the role of carbon dioxide during the onset of antarctic glaciation earth s modern climate characterized by polar ice sheets and large equator to pole temperature gradients is rooted in environmental changes that promoted antarctic glaciation 33 7 million years ago onset of antarctic glaciation reflects a critical tipping point for earth s climate and provides a framework for investigating the role of atmospheric carbon dioxide co2 during major climatic change previously published records of alkenone based co2 from high and low latitude ocean localities suggested that co2 increased during glaciation in contradiction to theory here we further investigate alkenone records and demonstrate that antarctic and subantarctic data overestimate atmospheric co2 levels biasing long term trends our results show that co2 declined before and during antarctic glaciation and support a substantial co2 decrease as the primary agent forcing antarctic glaciation consistent with model derived co2 thresholds

the foreslope and toe of slope facies of the middle triassic latemar buildup dolomites northern italy abstract the latemar buildup was a circular carbonate buildup 4 km wide with a central platform core flat bedded interior platform and massive reef margin flanked on all sides by slope facies steeply dipping 30 35 foreslope breccias are present adjacent to the margin and flat lying graded grainstones at the toe of slope slope facies relate directly to depositional profile and slope angle the steeply dipping foreslopes consist of lobate breccia beds that are 25 m thick and a few tens of meters across and extend tens to hundreds of meters downslope some beds are conformably overlain by thinner 1 m thick beds of finer grained carbonate sediment the basal surfaces of the breccias are erosional and are anastamosing in both strike and dip views the breccia rains was derived principally from margin boundstones and deposited by rockfalls and avalanches planar clinoforms extend the entire height of the foreslope hundreds of meters and bracket depositional units clinothems tens of meters thick clinoforms appear to be shear surfaces formed during large slope failures avalanches graded grainstone beds less than 1 m thick are present at the nearly flat lying toe of slope these consist of redeposited shallow water platform interior and reef margin carbonate sands some with nodular limestone caps that are interpreted as proximal carbonate turbidites toe of slope breccias are the downdip extensions of foreslope breccias and pinch out abruptly basinward some slope depositional processes are related to high frequency fourth order and fifth order sea level changes toe of slope graded grainstones correspond to times of platform submergence in contrast foreslope breccia was deposited during both platform submergence and exposure the slope deposits do not record the high frequency cyclic rhythms identified in shallow water platform sections this is attributed to the nature of slope deposition downslope talus transport was episodic and localized graded grainstone beds reflect storm redeposition

the carbonate factory of middle triassic buildups in the dolomites italy a quantitative analysis middle triassic carbonate buildups of the dolomites were high in relief 500 1000m and small in size one to a few square kilometres in area a paradox results from the carbonate platform model that invokes the platform top including reef rims as the carbonate factory and flanking beds as talus deposits most buildups consist largely of clinoforms inclined at 10 50 whereas massive reef rocks and stratified buildup interiors are poorly developed or absent facies and modal analysis of 323 thin sections from buildups of the marmolada indicate that clinoforms are i predominantly composed of in situ boundstones 56 of all samples ii primarily made up of early cements 37 vol microbial crusts 17 vol micritic intraclasts 10 vol and tubiphytes 8 vol and iii contain diagnostic shallow water grains dasyclads coated grains that are less abundant by 1 2 orders of magnitude compared with buildup interior facies these data suggest that the clinoforms themselves were the main carbonate factory of the triassic buildups stratified buildup interior rocks and massive reef rocks were apparently not a prerequisite for buildup growth and clinoform progradation

transition from the cretaceous ocean to cenozoic circulation in the western south atlantic a twofold reconstruction abstract the cretaceous oceanic circulation has been quite different from the modern with a different distribution of the continents on the globe this has resulted in a much lower temperature gradient between poles and equator we have studied seismic reflection data and used numerical simulations of atmosphere and ocean dynamics to identify important steps in modifications of the oceanic circulation in the south atlantic from the cretaceous to the cenozoic and the major factors controlling them starting in the albian we could not identify any traces of an overturning circulation for the south atlantic although a weak proto antarctic circumpolar current acc was simulated no change in circulation was observed for the paleocene early eocene south atlantic which indicated that this period has witnessed a circulation similar to the albian and cenomanian turonian circulation the most drastic modifications were observed for the eocene oligocene boundary and the oligocene early miocene with the onset of an acc and atlantic meridional overturning circulation amoc and hence southern sourced deep and bottom water masses in the western south atlantic a modern amoc which intensified in strength after closure of the central american seaway cas and a strong acc have resulted in current controlled sedimentary features and wide spread hiatusses in the south atlantic since the middle miocene the opening of drake passage in early oligocene times and the closure of the cas at 6 ma i e tectonic processes have been identified as the key triggers for the observed most severe changes in oceanic circulation in the south atlantic

effects of drake passage on a strongly eddying global ocean the climate impact of ocean gateway openings during the eocene oligocene transition is still under debate previous model studies employed grid resolutions at which the impact of mesoscale eddies has to be parameterized we present results of a state of the art eddy resolving global ocean model with a closed drake passage and compare with results of the same model at noneddying resolution an analysis of the pathways of heat by decomposing the meridional heat transport into eddy horizontal and overturning circulation components indicates that the model behavior on the large scale is qualitatively similar at both resolutions closing drake passage induces i sea surface warming around antarctica due to equatorward expansion of the subpolar gyres ii the collapse of the overturning circulation related to north atlantic deep water formation leading to surface cooling in the north atlantic and iii significant equatorward eddy heat transport near antarctica however quantitative details significantly depend on the chosen resolution the warming around antarctica is substantially larger for the noneddying configuration 5 5 c than for the eddying configuration 2 5 c this is a consequence of the subpolar mean flow which partitions differently into gyres and circumpolar current at different resolutions we conclude that for a deciphering of the different mechanisms active in eocene oligocene climate change detailed analyses of the pathways of heat in the different climate subsystems are crucial in order to clearly identify the physical processes actually at work

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

environmental control on granular clinoforms of ancient carbonate shelves the purpose of this paper is to document the influence of depositional environments on shallow water low relief clinoforms from the description of five ancient carbonate platforms the neoproterozoic namibia middle jurassic france lower cretaceous france upper cretaceous oman and miocene turkey these examples have been investigated on the basis of field observations the clinoforms are described with reference to geometric and compositional attributes declivity shape height sedimentary structures sediment fabric and components the results show great variability in stratal geometry declivity and facies distribution 1 depositional profiles vary from exponential to sigmoidal to oblique 2 maximal slope angles range from 3 to 25 most of them being grouped between 10 and 18 3 facies differentiation identified from lateral facies successions along beds and vertical facies successions through beds is pronounced to subtle this study documents linkages between depositional environments and clinoform attributes proximal shallow clinoforms display round edged exponential profiles sediment deposition has resulted from unidirectional currents in the upper convex section and storm generated oscillatory currents in the lower concave part the sediment fabric changes gradually along this type of clinoform there is little vertical facies differentiation through these clinobeds which have formed from a continuous amalgamation of deposits by contrast distal clinoforms shelf break distally steepened ramp settings yield a much broader spectrum of profiles and are generally shorter and steeper sedimentary structures in gravel sized deposits of the upper slope indicate pure traction by unidirectional currents conversely marks of oscillatory flows undular wavy top bounding surfaces of clinobeds are common in the lower slope intercalation of massive fine grained deposits suggests offshore transport of carbonate mud by suspension each distal clinobed represents a single flow event accordingly facies differentiation is weak laterally but may be pronounced through the clinobeds our study suggests that low relief forms of proximal shallow environments which contain coarse grained and photo independently produced debris record hydrodynamic equilibrium profiles whereas the higher relief forms of this setting rather reflect a high differential production rate of carbonate sediment with water depth the carbonate sediment of the distal clinobeds mainly derives from skeletal production by oligophotic and photo independent biota of the middle shelf ramp and upper portion of the clinoforms the contribution by in situ skeletal biota only becomes significant on the lower slope indicating that the distal submerged slopes of carbonate platforms are not organically but hydrodynamically generated our compilation shows that the slope angles of shallow marine low relief clinoforms do not simply correlate to the sediment grain size and fabric in contrast to what has been documented for the high linear slope profiles this difference stems from the depositional settings namely the involved transport mechanisms low relief clinoform accretion seems to be dominantly influenced by wave induced sediment transport in contrast to linear flanks of high relief clinoforms that build to the angle of repose and for which gravity is the primary transport process

impact of antarctic circumpolar current development on late paleogene ocean structure global cooling and the development of continental scale antarctic glaciation occurred in the late middle eocene to early oligocene 38 to 28 million years ago accompanied by deep ocean reorganization attributed to gradual antarctic circumpolar current acc development our benthic foraminiferal stable isotope comparisons show that a large 13c offset developed between mid depth 600 meters and deep 1000 meters western north atlantic waters in the early oligocene indicating the development of intermediate depth 13c and o2 minima closely linked in the modern ocean to northward incursion of antarctic intermediate water at the same time the ocean s coldest waters became restricted to south of the acc probably forming a bottom ocean layer as in the modern ocean we show that the modern four layer ocean structure surface intermediate deep and bottom waters developed during the early oligocene as a consequence of the acc

progradation geometries of carbonate platforms examples from the triassic of the dolomites northern italy various types of progradation of triassic carbonate platforms are described from the dolomites of the southern alps the internal and external geometric relationships are exposed in spectacular natural sections and moreover their scale 500 1000 m of thickness is such that they can be compared with features found in seismic profiles the different types of progradation are controlled by a number of factors which normally interact with each other these factors include rate of basinal sedimentation rate of subsidence width of the platform depth of the surrounding basin and eustatic variations of sea level progradation is not a continuous process but episodic moments of massive debris input during which the platform advances alternate with long periods of negligible progradation during which basinal sediments accrete and onlap the toe of slope upper boundary relationships of the prograding platforms include offlap toplap and erosional truncation lower boundary relationships are horizontal climbing and descending progradations a variety of phenomena and circumstances have caused the cessation of progradation of the triassic platforms they include volcanism collapse of margins drowning rapid relative rise of sea level subaerial exposure relative fall of sea level and probably a natural decay of the system in the triassic of the dolomites two main progradation models can be put forward in the ladinian model progradation took place simultaneously with aggradation relative rise of sea level whereas the characteristic feature of the carnian model is toplap relative stillstand of sea level

atmospheric and oceanic impacts of antarctic glaciation across the eocene oligocene transition the glaciation of antarctica at the eocene oligocene transition approx 34 million years ago was a major shift in the earth s climate system but the mechanisms that caused the glaciation and its effects remain highly debated a number of recent studies have used coupled atmosphere ocean climate models to assess the climatic effects of antarctic glacial inception with often contrasting results here using the hadcm3l model we show that the global atmosphere and ocean response to growth of the antarctic ice sheet is sensitive to subtle variations in palaeogeography using two reconstructions representing eocene and oligocene geological stages the earlier stage eocene priabonian which has a relatively constricted tasman seaway shows a major increase in sea surface temperature over the pacific sector of the southern ocean in response to the ice sheet this response does not occur for the later stage oligocene rupelian which has a more open tasman seaway this difference in temperature response is attributed to reorganization of ocean currents between the stages following ice sheet expansion in the earlier stage the large ross sea gyre circulation decreases in size stronger zonal flow through the tasman seaway allows salinities to increase in the ross sea deep water formation initiates and multiple feedbacks then occur amplifying the temperature response this is potentially a model dependent result but it highlights the sensitive nature of model simulations to subtle variations in palaeogeography and highlights the need for coupled ice sheet climate simulations to properly represent and investigate feedback processes acting on these time scales

