oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

the progressive intensification of northern hemisphere glaciation as seen from the north pacific ocean drilling project odp site 882 50 22 n 167 36 e provides the first high resolution grape density magnetic susceptibility carbonate opal and foraminifera planktonic and benthic stable isotopes records between 3 2 and 2 4 ma in the northwest pacific we observed a dramatic increase in ice rafting debris at site 882 at 2 75 ma which is coeval with that found in the norwegian sea suggesting that the eurasian arctic and northeast asia were significantly glaciated from 2 75 ma onwards prior to 2 75 ma planktonic foraminifera 18o records indicate a warming or freshening trend of 4 c or 2 over 80 ka if this is interpreted as a warm pre glacial pliocene north pacific it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet the dramatic drop in sea surface temperatures sst 7 5 c at 2 75 ma ended this suggested period of enhanced sst and thus the proposed moisture pump moreover at 2 79 and 2 73 ma opal mass accumulation rates mar decrease in two steps by five fold and is accompanied by a more gradual long term decrease in caco3 mars evidence from the southern ocean odp site 704 indicates that just prior to 2 6 ma there is a massive increase in opal mars the opposite to what is found in the north pacific this indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget possibly caused by changes in deep ocean circulation the initiation of northern hemisphere glaciation occurred in the late miocene with a significant build up of ice on southern greenland however the progressive intensification did not occur until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia glaciated at 2 75 ma approximately 100 ka before the glaciation of alaska 2 65 ma and 200 ka before the glaciation of the north east american continent 2 54 ma

cenozoic ice volume history development of a composite oxygen isotope record to view cenozoic ice volume and ocean temperature history a composite 18 o time series was constructed for tropical shallow dwelling planktonic foraminifers and for deep water benthic foraminifers we conclude that cenozoic benthic 18 o primarily reflect considerable deep ocean temperature variation and that tropical planktonic 18 o afford the best record of cenozoic ice volume the planktonic composite indicates the presence of a significant ice budget for the past 40 m y the difference between the benthic and planktonic 18 o composites suggests that low latitude production of warm saline bottom water dominated tertiary thermohaline circulation

origin nature and world climate effect of arctic ocean ice cover during the cenozoic an open water arctic ocean changed to the modern permanently ice covered condition significant world climate modification accompanied this change but the precise role of the arctic ocean in major pleistocene climate events is controversial the present ice cover averages 3 m thickness but there are theories that during the pleistocene it was antarctic like several thousand metres thick the time of origin of the ice cover is placed as young as 0 7 myr ago and as old as the middle miocene any theory concerned with origin nature and climatic response of the arctic ice cover must consider the ocean s sediment record

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

the time transgressive initiation of boreal ice caps continental and oceanic evidence reconciled abstract oxygen isotope analyses of planktonic foraminifera and organic carbon 13c measurements of the sediment at dsdp site 116 compared with planktonic foraminiferal counts and sedimentological investigations previously published by poore and berggren indicate 1 that the hatton rockall basin did not undergo any significant temperature change 3 1 ma ago when the first boreal ice caps were established on the western side of the north atlantic 2 that the ice rafted detrital grains appeared close to 2 7 ma ago still without noticeable change in the growth temperature of the plankton and 3 that the major cooling took place at about 2 3 ma and can be correlated with the pretiglian first cold phase in northern europe thispattern of climatic change shows the existence of a lag in the initial glaciation of the western and eastern shores of the atlantic and can be explained by the persistence of the north atlantic drift between 3 1 and 2 3 ma in the northeastern atlantic ocean

application of a seasonal climate model to cenozoic glaciation mathematical modelling of climate has matured as a discipline to the point that it can be useful in palaeoclimatology as an example a new two dimensional energy balance model is described and applied to several problems of current interest the model includes the seasonal cycle and the detailed land sea geographical distribution by examining the changes in the seasonal cycle when external perturbations are forced upon the climate system it is possible to construct hypotheses about the origin of mid latitude ice sheets and polar ice caps in particular the model predicts a rather sudden potential for glaciation over large areas when the earth s orbital elements are only slightly altered similarly the drift of continents or the change of atmospheric carbon dioxide over geological time can induce radical changes in continental ice cover with the advance of computer technology and our improved understanding of the individual components of the climate system it should be possible to test these ideas in far more realistic models in the near future

