influence of surface topography on the critical carbon dioxide level required for the formation of a modern snowball earth abstractthe influence of continental topography on the initiation of a global glaciation i e snowball earth is studied with both a fully coupled atmosphere ocean general circulation model aogc

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

is there a conflict between the neoproterozoic glacial deposits and the snowball earth interpretation an improved understanding with numerical modeling the behavior of the terrestrial glacial regime during the neoproterozoic glaciations is still a matter of debate some papers claim that the glacial sequences cannot be explained with the snowball earth scenario indeed the near shutdown of the hydrological cycle simulated by climatic models once the earth is entirely glaciated has been put in contrast with the need for active wet based continental ice sheets to produce the observed thick glacial deposits a climate ice sheet model is applied to the older extreme neoproterozoic glaciation around 750 ma with a realistic paleogeographic reconstruction of rodinia our climate model shows that a small quantity of precipitation remains once the ocean is completely ice covered thanks to sublimation processes over the sea ice at low latitudes acting as a water vapor source after 10 ka of the ice sheet model the ice volume in the tropics is small and confined as separate ice caps on coastal areas where water vapor condenses however after 180 ka large ice sheets can extend over most of the supercontinent rodinia several areas of basal melting appear while ice sheets reach their ice volume equilibrium state at 400 ka they are located either under the two single domed ice sheets covering the antarctica and the laurentia cratons or near the ice sheet margins where fast flow occurs only the isolated and high latitude cratons stay cold based finally among the simulated ice sheets most have a dynamic behavior in good agreement with the needs inferred by the preserved thick formations of diamictite and share the features of the antarctica present day ice sheet therefore our conclusion is that a global glaciation would not have hindered the formation of the typical glacial structures seen everywhere in the rock record of neoproterozoic times

holocene paleoseismicity temporal clustering and probabilities of future large m 7 earthquakes on the wasatch fault zone utah the chronology of m 7 paleoearthquakes on the central five segments of the wasatch fault zone wfz is one of the best dated in the world and contains 16 earthquakes in the past 5600 years with an average repeat time of 350 years repeat times for individual segments vary by a factor of 2 and range from about 1200 to 2600 years four of the central five segments ruptured between 620 30 and 1230 60 calendar years b p the remaining segment brigham city segment has not ruptured in the past 2120 100 years comparison of the wfz space time diagram of paleoearthquakes with synthetic paleoseismic histories indicates that the observed temporal clusters and gaps have about an equal probability depending on model assumptions of reflecting random coincidence as opposed to intersegment contagion regional seismicity suggests that for exposure times of 50 and 100 years the probability for an earthquake of m 7 anywhere within the wasatch front region based on a poisson model is 0 16 and 0 30 respectively a fault specific wfz model predicts 50 and 100 year probabilities for an m 7 earthquake on the wfz itself based on a poisson model as 0 13 and 0 25 respectively in contrast segment specific earthquake probabilities that assume quasi periodic recurrence behavior on the weber provo and nephi segments are less 0 01 0 07 in 100 years than the regional or fault specific estimates 0 25 0 30 in 100 years due to the short elapsed times compared to average recurrence intervals on those segments the brigham city and salt lake city segments however have time dependent probabilities that approach or exceed the regional and fault specific probabilities for the salt lake city segment these elevated probabilities are due to the elapsed time being approximately equal to the average late holocene recurrence time for the brigham city segment the elapsed time is significantly longer than the segment specific late holocene recurrence time

faunal turnover and changing oceanography late palaeozoic warm to cool water carbonates sverdrup basin canadian arctic archipelago abstract carbonate sedimentary rocks in the fosheim hamilton sub basin at the eastern end of the sverdrup basin contain a particularly sensitive record of changing palaeoceanography and faunal turnover during the northward movement of pangaea through the late palaeozoic carboniferous and earliest permian inner ramp carbonates are a photozoan association of colonial corals fusulinids algae and ooids with sparse heterozoan elements crinoids brachiopods and bryozoans based on modern analogues these biotic components reflect warm water oligotrophic marine environments contemporaneous mid ramp and basin biotas are dominated by a heterozoan fauna solitary corals crinoids bryozoans and brachiopods that grew in cooler deeper waters that may have been beneath a thermocline initial cooling began in the latest sakmarian with an influx of cool deep water and climatic deterioration allowing cool and warm waters to mix disrupting the thermocline and producing a sub tropical marine biota whose remains were reworked by storms and re deposited as tempestites faunas are heterozoan crinoids bryozoans brachiopods and sponges with photozoan elements colonial corals and symbiont bearing fusulinids prominent only in inner ramp facies by late artinskian these photozoan components are only present in shallowest basin margin environments artinskian subtropical waters contained somewhat elevated trophic resources that together with mixing of photozoan and heterozoan elements in the subtropical inner ramp produced the greatest faunal diversity seen in the sverdrup basin the biota was completely boreal in nature and warm shallow waters with a warm refuge biota were now supplemented by cool waters derived from the panthalassa ocean profound change took place in the kungurian coincident with localised uplift during the melville disturbance and increased siliciclastic input neritic storm dominated sediments are wholly heterozoan brachiopods bryozoans crinoids and sponges with no remaining photozoan elements nutrient levels are elevated but not eutrophic as indicated by phosphate and glauconite extensive bioerosion numerous infaunal foraminifers and an impressive and diverse shelly biota that during times of high siliciclastic input was replaced by a profuse zoophycos infauna brachiopod and bryozoan faunas are distinctly boreal continued cooling relatively high nutrients as indicated by abundant glauconite and phosphate and decreased siliciclastic input eventually resulted in an abundant heterozoan biota brachiopods bryozoans crinoids and sponges with local gigantism but reduced brachiopod and bryozoan diversity these middle permian rocks may be the coolest water deposits in the sverdrup basin the faunas are still part of a boreal arctic province with strong ties to cool water faunas of uralian basin the succession ends with late permian biosiliceous spiculitic cherts containing accessory heterozoan components brachiopods bryozoans and few crinoids these sediments in part coeval with evaporites and terrestrial red beds on the eastern european platform are interpreted to reflect a combination of cool waters elevated nutrients and mid latitude storminess

