asian origin of interannual variations of summer climate over the extratropical north atlantic ocean abstractthe authors have identified an interannual relationship between asian tropospheric temperature and the north atlantic ocean sea surface temperature sst during summer may september and discussed the associated features of atmospheric circulation over the atlantic eurasian region when tropospheric temperature is high low over asia positive negative sst anomalies appear in the extratropical north atlantic this relationship is well supported by the changes in background atmospheric circulation and ocean atmosphere land thermodynamic processes when heat transfer from the land surface to the atmosphere over asia strengthens local tropospheric temperature increases and positive temperature anomalies propagate westward from asia to the north atlantic leading to an increase in summer tropospheric temperature over the atlantic eurasian region accordingly a deep anomalous ridge occurs over the extratropical north atlantic ocean with low level southerly anomalies over the western portion of t

de glauconiarum origine the glauconitic facies is widespread on present day continental shelves from 50 s to 65 n and at water depths between 50 and 500 m and is in particularly great abundance on the upper slope and outer shelf between 200 and 300 m it is also common in many ancient rocks of post late precambrian age it occurs as sand to pebble sized essentially green particles granular facies but also as a surface coating on particles and hardgrounds and as a diffuse impregnation film and diffuse facies we suggest the replacement of the term glauconite which has been interchangeably used to designate a morphological form and a specific mineral by glaucony facies and glauconitic smectite and glauconitic mica as end members of the glauconitic mineral family the widely accepted model of burst and hower for glauconitization requires a degraded micaceous 2 1 layer lattice structure parent clay mineral however detailed analysis of numerous samples of recent glaucony reveals that such a parent substrate is exceptional the model therefore requires modification generally the parent material is carbonate particles argillaceous kaolinitic faecal pellets infillings of foraminiferal tests various mineral grains and rock fragments that pass gradually into the commonly occurring green grains we show that the process of glauconitization is achieved by de novo authigenic growth of automorphous crystallites in the pores of the substrate accompanied by progressive alteration and replacement of the substrate it is this two fold evolution that causes the verdissement of granular substrates macrofossils and hardgrounds the authigenic mineral is an iron rich and potassium poor glauconitic smectite while new smectites are growing into the remaining pore space the earlier smectites are modified by incorporation of potassium producing decreasingly expandable minerals with a non expandable glauconitic mica as the end member this mineralogical diversity of the glauconitic mineral family explains the highly variable physical and chemical properties of glaucony four categories nascent little evolved evolved and highly evolved glaucony are distinguished glauconitization appears to be controlled by a delicate balance between degree of physical confinement of a particle and the amount of ionic exchange between the micro environment and ambient open marine sea water the optimum conditions for glauconitization are those of semi confinement as a result the interior of a grain is more glauconitized than its less confined periphery similarly for identical substrate types large grains 500 m provide more favourable substrates for glauconitization than lesser confined small grains on a larger scale the formation of glaucony is governed by the availability of iron and potassium and the balance between detrital influx and winnowing low accumulation rates expose grains to the open marine environment for sufficiently long times 105 106 years for highly evolved glaucony

equifinality of basal ice facies from an antarctic cold based glacier threedebris bearingicefacieswererecognizedatthebaseofsuessglacier a cold basedglacierdamminga lakeintaylorvalley southvictoria land antarctica these faciesaretermed amber ice solidfacies and basal stratifiedfacies thispaper uses stable isotope composition dd and d 18 o gas content and gas composition co 2 o2 and n2 to develop an understanding of the processes responsible for the formation of these facies the basal iceischaracterizedbya strikingdifferencein icepropertiesbetweentheinnermostend of a 25m long tunnel dug 200m upstream fromthe glacier front and the front itself at the glacier front co isotopic data plot along a well defined freezing slope s 5 6 whereas insidethetunnel the isotopic data offset fromthefreezing slope and fromthe local meteoric water line which has a slope of 8 2 co 2 concentrations rise from a minimum of about 1000ppmv inthetunnelto about 220000ppmvatthe front takentogether these character istics strongly suggest an increasing contribution of liquidwater inthe formation of basal ice towards the glacier terminus we therefore conclude that visually similar basal ice facies can have differentorigins

characteristics of the atlantic storm track eddy activity and its relation with the north atlantic oscillation abstract this study focuses on feedbacks of the high frequency eddy activity onto the quasi stationary circulation particularly with regard to the north atlantic oscillation nao the methodology consists of analyzing ncep ncar reanalysis data and sensitivity runs from a high resolution nonhydrostatic regional model consistent with recent studies results show that the jet displacement characteristic of the nao phenomenon depends strongly on the dynamics of the synoptic scale waves and the way they break positive and negative phases of the nao are closely related to anticyclonic and cyclonic wave breaking respectively indeed the high frequency momentum flux whose sign is directly related to the type of wave breaking is correlated with the nao index over the atlantic the peak of the momentum flux signal precedes that of the nao by a few days suggesting that wave breaking is triggering nao events two examples illustrate the significant impact of single storms in particular those occurring in the e

upstream subtropical signals preceding the asian summer monsoon circulation in this study the authors address several issues with respect to the antecedent signals of the large scale asian summer monsoon that were earlier identified by webster and yang in particular they revisit the changes in the subtropical upper tropospheric westerlies preceding the monsoon depict the detailed structure of the monsoon s antecedent signals and investigate the physical processes from the signals to the monsoon they also explore the teleconnection of these signals to various large scale climate phenomena and emphasize the importance of the upstream location of the signals relative to the tibetan plateau and the monsoon before a strong weak asian summer monsoon the 200 mb westerlies over subtropical asia are weak strong during the previous winter and spring a significant feature of these signals is represented by the variability of the middle east jet stream whose changes are linked to the arctic oscillation north atlantic oscillation el

40ar39ar and kar dating of altered glassy volcanic rocks the dabi volcanics p n g k ar and 40ar39ar ages have been determined for altered submarine tholeiitic and boninite high mg andesite lavas from the dabi volcanics cape vogel peninsula papua new guinea 40ar39ar whole rock total fusion and plateau ages identify a late paleocene age for the tholeiitic lavas 58 9 1 1 ma and also for the boninitic lavas 58 8 0 8 ma apparent k ar ages for the same samples range from 27 2 0 7 to 63 9 4 5 ma and young k ar ages for glassy boninites are probably due to variable radiogenic 40ar 40ar loss these new ages effectively reconcile previously ambiguous age data for the dabi volcanics and indicate contemporaneous tholeiitic and boninitic volcanism occurring in southeast png during the late paleocene smectites developed as alteration products after glass in oceanic lavas commonly do not retain 39ar during or subsequent to irradiation but in some cases may contain 40ar in the absence of other factors modifying k and ar contents samples which have not lost 40ar from smectite and suffer 39ar loss only are interpreted to have been altered immediately subsequent to the crystallization of the lava whereas samples which have lost 40ar as well as 39ar may be the result of either recent alteration or of continuous 40ar loss since the time of crystallization

a k ar and 40 ar 39 ar study on white micas from the brixen quartzphyllite southern alps the brixen quartzphyllite basement of the southern alps italy consists of metasediments which had suffered progressive deformation and low grade metamorphism pmax 4 kbar tmax 375 25 c during the palaeozoic it has been excavated by pre permian erosion buried again beneath a pile of permo mesozoic to cainozoic sediments estimated tmax 150 c and is now exposed anew due to late alpine uplift and erosion the behavior of the k ar system of white micas is investigated taking advantage of the narrow constraints on their thermal history imposed by the geological stratigraphic reference systems

excess argon in amphiboles from fluid interaction and short intrusion interval at the epizonal marangudzi complex zimbabwe the epizonal marangudzi complex of the karoo associated nuanetsi igneous province in southern zimbabwe was emplaced into precambrian gneisses and consists of a gabbro mass intruded in turn by ring dikes of quartz and nepheline syenites amphibole and biotite from various lithologies have been examined using 40ar 39ar techniques in order to investigate the temporal distribution of intrusions and the possible occurrence of excess ar with one important exception samples give internally concordant incremental release spectra average 40ar 39ar dates range from 177 6 to 181 3 ma three amphiboles give dates which are significantly older than the other samples and contain small yet discernible quantities of excess 40ar excess ar is restricted to amphiboles displaying substantial fe mg zoning which is interpreted as reflecting late magmatic or early sub solidus reaction with fluid phases argon was apparently acquired from the fluid during alteration and ultimately could have been magmatic or could have come from degassing of the country rocks the remaining samples both amphibole and biotite show only a restricted range 1 m y in apparent age and are essentially analytically indistinguishable implying rapid cooling of the complex the average for these analyses 178 1 ma reflects the mean age of emplacement of cogenetic intrusions within a short interval 1 m y in duration this revised age of the marangudzi complex fits well within the temporal framework of karoo province magmatism in the region

