isotopically depleted carbon in the mid depth south atlantic during the last deglaciation 1 the initial rise in atmospheric co2 during the last deglaciation was likely driven by input of carbon from a 13c depleted reservoir here we show that high resolution benthic foraminiferal records from the mid depth brazil margin display an abrupt drop in 13c during heinrich stadial 1 hs1 that is similar to but larger than in the atmosphere comparing the brazil margin results to published records from the north atlantic we are unable to account for the south atlantic 13c data with conservative mixing between northern and southern component water masses rapid input of abyssal water from the southeast atlantic could account for deglacial 13c anomalies at the brazil margin but it would require a reversal in deep water flow direction compared to today a new mid depth water mass may explain similar hs1 13c values in both the north and south atlantic but contrasting oxygen isotopic values between the two basins do not support such a scenario instead it appears that 13c behaved non conservatively during the deglaciation possibly reflecting the input of carbon from an isotopically depleted source

effects of particle size and cushioning thickness on the performance of gabions against boulder impact a gabion is one of the most commonly used cushioning layers to shield protection structures against boulders entrained in debris flow despite the prevalence of gabions their cushioning performanc

north atlantic versus southern ocean contributions to a deglacial surge in deep ocean ventilation past glacial interglacial climate transitions were accompanied by millennial scale pulses in atmospheric co2 that are widely thought to have resulted from the release of co2 via the southern ocean however direct proxy evidence for a southern ocean role in regulating past ocean atmosphere co2 exchange is scarce here we use combined radiocarbon and neodymium isotope measurements from the last deglaciation to confirm greatly enhanced overturning and or air sea exchange rates relative to today in particular during the bolling allerod warm interval we show that this deglacial pulse in ocean ventilation was not driven by the north atlantic overturning alone and must have involved an increase in the ventilation of southern sourced deep waters our results thus confirm the removal of a physical and or dynamical barrier to effective air sea co2 exchange in the southern ocean during deglaciation and highlight the antarctic region as a key locus for global climate carbon cycle feedbacks

large scale successive boulder impacts on a rigid barrier shielded by gabions debris flows occur in multiple surges boulders entrained within the flow have been reported to incapacitate structures within its flow path single layer cushions such as gabions are often installed to shield debris resisting barriers from boulder impact however most relevant works only focus on single impact and the performance of gabions subjected to successive loading is still not well understood a new large scale pendulum facility was established to induce impact energy of up to 70 kj on an instrumented rigid barrier shielded by 1 m thick gabions the response of the gabions under six successive impacts was investigated results show that the peak boulder impact force given by the hertz equation is at least four times the measured values the recommended load reduction factor kc used in practice can be reduced by a factor of two after six successive impacts at an energy level of 70 kj the transmitted force increases by up to 40 based on the swiss guidelines a 13 increase of gabion thickn

rates of shortening propagation underthrusting and flexural wave migration in continental orogenic systems the rate of horizontal shortening in an orogenic wedge is the rate at which the length of undeformed crust decreases as it is incorporated into the orogen this rate equals the rate of convergence of the foreland lithosphere toward the central surface of the orogenic belt and the rate of subduction of foreland lithosphere beneath the central surface the rate of propagation of an orogenic wedge is the rate at which it elongates in the direction of horizontal shortening this rate is controlled by the rates of mass accretion to the orogenic wedge and erosion the orogenic belt drives a flexural isostatic wave through the foreland lithosphere at a velocity equal to the rate of propagation plus the rate of subduction or convergence or shortening in orogenic belts where the total amount of shortening cannot be reliably estimated from balanced regional cross sections it may be possible to determine total shortening from the distance of flexural wave migration in the foreland basin and the width of the orogenic wedge in addition orogenic wedges may accelerate solely in response to a reduction in taper

erosional control of the kinematics of the aconcagua fold and thrust belt from numerical simulations and physical experiments we investigate the impact of erosion on the geometry and kinematics of the aconcagua fold and thrust belt in central argentina using analog and numerical models in these models the surfaces are eroded according to a rule in which mass removal is limited by the rate of fluvial bedrock incision this approach unifies principles of frictional failure used in critical coulomb wedge theory with a quasi mechanistic erosion rule which allows us to explicitly relate temporal changes in erosional efficiency in this fold and thrust belt to its kinematics we show that theoretical predictions of the fold and thrust belt geometry as well as the kinematics predicted by both physical and numerical experiments are both internally consistent and correctly predict the interpreted and measured field geometries specifically the geometric evolution of the aconcagua fold and thrust belt requires relatively high erosion efficiency values k during the initial stage of deformation and relatively low k values during the latter stages consistent with the progressive exposure of different rock types during the different stages of deformation model results indicate that the activity of the faults in the hinterland is high when erosion is most efficient during the initial stage of deformation this activity is facilitated by increased out of sequence thrusting in contrast the models predict that forward propagating thrusts dominate the latter stages of deformation when erosion is far less efficient comparing the geometry of models subjected to erosion with those in which the surface remains uneroded suggests that erosional mass removal is required to explain the geometry of this fold and thrust belt by implication the results indicate that the kinematics of this and perhaps other fold and thrust belts may be intimately tied to the temporal history of erosion of the surface topography of these features

the hafnium neodymium isotopic composition of atlantic seawater the first full water column hafnium isotopic compositions of atlantic seawater have been obtained at seven locations from the labrador sea to the drake passage despite subpicomolar concentrations in seawater a precision of the hf isotopic measurements of 03 epsilon hf units was achieved an overall epsilon hf range between 3 1 in the labrador sea and 4 4 in antarctic bottom water was determined the distribution of which broadly reflects continental weathering inputs within particular water column profiles significant differences of up to 4 epsilon hf units occur combined with nd isotope data of the same samples it is evident that the hf isotopic composition of seawater is too radiogenic for a given nd isotopic composition and that the largest difference between expected and measured hf isotopic compositions in seawater occurs near the oldest continental crust in the labrador sea this corroborates the previous proposition which was mainly based on ferromanganese crust data that the hf isotopic composition of seawater is controlled by incongruent weathering of continental crust and possibly to some extent by hydrothermal contributions hafnium concentrations in the ocean do not increase along the deep ocean conveyer indicating an oceanic residence time of only a few hundred years which is significantly shorter than previously assumed the hf isotopic composition of past seawater can therefore serve as a proxy for short distance basin scale mixing processes and the regime and intensity of nearby continental weathering processes c 2009 elsevier b v all rights reserved

