three dimensional representation of tubular horizons in sandy soils soil horizons are three dimensional bodies and this is widely recognised however many soil descriptions are still based on the soil profile and the move to three dimensional diagrams to represent horizons or other soil phenomena is just starting in the present study computer reconstruction and visualization techniques were used to illustrate the geometry of the illuvial bh horizon in a buried podzol the 3d computer representation revealed a complex of tubular forms with diameters varying from 10 to 25 cm and length around 100 cm similar tubular shapes are found in australian podzols

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

impact of drainage on soil forming mechanisms in a french albeluvisol input of mineralogical data in mass balance modelling research on soil pedogenesis has mainly focused on the long term soil formation and has most often neglected recent soil evolutions in response to human practices such recent soil evolutions are however of considerable interest to study the timing of soil forming processes in response to changes in environmental conditions in this paper we model the albeluvisol evolution in response to agricultural drainage this was considered as a model case to study the velocity of mineralogical changes in soil as a result of eluviation and redox processes we used a space for time substitution approach in combination with mass balance modelling based on mineralogical data in order to identify and characterise the mineralogical transformations responsible for the recent soil evolution in response to subsurface drainage this approach allowed demonstrating that the main effects of subsurface drainage are i increasing precipitation of mn oxides and mn rich ferrihydrite with decreasing distance to the drain as a result of the change in redox conditions and ii increasing loss of clay sized oxides and smectites due to the enhanced eluviation in the vicinity of the drain both processes induce significant matter fluxes in comparison with those that occurred over the long term soil formation nowadays the precipitation of mn oxides and mn rich ferrihydrite seems to still be active in the studied soil on the opposite the eluviation process appears less active than immediately after the drainage network installation if not totally inactive it thus demonstrates that some soil processes may have significant impact on the soil mineralogical composition even if they are only active over very short periods of time after a change in environmental conditions

a numerical comparison of 2d resistivity imaging with 10 electrode arrays numerical simulations are used to compare the resolution and efficiency of 2d resistivity imaging surveys for 10 electrode arrays the arrays analysed include polepole pp pole dipole pd half wenner hw wenner wn schlumberger sc dipole dipole dd wenner wb array gm multiple or moving gradient array gd and midpoint potential referred measurement mpr arrays five synthetic geological models simulating a buried channel a narrow conductive dike a narrow resistive dike dipping blocks and covered waste ponds were used to examine the surveying efficiency anomaly effects signal to noise ratios and the imaging capabilities of these arrays the responses to variations in the data density and noise sensitivities of these electrode configurations were also investigated using robust l1 norm inversion and smoothness constrained least squares l2 norm inversion for the five synthetic models the results show the following i gm and wn are less contaminated by noise than the other electrode arrays ii the relative anomaly effects for the different arrays vary with the geological models however the relatively high anomaly effects of pp gm and wb surveys do not always give a high resolution image pd dd and gd can yield better resolution images than gm pp wn and wb although they are more susceptible to noise contamination sc is also a strong candidate but is expected to give more edge effects iii the imaging quality of these arrays is relatively robust with respect to reductions in the data density of a multi electrode layout within the tested ranges iv the robust inversion generally gives better imaging results than the l2 norm inversion especially with noisy data except for the dipping block structure presented here v gd and mpr are well suited to multichannel surveying and gd may produce images that are comparable to those obtained with dd and pd accordingly the gd pd dd and sc arrays are strongly recommended for 2d resistivity imaging where the final choice will be determined by the expected geology the purpose of the survey and logistical considerations

decadal interactions between the western tropical pacific and the north atlantic oscillation the relationship between interdecadal variations of tropical sea surface temperature sst in the last 120 years and circulation anomalies related to the north atlantic oscillation nao is investigated in this study using an atmospheric general circulation model agcm we confirm observational evidence that variations in the sst gradient in the western tropical pacific are related to the nao anomalies on decadal timescale and may be contributing to the shift towards the positive nao phase observed in the late 20th century the role played by the indian ocean nao teleconnection advocated in recent studies focused on the last 50 years is also assessed in the context of the 120 year long record it is suggested that a positive feedback between the pacific sst and the hemispheric circulation pattern embedding the decadal nao signal may act to enhance the internal variability of the coupled ocean atmosphere system and justify the stronger teleconnection found in observational data than in sst forced agcm experiments

a 3d electrical resistivity tomography survey to characterise the structure of a albeluvic tonguing horizon composed of distinct elementary pedological volumes abstract water and gas transfer in porous media like soils are determined by their porous network described by their structure in soil the horizon is usually considered to be elementary and homogeneous functioning system in the description of gas and water functioning however in some cases a horizon is heterogeneous and its structure is defined by the 3d arrangement of elementary pedological volumes epvs the horizon needs to be described in three dimensions to improve the characterisation of the structure and consequently the prediction of its hydraulic functioning the aim of this study was to determine the feasibility of describing the 3d structure of a heterogeneous albeluvic tonguing soil horizon composed of a juxtaposition of silty white and clayey ochre epvs using 3d electrical resistivity tomography ert electrical measurements were compared with geostatistical analyses from soil photographs we demonstrated that the resistivity of the white epvs was greater than that of the ochre epvs in addition the general soil structure and organisation of the soil horizon could be derived from the electrical resistivity data we proposed a method to discretise the soil electrical resistivity into a binary system that corresponded to white and ochre volumes finally a 3d representation of the soil structure was created that could be used to improve soil hydraulic models

ocean heat transport sea ice and multiple climate states insights from energy balance models abstract several extensions of energy balance models ebms are explored in which i sea ice acts to insulate the atmosphere from the ocean and ii ocean heat transport is allowed to have some meridional structure controlled by the wind with minima at which the ice edge can rest these new models support multiple stable ice edges not found in the classical ebm and a hysteresis loop capable of generating abrupt warming as the ice edge jumps from mid to high latitudes the new equilibria are demonstrated in two classes of model in which the wind stress is either specified externally or generated interactively wind stress is computed by introducing a dynamical constraint into the ebm to represent the simultaneous meridional transport of energy and angular momentum in the atmosphere this wind stress is used to drive ocean gyres with associated structure in their meridional heat transport so that the atmosphere and ocean are coupled together both thermally and mechanically

co existing climate attractors in a coupled aquaplanet the first step in exploring the properties of dynamical systems like the earth climate is to identify the different phase space regions where the trajectories asymptotically evolve called attractors in a given system multiple attractors can co exist under the effect of the same forcing at the boundaries of their basins of attraction small changes produce large effects therefore they are key regions for understanding the system response to perturbations here we prove the existence of up to five attractors in a simplified climate system where the planet is entirely covered by the ocean aquaplanet these attractors range from a snowball to a hot state without sea ice and their exact number depends on the details of the coupled atmosphere ocean sea ice configuration we characterise each attractor by describing the associated climate feedbacks by using the principal component analysis and by measuring quantities borrowed from the study of dynamical systems namely instantaneous dimension and persistence

sr nd isotopic evidence of terrigenous flux variations in the bay of bengal implications of monsoons during the last 34 000 years 1 sr and nd isotopic compositions of a sediment core from the bay of bengal are used to constrain the provenance and transport pathways of their terrigenous component during the 3 to 34 14c kyr bp the results clearly demonstrate a distinctly different source for detrital fluxes on the ninetyeast ridge from that of distal and western fan sediments there is a systematic pattern of climate related variability in 87sr 86sr and nd o values at the studied location pulses of low 87sr 86sr higher radiogenic nd and high silt content occurring at 5 7 kyr intervals suggest significant changes in the detrital source increased supply of irrawaddy derived sediments appears to be the dominant source for these pulses our results support the hypothesis that rapid cold events of north atlantic heinrich events are characterized by the intensified northeast monsoon

arctic ice ocean simulation with optimized model parameters approach and assessment 1 we present an optimized 1992 2008 coupled ice ocean simulation of the arctic ocean a green s function approach adjusts a set of parameters for best model data agreement overall model data differences are reduced by 45 the optimized simulation reproduces the negative trends in ice extent in the satellite records volume and thickness distributions are comparable to those from the ice cloud and land elevation satellite 2003 2008 the upper cold halocline is consistent with observations in the western arctic the freshwater budget of the arctic ocean and volume heat transports of pacific and atlantic waters across major passages are comparable with observation based estimates we note that the optimized parameters depend on the selected atmospheric forcing the use of the 25 year japanese reanalysis results in sea ice albedos that are consistent with field observations simulated pacific water enters the bering strait and flows off the chukchi shelf along four distinct channels this water takes 5 10 years to exit the arctic ocean at the canadian arctic archipelago nares or fram straits atlantic water entering the fram strait flows eastward merges with the st ana trough inflow and splits into two branches at the southwest corner of the makarov basin one branch flows along lomonosov ridge back to fram strait the other enters the western arctic circulates cyclonically below the halocline and exits mainly through the nares and fram straits this work utilizes the record of available observations to obtain an arctic ocean simulation that is in agreement with observations both within and beyond the optimization period and that can be used for tracer and process studies

