discriminating between subglacial and proglacial lake sediments an example from the danischer wohld peninsula northern germany subglacial lakes are common features of contemporary ice masses however they are rarely identified in the geological record this is due to the difficulty in discriminating between subglacial and proglacial lake sediments a proglacial origin is typically preferred as the simplest explanation we hypothesise that numerous deposits currently interpreted to record proglacial lake sedimentation may actually have a subglacial origin here we try and find ways of distinguishing proglacial from subglacial lake sediments by investigating three sites along the danischer wohld peninsula northern germany which have been interpreted to record both proglacial and subglacial sedimentation we identify two major phases of ice activity and associated lake formation during the late weichselian glaciation 1 proglacial lake formation at 23 ka in front of the advancing baltic ice stream this lake was subsequently overridden and the sediments glaciotectonised as ice continued to advance to its maximum extent 2 retreat of ice back into the baltic basin at 19 ka and formation of a proglacial lake that persisted for 4 ka we suggest that subglacial lake activity may have occurred at two of the sites between 23 and 19 ka this is based on the presence of aggrading sediment deposits characterised by stratified laminated diamictons and interbedded tabular to channelized sorted sediments the juxtaposition of relatively undeformed waterlain sediment and subglacial till absence of glaciotectonic thrusting and folding or of fining coarsening successions and the geomorphic association with tunnel valleys to the south of the study area the style of sedimentation and deformation provided the greatest insight into the discrimination of proglacially vs subglacially deposited glaciolacustrine sediments the luminescence signal palaeodose distributions also offers a potentially powerful means of fingerprinting sediment transport pathways of young glacial systems

geoid and topography over subduction zones the effect of phase transformations 1 the association between local maxima in the geoid and subduction zones is examined while it is well known that subduction zones are associated with broad local maxima in the geoid at spherical harmonic degrees 4 9 there is an impressive correlation between back arc geoid maxima at the 5000 km length scale i e spherical harmonic degrees 9 and subduction zones with the exception of the scotia and caribbean arcs geoid maxima are also observed in the forearc regions of the aleutian and central american subduction zones numerical modeling of compressible convection with multiple phase transformations indicates that an increase in viscosity at or near the 660 km phase transformation is necessary to explain the pattern of geoid maxima associated with subduction zones the addition of an endothermic phase transformation at 660 km depth does not provide sufficient resistance to the slab to eliminate the need for a viscosity increase at or near 660 km short wavelength geoid and topography profiles might provide an additional constraint on the deformation at subduction zones however it may be necessary to incorporate geologic history into subduction calculations to further improve the results presented here

lateglacial holocene environmental changes in the mediterranean alps inferred from lacustrine sediments this study investigates sediment cores from the mediterranean alpine lakes located in upvalley cirques upper than 1700 metres a s l using sedimentological palynological and geomorphological studies in order to document environmental changes following the last phase of glacier retreat these results are considered in the framework of the deglaciation characterized from 16 sediment cores from high altitude lakes and mires including 104 14c ages and geomorphological studies of the mediterranean alps considering each sediment core proxy as an independent observation i e comparisons between 14c ages and palynostratigraphy between 14c ages and lithostratigraphy between palynostratigraphy and lithostratigraphy these data are aimed at contributing to a better understanding of the timing of postglacial environmental changes the 14c ages combined with pollen biostratigraphy indicate that the deglaciation of cirque catchments is dated between 14 500 and 13 000 cal bp i e during the lateglacial interstadial greenland interstadial 1e the sixteen lacustrine and mire sediment records are systematically characterized by three units from bottom to top organic poor blue clay beige to light brown silty clay and organic rich dark brown gyttja lithotype during the younger dryas lakes located below 2300 m a s l were ice free and their pollen record indicates steppe conditions the sedimentary facies also informs on the timing of glacial dominated processes the onset of organic rich gyttja is dated at 11 000 cal bp suggesting the last influence of cirque glaciers in these lakes at the beginning of the holocene the timing of the onset of this organic rich unit differs in sites 2000 years probably due to an altitudinal and exposure gradient of the glacial cirques the presence of gyttja from 11 000 cal bp to present indicates biogenic infilling lake for all the holocene even though the literature have indicated rock glacier advances occurred during the holocene subboreal and lia in the south of the alps no significant sedimentological patterns related to glacier fluctuations are recorded in lake vens the glacier fluctuations in the mediterranean alps are concomitant with those dated in the non mediterranean alps thus suggesting a main common climate forcing however the increase in terrigenous sediment inputs since 1800 cal bp is mainly due to human activities

toward direct micron scale xrf elemental maps and quantitative profiles of wet marine sediments 1 here we describe a chemical analysis technique for ca fe k sr ti and s using a recently developed micro xrf analyzer micro xrf with a 100 m resolution and an xrf whole core scanner xrf s with a 5 mm resolution for selected sediment sections from a continental margin sediment core the micro xrf produces highly resolved element maps of individual sections and the calculation of individual continuous element profiles is based on overlap measurements of successive sections by means of discrete subsamples analyzed by icp oes the two xrf data sets are successfully calibrated to provide quantitative profiles of ca fe k sr and ti we discuss the advantages and limitations of both xrf techniques a comparison of the two independent xrf data sets demonstrates the overall high consistency and accuracy of both techniques the resulting element profiles and detailed xrf maps clearly show that the micro xrf is a powerful tool for studying at high resolution the chemical transitions linked to paleoenvironmental changes for example the discrimination between provenance changes and diagenetical effects on the fe profile can be achieved by the combined inspection of the fe ti profile and s maps this highlights the usefulness of the xrf maps for clarification of profile ambiguities and clearly distinguishes the micro xrf from other technical devices producing elemental profiles only

the dynamical control of subduction parameters on surface topography the long wavelength surface deflection of earth s outermost rocky shell is mainly controlled by large scale dynamic processes like isostasy or mantle flow the largest topographic amplitudes are therefore observed at plate boundaries due to the presence of large thermal heterogeneities and strong tectonic forces distinct vertical surface deflections are particularly apparent at convergent plate boundaries mostly due to the convergence and asymmetric sinking of the plates having a mantle convection model with a free surface that is able to reproduce both realistic single sided subduction and long wavelength surface topography self consistently we are now able to better investigate this interaction we separate the topographic signal into distinct features and quantify the individual topographic contribution of several controlling subduction parameters results are diagnosed by splitting the topographic signal into isostatic and residual components and by considering various physical aspects like viscous dissipation during plate bending performing several systematic suites of experiments we are then able to quantify the topographic impact of the buoyancy rheology and geometry of the subduction zone system to each and every topographic feature at a subduction zone and to provide corresponding scaling laws we identify slab dip and slightly less importantly slab buoyancy as the major agents controlling surface topography at subduction zones on earth only the island arc high and the back arc depression extent are mainly controlled by plate strength overall his modeling study sets the basis to better constrain deep seated mantle structures and their physical properties via the observed surface topography on present day earth and back through time

three dimensional numerical simulation of the subduction dynamics in the sunda arc region southeast asia abstract the sunda arc has been modelled as a test subduction zone with geometrical complexities and varying dynamics we simulated spatially the structural heterogeneities of the subduction zone and carried out our computations by a three dimensional finite element approach the aim is to estimate the lateral variation in the effective horizontal compressive stress in the interplate region which can produce the present day observed seismogenic stress field in our simplified approach the stress field has been modelled by varying the traction ridge push while keeping the age dependent gravitational body force slab pull constant our result suggests that there is a considerable amount of stress dissipation in the decoupled segment of java at sumatra the required traction is much greater than that expected from the age dependency relations in our modelling the transition from the dominance of the horizontal compressive stress to that of the gravitational pull in the regional stress field occurs around a depth range of 150 200 km lateral variation in the subducted slab volume emerges crucial to the seismogenic stress field and the derived pattern of displacement subduction of the lighter oceanic rise material should enhance the stress level the effect of abrupt lateral variation in structure e g sudden changes in the slab dip or slab depth may also be significant on the regional stress field viscoelastic modelling attempted for estimating the temporal variation in subduction dynamics suggests that the thrust level will increase southward of the present day thrust zone in java while strike slip fault type stress field will be developed south of sumatra

on the initiation of subduction estimates of shear resistance associated with lithospheric thrusting and convergence represent lower bounds on the force necessary to promote trench formation three environments proposed as preferential sites of incipient subduction are investigated passive continental margins transform faults fracture zones and extinct ridges none of these are predicted to convert into subduction zones simply by the accumulation of local gravitational stresses subduction cannot initiate through the foundering of dense oceanic lithosphere immediately adjacent to passive continental margins the attempted subduction of buoyant material at a mature trench can result in large compressional forces in both subducting and overriding plates this is the only tectonic force sufficient to trigger the nucleation of a new subduction zone the ubiquitous distribution of transform faults and fracture zones combined with the common proximity of these features to mature subduction complexes suggests that they may represent the most likely sites of trench formation if they are even marginally weaker than normal oceanic lithosphere

residual geoid anomalies of the north atlantic ocean and their tectonic implications residual geoid undulations of the north atlantic ocean are obtained and interpreted in terms of upper mantle processes starting from the 1 1 averaged seasat altimeter derived geoid the effects of long wavelength features were first removed by subtracting the degree and order 10 geoid of gem 10c standard earth model the empirical geoid age relationship of the north atlantic after removing the long wavelength features shows closer affinity to the geoid age relationship of the plate model than to that of the half space model for the older part greater than 100 m y of the ocean floor the geoid effects associated with the thermal evolution of the oceanic lithosphere mask the geoid signal associated with deeper processes we thus removed these effects and compared the resulting geoid with residual depth in order to investigate upper mantle processes a principal conclusion here is that the axis of the azores geoid high associated with the azores triple junction shifts east to azores islands after we account for the thermal effects this may indicate that the main axis of smaller scale upper 600 km convective upwellings does not lie beneath the present day spreading center but beneath the azores islands further areas of extensive volcanism such as the bermuda rise and cape verde rise in the older part of the ocean floor ages greater than 100 m y exhibit relative residual geoid highs which correlate very well with the residual depth anomalies

