structural characterization of natural loess and remolded loess under triaxial tests this paper characterizes the microstructural evolution of saturated natural loess from a site in jingyang china during triaxial test along two stress paths for comparison the same soil in remolded state is also characterized mercury intrusion porosimetry mip scanning electron microscopy sem and environmental scanning electron microscopy esem were used for the microstructure investigation results show that the microstructure of natural loess is similar to that of remolded loess before the consolidated undrained cu triaxial tests including conventional triaxial compression ctc test and reduced triaxial compression rtc test on the contrary their microstructures are different after the tests deeper examination shows that loading led to a significant change of inter aggregate pores without modifying the intra aggregate pores in addition the volume of inter aggregate pores after the rtc test is greater than that after the ctc test under the same consolidation stress the microstructure features of natural and remolded loess after the tests are further used to analyze the macro mechanical behavior for better understanding the relationship between them the results show that it is the cementation bonds of which breakage is influenced by stress path and confining pressure that play important roles in the strength and deformation behavior

permeability anisotropy of natural clays as a function of strain seven series of tests have been performed on specimens from five natural soft clay sites to determine the variation of the vertical and horizontal permeabilities when the soil is unidimensionally compressed the results show that the permeability anisotropy does not increase significantly with compression up to strains of 25 for marine clays in varved clays mostly because the clay laminae are more compressible than the silty laminae the anisotropy increases with vertical compression key words permeability clay anisotropy laboratory compression

millennial scale changes in north atlantic circulation since the last glaciation ocean circulation is closely linked to climate change on glacial interglacial and shorter timescales extensive reorganizations in the circulation of deep and intermediate depth waters in the atlantic ocean have been hypothesized for both the last glaciation1 2 3 4 5 6 and the subsequent younger dryas cold interval3 6 7 8 9 10 but there has been little palaeoceanographic study of the subtropical gyres11 12 13 these gyres are the dominant oceanic features of wind driven circulation and as such they reflect changes in climate and are a significant control on nutrient cycling and possibly atmospheric co2 concentrations here we present cd ca ratios in the shells of benthic foraminifera from the bahama banks that confirm previous suggestions11 12 that nutrient concentrations in the north atlantic subtropical gyre were much lower during the last glacial maximum than they are today up to 50 lower according to our data these contrasting nutrient burdens imply much shorter residence times for waters within the thermocline of the last glacial maximum below the glacial thermocline nutrient concentrations were reduced owing to the presence of glacial north atlantic intermediate water a high resolution cd ca record from an intermediate depth indicates decreased nutrient concentrations during the younger dryas interval as well mirroring opposite changes at a nearby deep site3 9 together these observations suggest that the formation of deep and intermediate waters north atlantic deep water and glacial north atlantic intermediate water respectively wax and wane alternately on both orbital and millennial timescales

abrupt changes in antarctic intermediate water circulation over the past 25 000 years the formation and circulation of antarctic intermediate water has varied over glacial interglacial timescales a neodymium record from the atlantic ocean basin suggests that changes in circulation may have been driven by changes both in antarctic intermediate water formation in the southern ocean and in the strength of north atlantic meridional overturning

measurement and estimation of pore shrinkage and pore distribution in a clayey till during soil water characteristic curve tests the soil water characteristic curve swcc of fine grained soils is usually determined experimentally in many applications such as design of mine waste covers and landfill liners the unsaturated permeability function k h is often derived theoretically from the measured swcc implicit in these derivations is the transformation of the swcc to a pore size distribution psd typically assumed to be constant and mono modal psds of a clayey till compacted at various water contents were measured after compaction after flexible wall permeability testing and during and after swcc tests the measurements show that the psd changes significantly during permeability and swcc testing a method is advanced for predicting the observed changes in psd during swcc testing psds are determined for soil samples subjected to the highest and lowest suctions applied during the swcc test the measured psds are transformed to account for pore trapping the transform assumes that flow occurs through two sets of randomly d

sources and flow patterns of deep ocean waters as deduced from potential temperature salinity and initial phosphate concentration through the deconvolution of ocean chemical data it has been shown that the ratio of o2 utilization to phosphate production in the sea is 175 6 rather than 138 as proposed by redfield et al 1963 we find no evidence that this ratio changes significantly with location or depth in the sea we have used this new ratio to calculate the initial phosphate concentrations for the waters sampled during the geosecs and tto programs the important application of these new results is in constraining the origin and flow patterns of deep waters in the ocean we believe that a strong case can be made that antarctic salinity maximum water i e the common water of montgomery 1958 is produced by the mixing of waters entering the antarctic from mid depths in the indian pacific and atlantic with weddell sea bottom water southern component antarctic common water consists of about 45 weddell sea bottom water 30 intermediate waters from the pacific and indian oceans and 25 deep water originating from the northern atlantic

carbon isotopic changes in benthic foraminifera from the western south atlantic reconstruction of glacial abyssal circulation patterns oxygen and carbon isotopic analyses have been performed on the benthic foraminifer planulina wuellerstorfi in seven late quaternary cores from the vema channel rio grande rise region the cores are distributed over the water depth interval of 2340 to 3939 m which includes the present transition from north atlantic deep water nadw to antarctic bottom water aabw the carbon isotopic records in the cores vary as a function of water depth the shallowest and deepest cores show no significant glacial interglacial difference in 13c four of the five cores presently located in the nadw have benthic foraminiferal 13c that is lower during glacial isotopic stages based on bathymetric gradients in 13c we conclude that like today there were two water masses present in the vema channel during glacial intervals a water mass enriched in 13c overlying another water mass depleted in 13c the largest gradient of change of 13c with depth however occurred at 2 7 km 1 km shallower than the present position of this gradient on the basis of paleontologic and sedimentologic evidence we consider it unlikely that the nadw aabw transition shallowed to this level reduced carbon isotopic gradients between the deep basins of the north atlantic and pacific oceans during the last glaciation suggest that production of nadw was reduced lower production of nadw may have modified the local abyssal circulation pattern in the vema channel region

mercury intrusion and permeability of louiseville clay several theories have been proposed to correlate the permeability hydraulic conductivity with the pore size distribution of soils and it seemed interesting to determine if these theories could be applied to natural clays for this purpose permeability and mercury intrusion porosimetry tests were performed on a champlain sea clay for both intact and remoulded conditions after compression of the specimens to strains varying from 0 to 42 the results show that for either intact or remoulded soil conditions there is a relationship between the pore size parameters and the permeability of the clay however there is no unique relationship for both intact and remoulded clays and for the silt and clay considered in previous studies consequently mercury intrusion porosimetry alone cannot be usepto evaluate the permeability of soils in general plusieurs thkories ont ctc proposces pour corrcler la permiabilite conductivitk hydraulique avec la distribution des grosseurs de pore des sols et il a semblc intiressant de verifier si ces theories pourraient 2tre appliquees aux argiles naturelles a cette fin des essais de permcabilitc et de porosimctrie a intrusion de mercure okt ctc rcaliscs sur l argile de la mer champlain dans des conditions tant intactes que remanikes apris la compression des specimens a des dcformations variant de 0 a 42 les rcsultats demontrent que pour des conditions soit intactes ou remanices il existe une relation entre les paramitres de grosseur de pore et la permcabilitc de l argile cependant il n existe pas de relation unique pour les argiles tant intactes que remanices et pour le limon et l argile ctudics antkrieurement en conscquence la porosimctrie a intrusion de mercure ne peut pas a elle seule tre utilisce pour cvaluer la permcabilitc des sols en general mots clds permcabilitc argile porosimctrie a intrusion de mercure structure traduit par la rcdaction

probabilistic modelling of saturated unsaturated hydraulic conductivity for compacted glacial tills a probabilistic model including some previous probabilistic studies is proposed to evaluate hydraulic conductivity from pore entrance size distribution the model considers multi pores in series of paths through capillary networks in the soil fabric the average number of connected pores is a representative value of the fabric greater than two but not too large the hydraulic conductivity of three glacial tills from northern quebec with different grain size distributions has been examined by horizontal permeability tests in saturated conditions and suction tests with vertical permeability measurement in unsaturated conditions the hydraulic conductivity is strongly influenced by compaction conditions corresponding to different microfabrics the model is applicable not only in saturated conditions but also in unsaturated conditions with different microfabrics

