iron snow in the martian core abstract the decline of mars global magnetic field some 3 8 4 1 billion years ago is thought to reflect the demise of the dynamo that operated in its liquid core the dynamo was probably powered by planetary cooling and so its termination is intimately tied to the thermochemical evolution and present day physical state of the martian core bottom up growth of a solid inner core the crystallization regime for earth s core has been found to produce a long lived dynamo leading to the suggestion that the martian core remains entirely liquid to this day motivated by the experimentally determined increase in the fe s liquidus temperature with decreasing pressure at martian core conditions we investigate whether mars core could crystallize from the top down we focus on the iron snow regime where newly formed solid consists of pure fe and is therefore heavier than the liquid we derive global energy and entropy equations that describe the long timescale thermal and magnetic history of the core from a general theory for two phase two component liquid mixtures assuming that the snow zone is in phase equilibrium and that all solid falls out of the layer and remelts at each timestep formation of snow zones occurs for a wide range of interior and thermal properties and depends critically on the initial sulfur concentration 0 release of gravitational energy and latent heat during growth of the snow zone do not generate sufficient entropy to restart the dynamo unless the snow zone occupies at least 400 km of the core snow zones can be 1 5 2 gyrs old though thermal stratification of the uppermost core not included in our model likely delays onset models that match the available magnetic and geodetic constraints have 0 10 and snow zones that occupy approximately the top 100 km of the present day martian core

environmental changes during the holocene climatic optimum in central europe human impact and natural causes abstract the priority programme changes of the geo biosphere aimed to reconstruct the environmental history of central europe with emphasis on the time interval from 9000 to 5500 cal bp time slice ii coinciding with the holocene climatic optimum during this period the onset of human activities such as settlement agriculture and animal husbandry caused environmental changes studies of different landscape units in germany were carried out to identify these anthropogenically induced changes and to distinguish them from natural effects on the environmental system the investigated archives included laminated lake sediments fluvial sediments colluvia and soils speleothems peat and coastal sediments the different archives were examined using refined research methods including a variety of sedimentary and geochemical analyses together with pollen analysis and dating methods for the establishment of a reliable chronology the results of the various research groups are summarised and critically discussed based on these results the climatic optimum can be subdivided into three periods 1 the early atlantic from 9000 to 7500 cal bp with negligible human impact and stable environmental conditions 2 the late atlantic during early and middle neolithic from 7500 to 6300 cal bp with pollen evidence for vegetation changes but only negligible changes detectable in other proxy records and 3 the late atlantic during the younger neolithic jungneolithikum after 6300 cal bp with human impact observed in many archives and proxy records especially in the pollen record but also in lacustrine and fluvial sediments during the whole climatic optimum natural causes such as minor shifts of temperature did not induce substantial environmental changes though some changes such as temporary droughts may have facilitated and amplified the observed human impact

integrated two dimensional lithospheric conductivity modelling in the pyrenees using field scale and laboratory measurements abstract recent magnetotelluric mt studies have shown that the lower crust in the pyrenees contains a high conductivity zone consistent with a subducting continental slab whose conductivity is 0 33 s m partial melting has been interpreted to be the most plausible explanation for this high conductivity here we report a two dimensional conductivity model of the lithosphere by integrating field scale and laboratory determinations of the conductivity of continental crustal and mantle rocks the laboratory data provide empirical formulas which allow us to determine the fluid saturated rock and melt conductivity when temperature pressure and lithology are known consequently we have also calculated the density lithostatic pressure and several alternative temperature profiles for use in the model from gravity seismic and thermal field data these can be used with a prescribed melt fraction to predict the electrical conductivity at depth which can be compared with the mt conductivity data alternatively the laboratory data can be combined with the mt conductivity data to predict the melt fraction at depth the primary outputs of the modelling are conductivity and melt fraction prediction profiles for six mixing models i waff s model hashin shtrikman hs upper bound ii hs lower bound iii parallel layers iv perpendicular layers v random melt areas and vi a modified archie s law that takes account of the presence of two conducting phases the modelling results indicate that a good match to the mt data can be obtained along the whole profile by the influence of pressure temperature and the fluid phase with the only exception being the subducted slab where a minimum of 4 7 melt fraction is necessary to explain the data

are mid latitude slopes sensitive to climatic oscillations implications from an early holocene sequence of slope deposits and buried soils from eastern germany abstract on a straight slope within the lake catchment of kleiner tornowsee brandenburg germany a sequence of slope sediments has been deposited during the late glacial the early holocene and around cal 4 2 ka before today 800 500 and 300 years ago the chronology is based on 21 radiocarbon dates and 11 osl dates and a deposition model including the numerical data as well as stratigraphic information has been calculated with oxcal 4 1 a comparison of the woody taxa of charcoal particles n 566 embedded within the sediments with the known regional vegetation history confirmed the reliability of the dates according to the age volume and distribution the deposition of the early holocene sediments at ca 10 3 kyrs ca 9 5 kyrs and ca 8 2 to 7 7 kyrs before today strongly suggests an influence of known climatic deteriorations phases on geomorphologic processes cold and dry climatic conditions probably promoted wildfires in pinus dominated forests and therefore triggered the observed repeated slope instability in consequence mid latitude slope deposits provide a potential to reconstruct the geomorphological response to climatic events at a high spatial resolution in contrast the recorded mid to late holocene soil erosion phases on the slope have been triggered by land use activities apart from traditional environmental archives slope deposits provide valuable information about the vegetation and climate history

electrical resistivity of solid and liquid pt insight into electrical resistivity of e fe abstract knowledge of the transport properties of fe and its alloys at extreme pressure p and temperature t conditions are essential for understanding the generation and sustainability of the magnetic field of the rocky planets with a metallic core since pt an unfilled d band late transition metal with an electronic structure of xe 4 f 14 5 d 9 6 s 1 is paramagnetic and close packed structure at ambient and high p t conditions it is expected that its transport properties at these conditions would be similar to those of e fe we investigated the t dependent electrical resistivity of solid and liquid pt up to 8 gpa and found it constant along its melting curve on the liquid side in agreement with theoretical investigations and experimental results estimated from thermal conductivity measurements our results suggest that the t dependent resistivity of e fe could be linear and would not saturate at high p t conditions this in turn suggests that the thermal conductivity of liquid fe at earth s core conditions may not be as high as previously suggested by models employing saturation resistivity hence thermal convection could have powered the geodynamo before the birth of the inner core the electrical resistivity and thermal conductivity on the liquid and solid sides of the inner core boundary of the earth could be different in values

influence of sulfur on the electrical resistivity of a crystallizing core in small terrestrial bodies abstract electrical experiments were performed on core analogues in the fe s system and on fesi2 up to 8 gpa and 1850 c in the multi anvil apparatus electrical resistivity was measured using the four electrode method for all samples resistivity increases with increasing temperature the higher the s content the higher the resistivity and the resistivity increase upon melting at 4 5 gpa liquid fes is up to 10 times more resistive than fe 5 wt s and twice more resistive than fesi2 suggesting a stronger influence of s than si on liquid resistivity electrical results are used to develop crystallization resistivity paths considering both equilibrium and fractional crystallization in the fe s system at 4 5 gpa equilibrium crystallization as expected locally in thin snow zones during top down core crystallization presents electrical resistivity variations from about 300 to 190 microhm cm for a core analogue made of fe 5 wt s depending on temperature fractional crystallization which is relevant to core scale cooling leads to more important electrical resistivity variations depending on s distribution across the core temperature and pressure estimates of the lower bound of thermal resistivity are calculated using the wiedemann franz law comparison with previous works indicates that the thermal conductivity of a metallic core in small terrestrial bodies is more sensitive to the abundance of alloying agents than that of the earth s core application to ganymede using core adiabat estimates from previous studies suggests important thermal resistivity variations with depth during cooling with a lower bound value at the top of the core that can be as low as 3 w m k it is speculated that the generation and sustainability of a magnetic field in small terrestrial bodies might be favored in light element depleted cores

electrical investigation of metal olivine systems and application to the deep interior of mercury we report electrical conductivity measurements on metal olivine systems at about 5 and 6 gpa and up to 1 675 c in order to investigate the electrical properties of core mantle boundary cmb systems electrical experiments were conducted in the multianvil apparatus using the impedance spectroscopy technique the samples are composed of one metal layer fe fes fesi2 or fe ni s si and one polycrystalline olivine layer with the metal olivine ratio ranging from 1 0 7 to 1 9 2 for all samples we observe that the bulk electrical conductivity increases with temperature from 10 2 5 to 101 8 s m which is higher than the conductivity of polycrystalline olivine but lower than the conductivity of the pure metal phase at similar conditions in some experiments a conductivity jump is observed at the temperature corresponding to the melting temperature of the metallic phase both the metal olivine ratio and the metal phase geometry control the electrical conductivity of the two layer samples by combining electrical results textural analyses of the samples and previous studies of the structure and composition of mercury s interior we propose an electrical profile of the deep interior of the planet that accounts for a layered cmb outer core structure the electrical model agrees with existing conductivity estimates of mercury s lower mantle and cmb using magnetic observations and thermodynamic calculations and thus supports the hypothesis of a layered cmb outermost core structure in the present day interior of mercury we propose that the layered cmb outer core structure is possibly electrically insulating which may influence the planet s structure and cooling history

mercury s thermal evolution controlled by an insulating liquid outermost core abstract the weak intrinsic magnetic field of mercury is intimately tied to the structure and cooling history of its metallic core recent constraints about the planet s internal structure suggest the presence of a fes layer overlying a silicon bearing core we performed 4 electrode resistivity experiments on core analogues up to 10 gpa and over wide temperature ranges in order to investigate the insulating properties of core materials our results show that the fes layer is liquid and insulating and that the electrical resistivity of a miscible fe si s core is comparable to the one of an immiscible fe s fe si core the difference in electrical resistivity between the fes rich layer and the underlying fe si s core is at least 1 log unit at pressure and temperature conditions relevant to mercury s interior estimates of the lower bound of thermal conductivity for fes and fe si s materials are calculated using the wiedemann franz law a thick 40 km fes rich shell is expected to maintain high temperatures across the core and if temperature in this layer departs from an adiabat then this might affect the core cooling rate the presence of a liquid and insulating shell is not inconsistent with a thermally stratified core in mercury and is likely to impact the generation and sustainability of a magnetic field

impact of local morphology on sedimentation in a submarine canyon rov studies in eel canyon northern california u s a abstract despite existing paradigms about marine sedimentation some submarine canyons are receiving large amounts of sediment during the present highstand of sea level these modern examples can be used to unlock secrets of past canyon sedimentation however submarine canyons have complex morphology and consequently dramatic variations in sedimentary processes and deposits can occur over a range of spatial scales as small as meters to tens of meters operations from surface ships usually cannot place sampling devices on the canyon seabed with this level of accuracy the purpose of the present study was to investigate the variability of sedimentation over a range of scales in order to delineate accurate trends along and among channels at the head of a canyon sampling with the rov ventana facilitated detailed examination of microenvironments i e wall thalweg in eel submarine canyon the combination of intense sedimentation from nepheloid layers and gravity flows in a complicated morphologic system leads to clear distinctions between microenvironments as well as some recognizable and unifying trends in sedimentation inherent small scale variability due to canyon morphology is evident in narrow and steep channels at 1 m horizontal resolution cores exhibit consistent sediment fabric but laminae can differ between cores at the 10 m horizontal scale the fabric is not consistent broader more gently sloping channels reveal consistent sediment fabric at the 10 m scale in most cases physical stratification decreases along the thalwegs of channels as water depths increase in contrast channel walls generally exhibit elevated impacts of bioturbation and variable amounts of physical stratification radiochemical profiles 210pb 137cs and the predominance of physical stratification including discrete laminae with high sand content suggest that the northern entrants are receiving more sediment than their southern counterparts however 210pb profiles in this study demonstrate rapid accumulation of sediment everywhere in the head of eel canyon with the highest rates of accumulation 40 mm yr found in the channel thalwegs in thalwegs evidence from sedimentary structures e g erosional bases cross bedded sand layers demonstrates that gravity flows occur frequently many times each year and have been linked by other investigations to storm impacts on the adjacent continental shelf on decadal timescales these processes are temporarily depositing sediment in the head of the canyon which is removed over longer timescales probably as larger gravity flows triggered by earthquakes the radiochemical and sedimentological data collected at the base of entrant channels confirm that modern sediment is moving to deeper portions of the canyon

stratification of the top of the core due to chemical interactions with the mantle 1 chemical interactions between the core and the mantle have been proposed as a mechanism to transfer o and si to the core adding light elements to the top of the core creates a stratified layer which grows by chemical diffusion into the underlying convecting region we develop a physical model to describe the evolution of the layer and estimate physical properties to aid in its detection the interface between the stratified layer and the convecting interior is defined by the onset of double diffusive instabilities oscillatory instabilities arise from the interplay of a stable compositional stratification and an unstable thermal stratification due to a superadiabatic heat flow at the core mantle boundary double diffusive convection in the region of neutral stratification establishes the base of the layer and sets the rate of entrainment of excess light element into the interior of the core growth of the layer by diffusion is interrupted by nucleation of the inner core which segregates light elements into the convecting part of the core for calculations using o as the sole light element we find that the base of the stratified layer retreats toward the core mantle boundary as the radius of the inner core increases representative but uncertain model parameters yield a present day layer thickness of 60 to 70 km we also calculate the anomaly in p wave velocity relative to the value for a well mixed core the velocity anomaly decreases almost linearly across the layer with a peak value of 2 at the core mantle boundary this anomaly should be large enough to detect in seismic observations although the sign of the anomaly is opposite to estimates obtained in previous seismic studies we suggest possible explanations for this discrepancy and speculate about the implications for the structure of the earth s interior

vertic properties and gilgai related subsurface features in soils of south western poland abstract more than 650 subsurface concave structures 1 20 m long 0 5 7 m wide and 0 1 0 9 m deep were described in soils developed of clays overlain by loess in a large scale archeological excavation in sw poland the structures are considered to be microlows and microhighs similar to those in gilgaied vertisols which have never been reported in central europe until now soils do not have a clayey texture throughout the profile however the thick and humus rich mollic horizons as well as a clay enriched argic layers developed directly above vertic horizons have favored soil cracking and shrink swell phenomena in the clayey subsoil as a result well developed wedge shaped lenticular aggregates have formed in the clayey subsoil aggregates have grooved surfaces with an oriented matrix slickensides and are ordered under variable angles from 10 to 60 a periglacial origin of these structures has been rejected and the mid to late holocene period since the neolithic epoch has been considered to be favorable for intense shrink swell phenomena vertic horizon development and clayey mass cycling responsible for the subsurface bowl and chimney structure development a micro mosaic of soil units related to these structures has been distinguished including non or deep vertic stagnic chernozems phaeozems above the microlow centers mollic planosols vertic above the microslopes and mollic planosols protovertic over the microhighs chimneys it is concluded that a temperate climate as in central europe allows the formation of vertic properties and subsurface mass reorganization similar to those in soils with gilgai microrelief if specific conditions clayey substratum position in landscape soil moisture regime and the land use connected with vegetation type support deep seasonal changes of soil moisture and shrink swell phenomena in the subsoil

