climate and environment of a pliocene warm world the pliocene epoch 5 33 2 58 million years ago ma was a generally warmer and wetter interval with atmospheric co2 concentrations at or slightly above modern levels this paper provides an overview of pliocene vegetation sea surface temperatures and climate modelling outcomes most prominent changes in pliocene biome distribution compared to today include a northwards shift of temperate and boreal vegetation zones in response to a warmer and wetter climate as well as an expansion of tropical savannas and forests at the expense of deserts faunal analysis techniques and modelling experiments using the hadley centre climate model identified significantly higher pliocene sea surface temperatures at mid and high latitudes of the northern hemisphere with cooling or unchanged sea surface temperatures at low latitudes global mean annual surface temperatures mat are estimated to have been 2 to 3 c higher during the piacenzian 3 6 2 58 ma than today with a reduced equator to pole gradient the marine realm during the pliocene was characterised by a reconfiguration of ocean gateways particularly the narrowing of the indonesian seaway and closure of the central american isthmus which produced essentially a modern pattern of ocean circulation in the southern ocean a warm early pliocene gave way to late piacenzian cooling proxy data indicate a reduced east to west sea surface temperature gradient in the tropical pacific during the pliocene warmth the pliocene is one of the most intensively studied geological intervals of the pre quaternary no other warm period in the geological past yields such a unique combination of near modern atmospheric co2 concentrations palaeogeography and palaeobiology however this paper also identifies data gaps and shortcomings in the reconstruction of pliocene environments using proxy data and climate models on which future research should focus

river bed aggradation due to overloading this paper presents the analytical solution of the aggradation problem for a more appropriate boundary condition the analytical results are compared with the laboratory experimental data

effect of early pliocene uplift on late pliocene cooling in the arctic atlantic gateway despite the undisputed role of the arctic ocean in the modern and pliocene climate system the arctic has only recently attracted public awareness that ongoing fundamental change in the arctic cryosphere could be a response to global warming clarification of the arctic s role in global climate during the pliocene is however largely hampered by equivocal stratigraphic constraints from a well dated pliocene sequence from the yermak plateau off nw spitsbergen we present sedimentological and geochemical data indicating that 4 million years ago terrigenous sediment supply and sources changed abruptly in response to a regional tectonic uplift event we argue that this event together with contemporary uplift and tilting along the northwestern european continental margin preconditioned the landmasses for glacial ice build up during intensification of the northern hemisphere glaciation inhg our data further suggest that the final deepening widening of the arctic atlantic gateway the fram strait between 6 5 and 5 ma gradually caused increased deep water mass exchange which in turn likely contributed to the intensification of the north atlantic thermohaline circulation coupled to the north atlantic warm pool as a regional moisture source declining atmospheric co2 levels and other feedback mechanisms during the pliocene the regional tectonic activities in the high northern latitudes caused decreased summer ablation and thus allowed the initial build up of glacial ice both in scandinavia and the sub aerially exposed svalbard barents sea culminating in the first large scale coastline shelf edge glaciations at 2 75 ma

the disappearance of the european north african sirenia mammalia abstract sirenia inhabited the coastal waters of europe and north africa from the eocene until the end of the pliocene they are the only herbivorous marine mammals and their presence in the european north african realm is supported by almost 400 fossil records their dependence on seagrass as well as their ecological needs limited their capability to adapt to the climate changes that occurred during the cenozoic their disappearance from european and mediterranean shores occurred in two different steps 1 the european atlantic extinction related to global cooling and fragmentation of the seagrass meadows which greatly reduced sirenia habitats and resources 2 their disappearance from the mediterranean linked not to declining resources but to the onset of continental glaciations in the northern hemisphere

on the causes of mid pliocene warmth and polar amplification the mid pliocene 3 to 3 3 ma ago is a period of sustained global warmth in comparison to the late quaternary 0 to 1 ma ago and has potential to inform predictions of long term future climate change however given that several processes potentially contributed relatively little is understood about the reasons for the observed warmth or the associated polar amplification here using a modelling approach and a novel factorisation method we assess the relative contributions to mid pliocene warmth from elevated co2 lowered orography and vegetation and ice sheet changes the results show that on a global scale the largest contributor to mid pliocene warmth is elevated co2 however in terms of polar amplification changes to ice sheets contribute significantly in the southern hemisphere and orographic changes contribute significantly in the northern hemisphere we also carry out an energy balance analysis which indicates that that on a global scale surface albedo and atmospheric emmissivity changes dominate over cloud changes we investigate the sensitivity of our results to uncertainties in the prescribed co2 and orographic changes to derive uncertainty ranges for the various contributing processes

numerical modeling of aggradation and degradation in alluvial channels the saint venant equations describing unsteady flow in open channels and the continuity equation for the conservation of sediment mass are numerically solved to determine the aggradation and degradation of channel bottom due to an imbalance between water flow and sediment discharge for this purpose the maccormack explicit finite difference scheme is introduced this scheme is second order accurate handles shocks and discontinuities in the solution without any special treatment and allows simultaneous solution of the water and sediment equations thereby obviating the need for iterations the sediment transport relationship in any form may be included in the computations computational procedures are outlined for incorporating the typical boundaries for hydraulic engineering applications the mathematical model presented here is applied to predict 1 bed level changes due to sediment overloading 2 development of longitudinal profile due to base level lowering 3 and bed level changes associated with the migration of knickpoints the computed results are compared with the available experimental data obtained on laboratory flumes the agreement between the computed and experimental results is satisfactory