lake sediments record cycles of sediment flux driven by large earthquakes on the alpine fault new zealand large earthquakes in mountain regions commonly trigger extensive landsliding and are important drivers of erosion but the contribution of this landsliding to long term erosion rates and seismic hazard remains poorly understood here we show that lake sediments record postseismic landscape response as a sequence of turbidites that can be used to quantify erosion related to large moment magnitude m w 7 6 earthquakes on the alpine fault new zealand alpine fault earthquakes caused a threefold increase in sediment flux over the 50 yr duration of each postseismic landscape response this represents considerable delayed hazard following earthquake induced strong ground motion earthquakes were responsible for 27 of the sediment flux from the lake catchment over the past 1100 yr leading us to conclude that alpine fault earthquakes are one of the most important drivers of erosion in the range front of the southern alps

mudball surface dust and snowball earth deglaciation 1 recent modeling results have raised doubts about the ability to deglaciate from a global glaciation at atmospheric carbon dioxide levels that are realistic for a neoproterozoic snowball earth here we argue that over the lifetime of a snowball event ice dynamics should lead to the development of a layer of continental and volcanic dust at the ice surface in the tropics that would significantly lower the tropical surface albedo and encourage deglaciation this idea leads to the prediction that clay drapes found on top of neoproterozoic glaciations should be thicker in tropical than extratropical regions we test this idea by running the foam general circulation model gcm with an added tropical dust layer of different sizes and albedos and find that the tropical dust layer causes snowball deglaciation at pco2 0 01 0 1 bar in a reasonable regime of these parameters we find similar though more nuanced results from a limited number of test cases using national center for atmospheric research s cam gcm

history and dynamics of the greater yellowstone glacial system during the last two glaciations abstract the greater yellowstone glacial system gygs covered about 20 000 km2 at its maximum pleistocene extent the initiation culmination and ultimate decay of the gygs involved complex interactions between several coalescent ice masses flowing from glacial source areas adjoining and including the yellowstone plateau here we present an updated review of the history and dynamics of the gygs during the penultimate bull lake and last pinedale glaciations drawing upon an integration of glacial geologic mapping with 130 cosmogenic 10be and 3he exposure ages bull lake glacial deposits in greater yellowstone are dated to ca 150 140 ka and correlate with marine isotope stage 6 the bull lake glaciation extended well beyond the pinedale along the southern and western gygs margins but pinedale glaciers overrode bull lake ice limits on the north and east sides the northeastward shift of the center of ice mass from bull lake to pinedale time may be explained by uplift on the leading edge of the yellowstone hotspot and subsidence on the trailing margin in early pinedale time 22 18 ka ice buildup culminated in the high terrain of the beartooth uplift and high absaroka range glaciers from these source regions flowed onto the northeastern margin of the yellowstone plateau and advanced to terminal moraines beyond clarks fork canyon and in jackson hole by middle pinedale time 18 16 ka the yellowstone plateau ice cap surface had risen above the equilibrium line altitude stimulating orographic glacial buildup nourished by storms funneled eastward through the snake river plain the plateau ice cap eventually thickened to 1000 m and joined glaciers from the beartooth uplift and gallatin range to form the northern yellowstone outlet glacier terrain east and downwind of the ice cap crest was placed in a precipitation shadow resulting in glacial recession in these regions during the late pinedale 16 13 ka the plateau ice cap prograded southwestward toward the direction of moisture supply leading to advances along the southern and western margins of the gygs northern sectors of the plateau ice cap were nearly stagnant at this time the yellowstone region experienced widespread deglaciation ca 15 14 ka in response to warming climate unloading of the 1 km thick plateau ice cap and consequent release of pressure on the magmatic system beneath yellowstone was not accompanied by volcanism indicating that the magma chamber was not primed to erupt via decompression during the last deglaciation

migration of air bubbles in ice under a temperature gradient with application to snowball earth 1 to help characterize the albedo of sea glaciers on snowball earth a study of the migration rates of air bubbles in freshwater ice under a temperature gradient was carried out in the laboratory the migration rates of air bubbles in both natural glacier ice and laboratory grown ice were measured for temperatures between 36 c and 4 c and for bubble diameters of 23 2000 m the glacier ice was sampled from a depth near close off 74 m in the jems2 ice core from summit greenland migration rates were measured by positioning thick sections of ice on a temperature gradient stage mounted on a microscope inside a freezer laboratory the maximum and minimum migration rates were 5 45 m h 1 k cm 1 1 at 4 c and 0 03 m h 1 k cm 1 1 at 36 c besides a strong dependence on temperature migration rates were found to be proportional to bubble size we think that this is due to the internal air pressure within the bubbles which may correlate with time since close off and therefore with bubble size migration rates show no significant dependence on bubble shape estimates of migration rates computed as a function of bubble depth within sea glaciers indicate that the rates would be low relative to the predicted sublimation rates such that the ice surface would not lose its air bubbles to net downward migration it is therefore unlikely that air bubble migration could outrun the advancing sublimation front transforming glacial ice to a nearly bubble free ice type analogous to low albedo marine ice

comparison of geodetic and geologic data from the wasatch region utah and implications for the spectral character of earth deformation at periods of 10 to 10 million years the wasatch fault and adjacent fault zones provide an opportunity to compare present day deformation rate estimates obtained from space geodesy with geologic displacement rates over at least four temporal windows ranging from the last millennium up to 10 myr the three easternmost gps sites of the basin and range geodetic network bargen at this latitude define a 130 km wide region spanning three major normal faults extending east west at a total rate of 2 7 0 4 mm yr with an average regional strain rate estimated to be 21 4 nstrain yr about twice the basin and range average on the wasatch fault the vertical component of the geologic displacement rate is 1 7 0 5 mm yr since 6 ka 0 6 mm yr since 130 ka and 0 5 0 7 mm yr since 10 ma however it appears likely that at the longest timescale rates slowed over time from 1 0 to 1 4 mm yr between 10 and 6 ma to 0 2 to 0 3 mm yr since 6 ma the cumulative vertical displacement record across all three faults also shows time variable strain release ranging from 2 to 4 mm yr since 10 ka to 1 mm yr averaged over the past 130 kyr conventional earthquake recurrence models reid type behavior would require an accordingly large variation in strain accumulation or loading rate on a 10 kyr timescale for which there appears to be no obvious geophysical explanation alternatively seismic strain release given a wide range of plausible constitutive behaviors for frictional sliding may be clustered on the 10 kyr timescale resulting in the high holocene rates with comparatively low uniform strain accumulation rates on the 100 kyr timescale wallace type behavior the latter alternative combined with observations at the million year timescale and the likelihood of a significant contribution of postseismic transients implies maxima of spectral amplitude in the velocity field at periods of 10 myr variations in tectonic loading 10 kyr clustered strain release and of 100 years postseismic transients if so measurements of strain accumulation and strain release may be strongly timescale dependent for any given fault system

