transient sediment supply in a high altitude alpine environment evidenced through a 10be budget of the etages catchment french western alps although beryllium 10 10be concentrations in stream sediments provide useful synoptic views of catchment wide erosion rates little is known on the relative contributions of different sediment supply mechanisms to the acquisition of their initial signature in the headwaters here we address this issue by conducting a 10be budget of detrital materials that characterize the morphogenetic domains representative of high altitude environments of the european alps we focus on the etages catchment located in the ecrins pelvoux massif southeast france and illustrate how in situ 10be concentrations can be used for tracing the origin of the sand fraction from the bedload in the trunk stream the landscape of the etages catchment is characterized by a geomorphic transient state high topographic gradients and a large variety of modern geomorphic domains ranging from glacial environments to scarcely vegetated alluvial plains beryllium 10 concentrations measured in the etages catchment vary from similar to 1 x 104 to 4 5 x 105 atoms per gram quartz while displaying consistent 10be signatures within each representative morphogenetic unit we show that the basic requirements for inferring catchment wide denudation from 10be concentration measurements are not satisfied in this small dynamic catchment however the distinct 10be signature observed for the geomorphic domains can be used as a tracer we suggest that a terrestrial cosmogenic nuclide tcn budget approach provides a valuable tool for the tracing of material origin in basins where the let nature do the averaging principles may be violated

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

complex multiple cosmogenic nuclide concentration and histories in the arid rio lluta catchment northern chile terrestrial cosmogenic nuclide tcn concentrations measured in river sediments can be used to estimate catchment wide denudation rates by investigating multiple tcn the steadiness of sediment generation transport and depositional processes can be tested measurements of 10be 21ne and 26al from the hyper to semi arid rio lluta catchment northern chile yield average single denudation rates ranging from 12 to 75 m myr 1 throughout the catchment paired nuclide analysis reveals complex exposure histories for most of the samples and thus the single nuclide estimates do not exclusively represent catchment wide denudation rates the lower range of single nuclide denudation rates 12 17 m myr 1 established with the noble gas 21ne is in accordance with palaeodenudation rates derived from 21ne 10be and 26al 10be ratio analysis since this denudation rate range is measured throughout the system it is suggested that a headwater signal is transported downstream but modulated by a complex admixture of sediment that has been stored and buried at proximal hillslope or terrace deposits which are released during high discharge events that is best evidenced by the stable nuclide 21ne which preserves the nuclide concentration even during storage intervals the catchment wide single 21ne denudation rates and the palaeodenuation rates contrast with previous tcn derived erosion rates from bedrock exposures at hillslope interfluves by being at least one order of magnitude higher especially in the lower river course these results support earlier studies that identified a coupling of erosional processes in the western cordillera contrasting with decoupled processes in the western escarpment and in the coastal cordillera copyright 2008 john wiley sons ltd

multiproxy summer and winter surface air temperature field reconstructions for southern south america covering the past centuries we statistically reconstruct austral summer winter surface air temperature fields back to ad 900 1706 using 22 20 annually resolved predictors from natural and human archives from southern south america ssa this represents the first regional scale climate field reconstruction for parts of the southern hemisphere at this high temporal resolution we apply three different recon struction techniques multivariate principal component regression composite plus scaling and regularized expectation maximization there is generally good

the migration history of the nazca ridge along the peruvian active margin a re evaluation abstract the collision zone of the 200 km wide and 1 5 km high nazca ridge and the peruvian segment of the convergent south american margin between 14 s and 17 s is characterized by deformation of the upper plate and several hundred meters of uplift of the forearc this is evident by a narrowing of the shelf a westward shift of the coastline and the presence of marine terraces as the nazca ridge is oblique with respect to both trench and convergence direction of the nazca plate it migrates southward along the active plate boundary for reconstructing the migration history of the nazca ridge this study uses updated plate motion data resulting from a revision of the geomagnetic time scale the new model suggests that the ridge crest moved laterally parallel to the margin at a decreasing velocity of 75 mm a before 10 8 ma 61 mm a 10 8 4 9 ma and 43 mm a 4 9 ma to present intra plate deformation associated with mountain building in the peruvian andes since the miocene reduces the relative convergence rate between nazca plate and peruvian forearc taking an intra plate deformation at a rate of 10 mm a estimated from space geodetic and geological data into account does not significantly reduce these lateral migration velocities constraining the length of the original nazca ridge by its conjugate feature on the pacific plate yields a length of 900 km for the subducted portion of the ridge using this constraint ridge subduction began 11 2 ma ago at 11 s therefore the nazca ridge did not affect the northern sites of ocean drilling program odp leg 112 located at 9 s this is supported by benthic foraminiferal assemblages in odp leg 112 cores indicating more than 1000 m of subsidence since at least middle miocene time and by continuous shale deposition on the shelf from 18 to 7 ma recorded in the ballena industrial well at 11 5 s the model predicts the passage of the ridge crest 9 5 ma ago this agrees with the sedimentary facies and benthic foraminiferal stratigraphy of odp leg 112 cores which argue for deposition on the shelf in the middle and late miocene with subsequent subsidence of a minimum of several hundred meters onshore at 12 s the sedimentary record shows at least 500 m uplift prior to the end of the miocene also in agreement with the model

