antarctic climate at the eocene oligocene boundary climate model sensitivity to high latitude vegetation type and comparisons with the palaeobotanical record abstract simulated climate for the antarctic continent using the genesis version 2 1 global climate model with 34 ma boundary conditions is shown to be highly sensitive to polar vegetation type six experiments were run using different levels of atmospheric co2 orbital configurations ice sheet geometries and vegetation types to assess model sensitivity to antarctica being covered with either a needle leaf evergreen forest or tundra simulations using 2 pre industrial levels of co2 combined mean annual temperature mat 19 c are about 7 c cooler than minimum estimates from the antarctic cenozoic plant record mat 12 to 15 c however simulations using 3 co2 mat 7 c are in good agreement with our empirical estimates of mean annual temperature with ice sheets and orbits set up to represent early oligocene interglacial conditions the tundra climate is significantly cooler than the evergreen forest climate with local austral summer averages up to 6 c cooler in non glaciated areas and continental averages 2 5 c cooler in the model this is mainly due to higher albedo and decreases in net radiation and sensible and latent heat flux especially during spring and summer feedbacks between coastal and continental cooling marginal sea surface temperatures and sea ice also appear to be significant a review of the late palaeocene to earliest miocene plant fossil record in the antarctic peninsula and ross sea regions shows that the vegetation was in transition 34 ma from a relatively diverse mainly evergreen forest to a tundra vegetation the modelled sensitivity of continental temperatures to a change from forest to tundra suggests vegetation climate feedbacks during the eocene oligocene transition played a significant role in the initial rapid glaciation of the continent

40ar 39ar dating of the manson impact structure a cretaceous tertiary boundary crater candidate the mineralogy of shocked mineral and lithic grains in the cretaceous tertiary k t boundary claystone worldwide is most consistent with a bolide impact on a continent both the concentrations and sizes of these shocked grains are greatest in the western interior of north america these data suggest that the manson impact structure in north central iowa is a viable candidate for the k t boundary impact event argon 40 argon 39 age spectrum dating of shocked microcline from the crystalline central uplift of the manson impact structure indicates that there was severe argon 40 loss at 65 7 1 0 million years ago an age that is indistinguishable from that of the k t boundary within the limits of analytical precision

shock induced microdeformations in quartz and other mineralogical indications of an impact event at the cretaceous tertiary boundary abstract the event terminating the cretaceous period and the mesozoic era caused massive extinctions of flora and fauna worldwide theories of the nature of this event can be classed as endogenic volcanic climatic etc or exogenic extraterrestrial causes mineralogical evidence from the boundary clays and claystones strongly favor the impact of an extraterrestrial body as the cause of this event nonmarine k t boundary claystones are comprised of two separate layers an upper layer composed of high angle ejecta material shocked quartz altered glass and spinel and a basal kaolinitic layer containing spherules clasts and altered glass together with some shocked grains recognition of this dual layered nature of the boundary clay is important for the determination of the timing and processes involved in the impact event and in the assignment and interpretation of geochemical signatures multiple sets of shock induced microdeformations planar features in quartz grains separated from k t boundary clays provide compelling evidence of an impact event this mineralogical manifestation of shock metamorphism is associated worldwide with a large positive anomaly of iridium in these boundary clays which has also been considered indicative of the impact of a large extraterrestrial body global distributions of maximum sizes of shocked quartz grains from the boundary clays and the mineralogy of the ejecta components favor an impact on or near the north american continent spinel crystals magnesioferrite occur in the boundary clays as micrometer sized octahedra or skeletal forms their composition differs from that of spinels found in terrestrial oceanic basalts magnesioferrite crystals are restricted to the high angle ejecta layer of the boundary clays and their small size and skeletal morphology suggest that they are condensation products of a vaporized bolide hollow spherules ranging up to 1 mm in size are ubiquitously associated with the boundary clays in nonmarine sections where a high angle ejecta layer and an underlying kaolinitic layer can be distinguished the spherules are found only in the kaolinitic layer the morphologies and surface features of these spherules suggest that they are original forms and not secondary growths or algal bodies these impact spherules closely resemble microtektites in size and shape all of these features of the boundary clay are uniquely associated with impact and cannot have been formed by volcanic or other terrestrial processes

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

authigenic spherules in k t boundary sediments at caravaca spain and raton basin colorado and new mexico may not be impact derived the k t boundary interval at barranco del gredero caravaca spain consists of three units a light gray cretaceous marl a 1 to 3 mm thick ferruginous clay called the k t boundary impact layer because of its content of shock metamorphosed quartz grains and an overlying greenish gray clay a conspicuous feature of the impact layer is its content of potassium feldspar particles called sanidine spherules by some authors the particles consist of a porous mesh work of prismatic potassium feldspar crystals clearly of authigenic origin their shape distribution and texture suggest that they are not altered basaltic melt droplets formed during impact of an extraterrestrial object as advocated by some proponents of the impact extinction theory of alvarez moreover authigenic spherules also occur in a thin kaolinitic claystone layer at the k t boundary in continental sedimentary rocks of the raton basin colorado and new mexico this layer is overlain by another claystone 5 8 mm thick that records the abrupt appearance of shock metamorphosed quartz grains in the local stratigraphic section four compositional types of spherules kaolinite goyazite layered goyazite kaolinite and jarosite occur in the lower of the two claystone layers because the spherules are 1 not in a bed containing shock metamorphosed minerals 2 common at some and rare at other localities and 3 hollow and form peculiarly shaped intergrown masses suggest that they are not altered microtektites or melt droplets

surface wind measurements in sequal i data from meteorological recorders at 29 37w 24 00w and 14 93w all within one degree latitude of the equator show that a relaxation event in the wind speed occurred nearly simultaneously at all three during late march 1983 during sequal i wind stress subsequently increased by approximately a factor of two the event was not recognizable in the data from a fourth recorder at 6 10n 27 88w

neogene vegetation of the meyer desert formation sirius group transantarctic mountains antarctica a tundra vegetation consisting of at least 18 plant species is described from the meyer desert formation which outcrops along the beardmore glacier in the transantarctic mountains about 500 km from the south pole the fossils include pollen seeds fruits flowers leaves wood and in situ plants of which wood and leaves of nothofagus and a pollen assemblage had been previously reported the plants include a cryptogamic flora of mosses and liverworts conifers and angiosperms in the families gramineae cyperaceae nothofagaceae ranunculaceae hippuridaceae caryophyllaceae and chenopodiaceae or myrtaceae the plants grew in a weakly developed soil formed within a complex periglacial environment that included moraines glacial outwash streams well drained gravel ridges and poorly drained depressions in which peat and marl were being deposited d 2004 elsevier b v all rights reserved

proximal cretaceous tertiary boundary impact deposits in the caribbean trace element isotopic and mineralogic studies indicate that the proposed impact at the cretaceous tertiary k t boundary occurred in an ocean basin although a minor component of continental material is required the size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact wave deposits suggest an impact between the americas coarse boundary sediments at sites 151 and 153 in the colombian basin and 5 to 450 meter thick boundary sediments in cuba may be deposits of a giant wave produced by a nearby oceanic impact on the southern peninsula of haiti a approximately 50 centimeter thick ejecta layer occurs at the k t boundary this ejecta layer is approximately 25 times as thick as that at any known k t site and suggests an impact site within approximately 1000 kilometers seismic reflection profiles suggest that a buried approximately 300 km diameter candidate structure occurs in the colombian basin

production and destruction control of biogenous sedimentation in the tropical atlantic 0 300 000 years b p late pleistocene signals of calcium carbonate organic carbon and opaline silica concentration and accumulation are documented in a series of cores from a zonal meridional depth transect in the equatorial atlantic ocean to reconstruct the regional sedimentary history spectral analysis reveals that maxima and minima in biogenous sedimentation occur with glacial interglacial cyclicity as a function of both 1 primary production at the sea surface modulated by orbitally forced variation in trade wind zonality and 2 destruction at the seafloor by variation in the chemical character of advected intermediate and deep water from high latitudes modulated by high latitude ice volume from these results a pattern emerges in which the relative proportion of signal variance from the productivity signal centered on the precessional 23 kyr band decreases while that of the destruction signal centered on the obliquity 41 kyr and eccentricity 100 kyr periods increases below 3600 m ocean depth

the evolution of the subglacial landscape of antarctica the aim is to investigate the evolution of the subglacial landscape of antarctica using an ice sheet and erosion model we identify different stages of continental glaciation and model the erosion processes associated with each stage the model links erosion to the basal thermal regime and indicates that much of the antarctic interior may have been subject to less than 200 m of erosion the depth of erosion reflects the presence or absence of warm based ice and the consistency of ice flow direction this information linked with knowledge about landscapes of glaciation in the northern hemisphere and some simple but robust assumptions about initial topography is used to generate a map of the subglacial antarctic landscape in which much of the lowland interior resembles the landscapes of areal scouring typical of the laurentian and scandinavian shields near the continental margins selective linear erosion has overdeepened pre existing river valleys by as much as 2 8 km high elevation plateaus adjacent to such drainage systems have survived largely unmodified under cold based ice high erosion rates result from steep thermal gradients in basal ice mountain regions such as the gamburtsev mountains uplands in dronning maud land and massifs in west antarctica are likely to bear features of local alpine glaciation such landscapes may have been protected under cold based ice for the last 34 myrs or possibly longer

