detrital carbonate peaks on the labrador shelf a 13 7 ka template for freshwater forcing from the hudson strait outlet of the laurentide ice sheet into the subpolar gyre abstract the laurentide ice sheet lis was a large dynamic ice sheet in the early holocene the glacial events through hudson strait leading to its eventual demise are recorded in the well dated labrador shelf core md99 2236 from the cartwright saddle we develop a detailed history of the timing of ice sheet discharge events from the hudson strait outlet of the lis during the holocene using high resolution detrital carbonate ice rafted detritus ird 18o and sediment color data eight detrital carbonate peaks dcps associated with ird peaks and light oxygen isotope events punctuate the md99 2236 record between 11 5 and 8 0 ka we use the stratigraphy of the dcps developed from md99 2236 to select the appropriate r to calibrate the ages of recorded glacial events in hudson bay and hudson strait such that they match the dcps in md99 2236 we associate the eight dcps with h0 gold cove advance noble inlet advance initial retreat of the hudson strait ice stream hsis from hudson strait opening of the tyrrell sea and drainage of glacial lakes agassiz and ojibway the opening of foxe channel and retreat of glacial ice from foxe basin are represented by a shoulder in the carbonate data r of 350 years applied to the radiocarbon ages constraining glacial events h0 through the opening of the tyrell sea provided the best match with the md99 2236 dcps r values and ages from the literature are used for the younger events a very close age match was achieved between the 8 2 ka cold event in the greenland ice cores dcp7 8 15 ka bp and the drainage of glacial lakes agassiz and ojibway our stratigraphic comparison between the dcps in md99 2236 and the calibrated ages of hudson strait bay deglacial events shows that the retreat of the hsis the opening of the tyrell sea and the catastrophic drainage of glacial lakes agassiz and ojibway at 8 2 ka are separate events that have been combined in previous estimates of the timing of the 8 2 ka event from marine records sw iceland shelf core md99 2256 documents freshwater entrainment into the subpolar gyre from the hudson strait outlet via the labrador north atlantic and irminger currents the timing of freshwater release from the lis hudson strait outlet in md99 2236 matches evidence for freshwater forcing and lis icebergs carrying foreign minerals to the sw iceland shelf between 11 5 and 8 2 ka the congruency of these records supports the conclusion of the entrainment of freshwater from the retreat of the lis through hudson strait into the subpolar gyre and provides specific time periods when pulses of lis freshwater were present to influence climate

the u series toolbox for paleoceanography the geochemistry of marine sediments is a major source of information about the past environment of the many measurements that provide such information those of the u series nuclides are unusual in that they inform us about the rate and timescales of processes oceanic processes such as sedimentation productivity and circulation typically occur on timescales too short to be assessed using parent daughter isotope systems such as rb sr or sm nd so the only radioactive clocks that we can turn to are those provided by cosmogenic nuclides principally 14c or the u series nuclides this makes the u series nuclides powerful allies in the quest to understand the past ocean climate system and has led to their widespread application over the last decade as in other applications of the u series those in paleoceanography rely on fractionation of the nuclides away from secular equilibrium in the oceanic setting this fractionation is generally due to differences in the solubility of the various nuclides the behavior of the u series nuclides in the ocean environment was widely researched in the middle decades of the twentieth century this work established knowledge of the concentrations of the nuclides in the various compartments of the ocean system and of their fluxes between these compartments such understanding was comprehensively summarized in the ivanovich and harmon u series volume 1992 particularly by cochran 1992 understanding of the behavior of the u series nuclides has not advanced very dramatically in the decade since that summary but a major theme of research has been the use of this geochemical understanding to develop u series tools to assess the past environment table 1 view this table table 1 summary of seawater data for u series nuclides with paleoceanographic applications s soluble i insoluble full descriptions of the paleoceanographic uses and references are provided in the text further details of the half

weathering mechanisms and their effects on the landsliding of ignimbrite subject to vapor phase crystallization in the shirakawa pyroclastic flow northern japan abstract ignimbrite which is consolidated by vapor phase crystallization is weathered in humid regions to form a special type of weathering profile that consists of a hydrated zone an exfoliated zone and a disintegrated zone from the depth to the ground surface with each zone having a basal front the ignimbrite is hydrated first and loses a significant amount of phosphorous at the hydration front where rock forming tridymite is dissolved and cristobalite is precipitated the ignimbrite further loses its alkali and alkali earth components at the top of the hydrated zone by reacting with reactive water from the exfoliated zone then the leached layers are exfoliated and become part of the exfoliated zone and then they soften significantly at the top of the exfoliated zone rock is disintegrated so completely that rock texture disappears water from rainstorms infiltrates down to the exfoliation front but penetrates only slightly further downward thus saturating the weathered rock in the exfoliated and disintegrated zones and leading to a landslide with a slip surface within the exfoliated zone

a giant deep seated slope deformation in the italian alps studied by paleoseismological and morphometric techniques this work proves the existence of a large deep seated gravitational slope deformation dgsd in a hilly region of the southwestern alps whereas dgsd are usually linked with high relief energy in mountain environments moreover we describe the usefulness of applying paleoseismological techniques by means of trench excavation to date and understand the deformation history and genesis of recent morphostructures and we found evidence of causative relationships between dgsd and surface landslides the studied dgsd of mt croce della tola mt scincina italy is the largest of the western alps it is 7 km long and involves a minimum area of 16 km2 with a volume 3 5 km3 probably extending further ne beneath lake maggiore surface several parallel scarps representing the surface expression of slip planes affect the upper part of the slope whereas the lower part presents a convex profile dgsd at mt croce della tola started in the last interglacial period 120 40 ka bp and the following glacial phase was not able to significantly modify the general slope geometry post glacial deformation also occurred especially at mt scincina after 25 ka bp post glacial and active surface landslides developed on the convex lower part of the slope suggesting that they resulted from instability due to the new profile assumed by the slopes during the deep seated deformation the occurrence of mt scincina dgsd with a very low topographic gradient is interpreted as an effect induced by on other large dgsd

buckling deformations at the 2017 xinmo landslide site and nearby slopes maoxian sichuan china abstract a large catastrophic rock avalanche with a total volume of 18 0 106 m3 occurred at 5 38 am 24th june 2017 at xinmo village maoxian sichuan china resulting in 102 casualties 10 deaths 3 injuries and 89 missing we have been conducting a geological and geomorphological investigation in and around the xinmo landslide site since 2015 and we present our results here including data obtained before and after the landslide event the landslide which had an initial volume of 4 46 106 m3 of its source area was induced by rainfall on a previous landslide scar near the ridge top this initial landslide then struck and remobilized older landslide deposits in the middle and lower parts of the slope which subsequently buried xinmo village at the landslide toe the landslide occurred on a dip slope of triassic calcareous psammitic and pelitic schists the bedding plane which dips downslope to the south with an orientation of n80 w 48 s and high angle ne sw striking joints bounded the landslide source area at its base and sides respectively satellite image analysis and field observations of the slope of the landslide scar before and after the landslide strongly suggest that the beds in the source area had already begun gravitationally deforming e g buckling prior to the 2017 landslide moreover pits on the slip surface were likely the result of the dissolution of calcareous material dissolution probably reduced the rock strength along the bedding plane a rainfall event from the 16th to 24th of june 2017 probably dominated the groundwater drainage and finally triggered the catastrophic rock avalanche in addition to the 2017 landslide the hillslope just to the east of the xinmo landslide exhibits pronounced gravitational slope deformation including a tent like structures and warps induced by buckling this suggests that this slope could also fail like the xinmo rock avalanche during a future rainfall or earthquake event

assessment of landslide occurrences in serra do mar mountain range using kinematic analyses due to its meteorological geological and geomorphological settings brazilian s atlantic coast have suffered severe landslide phenomena particularly along the cost of sao paulo rio de janeiro and santa catarina states studies have shown that these processes are complex and triggered by several factors however within the study area many landslide locations are placed on gneiss migmatitic terrain with pronounced geological discontinuities the objective of this paper is to assess landslide occurrences in serra do mar caraguatatuba sp and investigate by means of kinematic analysis how they correlate with foliation and fractures present on the rocks kinematic analysis is used to investigate which discontinuities are more favorable to landslides occurrence and their relationship with slope directions structural information and kinematic data models are used to evaluate cause effect relationship of landslide processes results show that dip slopes with ne sw direction have greatest potential for the occurrence of planar landslides on the other hand anti dip and cross dip slopes have a greater potential to develop wedge landslides rock weathering and fluid flux along foliation planes can intensify mass movement such effect is also seen in residual soil since they are able to preserve relict structures of the rock this study contributes to a better understanding of how geological structures preserved in tropical residual soils influence shallow landslides

stability analysis and reinforcement evaluation of high steep rock slope by microseismic monitoring abstract the stability of excavated high steep rock slopes is most significant in the long term safety of large scale hydropower projects dagangshan rock slope had an unloading fractured zone xl 316 and a fault f231 during excavation which resulted in a high risk of slope instability anti shear tunnels were constructed for enhancing the overall shear resistance and reinforcing the slope at six different elevations the microseismic technique was employed to investigate microseismic activities during excavation and after reinforcement an integrated method of microseismic energy density and the magnitude frequency relation based on microseismic monitoring was proposed to analyse the stability and reinforcement effect of the slope during excavation a large number of microseismic events took place with few low magnitude events and numerous high magnitude events the aggravated damage occurred in the major discontinuities during excavation the number of low magnitude microseismic events increased after reinforcement and the b value obviously increased which means the slope stability was substantially enhanced microseismic activities were evidently reduced and the accumulated microseismic energy increased slowly the stresses were transferred towards the edge of the anti shear tunnel and a small number of low energy events occurred the targeted reinforcement has served well for its purpose and improves the mechanical performance of the discontinuities the application of the proposed method was verified by 3d rfpa centrifuge software the proposed method can be considered as an effective way to evaluate the reinforcement effect and stability of high steep rock slopes

long term gravitational deformation of rocks by mass rock creep abstract subsurface rocks beneath slopes are deformed to various degrees in various ways by mass rock creep mrc when they are subjected to a gravitationally unstable state for a long period mrc forms folds faults and numerous kinds of fractures such deformation is one of the main factors for deteriorating rock masses on slopes and also precursors of many landslides mrc deformations which have often been ascribed to tectonic origins can be distinguished from tectonic ones by their deformational features landforms and relationships between slope morphology and subsurface structures mrc folds are flexural slip folds that have the following mesoscopic to microscopic characteristics their axial surfaces are not smooth but are jagged and many visible openings or open fractures develop in association with the folds the jagged axial surfaces become smoother at depth and openings decrease in width with increasing overburden at the deformation site macroscopic types of mrc folds change according to the relationship between foliations and slopes buckling folds form in consequent slopes drag folds form in a deeper part of obsequent slopes and bending folds form in slopes with steep dipping foliations consequent or obsequent by downslope bowing of foliations shear fractures and tension fractures are the main deformational structures formed by mrc in massive rocks among shear fractures those of listric origin are remarkable tension fractures in general occur either in networks dividing rocks into fragments that slip and rotate irregularly in relation to each other or in parallel arrays of steeply dipping fractures an mrc fault has a shear zone consisting of a pulverized zone with gouge and a phyllitic or brecciated zone in a densely foliated rock the phyllitic zone is formed by microscopic slip along foliations in a sparsely foliated rock the brecciated zone is formed by random crushing except for the faults made through the shear fractures in massive rocks landforms due to mrc are gentle slopes bounded by horseshoe knicklines upslope convex slopes ridge top depressions multiple ridges uphill facing scarps and ridge crossing depressions

weathering mechanisms and their effects on landsliding in pelitic schist physical chemical and mineralogical analyses of undisturbed drill cores of pelitic schist from a landslide area in japan clarified the mechanisms of chemical weathering of pelitic schist oxidizing surface water percolates downward and reaches an oxidation front where chlorite is altered to al vermiculite graphite and pyrite are oxidized and depleted and goethite precipitates oxidation of pyrite also occurs just below the oxidation front probably by ferric iron pyrite oxidation yields sulphuric acid which penetrates further downward interacting with and weakening the rocks in addition to this chemical weakening stress release and shearing along schistosities form an incipient shear zone which propagates to a sliding zone that forms the rupture surface of a landslide once a sliding zone has developed it inhibits downward groundwater flow across it because of its low permeability slowing the downward propagation of the weathering zone until this filtration barrier is broken by landslide movement copyright 2010 john wiley sons ltd

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

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

improving past sea surface temperature estimates based on planktonic fossil faunas a new method of past sea surface temperature sst reconstruction based on the modern analog technique prell 1985 and on the indirect approach bartlein et al 1986 has been developed the revised analog method ram applied to planktonic foraminifera this technique leads to significant improvements in modern sst reconstruction with respect to former methods our estimates are characterized by much lower residuals and a better coverage of the observed sst range moreover the error of ram estimates of past ssts is lower than that associated with former reconstructions particularly at middle and high latitudes in low latitudes cold season ssts reconstructed by ram during glacials are 1 3 c lower than previously estimated our results tend thus to reconcile paleoestimates of glacial temperatures based on planktonic microfossils and on continental data in the tropics

high definition analysis of fluid induced seismicity related to the mesoscale hydromechanical properties of a fault zone interactions between pore pressure strain and seismicity were analyzed in a 30 m thick shallow fault zone that was subjected to a small overpressure of 80 kpa to produce small changes in effective stress simultaneous pressure strain and seismic measurements taken in the fractured damage zone during the pressurization indicated that seismicity is triggered along low permeable highly rigid low dip angle mesoscale inherited fractures where deformation is controlled by the hydromechanical behavior of the surrounding high permeability not so rigid aseismic sub vertical fault related fractures using a three dimensional distinct element representation of the fractures network we show that the seismicity observed is mainly due to shear slip along inherited planes in response to the mechanical loading induced by the opening by a few microns of the surrounding subfaults

similar rates of modern and last glacial ocean thermohaline circulation inferred from radiochemical data today the ocean thermohaline circulation transports half of the 231pa produced by radioactive decay in the atlantic ocean water column to the southern ocean this export respectively imparts low and high 231pa 230th ratios to the surface sediments of these oceans ocean sediments from the last glacial maximum bear a similar isotopic fingerprint implying that advection of north atlantic deep intermediate water into the circumpolar deep water of the southern ocean occurred at a similar or slightly higher rate during the last glacial period

improved determination of marine sedimentation rates using 230thxs measurements of excess 230th 230thxs have proved to be a useful tool in constraining changes in sedimentation rate and improving our understanding of the fluxes of other components into marine sediments to obtain the initial activity of 230thxs 230thxs0 in sediment the total measured 230th must be corrected for the presence of 230th associated with detrital minerals for ingrowth from uranium bearing authigenic phases and then also corrected for the decay of 230thxs since deposition we describe a number of improvements in the way these corrections are applied to obtain more accurate determinations of 230thxs0 we present a new method for the determination of a local estimate for the detrital 238u 232th activity ratio suggest more appropriate values for the isotopic composition of authigenic uranium and question the assumption of secular equilibrium in detrital material we also present a new freely available matlab script called xsage that can calculate 230thxs0 from user supplied datasets of uranium and thorium isotope activities from sedimentary samples following the theoretical approach described xsage can determine variations in sedimentation rate between stratigraphic horizons of known age and thus produce high resolution age models using a monte carlo approach the program calculates uncertainties for these age models and on the durations of intervals between tie points an example of the application of the xsage program using a previously published record is provided

seismic precursory patterns before a cliff collapse and critical point phenomena 1 we analyse the statistical pattern of seismicity before a 1 2 103 m3 chalk cliff collapse on the normandie ocean shore western france we show that a power law acceleration of seismicity rate and energy in both 40 hz 1 5 khz and 2 hz 10khz frequency range is defined on 3 orders of magnitude within 2 hours from the collapse time simultaneously the average size of the seismic events increases toward the time to failure these in situ results are derived from the only station located within one rupture length distance from the rock fall rupture plane they mimic the critical point like behavior recovered from physical and numerical experiments before brittle failures and tertiary creep failures our analysis of this first seismic monitoring data of a cliff collapse suggests that the thermodynamic phase transition models for failure may apply for cliff collapse

downcore variations of sedimentary detrital 238 u 232 th ratio implications on the use of 230 th xs and 231 pa xs to reconstruct sediment flux and ocean circulation excess 231 pa and 230 th 231 pa xs and 230 th xs can be used to reconstruct past oceanic sedimenta tion 230 th normalized flux and circulation changes 231 pa 230 th xs 0 hereafter pa th these quantities are determined by computing the detrital and authigenic contributions from bulk sediment measurement the method relies on the use of a chosen constant value of the detrital 238 u 232 th activity ratio hereafter u th det in this study we have extracted the detrital fraction of the sediments from north atlantic deep sea core su90 08 43803 0 1n 30802 0 5w 3 080 m and determined its u th det value over the last 40 ky we find that u th det varied significantly through time with a minimum value of 0 4 during the holocene and a maximum value of 0 7 during the last glacial maximum lgm the sensitivity of sedimentary 230 th normalized flux and pa th is tested for our study site and for other north atlantic sites we show that the sensitivity is highly dependent on the core location and its terrigenous material supply the 230 th normalized flux and pa th signals are very robust in cores with low detrital contributions whereas they are very sensitive to u th det changes in cores with higher detrital contribution in the latter case changes in 230 th normalized flux and pa th due to the choice of a constant u th det can largely exceed the uncertainty on the 230 th normalized flux and pa th inducing potential biases in the amplitude and temporal variability of reconstructed sedimentation and ocean circulation changes

fault gouge evolution in highly overconsolidated claystones processes of fault gouge evolution in hard claystones start with cataclasis that produces a soft clay gouge which fills the space between the initial fragments this re seals the initially highly porous and permeable damage zone without diagenetic processes we studied this process in shales and sandstones deformed in normal faults after uplift to shallow crustal depths in the ardennes and eifel detailed mapping shows four different lithotypes from intact shale in the wall rock broken wall rock fragments with various amounts of clay to a fully reworked gouge these lithotypes reflect different evolutionary stages the similar mineralogy of the different lithotypes suggests that the main process involved is mechanical fragmentation with minor contribution by diagenetic changes or weathering accompanied by large changes in microstructure porosity and transport properties while the wall rock has a very low porosity and permeability initial deformation results in a much higher porosity with large pores the reworked clay gouge also has a high porosity but its pore size corresponds to a lower permeability and higher capillary seal capacity in upper crustal fault zones in strong brittle lithologies this early re sealing in sections consisting of claystone will lead to local barriers to along fault fluid flow

carbonaceous material in pelitic schists of the sanbagawa metamorphic belt in central shikoku japan abstract carbonaceous material in pelitic schists of the sanbagawa metamorphic belt in central shikoku japan was separated from the host rocks and its x ray diffraction and chemical composition were studied its crystal structure and chemistry change continously with increasing metamorphic grade and approach those of well ordered graphite near the biotite isograd as graphitization is a rate process the temperature of complete graphitization differs from one metamorphic terrain to another as a function of the duration of metamorphism in an individual metamorphic terraan however the degree of graphitization is a useful indicator of relative metamorphic temperature in lower grade rocks

weathering mechanism of arenite sandstone with sparse calcite cement content abstract we conducted a multifaceted analysis of the weathering zones of arenite containing a minute amount of calcite cement based on mineralogical chemical and physical properties the survey targeted sandstone with mudstone interbeds belonging to the cretaceous izumi group the survey revealed that the weathering mechanism is a chain reaction the most important process is the pore opening between the grains caused by the dissolution of calcite cement in the initial stage of weathering subsequently the pores between the grains connect and widen separating the sand grains within the sandstone this primary weathering action may be a major difference from wacke during calcite dissolution in the initial stage sulfuric acid generated by pyrite oxidation in sandstone plays an important role chlorite breaks down as calcite dissolves however iron resulting from the breakdown disappears only after the pore water has been replaced by acidic water sandstones with advanced diagenesis are dense and hard and it was previously assumed that thick weathering zones could not develop because they were less susceptible to weathering however we discovered that weathering caused arenite with a minute amount of calcite cement to disintegrate into grains down to a depth of 30 m the surface layer of the weathered arenite lost fine particle fraction and crept to form a fragile soil layer susceptible to landslides

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

a microseismic based procedure for the detection of rock slope instabilities abstract the accumulation and spatial location of damage can lead to the progressive formation of macroscale discontinuities and the possible collapse of portions of rock slopes since rock fracturing is accompanied by the generation and transmission of elastic waves that travel through the affected material an analysis procedure that is able to interpret data recorded by means of a microseismic monitoring system has been developed the procedure is made up of three main parts the identification and grouping of similar events the hypocenter location of grouped events and the cross analysis of the spatial distribution of the source events with the structural setting of the investigated area the application of this methodology to a dataset recorded by a monitoring system installed on the matterhorn mountain has pointed out that this approach can contribute to recognizing areas subjected to a common rupture mechanism which can concern one single fracture or a set of neighboring fractures if signals that are generated over time from a certain area have a waveform with similar characteristics the rupture mechanism that causes the signals is the same at this regard a good knowledge of the local structural setting of the slope and of the characteristics of some documented rockfall events can contribute in supporting the above statement and help focus on areas where failures are kinematically possible

analysis of climatic influences on slope microseismic activity and rockfalls case study of the matterhorn peak northwestern alps abstractrock instability and rockfalls are commonly preceded by the initiation and propagation of cracks this process is accompanied by the release of microseismic energy which can be detected by means of an appropriate monitoring system because an increase in rockfall events have been observed in the matterhorn peak area since 2003 in 2007 a microseismic monitoring system and a thermometric monitoring system were installed on the italian side of the matterhorn peak close to the j a carrel hut as part of the interreg iiia alcotra permadataroc project the objective of the installation was to determine whether this instability increase was connected to climatic fluctuations detailed analysis of the recorded microseismic data shows a spatial concentration of microseismic activity on the western side of the investigated slope and a correlation of these data with thermal information shows that the temporal concentration of the microseismic activity could be traced back to the transitions from warm

changes in north atlantic radiocarbon reservoir ages during the allerod and younger dryas estimates of the radiocarbon age of seawater are required in correlations between marine and terrestrial records of the late quaternary climate we radiocarbon dated marine shells and terrestrial plant remains deposited in two bays on norway s west coast between 11 000 and 14 000 years ago a time of large and abrupt climatic changes that included the younger dryas yd cold episode the radiocarbon age difference between the shells and the plants showed that sea surface reservoir ages increased from 400 to 600 years in the early yd stabilized for 900 years and dropped by 300 years within a century across the yd holocene transition

characterising the spatial distribution frequency and geomorphic controls on landslide occurrence molise italy abstract an 815 km2 area in molise central italy was used as a natural laboratory to characterise the lithological topographic and fluvial controls on the spatial distribution and frequency of active landslides in temperate climates the study area is part of the central apennines fold and thrust belt and is characterised by the presence of a tectonic melange of scaly clays known as argille varicolori as well as more competent limestone and sandstone units the area has been subjected to a cumulative stream incision of up to 400 m since the mid pleistocene the landslide inventory was developed by combining satellite image interpretation and existing data sets ground truthed in the field statistical analysis of the inventory data demonstrates that the coupling between landslide occurrence in the area and lithology is strong with landslides occurring 3 10 times more frequently where the mechanically weak argille varicolori scaly clays outcrops compared to other lithologies analysis of the relationship between landslide occurrence and hillslope gradients shows that 50 of all landslides occur on slopes between 10 and 15 despite this interval representing only 30 of hillslope gradients in the study area these results demonstrate the major control that the properties of the regionally significant argille varicolori have on landslide occurrence in the area directly and through their control on hillslope gradients additionally our results show that more than 50 of the landslides occur at a distance of

microseismic investigation of an unstable mountain slope in the swiss alps 1 risks associated with unstable rocky slopes are growing as a result of climate change and rapid expansions of human habitats and critical infrastructure in mountainous regions to improve our understanding of mountain slope instability we developed a microseismic monitoring system that operates autonomously in remote areas afflicted by harsh weather our microseismic system comprising 12 three component geophones was deployed across 60 000 m 2 of rugged crystalline terrain above a huge 30 million m 3 recent rockfall in the swiss alps during its 31 month lifetime signals from 223 microearthquakes with approximate moment magnitudes ranging from 2 to 0 were recorded determining the hypocenters was challenging for several reasons 1 p wave velocities were highly heterogeneous varying abruptly from 3 8 km s 2 first break picks were either inaccurate or lacking for some microearthquakes 3 there were no reliable s wave picks 4 numerous microearthquakes occurred just outside the network boundaries these issues were addressed by using a three dimensional 3 d p wave velocity model of the mountain slope determined from refraction tomography in a nonlinear inversion for hypocenter parameters and their probability density functions recordings from geophones at different altitudes and in boreholes constrained microearthquake depth estimates most microearthquakes were concentrated within 50 100 m of the surface in two zones one that followed the recent rockslide scarp and one that spanned the volume of highest fracture zone fault density these two active zones delineated a mass of rock that according to geodetic measurements has moved toward the scarp at 1 2 cm yr

atlantic ocean circulation changes preceded millennial tropical south america rainfall events during the last glacial during the last glacial period greenland s climate shifted between cold stadial and warm interstadial phases that were accompanied by ocean circulation changes characterized by reduced atlantic meridional overturning circulation amoc during stadials here we present new data from the western tropical atlantic demonstrating that amoc slowdowns preceded some of the large south american rainfall events that took place during stadials based on 231pa 230th and ti ca measurements in the same sediment core we determine that the amoc started to slowdown 1420 250 and 690 180 1 years before the onset of two large precipitation events associated with heinrich stadials our results bring unprecedented evidence that amoc changes could be at the origin of the large precipitation events observed in tropical south america during heinrich stadials in addition we propose a mechanism explaining the differences in the extent and timing of amoc slowdowns associated with shorter and longer stadials

mechanisms of abrupt climate change of the last glacial period 1 more than a decade ago ice core records from greenland revealed that the last glacial period was characterized by abrupt climate changes that recurred on millennial time scales since their discovery there has been a large effort to determine whether these climate events were a global phenomenon or were just confined to the north atlantic region and also to reveal the mechanisms that were responsible for them in this paper we review the available paleoclimate observations of abrupt change during the last glacial period in order to place constraints on possible mechanisms three different mechanisms are then reviewed ocean thermohaline circulation sea ice feedbacks and tropical processes each mechanism is tested for its ability to explain the key features of the observations particularly with regard to the abruptness millennial recurrence and geographical extent of the observed changes it is found that each of these mechanisms has explanatory strengths and weaknesses and key areas in which progress could be made in improving the understanding of their long term behavior both from observational and modeling approaches are suggested finally it is proposed that a complete understanding of the mechanisms of abrupt change requires inclusion of processes at both low and high latitudes as well as the potential for feedbacks between them some suggestions for experimental approaches to test for such feedbacks with coupled climate models are given

lead isotopes in the eastern equatorial pacific record quaternary migration of the south westerlies abstract the influence of atmospheric dust on climate and biogeochemical cycles in the oceans is well understood but poorly quantified glacial atmospheric dust loads were generally greater than those during the holocene as shown for example by the covariation of dust fluxes in the equatorial pacific and antarctic ice cores nevertheless it remains unclear whether these increases in dust flux were associated with changes in sources of dust which would in turn suggest variations in wind patterns climate or paleo environment such questions can be answered using radiogenic isotope tracers of dust provenance here we present a 160 kyr high precision lead isotope time series of dust input to the eastern equatorial pacific eep from core odp leg 138 site 849 0 11 59 n 110 31 18 w the pb isotope record combined with nd isotope data rules out contributions from northern hemisphere dust sources north of the intertropical convergence zone such as asia or north africa sahara similarly eolian sources in australia central america the northern andes and patagonia appear insignificant based upon the radiogenic isotope data fluctuations in pb isotope ratios throughout the last 160 kyr show instead that south america remained the prevailing source of dusts to the eep there are two distinct south american pb isotope end members constrained to be located in the south central volcanic zone cvz 22 s 27 5 s and the south volcanic zone svz 33 s 43 s with the former most likely originating in the atacama desert dust availability in the svz appears to be related to the weathering of volcanic deposits and the development of ash derived andosols and influenced by local factors that might include vegetation cover variations in the dust fluxes from the two sources are in phase with both the dust flux and temperature records from antarctican ice cores we show that the forcing of dust provenance over time in the eep overall is influenced by high southerly latitude climate conditions leading to changes in the latitudinal position and strength of the south westerlies as well as the coastal winds that blow northward along the chilean margin the net result is a modulation of dust emission from the atacama desert and the svz via a northward migration of the south westerlies during cold periods and southward retreat during glacial terminations

lateglacial rock slope failures in north west ireland age causes and implications nine postglacial quartzite rock slope failures rsfs in north west ireland were dated using cosmogenic 10be weighted mean rsf ages range from 17 7 0 9 to 12 5 0 7 ka or 16 6 0 7 to 11 7 0 5 ka depending on assumed 10be production rate all dated rsfs occurred within 5000 years following ice sheet deglaciation at 17 4ka 16 3 ka and all but two occurred within 2000 years after deglaciation the timing of rsfs rules out glacial debuttressing permafrost degradation and enhanced deglacial cleft water pressures as triggers of failure in most cases we infer that paraglacial stress release and associated fracture propagation were critical in reducing rock masses to critical stability although earthquakes caused by lateglacial glacio isostatic rebound and or release of stored tectonic stresses may have triggered failure in some or all cases in conjunction with data from related studies our results imply that most undated rsfs outside the limit of younger dryas glaciation in the british isles are of lateglacial age and that numerous lateglacial rsfs occurred inside these limits with subsequent removal of debris by glaciers they support the view that paraglacial rsf activity in tectonically stable intraplate terrains was concentrated within a few millennia following deglaciation

analysis of seismic signals recorded on a prone to fall rock column vercors massif french alps summary a small aperture 40 m short period seismic array was installed during four months on the vercors massif western french alps at the top of a limestone column which collapsed one month and a half later during this monitoring period 193 seismic events were recorded by the seven seismometers of the array signal analysis yielded three main types of nearby seismic events to be identified from temporal and spectral characteristics microearthquakes single or multiple events individual block falls and rock falls it turned out that 60 per cent of the 193 events were classified as microearthquakes exhibiting distinct p and s waves while 17 per cent of these events remained unclassified out of the microearthquakes 40 events with a good signal to noise ratio were selected and processed p and s wave traveltimes were picked on the records and the inferred hypocentral distances agree with the two zones of the scarp exhibiting fresh ruptures after the fall polarization analysis of the 3 c records along with numerical simulations allowed discriminating between the two possible rupture mechanisms toppling and sliding shear rupture sliding was the predominant mode in the lower part of the column whereas traction rupture toppling affected the upper part finally the comparison between the ground motions recorded on the column and on the rock mass showed a systematic amplification on the column signal processing and numerical modelling both suggest that this amplification resulted from the excitation of the natural frequencies of the column and is particularly high 3 for microearthquakes occurring at the column to mass interface

glacial interglacial circulation changes inferred from 231pa 230th sedimentary record in the north atlantic region 1 studies from the subtropical western and eastern atlantic ocean using the 231pa 230th ratio as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation in this study we present a compilation of existing and new sedimentary 231pa 230th records from north atlantic cores between 1710 and 4550 m water depth comparing sedimentary 231pa 230th from different depths provides new insights into the evolution of the geometry and rate of deep water formation in the north atlantic during the last 20 000 years the 231pa 230th ratio measured in upper holocene sediments indicates slow water renewal above 2500 m and rapid flushing below consistent with our understanding of modern circulation in contrast during the last glacial maximum lgm glacial north atlantic intermediate water gnaiw drove a rapid overturning circulation to a depth of at least 3000 m depth below 4000 m water renewal was much slower than today at the onset of heinrich event 1 transport by the overturning circulation declined at all depths gnaiw shoaled above 3000 m and significantly weakened but did not totally shut down during the bolling allerod ba that followed water renewal rates further decreased above 2000 m but increased below our results suggest for the first time that ocean circulation during that period was quite distinct from the modern circulation mode with a comparatively higher renewal rate above 3000 m and a lower renewal rate below in a pattern similar to the lgm but less accentuated moc during the younger dryas appears very similar to ba down to 2000 m and slightly slower below

detrital carbonate rich sediments northwestern labrador sea implications for ice sheet dynamics and iceberg rafting heinrich events in the north atlantic much of the bed of the central and eastern sectors of the laurentide ice sheet was underlain by paleozoic carbonates we propose that pulses of detrital carbonate rich sediments in two cores from the northwestern labrador sea reflect episodes when an ice stream from the hudson strait extended to the shelf break and delivered sediment onto the slope and deep sea plain atomic mass spectroscopy 14 c dating of planktonic foraminifera in cores hu75 009 iv 55 2 4 km water depth and hu87 033 009 1 4 km water depth and 150 km north northwest indicates that the youngest event occurred between ca 14 and 15 ka and another occurred between 19 and 21 ka the two carbonate intervals in northwestern labrador sea cores are coeval with heinrich events 1 and 2 in the eastern north atlantic lat 45 50 n long 20 w where they are associated with an increase in lithic fragments and a drastic reduction in the numbers of foraminifera these changes have been linked with the massive production of icebergs associated with ice sheet surges our evidence indicates that heinrich events 1 and 2 are associated with the dynamics of the hudson strait ice stream and denote considerable glaciological instability

microscopic features of quartz and clay particles from fault gouges and infilled fractures in granite discriminating between active and inactive faulting abstract to assist in identifying faults that have a significant potential for displacement at or near the ground surface we carried out in depth investigations on fault gouges and a fracture infilled with clay clay vein in the kojaku granite on the tsuruga peninsula central japan we sampled several fault gouges at different stages of evolutions and clay rich infilling of a fracture with no evidence of offset based on our field observations gouge in an active fault is characterized by 1 stacked layers of different colors made up of comminuted fragments and clays and 2 injection of the fragments and clays from the gouge into the surrounding rocks indicating an accumulation of seismic induced shearing our thin section observations and x ray diffraction analyses show that all our samples are similar in the degree of fragmentation and mineral composition and because of this our study became focused mainly on microscopic features using laser diffraction particle size analysis scanning electron microscopy sem and transmission electron microscopy tem we identified the mineralogical and textural characteristics of the samples in order to improve our ability to discriminate between active and inactive faulting particle size distribution analysis showed that the gouge in the active fault contains the greatest abundance of finer particles due to multiple slip events which contrasts with the clay rich infilling of a fracture sem examination of the quartz particles showed that the gouge in the active fault contains more particles that have retained sharp and smooth crystal surfaces formed by fracturing than do either the gouges in minor faults that show no evidence of recent shear or the clay rich infilling of a fracture in contrast tem observations of very fine clay minerals approximately

rapid and accurate u th dating of ancient carbonates using inductively coupled plasma quadrupole mass spectrometry here the potential for rapid and accurate u th dating technique of marine aragonite skeletons deep sea corals lophelia pertusa and secondary calcite deposits speleothems and stalagmites has been explored using inductively coupled plasma quadrupole mass spectrometry icp qms the analytical procedure includes a largely simplified chemical separation technique for uranium u and thorium th using uteva resin the developed technique permits simultaneous quantification of uranium 238u and thorium 232th concentrations and their respective isotopic composition required for u series disequilibrium dating up to 50 u th dates per day can be achieved through icp qms with 234u and 230th reproducibility 2 of 3 4 and 1 respectively the high sensitivity 3 0 105 cps ppb together with low background 0 5 cps on each mass between 228 and 236 amu allowed u th dating of ancient deep water corals 15 260 kyr and stalagmites 30 85 kyr at precision levels of less than 2 consequently the combination of simplified chemistry using uteva with state of the art icp qms isotopic measurements that do not require a u th separation step now provides an extremely rapid and low cost u series dating technology the level of precision is most convenient for numerous geochronological applications such as the determination of climatic influences on ecosystem development and carbonate precipitation as a first example application we present icp qms u th dates of north atlantic deep water coral fragments retrieved in the southeastern porcupine seabight md01 2463g mound therese indicating a purely interglacial growth of deep water corals on so called carbonate mounds over several climate cycles

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

color development of iron oxides during rhyolite weathering over 52 000 years abstract to evaluate the behavior of iron during weathering colors of four rhyolites with different degrees of weathering eruption ages 1 1 1 8 26 and 52 ka were studied because the initial chemical compositions of the four lavas were similar to one another it is considered that the four lavas had similar whitish color at the time of eruption however at present more weathered lavas have more yellow brownish color indicating the formation of iron hydr oxides or fe bearing clays in order to characterize those weathering products spectro colorimetry and differential dissolution method were combined the colors of 1 1 and 1 8 ka lavas are close to the color of ferrihydrite whereas those of 26 and 52 ka lavas approach to the color of goethite this indicates that the initial stage of weathering is dominated by the formation of ferrihydrite and with increasing weathering the transformation from ferrihydrite to goethite proceeds it is estimated from the change of rock color that the half life for the transformation reaction of ferrihydrite to goethite in the field is 1100 years which is at least 80 times longer than previously reported values based on laboratory experiments the presence of impurities such as si and al in ferrihydrite can be a possible origin for retarding the transformation rate in the field

acoustic emission microseismic source location analysis for a limestone mine exhibiting high horizontal stresses a thin and rigid limestone roof and high horizontal stresses in an underground limestone mine have caused severe roof fall problems to help the mine address these problems an acoustic emission microseismic system was installed at the mine however the efficiency of this system was hampered by high background noise and inadequate source locations the focus of this research was therefore to resolve these problems the most beneficial outcome of this research was to demonstrate that the source location calculation at the mine could be improved through a comprehensive source location approach which includes digital filtering an absolute value based optimization method an advanced simplex location algorithm and reliability analysis

lower export production during glacial periods in the equatorial pacific derived from 231pa 230th xs 0 measurements in deep sea sediments 1 the 231pa 230th xs 0 records obtained from two cores from the western md97 2138 1 25 s 146 24 e 1900 m and eastern ocean drilling program leg 138 site 849 0 11 59 n 110 31 18 w 3851 m equatorial pacific display similar variability over the last 85 000 years i e from isotopic stages 1 to 5a with systematically higher values during the holocene isotopic stage 3 and isotopic stage 5a and lower values approaching the production rate ratio of the two isotopes 0 093 during the colder periods corresponding to isotopic stages 2 and 4 we have also measured the 230th normalized biogenic preserved and terrigenous fluxes as well as major and trace elements concentrations in both cores the 231pa 230th xs 0 results combined with the changes in preserved carbonate and opal fluxes at the eastern site indicate lower productivity in the eastern equatorial pacific during glacial periods the 231pa 230th xs 0 variations in the western equatorial pacific also seem to be controlled by productivity carbonate and or opal the generally high 231pa 230th xs 0 ratios 0 093 of the profile could be due to opal and or mno2 in the sinking particles the profiles of 231pa 230th xs 0 and 230th normalized fluxes indicate a decrease in exported carbonate and possibly opal during isotopic stages 2 and 4 in md97 2138 using 230th normalized flux we also show that sediments from the two cores were strongly affected by sediment redistribution by bottom currents suggesting a control of mass accumulation rates by sediment focusing variability

the greenland ice core chronology 2005 15 42 ka part 2 comparison to other records a new greenland ice core chronology gicc05 based on multi parameter counting of annual layers has been obtained for the last 42 ka here we compare the glacial part of the new time scale which is based entirely on records from the northgrip ice core to existing time scales and reference horizons covering the same period these include the grip and northgrip modelled time scales the meese sowers gisp2 counted time scale the shackleton fairbanks grip time scale sfcp04 based on 14c calibration of a marine core the hulu cave record three volcanic reference horizons and the laschamp geomagnetic excursion event occurring around greenland interstadial 10 gicc05 is generally in good long term agreement with the existing greenland ice core chronologies and with the hulu cave record but on shorter time scales there are significant discrepancies around the last glacial maximum there is a more than 1 ka age difference between gicc05 and sfcp04 and a more than 0 5 ka discrepancy in the same direction between gicc05 and the age of a recently identified tephra layer in the northgrip ice core both sfcp04 and the tephra age are based on 14c dated marine cores and fixed marine reservoir ages for the laschamp event gicc05 agrees with a recent independent dating within the uncertainties

the role of graphite layers in gravitational deformation of pelitic schist abstract deep seated landslides in pelitic schists are common in many countries but are poorly investigated and understood in this study we present the first detailed examination and modelling of landslide mechanisms in these materials we found that pelitic schist commonly contains black graphite rich layers on a scale of millimeter to centimeter thickness that are typically weaker than neighboring layers by examining microscopic textures in borehole samples obtained from landslide masses of pelitic schist we find that ductile gravitational shearing commonly occurs within these weaker layers accompanied by brittle fracture in the surrounding layers to investigate these mechanisms we have performed high precision direct shear tests using a novel back pressured shearbox on artificial rock samples both with and without graphite layers placed between pre cut shear surfaces the tests used normal stresses up to 800 kpa equivalent to 32 m depth of burial we found that the coefficients of friction for samples with graphite layers embedded in the artificial rock samples 0 30 representing an angle of internal friction of 16 7 were much lower than those without graphite layers on the pre cut surface 0 85 the shear strength of the artificial rocks with embedded layers of graphite decreased abruptly with increasing areal extent of the graphite layer along the shear surface from which it can be inferred that the continuity of a graphite layer in natural pelitic schist has a considerable effect on shear resistance these results suggest that even comparatively low dip angles of schistosity in pelitic schist could initiate microscopic slip along the graphite rich layers

introduction to u series geochemistry during the last century the earth sciences underwent two major revolutions in understanding the first was the recognition of the great antiquity of the earth and the second was the development of plate tectonic theory these leaps in knowledge moved geology from its largely descriptive origins and established the modern quantitative earth sciences for any science and particularly for the earth sciences time scales are of central importance until recently however the study of time scales in the earth sciences was largely restricted to the unraveling of the ancient history of our planet for several decades earth scientists have used a variety of isotope chronometers to unravel the long term evolution of the planet a fuller understanding of the physical and chemical processes driving this evolution often remained elusive because such processes occur on time scales 1 105 years which are simply not resolvable by most conventional chronometers the u series isotopes however do provide tools with sufficient time resolution to study these earth processes during the last decade the earth sciences have become increasingly focused on fundamental processes and u series geochemistry has witnessed a renaissance with widespread application in disciplines as diverse as modern oceanography and igneous petrology the uranium and thorium decay series contain radioactive isotopes of many elements in particular u th pa ra and rn the varied geochemical properties of these elements cause nuclides within the chain to be fractionated in different geological environments while the varied half lives of the nuclides allows investigation of processes occurring on time scales from days to 105 years u series measurements have therefore revolutionized the earth sciences by offering some of the only quantitative constraints on time scales applicable to the physical processes that take place on the earth the application of u series geochemistry to the earth sciences was thoroughly summarized in 1982

removal of 230th and 231pa at ocean margins abstract uranium thorium and protactinium isotopes were measured in particulate matter collected by sediment traps deployed in the panama basin and by in situ filtration of large volumes of seawater in the panama and guatemala basins concentrations of dissolved th and pa isotopes were determined by extraction onto mno 2 adsorbers placed in line behind the filters in the in situ pumping systems concentrations of dissolved 230 th and 231 pa in the panama and guatemala basins are lower than in the open ocean whereas dissolved 230 th 231 pa ratios are equal to or slightly greater than ratios in the open ocean particulate 230 th 231 pa ratios in the sediment trap samples ranged from 4 to 8 in contrast to ratios of 30 or more at the open ocean sites previously studied particles collected by filtration in the panama basin and nearest to the continental margin in the guatemala basin contained 230 th 231 pa ratios similar to the ratios in the sediment trap samples the ratios increased with distance away from the continent suspended particles near the margin show no preference for adsorption of th or pa and therefore must be chemically different from particles in the open ocean which show a strong preference for adsorption of th ocean margins as typified by the panama and guatemala basins are preferential sinks for 231 pa relative to 230 th furthermore the margins are sinks for 230 th and to a greater extent 231 pa transported by horizontal mixing from the open ocean

implications for sedimentation changes on the iberian margin over the last two glacial interglacial transitions from 230thexcess 0 systematics abstract the portuguese margin is well suited for studies of the contrasts in north atlantic circulation during glacial and interglacial times because of its rapid sediment accumulation rate this paper reports a 230thexcess 0 based study of sediment accumulation over the past 140 ky a period which includes the last two glacial interglacial transitions in two cores at 2 4 and 3 5 km water depth on a slope transect at 40 n although the independently determined mean sediment accumulation fluxes over the past 140 ky are unequivocally high with means of 13 2 and 10 5 g cm 2 ky 1 in the two cores conventional application of the 230thexcess 0 method yields consistently lower fluxes with means of 3 5 and 3 8 g cm 2 ky 1 these 230thexcess 0 estimates are interpreted as representations of the regional depositional flux through time this 230thexcess 0 regional flux is composed of a carbonate flux of

clay mineral evidence of nepheloid layer contributions to the heinrich layers in the northwest atlantic abstract the clay fraction of four cores drilled in the north atlantic ocean was studied at a very high resolution over the last 150 ka in order to record the mineralogical signature of heinrich events factor analysis of clay mineralogy establishes that three independent factors represent the main variations a detrital factor illite chlorite kaolinite a smectite factor and a mixed layer factor ivml illite vermiculite mixed layered clay the clay mineral fraction of core su90 38 drilled in the northeastern atlantic basin did not record any heinrich event whereas large changes in the clay mineral fraction occurred during heinrich events h1 h2 h4 and h5 in the three cores from the northwestern atlantic basin cores su90 08 su90 11 and su90 12 heinrich layers are characterized by increases in the detrital factor in cores su90 08 and su90 11 and sharp increases in the mixed layer factor in cores su90 11 and su90 12 the geographical setting of the cores the pattern of surface intermediate and deep water circulation and the main sources of clay minerals allow recognition of two major mechanisms involved in the deposition of the heinrich layers 1 an increased supply of detrital clay minerals by the icebergs and 2 a specific input of illite vermiculite mixed layer clay minerals by a nepheloid layer

location of seismic signals associated with microearthquakes and rockfalls on the sechilienne landslide french alps the sechilienne rockslide in the french alps has recently been instrumented with three seismic arrays this network has recorded numerous rockfalls and local microearthquakes because the media is highly fractured it is difficult to identify and pick first arrivals beam forming methods were therefore used to locate these events the method has been adapted to take into account the heterogeneity of seismic wave velocities the location accuracy has been estimated to be about 50 m for epicenters by applying the method to calibration shots depth is less constrained due to uncertainties on the velocity model and due to the seismic network geometry this method of location has then been applied to rockfalls and microearthquakes most rockfalls initiate in the most active part of the rockslide called les ruines the others are located on a recent eroded area aside from les ruines the network also allows the estimation of the rockfall trajectory and propagation speed finally 55 microearthquakes have been located within two zones microearthquakes are located within the first 250 m below the surface most microearthquakes are located in les ruines the most active part of the rockslide where the velocity has increased from 0 5 m yr in 1996 to 1 4 m yr in 2008 these events are located close to three faults that delimit a mass of about 3 6 million m3 other events are located close to the summital scarp in a zone moving at a few centimeters per year the western part of the rockslide which moves more slowly did not produce any event large enough to be detected simultaneously by all stations this seismic monitoring suggests that only a very small fraction of the deformation is released through seismic events

strong and deep atlantic meridional overturning circulation during the last glacial cycle extreme abrupt northern hemisphere climate oscillations during the last glacial cycle 140 000 years ago to present were modulated by changes in ocean circulation and atmospheric forcing1 however the variability of the atlantic meridional overturning circulation amoc which has a role in controlling heat transport from low to high latitudes and in ocean co2 storage is still poorly constrained beyond the last glacial maximum2 3 4 here we show that a deep and vigorous overturning circulation mode has persisted for most of the last glacial cycle dominating ocean circulation in the atlantic whereas a shallower glacial mode with southern sourced waters filling the deep western north atlantic prevailed during glacial maxima3 5 our results are based on a reconstruction of both the strength and the direction of the amoc during the last glacial cycle from a highly resolved marine sedimentary record in the deep western north atlantic parallel measurements of two independent chemical water tracers the isotope ratios of 231pa 230th and 143nd 144nd 6 7 8 which are not directly affected by changes in the global cycle reveal consistent responses of the amoc during the last two glacial terminations any significant deviations from this configuration resulting in slowdowns of the amoc were restricted to centennial scale excursions during catastrophic iceberg discharges of the heinrich stadials severe and multicentennial weakening of north atlantic deep water formation occurred only during heinrich stadials close to glacial maxima with increased ice coverage probably as a result of increased fresh water input in contrast the amoc was relatively insensitive to submillennial meltwater pulses during warmer climate states and an active amoc prevailed during dansgaard oeschger interstadials greenland warm periods

glacial interglacial changes in sediment rain rate in the sw indian sector of subantarctic waters as recorded by 230th 231pa u and δ15n high resolution records of opal carbonate and terrigenous fluxes have been obtained from a high sedimentation rate core md84 527 43 50 s 51 19 e 3269 m by normalization to 230th this method estimates paleofluxes to the seafloor on a point by point basis and distinguishes changes in sediment accumulation due to variations in vertical rain rates from those due to changes in syndepositional sediment redistribution by bottom currents we also measured sediment 15n to evaluate the changes in nitrate utilization in the overlying surface waters associated with paleoflux variations our results show that opal accumulation rates on the seafloor during the holocene and stage 3 based on 14c dating were respectively tenfold and fivefold higher than the vertical rain rates at this particular location changes in opal accumulation on the seafloor appear to be mainly controlled by sediment redistribution by bottom currents rather than variations in opal fluxes from the overlying water column correction for syndepositional sediment redistribution and the improved time resolution that can be achieved by normalization to 230th disclose important variations in opal rain rates we found relatively high but variable opal paleoflux during stage 3 with two maxima centered at 36 and 30 kyr b p low opal paleoflux during stage 2 and deglaciation and a pronounced maximum during the early holocene we interpret this record as reflecting variations in opal production rates associated with climate induced latitudinal migration of the southern ocean frontal system sediments deposited during periods of high opal paleoflux also have high authigenic u concentrations suggesting more reducing conditions in the sediment and high pa 231 th 230 ratios suggesting increased scavenging from the water column sediment 15n is circa 1 5 per mil higher during isotopic stage 2 and deglaciation the low opal rain rates recorded during that period appear to have been associated with increased nitrate depletion this suggests that opal paleofluxes do not simply reflect latitudinal migration of the frontal system but also changes in the structure of the upper water column increased stratification during isotopic stage 2 and deglaciation could have been produced by a meltwater lid leading to lower nitrate supply rates to surface waters

observations and predictions of the behaviour of large slow moving landslides in schist clyde dam reservoir new zealand abstract major remedial works involving toe buttressing pumped drainage gravity drainage and or infiltration protection were undertaken at nine of the seventeen large landslides along the clyde dam reservoir margins prior to lake filling in 1992 1993 all 17 landslides continue to be routinely monitored and inspected as part of the dam safety assurance programme undertaken by contact energy movement of the landslides is monitored by a combination of inclinometers extensometers and survey and is correlated with controlling events including lake filling storms floods prolonged wet periods and earthquakes most monitoring records extend over periods of 15 years with some histories as long as 25 years over 100 years of rainfall records are available for nearby locations very small deformation responses attributable to lake filling occurred at four of the stabilized slides slightly accelerated movement occurred at one slide that had not been stabilized and minor reactivation was detected at three others two landslides have demonstrated movement rate sensitivity to rainfall events neither slide was significantly affected by lake filling monitoring records show that movement of a known active part of the brewery creek landslide is triggered when a key piezometer reaches or exceeds a critical threshold level movement continues until the piezometer drops below that level movement of part of ripponvale landslide increases following prolonged rainfall events the slide was barely affected by lake filling and has not responded to subsequent transient increases in toe inundation levels floods data from zone a of the slide mass which is entirely above the lake shows the slide to be very sensitive to the effects of prolonged wet periods movement rates increase over a period of months and then gradually reduce based on the records to date it can be predicted that the slide will exhibit an increased movement rate when the cumulative rainfall over a period of 3 to 4 months exceeds about 300 mm

large sackung along major tectonic features in the central italian alps deep seated gravitational slope deformation sackung is common in alpine mountain belts it is controlled by lithological geomorphological and structural features we describe and discuss five examples of dsgsd along the insubric line periadriatic fault in the central italian alps the five examples are different in morphology size state of activity and distribution and are located along both primary and secondary valleys we demonstrate relations between structural and gravitational features and discuss the possibility that structural has both passive and active roles in sackung development analysis of ps sar data shows that the studied examples are not active today numerical modelling demonstrates the importance of lithological and structural constraints postglacial debuttressing groundwater fluctuations and weathering on sackung triggering and development

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

enhanced scavenging of 231pa relative to 230th in the south atlantic south of the polar front implications for the use of the 231pa 230th ratio as a paleoproductivity proxy abstract the fractionation of 230th and 231pa was investigated throughout the atlantic sector of the southern ocean published scavenging models generally assume that the 231pa 230t ratio of surface sediments is primarily determined by the mass flux of particles this relationship holds north of the polar front where low primary productivity coincides with ratios of unsupported 231pa 230th xs 231pa 230th in surface sediments below the production ratio of both radionuclides in the water column however we observed high xs231pa 230th ratios conventionally interpreted as a high productivity signal in surface sediments south of the polar front especially throughout the weddell sea in contradiction with the low particle flux of this region measurements of both dissolved and particulate fractions of 231pa and 230th in the water column revealed a strong n s decrease in the th pa fractionation factor from typical open ocean values around 10 north of the polar front to values between 1 and 2 south of 60 s this observation clearly indicates that the high xs231pa 230th ratios in surface sediments south of the antarctic circumpolar current are produced by a n s increase in the relative scavenging efficiency of 231pa relative to 230th most probably due to a change in the chemical composition of particulate matter and not by a high mass flux it is speculated that biogenic opal suggested not to significantly fractionate231pa and 230th may explain the enhanced scavenging of 231pa to the south this assumption is further supported by extremely high 231pa 230th ratios up to 0 34 in material collected with sediment traps south of the polar front where fluxes are primarily determined by biogenic opal based on these results we conclude that in regions where the sedimenting flux is dominated by biogenic opal the 231pa 230th ratio is not a reliable indicator for the mass flux of particles thus limiting its use as a paleoproductivity proxy in the southern ocean

deformation and stability of a discontinuity controlled rock slope at dagangshan hydropower station using three dimensional discontinuous deformation analysis abstract the right bank slope of the dagangshan hydropower station has undergone large deformation during excavation which may continue to increase and cause slope instability and failure threatening dam construction and safe operation this study analysed the deformation and instability of this discontinuity controlled rock slope by three dimensional discontinuous deformation analysis 3d dda a microseismic monitoring technique was adopted to capture the spatial and temporal distributions of microseismic events the unknown geological discontinuities and the potential slip surface inside the slope were determined by combining monitoring data with the geological information the 3d dda model was established to analyse the 3d deformation characteristics of the slope in addition the slope deformation and failure under various conditions such as over excavations as well as various joint penetrations joint dip directions and friction angles were further investigated it was found that the simulation of the critical sliding state of blocks by 3d dda is effective after improvement of the critical sliding model of joint contact between blocks and the computational results showed good agreement with monitoring results slope deformation is caused by the accumulation of micro crack damage in deep rock masses and it is closely related to its internal and external conditions furthermore the failure modes and mechanisms of the slope with 3d topography are presented which may be helpful for the design of a slope reinforcement scheme

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

timing and periodicity of paraglacial rock slope failures in the scottish highlands abstract many formerly glaciated mountains exhibit a high density of postglacial rock slope failures rsfs in the form of rockslides rock avalanches or deep seated gravitational slope deformations such rsfs are often termed paraglacial as they reflect pre conditioning by glaciation and deglaciation the temporal pattern of paraglacial rsfs is unknown we employ 47 cosmogenic isotope exposure ages obtained for 17 catastrophic rsfs in the scottish highlands to test models of changes in rsf frequency since deglaciation our results show that rsf activity spans almost the entire postglacial period from 17 ka until 1 5 ka and that the periodicity of sampled postglacial rsfs is statistically indistinguishable from a pattern of uniform periodicity 1 ka 1 our data do not conform to proposed models of declining rsf frequency with time elapsed since deglaciation but suggest that the temporal distribution of postglacial rsfs is best described by a combination of rapid response enhanced rsf frequency during or immediately after deglaciation followed by approximately constant periodicity our findings are consistent with near surface fracturing of rock when glacially induced confining stresses are removed causing some failures during or immediately after deglaciation and reducing other slopes to critical conditional stability so that failure is triggered by progressive rock mass weakening or by transient triggering mechanisms neither permafrost degradation thaw of ice in joints nor seismic activity offers a general explanation for triggering scottish rsfs but could be contributory in some cases the quasi constant periodicity inferred for holocene rsfs implies that the probability of rsfs in this seismically quiescent intraplate area has not changed in the past 10 ka and that further though infrequent catastrophic rsfs are likely to occur in the future

late slowdown of the atlantic meridional overturning circulation during the last glacial inception new constraints from sedimentary 231 pa 230 th our study gives new constraints on the response of atlantic meridional overturning circulation amoc export to various forcings during the last glacial inception the decay corrected excess sedimentary 231 pa 230 th activity ratio hereafter referred to as pa th has been measured over that period in two deep cores from the western su90 11 44 degrees 04 n 40 degrees 01 w 3645 m and eastern md01 2446 39 degrees 03 n 12 degrees 37 w 3547 m basins of the north atlantic both records display significant changes despite the relatively short half life of 231 pa similar to 32 kyr compared to the period we investigate the pa th variability does not correlate to changes in local opal flux normalized to 230 th moreover the pa th profiles display a high degree of coherency with indirect proxies of amoc activity such as the benthic foraminifera delta 13 c and the mid latitude summer sea surface temperature in nearby reference cores these additional pieces of evidence support our interpretation of the pa th as reflecting amoc export the pa th repeatedly underwent rapid changes during the last glacial inception associated with the extension of ice rafted detritus in the north atlantic highlighting the control of ice sheet dynamics through freshwater forcing on amoc export amoc export remains large during periods of ice sheet growth and its decreases lag the northern hemisphere summer insolation forcing amoc modulation appears driven by ice sheet dynamics itself driven by the seasonal insolation gradient between low and high northern hemisphere latitudes and the associated intensity of the meridional oceanic and atmospheric circulation c 2009 elsevier b v all rights reserved

a mechanism of chemical weathering of mudstone in a mountainous area abstract the chemical weathering of marine mudstone in humid mountainous areas of japan is dominated by the oxidation of pyrite a common mineral in marine sedimentary rocks this process occurs at the oxidation front that is the base of the oxidized zone and sulfuric acid is formed chlorite is transformed into smectite due to the oxidizing and acidic conditions as sulfuric acid migrates downward from the oxidation front minerals are dissolved and components are leached out from the underlying dissolved zone whose lower boundary is the dissolution front the oxidation and dissolution fronts migrate downward as weathering progresses in mountainous areas

spheroidal weathering of granite porphyry with well developed columnar joints by oxidation iron precipitation and rindlet exfoliation spheroidal weathering one of the important rock weathering styles has been attributed to chemical weathering by the water from joint surfaces and mechanical aspects of the weathering have not been well addressed we made an investigation on spheroidal weathering of miocene granite porphyry with well developed columnar joints and found that this spheroidal weathering proceeds through chemical processes and accompanying mechanical processes the investigation of the textures physical properties mineralogy and chemistry of the porphyry revealed the presence of a brown band on the surface margins of corestones representing the oxidation of pyrite and chlorite and the precipitation of iron hydroxides and the consequent generation of micro cracks within the band during weathering oxidation progresses inwards from joints that surround the rindlets including both high angle columnar and low angle planar joints and causes rounding of the unweathered interior portion of the rock microscopic observations of the brown band embedded with fluorescent resin show that pores are first filled with iron hydroxides and that micro cracks then form parallel to the oxidation front in the outer portion of the brown band iron hydroxide precipitation increases the p wave velocity in the brown band while micro crack formation decreases the tensile strength of the rock where the brown band has thickened to 6 cm the micro cracks are connected to one another to create continuous cracks which separate the rindlets from the corestone micro crack formation parallel to the corestone surface may be attributed to compressive stresses generated by small amounts of volumetric expansion due to the precipitation of iron hydroxides in the brown band earth surface is under oxidizing environments so that precipitation of iron hydroxides commonly occurs the spheroidal weathering in this paper is a typical example of the combination of chemical and mechanical processes under such environments copyright 2016 john wiley sons ltd

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

changes in sea surface hydrology associated with heinrich event 4 in the north atlantic ocean between 40 and 60 n abstract the changes in distribution of sea surface temperature and salinity in the north atlantic between 40 and 60 n were reconstructed for the time interval between 40 and 30 kyr bp which includes the large iceberg discharge event associated with the deposition of heinrich layer 4 we found that the meltwater input during deposition of heinrich layer 4 resulted in a 1 2 kyr temperature decrease of about 2 c and a salinity decrease in the range of 1 5 3 5 between 40 and 50 n sites above 50 n did not experience significant salinity variations a much larger area was affected by the reduction in sea surface temperature the amplitude of the sea surface temperature shift was however much smaller than the atmospheric temperature changes over greenland at gisp and grip sites