samarium neodymium and rubidium strontium systematics of nakhlite governador valadares abstract the sm nd systematics of whole rock and mineral separate samples from nakhlite governador valadares define a good 147sm 143nd mineral isochron age of 1 37 0 02 ga this age is in excellent agreement with the 39ar 40ar and rb sr ages obtained previously for this meteorite however the rb sr isotopic data for our sample show that the isotopic system is disturbed the lack of isotopic equilibrium is probably caused by the weathering of the sample as indicated by the presence of secondary alteration phases the whole rock and acid washed mineral data yield a rb sr age of 1 20 0 05 ga which probably represents a lower limit to the crystallization age of the rock the petrographic evidence indicates that this meteorite is a clinopyroxene cumulate that probably crystallized in a subsurface sill mcsween 1994 thus the sm nd isotopic age probably represents the age of such a magmatic event the initial e143nd value determined for the rock at 1 37 ga is 17 1 indicating that the parent magma of the rock came from a light rare earth element depleted source of 147sm 144nd 0 237 based on a simple two stage evolution model results of the same model calculation for the initial 87sr 86sr ratio of the rock suggest that its source material was depleted in 87rb 86sr by 50 relative to the estimated martian value at 1 37 ga both the high sm nd and low rb sr values support a clinopyroxene rich cumulate source for the genesis of the nakhlite governador valadares furthermore our sm nd age and e143nd data and the previously published e142nd datum for the rock harper et al 1995 are consistent with early differentiation of the parent planet formation of cumulate sources 4 56 ga ago and late melting of the sources and formation of the rock 1 37 ga ago the good agreement of isotopic ages and petrographic features among governador valadares nakhla and lafayette strongly suggests that all three nakhlites have undergone similar evolutionary histories the nakhlite age data suggest that isotopic heterogeneity in the martian mantle sources existed up to 1 37 ga ago and early mantle structures probably have not been disturbed for a significant portion of martian history

a 10 15 yr modulation cycle of enso intensity abstract this study examines the slow modulation of el nino southern oscillation enso intensity and its underlying mechanism a 10 15 yr enso intensity modulation cycle is identified from historical and paleoclimate data by calculating the envelope function of boreal winter nino 3 4 and nino 3 sea surface temperature sst indices composite analyses reveal interesting spatial asymmetries between el nino and la nina events within the modulation cycle in the enhanced intensity periods of the cycle el nino is located in the eastern tropical pacific and la nina in the central tropical pacific the asymmetry is reversed in the weakened intensity periods el nino centers in the central pacific and la nina in the eastern pacific el nino and la nina centered in the eastern pacific are accompanied with basin scale surface wind and thermocline anomalies whereas those centered in the central pacific are accompanied with local wind and thermocline anomalies the el nino la nina asymmetries provide a possible m

the normality of el nino the amplitude of the el nino southern oscillation enso would be normally distributed if the coupled pacific ocean atmosphere were a linear system forced by gaussian weather noise moment estimates of skewness and kurtosis demonstrate that this is not the case for monthly mean anomalies in pacific sea surface temperatures during 1950 97 the noted predominance of el nino events compared to la nina events is related to the high skewness in the eastern pacific skewness and kurtosis both exhibit an intriguing geographical variation from positive in the eastern to negative in the western pacific we have also examined nino 3 indices generated by three climate models having widely different complexity these exhibit a wide range of skewness and kurtosis values rather different from those found for the observations skewness and kurtosis can be used to diagnose non linear processes and provide powerful tools for validating models and for testing observed sea surface temperatures for the presence of possible climate change

39ar 40ar ages of martian nakhlites abstract we report 39ar 40ar ages of whole rock wr and plagioclase and pyroxene mineral separates of nakhlites mil 03346 and y 000593 and of wr samples of nakhlites nwa 998 and nakhla all age spectra are complex and indicate variable degrees of 39ar recoil and variable amounts of trapped 40ar in the samples thus we examine possible ar ar ages in several ways from consideration of both limited plateau ages and isochron ages we prefer ar ar ages of nwa 998 1334 11 ma mil 03346 1368 83 ma mesostasis and 1334 54 ma pyroxene y 000593 1367 7 ma and nakhla 1357 11 ma 2 errors for nwa 998 and mil 03346 the ar ar ages are within uncertainties of preliminary rb sr isochron ages reported in the literature these ar ar ages for y 000593 and nakhla are several ma older than sm nd ages reported in the literature we conclude that the major factor in producing ar ar ages slightly too old is the presence of small amounts of trapped martian or terrestrial 40ar on weathered grain surfaces that was degassed along with the first several percent of 39ar a total k 40ar isochron for wr and mineral data from five nakhlites analyzed by us plus lafayette data in the literature gives an isochron age of 1325 18 ma 2 we emphasize the precision of this isochron over the value of the isochron age our ar ar data are consistent with a common formation age for nakhlites the cosmic ray exposure cre age for nwa 998 of 12 ma is also similar to cre ages for other nakhlites

nonlinear principal component analysis tropical indo pacific sea surface temperature and sea level pressure abstract nonlinear principal component analysis nlpca is a generalization of traditional principal component analysis pca that allows for the detection and characterization of low dimensional nonlinear structure in multivariate datasets the authors consider the application of nlpca to two datasets tropical pacific sea surface temperature sst and tropical indo pacific sea level pressure slp it is found that for the sst data the low dimensional nlpca approximations characterize the data better than do pca approximations of the same dimensionality in particular the one dimensional nlpca approximation characterizes the asymmetry between spatial patterns characteristic of average el nino and la nina events which the 1d pca approximation cannot the differences between nlpca and pca results are more modest for the slp data indicating that the lower dimensional structures of this dataset are nearly linear

an evaluation of enso asymmetry in the community climate system models a view from the subsurface abstract the asymmetry between el nino and la nina is a key aspect of enso that needs to be simulated well by models in order to fully capture the role of enso in the climate system here the asymmetry between the two phases of enso in five successive versions of the community climate system model ccsm1 ccsm2 ccsm3 at t42 resolution ccsm3 at t85 resolution and the latest ccsm3 nr with the neale and richter convection scheme is evaluated different from the previous studies not only is the surface signature of enso asymmetry examined but so too is its subsurface signature by comparing the differences among these models as well as the differences between the models and the observations an understanding of the causes of the enso asymmetry is sought an underestimate of the enso asymmetry is noted in all of the models but the latest version with the neale and richter scheme ccsm3 nr is getting closer to the observations than the earlier versions the net surface heat flux is found to damp th

decadal amplitude modulation of two types of enso and its relationship with the mean state in this study we classified two types of el nino southern oscillation enso events within the decadal enso amplitude modulation cycle using a long term coupled general circulation model simulation we defined two climate states strong and weak enso amplitude periods and separated the characteristics of enso that occurred in both periods there are two major features in the characteristics of enso the first is the asymmetric spatial structure between el nino and la nina events the second is that the el nino la nina asymmetry is reversed during strong and weak enso amplitude periods el nino events during strong weak enso amplitude periods resemble the eastern pacific central pacific el nino in terms of the spatial distribution of sea surface temperature anomalies ssta and physical characteristics based on heat budget analysis the spatial pattern of the thermocline depth anomaly for strong weak el nino is identical to that for weak strong la nina but for an opposite sign and slightly different amplitude the accumulated residuals of these asymmetric anomalies dominated by an east west contrast structure could feed into the tropical pacific mean state moreover the residual pattern associated with el nino la nina asymmetry resembles the first principal component analysis pca mode of tropical pacific decadal variability indicating that the accumulated residuals could generate the change in climate state thus the intensified enso amplitude yields the warm residuals due to strong el nino and weak la nina over the eastern tropical pacific this linear relationship between enso and the mean state is strong during the mature phases of decadal oscillation but it is weak during the transition phases furthermore the second pca mode of tropical pacific decadal variability plays an important role in changing the phase of the first mode consequently the feedback between enso and the mean state is positive feedback to amplify the first pca mode whereas the second pca mode is a negative feedback to lead the phase change of the first pca mode due to their lead lag relationship these features could be regarded as evidence that the decadal change in properties of enso could be generated by the nonlinear interaction between enso and the mean state on a decadal to interdecadal time scale

interdecadal change of the structure of the enso mode and its impact on the enso frequency in the late 1970s the enso cycle exhibited frequency change the oscillation period increased from 2 4 yr high frequency during 1962 75 to 4 6 yr low frequency during 1980 93 observations suggest that this frequency change was accompanied by a significant change in the structure of the coupled enso mode in comparison with the high frequency regime the structure of the coupled mode in the low frequency regime shows three distinctive features during the warm phase of enso the eastward shift of the westerly anomalies the meridional expansion of the westerly anomalies and the weaker intensity of the easterly anomalies in the eastern pacific to test the robustness of the relationship between the oscillation period and the structure of the coupled mode the authors designed empirical atmospheric models based on observations and coupled them with the ocean model of zebiak and cane numerical experiments demonstrate that the enso period is sensitive to changes in the wind anomaly pattern in a way much like the observed enso frequency structure relation the increase of the enso period after 1980 is mainly due to the eastward shift of the zonal wind stress with respect to the sst anomalies physical explanations of the dependence of enso frequency on the structure of the coupled mode are provided by diagnosing the relative contributions of the thermocline feedback and zonal advection feedback on enso evolution

disentangling xenon components in nakhla martian atmosphere spallation and martian interior abstract a powdered sample of nakhla was separated into 3 subsamples one was left otherwise untreated one was washed in water and one etched with hno3 removing 6 of the original mass we report results of isotopic analysis of xenon released by laser step heating on aliquots of each of these subsamples some aliquots were neutron irradiated before isotopic analysis to allow determination of i ba and u as daughter xenon isotopes and some were not there is evidence that water soluble phases contain both martian atmospheric xenon and a component with low 129xe 132xe either martian interior xenon or terrestrial atmosphere higher temperature data from unirradiated aliquots of the water and acid treated samples reveal two component mixing one is a trapped xenon component with 129xe 132xe 2 350 0 026 isotopically identical to the martian atmosphere as measured in shock glass from shergottites it is associated with leachable iodine suggesting it is trapped close to grain boundaries it may be a result of shock incorporation of adsorbed atmospheric gas the second component is best explained as an intimate mixture of martian interior xenon and spallation xenon the martian interior component is present at a concentration of 10 12 cm3 stp g 1 132xe around 40 times lower than that observed in chassigny its association with spallation xenon produced from ba and light rare earth elements suggests it is in the feldspathic mesostasis we propose that it was trapped during crystallisation and reflects the mantle source of the parental magma