the tectonic history of drake passage and its possible impacts on global climate this study provides an integrated review of plate tectonic models of the evolution of the antarctica patagonia connection compared to geological records collected on land in patagonia and tierra del fuego and offshore along the northern edge of the scotia sea a temporal framework for the sedimentary and tectonic events of the north scotia ridge and tierra del fuego is constructed with additional data compiled from entire patagonia and the austral basin this review provides robust correlations of seaways and tectonic events along the scotia and south america plates and indicates that the opening of the drake passage was not steady state since ca 30 ma rather the regions forming the present day northern limit of this gateway experienced important paleogeographic changes from deep marine basins to shallow ridges and emerged regions during the late oligocene and early middle miocene time our compilation of geological data shows that emergence along the north scotia ridge and tierra del fuego was achieved at 23 22 ma and has been followed by elimination of the patagoniano sea in patagonia starting at 22 23 ma and achieved at 20 ma this transition towards more continental sedimentation in southern south america is correlated with more shallow marine conditions in the austral basin this succession of events had a strong influence on the general geometry of the drake passage corresponding to a constriction of its northern limit starting in the window 29 22 ma and achieved at 21 ma this period of active deformation in southern south america also corresponds to a period of the global climate having two anomalies well known from the isotopic records the late oligocene warming around 26 ma and the mid miocene climatic optimum which ended between 15 and 14 ma the possible effects of the post oligocene tectonic evolution of the drake passage region on general oceanic circulation are discussed causes for the synchronicity between tectonic events and these global warming events are examined

cenomanian early turonian carbonate platform of northern oman stratigraphy and palaeo environments abstract the jebel akhdar and adam foothills outcrops in northern oman arabian peninsula offer the opportunity to study in detail the lateral and vertical changes of a cenomanian early turonian carbonate platform formed by the natih formation wasia group eleven sections with less than 5 km offset were logged to express metre scale lithological and biostratigraphical vertical changes the first rudist zonation is established complementing classical benthonic foraminifer and ammonite biozones typical cenomanian rudist association caprinids and radiolitids occur in the natih e c d a lower part whereas lower turonian hippuritid rudists are represented in the upper part of the natih a a sedimentological and palaeoecological approach leads to identification and interpretation the facies and discontinuities of the natih carbonate platform and to a reconstruction of its spatial organization application of the concepts of sequence stratigraphy allows interpretation of the units of the natih in terms of systems tracts an attempt is made to correlate the sequence stratigraphical model to eustatic sea level changes and regional tectonic events three palaeoenvironmental models taking into account bio and lithofacies are proposed

mathematical model of a hot dry rock system summary we derive a mathematical model which can be used to determine the evolution of the temperature in a hot dry rock system the essential feature of this approach is given by the fact that the solution is available by analytical methods therefore long term predictions of the evolution of the temperature as well as a detailed study concerning the influence of critical parameters become available although this approach is based on simplifying hypotheses it provides a good overview of the evolution of the temperature in a hot dry rock system which can be used for efficiency calculations

simulation of groundwater flow in fractured rocks using a coupled model based on the method of domain decomposition groundwater flow in fractured rocks is modeled using a coupled model based on the domain decomposition method in the model the fractured porous medium is divided into two non overlapping sub domains one is the rock matrix in which the medium is described using a continuum model the other consists of deep fractures and fissure zones where the medium is described using a discrete fracture network dfn model the two models are coupled through the continuity of the hydraulic heads and fluxes on the common boundaries the coupled model is used to simulate groundwater flow in a hydropower station the results show that the model simulates groundwater levels that are in agreement with the measured groundwater levels furthermore the model s parameters relating to deep fractures and fissure zones are verified by comparing three different models the continuum model coupled model and dfn model the results show that the coupled model can capture and duplicate the hydrogeological conditions in the study domain whereas the continuum model overestimates and the dfn model underestimates the measured hydraulic heads a sensitivity analysis shows that fracture aperture has a considerable effect on the groundwater level so when the fracture aperture is large the coupled model or dfn model is more appropriate than the continuum model in the fracture domain

onset and ending of the late palaeozoic ice age triggered by tectonically paced rock weathering the onset of the late palaeozoic ice age about 340 million years ago has been attributed to a decrease in atmospheric co2 concentrations associated with expansion of land plants as plants both enhance silicate rock weathering which consumes co2 and increase the storage of organic carbon on land however plant expansion and carbon uptake substantially predate glaciation here we use climate and carbon cycle simulations to investigate the potential effects of the uplift of the equatorial hercynian mountains and the assembly of pangaea on the late palaeozoic carbon cycle in our simulations mountain uplift during the late carboniferous caused an increase in physical weathering that removed the thick soil cover that had inhibited silicate weathering the resulting increase in chemical weathering was sufficient to cause atmospheric co2 concentrations to fall below the levels required to initiate glaciation during the permian the lowering of the mountains led to a re establishment of thick soils whilst the assembly of pangaea promoted arid conditions in continental interiors that were unfavourable for silicate weathering these changes allowed co2 concentrations to rise to levels sufficient to terminate the glacial event based on our simulations we suggest that tectonically influenced carbon cycle changes during the late palaeozoic were sufficient to initiate and terminate the late palaeozoic ice age the late palaeozoic was characterized by glacial cycles numerical simulations suggest that increased silicate weathering due to mountain uplift and soil removal caused atmospheric co2 to fall below the threshold for glaciation

influence of the central american seaway and drake passage on ocean circulation and neodymium isotopes a model study the sensitivity of the neodymium isotopic composition nd to tectonic rearrangements of seaways is investigated using an earth system model of intermediate complexity the shoaling and closure of the central american seaway cas is simulated as well as the opening and deepening of drake passage dp multiple series of equilibrium simulations with various intermediate depths are performed for both seaways providing insight into nd and circulation responses to progressive throughflow evolutions furthermore the sensitivity of these responses to the atlantic meridional overturning circulation amoc and the neodymium boundary source is examined modeled nd changes are compared to sediment core and ferromanganese fe mn crust data the model results indicate that the north atlantic nd response to the cas shoaling is highly dependent on the amoc state i e on the amoc strength before the shoaling to shallow depths preclosure three scenarios based on different amoc forcings are discussed of which the model data agreement favors a shallow preclosure miocene amoc 6 sv the dp opening causes a rather complex circulation response resulting in an initial south atlantic nd decrease preceding a larger increase this feature may be specific to our model setup which induces a vigorous cas throughflow that is strongly anticorrelated to the dp throughflow in freshwater experiments following the dp deepening odp site 1090 is mainly influenced by amoc and dp throughflow changes while odp site 689 is more strongly influenced by southern ocean meridional overturning circulation and cas throughflow changes the boundary source uncertainty is largest for shallow seaways and at shallow sites

paleogeographic controls on the onset of the antarctic circumpolar current development of the antarctic circumpolar current acc during the cenozoic is controversial in terms of timing and its role in major climate transitions some propose that the development of the acc was instrumental in the continental scale glaciation of antarctica and climate cooling at the eocene oligocene boundary here we present climate model results that show that a coherent acc was not possible during the oligocene due to australasian paleogeography despite deep water connections through the drake passage and tasman gateway and the initiation of antarctic glaciation the simulations of ocean currents compare well to paleoenvironmental records relating to the physical oceanography of the oligocene and provide a framework for understanding apparently contradictory dating of the initiation of the acc we conclude that the northward motion of the australasian land masses and the reconfiguration of the tasman seaway and drake passage are necessary preconditions for the formation of a strong coherent acc

evaluating southern ocean sea ice for the last glacial maximum and pre industrial climates pmip 2 models and data evidence sea ice is recognized as an important factor controlling climate conditions at high latitudes it has a major impact in controlling the ocean to atmosphere exchanges e g for co2 as well as surface oceanic conditions and deep water formation in the high latitude oceans being at the interface of two major components of the climate system sea ice is useful to evaluate and intercompare different climate models we here analyze the results of eight coupled climate models from which seven are from the pmip 2 database against available reconstructions for winter and summer sea ice extent around antarctica to evaluate the ability of models in representing different climate states we compare their results for both the pre industrial and the last glacial maximum lgm we find that models generally have identical seasonal ranges for the two climate states analyzed which is not supported by data inferences indeed data indicate that the lgm seasonality was enhanced compared to the pre industrial the shape of the sea ice distribution is also different in models circular around the antarctic continent and in reconstructions oval shaped distribution similar to modern sea ice distribution we show that models underestimating the sea ice extent for the pre industrial are also underestimating the last glacial maximum extent our results thus point to difficulties for climate models in representing the sea ice dynamics in the southern ocean

twentieth century simulation of the southern hemisphere climate in coupled models part ii sea ice conditions and variability we examine the representation of the mean state and interannual variability of antarctic sea ice in six simulations of the twentieth century from coupled models participating in the intergovernmental panel on climate change fourth assessment report the simulations exhibit a largely seasonal southern hemisphere ice cover as observed there is a considerable scatter in the monthly simulated climatological ice extent among different models but no consistent bias when compared to observations the scatter in maximum winter ice extent among different models is correlated to the strength of the climatological zonal winds suggesting that wind forced ice transport is responsible for much of this scatter observations show that the leading mode of southern hemisphere ice variability exhibits a dipole structure with anomalies of one sign in the atlantic sector associated with anomalies of the opposite sign in the pacific sector the observed ice anomalies also exhibit eastward propagation with the antarctic circumpolar current as part of the documented antarctic circumpolar wave phenomenon many of the models do simulate dipole like behavior in sea ice anomalies as the leading mode of ice variability but there is a large discrepancy in the eastward propagation of these anomalies among the different models consistent with observations the simulated antarctic dipole like variations in the ice cover are led by sea level pressure anomalies in the amundsen bellingshausen sea these are associated to different degrees in different models with both the southern annular mode and the el nino southern oscillation enso there are indications that the magnitude of the influence of enso on the southern hemisphere ice cover is related to the strength of enso events simulated by the different models

high resolution 104 years deep sea foraminiferal stable isotope records of the eocene oligocene climate transition we have constructed high resolution 104 105 years benthic foraminiferal 13c and 18o records for the upper eocene through lower oligocene of two pelagic sequences deep sea drilling project dsdp site 522 in the angola basin south atlantic ocean and ocean drilling program odp site 744 in the southern indian ocean these records provide improved constraints on both the timing and magnitude of marine oxygen and carbon isotope events from 30 to 35 ma the oxygen isotope records indicate that the ubiquitous 18o increase oi 1 which marks the rapid expansion of continental ice sheets and a minimum of 3 to 4 c of cooling of bottom waters in the earliest oligocene 33 6 ma occurred in 350 kyr more than half the transition occurred over the final 40 50 kyr this period of lower temperatures and widespread continental glaciation persisted for roughly 400 kyr i e the duration of magnetochron c13n these records also indicate that this interval was characterized by at least two 100 kyr waxing and waning cycles oi 1a and oi 1b and possibly several higher frequency events the benthic foraminiferal 13c records show a positive 0 8 excursion that is nearly isochronous with the oi 1 oxygen isotope increase similar magnitude 13c increases at other sites indicate this was a global phenomenon suggestive of an unusually large perturbation to the carbon cycle this excursion was followed by smaller amplitude 13c oscillations with periods of roughly 400 kyr we suspect that the ubiquitous oi 1 13c excursion resulted from a brief but substantial increase in export production and carbon burial

