dust a diagnostic of the hydrologic cycle during the last glacial maximum dust concentrations in ice of the last glacial maximum lgm are high in ice cores from greenland and antarctica the magnitude of the enhancements can be explained if the strength of the hydrologic cycle during the lgm was about half of that at present this notion is consistent with a large decrease 5 c in ocean temperature during the lgm as recently deduced from measurements of strontium and calcium in corals

10 be in ice at vostok antarctica during the last climatic cycle we have previously reported accelerator mass spectrometer measurements of the cosmogenic isotope 10be half life 1 5 myr in an 906 m ice core recovered at dome c antarctica1 in addition to an enhanced concentration during a period of reduced solar activity maunder minimum ad 1645 1715 2 we found substantially increased concentrations during that part of the core corresponding to the last ice age both effects have been confirmed and extended in greenland ice cores3 4 the recovery of a 2 083 m ice core at vostok antarctica5 together with an extended oxygen isotope chronology reported elsewhere in this issue6 permits an extension of 10be studies over the whole of the last climatic cycle 125 kyr we report here such measurements which show an excellent correlation with the oxygen isotope and thus presumably climate record over the whole of this period the results imply that precipitation rates in the antarctic during the last interglacial were similar to those of the holocene but were roughly halved during the last glaciation

hydrogeological characterization of carbonated jurassic aquifers in the gijon villaviciosa basin asturias n spain by means of geochemical and isotopic techniques chemical and isotopic analyses of groundwater from the carbonated jurassic aquifers in the gijon villaviciosa basin asturias northern spain were carried out nine springs were sampled to determine major cations and anions as well as the stable isotopes of the water molecule 2h and 18o and sulphate 34s values also 34s values from gypsum coming both from triassic rocks and bottom of jurassic sequence were also determined the results obtained were used to classify the waters with a genetic criteria in three groups 1 waters with a high gypsum influence with sulphate coming from jurassic gypsum 2 waters without gypsum influence where sulphate source could be atmospheric deposition from industrial processes and marine aerosol and 3 waters with some gypsum influence in which sulphate origin could be a combination of different sources in relation to recharge 2h and 18o values were close to those of global meteoric water line and fit a local line that suggests a meteoric origin the estimated elevations for spring recharge are in agreement with those obtained from hydrogeological maps

high resolution ammonium ice core record covering a complete glacial interglacial cycle high resolution ammonium measurements were performed along the greenland ice core program grip deep ice core covering a complete climatic cycle no overall anthropogenic increase is observed over the last 300 years however springtime concentrations have roughly doubled since 1950 biomass burning is estimated to be a major source for ammonia emissions for preindustrial times it contributes between 10 to 40 to the total ammonium deposited on the central greenland ice sheet during the holocene no correlation is found between the ammonium summer concentrations recorded over the last 100 years and the area burned in northern north america which is considered to be the main source area for ammonium deposited on the central greenland ice sheet this suggests that the meteorological factor is predominant for the pattern of ammonium spikes observed in the ice core if unchanged meteorological conditions are assumed for the holocene as indicated by the 18o ice record a decreasing biomass burning activity toward present time can be derived from the ammonium ice record soil and vegetation emissions are responsible for the ammonium background concentrations in the ice the record therefore may be used to trace back the biomass history of the north american continent a pronounced decreasing trend in background ammonium is found during the holocene reflecting decreasing temperature and therefore lower nh3 emissions in the source region variations in the ammonium concentration during the glacial age are discussed in terms of changes in transport and deposition mechanisms and changes in source strength which can be related to the extent of the laurentide ice sheet the data suggest that the laurentide ice sheet was built up immediately after the last interglacial and went through several large fluctuations during the last ice age

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

δ15n of n2 in air trapped in polar ice a tracer of gas transport in the firn and a possible constraint on ice age gas age differences with respect to gas transport the fim near the surface of an ice sheet can be divided into three zones the uppermost is a convective zone located just below the surface of the ice sheet in which the air is rapidly flushed by convective exchange with the overlying atmosphere below the convective zone there is a diffusive air column in which diffusion is rapid but there is no convection between the bottom of the diffusive air column and the bubble close off region there may be a nondiffusive zone in which diffusion is so slow that negligible gas transport occurs the diffusive air column is characterized by progressive enrichment with depth of 15n in n2 and heavy isotopes of gases in general as predicted using the barometric equation in this paper we present data on the 15n of n2 in recently trapped air samples from 12 ice cores along with numerous downcore samples from byrd vostok and dome c bubble close off depths for these cores calculated from a densification model ranged from 51 to 114 meters below the surface mbs we used these data and the barometric equation to calculate the thickness of the diffusive air column and found that it comprised 46 to 93 of the total firn thickness at our study sites paleo close off depths calculated from the densification model for glacial sections of byrd vostok and dome c are 15 25 m deeper than close off depths today diffusive column heights calculated from 15n varied in a more complex manner the diffusive column height at byrd appears to have decreased from 74 m during the last glacial period to 50 m during the holocene at vostok and dome c the diffusive column height calculated from 15n increase from about 65 m during the last glacial period to about 80 m in the holocene we use records of surface temperature and co2 at byrd and vostok along with their respective chronologies to constrain the ice age gas age difference age throughout the section of the vostok ice core corresponding to the last glacial termination in principle age values calculated from these data can be used to discriminate whether gas in the fim mixes to the bubble close off depth or to a depth equivalent to the diffusive column height in practice however uncertainties in the chronology of byrd and vostok are too great to allow us to distinguish between these two possibilities one can only say that at the time of the last termination age for vostok was between 3 and 10 5 kyr previous estimates fall within this range

impurity sources of f cl no3 and so4 2 in greenland and antarctic precipitation five polar impurity sources are proposed anthropogenic no3 and so42 in recent greenland but not antarctic snow marine aerosols the dominant cl source volcanic eruptions which produce detectable but variable peaks in so42 f and or cl concentrations biogenic sulfurous gases from soil and coastal waters the dominant source for so42 in nonvolcanic strata an unidentified source of background nitrate which is more active in the northern hemisphere and which displays a summer concentration maximum solar activity and supernova events do not modulate no3 concentrations in greenland snow

the holocene and upper pleistocene pollen record from padul granada spain a new study two borings were made at the site of padul granada pollen analysis of 200 spectra from two successive sequences 14 8 and 8 m deep enables a description of the vegetational and climatic history of this region the most southern one in europe from early wurmian times the chronology is supported by twenty one 14c dates original equivalents are found for the great european prewurm interstadials a markedly arid though thermically not extreme episode exactly equivalent to stage 4 of the marine isotopic stratigraphy closes this relatively temperate period the middle part of the last glacial shows climatic fluctuations that are poorly characterized as is often the case in europe for this period a long section very probably corresponding to the complete last pleniglacial does not show any climatic amelioration towards 15 000 yr b p a change in the diagram is noted that can only be interpreted as reflecting a larger expansion of a regional steppe cover this event also reported on three occasions in southeast france marks the beginning of the oldest dryas the climatic amelioration of ca 13 000 yr b p is far more pronounced here than anywhere else in europe whereas that at 10 000 yr b p is not so clearly marked this unexpected result may be accounted for by the fact that padul is the first continental site so far south and so near pleniglacial refuges to be known on the other hand this result is consistent with what is known from oceanic isotopic stratigraphy a quite new late glacial and holocene vegetational history is revealed characterized by the early appearance and dominance of quercus ilex oak forests of a southern type and the early occurrence of quercus suber and olea it is the first account of a complete history of the postglacial reafforestation in a region with a modern semi arid mediterranean climate from the palaeoclimatic point of view it shows that the hot and humid holocene optimum was attained slightly before 8000 yr b p and that the holocene climatic fluctuations were of but small amplitude

