climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

south america and a few grains of sand part 1 beach sands to study correlations between petrography and provenance of modern sands and thus contribute to improved interpretation of ancient sandstones this study reports on the petrography of 218 modern south american beach sands obtained from a shoreline of 25 300 km judged by quartz feldspar rock fragment ratios there are five major associations pacific 24 16 60 argentina 28 14 58 brazil 91 4 5 caribbean east 59 8 23 and caribbean west 54 17 29 study of potash feldspar volcanic rock fragments and the sio 2 al 2 o 3 ratio supplement q f rf ratios tectonics are the dominant control on the mineralogy both the pacific and brazilian associations which form 75 of south america s coastline identify correctly tectonic setting that is active margin composition for the pacific and passive margin for the brazilian however the argentine association would yield a serious error because sand with active margin composition overprints a passive margin variation of total quartz and feld

oxygen isotope compositions of phosphate from arvicoline teeth and quaternary climatic changes gigny french jura oxygen isotope compositions of biogenic phosphates from mammals are widely used as proxies of the isotopic compositions of meteoric waters that are roughly linearly related to the air temperature at high and mid latitudes an oxygen isotope fractionation equation was determined by using present day european arvicoline rodents tooth phosphate d 18 op 20 98 f0 59 0 572 f0 065 d 18 ow this fractionation equation was applied to the late pleistocene karstic sequence of gigny french jura comparison between the oxygen isotope compositions of arvicoline tooth phosphate and greenland ice core records suggests to reconsider the previously established hypothetical chronology of the sequence according to the d 18 o value of meteoric water mean air temperature relationships the d 18 o value of arvicoline teeth records variations in mean air temperatures that range from 0j to 15jc

electrical conductivity measurements from the gisp2 and grip greenland ice cores the direct current electrical conductivity of glacial ice depends on its acidity1 3 and can also indicate changes in climate as ice formed in cold dusty periods has a high concentration of alkaline dust1 4 5 which significantly reduces the conductivity6 7 compared to warmer less dusty periods here we present electrical conductivity records for the greenland ice sheet project 2 gisp2 and greenland ice core project grip ice cores drilled 28 km apart to enable direct comparison of the results the upper parts of both records are consistent with previous evidence from other greenland cores4 8 12 for a stable greenland climate during the holocene and a series of warm events punctuating the last glacial period however there is a significant discrepancy between the two records in the bottom 10 of the cores calling into question recent reports of climate variability in the last interglacial4 8 and the penultimate glaciation8 at this stage it is too early to say what exactly is causing the discrepancy although ice flow may have introduced some discontinuities into the records further work will be necessary to establish how much climatic information it will eventually be possible to extract from the lower parts of the two cores

incorporating δ18o values of past waters in the calibration of radiocarbon dating all scientists who study the late quaternary are confronted by the problem of radiocarbon calibration since 1969 numerous high frequency time series have been developed through the use of several stable isotopes e g 1 8 o such time series are inefficient as dating methods because too many age possibilities are obtained for a given unique value however the bayesian framework permits incorporation of these time series as a prior assumption on ages in order to improve calibrated ages obtained from a more precise absolute dating approach such as that using radiocarbon the method is tested on data obtained from the gigny cave french jura highly discontinuous posterior distributions are obtained with narrow highest posterior density regions thus when the radiocarbon method alone gives large uncertainties the incorporation of 1 8 o values of meteoric waters largely diminishes these uncertainties

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

basal melt at northgrip modeled from borehole ice core and radio echo sounder observations from temperature measurements down through the 3001 m deep borehole at the north greenland icecore project northgrip drill site it is now clear that the ice at the base 3080 m below the surface is at the pressure melting point this is supported by the measurements on the ice core where the annual layer thicknesses show there is bottom melting at the site and upstream from the borehole surface velocity measurements internal radio echo layers borehole and ice core data are used to constrain a time dependent flow model simulating flow along the north northwest trending ice ridge flow line leading to the northgrip site also time dependent melt rates along the flowline are calculated with a heat flow model the results show the geothermal heat flow varies from 50 to 200 mw m 2 along the 100km section of the modeled flowline the melt rate at the northgrip site is 0 75 cm a 1 but the deep ice in the northgrip core originated 50 km upstream and has experienced melt rates as high as 1 1 cm a 1

conceptual hydrogeological model of flow and transport of dissolved organic carbon in a small jura karst system summary this paper aims at characterizing infiltration and solute transport processes in a karst system during flood events in order to build a conceptual model of hydrogeological functioning the study site is the small karst system of fertans in the french jura soil cover rock matrix and a small spring were monitored to measure hydrological and hydrochemical parameters and particularly a continuous dissolved organic carbon doc signal which is a relevant environmental tracer of fast infiltration we used two combined approaches first from hydrodynamic and hydrochemical data we identified the system structure consistent with a dual porosity scheme and characterized the main processes occurring during flood events second on the basis of this scheme we built a new conceptual hydrogeological model coupled with doc transport to numerically validate the hydrological functioning this modelling approach is based on a rainfall discharge model to simulate spring flow solute transport is modelled using mixing equations including an empirical retardation factor as well as a first order solute decay the model was calibrated and validated on a set of nineteen flood events showing its performances in simulating spring hydrographs and delayed doc signals during flood events with various rainfall intensities we showed that the recharge area of the karst system varied largely with low and high groundwater periods which was attributed to the state of hydraulic connectivity in the unsaturated zone the soil cover appeared to play an important role of mixing and transfer for the recharge water the model simulated the contributions of pre event and event waters during flood events and allowed a better quantification of the available resource it showed in particular that total discharge of some flood events during low water periods is mainly composed of pre event water via piston flow type processes finally this study shows that the mixing model can simulate solute transport correctly taking into account degradation and retardation processes it highlights the need for a quantitative approach on hydrochemical studies of karst systems in order to understand them better

quantitative analysis of detrital modes statistically rigorous confidence regions in ternary diagrams and their use in sedimentary petrology abstract detrital modes are the basic type of quantitative data used in sedimentary petrology they represent estimates of the petrographic framework composition of sand or sandstone obtained by point counting of thin sections at present geological inferences from analysis of these numerical data are semi quantitative only because many of the data processing methods employed in sedimentary petrology lack a firm theoretical basis a review of existing methods reveals a number of fundamental statistical problems associated with the use of univariate statistics and the construction of so called hexagonal fields of compositional variation it is shown that these problems can be overcome by using multivariate methods that honour the non negativity and unit sum constraints on compositional data and incorporate the covariance structure spread in compositional data can be modelled on two levels 1 by regarding the grain as unit of observation and the total point count as a sample from a multinomial distribution 2 by regarding the total count as unit of observation and a set of counts as a sample from an additive logistic normal distribution numerical methods are presented for constructing statistically rigorous confidence regions in ternary diagrams by inversion of significance tests for these two distributions statistical analyses of the framework composition and heavy mineral assemblages of modern beach and river sands illustrate their use the case histories are followed by a brief overview of popular multivariate methods for reconstructing sediment provenance

heavy minerals as a guide to turbidite provenance in the lower palaeozoic southern welsh basin a pilot study a pilot study has demonstrated that heavy mineral analysis is a useful guide to the provenance of silurian turbidites in the southern welsh basin the results confirm the sedimentological evidence for two distinct source areas of coarse clastic detritus one lying to the south and the other to the east they also provide mineralogical criteria by which the two source areas may be distinguished the southern area provided material with relatively low mineral diversity and is characteristic in having low rutile zircon ratios whereas the eastern source provided more diverse assemblages generally with high rutile zircon ratios the southern source shows variations in terms of apatite tourmaline ratio with the older aberystwyth grits group tending to contain relatively low apatite compared with the younger cwmystwyth grits group rhuddnant and pysgotwr grits formations there is evidence for polycyclic material and volcanic detritus in both southerly and easterly derived samples however easterly sourced sandstones apparently tapped a more lithologically diverse terrain

