a new mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of poc with ballast minerals abstract in simulation studies of the ocean s role in the global carbon cycle predicting the depth distribution for remineralization of particulate organic carbon poc is of particular importance following sarmiento et al global biogeochemical cycles 7 1993 417 most simulation models have the power law curve of martin et al deep sea research 34 1987 267 for this purpose the martin et al curve is an empirical fit to data most of which is from shallow floating sediment traps using such a fit implies that all the information necessary for prediction is contained in the carbon flux itself so that the organic carbon flux f oc z at any depth z can be predicted from the flux of organic carbon f oc z 0 at some near surface depth z 0 here we challenge this basic premise arguing that fluxes of ballast minerals silicate and carbonate biominerals and dust determine deep water poc fluxes so that a mechanism based model of poc flux must simultaneously predict fluxes of both poc and ballast minerals this assertion is based on the empirical observation that poc fluxes are tightly linked quantitatively to fluxes of ballast minerals in the deep ocean here we develop a model structure that incorporates this observation and fit this model to us jgofs eqpac data this model structure plus the preliminary parameter estimates we have obtained can be used to explore the implications of our model in studies of the ocean carbon cycle

evaluation of sample quality of sensitive clay using intrinsic compression concept a simple index the degree of sample disturbance is proposed in this study to quantitatively evaluate the quality of sensitive clay samples based on the concept of void index proposed by burland in 1990 the degree of sample disturbance is defined as the ratio of the difference between the in situ void index and the void index of the undisturbed sample tested in the laboratory to the difference between the in situ void index and the void index of the completely remolded clay all these indices are determined at the same effective overburden stress theoretically the degree of sample disturbance varies from 0 perfect undisturbed sample to 100 completely remolded sample the proposed index is used in this study to evaluate the sensitive ariake clay in japan oedometer tests on undisturbed samples of natural ariake clay obtained from the field using the current sampling practice in japan show the degree of sample disturbance ranging from approximately 5 to 38 the clay sample with an in situ void index closer to the intrinsic compression line has a lower degree of sample disturbance in addition a series of consolidation and unconfined compression tests were conducted on artificially disturbed samples in the laboratory to demonstrate the change of consolidation yield stress unconfined compressive strength and compression index with the degree of sample disturbance a simple method is proposed in this paper to correct the mechanical parameters measured in a laboratory setting considering the degree of sample disturbance

speciation bioavailability and preservation of phosphorus in surface sediments of the changjiang estuary and adjacent east china sea inner shelf abstract the speciation potential bioavailability and preservation of phosphorus p in surface sediments of the changjiang yangtze river estuary and adjacent east china sea ecs inner shelf were investigated through the analyses of p fractions and sediment bulk properties a sequential extraction method sedex was used to separate and quantify the following six sedimentary p reservoirs exchangeable p ex p authigenic p au p detrital p de p organic p or p refractory p re p and fe bound p fe p total p tp in surface sediments ranged from 15 0 to 21 4 mol g 1 and was highest near the changjiang river mouth the average contribution of each form of p to tp was 55 6 de p 17 8 re p 16 1 or p 5 5 au p 2 5 ex p and 2 5 fe p respectively de p showed relatively higher concentrations in the river mouth and the ecs shelf region off the changjiang estuary high concentrations of or p were found mainly in mud areas showing a similar distribution pattern with silt sediment surface area ssa and total organic carbon toc re p was mainly distributed near the estuarine area and the zhe min coast bioavailable p bap accounted for 9 5 32 0 of tp with a mean of 21 2 and showed a similar distribution pattern to that of or p de p ssa and toc ssa loadings both decreased with increasing of ssa while or p ssa loadings varied little with ssa indicating that or p may have reached an adsorption desorption equilibrium on mineral surfaces toc to total organic p top sum of re p and or p ratios less than the redfield ratio 84 in average may have indicated efficient remineralization of organic matter in mobile muds of the changjiang estuary and adjacent ecs inner shelf furthermore the relatively high toc or p ratios 72 422 with a mean of 188 likely suggest a higher degree of preferential regeneration of labile or p over toc in sediments

reliability of dipole dipole electrical resistivity tomography for defining depth to bedrock in covered karst terranes sinkhole collapse is one of the main limitations on the development of karst areas especially where bedrock is covered by unconsolidated material studies of sinkhole formation have shown that sinkholes are likely to develop in cutter enlarged joint zones as a result of subterranean erosion by flowing groundwater because of the irregular distribution of pinnacles and cutters on the bedrock surface uncertainties arise when hit or miss borehole drilling is used to locate potential collapse sites a high resolution geophysical technique capable of depicting the details of the bedrock surface is essential for guiding the drilling program dipole dipole electrical resistivity tomography ert was used to map the bedrock surface at a site in southern indiana where limestone is covered by about 9 m of clayey soils forty nine transects were conducted over an area of approximately 42 037 m2 the electrode spacing was 3 m the length of the transects varied from 81 to 249 m the tomographs were interpreted with the aid of soil borings the repeatability of ert was evaluated by comparing the rock surface elevations interpreted from pairs of transects where they crossed each other the average difference was 2 4 m with a maximum of 10 m the discrepancy between interpreted bedrock surface elevations for a transect intersection may be caused by variations in the subsurface geology normal to the transect averaging the elevation data interpreted from different transects improved the ert results a bedrock surface map was generated using only the averaged elevation data at the transect junctions the accuracy of the map was further evaluated using data from four exploratory boreholes the average difference between interpreted and actual bedrock surface elevations was less than 0 4 m the map shows two large troughs in the limestone surface one coinciding with an existing sinkhole basin while the other is in alignment with a small topographic valley because sinkholes were observed at the same elevation interval in similar valleys in the vicinity the delineated trough may have implications for future land use at the site

controls on phosphorus concentration and accumulation in oceanic sediments understanding phosphorus p sedimentation in the ocean is important both for quantifying outputs in the marine phosphorus cycle and for determining the controls on phosphogenesis the authigenic formation of carbonate fluorapatite and phosphorite deposition large accumulations of p rich sediments on continental margins in this study i have compiled literature data on sedimentary p concentrations and sedimentation rates from continental margins phosphogenic continental margins and open ocean environments i have also calculated p accumulation rates the product of p concentration sediment density and sedimentation rate in these settings sedimentary p concentrations exhibit a similar range in a wide variety of oceanic environments and sedimentation rate conditions for example p concentrations in continental margin sediments range from 8 to 108 mol p g 1 with sedimentation rates from 80 to 8 000 m my 1 in open ocean sediments the p concentration range is similar 7 307 mol p g 1 even though sedimentation rates are generally about 100 times lower 2 50 m my 1 the exception to this are phosphogenic environments where p concentrations are exceptionally high 580 3 700 mol p g 1 while sedimentation rates are relatively low 20 310 m my 1 phosphorus accumulation rates appear to be controlled by sedimentation rate in ocean sediments although p concentrations generally exhibit similar ranges the large difference in sedimentation rates between various environments results in p accumulation rates that are several orders of magnitude higher in continental margins 90 8 000 mol p cm 2 kyr 1 compared to open ocean sediments 2 75 mol p cm 2 kyr 1 in the case of phosphogenic environments low sedimentation rates result in p accumulation rates 80 6 300 mol p cm 2 kyr 1 that are surprisingly similar to those of non phosphogenic continental margin sediments

the nature and hydrogeologic significance of mud diapirs and diatremes for accretionary systems in accretionary wedges often morphologically similar sedimentary intrusions when observed by remote geophysical means may have one of two quite different driving mechanisms and a highly variable significance for the regional hydrogeologic picture for example mud diapirs are driven by buoyancy forces that arise from bulk density contrasts in them mud and pore fluid upwell en masse and fluid migration is a related sometimes important but generally subsidiary process in contrast diatremes contain sediments fluidized during rapid fluid advection and are forcibly and directly driven by the hydrogeologic system the nature of fluid input from local and exotic source regions can therefore strongly affect sedimentary intrusive processes and vice versa this complicates the process of defining the main features of the hydrogeological systems operating in accretionary wedges focused vertical advection through steep sided piercement mud diapirs requires conduit systems otherwise flow will be diffuse and directed more horizontally out of the low permeability mud mass however where the permeability of the overburden is less than that of the diapir the whole diapir may act as a conduit apart from this special case conduits will be associated with highly anisotropic scaly fabrics that can sometimes develop in the marginal shear zone of diapirs scaly fabrics form during deformation and compaction of a mud matrix under conditions of constant or increasing effective stress however the effective stress path can be complex as it is both controlled by the relative rates of upward intrusion and burial by sedimentation and or structural thickening and the hydrogeologic system due to this it appears likely that even in a geographically related group of diapirs effective stress histories will vary widely between intrusions so that some can form advective pathways for fluids and some cannot mixed systems of behavior may also be present with local diatremes developing within diapirs above the terminations of conduit systems and rapidly expanding methane gas pockets the potentially heterogeneous near surface behavior may be why the surface manifestations of sedimentary intrusions are so variable when observed in the field diatremes can also form separately as large primary features above any structural or stratigraphic conduit that rapidly expels water or gas into the base of an unlithified sediment column when active large diatremes require enormous quantities of fluid water or gas to drive them particularly if they are long lived features and hence are a direct indication of at least an episodically vigorous hydrogeologic system

origin of bermuda s clay rich quaternary paleosols and their paleoclimatic significance red clayey paleosols that are chiefly the product of aerosolic dust deposition are interbedded in the quaternary carbonate formations of the bermuda oceanic island system these paleosols provide a basis for reconstructing quaternary atmospheric circulation patterns in the northwestern atlantic geochemical analyses were performed on representative paleosol samples to identify their parent dust source fine grained fractions were analyzed by energy dispersive x ray fluorescence to determine trace element zr y la ti and nb concentrations and to derive geochemical signatures based on immobile element ratios these ratios were compared with geochemical signatures determined for three possible sources of airborne dust 1 great plains loess 2 mississippi river valley loess and 3 saharan dust the zr y and zr la ratios provided the clearest distinction between the hypothesized dust sources the low ratios in the paleosol b horizons most closely resemble saharan dust in the 2 m size class fraction contributions from the two north american loessial source areas could not be clearly detected thus bermuda paleosols have a predominantly saharan aerosolic dust signature saharan dust deposition on bermuda during successive quaternary glacial periods is consistent with patterns of general circulation models which indicate that during glacial maxima the northeast summer trade winds were stronger than at present and reached latitudes higher than 30on despite lower than present sea surface temperatures in the north atlantic

association of sinking organic matter with various types of mineral ballast in the deep sea implications for the rain ratio 1 we compiled and standardized sediment trap data below 1000 m depth from 52 locations around the globe to infer the implications of the armstrong et al 2002 ballast model to the ratio of organic carbon to calcium carbonate in the deep sea the rain ratio we distinguished three forms of mineral ballast calcium carbonate opal and lithogenic material we concur with armstrong et al 2002 that organic carbon sinking fluxes correlate tightly with mineral fluxes based on the correlations seen in the trap data we conclude that most of the organic carbon rain in the deep sea is carried by calcium carbonate because it is denser than opal and more abundant than terrigenous material this analysis explains the constancy of the organic carbon to calcium carbonate rain ratio in the deep sea today and argues against large changes in the mean value of this ratio in the past however sediment trap data show variability in the ratio in areas of high relative calcium carbonate export mass caco3 mass ratio 0 4 unexplainable by the model leaving open the possibility of regional variations in the rain ratio in the past

evaluation of electrical resistivity tomography ert for mapping the soil rock interface in karstic environments rocky desertification is a significant threat in the karst regions of southwest china studies of soil distribution can contribute to protecting and recovering the fragile karst ecosystem that is prevalent in this region with an underlying aim of being able to assess soil stocks in karstic environments this study evaluates the use of electrical resistivity tomography ert for delineating the soil rock interface using a synthetic model that recognizes the three dimensional nature of the subsurface experiments are performed to assess the impact of measurement errors and measurement configuration on recovery of the interface the inverted results show that the accuracy of the delineation of the soil rock interface decreases with the increase of measurement error and dipole spacing the results also show the importance of reliable estimation of measurement errors field based applications of ert at five exposed profiles in southwest china are also reported for the field data three dimensional modelling was necessary to account for the exposed face the field experiments show that ert can be effective at delineating the interface between soil and bedrock but resolution can be limited due to the scale of features or lack of contrast between soil and bedrock the method shows great promise as a means of assessing in a non invasive manner the soil bedrock interface and perhaps more significantly quantifying estimates of total soil stocks as we seek to quantify the vulnerability or resilience of this important landscape to anthropogenic and natural stresses

crystallinity and diagenesis of sedimentary apatites the crystallinity of sedimentary apatites was determined by fourier transform infrared spectroscopy ft ir using the splitting of a triply degenerate antisymmetric bending vibration of orthophosphate the crystallinity indices of recent marine apatites are low 3 0 3 6 while those of onland ancient apatites are high 4 5 7 8 indicating post depositional recrystallization the infrared spectra reveal that recrystallization is associated with a decrease in carbonate content substituting for po43 and an increase in fluoride order within the apatite structure the relationship between the crystallinity index and po43 18o suggests alteration of the primary isotopic composition by exchange reactions between po43 oxygens and surrounding waters the monterey samples have a large range of crystallinity index that reflects a set of complex and highly variable diagenetic conditions this demonstrates the use of ft ir criteria for differentiating between pristine and altered apatites and as a consequence for relating geochemical markers to formation or diagenetic environments it is suggested that only those samples that have low crystallinity indices c i 3 8 should be considered as pristine apatite spectra of fish remains indicate that differences in rare earth element ree patterns correspond to variations in crystallinity carbonate content and f order in the apatite lattice the fact that crystallinity is not correlated with geologic age suggests that environmental factors such as accumulation rate and pore water chemistry govern the recrystallization process in general sr content decreases and 18op exhibits high variability with increasing crystallinity