chironomid and pollen evidence for climate fluctuations during the last glacial termination in nw patagonia abstract we present chironomid and pollen records from the huelmo site 41 30 s nw patagonia to examine in detail the timing and structure of climate changes during the last glacial termination in the southern mid latitudes the chironomid record has the highest temporal and taxonomic resolution for this critical interval and constitutes the first account of midge faunas at the culmination of the last glacial maximum lgm for the region the chironomid record suggests cold and wet conditions during the lgm followed by deglacial warming between 17 6 and 16 8 cal kyr bp relatively warm conditions prevailed between 15 14 cal kyr bp followed by a reversal in trend with cooling pulses at 14 and 13 5 cal kyr bp and warming at the beginning of the holocene cool temperate conditions prevailed during the huelmo mascardi cold reversal hmcr which according to chironomid data exhibits a wet phase 13 5 12 8 cal kyr bp followed by a conspicuous drier phase 12 8 11 5 cal kyr bp the chironomid and pollen records from the huelmo site indicate step wise deglacial warming beginning at 17 6 cal kyr bp in agreement with other paleoclimate records from nw patagonia and isotopic signals from antarctic ice cores peak warmth during the last glacial termination was achieved by 14 5 cal kyr bp followed by a cooling trend that commenced during the antarctic cold reversal which later intensified and persisted during the hmcr 13 5 11 5 cal kyr bp we observe a shift toward drier conditions at 12 8 cal kyr bp superimposed upon the hmcr coeval with intense fire activity and vegetation disturbance during younger dryas time

the climate of the altiplano observed current conditions and mechanisms of past changes abstract the large scale controls on the climate of the south american altiplano are investigated using local observations reanalysis data and general circulation model experiments the objective is to gain understanding of causes of climate variability and climate change by relating mechanisms that operate on timescales ranging from the intraseasonal to the glacial interglacial our results suggest that on all timescales the climatic conditions on the altiplano are closely related to the upper air circulation with an easterly zonal flow aloft favoring wet conditions and westerly flow causing dry conditions different factors influence the upper air circulation on the different timescales intraseasonal variability is a reflection of the position and intensity of the bolivian high which is modulated by rossby waves emanating from the midlatitude south pacific the annual cycle of dry winter and wet summer conditions is caused by the seasonal expansion of the equatorial easterlies in the upper troposphere rather than direct insolation forcing over the altiplano or moisture changes in the source area interannual variability is primarily related to changes in the mean zonal flow over the altiplano reflecting changes in meridional baroclinicity between tropical and subtropical latitudes which in turn is a response to sea surface temperature changes in the tropical pacific orbitally forced changes in the land sea contrast drive continental scale circulation changes which significantly alter the zonal flow over the altiplano on glacial interglacial timescales the contrast in heating between northern and southern hemispheres during the glacial leads to upper air easterly anomalies throughout the tropics on modern timescales the marked submonthly seasonal and interannual changes of moisture over the altiplano cannot be accounted for by moisture changes in the humid tropical lowlands however the model experiments suggest that cooler conditions during a glacial reduce moisture availability from the tropical lowlands which counteracts the effect of the upper level circulation resulting in little overall change in precipitation this observational and modeling analysis provides a physical framework for relating the mechanisms of both internal and forced climate change on the altiplano on a wide range of timescales

the ad 1717 rock avalanche deposits in the upper ferret valley italy a dating approach with cosmogenic 10be on 12 september ad 1717 a rock volume larger than 10 million m3 collapsed onto the triolet glacier mobilized a mass composed of ice and sediment and travelled more than 7 km downvalley in the upper ferret valley mont blanc massif italy this rock avalanche destroyed two small settlements causing seven casualties and loss of livestock no detailed maps were made at the time later investigators attributed accumulations of granitic boulders and irregular ridges on the upper valley floor to either glacial deposition or the ad 1717 rock avalanche or a complex mixture of glacial deposition earlier rock avalanche and ad 1717 rock avalanche origin in this study we present cosmogenic 10be exposure ages from nine boulders in the extensive chaotic boulder deposit with irregular ridges two from holocene glacier free areas and one from a little ice age moraine exposure ages between 330 23 and 483 123 a from eight of nine boulders from the chaotic deposit indicate that at least seven were deposited by the ad 1717 rock avalanche the other three boulders yielded 10be exposure ages of 10 900 400 9700 400 and 244 97 a respectively our results are in good agreement with the existing chronology from dendrochronology and lichenometry and radiocarbon analysis of wood samples but not with older 14c ages from a peat bog in the upper part of the valley based on the new age control the rock avalanche deposits cover the whole bottom of the upper ferret valley copyright 2012 john wiley sons ltd

geochronologic and stratigraphic constraints on canyon incision and miocene uplift of the central andes in peru the deepest valleys of the andes have been cut in southern peru by the rios cotahuasi ocona and colca majes these canyons are late miocene landforms based on a new ignimbrite stratigraphy supported by 42 new 40ar 39ar age determinations obtained on plateau forming and valley filling ignimbrites between 19 and 13 ma a gently sloping surface bevelling the clastic wedge southeast of the developing mountain front was mantled by widespread ignimbrites after 13 ma this paleosurface was tilted up from 2 2 km a s l at the mountain front to 4 3 km a s l at the base of the pliocene and pleistocene volcanoes that crown the southwestern edge of the altiplano the canyons incised this topography after 9 ma while the dated base of younger ignimbrite valley fills suggests that these canyons had been cut down to near their present depths as early as 3 8 ma by 1 4 ma however the canyons had been almost completely refilled by 1 3 km thick unwelded pyroclastic deposits which were subsequently eroded valley incision since 9 ma at an average rate of 0 2 mm yr 1 is the response to topographic uplift after 13 ma combined with increasing runoff due to a wetter climate recorded after 7 ma although long term aridity generated an imbalance between high long term uplift rates and low plateau denudation rates the combination of aridity and volcanism still promoted canyon incision because episodic volcanic fills maintained a cycle of catastrophic debris avalanches and subsequent dam breakouts