building stone evaluation a case study of the sub himalayas muzaffarabad region azad kashmir pakistan abstract building stone is one of the oldest material used in construction the present study evaluated the physical and mechanical characteristics of dolomite limestone and sandstone as building stones these rocks were selected from the foothills of himalaya as a case study compressive strength tensile strength specific gravity durability under wetting drying water absorption pulse velocity and petrography of the selected rocks were evaluated relationships were established among these properties of the rocks total reserves of these rocks in the selected area were approximated and the influence of geological structures on the rock properties were also considered kashmir boundary thrust and kawai fault present in the study area have adversely affected the physico mechanical characteristics of the rocks dolomite shows a higher water absorption and lower strength values than expected kamsar dolomite shows high degree of fracturing and weathering which lowers its polishing character and degrades its quality as building and ornamental stone however yadgar dolomite reflects fair degree of polishing and could be used as ornamental stone and as non load bearing masonry units limestone also shows lower strength values but its good degree of polishing and other characteristics are suggestive of its use in internal flooring cladding stone veneer wall stone tabletops risers and treads the most suitable rock proven as building stone is pattika sandstone due to its sound petrographic characters higher tensile and compressive strengths very high durability and lower water absorption values deolian sandstone should be avoid in load bearing masonry units because of its lower strength values pattika sandstone can be used as curbs copings sills facing stone external pavements and as ashlar and rubble stone strength properties were found to be largely dependent on each other ultrasonic pulse velocity in these rocks shows close relation to the density than the strength characteristics durability under wetting drying was found to be more relevant to the water absorption and less relevant to the strength of rocks sandstone has fairly large reserves in the study area followed by dolomite and limestone

sandstone detrital modes central utah foreland region stratigraphic record of cretaceous paleogene tectonic evolution abstract within a sedimentary basin the analysis of sandstone petrofacies defined by detrital modes of framework grains is a powerful means to detect areal or temporal changes in provenance related to evolving paleotectonics and paleogeography in the central utah foreland the regional tectonic transition from thin skinned sevier thrusting during the late cretaceous to deep seated laramide deformation during the paleogene is recorded by four contrasting petrofacies in uppermost cretaceous and paleogene sandstones of fluvial and deltaic facies coeval subaqueous environments were marine during the cretaceous and lacustrine during the paleogene the cretaceous quartzose petrofacies qm93 f1 lt6 of mainly campanian age was derived from sedime tary sources in the active sevier thrust belt and transported into a broad adjacent foreland basin by transverse paleocurrents the heterogeneous cretaceous quartzolithic petrofacies qm40 70 f5 20 lt25 40 of uppermost campanian age was derived from the sevier orogenic belt during the waning phases of sevier tectonism and was distributed by longitudinal paleocurrents within a foreland basin whose floor had begun to be deformed by incipient laramide tectonism the paleogene feldspathic petrofacies qm50 f35 lt15 in paleocene and eocene strata is composed of arkosic detritus that was derived principally from basement rocks then exposed in the extensive san luis uplift of laramide age in south central colorado the feldspathic sand was transported to the laramide uinta basin and vicinity in utah by a trunk river which flowed generally northwestward between monoclinal laramide uplifts of the colorado plateau the paleogene quartzolithic petrofacies qm75 f2 lt23 of dominantly eocene age was derived mainly from sedimentary sources in the laramide uinta uplift to the north but also in part from similar sources in the dormant sevier thrust belt to the west in the rocky mountain and intermountain regions more widespread and systematic use of petrofacies analysis in combination with standard paleocurrent and lithofacies analyses could lead to better definition of the timing of laramide uplift and improved understandi g of the evolution of complex laramide paleogeography

dissolved organic carbon of infiltration within the autogenic karst hydrosystem this work aims at using the dissolved organic carbon doc as a tracer of infiltration in karstic aquifers with only diffuse recharge regular measurements of doc have been carried out in three karstic systems located in south eastern france during an hydrogeological cycle considering that the doc is mainly located in the soil it might be used as a tracer of the infiltration the behavior of the tracer considerably varies between the high and low flow periods the low concentrations of doc occur when the flow is mainly due to a long residence time of the water in the saturated zone whereas the concentration of doc increases with the contribution of recent waters during the flood period so the doc can be used as a tracer of the infiltration a comparison between the magnesium and the doc allows to demonstrate the ability of using the doc as a tracer of the water residence time

provenance of the lower tertiary murree redbeds hazara kashmir syntaxis pakistan and initial rising of the himalayas abstract the murree supergroup of northern pakistan is represented by an over 6 km thick succession of deltaic redbeds and intercalated impure foraminiferal limestones of latest palcocene to middle eocene ilerdian to lutetian age cropping out in the northern part of the hazara syntaxis and by redbeds of younger age early middle eocene to early miocene cropping out in the southern part of the syntaxis rawalpindi area the quartzolithic composition of the murree redbeds testifies to a collision orogen provenance detritus was derived from a suture belt including thrust sheets of metasedimentary and subordinately sedimentary rocks volcanic or volcaniclastic rocks and ophiolites phyllite rock fragments are most common in the ilerdian sandstones whereas volcanic and carbonate rock fragments are more abundant in the lutetian sandstones minor quantities of chert and serpentineschist indicating contribution from uplifted subduction complex sources as well as siltstone shale and limestone grains are invariably present detrital modes of sandstones and southwestward progradation of tertiary clastic wedges both testify to provenance from the proto himalayan chain located to the north and uplifted since the very first stages of the india asia continental collision at the end of the paleocene the coeval chulung la redbeds of the tethys himalaya instead consisting of volcanic and subordinate ophiolitic detritus testify to exclusive provenance from the obducting trans himalayan are trench system this major petrographic difference may be accounted for by the different structural setting of the chulung la piggy back and murree foreland basins these two distinct collisional basins have been separated probably since the onset of collision by a fold thrust belt beginning to rise in the position occupied today by the high and lesser himalayan structural domains throughout the murree supergroup main petrographic parameters do not vary greatly and volcanic sedimentary low grade metasedimentary and ophiolitic detritus persisted until the early miocene indicating slow progressive growth of the chain only during the middle miocene when the highly metamorphosed rocks of the high himalaya were carried southward along the main central thrust mct the mountain range began to rise to dramatic heights and huge amounts of detritus started to feed the siwalik foreland basin sandstones and the remnant ocean turbidites of the indus and bengal fans

n2o and ch4 variations during the last glacial epoch insight into global processes 1 greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere its natural variations and the responses to fast climatic changes in the past we present high resolution nitrous oxide n2o and methane ch4 records measured along two ice cores from central greenland covering part of marine isotope stages 3 and 4 in the last glacial epoch the n2o data confirm the hypothesis that n2o shows variations in phase to fast climatic changes observed in the northern hemisphere the so called dansgaard oeschger d o events variations exist not only for events with a long duration 1500 years and more but also for the shorter ones the comparison with ch4 unveils interesting differences between the response of ch4 and n2o to d o events while the average amplitudes of ch4 oscillations associated with d o events are similar to those of the northern hemisphere summer insolation the magnitude of the n2o concentration change instead correlates with the duration of the d o events the records give further insight into the timing of concentration changes at the beginning of d o events they show that for long lasting events the n2o concentration starts to increase before both the sharp increase in the ch4 concentration and the temperature reconstructed for greenland

contribution of environmental isotopes to the understanding of complex hydrologic systems a case study sierra de gador se spain determining the content of 18o and deuterium in the groundwater at the southern edge of the sierra de gador between october 1991 and march 1993 has enabled identification of the flow system of the waters the recharge and mixing processes and the possible mechanisms of salinization analysis of the precipitation indicates the dominant source and direction of the air masses the local meteoric water line that is established indicates a primarily mediterranean origin for the precipitation recharging the aquifers the variation of 18o content with altitude 0 35 per mille per 100 m enables an estimation of the principal recharge area which corresponds to a zone between 1200 and 1800 m a s l 1997 john wiley sons ltd

