thermochronological investigation of fault zones abstract the timing of faulting episodes can be constrained by radiometric dating of fault zone rocks fault zone material suitable for dating is produced by tectonic processes such as 1 fragmentation of host rocks followed by grain size reduction and recrystallization to form mica and clay minerals 2 secondary heating melting of host rocks by frictional fault motions and 3 mineral vein formation as a result of fluid advection associated with the fault motions the thermal regime of fault zones consists primarily of the following three factors a regional geothermal structure across the fault zone and background thermal history of studied province bounded by fault systems b frictional heating of wall rocks by fault motions and c heating of host rocks by hot fluid advection in and around the fault zone thermochronological methods widely applied in fault zones are k ar 40ar 39ar fission track and u th methods for which methodological principles as well as analytical procedures are briefly described the thermal sensitivities of individual thermochronological systems are then reviewed which critically control the response of each method against the thermal processes based on the knowledge above representative examples as well as key issues are highlighted to date fault gouges pseudotachylytes mylonites and carbonate veins placing new constraints upon geological geomorphological and seismological frames finally the nojima fault is presented as an example for multiple applications of thermochronological methods in a complex fault zone

timing of millennial scale climate change at siple dome west antarctica during the last glacial period using atmospheric methane and the isotopic composition of o2 as correlation tools we place the dd record of ice from the siple dome west antarctica ice core on a precise common chronology with the gisp2 greenland ice core for the period from 9 to 57 ka the onset of major millennial warming events in siple dome preceded major abrupt warmings in greenland and the pattern of millennial change at siple dome was broadly similar though not identical to that previously observed for the byrd ice core also in west antarctica the addition of siple dome to the database of well dated antarctic paleoclimate records supports the case for a coherent regional pattern of millennial scale climate change in antarctica during much of the last ice age and glacial interglacial transition

north sea rift system abstract the mesozoic north sea rift forms an integral part of the arctic north atlantic rift system rifting activity in the north sea commenced during the earliest triassic during the mid jurassic the central north sea underwent a temporary doming stage crustal extension peaked during the late jurassic earliest cretaceous abated subsequently and terminated altogether during the paleocene the saucer shaped cenozoic post rift basin straddles the axis of the viking and central grabens this speaks for the applicability of a depth dependent pure shear model rather than a simple shear model geophysical data indicate an important discrepancy between upper and lower crustal attenuation across the north sea rift suggesting that during rifting processes the mono discontinuity was seriously destabilized this requires a basic modification of currently favoured crustal stretching models

in situ cosmogenic radiocarbon production and 2 d ice flow line modeling for an antarctic blue ice area surface 14 c activity that differs by up to 25 from the activity calculated using an ablation only approximation which is used in all prior work and 3 that at high ablation margin sites solar modulation of the cosmic ray flux may change the strength of the dominant spallogenic production by up to 10 as part of this effort we model twodimensional ice flow along the central flow line of taylor glacier we present two methods for parameterizing vertical strain rates and assess which method is more reliable for taylor glacier finally we present a sensitivity study from which we conclude that uncertainties in published cosmogenic production rates are the largest source of potential error the results presented here can inform ongoing and future 14 c and ice flow studies at ice margin

pleistocene ice and paleo strain rates at taylor glacier antarctica ice exposed in ablation zones of ice sheets can be a valuable source of samples for paleoclimate studies and information about long term ice dynamics we report a 28 km long stable isotope sampling transect along a flowline on lower taylor glacier antarctica and show that ice from the last glacial period is exposed here over tens of kilometers gas isotope analyses on a small number of samples confirm our age hypothesis these chronostratigraphic data contain information about past ice dynamics and in particular should be sensitive to the longitudinal strain rate on the north flank of taylor dome averaged over millennia the imprint of climatic changes on ice dynamics may be discernible in these data