a note on 10be derived mean erosion rates in catchments with heterogeneous lithology examples from the western central andes millennial catchment mean erosion rates derived from terrestrial cosmogenic nuclides are generally based on the assumption that the lithologies of the parent rock each contain the same proportion of quartz this is not always true for large catchments in particular at the edge of mountainous plateaus where quartz rich basement rocks may adjoin sedimentary or volcano sedimentary rocks with low quartz content the western central andes is an example of this type of situation different quartz contents may be taken into account by weighting the tcn production rates in the catchment we recall the underlying theory and show that weighting the tcn production rate may also lead to bias in the case of a spatial correlation between erosion rate and lithology we illustrate the difference between weighted and unweighted erosion rates for seven catchments 16 samples in southern peru and northern chile and show variations up to a factor of 2 between both approaches in this dataset calculated erosion rates considering only granitoid outcrops are better correlated with catchment mean slopes than those obtained without taking into account the geological heterogeneity of the drained watershed this dataset analysis demonstrates that weighting erosion rates by relative proportions of quartz is necessary to evaluate the uncertainties for calculated catchment mean erosion rates and may reveal the correlation with geomorphic parameters copyright 2015 john wiley sons ltd

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

uplift of the central andean plateau and bending of the bolivian orocline the topography of the central andes can be considered the primary tectonic signal of late cenozoic mountain building in an arid region where the effects of uplift and magmatism are little obscured by denudation the spatial coverage of the topographic signal is more complete than that for sparsely sampled geological and geophysical data a color coded image of digitized topography between 12 s and 37 s highlights the altiplano puna one of the world s most remarkable plateaus and reveals important physiographic clues about the formation of that major feature the topographic data combined with information on structure magmatism seismicity and paleomagnetism support a simple kinematical model for the late cenozoic evolution of the central andes the model does not require collisional effects or enormous volumes of intrusive additions to the crust but instead calls upon plausible amounts of crustal shortening and lithospheric thinning the model interrelates andean uplift a changing geometry of the subducted nazca plate and a changing outline in map view of the leading edge of the south american plate crustal shortening has accommodated convergence between the chilean peruvian forearc and the south american foreland the altiplano puna plateau can be constructed by a combination of crustal shortening and thickening and lithospheric thinning above a shallow dipping 20 30 subducted plate the seawardly concave bend of western south america the bolivian orocline was enhanced but not completely produced by an along strike variation in the amount of late cenozoic shortening maximum shortening in bolivia both produced the widest part of the plateau and increased the seaward concavity of the bolivian orocline the along strike variations of shortening are hypothesized to result from corresponding along strike variations in the width of a weakened zone in the overriding plate weakening occurs above the wedge of asthenosphere located between the subducted and overriding plates hence the width of the zone of weakening depends upon the dip of the subducted plate two types of shortening are recognized 1 a widespread basin and range laramide like shortening that characterizes modem activity in the sierras pampeanas and late miocene deformation of the altiplano puna and 2 on the eastern side of the cordilleras and plateau an east verging foreland fold thrust belt in which the underthrust foreland compresses and thickens the ductile lower crust and produces a plateau uplift of the upper crust the second type of shortening can be applied to plio quaternary deformations throughout the central andes but with a substantial narrowing of the region of plateau uplift in peru and south of 28 s a proposed monoclinal flexure of the upper crust on the western side of the plateau uplift explains the remarkably simple and regular morphology of the main western slope of the central andes the monocline is located above the tip of the asthenospheric wedge between the converging plates it is postulated to occur above the western limit of lower crustal thickening in the regions of horizontal subduction the monocline can be associated with a late miocene asthenospheric wedge tip

the environmental impact of the minoan eruption of santorini thera statistical analysis of palaeoecological data from golhisar southwest turkey eastwood w j tibby j roberts n birks h j b lamb h f 2002 the environmental impact of the minoan eruption of santorini thera statistical analysis of palaeoecological data from golhisar southwest turkey holocene 12 4 431 444

renewed uplift of the central andes forearc revealed by coastal evolution during the quaternary most of the pacific coast of the central andes between 15 s and 30 s displays a wide a couple of kilometres planar feature gently dipping oceanwards and backed by a cliff this morphology usually of marine orgin is called rasa and argues for a recent and spatially continuous uplift of the margin over the 1 500 km long coastal region we describe the cliff foot is found at a similar elevation 110 m amsl all over the studied area with the exception of peninsulas such as the mejillones peninsula the compilation of published chronological data and the extrapolation of re appraised uplift rates provide evidence for a common cliff foot age of around 400 ka i e marine isotopic stage mis 11 this together with other geological constraints indicates a quaternary renewal of uplift in the central andes forearc after a late pliocene quiescence or subsidence