soils in the mediterranean region what makes them different mediterranean climates are characterized by winter rains with some months of excess rainfall over evatranspiration warm and dry summer months with moisutre deficits drying out soils and their annual vegetation xeric moisture regime they are found on western parts of all continents between the cooler temperature zone and the hot dry desert zone the largest mediterranean region surrounding the mediterranean sea extends over 4 300 000 km2 and exhibits a wide variety of soils and geo ecosystems characteristics landscape attributes are the high proportion of mountains with sleep slopes significant additions of saharan desert dust to practically all soils of the region and a large proportion of limestone and other calcareous rocks as soil parent materials characteristics soil behavior features are moderate weathering with pervection leaching lessivage of mostly 2 1 clays into b horizons xeralfs luvisols hematite induced reddening of the clays due to summer dehydration of free iron oxyhydroxides carbonate dissolution and reprecipitation with prevalence of calcic horizons xerolls calcisols in semiarid regions and development of vertisols mostly in lowlands where deep layers of swelling cracking clays have sedimented shallows soils on nearly bare slopes mostly a result of erosion subsequent to deforestation are frequent leptosols cambiosols inceptisols entisols red or brown mediterranean soils are no longer used as a separate classification group in modern well defined soil property controlled taxonomies soil taxonomy fao system but were partially replaced by duchaufour s term fersiallitic soils in some classification systems terra rossa continues to be used in some classification for hard limestone derived red soils mostly shallow the effects of man s past and current interference with the lanscape are pervasive in most regions and predictions for possible future effects on the soils and ecosystems due to greenhouse gas induced warming and rainfall change are partly negative partly still too uncertain

erosion creep collapse mechanism of underground soil loss for the karst rocky desertification in chenqi village puding county guizhou china carbonate rocks distribute widely in china the total area of the carbonate rocks is about 3 430 000 km 2 and the exposed area of the carbonate is approximately 13 of china s territory in 2003 soil loss in yunnan guizhou and guangxi provinces reached 179 600 km 2 which is almost 40 1 of the total area causing rocky desertification in this study the erosion creep collapse mechanism of underground soil loss for the karst rocky desertification in chenqi village puding county guizhou province is proposed the mechanism occurs under the following geological environment slope surface undulation underlying bedrock surface fluctuation and thin and inhomogeneous soil overlying overlying soil generation by bedrock weathering underground karst development and large groundwater depth and lying water table under the bottom of soils the erosion creep collapse mechanism of underground soil loss in the karst slopes is explained as follows power loss due to human cultivation activities that destroy the soil structure hydraulic force formed by rainfall infiltration wet dry cycle generated by rainfall erosion effect caused by rainfall penetration creeping and flowing of plastic stream soil and collapse the erosion creep collapse mechanism of underground soil loss has seven steps disturbance of soils filled in underground karst cave by human activities internal soil erosion and partial collapse caused by hydraulic power internal free surface formation within the soil in the filled karst cave internal soil creeping soil pipe formation soil pipe collapse and ground surface collapse and filling soil loss develops slowly and sudden transportation occurs by collapse soil loss can be explained by the proposed mechanism and soil loss can be prevented by controlling soil collapse

prediction of impending failure of embankments on soft ground the deformation behaviour and excess pore pressure response of 13 well monitored embankments on soft ground that were constructed to failure have been analyzed the analysis shows that by monitorin

age and origin of terra rossa soils in the coonawarra area of south australia abstract the famous terra rossa soil in the coonawarra area south australia is dominated by locally derived aeolian detritus which probably accumulated over the last 120 130 ka four soil profiles and associated limestone and lunette deposits were investigated using the following methods mass balance geochemistry of bulk soil samples major and trace elements quantitative x ray diffraction xrd mineralogy strontium isotopes 87 86 as well as grain size analysis and cation exchange capacity these data show that the terra rossa soil from the coonawarra has a thick clayey b horizon which is geochemically homogeneous and dominated by smectite and kaolinite mass balance calculations show unrealistic weathering scenarios when plotted using silicate residuum from the underlying limestone as parent realistic weathering scenarios are produced with fine grained silicate material from local lunette deposits as parent strontium isotopes of silicate residuum from gambier limestone 0 78 contrast strongly with the clayey b horizon 0 726 strontium isotope ratios of silicate material from a local lunette 0 725 are similar to the b horizon soil values strontium isotope ratios from regional geological units indicate that the strontium signature in the lunette and soil b horizon is dominated by weathering products from the palaeozoic kanmantoo shales extensively exposed upwind to the west on kangaroo island and the fleurieu peninsula optical optically stimulated luminescence osl dating of 61 individual quartz grains single aliquot from three samples in the coonawarra soil profile one from the a horizon and two from the b horizon shows that most of the quartz sand grains have been buried for only a few thousand years many of the grains however have been buried for tens of thousands of years with three grains having exposure ages of between 105 and 109 ka the large population of young exposure dates represents quartz sands recently exposed in the a horizon and which have been translocated down to the b horizon the older exposure dates are interpreted as representing grains that were buried during or soon after the accumulation of wind blown silt and clay our current model concerning the timing and conditions of aeolian deposition of the coonawarra soil is that much of it accumulated during the relatively wet last interglacial period around 120 130 ka during that time span it is thought that the playa lunette systems in the low lying areas to the west were particularly active and generated a significant local dust flux

implications of replacement for reaction transport modeling abstract mineral replacement in rocks consists of growth of guest mineral and dissolution of host the two reactions are coupled by the grain grain stress generated by growth of the guest grain in a rigid or very viscous rock in which it has initially no available room this stress self adjusts to make the volumetric rates of guest growth and host dissolution equal to each other which accounts for the volume conservation typical of replacement volume preservation during replacement is required by conservation of mass and momentum as well the two reactions are also simultaneous and proceed by a sequence of many tiny alternating increments where these increments are small enough internal textural details of the host grain or grain aggregate are morphologically preserved as ghost textures by the replacement the strong variation of mineral reaction rates with stress required by replacement is evidenced also experimentally reported widespread replacement in many rocks laterites diagenesis of siliciclastics and carbonates metasomatic ores metamorphic rocks and hydrothermal alteration warrants creating water rock reactive transport models that predict when and where in a system replacement should take place current geochemical models implicitly view replacement as sequential uncoupled dissolution of host and growth of guest this sequence of reactions may also occur in rocks but crucially differs from replacement implications of replacement for water rock reaction modeling include 1 balancing of replacement reactions on volume 2 use of helmholtz rather than gibbs free energies of minerals involved in replacement 3 taking account of the strong stress dependence of mineral growth and dissolution rates in rocks and 4 taking account of possible accommodation of growth by local deformation as well as pressure solution of the host rock and of the effect of strain rate growth rate on local rock viscosity

