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

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

sulfur isotopic composition of surface snow along a latitudinal transect in east antarctica the sulfur stable isotopic values 34s of sulfate aerosols can be used to assess oxidation pathways and contributions from various sources such as marine biogenic sulfur volcanoes and sea salt however because of a lack of observations the spatial distribution of 34s values in antarctic sulfate aerosols remains unclear here we present the first sulfur isotopic values from surface snow samples along a latitudinal transect in eastern dronning maud land east antarctica the 34s values of sulfate showed remarkably uniform values in the range of 14 8 16 9 and no significant decrease toward the inland part of the transect was noted these results suggest that net isotopic fractionation during long range transport is insignificant thus the 34s values can be used to infer source contributions the 34s values suggest that marine biogenic sulfur is the dominant source of sulfate aerosols with a fractional contribution of 84 16

variations in the zn si record over the last interglacial glacial transition we examined the zinc content of diatom frustules as an indicator of past changes in surface seawater zn2 concentration zn si data of samples from three cores located in the south atlantic sector of the southern ocean spanning the last interglacial glacial transition are presented changes in the zn si record are linked to changes in the surface water zn2 concentration the source of variation in zn2 concentration appears to be via changes in deep water upwelling and circulation we rule out changes in phytoplankton productivity and aeolian dust input as a source of variation in the zn si record likewise the zn si data are not linked to shifts in the diatom species composition of the sediment or sediment preservation effects the zn si results presented do not support the zinc hypothesis there is no link between the uptake of co2 by phytoplankton as inferred from the 13c record and the zn si record

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

present antarctic aerosol composition a memory of ice age atmospheric dust the data obtained from the chemical analysis na al and ca concentrations of deep antarctic ice cores has been reexamined the correlations found between the concentrations of these elements suggest that the patagonian continental shelf was the dominant aerosol source during the last ice age the dust being an intimate mixture of marine clay and carbonates in addition it is proposed that sea salt deposited on the continental shelf sediments during drop in sea level was emitted and transported jointly with this dust the present antarctic aerosol composition is very similar to the one deduced from ice core studies for glacial climatic conditions it is concluded that present antarctic aerosol originates mainly from ice age aeolian deposits in south american cold deserts

palaeoclimatological and chronological implications of the vostok core dust record the2 083 m vostok ice core recovered by the soviet antarctic expeditions has provided much information of climatic and environmental interest for a period covering a full glacial inter glacial cycle1 6 here we present and discuss the dust record obtained down to 2 202 m the final depth to which this core was extended in 1986 first we document the fact that major changes in aeolian deposits as recorded in the vostok core appear to be of global significance and confirm the existence of a link between high latitude aeolian deposits and the earth s orbital parameters7 8 second we propose atmospheric dust as a strati graphic marker to compare timing with other records of palaeocli mate and use the magnetic susceptibility profile measured along the rc11 120 indian ocean core9 for this purpose assuming that major dust events correspond to common aeolian inputs this approach indicates that the vostok and marine records were roughly in phase at the previous glacial interglacial transition

diatoms in antarctic ice cores some implications for the glacial history of antarctica the presence of reworked pliocene and older marine microfossils in glacial tills of the sirius group suggests that these sediments were emplaced during the pliocene or later by glaciers riding up the eastern east antarctic slope of the transantarctic mountains this interpretation implies that there was considerable fluctuation in the size of the east antarctic ice sheet as recently as ca 3 ma here we test an alternate scenario eolian emplacement of the pliocene microfossils by comparing diatoms in the sirius group with diatoms in holocene and last glacial maximum ice from the dome c core from the central antarctic plateau since the diatoms in dome c ice are known to be eolian in origin we hypothesize that if the sirius diatoms are also eolian then the two antarctic sites dome c and the sirius group equally remote from the southern ocean will have the same exotic flora i e windblown diatoms from either a fresh water or marine source however whereas the dome c diatoms are predominantly fresh water those of the sirius are predominantly marine we conclude from these data that the sirius and dome c diatoms each reflect a different mode of emplacement and that the diatoms in the sirius till were not emplaced via wind transport this conclusion does not prove that the pliocene diatoms in the sirius till record a deglaciation and pliocene reglaciation of east antarctica but rather it removes an alternate mechanism eolian transport raised by those who oppose this scenario

climate and marine carbon cycle response to changes in the strength of the southern hemispheric westerlies 1 it has been previously suggested that changes in the strength and position of the southern hemisphere westerlies could be a key contributor to glacial interglacial atmospheric co2 variations to test this hypothesis we perform a series of sensitivity experiments using an earth system model of intermediate complexity a strengthening of the climatological mean surface winds over the southern ocean induces stronger upwelling and increases the formation of antarctic bottom water enhanced ekman pumping brings more dissolved inorganic carbon dic rich waters to the surface however the stronger upwelling also supplies more nutrients to the surface thereby enhancing marine export production in the southern hemisphere and decreasing the dic content in the euphotic zone the net response is a small atmospheric co2 increase 5 ppmv compared to the full glacial interglacial co2 amplitude of 90 ppmv roughly the opposite results are obtained for a weakening of the southern hemisphere westerly winds

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

aerosol deposited in east antarctica over the last glacial cycle detailed apportionment of continental and sea salt contributions 1 the major ions sodium na calcium ca2 and chloride cl deposited in central antarctica and preserved in ice cores originate from both marine and continental sources they provide important proxy records helping to reconstruct past climatic processes however it is difficult to clearly separate the individual contributions from the two sources particularly the continental one during glacial periods on the basis of na and ca2 records at an unprecedented resolution from the european project for ice coring in antarctica epica dome c ice core back to the penultimate glacial period mean ion mass ratios were deduced for the continental and the sea salt aerosol body over east antarctica the sea salt ion mass ratios are in the range predicted for both wind induced bubble bursting of breaking waves on the open ocean and sea ice brine derived aerosols respectively thus allowing no clear decision on the contribution of sea ice to the central antarctic sea salt aerosol the continental ion mass ratios point to a substantial contribution by halide aerosols which is in agreement with the source properties in southern south america although these ratios do not rule out the continental shelf exposed during glacial stages as an additional source while during cold glacial periods continental sources accounted for more than 90 of the total ca2 input this contribution was highly variable during the remaining glacial periods covarying with the antarctic warm events during the holocene it was less than 50 but it was significantly higher during the last interglacial period the sea salt aerosol contribution to the total na input which was mostly dominant and higher than 90 was reduced to only two thirds during the last two glacial maxima and the period around 60 ka thus the glacial continental na contribution appears to be more important than previously assumed implying that na records not corrected for continental na do not represent a pure marine signal at the east antarctic plateau during glacial times

sulfur isotopic measurements from a west antarctic ice core implications for sulfate source and transport measurements of d 34 s covering the years 1935 76 and including the 1963 agung indonesia eruption were made on a west antarctic firn core ridsa 78 738 s 116 338 w 1740 m a s l and results are used to unravel potential source functions in the sulfur cycle over west antarctica the d 34 s values of so4 2 range from 3 1 to 9 9 these values are lower than those reported for central antarctica from near south pole station of 9 3 18 1 patris and others 2000 while the agung period is isotopically distinct at south pole it is not in the ridsa dataset suggesting differences in the source associations for the sulfur cycle between these two regions given the relatively large input of marine aerosols at ridsa determined from na data and the seasonal so4 2 cycle there is likely a large marine biogenic so4 2 influence the d 34 s values indicate however that this marine biogenic so4 2 with a well established d 34 so f 18 is mixing with so4 2 that has extremely negative d 34 s values to produce the measured isotope values in the ridsa core we suggest that the transport and deposition of stratospheric so4 2 in west antarctica combined with local volcanic input accounts for the observed variance in d 34 s values

multiple oxygen and sulfur isotopic analyses on water soluble sulfate in bulk atmospheric deposition from the southwestern united states 1 sulfate is a major component of bulk atmospheric deposition including dust aerosol fog and rain we analyzed sulfur and oxygen isotopic compositions of water soluble sulfate from 40 sites where year round dust traps collect bulk atmospheric deposition in the southwestern united states average sulfur and oxygen isotopic compositions 34s and 18o are 5 8 1 4 cdt and 11 2 1 9 smow n 47 respectively samples have an oxygen 17 anomaly 17o with an average value of 1 0 0 6 except for a weak positive correlation between 18o and 17o values r2 0 4 no correlation exists for 18o versus 34s 17o versus 34s or any of the three isotopic compositions versus elevation of the sample site exceptional positive 17o values up to 4 23 are found in samples from sites in the vicinity of large cities or major highways and near zero 17o values are found in samples close to dry lakes comparison of isotopic values of dust trap sulfate and desert varnish sulfate from the region reveals that varnish sulfate has average isotopic values that are 4 8 lower for 18o 2 1 higher for 34s and 0 3 lower for 17o than those of the present day bulk deposition sulfate although other factors could cause the disparity this observation suggests a possibility that varnish sulfate may have recorded a long term atmospheric sulfate deposition during the holocene or pleistocene as well as the differences between sulfur and oxygen isotopic compositions of the preindustrial bulk deposition sulfate and those of the industrial era