calcitic foraminiferal data confirmed by cadmium in aragonitic hoeglundina application to the last glacial maximum in the northern indian ocean a core top study of cadmium uptake into the shells of the aragonitic benthic foraminifera hoeglundina elegans demonstrates that the hoeglundina cd ca partition coefficient is close to 1 0 throughout the ocean cd uptake by hoeglundina is far less depth dependent than that of calcitic benthic foraminifera furthermore manganese carbonate does not precipitate on these aragonitic shells allowing for the recovery of cd estimates in some samples where calcitic species are spoiled by contaminating overgrowths because cd incorporation into hoeglundina shows little depth dependence a comparison of calcitic and hoeglundina cd data can be used to verify the assumption that the depth dependence observed for calcitic benthic foraminifera is time invariant this comparison has been undertaken in downcore and last glacial maximum lgm samples from the northern indian ocean aragonitic and calcitic foraminiferal estimates for cd in the lgm ocean are in excellent agreement this result indicates upper ocean estimates of lgm cd are reliable despite a factor of two variation in cd uptake by calcitic species over this depth range cd and 13c data indicate that the uppermost waters of the lgm arabian sea were strongly nutrient depleted relative to today but that the deepest waters of the northern bay of bengal had nutrient concentrations at least as high as or higher than modern levels a strong vertical gradient of increasing nutrients with increasing depth existed in both basins during the lgm a west to east gradient of increasing nutrient concentrations also is evident at all depths in the bay of bengal there is evidence for an enhanced gradient of nutrients increasing from south to north the lgm deep arabian sea and intermediate depth bay of bengal were nutrient depleted compared to the modern ocean however cd and 13c data indicate that nutrient depletion in the northern indian ocean did not exceed that of the deep eastern tropical pacific except during the latest part of oxygen isotope stage 2 and according to cd data only the early stages of deglaciation during oxygen isotope stage 3 and early stage 2 cd in the northern indian ocean and cd in the eastern tropical pacific were indistinguishable although both regions have lower cd at these times compared to the holocene

millennial scale evolution of the southern ocean chemical divide abstract the chemical properties of the mid depth and deep southern ocean are diagnostic of the mechanisms of abrupt changes in the global ocean throughout the late pleistocene because the regional water mass conversion and mixing help determine global ocean gradients here we define continuous time series of southern ocean vertical gradients by differencing the records from two high deposition rate deep sea sedimentary sequences that span the last several ice age cycles the inferred changes in vertical carbon and oxygen isotopic gradients were dominated by variability on the millennial scale and they followed closely the abrupt climate events of the high latitude northern hemisphere in particular the stadial events of at least the last 200 kyr were characterized by enhanced mid deep gradients in both 13 c dissolved inorganic carbon and 18 o temperature interstadial events conversely featured reduced vertical gradients in both properties the glacial terminations represented exceptions to this pattern of variability as the vertical carbon isotopic gradient flattened dramatically at times of peak warmth in the southern ocean surface waters and with little or no corresponding change 18 o gradient the available evidence suggests that properties of the upper layer of the southern ocean antarctic intermediate water were influenced by an atmospherically mediated teleconnection to high latitude northern hemisphere

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

deepwater circulation on blake outer ridge western north atlantic during the holocene younger dryas and last glacial maximum three depth transects containing a total of 33 sediment cores were investigated along the blake outer ridge in the western subtropical north atlantic sortable silt mean grain size and stable isotope records were used to assess the position and relative intensity of the western boundary undercurrent wbuc during the holocene the last glacial maximum lgm and the younger dryas yd intervals the holocene reconstruction is consistent with modern physical and chemical hydrographic measurements in the area suggesting a deep position for the fast flowing core of the wbuc 3000 4000 m deepening to 4500 m water depth on the ridge flanks and a water column dominated by north atlantic deep water nadw the lgm and yd reconstructions show that a comparable hydrographic regime was present during both these intervals suggesting a similar mode of circulation that was appreciably different from the holocene reconstruction the wbuc s zone of maximum flow speed during these intervals is suggested to have shifted above 2500 m water depth consistent with nutrient depleted glacial north atlantic intermediate water formation with an increasing influence of southern source water ssw beneath below 4000 m water depth results hint at increased ssw flow vigor during both the lgm and yd with higher flow speeds than during the holocene this study provides a framework for aiding the interpretation of time series records of paleocurrent flow speed changes in the region of the wbuc

mineralogy chemistry and physical properties interrelationships of some sensitive clays from eastern canada this paper describes the use of quantitative mineralogy and specific surface area in interpreting the index properties of clayey soils from nine sites in eastern canada samples representative of t

resistivity monitoring of an active volcano using the controlled source electromagnetic technique kilauea hawaii a controlled source electromagnetic monitoring system located near the summit of kilauea has been in operation since mid 1979 prominent changes in the controlled source magnetic fields have been observed both preceding and following two seismic swarms that are interpreted to be related to shallow magma intrusions in august 1980 and january 1981 the vertical magnetic field hz sensor nearest the sites of intrusion showed the largest field changes all comparisons to date have been made at 1 hz which corresponds to a depth of penetration of several kilometers large and rapid vertical magnetic field changes were measured following the intrusion into the upper east rift of kilauea on august 27 1980 similar fluctuations were measured both before and during the intrusion into the southern caldera on january 20 1981 located earthquakes and data from a recording tiltmeter within 2 km of the hz sensor which showed anomalous field changes over the january 20 event indicate that the hz sensor was located nearly over the zone of intrusion the hz field changes recorded over both the august 1980 and january 1981 intrusive events appear too large to have been caused by conductivity changes within a horizontally layered section more probably they were caused by relatively shallow intrusion of high conductivity magma into open high angle fractures or by establishing continuity of short sections of preexisting magma storage zones thereby producing long linear conductors from short normally discontinuous conductive segments

cadmium chemical tracer of deepwater paleoceanography the oceanic distribution of cadmium resembles that of phosphorus because the cadmium content of foraminiferal shells is governed by the cadmium content of seawater planktonic and benthic fossil shells can be used to infer nutrient distributions within ancient oceans empirical studies demonstrate that cadmium in benthic foraminiferal shells is related to the bottom water composition through a proportionality constant d 2 9 this constant is the same for each of the species studied cibicidoides wuellerstorfi cibicidoides kullenbergi nuttallides umbonifera and uvigerina spp downcore cadmium data from high quality pacific and atlantic sediment cores suggest that the cadmium inventory of the ocean did not change significantly between the most recent glacial maximum and the present hence changes in the cadmium content of fossils at a site directly reflect changes in nutrient distributions due to altered oceanic circulation patterns studies of cadmium in pleistocene sediments show that deep ocean circulation patterns were significantly different during the most recent glacial maximum in the western north atlantic ocean the nutrient content of waters from 2500 to 3500 m was twice as high during glacials as during interglacial periods signifying an increase in the proportion of waters of antarctic origin in this depth interval and a decrease but not a cessation in the flux of north atlantic deep waters through this depth range below 3500 m the nutrient increase was greater indicating a higher proportion of antarctic bottom water above 2500 m the nutrient content was lower during glacial periods than it has been during interglacial times the cd content of high latitude north atlantic and southern ocean surface waters does not show a significant glacial interglacial change which argues against theories for changes atmospheric carbon dioxide that require changes in high latitude nutrient concentrations