properties and formation of black soils on the island of poel ne germany abstract recent soil mapping on the island of poel situated in the southern baltic sea shows an abundance of black soils developed in stratified parent material whereby the upper layers are of periglacial origin covering calcareous till the black soils have been formed in the upper layer overlying luvisols developed in decalcified till with different degrees of stagnic influence the luvisols are not the result of a degradation of the black soil as no humic clay coatings were detected in their bt horizons with a simplified ap ah eb ah 2 e 2bt g b c horizon sequence these soils differ from the better known degraded phaeozems on fehmarn and the uckermark region the properties of three pedons are presented and their pedogenesis is discussed ams 14c ages from soil organic carbon of the ah horizons from the black soils suggest that the development of the luvisols stopped within the first half of the subatlantic period

effect of hydrogen on the melting temperature of fes at high pressure implications for the core of ganymede abstract we have carried out in situ x ray diffraction experiments on the fes h system up to 16 5 gpa and 1723 k using a kawai type multianvil high pressure apparatus employing synchrotron x ray radiation hydrogen was supplied to fes from the thermal decomposition of lialh 4 and fesh x was formed at high pressures and temperatures the melting temperature and phase relationships of fesh x were determined based on in situ powder x ray diffraction data the melting temperature of fesh x was reduced by 150 250 k comparing with that of pure fes the hydrogen concentration in fesh x was determined to be x 0 2 0 4 just before melting occurred between 3 0 and 16 5 gpa it is considered that sulfur is the major light element in the core of ganymede one of the galilean satellites of jupiter although the interior of ganymede is differentiated today the silicate rock and the iron alloy mixed with h 2 o and the iron alloy could react with h 2 o as ice or water or the hydrous silicate before the differentiation occurred in an early period resulting in a formation of iron hydride therefore ganymede s core may be composed of an fe s h system according to our results hydrogen dissolved in ganymede s core lowers the melting temperature of the core composition and so today the core could have solid fesh x inner core and liquid feh x fesh x outer core and the present core temperature is considered to be relatively low

phase relations in the fe fesi system at high pressures and temperatures the earth s core is comprised mostly of iron and nickel but it also contains several weight percent of one or more unknown light elements which may include silicon therefore it is important to understand the high pressure high temperature properties and behavior of alloys in the fe fesi system such as their phase diagrams we determined melting temperatures and subsolidus phase relations of fe 9 wt si and stoichiometric fesi using synchrotron x ray diffraction at high pressures and temperatures up to 200 gpa and 145 gpa respectively combining this data with that of previous studies we generated phase diagrams in pressure temperature temperature composition and pressure composition space we find the b2 crystal structure in fe 9si where previous studies reported the less ordered bcc structure and a shallower slope for the hcp b2 to fcc b2 boundary than previously reported in stoichiometric fesi we report a wide b2 b20 two phase field with complete conversion to the b2 structure at 42 gpa the minimum temperature of an fe si outer core is 4380 k based on the eutectic melting point of fe 9si and silicon is shown to be less efficient at depressing the melting point of iron at core conditions than oxygen or sulfur at the highest pressures reached onlymore the hcp and b2 structures are seen in the fe fesi system we predict that alloys containing more than 4 8 wt silicon will convert to an hcp b2 mixture and later to the hcp structure with increasing pressure and that an iron silicon alloy in the earth s inner core would most likely be a mixture of hcp and b2 phases less

in situ measurements of velocity structure within turbidity currents 1 turbidity currents are thought to be the main mechanism to move 500 000 m3 of sediments annually from the head of the monterey submarine canyon to the deep sea fan indirect evidence has shown frequent occurrences of such turbidity currents in the canyon but the dynamic properties of the turbidity currents such as maximum speed duration and dimensions are still unknown here we present the first ever in situ measurements of velocity profiles of four turbidity currents whose maximum along canyon velocity reached 190 cm s two turbidity currents coincided with storms that produced the highest swells and the biggest stream flows during the year long deployment

landscape related transformation and differentiation of chernozems catenary approach in the silesian lowland sw poland abstract the unfavourable environmental conditions to chernozem development in central europe has led to questions regarding their origin and age and conditions necessary for chernozem persistence in central europe under a humid climate this paper deals with chernozem transformation during the holocene period in sw poland in relation to land morphology the study was based on a catenary approach with additional remarks on parent material homogeneity and soil classification based on textural and geochemical indices the homogeneity of aeolian material loess was proven in the main part of the catena which confirmed that the differentiation of dry and wet chernozemic soil across the catena did not result from the variability of parent material no differences in morphological or physicochemical characteristics of mollic horizons were identified between the well drained and wet sections of the catena the strong redoximorphic features manifested as stagnic or gleyic properties in the lowermost part of catena are therefore secondary features i e developed after the mollic horizon development presumably in late holocene period chernozems with chernic horizon weakly developed subsurface argic horizon and free of redoximorphic features prevail in the central well drained and not eroded section of the catena it has been hypothesized that the loess soils in the uppermost more inclined part of the catena have been truncated by erosion during the first agricultural period then afforested and transformed into luvisols probably due to temporary abandonment of those sites less favourable for farming the soils in the transitional zone received the colluvial addition of humus material from the eroded hill summit however the colour of the humus layer has a chroma too high for a chernic horizon that surprisingly shifted these soils to the kastanozems group this study showed that the direction of transformation of native chernozems in the holocene period was strongly related to their position in the landscape which affected the erosion accumulation intensity and water drainage conditions soil moisture regime as a final result of these transformations a relief related zonality of soils has developed with stagnic gleyic chernozems luvic chernozems colluvial kastanozems haplic luvisols in the lower moist middle well drained and upper colluvial eroded sections of the undulating loess plain respectively

