dynamic friction and the origin of the complexity of earthquake sources abstract we study a simple antiplane fault of finite length embedded in a homogeneous isotropic elastic solid to understand the origin of seismic source heterogeneity in the presence of nonlinear rate and state dependent friction all the mechanical properties of the medium and friction are assumed homogeneous friction includes a characteristic length that is longer than the grid size so that our models have a well defined continuum limit starting from a heterogeneous initial stress distribution we apply a slowly increasing uniform stress load far from the fault and we simulate the seismicity for a few 1000 events the style of seismicity produced by this model is determined by a control parameter associated with the degree of rate dependence of friction for classical friction models with rate independent friction no complexity appears and seismicity is perfectly periodic for weakly rate dependent friction large ruptures are still periodic but small seismicity becomes increasingly nonstationary when friction is highly rate dependent seismicity becomes nonperiodic and ruptures of all sizes occur inside the fault highly rate dependent friction destabilizes the healing process producing premature healing of slip and partial stress drop partial stress drop produces large variations in the state of stress that in turn produce earthquakes of different sizes similar results have been found by other authors using the burridge and knopoff model we conjecture that all models in which static stress drop is only a fraction of the dynamic stress drop produce stress heterogeneity

self healing slip pulses in dynamic rupture models due to velocity dependent strength abstract seismological observations of short slip duration on faults short rise time on seismograms during earthquakes are not consistent with conventional crack models of dynamic rupture and fault slip in these models the leading edge of rupture stops only when a strong region is encountered and slip at an interior point ceases only when waves from the stopped edge of slip propagate back to that point in contrast some seismological evidence suggests that the duration of slip is too short for waves to propagate from the nearest edge of the ruptured surface perhaps even if the distance used is an asperity size instead of the entire rupture dimension what controls slip duration if not dimensions of the fault or of asperities in this study dynamic earthquake rupture and slip are represented by a propagating shear crack for all propagating shear cracks slip velocity is highest near the rupture front and at a small distance behind the rupture front the slip velocity decreases as pointed out by heaton 1990 if the crack obeys a negative slip rate dependent strength relation the lower slip velocity behind the rupture front will lead to strengthening that further reduces the velocity and under certain circumstances healing of slip can occur the boundary element method of hamano 1974 is used in a program adapted from andrews 1985 for numerical simulations of mode ii rupture with two different velocity dependent strength functions for the first function after a slip weakening displacement the crack follows an exponential velocity weakening relation the characteristic velocity v 0 of the exponential determines the magnitude of the velocity dependence at dynamic velocities the velocity dependence at high velocity is essentially zero when v 0 is small and the resulting slip velocity distribution is similar to slip weakening if v 0 is larger rupture propagation initially resembles slip weakening but spontaneous healing occurs behind the rupture front the rise time and rupture propagation velocity depend on the choice of constitutive parameters the second strength function is a natural log velocity dependent form similar to constitutive laws that fit experimental rock friction data at lower velocities slip pulses also arise with this function for a reasonable choice of constitutive parameters slip pulses with this function do not propagate at speeds greater than the raleighwave velocity the calculated slip pulses are similar in many aspects to seismic observations of short rise time in all cases of self healing slip pulses the residual stress increases with distance behind the trailing edge of the pulse so that the final stress drop is much less than the dynamic stress drop in agreement with the model of brune 1976 and some recent seismological observations of rupture

simulating the impact of glaciations on continental groundwater flow systems 1 relevant processes and model formulation 1 in the recent literature it has been shown that pleistocene glaciations had a large impact on north american regional groundwater flow systems because of the myriad of complex processes and large spatial scales involved during periods of glaciation numerical models have become powerful tools to examine how ice sheets control subsurface flow systems in this paper the key processes that must be represented in a continental scale 3 d numerical model of groundwater flow during a glaciation are reviewed including subglacial infiltration density dependent i e high salinity groundwater flow permafrost evolution isostasy sea level changes and ice sheet loading one dimensional hydromechanical coupling associated with ice loading and brine generation were included in the numerical model hydrogeosphere and tested against newly developed exact analytical solutions to verify their implementation other processes such as subglacial infiltration permafrost evolution and isostasy were explicitly added to hydrogeosphere a specified flux constrained by the ice sheet thickness was found to be the most appropriate boundary condition in the subglacial environment for the permafrost frozen and unfrozen elements can be selected at every time step with specified hydraulic conductivities for the isostatic adjustment the elevations of all the grid nodes in each vertical grid column below the ice sheet are adjusted uniformly to account for the earth s crust depression and rebound in a companion paper the model is applied to the wisconsinian glaciation over the canadian landscape in order to illustrate the concepts developed in this paper and to better understand the impact of glaciation on 3 d continental groundwater flow systems

deglacial radiocarbon history of tropical atlantic thermocline waters absence of co2 reservoir purging signal abstract a current scenario to explain much of the atmospheric co 2 increase during the glacial to holocene climate transition requires the outgassing of a deep old oceanic co 2 reservoir thought to be located in the southern ocean in this scenario co 2 rich and 14 c depleted subsurface antarctic sourced water ventilates the thermocline where it is purged to the atmosphere in the equatorial regions a view that has been met with conflicting results using a novel approach paired surface and deep dwelling planktonic foraminifer radiocarbon analyses we document that the equatorial atlantic thermocline did not see old 14 c depleted water which would be characteristic of the proposed isolated deep ocean co 2 reservoir data from several studies concur that during the deglaciation antarctic intermediate waters were contributing to atlantic thermocline waters even more than today therefore our observations challenge the current purging hypothesis together with other studies these results suggest that the mechanism responsible for the deglacial co 2 rise cannot invoke contemporary circulation modes and or thermocline ventilation pathways

model of earthquake recurrence role of elastic wave radiation relaxation of friction and inhomogeneity we have constructed a dynamical model of seismicity wherein a fault is embedded in an infinite continuous elastic medium therefore the influence of the energy dissipated in seismic wave radiation oil the sequential history of model earthquakes is fully taken into account in this model the drop in friction at rupture takes place gradually thus introducing a relaxation dimension as an example we consider a finite homogeneous fault that is terminated by infinitely strong barriers at the ends the features of the seismicity are dominated by the stresses that are reflected from the unbreakable barriers there is a strong dependence of the patterns of seismicity on the ratio of the relaxation dimension to the distance between the barriers at the ends for large values of this parameter we find that periodicity begins after a short transient interval and a dominance of the statistical distributions by large events that break completely through the fault from end to end for small values of this parameter smaller scale seismicity is interspersed with the large events and no periodicity is observed within the time spanned by the computations we conclude that major unquenched heterogeneities such as those found at barriers which we suppose arise in nature due to the nonuniform geometry of faults are vital ingredients for generating complex seismic histories as well as giving rise to the complex features of individual earthquake source time functions in models of seismicity as a dynamical process

strike slip earthquakes on quasi vertical transcurrent faults inferences for general scaling relations the recent occurrence of several large strike slip earthquakes provides the opportunity to review and complement available data on the scaling of seismic moment mo with length of rupture l for large earthquakes depending on their tectonic setting and mechanism for strike slip earthquakes on quasi vertical transcurrent faults the mo versus l relation has a significant change of slope around mo 0 6 0 8 1020 n m and for larger earthquakes mo scales linearly with l this is compatible with models where slip is controlled by the width of the fault also it appears to be easier to categorize large earthquakes by their mechanism strike slip on vertical transcurrent fault versus pure thrust normal than their tectonic setting interplate intraplate

simulation of co seismic secondary fracture displacements for different earthquake rupture scenarios at the proposed nuclear waste repository site in forsmark simulation of co seismic secondary fracture displacements for different earthquake rupture scenarios at the proposed nuclear waste repository site in forsmark