high latitude dust deposition in snow on the glaciers of james ross island antarctica high latitude dust hld depositions on four glaciers of james ross island the ulu peninsula were analysed the deposition rate on the selected glaciers varies from 11 8 to 64 0 g m 2 which is one order of magnitude higher compared to the glaciers in antarctica or elsewhere in the world a strong negative relationship between the sediment amount and altitude of a sampling site was found this is most likely caused by the higher availability of aeolian material in the atmospheric boundary layer general southerly and south westerly wind directions over the ulu peninsula with exceptions based on local terrain configuration help to explain the significantly lower level of sediment deposition on san jose glacier and the high level on triangular glacier x ray fluorescence xrf spectrophotometry was used to estimate the relative proportions of the main and trace lithophile elements in the sediment samples both the sediment amount and the xrf results are analysed in a depth profile at each locality and compared among the glaciers suggesting long range transport of fine mineral material from outside james ross island the distribution of aeolian sediment among the glaciers corresponds well with the prevailing wind direction on the ulu peninsula

quantifying sulfate components and their variations in soils of the mcmurdo dry valleys antarctica 1 many soils of the mcmurdo dry valleys mdv antarctica being old hyperarid and frigid have accumulated abundant atmospheric salts over the last several million years this salt repository offers an opportunity to study atmospheric chemistry past and present the origin and transport of ions in soils the weathering activity of soils and postdepositional soil leaching processes within this unique environment in particular soil sulfate in the mdv is known to have multiple origins but the precise proportions of different sulfate components remain elusive here we test a hypothesis that soil sulfate in the mdv is a predictable mixture of three major components sea salt sulfate non sea salt sulfate and background sulfate derived from weathering and volcanic sources that to a large extent varies as a function of elevation and distance from the coast by measuring sulfate s three stable isotope parameters i e 17o 18o and 34s plus estimating independently the end member stable isotope parameters for the three components on the basis of published reports and our measured data we solve explicitly the mixing proportion for each component using a set of three simultaneous linear equations the results from four spatially representative soil profiles show that the sum of such calculated proportions for the three components is very close to unity in most samples suggesting that a simple three component mixing model is a good representation of the soil sulfate budget while significant uncertainties still exist in the isotope compositions of different sulfate end members these data provide important initial constraints on sulfate diversity as well as its spatial and vertical distribution in the mdv

variations in atmospheric sulphate recorded in stalagmites by synchrotron micro xrf and xanes analyses abstract we report here the first speleothem time series of the variability of sulphate a species whose abundance in catchments is strongly influenced by atmospheric anthropogenic and volcanic sources annually resolved archives of s mg si and p were generated by applying synchrotron radiation micro x ray fluorescence xrf to two speleothems from different sites in northern italy x ray absorption edge spectrometry proves that the s is in the form of sulphate and xrf mapping demonstrates that s is within calcite and enriched zones are predominantly as layers a post 1850 a d record from the ernesto cave shows a substantial rise in sulphate interpreted as reflecting the largely anthropogenically forced variation of sulphate of the atmospheric boundary layer moderated by some ecosystem storage analysis of the circa 5 2 to circa 5 0 ka interval of a speleothem from savi cave where ecosystem retention of s is likely to have been minimal shows a spiky sulphate record resembling that of ice cores a series of sulphate peaks suggest that multiple volcanic sulphate aerosol emissions at that time this probably enhanced summer temperature cooling thus favouring the preservation of the human mummy of neolithic copper age the iceman on the watershed between italy and austria both examples illustrate the power of speleothems to record atmospheric sulphate variability

neodymium isotopes as tracers in marine sediments and aerosols north atlantic nd and sm concentrations and nd isotopic compositions were measured on the detrital fraction of deep sea surface sediments and on aerosols sampled over the north atlantic and mediterranean sea the data expressed asend 0 and as model ages ranged from 14 5 end 0 4 9 and from 0 01 to 2 21 ga respectively two areas where the sediments contain relatively less radiogenic nd are to the west off north africa and eastward of the canadian shield this distribution is consistent with other tracers in suggesting that a significant fraction of the sediments are derived from aeolian material transported by major wind systems saharan dust transported in the equatorial trade winds belt and north american soil material transported in the latitudes of the westerlies between these aeolian dominated belts along an axis from the azores to gibraltar and the mediterranean lies a zone of more radiogenicend 0 values in sediments and aerosols influenced by the recent volcanism of this region previously reported distributions of nd isotopes in bottom formed iron manganese crusts and coatings are similar to distributions of nd isotope values in detrital sediments and aerosols this suggests that the detrital fraction has undergone partial dissolution and desorption in the water column and or in the pore waters of near surface sediments and that a significant proportion of nd in the authigenic ferromanganese phases is derived from this source and may therefore not represent strictly dissolved seawater nd isotope ratios useful as watermass tracers

ice core palaeoclimate records in tropical south america since the last glacial maximum ice core records spanning the last 25 000 yr from the tropical andes of south america are reviewed these records from quelccaya huascaran and sajama present a high temporal resolution picture of both the late glacial stage lgs and the holocene climatic and environmental conditions in the south american andes late glacial stage conditions at high elevations appear to have been cooler than today although the magnitude of the inferred cooling differs with the particular proxy used e g snowline depression pollen ice cores insoluble dust and anion concentrations in the ice cores reveal that lgs hydrological conditions in the tropics 9 s were much drier than today whereas in the subtropics 18 s lgs conditions were much wetter this probably reflects the migration of the tropical hadley cell in response to a different meridional temperature gradient low nitrate concentrations in the lgs ice from both huascaran and sajama suggest that the amazon basin forest cover may have been much less extensive discussed is the conundrum surrounding the use of d 18 o as a palaeothermometer in the tropics where temperatures exhibit little seasonal variation yet the ice core records suggest that d 18 o records temperature variations on decadal to millennial time scales finally evidence is presented for a strong twentieth century warming copyright 2000 john wiley sons ltd

glacier climate interaction at low latitudes in the low latitudes there is an absence of major thermal seasonality yet there are three different climate regimes related to global circulation patterns and their seasonal oscillation the humid inner tropics the dry subtropics and intermediate between these two the outer tropics for the respective glacier regimes the vertical profiles of specific mass balance vbps are modeled considering vertical gradients of accumulation air temperature and albedo the duration of the ablation period and a factor for the ratio between melting and sublimation the model is first calibrated with data from hintereisferner austrian alps and is then applied to tropical conditions the simulated vbp matches well the measured profiles from irian jaya and mount kenya due to lack of field evidence the subtropical vbp cannot be verified directly however application of the respective model versions separately to the humid and dry seasons of the outer tropical glaciar uruashraju cordillera blanca peru provides reasonable results glaciers in the humid inner tropics are considered to be most sensitive to variations in air temperature while dry subtropical glaciers are most sensitive to changes in air humidity the two seasons of the outer tropics have to be viewed from these different perspectives

ammonium and non sea salt sulfate in the epica ice cores as indicator of biological activity in the southern ocean sulfate so42 and ammonium nh4 flux records over the last 150 000 years from both antarctic epica ice cores european project for ice coring in antarctica are presented the ice core record from dome c is influenced by the indian sector of the southern ocean so whereas dronning maud land is facing the atlantic sector generally they reflect the past atmospheric aerosol load and thus potentially reveal the fingerprint of marine biogenic sources from the so the most important feature of both the nssso 4 2 as well as nh4 flux records is the absence of any significant glacial cycles in contrary to the distinct transitions for mineral dust and sea salt aerosol over the last 150 000 years this finding challenges the iron fertilization hypothesis on long time scales as the significant changes in dust e g from the last glacial maximum toward the holocene have neither an impact on nssso 4 2 nor on nh4 fluxes found in interior antarctica the inter site correlation of both species is weak r 2 0 42 for the nssso 4 2 flux and r 2 0 12 for the nh4 flux respectively emphasizing the local source characteristics of biogenic aerosol from the so millennial variability in nh4 and nssso 4 2 is within the uncertainty of our flux estimates correlation with mineral dust and sea ice derived sodium shows only a very weak influence of dust deposition on those insignificant changes in nssso 4 2 flux for the atlantic sector of the southern ocean but also small transport changes or terrigeneous sulfate contributions may contribute to those variations at edml c 2009 elsevier ltd all rights reserved

