late eocene to early miocene ice sheet dynamics and the global carbon cycle paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial pacific ocean drilling program site 1218 the records include the two largest abrupt 1 myr increases in the cenozoic benthic oxygen isotope record oi 1 in the earliest oligocene 34 ma and mi 1 in the earliest miocene 23 ma the paired mg ca and oxygen isotope records are used to calculate seawater 18o w calculated w suggests that a large antarctic ice sheet formed during oi 1 and subsequently fluctuated throughout the oligocene on both short 0 5 myr and long 2 3 myr timescales between about 50 and 100 of its maximum earliest oligocene size the magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy the transient expansion of the antarctic ice sheet at mi 1 is marked in the benthic 18o record by two positive excursions between 23 7 and 22 9 ma each with a duration of 200 300 kyr bottom water temperatures decreased by 2 c over the 150 kyr immediately prior to both rapid 18o excursions however the onset of each of these phases of ice growth is synchronous within the resolution of the records with the onset of a 2 c warming over 150 kyr we suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as antarctic basement silicate rocks became blanketed by an ice sheet this represents a negative feedback process that might have operated during major abrupt growth phases of the antarctic ice sheet

seasonal and interannual variation of coccolithophore fluxes and species composition in sediment traps north of gran canaria 29 n 15 w abstract coccolithophore flux variations in sediment traps of the time series station estoc european station for time series in the ocean canary islands located 60 nm north of gran canaria were recorded from april 1993 to december 1996 the 20 cup particle traps were deployed at 1000 and 3000 m below sea surface and sampling intervals ranged from eight days to three weeks coccolith and coccosphere fluxes at both trap depths were characterized by a strong seasonality at 1000 m maximum coccolith fluxes were reached during spring from march to april 1995 and from february to march 1996 highest coccolith fluxes of 4538 106 coccoliths m 2 d 1 occurred at the beginning of march 1996 whereas lowest values of 19 8 106 coccoliths m 2 d 1 were recorded in june 1994 total coccosphere fluxes were constantly low during most of the investigated time interval and showed only high values during the main sedimentation phases from january to march 1995 up to 6 2 106 spheres m 2 d 1 and in march 1996 36 4 106 spheres m 2 d 1 at 3000 m water depth the sedimentation pattern was rather similar to the pattern observed at 1000 m maximum coccolith and coccosphere fluxes were also reached during spring time in february 1994 8200 106 and 15 6 10 6 m 2 d 1 respectively and in march 1996 8114 106 and 32 3 10 6 m 2 d 1 respectively however total coccolith flux peaks at 3000 m were about 2 4 times higher compared to the upper traps probably due to horizontal advection from phytoplankton material from north of the study site this effect also influenced the coccolith caco3 flux estimates mean calculated coccolith caco3 fluxes ranged between 3 9 mg m 2 d 1 for the upper traps 1995 1996 and 9 9 mg m 2 d 1 for the lower traps 1996 coccoliths contributed for about 8 78 of the measured total caco3 fluxes the coccolithophore assemblages were dominated by emiliania huxleyi florisphaera profunda and gephyrocapsa ericsonii during the entire sampling period whereas all other species together generally contributed less than 40 to the total assemblages variability of species compositions at either trap depth was very low indicating similar seasonal flux patterns of the different species

the sea level fingerprint of west antarctic collapse recent projections of sea level rise after a future collapse of thewest antarctic ice sheet for example the fourth intergovernmental panel on climate change assessment report assume that meltwater will spread uniformly that is eustatically across the oceans once marine based sectors of the west antarctic are filled a largely neglected 1977 study predicted that peak values would be 20 higher than the eustatic in the north pacific and 5 to 10 higher along the u s coastline we show with use of a state of the art theory that the sea level rise in excess of the eustatic value will be two to three times higher than previously predicted for u s coastal sites

seasonal variability of the long chain alkenone flux and the effect on the u37k index in the norwegian sea a seasonally varying sedimentation pattern was observed for the alkenone flux measured with sediment traps in the northern north atlantic in the norwegian sea traps were set at 500 1000 and 3000 m the alkenone flux varied between 0 1 and 7 1 g m 2 d 1 and followed the seasonal pattern of the bulk parameters maximum fluxes occurred from mid october until mid november and were also high in may a surprising result was that considerably higher particle fluxes were observed at 3000 m for the alkenone flux the highest additional input of 250 was observed during the period when sediment resuspension was greatest in summer at the barents sea continental margin traps at 1840 and 1950 m the alkenone fluxes follow the sedimentation pattern of the bulk parameters with a less visible signal of distinct seasonality observed in the 1950 m trap the sedimentation of total alkenones varied between 0 8 and 144 g m 2 d 1 at 1840 m and between 0 5 and 31 0 g m 2 d 1 at 1950 m resuspension and lateral advection contributed significantly to measured fluxes in the two near bottom traps alkenone concentrations were determined in faecal pellets of appendicularia ostracods and euphausids from selected samples at the barents sea site the alkenone flux in pellets 4 to 24 of total was 5 to 6 times higher at 1950 m depth than at 1840 m and the major part 77 78 of the total flux of c37 3 reaching the near bottom trap at 1950 m was associated with faecal pellets of the meso zooplankton spatial and temporal variations of the u37k signals were observed indicating that the imprint in the alkenone signal depends on the origin and transport pathway of the organic material strong deviations occur in areas where nepheloid layers contribute particles of long residence times to the primary flux

reconstructing past seawater mg ca and sr ca from mid ocean ridge flank calcium carbonate veins proxies for past seawater chemistry such as mg ca and sr ca ratios provide a record of the dynamic exchanges of elements between the solid earth the atmosphere and the hydrosphere and the evolving influence of life we estimated past oceanic mg ca and sr ca ratios from suites of 1 6 to 170 million year old calcium carbonate veins that had precipitated from seawater derived fluids in ocean ridge flank basalts our data indicate that before the neogene oceanic mg ca and sr ca ratios were lower than in the modern ocean decreased ocean spreading since the cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early tertiary may explain the recent rise in these ratios

present day climatic equivalents of european cenozoic climates abstract recently continental climate evolution in central europe over the last 45 ma has been reconstructed from the palaeobotanical record using a nearest living relative methodology coexistence approach ca the reconstructed climate curves document in detail the transition from almost tropical conditions in the mid eocene to a temperate climate at the pliocene pleistocene transition the observed climatic shifts are primarily expressed as non proportional changes of the different variables taken into account in the present study a published palaeoclimate data set for a total of 42 macrofloras complemented by new calculations is used as base to analyse the climatic space in which a fossil flora existed to define these spaces ca intervals calculated for 3 temperature mean annual temperature cold and warm month mean and 3 precipitation variables mean annual precipitation mean monthly precipitation of the driest and of the wettest month are combined using a global gridded climatology 10 resolution this climate space is then utilized to identify recent climate analogues with respect to the variables regarded for 18 macrofloras climatic analogue regions with respect to 6 variables are identified on the globe for 16 macrofloras analogues exist when three temperature parameters and mean annual precipitation are regarded no recent equivalents are found in 8 cases this corroborates the assumption of the temporary existence of non analogue climates in the cenozoic as shown by multivariate statistics the observed anomalies with respect to present day conditions basically refer to high winter temperatures deploying a gis the recent climate analogues can be presented as sets of grid cells for each flora that can be mapped on a globe once identified these regions can be merged with adequate thematic layers to assess additional proxy data for the palaeofloras to exemplify the procedure koeppen climate type numbers of days with ground frost as well as matthews biome classes are reconstructed the resulting koeppen types ranging from a to c are largely consistent with data previously published the ground frost record shows almost frost free conditions for the mid eocene greenhouse and for the mid miocene climatic optimum for the chattian up to 7 days with ground frost result during the late miocene cooling the number of days with ground frost significantly increased the inferred matthews biomes reveal changing patterns of evergreen and deciduous forest cover when recent climate analogues are found for a fossil flora present climate can be used to calibrate the original ca data it is shown that calibration considerably improves the resolution of the continental climate records