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

deep water formation in the north pacific and deglacial co2 rise deep water formation in the north atlantic and southern ocean is widely thought to influence deglacial co 2 rise and climate change here we suggest that deep water formation in the north pacific may also play an important role we present paired radiocarbon and boron isotope data from foraminifera from sediment core md02 2489 at 3640 m in the north east pacific these show a pronounced excursion during heinrich stadial 1 with benthic planktic radiocarbon offsets dropping to 350 years accompanied by a decrease in benthic 11 b we suggest that this is driven by the onset of deep convection in the north pacific which mixes young shallow waters to depth old deep waters to the surface and low ph water from intermediate depths into the deep ocean this deep water formation event was likely driven by an increase in surface salinity due to subdued atmospheric monsoonal freshwater flux during heinrich stadial 1 the ability of north pacific deep water npdw formation to explain the excursions seen in our data is demonstrated in a series of experiments with an intermediate complexity earth system model these experiments also show that breakdown of stratification in the north pacific leads to a rapid 30 ppm increase in atmospheric co 2 along with decreases in atmospheric 13 c and 14 c consistent with observations of the early deglaciation our inference of deep water formation is based mainly on results from a single sediment core and our boron isotope data are unavoidably sparse in the key hs1 interval so this hypothesis merits further testing however we note that there is independent support for breakdown of stratification in shallower waters during this period including a minimum in 15 n younging in intermediate water 14 c and regional warming we also re evaluate deglacial changes in north pacific productivity and carbonate preservation in light of our new data and suggest that the regional pulse of export production observed during the bolling allerod is promoted by relatively stratified conditions with increased light availability and a shallow potent nutricline overall our work highlights the potential of npdw formation to play a significant and hitherto unrealized role in deglacial climate change and co 2 rise

a high resolution record of southern ocean intermediate water radiocarbon over the past 30 000 years the circulation of intermediate waters plays an important role in global heat and carbon transport in the ocean and changes in their distribution are closely tied to glacial interglacial climate change coupled radiocarbon and u th measurements on deep sea desmophyllum dianthus corals allow for the reconstruction of past intermediate water ventilation we present a high resolution time series of antarctic intermediate water radiocarbon from 44 corals spanning 30 ka through the start of the holocene encompassing the transition into the last glacial maximum lgm and the last deglaciation corals were collected south of tasmania from water depths between 1430 and 1950 m with 80 of them between 1500 and 1700 m giving us a continuous record from a narrow depth range the record shows three distinct periods of circulation the mis 3 2 transition the lgm heinrich stadial 1 extending from 22 to 16 kyr bp and the antarctic cold reversal acr the mis 3 2 transition and the acr are characterized by abrupt changes in intermediate water radiocarbon while the lgm time period generally follows the atmosphere at a constant offset in support of the idea that the lgm ocean was at steady state for its 14 c distribution closer inspection of the lgm time period reveals a 40 jump at 19 ka from an atmospheric offset of roughly 230 to 190 coincident with an observed 10 15 m rise in sea level and a southward shift of the subantarctic and polar fronts an abrupt change not seen in deeper records during the acr time period intermediate water radiocarbon is on average less offset from the atmosphere 110 110 and much more variable this variability has been captured within the lifetimes of three individual corals with changes of up to 35 over 40 yr likely caused by the movement of southern ocean fronts this surprising result of relatively young and variable intermediate water radiocarbon during the acr seems to go against the canonical idea of reduced circulation and ventilation in the south during this time period however comparisons with other records from the southern ocean highlight zonal asymmetries which can explain the deviation of our tasmanian record from those in drake passage and the eastern pacific these signals seen in tasmanian intermediate water 14 c can also be found in greenland ice core 18 o and east asian monsoon strength throughout the lgm and the deglaciation our tasmanian intermediate water record is sensitive to times when the upper and lower cells of the meridional overturning circulation are more or less interconnected which has important implications for the global climate system on glacial interglacial time scales

stress diffusion along rupturing plate boundaries an analysis is made of viscoelastic lithosphere asthenosphere coupling in the time dependent redistribution of stress along plate boundaries or other seismic lineaments following great earthquakes the study is based on a generalization by rice of elsasser s model of stress diffusion in which general elastic plane stress deformations are allowed in lithospheric plates which are coupled in an elementary way to a maxwellian viscoelastic asthenosphere solutions are developed which describe the large scale quasistatic distribution of thickness averaged in the lithosphere at or near stationary or travelling rupture zones modeled here by either crack like zones of fixed stress drop or dislocation type slip zones sudden ruptures shed load onto the asthenosphere which is gradually transferred back to the lithosphere by a slow relaxation process the spatial and temporal characteristics of the predicted stress alterations suggest a significant role of lithosphere asthenosphere coupling effects in triggering interactions of great earthquakes patterns of prolonged aftershock activity and the breaking of barriers or gaps by time dependent stressing

decovalex iii bmt3 benchpar wp4 the thermo hydro mechanical responses to a glacial cycle and their potential implications for deep geological disposal of nuclear fuel waste in a fractured crystalline rock mass a number of studies related to past and on going deep repository performance assessments have identified glaciation deglaciation as major future events in the next few hundred thousand years capable of causing significant impact on the long term performance of the repository system benchmark test 3 bmt3 of the international decovalex iii project has been designed to provide an illustrative example that explores the mechanical and hydraulic response of a fractured crystalline rock mass to a period of glaciation the primary purpose of this numerical study is to investigate whether transient events associated with a glacial cycle could significantly influence the performance of a deep geological repository in a crystalline shield setting a conceptual site scale tens of kilometres hydro mechanical hm model was assembled based primarily on site specific litho structural hydrogeological and geomechanical data from the whiteshell research area in the canadian shield with simplification and generalization continental glaciological modelling of the laurentide ice sheet through the last glacial cycle lasting approximately 100 000 years suggests that this site was glaciated at about 60 ka and between about 22 5 and 11 ka before present with maximum ice sheet thickness reaching 2500 m and maximum basal water pressure head reaching 2000m the ice sheet drainage model was scaled down to generate spatially and temporally variable hydraulic and mechanical glaciated surface boundary conditions for site scale subsurface hm modelling and permafrost modelling under extreme periglacial conditions permafrost was able to develop down to the assumed 500 m repository horizon two and three dimensional coupled hm finite element simulations indicate during ice sheet advance there is rapid rise in hydraulic head high transient hydraulic gradients and high groundwater velocities 2 3 orders of magnitude higher than under nonglacial conditions surface water recharges deeper than under nonglacial conditions upon ice sheet retreat the gradients reverse fracture zone network geometry interconnectivity and hydraulic properties significantly influence flow domain response residual elevated heads are preserved for 10 000s in the low diffusivity rock and no hydraulic jacking or shear failure occurs at depth it was found that transient coupled modelling is necessary to capture the essence of glacial effects on performance assessment model dimensionality also significantly affects simulated results