environmental changes during the holocene climatic optimum in central europe human impact and natural causes abstract the priority programme changes of the geo biosphere aimed to reconstruct the environmental history of central europe with emphasis on the time interval from 9000 to 5500 cal bp time slice ii coinciding with the holocene climatic optimum during this period the onset of human activities such as settlement agriculture and animal husbandry caused environmental changes studies of different landscape units in germany were carried out to identify these anthropogenically induced changes and to distinguish them from natural effects on the environmental system the investigated archives included laminated lake sediments fluvial sediments colluvia and soils speleothems peat and coastal sediments the different archives were examined using refined research methods including a variety of sedimentary and geochemical analyses together with pollen analysis and dating methods for the establishment of a reliable chronology the results of the various research groups are summarised and critically discussed based on these results the climatic optimum can be subdivided into three periods 1 the early atlantic from 9000 to 7500 cal bp with negligible human impact and stable environmental conditions 2 the late atlantic during early and middle neolithic from 7500 to 6300 cal bp with pollen evidence for vegetation changes but only negligible changes detectable in other proxy records and 3 the late atlantic during the younger neolithic jungneolithikum after 6300 cal bp with human impact observed in many archives and proxy records especially in the pollen record but also in lacustrine and fluvial sediments during the whole climatic optimum natural causes such as minor shifts of temperature did not induce substantial environmental changes though some changes such as temporary droughts may have facilitated and amplified the observed human impact

a mid european decadal isotope climate record from 15 500 to 5000 years b p oxygen isotope ratios of precipitation delta18op inferred from deep lake ostracods from the ammersee southern germany provide a climate record with decadal resolution the record in detail shows many of the rapid climate shifts seen in central greenland ice cores between 15 000 and 5000 years before the present b p negative excursions in the estimated delta18op from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the north atlantic deviating millennial scale trends however indicate that climate gradients between europe and greenland changed systematically reflecting a gradual rearrangement of north atlantic circulation during deglaciation

palaeolimnological approaches to climate change with special regard to the biological record abstract lakes systems respond physically chemically and biologically to changes in climate and these responses are registered in many various ways in lake sediment records this paper focuses principally on the biological record and describes recent research that aims to reconstruct i past variability in effective moisture and ii past variability in temperature changes in effective moisture are manifested especially by changes in lake water level in closed lake basins water level change can cause significant changes in water salinity that is registered in sediments by changes in the composition of fossil assemblages especially diatoms in open freshwater lake basins changes in water level are best reconstructed from the aquatic macrofossil record and potentially from the ratio of open water to littoral species of cladocera ostracods and diatoms the most promising biological method for reconstructing past temperature is chironomid analysis and a range of new chironomid temperature transfer functions are being developed however biological responses to changing temperature are usually indirect as a result of temperature effects on water column stratification nutrient cycling and alkalinity generation and in most cases a correct interpretation of the climatic significance of changes in the fossil record requires an understanding of the processes that are operating in the water column a multi proxy whole lake approach is advocated as the best way forward not only as a means of reconstructing past climate but also as a means of assessing the impact of climate change on lake systems

interaction of rhyolite melts with monazite xenotime and zircon surfaces the interfacial contact region between a rhyolite melt and the accessory minerals monazite xenotime and zircon is investigated using molecular dynamics simulations on all surfaces major structural rearrangement extends about 1 nm into the melt from the interface as evidenced by the structural perturbations in the ion distribution profiles the affinity of the melt for the surface increases in going from monazite to xenotime to zircon alkali ions are enriched in the melt in contact with an inert wall as well as at the mineral surfaces melt in contact with zircon has a particularly strong level of aluminum enrichment in xenotime the enrichment of aluminum is less than that in zircon but still notable in monazite the aluminum enrichment in the contact layer is much less it is expected that the relative surface energies of these accessory minerals will be a strong function of the aluminum content of the melt and that nucleation of zircon in particular would be easier for melts with higher aluminum concentration the crystal growth rate for zircon is expected to be slower at a higher aluminum concentration because of the effectiveness of aluminum in solvating the zircon surface the variable interfacial concentration profiles across the series of accessory minerals will likely affect the kinetics of trace element incorporation as the trace elements must compete with the major elements for surface sites on the growing accessory minerals

deep fluids and volatile recycling crust to mantle abstract there is now clear evidence that geofluids are involved in many stress release processes at many depths modern studies of crustal regions show that surface fluids may penetrate to depths of many kilometres at subduction zones volatiles may be recycled to mantle depths there is increasing evidence for the complexity of subduction structures with flaking off of major fragments which may devolatilize and revolatilize lower crust and upper mantle the same processes may be associated with massive magma underplating of continental crust the new techniques of modern surface chemistry open new possibilities for the study of fluid tracks thin films on mineral grains which may influence many properties like deep electrical conductivity

on the initiation of subduction zones analysis of the relation between intraplate stress fields and lithospheric rheology leads to greater insight into the role that initiation of subduction plays in the tectonic evolution of the lithosphere numerical model studies show that if after a short evolution of a passive margin time span a few tens of million years subduction has not yet started continued aging of the passive margin alone does not result in conditions more favorable for transformation into an active margin

slab pull and the seismotectonics of subducting lithosphere this synthesis links many seismic and tectonic processes at subduction zones including great subduction earthquakes to the sinking of subducted plate earthquake data and tectonic modeling for subduction zones indicate that the slab pull force is much larger than the ridge push force interactions between the forces that drive and resist plate motions cause spatially and temporally localized stresses that lead to characteristic earthquake activity providing details on how subduction occurs compression is localized across a locked interface thrust zone because both the ridge push and the slab pull forces are resisted there the slab pull force increases with increasing plate age thus because the slab pull force tends to bend subducted plate downward and decrease the force acting normal to the interface thrust zone the characteristic maximum earthquake at a given interface thrust zone is inversely related to the age of the subducted plate the 1960 chile earthquake mw 9 5 the largest earthquake to occur in historic times began its rupture at an interface bounding oceanic plate 30 m y old however this rupture initiation was associated with the locally oldest subducting lithosphere weakest coupling the rupture propagated southward along an interface bounding progressively younger oceanic lithosphere terminating near the subducting chile rise prior to a great subduction earthquake the sinking subducted slab will cause increased tension at depths of 50 200 km with greatest tension near the shallow zone resisting plate subduction plate sinking not only leads to compressional stresses at a locked interface thrust zone but may load compressional stresses at plate depths of 260 350 km provided that the shallow sinking occurs faster than the relaxation time of the deeper mantle this explains k mogi s observations of m 7 thrust earthquakes at depths of 260 350 km immediately downdip and within 3 years prior to five great shallow earthquakes of northern japan the slab pull model explains the lower layer of double seismic zones as due to tension from the deeper sinking plate and the upper layer as due to localized in plate compression as plate motion is resisted by the bounding mantle just downdip of the interface thrust zone there occurs an aseismic 20 50 dip increase of subducted plate this slab bend reflects the summed slab pull force of deeper plate and probably is at the crustal basalt to eclogite phase change resistance to subduction provided by a continually developing slab bend may be an important factor in the size of slab pull force delivered to an interface thrust zone

late holocene drought responsible for the collapse of old world civilizations is recorded in an italian cave flowstone a severe drought in parts of low latitude northeastern africa and southwestern asia 4200 yr ago caused major disruption to ancient civilizations stable isotope trace element and organic fluorescence data from a calcite flowstone collected from the well watered alpi apuane karst of central western italy indicate that the climatic event responsible for this drought was also recorded in mid latitude europe although the timing of this event coincides with an episode of increased ice rafted debris to the subpolar north atlantic the regional ocean atmosphere response seems atypical of similar holocene ice rafting events furthermore comparison of the flowstone data with other regional proxies suggests that the most extreme part of the dry spell occurred toward the end of a longer term climate anomaly

non reversible geosystem destabilisation at 4200 cal bp sedimentological geochemical and botanical markers of soil erosion recorded in a mediterranean alpine lake a 144 cm long core was obtained in lake petit 2200 m a s l mediterranean french alps in order to reconstruct past interactions between humans the environment and the climate over the last five millennia using a multidisciplinary approach involving sedimentological geochemical and botanical analyses we show a complex pattern of environmental transformation from 4800 to 4200 cal bp podzol type soils progressively developed under forest cover this stable situation was interrupted by a major detrital pulse at 4200 cal bp that we consider as a tipping point in the environmental history at this point pedogenetic processes drastically regressed leading to the development of moderately weathered soils more frequent detrital inputs are recorded since 3000 cal bp ad 1050 as the human impact significantly increased in the catchment area we conclude that destabilisation of the environment was triggered by climate and exacerbated by human activities to a stage beyond resilience

three dimensional modeling of lacustrine diatom habitat areas improving paleolimnological interpretation of planktic benthic ratios three dimensional modeling of lake morphometry enables the calculation of lake volume planar surface area and basin surface area which are critical components of a conceptual model of how planktic and benthic habitat areas change with changing lake level we have applied three dimensional modeling to foy lake montana and compared model results of changing ratios of planktic and benthic habitat areas at all possible lake levels to sediment cores recovered from the lake the model allows us to produce semiquantitative depth reconstructions and greatly improves lake level reconstruction of this morphometrically complex basin the conceptual model also was modified to examine the influence of resuspension versus gravity redistribution of diatomaceous material on the sedimentary record comparison of the model results with both long and short sedimentary records from foy lake montana suggests that planktic benthic ratios may be a better predictor of mean lake depth than maximum lake depth the model developed here is simple enough to be easily implemented has few requirements can be adapted to suit any lake basin and can be augmented to examine a variety of different lake processes that affect habitat availability

large scale deformation associated with ridge subduction summary continuum models are used to investigate the large scale deformation associated with the subduction of aseismic ridges formulated in the horizontal plane using thin viscous sheet theory these models measure the horizontal transmission of stress through the arc lithosphere accompanying ridge subduction modelling was used to compare the tonga arc and louisville ridge collision with the new hebrides arc and d entrecasteaux ridge collision which have disparate arc ridge intersection speeds but otherwise similar characteristics models of both systems indicate that diffuse deformation low values of the effective stress strain exponent n are required to explain the observed deformation deformation is somewhat insensitive to the vertically integrated strength of the arc inversely proportional to the argand number ar but indicates that the arc lithosphere is not extremely weak ar 100 low values of both ar and n suggest that the thermal structure is typical of cold or normal arcs and that deformation is dominated by flow in the lower crust and mantle in addition low values of n approaching newtonian flow may indicate that specific deformation mechanisms dictate deformation of the arc lithosphere possible mechanisms include low stress grain size dependent creep pyroxenite controlled rheology and mechanisms associated with water weakening changes in the boundary conditions greatly affect deformation within island arcs high rates of arc ridge intersection speed tonga louisville system yield arc parallel tension and crustal thickening in the wake of ridge subduction in contrast low rates of arc ridge intersection speed new hebrides d entrecasteaux system yield compressional deformation directly arcward of the collision zone and transverse strike slip faulting adjacent to the region of compressional deformation localized regions of extensional deformation along the frontal part of the arc adjacent to the collision zone may contribute to the formation of re entrants

seasat geoid anomalies and the macquarie ridge complex abstract the seismically active macquarie ridge complex forms the pacific india plate boundary between new zealand and the pacific antarctic spreading center the late cenozoic deformation of new zealand and focal mechanisms of recent large earthquakes in the macquarie ridge complex appear consistent with the current plate tectonic models these models predict a combination of strike slip and convergent motion in the northern macquarie ridge and strike slip motion in the southern part the hjort trench is the southernmost expression of the macquarie ridge complex regional considerations of the magnetic lineations imply that some oceanic crust may have been consumed at the hjort trench although this arcuate trench seems inconsistent with the predicted strike slip setting a deep trough also occurs in the romanche fracture zone geoid anomalies observed over spreading ridges subduction zones and fracture zones are different therefore geoid anomalies may be diagnostic of plate boundary type we use seasat data to examine the macquarie ridge complex and find that the geoid anomalies for the northern hjort trench region are different from the geoid anomalies for the romanche trough the hjort trench region is characterized by an oblique subduction zone geoid anomaly e g the aleutian komandorski region also limited first motion data for the large 1924 earthquake that occurred in the northern hjort trench suggest a thrust focal mechanism we conclude that subduction is occurring at the hjort trench the existence of active subduction in this area implies that young oceanic lithosphere can subduct beneath older oceanic lithosphere

flood and earthquake disturbance of 210pb geochronology lake anterne nw alps dating recent lake sediment records yielding disturbed 210pb profiles has been a problem of wide interest in palaeoclimatic and palaeoseismic studies over the last few centuries when applied to an alpine lake sedimentary record a high resolution sedimentological study reveals that the 210pb profile is disturbed by the occurrence of single event deposits triggered by two different mechanisms flood events deposits and gravity reworking removing disturbed layers from the 210pb profile yields a logarithmic depth activity relationship using a simple 210pb decay model cfcs provides an assessment of mean accumulation rate of continuous sedimentation as opposed to event linked sedimentation the correlation of the thickest four gravity reworked deposits with historically known earthquakes permits both validation and refinement of the age depth relationship this refinement highlights variations in accumulation rate consistent with post little ice age climatic variations

impact of bolivian paleolake evaporation on the δ18o of the andean glaciers during the last deglaciation 18 5 11 7 ka diatom inferred δ18o values and hydro isotopic modeling abstract during the last deglaciation the bolivian altiplano 15 23 s 66 70 w was occupied by paleolake tauca covering at least 51 000 km 2 at its maximum highstand between 16 5 and 15 ka twenty five hundred years later after a massive regression a new transgressive phase produced paleolake coipasa smaller than tauca and restricted to the southern part of the basin these paleolakes were overlooked at the west by the sajama ice cap the latter provides a continuous record of the oxygen isotopic composition of paleo precipitation for the last 25 ka contemporaneously to the end of paleolake tauca around 14 3 ka the sajama ice cap recorded a significant increase in ice oxygen isotopic composition 18 o ice this paper examines to what extent the disappearance of lake tauca contributed to precipitation on the sajama summit and this specific isotopic variation the water 18 o values of paleolakes tauca and coipasa 18 o lake were quantitatively reconstructed from 18 5 to 11 7 ka based on diatom isotopic composition 18 o diatoms and ostracod isotopic composition 18 o carbonates retrieved in lacustrine sediments at a centennial time scale a strong trend appears abrupt decreases of 18 o lake during lake fillings are immediately followed by abrupt increases of 18 o lake during lake level stable phases the highest variation occurred at 15 8 ka with a 18 o lake decrease of about 10 concomitant with the lake tauca highstand followed 400 years later by a 7 increase in 18 o lake a simple hydro isotopic modeling approach reproduces consistently this rapid decrease increase feature moreover it suggests that this unexpected re increase in 18 o lake after filling phases can be partly explained by an equilibration of isotopic fluxes during the lake steady state based on isotopic calculations during lake evaporation and a simple water stable isotopes balance between potential moisture sources at sajama advection versus lake evaporation we show that total or partial evaporation from 5 to 60 of paleolake tauca during its major regression phase at 14 3 ka could explain the pronounced isotopic excursion at sajama ice cap these results suggest that perturbations of the local hydrological cycle in lacustrine areas may substantially affect the paleoclimatic interpretation of the near by isotopic signals e g ice core or speleothems

small scale mantle flows and induced lithospheric stress near island arcs summary this paper explores the middle ground between complex thermallycoupled viscous flow models and simple corner flow models of island arc environments the calculation retains the density driven nature of convection and relaxes the geometrical constraints of corner flow yet still provides semianalytical solutions for velocity and stress a novel aspect of the procedure is its allowance for a coupled elastic lithosphere on top of a newtonian viscous mantle initially simple box like density drivers illustrate how vertical and horizontal forces are transmitted through the mantle and how the lithosphere responds by trench formation the flexural strength of the lithosphere spatially broadens the surface topography and gravity anomalies relative to the functional form of the vertical flow stresses applied to the plate base i find that drivers in the form of inclined subducting slabs cannot induce selfdriven parallel flow however the necessary flow can be provided by supplying a basal drag of 1 5mpa to the mantle from the oceanic lithosphere these basal drag forces create regional lithospheric stress and they should be quantifiable through seismic observations of the neutral surface the existence of a shallow elevated phase transition is suggested in two slab models of 300 km length where a maximum excess density of 0 2 g m was needed to generate an acceptable mantle flow a north new hebrides subduction model which satisfies flow requirements and reproduces general features of topography and gravity contains a high shear stress zone 75mpa around the upper slab surface to a depth of 150 km and a deviatoric tensional stress in the back arc to a depth of 70 km the lithospheric stress state of this model suggests that slab detachment is possible through whole plate fracture

subduction zone seismicity and the thermo mechanical evolution of downgoing lithosphere in this paper we discuss characteristic features of subduction zone seismicity at depths between about 100 km and 700 km with emphasis on the role of temperature and rheology in controlling the deformation of and the seismic energy release in downgoing lithosphere this is done in two steps after a brief review of earlier developments we first show that the depth distribution of hypocentres at depths between 100 km and 700 km in subducted lithosphere can be explained by a model in which seismic activity is confined to those parts of the slab which have temperatures below a depth dependent critical valuetcr

orbital and solar forcing of shifts in mid to late holocene flood intensity from varved sediments of pre alpine lake ammersee southern germany abstract microfacies analyses and x ray fluorescence scanning xrf at sub mm resolution were conducted on the varved mid to late holocene interval of two sediment profiles from pre alpine lake ammersee southern germany the coring sites are located in a proximal as10prox and distal as10dist position towards the main tributary river ammer in 1 8 km distance from each other to shed light on sediment distribution within the lake particular emphasis was 1 the detection of intercalated detrital layers and their micro sedimentological features and 2 intra basin correlation of these event deposits detrital layers were dated by microscopic varve counting verified by accelerator mass spectrometry 14c dating of terrestrial plant macrofossils since 5500 varve years vyr bp in total 1573 detrital layers were detected in either one or both of the investigated sediment profiles based on their microfacies geochemistry and proximal distal deposition pattern detrital layers were interpreted as river ammer flood deposits earlier studies on flood layer seasonality have proven that flood layer deposition occurs predominantly during spring and summer the flood season at lake ammersee most prominent features of the record are the onset of regular flood layer deposition at 5500 vyr bp in as10prox and 2800 vyr bp in as10dist as well as three major increases in mean flood layer thickness at 5500 2800 and 400 vyr bp integrating information from both sediment profiles allowed to interpret these changes in terms of shifts towards higher mean flood intensity proposed triggering mechanisms are gradual reduction in northern hemisphere orbital summer forcing and superimposed centennial scale solar activity minima likely responses to this forcing are enhanced equator to pole temperature gradients and changes in synoptic scale atmospheric circulation the consequences for the ammersee region are more intense cyclones leading to extremer rainfall and flood events in spring and summer

