impacts tillites and the breakup of gondwanaland a second discussion i read with interest the paper by oberbeck et al 1993a as well as the subsequent discussion and reply young 1993 oberbeck et al 1993b to me the main question is not whether some of the gondwana diamictites are of impact origin but whether there is enough general evidence to link these rocks and related phenomena to the breakup of gondwanaland as reflected in the title of their paper oberbeck et al 1993a seem to favor the latter hypothesis they also suggest that the cape fold belt and associated basins may be possible remnants of large impact basins left after continental breakup the purpose of this discussion is to review some of the evidence indicating that in the karoo gondwana basin of south africa a the dwyka formation is predominantly of glacial origin and b the cape fold belt cannot be the result of a single bolide impact as concerns the dwyka formation field evidence indicating widespread glaciation includes inter alia 1 divergent directions of transport at many localities for example striae on polished pavements in natal are locally at right angles to one another on the same outcrop du toit 1921 at several other localities transport directions differ by more than 900 visser and loock 1982 visser 1990a von brunn and marshall 1989 young 1993 also mentions curved striations in the sturtian succession of south australia a problem which oberbeck et al 1993b sidestep in their reply by focusing on the fact that nailhead striations previously considered unique to glacial environments also formed on clasts from the ries impact crater by extrapolation they imply that cross cutting striae may still be found in ejecta deposits however it is difficult to imagine how such divergent directions can be

el chichon volcanic ash in the stratosphere particle abundances and size distributions after the 1982 eruption volcanic ash particles collected from the stratosphere after the march april 1982 explosive eruption of el chichon volcano mexico were mostly 2 40 m vesicular shards of silicic volcanic glass that varied in abundance at 16 8 19 2 km altitude from 200 m 3 30 49 n lat in may to 1 3 m 3 45 75 n in october at the minimum the ash cloud covered latitudes 10 60 n in july and 10 s 75 n in october in may and july ash particles were mostly free individual shards and clusters of shards but by october were intimately associated with liquid droplets presumably sulfuric acid in may 1982 the total stratospheric burden of ash was at least 240 tons 2 2 108 g although the total ash injected into the stratosphere by the eruption was probably 480 8400 tons

effects of nearshore recharge on groundwater interactions with a lake in mantled karst terrain the recharge and discharge of groundwater were investigated for a lake basin in the mantled karst terrain of central florida to determine the relative importance of transient groundwater inflow to the lake water budget variably saturated groundwater flow modeling simulated water table responses observed beneath two hillsides radiating outward from the groundwater flow through lake modeling results indicated that transient water table mounding and groundwater flow reversals in the nearshore region following large daily rainfall events generated most of the net groundwater inflow to the lake simulated daily groundwater inflow was greatest following water table mounding near the lake not following subsequent peaks in the water level of upper basin wells transient mounding generated net groundwater inflow to the lake that is groundwater inflow in excess of the outflow occurring through the deeper lake bottom the timing of the modeled net groundwater inflow agreed with an independent lake water budget however the quantity was considerably less than the budget derived value

comparison of measured and estimated unsaturated hydraulic conductivities during snowmelt estimates of unsaturated flow often require an assessment of the relationship between unsaturated hydraulic conductivity ku and moisture content measured ku relationships for a well sorted sandy soil were obtained using the instantaneous profile method during snowmelt recharge these values are compared with estimates from three approaches the campbell equation a modified version of the campbell model that considers residual water and the rate of isotopic tracer displacement during infiltration the modified campbell model provided the best fit to the observed data although all three methods overpredicted ku the isotopic tracer method overestimated observed ku values by 2 6 4 5 times this may reflect the role of macropores upon hydraulic conductivities during infiltration since the tracer method is employed during recharge while the instantaneous profile method is generally used during drainage periods when macropores are nonconductive whereas ku estimates derived from empirical approaches such as the campbell model may be valid during conditions of drainage the isotopic tracer model appears to provide more realistic conductivity values during infiltration the latter method also provides a direct means of estimating the immobile fraction of total soil water

volcanic aerosol perturbations and strong el nino events no general correlation we test the hypothesis that el nino southern oscillation enso events are caused or enhanced by volcanic aerosol perturbations using two methods 1 a case by case comparison of the 16 strongest el nino events of the last 150 years with the characteristics of the largest concurrent volcanic events and 2 comparison of the timing of strong el nino events and the independently determined record of stratospheric optical depth perturbations many eruptions that occurred near times of strong el nino years produced small amounts of stratospheric aerosols in many cases the relative timing of the two events argues against triggering the correlation of 4 of 11 peaks in global stratospheric optical depth 0 025 within 3 years of strong el nino events over the last 150 years is what would be expected by chance moreover five strong el ninos occurred between 1915 and 1960 when the stratosphere was largely free of volcanic aerosols of the three strongest tropical volcanic aerosol perturbations that coincided with or were followed by strong el ninos in the period studied krakatau in 1883 el chichon in 1982 and pinatubo in 1991 the two modern ones occurred after the earliest sst warming of the el nino events the coincidence of these two phenomena indicates no causative relationship

palaeomagnetism and magnetic anisotropy of proterozoic banded iron formations and iron ores of the hamersley basin western australia abstract rock magnetic properties and palaeomagnetism of weakly metamorphosed banded iron formations bifs of the palaeoproterozoic hamersley group western australia and proterozoic bif derived iron ores have been investigated the bif units sampled here are slightly younger than 2500 ma at paraburdoo mount tom price and mount newman iron ore formation was completed before 1850 ma sampling was mainly from the mount tom price and paraburdoo mining areas and for the first time a palaeomagnetic fold test on fresh unweathered and unaltered bif samples has allowed the nature of the remanence of the bifs to be defined the remanence of the bifs is carried by late diagenetic low grade metamorphic magnetite after primary haematite this remanence is pre folding and is unlikely to be greatly affected by the high anisotropy because the palaeofield inclination was demonstrably low determination of palaeofield directions from measured remanence directions is complicated by self demagnetization effects in strongly magnetic highly anisotropic bif specimens we present a method for correcting measured directions for the effects of self demagnetization and anisotropy for typical bifs the effect of magnetic anisotropy on measured remanence inclinations and inferred palaeolatitudes is minor for low palaeolatitudes but can lead to large errors in calculated palaeopoles for intermediate to moderately steep palaeolatitudes anisotropy also causes cones of confidence to be underestimated due to compression of the range of inclinations in principle deflection of post folding remanence towards the bedding plane by high magnetic anisotropy can produce an apparent syn folding signature with best agreement between directions from different fold limbs after partial unfolding thus high anisotropy cannot only bias estimated palaeofield directions and cause underestimation of errors but can also mislead interpretation of the time of remanence acquisition the anisotropy of anhysteretic remanent magnetization arm probably yields an upper limit to the anisotropy of the chemical remanent magnetization crm carried by the bifs therefore from the anisotropy of arm a maximum inclination deflection of 9 is suggested for the sampled bifs this corresponds to less than 5 change of palaeolatitude the palaeomagnetic pole position calculated for bifs at paraburdoo is 40 9 s 225 0 e dp 2 9 dm 5 8 after tilt correction but without correction for anisotropy other pole positions reported include that from flat lying bifs from wittenoom at 36 4 s 218 9 e dp 4 6 dm 9 1 from mount tom price iron ore at 37 4 s 220 3 e dp 5 7 dm 11 3 and from paraburdoo ore at 36 4 s 209 9 e dp 4 7 dm 8 8 the poles from the bifs the paraburdoo ore and the part of the tom price deposit that was sampled in this study are indistinguishable from each other and from the mount jope volcanics overprint pole the magnetization of the bifs was probably acquired during burial metamorphism of the hamersley group soon before the main folding and uplift event in the southern part of the hamersley province this tectonic event exposed magnetite rich bifs to near surface oxidizing conditions producing extensive martite goethite orebodies and also appears to have produced the syn folding overprint magnetization recorded by the mount jope volcanics of the underlying fortescue group ages of magnetization are tentatively interpreted as 2200 100 ma for the bifs 2000 100 ma for the supergene enrichment of bif to martite goethite ore recorded by the parabudoo and mount tom price orebodies and 1950 100 ma for the metamorphic martite microplaty haematite ore recorded as an overprint by the tom price orebody and as the only surviving magnetization of the mount newman orebody