controls on the strength of coupling among climate erosion and deformation in two sided frictional orogenic wedges at steady state 1 many important insights regarding the coupling among climate erosion and tectonics have come from numerical simulations using coupled tectonic and surface process models however analyses to date have left the strength of the coupling between climate and tectonics uncertain and many questions unanswered we present an approximate analytical solution for two sided orogenic wedges obeying a frictional rheology and in a condition of flux steady state that makes explicit the nature and sensitivity of the coupling between climate and deformation we make the simplifying assumption that the wedge grows in a self similar fashion consistent with airy isostasy such that topographic taper is invariant with orogen width tectonic influx rate and climate we illustrate first how and why the form of the erosion rule matters to orogen evolution and then derive a physically based orogen scale erosion rule we show that steady state orogen width crest elevation and crustal thickness are controlled by the ratio of accretionary flux to erosional efficiency to a power dictated by the erosion process remarkably we show that for most combinations of parameters in the erosion law rock uplift rate is more strongly controlled by erosional efficiency than it is by the accretionary flux further assuming frontal accretion with no underplating the spatial distribution of erosional efficiency dictates the relative rock uplift rates on the pro wedge and retro wedge and the time averaged trajectories of rocks through the orogen the restriction to invariant frictional properties is conservative in these respects systems subject to positive feedback between erosion and rheology will exhibit even stronger coupling among climate erosion and deformation than shown here

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

the timing of deglacial circulation changes in the atlantic 1 well dated benthic foraminifer oxygen isotopic records 18o from different water depths and locations within the atlantic ocean exhibit distinct patterns and significant differences in timing over the last deglaciation this has two implications on the one hand it confirms that benthic 18o cannot be used as a global correlation tool with millennial scale precision but on the other hand the combination of benthic isotopic records with independent dating provides a wealth of information on past circulation changes comparing new south atlantic benthic isotopic data with published benthic isotopic records we show that 1 circulation changes first affected benthic 18o in the 1000 2200 m range with marked decreases in benthic 18o taking place at 17 5 cal kyr b p ka due to the southward propagation of brine waters generated in the nordic seas during heinrich stadial 1 hs1 cold period 2 the arrival of 18o depleted deglacial meltwater took place later at deeper north atlantic sites 3 hydrographic changes recorded in north atlantic cores below 3000 m during hs1 do not correspond to simple alternations between northern and southern sourced water but likely reflect instead the incursion of brine generated deep water of northern as well as southern origin and 4 south atlantic waters at 44 s and 3800 m depth remained isolated from better ventilated northern sourced water masses until after the resumption of north atlantic deep water nadw formation at the onset of the bolling allerod which led to the propagation of nadw into the south atlantic

southwest atlantic water mass evolution during the last deglaciation the rise in atmospheric co2 during heinrich stadial 1 hs1 14 5 17 5 kyr b p may have been driven by the release of carbon from the abyssal ocean model simulations suggest that wind driven upwelling in the southern ocean can liberate 13c depleted carbon from the abyss causing atmospheric co2 to increase and the 13c of co2 to decrease one prediction of the southern ocean hypothesis is that water mass tracers in the deep south atlantic should register a circulation response early in the deglaciation here we test this idea using a depth transect of 12 cores from the brazil margin we show that records below 2300 m remained 13c depleted until 15 kyr b p or later indicating that the abyssal south atlantic was an unlikely source of light carbon to the atmosphere during hs1 benthic 18o results are consistent with abyssal south atlantic isolation until 15 kyr b p in contrast to shallower sites the depth dependent timing of the 18o signal suggests that correcting 18o for ice volume is problematic on glacial terminations new data from 2700 to 3000 m show that the deep sw atlantic was isotopically distinct from the abyss during hs1 as a result we find that mid depth 13c minima were most likely driven by an abrupt drop in 13c of northern component water low 13c at the brazil margin also coincided with an 80 decrease in 14c our results are consistent with a weakening of the atlantic meridional overturning circulation and point toward a northern hemisphere trigger for the initial rise in atmospheric co2 during hs1

evidence from the northeastern atlantic basin for variability in the rate of the meridional overturning circulation through the last deglaciation a first study from the subtropical western atlantic using 231pa 230th ratios as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation however these results warrant confirmation from additional locations and water depths because the interpretation of the sedimentary 231pa 230th ratio in terms of circulation vigor can be biased by variations in particle flux and composition we have measured 231pa 230th in a core from the iberian margin in the northeastern atlantic basin and have compared these new results to the data from the western atlantic basin we find that the reduction in the circulation during h1 and yd and the subsequent increases first recognized in the sediment deposited on bermuda rise are also evident in the eastern basin in a totally different sedimentary regime confirming that sedimentary 231pa 230th ratios record basin wide changes in deep water circulation however some differences between the eastern and western records are also recognized providing preliminary evidence to differentiate between renewal rates in the two north atlantic basins and between shallower and deeper overturning our results suggest the possible existence of two sources of glacial north atlantic intermediate deep water gnaiw one in the south labrador sea and another west of rockall plateau both sources contributed to the meridional overturning but the two had different sensitivity to meltwater from the laurentide and the fennoscandian ice sheets during the deglaciation these results indicate that additional information on the geometry and strength of the ventilation of the deep atlantic can be obtained by contrasting the evolution of sediment 231pa 230th in different sections of the atlantic ocean

