sensitivity studies with a sea ice mixed layer pycnocline model in the weddell sea the sensitivity of a dynamic thermodynamic sea ice model coupled to a one dimensional mixed layer pycnocline model to variations of dynamic and thermodynamic model parameters is investigated furthermore the modifications of the model results due to the inclusion of a prognostic snow cover and the implementation of simplified sea ice rheologies are investigated in these comparisons special emphasis is placed upon the ice ocean boundary conditions buoyancy fluxes and the mixed layer properties

spatial variability in selected geotechnical property measurements from three sedimentary provinces in the venezuela basin abstract relatively undisturbed surficial sediment samples from three sedimentary provinces pelagic turbidite dominated and hemipelagic in the venezuela basin were examined for spatial variability in water content and undrained shear strength a miniature vane shear apparatus boring method which minimized sample disturbance was used to determine variability of sediment shear strength directly within individual box core samples the variability of water content and sediment shear strength was also determined from subsamples 61 mm id cores collected from replicate box cores at each province sediments at the turbidite site yielded a higher average lateral coefficient of variation in water content and sediment shear strength both methods of measurement than sediments from the pelagic and hemipelagic sites vertical coefficients of variation were consistently higher than lateral coefficients of variations for all measured parameters between box core variability in sediment shear strength was less than within box core variability reflecting differences in measuring techniques and sample disturbance rather than actual differences biological activity primarily compaction by burrowing polychaetes maintains steep gradients of decreasing water content and increasing shear strength in the upper 100 200 mm of sediments at all three sites the biologically controlled gradients and the occasional deposition of turbidites results in much higher vertical compared to lateral variability of some sediment geotechnical properties on scales of tens of millimeters within box cores and kilometers between box cores collected at the same site

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

significant southern ocean warming event in the late middle eocene a prominent middle eocene warming event is identified in southern ocean deep sea cores indicating that long term cooling through the middle and late eocene was not monotonic at sites on maud rise and the kerguelen plateau a distinct negative shift in 1 8 o values 1 0 is observed ca 41 5 ma this excursion is interpreted as primarily a temperature signal with a transient warming of 4 c over 600 k y affecting both surface and middle bathyal deep waters in the indian atlantic region of the southern ocean this isotopic event is designated as the middle eocene climatic optimum and is interpreted to represent a significant climatic reversal in the midst of middle to late eocene deep sea cooling the lack of a significant negative carbon isotope excursion as observed during the paleocene eocene thermal maximum and the gradual rate of high latitude warming suggest that this event was not triggered by methane hydrate dissociation rather a transient rise in pco 2 levels is suspected possibly as a result of metamorphic decarbonation in the himalayan orogen or increased ridge arc volcanism during the late middle eocene

sea ice drift variability in arctic ocean model intercomparison project models and observations drift is a prominent parameter characterizing the arctic sea ice cover that has a deep impact on the climate system hence it is a key issue to both the remote sensing as well as the modeling community to provide reliable sea ice drift fields this study focuses on the comparison of sea ice drift results from different sea ice ocean coupled models and the validation with observational data in the period 19792001 the models all take part in the arctic ocean model intercomparison project aomip and the observations are mainly based on satellite imagery according to speed distributions one class of models has a mode at drift speeds around 3 cm s and a short tail towards higher speeds another class shows a more even frequency distribution with large probability of drift speeds of 10 to 20 cm s observations clearly agree better with the first class of model results reasons for these differences are manifold and lie in discrepancies of wind stress forcing as well as sea ice model characteristics and sea ice ocean coupling moreover we investigated the drift patterns of anticyclonic and cyclonic wind driven regimes the models are capable of producing realistic drift pattern variability the winter of 1994 95 stands out because of its maximum in fram strait ice export although export estimates of some models agree with observations the corresponding inner arctic drift pattern is not reproduced the reason for this is found in the wind forcing as well as in differences in ocean velocities