persistently well ventilated intermediate depth ocean through the last deglaciation during the last deglaciation 18 11 thousand years ago existing radiocarbon 14c reconstructions of intermediate waters in the mid to low latitude oceans show widely diverging trends with some broadly tracking the atmosphere and others suggesting extreme depletions these discrepancies cloud our understanding of the deglacial carbon cycle because of the diversity of hypotheses needed to explain these diverging records for example injections of 14c dead geological carbon mixing of extremely isolated waters from the abyssal ocean or changes in sites of deep water ventilation here we present absolutely dated deglacial deep sea coral 14c records of intermediate waters from the galapagos platform close to the largest reported deglacial 14c depletions together with data from the low latitude atlantic our records indicate coherent well equilibrated intermediate water 14c ventilation in both oceans relative to the atmosphere throughout the deglaciation the observed overall trend towards 14c enriched signatures in our records is largely due to enhanced air sea carbon isotope exchange efficiency under increasing atmospheric p rm co 2 these results suggest that the 14c depleted signatures from foraminifera are likely sedimentary rather than water mass features and provide tight 14c constraints for modelling changes in circulation and carbon cycle during the last deglaciation intermediate depth waters in the atlantic and pacific oceans were well equilibrated with the atmosphere through the last deglaciation according to radiocarbon data from deep sea corals

no signature of abyssal carbon in intermediate waters off chile during deglaciation the rise in atmospheric carbon dioxide at the end of the last glacial maximum has been attributed to the release of carbon dioxide from the deep southern ocean however reconstructions of the radiocarbon signature of chilean margin intermediate waters during the glacial termination do not reflect the influence of such a release

complexity of seismicity due to highly rate dependent friction we study a simple antiplane fault of finite length embedded in a homogeneous isotropic elastic solid in order to understand the origin of seismic source heterogeneity in the presence of nonlinear rate dependent friction all the mechanical properties of the medium and friction are assumed to be homogeneous starting from a heterogeneous initial stress distribution we apply a slowly increasing uniform stress load far from the fault and we simulate the seismicity for more than 20 000 events in some cases the style of seismicity produced by this model is determined by a control parameter which measures the degree of rate dependence of friction for classical friction models with rate independent friction no complexity appears and seismicity is perfectly periodic for weakly rate dependent friction seismicity becomes slightly nonperiodic but most events are still characteristic earthquakes when friction is highly rate dependent seismicity is completely irregular and ruptures of all sizes occur inside the fault highly rate dependent friction destabilizes the healing process producing premature healing of slip and partial stress drop premature healing causes rupture to take the form of narrow propagating slip episodes the so called heaton s 1990 pulses partial stress drop produces large variations in the state of stress which in turn produce earthquakes of different sizes we make the conjecture that all models in which static stress drop is only a fraction of the dynamic stress drop produce stress heterogeneity

modelling of the hydro mechanical response of sedimentary rocks of southern ontario to past glaciations abstract glaciation is considered as one of the main natural processes that can have a significant impact on the long term performance of a deep geological nuclear waste repository dgr located in the northern hemisphere the northern part of the american continent has been subjected to a series of strong glaciation and deglaciation events over the past million years the last glacial cycle in the northern hemisphere started approximately 110 000 year ago during that cycle southern ontario was buried under a continental ice sheet with a maximum thickness of up to 3000 m at about 20 000 years ago the ice cap retreated approximately 10 000 years ago however field data from deep boreholes in sedimentary rocks of southern ontario show anomalous pore water pressure including underpressure and overpressure zones in this paper a large scale coupled hydro mechanical hm model is developed to investigate the hydro mechanical hm response of the sedimentary rocks of southern ontario to past glacial cycles particular emphasis has been placed on the evolution of pore water pressures and surface displacements the hm model is verified using analytical solutions the results of the large scale hm modeling study shows that the past glaciation particularly the second cycle 22 000 apb had significant impact on the pore water pressure gradient and effective stress distribution in the sedimentary rocks of southern ontario furthermore good agreement between the large scale modeling results and anomalous pressures leads us to the conclusion that these anomalies could be glacially induced the results of this research can provide information that will contribute to a better understanding of the impact of future glaciations on the long term performance of drgs in sedimentary rocks

deep sea corals off brazil verify a poorly ventilated southern pacific ocean during h2 h1 and the younger dryas abstract simultaneous 14 c and th u dating of deep sea corals are useful for reconstructing the intensity of deep ocean circulation in the past as they deliver the time between the gas exchange of the water with the atmosphere and the incorporation of the 14 c in the carbonates adkins and boyle 1997 adkins et al 1998 mangini et al 1998 th u ages of deep sea corals sampled in sediment cores from locations off the coast of brazil bathed by antarctic intermediate water at depths between 600 and 800 m group close to heinrich events h2 h1 and the younger dryas the 14 c of the water bathing the corals starts to decrease approximately 2 kyr before the heinrich events and decreases to values 400 lower than the corresponding back tracked atmospheric values the timing and the magnitude of the decrease is similar to that observed in intermediate water in the n pacific off baja california marchitto et al 2007 and in the eastern pacific stott et al 2009 high ventilation ages partly exceeding 4000 years are an unambiguous indication for a reduction of north atlantic deep water formation during h2 h1 and the yd as deduced from higher 231 pa 230 th activity ratios and from end in n atlantic ocean sediments mcmanus et al 2004 pahnke et al 2008 yu et al 1996 they also could indicate a poorly oxygenated southern pacific ocean at the end of the heinrich events

deepwater formation in the north pacific during the last glacial termination between approximately 17 500 and 15 000 years ago the atlantic meridional overturning circulation weakened substantially in response to meltwater discharges from disintegrating northern hemispheric glacial ice sheets the global effects of this reorganization of poleward heat flow in the north atlantic extended to antarctica and the north pacific here we present evidence from north pacific paleo surface proxy data a compilation of marine radiocarbon age ventilation records and global climate model simulations to suggest that during the early stages of the last glacial termination deep water extending to a depth of approximately 2500 to 3000 meters was formed in the north pacific a switch of deepwater formation between the north atlantic and the north pacific played a key role in regulating poleward oceanic heat transport during the last glacial termination

ventilation history of nordic seas overflows during the last de glacial period revealed by species specific benthic foraminiferal 14c dates formation of deep water in the high latitude north atlantic is important for the global meridional ocean circulation and its variability in the past may have played an important role in regional and global climate change here we study ocean circulation associated with the last de glacial period using water column radiocarbon age reconstructions in the faroe shetland channel southeastern norwegian sea and from the iceland basin central north atlantic the presence of tephra layer faroe marine ash zone ii dated to 26 7 ka enables us to determine that the middepth 1179 m water depth and shallow subsurface reservoir ages were 1500 and 1100 14c years respectively older during the late glacial period compared to modern suggesting substantial suppression of the overturning circulation in the nordic seas during the late last glacial maximum and the onset of deglaciation 20 18 ka nordic seas overflow was weak but active during the early deglaciation 17 5 14 5 ka our data reveal large differences between 14c ventilation ages that are derived from dating different benthic foraminiferal species pyrgo and other miliolid species yield ventilation ages 6000 14c years while all other species reveal ventilation ages 2000 14c years these data either suggest subcentennial regional circulation changes or that miliolid based 14c ages are biased due to taphonomic or vital processes implications of each interpretation are discussed regardless of this enigma the onset of the bolling allerod interstadial 14 5 ka is clearly marked by an increase in middepth nordic seas ventilation and the renewal of a stronger overflow