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

results of global atmospheric circulation experiments on an earth with a meridional pole to pole continent four general circulation models forced by mean annual insolation and having an energy balance ocean have been run for pole to pole continents 1 low relief 750 m average elevation 2 high plateau 1500 m average elevation 3 mostly low 750 m but with 3 km mountains on the west and 4 mostly low 750 m but with 3 km mountains on the east the high plateau continent emphasizes the contrast between high and low pressure systems marginal mountains on either coast enhance moisture transport from the west to the continental interior but mountains on the east eliminate the tropical wet belt and produce the most arid scenario in none of the experiments do zonal climate boundaries trend steeply equatorward from east to west all of the models produce more arid continental conditions than exist today

the analysis and interpretation of stratification cycles beds in carbonate successions often form regular patterns either there is a cyclic repetition of beds with different thicknesses or bundles of beds occur separated from each other by some distinct layer any such group will be called a stratification cycle cycles of this type are from 0 5 m to several meters in thickness and they seem to be present throughout the geological column the analysis of sedimentary cycles involves three stages 1 regional mapping is necessary to understand the facies of the sediment establishing the lateral persistence of bedding eliminates the possibility that bedding is caused by diagenetic processes 2 petrographic examination and in particular analyses of primary structures are used to reconstruct the sedimentation conditions during cycle formation such conditions are extremely important for judging the time content of individual beds 3 the quantitative analysis of vertical sections using power spectral methods can find superimposed cycles and enables one to judge their degree of regularity the latter approach is illustrated using lower carboniferous limestone sections from nw ireland as an example spectral analysis finds a stratification cycle of 1 to 3 m in thickness each cycle consists of between five to seven limestone beds upper jurassic limestone marl successions from southern germany and late cretaceous and early tertiary successions from italy show a very similar cyclic pattern the scale of the cycles and their regularity suggest that they are ultimately caused by variations in the earth s orbit possibly by climatic cycles as was postulated by milankovitch however the exact mechanism which links sedimentation with orbital variations is not known

attenuation of coda waves in the dead sea region abstract coda waves of local small earthquakes in the dead sea region part of the jordan rift structure show frequency invariant codas that is q c q 0 f f 0 n with q 0 65 5 f 0 1 hz and n 1 05 0 04 for hypocentral distances between 10 and 55 km and lapse times less than 60 sec this justifies for example the use of part of the coda for relative site response studies lacking direct q measurements q c might be considered as a first approximation of q for the region for short hypocentral distances r q c with lapse time t has been observed

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

cretaceous climate a comparison of atmospheric simulations with the geologic record abstract atmospheric simulations using realistic cretaceous geography 100 million years ago suggest that paleography is an important factor governing the nature of the circulation the simulated cretaceous atmospheric circulations are markedly different both from the present day atmospheric circulation and from the classical hypotheses of a weaker circulation and poleward displacement of circulation features e g the subtropical high therefore they pose specific questions which can be tested against the geologic record aspects of the cretaceous simulations are verified in comparisons with the geologic record the simulations serve to guide areas of future paleoclimatic research and to formulate better the nature of the problem of warm equable climates

the late cenozoic uplift climate change paradox the geologic evidence for worldwide uplift of mountain ranges in the neogene is ambiguous estimates of paleoelevation vary according to whether they are based on the characteristics of fossil floras on the masses and grain sizes of eroded sediments or on calculations of increased thickness of the lithosphere as a result of faulting detrital erosion rates can be increased both by increased relief in the drainage basin and by a change to more seasonal rainfall patterns the geologic record provides no clear answer to the question whether uplift caused the climatic deterioration of the neogene or whether the changing climate affected the erosion system in such a way as to create an illusion of uplift we suggest that the spread of c4 plants in the late miocene may have altered both the erosion and climate systems these changes are responsible for the apparent contradictions between data supporting uplift and those supporting high elevations in the past

the cause of the late cenozoic northern hemisphere glaciations a climate change enigma the ultimate cause of the onset of glaciations remains elusive but in the case of northem hemisphere glaciation it is probable that several factors acted in combination general global cooling resulted from reduction of atmospheric c02 by weathering of silicate rocks exposed by erosion of late cenozoic uplifts uplifts in south asia southwestern north america and scandinavia occurred at distances appropriate for the generation of quasi permanent rossby waves in the atmosphere the resulting winds given suitable moisture sources were favourable for causing large scale precipitation at mid latitudes on the northern continents moisture sources were provided by the closure of the central american isthmus gulf stream flow increased carrying warm subtropical waters to high latitudes the denmark strait deepened permitting greater outflow of deep water from the norwegian greenland sea the relative importance of each of these factors should be investigated by additional atmospheric and ocean climate model sensitivity studies

neogene stratigraphy paleoceanography and paleobiogeography in northwest south america and the evolution of the panama seaway abstract the atrato basin in the pacific coastal region of nw south america colombia exhibits stratigraphic and biostratigraphic characteristics similar to other neogene pacific coastal basins of southern central america and northern south america an evaluation of the neogene stratigraphy and foraminiferal biostratigraphy with emphasis on paleoceanographic and paleobiogeographic phenomena indicate the following 1 previous to the middle miocene well aerated deep and open oceanic conditions and free and active water circulation prevailed along the steep continental margins of nw south america 2 during the early middle miocene right after the neogene hiatus nh 2 15 2 ma tectonic disturbances triggered the initial uplift of the panama sill bottom water circulation foraminiferal and sedimentation changes are observed in both the pacific and caribbean coastal areas of nw south america 3 during the middle miocene coinciding with the neogene hiatus nh 3 12 9 11 8 ma an abrupt paleobathymetric change from lower to middle bathyal depths indicates a major uplift of the panama sill to about 1000 m reflecting the middle miocene tectonic disturbances in nw south america 4 during the late middle miocene immediately following this uplift a distinctive pacific benthic foraminiferal fauna abruptly appeared and extended from ecuador to california because these assemblages do not occur in the adjacent caribbean region a circulation barrier between the atlantic and pacific oceans as a result of intensification of the cool marginal california current is proposed anoxic middle to upper bathyal environments prevailed under well aerated cool surface waters in the pacific coastal areas of nw south america 5 during the latest miocene immediately following the neogene hiatus nh 6 7 0 6 3 ma surface water circulation between the caribbean and the pacific was re established and the previous influence of the california current disappeared a rapid filling and shallowing of the basin to mostly neritic depths is indicated along the pacific and caribbean coastal basins of colombia as well as a progressive increase in similarity between the coastal pacific and caribbean benthic biotas this shallowing in the early late miocene also appears to have been associated with the earliest terrestrial interchange of ground sloths to north america and raccoons and their allies to south america 6 immediately following early pliocene time the panamanian isthmus became completely emergent providing a terrestrial environment favourable for intermingling of terrestrial faunas and floras between north and south america i correlate this pliocene uplift with the neogene hiatus nh 8 3 7 3 1 ma four regional unconformities associated with tectonic disturbances in the nw corner of south america have also been recognized and correlated with neogene hiatuses recorded from the oceans early middle miocene middle miocene late miocene and early pliocene