cathodoluminescence petrography of syntectonic quartz fibres abstract the cathodoluminescence of low grade metamorphic quartz is reported in the literature to be uniformly brown this study describes an investigation of syntectonic quartz fibres from veins and pressure shadows contained in different carbonate units of the helvetic alps switzerland and of anglesey u k with the scanning electron microscope in the cathodoluminescence mode the cathodoluminescence spectra measured show systematic variations between older and younger parts of the same fibre and between fibres from different tectonic units these variations can be related first to variations in the temperature of formation of the quartz fibres and second to deformation induced differences in the microstructure of the earlier formed parts of fibres during later imposed strains

seasonal variability from a model of the tropical atlantic ocean abstract a numerical model incorporating a single baroclinic mode and realistic coastline geometry is used to analyze the linear dynamic response to estimates of the seasonal wind field over the tropical atlantic ocean the forced periodic response consists of a spatially dependent combination of a locally forced response kelvin waves rossby waves and multiple wave reflections the seasonal displacements of the model pycnocline are compared with observed dynamic height annual and semiannual fluctuations dominate the seasonal signal throughout the basin in general the distribution of amplitude and phase are similar for annual changes in dynamic height and pycnocline depth major features of the seasonal response are reproduced e g east west changes in pycnocline depth about a nodal point at the equator the seasonal pycnocline movement along the northern and southern coast of the guinea gulf and a significant changes of phase in the ocean variability north and south of the itcz the relative impo

evidence of remote forcing in the equatorial atlantic ocean abstract an analysis of sea surface temperature sst and surface winds in selected areas of the tropical atlantic indicates that the nonseasonal variability of sst in the eastern equatorial atlantic gulf of guinea is highly correlated with the nonseasonal variability of the zonal wind stress in the western equatorial atlantic a negative positive anomaly of the zonal wind stress near the north brazilian coast is followed by a positive negative sst anomaly in the gulf of guinea about one month later furthermore the correlation between the local wind stress anomaly and sst anomaly in the gulf of guinea is considerably smaller these preliminary results indicate that remote forcing in the western equatorial atlantic ocean is an important factor affecting the eastern equatorial atlantic sea surface temperature recent equatorial theories are consistent with these observations

vegetation and climate from two oligocene glacioeustatic sedimentary cycles 31 and 24 ma cored by the cape roberts project victoria land basin antarctica abstract the cape roberts project recovered over 1500 m of coastal glaciomarine sediments of oligocene and early miocene age off the ross sea margin of antarctica the strata are characterised by cyclic repetition of facies in a glaciomarine setting and are interpreted to be a record of glacial interglacial episodes involving significant changes in eustatic sea level on milankovitch frequencies we have undertaken a detailed study of pollen and spores miospores from an early oligocene 31 ma and a late oligocene 24 ma cycle although miospores are sparse in the core averaging only 1 grain per gram of sediment processed over 1200 cenozoic miospores were recovered for this study previous studies of miospores from ross sea sediments have encountered problems differentiating between reworked and in situ palynomorphs here only samples containing a low relative abundance of an eocene dinoflagellate cyst assemblage the transantarctic flora have been used to infer the contemporaneous oligocene miospore flora the flora of the early oligocene cycle is dominated by three species of nothofagidites and four types of podocarpidites the assemblage from the upper oligocene cycle is also dominated by nothofagidites and podocarpidites but with the addition of two distinctive taxa an angiosperm pollen and a bryophyte spore notwithstanding these additions there is a slight decrease in floral diversity between the two cycles while this study confirms that some floristic changes did occur between early and late oligocene time on the victoria land coast the present data suggest that the changes were not extensive it is likely that the vegetation of both cycles was a low diversity scrub of low stature consisting of mainly nothofagus podocarps and bryophytes modern analogues suggest that this vegetation was growing in a climate significantly warmer mean summer monthly temperature 4 12 c than is found on the present day victoria land msmt 5 c although colder that the temperate climate suggested by the diverse flora found in ross sea sediments of eocene age

forcing of atlantic equatorial and subpolar millennial cycles by precession abundance cycles of the marine alga florisphaera profunda centered on a period of 7600 carbon 14 years 8400 calendar years are present in high resolution records from the equatorial atlantic spanning 0 to 45 000 years ago these cycles correlate with heinrich events 1 through 5 which document rapid changes in continental ice melting around the subpolar north atlantic these variations in f profunda are a direct response to modulation in zonal wind driven divergence produced by a precessional component of orbital variation during a time of reduced eccentricity modulation

upper equatorial atlantic variability during 2002 and 2005 associated with equatorial kelvin waves on the basis of moored 35 degrees w 0 degrees and 23 degrees w 0 degrees and satellite observations we contrast the upper equatorial atlantic variability during 2002 with those during 2005 inspection of the interannual boreal summer cold tongue variability revealed a warm cold event in 2002 2005 with relaxed intensified winds in the west and the equatorial undercurrent euc embedded in a shallower deeper thermocline at 23 degrees w during both years 2002 and 2005 equatorial kelvin waves are present in moored observations as 20 degrees c isotherm depth anomalies and dynamic height anomalies basin wide sea surface height anomalies are used to derive an equatorial kelvin wave mode the time evolution of this mode represents the basis for a regression analysis to investigate related oceanic variability compared to the exceptionally strong wave activity in 2002 equatorial kelvin waves were generally weaker during 2005 the main effect of equatorial kelvin waves on zonal velocity anomalies at 23 degrees w 0 degrees is evident well below the euc core their direct influence on cold tongue sea surface temperature is small but they are found to affect the equatorial thermocline slope prior to the cold tongue onset in 2002 2005 the presence of equatorial kelvin waves is associated with a flattened steeper thermocline slope that is crucial for the shallowing deepening of the euc core at 23 degrees w and that might precondition the development of the warm cold event

provenance of mineral phases in the cretaceous tertiary boundary sediments exposed on the southern peninsula of haiti abstract acid insoluble mineral residua of tektite bearing cretaceous tertiary boundary sediments in the beloc formation of haiti contain abundant shocked quartz and lesser amounts of shocked plagioclase the shocked quartz grains typically have 2 or 3 sets of planar deformation features although grains with up to 15 sets were observed the proportion of shocked quartz in the boundary sediments increases with stratigraphic height at least 70 11 of the quartz grains are shocked in the uppermost stratigraphic interval the proportion of shocked quartz throughout the boundary sediments indicates that these grains were excavated primarily from crystalline silicate units which may have been covered with a small amount of porous quartz bearing sediments polyhedral and moderately sutured margins in shocked polycrystalline quartz grains the size of the crystal units in these grains and the presence of shocked plagioclase indicate these ejecta components were excavated from a target with continental affinities containing quartzites or metaquartzites and a sialic metamorphic and or igneous component other evidence suggests the target may also have contained a significant amount of calcium carbonate and or sulfate the large size and amount of shocked quartz grains deposited in haiti indicate the crater from which they were excavated was produced in the proto caribbean region

the last forests on antarctica reconstructing flora and temperature from the neogene sirius group transantarctic mountains abstract fossil bearing deposits in the transantarctic mountains antarctica indicate that despite the cold nature of the continent s climate a tundra ecosystem grew during periods of ice sheet retreat in the mid to late neogene 17 2 5 ma 480 km from the south pole to date palaeotemperature reconstruction has been based only on biological ranges thereby calling for a geochemical approach to understanding continental climate and environment there is contradictory evidence in the fossil record as to whether this flora was mixed angiosperm conifer vegetation or whether by this point conifers had disappeared from the continent in order to address these questions we have analysed for the first time in sediments of this age plant and bacterial biomarkers in terrestrial sediments from the transantarctic mountains to reconstruct past temperature and vegetation during a period of east antarctic ice sheet retreat from tetraether lipids mbt cbt palaeothermometer we conclude that the mean continental summer temperature was ca 5 c in agreement with previous reconstructions this was warm enough to have allowed woody vegetation to survive and reproduce even during the austral winter biomarkers from vascular plants indicate a low diversity and spatially variable flora consisting of higher plants moss and algal mats growing in microenvironments in a glacial outwash system abietane type compounds were abundant in some samples indicating that conifers most likely podocarpaceae grew on the antarctic continent well into the neogene this is supported by the palynological record but not the macrofossil record for the continent and has implications for the evolution of vegetation on antarctica

early east antarctic ice sheet growth recorded in the landscape of the gamburtsev subglacial mountains the gamburtsev subglacial mountains are regarded as a key nucleation site for the antarctic ice sheet and they retain a unique long term record of pre glacial and early glacial landscape evolution here we use a range of morphometric analyses to constrain the nature of early glaciation and subsequent ice sheet evolution in the interior of east antarctica using a new digital elevation model of the gamburtsev subglacial mountains derived from an extensive airborne radar survey we find that an inherited fluvial landscape confirms the existence of the gamburtsev subglacial mountains prior to the onset of glaciation at the eocene oligocene climate boundary ca 34 ma features characteristic of glaciation at a range of scales are evident across the mountains high elevation alpine valley heads akin to cirques identified throughout the mountains are interpreted as evidence for early phases of glaciation in east antarctica the equilibrium line altitudes associated with these features combined with information from fossil plant assemblages suggest that they formed at or prior to 34 ma it cannot be ruled out that they may have been eroded by ephemeral ice between the late cretaceous and the eocene 100 34 ma hanging valleys overdeepenings truncated spurs and steep sided linear valley networks are indicative of a more widespread alpine glaciation in this region these features represent ice growth at or before 33 7 ma and provide a minimum estimate for the scale of the east antarctic ice sheet between ca 34 and 14 ma when dynamic fluctuations in ice extent are recorded at the coast of antarctica the implications are that the early east antarctic ice sheet grew rapidly and developed a cold based core that preserved the alpine landscape the patterns of landscape evolution identified provide the earliest evidence for the development of the east antarctic ice sheet and can be used to test coupled ice climate evolution models