k ar illite age constraints on the proterozoic formation and reactivation history of a brittle fault in fennoscandia k ar ages of authigenic illite from two drill core gouge samples of a fault in the palaeoproterozoic basement of finland record two distinct faulting events the older sample yields apparent ages from 1240 26 to 1006 21 ma for four grain size fractions between 6 and 0 1 m the second sample is structurally younger and yields statistically distinct ages ranging from 978 20 to 886 18 ma we interpret the ages of the 0 1 m fractions which are the youngest as representing the actual time of faulting xrd analysis and age modelling exclude significant age contamination of the finest dated fractions with inherited host rock components these results provide therefore an example of meaningful isotopic dating of illite type clay material formed during precambrian faulting demonstrate and constrain fault reactivation and give evidence for brittle sveconorwegian mesoproterozoic shortening and neoproterozoic extension in fennoscandia

on the origin and timing of rapid changes in atmospheric methane during the last glacial period we present high resolution records of atmospheric methane from the gisp2 greenland ice sheet project 2 ice core for four rapid climate transitions that occurred during the past 50 ka the end of the younger dryas at 11 8 ka the beginning of the bolling allerod period at 14 8 ka the beginning of interstadial 8 at 38 2 ka and the beginning of interstadial 12 at 45 5 ka during these events atmospheric methane concentrations increased by 200 300 ppb over time periods of 100 300 years significantly more slowly than associated temperature and snow accumulation changes recorded in the ice core record we suggest that the slower rise in methane concentration may reflect the timescale of terrestrial ecosystem response to rapid climate change we find no evidence for rapid massive methane emissions that might be associated with large scale decomposition of methane hydrates in sediments with additional results from the taylor dome ice core antarctica we also reconstruct changes in the interpolar methane gradient an indicator of the geographical distribution of methane sources associated with some of the rapid changes in atmospheric methane the results indicate that the rise in methane at the beginning of the bolling allerod period and the later rise at the end of the younger dryas were driven by increases in both tropical and boreal methane sources during the younger dryas a 1 3 ka cold period during the last deglaciation the relative contribution from boreal sources was reduced relative to the early and middle holocene periods

microstructurally constrained versus bulk fault gouge k ar dating abstract structural mineralogical and geochronological data were collected from two brittle fault zones fault i and ii deforming the ordovician rolvsnes granodiorite in sw norway microstructurally constrained k ar data from cohesive damage zone samples are compared to bulk k ar data from fault gouges from the adjacent fault cores in fault i fluid ingress along the fault core caused pervasive alteration of the host granodiorite plagioclase and biotite are almost completely altered to kaolinite quartz illite and smectite in fault ii a complex deformation history is recorded by multiple fault rock microdomains including an ultracataclasite with 50 authigenic illite and an illite jarosite bearing pseudotachylyte microdomains hosting authigenic illite jarosite from both studied faults were separated characterized mineralogically and dated by k ar results confirm that each domain contains only one generation of authigenic illite jarosite and provide robust time constraints on fault initiation in the carboniferous 339 8 ma and reactivation in the permian 289 6 ma k ar geochronology of the adjacent fault gouges yields inclined age versus grain size relationships the ages of the coarsest grain size fractions are similar to the age range of the damage zone data whereas the ages of the finer fractions are significantly younger our study provides new and important insights into the dynamics of long lived fault zones isotopic signatures and structural features representative of fault initiation are preserved in the damage zones while they are progressively overprinted due to cumulative strain localization in the fault cores finally our study further clarifies the significance of age plateaus in age versus grain size plots which allows for a robust and geologically meaningful interpretation of k ar data

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

evidence of microbial consortia metabolizing within a low latitude mountain glacier carbon dioxide co 2 nitrous oxide n 2 o and methane ch 4 concentrations of ice samples from a south american mountain glacier are larger than those in coeval polar ice cores of the six possible mechanisms that may cause the composition of air measured in ice cores to depart from that of the overlying troposphere gravitational fractionation thermal fractionation gases trapped in refrozen meltwater atmospheric heterogeneity abiotic chemical reactions and biologically mediated chemical reactions only metabolism of a consortium of microorganisms within the ice can explain our data

early carboniferous unroofing in western norway a tale of alkali feldspar thermochronology abstract 40ar 39ar thermochronologic data from an extensional detachment zone in western norway document punctuated late paleozoic through mesozoic tectonothermal activity diffusion and thermal modeling of alkali feldspars sampled in a profile through the detachment replicate laboratory argon release patterns when feldspars comprise three or four diffusion domains with differing activation energies that represent high intermediate and low closure temperatures these domains correspond to distinct changes in late paleozoic cooling rates 1 slow cooling at 0 4 2 2 c m yr from ca 380 360 ma 2 rapid cooling at 15 c m yr in late devonian early carboniferous time 360 340 ma 3 slow cooling at 0 4 1 7 c m yr after ca 340 ma with partial argon loss in permian and late jurassic early cretaceous times the early carboniferous rapid cooling event recorded by the feldspars links the western norway margin to contemporaneous unconformities regional extension basin inversion and igneous activit

radiometric 81kr dating identifies 120 000 year old ice at taylor glacier antarctica we present successful 81kr kr radiometric dating of ancient polar ice krypton was extracted from the air bubbles in four 350 kg polar ice samples from taylor glacier in the mcmurdo dry valleys antarctica and dated using atom trap trace analysis atta the 81kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 2 5 ka our experimental methods and sampling strategy are validated by i 85kr and 39ar analyses that show the samples to be free of modern air contamination and ii air content measurements that show the ice did not experience gas loss we estimate the error in the 81kr ages due to past geomagnetic variability to be below 3 ka we show that ice from the previous interglacial period marine isotope stage 5e 130 115 ka before present can be found in abundance near the surface of taylor glacier our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available greatly enhancing their scientific value as archives of old ice and meteorites at present atta 81kr analysis requires a 40 80 kg ice sample as sample requirements continue to decrease 81kr dating of ice cores is a future possibility

illite and hydrocarbon exploration illite is a general term for the dioctahedral mica like clay mineral common in sedimentary rocks especially shales illite is of interest to the petroleum industry because it can provide a k ar isotope date that constrains the timing of basin heating events it is critical to establish that hydrocarbon formation and migration occurred after the formation of the trap anticline etc that is to hold the oil illite also may precipitate in the pores of sandstone reservoirs impeding fluid flow illite in shales is a mixture of detrital mica and its weathering products with diagenetic illite formed by reaction with pore fluids during burial k ar ages are apparent ages of mixtures of detrital and diagenetic end members and what we need are the ages of the end members themselves this paper describes a methodology based on mineralogy and crystallography for interpreting the k ar ages from illites in sedimentary rocks and for estimating the ages of the end members

patterns of mineral transformations in clay gouge with examples from low angle normal fault rocks in the western usa abstract neoformed minerals in shallow fault rocks are increasingly recognized as key to the behavior of faults in the elasto frictional regime but neither the conditions nor the processes which wall rock is transformed into clay minerals are well understood yet understanding of these mineral transformations is required to predict the mechanical and seismogenic behavior of faults we therefore present a systematic study of clay gouge mineralogy from 30 outcrops of 17 low angle normal faults lanf s in the american cordillera to demonstrate the range and type of clay transformations in natural fault gouges the sampled faults juxtapose a wide and representative range of wall rock types including sedimentary metamorphic and igneous rocks under shallow crustal conditions clay mineral transformations were observed in all but one of 28 faults one fault contains only mechanically derived clay rich gouge which formed entirely by cataclasis clay mineral transformations observed in gouges show four general patterns 1 growth of authigenic 1m d illite either by transformation of fragmental 2m 1 illite or muscovite or growth after the dissolution of k feldspar illitization of fragmental illite smectite is observed in lanf gouges but is less common than reported from faults with sedimentary wall rocks 2 retrograde diagenesis of an early mechanically derived chlorite rich gouge to authigenic chlorite smectite and saponite mg rich tri octahedral smectite 3 reaction of mechanically derived chlorite rich gouges with mg rich fluids at low temperatures 50 150 c to produce localized lenses of one of two assemblages sepiolite saponite talc lizardite or palygorskite chlorite quartz and 4 growth of authigenic di octahedral smectite from alteration of acidic volcanic wall rocks these transformation groups are consistent with patterns observed in fault rocks elsewhere the main controls for the type of neoformed clay in gouge appear to be wall rock chemistry and fluid chemistry and temperatures in the range of 60 180 c