role of epikarst in near surface hydrological processes in a soil mantled subtropical dolomite karst slope implications of field rainfall simulation experiments epikarst exerts a strong control on run off generation in karst regions but it is still unclear in karst regions our study aimed to demonstrate the effect of epikarst on near surface hydrological processes in a subtropical cockpit karst region of southwest china using plot scale rainfall simulation experiments with different rainfall intensities low and high and antecedent moisture conditions dry and wet a trench excavated to the epikarst lower boundary allowed identification of flow pathways in the entire soil epikarst architecture system thus facilitating the water balance calculations using a conceptual model with the assumption of a two stage hydrological evolution more than 70 of the total rainfall water moved vertically through the shallow soil layer and then was redistributed by the epikarst as subsurface flow occurring on the soil epikarst interface depression filling on epikarst surface water held by epikarst and deep percolation epikarst water regulation capacity defined as the sum of depression filling on epikarst surface water held by epikarst epikarst seepage flow and deep percolation was 58 mm wet antecedent condition and 223 mm dry antecedent condition total run off from the soil epikarst system was dominated by saturated subsurface flow showing a threshold process controlled by epikarst storage capacity storing as much as 181 mm of rainfall water under dry antecedent condition our study proved that despite the epikarst being relatively poorly developed and covered by a soil mantle it still exerted a strong influence on near surface hydrological processes and thus should be adequately considered in future modelling of water recharge and depletion dynamics in this integrated soil epikarst system copyright 2015 john wiley sons ltd

diagenetic replacement controlled by force of crystallization many diagenetic replacements in sedimentary rocks occur along thin solution films between the authigenic and host phases rather than conventionally invoking bulk pore water undersaturation for host phase dissolution we propose that many diagenetic replacements occur by a force of crystallization controlled replacement mechanism whereby nonhydrostatic stresses resulting from authigenic crystal growth are principally responsible for host phase dissolution this model explains diagenetic features such as the restriction of host phase dissolution to authigenic host crystal contacts and euhedral authigenic crystal faces in planar contact with unreplaced host phases as well as the relative replacement tendencies of some common authigenic minerals

the sahara east mediterranean dust and climate connection revealed by strontium and uranium isotopes in a jerusalem speleothem this paper explores the potential of sr and u isotope systems in speleothems as tracers of eolian dust transport and hydrological conditions the study focuses on a speleothem from jerusalem spanning the past 220 kyr this speleothem provides a precisely dated record of dust flux from the sahara to the east mediterranean enhanced dust flux and terra rossa soil development are reflected by elevated 87sr 86sr ratios in the speleothem 0 7082 0 7086 while lower 87sr 86sr ratios 0 7078 indicate higher contribution of the local bedrock due to low dust flux and low soil accumulation the strontium isotope system in the speleothem is a robust monitor of the sahara monsoon modulated climate since dust uptake is related to development or reduction in vegetation cover of sahara soil the 234u 238u activity ratios in the speleothem range between 1 12 and 1 0 the high activity values may indicate selective removal of 234u from the soil while the low values converge to the bedrock the migration of 234u to the cave reflects mainly the regional hydrological conditions that are modulated by the north atlantic mediterranean climate system thus the speleothem provides a combined record of the monsoon north atlantic climatic systems long term stability in glacial 87sr 86sr ratios 0 7083 0 0001 over the past 220 kyr suggests an overall similarity in eolian dust sources and uniformity in the synoptic conditions that dominate the dust storm tracks during glacial periods

sediment carbon nitrogen and phosphorus cycling in an anoxic fjord effingham inlet british columbia sediment geochemistry as well as benthic exchange of nutrients was investigated in effingham inlet a fjord located on the west coast of vancouver island in barkley sound the effect of bottom water oxygenation on sediment carbon nitrogen and phosphorus cycling was compared at sites overlain by oxic and anoxic bottom waters the sites separated by only 3 kilometers were similar in terms of key diagenetic parameters including mass accumulation rate and bulk sediment organic carbon content thus allowing a focus on diagenetic effects attributable to depositional oxygen availability benthic flux chamber incubations sulfate reduction rate measurements measurements of solid phase and pore water chemical profiles were compared for the sites these comparisons reveal that diagenetic processes in the site overlain by oxic waters act to retain more phosphorus in the sediment relative to the anoxic site differences in phosphorus benthic fluxes and burial between the two sites most likely result from differences in organic matter cycling under aerobic versus anaerobic conditions and are not strongly influenced by cycling of p associated with metal oxide phases

seepage leaching and embankment instability water retention dykes at a hydroelectric generating station in southeastern manitoba experienced irregular instabilities over many years after they were heightened in the late 1940s samples from an unstable section of dyke showed considerable reductions in gypsum content and increased brittleness compared with those of neighbouring unloaded clay the samples also showed that lowering the content of gypsum reduced the sizes of yield loci and the strains required for strain softening to occur these observations and the time dependent nature of the problem suggested that seepage from the forebay had leached naturally occurring cementation from the foundation clay and subsequently changed its behaviour stress deformation modeling indicated the foundation clay had yielded during initial construction and again when the dykes were heightened seepage from the forebay occurred at different rates in different locations through the irregular sand silt partings that are generally present in proglacial clays leac

influence of boundary scavenging and sediment focusing on 234th 228th and 210pb fluxes in the santa barbara basin abstract sediment trap samples were collected from the santa barbara basin to examine the flux of 234 th 228 th and 210 pb mean ratios of measured to predicted fluxes are 2 10 and 21 for 234 th 228 th and 210 pb respectively boundary scavenging may supply a portion of all three radionuclides however sediment focusing supplies additional 228 th and 210 pb but little 234 th sediment temporarily deposited on the shelf around the basin contains little excess 234 th due to its short half life 228 th and 210 pb fluxes to the sediments in the santa barbara basin are several times greater than predicted from their supply in the overlying water column these enhanced fluxes require lateral transport of 228 th and 210 pb to the basin through boundary scavenging and sediment focusing 234 th flux is poorly correlated with 228 th and 210 pb fluxes because individual radionuclide sources to the basin differ i e water column production boundary scavenging and or sediment focusing correlations between 228 th and 210 pb fluxes are high due to the strong influence of sediment focusing on both radionuclides there is a strong correlation between both the 228 th and 210 pb flux and total mass flux and lithogenic flux but a weak correlation with the other major sediment components e g organic carbon carbonate and biogenic opal in the santa barbara basin a large fraction of the total mass flux is lithogenic material 50 80 hence the strong correlation between 228 th and 210 pb fluxes and both total mass and lithogenic fluxes 234 th flux is poorly correlated with total mass and major sediment component fluxes