seismicity and earthquake hazard analysis of the teton yellowstone region wyoming abstract earthquakes of the teton yellowstone region represent a high level of seismicity in the intermountain west u s a that is associated with intraplate extension associated with the yellowstone hotspot including the nearby teton and hebgen lake faults the seismicity and the occurrence of high slip rate late quaternary faults in this region leads to a high level of seismic hazard that was evaluated using new earthquake catalogues determined from three dimensional 3 d seismic velocity models followed by the estimation of the probabilistic seismic hazard incorporating fault slip and background earthquake occurrence rates the 3 d p wave velocity structure of the teton region was determined using local earthquake data from the jackson lake seismic network that operated from 1986 2002 an earthquake catalog was then developed for 1986 2002 for the teton region using relocated hypocenters the resulting data revealed a seismically quiescent teton fault at m l local magnitude 3 with diffuse seismicity in the southern jackson hole valley area but notable seismicity eastward into the gros ventre range relocated yellowstone earthquakes determined by the same methods highlight a dominant e w zone of seismicity that extends from the aftershock area of the 1959 m s surface wave magnitude 7 5 hebgen lake montana earthquake along the north side of the 0 64 ma yellowstone caldera earthquakes are less frequent and shallow beneath the yellowstone caldera and notably occur along northward trending zones of activity sub parallel to the post caldera volcanic vents stress field orientations derived from inversion of focal mechanism data reveal dominant e w extension across the teton fault with a ne sw extension along the northern teton fault area and southern yellowstone the minimum stress axes directions then rotate to e w extension across the yellowstone caldera to n s extension northwest of the caldera and along the hebgen lake fault zone the combination of accurate hypocenters unified magnitudes and seismotectonic analysis helped refine the characterization of the background seismicity that was used as input into a probabilistic seismic hazards analysis our results reveals the highest seismic hazard is associated with the teton fault because of its high slip rate of approximately 1 3 mm yr compared to the highest rate of 1 4 mm yr in southern yellowstone on the mt sheridan fault this study demonstrates that the teton yellowstone area is among the regions highest seismic hazard in the western u s

robust elements of snowball earth atmospheric circulation and oases for life 1 atmospheric circulation in a snowball earth is critical for determining cloud behavior heat export from the tropics regions of bare ice and sea glacier flow these processes strongly affect snowball earth deglaciation and the ability of oases to support photosynthetic marine life throughout a snowball earth here we establish robust aspects of the snowball earth atmospheric circulation by running six general circulation models with consistent snowball earth boundary conditions the models produce qualitatively similar patterns of atmospheric circulation and precipitation minus evaporation the strength of the snowball hadley circulation is roughly double modern at low co2 and greatly increases as co2 is increased we force a 1 d axisymmetric sea glacier model with general circulation model gcm output and show that neglecting zonal asymmetry sea glaciers would limit ice thickness variations to o 10 global mean ice thickness in the 1 d sea glacier model is well approximated by a 0 d ice thickness model with global mean surface temperature as the upper boundary condition we then show that a thin ice snowball solution is possible in the axysymmetric sea glacier model when forced by output from all the gcms if we use ice optical properties that favor the thin ice solution finally we examine snowball oases for life using analytical models forced by the gcm output and find that conditions become more favorable for oases as the snowball warms so that the most critical time for the survival of life would be near the beginning of a snowball earth episode

snowball earth asynchronous coupling of sea glacier flow with a global climate model during snowball earth episodes of the neoproterozoic and paleoproterozoic limited amounts of tropical open ocean jormungand or tropical ocean with thin ice cover would help to explain 1 vigorous glacial activity in low latitudes 2 survival of photosynthetic life and 3 deglacial recovery without excessive buildup of atmospheric co2 some previous models have suggested that tropical open ocean or thin ice cover is possible however its viability in the presence of kilometer thick sea glaciers flowing from higher latitudes has not been demonstrated conclusively here we describe a new method of asynchronously coupling a zonal sea glacier model with a 3 d global climate model and apply it to snowball earth equilibrium curves of ice line vs co2 are mapped out as well as their dependence on ocean heat transport efficiency sea glacier flow and other model parameters no climate states with limited tropical open ocean or thin ice are found in any of our model runs including those with sea glaciers if this result is correct then other refugia such as cryoconite pans would have been required for life to survive however the reasons for the differences between our results and others should first be resolved it is suggested that small scale convective dynamics affecting fractional snow cover in low latitudes may be a critical factor accounting for these differences

a 12 000 year record of vertical deformation across the yellowstone caldera margin the shorelines of yellowstone lake the 600 ka yellowstone caldera exhibits several signs of unrest the most evident of which is historic ground deformation including both uplift and subsidence we document deformation in the area of the southeastern caldera across 12 000 years using the postglacial shoreline terraces of yellowstone lake raised shoreline elevations were interpreted from 230 leveling profiles surveyed across flights of terraces with an accuracy of 0 5 m of about 11 recognizable terraces the five most continuous raised shorelines were correlated around the lake basin to reveal deformation patterns shoreline ages are based on minimum and maximum limiting radiocarbon and obsidian hydration dates each terrace is interpreted as representing an episode of uplift 1 kyr 1 of the caldera interior and subsequent subsidence with little net volume change this cyclic behavior may result from magma emplacement and subsequent withdrawal or cooling and crystallization and or episodic trapping and release of magmatic fluids evolved during cooling and crystallization in a self sealing reservoir as hypothesized by dzurisin et al 1990 early postglacial shoreline deformation reveals substantial intracaldera subsidence possibly reflecting cooling and loss of trapped hydrothermal fluids extension along north south trending normal faults and related structures is also apparent in early to middle postglacial deformation both inside and outside of the caldera margin including downwarping and local faulting of hot weak intracaldera crust net deformation over the past 3 kyr has been dominantly up within the caldera interior and slightly down along the caldera rim relative to the extracaldera region this uplift is roughly similar to the historic pattern and may largely represent the effects of the most recent inflation episode subtraction of the total estimated magnitude of inflation in this episode suggests that the overall trend of postglacial deformation has been subsidence the cause of this trend is undetermined but is most likely related to the effects of regional extension and long term cooling within the yellowstone caldera

lacustrine turbidites produced by surficial slope sediment remobilization a mechanism for continuous and sensitive turbidite paleoseismic records turbidite records along ocean margins and in lake basins are increasingly used as paleoseismic proxies however the slope remobilization processes that formed the earthquake related turbidity currents are poorly understood and therefore it is difficult to assess the consistency of turbidite paleoseismic records we analyzed the sedimentary imprint of the giant ad 1960 mw 9 5 chile earthquake in four south central chilean lakes mass transport deposits and turbidites were compared by interpreting reflection seismic profiles sedimentary facies volume balances and proxies for turbidite composition i e grain size radionuclides sediment color organic matter sediment lightness was used as a proxy for organic matter content comparison of lightness of turbidites and the underlying sediments shows that earthquake triggered turbidites in the four lakes result from remobilization of a thin veneer on average about 5 cm of slope sediments and do not result from disintegration of subaquatic landslides statistical analysis of 34 turbidites in a new 5200 year sedimentary record does not show any correlation between inter event time and turbidite thickness and thus volume this means that inter event slope recharging is not a dominant factor governing turbidite recurrence and that initiation of turbidity currents by remobilization of surficial sediments is different to slope failure related to subaquatic landslides we conclude that surficial slope sediment remobilization forms a valid mechanism that explains why turbidite paleoseismic records can be of excellent continuity and high sensitivity moreover based on correlations between seismic intensity turbidite volume and stratigraphic remobilization depth we propose that surficial slope sediment remobilization allows for turbidite records containing information about paleo earthquake intensity

postglacial slip rate increase on the teton normal fault northern basin and range province caused by melting of the yellowstone ice cap and deglaciation of the teton range along the eastern front of the teton range wyoming prominent fault scarps offset pinedale deposits by up to 30 m and document that multiple earthquakes ruptured the range bounding teton normal fault after the last glacial period paleoseismological data suggest that 70 of the postglacial slip on the southern teton fault accumulated during or shortly after deglaciation before 8 ka here we use a three dimensional fi nite element model to show that melting of the yellowstone ice cap and the valley glaciers in the teton range may have caused the postglacial slip rate increase on the teton fault during deglaciation slip on our model fault accelerates by a factor of 6 with respect to the long term rate our model further shows that the impact of the melting yellowstone ice cap on fault slip increases along strike of the fault from south to north and is everywhere larger than the effect of the former valley glaciers in the teton range the results demonstrate that postglacial slip on faults in glaciated regions may not have been uniform through time rather a signifi cant fraction of slip may have accumulated within a few thousand years after the last glaciation we hypothesize that the rebound caused by the yellowstone ice cap has also triggered clusters of earthquakes on other normal faults in the surrounding basin and range province

carbon isotopic composition of neoproterozoic glacial carbonates as a test of paleoceanographic models for snowball earth phenomena consistently positive carbon isotopic values were obtained from in situ peloids ooids and stromatolitic carbonate within neoproterozoic glacial successions in northern namibia central australia and the north american cordillera because positive values continue upward into the immediately overlying postglacial cap carbonates the negative isotopic excursions widely observed in those carbonate rocks require an explanation that involves a short term perturbation of the global carbon cycle during deglaciation the data do not support the ecological consequences of complete coverage of the glacial ocean with sea ice as predicted in the 1998 snowball earth hypothesis of p f hoffman et al in the snowball earth hypothesis the postglacial cap carbonates and associated 5 negative carbon isotopic excursions represent the physical record of co2 transfer from the high p co2 snowball atmosphere 0 12 bar to the sedimentary reservoir via silicate weathering in the snowball aftermath stratigraphic timing constraints on cap carbonates imply weathering rates of 1000 times preglacial levels to be consistent with the hypothesis the absence of sr isotopic variation between glacial and postglacial deposits and calculations of maximum weathering rates do not support a post snowball weathering event as the origin for cap carbonates and associated isotopic excursions

late quaternary lacustrine paleo seismic archives in north western alps examples of earthquake origin assessment of sedimentary disturbances abstract the late quaternary sedimentary fills of several lakes of the north western alps are revealed to be possible paleo seismological archives in a moderately active seismo tectonic region the strongest historically reported events can be correlated with specific layers whose textures result from different processes i mass failures of sub aqueous slope deposits especially delta foresets evolving into hyperpycnal currents influenced by seiche effects and or multiple reflections on lake basin slopes ii in situ liquefaction and flowage and iii micro fracturing based on identification of the sedimentary signature of a well documented historical earthquake the paleoseismic interpretation can be extrapolated back to 16 000 yrs bp with a reconstruction of a time series and textural identification of slope failure related turbidites the most frequent earthquake signature the obtained time series are compatible with historical seismicity in terms of recurrence interval