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

planktonic foraminifera calcareous nannoplankton and ascidian variations during the last 25 kyr in the southwestern atlantic a paleoproductivity signature micropaleontological and geochemical analyses from western south atlantic core san 76 off southeast brazil revealed changes in stable isotope values and in the assemblages of calcareous nannoplankton and planktonic foraminifera during the past 25 kyr that point to significant paleoceanographic and climatic changes leading to an increase in productivity during the last deglaciation the enhanced surface productivity was clearly indicated by increased relative abundances of the planktonic foraminifera globigerina bulloides and neogloboquadrina dutertrei and the decreased values of 13 c in planktonic foraminiferal tests a coeval shoaling of the nutricline and thermocline was indicated by decreased relative abundances of the calcareous nannoplankton florisphaera profunda and an increased relative abundance of the planktonic foraminifera globorotalia truncatulinoides right coiling we speculate that these changes are related to n s shifts of the atlantic intertropical convergence zone itcz a significant increase in the cd ca ratio and decrease in 13 c values in the benthic foraminifer hoeglundina elegans along with a significant increase in the relative abundance of ascidian spicules during the deglaciation suggest that benthic communities in this area strongly benefited from increased surface water productivity 2007 elsevier b v all rights reserved

evolution of microstructure in compacted london clay during wetting and loading the influence of fabric on mechanical behaviour is explicitly considered in some of the current constitutive models for unsaturated soils these are based on assumptions regarding the interaction b

behaviour of the stiff and sensitive saint jean vianney clay in intact destructured and remoulded conditions the role of the degree of microstructure on the behaviour of clayey soils has been the focus of many studies however none so far have quantified the evolution of the shear strength parameters for

paired benthic foraminiferal cd ca and zn ca evidence for a greatly increased presence of southern ocean water in the glacial north atlantic benthic foraminiferal 13c and cd ca studies suggest that deep atlantic circulation during the last glacial maximum was very different from today with high nutrient low 13c high cd deep southern ocean water sow penetrating far into the north atlantic however if some glacial 13c values are biased by productivity artifacts and or air sea exchange processes then the existing 13c data may be consistent with the continual dominance of north atlantic deep water nadw cibicidoides wuellerstorfi cd ca results presented here indicate that the glacial north atlantic was strongly enriched in dissolved cd below 2500 m depth if nadw formation was still vigorous relative to sow formation these data could be explained by either increased preformed nutrient levels in the high latitude north atlantic or by increased organic matter remineralization within lower nadw high glacial zn ca values in the same samples however are best explained by a substantially increased mixing with zn rich sow the cause was most likely a partial replacement of nadw by less dense glacial north atlantic intermediate water this reorganization also lowered deep north atlantic co32 concentrations by perhaps 10 to 15 mol kg 1

glacial interglacial differences in circulation and carbon cycling within the upper western north atlantic we investigated glacial interglacial changes in the circulation and carbon cycling in the western north atlantic subtropical gyre using hydrographic data and downcore records of the stable isotopic compositions of individual shells of bahamian benthic foraminifera potential temperature salinity depth relations show that modern thermocline 200 1000 m and deep 1000 2000 m waters in the providence channels bahamas originate in the sargasso sea and are typical of the subtropical gyre gradients in the stable isotopic compositions of late holocene planulina and cibicidoides species from the bank margins 400 to 1500 m depth reflect temperature nutrient and isotopic gradients of modern subtropical gyre waters the difference between the 18o of glacial maximum and late holocene foraminifera is 2 1 for the upper 900 m of the water column and 1 6 for deeper waters indicating that these waters were 4 c and 2 c cooler respectively during glacial time the glacial temperature gradient dt dz was similar to today while the base of the thermocline was 100 m shallower these results differ significantly from our earlier results from multiple shell 18o analyses which implied upper thermocline waters were only 1 c cooler and dt dz was greater during the glacial maximum the difference occurs because bioturbation adversely affects multiple shell analyses of glacial aged samples from shallow water depths at all depths above 1500 m foraminiferal 13c are greater during the glacial maximum than the late holocene by at least 0 1 to 0 2 as much as 0 6 in the lower thermocline indicating that nutrient concentrations throughout the thermocline were reduced and there was no oxygen minimum zone during the glacial maximum this suggests greater more uniform ventilation of the thermocline results of single and multiple shell 13c analyses of glacial age foraminifera compare favorably because samples most affected by mixing correspond to water depths where the glacial interglacial change of 13c was small cooler upper ocean waters during the glacial maximum reflect cooler temperatures at the ocean surface where isopycnal surfaces outcrop including large areas of the subtropical ocean a shallower thermocline base is consistent with southward migration of the northern edge of the subtropical gyre or increased mode water production enhanced thermocline ventilation is consistent with more vigorous winds and all isopycnal surfaces outcropping in the area of ekman downwelling

atlantic ocean circulation during the younger dryas insights from a new cd ca record from the western subtropical south atlantic author posting american geophysical union 2003 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in paleoceanography 18 2003 1086 doi 10 1029 2003pa000888

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

model test of soil deformation response to draining recharging conditions based on dfos abstract intense groundwater exploitation and seasonal fluctuations of water level in phreatic aquifer cause land subsidence disasters to better understand the land subsidence mechanism caused by groundwater withdrawal a small scale sand clay interbedded model box was built to carry out consolidation and rebound tests during two drainage recharge cycles distributed fiber optical sensing dfos technologies were introduced for coupled monitoring of soil strain and water content to analyze response characteristics of each layer to water level changes the results indicate that soil layers were compressed during drainage and rebound during recharge with clay layer deformation more obvious than sand layer deformation deformation of the sand layer was synchronous with water content changes while that of the clay layer lagged behind water content changes due to its lower permeability coefficient the segmented compression clay layer curve shows that the water content rapidly decreased when it was lower than the liquid limit while the clay layer compression rate obviously accelerated during drainage when the water content was higher than that of the liquid limit during recharge the rebound rate significantly increased under the condition of repeated drainage and recharge the soil microstructure changed with decreasing porosity and permeability coefficient leading to a longer consolidation time with increasing cycling times the soil gradually tended toward elastic deformation the observations propose a novel technology dfos technology for monitoring land subsidence caused by seasonal water level fluctuations and dewatering projects the test results are of great significance to investigate land subsidence mechanisms and evaluate soil layer compression potential

slip rate of the western garlock fault at clark wash near lone tree canyon mojave desert california the precise tectonic role of the left lateral garlock fault in southern california has been controversial three proposed tectonic models yield significantly different predictions for the slip rate history orientation and total bedrock offset as a function of distance along strike in an effort to test these models we present the first slip rate estimate for the western garlock fault that is constrained by radiocarbon dating a channel referred to here as clark wash incised into a latest pleistocene alluvial fan has been left laterally offset at least 66 6 m and no more than 100 m across the western garlock fault indicating a left lateral slip rate of 7 6 mm yr 95 confidence interval of 5 3 10 7 mm yr using dendrochronologically calibrated radiocarbon dates the timing of aggradational events on the clark wash fan corresponds closely to what has been documented elsewhere in the mojave desert suggesting that much of this activity has been climatically controlled the range front fault located a few hundred meters northwest of the gar lock fault has probably acted primarily as a normal fault with a holocene rate of dip slip of 0 4 0 7 mm yr the record of prehistoric earthquakes on the garlock fault at this site though quite possibly incomplete suggests a longer interseismic interval 1200 2700 yr for the western garlock fault than for the central garlock fault the relatively high slip rate determined here indicates that the western and central segments of the garlock fault show similar rates of movement that are somewhat faster than rates inferred from geodetic data the high rate of motion on the western garlock fault is most consistent with a model in which the western garlock fault acts as a conjugate shear to the san andreas fault other mechanisms involving extension north of the garlock fault and block rotation at the eastern end of the fault may be relevant to the central and eastern sections of the fault but they cannot explain a high rate of slip on the western garlock fault

what do benthic δ13c and δ18o data tell us about atlantic circulation during heinrich stadial 1 approximately synchronous with the onset of heinrich stadial 1 hs1 13c decreased throughout most of the upper 1000 2500 m atlantic and at some deeper north atlantic sites this early deglacial 13c decrease has been alternatively attributed to a reduced fraction of high 13c north atlantic deep water nadw or to a decrease in the nadw 13c source value here we present new benthic 18o and 13c records from three relatively shallow 1450 1650 m subpolar northeast atlantic cores with published data from other cores these data form a depth transect 1200 3900 m in the subpolar northeast atlantic we compare last glacial maximum lgm and hs1 data from this transect with data from a depth transect of cores from the brazil margin the largest lgm to hs1 decreases in both benthic 13c and 18o occurred in upper waters containing the highest nadw fraction during the lgm we show that the 13c decrease can be explained entirely by a lower nadw 13c source value entirely by a decrease in the proportion of nadw relative to southern ocean water or by a combination of these mechanisms however building on insights from model simulations we hypothesize that reduced ventilation due to a weakened but still active atlantic meridional overturning circulation also contributed to the low 13c values in the upper north atlantic we suggest that the benthic 18o gradients above 2300 m at both core transects indicate the depth to which heat and north atlantic deglacial freshwater had mixed into the subsurface ocean by early hs1