preliminary geological geochemical and numerical study on the first egs project in turkey geothermal energy is attracting more and more attention due to its large capacity and lack of dependency on the weather currently many countries have planned enhanced geothermal system egs projects in this paper the first egs project in turkey which is being implemented at the license area of sds energy inc in dikili of the izmir province is introduced extensive geological paleostress 279 fault slip data from 33 locations geophysical magnetotelluric and vertical electrical sounding at 80 and 129 locations respectively and geochemical studies as well as paleostress measurements have been conducted in this area within the scope of this project in the light of all these studies it has been determined that the dikili region is remarkable in terms of its high thermal gradient of about 7 c 100 m the geothermal reservoir formation the kozak granodiorite is a homogeneous crystalline volcanic rock mass with high radiogenic heat production and suitable for an egs application the analysis shows that the dominating fault system is normal and the corresponding primary stress regime is extensional based on the geological geophysical surveys and the estimated in situ stresses numerical studies were carried out to assess the results of the hydraulic fracturing and geothermal energy production using the numerical codes flac3dplus and tough2mp respectively in the area a of the dikili site the simulation results show that the stimulated reservoir volume and area could reach 44 5 million m3 and 1 km2 respectively with an injection volume of 122 931 m3 assuming the fractured zone has a height of 1000 m and a half length of 1200 m the distance between injection and production wells being 1000 m an average overall geothermal capacity of 83 7 mwth in 20 years could be reached with an injection rate of 250 l s the injection strategy and design parameters of the reservoir stimulation and geothermal production will be further optimized with the project running

eocene circulation of the southern ocean was antarctica kept warm by subtropical waters 1 near the eocene s close 34 million years ago the climate system underwent one of the largest shifts in earth s history antarctic terrestrial ice sheets suddenly grew and ocean productivity patterns changed previous studies conjectured that poleward penetration of warm subtropical currents the east australian current eac in particular caused eocene antarctic warmth late eocene opening of an ocean gateway between australia and antarctica was conjectured to have disrupted the eac cooled antarctica and allowed ice sheets to develop here we reconstruct eocene paleoceanographic circulation in the tasmanian region using 1 biogeographical distributions of phytoplankton including data from recently drilled ocean drilling program leg 189 sites and 2 fully coupled climate model simulations we find that the eac did not penetrate to high latitudes and ocean heat transport in the region was not greater than modern our results do not support changes in thermal isolation as the primary driver of the eocene oligocene climatic transition

ice atmosphere feedbacks dominate the response of the climate system to drake passage closure abstractthe response of the global climate system to drake passage dp closure is examined using a fully coupled ocean atmosphere ice model unlike most previous studies a full three dimensional atmospheric general circulation model is included with a complete hydrological cycle and a freely evolving wind field as well as a coupled dynamic thermodynamic sea ice module upon dp closure the initial response is found to be consistent with previous ocean only and intermediate complexity climate model studies with an expansion and invigoration of the antarctic meridional overturning along with a slowdown in north atlantic deep water nadw production this results in a dominance of southern ocean poleward geostrophic flow and antarctic sinking when dp is closed however within just a decade of dp closure the increased southward heat transport has melted back a substantial fraction of antarctic sea ice at the same time the polar oceans warm by 4 6 c on the zonal mean and the maximum strength of the so

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

the ocean circulation in the southern hemisphere and its climatic impacts in the eocene abstract opening of southern ocean gateways may have had a controlling influence on the evolution of global climate the largest step in the history of cenozoic climate from an eocene greenhouse toward the modern glaciated state is correlated with opening of a deep water connection between the southern indian and southern pacific oceans this study synthesizes results from previous work assesses the possibility that ocean heat transport was much greater than modern during the globally warm eocene and explores the sensitivity of polar climate to large changes in ocean heat transport the magnitudes of these sensitivities are compared with those due to greenhouse gas concentration changes we find that ocean heat transport was unlikely to have been sufficiently greater than modern during the eocene to explain the change in the climate specifically in order to have significantly affected antarctic climate ocean heat transport changes would have had to change by an order of magnitude much greater than the largest change produced in our simulations in coupled climate model simulations changes in co2 concentrations from 1120 to 560 ppm supported by proxy records lead to significant antarctic responses in the absence of ocean heat transport changes the results show that antarctic snow accumulation is primarily controlled by changes in summer temperature not precipitation and that snow did not remain on antarctica during summer months in eocene even at low greenhouse gas concentrations greenhouse gas concentration changes and subsequent processes such as ice albedo and weathering feedbacks were more likely to have been the primary cause of antarctic glaciation than ocean heat transport changes

systems tracts and depositional sequences in a carbonate setting a study of continuous outcrops from platform to basin at the scale of seismic lines abstract the application of sequence stratigraphy concepts to carbonates is feasible and this paper presents an example of its successful application the continuity and lateral extent of outcropping sedimentary sections observed at the scale of a seismic line from platform to basin in the southern vercors plateau western alps france confirm the validity of sequence stratigraphy concepts when applied to carbonate depositional systems from the stratal patterns displayed in outcrop we determined that carbonate lowstand systems tracts are major components in the basin even in the deep pelagic realm transgressive and highstand systems tracts are very thin a response to starvation in contrast on the shelf transgressive and highstand systems tracts are the major components carbonate lowstand and shelf margin systems tracts pinch out in the vicinity of the offlap break it clearly appears that the stratal patterns and stratal termination patterns of carbonate systems tracts especially of carbonate lowstand systems tracts are basically similar to those of siliciclastic systems tracts this study documents that carbonate platforms may provide the basin with carbonate clastics during periods of relative sea level falls and lowstand this is one of the most controversial aspects of the application of sequence stratigraphy concepts in carbonate environments a second controversial aspect of the application of sequence stratigraphy concepts to carbonate rocks is the distinction between transgressive and regressive facies cycles and depositional sequences and systems tracts this paper demonstrates that the shoreline position for carbonates which indicates the facies transgression or regression is independent of prograding or retrograding shelf breaks the stratal pattern and facies within systems tracts vary depending on the overall evolution of the accommodation space i e on their position within the transgressive and regressive cycles

antarctic glaciation caused ocean circulation changes at the eocene oligocene transition a climate model is used to show that the growth of the antarctic ice sheet at about 34 myr ago drove changes in ocean circulation but the opening of ocean gateways had relatively little impact antarctica developed an ice sheet about 34 million years ago following a period of ice free conditions known as the super greenhouse climate previous research has suggested that ice sheet growth was driven by either the thermal isolation of antarctica arising from the opening of ocean gateways or by progressively lower atmospheric co2 content matt huber and colleagues now use a climate model to show that the growth of the ice sheet forced by changes in co2 drove the changes in ocean circulation in contrast the opening of the gateways had relatively little impact on ocean circulation two main hypotheses compete to explain global cooling and the abrupt growth of the antarctic ice sheet across the eocene oligocene transition about 34 million years ago thermal isolation of antarctica due to southern ocean gateway opening1 2 3 4 and declining atmospheric co2 refs 5 6 increases in ocean thermal stratification and circulation in proxies across the eocene oligocene transition have been interpreted as a unique signature of gateway opening2 4 but at present both mechanisms remain possible here using a coupled ocean atmosphere model we show that the rise of antarctic glaciation rather than altered palaeogeography is best able to explain the observed oceanographic changes we find that growth of the antarctic ice sheet caused enhanced northward transport of antarctic intermediate water and invigorated the formation of antarctic bottom water fundamentally reorganizing ocean circulation conversely gateway openings had much less impact on ocean thermal stratification and circulation our results support available evidence that co2 drawdown not gateway opening caused antarctic ice sheet growth and further show that these feedbacks in turn altered ocean circulation the precise timing and rate of glaciation and thus its impacts on ocean circulation reflect the balance between potentially positive feedbacks increases in sea ice extent and enhanced primary productivity and negative feedbacks stronger southward heat transport and localized high latitude warming the antarctic ice sheet had a complex dynamic role in ocean circulation and heat fluxes during its initiation and these processes are likely to operate in the future

origin signature and palaeoclimatic influence of the antarctic circumpolar current the antarctic circumpolar current acc is today the strongest current in the world s ocean with a significant influence on global climate its assumed history and influence on palaeoclimate while almost certainly equally profound are here called into question in this paper we review 30 years of accumulated data interpretation and speculation about the acc deriving mainly from dsdp and odp drilling in the southern ocean for most of this time a conventional view of acc development signature and influence has held sway among palaeoceanographers and marine geologists in this view the acc began at about 34 ma close to the eocene oligocene boundary the time of onset of significant antarctic glaciation and the time of creation of a deep water gap tasmanian seaway between australia and antarctica as the south tasman rise separated from north victoria land this is the smoking gun of synchroneity the southern ocean sediment record shows a latest eocene development and subsequent geographic expansion of a siliceous biofacies its northern limit taken to indicate the palaeoposition of the acc axis in addition the acc was considered to have caused antarctic glaciation by isolating the continent within a cold water annulus reducing north south heat transport a different and later date for antarctic south american opening drake passage was proposed but the timing of acc onset there was disputed and the simple story survived recent developments however call it into question modern physical oceanography shows that all or most of present day acc transport is confined to narrow jets within deep reaching circumpolar fronts and numerical modelling has suggested that a steady reduction in greenhouse gas concentration through the cenozoic could cause antarctic glaciation with or without a contribution from ocean circulation change the rapidity of antarctic glacial onset at the eocene oligocene boundary and coeval creation of a deep water gap south of tasmania both survive but in light of the new information the presence of a siliceous biofacies cannot be claimed as evidence of the existence of a continuous deep reaching oceanic front and therefore of an acc and the possibility arises that cool and cold sea surface temperatures were effects of antarctic glaciation rather than evidence of a major contributor to its cause in considering future work we emphasise the importance of additional information from ancillary fields better definition of the necessary and sufficient properties of oceanic fronts additional determinations of cenozoic atmospheric pco2 and further developments in models of antarctic glaciation but also suggest the way forward in marine geology our knowledge of the development and palaeoclimatic significance of the acc will be best served by grainsize studies of bottom current strength at selected locations and geochemical or mineralogical studies of clays and ird as a way of examining provenance and therefore surface and bottom current directions and the existence of interocean connections

sub wavebase cross bedded grainstones on a distally steepened carbonate ramp upper miocene menorca spain cross bedded grainstones on carbonate ramps and shelves are commonly related to the locus of major wave energy absorption such as shorelines shoals or shelf breaks in contrast on the early tortonian carbonate platform of menorca balearic islands coarse grained cross bedded grainstones are found at a distance from the palaeoshoreline where they were deposited below the wavebase excellent exposures along continuous outcrops on the sea cliffs of menorca reveal the depositional profile and three dimensional distribution of the different facies belts of the tortonian ramp depositional system basinward from the palaeoshoreline fan deltas and beach deposits pass into 5 km wide gently dipping bioturbated dolopackstone inner and middle ramp then into 12 20 dipping dolograinstone rudstone clinobeds ramp slope and finally into subhorizontal fine grained basinal dolowackestone to dolopackstone outer ramp in this miocene example coarse grained grainstones exist in five different settings other than beach deposits 1 on the middle ramp where cross bedded grainstones were deposited by currents roughly parallel to the shoreline at 40 70 m estimated water depth and are interbedded with gently dipping bioturbated dolomitized packstones 2 on the upper slope where clinobeds are composed mostly of in situ rhodoliths and red algae fragments 3 on the lower slope as small scale bedforms small three dimensional subaqueous dunes migrating parallel to the slope 4 at the transition between the lower slope and the outer ramp where mollusc rich and rhodolithic rudstones and grainstones interbedded in dolomitized laminated wackestones containing abundant planktonic foraminifera infill slide slump scars as upslope backstepping bodies backsets 5 at the toe of the slope where coarse skeletal grainstones indicate bedform migration parallel to the platform margin induced by currents at more than 150 m estimated water depth this late miocene example also illustrates how changes in intrabasinal environmental conditions nutrients and or temperature may produce changes in stratal patterns and facies architecture if they affect the biological system two depositional sequences compose the miocene platform on menorca where a reef rimmed platform prograded onto an earlier distally steepened ramp the transition from the ramp to the reef rimmed platform was effected by an increase in accommodation space caused by ecological changes promoting a shift from a grain to a framework producing biota

paleogene opening of drake passage the timing of events leading to the earliest connection between the pacific and atlantic oceans at drake passage is controversial but important because gateway opening probably had a profound effect on global circulation and climate a rigorous new analysis of marine geophysical data demonstrates a major change in the motion of the south american and antarctic plates at about 50 ma from n s to wnw ese accompanied by an eightfold increase in separation rate this would have led to crustal extension and thinning and perhaps the opening of small oceanic basins with the probable formation of a shallow b1000 m gateway during the middle eocene no change in south american antarctic motion is observed near the eocene oligocene boundary but a deep water connection developed between 34 and 30 ma when continued extension led to the initiation of seafloor spreading at the west scotia ridge these timings correlate with events seen in the oxygen isotope record from benthic foraminera and support the view that drake passage opening was the trigger for abrupt eocene oligocene climate deterioration and the growth of extensive antarctic ice sheets d 2005 elsevier b v all rights reserved

stratal patterns sediment composition and sequence stratigraphy at the margin of the vercors carbonate platform lower cretaceous se france abstract conventional sequence stratigraphic concepts relate the large scale stratal architecture of sediment bodies to changes in relative sea level this paper evaluates the relationship between stratal geometry and sea level stand based on a study of large semicontinuous outcrops of cretaceous carbonate platform strata in the vercors southeastern france multiple lines of evidence for sea level change are combined including stratal geometry detailed quantitative microfacies analyses and diagenetic patterns at platform top hardground surfaces the studied outcrops of the cirque d archiane show two main prograding platform tongues both over 100 m thick the stratal geometries at the boundary between these platform tongues including an apparent pinchout of a wedge of slope sediments suggest the presence of a major lowstand unconformity however this stratal boundary does not coincide with the horizon containing the most extensive meteoric alteration furthermore detailed platform to basin correlation shows that the wedge of slope sediments is not basin restricted but makes a thin drape over the platform top the sedimentologic and diagenetic evidence suggest incipient drowning of the platform at the boundary between the two main platform tongues preceded by a minor exposure event only internally the main platform tongues consist of smaller 10 30 m thick units that prograde towards the basin and aggrade on the platform top and which are interpreted as stacked highstand wedges these wedges are usually topped by hardground surfaces with minor evidence for subaerial exposure the platform top horizon with the most extensive subaerial diagenesis and erosion correlates with a distinct but relatively thin unit of lithoclastic debris on the slope a pronounced scour in the clinoforms of the vercors does not correlate with a major exposure surface on the platform top this study shows that stratal geometries alone are a rather ambiguous guide to sea level history without the accompanying sedimentologic and diagenetic evidence for sea level change most of the stratal architecture of the vercors platform can be explained by either changes in accommodation or changes in carbonate production

sedimentological evidence for the formation of an east antarctic ice sheet in eocene oligocene time middle eocene to late oligocene sediments recovered at ocean drilling program sites 689 and 690 on maud rise in the southernmost atlantic ocean and at sites 738 and 744 on kerguellen plateau in the southernmost indian ocean were analysed in order to study the depositional environment and the palaeoclimate special emphasis was placed on the reconstruction of the formation of a cryosphere on the antarctic continent the investigations include quantifications of carbonate and opal contents grain size analyses and studies of clay mineral assemblages the sedimentary sequence at all sites under investigation is highly pelagic with nannofossil oozes and chalks dominant the first indication of probable glacierization at sea level is in the form of isolated gravel and terrigenous sand grains which indicate ice rafting from middle eocene time at c 45 5 ma this is supported by enhanced concentrations of detrital chlorite and reworked kaolinite probably some glaciers reached the sea while most of the continent remained under the influence of a humid and warm to temperate climate the growth of the inland ice resulted in enhanced physical weathering and in increased contents of detrital chlorite and kaolinite from about 40 ma a strengthening of the glacial conditions and the onset of continental east antarctic glaciation is recorded in early oligocene sediments with an age of 36 ma all major sediment parameters document this event the clay mineralogy changed between c 36 3 ma and c 35 5 ma from smectite dominated assemblages to illite and chlorite dominated assemblages the latter being indicative of physical weathering under cooler climates large quantities of ice rafted gravel and sand accumulated on the kerguelen plateau between 36 0 ma and 35 8 ma at the same time an increase in opal content occurred as well as a decrease in carbonate the sediment parameters imply that the east antarctic continent was more or less totally buried beneath the ice during oligocene time the ice sheet however probably did not have a polar but a temperate character as indicated by the occurrence of nothofagus and relatively warm surface water temperatures prohibiting the long distance transport of debris by icebergs

quantifying the geometry and sediment fabric of linear slopes examples from the tertiary of italy southern alps and gargano promontory the geometries and sediment characteristics of two well exposed submarine slope successions of ancient carbonate platforms were studied to analyse the relationship between inclinations of linear slopes and sediment fabric the two examples are an oligocene platform to slope succession exposed on the brione mountain in the southern alps and an eocene slope tobasin succession exposed on the saraceno mountain in the gargano promontory the planar slope of the brione mountain outcrop is inclined up to 20 25j and consists of fine to coarse sand sized skeletal packstones and grainstones and that of the saraceno mountain outcrop has a modal angle of 15 22 5j and comprises very fine to coarse sand sized poorly washed skeletal packstones grainstones and rudstones the good agreement between the inclinations of the linear slope profiles and angles of repose published in the literature implies that these slopes are at or very close to the angle of repose the general rule that in systems built to the angle of repose slope angle is directly correlated to sediment fabric can be applied to linear slopes d 2002 elsevier science b v all rights reserved

the respective role of atmospheric carbon dioxide and orbital parameters on ice sheet evolution at the eocene oligocene transition the continental scale initiation of the antarctic ice sheet at the eocene oligocene boundary eocene oligocene transition eot 34 ma is associated with a global reorganization of the climate if data studies have assessed the precise timing and magnitudes of the ice steps modeling studies have been unable to reproduce a transient ice evolution during the eocene oligocene transition in agreement with the data here we simulate this transition using general circulation models coupled to an ice sheet model our simulations reveal a threshold for continental scale glaciation of 900 ppm 100 to 150 ppm higher than previous studies this result supports the existence of ephemeral ice sheets during the middle eocene as similar co 2 levels 900 1000 ppm have been reached episodically during this period transient runs show that the ice growth is accurately timed with eot 1 and oi 1 the two 18 o excursions occurring during the transition we show that co 2 and orbital variations are crucial in initiating these steps with eot 1 corresponding to the occurrence of low summer insolation whereas oi 1 is controlled by a major co 2 drop the two 18 o steps record both ice growth and temperature representing some 10 30 m eustatic sea level fall and 2 4 c cooling at eot 1 and 70 20 m and 0 2 c for oi 1 the simulated magnitude of the ice steps 10 m for eot 1 and 63 m for oi 1 and the overall cooling at various locations show a good agreement with the data which supports our results concerning this critical transition

the non analogue nature of pliocene temperature gradients abstract the strong warming of the north atlantic and high latitudes in the pliocene 5 3 2 6 million years ago continually fails to be simulated in climate model simulations being the last period of earth history with higher global temperatures and carbon dioxide levels similar to today it is an important target period for palaeoclimate models one of the key features of the pliocene climate is the reduced meridional gradients particularly in the high latitudes of the northern hemisphere here we show that previously unconsidered palaeogeographic changes river routing ocean bathymetry and additional landmass in the modern barents sea in the north atlantic region can produce significant temperature responses at high latitudes along with orbital forcing this can significantly decrease equator to pole temperature gradients in the atlantic ocean these additional forcings show that the large arctic warming and significantly reduced temperature gradients in the pliocene are not analogous to future warming and that careful consideration of all the possible climatic forcings is required to accurately simulate pliocene climate

reef geometries erosion surfaces and high frequency sea level changes upper miocene reef complex mallorca spain the upper miocene reef complex of mallorca is a 20 km prograding unit which crops out in sea cliffs along the southern side of the island these vertical and exceptionally clean outcrops permit i identification of different facies lagoon reef front reef slope and open platform and their geometries and boundaries at different scales ranging from metre to kilometre and ii construction of a 6 km long high resolution cross section in the direction of reef progradation this cross section shows vertical shifts of the reefal facies and erosion surfaces linked to a general progradational pattern that defines the accretional units four hierarchical orders of magnitude 1 m to 4 m of accretional units are identified by consideration of the vertical facies shifts and by which erosion surfaces are truncated by other erosion surfaces all these orders show similar patterns horizontal beds of lagoonal facies in the upper part landward reefal and slope facies with sigmoidal bedding in the central part and open platform facies with subhorizontal bedding in the lower part basinwards the boundaries are erosion surfaces horizontal over the lagoon facies dipping basinwards over the reef front facies and connecting basinwards with their correlative conformities over the reef slope and open platform facies the four orders of accretional units are interpreted in terms of four 1 m to 4 m hierarchies of sea level cycles because i there is a close relation between the coral growth and the sea surface ii there are vertical shifts in the reefal facies and their relation to the erosion surfaces and iii there was very little tectonic subsidence in the study area during the late miocene additionally all these units can be described in terms of their position relative to the sea level cycle i the reefs prograde on the open platform sediments during low stands of sea level ii aggradation of the lagoon reef and open platform facies dominates during sea level rises and the lagoonal beds onlap landwards upon the previous erosion surface iii reefal progradation occurs during high stands of sea level and iv the 2 m sea level fall produces an off lapping reef and there is progradation with downward shifts of the reefal facies and erosion landward on the emerged older reefal units a erosion surfaces the 3 m and 4 m sea level falls produce only erosion b and c erosion surfaces although precise age data do not exist at present some speculations upon the frequency of these miocene relative sea level cycles can be made by comparisons with pleistocene cyclicity there is a good correlation between the miocene 2 m cycles and the 100 ka pleistocene cycles consequently the 1 m cycles can be assigned to a fourth order in relation to previously proposed global cycles and the 2 m to fifth order cycles all these accretional units could be defined as sequences according to the definition as commonly used in sequence stratigraphy however they represent higher than third order sea level cycles but are not parasequences the term subsequence therefore is suggested to define a part of a sequence bounded by erosion surfaces mostly subaerial and their correlative conformities basinwards a hierarchy of subsequences can be established

deep 3d thermal modelling for the city of berlin germany this study predicts the subsurface temperature distribution of germany s capital berlin for this purpose a data based lithosphere scale 3d structural model is developed incorporating 21 individual geological units this model shows a horizontal grid resolution of 500 500 m and provides the geometric base for two different approaches of 3d thermal simulations 1 calculations of the steady state purely conductive thermal field and 2 simulations of coupled fluid flow and heat transport the results point out fundamentally different structural and thermal configurations for potential geothermal target units the top of the triassic middle buntsandstein strongly varies in depth 159 2 470 m below sea level and predicted temperatures 15 95 c mostly because of the complex geometry of the underlying permian zechstein salt the top of the sub salt sedimentary rotliegend is rather flat 2 890 3 785 m below sea level and reveals temperatures of 85 139 c the predicted 70 c isotherm is located at depths of about 1 500 2 200 m cutting the middle buntsandstein over large parts of berlin the 110 c isotherm at 2 900 3 700 m depth widely crosscuts the sedimentary rotliegend groundwater flow results in subsurface cooling the extent of which is strongly controlled by the geometry and the distribution of the tertiary rupelian clay the cooling effect is strongest where this clay rich aquitard is thinnest or missing thus facilitating deep reaching forced convective flow the differences between the purely conductive and coupled models highlight the need for investigations of the complex interrelation of flow and thermal fields to properly predict temperatures in sedimentary systems