contributions and unrealized potential contributions of cosmogenic nuclide exposure dating to glacier chronology 1990 2010 abstract this paper reviews the application of cosmogenic nuclide exposure dating to glacier chronology exposure dating of glacial landforms has made an outsize impact on this field because the technique filled an obvious need that had already been recognized by glacial geologists by now hundreds of studies have used cosmogenic nuclide exposure dating to date glacial deposits and in fact it is rare to find a study of glacial geology or glacier chronology or any paleoclimate synthesis that makes use of such studies that does not involve exposure dating these developments have resulted in major contributions to glacier chronology and paleoclimate in particular i reconstructing antarctic ice sheet change ii establishing the chronology of late pleistocene and holocene glacier change in mountain regions where it was previously unknown iii establishing the broad chronological outlines of mountain glaciations prior to the last glacial maximum and iv gaining insight into subglacial erosional processes through the observation that many glaciated surfaces preserve cosmogenic nuclide inventories from long past ice free periods as well as the present one an important potential future contribution will be the application of the large data set of exposure dated glacier chronologies to better understand global and regional climate dynamics during lateglacial and holocene millennial scale climate changes however this contribution cannot be realized without significant progress in two areas i understanding and accounting for geologic processes that cause apparent exposure ages on glacial landforms to differ from the true age of the landform and ii minimizing systematic uncertainties in exposure ages that stem from cosmogenic nuclide production rate estimates and scaling schemes at present there exists an enormous data set of exposure ages on glacial deposits but these data cannot be used to their full potential in paleoclimate syntheses due to an inadequate understanding of geologic scatter and production rate uncertainties the intent of this paper is to highlight this situation and suggest some strategies for realizing this potential

slip rate variations on normal faults during glacial interglacial changes in surface loads geologic and palaeoseismological data document a marked increase in the slip rates of the wasatch fault and three adjacent normal faults in the basin and range province during the late pleistocene early holocene epochs the cause of this synchronous acceleration of fault slip and the subsequent clustering of earthquakes during the holocene has remained enigmatic although it has been suggested that the coincidence between the acceleration of slip and the shrinkage of lake bonneville after the last glacial maximum may indicate a causal relationship here we use finite element models of a discrete normal fault within a rheologically layered lithosphere to evaluate the relative importance of two competing processes that affect fault slip postglacial unloading the removal of mass which decreases the slip rate and lithospheric rebound which promotes faster slip we show that lithospheric rebound caused by regression of lake bonneville and deglaciation of adjacent mountain ranges provides a feasible mechanism for the high holocene rates of faulting in the wasatch region our analysis implies that climate controlled changes in loads applied to earth s surface may exert a fundamental control on the slip history of individual normal faults

snowball earth a thin ice solution with flowing sea glaciers 1 the late neoproterozoic era 600 800 myr ago was marked by at least two intervals of widespread cold that left glacial deposits at low paleolatitudes both snowball solutions with global ice cover and slushball solutions with ice free tropical oceans have been proposed to explain the paleomagnetic data the snowball model is best able to explain the auxiliary geological evidence particularly the existence of cap carbonates but it implies drastic survival pressure on the photosynthetic biota if the ice cover was everywhere thick enough to prevent sunlight from reaching the underlying ocean a thin ice solution that avoids this problem has been proposed but is thought to be inconsistent with realistic optical properties of sea ice and with the equatorward flow of sea glaciers here we use a coupled energy balance climate sea glacier model to argue that these apparent difficulties can be overcome and that thin tropical ice may have prevailed during these remarkable glacial episodes we also suggest that 1 some processes beyond the scope of zonal mean energy balance models may significantly affect the solutions and 2 thin ice could have prevailed on low latitude seas or large lakes protected from large scale sea glacier flow by surrounding land even if most of the earth was in a hard snowball state

fault segmentation new concepts from the wasatch fault zone utah usa the question of whether structural segment boundaries along multisegment normal faults such as the wasatch fault zone wfz act as persistent barriers to rupture is critical to seismic hazard analyses we synthesized late holocene paleoseismic data from 20 trench sites along the central wfz to evaluate earthquake rupture length and fault segmentation for the youngest 3 ka and best constrained earthquakes differences in earthquake timing across prominent primary segment boundaries especially for the most recent earthquakes on the north central wfz are consistent with segment controlled ruptures however broadly constrained earthquake times dissimilar event times along the segments the presence of smaller scale subsegment boundaries and areas of complex faulting permit partial segment and multisegment e g spillover ruptures that are shorter 20 40 km or longer 60 100 km than the primary segment lengths 35 59 km we report a segmented wfz model that includes 24 earthquakes since 7 ka and yields mean estimates of recurrence 1 1 1 3 kyr and vertical slip rate 1 3 2 0 mm yr for the segments however additional rupture scenarios that include segment boundary spatial uncertainties floating earthquakes and multisegment ruptures are necessary to fully address epistemic uncertainties in rupture length we compare the central wfz to paleoseismic and historical surface ruptures in the basin and range province and central italian apennines and conclude that displacement profiles have limited value for assessing the persistence of segment boundaries but can aid in interpreting prehistoric spillover ruptures our comparison also suggests that the probabilities of shorter and longer ruptures on the wfz need to be investigated

comment on snowball earth a thin ice solution with flowing sea glaciers by david pollard and james f kasting 1 pollard and kasting 2005 hereinafter referred to as pk have coupled an energy balance climate model to an ice shelf flow model to investigate the snowball earth episodes of the neoproterozoic 600 800 million years ago when the ocean apparently froze all the way to the equator hoffman and schrag 2002 pk s particular concern was to investigate the possibility that over a wide equatorial band where sublimation exceeded snowfall the bare ice may have been thin enough to permit transmission of sunlight to the water below providing an extensive refugium for the photosynthetic eukaryotes that survived the snowball events this possibility was first proposed by mckay 2000 whose model of radiative transfer and heat conduction predicted tropical ice only a few meters thick for ice albedo up to 0 7 under assumed conditions of sunlight and temperature at the snowball equator however when spectral resolution was incorporated into the radiative transfer model warren et al 2002 the ice albedo had to be reduced below 0 4 to obtain the thin ice solution under otherwise identical conditions it seemed unlikely that such dark sea ice could avoid melting under the equatorial sun but even if it could avoid melting the thin ice would risk being crushed by the inflow of kilometer thick sea glaciers from higher latitudes goodman and pierrehumbert 2003 to further investigate the feasibility of tropical thin ice it was therefore necessary to couple a climate model to models of sea ice thermodynamics and sea glacier flow this is what pk have done surprisingly they conclude that thin ice 3 m thick may have prevailed in a 20 degree latitude band centered on the equator we argue here that this conclusion is too optimistic because pk s thin ice solution apparently required that several controlling variables be set outside their measured ranges the albedo of cold glacier ice the depth of transition from snow to ice and the thermal conductivity of ice we then raise the more general question of how wide is the thin ice domain in the parameter space of model variables 2 choices of model variables that favor thin ice 2 1 albedo of cold glacier ice 2 as sea glaciers flowed equatorward into the tropical region of net sublimation their surface snow and subsurface firn would sublimate away exposing bare glacier ice to the atmosphere and solar radiation this ice would be freshwater meteoric ice which originated from compression of snow so it would contain numerous bubbles giving a high albedo the albedo of cold nonmelting glacier ice exposed by sublimation antarctic blue ice has been measured as 0 55 0 65 in four experiments in the atlantic sector of antarctica bintanja and van den broeke 1995 bintanja et al 1997 liston et al 1999 reijmer et al 2001 0 63 in the transantarctic mountains warren et al 2002 and 0 66 near the coast of east antarctica weller 1968 weller s blue ice albedo is often quoted as 0 69 e g weller 1980 king and turner 1997 but that is an average value which included a few times with patchy snow cover on the ice not all glacier ice is bubbly under several hundred meters of ice thickness the pressure becomes so great that each air bubble dissolves in the ice to form a clathrate crystal and the ice becomes relatively clear price 1995 however when this ice becomes depressurized as its cover sublimates away as in the antarctic blue ice areas where the albedos were measured the bubbles reform lipenkov 2000 so that the albedo of 0 55 0 66 is observed at the surface 3 in contrast to glacier ice which forms by compression of snow sea ice forms by freezing of liquid water in their model pk tried two values of scattering coefficient each of which they applied uniformly to both sea ice and glacier ice with albedo 0 47 a reasonable value for meter thick snowfree sea ice brandt et al 2005 figure 1 the sea glaciers terminated at 9 degrees latitude leaving an equatorial strip of thin ice but with albedo 0 64 i e within the measured range for glacier ice the sea glaciers advanced to the equator with a thickness of 1 km to add realism to the model it would be good to assign different values of scattering coefficient to these two very different types of ice

a complex microbiota from snowball earth times microfossils from the neoproterozoic kingston peak formation death valley usa a thin carbonate unit associated with a sturtian age 750 700 million years ago glaciogenic diamictite of the neoproterozoic kingston peak formation eastern california contains microfossil evidence of a once thriving prokaryotic and eukaryotic microbial community preserved in chert and carbonate stratiform stromatolites oncoids and rare columnar stromatolites also occur the microbial fossils which include putative autotrophic and heterotrophic eukaryotes are similar to those found in chert in the underlying preglacial units they indicate that microbial life adapted to shallow water carbonate environments did not suffer the significant extinction postulated for this phase of low latitude glaciation and that trophic complexity survived through snowball earth times

growth and demise of permian biogenic chert along northwest pangea evidence for end permian collapse of thermohaline circulation abstract the permian chert event pce was a 30 ma long episode of unusual chert accumulation along the northwest margin of pangea and possibly worldwide the onset of the pce occurred at about the sakmarian artinskian boundary in the sverdrup basin canadian arctic where it coincides with a maximum flooding event the ending of high frequency high amplitude shelf cyclicity the onset of massive biogenic chert deposition in deep water distal areas and a long term shift from warm to cool water carbonate sedimentation in shallow water proximal areas a similar and coeval shift is observed from the barents sea to the northwestern usa a landward and southward expansion of silica factories occurred during the middle and late permian at which time warm water carbonate producers disappeared completely from the northwest margin of pangea biotically impoverished and increasingly narrow cold water carbonate factories characterised by non cemented bioclasts of sponges bryozoans echinoderms and brachiopods were then progressively replaced by silica factories by late permian time little carbonate sediments accumulated in the barents sea and in the sverdrup basin where the deep to shallow water sedimentary spectrum was occupied by siliceous sponge spicules by that time biogenic silica sedimentation was common throughout the world silica factories collapsed in the late permian abruptly bringing the pce to an end in northwest pangea the end permian collapse of the pce was associated with a major transgression and with a return to much warmer oceanic and continental climatic conditions chert deposition resumed in the distal oceanic areas during the early middle triassic anisian after a 8 10 ma interruption early triassic chert gap the conditions necessary for the onset expansion and zenith of the pce were provided by the thermohaline circulation of nutrient rich cold waters along the northwestern and western margin of pangea and possibly throughout the world oceans these conditions provided an efficient transportation mechanism that constantly replenished the supply of silica in the area created a nutrient and oxygen rich environment favouring siliceous biogenic productivity established cold sea floor conditions hindering silica dissolution while increasing calcium carbonate solubility and provided conditions adverse to organic and inorganic carbonate production the northwest margin of pangea was for nearly 30 ma bathed by cold waters presumably derived from the seasonal melting of northern sea ice the assumed engine for thermohaline circulation this process started near the sakmarian artinskian boundary intensified throughout middle and late permian time and ceased suddenly in latest permian time it led to oceanic conditions much colder than normally expected from the palaeolatitudes and the influence of cold northerly derived water was felt as far south southern nevada the demise of silica factories was caused by the rapid breakdown of these conditions and the establishment of a much warmer marine environment accompanied by sluggish circulation and perhaps a reduced input of dissolved silica to the ocean complete thawing of northern sea ice would have ended thermohaline circulation and led to warm and sluggish oceanic conditions inimical to the production accumulation and preservation of biogenic silica

the importance of ice vertical resolution for snowball climate and deglaciation sea ice schemes with a few vertical levels are typically used to simulate the thermodynamic evolution of sea ice in global climate models here it is shown that these schemes overestimate the magnitude of the diurnal surface temperature cycle by a factor of 2 3 when they are used to simulate tropical ice in a snowball earth event this could strongly influence our understanding of snowball termination which occurs in global climate models when the midday surface temperature in the tropics reaches the melting point a hierarchy of models is used to show that accurate simulation of surface temperature variation on a given time scale requires that a sea ice model resolve the e folding depth to which a periodic signal on that time scale penetrates this is used to suggest modifications to the sea ice schemes used in global climate models that would allow more accurate simulation of snowball deglaciation

