the fold test in palaeomagnetism summary the fold test suggested by mcelhinny is shown to be inappropriate more correctly one should determine whether the mean direction of a group of sites from one limb of a fold may be distinguished statistically from the mean direction of a group of sites from another limb details of the application of this test are given with examples it is shown that the test indicates significance under far less severe folding than does the test suggested by mcelhinny

climate tectonics and the morphology of the andes large scale topographic analyses show that hemisphere scale climate variations are a first order control on the morphology of the andes zonal atmospheric circulation in the southern hemisphere creates strong latitudinal precipitation gradients that when incorporated in a generalized index of erosion intensity predict strong gradients in erosion rates both along and across the andes cross range asymmetry width hypsometry and maximum elevation reflect gradients in both the erosion index and the relative dominance of fluvial glacial and tectonic processes and show that major morphologic features correlate with climatic regimes latitudinal gradients in inferred crustal thickening and structural shortening correspond to variations in predicted erosion potential indicating that like tectonics nonuniform erosion due to large scale climate patterns is a first order control on the topographic evolution of the andes

ice sheet control of continental erosion in central and southern chile 36 41 s over the last 30 000 years bulk sediment chemistry from three chilean continental margin ocean drilling program sites constrains regional continental erosion over the past 30 000 years sediments from thirteen rivers that drain the mostly igneous andes and the mostly metamorphic coast range along with existing rock chemistry datasets define terrestrial provenance for the continental margin sediments andean river sediments have high mg al relative to coast range river sediments near 36 s marine sediments have high mg al i e more andean sources during the last glacial period and lower mg al less andean sources during the holocene near 41 s a ti rich source likely from coast range igneous intrusions is prevalent during holocene time whereas high mg al andean sources are more prevalent during the last glacial period we infer that there is a dominant ice sheet control of sediment sources at 36 s andean sourced sediment decreased as andean mountain glaciers retreated after w17 6 ka coincident with local oceanic warming and southward retreat of the patagonian forest and by inference westerly winds at 41 s andean sediment dominance peaks and then rapidly declines at w19 ka coincident with local oceanic warming and the earliest deglacial sea level rise we hypothesize that this decreased flux of andean material in the south is related to rapid retreat of the marine based portion of the patagonian ice sheet in response to global sea level rise as the resulting flooding of the southern portion of the central valley created a sink for andean sediments in this region reversal of the decreasing deglacial mg al trend at 41 s from 14 5 to 13 0 ka is consistent with a brief re advance of the patagonian ice sheet coincident with the antarctic cold reversal

abnormal monsoon years and their control on erosion and sediment flux in the high arid northwest himalaya abstract the interplay between topography and indian summer monsoon circulation profoundly controls precipitation distribution sediment transport and river discharge along the southern himalayan mountain front shf the higher himalayas form a major orographic barrier that separates humid sectors to the south and arid regions to the north during the indian summer monsoon vortices transport moisture from the bay of bengal swirl along the shf to the northwest and cause heavy rainfall when colliding with the mountain front in the eastern and central parts of the himalaya precipitation measurements derived from passive microwave analysis ssm i show a strong gradient with high values at medium elevations and extensive penetration of moisture along major river valleys into the orogen the end of the monsoonal conveyer belt is near the sutlej valley in the nw himalaya where precipitation is lower and rainfall maxima move to lower elevations this region thus comprises a climatic transition zone that is very sensitive to changes in indian summer monsoon strength to constrain magnitude temporal and spatial distribution of precipitation we analyzed high resolution passive microwave data from the last decade and identified an abnormal monsoon year amy in 2002 during the 2002 amy violent rainstorms conquered orographic barriers and penetrated far into otherwise arid regions in the northwest himalaya at elevations in excess of 3 km asl while precipitation in these regions was significantly increased and triggered extensive erosional processes i e debris flows on sparsely vegetated steep hillslopes mean rainfall along the low to medium elevations was not significantly greater in magnitude this shift may thus play an important role in the overall sediment flux toward the himalayan foreland using extended precipitation and sediment flux records for the last century we show that these events have a decadal recurrence interval during the present day monsoon circulation hence episodically occurring amys control geomorphic processes primarily in the high elevation arid sectors of the orogen while annual recurring monsoonal rainfall distribution dominates erosion in the low to medium elevation parts along the shf

holocene rainfall variability in southern chile a marine record of latitudinal shifts of the southern westerlies geochemical and clay mineral parameters of a high accumulation marine sediment core from the chilean continental slope 41 s provide a 7700 yr record of rainfall variability in southern chile related to the position of the southern westerlies we especially use the iron content measured with a time resolution of ca 10 yr on average of 14 caccelerator mass spectrometry dated marine sediments as a proxy for the relative input of iron poor coastal range and iron rich andean source rocks variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position based on these interpretations we find a pronounced rainfall variability on multicentennial to millennial time scales superimposed on generally more arid conditions during the middle holocene 7700 to 4000 cal yr b p compared to the late holocene 4000 to present this variability and thus changes in the position of the southern westerlies are first compared to regional terrestrial paleoclimate data sets from central and southern chile in order to derive possible wider implications and forcing mechanisms of the holocene latitudinal shifts of the southern westerlies we then compare our data to ice core records from both tropical south america and coastal antarctica these records show similar bands of variability centered at ca 900 and 1500 yr comparisons of band pass filters suggest a close connection of shifts of the southern westerlies to changes within the tropical climate system the correlation to climate conditions in coastal antarctica shows a more complicated picture with a phase shift at the beginning of the late holocene coinciding with the onset of the modern state of el nin o southern oscillation system the presented data provide further evidence that the well known millennial scale climate variability during the last glacial continued throughout the holocene fl 2001 elsevier science b v all rights reserved

erosion rates in and around shenandoah national park virginia determined using analysis of cosmogenic 10be we use cosmogenic 10be analysis of fluvial sediments and bedrock to estimate erosion rates 104 105 year timescale and to infer the distribution of post orogenic geomorphic processes in the blue ridge province in and around shenandoah national park virginia our sampling plan was designed to investigate relationships between erosion rate and lithology mean basin slope basin area and sediment grain size fifty nine samples were collected from a variety of basin sizes inferred erosion rates for the medium sand fraction of all fluvial samples from all lithologies range from 3 0 to 21 m my the area weighted mean erosion rate for single lithology basins in the park is 12 2 m my single lithology erosion rate ranges for fluvial samples are granite 7 0 to 20 m my metabasalt 3 8 to 21 m my quartzite 3 8 to 15 m my and siliciclastic rocks 5 2 to 15 m my multilithology basins erode at rates between 3 0 16 m my the shenandoah river basin 3305 km2 is eroding at 6 6 m my bedrock erosion rates range from 1 8 to 11 m my across all lithologies with a mean of 6 5 4 3 m my grain size specific 10be analysis of four samples showed no consistent trend of concentration with grain size cosmogenic analysis of bedrock and sediment from the shenandoah national park area allows us to speculate about why some parts of the appalachian mountains erode more slowly and some more rapidly overall it appears that steep drainage basins erode more rapidly than gently sloped basins climate and lithology may also influence basin scale rates of erosion as suggested by the difference in average erosion rates east and west of the divide and the difference between the erosion rates of quartzite and granite dominated basins data are conflicting in regards to the evolution of relief over time analyses made of exposed bedrock along ridgelines suggest that such rock is eroding either more slowly than adjacent drainage basins susquehanna river shenandoah national park region or at similar rates great smoky mountains providing a mechanism for growing relief at the scale of individual ridgelines however considering relief on a landscape or physiographic province scale by comparing erosion rates of the highlands versus the lowlands suggests that relief of the range as a whole is either steady or very slowly decreasing over multi millennial timescales the presence of significant erosion rate slope relationships negates a broad hackian view of the landscape because there is not uniform erosion across this landscape the aspect erosion rate and slope erosion rate relationships present in the shenandoah area suggest that the landscape is not fully adjusted to rock strength