modeling evidences for global warming arctic seawater freshening and sluggish oceanic circulation during the early toarcian anoxic event 1 the paleoecological disturbances recorded during the early toarcian warming event 183 myr ago including marine anoxia sea level rise seawater acidification carbonate production crisis and species extinctions are often regarded as past examples of earth s possible responses to the rapid emergence of super greenhouse conditions however physical mechanisms explaining both the global and local expressions of paleoenvironmental events are still highly debated here we analyze the paleoclimatic and paleoceanographic consequences of increases in atmospheric pco2 levels at a multiscale resolution using a fully coupled ocean atmosphere model foam we show that in association with stronger high latitude precipitation rates and enhanced continental runoff the demise of polar sea ice due to the global warming event involved a regional freshening of arctic surface seawaters these disturbances lead to progressive slowdowns of the global oceanic circulation accountable for widespread ocean stratification and bottom anoxia processes in deep oceanic settings and epicontinental basins in agreement with very negative oxygen isotope values measured on fossil shells from the nw tethys our simulations also show that recurrent discharges of brackish and nutrient rich arctic surface waters through the viking corridor could have led to both vertical and geographical gradients in salinity and seawater 18o in the nw tethyan seas locally contrasted conditions in water mass density and rises in productivity rates due to strong nutrient supplies could partly explain the regional severity of the anoxic event in the restricted euro boreal domains as it has been previously suggested and modeled regionally

the early cretaceous platform off northwest florida controls on morphologic development of carbonate margins abstract an analysis of approximately 3500 km of multifold and 1000 km of singlefold seismic reflection data correlated with two exploration wells and other available geologic information records the morphologic development of the early cretaceous carbonate platform margin off northwest florida early cretaceous depositional patterns apparently controlled the concurrent formation of gently dipping declivities 10 carbonate platform margin slopes in the vicinity of desoto canyon northeastern gulf of mexico we suggest that the pronounced along strike change in morphology reflects variations in platform width input of terrestrial clastics and overall sediment availability to the platform s seaward margin slope southeast of the canyon the early cretaceous slope bordered a relatively broad platform removed from terrigenous sediment input environmental conditions favored the uninterrupted development of skeletal and nonskeletal buildups along the paleo shelf edge which effectively prevented large quantities of shelf derived clastic sediments from moving seaward consequently as the carbonate platform grew and its height increased the declivity of its seaward slope also increased as predicted by models of long term carbonate platform development in contrast northwest of the canyon the slope bordered a narrower platform adjacent to a source of terrigenous clastics more vigorous cross platform transport of clastics and resultant adverse environmental conditions at the paleo shelf edge inhibited consistent development of carbonate buildups thereby creating only an intermittent sediment barrier to the adjacent slope resultant higher sedimentation rates on the slope caused it to aggrade and prograde along with the carbonate platform allowing the margin slope to maintain its gentle morphology throughout the early cretaceous

high dependence of ordovician ocean surface circulation on atmospheric co2 levels abstract life on earth radiated dramatically during the ordovician period 485 444 ma at all taxonomic levels during an evolutionary episode known as the great ordovician biodiversification event abundant scientific literature has documented the pattern of biodiversification for numerous organism groups however fully understanding this event also requires detailed knowledge about the spatial distribution of the organisms the full potential of the palaeobiodiversity patterns remains under explored due to the lack of knowledge about past ocean circulation surface circulation significantly conditions the dispersal of organisms in creating preferential ocean migration pathways or in contrast by isolating specific regions and thus establishing major physical barriers these uncertainties persist because neither direct observational data nor proxy data independent from the fossil record are available to reconstruct the ocean surface circulation here we present new maps of ordovician ocean surface circulation based on simulations using the general circulation model foam this is a coupled ocean atmosphere general circulation model and represents a methodological improvement over previously published work in addition we use the most up to date palaeogeographical reconstructions to increase compatibility with recent palaeontological databases in providing clear synthetic maps of ocean surface circulation in addition to raw model outputs we aim to facilitate data model comparison to assist in interpretation of palaeontological datasets and to promote renewed discussion about ordovician biogeography finally we investigate the sensitivity of the circulation pattern to the atmospheric co2 content which remains poorly constrained in the ordovician potentially ranging from more than 15 times the preindustrial atmospheric co2 level pal to 5 pal maps are systematically constructed for a high 16 pal medium 8 pal and low 4 pal co2 value we show that the circulation pattern is much more sensitive to co2 than previously suggested

growth and demise of late carboniferous carbonate platforms in the eastern cantabrian zone asturias northwestern spain abstract geometric relationships of seismic scale stratal patterns observed on aerial photographs of late carboniferous carbonate platforms in the cuera region in asturias northwestern spain allow the identification of two discrete stages of platform development with different styles of deposition the first phase represented by the bashkirian valdeteja formation is characterized by progradation of more than 10 km with steep clinoforms of up to 35 and slope heights up to 650 m during the second phase corresponding to the moscovian picos de europa formation the platform aggraded mainly vertically nearly 850 m both phases of platform growth were terminated by major relative sea level lowstands in conjunction with local filling of the adjacent basins by shales and mudstones that onlap the platform flanks calibration with outcrops suggests a subdivision into the following lithofacies directly related to the depositional profile 1 platform interior parallel well to thick bedded skeletal pack to grainstones 2 margin algal and sponge dominated bioherms with little internal structure 3 slope clinothems of medium to thick bedded margin derived breccia beds 4 toe of slope alternating grain and packstones with spiculites and 5 basin marly shales shales sandstones and calcareous mudstones relative sea level changes caused by regional tectonic movements are suggested to be responsible for the generation of the two platform phases sea level highstands triggered the nucleation and growth of the platforms whereas major sea level lowstands in combination with terrigenous infill of the basins terminated the platform growth in addition it is proposed that the termination of late carboniferous carbonate platforms is caused by the combined effect of a sea level fall subaerial exposure and erosion and finally a rapid transgression that drowned and polluted the platform with shales and mudstones local variations in the infilling of the basins controlled the variations in the style of progradation the subsidence rates for the vertically aggrading phase picos de europa formation were approximately twice that for the progradational phase valdeteja formation and may explain the aggradational versus progradational character

role of the drake passage in controlling the stability of the ocean s thermohaline circulation the role of a southern ocean gateway in permitting multiple equilibria of the global ocean thermohaline circulation is examined in particular necessary conditions for the existence of multiple equilibria are studied with a coupled climate model wherein stable solutions are obtained for a range of bathymetries with varying drake passage dp depths no transitions to a northern hemisphere nh overturning state are found when the drake passage sill is shallower than a critical depth 1100 m in the model described herein this preference for southern hemisphere sinking is a result of the particularly cold conditions of the antarctic bottom water aabw formation regions compared to the nh deep water formation zones in a shallow or closed dp configuration this forces an exclusive production of deep bottom water in the southern hemisphere increasing the depth of the drake passage sill causes a gradual vertical decoupling in atlantic circulation removing the influence of aabw from the upper 2000 m of the atlantic ocean when the dp is sufficiently deep this shifts the interaction between a north atlantic deep water nadw cell and an aabw cell to an interaction between an shallower antarctic intermediate water cell and an nadw cell this latter situation allows transitions to a northern hemisphere overturning state

application of the geomechanical facies approach and comparison of exploration and evaluation methods used at soultz sous forets france and spa urach germany geothermal sites earth reservoirs are increasingly exploited today with the extraction of resources such as heat and hydrocarbons and the large scale emplacement of waste such as co2 sequestration the characterization site investigation predictive modeling and long term monitoring are dependent on the processes being investigated and modeled in most cases complex coupled processes have to be addressed in a geologically complex rock mass system in this paper we present a conceptual holistic framework known as geomechanical facies linking all the scales of investigation characterization and reservoir development methods we demonstrate this concept on the work undertaken during the design and development of the enhanced geothermal systems egs systems at the forefront of european hot dry rock hdr technology soultz sous forets france and spa urach germany soultz sous forets is situated within granitic rocks and an active tectonic graben system in the central part of the rhine graben it presents conditions of lithology temperature stress hydraulics and geochemistry that are very different from those at spa urach located in a very dense gneiss formation in the south german crystalline complex spa urach exhibits more elastic behavior and is set tectonically within an almost inactive strike slip stress field described in more detail in sects drill core analysis and hydraulic stimulation at spa urach this paper compares the exploration and field development methods used at these two sites against the back drop of the geomechanical facies concept issues addressed include the key parameters for flow and heat transport properties coupled hydro mechanical process identification the success of the hdr reservoir as a heat exchanger and exploration techniques applicable to the different facies identification of the key geomechanical facies gives an indication as to which technologies will prove more efficient in the application of hdr technology the results of this study will hopefully help in developing heat recovery schemes for the long term economical operation of future hdr plants and egs as well as assist in the understanding of engineered geosystems

magnetobiostratigraphic chronology of the eocene oligocene transition in the ciros 1 core victoria land margin antarctica implications for antarctic glacial history in 1986 cores were obtained to a depth of 702 m with 98 recovery from the ciros 1 drill hole beneath the ross sea on the victoria land margin glaciogene sediments identified near the base of the hole mark the earliest known record of antarctic glaciation initial biostratigraphic analysis indicated that the lower 336 m of the core is early oligocene in age and that the upper 366 m is of late oligocene early miocene age recently the chronology of the ciros 1 core has been questioned we developed a magnetostratigraphy for the lower 400 m of the ciros 1 core to clarify the chronology our magnetobiostratigraphic results indicate that the base of the ciros 1 core is early late eocene in age corresponding to chron c16r ca 36 5 ma we identify the eocene oligocene boundary at about 410 420 m within a 20 m thick poorly stratified bioturbated sandy mudstone this makes the ciros 1 core the highest latitude site 77 1 s from which this datum event has been recognized at 366 m a 4 m y hiatus which lies immediately beneath fluvial sediments accounts for most of chrons c11 and c12 we recognize three major climatic episodes in the ciros 1 core 1 the late eocene 34 5 36 5 ma 430 702 m when relatively warm conditions dominated and there were high sedimentation rates and some glacial activity 2 the late eocene early oligocene boundary interval 28 5 34 5 ma 340 430 m which was a transition from relatively warm to cooler conditions that coincided with glacial intensification sea level fall and subaerial erosion of the shelf and 3 the late oligocene early miocene 22 28 5 ma 50 340 m when large scale glaciation dominated the region and glaciers grounded across the continental shelf from correlation with global oxygen isotope and sea level records we infer that the antarctic climate and surrounding oceans cooled after separation of australia and antarctica and development of deep water circulation between them this marked the onset of the eocene oligocene transition at ca 34 5 ma a major east antarctic ice sheet did not develop until the early late oligocene boundary toward the end of the eocene oligocene transition ca 28 5 ma outlet glaciers did not breach the transantarctic mountains and ground across the ross sea shelf until 0 5 m y later ca 28 ma