the capillary fringe and its effect on water table response abstract shallow water tables are often observed to respond in a highly disproportionate manner to precipitation events that is the magnitude of the response is often much greater than would be predicted on the basis of the specific yield of the geologic material and the amount of rainfall physical arguments are presented to show that if the capillary fringe the zone of tension saturation extends to ground surface then the addition of a very small amount of water can result in an immediate and large rise in the water table the arguments are supported by a field experiment in which the addition of 0 3 cm of water caused the water table to rise 30 cm in 0 25 min thus demonstrating the large and highly transient influence of the capillary fringe on the position of the water table the evidence in this study as well as recent work of others suggests that the capillary fringe effect could have a major influence on the process of stream flow generation contaminant transport to surface waters and contaminant transport in hydrogeologic regimes having shallow water tables it is further shown that calculations of groundwater recharge and consumptive use based on water table response and an assumed specific yield could be substantially in error

on the structure of the southern oscillation abstract a realistic oceanic general circulation model is forced with winds observed over the tropical pacific between1967 and 1979 the structure of the simulated southern oscillation is strikingly different in the western andeastern sides of the basin because the principal interannual zonal wind fluctuations are confined to the westand are in the form of an equatorial jet this causes thermocline displacements to have maxima offthe equatorin the west where the curl of the wind is large but on the equator in the east zonal phase propagation bothon and offthe equator is at different speeds in the west and east the phase pattern is complex and there is on interannual time scale no explicit evidence ofindividuai equatorial waves these results lead to a modificationof the delayed oscillator mechanism originally proposed by schopfand suarez to explain a continual southernoscillation the results also permit an evaluation of the various coupled ocean atmosphere models that simulatethe southern osci

a hydrometric and geochemical approach to test the transmissivity feedback hypothesis during snowmelt to test the transmissivity feedback hypothesis of runoff generation surface and subsurface waters were monitored and sampled during the 1996 snowmelt at various topographic positions in a 41 ha forested headwater catchment at sleepers river vermont two conditions that promote transmissivity feedback existed in the catchment during the melt period first saturated hydraulic conductivity increased toward land surface from a geometric mean of 3 6 mm h 21 in glacial till to 25 6 mm h 21 in deep soil to 54 0 mm h 21 in shallow soil second groundwater levels rose to within 0 3 m of land surface at all riparian sites and most hillslope sites at peak melt the importance of transmissivity feedback to streamflow generation was tested at the catchment scale by examination of physical and chemical patterns of groundwater in near stream discharge and hillslope recharge lateral flow zones and within a geomorphic hollow convergent flow the presence of transmissivity feedback was supported by the abrupt increase in streamflow as the water table rose into the surficial transmissive zone a flattening of the groundwater level vs streamflow curve occurred at most sites this relation had a clockwise hysteresis higher groundwater level for given discharge on rising limb than at same discharge on falling limb at riparian sites suggesting that the riparian zone was the dominant source area during the rising limb of the melt hydrograph hysteresis was counterclockwise at hillslope sites suggesting that hillslope drainage controlled the snowmelt recession end member mixing analysis using ca mg na dissolved organic carbon doc and si showed that stream chemistry could be explained as a two component mixture of groundwater high in base cations and an o horizon overland flow water high in doc the dominance of shallow flow paths during events was indicated by the high positive correlation of doc with streamflow r 2 a 0 82 despite the occurrence of transmissivity feedback hillslope till and soil water were ruled out as end members primarily because their distinctive high si composition had little or no effect on streamwater composition till water from the geomorphic hollow had a chemistry very close to streamwater base flow and may represent the base flow end member better than the more concentrated riparian groundwater during snowmelt streamwater composition shifted as this base flow was diluted not by shallow groundwater from the hillslope but rather by a more surficial o horizon overland flow water q 1999 elsevier science b v all rights reserved

stratigraphy sedimentology and isotopic geochemistry of australian neoproterozoic postglacial cap dolostones deglaciation delta 13 c excursions and carbonate precipitation abstract thin d13c excursions in the geologic record they are interpreted to record a brief postglacial anomaly in ocean chemistry in australia the marinoan varanger equivalent 600 ma cap dolostone units exhibit many of the characteristics displayed by such deposits elsewhere around the globe including fine grained dolomitic mineralogy lateral persistenc at basinal scales thin laminae graded beds intervals with abundant marine cements crystal fans and a distinctive negative d13c isotopic signature of up to 5 pdb on the basis of these features the australian examples are interpreted here to be deeper water deposits below storm wave base resulting from an anomalous flux of inorganic carbonate to the sea floor during postglacial transgression detailed isotopic analysis of australian cap dolostones indicates d13c values ranging from 1 to 5 and gen rally becoming more depleted in 13c upsection trace element data indicate some diagenetic stabilization but textural evidence and the presence of similar profiles in different basins argue against a pervasive recrystallization event the range in d13c values between sections as well as more negative 13c values appear to correlate with greater paleobathymetry within basins this implies either 1 only partial preservation of the complete oceanic variation of d13c or 2 precipitation of this peculiar facies owes its genesis to basinal specific oceanographic processes such as proximi y of a given section to a postglacial upwelling zone in the later case d13c values would not represent whole ocean values stratigraphic constraints and paleoenvironmental interpretations suggest that much of this excursion lies within the geologically brief period of postglacial transgression this implies that the cause s of d13c variation likely operated on time scales significantly less than the residence time of carbon in the oceans 105 yr the continent wide and perhaps global nature of cap dolostones indicates that large volumes of carbonate were precipitated during the postglacial transgressive period such large scale carbonate precipitation over the hypothesized short time interval of postglacial transgression must have caused or have been the product of profound changes in the carbon cycle and global climate at tha time similar evidence for transgression and increased carbonate deposition in the holocene are attributed to the changing basin shape and ph of the oceans the coral reef hypothesis of berger 1982 cap dolostones may record a proterozoic equivalent of this process with the substitution of abiotic carbonate precipitation for skeletal precipitation by reef organisms

a robust equatorial pacific westerly response to tropical volcanism in multiple models after each of the 1963 agung 1982 el chichon and 1991 pinatubo eruptions an el nino was observed the increased likelihood of an el nino after a tropical eruption has also been found in long term reconstructed proxy data through examining simulations over the last millennium by 11 different models we show that a tropical volcano eruption can robustly excite a western to central equatorial pacific wcep westerly anomaly at 850 hpa in eight out of the 11 models such a westerly anomaly is favorable for el nino development under the volcanic forcing there are significant extratropical continent surface cooling and tropical drying with negative precipitation anomalies over the south south east asia ssea west african monsoon and intertropical convergence zone itcz regions this common precipitation suppression response occurs in most of the models sensitivity experiments show that a wcep westerly anomaly can be excited by the tropical land cooling especially the ssea cooling induced precipitation suppression rather than by the extratropical land surface cooling theoretical results show that a wcep westerly anomaly is excited due to a gill response to reduced precipitation over the ssea and west african monsoon regions and the ssea contributes more than the west african monsoon does the itcz weakening however excites an easterly wind anomaly the models with more sensitive convective feedback tend to simulate an el nino more easily while a failed simulation of an el nino after a robust westerly anomaly in some models calls for further studies on these models delayed responses to radiative forcing induced by volcano eruptions

comment on the neoproterozoic 1000 540 ma glacial intervals no more snowball earth by joseph g meert and rob van der voo

runoff generation processes estimated from hydrological observations on a steep forested hillslope with a thin soil layer abstract in order to understand runoff generation processes on a forested hillslope involving large heterogeneities this study monitored runoff from a steep hillslope with a thin soil layer as well as matric potential within it and analyzed their responses to storm rainfall a comparison of storm runoff responses from the study slope with those from two adjacent catchments one of which includes it showed that physical properties of the slope reflected the runoff characteristics although no responses occurred in very dry conditions because of the absence of wet zones near the stream the area contributing to storm runoff more rapidly extended to the whole slope due to its topographic properties they also caused its steep hydrographs produced in the wettest condition where almost all the rainfall contributed to storm runoff in this wettest condition tensiometric responses near bedrock showed the vertical quick propagation of the rainfall pulse and a good agreement of storm hydrograph simulated through a kinematic wave runoff model suggested that runoff from the slope was produced by a lateral flow on the bedrock receiving the quick propagation in a transition process from dry to the wettest conditions the development of the lateral flow producing smaller responses at the downslope end was estimated from decreasing of matric potential near bedrock from high negative to low values with increasing cumulative rainfall

on the trigger of el nino southern oscillation by the forcing of early el chichon volcanic aerosols after the volcanic eruption of el chichon in 1982 the distribution of volcanic aerosols in the upper atmosphere was zonally very inhomogeneous for about a month or more and was located in a fairly uniform zonal band around the earth in the northern subtropical region for the ensuing several months the impact of those aerosols absorbing radiation on the atmospheric motion is discussed in the model of gill 1980 it is shown that the mean westerly wind induced near the central pacific equatorial region would be able to trigger or amplify the el nino southern oscillation several observed results related to the simulation are discussed in some detail the location of the initial center of most aerosols relative to the central pacific is important in the model and the impact of the forcing at the agung event of 1963 is estimated to be smaller than that of the present event which seems to agree with observed results

the volcanic signal in goddard institute for space studies three dimensional model simulations abstract transient calculations of the goddard institute for space studies general circulation model for the climatic signal of volcanic eruptions are analyzed by compositing the output for two different volcanoes for scenario a and five different volcanoes for scenario b the natural variability is suppressed and the volcanic signals am extracted significant global mean surface air temperature cooling and precipitation reduction are found for several years following the eruptions with larger changes in the northern hemisphere nh than in the southern hemisphere the global average temperature response lasts for more than four years but the precipitation response disappears after three years the largest cooling in the model occurs in the nh summer of the year after spring eruptions significant zonal average temperature reductions begin in the tropics immediately after the eruptions and extend to 45 s 45 n in the year after the eruptions in the second year cooling is still seen from 30 s to 30 n

an estimate of average lower mantle conductivity by wavelet analysis of geomagnetic jerks it has recently been proposed that geomagnetic jerks observed at the earth s surface could be viewed as singularities in the time behavior of the geomagnetic field with a regularity of about 1 5 when wavelet analyzed such a signal should have suffered some distortion when diffusing from the core mantle boundary cmb through the conducting mantle assuming that the upper mantle is an insulator and given the electromagnetic time constant of the mantle we compute the distortion that a pure singularity introduced at the cmb suffers as it traverses the mantle we compute this distortion through its effects on the so called ridge functions extracted from the wavelet transform of the signal this distortion is very similar to the small but significant one that we observe in real data we therefore speculate that jerks must have been pure singularities at the base of the mantle and infer an average estimate for the mantle electromagnetic time constant from the way the signal is distorted by fitting the synthetic ridge functions to the experimental ones assuming for example a thickness of 2000 km for a uniform lower conducting mantle we find an electrical conductivity smaller than 10 s m 1 this value is in reasonable agreement with values derived from high pressure experiments for a silicate mantle

the identification of runoff production mechanisms using environmental isotopes in a tussock grassland catchment eastern otago new zealand a previous hydrometric study of runoff production in tussock grassland drainage basins in otago 45 50 s 169 45 e new zealand revealed a marked change of slope in storm hydrograph recessions an environmental isotope study was initiated to investigate the runoff mechanisms operating and to test specific hypotheses to explain this break in the hydrograph recession the results indicated that for quickflow volumes in excess of 10mm the first part of the storm hydrograph can be attributed to two separate sources namely old water from a shallow unconfined groundwater reservoir and new water from saturation overland flow on the lower wetlands of concave slopes despite the extensive area of wetlands old water runoff from the unconfined groundwater reservoir is delivered more rapidly to the stream than new water from saturation overland flow substantial surface storage in the wetlands has first to be exceeded before rain becomes a significant part of stream discharge for quickflow volumes less than 10mm only old water from groundwater contributes to the first part of the hydrograph recession this means that only the largest 7 per cent of storms in terms of quickflow volume generate quickflow containing significant amounts of new water the second part of the recession of the storm hydrograph consists of old water derived from a remarkably well mixed shallow unconfined groundwater body

effect of the eruption of el chichon on stratospheric aerosol size and composition dominant effects of the el chichon eruption on stratospheric aerosols at 19 8 to 20 7 km are 1 vapor depositional growth of the small aerosol background mode 2 development of a large particle mode by sedimentation from the highest altitudes in the cloud 3 a change in the large particle mode from sulfate coated silicates to sulfate aerosols some with silicate cores 4 a 100 fold increase in sulfate mass in the large particle mode terminal velocities of large silicate particles maximum r 2 3 m sampled 1 month after eruption and calibrated with the aid of lidar data indicate initial injection to 26 to 27 km smaller velocities of sulfate aerosols median r 0 5 m are compatible with major growth in 2 to 3 months at 27 to 28 km aerosol settling accounts for the descent of the main lidar return to 26 5 km in august and to 20 to 21 km in december additional growth by condensation and or coalescence during descent is required to explain the largest aerosols r 0 5 to 0 9 m although sedimentation is the dominant cause of bimodality mixing of air from low and high latitudes can produce bimodal or trimodal distributions