late pleistocene landscape evolution in south central chile constrained by luminescence and stable cosmogenic nuclide dating landscapes in tectonically active regions develop in response to a complex interplay between rapid tectonic deformation and surface processes in order to understand the evolution of these environments and distinguish between the different factors it is fundamental to identify and quantify geomorphic processes and rates on different time scales the forearc of south central chile provides an ideal setting to elucidate the response of surface processes to climatic and tectonic forcing however in contrast to northern chile this region has attracted little attention due to difficulties in quantifying the age of geomorphic surfaces we use luminescence and stable cosmogenic nuclides 3 he 21 ne on conglomeratic units in the central depression and fluvial valley fills in the coastal cordillera to constrain exposure and burial ages of these units that form major landscape elements in the southern chilean forearc our data indicate that disturbances in the drainage network are controlled by local uplift which may be caused by deformation above an active blind thrust in the coastal cordillera local short term uplift rates reach a minimum of 0 27 mm a 1 and are on the same order as late quaternary minimum incision rates of 0 15 mm a 1 to 0 43 mm a 1 the valley fills in the coastal cordillera have depositional ages of 80 ka and 255 ka respectively exposure ages of the extensive alluvial surfaces in the central depression cluster between 135 ka and 175 ka and between 240 ka and 280 ka hence the deposition of these surfaces broadly coincides with marine isotope stages mis 6 and 8 and appears to be climatically driven

permo triassic paleomagnetism of the north pamir tectonic implications abstract after stepwise thermal demagnetization of upper permian tuffaceous red beds localities 1 and 2 and triassic volcanics locality 3 of north pamir central asia the following mean directions of characteristic magnetization components were obtained 1 upper permian locality 1 d 179 3 i 38 0 95 5 4 29 samples 2 upper permian locality 2 d 137 4 i 42 0 95 6 6 20 samples 3 middle upper triassic locality 3 d 226 8 i 63 8 95 4 4 16 samples the conglomerate and fold tests are positive for the first and third results whereas no field test could be performed for the second one the late permian locality mean inclinations are statistically indistinguishable and the observed difference in mean declinations closely matches that in structural trends between localities 1 and 2 this constitutes a positive fold test and at the same time points to oroclinal bending of the pamir structures thus confirming an earlier conclusion about the secondary origin of this arc permian and triassic paleolatitudes together with earlier published early cretaceous data fall close to the european reference inclination curve this implies that north pamir has been close to the eurasia landmass at least since the late permian and the major part of the india eurasia convergence was absorbed to the south of this zone

3 d sediment basement tomography of the northern marmara trough by a dense obs network at the nodes of a grid of controlled source profiles along the north anatolian fault a 3 d tomographic inversion of first arrival times of shot profiles recorded by a dense 2 d obs network provides an unprecedented constraint on the p wave velocities heterogeneity of the upper crustal part of the north marmara trough nmt over a region of 180 km long by 50 km wide one of the specific aims of this controlled source tomography is to provide a 3 d initial model for the local earthquake tomography let hence in an original way the controlled source inversion has been performed by using a code dedicated to let after several tests to check the results trade off with the inversion parameters we build up a 3 d a priori velocity model in which the sea bottom topography the acoustic and the crystalline basements and the moho interfaces have been considered the reliability of the obtained features has been checked by checkerboard tests and also by their comparison with the deep penetration multichannel seismic profiles and with the wide angle reflection and refraction modelled profiles this study provides the first 3 d view of the basement topography along the active north anatolian fault beneath the marmara sea even beneath the deepest part of three sedimentary basins of nmt clear basement depressions reaching down 6 km depth below the sea level bsl have been found beneath these basins the north imrali basin located on the southern continental shelf is observed with a similar sedimentary thickness as its northern neighbours between central and cinarcik basins the central high rises up to 3 km depth below bsl its crest position is offset by 10 km northwestward relatively to the bathymetric crest on the contrary tekirdag and central basins appear linked forming a 60 km long basement depression beneath the bathymetric relief of western high low velocities are observed down to 6 km depth bsl and no basement high have been found the obtained 3 d vp heterogeneity model allows the consideration of the 3 d supracrustal heterogeneity into the future earthquake relocations in this region the topographic map of the pre kinematic basement offers the possibility to take into account the locking depth variations in future geohazard estimations by geomechanical modelling in this region

review of erosion dynamics along the major n s climatic gradient in chile and perspectives abstract chile is an elongated country running in a north south direction for more than 30 along a subduction zone its climate is progressively wetter and colder from north to south this particular geography has been used positively by a growing number of studies to better understand the relationships between erosion processes and climate land use slope tectonics volcanism etc here we review the erosion rates factors and dynamics over millennial to daily periods reported in the literature in addition 21 new catchment mean erosion rates suspended sediment and 10be are provided and previous suspended sediment derived erosion rates are updated a total of 485 local and catchment mean erosion rates are reported erosion rates vary between some of the smallest values on earth 10 5 mm a to moderate values 0 5 mm a compared to other active ranges this review highlights strong limitations concerning the quantification of local erosion factors because of uncertainties in sampling point location slope and rainfall data for the mean erosion rates e for the millennial and decennial catchments a model of the form e s 1 s 0 6 2 r with 0 3 0 8 accounts for 40 to 70 of the erosion variance confirming a primary role of slope s compared to precipitation rate r over this time scale over the long term this review points to the long 5 to 10 ma response time of rivers to surface uplift in north central arid chile over millennia data provide evidence for the progressive contribution of extreme erosion events to millennial averages for drier climates as well as the link between glacier erosion and glacier sliding velocity in this period of time a discrepancy exists between the long term offshore sedimentological record and continental decennial or millennial erosion data for which no single explanation appears still little information is available concerning the magnitude of variation of millennial erosion rates over centuries data show the variable role of groundwater in the dynamics of suspended load and document a decrease in erosion over hundreds of years probably associated with historical harvesting