sea ice and polar climate in the ncar csm the climate system model csm consists of atmosphere ocean land and sea ice components linked by a flux coupler which computes fluxes of energy and momentum between components the sea ice component consists of a thermodynamic formulation for ice snow and leads within the ice pack and ice dynamics using the cavitating fluid ice rheology which allows for the compressive strength of ice but ignores shear viscosity the results of a 300 yr climate simulation are presented with the focus on sea ice and the atmospheric forcing over sea ice in the polar regions the atmospheric model results are compared to analyses from the european centre for medium range weather forecasts and other observational sources the sea ice concentrations and velocities are compared to satellite observational data the atmospheric sea level pressure slp in csm exhibits a high in the central arctic displaced poleward from the observed beaufort high the southern hemisphere slp over sea ice is generally 5 mb lower than observed air temperatures over sea ice in both hemispheres exhibit cold biases of 2 4 k the precipitationminus evaporation fields in both hemispheres are greatly improved over those from earlier versions of the atmospheric gcm the simulated ice covered area is close to observations in the southern hemisphere but too large in the northern hemisphere the ice concentration fields show that the ice cover is too extensive in the north pacific and subarctic north atlantic oceans the interannual variability of the ice area is similar to observations in both hemispheres the ice thickness pattern in the antarctic is realistic but generally too thin away from the continent the maximum thickness in the arctic occurs against the bering strait not against the canadian archipelago as observed the ice velocities are stronger than observed in both hemispheres with a consistently greater turning angle to the left in the southern hemisphere they produce a northward ice transport in the southern hemisphere that is 3 4 times the satellite derived value sensitivity tests with the sea ice component show that both the pattern of wind forcing in csm and the air ice drag parameter used contribute to the biases in thickness drift speeds and transport plans for further development of the ice model to incorporate a viscousplastic ice rheology are presented in spite of the biases of the sea ice simulation the 300 yr climate simulation exhibits only a small degree of drift in the surface climate without the use of flux adjustment this suggests a robust stability in the simulated climate in the presence of significant variability

integrated characterization of carbonate ramp reservoirs using permian san andres formation outcrop analogs the san andres formation permian guadalupian of the permian basin is representative of carbonate ramp reservoirs in that it has highly stratified character complex facies and permeability structure and generally low recovery efficiencies of 30 of original oil in place the approach used here to describe carbonate ramp reservoirs such as the san andres formation produces detailed reservoir models based on integration of sequence stratigraphic analysis petrophysical quantification through definition of rock fabric flow units and fluid flow simulation synthesis of these subdisciplines clarifies which aspects of the geologic petrophysical model are most significant in predicting reservoir performance and ultimately in understanding the location of remaining oil satur tion the san andres formation crops out along the algerita escarpment a long oblique dip continuous shelf to basin exposure in the central guadalupe mountains these outcrops provide a unique opportunity to study lateral relationships in geologic and petrophysical structure analogous to those occurring between wells in subsurface reservoirs on the basis of sequence stratigraphic analysis three scales of cyclicity are recognized depositional sequences high frequency sequences and cycles examination of the cycles in two detailed window areas provides a practical scale for petrophysical quantification and fluid flow simulation an understanding of cycle position within the high frequency sequence framework also provides predictive information petrophysical analysis revealed six rock fabric groups dominated by intergranular separate vug or dense intercrystalline pore types comparison of these rock fabric groups with facies descriptions produced a rock fabric flow unit model that honors the geologic structure of the cycle and sequence framework permeability data were averaged within rock fabric flow units using a geometric mean approach based on fine scale fluid flow modeling of deterministic and stochastically generated permeability fields two dimensional black oil fluid flow models illustrate that 1 major differences in sweep efficiency and fluid flow performance are predicted when linear interwell interpolations are compared with actual interwell scale geologic structure as determined by outcrop geologic and petrophysical mapping 2 an understanding of static geologic petrophysical conditions provides only a partial understanding of reservoir performance defined by the interaction of these static properties and dynamic properties of fluid flow interaction within the flow unit architecture and 3 because of the orderly distribution of high and low permeability facies within cycle stacks of high frequency sequences this larger scale of geologic description can give a reasonable first order approximation of fluid flow patterns and early breakthrough end page 181

evidence for late oligocene establishment of the antarctic circumpolar current removal of the last impediment to circum antarctic flow opening of the drake passage between antarctica and south america is essential to establishment of the acc and has been placed in both the earliest oligocene and earliest miocene on the basis of paleomagnetic reconstructions the tasman gateway between antarctica and tasmania notably deepened following 33 5 ma completion of the acc circuit has been seen as the key to major growth of the east antarctic ice sheet by thermal isolation of the continent an alternative argument attributes ice sheet growth to changes in atmospheric pco2 we present evidence on current strength and water mass properties suggesting a clear increase in flow speed and homogeneity of southern ocean water masses in the latest oligocene after about 23 95 ma marking establishment of the acc attributable to deep opening of drake passage the mi 1 glaciation may be a consequence establishment of a permanent low altitude ice sheet does not appear to take place prior to mid miocene cooling

lithofacies and depositional processes on a high steep margined carboniferous bashkirian moscovian carbonate platform slope sierra del cuera nw spain the depositional slope of the sierra del cuera a carboniferous bashkirian moscovian high steep margined carbonate platform provides excellent cross sections of lithofacies zonations and associated stratal geometries the steep 30 40 and nearly planar upper slope is dominated by massive sheet like layers of microbial cement rich boundstone which alternate with intercalations of red stained bryozoan cementstone with crinoids and brachiopods the slightly gentler 20 26 and concave upward lower slope is characterized by clast supported resedimented deposits the upper slope extended from platform break to ca 300 m water depth whereas lower slope sediments were deposited in water depths up to 600 700 m at which level the slope beds flatten to a few degrees toe of slope and interfinger with spiculitic and argillaceous basinal sediments between 250 and 450 m water depth boundstones and breccias alternated in a transitional zone the lower slope sediments include clast supported breccias with radiaxial fibrous cement in interparticle space mud to clast supported breccias with red stained carbonate mud matrix and packstone to grainstone and rudstone beds most of the clasts comprise boundstone reworked from an upper slope setting and smaller grains are platform and slope derived a pervasive submarine cementation occurs along the upper two thirds of the flank and this stabilized the slope slope deposition is interpreted as follows during active boundstone accretion microbial boundstone layers slid off and formed breccia tongues extending from the lower upper slope down to the toe of slope rock falls and avalanches were generated whenever the shear strength of the substrate of loose or partly lithified sediment was exceeded upper slope boundstone accretion and shedding independent of the depth of light penetration controlled most of the depositional processes on the slope cement dominated intervals are considered to be related to early highstand and or flooding phases relative sea level fluctuations and or associated changes in the water conditions are believed to be responsible for intervals of low boundstone production or cement precipitation whether the in situ boundstone and breccia are preferentially related to lowstand or highstand periods is as yet unclear

tectonic controls on stratigraphic evolution of the adana basin turkey the neogene adana basin of se turkey was initiated after thrust emplacement of the tauride belt to the north of the basin seismic reflection profiles across the southern part of the adana basin provide information on structural and stratigraphic evolution of the basin based on seismic character and the identification of unconformities three megasequences and two mega sequence boundaries are identified the first megasequence is partly coincident with an early miocene rifting event and it comprises reefs that have grown on fault footwall crests with fore and back reef sediments in intervening lows subsequent rapid flexurally induced subsidence generated an underfilled basin which was then passively filled by turbiditic sediments megasequence 2 showing aggradational character on seismic profiles further extensional faulting and coupled sinistral wrench faulting took place after the deposition of megasequence 2 erosional truncation of its upper part is followed by the deposition of continental and shallow marine sediments of megasequence 3 which shows localized progradational sequences characteristic of shallow water deposition further minor extensional faulting took place after the deposition of megasequence 3

factors that inhibit snowball earth simulation 1 a coupled ocean atmosphere general circulation model with a thermodynamic sea ice model the fast ocean atmosphere model version 1 5 is used to investigate the factors that inhibit the simulation of global sea ice in the control experiment with reduced solar luminosity 93 of modern low atmospheric pco2 140 ppm and an idealized tropical continent the sea ice margin equilibrates at 27 latitude a series of experiments was completed to systematically test the influence of deep ocean circulation wind driven ocean circulation convective mixing sea ice treatment and radiative cloud forcing on the sea ice extent model results indicate that both wind driven circulation and cloud radiative forcing are critical factors that inhibit sea ice advance into the low latitudes the wind driven ocean circulation transports heat to the sea ice margin stabilizing the sea ice margin clouds yield a positive radiative forcing over ice warming the air overlying sea ice and decreasing sensible heat loss at the sea ice margin in the absence of either factor sea ice expands to the equator within 15 model years yielding a snowball earth we also find that intensification of the hadley circulation as sea ice enters the hadley domain promotes the climate instability that leads to global sea ice cover results from this study help explain the wide disparity in conditions necessary to simulate global ice cover in previous climate models of the neoproterozoic

late oligocene initiation of the antarctic circumpolar current evidence from the south pacific the antarctic circumpolar current acc is a key feature of the southern ocean its development may have helped cool antarctica and initiate southern hemisphere glaciation the deep circulation of the acc must have been established after both the tasman gateway between antarctica and australia and the drake passage between south america and antarctica opened however estimates for acc initiation range over 20 m y from the middle eocene to early miocene a new piston core of upper oligocene to holocene sediments from the south pacific has allowed us to delimit the formation of the acc to the late oligocene ca 25 23 ma upper oligocene current worked sediments and a hiatus to the upper miocene result from the beginning of the modern acc flow i e when strong currents and mixing throughout the water column were established previously published nd isotope data date the first intrusion of pacific water into the atlantic much earlier the discrepancy with our results can be reconciled by the different methods measuring different flow regimes tracer methods such as nd are sensitive to relatively small and shallow incursions of water whereas pelagic erosional regimes require vigorous deep flow

development of a semi analytical method to calculate depth dependent temperature and stress changes investigation of micro seismicity at unterhaching uha gt 2 geothermal well since october 2007 when the hydrothermal production of geothermal energy from the deep underground started at unterhaching near munich germany several micro seismic events have been observed three of the five strongest events with local magnitudes ml ranging from 2 0 to 2 4 occurred in 2008 and were partially felt by the residents the reasons for these events are not clear these micro seismic events could have been induced by a variety of factors the strongest micro seismic event was observed soon after the injection of cold water pointing to an intrinsic relationship between micro seismic event and cold water injection one of the possible reasons for the observed micro seismic events could be the reinjection of cooled thermal water into the hotter underground inducing stress redistribution and shear failures in the reservoir formations around the injection wellbore uha gt 2 to justify this reason further investigation will be carried out in another simulation study to verify whether the shear failures induced by cold water injection were the major cause for the occurrence of these micro seismic events nevertheless before the simulation of shear failures temperature profiles in both the wellbore and surrounding rocks as well as their corresponding thermal stresses during cold water injection should be established in this study in this paper a new semi analytical simulation method has been developed to calculate simultaneously the temperature profiles in the wellbore and the surrounding rock formations and also determine the corresponding thermal stresses in the surroundings near wellbore field and subsequently verified by analytical solution results show that great tensile thermal stresses in the reservoir were initiated by the injection of the cooled thermal water in the injection wellbore uha gt 2 the results of the simulated thermal stresses indicate a great potential for the ensuing shear failures to affect an extensive area and could be used as input data for the planned shear failure simulations in the future