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

shifts in north atlantic planktic foraminifer biogeography and subtropical gyre circulation during the mid piacenzian warm period abstract the mid piacenzian mp warm period 3 264 3 025 ma has been identified as the most recent time in geologic history during which mean global surface temperatures were considerably warmer than today for a sustained period this interval has therefore been proposed as a potential albeit imperfect analog for future climate change and as such has received much scientific attention over the past two decades central to this research effort is the pliocene research interpretation and synoptic mapping prism project an iterative paleoenvironmental reconstruction of the mp focused on increasing our understanding of warm period climate forcings dynamics and feedbacks by providing three dimensional data sets for general circulation models a mainstay of the prism project has been the development of a global sea surface temperature sst data set based primarily upon quantitative analyses of planktic foraminifer assemblages supplemented with geochemical sst estimates wherever possible in order to improve spatial coverage of the prism faunal data set in the low and mid latitude north atlantic this study provides a description of the mp planktic foraminifer assemblage from five ocean drilling program sites 951 958 1006 1062 and 1063 in the subtropical gyre a region critical to atlantic ocean circulation and tropical heat advection assemblages from each core provide evidence for a temperature and circulation driven 5 10 northward displacement of mp faunal provinces as well as regional shifts in planktic foraminifer populations linked to species ecology and interactions general biogeographic trends also indicate that relative to modern conditions gyre circulation was stronger particularly the gulf stream north atlantic current and north equatorial current and meridionally broader a comparison of mid piacenzian and modern north atlantic planktic foraminifer assemblages suggests that low latitude western boundary currents were less than 1 c warmer while eastern boundary currents were 1 2 c warmer supporting the hypothesis of enhanced northward heat advection along western boundary currents and warming of high latitude northeast atlantic source regions for the canary current these findings are consistent with a model of reduced meridional sst gradients with little to no low latitude warming and more vigorous ocean circulation results therefore support the theory that enhanced meridional overturn circulation and associated northward heat advection made an important contribution in conjunction with elevated atmospheric co2 concentrations to the 2 3 c global surface temperature increase relative to today and strong polar amplification of sst warmth during the mp warm period

a contourite drift system on the baffin bay west greenland margin linking pliocene arctic warming to poleward ocean circulation terrestrial records from the canadian arctic archipelago indicate that a temperate and moist climate prevailed during the pliocene i e before the intensification of northern hemisphere glaciations but the controlling factors causing these conditions remains elusive here we present marine seismic reflection evidence of contiguous kilometer scale sedimentary drifts or contourites buried below the west greenland shelf which relates high latitude pliocene warmth to intense geostrophic currents along the eastern baffin bay margin seismic to borehole correlation indicates that enhanced current induced deposition began during the middle miocene ca 17 15 ma and terminated during the late pliocene onset of global cooling the transition from along slope sediment transport to trough mouth fan progradation designates the onset of greenland ice sheet glaciers advancing across the continental shelf and coincides with increasing iceberg productivity in baffin bay and the nordic seas from 3 3 to 2 7 ma our results suggest that the baffin bay west greenland margin formed a late neogene passageway for persistent ocean boundary currents and we infer that the pliocene high latitude warmth was to a significant extent caused or enhanced by advection of subtropical heat and moisture to the arctic regions attenuation of the poleward heat flux conveyed by the paleo current system may have been critical for allowing glacial buildup in the canadian arctic and northern greenland during the late pliocene we further surmise that vertical tectonic adjustments of the continental margin played a role in this attenuation which eventually caused the demise of meridional ocean circulation through baffin bay

carbonate preservation records of the past 3 myr in the norwegian greenland sea and the northern north atlantic implications for the history of nadw production carbonate preservation records from a number of drill sites in the north atlantic and adjacent norwegian greenland sea ngs are used to reconstruct variations in north atlantic deep water nadw production over the past 3 myr before the initiation of major northern hemisphere glaciation good carbonate preservation was recorded in the north atlantic and the ngs supporting the superconveyor model of accelerated nadw formation in the late pliocene after the inception of main northern hemisphere glaciation nadw formation in the ngs was blocked off during the period 2 8 1 9 ma carbonate was only badly preserved due to 1 low production of carbonate shells in surface waters 2 sluggish renewal of deep waters induced by a rather stable sea ice cover and or 3 production of carbonate corrosive dense brines during sea ice formation e g sea ice dissolution mode in contrast contemporaneous good preservation in the adjacent north atlantic indicates efficient nadw production during the middle matuyama 1 9 1 4 ma the first intrusions of the proto norwegian current into a narrow corridor in the southeastern ngs are evidenced by much better carbonate preservation a decrease both in carbonate content and preservation towards the north and west of this corridor indicates the proximity of the polar front and gives evidence that nadw production was efficiently triggered by the atlantic water entrainment mode during the past 1 2 myr carbonate preservation patterns in the ngs clearly reflect major global events like the mid pleistocene transition and the mid brunhes dissolution event the onset of the mid pleistocene transition at 1 2 ma is characterized by a complete shift to higher carbonate contents in the southeastern ngs and labrador sea overall good preservation during both interglacials and glacials is only interrupted by high frequency short term dissolution spikes which were induced by ice sheet collapse and development of extensive meltwater lids as a consequence nadw was produced nearly continuously during glacials in the nordic seas however due to its lower density it was entrained into intermediate water levels in the north atlantic and thus enforced the intermediate water circulation loop whereas a decrease in lower nadw production is observed contemporaneously

coupled and decoupled numerical modeling of flow and morphological evolution in alluvial rivers existing numerical river models are mostly built upon asynchronous solution of simplified governing equations the strong coupling between water flow sediment transport and morphological evolution is thus ignored to a certain extent an earlier study led to the development of a fully coupled model and identified the impacts of simplifications in the water sediment mixture and global bed material continuity equations as well as of the asynchronous solution procedure for aggradation processes this paper presents the results of an extended study along this line highlighting the impacts on both aggradation and degradation processes simplifications in the continuity equations for the water sediment mixture and bed material are found to have negligible effects on degradation this is however in contrast to aggradation processes in which the errors purely due to simplified continuity equations can be significant transiently the asynchronous solution procedure is found to entail appreciable inaccuracy for both aggradation and degradation processes further the asynchronous solution procedure can render the physical problem mathematically ill posed by invoking an extra upstream boundary condition in the supercritical flow regime finally the impacts of simplified continuity equations and an asynchronous solution procedure are shown to be comparable with those of largely tuned friction factors indicating their significance in calibrating numerical river models it is concluded that the coupled system of complete governing equations needs to be synchronously solved for refined modeling of alluvial rivers