denudation and deformation in a glaciated orogenic wedge the st elias orogen alaska apatite u th he dating from the st elias orogen in southern alaska illustrates a potential association between long term denudation and glacier sliding cooling ages as young as 0 4 ma exhumation 4 5 mm yr are concentrated in a narrow band near the glacier equilibrium line altitude ela front where mean quaternary ela intersects the windward flank of the orogen this band of denudation is not correlated with individual faults structural trends or known concentrations of precipitation and we propose that it is produced by focused glacier sliding at or near the ela front this implies that long term glacial erosion is a maximum at ela which corroborates model predictions that glaciers and climate can control the pattern of crust removal from orogens denudation rates do not covary with fluctuations in glacier size along the ela front suggesting that small glaciers are capable of keeping pace with incision by larger ones and tectonic rock uplift ice discharge may thus play a critical but complex role in excavating glaciated orogens

the reconstruction and climatic implication of an independent palaeo ice cap within the andean rain shadow east of the former patagonian ice sheet santa cruz province argentina abstract this paper describes the reconstruction of the previously undocumented meseta cuadrada palaeo ice cap on south west meseta del lago buenos aires santa cruz province patagonia based on theoretical surface profiles the reconstruction of the meseta cuadrada palaeo ice cap indicates an ice mass covering at least 78 km2 with a total ice volume around 9 2 km3 the inferred equilibrium line altitude ela of the palaeo ice cap 2031 m asl represents a drop of 286 m compared to the ela of the current meseta cuadrada glacier 2317 m asl we explain this small change in ela with reference to the flat hypsometry of the palaeo ice cap and an enhanced aridity to the west of the patagonian andes caused by the existence of the last glacial maximum lgm patagonian ice sheet calculated annual accumulation values of ca 402 to 957 mm a at the ela of the meseta cuadrada palaeo ice cap derived by a degree day model ddm during the last local glacial maximum extent are low compared with estimations of the current accumulation at the ela of the remaining glacierized area of around 3789 mm a this strongly supports the existence of increased aridity and seasonality east of the patagonian andes during the last glacial maximum provided both maximum extents were synchronous

seismic evidence of up to 200 m lake level change in southern patagonia since marine isotope stage 4 maar lake laguna potrok aike is located north of the strait of magellan south eastern patagonia seismic reflection profiles revealed a highly dynamic palaeoclimate history dunes were identified

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

geomorphologic evidence for the late pliocene onset of hyperaridity in the atacama desert the atacama desert has experienced a long and protracted period of hyperaridity that has resulted in what may be the most unusual biome on earth but the duration of this aridity is poorly constrained we reconstructed aspects of the fluvial and geochemical history of this region using integrated landscape features alluvial fans hillslope soils soil chemistry river profiles in the southern portion of the present desert topographic reconstructions of a large watershed 11 000 km 2 show deep incision and sediment removal between the late miocene and the end of the pliocene and modest to negligible incision in post pliocene times these changes in incision suggest an 50 280 reduction in river discharge which should reflect corresponding changes in precipitation changes in the nature of hillslope soils in the atacama desert indicate that in the pliocene or earlier hillslopes were mantled with silicate derived soil this mantle was stripped off and locally deposited as alluvial fans late pliocene to early pleistocene that now block or otherwise cause a rearrangement of pliocene and earlier river channels finally the hillslopes have largely accreted a soil mantle of dust and salt since the apparent late pliocene stripping suggesting a decline in annual precipitation of at least 125 mm yr 1 or more mean annual precipitation map is now 1 embedded in the long post pliocene era of salt accumulation there are a variety of features suggesting overland flow on hillslopes rills striped gravel deposits piping and water spouts and large infrequent storms that infiltrated gentle alluvial fans due to the depth of salt rich horizons despite evidence for episodes that punctuate the hyperaridity the magnitude and duration of these pluvial events have been insufficient to remove the regional accumulations of sulfate chloride and nitrate the late pliocene cessation of many fluvial features is coincident with recent research on the tropical pacific which shows that the pacific was in a permanent el nino state until ca 2 2 ma at which time sea surface temperatures offshore of south america declined greatly relative to those of the western pacific in turn setting up the present el nino southern oscillation enso climate system these observations indicate that the latest period of aridity has been prolonged and largely continuous and it appears to have occurred in step with the onset of the enso climate system beginning 2 m y ago

turbiditic trench deposits at the south chilean active margin a pleistocene holocene record of climate and tectonics the active plate margin of south america is characterized by a frequent occurrence of large and devastating subduction earthquakes here we focus on marine sedimentary records off southern chile that are archiving the regional paleoseismic history over the holocene and late pleistocene the investigated records ocean drilling program odp site 1232 and sonne core 50sl are located at 40 s and 38 s within the peru chile trench and are characterized by frequent interbedded strata of turbiditic and hemipelagic origin on the basis of the sedimentological characteristics and the association with the active margin of southern chile we assume that the turbidites are mainly seismically triggered and may be considered as paleo megaearthquake indicators however the long term changes in turbidite recurrence times appear to be strongly influenced by climate and sea level changes as well during sea level highstands in the holocene and marine isotope stage mis 5 recurrence times of turbiditic layers are substantially higher primarily reflecting a climate induced reduction of sediment availability and enhanced slope stability in addition segmented tectonic uplift changes and related drainage inversions likely influenced the postglacial decrease in turbidite frequencies glacial turbidite recurrence times including mis 2 mis 3 cold substages of mis 5 and mis 6 on the other hand are within the same order of magnitude as earthquake recurrence times derived from the historical record and other terrestrial paleoseismic archives of the region only during these cold stages sediment availability and slope instability were high enough to enable recording of the complete sequence of large earthquakes in southern chile our data thus suggest that earthquake recurrence times on the order of 100 to 200 years are a persistent feature at least during the last glacial period 2008 elsevier b v all rights reserved

quantifying the role of geographic change in cenozoic ocean heat transport using uncoupled atmosphere and ocean models abstract a series of five cenozoic atmospheric general circulation model agcm experiments has been performed using a new set of paleogeographic reconstructions for 55 40 33 20 and 14 ma the five continental reconstructions incorporate the tectonic evolution of early eocene to middle miocene continental positions and topography with all other model boundary conditions and forcings held constant the series of agcm experiments captures a

magnitude geomorphologic response and climate links of lake level oscillations at laguna potrok aike patagonian steppe argentina abstract laguna potrok aike is a large maar lake located in the semiarid steppe of southern patagonia known for its lateglacial and holocene lake level fluctuations based on sedimentary seismic and geomorphological evidences the lake level curve is updated and extended into the last glacial period and the geomorphological development of the lake basin and its catchment area is interpreted abrasion and lake level oscillations since at least 50 ka caused concentric erosion of the surrounding soft rocks of the miocene santa cruz formation and expanded the basin diameter by approximately 1 km a high lake level and overflow conditions of the lake were dated by luminescence methods and tephra correlation to the early lateglacial as well as to 45 ka the lowest lake level of record occurred during the mid holocene a further lake level drop was probably prevented by groundwater supply this low lake level eroded a distinct terrace into lacustrine sediments collapse of these terraces probably caused mass movement deposits in the profundal zone of the lake after the mid holocene lake level low stand a general and successive transgression occurred until the little ice age maximum i e ca 40 m above the local groundwater table frequent lake level oscillations caused deflation of emerged terraces only along the eastern shoreline due to prevailing westerly winds preservation of eolian deposits might be linked to relatively moist climate conditions during the past 2 5 ka precisely dated lake level reconstructions in the rain shadow of the andes document high last glacial and low holocene lake levels that could suggest increased precipitation during the last glacial period as permafrost in semiarid patagonia is documented and dated to the last glacial period we argue that the frozen ground might have increased surficial runoff from the catchment and thus influenced the water balance of the lake this is important for investigating the glacial to holocene latitudinal shift and or strengthening of the southern hemispheric westerlies by using lake level reconstructions as a means to assess the regional water balance our interpretation explains the contradiction with investigations based on pollen data indicating drier climatic conditions for the last glacial period