orbitally influenced vegetation record of the mid pleistocene climate transition offshore eastern new zealand odp leg 181 site 1123 a census of plio pleistocene 5 0 ma terrestrial palynomorph assemblages from odp site 1123 located 1100 km offshore eastern new zealand and in a water depth of 3290 m reveals marked variations in warm cyathea tall tree podocarpus prumnopitys dacrydium cupressinum and cold halocarpus phyllocladus nothofagus fusca type coprosma climate indicator species at milankovitch scale periodicities time series analysis indicates that the vegetation record is covariant with marine climate proxies carbonate content and is strongly coherent at the 40 ka and 100 ka orbital frequency a pronounced increase in amplitude and a coeval decrease in frequency of climate cycles from 40 to 100 ka occurs between 0 92 and 0 62 ma and provides a rare vegetation record of a fundamental reorganisation of earth s climate system the mid pleistocene climate transition despite the long distance from land and great water depth terrestrial palynomorphs are relatively abundant in this high resolution marine sediment record where they reflect a southern north island source the predominance of robust spores and buoyant pollen cyathea podocarpus prumnopitys indicates considerable current sorting and degradation of more delicate morphotypes during transport across the eastern north island shelf little evidence is found for sorting and transport processes being significantly modulated by climate

a quantitative analysis of calcareous nannofossils across a late oligocene paleolatitudinal transect of the north atlantic ocean abstract samples from six ocean drilling sites were analyzed quantitatively across a paleolatitude transect of the north atlantic ocean to determine the paleolatitudinal distribution of calcareous nannofossils in the late oligocene and the effects of that distribution on biostratigraphic resolution quantitative methodology utilized a detrended correspondence analysis dca nannofossil temperature index nti and shannon index h to examine the paleoenvironmental gradients which exerted the most control over the distribution of species and their abundances the dca produced two axes which explain 82 of the data matrix the dca1 explaining 57 of the variance significantly correlates with the nti suggesting that thermal controls were the most important factor in the paleoceanographic distribution of nannofossils the dca2 explained 25 of the variance and significantly correlates with the percent abundance of the taxon reticulofenestra minuta as well as the shannon index suggesting that surface water productivity was an important secondary control the characteristics of the nannofossil assemblage distributions indicate the existence of a well developed latitudinal diversity gradient in the late oligocene of the north atlantic based on the loss of biostratigraphic index taxa in higher paleolatitudes the primary limiter on biostratigraphic resolution for the late oligocene north atlantic is sea surface temperature particularly cold water regimes

annual change of sea surface slope along the equator of the atlantic ocean in 1983 and 1984 for two years beginning in october 1982 oceanographic observations were made in the equatorial atlantic to investigate the relationship between sea level wind stress sea surface slope zonal pressure gradient thermocline depth and equatorial currents here we describe the sea surface slope derived from three complementary methods hydrographic stations pressure gauges and inverted echo sounders the latter two have the advantage of yielding continuous time series but depend on the hydrographic stations for an absolute reference together the three provide a detailed description of the temporal variation of the sea surface slope which is then compared to a wind stress time series the dominant signal in both sea slope and wind stress is the annual cycle although amplitude and phase vary interannually the annual increase in sea surface slope along the equator in the western and central basins lags the onset of the south east trade wind during the boreal winter of 1983 84 a strong rise in sea level occurred against the african coast accompanied by a levelling of the sea surface to the west at the same time an almost complete relaxation of eastward wind stress on the equator was observed near the centre of the basin

tropical atlantic seasonal dynamics in the early middle eocene from stable oxygen and carbon isotope profiles of mollusk shells there are disagreements whether the tropical sea surface temperature during the warm early to early middle eocene was equal to the present temperature or significantly lower in order to determine the sea surface temperature of the eastern tropical atlantic in the early middle eocene we have established 18o and 13c profiles along the transect of growth of excellently preserved shells of turritella gastropods and a macoma bivalve from tropical west africa this method makes possible a distinction between the winter and the summer temperature the 18o and 13c data indicate sea surface temperatures of 29 31 c which declined to 23 25 c during seasonal upwelling these conditions are similar to those of today and suggest that significant seasonal dynamics prevailed in the early middle eocene tropics the new data further contradict that the tropics cooled during the generally warm early to early middle eocene as inferred in studies on foraminifera 18o

impact production of co2 by the cretaceous tertiary extinction bolide and the resultant heating of the earth evidence at the cretaceous tertiary boundary suggests that the proposed extinction bolide struck a continental or shallow marine terrane this evidence includes shocked quartz and feldspar grains found in the boundary layer inherited from a range of rock types a high 87 sr 86 sr ratio in some planktonic fossils which could reflect continental derived sr ref 5 and evidence that the platinum group element rich clay layer is underlain at some localities by a deposit of possible tsunamic origin these observations and data demonstrate that sea level at the end of the cretaceous was 150 200 m higher than at present suggesting the possibility that the extinction bolide struck a shallow marine carbonate rich sedimentary section here we show that the impact of such a bolide 5km in radius onto a carbonate rich terrane would increase the co 2 content of the atmosphere by a factor of two to ten additional dissolution of co 2 from the ocean s photic zone could release much larger quantities of co 2 the impact induced release of co 2 by itself would enhance atmospheric greenhouse heating and give rise to a worldwide increase in temperature from 2 k to 10 k for periods of 10 4 to 10 5 years

precessional forcing of nutricline dynamics in the equatorial atlantic climate control of nutricline depth in the equatorial atlantic can be monitored by variations in the abundance of the phytoplankton species florisphaera profunda a conceptual model based on in situ evidence associates high abundances of f profunda with a deep nutricline and low abundances with a shallow nutricline a 200 000 year record of f profunda relative abundances obtained from a deep sea core sited beneath the region of maximum equatorial divergence at 10 w has 52 percent of its variance centered on the 23 000 year precessional band cross spectral analysis between the signals of f profunda and sea surface temperature independently derived from zooplankton species shows their 23 000 year cycles to be coherent and nearly in phase abundance minima of f profunda coincide with times of december perihelion whereas abundance maxima coincide with june perihelion these relations indicate that nutricline dynamics in the divergence region of the equatorial atlantic are controlled by variations in the tropical easterlies forced by the precessional component of orbital insolation on time scales greater than 10 000 years

observing the seasonal variability in the tropical atlantic from altimetry the tropical atlantic circulation is dominated by a strong wind driven seasonal cycle which is here described by means of the sea level heights measured by geos 3 and seasat altimeters seasat worked for just 3 months and geos 3 yielded an inhomogeneous space time coverage during its 3 5 years of operation to remedy this coverage shortfall all geos 3 and seasat data were merged together on a monthly basis without regard to year thereby ignoring the weak interannual perturbations of the tropical atlantic in this way a complete time series was produced for 1 year along each profile altirnetric heights were referenced to a global mean sea surface and then filtered to remove high and low frequency noise the residual heights were objectively analyzed to produce monthly maps of sea level anomaly between 10 s and 20 n these maps show a large annual signal in the western side of the basin between the equator and 10 n where the north equatorial countercurrent and south equatorial current are predominant the signal has an amplitude of 8 cm from a minimum in april may to a maximum in october november in the east the signal is weaker and depicts a semiannual cycle these results have been compared to similar maps obtained from historical hydrographic data merle and arnault 1985 the two sets of maps are in good agreement especially north of the equator where the largest seasonal variability occurs the major difference comes from underestimation of the altimetric signal amplitude due to the strong filtering and uneven distribution of the data

in situ wind measurements and the ocean response in the equatorial atlantic during the programme francais ocean et climat dans l atlantique equatorial and seasonal response of the atlantic ocean experiment in situ wind measurements collected as part of the programme francais ocean et climat dans l atlantique equatorial focal seasonal response of the equatorial atlantic sequal experiment 1983 1984 in the western and eastern parts of the equatorial atlantic basin are described they were obtained from meteorological stations placed saint peter peter and saint paul rocks spp 1 n 29 w and at the top of a surface buoy moored in the gulf of guinea 0 n 4 w from the wind observations the wind stress was inferred and results are compared with climatology the wind stress time series show the abrupt increase of the winds during the spring that at spp reaches a value as high as 0 35 dyn cm2 in 2 weeks for both observed years the 11 day running mean time series shows that the onset of the zonal component of the wind stress occurs at spp on april 10 1983 and on may 17 1984 and in the gulf of guinea gg on april 5 1983 and april 10 1984 the monthly mean observations show an interannual variability both in the time of the onset and in the strength of the trade winds at spp and gg the total wind stress increases 1 month earlier than climatology in 1983 but at the same time as climatology in 1984 at spp the zonal component of the wind stress also intensifies 1 month earlier than climatology in 1983 but 1 month later in 1984 the equatorial temperature records at 28 w and 4 w show that the depth of the 20 c isotherm on a seasonal time scale decreases during the relaxation period of the trade winds boreal winter in 1983 1984 this occurred in december 1983 at 28 w and in march 1984 at 4 w after the onset of the local trade winds the thermocline continues to move upward during 1 month at 28 w and during 3 months at 4 w thereafter the thermocline deepens at both locations at the surface the temperature decreases when the trade winds intensify and remains low as long as the trade winds are blowing the seasonal variations of the temperature both at the surface and below the surface at 28 w and 4 w are interpreted in the light of the results of a nonlinear multilevel model in the cases of a sudden increase and a sudden relaxation of the trade winds