the sequence of events surrounding termination ii and their implications for the cause of glacial interglacial co2 changes events surrounding termination ii as preserved in the vostok ice core provide a number of clues about the mechanisms controlling glacial to interglacial climate change antarctic temperature and the atmosphere s co2 content increased together over a period of 8000 years this increase is bounded by a drop in dust flux at its onset and by a drop in the 18o of trapped air at its finish a similar lag between dust flux and foraminiferal 18o is seen in a southern ocean marine record suggesting that the 18o in air trapped in vostok ice is a valid proxy for ice volume the synchronous change of atmospheric co2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets this observation coupled with the fact that nutrient reorganization in the north atlantic occurs with or after the sea level rise eliminates many scenarios proposed to explain the co2 rise including those which rely on sea level change conveyor related nutrient redistribution or north atlantic cooling southern ocean scenarios become the front runners but the most popular mechanism iron fertilization has two problems in explaining the co2 rise before termination ii first much of the dust demise occurs prior to the change in co2 so if iron is the villain a threshold value of its supply must be called upon above which productivity does not continue to increase second the co2 rise continues for some 4 5 kyr after the dust flux has fallen to close to zero these problems may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during the glacial periods in this case the residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon and would explain the slow rampup of atmospheric co2

sulphate concentration in cave dripwater and speleothems long term trends and overview of its significance as proxy for environmental processes and climate changes sulphate concentrations in speleothems identify major volcanic eruptions provide useful information on soil and aquifer dynamics and in similar fashion to the 14c bomb peak its anthropocene peak can be used to date recent cave formations however the transmission of s from the atmosphere to cave dripwater and its incorporation in speleothems is subjected to biogeochemical cycling and accurate studies of each cave site are needed in order to assess how the s atmospheric signal is modified and eventually encoded in speleothems this study investigates the role of biogeochemical cycling and aquifer hydrology by utilising published and new dripwater and speleothem data from grotta di ernesto er in northern italy here we provide the first long term record of sulphate concentration in cave dripwater based on over 20 years of measurements fast drip site st er1 is characterised by a continuous decrease in so4 concentration from a high of 7 5 0 8 mg l in 1993 1994 to a low of 2 2 0 2 mg l in 2013 2014 and replicates with a delay of 15 years the decline in the atmospheric so2 emissions the s series of slow flow er78 site is further delayed by 4 5 years in relation to the s retention in the aquifer matrix the dripwater data are used to extend the previously published s record 1810 1998 ad of stalagmite er78 and reconstruct the anthropogenic s peak this displays a delay of 20 years with respect to the atmospheric s emission peak due to biogeochemical cycling and aquifer storage however sulphur recycling above the cave did not operate with the same degree of efficiency through time which resulted in a variable time delay between s deposition and incorporation into the stalagmite in the pre anthropocene era and in particular during the cold little ice age biogeochemical cycling was far less efficient than today and the fast transmission of the atmospheric signal allowed capture of s released during major volcanic eruptions by stalagmites

migration of volcanism in the san francisco volcanic field arizona the remanent magnetization of volcanic rocks has been determined at 650 sites in the san francisco volcanic field in the southern part of the colorado plateau the polarity of remanent magnetization combined with k ar age determinations spatial and petrographic associations stratigraphic relations and state of preservation of the cinder cones provides a basis for assignment to known magnetic polarity epochs of 610 mafic vents and 100 intermediate to silicic flows flow sequences and vents the age assignments for basaltic rocks include 243 brunhes 0 73 ma vents 220 matuyama 0 73 to 2 48 ma vents and 147 pre matuyama 2 48 to about 5 0 ma vents basaltic volcanism migrated northeastward before matuyama time at a rate of 1 2 cm yr and eastward s87 5 e over the past 2 5 m y at a rate of 2 9 0 3 cm yr concomitant acceleration in total magma production from 75 to 1 400 10 6 km3 yr and frequency of basaltic eruptions from 1 per 17 000 yr to 1 per 3 000 yr occurred between 5 and 0 25 ma for the past 0 25 m y magma production 180 10 6 km3 yr and perhaps eruption frequency have decreased this evolutionary sequence coupled with the lead and strontium isotopic composition of the rocks can be explained by magmatism caused by shear heating at the base of the lithosphere we propose that this eastward drift of volcanic activity represents absolute westward motion of the north american plate our model is in agreement with a model in which the african plate is fixed to the deep mantle

a chronology for the dome c deep ice core site through radio echo layer correlation with the vostok ice core antarctica ice at the new dome c drill site is correlated directly with the vostok ice core record using internal radio echo layering in the antarctic ice sheet layering observed on 60 mhz radar records at ice depths greater than 1000 m is a result of electro magnetic wave reflections from acidic ice layers formed it is assumed by volcanic eruption derived aerosols these acidic layers represent isochronous surfaces within the ice sheet we are able to trace five prominent layers for over 500 km across the antarctic ice sheet between vostok and the new ice core site at dome c this correlates the stratigraphy and depth age relationship between the two sites the thickness of ice deposited over the last glacial cycle 120 000 years at dome c is 300 m greater than at vostok and at comparable depths the ice at dome c is between about 10 000 and 25 000 years younger than at vostok

sulfate sources and oxidation chemistry over the past 230 years from sulfur and oxygen isotopes of sulfate in a west antarctic ice core 1 the sulfur and oxygen isotopic composition of sulfate in polar ice cores provides information about atmospheric sulfate sources and formation pathways which have been impacted regionally by human activity over the past several centuries we present decadal scale mean ice core measurements of 17o 34s 33s and 36s of sulfate over the past 230 years from the west antarctic ice sheet wais divide deep ice core drill site wdc05 a the low mean 34s of non sea salt sulfate at wais divide 6 0 0 2 relative to east antarctic coastal and plateau sites may reflect a combination of stronger influence of volcanogenic and or stratospheric sulfate with low 34s and the influence of frost flowers on the sea salt sulfate to sodium ratio 33s and 36s measurements are all within analytical uncertainty of zero but do not contradict a contribution of stratospheric sources to background sulfate deposition at wais divide 17o of non sea salt sulfate shows a small but significant increase between the late 1700s 1 8 0 2 and late 1800s 2 6 0 2 but the influence of stratospheric scale volcanic events on 17o in the early 1800s remains uncertain an isotope mass balance model shows that the lack of change in 17o of non sea salt sulfate from the mid 1800s to early 2000s 2 4 2 6 0 2 is consistent with previous atmospheric chemistry model estimates indicating preindustrial to industrial increases in o3 as high as 50 and decreases in oh of 20 in the southern polar troposphere as long as h2o2 concentrations also increase by over 50

anomalous sulfur isotope compositions of volcanic sulfate over the last millennium in antarctic ice cores 1 the reconstruction of past volcanism from glaciological archives is based on the measurement of sulfate concentrations in ice this method does not allow a proper evaluation of the climatic impact of an eruption owing to the uncertainty in classifying an event between stratospheric or tropospheric this work develops a new method using anomalous sulfur isotope composition of volcanic sulfate in order to identify stratospheric eruptions over the last millennium the advantages and limits of this new method are established with the examination of the 10 largest volcanic signals in ice cores from dome c and south pole antarctica of the 10 seven are identified as stratospheric eruptions among them three have been known to be stratospheric tambora kuwae the 1259 unknown event and they exhibit anomalous sulfur isotope compositions three unknown events circa 1277 1230 1170 a d and the serua eruption have been identified as stratospheric eruptions which suggests for the first time that they could have had significant climatic impact however the kuwae and the 1259 unknown event stratospheric eruptions exhibit different anomalous sulfur isotope compositions between south pole and dome c samples differences in sulfate deposition and preservation patterns between the two sites can help explain these discrepancies this study shows that the presence of an anomalous sulfur isotope composition of volcanic sulfate in ice core indicates a stratospheric eruption but the absence of such composition does not necessarily lead to the conclusion of a tropospheric process because of differences in the sulfate deposition on the ice sheet

tropical ice core records evidence for asynchronous glaciation on milankovitch timescales over the last 28 years ice core records have been systematically recovered from ten high elevation ice fields nine of which are located in the low latitudes each core has provided new information about the regional climate and environmental change and together their records challenge existing paradigms about the earth s climate system when viewed collectively these ice core histories provide compelling evidence that the growth glaciation and decay deglaciation of large ice fields in the lower latitudes are often asynchronous both between the hemispheres and with high latitude glaciation that occurs on milankovitch timescales although stable isotopic records suggest that global scale cooling occurred during the last glacial stage lgs we contend that precipitation is the primary driver of glaciation in the low latitudes this is consistent with the time transgressive nature of precession driven changes in insolation and hence precipitation such that glaciers advance retreat in the tropics north of the equator while glaciers retreat advance in the tropics south of the equator thus the coeval inter hemispheric retreat of glaciers in the 20th century and the beginning of the 21st century is atypical copyright 2005 john wiley sons ltd

evidence of sea ice source in aerosol sulfate loading and size distribution in the canadian high arctic from isotopic analysis the influence of frost flowers and seawater brine on ion chemistry in snow snowpack ice cores and aerosols is detected when a lower sulfate to sodium ratio than in seawater is present in polar regions this evidence can be masked when large amounts of non sea salt sulfate are present from other sources such as biogenic and anthropogenic sulfate frost flower 34s values were measured for the first time in frost flower sulfates and did not differ significantly from the sea salt 34s values of 21 a method using stable isotopes is introduced to determine the limit of contributions from sea salt and sea ice sources including frost flowers and brine on sulfate concentrations in aerosol samples from alert canada knowledge of the range of values of 34snss and the so4 na ratio found in sea ice sources i e frost flowers is used to quantitatively constrain the contributions from frost flowers and sea salt in the arctic aerosol mass during the onset of winter in 2007 and 2008 allowing for quantification of non sea salt sulfate amounts during times when frost flowers are present frost flower and or brine influence was found predominantly in the coarse mode aerosols 0 95 m this method to determine the contributions from sea salt and sea ice sources can be carried over to future studies with snow and ice cores

multiple oxygen 16o 17o and 18o and sulfur 32s 33s 34s and 36s isotope signatures of the dissolved sulfate from deception island antarctic peninsula implications on sulfate formation transportation and deposition in the antarctic region abstract oxygen 16 o 17 o and 18 o and sulfur 32 s 33 s 34 s and 36 s isotope ratios of and major ion na ca 2 cl no 3 and so 4 2 concentrations in lakes ponds and creeks from deception island antarctic peninsula were analyzed to study the sources of sulfate its oxidation and the surficial processes of the dissolved sulfate the positive relationship between the 34 s sulfate 8 1 to 17 3 and the cl so 4 2 molar ratio suggests mixing of sulfate from atmospheric deposition and from oxidation of sulfide minerals the average sea salt fraction 28 and 34 s nss values from 5 6 to 15 9 indicate that a combination of sea salt and marine biogenic sulfide provide the high 34 s end member of the dissolved sulfates the relatively low 18 o sulfate from 4 6 to 0 7 of deception island water suggests a role of local water in the formation of sulfate slightly negative but mass dependent 17 o sulfate values imply that atmospheric oxidation by o 3 and h 2 o 2 are negligible while these values might suggest a significant role of oxidation by molecular oxygen and oh the distinctly low 34 s sulfate value of two samples dcw 2 and dcw 3 suggests the input of sulfate from sulfide oxidation slight elevation of 34 s sulfate values up to 17 3 compared to a typical atmospheric value indicates a minimal role for dissimilatory microbial sulfate reduction of deception island water and sediments both 33 s sulfate and 36 s sulfate values are homogeneous and near zero implying that the dominant atmospheric oxidation process is tropospheric and that there are minimal to no contributions of stratospheric sulfate to deception island water

antarctic dome c ice core dust at 18 k y b p isotopic constraints on origins we have determined the source area from which dusts from the last glacial maximum lgm section of the dome c ice core were derived by comparing their strontium and neodymium isotopic ratios with those of samples from potential source areas the87sr 86sr and143nd 144nd isotope ratios of the dusts deposited 18 k y b p at the east antarctic dome c site were compared with potential antarctic australian southern african and south american sources the isotope ratios clearly define the patagonian provenance of the dust with the other potential source areas being at most minor contributors contributions by volcanic ash and tephra to the dust sample were also determined to be minimal based on the patterns of rare earth elements knowing the source of the dusts places constraints on the aeolian trajectory by which it was transported to antarctica and this serves as a test of the simulation of southern hemispheric circulation by atmospheric global circulation models during the lgm

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

sr and nd isotopic and trace element compositions of quaternary volcanic centers of the southern andes isotopic compositions of samples from six quaternary volcanoes located in the northern and southern extremities of the southern volcanic zone svz 33 46 s of the andes and from four centers in the austral volcanic zone avz 49 54 s range for 87sr 86sr from 0 70280 to 0 70591 and for 143nd 144nd from 0 51314 to 0 51255 the ranges are significantly greater than previously reported from the southern andes but are different from the isotopic compositions of volcanoes in the central and northern andes basalts and basaltic andesites from three centers just north of the chile rise trench triple junction have 87sr 86sr 143nd 144nd la yb ba la and hf lu that lie within the relatively restricted ranges of the basic magmas erupted from the volcanic centers as far north as 35 s in the svz of the andes the trace element and sr and nd isotopic characteristics of these magmas may be explained by source region contamination of subarc asthenosphere with contaminants derived from subducted pelagic sediments and seawater altered basalts by dehydration of subducted oceanic lithosphere in the northern extremity of the svz between 33 and 34 s basaltic andesites and andesites have higher 87sr 86sr rb cs and hf lu and lower 143nd 144nd than basalts and basaltic andesites erupted farther south in the svz which suggests involvement of components derived from the continental crust in the avz the most primitive sample high mg andesite from the southernmost volcanic center in the andes 54 s has sr and nd isotopic compositions and kr b and ba la similar to morb the high la yb of this sample suggests formation by small degrees of partial melting of subducted morb with garnet as a residue samples from centers farther north in the avz show a regionally regular northward increase in sio2 k2o rb ba ba la and 87sr 86sr and decrease in mgo sr kr b rb cs and 143nd 144nd suggesting increasingly greater degrees of fractional crystallization and associated intra crustal contamination

isotopic signatures of sulfur in shallow antarctic ice cores sulfur stable isotopes from antarctic snow samples have been used to assess sources of sulfate the novel experimental procedure presented here is suitable for the determination of sulfur isotopic composition at the micromolar level and has been adapted to polar ice samples measurements were carried out on three contiguous firn cores ps6 ps7 and ps8 collected near amundsen scott station south pole covering the record of the agung eruption march 1963 taking into account the minimum amount of sulfate required for the isotope analysis it has been possible to delineate three time periods along the cores pre 1964 years background sulfate level 1964 1965 volcanic deposition peak and 1966 1968 volcanic peak tail a deeper part of another core ps12 has been used to extend the background picture assuming the conservation of isotopic signatures during long range transport and deposition processes results demonstrate the significant volcanic contribution to sulfate deposition on the central antarctic ice cap a few months after a major low latitude eruption they also confirm the marine biogenic origin of present background sulfate isotopic signatures 34s of marine biogenic sulfate and volcanic sulfate from mt agung have been found to be 18 6 0 9 and 2 7 1 respectively

alteration assemblages in the miller range and elephant moraine regions of antarctica comparisons between terrestrial igneous rocks and martian meteorites the weathering products present in igneous terrestrial antarctic samples were analyzed and compared with those found in the four miller range nakhlite martian meteorites the aim of these comparisons was to determine which of the alteration phases in the miller range nakhlites are produced by terrestrial weathering and what effect rock composition has on these phases antarctic terrestrial samples mil 05031 and eet 96400 along with the miller range nakhlites mil 03346 and 090032 were found to contain secondary alteration assemblages at their externally exposed surfaces despite the difference in primary mineralogy the assemblages of these rocks consist mostly of sulfates jarosite in mil 05031 jarosite and gypsum in eet 96400 and iddingsite like fe clay as neither of the terrestrial samples contains sulfur bearing primary minerals and these minerals are rare in the miller range nakhlites it appears that so42 possibly along with some of the na k and ca in these phases was sourced from wind blown sea spray and biogenic emissions from the southern ocean cl enrichment in the terrestrially derived iddingsite of mil 05031 and mil 03346 and the presence of halite at the exterior edge of mil 090032 can also be explained by this process however jarosite within and around the olivine bound melt inclusions of mil 090136 is present in the interior of the meteorite and therefore is probably the product of preterrestrial weathering on mars

time correlation analysis of the microseismicity of the low eastern flank of mt etna volcano italy an analysis in terms of time correlation functions has been applied to the time distribution of microseismicity we considered the single station detections m 2 recorded by each one of the four working stations of the network of the osservatorio sismologico di protezione civile acireale catania located on the active faults systems timpe of the low eastern flank of mt etna information obtained on the time regularity of seismic crisis and on the time correlation between the activities recorded by different stations allowed a better understanding of the role of the two main structures the timpa di santa tecla is the most seismogenic structure in the area and probably played a role in the magma transfer process for the 1989 eruption modifications of the local stress field by actions of this feature may have produced gravitational instability along a second structural system the timpa di s leonardello with a time delay of about 100 days by contrast magma penetration associated with the larger eruption of 1991 1993 had a deeper rise system and had no effect on local stress conditions consequently there was no correlation between volcanism and seismicity

major element rare earth element and sulfur isotopic composition of a high elevation firn core sources and transport of mineral dust in central asia 1 the arid region extending from the caspian sea into china contains some of the most extensive dust aerosol production areas in the world major element al fe ca and s rare earth element ree and isotopic 34s and 18o data from a 14 4 m long firn core recovered on the inilchek glacier tien shan mountains kyrgyzstan 5100 m elevation are presented and used to investigate the composition sources and transport of mineral dust to this central asian site the combination of geochemical compositions points to three distinct types of mineral deposits loess calcium carbonate and gypsum which do not covary in a linear fashion during the period recorded in the firn core 1992 1998 loess identified by its ree composition is characterized by distinct large scale deposition events and by ubiquitous background deposition at other times significant interannual scale variability is evident with the two largest loess events occurring within a single accumulation year 1997 and background conditions prevailing during 1994 1996 ree compositions specifically nd yb ratios point to multiple sources and transport directions of loess to inilchek glacier nonloess sources provide a significant fraction of the total ca and s deposited at the inilchek glacier hence the downcore profiles of ca and s reflect variability in the deposition of calcium carbonate and gypsum differences in the sulfur isotopic composition 34s of high dust period 15 0 and low background dust period 5 4 samples provide strong evidence for two sources of sulfate the former isotopic composition reflects a marine evaporite source of which there are many to the west of the tien shan mountains the latter composition indicates that a major portion of the atmospheric so42 was derived from anthropogenic emissions while the deposition of non loess ca calcite and non loess s gypsum is also high during the periods of high loess deposition there is pronounced ca and s variability during background loess periods 1994 1996 we suggest that the observed geochemical variability in the firn core can be explained by changes in local to regional scale atmospheric circulation and associated transport from multiple dust sources western kyrgyzstan kazakhstan versus the taklimakan desert china

spatial patterns and seasonal variation of snowpack sulphate isotopes of the prince of wales icefield ellesmere island canada ion chemistry and sulphate isotope values for snow samples from the prince of wales icefield ellesmere island canada show distinct seasonal trends and spatial patterns sixteen surface snow samples from two transects and 30 samples from five depth profiles representing fall 2003 to spring 2004 accumulation have been analyzed surface snow samples show decreasing so4 2 and na concentrations along with decreasing d 34 s values with distance inland and increased elevation these trends follow an expected pattern of decreasing sea salt aerosol impact with greater vertical and horizontal distance from sea water sources depth profile total sulphate and non sea salt sulphate increase in concentration with height in the snowpack and these results combined with d 34 s values that are more positive in fall snow are consistent with increased amounts of anthropogenic sulphate in surface spring snow sulphate apportionment was performed on surface snow assuming an isotopically light sulphate source anthropogenic plus volcanic mixed with isotopically heavier sulphate from dimethylsulphide dms oxidation and sea water isotopically light sulphate in surface snow was apparent at all elevations at a reasonably uniform concentration dms sulphate however decreased exponentially with altitude reflecting an ocean level source with oxidation occurring during transport and deposition the significance to multi year deposition studies is that sulphate from dms oxidation may be related to sea ice conditions in the region

recent glacial recession in the rwenzori mountains of east africa due to rising air temperature based on field surveys and analyses of optical spaceborne images landsat5 landsat7 we report recent decline in the areal extent of glaciers in the rwenzori mountains of east africa from 2 01 0 56 km 2 in 1987 to 0 96 0 34 km 2 in 2003 the spatially uniform loss of glacial cover at lower elevations together with meteorological trends derived from both station and reanalysis data indicate that increased air temperature is the main driver clear trends toward increased air temperatures over the last four decades of similar to 0 5 degrees c per decade exist without significant changes in annual precipitation extrapolation of trends in glacial recession since 1906 suggests that glaciers in the rwenzori mountains will disappear within the next two decades

isotopic archives of sulphate in speleothems the hemispheric impact of industrial emissions upon atmospheric sulphur loading is reflected in the sulphur depositional history recorded in cores from ice sheets however these do not reveal regional variations recently deposited speleothems are used here as archives of regional sulphur depositional history at two locations within the united kingdom and ireland 34s so4 and 18o so4 present within speleothem carbonate are measured for the first time as part of a dual isotope approach to decode the speleothem sulphur record the largely refractory nature of 34s so4 under oxidising conditions enables source provenance of atmospheric so2 whereas the complex cycles of isotopic exchange and fractionation during incorporation of oxygen into sulphate molecules enable 18o so4 signatures to yield insights into ambient environmental conditions and biogeochemical cycling in the ecosystem above the cave 34s so4 values extracted from speleothem carbonate formed within browns folly mine uk range from 3 5 to 5 5 and 18o so4 10 3 to 13 7 both signatures lie within the range expected from sulphate deposition in industrial locations and reflect the transfer of sulphate into speleothem calcite with little fractionation however 18o so4 signatures at crag cave western ireland are isotopically heavier than expected and approach isotopic equilibrium with 18o h2o under reducing conditions dual isotope analysis of 34s so4 and 18o so4 optimises the correct identification of sulphur sources and biogeochemical cycling prior to incorporation into the speleothem record at carefully selected cave sites where drip water flowpaths into the cave remain oxic speleothems hold the potential to retain records of atmospheric sulphur loading at the local and regional scale

delineation of carbonate dust aluminous dust and sea salt deposition in a greenland glaciochemical array using positive matrix factorization 1 high resolution trace element records from polar ice cores are fundamental to identifying spatial and temporal variability in dust and sea salt aerosols here we developed high temporal resolution glaciochemical records over recent centuries from an array of seven recently collected greenland ice cores positive matrix factorization pmf was used to assess apportionment of trace elements between three unique sources which were identified as proxies of carbonate dust aluminous dust and sea salt the three pmf factors agree well with literature values and represent the first time carbonate and aluminous dust sources have been quantifiably differentiated using high resolution glaciochemistry the concentrations of all three sources varied with ice core site however the large array of ice cores provided a regional scale understanding of the sources and magnitude of dust and sea salt impurities deposited on the greenland ice sheet at the regional level all three sources varied on seasonal annual and multiyear timescales the seasonal deposition of sea salt impurities reached a maximum in the winter followed by spring peaks of carbonate and aluminous dust over the 331 year composite record only aluminous dust exhibited a long term increasing trend that peaked in the 1930s and was followed by a 20 decline in recent decades

patagonian origin of glacial dust deposited in east antarctica vostok and dome c during glacial stages 2 4 and 6 abstract the source area of continental dust deposited at both vostok and dome c sites east antarctica during the glacial stages stage 2 18 ka last glacial maximum stage 4 60 ka and stage 6 160 ka of the last two climatic cycles has remained constant the isotopic composition 87 sr 86 sr and 143 nd 144 nd of the ice core dust has been compared with the isotopic composition of the potential source areas antarctica new zealand southern africa australia and south america this comparison reveals the southern south american provenance of the dust for all three glacial periods as has already been shown for the lgm 1 we show that the patagonian loess and the marine shelf sediments from the argentine continental shelf which was variably emerged during glacial periods display different isotopic compositions and that the composition of the patagonian loess best matches the signature of the ice core dust the identification of the patagonian region as the source of the windblown dust deposited over east antarctica during all the latest glacial periods permits a better understanding of paleo atmospheric circulations of the last climatic cycles and a better constraint on the parametrization of dust sources for paleoatmospheric general circulation models

tales of volcanoes and el nino southern oscillations with the oxygen isotope anomaly of sulfate aerosol the ability of sulfate aerosols to reflect solar radiation and simultaneously act as cloud condensation nuclei renders them central players in the global climate system the oxidation of s iv compounds and their transport as stable s vi in the earth s system are intricately linked to planetary scale processes and precise characterization of the overall process requires a detailed understanding of the linkage between climate dynamics and the chemistry leading to the product sulfate this paper reports a high resolution 22 y 1980 2002 record of the oxygen triple isotopic composition of sulfate so4 aerosols retrieved from a snow pit at the south pole observed variation in the o isotopic anomaly of so4 aerosol is linked to the ozone variation in the tropical upper troposphere lower stratosphere via the ozone el nino southern oscillations enso index oei higher 17o values 3 3 4 5 and 4 2 were observed during the three largest enso events of the past 2 decades volcanic events inject significant quantities of so4 aerosol into the stratosphere which are known to affect enso strength by modulating stratospheric ozone levels oei 6 and 17o 3 3 oei 11 and 17o 4 5 and normal oxidative pathways our high resolution data indicated that 17o of sulfate aerosols can record extreme phases of naturally occurring climate cycles such as ensos which couple variations in the ozone levels in the atmosphere and the hydrosphere via temperature driven changes in relative humidity levels a longer term higher resolution oxygen triple isotope analysis of sulfate aerosols from ice cores encompassing more enso periods is required to reconstruct paleo enso events and paleotropical ozone variations

microparticle concentration variations linked with climatic change evidence from polar ice cores the microparticle concentrations in three deep ice cores reveal a substantial increase in the concentration of insoluble particles in the global atmosphere during the latter part of the last major glaciation the ratio of the average particle concentration in the late glacial strata to that in the holocene strata is 6 1 for the core from dome c antarctica 3 1 for the core from byrd station antarctica and 12 1 for the core from camp century greenland whether this temporal correlation between increased atmospheric particle load and the lower surface temperatures is directly causal is unknown however the variations in these two parameters must be satisfactorily resolved in any successful hypothesis that addresses the causes of climatic change

long continental records of climate an introduction abstract the symposium on long continental records presented new information on past climates on land it seems that throughout the last 2 5 million years the climate in the middle latitudes changed in the same complex fashion as during the better known late pleistocene and holocene times over 40 interglacial glacial shifts took place during this interval out of those 40 10 12 glacials were markedly stronger and or longer lasting than the others the apparently abrupt shifts from interglacials to glacials were probably gradual oscillatory coolings interrupted by warming episodes in that respect the detailed anatomy of the past climate changes does not differ substantially from the climate oscillations documented by instrumental weather records in the last two centuries the pronounced expansions of dry and cold steppes on land were accompanied by corresponding increases of the ice volume indicated by the oxygen isotope ratio the two exceptions occurred around 1 4 ma ago and 1 6 ma ago the reason for this discrepancy is not known by far the most expressed change of land environments occurred at about 2 4 ma ago

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

climatic interpretation of the recently extended vostok ice records a new ice core drilled at the russian station of vostok in antarctica reached 2755 m depth in september 1993 at this depth the glaciological time scale provides an age of 260 ky bp 25 we refine this estimate using records of dust and deuterium in the ice and of 18o of o2 in the entrapped air 18o of o2 is highly correlated with insolation over the last two climatic cycles if one assumes that the egt chronology overestimates the increase of age with depth by 12 for ages older than 112 ky bp this modified age depth scale gives an age of 244 ky bp at 2755 m depth and agrees well with the age depth scale of walbroeck et al in press derived by orbital tuning of the vostok d record we discuss the temperature interpretation of this latter record accounting for the influence of the origin of the ice and using information derived from deuterium excess data we conclude that the warmest period of stage 7 was likely as warm as today in antarctica a remarkable feature of the vostok record is the high level of similarity of proxy temperature records for the last two climatic cycles stages 6 and 7 versus stages 1 5 this similarity has no equivalent in other paleorecords

dust transport to dome c antarctica at the last glacial maximum and present day the antarctic polar ice core records show large changes in the concentration of dust over glacial interglacial timescales this paper explores how much of this variation is due to changes in the transport of dust from arid regions to the ice cores back trajectories initialised from the site of dome c ice core antarctica are calculated using an offline trajectory code forced by modelled winds output from the ukmo unified model running under present day and lgm boundary conditions as well as comparing the present day and lgm back trajectories their seasonal and interannual variability is also explored the results suggest that the patagonian provenance of the dome c dust can be understood in terms of the atmospheric transport whereas the total change in dust concentration requires changes to the sources or sinks

mineralogy of insoluble particles in the vostok antarctic ice core over the last climatic cycle 150 kyr mineralogical characterisation of insoluble microparticles entrapped in ice layers successively deposited on the antarctic continent is a useful tool for paleoclimate reconstruction indeed it is likely to provide information on the distribution of potential source areas and of climatic conditions prevailing over different time periods a first study covering the last 30 kyr and including the end of the last glacial age has shown that over central east antarctica continental input was soil derived and originated probably from south america in this work the time period covered is l60 kyrs which includes a complete climate cycle clay species and particle size considerations suggest that local sources and australia have been of minor importance for the studied area over the last 160 kyr they support the hypothesis of colder and drier conditions prevailing over the source areas during glacial extrema lastly the predominance of illite feldspar and quartz in association with presumably weathered volcanic products is consistent with a continental input originating from south america for the east antarctic area but is not in complete agreement with the results of general circulation models

high resolution sulphur isotope analysis of speleothem carbonate by secondary ionisation mass spectrometry sulphur emitted into the atmosphere from industrial activity is regarded as a key mechanism in forcing recent climate and has impacts upon the environment and human health at both local and regional scales trace amounts of sulphate present within speleothem carbonate can be used to provide an emissions inventory for regional sulphur loading to the atmosphere where sulphur isotopes can be extracted and used as a tool for provenance however speleothem sulphur concentrations are low and manual techniques for sulphur isotope analysis allow only low sampling resolution sims secondary ionisation mass spectrometry is used here to develop records of sulphur isotopic change in speleothems from the italian and austrian alps where annual laminae are less than 100 mu m thick analysis at annual resolution over the past 100 years demonstrates an excursion in sulphur isotopic composition from values close to the carbonate bedrock end member composition in the pre industrial era to values isotopically depleted in 34 s this trend is mirrored by increasing concentrations of sulphate and is suggested to reflect the increase in so2 emissions with industrial activity subsequent decline in speleothem sulphate concentrations in one of the stalagmites reflects the recent european decline in industrial atmospheric so2 content and is matched by a rebound in sulphur isotopic composition to values more enriched in 345 superimposed on this general secular trend are smaller annual variations in concentration reflecting cave environmental conditions high magnitude events of short duration potentially reflect volcanic inputs of so2 or the incorporation of dust particulates into the speleothem carbonate this is the first micro analysis of carbonate associated sulphate cas sulphur isotopes by sims sims analysis of delta s 34 so4 in speleothem carbonate reveals a high resolution archive depicting a regional sulphur emissions inventory for so2 loading to the atmosphere c 2010 elsevier b v all rights reserved

geomorphologic proxies for bedrock rivers a case study from the rwenzori mountains east african rift system geomorphic proxies yield useful insights into understanding long term endogenic and exogenic response to erosion and or rock uplift rates by evaluating areal proxies including asymmetry factor af mountain front sinuosity smf hypsometric integral hi geophysical relief and shape factor shp and linear proxies including normalized steepness index ksn length gradient index slk and chi gradient m the erosion and or rock uplift rates can be quantified we carried out morphotectonic analysis in the rwenzori mountains which represents an anomalously uplifted precambrian horst within the western branch of the east african rift system ears this study aims to 1 evaluate the relationship between geomorphic proxies and drainage basin s maturity 2 evaluate the usefulness of geomorphic proxies as recorders of erosion and or rock uplift rates 3 evaluate the sensitivity of each geomorphic proxy to the drainage basin size and geometry stream order glaciers extent and local structures 4 explore internal correlation within the geomorphic proxies and 5 contribute to the understanding of morphotectonic evolution of the rwenzori mountains for this we computed the stream s good of fitness r2 an indicator of the drainage basin s maturity and geomorphic proxies for the drainage basins and their streams in the rwenzori mountains from the advanced spaceborne thermal emission and reflection radiometer aster digital elevation model dem subsequently we correlated the areal geomorphic proxies with each other and with r2 also we correlated the linear geomorphic proxies with each other and with published erosion rates obtained from cosmogenic 10be analysis our results show that the areal geomorphic proxies af smf hi relief and shp considering the drainage basin size and geometry stream order glacier extent and local structures can be applied to locally evaluate the maturity of the drainage basin we also found that the linear geomorphic proxies ksn slk and m have strong positive correlation with the erosion rates they are effective in detecting fault activities and some of them ksn and m are highly correlated with each other additionally our geomorphic proxy results suggest that the north and south sectors of the rwenzori mountains are in relative tectonic quiescence but that the central sector is experiencing higher levels of erosion and rock uplift

east antarctic ice core sulfur isotope measurements over a complete glacial interglacial cycle 1 both sulfur and oxygen isotopes of sulfate preserved in ice cores from greenland and antarctica have provided information on the relative sources of sulfate in the ice and their chemical transformation pathways in the atmosphere over various time periods the mass independent fractionation in the oxygen isotopes of sulfate from the vostok ice core from east antarctica suggests that gas phase oxidation by the hydroxyl radical oh was relatively greater than aqueous phase oxidation by o3 and h2o2 during the last glacial period than during the eemian and preindustrial holocene the complete sulfur isotopic composition 33s 34s 36s from the same vostok ice core samples along with 34s measurements from the dome c east antarctic ice core from this study lend support to these conclusions and reveal significant isotopic fractionation of 34s during chemical transformation and transport to east antarctica these findings reveal that conservation of sulfur isotopic signatures upon transport cannot be assumed for the east antarctic plateau over the time periods considered

the oxygen cycle of the terrestrial planets insights into the processing and history of oxygen in surface environments physical and chemical processes that operate at low temperature in earth s surface environments and in other planetary settings have left an indelible record of the evolution and interactions of planetary surface and near surface reservoirs this chapter reviews the chemistry of oxygen elemental and isotopic in lunar planetary and earth surface reservoirs the discussion begins with a brief review of the relative abundances of oxygen isotopes in planetary materials including lunar samples the snc martian meteorites and components that are inferred to come from martian surface pools this is followed by a brief largely historical account of the development of oxygen isotope geochemistry in earth surface materials the discussion then transitions using an earth systems perspective into an overview of developments in oxygen isotope geochemistry of atmospheric compounds this treatment includes recent studies that 1 use high precision measurements of 17 o and 18 o to characterize atmospheric oxygen 2 apply information about isotopically substituted species isotopologs for characterizing the position dependent isotopic fractionations of some oxygen bearing atmospheric species and 3 investigate non mass dependent isotopic fractionations in ozone and other atmospheric species the discussion then examines the evidence and models that point to change in the oxygen cycle and oxidation chemistry in earth surface environments over the course of geologic time we use the subdivisions of the earth systems the hydrosphere geosphere and biosphere as a basis for examining these changes this record is explored in the context of hypotheses and data that relate to the nature of the changes and transformations in the oxidation state of these different components of the earth s surface environments we conclude with a brief accounting of areas of research where scientifi c inquiry is presently very active

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

so2 photoexcitation mechanism links mass independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism natural climate variation such as that caused by volcanoes is the basis for identifying anthropogenic climate change however knowledge of the history of volcanic activity is inadequate particularly concerning the explosivity of specific events some material is deposited in ice cores but the concentration of glacial sulfate does not distinguish between tropospheric and stratospheric eruptions stable sulfur isotope abundances contain additional information and recent studies show a correlation between volcanic plumes that reach the stratosphere and mass independent anomalies in sulfur isotopes in glacial sulfate we describe a mechanism photoexcitation of so2 that links the two yielding a useful metric of the explosivity of historic volcanic events a plume model of s iv to s vi conversion was constructed including photochemistry entrainment of background air and sulfate deposition isotopologue specific photoexcitation rates were calculated based on the uv absorption cross sections of 32so2 33so2 34so2 and 36so2 from 250 to 320 nm the model shows that uv photoexcitation is enhanced with altitude whereas mass dependent oxidation such as so2 oh is suppressed by in situ plume chemistry allowing the production and preservation of a mass independent sulfur isotope anomaly in the sulfate product the model accounts for the amplitude phases and time development of 33s 34s and 36s 33s found in glacial samples we are able to identify the process controlling mass independent sulfur isotope anomalies in the modern atmosphere this mechanism is the basis of identifying the magnitude of historic volcanic events

hazard area and recurrence rate time series for determining the probability of volcanic disruption of the proposed high level radioactive waste repository at yucca mountain nevada usa the post 12 ma volcanism at yucca mountain ym nevada a potential site for an underground geologic repository of high level radioactive waste in the usa is assumed to follow a poisson process and is characterized by a sequence of empirical recurrence rate time series the last ten time series are used as a prediction set to check the predictive ability of the candidate model produced by a training sample using autoregressive integrated moving average modeling techniques the model is used to forecast future recurrence rates that in turn are used to develop a continuous mean function of the volcanic process which is not only required to evaluate the probability of site disruption by volcanic activity but accommodates a long period of compliance at the model validation stage our candidate model forecasts a mean number of 6 196 eruptions for the prediction set which accounts for seven volcanic events of the 33 post 12 ma eruptions at the ym site for a full scaled forecasting our fitted model predicts a waning volcanism producing only 3 296 new eruptions in the next million years we then present the site disruption probability as the chance that a new eruption will occur in the hazard area based on a model developed for licensing commercial space launch and reentry operations in the space transportation industry the results of the site disruption probability and sensitivity analysis are summarized with a numerical table generated from a simple equation sufficient for practical use we also produce three dimensional plots to visualize the nonlinearity of the intensity function associated with the underlying model of a nonhomogeneous poisson process and emphasize that the interpretation of site disruption probability should always be accompanied by a compliance period

first sulfur isotope measurements in central greenland ice cores along the preindustrial and industrial periods 1 sulfur isotopes of sulfate have been measured in a discontinuous set of polar ice core samples from summit central greenland covering the preindustrial from the fourteenth to the eighteenth century and industrial from 1872 to 1969 a d periods results have been used to estimate the different source contributions to the deposited sulfate and their evolution along the last centuries they indicate that the preindustrial background sulfate budget is slightly dominated on a year round average by marine biogenic emissions amounting to close to half of the non sea salt sulfate 49 the second contribution is provided by continental sources of secondary sulfate including background volcanism and to a lesser extent continental biota 44 of the non sea salt sulfate sulfur emitted by relatively weak eruptions is found to be largely depleted in 34s compared to bulk volcanic s suggesting an efficient washout of the heavier isotope during the tropospheric transport the impact of human driven emissions on the sulfate deposited in central greenland ice is visible in isotope data as early as 1870 a d the isotopic signature of anthropogenic sulfur deposited during the twentieth century is found to be constant 34s 3 0 1 5 regardless of the changes of dominant source regions and emission processes this signature is slightly but measurably lighter than the one reported for arctic haze pollution events

the first greenland ice core record of methanesulfonate and sulfate over a full glacial cycle methanesulfonate msa in ice cores has attracted attention as a possible tracer of past oceanic emissions of dimethylsulfide dms after sulfate msa is the second most prevalent aerosol oxidation product of dms but in contrast to sulfate dms oxidation is the only known source of msa the hypothesis by charlson et al 1987 of a climate feedback mechanism with sulfur emissions from marine phytoplankton influencing the cloud albedo adds to the interest in establishing long records of msa and non seasalt sulfate spanning large climatic changes records of msa and non seasalt sulfate covering time periods from a few years to thousands of year have been extracted from antarctic ice cores ivey et al 1986 saigne and legrand 1987 legrand and feniet saigne 1991 mulvaney et al 1992 but only the record from the vostok ice core legrand et al 1991 covers a full glacial cycle the concentrations of msa and non seasalt sulfate in antarctica have been found to increase under glacial conditions here we present the first northern hemisphere record of msa and the first continuous record of non seasalt sulfate both extracted from the renland ice core east greenland the records are extending from the holocene to the eem interglacial 130 000 years b p the contrast to the southern hemisphere records is striking with a decreasing concentration of msa with the advance of glaciation but an increasing concentration of non seasalt sulfate a strong linear relationship is found in the renland ice core between the ratio of msa to non seasalt sulfate and the temperature with higher ratios associated with warmer climatic stages while the opposite relationship to temperature is found in the vostok ice core a more complicated picture is emerging of the use of msa in ice cores as a quantitative tracer which suggests that previous interpretations can have been overly simplistic

rare sulfur and triple oxygen isotope geochemistry of volcanogenic sulfate aerosols we present analyses of stable isotopic ratios 17 o 16 o 18 o 16 o 34 s 32 s and 33 s 32 s 36 s 32 s in sulfate leached from volcanic ash of a series of well known large and small volcanic eruptions we consider eruptions of mt st helens washington 1980 1 km 3 mt spurr alaska 1953 1 km3 gjalp iceland 1996 1998 1 km 3 pinatubo phillipines 1991 10 km 3 bishop tuff long valley california 0 76 ma 750 km 3 lower bandelier tuff toledo caldera new mexico 1 61 ma 600 km 3 and lava creek and huckleberry ridge tuffs yellowstone wyoming 0 64 ma 1000 km 3 and 2 04 ma 2500 km 3 respectively this list covers much of the diversity of sizes and the character of silicic volcanic eruptions particular emphasis is paid to the lava creek tuff for which we present wide geographic sample coverage this global dataset spans a significant range in 34 s 18 o and 17 o of sulfate 29 30 and 3 3 respectively with oxygen isotopes recording mass independent 17 o 0 2 and sulfur isotopes exhibiting mass dependent behavior products of large eruptions account for most of these isotopic ranges sulfate with 17 o 0 2 is present as 1 10 m gypsum crystals on distal ash particles and records the isotopic signature of stratospheric photochemical reactions sediments that embed ash layers do not contain sulfate or contain little sulfate with 17 o near 0 suggesting that the observed sulfate in ash is of volcanic origin mass dependent fractionation of sulfur isotopic ratios suggests that sulfate forming reactions did not involve photolysis of so2 like that inferred for pre 2 3 ga sulfates from archean sediments or antarctic ice core sulfate associated with few dated eruptions even though the sulfate sulfur isotopic compositions reflect mass dependent processes the products of caldera forming eruptions display a large 34 s range and exhibit fractionation relationships that do not follow the expected equilibrium slopes of 0 515 and 1 90 for 33 s 32 s vs 34 s 32 s and 36 s 32 s vs 34 s 32 s respectively the data presented here are consistent with modification of a chemical mass dependent fractionation of sulfur isotopes in the volcanic plume by either a kinetic gas phase reaction of volcanic so 2 with oh and or a rayleigh processes involving a residual rayleigh reactant volcanic so 2 gas rather than a rayleigh product these results may also imply at least two removal pathways for so 2 in volcanic plumes above zero 17 o values and their positive correlation with 18 o in sulfate can be explained by oxidation by high 18 o and high 17 o compounds such as ozone and radicals such as oh that result from ozone break down large caldera forming eruptions have the highest 17 o values and the largest range of 18 o which can be explained by stratospheric reaction with ozone derived oh radicals these results suggest that massive eruptions are capable of causing a temporary depletion of the ozone layer such depletion may be many times that of the measured 3 8 depletion following 1991 pinatubo eruption if the amount of sulfur dioxide released scales with the amount of ozone depletion

isotopic composition of sulfur in size resolved marine aerosols above the atlantic ocean sulfur isotope measurements were performed on size segregated aerosols collected during the albatross oceanographic campaign from 61 n to 35 s above the atlantic ocean in october and november 1996 results obviously showed the dependence of the sulfur isotope ratio upon particle size the finest particles being depleted in 34s compared to coarse particles suggesting a heavier continental influence in the fine mode in the coarse mode 50 90 of the excess sulfate in both hemispheres was found to be of biogenic origin in the fine mode a different picture was obtained in the northern hemisphere the contribution of biogenic sulfur was found to be less than 35 of the excess sulfur even in relatively clean air masses on the other hand in the southern hemisphere the participation of biogenic sulfur was about 60 of the excess sulfur in purely marine air the contribution of continental sulfur to the fine fraction in the southern hemisphere was up to 40 25 even under pure oceanic conditions and far more in the northern hemisphere these results attest to the possible importance of long range transport of fine sulfate particles or so2 possibly through the free troposphere or the importance of anthropogenic emissions due to shipping

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

a 150 000 year climatic record from antarctic ice during much of the quaternary the earth s climate has undergone drastic changes most notably successive glacial and interglacial episodes the past 150 kyr includes such a climatic cycle the last interglacial the last glacial and the present holocene interglacial a new climatic time series for this period has been obtained using 18 o data from an antarctic ice core

primary aerosol sea salt and soil dust deposited in greenland ice during the last climatic cycle comparison with east antarctic records ion chromatography data of ca mg cl and ca and coulter counter particle measurements are used to study the cycle of marine and continental primary aerosol reaching greenland in relation to climatic changes over the last 150 kyr a detailed comparison between greenland dome summit and antarctic vostok records provides new insight on a potential link between northern and southern patterns ca is a good indicator of continental input and is mainly emitted as caco3 an attempt is made to estimate the contribution of aluminosilicates using the concentration of insoluble particles greater than 0 5 m in diameter the relative abundance of non sea salt mg and ca and of aluminosilicate shows that the calcium content of continental background aerosol over greenland was much higher during the glacial age the neutralization capacity of carbonaceous aerosol is estimated the inverse relationship between 18o and continental input as well as the response of this input to the rapid climatic variations that have occurred during the second part of the glacial age are discussed in terms of source and transport modification in relation to the presence and the extent of the great laurentide ice cap the corresponding vostok profiles strongly suggest that some of the phenomena observed at high northern latitudes are of global concern the marine component of na nam is a good tracer of sea salt aerosol similarly to continental input it shows an inverse but more linear relationship with 18o the sensitivity of greenland and antarctic marine input to climate variations of small and large amplitude is compared and a corresponding estimation is made for the aeolian contribution the respective influence of atmospheric circulation and the water vapor cycle is discussed the chlorine to marine sodium weight ratio increases with temperature from values very close to the bulk seawater ratio during the last glacial maximum 18 20 kyr b p to values significantly higher during the holocene and warm eemian the corresponding excess of chloride hcl is discussed in terms of atmospheric transport taking into account the role of atmospheric acidity on sea salt fractionation processes owing to postdepositional phenomena similar vostok data must be considered cautiously nevertheless aerosol fractionation seems to have been much more important over the vostok site except during glacial extrema

ground satellite observations and atmospheric modeling of dust storms originating in the high puna altiplano deserts south america implications for the interpretation of paleo climatic archives 1 this study provides a detailed description of the sources transport dispersion and deposition of two major dust events originating from the high altitude subtropical puna altiplano plateau 15 26 s 65 69 w in south america a long and severe drought provided the right conditions for the onset of both events in july 2009 and 2010 dust was transported se and deposited over the pampas region and was observed to continue to the atlantic ocean dust monitoring stations located downwind recorded both events and samples were characterized through chemical and textural analysis through a combination of meteorological data and satellite observations calipso and modis detectors we estimate the emission flux for the 2010 event this estimate was used to constrain the hybrid single particle lagrangian integrated trajectory hysplit transport model and simulate the dust event both satellite imagery and model results agree in the location and extension of the dust cloud calipso detected dust between 6000 and 8500 m a s l which remained at this height during most of its trajectory the dust cloud mixed with a strong convective system in the region and the associated precipitation brought down significant amounts of dust to the ground dust particle size analysis for both events indicates that near the sources dust samples show median modes of 12 4 14 1 m similar to modes observed 1300 km away chemical composition of sediments from potential dust sources shows distinct signatures within the puna altiplano plateau the puna sector being clearly different from the altiplano area in addition both sources are markedly different from the patagonian chemical fingerprint these results have important implications to improve the interpretation of paleo environmental archives preserved on the argentine loess antarctic ice cores and southern ocean marine sediments

changes in continental and sea salt atmospheric loadings in central greenland during the most recent deglaciation model based estimates by fitting a very simple atmospheric impurity model to high resolution data on ice accumulation and contaminant fluxes in the gisp2 ice core we have estimated changes in the atmospheric concentrations of soluble major ions insoluble particulates and 10 be during the transition from glacial to holocene conditions for many species changes in concentration in the ice typically overestimate atmospheric changes and changes in flux to the ice typically underestimate atmospheric changes because times of increased atmospheric contaminant loading are also times of reduced snowfall the model interpolates between the flux and concentration records by explicitly allowing for wet and dry deposition processes compared to the warm preboreal that followed we estimate that the atmosphere over greenland sampled by snow accumulated during the younger dry as cold event contained on average four seven times the insoluble particulates and nearly seven times the soluble calcium derived from continental sources and about three times the sea salt but only slightly more cosmogenic 10 be

paleoclimatic tracers an investigation using an atmospheric general circulation model under ice age conditions 2 water isotopes the linear relationship observed between the water isotopic contents of precipitation and surface air temperatures leads to the use of the water isotopes h218o and hdo in paleoclimatology applied to the measurements of the isotopic content of paleowaters like groundwaters and deep ice cores this relationship is used to infer paleotemperatures however this interpretation of paleo isotopic contents is only valid if the isotope temperature relationship is not affected by climate change to address this problem we have developed a water isotope modeling inside an atmospheric general circulation model agcm and performed simulations of both the present day and last glacial maximum lgm climatic conditions agcms are indeed the only appropriate tools able to account the whole complexity of the atmospheric circulation for the present day climate preliminary results for january were presented by joussaume et al 1984 and are complemented by new simulations performed for both february and august climatic conditions with a higher resolution version of the model model results are well corroborated by observations they also exhibit some effects of the atmospheric circulation on the isotopic fields for the simulated lgm climate the model results compare well with paleoclimatic data of water isotopic contents except for a higher than observed spatial variability the overall patterns of the simulated 18o temperature relationship for the lgm climate are practically unchanged which tends to comfort the use of water isotopes in paleoclimatology however concerning the deuterium excess i e the relationship between oxygen 18 and deuterium the model results are not sufficiently valid to allow a discussion of the use of deuterium excess in paleoclimatology

sources of aerosol sulphate at alert apportionment using stable isotopes from july 1993 to september 1994 seasonal variations in the sources of so42 aerosols in the arctic lower atmosphere at alert canada 82 30 n 62 20 w were investigated using the sulphur isotope abundance of as little as 10 g of sulphur analyzed by combustion flow isotope ratio mass spectrometry in conjunction with air mass trajectories and in parallel with measurements of aerosol composition the sulphur isotope composition was used to discern sources of aerosol so42 total so42 is composed of sea salt so42 marine biogenic and nonmarine so42 from june through september the fraction of biogenic so42 in the non sea salt nss component ranged from 0 09 to 0 40 with an average of 0 31 0 11 summertime nonmarine so42 is likely anthropogenic in origin since it is isotopically indistinguishable from so42 in the polluted winter spring period of arctic haze 34s 5 in summer there was no significant difference in isotope composition of aerosol sulphate between air which recently traversed eurasia and the arctic ocean and air arriving from north america in contrast to summer and late winter spring 34s values for nonmarine so42 in fall and early winter were often less than 5 these isotopically light samples were divisible into two groups 1 those associated with air mass trajectories potentially affected by north american soils and or smelters and 2 three weekly samples between october and december which could be attributed to fractionated sea salt aerosol formed on refrozen arctic ocean leads for the latter the ratio of so42 na was estimated to be a factor of 3 6 lower than in bulk seawater from november to may nonmarine aerosol so42 was apportioned into 10 aerosol components using positive matrix factor analysis of 18 aerosol ions and trace elements sirois and barrie this issue in turn a multiple linear regression of 34s values against the scores of the components was used to predict the isotope composition of six components it was concluded that the main mass of anthropogenic so42 had a 34s value near 5 and that biogenic so42 had a 34s of 16 3 9 reasonable agreement between model results and sulphur isotope measurements at alert show that so42 apportionment using positive matrix factor analysis is a reasonable approach which gives realistic results

k ar dating of the cima volcanic field eastern mojave desert california late cenozoic volcanic history and landscape evolution thirty four k ar ages and supporting paleomagnetic measurements from flows of the cima volcanic field provide a detailed volcanic history and a temporal basis for analysis of evolving landforms the cima field has undergone three periods of volcanic activity spanning late miocene through latest pleistocene time 1 7 6 to 6 5 2 4 5 to 3 6 and 3 1 0 to at least 0 015 m y ago these precisely dated sequences afford a unique opportunity to quantify the long term effects of pedogenesis and erosion on volcanic landforms in an arid environment morphologic and pedologtc data indicate that the most stable geomorphic surfaces in the field occur on flows between 0 25 and 0 75 m y old younger flows are dominated by eolian aggradation and outcrop rubbling and older flows are dominated by surface runoff and fluvial dissection a process response model involving progressive pedogenesis and a subsequent shift from infiltration to surface runoff is proposed to explain this temporal variation in land surface stability