mid latitude glacial erosion hotspot related to equatorial shifts in southern westerlies glaciation has affected the shape of mountain ranges and has induced a global increase in erosion rates during the past 2 m y the observed increase in erosion rates appears to vary with latitude reaching a maximum at mid latitudes that is particularly well defined in the southern hemisphere although it is likely that climate played an important role the processes responsible for such latitudinal distribution of erosion are unclear here we exploit the meridional extent of the patagonian andes and identify an erosion hotspot at 44 s using a glacial erosion model and formally inverting the available thermochronometric and geobarometric data we show that this hotspot coincides with the location of maximum precipitation that follows the southern hemisphere westerlies during glacial periods we propose that the increased precipitation rates at 44 s led to greater ice sliding velocities and faster glacial erosion our results imply that the migration of the westerly wind belt toward the equator since 2 3 ma may have played an important role in determining the distribution of mountain erosion in the southern hemisphere

late cenozoic geomorphic and tectonic evolution of the patagonian andes between latitudes 42 s and 46 s an appraisal based on fission track results from the transpressional intra arc liquine ofqui fault zone fission track ft thermochronology has been applied to investigate the low temperature cooling and denudation history of the patagonian andes along the southern part of the intra arc transpressional liquine ofqui fault zone between 42 and 46 s the liquine ofqui fault is shown to have been the focus of enhanced cooling and denudation initiated between ca 16 and 10 ma several fault blocks with different cooling histories are identified these are separated by major oblique or reverse slip faults proposed to form the eastern part of a major crustal scale dextral transpression zone local very fast rates of cooling and denudation between ca 7 and 2 ma were coeval with collision of the chile rise an active mid oceanic ridge with the peru chile trench between 47 and 48 s this location is close to the southern termination of the liquine ofqui fault implying that the collision of the ridge was a major force driving late cenozoic transpression the lack of significant cooling and denudation before ca 16 ma is indicative of pure strike slip or transtensional movement along the liquine ofqui fault before the collision of the ridge digital landscape analysis supports glacial and periglacial erosion as the main contributor to denudation since ca 7 ma leading to restriction of topographic development the combination of transpression induced rock uplift and glacial erosion is shown to be very effective at causing localized denudation anomalously young ft ages along the liquine ofqui fault are attributed to the existence of a late cenozoic localized heat flow anomaly along the fault

high resolution marine record of climatic change in mid latitude chile during the last 28 000 years based on terrigenous sediment parameters abstract marine sediment cores from the continental slope off mid latitude chile 33 s were studied with regard to grain size distributions and clay mineral composition the data provide a 28 000 yr14c accelerator mass spectrometry dated record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland these variations can be interpreted in terms of the paleoclimatic evolution of mid latitude chile and are compared to existing terrestrial records glacial climates 28 000 18 000 cal yr b p were generally cold humid with a cold semiarid interval between 26 000 and 22 000 cal yr b p the deglaciation was characterized by a trend toward more arid conditions during the middle holocene 8000 4000 cal yr b p comparatively stable climatic conditions prevailed with increased aridity in the coastal range the late holocene 4000 0 cal yr b p was marked by more variable paleoclimates with generally more humid conditions variations of rainfall in mid latitude chile are most likely controlled by shifts of the latitudinal position of the southern westerlies compared to the holocene the southern westerly wind belt was located significantly farther north during the last glacial maximum less important variations of the latitudinal position of the southern westerlies also occurred on shorter time scales

holocene sediments from the southern chile trench a record of active margin magmatism tectonics and palaeoseismicity abstract sedimentology petrography and the provenance of holocene sediments from the southern chile trench 36 47 s were investigated in an integrated approach combining description of a collection of gravity cores measurements of physical properties quantitative x ray petrography and modal analysis the sediments studied were trench hemipelagic sediments fan deposits and more distal hemipelagic sediments from the nazca plate the trench is mostly fed by multiple point sources via submarine canyons sandy turbidites show a southward increase in sediment maturity whereas volcanic lithic fragments and plagioclase represent the dominant fraction in the north quartz content strongly increases in the southern part of the study area in line with source lithologies further north active volcanoes in the main cordillera represent almost the entire provenance signal as a result of a strong contribution of highly erodible volcanic rocks recurrence rates of sandy and silty turbidites in the trench fan sediments indicate a link to the palaeoseismic record on land our study documents the potential usefulness of proximal turbidites to reconstruct palaeoseismicity even at a scale of single segments of the plate boundary

enormous ganges brahmaputra sediment discharge during strengthened early holocene monsoon rivers are the main source of terrigenous sediment delivered to continental margins and thus exert a major control on coastal evolution and sequence development however little is known about past changes in fluvial sediment loads despite the recognition of significant variation under changing climatic regimes in this study we present the first quantified estimate of sediment discharge for a major river system under conditions of an intensified early holocene monsoon development of the ganges brahmaputra river delta began ca 11000 yr b p when rising sea level flooded the bengal basin thereby trapping most of the river s discharge on the inner margin chronostratigraphic data from these deltaic deposits are used to calculate the rates of sediment storage on the margin which provide a minimum estimate of the river s past sediment load results reveal that 5 1012 m3 of sediment was stored in the bengal basin from ca 11000 to 7000 yr b p which corresponds to a mean load of 2 3 109 t yr in comparison modern sediment load of the ganges brahmaputra is 1 109 t yr ranking it first among the world s rivers and underscoring the significance of a two fold increase sustained over 4 k y furthermore the timing of immense discharge in the early holocene strongly suggests its relation to a stronger than present southwest monsoon in south asia similar patterns of high monsoon related sediment discharge have been noted throughout the tropics and subtropics suggesting a widespread fluviosedimentary response the potential magnitude of which is showcased by the ganges brahmaputra system

