bulk chondrite variability in mass independent magnesium isotope compositions implications for initial solar system 26al 27al and the timing of terrestrial accretion abstract we have determined 26 mgdsm 3 the mass independent variations in 26mg 24mg of primitive bulk meteorites to precisions better than 3 ppm 2se our measurements of samples from 10 different chondrite groups show 26 mgdsm 3 that vary from 5 to 22 ppm our data define an array with a positive slope in a plot of 26 mgdsm 3 against 27al 24mg which can be used to determine 26al 27al 0 i e initial 26al 27al and 26 mgdsm 3 0 i e initial 26 mgdsm 3 on such an isochron plot the best fit of our new measurements combined with literature data implies 26al 27al 0 of 4 67 0 78 10 5 and 26 mgdsm 3 0 of 31 6 5 7 ppm 2se for ordinary and carbonaceous chondrites other than cr chondrites which have anomalously low 26 mgdsm 3 these parameters are within uncertainty of those defined by previous measurements of bulk calcium aluminium rich inclusions cais that set canonical 26al 27al 0 5 10 5 the most straightforward interpretation of all these observations is that differences in the al mg of bulk ordinary and carbonaceous chondrites are dominantly controlled by variable contributions of early formed refractory and major silicate components derived from a common canonical reservoir the 26 mgdsm 3 of enstatite chondrites are slightly more radiogenic 3 ppm at similar al mg to the ordinary chondrites we speculate that this is related to the timing of removal of a refractory component from the source reservoirs of these different meteorite groups the higher 26 mgdsm 3 of the enstatite chondrites suggests later 0 5 ma post cais condensation and loss of this refractory component despite inferred consistency of 26al 27al 0 and 26 mgdsm 3 0 across most chondrite groups some nebular heterogeneity is required to account for the compositions of cr chondrites our preferred interpretation is that the cr source region has lower 26 mgdsm 3 0 as the most appropriate isotopic reference for the earth our new mean enstatite chondrite composition allows us to assess possible ingrowth of 26mg from live 26al during accretion of the earth the earth has 26 mgdsm 3 within uncertainty of enstatite chondrites despite its higher al mg this requires that the terrestrial increase in al mg which we attribute to vapour loss during accretion must have happened 1 5 ma post cai formation in an instantaneous fractionation model

26al 26mg systematics in d orbigny and sahara 99555 angrites implications for high resolution chronology using extinct chronometers abstract we report on an investigation of the 26al 26mg isotope systematics in the d orbigny and sahara 99555 angrites high precision mg isotope compositions and al mg ratios were measured in mineral separates and whole rock samples from d orbigny and sahara 99555 using multiple collector inductively coupled plasma mass spectrometry mc icpms plagioclase separates from both angrites have resolvable excesses in 26mg 26mg that correlate with their respective al mg ratios 26al 26mg systematics in the mineral separates and whole rocks define precise isochrons that correspond to 26al 27al ratios of 5 06 0 92 10 7 and 5 13 1 90 10 7 and initial 26mg values of 0 006 0 040 and 0 016 0 047 for d orbigny and sahara 99555 respectively the slopes and initial 26mg values are identical for these two meteorites within errors and the data for both angrites considered together define an isochron corresponding to a 26al 27al ratio of 5 10 0 55 10 7 and initial 26mg value of 0 012 0 019 relative to the efremovka e60 cai the 26al 27al values reported here for these angrites imply 26al 26mg ages of 4562 42 0 29 ma and 4562 43 0 53 ma for d orbigny and sahara 99555 respectively these 26al 26mg ages are concordant with model ages determined using other extinct radionuclide chronometers e g 53mn 53cr and 182hf 182w but are 2 myr younger than the absolute 207pb 206pb ages that have been reported recently for these angrites the reason for this discrepancy is not presently known but may imply disturbance of one or more of the isotope systems under consideration or a possible bias in the 207pb 206pb ages of the angrites resulting from natural or analytical causes

revisited relationship between tropical and north pacific sea surface temperature variations 1 the relationship between the tropical and north pacific sea surface temperature sst variations is reexamined following the results of deser and blackmon 1995 db95 based on a much longer period of data 1949 2010 as in db95 the two leading sst modes the el nino southern oscillation enso mode and the north pacific mode represent the sst variations in the pacific domain before 1992 considering the period after 1992 however one needs to consider a new mode of sst variation along with the two modes mentioned to understand the relationship between the tropical and north pacific sst variations a new sst mode known as the warm pool mode exhibits a strong variance in the warm pool region and undergoes a phase shift after the mid 1990s reflecting a warming in the warm pool region and a cooling in the central and eastern equatorial pacific it is found that the warm pool mode accompanies the north pacific oscillation like atmospheric variability over the north pacific through this teleconnection the warm pool mode mostly shows a relationship between the warm pool sst and the associated north pacific sst component and which has some similarities with the north pacific gyre oscillation

observational evidences of walker circulation change over the last 30 years contrasting with gcm results in order to examine the changes in walker circulation over the recent decades we analyzed the sea surface temperature sst deep convective activities upper tropospheric moistening sea level pressure slp and effective wind in the boundary layer over the 30 year period of 1979 2008 the analysis showed that the eastern tropical pacific has undergone cooling while the western pacific has undergone warming over the past three decades causing an increase in the east west sst gradient it is indicated that the tropical atmosphere should have responded to these sst changes increased deep convective activities and associated upper tropospheric moistening over the western pacific ascending region increased slp over the eastern pacific descending region in contrast to decreased slp over the western pacific ascending region and enhanced easterly wind in the boundary layer in response to the slp change these variations recognized from different data sets occur in tandem with each other strongly supporting the intensified walker circulation over the tropical pacific ocean since the sst trend was attributed to more frequent occurrences of central pacific type el nino in recent decades it is suggested that the decadal variation of el nino caused the intensified walker circulation over the past 30 years an analysis of current climate models shows that model results deviate greatly from the observed intensified walker circulation the uncertainties in the current climate models may be due to the natural variability dominating the forced signal over the tropical pacific during the last three decades in the twentieth century climate scenario runs by cmip3 cgcms

accuracy of stable mg and ca isotope data obtained by mc icp ms using the standard addition method the standard addition method is evaluated to verify the accuracy and precision of mg and ca isotope data with complex matrices using the standard sample bracketing technique and analysis by mc icp ms the 44ca 42ca ratio of seawater expressed as 44 42ca relative to srm915a was determined as 0 93 0 03 95 confidence in agreement with estimates obtained by the double spike method using standard addition the seawater 26mg 24mg ratio expressed as 26mg relative to the dsm3 standard was determined as 0 80 0 06 95 confidence in agreement with previous estimates four terrestrial silicate rocks morb flood basalt glacial flour and granodiorite and olivine mineral separates from an island basalt are shown to exhibit no scatter within the error of the method averaging a 26mg of 0 20 0 05 95 confidence although a number of silicate rock data for mg isotope ratios have already been reported this is the first detailed effort to validate the accuracy of such data and test for residual analytical artifact after chemical purification of samples data regressions were evaluated statistically using the mean square weighted deviate mswd demonstrating that the uncertainty on individual data points are generally over estimated the external two standard deviation uncertainty on individual data points is estimated by monte carlo simulation as b0 075 about a factor of two improvement on early publications of mg isotope data the consistency of the standard addition estimates of 26mg in silicate rocks imply that if any residual matrix effects are present then they must be less than the spread of the data 0 11 given the diverse range of matrices in each of the samples the 26mg values of the silicate rocks suggest that mg isotope ratios in silicate material may only have a very restricted range the 26mg values of silicate material in the present study falls between the average values reported by teng et al teng f z wadhwa m helz r t 2007 investigation of magnesium isotope fractionation during basalt differentiation implications for a chondritic composition of the terrestrial mantle earth and planetary science letters 261 84 92 doi 10 1016 j epsl 2007 06 004 and wiechert and halliday wiechert u halliday a n 2006 non chondritic magnesium and the origins of the inner terrestrial planets earth and planetary science letters 256 360 371 doi 10 1016 j epsl 2007 01 007 and given the spread of published 26mg values for chondritic material a chondritic composition for terrestrial mg cannot be ruled out we suggest that some of the small discrepancies between our data and analysis of the same samples in earlier studies may have arisen because the chemical purification of mg prior to analysis can easily induce analytical artifact this method could be expanded to the isotope ratios of other elements which also rely on correcting for mass bias using the standard sample bracketing method where similar analytical discrepancies may also exist