deglacial pulses of deep ocean silicate into the subtropical north atlantic ocean records of biogenic opal export in the north atlantic ocean show pronounced maxima during each glacial termination over the past 550 000 years consistent with a strong deglacial reduction in the formation of silicate poor glacial north atlantic intermediate water and a consequent increase in upward silicate transport the southern ocean is thought to have an important role in driving glacial interglacial changes in atmospheric carbon dioxide concentrations but the mechanism responsible for carbon dioxide release upon deglaciation remains unclear based on a record of biogenic opal export that exhibits opal maxima during each glacial termination of the past 550 000 years nele meckler et al propose that deglacial reduction in glacial north atlantic intermediate water led to downward mixing of warm low density surface water ultimately triggering antarctic overturning and carbon dioxide release to the atmosphere growing evidence suggests that the low atmospheric co2 concentration of the ice ages resulted from enhanced storage of co2 in the ocean interior largely as a result of changes in the southern ocean1 early in the most recent deglaciation a reduction in north atlantic overturning circulation seems to have driven co2 release from the southern ocean2 3 4 5 but the mechanism connecting the north atlantic and the southern ocean remains unclear biogenic opal export in the low latitude ocean relies on silicate from the underlying thermocline the concentration of which is affected by the circulation of the ocean interior here we report a record of biogenic opal export from a coastal upwelling system off the coast of northwest africa that shows pronounced opal maxima during each glacial termination over the past 550 000 years these opal peaks are consistent with a strong deglacial reduction in the formation of silicate poor glacial north atlantic intermediate water2 gnaiw the loss of gnaiw allowed mixing with underlying silicate rich deep water to increase the silicate supply to the surface ocean an increase in westerly wind driven upwelling in the southern ocean in response to the north atlantic change has been proposed to drive the deglacial rise in atmospheric co2 refs 3 4 however such a circulation change would have accelerated the formation of antarctic intermediate water and sub antarctic mode water which today have as little silicate as north atlantic deep water and would have thus maintained low silicate concentrations in the atlantic thermocline the deglacial opal maxima reported here suggest an alternative mechanism for the deglacial co2 release5 6 just as the reduction in gnaiw led to upward silicate transport it should also have allowed the downward mixing of warm low density surface water to reach into the deep ocean the resulting decrease in the density of the deep atlantic relative to the southern ocean surface promoted antarctic overturning which released co2 to the atmosphere

modeling the three dimensional structure of macroscopic magma transport systems application to kilauea volcano hawaii we report the results of modeling the three dimensional internal structure of kilauea s magmatic passageways the approach uses a clear plexiglass model containing equally spaced levels upon which well located seismic hypocenters are plotted application of constraining geologic and geophysical criteria to this distributed volume of earthquakes permits the interpretation of seismic structures produced by fracturing in response to locally high fluid pressures four magma transport and storage structures have been identified within and beneath kilauea 1 primary conduit the conduit transporting magma into kilauea s summit storage reservoir rises from the model base 14 6 km to the 6 5 km depth level it is a zone of intense fracturing and inferred intrusion whose horizontal sections are elliptical in planform over its height the average major axis of the component horizontal sections is 3 3 km with an average minor axis of 1 7 km this yields an aspect ratio of 0 52 at the 14 6 km level the strike of the major axis is n67 e during passage from the upper mantle through the oceanic crust this axis rotates in a right handed sense until the strike is n41 w at the 6 5 km level 2 magma chamber complex floor the interval from 6 5 to 5 7 km immediately over the primary conduit is aseismic this suggests differentially high fluid to rock ratios and relatively weak pathways for further vertical transport into higher levels of the storage complex as well as lateral leakage eastward into the mauna ulu staging area for later vertical ascent beneath the upper east rift zone seismicity within the immediately subjacent rocks that form the top of the primary conduit at 6 5 km suggests that this inferred magma rich horizon forms the effective floor of the summit storage complex 3 magma chamber crown intense seismicity over the 1 1 1 9 km depth interval defines an elliptical region in plan view the top of this region has a broad apex with an average major axis of 1 5 km and an average minor axis of 1 1 km producing an aspect ratio of 0 73 this region coincides with the epicentral position of summit vertical displacement maxima during inflationary deformation and is interpreted as a region of intense diking crowning the summit storage complex 4 upper east rift zone pipe from a depth of 5 7 km a cylindrical region of seismicity rises beneath the upper east rift zone to the 1 9 km level where it merges with the subhorizontal upper east rift zone duct this pipe like zone has a mean diameter of 1 4 km and a vertical axis that pierces the surface of the volcano at the intersection of the koae fracture system and the upper east rift zone we suggest this pipe forms a principal connection between the base of the summit storage reservoir and near surface storage compartments and ducts in the upper east rift zone in this role the pipe is suggested to have contributed heavily to mauna ulu s magma supply during 1969 1974 the model of magma transport and storage thus constructed provides a context in which other types of data e g ground deformation and electrical conductivity may be interpreted as well as a means of refining petrological inferences based on lava chemistry

a microstructural investigation of osaka bay clay the impact of microfossils on its mechanical behaviour a recent microstructural investigation of osaka bay clay sediments has revealed the presence of abundant microfossils particularly in the marine layers which appear to influence directly the micr

mechanical limits to microbial activity in deep sediments the observed decline in microbial abundance with increasing depth has been associated to various environmental factors meanwhile the role of geometrical constraints and soil bacteria mechanical interactions remains poorly analyzed pore and pore throat sizes may restrict habitable pore space and traversable interconnected porosity and sediment cell interaction may cause puncture or tensile failure of the cell membrane in this study we compile published evidence on the presence of bacteria in deep sediments as well as pore and pore throat size data in sediments at different depths to establish possible geometrical conditions for the sediment cell complex compiled data are complemented with experimental results gathered through controlled axial compression experiments that reproduce the mechanical consolidation of deep sediment sequences then we analyze the mechanical interaction between bacteria and sediments that may cause cell death finally we combine data and model predictions to define the main regions in a particle size versus depth space that characterize the fate of bacteria active and motile trapped inside pores and dead or dormant these regions constrain hypotheses related to the role of biological activity in deep sediments research protocols and sampling methods the viability of bioremediation strategies for contaminated sites and the potential development of bioengineered sediments

radiocarbon and stable isotope constraints on last glacial maximum and younger dryas ventilation in the western north atlantic 1 foraminiferal abundance 14c ventilation ages and stable isotope ratios in cores from high deposition rate locations in the western subtropical north atlantic are used to infer changes in ocean and climate during the younger dryas yd and last glacial maximum lgm the 18o of the surface dwelling planktonic foram globigerinoides ruber records the present day decrease in surface temperature sst of 4 c from gulf stream waters to the northeastern bermuda rise if during the lgm the modern 18o salinity relationship was maintained this sst contrast was reduced to 2 c with lgm to interglacial 18o changes of at least 2 2 ssts in the western subtropical gyre may have been as much as 5 c colder above 2 3 km glacial 13c was higher than today consistent with nutrient depleted younger bottom waters as identified previously below that 13c decreased continually to 0 5 about equal to the lowest lgm 13c in the north pacific ocean seven pairs of benthic and planktonic foraminiferal 14c dates from cores 2 5 km deep differ by 1100 340 years with a maximum apparent ventilation age of 1500 years at 4250 m and at 4700 m apparent ventilation ages are presently unavailable for the lgm 2 5 km because of problems with reworking on the continental slope when sea level was low because lgm 13c is about the same in the deep north atlantic and the deep north pacific and because the oldest apparent ventilation ages in the lgm north atlantic are the same as the north pacific today it is possible that the same water mass probably of southern origin flowed deep within each basin during the lgm very early in the yd dated here at 11 25 0 25 n 10 conventional 14c kyr bp equal to 12 9 calendar kyr bp apparent ventilation ages 2 3 km water depth were about the same as north atlantic deep water today below 2 3 km four yd pairs average 1030 400 years the oldest apparent ventilation age for the yd is 1600 years at 4250 m this strong contrast in ventilation which indicates a front between water masses of very different origin is similar to glacial profiles of nutrient like proxies this suggests that the lgm and yd modes of ocean circulation were the same

deep water mass geometry in the glacial atlantic ocean a review of constraints from the paleonutrient proxy cd ca 1 paleonutrient proxies currently provide the strongest constraints on the past spatial distribution of deep water masses we review the state of knowledge derived from the trace metal proxy cd ca for the atlantic ocean during the last glacial maximum lgm we compile published benthic foraminiferal cd ca data supplemented with new data to reconstruct meridional cd sections through the holocene and lgm atlantic holocene cd ca reflects the modern water masses north atlantic deep water nadw antarctic bottom water aabw and antarctic intermediate water aaiw reasonably well except for anomalously high values in the intermediate to mid depth far north atlantic lgm cd ca clearly shows that nadw was replaced by the shallower glacial north atlantic intermediate water gnaiw with significant northward expansion of aabw the boundary level between gnaiw and aabw was very abrupt occurring between 2200 and 2500 m modern water depth combined cd ca and cibicidoides d 13 c data allow us to also calculate the air sea signature of d 13 c d 13 cas the lgm atlantic can be explained entirely by mixing between high d 13 cas gnaiwand low d 13 cas aabw negative d 13 cas values in glacial aabw were likely caused by poor ventilation during formation probably associated with extensive sea ice coverage overall our knowledge base would benefit from improved data coverage in the south atlantic and southern ocean and a better understanding of ancillary effects on the cd ca proxy itself