sediment residence time and connectivity in non equilibrium and transient geomorphic systems abstract growing empirical evidence shows that many geomorphic systems are in transient state or out of equilibrium with respect to the external driving forces the transient state is often related to the dis connectivity of the many constituent parts of geomorphic systems as a result of sediment storage along the sediment flow path from its source to the final sink the response time of geomorphic systems to external changes is thus dependent on the residence time of sediment in various storage compartments here i present a mathematical concept based on reservoir theory to model residence time of sediment using millennial scale sediment budgets the framework sheds light on the limitation of the sediment delivery ratio which is often used as a measure of sediment connectivity in geomorphic systems and provides analytical information on process type pace of sediment flux and connectivity of storage compartments along the sediment cascade the application of the reservoir theory to geomorphic systems under agricultural land use shows that sediment delivery ratios are linked to the virtual velocity of the eroded sediment the time since the onset of agricultural land use and the size of the studied basins with respect to the temporal evolution of sediment storages that temporarily remove sediment from the conveyor belt the framework aims to estimate the sediment residence time in storages which is linked to the effective time scale of disconnectivity reanalysis of a long term empirical sediment budget from central europe reveals that the response to agricultural land use which started 5000 years bp is mainly buffered by the long residence time of sediment on hillslopes in the order of 10 3 years which results in a delayed floodplain aggradation furthermore the framework was applied to paraglacial mountain systems that inherit striking evidences of pleistocene glacial erosion and still recover from the change from glacial to interglacial conditions as a consequence of the reduced lateral and longitudinal connectivity i show that paraglacial response times of sediment flux in mountain headwater in the canadian rocky mountains range in the order of 100 400 ka the results indicate that response times at the transition from glacial to interglacial conditions are much longer than the return interval of the major glaciations causing a transient behavior of mountain headwater basins during interglacial periods the presented reanalysis of millennial scale sediment budgets of agricultural and mountain geosystems provides an integrative framework to link paleo environmental reconstructions and the connectivity of transient geomorphic system to external changes

changes in erosion patterns during the holocene in a currently treeless subalpine catchment inferred from lake sediment geochemistry lake anterne 2063 m a s l nw french alps the role of climate and human activities a high resolution sedimentological and geochemical study was performed on a 20 m long core from the alpine lake anterne 2063 m a s l nw french alps spanning the last 10 ka sedimentation is mainly of minerogenic origin the organic matter quantity toc as well as its quality hydrogen hi and oxygen oi indices both indicate the progressive onset and subsequent stabilization of vegetation cover in the catchment from 9950 to 5550 cal bp during this phase the pedogenic process of carbonate dissolution is marked by a decrease in the calcium content in the sediment record between 7850 and 5550 cal bp very low manganese concentrations suggest anoxic conditions in the bottom water of lake anterne these are caused by a relatively high organic matter terrestrial and lacustrine content a low flood frequency and longer summer stratification triggered by warmer conditions from 5550 cal bp a decrease in toc stabilization of hi and higher sedimentation rates together reflect increased erosion rates of leptosols and developed soils probably due to a colder and wetter climate then three periods of important soil destabilization are marked by an increased frequency and thickness of flood deposits during the bronze age and by increases in topsoil erosion relative to leptosols hi increases during the late iron age roman period and the medieval periods these periods are also characterized by higher sedimentation rates according to palynological data human impact deforestation and or pasturing activity probably triggered these periods of increased soil erosion

a historical ecology of the ecrins southern french alps archaeology and palaeoecology of the mesolithic to the medieval period this paper elucidates the nature of human environment interactions in a mountainous landscape the southern zone of the ecrins french alps from the mesolithic through to the post medieval period we present an integrated programme of palynology pedo and archaeo anthracology and archaeology these data permit the development of a historical ecology that allows us to differentiate between climatic and anthropogenic influences on vegetation and the development of anthropogenic landscapes in an alpine region this study is of profound relevance for the broader understanding of human environment interactions in ecologically sensitive environments both within the alpine arc but also beyond this region we identify and explain evidence for possible human landscape management practices in a high altitude landscape palynology defines the broad floral context and evolution of the environment through the holocene palynology also permits an assessment of human activities and practices arable agriculture pastoralism and haymaking the combination of these data with anthracological and archaeological evidence permits a nuanced assessment of human interaction with the landscape we consider phases of anthropological ecological succession across the range of altitudes from valley bottom to the alpine zones in the ecrins national park four important stages of landscape use and change have been inferred from our evidence the mesolithic the chalcolithic bronze age iron age and roman and post medieval during the mesolithic c 8000 4500 bc a major event is the expansion of fir in the montane stage at higher altitudes people exploit the ecotone defined by the forest edge or tree line an ideal zone for hunting the neolithic sees low altitude clearances but a continuation of hunting and low levels of human impact on high altitude vegetation the chalcolithic bronze age 2400 1000 bc sees complex interplay of climatic changes and the appearance of direct human intervention in the high altitude landscape as part of a new transhumant system although the roman period is characterised by phases of climatic amelioration after the deterioration of the iron age the increase in human activity that is usually seen in low lying areas is not reflected in the sub alpine and alpine altitudes the medieval period including the little ice age witnesses a steady increase in human use of these landscapes with forest manipulation and clearance becoming the defining characteristics of these areas despite the supposed inclement nature of the little ice age human activity achieves its zenith and the combination people and climate produces the most open and managed landscape of the holocene

reconstruction and paleoclimatic interpretation of holocene lake level changes in lac de saint leger haute provence southeast france abstract lac de saint leger is located in the transitional region between central europe and the mediterranean the reconstruction of the past lake level changes was based on plant macrofossil and mollusc analyses of two stratigraphic transects correlated by pollen analysis past changes in lake level were quantitatively reconstructed from changes in the recorded level of overgrowth in the beginning of the holocene the lake level was high however a progressive lowering occurred from about 7500 b p between about 4500 b p and 4000 b p there was a moderate rise in lake level subsequently the lowering was continued and culminated between about 3300 b p and 2500 b p from the reconstruction there then occurred a progressive rise in lake level until the present the lake level changes recorded in lac de saint leger are compared with a compilation of lake level data from southern france the major long term changes can be supposed to be regionally significant and related to climatic changes to obtain a basis for paleoclimatic interpretation of the changes in lake level the reference pollen diagram from lac de saint leger was used for a quantitative reconstruction of paleoclimate during the middle and later part of the holocene there is a reasonable consistency between the recorded pattern of lake level changes and the paleoclimatic reconstruction during the earlier part of the holocene there are some disagreements which may be explained by the shortage in adequate modern pollen analogues the paleoclimatic reconstruction indicates that the major changes in lake level were mostly related to changes in precipitation

stresses and plate boundary forces associated with subduction plate margins primary tectonic stress in the lithosphere is predominantly caused by lateral density variations within the earth and associated topographical loading when such a stress system caused by major sublithospheric density anomalies is intersected by a weak zone which cuts across the lithosphere plate boundary forces develop and modify the plate interior stresses in this paper unite element analysis is used to model the stresses and plate boundary forces associated with subduction plate boundaries with dipping and vertical slabs extending to about 270 and 400 km depths having the subduction fault both locked and unlocked in such regions several types of horizontal deviatoric stress may occur including 1 local compression in the trench arc region caused by the dense sinking slab and the associated surface downflexure 2 plate interior tension which occurs when this compression is intersected by a weak subduction fault 3 local tension associated with thickening of the crust at the arc and elsewhere 4 local tension in the back arc region produced by the underlying low density upper mantle and 5 downbending stresses in the subducting slab thermal stresses and transmitted ridge push which are not included in the modelling here a gradient from compression in the forearc to tension in the back arc can be modelled in terms of these stresses when the fault is partially locked it is however the intersection of the local compression 1 by an unlocked or partially locked subduction fault that modifies the plate interior stresses and gives rise to the slab pull and trench suction plate boundary forces the state of stress in the interior of the overriding plate is also crucially influenced by back arc spreading where this occurs plate boundary forces have been evaluated for each of the models it is shown that slab pull and trench suction may be of comparable magnitude

limnological changes in south carpathian glacier formed lakes retezat mountains romania during the late glacial and the holocene a synthesis abstract remains of aquatic biota preserved in mountain lake sediments provide an excellent tool to study lake ecosystem responses to past climate change in the prolong project a multi proxy study was performed on sediments of glacier formed lakes from the retezat mountains southern carpathians romania the studied lakes lake brazi and gales are situated on the northern slope of the mountain at different altitudes 1740 m and 1990 m a s l our main objectives were 1 to describe the main limnological changes in these lakes during the last ca 15 000 years and 2 to summarize the environmental history of the studied lakes based on taxonomical and functional patterns of the biological proxies for this synthesis we used the results of diatom and chironomid analyses and indirect biotic and abiotic parameters including sediment organic matter loi content geochemical element concentrations al ca s sr and biogenic silica content using multivariate numerical approaches we analysed changes in the assemblage structure of siliceous algae and chironomids compared temporal patterns among proxies examined the relationship between potential driving factors chironomid and diatom assemblage changes and identified paleolimnological phases of the lake successions changes in assemblage composition and aquatic ecosystem state apparently followed summer insolation local climatic conditions and local productivity changes driven by these diatom and chironomid assemblages generally changed in a similar direction and at a similar time within a lake but differed to some extent between lake brazi and gales at both lakes the strongest variations were observed in the late glacial and the first half of the holocene the strongest holocene assemblage changes took place in the earliest holocene in lake brazi but extended into the mid holocene in lake gales following long term insolation changes and climatic changes in addition three common zone boundaries were identified at ca 14 200 and at ca 6500 cal yr bp for every records and at ca 3100 cal yr bp for diatom records in both of the lakes and for the chironomid record of lake brazi this multi proxy synthesis provides comprehensive data that increase our understanding of the past variability of lake ecosystem functioning and biodiversity in east central europe