petroleum systems in the jiangling dangyang area jianghan basin china source related geochemical data define at least four petroleum systems in the jiangling dangyang area of the jianghan basin eocene paleocene anoxic evaporitic lacustrine source rocks generated most of the crude oils in the area eocene qianjiang rock from the sha 13 well 1322 m contains fast reacting sulfur rich type is organic matter and its extract is most similar to the sha 13 oil sand bitumen qianjiang reservoir lower eocene paleocene xingouzhui rocks from the xin 73 well 842 and 862 m contain slow reacting low sulfur type i organic matter and their extracts are most similar to the sha 26 oil sand bitumen eocene jinsha reservoir and the ling 2 sha 24 and tuo 3 oils xingouzhui reservoirs two unidentified middle triassic or older marine carbonate evaporite source rocks or different facies of the same source rock generated the daxiakou oil triassic jialingjiang formation outcrop xingshan county and the moderately biodegraded tianwan seep oil permian changxing outcrop chengxi county respectively one or more unidentified marine source rocks which could include the lower permian qixia or the upper sinian doushantuo formations generated the miaoshi and yanmenkuo seep oils permian qixia outcrops the jingshan seep oil ordovician baota outcrop probably is related to these oils but could represent another petroleum system different kinetics for hydrocarbon generation among eocene qianjiang and lower eocene paleocene xingouzhui formation source rocks and chemical differences among the related oils are caused by organic facies variations high salinity and low eh enhanced the preservation of oil prone organic matter in these lacustrine settings and facilitated incorporation of sulfur into the organic matter anoxia and the unusual presence of abundant sulfate as gypsum resulted in the microbial reduction of sulfate to sulfide and incorporation of this sulfur into the kerogen for example biomarkers show that source rock in the sha 13 well 1322 m was deposited under more saline lower eh conditions than that in the ling 80 well 1808 m although both are from the qianjiang formation the sha 13 rock sample is more organic rich 6 62 vs 1 27 wt toc and has a higher hydrogen index 794 vs 501 mg hc g toc and faster reaction kinetics than the ling 80 sample kerogen from the sha 13 sample is type is because it has a high hydrogen index and an atomic s c ratio 0 074 in the range of sulfur rich fast reacting kerogens of the monterey formation s c 0 040 organic rich lower jurassic coaly rocks from outcrops at daxiakou contain immature to mature gas prone organic matter that is not related to any oils in the study several organic rich upper sinian to permian samples could have been source rocks in the past but are now highly mature based on high tmax 464 540 c and estimated vitrinite reflectance ro values mass balance calculations were used to estimate the original toc toc c in these samples prior to maturation these samples could not be correlated with the oils using biomarkers because of high maturities and low extract yields however stable carbon isotope type curves suggest that the miaoshi yanmenkuo permian qixia formation and the jingshan ordovician baota formation seep oils originated from source rocks in the lower permian qixia 3 00 wt toc or upper sinian doushantuo formations 5 96 wt toc lack of triaromatic dinosteroids in the miaoshi and yanmenkuo seep oils supports but does not prove a permian source rock very negative stable carbon isotope ratios for kerogens from the lower cambrian shuijintuo formation 33 5 to 33 6 8 85 16 64 wt toc show that they are not related to any of the analyzed oils

a case study of the anomalous arctic sea ice conditions during 1990 insights from coupled and uncoupled regional climate model simulations 1 the regional coupled atmosphere ice ocean model hirham mom has been developed to simulate the arctic climate the model has been applied for the year 1990 which was characterized by anomalous ice retreat along the eastern arctic coasts many observed features of the anomalous atmospheric circulation and sea ice concentration pattern during spring to early summer are reproduced by the model it was even able to generate the extreme summer sea ice conditions in the eurasian arctic and the associated high surface air temperatures the model shows less success in simulating the large ice retreat in the siberian arctic in late summer this is explained mainly by deviations in the simulated atmospheric circulations results from an ocean ice alone model confirm that the atmospheric forcing dominates the simulated ice retreat on the other hand a sensitivity study with the atmosphere alone model shows the impact of the sea ice conditions on the atmospheric circulation only with the accurate satellite derived sea ice data is the model able to reproduce the anomalous late summer atmospheric pressure patterns