different impacts of northern tropical and southern volcanic eruptions on the tropical pacific sst in the last millennium abstractthe impact of northern tropical and southern volcanic eruptions on the pacific sea surface temperature sst and the different response mechanisms arising due to differences in the volcan

impacts of a pinatubo size volcanic eruption on enso observations and model simulations of the climate responses to strong explosive low latitude volcanic eruptions suggest a significant increase in the likelihood of el nino during the eruption and post eruption years though model results have been inconclusive and have varied in magnitude and even sign in this study we test how this spread of responses depends on the initial phase of el nino southern oscillation enso in the eruption year and on the eruption s seasonal timing we employ the gfdl cm2 1 global coupled general circulation model to investigate the impact of the pinatubo 1991 eruption assuming that in 1991 enso would otherwise be in central or eastern pacific el nino la nina or neutral phases we obtain statistically significant el nino responses in a year after the eruption for all cases except la nina which shows no response in the eastern equatorial pacific the eruption has a weaker impact on eastern pacific el ninos than on central pacific el ninos we find that the ocean dynamical thermostat and to a lesser extent wind changes due to land ocean temperature gradients are the main feedbacks affecting el nino development after the eruption the el nino responses to eruptions occurring in summer are more pronounced than for winter and spring eruptions that the climate response depends on eruption season and initial enso phase may help to reconcile apparent inconsistencies among previous studies

low latitude glaciation in the palaeoproterozoic era one of the most fundamental enigmas of the earth s palaeoclimate concerns the temporal and spatial distributions of precambrian glaciations through four billion years of precambrian history unequivocally glacial deposits have been found only in the palaeoproterozoic and neoproterozoic record nonetheless some of these deposits are closely associated with tropical rather than just polar palaeolatitudinal indicators such as carbonate rocks red beds and evaporites these observations are quantitatively supported by palaeomagnetic results indicating a 5 latitude for neoproterozoic glaciogenic rocks in australia similarly reliable palaeolatitudes for the older palaeoproterozoic glaciogenic rocks have not yet been obtained as such deposits commonly suffer from poor preservation and secondary magnetic overprinting the archaean palaeoproterozoic transvaal supergroup on the kaapvaal craton in south africa is however exceptionally well preserved and is thus amenable to the palaeomagnetic determination of depositional palaeolatitudes within this supergroup the 2 2 billion year old ongeluk lavas are a regionally extensive largely undeformed and unmetamorphosed extrusive volcanic succession which conformably overlies glaciogenic deposits the makganyene diamictite here we report a palaeomagnetic estimate of 11 5 depositional latitude for the lavas and hence for the underlying contemporaneous glacial rocks the palaeoclimate enigma is thus deepened a largely ice free precambrian world was apparently punctuated by two long ice ages both yielding glacial deposits well within tropical latitudes

ebb tidal jets a model of suspended sediment and mass transport at tidal inlets abstract mass transport by turbulent jets issuing from tidal inlets is investigated through a model that includes lateral mixing and entrainment bottom friction bathymetric changes settling rate of particles size possible deposition erosion at the bottom and ambient currents and concentrations the bottom frictional jet becomes diluted more slowly than a classical jet a non vanishing concentration may result offshore and a maximum may occur in the core the concentration of a jet on a sloping bottom decreases more rapidly due to increased dilution by entraiment the effects of bottom friction and bottom slope compete in determining the jet concentration deposition to the bottom occurs within the jet mainly on both sides of the centre line and at lower rates on the centre line erosion or deposition may occur at the jet core depending on the inlet flow conditions in the case of erosion at the core the material extracted is deposited on the margins and the offshore areas sorting of the sediments is expected with coarser materials mainly deposited in the marginal areas while the finer sediments are more uniformly distributed and jetted further off shore the main features of the model are verified through a limited set of observations the qualitative agreement is enhanced for micro and meso tidal inlets that are dominated by tidal hydraulics

a new analytical expression for ultimate specific yield and shallow groundwater drainage the ultimate specific yield i e the specific yield under steady state condition is generally dependent on the water table depth in the shallow groundwater systems this paper presents a new expression to describe this relationship the expression is based on the relationship between soil water content soil depths below ground surface near the saturation zone i e water content profile which can be fitted by the van genuchten model because this model is highly nonlinear a taylor series expansion was used to solve the integral equation for specific yield in our study the new expression was verified by a drainage experiment and the results demonstrated that the new expression is reliable for eolian sand when the range of water table fluctuation is less than 30 cm the expression is easily applicable because knowledge of the water content profile near the saturation zone is the only requirement compared with the expression obtained from the brooks corey model the new expression can be used for a variety of aquifer and soil media the improved accuracy of the specific yield provides a better estimate of discharge rates in shallow groundwater systems with water table fluctuations copyright 2014 john wiley sons ltd

a zonally symmetric model for volcanic influence upon atmospheric circulation we consider the effects of volcanic activity upon zonal wind flow in a model atmosphere a low latitude volcanic eruption could lower the tropospheric pole to equator temperature difference and thereby affect the atmospheric motions when the temperature contrast decreases the zonal wind velocities at high altitudes are reduced to conserve angular momentum the velocities in the lower atmosphere near the surface must increase thus providing a momentum source for ocean currents we suggest that this momentum source may have played a role as a trigger for inducing the 1982 83 anomalous el nino and possibly other climate changes

a water balance study in lateritic terrain the water balance of a 600 m2 field site on a lateritic hillslope in kerala southwest india has been studied during two southwest monsoon seasons surface runoff was of minor importance while infiltration and evapotranspiration were the major components amounting to approximately 2 3 and 1 3 of the rainfall respectively groundwater response was rapid involving fluctuations of several metres recharge mechanisms hypothesized are water movement via preferred pathways from the ground surface to the capillary fringe where rapid rise in groundwater level is brought about by a transmitted pressure pulse groundwater recharge was found normally to take place during the southwest monsoon season only the field study demonstrates that seasonal shallow groundwater recharge representing the major portion of the rainfall may be observed in this lateritic terrain in the humid tropics it indicates a good potential for further groundwater development moreover conditions are conducive to a considerable contribution to possible recharge to deeper aquifers the observed groundwater recharge is the result of a complex process on which further research will throw more light

dynamic winter climate response to large tropical volcanic eruptions since 1600 1 we have analyzed the mean climate response pattern following large tropical volcanic eruptions back to the beginning of the 17th century using a combination of proxy based reconstructions and modern instrumental records of cold season surface air temperature warm anomalies occur throughout northern eurasia while cool anomalies cover northern africa and the middle east extending all the way to china in north america the northern portion of the continent cools with the anomalies extending out over the labrador sea and southern greenland the analyses confirm that for two years following eruptions the anomalies strongly resemble the arctic oscillation northern annular mode ao nam or the north atlantic oscillation nao in the atlantic eurasian sector with our four century record the mean response is statistically significant at the 95 confidence level over much of the northern hemisphere land area however the standard deviation of the response is larger than the mean signal nearly everywhere indicating that the anomaly following a single eruption is unlikely to be representative of the mean both the mean response and the variability can be successfully reproduced in general circulation model simulations driven by the solar heating induced by the stratospheric aerosols these models produce enhanced westerlies from the lower stratosphere down to the surface the climate response to volcanic eruptions thus strongly suggests that stratospheric temperature and wind anomalies can affect surface climate by forcing a shift in the ao nam or nao