k ar illite and apatite fission track constraints on brittle faulting and the evolution of the northern norwegian passive margin abstract determining the timing of post caledonian brittle faulting in northern norway is important for the understanding of the extensional tectonic evolution of the north norwegian continental margin fault gouges from the troms and vesteralen regions of northern norway yield carboniferous to permian and carboniferous to cretaceous k ar illite ages respectively the results show a contrast in fault activity and exhumation between the troms and the vesteralen regions while major faulting in the troms region appears to have ceased after the permian faulting event faulting continued into at least the cretaceous in the vesteralen region the findings highlight the importance of a widespread permian tectonic event followed by a distinct southwestward migration of post permian tectonic activity on the north norwegian passive margin late triassic to early jurassic apatite fission track ages do not show significant age offsets across major fault zones in troms indicating that most or all of fault activity took place prior to the late triassic the thermal history models are consistent and indicate continuous cooling to about 60 c in the late permian triassic

the k ar and 40ar 39ar methods revisited for dating fine grained k bearing clay minerals abstract the strengths and weaknesses of the two ar isotopic methods k ar and 40ar 39ar were evaluated on the basis of respective recent applications mainly on low temperature k bearing illite type clay minerals this review includes a presentation of basic analytical and technical aspects for both methods as well as a discussion of varied claims on the two methods and of requests about sample preparation and characterization whenever possible the advantages and weaknesses of each method were compared on coeval results obtained by both methods on the same mineral separates the comparative review examines stratigraphic dating of glauconites indirect dating of low temperature ore deposits dating of burial related illitization and dating of polyphased tectono thermal activity more specifically of fault gouges some pending questions such as the necessary encapsulation due to 39ar recoil and its restoration into step heating patterns are also raised together with the new potential of ar dating of nanometric illite crystals weakness of the k ar method is in its pioneering status that makes many believe that it is no longer accurate because of its traditional analytical aspects and of the k determinations leading to somewhat large uncertainties however precise evaluation of varied applications points to a k ar method having probably larger applicability in sedimentary to diagenetic environments than the 40ar 39ar method the drawbacks become less important if the method is applied to nanometer sized clay minerals in diagenetic to low grade metamorphic environments in this instance the extracted size fractions are generally homogeneous and the relative uncertainty given by the age calculations if mathematically justified can be reduced by duplicate analyses weakness of the 40ar 39ar method is in its basics such as the 39ar recoil the necessary encapsulation the reintegration of the 39ar into the step heating patterns and the meaning of the step heating patterns that are more suggestive of variable 39ar reservoirs created among the clay particles by irradiation than of meaningful geologic ages if the k ar method is the preferred method for dating diagenetic clay processes such as glauconitization illite crystal nucleation and growth or low temperature hydrothermal activities then the 40ar 39ar method has more potential in dating low temperature tectono thermal activities and in detailing mixtures of multi generation illite

high precision 14c measurements demonstrate production of in situ cosmogenic 14ch4 and rapid loss of in situ cosmogenic 14co in shallow greenland firn abstract measurements of radiocarbon 14 c in carbon dioxide co 2 methane ch 4 and carbon monoxide co from glacial ice are potentially useful for absolute dating of ice cores studies of the past atmospheric ch 4 budget and for reconstructing the past cosmic ray flux and solar activity interpretation of 14 c signals in ice is complicated by the fact that the two major 14 c components trapped atmospheric and in situ cosmogenic are present in a combined form as well as by a very limited understanding of the in situ component this study measured 14 ch 4 and 14 co content in glacial firn with unprecedented precision to advance understanding of the in situ 14 c component 14 ch 4 and 14 co were melt extracted on site at summit greenland from three very large 1000 kg each replicate samples of firn that spanned a depth range of 3 6 5 6 m non cosmogenic 14 c contributions were carefully characterized through simulated extractions and a suite of supporting measurements in situ cosmogenic 14 co was quantified to better than 0 6 molecules g 1 ice improving on the precision of the best prior ice 14 co measurements by an order of magnitude the 14 co measurements indicate that most 99 of the in situ cosmogenic 14 c is rapidly lost from shallow summit firn to the atmosphere despite this rapid 14 c loss our measurements successfully quantified 14 ch 4 in the retained fraction of cosmogenic 14 c to 0 01 molecules g 1 ice or better and demonstrate for the first time that a significant amount of 14 ch 4 is produced by cosmic rays in natural ice this conclusion increases the confidence in the results of an earlier study that used measurements of 14 ch 4 in glacial ice to show that wetlands were the likely main driver of the large and rapid atmospheric ch 4 increase approximately 11 6 kyr ago