response of chironomid assemblages to environmental change during the early late glacial at gerzensee switzerland prior to ca 14 660 yr bp during the early late glacial oldest dryas larval assemblages of chironomidae insecta diptera in gerzensee switzerland were dominated by cold stenothermic taxa as well as by taxa typical of subalpine lakes today this was the coldest period of the entire sequence after ca 14 660 yr bp in the late glacial interstadial bolling allerod a temperature increase is recorded by a sharp rise in the oxygen isotope ratio in lake marl and by an increase in the organic matter content of the sediments changes in the chironomid fauna then are consistent with rising temperatures this warming trend is interrupted between 14 070 and 13 940 yr bp coinciding with the gi 1d cold oscillation but the change in the chironomid assemblage is more consistent with a response to increasing lake depth and density of aquatic macrophytes than falling temperature a rise in cold adapted chironomid taxa between 13 840 and 13 710 yr bp suggests that summer air temperatures may have declined changes in the chironomid assemblage after 13 710 yr bp suggest a decline in submerged macrophytes coupled with a rise in lake productivity and summer temperature although the latter is not reflected in the oxygen isotope record this suggests that there may have been increasing seasonality during this period when summer temperatures were rising driven by rising summer insolation and winters becoming cooler which is largely reflected in the oxygen isotope record a decline in thermophilic chironomids and a rise in cold adapted taxa after 13 180 yr bp suggest a response to cooling at the beginning of the gerzensee oscillation

motion of continental slivers and creeping subduction in the northern andes regions of intense continental deformation termed continental slivers have been identified in chile bolivia and ecuador analyses of gps data now identify another large sliver in peru the inca sliver that is moving away from a neighbouring sliver in ecuador implying that moving continental slivers control the deformation of almost the entire andean mountain range

uplift of the western margin of the andean plateau revealed from canyon incision history southern peru we explore canyon incision history of the western margin of the andean altiplano puna plateau in the central andes as a proxy for surface uplift u th he apatite data show rapid cooling beginning at ca 9 ma and continuing to ca 5 1 ma in response to incision a minimum of 1 0 km of incision took place during that interval the youngest apatite date and a volcanic fl ow perched 125 m above the present valley fl oor dated at 2 261 0 046 ma 40 ar 39 ar show that an additional 1 4 km of incision occurred between ca 5 1 and 2 3 ma thus we infer that a total of at least 2 4 km or 75 of the present canyon depth was incised after ca 9 ma u th he zircon data collected along the same transect imply that the western margin of the plateau was warped upward into its present monoclinal form rather than uplift being accommodated on major surface breaking faults

geochemical and mineralogical characterization of sediments from lake futalaufquen 42 8 s andean patagonia to evaluate their potential as paleoclimatic proxies lake sediments are key archives for paleoenvironmental investigation as they provide continuous records of the depositional history of the lake and its watershed lake futalaufquen 42 8 s is an oligotrophic waterbody located in los alerces national park in the andes of northern patagonia south america a sedimentary sequence covering 1600 years was recovered to analyze the potential for paleoenvironmental reconstructions of the last millennia integration of different geochemical and mineralogical parameters and comparison with climatic reconstructions from other patagonian records give clues for the identification of a warm period around ad 800 1000 associated with the medieval climatic anomaly the high frequency of tephra layers beginning in the mid sixteenth century precludes identification of the little ice age recorded in northern patagonia as a cold period from the fourteenth to the eighteenth century furthermore the parameters analysed do not provide evidence of late twentieth century global warming however zn deposition a long distance atmospheric transport process of anthropogenic origin was identified during the last century

el nino forcing on 10be based surface denudation rates in the northwestern peruvian andes abstract high magnitude precipitation events provide large contributions to landscape formation and surface denudation in arid environments here we quantify the precipitation dependent geomorphic processes within the rio piura drainage basin located on the western escarpment of the northern peruvian andes at 5 s latitude in this region monsoonal easterly winds bring precipitation to the 3000 m asl high headwaters from where the annual amount of precipitation decreases downstream toward the pacific coast denudation rates are highest in the knickzones near the headwaters 200 300 mm ky 1 and sediment discharge is limited by the transport capacity of the channel network every few years this situation is perturbed by westerly wind driven heavy precipitation during el nino events and results in supply limited sediment discharge as indicated by bedrock channels the detailed analysis of the stream long profiles of two river basins within the rio piura catchment reveals a distinct knickzone in the transition zone between the easterly and westerly climatic influences suggesting an en nino forcing on the longitudinal channel profiles over at least holocene timescales measured trunk stream catchment wide denudation rates are up to ca 300 mm ky 1 and decrease successively downstream along the river profiles denudation rates of tributary rivers are ca 200 mm ky 1 near the plateau and show a stronger downstream decreasing trend than trunk stream rates this suggests that the landscape is in a transient stage of local relief growth which is driven by fluvial incision this corroborates the results of paleoclimate studies that point towards higher el nino frequencies during the past ca 3000 years leading to higher runoff and more erosion in the trunk channel compared to the hillslopes and thus growth of local relief downstream increases in channel gradient spatially coincide with the reaches of highest precipitation rates during el nino events we therefore interpret that holocene landscape evolution has largely been controlled by climate the ky timescale of the 10 be data together with the transience of the landscape implies that el nino events in northwestern peru have occurred since at least the holocene and that adjustment to channel incision is still taking place