foraminiferal end in the deep north western subtropical pacific ocean tracing changes in weathering input over the last 30 000 years abstract this study focuses on the neodymium isotopic composition end of mixed planktonic foraminifera species in sediment cores collected on the north western margin of the south china sea scs and in the western equatorial pacific the aim was to identify temporal changes in the end of the upper circumpolar deep water ucdw during its northward penetration in the western subtropical pacific and to re evaluate the significance of deep water end changes at the northern margin of the scs over the past 25 kyr the past seawater end record derived from sediments of the subtropical western pacific displays a narrow range from 2 9 0 3 to 1 6 0 4 this suggests that the end of the ucdw is greatly modified during its northward penetration through the process of boundary exchange along the western volcanic margin of the south pacific and that the unradiogenic end signature of the ucdw observed in the south pacific about 6 has not been propagated beyond the equatorial pacific at least not over the last 25 kyr seawater end values obtained from the northern scs display large variations with values that are lower 6 8 0 3 to 5 6 0 2 for the last glacial period than for the late holocene 5 7 0 3 to 4 1 0 2 such glacial end cannot be attributed to a higher proportion of southern sourced water ssw as end values of the ucdw in the equatorial western pacific are more radiogenic than those observed in the scs the evolution of the seawater end values of the northern scs during the last glacial period and the last climatic transition is coeval with variations in the contribution of sediments from the pearl river the low sea level stand of the last glacial period resulted in a more proximal position of the pearl river mouth relative to core md05 2904 which a higher input of freshwater and in particular detrital sedimentary particles originating from the pearl river that partially dissolved during sinking led to a decrease in the seawater end along the north western margin of the scs enhanced rainfalls associated with intensified monsoon and more frequent typhoon activities during the early holocene climatic optimum from 9 to 7 cal kyr bp are linked to a decrease in sea surface salinity lower 18o values of planktonic foraminifera and a decrease in end values 6 2 0 3 induced by lithogenic nd input from pronounced freshwater and sediment discharge from distal rivers

substantial contribution to sea level rise during the last interglacial from the greenland ice sheet during the last interglacial period the eemian global sea level was at least three metres and probably more than five metres higher than at present1 2 complete melting of either the west antarctic ice sheet or the greenland ice sheet would today raise sea levels by 6 7 metres but the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the west antarctic ice sheet3 with model studies attributing only 1 2 m of sea level rise to meltwater from greenland4 5 this result was considered consistent with ice core evidence4 although earlier work had suggested a much reduced greenland ice sheet during the last interglacial period6 here we reconsider the eemian evolution of the greenland ice sheet by combining numerical modelling with insights obtained from recent central greenland ice core analyses our results suggest that the greenland ice sheet was considerably smaller and steeper during the eemian and plausibly contributed 4 5 5 m to the sea level highstand during that period we conclude that the high sea level during the last interglacial period most probably included a large contribution from greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the west antarctic ice sheet

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

comparison between greenland ice margin an ice core oxygen 18 records old ice for paleoenvironmental studies retrieved by deep core drilling in the central regions of the big ice sheets can also be retrieved from the ice sheet margins the d18o content of the surface ice was studied at 15 different greenland ice margin locations at some locations two or more records were obtained along closely spaced parallel sampling profiles showing good reproducibility of the records we present ice margin d18o records reaching back into the pleistocene many of the characteristic d18o variations known from greenland deep ice cores can be recognized allowing an approximate time scale to be established along the ice margin records a flow line model is used to determine the location on the ice sheet where the margin ice was originally deposited as snow the pleistocene holocene d18o change at the deposition sites is determined by comparing the d18o values in the ice margin record to the present 18o values of the surface snow at the deposition sites on the northern slope of the greenland ice sheet the pleistocene holocene d18o change is c 10 per mil in contrast to a change of 6 7 per mil at locations near the central ice divide this is in accordance with deep ice core results we conclude that d18o records measured on ice from the greenland ice sheet margin provide useful information about past climate and dynamics of the ice sheet and thus are important and cheap supplements to deep ice core records

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

δ18o of atmospheric oxygen measured on the grip ice core document stratigraphic disturbances in the lowest 10 of the core 18 o measured on oxygen in the bubble air from ice cores is a proxy for continental ice volume and is used to synchronize cores from greenland and antarctica a record measured on ice samples from the central greenland deep ice core grip spanning the last glacial maximum and the holocene shows that 18 o of atmospheric oxygen lags 18 o of ice by about 4000 to 1000 years the smooth isotope record of atmospheric oxygen shows a steady ice sheet decay beginning around 18 000 years bp taking the time lag into account however measurements performed on ice from the grip core older than 100 kyrs do not correlate with the corresponding vostok record and show transitions too fast to be typical for ice sheet build up or decay furthermore the expected time lag between 18 o atm and 18 o of seawater or 18 o of ice is absent or has even turned into a lead climatic interpretation of the fast 18 o ice transitions is not consistent with our 18 o atm results the stratigraphy is possibly irregular and if so this stops us from constructing a steady age depth relation in the deepest part of the grip ice core

functioning of a karst aquifer from s spain under highly variable climate conditions deduced from hydrochemical records over a period of three hydrological years during which precipitation was highly variable measurements of discharge electrical conductivity temperature and chemical components of the water at the canamero spring southern spain were taken in order to characterise the hydrogeological functioning of the karst aquifer that it drains the results obtained from analysis of the frequency distribution of electrical conductivity data revealed histograms with a plurimodal morphology up to 5 modes and a range of variation that increased with greater pluviometry during the study period the discharge from this spring increased sharply a few days after major rainfall episodes and when the discharge reached a value of approximately 3 73 m3 s an overflow spring started to function during high water periods there were sudden and large falls in ec temperature and all the chemical components dissolved in the water this high variability reflects the predominance of groundwater flow through karst drains a typical feature of conduit flow systems the considerable hydrochemical heterogeneity observed is caused by the mobilisation of important volumes of recharge waters from shallow areas of the aquifer soil epikarst towards the discharge point with greater participation of the unsaturated zone during high water conditions and a more active role played by the saturated zone during low water conditions in karst systems such as the one drained by the canamero spring it is important to monitor several responses hydrodynamic hydrothermal hydrochemical etc with an appropriate sampling frequency and under different hydrometeorological conditions in order to achieve an adequate hydrological characterisation this is fundamental for planning management and protection of groundwater in karst aquifers

how long and how stable was the last interglacial abstract surface ocean indicators in the north atlantic during marine isotope stage mis 5 correlate closely with the vegetational succession in northeastern france the melisey i silty layer which marks the end of the last interglacial biozone in la grande pile pollen record appears coeval with the polar front advance c24 registered in the core v29 191 by a sharply increased presence of ice rafted detritus and the cold water foraminifer neogloboquadrina pachyderma sinistral since this event is younger than the peak of mis 5d the last interglacial as recognized in northern france correlates not only with the mis 5e but also with a substantial part of mis 5d the last interglacial in la grande pile was twice as long as the holocene and the climate in its first half was apparently not less stable than during the current interglacial if the future natural climates were to develop as analogs of the past then the onset of the next glacial environments on land would be still many millennia ahead

a tentative reconstruction of the last interglacial and glacial inception in greenland based on new gas measurements in the greenland ice core project grip ice core parameters the grip d 18 oice chronological sequence is obtained by comparing a new set of d 18 o of atmospheric o2 and ch4 measurements from the bottom section of the grip core with their counterpart in the vostok antarctic profiles this comparison clearly identifies ice from the penultimate glacial maximum mis 6 190 130 kyr b p in the grip core further it allows rough reconstruction of the last interglacial period and of the last glacial inception in greenland which appears to lay its antarctic counterpart our data suggest that while antarctica is already entering into a glaciation greenland is still experiencing a warm maximum during mis 5e index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology keywords interglacial ice cap firn