variations in rupture process with recurrence interval in a repeated small earthquake in theory and in laboratory experiments friction on sliding surfaces such as rock glass and metal increases with time since the previous episode of slip1 this time dependence is a central pillar of the friction laws widely used to model earthquake phenomena2 3 on natural faults other properties such as rupture velocity4 5 porosity and fluid pressure6 11 may also vary with the recurrence interval eighteen repetitions of the same small earthquake separated by intervals ranging from a few days to several years allow us to test these laboratory predictions in situ the events with the longest time since the previous earthquake tend to have about 15 larger seismic moment than those with the shortest intervals although this trend is weak in addition the rupture durations of the events with the longest recurrence intervals are more than a factor of two shorter than for the events with the shortest intervals both decreased duration and increased friction are consistent with progressive fault healing during the time of stationary contact

dynamic faulting under rate dependent friction we discuss the effects of rate dependent friction on the propagation of seismic rupture on active faults several physicists using burridge and knopoff s box and spring model of faulting have proposed that fault complexity may arise from the spontaneous development of a self similar stress distribution on the fault plane if this model proves to be correct it has important consequences for the origin of the complexity of seismic sources in order to test these ideas on a more realistic earthquake model we developed a new boundary integral equation method for studying rupture propagation along an antiplane fault in the presence of nonlinear rate dependent friction we study rupture dynamics of models with single and twin asperities in our models asperities are places on the fault with a higher value of prestress othewise all fault parameters are homogeneous we show that for models with such asperities a slip velocity weakening friction leads to the propagation of supersonic healing phases and to the spontaneous arrest of fracture if the prestress outside the asperities is low enough for models with asperities we can also observe narrow slip velocity pulses qualitatively similar to the so called heaton pulses observed in some earthquake accelerograms we also observe a complex distribution of stress after the rupture that depends on details of the initial distribution of asperities and on the details of the friction law

the impact of atmospheric pco2 on carbon isotope ratios of the atmosphere and ocean it is well known that the equilibration timescale for the isotopic ratios 13c 12c and 14c 12c in the ocean mixed layer is on the order of a decade 2 orders of magnitude slower than for oxygen less widely appreciated is the fact that the equilibration timescale is quite sensitive to the speciation of dissolved inorganic carbon dic in the mixed layer scaling linearly with the ratio dic co2 which varies inversely with atmospheric pco2 although this effect is included in models that resolve the role of carbon speciation in air sea exchange its role is often unrecognized and it is not commonly considered in the interpretation of carbon isotope observations here we use a global three dimensional ocean model to estimate the redistribution of the carbon isotopic ratios between the atmosphere and ocean due solely to variations in atmospheric pco2 under last glacial maximum lgm pco2 atmospheric 14c is increased by 30 due to the speciation change all else being equal raising the surface reservoir age by about 250 years throughout most of the ocean for 13c enhanced surface disequilibrium under lgm pco2 causes the upper ocean atmosphere and north atlantic deep water 13c to become at least 0 2 higher relative to deep waters ventilated by the southern ocean conversely under high pco2 rapid equilibration greatly decreases isotopic disequilibrium as a result during geological periods of high pco2 vertical 13c gradients may have been greatly weakened as a direct chemical consequence of the high pco2 masquerading as very well ventilated or biologically dead strangelove oceans the ongoing anthropogenic rise of pco2 is accelerating the equilibration of the carbon isotopes in the ocean lowering atmospheric 14c and weakening 13c gradients within the ocean to a degree that is similar to the traditional fossil fuel suess effect

implications of subsurface thermal hydraulic mechanical processes associated with glaciation on shield flow system evolution and performance assessment a deep geologic repository dgr situated on the canadian shield will be subject to long term climate change that will markedly alter surface conditions as a result of glaciation and permafrost penetration systematic two dimensional and three dimensional coupled thermal hydraulic mechanical finite element simulations with varying degrees of coupling including depth dependent salinity represented as a change in groundwater density and temperature dependent density and viscosity were undertaken to address the implications of glaciation on groundwater flow system dynamics as it could affect dgr performance the modelling domain consisted of a 1 6 km deep sub regional scale 100 km2 fractured shield flow system initial and transient thermal hydraulic and mechanical boundary conditions were developed from two realizations of the university of toronto glacial systems model of the last laurentide glaciation results indicate that during the glacial loading unloading cycle for this particular conceptual model there is limited penetration of glacial meltwaters to depth and small residual anomalous hydraulic head during glacial coverage the mechanical factor of safety increases in the moderately fractured and sparsely fractured rock mass but principal effective stress reorientation also occurs given the assumed nonglacial in situ state of stress and mechanical properties the fracture zones were predicted to be less stable under glacial conditions

extreme deepening of the atlantic overturning circulation during deglaciation glacial terminations during the late pleistocene epoch are associated with changes in insolation they are also punctuated by millennial scale climate shifts characterized by a weakening and subsequent strengthening of the atlantic meridional overturning circulation this ubiquitous association suggests that these oscillations may be a necessary component of deglaciation model simulations have suggested that the period of weakened circulation during these terminal oscillations would be followed by an overshoot of the circulation on its resumption but this phenomenon has not yet been observed here we use radiocarbon measurements of benthic foraminifera and carbonate preservation indices to reconstruct ventilation changes in the deep south atlantic ocean over the past 40 000 years we find evidence for a particularly deep expansion of the atlantic overturning cell directly following the weak mode associated with heinrich stadial 1 our analysis of an ocean general circulation model simulation suggests that north atlantic deep water export during the expansion was greater than that of interglacial conditions we find a similar deep expansion during dansgaard oeschger interstadial event 8 38 000 years ago which followed heinrich stadial 4 we conclude that the rise in atmospheric co2 concentrations and resultant warming associated with an especially weak overturning circulation are sufficient to trigger a switch to a vigorous circulation but a full transition to interglacial conditions requires additional forcing at an orbital scale

modeling of the thermo hydro mechanical chemical response of sedimentary rocks to past glaciations abstract thermo hydro mechanical chemical thmc coupled processes that have resulted from long term past climate changes and glaciation cycles in the sedimentry rocks of southern ontario are investigated a conceptual numerical model has been developed to solve four coupled partial differential equations pdes which represent hydraulic thermal mechanical and chemical processes the finite element method is used to solve the pdes under transient surface boundary conditions imposed by past glaciation cycles to predict the hydraulic mechanical thermal and geochemical responses of the geological system the results show that past glaciations have a significant impact on the hydraulic gradient and pressure vertical effective stress and salinity profiles and a limited effect on the permafrost depth the predicted results show good agreement when compared with the field data for the total dissolved solid rock strength and quality the results show relatively good agreement with the anomalous pore water pressure profile in the field the modeling results indicate that the infiltration depth of glacial melted water is less than 300 m and are consistent with the field observation of total dissolved solids at the level of a deep geological repository dgr for low and intermediate level radioactive wastes being planned in these rock formations a safety factor of 6 9 is predicted against failure by using hoek brown failure envelopes while a low safety factor of 0 83 is predicted at the shallower level of the silurian salina formation it is found that solute transport at the middle and upper ordovician formations are diffusion dominated at depths of 300 m or more and controlled by diffusion advection above 300 m based on the results obtained the modeling of a past glaciation can be used with reasonable confidence in predicting the impact of future glaciations related to the long term safety and stability of the proposed dgr in the sedimentry formation however for site specific conditions thmc modeling is very sensitive to material properties and sensitivity analysis is required for future model development