resolving a late oligocene conundrum deep sea warming and antarctic glaciation abstract changes in ice volume and resulting changes in sea level were determined for the late oligocene 26 23 ma astronomical timescale ats by applying 18 o to sea level calibrations to deep sea 18 o records from odp sites 689 690 929 1090 and 1218 our results show that maximum global ice volume occurred during two late oligocene 18 o events oi2c 24 4 ma and mi1 23 0 ma inferred glacioeustatic lowering with volumes up to 25 greater than the present day east antarctic ice sheet eais ice volume during glacial minima was on the order of about 50 of the present day eais this is supported by late oligocene stratigraphic records from antarctica that contain evidence of cold climates and repeated episodes of glaciation at sea level and grounding lines of glacial ice on the antarctic continental shelf in the ross sea and prydz bay in contrast composite deep sea 18 o records show a significant decrease 1 between 26 7 and 23 5 ma which have long been interpreted as bottom water warming combined with deglaciation of antarctica however a close examination of individual 18 o records indicates a clear divergence after 26 8 ma between records from southern ocean locations i e ocean drilling program sites 689 690 744 and those of other ocean basins high 18 o values 2 9 3 3 from these southern ocean 18 o records are consistent with an ice sheet on the east antarctic continent equivalent to present day values and cold bottom water temperatures 2 0 c these differences suggest a reduction in deep water produced near the antarctic continent i e proto antarctic bottom water proto aabw which were quickly entrained and mixed with warmer and presumably more saline bottom water originating from lower latitudes expansion of a warmer deep water mass and the weakening of the proto aabw may explain the large intra basinal isotopic gradients that developed among late oligocene benthic 18 o records these conclusions are also supported by ocean modeling suggesting a reduction of deep water formed in the southern ocean strengthening of deep water from the northern hemisphere and decreasing temperatures in high southern latitudes occurred as the drake passage opened to deep water low 18 o values reported from deep sea locations other than the southern ocean are shown to bias estimates of antarctic ice volume calling for a re evaluation of the notion that antarctic ice volume was significantly reduced during the late oligocene

small scale mantle convection produces stratigraphic sequences in sedimentary basins cyclic sedimentary deposits link stratigraphic sequences that are now geographically distant but were once part of the same depositional environment some of these sequences occur at periods of 2 to 20 million years and eustatic sea level variations or regional tectonic events are likely causes of their formation using numerical modeling we demonstrate that small scale mantle convection can also cause the development of stratigraphic sequences through recurrent local and regional vertical surface movements small scale convection driven stratigraphic sequences occur at periods of 2 to 20 million years and correlate only at distances up to a few hundred kilometers these results suggest that previous sequence stratigraphic analyses may contain erroneous conclusions regarding eustatic sea level variations

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

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

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

southern ocean seasonal temperature and subtropical front movement on the south tasman rise in the late quaternary 1 the subtropical front stf marking the northern boundary of the southern ocean has a steep gradient in sea surface temperature sst of approximately 4c over 0 5 of latitude presently in the region south of tasmania the stf lies nominally at 47s in the summer and 45s in the winter we present here sst reconstructions in a latitudinal transect of cores across the south tasman rise southeast of australia during the late quaternary sst reconstructions are based on two paleotemperature proxies alkenones and faunal assemblages which are used to assess past changes in sst in spring and summer the north south alignment in core locations allows reconstruction of movement of the stf over the last 100 ka surface water temperatures during the last glaciation in this region were 4c colder than today additional temperature changes greater in magnitude than 4c seen in individual cores can be attributed to changes in the water mass overlying the core site caused by the movement of the front across that location during the penultimate interglacial sst was 2c warmer and the stf was largely positioned south of 47s movement of the stf to the north occurred during cool climate periods such as the last marine isotope stages 3 and 4 in the last glaciation the front was at its farthest north position becoming pinned against the tasmanian landmass it moved south by 4 latitude to 47s in summer during the deglaciation but remained north of 45s in spring throughout the early deglaciation after 11 ka b p inferred invigoration of the east australia current appears to have pushed the stf seasonally south of the east tasman plateau until after 6 ka b p when it achieved its present configuration

constraints on glaciation in the middle eocene 46 37 ma from ocean drilling program odp site 1209 in the tropical pacific ocean the presence of glacial ice in the late middle eocene has been vigorously debated recently published sedimentary data from the high latitudes is suggestive of episodic cooling events and near freezing sea surface temperatures during parts of the late middle eocene constraints on ice volumes and the significance of excursions in open ocean foraminifera and seawater 18o reconstructions are less clear and there are few high resolution 18o records we present a new detailed record of benthic foraminiferal 18o from site 1209 that exhibits variations 18o benthic of 0 6 1 3 different approaches have previously been used to interpret 18o benthic including 1 an a priori assumption of a 50 contribution of temperature similar to what is reconstructed for the last glacial maximum recent change 2 applying oligocene calibrations between apparent sea level asl and 18o benthic or 3 assuming temperature and seawater 18o contributions can be partitioned through comparison with benthic mg ca using assumption 1 the record from site 1209 indicates changes in seawater 18o of 0 3 0 7 equivalent to 33 72 m m of asl assuming mean ice 18o of 45 using assumption 2 and two different end member calibrations the 18o benthic record implies changes in asl of 23 50 m or 50 108 m the third approach yields changes in seawater 18o of up to 0 6 to 1 4 we explore the compatibility of the results of each of these approaches with other studies that discuss evidence for ephemeral glaciations during the middle eocene with variable ice storage at one or both poles

microstructural and geochemical perspectives on planktic foraminiferal preservation glassy versus frosty in recent years it has become apparent that the cool tropic paradox of paleogene and cretaceous greenhouse climates arises because of the diagenetic alteration of tropical planktic foraminiferal calcite near the seafloor yielding artificially high 18o values because the mg ca compositions of foraminiferal and inorganic calcite are thought to be quite different mg ca measurements should be a sensitive way of monitoring diagenetic alteration here we examine the extent of diagenetic alteration of eocene planktic foraminiferal calcite using scanning electron microscope imaging of foraminiferal test microstructures and geochemical 18o and mg ca analyses we compare microstructural and geochemical characteristics between given species exhibiting two contrasting states of preservation those that appear frosty under reflected light and those that appear glassy microstructural evidence reveals extensive diagenetic alteration of frosty foraminiferal tests at the micron scale while 18o analyses document consistently higher 18o and therefore lower paleotemperatures in this material yet we find that 18o offsets between species in these frosty foraminiferal assemblages appear to be generally preserved suggesting that frosty foraminifera remain valuable for generating relatively short approximately 1 myr paleoceanographic time series that do not demand absolute estimates of paleotemperature we also find that the observed increase in mg ca for planktic foraminifera exhibiting diagenetic alteration compared to glassy taphonomies is far smaller than would be expected from the addition of inorganic calcite based on laboratory derived mg2 partition coefficients our findings imply that a much lower mg2 partition coefficient controls inorganic calcite formation in deep sea sedimentary sections in accordance with the findings of baker et al 1982

remote sensing of breaking wave phase speeds with application to non linear depth inversions abstract a number of existing models for surface wave phase speeds linear and non linear breaking and non breaking waves are reviewed and tested against phase speed data from a large scale laboratory experiment the results of these tests are utilized in the context of assessing the potential improvement gained by incorporating wave non linearity in phase speed based depth inversions the analysis is focused on the surf zone where depth inversion accuracies are known to degrade significantly the collected data includes very high resolution remote sensing video and surface elevation records from fixed in situ wave gages wave phase speeds are extracted from the remote sensing data using a feature tracking technique and local wave amplitudes are determined from the wave gage records and used for comparisons to non linear phase speed models and for non linear depth inversions a series of five different regular wave conditions with a range of non linearity and dispersion characteristics are analyzed and results show that a composite dispersion relation which includes both non linearity and dispersion effects best matches the observed phase speeds across the domain and hence improves surf zone depth estimation via depth inversions incorporating non linearity into the phase speed model reduces errors to o 10 which is a level previously found for depth inversions with small amplitude waves in intermediate water depths using linear dispersion considering the controlled conditions and extensive ground truth this appears to be a practical limit for phase speed based depth inversions finally a phase speed sensitivity analysis is performed that indicates that typical nearshore sand bars should be resolvable using phase speed depth inversions however increasing wave steepness degrades the sensitivity of this inversion method