climatic inferences from glacial and palaeoecological evidence at the last glacial termination southern south america there is uncertainty about the interhemispheric timing of climatic changes during the last glacial interglacial transition different hypotheses relying on different lines of evidence point variously to the northern hemisphere leading the southern hemisphere and vice versa or to synchrony between the hemispheres southern south america is well placed to test the various alternatives using both glacial and palaeoecological evidence we argue here from a synthesis of key proxy records that there was a sudden rise in temperature that initiated deglaciation sychronously over 16 of latitude at 14 600 14 300 14 c yr bp 17 500 17 150 cal yr there was a second step of warming in the chilean lake district at 13 000 12 700 14 cy r bp 15 650 15 350 cal yr which saw temperatures rise to close to modern values a third warming step particularly clear in the south occurred at ca 10 000 14 c yr bp 11 400 cal yr the latter achieving holocene levels of warmth following the initial warming there was a lagged response in precipitation as the westerlies after a delay of ca 1600 yr migrated from their northern glacial location to their present latitude which was attained by 12 300 14 cy r bp 14 300 cal yr the latitudinal contrasts in the timing of maximum precipitation are reflected in regional contrasts in vegetation change and in glacier behaviour the large scale of a 80 km glacier advance in the strait of magellan at 12 700 10 300 14 c yr bp 15 350 12 250 cal yr which spans the antarctic cold reversal and the younger dryas was influenced by the return of the westerlies to southern latitudes the delay in the migration of the westerlies coincides with the heinrich 1 iceberg event in the north atlantic the suppressed global thermohaline circulation at the time may have affected sea surface temperatures in the south pacific and the return of the westerlies to their present southerly latitude only followed ocean reorganisation to its present interglacial mode copyright 2000 john wiley sons ltd

active faulting mountain growth and erosion at the margins of the tibetan plateau constrained by in situ produced cosmogenic nuclides abstract the india asia collision zone is a key area for understanding continental plateau formation and mountain building two fundamental questions in this context are how the northeastward motion of india is partitioned between strike slip and thrust faults and how mountain building is counteracted by erosion cosmogenic nuclides allow us to address these questions because they provide age constraints on tectonically offset landforms and constraints on erosion rates after considerable debate on whether or not major strike slip faults move at high rates of up to 20 30 mm yr and absorb most of the continental deformation it now appears that the three largest faults altyn tagh haiyuan kunlun have millennial slip rates of no more than 8 13 mm yr consistent with rates of elastic strain accumulation determined by geodetic methods furthermore a significant portion of the lateral slip on these faults is transferred to thrust faults within the collision zone both observations indicate that the eastward tectonic escape of material along these faults is less important than often assumed with respect to mountain building and erosion cosmogenic nuclide studies show that thrust faults at the northeastern and eastern margins of tibet qilian shan longmen shan have vertical slip rates of 0 3 to 2 mm yr while catchment wide erosion rates vary from 0 02 to 1 0 mm yr with high relief areas eroding significantly faster than the plateau interior and growing mountains in the foreland the deeply incised regions have apparently reached an erosional steady state in which rock uplift is balanced by erosion river terraces at active mountain fronts document repeated changes between sediment deposition and fluvial incision during the quaternary incision and terrace formation occurred predominantly at glacial interglacial transitions but also during interglacial periods hence flights of terraces at the fault bounded mountain fronts record the interplay between sustained rock uplift and a temporally variable climate

the sensitivity of hillslope bedrock erosion to precipitation decoupling the impacts of climate and tectonics on hillslope erosion rates is a challenging problem hillslope erosion rates are well known to respond to changes in hillslope boundary conditions e g channel incision rates through their dependence on soil thickness and precipitation is an important control on soil formation surprisingly though compilations of hillslope denudation rates suggest little precipitation sensitivity to isolate the effects of precipitation and boundary condition we measured rates of soil production from bedrock and described soils on hillslopes along a semi arid to hyperarid precipitation gradient in northern chile in each climate zone hillslopes with contrasting boundary conditions actively incising channels versus non eroding landforms were studied channel incision rates which ultimately drive hillslope erosion varied with precipitation rather than tectonic setting throughout the study area these precipitation dependent incision rates are mirrored on the hillslopes where erosion shifts from relatively fast and biologically driven to extremely slow and salt driven as precipitation decreases contrary to studies in humid regions bedrock erosion rates increase with precipitation following a power law from 1 m ma 1 in the hyperarid region to 40 m ma 1 in the semi arid region the effect of boundary condition on soil thickness was observed in all climate zones thicker soils on hillslopes with stable boundaries compared to hillslopes bounded by active channels but the difference in bedrock erosion rates between the hillslopes within a climate region slower erosion rates on hillslopes with stable boundaries decreased as precipitation decreased the biotic abiotic threshold also marks the precipitation rate below which bedrock erosion rates are no longer a function of soil thickness our work shows that hillslope processes become sensitive to precipitation as life disappears and the ability of the landscape to respond to tectonics decreases copyright 2010 john wiley sons ltd

holocene denudation rates from the superhumid southernmost chilean patagonian andes 53 s deduced from lake sediment budgets abstract holocene denudation rates and their regional variations in the superhumid and temperate climate of the southernmost patagonian andes are poorly surveyed therefore we have investigated denudation in five small lake catchments 0 11 1 62 km 2 across a precipitation gradient from 600 to 9000 mm yr 1 in southernmost chile at 53 s variations in denudation rates can be defined most precisely by using small catchments and short time spans holocene thus can be related to variable bedrock types vegetation cover elevation and climate minimum physical denudation rates were determined from sediment budgets based on sediment echosounder data and physical properties of sediment cores the holocene denudation rates vary from 0 08 mm kyr 1 in the highly elevated bare granitic rock catchments to 9 01 mm kyr 1 in the low and vegetated catchments with a basement of sedimentary rocks these values are comparable with those from similar areas in norway sweden and nw iceland the high annual precipitation in the study area has only a minor effect on denudation enhanced geomorphic activity during paraglacial conditions caused a faster denudation after the glacier retreat until either the clastic glacial detritus was removed or the catchment was covered with vegetation chemical comparisons between basement rocks and lake sediments indicate a pronounced chemical denudation in catchments with peaty soils and low soil water ph values of 3 to 5 the holocene surface lowering rates are on average 200 fold lower than cenozoic surface lowering rates calculated from fission track data for the southern andes this discrepancy can be explained by significantly higher erosion rates during glacial periods

mechanisms and variations of the paleoproductivity off northern chile 24 s 33 s during the last 40 000 years 1 a multiparameter investigation including organic carbon carbonate opal and planktic foraminifera was carried out on five sediment cores from the coastal upwelling area between 24 s and 33 s along the peru chile current to reconstruct the history of the paleoproductivity and its driving mechanisms during the last 40 000 years inferred from our data we conclude that the antarctic circumpolar current as the main nutrient source in this region mainly drives the productivity by its latitudinal shifts associated with climate change simplified its northerly position during the last glacial led to enhanced productivities and its southerly position during the holocene caused lower productivities at 33 s the paleoproductivity was additionally affected by the southern westerlies and records highest levels during the last glacial maximum lgm north of 33 s several factors e g position and strength of the south pacific anticyclone wind stress continental runoff and el nino southern oscillation events supplementary influenced upwelling and paleoproductivity where maximum values occurred prior to the lgm and during the deglaciation

paleoproductivity evolution off central chile from the last glacial maximum to the early holocene a geochemical and paleontological reconstruction of paleoproductivity upwelling intensity and sea surface temperature sst off central chile at 35 s geob3359 3 reveals marked changes from the last glacial maximum lgm through the early holocene surface water productivity was determined by the interaction between the atmospheric the southern westerlies and oceanographic the antarctic circumpolar current acc systems from the lgm through early termination i ti the northward shift of the climate zones during the lgm brought the acc as the main macronutrient source closer to the geob3359 3 sst lowered and surface water productivity and accumulation rates of biogenic components enhanced with the poleward return of the southern westerlies and the acc the subtropical high pressure system became the dominant atmospheric component southward till 35 s during the late ti and early holocene and caused surface water productivity to increase through enhanced upwelling

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

observed latitudinal variations in erosion as a function of glacier dynamics erosion and velocity data from 15 outlet glaciers covering temperate to polar glacier thermal regimes from patagonia to the antarctic peninsula reveal that over the past century the basin averaged erosion rates vary by three orders of magnitude as a function of climate across this latitudinal transect glacial erosion plays an important role in shaping the earth s landscape but attempts to quantify the long term effect of the erosion of glaciers have proven inclusive and contradictory glacial erosion rates are expected to decrease towards the poles where lower temperatures limit meltwater production thereby reducing glacial sliding erosion and sediment transfer this study presents erosion and velocity data from 15 outlet glaciers covering temperate to polar glacier thermal regimes from patagonia to the antarctic peninsula the dataset reveals that during the past century the basin averaged erosion rates vary by three orders of magnitude as a function of climate across this latitudinal transect the authors suggest that climate and the glacier thermal regime exert more control over erosion rates than the extent of ice cover ice flux or sliding speeds glacial erosion is fundamental to our understanding of the role of cenozoic era climate change in the development of topography worldwide yet the factors that control the rate of erosion by ice remain poorly understood in many tectonically active mountain ranges glaciers have been inferred to be highly erosive and conditions of glaciation are used to explain both the marked relief typical of alpine settings and the limit on mountain heights above the snowline that is the glacial buzzsaw1 in other high latitude regions glacial erosion is presumed to be minimal where a mantle of cold ice effectively protects landscapes from erosion2 3 4 glacial erosion rates are expected to increase with decreasing latitude owing to the climatic control on basal temperature and the production of meltwater which promotes glacial sliding erosion and sediment transfer this relationship between climate glacier dynamics and erosion rate is the focus of recent numerical modelling5 6 7 8 yet it is qualitative and lacks an empirical database here we present a comprehensive data set that permits explicit examination of the factors controlling glacier erosion across climatic regimes we report contemporary ice fluxes sliding speeds and erosion rates inferred from sediment yields from 15 outlet glaciers spanning 19 degrees of latitude from patagonia to the antarctic peninsula although this broad region has a relatively uniform tectonic and geologic history the thermal regimes of its glaciers range from temperate to polar we find that basin averaged erosion rates vary by three orders of magnitude over this latitudinal transect our findings imply that climate and the glacier thermal regime control erosion rates more than do extent of ice cover ice flux or sliding speeds

southern ocean and glaciogenic nutrients control diatom export production on the chile margin abstract biogenic particle flux was reconstructed using 230 thorium normalization at two sites on the southern chile margin odp site 1233 at 41 s 838 m depth is at the southern limit of the peru chile upwelling system where the northern extent of the antarctic circumpolar current impinges on the south american continental margin odp site 1234 at 36 s 1014 m depth is located within the core of the coastal upwelling system near the mouths of the bio bio and itata rivers at 41 s opal lithogenic and carbonate fluxes are greatest during the last glacial interval 26 20 ka carbonate has a secondary peak during the mid holocene 8 ka and organic carbon fluxes increase slightly from 17 ka to the present at 36 s large lithogenic fluxes are observed both during the last glacial interval and the holocene and a maximum in organic carbon flux is observed during the late holocene 5 ka without an accompanying peak in opal flux these reconstructed fluxes at 36 s and 41 s fit within a larger latitudinal pattern of a poleward increase in the magnitude of opal flux during the glacial period the pattern of normalized opal flux opal mass accumulation rate and opal carbonate ratios is consistent with either i enhanced supply of si from the southern ocean as proposed by the silicic acid leakage hypothesis or ii enhanced si and fe delivery from land driven by glacial erosion the pattern of reconstructed export production supports our view that the appearance of more reducing conditions in the sediments upon deglaciation was most likely driven by decreased ventilation rather than increased local productivity

surface sediment distribution along the chilean continental slope related to upwelling and productivity abstract the coastal upwelling system of the peru chile current belongs to the most productive regions in the world oceans in spite of this remarkable fact only very little is known about the sediment distribution in its southern part off the coast of chile to increase the knowledge about this region a multiparameter study of the surface sediment distribution along the chilean continental slope between 27 and 42 s has been carried out detailed analyses of sedimentary data toc and carbonate contents 13corg 15n of the species composition of planktic foraminifera and of the stable isotope composition of the two planktic foraminifera species neogloboquadrina pachyderma dex and globigerina bulloides reveal a close relation to environmental conditions in the region the pattern of a southward increase of surface water productivity known from satellite data is closely reflected in the organic carbon and 15n data information about the water mass distribution especially about varying influences of upwelling waters and warmer subtropical surface waters can be derived from the species composition of the planktic foraminifera while the stable isotope data provide additional clues about water mass characteristics high productivity along the chilean margin north of 40 s is sustained by coastal upwelling while further to the south advection of nutrients with the antarctic circumpolar current and a significant riverine input fuel the highest productivity found in the study area this data set will provide the base for future paleoclimatic and paleoceanographic reconstructions of the southeast pacific region

tracing the impact of glacial interglacial climate variability on erosion of the southern andes sediment accumulation rates of well dated primarily terrigenous marine sediments collected along the chilean continental margin were used to infer erosion rates of the southern andes and the adjacent coastal cordillera compared to the holocene sediment supply to the margin and thus erosion were substantially enhanced during the last glacial when continental rainfall in the region was higher major changes in precipitation forcing to the southern andes on such glacial interglacial time scales appear to be transferred to offshore sedimentation rates by a fixed relation these data show that marine archives can make it possible to trace variability in erosion at adjacent continents on time scales to 10 3 yr a much better resolution than provided by commonly used methods such as thermochronometry or seismic studies

changes in the advection of antarctic intermediate water to the northern chilean coast during the last 970 kyr 1 the antarctic intermediate water aaiw is a key player in global scale oceanic overturning processes and an important conduit for heat fresh water and carbon transport the aaiw past variability is poorly understood mainly due to the lack of sedimentary archives at intermediate water depths we present records of benthic stable isotopes from sediments retrieved with the seafloor drill rig marum mebo at 956 m water depth off northern chile geob15016 27 29 48 s 71 07 58 w that extend back to 970 ka the sediments at this site are presently deposited at the boundary between aaiw and pacific deep water pdw for previous peak interglacials our results reveal similar benthic 13c values at site geob15016 and of a newly generated stack of benthic 13c from various deep pacific cores representing the average pdw this suggests unlike today the absence of aaiw at the site and the presence of nearly pure pdw in contrast more positive 13c values at site geob15016 compared to the stack imply a considerable aaiw contribution during cold phases of interglacials and especially during glacials besides we used three short sediment cores to reconstruct benthic 13c values from the aaiw core during the last glacial and found a 13c signature similar to today s assuming that this was the case also for the past 970 kyr we demonstrate that sea level changes and latitudinal migrations of the aaiw formation site can only account for about 50 of the full range of past 13c increases at site geob15016 during cold periods other processes that could explain the remaining of the positive 13c anomalies are increases in glacial aaiw production and or deeper convection of the aaiw with respect to preceding interglacials

decoupling of erosion and precipitation in the himalayas the hypothesis that abrupt spatial gradients in erosion can cause high strain rates in active orogens has been supported by numerical models that couple erosional processes with lithospheric deformation via gravitational feedbacks1 2 3 most such models invoke a stream power rule in which either increased discharge or steeper channel slopes cause higher erosion rates spatial variations in precipitation and slopes are therefore predicted to correlate with gradients in both erosion rates and crustal strain here we combine observations from a meteorological network across the greater himalaya nepal along with estimates of erosion rates at geologic timescales greater than 100 000 yr from low temperature thermochronometry across a zone of about 20 km length spanning the himalayan crest and encompassing a more than fivefold difference in monsoon precipitation significant spatial variations in geologic erosion rates are not detectable decreased rainfall is not balanced by steeper channels instead additional factors that influence river incision rates such as channel width and sediment concentrations must compensate for decreasing precipitation overall spatially constant erosion is a response to uniform upward tectonic transport of greater himalayan rock above a crustal ramp

lower and middle jurassic paleomagnetic results from the south lesser caucasus and the evolution of the mesozoic tethys ocean abstract we studied lower jurassic pliensbachian toarcian basalts and tuffs and middle jurassic bajocian limestones and marls from 9 sites in the southern part of the lesser caucasus ca 39 3 n 45 4 e a component showing rectilinear decay to the origin was reliably isolated from most volcanics this characteristic component reveals nearly antipodal directions for both polarities and passes the fold test the conglomerate test performed on lava boulders from the aalenian basal conglomerates is also positive we think that a primary remanence d 20 i 38 a 95 5 was isolated from the volcanics in contrast middle jurassic sediments yielded controversial results and the only reliably isolated intermediate temperature component itc does not pass the fold test the itc directions show a considerable improvement in data grouping during incremental unfolding with a maximum at 40 unfolding we argue however that the thus obtained mean direction does not correspond to any paleofield and is most probably an artefact when compared to reference data for the eurasian and african plates the lower jurassic mean inclination of 21 n 4 agrees well with the latter thus implying that in the early jurassic the area studied belonged to gondwana and was separated by the tethys ocean from eurasia in agreement with paleontological data we tried to locate the position of the boundary between the eurasian and gondwanian realms in the caucasus region in the early middle jurassic unfortunately the available jurassic paleomagnetic data from other tectonic units of the region did not reveal any clear pattern

a new conglomerate test in palaeomagnetism summary the conglomerate test is widely used in palaeomagnetism to date components of natural remanent magnetization with respect to deposition of conglomerates it has been demonstrated however that this test may be positive even if the data are strongly contaminated by a secondary remanence especially for the commonly used small number of clasts starkey palmer 1970 here we show with the aid of numerical simulations that diverent statistical procedures employed in this test have similar low sensitivities to remagnetization we suggest a new conglomerate test which incorporates additional information on the direction of a secondary palaeomagnetic component which is isolated from either clasts themselves or their host rocks numerical simulations show that this new test is about twice as sensitive to remagnetization as the previous procedures and is robust with respect to small errors in the direction of a secondary component

antarctic timing of surface water changes off chile and patagonian ice sheet response marine sediments from the chilean continental margin are used to infer millennial scale changes in southeast pacific surface ocean water properties and patagonian ice sheet extent since the last glacial period our data show a clear antarctic timing of sea surface temperature changes which appear systematically linked to meridional displacements in sea ice westerly winds and the circumpolar current system proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore but reveal a variable glacier response time of up to 1000 years which may explain some of the current discrepancies among terrestrial records in southern south america

shelfal sediment transport by an undercurrent forces turbidity current activity during high sea level along the chile continental margin terrigenous sediment supply marine transport and depositional processes along tectonically active margins are key to decoding turbidite successions as potential archives of climatic and seismic forcings sequence stratigraphic models predict coarse grained sediment delivery to deep marine sites mainly during sea level fall and lowstand marine siliciclastic deposition during transgressions and highstands has been attributed to sustained connectivity between terrigenous sources and marine sinks facilitated by narrow shelves to decipher the controls on holocene highstand turbidite deposition we analyzed 12 sediment cores from spatially discrete coeval turbidite systems along the chile margin 29 40 s with changing climatic and geomorphic characteristics but uniform changes in sea level sediment cores from intraslope basins in north central chile 29 33 s offshore a narrow to absent shelf record a shut off of turbidite deposition during the holocene due to postglacial aridification in contrast core sites in south central chile 36 40 s offshore a wide shelf record frequent turbidite deposition during highstand conditions two core sites are linked to the biobio river canyon system and receive sediment directly from the river mouth however intraslope basins are not connected via canyons to fluvial systems but yield even higher turbidite frequencies high sediment supply combined with a wide shelf and an undercurrent moving sediment toward the shelf edge appear to control holocene turbidite sedimentation and distribution shelf undercurrents may play an important role in lateral sediment transport and supply to the deep sea and need to be accounted for in sediment mass balances

spatial and temporal variations in landscape evolution historic and longer term sediment flux through global catchments abstractsediment generation and transport through terrestrial catchments influence soil distribution geochemical cycling of particulate and dissolved loads and the character of the stratigraphic record of earth history to assess the spatiotemporal variation in landscape evolution we compare global compilations of stream gauge derived and cosmogenic radionuclide crn derived predominantly 10be denudation of catchments mm yr and sediment load of rivers mt yr stream gauges measure suspended sediment loads of rivers during several to tens of years whereas crns provide catchment integrated denudation rates at 102 105 yr time scales stream gauge derived and crn derived sediment loads in close proximity to one another 500 km exhibit broad similarity stream gauge samples crn samples nearly two thirds of crn derived sediment loads exceed historic loads measured at the same locations excessive longer term sediment loads likely are a result of longer term recurrence of large magnitude

southern westerlies during the holocene deduced from geomorphological and pedological studies in the norte chico northern chile 27 33 s abstract in the norte chico precipitation is controlled by atmospheric perturbations and frontal systems associated with the belt of westerly wind circulation the holocene climatic history of the region can be reconstructed from geomorphic and pedologic investigations in comparison to modern climatic conditions increased influence of the westerlies is deduced for the time periods prior to 7300 yr b p between 5000 3700 yr b p 3000 1800 yr b p and around 270 yr b p it remains uncertain whether the increased influence of the westerlies was the consequence of northward shifts of the westerlies as a whole of a meridional expansion of the westerly belt or only of intensity changes of the atmospheric dynamics almost synchronous with changes in the westerlies the coastal fogs in the region were apparently reduced or the fog belt in the coastal range was elevated probably due to a weakened upwelling and warmer water conditions in the eastern pacific in general the climate of the norte chico has become more variable since 5000 yr b p especially since 3000 yr b p with frequent changes of the geoecological conditions

the topographic imprint of a transient climate episode the western andean flank between 15 5 and 41 5 s mountain range topography is determined by the complex interplay between tectonics and climate however often it is not clear to what extent climate forces topographic evolution and how past climatic episodes are reflected in present day relief the andes are a tectonically active mountain belt encompassing various climatic zones with pronounced differences in rainfall erosion and glacier extent under similar plate boundary conditions in the central to south western andes climatic zones range from hyperarid desert with mean annual rainfall of 5 mm a 22 5 s to year round humidity with 2500 mm a 40 s the andes thus provide a unique setting for investigating the relationship between tectonics climate and topography we present an analysis of 120 catchments along the western andean watersheds between 15 5 and 41 5 s which is based on srtmv3 90m data and new medium resolution rainfall tropical rainfall measurement mission trmm dataset for each basin we extracted geometry relief and climate parameters to test whether andean topography shows a climatic imprint and to analyze how climate influences relief our data document that elevation and relief decrease with increasing rainfall and descending snowline elevation furthermore we show that local relief reaches high values of 750 m in a zone between 28 s to 35 s during pleistocene glacial stages this region was affected by the northward shifting southern hemisphere westerlies which provided moisture for valley glacier formation and extended glacial coverage as well as glacial erosion in contrast the southern regions between 35 s to 40 s receive higher rainfall and have a lower local relief of 200 m probably related to an increased drainage density we distinguish two different climatically controlled mechanisms shaping topography 1 fluvial erosion by prolonged channel hillslope coupling which smoothes relief and 2 erosion by valley glaciers that generates relief finally our results suggests that the catchment scale relief of the andes between 28 s to 35 s is characterized by a pronounced transient component reflecting past climatic conditions copyright 2010 john wiley sons ltd

consistent slow exhumation in a late cenozoic glaciated landscape the presidential and carter ranges of the white mountains in new hampshire usa abstract to investigate the ability of the onset of quaternary glaciations to drive an acceleration in erosion rates we compare short timescale 103 104 yr erosion rates using the in situ terrestrial cosmogenic nuclide tcn 10be to longer time scale exhumation rates 106 107 yr using the apatite u th he method in the presidential and carter ranges of the white mountains in new hampshire usa our results are generally consistent with but refine previous studies using similar techniques resulting u th he ages and thermal modeling from mt washington in the presidential range n 4 91 7 to 117 3 ma suggest that exhumation rates from the late cretaceous to the present were slow

late quaternary intensified monsoon phases control landscape evolution in the northwest himalaya the intensity of the asian summer monsoon circulation varies over decadal to millennial time scales and is reflected in changes in surface processes terrestrial environments and marine sedi ment records however the mechanisms of long lived 2 5 k y intensified monsoon phases the related changes in precipitation distribution and their effect on landscape evolution and sedimen tation rates are not yet well understood the arid high elevation sectors of the orogen correspond to a climatically sensitive zone that currently receives rain only during abnormal i e strength ened monsoon seasons analogous to present day rainfall anom alies enhanced precipitation during an intensified monsoon phase is expected to have penetrated far into these geomorphic threshold regions where hillslopes are close to the angle of failure we as sociate landslide triggering during intensified monsoon phases with enhanced precipitation discharge and sediment flux leading to an increase in pore water pressure lateral scouring of rivers and ov ersteepening of hillslopes eventually resulting in failure of slopes and exceptionally large mass movements here we use lacustrine deposits related to spatially and temporally clustered large land slides 0 5 km 3 in the sutlej valley region of the northwest him alaya to calculate sedimentation rates and to infer rainfall patterns during late pleistocene 29 24 ka and holocene 10 4 ka inten sified monsoon phases compared to present day sediment flux measurements a fivefold increase in sediment transport rates re corded by sediments in landslide dammed lakes characterized these episodes of high climatic variability these changes thus em phasize the pronounced imprint of millennial scale climate change on surface processes and landscape evolution

turbidite paleoseismology along the active continental margin of chile feasible or not abstract much progress has been made in estimating recurrence intervals of great and giant subduction earthquakes using terrestrial lacustrine and marine paleoseismic archives recent detailed records suggest these earthquakes may have variable recurrence periods and magnitudes forming supercycles understanding seismic supercycles requires long paleoseismic archives that record timing and magnitude of such events turbidite paleoseismic archives may potentially extend past earthquake records to the pleistocene and can thus complement commonly shorter term terrestrial archives however in order to unambiguously establish recurring seismicity as a trigger mechanism for turbidity currents synchronous deposition of turbidites in widely spaced isolated depocenters has to be ascertained furthermore characteristics that predispose a seismically active continental margin to turbidite paleoseismology and the correct sample site selection have to be taken into account here we analyze 8 marine sediment cores along 950 km of the chile margin to test for the feasibility of compiling detailed and continuous paleoseismic records based on turbidites our results suggest that the deposition of areally widespread synchronous turbidites triggered by seismicity is largely controlled by sediment supply and hence the climatic and geomorphic conditions of the adjacent subaerial setting the feasibility of compiling a turbidite paleoseismic record depends on the delicate balance between sufficient sediment supply providing material to fail frequently during seismic shaking and sufficiently low sedimentation rates to allow for coeval accumulation of planktonic foraminifera for high resolution radiocarbon dating we conclude that offshore northern central chile 29 32 5 s holocene turbidite paleoseismology is not feasible because sediment supply from the semi arid mainland is low and almost no holocene turbidity current deposits are found in the cores in contrast in the humid region between 36 and 38 s frequent holocene turbidite deposition may generally correspond to paleoseismic events however high terrigenous sedimentation rates prevent high resolution radiocarbon dating the climatic transition region between 32 5 and 36 s appears to be best suited for turbidite paleoseismology

tracking paraglacial sediment with cosmogenic 10 be using an example from the northwest scottish highlands abstract beryllium 10 concentrations in samples of sediment and bedrock from five study sites across the scottish highlands trace paraglacial sediment sources and define the nature of glacial erosion for the late quaternary exposure ages derived from 10 be concentrations in ridge and lower elevation bedrock range from 10 to 33 ka which suggest that polythermal ice and warm based ice were primarily responsible for producing glacial sediment comparisons of 10 be concentrations between catchment wide sediment 2 06 0 34 10 4 to 11 24 1 54 10 4 atoms g 1 sio 2 n 33 near surface deposits 2 71 0 33 10 4 to 3 48 0 49 10 4 atoms g 1 sio 2 n 6 4 m thick deep till 0 68 10 4 10 be atoms g 1 sio 2 n 1 ridge bedrock 8 93 0 47 10 4 to 34 05 1 66 10 4 atoms g 1 sio 2 n 20 and lower elevation polished bedrock 6 74 0 67 10 4 to 12 65 0 7 10 4 atoms g 1 sio 2 n 5 indicate that most sand fluxing through catchments in the scottish highlands is sourced from the remobilization and vertical mixing of near surface deposits these findings indicate that glaciogenic material continues to dominate paraglacial sediment budgets more than 11 ka after deglaciation