comparison of changes in vegetation in northeast greece with records of climate variability on orbital and suborbital frequencies over the last 450 000 years abstract a new direct pollen orbital tuning procedure based on a correspondence between changes in certain vegetation elements and march and june perihelion configurations is applied to the tenaghi philippon record northeast greece the development of a refined chronological scheme allows comparisons to be made with records of climate variability from the north atlantic as well as of global sea level ice volume and atmospheric co2 content on orbital frequencies the comparison reveals a close correspondence between relative ice volume extent and tree population size during glacial intervals during interglacial and interstadial periods the degree of forest development is more closely associated with high latitude insolation and related climate regimes rather than extent of residual ice volume on suborbital frequencies the greek record shows similar repeat times in peaks of steppe vegetation with north atlantic ice rafting events but the amplitude of this variability in the two records is not always proportional overall what emerges is that the major shifts in the relative abundance of forest v open vegetation communities at tenaghi philippon on orbital and suborbital frequencies over the last 450 000 years are coherent with high latitude changes affecting atmospheric and oceanic circulation glacial decreases in atmospheric co2 content contributed to the elimination of tree populations by exacerbating water stress conditions during arid intervals but do not appear to be the primary driver of the observed vegetation changes at this latitude variations in co2 levels in the order of 40 ppmv between different interglacial interstadials periods with adequate moisture availability appear to have had a limited effect on the nature and size of tree populations

the chemistry and origin of groundwater in triassic sandstone and quaternary deposits northwest england and some uk comparisons abstract the triassic sherwood sandstone group is a major uk aquifer in this study the groundwater geochemistry of a 60 km2 area has been investigated to improve the understanding of the hydrogeology of the area and to determine the origin of groundwater archived analyses of groundwater samples were interpreted to determine the dominant geochemical processes and subsequently samples were taken from selected sites for stable and radio isotope measurements near areas of direct recharge of the sherwood sandstone groundwaters are unsaturated with respect to carbonate minerals sulphate and chloride are contributed to the groundwater in the sherwood sandstone from the overlying quaternary glacial drift deposits and mercia mudstone the groundwater chemistry and isotopes of sulphate indicate that the source of sulphate is gypsum in the triassic sequence and the triassic derived glacial deposits a significant proportion of the calcium in groundwater is shown to be exchanged for sodium in the aquifer matrix however in the more mineralised waters carbonate minerals are precipitated because of contributions to the groundwater of calcium from dissolution of gypsum up piezometric gradient groundwaters are modem and have relatively high 14c and tritium contents the oldest water which was sampled for 14c is estimated to be about 4000 years older than the modern waters which were sampled from near recharge zones the groundwater regime in the study area may be compared and contrasted with triassic sandstone aquifers elsewhere in the uk incongruent carbonate dissolution occurs as described in the triassic of the east midlands the lower mersey basin and southwest england exchange reactions are important in determining the groundwater chemistry as found elsewhere in the triassic of northwest england and in contrast to the east midlands and southwest england

the co2 concentration of air trapped in gisp2 ice from the last glacial maximum holocene transition measurements of the co2 concentration of air trapped in greenland ice sheet project two ice show an increase from approximately 190 ppm to 270 ppm during the 8000 years between the end of the last glacial maximum and the beginning of the holocene this increase is in agreement with other parallel records from both greenland and antarctica although the gisp2 data exhibit considerable variability over periods as small as 50 100 years and show that co2 can be affected by processes occurring within the ice after bubble formation the in situ reactions which contribute to the modification of the concentrations of paleoatmospheric co2 may include both co2 uptake as well as co2 production the existence of two major episodes of co2 enrichment in addition to the variability of the data prevents a precise determination of the progression of the increase in atmospheric co2 although the 80 ppm rise between 18 0 kybp and 10 4 kybp is evident these results strongly suggest that some intervals of the gisp2 co2 record must be interpreted in the context of the chemical composition of the ice and that records of atmospheric co2 in polar ice can be considered accurate only if the ice is either essentially carbonate free or contains abundant carbonate

interpreting ancient ice in a shallow ice core from the south yamato antarctica blue ice area using flow modeling and compositional matching to deep ice cores 1 we explore methods of dating a 101 m ice core from a bare ice ablation area in the yamato mountains dronning maud land east antarctica there are two unknowns the age of the ice at the surface and the age spanned by the core the ice crystal growth rate was used to estimate the age span of the core at about 5 kyr co2 ch4 and n2o data on the core were compared with well dated records from deep cores leading to two plausible matches both within isotope stage c detailed comparison of high resolution dep records from this core and the dome fuji core support the 55 61 kyr bp fit best oxygen isotope values in the core were then used to constrain the source elevation of the snow in the core and hence the velocities in a simple flow line model we inverted the ice core surface age age span and origin site and their confidence intervals in a sensitivity study of flow model parameter space the flow line model predicts good matches to the core by reducing glacial flow rates to 70 of present day accumulation rates by 45 with 10 confidence intervals the modeled surface age for the whole meteorite field yields maximum surface ages of about 90 kyr which is consistent with known but poorly constrained tephra dating meteorite terrestrial ages and the frequency of meteorite discoveries this approach can be used quite generally to link deep ice cores to surface outcrops on blue ice fields

the transition from temperate phases to stadials in the long upper pleistocene sequence from les echets france abstract from two sections of the long sequence of les echets corresponding to the end of the eemian and to the end of st germain ii interstadial respectively detailed pollen diagrams have been established which provide information about the climatic conditions prevailing during the transitions from very temperate periods to the following cold stadials

a mis 15 mis 12 record of environmental changes and lower palaeolithic occupation from valle giumentina central italy abstract an integrated geological study including sedimentology stable isotope analysis 18o 13c geochemistry micromorphology biomarker analysis 40ar 39ar geochronology and tephrochronology was undertaken on the quaternary infill of the valle giumentina basin in central italy which also includes an outstanding archaeological succession composed of nine human occupation levels ascribed to the lower and middle palaeolithic 40ar 39ar dating and other palaeoenvironmental and tephrochronological data constrain the sedimentary history of the whole succession to the mis 15 mis 12 interval between 618 13 ka and 456 2 ka palaeoenvironmental proxies suggest that over this time interval of about 150 ka sedimentary and pedogenic processes were mainly influenced by climatic changes in particular by the pulsing of local mountain glaciers of the majella massif specifically the valle giumentina succession records glacio fluvial and lacustrine sedimentation during the colder glacial periods and pedogenesis and or alluvial sedimentation during the warmer interglacial and or interstadial periods during this interval tectonics played a negligible role as a driving factor of local morphogenesis and sedimentation whereas the general regional uplift experienced in the middle pleistocene led to capture of the basin and its definitive extinction after mis 12 these data substantially improve previous knowledge of the chronology and sedimentary evolution of the succession providing for the first time a well constrained chronological and palaeoenvironmental framework for the archaeological and human palaeoecological record of valle giumentina

electrical resistivity sounding of the east antarctic ice sheet electrical resistivity soundings using a schlumberger array have been carried out at dome c east antarctica 74 39 s 124 10 e elevation 3400 m to sound the entire 3500 m depth of the ice sheet changes in density and temperature are largely separated in the ice at dome c so activation energies for both firn and ice could be determined we find an activation energy of 0 25 ev in both solid ice and firn between 15 c and 58 c a common value of the activation energy points to a single transport regime in which the charge carriers and conduction paths are the same in firn and ice to evaluate the variation of resistivity with density we have considered five dielectric mixture models that fit the available data on the high frequency dielectric constant of firn only looyenga s equation fits the field data for dc resistivity in the upper 900 m of the ice sheet where impurity concentrations are known from core samples we find no correlation between resistivities and the concentrations of salts or acids instead we find it likely that resistivities are correlated with the crystal size hence with the holocene wisconsin boundary in the ice column a pronounced increase in resistivity to a value comparable with that in temperate glacier ice occurs deep within the ice sheet we attribute this to a large increase in the size and irregularity of the ice crystals which destroys the continuity of the impurity shells surrounding the ice crystals that we believe supply the conduction paths shabtaie and bentley 1994a high resistivity does not imply removal of the impurities from the system moderate concentrations of impurities can be accommodated by locating them in disconnected domains

late glacial to holocene depositional architecture of the ombrone palaeovalley system southern tuscany italy sea level climate and local control in valley fill variability the ombrone palaeovalley was incised during the last glacial sea level fall and was infilled during the subsequent late glacial to holocene transgression a detailed sedimentological and stratigraphic study of two cores along the palaeovalley axis led to reconstruction of the post last glacial maximum valley fill history stratigraphic correlations show remarkable similarity in the late glacial to early holocene succession but discrepancy in the holocene portion of the valley fill above the palaeovalley floor about 60 m below sea level late glacial sedimentation is recorded by an unusually thick alluvial succession dated back to ca 18 cal kyr bp the holocene onset was followed by the retrogradational shift from alluvial to coastal facies in seaward core om1 the transition from inner to outer estuarine environments marks the maximum deepening of the system by comparison in landward core om2 the emplacement of estuarine conditions was interrupted by renewed continental sedimentation swamp to lacustrine facies stratigraphically equivalent to the fully estuarine facies of core om1 represent the proximal expression of the maximum flooding zone this succession reflects location in a confined segment of the valley just landward of the confluence with a tributary valley it is likely that sudden sediment input from the tributary produced a topographic threshold damming the main valley course and isolating its landward segment from the sea the seaward portion of the ombrone palaeovalley presents the typical estuarine backfilling succession of allogenically controlled incised valleys in contrast in the landward portion of the system local dynamics completely overwhelmed the sea level signal following marine ingression this study highlights the complexity of palaeovalley systems where local morphologies changes in catchment areas drainage systems and tributary valleys may produce facies patterns significantly different from the general stratigraphic organization depicted by traditional sequence stratigraphic models

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

holocene volcanic history as recorded in the sulfate stratigraphy of the european project for ice coring in antarctica dome c edc96 ice core 1 a detailed history of holocene volcanism was reconstructed using the sulfate record of the european project for ice coring in antarctica dome c edc96 ice core this first complete holocene volcanic record from an antarctic core provides a reliable database to compare with long records from antarctic and greenland ice cores a threshold method based on statistical treatment of the lognormal sulfate flux distribution was used to differentiate volcanic sulfate spikes from sulfate background concentrations ninety six eruptions were identified in the edc96 ice core during the holocene with a mean of 7 9 events per millennium the frequency distribution events per millennium showed that the last 2000 years were a period of enhanced volcanic activity edc96 volcanic signatures for the last millennium are in good agreement with those recorded in other antarctic ice cores for older periods comparison is in some cases less reliable mainly because of dating uncertainties sulfate depositional fluxes of individual volcanic events vary greatly among the different cores a volcanic flux normalization volcanic flux tambora flux ratio was used to evaluate the relative intensity of the same event recorded at different sites in the last millennium normalized flux variability for the same event showed the highest value in the 1100 1500 ad period this pattern could mirror changes in regional transport linked to climatic variations such as slight warming stages in the southern hemisphere southern hemisphere medieval warming like period

evidence for an early glacial maximum in the french vosges during the last glacial cycle the last glacial maximum is observed to have occurred between 18 000 and 20 000 years ago throughout northern europe here we present evidence for the surprising result that in the region of the french vosges the regional ice sheet advanced during the early part of the last glacial cycle and this expansion was considerably larger than that which occurred during the last glacial maximum from these results we conclude that the glacial maximum may not have occurred at the same time worldwide contrary to what has usually been assumed1

the co2 concentration of air trapped in greenland ice sheet project 2 ice formed during periods of rapid climate change the co2 content of air occluded in greenland ice sheet project 2 gisp2 ice formed over two separate intervals of rapidly changing climate centered at approximately 46 and 63 kyr b p is as much as 90 ppm more during warm periods interstadials than during cold periods stadials these co2 variations are superimposed on changes in annual layer thickness and 18o of the ice and do not show the 200 to 700 year offsets which would be expected for concurrent variations in the atmosphere and the ice the co2 concentrations during the stadials are similar to the atmospheric values recorded by antarctic ice of the same age so processes occurring in the ice after bubble enclosure must be enriching the air trapped in gisp2 ice formed during the interstadials this conclusion is supported by ca content and electrical conductivity measurements of the ice which show that adequate carbonate is present to produce these enrichments and that co2 content is high only when the electrical conductivity a proxy for h concentration is high high resolution mapping of one 4 cm section of ice shows a 200 ppm increase in the co2 content of the trapped air from approximately 275 to 475 ppm analyses of the total inorganic carbon of ice from both the lgm and holocene show that most of the ca in the ice is from caco3 and that the 13co2 approaches that of soil and marine carbonates these results show that the co2 record preserved in ice can be altered by in situ decarbonation reactions and that only ice containing either abundant carbonate or essentially no carbonate contains a reliable record of paleoatmospheric co2

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

radiogenic isotopic compositions of low concentration dust and aerosol from the gisp2 ice core abstract we have produced a record of radiogenic isotope compositions of particulate and soluble dust fractions from the gisp2 ice core from basal ice to the surface for each respective dust fraction we measured sr and nd isotope values to constrain the provenance of mineral dust and sea salt aerosol transported to the greenland ice sheet we have produced high precision measurements of end values on sub ng quantities of nd in ice core samples via tims with 1013 ohm resistors the range of measured end values of soluble material 12 9 2 6 to 7 3 0 9 is interpreted to represent sea salt aerosol based on sr isotope compositions that resemble seawater values 0 711007 0 000030 to 0 709416 0 000072 therefore the end potentially provides important insights to the atmospheric circulation patterns at high latitudes at least through mis 5 we compare end values of surface seawater from ocean basins and deltas at high latitudes to alternating relatively radiogenic and unradiogenic end at gisp2 we suggest these changes represent transitions between a climate system dominated by enhanced and persistent arctic oscillation positive anomalies as determined from sea level and ocean bottom pressure measurements and a state representative of modern atmospheric circulation which typically exhibits either negative anomalies or none altogether

pollen analysis of a long upper pleistocene continental sequence in a velay maar massif central france abstract a new 20 m sequence is presented which is based on 279 spectra derived from a coring at le bouchet lake massif central france the vegetational history of this region is described back to the end of the last interglacial ribains interglacial the two preglacial early glacial forested interstadials st geneys 1 and st geneys 2 are evidence for the first time in the massif central in spite of the altitude of the site 1200 m they suggest a quite temperate vegetation with the same mesophilous character as during the holocene the pleniglacial appears to be threefold with two cold episodes lower and upper pleniglacial divided by a long complex period of moderate climatic improvement the vegetation history of this mountain region is compared with that evidenced for the same period on the basis of the sequence of les echets at a lower altitude 267 m botanical and climatic inferences are discussed

atmospheric co2 concentration from 60 to 20 kyr bp from the taylor dome ice core antarctica a high resolution record of the atmospheric co2 concentration from 60 to 20 thousand years before present kyr bp based on measurements on the ice core of taylor dome antarctica is presented this record shows four distinct peaks of 20 parts per million by volume ppmv on a millennial time scale good correlation of the co2 record with temperature reconstructions based on stable isotope measurements on the vostok ice core antarctica is found

location of cation impurities in ngrip deep ice revealed by cryo cell uv laser ablation icpms in polar ice sheets the average grain size varies with depth ice grain size increases due to several factors including ice temperature and impurity content which in turn varies with climate the effect of impurities on grain growth is thought to be crucial but has never been observed experimentally using a methodology recently developed at royal holloway university of london in situ chemical analysis of frozen ice at sub ppm concentrations with unprecedented spatial resolution 150 m is achievable using ultraviolet laser ablation inductively coupled plasma mass spectrometry uv la icpms featuring a two volume cryo la cell following surface cleaning with a custom built vice equipped with a ceramic blade ngrip ice slabs 86 ka before ad 2000 have been analysed using a series of one dimensional profiles and two dimensional maps of laser spots at a resolution of 200 300 m results demonstrate that cation impurities are not uniformly distributed in ice layers and show significant variations in concentration on a sub millimetre scale furthermore a different pattern of elemental distribution between clear ice and layers enriched in impurities cloudy bands has been identified while concentration differences for cloudy bands are not resolvable between boundaries and inner grain domains within clear ice grain boundaries and junctions are significantly up to 100 times impurity enriched relative to corresponding grain interiors

atmospheric co2 over the last 1000 years a high resolution record from the west antarctic ice sheet wais divide ice core 1 we report a decadally resolved record of atmospheric co2 concentration for the last 1000 years obtained from the west antarctic ice sheet wais divide shallow ice core the most prominent feature of the pre industrial period is a rapid 7 ppm decrease of co2 in a span of 20 50 years at 1600 a d this observation confirms the timing of an abrupt atmospheric co2 decrease of 10 ppm observed for that time period in the law dome ice core co2 records but the true magnitude of the decrease remains unclear atmospheric co2 variations over the time period 1000 1800 a d are statistically correlated with northern hemispheric climate and tropical indo pacific sea surface temperature however the exact relationship between co2 and climate remains elusive due to regional climate variations and or uneven geographical data density of paleoclimate records we observe small differences of 0 2 0 6 ppm among the high precision co2 records from the law dome epica dronning maud land and wais divide antarctic ice cores however those records share common trends of co2 change on centennial to multicentennial time scales and clearly show that atmospheric co2 has been increasing above preindustrial levels since 1850 a d

atmospheric co2 and climate from 65 to 30 ka b p 1 using new and existing ice core co2 data from 65 30 ka a new chronology for co2 is established and synchronized with greenland ice core records to study how high latitude climate change and the carbon cycle were linked during the last glacial period atmospheric co2 rose several thousand years before abrupt warming in greenland associated with dansgaard oeschger events 8 12 14 17 four large warm events that follow heinrich events the co2 rise terminated at the onset of greenland warming for each of these events atmospheric co2 is strongly correlated with the antarctic isotopic temperature proxy with an average time lag of 720 370 yr mean 1 during the time interval studied the new data and chronology should provide a better target for models attempting to explain co2 variability and abrupt climate change

quantification of bioturbation in hemipelagic sediments via thin section image analysis traditional ichnofabric descriptive semiquantitative l schemes rely upon subjective estimates of the degree to which original sedimentary fabrics have been disrupted this paper presents an objective method of quantifying bioturbation in hemipelagic sediments based on a thin section image analysis technique in order to perform these analyses optical or backscattered electron micrographs are processed in order to obtain black and white images in these images black pixels are silt size larger grains and the clay size sedimentary matrix are white pixels once the initial processing has been accomplished an index h is defined to quantify the horizontal orientation of the larger grain size fraction of the sediment h is low for bioturbated fabric and high for laminated sediments in hemipelagic suspension deposits h can he used to quantify bioturbation assuming that no other sedimentary processes have disrupted the original depositional fabric the quantitive bioturbation scheme described here is consistent with existing semiquantitative bioturbation schemes in addition it is objective and provides higher resolution descriptions of biological processes that disrupted the sediment after deposition applying this quantitative scheme should refine future paleoecological reconstruction derived from lacustrine and marine successions

handbook of environmental isotope geochemistry vol 1 the terrestrial environment a p fritz and j ch fontes editors elsevier amsterdam 1980 xii 532 pp u s 90 25 dfl 185 00

late pleistocene climatic variations as recorded in two italian maar lakes lago di mezzano lago grande di monticchio abstract sediment profiles from two maar lakes lago di mezzano central italy and lago grande di monticchio southern italy were investigated with respect to their minerogenic and biogenic sediment accumulation rates for a time window spanning the final 20 000 yr of the last glaciation the chronological framework is provided by calibrated radiocarbon ages varve counting calculation of sedimentation rates and tephrochronology in the time slice between 34 000 and 14 000 cal bp periods of increased minerogenic input are observed in both lacustrine records interrupted by periods of low minerogenic input these cyclic variations have an average recurrence time of 1785 yr for lago di mezzano and 2875 yr for lago grande di monticchio comparing well with marine and ice core data explanations for these pulses of increased minerogenic sedimentation include enhanced erosion and runoff the higher precipitation evaporation ratio required for this interpretation was possibly restricted to winter months as earlier published pollen analyses on sediments from lago grande di monticchio show a contemporary development of steppe vegetation an indicator for cool dry climatic conditions this may be connected with a southward shift of the westerlies and a reinforced jet stream agreement of lacustrine data from italy with late pleistocene glacial events in central italy with events recorded in marine archives from the north atlantic heinrich events and with oxygen isotope data from greenland ice cores is interpreted as evidence for the late pleistocene climate in europe being influenced by north atlantic climatic forcing which may be related to dansgaard oeschger cycles

comparison of holocene electrical records from dome c and vostok antarctica as part of the european project for ice coring in antarctica a new deep ice core is being drilled at dome c two electrical methods have been used on the core drilled so far a new design of electrical conductivity method ecm instrument and a traditional dielectric profiler the two profiles are very similar in both peaks and background consistent with acidity being the dominant influence on both in this part of the record the dome c records have been compared to ecm records from vostok and a tentative match has been made between them this suggests a long term average ratio of accumulation rate of 1 36 between this dome c core and vostok and that the dome c core analyzed so far to 358 m probably includes the very end of the glacial holocene transition

soluble impurities in the byrd station ice core antarctica their origin and sources polar ice cores contain long and detailed records of paleoatmospheric composition paleoclimate and their evolution through time by making a complete ionic balance in melted samples of ice it is possible to evaluate the origin identification of chemical compounds and sources continental marine volcanic extraterrestrial of soluble impurities contained in these ice cores once these are known an attempt can be made to try and explain the cause of any observed changes in this paper we present results of analyses of the major soluble impurities h na nh4 k so4 no3 cl made on bulk samples selected at approximately 50 m intervals down the length of an ice core from byrd station antarctica 80 01 s 119 31 w 1530 m most samples are in ionic balance and it is therefore possible to suggest with which compounds the ionic impurities are linked these compounds include an important contribution from both sea salts nacl and na2so4 and strong acids approximately equal amounts of hno3 and h2so4 the cl na mole ratio is found to be quite stable throughout the core and hovers about the expected bulk sea water ratio in general the marine derived components at byrd station decreased by a factor of 2 between the late glacial maximum and holocene while the gas derived acid components decreased by a factor of only 1 5 some possible causes of these variations are suggested

tyrrhenian sea tephrochronology of the oxygen isotope record for the past 60 000 years abstract a chronology of the marine oxygen isotope record of the past 60 ka is proposed by correlating eight marine ash layers with terrestrial volcanic deposits dated by the 14c and or k ar methods detailed oxygen isotope analyses were made on the planktonic foraminifera of three cores collected in the central tyrrhenian sea the origin of the ash layers was determined by major and trace elements analyses then the major pyroclastic terrestrial deposits were sampled and analysed in order to provide land sea correlations two ash layers occurred during the warm event that followed the first step of the deglaciation and which was dated at 12 6 0 5 ka b p another ash layer is present near the last glacial maximum that we have dated at 17 5 0 3 ka b p during isotopic stage 3 five ash layers were recognized and dated which allowed us to assign ages to the isotopically light oxygen peaks warmer interstadials at 31 1 5 ka and 33 4 1 6 ka denekamp at 37 5 2 ka hengelo and successively at 49 2 ka 52 4 2 2 ka 57 2 2 ka and 60 5 2 2 ka moershoofd complex

limited dechlorination of sea salt aerosols during the last glacial period evidence from the european project for ice coring in antarctica epica dome c ice core 1 chloride cl and sodium na in ice cores originate mainly from sea salt and one would thus expect the cl na ratio to reflect the seawater ratio however at dome c a low accumulation site in east antarctica this is not the case in present day snow instead a cl excess relative to na is observed in surface snow and within a few meters depth the cl concentration decreases and the cl na ratio becomes significantly lower than the seawater ratio aerosol studies at coastal antarctic sites have shown that the reaction of sea salt aerosols with nitric and sulphuric acid leads to the formation of hcl that eventually escapes the sea salt aerosol the observed decrease in cl concentrations in the uppermost snow layers is due to reemission of hcl from the snow postdepositional loss of hcl depends among other factors on the accumulation rate at the site with lower accumulation rates leading to larger losses during the last glacial maximum lgm the cl na ratio is relatively stable and close to the seawater ratio despite the even lower accumulation rate during that time the likely explanation for this conflicting observation is that high levels of dust neutralized nitric and sulphuric acids during the lgm which in turn reduced the formation of hcl from sea salt aerosol with less or no hcl formed postdepositional loss would be prevented keeping the cl na ratio close to that of sea water

coastal antarctic aerosol and snowfall chemistry aerosol samples have been collected at three stations on the coast of antarctica at dumont d urville station samples have been collected for 4 years at halley station for 2 years and at neumayer station for 12 years fresh snow samples have also been collected at the three sites at halley daily surface snow samples were taken as well as firn cores covering the sampling period meteorological including upper air data are available at the three sites in the subsequent papers of this special section the data from the three stations have been combined in order to make general statements about the chemistry of aerosol in coastal antarctica about the differences between sectors of antarctica and about the relationship between air concentrations and the chemistry that is eventually seen in ice cores this paper summarizes the samples collected and the sampling methods used at the three sites it also highlights the main role of each paper in this special section

controls on δ 34 s and δ 18 o of dissolved sulfate in aquifers of the murray basin australia and their use as indicators of flow processes the usefulness of stable isotopes of dissolved so4 34s and 18o to study recharge processes and to identify areas of significant inter aquifer mixing was evaluated in a large semi arid groundwater basin in south eastern australia the murray basin the distinct isotopic signatures in the oxidizing unconfined murray group aquifer and the deeper reducing renmark group confined aquifer may be more sensitive than conventional chemical tracers in establishing aquifer connections 34s values in the unconfined murray group aquifer in the south and central part of the study area decrease along the hydraulic gradient from 20 8 to 0 3 the concomitant increasing so4 cl ratios as well as relatively low 18oso4 values suggest that vertical input of biogenically derived so4 via diffuse recharge is the predominant source of dissolved so4 to the aquifer further along the hydraulic gradient towards the discharge area near the river murray 34s values in the unconfined murray group aquifer increase and so4 cl ratios decrease due to upward leakage of waters from the confined renmark group aquifer which has a distinctly low so4 cl and high 34s 14 9 56 4 relatively positive 34s and 18oso4 values and low so4 cl in the renmark group aquifer is typical of so4 removal by bacterial reduction the s isotope fractionation between so4 and hs of 24 estimated for the confined aquifer is similar to the experimentally determined chemical fractionation factor for the reduction process but much lower than the equilibrium fractionation 70 even though the confined groundwater residence time is 300 ka years mapping the spatial distribution of 34s and so4 cl of the unconfined murray group aquifer provides an indicative tool for identifying the approximate extent of mixing however the poorly defined end member isotopic signatures precludes quantitative estimates of mixing fractions

seasonal variations of glaciochemical isotopic and stratigraphic properties in siple dome antarctica surface snow six snow pit records recovered from siple dome west antarctica during 1994 are used to study seasonal variations in chemical major ion and h 202 isotopic deuterium and physical stratigraphic properties during the 1988 94 period comparison of d measurements and satellite derived brightness temperature for the siple dome area suggests that most seasonal sd maxima occur within 4 weeks of each 1 january several other chemical species h 2o2 non sea salt nss so 4 2 methanesulfonic acid and no3 show coeval peaks with sd together providing an accurate method for identifying summer accumulation sea salt derived species generally peak during winter spring but episodic input is noted throughout some years no reliable seasonal signal is identified in species with continental sources nssca 2 nss mg 2 nh 4 or nsscl visible strata such as large depth hoar layers 5 cm are associated with summer accumulation and its metamorphosis but smaller hoar layers and crusts are more difficult to interpret a multi parameter approach is found to provide the most accurate dating of these snow pit records and is used to determine annual layer thicknesses at each site significant spatial accumulation variability exists on an annual basis but mean accumulation in the sampled 10 km 2 grid for the 1988 94 period is fairly uniform

last glacial climate instability documented by coarse grained sediments within the loess sequence at fanjiaping lanzhou china optically stimulated luminescence dating grain size analysis and magnetic susceptibility measurements were conducted on the fanjiaping loess section from the western chinese loess plateau the results confirm that last glacial high frequency climatic shifts were documented in mid latitude continental archives the grain size record indicated that coarse grained sediments with horizontal bedding and channel fill structures were only deposited in several short intervals equivalent to the beginning of marine oxygen isotope stage mis 4 and the early to middle mis 3 this probably implies brief rainfall intensification of the asian summer monsoon and its disappearance since the late mis 3 to mis 2 may have been a response to significant glacial cooling in the northern hemisphere previous investigations revealed high sea surface temperatures at high latitudes at the start of mis 4 and the early to middle mis 3 intensification of summer insolation in the northern hemisphere implying evident climate amelioration climate improvement favors boreal forest recovery enhancing both winter and summer air temperatures the resultant smaller equator polar temperature gradient probably helped the moisture laden summer monsoon to penetrate northward this study thus provides new significant information about the response of terrestrial loessic palaeoenvironments to millennial timescale climatic fluctuations during the last glacial period

vegetation reconstruction on the basis of pollen in late pleistocene hyena coprolites from san teodoro cave sicily italy vegetation reconstruction based on pollen from coprolites of extinct spotted hyena crocuta crocuta spelaea goldfuss 1832 recovered from excavations carried out in 1998 at san teodoro cave sicily italy supports previous indications of pre late glacial conditions eight of the twelve coprolites analysed contained well preserved pollen grains there is a general similarity between the pollen contents from the coprolites but they show variability they suggest a main vegetation type dominated by steppic taxa poaceae artemisia ephedra chenopodiaceae and asteraceae but also including arboreal taxa pinus and cupressaceae low percentages of pollen of mesophilous woody taxa quercus betula abies alnus pistacia among others are noticeable suggesting the existence of nearby refugia for temperate and mediterranean vegetation a reconstruction of the landscape using the coprolite pollen record and other pollen records from sicily and south italy shows the predominance during the pre late glacial of a wooded steppe biome with elements representing a variety of local environmental conditions

palaeoenvironmental and palaeoclimatic implications of the late quaternary sediment record of vico volcanic lake central italy a 15 m long sediment core recovered from the lago di vico caldera lake in central italy has been the subject of macrofacies description and sedimentological organic carbon content grain size and mineralogy investigation the results have been integrated with the pollen data from the same core in order to provide a regional climatic and environmental history with inferences on past lake levels and on moisture and temperature regimes radiometric 14c and 40ar 39ar dating biostratigraphical considerations and tephra analyses provide a chronological framework and indicate that the sequence spans the last 90 000 yr several moist periods have been identified that were characterised by enhanced weathering by hydrolysis of the catchment rocks these alternated with relatively dry phases associated with lowering of lake levels the lowest hydrolysis efficiency of the whole record accompanied by notable aeolian deposition was attained during the last glacial phase but moisture conditions were such that the lake level did not decrease probably owing to reduced temperatures evidence for cool climate also emerges for the early pleniglacial the highest available moisture was achieved within the holocene at 5 kyr bp the late holocene does not show either increase of aridity or degradation of the vegetation cover until at least roman times copyright 2001 john wiley sons ltd

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

the last climatic cycle at kopais central greece thick lacustrine sequences from southern europe provide an opportunity to derive continuous records where the chronostratigraphical position of pre holocene stages can be determined with increased confidence here high resolution sediment and pollen analytical results from a 60 m core recovered from the kopais basin central greece spanning the interval from the last interglacial to the early holocene are presented the record shows distinct shifts between open vegetation periods of increased erosion with sediment inwashing and forest periods associated with calcite precipitation in the lake the sequence of major events of the last climatic cycle contained at kopais bears strong similarities to other records in greece but also reveals the presence of high frequency oscillations with higher amplitudes than previously seen at other sites

holocene carbon cycle dynamics based on co2 trapped in ice at taylor dome antarctica a high resolution ice core record of atmospheric co2 concentration over the holocene epoch shows that the global carbon cycle has not been in steady state during the past 11 000 years analysis of the co2 concentration and carbon stable isotope records using a one dimensional carbon cycle model uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial scale changes of atmospheric co2 concentrations

co2 and o2 n2 variations in and just below the bubble clathrate transformation zone of antarctic ice cores co2 measurements on the epica european project for ice coring in antarctica dml ice core in depth levels just below the bubble ice clathrate ice transformation zone 1230 2240 m depth were performed in the youngest part 1230 1600 m they reveal variations of up to 25 ppmv around the mean atmospheric concentration within centimetres corresponding to a snow deposition interval of a few years similar results are found at corresponding depth regions of the dome c and the talos dome ice cores since we can exclude all hitherto known processes altering the concentration of co2 in ice cores we present a hypothesis about spatial fractionation of air components related to episodically increasing clathrate formation followed by diffusion processes from bubbles to clathrates this hypothesis is supported by optical line scan observations and by o2 n2 measurements at the same depth where strong co2 variations are detected below the clathrate formation zone this small scale fractionation process is slowly smoothed out most likely by diffusion regaining the initial mean atmospheric concentration although this process compromises the representativeness of a single co2 measurement on small ice samples in the clathrate formation zone of an ice core it does not affect the mean atmospheric co2 concentration if co2 values are averaged over a sufficiently long depth scale 10 cm in case of the epica dml ice core

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

oxygen 18 16 variability in greenland snow and ice with 10 3 to 105 year time resolution the 3 km long greenland ice sheet project 2 gisp2 ice core presents a 100 000 year detailed oxygen isotope profile covering almost a full glacial interglacial cycle measuranents of isotopic fluctuations in snow frost and atmospheric water vapor samples collected during summer field seasons up to 20 0 are compatible with the large and abrupt 80 160 changes observed in accumulated tim snow pit 15 80 profiles from the gisp2 summit area however show rapid smoothing of the 180 160 signal near the surface beyond about 2 m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate the longer climate fluctuations also have regional and often global significance in the older part of the record corresponding to marine isotope stages mis 5a to 5d the effect of orbital climate forcing via the 19 and 23 kyr precession cycles and the 41 kyr obliquity cycle is obvious from the end ofmis 5a at about 75 000 years b p till the end of the glacial at the younger dryas preboreal transition at 11 650 years b p the o180 160 record shows frequent rapid switches between intermediate interstadial and low stadial values fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1 5 kyr a broad peak at 4 0 kyr and additional shorter periods detailed comparison of the gisp2 180 160 record with the vostok antarctica 15d record pacific ocean foraminiferal 180 160 grande pile france tree pollen and insolation indicates that a counterpart to many of the rapid 180 160 fluctuations of gisp2 can be found in the other records and that the gisp2 isotopic changes clearly are the local expression of climate changes of worldwide extent correlation of events on the independent gisp2 and specmap time scales for the interval 10 000 50 000 years b p shows excellent chronometric agreement except possibly for the event labeled 3 1 the glacial to interglacial transition evidently started simultaneously in the arctic and the antarctic but its development and its expression in greenland isotopes was later suppressed by the influence of meltwater especially from the barents sea ice sheet on deep water formation and ocean circulation meltwaters from different ice sheets bordering the north atlantic also influenced ocean circulation during the bolling allerod interstadial complex and the younger dryas and led to a distinct development of european climate and greenland 180 160 values the holocene interval with long term stable mean isotopic values contains several fluauations with periods from years to millennia dominant is a 6 3 year oscillation with amplitude up to 3 to 4 0 periodicities of 11 and 210 years also found in the solar modulated records of the cosmogenic isotopes 1obe and 14c suggest solar processes as the cause of these cycles depression of180 160 values cooling by volcanic eruptions is observed in stacked gisp215 80 records but the effect is small and not likely to trigger major climate changes

glacio chemical study spanning the past 2 kyr on three ice cores from dronning maud land antarctica 2 seasonally resolved chemical records the ammonium calcium and sodium concentrations from three intermediate depth ice cores drilled in the area of dronning maud land east antarctica have been investigated since all measurements were performed by a high resolution continuous flow analysis system for the first time seasonal signals of chemical trace species could be obtained from the interior of central antarctica over a period of approximately 2 millennia although the elevation as well as the accumulation rate differ between the drilling sites similar values were obtained by comparing mean concentrations spanning the last 900 years however a distinct lack of intersite correlation was found on decadal timescales despite a noticeable accumulation change apparent in one core no significant concentration change of all three species has occurred all the measured ions show clear seasonal signals over the whole records while the sea salt related component sodium peaks simultaneously with calcium the maximum ammonium concentration occurs in the snow with a time lag of 2 months after the sea salt peak more than 60 of the calcium concentration can be attributed to an ocean source elevated sodium concentrations were found within this millennium compared to mean values of the whole records but the spatially varying shape of the increase suggests that a possible climatic signal is biased by local deposition effects

a high precision method for measurement of paleoatmospheric co2 in small polar ice samples we describe a high precision method now in use in our laboratory for measuring the co 2 mixing ratio of ancient air trapped in polar ice cores occluded air in ice samples weighing 8 15 g is liberated by crushing with steel pins at 35 c and trapped at 263 c in a cryogenic cold trap co 2 in the extracted air is analyzed using gas chromatography replicate measurements for several samples of high quality ice from the siple dome and taylor dome antarctic ice cores have pooled standard deviations of 0 9 ppm this high precision technique is directly applicable to high temporal resolution studies for detection of small co 2 variations for example co 2 variations of a few parts per million on millennial to decadal scales

reply to the comment on environmental impact of the 73 ka toba super eruption in south asia by m a j williams s h ambrose s van der kaars c ruehlemann u chattopadhyaya j pal p r chauhan palaeogeography palaeoclimatology palaeoecology 284 2009 295 314 abstract haslam and petraglia raise three broad questions concerning our paper environmental impact of the 73 ka toba super eruption in south asia by martin a j williams stanley h ambrose sander van der kaars carsten ruehlemann umesh chattopadhyaya jagannath pal parth r chauhan palaeogeography palaeoclimatology palaeoecology 284 2009 295 314 a what was the relationship between the 73 ka toba eruption and the cold stade between the dansgaard oeschger interstades 20 and 19 b what was the regional impact of the eruption on vegetation c what was the possible effect of the eruption upon humans and mammals in response to questions a and b we note that the 73 ka toba eruption was followed by several centuries of intense cooling and wind blown dust accession in the greenland gisp2 ice core by a change from forest to grassland or open woodland in central india carbon isotopic analysis and in the wider region pollen analysis of a marine sediment core in the bay of bengal in regard to c the genetic evidence is as yet too imprecisely dated to demonstrate causality as is the archaeological evidence cited by haslam and petraglia in favour of minimal impact future work supported by higher resolution chronologies than are presently available is needed to provide a less equivocal picture of the environmental impact of the 73 ka toba eruption

the last climatic cycle at la grande pile vosges france a new pollen profile a new pollen diagram has been made from an old unanalyzed core from la grande pile gp xx correlations with the previous work of woillard 1975 1978 leads to the following conclusions the end of the eemian was marked by a minor climatic change prior to the melisey i stadial the ognon ii and ognon iii interstadials are not consistent and correspond to the level of reworking of mesophilous taxa during the last pleniglacial the limitations of the botanical interpretation of pollen spectra from the last pleniglacial are underlined lastly bruckenthalia and larix are identified for the first time at la grande pile the respective roles of these taxa following the eemian are additional arguments for correlating the st germain i and ii with the early weichsel interstadials in the north of middle europe

uth fractionation by fluids in k rich magma genesis the vico volcano central italy abstract the 230th 238u disequilibrium method has been applied to the potassic volcanic series of vico latium central italy the 3 main events of the recent volcanic activity have been dated using whole rock isochrons the lava flows of the main cone were erupted between 260 and 180 ky pyroclastic flows are dated around 90 ky and the final effusive activity mte venere around 60 ky these results are in good agreement with previous k ar ages the intense th u fractionation th u varying from 3 2 to 11 is apparently not related to processes of partial melting and crystal fractionation the th u fractionation is the most intense in basic terms of the first episode and is due to the percolation of a deep hydrothermal fluid which impoverishes u in different batches of primary magmas more limited th u fractionations in highly differentiated magma are due to u accompanied by sb and alkalies enrichments in the shallow magma chambers a time integrated model is proposed for the evolution of the 230th 232th ratio in the mantle source of vico it shows that th u and th ta fractionations are probably related to the bulk k u and th enrichment of the mantle of the roman province around 300 ky ago a metasomatic enrichment by a silicate melt is proposed to explain the anomalously high th u and th ta fractionations

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

co 2 diffusion in polar ice observations from naturally formed co 2 spikes in the siple dome antarctica ice core this is the publisher s final pdf the published article is copyrighted by the international glaciological society and can be found at http www igsoc org journal

the role of the deep ocean in north atlantic climate change between 70 and 130 kyr ago the suggestion1 that changes in north atlantic deep water nadw production are linked through surface heat flux to the atmospheric temperature over greenland is supported by earlier indications2 3 that nadw production decreased during glacial times and by the subsequent finding4 6 that it declined during the younger dryas cool period at the end of the last glaciation changes in north atlantic surface temperatures have been found7 to mirror high frequency temperature changes recorded in greenland ice cores over the past 80 kyr but the connection to abyssal circulation has yet to be established except for one or two isolated oscillations8 9 here we present carbon and oxygen isotope analyses of benthic foraminifera in a high resolution north atlantic deep sea sediment core for the period 70 130 kyr ago these data allow us to reconstruct the history of nadw production which shows a close correlation with greenland climate variability for much of this time interval suggesting that the climate influence of nadw variability was widespread we see no evidence however for changes in nadw production during substage 5e the eemian interglacial period in contrast with recent ice core data10 which suggest severe climate instability in greenland during this time period our results may support suggestions based on data from a second ice core that this apparent instability is an artefact caused by ice flow11 alternatively the eemian climate instability may have had a different origin from the subsequent climate events

holocene electrical and chemical measurements from the epica dome c ice core the comparison between electric electric conductivity measurement ecm and dielectric profiling dep and chemical sulphate and chloride depth profiles along the first 400 m of the epica dome c ice core revealed a very good fit especially for peaks related to volcanic emissions from the comparison between these profiles a dominant contribution of sulphuric acid to the ionic balance of antarctic ice for the holocene was confirmed a progressive increase with depth was observed for chloride concentrations showing a change of relative contribution between sulphate and chloride a higher increase of chloride was evident between 270 and 360 m depth probably due to a change in source or transport processes or to an increase of the annual snow accumulation rate the dep ecm and sulphate ice signatures of tambora ad 1816 and el chichon ad 1259 eruptions are described in detail a characteristic peak series due to hcl deposition was identified at 103 109 m depth from the ecm dep and chloride profiles

cyclic water level oscillations of the karabogazgol caspian sea system abstract the karabogazgol kbg water level oscillations were reconstructed in the last 200 years using the geochemical evolution of the uppermost meter of its sedimentary infill high resolution studies of the mineralogical composition of the kbg sediments show alternating periods of high concentration brines followed by periods of more dilute waters the relative water level reconstruction was based on statistical models factor analysis fa correspondence analyses ca and detrended correspondence analyses dca whilst the chronological framework was established using the 210 pb technique this reconstruction was compared with the instrumental water level record of the caspian sea showing a high degree of correlation r 2 0 83 the agreement between the reconstructed and the measured water level oscillations of the caspian sea indicates that environmental changes can be reconstructed from closed lakes provided that an accurate chronological control of sedimentary processes is available the water level reconstruction shows that the caspian sea water level fluctuations follow a cyclical pattern rather than an erratic one as has been suggested in the literature two main periodicities of 62 5 and 38 46 years have been found

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

evidence for substantial accumulation rate variability in antarctica during the holocene through synchronization of co 2 in the taylor dome dome c and dml ice cores high resolution records of atmospheric co2 concentration during the holocene are obtained from the dome concordia and dronning maud land antarctica ice cores these records confirm that the co2 concentration varied between 260 and 280 ppmv in the holocene as measured in the taylor dome ice core however there are differences in the co2 records most likely caused by mismatches in timescales matching the taylor dome timescale to the dome c timescale by synchronization of co2 indicates that the accumulation rate at taylor dome increased through the holocene by a factor two and bears little resemblance to the stable isotope record used as a proxy for temperature this result shows that different locations experienced substantially different accumulation changes and casts doubt on the often used assumption that accumulation rate scales with the saturation vapor pressure as a function of temperature at least for coastal locations d 2004 elsevier b v all rights reserved

the high sensitivity of the palynological record in the vico maar lacustrine sequence latium italy highlights the climatic gradient through europe for the last 90 ka the palynological study of the vice maar lacustrine sequence italy is realized from the correlation of three drillholes the time span covers a period from the end of oxygen isotope substage 5b till the beginning of stage 1 from ca 90 to ca 10 ka bp at the base of the pollen diagram pollen zone 0 a younger dryas like fluctuation is observed after pollen zone 1 which is a well developed forest period substage 5a the forests of pollen zones 3 and 5 correspond to extensive climate improvements these last two zones are correlated to the ognon complex of the grande pile france and to interstadial periods 20 and 19 defined in the grip ice core greenland 72 6 66 2 ka before the stage 5 4 transition these two interstadial periods are global events found in the greenland and antarctica ice sheets as well as in north atlantic marine cores in other pollen records from north of the alps changes have been recorded but they are less pronounced than in vico pollen zone 7 stage 3 shows ca 7 warm humid fluctuations that might have a link to the dansgaard oeschger events greenland during zone 9 the lateglacial interstadial is recorded as well as the younger dryas event the localization of vice near plant refugia and far from the ice cap enables its pollen diagram to record abrupt and intense response to climate changes possibly through a link to the atlantic ocean via westerly winds c 1996 elsevier science ltd

environmental impact of the 73 ka toba super eruption in south asia abstract the cooling effects of historic volcanic eruptions on world climate are well known but the impacts of even bigger prehistoric eruptions are still shrouded in mystery the eruption of toba volcano in northern sumatra some 73 000 years ago was the largest explosive eruption of the past two million years with a volcanic explosivity index of magnitude 8 but its impact on climate has been controversial in order to resolve this issue we have analysed pollen from a marine core in the bay of bengal with stratified toba ash and the carbon isotopic composition of soil carbonates directly above and below the ash in three sites on a 400 km transect across central india pollen evidence shows that the eruption was followed by initial cooling and prolonged desiccation reflected in a decline in tree cover in india and the adjacent region carbon isotopes show that c 3 forest was replaced by wooded to open c 4 grassland in central india our results demonstrate that the toba eruption caused climatic cooling and prolonged deforestation in south asia and challenge claims of minimal impact on tropical ecosystems and human populations

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

character of vegetational and environmental changes in southern europe during the last glacial period evidence from lesvos island greece this paper presents high resolution results of palynological and sedimentological analyses undertaken on two sediment cores from the megali limni ml basin an area characterised by serpentine soils in the southeastern part of lesvos island greece six tephra horizons and multiple radiocarbon dates provide independent controls towards the development of a chronological framework the composite pollen record spans the period from 22 to 62 thousand years ago ka bp and shows a number of oscillations between steppe forest steppe and forest in concert with north atlantic millennial scale variability vegetation during the late marine isotope stage mis 4 was grassland steppe indicating cold and arid conditions while sediment composition suggests increased erosion rates arboreal populations dominated by pinus and to a lesser extent deciduous quercus expanded during mis 3 interstadials suggesting increases in precipitation and temperature within the course of the longer interstadials changes in vegetation composition point to a trend towards increased aridity and sometimes decreasing winter temperatures during intervening stadials vegetation was composed mainly of artemisia chenopodiaceae and gramineae indicating reversals to arid and cold conditions with most extreme conditions recorded during stadials corresponding to heinrich events during the course of mis 3 the basin was progressively infilled with sediments only a small portion of mis 2 is represented in the sequence showing a short lived expansion of arboreal populations comparisons with other pollen sequences from southern europe underscore the important role of pinus throughout the last glacial period a reflection of the serpentine soils of the megali limni area where pinus brutia dominates today

reconstructing past atmospheric co2 concentration based on ice core analyses open questions due to in situ production of co2 in the ice analysis of air extracted from bubbles of polar ice showed the anthropogenic increase of atmospheric co2 concentration during the past few hundred years preindustrial concentration 280 ppmv and unexpectedly that the concentration also increased due to natural causes from 200 to 280 ppmv during the transition from the last glacial epoch to the holocene however more detailed reconstructions based on ice core analyses suggested that some of the additional observed variations were actually due to the modification of co2 concentration in the bubbles by chemical reactions between impurities in the ice detailed analyses of acidity the carbonate concentration the concentration of oxidation agents like hydrogen peroxide h2o2 and organic compounds e g formaldehyde hcho along short intervals of ice cores representing only a few annual layers allowed us to investigate these chemical reactions the records are not conclusive but they indicate that the oxidation of organic compounds is at least as important as acid carbonate reactions ice containing a low mean carbonate and a low h2o2 concentration as well as a small scattering of co2 results obtained on several adjacent samples representing a few annual layers at most is at present the best guarantee for reliable results of the atmospheric co2 concentration

year round record of size segregated aerosol composition in central antarctica concordia station implications for the degree of fractionation of sea salt particles the origin of sea salt aerosol that reaches the high antarctic plateau and is trapped in snow and ice cores remains still unclear in particular the respective role of emissions from the open ocean versus those from the sea ice surface is not yet quantified to progress on this question the composition of bulk and size segregated aerosol was studied in 2006 at the concordia station 75 s 123 e located on the high antarctic plateau a depletion of sulfate relative to sodium with respect to the seawater composition is observed on sea salt aerosol reaching concordia from april to september that suggests that in winter when the sea salt atmospheric load reaches a maximum emissions from the sea ice surface significantly contribute to the sea salt budget of inland antarctica citation jourdain b s preunkert o cerri h castebrunet r udisti and m legrand 2008 year round record of size segregated aerosol composition in central antarctica concordia station implications for the degree of fractionation of sea salt particles

antarctic aerosol and snowfall chemistry implications for deep antarctic ice core chemistry in this paper we first summarise major findings of recent atmospheric studies of nitrogen and sulphur species present in the boundary layer of coastal antarctic regions we then discuss the implications of such atmospheric data for the interpretation of nitrate ammonium methanesulphonate and sulphate records in deep ice cores extracted from central antarctica in terms of past atmospheric chemistry changes

a record of atmospheric co2 during the last 40 000 years from the siple dome antarctica ice core 1 we have measured the co2 concentration of air occluded during the last 40 000 years in the deep siple dome a hereafter siple dome ice core antarctica the general trend of co2 concentration from siple dome ice follows the temperature inferred from the isotopic composition of the ice and is mostly in agreement with other antarctic ice core co2 records co2 rose initially at 17 5 kyr b p thousand years before 1950 decreased slowly during the antarctic cold reversal rose during the younger dryas fell to a local minimum at around 8 kyr b p and rose continuously since then the co2 concentration never reached steady state during the holocene as also found in the taylor dome and epica dome c hereafter dome c records during the last glacial termination a lag of co2 versus siple dome isotopic temperature is probable the siple dome co2 concentrations during the last glacial termination and in the holocene are at certain times greater than in other antarctic ice cores by up to 20 ppm mol co2 mol air while in situ production of co2 is one possible cause of the sporadic elevated levels the mechanism leading to the enrichment is not yet clear

changes in atmospheric circulation and ocean ice cover over the north atlantic during the last 41 000 years high resolution continuous multivariate chemical records from a central greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41 000 years these chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to greenland defined here as the polar circulation index pci and in the extent of ocean ice cover massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in pci during stadials without discharge events ocean ice cover appears to reach some common maximum level the massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

changes in environment over the last 800 000 years from chemical analysis of the epica dome c ice core the epica ice core from dome c extends 3259 m in depth and encompasses 800 ka of datable and sequential ice numerous chemical species have been measured along the length of the cores here we concentrate on interpreting the main low resolution patterns of major ions we extend the published record for non sea salt calcium sea salt sodium and non sea salt sulfate flux to 800 ka the non sea salt calcium record confirms that terrestrial dust originating from south america closely mirrored antarctic climate both at orbital and millennial timescales a major cause of the main trends is most likely climate in southern south america which could be sensitive to subtle changes in atmospheric circulation sea salt sodium also follows temperature but with a threshold at low temperature we re examine the use of sodium as a sea ice proxy concluding that it is probably reflecting extent with high salt concentrations reflecting larger ice extents with this interpretation the sodium flux record indicates low ice extent operating as an amplifier in warm interglacials non sea salt sulfate flux is almost constant along the core confirming the lack of change in marine productivity for sulfur producing organisms in the areas of the southern ocean contributing to the flux at dome c for the first time we also present long records of reversible species such as nitrate and chloride and show that the pattern of post depositional losses described for shallower ice is maintained in older ice it appears possible to use these concentrations to constrain snow accumulation rates in interglacial ice at this site and the results suggest a possible correction to accumulation rates in one early interglacial taken together the chemistry records offer a number of constraints on the way the earth system combined to give the major climate fluctuations of the late quaternary period

abrupt climatic changes during the last glaciation based on pollen analysis of the abric romani catalonia spain the abric romani continental pollen record provides evidence of abrupt climate variations during the last glaciation the pollen record reveals a pattern of high frequency variations similar to that in ice cores as shown by oxygen isotopes or dust content analyses of 14 travertine samples yield coherent u series ages in correct stratigraphic order ranging from 40 000 to 70 000 yr according to changes in the composition and structure of the vegetation five paleoclimatic phases have been differentiated the oldest ranging from 70 200 to 65 500 yr ago records thermophilous taxa which correspond to the last warm events of isotopic stage 5 the next phase from 65 500 to 56 800 yr records a cold humid climate that correlates with isotope stage 4 during the third phase from 56 800 to 49 500 yr relatively warm and cold events alternate the fourth phase from 49 500 to 46 200 yr records a cold dry climate the fifth phase ranging from 46 200 to 40 800 yr records a milder phase that is similar in appearance to the beginning of the holocene

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr