permeability evolution of shale under anisotropic true triaxial stress conditions abstract although permeability data for shale have been reported previously and permeability models have been proposed studies on permeability for shale under anisotropic true triaxial stress conditions are lacking in this work the permeability of shale under true triaxial stress conditions was measured using a newly developed true triaxial geophysical apparatus the permeability always decreased with increasing principal stress the permeability variations induced by varying each principal stress were distinct the greatest permeability reductions were observed with increasing stress normal to the bedding planes based on a consideration of shale anisotropy a permeability model was established to be applicable to shale under anisotropic true triaxial stress conditions ttp model this model was verified by matching the permeability data in our experiments it was found that a more accurate match could be obtained using the ttp model which showed advantages in reflecting the permeability changes related to increments in each principal stress

anisotropy of gas permeability associated with cleat pattern in a coal seam of the kushiro coalfield in japan an underground investigation has been performed in a subbituminous coal seam exhibiting a particular cleat pattern in the kushiro coalfield japan the coal cleat pattern shows some analogy to isolated straight joints and is believed to have been formed during the late tertiary period by a compressive tectonic stress roughly in the east west direction three cylindrical coal specimens representing the three orthogonal axes of the coal seam with respect to the bedding plane and its associated cleat were cored from a large block of coal gas permeabilities of the three coal specimens were measured under the same hydrostatic pressure conditions results clearly revealed anisotropy in permeability of the coal seam under relatively low confining pressures of less than about 12 mpa the specimen cored parallel to both the bedding plane and cleat strike showed the highest permeability even though the cleats were partly filled with calcite and clay minerals the permeability in this direction was 2 5 times higher than perpendicular to the bedding plane and 3 times higher than in the direction parallel to the bedding plane but perpendicular to the cleat strike this suggests that the cleats play a greater role than bedding planes in controlling fluid flow in the coal seam the permeability in the three orientations however converged to the same value at confining pressures above about 16 mpa this may suggest that both cleats and bedding planes in a coal seam can close due to earth pressure if the coal seam is located below a certain depth it further indicates that the traditional view that gas permeability is always greater parallel to the coal bedding than perpendicular to it should be reconsidered

an analytical coal permeability model for tri axial strain and stress conditions coal permeability is sensitive to the effective stress and is therefore coupled to the geomechanical behaviour of the seam during gas migration as coal shrinks with gas desorption and swells with adsorption understanding this coupling to geomechanical behaviour is central to interpreting coal permeability existing coal permeability models such as those proposed by shi and durucan 2004 and palmer and mansoori 1996 simplify the geomechanical processes by assuming uni axial strain and constant vertical stress however it is difficult to replicate these conditions in laboratory tri axial permeability testing and during laboratory core flooding tests for enhanced coal bed methane often laboratory tests involve a hydrostatic stress state where the pressure in the confining fluid within the tri axial cell is uniformly applied to the sample exterior in this experimental arrangement the sample is allowed to undergo tri axial strain this paper presents two new analytical permeability model representations derived from the general linear poroelastic constitutive law that include the effects of tri axial strain and stress for coal undergoing gas adsorption induced swelling a novel approach is presented to the representation of the effect of coal sorption strain on cleat porosity and thus permeability this involves distinguishing between the sorption strain of the coal matrix the pores or cleats and the bulk coal the developed model representations are applied to the results from a series of laboratory tests and it is shown that the models can predict the laboratory permeability data as part of this characterisation the various sorption strains are identified and it is shown that the pore strain is significantly larger than approximately 50 times the bulk sorption strain the models also provide further insight into how coal permeability varies with coal shrinkage and swelling and how the permeability rebound pressure depends upon the effective stress applied

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

eddy zonal flow feedback in the southern hemisphere abstract the variability of the zonal mean zonal wind in the southern hemisphere is studied using eof analysis and momentum budget diagnostics of ncep reanalysis data 1978 97 the leading eof of the zonal mean zonal wind is well separated from the remaining eofs and represents the north south movement of the midlatitude jet analysis of the momentum budget shows that a positive feedback between the zonal mean wind anomalies and the eddy momentum fluxes accounts for the unusual persistence of eof1 and plays an important role in the selection of the leading eof of midlatitude variability further analysis also shows a propagating feedback common to both eof1 and eof2 which is responsible for the poleward drift of wind anomalies with time the observations support the following feedback mechanism anomalous baroclinic wave activity is generated at the latitude of anomalous temperature gradient that by thermal wind coincides with the latitude of the anomalous zonal jet the net propagation of baroclinic

middle miocene southern ocean cooling and antarctic cryosphere expansion magnesium calcium data from southern ocean planktonic foraminifera demonstrate that high latitude similar to55degreess southwest pacific sea surface temperatures ssts cooled 6degrees to 7degreesc during the middle miocene climate transition 14 2 to 13 8 million years ago stepwise surface cooling is paced by eccentricity forcing and precedes antarctic cryosphere expansion by similar to60 thousand years suggesting the involvement of additional feedbacks during this interval of inferred low atmospheric partial pressure of co2 pco 2 comparing ssts and global carbon cycling proxies challenges the notion that episodic pco2 drawdown drove this major cenozoic climate transition sst salinity and ice volume trends suggest instead that orbitally paced ocean circulation changes altered meridional heat vapor transport triggering ice growth and global cooling

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

past and future grounding line retreat of the west antarctic ice sheet the history of deglaciation of the west antarctic ice sheet wais gives clues about its future southward grounding line migration was dated past three locations in the ross sea embayment results indicate that most recession occurred during the middle to late holocene in the absence of substantial sea level or climate forcing current grounding line retreat may reflect ongoing ice recession that has been under way since the early holocene if so the wais could continue to retreat even in the absence of further external forcing

plio pleistocene sedimentation in ferrar fiord antarctica a 166 m thick plio pleistocene sequence of glacial sediments has been cored in ferrar fiord in the southwestern corner of the ross sea antarctica the core has the following lithofacies massive diamictite 33 of the core interpreted as lodgement or waterlain till weakly stratified diamictite 25 waterlain till or proximal glaciomarine sediment well stratified diamictite 8 proximal glaciomarine or glaciolacustrine sediment sandstone 25 sand of aeolian or supraglacial origin mudstone 7 derived from subglacial debris and transported offshore in suspension and minor amounts of rhythmite and tuff the range of facies in this polar setting differs from those normally found in subpolar and temperate glacier fiord settings in the high proportion of aeolian derived sand and the low proportion of mudstone facies the core can be divided into two sequences based on composition and texture the sequence from 162 to 100 mbsf metres below the sea floor comprises alternations of diamictite dominated by basement lithologies and thin marine mudstone beds it is pliocene in age 4 9 2 0 ma and records several advances and retreats of ice through the transantarctic mountains and across the drill site from the west the sequence from 100 mbsf to the sea floor of pleistocene age consists of alternations of diamictite interpreted as lodgement and waterlain till and sandstone of aeolian origin deposited in a glaciolacustrine setting similar to ice covered lakes in the dry valleys today these sediments have a high volcanic component and hence are thought to have been derived by the grounding and advance of the ross ice shelf from the east past volcanic ross island this change in source is attributed to the rising transantarctic mountains increasingly containing east antarctic ice the pleistocene sequence above 100 mbsf clearly represents polar glacial sedimentation with alternations of till and glaciolacustrine sand mudstones from the pliocene sequence beneath include palynomorphs indicating times when the landscape was at least partially vegetated but contain no evidence of meltwater influence

greatly expanded tropical warm pool and weakened hadley circulation in the early pliocene the pliocene warm interval has been difficult to explain we reconstructed the latitudinal distribution of sea surface temperature around 4 million years ago during the early pliocene our reconstruction shows that the meridional temperature gradient between the equator and subtropics was greatly reduced implying a vast poleward expansion of the ocean tropical warm pool corroborating evidence indicates that the pacific temperature contrast between the equator and 32 n has evolved from 2 c 4 million years ago to 8 c today the meridional warm pool expansion evidently had enormous impacts on the pliocene climate including a slowdown of the atmospheric hadley circulation and el nino like conditions in the equatorial region ultimately sustaining a climate state with weak tropical sea surface temperature gradients may require additional mechanisms of ocean heat uptake such as enhanced ocean vertical mixing