deglaciation and postglacial environmental changes in the teton mountain range recorded at jenny lake grand teton national park wy abstract sediments contained in lake basins positioned along the eastern front of the teton mountain range preserve a continuous and datable record of deglaciation and postglacial environmental conditions here we develop a multiproxy glacier and paleoenvironmental record using a combination of seismic reflection data and multiple sediment cores recovered from jenny lake and other nearby lakes age control of teton lake sediments is established primarily through radiocarbon dating and supported by the presence of two prominent rhyolitic tephra deposits that are geochemically correlated to the widespread mazama 7 6 ka and glacier peak 13 6 ka tephra layers multiple glacier and climate indicators including sediment accumulation rate bulk density clastic sediment concentration and flux organic matter concentration flux 13c 15n and c n ratios and biogenic silica track changes in environmental conditions and landscape development sediment accumulation at jenny lake began centuries prior to 13 8 ka and cores from three lakes demonstrate that teton glacier extents were greatly reduced by this time persistent ice retreat in cascade canyon was slowed by an interval of small glacier activity between 13 5 and 11 5 ka prior to the end of glacial lacustrine sedimentation 11 5 ka the transition to non glacial sediments marks the onset of holocene conditions at jenny lake and reflects a shift toward warmer summers increased vegetation cover and landscape stability in the tetons we discuss the teton lake sediment records within the context of other regional studies in an effort to construct a comprehensive overview of deglaciation and postglacial environmental conditions at grand teton national park

the jormungand global climate state and implications for neoproterozoic glaciations 1 geological and geochemical evidence can be interpreted as indicating strong hysteresis in global climate during the neoproterozoic glacial events 630 ma and 715 ma standard climate theory only allows such strong hysteresis if global climate enters a fully glaciated snowball state however the survival of photosynthetic eukaryotic marine species through these glaciations may indicate that there were large areas of open ocean a previously proposed slushball model for neoproterozoic glaciations could easily explain the survival of these organisms because it has open ocean throughout the tropics but there is only a small amount of hysteresis associated with the slushball state in this paper a new state of global climate the jormungand state is proposed in this state the ocean is very nearly globally ice covered but a very small strip of the tropical ocean remains ice free the low ice latitude of the jormungand state is a consequence of the low albedo of snow free bare sea ice if the ice latitude propagates into the subtropical desert zone it can stabilize without collapsing to the equator because subtropical ice covered regions have a relatively low top of atmosphere albedo as a result of the exposure of bare sea ice and relatively lower cloud cover moreover there is strong hysteresis associated with the jormungand state as greenhouse gas levels are varied because of the high albedo contrast between regions of bare and snow covered sea ice the jormungand state is illustrated here in two different atmospheric global climate models and in the budyko sellers model by offering a scenario that could explain both strong hysteresis in global climate and the survival of life the jormungand state represents a potential model for neoproterozoic glaciations although further study of this issue is needed

snowball earth ice thickness on the tropical ocean 1 on the tropical oceans of a neo proterozoic snowball earth snow free ice would have existed in regions of net sublimation photosynthesis could have continued beneath this bare ice if it was sufficiently thin and sufficiently clear the steady state ice thickness is determined by the necessity to balance the upward conduction of heat with three subsurface heating rates the heat flux from the ocean to the ice base the latent heat of freezing to the ice base and the solar energy absorbed within the ice a preliminary study using a broadband model for solar radiation and assuming a large freezing rate had indicated that tropical ice might be only a few meters thick here we show that the vertical throughput of ice by surface sublimation and basal freezing would be too slow to keep the ice thin and that the broadband model had exaggerated the absorption depth of sunlight we use a spectral model for solar absorption computing radiative transfer at 60 wavelengths considering absorption by the ice and scattering by bubbles with the spectral model the computed ice thickness is much greater for a solar flux of 320 w m 2 at the equatorial surface and expected albedo of 0 5 for bare sea ice we find that surface temperatures below 12 c generate ice layers too thick for photosynthesis 100 m if the albedo were as low as 0 4 thick ice would occur only for surface temperatures below 25 c but such low temperatures would be difficult to maintain with such low albedo for surface temperatures warmer than these limits the ice becomes thin 1 m and is unlikely to represent a coherent ice layer however glacial deformation of thick floating ice from nearby oceanic regions may preclude the existence of thin or ice free patches

effects of bubbles cracks and volcanic tephra on the spectral albedo of bare ice near the transantarctic mountains implications for sea glaciers on snowball earth 1 spectral albedo was measured along a 6 km transect near the allan hills in east antarctica the transect traversed the sequence from new snow through old snow firn and white ice to blue ice showing a systematic progression of decreasing albedo at all wavelengths as well as decreasing specific surface area ssa and increasing density broadband albedos under clear sky range from 0 80 for snow to 0 57 for blue ice and from 0 87 to 0 65 under cloud both air bubbles and cracks scatter sunlight their contributions to ssa were determined by microcomputed tomography on core samples of the ice although albedo is governed primarily by the ssa and secondarily by the shape of bubbles or snow grains albedo also correlates highly with porosity which as a proxy variable would be easier for ice sheet models to predict than bubble sizes albedo parameterizations are therefore developed as a function of density for three broad wavelength bands commonly used in general circulation models visible near infrared and total solar relevance to snowball earth events derives from the likelihood that sublimation of equatorward flowing sea glaciers during those events progressively exposed the same sequence of surface materials that we measured at allan hills with our short 6 km transect representing a transect across many degrees of latitude on the snowball ocean at the equator of snowball earth climate models predict thick ice or thin ice or open water depending largely on their albedo parameterizations our measured albedos appear to be within the range that favors ice hundreds of meters thick