study of the structure of a sensitive champlain clay and of its evolution during consolidation scanning electron microscopy and mercury intrusion porosimetry are used in parallel to identify the structure of a medium sensitivity champlain clay the clay structure is observed firstly on intact remolded and oven dried soils and secondly on soils consolidated at various levels in one dimensional compression both methods of investigation reveal for the intact soil the existence of an aggregated structure characterized by an interaggregate and an intra aggregate porosity remolding affects interaggregate links but does not destroy aggregates the observation of clay structure at various levels of one dimensional compression shows that the collapse of the structure is progressive the largest interaggregate pores being the first affected as the consolidation proceeds smaller and smaller pores are affected for a given pressure increment only the largest existing pores are affected a structure anisotropy has been seen to develop with increasing compression the scanning electron microscope and the me

a method for precise analysis of trace element calcium ratios in carbonate samples using quadrupole inductively coupled plasma mass spectrometry an improved method has been developed using a quadrupole inductively coupled plasma mass spectrometer q icp ms to analyze carbonate samples for multiple trace element to calcium ratios problems alleviating shorter term drift have been overcome by manipulating the instrument to bracket each trace metal measurement with a calcium measurement while longer term drift is corrected by bracketing each sample analysis with external matrix matched standards of typical foram composition our method is optimized for measuring the ratios sr ca mg ca zn ca cd ca ba ca mn ca and u ca from a single carbonate sample but could be adapted to include a range of alternative ratios evaluation has shown the method to be extremely precise at less than 1 rsd 1 for 3 trace metal to calcium ratios we have achieved comparable precision to a sector field icp ms instrument and an advance over previous methods using the q icp ms instrument precision rsd for each ratio based on 96 sample analyses in 5 batches made over a period of 9 months using a 100 mg l ca standard is 2 2 for u ca 1 7 for cd ca 1 9 for zn ca 1 1 for ba ca 0 7 for mn ca and 0 7 and 0 6 for sr ca and mg ca respectively accuracy of the method is confirmed by comparing standard ratios with those obtained from an icp aes instrument and by comparing sample analyses of neap4b material from the north atlantic with data measured using thermal ionization mass spectrometry tims and flame atomic absorption spectroscopy faas

regional and global benthic δ18o stacks for the last glacial cycle although detailed age models exist for some marine sediment records of the last glacial cycle 0 150 ka age models for many cores rely on the stratigraphic correlation of benthic 18o which measures ice volume and deep ocean temperature change the large amount of data available for the last glacial cycle offers the opportunity to improve upon previous benthic 18o compilations such as the lr04 global stack not only are the age constraints for the lr04 stack now outdated but a single global alignment target neglects regional differences of several thousand years in the timing of benthic 18o change during glacial terminations here we present regional stacks that characterize mean benthic 18o change for 8 ocean regions and a volume weighted global stack of data from 263 cores age models for these stacks are based on radiocarbon data from 0 to 40 ka correlation to a layer counted greenland ice core from 40 to 56 ka and correlation to radiometrically dated speleothems from 56 to 150 ka the regional 18o stacks offer better stratigraphic alignment targets than the lr04 global stack and furthermore suggest that the lr04 stack is biased 1 2 kyr too young throughout the pleistocene finally we compare global and regional benthic 18o responses with sea level estimates for the last glacial cycle

refined modeling and14c plateau tuning reveal consistent patterns of glacial and deglacial14c reservoir ages of surface waters in low latitude atlantic atlantic surface water reservoir ages

rapid deglacial injection of nutrients into the tropical atlantic via antarctic intermediate water highlights first high resolution cdw record from caribbean intermediate waters rapid nutrient enrichment during hs1 and yd tropical n atlantic aaiw nutrient content controlled by southern ocean enhanced aaiw nutrient content likely fed low to high latitude productivity dampening of the deglacial global co2 rise by aaiw nutrient enrichment as part of the return flow of the atlantic overturning circulation antarctic intermediate water aaiw redistributes heat salt co2and nutrients from the southern ocean to the tropical atlantic and thus plays a key role in ocean atmosphere exchange it feeds sub tropical upwelling linking high and low latitude ocean biogeochemistry but the dynamics of aaiw during the last deglaciation remain poorly constrained we present new multi decadal benthic foraminiferal cd ca and stable carbon isotope 13c records from tropical w atlantic sediment cores indicating abrupt deglacial nutrient enrichment of aaiw as a consequence of enhanced deglacial southern ocean upwelling intensity this is the first clear evidence from the intermediate depth tropical w atlantic that the deglacial reconnection of shallow and deep atlantic overturning cells effectively altered the aaiw nutrient budget and its geochemical signature the rapid nutrient injection via aaiw likely fed temporary low latitude productivity thereby dampening the deglacial rise of atmospheric co2

a deep sea coral record of north atlantic radiocarbon through the younger dryas evidence for intermediate water deepwater reorganization requires the existence of large mobile gradients of d 14 c in the ocean during the younger dryas the d 14 c water column profile from keigwin 2004 provides direct evidence for the presence of one such gradient at the beginning of the younger dryas 12 9 ka with a 100 offset between shallow 2400 m and deep water our early younger dryas data are consistent with this profile and also show a d 14 c inversion with 35 more enriched water at 2400 m than at 1700 m this feature is probably the result of mixing between relatively well 14 c ventilated northern source water and more poorly 14 c ventilated southern source intermediate water which is slightly shallower over the rest of the younger dryas our intermediate water deepwater coral d 14 c data gradually increase while the atmosphere d 14 c drops for a very brief interval at 12 0 ka and at the end of the younger dryas 11 5 ka intermediate water d 14 c 1200 m approached atmospheric d 14 c these enriched d 14 c results suggest an enhanced initial d 14 c content of the water and demonstrate the presence of large lateral d 14 c gradients in the intermediate deep ocean in addition to the sharp vertical shift at 2500 m the transient d 14 c enrichment at 12 0 ka occurred in the middle of the younger dryas and demonstrates that there is at least one time when the intermediate deep ocean underwent dramatic change but with much smaller effects in other paleoclimatic records

influence of compaction conditions on pore size distribution and saturated hydraulic conductivity of a glacial till the paper examines the hydraulic conductivity of a nonplastic till from northern quebec it is shown that the hydraulic conductivity is strongly influenced by the compaction degree of saturation and the variation of hydraulic conductivity with void ratio is influenced by compaction conditions determination of pore size distributions and microphotographs provide evidence that changes in hydraulic conductivity are related to the fabric of the compacted specimens and macroporosity developing when the soil is compacted at degrees of saturation less than that at the optimum key words till hydraulic conductivity microfabric

authigenic cadmium enrichments in suboxic sediments precipitation and postdepositional mobility the postdepositional mobility of cd and u has been investigated in north atlantic turbidites in order to validate their utility as proxies of paleo organic carbon fluxes in this region pelagic sediments are interspersed with relatively organic rich turbidites following instantaneous emplacement of turbidite units an oxidation front progressively migrated downwards into the suboxic turbidite thereby leading to redistribution of authigenic phases according to their affinity to different redox conditions authigenic cd concentrations show a large peak at the redox boundary and are significantly lower in the oxidized portion than in the deeper unoxidized part of the turbidite this distribution indicates that cd has been continuously remobilized by the oxidation front thereby suggesting high sensitivity of the cd species to the redox state and an efficient immobilization mechanism for cd under reducing conditions we propose the precipitation of cds as a plausible mechanism for removal of cd in reducing sediments rather than adsorption onto mineral surfaces this proposal is consistent with porewater data indicating diffusion of cd toward and uptake by suboxic sediments solubility calculations suggest that precipitation of cds may occur in suboxic sediments in the presence of trace levels of h2s below routine detection limits there is no evidence for release of cd or u back into seawater upon oxidation of reducing sediments the strong coupling between precipitation of authigenic cd and u and the early diagenetic degradation of organic carbon offers the potential of reconstructing paleo productivity using records of cd and u however postdepositional redistribution of authigenic cd and u may significantly alter records of authigenic cd and u thereby rendering paleo productivity reconstructions uncertain we propose that the cd u authigenic ratio may provide a qualitative indicator to assess the relative role of steady state incorporation relative to transient burn down enrichments

