osmotic generation of anomalous fluid pressures in geological environments osmotic pressures are generated by differences in chemical potential of a solution across a membrane but whether osmosis can have a significant effect on the pressure of fluids in geological environments has been controversial because the membrane properties of geological media are poorly understood anomalous pressures large departures from hydrostatic pressure that are not explicable in terms of topographic or fluid density effects are widely found in geological settings and are commonly considered to result from processes that alter the pore or fluid volume which in turn implies crustal changes happening at a rate too slow to observe directly yet if osmosis can explain some anomalies there is no need to invoke such dynamic geological processes in those cases here i report results of a nine year in situ measurement of fluid pressures and solute concentrations in shale that are consistent with the generation of large up to 20 mpa osmotic pressure anomalies which could persist for tens of millions of years osmotic pressures of this magnitude and duration can explain many of the pressure anomalies observed in geological settings they require however small shale porosity and large contrasts in the amount of dissolved solids in the pore waters criteria that may help to distinguish between osmotic and crustal dynamic origins of anomalous pressures

lateglacial and early holocene climate oscillations in the matanuska valley south central alaska abstract here we present multi proxy data from two cores taken from hundred mile lake in the matanuska valley of south central alaska to investigate the climate vegetation and deglaciation history of the last 14 000 years the chronology of the cores was controlled by five ams dates sediment lithology changes from clay at 14 13 ka 1 ka 1000 cal bp through marl at 13 8 ka to gyttja at 8 0 ka the transition from clay to marl probably represents increased productivity of the lake in a stabilizing watershed induced by initial allerod climate warming after ice retreat as calcite precipitation of marl was facilitated by chara photosynthesis under high water temperature in summer the 18o record obtained from bivalve pisidium mollusc shells shows several large shifts between 13 and 8 ka a negative excursion of 2 in 18o at 12 4 11 5 ka is suggestive of a regional expression of the younger dryas gs 1 cooling event a 4 5 negative shift from 10 5 at 13 11 ka to 15 at 10 5 8 ka occurred during the peak carbonate interval around 10 5 ka this surprisingly large negative shift in 18o values during the early holocene thermal maximum has not been documented elsewhere in the region this shift suggests a major change in atmospheric circulation patterns possibly through more frequent easterly flow of warm and dry air masses that are also depleted in 18o pollen results from marl sediments indicate vegetation change from a herb tundra through shrub birch dominated tundra to an alder forest which follows closely with other regional pollen sequences in south central alaska the results from this study suggest that the climatic shift during the early holocene was of greater magnitude than the younger dryas event implying the importance of regional feedback processes in high latitudes in controlling regional climate response to large scale forcing

multiple stage deglacial retreat of the southern greenland ice sheet linked with irminger current warm water transport 1 there is limited knowledge pertaining to the history of the greenland ice sheet gis during the last glacial interglacial transition as it retreated from the continental margins to an inland position here we use multiproxy data including ice rafted debris ird planktonic isotopes alkenone temperatures and tephra geochemistry from the northern labrador sea off southwest greenland to investigate the deglacial response of the gis and evaluate its implications for the north atlantic deglacial development the results imply that the southern gis retreated in three successive stages 1 early deglaciation of the east greenland margins by tephra rich ird that embrace heinrich event 1 2 progressive retreat during allerod culminating in major meltwater releases 18o depletion of 1 2 at the allerod younger dryas transition 12 8 13 0 kyr b p and 3 a final stage of glacial recession during the early holocene 9 11 kyr b p rather than indicating local temperatures of ambient surface water the alkenones likely were transported to the core site by the irminger current we attribute the timing of gis retreat to the incursion of warm intermediate waters along the base of grounded glaciers and below floating ice shelves on the continental margin the results lend support to the view that gis meltwater presented a forcing factor for the younger dryas cooling

osmotic model to explain anomalous hydraulic heads laboratory experiments have shown that compacted clays act as osmotic membranes when they separate aqueous solutions of unequal ionic concentration theoretically osmotically induced differential hydraulic pressure in groundwater systems can be relatively high the magnitude depends primarily upon concentration differences across the membrane type of ions type of clay and pore size in experiments thin compacted clay membranes commonly exhibit varying degrees of osmotic efficiency due to ion leak age through the clay in natural systems the membrane and the solution containers are not as distinct and well defined as they are in the laboratory moreover the membrane is commonly thick inhomogeneous and composite in a buried triassic basin at the savannah river plant near aiken south carolina it is suspected that osmosis causes the saline water in the basin center to be slightly geopressurized in relation to freshwater in the overlying coastal plain aquifer two wells have heads of 7 88 and 12 98 bars 114 3 and 188 3 psi above the head in the coastal plain aquifer the head in each of these wells approximates the osmotic equilibrium head calculated from solution concentration of water produced by each well 12 000 and 18 500 mg l respectively other wells penetrating the top and edge of the triassic basin probably penetrate a zone where ion leakage gives rise to less saline water thus these wells are not geopressurized