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

beyond debuttressing mechanics of paraglacial rock slope damage during repeat glacial cycles cycles of glaciation impose mechanical stresses on underlying bedrock as glaciers advance erode and retreat fracture initiation and propagation constitute rock mass damage and act as preparatory factors for slope failures however the mechanics of paraglacial rock slope damage remain poorly characterized using conceptual numerical models closely based on the aletsch glacier region of switzerland we explore how in situ stress changes associated with fluctuating ice thickness can drive progressive rock mass failure preparing future slope instabilities our simulations reveal that glacial cycles as purely mechanical loading and unloading phenomena produce relatively limited new damage however ice fluctuations can increase the criticality of fractures in adjacent slopes which may in turn increase the efficacy of fatigue processes bedrock erosion during glaciation promotes significant new damage during first deglaciation an already weakened rock slope is more susceptible to damage from glacier loading and unloading and may fail completely we find that damage kinematics are controlled by discontinuity geometry and the relative position of the glacier ice advance and retreat both generate damage we correlate model results with mapped landslides around the great aletsch glacier our result that most damage occurs during first deglaciation agrees with the relative age of the majority of identified landslides the kinematics and dimensions of a slope failure produced in our models are also in good agreement with characteristics of instabilities observed in the field our results extend simplified assumptions of glacial debuttressing demonstrating in detail how cycles of ice loading erosion and unloading drive paraglacial rock slope damage

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

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

simulating earthquake rupture and off fault fracture response application to the safety assessment of the swedish nuclear waste repository abstract to assess the long term safety of a deep repository of spent nuclear fuel upper bound estimates of seismically induced secondary fracture shear displacements are needed for this purpose we analyze a model including an earthquake fault which is surrounded by a number of smaller discontinuities representing fractures on which secondary displacements may be induced initial stresses are applied and a rupture is initiated at a predefined hypocenter and propagated at a specified rupture speed during rupture we monitor shear displacements taking place on the nearby fracture planes in response to static as well as dynamic effects as a numerical tool we use the 3dimensional distinct element code 3dec because it has the capability to handle numerous discontinuities with different orientations and at different locations simultaneously in tests performed to benchmark the capability of our method to generate and propagate seismic waves 3dec generates results in good agreement with results from both stokes solution and the compsyn code package in a preliminary application of our method to the nuclear waste repository site at forsmark southern sweden we assume end glacial stress conditions and rupture on a shallow gently dipping highly prestressed fault with low residual strength the rupture generates nearly complete stress drop and an m w 5 6 event on the 12 km 2 rupture area of the 1584 secondary fractures 150 m radius with a wide range of orientations and locations relative to the fault a majority move less than 5 mm the maximum shear displacement is some tens of millimeters at 200 m fault fracture distance

links between eastern equatorial pacific stratification and atmospheric co2 rise during the last deglaciation it is difficult to untangle the mixed influences of high and low latitude climate forcing in the eastern equatorial pacific eep here we test the hypothesis that the southern ocean drove change in the eep via subsurface intermediate waters during the last deglaciation we use the 18o signature of benthic foraminifera to reconstruct water density changes during the last 25 kyr at three intermediate water depths 370 m 600 m and 1000 m in the eep carbonate 18o records a combined signature of temperature and salinity and is therefore more closely related to density than temperature or salinity alone we find that benthic foraminiferal 18o values decreased first in the subsurface simultaneously with rising temperatures over antarctica and propagated up to the surface within 3 kyr the early subsurface response initiated a rapid decrease in density stratification over the upper water column as indicated by reduced 18o gradients between surface and intermediate depths stratification of the upper water column remained low through the termination with stratification minima reached during heinrich stadial 1 and the younger dryas yd synchronous with the two part deglacial rise in atmospheric co2 centennial scale shifts toward heavier 18o signatures at 370 and 600 m during the yd indicate short lived shifts in the subantarctic mode water antarctic intermediate water boundary to shallower intermediate depths we suggest that decreased density gradients during the deglaciation accelerated vertical mixing across the eep and potentially the entire south pacific subtropical gyre which enhanced co2 delivery from depth to the surface ocean and atmosphere

subsurface hydro mechanical hm impacts of glaciation sensitivity to transient analysis hm coupling fracture zone connectivity and model dimensionality abstract benchmark test 3 bmt3 of the international decovalex iii project has been designed to provide an illustrative example that explores the mechanical and hydraulic response of a fractured crystalline rock mass to a period of glaciation the primary purpose of this numerical study is to investigate whether transient events associated with a glacial cycle could significantly influence the performance of a deep geological repository in a crystalline shield setting a conceptual site scale tens of kilometres hydro mechanical hm model was assembled based primarily on site specific litho structural hydrogeological and geomechanical data from the whiteshell research area on the canadian shield with simplification and generalization to accommodate fennoscandian shield information this site scale hm model was driven by transient hydraulic and mechanical glaciated surface boundary conditions generated by the university of edinburgh s continental scale model of laurentide ice sheet history during the last glacial cycle which lasted approximately 100 000 years an overview of the bmt3 study has been presented in a companion paper chan t christiansson r boulton gs ericsson lo hartikainen j jensen mr mas ivars d stanchell fw vidstrand p wallroth t decovalex iii bmt3 benchpar wp4 the thermo hm responses to a glacial cycle and their potential implications for deep geological disposal of nuclear fuel waste in a fractured crystalline rock mass this issue this paper describes two and three dimensional coupled hm finite element simulations with the motif model of transport in fractured porous media code the mathematical and numerical modelling approaches are described and example results are presented to illustrate a transient coupled modelling is necessary to capture the essence of glacial effects on groundwater flow system evolution b fracture zone network geometry interconnectivity and hydraulic properties significantly influence the magnitude and rate of flow domain response and c model dimensionality can significantly affect simulated results

the glacial mid depth radiocarbon bulge and its implications for the overturning circulation published reconstructions of radiocarbon in the atlantic sector of the southern ocean indicate that there is a mid depth maximum in radiocarbon age during the last glacial maximum lgm this is in contrast to the modern ocean where intense mixing between water masses results in a relatively homogenous radiocarbon profile ferrari et al 2014 suggested that the extended antarctic sea ice cover during the lgm necessitated a shallower boundary between the upper and lower branches of the meridional overturning circulation this shoaled boundary lay above major topographic features associated with strong diapycnal mixing isolating dense southern sourced water in the lower branch of the overturning circulation this isolation would have allowed radiocarbon to decay and thus provides a possible explanation for the mid depth radiocarbon age bulge we test this hypothesis using an idealized 2 d residual mean dynamical model of the global overturning circulation concentration distributions of a decaying tracer that is advected by the simulated overturning are compared to published radiocarbon data we find that a 600 km 5 of latitude increase in sea ice extent shoals the boundary between the upper and lower branches of the overturning circulation at 45 s by 600 m and shoals the depth of north atlantic deep water convection at 50 n by 2500 m this change in circulation configuration alone decreases the radiocarbon content in the mid depth south atlantic at 45 s by 40 even without an increase in surface radiocarbon age in the source region of deep waters during the lgm