use of dinoflagellate cysts to determine changing quaternary sea surface temperature in southern australia abstract cluster analysis and principal component analysis of dinoflagellate cyst assemblage data from two cores so36 7 and v18 222 off southern australia clearly separate glacial from interglacial environments however those species causing much of the differentiation respond differently to changing sea surface temperature in the two cores this varying response emphasises the complexity of dinoflagellate interactions with the environment and underlines the need for caution in interpretation particularly with sea surface temperature

the forced annual reversal of the atlantic north equatorial countercurrent abstract we analyze the variability of the thermal structure associated with the atlantic north equatorial countercurrent necc and its relation to the seasonally varying winds the analysis performed allows us to establish the period of time and the region where the necc reverses direction west of 25 w the depth of the thermocline in the southern side of the necc 4 to 7 n annually oscillates 180 out of phase to the oscillations on the northern side 7 to 10 n east of 25 w the thermocline rises and falls nearly in phase across the countercurrent if the flow can be uniquely presumed from the thermal structure the necc disappears during the boreal spring in the western basin the reversal of phase from north to south over one part of the ocean but no the other is shown to be mirrored in the annual variation of the curl of the stress induced at the surface by the winds in order to quantify this result the different terms of the vorticity equation are calculated from the data we conclude that t

response of equatorial oceans to periodic forcing oscillating wind with a period p induce variability with the following characteristics in the upper few hundred meters of the equatorial zone 5 sup 0 n to 5 sup 0 s of the ocean 1 p 10 days these winds fluctuate too rapidly to generate strong currents and excite primarily waves 2 10 days 150 days the amplitude of variability is almost independent of frequency an equilibrium response which is in phase with the forcing and which corresponds to a succession of steady states is approached asymptotically these time scales are for a basin 5000 km wide if the width of the basis exceeds 5000 km then the 150 daytime scale increases in the deep ocean below the thermocline motion corresponds to propagating waves generated by the divergence of the nonlinear currents in the upper ocean

the response of equatorial oceans to a relaxation of the trade winds abstract the trade winds over the central pacific are observed to weaken several months after the appearance of anomalously warm surface waters in the eastern equatorial pacific ocean the following results obtained with a numerical model indicate how this relaxation of the winds affect the later stages of el nino a weakening of the westward trade winds causes a zonal redistribution of heat in the equatorial oceans and a warming of the eastern part of the basin the warming depends on the zonal extent of the region over which the winds relax and on the length of time t for which the winds relax as t increases the warming in the east increases until it asymtotes to a maximum value when t exceeds the adjustment time of the basin which is 400 days in the case of the pacific ocean maximum heating is associated with a permanent weakening of the winds unless the winds reverse direction and become eastward even weak eastward winds for a short period can cause disproportionately large temperature increa

seasonal cycle in the upper equatorial atlantic ocean the dynamics of the seasonal cycle in the upper equatorial atlantic ocean are studied using observations and a hierarchy of ocean models distinctive features of the seasonal cycle are strong annual and semiannual components eastward westward propagating sea surface height ssh and thermocline depth at the equator off the equator and westward propagating surface zonal currents at the equator modelling results show that linear theory can explain the seasonal cycle in thermocline depth and ssh while first order linear theory can also explain the structure of the seasonal cycle of surface zonal currents at the equator nonlinear terms are required they weaken the variability and improve its phase and zonal extent the important terms are meridional and vertical advection and vertical diffusion of zonal momentum the linear solution is essentially determined by the four gravest baroclinic modes and kelvin and first meridional mode rossby waves the eastward propagation in thermocline depth at the equator results from the kelvin wave contribution while the westward propagation in thermocline depth off the equator and surface zonal currents at the equator result from the first meridional mode rossby wave the contribution of kelvin and rossby waves generated by boundary reflections equals that of the directly forced waves the semiannual cycle in zonal winds although much weaker than the annual component forces a strong semiannual component in ssh and surface zonal currents because it excites the basin mode of the second baroclinc mode this explains the observed feature in the seasonal cycle from march to august

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

seasonal variations in equatorial atlantic ocean zonal volume transport at 28 w zonal volume transport is examined over the upper 150 m of the water column at 28 w using the seasonal response of the equatorial atlantic experiment moored current meter data at 0 75 s 0 0 and 0 75 n and a time domain empirical orthogonal function eof analysis to improve spatial and temporal resolution gaussian distributions are fit to the mean volume transports per unit width and the fluctuations about these means that are found to be represented by a single eof mode the mean volume transport is distributed symmetrically both about the equator and about 75 m depth with a meridional scale width of 101 km and a magnitude of 20 3 sv the standard deviation for the fluctuations is 4 7 sv and in contrast to the mean the fluctuations are confined to above 100 m depth with a larger meridional scale width the scale width for the mean is consistent with an inertial scale associated with conservation of potential vorticity while the scale width for the fluctuations is consistent with an equatorial rossby radius of deformation associated with equatorially trapped waves these findings support a hypothesis that different physical processes are controlling the volume transport as integrated from the surface across the equatorial undercurrent over different time scales on the time scale of the record length average inertial dynamics appear to be controlling while on the time scales of the seasonal fluctuations linear equatorial long wave dynamics appear to be controlling however given the limited record length there are insufficient degrees of freedom to test this hypothesis statistically

terminal cretaceous environmental events the geologic record of terminal cretaceous environmental events indicates that iridium and other associated elements were not deposited instantaneously but during a time interval spanning some 10 000 to 100 000 years the available geologic evidence favors a mantle rather than meteoritic origin for these elements these results are in accord with the scenario of a series of intense eruptive volcanic events occurring during a relatively short geologic time interval and not with the scenario of a single large asteroid impact event

the terminal triassic catastrophic extinction event in perspective a review of carboniferous through early jurassic terrestrial vertebrate extinction patterns abstract a catastrophic terminal triassic extinction event among terrestrial vertebrates is not supported by available evidence the current model for such an extinction is based on at least eight weak or untenable assumptions 1 a terminal triassic extinction inducing asteroid impact occurred 2 a terminal triassic synchronous mass extinction of terrestrial vertebrates occurred 3 a concurrent terminal triassic marine extinction occurred 4 all terrestrial vertebrate families have similar diversities and ecologies 5 changes in familial diversity can be gauged accurately from the known fossil record 6 extinction of families can be compared through time without normalizing for changes in familial diversity through time 7 extinction rates can be compared without normalizing for differing lengths of geologic stages and 8 catastrophic mass extinctions do not select for small size these assumptions have resulted in unsupportable and or erroneous conclusions carboniferous through early jurassic terrestrial vertebrate families mostly have evolution and extinction patterns unlike the vertebrate evolution and extinction patterns during the terminal cretaceous event only the serpukhovian mid carboniferous extinction event shows strong analogy to the terminal cretaceous event available data suggest no terminal triassic extinction anomaly but rather a prolonged and nearly steady decline in the global terrestrial vertebrate extinction rate throughout the triassic and earliest jurassic

dinosaurs spherules and the magic layer a new k t boundary clay site in wyoming a new cretaceous tertiary k t boundary clay site has been found along dogie creek in wyoming in the drainage of lance creek the type area of the lance formation of latest cretaceous age the boundary clay was discovered in the uppermost part of the lance formation 4 7 cm beneath the lowest lignite in the paleocene fort union formation and approximately 1 m above a fragmented dinosaur bone the boundary clay consists of a basal kaolinitic claystone layer as much as 3 cm thick containing hollow goyazite spherules overlain by a 2 3 mm smectitic layer the magic layer containing both shock metamorphosed minerals and an iridium anomaly of 21 ppb a palynological break coincides with the base of the claystone layer numerous late cretaceous palynomorph species terminate at this boundary the paleontological significance of this new boundary site lies in its close association with the well studied assemblage of dinosaurs and other vertebrates and flora within the type area of the lance formation the spherules at the dogie creek site are extremely well preserved by virtue of their replacement by the mineral goyazite this preservation should facilitate the resolution of the origin of the spherules and of their host layer