application of benthic foraminiferal mg ca ratios to questions of cenozoic climate change abstract we investigate the evolution of cenozoic climate and ice volume as evidenced by the oxygen isotopic composition of seawater 18osw derived from benthic foraminiferal mg ca ratios to constrain the temperature effect contained in foraminiferal 18o values we have constructed two benthic foraminiferal mg ca records from intermediate water depth sites ocean drilling program sites 757 and 689 from the subtropical indian ocean and the weddell sea respectively together with the previously published composite record of lear et al science 287 2002 269 272 and the neogene record from the southern ocean of billups and schrag paleoceanography 17 2002 10 1029 2000pa000567 we obtain three almost complete representations of the 18osw for the past 52 myr we discuss the sensitivity of early cenozoic mg ca derived paleotemperatures and hence the 18osw to assumptions about seawater mg ca ratios we find that during the middle eocene 49 40 ma modern seawater ratios yield mg ca derived temperatures that are in good agreement with the oxygen isotope paleothermometer assuming ice free conditions intermediate waters cooled during the middle eocene reaching minimum temperatures by 40 ma the corresponding 18osw reconstructions support ice growth on antarctica beginning by at least 40 ma at the eocene oligocene boundary mg ca ratios and hence temperatures from weddell sea site 689 display a well defined maximum we caution against a paleoclimatic significance of this result and put forth that the partitioning coefficient of mg in benthic foraminifera may be sensitive to factors other than temperature throughout the remainder of the cenozoic the temporal variability among 18osw records is similar and similar to longer term trends in the benthic foraminiferal 18o record an exception occurs during the pliocene when 18osw minima in two of the three records suggest reductions in global ice volume that are not apparent in foraminiferal 18o records which provides a new perspective to the ongoing debate about the stability of the antarctic ice sheet maximum 18osw values recorded during the pleistocene at southern ocean site 747 agree well with values derived from the geochemistry of pore waters schrag et al science 272 1996 1930 1932 further highlighting the value of the new mg ca calibrations of martin et al earth planet sci lett 198 2002 193 209 and lear et al geochim cosmochim acta 66 2002 3375 3387 applied in this study we conclude that the application of foraminiferal mg ca ratios allows a refined view of cenozoic ice volume history despite uncertainties related to the geochemical cycling of mg and ca on long time scales

archaeal tetraether membrane lipid fluxes in the northeastern pacific and the arabian sea implications for tex86 paleothermometry the newly introduced temperature proxy the tetraether index of archaeal lipids with 86 carbon atoms tex86 is based on the number of cyclopentane moieties in the glycerol dialkyl glycerol tetraether gdgt lipids of marine crenarchaeota the composition of sedimentary gdgts used for tex86 paleothermometry is thought to reflect sea surface temperature sst however marine crenarchaeota occur ubiquitously in the world oceans over the entire depth range and not just in surface waters we analyzed the gdgt distribution in settling particulate organic matter collected in sediment traps from the northeastern pacific ocean and the arabian sea to investigate the seasonal and spatial distribution of the fluxes of crenarchaeotal gdgts and the origin of the tex86 signal transported to the sediment in both settings the tex86 measured at all trap deployment depths reflects sst in the arabian sea analysis of an annual time series showed that the sst estimate based on tex86 in the shallowest trap at 500 m followed the in situ sst with a 1 to 3 week time delay likely caused by the relatively low settling speed of sinking particles this revealed that the gdgt signal that reaches deeper water is derived from the upper water column rather than in situ production of gdgts the gdgt temperature signal in deeper traps at 1500 m and 3000 m did not show a seasonal cyclicity observed in the 500 m trap but rather reflected the annual mean sst this is probably due to a homogenization of the tex86 sst signal carried by particles as they ultimately reach the interior of the ocean our data confirm the use of tex86 as a temperature proxy of surface ocean waters

transient nature of the earth s climate and the implications for the interpretation of benthic δ18 o records abstract from the marine benthic 18 o records it is known that the earth s climate has experienced significant variability over the past 40 million years in general a number of assumptions are often needed to disentangle the benthic 18 o data into its temperature and ice volume contributions in this study a transient 1 d ice sheet model is used which overcomes these shortcomings by relating temperature to the benthic 18 o data leading to a self consistent and continuous record of 18 o temperature and sea level the contribution of land ice to benthic 18 o is examined with a set of sensitivity experiments varying the mean 18 o of the ice for different ice sheets it is shown that the scaling factor of sea water 18 o w to sea level is not constant over the long time scales however our sensitivity experiments do show that over the long time scale the general assumed 1 0 1 1 per 100 m of sea level is in reasonable agreement with our model results moreover the sea level ice volume response to temperature s t is shown to vary through time with the largest response found when variations in antarctic ice volume dominates the sea level variations during the oligocene to early miocene furthermore this response is quite large compared to the individual response of ice sheets during the plio pleistocene whereas the combined s t in this period is comparable to that during the oligocene accordingly the transient behaviour is very important for the interpretation of data records with respect to climate sensitivity and climate change during the past 40 million years

accurate estimation of sea surface temperatures using dissolution corrected calibrations for mg ca paleothermometry 1 paired 18o and mg ca measurements on the same foraminiferal shells offer the ability to independently estimate sea surface temperature sst changes and assess their temporal relationship to the growth and decay of continental ice sheets the accuracy of this method is confounded however by the absence of a quantitative method to correct mg ca records for alteration by dissolution here we describe dissolution corrected calibrations for mg ca paleothermometry in which the preexponent constant is a function of size normalized shell weight 1 for g ruber 212 300 m mg ca ruber 0 025 wt 0 11 e0 095t and b for g sacculifer 355 425 m mg ca sacc 0 0032 wt 0 181 e0 095t the new calibrations improve the accuracy of sst estimates and are globally applicable with this correction eastern equatorial atlantic sst during the last glacial maximum is estimated to be 2 9 0 4 c colder than today

deep sea temperature and ice volume changes across the pliocene pleistocene climate transitions earth has undergone profound changes since the late pliocene which led to the development 2 7 million years ago ma and intensification 0 9 ma of large scale northern hemisphere ice sheets recorded as transitions in the benthic foraminiferal oxygen isotope 18ob record here we present an orbitally resolved record of deep ocean temperature derived from benthic foraminiferal magnesium calcium ratios from the north atlantic which shows that temperature variations are a substantial portion of the global 18ob signal the record shows two distinct cooling events associated with the late pliocene lpt 2 5 to 3 ma and mid pleistocene mpt 1 2 to 0 85 ma climate transitions whereas the lpt increase in ice volume is attributed directly to global cooling the shift to 100 000 year cycles at the mpt is more likely to be a response to an additional change in ice sheet dynamics

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

the mid pleistocene transition in the tropical pacific a sea surface temperature sst record based on planktonic foraminiferal magnesium calcium ratios from a site in the western equatorial pacific warm pool reveals that glacial interglacial oscillations in sst shifted from a period of 41 000 to 100 000 years at the mid pleistocene transition 950 000 years before the present sst changes at both periodicities were synchronous with eastern pacific cold tongue ssts but preceded changes in continental ice volume the timing and nature of tropical pacific sst changes over the mid pleistocene transition implicate a shift in the periodicity of radiative forcing by atmospheric carbon dioxide as the cause of the switch in climate periodicities at this time

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

long chain alkenones and alkyl alkenoates and the fossil coccolith record of marine sediments long chain n c37 c39 alkenones and alkyl alkenoates are biological markers for sediment inputs of algae from the class prymnesiophyceae which includes the coccolithophorids these compounds have been recognized in many recent and ancient marine sediments but in only a few living algal species notably the ubiquitous coccolithophorid emiliania huxleyi the proven value of long chain alkenones in palaeotemperature assessment prompts an evaluation of their sedimentary record especially their correspondence with coccolithophorid fossils in ancient marine sediments synthesis of available micropalaeontological and molecular data suggests that morphologically related species of the genera crenalithus dictyococcites emiliania gephyrocapsa pseudoemiliania and reticulofenestra all belonging to the family gephyrocapsaceae were potential biological sources of alkenones and alkyl alkenoates in marine sediments deposited since the eocene 45 ma the occurrence of alkenones in cenomanian and albian sediments devoid of nannofossils may be presumed to reflect contributions from ancestors of the gephyrocapsaceae although an investigation of cretaceous samples containing both coccoliths and alkenones would provide further evidence of this proposed correspondence the combination of palaeontological and molecular chemotaxonomic information offers a novel approach to the evaluation of the phylogenetic lineages that link living and extinct algae