effects of land use land cover and rainfall regimes on the surface runoff and soil loss on karst slopes in southwest china abstract surface runoff and soil loss from 2007 to 2010 related to land use and rainfall regimes in karst hill slopes in guizhou province southwest china were analyzed using the hierarchical clustering method sixty one rainfall events under the subtropical monsoon climate condition were classified into 5 types of rainfall regimes according to the depth maximum 30 min intensity and duration of rainfall in our study we first demonstrated that the amounts of surface runoff and soil loss on the karst hill slopes were very small compared to the non karst areas because the dual hydrological structure in the karst region including ground and underground drainage systems could influence the processes of rainfall recharge and runoff generation most rainfall water was transported underground through limestone fissures and fractures while little was in the form of surface runoff second the runoff and soil loss were affected by land use management and vegetation cover soil loss was intensified in a descending order to five types of land uses pastureland burned area cropland combination vegetation land young forestland third the runoff and soil loss exhibited remarkable variances among different rainfall regimes large runoff and soil loss were mainly created by heavy rainfall storms with a rainfall depth of more than 40 mm and a maximum 30 min rainfall intensity of over 30 mm h 1 in addition rainfall storms with large antecedent precipitations could also produce large runoff and soil loss these observations indicated that limestone fissures and fractures play important roles in surface runoff generation on karst limestone slopes due to their large storage capacity and high infiltration rate lastly the soil erosion risk in the karst pure limestone slope is quite high and should be paid particular attention especially in regards to over grazing because the soil loss created by a single heavy rainstorm in pastureland was 5 times the annual soil loss tolerance

mineral growth in rocks kinetic rheological models of replacement vein formation and syntectonic crystallization abstract we model three cases of coupling between mineral growth kinetics and mechanical response of the rock i dispersed spherical crystals growing by replacement in a hydrostatically stressed elastic rock ii growth of veins or vein networks accommodated by viscous relaxation of surrounding rock and iii syntectonic crystallization in a rock undergoing bulk pure shear such models for the microscopic environment of mineral growth together with additional assumptions or knowledge about rheological behavior and aggregate geometry provide refined estimates of the behavior of a macroscopic volume element which could be combined with geochemical reaction transport models crucial in the models are the various consequences pressure solution creep fracturing of the local stress that is necessarily generated by mineral growth in rocks other than in pores in the first model the dispersed spherical crystals of mineral a are assumed to grow within a spherical volume of rock consisting of mineral b the mineralized zone mz itself embedded in elastic rock the macroscopic stress in the mz and the far field stress in the surrounding rock are uniform and hydrostatic mineral growth of the a crystals is driven by supersaturation with respect to mineral a is accommodated by replacement of b grains and leads to an expansion of the mz described by an infinitesimal strain the radial growth rate of a spherical crystal of mineral a with replacement of mineral b is da dt k a r tln a k b v 0 b k b v 0 b k a v 0 a where ka and kb are kinetic constants r is the gas constant t the temperature in kelvin and v0a and v0b are specific volumes reference saturation states of mineral a a 1 and host mineral b b 1 are specified at the far field hydrostatic stress 0 the microscopic environment of each crystal of a is modeled by a representative volume element rve consisting of a sphere of mineral a embedded in a spherical shell of mineral b in each rve stress is neither uniform nor hydrostatic the model links the local microscopic stress with the macroscopic stress in the mz and surrounding rock the second model refers to veins that make room for themselves by growing not to veins that form by cementation of previously opened or opening cracks if the growth of mineral a as propagating veins or as an interconnected vein network takes place by deformation and expansion of the mz with the deformation itself driven by the stress arising from the supersaturation driven growth the surrounding rock undergoes deformation and is treated as viscous the rate of growth in vein width w is dw dt 2 k a rtln a sv 0 a 1 m where m 16 kav0ac2 3b3 is the medium viscosity c is the vein radius and each vein is treated as centered in a spherical rve of radius b s is an effective tensile stress required for vein propagation for a vein network in which veins surround equant polyhedra of rock of radius b we set c b and drop the term in s for simplicity veins may also widen by replacement the ratio of vein widening by expansion to that by replacement is dw dt expansion dw dt replacement 3 b 16 3 b 16 k a v 0 a k b v 0 b k b v 0 b k a v 0 a both mechanisms of accommodation contribute equally when 3b 16kbv0b at higher viscosity replacement is dominant the incipient growth of a cylindrical crystal with circular cross section in a medium deforming in pure shear simulates syntectonic crystallization both dissolution and deformation of the host accommodate growth in the model the crystal tends to grow faster in the direction of maximum rate of extension in this direction the host mineral may either dissolve to accommodate growth or precipitate to form a pressure shadow accommodation by host dissolution is greatest in the direction of maximum rate of shortening

phosphorus speciation and its bioavailability in sediments of the jiaozhou bay abstract phosphorus p is an important macronutrient that can limit primary productivity in coastal marine ecosystems in this study four sediment cores were collected in the jiaozhou bay to study the phosphorus forms and their bioavailability including exchangeable or loosely sorbed p ex p iron bound p fe p authigenic p ca p detrital p de p and organic p op which were separated and quantified using a sequential extraction method sedex the results showed that the concentration of total p tp in core sediments ranged from 6 23 to 10 46 mol g and inorganic p ip was the dominated p form fe p and de p were the main chemical forms of ip in core sediments the profile variation of op presented the most significant among the phosphorus forms whereas the concentrations of ex p fe p and ca p varied slightly with depth indicating that the transformation of ex p fe p ca p and op could occur during sedimentary p burial moreover the distribution of p species was influenced by many factors including terrigenous input biological processes organic matter degradation and increasing human activities high total organic carbon toc op ratio occurred in the jiaozhou bay ranging from 73 to 472 average 180 81 in core sediments which was caused by the increasing terrestrial organic matter the ratio of toc p reactive ranged from 24 to 101 average 46 15 in core sediments lower than the redfield ratio implying a surplus of sedimentary reactive p compared with toc potential bioavailable p bap accounted for about 28 2 60 8 average 47 1 7 4 of tp in core sediments and presented an increasing trend since 1980s which might be responsible for the shift of phytoplankton community composition during these decades

terra rossa genesis implications for karst and eolian dust a geodynamic thread abstract although terra rossa has long been thought to form by residual dissolution of limestone and or by accumulation of detrital mud ash or dust on preexisting karst limestones we present conclusive new field and petrographic evidence that terra rossa forms by replacement of limestone by authigenic clay at a moving metasomatic front several centimeters wide the red clay s major chemical elements al fe and si probably come from dissolved eolian dust the replacement of calcite by clay exhibits a serrated microstylolitic texture that helps prove that replacement happens not by dissolution precipitation as conventional wisdom has it but by pressure solution of calcite driven by the crystallization stress generated by the growth of clay crystals the acid produced by the isovolumetric replacement of limestone by clay quickly dissolves out additional porosity permeability in an adjacent slice of limestone within the front triggering a reactive infiltration instability that should theoretically

particulate organic carbon fluxes along upwelling dominated continental margins rates and mechanisms 1 time series sediment trap samples were used to examine the rates and mechanisms of particulate organic carbon poc flux at three continental margin locations santa barbara basin cariaco basin and guaymas basin marked by seasonal upwelling and high primary production the mean poc flux in santa barbara basin 0 096 g m 2 d 1 is nearly twice that of cariaco basin and 4 times higher than that in guaymas basin with all three sites having poc fluxes significantly higher than the open ocean average 0 007 g m 2 d 1 in cariaco basin the only site with available primary production numbers there is no significant relationship between poc flux and monthly primary production rather poc fluxes in all three areas strongly correlate with mineral carbonate opal and lithogenic material fluxes this supports the mineral ballast hypothesis where it has been suggested that higher density minerals enhance the flux of organic matter to the deep ocean on the basis of multiple regression analysis the three mineral components explain 72 of the total variance in poc fluxes at the three study sites with biogenic carbonate particles being the most effective transport mineral

accretion of asian dust to hawaiian soils isotopic elemental and mineral mass balances hawaiian soils contain a mixture of material derived from in situ weathering of parent material plus atmospheric inputs including sea salt aerosols and asian dust we use soil mineralogy and radiogenic isotope geochemistry sr and nd to evaluate the impact of asian dust on a chronosequence of hawaiian soils dust becomes an important constituent of soils 20 ky and older near surface 50 cm depth horizons contain as much as 30 quartz a mineral absent from local parent material basaltic sr and nd isotope signatures in these horizons have been completely overprinted by asian dust signatures with 87sr 86sr ratios as high as 0 723 and end values as low as 7 ree patterns in these soils are indistinguishable from that of average upper continental crust quartz abundance and nd isotopes provide two independent tracers of long term dust additions to the chronosequence soils the two tracers indicate a minimum long term average dust accretion rate of 125 mg cm 2 ky 1 at the 150 ka chronosequence site roughly a factor of three higher than holocene dust accumulation rates estimated from north pacific sediment cores we find that the mass of dust preserved in these soil profiles does not increase with age in soils 150 ka and older requiring a loss mechanism for accreted dust on the basis of the geomorphic stability of these sites observed preferential loss of dust derived mica relative to quartz and estimates of soil si leaching rates we argue that chemical weathering is the dominant loss mechanism for dust from these soils dust has a profound effect on the budgets of elements that are susceptible to leaching losses dust becomes the dominant source of soil nutrients si and p in the oldest most intensely weathered soils we calculate a dust derived p input flux of 0 8 mg cm 2 ky 1 and a dust derived si input flux of 35 mg cm 2 ky 1 si leaching fluxes are high 1400 mg cm 2 ky 1 in the youngest 2 ka soils and drop systematically with soil age to a value that closely balances the dust derived si input flux by 4100 ka extremely refractory elements such as nb which are concentrated in soils by residual enrichment processes are much less readily impacted by dust addition although dust has had a pronounced impact on sr and nd isotopic budgets and on soil mineral composition at the 150 ka site dust cannot have contributed 4 of the total nb contained in this soil profile

epikarst mapping by remote sensing abstract epikarst the shallow surficial part of a karstic massif has a significant influence on the spatio temporal variability of recharge and the hydrodynamic functioning of many karst aquifers in the mediterranean morphoclimatic zone the average thickness of a well developed epikarst is around ten metres but the spatial patterns of its degree of development are very heterogeneous due to the complex interaction of a number of different factors such as lithology fracturing weathering soil and vegetation in addition direct field observation is difficult because good outcropping conditions are restricted to particular locations some areas are not accessible and the size of the study area is often too large for exhaustive field surveys satellite based remote sensing however provides a complete coverage of an entire area with spectral resolutions that detect variability in features that can define image textures related to the development of the epikarst this paper describes a quantitative methodology for epikarst mapping using satellite images and field data the proposed method comprises an unsupervised classification to define the spectral signature of each of three epikarst development categories in a high resolution satellite image followed by a supervised classification of the terrain into one of the three categories on a low spatial resolution scale the training areas in the field are assigned to the three categories by a panel of experts using the delphi method geophysical data are used for validation to overcome any bias that may be introduced by the panel the proposed methodology has been applied to the sierra de las nieves karstic aquifer malaga southern spain the outcome is a map of estimated epikarst development that is an approximation to reality and which can be improved as more experimental data become available

authigenic apatite formation and burial in sediments from non upwelling continental margin environments abstract evidence for precipitation of authigenic carbonate fluorapatite cfa in long island sound and mississippi delta sediments suggests that formation of cfa is not restricted to environments of active coastal upwelling we present porewater data suggestive of cfa formation in both these areas application of a sequential leaching procedure designed specifically to separate authigenic carbonate fluorapatite from other phosphorus containing phases including detrital apatite of igneous or metamorphic origin provides strong supporting evidence for authigenic apatite formation in these sediments the size of the authigenic apatite reservoir increases with depth indicating continued formation of cfa during early diagenesis this depth increase is mirrored by a decrease in solid phase organic p at both sites suggesting that cfa is forming at the expense of organic p mass balance considerations application of diagenetic models to interstitial water nutrient data and the saturation state of the interstitial water are consistent with this interpretation diagenetic redistribution of phosphorus among the different solid phase reservoirs is observed at both sites and results in near perfect retention of p by these sediments over the depth intervals sampled formation of cfa in continental margins which do not conform to the classically defined regions of phosphorite formation renders cfa a quantitatively more important sink than has previously been recognized including this reservoir as a newly identified sink for reactive p in the ocean the residence time of p in the modern ocean must be revised downward the implication for ancient oceans of cfa formation in continental margin sediments other than phosphorites is that phosphorite formation may be less a representation of episodicity in removal of reactive p from the oceans than of localized concentration of cfa in phosphatic sediments by secondary physical processes

spatial distribution vertical and horizontal and partitioning of dissolved and particulate nutrients c n and p in the campos basin southern brazil abstract tropical oceans are characterized by low amounts of dissolved nutrients and high amounts of particulates in the biogenic layer and by increased dissolved nutrients and reduced particulates in the water masses of the biolytic layer in this study the hydrochemistry of the area included in the campos basin was evaluated at 72 sampling sites and six depths surface a second depth and the cores of deep water masses up to 2300 m during the summer and winter seasons of 2009 the vertical distribution of dissolved and particulate nutrients had patterns typical of permanently stratified tropical waters and greater values were found on the continental shelf than on the slope as expected these results confirm that the continent is an important source of the materials found in the studied water masses additionally the spatial variations observed are likely related to the south atlantic central water sacw intrusion into the continental shelf in the cabo frio region and to eddies formation in the cabo de sao tome region where higher concentrations of dissolved and particulate nutrients were found despite the n p ratio indicates limitation of primary producers by inorganic nitrogen the particulated and dissolved organic n p indicate a strong depletion of p relative to n suggesting preferential degradation of that

evaluation of the predictive ability of two elastic viscoplastic constitutive models two elastic viscoplastic constitutive formulations are evaluated using laboratory and field data from sackville new brunswick and gloucester ontario both constitutive models have been implemented in a finite element program and formulated for undrained analysis and fully coupled analysis based on biot consolidation theory a laboratory study of the rate sensitive behaviour of sackville clay is described the response of sackville clay during consolidated anisotropic undrained cau triaxial creep cau triaxial compression and incremental oedometer consolidation is compared with the calculated behaviour the comparisons demonstrate the general ability of three parameter elastic viscoplastic constitutive models to satisfactorily describe the rate dependent behaviour of sackville clay the measured response of gloucester clay during long term rowe cell consolidation tests is compared with the calculated behaviour and the predictive ability of both constitutive formulations is evaluated using the field p