massive perturbation in terrestrial ecosystems of the eastern mediterranean region associated with the 8 2 kyr b p climatic event the climatic perturbation at ca 8 2 kyr b p is the strongest short term climate anomaly within the holocene it is generally attributed to a meltwater induced slowdown of the thermohaline circulation in the north atlantic model simulations and available proxy data suggest that it was strongest in the high to middle latitudes around the north atlantic based on new pollen data from tenaghi philippon northeastern greece we provide evidence for a massive climate induced turnover in terrestrial ecosystems of the aegean region associated with the 8 2 kyr b p event the reconstructed winter temperature decline of 4 c is much stronger than suggested by model simulations and proxy data from more northern latitudes of europe although the latter provide a direct downstream response to a north atlantic thermohaline circulation slowdown we attribute this discrepancy to mesoclimatic effects a stronger influence of the siberian high during the 8 2 kyr b p event may have enhanced the katabatic air flow from the mountains bordering the study site via a larger longer persisting snow cover our data demonstrate that high amplitude temperature anomalies and increased seasonality connected to the 8 2 kyr b p event may also have occurred in the lower mid latitudes much farther south than previously thought the magnitudes of these anomalies appear to have been strong enough to have seriously affected neolithic settlers in the northeastern mediterranean region

the tectonic development of the hellenic arc and the sea of crete a synthesis abstract we use field analyses together with interpretation of aerial photographs orbital imagery and sea beam data to define more accurately the geometry of fault systems in the hellenic arc the tectonics of the area are dominated by extensional processes related to normal faulting we then use sea beam data previous oceanographic studies and extrapolation of field analyses on surrounding islands to describe the fault pattern of the cretan sea basin which is found consistent with the land fault pattern the mechanisms of the late neogene and quaternary deformation of the central and southern aegean region are analysed in terms of stress trajectories as revealed by field studies of fault populations we then examine the subsidence of the sea of crete in terms of a model of uniform stretching of the lithosphere the opening of the sea of crete was cylindrical and did not result in bending of crete this leads us to modify the southern portion of an earlier kinematic reconstruction of aegea in agreement with recent paleomagnetic results the implications of the opening of the sea of crete on the tectonic evolution of the straits to the west and east of crete are discussed finally the uplift of the outer arc is explained by underplating due to subduction

inelastic models of lithospheric stress 11 implications for outer rise seismicity and dynamics summary outer rise seismicity and dynamics are examined using inelastic models of lithospheric deformation which allow a more realistic characterization of stress distributions and failure behaviour we conclude that thrust and normal faulting outer rise earthquakes represent substantially different states of stress within the oceanic lithosphere specifically the normal faulting events occur in response to downward plate bending which establishes the standard bending dominated state of outer rise stress and the thrust faulting events occur in response to an elevated level of in plane compression which develops only in response to exceptional circumstances this interpretation accounts for the observation that normal faulting outer rise earthquakes occur more frequently and are more widely distributed than their thrust faulting counterparts an observation for which the simple bending model offers no explanation in addition attributing both thrust and normal faulting outer rise earthquakes to plate bending implies that both classes of events should occur within relatively close lateral proximity to one another because both are allegedly a manifestation of the same bendingdominated stress distribution whereas in reality this is not observed we propose that the tendency for thrust faulting outer rise earthquakes to exhibit greater source depths than their normal faulting counterparts an observation that is frequently cited in support of the bending interpretation of the former is merely a consequence of the fact that bending induced tension is confined to the upper lithosphere our model predicts that outer rise in plane force variations may promote thrust faulting outerrise activity prior to an underthrusting interplate subduction earthquake and normalfaulting outer rise activity following such an earthquake but that both forms of outerrise activity are unlikely to be associated with the same subduction earthquake a corollary implication of our model is that subduction earthquakes are likely to be either preceded by or followed by an absence of large outer rise earthquakes levels of in plane compression necessary to generate thrust faulting outer rise earthquakes are attributed to stress concentrations within the subducting plate that are induced by relatively localized resistance to regionally distributed plate driving forces resistance of this nature may result from either the attempted subduction of relatively buoyant i e isostatically compensated bathymetric features or the existence of strong interplate

application of continuum models to deformation of the aleutian island arc continuum models were constructed to describe large scale deformation of the aleutian island arc over the past 5 m y these models consider the island arc as a continuum in the horizontal plane with the velocity boundary condition at the pacific edge stated as a fraction of pacific plate convergence transferred to the arc first a simple model of uniformly distributed strain is formulated to illustrate the mechanics of continuous deformation lineaments along the arc massif rotated about a vertical axis are matched by small element rotation calculated from the model however this model does not predict across arc variations in deformation and produces an unrealistic amount of crustal thickening after 5 m y a physically more meaningful model of deformation is the thin viscous sheet model based on averages of stress and rheology throughout the lithosphere the amount of motion transferred from the pacific plate to the arc is constrained by the rotated lineaments while the effective stress strain exponent n and the ability the lithosphere has to sustain crustal thickness contrasts the argand number are independent variables primarily bathymetry earthquake focal mechanisms and styles of faulting are used to evaluate the models the preferred model is one where the amount of motion transferred from the pacific plate is greater in an arc parallel direction than in an arc normal direction producing stresses consistent with strike slip faulting at the far western end of the arc and tensional stresses consistent with transverse normal faulting elsewhere in the arc massif this model agrees with observations of slip vectors by ekstr6m and engdahl 1989 who conclude that a portion of the arc parallel component of relative plate motion is taken up in the overriding plate this model implies that compressive stress transferred to the arc is small in comparison to along arc shear stress and that stresses conducive to strikeslip faulting are prevalent throughout the arc

granites and thermal structures in the lithosphere the production of melts of the granite clan on a significant scale requires participation of continental crust such crust will melt when heated from below by a mantle thermal anomaly or when thickend to 40 km or more sites of melting and the time sequences of melting associated with subduction and underplating processes and collision processes are complex in both these processes at least six melting sites may be involved the final chemical and isotopic composition of granitic melts depends on a very complex array of processes which include source composition composition of subducted materials magma mixing magma underplating assimilation fractionation cooling processes resolution of granite melt dynamics requires an integrated attack using modern seismic and electrical measurements in regions where the continental crust is abnormally thick or hot

subduction zone stresses constraints from mechanics and from topographic and geoid anomalies abstract there are in principle direct relations between several important phenomena associated with subduction zones the depth of oceanic trenches the magnitude of the net force from trenches acting on subducting plates the distribution and fault plane orientations of earthquakes the magnitude of stresses on subduction faults the bathymetry of back arc regions and the magnitudes of gravity and geoid anomalies these phenomena are related through the stresses transmitted through surface and subducted lithosphere and are associated with the mass anomaly of the subducted lithosphere quantitative estimates suggest that observed trench depths imply a trench pull force on subducting plates which is comparable to the ridge push force but much less than the excess weight of the subducted lithospheric slab it is further suggested that either the mass anomaly of subducted lithosphere is much less than would be expected on the basis of conventional thermal and compositional models or that a a large resistance acts on the upper part of slabs due to high stress corner flow and b the mass anomaly of the slab is 70 90 compensated either by a broad 1 km deep back arc depression or a low density mantle wedge above the slab or both

monazite and xenotime u th pb geochronology by ion microprobe dating highly fractionated granites at xihuashan tungsten mine se china zircon monazite and xenotime have proven to be valuable chronometers for various geological processes due to their commonly high u th and low common pb contents however zircons that have crystallized in highly fractionated granites often have such high u contents that radiation damage can lead to scattered u pb ages when measured with secondary ion mass spectrometry sims in this study monazite and xenotime were separated from a number of highly fractionated granites at the xihuashan tungsten mine southeast china for alternative dating methods by sims for monazite analysis obvious excess 204 pb signal mainly from interference of 232 th 144 nd 16 o 2 was observed in high th 2 wt monazite which hinders 204 pb based common pb correc tions a 207 pb based common pb correction method was used instead by employing power law relationships between pb u versus uo2 u p b th versus tho2 th and suitable exponentials monazites with tho2 contents in the range of 3 19 do not exhibit this matrix effect inde pendent sims u pb ages and th pb ages of three phases of xihuashan granite samples were consistent with each other and yielded dates of 158 7 0 7 158 0 0 7 and 156 9 0 7 ma respectively xenotime does show marked matrix effects due to variations of u th and y or total rare earth element ree referred as rree hereafter contents suitable correction factors require end member standards with extremely high or low u th and y or rree con tents no excess 204 pb was observed indicating that the 204 pb based common pb correction method is feasible independent 207 pb 206 pb ages can be obtained although multi collector mode is necessary to improve precision the main difficulties with dating xenotime are when high th u mineral inclusions are ablated we can identify when this occurs however by comparing the measured uo2 u and tho2 th with those in xenotime standards three xeno time samples from the first phase of xihuashan granite yielded a weighted mean 207 pb 206 pb date of 159 5 4 4 ma mswd 1 0 and a 206 pb 238 u date of 159 4 0 9 ma mswd 1 6 which are consistent with mona zite u pb and th pb ages from the same granites this study demonstrates that monazite and xenotime are better sims chronometers for highly fractionated granites than zircon which can yield doubtful ages due to high u contents

late glacial chironomid based temperature reconstructions for lago piccolo di avigliana in the southwestern alps italy chironomid headcapsules were used to reconstruct late glacial and early holocene summer temperatures at lago piccolo di avigliana lpa two training sets northern sweden north america were used to infer temperatures the reconstructed patterns of temperature change agreed well with the grip and ngrip 18o records inferred temperatures were high during the bolling ca 19 c slowly decreased to ca 17 5 c during the allerod reached lowest temperatures ca 16 c during the younger dryas and increased to ca 18 5 c during the preboreal the amplitudes of change at climate transitions i e oldest dryas bolling 3 c allerod younger dryas 1 5 c and younger dryas preboreal 2 5 c were smaller than in the northern alps but similar to those recorded at another site in northeastern italy our results suggest that 1 allerod temperatures were higher in the southern alps and 2 higher during the preboreal 1 c than during the allerod these differences might provide an explanation for the different responses of terrestrial vegetation to late glacial and early holocene climatic changes in the two regions other sites on both sides of the alps should be studied to confirm these two hypotheses

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

multiproxy analyses of lake allos reveal synchronicity and divergence in geosystem dynamics during the lateglacial holocene in the alps abstract palaeoenvironmental reconstructions of ecosystem responses to external forcing are generally limited by the difficulty of understanding the geosystem as a whole because of the complex interactions between ecological compartments therefore identifying which geosystem compartments or proxies co vary is a prerequisite in unravelling the propagation of disturbances e g climatic or anthropogenic from one compartment to another a multiproxy study of a continuous 13 500 year sedimentary profile cored in lake allos european alps 2200 m a s l was carried out on the basis of high resolution sedimentological geochemical and botanical analyses as well as determination of aquatic biotic proxies diatoms ostracods these multiproxy datasets are rare at these high altitudes major changes occurred in the course of the palaeoenvironmental history of this alpine watershed at 12 000 8600 7200 and 3000 cal bp during the holocene two main transitions were recorded in all the ecological compartments 8600 and 3000 cal bp but the period 4500 3000 cal bp stands out because of major changes that concerned only the lacustrine ecosystem the frequent switches in lake level might correspond to the 4 2 ka climatic event proximity of this alpine lake to climatically sensitive thresholds ice cover thermal stratification hydrological balance may have amplified climatic signals in the lake ecosystem this study illustrates the difficulties inherent to the use of common intra holocene stratigraphical limits given that ecological compartments are likely to have different responses to forcing factors depending on the characteristics of the watershed and its capacity to accommodate disturbances

geoid heights over the louisville ridge south pacific geoid heights over the louisville ridge seamount chain deduced from the seasat satellite altimeter data have been analyzed and interpreted two uncharted seamounts belonging to the chain have been detected the elastic thickness of the oceanic lithosphere has been determined along the chain this was done rigorously using the three dimensional geoid and bathymetry maps and was also computed approximately using spectral methods on geoid and bathymetry profiles a slightly increasing elastic thickness from the southeast to the northwest in the range 15 5 22 5 km has been estimated

long term changes in alpine pedogenetic processes effect of millennial agro pastoralism activities french italian alps human activities are known to modify soil properties however the associated modifications to soil processes are poorly documented as they must be studied over long time scales lake verney which is on the italian side of the petit saint bernard pass in the french italian alps 2188 m a s l provides a sediment record of the last 11 000 cal yrs bp analysis of multiple proxies within this sediment sequence including sedimentological characteristics mineral geochemistry as determined using xrf and extractable fe fractions pollen and non pollen palynomorphs npps and sediment dna seddna analysis is compared with analyses of current soils and paleosols within this mountain ecosystem in order to understand the main drivers of long term pedogenesis we performed principle component analysis on both the sediment proxies and the soil geochemical properties to identify different sediment endmembers that reflect different types of soil horizons mainly stagnic and spodic these horizons are characteristic of specific soil processes and their associated land uses during the first part of the holocene a decrease in the carbonate fraction in the sediment reflects the loss of carbonate material from soils that occurred as early as postglacial vegetation became established the migration of fe complexes until 6000 cal yrs bp indicates the development of podzols in the catchment the first signs of human land use are detected at 4300 cal yrs bp according to analyses of seddna and npps increases in the input of terrestrial organic matter associated with forest clearance suggests degradation of the surface horizons of the podzols erosion increased during the roman period due to sheep grazing then while erosion was still increasing podzols developed into stagnosols after the middle ages with cow grazing which is consistent with the current functioning of the soils the history of the paleosols and archaeological stratigraphy within the study area confirm the model of soil evolution inferred from the lake sediments and allow us to characterize the human induced metapedogenetic phase of the evolution of the soil cycle anthropo pedogenesis may define the development of soils during the anthropocene the main consequence of this change in the functioning of the soils is a reduced sequestration of soil carbon

the overlooked human influence in historic and prehistoric floods in the european alps understanding the role of climate and humans in generating mountain slope instability is crucial because such instability influences downstream fluvial activity and is a major threat to societies here we use the sedimentary archive of lake allos southeastern france a mountain lake in the european alps to characterize mountain flood deposits and vegetation dynamics over the past 7000 yr our results support the interpretation of a critical threshold in catchment sensitivity to erosion at 1700 calibrated cal yr b p a d 250 probably resulting from long term uninterrupted impacts of human activity the frequency and severity of floods increased dramatically after this date these results demonstrate that underestimation of human impacts over the holocene may pose a challenge to a clear understanding of past climate changes because paleoflood records are highly likely to have been affected by geomorphic thresholds natural reforestation since the end of the 19th century does not appear to be sufficient to induce a flood regime comparable to that which occurred prior to 1700 cal yr b p this poses the question as to whether forest restoration in high altitude environments is liable to foster a return to a low erosion regime over the next decades or whether the overall severity of soil degradation has been such as to preclude a return to previous conditions

flood stratigraphies in lake sediments a review abstract records of the frequency and magnitude of floods are needed on centennial or millennial timescales to place increases in their occurrence and intensity into a longer term context than is available from gauged river flow and historical records recent research has highlighted the potential for lake sediment sequences to act as a relatively untapped archive of high magnitude floods over these longer timescales abyssal lake sediments can record past floods in the form of coarser grained laminations that reflect the capacity for river flows with greater hydrodynamic energy to transport larger particles into the lake this paper presents a framework for investigating flood stratigraphies in lakes by reviewing the conditioning mechanisms in the lake and catchment outlining the key analytical techniques used to recover flood records and highlighting the importance of appropriate field site and methodology selection the processes of sediment movement from watershed to lake bed are complex meaning relationships between measureable sedimentary characteristics and associated river discharge are not always clear stratigraphical palaeoflood records are all affected to some degree by catchment conditioning fluvial connectivity sequencing of high flows delta dynamics as well as within lake processes including river plume dispersal sediment focussing re suspension and trapping efficiency with regard to analytical techniques the potential for direct e g laser granulometry and indirect e g geochemical elemental ratios measurements of particle size to reflect variations in river discharge is confirmed we recommend care when interpreting fine resolution geochemical data acquired via micro scale x ray fluorescence xrf core scanning due to variable down core water and organic matter content altering x ray attenuation we also recommend accounting for changes in sediment supply through time as new or differing sources of sediment release may affect the hydrodynamic relationship between particle size and or geochemistry with stream power where these processes are considered and suitable dating control is obtained discrete historical floods can be identified and characterised using palaeolimnological evidence we outline a protocol for selecting suitable lakes and coring sites that integrates environmental setting sediment transfer processes and depositional mechanisms to act as a rapid reference for future research into lacustrine palaeoflood records we also present an interpretational protocol illustrating the analytical techniques available to palaeoflood researchers to demonstrate their utility we review five case studies of palaeoflood reconstructions from lakes in geographically varied regions these show how lakes of different sizes and geomorphological contexts can produce comprehensive palaeoflood records these were achieved by consistently applying site validated direct and proxy grain size measurements well established chronologies validation of the proxy process interpretation and calibration of the palaeoflood record against instrumental or historical records

formal subdivision of the holocene series epoch a discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommission on quaternary stratigraphy international commission on stratigraphy this discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommision on quaternary stratigraphy sqs of the international commission on stratigraphy ics considers the prospects for a formal subdivision of the holocene series epoch although previous attempts to subdivide the holocene have proved inconclusive recent developments in quaternary stratigraphy notably the definition of the pleistocene holocene boundary and the emergence of formal subdivisions of the pleistocene series epoch mean that it may be timely to revisit this matter the quaternary literature reveals a widespread but variable informal usage of a tripartite division of the holocene early middle or mid and late and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology we propose an early middle holocene boundary at 8200 a bp and a middle late holocene boundary at 4200 a bp each of which is linked to a global stratotype section and point gssp should the proposal find a broad measure of support from the quaternary community a submission will be made to the international union of geological sciences iugs via the sqs and the ics for formal ratification of this subdivision of the holocene series epoch copyright 2012 john wiley sons ltd

regional compensation of subducted lithosphere effects on geoid gravity and topography from a preliminary model abstract it is proposed that the anomalous mass of subducted lithospheric slabs is partially compensated by two mechanisms a by stresses transmitted up the slab to the surface lithosphere causing the trench and b by stresses transmitted through the mantle wedge overlying the slab which cause a broad shallow depression results calculated from a preliminary two dimensional model show that it can give a first order account of observed topography gravity and geoid anomalies in particular the model can reconcile the large mass anomaly predicted for the slab by thermal conduction theory with the smaller than expected gravity and geoid anomalies preliminary results indicate substantial compensation by mechanism a implying rather large stresses at the top of the slab these could be important for theories of earthquake mechanisms and plate driving mechanisms roughly 50 of the possible compensation by mechanism b is indicated the resulting depression the order of 500 m deep and over 500 km wide could explain anomalously deep marginal basins and some marine transgressions of continents

climatic and human impacts on mountain vegetation at lauenensee bernese alps switzerland during the last 14 000 years lake sediments from lauenensee 1381 m a s l a small lake in the bernese alps were analysed to reconstruct the vegetation and fire history the chronology is based on 11 calibrated radiocarbon

underthrusting at the hjort trench australian pacific plate boundary incipient subduction 1 the southernmost portion of the macquarie ridge complex mrc comprises the hjort ridge trench and plateau the topographic expression of the australian pacific plate boundary south of new zealand on the basis of marine geophysical swath bathymetry reflectivity seismic reflection gravity magnetic data teleseismic data and gravity modeling we argue that the australian plate is actively underthrusting the pacific plate along the hjort trench but self sustaining subduction does not yet appear to have commenced we interpret a crustal discontinuity in the trench as a shallowly dipping thrust splay off a sub vertical transform fault in the crest of the hjort ridge hjort fault the hjort fault separates oceanic crust generated at the southeast indian ridge seir crust located to the south from oceanic crust generated at the extinct australian pacific spreading center located to the north mrc crust oblique convergence on the transform has initiated a significant plate boundary decollement in the trench but our estimate of 50 km of underthrusting does not support the existence of an eastwardly dipping australian slab below 20 km depth for the length of the hjort ridge and trench system oblique convergence is partitioned between the decollement in the trench and the hjort fault south of 57 5 s the trench decollement accommodates thrusting north of 57 5 s the boundary parallel component of convergence becomes dominant the trench gradually shallows and the trench decollement evolves into a low angle oblique slip fault the trench decollement and strike slip system in the hjort ridge are structural boundaries that contain tectonic slivers of inferred seir crust of the western flank of the hjort ridge that currently belong to neither the australian nor the pacific plates

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

structure and seismicity of the aegean subduction zone tomographic results show the presence of a high velocity anomaly dipping north beneath the aegean sea hellenic arc down to a depth of at least 600 km this anomaly is interpreted as the image of the subducting lithosphere of the african plate no deep seismicity however is associated with this downgoing slab although this would be expected on the basis of the age of the downbending lithosphere approximately 100 myr and the inferred duration of the present ongoing episode of subduction using a thermo mechanical model for the subduction zone we find that the non stationary input of the subduction zone both in convergence rate and in thermal structure of the downgoing lithosphere adequately accounts for both the presence of a velocity anomaly associated with a slab and the absence of deep seismicity the non stationarity follows from the large scale tectonic setting of the eastern mediterranean basin

crystal chemistry of the monazite and xenotime structures monazite and xenotime the re p04 dimorphs are the most ubiquitous rare earth re minerals yet accurate structure studies of the natural phases have not been reported here we report the results of high precision structure studies of both the natural phases and the synthetic re p04 phases for all individual stable rare earth elements monazite is monoclinic p2 n and xenotime is isostructural with zircon space group 14 amd both atomic arrangements are based on 001 chains of intervening phosphate tetrahedra and re polyhedra with a reogpolyhedron in xenotime that accommodates the heavy lanthanides tb lu in the synthetic phases and a re09 polyhedron in monazite that preferentially incorporates the larger light rare earth elements la gd as the structure transforms from xenotime to monazite the crystallographic properties are comparable along the 00i chains with structural adjustments to the different sizes of re atoms occurring principally in 00i there are distinct similarities between the structures that are evident when their atomic arrangements are projected down 001 in that projection the chains exist in 100 planes with two planes per unit cell in monazite the planes are offset by 2 2 a along 010 relative to those in xenotime in order to accommodate the larger light re atoms the shift of the planes in monazite allows the re atom in that phase to bond to an additional 02 atom to complete the re09 polyhedron

controls on trench topography from dynamic models of subducted slabs a finite element method with constrained elements and lagrange multipliers is used to study tectonic faults in a viscous medium a fault representing the interface between overriding and subducting plates has been incorporated into a viscous flow model of a subduction zone in which both thermal buoyancy and the buoyancy associated with the phase change from olivine to spinel are included the fault causes stress to concentrate in its vicinity giving rise to a weak plate margin and a mobile plate if a power law rheology is used surface dynamic topography with either a newtonian or a power law rheology and with typical subduction zone parameters is characterized by a narrow and deep trench and a broadly depressed back arc basin this suggests that oceanic trenches and back arc basins over subduction zones are dynamically compensated by viscous flow our models show that trench depth increases with fault dip angle slab dip angle slab length and age of oceanic lithosphere just prior to subduction the influence of fault dip angle and age of lithosphere on trench depth is greater than the influence of slab dip angle and slab length these relationships of trench depth versus subduction zone parameters explain well the statistics of observed trench depths for those subduction zones with oceanic lithosphere on both sides of the trench observed trench depths have been corrected for fault and slab dip angles based on the relationships from the dynamic models after correction to a common set of parameters trench depth correlates linearly with age of lithosphere prior to subduction with a slope which is close to what models having high viscosities within the transition zone and lower mantle predict comparison between the trench depths corrected for fault and slab dip angles and model trench depths suggests that the resisting tangential stress on faults in subduction zones may range from 15 mpa to 30 mpa depending on model details

a critical assessment of viscous models of trench topography and corner flow stresses for newtonian viscous flow in a simple geometry e g corner flow bending flow are obtained in order to study the effect of imposed velocity boundary conditions stress for a delta function velocity boundary condition decays as 1 r 2 for a step function velocity stress goes as 1 r for a discontinuity in curvature the stress singularity is logarithmic for corner flow which has a discontinuity of velocity at a certain point the corresponding stress has a 1 r singularity however for a more realistic circular slab model the stress singularity becomes logarithmic thus the stress distribution is very sensitive to the boundary conditions and in evaluating the applicability of viscous models of trench topography it is essential to use realistic geometries topography and seismicity data from northern hoshu japan were used to construct a finite element model with flow assumed tangent to the top of the grid for both newtonian and non newtonian flow power law 3 rheology normal stresses at the top of the grid are compared to the observed trench topography and gravity anomalies there is poor agreement purely viscous models of subducting slables with specified velocity boundary conditions do not predict normal stress patterns compatible with observed topography and gravity elasticity and plasticity appear to be important for the subduction process

synchronisation of palaeoenvironmental records over the last 60 000 years and an extended intimate event stratigraphy to 48 000 b2k the intimate protocol for the correlation of marine ice core and terrestrial records is here updated reflecting recent developments in palaeoclimate research originally focussed on last glacial to interglacial transition lgit 22 000 11 500 years b p the intimate group has now extended its study period back to 60 000 years as a first step the intimate event stratigraphy has now been extended to include 8000 48 000 b2k based on a combined ngrip and grip isotope profile against a gicc05 chronology and key tephra horizons from iceland and continental european volcanic sources in this lead article of this intimate special issue we introduce some of the recent achievements of the intimate community and discuss the challenges associated with extending the intimate approach back in time focussing in particular on the chronological problems inherent in comparing different proxy records the intimate approach has thus far been limited predominantly to the north atlantic and australasian regions and we also discuss the potential to extend the intimate protocol beyond these regions

1400 years of extreme precipitation patterns over the mediterranean french alps and possible forcing mechanisms investigation of lake allos sediments revealed 160 graded layers interpreted as flood deposits over the last 1400 yr comparisons with records of historic floods support the interpretation of flood deposits and suggest that most recorded flood events are the result of intense meso scale precipitation events as there is no evidence for any major changes in erosion processes in the catchment since the medieval warm period mwp we interpret the allos record in terms of repeated intense precipitation events over the last millennium with a low flood frequency during the mwp and more frequent and more intense events during the little ice age this interpretation is consistent with the pattern of increasingly humid conditions in the northwestern mediterranean region this long term trend is superimposed on high frequency oscillations that correlate with solar activity and autumnal north atlantic oscillation nao finally a comparison of flood records across the northwestern mediterranean region showed that intense precipitation events in allos east of the rhone valley were out of phase with events in the cevennes west of the rhone but in phase with events in eastern spain supported by meteorological analyses this suggests an oscillation in atmospheric circulation patterns over the northwestern mediterranean

a back arc basin formed within continental lithosphere the central volcanic region of new zealand abstract the central volcanic region is an area of quaternary volcanism and tensional tectonics within the north island of new zealand that appears to be a direct continuation of a young oceanic back arc basin the havre trough into the continental structure of new zealand volcanism is predominantly rhyolitic yet the region possesses many of the geophysical characteristics often associated with oceanic back arc basins upper mantle seismic velocities are low pn and sn velocities of 7 4 and 3 95 km s respectively the crust is anomalously thin for its continental setting and the heat flow almost all of which is expressed in the discharge of hot water through geothermal systems is about 700 mw m2 i e some twelve times greater than normal continental heat flow in order to account for such a high heat flow a large scale mass transfer of heat is required it is proposed therefore that the central volcanic region represents a site of active back arc spreading within a continental lithosphere

lithospheric rheology and flexure at artemis chasma venus artemis chasma is an arcuate 2000 km diameter zone of convergence and lithospheric underthrusting on venus inelastic flexure modeling of the topography at artemis combined with observations of trench tectonics allow us to document local temperature gradients below 4 k km 1 and an immense compressive in plane force at the trench lithospheric rheology on venus may be stronger than would be predicted from conventional extrapolations of rock mechanics experiments in particular the brittle surface strength must reach a few tens of megapascals to satisfy the observed lack of flexurally induced surface faulting elastic plate bending models provide an adequate estimate of the bending moment at artemis but they fail to constrain or even recognize the in plane force the inelastic analysis implies an in plane force of the order of 1 1014 n m 1 a potential driving force is thermal thinning of regionally thick lithosphre in the highlands to the north the low heat flux at artemis which is a comparatively young structure is compatible with the notion that venus has experienced a prolonged period of cooling in the last several hundred million years the inference of such exceptionally low thermal gradients embraces three end member possibilities 1 the surface age is 600 ma 2 the lithospheric thermal age is greater than the surface age and or 3 the upper mantle temperature is anomalously low 1550 k

energy flow and geosphere interactions archaean to the present the foundation of the global resource base abstract direct observation of processes on modern earth have shown that the cooling processes lead to geochemical mixing influencing all the geospheres and the continental crust in the past two decades the importance of water cooling and hydrosphere interactions with the outer 10 km or so of the crust have explained a host of chemical and isotopic features today new attention is being focused on the role of the biomass in earth chemistry and the scale of the processes almost all of our most basic resources metals fossil fuels fertile soils involved the interactions of atmosphere hydrosphere biosphere with the outer shells of earth new needs in waste management technologies involve use of the same knowledge while there can be no doubt that the ancient earth was more energetic there is still no general agreement on the main styles of convection perhaps reflecting more chaotic tectonics but for sure the biosphere was alive and well

tracing bottom water oxygenation with sedimentary mn fe ratios in lake zurich switzerland abstract redox dynamics of manganese mn were studied in the sediment of lake zurich using precise sediment core age models monthly long term oxygen o 2 monitoring data of the water column 1936 2010 and high resolution xrf core scanning the age models were based on bi annual lamination and calcite precipitation cycles if present mn exhibits distinct maxima which coincide with the annual maximum deep water o 2 concentrations in spring according to the monitoring data in contrast the iron fe signal is mainly the result of calcite dilution as indicated by a strong negative correlation between fe and calcium ca xrf data the mn fe ratio in the core from the maximum lake depth zh10 15 137 m revealed a moderate correlation with o 2 measurements in the lake bottom water confirming the successful application of the mn fe ratio to semi quantitatively reconstruct bottom water oxygenation in the lake mostly low ratios were observed between 1895 and the mid 1960s as a result of eutrophication however geochemical focusing and sedimentological factors can reduce the applicability of the mn fe ratio in reconstructing o 2 concentrations in the bottom water of lakes

dynamically supported trench topography a viscous flow model of a subduction zone is used to calculate the near trench deformation and topography of the overriding plate in response to tectonic and buoyancy forces the tectonic force which is associated with global plate motion arises from subduction of a cold oceanic lithosphere that shears the overriding lithosphere along the contact between the two plates the buoyancy force arises in response to horizontal density variations and tends to relax the existing topography the time evolution of the near trench topography is investigated via a finite element technique that solves for the flow field in the overriding plate the results indicate that the near trench topography approaches a steady state configuration in which the upper surface topography produces a buoyancy force that balances the tectonic force induced by the subducting slab the model predicts that the steady state trench depth increases with the subduction rate and hence explains the correlation between trench depth and subduction rate observed by grellet and dubois 1982 transition from one steady state trench topography to another adds or removes material from the overriding plate this may result from a change in subduction rate angle of subduction or subduction of a seamount during a transition to a deeper steady state configuration the near trench stress field has an extensional component which agrees with the observed extension in regions of tectonic erosion similarly during a transition to a shallower steady state configuration the near trench stress field has a compressional component which agrees with the observed compression of accretionary wedges hence the model explains tectonic erosion and accretion at trenches as transitional features that indicate a change from one steady state configuration to another

holocene climate variability vegetation dynamics and fire regime in the central pyrenees the basa de la mora sequence ne spain abstract high resolution multiproxy data pollen sedimentology geochemistry chironomids and charcoal from the basa de la mora bsm lake sequence 42 32 n 0 19 e 1914 m a s l show marked climate variability in the central southern pyrenees throughout the holocene a robust age model based on 15 ams radiocarbon dates underpins the first precise reconstruction of rapid climate changes during the holocene from this area during the early holocene increased winter snowpack and high snowmelt during summer as a consequence of high seasonality led to higher lake levels a chironomid community dominated by non lacustrine taxa orthocladiinae related to higher inlet streams and a forested landscape with intense run off processes in the watershed from 9 8 to 8 1 cal ka bp climate instability is inferred from rapid and intense forest shifts and high fluctuation in surface run off shifts among conifers and mesophytes reveal at least four short lived dry events at 9 7 9 3 8 8 and 8 3 cal ka bp between 8 1 and 5 7 cal ka bp a stable climate with higher precipitation favoured highest lake levels and forest expansion with spread of mesophytes withdrawal of conifers and intensification of fires coinciding with the holocene climate optimum at 5 7 cal ka bp a major change leading to drier conditions contributed to a regional decline in mesophytes expansion of pines and junipers and a significant lake level drop despite drier conditions fire activity dropped as consequence of biomass reduction two arid intervals occurred between 2 9 and 2 4 cal ka bp and at 1 2 0 7 cal ka bp 800 1300 ad the latter coincides with the medieval climate anomaly and is one of the most arid phases of the holocene in bsm sequence anthropogenic disturbances were small until 700 ad when human pressure over landscape intensified with olea cultivation in the lowlands and significant deforestation in highlands colder and unfavourable weather conditions during the second part of the little ice age caused a temporary cease of high land management the most intense anthropogenic disturbances occurred during the second half of 19th century last decades are characterized by recovery of the vegetation cover as a result of land abandonment and lowered lake levels probably due to higher temperatures

lagging mantle convection the geoid and mantle structure abstract in numerical models of convection incorporating migration of a simulated subduction zone the main descending flow lags far behind the migrating trench and a geoid low is associated with the main descending flow this provides physical plausibility for the suggestion by chase and sprowl that present very long wavelength degree 2 4 geoid lows are associated with mesozoic trench locations and suggests further that the present long wavelength geoid deep mantle structure and hotspot distribution may be straightforward consequences of plate evolution since the upper paleozoic

deep earthquakes and the thermal assimilation of subducting lithosphere two problematic aspects of deep seismic zones are investigated the maximum depth about 700 km of seismic activity and the relative maximum in seismic energy release in the 500 700 km depth range it is shown that both features can be accounted for by a model based on thermal assimilation this implies that no barrier is required at a depth of 650 700 km to explain the observations

sediment budget quantification of a sub alpine river catchment since the end of the last glaciation changes in sediment budget and quantification of sediment fluxes of a small 5 3 km2 mediterranean sub alpine river catchment charanc catchment southern french alps 44 30 44n 5 51 55e are estimated for the last 20 000 years using a gis based approach and 3d palaeotopographic reconstructions following field surveys a high resolution morphometric map was established ten 14c ages of sub fossil trees and charcoal beds were compiled all datasets were integrated into a geographic information system we computed three palaeosurfaces by masking the digital elevation model of the current topography and calculated the sediment budget of the catchment estimations of specific hillslope erosion sedimentation and export rates highlight the evolution of the catchment and its sensitivity to variations in the ratio of sediment load to stream discharge between 20 000 and 14 500 cal bp sediment that was eroded 37 million m3 within the charanc catchment was entirely exported a change to a sedimentation regime commenced at around 14 500 cal bp between 9000 cal bp and 7000 cal bp footslopes were buried by fan shaped deposits at a rate of 6700 m3 yr since 7000 cal bp the overall morphogenetic regime has been one of vertical incision 73 of the material eroded over the last 14 500 years 14 million m3 was stored in fan shaped deposits at the present time 46 of this volume 6 million m3 is still stored in the catchment 8 million m3 of sediments have thus been exported out of the charanc catchment since 14 500 cal bp annual specific erosion rates on marly slopes are estimated at 1 98 to 111 t ha yr for the period 20 000 14 500 cal bp which is comparable to present rates measured on denudated marls in the southern french alps under a probably climate driven erosion regime and 2 17 to 20 t ha yr since 14 500 cal bp a reduction in erosion rate that may have been favoured by a more extensively wooded landscape

is a regional flood signal reproducible from lake sediments the evolution of flood activity with global warming remains uncertain to better assess flood climate relationships lake sediments are increasingly being investigated because they could provide regional flood histories long enough to cover past climate changes however site specific sedimentary processes may bias flood reconstructions the aim of this article is to investigate these effects through the reconstruction of two distinct flood records from independent neighbouring sedimentary basins of the same lake lake allos in the mediterranean french alps i e under the same climate conditions understanding of sedimentary processes is crucial in order to adapt the sampling strategy and the flood intensity proxy to each sedimentary system and thereby reconstruct a complete and reliable flood history thanks to this detailed approach the main trends of the regional flood variability can be reproduced i e periods of high flood frequency ranges of flood frequency values and timing of the most intense events in detail some differences appeared associated to the various stream capacities to erode and transport flood sediments to the lake system implying variable sensitivity of sedimentary systems in recording floods comparing regional flood records based on independent sedimentary systems from similar environments could thus be a complementary approach to assessing past flood intensity such an approach could open particularly interesting perspectives because reconstructing the long term evolution of flood intensity is a key challenge in the geosciences

holocene history of lac des lauzons 2180 m a s l reconstructed from multiproxy analyses of coleoptera plant macroremains and pollen hautes alpes france a 1 70 m core extracted from the lac des lauzons haut champsaur french alps at 2180 m altitude provided a detailed holocene record of beetles pollen and plant macrofossils enabling the reconstruction of local palaeoenvironmental changes during the last 10 000 years after an early phase of colonization by plants and insects corresponding to the lateglacial interstadial a long phase of relative stability of the ecosystems at least in the vicinity of the lake is recorded strikingly there is no evidence from beetle and plant macrofossils that the treeline reached the altitude of lauzons during the holocene climate optimum although this period is characterized by major forest expansion in many high altitude sites in the southern french alps the uppermost part of the record is blurred by the infilling of the lake progressively turning into a peat bog this sequence also provides an opportunity to compare the records of coprophilous fungal spores and coprophilous beetles and to improve the interpretation of these proxies in terms of their significance as proxies for pastoralism