low frequency pliocene climate variability in the eastern nordic seas the pliocene 5 3 2 6 ma is often described as a relatively stable climatic period with warm temperatures characterizing high latitudes new suborbital resolved stable isotope records from ocean drilling program hole 642b in the eastern nordic seas document that the pliocene was not a stable period characterized by one climate rather seven distinct climate phases each lasting between 150 000 and 400 000 years are identified and characterized in the time interval 5 1 3 1 ma four of the transitions between the defined climate phases occurred close to an eccentricity minimum and a minimum in amplitude of change for northern hemisphere summer insolation while two occurred around an eccentricity maximum and a maximum in amplitude in insolation change hence a low frequency response of the nordic seas to insolation forcing is indicated in addition paleogeographic and related paleoceanographic changes expansion of the arctic sea ice cover and onset of northern hemisphere glaciation were important factors behind the evolving pliocene low frequency variability in the eastern nordic seas it is likely that the identified climate phases and transitions are important beyond the nordic seas due to their association with changes to both insolation and paleogeography however a strong and variable degree of diagenetic calcite overgrowth is documented for the planktic foraminifera especially influencing the planktic 18o results the absolute values and amplitude of change cannot be taken at face value

significantly warmer arctic surface temperatures during the pliocene indicated by multiple independent proxies temperatures in the arctic have increased by an astounding 1 c in response to anthropogenic forcing over the past 20 years and are expected to rise further in the coming decades the pliocene 2 6 5 3 ma is of particular interest as an analog for future warming because global temperatures were signifi cantly warmer than today for a sustained period of time with continental confi gurations similar to present here we estimate mean annual temperature mat based upon three independent proxies from an early pliocene peat deposit in the canadian high arctic our proxies including oxygen isotopes and annual ring widths mat 0 5 1 9 c coexistence of paleovegetation mat 0 4 4 1 c and bacterial tetraether composition in paleosols mat 0 6 5 0 c yield estimates that are statistically indistinguishable the consensus among these proxies suggests that arctic temperatures were 19 c warmer during the pliocene than at present while atmospheric co 2 concentrations were 390 ppmv these elevated arctic pliocene temperatures result in a greatly reduced and asymmetrical latitudinal temperature gradient that is probably the result of increased poleward heat transport and decreased albedo these results indicate that arctic temperatures may be exceedingly sensitive to anthropogenic co 2 emissions

sea surface temperatures of the mid piacenzian warm period a comparison of prism3 and hadcm3 it is essential to document how well the current generation of climate models performs in simulating past climates to have confidence in their ability to project future conditions we present the first global in depth comparison of pliocene sea surface temperature sst estimates from a coupled ocean atmosphere climate model experiment and a sst reconstruction based on proxy data this enables the identification of areas in which both the climate model and the proxy dataset require improvement in general the fit between model produced sst anomalies and those formed from the available data is very good we focus our discussion on three regions where the data model anomaly exceeds 2 c 1 in the high latitude north pacific a systematic model error may result in anomalies that are too cold also the deeper pliocene thermocline may cause disagreement along the california margin either the upwelling in the model is too strong or the modeled thermocline is not deep enough 2 in the north atlantic the model predicts cooling in the center of a data based warming trend that steadily increases with latitude from 1 5 c to 6 c the discrepancy may arise because the modeled north atlantic current is too zonal compared to reality which is reinforced by the lowering of the altitude of the pliocene western cordillera mountains in addition the model s use of modern bathymetry in the higher latitudes may have led the model to underestimate the northward penetration of warmer surface water into the arctic 3 finally though the data and model show good general agreement across most of the southern ocean a few locations show offsets due to the modern land sea mask used in the model additional considerations could account for many of the modest data model anomalies such as differences between calibration climatologies the oversimplification of the seasonal cycle and differences between sst proxies i e seasonality and water depth new sst estimates from data sparse and regionally important areas will greatly enhance our ability to judge model performance

modelling pliocene warmth contribution of atmosphere oceans and cryosphere the relative role of the atmosphere oceans and cryosphere in contributing towards middle pliocene warmth ca 3 ma bp is investigated using the hadcm3 coupled ocean atmosphere general circulation model the model was initialised with boundary conditions from the usgs prism2 data set and a pliocene atmospheric co2 level of 400 ppmv and run for 300 simulated years the simulation resulted in a global surface temperature warming of 3degreesc compared to present day in contrast to earlier modelling experiments for the pliocene surface temperatures warmed in most areas including the tropics 1 5degreesc compared with present day the model predicts a general pattern of ocean warming 1 5degreesc in both hemispheres to a depth of 2000 m below which no significant differences are noted sea ice coverage is massively reduced up to 90 the flow of the gulf stream north atlantic drift is up to 100 mm s 1 greater in the pliocene case analysis of the model predicted meridional streamfunction suggests a global pattern of reduced outflow of antarctic bottom water aabw up to 5 sv a shallower depth for north atlantic deep water formation and weaker thermohaline circulation 3 sv the decrease in aabw occurs mainly in the pacific rather than atlantic ocean model diagnostics for heat transports indicate that neither the oceans nor the atmosphere are transporting significantly more heat in the pliocene scenario rather these results indicate that the major contributing mechanism to global pliocene warmth was the reduced extent of high latitude terrestrial ice sheets 50 reduction on greenland 33 reduction on antarctica and sea ice cover resulting in a strong ice albedo feedback these results highlight the need for further studies designed to improve our knowledge regarding pliocene terrestrial ice configurations

quantifying uncertainty in model predictions for the pliocene plio qump initial results examination of the mid pliocene warm period mpwp 3 3 to 3 0 ma bp provides an excellent opportunity to test the ability of climate models to reproduce warm climate states thereby assessing our confidence in model predictions to do this it is necessary to relate the uncertainty in model simulations of mpwp climate to uncertainties in projections of future climate change the uncertainties introduced by the model can be estimated through the use of a perturbed physics ensemble ppe developing on the uk met office quantifying uncertainty in model predictions qump project this paper presents the results from an initial investigation using the end members of a ppe in a fully coupled atmosphere ocean model hadcm3 running with appropriate mpwp boundary conditions prior work has shown that the unperturbed version of hadcm3 may underestimate mpwp sea surface temperatures at higher latitudes initial results indicate that neither the low sensitivity nor the high sensitivity simulations produce unequivocally improved mpwp climatology relative to the standard whilst the high sensitivity simulation was able to reconcile up to 6 c of the data model mismatch in sea surface temperatures in the high latitudes of the northern hemisphere relative to the standard simulation it did not produce a better prediction of global vegetation than the standard simulation overall the low sensitivity simulation was degraded compared to the standard and high sensitivity simulations in all aspects of the data model comparison the results have shown that a ppe has the potential to explore weaknesses in mpwp modelling simulations which have been identified by geological proxies but that a best fit simulation will more likely come from a full ensemble in which simulations that contain the strengths of the two end member simulations shown here are combined