abrupt changes in high latitude nutrient supply to the atlantic during the last glacial cycle the supply of nutrients to the low latitude thermocline is largely controlled by intermediate depth waters formed at the surface in the high southern latitudes silicic acid is an essential macronutrient for diatoms which are responsible for a significant portion of marine carbon export production changes in ocean circulation such as those observed during the last deglaciation would influence the nutrient composition of the thermocline and therefore the relative abundance of diatoms in the low latitudes here we present the first record of the silicic acid content of the atlantic over the last glacial cycle our results show that at intermediate depths of the south atlantic the silicic acid concentration was the same at the lgm as it is today overprinted by high silicic acid pulses that coincided with abrupt changes in ocean and atmospheric circulation during heinrich stadials and the younger dryas we suggest these pulses were caused by changes in intermediate water formation resulting from shifts in the subpolar hydrological cycle with fundamental implications for the nutrient supply to the atlantic

response of eastern tropical atlantic central waters to atlantic meridional overturning circulation changes during the last glacial maximum and heinrich stadial 1 shows a mg ca temperature sensitivity of 0 19 mmol mol perc estimates of the lgm and hs1 thermocline temperatures are comparable to the present day values between 200 and 400 m water depth but were 1 2 1 5 c warmer at 550 570 m depth the hs1 thermocline waters 200 570 m depth did not show any warming relative to the lgm this is in contrast to previous climate model studies which concluded that tropical atlantic thermocline waters warmed significantly when atlantic meridional overturning circulation was reduced however our results suggest that thermocline temperatures of the northeastern tropical atlantic show no pronounced sensitivity to changes in the thermohaline circulation during glacial periods in contrast we find a significant increase in thermocline water salinity during the lgm 200 550 m depth and hs1 200 400 m depth with respect to the present day which we relate to changes in the wind driven circulation we infer that the lgm thermocline 200 550 m depth and the hs1 upper thermocline 200 400 m depth in the northeastern tropical atlantic was ventilated by surface waters from the north atlantic rather than the southern sourced waters this suggests that the frontal zone between the modern south atlantic and north atlantic central waters was probably shifted southward during the lgm and hs1

hydraulic conductivity and compressibility of mixtures of nagoya clay with sand or bentonite in this study a series of incremental loading oedometer tests and microscopic observations is carried out in order to investigate the influence of sand bentonite fractions on hydraulic conductivity and compressibility if sand particles do not form a skeletal structure and each particle is independent in the clay matrix an additive fraction of sand causes a decrease in the compressibility however it does not affect the hydraulic conductivity under the same consolidation pressure the additive fraction of bentonite contributes to a decrease in the hydraulic conductivity even for clayey materials in addition the relationship between the pore size parameter which represents the pore entrance size distribution and the hydraulic conductivity is discussed using a probabilistic model known as the general capillary model

science at the policy interface volcano monitoring technologies and volcanic hazard management this paper discusses results from a survey of volcanologists carried out on the volcano listserv during late 2008 and early 2009 in particular it examines the status of volcano monitoring technologies and their relative perceived value at persistently and potentially active volcanoes it also examines the role of different types of knowledge in hazard assessment on active volcanoes as reported by scientists engaged in this area and interviewees with experience from the current eruption on montserrat conclusions are drawn about the current state of monitoring and the likely future research directions and also about the roles of expertise and experience in risk assessment on active volcanoes while local knowledge is important it must be balanced with fresh ideas and expertise in a combination of disciplines to produce an advisory context that is conducive to high level scientific discussion

high resolution radiocarbon records trace episodes of zoophycos burrowing the unknown zoophycos producing organism potentially reworks marine sediments far deeper up to 1 m than common bioturbational mixing of the topmost sediment layer the zoophycos producer displaces planktonic foraminifera tests down to deep sediment levels hence may seriously bias the faunal and isotopic composition and in particular the radiocarbon age 14c of the ambient host sediment here we present three high resolution 14c records from sediment cores retrieved at intermediate water depths off brazil new zealand and norway where zoophycos burrows have biased 14c ages by 1000 5000 years based on closely spaced 14c ages and 14c plateau tuning we distinguish particular episodes with enhanced zoophycos production that coincide with time spans of decreased sedimentation and thus with probably reduced benthic nutrition off new zealand the actual burrowing activity was dated close to the bolling allerod younger dryas boundary displaced grains are traced from the ancient sediment surface of the younger dryas as far back as to the onset of heinrich stadial 1 and the terminal last glacial maximum these displaced 14c ages and similar 14c records obtained from two other sediment cores suggest that zoophycos producers generally mount a burrowing campaign during times when environmental conditions are switching toward a starved sedimentation regime during these tipping points zoophycos spreiten probably serve as storage space for nutrient rich particles foraged at the sediment surface and bioturbational mixed layer

rapid climate transitions in a coupled ocean atmosphere model recent geochemical data1 2 have challenged the view that rapid climate fluctuations in the north atlantic at the end of the last glacial were caused by the thermohaline circulation of the ocean being switched on or off instead these data suggest that the circulation pattern must have switched between a warm deep mode and a cold shallow mode probably associated with different sites of deep convection3 here i present simulations with a three dimensional ocean model coupled to an idealized atmosphere which show this kind of transition the mechanism for the transition is a rearrangement of convection in the north atlantic triggered by a brief freshwater pulse this results in a drop in sea surface temperature in the north atlantic by up to 5 c within less than 10 years the rate of north atlantic deep water nadw forma tion is the same in the cold climate as in the warm climate but nadw sinks to intermediate depths only while antarctic bottom water pushes north to fill the entire abyssal atlantic

internal structure of mount merapi indonesia derived from long offset transient electromagnetic data 1 a long offset transient electromagnetic lotem survey was carried out on merapi volcano indonesia in 1998 lotem data have been recorded at 41 receiver locations which cover a 10 km w e and a 15 km s n profile the signals were transmitted at four locations on the south west and north sides of merapi the data were interpreted with one dimensional 1 d inversions in addition two particular features were investigated with 3 d modeling on the south flank the magnetic field data show strong 3 d distortions consistently over the profile which can only be explained by a conductive near surface structure like a fracture filled with conductive fluids the simulation of topographic effects shows that the interpretation is not significantly affected on both profiles the most striking feature is a conductive layer of 20 m at depths of 500 1000 m below the surface and a thickness of 1 2 km the cause of the increased conductivity may be different for the summit area the intermediate zone and at the flanks below the summit in vicinity of the conduit the decrease in resistivity is produced either by hydrothermal fluids by partial melts or rocks altered by the hydrothermal system or by a combination in the intermediate zone between the conduit and the flanks either alteration or hydrothermal fluids may be the source of the conductivity increase fluids seem to be the most likely cause for the conductive layer at the flanks and the west east striking anomaly from the resistivity of the conductive layer and the typical porosity of volcanic rock we estimate fluid resistivities of 0 2 1 m

pore size distribution of a compacted silty soil after compaction saturation and loading soil microstructure is an important feature that controls soil behaviour at the macroscale this microstructure depends on the sample preparation method and evolves during saturation and loading this paper investigates the effects of compaction water content drying techniques adopted prior to performing porosimetry saturation and loading on the evolution of the microstructure of a silty soil mercury intrusion porosimetry is used to obtain the pore size distribution at different states of soil presenting single and double porosity it is observed that in presence of aggregates obtained from a compaction on the dry side of optimum the bimodal pore size distribution is not significantly affected by the saturation process at zero stress this feature of behaviour is quite specific to low plasticity silty soil conversely loading under saturated conditions has a more significant effect on the pore size distribution this bimodal distribution converges into a single mode of pore size when the stress is

suborbital intermediate water variability inferred from paired benthic foraminiferal cd ca and δ13c in the tropical west atlantic and linking with north atlantic climates abstract paired benthic cd ca and 13c records have been generated along core m35003 in the western tropical atlantic decreased glacial water column dissolved cadmium cdw and increased benthic 13c indicate enhanced ventilation with nutrient deplete intermediate waters in line with similar inferences from other north atlantic mid depth records an abrupt early deglacial 13c collapse that is associated with a marked positive cdw anomaly indicates a transient collapse of mid depth ventilation from north atlantic sources conceivably in conjunction with the h1 meltwater anomaly the cdw record displays fine scale fluctuations that mimic the greenland dansgaard oeschger d o cycles and show decreased cdw during stadials this pattern is opposite to cdw variations in a deep water record from bermuda rise that display increased cdw concentrations during stadials the divergent pattern between mid depth and deep water cdw records indicates millennial scale switches between deep and shallow convection in the glacial north atlantic at the pace of the d o climatic cycles several high amplitude anomalies occur in the cdw record that reach levels similar to those observed today in the north pacific while a substantial nutrient increase in the mid depth north atlantic cannot be ruled out during these events changes of pore water chemistry and cd p fractionation during biological uptake offer alternative scenarios to explain the peak cdw maxima

changes of the pore distribution of silty clay under the subway train loads vibrations induced by the passage of subway trains are a major concern in urban areas these vibrations can cause annoyance to people meanwhile they can cause the settlement of tunnels by loading on the structured soft soil around the tunnel it is known that the engineering behaviors of soft soil are determined by its microstructure therefore the changes of pore distribution under characteristic dynamic loads were studied in this paper through a series of dynamic triaxial tests and mercury intrusion porosimeter tests it is worth mentioning that the low order fundamental frequency should be paid more attention to the similar research under the dynamic loads the silty clay and mucky silty clay samples were all compacted the volume of large pores pore radius 400 nm significantly decreased while the volume of medium and small pores pore radius 400 nm increased due to the transformation of large pores the changes of pore distribution can be well reflected by the fractal dimensions in thermodynamic model

are great salinity anomalies advective abstract great salinity anomalies gsas have been observed to propagate around the north atlantic subpolar gyre similar anomalies occur in the third hadley centre coupled atmosphere ocean gcm hadcm3 of preindustrial climate it has been hypothesized that these salinity anomalies result from the advection of anomalously low salinity waters around the subpolar gyre here the consequences of using passive tracers in the hadcm3 climate model to tag the anomalously low salinity water associated with a gsa in the greenland and labrador seas are reported rather than predominantly advecting around the modeled subpolar gyre in accordance with the upper ocean salinity anomaly the tracers mix to intermediate depths before becoming incorporated into the model s north atlantic deep water horizontal advection of the tracer in the upper ocean is limited to around 1000 km compared with the gyre scale propagation of the salinity anomalies it is concluded that gsas are unlikely to be caused by the advection of

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

evidence from the high latitude north atlantic for variations in antarctic intermediate water flow during the last deglaciation we present evidence that the characteristic chemical signature based on coupled benthic foraminiferal cd ca and d13c of antarctic intermediate waters aaiw penetrated throughout the intermediate depths of the atlantic basin to the high latitude north atlantic during the abrupt cooling events of the last deglaciation heinrich 1 and the younger dryas aaiw may play the dynamic counterpart to the bipolar seesaw when near freezing salty bottom waters from the antarctic aabw sluggishly ventilate the deep ocean our data reinforce the concept that interglacial circulation is stabilized by salinity feedbacks between salty northern sourced deep waters nadw and fresh southern sourced waters aabw and aaiw further the glacial ocean may be susceptible to the more finely balanced relative densities of nadw and aaiw due to either freshwater input or a reversal of the salinity gradient such that the ocean is poised for nadw collapse via a negative salinity feedback the unstable climate of the glacial period and its termination may arise from the closer competition for ubiquity at intermediate depths between northern and southern sourced intermediate waters

the permeability of natural soft clays part ii permeability characteristics reply the permeability characteristics of a number of intact natural soft clays from quebec the usa and sweden have been investigated in the laboratory the variation of permeability with void ratio is best represented in terms of a linear e vs lg k relation which is generally valid in the range of volumetric strains encountered in engineering practice the permeability at the in situ void ratio is shown to be a complex function of such parameters as the void ratio the clay fraction the plasticity index and the fabric of the clay permeability anisotropy is negligible in marine clays the e vs lg k relationships of the various clays tested are well ordered in terms of an empirical parameter ip clay fraction irrespective of the geological origin of the clay the slope of the e vs lg k relationship referred to as permeability change index ck is simply related to the initial void ratio by ck 0 5eo keywords permeability clays laboratory tests permeability anisotropy permeability void ratio re

glacial deep water geometry south atlantic benthic foraminiferal cd ca and δ13c evidence a depth transect of cores from 1268 to 3909 m water depth in the western south atlantic are ideally situated to monitor the interocean exchange of deep water and variations in the relative strength of northern and southern sources of deep water production benthic foraminiferal cd ca and 13c data suggest that glacial north atlantic intermediate water gnaiw extended at least as far south as 28 s in the western south atlantic the core of nutrient depleted water was situated at 1500 m above and below water masses with higher nutrient concentrations when examined in conjunction with published paired cd ca and 13c from intermediate depth cores from other basins it appears that the extent of gnaiw influence on the intermediate waters of the world s oceans was less than suggested previously differentiating among possible pathways for the glacial deep ocean 3 km requires a better understanding of the controls on cd ca and 13c values of benthic foraminifera

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

land subsidence and pore structure of soils caused by the high rise building group through centrifuge model test abstract in the urban area of shanghai the dewatering of groundwater was controlled strictly and the engineering environment effect of the high rise building group became to be the main cause of land subsidence in shanghai based on the high rise building group in the soft soil area in shanghai the mechanism of land subsidence was studied in this paper by the centrifuge model test the central area of the building group has larger subsidence and the subsidence superimposition effect is obvious it can exceed the allowance and cause land subsidence hazard the land subsidence affected by the different building distances was also studied for smaller building distances the subsidence superimposition effect is more obvious the engineering characteristics of soils are controlled by the state of pore structure of soils to a great extent the parameter of specific subsidence was put forward as a tie to analyze the relationship between land subsidence and pore structure of soils the pore structure of each soil layer was studied by the mercury intrusion porosimetry test mip and the pore distribution of each soil layer was studied by the fractal theory there are mainly macropores in silty clay of layer no 4 clayey soil of layer no 8 silty sand of layer no 7 and layer no 9 in shanghai the ink bottle effect exists in the intrusion stage in the mip test there are four different fractal dimensions in silty clay of layer no 4 and clayey soil of layer no 8 and three different fractal dimensions in silty sand of layer no 7 and layer no 9

changes in the distribution of δ13c of deep water σco2 between the last glaciation and the holocene carbon isotopic measurements on the benthic foraminiferal genus cibicidoides document that mean deep ocean 13c values were 0 46 lower during the last glacial maximum than during the late holocene the geographic distribution of 13c was altered by changes in the production rate of nutrient depleted deep water in the north atlantic during the late holocene north atlantic deep water with high 13c values and low nutrient values can be found throughout the atlantic ocean and its effects can be traced into the southern ocean where it mixes with recirculated pacific deep water during the glaciation decreased production of north atlantic deep water allowed southern ocean deep water to penetrate farther into the north atlantic and across low latitude fracture zones into the eastern atlantic mean southern ocean 13c values during the glaciation are lower than both north atlantic and pacific 13c values suggesting that production of nutrient depleted water occurred in both oceans during the glaciation enriched 13c values in shallow cores within the atlantic ocean indicate the existence of a nutrient depleted water mass above 2000 m in this ocean

cadmium and delta13c paleochemical ocean distributions during the stage 2 glacial maximum changes in heat and salt transport by ocean currents have been implicated in ice age climate cycles weyl 1 968 newell 1 974 broecker et al 1 990b in addition to the direct physical effects of the ocean on climate the ocean carbon system controls atmospheric co2 and the co2 fluctuations documented in ice core bubbles barnola et a1 1 987 neftel et a1 1 988 are thought to be a significant factor in climate oscillations hansen et al 1 984 dramatic changes in oceanic circulation patterns and carbon system chemistry have occurred during the late quaternary glacial interglacial global climate cycles boyle keigwin 1 982 curry lohmann 1 983 shackleton pisias 1 984 boyle keigwin 1 987 duplessy et al 1 988 curry et al 1 988 broecker et al i 990a these changes in the ocean system may be significant driving forces in the progression of ice age co2 cycles toggweiler sarmiento 1 985 ennever mcelroy 1 985 wenk siegenthaler 1 985 boyle 1 988a b broecker peng 1 990 the oceanic distributions of c513c cd and other carbon system linked properties are controlled by the interaction between biological uptake and decomposition with the general circulation of the ocean because records of past oceanic cd and c5 1 3c are preserved in shells of planktonic and benthic foraminifera