ocean and climate response to north atlantic seaway changes at the onset of long term eocene cooling abstract around the early middle eocene boundary the first occurrence of contourite drift sediments and widespread deep ocean erosion indicate changes in the north atlantic ocean circulation interestingly these changes coincide with the first steps of cenozoic cooling from the paleogene greenhouse climate towards the modern icehouse the cause for this ocean circulation reorganization is poorly understood since modern water mass tracers may have worked fundamentally different in the past and the paleoceanographic proxy record is limited in both time and space as a result it is challenging to reliably reconstruct the climatic and tectonic boundary conditions e g atmospheric greenhouse gas concentration and the depth and geometry of developing and closing passages between ocean basins in this study we attempt to identify thresholds in tectonic gateway passages and atmospheric co2 concentration using the fully coupled earth system model cosmos indeed the simulation of earth s past climates can unravel the physical processes driving deep water formation in a greenhouse world specifically we use cosmos to evaluate the impact of changes in the north atlantic gateways at the early middle eocene boundary on the north atlantic deep western boundary currents under low obliquity configuration we find that northern component waters start to form when the greenland scotland ridge reaches a threshold depth of deeper than 200 m while the arctic ocean is still shut off from the north atlantic in this scenario the relatively deep greenland scotland ridge allows for sufficient inflow of warm salty atlantic surface waters into the nordic seas to initiate convection during winter cooling opening the seaway towards the arctic leads to a cessation of northern component water formation as it allows for inflow of brackish surface waters into the northern nordic seas hindering northern component water formation

investigation of a new hdr system with horizontal wells and multiple fractures using the coupled wellbore reservoir simulator tough2mp well eos3 geothermal energy is renewable sustainable and available in large amounts the hot dry rock hdr systems in particular have the largest potential for long term sustainability and therefore draw a lot of attention the combination of horizontal wells and the technology of multiple transverse fractures technology is an attractive approach of such hdrs which is called in this paper as the specific egs enhanced geothermal system the main objective of this paper is to study the heat extraction over a period of 20 years by water circulating in a deep geothermal reservoir using this specific egs the wellbore flow module t2well eco2n is implemented in the parallelized simulator tough2mp as a new code tough2mp well eos3 which enables coupled wellbore reservoir simulations using this newly developed code the sensitivity of heat extraction against various parameters of the formation and fractures is assessed the influences of the fracture geometry and the space of two neighborhood fractures on the geothermal energy performance are analyzed according to the results in this paper the injection rate the wellbore radius and the fracture permeability are three main influence factors for the distribution of total flow through individual fractures a large injection rate a small wellbore radius and a large fracture width will cause the short circuit effect which reduces the performance of this specific egs compared with the classic hdr system doublet or triplet vertical wells single fracture this specific egs has a much higher performance and a longer duration of the economic production furthermore the horizontal wells can also be drilled in both directions of the minimum horizontal stress instead of in just one direction so that the energy performance is doubled and the investment cost per kw energy production is decreased and the advantage of this specific egs is significantly enlarged

vertical structure and transport of the antarctic circumpolar current in drake passage from direct velocity observations 1 the structure of the antarctic circumpolar current acc in drake passage is examined using 4 5 years of shipboard acoustic doppler current profiler adcp velocity data the extended 1000 m depth range available from the 38 khz adcp allows us to investigate the vertical structure of the current the mean observed current varies slowly with depth while eddy kinetic energy and shear variance exhibit strong depth dependence objectively mapped streamlines are self similar with depth consistent with an equivalent barotropic structure vertical wavenumber spectra of observed currents and current shear reveal intermediate wavenumber anisotropy and rotation indicative of downward energy propagation above 500 m and upward propagation below 500 m the mean observed transport of the acc in the upper 1000 m is estimated at 95 2 sv or 71 of the canonical total transport of 134 sv mean current speeds in the acc jets remain quite strong at 1000 m 10 20 cm s 1 vertical structure functions to describe the current and extrapolate below 1000 m are explored with the aid of full depth profiles from lowered adcp and a 3 year mean from the southern ocean state estimate sose a number of functions including an exponential are nearly equally good fits to the observations explaining 75 of the variance fits to an exponentially decaying function can be extrapolated to give an estimate of 154 38 sv for the full depth transport

descent toward the icehouse eocene sea surface cooling inferred from gdgt distributions the tex86 proxy based on the distribution of marine isoprenoidal glycerol dialkyl glycerol tetraether lipids gdgts is increasingly used to reconstruct sea surface temperature sst during the eocene epoch 56 0 33 9 ma here we compile published tex86 records critically reevaluate them in light of new understandings in tex86 palaeothermometry and supplement them with new data in order to evaluate long term temperature trends in the eocene we investigate the effect of archaea other than marine thaumarchaeota upon tex86 values using the branched to isoprenoid tetraether index bit the abundance of gdgt 0 relative to crenarchaeol gdgt 0 and the methane index mi we also introduce a new ratio gdgtrs which may help identify red sea type gdgt distributions in the geological record using the offset between tex86h and tex86l h l and the ratio between gdgt 2 and gdgt 3 2 3 we evaluate different tex86 calibrations and present the first integrated sst compilation for the eocene 55 to 34 ma although the available data are still sparse some geographic trends can now be resolved in the high latitudes 55 there was substantial cooling during the eocene 6 c our compiled record also indicates tropical cooling of 2 5 c during the same interval using an ensemble of climate model simulations that span the eocene our results indicate that only a small percentage 10 of the reconstructed temperature change can be ascribed to ocean gateway reorganization or paleogeographic change collectively this indicates that atmospheric carbon dioxide pco2 was the likely driver of surface water cooling during the descent toward the icehouse

timing and nature of the deepening of the tasmanian gateway 1 tectonic changes that produced a deep tasmanian gateway between australia and antarctica are widely invoked as the major mechanism for antarctic cryosphere growth and antarctic circumpolar current acc development during the eocene oligocene e o transition 34 33 ma ocean drilling program odp leg 189 recovered near continuous marine sedimentary records across the e o transition interval at four sites around tasmania these records are largely barren of calcareous microfossils but contain a rich record of siliceous and organic walled marine microfossils in this study we integrate micropaleontological sedimentological geochemical and paleomagnetic data from site 1172 east tasman plateau to identify four distinct phases a d in the e o tasmanian gateway deepening that are correlative among odp leg 189 sites phase a prior to 35 5 ma minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes phase b 35 5 33 5 ma increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom water currents phase c 33 5 30 2 ma further deepening to bathyal depths with episodic erosion by increasingly energetic bottom water currents phase d 30 2 ma establishment of stable open ocean warm temperate oligotrophic settings characterized by siliceous carbonate ooze deposition our combined evidence indicates that this early oligocene tasmanian gateway deepening initially produced an eastward flow of relatively warm surface waters from the australo antarctic gulf into the southwestern pacific ocean this proto leeuwin current fundamentally differs from previous regional reconstructions of eastward flowing cool water e g a proto acc during the early oligocene and thereby represents an important new constraint for reconstructing regional to global scale dynamics for this major global change event

sedimentation on a lower jurassic carbonate platform flank geometry sediment fabric and related depositional structures djebel bou dahar high atlas morocco abstract along the southern margin of the high atlas morocco carbonate platforms of lower jurassic age developed in a transtensional basin the south atlas trough complete exposure and preservation of the platform margin flank and basin of the djebel bou dahar allowed the subdivision of the slope into an upper mid and lower slope based on geometry sediment fabric and depositional structures at ca 50 m below the platform margin coral algal patch reefs and ooid sand shoals grade into the depositional slope the straight upper slope showing discontinuous bedding at angles up to 29 extends down to ca 250 m and consists mainly of poorly sorted mixtures of sand and gravel almost devoid of mud avalanching rockfall and shearing of the coarse gravelly sediment are the dominant processes readjusting the upper slope the middle and lower part of the slope profile extending down to ca 500 m below the margin is separated from the upper slope by a distinct slope break slope angles range from 19 near the slope break down to 4 8 where the slope merges with the basin plain the irregularly bedded mid slope is characterized by scouring and deposition of muddy sands and non cohesive gravelly debris flows sedimentation on the dominantly muddy concave upwards lower slope can be separated into evenly bedded shales muddy sands and mud free gravel sand mixtures deposited as debris sheets the results of this study emphasize the relationship between sediment fabric and the slope geometry of a carbonate platform flank the overall geometry internal heterogeneity and depositional structures are suggested to be strongly related to the original character of the sediment supplied to the djebel bou dahar platform flank

what sets the mean transport through drake passage twelve experiments with two coarse resolutions of a global ocean model using a variety of surface forcings are analyzed to address the question of what sets the mean transport through drake passage seven of the experiments do not have an active sea ice model but the remaining five do previous theories have suggested that the drake passage transport is governed by the cape horn sverdrup transport or alternatively is proportional to the square root of the meridional ekman transport at the latitude of drake passage the results presented here do not support either of these theories the drake passage transport depends quite strongly on the isopycnal diffusivity parameter in the model and less strongly on the background vertical diffusivity and horizontal viscosity parameters however when the magnitudes of these parameters are fixed the results show a very strong correlation between drake passage transport and both the strength of the meridional ekman transport at the latitude of drake passage and the thermohaline circulation off the antarctic shelf the relationships are monotonic but not linear the best estimate is that the meridional ekman transport drives 100 sv of drake passage transport while the remaining 30 sv are driven by the global thermohaline circulation

effect of the deepening of the tasman gateway on the global ocean 1 we examine the effect of the deepening of the tasman seaway at the end of the eocene in a climate model with realistic late eocene bathymetry and winds for this we have constructed an eocene numerical model based on the university of victoria climate model with wind forcing derived from a fully coupled eocene simulation the model climate state is characterized by an oceanic meridional overturning circulation moc involving southern hemisphere sinking and a northward atmospheric moisture transport across the equator the deepening of the tasman seaway in the presence of an open drake passage and the associated establishment of the antarctic circumpolar current acc have a limited climatic impact on antarctica nonetheless the antarctic deep sinking regions cool sufficiently to lead to a global deep ocean cooling of 3 c no initiation of northern component water is found indicating that this may require the development of a more mature acc previous studies suggest that the ross sea gyre cools the east coast of australia and expected the deepening of the tasman seaway to lead to a warming east of australia due to the introduction of warmer water from the australo antarctic gulf we here find that this warming is limited to close to the australian coast and that widespread cooling prevails further off shore

transport and variability of the antarctic circumpolar current in drake passage the baroclinic transport of the antarctic circumpolar current acc above 3000 m through drake passage is 107 3 10 4 sv and has been steady between 1975 and 2000 for six hydrographic sections 1993 2000 along the world ocean circulation experiment woce line sr1b the baroclinic transport relative to the deepest common level is 136 7 7 8 sv the acc transport is carried in two jets the subantarctic front 53 10 sv and the polar front pf 57 5 5 7 sv southward of the acc the southern antarctic circumpolar current transports 9 3 2 4 sv we observe the pf at two latitudes separated by 90 km this bimodal distribution is related to changes in the circulation and properties of antarctic bottom water three realizations of the instantaneous velocity field were obtained with lowered adcps from these observations we obtain near bottom reference velocities for transport calculations net transport due to these reference velocities ranges from 28 to 43 sv consistent with previous estimates of variability the transport in density layers shows systematic variations due to seasonal heating in near surface layers volume transport weighted mean temperatures vary by 0 40 c from spring to summer a seasonal variation in heat flux of about 0 22 pw finally we review a series of papers from the international southern ocean studies program the average yearlong absolute transport is 134 sv and the standard deviation of the average is 11 2 sv the error of the average transport is 15 to 27 sv we emphasize that baroclinic variability is an important contribution to net variability in the acc