the high supply current dominated continental margin of southeastern south america during the late quaternary the continental margin off the la plata estuary se south america is characterized by high fluvial sediment supply and strong ocean currents high resolution sediment acoustic data combined with sedimentary facies analysis ams 14c ages and neodymium isotopic data allowed us to reconstruct late quaternary sedimentary dynamics in relation to the two major sediment sources the la plata estuary and the argentine margin sediments from these two provinces show completely different dispersal patterns we show that the northward trending la plata paleo valley was the sole transit path for the huge volumes of fluvial material during lower sea levels in contrast material from the argentine margin sector was transported northwards by the strong current system despite the large sediment volumes supplied by both sources wide parts of the shelf were characterized by either persistent non deposition or local short term depocenter formation the location and formation history of these depocenters were primarily controlled by the interplay of sea level with current strength and local morphology the high sediment supply was of secondary importance to the stratigraphic construction though locally resulting in high sedimentation rates thus the shelf system off the la plata estuary can be considered as a hydrodynamic controlled end member

analogue models of orogenic wedges controlled by erosion abstract indentation in the upper brittle crust where one plate is stiffer than the other produces vertical extrusion of a doubly vergent orogenic wedge sandbox models of this process show that erosion with or without deposition of the eroded material onto one or both margins significantly changes the internal patterns of orogenic shear and compaction within the orogens erosion decreases the vertical stress and changes the criticality of the orogenic wedge whereas redeposition increases the vertical stress on its margins effective indenters of accreted sand which develop in models without erosion if the rigid indenter face dip is 75 e g 45 or 15 are strongly affected by erosion rapid erosion favors thrusting over compaction and decreases both the size and the relevance of the effective indenters redeposition of eroded material on the margins also expands the lifetime of the active shear as the additional load delays initiation of underlying new shears

sedimentary basins and crustal thickening abstract we consider the development of sedimentary basins in a tectonic context dominated by horizontal shortening and vertical thickening of the crust well known examples are foreland basins others are ramp basins and buckle basins we have reproduced various styles of compressional basins in experiments properly scaled for gravity a multilayered model lithosphere with brittle and ductile layers floats on a model asthenosphere a computer driven piston provides shortening and thickening synchronous with erosion and sedimentation after a first stage of lithospheric buckling thrust faults appear mainly at inflection points slip on an isolated reverse fault is accompanied by flexure footwall flexure results in a foreland basin and becomes accentuated by sedimentation hangingwall flexure is less marked but may become accentuated by erosion motion on a fault leads to hangingwall collapse at the surface either footwall sedimentation or hangingwall erosion tends to prolong the active life of a reverse fault slip on any pair of closely spaced reverse faults of opposite vergence results in a ramp basin simultaneous slip produces a symmetric ramp basin whereas alternating slip results in a butterfly shaped basin with superposed foredeeps some well developed ramp basins become pushed down until bounding faults meet at the surface and the basin disappears from view at this stage the basin depth is equivalent to 15 km or more slip on any pair of widely spaced reverse faults of opposite vergence results in a pronounced central anticline between two distinct foredeeps in central asia and in western europe cenozoic crustal thickening is due to continental collision for central asia western china kyrgyzstan uzbekistan tajikistan we have compiled a regional structure contour map on the base of the tertiary as well as 4 regional sections foreland basins and ramp basins are numerous and associated with cenozoic thrusts large basins tarim junggar fergana tajik occur around and between mountain ranges but smaller basins issyk kul naryn occur within them in western europe the alps and pyrenees are surrounded by foreland basins ramp basins or intermediate styles in the andes and its foreland neogene thrusts and compressional basins are due to subduction of oceanic lithosphere in colombia they account for much of the cordillera oriental in nw argentina for the altiplano in west central argentina for the sierras pampeanas compressional basins are also common in other areas of older crustal thickening

millennial scale fluctuations in north atlantic heat flux during the last 150 000 years abstract surface water and deep ocean palaeoclimate records obtained from north atlantic core su90 03 40 n 32 w exhibit pronounced fluctuations at sub orbital time scales surface temperature variability in the mid latitude atlantic over the last 150 kyr is dominated by forcing at precession 21 kyr and semi precession harmonics 11 kyr abrupt changes in sea surface temperatures show that the northward transport of heat by the north atlantic current was curtailed during ice rafting events sea surface temperatures were about 12 c colder than modern values during the most intense cooling episodes associated with major ice rafting events heinrich events 1 4 6 and 11 and 10 c below modern values during the later part of isotope stage 3 40 30 ka during these cold intervals the north atlantic current was displaced to south of 40 n as the cold meltwaters penetrated southwards into what is now the subtropical ocean these changes in surface ocean heat exchange were most probably allied to a latitudinal migration and increase in zonality of atmospheric circulation patterns concurrent shifts in ird concentration sea surface temperatures and benthic 13 c values provide evidence of coupling between sea surface processes and the deep water circulation and suggest that decreases in surface temperature and salinity during ice rafting events culminated in a significant reorganisation of north atlantic deep water production

temporal variation in climate and tectonic coupling in the central andes analog and numerical models predict a coupling between climate and tectonics whereby erosion infl uences the deformation of orogens a testable prediction from modeling studies is the decrease in width of mountain ranges as a result of increased precipitation here we evaluate the effect of climate on a critically tapered orogen the central andes using sequentially restored balanced cross sections through wet 15 16 s and dry 21 s regions of the orogen in these regions tectonics basin geometry and style of deformation are similar allowing us to use variations in propagation or changes in percent shortening to evaluate whether alongstrike changes in width and morphology are climate driven in the north results indicate similar total percent shortening along the northern 40 and southern 37 sections suggesting that a wetter climate has not limited the width propagation in the north however comparison of early 45 25 ma and recent ca 20 0 ma shortening indicates that early deformation produced 45 2 shortening of both sections while recent deformation produced 41 2 north versus 32 2 south in the actively deforming subandes the latter suggests a coupling between climate and tectonics that began between ca 19 and 8 ma and continues to 0 ma potentially limiting the width of the northern subandes by 40 km