linear and planar structure in ordered multivariate data as applied to progressive demagnetization of palaeomagnetic remanence summary consider a sequence of say 10 to 20 vector observations in threedimensional space it is suspected that a few subsets of consecutive observations are made up of collinear points the purpose of this paper is to construct a statistically based algorithm to find such linear segments and to assess their accuracy a similar assessment is made for coplanar sets of points this algorithm is applied here to palaeomagnetic data and is claimed to be superior to previous methods of palaeomagnetic analysis in terms of completeness and balance of analysis treatment of measurement errors and other sources of scatter criteria for identification of linear and planar sets of points and statistical rigour stability spectra with statistically based confidence limits are obtained as a by product 1 palaeomagnetic analysis background to the geometrical problem the natural remanent magnetization nrm in rocks is known in general to have originated in one or more relatively short time intervals during their formation and subsequent history i e during rock forming or metamorphic events during which nrm is frozen in stabilized by falling temperature grain growth etc the nrm acquired during each such event is a single vector magnetization parallel to the then prevailing geomagnetic field and is called a component of nrm rocks which have suffered more than one event of this kind are therefore liable to carry multi component nrm in the laboratory these components can be identified by demagnetizing the rock step by step usually by thermal alternating field or chemical demagnetization which involves the analysis of the distribution of blocking rzmperature coercivity and chemical leaching respectively resistance to these treatments is called stability of remanence and the range of treatment over which a particular component is removed is called the stability range of the component the various discrete

the vendian succession of northeastern spitsbergen petrogenesis of a dolomite tillite association abstract the sedimentary record of late precambrian time is magnificently displayed in the highland snowfields of northeastern spitsbergen svalbard vendian strata are represented essentially by the polarisbreen group which consists mostly of dolostone and includes two dolomitic glacial units the oldest sediments in the polarisbreen group compose the elbobreen formation c 400 m which is divided into four laterally persistent members the lower carbonate member e1 125 m contains a distinctive basal dark grey limestone with microspar filled synaeresis cracks suggested to be of lagoonal origin and associated with minor dolostone shale and chert higher parts of the member are dominantly dolostone partly stromatolitic with some shale and sandstone shallow subtidal to intertidal deposition is indicated by the dominance of intraclastic lithologies and relics of anhydrite penecontemporaneous dolomite is partially overprinted by microsparry dolomite thought to be of groundwater origin the redefined petrovbreen member e2 consists of diamictite and other detrital dolostone pronounced thickness variations 2 40 m are thought to be original depositional features the member represents the deposits of a short glacial period in which the following depositional processes are inferred lodgement massive diamictite subaqueous meltout massive and bedded diamictite ice rafting lithologies bearing dropstones and possibly also diamictite redeposition by sediment gravity flows some diamictite and conglomerate rhythmite and shale current winnowing thin tabular conglomerate subaerial or subaqueous meltwater action channelled conglomerate and sandstone periglacial shrinkage diamictite wedge fillings the macdonaldryggen member e3 230 m is a monotonous succession of shaly dolostone of lagoonal origin it grades up into the slangen member e4 25 m which consists of subtidal to intertidal dolarenite with anhydrite relics succeeded by fenestral dolostone that was fractured and cemented by saline groundwaters in an emergent environment the wilsonbreen formation 160 m represents a return to glacial deposition but this time longer lasting and with substantial extra basinal material represented the gropbreen member w1 28 107 m and the ormen member w3 44 139 m consist dominantly of dolomitic diamictite with subordinate conglomerate and sandstone and are separated by a middle carbonate member w2 3 30 m which contains distinctive rhythmitic and stromatolitic limestone as well as sandstone the same depositional processes can be recognised as in the petrovbreen member but the wilsonbreen formation is overall of somewhat more continental aspect lower proportion of rhythmite and dropstone structures in addition there are basal breccia and crack fillings formed by frost shattering of the underlying cemented dolostone tabular sandstone thought to be formed by wave reworking of outwash a striated terrestrial cobble pavement supraglacially derived breccia horizons periglacial wedges filled by sand and the w2 assemblage of possible lacustrine origin the dracoisen formation 525 m represents an abrupt return to non glacial conditions an upward deepening wave dominated succession of pure dolostone d1 20 m and impure dolostone d2 105 m is succeeded by offshore black shale d3 150 m and then by a very shallow water succession of evaporite lacustrine aspect with a dolostone containing evaporite relics d5 10 m separating dolomitic sandstone and shale d4 80 m and d6 150 m the contact with the transgressive cambrian sandstones above is poorly exposed deposition of the succession dominantly under marine conditions is inferred but it is difficult to rule out a lacustrine environment at any particular horizon this dolomite tillite association can be explained by penecontemporaneous and minor secondary dolomite formation in marginal environments with warm climatic indicators at some levels being sharply interrupted because of rapid climatic changes by glacial sediments containing abundant detrital dolomite since the latter sediments make up only 17 of the 1080m thick succession glacial conditions only occupied a small proportion of vendian time

assessment of depositional ash loadings from the 2009 eruption of mt redoubt abstract volcanic ash deposited onto ice and snow in the arctic has the potential to perturb the regional radiation balance by altering the surface reflectivity in order to determine changes in surface albedo loading fields of deposits must be quantified loading fields are defined as the total mass of ash deposited over an area we assessed the areal extent and loading of ash deposits from the 2009 eruption of mt redoubt using an eulerian volcanic ash transport and dispersion model fall3d combined with satellite and deposit observations because direct observations are often limited in remote arctic regions we devised a novel method for modeling ash deposit loading fields for the entire eruption based on best fit parameters of a well studied eruptive event the major land depositing eruptive events events 2 6 on march 23 24 were chosen for analyses realistic ranges of model parameters were selected based on the well described event 5 march 23 and were estimated for other events the model results were validated against nasa a train satellite data and field measurements reported by the alaska volcano observatory overall good to moderate agreement was found a total cumulative deposit area of 3 7 106 km2 was produced and loadings ranged from 7000 3000 g m 2 near the vent to

surface temperature patterns associated with the southern oscillation abstract the typical global and large scale regional temperature patterns associated with the low warm and high cold phases of the southern oscillation so are investigated a total of 12 separate regions were found to have consistent temperature patterns associated with low phase of the so while 11 areas were found to have temperature patterns associated with the high phase of these areas 9 have expected temperature patterns during both phases of the so in the tropics temperature anomalies are of the same sign as the so related sea surface temperature sst anomaly in all land regions except for one area in the west pacific three extratropical responses to the low phase of the so are found over north america and one is found in japan high so temperature patterns were found in the extratropies for japan western europe and northwestern north america the identified temperature responses are more consistent in tropical regions than in the extratropies the so can influence the estimation of