glaciation across the oligocene miocene boundary in southern mcmurdo sound antarctica new chronology from the ciros 1 drill hole few palaeogene and neogene sediment cores from the antarctic continental margin have been dated with sufficient precision to enable establishment of direct linkages between glacial events on the antarctic continent and marked events in deep sea delta 18o records as a result much of our knowledge of the gradual but stepwise shift from greenhouse climates of the cretaceous to the ice house climates of the quaternary is inferred from well dated and more continuously deposited deep sea sediments in this study we present new magnetostratigraphic results from the ciros 1 drill core from mcmurdo sound antarctica along with a reinterpretation of a published diatom biostratigraphic zonation that is constrained by correlation to a high precision age model from the nearby crp 2 2a drill core our results suggest that most of the upper 350 m of the ciros 1 drill core represents rapid sediment accumulation during a short time interval spanning the oligocene miocene boundary chronostratigraphic control is precise enough to enable correlation of this interval of glacimarine sedimentation with the mi 1 deep sea delta 18o event which confirms that the mi 1 event was related to a major expansion of antarctic ice a major unconformity at 366 m in the ciros 1 drill core which is widely observed in regional seismic reflection studies represents 9 myr of missing time this unconformity can be traced offshore into the ross sea using seismic stratigraphy and is interpreted to indicate significant east antarctic ice sheet development during the mi 1 glaciation the stratigraphic expression of this 400 kyr glacial event is evidently multiphase and complex in the victoria land basin probably because it was punctuated by higher frequency orbitally induced glacial oscillations the presence of nothofagidites pollen throughout the ciros 1 drill core and the presence of a nothofagus southern beech leaf within the early miocene portion of the core indicate that antarctic mean summer temperatures did not decrease below 5 deg c throughout the mi 1 glaciation these temperatures are significantly warmer than present day mean summer temperatures at sea level in mcmurdo sound the persistence of a nothofagus forest in coastal southern victoria land throughout this time interval suggests that the present state of deep refrigeration was not reached until some time after the mi 1 glaciation

oligocene miocene antarctic continental weathering record and paleoclimatic implications cape roberts drilling project ross sea antarctica abstract the bulk chemistry of mudrocks in ross sea drillcores on the antarctic inner shelf is re evaluated to extract records of continental paleotemperatures and ice extent the chemical index of alteration cia of the sedimentary sequence derived from the composite of the cape roberts cores changes in accordance with pco 2 pagani m zachos j c freeman k h tipple b bohaty s 2005 marked change in atmospheric carbon dioxide concentrations during the paleogene science 309 600 603 the k 2 o na 2 o al 2 o 3 molar ratio of the mudrocks is used as a mean summer temperature proxy for continental antarctica and it shows similarities with benthic mg ca temperatures for the southern ocean billups k schrag d p 2002 paleotemperatures and ice volume of the past 27 myr revisited with paired mg ca and stable isotope measurements on benthic foraminifera paleoceanography 17 doi 10 1029 2000pa000567 the ratio is calibrated using intervals with significant pollen assemblages and the temperature proxy enables extrapolation of the paleoclimatic data over a larger portion of the drilled record the cia and k na al ratios support a persistent cooling and drying of climate through the oligocene miocene transition the results reinforce the strong coupling between east antarctic continental temperatures and ice volume with deep sea temperatures and concentrations of atmospheric carbon over long timescales

cathodoluminescence as a tool to discriminate impact melt shocked and unshocked volcanics a case study of samples from the el gygytgyn impact structure el gygytgyn chukotka arctic russia is a well preserved impact structure mostly excavated in siliceous volcanic rocks for this reason the el gygytgyn structure has been investigated in recent years and drilled in 2009 in the framework of an icdp international continental scientific drilling program project the target rocks mostly consist of rhyodacitic ignimbrites and tuffs which make it difficult to distinguish impact melt clasts from fragments of unshocked target rock within the impact breccia several chemical and petrologic attempts other than dating individual clasts have been considered to distinguish impact melt from unshocked volcanic rock of the targets but none has proven reliable here we propose to use cathodoluminescence imaging and spectrometry whose intensity is inversely correlated with the degree of shock metamorphism experienced by the investigated lithology to aid in such a distinction specifically impact melt rocks display low cathodoluminescence intensity whereas unshocked volcanic rocks from the area typically show high luminescence this high luminescence decreases with the degree of shock experienced by the individual clasts in the impact breccia down to almost undetectable when the groundmass is completely molten this might apply only to el gygytgyn because the luminescence in volcanic rocks might be due to devitrification and recrystallization processes of the relatively old cretaceous target rock with respect to the young impactites 3 58 ma the alteration that affects most samples from the drill core does not have a significant effect on the cathodoluminescence response in conclusion cathodoluminescence imaging and spectra supported by raman spectroscopy potentially provide a useful tool for in situ characterization of siliceous impactites formed in volcanic target

velocity and temperature observations during the seasonal response of the equatorial atlantic experiment at 0 28 w continuous 2 7 year time series of upper ocean currents and temperature at 0 28 w collected during the seasonal response of the equatorial atlantic experiment are presented the thermocline underwent distinctive annual cycles in response to forcing by the surface wind stress and the core of the equatorial undercurrent tracked the thermocline while the vertical position of the thermocline and the undercurrent appear to be simply related the transport of the undercurrent did not show a replicating annual cycle and the speed at the undercurrent core remained relatively constant near surface flow when averaged over the 2 7 years was not statistically different from zero and a westward flowing south equatorial current was rarely established despite strong easterly wind stress in all 3 years cross equatorial flow was also zero in the mean at this location

dynamic deformation of volcanic ejecta from the toba caldera possible relevance to cretaceous tertiary boundary phenomena plagioclase and biotite phenocrysts in ignimbrites erupted from the toba caldera sumatra show microstructures and textures indicative of shock stress levels higher than 10 gpa strong dynamic deformation has resulted in intense kinking in biotite and with increasing shock intensity the development of plagioclase of planar features shock mosaicism incipient recrystallization and possible partial melting microstructures in quartz indicative of strong shock deformation are rare however and many shock lamellae if formed may have healed during post shock residence in the hot ignimbrite they might be preserved in ash falls peak shock stresses from explosive silicic volcanism and other endogenous processes may be high and if so would obviate the need for extraterrestrial impacts to produce all dynamically deformed structures possibly including shock features observed near the cretaceous tertiary boundary 38 references 3 figures

the mean and annual cycle of upper layer temperature fields in relation to sverdrup dynamics within the gyres of the atlantic ocean using 28 years of expendable bathythermograph data 1967 1994 we describe the mean and annual cycle of the upper ocean temperature fields in the atlantic from 30 s to 50 n in the context of the basin scale wind driven gyres sverdrup stream function field which provide a framework for describing the oceanographic measurements we examine the circulation field implied by the temperature distributions which are used as a proxy for the field of mass similarities between the temperature and stream function fields increase with depth in the lower to subthermocline depths of the tropical and equatorial gyres the zonal currents form a closed circulation a southeastward boundary current is suggested near and below 150 m that provides closure for the tropical gyre and the equatorial gyre axis is southward of that suggested by the stream function field higher in the water column the north equatorial countercurrent necc may be a surface manifestation of the north equatorial undercurrent neuc where the latter can be interpreted as the southern limb of the tropical gyre because there are large vertical shears in the tropics the equatorial gyre is not clearly indicated in the vertically integrated temperature field but appears below about 200 m here the south equatorial undercurrent seuc can be interpreted as the eastward flowing northern limb of the equatorial gyre and is opposite in direction to the westward flowing south equatorial current above both the neuc and seuc are analagous to currents in the pacific that are governed by non sverdrup dynamics despite the shortcomings of the data the mean annual cycle appears to be relatively stable and we have discounted the possibility that in regions where it represents a significant percentage of the total variance it is changing slowly over the 28 years of record the wind forcing fields which undergo large meridional movements 5 6 of latitude during their annual cycle with some exceptions have essentially no counterpart in gyre movements between their seasonal extremes most of the variability associated with the annual cycle is confined to the upper 300 m greatest variability where ranges exceed 6 c occurs in the northwestern atlantic in late winter and early spring during this time of year south of the gulf stream and below about 100 m water temperatures exhibit a systematic phase lag with depth the next largest area of variability where ranges can also exceed 6 c resides in the tropical western basin between the equator and 10 n just below 100 m in the eastern basin ranges decrease and shoal additionally the phase fields are consistent with the intensification and relaxation of the tropical ridge trough system where the necc disappears in march in the west but the necc neuc complex is strongest in september

the cretaceous tertiary boundary in the gosau basin austria the cretaceous tertiary boundary has been identified in the gosau beds elendgraben near salzburg austria the undisturbed 2 mm thick boundary clay in the palaeomagnetic g zone differs from the surrounding sediments in having significant colour no biogenic calcite and different contents of rare earth and siderophile elements carbon and magnetic minerals the clay also contains shocked quartz and plagioclase particles and indicates a dramatic change in sedimentation caused by a short lived event

paleotemperatures and ice volume of the past 27 myr revisited with paired mg ca and 18o 16o measurements on benthic foraminifera 1 we explore the applicability of paired mg ca and 18o 16o measurements on benthic foraminifera from southern ocean site 747 to paleoceanographic reconstructions on pre pleistocene timescales we focus on the late oligocene through pleistocene 27 0 ma history of paleotemperatures and the evolution of the 18o values of seawater 18osw at a temporal resolution of 100 200 kyr absolute paleotemperature estimates depend on assumptions of how mg ca ratios of seawater have changed over the past 27 myr but relative changes that occur on geologically brief timescales are robust results indicate that at the oligocene to miocene boundary 23 8 ma temperatures lag the increase in global ice volume deduced from benthic foraminiferal 18o values but the smaller scale miocene glaciations are accompanied by ocean cooling of 1 c during the mid miocene phase of antarctic ice sheet growth 15 13 ma water temperatures cool by 3 c unlike the benthic foraminiferal 18o values which remain relatively constant thereafter temperatures vary by 3 c and reach maxima at 12 and 8 5 ma the onset of significant northern hemisphere glaciation during the late pliocene is synchronous with an 4 c cooling at site 747 a comparison of our 18osw curve to the haq et al 1987 sea level curve yields excellent agreement between sequence boundaries and times of increasing seawater 18o 16o ratios at 12 11 ma in particular when benthic foraminiferal 18o values do not support a further increase in ice volume the 18osw curve comes to a maximum that corresponds to a major mid miocene sea level regression the agreement between the character of our mg ca based 18osw curve and sequence stratigraphy demonstrates that benthic foramaniferal mg ca ratios can be used to trace the 18osw on pre pleistocene timescales despite a number of uncertainties related to poorly constrained temperature calibrations and paleoseawater mg ca ratios the mg ca record also highlights that deep ocean temperatures can vary independently and unexpectedly from ice volume changes which can lead to misinterpretations of the 18o record