interannual variability in a tropical atmosphere ocean model influence of the basic state ocean geometry and nonlinearity abstract the behavior of a tropical coupled atmosphere ocean model is analyzed for a range of different background states and ocean geometries the model is essentially that of cane and zebiak for the tropical pacific except only temporally constant background states are considered here for realistic background states and ocean geometry the model solutions feature oscillations of period of 3 5 yr by comparing the full model solution with a linearized version of the model it is shown that the basic mechanism of the oscillation is contained within linear theory a simple linear analog model is derived that describes the nature of the interannual variability in the coupled tropical atmosphere ocean system the analog model highlights the properties that produce coupled atmosphere ocean instability in the eastern ocean basin and the equatorial wave dynamics in the western ocean basin that are responsible for a delayed negative feedback into this instability growth the growth rate of the local instabil

the 154 year record of sea level at san francisco extracting the long term trend recent changes and other tidbits a data adaptive method called ensemble empirical mode decomposition eemd is used to examine the 154 year record of monthly sea level at san francisco the mode that is lowest in frequency corresponds to the long term trend the next highest mode corresponds to an oscillation with a period of 100 years and may be related to solar variability when this mode is combined with the long term trend the rate of increase in sea level starts to decrease by 1980 the next lower mode corresponds to interdecadal time scales and thus includes the pacific decadal oscillation when combined with the two lower modes sea level itself starts to decrease by the mid 1990s these results are consistent with the most recent results from the intergovernmental panel on climate change ipcc and may be the first obtained from a tidal record prior to conducting eemd corrections for glacial isostatic adjustment gia and the inverse barometer ib effect were applied the effect of applying the gia correction was relatively small but the ib correction reduced the slope of the long term trend in sea level by almost 15 this reduction is due to a long term increase in the variance of sea level pressure to determine if the 10 15 year enso modulation cycle could be detected from the decomposition we first compared the envelope from the mode associated with enso with the two adjacent modes that were lower in frequency spectral analysis revealed no significant maxima in the enso mode envelope but a major peak in the spectrum for the two adjacent modes with a period of 12 8 years this is consistent with a local response to el nino warming for the enso mode but a non local response for the two adjacent modes a similar analysis was performed for the southern oscillation index and a spectral maximum was found between 12 and 16 years consistent with our non local interpretation of the previous two modes

martian gases in an antarctic meteorite significant abundances of trapped argon krypton and xenon have been measured in shock altered phases of the achondritic meteorite elephant moraine 79001 from antarctica the relative elemental abundances the high ratios of argon 40 to argon 36 2000 and the high ratios of xenon 129 to xenon 132 2 0 of the trapped gas more closely resemble viking data for the martian atmosphere than data for noble gas components typically found in meteorites these findings support earlier suggestions made on the basis of geochemical evidence that shergottites and related rare meteorites may have originated from the planet mars

enso like and enso induced tropical pacific decadal variability in cgcms abstractoutputs from coupled general circulation models cgcms are used in examining tropical pacific decadal variability tpdv and their relationships with el nino southern oscillation enso herein tpdv is classified as either enso induced tpdv eit or enso like tpdv elt based on their correlations with a decadal modulation index of enso amplitude and spatial pattern eit is identified by the leading eof mode of the low pass filtered equatorial subsurface temperature anomalies and is highly correlated with the decadal enso modulation index this mode is characterized by an east west dipole structure along the equator elt is usually defined by the first eof mode of subsurface temperature of which the spatial structure is similar to enso generally this mode is insignificantly correlated with the decadal modulation of enso eit closely interacts with the residuals induced by enso asymmetries both of which show similar spatial structures on the other hand elt is controlled by slowly varying oc

the role of mean state on changes in el nino s flavor recently many studies have argued for the existence of two types of el nino phenomena based on different spatial distributions the conventional el nino or eastern pacific ep el nino and the central pacific cp el nino here we investigate the decadal modulation of cp el nino occurrences using a long term coupled general circulation model simulation focusing in particular on the role of climate state in the regime change between more and fewer cp el nino events the higher occurrence regime of the cp el nino coincides with the lower occurrence regime of ep el nino and vice versa the climate states associated with these two opposite regimes resemble the leading principal component analysis pca modes of tropical pacific decadal variability indicating that decadal change in climate state may lead to regime change in terms of two different types of el nino in particular the higher occurrence regime of cp el nino is associated with a strong zonal gradient of mean surface temperature in the equatorial pacific along with a strong equatorial trade wind over the area east of the dateline in addition the oceanic variables the mixed layer depth and the thermocline depth show values indicating increased depth over the western to central pacific the aforementioned climate states obviously intensify zonal advective feedback which promotes increased generation of the cp el nino frequent cp el nino occurrences are not fully described by oceanic subsurface dynamics and dynamical or thermodynamical processes in the ocean mixed layer and air sea interaction are important contributors to the generation of the cp el nino furthermore the atmospheric response with respect to the ssta tends to move toward the west which leads to a weak air sea coupling over the eastern pacific these features could be regarded as evidence that the climate state can provide a selection mechanism of the el nino type

noble gases in iddingsite from the lafayette meteorite evidence for liquid water on mars in the last few hundred million years we analyzed noble gases from 18 samples of weathering products iddingsite from the lafayette meteorite potassium argon ages of 12 samples range from near zero to 670 91 ma these ages confirm the martian origin of the iddingsite but it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration or incorporation of martian atmospheric 40ar in any case because iddingsite formation requires liquid water this data requires the presence of liquid water near the surface of mars at least as recently as 1300 ma ago and probably as recently as 650 ma ago krypton and xe analysis of a single 34 g sample indicates the presence of fractionated martian atmosphere within the iddingsite this also confirms the martian origin of the iddingsite the mechanism of incorporation could either be through interaction with liquid water during iddingsite formation or a result of shock implantation of adsorbed atmospheric gas our strongest conclusion is that the iddingsite in lafayette formed on mars in agreement with the microstratigraphic arguments of gooding et al 1991 and treiman et al 1993 a preterrestrial origin of the iddingsite is required both by the many non zero k ar ages and by the presence of xe that is isotopically distinct from any terrestrial xe the xe is accompanied by kr but the kr and xe have been fractionated if they are derived from the present martian atmosphere this is presumably the result of either incorporation via interaction with liquid water drake et al 1994 bogard and garrison 1998 or by adsorption from the martian atmosphere perhaps accompanied by shock see also gilmour et al 1998 1999 although the iddingsite is enriched in kr and xe compared to whole rock analyses it is not clear whether iddingsite is the dominant carrier of the atmospheric derived gas drake et al 1994 or merely a minor carrier gilmour et al 1999 our 40ar 39ar experiment was disappointing in that it mostly served to confirm that the iddingsite which contains fine grained clays is susceptible to recoil loss of 39ar during irradiation only one sample of five gave a clear signal of radiogenic or extraterrestrial 40ar and that was only by 3 potassium argon ages of the second set of samples were more successful ranging from near 0 to 670 91 ma it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration the fact that a rb sr experiment shih et al 1998 gave an apparent age for iddingsite of 679 66 ma 2a suggests that perhaps formation of iddingsite occurred or began 650 ma ago and that some samples either formed or were thermally altered later the ages could be even younger than 650 ma if the samples have incorporated martian atmospheric 40ar this means that liquid water was certainly present on mars in the last 1300 ma the formation age of lafayette and probably within the last 650 ma

40ar 39ar dating and cosmic ray exposure time of desert meteorites dhofar 300 and dhofar 007 eucrites and anomalous achondrite nwa 011 we performed high resolution 40ar 39ar dating of mineral separates and whole rock samples from the desert meteorites dhofar 300 dhofar 007 and northwest africa nwa 011 the chronological information of all samples is dominated by plagioclase of varying grain size the last total reset age of the eucrites dhofar 300 and dhofar 007 is 3 9 0 1 ga coeval with the intense cratering period on the moon some large plagioclase grains of dhofar 007 possibly inherited ar from a 4 5 ga event characteristic for other cumulate eucrites due to disturbances of the age spectrum of nwa 011 only an estimate of 3 2 3 9 ga can be given for its last total reset age secondary events causing partial 40ar loss 3 4 ga ago are indicated by all age spectra furthermore ar extractions from distinct low temperature phases define apparent isochrons for all samples these isochron ages are chronologically irrelevant and most probably caused by desert alterations in which radiogenic 40ar and k from the meteorite and occasionally k induced by weathering are mixed accompanied by incorporation of atmospheric ar additional uptake of atmospheric ar by the alteration phase s was observed during mineral separation i e crushing and cleaning in ultrasonic baths consistent cosmic ray exposure ages were obtained from plagioclase and pyroxene exposure age spectra of dhofar 300 25 1 ma and dhofar 007 13 1 ma using the minerals specific target element chemistry and corresponding 38ar production rates

reversed spatial asymmetries between el nino and la nina and their linkage to decadal enso modulation in cmip3 models abstractthis study examines preindustrial simulations from coupled model intercomparison project phase 3 cmip3 models to show that a tendency exists for el nino sea surface temperature anomalies to be located farther eastward than la nina anomalies during strong el nino southern oscillation enso events but farther westward than la nina anomalies during weak enso events such reversed spatial asymmetries are shown to force a slow change in the tropical pacific ocean mean state that in return modulates enso amplitude cmip3 models that produce strong reversed asymmetries experience cyclic modulations of enso intensity in which strong and weak events occur during opposite phases of a decadal variability mode associated with the residual effects of the reversed asymmetries it is concluded that the reversed spatial asymmetries enable an enso tropical pacific mean state interaction mechanism that gives rise to a decadal modulation of enso intensity and that at least three cmip3 models realistically simu

glass bearing inclusions in olivine of the chassigny achondrite heterogeneous trapping at sub igneous temperatures three types of glass bearing inclusions are present in olivine and chromite of the chassigny achondrite pure glass monocrystal glass plus a single mineral grain and multiphase glass plus a variety of minerals inclusions the occurrence texture and mineralogy of these inclusions and the chemical composition of the glass suggest an origin by heterogeneous trapping of these phases the glass is rich in sio2 al2o3 na2o k2o and poor in mgo feo and cao and contains appreciable amounts of cl the compositional variability of the glass is independent of the mineral content of the inclusions heating experiments with final temperatures of 900 1000 and 1200 c were performed with chassigny inclusions for the first time the glass of the heated inclusions has a chemical composition similar to that of unheated inclusions this situation suggests that the glass cannot be a residual melt but rather is an independent component that was trapped with or without mineral phases the extreme heterogeneity in alkali contents and in particular rb and sr contents also suggests precipitation and mixing of solid precursors the most rb rich glasses have near chondritic rb sr ratios possibly indicating a chondritic source for their precursor s none of the inclusions contain bubbles like those of typical melt inclusions in terrestrial igneous minerals furthermore many inclusions are at the center of radial cracks in the host olivine which indicates development of an overpressure within the inclusions at some time a volume increase of the inclusions could have been achieved by differential thermal expansion of the content of the inclusion during a heating event that mechanism requires bubble free and solid preheating inclusion contents these features are incompatible with an origin of the inclusions by trapping of a silicate melt and point toward heterogeneous trapping of solid phases the first n analyses performed in chassigny glass bearing inclusions by nuclear reaction analysis nra revealed high and variable n contents of the glass which suggests trapping of a solid precursor presumably at relatively low temperatures from a fluid rather than a melt in conclusion the glass bearing inclusions in chassigny olivine are not residuals after a closed system evolution of a trapped melt but rather heterogeneously trapped precipitates of a fluid that existed during formation of chassigny constituents consequently it is very unlikely that the host olivine has an igneous origin

shergottites dhofar 019 sau 005 shergotty and zagami 40ar 39ar chronology and trapped martian atmospheric and interior argon we report a high resolution 40ar 39ar study of mineral separates and whole rock samples of olivine phyric dhofar 019 sayh al uhaymir sau 005 and basaltic shergotty zagami shergottites excess argon is present in all samples the highest 40ar 36ar trapped ratios are found for argon in pyroxene melt inclusions 1500 maskelynite 1200 impact glass 1800 of shergotty and impact glass of sau 005 1200 a high 40ar 36ar trapped componentusually uniquely ascribed to martian atmosphere can also originate from the martian interior indicating a heterogeneous martian mantle composition as additional explanation of variable high 40ar 36ar trapped ratios in shocked shergottites we suggest argon implantation from a transient atmosphere during impact induced degassing the best 40ar 39ar age estimate for dhofar 019 is 642 72 ma maskelynite sau 005 samples are between 700900 ma old relatively high 40ar 39ar ages of melt inclusions within dhofar 019 1086 252 ma and sau 005 olivine 885 66 ma could date entrapment of a magmatic liquid during early olivine crystallization or reflect unrecognized excess 40ar components the youngest 40ar 39ar age of shergotty separates maskelynite is 370 ma that of zagami is 200 ma the 40ar 39ar chronology of dhofar 019 and sau 005 indicate 1 ga ages apparent ages uncorrected for trapped e g martian atmosphere mantle argon components approach 4 5 ga but are not caused by inherited 40ar because excess 40ar is supported by 36artrapped young ages obtained by 40ar 39ar and other chronometers argue for primary rather than secondary events the cosmic ray exposure ages calculated from cosmogenic argon are 15 7 0 7 ma dhofar 019 1 0 1 6 ma sau 005 2 1 2 5 ma shergotty and 2 2 3 0 ma zagami

enso impact on kelvin waves and associated tropical convection abstractthe impact of el nino southern oscillation enso on atmospheric kelvin waves and associated tropical convection is investigated using the ecmwf re analysis noaa outgoing longwave radiation olr and the analysis technique introduced in a previous study it is found that the phase of enso has a substantial impact on kelvin waves and associated convection over the equatorial central eastern pacific el nino la nina events enhance suppress variability of the upper tropospheric kelvin wave and the associated convection there in both extended boreal winter and summer the mechanism of the impact is through changes in the enso related thermal conditions and the ambient flow in el nino years because of sst increase in the equatorial central eastern pacific variability of eastward moving convection which is mainly associated with kelvin waves intensifies in the region in addition owing to the weakening of the equatorial eastern pacific westerly duct in the upper troposphere in el nino years

contrasting eastern pacific and central pacific types of enso abstract surface observations and subsurface ocean assimilation datasets are examined to contrast two distinct types of el nino southern oscillation enso in the tropical pacific an eastern pacific ep type and a central pacific cp type an analysis method combining empirical orthogonal function eof analysis and linear regression is used to separate these two types correlation and composite analyses based on the principal components of the eof were performed to examine the structure evolution and teleconnection of these two enso types the ep type of enso is found to have its sst anomaly center located in the eastern equatorial pacific attached to the coast of south america this type of enso is associated with basinwide thermocline and surface wind variations and shows a strong teleconnection with the tropical indian ocean in contrast the cp type of enso has most of its surface wind sst and subsurface anomalies confined in the central pacific and tends to onset develop and decay in situ

40ar 39ar studies of whole rock nakhlites evidence for the timing of formation and aqueous alteration on mars 20 25 mg whole rock samples of the nakhlites lafayette and nakhla have been analyzed via the 40ar 39ar technique in part to verify their formation ages but primarily in an attempt to determine the timing of aqueous alteration in these martian meteorites as in previous studies plateaus in apparent age are observed at about 1300 ma 1322 10 for lafayette 1332 10 and 1323 11 for nakhla presumably corresponding to crystallization ages the plateaus are not entirely flat perhaps reflecting the effects of recoil during creation of 39ar in the nuclear irradiation the first 5 20 of the k derived ar released from all three samples give apparent ages 1300 ma coupled with the fact that chronometric isotopic studies of nakhlites typically show some disturbance we believe the low temperature pattern represents more recent than 1300 ma formation of martian aqueous alteration products such as iddingsite no low temperature plateaus are observed this is consistent with petrographic evidence for multiple formation events although the lack of low temperature plateaus is far from conclusive on the other hand if there was a single time of alteration we believe that it will be difficult if not impossible to determine it using the k ar system

modes of interannual and interdecadal variability of pacific sst abstract the multichannel singular spectrum analysis has been used to characterize the spatio temporal structures of interdecadal and interannual variability of sst over the pacific ocean from 20 s to 58 n using the comprehensive ocean atmosphere data set from 1950 to 1993 three modes with distinctive spatio temporal structures were found they are an interdecadal mode a quasi quadrennial qq oscillation with a period of 51 months and a quasi biennial qb oscillation with a period of 26 months the interdecadal mode is a standing mode with opposite signs of sst anomalies in the north pacific and in the tropical pacific the amplitude of this mode is larger in the central north pacific than in the tropical pacific this mode contributes 11 4 to the total variance it is associated with cooling in the central north pacific and warming in the equatorial pacific since around 1976 77 the qq oscillation exhibits propagation of sst anomalies northeastward from the philippine sea and then eastward along 4

clues to martian brines based on halogens in salts from nakhlites and mer samples 1 chlorine and br abundances in fracture filling secondary salts in nakhla veins determined in this study by synchrotron x ray microprobe br and electron microprobe cl techniques compare well to the halogens determined recently by apxs instruments in soils and rock rinds at the gusev and meridiani sites the salts in these mars rocks arise from martian brines that have undergone evaporative or freezing concentration the halogen abundances in these salts are corrected for dilution effect because of mixing with halogen poor phases to obtain their true abundances which seem to be close to the halogen abundances in terrestrial sea brines consistent with the petrographic evidence for evaporative salt deposition sequence of carbonate sulfate halite in nakhlite meteorites nakhla veins yield high br 250 ppm and low cl br ratios 10 50 suggesting possible salt deposition from concentrated brines whereas lafayette iddingsite with low br 11 ppm and high cl br ratios 250 300 indicates salt deposition from dilute brines on mars the low cl br ratios 20 to 80 in salts from gusev and meridiani rock rinds indicate that they presumably originate from concentrated subsurface martian brines the high cl br ratio 270 in salts deposited by dilute solutions in lafayette and adirondack is similar to the chondritic cl br ratio which seems to characterize the dilute brines on mars prior to halite precipitation including early mars waters noachian or earlier our results seem to be consistent with the burt knauth model involving density stratification during evaporation freezing of brine solutions in martian regolith

changes in the relationship in the sst variability between the tropical pacific and the north pacific across the 1998 1999 regime shift this study shows that sea surface temperature sst variability in the central to eastern tropical pacific has a strong negative correlation with that of the central to eastern north pacific in the boreal winter after the 1998 1999 regime shift this phenomenon is in contrast to before the 1998 1999 regime shift the anomalous aleutian low pressure associated with the tropical sst forcing became stronger and its center shifted to the south and to the west after 1998 1999 such a modulation caused the change in the north pacific sst response this also resulted in a close relationship between the tropical pacific and north pacific sst variability the modulation of the aleutian low pressure is primarily due to the westward shift in the location of the tropical convective heating around the dateline which occurred during 1998 1999 the results of simple atmospheric model experiments support this hypothesis that the shift in the tropical convective heating to the west is responsible for the modulation of the aleutian low pressure and the associated change in the relationship of the sst variability between the tropical pacific and north pacific these results imply that the seasonal predictability of the north pacific sst has increased since 1998 1999 due to its increased correlation with the tropical pacific sst variability

analysis of the non linearity in the pattern and time evolution of el nino southern oscillation in this study the observed non linearity in the spatial pattern and time evolution of el nino southern oscillation enso events is analyzed it is shown that enso skewness is not only a characteristic of the amplitude of events el ninos being stronger than la ninas but also of the spatial pattern and time evolution it is demonstrated that these non linearities can be related to the non linear response of the zonal winds to sea surface temperature sst anomalies it is shown in observations as well as in coupled model simulations that significant differences in the spatial pattern between positive el nino versus negative la nina and strong versus weak events exist which is mostly describing the difference between central and east pacific events central pacific events tend to be weak el nino or strong la nina events in turn east pacific events tend to be strong el nino or weak la nina events a rotation of the two leading empirical orthogonal function modes illustrates that for both el nino and la nina extreme events are more likely than expected from a normal distribution the bjerknes feedbacks and time evolution of strong enso events in observations as well as in coupled model simulations also show strong asymmetries with strong el ninos being forced more strongly by zonal wind than by thermocline depth anomalies and are followed by la nina events in turn strong la nina events are preceded by el nino events and are more strongly forced by thermocline depth anomalies than by wind anomalies further the zonal wind response to sea surface temperature anomalies during strong el nino events is stronger and shifted to the east relative to strong la nina events supporting the eastward shifted el nino pattern and the asymmetric time evolution based on the simplified hybrid coupled rechoz model of enso it can be shown that the non linear zonal wind response to sst anomalies causes the asymmetric forcings of enso events this also implies that strong el ninos are mostly wind driven and less predictable and strong la ninas are mostly thermocline depth driven and better predictable which is demonstrated by a set of 100 perfect model forecast ensembles

common asteroid break up events of eucrites diogenites and howardites and cosmic ray production rates for noble gases in achondrites we determined the cosmic ray produced noble gas abundances in eight diogenites four eucrites and four howardites using these and additional noble gas and chemical data from the literature composition and shielding dependent production rates of achondrites for 3he 21ne 38ar 78kr 83kr and126xe were derived based on 81krkr exposure ages the cosmogenic ratio 22ne 21ne is found to be a valid shielding indicator for all howardites eucrites and diogenites heds this ratio correlates with other shielding dependent ratios such as 78kr 83kr 80kr 83kr 124xe 131xe 126xe 131xe and 128xe 131xe we show that strong correlations for these ratios also exist for basaltic lunar rocks the new production rates were used for the calculation of exposure ages for all heds with known noble gas abundances two major exposure age clusters at 21 ma and 38 ma are observed in all three classes we find that five asteroid break up events characterized by exposure ages 6 1 ma 12 2 ma 21 4 ma 38 8 ma and 73 3 ma produced all diogenites fifteen out of seventeen howardites and twenty eight out of thirty nine eucrites we conclude that asteroidal or cometary impact events at such times on one or several parent bodies are responsible for the ejection of eucrites howardites and diogenites probable parent bodies are multiple 4 vesta derived kilometer sized objects of basaltic achondritic composition reaching the 3 1 resonance region a proposed source area for meteorites the direct ejection from vesta and capture by earth of basaltic meteorites has been shown to be dynamically difficult in such a scenario large events 38 ma and 21 ma ago are required liberating simultaneously material representing vesta s surface eucrites howardites and interior regions diogenites

formation of a martian pyroxenite a comparative study of the nakhlite meteorites and theo s flow the unusual composition of the nakhlites a group of pyroxenitic martian meteorites with young ages presents an opportunity to learn about nonbasaltic magmatic activity on another planet however the limited number of these meteorites makes unraveling their history difficult a promising terrestrial analog for the formation of the nakhlites is theo s flow in ontario canada this atypical 120 m thick flow differentiated in place forming distinct layered lithologies of peridotite pyroxenite and gabbro theo s pyroxenite and the nakhlites share strikingly similar petrographies with concentrated euhedral to subhedral augite grains set in a plagioclase rich matrix these two suites of rocks also share specific petrologic features mineral and whole rock compositional features and size and spatial distributions of cumulus grains the numerous similarities suggest that the nakhlites formed by a similar mechanism in a surface lava flow or shallow intrusion their formation could have involved settling of crystals in a phenocryst laden flow or in situ nucleation and growth of pyroxenes in an ultramafic lava flow the latter case is more likely and requires steady state nucleation and growth of clusters of pyroxene grains and olivine in the nakhlites circulating in a strongly convecting melt pool followed by settling and continued growth in a thickening cumulate pile trapped pockets of intercumulus liquid in the pile gradually evolved finally growing fe enriched rims on cumulus grains with sufficient evolution the melt reached plagioclase supersaturation causing rapid growth of plagioclase sprays and late stage mesostasis growth

argon 39 argon 40 ages and trapped argon in martian shergottites chassigny and allan hills 84001 abstract argon isotopic abundances were measured in neutron irradiated samples of martian meteorites chassigny allan hills alh 84001 alh 77005 elephant moraine eet 79001 yamato y 793605 shergotty zagami and queen alexandra range que 94201 and in unirradiated samples of alh 77005 chassigny gives a 39ar 40ar age of 1 32 0 07 ga which is similar to radiometric ages of the nakhlites argon 39 argon 40 data for alh 84001 indicate ages between 3 9 and 4 3 ga a more precise definition of this age requires detailed characterization of the multiple trapped ar components in alh 84001 and of 39ar recoil distribution all six shergottite samples show apparent 39ar 40ar ages substantially older than the 165 200 ma range in ages given by other isotope dating techniques shergottites appear to contain ubiquitous ar components acquired from the martian atmosphere the martian mantle and commonly terrestrial atmospheric contamination zagami feldspar also suggests inherited radiogenic 40ar these data analyses indicate that the recent martian atmospheric component trapped in shergottites has a 40ar 36ar ratio possibly as low as 1750 and no greater than 1900 these ratios are less than the value of 3000 500 reported by viking the 40ar 36ar ratio for the martian mantle component is probably 500 but is poorly constrained the correlation between trapped 40ar 36ar and 129xe 132xe ratios in shergottite impact glasses and unirradiated samples of alh 77005 shows considerable scatter and suggests that the 36ar 132xe ratio in the martian components may vary resolution of martian atmospheric 40ar 36ar ratio at different time periods i e at 4 0 and 0 2 ga is also difficult without an understanding of the composition of various trapped components

ejection of martian meteorites we investigated the transfer of meteorites from mars to earth with a combined mineralogical and numerical approach we used quantitative shock pressure barometry and thermodynamic calculations of post shock temperatures to constrain the pressure temperature conditions for the ejection of martian meteorites the results show that shock pressures allowing the ejection of martian meteorites range from 5 to 55 gpa with corresponding post shock temperature elevations of 10 to about 1000 c with respect to shock pressures and post shock temperatures an ejection of potentially viable organisms in martian surface rocks seems possible a calculation of the cooling time in space for the most highly shocked martian meteorite allan hills alh 77005 was performed and yielded a best fit for a post shock temperature of 1000 c and a meteoroid size of 0 4 to 0 6 m the final burial depths of the sub volcanic to volcanic martian rocks as indicated by textures and mineral compositions of meteorites are in good agreement with the postulated size of the potential source region for martian meteorites during the impact of a small projectile 200 m as defined by numerical modeling artemieva and ivanov 2004 a comparison of shock pressures and ejection and terrestrial ages indicates that on average highly shocked fragments reach earth crossing orbits faster than weakly shocked fragments if climatic changes on mars have a significant influence on the atmospheric pressure they could account for the increase of recorded ejection events of martian meteorites in the last 5 ma

martian atmospheric xenon contents of nakhla mineral separates implications for the origin of elemental mass fractionation abstract analyses of mineral separates from nakhla reveal that martian atmosphere derived xenon is present in olivine and pyroxene in concentrations close to that of the bulk meteorite and at elevated concentrations in mesostasis we argue that neither aqueous alteration nor adsorption followed by shock incorporation are plausible mechanisms for incorporating this gas component into the meteorite and suggest trapping occurred on formation direct dissolution of martian atmosphere in the parent melt is unlikely since it would require a partial pressure of xenon in the martian atmosphere greater than consideration of the i xe system realistically allows the melt appears to have been insufficiently hydrated for water transport to have been solely responsible addition of as little as 500 ppm of martian soil to the melt could account for the observed composition and elemental mass fractionation

indo pacific variability on seasonal to multidecadal time scales part i intrinsic sst modes in models and observations abstractthe variability of indo pacific sst on seasonal to multidecadal time scales is investigated using a recently introduced technique called nonlinear laplacian spectral analysis nlsa through this technique drawbacks associated with ad hoc prefiltering of the input data are avoided enabling recovery of low frequency and intermittent modes not previously accessible via classical approaches here a multiscale hierarchy of spatiotemporal modes is identified for indo pacific sst in millennial control runs of ccsm4 and gfdl cm3 and in hadisst data on interannual time scales a mode with spatiotemporal patterns corresponding to the fundamental component of enso emerges along with enso modulated annual modes consistent with combination mode theory the enso combination modes also feature prominent activity in the indian ocean explaining a significant fraction of the sst variance in regions associated with the indian ocean dipole and suggesting a deterministic relationship between these patterns a p

modified sulfur isotopic compositions of sulfides in the nakhlites and chassigny variable sulfur isotopic ratios of sulfide minerals in the nakhlites and chassigny have been measured by ion microprobe the ranges and means of 34s values of pyrrhotite and pyrite in nakhlites become more negative in the sequence nakhla 34s 1 7 to 4 9 mean 34s 1 5 2 0 governador valadares 34s 2 4 to 3 8 mean 34s 0 7 2 4 lafayette 6 1 to 0 1 mean 34s 3 2 2 1 this is also the sequence of increasing degrees of subsolidus re equilibration suggesting that 32s enrichment may be related to the subsolidus thermal history a chalcopyrite vein cross cutting a pyrrhotite in nakhla coupled with chalcopyrite having slightly lighter 34s values suggests that subsolidus fluids may have become isotopically lighter with respect to sulfur in nakhla with time pyrite has replaced pyrrhotite in lafayette suggesting that fo2 and or fs2 increased after pyrrhotite crystallization a model involving subsolidus hydrothermal modification of igneous sulfide minerals with 34s 0 due to late stage oxidation of fluids provides a reasonable explanation for the sulfur isotopic systematics of the nakhlites and chassigny sulfur isotopic alteration is believed to have occurred during the waning stages of nakhlite magmatism rather than during a much later low temperature 100 c iddingsite formation event based on the ineffectiveness of abiogenic sulfur isotopic fractionation below 200 c variable mixing of two isotopically different fluids also could have produced the observed fractionations although an isotopically light reservoir of sulfur is problematic other possible mechanisms evaluated to explain the sulfur isotopic values of the sulfide minerals include martian mantle heterogeneity possible influence of martian biological processes and magmatic degassing of so2

40ar 39ar and cosmic ray exposure ages of nakhlites nakhla lafayette governador valadares and chassigny we present 40ar 39ar dating results of handpicked mineral separates and wholerock samples of nakhla lafayette and chassigny our data on nakhla and lafayette and recently reported ages for some nakhlites and chassigny misawa et al 2006 park et al 2009 point to formation ages of approximately 1 4 ga rather than 1 3 ga that is consistent with previous suggestions of close in time formation of nakhlites and chassigny in lafayette mesostasis we detected a secondary degassing event at approximately 1 1 ga which is not related to iddingsite formation it may have been caused by a medium grade thermal event resetting the mesostasis age but not influencing the k ar system of magmatic inclusions and the original igneous texture of this rock cosmic ray exposure ages for these meteorites and for governador valadares were calculated from bulk rock concentrations of cosmogenic nuclides 3he 21ne and 38ar individual results are similar to literature data the considerable scatter of t3 t21 and t38 ages is due to systematic uncertainties related to bulk rock and target element chemistry production rates and shielding effects this hampers efforts to better constrain the hypothesis of a single ejection event for all nakhlites and chassigny from a confined martian surface terrain eugster 2003 garrison and bogard 2005 cosmic ray exposure ages from stepwise release age spectra using 38ar and neutron induced 37ar from ca in irradiated samples can eliminate errors induced by bulk chemistry on production rates although not from shielding conditions

the parent magma of the nakhla snc meteorite inferred from magmatic inclusions abstract the nakhla meteorite one of the snc group of putative martian origin is an igneous rock a cumulate of augite and olivine that does not represent a magma composition samples of its parent magma were trapped as magmatic inclusions in its cumulus olivine crystals the inclusions range from 10 350 m in diameter and consist of augite rich in ti and al silica rich glass iron oxides ilmenite apatite and rare amphibole each inclusion has a rind of augite and chromite against its host olivine and a core of radiating sprays of augite set in glass and feldspar these textures are consistent with an origin as trapped silicate liquid twenty four inclusions were analyzed by electron microprobe by averaging series of rastered beam analyses on average the analyses are independent of the size of the inclusion most clearly for inclusions larger than 70 m diameter and variations among analyses are consistent with small differences in the proportions of augite glass and iron oxides exposed on thin section surfaces the average inclusion analysis is calculated to represent 28 host olivine and 72 inclusion composition the inclusion rinds are calculated to be 13 of the inclusion composition for which a small correction is made the inclusion composition is then corrected for mg fe exchange with the host olivine to chemical equilibrium with the cumulus augite cores and crystallization of 13 olivine onto the host crystal to yield a magma composition with the proper mgo feo ratio and with olivine and augite on its liquidus this composition nk93 is an estimate of nakhla s parent magma originally trapped in the inclusions nk93 is basaltic rich in iron and poor in aluminum compared to terrestrial basalts its abundances of al ti and na are consistent with the geochemistry of the snc meteorites as a whole nk93 is similar to the parent magmas proposed in an independent study of magmatic inclusions in nakhla but unlike other proposed compositions one proposed parent magma based on mass balance and the assumption that nakhla was a closed system after crystal accumulation is inconsistent with the magmatic inclusion studies and nakhla s petrography this suggests that nakhla was not a closed system but was infiltrated by post cumulus basaltic magmas another suggested parent magma was derived from element distribution between augite and basaltic magma but that calculation relied on an incorrect augite composition using a correct augite composition in that calculation yields a parent magma much closer in composition to nk93 thus three independent approaches converge in requiring that nakhla originally formed from a low al low mgo feo basalt like nk93

indo pacific variability on seasonal to multidecadal time scales part ii multiscale atmosphere ocean linkages abstractthe coupled atmosphere ocean variability of the indo pacific domain on seasonal to multidecadal time scales is investigated in ccsm4 and in observations through nonlinear laplacian spectral analysis nlsa it is found that enso modes and combination modes of enso with the annual cycle exhibit a seasonally synchronized southward shift of equatorial surface zonal winds and thermocline adjustment consistent with terminating el nino and la nina events the surface winds associated with these modes also generate teleconnections between the pacific and indian oceans leading to sst anomalies characteristic of the indian ocean dipole the family of nlsa enso modes is used to study el nino la nina asymmetries and it is found that a group of secondary enso modes with more rapidly decorrelating temporal patterns contributes significantly to positively skewed sst and zonal wind statistics besides enso fundamental and combination modes representing the tropospheric biennial oscillation tbo are found to

interannual to decadal predictability of tropical and north pacific sea surface temperatures abstract a multivariate empirical model is used to show that predictability of the dominant patterns of tropical and north pacific oceanic variability el nino southern oscillation enso and the pacific decadal oscillation pdo is mostly limited to little more than a year despite the presence of spectral peaks on decadal time scales the model used is a linear inverse model lim derived from the observed simultaneous and 1 yr lag correlation statistics of july june averaged sst from the hadley centre global sea ice and sea surface temperature hadisst dataset for the years 1900 2002 the model accurately reproduces the power spectra of the data including interannual and interdecadal spectral peaks that are significant relative to univariate red noise eigenanalysis of the linear dynamical operator yields propagating eigenmodes that correspond to these peaks but have very short decay times and thus limited predictability longer term predictability does exist however due to two stationary eigen

observed changes in baroclinic wave activity during the life cycles of low frequency circulation anomalies abstract anomalous baroclinic wave activity during the onset and decay of blocking patterns in the northern hemisphere winter is investigated based upon a 30 year record of 500 mb height and sea level pressure a slowly varying envelope function is defined at each gridpoint in order to represent the modulation of the amplitude of baroclinic wave activity by the low frequency circulation anomalies related to blocking the envelope function fields and the low frequency circulation fields are composited relative to the onset and decay times of four persistent dipole patterns in low frequency circulation anomalies located downstream of the climatological mean stormtracks one polarity of the anomaly patterns corresponds to dipole or modon like blocking patterns over the eastern oceans and the other to strong zonal flow patterns each of the eight composites is comprised of more than 50 persistent blocking or zonal flow episodes the most striking common feature observed during the onset of blocking over th

petrogenesis of the nakhlite meteorites evidence from cumulate mineral zoning abstract a simple igneous petrogenesis for the meteorite nakhla has previously been called into question because mg fe ratios in olivine indicate substantial disequilibrium between the predominant cumulus minerals olivine and augite comparative analyses of simulated diffusive zoning and the observed cumulus mineral zoning for all three nakhlites nakhla governador valadares and lafayette show that their current compositions do not necessarily reflect parental magma compositions instead diffusion has altered primary cumulus compositions to varying degrees nakhla being the least affected and lafayette being almost completely re equilibrated only the cores of augite grains in nakhla and governador valadares appear to have preserved their original compositions mineral zoning in each meteorite is strongly concentric around mesostasis areas suggesting that reaction with intercumulus liquid has controlled the observed zoning the presence of pigeonite and orthopyroxene overgrowths in nakhla and governador valadares and of poikilitic orthopyroxene enclosing olivine relicts in lafayette indicate substantial late magmatic reactions two pyroxene geothermometry for lafayette indicates temperatures around 950 c suggesting subsolidus equilibration as well the nakhlites appear to be a series of relatively simple cumulate rocks which have undergone various amounts of late magmatic and subsolidus diffusion possibly reflecting their relative positions in a cooling cumulate pile

noble gases in mineral separates from three shergottites shergotty zagami and eeta79001 this study provides a complete data set of all five noble gases for bulk samples and mineral separates from three martian shergottites shergotty bulk pyroxene maskelynite zagami bulk pyroxene maskelynite and elephant moraine eet a79001 lithology a bulk pyroxene we also give a compilation of all noble gas and nitrogen studies performed on these meteorites our mean values for cosmic ray exposure ages from 3he 21ne and 38ar are 2 48 myr for shergotty 2 73 myr for zagami and 0 65 myr for eeta79001 lith a serious loss of radiogenic 4he due to shock is observed cosmogenic neon results for bulk samples from 13 martian meteorites new data and literature data are used in addition to the mineral separates of this study in a new approach to explore evidence of solar cosmic ray effects while a contribution of this low energy irradiation is strongly indicated for all of the shergottites spallation ne in chassigny allan hills alh 84001 and the nakhlites is fully explained by galactic cosmic ray spallation implanted martian atmospheric gases are present in all mineral separates and the thermal release indicates a near surface siting we derive an estimate for the 40ar 36ar ratio of the martian interior component by subtracting from measured ar in the k poor pyroxenes the small radiogenic component as well as the implanted atmospheric component as indicated from 129xe excesses unless compromised by the presence of additional components a high ratio of 2000 is indicated for martian interior argon similar to that in the martian atmosphere since much lower ratios have been inferred for chassigny and alh 84001 the result may indicate spatial and or temporal variations of 40ar 36ar in the martian mantle