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

pleistocene collapse of the west antarctic ice sheet some glacial sediment samples recovered from beneath the west antarctic ice sheet at ice stream b contain quaternary diatoms and up to 108 atoms of beryllium 10 per gram other samples contain no quaternary diatoms and only background levels of beryllium 10 less than 10 6 atoms per gram the occurrence of young diatoms and high concentrations of beryllium 10 beneath grounded ice indicates that the ross embayment was an open marine environment after a late pleistocene collapse of the marine ice sheet

exploring uncertainties in the relationship between temperature ice volume and sea level over the past 50 million years over the past decade efforts to estimate temperature and sea level for the past 50 ma have increased in parallel efforts to model ice sheet changes during this period have been ongoing we review published paleodata and modeling work to provide insights into how sea level responds to changing temperature through changes in ice volume and thermal expansion to date the temperature to sea level relationship has been explored for the transition from glacial to interglacial states attempts to synthesize the temperature to sea level relationship in deeper time when temperatures were significantly warmer than present have been tentative we first review the existing temperature and sea level data and model simulations with a discussion of uncertainty in each of these approaches we then synthesize the sea level and temperature data and modeling results we have reviewed to test plausible forms for the sea level versus temperature relationship on this very long timescale there are no globally representative temperature proxies and so we investigate this relationship using deep sea temperature records and surface temperature records from high and low latitudes it is difficult to distinguish between the different plausible forms of the temperature to sea level relationship given the wide errors associated with the proxy estimates we argue that for surface high latitude southern hemisphere temperature and deep sea temperature the rate of change of sea level to temperature has not remained constant i e linear over the past 50 ma although the relationship remains ambiguous for the available low latitude surface temperature data a nonlinear form between temperature and sea level is consistent with ice sheet modeling studies this relationship can be attributed to 1 the different glacial thresholds for southern hemisphere glaciation compared to northern hemisphere glaciation and 2 the ice sheet carrying capacity of the antarctic continent

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

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

a record of bottom water temperature and seawater δ18o for the southern ocean over the past 440 kyr based on mg ca of benthic foraminiferal uvigerina spp the sensitivity to temperature of mg ca ratios in the shallow infaunal benthic foraminifera uvigerina spp has been assessed core top calibrations over 1 20 c show a range in sensitivity of 0 065 0 084 mmol mol c but few data are available spanning the temperature range anticipated in deep sea records over glacial interglacial cycles in contrast to epibenthic foraminiferal species carbonate ion saturation appears not to affect mg ca significantly a method based on estimating the ratio of the temperature sensitivity of foraminiferal mg ca to that of 18ocalcite shows that sensitivity for mg ca at the high end of the observed core top range 0 1 mmol mol c is required for consistency with lgm holocene differences in each property as constrained by independent proxy data this is supported by a mg ca record for uvigerina spp generated for the southern ocean over the past 440 000 years from ocean drilling program site 1123 chatham rise new zealand the record shows variability that correlates with climate oscillations the lgm deep ocean temperature derived from the mg ca record is 1 1 0 3 c transformation to temperature allows estimates to be made of changes in bottom water temperature and seawater 18o and comparison made with literature records analysis reveals a 2 5 kyr lead in the record of temperature over calcite 18o and a longer lead over seawater 18o this is a reflection of larger phase offsets at eccentricity periods phase offsets at tilt and precession are within error zero

extremely low long term erosion rates around the gamburtsev mountains in interior east antarctica the high elevation and rugged relief 3 km of the gamburtsev subglacial mountains gsm have long been considered enigmatic orogenesis normally occurs near plate boundaries not cratonic interiors and large scale tectonic activity last occurred in east antarctica during the pan african 480 600 ma we sampled detrital apatite from eocene sands in prydz bay at the terminus of the lambert graben which drained a large pre glacial basin including the northern gamburtsev mountains apatite fission track and u th he cooling ages constrain bedrock erosion rates throughout the catchment we double dated apatites to resolve individual cooling histories erosion was very slow averaging 0 01 0 02 km myr for 250 myr supporting the preservation of high elevation in interior east antarctica since at least the cessation of permian rifting long term topographic preservation lends credence to postulated high elevation mountain ice caps in east antarctica since at least the cretaceous and to the idea that cold based glaciation can preserve tectonically inactive topography

variations in mg ca and sr ca ratios of planktonic foraminifera caused by postdepositional dissolution evidence of shallow mg dependent dissolution a comparative study has been made of two species of planktonic foraminifera g tumida and g sacculifer in a depth transect on the ontong java plateau western equatorial pacific g tumida tests from core top sediments showed decreasing mg ca 2 65 1 25 mmol mol and sr ca 1 50 1 16 mmol mol ratios with increasing water depth 1600 4400 m while no such variation was found in g sacculifer tests in excess of 355 m average mg ca 3 6 mmol mol sr ca 1 4 mmol mol artificial dissolution of g tumida tests led to a decrease in both mg ca and sr ca but in g sacculifer there was no significant change in the ratios analyses by electron microprobe revealed that mg ca of the inner chamber calcite in g tumida tests was much higher than that of the calcite crust keel whereas sr ca was only slightly elevated there were no consistent spatial differences in either mg ca or sr ca for g sacculifer tests dissolution in the oceans gives rise to the removal of the chamber calcite in g tumida about 30 of the total calcite leaving the keel calcite although g tumida is thought of as a dissolution resistant form the majority of mg ca and sr ca depletion and chamber loss occurs above the lysocline it is also possible that much of the mg enriched gametogenic calcite has been lost by dissolution from g sacculifer above 1600 m mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera calculations show that the saturation horizon for mg rich parts of tests may be elevated by several hundred meters compared with normal calcite

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

physiological impacts on alkenone paleothermometry we conducted isothermal 15 c batch culture experiments with the coccolithophorid emiliania huxleyi strain nepcc 55a to evaluate the extent to which nutrient and light stress contribute to variability in the alkenone unsaturation index u37k alkenone content and composition were constant throughout exponential growth in both experiments when nutrients nitrate and orthophosphate were replete stationary phase nutrient starved cells continued to produce alkenones amassing concentrations alk 3 times higher than those dividing exponentially 1 5 2 pg cell 1 and the u37k of excess alkenone dropped by 0 11 units in contrast 5 days of continuous darkness resulted in a 75 decrease in cellular alk and a significant u37k increase 0 11 units given an established 0 034 unit c response for exponentially growing cells of this strain the observed range of u37k variability at 15 c corresponds to an uncertainty of 3 2 c in predicted growth temperature this level of variability matches that of the global u37k annual mean sea surface temperature calibration for surface marine sediments begging the question what is the physiological condition of alkenone producing cells exported to marine sediments comparison of our laboratory results for a strain of e huxleyi isolated from the subarctic pacific ocean with depth profiles for alkenones in surface waters from two contrasting sites in the northeast pacific ocean suggests that the answer to this question depends on the ocean regime considered a possibility with significant bearing on how stratigraphic u37k records in marine sediments are to be interpreted paleoceanographically

how is the ocean filled 1 the ocean surface rapidly exchanges heat freshwater and gases with the atmosphere but once water sinks into the ocean interior the inherited properties of seawater are closely conserved previous water mass decompositions have described the oceanic interior as being filled by just a few different property combinations or water masses here we apply a new inversion technique to climatological tracer distributions to find the pathways by which the ocean is filled from over 10 000 surface regions based on the discretization of the ocean surface at 2 by 2 resolution the volume of water originating from each surface location is quantified in a global framework and can be summarized by the estimate that 15 of the surface area fills 85 of the ocean interior volume ranked from largest to smallest the volume contributions scaled by surface area follow a power law distribution with an exponent of 1 09 0 03 that appears indicative of the advective diffusive filling characteristics of the ocean circulation as demonstrated using a simple model this work quantifies the connection between the surface and interior ocean allowing insight into ocean composition atmosphere ocean interaction and the transient response of the ocean to a changing climate

cenozoic global sea level sequences and the new jersey transect results from coastal plain and continental slope drilling the new jersey sea level transect was designed to evaluate the relationships among global sea level eustatic change unconformity bounded sequences and variations in subsidence sediment supply and climate on a passive continental margin by sampling and dating cenozoic strata from coastal plain and continental slope locations we show that sequence boundaries correlate within 0 5 myr regionally onshore offshore and interregionally new jersey alabama bahamas implicating a global cause sequence boundaries correlate with 18o increases for at least the past 42 myr consistent with an ice volume glacioeustatic control although a causal relationship is not required because of uncertainties in ages and correlations evidence for a causal connection is provided by preliminary miocene data from slope site 904 that directly link 18o increases with sequence boundaries we conclude that variation in the size of ice sheets has been a primary control on the formation of sequence boundaries since 42 ma we speculate that prior to this the growth and decay of small ice sheets caused small amplitude sea level changes 20 m in this supposedly ice free world because eocene sequence boundaries also appear to correlate with minor 18o increases subsidence estimates backstripping indicate amplitudes of short term million year scale lowerings that are consistent with estimates derived from 18o studies 25 50 m in the oligocene middle miocene and 10 20 m in the eocene and a long term lowering of 150 200 m over the past 65 myr consistent with estimates derived from volume changes on mid ocean ridges although our results are consistent with the general number and timing of paleocene to middle miocene sequences published by workers at exxon production research company our estimates of sea level amplitudes are substantially lower than theirs lithofacies patterns within sequences follow repetitive predictable patterns 1 coastal plain sequences consist of basal transgressive sands overlain by regressive highstand silts and quartz sands and 2 although slope lithofacies variations are subdued reworked sediments constitute lowstand deposits causing the strongest most extensive seismic reflections despite a primary eustatic control on sequence boundaries new jersey sequences were also influenced by changes in tectonics sediment supply and climate during the early to middle eocene low siliciclastic and high pelagic input associated with warm climates resulted in widespread carbonate deposition and thin sequences late middle eocene and earliest oligocene cooling events curtailed carbonate deposition in the coastal plain and slope respectively resulting in a switch to siliciclastic sedimentation in onshore areas oligocene sequences are thin owing to low siliciclastic and pelagic input and their distribution is patchy reflecting migration or progradation of depocenters in contrast miocene onshore sequences are thicker reflecting increased sediment supply and they are more complete downdip owing to simple tectonics we conclude that the new jersey margin provides a natural laboratory for unraveling complex interactions of eustasy tectonics changes in sediment supply and climate change

autostepping during the transgressive growth of deltas results from flume experiments a series of three dimensional flume experiments on the transgressive growth of deltas conducted with constant rate of relative sea level rise a constant sediment discharge s and constant upstream water discharge q reveals an inbuilt geomorphic process that inevitably forms discrete steps on the abandoned subaqueous deltaic slope the stepped topography and its process of formation are here referred to as autostep s and autostepping respectively the stepped topography is caused by the lateral migration of delta front lobes that inevitably shift landward but fail to cover lobes of older cycles the autostepping arises from the principle of autoretreat combined with autocyclic lateral shifting of the feeder system discrete changes of a s a s or q s are not required to explain the origin of episodic backstepping in an overall transgressive regime allocyclic changes in a and s as commonly invoked in the sequence stratigraphy literature are not an alternative to autostepping but would only enhance or reduce the inbuilt process of autostepping in river dominated delta systems

accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf acceleration exceeds 27 km 3 per year and ice is thinning at rates of tens of meters per year we attribute this abrupt evolution of the glaciers to the removal of the buttressing ice shelf the magnitude of the glacier changes illustrates the importance of ice shelves on ice sheet mass balance and contribution to sea level change index terms 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 3349 meteorology and atmospheric dynamics polar meteorology 6924 radio science interferometry 9310 information related to geographic region antarctica citation rignot e g casassa p gogineni w krabill a rivera and r thomas 2004 accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf geophys res lett 31 l18401 doi 10 1029 2004gl020697

a new high resolution digital elevation model of greenland fully validated with airborne laser altimeter data a new digital elevation model of the greenland ice sheet and surrounding rock outcrops has been produced at 1 km postings from a comprehensive suite of satellite remote sensing and cartographic data sets height data over the ice sheet were mainly from ers 1 and geosat radar altimetry these data were corrected for a slope dependent bias that had been identified in a previous study the radar altimetry was supplemented with stereophotogrammetric data sets synthetic aperture radar interferometry and digitized cartographic maps over regions of bare rock and where gaps in the satellite altimeter coverage existed the data were interpolated onto a regular grid with a spacing of 1 km the accuracy of the resultant digital elevation model over the ice sheet was assessed using independent and spatially extensive measurements from an airborne laser altimeter that had an accuracy of between 10 and 12 cm in a comparison with the laser altimetry the digital elevation model was found to have a slope dependent accuracy ranging from 1 04 1 98 m to 0 06 14 33 m over the ice sheet for a slope range of 0 0 1 0 the mean accuracy over the whole ice sheet was 0 33 6 97 m over the bare rock areas the accuracy ranged from 20 to 200 m dependent on the data source available the new digital elevation model was used as an input data set for a positive degree day model of ablation the new elevation model was found to reduce ablation by only 2 compared with using an older 2 5 km resolution model which suggests that resolution induced errors in estimating ablation are no longer important

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

insights from the paleogene tropical pacific foraminiferal stable isotope and elemental results from site 1209 shatsky rise 1 stable isotope and elemental measurements were conducted on foraminifera from a sequence of calcareous pelagic ooze at ocean drilling program site 1209 to document the thermal evolution of the north pacific water column over shatsky rise and to address long standing questions about the nature of oceanic circulation in the early paleogene a major change in seasonality and water column structure in the early eocene marks a change in tropical pacific climate and circulation just prior to the early eocene climatic optimum subsequent long term cooling is interrupted by a transient positive 18o excursion identified in planktonic and benthic foraminifera during the late early eocene that is interpreted as evidence for ephemeral formation of deep water from a low latitude saline source paired analysis of benthic mg ca and 18o was undertaken to assess the relative contribution of temperature and seawater oxygen isotope composition to the benthic 18o record stratigraphic trends of benthic 18o and mg ca decouple during two intervals in the early eocene and early middle eocene although variable seawater 18o is the most likely candidate to explain decoupling of benthic 18o and mg ca it is difficult to argue for substantial change in continental ice volume during a presumably ice free interval of time

the neogene of eurasia spatial gradients and temporal trends the second synthesis of neclime article i nfo this volume represents the second synthesis of the international open research network neclime neogene climate evolution in eurasia that was established in 2000 to study climate change in eurasia during the neogene and its impact on ecosystems the main objectives of neclime research are 1 proxy data based quantitative reconstructions of neogene climate in eurasia by means of standardised techniques 2 the modelling of atmospheric and oceanic circulation and of biomes using neogene boundary conditions and 3 the analysis of the interaction between palaeogeography vegetation and climate presently 94 scientists from 34 countries are neclime members contributing with their published data to a collective data base integrating proxies from various sources such as palaeobotany vertebrate palaeontology and geology the following core topics are addressed in the volume precipitation patterns and landscape opening the asian monsoon systems the potential of past climates for the evaluation of future climate change scenarios as well as short term change and variability of climate highlights of the single contributions are summarised in a proxy data section and in a modelling section respectively it is shown that the integrative approach presented in this volume brings about a much better and much more detailed understanding of neogene climate dynamics in eurasia than previously achieved even though neogene climate changes may have regional aspects differing considerably from each other and from the general global trend the results from the various proxy and modelling studies consistently show that later neogene cooling implicated more pronounced latitudinal and longitudinal gradients on the other hand the issue reveals a number of problems and questions resulting from the contrary nature of palaeozoological and palaeobotanical palaeoclimate proxies and modelling results mainly at a more regional level the models can not yet explain the relatively warm high latitudes during the neogene and we still do not sufficiently understand the role of the various boundary conditions such as co2 palaeogeography and palaeovegetation in the observed neogene climate change and its regional differentiation these apparent uncertainties underline the importance of the study of palaeo scenarios in order to enhance the reliability of future climate projections

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

increased seasonality through the eocene to oligocene transition in northern high latitudes a profound global climate shift took place at the eocene oligocene transition approximately 33 5 million years ago when cretaceous early palaeogene greenhouse conditions gave way to icehouse conditions during this interval changes in the earth s orbit and a long term drop in atmospheric carbon dioxide concentrations resulted in both the growth of antarctic ice sheets to approximately their modern size and the appearance of northern hemisphere glacial ice however palaeoclimatic studies of this interval are contradictory although some analyses indicate no major climatic changes others imply cooler temperatures increased seasonality and or aridity climatic conditions in high northern latitudes over this interval are particularly poorly known here we present northern high latitude terrestrial climate estimates for the eocene to oligocene interval based on bioclimatic analysis of terrestrially derived spore and pollen assemblages preserved in marine sediments from the norwegian greenland sea our data indicate a cooling of approximately 5 degrees c in cold month winter mean temperatures to 0 2 degrees c and a concomitant increased seasonality before the oi 1 glaciation event these data indicate that a cooling component is indeed incorporated in the delta 18 o isotope shift across the eocene oligocene transition however the relatively warm summer temperatures at that time mean that continental ice on east greenland was probably restricted to alpine outlet glaciers

a late miocene climate model simulation with echam4 ml and its quantitative validation with terrestrial proxy data abstract for the tortonian late miocene 11 to 7 ma we present a model simulation using the atmospheric general circulation model agcm echam4 coupled to a mixed layer ml ocean model the tortonian simulation with echam4 ml includes an adjusted weaker than present ocean heat transport a generally lower palaeorography and an appropriate palaeovegetation we analyse the climatic differences between the tortonian run and the present day control experiment and we validate our tortonian model results for the mean annual temperature and the annual precipitation with quantitative terrestrial proxy data globally the tortonian run is slightly warmer 0 6 c and the global precipitation indicates more humid conditions 27 mm a than the pd control run particularly the northern high latitudes are warmer 3 5 c in the tortonian simulation which leads to a weaker meridional temperature gradient than today as well as to a reduction of polar sea ice we attribute the polar warming to the lowering of the greenland elevation 20 c in the miocene and to the effects of the palaeovegetation the reduced altitude of the tibetan plateau causes a warming 20 c as compared to today and leads to a weaker asian monsoon in the tortonian run for europe the mean annual temperature is almost unaffected as compared to today because a cooling effect of the weak palaeocean heat transport is compensated by the palaeovegetation when validating our model results we find that the tortonian run is largely consistent with quantitative proxy data however the high latitudes tend to be generally too cool in the palaeoclimate simulation and the equator to pole temperature gradient is too steep as compared to proxy data for europe the comparison with proxy data indicates that the tortonian simulation underestimates the mean annual temperatures but precipitation patterns are quite consistent between model results and proxy data overall the tortonian run is quite realistic and hence the model simulation contributes to a better understanding of the relevant climate processes in the miocene however the discrepancies to proxy data demonstrate that we still do not sufficiently understand the late miocene climate

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

large temperature drop across the eocene oligocene transition in central north america the eocene oligocene transition about 33 5 million years ago was a major global climate event the end of the eocene was unusually warm with no significant ice on antarctica but the oligocene saw the arrival of a permanent antarctic ice sheet two papers this week relate to the continental effects of this global change dupont nivet et al examined sedimentary records from the tibetan plateau and find a drop in atmospheric water which caused cooling and aridification coincident with antarctic cooling previous studies attributed this phenomenon to the rapid uplift of the tibetan plateau but this new work suggests that regional tibetan climate was influenced by global events in an unrelated paper on the same climate transition zanazzi et al explore the cooling in north america at the time using stable isotope measurements from fossil teeth and bones to create a proxy temperature record they find a large drop in mean annual temperature of 8 2 c a greater fall than seen in the oceans this continental transition may explain why many cold blooded reptiles and amphibians became extinct whereas mammals able to regulate their body temperature escaped relatively unscathed an analysis of fossil tooth enamel and fossil bones is used to derive a continental temperature record for the eocene oligocene transition and reports a large drop in mean annual temperature over roughly 400 000 years this cooling explains the decline in cold blooded terrestrial animals whereas most mammals in the region were unaffected the eocene oligocene transition towards a cool climate 33 5 million years ago was one of the most pronounced climate events during the cenozoic era1 the marine record of this transition has been extensively studied however significantly less research has focused on continental climate change at the time yielding partly inconsistent results on the magnitude and timing of the changes2 3 4 5 6 7 8 here we use a combination of in vivo stable isotope compositions of fossil tooth enamel with diagenetic stable isotope compositions of fossil bone to derive a high resolution about 40 000 years continental temperature record for the eocene oligocene transition we find a large drop in mean annual temperature of 8 2 3 1 c over about 400 000 years the possibility of a small increase in temperature seasonality and no resolvable change in aridity across the transition the large change in mean annual temperature exceeding changes in sea surface temperatures at comparable latitudes9 10 and possibly delayed in time with respect to marine changes by up to 400 000 years explains the faunal turnover for gastropods amphibians and reptiles whereas most mammals in the region were unaffected our results are in agreement with modelling studies that attribute the climate cooling at the eocene oligocene transition to a significant drop in atmospheric carbon dioxide concentrations

deep water temperature carbonate ion and ice volume changes across the eocene oligocene climate transition 1 paired benthic foraminiferal stable isotope and mg ca data are used to estimate bottom water temperature bwt and ice volume changes associated with the eocene oligocene transition eot the largest global climate event of the past 50 myr we utilized odp sites 1090 and 1265 in the south atlantic to assess seawater 18o w antarctic ice volume and sea level changes across the eot 33 8 33 54 ma we also use benthic 13c data to reconstruct the sources of the deep water masses in this region during the eot our data together with previously published records indicate that a pulse of northern component water influenced the south atlantic immediately prior to and following the eot benthic 18o records show a 0 5 increase at 33 8 ma eot 1 that represents a 2 c cooling and a small 10 m eustatic fall that is followed by a 1 0 increase associated with oi 1 the expected cooling of deep waters at oi 1 33 54 ma is not apparent in our mg ca records we suggest the cooling is masked by coeval changes in the carbonate saturation state co32 which affect the mg ca data to account for this the bwt ice volume and w estimates are corrected for a change in the co32 of deep waters on the basis of recently published work corrected bwt at sites 1090 and 1265 show a 1 5 c cooling coincident with oi 1 and an average w increase of 0 75 the increase in ice volume during oi 1 resulted in a 70 m drop in global sea level and the development of an antarctic ice sheet that was near modern size or slightly larger

eocene sea temperatures for the mid latitude southwest pacific from mg ca ratios in planktonic and benthic foraminifera abstract we have used laser ablation inductively coupled plasma mass spectrometry la icp ms to measure elemental mg ca al ca mn ca zn ca sr ca and ba ca ratios of 13 species of variably preserved early to middle eocene planktonic and benthic foraminifera from new zealand the foraminifera were obtained from ashley mudstone mid waipara river south island which was deposited at bathyal depth ca 1000 m on the northern margin of the east facing canterbury basin at a paleo latitude of ca 55 s la icp ms data yield trace element depth profiles through foraminifera test walls that can be used to identify and exclude zones of surficial contamination and infilling material resulting from diagenetic coatings mineralisation and detrital sediment screened mg ca ratios from 5 species of foraminifera are used to calculate sea temperatures from late early to early middle eocene ca 51 to 46 5 ma a time interval that spans the termination of the early eocene climatic optimum eeco during this time sea surface temperatures sst varied from 30 to 24 c and bottom water temperatures bwt from 21 to 14 c comparison of mg ca sea temperatures with published 18o and tex86 temperature data from the same samples hollis et al 2009 shows close correspondence indicating that la icp ms can provide reliable mg ca sea temperatures even where foraminiferal test preservation is variable agreement between the three proxies also implies that mg ca temperature calibrations for modern planktonic and benthic foraminifera can generally be applied to eocene species although some species e g v marshalli show significant calibration differences the mg ca ratio of the eocene ocean is constrained by our data to be 35 50 lower than the modern ocean depending on which tex86 temperature calibration kim et al 2008 liu et al 2009 is used to compare with the mg ca sea temperatures sea temperatures derived from 18o analysis of foraminifera from waipara show amplified variability relative to the mg ca and tex86 proxies this amplified variability is probably a diagenetic effect although it is possible that this eocene 18o record contains an ice volume component the amplification signalling that temperature changes may have been accompanied by growth and collapse of ephemeral polar ice sheets on timescales of ca 0 5 myr

a study of the tex86 paleothermometer in the water column and sediments of the santa barbara basin california 1 particulate organic matter collected during a 2 year period as part of an ongoing sediment trap study and a high resolution sediment record from 1850 to 1987 a d from the santa barbara basin were analyzed for tex86 a temperature proxy based on marine crenarchaeotal membrane lipids highest fluxes of crenarchaeotal lipids in the water column were found in may june 1996 and from october 1996 to january 1997 and in general showed a good correlation with mass fluxes tex86 reconstructed temperatures from the sediment trap series ranged from 8 to 11 c and were usually substantially lower than sea surface temperatures sst indicating that unlike in previous studies the tex86 corresponds to subsurface temperatures likely between 100 and 150 m tex86 temperature variations observed in trap samples were not coupled to changes in sst or deep water temperatures and only to some degree with crenarchaeotal lipid fluxes this suggests that a complex combination of different depth origins and seasonal growth periods of crenarchaeota contributed to the variations in tex86 signal during the annual cycle tex86 temperatures in the two sediment cores studied 8 13 c were also substantially lower than those of instrumental sst records 14 17 5 c confirming that tex86 records a subsurface temperature signal in the santa barbara basin this result highlights the importance of performing calibration studies using sediment traps and core tops before applying the tex86 temperature proxy in a given study area

timing and magnitude of miocene eustasy derived from the mixed siliciclastic carbonate stratigraphic record of the northeastern australian margin article eustasy is a key parameter to understand sedimentary sequences on continental margins and to reconstruct continental ice volume in the cenozoic but timing and magnitude of global sea level changes remain controversial especially for the miocene epoch we analyzed sediment cores recovered from the marion plateau offshore northeastern australia during ocean drilling program odp leg 194 to define the mechanisms and timing of sequence formation on mixed carbonate siliciclastic margins and to estimate the amplitude of miocene eustatic adjustments we identified sequence boundaries on seismic reflection lines significantly revised the existing biostratigraphic age models and investigated the sedimentary response to sea level changes across the marion plateau we subdivided the miocene sediments into three sequence sets comprising a set of prograding clinoforms a muddy prograding carbonate ramp evolving into an aggrading platform and a lowstand ramp evolving into a backstepping ramp we recognized eight individual sequences dated at 18 0 ma 17 2 ma 16 5 ma 15 4 ma 14 7 ma 13 9 ma 13 0 ma and 11 9 ma we demonstrate that sequences on the marion plateau are controlled by glacio eustasy since sequence boundaries are marked by increases in 18 o deep sea miocene isotope events mi1b mbi 3 mi2 mi2a mi3a mi3 mi4 and mi5 respectively which reflects increased ice volume primarily on antarctica our backstripping estimates suggest that sea level fell by 26 28 m at 16 5 ma 26 29 m at 15 4 ma 29 38 m at 14 7 ma and 53 81 m at 13 9 ma combining backstripping with 18 o estimates yields sea level fall amplitudes of 27 1 m at 16 5 ma 27 1 m at 15 4 ma 33 3 m at 14 7 ma and 59 6 m at 13 9 ma we use a similar approach to estimate eustatic rises of 19 1 m between 16 5 and 15 4 ma 23 3 m between 15 4 and 14 7 ma and 33 3 m between 14 7 and 13 9 ma these estimates can be combined into a eustatic curve that suggests that sea level fell by 53 69 m between 16 5 and 13 9 ma this implies that at least 90 of the east antarctic icesheet was formed during the middle miocene the new independent amplitude estimates are crucial as the miocene is the geologic epoch for which the new jersey margin sea level record is poorly constrained

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

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

sea ice feedback and cenozoic evolution of antarctic climate and ice sheets 1 the extent and thickness of antarctic sea ice have important climatic effects on radiation balance energy transfer between the atmosphere and ocean and moisture availability this paper explores the role of sea ice and related feedbacks in the cenozoic evolution of antarctic climate and ice sheets using a numerical climate model with explicit dynamical representations of sea ice and continental ice sheets in a scenario of decreasing cenozoic greenhouse gas concentrations our model initiates continental glaciation before any significant sea ice forms around the continent once variable ice sheets are established seasonal sea ice distribution is highly sensitive to orbital forcing and ice sheet geometry via the ice sheet s control on regional temperature and low level winds although the expansion of sea ice has significant climatic effects near the coast it has only minimal effects in the continental interior and on the size of the ice sheet therefore the cenozoic appearance of antarctic sea ice was primarily a response to the growth of grounded ice sheets and was not a critical factor in episodes of paleogene and neogene glaciation the influence of the east antarctic ice sheet on sea ice southern ocean surface temperatures and winds has important implications for ocean circulation the marine carbon cycle and the development of the west antarctic ice sheet the sensitivity of sea ice to grounded ice sheets implies reconstructions of sea ice based on marine diatoms are good indicators of glacial conditions in the continental interior and may provide insight into the long term stability of antarctic ice sheets

alkenones and alkenes in surface waters and sediments of the southern ocean implications for paleotemperature estimation in polar regions abstract the concentration of c37 c39 long chain alkenones and alkenes were determined in surface water and surface sediment samples from the subpolar waters of the southern ocean distributions of these compounds were similar in both sample sets indicating little differential degradation between or within compound classes the relative amounts of the tri to tetra unsaturated c37 alkenones increased with increasing temperature for temperatures below 6 c similar to the di and tri unsaturated c37 alkenones the c37 di tri and tetra unsaturated methyl alkenones are used in paleotemperature calculations via the u37k and the u37k ratios in these datasets the relative abundances of the c37 2 and the c37 3 alkenones as a proportion of the total c37 alkenones were opposite and strongly related to temperature the latter with more scatter but the abundance of the c37 4 alkenone showed no relationship with temperature the original definition of u37k includes the abundance of 37 4 in both the numerator and denominator and thus it is perhaps not surprising that there is considerable scatter in the values obtained for u37k at low temperatures of the two we suggest that u37k is the better parameter for use in paleotemperature estimations even in cold locations u37k values in the sediments fall on virtually the same regression line obtained for the water column samples of sikes and volkman 1993 indicating that their calibration is suitable for use in southern ocean sediments the comparison of water column data with sedimentary temperature estimates suggests that the alkenone distributions are dominated by contributions from the summer when the biomass of emiliania huxleyi and presumably flux to the sediment is expected to be high

weathering profiles in granitoid rocks of the sila massif uplands calabria southern italy new insights into their formation processes and rates abstract in this paper we characterized several weathering profiles developed on granitoid rocks in the sila massif upland calabria southern italy integrating detailed macro and micromorphological observations with physico mechanical field tests and petrographic mineralogical and geochemical analyses we focused our attention on the main weathering and pedogenetic processes trying to understand apparent discrepancies between weathering grade classes based on field description and geomechanical properties and two common weathering indices such as the micropetrographic index ip and the chemical index of alteration cia our results showed that sericite on plagioclase and biotite chloritization that represent inherited features formed during late stage hydrothermal alteration of granitoid rocks may cause an overestimation of the real degree of weathering of primary mineral grains under meteoric conditions especially in lower weathering grade classes moreover the frequent identification of fe mn oxides and clay coatings of illuvial origin rather than or in addition to those formed in situ both at the macro and microscale may also explain an overestimation of the weathering degree with respect to field based classifications finally some apparent inconsistencies between field geomechanical responses and chemical weathering were interpreted as related to physical weathering processes cryoclastism and thermoclastism that lead to rock breakdown even when chemical weathering is not well developed hence our study showed that particular caution is needed for evaluating weathering grades because traditional field and geochemical petrographic tools may be biased by inherited hydrothermal alteration physical weathering and illuvial processes on the basis of chronological constraints to soil formation obtained from a 42 ka old volcanic input mixed to granite parent materials detected in the soil cover of the sila massif upland a first attempt to estimate soil formation rates was achieved for different depths of corresponding weathering profile zones soil formation rates ranged from 0 01 0 07 mm a 1 for a and bw horizons weathering class vi to 0 04 0 36 mm a 1 for the underlying saprolite c and cr layers class v by comparing these results with the corresponding erosion rates available in the literature for the study area that range from

middle miocene ice sheet dynamics deep sea temperatures and carbon cycling a southern ocean perspective 1 relative contributions of ice volume and temperature change to the global 1 18o increase at 14 ma are required for understanding feedbacks involved in this major cenozoic climate transition a 3 ma benthic foraminifer mg ca record of southern ocean temperatures across the middle miocene climate transition reveals 2 2 c cooling 14 2 13 8 ma indicating that 70 of the increase relates to ice growth seawater 18o calculated from mg ca and 18o suggests that at 15 ma antarctica s cryosphere entered an interval of apparent eccentricity paced expansion glaciations increased in intensity revealing a central role for internal climate feedbacks comparison of ice volume and ocean temperature records with inferred pco2 levels indicates that middle miocene cryosphere expansion commenced during an interval of southern ocean warmth and low atmospheric pco2 the antarctic system appears sensitive to changes in heat moisture supply when atmospheric pco2 was low suggesting the importance of internal feedbacks in this climate transition

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

temperature control on the incorporation of magnesium strontium fluorine and cadmium into benthic foraminiferal shells from little bahama bank prospects for thermocline paleoceanography surface sediments from little bahama bank lbb intersecting the subtropical thermocline were used to assess the influence of temperature on the incorporation of mg sr f and cd into shells of benthic foraminifera samples were obtained from twelve cores along the southern slope of lbb covering a temperature range of 18 4 5 c between 301 and 1585 m we studied the composition of ten calcitic and one aragonitic species which are often used in paleochemical reconstructions mg ca ratios decrease with increasing water depth in all benthic species both with calcitic and aragonitic mineralogy showing a strong correlation with water temperature similar decrease is seen in sr ca but with no correlation with temperature none of the benthic species studied here exhibits a depth or temperature related change in f ca similar trends are observed when using an ocean wide dataset which includes shallow and deep core tops 300 5000 m we suggest that temperature is the primary control on the mg content of benthic foraminifera based on inorganic precipitation experiments and thermodynamic considerations presented here a 30 40 decrease in the mg distribution coefficient in calcite may be expected as a result of a temperature change from 25 c to 5 c which is about half the observed change in lbb a calibration curve applied to c pachyderma data from core tops along the slope of little bahama bank suggests that water temperature may be inferred from mg ca ratios with an uncertainty of about 0 8 c therefore the mg content of benthic foraminifera may provide a new independent temperature proxy for studying shallow waters paleoceanography the linear decrease in sr ca with increasing depth is not correlated with temperature the trend is constant from the ocean surface down to 5 km suggesting that pressure related effects on the calcification process are a more likely explanation than post depositional dissolution mg ca ratios in aragonitic shells of h elegans covary with temperature in accord with recent observations from corals in contrast the sr and f chemistry of h elegans is very different than that of corals and inorganically precipitated aragonites the disparities between the elemental composition of biogenic and inorganic phases and the large intergeneric and interspecific differences observed both in planktonic and benthic foraminifera implicate temperature related physiological processes in regulating the coprecipitation of elements in foraminiferal shells our work demonstrates that cd ca ratios of shallow calcitic species reflect the vertical distribution of nutrients no significant influence of temperature on the partitioning of cd into the shells was found our data extend the previous deep water calibration boyle 1992 thereby allowing for the reconstruction of the nutrient chemistry of shallow thermocline waters

combined coccolith foraminiferal and biomarker reconstruction of paleoceanographic conditions over the past 120 kyr in the northern north atlantic 59 n 23 w we present data for north atlantic core biogeochemical ocean flux study bofs 16k 59 n 23 w water depth 2370 m including coccolith flora 18o planktonic foraminiferal sea surface temperatures ssts by fa20 and simmax methods and alkenone based u37k and u37k ssts a good correlation exists between the abundances of cold water coccolith species and foraminifera and a broad correlation exists between coccolith and alkenone abundances except in the holocene reworked cretaceous coccoliths at the last glacial maximum are coincident with warm deviations of the u37k signal assessment of various calibrations of u37k and u37k with paleotemperature shows the inappropriateness of a global correlation we have produced a north atlantic u37k calibration on the basis of north atlantic data alone u37k 0 026t 0 186 which produces sst data for summer season at 0 m water depth comparable to the warm season foraminiferal ssts except during the intervals 26 36 58 65 and 100 120 ka when the alkenones indicate somewhat cooler surface waters

late cretaceous neogene trends in deep ocean temperature and continental ice volume reconciling records of benthic foraminiferal geochemistry δ18o and mg ca with sea level history 1 we reconstruct trends in ice volume and deep ocean temperature for the past 108 myr resolving variations on timescales of 2 myr and longer we use a sea level record as a proxy for ice volume a benthic foraminiferal mg cabf record as a proxy for temperature and a benthic foraminiferal 18obf record as a proxy for both this allows us to construct dual estimates of temperature and ice volume variations for the interval 10 60 ma extracting temperature from 18obf by using sea level as a proxy for ice volume to constrain the 18osw component and extracting seawater 18osw which reflects ice volume from 18obf by using mg cabf to constrain the temperature component each of these approaches requires numerous assumptions but the range of plausible solutions are concordant on timescales 2 myr and within an uncertainty of 2 c temperature and 0 4 18osw the agreement between the two approaches for the last 50 myr provides empirical justification for the use of 18obf mg cabf and sea level records as robust climate proxies our reconstructions indicate differences between deep ocean cooling and continental ice growth in the late cenozoic cooling occurred gradually in the middle late eocene and late miocene pliocene while ice growth occurred rapidly in the earliest oligocene middle miocene and plio pleistocene these differences are consistent with climate models that imply that temperatures set by the long term co2 equilibrium should change only gradually on timescales 2 myr but growth of continental ice sheets may be rapid in response to climate thresholds due to feedbacks that are not yet fully understood

modeling geographic impacts on early eocene ocean temperature 1 a general circulation model is used to evaluate the impact of geographic differences between the early eocene and the present day on ocean thermal structure the model includes reconstructed eocene bathymetry and surface thermal boundary conditions that mimic a diffusive atmosphere the model estimates that bathymetric changes alone caused surface waters to cool by 3 4 c in high latitudes and warm by 1 2 c in low latitudes over the last 55 million years which would account for as much as half 4 5 c of the increase in the meridional sea surface temperature gradient during this time other changes include a cooling 2 c of deep ocean waters a warming of low latitude intermediate waters 2 c and decreases in southern ocean zonal sea surface temperature gradients

a coupled climate ice sheet modeling approach to the early cenozoic history of the antarctic ice sheet abstract the sudden widespread glaciation of antarctica and the associated shift toward colder temperatures near the eocene oligocene boundary 34 ma represents one of the most fundamental reorganizations of the global climate system recognized in the geologic record this glacial inception and the subsequent evolution of the early east antarctic ice sheet eais are simulated using a new coupled global climate dynamical ice sheet model accounting for the paleogeography greenhouse gas concentrations changing orbital parameters and varying ocean heat transport suites of long 105 yr climate ice sheet simulations are used to investigate the effects of declining atmospheric co2 compared to those of the tectonic opening of southern ocean gateways and the timing of mountain uplift in the antarctic interior in contrast to the established paradigm for the glaciation of antarctica which centers on the opening of the southern ocean gateways and the thermal isolation of the continent our results show that declining cenozoic pco2 may have played the dominant role first small isolated ice caps formed on the highest antarctic plateaus then as a co2 threshold between 3 and 2 pre industrial level pal was crossed height mass balance feedbacks were initiated during orbital periods with cold austral summers triggering much larger highly dynamic terrestrial ice sheets as co2 continued to decline these isolated ice caps eventually merged into a permanent continental scale eais in our model neither the opening of the southern ocean gateways nor mountain uplift significantly affected the timing of the major ice sheet transition given a scenario of gradually declining co2 from 4 to 2 pal over 10 million years around the eocene oligocene boundary

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

temperature dependent variation in the distribution of tetraether membrane lipids of marine crenarchaeota implications for tex86 paleothermometry 1 recently a new geochemical temperature proxy the tex86 was introduced this proxy is based on the number of cyclopentane moieties in the glycerol dialkyl glycerol tetraethers gdgts of the membrane lipids of marine crenarchaeota which changes as a response to temperature however until now only sediment data have been used to establish this proxy and experimental work is missing we performed mesocosm studies with marine crenarchaeota incubated at temperatures ranging from 5 to 35 c and salinities of 27 and 35 to test the validity of the tex86 proxy growth of marine crenarchaeota in these mesocosms was evident from the substantial increase in the concentration of marine crenarchaeotal membrane lipids with amounts up to 3400 ng l with increasing temperature an increase in the number of cyclopentane moieties in the crenarchaeotal membrane lipids was observed different salinities did not show any effect on the gdgt distribution the tex86 showed a significant linear correlation to incubation temperature tex86 0 015 t 0 10 r2 0 79 this equation has a similar slope to the correlation obtained from core tops but differs in the intersection tex86 0 015 t 0 28 r2 0 92 this difference is mainly determined by the smaller amount of the regioisomer of crenarchaeol in the incubation series compared to core top samples these incubation experiments indicates that water temperature is indeed the major controlling factor for the membrane distribution of marine crenarchaeota and confirms that the tex86 proxy depends on a physiological response to regulate membrane fluidity

effects of long term oxic degradation on the u37k tex86 and bit organic proxies abstract one of the primary prerequisites for the application of organic proxies is that they should not be substantially affected by diagenesis however studies have shown that oxic degradation of biomarker lipids can affect their relative distribution we tested the diagenetic stability of the u 37 k and tex86 palaeothermometers upon long term oxygen exposure for this purpose we studied the distributions of alkenones and glycerol dialkyl glycerol tetraethers gdgts in different sections of turbidites at the madeira abyssal plain map that experienced different degrees of oxygen exposure sediments were deposited anoxically on the shelf and then transported by turbidity currents to the map which has oxic bottom water this resulted in partial degradation of the turbidite organic matter as a result of long term exposure to oxic bottom water concentrations of gdgts and alkenones were reduced by one to two orders of magnitude in the oxidized parts of the turbidites compared to the unoxidized parts indicating substantial degradation high resolution analysis of the pleistocene f turbidite showed that the u 37 k index of long chain alkenones increased only slightly 0 01 corresponding to u 37 k while for other pliocene miocene turbidites it either remained unchanged or decreased substantially up to 0 06 corresponding to 6 c previous observations showed that the bit index a proxy for the contribution of soil organic matter to total organic carbon was always substantially higher in the oxidized part in all the turbidites as a result of preferential degradation of marine derived gdgts this relative increase in soil derived gdgts affects tex86 as the isoprenoid gdgt distribution on the continent can be quite different from that in the marine environment our results indicate that the organic proxies are affected by long term oxic degradation to different extents this should be taken into account when applying these proxies in palaeoceanographic studies of sediments which have been exposed to prolonged oxic degradation

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

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