some simple analytical solutions to the problem of forced equatorial long waves this paper describes some simple time dependent analytical solutions to the problem of a sudden switch on of heating localized about the equator the equations used are the shallow water equations on the plane under the long wave approximation it is shown that with a reasonable amount of dissipation it can take several days for a steady state response to be established in the early stages the circulation differs considerably from that of the steady state the long time scale for the adjustment process has implications in numerical weather prediction since it implies that if the initial data are not in balance with the model s forcing it may take several days for a balance to be established by which time the quasi stationary tropical flow may have been irrevocably changed

mineralogic evidence for an impact event at the cretaceous tertiary boundary a thin claystone layer found in nonmarine rocks at the palynological cretaceous tertiary boundary in eastern montana contains an anomalously high value of iridium the nonclay fraction is mostly quartz with minor feldspar and some of these grains display planar features these planar features are related to specific crystallographic directions in the quartz lattice the shocked quartz grains also exhibit asterism and have lowered refractive indices all these mineralogical features are characteristic of shock metamorphism and are compelling evidence that the shocked grains are the product of a high velocity impact between a large extraterrestrial body and the earth the shocked minerals represent silicic target material injected into the stratosphere by the impact of the projectile

shocked quartz in the cretaceous tertiary boundary clays evidence for a global distribution shocked quartz grains displaying planar features were isolated from cretaceous tertiary boundary clays at five sites in europe a core from the north central pacific ocean and a site in new zealand at all of these sites the planar features in the shocked quartz can be indexed to rational crystallographic planes of the quartz lattice the grains display streaking indicative of shock in x ray diffraction photographs and also show reduced refractive indices these characteristic features of shocked quartz at several sites worldwide confirm that an impact event at the cretaceous tertiary boundary distributed ejecta products in an earth girdling dust cloud as postulated by the alvarez impact hypothesis

seasonal adjustments in the equatorial atlantic during 1983 as seen by surface moorings upper ocean seasonal variations in velocity and temperature observed with current meters on surface moorings along the equator in the atlantic during february september 1983 are shown the longitudinal variation in the duration of upwelling and downwelling responses to zonal wind stress changes are discussed these responses exhibit an integral character dependent upon longitudinal position which is consistent with forced linear long wave theory

vertical structure of the seasonal cycle in the central equatorial atlantic ocean xbt sections from 1980 to 1988 abstract a set of temperature profiles from expendable bathythermographs collected from 1980 to april 1988 along two ship routes transecting the equatorial atlantic from 11 n to 11 s is analyzed to inter the vertical structure of the annual variability of the temperature and the currents in the upper ocean during the average seasonal cycle the vertical isotherm displacements occur earlier below 300 meters than near the surface at most locations within 4 degrees of the equator at the equator the amplitude of the displacements does not decrease with depth in the upper 500 meters this still holds down to 700 meters but there are less data at these depths the lead of the deeper isotherm displacements with respect to those in the upper thermocline implies that there is a contribution to the pressure forces from these layers that is not in phase with the contribution of the upper thermocline this also suggests that the energy source of the seasonal variability is close to the surface dynamic height and

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

constraining the amplitude of late oligocene bathymetric changes in western ross sea during orbitally induced oscillations in the east antarctic ice sheet 2 implications for global sea level changes abstract calibrations of deep sea 18 o ice volume records imply glacial interglacial g i eustatic sea level fluctuations of 10 30 m during the late oligocene but it has hitherto not been possible to evaluate these inferred changes from direct evidence for coeval oscillations of sea level and changes in the volume of the antarctic ice sheets here we utilise a grainsize derived paleobathymetry curve dunbar g b naish t r powell r p barrett p j this volume constraining the amplitude of late oligocene bathymetric changes in western ross sea during orbitally induced oscillations in the east antarctic ice sheet 1 implications for cycle stratigraphic models palaeogeography palaeoclimatology palaeoecology to determine the amplitude of eustatic sea level fluctuations from three well dated late oligocene shallow glacimarine sedimentary cycles cored by the cape roberts project in western ross sea our approach estimates the eustatic sea level contribution to the paleobathymetry curve by placing constraints on total subsidence decompacted sediment accumulation and glacio isostasy these sedimentary cycles link the extent of the east antarctic ice sheet and local paleobathymetry changes directly to orbital cycles by using a new chronostratigraphy that enables the three sedimentary cycles to be correlated with individual cycles on the new astronomically tuned 18 o timescale our new eustatic estimates are consistent with the late oligocene 18 o to sea level calibrations of pekar et al pekar s f deconto r m harwood d m 2006 resolving a late oligocene conundrum deep sea warming and antarctic glaciation palaeogeography palaeoclimatology and palaeoecology 231 29 40 and show that eustatic sea level fluctuated between 10 m and 40 m and represented ice volume fluctuations involving 15 to 60 of the present day antarctic ice sheet moreover our eustatic estimates imply a 18 o calibration for the mi 1 excursion that supports a significant expansion of ice on antarctica perhaps equivalent to 120 of the present day eais assuming no northern hemisphere ice with an attendant fall in global sea level of 50 m

distribution of noble metals across the cretaceous tertiary boundary at gubbio italy iridium variation as a constraint on the duration and nature of cretaceous tertiary boundary events iridium pd pt and au were determined in sections from the bottaccione gorge and contessa valley gubbio italy by radiochemical neutron activation shales and limestones were sampled from 2 85 m above to 219 m below the cretaceous tertiary k t boundary metal enrichment was evaluated by comparing the boundary shale region with the lower part of the section background iridium is concentrated by 63 times in the boundary shales in comparison with the background whereas other metals are enriched by no more than 2 2 times the enrichment of ir is not confined to the boundary shales but extends approximately 2 m above and below this horizon within this ir rich region there are four distinct ir maxima in addition to the major ir enrichment in the k t boundary shales iridium maxima are stratigraphically coincident with maxima in abundances of shocked minerals characteristic of explosive volcanism limestones are much lower in noble metals than shales and their ir contents in the k t boundary region are largely accounted for by their minor clay mineral contents the time represented by the 4 m of ir rich section is at least 3 x 10 5 yr if published sedimentation rates are used to sustain an increased ir flux over this period and to account for the ir distribution near the k t boundary intense volcanic activity is a preferred alternative to impact of extraterrestrial material

antarctic cenozoic climate history from sedimentary records andrill and beyond mounting evidence from models and geological data implies that the antarctic ice sheet may behave in an unstable manner and retreat rapidly in response to a warming climate which is a key factor motivating efforts to improve estimates of antarctic ice volume contributions to future sea level rise here we review antarctic cooling history since peak temperatures of the middle eocene climatic optimum approx 50 ma to provide a framework for future initiatives to recover sediment cores from subglacial lakes and sedimentary basins in antarctica9s continental interior while the existing inventory of cores has yielded important insights into the biotic and climatic evolution of antarctica strata have numerous and often lengthy time breaks providing a framework of snapshots through time further cores and more work on existing cores are needed to reconcile antarctic records with the more continuous far field records documenting the evolution of global ice volume and deep sea temperature to achieve this we argue for an integrated portfolio of drilling and coring missions that encompasses existing methodologies using ship and sea ice ice shelf based drilling platforms as well as recently developed seafloor based drilling and subglacial access systems we conclude by reviewing key technological issues that will need to be overcome

laboratory simulation of explosive volcanic loading and implications for the cause of the k t boundary intense explosive volcanism was simulated by preheating samples to 600 c and subjecting them to dynamic stress pulses of 0 9 and 1 3 gpa the resultant ejecta was examined optically and by transmission electron microscopy tem deformation and failure was entirely by brittle fracture and most fractures were irregular and intergranular none of the features typical of k t boundary sediments and of ejecta from meteorite impact craters planar deformation features amorphization mosaicism were observed there were also no signs of intracrystalline plasticity we conclude that explosive volcanism is incapable of producing the microstructural features seen at the k t boundary and that they must have been caused by impact of a large meteorite