effect of the drake passage throughflow on global climate abstract the role of the southern ocean in global climate is examined using three simulations with a coupled model employing geometries different only at the location of drake passage dp the results of three main experiments are examined 1 a simulation with dp closed 2 an experiment with dp at a shallow 690 m depth and 3 a realistic dp experiment the climate with dp closed is characterized by warmer southern hemisphere surface air temperature sat little antarctic ice and no north atlantic deep water nadw overturn on opening the dp to a shallow depth of 690 m there is an increase in antarctic sea ice and a cooling of the southern hemisphere but still no north atlantic overturn on fully opening the dp the climate is mostly similar in the southern hemisphere to dp at 690 m but the model now simulates nadw formation and a warming in the northern hemisphere this suggests the north atlantic thermohaline circulation depends not only on the existence of a dp throughflow but also on the dep

deciphering the role of southern gateways and carbon dioxide on the onset of the antarctic circumpolar current 1 growth of antarctic ice sheet during the cenozoic 34 million years ago appears as a potential tipping point in the long term cooling trend that began 50 ma ago for decades the onset of the antarctic circumpolar current acc following the opening of the drake passage and of the tasman seaway has been suggested as the main driver of the continental scale antarctic glaciation however recent modeling works emphasized that the eocene oligocene atmospheric carbon dioxide co2 lowering could be the primary forcing of the antarctic glaciation questioning the acc theory here we investigate the response of the acc to changes in co2concentrations occurring from the late eocene to the late oligocene we used a fully coupled atmosphere ocean model foam with a mid oligocene geography we find that the opening of southern oceanic gateways does not trigger the onset of the acc for co2typical of the late eocene 840 ppm a cooler background climatic state such as the one prevalent at the end of the oligocene is required to simulate a well developed acc in this cold configuration the intensified sea ice development around antarctica and the resulting brine formation lead to a strong latitudinal density gradient in the southern ocean favoring the compensation of the ekman transport and consequently the acc our results imply that the acc has acted as a feedback rather than as a driver of the global cooling

coupled climate impacts of the drake passage and the panama seaway tectonically active gateways between ocean basins have modified ocean circulation over earth history today the atlantic and pacific are directly connected via the drake passage which forms a barrier to the time mean geostrophic transport between the subtropics and antarctica in contrast during the warm early cenozoic era when antarctica was ice free the drake passage was closed instead at that time the separation of north and south america provided a tropical seaway between the atlantic and pacific that remained open until the isthmus of panama formed in the relatively recent geological past ocean circulation models have previously been used to explore the individual impacts of the drake passage and the panama seaway but rarely have the two gateways been considered together and most explorations have used very simple atmospheric models here we use a coupled ocean ice atmosphere model gfdl s cm2mc to simulate the impacts of a closed drake passage both with and without a panama seaway we find that the climate response to a closed drake passage is relatively small when the panama seaway is absent similar to prior studies although the coupling to a dynamical atmosphere does increase the temperature change however with a panama seaway closing drake passage has a much larger effect due to the cessation of deep water formation in the northern hemisphere both gateways alter the transport of salt by ocean circulation with the panama seaway allowing fresh pacific water to be imported to the north atlantic and the drake passage preventing the flow of saline subtropical water to the circum antarctic a flow that is particularly strong when the panama seaway is open thus with a panama seaway and a closed drake passage the southern ocean tends to be relatively salty while the north atlantic tends to be relatively fresh such that the deep ocean is ventilated from the circum antarctic ensuing changes in the ocean heat transport drive a bi polar shift of surface ocean temperatures and the intertropical convergence zone migrates toward the warmer southern hemisphere the response of clouds to changes in surface ocean temperatures amplifies the climate response resulting in temperature changes of up to 9 c over antarctica even in the absence of land ice feedbacks these results emphasize the importance of tectonic gateways to the climate history of the cenozoic and support a role for ocean circulation changes in the glaciation of antarctica

timing and climatic consequences of the opening of drake passage age estimates for the opening of drake passage range from 49 to 17 million years ago ma complicating interpretations of the relationship between ocean circulation and global cooling secular variations of neodymium isotope ratios at agulhas ridge southern ocean atlantic sector suggest an influx of shallow pacific seawater approximately 41 ma the timing of this connection and the subsequent deepening of the passage coincide with increased biological productivity and abrupt climate reversals circulation productivity linkages are proposed as a mechanism for declining atmospheric carbon dioxide these results also indicate that drake passage opened before the tasmanian gateway implying the late eocene establishment of a complete circum antarctic pathway

response of a comprehensive climate model to a broad range of external forcings relevance for deep ocean ventilation and the development of late cenozoic ice ages over the past few million years the earth descended from the relatively warm and stable climate of the pliocene into the increasingly dramatic ice age cycles of the pleistocene the influences of orbital forcing and atmospheric co2 on land based ice sheets have long been considered as the key drivers of the ice ages but less attention has been paid to their direct influences on the circulation of the deep ocean here we provide a broad view on the influences of co2 orbital forcing and ice sheet size according to a comprehensive earth system model by integrating the model to equilibrium under 40 different combinations of the three external forcings we find that the volume contribution of antarctic aabw vs north atlantic nadw waters to the deep ocean varies widely among the simulations and can be predicted from the difference between the surface densities at aabw and nadw deep water formation sites minima of both the aabw nadw density difference and the aabw volume occur near interglacial co2 270 400 ppm at low co2 abundant formation and northward export of sea ice in the southern ocean contributes to very salty and dense antarctic waters that dominate the global deep ocean furthermore when the earth is cold low obliquity i e a reduced tilt of earth s rotational axis enhances the antarctic water volume by expanding sea ice further at high co2 aabw dominance is favoured due to relatively warm subpolar north atlantic waters with more dependence on precession meanwhile a large laurentide ice sheet steers atmospheric circulation as to strengthen the atlantic meridional overturning circulation but cools the southern ocean remotely enhancing antarctic sea ice export and leading to very salty and expanded aabw together these results suggest that a sweet spot of low co2 low obliquity and relatively small ice sheets would have poised the amoc for interruption promoting dansgaard oeschger type abrupt change the deep ocean temperature and salinity simulated under the most representative glacial state agree very well with reconstructions from the last glacial maximum lgm which lends confidence in the ability of the model to estimate large scale changes in water mass geometry the model also simulates a circulation driven increase of preformed radiocarbon reservoir age which could explain most of the reconstructed lgm preindustrial ocean radiocarbon change however the radiocarbon content of the simulated glacial ocean is still higher than reconstructed for the lgm and the model does not reproduce reconstructed lgm deep ocean oxygen depletions these ventilation related disagreements probably reflect unresolved physical aspects of ventilation and ecosystem processes but also raise the possibility that the lgm ocean circulation was not in equilibrium finally the simulations display an increased sensitivity of both surface air temperature and aabw volume to orbital forcing under low co2 we suggest that this enhanced orbital sensitivity contributed to the development of the ice age cycles by amplifying the responses of climate and the carbon cycle to orbital forcing following a gradual downward trend of co2

asian monsoons in a late eocene greenhouse world the strong present day asian monsoons are thought to have originated between 25 and 22 million years myr ago driven by tibetan himalayan uplift however the existence of older asian monsoons and their response to enhanced greenhouse conditions such as those in theeocene period 55 34myrago are unknownbecause of the paucity of well dated records here we show late eocene climate records revealing marked monsoon like patterns in rainfall and wind south and north of the tibetan himalayan orogen this is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from myanmar and by aeolian dust deposition in northwest china our climate simulations support modern like eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhancedgreenhouse conditions counterbalanced the negative effect of lowertibetanrelief onprecipitation these strong monsoons later weakened with the global shift to icehouse conditions 34myr ago

bioclastic sediment lobes on a supply dominated upper cretaceous carbonate platform margin montagna della maiella italy a thick bioclastic sediment wedge was deposited on the slope of the maiella carbonate platform margin in the late campanian to late maastrichtian the wedge consists of lobate depositional units laterally and vertically convex structures the complex internal geometries of the lobes combine characteristics of unidirectional sandwaves and the alternating point sources of deltas excellent outcrop permits a detailed documentation and discussion of the depositional processes the sediment wedge constitutes a supersequence which prograded along the platform margin as a result of high sediment supply and forced regression within the supersequence a hierarchy of higher order stratigraphic units sequence sets and sequences are developed the individual bioclastic sediment lobes are interpreted as systems tracts and parasequences of the sequences within the sequence sets

injection and thermal breakthrough in fractured geothermal reservoirs lbl 12698 preprint submitted to the journal of geophysical research injection and thermal breakthrough in fractured geothermal reservoirs gudmundur s bodvarsson and chin fu tsang may 1981 two week loan copy this is a library circulating copy which may be borrowed for two weeks for a personal retention copy call tech info division ext 6782 prepared for the u s department of energy under contract w 7405 eng 48

heat transport deep waters and thermal gradients coupled simulation of an eocene greenhouse climate for the first time a coupled general circulation model with interactive and dynamical atmospheric oceanic and sea ice components is used to simulate an eocene 50 ma greenhouse climate we introduce efficient ocean spin up methods for coupled paleoclimate modeling sea surface temperatures ssts and salinities evolve unconstrained producing the first proxy data independent estimates for these eocene climate parameters tropical and extratropical model predicted ssts are warmer than modern values by 3 and 5 c respectively salinity driven deep water formation occurs in the north atlantic and tethys the zonal average overturning circulation is weaker than modern eocene ocean heat transport is 0 6 pw less than modern in the northern hemisphere and 0 4 pw greater in the southern hemisphere the model predicted near modern vertical and meridional eocene temperature gradients imply that the dominant theory for maintaining low gradients increased ocean heat transport is incorrect or incomplete and other mechanisms should be explored

volume transport of the antarctic circumpolar current from bottom pressure measurements abstract meausrements from bottom pressure gauges located at the north and south sides of drake passage are used to extend the one year time series of volume transport of the antarctic circumpolar current acc given previously by whitworth a small error in that paper is corrected and a revised transport time series is presented which shows the importance of including the transport in the northern and southern margins of drake passage direct measurements of vertical shear averaged across the passage are in good agreement with geostrophic shear and suggest that the acc is in geostrophic balance although most of the acc transport is in the baroclinic field transport fluctuations are mainly barotropic transport estimates based on pressure difference alone differ from the estimates of whitworth by less than 10 106 m3 s 1 fluctuations in transport of almost half of the mean value occur over periods as short as two weeks

early cenozoic glaciation antarctic weathering and seawater 87sr 86sr is there a link abstract stable and radiogenic isotopic and sedimentological data from sub antarctic deep sea sediment cores reveal a temporal link between changes in seawater 87 sr 86 sr ratios and major episodes of late eocene early oligocene climate change the 87 sr 86 sr records show two major inflections one at 38 39 ma near the middle late eocene boundary followed by another at 33 4 ma similarly the oxygen isotope ice rafted debris and clay assemblage records indicate two important climatic events the appearance of alpine glaciers and or small ice sheets on antarctica in the late eocene at 38 39 ma followed by a rapid transition to larger and more permanent temperate ice sheets in the early oligocene at 33 4 ma moreover during the early oligocene 30 33 ma three to four inferred peaks in glacial activity appear to coincide with subtle steps in the 87 sr 86 sr record the coupled variations in climate and seawater sr isotope ratios during the eocene oligocene imply a strong causal link between the two either changes in climate directly influenced patterns of continental weathering and hence seawater chemistry and or a tectonic event e g uplift as reflected in weathering and seawater chemistry triggered relatively abrupt changes in global climate