the key role of global solid earth processes in preconditioning greenland s glaciation since the pliocene after 500 ma of absence major northern hemisphere glaciations appeared during the plio pleistocene with greenland leading other northern areas here we propose that three major solid earth processes underpinned build up of the greenland ice sheet first a mantle plume pulse responsible for the north atlantic igneous province at 60 ma regionally thinned the lithosphere younger plume pulses led to uplift which accelerated at 5 ma lifting the parts of the east greenland margin closest to iceland to elevations of more than 3 km above sea level second plate tectonic reconstruction shows a 6 northward component of greenland motion relative to the mantle since 60 ma third a concurrent northward rotation of the entire mantle and crust towards the pole dubbed true polar wander tpw contributed an additional 12 change in latitude these global geodynamic processes preconditioned greenland to sustain long term glaciation emphasizing the role of solid earth processes in driving long term global climatic transitions

topological constraints by the greenland scotland ridge on amoc and climate abstractchanges in the geometry of ocean basins have been influential in driving climate change throughout earth s history here we focus on the emergence of the greenland scotland ridge gsr and

amplified north atlantic warming in the late pliocene by changes in arctic gateways under previous reconstructions of late pliocene boundary conditions climate models have failed to reproduce the warm sea surface temperatures reconstructed in the north atlantic using a reconstruction of mid piacenzian paleogeography that has the bering strait and canadian arctic archipelago straits closed however improves the simulation of the proxy indicated warm sea surface temperatures in the north atlantic in the community climate system model we find that the closure of these small arctic gateways strengthens the atlantic meridional overturning circulation by inhibiting freshwater transport from the pacific to the arctic ocean and from the arctic ocean to the labrador sea leading to warmer sea surface temperatures in the north atlantic this indicates that the state of the arctic gateways may influence the sensitivity of the north atlantic climate in complex ways and better understanding of the state of these arctic gateways for past time periods are needed

the amplification of arctic terrestrial surface temperatures by reduced sea ice extent during the pliocene abstract many past warm periods exhibited greatly reduced latitudinal temperature gradients as a result of amplified arctic surface temperatures as well as more seasonably equable temperatures the pliocene is a period of particular interest because co2 forcing was comparable to today and yet arctic temperatures were significantly warmer than today here we describe an atmospheric general circulation model experiment assessing the response of terrestrial temperatures in the mid pliocene 3 02 to 3 26 ma to an ice free arctic and we compare the simulation with a compilation of proxy based pliocene paleotemperature reconstructions our experiments indicate that the amplification of arctic surface temperatures is much more sensitive to the extent of sea ice than continental ice the removal of arctic sea ice results in simulated mean annual surface temperatures that better match terrestrial proxy data rmse 2 9 c than experimental conditions that included seasonal sea ice rmse 4 5 c our simulations also show a decrease in the seasonal amplitude of temperatures in the absence of sea ice which is consistent with theory predicting more equable climates in the arctic during warmer intervals in earth s history our results demonstrate that once sea ice is removed latent heat is lost from the ocean to the atmosphere as water vapor that can be circulated by the atmosphere which results in warming of continental interiors although our sensitivity experiment does not help to identify the full array of feedback mechanisms responsible for the amplification of arctic surface temperatures during the pliocene it does demonstrate that arctic terrestrial surface temperatures are extremely sensitive to the spatial and seasonal extent of sea ice

a combined magnetometry and gravity study across zagros orogeny in iran abstract in this work the structural geology and the tectonic conditions of the zagros orogeny along the route of qom to kermanshah cities were investigated using the combined geophysical methods of the airborne magnetometry and the ground based gravity data airborne magnetometry data of iran with a line space of survey 7 5 km were used to model the magnetic susceptibility property along the route at first the airborne magnetic data were stably 500 m downward continued to the ground surface in order to enhance minor changes of the earth s magnetic field over the studied region afterward 3d inverse modeling of the magnetic data was implemented to the downward continued data and subsequently the section of magnetic susceptibility variation along the desired route was extracted and imaged at depth the acquired model could appropriately predict the observed magnetic data showing low misfit values between the observation and the predicted data the analytic signal filter was applied to the reduced to pole rtp magnetic data leading to the determination of the active and probable hidden faults in the structural zones of the zagros such as sanandaj sirjan central domain cd and urumieh dokhtar based upon the generated peaks along the profile of analytic signal filter in addition the density variations of the subsurface geological layers were determined by 3d inverting of the ground based gravity data over the whole study area and extracting this property along the route the joint models of magnetic susceptibility and density variation could appropriately localize the traces of faults along with the geologically and tectonically structural boundaries in the region the locations of faults correspond well to the variation of geophysical parameters on the inverted sections probable direction slope and extension at depth of these faults were also determined on the sections indicating a high tectonized zone of the sanandaj sirjan zone ssz parallel to the zone of the urumieh dokhtar magmatic assemblage udma the udma zone increases the magnetic and the bouguer anomalies by intruding into the cd zone as well

amplified late pliocene terrestrial warmth in northern high latitudes from greater radiative forcing and closed arctic ocean gateways abstract proxy reconstructions of the mid piacenzian warm period mpwp between 3 264 and 3 025 ma suggest terrestrial temperatures were much warmer in the northern high latitudes 55 90 n referred to as nhl than present day climate models participating in the pliocene model intercomparison project phase 1 pliomip1 tend to underestimate this warmth for instance the underestimate is 10 c on average across nhl and up to 17 c in the canadian arctic region in the community climate system model version 4 ccsm4 here we explore potential mpwp climate forcings that might contribute to this mpwp mismatch we carry out seven experiments to assess terrestrial temperature responses to pliocene arctic gateway closure variations in co 2 level and orbital forcing at millennial time scale to better compare the full range of simulated terrestrial temperatures with sparse proxy data we introduce a pattern recognition technique that simplifies the model surface temperatures to a few representative patterns that can be validate with the limited terrestrial proxy data the pattern recognition technique reveals two prominent features of simulated pliocene surface temperature responses first distinctive patterns of amplified warming occur in the nhl which can be explained by lowered surface elevation of greenland pattern and amount of arctic sea ice loss and changing strength of atlantic meridional overturning circulation second patterns of surface temperature response are similar among experiments with different forcing mechanisms this similarity is due to strong feedbacks from responses in surface albedo and troposphere water vapor content to sea ice changes which overwhelm distinctions in forcings from changes in insolation co 2 forcing and arctic gateway closure by comparing ccsm4 simulations with proxy records we demonstrate that both model and proxy records show similar patterns of mpwp nhl terrestrial warmth but the model underestimates the magnitude high insolation greater co 2 forcing and arctic gateways closure each contributes to reduce the underestimate by enhancing the arctic warmth of 1 2 c these results highlight the importance of considering proxy nhl warmth in the context of pliocene arctic gateway changes and variations in insolation and co 2 forcing