temporal evolution of sediment supply in lago puyehue southern chile during the last 600 yr and its climatic significance short term climate changes in southern chile are investigated by a multi proxy analysis of a 53 cm long sedimentary sequence selected among eight short cores retrieved in lago puyehue chile 40 s this core contains a 600 yr long undisturbed record of paleo precipitation changes two measurement methods for sediment density organic matter and biogenic silica contents are compared and the most appropriate techniques are selected together with aluminium and titanium concentrations grain size and geochemical properties of the organic matter these proxies are used to demonstrate paleo precipitation changes around 40 s increase of terrigenous particle supply between a d 1490 and a d 1700 suggests a humid period contemporaneously y 13 c data show increasing lake productivity in response to the high nutrient supply the a d 1700 1900 interval is characterized by a decreasing terrigenous supply and increasing y 13 c values interpreted as a drying period the magnetic susceptibility signal reflecting the terrigenous biogenic ratio demonstrates that similar variations occur in all the undisturbed sedimentary environments of lago puyehue the a d 1490 1700 wet period is associated with the onset of the european little ice age lia andinterpreted asits local signature this worksupports the fact that the liawasaglobal event not only restricted to thenorthern hemisphere d 2005 university of washington all rights reserved

production of cosmogenic radionuclides at great depth a multi element approach abstract for the last two decades in situ produced cosmogenic nuclides are increasingly applied in earth sciences to quantify surface processes in parallel significant reduction of the analytical uncertainties linked to advances in accelerator mass spectrometry ams allows more precise measurements however among all the published works on cosmogenic nuclides only few studies are dedicated to a better understanding of their production systematic or to a better constrain of the physical parameters involved in their production thus an approach to investigate in situ produced cosmogenic nuclides 10 be 26 al and 36 cl along a single 11 meter long core drilled from the surface and composed of carbonates and quartzose conglomerates has been launched these measurements have been used to quantify muon induced productions based on natural samples for each studied nuclide contrary to the current most oftenly used calculation of muon induced production parameters which are based on irradiation experiments at discrete energies productions based on natural samples are considering the entire energy range of particles reaching the ground surface the evolution of 36 cl concentrations with depth needs to agree with those parameters deduced from 10 be and 26 al data this is optimized when considering a fast muon induced 36 cl production contribution and a spallation production rate at sea level high latitude slhl of 42 0 2 0 atoms 36 cl g ca 1 a 1 1 sigma uncertainty

climatic fluctuations in northern patagonia during the last 1000 years as inferred from tree ring records abstract millennium old alerce trees fitzroya cupressoides mol johnst have been used to develop a 1120 year reconstruction of the summer temperature departures for the andes of northern patagonia in argentina four main climatic episodes can be distinguished in this proxy paleoclimatic record the first a cold and moist interval from a d 900 to 1070 was followed by a warm dry period from a d 1080 to 1250 correlative with the medieval warm epoch of europe afterward a long cold moist period followed from a d 1270 to 1670 peaking around a d 1340 and 1650 these cold maxima are contemporaneous with two principal little ice age events registered in the northern hemisphere warmer conditions then resumed between a d 1720 and 1790 these episodes are supported by glaciological and palynological data in patagonia following a cold period in the early 1800s tree ring indices have oscillated around the long term mean except for a warmer period from a d 1850 to 1890 correlations between the rio alerce reconstruction and the regional weather stations indicate that the tree ring variations are correlated with a homogeneous summer weather pattern covering patagonia east of the andes from 38 to 50 s

anthropogenic versus climatic control in a high resolution 1500 year chironomid stratigraphy from a southwestern greenland lake we performed a high resolution study of chironomid assemblages in a sediment core retrieved from lake igaliku in southern greenland the well dated core is located within the former norse eastern settlement and covered the last 1500 yr the comparison of chironomid stratigraphy pca axis scores with instrumental temperature data land use history and organic matter in the sediment over the last 140 yr suggested that the primary changes in chironomid fauna in 1988 2 yr were driven by the shift to modern agriculture in the catchment this unprecedented change in chironomid fauna was most likely triggered by a shift in in lake processes within the instrumental period subtle variations in the chironomid assemblages that occurred before 1988 2 yr were significantly correlated with summer temperatures even in times of traditional extensive sheep farming in the catchment the relevance of the chironomid derived climate signal over the last 1500 yr was supported by its good concordance with previous studies in west greenland and in the arctic the chironomid assemblage therefore appeared to be a valuable proxy for climate changes within the norse colony area synchronous changes in norse diet and chironomid reconstructed climate give new insights into the interplay of norse society with climate

erosion rates and mechanisms of knickzone retreat inferred from 10be measured across strong climate gradients on the northern and central andes western escarpment escarpment edge deep gorges and distinct knickzones in river profiles characterize the landscape on the western escarpment of the andes between 5 s and 18 s northern peru to northern chile th

environmental controls on 10 be based catchment averaged denudation rates along the western margin of the peruvian andes we present 10be based basin averaged denudation rates for the entire western margin of the peruvian andes denudation rates range from c 9 mm ka 1 to 190 mm ka 1 and are related neither to the subduction of the nazca plate nor to the current seismicity along the pacific coast and the occurrence of raised quaternary marine terraces therefore we exclude a tectonic control on denudation on a millennial time scale instead we explain 60 of the observed denudation rates with a model where erosion rates increase either with mean basin slope angles or with mean annual water discharge these relationships suggest a strong environmental control on denudation

tephrochronology of recent events in the andean range northern patagonia spatial distribution and provenance of lacustrine ash layers in the nahuel huapi national park tephrochronology is a powerful tool for dating sedimentary sequences especially in patagonia where a large number of active volcanoes have produced frequent historical eruptions short lacustrine sedimentary sequences were extracted from the lakes moreno oeste and ton cek nahuel huapi national park seventeen volcanic ash layers were identified in both cores 210 pb and 137 cs were used for dating techniques and historical volcanic records were employed for correlation white pumice and glass shards from the tephras were characterised by measuring major and trace element contents by instrumental neutron activation analysis two volcanic sources the cordon caulle and the calbuco volcanoes were recognised as the prevailing systems that impacted the area in the past 800 1000 a the calbuco volcano was mainly responsible for the nine tephras identified in the lake ton cek sequence four of these nine tephras also contained material from the cordon caulle complex and could be interpreted as composite tephras or possible reworked ones the calbuco volcano showed predominant influences in the lake moreno oeste sequence six of the eight tephras identified in such a sequence were from the calbuco volcano and three of these six contained material from the cordon caulle complex the other two were from the cordon caulle complex with contributions from the calbuco volcano in one of them these findings show that the high frequency of volcanic events in the study region demands an accurate characterisation of the products generated by each source as well as an evaluation of their spatial distribution to obtain a consistent framework for dating recent environmental changes copyright 2010 john wiley sons ltd supporting information can be found in the online version of this article

millennial scale record of landslides in the andes consistent with earthquake trigger landslide deposits are often interpreted as the consequence of precipitation a millennial scale record of landslides inferred from river cobbles in the arid andes is instead consistent with earthquake triggering

paleo erosion rates and climate shifts recorded by quaternary cut and fill sequences in the pisco valley central peru fluvial cut and fill sequences have frequently been reported from various sites on earth nevertheless the information about the past erosional regime and hydrological conditions have not yet been adequately deciphered from these archives the quaternary terrace sequences in the pisco valley located at ca 13 s offer a manifestation of an orbitally driven cyclicity in terrace construction where phases of sediment accumulation have been related to the minchin 48 36 ka and tauca 26 15 ka lake level highstands on the altiplano here we present a 10be based sediment budget for the cut and fill terrace sequences in this valley to quantify the orbitally forced changes in precipitation and erosion we find that the minchin period was characterized by an erosional pulse along the pacific coast where denudation rates reached values as high as 600 80 mm ka600 80 mm ka for a relatively short time span lasting a few thousands of years this contrasts to the younger pluvial periods and the modern situation when 10be based sediment budgets register nearly zero erosion at the pacific coast we relate these contrasts to different erosional conditions between the modern and the minchin time first the sediment budget infers a precipitation pattern that matches with the modern climate ca 1000 km farther north where highly erratic and extreme el nino related precipitation results in fast erosion and flooding along the coast second the formation of a thick terrace sequence requires sufficient material on catchment hillslopes to be stripped off by erosion this was most likely the case immediately before the start of the minchin period because this erosional epoch was preceded by a 50 ka long time span with poorly erosive climate conditions allowing for sufficient regolith to build up on the hillslopes finally this study suggests a strong control of orbitally and ice sheet forced latitudinal shifts of the itcz on the erosional gradients and sediment production on the western escarpment of the peruvian andes at 13 during the minchin period

the equivalent pore aspect ratio as a tool for pore type prediction in carbonate reservoirs the equivalent pore aspect ratio provides a tool to detect pore types by combining compressional and shear wave velocities porosity bulk density and mineralogical composition of carbonate rocks the integration of laboratory measurements well logs and petrographic analysis of carbonate rocks from various depositional and diagenetic settings lower cretaceous presalt nonmarine carbonates from offshore brazil lower cretaceous shallow water platform carbonates from southeast france and upper cretaceous deep water carbonate from the gargano peninsula italy allowed the acoustic signature of a wide range of pore types to be quantified the equivalent pore aspect ratios are shown to be independent of pore volume and mineralogy they can therefore be regarded as relevant parameters for discriminating selected pore network architectures in carbonate reservoirs interparticle and intercrystalline microporosity and macroporosity may include a variety of distinct pore network structures and a wide range of acoustic signatures depending on particle shape nature of contacts packing and cementation intergranular macroporosity in a densely packed granular sediment secondary pseudofenestral etc the acoustic response of moldic pores appears to be mainly controlled by the shape of the dissolved allochems the present work reveals also that correct pore type detection from acoustic and porosity measurements is highly dependent on the pore type classification used a selection of petrographic and diagenetic features to be considered for the construction of a suitable pore type classification is proposed to improve the detection of the pore type effect on the acoustic properties of carbonate reservoirs at plug and well log scale