sea ice thickness in the weddell sea antarctica a comparison of model and upward looking sonar data sea ice thickness is a key parameter for estimates of salt fluxes to the ocean and the contribution to global thermohaline circulation observations of sea ice thickness in the southern ocean are sparse and difficult to collect an exception to this data gap is time series data from upward looking sonars uls which sample the drifting sea ice continuously in this study we use uls data from ten different locations over periods ranging from 9 to 25 months to compare with model data although these data are limited in space and time they provide a qualitative indication of the ability of global climate models gcms to adequately represent southern ocean sea ice we compare the uls data to output from four different gcms bccr bcm2 0 echam5 mpi om ukmo hadcm3 and ncar ccsm3 which were used for the fourth assessment report of the intergovernmental panel on climate change they simulate the ice thickness reasonably well but in most cases average model ice thickness is less than thicknesses derived from uls data the seasonal cycle produced by the models correlates well with the uls except for locations near maud rise where in summer the uls find a low concentration of thick ice floes this overly thin ice will have implications for both the salt flux to the central weddell sea during the growth season and the freshwater flux during the melt season using satellite derived ice drift data to calculate transports in the weddell sea we find that the underestimation of ice thickness results in underestimated salt fluxes

results of the sea ice model intercomparison project evaluation of sea ice rheology schemes for use in climate simulations a hierarchy of sea ice rheologies is evaluated on the basis of a comprehensive set of observational data the investigations are part of the sea ice model intercomparison project simip four different sea ice rheology schemes are compared a viscous plastic rheology a cavitating fluid model a compressible newtonian fluid and a simple free drift approach with velocity correction the same grid land boundaries and forcing fields are applied to all models as verification data there are 1 ice thickness data from upward looking sonars uls 2 ice concentration data from the passive microwave radiometers smmr and ssm i 3 daily buoy drift data obtained by the international arctic buoy program iabp and 4 satellite derived ice drift fields based on the 85 ghz channel of ssm i all models are optimized individually with respect to mean drift speed and daily drift speed statistics the impact of ice strength on the ice cover is best revealed by the spatial pattern of ice thickness ice drift on different timescales daily drift speed statistics and the drift velocities in fram strait overall the viscous plastic rheology yields the most realistic simulation in contrast the results of the very simple free drift model with velocity correction clearly show large errors in simulated ice drift as well as in ice thicknesses and ice export through fram strait compared to observation the compressible newtonian fluid cannot prevent excessive ice thickness buildup in the central arctic and overestimates the internal forces in fram strait because of the lack of shear strength the cavitating fluid model shows marked differences to the statistics of observed ice drift and the observed spatial pattern of ice thickness comparison of required computer resources demonstrates that the additional cost for the viscous plastic sea ice rheology is minor compared with the atmospheric and oceanic model components in global climate simulations

effects of rheology and ice thickness distribution in a dynamic thermodynamic sea ice model realistic treatment of sea ice processes in general circulation models is needed to simulate properly global climate and climate change scenarios as new sea ice treatments become available it is necessary to evaluate them in terms of their accuracy and computational time here several dynamic ice models are compared using both a 2 category and 28 category ice thickness distribution simulations are conducted under normal wind forcing as well as under increased and decreased wind speeds it is found that the lack of a shear strength parameterization in the cavitating fluid rheology produces significantly different results in both ice thickness and ice velocity than those produced by an elliptical rheology furthermore use of a 28 category ice thickness distribution amplifies differences in the responses of the various models while the choice of dynamic model is governed by requirements of accuracy and implementation it appears that in terms of both parameterization of physical properties and computational time the elliptical rheology is well suited for inclusion in a gcm

rapid fluctuations in mid latitude siliceous plankton production during the middle eocene climatic optimum odp site 1051 western north atlantic abstract the middle eocene climatic optimum meco 40 million years ago ma is one of the most prominent transient global warming events in the paleogene although the event is well documented in geochemical and isotopic proxy records at many locations the marine biotic response to the meco remains poorly constrained we present new high resolution quantitative records of siliceous microplankton assemblages from the meco interval of ocean drilling program odp site 1051 in the subtropical western north atlantic ocean which are interpreted in the context of published foraminiferal and bulk carbonate stable isotope 18o and 13c records high diatom radiolarian and silicoflagellate accumulation rates between 40 5 and 40 0 ma are interpreted to reflect an 500 thousand year kyr interval of increased nutrient supply and resultant surface water eutrophication that was associated with elevated sea surface temperatures during the prolonged onset of the meco relatively low pelagic siliceous phytoplankton sedimentation accompanied the peak meco warming interval and the termination of the meco during an 70 kyr interval centered at 40 0 ma following the termination of the meco an 200 kyr episode of increased siliceous plankton abundance indicates enhanced nutrient levels between 39 9 and 39 7 ma throughout the site 1051 record abundance and accumulation rate fluctuations in neritic diatom taxa are similar to the trends observed in pelagic taxa implying either similar controls on diatom production in the neritic and pelagic zones of the western north atlantic or fluctuations in sea level and or shelf accommodation on the north american continental margin to the west of site 1051 these results combined with published records based on multiple proxies indicate a geographically diverse pattern of surface ocean primary production changes across the meco notably however increased biosiliceous accumulation is recorded at both odp sites 1051 and 748 southern ocean in response to meco warming this may suggest that increased biosiliceous sediment accumulation if indeed a widespread phenomenon resulted from higher continental silicate weathering rates and an increase in silicic acid supply to the oceans over several 100 kyr during the meco

choosing the best ancient analogue for projected future temperatures a case using data from fluid inclusions of middle late eocene halites abstract after the paleocene eocene thermal maximum petm global temperature and co2 levels decreased concurrently in the middle late eocene using different approaches estimated co2 levels of the middle late eocene are very similar to the 1000 ppm co2 level projected for the next 100 years as a result of increasing greenhouse gas concentrations the average global temperature is projected to increase from 1 4 to 5 8 c by 2100 relative to 2001 levels thus the middle late eocene may be the best ancient analogue for a future with increased temperatures due to burning of fossil fuels in order to explore the sensitivity range of global annual temperature with respect to co2 concentration exact atmospheric co2 concentrations and air temperatures of ancient analogs must be known previous palynological studies provide only indirect estimates of temperature however the homogenization temperature of fluid inclusions in halites obtained by the cooling nucleation method can provide the exact temperature of saline lake water which is similar to overlying air temperature in shallow lakes in this paper we measured the range of homogenization temperatures from 5 8 to 43 3 c of fluid inclusions in middle late eocene halites of the yunying depression central china the maximum homogenization temperature of fluid inclusions thmax in these middle late eocene halites is 4 6 c higher than the modern extreme highest temperature 38 7 c recorded for this area

sea ice dynamics in the weddell sea simulated with an optimized model the advection of sea ice and associated freshwater salt fluxes in the weddell sea in 1986 and 1987 are investigated with a large scale dynamic thermodynamic sea ice model the model is validated and optimized by comparison of simulated sea ice trajectories with observed drift paths of six buoys deployed on the weddell sea ice the skill of the model is quantified by an error function that measures the deviations of simulated trajectories from observed 30 day sea ice drift a large number of sensitivity studies show how simulated sea ice transports and associated freshwater salt fluxes respond to variations in physical parameterizations the model reproduces the observed ice drift well provided ice dynamics parameters are set to appropriate values optimized values for the drag coefficients and for the ice strength parameter are determined by applying the error function to various sensitivity studies with different parameters the optimized model yields a mean northward sea ice volume export out of the southern weddell sea of 1693 km3 in 1986 and 2339 km3 in 1987 this shows the important role of sea ice transport for the freshwater budget of the weddell sea and gives an indication of its high interannual variability

the major composition of a middle late eocene salt lake in the yunying depression of jianghan basin of middle china based on analyses of fluid inclusions in halite abstract during the cretaceous tertiary transition in eastern china abundant halites formed in non marine areas many continental salt deposits from inland salt lakes were formed in eastern china in faulted basins as a result of the northward movement and collision of the indo china plate with the eurasian plate including the bohai gulf basin however a marine transgression versus a non marine origin of these evaporites remains to be determined primary fluid inclusions trapped in halite deposits can directly record the composition of evaporated seawater or salt lake water such as those in the cretaceous halite in the khorat plateau laos and thailand area can resolve the origins of the evaporate deposits recent fluid inclusions data in the khorat plateau coincide with the predicted secular variation of seawater and are comparable to other fluid inclusions in cretaceous marine halite indicating these fluid inclusions are directly related to a marine transgression our analyses in this study shows that the average k mg2 and so 4 2 contents are 8 8 5 0 and 6 8 g l respectively in the primary fluid inclusions in halite of middle late eocene from the yunying depression of china these numbers are much less than those in the contemporary spanish primary fluid inclusions in halite precipitated from seawater 16 4 36 3 and 12 5 g l for k mg2 and so 4 2 respectively furthermore br contents of all fluid inclusion samples in halite from the yunying depression are lower than 2 ppm vs 55 58 ppm at the base of spanish contemporary marine halite and their 37cl values range from 0 11 to 2 94 vs 0 09 to 0 24 in sylvite of spanish deposit indicating that the compositions of the middle late eocene brines trapped in halite in the yunying depression of china are very different from those derived from the contemporary seawater and are considered to be resulted from evaporation of an inland saline lake water with little influence of seawater

spectral analysis of the lower eocene wilkins peak member green river formation wyoming support for milankovitch cyclicity abstract this study is the first to employ spectral analysis to examine meter scale sedimentary cyclicity in the wilkins peak member of the lower eocene green river formation of wyoming generally regarded as the classic example for orbital forcing of lacustrine sediments at eccentricity and precession time scales this long standing interpretation was recently contested with a much shorter duration 10 ky inferred for the dominant cyclicity earlier work lacked adequate age control or spectral analysis or both our analysis is based upon an evaluation in the frequency domain of oil yield values from four boreholes accuracy estimation for suggested orbital interpretations and comparison to independent geochronology cored intervals 266 364 m thick represent a span of 1 2 1 7 m y with temporal resolution of 3 5 ky 1 m for oil yield values variations in spectral power with depth within the original records are interpreted to reflect changes in the rate of sediment accumulation these changes are corrected prior to testing the orbital forcing hypothesis by using two methods 1 a minimal adjustment three segments accounting for the dominant changes of spectral frequency with depth and 2 correlating the published definitions of precessional cycles in these records to a 21 ky cosine curve orbital age models resulting from the two tuning methods are compared to available chronology and the tuned records are tested for the expected spectral peaks from orbitally forced records we conclude that the dominant cyclicity of the wilkins peak member is orbitally forced orbital age models overlap 40 ar 39 ar ages and inferred periods include long and short eccentricity weak obliquity and precession eccentricity is resolved in the analyzed records but the expected 95 and 125 ky periods are not resolved controlling the range of possible tuning periods and the accuracy of orbital age models sub milankovitch variability exists and can be resolved to a minimum period of 3 5 ky by the analyzed records however it cannot be characterized fully with the available chronology or by the previously calculated mean cycle duration

early eocene carbon isotope excursions and landscape destabilization at eccentricity minima green river formation of wyoming repeated global reorganizations of carbon cycling and biotic oceanic and terrestrial processes occurred during the early eocene and appear to have been paced by cyclic variations in the eccentricity of the earth s orbit the phase relationship s between insolation variation terrestrial paleoclimate and atmospheric pco2 during these events remains enigmatic however due to their poorly constrained timing relative to specific orbital configurations here we use tiered interpolation between radioisotopic ages and paleomagnetic polarity chrons to compare high resolution 13c and lithofacies records from the wilkins peak member of the green river formation of western north america to a fe intensity xrf record from the western atlantic ocean and to numerical solutions for earth s orbital configuration wilkins peak member lithofacies stacking patterns record cyclic geomorphic responses to insolation and climate fluctuations spanning an interval of 1 8 ma previous macrostratigraphic analyses using 40ar 39ar and u pb ash bed ages indicate that these cycles reflect long and short eccentricity modulation of precession hydrologic variance appears to have occurred inversely with intervals of maximum sediment advection with carbonate and evaporite dominated lacustrine modes during eccentricity maxima and siliciclastic dominated alluvial modes during eccentricity minima stable carbon isotope analyses of 126 meters of wilkins peak member strata reveal a regular 5 per mil oscillation between high 13c lacustrine modes and low 13c alluvial modes tiered interpolation between paleomagnetically characterized terrestrial ash beds facilitates the integration of 11 radioisotopic ages with the geomagnetic polarity timescale resulting in significant expansion of chron c23 and shortening of chron c22 relative to timescales based on seafloor magnetic anomaly profiles the new proposed timescale permits direct comparison of terrestrial and marine climate proxy records from the early eocene climatic optimum at ca 250 kyr 250 kyr resolution and reveals prominent 100 kyr and 405 kyr scale oscillations within both records wilkins peak member 13c minima which occurred during low eccentricity alluvial modes likely coincided with global 13c minima scenario 1 but may alternatively reflect productivity driven local effects within lake gosiute scenario 2 if scenario 1 proves accurate early eocene negative 13c hyperthermal excursions occurred during eccentricity minima rather than maxima as formerly believed

sea ice transport a highly variable link between arctic and north atlantic the variability of the ice volume flux into the northeast atlantic is investigated with an optimized dynamic thermodynamic sea ice model using 40 years 1958 1997 of atmospheric forcing fields derived from the ncep ncar reanalysis project the simulated sea ice export from the arctic exhibits considerable interannual to decadal variability and is primarily a linear response to sea level pressure anomalies over greenland and over the barents and kara seas our model results suggest that ice export anomalies such as in 1968 which supposedly caused the so called great salinity anomaly in the northern north atlantic are not unique but rather frequent events as part of the variability of the arctic climate system

clay mineral changes across the eocene oligocene transition in the sedimentary sequence at xining occurred prior to global cooling abstract during the cenozoic high quality long term sedimentary sequences formed in xining basin at the northeastern margin of the tibetan plateau which are characterized by alternating gypsiferous layers and reddish mudstone beds the tashan section was previously dated in detail by magnetostratigraphy which yielded an age span of 16 to 35 7 ma in this study bulk and clay mineral assemblages and magnetic parameters of the 33 1 35 7 ma portion were analyzed using x ray diffraction and magnetic methods to determine the behavior of the eocene oligocene climate transition quartz calcite feldspar and clay fractions in sediments that are mainly derived from the surrounding catchments gypsum and dolomite are authigenic minerals illite chlorite irregular mixed layer illite smectite and smectite are the four main clay sized fractions

large scale drift of arctic sea ice retrieved from passive microwave satellite data a method of determining the large scale sea ice drift using 85 5 ghz special sensor microwave imager data are presented a cross correlation method is applied to sequential images of gridded data covering the entire arctic individual correlation results are validated with ice velocities derived from buoy data the satellite derived mean drift values and the variabilities of the ice drift correspond closely with the buoy data similarly time series of buoy data and associated satellite data are in good agreement even over large time periods an example of a satellite retrieved 3 day mean drift field demonstrates the potential of the method for providing large scale ice circulation patterns mean drift fields of the winter periods 1987 1988 and 1992 1993 indicate a considerable interannual variability of the sea ice drift pattern in the arctic ocean the arctic region is divided into seven larger areas and the area flux between these regions has been derived the kara sea and the laptev sea show the largest area ice export with 0 02 and 0 015 km 2 s 1 respectively the central arctic export through fram strait amounts to 0 12 sv during the winter of 1992 1993 with a maximum of 0 15 sv in january

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

on the improvement of sea ice models for climate simulations the sea ice model intercomparison project experiments with dynamic thermodynamic sea ice models indicate a strong dependence of the net freezing rate sea ice transport and variability on dynamic model parameters although current dynamic thermodynamic sea ice models show relatively good agreement with observations an optimization seems to be necessary especially for the parameterizations of dynamic processes presently only a few coupled climate models use dynamic thermodynamic sea ice models in order to promote by means of coordinated numerical experiments the development of an optimal sea ice model for climate research the sea ice ocean modelling panel of the arctic climate system study acsys a project of the world climate research programme has initiated the sea ice model intercomparison project simip the first results from this model hierarchy approach are presented

coupled greenhouse warming and deep sea acidification in the middle eocene 1 the middle eocene climatic optimum meco is an enigmatic warming event that represents an abrupt reversal in long term cooling through the eocene in order to further assess the timing and nature of this event we have assembled stable isotope and calcium carbonate concentration records from multiple deep sea drilling project and ocean drilling program sites for the time interval between 43 and 38 ma revised stratigraphy at several sites and compilation of 18o records place peak warming during the meco event at 40 0 ma chron c18n 2n the identification of the 18o excursion at sites in different geographic regions indicates that the climatic effects of this event were globally extensive the total duration of the meco event is estimated at 500 ka with peak warming lasting 100 ka assuming minimal glaciation in the late middle eocene 4 6 c total warming of both surface and deep waters is estimated during the meco at the study sites the interval of peak warming at 40 0 ma also coincided with a worldwide decline in carbonate accumulation at sites below 3000 m depth reflecting a temporary shoaling of the calcite compensation depth the synchroneity of deep water acidification and globally extensive warming makes a persuasive argument that the meco event was linked to a transient increase in atmospheric pco2 the results of this study confirm previous reports of significant climatic instability during the middle eocene furthermore the direct link between warming and changes in the carbonate chemistry of the deep ocean provides strong evidence that changes in greenhouse gas concentrations exerted a primary control on short term climate variability during this critical period of eocene climate evolution

the middle eocene climatic optimum meco a multiproxy record of paleoceanographic changes in the southeast atlantic odp site 1263 walvis ridge the middle eocene climatic optimum meco 40 ma was a transient period of global warming that interrupted the secular cenozoic cooling trend we investigated the paleoceanographic paleoenvironmental and paleoecological repercussions of the meco in the southeast atlantic subtropical gyre ocean drilling program site 1263 tex86 and 18o records support an 4 c increase in surface and deepwater temperatures during the meco there is no long term negative carbon isotope excursion cie associated with the early warming consistent with other sites and there is no short term negative cie 50 kyr during the peak of the meco in contrast to what has been observed at some sites this lack of a cie during the peak of the meco at site 1263 could be due to poor sediment recovery or geographic heterogeneity of the 13c signal benthic and planktic foraminiferal mass accumulation rates markedly declined during meco indicating a reduction of planktic foraminiferal production and export productivity vertical 13c gradients do not indicate major changes in water column stratification and there is no biomarker or micropaleontological evidence that hypoxia developed we suggest that temperature dependency of metabolic rates could explain the observed decrease in foraminiferal productivity during warming the kinetics of biochemical reactions increase with temperature more so for heterotrophs than for autotrophs steady warming during meco may have enhanced heterotroph i e foraminiferal metabolic rates so that they required more nutrients these additional nutrients were not available because of the oligotrophic conditions in the region and the lesser response of primary producers to warming the combination of warming and heterotroph starvation altered pelagic food webs increased water column recycling of organic carbon and decreased the amount of organic carbon available to the benthos

astronomically forced climate evolution in a saline lake record of the middle eocene to oligocene jianghan basin china abstract following the early eocene climatic optimum some 50 million years ago the marine paleoclimate record indicates that a long interval of global cooling took place punctuated by a series of short term warming reversals and culminating with the glaciation of antarctica at the eocene oligocene transition we investigate a saline lake record from the qianjiang and jinghezhen formations jianghan basin china for the corresponding continental climate response a 20 25 myr long astronomical time scale is constructed based on 405 kyr orbital eccentricity cycle tuning of gamma ray gr series measured from the qianjiang and jinghezhen formations the halite rich interval between 41 40 4 ma correlates well with the middle eocene climate optimum recorded in the deep sea 18 o record confirming predominantly halite deposition during the warming silt mudstone rich intervals were deposited during 2 4 myr orbital eccentricity minima the evidence indicates a history of alternating fresh water humid cool and saline water dry hot lake cycles paced by 100 kyr orbital eccentricity cycles analysis of gr series from the deepest part of the lake indicates strong astronomical forcing of halite deposition throughout the middle late eocene and a shift to siliciclastic deposition and cooler climates at 33 9 ma early oligocene wet cool climate in the jianghan basin signals east asian summer monsoon intensification and a reduction from northwest winter monsoon in response to tibetan plateau uplift northern hemisphere summer insolation minima in the middle late eocene with temperatures that are 4 6 c higher than present may provide an analogy for near future climate change in jianghan basin