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

chronology of greenland scotland ridge overflow what do we really know abstract as a sill constricting the exchange of deep water masses between the nordic seas and the north atlantic which forms an essential part of the atlantic meridional overturning circulation the dynamic height of the greenland scotland ridge and thus its overflow have an important influence on global climate several dsdp odp and iodp sites have been drilled in the north atlantic to shed light on the overflow and climate development reconstructions of bathymetry and sediment thickness have been put forward as well as calculations of the potential temperature of the conduit feeding the iceland plume the available studies have been screened to construct a conceptual model for the evolution of the palaeo circulation in the north atlantic and identify possible weaknesses in our knowledge details e g timing and location about the onset of the overflow are unknown and especially the paleogene development remains enigmatic the database for this period is inadequate and covers only small areas the discussion centres on the earliest traces of the overflow leading to formation of sediment drifts in the eastern north atlantic more data provide a better base to reconstruct variations for the neogene overflow but also appears insufficient for in depth analyses in time and space sediment drifts in the iceland basin indicate a first iceland faroe ridge overflow for the early miocene denmark strait overflow appears to have started in mid miocene times but evidence for this still is sparse grids of high resolution seismic reflection data across all sediment drifts and all limbs of the greenland scotland ridge combined with deeper drill sites targeting the complete sedimentary column down to basement are needed to fully understand the chronology of the greenland scotland ridge overflow and its detailed impact on climate

aggradation and degradation of alluvial channel beds a nonlinear parabolic model for nonequilibrium processes in alluvial rivers is presented analytical expressions for the characteristic parameters of relevant aggradation and degradation processes are derived the validity and limitations of the model are assessed by comparing the analytical results with the available experimental data

isotopic evidence of cool winter conditions in the mid piacenzian pliocene of the southern north sea basin oxygen isotope thermometry of aequipecten opercularis and atrina fragilis bivalves which demonstrate all year growth provides quantitative evidence of cool temperate winter conditions below 10 c during deposition of the mid piacenzian oorderen sands and time equivalent strata in the southern north sea basin snsb isotopic summer temperatures seafloor are within or only marginally above the cool temperate range upper limit 20 c the occurrence of warm temperate dinoflagellate cysts alongside and presumably contemporaneous with the bivalves indicates the development of a correspondingly warm surface layer in summer encystment allowing the dinoflagellates to survive cool winter conditions this evidence of greater surface seasonality than now is consistent with greater global warmth and a reduction in the vigour of the gulf stream north atlantic drift gs nad leading to a reduced supply of winter heat this reduction in gs nad strength may be linked to breaching of the emerging isthmus of panama

microfaunal evidence for elevated pliocene temperatures in the arctic ocean the migration of thermophilic marine ostracoda into the arctic ocean during the pliocene indicates that winter and summer ocean temperatures around arctic margins were 0 c and 3 c respectively and that ice free conditions existed for most or all of the arctic by at least 3 5 3 0 ma probably earlier the opening of the bering strait allowed marine organisms to migrate through the arctic ocean mostly from the pacific ocean migrant taxa such as cythere hemicythere and neomonoceratina are known from pliocene deposits of alaska and canada as well as neogene deposits of the north pacific and atlantic oceans on the basis of ecological and zoogeographic information on ostracode species from more than 800 modern core top samples for the north atlantic north pacific and arctic oceans we determined winter and summer temperature tolerances for migrant taxa to be at or above about 0 c and 3 c this suggests ice free summers and probably a perennially ice free arctic ocean in some regions elevated water temperatures in the arctic ocean between 3 5 and 2 0 ma is supported by evidence for late pliocene increased meridional heat transport in the north atlantic ocean

mid pliocene warmth stronger greenhouse and stronger conveyor abstract three million years ago prior to the onset of northern hemisphere glaciation global mean temperatures may have been as much as 3 5 c warmer than at present we present evidence based on the carbon isotopic composition of marine organic matter that atmospheric co2 levels at this time were on average only about 35 higher than the preindustrial value of 280 ppm we also present carbon isotopic evidence for stronger thermohaline circulation in the atlantic ocean during the warmest intervals and propose that the north atlantic conveyor belt may act as a positive feedback to global warming by enhancing sea ice retreat and decreasing high latitude albedo based on our results it seems unlikely that the mid pliocene warm period was a doubled co2 world

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

bathymetric controls on pliocene north atlantic and arctic sea surface temperature and deepwater production the mid pliocene warm period mpwp 3 3 to 3 0 ma is the most recent interval in earth s history in which global temperatures reached and remained at levels similar to those projected for the near future the distribution of global warmth however was different than today in that the high latitudes warmed more than the tropics multiple temperature proxies indicate significant sea surface warming in the north atlantic and arctic oceans during the mpwp but predictions from a fully coupled ocean atmosphere model hadcm3 have so far been unable to fully predict the large scale of sea surface warming in the high latitudes if climate proxies accurately represent pliocene conditions and if no weakness exists in the physics of the model then model boundary conditions may be in error here we alter a single boundary condition bathymetry to examine if pliocene high latitude warming was aided by an increase in poleward heat transport due to changes in the subsidence of north atlantic ocean ridges we find an increase in both arctic sea surface temperature and deepwater production in model experiments that incorporate a deepened greenland scotland ridge these results offer both a mechanism for the warming in the north atlantic and arctic oceans indicated by numerous proxies and an explanation for the apparent disparity between proxy data and model simulations of pliocene northern north atlantic and arctic ocean conditions determining the causes of pliocene warmth remains critical to fully understanding comparisons of the pliocene warm period to possible future climate change scenarios

euro north african sirenia biodiversity as a response to climate variations abstract earth has a latitudinal biodiversity gradient in which more species inhabit tropical than polar regions frequently attributed to seasonality this ecological pattern is applied to the evolution of the euro north african sirenians and its relation to cenozoic climate change climate disruption changes in seasonality and geological processes such as sea level variations are statistically tested as primary drivers to explain sirenian evolution and regional amphi mediterranean sirenian speciation and biodiversity

micropaleontological evidence for increased meridional heat transport in the north atlantic ocean during the pliocene the middle pliocene approximately 3 million years ago has been identified as the last time the earth was significantly warmer than it was during the last interglacial and holocene a quantitative micropaleontological paleotemperature transect from equator to high latitudes in the north atlantic indicates that middle pliocene warmth involved increased meridional oceanic heat transport

control of north atlantic deep water circulation by the greenland scotland ridge coherent bathymetric features along the reykjanes ridge indicate that there were significant changes in the flux of buoyant material within the icelandic hot spot during the neogene the radial extent of the topographic swell associated with this hot spot is of the order of 1000 to 2000 km and therefore these changes affected the greenland scotland ridge gsr at present sill depths along the gsr are generally less than 500 m with the deepest passage being less than 1000 m making the overflow water sensitive to even small changes in the ridge depths reconstructions of neogene mantle plume activity correlate with the deepwater circulation patterns in the north atlantic times of high mantle plume activity caused northern component water ncw production to cease ncw fluxes resumed once this phase of high mantle plume activity slowed the long term climate change during the neogene must be controlled by factors other than ncw production however climatic optima during the late early miocene and early pliocene appear to have been augmented by high ncw fluxes while subsequent middle miocene and middle pliocene coolings correlate with uplifts on the gsr and reduced ncw flux we suggest that reductions in ncw may have contributed to both of these cooling events

architecture of north atlantic contourite drifts modified by transient circulation of the icelandic mantle plume overflow of northern component water the precursor of north atlantic deep water appears to have varied during neogene times it has been suggested that this variation is moderated by transient behavior of the icelandic mantle plume which has influenced north atlantic bathymetry through time thus pathways and intensities of bottom currents that control deposition of contourite drifts could be affected by mantle processes here we present regional seismic reflection profiles that cross sedimentary accumulations bjorn gardar eirik and hatton drifts prominent reflections were mapped and calibrated using a combination of boreholes and legacy seismic profiles interpreted seismic profiles were used to reconstruct solid sedimentation rates bjorn drift began to accumulate in late miocene times its average sedimentation rate decreased at 2 5 ma and increased again at 0 75 ma in contrast eirik drift started to accumulate in early miocene times its average sedimentation rate increased at 5 5 ma and decreased at 2 2 ma in both cases there is a good correlation between sedimentation rates inferred northern component water overflow and the variation of icelandic plume temperature independently obtained from the geometry of diachronous v shaped ridges between 5 5 and 2 5 ma the plume cooled which probably caused subsidence of the greenland iceland scotland ridge allowing drift accumulation to increase when the plume became hotter at 2 5 ma drift accumulation rate fell we infer that deep water current strength is modulated by fluctuating dynamic support of the greenland scotland ridge our results highlight the potential link between mantle convective processes and ocean circulation

numerical simulation of degradation of alluvial channel beds the bed degradation in alluvial channels resulting from sediment interruption is simulated numerically by solving the one dimensional momentum and continuity equations for water and sediment a simple bed layer model is proposed to simulate the plane bed armoring process the model does not contain any parameter that needs calibration the agreement between the numerical results and the available experimental data is satisfactory

new constraints on upper mantle s velocity structure and crustal thickness of the iranian plateau using partitioned waveform inversion summary the continental collision between the african and eurasian plates resulted in a tectonically young and complex deformation in the iranian plateau the present day iranian plateau is characterized by diverse tectonic domains including the continental collisions e g zagros and alborz and the oceanic plate subduction e g makran partitioned waveform inversion method is used here to image the s velocity structure of the upper mantle and moho depth variations in the iranian plateau of nearly 3000 waveforms originally selected for the analysis we have fitted 974 waveforms from 101 events and 39 stations which result in 11 688 linear constraints on the upper mantle s velocity structure and moho depth for the region our new seismic images show seismically faster upper mantle beneath the zagros and the arabian plate compared to the central iran and alborz this high velocity anomaly has descended beneath the central iran along the main zagros thrust across the zagros collision zone the tomographic images show a slab stagnation in the transition zone at about 410 km depth in the form of a horizontal high velocity zone which does not penetrate the deeper parts of the mantle the lowest s velocities are concentrated beneath the central iran and alborz according to our velocity models a strong high velocity anomaly is resolved beneath the trapped south caspian basin with clear indication of westward underthrusting beneath the talesh and western alborz in makran southeast iran there is a clear evidence of subduction of oceanic crust of the arabian plate beneath the makran belt which is correlated with seismicity pattern across the makran zone also the inverted moho map using a priori information of crustal thickness constraints shows the large crustal thickness beneath the zagros suture zone in some places to a maximum depth of 65 km which indicates the influence of crustal thickening and shortening beneath arabian eurasian plate boundary a significantly crustal thinning is observable across the south caspian basin compared to its margins

neogene overflow of northern component water at the greenland scotland ridge in the north atlantic ocean flow of north atlantic deep water nadw and of its ancient counterpart northern component water ncw across the greenland scotland ridge gsr is thought to have played an important role in ocean circulation over the last 60 ma the iceland plume has dynamically supported an area which encompasses the gsr consequently bathymetry of the gsr has varied with time due to a combination of lithospheric plate cooling and fluctuations in the temperature and buoyancy within the underlying convecting mantle here we reassess the importance of plate cooling and convective control on this northern gateway for ncw flow during the neogene period following wright and miller 1996 to tackle the problem benthic foraminiferal isotope data sets have been assembled to examine 13c gradients between the three major deep water masses i e northern component water southern ocean water and pacific ocean water composite records are reported on an astronomical timescale and a nonparametric curve fitting technique is used to produce regional estimates of 13c for each water mass confidence bands were calculated and error propagation techniques used to estimate ncw and its uncertainty despite obvious reservations about using long term variations of 13c from disparate analyses and settings and despite considerable uncertainties in our understanding of ancient oceanic transport pathways the variation of ncw through time is consistent with independent estimates of the temporal variation of dynamical support associated with the iceland plume prior to 12 ma 13c patterns overlap and ncw cannot be isolated significant long period variations are evident which are consistent with previously published work from 12 ma when lithospheric cooling probably caused the gsr to submerge completely long period 13c patterns diverge significantly and allow reasonable ncw estimates to be made our most robust result is a dramatic increase in ncw overflow between 6 and 2 ma when dynamical support generated by the iceland plume was weakest between 6 and 12 ma a series of variations in ncw overflow have been resolved

pliocene climate variability northern annular mode in models and tree ring data the northern annular mode nam and its regional expression the north atlantic oscillation nao are the primary interannual oscillatory systems in the northern hemisphere in the modern climate nam has been linked with a number of weather extremes including large terrestrial temperature increases and extreme snowfalls its connection to climate is more controversial although a change in its behaviour between 1970 and 2000 coincided with rapid temperature increases in the northern hemisphere the north atlantic and nordic seas are a key component in pliocene climate showing the largest increases from modern sea surface temperature to understand these changes and the ability of climate models to reproduce them we must consider simulations of the nam here we show that existing mid pliocene simulations exhibit large changes to the mean state and variability in the north atlantic and a significant dampening of the nao through sensitivity experiments this change is primarily attributed to the impact of the lowering of the rocky mountains as the timing of rocky mountains uplift is still disputed simulations of the north atlantic region contain significant uncertainty particularly relating to interannual variability and its climate feedbacks new high temporal resolution climate proxy data is required to test these model reconstructions here we report new annual resolution data and an analysis of climate variability from fossil tree rings these fossils from sites in the canadian arctic provide support for a strong north atlantic oscillation during the pliocene

growth of subtropical forests in miocene europe the roles of carbon dioxide and antarctic ice volume the middle miocene is a crucial period for the evolution of apes and it corresponds to their appearance in europe the dispersion of apes was made possible by tectonic changes and the expansion of their habitat sub tropical forest in europe the context in which the middle miocene climatic optimum occurred still lacks constraints in terms of atmospheric p co 2 and ice sheet volume and extent using a coupled atmosphere ocean general circulation model gcm and dynamic vegetation model we investigated the sensitivity of miocene climate and vegetation to p co 2 levels and antarctic ice sheet configurations our results indicate that higher than present p co 2 is necessary to simulate subtropical forest in western and central europe during the middle miocene but that a threshold at high p co 2 makes subtropical forest partly collapse moreover removing ice over antarctica modifies oceanic circulation and induces warmer and slightly wetter conditions in europe which are consistent with the expansion of subtropical forest these results suggest that a small east antarctic ice sheet 25 of present day ice volume together with higher than present p co 2 values are in better agreement with available european middle miocene data

the relationship between neogene dinoflagellate cysts and global climate dynamics abstract the neogene period 23 03 2 58 ma underwent a long term relatively gradual cooling trend culminating in the glacial interglacial climate of the quaternary palaeoclimate studies on the neogene have provided important information for understanding how modern patterns of atmospheric and oceanic circulation developed and how they may relate to wider environmental change here we use a newly created global database of neogene dinoflagellate cysts the tertiary oceanic parameters information system topis to investigate how dinoflagellate cysts recorded the cooling of neogene surface marine waters on a global scale species with warm and cold water preferences were determined from previously published literature and extracted from the database percentages of cold water species were calculated relative to the total number of species with known temperature preferences from each site and compared throughout the neogene at differing latitudes overall the percentage of cold water species increases gradually through the neogene this trend indicates a gradual global cooling that is comparable to that reported from other marine and terrestrial proxies this also demonstrates the use of dinoflagellate cysts in determining temperature change on both extended temporal and wide geographical scales the increase in the percentage of cold water species of dinoflagellate cysts recorded worldwide from the early and middle miocene to the late pliocene indicates a global scale forcing agent on neogene climate such as co2

modeling the miocene climatic optimum ocean circulation 1 ocean circulation is investigated using the community climate system model 3 ccsm3 forced with early to middle miocene 20 14 ma topography bathymetry vegetation and modern co2 significant bottom water formation is modeled in the weddell sea along with intermediate north component water formation in the north atlantic this is attributed primarily to stronger and weaker than modern convective preconditioning in the weddell and labrador seas respectively global meridional overturning and gyre circulation is weaker in the miocene due to weaker midlatitude westerlies in the southern hemisphere caused by lowering of the meridional surface temperature gradient in addition to regional influences on convection subsurface temperatures in the miocene are significantly higher in the far north atlantic greenland norwegian seas and arctic basin compared to the present ocean heat transport is symmetrical about the equator and resembles that simulated for late cretaceous and early cenozoic climates suggesting the northern hemisphere dominated ocean heat transport active today developed after the middle miocene simulated deep water warming in the miocene is more than an order of magnitude lower than indicated by proxies this discrepancy is not reconciled by higher co2 due to the persistence of sea ice at sites of deep water formation this suggests that either the ccsm3 is insufficiently sensitive to miocene boundary conditions greater greenhouse forcing existed than is currently reconstructed or that proxy records of warming are exaggerated given the diversity of global miocene proxy records and their near unanimous estimate of a significantly warmer earth the first two options are more likely

variability in the deep and intermediate water circulation of the atlantic ocean during the past 25 000 years northern hemisphere modulation of the southern ocean the relative flux of north atlantic deep water nadw out of the atlantic can be monitored in the southern ocean where high 13c nadw mixes rapidly with low 13c recirculated pacific water before forming antarctic bottom water aabw by using 13c measured in benthic foraminifera as a water mass tracer it is shown that the southern ocean was dominated by pacific water with little nadw contribution during the last glaciation these tracer results document the direct physical connection between insolation controlled northern hemisphere oscillations and changes in the chemical and physical properties of southern ocean water the 13c records from the deep tropical atlantic document the transition from an atlantic dominated by southern ocean water during the last glaciation to an atlantic dominated by nadw during the holocene with more southern ocean water in the deep atlantic during the last glaciation the boundary between nadw and southern ocean water was north of its modern position allowing more southern ocean water to enter the eastern atlantic through the romanche fracture zone carbon isotope records from the caribbean and mediterranean seas suggest that the influence of mediterranean overflow water mow extended to the caribbean during the last glaciation and therefore was a volumetrically much more important water mass in the intermediate depth atlantic than it is today