crustal channel flows 1 numerical models with applications to the tectonics of the himalayan tibetan orogen 1 plane strain thermal mechanical numerical models are used to examine the development of midcrustal channel flows in large hot orogens in the models radioactive self heating reduces the viscosity of tectonically thickened crust and increases its susceptibility to large scale horizontal flow channels can be exhumed and exposed by denudation focused on the high relief transition between plateau and foreland we interpret the himalaya to have evolved in this manner channel flows are poorly developed if the channel has a ductile rheology based on wet quartz flow laws and well developed if there is an additional reduction in viscosity to 1019 pa s this reduction occurs from 700 c to 750 c in the models and is attributed to a small percentage of in situ partial melt melt weakening model ht1 provides an internally consistent explanation for the tectonic evolution of many features of the himalayan tibetan orogenic system erosional exhumation exposes the migmatitic channel equivalent to the greater himalayan sequence ghs between coeval normal and thrust sense ductile shear zones corresponding to the south tibetan detachment and the main central thrust systems outward flow of unstable upper crust rotates these shears to low dip angles in the model both the ghs and the lesser himalayan sequence are derived from indian crust with the latter from much farther south similar models exhibit a range of tectonic styles including the formation of domes resembling north himalayan gneiss domes model results are relatively insensitive to channel heterogeneities and to variations in the behavior of the mantle lithosphere beneath the model plateau

what do benthic δ13c and δ18o data tell us about atlantic circulation during heinrich stadial 1 approximately synchronous with the onset of heinrich stadial 1 hs1 13c decreased throughout most of the upper 1000 2500 m atlantic and at some deeper north atlantic sites this early deglacial 13c decrease has been alternatively attributed to a reduced fraction of high 13c north atlantic deep water nadw or to a decrease in the nadw 13c source value here we present new benthic 18o and 13c records from three relatively shallow 1450 1650 m subpolar northeast atlantic cores with published data from other cores these data form a depth transect 1200 3900 m in the subpolar northeast atlantic we compare last glacial maximum lgm and hs1 data from this transect with data from a depth transect of cores from the brazil margin the largest lgm to hs1 decreases in both benthic 13c and 18o occurred in upper waters containing the highest nadw fraction during the lgm we show that the 13c decrease can be explained entirely by a lower nadw 13c source value entirely by a decrease in the proportion of nadw relative to southern ocean water or by a combination of these mechanisms however building on insights from model simulations we hypothesize that reduced ventilation due to a weakened but still active atlantic meridional overturning circulation also contributed to the low 13c values in the upper north atlantic we suggest that the benthic 18o gradients above 2300 m at both core transects indicate the depth to which heat and north atlantic deglacial freshwater had mixed into the subsurface ocean by early hs1

interactions between tectonics erosion and sedimentation during the recent evolution of the alpine orogen analogue modeling insights 1 on the basis of a section across the northwestern alpine wedge and foreland basin analogue modeling is used to investigate the impact of surface processes on the orogenic evolution the basis model takes into account both structural and lithological heritages of the wedge during shortening erosion and sedimentation are performed to maintain a critical wedge frontal accretion leads to the development of a foreland thrust belt underplating leads to the formation of an antiformal nappe stack in the internal zones important volumes of analogue materials are eroded out of the geological record which in the case of the alps suggests that the original lengths and volumes may be underestimated the foreland basin evolves differently depending on the amounts of erosion sedimentation its evolution and internal structuring is governed by the wedge mechanics thought to be the main controlling mechanism in the development of the molasse basin in a feedback interaction with surface processes

similar mid depth atlantic water mass provenance during the last glacial maximum and heinrich stadial 1 abstract the delivery of freshwater to the north atlantic during heinrich stadial 1 hs1 is thought to have fundamentally altered the operation of atlantic meridional overturning circulation amoc although benthic foraminiferal carbon isotope records from the mid depth atlantic show a pronounced excursion to lower values during hs1 whether these shifts correspond to changes in water mass proportions advection or shifts in the carbon cycle remains unclear here we present new deglacial records of authigenic neodymium isotopes a water mass tracer that is independent of the carbon cycle from two cores in the mid depth south atlantic we find no change in neodymium isotopic composition and thus water mass proportions between the last glacial maximum lgm and hs1 despite large decreases in carbon isotope values at the onset of hs1 in the same cores we suggest that the excursions of carbon isotopes to lower values were likely caused by the accumulation of respired organic matter due to slow overturning circulation rather than to increased southern sourced water as typically assumed the finding that there was little change in water mass provenance in the mid depth south atlantic between the lgm and hs1 despite decreased overturning suggests that the rate of production of mid depth southern sourced water mass decreased in concert with decreased production of northern sourced intermediate water at the onset of hs1 consequently we propose that even drastic changes in the strength of amoc need not cause a significant change in south atlantic mid depth water mass proportions

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

climatic forcing of erosion landscape and tectonics in the bhutan himalayas a fundamental objective in studies of climate erosion tectonics coupling is to document convincing correlation between observable indicators of these processes on the scale of a mountain range the eastern himalayas are a unique range to quantify the contribution of tectonics and climate to long term erosion rates because uniform and steady tectonics have persisted for several million years while monsoonal precipitation patterns have varied in space and time specifically the rise of the shillong plateau the only orographic barrier in the himalayan foreland has reduced the mean annual precipitation downwind in the eastern bhutan himalaya at the miocene pliocene transition apatite fission track aft analyses of 45 bedrock samples from an e w transect along bhutan indicate faster long term erosion rates outside of the rain shadow in the west 1 0 1 8 mm yr than inside of it in the east 0 55 0 85 mm yr furthermore an aft vertical profile in the latter segment reveals a deceleration in erosion rates sometime after 5 9 ma in this drier segment of bhutan there are remnants of a relict landscape formed under a wetter climate that has not yet equilibrated to the present climatic conditions uplift and preservation of the paleolandscape are a result of a climate induced decrease in erosion rates rather than of an increase in rock uplift rate this study documents not only a compelling spatial correlation between long term erosion and precipitation rates but also a climatically driven erosion rate change on the scale of the eastern himalayas a change that in turn likely influences that region s recent tectonic evolution