increased glacial age ventilation of the chilean margin by antarctic intermediate water antarctic intermediate water is an oxygen rich water mass that spreads throughout the southern hemisphere oceans marine sediment chemistry indicates that the water mass was produced at higher rates and had higher oxygen concentrations during the last glacial maximum antarctic intermediate water is at present a water mass that brings oxygen to intermediate depths throughout the southern hemisphere oceans models have suggested that intermediate waters had higher concentrations of oxygen during the last glacial period1 2 consistent with globally reduced denitrification3 and increased production of antarctic intermediate water4 however some palaeoceanographic reconstructions5 6 have indicated that production decreased in the southeast pacific ocean at this time here we analyse the concentrations of re and mn the sedimentary concentrations of which are controlled by the amount of dissolved oxygen at the sea floor from three sediment cores located along the chilean margin for the past 30 000 years our results from the cores which bracket the present day water column extent of antarctic intermediate water show that the depth range of well oxygenated antarctic intermediate water increased off chile during the last glacial maximum dissolved oxygen content began to decrease approximately 17 000 years ago coincident with rapid antarctic warming and a poleward shift of the southern westerly winds7 our estimates of productivity from accumulation rates of organic carbon and opal do not co vary with the seafloor oxygen variations ruling out local control of seafloor oxygenation we conclude that the data are best explained by a combination of increased oxygenation and increased flux of antarctic intermediate water during the last glacial maximum

late pliocene greenland glaciation controlled by a decline in atmospheric co2 levels it is thought that the northern hemisphere experienced only ephemeral glaciations from the late eocene to the early pliocene epochs about 38 to 4 million years ago and that the onset of extensive glaciations did not occur until about 3 million years ago several hypotheses have been proposed to explain this increase in northern hemisphere glaciation during the late pliocene here we use a fully coupled atmosphere ocean general circulation model and an ice sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the greenland ice sheet in particular we find that greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the late pliocene by contrast our model results suggest that climatic shifts associated with the tectonically driven closure of the panama seaway with the termination of a permanent el nino state or with tectonic uplift are not large enough to contribute significantly to the growth of the greenland ice sheet moreover we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the earth s orbit

geotechnical sedimentology its use in underground coal mining from a geotechnical perspective bedding is a discontinuity in a rock mass sedimentology is concerned in part with the origin of bedding there is much to be gained by a melding of the two disciplines in the underground coal mining sector bedding controls the strength of rock units in coal measures by defining beams that may or may not span openings voussoir beam theory can be used to explain how massive sandstone conglomerate units can span longwall panels and what thickness of roof beam is required to span a coal mine roadway bedding also controls the way in which stresses are distributed about coal mine openings by utilizing transverse isotropic elastic properties the effect of bedding can be readily implemented in continuum numerical codes geologists logging core need to discriminate between bedding as a textural element in the rock and bedding as a geotechnical discontinuity geotechnical engineers need to explicitly consider bedding when formulating their design models

eddy transport and mixing in a wind and buoyancy driven jet on the sphere abstract the baroclinically unstable wind and buoyancy driven flow in a zonally reentrant pie shaped sector on a sphere is numerically modeled and then analyzed using the transformed eulerian mean tem formalism mean fields are obtained by zonal and time averaging performed at fixed height the very large latitudinal extent of the basin 50 7 s latitude to the equator allows the latitude variation of the coriolis parameter to strongly influence the flow persistent zonal jets are observed in the statistically steady state reynolds stress terms play an important role in redistributing zonal angular momentum convergence of the lateral momentum flux gives rise to a strong eastward jet with an adjacent westward jet equatorward and weaker multiple jets poleward an equally prominent feature of the flow is a strong and persistent eddy that has the structure of a kelvin cat s eye and generally occupies the zonal width of the basin at latitudes 15 10 s a strongly mixed surface diabatic zone overlies the

cenozoic marine sedimentation and ice volume variation on the east antarctic craton recycled cretaceous and cenozoic marine microfossils have been recovered from samples of the pliocene sinus formation samples were collected from outcrops in the reedy beardmore and ferrar glacier areas of the transantarctic mountains between lat 77 and 86 s the glaciogene sediments contained diatoms foraminifera calcareous nannoplankton silicoflagellates radiolarians sponge spicules palynomorphs and ostracodes of late cretaceous paleocene eocene late oligocene late miocene and pliocene age this suggests the presence of open marine basins on the east antarctic craton during late mesozoic and cenozoic time the apparent absence of early oligocene and early through middle and earliest late miocene assemblages suggests either that marine regression exposed the basin floors or that ice filled the basins during these times the high elevation setting of sirius formation outcrops suggests one of two hypotheses for their origin 1 they are in situ pliocene glaciomarine deposits that were uplifted 1 750 2 500 m with the transantarctic mountains to their present elevation 2 the sirius formation deposits are a mixture of derived sediments stripped from sub ice intracratonic basins and subsequently redeposited by ice flowing up the inland slope of the transantarctic mountains we favor the second hypothesis with transport to sites sometime within the past 3 m y

were west antarctic ice sheet grounding events in the ross sea a consequence of east antarctic ice sheet expansion during the middle miocene abstract seismic correlation of glacial unconformities from the ross sea outer continental shelf to chronostratigraphic control at dsdp sites 272 and 273 indicates that at least two west antarctic ice sheet wais expansions occurred during the early part of the middle miocene i e well before completion of continental scale expansion of the east antarctic ice sheet eais inferred from 18o and eustatic shifts therefore if the volume of the eais was indeed relatively low and if the ross sea age model is valid then these wais expansions contractions were not a direct consequence of eais expansion over the transantarctic mountains onto west antarctica an in situ development of the wais during the middle miocene suggests that either west antarctic land elevations were above sea level and or that air and water temperatures were sufficiently cold to support a marine based ice sheet additional chronostratigraphic and lithologic data are needed from antarctic margins to test these speculations

alkenone and boron based pliocene pco2 records abstract the pliocene period is the most recent time when the earth was globally significantly 3 c warmer than today however the existing pco2 data for the pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo pco2 this disagreement coupled with the general low temporal resolution of the published records does not allow a robust assessment of the role of declining pco2 in the intensification of the northern hemisphere glaciation inhg and a direct comparison to other proxy records are lacking for the first time we use a combination of foraminiferal 11b and organic biomarker alkenone derived carbon isotopes proxies to determine the concentration of atmospheric co2 over the past 5 ma both proxy records show that during the warm pliocene pco2 was between 330 and 400 ppm i e similar to today the decrease to values similar to pre industrial times 275 285 ppm occurred between 3 2 ma and 2 8 ma coincident with the inhg and affirming the link between global climate the cryosphere and pco2

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

evolution of the eastern tropical pacific through plio pleistocene glaciation a tropical pacific climate state resembling that of a permanent el nino is hypothesized to have ended as a result of a reorganization of the ocean heat budget 3 million years ago a time when large ice sheets appeared in the high latitudes of the northern hemisphere we report a high resolution alkenone reconstruction of conditions in the heart of the eastern equatorial pacific eep cold tongue that reflects the combined influences of changes in the equatorial thermocline the properties of the thermocline s source waters atmospheric greenhouse gas content and orbital variations on sea surface temperature sst and biological productivity over the past 5 million years our data indicate that the intensification of northern hemisphere glaciation 3 million years ago did not interrupt an almost monotonic cooling of the eep during the plio pleistocene sst and productivity in the eastern tropical pacific varied in phase with global ice volume changes at a dominant 41 000 year obliquity frequency throughout this time changes in the southern hemisphere most likely modulated most of the changes observed

southern ocean wind response to north atlantic cooling and the rise in atmospheric co2 modeling perspective and paleoceanographic implications 1 a recent study found enhanced upwelling rates in the southern ocean during the last glacial termination that coincided with the deglacial warming in antarctica and the rise in atmospheric co2 they hypothesized that the intensification of southern hemisphere midlatitude westerlies the presumed cause of the increased wind driven upwelling was triggered by an initial cooling within the glacial north atlantic whose influence was then communicated to the southern midlatitudes through an atmospheric teleconnection in this study we explore the viability of the above hypothesis using a modeling strategy focusing on the atmospheric teleconnection in simulations where north atlantic cooling was applied the model intertropical convergence zone shifted southward and westerlies and wind stress over southern ocean increased by as much as 25 while the perennial westerly anomalies occur over the entire southern ocean they are strongest over the south pacific during the austral winter when the wind stress anomalies were applied to an earth system model incorporating interactive marine biogeochemistry atmospheric co2 rises between 20 and 60 ppm depending on the biological response we thus confirm the viability of the proposed atmospheric teleconnection hypothesis the teleconnection appears to involves two distinct steps first the north atlantic cooling shifts the intertropical convergence zone southward weakening the southern branch of the hadley circulation and second how the altered hadley circulation in turn modifies the structure of midlatitude westerlies in the south pacific via the former s influence on the southern hemisphere subtropical jet this study underscores the control of the northern hemisphere has on southern midlatitude westerlies mediating by tropical circulation in contrast to past paleoclimate hypotheses that the magnitude and position of the southern midlatitude westerlies was controlled by global mean temperature our results do not preclude other potential mechanisms for affecting southern ocean ventilation in particular through oceanic pathways

flow and water property structures between the bering sea and fiji in the summer of 1993 an overview is given of the top to bottom flow thermohaline oxygen and nutrient structures between the bering sea and the fiji islands based on high resolution field measurements along 179 e the zonal flow is dominated by a banded mesoscale structure reflecting the highly sheared structure and instabilities of the major ocean currents crossing the date line the major midlatitude currents are 100 200 km wide have maximum speeds of 40 cm s 1 and extend to 2000 m when measured by the 5 cm s 1 isotach el nino conditions in 1993 caused a merger of the north equatorial countercurrent with the equatorial undercurrent leading to a 600 km wide band of equatorial eastward flow 40 60 cm s 1 in the upper 300 m beneath a 400 km wide and 1 2 km deep westward jet 10 30 cm s 1 is found between 1500 and 3500 m the equatorial flow is predominately to the southeast and between 3500 and 5000 m it is toward the northwest consonant with banded shear flow and flow topography interactions the physical and chemical property distributions along 179 e are complicated reflecting the effects of differential property advection mixing and water mass transformation well defined property fronts occur in shear zones between currents of different origin the thermohaline oxygen and nutrient tongues associated with north and south pacific intermediate and deep waters have considerable internal structure indicative of mesoscale processes and contorted flow paths the abyssal flow near the date line indicates northward movement of lower circumpolar water to the hess rise whence it turns westward and north west of the emperor seamounts properties east of this seamount chain are very uniform the deep and abyssal waters of the isolated aleutian basin differ substantially from those in the adjacent pacific by being warmer 0 1 c less saline 0 01 poorer in oxygen 50 mol kg 1 and much richer in silicate 80 mol kg 1 an isolated basin within the wake necker ridge also shows some unusual bottom water characteristics below sill depth

annular variability and eddy zonal flow interactions in a simplified atmospheric gcm part i characterization of high and low frequency behavior abstract experiments have been performed using a simplified newtonian forced global circulation model to investigate how variability of the tropospheric jet can be characterized by examining the combined fluctuations of the two leading modes of annular variability eddy forcing of this variability is analyzed in the phase space of the leading modes using the vertically integrated momentum budget the nature of the annular variability and eddy forcing depends on the time scale at low frequencies the zonal flow and baroclinic eddies are in quasi equilibrium and anomalies propagate poleward the eddies are shown primarily to reinforce the anomalous state and are closely balanced by the linear damping leaving slow evolution as a residual at high frequencies the flow is strongly evolving and anomalies are initiated on the poleward side of the tropospheric jet and propagate equatorward the eddies are shown to drive this evolution strongly eddy location and amplitude reflect the past baroclinicity while

mechanisms of zonal index variability in an aquaplanet gcm abstract data from a 2025 day geophysical fluid dynamics laboratory aquaplanet gcm integration are used to examine the temporal evolution of the zonal index defined as the principal component of the first eof of the zonally and vertically integrated absolute angular momentum this eof represents meridional displacements of the subtropical jet positive negative values of the zonal index correspond to poleward equatorward displacements of the subtropical jet and are referred to as the high low zonal index composites of various quantities are used to examine the temporal evolution of both the zonal mean zonal winds and the eddy fields associated with either index the high index is initiated by an enhancement in the equatorward wave activity propagation which causes the subtropical jet to move in a poleward direction the low index is led by a weakening in the equatorward propagation which results in an equatorward displacement of the subtropical jet more importantly for the high index the corr

thresholds for cenozoic bipolar glaciation the long standing view of earth s cenozoic glacial history calls for the first continental scale glaciation of antarctica in the earliest oligocene epoch 33 6 million years ago1 followed by the onset of northern hemispheric glacial cycles in the late pliocene epoch about 31 million years later2 the pivotal early oligocene event is characterized by a rapid shift of 1 5 parts per thousand in deep sea benthic oxygen isotope values3 oi 1 within a few hundred thousand years4 reflecting a combination of terrestrial ice growth and deep sea cooling the apparent absence of contemporaneous cooling in deep sea mg ca records4 5 6 however has been argued to reflect the growth of more ice than can be accommodated on antarctica this combined with new evidence of continental cooling7 and ice rafted debris8 9 in the northern hemisphere during this period raises the possibility that oi 1 represents a precursory bipolar glaciation here we test this hypothesis using an isotope capable global climate ice sheet model that accommodates both the long term decline of cenozoic atmospheric co2 levels10 11 and the effects of orbital forcing12 we show that the co2 threshold below which glaciation occurs in the northern hemisphere 280 p p m v is much lower than that for antarctica 750 p p m v therefore the growth of ice sheets in the northern hemisphere immediately following antarctic glaciation would have required rapid co2 drawdown within the oi 1 timeframe to levels lower than those estimated by geochemical proxies10 11 and carbon cycle models13 14 instead of bipolar glaciation we find that oi 1 is best explained by antarctic glaciation alone combined with deep sea cooling of up to 4 c and antarctic ice that is less isotopically depleted 30 to 35 than previously suggested15 16 proxy co2 estimates remain above our model s northern hemispheric glaciation threshold of 280 p p m v until 25 myr ago but have been near or below that level ever since10 11 this implies that episodic northern hemispheric ice sheets have been possible some 20 million years earlier than currently assumed although still much later than oi 1 and could explain some of the variability in miocene sea level records

low frequency variability of southern ocean jets both observations and high resolution numerical models show that the southern ocean circumpolar flow is concentrated in a large number approximately 8 to 12 of narrow filamentary jets it is shown here that coherent jets exhibit a range of low frequency variability on timescales of months to years that can lead to displacement and to intermittent formation and dissipation of jets using output from an eddy resolving ocean general circulation model in local regions near topographic features the impact of energy exchange between eddy and mean flow components on jet persistence and variability is examined a novel approach that uses a time dependent definition of the mean flow provides a clearer picture of eddy mean flow interactions in regions with spatially and temporally varying flow structure the dynamics are largely consistent with those in idealized quasi geostrophic models including topographically organized and surface enhanced reynolds stress forcing of the mean flow jets form during periods of enhanced eddy activity but may persist long after the eddy activity has decayed similarly jets may evolve in a downstream sense with jet formation localized near topography and undergoing modification in response to changing bathymetry the evolution of both temperature and potential vorticity is used to show that the low frequency variability of the jets impacts water mass structure and tracer transport this study highlights various examples of southern ocean dynamics that will prove difficult to capture through parameterizations in coarser climate models

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

annular modes in a multiple migrating zonal jet regime the authors investigate the dynamics of zonal jets in a semihemisphere zonally reentrant ocean model the forcings imposed in the model are an idealized atmospheric wind stress and relaxation to a latitudinal temperature profile held constant in time while there are striking similarities to the observed atmospheric annular modes where the leading mode of variability is associated with the primary zonal jet s meridional undulation secondary weaker jets emerge and systematically migrate equatorward the model output suggests the following mechanism for the equatorward migration while the eddy momentum fluxes sustain the jets the eddy heat fluxes have a poleward bias causing an anomalous residual circulation with poleward equatorward flow on the poleward equatorward flanks by conservation of mass there must be a rising residual flow at the jet from the thermodynamics equation the greatest cooling occurs at the jet core thus creating a tendency to reduce the baroclinicity on the poleward flank while enhancing it on the equatorward flank consequently the baroclinic zone shifts perpetuating the jet migration

on the relationship between stress and elastic strain for porous and fractured rock modeling the mechanical deformations of porous and fractured rocks requires a stress strain relationship experience with inherently heterogeneous earth materials suggests that different varieties of hooke s law should be applied within regions of the rock having significantly different stress strain behavior we apply this idea by dividing a rock body conceptually into two distinct parts the natural strain volume change divided by rock volume at the current stress state rather than the engineering strain volume change divided by the unstressed rock volume should be used in hooke s law for accurate modeling of the elastic deformation of that part of the pore volume subject to a relatively large degree of relative deformation i e cracks or fractures this approach permits the derivation of constitutive relations between stress and a variety of mechanical and or hydraulic rock properties we show that the theoretical predictions of this method are generally consistent with empirical expressions from field data and also laboratory rock experimental data

propagation of planetary waves between the troposphere and stratosphere abstract the propagation of planetary waves between the troposphere and stratosphere is investigated using a linear time dependent primitive equation model it is found that the tropopause acts like a valve for the propagation of planetary waves the key parameters controlling the valve are the vertical gradient of buoyancy frequency and the vertical shear of the zonal winds at the tropopause for a given wind profile smaller gradient of buoyancy frequency enhances the propagation of planetary waves for a given profile of buoyancy frequency the larger the shear the more the wave activity is trapped in the troposphere and therefore there is less left to propagate into the stratosphere the transmission across the tropopause is however not sensitive to zonal winds in the upper stratosphere the propagation of planetary waves is very sensitive to transience more transient waves propagate more vertically within the troposphere and for more transient waves more wave activity is transferred into the

permeability evolution of slowly slipping faults in shale reservoirs slow slip on preexisting faults during hydraulic fracturing is a process that significantly influences shale gas production in extremely low permeability shale unconventional reservoirs we experimentally examined the impacts of mineralogy surface roughness and effective stress on permeability evolution of slowly slipping faults in eagle ford shale samples our results show that fault permeability decreases with slip at higher effective stress but increases with slip at lower effective stress the permeabilities of saw cut faults fully recover after cycling effective stress from 2 5 to 17 5 to 2 5 mpa and increase with slip at constant effective stress due to asperity damage and dilation associated with slip however the permeabilities of natural faults only partially recover after cycling effective stress returns to 2 5 mpa and decrease with slip due to produced gouge blocking fluid flow pathways our results suggest that slowly slipping faults have the potential to enhance reservoir stimulation in extremely low permeability reservoirs

effects of bedding on the dynamic indirect tensile strength of coal laboratory experiments and numerical simulation abstract dynamic indirect tensile tests were carried out by using a split hopkinson pressure bar shpb for coal sampled from the datong mine in china the principal purpose was to explore the influence of bedding structure in the coal on its dynamic indirect tensile strength however to resolve some contradictions x ray micro ct high speed optical imaging and a discrete element based modelling approach were combined to analyze the test results the x ray micro ct was used to detect the actual bedding structure in the coal the high speed imaging captured failure patterns of the specimens with different bedding directions and the numerical modelling was utilized to investigate the influence of different bedding structures on dynamic strength the shpb and numerical results illustrate that dynamic indirect tensile strength reliably correlates with impact velocity in addition the dynamic indirect tensile strength is not only influenced by the bedding direction but also by the roughness and discontinuity of the bedding based on these findings a method is developed to further process the test data including a model to describe the dynamic indirect tensile strength of datong coal

transformed eulerian mean theory part ii potential vorticity homogenization and the equilibrium of a wind and buoyancy driven zonal flow the equilibrium of a modeled wind and buoyancy driven baroclinically unstable flow is analyzed using the transformed eulerian mean tem approach described in part i within the near adiabatic interior of the flow ertel potential vorticity is homogenized along mean isopycnals a finding readily explained using tem theory given the geometry of the domain the equilibrium zonal mean buoyancy structure at the surface is determined entirely by a balance between imposed surface fluxes and residual mean and eddy buoyancy transport within a surface diabatic layer balance between these same processes and the wind stress determines the stratification and hence potential vorticity immediately below this layer ertel potential vorticity homogenization below then determines the mean buoyancy structure everywhere accordingly the equilibrium structure of this flow can be described and quantitatively reproduced from knowledge of the eddy mixing rates within the surface diabatic zone and the depth of this zone together with potential vorticity homogenization beneath these results emphasize the need to include near surface buoyancy transport as well as interior pv transport in eddy parameterization schemes they also imply that in more realistic models the surface buoyancy balances may be impacted by processes in remote locations that allow diapycnal flow

the biogeography of major diatom taxa in southern ocean sediments 2 open ocean related species diatoms from 228 southern ocean core top sediment samples were examined to determine the geographic distributions of 32 major diatom species taxa preserved in the sediments of three zonally distinct regions sea ice open ocean and the tropical subtropical in the first of three papers 14 species taxa occurring in the region where sea ice covers the ocean surface on an annual basis are geographically documented comparisons are drawn between the diatom abundances on the sea floor sea ice parameters annual duration and concentration in february and september and february sea surface temperature such parameters are commonly used in reconstructing past oceanographic conditions in the sea ice and open ocean zones analysis of the geographic patterns and sea surface parameter correlations reveals species specific distributions regulated primarily by sea ice coverage and sea surface temperature which support the use of diatom remains for the estimation of these past seasurface environmental parameters comparison with reliable accounts of the 14 species from the sediments or plankton also provides the first glimpses into species specific ecology and habitat linkages d 2005 elsevier b v all rights reserved

west antarctic paleotopography estimated at the eocene oligocene climate transition 1 one generally recognized limitation of models for rapid growth of antarctic ice near the eocene oligocene transition is that they are based on present topography corrected only for removal of modern ice for west antarctica this results in large areas below sea level that would not readily host ice in the recently active west antarctic rift system other factors may have contributed to significant vertical motions since the eocene additional corrections for thermal contraction resulting from tectonic extension and for erosion and sedimentation since 34 ma restore most of west antarctica to above sea level increasing total antarctic land area by 10 20 because ice sheets have convex slopes the potential increase in ice volume is larger than the increase in land area accounting for large changes in west antarctic topography may resolve conflicts between ice models and data by demonstrating the possibility of an early large west antarctic ice sheet

an observational study of the intraseasonal poleward propagation of zonal mean flow anomalies abstract the poleward propagation of zonal mean relative angular momentum mr anomalies is examined using ncep ncar reanalysis data for both the winter and summer seasons of the northern and southern hemisphere this analysis is performed with a regression analysis using base latitudes in the subtropics midlatitudes and high latitudes it is found that the poleward mr anomaly propagation occurs at all latitudes with the propagation speed being greater in the subtropics and high latitudes compared to midlatitudes other fields such as eddy angular momentum flux convergence eddy heat flux friction torque and 300 mb streamfunction are regressed for the northern hemisphere winter and the southern hemisphere summer the main finding is that in the subtropics and midlatitudes the poleward mr anomaly propagation is primarily due to high frequency 10 day transient eddy angular momentum flux convergence and in high latitudes the propagation is mostly due to the summation of cross frequency and low fr

carbon 13 carbon 12 ratios of sedimentary organic matter from the ross sea antarctica a record of phytoplankton bloom dynamics suspended and sea ice particulate organic carbon poc collected from the ross s 13 in r sea antarctica shows seasonal enrichments in c unrelated to at osphe ic pco2 varia tions the carbon isotopic composition of phytoplankton bloom related poc 5 3cpoc col lected from the southwestern ross sea during a 1992 bloom event is strongly correlated with poc concentration this correlation may be attributed to high growth rates species specific fractionation input from sea ice communities enriched in 3c increased heterotrophic recy cling or high rates of bloom related co2 aq drawdown in the upper water column while all these factors likely contribute to poc 3c enrichment we favor the latter hypothesis because of the link betweenc enrichment and partial isolation of the surface water co2 pool in ar eas of sea ice melt induced stratification of the upper water column the co2 drawdown hy pothesis is further supported by dissolved inorganic carbon 5 3c enrichments of up to 2 3 0 in the vicinity of phytoplankton blooms patterns of isotopic composition and organic carbon concentration in ross sea surface sediments resemble that of the upper water column par ticularly in areas of frequent annually recurrent phytoplankton blooms overall surface sediment 5 c values are 1 3 o enriched relative to surface water poc with the highest 5 3c values found in areas that receive large amounts of phytoplankton bloom detritus future downcore carbon isotopic analyses may prove useful as tracers of bloom dynamics in melt water influenced areas where large enrichments in 3c coincide with high productivity

wave zonal flow interaction and ultra low frequency variability in a simplified global circulation model the interactions between baroclinic waves and the zonal mean mid latitude flow are investigated using a multilevel primitive equation model of moderate resolution with idealized surface friction and diabatic heating terms integrations corresponding to 100 years were performed under perpetual solstice conditions empirical orthogonal function eof analyses were carried out on the zonal mean zonal wind u adjustments to the winter hemisphere zonal jet due to the growth and decay of baroclinic waves can be described in terms of the first two eof patterns which exhibit substantial interannual variability for a single lifecycle such adjustments take the form of a circuit of a phase space whose axes are defined by the amplitudes of the two eofs the cumulative effects of multiple lifecycles lead to a low frequency circulation in the phase space with a timescale of about 150 days we suggest that this effect may be intrinsically related to the internal generation of ultra low frequency variability in the model normal mode lifecycle calculations including dissipation reveal similar phase space properties the growth rates of normal mode disturbances are shown to be highly sensitive to the phase of the first eof

upper ocean nitrogen fluxes in the polar antarctic zone constraints from the nitrogen and oxygen isotopes of nitrate 1 we report nitrate nitrogen n and oxygen o isotope measurements from the seasonally sea ice covered polar antarctic zone paz south of the southern antarctic circumpolar front the 15n 14n and 18o 16o ratios of nitrate both increase into the summertime surface mixed layer in strong correlation with the upward decrease in nitrate concentration the expected result of nitrate assimilation by phytoplankton culture studies indicate that algal assimilation of nitrate fractionates the nitrate n and o isotopes equally while previous field studies suggest that nitrate n and o isotope behavior can be decoupled by euphotic zone nitrification our data for the paz show strong coupling of the dual isotopes of nitrate and a numerical model of antarctic summertime surface layer n cycling fits our observations including isotopic compositions of both nitrate and suspended particulate n if the nitrification rate is no more than 6 of the nitrate assimilation rate by phytoplankton the model estimates that the n isotope effect of nitrate assimilation is 5 0 0 7 this estimate lacks some of the uncertainties associated with previous studies within the antarctic circumpolar current and it is at the low end of most recent estimates from the southern ocean the range of which we speculatively attribute to an effect of mixed layer depth on the amplitude of isotope discrimination

sea ice control of plio pleistocene tropical pacific climate evolution marine proxies of sea surface temperature sst indicate that the tropical pacific thermal gradient intensified through the plio pleistocene and peaked during pleistocene glaciations the cause of this variability which has been linked to the initiation of the walker circulation is uncertain here we hypothesize that plio pleistocene tropical climate variability was coupled to high latitude southern hemisphere climate change specifically sea ice extent we use a coupled ocean atmosphere general circulation model to investigate the influences of sea ice extent and atmospheric co2 on the tropical pacific thermal structure in the model co2 radiative forcing in the absence of any sea ice feedbacks has little influence on the tropical sst gradient a 180 ppm reduction in co2 causes the sst gradient to decrease by 0 4 c in comparison an expansion of southern hemisphere high latitude sea ice reduces tropical ssts and enhances the sst gradient in the tropical pacific by as much as 3 5 c tropical cooling is primarily due to the advection and upwelling of waters into the eastern equatorial pacific that were cooled by sensible heat loss at the sea ice margin in the southern pacific an energy balance analysis indicates that the ocean heat flux into the eastern equatorial pacific decreases by 44 this mechanism provides an intimate coupling between the tropical pacific and the high latitude southern hemisphere through the thermocline circulation

polar stratification a critical view from the southern ocean oceanic stratification represents an effective mechanism to reduce vertical mixing of the water column thereby locking up carbon dioxide co2 in the deep sea and preventing air sea exchange of co2 it has been proposed that enhanced stratification of the upper water column in polar oceans during late cenozoic cooling episodes limited the upwelling of co2 rich deep waters and thus co2 release to the atmosphere resulting in a net global drawdown of atmospheric co2 increased stratification in the subarctic northwest pacific during both the onset of northern hemisphere glaciation at 2 73 ma and late quaternary glacial periods has been recently linked to enhanced ocean stratification south of the antarctic polar front apf in the pacific and atlantic sectors of the southern ocean increased stratification of southern ocean surface waters was mainly deduced from a reduction of biological production during these cooling episodes manifested by the decrease of geochemical proxies for productivity such as biogenic opal and barium in the marine sediment records however the records chosen from the southern ocean do not provide evidence for a more stratified upper water column rather the observed decrease in biological productivity is likely to have resulted from an expansion of annual sea ice coverage the sediment records suggest that south of the apf in the pacific and atlantic sectors of the southern ocean extensive sea ice may have contributed to the global co2 drawdown during glacial periods with hypothetical glacial increase of stratification in today s permanent open ocean zone merely being an add on caused by this expansion

deformation and permeability evolution of coals considering the effect of beddings abstract coal belongs to sedimentary rock with obvious bedding planes the existence of bedding weakens the continuity and integrity of coal deformation and permeability anisotropy of coals to a certain extent is attributed to the bedding planes we performed experiments of deformation and permeability evolution of coals under true triaxial stress conditions the experimental results indicate that the volumetric strain and bedding jointly affect permeability an analytical model for stress strain relationship of coals containing beddings is developed to quantify the bedding effects under true triaxial stress conditions in the model the deformation and permeability of the bedding and non bedding are separated through bedding ratio and bedding elastic modulus the bedding ratio is defined as the ratio of the total length of bedding to the total length of coal normal to bedding planes which is a parameter closely related to the porosity the elastic modulus is divided into four parts a bedding elastic modulus and a non bedding elastic modulus in the direction normal to bedding planes and two elastic moduli in the direction parallel to bedding planes the four elastic moduli are calculated by the analytical model the bedding elastic modulus is relatively small which shows that the bedding effect cannot be ignored the permeability is highly sensitive to the bedding of coal with low stress in the direction normal to the bedding the bedding ratio always affects the volumetric strain the permeability of the coal is divided into bedding and non bedding permeability the ratio of the bedding permeability to the total permeability is different due to different stresses in the direction normal to bedding planes which is linking with the compression of bedding a permeability model which can reflect the different effects of beddings and non beddings to the total permeability is proposed and verified

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

multiple zonal jets in a quasigeostrophic model of the antarctic circumpolar current abstract the presence of multiple zonal fronts in the antarctic circumpolar current acc a phenomenon described as zonation has been confirmed by many observations suggesting that the fronts are circumpolar in extent in the context of quasigeostrophic turbulence models panetta has shown that fronts associated with long lived zonal jets develop spontaneously in very wide baroclinically unstable regions of width large compared with the rossby radius of deformation the present paper examines the relevance of this mechanism to the zonation of the acc using a quasigeostrophic wind forced channel model multiple jets appear when the forcing scale is wide enough and they have horizontal scales and a strength that compares well with observations however in the presence of large scale random topography a different dynamical regime emerges in which the flow structure depends on the topographically controlled stationary eddies

modelling permeability for coal reservoirs a review of analytical models and testing data abstract as with other reservoir types permeability is a key controlling factor for gas migration in coalbed methane reservoirs the absolute permeability of coal reservoirs changes significantly during gas production often initially decreasing but then increasing as the reservoir pressure and gas content is drawn down it has also been observed to decrease markedly during co2 injection to enhance coalbed methane recovery in order to predict gas migration models for coal permeability must represent the mechanisms leading to these observed behaviours the permeability of coal reservoirs behaves in a similar fashion to other fractured reservoirs with respect to effective stress decreasing exponentially as the effective stress increases however a unique effect of coal is that it shrinks with gas desorption and swells with adsorption within the reservoir this swelling shrinkage strain leads to a geomechanical response changing the effective stress and thus the permeability modelling coal permeability incorporating the impacts from both effective stress and coal swelling shrinkage dates back about 25 years since then a number of permeability models have been developed in recent years this topic has seen a great deal of activity with a growing body of research on coal permeability behaviour and model development this article presents a review of coal permeability and the approaches to modelling its behaviour as an important part of this the field and laboratory data used to test the models are reviewed in detail this article also aims to identify some potential areas for future work

the pliocene paradox mechanisms for a permanent el nino during the early pliocene 5 to 3 million years ago globally averaged temperatures were substantially higher than they are today even though the external factors that determine climate were essentially the same in the tropics el nino was continual or permanent rather than intermittent the appearance of northern continental glaciers and of cold surface waters in oceanic upwelling zones in low latitudes both coastal and equatorial signaled the termination of those warm climate conditions and the end of permanent el nino this led to the amplification of obliquity but not precession cycles in equatorial sea surface temperatures and in global ice volume with the former leading the latter by several thousand years a possible explanation is that the gradual shoaling of the oceanic thermocline reached a threshold around 3 million years ago when the winds started bringing cold waters to the surface in low latitudes this introduced feedbacks involving ocean atmosphere interactions that along with ice albedo feedbacks amplified obliquity cycles a future melting of glaciers changes in the hydrological cycle and a deepening of the thermocline could restore the warm conditions of the early pliocene

horizontal stress anisotropy and effective stress as regulator of coal seam gas zonation in the sydney basin australia abstract coal seam gas zonation in the sydney basin nsw australia is related to basin hydrodynamics and hydrochemical facies evolution along the flow path from the subcrop to the basin center biogenic methane corresponds with meteoric water under hydrostatic pressure and persists down to the top of the geopressured zone 800 to 1000 m thermogenic gases including wet hydrocarbons can reach up to relatively shallow horizons of less than 500 600 m depth in the transition zone between the top of the geopressured and base of the hydrostatic zone a mixed water and gas regime prevails comprising brackish waters and gases of mixed biogenic thermogenic and inorganic origins including co 2 mechanisms for and the role of stress in the development of this layered hydrogeological and gas environment are investigated in this paper the inverse relationship between effective horizontal stress and permeability in coals through regulation of cleat volumes is well documented and there is evidence of regionally compartmentalized stress regimes with depth within the sydney and other eastern australian coal basins this regional stress regime can be overprinted by the effect of localized geological features it is hypothesized that the in situ stress regime plays an important role in the regulation of groundwater flow regimes and extents resulting in the development of the reported gas content and compositional zonation analysis of regional gas and stress data obtained from public and private databases as well as literature supports this hypothesis changes in gas concentration and composition with depth correspond with discernable variations in horizontal stress anisotropy gas contents generally increase with depth down to a peak gas horizon below which concentrations decrease this peak gas zone is coincident with a horizontal stress anisotropy change from moderately high to low levels associated with reverse to strike slip faulting conditions respectively the stress release zone also marks the top of the thermogenic gas zone identified by the first appearance of ethane in the vertical profile this zone also hosts gases of mixed origins biogenic thermogenic and inorganic co 2 and represents a mixed transitional groundwater flow environment the base of the mixed gas zone is the top of the geopressured only flow associated with thermogenic gases and is signaled by the return to high stress reverse faulting conditions below 850 900 m depth in the sydney basin

the contribution of orbital forcing to the progressive intensification of northern hemisphere glaciation in this study we reconstruct the timing of the onset of northern hemisphere glaciation this began in the late miocene with a significant build up of ice on southern greenland however progressive intensification of glaciation did not begin until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia were glaciated at approximately 2 74 ma 40 ka before the glaciation of alaska 2 70 ma and about 200 ka before significant glaciation of the north east american continent 2 54 ma we also review the suggested causes of northern hemisphere glaciation tectonic changes such as the uplift of the himalayan and tibetan plateau the deepening of the bering strait and the emergence of the panama isthmus are too gradual to account entirely for the speed of northern hemisphere glaciation we therefore postulate that tectonic changes may have brought global climate to a critical threshold but the relatively rapid variations in the earth s orbital parameters and thus insolation triggered the intensification of northern hemisphere glaciation this theory is supported by computer simulations which despite the relative simplicity of the model and the approximation of some factors e g using a linear carbon dioxide scenario neglecting the geographical difference between the pliocene and the present suggest that it is possible to build up northern hemisphere ice sheets between 2 75 and 2 55 ma by varying only the insolation controlled by the orbital parameters c 1998 elsevier science ltd all rights reserved

subpolar link to the emergence of the modern equatorial pacific cold tongue the cold upwelling tongue of the eastern equatorial pacific is a central energetic feature of the ocean dominating both the mean state and temporal variability of climate in the tropics and beyond recent evidence for the development of the modern cold tongue during the pliocene pleistocene transition has been explained as the result of extratropical cooling that drove a shoaling of the thermocline we have found that the sub antarctic and sub arctic regions underwent substantial cooling nearly synchronous to the cold tongue development thereby providing support for this hypothesis in addition we show that sub antarctic climate changed in its response to earth s orbital variations from a subtropical to a subpolar pattern as expected if cooling shrank the warm water sphere of the ocean and thus contracted the subtropical gyres

antarctic and southern ocean influences on late pliocene global cooling the influence of antarctica and the southern ocean on late pliocene global climate reconstructions has remained ambiguous due to a lack of well dated antarctic proximal paleoenvironmental records here we present ice sheet sea surface temperature and sea ice reconstructions from the andrill and 1b sediment core recovered from beneath the ross ice shelf we provide evidence for a major expansion of an ice sheet in the ross sea that began at 3 3 ma followed by a coastal sea surface temperature cooling of 2 5 c a stepwise expansion of sea ice and polynya style deep mixing in the ross sea between 3 3 and 2 5 ma the intensification of antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation the associated northward migration of southern ocean fronts has been linked with reduced atlantic meridional overturning circulation by restricting surface water connectivity between the ocean basins with implications for heat transport to the high latitudes of the north atlantic while our results do not exclude low latitude mechanisms as drivers for pliocene cooling they indicate an additional role played by southern high latitude cooling during development of the bipolar world

deformation metamorphism of bituminous and anthracite coals from china abstract tectonic displacement of coal seams in china has resulted in faulting parallel to coal bedding displacement along these faults caused significant comminution of the coal on the footwall contributing to various mining problems the worst of which is catastrophic failure or outbursting of the working face during mining the granular texture and mostly unconsolidated nature of the coal suggests that faulting occurred relatively late in the coalification sequence at a time of maximum tectonic stress coal samples taken on either side of the fault plane normal and deformed coal layers were obtained in an effort to establish what influence these tectonic stresses might have had on coal properties as well as what they might reveal about the influence of tectonic pressure on organic maturity sample sets were collected within coal beds from undisturbed and adjacent deformed layers including 21 bituminous samples from the pingdingshan coal field and nine anthracite samples from the jiaozuo coal field the tieshenggou coal mine of the yuxi coal field in henan province the beijing xishan coal field the baijiao mine of the furong coal field in sichuang province and the baisha coal field in hunan province china results from vitrinite reflectance proximate and ultimate analyses show some differences in reflectance hydrogen content and nitrogen content of anthracite coal no significant difference was found between volatile matter yields of normal and deformed coal specimens gc measurements of the saturated hydrocarbon fraction of chloroform extracts from bituminous coals showed that lower molecular weight carbon fragments were concentrated in the deformed samples therefore although changes in the gross chemical properties of the deformed coal were insignificant some modification of the chemical structure is seen to have occurred as a result of exposure to tectonic pressure

departures from eustasy in pliocene sea level records estimates for sea level three million years ago a period with similar atmospheric co2 levels to today vary from 10 to 40 m above present glacial isostatic adjustment modelling suggests that variations in the height of palaeoshorelines result from the residual adjustment of continental flexure following recent glaciations

holocene southern ocean surface temperature variability west of the antarctic peninsula the antarctic peninsula is currently one of the fastest warming locations on earth but its long term variability has remained unclear amelia shevenell and colleagues now use the tex86 proxy a palaeothermometer that tracks membrane lipids of the marine picoplankton crenarchaeota to show that a long term cooling of about 4 c occurred in waters near the tip of antarctic peninsula over the past 12 000 years this is consistent with orbitally controlled changes in insolation shorter term variability in temperature seems to have been strongly influenced by the position of the westerly winds this work suggests that the present influence of the el nino southern oscillation system on the antarctic peninsula is a relatively recent phenomenon dating to the late holocene the antarctic peninsula is currently one of the fastest warming locations on earth but its long term variability has remained unclear this study uses tex86 sea surface temperature proxy evidence to show that a long term cooling of about 3 4 c occurred in waters near the tip of the antarctic peninsula over the past 12 000 years consistent with orbitally controlled changes in insolation shorter term variability in temperature at the antarctic peninsula appears to have been strongly influenced by the position of westerly winds the present influence of the el nino southern oscillation system on the antarctic peninsula may have arisen only during the late holocene the disintegration of ice shelves reduced sea ice and glacier extent and shifting ecological zones observed around antarctica1 2 highlight the impact of recent atmospheric3 and oceanic warming4 on the cryosphere observations1 2 and models5 6 suggest that oceanic and atmospheric temperature variations at antarctica s margins affect global cryosphere stability ocean circulation sea levels and carbon cycling in particular recent climate changes on the antarctic peninsula have been dramatic yet the holocene climate variability of this region is largely unknown limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms here we show that surface ocean temperatures at the continental margin of the western antarctic peninsula cooled by 3 4 c over the past 12 000 years tracking the holocene decline of local 65 s spring insolation our results based on tex86 sea surface temperature sst proxy evidence from a marine sediment core indicate the importance of regional summer duration as a driver of antarctic seasonal sea ice fluctuations7 on millennial timescales abrupt sst fluctuations of 2 4 c coincide with globally recognized climate variability8 similarities between our ssts southern hemisphere westerly wind reconstructions9 and el nino southern oscillation variability10 indicate that present climate teleconnections between the tropical pacific ocean and the western antarctic peninsula11 strengthened late in the holocene epoch we conclude that during the holocene southern ocean temperatures at the western antarctic peninsula margin were tied to changes in the position of the westerlies which have a critical role in global carbon cycling9 12

the biogeography of major diatom taxa in southern ocean surface sediments 3 tropical subtropical species abstract this paper gives a modern circumscription of tropical subtropical diatoms regarding their relationship with sea surface temperatures sst and sea ice cover diatoms from 228 core top sediment samples collected from the southern ocean were studied to determine the geographic distribution of eight major diatom species taxa preserved in surface sediments generally located north of the subantarctic front the comparison of the relative contribution of diatom species with modern february sst and sea ice cover reveals species specific sedimentary distributions regulated both by water temperatures and sea ice conditions although selective preservation might have played some role their presence in surface and downcore sediments from the southern ocean are reliable indicators of high sst and poleward transport of waters from the tropical subtropical atlantic our work supports the use of diatom remains to reconstruct past variations of these environmental parameters via qualitative and transfer function approaches

late neogene history of deepwater ventilation in the southern ocean we compiled carbon isotope records from the north atlantic south atlantic and pacific oceans to estimate changes in vertical and interbasinal 13c gradients for the last 9 myr benthic 13c values of deep water in the south atlantic decreased in a series of steps at 7 2 75 and 1 55 ma away from the north atlantic and toward the pacific the benthic 13c of intermediate water in the south atlantic evolved differently from deep waters resulting in an increase in the intermediate to deep 13c gradient 13cid the 13cid increased in steps at 2 75 and 1 55 ma marking the development and intensification of a chemical divide in the atlantic ocean between well ventilated intermediate water and poorly ventilated deep water we suggest these changes in interbasinal and vertical gradients resulted from decreasing northern component water and reduced ventilation of southern component water scw the latter was caused by several interrelated processes in antarctic sources areas including increased sea ice cover enhanced surface water stratification decreased ekman induced upwelling and reduced vertical mixing across the thermocline because antarctic surface water processes and deepwater ventilation rates ultimately influence atmospheric co2 concentration these processes may have acted as a positive feedback that contributed to the major cooling steps in late neogene climate

past hydrographic and climatic changes in the subantarctic zone of the south atlantic the pleistocene record from odp site 1090 abstract pleistocene summer sea surface temperatures ssst have been reconstructed on a composite core section recovered in the subantarctic zone of the southern ocean from planktonic foraminifers applying the modern analog technique the composite consists of core ps2489 2 and the sections recovered at odp site 1090 and documents the last 1 83 ma three distinct climatic periods can be identified that mirror the pleistocene development of the southern ocean hydrography cold climatic conditions prevailed at 43 s during glacial as well as during interglacial periods during the early pleistocene 1 83 0 87 ma indicating a northward shift of isotherms that characterize the present day polar front zone by about 7 of latitude evidence shows a strong linkage between southern ocean and low latitude climate during that interval time between the mid pleistocene revolution ca 0 9 ma and the mid brunhes event ca 0 4 ma we observe higher amplitude fluctuations in the ssst between glacial and interglacial periods corresponding to the temperature range between the present polar front and subantarctic front these climatic variations have been related to changes in the northern hemisphere ice sheets the past 0 4 ma are characterized by strong ssst variations of up to 8 c between glacials and interglacials only during the climatic optima stages 11 3 9 3 7 5 7 1 5 5 and the early holocene ssst exceeded present ssst at the core locality 10 2 c although the carbonate dissolution record exhibits high variability during the pleistocene it can be shown that ssst estimates were not significantly biased the mid brunhes dissolution cycle as well as the mid pleistocene enhanced carbonate preservation appear to belong to a global long term variability in carbonate preservation

major neogene fluctuations of the east antarctic ice sheet stratigraphic evidence from the lambert glacier region stratigraphic and sedimentological data are presented from a region likely to directly record the evolution of the east antarctic ice sheet along the western margin of the lambert graben which now drains 1 106 km2 or one eighth of the total area of the east antarctic ice sheet extensive remnants of cenozoic glaciomarine fjordal sediment known as the pagodroma group are preserved as far as several hundred kilometers inland from the open coast the sediments resemble those produced by tidewater glaciers in the arctic rather than those of modern antarctica four separate formations of the pagodroma group spanning the interval from early miocene or older to pliocene or early pleistocene are preserved the oldest and highest crop out at nearly 1500 m above sea level each formation was deposited in close proximity to an ice margin grounded on the fjord bottom during major recessional phases of the lambert glacier underlying each formation is a glacially cut erosion surface each surface records a separate stage of fjord excavation when ice expanded onto the continental shelf in prydz bay evidence from offshore drilling in prydz bay and these data indicate fluctuations of the lambert glacier terminus in excess of 500 km in neogene time thereby reflecting large changes in the volume of the ice sheet depositional episodes were succeeded by phases of uplift totalling more than 1500 m

modelling west antarctic ice sheet growth and collapse through the past five million years changes in earth s orbit are known to influence climate shifts from cold glacials to warm interglacials how the vast west antarctic ice sheet responds to these fluctuations is uncertain but because its collapse could raise sea levels by about 5 metres of great interest naish et al have analysed the and 1b ocean sediment core extracted from beneath the ross ice shelf as part of the andrill drilling project and find evidence that the ice sheet collapsed periodically during the early pliocene 3 5 million years ago when atmospheric co2 levels were similar to or slightly higher than today s the pattern of collapse suggests an influence of approximately 40 000 year cycles in the tilt of earth s rotational axis obliquity also in this issue of nature in a numerical modelling study focused on the past 5 million years in antarctica david pollard and robert deconto combine ice sheet land supported and ice shelf water supported modelling approaches to simulate the movement of the grounding line the border between land and sea ice their results show that over the past 5 million years the west antarctic ice sheet transitioned between full intermediate and collapsed states in just a few thousand years this means that the ice sheet is likely to disintegrate if ocean temperatures in the area rise by 5 c if the west antarctic ice sheet wais melted sea levels would rise by about 5 m such changes are thought to have occurred in the past but could not be simulated by models pollard and deconto combine ice sheet with ice shelf modelling and show that over the past 5 million years the wais transitioned among full intermediate and collapsed states in only a few thousand years suggesting possible disintegration of the wais if ocean temperatures in the area rise by 5 c the west antarctic ice sheet wais with ice volume equivalent to 5 m of sea level1 has long been considered capable of past and future catastrophic collapse2 3 4 today the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams grounding lines are several hundred metres below sea level and the bed deepens upstream raising the prospect of runaway retreat3 5 projections of future wais behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms6 7 its variation since the last glacial maximum is best known with grounding lines advancing to the continental shelf edges around 15 kyr ago before retreating to near modern locations by 3 kyr ago8 prior collapses during the warmth of the early pliocene epoch9 and some pleistocene interglacials have been suggested indirectly from records of sea level and deep sea core isotopes and by the discovery of open ocean diatoms in subglacial sediments10 until now11 however little direct evidence of such behaviour has been available here we use a combined ice sheet ice shelf model12 capable of high resolution nesting with a new treatment of grounding line dynamics and ice shelf buttressing5 to simulate antarctic ice sheet variations over the past five million years modelled wais variations range from full glacial extents with grounding lines near the continental shelf break intermediate states similar to modern and brief but dramatic retreats leaving only small isolated ice caps on west antarctic islands transitions between glacial intermediate and collapsed states are relatively rapid taking one to several thousand years our simulation is in good agreement with a new sediment record andrill and 1b recovered from the western ross sea11 indicating a long term trend from more frequently collapsed to more glaciated states dominant 40 kyr cyclicity in the pliocene and major retreats at marine isotope stage 31 1 07 myr ago and other super interglacials

upwelling intensification as part of the pliocene pleistocene climate transition a deep sea sediment core underlying the benguela upwelling system off southwest africa provides a continuous time series of sea surface temperature sst for the past 4 5 million years our results indicate that temperatures in the region have declined by about 10 c since 3 2 million years ago records of paleoproductivity suggest that this cooling was associated with an increase in wind driven upwelling tied to a shift from relatively stable global warmth during the mid pliocene to the high amplitude glacial interglacial cycles of the late quaternary these observations imply that atlantic ocean surface water circulation was radically different during the mid pliocene

early pliocene increase in thermohaline overturning a precondition for the development of the modern equatorial pacific cold tongue unraveling the processes responsible for earth s climate transition from an el nino like state during the warm early pliocene into a modern like la nina dominated state currently challenges the scientific community recently the pliocene climate switch has been linked to oceanic thermocline shoaling at 3 million years ago along with earth s final transition into a bipolar icehouse world here we present pliocene proxy data and climate model results which suggest an earlier timing of the pliocene climate switch and a different chain of forcing mechanisms we show that the increase in north atlantic meridional overturning circulation between 4 8 and 4 0 million years ago initiated by the progressive closure of the central american seaway triggered overall shoaling of the tropical thermocline this preconditioned the turnaround from a warm eastern equatorial pacific to the modern equatorial cold tongue state about 1 million years earlier than previously assumed since 3 6 3 5 million years ago the intensification of northern hemisphere glaciation resulted in a strengthening of the trade winds thereby amplifying upwelling and biogenic productivity at low latitudes

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

a mechanism for the poleward propagation of zonal mean flow anomalies abstract observational studies have shown that tropospheric zonal mean flow anomalies frequently undergo quasi periodic poleward propagation a set of idealized numerical model runs is examined to investigate the physical mechanism behind this poleward propagation this study finds that the initiation of the poleward propagation is marked by the formation of negative zonal wind anomalies in the tropics these negative anomalies arise from meridional overturning breaking of waves that originate in midlatitudes this wave breaking homogenizes the potential vorticity pv within the region of negative zonal wind anomalies and also leads to the formation of positive zonal wind anomalies in the subtropics subsequent equatorward radiation of midlatitude waves is halted which results in wave breaking at the poleward end of the homogenized pv region this in turn generates new positive and negative zonal wind anomalies which enables a continuation of the poleward propagation the shielding of the homogenized

southern ocean dust climate coupling over the past four million years dust plays a central part in ocean biogeochemical cycles by supplying iron and other essential micronutrients to regions where marine productivity is limited by the availability of iron martinez garcia et al present a marine record of dust and iron supply to the southern ocean during the past four million years the data derived from leaf waxes establish that previous records of dust flux from antarctic ice cores are broadly representative of a larger area importantly the dust and iron supply rose sharply 1 25 million years ago suggesting that increased dust supply may be a major influence on the more severe swings between the glacial and interglacial climate of the late pleistocene dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean1 2 indeed dust supply to the southern ocean increases during ice ages and iron fertilization of the subantarctic zone may have contributed up to 40 parts per million by volume p p m v of the decrease 80 100 p p m v in atmospheric carbon dioxide observed during late pleistocene glacial cycles3 4 5 6 7 so far however the magnitude of southern ocean dust deposition in earlier times and its role in the development and evolution of pleistocene glacial cycles have remained unclear here we report a high resolution record of dust and iron supply to the southern ocean over the past four million years derived from the analysis of marine sediments from odp site 1090 located in the atlantic sector of the subantarctic zone the close correspondence of our dust and iron deposition records with antarctic ice core reconstructions of dust flux covering the past 800 000 years refs 8 9 indicates that both of these archives record large scale deposition changes that should apply to most of the southern ocean validating previous interpretations of the ice core data the extension of the record beyond the interval covered by the antarctic ice cores reveals that in contrast to the relatively gradual intensification of glacial cycles over the past three million years southern ocean dust and iron flux rose sharply at the mid pleistocene climatic transition around 1 25 million years ago this finding complements previous observations over late pleistocene glacial cycles5 8 9 providing new evidence of a tight connection between high dust input to the southern ocean and the emergence of the deep glaciations that characterize the past one million years of earth history

sensitivity of pliocene ice sheets to orbital forcing the stability of the earth s major ice sheets is a critical uncertainty in predictions of future climate and sea level change one method of investigating the behaviour of the greenland and the antarctic ice sheets in a warmer than modern climate is to look back at past warm periods of earth history for example the pliocene this paper presents climate and ice sheet modelling results for the mid pliocene warm period mpwp 3 3 to 3 0 million years ago which has been identified as a key interval for understanding warmer than modern climates jansen et al 2007 using boundary conditions supplied by the united states geological survey prism group pliocene research interpretation and synoptic mapping the hadley centre coupled ocean atmosphere climate model hadcm3 and the british antarctic survey ice sheet model basism we show large reductions in the greenland and east antarctic ice sheets gris and eais compared to modern in standard mpwp experiments we also present the first results illustrating the variability of the ice sheets due to realistic orbital forcing during the mid pliocene while gris volumes are lower than modern under even the most extreme cold mid pliocene orbit losing at least 35 of its ice mass the eais can both grow and shrink losing up to 20 or gaining up to 10 of its present day volume the changes in ice sheet volume incurred by altering orbital forcing alone means that global sea level can vary by more than 25 m during the mid pliocene however we have also shown that the response of the ice sheets to mpwp orbital hemispheric forcing can be in anti phase whereby the greatest reductions in eais volume are concurrent with the smallest reductions of the gris if this anti phase relationship is in operation throughout the mpwp then the total eustatic sea level response would be dampened compared to the ice sheet fluctuations that are theoretically possible this suggests that maximum eustatic sea level rise does not correspond to orbital maxima but occurs at times where the anti phasing of northern and southern hemisphere ice sheet retreat is minimised

experimental investigation of mechanical properties of bedded salt rock abstract because of salt cavern utilization for liquid gas and solid waste storage salt rock mechanical properties are needed for assessments of facility stability and safety bedded salt deposits are widespread and used as much or more than diapiric salt bodies as storage facility hosts but experimental data on the mechanical properties of bedded salt rock with impurities are far less common than data available on relatively pure diapiric salt rocks through laboratory uniaxial and triaxial compression experiments on rock salt halite interlayers anhydrite and bedded composite specimens anhydrite halite and mudstone halite differences in mechanical properties of the various lithologies are explored in the composite specimens the weakest or the most deformable component governs the behavior also the properties of bedded composite lithology specimens tend to be in between the property ranges of the pure lithologies the elastic modulus of the bedded salt rock increases from 5 3 to 24 1 gpa with an increase in the confining stress from 0 to 15 mpa with some evidence of sample damage the ductile transition for halite at the strain rates used is at about 3 10 mpa with increasing 3 the anhydrite halite composite lithology deformation showed strain hardening and a strong trend to ductile behavior as the halite bands tended to dominate the behavior strain incompatibility effects exist along interfaces between creeping and non creeping phases in anhydrite halite composite lithologies mudstone halite rocks tended to be extremely weak compared with all other specimens