sr isotope evidence for sources of terrigenous sediment in the southeast atlantic ocean is there increased available fe for enhanced glacial productivity 1 sr isotope ratios of the terrigenous sediments from the cape basin southeast atlantic ocean exhibit a systematic pattern of climate related variability from the holocene through the last glacial period values are high during warm climate intervals marine isotope stages miss 1 and 3 and lower during full glacial periods miss 2 and 4 the variability is large 87sr 86sr 0 717 0 723 and the rapid changes correspond temporally to abrupt climate change during the mis 5a 4 and 2 1 transitions and through mis 3 the sr isotope variability corresponds to changes in 13c of benthic foraminifera at orbital frequencies and within periods of rapid variability prior studies have suggested that benthic 13c records from the cape basin follow greenland ice core variability and thus global overturning circulation other studies suggest that these benthic 13c records contain a strong overprint from isotopically light carbon possibly associated with high fluxes of organic matter to the seabed we explore the scenario that the relationship between lower terrigenous 87sr 86sr and lighter benthic 13c may reflect high productivity during cold climatic intervals as a result of iron fertilization of the southern atlantic ocean increased supply of iron during cold periods may be associated with greater terrigenous sediment fluxes from south america characterized by a less radiogenic sr isotopic signature

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

linking glacial interglacial states to multiple equilibria of climate glacial interglacial cycles are often described as an amplified global response of the climate to perturbations in solar radiation caused by oscillations of earth s orbit however it remains unclear whether internal feedbacks are large enough to account for the radically different glacial and interglacial states here we provide support for an alternative view glacial interglacial states are multiple equilibria of the climate system which exist for the same external forcing we show that such multiple equilibria resembling glacial and interglacial states can be found in a complex coupled general circulation model of the ocean atmosphere sea ice system the multiple states are sustained by ice albedo feedback modified by ocean heat transport and are not caused by the bi stability of the ocean s overturning circulation in addition expansion contraction of the southern hemisphere ice pack over regions of upwelling regulating outgassing of co 2 to the atmosphere is the primary mechanism behind a large pco 2 change between states

water movement in a glossaqualf as measured by two tracers abstract the relationships between soil organization and water movement were investigated in a glossaqualf this soil is characterized by a clear discontinuity between the tongues and the matrix in both material texture and mineralogy and structure porosity and pedality two tracer approaches have been used to evaluate water movement 1 methylene blue for studying the transfer in saturated conditions in the field and on undisturbed cores and 2 an environmental isotope oxygen 18 for studying the actual behaviour under natural conditions the different approaches show that tongues are preferential paths of water transfer the matrix is nearly short circuited under saturated conditions analogous results were obtained in the laboratory and under natural conditions these results are attributed to the shapes sizes distribution and overall continuity of the system of pores

the role of oceans and sea ice in abrupt transitions between multiple climate states the coupled climate dynamics underlying large rapid and potentially irreversible changes in ice cover are studied a global atmosphere ocean sea ice general circulation model with idealized aquaplanet geometry is forced by gradual multi millennial variations in solar luminosity the model traverses a hysteresis loop between warm ice free conditions and cold glacial conditions in response to 6 5wm 22 variations in global annual mean insolation comparison of several model configurations confirms the importance of polar ocean processes in setting the sensitivity and time scales of the transitions a sawtooth character is found with fasterwarmingandslowercooling reflectingtheopposingeffectsofsurfaceheatingandcoolingonupper ocean buoyancy and thus effective heat capacity the transition from a glacial to warm equable climate occurs in about 200 years in contrast to the freshwater hosing scenario transitions are driven by radiative forcing and sea ice feedbacks the ocean circulation and notably the meridional overturning circulation moc does not drive the climate change the moc and associated heat transport collapses poleward of the advancing ice edge but this is a purely passive response to cooling and ice expansion the moc does however play a key role in setting the time scales of the transition and contributes to the asymmetry between warming and cooling