the role of vertical chemical fractionation in controlling late quaternary atmospheric carbon dioxide the 30 decrease in atmospheric carbon dioxide during glacial maxima must be driven by some change in the chemical circulation of the ocean here a new model for late quaternary co2 variability is presented which resolves some problems occurring in previous models including the timing of carbon dioxide response and changes in the oxygen content of the deep ocean the primary driving factor in this model is a rearrangement of chemical distributions in the ocean whereby labile nutrients and metabolic co2 are concentrated in deep waters rather than in intermediate waters as observed in the modern ocean this new bottom heavy chemical structure does not affect atmospheric carbon dioxide directly instead co2 induced acidity lowers the deep ocean carbonate ion concentration and temporarily increases carbonate dissolution rates oceanic alkalinity then rises until the deep ocean carbonate ion is restored to its steady state value the resulting increase in oceanic alkalinity draws co2 out of the atmosphere into the ocean alkalinity and atmospheric co2 lag several thousand years behind the change in oceanic chemical structure this delayed response is determined by the limited rate of continental weathering and deep ocean carbonate dissolution relative to the oceanic alkalinity inventory it is proposed that characteristic deglacial and preglacial states of the ocean are leading factors driving glacial interglacial climate changes this concept reinterprets the carbon isotope contrast between surface water and deep waters 13c p b as due to a shift of light metabolic carbon from intermediate waters into deep waters the process is illustrated here by a simple equilibrium five box ocean model the observed intermediate depth nutrient depletion is not sufficient in itself to determine which of several possible mechanisms are operating and some mechanisms are not as effective in changing atmospheric co2 as others the largest response is seen from deepening the regeneration cycle of organic carbon the least response is seen from converting north atlantic deep water into intermediate water

mass balanced paleogeographic reconstructions paleogeography paleotopography and paleobathymetry of a closed erosion depositional system can be reconstructed by restoring sedimentary masses to elevated surfaces in a drainage basin based on the inverse of present erosion equations and adjusting for isostasy sea level changes sediment compaction and thermal subsidence the erosion deposition history of the northwestern gulf of mexico margin and its western central north american source area during the cenozoic is used to explore the sensitivity of mass balance reconstructions and changes in assumptions concerning erosion rate parameters and sea level

the role of co2 decline for the onset of northern hemisphere glaciation the pliocene pleistocene transition ppt from around 3 2 to 2 5 million years ago ma represented a major shift in the climate system and was characterized by a gradual cooling trend and the appearance of large continental ice sheets over northern eurasia and north america paleo evidence indicates that the ppt was accompanied and possibly caused by a decrease in atmospheric co2 but the temporal resolution of co2 reconstructions is low for this period of time and uncertainties remain large therefore instead of applying existent co2 reconstructions we solved an inverse problem by finding a schematic co2 concentration scenario that allows us to simulate the temporal evolution of key climate characteristics in agreement with paleoclimate records to this end we performed an ensemble of transient simulations with an earth system model of intermediate complexity from which we derived a best guess transient co2 scenario for the interval from 3 2 to 2 4 ma that gives the best fit between the simulated and reconstructed benthic 18o and global sea surface temperature evolution our data constrained co2 scenarios are consistent with recent co2 reconstructions and suggest a gradual co2 decline from 375 425 to 275 300 ppm between 3 2 and 2 4 ma in addition to a gradual decline the best fit to paleoclimate data requires the existence of pronounced co2 variability coherent with the 41 kyr 1 kyr 1000 years obliquity cycle in our simulations the long term co2 decline is accompanied by a relatively abrupt intensification of northern hemisphere glaciation at around 2 7 ma this is the result of a threshold behaviour of the ice sheets response to gradual co2 decrease and orbital forcing the simulated northern hemisphere ice sheets during the early pleistocene glacial cycles reach a maximum volume equivalent to a sea level drop of about 40 m both ice volume and benthic 18o are dominated by 41 kyr cyclicity our simulations suggest that before 2 7 ma greenland was ice free during summer insolation maxima and only partly ice covered during periods of minimum summer insolation a fully glaciated greenland comparable to its present day ice volume is modelled only during glacial maxima after 2 7 ma and more continuously after 2 5 ma

palaeotectonic implications of increased late eocene early oligocene volcanism from south pacific dsdp sites late eocene early oligocene 42 35 myr sediments cored at two dsdp sites in the south west pacific contain evidence of a pronounced increase in local volcanic activity particularly in close association with the eocene oligocene boundary this pulse of volcanism is coeval with that in new zealand and resulted from the development of an indo australian pacific plate boundary through the region during the late eocene the late eocene earliest oligocene was marked by widespread volcanism and tectonism throughout the pacific and elsewhere and by one of the most important episodes of cenozoic climatic cooling

geochemical evidence supporting t c chamberlin s theory of glaciation in 1899 t c chamberlin proposed that the co sub 2 content of the atomsphere decreased during times of enhanced continental erosion ultimately resulting in glacial epochs he ascribed the increase in the rate of chemical weathering relative to the rate of supply of co sub 2 from earth s interior to increased orogenic activity and globally higher average elevations which promoted rapid chemical erosion of silicates the oceanic record of strontium isotopes preserved in marine sediment supports his suggestion that glacial climates during the phanerozoic are in part linked to increases in the rate of global chemical erosion relative to outgassing from earth s interior further the close correspondence of the major tectonic episodes of the late cenozoic to times of increased continental erosion and glaciation suggests that chamberlin s hypothesis of the cause of glacial periods should be revived

the northern red sea and the dead sea rift abstract the results of geophysical measurements at sea when combined with mesostructural measurements on land demonstrate systematic extensional features in the region of the northern red sea and the dead sea rift rifts and diapirs were encountered in the northern red sea showing an arcuate trend whereas the faulted continental margins at that region are oriented nw se the rifts and the diapirs changed their trend northwards from nnw sse to n s systems of rifts and diapirs are considered to be extensional features therefore the tectonic extensional axis probably changed its orientation accordingly a series of rifts and diapirs was found also in the gulf of elat trending approximately parallel to the coastlines and is interpreted to be the northern extension of the red sea rift and diapir system mesostructural measurements that were carried out in the western flank of the dead sea rift indicated further evidence for structural extension trending e w to ene wsw in addition to measurements of left lateral offset of approximately 10 km all these data when combined with the geophysical measurements of the characteristics of the earth crust underneath the dead sea rift suggest a tectonic regime of oblique extension in the region of the red sea and the dead sea rift this tectonic regime indicates that the red sea spreading center extends northwards along the dead sea rift and the clockwise change of the axial trend imposed a sinistral offset to the tectonic extension thus it is suggested that the dead sea rift is an incipient oblique spreading center

sea level change a philosophical approach the present cenozoic era is an lsquoicehousersquo episode characterized by a low sea level since the beginning of the industrial revolution the human race has been emitting greenhouse gases increasing the global atmospheric temperature and causing a rise in sea level if emissions continue to increase at the present rate average global temperatures may rise by 1 5 c by the year 2050 accompanied by a rise of about 30 cm in sea level however the prediction of future climatic conditions and sea level is hampered by the difficulty in modelling the interactions between the lithosphere kryosphere biosphere and atmosphere in addition the buffering capacity of our planet is still poorly understood as scientists cannot offer unambiguous answers to simple questions sorcerer s apprentices fill in the gaps presenting plans to save planet without inconveniencing us the geological record can help us to learn about the regulation mechanisms of our planet many of which are connected with or expressed as sea level changes global changes in sea level are either tectono eustatic or glacioeustatic plate tectonic processes strongly control sea levels and climate in the long term there is a strong feed back mechanism between sea level and climate both can influence and determine each other although high sea levels are a powerful climatic buffer falling sea levels accelerate climatic accentuation the growth of the polar ice caps and will hence amplify the drop in sea level important sources of fossil greenhouse gases are botanic co2 production co2 released by volcanic activity and water vapour the latter is particularly important when the surface area of the sea increases during a rise in sea level lsquomaritime greenhouse effectrsquo a lsquovolcanogenic greenhouse effectrsquo release of volcanogenic co2 is possibly not equally important as intense volcanic activity may take place both during icehouse episodes as well as during greenhouse episodes the hydrosphere land vegetation and carbonate platforms are major co2 buffers which may both take up and release co2 co2 can be released from the ocean due to changes in the pco2 caused by growth of coral reefs and by uptake of co2 rich freshwater from karst provinces efficient sinks of co2 are the weathering products of silicate rocks long term sinks are organic deposits caused by regional anoxic events which preferrably develop during sea level rises and highstands and coal bearing strata deposition of limestone also removes co2 from the atmospheric hydrospheric cycle at a long term biotic crises are often related to either sea level lows or sea level highs long term sea level lows characteristic of glacial periods indicate cooling as major cause of extinction during verly long lasting greenhouse episodes the sea level is very high climate and circulation systems are stable and biotic crises often develop as a consequence of oxygen depletion on land niche splitting complex food web structures and general overspecialization of biota will occur whether the crisis is caused by a single anoxic event e g in the late devonian or a disturbance by an asteroid impact e g the cretaceous tertiary boundary it will only trigger total collapse of an ecosystem if a large part of it was already in decline the regulatory mechanisms and buffers are thermodynamically extremely efficient if they are given sufficient time in which to deploy their power however after major catastrophes the re establishment of successful ecosystems will take millions of years the present rate of sea level and associated temperature rise is much too fast to be compensated and buffered by the network of natural controls it is likely that the transitional time towards a new steady state will be an extremely variable and chaotic episode of unpredictable duration

energy flux model of seismic coda separation of scattering and intrinsic attenuation a new model of seismic coda is presented based on the balance between the energy scattered from the direct wave and the energy in the seismic coda this energy flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic anelastic attenuation of the medium this formula is valid for both weak and strong scattering and implicitly includes multiple scattering the model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity some of the simulations also included intrinsic dissipation the energy flux model explains the coda decay and amplitude observed in the synthetics for random media with a wide range of scattering q in contrast the single scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation scattering q less than or equal to 150 the simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate as predicted by the energy flux model the coda decay rate is sensitive however more to the intrinsic q of the medium the ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation thus analysis of the decay rate and amplitude of the coda can in principle produce separate estimates for the scattering and intrinsic q values of the crust we analyze the coda from two earthquakes near anza california intrinsic q values determined from these seismograms using the energy flux model are comparable to coda q values found from the single scattering theory the results demonstrate that coda q values are at best measures of the intrinsic attenuation of the lithosphere and are unrelated to the scatteing q less

co 2 record in the byrd ice core 50 000 5 000 years bp the analysis of air in polar ice cores revealed 30 lower co2 values during glacial periods than during interglacial periods at present this is confirmed by results from six different ice cores two from greenland and four from antarctica1 5 in all cores the co2 change coincides with the change in the isotopic composition of the ice expressed as either the 18o or d ratio both are indicators for the mean annual surface temperature6 to investigate the relationship between atmospheric co2 concentration changes with changes in climate the atmospheric co2 concentration during and at the end of the last glaciation has to be known in detail to achieve this we have studied a great number of samples from the deep ice core from byrd station westantarctica drilled in 1968 these measurements allow us to reconstruct the atmospheric co02 concentration in the time period 50 000 15 000 yr bp in great detail

sensitivity of climate to late cenozoic uplift in southern asia and the american west numerical experiments experiments with general circulation models with no mountains half mountains and full modern mountains show the sensitivity of atmospheric circulation patterns to progressive amounts of uplift the experiments were motivated by geologic evidence for large kilometer scale uplift in the late cenozoic in southern asia and the american west particularly within the last 10 m y in january the amplitude of the mid latitude upper tropospheric planetary waves increased with uplift and the low level winds were progressively blocked or diverted around the topographic features in july the progressive uplift caused monsoonlike circulations to develop in the vicinity of the colorado and tibetan plateaus atmospheric heating rates midtroposphere vertical motion and upper tropospheric planetary wave amplitudes varied approximately linearly with progressive uplift these results suggest that geologically recent kilometer scale uplift may have had climatic consequences comparable in magnitude and pattern to those of earlier stages of uplift comparison of the simulated climatic effects of uplift with the geologic evidence for late cenozoic climatic change especially for the last 10 m y is given in accompanying papers

climatic effects of reduced arctic sea ice limits in the giss ii general circulation model in this paper we present results of an atmospheric general circulation model gcm experiment in which arctic sea ice limits were substantially reduced in all months march sea ice limits were set equivalent to modern september limits and all sea ice was removed in september sea ice coverage for other months varied between these two extremes this climate sensitivity experiment makes predictions about mean northern hemisphere atmospheric conditions including temperature pressure wind patterns and precipitation consistent with these boundary constraints the major effects of reduced sea ice limits are observed in winter they include large regional warming of the circum arctic region northward migration of the icelandic low pressure system and strengthening of the azores high changes in net heating over the north atlantic ocean suggest that increases in sea surface temperatures and salinities in this region would also accompany reductions in arctic sea ice limits in the wind field a weakening of the polar easterlies and an intensification of cyclonic circulation over the norwegian greenland sea suggest that surface water exchange between the atlantic and arctic would increase when sea ice limits are reduced however zonally averaged changes in strength of the westerlies or upper level jet stream are minimal the late pliocene cooling of the north atlantic ocean and north american arctic margin may have been linked in part to the development of perennial sea ice cover