erosional control of the kinematics and geometry of fold and thrust belts imaged in a physical and numerical sandbox 1 we investigate the effect of systematically varying erosion intensity k on the geometry and kinematics of fold and thrust belts modeled using equivalent conditions in physical and numerical experiments similar material properties and boundary conditions were used to compare numerical experiments to those modeled in the sandbox using an erosion rule that removes mass from the scaled sand wedges according to rates expected from bedrock fluvial incision the geometry of both modeling approaches is quantitatively compared with that expected from analytical theory the fold and thrust belt growth rate is inversely proportional to k and is well predicted by theory except for the high erosion case in which both the numerical and the experimental sandbox grows supercritically a direct relationship exists between the erosion intensity and the number of fore shear bands and shear strain magnitude the number of fore shear bands decreases and their strain increases with erosion intensity the results indicate that realistic and mechanistic erosion rules can be applied to physical experiments to model mass removal and this approach opens up the possibility of calibrating strain history to erosion intensities for predictions in natural settings quantitative comparisons between the physical and numerical sandbox experiments indicate that deformation style and geometry of the thrust and fold belts are similar when identical rheologies and boundary conditions are used this benchmarking suggests that numerical experiments realistically model conditions observed in the simple cohesionless rheologies commonly employed in sandbox experiments this suggests that numerical simulation may reliably model experimental deformation in geological situations that are difficult to represent in scaled experiments because of the different scales and rheologies of natural orogenic wedges

erosion and exhumation in accretionary orogens experimental and geological approaches 1 this study examines the role of erosion on exhumation and deformation history of accretionary orogens through experimental and geological methods fault propagation kinematics and exhumation rates in an eroded thrust wedge are analyzed through scaled sandbox simulations by testing different parameters friction rheologic layering and sediment input output ratio a model coulomb wedge is submitted to erosion under flux steady state conditions that is the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during shortening results show that the way of exhumation depends on the internal dynamics of thrust wedges and conversely on how this dynamics is modified by erosion in the eroded thrust wedges the diversity of exhumation patterns is controlled by the mode of fault propagation depending on the basal friction high or low the vertical component of exhumation is generally higher for the wedges with high basal friction than for low friction wedges the uplift of material occurs along a cluster of subvertical thrusts in the middle part of the eroded thrust wedge with low basal friction the material is exhumed along a series of inclined 20 50 thrusts in the rear of the high friction wedge the zone of maximum exhumation is generally localized in the middle part of the thrust wedge and migrates toward the backstop with continued shortening the vertical exhumation rate increases with time and the material accreted later is rapidly transferred to the main exhumation zone compared to the material accreted during the early stages the exhumation occurs at rates 2 times faster in the wedges with half the thickness than in full thickness wedges the total quantity of eroded material at the end of convergence constitutes 36 50 of initial model area for the thrust wedges with low basal friction and 20 40 for the high basal friction wedges the extent of basal underplating increases with total shortening the area of basal underplated material constitutes up to 30 and 40 of the eroded thrust wedge area for the models with low and high basal friction respectively presence of decollements in the accreted series allows underplating of thrust units developing an anticlinal stack whose growth and location is favored by erosion our results are compared to different present day active and ancient convergent orogens himalaya taiwan southern alps of new zealand and cascadia orogen allowing the different specific exhumation processes to be characterized

evolution of fault efficiency at restraining bends within wet kaolin analog experiments abstract restraining bends are regions of mechanical inefficiency along strike slip faults where faults evolve to improve efficiency analog experiments using wet kaolin examine the evolution of a variety of restraining bends restraining bends with 15 bends continue to slip while systems with greater bends develop new faults the new faults which flank the uplifted region accommodate right lateral slip when parallel to the plate movement and oblique slip motion when parallel to the restraining segment within the wet kaolin strain is partitioned into fault slip and off fault deformation such as distributed shear and uplift the wet kaolin produces restraining bend deformation patterns fault sequence and mechanical efficiency similar to dry sand experiments and natural restraining bends the propagation of new faults in the wet kaolin improves the mechanical efficiency of the fault system by increasing the ratio of fault slip to off fault deformation local inefficiencies such as linkage of faults via a sharp kink do not affect the overall increase in efficiency of the linked fault system furthermore wider restraining bend stepovers have lower mechanical efficiency than close stepovers but the difference in mechanical efficiency decreases as faults grow and link up around the restraining bends this study demonstrates that restraining bend fault systems evolve toward greater mechanical efficiency

quantifying frictional variations and erosion in the mexican fold thrust belt abstract the impact of frictional crustal heterogeneities and surface processes on the evolution of the ancient thin skinned mexican fold and thrust belt mftb is investigated and quantified using numerical finite element simulations these simulations explore the evolution total shortening and structural styles of deforming orogenic wedges the models include spatial lateral variations in the internal friction and the topographic erodibility k using the power law incision rule the mftb exhibits paleogeographical elements manifested as lateral facies changes across two platforms units and two sedimentary basins that show different degrees of deformation the observed kinematics of the mftb requires based on the parameters considered in this study a rheologically heterogeneous crust with at least laterally varying internal friction yet only limited syntectonic and post tectonic erosion are necessary to explain the geometries and internal total shortening constrained by field observations and interpretations application of the analytical and homogeneous critical coulomb wedge ccw theory to the mftb closely predicts the external wedge geometry but fails to predict the observed shortening of the individual litho tectonic units and structural styles

possible erosional control on lateral growth of the european central alps between the middle and late miocene the central alps of switzerland and northern italy underwent a major phase of lateral crustal growth as recorded by the formation of the southern alps and the jura fold and thrust belt this period of dominantly outward directed deformation differs from the late oligocene and early miocene deformation style which was characterized mainly by rapid vertical exhumation sediment budgets from circum alpine sedimentary basins indicate a decrease in the erosional efficiency in the alpine hinterland several million years before lateral orogen growth was initiated and decreasing magnitudes of sediment discharge thereafter this decrease in erosional efficiency of the hinterland coincides approximately with widespread exposure of the crystalline core in the alpine hinterland as indicated by clast types in conglomerates of synorogenic deposits and with a contemporaneous increase in the continental influence in the paleoclimate as suggested by the fossiliferous plant record we suggest that the observed decrease in erosional efficiency caused gravitational forces to increase relative to tectonic forces driving the orogenesis which led to a transition from dominantly vertical to horizontally directed extrusion the data thus can be interpreted to indicate an active link between surface erosion and orogenic evolution

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

temporal stability of the neodymium isotope signature of the holocene to glacial north atlantic the neodymium isotopic composition of marine precipitates is increasingly recognized as a powerful tool for identifying changes in ocean circulation and mixing on million year to millennial timescales unlike nutrient proxies such as 13 c or cd ca nd isotopes are not thought to be altered in any significant way by biological processes and thus they can serve as a quasi conservative water mass tracer however the application of nd isotopes in understanding the role of thermohaline circulation in rapid climate change is currently hindered by the lack of direct constraints on the signature of the north atlantic end member through time here we present the first results of nd isotopes measured in u th dated deep sea corals from the new england seamounts in the northwest atlantic ocean our data are consistent with the conclusion that the nd isotopic composition of north atlantic deep and intermediate water has remained nearly constant through the last glacial cycle the results address long standing concerns that there may have been significant changes in the nd isotopic composition of the north atlantic end member during this interval and substantiate the applicability of this novel tracer on millennial timescales for paleoceanography research

abrupt pre bolling allerod warming and circulation changes in the deep ocean several large and rapid changes in atmospheric temperature and the partial pressure of carbon dioxide in the atmosphere probably linked to changes in deep ocean circulation occurred during the last deglaciation the abrupt temperature rise in the northern hemisphere and the restart of the atlantic meridional overturning circulation at the start of the bolling allerod interstadial 14 700 years ago are among the most dramatic deglacial events but their underlying physical causes are not known here we show that the release of heat from warm waters in the deep north atlantic ocean probably triggered the bolling allerod warming and reinvigoration of the atlantic meridional overturning circulation our results are based on coupled radiocarbon and uranium series dates along with clumped isotope temperature estimates from water column profiles of fossil deep sea corals in a limited area of the western north atlantic we find that during heinrich stadial 1 the cool period immediately before the bolling allerod interstadial the deep ocean was about three degrees celsius warmer than shallower waters above this reversal of the ocean s usual thermal stratification pre dates the bolling allerod warming and must have been associated with increased salinity at depth to preserve the static stability of the water column the depleted radiocarbon content of the warm and salty water mass implies a long term disconnect from rapid surface exchanges and although uncertainties remain is most consistent with a southern ocean source the heinrich stadial 1 ocean profile is distinct from the modern water column that for the last glacial maximum and that for the younger dryas suggesting that the patterns we observe are a unique feature of the deglacial climate system our observations indicate that the deep ocean influenced dramatic northern hemisphere warming by storing heat at depth that preconditioned the system for a subsequent abrupt overturning event during the bolling allerod interstadial

evidence from the high latitude north atlantic for variations in antarctic intermediate water flow during the last deglaciation we present evidence that the characteristic chemical signature based on coupled benthic foraminiferal cd ca and d13c of antarctic intermediate waters aaiw penetrated throughout the intermediate depths of the atlantic basin to the high latitude north atlantic during the abrupt cooling events of the last deglaciation heinrich 1 and the younger dryas aaiw may play the dynamic counterpart to the bipolar seesaw when near freezing salty bottom waters from the antarctic aabw sluggishly ventilate the deep ocean our data reinforce the concept that interglacial circulation is stabilized by salinity feedbacks between salty northern sourced deep waters nadw and fresh southern sourced waters aabw and aaiw further the glacial ocean may be susceptible to the more finely balanced relative densities of nadw and aaiw due to either freshwater input or a reversal of the salinity gradient such that the ocean is poised for nadw collapse via a negative salinity feedback the unstable climate of the glacial period and its termination may arise from the closer competition for ubiquity at intermediate depths between northern and southern sourced intermediate waters

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

brittle frictional mountain building 1 deformation and mechanical energy budget an active fold and thrust belt is analogous to a wedge of soil or snow that forms in front of a moving bulldozer such wedges exhibit a critical taper and a regional state of stress that is everywhere on the verge of coulomb failure the width of such a critically tapered fold and thrust belt does not depend on its brittle strength or frictional properties but rather on the accretionary influx rate of fresh material at its toe and on the rate of erosion a steady state fold and thrust belt is one in which the accretionary influx is balanced by the erosive efflux rocks are accreted at the toe and then horizontally shortened as they are transported toward the rear those that enter lower in the accreted section are more deeply buried before being uplifted by erosion mass balance and isotropy constrain the kinematics of this large scale deformation enabling us to infer the trajectories residence times and stress strain histories of rocks incorporated into eroding fold and thrust belts a typical rock resides in the steady state taiwan wedge for 2 3 m y before it is uplifted and eroded during its motion through the wedge it experiences strain rates in the range 10 13 to 10 14 s 1 the mechanical energy budget of brittle frictional mountain building is described by the equation where is the rate of work performed on the base and front of the fold and thrust belt by the subducting plate is the rate at which energy is dissipated against friction on the decollement fault is the rate at which energy is dissipated by internal frictional processes within the deforming brittle wedge and is the rate of work performed against gravitational body forces in a reference frame attached to the overriding plate the total mechanical power being supplied by the subducting eurasian plate to the active fold and thrust belt in taiwan is slightly over 3 gw approximately 60 of this work of steady state mountain building is being dissipated against friction on the decollement fault and about another 25 is being dissipated against internal friction this leaves only 15 or roughly half a gigawatt available to do useful work against gravity in general fold and thrust belts with moderate pore fluid pressures are dominated by work done against friction on the decollement fault however those with nearly lithostatic pore fluid pressures may be dominated by work done against gravity internal frictional dissipation is always less than basal frictional dissipation as it is in taiwan an alternative and equivalent description of the mechanical energy balance of a steady state fold and thrust belt is provided by the equation in this version the quantity on the left is the rate at which work is performed on the back of the wedge by the overriding plate and is the rate of work performed against gravity in a reference frame attached to the subducting plate the latter quantity is always positive for any critically tapered fold and thrust belt whose decollement fault dips toward its rear in contradiction to the central premise of the gravity spreading theory of fold and thrust tectonics

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

reduced advection into atlantic ocean deep eastern basins during last glaciation maximum causes of change in deep water 13c can be either global or local in extent global causes include 1 climatically induced changes in the amount of terrestrial biomass which alter the average carbon isotopic composition of the oceanic reservoir1 and 2 erosion and deposition of organic rich continental shelf sediments during sea level fluctuations which change the mean oceanic carbon phosphorus ratio2 regional gradients of 13c are created by remineralization of organic detritus within the deep ocean itself thus reflecting the distribution of water masses and modern thermohaline flow changes in a single geological record of benthic foraminiferal 13c can result from any combination of these global and abyssal circulation effects by sampling a large number of cores collected over a wide bathymetric range yet confined to a small geographical region we have minimized the ambiguity we can assume that each 13c record was equally affected by global causes of 13c variation the differences seen between the 13c records must therefore reflect changes in the distribution of 13c in the deep ocean we interpret these differences in distribution in terms of changes in the ocean s abyssal circulation benthic foraminiferal carbon isotopic evidence from a suite of sierra leone rise cores indicates that the deeper parts of the eastern atlantic basins underwent a reduction in o2 during the maximum of the last glaciation reduced advection of o2 rich deep water through low latitude fracture zones associated with increased delivery of organic matter to the deep ocean lowered the 13c of deep water co2 at all depths below the sill separating the eastern and western atlantic basins 3 this decreased advection into the eastern atlantic ocean coincides with the overall decrease in deep water production in the north atlantic during the last glacial maximum4 7

geologic constraints on bedrock river incision using the stream power law denudation rate in unextended terranes is limited by the rate of bedrock channel incision often modeled as work rate on the channel bed by water and sediment or stream power the latter can be generalized as ka m s n where k represents the channel bed s resistance to lowenng whose variation with lithology is unknown a is drainage area a surrogate for discharge s is local slope and m and n are exponents whose values are debated we address these uncertainties by simulating the lowering of ancient river profiles using the finite difference method we vary m n and k to match the evolved profile as closely as possible to the corresponding modern river profile over a time period constrained by the age of the mapped paleoprofiles we find at least two end member incision laws ka 0 3 0 5 s for australian rivers with stable base levels and k f a 0 1 0 2 s n for rivers in kauai subject to abrupt base level change the long term lowering rate on the latter expression is a function of the frequency and magnitude of knickpoint erosion characterized by k f incision patterns from japan and california could follow either expression if they follow the first expression with m 0 4 k varies from 10 7 10 6 m 0 2 yr for granite and metamorphic rocks to 10 5 10 4 m 0 2 yr for volcaniclastic rocks and 10 4 10 2 m 0 2 yr for mudstones this potentially large variation in k with lithology could drive strong variability in the rate of long term landscape change including denudation rate and sediment yield

comparison of cushioning mechanisms between cellular glass and gabions subjected to successive boulder impacts abstractgabions are the most commonly adopted cushion layer for shielding rigid debris resisting barriers against boulder impact despite the prevalent use of gabions they comprise heavy rock frag

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

southern ocean evidence for reduced export of north atlantic deep water during heinrich event 1 deep sea corals form unique high resolution archives of ocean circulation that can be dated using the decay of uranium to thorium they are abundant in the southern ocean and can provide unprecedented insights into ocean circulation and ocean chemistry on sub millennial time scales in areas where application of traditional paleoceanographic proxies is difficult here we present the first coupled neodymium nd isotope and radiocarbon data from deep sea corals in the drake passage southern ocean adding new constraints on ocean circulation during the last heinrich event h1 16 7 ka the modern day drake passage water column is homogeneous with respect to nd isotopes expressed in epsilon units nd its isotopic value of close to 9 is largely controlled by the mixture of north atlantic deep water and pacific deep water the aragonite of modern drake passage corals reflects this water column value whereas a fossil coral from h1 is significantly higher at 6 4 0 4 we interpret this 2 5 unit shift as a reduction in the influence of north atlantic sourced nd in the southern ocean during h1 this interpretation is supported by a series of radiocarbon analyses on the same sample and is consistent with a twofold or greater reduction in export of north atlantic waters from the atlantic basin combining analyses of radiocarbon and nd isotopes on u series dated deep sea coral skeletons holds great potential for quantification of past ocean ventilation rates

messinian climate change and erosional destruction of the central european alps at the end of the miocene the european alps ceased outward expansion and tectonic uplift and exhumation shifted into the orogen interior this shift is consistent with a change from orogenic construction to orogenic destruction reflecting an increase in the ratio of erosional flux to accretionary flux the coincidence of this change with an increase in sediment yield from the alps suggests a climate driven increase in erosional flux the timing of deformation and sediment release from the southern alps indicates that the tectonic change occurred synchronous with the last phase of the messinian salinity crisis we attribute the increase in erosional flux to a climatic shift to wetter conditions throughout europe likely augmented by the base level fall that occurred during the mediterranean dessication this climate change is represented in the stratigraphic record by the lago mare deposits of the mediterranean salinity crisis