alluvial sandstone composition and paleoclimate i framework mineralogy abstract systematic variations in compositional maturity of first cycle fluvial sandstones are found in the cutler formation permian and fountain formation permian pennsylvanian in colorado and in the gondwana supergroup permian triassic of peninsular india these variations reflect changing climate during deposition climate is considered to be the critical factor affecting maturity because source rocks granite granite gneiss and tectono environmental setting alluvial systems associated with basement cored block uplifts were similar and remained relatively unchanged throughout deposition of all three of the units the roughly 3 200 m thick gondwana succession consisting of five sandstone petrofacies is characterized by the following sequence of change oldest to youngest in compositional maturity expressed in q f r percentages 54 42 4 88 10 2 62 34 4 82 16 2 99 1 0 this sequence is a function of the changing paleoclimate glacial arid temperate humid warm semiarid warm semihumid warm humid associated with the overall global limatic change and the changing latitudinal location of india as it moved from a location close to the south pole northward during the interval of time represented by gondwana deposition lithologic and fossil evidence indicates that during deposition of the fountain formation climate gradually changed from relatively wet and warm to at least semiarid and warm this climatic change is the main factor responsible for the difference in compositional maturity of the older fountain sandstone q f r 65 26 9 relative to the younger q f r 54 36 10 cutler sandstone was deposited in an arid climate and has maximum compositional immaturity q f r 49 44 7 a log log plot of the ratio of total quartz to total feldspar plus rock fragments against the ratio of total polycrystalline quartz to to al feldspar plus rock fragments is a sensitive discriminator of first cycle sandstones with differing climatic heritage bulk chemical composition data support interpretation of climate from framework mineralogy but by themselves are not sensitive enough to be unequivocal indicators the same is true for the ztr index and observations of degree and abundance of solution pits embayments on detrital quartz results of this study support the conclusion of earlier empirical and theoretical analyses which suggest that the optimum conditions for the production and preservation of a distinctive climatic signature on sand composition are met in extensional plate tectonic settings such settings are characterized by coarse grained crystalline parent rocks short transport distances in low order streams deposition in nonroutine environments and shallow burial diagenesis however even in such optimum settings only rarely will climate be a more important determinant of sandstone composition than the tectonic setting itself

a novel method to study the phase relationship between antarctic and greenland climate 1 a classical method for understanding the coupling between northern and southern hemispheres during millennial scale climate events is based on the correlation between greenland and antarctic ice core records of atmospheric composition here we present a new approach based on the use of a single antarctic ice core in which measurements of methane concentration and inert gas isotopes place constraints on the timing of a rapid climate change in the north and of its antarctic counterpart we applied it to the marine isotope stage mis 5d c transition early in the last glaciation 108 ky bp our results indicate that the antarctic temperature increase occurred 2 ky before the methane increase which is used as a time marker of the warming in the northern hemisphere this result is in agreement with the bipolar seesaw mechanism used to explain the phase relationships documented between 23 and 90 ky bp blunier and brook 2001

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

oxygen isotope analyses of co existing carbonate and phosphate in biogenic apatite a way to monitor diagenetic alteration of bone phosphate abstract the oxygen isotopic composition of phosphate 18 op and structural carbonate 18 oc of hydroxylapatite was determined in 31 bone and tooth samples of modern mammals from different countries these two variables are highly correlate r 2 0 98 and the calculated best fit of linear regression is very similar to the equation calculated from the phosphate and carbonate palaeotemperature equations 1 2 according to previous measurements 3 6 on fossils of different ages from different areas it seems quite improbable to find isotopically altered skeletal remains showing a good correlation between 18 op and 18 oc as is the case with modern samples it therefore seems possible at least in some cases to use these measurements for monitoring fossil bone and tooth diagenetic alteration when a set of points lie on the equilibrium line or close to it the 18 o values could be considered close to the original values in contrast when the points lie to the left or to the right of this line this probably means that the values are diagenetically modified due to interaction with meteoric water or 18 o enriched water respectively

chemical weathering of fluvial sediments during alluvial storage the macuapanim island point bar solimoes river brazil abstract modification of sediment composition by chemical weathering depends both on the overall intensity of weathering and on its duration at macuapanim island solimboes river amazon main channel brazil a number of alluvial deposits have been exposed to intense tropical weathering for differing lengths of time in the very fine sand fraction the detrital component shows a steady and marked increase in compositional maturity with increasing sediment age immature sands of arkosic to litharenitic composition show a progressive loss of lithic fragments feldspars and accessory minerals with a concomitant enrichment in quartz this process produces first cycle sands whose detrital component is of quartz arenite composition among the salts quartz is enriched over time relative to more nstable phases particularly plagioclase this enrichment is probably largely caused by the destruction of plagioclase through chemical weathering but silt size quartz may also be produced through the breakdown of sedimentary and metasedimentary lithic fragments in the sand fraction in the clay fraction an increase in the relative abundance of smectite accompanies the breakdown of volcanic lithic fragments in the sand fraction and probably reflects the degradation of volcanic glass the clay fractions of the oldest samples examined contain less smectite somewhat more kaolinite and markedly more vermiculite as compared to younger samples but an extensively leached cation poor clay fraction analogous to the quartz dominated silts and sands is never attained the compositional mat rity of the clay fraction is everywhere lower than that of associated silts and sands perhaps because of a continual influx into the clay fraction of immature cation rich clays derived from the physical breakdown of lithic fragments in coarser size fractions this effect is enhanced by the translocation of fines whereby younger less weathered fine material is juxtaposed with older more mature coarse material in the lower levels of the alluvial stratigraphy reworking of floodplains during channel migration results in the reincorporation of older material stored on the floodplains into the sediment load if sediments have been intensely weathered during storage on the floodplain then the result will be a net dilution and replacement of younger relatively immature sands transported by the river by older more mature material from the floodplain the relative proportion of the older sands in the bedload will increase downstream resulting in a progressive downstream increase in the compositional maturity of the bedload of the river

contribution of time tracers mg2 toc δ13ctdic no3 to understand the role of the unsaturated zone a case study karst aquifers in the doubs valley eastern france 1 time tracers no 3 a toc d 13 c tdic mg 2 have been used to define the hydrodynamic behavior of a karst system high values in no 3 a and toc reflect rapid infiltration and consequently a short residence time within the aquifer whereas enriched d 13 c tdic and high mg 2 are expected for old water 9 springs and 5 boreholes have been sampled during three field campaigns in the doubs valley karst aquifer low water flood and recession periods a clear differentiation can be highlighted between boreholes characterized by a long residence time and springs that show a rapid infiltration considering only the springs values it appears that toc and d 13 c tdic contents can easily be correlated to the sampling period we show then the contribution of the unsaturated zone to the discharge during the low water period and the existence of reserves that seem badly connected to the drainage network and that contribute poorly to the minimal flow

steady state characteristics of the greenland ice sheet under different climates the greenland ice sheet is modelled to simulate its extent and volume in warmer climates and also to find out whether the ice sheet would re form on theice free bedrock under present climatic conditions the ice sheet model is a three dimensional thermo mechanical model with a fine resolution grid thebedrock surface beneath the ice sheet was mapped using radio echo sounding measurements by the electromagnetic institute copenhagen the modelexperiments show that increased temperature will result in ice margin retreat but the ice sheet is relatively stable it takes a rather high temperature rise of atleast 6ic for the ice sheet to disappear completely which indicates that the ice sheet probably survived the last interglacial also it appears that the greenlandice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re form on the bare bedrock under the present or evenslightly warmer climatic conditions

homogeneous climate variability across east antarctica over the past three glacial cycles recent ice core studies have raised the disturbing possibility that glacial interglacial climate changes may be non uniform across antarctica1 2 these findings have been confined to records from the ross sea sector of the continent but significant deviations in other areas would call into question the widely assumed validity of the climate record obtained from vostok east antarctica on large spatial scales3 here we present an isotopic profile from a core drilled at dome fuji4 5 situated 1 500 km from vostok in a different sector of east antarctica the two records show remarkable similarities over the past three glacial cycles the extent of the dome fuji record in both large amplitude changes such as terminations interglacials and interstadials and more subtle glacial events even when the origin of precipitation is accounted for our results indicate that antarctic climate is essentially homogeneous at the scale of the east antarctic plateau possibly as a consequence of the symmetry of the plateau and the adjacent ocean

vegetation and environmental responses to climate forcing during the last glacial maximum and deglaciation in the east carpathians attenuated response to maximum cooling and increased biomass burning the carpathian mountains were one of the main mountain reserves of the boreal and cool temperate flora during the last glacial maximum lgm in east central europe previous studies demonstrated lateglacial vegetation dynamics in this area however our knowledge on the lgm vegetation compo sition is very limited due to the scarcity of suitable sedimentary archives here we present a new record of vegetation fire and lacustrine sedimentation from the youngest volcanic crater of the carpathians lake st anne lacul sf ana szent anna tto examine environmental change in this region during the lgm and the subsequent deglaciation our record indicates the persistence of boreal forest steppe vegetation with pinus betula salix populus and picea in the foreland and low mountain zone of the east carpathians and juniperus shrubland at higher elevation we demonstrate attenuated response of the regional vegetation to maximum global cooling between 22 870 and 19 150 cal yr bp we find increased regional biomass burning that is antagonistic with the global trend increased regional fire activity suggests extreme continentality likely with relatively warm and dry summers we also demonstrate xerophytic steppe expansion directly after the lgm from 19 150 cal yr bp and regional increase in boreal woodland cover with pinus and betula from 16 300 cal yr bp plant macrofossils indicate local 950 m a s l establishment of betula nana and betula pubescens at 15 150 cal yr bp pinus sylvestris at 14 700 cal yr bp and larix decidua at 12 870 cal yr bp pollen data furthermore support population genetic inferences regarding the regional presence of some temperate deciduous trees during the lgm fagus sylvatica corylus avellana fraxinus excelsior our sedimentological data also demonstrate intensified aeolian dust accumulation between 26 000 and 20 000 cal yr bp

petrography and provenance of the early miocene murree formation himalayan foreland basin muzaffarabad pakistan murree formation lies in the core of hazara kashmir syntaxis sub himalayas pakistan in the muzaffarabad area the murree formation extends from ghori to nauseri the early miocene murree formation is underlain unconformably by the ypresian to early lutetian kuldana formation and is in a fault contact with the permian panjal formation the murree formation contains litharenite and feldspathic litharenite all of the plots in the qtfl diagram fall in recycled orogen provenance field whereas ternary diagram qmflt also suggests transitional recycled to quartzose recycled orogenic provenance for the sandstone of murree formation orogenic recycling occurs in the lesser and higher himalayas where stratified rocks are deformed uplifted and eroded the detritus was then deposited in the himalayan foreland basin by river meandering system the detritus of rock fragments strongly suggests mixed sources of the murree formation sandstones the modal analysis data were plotted in a diamond diagram for the recognition of the sediment source and tectonic setting of the provenance the frequency of the non undulatory monocrystalline quartz qnu is larger in the sandstone as compared to the frequency of the undulatory monocrystalline quartz qu and polycrystalline quartz qp the greater abundance of qnu suggests plutonic provenance for these sandstones the plot of q f l against qp f l reveals that during the deposition of murree formation the climatic conditions were semi arid to semi humid the xrd analyses of shale samples indicate quartz carbonate and clays vary from 66 89 1 25 and 1 21 respectively

provenance of eocene foreland basin sediments nepal constraints to the timing and diachroneity of early himalayan orogenesis in contrast to eocene himalayan foreland basin sedimentary deposits in india and pakistan coeval sedimentary rocks of the bhainskati formation in nepal contain scant petrographic evidence of orogenic input such data have been used as evidence to promote models of diachroneity of india asia collision in this paper we document orogenic input into the eocene foreland basin rocks of nepal from fission track analyses of detrital zircons our data provide evidence that significantly reduces the possible duration of any diachroneity of collision and brings the interpretation of the sedimentary record into better agreement with ages of early thrusting and metamorphism in the orogen we also use our detrital fission track data to bolster previous age determinations of the overlying dumri formation confirming the basin wide occurrence of a major unconformity comparison of our data set with that from coeval along strike rocks in india suggests that there is no evidence of diachroneity in early stages of the orogen s exhumation

high geothermal heat flow basal melt and the origin of rapid ice flow in central greenland age depth relations from internal layering reveal a large region of rapid basal melting in greenland melt is localized at the onset of rapid ice flow in the large ice stream that drains north off the summit dome and other areas in the northeast quadrant of the ice sheet locally high melt rates indicate geothermal fluxes 15 to 30 times continental background the southern limit of melt coincides with magnetic anomalies and topography that suggest a volcanic origin

cooling history of the nw himalaya pakistan fission track and 40ar 39ar cooling ages indicate that the late tertiary cooling history of the himalayan ranges of northern pakistan is largely a function of uplift and erosion interpretation of cooling ages which range from under 0 5 ma to over 80 ma suggests that during the late tertiary long term uplift rates at least doubled from under 0 2 mm yr to in some cases well over 0 5 mm yr uplift rates show strong and systematic regional variations as well which reflect the greater uplift of eastern and northern regions the association of very rapid uplift and erosion with the nanga parbat haramosh massif can be explained by a locally vigorous collision of india with eurasia near a promontory of indian crust the resultant rapid uplift of the nanga parbat haramosh massif reactivated the main mantle thrust melange zone with a reversed sense of motion discontinuities in the coolingage distribution along the main mantle thrust in the southern swat hazara region may be the result of the thermal effects of overthrusting

ice stream related patterns of ice flow in the interior of northeast greenland ice flow in the interior of the ne quadrant of the greenland ice sheet is focused on the large ice stream draining the north side of the summit dome the rapid ice flow in the stream is apparent in the surface features in the stream and at the margins in the broad scale topography that drives ice flow and in satellite derived ice motion information the patterns of ice flow in the upper half of the stream are remarkable for their level of organization simple geometry and effects on local surface topography the stream begins less than 100 km from the ice divide as a current 15 km wide and then broadens symmetrically downstream by the addition of ice from the sides to a width of more than 60 km elevation data and visible band imagery show that the stream has marginal troughs tens of meters deep in its upper reach which are coincident with regions of high shear strain rate the topography of the margins and undulating surface of the stream is generated by the ice flow the surface undulations in the stream are fixed in location and shape over the 5 year period from 1994 to 1999 the enhanced flow presents a challenge for researchers trying to understand the history of ice discharge from a significant area in the interior of the ice sheet

millennial variability in an idealized ocean model predicting the amoc regime shifts abstracta salient feature of paleorecords of the last glacial interval in the north atlantic is pronounced millennial variability commonly known as dansgaard oeschger events it is believed that these events are related to variations in the atlantic meridional overturning circulation and heat transport here the authors formulate a new low order model based on the howard malkus loop representation of ocean circulation capable of reproducing millennial variability and its chaotic dynamics realistically it is shown that even in this chaotic model changes in the state of the meridional overturning circulation are predictable accordingly the authors define two predictive indices which give accurate predictions for the time the circulation should remain in the on phase and then stay in the subsequent off phase these indices depend mainly on ocean stratification and describe the linear growth of small perturbations in the system thus monitoring particular indices of the ocean state could help predict

sandstone petrology and provenance of the siwalik group northwestern pakistan and western southeastern nepal abstract the siwalik group consists of a neogene sedimentary succession 5 8 km thick deposited as the himalayan foreland basin developed following collision between the indian and eurasian continents it consists of fluvial deposits composed of shale siltstone and sandstone in the lower part and thick sandstone and conglomerate in the upper part this paper presents new petrologic data on the sandstone composition of two coeval petrofacies of siwalik group in two areas the potwar plateau of northwestern pakistan and the surai khola and bakiya khola localities of western and southeastern nepal in both regions detrital modes reflect a collisional orogen provenance petrologic parameters indicate derivation from mid crustal rocks and overlying sedimentary strata ascribed to different tectonostratigraphic units of the high himalaya and tibetan zone the siwalik sandstones of the potwar plateau nw pakistan are composed of low to medium grade metamorphic and sedimentary detritus and subordinately of ophiolitic and volcanic detritus abundant metamorphic detritus consists of phyllite fine grained schist lithics and coarse grained gneiss derived from the high and or lesser himalaya sedimentary detritus is represented by abundant limestone radiolarian chert siltstone shale very fine grained quartzarenite and other sandstone grains the siliciclastic grains probably were eroded from older terrigenous sequences belonging to the tethys himalayan and lesser himalayan zones uplifted during the india eurasia collision ophiolitic volcanic lithic grains and radiolarian chert reflect a provenance from the indus suture and tran himalayan belt the sandstones of western and southeastern nepal surai khola and bakiya khola sections have higher quartz and lower feldspar contents than those of northwestern pakistan and contain sedimentaclastic western nepal and metamorphiclastic sandstones southeastern nepal comparison of the data presented here with previous work on pre and post siwalik sandstones of the himalaya range and of the remnant ocean basins along both sides of the indian peninsula also derived from the himalayan suture belt suggests abundant quartzolithic detritus from the eocene to the present varying proportions of lithic populations in time are related to rapid uplift of the himalayas and intense unroofing of sedimentary metasedimentary and deeper terranes