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

gas records from the west greenland ice margin covering the last glacial termination a horizontal ice core abstract certain sites along ice sheet margins provide an easily accessible and almost unlimited supply of ancient ice at the surface measurements of gases in trapped air from ice outcropping at pakitsoq west greenland demonstrate that ancient air is mostly well preserved no alterations in 18 o atm and 15 n of n 2 are apparent and alterations in methane are found in only a few ice sections using measurements of these gases we have unambiguously identified a stratigraphic section containing ice from the end of last glacial period as well as bolling allerod younger dryas and preboreal intervals extensive sections of ice from the holocene and most ages within the last glacial period are probably also present very accurate dating has been possible in the ice section containing the younger dryas preboreal abrupt climate transition signal the ice at pakitsoq is folded and non uniformly thinned with many cross cutting bands of bubble free ice and dust the cross cutting features are associated with anomalies in both the gas and the ice records with careful sampling to avoid these the ice at pakitsoq is suitable for recovery of large volume samples of the ancient atmosphere for analysis of trace constituents such as 14 ch 4

timing of alpine fault gouges k ar ages from clay rich fault gouges in the european alps are consistent internally with established field constraints and with fission track ages demonstrating the applicability of this method for direct dating of brittle deformation illite grown by retrograde hydration of granitic and or high grade metamorphic protoliths is the major k bearing mineral in the fractions that have been separated 0 1 to 6 10 m the ages obtained are bracketed by apatite and zircon fission ages from adjacent localities this together with the interpreted cooling curve for one well constrained sample from the simplon fault indicates that illite grew or the k ar isotopic system in illite closed at temperatures in the range 120 150 c consistent with the stability of illite alone rather than illite smectite average ages obtained for fractions finer than 2 m were 1 5 2 2 6 ma 2 for 11 analyses from the detachment and footwall of the simplon fault 2 8 8 0 6 ma for four analyses from the centovalli fault at trontano 3 19 9 2 6 ma for two analyses from a major riedel fault related to the periadriatic fault offsetting the tertiary bergell tonalite at gesero 4 21 5 5 5 ma for two analyses from a zone parallel to the periadriatic fault in the adjacent southern alps in val morobbia and 5 14 5 3 9 ma for two analyses from a gouge zone on the northern rim of the tertiary mauls tonalite in the eastern alps the ages from the simplon centovalli and periadriatic faults are not identical and do not lend support to models linking these three faults as a single coeval structure

disappearing ink how pseudotachylytes are lost from the rock record abstract melt origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record however reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed in this paper we document the processes whereby pseudotachylytes are overprinted destroyed and otherwise removed from the rock record we present examples of recrystallized altered and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults based on these observations we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes our results imply that pseudotachylytes are vastly under reported due to their vulnerability to destruction and the resulting difficulty in identification as a consequence the significance of frictional melting is underestimated the criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record

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

basin wide estimates of the input of methane from seeps and clathrates to the black sea numerous methane emitting bottom features such as seeps methane clathrate hydrates clathrates and mud volcanoes have been identified recently in the black sea the fluxes of methane from these sources averaged over large spatial scales are unknown here we take advantage of the fact that the black sea is a semi enclosed basin with restricted deep water circulation to establish first order estimates of basin wide fluxes of methane from these sources to the water column and atmosphere first we measured the natural radiocarbon content of methane 14c ch4 dissolved in the water column and emitted from seeps the 14c ch4 results showed that the dominant source of methane to the water column is emitted from seeps and a smaller source is diagenetically produced in relatively modern sediments the 14c ch4 results were then used to partition a basin wide total methane budget this analysis estimated the basin wide flux of methane from seeps and clathrates to the water column to be 3 60 to 4 28 tg yr 1 second a geochemical box model was used to calculate possible distributions of methane inputs from seeps and clathrates as well as provide additional estimates of the basin wide flux of methane from seeps and clathrates to the water column 4 95 to 5 65 tg yr 1 2006 elsevier b v all rights reserved

a method for precise measurement of argon 40 36 and krypton argon ratios in trapped air in polar ice with applications to past firn thickness and abrupt climate change in greenland and at siple dome antarctica we describe a method for measuring the 40ar 36ar ratio and the 84kr 36ar ratio in air from bubbles trapped in ice cores these ratios can provide constraints on the past thickness of the firn layer at the ice core site and on the magnitude of past rapid temperature variations when combined with measured 15n 14n both variables contribute to paleoclimatic studies and ultimately to the understanding of the controls on earth s climate the overall precision of the 40ar 36ar method 1 standard error of the mean is 0 012 for a sample analyzed in duplicate corresponding to 0 6 m in reconstructed firn thickness we use conventional dynamic isotope ratio mass spectrometry with minor modifications and special gas handling techniques designed to avoid fractionation about 100 g of ice is used for a duplicate pair of analyses an example of the technique applied to the gisp2 ice core yields an estimate of 11 3k of abrupt warming at the end of the last glacial period 15 000 years ago the krypton argon ratio can provide a diagnostic of argon leakage out of the bubbles which may happen naturally during bubble close off or artifactually if samples are warmed near the freezing point during core retrieval or storage argon leakage may fractionate the remaining 40ar 36ar ratio by 0 007 per change in 84kr 36ar introducing a possible bias in reconstructed firn thickness of about 2 m if thermal diffusion is not accounted for or 6 m if thermal diffusion effects are quantified with measured 15n 14n reproducibility of 84kr 36ar measured in air is about 0 2 1 standard error of the mean but is about 1 for ice core samples ice core samples are systematically enriched in 84kr 36ar relative to atmosphere by 5 probably reflecting preferential size dependent exclusion of the smaller argon atom during bubble entrapment recent results from the siple dome ice core reveal two climate events during the last deglaciation including an 18 m reduction in firn thickness associated with an abrupt warming at sometime between 18 and 22 kyr bp and a partial or total removal of the firn during an ablation event at 15 3 kyr bp

a method to measure kr n2 ratios in air bubbles trapped in ice cores and its application in reconstructing past mean ocean temperature 1 we describe a new method for precise measurement of kr n2 ratios in air bubbles trapped in ice cores and the first reconstruction of atmospheric kr n2 during the last glacial maximum lgm 20 000 years ago after gravitational correction the kr n2 record in ice cores should represent the atmospheric ratio which in turn should reflect past ocean temperature change due to the dependence of gas solubility on temperature the increase in krypton inventory in the glacial ocean due to higher gas solubility in colder water causes a decrease in the atmospheric inventory of krypton assuming kr and n2 inventories in the ocean atmosphere system are conserved we use a mass balance model to estimate a mean ocean temperature change between the lgm and today we measured kr n2 in air bubbles in greenland gisp2 ice from the late holocene and lgm using the present atmosphere as a standard the late holocene kr n2 means from two sets of measurements are not different from zero 0 07 0 30 and 0 14 0 93 as expected from the relatively constant climate of the last millennium the mean kr n2 in air bubbles from the lgm is 1 34 0 37 using the mass balance model we estimate that the mean temperature change between the lgm ocean and today s ocean was 2 7 0 6 c although this error is large compared to the observed change this finding is consistent with most previous estimates of lgm deep ocean temperature based on foraminiferal 18o and sediment pore water 18o and chlorinity

measurements of 14c in ancient ice from taylor glacier antarctica constrain in situ cosmogenic 14ch4 and 14co production rates abstract carbon 14 14c is incorporated into glacial ice by trapping of atmospheric gases as well as direct near surface in situ cosmogenic production 14c of trapped methane 14ch4 is a powerful tracer for past ch4 emissions from old carbon sources such as permafrost and marine ch4 clathrates 14c in trapped carbon dioxide 14co2 can be used for absolute dating of ice cores in situ produced cosmogenic 14c in carbon monoxide 14co can potentially be used to reconstruct the past cosmic ray flux and past solar activity unfortunately the trapped atmospheric and in situ cosmogenic components of 14c in glacial ice are difficult to disentangle and a thorough understanding of the in situ cosmogenic component is needed in order to extract useful information from ice core 14c we analyzed very large 1000 kg ice samples in the 2 26 19 53 m depth range from the ablation zone of taylor glacier antarctica to study in situ cosmogenic production of 14ch4 and 14co all sampled ice is 50 ka in age allowing for the assumption that most of the measured 14c originates from recent in situ cosmogenic production as ancient ice is brought to the surface via ablation our results place the first constraints on cosmogenic 14ch4 production rates and improve on prior estimates of 14co production rates in ice we find a constant 14ch4 14co production ratio 0 0076 0 0003 for samples deeper than 3 m which allows the use of 14co for correcting the 14ch4 signals for the in situ cosmogenic component our results also provide the first unambiguous confirmation of 14c production by fast muons in a natural setting ice or rock and suggest that the 14c production rates in ice commonly used in the literature may be too high

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

formation and ascent of granitic magmas new results obtained by the investigation of liquidus and solidus phase relationships in the haplogranite system qz ab or are used to discuss the evolution of magmas during their ascent in the crust it is assumed that the magmas are formed at 720 c 820 c 920 c and at a depth corresponding to a pressure of 8 kbar the starting composition of the magma is taken as 50 melt plus 50 quartz and feldspars in case of a closed system no heat exchange and no transfer of elements the melt fraction of magmas the water activity and the viscosity increase with decreasing pressure the temperature slightly decreases at 700 c the viscosity is approximatively 2 orders of magnitude lower than at 900 c this is related to the higher amount of water in the h2o undersaturated melt at low t it is also shown that dehydration melting is only realistic at high t 900 c at lower temperatures water has to be added from outside to obtain an intrusive magma with approximatively 50 melt

multidecadal variability of atmospheric methane 1000 1800 c e 1 we present a new high precision high resolution record of atmospheric methane from the west antarctic ice sheet wais divide ice core covering 1000 1800 c e a time period known as the late preindustrial holocene lpih the results are consistent with previous measurements from the law dome ice core the only other high resolution record of methane for this time period and confirm most of the observed variability multidecadal variability in methane concentrations throughout the lpih is weakly correlated or uncorrelated with reconstructions of temperature and precipitation from a variety of geographic regions correlations with temperature are dominated by changes in northern hemisphere high latitude temperatures between 1400 and 1600 c e during the onset of the little ice age times of war and plague when large population losses could have reduced anthropogenic emissions are coincident with short periods of decreasing global methane concentrations

instruments and methods a novel method for obtaining very large ancient air samples from ablating glacial ice for analyses of methane radiocarbon we present techniques for obtaining large 100 l stp samples of ancient air for analysis of 14 c of methane 14 ch4 and other trace constituents paleoatmospheric 14 ch4 measurements should constrain the fossil fraction of past methane budgets as well as provide a definitive test of methane clathrate involvement in large and rapid methane concentration ch4 increases that accompanied rapid warming events during the last deglaciation air dating to the younger dryas preboreal and oldest dryas bolling abrupt climatic transitions was obtained by melt extraction from old glacial ice outcropping at an ablation margin in west greenland the outcropping ice and occluded air were dated using a combination of d 15 no f n 2 d 18 oo f o 2 d 18 oice and ch4 measurements the ch4 blank of the melt extractions was 4 ppb measurements of d 18 o and d 15 n indicated no significant gas isotopic fractionation from handling measured ar n2 cfc 11 and cfc 12 in the samples indicated no significant contamination from ambient air ar n2 kr ar and xe ar ratios in the samples were used to quantify effects of gas dissolution during the melt extractions and correct the sample ch4 corrected ch4 is elevated over expected values by up to 132 ppb for most samples suggesting some in situ ch4 production in ice at this site