geometric morphology and soil properties of shallow karst fissures in an area of karst rocky desertification in sw china abstract serious soil erosion and an extremely low rate of soil formation leads to a thin layer of surface soil that makes tree growth difficult in areas of karst meanwhile surface soil driven by runoff enters shallow karst fissures skfs these skfs filled with soil have become the major habitat type in the area here we explore the morphological characteristics of shallow karst fissures as well as the soil physical and chemical properties of the skfs and comprehensively analyse the factors that influence the soil properties three key results are presented first a high heterogeneity of morphological characteristics exists for shallow karst fissures according to the different characteristics of the vertical section the skfs can be divided into 5 types these types are rectangle type pyramid type funnel type net type and diamond type in addition the skf dip angles were mainly between 60 and 90 76 39 the width of the top aperture was mainly between 20 and 40 cm 51 39 and the trace lengths were mainly between 80 and 160 cm 76 39 second compared with their characteristics of surface soil the bulk density and fractal dimension of soil particles of the skfs were both large and the main composition of the skf soil was clay third the soil nutrients of the skfs the organic matter total nitrogen and total phosphorus were lower than the surface soil nutrients but not significantly so the total potassium tk of the skfs was greater than that observed for the surface and increased as the depth of the skf increased the soil nutrients of the skfs were significantly affected by the fissure morphology the poorly connected fissures had better soil fertility when the morphological characteristics and soil properties of the skfs were comprehensively considered the vegetation types that were determined to be the best for use in the ecological restoration of areas of karst rocky desertification were deep rooted plants with especially strong root penetration the result of this study can supply some reference for future studies of karst rocky desertification control and vegetation restoration in the karst area of southwest china in the south claw silicon island in yogyakarta province indonesia and in other karst regions with the same ecological background

estimation of in situ stresses using anisotropic elasticity and suction measurements sampling and specimen preparation produce changes in mean effective stresses and pore water pressures even with perfect sampling the paper takes an existing simplified three parameter cross anisotropic elastic model and uses it to model these changes the required ratio of cross anisotropic parameters j 3g can be obtained from standard ciu triaxial tests if measurements are also made of suctions in unloaded specimens in the laboratory then a combination of j 3g the measured suction and the effective overburden pressure permits an estimation of the horizontal effective pressure and the k0 at rest coefficient this can be helpful in numerical modelling that needs to start from in situ conditions and in planning pressure levels for reconsolidation of clay specimens in the laboratory tests were done on belfast upper boulder clay from a depth of 28 m values of horizontal in situ effective stress estimated from these measurements compare favorably with conventional estimates of the at rest coef

terra rossa genesis by replacement of limestone by kaolinite iii dynamic quantitative model abstractwe model quantitatively the chemical dynamics of terra rossa formation that we deduced earlier from new field and petrographic evidence the key phenomenon is that authigenic kaolinite a proxy for kaolinite solid solutions and other clays replaces limestone at a downward moving reaction front at the base of the existing terra rossa the chemical elements needed to make the authigenic clay are assumed to come from dissolution of eolian clay dust deposited at the surface the model consists of equations of mass conservation in one spatial dimension that incorporate infiltration diffusion and replacement and dissolution reactions distinctive elements of the model are that 1 the kinetics of the kaolinite for calcite replacement is dominated by the crystallization stress generated by the kaolinite growth in accordance with the view that replacement happens not by dissolution precipitation but by guest mineral growth driven pressure solution of the host 2 the field observation that the terr

magnitude and composition of sinking particulate phosphorus fluxes in santa barbara basin california examined particulate p cycling in the santa barbara basin sbb off the coast of southern california using a 520 m deep moored sediment trap deployed from 1993 2006 and a sediment core collected in 2005 directly beneath the sediment trap at 590 m total particulate p tpp particulate inorganic p pip and particulate organic p pop were quantified using a 5 step sequential extraction method sedex that chemically separates pip into loosely bound oxide bound authigenic and detrital p phases pop fluxes while similar in magnitude to other coastal regions 22 10 mmol m 2 d 1 were a small component of the tpp pool 15 seasonal trends revealed significant increases in pop fluxes during upwelling due to increased biological production in surface waters by organisms that increased mineral ballast high particulate organic carbon poc to pop ratios 337 18 further indicated rapid and efficient remineralization of pop relative to poc as particles sank through the oxic water column however further reduction of pop ceased in the deeper anoxic waters loosely bound oxide bound and authigenic p dominated the tpp pool with pip fluxes substantially higher than those measured in other coastal settings strong correlations between oxide associated authigenic and detrital p fluxes with lithogenic material indicated a terrestrial source associated with riverine discharge furthermore more than 30 of the loosely bound and oxide bound p was remineralized prior to burial with the magnitude of dissolution far exceeding that of pop these results highlight the dynamic nature of the particulate p pool in coastal ecosystems and how changes in p source can alter the composition and lability of p that enters coastal waters

phosphorus cycling in marine sediments advances and challenges abstract phosphorus p is a critical macronutrient for all living cells as it provides the phosphate ester backbone of nucleic acids plays a crucial role in the transmission of chemical energy by the atp molecule and is also a structural constituent in many cell components while p cycling in the marine water column has been the subject of many studies and reviews many aspects of the sedimentary p cycling remain poorly understood this is mainly due to low p concentrations in sediments and analytical difficulties associated with isolating distinct p forms from sediment samples the aim of this review is to highlight the advances made in our understanding of p cycling in marine sediments as a result of improved instrumentation and novel approaches some of these techniques range from sediment sequential extractions sedex to spectroscopic techniques 31p nmr and innovative isotope tracer experiments stable oxygen ratios in phosphate radioactive p isotopes while our understanding of p cycling has considerably improved numerous aspects of sedimentary p cycling including the fate of organic p in sediments as a function of redox conditions organic matter content and burial depth as well as turnover rates of different sedimentary p compounds remain poorly constrained the techniques presented in this review along with yet to be utilized innovative approaches used in soil and lacustrine sediment p research will play an important role in addressing these important questions and in furthering our understanding of this critical component of the p global biogeochemical cycle

phosphorus composition of sinking particles in the guaymas basin gulf of california phosphorus p composition and fluxes were measured in samples collected using a moored sediment trap located at 500 m in depth in the center of guaymas basin gulf of california from february 1991 through september 1997 p composition was measured using a sequential extraction technique that chemically separates the particulate inorganic p pip pool into exchangeable oxide bound authigenic and detrital phases pip comprised 69 6 15 of the total particulate p pool with significantly higher concentrations during the rainy summer strong relationships between authigenic and detrital p fluxes with lithogenic material r2 0 85 indicate that a significant component of pip is terrestrially derived and varies with large scale changes in regional climate particulate organic p pop fluxes were significantly higher during the winter as a result of stimulation of biological production during upwelling average particulate organic carbon poc pop ratios also varied seasonally with higher ratios in the summer 221 vs the winter 158 the fact that poc fluxes remained relatively constant throughout the year indicates that in winter fresher less degraded organic material was more effectively transported to depth strong correlations between pop and opal fluxes r2 5 0 63 further support a ballast mechanism whereby enhanced sinking rates reduce the time during which organic matter is subjected to water column degradation compared to trap concentrations pop is preferentially remineralized over pip in concert with an increase in the authigenic p pool this signifies rapid diagenetic transformations of sedimentary p between the sediment trap and underlying sediments

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

feedbacks between oceanic redox states and marine productivity a model perspective focused on benthic phosphorus cycling a new model for the marine cycles of particulate organic carbon poc oxygen nitrate and phosphorus has been developed and applied to explore the controls and constraints on marine productivity and nutrient inventories the coupled benthic pelagic model uses a new approach for the simulation of the reactive phosphorus turnover preac corresponding to the sum of organic p authigenic p and adsorbed phosphate in marine sediments the simulated poc preac burial ratio in shelf slope and rise and deep sea sediments increases under strongly reducing conditions in agreement with field observation the model runs revealed that the spread of anoxia in bottom waters may enhance the productivity of the global ocean by one order of magnitude if sufficient nitrate is provided by n2 fixation thus anoxic bottom waters promote eutrophic conditions and vice versa additional model runs showed that the productivity and nutrient inventory of the glacial ocean were probably enhanced due to the falling sea level marine regression induced a narrowing of the depositional areas on the continental shelves and thereby an increase in the fraction of poc exported to the deep ocean the accelerated poc delivery in turn decreased the oxygen contents of the deep water and thus favored the release of phosphate from deep sea and rise sediments enhanced recycling of phosphate at the seafloor promoted further poc export in a positive feedback loop

phosphorus imbalance in the global ocean the phosphorus budget of the pre human modern ocean is constrained applying the most recent estimates of the natural riverine eolian and ice rafted input fluxes the phosphorus burial in marine sediments and the hydrothermal removal of dissolved phosphate from the deep ocean this review of current flux estimates indicates that the phosphorus budget of the ocean is unbalanced since the accumulation of phosphorus in marine sediments and altered oceanic crust exceeds the continental input of particulate and dissolved phosphorus the phosphorus mass balance is further tested considering the dissolved phosphate distribution in the deep water column the marine export production of particulate organic matter rain rates of phosphorus to the seafloor benthic dissolved phosphate fluxes and the organic carbon to phosphorus ratios in marine particles these independent data confirm that the phosphate and phosphorus budgets were not at steadystate in the pre human global ocean the ocean is losing dissolved phosphate at a rate of 11 6 x 1010 mol yr 1 corresponding to a decline in the phosphate inventory of 4 5 kyr 1 benthic data show that phosphate is preferentially retained in pelagic deep sea sediments where extended oxygen exposure times favor the degradation of particulate organic matter and the up take of phosphate in manganese and iron oxides and hydroxides enhanced c p regeneration ratios observed in the deep water column 400 m water depth probably reflect the preferential burial of phosphorus in pelagic sediments excess phosphate is released from continental margin sediments deposited in low oxygen environments the dissolved oxygen threshold value for the enhanced release of dissolved phosphate is 20 m benthic phosphate fluxes increase drastically when oxygen concentrations fall below this value

tenth canadian geotechnical colloquium recent developments in consolidation of natural clays a global analysis of the consolidation of natural clays is realized considering the consolidation process to be a combination of the effects of compressibility and of permeability the compressibil

phosphorus burial and diagenesis in the central bering sea bowers ridge iodp site u1341 perspectives on the marine p cycle abstract to reconstruct the cycling of reactive phosphorus p in the bering sea a p speciation record covering the last 4 ma was generated from sediments recovered during integrated ocean drilling program iodp expedition 323 at site u1341 bowers ridge a chemical extraction procedure distinguishing between different operationally defined p fractions provides new insight into reactive p input burial and diagenetic transformations reactive p mass accumulation rates mars are 20 110 mol cm2 ka which is comparable to other open ocean locations but orders of magnitude lower than most upwelling settings we find that authigenic carbonate fluorapatite cfa and opal bound p are the dominant p fractions at site u1341 an overall increasing contribution of cfa to total p with sediment depth is consistent with a gradual sink switching from more labile p fractions fish remains fe oxides organic matter to stable authigenic cfa however the positive correlation of cfa with al content implies that a significant portion of the supposedly reactive cfa is non reactive detrital contamination by eolian and or riverine cfa in contrast to cfa opal bound p has rarely been studied in marine sediments we find for the first time that opal bound p directly correlates with excess silica contents this p fraction was apparently available to biosiliceous phytoplankton at the time of sediment deposition and is a long term sink for reactive p in the ocean despite the likelihood for diagenetic re mobilisation of this p at depth indicated by increasing ratios of excess silica to opal bound p average reactive p mars at site u1341 increase by 25 if opal bound p is accounted for but decrease by 25 if 50 of the extracted cfa fraction based on the lowest cfa value at site u1341 is assumed to be detrital combining our results with literature data we present a qualitative perspective of terrestrial cfa and opal bound p deposition in the modern ocean riverine cfa input has mostly been reported from continental shelves and margins draining p rich lithologies while eolian cfa input is found across wide ocean regions underlying the northern hemispheric dust belt opal bound p burial is important in the southern ocean north pacific and likely in upwelling areas shifts in detrital cfa and opal bound p deposition across ocean basins likely occurred over time responding to changing weathering patterns sea level and biogenic opal deposition

detection of undercover karst features by geophysics ert lascaux cave hill abstract the study of karst features under a detrital cover is difficult to obtain using punctual traditional tools this paper presents a 3d geostatistical modeling of ert electrical resistivity tomography data to describe undercover karst features a case study was carried out on the karstic site of the prehistoric decorated lascaux cave france geophysical measurements were used to define the limit between outcropping coniacian or santonian limestones southwest and clayey sands northeast with a main orientation of n140 a geometrical description of the scarp was also constructed pinnacles and notches were found under the clayey sand detrital formation by combining 3d ert with geomorphological and geological observations the geometry of the stratigraphic limit between the coniacian and santonian limestone could be determined this stratigraphic limit separates two domains one is a potential aquifer and acts as a feeder for the intermittent spring at the cave entrance while the other is less permeable resulting in a permeability contrast with the later rock type all these observations help define the geological cave environment and ensure better protection for the paintings

effective stress paths and yielding in soft clays below embankments current methods of predicting the response of soft clays to surface loading are often unsuccessful because the assumed constitutive relationships including effective stress path behaviour are incorrect in particular the transition from small strain to large strain behaviour i e yielding is frequently not taken into account recent laboratory testing has demonstrated that the behaviour of soft clays is largely controlled by yielding the locus of effective stress states causing yield is known as the yield envelope ye the effective stress paths esp s in soft clay foundations below the centre of six fills were determined from computed total stresses and measured pore water pressures yield behaviour is clearly indicated by esp shapes the yield envelopes inferred from analyses of field data are similar to those obtained from laboratory testing effective stress path shapes vary widely depending on a variety of factors including imposed stress level rate of construction and boundary drainage co