the role of deep ocean circulation in setting glacial climates the glacial cycles of the pleistocene involve changes in the circulation of the deep ocean in important ways this review seeks to establish what were the robust patterns of deep sea water mass changes and how they might have influenced important parts of the last glacial cycle after a brief review of how tracers in the modern ocean can be used to understand the distribution of water masses i examine the data for biogeochemical circulation rate and conservative tracers during glacial climates some of the robust results from the literature of the last 30 years include a shoaled version of northern source deep water in the atlantic expanded southern source water in the abyss and deep ocean salt rather than heat stratification of the last glacial maximum lgm deep sea and several lines of evidence for slower overturning circulation in the southern deep cell we combine these observations into a new idea for how the ocean atmosphere system moves from interglacial to glacial periods across a single cycle by virtue of its influence on the melting of land based ice around antarctica cooling north atlantic deep water nadw leads to a cold and salty version of antarctic bottom water aabw this previously underappreciated feedback can lead to a more stratified deep ocean that operates as a more effective carbon trap than the modern helping to lower atmospheric co 2 and providing a mechanism for the deep ocean to synchronize the hemispheres in a positive feedback that drives the system to further cooling

effects of soil structure on the permeability of saturated maryland clay this study focuses on the permeability of saturated maryland clay a natural expansive soil that can be found close to the university of newcastle australia previous studies on this material cond

a discussion of the application of mercury intrusion porosimetry for the investigation of soils including an evaluation of its use to estimate volume change in compacted clayey soils

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

the relationship between earthquake swarms and magma transport kilauea volcano hawaii a detailed investigation of earthquake locations and focal mechanisms for swarms associated with intrusive events at kilauea volcano hawaii further illuminates the relationships among stress state faulting and magma transport we determine the earthquake locations and mechanisms using a three dimensional crustal model to improve their accuracy and consistency swarms in kilauea s upper east and southwest rift zones from the years 1980 through 1982 provide clear evidence for the propagation and or dilation of dikes focal mechanisms are predominantly strike slip and the faulting and inferred dike orientations can be interpreted quite consistently in terms of the model ofhill 1977 stresses induced by the summit magma reservoir system strongly control faulting and magma transport in the rift zones close to the summit

geothermal evolution of an intruded dike in the rift zone of kilauea volcano hawaii from vlf and self potential measurements abstract self potential sp and vlf measurements were made in 1973 1975 1995 1997 and 2012 across a basaltic dike that intruded into the koae fault zone of kilauea volcano hawaii in may 1973 the sp anomaly remained strong throughout in 2012 it was at about 60 of the strength it had in 1973 in contrast the vlf anomaly though diminished was still observable in 1995 1997 but by 2012 it had disappeared a hydrothermal dike model with parameters calibrated by modeling the solidification of kilauea iki lava lake is used to calculate temperatures and conductivity variation following jaeger s 1957 method we find that the time in years for a dike of width w m to solidify is 0 0075w2 thus a 1 m dike solidifies within the first few days and after 39 years is only tens of degrees above ambient given the orders of magnitude difference between the conductivities of wet and dry basalt we infer that after solidification the vlf anomalies were caused by induction in a localized veil of wet hot basalt enveloping the dike that was generated initially by condensation of steam and subsequently by condensation of evaporated water as temperatures reduced the conductivity anomaly persisted until the mid nineties by 2012 temperatures and condensation were too small for a vlf signal the persistent sp anomaly is attributed to localized fluid disruption with evaporation mainly at the water table and in the vadose zone streaming potentials are associated with evaporative circulation in the vadose zone next to the dike a positive potential is generated by upward flow of moisture laden air with a smaller negative potential on its flanks from downward infiltrating rainwater the analysis indicates that the combination of sp and vlf measurements can characterize the evolving geothermal regime of intrusions above the water table

a microstructure approach to the sensitivity and compressibility of some eastern canada sensitive clays investigation of micro macro relationships in soils most often concerns granular soils in which both the elemental unit the grain and the physical laws governing inter grain interactions appear to be better known the situation is different for clays because the elementary unit and the inter unit interactions at the micro scale are more difficult to characterise in fine grained soils it has been shown that an intermediate level corresponding to the way clay and fine grained particles are arranged together had to be considered so as to link microscopic features to macroscopic behaviour an investigation of the change in microstructure during compression carried out some time ago on a sensitive clay from canada demonstrated that studying the changes in pore size distribution provides a satisfactory description of microstructure changes during compression the analysis is applied here to six other sensitive clays first a careful examination of the intact and remoulded microstructure is conducted in o

no evidence for a deglacial intermediate water δ14c anomaly in the sw atlantic abstract the last deglaciation was characterized by an increase in atmospheric pco 2 and decrease in atmospheric radiocarbon activity one hypothesis is that these changes were due to out gassing of 14 c depleted carbon from the abyssal ocean reconstructions of foraminiferal 14 c from the eastern tropical pacific arabian sea and high latitude north atlantic show that severe depletions in 14 c occurred at intermediate water depths during the last deglaciation it has been suggested that 14 c depleted water from the abyss upwelled in the southern ocean and was then carried by antarctic intermediate water aaiw to these sites however locations in the south pacific in the direct path of modern day aaiw do not exhibit the 14 c excursion and therefore cast doubt upon the aaiw mechanism de pol holz et al 2010 rose et al 2010 here we evaluate whether or not a deglacial 14 c anomaly occurred at intermediate depths in the southwest atlantic we find that the deglacial benthic 14 c trend at our site is similar to the atmospheric 14 c trend our results are also largely consistent with results from u th dated corals at shallower water depths on the brazil margin mangini et al 2010 we find no evidence in the southwestern atlantic of a 300 decrease in intermediate water 14 c from 18 to 14 kyr bp like that observed in the eastern tropical pacific marchitto et al 2007 when our results are paired with those from the south pacific it appears aaiw did not carry a highly 14 c depleted signal during the deglaciation another source of carbon is apparently required to explain the intermediate depth 14 c anomalies in the north atlantic indian and pacific oceans

deglacial variability in the surface return flow of the atlantic meridional overturning circulation 1 benthic foraminiferal cd ca from a florida current sediment core documents the history of the northward penetration of southern source waters within the surface return flow of the atlantic meridional overturning circulation amoc cd seawater estimates cdw indicate that intermediate depth southern source waters crossed the equator and contributed to the florida current during the bolling allerod warm period of the last deglaciation consistent with evidence of only a modest amoc reduction compared to today the cdwestimates also provide the first paleoceanographic evidence of a reduction in the influence of intermediate depth southern source waters within the florida current during the younger dryas a deglacial cold event characterized by a weak north atlantic amoc our results reveal a close correspondence between the northward penetration of intermediate depth southern source waters and the influence of north atlantic deep water suggesting a possible link between intermediate depth southern source waters and the strength of the atlantic amoc

antarctic intermediate water circulation in the south atlantic over the past 25 000 years antarctic intermediate water is an essential limb of the atlantic meridional overturning circulation that redistributes heat and nutrients within the atlantic ocean existing reconstructions have yielded conflicting results on the history of antarctic intermediate water penetration into the atlantic across the most recent glacial termination in this study we present leachate foraminiferal and detrital neodymium isotope data from three intermediate depth cores collected from the southern brazil margin in the south atlantic covering the past 25 kyr these results reveal that strong chemical leaching following decarbonation does not extract past seawater neodymium composition in this location the new foraminiferal records reveal no changes in seawater nd isotopes during abrupt northern hemisphere cold events at these sites we therefore conclude that there is no evidence for greater incursion of antarctic intermediate water into the south atlantic during either the younger dryas or heinrich stadial 1 we do however observe more radiogenic nd isotope values in the intermediate depth south atlantic during the mid holocene this radiogenic excursion coincides with evidence for a southward shift in the southern hemisphere westerlies that may have resulted in a greater entrainment of radiogenic pacific sourced water during intermediate water production in the atlantic sector of the southern ocean our intermediate depth records show similar values to a deglacial foraminiferal nd isotope record from the deep south atlantic during the younger dryas but are clearly distinct during the last glacial maximum and heinrich stadial 1 demonstrating that the south atlantic remained chemically stratified during heinrich stadial 1