ocean mixing and ice sheet control of seawater 234u 238u during the last deglaciation seawater 234u 238u provides global scale information about continental weathering and is vital for marine uranium series geochronology existing evidence supports an increase in 234u 238u since the last glacial period but the timing and amplitude of its variability has been poorly constrained here we report two seawater 234u 238u records based on well preserved deep sea corals from the low latitude atlantic and pacific oceans the atlantic 234u 238u started to increase before major sea level rise and overshot the modern value by 3 per mil during the early deglaciation deglacial 234u 238u in the pacific converged with that in the atlantic after the abrupt resumption of atlantic meridional overturning we suggest that ocean mixing and early deglacial release of excess 234u from enhanced subglacial melting of the northern hemisphere ice sheets have driven the observed 234u 238u evolution

slip complexity in earthquake fault models we summarize studies of earthquake fault models that give rise to slip complexities like those in natural earthquakes for models of smooth faults between elastically deformable continua it is critical that the friction laws involve a characteristic distance for slip weakening or evolution of surface state that results in a finite nucleation size or coherent slip patch size h models of smooth faults using numerical cell size properly small compared to h show periodic response or complex and apparently chaotic histories of large events but have not been found to show small event complexity like the self similar power law gutenberg richter frequency size statistics this conclusion is supported in the present paper by fully inertial elastodynamic modeling of earthquake sequences in contrast some models of locally heterogeneous faults with quasi independent fault segments represented approximately by simulations with cell size larger than h so that the model becomes inherently discrete do show small event complexity of the gutenberg richter type models based on classical friction laws without a weakening length scale or for which the numerical procedure imposes an abrupt strength drop at the onset of slip have h 0 and hence always fall into the inherently discrete class we suggest that the small event complexity that some such models show will not survive regularization of the constitutive description by inclusion of an appropriate length scale leading to a finite h and a corresponding reduction of numerical grid size

north atlantic circulation and reservoir age changes over the past 41 000 years 1 constraints on the timing of atlantic meridional overturning circulation amoc changes during the last deglaciation are fundamental to understanding the climate s rapid response to insolation forcing however uncertainty about high latitude north atlantic hlna radiocarbon reservoir ages has previously precluded robust age model development for this critical region hlna reservoir ages also serve as a proxy for amoc strength we present regionally averaged hlna reservoir ages for 0 to 41 thousand years before the present kyr bp based on over 500 radiocarbon dates from 33 north atlantic cores an early deglacial increase to 1000 14c yr reservoir ages between 18 5 and 16 5 kyr bp suggests reduced amoc before peak heinrich stadial 1 hs1 ice rafted debris ird a rapid decrease in reservoir ages coincident with the ird maximum at 16 kyr bp indicates strong stratification of the upper water column caused by massive freshwater release

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

marine radiocarbon reservoir age simulations for the past 50 000 years radiocarbon 14c dating calibration for the last glacial period largely relies on cross dated marine 14c records however marine reservoirs are isotopically depleted with respect to the atmosphere and therefore have to be corrected by the marine radiocarbon ages of surface waters mras whose temporal variabilities are largely unknown here we present simulations of the spatial and temporal variability in mras using a three dimensional ocean circulation model covering the past 50 000 years our simulations are compared to reconstructions of past surface ocean 14c running the model with different climatic boundary conditions we find that low latitude to midlatitude mras have varied between 400 and 1200 14c years with values of about 780 14c years at the last glacial maximum reservoir ages exceeding 2000 14c years are simulated in the polar oceans our simulation results can be used as first order approximation of the mra variability in future radiocarbon calibration efforts

radiocarbon age anomaly at intermediate water depth in the pacific ocean during the last deglaciation 1 benthic and planktonic 14c ages are presented for the last glacial termination from marine sediment core vm21 30 from 617 m in the eastern equatorial pacific the benthic planktonic 14c age differences in the core increased to more than 6000 years between heinrich 1 time and the end of the younger dryas period several replicated 14c ages on different benthic and planktonic species from the same samples within the deglacial section of the core indicate a minimal amount of bioturbation scanning electron microscopy reveals no evidence of calcite alteration or contamination the oxygen isotope stratigraphy of planktonic and benthic foraminifera does not indicate anomalously old glacial age values and there is no evidence of a large negative stable carbon isotope excursion in benthic foraminifera that would indicate input of old carbon from dissociated methane it appears therefore that the benthic 14c excursion in this core is not an artifact of diagenesis bioturbation or a pulse of methane a benthic 14c stratigraphy reconstructed from the 14c ages from the deglacial section of vm21 30 appears to match that of baja margin core mv99 mc19 gc31 pc08 705 m but the magnitude of the low 14c excursion is much larger in the vm21 30 record this would seem to imply that the vm21 30 core was closer to the source of 14c depleted waters during the deglaciation but the source of this co2 remains elusive

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

radiocarbon evidence for a possible abyssal front near 3 1 km in the glacial equatorial pacific ocean abstract we investigate the radiocarbon ventilation age in deep equatorial pacific sediment cores using the difference in conventional 14c age between coexisting benthic and planktonic foraminifera and integrate those results with similar data from around the north pacific ocean in a reconstruction for the last glaciation 15 to 25 conventional 14c ka most new data from both the equatorial pacific and the emperor seamounts in the northwestern pacific come from maxima in abundance of benthic taxa because this strategy reduces the effect of bioturbation although there remains considerable scatter in the ventilation age estimates on average ventilation ages in the equatorial pacific were significantly greater below 3 2 km 3080 1125 yrs n 15 than in the depth interval 1 9 to 3 0 km 1610 250 yrs n 12 when compared to the average modern seawater c 14 profile for the north pacific the equatorial pacific glacial data suggest an abyssal front located somewhere between 3 0 and 3 2 km modern water depth above that depth the data may indicate slightly better ventilation than today and below that depth glacial equatorial pacific data appear to be as old as last glacial maximum lgm deep water ages reported for the deep southern atlantic this suggests that a glacial reservoir of aged waters extended throughout the circumpolar southern ocean and into the equatorial pacific renewed ventilation of such a large volume of aged and by corollary carbon rich water would help to account for the rise in atmospheric pco2 and the fall in c 14 as the glaciation drew to a close