a mid european decadal isotope climate record from 15 500 to 5000 years b p oxygen isotope ratios of precipitation delta18op inferred from deep lake ostracods from the ammersee southern germany provide a climate record with decadal resolution the record in detail shows many of the rapid climate shifts seen in central greenland ice cores between 15 000 and 5000 years before the present b p negative excursions in the estimated delta18op from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the north atlantic deviating millennial scale trends however indicate that climate gradients between europe and greenland changed systematically reflecting a gradual rearrangement of north atlantic circulation during deglaciation

a 14 000yr paleoenvironmental record from windmill lake central alaska lateglacial and holocene vegetation in the alaska range abstract a 14 000 yr high resolution pollen and lake level record from windmill lake in central alaska provides new evidence for the late pleistocene and holocene paleoenvironments of this region at 14 000 14 c yr bp sparse herb tundra and low lake levels indicate a cold arid environment about 11 800 14 c yr bp the vegetation abruptly shifted to a shrub tundra and lake levels increased suggesting warmer and more mesic conditions ca 10 500 10 200 14 c yr bp herbaceous taxa increased at the expense of the shrubs suggesting a transient episode of climatic deterioration nearly contemporaneous with the younger dryas chronozone by 8000 14 c yr bp spruce was present in the watershed and alder grew locally by 6500 14 c yr bp the ams radiocarbon chronology indicates later expansions of betula picea and alnus than at most sites in central alaska which are conventionally dated

magma migration and magmatic solitary waves in 3 d numerical studies of fluid flow in the mantle sug gest that magma migration is an inherently time dependent process that produces magmatic solitary waves from obstruc tions in melt flux previous work has considered one and two dimensional problems here we present the results of three dimensional calculations that utilize a new efficient multi grid scheme we demonstrate that one and two dimensional solitary waves are unstable and break up into sets of 3 d solitary waves which are perfectly spherical when propagat ing through a uniform porosity medium while these waves are not solirons their non linear interactions are qualitatively similar the solitary waves are highly opportunistic and es tablish efficient pathways for migration by linking up with nearby waves when the initial condition is a random dis tribution of porosity the porosity structure can organize into elongate time dependent channels formed from chains of solitary waves these results are natural consequences of the assumptions that the matrix is permeable and viscously deformable we suggest that solitary waves are likely to exist in the mantle and may contribute to the episodicity of mantle magmatism

vegetation history of pleasant island southeastern alaska since 13 000 yr b p abstract a 13 000 year history of late quaternary vegetational and climatic change has been derived from lacustrine sediments from pleasant island in the glacier bay region of southeastern alaska early arrival of lodgepole pine and mountain hemlock indicated by the presence of pollen and conifer stomata suggests expansion from refugia in the alexander archipelago a short term climatic reversal possibly correlated with the european younger dryas is inferred from the expansion of tundra elements and deposition of inorganic sediments between 10 600 and 9900 14 c yr b p two peat cores from the lake catchment verify holocene vegetation changes and aid in the separation of biogenic from climatic forces affecting vegetation history differences in pollen representation among the three cores illustrate the variation among pollen collecting substrates as well as the spatial heterogeneity of peatland development and its dependence on local hydrology initial peat accumulation and soil paludification occasioned by increases in temperature and precipitation in the early holocene allowed western and mountain hemlock to replace sitka spruce 8500 8000 yr b p open muskeg became widespread about 7000 yr b p and allowed lodgepole pine to reinvade the region after a 2000 yr absence the extensive replacement of fen elements by bog taxa at 3400 yr b p suggests increased paludification due to changing hydrologic conditions its correlation with the upland expansion of tsuga heterophylla suggests the onset of a cooler wetter neoglacial climate in southeastern alaska

creep and time dependent damage in argillaceous rocks abstract this paper presents the results of laboratory tests on the time dependent behaviour of three rocks characterized by a high proportion of clay particles the viscosity of these sedimentary rocks was studied under different loading conditions in uniaxial compression static or cyclic creep tests and quasistatic tests low loading strain rate were performed across various orientations of fabric planes the quasistatic tests showed similarities in the mechanical response of these three argillaceous rocks a late phase of dilation and a linear development of volumetric deformation before the beginning of unstable crack propagation the development of secondary and tertiary creep phases during the creep tests highlighted the existence of a deviatoric stress threshold below which only primary creep is observed long term creep tests also showed that the volumetric variation is not constant during the development of viscoplastic deformations a microstructural analysis of thin sections extracted from specimens after the tests gave evidence of cataclastic and granular creep damage to the argillaceous matrix occurs and no cracks were observed in the quartz and carbonate grains this evidence was also demonstrated for tests with loading at a high strain rate finally this study highlights the significant viscoplasticity of argillaceous rocks the mechanical properties deteriorate rapidly when crack propagation becomes unstable and the viscoplastic strains seem to be due to clay particle slips known as granular creep

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

abrupt climate oscillations during the last deglaciation in central north america evidence from stable isotopes and a variety of proxies from two ontario lakes demonstrate that many of the late glacial to early holocene events that are well known from the north atlantic seaboard such as the gerzensee killarney oscillation also known as the intra allerod cold period younger dryas and preboreal oscillation also occurred in central north america these results thus imply that climatic forcing acted in the same manner in both regions and that atmospheric circulation played an important role in the propagation of these events

unstable younger dryas climate in the northeast north atlantic the younger dryas stadial greenland stadial 1 has long been recognized in proxy records throughout the north atlantic region as a stable cool period that started and ended abruptly however modeling experiments in which the younger dryas cooling was forced by meltwater predict much more unstable climatic conditions compared to the proxy records here we present evidence of a climatically unstable younger dryas based on a decadal resolution marine proxy record from the norwegian continental shelf this record shows that the north atlantic was characterized in the early younger dryas by arctic water and an increasing accumulation of fresh surface water that peaked at 12 500 calendar yr b p for 300 yr during the late younger dryas the sea surface temperatures fluctuated between glacial values 2 c and interglacial values 10 c on a subdecadal to multidecadal time scale this period of extreme instability preceded the more stable and warm holocene starting ca 11 500 calendar yr b p these results are consistent with modeling experiments that link the younger dryas climate changes to fluctuations of the north atlantic thermohaline circulation

osmotic flow through a cretaceous clay in southern saskatchewan canada clays and shales can act as semipermeable membranes causing osmotic flow and or osmotically induced fluid pressures despite laboratory proof of the osmotic behaviour of clay rich geologic material the influence of this osmotic behaviour on in situ groundwater flow and solute transport is inconclusive this is due in part to the lack of laboratory experimental work involving undisturbed core samples and to the lack of field scale research the ability of undisturbed clay samples to conduct flow hydraulically and osmotically was investigated using dilute salt solutions undisturbed cretaceous clay samples from southern saskatchewan were used in a laboratory experimental program the experiments included constant head hydraulic conductivity kh tests and osmotic flow tests conducted over a range of pore fluid concentrations of 0 054 1 12 equiv l the clay samples exhibited semipermeable membrane behaviour by conducting flow osmotically the hydraulic conductivity of the clay increased by a factor of

on the theory of solitons of fluid pressure and solute density in geologic porous media with applications to shale clay and sandstone we here analyze a new model of transients of pore pressure p and solute density in geologic porous media this model is rooted in the nonlinear wave theory its focus is on advection and effect of large pressure jumps on strain it takes into account nonlinear and also time dependent versions of the hooke law about stress rate and strain the model solutions strictly relate p and evolving under the effect of a strong external stress as a result the presence of quick and sharp transients in low permeability rocks is unveiled i e the nonlinear burgers solitons we therefore show that the actual transport process in porous rocks for large signals is not only the linear diffusion but also a solitons presence could control the process a test of a presence of solitons is applied to pierre shale bearpaw shale boom clay and oznam mugu silt and clay an application about the presence of solitons for nuclear waste disposal and salt water intrusions is also discussed finally in a kind of theoretical experiment we show that solitons could also be present in higher permeability rocks jordan and st peter sandstones thus supporting the idea of a possible occurrence of osmosis also in sandstones

evaluation of solitary waves as a mechanism for oil transport in poroelastic media a case study of the south eugene island field gulf of mexico basin abstract hydrocarbons in shallow reservoirs of the eugene island 330 field in the gulf of mexico basin are thought to have migrated rapidly along low permeability sediments of the red fault zone as discrete pressure pulses from source rocks at depths of about 4 5 km the aim of this research was to evaluate the hypothesis that these pressure pulses represent solitary waves by investigating the mechanics of solitary wave formation and motion and wave oil transport capability a two dimensional numerical model of eugene island minibasin formation predicted overpressures at the hydrocarbon source depth to increase at an average rate of 30 pa yr reaching 52 mpa by the present day and oil velocities of 10 12 m yr far too low for kilometer scale oil transport to fill shallow plio pleistocene reservoirs within the 3 6 million year minibasin history calculations from a separate one dimensional model that used the pressure generation rate from the two dimensional model showed that solitary waves could only form and migrate within sediments that have very low permeabilities between 10 25 and 10 24 m 2 and that are highly overpressured to 91 93 of lithostatic pressure solitary waves were found to have a maximum pore volume of 10 5 m 3 to travel a maximum distance of 1 2 km and to have a maximum velocity of 10 3 m yr based on these results solitary waves are unlikely to have transported oil to the shallowest reservoirs in the eugene island field in a poroelastic fault gouge rheology at the pressure generation rates likely to have been caused by disequilibrium compaction and hydrocarbon generation however solitary waves could perhaps be important agents for oil transport in other locations where reservoirs are closer to the source rocks where the pore space is occupied by more than one fluid or where sudden fracturing of overpressured hydrocarbon source sediments would allow the solitary waves to propagate as shock waves

regional atmospheric circulation change in the north pacific during the holocene inferred from lacustrine carbonate oxygen isotopes yukon territory canada analyses of sediment cores from jellybean lake a small evaporation insensitive groundwater fed lake provide a record of changes in north pacific atmospheric circulation for the last 7500 yr at 5 to 30 yr resolution isotope hydrology data from the southern yukon indicate that the oxygen isotope composition of water from jellybean lake reflects the composition of mean annual precipitation 18op recent changes in the 18o of jellybean sedimentary calcite 18oca correspond to changes in the north pacific index npi a measure of the intensity and position of the aleutian low al pressure system this suggests that 18op variability was related to the degree of fractionation during moisture transport from the gulf of alaska across the st elias mountains and that holocene shifts were controlled by the intensity and position of the al following this model between 7500 and 4500 cal yr b p long term trends suggest a predominantly weaker and or westward al between 4500 and 3000 cal yr b p the al shifted eastward or intensified before shifting westward or weakening between 3000 and 2000 cal yr b p rapid shifts eastward and or intensification occurred 1200 and 300 cal yr b p holocene changes in north pacific atmospheric circulation inferred from jellybean lake oxygen isotopes correspond with late holocene glacial advances in the st elias mountains changes in north pacific salmon abundance and shifts in atmospheric circulation over the beaufort sea

importance of thermo osmosis for fluid flow and transport in clay formations hosting a nuclear waste repository abstract three osmotic processes have been identified in clay rich media electro and chemo osmosis flows of water caused by salinity and electrical potential gradients have so far attracted almost exclusive attention but despite the recurring concern about the importance of thermo osmosis a flow of water driven by a temperature gradient in argillaceous media it remains largely neglected here we propose a new formalism for estimating the thermo osmotic permeability based on a theoretical analysis at the molecular and pore scale then upscaled we show that the thermo osmotic permeability can be estimated only from surface charge density temperature pore size and salinity the possible prominent role of thermo osmosis in compacted shale layers with a temperature gradient is then exemplified this first general estimate of the thermo osmotic permeability can be used to improve our understanding of the influence on fluid flow and pressure fields of the natural geothermal gradient in sedimentary basins which is required e g for safety assessments of nuclear waste repositories in shale layers

elastic wave velocity in marine sediments with gas hydrates effective medium modeling we offer a first principle based effective medium model for elastic wave velocity in unconsolidated high porosity ocean bottom sediments containing gas hydrate the dry sediment frame elastic constants depend on porosity elastic moduli of the solid phase and effective pressure elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation to model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions a hydrate modifies the pore fluid elastic properties without affecting the frame b hydrate becomes a component of the solid phase modifying the elasticity of the frame the goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data we apply the model to sonic and vsp data from odp hole 995 and obtain hydrate concentration estimates from assumption b consistent with estimates obtained from resistivity chlorinity and evolved gas data

historical linkage between atmospheric circulation patterns and the oxygen isotopic record of sedimentary carbonates from lake mendota wisconsin usa stratigraphic variations in the delta 18o values of sedimentary carbonate in lake mendota wisconsin usa correlate with changes in atmospheric circulation patterns over the past century carbonate delta 18o values trend toward 18o depletion in progressively younger sediments archives of historical water column data and climate data from the surrounding drainage basin indicate that this trend cannot reflect changes in water temperature timing of carbonate precipitation disequilibrium isotope fractionation air temperature or seasonal precipitation patterns however significant correlations with the frequency and direction of cyclones indicate that the isotopic record has been significantly influenced by subtle changes in atmospheric circulation over the past 100 yr two atmospheric circulation models can account for this relationship 1 greater contributions of 18o depleted precipitation associated with air masses from the pacific ocean or 2 a progressive increase in the altitude of condensation leading to 18o depletion of precipitation originating from the gulf of mexico because the pacific ocean generally contributes little moisture to the midcontinent the first model is an unlikely mechanism to generate the isotopic trends observed in the sediments intrusions of dry dense air from the west however could force moisture originating from the gulf of mexico to higher altitudes of condensation and thus account for the trends in the carbonate isotopic record this study demonstrates that historic data used in conjunction with lacustrine delta 18o stratigraphy provide a method to reconstruct past atmospheric circulation regimes in continental environments comparisons of sedimentary isotopic records from lakes in north america and europe indicate that these reconstructions of regional atmospheric circulation patterns can be integrated to assess circulation changes on the global scale