chironomids as indicators of natural and human impacts in a 700 yr record from the northern patagonian andes abstract chironomid communities were studied in a sediment core collected from lake moreno oeste located in nahuel huapi national park a major change in midge assemblages occurred at ad 1760 which was characterized by a decrease of cold taxa including polypedilum sp 2 and dicrotendipes and an increase of warm taxa including apsectrotanypus and polypedilum sp 1 these taxa are likely related to climatic conditions concurrent with the end of a cold period at ad 1500 1700 and the beginning of a drying climate at ad 1740 1900 in northern patagonia coarse tephra layers had low midge diversity however they did not disrupt the climatic trend as the community recovered rapidly after the event since ad 1910 after the increase in suburban housing fish introduction and the construction of a road there was an increase in the relative abundances of taxa typically associated with the littoral zone such as parapsectrocladius riethia apsectrotanypus and some tanytarsini morphotypes the main change in the chironomid community appears to be associated with long term climate change at the beginning of the 20th century other site specific environmental factors catchment change and fish introduction altered the chironomid assemblages making it more difficult to understand the relative importance of each driver of assemblage change

the dynamics of chironomid assemblages and vegetation during the late quaternary at laguna facil chonos archipelago southern chile abstract we compare high resolution pollen and chironomid records from the last 15 000 yr in laguna facil southern chile major vegetation and chironomid changes are recorded between ca 14 900 and 14 700 cal yr bp during the lateglacial changes in the chironomid stratigraphy lag behind changes in the pollen stratigraphy suggesting that the chironomids are responding to changes in the tree canopy or in soil chemistry brought about by vegetational development at about 7200 cal yr bp there is a change in the chironomid stratigraphy in advance of changes in the vegetation this suggests that the response is to regional climatic change the relatively close correlation of the chironomid and pollen stratigraphies with changes in charcoal concentrations also implicates the importance of fire and or vulcanism in influencing the dynamics of forest and limnological systems there is no clear evidence of cooling during the younger dryas chronozone in laguna facil

response of chironomid assemblages to east asian summer monsoon precipitation variability in northern china since the last deglaciation we investigate chironomid assemblages in a sediment core from gonghai lake which is located on the east asian summer monsoon easm boundary in northern china to quantify easm variability during the past 13 5 ka bp six significantly different chironomid assemblage zones indicate that maximum precipitation and water depth occurred in the mid holocene 8270 2700 cal a bp and the minimum period was the past 1250 years a modern dataset of 44 lakes near gonghai lake was sampled to calibrate the response of chironomid assemblages to precipitation our results demonstrate that mean annual precipitation is the most significant environmental variable influencing modern chironomid assemblages in this monsoonal region maximum easm precipitation in the mid holocene indicated by chironomid assemblages in the monsoon fringe contrasts with the early holocene easm maximum suggested by stalagmite delta o 18 data from southern china but is consistent with other evidence our findings are compatible with the proposal that the stalagmite delta o 18 variations in southern china may not reliably reflect the evolution of easm since the last deglaciation copyright c 2016 john wiley sons ltd

response of chironomidae to environmental disturbances in a high mountain lake in patagonia during the last millennium through the last millennium patagonia has been affected by changing climate conditions and successive volcanic eruptions lake toncek is a high altitude lake in the southern volcanic zone in the northern patagonian andes we documented the responses of the subfossil chironomid community to the effects of successive volcanic and different conditions in a sedimentary sequence from this lake comprising the last 900 years the community composition and structure abundance diversity and richness and the development of morphological anomalies in the chironomid mouthparts were evaluated throughout the core both climatic conditions and volcanism affected the chironomid community differentially the chironomid community changed following short term climate change patterns being affecting not only by temperature changes but also by variations in the regional precipitation regime decreases in abundance and diversity were only observed in coarse volcanic layers in these samples we recorded a high percentage of damaged chironomid mouthparts caused by mechanical wear breakage or abrasion possibly due to the increase of mineral particles our results represent important baseline data about the responses of chironomid communities to environmental disturbances in high altitude lakes over long time frames

glacier fluctuations in extratropical south america during the past 1000 years article i nfo this paper presents an updated extensive review of glacier fluctuations during the past 1000 years in the extratropical andes of south america between ca 17 and 55 s given the variety of environmental conditions and evidence available for glacier fluctuations across this wide latitudinal range regional accounts are given for the desert andes 17 31 s the andes of central chile and argentina 31 36 s and the north 36 45 s and south 45 55 s patagonian andes the techniques dating limitations and interpretations of the glacier records along this transect are also discussed information on glacier fluctuations in the desert andes is limited to the 20th century documentation on past glacier variations is more abundant in the central chilean argentinean andes but the number of chronologies dealing with glacier fluctuations prior to the 1900s is also limited most records indicate that glaciers were generally more extensive prior to the 20th century with dates of maximum expansion ranging from the 16th to the 19th centuries the number and extent of glaciers increase significantly in the patagonian region where the evidence available for dating glacier variations during the past centuries is more abundant and the dating control for glacier events is generally better than in the northern parts of the study area for some patagonian glaciers maximum little ice age lia or post lia advances have been precisely dated by dendro geomorphological determinations or in situ measurements however for most sites the evidence available is still preliminary and there is considerable variability in the extent and timing of events related to the maximum lia expansion identified in most areas between the 16th and 19th centuries evidence is starting to appear at a growing number of sites for glacier advances during the first half of the past millennium these events were generally less extensive than the lia maximum pulses despite the occurrence of several post lia readvances over the past 100 110 years most areas in the andes of extratropical south america have experienced a general pattern of glacier recession and significant ice mass losses the differences in the glacier histories observed at local and regional scales probably reflect the inherent limitations associated with the glacier records and or the dating techniques used in each case together with the varying dominance of precipitation temperature and other climatic and non climatic factors on glacier mass balance and glacier dynamics these differences indicate that the late holocene glacier history of southern south america is more complex than commonly assumed the evidence discussed in this study highlights not only the immense potential for glaciological studies of this region but also a significant need for an increased number of detailed well dated records of glacier fluctuations