intercalibration of 40ar 39ar age standards nl 25 hb3gr hornblende ga1550 sb 3 hd b1 biotite and bmus 2 muscovite abstract 40 ar 39 ar dating requires precise and accurate age data of standard fluence monitors besides primary calibration of k and 40 ar concentrations i e the ages are calculated with precise k ar dating intercalibration of the different monitors in use provides important cross checks of the validity of standard ages and implicitly reliability and uncertainty of chronological studies that rely on these standards here we report intercalibration of 5 primary international 40 ar 39 ar standards and one internal laboratory monitor a major goal of this study was to check the ages of the nl 25 hornblende standard and of the muscovite laboratory standard bmus 2 against the international standards hd b1 ga1550 sb 3 and hb3gr in replicate measurements of three irradiation series 40 ar 39 ar ages for the fluence monitors were found which agree within 1 error limits with the reported age values of 2660 9 ma for nl 25 hb3gr 1073 6 4 6 ma bmus 2 328 5 1 1 ma sb 3 162 9 0 8 ga1550 98 79 0 54 and 24 21 0 32 for hd b1 for the hornblende nl 25 fluence monitor a new slightly different 40 ar 39 ar age of 2657 4 ma is suggested for the age of the muscovite bmus 2 laboratory standard we recommend 328 5 1 1 ma and for biotite hd b1 a more precise value of 24 18 0 09 ma

the case for old basaltic shergottites abstract the crystallization age of shergottites is currently not agreed upon although mineral 87 rb 87 sr 147 sm 143 nd 176 lu 176 hf and u pb isochrons all give very young ages typically in the range of 160 180 ma 207 pb 206 pb data support a much older crystallization age at 4 1 ga which is consistent with published whole rock 87 rb 87 sr data on basaltic shergottites different isotopic systems present different complexities but crater counting chronology which shows that a substantial fraction of the martian surface was resurfaced during the late heavy bombardment is in favor of an old martian lithosphere with ages in accordance with pb pb and rb sr isotopic data a 4 1 ga pb pb age of shergottites also agrees with the 142 nd and 182 w anomalies found in these rocks and concur with the presence of an actively convecting mantle during the first 500 myr of the planet s history we here present new sm nd lu hf and pb pb mineral isochrons for the basaltic shergottites shergotty and los angeles complementing our previous results on zagami bouvier a blichert toft j vervoort j d and albarede f 2005 the age of snc meteorites and the antiquity of the martian surface earth planet sci lett 240 221 233 the internal 147 sm 143 nd and 176 lu 176 hf isochrons give young ages of respectively 172 40 mswd 2 0 and 188 91 mswd 3 1 for shergotty and 181 13 mswd 0 14 and 159 42 mswd 0 01 for los angeles in contrast the pb isotope compositions of the leached whole rock fragments and maskelynite separates of shergotty and los angeles fall on the whole rock isochron previously established for zagami and other shergottite samples and collectively yield a pb pb age of 4050 70 ma for the crystallization of the basaltic shergottite suite the contrast between the 170 ma ages of internal isochrons and the 4 1 ga age supported by pb pb and 87 rb 87 sr on whole rocks simply reflects that the younger age dates the perturbation of a suite of rocks of noachian age the internal rb sr sm nd lu hf and u pb errorchrons are heavily biased by the presence of disseminated phosphate minerals and inclusions for which d h ratios d 4600 indicate strong interaction with martian subsurface waters in contrast baddeleyite occasionally present in sncs and also having extremely young u pb ages reflect resetting under the shock conditions that prevailed either during shergottite extraction from the planet or from impacts associated with a major break up event of planetesimals in the main asteroid belt we finally also re examine 39 ar 40 ar data on snc meteorites and suggest that they as well support old crystallization ages

the parental magma of the nakhla achondrite ultrabasic volcanism on the shergottite parent body the nakhla meteorite is an augite rich igneous cumulate rock magma trapped among the cumulus grains is now represented by fine grained mesostasis and post cumulus overgrowths on cumulus grains the composition of the intercumulus magma calculated by mass balance is ultrabasic sio2 45 and enriched in incompatible elements lalu 6 ci the cumulus augite and intercumulus magma were in chemical equilibrium implying that the intercumulus magma is a sample of nakhla s parental magma complex processes like infiltration metasomatism were therefore unimportant nakhla contains olivine crystals which are as large or larger than the cumulus augite crystals the largest olivine crystals probably xenocrysts preserve core compositions too fe rich to have been in equilibrium with the intercumulus magma other smaller olivine grains may have been phenocrysts the closest terrestrial analogs to nakhla and the other nakhlites are pyroxene rich cumulate layers in differentiated picrite and komatiite flows and shallow sills spinel or garnet was fractionated from the parental magmas of the nakhlites or their parental mantle based on the superchondritic caoal2o3 ratio of nakhla s intercumulus magma and its lack of an eu anomaly the three nakhlites and chassigny are half of the known samples of the shergottite parent body spb one may tentatively infer that ultrabasic volcanism was much more important on the spb than on the moon eucrite parent body or present day earth

cold tongue and warm pool enso events in cmip5 mean state and future projections abstractthe representation of the el nino southern oscillation enso under historical forcing and future projections is analyzed in 34 models from the coupled model intercomparison project phase 5 cmip5 most models realistically simulate the observed intensity and location of maximum sea surface temperature sst anomalies during enso events however there exist systematic biases in the westward extent of enso related sst anomalies driven by unrealistic westward displacement and enhancement of the equatorial wind stress in the western pacific almost all cmip5 models capture the observed asymmetry in magnitude between the warm and cold events i e el ninos are stronger than la ninas and between the two types of el ninos that is cold tongue ct el ninos are stronger than warm pool wp el ninos however most models fail to reproduce the asymmetry between the two types of la ninas with ct stronger than wp events which is opposite to observations most models capture the observed peak in enso

on the relationship between indian ocean sea surface temperature and the transition from el nino to la nina the relationship between indian ocean sea surface temperature and the transition of el nino events into either la nina or el nino southern oscillation neutral conditions is examined in both observations and the retrospective ensemble hindcasts of the national center for environmental prediction climate forecast system the southern indian ocean is shown to demonstrate a particularly robust and consistent relationship with the evolution of these transitions these associations are described and a physical mechanism involving air sea interaction in the indian and western pacific oceans is proposed observations suggest that easterly surface wind anomalies in the western pacific ocean are associated with the emergence of la nina during boreal summer and fall here it is shown that these winds are significantly correlated to southern indian ocean sea surface temperature in the preceding spring that is characterized by a large scale zonal dipole of cool and warm anomalies in the southwestern and southeastern indian oceans respectively these associations are particularly pronounced for strong el nino conditions during the dissipation of which a pronounced wavetrain like atmospheric pattern accompanies sea surface temperature anomalies in the southern indian ocean together the circulation and sea surface temperature anomalies increase the meridional cross equatorial temperature gradient in the western indian ocean and mute intraseasonal variability while strengthening surface equatorial easterly winds in the indo pacific warm pool collectively these anomalies favor subsequent la nina development on the basis of these observed associations a predictive model that demonstrates skill in anticipating the nature of el nino transitions involving the southern indian ocean asian monsoon and el nino southern oscillation is proposed in the national center for environmental prediction climate forecast system the relationships described above are simulated both consistently and realistically despite model weaknesses further bolstering a key role of southern indian ocean and predictive relationship comparison of fully coupled and sea surface temperature forced simulations suggests a key role for air sea interaction in the observed associations moreover it is demonstrated that coupled simulations of el nino southern oscillation may benefit substantially from improved representation of indian ocean variability and indo pacific interaction

connections between the pacific ocean tropics and midlatitudes on decadal timescales abstract connections between the tropical and midlatitude pacific on decadal timescales are examined using a 137 yr run of a fully coupled ocean atmosphere general circulation model it is shown that the model does a credible job of simulating both enso scale and decadal scale variability and that there are statistically significant correlations between the midlatitudes and tropics on decadal timescales three physical mechanisms linking the regions are examined 1 oceanic advection along isopycnal surfaces from the midlatitude subduction regions to the tropics 2 coastally trapped or kelvin wave propagation between the tropics and midlatitudes and 3 near simultaneous communication between the regions affected by changes in the atmosphere it is found that communication via the atmosphere explains the strongest correlations found in the model further evidence is presented that is consistent with the idea that midlatitude sea surface temperature anomalies drive changes in the trade wind system that a

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

decadal changes of enso persistence barrier in sst and ocean heat content indices 1958 2001 decadal changes of el nino southern oscillation enso persistence barriers in various indices of sea surface temperature sst and ocean heat content ohc are examined in this study using observations and ocean data assimilation products for the period 1958 2001 it is found that the sst indices in the eastern and central equatorial pacific exhibit very different decadal barrier variability the variability is large for the eastern pacific sst indices nino1 2 and nino3 whose persistence barriers shifted abruptly in 1976 1977 and 1989 1990 in contrast the central pacific sst indices nino3 4 and nino4 experienced little decadal barrier variability and have had their persistence barriers fixed in spring in the past four decades the zonal mean ohc index averaged over the equatorial pacific shows decadal barrier changes similar to those in the eastern pacific sst indices and always leads the nino3 sst barrier by about one season it is noticed that the sst persistence barrier appeared first in the eastern pacific before 1976 1977 first in the central pacific between 1976 1977 and 1989 1990 and almost simultaneous in both the eastern and central pacific after 1989 1990 these timings coincide with the westward propagating eastward propagating and standing pattern of enso sst anomalies observed in these three periods these results suggest that enso sst anomalies in the equatorial pacific can be considered to consist of two different processes a central pacific process whose phase transition such as onset and barrier always happen in spring and an eastern pacific process whose phase transition and barrier change from decade to decade and are influenced by changes in the mean thermocline depth along the equatorial pacific

enso diversity and the recent appearance of central pacific enso enso diversity refers to the appearance in recent decades of different el nino types in the tropical pacific in addition to the canonical el nino the newly discovered type called central pacific cp el nino has its center of warming shifted more to the central equatorial pacific whether these enso types are really distinct or are different manifestations of a continuum is currently under debate the mechanisms for the recent appearance of the additional type of enso have not been clarified while previously it was claimed that the increased cp el nino occurrence in recent decades were due to tropical trade winds weakened by global warming the observed trade winds actually intensified we systematically study the variability of the pacific sea surface temperature sst using the new method of rotated principal component analysis rpca the essential statistical characteristics of these two el nino types are found to be describable by only three fundamental modes of pan pacific sst with different proportions the enso cycle the pan pacific counterpart of the regionally defined pacific decadal oscillation pdo and a new climate mode we call the central pacific variability cpv it is shown that cp el nino can be described by the pdo and the cpv the latter has a horseshoe shaped warm sst pattern in the central pacific flanked by cold sst to the east roughly similar to the original definition of enso modoki by ashok et al j geophys res oceans 112 c11007 2007 as the second empirical orthogonal function in a narrow tropical domain decomposition the principal component pc of this mode called modoki pc mpc was thought to characterize the occurrence of this new phenomenon but it has been shown to be unable to separate it from the canonical enso in contrast we demonstrate that central pacific el nino occurs when the cpv index is larger than 0 5 the intensity of the cpv mode has increased dramatically since 1970s likely as a result of the intensification of the easterly trade winds in the tropical pacific which tilts the thermocline along the tropical pacific and raises the sst in the central equatorial pacific moderate el ninos are more prone to stalling in the central pacific becoming cp el ninos

on the structure and teleconnections of north atlantic decadal variability abstractdecadal variability in the north atlantic has been associated in the literature with a tripolar pattern of sea surface temperature sst anomalies that show one sign in the western midlatitudinal north atlantic and the opposite in the subpolar and tropical north atlantic the present analysis of observed sst from 1870 to 2009 leads to the dissection of the sst tripole into two components each with a different time scale in the decadal band and different teleconnections in the atlantic basin while the subpolar and tropical poles present quasi decadal variations with a period of about 9 years essentially uncorrelated with other parts of the basin the center of action in the western midlatitudes is characterized by a longer time scale of about 14 years and significant correlations with the tropical south atlantic and the norwegian and north sea s the 9 yr period variations are associated with an atmospheric configuration resembling the east atlantic pattern whereas the 14 yr period fluctuation

depth extent of damage zones around the central calaveras fault from waveform analysis of repeating earthquakes summary we systematically investigate spatial variations of temporal changes and depth extent of damage zones along the calaveras fault that ruptured during the 1984 morgan hill earthquake by the waveform analysis of 333 sets of repeating earthquakes we use a sliding window waveform cross correlation technique to measure traveltime changes in waveforms generated by each repeating cluster we find clear traveltime delays in the s and early s coda waves for events immediately after the morgan hill main shock the amplitudes of the time delays decrease logarithmically with time since the main shock indicating a time dependent recovery healing process following the abrupt coseismic temporal changes the largest temporal changes are observed at station cco that is the closest to the rupture zone of the morgan hill main shock the time delays at this station are larger for clusters in the top 6 km and decrease systematically at larger depth in comparison the time delays observed at other five stations are much smaller and do not show clear relationship with hypocentral depth we suggest that the temporal changes at these five stations mostly occur in the top few hundred metres of the near surface layers while the temporal changes at station cco are likely associated with the damage zone around the calaveras fault that is well developed in the top few kilometres of the upper crust our results are consistent with the inference of a widespread damage and non linearity in the near surface layers associated with strong ground motions of nearby large earthquakes and localized damages and flower type structures around active faults based on previous studies of fault zone structures and recent 3 d numerical simulations

asymmetry between el nino and la nina in a global coupled gcm with an eddy permitting ocean resolution observations show the asymmetric nature of el nino and la nina sea surface temperature sst anomalies warm events are often stronger than cold events this asymmetric behavior is an important feature that can be used to validate coupled models to test their ability to represent the climate system the asymmetry of el nino and la nina sst anomalies has been investigated in a simulation of the hadley centre eddy permitting coupled general circulation model it is found that the asymmetric behavior is captured by the model with sst anomalies associated with strong el nino events being greater than those associated with strong la nina events the pattern of the sst asymmetry also bears some similar characteristics to those based on observations despite the deficiency that sst anomalies associated with both el nino and la nina extend too far westward in the model through a heat budget analysis of the ocean mixed layer it is shown that nonlinear dynamic heating ndh is important in generating intense el nino and the sst asymmetry between el nino and la nina events especially in the eastern tropical pacific ocean this nonlinear dynamic heating enhances the amplitude of el nino and reduces the amplitude of la nina and therefore leads to the asymmetry between el nino and la nina events with el nino being stronger however the skewness and asymmetry in the model are relatively weak being consistent with a relatively weak nonlinear dynamical heating it is also shown that the eastward propagating feature of subsurface anomalies provides a favorable phase relationship between temperature and current anomalies that results in strong nonlinear dynamical heating that tends to produce stronger el ninos in addition in the model simulation the nonlinear nature of zonal wind stress anomalies between el nino and la nina events also plays an important role in the central tropical pacific these different mechanisms work constructively to determine the asymmetry between el nino and la nina events in the model and they are similar to those proposed in recent studies based on observations the ability of the model to simulate this asymmetric feature is encouraging and offers hope to the challenge of predicting the amplitude of strong el nino events

factors that affect the amplitude of el nino in global coupled climate models historically el nino like events simulated in global coupled climate models have had reduced amplitude compared to observations here el nino like phenomena are compared in ten sensitivity experiments using two recent global coupled models these models have various combinations of horizontal and vertical ocean resolution ocean physics and atmospheric model resolution it is demonstrated that the lower the value of the ocean background vertical diffusivity the greater the amplitude of el nino variability which is related primarily to a sharper equatorial thermocline among models with low background vertical diffusivity stronger equatorial zonal wind stress is associated with relatively higher amplitude el nino variability along with more realistic east west sea surface temperature sst gradient along the equator the sst seasonal cycle in the eastern tropical pacific has too much of a semiannual component with a double intertropical convergence zone itcz in all experiments and thus does not affect nor is it affected by the amplitude of el nino variability systematic errors affecting the spatial variability of el nino in the experiments are characterized by the eastern equatorial pacific cold tongue regime extending too far westward into the warm pool the time scales of interannual variability as represented by time series of nino3 ssts show significant power in the 3 4 year enso band and 2 2 5 year tropospheric biennial oscillation tbo band in the model experiments the tbo periods in the models agree well with the observations while the enso periods are near the short end of the range of 3 6 years observed during the period 1950 94 the close association between interannual variability of equatorial eastern pacific ssts and large scale sst patterns is represented by significant correlations between nino3 time series and the pc time series of the first eofs of near global ssts in the models and observations

the interconnected global climate system a review of tropical polar teleconnections abstractthis paper summarizes advances in research on tropical polar teleconnections made roughly over the last decade elucidating el nino southern oscillation enso impacts on high latitudes has remained an important focus along different lines of inquiry tropical to polar connections have also been discovered at the intra seasonal timescale associated with madden julian oscillations mjo on the timescale of decades changes in mjo phases can result in temperature and sea ice changes in the polar regions of both hemispheres moreover the long term changes in sst of the western tropical pacific tropical atlantic and north atlantic ocean have been linked to the rapid winter warming around the antarctic peninsula while sst changes in the central tropical pacific have been linked to the warming in west antarctica rossby wave trains emanating from the tropics remain the key mechanism for tropical and polar teleconnections from intraseasonal to decadal timescales enso related tropical sst anomal

weakened interannual variability in the tropical pacific ocean since 2000 abstractan interdecadal shift in the variability and mean state of the tropical pacific ocean is investigated within the context of changes in el nino southern oscillation enso compared with 1979 99 the interannual variability in the tropical pacific was significantly weaker in 2000 11 and this shift can be seen by coherent changes in both the tropical atmosphere and ocean for example the equatorial thermocline tilt became steeper during 2000 11 which was consistent with positive negative sea surface temperature anomalies increased decreased precipitation and enhanced suppressed convection in the western central and eastern tropical pacific which reflected an intensification of the walker circulation the combination of a steeper thermocline slope with stronger surface trade winds is proposed to have hampered the eastward migration of the warm water along the equatorial pacific as a consequence the variability of the warm water volume was reduced and thus enso amplitude also decreased

improved extended reconstruction of sst 1854 1997 abstract an improved sst reconstruction for the 1854 1997 period is developed compared to the version 1 analysis in the western tropical pacific the tropical atlantic and indian oceans more variance is resolved in the new analysis this improved analysis also uses sea ice concentrations to improve the high latitude sst analysis and a modified historical bias correction for the 1939 41 period in addition the new analysis includes an improved error estimate analysis uncertainty is largest in the nineteenth century and during the two world wars due to sparse sampling the near global average sst in the new analysis is consistent with the version 1 reconstruction the 95 confidence uncertainty for the near global average is 0 4 c or more in the nineteenth century near 0 2 c for the first half of the twentieth century and 0 1 c or less after 1950

the age of the kara impact structure russia for the 65 km sized kara impact structure close to the polar ural we report an age of 70 3 2 2 ma 2s defined by the mean of 40ar 39ar plateau ages for three glassy or crystalline impact melt rocks cleaned from mineral and rock clasts the fine structure of the age spectra of these samples can quantitatively be simulated by modeling taking into account 39ar recoil effects without assuming the presence of excess ar the calculations corroborate our age results by showing that 39ar recoil does not affect the plateau fractions previously kara has been proposed as a probable k t impact site or was related to the campanian maastrichtian boundary at 73 ma at the 2s level both suggestions are ruled out by the well constrained age for the kara impact structure

enso asymmetry in cmip5 models abstractthe el nino la nina asymmetry is evaluated in 14 coupled models from phase 5 of the coupled model intercomparison project cmip5 the results show that an underestimate of enso asymmetry a common problem noted in cmip3 models remains a common problem in cmip5 coupled models the weaker enso asymmetry in the models primarily results from a weaker sst warm anomaly over the eastern pacific and a westward shift of the center of the anomaly in contrast sst anomalies for the la nina phase are close to observations corresponding atmospheric model intercomparison project amip runs are analyzed to understand the causes of the underestimate of enso asymmetry in coupled models the analysis reveals that during the warm phase precipitation anomalies are weaker over the eastern pacific and westerly wind anomalies are confined more to the west in most models the time mean zonal winds are stronger over the equatorial central and eastern pacific for most models wind forced ocean gcm experiments suggest

impact generated hydrothermal systems capable of forming phyllosilicates on noachian mars the early history of the terrestrial planets was punctuated by a period of heavy bombardment frequent large impacts condensed in a short 0 02 0 5 ga long time period resulted in heavily cratered planetary surfaces in volatile bearing planetary crusts each of these large impacts created a volume of hot rock and melt that drove vast subsurface hydrothermal systems in mars basaltic crust these systems produced a variety of alteration phases the nature of which we explored with thermochemical modeling using the computer code chiller we found a variety of oxides hydroxides and hydrous and water free silicates resulting from the hydrothermal alteration the main hydrous silicates are serpentine chlorite nontronite and other clay minerals some of the resulting assemblages contain up to 15 wt bound water our results constrain the temperature and water rock ratio at the time of alteration and compare well to the mineral assemblages found on mars by omega observatoire pour la mineralogie l eau les glaces et l activite and crism compact reconnaissance imaging spectrometer for mars and therefore provide an interpretative framework for analyzing martian mineralogy from orbital data our results also provide a geological template needed to select landing locations for future missions that search for water and energy sources associated with potential habitats on early mars

el nino la nina and the nonlinearity of their teleconnections the paradigm of an atmospheric system varying linearly with respect to extreme phases of the el nino southern oscillation is questioned it is argued that the global response to tropical pacific sea surface temperature forcing will be inherently nonlinear a physical basis for this intrinsic nonlinearity is the thermodynamic control on deep convection climate statistics for warm and cold events of the tropical pacific are analyzed separately for the northern winter periods during 1950 96 composite analysis of 500 mb heights reveal planetary scale teleconnection patterns as noted in earlier studies a new result is the evidence for an appreciable 358 longitude phase shift between the warm and cold event circulation composites and the two wave trains appear to have different tropical origins a large nonlinear component in north american surface climate anomalies is also found which is consistent with such a phase shift in teleconnections in the tropics rainfall anomalies also show evidence of nonlinear behavior the maximum rain anomalies along the equator are located east of the date line during warm events but west of the date line during cold events the interpretation of this behavior is complicated however by the fact that composite warm event sst anomalies are not the exact inverse of their cold event counterparts idealized atmospheric general circulation model agcm experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system the model is forced with a composite sst anomaly that undergoes a realistic seasonally varying enso life cycle as described by e rasmusson and t carpenter both positive and negative phases of the sst anomaly are used and a 40 member ensemble of warm and cold event model simulations is conducted a nonlinear climate response in the agcm is found that closely resembles the observed composites including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns

ejection times of martian meteorites noble gas isotopic analyses were made for four meteorites whose origin is mars basaltic shergottites queen alexandra range 94201 zagami the iherzolite lew88516 and orthopyroxenite allan hills 84001 the latter one was separated into orthopyroxene chromite and maskelynite fractions ejection times were calculated for all martian meteorites using cosmic ray exposure ages based on 3he 21ne and 38ar concentrations and literature data on the terrestrial ages we discuss the arguments for a scenario in which they were ejected from mars by asteroidal or cometary impact as small meteoroids and were delivered to earth within and up to 15 million years the basaltic shergottites que94201 shergotty and zagami show an ejection age cluster at 2 76 ma the fourth basaltic shergottite eet79001 being younger 0 82 ma lherzolites lew88516 and alh77005 were ejected by a later event 3 84 ma ago all nakhlites nakhla governador valadares and lafayette originate from an event 11 0 ma ago although chassigny is chemically distinct from the nakhlites its ejection age is 11 6 ma whether this is a separate event cannot be decided from the available data finally orthopyroxenite alh84001 was launched from mars 14 4 ma ago the distribution of the delivery times for martian meteorites to earth reflect individual impact events onto five or six different source terrains this result is significant in the context of a comprehensive knowledge of the martian crust composition finally we derived the k 40ar gas retention age of alh84001 mineral fractions adopting two different models assuming a component of martian atmospheric ar with 40ar36ar 1790 trapped by this meteorite we obtained an age of 3390 ma on the other hand assuming no contribution of martian atmospheric ar the resulting k 40ar age is about 4100 ma that is roughly 500 ma younger than the reported sm nd crystallization age

rb sr sm nd and ar ar isotopic systematics of martian dunite chassigny abstract isotopic analysis of the martian meteorite chassigny yields a rb sr age of 1406 14 ma with an initial 87 sr 86 sr ratio of 0 702251 0 000034 a sm nd age of 1386 28 ma with an initial e 143nd value of 16 9 0 3 and an 39 ar 40 ar age of 1360 40 20 ma the concordance of these ages and the rb sr and sm nd initial isotopic signatures suggest that chassigny crystallized from low rb sr light rare earth element depleted source materials 1390 ma ago the ages and e 143nd values of chassigny and the nakhlites governador valadares and lafayette overlap suggesting that they could have come from very similar mantle sources nakhla northwest africa 998 and yamato 000593 appear to be from similar but distinct sources chassigny and all nakhlites so far studied have undergone similar evolution histories that is chassignites nakhlites were derived from a region where volcanism lasted at least 50 ma and crystallized from different lava flows or subsurface sills they probably were launched from mars by a single impact event the trapped martian atmospheric 40 ar 36 ar ratios in chassigny nakhlites and shergottite impact glass are similar and possibly indicate minimal change in this ratio over the past 600 ma

on the weakening relationship between the indian monsoon and enso analysis of the 140 year historical record suggests that the inverse relationship between the el nino southern oscillation enso and the indian summer monsoon weak monsoon arising from warm enso event has broken down in recent decades two possible reasons emerge from the analyses a southeastward shift in the walker circulation anomalies associated with enso events may lead to a reduced subsidence over the indian region thus favoring normal monsoon conditions additionally increased surface temperatures over eurasia in winter and spring which are a part of the midlatitude continental warming trend may favor the enhanced land ocean thermal gradient conducive to a strong monsoon these observations raise the possibility that the eurasian warming in recent decades helps to sustain the monsoon rainfall at a normal level despite strong enso events

martian atmospheric and interior volatiles in the meteorite nakhla abstract we report isotopic abundances of xenon argon and nitrogen for the observed distinct components in martian meteorite nakhla in a stepwise release the 129xe 132xe ratios in the 800 c and 1000 c fractions show the signature of the modern atmosphere and other xe ratios when corrected for the cosmogenic component confirm the isotopically fractionated modern atmospheric component on the other hand the xe isotope ratios in the 1000 c steps reveal an isotopically unfractionated interior component but with radiogenic 129xe excesses the isotopic composition of this interior component is consistent with chass s xe solar type but is augmented by 244pu derived fission xe the fission components in interior trapped xe in both nakhla and chassigny suggest that mars effectively retained 244pu derived fission gas a heavy relative to interior n nitrogen signature in the 600 900 c temperature steps also suggests a recent incorporation of martian atmospheric gases the n signatures in the high temperature 1000 c steps are strongly affected by cosmic ray produced 15nc and 36ar and 38ar abundances are dominated by the cosmogenic component we discuss the signatures of martian interior nitrogen and heavy noble gases and the constraints they provide on the evolutionary history of mars

a reappraisal of the martian 36ar 38ar ratio the currently used value of 4 1 0 2 for the 36 ar 38 ar isotopic ratio in the martian atmosphere is reappraised and a significantly lower ratio is suggested previous analyses of noble gases in impact glass from some martian meteorites demonstrate that large quantities of martian atmospheric gases were shock emplaced into these samples however several observations indicate that this trapped martian gas is composed of two components one atmospheric and one probably from the martian mantle these observations include large variations in 36 ar 38 ar during stepwise gas release variations in the ar kr xe elemental ratios among martian meteorites and variations in the cosmogenic corrected trapped 36 ar 38 ar ratios over 3 5 4 3 among shock glass samples uncertainties in applied corrections for cosmogenic ar cannot explain these variations by assuming a range of reasonable values for martian atmospheric and mantle 40 ar 36 ar the observed 40 ar 36 ar ratios in shock glass are used to correct for the mantle component and to derive a more precise ratio for the atmospheric component using this procedure one obtains an upper limit for martian atmospheric 36 ar 38 ar of 3 9 and a probable but poorly defined range for martian atmospheric 36 ar 38 ar of 3 0 3 6 these lower ratios imply that the degree of mass fractionation during ar loss from mars upper atmosphere is considerably larger than that previously calculated

trace and minor elements in minerals of nakhlites and chassigny clues to their petrogenesis abstract ion microprobe measurements of ree rare earth element and other selected trace and minor element concentrations were made in clinopyroxene olivine feldspar and chlorapatite in chassigny and the three nakhlites nakhla governador valadares and lafayette in chassigny we have found pigeonite occurring in a poikilitic habit it is the first reported occurrence of this mineral in this meteorite the most significant implication of this finding is that estimates of the major element composition of the chassigny parent melt will have to accommodate pigeonite as a primary mineral crystallizing before plagioclase chlorapatite contains the highest ree abundances in all meteorites studied here the ree patterns of chlorapatite plagioclase and augite in nakhlites and chassigny are similar although the downward trends of ree patterns are somewhat steeper for these minerals in chassigny than in the nakhlites pyroxenes in nakhlites and chassigny are extensively zoned in rees and other trace and minor elements such as y zr ti and al which appear to be resistant to diffusive reequilibration thus primary igneous zoning of these elements has been preserved in the pyroxenes of these meteorites and can be used to infer their crystallization histories the calculated ree patterns of the parent melts of nakhlites and chassigny are lree enriched and parallel to their whole rock ree patterns indicating that once crystal accumulation occurred the intercumulus trapped melt fractionally crystallized in an essentially closed system and that infiltration i e metasomatism by lree enriched magmas need not be invoked to explain the lree enrichment in bulk samples of these meteorites fractional crystallization model calculations for nakhla also confirm these conclusions the distributions of trace and minor elements in augites in nakhlites and chassigny suggest that all three nakhlites could be samples from different horizons of the same lithologic unit but that chassigny was not comagmatic with the nakhlites