proximal impact deposits at the cretaceous tertiary boundary in the gulf of mexico a restudy of dsdp leg 77 sites 536 and 540 restudy of deep sea drilling project sites 536 and 540 in the southeast gulf of mexico gives evidence for a giant wave at cretaceous tertiary boundary time five units are recognized 1 cenomanian limestone underlies a hiatus in which the five highest cretaceous stages are missing possibly because of catastrophic k t erosion 2 pebbly mudstone 45 m thick represents a submarine landslide possibly of k t age 3 current bedded sandstone more than 2 5 m thick contains anomalous iridium tektite glass and shocked quartz it is interpreted as ejecta from a nearby impact crater reworked on the deep sea floor by the resulting tsunami 4 a 50 cm interval of calcareous mudstone containing small cretaceous planktic foraminifera and the ir peak is interpreted as the silt size fraction of the cretaceous material suspended by the impact generated wave 5 calcareous mudstone with basal tertiary forams and the uppermost tail of the ir anomaly overlies the disturbed interval dating the impact and wave event as k t boundary age like beloc in haiti and mimbral in mexico sites 536 and 540 are consistent with a large k t age impact at the nearby chicxulub crater

constraints on magnetic energy and mantle conductivity from the forced nutations of the earth observations of the earth s nutations are used to explore the possible presence of a conducting layer at the base of the mantle the existence of such a layer is suggested by recent experiments on iron and silicate mixtures at high pressures and temperatures knittle and jeanloz 1986 1989 which indicate that iron may react with silicate minerals to produce metallic compounds nutations provide an ideal tool for investigating the existence of such a layer because they are sensitive to the electrical properties within a thin magnetic boundary layer along the core mantle boundary cmb evidence in favor of a conducting layer is found in the effects of ohmic dissipation which cause the amplitude of the earth s nutation to be out of phase with tidal forcings although out of phase components in the earth s nutations are conventionally attributed to the dissipative influences of ocean tides and mantle anelasticity these effects appear incapable of explaining nutation amplitudes determined from very long baseline interferometry vlbi observations the additional effects of ohmic dissipation enhanced by the presence of a thin conducting layer at the cmb are sufficient to reconcile theory and observation the largest mismatch between observations and theory taking account of ocean tides and mantle anelasticity is a discrepancy of 0 39 0 04 milliarcseconds in the out of phase component of the retrograde annual nutation this discrepancy can be eliminated if the lowermost 200 m of the mantle has a conductivity of 5 105s m 1 and the magnetic energy in the spherical harmonic components of the field at the cmb in degrees l 12 is approximately 4 times greater than the energy inferred in degrees l 12 from surface observations unfortunately the vlbi observations do not uniquely resolve the mantle conductivity and magnetic energy so that trade offs exist between these two parameters nevertheless a high mantle conductivity is favored on the grounds that the alternative involving high levels of magnetic energy yields an excessive amount of ohmic heating other interpretations of the vlbi discrepancy are also discussed one such alternative involves viscous dissipation at the cmb requiring a kinematic viscosity of 0 1m2s 1

impacts tillites and the breakup of gondwanaland mathematical analysis demonstrates that substantial impact crater deposits should have been produced during the last 2 gy of earth s history textures of impact deposits are shown to resemble textures of tillites and diamictites of precambrian and younger ages the calculated thickness distribution for impact crater deposits produced during 2 gy is similar to that of tillites and diamictites leq 2 ga we suggest therefore that some tillites diamictites could be of impact origin extensive tillite diamictite deposits predated continental flood basalts on the interior of gondwanaland significantly other investigators have already associated impact cratering with flood basalt volcanism and continental rifting thus it is proposed that the breakup of gondwanaland could have been initiated by crustal fracturing from impacts

ocean response to volcanic eruptions in coupled model intercomparison project 5 simulations we examine the oceanic impact of large tropical volcanic eruptions as they appear in ensembles of historical simulations from eight coupled model intercomparison project phase 5 models these models show a response that includes lowering of global average sea surface temperature by 0 1 0 3 k comparable to the observations they show enhancement of arctic ice cover in the years following major volcanic eruptions with long lived temperature anomalies extending to the middepth and deep ocean on decadal to centennial timescales regional ocean responses vary although there is some consistent hemispheric asymmetry associated with the hemisphere in which the eruption occurs temperature decreases and salinity increases contribute to an increase in the density of surface water and an enhancement in the overturning circulation of the north atlantic ocean following these eruptions the strength of this overturning increase varies considerably from model to model and is correlated with the background variability of overturning in each model any cause effect relationship between eruptions and the phase of el nino is weak

storm water hydrograph separation of run off from a mine tailings impoundment formed by thickened tailings discharge at kidd creek timmins ontario the kidd creek cu zn sulphide mine is located near timmins ontario mill tailings are thickened and deposited as a thickened slurry in a circular conical shaped pile with an area of approximately 1200 ha deposition of tailings as a thickened slurry results in a relatively uniform grain size distribution and hydraulic conductivity and a thick tension saturated zone above the water table the tailings are drained by numerous small ephemeral stream channels which have developed in a radial pattern during storms water from these streams collects in catchment ponds where it is held before treatment the contribution of tailings pore water to the run off is of interest because of the potential for discharge of pore water containing high concentrations of fe ii acidity metals and so4 to the stream hydraulic head measurements measurements of water table elevation and groundwater flow modelling were conducted to determine the mechanisms responsible for tailings pore water entering the surface streams chemical hydrograph separation of storm run off in one of these streams during three rainfall events using na and cl as conservative tracers indicates that the integrated tailings pore water fraction makes up between less than 1 and 20 of the total hydrograph this range is less than the maximum fraction of tailings pore water of 22 65 reported for run off from a conventional tailings deposit at this site preferential flow through permeable fractures may be the dominant mechanism causing discharge of tailings pore water to storm run off estimates of the mass of fe ii that discharges to the surface run off from the pore water range up to 2800 mg s 1 during a moderate intensity long duration rainfall event the greatest potential for discharge of significant masses of solutes derived from the pore water exists during long duration rainfall events when the water table rises to the surface over large areas of the tailings impoundment

ice cores as an index of global volcanism from 1850 to the present to evaluate an important cause of past climate change climate researchers need reliable estimates of volcanic aerosol loading in the atmosphere previous indices the dust veil index volcanic explosivity index and those by mitchell 1970 sato et al 1993 and khmelevtsov et al unpublished manuscript 1993 all have drawbacks ice core acidity and sulfate records because they contain physical evidence of atmospheric loading are a promising source of information on past volcanic aerosols but these records contain large nonvolcanic signals as well we have compared northern hemisphere nh and southern hemisphere sh annual average versions of five indices with eight nh and six sh ice core records for the period 1850 to the present in an attempt to identify the volcanic signal common to all records the indices are all highly correlated with each other for the nh although the individual ice core records are in general not well correlated with each other or with any of the indices a composite derived from averaging the cores the ice core volcano index ivi shows promise as a new index of volcanic aerosol loading this new index correlates well with the existing non ice core volcanic indices and with high frequency temperature records for the sh the individual ice cores and indices are better correlated the shivi is again highly correlated with all indices and individual ice cores but not with high frequency temperature records for both hemispheres the southern oscillation index shows no significant correlation with the volcanic indices ice cores or the ivi thus providing no evidence for the impact of volcanic eruptions on el nino southern oscillation events

late precambrian paradoxical glaciation and obliquity of the earth a discussion of dynamical constraints abstract g e williams observations on late precambrian glaciogenic sequences pose some major challenges to the understanding of the dynamical evolution of the earth s orbit and spin that have not yet been adequately addressed in this paper we investigate whether dissipative core mantle coupling is an effective mechanism for reducing the obliquity by such a large amount as suggested by williams g e williams earth sci rev 112 1993 1 45 and we examine the relationship between the obliquity and spin rate in the presence of such coupling we show that this mechanism not only cannot explain the rapid and substantial decrease in obliquity but also that such a decrease is in contradiction with existing paleorotation evidence for the same period thus confirming the previous findings of neron de surgy and laskar o neron de surgy j laskar astron astrophys 318 1997 975 989

impacts tillites and the breakup of gondwanaland a discussion oberbeck et al 1993 have proposed that some ancient sedimentary rocks such as diamictites and associated deposits widely interpreted as glacigenic should be reassessed in the light of recent advances in the understanding of impact related phenomena such radical departures from accepted interpretations cf deitz 1964 can stimulate review of long accepted more traditional ideas and thus provide a catalyst for new avenues of research the proposed reinterpretations have potentially far reaching consequences for example the possible connections between long term climatic change and tectonic history of the earth fischer 1984 worsley et al 1984 young 1991 would be brought into question some aspects of atmospheric evolution hart 1978 interpretation of stable isotope distribution curves and ideas on the evolution of life knoll 1991 have been linked to inferences about cold climatic episodes glaciations based primarily on study of the rock record in the last two decades following publication of the benchmark paper by schermerhorn 1974 glacial specialists have been particularly circumspect in their interpretations and have developed what they consider to be a reliable set of criteria for the recognition of glacial deposits the following remarks are offered in an effort to reaffirm the validity of some of these criteria and to suggest that the proposed impact theory for the origin of many diamictite bearing sequences is correspondingly

volcanic eruptions large scale modes in the northern hemisphere and the el nino southern oscillation abstract the author analyzes the impact of 13 major stratospheric aerosol producing volcanic eruptions since 1870 on the large scale variability modes of sea level pressure in the northern hemisphere winter the paper focuses on the arctic oscillation ao and the north atlantic oscillation nao to address the question about the physical nature of these modes the hypothesis that the phase of the el nino southern oscillation enso may control the geographical extent of the dominant mode in the northern hemisphere is also investigated as well as the related possibility that the impact of the eruptions may be different according to the phase of enso the author finds that both the ao and the nao are excited in the first winter after the eruptions with statistical significance at the 95 level both the signal and the significance are larger for the nao than for the ao the excitation of the ao and the nao is connected with the excitation of a secondary mode which resembles an augmented pacific north ame

late proterozoic and paleozoic tides retreat of the moon and rotation of the earth the tidal rhythmites in the proterozoic big cottonwood formation utah united states the neoproterozoic elatina formation of the flinders range southern australia and the lower pennsylvanian pottsville formation alabama united states and mansfield formation indiana united states indicate that the rate of retreat of the lunar orbit is dxi dt approximately k2 sin 2delta where xi is the earth moon radius vector k2 is the tidal love number and delta is the tidal lag angle and that this rate has been approximately constant since the late precambrian when the contribution to tidal friction from the sun is taken into account these data imply that the length of the terrestrial day 900 million years ago was approximately18 hours

gcm evaluation of a mechanism for el nino triggering by the el chichon ash cloud the el chichon volcanic eruption in 1982 was immediately followed by the strongest el nino of the century in 1982 83 we investigate a possible mechanism proposed by hirono whereby volcanic eruptions might trigger or enhance el ninos three distributions of volcanic ash aerosol in the troposphere over the eastern pacific ocean were used to force simulations with a modified version of the ncar ccm1 atmospheric general circulation model for the month of april 1982 using observed sea surface temperatures only in the case of mid tropospheric heating is there a strong dynamical reaction in the atmosphere resulting in a weakening of the trade winds in the eastern pacific ocean north of the equator consistent with surface wind observations and with the first part of hirono s theory however the 1982 enso event had started before this wind anomaly and only trade wind collapses in the western equatorial pacific can initiate el ninos the results suggest that while tropospheric aerosols from volcanic eruptions can influence atmospheric circulation the timing and location of the el chichon eruption and the large enso event that followed was a coincidence and that hirono s mechanism was not responsible for the strength or timing of the el nino

field investigations of the nature of water table response to precipitation in shallow water table environments abstract several water table response tests performed in undulating topography at a field site near chalk river ontario are analysed the objective of the experiments was to gather detailed field information on the nature of the water table rise in response to precipitation in a shallow water table environment the tests were performed by applying simulated rainfall to a study site instrumented in detail with porous membrane tensiometers changes in hydraulic head were measured using a pressure transducer and a hydraulic switch a disproportionate rise in the water table was observed in areas where the zone of tension saturation capillary fringe extended to ground surface for example for rainfall of 5 mm over a duration of 5 3 min the water table in the lowest lying areas rose about 13 cm while the rise in the area of higher ground was only 5 cm furthermore as a result of the difference in response between the low lying and higher ground complex and transient hydraulic gradients were established directed away from the low lying area the magnitude of the response in the low lying area can only be explained by the presence of the capillary fringe

el chinchon eruption the dust cloud of the century on passe en revue les differentes methodes d observation du nuage de l eruption d el chichon satellite lidar observation aerienne

precambrian tidal and glacial clastic deposits implications for precambrian earth moon dynamics and palaeoclimate abstract over the past decade the study of precambrian clastic tidal rhythmites stacked laminae of sandstone siltstone and mudstone that display periodic variations in thickness reflecting a strong tidal influence on sedimentation has provided accurate palaeotidal and palaeorotational data palaeotidal records obtained from tidal rhythmites may be systematically abbreviated however and derived periods and frequencies can be misleading the validity of such values including past length of day can be assessed by testing for internal self consistency through application of the laws of celestial mechanics such a test supports the estimated length of day of 21 9 0 4 h derived from the late neoproterozoic 620 ma elatina reynella rhythmites in south australia and the indicated mean rate of lunar retreat of 2 16 0 31 cm year since 620 ma the validity of estimated lengths of day obtained from other precambrian tidal rhythmites remain unverified because the data sets contain only one primary value directly determined from the rhythmites the elatina reynella data militate against significant earth expansion at least since 620 ma and suggest that the free nutation or tipping of the earth s fluid core has undergone a resonance with the earth s annual forced nutation since the neoproterozoic glaciogenic deposits are readily distinguishable from ejecta resulting from impacts with earth crossing bodies palaeomagnetic data based on the geocentric axial dipole model for the geomagnetic field indicate that neoproterozoic and palaeoproterozoic glaciation and cold climate near sea level occurred in low palaeolatitudes this enigmatic finding may imply global glaciation or an increased obliquity of the ecliptic and is relevant to modelling the effect of ice sheet formation on the earth s obliquity history by obliquity oblateness feedback mechanisms through multidisciplinary studies clastic sedimentology and geophysics together can make substantial contributions to understanding precambrian earth moon dynamics and global palaeoenvironments