salt precipitation in sea ice and its effect on albedo with application to snowball earth during the initial freezing of the tropical ocean on snowball earth the first ice to form would be sea ice which contains salt within inclusions of liquid brine at temperatures below 23 c significant amounts of the salt begin to crystallize with the most abundant salt being hydrohalite nacl 2h2o these crystals scatter light increasing the ice albedo in this paper we present field measurements of the albedo of cold sea ice and laboratory measurements of hydrohalite precipitation precipitation of salt within brine inclusions was observed on windswept bare ice of mcmurdo sound at the coast of antarctica 78 s in early austral spring salinity and temperature were measured in ice cores spectral albedo was measured on several occasions during september and october the albedo showed a gradual increase with decreasing temperature consistent with salt precipitation laboratory examination of thin sections from the ice cores showed that the precipitation process exhibits hysteresis with hydrohalite precipitating over a range of temperatures between 28 c and 35 c but dissolving at about 23 c the causes of the hysteresis were investigated in experiments on laboratory grown sea ice with different solute mixtures all mixtures showed hysteresis suggesting that it may be an inherent property of hydrohalite precipitation within brine inclusions rather than being due to biological macromolecules or interactions between various salts in seawater this article is protected by copyright all rights reserved

geodetic evidence for aseismic reverse creep across the teton fault teton range wyoming the valley block hanging wall of the central segment of the teton fault rose 8 plus minus 0 7 mm during 1988 and 1989 relative to the mountain block west of the fault a displacement opposite to that expected on a normal fault the height change is based on first order leveling data over a 21 2 km long fault crossing line of 42 permanent bench marks established and initially surveyed in 1988 and resurveyed in 1989 the rapid height change took place across a 1 200 m wide zone coincident with the steep escarpment at the base of the range front including the surface trace of the east dipping teton fault a major active range front normal fault bounding the east side of the teton range at the northeastern edge of the basin and range province the total stratigraphic offset across the fault as much as 9 km accumulated over the last 7 to 9 million years quaternary fault scarps up to 52 m in height cut pinedale about 14 000 yr glacial and younger fluvial alluvial deposits indicating that the teton fault has been the locus of several large scarp forming earthquakes in the past 14 000 years and it exhibits up to 25 m of latest quarternary displacement where crossedmore by the level line although the relative uplift of the hanging wall may be local and unique to the teton fault this unexpected observation of aseismic reverse creep may have a variety of tectonic and non tectonic causes including hydrologic effects aseismic fault creep or tilt and pre seismic dilation less

refugium for surface life on snowball earth in a nearly enclosed sea a first simple model for sea glacier invasion 1 the existence of photosynthetic eukaryotic algae during the so called snowball earth events presents a conundrum if thick ice covered the oceans where could such life persist here we explore the possibility that photosynthetic life persisted at the end of long narrow seas analogous to the modern day red sea in this first analytical model we test the ability of the global sea glacier to penetrate a red sea analogue under climatic conditions appropriate during a snowball earth event we find the red sea is long enough to provide a refugium only if certain ranges of climatic conditions are met these ranges would likely expand if the restrictive effect of a narrow entrance strait is also considered

through thick and thin marine and meteoric ice in a snowball earth climate 1 marine ice cover in the frigid neoproterozoic climate system tends to isolate the ocean the thickness of this ice and thus the degree of isolation is an important unknown in geochemical and biological arguments regarding the fully glaciated snowball earth hypothesis the pollard and kasting 2005 coupled atmosphere ice model has been modified to track ice of marine and atmospheric origin separately and model their different optical properties in contrast to pollard and kasting s results a tropical region of thin ice is not stable in this model ice is hundreds of meters thick everywhere the overall pattern of the hydrological cycle in a snowball climate is also discussed

the teton fault wyoming topographic signature neotectonics and mechanisms of deformation we integrated geophysical and geological methods to evaluate the structural evolution of the active teton normal fault wyoming and its role in the development of the dramatic topography of teton range and jackson hole the teton fault bounds the precipitous eastern front of the teton range and is marked by large well preserved postglacial fault scarps that extend for 55 km along the range front comparison of variations in surface offsets with the topographic expression of the teton range crest and drainage divide and the overall structure of the range suggests that the effects of postglacial faulting cannot be discriminated from the influence of pre extensional structures and differential erosion on the footwall topography in contrast the effects of multiple scarp forming normal faulting earthquakes are expressed by the anomalous drainage pattern and westward tilt of the hanging wall jackson hole toward the teton fault kinematic boundary element fault models suggest that the westward tilt of the valley floor is the product of 110 125 m of displacement on a 45 75 e dipping teton fault in the past 25 000 75 000 years comparisons with historic normal faulting earthquake displacements imply that this range of displacement corresponds to 10 50 m 7 scarp forming earthquakes a total throw of 2 5 to 3 5 km across the teton fault is suggested by inverse ray tracing and forward gravity models these models also suggest that laramide age structures have been offset across the teton fault and obscure its geophysical signature but also continue to influence the structural and topographic expression of the footwall and hanging wall blocks paleomagnetic analyses of the 2 0 ma huckleberry ridge tuff suggest that the overall westward tilt of the teton range is a result of about 10 of west side down tilt across the teton fault since tuff emplacement this suggests that much if not all of the throw across the teton fault has accumulated in the past 2 m y complex demagnetization and rock magnetic behavior and local emplacement of the huckleberry ridge tuff on preexisting topography preclude determination of the amount or variations in throw along strike of the teton fault from the paleomagnetic data

the impact of atmospheric and oceanic heat transports on the sea ice albedo instability during the neoproterozoic in order to simulate the climatic conditions of the neoproterozoic we have conducted a series of simulations with a coupled ocean atmosphere model of intermediate complexity climber 2 using a reduced solar constant of 6 and varied co2 concentrations we have also tested the impact of the breakup of the supercontinent rodinia that has been hypothesized to play an important role in the initiation of an ice covered earth our results show that for the critical values of 89 and 149 ppm of atmospheric co2 a snowball earth occurs in the supercontinent case and in the dislocated configuration respectively the study of the sensitivity of the meridional oceanic energy transport to reductions in co2 concentration and to the dislocation of the supercontinent demonstrates that dynamics ocean processes can modulate the co2 threshold value below which a snowball solution is found but cannot prevent it the collapse of the overturning cells and of the oceanic heat transport is mainly due to the reduced zonal temperature gradient once the sea ice line reaches the 30 latitudinal band but also to the freshening of the tropical ocean by sea ice melt in term of feedbacks the meridional atmospheric heat transport via the hadley circulation plays the major role all along the co2 decrease by increasing the energy brought in the front of the sea ice margin but does not appear enough efficient to prevent the onset of the sea ice albedo instability in the case of the continental configurations tested in this contribution