fission track and 40ar39ar evidence for episodic denudation of the gangotri granites in the garhwal higher himalaya india abstract in order to document quantitatively the cooling and denudation history of the higher himalayan granites bordering the tethyan sedimentary zone fission track ft apatite and 40 ar 39 ar mica ages have been determined on the gangotri leucogranites and biotite granites in the garhwal region of india gangotri is the source area of the ganges river and lies in the midst of the highest himalayan peaks in india a total of 15 apatite ages from a vertical profile 2580 4370 m on the gangotri granites yields ft ages in the range of 1 5 0 6 to 2 4 0 5 ma indicating that the rock column with a relief of 1800 m cooled through 130 10 c within only 1 million years during the late pliocene an average denudation rate of 2 mm yr is estimated for the past 2 4 million years from the gangotri granites we also report a muscovite 40 ar 39 ar age of 17 9 0 1 ma and a biotite age of 18 0 0 1 ma these reflect cooling of the rocks through 300 350 c probably related to an early miocene pulse of denudation caused by a basement cover detachment the martoli normal fault above the leucogranites time temperature pathways indicate that the cooling of the rocks in the late pliocene quaternary was five to six times the magnitude of cooling between 18 and 2 ma indicating a distinct pulse of rapid denudation in the late pliocene quaternary we interpret these young apatite ages and fast denudation as a geomorphic response increased erosion and cooling of the rocks to a major pulse of tectonic uplift in the higher himalaya shortly before 2 4 ma the effect of climatic cooling on this denudation is considered secondary to the role of tectonic forcing and indeed produced a positive feedback to the primary cause although our study is confined to the garhwal region it is probable that other granitic bodies of the higher himalaya bordering the tethyan sedimentary rocks and forming the loftiest summits in the himalaya have also experienced episodic denudation one major pulse in the early miocene which was mainly tectonic denudation and another in the late pliocene quaternary which was mainly erosional the latter is well recorded by apatite ft data and is consistent with the hypothesis that rapid uplift and denudation of the himalayan rocks may have influenced the initiation of the ice ages in the northern hemisphere

composition and origin of amber ice and its influence on the behaviour of cold glaciers in the mcmurdo dry valleys antarctica this paper examines the basal ice sequence of rhone glacier a cold based glacier in the mcmurdo dry valleys antarctica using isotopic and solute chemistry data three different ice facies are identified englacial amber and stratified the englacial facies is clean bubbly ice of meteoric origin and is underlain by an amber facies amber ice is a characteristic of cold alpine glaciers in the mcmurdo dry valleys and is distinctive for its high solute concentrations and much higher strain rates compared with the overlying englacial ice and the underlying stratified ice analysis of the stratified facies reveals an isotopic signature indicative of melt then refreeze processes and it is most likely associated with apron entrainment at the margin by contrast the amber facies has a co isotopic slope of 8 and plots on a meteoric waterline the inclusion of impurities in the amber ice reveals prolonged contact with the bed and its depleted isotopic signature is consistent with ice formed during a cooler period comparison of the basal sequence of rhone glacier with other cold based glaciers in the mcmurdo dry valleys reveals strong similarities between valley side glaciers e g meserve and rhone glaciers whereas valley floor glacier basal sequences e g suess glacier are characterized by structurally complex amalgamations of ice and debris

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

effects of nao variability on the north atlantic ocean circulation 1 the ocean response to an idealised north atlantic oscillation like wind stress is evaluated as a function of the atmospheric forcing frequency in order to elucidate the relationship between internal and forced variability the nao is modulated with two specific timescales 10 and 50 years which characterise the spectrum of the system s internal variability different timescales of atmospheric variability select distinct sea surface temperature sst and large scale circulation patterns under a 50 year nao forcing period a lagged sst response is excited in the gulf stream extension region which is consistent with the spin up of the gyre circulation the thermohaline circulation varies in phase with the nao and shows a strong sensitivity to the forcing frequency a dipole mode of the overturning is excited by a 10 year modulation of the nao while an enhanced overturning response emerges under a 50 year nao with low enough lateral mixing the ocean exhibits an irregular response to a regular nao like forcing