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

decreased influence of antarctic intermediate water in the tropical atlantic during north atlantic cold events abstract antarctic intermediate water aaiw is a key player in the global ocean circulation contributing to the upper limb of the atlantic meridional overturning circulation amoc and influencing interhemispheric heat exchange and the distribution of salinity nutrients and carbon however the deglacial history of aaiw flow into the north atlantic is controversial here we present a multicore top neodymium isotope calibration which confirms the ability of unclean foraminifera to faithfully record bottom water neodymium isotopic composition e nd values in their authigenic coatings we then present the first foraminifera based reconstruction of e nd from three sediment cores retrieved from within modern aaiw in the western tropical north atlantic our records reveal similar glacial and interglacial contributions of aaiw and a pronounced decrease in the aaiw fraction during north atlantic deglacial cold episodes heinrich stadial 1 hs1 and younger dryas yd our results suggest two separate phases of reduced fraction of aaiw in the tropical atlantic during hs1 with a greater reduction during early hs1 if a reduction in aaiw fraction also reflects reduced amoc strength this finding may explain why in many regions there are two phases of hydrologic change within hs1 and why atmospheric co2 rose more rapidly during early than late hs1 our result suggesting less flow of aaiw into the atlantic during north atlantic cold events contrasts with evidence from the pacific where intermediate depth e nd records may indicate increased flow of aaiw into the pacific during the these same events antiphased e nd behavior between intermediate depths of the north atlantic and pacific implies that the flow of aaiw into atlantic and pacific seesawed during the last deglaciation

an experimental investigation of the response of slender protective structures to rockfall impacts this article investigates the mechanical response of slender rockfall protection embankments subjected to impacts based on real scale experiments more specifically it deals with rectangular in c

steady state erosion of critical coulomb wedges with applications to taiwan and the himalaya 1 orogenic structure appears to be partially controlled by the addition to and removal of material from the mountain belt by tectonic accretion and geomorphic erosion respectively we developed a coupled erosion deformation model for orogenic wedges that are in erosional steady state and deform at their coulomb failure limit erosional steady state is reached when all material introduced into the wedge is removed by erosion that is limited by the rate at which rivers erode through bedrock we found that the ultimate form of a wedge is controlled by the wedge mechanical properties sole out depth of the basal decollement erosional exponents basin geometry and the ratio of the added material flux to the erosional constant as this latter ratio is increased wedge width and surface slopes increase we applied these models to the taiwan and himalayan orogenic wedges and found that despite a higher flux of material entering the former the inferred ratio was larger for the latter calculated values for the erodibility of each wedge showed at least an order of magnitude lower value for the himalaya relative to taiwan these values are consistent with the lower precipitation regime in the himalaya relative to taiwan and the exposure of crystalline rocks within the himalayan orogenic wedge independently determined rock erodibility estimates are consistent with the accretionary wedge sediments and metasediments and the crystalline and high grade metamorphic rocks exposed within taiwan and the himalaya respectively therefore differences in rock type and climate apparently lead to key differences in the erosion and hence orogenic structure of these two mountain belts

growth and erosion of fold and thrust belts with an application to the aconcagua fold and thrust belt argentina 1 the development of topography within and erosional removal of material from an orogen exerts a primary control on its structure we develop a model that describes the temporal development of a frontally accreting critically growing coulomb wedge whose topography is largely limited by bedrock fluvial incision we present general results for arbitrary initial critical wedge geometries and investigate the temporal development of a critical wedge with no initial topography increasing rock erodibility and or precipitation decreasing mass flux accreting to the wedge front increasing wedge sole out depth decreasing wedge and basal decollement overpressure and increasing basal decollement friction lead to narrow wedges large power law exponent values cause the wedge geometry to quickly reach a condition in which all material accreted to the front of the wedge is removed by erosion we apply our model to the aconcagua fold and thrust belt in the central andes of argentina where wedge development over time is well constrained we solve for the erosional coefficient k that is required to recreate the field constrained wedge growth history and these values are within the range of independently determined values in analogous rock types using qualitative observations of rock erodibilities within the wedge we speculate that power law exponents of 1 3 m 0 4 and 2 3 n 1 characterize the erosional growth of the aconcagua fold and thrust belt this general model may be used to understand the development of mountain belts where orogenic wedges grow as they deform at their coulomb failure limit

the southern ocean s role in carbon exchange during the last deglaciation changes in the upwelling and degassing of carbon from the southern ocean form one of the leading hypotheses for the cause of glacial interglacial changes in atmospheric carbon dioxide we present a 25 000 year long southern ocean radiocarbon record reconstructed from deep sea corals which shows radiocarbon depleted waters during the glacial period and through the early deglaciation this depletion and associated deep stratification disappeared by 14 6 ka thousand years ago consistent with the transfer of carbon from the deep ocean to the surface ocean and atmosphere via a southern ocean ventilation event given this evidence for carbon exchange in the southern ocean we show that existing deep ocean radiocarbon records from the glacial period are sufficiently depleted to explain the 190 per mil drop in atmospheric radiocarbon between 17 and 14 5 ka

deformation exhumation and topography of experimental doubly vergent orogenic wedges subjected to asymmetric erosion we explore the effect of asymmetric erosion and dip angle of the indenter on the internal kinematics deformation and exhumation of an experimental doubly vergent orogenic wedge during transient and steady state flux conditions we calculate displacement fields and derive strain and exhumation for several erosion and non erosion cases using particle image velocimetry piv analysis we apply calculated displacement fields to a simple heat equation to explore virtual evolution of thermal structure erosion exerts a primary control in the internal kinematics of the experimental wedge in non erosion cases early formed fore shears rotate toward the indenter such that the shear bands become steeper this effect is more pronounced in prowedge erosion cases where shear bands become very steep and even overturned conversely retrowedge erosion results in back rotation of early formed fore shears and the shear bands evolved to gently dipping structures wedge erosion in combination with the condition of flux and topographic steady state increases density of fore shears and controls size width and topographic divide migration steeply dipping indenters produce overall gentle particle trajectories and gently dipping indenters favor steep trajectories particle velocity with respect to isotherms increases where erosion is concentrated and near active fore shears