ultrasonic monitoring of spontaneous imbibition experiments acoustic signature of fluid migration capillary rise experiments spontaneous imbibition tests were conducted in the laboratory with ultrasonic and x ray monitoring on the sherwood sandstone and the majella grainstone the aim was to provide a direct comparison between the variation in seismic attributes amplitude velocity spectral content and energy and the actual fluid distribution in the rock two pairs of ultrasonic p wave sensors located at different heights on a cylindrical rock specimen recorded every 5 s the waveforms when capillary forces make water rise up into the rock from the bottom in contact with a water tank simultaneously computerized tomography scan images of a vertical cross section were also recorded two important results were found i the amplitude of the first p wave arrival is impacted by the upward moving fluid front before the p wave velocity is while the fluid front has not yet reached the sensors level in contrast the p wave velocity decreases when the fluid front reaches the fresnel clearance zone the spectral analysis of the waveforms shows that the peak frequency amplitude is continuously decreasing without noticeable frequency shift ii a methodology based on the calculation of the analytical signal and instantaneous phase was designed to decompose each waveform into discrete wavelets associated with direct or reflected waves the energy carried by the wavelets is very sensitive to the fluid substitution process the coda wavelets related to reflections on the bottom end face of the specimen are impacted as soon as imbibition starts and can be used as a precursor for the arriving fluid

analytical expressions for drainable and fillable porosity of phreatic aquifers under vertical fluxes from evapotranspiration and recharge 1 in shallow unconfined aquifers the response of the water table wt to input and output water fluxes is controlled by two distinct storage parameters drainable and fillable porosity which are applicable for wt drawdown and rise respectively however only the drainable porosity estimated from the hydrostatic soil moisture profile is in common use in this study we show that under conditions of evapotranspiration and or recharge from or to a shallow water table drainable and fillable porosity have different values separate analytical expressions are developed for drainable and fillable porosity accounting for dynamic soil moisture conditions through the assumption of successive steady state fluxes in the unsaturated zone the equations are expressed in terms of soil hydraulic parameters and matric suction at the soil surface parametric evapotranspiration and recharge functions are used to estimate the suction at the soil surface the final expressions are independent of evapotranspiration or recharge function thus allowing the use of any appropriate function to estimate the storage parameters it is shown that the occurrence of unsaturated zone fluxes can result in significantly different values of drainable and fillable porosity even when hysteresis is neglected application of the two parameters in a boussinesq type groundwater model resulted in significantly improved estimates of field measured water table dynamics compared to the hydrostatic single parameter model

a palaeomagnetic test of the axial dipole assumption and implications for continental distribution through geological time the distribution of the magnetic inclination i in the global palaeomagnetic data is examined over broad windows of geological time extending from the cenozoic back to the archaean distributions are compared with the theoretical predictions from the uniform global sampling of dipolar and higher order geomagnetic field sources the distributions are found to accord more closely with a dipolar source than with a multipolar source over most of geological time reinforcing a conclusion by evans based on 10 of the present data base the exception is the interval 600 300 ma broadly coincident with palaeozoic times when the data critically fail to accord with any simple multipole assumption we interpret this to be a symptom of the remagnetisation effect the sedimentary derived and to a much lesser extent the igneous and metamorphic derived record from these times has been extensively remagnetised in late palaeozoic times as the result of a unique incidence of diagenetic tectonic and thermal processes otherwise we conclude that the palaeomagnetic data interpreted on the basis of the axial dipole assumption can be used reliably to evaluate tectonic models for older 600 ma and younger 250 ma parts of geological time models for the global distribution of the continental crust for those cases that have postulated episodic or long term accretion of the crust into quasi rigid supercontinents are also evaluated the proterozoic supercontinent yields the most acceptable solution to the i distribution observed over the long interval of precambrian times 3000 600 ma it also explains the variable ratios of high latitude palaeomagnetic poles from the ancient shield segments of continental crust owing to the failure of the palaeozoic data set to accord with the dipole assumption the i distributions cannot be used to test the relationship between the supercontinent of pangaea and the geoid symmetry during the earlier part of its history but after 250 ma it was most closely constrained to the form of the geoid positive over geological time as a whole the continental crust has shown a marked preference for the i distribution defined by the present geoid positive rather than the distribution defined by the geoid negative we therefore conclude that the deep mantle effects responsible for the geoid have on average had a surface response which has tended to move the continental crust towards this sector of the globe

reliability of lunar orbital periods extracted from ancient cyclic tidal rhythmites abstract ancient tidal periods extracted from the geologic record are useful to constrain and calibrate theoretical models of the evolution of the earth moon system analysis of rocks that contain such tidal periodicities termed cyclic rhythmites have tended to concentrate on long series and have focused on the more obvious periods for example neap spring periods have been the most widely discussed such information can be reliably extracted from bedform thickness series measured within laterally accreted tidal bundles and vertically accreted tidal laminae other lunar orbital data is also encoded in cyclic rhythmites however this additional information has been much less extensively applied to earth moon models herein short segments of well formed cyclic rhythmites are examined to determine how reliably the various tidal periods can be extracted via harmonic analysis rhythmite series analyzed here exhibit well formed neap spring tidal periods and also exhibit a prominent fortnightly inequality or a variation in the height of successive spring tides this inequality is related to the elliptical nature of the lunar orbit anomalistic month and it is demonstrated that this period can also be reliably extracted from cyclic rhythmites tropical periods which reflect the changing lunar declination that occurs during a tropical month have also been reported from cyclic rhythmites unlike synodic and anomalistic periods the apparent tropical periods extracted from some cyclic rhythmites do not always accurately correspond to the expected values in only a few cases can this period be reliably extracted from short segments of cyclic tidal rhythmite data this period is commonly only poorly encoded in rhythmites because 1 it tends to be masked by higher amplitude synodic periods and 2 it is not well expressed within predominantly semidiurnal tidal systems samples selected from the proterozoic and phanerozoic tend to be more common during specific intervals of geologic time these intervals were characterized by glacio eustatic flux and in some cases by unique continental configurations understanding these basic controls on rhythmite occurrences should aid in the discovery of additional examples

high obliquity simulations for the archean earth implications for climatic conditions on early mars global climate model simulations using high obliquity 70 higher co 2 and ch 4 but reduced o 3 concentrations produce warm climate conditions for archean boundary conditions reduced solar forcing solar radiation under high obliquity is distribution in such a way as to warm high latitudes and cool low latitudes global mean air temperatures of approximately 280 k are found with a 25 reduction in the solar forcing 4760 ppmv co 2 and 25 ppmv ch 4 high obliquity could also explain why polar oceans on mars may have occurred in its history a substantial increase in the amount of insolation is accounted for if mars had an obliquity of 70