the δ18o record along the greenland ice core project deep ice core and the problem of possible eemian climatic instability over 70 000 samples from the 3029 m long greenland ice core project grip ice core drilled on the top of the greenland ice sheet summit have been analyzed for 8o a highly detailed and continuous 8o profile has thus been obtained and is discussed in terms of past temperatures in greenland we also discuss a three core stacked annual 8o profile for the past 917 years the short term 50 years variability of the annual 8o signal is found to be 1 in the holocene and estimates for the coldest parts of the last glacial are 3 or higher these data also provide insights into possible disturbances of the stratigraphic layering in the core which seems to be sound down to the onset of the eemian spectral analysis of highly detailed sequences of the profile helps determine the smoothing of the 8o signal which for the holocene ice is found to be considerably stronger than expected we suggest this is due to a process involving diffusion of water molecules along crystal boundaries in the recrystallizing ice matrix deconvolution techniques were employed for restoring with great confidence the highly attenuated annual 8o signal in the holocene we confirm earlier findings of dramatic temperature changes in greenland during the last glacial cycle abrupt and strong climatic shifts are also found within the eem sangamon interglaciation which is normally recorded as a period of warm and stable climate in lower latitudes the stratigraphic continuity of the eemian layers is consequently discussed in section 3 of this paper in terms of all pertinent data which we are not able to reconcile

the influence of climate and topography on rock fragment abundance in modern fluival sands of the southern blue ridge mountains north carolina chemical weathering influences the detrital composition of sand size sediment derived from source areas subject to different amounts of precipitation in the coweeta basin north carolina of the grain types studied rock fragments are most sensitive to chemical degradation therefore their abundance is the best indicator of cumulative weathering effects destruction of sand size rock fragments by chemical weathering is a function of both the intensity and duration of chemical weathering experienced by grains in regoliths of the source area in the coweeta basin the intensity of chemical weathering is directly related to the climate via effective precipitation in individual subbasins whereas the duration of chemical weathering is inversely related to the relief ratio of the watershed therefore soils in watersheds with low relief ratios and high discharge per unit area experience the most extensive chemical weathering and sediments derived from these watersheds contain the lowest percentage of rock fragments the effects of climate alone cannot explain the systematic variation of rock fragment abundance in sediments from the coweeta basin the compositional imprint left on these sediments by chemical weathering is a function of both climate and topographic slope in the sediment source area

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

age scale of the air in the summit ice implication for glacial interglacial temperature change the air occluded in ice sheets and glaciers has in general a younger age defined as the time after its isolation from the atmosphere than the surrounding ice matrix because snow is first transformed into open porous firn in which the air can exchange with the atmosphere only at a certain depth firn ice transition the pores are pinched off and the air is definitely isolated from the atmosphere the firn ice transition depth is at around 70 m under present climatic conditions at summit central greenland the air at this depth is roughly 10 years old due to diffusive mixing whereas the ice is about 220 years old this results in an age difference between the air and the ice of 210 years this difference depends on temperature and accumulation rate and did thus not remain constant during the past we used a dynamic firn densification model to calculate the firn ice transition depth and the age of the ice at this depth and an air diffusion model to determine the age of the air at the transition past temperatures and accumulation rates have been deduced from the 18o record using time independent functions we present the results of model calculations of two paleotemperature scenarios yielding a record of the age difference between the air and the ice for the greenland ice core project grip and the greenland ice sheet project two gisp2 ice cores for the last 100 000 years during the holocene the age difference stayed rather stable around 200 years while it reached values up to 1400 years during the last glaciation for the colder scenario the model results are compared with age differences obtained independently by matching corresponding climate events in the methane and 18o records assuming a very small phase lag between variations in the greenland surface temperature and the atmospheric methane the past firn ice transition depths are compared with diffusive column heights obtained from 15n of n2 measurements the results of this study corroborate the large temperature change of 20 to 25 k from the coldest glacial to holocene climate found by evaluating borehole temperature profiles

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

sandstone detrital modes in the makran accretionary wedge southwest pakistan implications for tectonic setting and long distance turbidite transportation detrital modes of early miocene to early pliocene sandstones from the makran accretionary wedge in southwest pakistan show a mainly quartzolithic composition with an evolution from the transitional recycled to quartzose recycled the lithic types however indicate two distinct petrofacies accreted abyssal plain turbidites have qp11lvm27lsm62 and lm39lv27ls34 showing a predominant supply from sedimentary and metasedimentary source terranes whereas slope and shelf facies sediments deposited on the accretionary wedge have qp7lvm47lsm47 and lm22lv48ls30 due to an increase of volcanic detritus the detrital modes of the abyssal plain sediments suggest a recycled orogenic source probably the himalayan collision zone the facies and longitudinal dispersal pattern suggest deposition in an oligo miocene analogue of the present indus fan the sediment must have been transported across strike parallel to the transform structure linking the makran wedge to the himalayas chaman ornach nal fault system and fed into the fan at the western end of the subduction zone the detrital modes also show an increase in volcanic detritus with time lv l 0 27 for the early miocene abyssal plain sediments to 0 47 for the slope sequences this may have been derived from late mesozoic volcanic terrains in northern baluchistan or the ladakh himalayas or more probably from the early to middle miocene andesitic volcanic centre in the northern makran

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

estimation of temperature change and of gas age ice age difference 108 kyr b p at vostok antarctica air trapped in ice core bubbles provides our primary source of information about past atmospheres air isotopic composition 15n 14n and 40ar 36ar permits an estimate of the temperature shifts associated with abrupt climate changes because of isotope fractionation occurring in response to temperature gradients in the snow layer on top of polar ice sheets a rapid surface temperature change modifies temporarily the firn temperature gradient which causes a detectable anomaly in the isotopic composition of nitrogen and argon the location of this anomaly in depth characterizes the gas age ice age difference age during an abrupt event by correlation with the d or 18o anomaly in the ice we focus this study on the marine isotope stage 5d 5c transition 108 kyr b p a climate warming which was one of the most abrupt events in the vostok antarctica ice isotopic record petit et al 1999 a steplike decrease in 15n and 40ar 4 from 0 49 to 0 47 possibly a gravitational signal due to a change in firn thickness is preceded by a small but detectable 15n peak possibly a thermal diffusion signal we obtain an estimate of 5350 300 yr for age close to the model estimate of 5000 years obtained using the vostok glaciological timescale our results also suggest that the use of the present day spatial isotope temperature relationship slightly underestimates but by no more than 20 15 the vostok temperature change from present day at that time which is in contrast to the temperature estimate based on borehole temperature measurements in vostok which suggests that antarctic temperature changes are underestimated by up to 50 salamatin et al 1998

sea level changes at the lgm from ice dynamic reconstructions of the greenland and antarctic ice sheets during the glacial cycles abstract new experiments were performed with three dimensional thermomechanical models of the greenland and antarctic ice sheets to simulate their behaviour during the glacial cycles to reconstruct their thickness and extent at the last glacial maximum lgm and to estimate their glacio eustatic contribution to the global sea level stand the calculations used improved ice dynamic and isostatic treatments updated datasets on higher grid resolutions and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations results are discussed from a reference run with standard parameters that is compared with available glacial geological observations and from a series of sensitivity experiments focusing on isostatic adjustment thermomechanical coupling climatic forcing mass balance changes and basal melting rates and viscosity changes of antarctic ice shelves for the antarctic ice sheet we find that volume changes are closely linked with grounding line changes of the west antarctic ice sheet at the lgm the grounding line extended close to the continental shelf break almost everywhere ice over central east antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations for the greenland ice sheet melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the eemian at the lgm the greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas for a plausible range of parameters the experiments indicate that at the time of maximum sea level depression 21 kyr bp the antarctic ice sheet contributed 14 18 m to the sea level lowering and the greenland ice sheet 2 3 m significantly less than the older climap reconstructions whereas both ice sheets were at 21 kyr bp close to their maximum extent the experiments also indicate that their maximum volumes were reached only by 16 5 kyr bp greenland and 10 kyr bp antarctica equal to an additional sea level lowering of respectively 0 4 and 3 7 m holocene retreat was essentially complete by 5 kyr bp in greenland but is found to still continue today in west antarctica before reversing to growth during the next millenium the models were found to reproduce gross features of the ice sheet s history since the lgm in reasonably good agreement with available glacial geological data although observational control on ice thickness changes remains very limited

a comparison of the volcanic records over the past 4000 years from the greenland ice core project and dye 3 greenland ice cores since 1980 the electrical conductivity method ecm has been used to infer volcanic acid signals in greenland ice cores the method reveals the great majority of major volcanic eruptions including several known from historic records subsequent ion chromatographic analyses of the acid volcanic layers show the chemical composition i e the concentration of the volcanic acids h2so4 hci and hf plus e g the nonvolcanically derived hno3 while ecm data are available from a large number of shallow depth greenland ice cores covering the past 500 1500 years only the greenland ice core project grip greenland ice sheet project 2 gisp2 and dye 3 deep ice cores exist for a detailed comparative study of volcanic signals in greenland ice cores representing several thousand years comparison of the volcanic signals registered in the grip and gisp2 cores will be presented elsewhere the latter cores were augered 30 km apart and essentially represent the same atmospheric conditions such as temperature snow accumulation and chemical composition of the air here we present a comparison between the major volcanic signals over the past 4000 years in the grip core from central greenland and the dye 3 core from se greenland in order to investigate the depositional differences many of the major signals are detected in both cores but some of the differences in the records can be used to infer the latitudinal band of some eruption sites furthermore the influence of the amount of annual precipitation and glaciological postdepositional processes on the volcanic signals is discussed

ch4 and δ18o of o2 records from antarctic and greenland ice a clue for stratigraphic disturbance in the bottom part of the greenland ice core project and the greenland ice sheet project 2 ice cores the suggestion of climatic instability during the last interglacial period eem based on the bottom 10 of the greenland ice core project grip isotopic profile has been questioned because the bottom record from the neighboring greenland ice sheet project 2 gisp2 core 28 km away is strikingly different over the same interval and because records of the 18o of atmospheric o2 from both cores showed unexpected rapid fluctuations here we present detailed methane records from the vostok antarctica grip and gisp2 cores over the relevant intervals the grip and gisp2 data show rapid and large changes in methane concentration which are correlative with variations of the 18o of the ice while the vostok record shows no such variations this discrepancy reinforces the suggestion that the bottom sections of the greenland records are disturbed by combining the methane data with measurements of 18o of o2 in the same samples we attempt to constrain the nature of the stratigraphic disturbance and the age of the analyzed ice samples our results suggest that ice layers from part of the last interglacial period exist in the lower section of both ice cores and that some of the apparent climate instabilities in the grip core would be the result of a mixture of ice from the last interglacial with ice from the beginning of the last glaciation or from the penultimate glaciation

palaeomagnetic dating of the earliest continental himalayan foredeep sediments implications for himalayan evolution abstract between the time of the india eurasia collision 50 45 ma 1 and the climax of crustal shortening and thrust stacking in the himalaya when the main central thrust mct was active 21 ma 1 2 there is a ca 30 my gap about which little is known this paper aims to shed light on this period by dating the initiation of major erosion from the rising himalaya and the probable start of uplift a significant event in the orogen s history this was achieved by accurately dating for the first time the dagshai formation sediments of northern india which are interpreted as early himalayan foreland basin deposits that record initial large scale erosion of the orogen 3 oriented hand samples were collected from six sites and analysed using palaeomagnetic techniques both polarities are represented and the remanence passes a fold test fitting the measured palaeolatitude to that expected for the indian plate dates the dagshai formation at 35 5 ma 6 7 ma and this is taken as the time when the embryonic himalaya began to be strongly eroded and regionally uplifted

paleogeographic and paleotectonic evolution of the himalayan range as reflected by detrital modes of tertiary sandstones and modern sands indus transect india and pakistan detrital modes of sandstones derived from the himalayan suture belt record the history of the mountain range since initial collision between india and asia which began in latest paleocene time tertiary clastic wedges deposited in fore arc foreland and remnant ocean basins and exposed along the indus transect from northernmost india to the arabian sea represent the best opportunity to study sedimentary responses to successive tectonic events during continental collision quartzose continental block and feldspatholithic magmatic arc sandstones were deposited respectively on the passive indian tethys himalayan succession and active asian indus group continental margins during late cretaceous paleocene time closure of the neotethys was marked by sudden arrival of volcanic and ophiolitic detritus on the passive continental margin of the indian plate during deposition of sediments dated at foraminiferal zones p6 pakistan to p8 india starting in early eocene time deposition of chulung la formation and murree supergroup volcanic and ophiolitic to metasedimentary detritus was accumulated in rapidly subsiding piggy back and foreland basins homogeneous petrographic composition within the eocene lower miocene murree supergroup with only slight progressive increase of detrital feldspars suggests erosion of largely supracrustal rocks involved in thrusting in the north in middle miocene time marked enrichment in medium to high grade metamorphic detritus in foreland sandstones siwalik group reflects rapid uplift of a warm wedge of indian crust which was carried southward along the main central thrust this major paleogeographic change was recorded also by quartzolithic remnant ocean turbidites which were fed great distances along transverse fracture zones and later accreted in the coastal makran subduction complex panjgur association and makran group recycled orogen detritus derived from the elevated himalayan chain is still accumulating today in the indus fan enrichment in feldspars with respect to ancient sandstones reflects deep erosion levels into mid crustal rocks along the core of the growing orogen

simulating the amplification of orbital forcing by ocean feedbacks in the last glaciation according to milankovitch theory the lower summer insolation at high latitudes about 115 000 years ago allowed winter snow to persist throughout summer leading to ice sheet build up and glaciation1 but attempts to simulate the last glaciation using global atmospheric models have failed to produce this outcome when forced by insolation changes only2 3 4 5 these results point towards the importance of feedback effects for example through changes in vegetation or the ocean circulation for the amplification of solar forcing6 7 8 9 here we present a fully coupled ocean atmosphere model of the last glaciation that produces a build up of perennial snow cover at known locations of ice sheets during this period we show that ocean feedbacks lead to a cooling of the high northern latitudes along with an increase in atmospheric moisture transport from the equator to the poles these changes agree with available geological data10 11 12 13 14 15 and together they lead to an increased delivery of snow to high northern latitudes the mechanism we present explains the onset of glaciation which would be amplified by changes in vegetation in response to weak orbital forcing

climatically related millennial scale fluctuations in strength of california margin oxygen minimum zone during the past 60 k y a strong oxygen minimum zone omz currently exists along the california margin because of a combination of high surface water productivity and poor intermediate water ventilation however the strength of this omz may have been sensitive to late quaternary ocean circulation and productivity changes along the margin although sediment lamination strength has been used to trace ocean oxygenation changes in the past oxygen levels on the open margin are not sufficiently low for laminations to form in these regions benthic foraminifera are highly sensitive monitors of omz strength and their fossil assemblages can be used to reconstruct past fluctuations benthic foraminiferal assemblages from ocean drilling program site 1017 off point conception exhibit major and rapid faunal oscillations in response to late quaternary millennial scale climate change dansgaard oeschger cycles on the open central california margin these faunal oscillations can be correlated to and are apparently synchronous with those reported from santa barbara basin together they represent major fluctuations in the strength of the omz which were intimately associated with global climate change weakening perhaps disappearing during cool periods and strengthening during warm periods these rapid major omz strength fluctuations were apparently widespread on the northeast pacific margin and must have influenced the evolution of margin biota and altered biogeochemicalmore cycles with potential feedbacks to global climate change less

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

laser 40ar 39ar dating of single detrital muscovite grains from early foreland basin sedimentary deposits in india implications for early himalayan evolution in india the dagshai and overlying kasauli formations represent the oldest exposed continental foredeep sediments eroded from the himalayan orogen 40ar 39ar dating of individual detrital white micas from these sedimentary units has provided maximum depositional ages of 28 ma for the dagshai formation at one locality and 25 ma at a second locality whereas deposition of the kasauli formation occurred after 28 ma at two localities and after 22 ma at a third locality this timing suggests that in india the start of substantial exhumation and erosion from the rising himalayan orogen was delayed until 28 ma

seasonal precipitation timing and ice core records this is a commentary on global circulation model experiments of moisture source changes in greenland urging caution in how they are applied because they have important implications for paleoclimate reconstruction from ice cores the work comes from preliminary find is of a ice core gisp2 of the authors the authors conclude that at present anomalies in greenland ice core records should not be interpreted solely in terms of source region variations the combined use of oxygen 18 d and ionic species in the new summit greenland cores should make it possible to answer empirically some of the questions raised by the gcm experiments as to the interpretation of oxygen 18 records in terms of temperature 4 refs 1 fig

peregrinations of the greenland ice sheet divide in the last glacial cycle implications for central greenland ice cores abstract the superb quality of the climate chronology archived in the summit greenland ice cores grip gisp2 testifies that the greenland ice sheet divide has been generally stable through the last glacial cycle the ice sheet has experienced a broad range of paleoclimate conditions ice sheet margin configurations and internal dynamical adjustments in glacial interglacial transitions however it is unlikely that the summit region escaped shifts in ice divide position geometry elevation and flow characteristics details of this dynamical history are important to several aspects of ice core studies the magnitudes of pure and simple shearing reconstruction of vertical ice velocity the explicit location of the ice divide and the divide residence time at different locations are all of interest in interpretation of climatic variables and physical properties of ice in the ice cores we apply a three dimensional thermomechanical ice sheet model to examine the evolution of these dynamical variables over the last 160 kyr in central greenland while a high elevation ice dome is present in the summit region throughout the simulation ice divide migrations of up to 150 km are predicted all points in the vicinity of the summit ice cores including the modern divide have been subject to flowline shifts and variable non zero shear deformation during the adjustment from glacial to holocene conditions from ca 10 ka to the present modelled divide peregrinations and strain rate history are consistent with the observed disturbance of deep ice in the grip and gisp2 ice cores which has muddled paleoclimate reconstructions for the last interglacial eemian period in greenland dynamical excursions are also evident north of the modern summit where the ngrip ice core is currently being drilled dahl jensen et al j glaciol 43 1997 300 306 however the prevailing flow direction and deformation regime at the ngrip site are much more stable than those at grip and gisp2 in the simulations combined with the greater depth of ice at this site this lends cautious optimism to the hope that eemian ice at ngrip may contain an intact record of eemian climate

diagenesis and the reconstruction of paleoenvironments a method to restore original δ18o values of carbonate and phosphate from fossil tooth enamel abstract intra tooth 18 o variations within the carbonate 18 oc and phosphate 18 op components of tooth apatite were measured for miocene and pliocene hypsodont mammals from afghanistan greece and chad in order to evaluate the resistance of enamel to diagenetic alteration application of water apatite interaction models suggest that the different kinetic behaviours of the phosphate water and carbonate water systems can be used to detect subtle oxygen isotope disequilibria in fossil enamel when intra individual variations are considered selective alteration of the oxygen isotope composition from the carbonate component of afghan and greek enamels suggests inorganic isotopic exchange processes microbially induced isotopic exchange for phosphate is demonstrated for the first time in enamel samples from chad in association with extensive recrystallization in chad 18 op values were derived from partial isotopic exchange with fossil groundwater during early diagenesis mass balance calculations using average carbonate content in enamel as a proxy for recrystallization and the lowest 18 op value of dentine as a proxy for the isotopic composition of the diagenetic fluid indicate that diagenesis can alter 18 op by as much as 3 in some enamel samples this diagenetic alteration is also responsible for a decrease in intra individual variations of up to 1 in affected specimens the effects of diagenesis on 18 op values of fossil enamel are not systematic however and can only be estimated if sequential 18 op and 18 oc analyses are performed on fossil enamel and dentine reconstruction of large temporal or spatial scale paleoclimates based on 18 op analyses from mammalian teeth cannot be considered valid if enamel has been affected by bacterial activity or if the data cannot be corrected for diagenetic effects

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

sandstone petrofacies expressions of multiphase basinal tectonics and arc magmatism permian triassic north bowen basin australia abstract modal analyses of 209 sandstone samples from the permian triassic succession of the northern bowen basin eastern australia identify two stratigraphically and compositionally distinct petrofacies the lower to mid upper permian back creek group is characterised by petrofacies a which is quartz rich q82f8l10 it was sourced primarily from cratonic basement terranes to the west where relief was subdued and the quartz content of the sandstones may also reflect some reworking in the marine realm with a consequent loss of labile grains petrofacies b is volcanolithic and characterises alluvial sediments of the upper permian blackwater and lower triassic rewan groups it was sourced from an undissected to transitional magmatic arc provenance located in the contemporary new england orogen to the east which supplied abundant pyroclastic debris to the depositional complex petrofacies b of the northern bowen basin was derived primarily from felsic volcanics compared to an intermediate association recorded for the southern basinal sector indicating significant along arc variation in volcanic style as a consequence its framework grain population is enriched in quartz and is not readily accommodated in the schemes of provenance interpretation currently in use the consistency of framework detrital modes for sandstones distributed throughout the blackwater group q24f10l66 allows the recognition of subpetrofacies b1 and shows that the volcanism associated with the magmatic arc system was remarkably uniform in character and activity during deposition of the entire group the magmatic arc delivered almost identical sedimentary debris over a period of some 9 my in the late permian relative enrichment of quartz within the early triassic rewan group q49f6l45 relative to the blackwater group discriminates subpetrofacies b2 and is attributed to a climatic change and shift in palaeotemperature at the permian triassic boundary the contact between the marine back creek group petrofacies a and the coal bearing blackwater group petrofacies b represents an abrupt switch in provenance with little or no evidence of source mixing the boundary marks the onset of volcanism and associated tectonic uplift in the northern part of the new england orogen to the east sediment from the new source prograded rapidly westwards across the basin coincident with regression direct evidence of contemporaneous volcanism is widespread in the blackwater group as shown by tuffs and tonsteins which are distributed throughout the entire late permian succession

a search in north greenland for a new ice core drill site a new deep ice core drilling site has been identified in north greenland at 75 12 n 42 30 w 316 km north northwest nnw of the grip drill site on the summit of the ice sheet the ice thickness here is 3085 m the surface elevation is 2919 m the north grip ngrip site is identified so that ice of eemian age 115 130 ka bp calendar years before present is located as far above bedrock as possible and so the thickness of the eemian layer is as great as possible an ice flow model similar to the one used to date the grip ice core is used to simulate the flow along the nnw trending ice ridge surface and bedrock elevations surface accumulation rate distribution and ratio echo sounding along the ridge have been used as model input the surface accumulation rate drops from 0 23 m ice equivalent year 1 at grip to 0 19 m ice equivalent year 1 50 km from grip over the following 300 km the accumulation is relatively constant before is starts decreasing again further north ice thickness up to 3250 m bring the temperature of the basal ice up to the pressure melting point 100 250 km from grip the ngrip site is located 316 km from grip in a region where the bedrock is smooth and the accumulation rate is 0 19 m ice equivalent year 1 the modeled basal ice here has always been a few degrees below the pressure melting point internal radio echo sounding horizons can be traced between the grip and ngrip sites allowing us to date the ice down to 2300 m depth 52 ka bp an ice flow model predicts that the eemian age ice will be located in the depth range 2710 2800 m which is 285 m above the bedrock this is 120 m further above the bedrock and the thickness of the eemian layer of ice is 20 m thicker than at the grip ice core site

a monte carlo tuned model of the flow in the northgrip area the north greenland icecore project northgrip drill site was chosen in order to obtain a good eemian record at the present depth 3001 m the eemian interstadial has yet to be seen clearly the flow in this area is poorly understood and needs further investigation after a review of specific features of the bottom topography it is believed that the geology changes along the flowline in order to investigate whether this explains the observed age depth relationship at northgrip the inverse monte carlo method has been applied to a simple model the inversion reveals that the main reason no eemian is observed is a high basal melt rate 2 7 mma 1 the melting is a consequence of a higher geothermal heat flux than the expected 51 mwm 2 of the precambrian shield from our analyses it is concluded that the geothermal heat flux at northgrip is 98 mwm 2 the high basal melt rate also gives rise to sliding at the bed in addition to these results an accumulation model has been established specifically for northgrip these results are essential for further modelling of the northgrip flow and depth age relationship