stable waterbelt climates controlled by tropical ocean heat transport a nonlinear coupled climate mechanism of relevance to snowball earth ongoing controversy about neoproterozoic snowball earth events motivates a theoretical study of stability and hysteresis properties of very cold climates a coupled atmosphere ocean sea ice general circulation model gcm has four stable equilibria ranging from 0 to 100 ice cover including a waterbelt state with tropical sea ice all four states are found at present day insolation and greenhouse gas levels and with two idealized ocean basin configurations the waterbelt is stabilized against albedo feedback by intense but narrow wind driven ocean overturning cells that deliver roughly 100 w m 2 heating to the ice edges this requires three way feedback between winds ocean circulation and ice extent in which circulation is shifted equatorward following the baroclinicity at the ice margins the thermocline is much shallower and outcrops in the tropics sea ice is snow covered everywhere and has a minuscule seasonal cycle the waterbelt state spans a 46 w m 2 range in solar constant has a significant hysteresis and permits near freezing equatorial surface temperatures additional context is provided by a slab ocean gcm and a diffusive energy balance model both with prescribed ocean heat transport oht unlike the fully coupled model these support no more than one stable ice margin the position of which is slaved to regions of rapid poleward decrease in oht convergence wide ranges of different climates including the stable waterbelt are found by varying the magnitude and spatial structure of oht in both models some thermodynamic arguments for the sensitivity of climate and ice extent to oht are presented

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

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

snowball versus slushball earth dynamic versus nondynamic sea ice 1 modeling studies of the neoproterozoic snowball earth offer two variations for snowball conditions the original hard snowball earth where the ocean is completely covered by sea ice and an alternate slushball earth or soft snowball where there is an equatorial oasis of open water we use the university of victoria earth system climate model to show that the soft snowball result is only possible when dynamics are excluded from the sea ice component of the model using a purely thermodynamic sea ice component the soft snowball condition is stable whereas with a dynamic and thermodynamic sea ice component it is not as the behavior of dynamic sea ice largely depends on wind stress we compare simulations using two different wind fields a zonally averaged present day wind field and a wind field derived by a general circulation model the fast ocean atmosphere model using neoproterozoic conditions another consequence of using dynamic sea ice is that the sea ice does not become sufficiently thick to flow under its own weight when there is open water this suggests that sea glacier dynamics are not important for snowball inception

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

high sampling rate measurement and data treatment for mobile investigations kinematic electrical resistivity tomography kert abstract this paper presents an innovative system which adapts electrical resistivity tomography ert for fast investigation on long transects the device consists in a set of on the go sensors allowing high sampling rate measurement for mobile prospections the weak contact between the mobile sensors and the soil to allow fast investigations induces very noisy raw datasets kinematic electrical resistivity tomography named kert is then associated with a data treatment process a two step process reveals the information contained in the datasets the first focuses on the procedure to remove noise through the use of a low pass filter the assessment of cutoff frequency for smoothing is deduced from a fast fourier transform fft analysis thus the value is adapted to the site and the prospection the second phase consists in calibration of the kert on a conventional static ert at this point a classical static ert was used as a reference and directed on a reduced part of the kert transect the estimation of a factor of calibration xc to correct bias revealed the resistivity variations along the entire transect and in depth in the last part of the paper the validation of the investigation method and data treatment methodology is performed on a real case study a 450 m transect is investigated in 5 min mean speed about 6 km h integrating 10 depths of investigation the steps of data processing are detailed to show the final results consisting in a zonation along the transect

influence of rock fragments on the water retention and water percolation in a calcareous soil abstract the water retention properties of a calcareous soil containing rock fragments have been determined in the laboratory thanks to pressure plate measurements done on both the fine earth and the rock fragments from the soil the available water content awc has been calculated from these data we have shown that when the rock fragments are neglected the awc can be overestimated by 39 when we do not neglect their volume but when their hydraulic properties are not considered the awc can be underestimated by 34 by using a reservoir model we have also calculated the effect of rock fragments on water percolation to groundwater depending of the climatic characteristics of the year the underestimation of percolation when we neglect the rock fragments can reach up to 14 9 and the overestimation when we neglect their hydraulic properties can be equal to 15 8 these findings emphasise the role of the rock fragments on the water supply in stony soils