experimental modeling of role of gravity and lateral shortening in zagros mountain belt dynamically scaled analogs of the geologic structures of the zagros mountain belt are used to argue that different parts of the zagros mountains of iran record different combinations of the effects of a gravity driven overturn and a southwest northeast lateral shortening superimposed on the zagros overturn partially scaled material models have been used to simulate the zagros geodynamics which involve layer parallel compression of a 6 to 7 km thick phanerozoic carbonate cover containing a pattern of preshortening diapirs the folds in the zagros form rapidly 1 5 mm yr in a 20 to 30 km wide zone reactive some of the preshortening diapirs and generate new synshortening listric diapirs a third set of postshortening diapirs rises from the hormuz decollement behind the fold thrust front model buckle folds superimposed on diapirs or pillows tend to avoid and curve around preshortening diapirs which flatten in the synclines model profiles show that lateral shortening induces residual salt at depth to flow toward and rise through the anticlinal cores as synshortening or postshortening diapirs i suggest that any salt pillows in currently diapir free zones of the zagros fold thrust belt may surface as diapirs through the anticlines in the future in the absence of well data seismic and field observations i have used only three map pattern criteria to recognize the timing of diapirs these are locally obscured by extrusive salt sheets preshortening diapirs are generally small and elongate parallel to fold axes and are restricted to synclines synshortening diapirs are elongate perpendicular to the fold axes and are restricted to anticlines postshortening diapirs can be the same size as synshortening diapirs or larger and can be circular they are more common in the anticlines

river bed profiles with imposed sediment load the rate and extent of bed aggradation resulting from sediment overloading are determined by means of computer based numerical experiments a nondimensional momentum equation along with continuity equations for water and sediment of unsteady flow for a wide prismatic channel are solved numerically using recently developed relations for sediment discharge and friction factor numerical experiments are executed for a range of values of nondimensional input data principal dependent variables such as changes in bed levels from equilibrium levels and the length of aggradation determined from the computer experiments are correlated by multiple linear regression analysis to the independent nondimensional variables numerical results show that the sediment diffusion coefficient is a function of the rate of sediment overloading the agreement between the numerical results and the available experimental data is satisfactory

the structure and kinematics of the southeastern zagros fold thrust belt iran from thin skinned to thick skinned tectonics 1 we present the first complete balanced cross section across the southeastern zagros fold thrust belt zftb the following main structural features emerge from this section 1 in the south of the zftb the proterozoic to recent sedimentary sequence has been decoupled from its panafrican basement along the ductile basal evaporites and folded into a series of large detachment anticlines ongoing shortening of these structures has resulted in migration of the basal salt layers into the cores of the anticlines and propagation of forelimb thrusts 2 in the north of the zftb deep seated ramps have folded the hanging wall rocks and produced imbrications and duplex structures within the higher levels of the sedimentary sequence 3 out of sequence thrusts linked to major seismogenic basement faults have cut through the structures in the cover of the zftb a three step incremental restoration of the section shows that two main phases of deformation can be separated in the tectonic evolution of the zftb a mio pliocene thin skinned phase in the course of which most of the structures in the cover were generated followed by a pliocene to recent thick skinned phase expressed as out of sequence faulting in the cover which is currently underlined by the seismicity within the basement in plan view the initial structures of the southeastern zftb developed with a curved shape essentially controlled by the shape and thickness of the underlying proterozoic salt basin i e the jura style in the following basement involved phase out of sequence thrusts cut at oblique angles through the preexisting structures of the cover the total shortening absorbed in the cover amounts to at least 45 km corresponding to a ratio of 22

characteristic parameters of nonequilibrium processes in alluvial channels of finite length an analytical solution for the characteristic parameters of the nonequilibrium processes of aggradation due to sediment augmentation and degradation due to sediment diminution in alluvial channels of finite length is presented the analytical solution for small time agrees with that for a semi infinite channel the analytical solution is compared with the available experimental data the limitations of the analytical model are explained

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic

response of marine palynomorphs to neogene climate cooling in the iceland sea odp hole 907a abstract the present study on odp leg 151 hole 907a combines a detailed analysis of marine palynomorphs dinoflagellate cysts prasinophytes and acritarchs and a low resolution alkenone based sea surface temperature sst record for the interval between 14 5 and 2 5 ma and allows to investigate the relationship between palynomorph assemblages and the paleoenvironmental evolution of the iceland sea a high marine productivity is indicated in the middle miocene and palynomorphs and ssts both mirror the subsequent long term neogene climate deterioration the diverse middle miocene palynomorph assemblages clearly diminish towards the impoverished assemblages of the late pliocene parallel with a somewhat gradual decrease of ssts being as high as 20 c at 13 5 ma to around 8 c at 3 ma superimposed palynomorph assemblages not only reflect middle to late miocene climate variability partly coinciding with the short lived global miocene isotope events mi events but also the initiation of a proto thermohaline circulation across the middle miocene climate transition which led to increased meridionality in the nordic seas last occurrences of species cluster during three events in the late miocene to early pliocene and are ascribed to the progressive strengthening and freshening of the proto east greenland current towards modern conditions a significant high latitude cooling between 6 5 and 6 ma is depicted by the supraregional decahedrella event coeval with lowest miocene productivity and a sst decline in the early pliocene a transient warming is accompanied by surface water stratification and increased productivity that likely reflects a high latitude response to the global biogenic bloom the succeeding crash in palynomorph accumulation and a subsequent interval virtually barren of marine palynomorphs may be attributed to enhanced bottom water oxygenation and substantial sea ice cover and indicates that conditions seriously affecting marine productivity in the iceland sea were already established well before the marked expansion of the greenland ice sheet at 3 3 ma