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

ocean overturning since the late cretaceous inferences from a new benthic foraminiferal isotope compilation 1 benthic foraminiferal oxygen isotopic d 18 o and carbon isotopic d 13 c trends constructed from compilations of data series from multiple ocean sites provide one of the primary means of reconstructing changes in the ocean interior these records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records we present new benthic foraminiferal d 18 o and d 13 c compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to 80ma andtentatively to 110ma first order variations ininterbasinal isotopicgradients delineate transitions from interior ocean heterogeneity during the late cretaceous 65 ma to early paleogene 35 65 ma homogeneity and a return to heterogeneity in the late paleogene early neogene 35 0 ma we propose that these transitions reflect alterations in a first order characteristic of ocean circulation the ability of winds to make water in the deep ocean circulate we document the initiation of large interbasinal d 18 o gradients in the early oligocene and link the variations in interbasinal d 18 o gradients from the middle eocene to oligocene with the increasing influence of wind driven mixing due to the gradual tectonic opening of southern ocean passages and initiation and strengthening of the antarctic circumpolar current the role of wind driven upwelling possibly associated with a tethyan circumequatorial current in controlling late cretaceous interior ocean heterogeneity should be the subject of further research

constraints on the early uplift history of the tibetan plateau the surface uplift history of the tibetan plateau and himalaya is among the most interesting topics in geosciences because of its effect on regional and global climate during cenozoic time its influence on monsoon intensity and its reflection of the dynamics of continental plateaus models of plateau growth vary in time from pre india asia collision e g 100 ma ago to gradual uplift after the india asia collision e g 55 ma ago and to more recent abrupt uplift 7 ma ago and vary in space from northward stepwise growth of topography to simultaneous surface uplift across the plateau here we improve that understanding by presenting geologic and geophysical data from north central tibet including magnetostratigraphy sedimentology paleocurrent measurements and 40ar 39ar and fission track studies to show that the central plateau was elevated by 40 ma ago regions south and north of the central plateau gained elevation significantly later during eocene time the northern boundary of the protoplateau was in the region of the tanggula shan elevation gain started in pre eocene time in the lhasa and qiangtang terranes and expanded throughout the neogene toward its present southern and northern margins in the himalaya and qilian shan

on the influence of dsow in a numerical model of the north atlantic general circulation abstract two numerical experiments regarding the north atlantic circulation are compared the two experiments are initialized with climatological temperatures and salinities and are integrated for ten years with different surface boundary conditions in the lceland sea one case climatological wind stress sst and surface salinity to force the model it reproduces the atlantic circulation found in similar studies a change in surface boundary values in the iceland sea in order to improve the denmark strait overflow water properties in the second case results in major changes in circulation and hydrography the meridional overturning more than doubles and horizontal gyres are intensified recirculation cells occur north and south of the gulf stream the gulf stream separates from the north american coast in a more realistic manner and its further course is in better agreement with observations than in the reference run the subsurface temperature distribution differs by several kelvin in the subpolar and

continental ice in greenland during the eocene and oligocene the eocene and oligocene epochs approximately 55 to 23 million years ago comprise a critical phase in earth history an array of geological records supported by climate modelling indicates a profound shift in global climate during this interval from a state that was largely free of polar ice caps to one in which ice sheets on antarctica approached their modern size however the early glaciation history of the northern hemisphere is a subject of controversy here we report stratigraphically extensive ice rafted debris including macroscopic dropstones in late eocene to early oligocene sediments from the norwegian greenland sea that were deposited between about 38 and 30 million years ago our data indicate sediment rafting by glacial ice rather than sea ice and point to east greenland as the likely source records of this type from one site alone cannot be used to determine the extent of ice involved however our data suggest the existence of at least isolated glaciers on greenland about 20 million years earlier than previously documented at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher