transport and selective uptake of radium into natural clay minerals abstract understanding of the environmental behavior of ra is important from the viewpoint of the long termed repository safety of radioactive waste but investigation of ra behavior in natural environment is difficult to detect we found isotopic evidence of ra transportation and its selective uptake into clay minerals from pb isotopic analyses illite grains found in calcite veins included in sandstone near the oklo uranium deposit republic of gabon show extremely low 207 pb 206 pb 0 0158 isotopic ratios although the pb isotopic ratios of calcite and quartz coexisting with illite indicate the formation age of each component those of illite do not in addition illite grains having low 207 pb 206 pb isotopic ratios contain a strongly large amount of ba 1230 to 6010 ppm in contrast with low contents of ba in calcite and quartz 207 pb 206 pb isotopic data suggest an excess of 206 pb due to selective adsorption of 226 ra and also ba into illite grains this is a very rare example to show evidence of the selective adsorption behavior of ra from the isotopic excesses of 206 pb although the adsorption ability of ra itself in nature was largely reported

possible dust devils vortices on mars this paper presents the results of a study of local vortices and dust devils on mars as observed by viking landers 1 and 2 it is found that these vortices are most common during martian spring and summer as occurs on earth seven of the vortices involve wind speeds that may raise dust from the martian surface there is no indication that these possible dust devils contribute to the planet wide spread of major dust storms however it appears that they may help in maintaining the atmospheric dust content the data indicate that there is no preference in rotation direction at least to core diameters of 300 m corresponding to a region of influence of about 3 km diameter

226ra in marine barite new constraints on supported 226ra abstract following the pioneering work of paytan et al a paytan et al geochim cosmochim acta 60 1996 4313 4319 new investigations have been undertaken on marine barite separated from central and western equatorial pacific sediments these investigations are designed to achieve a better quantification of supported 226 ra activities in the separated samples enabling the use of excess 226 ra 226 ra ex in marine barite as a tool for dating holocene sediments instrumental neutron activation analysis allowed first to measure significant 238 u activities in the separated samples attributable to highly insoluble minerals that like barite are resistant to the chemical treatment used in this study tio 2 minerals zircon monazite within these u rich minerals 226 ra activities are in secular equilibrium with 238 u second the study of the 226 ra signal in old barite samples that do not contain any residual 226 ra ex activities provided accurate constraints on the amount of 226 ra produced by unsupported 230 th the remaining 226 ra activities corrected for the 238 u contribution appeared to decrease with depth with a slope comparable to that defined by the bulk 230 th ex activities the consistency of this deep trend allowed its extrapolation upwards to the sediment top in order to obtain an estimate of the 226 ra activities produced by unsupported 230 th in the holocene barite samples the total correction for supported 226 ra in the holocene barite samples used in this study therefore consists of the sum of 226 ra activities in secular equilibrium with 238 u within minerals and 226 ra activities produced by unsupported 230 th thus estimated the resulting correction is low for samples separated from central equatorial pacific sediments compared with both the total 226 ra activities measured in barite and results of previous studies the magnitude of the correction is nevertheless higher for samples from western equatorial pacific sediments which display a lower barite purity the corrected 226 ra in barite profiles are in agreement with the general trend observed for long half life radionuclides with a similar mixed layer in the sediment top thus adding confidence in the use of this tool below the mixed layer the exponential decay of 226 ra ex activities in barite allowed the determination of sedimentation rates that agree with the estimates for the two investigated sites ultimately one of the main uses for the 226 ra in barite dating method will be its application to holocene sediments from the southern ocean where dating is often problematic

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

monitoring mars with the hubble space telescope 1990 1991 observations images of mars obtained using the planetary camera on the hubble space telescope during 1990 and 1991 are described and analyzed multispectral images of mars record the martian season between ls 348 and 60 corresponding to late winter and spring in the northern hemisphere the wavelengths of these observations varied between 230 nm in the ultraviolet and 890 nm in the near infrared we use these images to discuss atmospheric and polar phenomena to constrain the aerosols and ozone in the martian atmosphere and to compare surface albedo features within this data set as well as with previous observations two methods are used to constrain the opacity of the martian atmosphere comparisons of ultraviolet images with atmospheric scattering models and examination of contrast changes of surface features observed at visible wavelengths our observations are consistent with a mars which was quite different from the planet when it was viewed by viking we estimate an upper limit of 0 1 for equatorial dust opacity near vernal equinox compared to values of 0 4 to 0 5 measured in chryse by viking lander 1 later at ls 60 an upper limit of 0 2 was found for dust in the southern hemisphere except for suggestions of local dust activity near the north polar cap in late spring there was no visual evidence of dust storms on the planet the hartley band of ozone is within the f230w filter bandpass and the 230w 336w ratio is therefore sensitive to ozone high latitude ozone is observed at a concentration similar to that observed by mariner 9 a seasonal dependence in ozone concentration was observed with concentration decreasing at northern arctic latitudes and increasing at southern midlatitudes as ls increases from 350 to 60 despite the difference in dust loading the behavior of condensate clouds and the recession of the north polar cap are consistent with those observed during viking years late winter images of the north polar region reveal an active north polar hood with a maximum uv opacity of about 0 25 near 50 latitude the hood seems to have an annular form with the central polar regions having smaller opacity clouds observed in the northern hemisphere to the south of the hood boundary are suggestive of fronts similar to those observed during the mariner 9 mission a diurnal variation in the hood clouds which is anti correlated with the amount of water vapor in the atmosphere is noted spring images show significant clouds in the tharsis elysium and arabia regions the most optically thick components of these clouds are those near elysium alba patera and tithonius in the afternoon although these regions also are bright on the morning limb the cloud associated with elysium had the largest optical depth for a cloud in the uv 0 4 most of the hst monitoring sequences were targeted on the syrtis major region an area which was intensively studied during the viking mission during viking there were major changes in the region which were attributed to the two major 1977 global dust storms on mars our series of images was projected onto map grids and photometrically corrected in order to study changes in the syrtis albedo features to first order syrtis does not change over the time period of these observations as would have been expected if they followed major global dust storms during the preceding season images were deconvolved using the richardson lucy iterative algorithm to remove the defocussing effects of the spherical aberration of the hst primary even when mars subtended less than 5 arcsec in may 1991 the images were scientifically useful and comparable to photographic images obtained at opposition although the data are subject to the solar pointing constraint for hst the relatively slow movement of the allowed observation window which is more than one half martian year with respect to the martian seasons will permit us to address the question of major variations in the martian atmosphere

on suspended barite and the oxygen minimum in the southern ocean particulate ba profiles were measured in the indian sector of the southern ocean the largest fraction 80 of this barium is present as barite microcrystals the profiles of total barium are characterized by a subsurface maximum between 200 and 500 m depth in the vicinity of the oxygen minimum highest barium values are found just south of the polar front while lowest values occur close to the antarctic divergence between the divergence and the polar front a tight inverse relationship is observed between oxygen in the oxygen minimum and barium in the barium maximum this relationship disappears north of the polar front since suspended barite is known to be of biological origin the correlation of barite with oxygen suggests that the observed decrease of oxygen in the oxygen minimum between the divergence and the polar front is due to local consumption of oxygen it is proposed that deep low oxygen water is advected towards the divergence where upwelling occurs and where this water subsequently partly spreads out to the north north east as entrained by the antarctic circumpolar current oxidation of locally produced organic matter with which barite crystals are associated consumes oxygen and sets free individual discrete barites as a result oxygen decreases and barite increases away from the divergence with barite integrating former biological processes

a precise high throughput method for determining sr ca sr ba and ca ba ratios in marine barite 1 recent evidence suggests that marine barite an inorganic phase preserved in oxic deep sea sediments may record seawater sr and ca concentrations here we describe a novel method for determining sr ca sr ba and ca ba ratios of discrete marine barite separates marine barite separated from deep sea sediments is dissolved in a basic ethylene diamine tetra acetic acid edta solution and subsequently analyzed using an inductively coupled plasma optical emission spectrometer icp oes since dissolution occurs within 2 5 days and 15 samples can be analyzed on the icp oes per hour data acquisition is rapid compared with other procedures the method yields precisions of 0 7 sr ca 0 6 sr ba and 1 0 ca ba which are reproducible within 1 7 sr ca 1 7 sr ba and 2 5 ca ba precise determination of trace element incorporation in marine barite has implications for paleoceanography development of seawater sr and ca concentration curves and calculation of barite solubility in both the modern and ancient ocean

hubble space telescope observations of the martian aphelion cloud belt prior to the pathfinder mission seasonal and interannual variations the presence of a globally extant equatorial belt of water ice clouds on mars is quantitatively investigated using data from three seasons of our hubble space telescope synoptic monitoring program 1993 1997 a subset of the 1996 1997 images covers the landing site of the mars pathfinder including a set of images taken after touchdown using multicolor imaging from the wide field planetary camera and the wide field planetary camera 2 we characterize both water ice cloud and dust optical depths as a function of latitude at several local times for each observing epoch the analysis technique models calibrated data using a multiple scattering radiative transfer code our results support the initial results of clancy et al 1996a regarding changes between the aphelion and perihelion climate of mars and provide a more detailed look at the development and decay of the cloud belt comparing our dust optical depths to those of the viking landers for the same seasons we note a trend toward lower dust loading in late northern winter and in spring our observations of the pathfinder site in july 1997 reveal a dust opacity in good agreement with that reported by pathfinder smith et al 1997b in addition the serendipitous occurrence of a dust storm in valles marineris in late june 1997 allows us to derive a set of dust single scattering albedos for use in more accurately modeling the dust s radiative properties and effects

three dimensional time lapse velocity tomography of an underground longwall panel three dimensional velocity tomograms were generated to image the stress redistribution around an underground coal longwall panel to produce a better understanding of the mechanisms that lead to ground failure especially rockbursts mining induced microseismic events provided passive sources for the three dimensional velocity tomography surface mounted geophones monitored microseismic activity for 18 days eighteen tomograms were generated and high velocity regions correlated with high abutment stresses predicted by numerical modeling additionally the high velocity regions were observed to redistribute as the longwall face retreated indicating that velocity tomography may be an appropriate technology for monitoring stress redistribution in underground mines

tornado like vortexgenesis in a simplified numerical model abstract a novel approach to the modeling of tornado like vortexgenesis has been developed and is used to articulate the sequence of events that leads to tornadogenesis the pseudostorm is an idealized thunderstorm representation and emulates the storm relative flow into an updraft of the horizontal streamwise vorticity that is baroclinically generated in cold air outflow by not explicitly simulating the morphology of a tornadic thunderstorm but instead concentrating on the development of low level rotation and tornado scale vortices the authors are able to transcend many of the experimental limitations encountered by cloud modelers intense near ground cyclonic vortices which are classified herein as tornado like evolve solely from horizontal streamwise vorticity due to buoyancy gradients and friction if present at the lower boundary regardless of the lower boundary condition none of the vortices exceed the thermodynamic speed limit based on the vertically integrated buoyancy or convect

mars atmospheric opacity effects observed in the northern hemisphere by viking orbiter imaging observations of changing mars contrasts by viking orbiter television cameras have provided a description of changing atmospheric opacity in the southern hemisphere paper 1 this report extends those measurements into the northern hemisphere over a greater time period and provides a detailed description of photometric changes at the lander sites as seen from orbit reflectivity changes compared with optical depth increases produced by four dust storms indicate mean particle scattering changes with storm evolution as well as substantial opacity in the northern hemisphere for the duration of nearly a martian year

the effect of sample disturbance on laboratory properties of lac du bonnet granite laboratory properties of lac du bonnet granite samples collected at depths ranging from near surface to 1000 m were established the laboratory properties indicated that either the in situ properties were changing with depth or the samples were changing with depth comparison of p wave velocities in the samples and in situ confirmed the latter i e sample disturbance was affecting the laboratory properties the strength of the damaged samples indicated that sample disturbance affected the cohesion of the material not the frictional properties and that the cohesion loss cannot be accounted for by applying a confining stress sample disturbance started to affect the laboratory properties of lac du bonnet granite when the maximum far field in situ stress exceeded about 10 of the unconfined compression strength key words sample disturbance core discing cohesion brittle rocks damage microcracks stress dependent young s modulus

mesoscale linear streaks on mars environments of dust entrainment abstract variable surface albedo features on mars are likely caused by the entrainment and deposition of dust by the wind most discrete markings are associated with topographic forms or with regional slopes that serve to alter the effective wind shear stress on the surface some of the largest variable features here termed mesoscale linear streaks are up to 400 km in length and repeatedly occur in one of the smoothest regions of mars amazonis planitia their orientations and apparent season of variability as observed by viking and mars orbiter cameras indicate linear streak formation by enhanced surface wind stresses during regional or local dust storms and during the initial stages of global dust storms they provide an example of the ability of large scale winds without significant local enhancement to initiate dust motion on mars the sizes and spacing of the linear streaks may be controlled by boundary layer rolls the repetitive formation of these streaks over a span of more than 11 mars years gives one measure of the stability of mars eolian processes

mars orbiter camera observations of martian dust devils and their tracks september 1997 to january 2006 and evaluation of theoretical vortex models 1 a multiyear planet wide survey of martian dust devils was conducted using observations from mars global surveyor mars orbiter camera acquired through 21 january 2006 a total of 223 350 images were surveyed and 11 456 dust devils were seen in 0 4 of the images 11 5 in the southern and 88 5 in the northern hemisphere dust devils were observed at latitudes from 71 9 s to 62 2 n over a range of surface albedos am 0 11 0 22 and elevations from hellas 8750 m to arsia mons 17 250 m the light and dark toned streaks created by dust devils were observed from 80 s to 80 n and changed on timescales as short as 1 month at mid to high latitudes seasonal changes in streak patterns contribute to the seasonal wave of darkening observed telescopically from earth dust devils were observed in all seasons in both hemispheres with the exception of ls 202 8 281 5 in the north peak activity occurred during midsummer in each hemisphere five regions in amazonis syria claritas meridiani and gusev were monitored regularly amazonis had the largest dust devils and was the most active planet wide with annual activity occurring from ls 8 5 197 interannual variability resulted from dust storms and planet encircling dust hazes which were observed to initiate and abate dust devil activity there was no evidence suggesting dust devils cause or lead to initiation of dust storms model derived tangential wind speeds of large vortices were 20 m s 1 at 20 m above the surface dust flux calculations suggest that dust devils are a contributor to the background dust opacity observed through northern spring and summer

barium sio2 excess and p2o5 as proxies of biological productivity in the middle east during the palaeocene and the latest palaeocene benthic extinction event the distribution of barium and other elements related to biological productivity has been studied in two palaeocene sections from the middle east in the bathyal ben gurion section israel ba ba al2o3 15 concentrations are low in the range 0 04 to 0 3 in the lower palaeocene and very high 1 to 2 throughout most of the upper palaeocene in the neritic gebel aweina section in egypt ba values are low 0 1 throughout the entire palaeocene the ba enrichments at ben gurion and their correlations with increases in p2o5 and opaline silica and local and global 13c maxima indicate that upwelling and high productivity were important in this region during the late palaeocene the absence of ba enrichments in the shallower gebel aweina section probably reflects the strong depth dependence of biobarium deposition in the uppermost palaeocene at the level where the global benthic extinction event is registered ba concentrations in the ben gurion section increase to anomalous 6 which suggests that upwelling and possibly wind strengths intensified during this event the results speak against deep water formation in this region since downwelling and not upwelling is required

an excess 226ra chronology for deep sea sediments from saanich inlet british columbia abstract to further explore the efficacy of 226 ra excess dating for deep sea sediments previously dated varve sediments from saanich inlet were investigated ages obtained using 226 ra excess are comparable to the varve ages in the upper 20 25 m of the sedimentary record but radiometric ages for those sediments older than c 4000 yr bp are significant underestimates this results from major changes in sedimentation within saanich inlet around 4000 yr bp linked to rising sea levels with younger sediments characterised by a higher biogenic contribution resulting from the establishment of an anoxic fjord environment the older sediments were deposited in a shallow water inlet characterised by variable ra mass balance and non radiogenic losses therefore while 226 ra excess can produce reliable dates its application may be limited where the relative significance of authigenic and allogenic input and bottom water anoxia has been variable and where closed system behaviour is compromised

terrigenous fe input and biogenic sedimentation in the glacial and interglacial equatorial pacific ocean many ocean regions important to the global carbon budget including the equatorial pacific ocean have low chlorophyll concentrations despite high levels of conventional nutrients iron may instead be the limiting nutrient and elevated input of terrigenous fe during windy glacial episodes has been hypothesized to stimulate oceanic productivity through time and thus regulate the oceanic and atmospheric co2 balance to test whether particulate fe input is related to the accumulation of biogenic matter in one important low chlorophyll high nutrient area that is the equatorial pacific ocean we present results from a suite of sediment cores that collectively record biogenic deposition through the last six glacial interglacial cycles 600 000 years our data set includes new chemical data on total fe terrigenous and biogenic components in three cores as well as previously published mineralogic records of coljan input to the region chemical spectral and stratigraphic analysis indicates that 1 terrigenous input to the region shows no consistent pattern of either glacial or interglacial maxima 2 the accumulation of particulate fe is closely related to the accumulation of terrigenous matter linear r 2 0 81 0 98 3 there are no coherent spectral relationships between fe input and glacial periodicity i e 5180 in any of the orbital frequency bands 4 the linear and cross spectral correlations between fe or coljan input and caco3 concentration are most commonly the strongest observed relationships between fe and any biogenic component yet indicate a largely inverse pattern with higher fe being associated with low caco3 5 there is no consistent linear r 2 correlation or spectral coherence between the accumulation of fe and that of caco3 corg or opal thus in total there is no relationship between terrigenous fe input and sedimentary sequestering of carbon additionally although we cannot specifically address the potential for changes in solubility of the terrigenous fraction that may be driven by a terrigenous compositional change the fe ti ratio which monitors first order mineralogic changes records only slight variations that also are linearly and spectrally unrelated to glacial periodicity the bulk fe flux and the accumulation of any biogenic component finally we find that the paleoceanographic flux of fe is several order of magnitudes larger than modem observations of coljan fe input suggesting that the long term importance of fe input by dust storms which deliver fe on the order of the sedimentary burial may be underestimated the removal of particulate terrigenous fe from the recently discovered source within the equatorial undercurrent however remains unquanfified and may also prove significant

mars dust devil track survey in argyre planitia and hellas basin dust devils and dust devil tracks have been frequently observed in viking orbiter and mars orbiter camera moc images but the parameters that control their distribution have been poorly constrained here we investigate the abundance of dust devil tracks in two large study areas argyre planitia and hellas basin using a survey of over 3000 moc narrow angle na images we report the effect of season elevation and surface properties on track distribution using measurements of dust devil track density the number of dust devil tracks per square kilometer in both areas dust devil tracks occur predominantly in summer and are rarely observed in winter the lifetime of dust devil tracks is inferred to be short i e less than a few months there is no unambiguous correlation of abundance with elevation rather the spatial distribution follows albedo patterns suggesting that dust availability controls the abundance of dust devil tracks we estimate the total dust lifting potential of dust devils using the average dust devil track density for argyre and hellas and conclude that unless the average dust devil track is greater than 20 m wide longer than 2 km and more than 40 mm deep they cannot account for the estimated global sedimentation rate in addition by comparing 2 mars years of observations we find no evidence of an increase in dust devil track density prior to the global dust storm that occurred in june 2001 we conclude that dust devils did not trigger this storm

the influence of particle composition on thorium scavenging in the ne atlantic ocean pomme experiment abstract 230th 232th and 234th were analyzed in sinking particles collected by moored and drifting sediment traps in the ne atlantic ocean pomme experiment in order to constrain the phase s carrying th isotopes in the water column it reveals a contrasted behaviour between 234th and 230th 234th is correlated to the particulate organic carbon suggesting that it is primarily scavenged by organic compounds in the surface waters 230thxs is correlated with mn ba and the lithogenic fraction that are enriched in small suspended particles and incorporated in the sinking particulate flux throughout the water column the lack of correlation between 230thxs and caco3 or biogenic silica bsi indicates that caco3 and bsi are not responsible for 230th scavenging in the deep waters of this oceanic region 230th is generally correlated with the lithogenic content of the trapped material but this correlation disappears in winter during strong atmospheric dust inputs suggesting that lithogenic matter is not directly responsible for 230th scavenging in the deep waters or that sufficient time is required to achieve particle solution equilibration mno2 could be the prevalent 230thxs bearing phase the narrow range of kd mno2th obtained for very contrasted oceanic environments supports a global control of 230thxs scavenging by mno2 and raises the possibility that the 230th 231pa fractionation is controlled by the amount of colloidal mno2 in seawater

fluxes of 226ra and barium in the pacific ocean the importance of boundary processes abstract the 226 ra ba ratio in particles collected in sediment traps decreases with depth fluxes of ba and al increase with depth these observations cannot be explained by simple vertical processes instead they require a component to the deep flux which originates at the ocean margins we suggest that the deep traps are enriched in ba through the advection of barite originally precipitated in biologically productive regions of the ocean margin this source is less important for 226 ra because some is lost by radioactive decay between the precipitation of barite on the margin and outward transport the boundary flux is an important source of material to the deep sea from 226 ra fluxes in the upper 1000 m of the water column we estimate that the residence time of 226 ra in the upper ocean is 400 years the removal of 226 ra in the particle flux is approximately balanced by the upwelling of waters enriched in 226 ra

barium and the late paleocene δ13c maximum evidence of increased marine surface productivity deep sea sediment ba ba al2o3 sample 15 ba aluminosilicate records show increasing values synchronous with the evolution of the late paleocene global 13c maximum reflecting an increase in marine surface primary production and biogenic barite formation at this time at two oligotrophic locations deep sea drilling project dsdp sites 384 and 527 in the north and south atlantic respectively ba increases from 160 360 ppm in the early paleocene to 1100 3000 ppm during the 13c maximum at equatorial dsdp site 577 positioned within or near the high productivity zone ba increases from 15 500 ppm in the early paleocene to 25 400 ppm in conjunction with late paleocene maximum 13c values linear fitted correlation plots of sediment ba content versus surface water 13c in all three regions support barite originating in the euphotic zone the early to late paleocene relative increase in ba illustrates how burial rates of corg relative to al2o3 accelerated by a factor of 1 8 and 6 0 in the eutrophic and oligotrophic areas respectively a tentative estimate weighing our result for the entire ocean suggests that accumulation rates of organic carbon increased by a factor of 2 during the late paleocene 13c maximum

bioturbation into a recently emplaced deep sea turbidite surface as revealed by210pbexcess 230thexcess and planktonic foraminifera distributions abstract this study concerns the surface of a single distal turbidite emplaced on the madeira abyssal plain a few hundred years ago the vertical and horizontal homogeneity of the unit and the low pelagic sediment accumulation rate enable a ready identification of the post emplacement signals of near surface bioturbation data have been gathered to define 210 pb excess 230 th excess and pelagic foraminifera profiles with depth these are used as constant input flux tracers and treated by models conventionally used to determine bioturbation parameters the mixed layer depths 7 11 cm bioturbation coefficients 0 08 0 18 cm 2 y 1 and inventory data 10 23 dpm cm 2 derived from the 210 pb excess data in five out of six cores are similar to those previously observed elsewhere with the same model in the deep sea under steady state sediment accumulation conditions although the mixed layer depths are similar for all three tracers the 210 pb excess bioturbation intensities are larger by a factor of 3 than those estimated from 230 th excess profiles and about an order of magnitude larger than those from the foraminifera profiles it is suggested that the conventional 210 pb excess model and those for other short lived tracers probably over estimate the intensity of biomixing of foraminifera for palaeontological and related geochemical purposes

