate induced by the precipitation change however the timing and amplitude of this decrease vary according to tp defining a delayed and damped erosion signal our data show that the landscape response to precipitation change is dictated by a critical water to rock ratio ratio of precipitation over uplift that likely corresponds to a geomorphic threshold our study suggests that variations in precipitation that occur at a geological time scale 106 years may have a weak impact on the erosion of landscapes and on the delivery of siliciclastic material to large rivers and sedimentary basins