buried a horizons in old bench terraces in les garrigues catalonia abstract a large part of les garrigues western catalonia is occupied by stone terraces locally known as bancals that were built up in the 18th century some soil surveys of the area noted the presence of buried thick a horizons with a well developed crumb structure and darker colour than the present day a horizons the objective of this study was to determine the conditions of the soil cover both at the time of the formation of these buried soils and at the onset of terracing the climate is semi arid and the landscape is defined by platforms and flat bottomed valleys four profiles were described from both slope and valley floor terraces and sampled for analyses a buried ahb horizon appears at various depths between 40 and 180 cm with thicknesses ranging from 35 to 160 cm probably due to earthworks since this depends on the position of the profile within the terrace many of these buried soils would correspond to phaeozems they are identified by an ahb having low values and chromas usually 4 or less a structure due to faunal activity 100 of the structural forms related to fauna either in the form of empty or infilled channels vermic qualifier and an organic matter content that is 1 7 3 3 which is higher but not significantly different than the som content of the present day topsoils p olsen is 1 6 ppm the present soils are non saline and highly calcareous 40 they show some calcium carbonate redistribution in the form of pseudomycelia and biogenic calcite charcoal is present in some of these buried horizons together with small ceramic fragments these buried horizons have several common micromorphological features a spongy highly porous structure due to high faunal activity frequent silt cappings charcoal fragments and biogenic carbonates queras in some cases the biogenic calcite has undergone dissolution and reprecipitated as micrite pollen assemblages of the buried horizons reveal a large forest cover mainly of oaks and pines which is also corroborated by the occurrence of quercus phytoliths but the presence of pollen of some deciduous crops such as cereals vitis vinifera and olea europaea at the top of the sequences points to a upper holocene origin of these soils the results from the charcoal study support the presence of perennial quercus and pines as well as shrubs in the period when the terraces were built the available information about present day similar soils indicates that the formation of these horizons took place under a moister milder climate in the past compared with the present one in the study area

environmental impact of the laacher see eruption at a large distance from the volcano integrated palaeoecological studies from vorpommern ne germany abstract in order to investigate the environmental impacts of the laacher see eruption 12 900 calendar years b p and the deposition of the laacher see tephra at a large distance from the volcano fine resolution micromorphological diatomological and palynological investigations were carried out on closely spaced areas in the reinberg basin vorpommern ne germany the lower part of the lst originates from atmospheric input whereas the upper part was washed in from the surrounding basin slopes diatom populations expanded as a consequence of the input of silica while simultaneously dissolution of dead diatoms decreased the tephra provided a favourable habitat for many epilithic and epipelic diatom taxa the diatoms show a slight acidification and an increase in specific conductivity of the water whereas no eutrophication is indicated these effects disappeared after lake sediments covered the tephra the pollen diagrams from the reinberg basin as well as many other pollen diagrams from ne germany indicate that the vegetation reacted to rising temperatures after the cooler gerzensee fluctuation to a short lived water level rise connected with higher precipitation after the volcanic eruption and to minor openings in the forest vegetation due to increased fire probably connected with severe thunderstorms

accumulation of modern sediment in quinault submarine canyon abstract twenty box cores have been studied from quinault submarine canyon a major pathway between the washington continental shelf and the deep sea for silt and clay originating from the columbia river sediment accumulation rates on a 100 yr time scale are calculated from profiles of excess 210pb and of 137cs accumulation rates decrease with increasing distance downcanyon from 14 10 2 g cm 2 yr 1 in the upper canyon lower head to 3 10 2 g cm 2 yr 1 in the lower canyon in the upper canyon lower head channel floor areas have a higher mean accumulation rate 12 10 2 g cm 2 yr 1 than channel wall areas 5 10 2 g cm 2 yr 1 the difference in accumulation rate between channel floor and channel wall areas indicates preferential accumulation i e focusing in topographic lows the decrease in accumulation rate from high rates in the channel floors of the upper canyon to low rates in the lower canyon may be caused by progressive depletion of a nepheloid layer source and or may be an artifact of sediment focusing in the upper canyon the silty clay and clayey silt accumulating in the canyon show no significant trend in grain size or clay mineralogy with depth in cores or with distance downcanyon the lack of sorting probably results from the transport of sediment in aggregate form with a nearly random distribution of size and mineralogy within aggregates quinault canyon is accumulating approximately 5 5 10 5 mt of sediment yr 1 the lithogenic component 64 accounts for 1 4 of the columbia river discharge similarity of sediment trap deposition rates including storm events and 210pb accumulation rates indicates that the vertical flux is a major input of sediment to quinault canyon and that storms are important in the accumulation of sediment on a 100 yr time scale

storm induced sediment gravity flows at the head of the eel submarine canyon northern california margin 1 as part of the strataform program a bottom boundary layer bbl tripod was deployed at 120 m depth in the northern thalweg of the eel canyon during winter 2000 increases of the near bottom suspended sediment concentrations ssc recorded at the canyon head were not directly related to the eel river discharge but were clearly linked to the occurrence of storms bbl measurements revealed that during intensifications of the wave orbital velocity sediment transport at the head of the canyon occurred as sediment gravity flows directed down canyon observational evidence for near bed sediment gravity flow transport included an increase toward the bed of the down canyon component of wave averaged velocity and high estimated ssc at higher sampling frequencies 1 hz the current components during these events fluctuated at the same periodicity as the pressure reflecting a clear influence of the surface wave activity on the generation and maintenance of the sediment gravity flows the origin of such flows is not related to the formation of fluid muds on the shelf or to intense wave current sediment resuspension around the canyon head region rather liquefaction of sediment deposited at the head of the canyon induced by wave load excess pore water pressures during storms combined with elevated slopes around the canyon head appear to be the mechanisms initiating sediment transport the resulting fluidized sediment layer can easily be eroded entrained into the water column and transported down canyon as a sediment gravity flow results from this study reveal that storm induced sediment gravity flows occur periodically in the eel canyon head and suggest that this kind of sediment transport process can occur in other submarine canyons more frequently than previously expected

prehistoric alteration of soil in the lower rhine basin northwest germany archaeological 14c and geochemical evidence in early holocene chernozems were assumed to have covered the entire loess landscape of the lower rhine basin today mirrored by the distribution of luvic phaeozems these luvic phaeozems have characteristic dark brown bht horizons accumulating clay and humus inherited and translocated from their precursors chernozem black humic a horizons we examined luvic phaeozems along a 33 km long and 2 0 2 5 m deep gas pipeline trench in the lower rhine basin west of cologne along this transect we discovered clusters of hundreds of regularly shaped pits these pits were always connected to the bht horizons of adjacent luvic phaeozems the luvic phaeozem horizons and the pits were investigated by combining methods from geo archaeology geographical distribution within the landscape shape of the pits soil texture geochemistry content of carbon nitrogen and black carbon palaeobotany species determination of charcoals and ams 14 c measurements we found that the luvic phaeozems occurred not only in the loess covered landscape but also in the sandy holocene floodplain and their distribution could not be limited to certain slope positions or parent material carbon and nitrogen concentrations in the luvic phaeozem horizons and pits were larger than in the surrounding luvisols whereas the c n ratios were small 10 material found in the luvic phaeozem pits was clearly different from material found in prehistoric settlements the pits investigated here never contained artifacts and carbon and nitrogen concentrations and c n ratios were smaller we found charcoal particles and black carbon contributed up to 46 of the total organic carbon the ams 14 c ages of charcoals and black carbon indicated that fire occurred from mesolithic 9500 5500 bc to the medieval ages 500 1500 ad and mainly in the late end neolithic period 4400 2200 bc we conclude that i the luvic phaeozem pits and horizons are man made formed during several archaeological epochs between mesolithic and middle ages ii these pits must have been formed outside the actual prehistoric settlements offsite and may serve as a novel archaeological feature iii the purpose of these pits at present is not clear and iv human activity has altered and ultimately formed the investigated soils of the lower rhine basin in prehistoric time

the high conductivity of iron and thermal evolution of the earth s core abstract we measured the electrical resistivity of iron and iron silicon alloy to 100 gpa the resistivity of iron was also calculated to core pressures combined with the first geophysical model accounting for saturation resistivity of core metal the present results show that the thermal conductivity of the outermost core is greater than 90 w m k these values are significantly higher than conventional estimates implying rapid secular core cooling an inner core younger than 1 ga and ubiquitous melting of the lowermost mantle during the early earth an enhanced conductivity with depth suppresses convection in the deep core such that its center may have been stably stratified prior to the onset of inner core crystallization a present heat flow in excess of 10 tw is likely required to explain the observed dynamo characteristics

a review of the history of the baltic sea 13 0 8 0 ka bp abstract the dynamic history of the baltic sea during the millennia following the last deglaciation has been one of the main topics for many generations of quaternary geologists around the baltic sea based on the present state of knowledge and certain hypotheses a model for the development during the baltic ice lake yoldia sea and ancylus lake stages are presented the oresund strait was the threshold of the initial stage of the baltic ice lake and was eroded down to bedrock as a result of the isostatic uplift the emerging threshold forced the baltic ice lake to rise above sea level at ca 12 0 ka bp this gradual up damming ended at ca 11 2 ka bp when the large glacial lake was lowered 5 10m by possible subglacial drainage at mt billingen a glacial readvance during the younger dryas ended a ca 400 year long land bridge between sweden and the continent by blocking the former drainage route once again the baltic ice lake had to rise above sea level to be drained over the oresund strait at ca 10 5 ka bp a gradual ice recession began and 200 years later when the receding ice sheet could not withhold the up dammed water masses the final drainage of the baltic ice lake occurred which rapidly lowered the water level within the baltic basin with ca 25 m and ended the baltic ice lake stage the next stage the yoldia sea was characterized by a complex pattern of relative sea level changes with large differences within the baltic basin a very restricted baltic sea in the south and thus an extensive landbridge at ca 9 9 ka bp a short 100 200 years saline ingression is seen in the baltic sediment records from stockholm in the north to the southernmost parts of the yoldia sea the gradually shallower strait in south central sweden the narke strait ended the saline influence 300 400 years later the two remaining outlets west of lake vanern gota alv and otteid steinselva had become too shallow to swallow the outflowing yoldia sea waters at this stage the baltic lake vanern level could thus not fall in pace with the relative sea level fall outside the outlet areas this was the isolation of lake vanern and the baltic from the sea and the beginning of the ancylus lake since the water depth of the larger gota alv outlet had to be more or less maintained the ancylus lake level had to rise in pace with the uplift of the outlet region this caused a significant and rapid transgression 10 30 m in ca 300 years in the southern baltic which flooded large areas with recently immigrated pine forests since the oresund strait during the yoldia sea stage had been uplifted more than southerly areas the ancylus transgression ended with a new drainage pathway at ca 9 2 ka bp through the darss sill area in the southern baltic and northwards through the store belt strait this so called dana river had cut off the former large land bridge the quaternary deposits of this new threshold were eroded and a fairly rapid regression set in at ca 9 0 ka bp the dana river had eroded down to the sea level which isolated lake vanern from the ancylus lake and created a land bridge between southern sweden and northwards ca 800 years later when the sea level rose above the oresund threshold marine water could enter the baltic and at ca 8 0 ka bp brackish water characterized the southern baltic this marks the end of the ancylus lake

micromorphology and late glacial holocene genesis of luvisols in mecklenburg vorpommern ne germany abstract in the german soil science literature luvisols formed in weichselian sediments except from the early weichselian are normally regarded as purely holocene soils with the main period of development assumed to have been during the atlantic phase although debated at some length since the 1960s the genesis of the widespread albic luvisols with a simplified ap bw eb ebtb btb g c horizon sequence and developed on the flat and slightly undulating till plains of the north german mecklenburgian stage deglaciation 14 000 bp has yet to be clarified periglacial climate during the late weichselian led to the formation of sand filled wedge shaped structures penetrating bt horizons systematic micromorphologic investigations of soil profiles with sand wedges revealed the occurrence of numerous fragments of rounded limpid clay coatings within periglacial formed lenticular microplates as well as in and at the margins of the sand wedge infillings assuming the younger dryas as the latest possible phase of formation the lenticular microplates and the undisturbed sand wedges postdate clay illuviation undisrupted clay coatings next to fragmented clay coatings prove a subsequent holocene clay illuviation clay illuviation must have occurred at least in warmer phases of the late glacial together with the already accepted pedogenic processes of decalcification organic matter accumulation ahb horizons podzolisation and silicate weathering bwb horizons on sites not influenced by groundwater

holocene relief and soil changes in loess covered areas of south western germany the pedosedimentary archives of bretten bauerbach kraichgau based on infrared stimulated luminescence irsl dating of loess borne sediments a chronometry of holocene landscape evolution is established for a representative study site in the early settled kraichgau area in south western germany the results show that the gently rolling relief is due essentially to soil erosion and colluvial deposition triggered by humans cultivating the loess soils since the onset of agriculture in the neolithic period levelling of relief is accompanied by alterations in soil type patterns from haplic luvisols before the impact of humans over variably truncated luvisols with bt horizons prevailing at the slope surfaces in the middle ages to calcaric regosols characterizing both sites of erosion and accumulation since then the tremendous changes show that the effects of human activities have been recorded over thousands of years indicating an early anthropocene in a geomorphological and pedological sense most landscapes are probably more modified by humans than thought at first sight as the results show this recognition requires considering that current geomorphological and soil forming processes might work at different frequencies or magnitudes e g by changes of internal system thresholds such as increased erodibility following the complete erosion of a more resistant bt horizon and or in a different direction e g accumulation instead of erosion or sediment transport due to slope angles decreased by former deposition of colluvium than they would in the absence of a human controlled pre history

occurrence formation and micromorphology of gypsum in soils from the central german chernozem region occurrence of gypsum in soils from loess of the central german chernozem region indicates that local climatic conditions with low precipitation average 500 mm a 1 and a real evaporation between 450 and 460 mm do not allow leaching of weakly soluble gypsum from soils at a site close to the strip mine etzdorf gypsum is accumulated in the ck horizon of a haplic chernozem down to a depth of about 1 5 m its distribution being nonuniform calculated total gypsum in the haplic chernozem amounts from 10 20 t ha 1 the highest accumulation of gypsum obviously by solution transport and evaporation can be observed in a profile exposed to the air since about 1960 in this profile maximum so42 values however are not found on the surface of the outermost aggregates with whitish efflorescence but at 20 cm depth in the profile in a eutric podzoluvisol the precipitation of gypsum developed on living roots as well as in pores of former roots in a buried chernozem large euhedral gypsum crystals with a diameter of up to 1 5 cm were found gypsum crystals occur in different shapes and sizes such as euhedral lenticular rosette like and equigranular ones even soils having undergone leaching processes reveal unusual increases of so42 at 40 50 cm depth this may be an indicator of more recent so42 input due to atmospheric deposition since the beginning of industrialization it is supposed that gypsum is formed by the reaction of atmogenic sulfuric acid with different ca sources in the soil

the fe snow regime in ganymede s core a deep seated dynamo below a stable snow zone ganymede shows signs of a present day magnetic field whose origin is thought to be in its core the fe snow regime has been suggested to be vital in ganymede s history in this regime fe crystals first form at the core mantle boundary and later settle to the deeper core due to their higher density fe snow a stable chemical gradient arises within the liquid of the snow zone below the snow zone the fe particles remelt we propose that the remelting of fe in the deeper entirely liquid core initiates compositional convection which could be the origin of the dynamo such a dynamo is restricted by the period of time the snow zone needs to grow across the core we investigate this time period with a 1 d core evolution model by varying the initial sulfur concentration the core heat flux and the thermal conductivity of the core for the proposed dynamo in the deeper liquid core we obtain necessary time periods of between 320 and 800 myr and magnetic field strengths at the surface that match the observed value of 719 nt to explain the present magnetic field we favor cores with high sulfur concentrations because those lead to a late start and a long duration of the dynamo furthermore a present dynamo below the snow zone suggests the absence of an inner core

a review on the potentiality of rare earth elements to trace pedogenetic processes abstract this review aims at considering the use of rees to trace pedogenetic processes in order to quantify the respective contribution of the successive processes on pedogenesis we first consider the origins and contents of rees in soils to assess their natural occurrence and tackle the common data treatment used to interpret their concentrations we review subsequently the impact of the different pedogenetic processes on the fate of rees in soils from their release into a soil solution by primary mineral heavy minerals phosphates silicates and carbonates dissolution during weathering to their fixation on or into main ree bearing secondary minerals clay minerals fe mn oxides and carbonates then their mobilization by plant recycling and organic matter and finally the impact of argilluviation and redox processes on their fractionation we conclude that rees much more than other trace elements can interestingly trace the considered processes that are encountered in a large diversity of non polluted soils arising from diverse parent materials weathering generally fractionates rees and accounts for a significant part of the variation in the initial ree stock of the soils plant recycling induces a weak mobilization of rees and their accumulation in topsoil argilluviation can be traced using the mree enrichment and the eu anomaly of the clay minerals redox processes can be traced by the ce anomaly caused by the precipitation of cerium on mn oxides to use rees as tracers of pedogenetic processes we recommend to i precisely characterize the ree bearing minerals ii adapt the choice of reference s for normalization and iii perform mass balance calculations

sediment transport events on the northern california continental shelf abstract a long term monitoring tripod has been maintained in 60 m water depth at the northern end of the strataform study site on the northern california continental shelf as part of this ongoing study tripod data for 1 year beginning 24 september 1995 are used to provide a sediment transport analysis on an event by event basis the objective of this paper is to highlight the energetic nature of this shelf region in terms of the frequency duration and magnitude of sediment suspension events and the associated particle flux analyses are based on measurements from two current meters and two optical backscatterance sensors located at 30 and 100 cm above the bed data from these instruments and a pressure sensor were averaged over 7 5 min every hour during the year of record 41 distinct sediment suspension events occurred i e sustained suspended sediment concentrations greater than 20 mg l above background level at 100 cm above bed suspended sediment events were associated with significant wave activity tidal currents and river discharge the average duration of a sediment suspension event was 3 1 days and varied from 0 7 to 8 days during events mean suspended sediment concentrations of 110 mg l were observed with peak hourly observations exceeding 1000 mg l concentrations between events averaged 35 mg l the overall sediment flux for the period of record was directed seaward and southward the distribution and magnitude of sediment suspension events and particle flux showed a strong seasonality for example of the sediment transport during events 98 of the net along shelf and 73 of the net across shelf sediment transport occurred in the winter three major winter storms could account for 72 of the total along shelf transport but only 10 of the across shelf transport the across shelf flux was more evenly distributed over the year and occurred as a result of mean currents and very low frequency seaward flows associated with mesoscale circulation patterns

the effect of nickel on the properties of iron at the conditions of earth s inner core ab initio calculations of seismic wave velocities of fe ni alloys abstract we have performed athermal periodic plane wave density functional calculations within the generalised gradient approximation on the bcc fcc and hcp structures of fe 1 x ni x alloys x 0 0 0625 0 125 0 25 and 1 in order to obtain their relative stability and elastic properties at 360 gpa and 0 k for the hcp structure using ab initio molecular dynamics we have also calculated the elastic properties and wave velocities for x 0 0 0625 and 0 125 at 360 gpa and 5500 k with further calculations for x 0 and 0 125 at 360 gpa and 2000 k at 0 k the hcp structure is the most stable for x 0 0 0625 0 125 and 0 25 with the fcc structure becoming the most stable above x 0 45 the bcc structure is not the most stable phase for any composition at 0 k compressional and shear wave velocities are structure dependent in the case of fcc the velocities are very similar to pure fe but for the hcp structure the addition of ni strongly reduces v s ni also reduced velocities in fcc iron but to a lesser extent however at 5500 k and 360 gpa ni has little effect on the wave velocities of the hcp structure which remain similar to those of pure iron throughout the range of compositions studied and in the case of v s 30 greater than that from seismological models the effect of temperature on fe ni alloys is therefore very significant indicating that conclusions based on the extrapolation of results obtained at much lower temperatures must be treated with great caution the significance of temperature is confirmed by the additional simulation at 2000 k for x 0 and 0 125 which reveals a remarkably linear temperature dependence of the change in v s relative to that of pure iron at 0 k the maximum anisotropy in v p is found to be only very weakly dependent on nickel content but dependent on structure being 15 for fcc and 8 for hcp for the hcp structure at 2000 and 5500 k the maximum anisotropy in v p is also 8 and almost independent of the ni content we conclude that ni can safely be ignored when considering its effect on the seismic properties of hcp fe under core pressures and temperatures and that the negligible effect of nickel on the physical properties of iron in the core arises not because of the chemical similarities between iron and nickel but because of the high temperature of the system