228ra 226ra and 226ra ba ratios in the western mediterranean sea barite formation and transport in the water column 226ra 228ra and ba distributions as well as 228ra 226ra and 226ra ba ratios were measured in seawater suspended and sinking particles at the dyfamed station in the western mediterranean sea at different seasons of year 2003 in order to track the build up and fate of barite through time the study of the 228raex 226raex ratios raex ra activities corrected for the lithogenic ra of suspended particles suggests that baex baex ba concentrations corrected for the lithogenic ba mostly barite formation takes place not only in the upper 500 m of the water column but also deeper i e throughout the mesopelagic layer temporal changes in the 228raex 226raex ratios of sinking particles collected at 1000 m depth likely reflect changes in the relative proportion of barite originating from the upper water column with a high 228ra 226ra ratio and formed in the mesopelagic layer with a low 228ra 226ra ratio 228raex 226raex ratios measured in sinking particles collected in the 1000 m trap in april and may suggest that barite predominantly formed in the upper water column during that period while barite found outside the phytoplankton bloom period february and june appears to form deeper in the water column combining ratios of both the suspended and sinking particles provides information on aggregation disaggregation processes high 226raex baex ratios were also found in suspended particles collected in the upper 500 m of the water column because celestite is expected to be enriched in ra bernstein r e byrne r h and schijf j 1998 acantharians a missing link in the oceanic biogeochemistry of barium deep sea res ii 45 491 505 acantharian skeletons may contribute to these high ratios in shallow waters the formation of both acantharian skeletons and barite enriched in 226ra may thus contribute to the decrease in the dissolved 226ra activity and 226ra ba ratios of surface waters observed between february and june 2003 at the dyfamed station

mars pathfinder convective vortices frequency of occurrence 1 the frequency of occurrence of small scale convective vortices at the mars pathfinder lander location exhibits a diurnal variation similar to terrestrial dust devil observations the 79 vortices detected via their pressure signatures during the 83 sol mission when combined with an assessment of the incompleteness of data temporal coverage implies that at least two vortices passed by the lander site each sol if the vortices are dust laden as inferred from lander imaging then the observed vortex frequency is capable of maintaining the observed atmospheric dust load against sedimentation loss the time of sol variation in vortex occurrence provided by pathfinder when combined with orbiter imaging of dust devils at a very limited time of sol offers a potential means of quantifying the effect of these small scale vortices upon the atmospheric dust cycle

martian and terrestrial dust devils test of a scaling theory using pathfinder data the mars pathfinder meteorological station recorded wind pressure and temperature fluctuations that have been interpreted as dust devils warm core vortices that form at the bottom of connective plumes we apply a scaling theory renno et al 1998 developed to explain terrestrial dust devil observations to test the validity of this interpretation and to provide a simple physical interpretation of the general characteristics of martian dust devils the theory is based on the thermodynamics of heat engines and predicts the central pressure and the wind speed of the connective vortices our findings are as follows for the best documented candidate event sol 25 observed wind and pressure fluctuations are consistent with those predicted by the model and hence strengthen the interpretation of this case as a dust devil a number of other candidates less well documented however also are consistent with passage of a dust devil over or near the lander temperature fluctuations observed on other sols permit dust devils an order of magnitude larger than the ones measured by the meteorology package the strongest dust devils predicted by our theory have a central pressure deficit of about 50 pa and wind speed of about 60 m s 1 the strongest dust devils are capable of lofting dust and hence support the interpretation of selected pathfinder images as showing the passage of dust devils within sight of the lander

the mars regional atmospheric modeling system model description and selected simulations the mars regional atmospheric modeling system mrams is introduced and selected model results are presented and compared with landed meteorological data when possible mrams is descended from a nonhydrostatic earth mesoscale and cloud scale model that is widely used for forecasting weather and simulating atmospheric systems over complex terrain mesoscale models such as mrams are ideal tools for making use of the high resolution data sets arriving from mars global surveyor experiments simulation of the mars pathfinder mpf landing site at lsd 142 using 1 2 degree mars orbiter laser altimeter mola derived topography and thermal emission spectrometer thermal inertia is shown to be in good agreement with observed near surface temperature pressure and wind direction simulations of topographically induced thermal circulations and mountain induced gravity waves are shown to be consistent with theory and earlier studies that tie large amplitude mountain waves to strong winds capable of producing dust streaks and local dust lifting events a large eddy simulation of the convective boundary layer provides estimates of vertical profiles of heat flux momentum flux turbulent kinetic energy and vertical velocity variance the model results suggest that the martian atmosphere is roughly two to three times more turbulent than the terrestrial atmosphere during the afternoon but fluxes are roughly an order of magnitude smaller due to the lower density dust devillike circulations are also predicted in the large eddy simulation finally a simulation that examines atmosphere surface interactions near big crater is discussed predicted surface wind stress patterns are consistent with aeolian processes inferred through mars orbiter camera imagery of big crater located near the mpf landing site c 2001 academic press

mars orbiter camera geodesy campaign during the geodesy campaign in may and june 1999 the wide angle system of the mars global surveyor mars orbiter camera imaged the visible surface of mars from latitudes 70 s to 90 n over 90 of this portion of the planet was covered at two viewing angles to obtain side looking stereo at a resolution of 250 m pixel and convergence angles of 21 27 continuous radiometric spacecraft tracking during this period provided precise orbit determination of spacecraft location this data set will become the basis of a new image mosaic of mars with the potential to exceed the geodetic precision and image quality of those presently available

moc observations of the 2001 mars planet encircling dust storm abstract from 15 september 1997 through 21 january 2006 only a single planet encircling martian dust storm was observed by mgs moc the onset of the storm occurred on 26 june 2001 l s 184 7 earliest recorded to date it was initiated in the southern mid to low latitudes by a series of local dust storm pulses that developed along the seasonal cap edge in malea and in hellas basin l s 176 2 184 4 the initial expansion of the storm though asymmetric was very rapid in all directions 3 32 m s 1 the main direction of propagation however was to the east with the storm becoming planet encircling in the southern hemisphere on l s 192 3 several distinct centers of active dust lifting were associated with the storm with the longest persisting for 86 sols syria claritas these regional storms helped generate and sustain a dust cloud haze which reached an altitude of about 60 km and a peak opacity of dust 5 0 by l s 197 0 the cloud had encircled the entire planet between 59 0 s and 60 0 n obscuring all but the largest volcanoes the decay phase began around l s 200 4 with atmospheric dust concentrations returning to nominal seasonal low levels at l s 304 0 exponential decay time constants ranged from 30 117 sols the storm caused substantial regional albedo changes darkening and brightening as a result of the redistribution removal and deposition of a thin veneer of surface dust at least 0 1 11 1 m thick it also caused changes in meteorological phenomena i e dust storms dust devils clouds recession of the polar caps and possibly surface temperatures that persisted for just a few weeks to more than a single mars year the redistribution of dust by large annual regional storms might help explain the long period 30 years between the largest planet encircling dust storms events

doppler radar observations of dust devils in texas abstract analyses of a dust devil dataset collected in northwest texas are presented the data were collected just above the ground at close range with a mobile w band 3 mm wavelength doppler radar having an azimuthal radial resolution of 3 5 m 30 m at the range of the dust devils most dust devils appeared as quasi circular rings of relatively high radar reflectivity four dust devil vortices were probed three of which were cyclonic and one anticyclonic documentation was obtained of a pair of adjacent cyclonic vortices rotating cyclonically around each other approximate radial profiles of azimuthal and radial wind components and of radar reflectivity are detailed and discussed the diameters of the core of the dust devils ranged from 30 to 130 m the latter diameters are much wider than that of typical dust devils in a homogeneous environment the widest vortex was cyclonic and exhibited evidence of a two cell structure i e sinking motion near the center and rising motion just outside the ra

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

a 210 000 year record of barium variability in the deep northwest atlantic ocean the deep ocean is the storehouse for most of the carbon and nutrients in the ocean atmosphere system together with its out crops at high latitudes the deep ocean is of great importance in driving glacial interglacial changes in the carbon dioxide content of the atmosphere1 3 the chemical and physical structure of the deep glacial oceans can be reconstructed by means of palaeochemical tracers for example the cadmium and carbon isotope contents of benthic foraminifera have been used to reconstruct the phosphate or labile nutrient compositions of deep waters4 14 recently it was proposed15 that barium in benthic foraminifera could be used to reconstruct the distribution of refractory deep regenerated chemical properties in the water masses of the glacial oceans a reconstruction of barium concentra tions in the oceans at the time of the last glacial maximum revealed the greatest changes in the north atlantic where barium concentrations in deep water were up to 50 higher than at present16 here we present a record of the benthic ba ca ratio in the deep northwest atlantic stretching back to interglacial stage 7 210 kyr ago encompassing two full glacial cycles a comparison of the barium record with that of the other nutrient like tracers lends confidence in the general agreement between these tracers while showing some spectral variability unique to barium thus underscoring its utility as an additional palaeoceanographic tracer

foraminiferal reconstruction of barium distributions in water masses of the glacial oceans foraminiferal ba can be used to reconstruct the distribution of deeply regenerated chemical components in past oceans the ba contents of benthic foraminifera recovered from cores in the atlantic ocean indicate that waters deeper than 2900 m had 30 60 higher ba during the last glacial maximum lgm these changes are consistent with previously observed glacial nutrient enrichments based on foraminiferal cd and 13c increases in deepwater nutrient contents in the atlantic can be explained by reductions in north atlantic deep water formation during the lgm ba ca of benthic foraminifera from the glacial sections of intermediate depth atlantic cores are equal to or lower than holocene values this ba evidence argues against the mediterranean as a greatly increased source to atlantic intermediate waters during the lgm since the mediterranean is enriched in ba today and apparently remained enriched during the lgm benthic foraminiferal ba from the glacial sections of cores from the eastern equatorial pacific suggest that deep waters of the glacial pacific were about 25 lower in ba at 3000 m taken together the foraminiferal evidence indicates that the ba content of deep waters of the atlantic antarctic and pacific were similar at the lgm since foraminiferal cd distributions indicate that cd remained significantly lower in the deep atlantic relative to the pacific at the last glacial maximum a seven box ocean model is used to explore several scenarios for reconciling lgm ba and cd distributions while the changed distribution of both tracers suggests diminishment in the flux of nutrient depleted waters to the deep atlantic during the lgm increased atlantic upwelling rates and consequently enhanced ba particle fluxes can account for the the lack of ba fractionation between the deep atlantic and pacific the model suggests that ba can be transferred efficiently to the deep atlantic by enhanced upwelling because the vast majority of the ba is regenerated in the deep atlantic box

early diagenesis impact on precise u series dating of deep sea corals example of a 100 200 year old lophelia pertusa sample from the northeast atlantic deep sea coral has proved useful for paleoceanographic reconstructions and for documenting 14 c ages of water masses using 230 th ages however for precise and accurate u series dating further information on coral age structure growth rate and diagenetic evolution is still needed to document such processes we used u th 226 ra systematics in a 40 cm diameter lophelia pertusa specimen collected in 1912 from the eastern atlantic sea of the hebrides external parts of the specimen are thought to have been alive when collected whereas more internal parts were likely dead the live collected and dead parts of the skeleton were sampled and analyzed for their 230 th 232 th 234 u 238 u 226 ra and ba contents by thermal ionization and multicollector inductively coupled plasma mass spectrometry 230 th 234 u ratios in the most recent parts yielded ages of 86 6 a and 92 9 a in agreement with the date of recovery the older parts yielded 230 th ages ranging from 169 15 to 211 10 a n 5 but had a 31 higher u content than more recent parts of the skeleton this raises concerns about the possibility of secondary diagenetic u uptake although an environmentally controlled u ca shift between coral growth stages cannot be ruled out 226 ra ba measurements were made and model 226 ra ba ages averaging 250 12 yr were calculated for the older part assuming a constant initial 226 ra ba ratio in bottom waters these ages are slightly older than 230 th ages suggesting either that 226 ra ba ratios of ambient seawater changed over time or that a diagenetic phenomenon have affected the u series system or both scanning electron microscope observations revealed bioerosion and secondary biomineralization in the older part of the coral skeleton supporting the hypothesis that diagenetic processes may have influenced the ages obtained by the u series toolbox modeled u series ages for such an open system are discussed however a comparison between 14 c and 230 th ages performed on both pristine and bioeroded parts of the coral gives coherent values ca 450 a for the preindustrial 14 c reservoir age of north atlantic waters it remains to be determined however whether diagenesis occurs rapidly over a short period of time or whether it continues for longer periods in the latter case diagenetic processes would hamper paleoceanographic interpretations as well as the precise calculation of 14 c ages of deep water masses based on comparative u th and 14 c chronologies copyright 2005 elsevier ltd

barium accumulation in the atlantic sector of the southern ocean results from 190 000 year records extensive investigations of sedimentary barium were performed in the southern south atlantic in order to assess the reliability of the barium signal in antarctic sediments as a proxy for paleoproductivity maximum accumulation rates of excess barium were calculated for the antarctic zone south of the polar front where silica accumulates at high rates the correspondence between barium and opal supports the applicability of barium as a proxy for productivity within the antarctic zone north of today s average sea ice maximum interglacial vertical rain rates of excess barium are high with a maximum occurring during the last deglaciation and early holocene and during oxygen isotope chronozone 5 5 during these periods the maximum silica accumulation was supposedly located south of the polar front glacial paleoproductivity instead was low within the antarctic zone north of the polar front significantly higher barium accumulation occurs during glacial times the vertical rain rates however are as high as in the glacial antarctic zone therefore there was no evidence for an increased productivity in the glacial southern ocean

determination of holocene sedimentation rates from a carbonate lake using excess 226ra profiles abstract research on the development of excess 226 ra decay as a novel technique for dating lake sediments has been undertaken on hawes water nw england investigation of the behaviour 226 ra and its precursors in the 238 u series in the lake environment supports the theoretical justification for dating carbonate sediments based on the decay of excess 226 ra activity that is transferred from the water column at the time of deposition via calcite coprecipitation depth profiles of excess 226 ra activity in bulk and biogenic carbonate phases of the sediment are exponential in form below a surface layer of lake sediment in which enhanced 226 ra influx can be identified application of a dating model that assumes a constant rate of supply and no significant post depositional mobility of 226 ra yields sedimentation rates for the lower parts of two cores of the order of 0 02 g cm 2 y 1 that compare well with those obtained from 210 pb dating whilst post depositional redistribution of 226 ra activity is shown to have negligible impact on the down core profile the approach is sensitive to changes in the rate of supply and the initial 226 ra activity both of which can be identified and are confirmed by comparison with the excess 210 pb activity profile

dust devils on mars columnar cone shaped and funnel shaped clouds rising 1 to 6 kilometers above the surface of mars have been identified in viking orbiter images they are interpreted as dust devils confirming predictions of their occurrence on mars and giving evidence of a specific form of dust entrainment

assessing in situ microcrack damage using ultrasonic velocity tomography abstract to characterize the damage induced during excavation of a test tunnel in granite ultrasonic wave velocity and amplitude measurements were made in situ around one quadrant of the tunnel sixteen 1 m deep boreholes were drilled into the tunnel wall these boreholes spanned the region from tensile stress induced damage in the sidewall to compressive stress induced damage in the well developed notch measurements were made by pulsing a source transducer at numerous points within a given borehole and on the tunnel surface and then capturing the transmitted ultrasonic waves at transducers located in the adjacent borehole the travel times of the waves between sources and receivers were used to compute the average velocities and to construct two dimensional 2d tomographic images wave velocities and amplitudes in the tensile stress region are low and show significant anisotropy indicating the presence of oriented microcracks even as deep as 1 m from the tunnel wall velocities and amplitudes are higher in the compressive stress region and show lower anisotropy indicating the rock is relatively undamaged away from the tunnel wall the velocity anisotropy indicates that the dominant orientation of microcrack planes is everywhere tangential to the tunnel wall even though the minimum principal stress is tangential and tensile in the sidewall the distribution of microcracks inferred from these results is consistent with the extensive microseismicity detected during and after excavation and suggests that both the stress history and current stress state have impacted the current state of damage around the tunnel

228ra 226ra and 226ra ba ratios to track barite formation and transport in the water column abstract we measured 228 ra ex 226 ra ex and 226 ra ex ba ex ratios in suspended and sinking particles collected at the oceanic flux program ofp time series site in the western sargasso sea and compared them to seawater ratios to provide information on the origin and transport of barite baso 4 in the water column the 228 ra ex 226 ra ex ratios of the suspended particles down to 2000 m are nearly identical to those of seawater at the same water depth these ratios are much lower than expected if suspended barite was produced in surface waters and indicate that barite is produced throughout the mesopelagic layer the 228 ra ex 226 ra ex activity ratios of sinking particles collected at 1500 and 3200 m varied mostly between 0 1 and 0 2 which is intermediate between the seawater ratio at these depths ex ba total ba lithogenic considered to be mainly barite present in the sinking flux is a mixture of crystals formed recently in the upper water column formed several years earlier in the upper water column or formed recently in deeper waters we observe a sizeable temporal variability in the 228 ra ex 226 ra ex ratios of sinking particles which indicates temporal variability in the relative proportion of barite crystals originating from surface with a high 228 ra ex 226 ra ex ratio and mesopelagic with a low 228 ra ex 226 ra ex ratio sources however we could not discern a clear pattern that would elucidate the factors that control this variability the 226 ra ba ratios measured in seawater are consistent with the value reported from the geosecs expeditions 2 3 dpm mol 1 below 500 m depth but are significantly lower in the upper 500 m high 226 ra ex ba ex ratios and elevated sr concentrations in suspended particles from the upper water column suggest preferential uptake of 226 ra over ba during formation of srso 4 skeletons by acantharians which must contribute to barite formation in shallow waters deeper in the water column the 226 ra ex ba ex ratios of suspended particles are lower than those of seawater since 228 ra ex 226 ra ex ratios demonstrate that suspended barite at these depths has been produced recently and in situ their low 226 ra ex ba ex ratios indicate preferential uptake of ba over ra in barite formed in mesopelagic water