on the baroclinic response of the zonal pressure gradient in the equatorial atlantic ocean temperature time series obtained from surface moorings deployed along the equator in the atlantic ocean during the seasonal response of the equatorial atlantic experiment and the programme francais ocean et climat dans l atlantique equatorial were used to investigate the baroclinic response of the zonal pressure gradient due to the sloping isopycnals the zonal pressure gradient evolved as a complicated function of time depth and zonal position the most rapid and spatially inhomogeneous variations corresponded to periods of rapidly changing easterly wind stress following these periods the baroclinic response due to the sloping isopycnals was observed to overshoot its intended equilibrium before relaxing to it in so doing it tended to buffer pressure gradient variations at the depth of the equatorial undercurrent euc over much of the year the isopycnal slopes opposed the surface slope after the winds relaxed in winter however the isopycnal slopes reversed and acted in concert with the surface slope thereby enhancing the pressure gradient at the depth of the euc relative to that at the surface this reversal might be important in maintaining the euc during times of weak easterly wind stress the vertical structure of the zonal pressure gradient varied with the depth of the thermocline when the winds were weak and the thermocline was shallow the baroclinic response of the zonal pressure gradient due to the sloping isopycnals was primarily effected in the upper 50 m after the winds intensified and the thermocline deepened the baroclinic response extended down to at least 150 m

how likely was a green antarctic peninsula during warm pliocene interglacials a critical reassessment based on new palynofloras from james ross island the question of whether pliocene climate was warm enough to support a substantial vegetation cover on antarctica is of great significance to the ongoing and controversial debate on the stability or dynamism of antarctic ice sheets during warm periods with high atmospheric greenhouse gas concentrations here we present a systematic palynological comparison of pollen and dinoflagellate cyst assemblages from early pliocene diamictites and underlying late cretaceous sediments collected from james ross island northern antarctic peninsula the diamictites are dated using a combination of 40ar 39ar and 87sr 86sr isotope ages on interbedded lavas and pristine bivalves well preserved pectinid shells and cheilostome bryozoans suggest that the palynomorph bearing sediments were probably deposited during warmer pliocene interglacials and later amalgamated into a diamictite formed by a major ice advance during cold glacial cycle the palynological analyses presented herein do not identify any in situ pollen and spores which indicate the presence of a substantial vegetation cover our study suggests a local i e james ross island provenance for most of the diamictites whilst sediments from the western coast might have been delivered by ice sheets from the antarctic peninsula whilst the acritarch leiosphaeridia might imply the presence of sea ice and near modern climate conditions during the late neogene the presence of the dinoflagellate cyst bitectatodinium tepikiense at one location suggests that sea surface temperatures might have been substantially warmer during some interglacials the absence of in situ pollen and spores in the james ross island diamictites cannot be taken as proof of non existence of vegetation however the combined palynological and geological evidence presented in this paper makes the presence of a substantial pliocene vegetation cover on james ross island unlikely and supports previous reconstructions of a permanent ice sheet on the antarctic peninsula throughout the late neogene

basin wide zonal wind stress and ocean thermal variations in the equatorial pacific ocean wind data obtained from the model results of the european centre for medium range weather forecasts ecmwf for the equatorial pacific ocean from 1985 to 1992 were employed to study the basin wide distributions for various constituents of zonal wind stress forcing the ocean by the individual constituent of zonal wind stress the upper ocean thermal variation was investigated using a linear analytical ocean model the interannual variation of zonal wind stress is largest in amplitude in the west central part of the basin and is dominated by an eastwardly propagating wave the upper layer thickness perturbation h shows an evolving eastward propagation over the region where the interannual wind stress variation occurs while to the east and west the region changes nearly in phase the evolution of h agrees well with the evolution of upper ocean heat content anomaly estimated from the tropical atmosphere ocean tao moored array the annual cycle of zonal wind stress can be described properly by a combination of annual and semiannual variations the annual variation of zonal wind stress was found to propagate westward with relative maxima out of phase to the west and east of the west central pacific the semiannual variation is stationary and is largest in amplitude in the western basin forced by the two components of the annual cycle of zonal wind stress the evolution of h shows a westward propagation this does not correlate well with the pattern of the evolution of the annual cycle of upper ocean heat content which emanates from the east central pacific and shows both eastward and westward propagation the seemingly anomalous eastward propagation is mainly related to the abrupt change during the relaxation intensification period of the easterly wind stress the abrupt change of the annual zonal wind stress variation in both time and space is then critical for the evolution of the pattern of the annual ocean response

end cretaceous mass extinction event argument for terrestrial causation the end cretaceous mass extinctions were not a geologically instantaneous event and were selective in character these features are incompatible with the original alvarez hypothesis of their being caused by a single asteroid impact that produced a world embracing dust cloud with devastating environmental consequences by analysis of physical and chemical evidence from the stratigraphic record it is shown that a modified extraterrestrial model in which stepwise extinctions resulted from encounter with a comet shower is less plausible than one intrinsic to the earth involving significant disturbance in the mantle

seasonal variations of the subsurface thermal structure in the gulf of guinea abstract the subsurface thermal structure in the gulf of guinea is analyzed using the historical hydrographic data file of particular interest is the rapid vertical displacement of the thermal structure from the warm march may season to the cold july august season this displacement field is trapped at the equator with vertical and meridional scales appropriate to a second or third mode baroclinic kelvin wave it has a maximum amplitude between 4 w and 10 w with a node near 2 e south of 4 s no seasonal displacement of the thermocline underlies the seasonal variation in the sea surface temperature along the eastern boundary north of the equator to 3 e the displacement field vanishes thus the coastal upwelling associated with a vertical displacement tightly bound to the northern coast from 2 e to 10 w appears detached from the equatorial regime

waves along the equator in the atlantic abstract spectra of two hundred days of data from five inverted echo sounders deployed along the equator in 1983 84 and a thousand days of 30 crossings of the equator by the topex poseidon altimeter in 1993 95 are both found to have enhanced variance of sea surface displacement in two frequency bands centered nominally about 50 1 and 25 1 cycles day complex empirical orthogonal function analysis of the two bands finds much of the variance being accounted for by eastward and westward propagating waves respectively that are coherent across the basin the eastward propagating wave is identifiable as a first mode kelvin wave with a period of 54 49 days in the sounder altimeter dataset a basinwide wavelength and a speed of 2 1 1 8 m s 1 it is suggested that the westward propagating wave is a surface expression of the meridional oscillation of the equatorial undercurrent about the equator presumably induced by a tropical instability wave with a period of 24 28 days a wavelength of 600 580 km

evidence from cathodoluminescence for non volcanic origin of shocked quartz at the cretaceous tertiary boundary bohor et al 1 have described shocked quartz displaying one or more sets of planar elements indexed to rational crystallographic planes associated with anomalous siderophile abundances at the cretaceous tertiary k t stratigraphic boundary in eastern montana shocked quartz has subsequently been shown at several k t boundary sections around the world and has been attributed to the effects of impact on crustal rocks2 7 this impact may have occurred within the scenario of comet or meteor collision8 9 or alternatively shocked quartz at the k t boundary could be the product of volcanic eruption rather than bolide impact10 14 here we describe a cathodoluminescence study of shocked quartz at the k t boundary in southeastern colorado that reveals a diversity of luminescence colours not present in quartz from known volcanic ejecta but typical of quartz in crustal supracrustal lithologies cathodoluminescence colour diversity indicates that the grains were originally derived from a variety of igneous metamorphic and sedimentary rocks subsequently overprinted with planar shock features these observations lend support to the hypothesis of bolide impact at the end of the cretaceous period

resolving apparent conflicts between oceanographic and antarctic climate records and evidence for a decrease in pco2 during the oligocene through early miocene 34 16 ma abstract an apparent mismatch between published oxygen isotopic data and other paleoclimate proxies for the span from 26 16 ma is resolved by calibration against global sea level estimates obtained from backstripping continental margin stratigraphy ice volume estimates from calibrated oxygen isotope data compare favorably with stratigraphic and palynological data from antarctica and with estimates of atmospheric pco2 throughout the oligocene to early miocene 34 16 ma isotopic evidence for an east antarctic ice sheet eais as much as 30 larger than its present day volume at glacial maxima during that span is consistent with seismic reflection and stratigraphic evidence for an ice sheet covering much of the antarctic continental shelf at the same glacial maxima palynological data suggest long term cooling during the oligocene with cold near tundra environments developing along the coast at glacial minima no later than the late oligocene a possible mechanism for this long term cooling is a decrease in atmospheric pco2 from the middle eocene to oligocene reaching near pre industrial levels by the latest oligocene and remaining at those depressed levels throughout the miocene