a three dimensional numerical model for thermohydromechanical deformation with hysteresis in a fractured rock mass abstract a three dimensional finite element solution to the problem of coupled thermohydromechanical deformation groundwater flow and heat transport in deformable fractured porous media is presented in this paper the governing equations are based on biot s consolidation theory for poroelastic materials extended to the non isothermal environment the normal and lateral deformations in joints are simulated by a new joint element the new joint element is based on the bandis barton models and is capable of simulating normal and lateral deformations with dilatancy contractancy and hysteresis due to irrecoverable damages rubblization a three dimensional finite element code model of transport in fractured porous media motif has been developed based on the theoretical framework presented herein verification results with experimental data and analytical solutions are presented in this paper an application example with flow of fluid through a non isothermally deforming joint is also presented results indicate that non isothermal deformation could play a major role in the transport of fluid and water borne substances in fractured rocks

marine radiocarbon evidence for the mechanism of deglacial atmospheric co2 rise we reconstructed the radiocarbon activity of intermediate waters in the eastern north pacific over the past 38 000 years radiocarbon activity paralleled that of the atmosphere except during deglaciation when intermediate water values fell by more than 300 per mil such a large decrease requires a deglacial injection of very old waters from a deep ocean carbon reservoir that was previously well isolated from the atmosphere the timing of intermediate water radiocarbon depletion closely matches that of atmospheric carbon dioxide rise and effectively traces the redistribution of carbon from the deep ocean to the atmosphere during deglaciation

shortcomings of the isolated abyssal reservoir model for deglacial radiocarbon changes in the mid depth indo pacific ocean severely negative 14c anomalies from the mid depth pacific and the arabian sea have been taken as support for the hypothesized deglacial release of a previously isolated extremely 14c deplete deep ocean carbon reservoir we report box model simulations that cast doubt on both the existence of the hypothesized deep reservoir and its ability to explain the mid depth 14c anomalies first the degree of ice age isolation needed to substantially reduce the deep 14c of the deep reservoir causes anoxia and the trapping of alkalinity from caco3 dissolution the latter increasing atmospheric co2 second even with a completely 14c free deep reservoir achieving the mid depth 14c anomalies of observed duration requires ad hoc stifling of aspects of deep circulation to prevent rapid dissipation of the anomalous 14c free carbon to the rest of the ocean and the atmosphere we suggest that the mid depth anomalies do not record basin scale 14c changes but are instead local phenomena

approach to estimating the maximum depth for glacially induced hydraulic jacking in fractured crystalline rock at forsmark sweden hydraulic jacking is a significant dilation of a fracture that occurs when the pore pressure within it exceeds the sum of the fracture s normal stress and tensile strength this phenomenon may occur during a glacial period because of changes in hydraulic and mechanical boundary conditions since hydraulic jacking may alter flow patterns and the transport capacity of the rock mass its possible effects on the long term performance of a nuclear waste repository should be considered we develop an approach to assess glacially induced hydraulic jacking in fractured crystalline rock and establish bounding estimates of the maximum jacking depth for the swedish nuclear fuel and waste management company s skb repository site at forsmark the pore pressure is estimated using mechanically uncoupled two dimensional poroelastic continuum models with hydraulic and mechanical conditions based on skb s reconstruction of the weichselian glaciation at this site 120 0kab p for warm based conditions the water pressure at the ice bed interface is set at 98 of the mechanical load whereas for glacial conditions with extensive proglacial permafrost the corresponding water pressure is set at a lower annual average value we demonstrate that the pore pressure within the uppermost kilometer of rock is mainly governed by the water pressure at the ice bed interface and that the mechanical impact of the ice load on the pore pressure is sufficiently small to be ignored given the current and estimated future stress conditions at forsmark hydraulic jacking is mainly of concern for subhorizontal fractures i e it is sufficient to consider situations when the pore pressure exceeds the vertical stress we conclude that hydraulic jacking at forsmark will be confined to the uppermost 200m of the rock mass

effects of seafloor diagenesis on planktic foraminiferal radiocarbon ages radiocarbon 14c ages obtained from planktic foraminiferal calcite are a mainstay for reconstructing ocean climate change and carbon cycle dynamics of the past 30 k y yet the effects of diagenesis on this vital chronometer are poorly constrained here we address this shortcoming by comparing 14c ages and trace element ratios mg ca mn ca of planktic foraminifera with white opaque shells deemed well preserved by traditional standards to those with exquisitely preserved translucent shells results support a diagenetic mechanism as opaque shells yield 14c ages invariably older and trace element ratios consistently higher than those of translucent shells radiocarbon age offsets are particularly pronounced in mono specific samples taken from stratigraphic horizons proximal to the 18o maximum marking the last glacial maximum lgm and the subsequent deglacial radiocarbon based calendar ages of translucent shells from the two intervals are congruent with the established age ranges for these climate events whereas those of co occurring opaque shells overestimate the lgm and deglacial by 8 15 k y and 14 22 k y respectively these results demonstrate that the use of translucent foraminifera enhances reproducibility and accuracy of 14c ages by minimizing the deleterious effects of diagenesis this study serves as a cautionary tale since white opaque foraminifera are common in pelagic sediments and 14c ages derived from their ostensibly well preserved shells can lead to discrepancies in the timing of quaternary climate events and ocean circulation reconstructions

changing controls on oceanic radiocarbon new insights on shallow to deep ocean exchange and anthropogenic co2 uptake 1 the injection of radiocarbon 14c into the atmosphere by nuclear weapons testing in the 1950s and 1960s has provided a powerful tracer to investigate ocean physical and chemical processes while the oceanic uptake of bomb derived 14c was primarily controlled by air sea exchange in the early decades after the bomb spike we demonstrate that changes in oceanic 14c are now primarily controlled by shallow to deep ocean exchange i e the same mechanism that governs anthropogenic co2 uptake this is a result of accumulated bomb 14c uptake that has rapidly decreased the air sea gradient of 14c c 14c and shifted the main reservoir of bomb 14c from the atmosphere to the upper ocean the air sea 14c gradient reduced further by fossil fuel dilution is now weaker than before weapons testing in most regions oceanic 14c and particularly its temporal change can now be used to study the oceanic uptake of anthropogenic co2 we examine observed changes in oceanic 14c between the woce save 1988 1995 and the clivar 2001 2007 eras and simulations with two ocean general circulation models the community climate system model ccsm and the estimating the circulation and climate of the ocean model ecco observed oceanic 14c and its changes between the 1980s 90s and 2000s indicate that shallow to deep exchange is too efficient in ecco and too sluggish in ccsm these findings suggest that mean global oceanic uptake of anthropogenic co2 between 1990 and 2007 is bounded by the ecco based estimate of 2 3 pg c yr 1 and the ccsm based estimate of 1 7 pg c yr 1

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

reply to comment by christopher talbot on approach to estimating the maximum depth for glacially induced hydraulic jacking in fractured crystalline rock at forsmark sweden as illustrated in figure 2 of our paper and as noted in numerous previous studies by talbot 1990 1999 and others e g chan et al 2005 vidstrand et al 2008 the water pressure at the ice bed interface many kilometers behind the margin of an advancing stationary or retreating ice sheet would be sufficient to jack open fractures at depths of several hundred meters in the region around the ice margin this has raised the question of whether or not hydraulic jacking should count as a potential concern for the nuclear waste repository projected at about 450m depth in forsmark however as explained in our paper for these high pressures to actually be effective in the region around the ice margin unrealistic assumptions regarding the fracture network and the background permeability have to be made the objective of our study and our calculations is to establish more realistic upper bound estimates of the water pressure around the margin and consequently of the maximum jacking depth by taking due account of the actual large scale hydrological conditions in the forsmark region the theoretical ice sheet profile assumed in our models has a significantly steeper slope than corresponding profiles of skb s reference reconstruction of the latest fennoscandian ice sheet its maximum height overestimates the reconstruction maximum height by about 1000mduring advance and by about 500mduring retreat this in combination with worst case assumptions regarding ice retreat speed distance between permafrost melt zone and ice margin and last but not least regarding the extension homogeneity and permeability of the proglacial permafrost is therefore highly likely to have given overestimated water pressures below the margin we are therefore not playing down the maximum depth to which this process hydraulic jacking can reach by making questionable assumptions as talbot 2014 claims the comment made by talbot 2014 regarding seasonal variations appears to be based on a misunderstanding that we are assuming that the supply of overpressured meltwater ceases soon after the first pre existing fracture is jacked open is incorrect although we note that shallow jacking is likely to reduce water pressures at larger depths and conclude that not accounting for this in our study probably has resulted in jacking depth overestimates

radiocarbon profiles of the nw pacific from the lgm and deglaciation evaluating ventilation metrics and the effect of uncertain surface reservoir ages during the last deglaciation the ventilation of the subarctic pacific is hypothesized to have changed dramatically including the rejuvenation of a poorly ventilated abyssal water mass that filled the deep ocean and fluctuations in the strength of north pacific intermediate and deep water formation at millennial timescales foraminiferal radiocarbon reconstructions of past ventilation changes in the pacific are valuable but are hampered by poor carbonate preservation low sediment accumulation rates bias from bioturbation and poorly constrained past surface reservoir age in this study we present paired benthic planktonic radiocarbon measurements from the okhotsk sea and emperor seamounts we take advantage of large contemporaneous peaks in benthic abundances from the last glacial maximum bolling allerod ba and early holocene to produce time slices of radiocarbon from 1 to 4 km water depth we explore the impact of uncertain surface reservoir age and evaluate several approaches to quantifying past ocean radiocarbon distribution using our nw pacific data and a compilation of published data from the north pacific both the calendar age and the absolute value of an ocean radiocarbon estimate depend on the assumed surface reservoir age but for a time slice from a small geographical area with radiocarbon independent stratigraphic correlation between cores the shape of a water column profile is independent of surface reservoir age the nw pacific profiles are similar in shape to the compilation profiles for the entire north pacific which suggests that deglacial surface reservoir age changes across the n pacific did not diverge dramatically across the areas sampled the last glacial maximum lgm profile 2 km spans a wide range of values ranging from values similar to today to lower than today however by the ba the profile has a similar shape to today ultimately local surface reservoir ages end member water mass composition and mixing ratios must each be constrained before a radiocarbon activity reconstruction can be used to confidently infer ventilation changes

resolving the cause of large differences between deglacial benthic foraminifera radiocarbon measurements in santa barbara basin 1 to better understand the deglacial upwelling pattern in the east pacific we have made radiocarbon 14c measurements on benthic foraminifera and macrofauna from a 3 5 m long interval in odp core 893a from santa barbara basin california representing early deglaciation this work serves to investigate the source of apparent disagreement between radiocarbon data sets from leibnitz laboratory kiel university kiel and carbon center for accelerator mass spectrometry lawrence livermore national laboratory llnl these data sets are based on measurements of mixed benthic and mixed planktonic foraminifera interlaboratory 14c results are similar for the planktonic foraminiferal analyses however kiel measurements on mixed benthic foraminifera are much older than mixed benthic measurements from equivalent depths measured at llnl our new results show distinct 14c differences between taxa with pyrgo sp giving ages consistently older than kiel measurements on mixed benthic taxa while ages for nonionellina sp buliminella sp uvigerina sp and benthic macrofauna were much younger even younger than the llnl mixed benthic data the new data supports benthic planktonic age offsets of no more than 300 years indicating that bottom waters within the basin remained significantly younger during early deglaciation than some previous results have suggested and are thus consistent with sedimentary and faunal evidence for well oxygenated conditions

radiocarbon variability in the western north atlantic during the last deglaciation we present a detailed history of glacial to holocene radiocarbon in the deep western north atlantic from deep sea corals and paired benthic planktonic foraminifera the deglaciation is marked by switches between radiocarbon enriched and depleted waters leading to large radiocarbon gradients in the water column these changes played an important role in modulating atmospheric radiocarbon the deep ocean record supports the notion of a bipolar seesaw with increased northern source deep water formation linked to northern hemisphere warming and the reverse in contrast the more frequent radiocarbon variations in the intermediate deep ocean are associated with roughly synchronous changes at the poles

reduced deep ocean ventilation in the southern pacific ocean during the last glaciation persisted into the deglaciation abstract marine radiocarbon 14c is widely used to trace ocean circulation and the 14c levels of interior ocean water masses can provide insight into atmosphere ocean exchange of co2 the since the last glaciation using tephras as stratigraphic tie points with which to estimate past atmospheric 14c we reconstructed a series of deep radiocarbon ages for several time slices from the last glaciation through the deglaciation and holocene in the southwestern pacific glacial ventilation ages were much greater in magnitude than modern and had a strong mid depth 14c minimum centered on 2500 m glacial radiocarbon ages of intermediate depth waters 600 1200 m were 800 to 1600 14c years about twice modern and persisted through the early deglaciation notably in the glaciation shallower depths were significantly more enriched in 14c than waters between 1600 and 3800 m which were 4000 to 6200 14c years or about 3 5 times older than modern abyssal waters deeper than 4000 m were also more 14c rich than the overlying deep water with radiocarbon ages of 1800 2300 14c years this was similar to modern values in the early deglaciation 14c depleted waters were flushed from shallower depths first and replaced with progressively younger waters such that by 18 ka the deep to intermediate age difference was reduced by half and by 14 ka a modern type 14c profile for deep ocean water masses was in place our results 1 confirm a deep 14c depleted water mass during the lgm and early deglaciation and 2 constrain the extent of this old water in the southern pacific as between 1600 m and 3800 m the availability of atmospheric ages from tephras reveals that the presence of older surface reservoir ages in the glaciation caused the estimation of ventilation ages from simple benthic planktonic offsets to significantly underestimate the depletion of 14c in deep waters this may have had a role in masking the large change in reservoir ages since the glaciation when using benthic planktonic reservoir age estimates

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

synchronous centennial abrupt events in the ocean and atmosphere during the last deglaciation antarctic ice core data reveal that the atmosphere experienced abrupt centennial increases in co2 concentration during the last deglaciation 18 thousand to 11 thousand years ago establishing the role of ocean circulation in these changes requires high resolution accurately dated marine records here we report radiocarbon data from uranium thorium dated deep sea corals in the equatorial atlantic and drake passage over the past 25 000 years two major deglacial radiocarbon shifts occurred in phase with centennial atmospheric co2 rises at 14 8 thousand and 11 7 thousand years ago we interpret these radiocarbon enriched signals to represent two short lived less than 500 years overshoot events with atlantic meridional overturning stronger than that of the modern era these results provide compelling evidence for a close coupling of ocean circulation and centennial climate events during the last deglaciation