dust devil tracks and wind streaks in the north polar region of mars a study of the 2007 phoenix mars lander sites 1 the 65 72 latitude band of the north polar region of mars where the 2007 phoenix mars lander will land was studied using satellite images from the mars global surveyor mgs mars orbiter camera narrow angle moc na camera dust devil tracks ddt and wind streaks ws were observed and recorded as surface evidence for winds no active dust devils dds were observed 162 moc na images 10 3 of total images contained ddt ws phoenix landing region c 295 315w had the highest concentration of images containing ddt ws per number of available images 20 9 region d 130 150w had the lowest 3 5 ddt and ws direction were recorded for phoenix landing regions a 110 130w b 240 260w and c to infer local wind direction region a showed dominant northwest southeast ddt ws region b showed dominant north south east west and northeast southwest ddt ws and region c showed dominant west northwest east southeast ddt ws results indicate the 2007 phoenix lander has the highest probability of landing near ddt ws in landing region c based on ddt ws linearity we infer phoenix would likely encounter directionally consistent background wind in any of the three regions

core top 14c ages as a function of latitude and water depth on the ontong java plateau radiocarbon measurements on core tops from the ontong java plateau confirm a previous finding by berger and killingley 1982 that at any given water depth cores taken on the equator have higher accumulation rates and younger core top ages than their off equator counterparts further these new results fortify the conclusion by broecker et al 1991 that the increase in core top radiocarbon age with water depth rules out homogeneous dissolution within the pore waters as the dominant mechanism either most of the dissolution must occur prior to burial or it must occur during the first pass through the respiration co2 rich upper pore waters after which the calcite grains become armored against further dissolution a puzzling aspect of this new data set is that despite the sizable difference in accumulation rate the extent of dissolution as measured by either the caco3 content or the ratio of caco3 in the 150 m size fraction to that in the 63 m fraction is no different off than on the equator in order to reconcile the results of this study with those obtained by hales and emerson 1996 using in situ electrodes it is necessary to call upon calcite armoring

box cores from the equatorial pacific 14c sedimentation rates and benthic mixing abstract carbon 14 determinations on box cores of calcareous ooze from the western and eastern equatorial pacific suggest that patterns of mixed layer ages sedimentation rates and mixed layer thicknesses are controlled by gradients of carbonate dissolution and fertility and by small scale redeposition processes mixed layer ages range from 3000 to 7000 years with a mode between 4000 and 5000 years sedimentation rates range from 0 8 to 2 4 cm 1000 years mixed layer depths calculated according to the box model of mixing range from 7 cm to 16 cm observed thicknesses are about one fourth smaller than calculated ones

sr ba in barite a proxy of barite preservation in marine sediments abstract the observation by bertram and cowen j mar res 55 1997 577 593 that the strontium content of marine barite decreased from the water column to the deep sea floor suggested that the sr ba ratio in barite was sensitive to barite dissolution following this observation we have investigated the potential of using the sr ba ratio in barite as a proxy of barite preservation by separating barite crystals from sediment cores collected at different water depths in the equatorial pacific and in the southern ocean our investigations do not reveal significant downcore variations in the sr ba ratios during the holocene period in the two basins and up to a few hundred thousand years in the equatorial pacific however a comparison of the mean sr ba ratios in individual cores suggests that the sr ba ratios in barite decrease with increasing water depth a feature that could be related to dissolution of barite crystals during settling to the deep sea floor and or at the sediment water interface if confirmed the sr ba ratios in barite could be used to infer the intensity of barite dissolution and the state of preservation of barite crystals in sediments such information could be employed usefully in paleoproductivity reconstructions for the purpose of distinguishing between productivity and dissolution signals affecting barite distributions in marine sediments

glacial to interglacial fluctuations in productivity in the equatorial pacific as indicated by marine barite an empirical correlation between marine barite baso4 accumulation rate in core top sediment samples from two equatorial pacific transects at 140 w and 110 w and the estimated primary productivity of the overlying water column were used to evaluate glacial to interglacial changes in productivity fluctuations in barite accumulation rates down core indicate that during glacial periods of the past 450 000 years the productivity in the central and eastern equatorial pacific was about two times that during intervening interglacial periods this result is consistent with other evidence that productivity was high in the eastern and central equatorial pacific during the last glacial

microseismicity monitoring and failure mechanism analysis of rock masses with weak interlayer zone in underground intersecting chambers a case study from the baihetan hydropower station china abstract a weak interlayer zone wiz is a rock mass system with poor mechanical properties large scale random distribution water softening causing an adverse effect on the safety of the construction and project progress to investigate the fracture process and the mechanism of rock masses with wizs in the intersecting chambers during the excavation process in situ microseismic ms monitoring was carried out in the underground powerhouse on the right bank of the baihetan hydropower station china during the monitoring the spatio temporal evolution process of the microseismicity of the rock masses around the intersecting chambers was obtained during the excavation unloading of multiple working faces the spatial evolution of ms events illustrates the dynamic progressive characteristics of ms activities as they propagate and accumulate along the wiz and finally form a cluster zone the fracture mechanism of moment tensor inversion reveals the distribution and evolution of ms events with respect to different fracture types tensile fracture events are distributed near the free surface while non tensile fracture events are far from the free surface finally the study proposes support measures restraining fracture development in surrounding rock masses with wiz the effectiveness of reinforced support measures is verified by ms events and the deformation of surrounding rocks the results of the study are particularly valuable for the stability analysis excavation and support optimization of similar engineering studies

226ra in barite absolute dating of holocene southern ocean sediments and reconstruction of sea surface reservoir ages absolute dating of marine sediments is necessary to achieve reliable correlations of paleoclimate records the 2 2 6 ra decay in barite separated from a deep sea core of the southern ocean was used to determine absolute ages for the holocene epoch comparison with 1 4 c ages measured on planktic foraminifers provides the first past sea surface reservoir ages in the antarctic zone of the southern ocean throughout the middle to late holocene our results indicate a reservoir age of ca 1100 yr comparable to modern estimates a significantly higher reservoir age ca 1900 yr is obtained for the early holocene which suggests a major change in the southern ocean circulation at that time