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

on the response of the equatorial thermocline in the atlantic ocean to the seasonally varying trade winds measurements made during the seasonal response of the equatorial atlantic experiment in 1983 when the easterly trade winds near the equator ceased and then intensified as part of their annual cycle show a sequence of events leading to an adjusted thermocline both the duration and extent of the downwelling and upwelling associated with the adjustment process were zonally inhomogeneous along the equator an analytical reduced gravity model was driven by a hierarchy of easterly wind stress forcing functions representative of the atlantic to compare the integral nature of the forced long wave responses with the observations qualitative agreement was found with upwelling and downwelling sequences within the forced region increasing to the east as observed apparent model propagation speeds differed significantly from the prescribed model wave speeds within the forced region owing to the growth parameters of the winds and boundary reflections distorted the responses to the east of the forced region the resulting interference patterns tended to separate the region 0 10 w along the equator from the african coast as one of maximum upwelling

origins and variations of fluoride in greenland precipitation summit greenland firn and ice core sections have been analyzed to determine the fluoride background level of high northern latitude precipitation and to investigate its temporal variations over various time periods a continuous profile covering the last century and a discontinuous study of the last 27 000 years spanning the entire holocene time period 0 to 11 500 years b p and the late part of the last glaciation have been achieved this first detailed study of the fluoride content of polar ice help us obtain a better understanding of the atmospheric cycle of inorganic fluoride in remote atmospheres first our data suggest that blown dust is among the nonvolcanic sources that contributed to the natural fluoride background level of this high latitude precipitation primary sea salt emissions represent an insignificant contribution our study also indicates that high latitude biomass burning debris which sometimes reaches the greenland ice cap represents an additional weak source of fluoride for greenland precipitation second this work provides useful information for evaluating the impact of the volcanic activity on the fluoride budget of these high northern latitude regions indeed our data demonstrate that although the natural background fluoride content of greenland snow is very often sporadically disturbed by volcanic emissions from iceland numerous hekla eruptions and the 1783 laki eruption for instance located relatively close to the greenland ice cap large explosive eruptions tambora in 1815 for instance only weakly disturb this background level our data suggest that even in the case of significant input within the stratosphere fluoride is rapidly scavenged probably along with ash particles finally our study of recent snow layers suggests that man made sources mainly coal burning represent an important contribution which has dominated this high northern hemisphere fluoride budget for the three last decades furthermore over the last 10 years a possible influence of the stratospheric reservoir builded up from the chlorofluorocarbons degradation cannot be ruled out and in the future this growing contribution may represent a significant part of the anthropogenic fluoride input compared to the input derived from coal burning

further studies on the response of the equatorial thermocline in the atlantic ocean to the seasonally varying trade winds upper ocean temperature data obtained during the seasonal response of the equatorial atlantic experiment and the francais ocean et climat dans l atlantique equatorial program are used to describe the variations of the thermocline observed along the equator from february 1983 to september 1984 in response to rapid seasonal changes in zonal wind stress the thermocline underwent sequences of upwelling followed by downwelling or conversely depending upon whether the winds were intensifying or relaxing these sequences increased systematically in magnitude and duration to the east both the sequential behavior and its zonal inhomogeneity represent departures from the slowly varying and in phase climatological description of the annual thermocline response an analytical reduced gravity equatorial long wave model forced by zonal wind stress distributions representative of the variations observed along the equator was employed to reconcile the differences between the 1983 1984 synoptic measurements and the climatologically averaged description qualitative agreements between the model results and the data were found for many salient features of the annual cycle including the zonal pressure gradient calculated by finite difference the features in the model arise as interference patterns between directly forced and reflected kelvin and long rossby waves that are generated with each change in the wind stress the manner in which the wind stress changes from year to year is therefore crucial to the equatorial ocean s response

high resolution ice volume estimates for the early miocene evidence for a dynamic ice sheet in antarctica ice volume estimates for the early miocene 23 16 ma ats were determined by applying d 18 o to sea level calibrations to high resolution d 18 o records from odp sites 1090 and 1218 these calibrated records indicate that ice volume ranged between 50 and 125 of the present day east antarctic ice sheet eais during most of the early miocene 23 17 ma maximum icevolume occurred at each of the early miocene isotopic events i e mi events concomitant with bottom water temperatures generally between 1 and 2 8c rapid bb 1 myr and high amplitude ice volume changes also occurred intermittently during this period with some fluctuations ranging from a fully glaciated east antarctic continent to a partial collapse of the ice sheet equivalent to a 50 70 reduction in the eais these large scale ice volume changes often occurred at b100 kyr time scales suggesting an orbitally driven dynamic eais existed during the early miocene in contrast the calibrated d 18 o record from site 1090 indicates significantly less ice volume 25 70 of the present day eais was present between 17 and 16 ma these results are supported by numerical climate ice sheet modeling studies that show increased orbitally driven ice volume variability with elevated levels of atmospheric co2 the distribution of bottom water masses during the miocene was likely significantly different from today owing to variability in the production of deep water near the antarctic continent i e proto antarctic bottom water proto aabw weakening of proto aabw is suggested to have occurred during the early miocene especially during glacial minima resulting in it becoming more spatially restricted to the southern ocean and becoming entrained into a warmer deep water mass increased production of a warmer bottom water mass is also considered to have been important in the lighter isotopic values observed in the atlantic and indian oceans these changes are supported by evidence of a large dynamic eais based on strata cored on the antarctic margin and require a reevaluation of the view that antarctic ice volume was significantly reduced for most of the early miocene previous estimates have been constrained by the lack of deep water isotopic records proximal to antarctica and unduly influenced by the expansion of warmer deep water into most of the ocean basins at this time d 2005 elsevier b v all rights reserved

satellite derived surface current divergence in relation to tropical atlantic sst and wind the relationships between tropical atlantic ocean surface currents and horizontal mass divergence sea surface temperature sst and winds on monthly to annual time scales are described for the time period from 1993 through 2003 surface horizontal mass divergence upwelling is calculated using surface currents estimated from satellite sea surface height surface vector wind and sst data with a quasi linear steadystate model geostrophic and ekman dynamical contributions are considered the satellite derived surface currents match climatological drifter and ship drift currents well and divergence patterns are consistent with the annual north south movement of the intertropical convergence zone itcz and equatorial cold tongue evolution while the zonal velocity component is strongest the meridional velocity component controls divergence along the equator and to the north beneath the itcz zonal velocity divergence is weaker but nonnegligible along the equator a strong divergence upwelling season in the central eastern equatorial atlantic peaks in may while equatorial sst is cooling within the cold tongue in addition a secondary weaker and shorter equatorial divergence occurs in november also coincident with a slight sst cooling the vertical transport at 30 m depth averaged across the equatorial atlantic ocean between 2 s and 2 n for the record length is 15 6 10 6 m 3 s 1 results are consistent with what is known about equatorial upwelling and cold tongue evolution and establish a new method for observing the tropical upper ocean relative to geostrophic and ekman dynamics at spatial and temporal coverage characteristic of satellite based observations

southern provenance of upper jackfork sandstone southern ouachita mountains cathodoluminescence petrology the source urea of the upper jackfork sandstone of the southern ouachita mountains of arkansas has been located by means of cathodoluminescence cl of quartz in conjunction with standard petrography comparison of frequency distributions of quartz cl colors between the jackfork and approximately coeval sandstones of the black warrior basin detected genetically based affinities which were not apparent by inspection of gross petrology the upper jackfork was derived from the same source area as the parkwood formation of the black warrior basin of alabama the parkwood is known to have come from the south and so the jackfork did also the jackfork represents a deep water lithologic equivalent of the deltaic and nearshore marine parkwood deposited as turbidites in the deeper water of the ouachita trough

changing oligocene climate recorded by palynomorphs from two glacio eustatic sedimentary cycles cape roberts project victoria land basin antarctica abstract two marine palynomorph assemblages recovered from two glacio eustatic sedimentary cycles from the cape roberts project crp which recovered over 1500 m of oligocene and miocene strata from the western margin of the victoria land basin are investigated we present results from one cycle dated as early oligocene and the other dated as late oligocene modest numbers of marine palynomorphs were recovered with an average abundance of 56 specimens per gram the assemblages recovered from both cycles are broadly similar and dominated by acritarchs and the phycoma of prasinophyte algae these include leiosphaeridia sp 2 leiosphaeridia sp 3 and the prasinophyte alga cymatiosphaera sp 2 in detail however the lower oligocene assemblage is different from that of the upper oligocene the lower oligocene cycle includes impagidinium cf dispertium and impagidinium cf elegans cymatiosphaera sp 6 and pyxidinopsis sp are abundant the upper oligocene cycle is characterized by an absence of cymatiosphaera invaganata cymatiosphaera sp 8 and pterospermella sp a it has very low numbers of acritarch sp b impagidinium and pyxidinopsis it contains tasmanites sp and brigantedinium pynei and it has higher abundances of lejeunecysta sp 1 and sigmopollis than the lower oligocene cycle the environmental interpretations of the crp core from other workers using sedimentological and paleontological indicators are used to infer environmental conditions that are likely to have influenced the marine palynomorph assemblages paleontological and sedimentological analysis suggests that both cycles were deposited in cold conditions with sea ice and melt water influence although the upper oligocene assemblage is inferred to have existed in colder marine conditions with more prolonged sea ice cover and less associated fresh water input than the assemblage of early oligocene times the application of modern analogues for some of the marine palynomorph taxa identified suggest the presence of sea ice and occasionally lowered salinity in both cycles this is broadly consistent with the findings of the other paleoenvironmental studies on the crp cores

nutricline variation in the equatorial atlantic coincident with the younger dryas variations in nutricline depth during the last deglaciation are recorded by the phytoplankton species florisphaera profunda a stacked record of six deep sea cores shows that across the entire equatorial atlantic there was a brief shallowing of the nutricline centered on 11 ka coincident with the younger dryas this shallowing is linked with high latitude north atlantic deglacial events we invoke high albedo and cool sea surface temperatures in the northern latitudes during 11 ka which steepened an already higher than expected winter insolation and hence temperature gradient for a time of june perihelion we postulate that the resultant increased pressure gradient caused an intensification of the northern hemisphere winter tropical easterlies which in turn caused equatorial divergence to occur in boreal winter

geologic framework of nonmarine cretaceous tertiary boundary sites raton basin new mexico and colorado iridium concentrations are anomalously high at the palynological cretaceous tertiary boundary in fluvial sedimentary rocks of the lower part of the raton formation at several localities in the raton basin of new mexico and colorado the iridium anomaly is associated with a thin bed of kaolinitic claystone in a discontinuous carbonaceous shale and coal sequence