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

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

rbsr and kar ages of paleozoic glauconites from ohio indiana and missouri u s a abstract glauconite pellets from the lower silurian brassfield formation on both limbs of the cincinnati arch in ohio and indiana give a rb sr age of 370 11 ma which is substantially younger than the stratigraphic age of the formation the age is concordantcwith conventional k ar ages of 355 6 and 368 5 ma for two of the same glauconites concordant ages were also obtained from the viburnum trend in missouri where glauconite pellets from the davis formation in an ore zone collapse structure into the underlying bonneterre formation give a rb sr age of 387 21 ma and conventional k ar ages of 368 5 and 369 5 and 369 5 ma a third suite of glauconite from the bonneterre formation in the old lead belt 10 km from the nearest ore body has given a rb sr age of 423 7 ma and slightly older conventional k ar ages of 434 6 445 6 and 441 11 ma because these glauconite bearing rocks have been buried to depths of less than 1 km thermal resetting of the rb sr and k ar systematics appears unlikely the initial 87 sr 86 sr ratios of the rb sr isochrons are similar to the ratios for vein and vug filling dolomite and calcite this is consistent with resetting of the rb sr and k ar systems during diagenetic changes which included the isotopic equilibration perhaps by cation exchange of the sr in the glauconite with that in the diagenetic and mississippi valley type ore fluids this interpretation implies that the age of the mississippi valley type mineralization in the viburnum trend is devonian rather than carboniferous permian as has been inferred from paleomagnetic measurements cation exchange experiments with a dilute sr bearing solution and an artificial oilfield brine indicate that glauconite adsorbs large amounts of sr some of which is sufficiently strongly attached to the glauconite lattice as to resist leaching with ammonium acetate the introduction of this strongly attached sr may be the first step in the resetting of the rb sr systematics of glauconite by cation exchange

is the north atlantic oscillation a breaking wave abstract given the recent observational evidence that the positive negative phase of the north atlantic oscillation nao is the remnant of anticyclonic cyclonic wave breaking this study uses a multilevel primitive equation model to investigate important dynamical attributes of the above wave breaking behavior for this purpose a hierarchy of different basic states two and three dimensional and initial perturbations are used with the three dimensional climatological flow as the basic state it is found that initial perturbations located equatorward poleward and upstream of the climatological atlantic jet lead to wave breaking similar to that of the positive negative nao phase consistently analysis of observational data indeed shows that the pacific storm track is displaced equatorward poleward prior the onset of the positive negative nao phase this result suggests that the latitudinal position of the pacific storm track plays an important role for determining the phase of the nao sen

on the isotopic composition in δd and δ18o of water and ice during freezing experiments on progressive unidirectional freezing are coi1 ducted to determine rhe evol ution in 00 and 51 bo of successive water samples and ice layers ta ken during the course of freezing r es ults indicate t hal lhi s evoluti on takes pl ace in a bd bibo diagram a long a strai ght line wi th a characteri sti c slope this slope different from that due to the precip itation effec t gives a finger print of the occurrence of a freezing or of a melt ing refreez ing process in the stud ied reservoir residual water was sampled at the beginning of the experiment after 40 80 85 90 and 95 of the material had frozen when the freezing process was complete the ice core was recovered and sectioned the samples covered the freezing ranges from 0 to 10 10 to 20 20 to 50 50 to 60 60 to 70 70 to 80

40ar39ar dating of glauconites measured 39ar recoil loss from well crystallized specimens abstract nine glauconite samples with relatively high k concentrations and which appear to be well crystallized using normal x ray diffraction techniques have been studied using the 40 ar 39 ar method the glauconite 40 ar 39 ar apparent ages exceed their k ar rb sr and in most cases stratigraphic ages by substantial amounts 40 ar 39 ar release spectra sometimes yield plateaus but these apparent ages have no geological significance the results indicate that 39ar is lost by recoil from mineral grains during neutron irradiation consistent with previously reported observations the amount of 39ar loss was measured by isotope dilution for four samples and varied from 29 to 17 in contrast radiogenic 40ar is quantitatively retained during irradiation the very fine blades which make up glauconite grains yield the mineral susceptible to large amounts of 39ar loss and unsuitable for 40 ar 39 ar dating

comparative 40ar 39ar and k ar dating of illite type clay minerals a tentative explanation for age identities and differences abstract the 40 k 40 ar k ar and 40 ar 39 ar dating methods are applied here to the same very small micrometric illite type particles that crystallized under low temperature 5 9 ma the same size fractions dated by the 40 ar 39 ar method give total gas ages ranging from 173 3 2 0 to 228 8 1 6 ma nearly all 40 ar 39 ar total gas ages are slightly older which cannot be explained by the recoil effect only the impact of which being amplified by the inhomogeneous shape of the clay minerals and their crystallographic characteristics with varied crystallinity indices and a particle width about 10 times large than thickness the 40 ar 39 ar data outline some advantages such as the plateaus obtained by incremental step heating of the various size fractions even if not translatable straight as ages of the illite populations they allow identification of two generations of authigenic illite that formed at about 200 and 175 ma and one detrital generation however 40 ar 39 ar dating of clay minerals remains challenging as technical factors such as the non standardized encapsulation may have potential unexpected effects both dating methods have their limitations 1 k ar dating requires relatively large samples ca 10 20 mg incurring potential sample homogeneity problems with two aliquots required for k and ar analysis for an age determination also inducing a higher analytical uncertainty 2 an identified drawback of 40 ar 39 ar dating is ar recoil and therefore potential loss that occurs during neutronic creation of 39 ar from 39 k mostly in the finer mineral particles if all the recoiled 39 ar is redistributed into adjacent grains minerals the final 40 ar 39 ar age of the analyzed size fraction remains theoretically identical but it is not systematic in clay type material the finest grain sizes e g 39 ar recoil and are therefore only datable by the 40 ar 39 ar method using an encapsulation technique that still needs to be technically evaluated in this study 39 ar recoil during irradiation was quantified by encapsulation it ranged from about 20 of the total 39 ar for the 39 ar recoil confirms that grain size increasing minimizes the recoil effect but how it proceeds has still to be explained despite recent developments in 40 ar 39 ar dating the conventional k ar method is still a valuable tool for clay dating due to a convenient and straightforward use supported by a standardized and well controlled technical approach the present comparison of the two ar dating methods as applied to clay material shows that neither method is presently outdated and that they are even of reciprocal use both methods have distinct application fields in clay geochronology and complementary application fields in clay crystallography

40ar39ar dating of very fine grained samples an encapsulated vial procedure to overcome the problem of 39ar recoil loss 40ar39ar dating of very fine grained materials is compromised by the loss of 39ar by recoil and also sometimes other ar isotopes during irradiation an encapsulated sample 40ar39ar procedure is described which overcomes this problem and which produces a k ar equivalent date measurements indicate that the procedure yields reliable and reproducible results it offers the potential for dating small amounts of material of many types for example very fine grained authigenic sheet silicates from rock cores which may suffer ar loss during irradiation

potassium argon dating of fine grained basalts with massive ar loss application of the 40ar39ar technique to plagioclase and glass from the kirkpatrick basalt antarctica 40ar39ar incremental heating measurements are reported for separated plagioclase and matrix fractions and a glass sample of the kirkpatrick basalt from victoria land antarctica these results are used to address the limitations of whole rock analyses of glassy or very fine grained basalts the use of plagioclase for determining ages of such rocks the ar behavior of matrix glass and feldspar components the use of k cl ratios in interpretation of step heating results and the age of the kirkpatrick basalt the precise age of the kirkpatrick basalt has been a long standing problem the wide range of reported k ar dates has been attributed to loss of ar despite massive ar loss from the matrix plagioclase is shown to yield good 40ar39ar plateaus plateaus are observed for increments above 700 c and are defined not only by consistent apparent ages but also appropriately low k ca and high k cl ratios cl relations help identify ar released from small amounts of matrix which can seriously contaminate a plagioclase separate an age of 176 8 1 8 ma defines the time of formation of the youngest lava at mt frustum in north victoria land a glass sample from south victoria land gives the same age indicating that terrestrial basaltic glasses as old as jurassic do not inherently lose ar the step heating profile of glass with very fine crystals shows discordance which is an artifact of ar recoil during irradiation

high resolution 40 ar 39 ar chronology of multiple intrusion igneous complexes the mount brome complex of the monteregian province of southern quebec canada consits of several major intrusions ranging compositionally from gabbro to syenite the relative ages of these intrusives have been investigated with high resolution 40ar 39ar analyses including a specially designed irradiation configuration to cancel the effects of fluence gradients small yet distinct apparent age differences are observed while a number of analytical and geological factors could be proposed to explain the small variations evaluation of these suggests the age differences reflect those in emplacement times the gabbro and nepheline diorite were emplaced within a short span 123 1 ma ago generally more evolved lithologies biotite monzodiorite pulaskite nordmarkite appear to have been emplaced within a restricted interval 1 4 0 3 ma later whole rock rb sr systematics do not give acceptable isochrons because of significant scatter interpreted to reflect initial 87sr 86sr heterogeneities resulting from crustal contamination considering the variations in initial ratio the rb sr data are consistent with the 40ar 39ar age

the dynamics of nao teleconnection pattern growth and decay this investigation performs both diagnostic analyses with ncep ncar re analysis data and forced barotropic model calculations to examine the dynamical mechanisms associated with the growth and decay of the north atlantic oscillation nao teleconnection pattern the diagnostic calculations include projection and composite analyses of each term in the stream function tendency equation the results of the analyses reveal a complete life cycle of growth and decay within approximately two weeks the positive nao phase is found to develop after anomalous wavetrain propagation across the north pacific to the east coast of north america this contrasts with the negative nao phase which appeared to develop in situ both high frequency period 10 days transient eddy fluxes drive the nao growth after the nao anomaly attains its maximum amplitude the high frequency transient eddy fluxes continue to drive the nao anomaly in a manner that is consistent with a positive feedback process the decay of the nao occurs through both the divergence term and the low frequency transient eddy fluxes the temporal and spatial properties of the divergence term are found to be consistent with ekman pumping these results illustrate many important differences between the nao and pacific north american pna teleconnection patterns perhaps most striking being that the nao life cycle is dominated by nonlinear processes whereas the pna evolution is primarily linear in addition the relation between the nao and the zonal index is discussed copyright 2003 royal meteorological society

on the significance of the interannual relationship between the asian pacific oscillation and the north atlantic oscillation using monthly data from the european centre for medium range weather forecasts 40 year re analysis this study investigated the interannual relationship between the asian pacific oscillation apo and the north atlantic oscillation nao for the period of may to august the nao is represented by the leading empirical orthogonal function of sea level pressure anomalies over the atlantic sector the difference of upper tropospheric eddy air temperature t between asia and the north pacific is used to measure the apo results clearly show that the apo and the nao correlated very well on the interannual time scale with the positive negative phase of the apo corresponding to the strong weak nao such a relationship is well supported by the atmospheric dynamic process when the apo is in the positive phase characterized by the positive t anomaly over asia and the negative t anomaly over the north pacific in the upper troposphere the upper tropospheric geopotential height increases over asia and decreases over the north pacific accordingly anticyclonic circulation and cyclonic circulation anomalies are introduced respectively over asia and south of the north pacific and a zonal teleconnection wave train is excited from asia to the north atlantic as a consequence an anomalous anticyclonic circulation prevails in the low level of the north atlantic and an anomalous cyclonic circulation appears to its north which corresponds to the atmospheric pattern of strong nao further study proposes that the quasi stationary wave pattern emanating from the western north pacific region may serve as a bridge for this linkage

mechanisms of basal ice formation in polar glaciers an evaluation of the apron entrainment model 1 previous studies of polar glaciers have argued that basal ice can form when these glaciers override and entrain ice marginal aprons that accumulate adjacent to steep ice cliffs to test this idea we have studied the morphology structure composition and deformation of the apron and basal ice at the terminus of victoria upper glacier in the mcmurdo dry valleys which are located on the western coast of the ross sea at 77 si n southern victoria land antarctica our results show that the apron has two structural elements an inner element that consists of strongly foliated ice that has a steep up glacier dip and an outer element that lacks a consistent foliation and has a down glacier slope parallel dip although strain measurements show that the entire apron is deforming the inner element is characterized by high strain rates whereas relatively low rates of strain characterize the outer part of the apron co isotopic analyses of the ice together with analysis of solute chemistry and sedimentary characteristics show that the apron is compositionally different from the basal ice our observations show that aprons may become deformed and partially entrained by advancing glaciers however such an ice marginal process does not provide a satisfactory explanation for the origin of basal ice observed at the ice margin our interpretation of the origin of basal ice is that it is formed by subglacial processes which are likely to include deformation and entrainment of subglacial permafrost

flow induced mixing in the grip basal ice deduced from the co2 and ch4 records this paper documents a larger degree of mixing in ice near the bottom of an ice sheet than described or suspected previously it shows thanks to favourable circumstances due to co2 and ch4 production underneath the ice that flow induced mixing within the basal ice has taken place at the scale of a few centimeters in the grip core such a mechanism must be considered when interpreting the ice properties in the bottom part of ice sheets and must be taken into account as a potential process of layer disruption in the low levels of the central greenland ice cores

a short interval of jurassic continental flood basalt volcanism in antarctica as demonstrated by 40ar39ar geochronology a continental flood basalt province the ferrar group kirkpatrick basalt and ferrar dolerite crops out along 3000 km of the transantarctic mountains in antarctica and is temporally related to the break up of gondwanaland although a wide range of dates between 90 and 193 ma have been published for the kirkpatrick basalt it is now recognized that the young dates reflect non ideal behavior of ar in the matrix in order to refine the geochronology feldspar separates have been analyzed by the 40ar39ar incremental heating method the main objectives are to constrain the duration of extrusive activity and the timing of volcanism along the outcrop belt basalt samples have been studied from the three principal outcrop areas yielding the following apparent ages central transantarctic mountains 176 8 0 5 ma south victoria land 176 4 0 4 ma north victoria land 176 6 0 7 ma ages from different stratigraphic levels within each area and from the three different areas are not analytically distinct the data imply that the eruptive activity which produced the kirkpatrick basalt occurred within a short interval of less than about 1 m y at 176 6 1 8 ma over an area which included more than 1200 km of the transantarctic mountains the jurassic volcanism in antarctica represents a short episode of magmatism comparable in duration with other well dated continental flood basalt provinces the linearly extensive outcrop of the ferrar province and the rapid eruption of the lavas suggests that lithospheric stretching exerted a major control on magmatism the poorly constrained age of the bajocian bathonian boundary makes the previously suggested connection between ferrar volcanism and an extinction event at that boundary uncertain

decadal variations of the relationship between the summer north atlantic oscillation and middle east asian air temperature 1 the relationship between the summer july september north atlantic oscillation snao and simultaneous east asian air temperature is investigated the results show that the snao is related to middle east asian summer air temperature however this linkage varies with time on decadal timescale a strong connection appears after the late 1970s but a weak connection before the late 1970s further analysis indicates that this instable relationship may have resulted from the shift of the snao mode around the late 1970s in the period of 1979 2003 the centers of the snao mode are located more eastward a positive phase negative phase snao produces a strong lower level divergence convergence over the asian jet entrance region in turn stimulates a strong upper level convergence divergence via the ekman pumping such a convergence divergence then excites a zonally oriented quasi stationary barotropical rossby wave train along the asian upper level jet thus the snao signal is transported eastward to east asia resulting in an anomalous summer air temperature over middle east asia however in the period of 1951 1975 the centers of the snao mode are located more westward the associated upper level divergence convergence is away from the asian jet entrance region and the snao signal cannot be transported eastward to east asia hence the connection is broken

physical and climatic parameters which influence the air content in polar ice abstract under present day climatic conditions the air content of polar ice v generally shows a high sensitivity to the atmospheric pressure and hence to the surface elevation of the ice sheet wherethe ice is formed the results presented here are from sixteen different sites fourteen in antartica one in greenland and one in the yukon territories canada and they allow a better understanding of the parameters which influence the air content in ice it is demonstrated the v can be expressed very simply as a function of the atmospheric pressure p i the temperature t i and the porous volume of ice v i at which the air in the firn becomes isolated in terms of pressure from the atmosphere during the process of pore close off our results confirm a v i increase with temperature and show no clear v i dependence on snow accumulation rate the possible non linearity of the v i t i relation we obtain could be due to a wind influence on v i and or to a second order effect of the accumulation rate our v i results are compared to measurements of the volume of closed pores versus depth in the firn to close we discuss the parameterization that we can obtain to interpret the air content variations observed in deep ice cores over periods covering glacial interglacial transitions in terms of paleoclimatic conditions prevailing at the surface of the ice sheet

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

apophyllite 40ar 39ar and rb sr geochronology potential utility and application to the timing of secondary mineralization of the kirkpatrick basalt antarctica apophyllite kca 4 si 8 o 20 f oh 8h 2 o which formed as a low temperature secondary mineral in the kirkpatrick basalt has been examined to evaluate its potential for geochronology using the k ar by the 40 ar 39 ar technique and rb sr methods the 40 ar 39 ar total gas ages for apophyllites from the kirkpatrick basalt are 114 133 ma for the central transantarctic mountains 95 114 ma for south victoria land and 76 100 ma for north victoria land within individual hand samples apophyllite 40 ar 39 ar apparent ages show variations of up to 24 m y and within single large up to 2 cm crystals differences of up to 14 m y are observed the 40 ar 39 ar incremental heating spectra are generally flat but have low and high temperature discordances attributed to 39 ar recoil rb sr model ages for the apophyllites range from 94 to 144 ma and vary from concordant with the 40 ar 39 ar dates to as much as 14 m y older the dates are consistent with other temporal indicators of low temperature alteration in the basalts and are interpreted to broadly reflect the time of apophyllite precipitation they document a geographically widespread early to middle cretaceous secondary mineralization which is inferred to be caused by a major period of groundwater movement associated with the initiation of uplift and denudation of the transantarctic mountains the results suggest that apophyllite can produce geologically meaningful ages by both rb sr and k ar methods although further work is required to fully understand the variations in age that may be attributed to ar loss alkali mobility or an extended history of mineral precipitation

very low oxygen concentration in basal ice from summit central greenland oxygen concentration as low as 3 has been detected in the basal silty ice of the grip core such values were never observed in ice from ice sheets they are most probably the consequence of organic matter oxidation in ice developed in a peaty deposit when the greenland ice sheet was not present at the site flow induced mixing has further incorporated this ice into glacier ice during the ice sheet build up the part of the local ice component in the mixing process diminishes with the distance from the bed this is the process which explains the oxygen profile

trapping of aeolian sediments and build up of the ice cover of a dry based antarctic lake among the perennially frozen lakes of the dry valleys of south victoria land antarctica some are dry based i e frozen to the bottom one of these is studied here by a multiparametric investigation isotopic composition in da nd 18 o ions gas and ice texture analyses a sediment layer about 10 cm thick appearing at a depth of 3 5m is also studied by grain size x ray diffraction and scanning electron microscope analyses the information retrieved indicates that this ice block lake results from a build up in two steps and explains how aeolian sediments were included as a layer into the ice copyright 2002 john wiley sons ltd

first 40ar 39ar geochronology of lateritic manganiferous pisolites implications for the palaeogene history of a west african landscape abstract a pisolitic superficial formation deriving from the geochemical degradation of a previous massive manganiferous crust has been investigated in west africa using 40 ar 39 ar laser probe analysis on different generations of cryptomelane from fe mn pisolites and their embedding lateritic matrices prior to the 40 ar 39 ar geochronological analysis a detailed petrographical study has allowed the identification of successive assemblages from mn pisolites to fe mn pisolites embedded in mn rich and fe rich matrices respectively the age spectra obtained for pisolites including cores cortices and matrices enables the definition of three age clusters around 56 59 44 47 and 24 27 ma the first two age clusters with the petrographical and geochemical results obtained on the different assemblages indicate that the development of the pisolitic crust first induced mn leaching and fe al accumulations due to warmer and wetter climatic conditions in the age interval 56 47 ma that characterizes the tertiary greenhouse effect period propitious to bauxite formation in west africa the absence of 40 ar 39 ar ages between 44 and 27 ma only means that geochemical conditions for cryptomelane crystallisation were not fulfilled but could still be favourable to fe and or al oxy hydroxides formation before drier climatic conditions became rather effective at the oligocene period to sustain mechanical erosion rather than chemical weathering processes the age cluster 24 27 ma indicates however a reactivation of the manganiferous lateritic weathering late oligocene the 40 ar 39 ar dating results are discussed in terms of climatic condition changes during the palaeogene that were favourable to the genesis of either al and fe or mn oxy hydroxides in the course of development and evolution of the pisolitic formation the 40 ar 39 ar dating also provides a new highlight to large scale geomorphological patterns of west africa

air content paleo record in the vostok ice core antarctica a mixed record of climatic and glaciological parameters under present day climatic conditions the air content of ice shows a high sensitivity to the atmospheric pressure and hence to the elevation at the surface of the ice sheet this observation has been used to infer past ice sheet thickness variations of antarctica and greenland a high resolution air content profile more than 1000 measurements covering approximately the last 200 000 years was obtained along the 2546 m long vostok ice core three analytical techniques were used leading to consistent results which show large amplitude and rapid air content variations the vostok results support thicker thinner ice in the central part of east antarctica during warm cold periods

entrainment at cold glacier beds here we present measurements of the gas content and isotopic composition of debris rich basal layers of a polar glacier meserve glacier antarctica which has a basal temperature of 17 c these measurements show that debris entrainment has occurred without alteration of the glacial ice and provide the most direct evidence to date that active entrainment occurs at the beds of cold glaciers without bulk freezing of water entrainment at subfreezing temperatures may have formed the u shaped trough containing meserve glacier in addition to possibly allowing some cold based glaciers to be important geomorphic agents entrainment at subfreezing temperatures provides a general mechanism for formation of the dirty basal layers of polar glaciers and ice sheets which are rheologically distinct and can limit the time span of ice core analyses furthermore accumulating evidence suggests that geomorphologists should abandon the assumption that cold based glaciers do not slide and abrade their beds