suction effects on bridge pier scour under clear water conditions abstractthe experimental study investigates how the application of point suction at different bed locations affects local scour around a cylindrical bridge pier under clear water conditions the results show that suction has a profound effect on pier scour development and the extent of the influence is related to the location of the suction source when the suction source is located at or upstream of the pier the equilibrium scour depth is reduced by up to 50 with qs qo 2 where qs and qo suction flow rate and undisturbed approach flow rate respectively the data also show that for the suction source that is located downstream of the pier the equilibrium scour depth is reduced by up to 30 with the same suction flow rate the extent of pier scour depth reduction at different locations from the suction source is closely associated with changes to the local effective shear and critical shear velocity results of this study show that bed suction may be used as an effective pier scour countermeasure

structural geometry and evolution of the dead sea jordan rift system as deduced from new subsurface data abstract analysis of deep drilling data and seismic reflection surveys obtained in recent years permit establishment of a tectonic model of the dead sea jordan rift system that is in part conformable with some of the many often controversial theories on this subject but which also introduces new information negating some concepts that are widely accepted in the literature the dead sea jordan rift system is not a tensional graben between two parallel sets of faults but instead can be best defined as a sinistral transform connecting an incipient oceanic ridge the red sea with an upthrusted collision zone the taurus range the shear is caused by the opening of the red sea and the motion of the arabian sub plate away from the african plate the shearing occurs along a largely south north trending slightly arcuate une consisting of a series of en echelon left stepping left lateral strike slip master faults of varying lengths these faults characteristically die out to the north by bending outward northeast and the movement is taken up by the strike slip faults to the left i e to the west where overlap of the two faults occurs very narrow and very deep grabens have evolved in places the width being equal to the depth the narrowness of these grabens is dictated by the closeness of the overlapping segments of the successive strike slip faults this feature points to the probability that the en echelon strike slip faults have a common root zone at great depth these grabens are not typical leaky pull aparts in that they have no gravimetric magnetic or heat flow anomalies nor are they closed on all four sides by large faults their northern ends are characterized by gradually rising graben floors without major diagonal cross faults the dead sea jordan rift system sensu stricto extends over a distance of 420 km from the northern shore of the gulf of elat to the northern margin of the hula valley southward it is connected with the red sea along the gulf of elat transition zone which has elements of strike slip as well as tensional opening a northern transition zone exists between the hula valley and the taurus arc where diminishing strike slip movement is compensated by several underthrust belts the time of the beginning of the movement along the rift can be established as pre middle miocene because mid miocene sediments overlie an upper cretaceous graben floor rifting has continued intermittently to the present volcanism in the northern fifth of the rift is genetically associated with the seismically active tensional golan hauran jebel drouz wadi sirhan tectonic trend which has a north west southeast orientation and not with the north south trending dead sea jordan rift

global atmospheric circulation experiments on an earth with polar and tropical continents two general circulation models forced by mean annual insolation and having an energy balance ocean have been run on an earth with polar continents and a tropical continent polar continents produce strong meridional temperature gradients and a maximum hydrological cycle a tropical continent produces the warmest planet and a minimal hydrological cycle both models produce more arid continents than exist today

links between climate and sea levels for the past three million years the oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on earth the ice sheets and the oceans since the latest of these oscillations the last glacial maximum between about 30 000 and 19 000 years ago approximately 50 million cubic kilometres of ice has melted from the land based ice sheets raising global sea level by approximately 130 metres such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere oceans ice sheets and solid earth all of which have different response timescales the trigger for the sea level fluctuations most probably lies with changes in insolation caused by astronomical forcing but internal feedback cycles complicate the simple model of causes and effects