southern westerly winds submit to the enso regime a multiproxy paleohydrology record from lake dobson tasmania abstract the el nino southern oscillation enso and southern westerly winds sww profoundly influence synoptic scale climate in the southern hemisphere although many studies have invoked either phenomenon to explain trends in proxy data few have demonstrated the transition from a climate dominated by sww flow to one controlled by el nino activity which is postulated to have occurred after 5 cal ka bp in the mid latitudes of the southern hemisphere tasmania southeast australia is ideally situated to detect changes in both of these climatic controls currently el nino and la nina events result in drier and wetter conditions island wide respectively with the greatest impact in the north further tasmania houses north south trending mountain ranges near its western coast as a result areas west of the mountains exhibit a positive correlation between sww flow and precipitation while eastern regions possess either no or a negative relationship here we present data from chironomid remains charcoal and geochemical proxies to investigate the paleohydrological history of lake dobson a site located in mount field national park tasmania the proxies revealed three broad periods 1 an early holocene 11 5 8 3 cal kyr bp characterised by generally high rainfall the occurrence of irregular fires and elevated charcoal influx at 11 4 and 10 2 cal ka bp conditions compatible with attenuated sww flow over the site 2 an ambiguous mid holocene 8 3 5 cal kyr bp that marks the transition from a sww to enso dominated climate and 3 a relatively dry and stable late holocene 5 cal kyr bp to present that is consistent with the onset of a climate controlled by enso activity i e characterised by a more mean el nino climate state the proxy record of lake dobson highlights the teleconnections between the equatorial pacific and southern australasia

end member models for andean plateau uplift abstract diverse techniques have been applied over the past decade to quantify the uplift history of the central andean plateau ap in this study opposing models for surface uplift are evaluated including a rapid rise of 2 5 km 10 6 ma and a slow and steady rise since 40 ma these end member models are evaluated by synthesizing observations of the ap lithosphere and the history of deformation sedimentation exhumation magmatism uplift and fluvial incision structural and geophysical studies estimate variable shortening magnitudes 530 150 km involving cover to basement rocks an isostatically compensated thick crust 80 65 km high heat flow and zones of variable velocity and attenuation in the crust and mantle these observations have invoked interpretations such as a hot weak lithosphere partial melt crustal flow and perhaps current localized delamination but do not provide strong support for massive delamination required by the rapid uplift model deformation and associated exhumation began 60 40 ma and generally migrated eastward with consistent long term average shortening rates 12 8 mm yr in bolivia favoring the slow uplift model volcanic and helium isotope evidence show an ap wide zone of shallow mantle melting and thin lithosphere that has existed since 25 ma which is inconsistent with the rapid rise model that suggests lithospheric thinning occurred 10 6 ma paleoaltimetry data suggest a rapid 2 5 km elevation gain 10 to 6 ma but are equally consistent within error with a linear rise since 25 ma widespread fluvial incision 2 5 1 km occurred along the western flank since 11 8 ma and may be associated with surface uplift as proposed by the rapid rise model however the paleoaltimetry and incision data can also be explained by regional climate change associated with plateau uplift implications of these results for reconstructions of ap evolution are that 1 substantial deformation of a weak lithosphere is essential 2 ap growth has taken significantly longer 40 myr and was more uniform along strike 1500 km than previously appreciated and 3 the slow and steady uplift model is most consistent with available constraints we conclude that the rapid uplift model may be an overestimate and that a more protracted cenozoic uplift history is tenable

evidence for nonlinear diffusive sediment transport on hillslopes and implications for landscape morphology steep soil mantled hillslopes evolve through the downslope movement of soil driven largely by slope dependent transport processes most landscape evolution models represent hillslope transport by linear diffusion in which rates of sediment transport are proportional to slope such that equilibrium hillslopes should have constant curvature between divides and channels on many soil mantled hillslopes however curvature appears to vary systematically such that slopes are typically convex near the divide and become increasingly planar downslope this suggests that linear diffusion is not an adequate model to describe the entire morphology of soil mantled hillslopes here we show that the interaction between local disturbances such as rainsplash and biogenic activity and frictional and gravitational forces results in a diffusive transport law that depends nonlinearly on hillslope gradient our proposed transport law 1 approximates linear diffusion at low gradients and 2 indicates that sediment flux increases rapidly as gradient approaches a critical value we calibrated and tested this transport law using high resolution topographic data from the oregon coast range these data obtained by airborne laser altimetry allow us to characterize hillslope morphology at 2 m scale at five small basins in our study area hillslope curvature approaches zero with increasing gradient consistent with our proposed nonlinear diffusive transport law hillslope gradients tend to cluster near values for which sediment flux increases rapidly with slope such that large changes in erosion rate will correspond to small changes in gradient therefore average hillslope gradient is unlikely to be a reliable indicator of rates of tectonic forcing or baselevel lowering where hillslope erosion is dominated by nonlinear diffusion rates of tectonic forcing will be more reliably reflected in hillslope curvature near the divide rather than average hillslope gradient