the north pacific as a regulator of summertime climate over eurasia and north america abstract the role of the north pacific as a regulator of boreal summer climate over eurasia and north america is investigated using observational data two summertime interannual climate modes associated with sea surface temperature sst variability in the north pacific are identified the first mode shows an elongated zone of warm cold sst anomalies in the central north pacific along 40 n with temporal variability significantly correlated with el nino during the preceding spring but its subsequent evolution is quite different from el nino the second mode exhibits a seesaw sst variation between the northern and southern north pacific and is independent of el nino both modes are linked to coherent sst anomalies over the north atlantic suggesting the presence of an atmospheric bridge linking the two extratropical oceans using the principal component of the most dominant mode as the north pacific index npi composite analyses show that the positive negative phase of npi features a warm cold

interlaboratory comparison of magnesium isotopic compositions of 12 felsic to ultramafic igneous rock standards analyzed by mc icpms to evaluate the interlaboratory mass bias for high precision stable mg isotopic analysis of natural materials a suite of silicate standards ranging in composition from felsic to ultramafic were analyzed in five laboratories by using three types of multicollector inductively coupled plasma mass spectrometer mc icpms magnesium isotopic compositions from all labs are in agreement for most rocks within quoted uncertainties but are significantly up to 0 3 in 26mg 24mg 4 times of uncertainties different for some mafic samples the interlaboratory mass bias does not correlate with matrix element mg ratios and the mechanism for producing it is uncertain but very likely arises from column chemistry our results suggest that standards with different matrices are needed to calibrate the efficiency of column chemistry and caution should be taken when dealing with samples with complicated matrices well calibrated standards with matrix elements matching samples should be used to reduce the interlaboratory mass bias

26al 26mg deficit dating ultramafic meteorites and silicate planetesimal differentiation in the early solar system abstract meteorites with significantly sub chondritic al mg that formed in the first 2 million years of the solar system should be characterised by deficits in the abundance of 26mg 26mg due to the absence of in growth of 26mg from the decay of short lived 26al t1 2 0 73 myr however these 26mg deficits will be small 26mg 0 037 even for material that formed at the same time as the solar system s oldest solids calcium aluminium rich inclusions and thus measurement of these deficits is analytically challenging here we report on a search for 26mg deficits in three types of ultramafic meteorites pallasites ureilites and aubrites by multiple collector inductively coupled plasma mass spectrometry a range of analytical tests were carried out including analysis of 1 a range of synthetic mg solution standards 2 mg gravimetrically doped with a high purity 26mg spike 3 mg cuts collected sequentially from cation exchange separation columns with fractionated stable mg isotope compositions 4 mg separated from samples that was bracketed by analyses of both dsm 3 and mg separated from a natural olivine sample subjected to the same chemical processing as the samples these tests confirm it is possible to resolve differences in 26mg from the terrestrial materials that are 0 005 however if mg yields from chemical separation are low or an inappropriate equilibrium isotopically fractionated standard is used this will generate analytical artefacts on 26mg when this is calculated with the kinetic exponential mass fractionation law as is the case when correcting for instrumental mass bias during mass spectrometric analysis olivine from four different main group pallasites and four bulk ureilites have small deficits in the abundance of 26mg with 26 mg dsm 3 0 0120 0 0018 and 26 mg dsm 3 0 0062 0 0023 respectively relative to terrestrial olivine 26 mg dsm 3 0 0029 0 0028 six aubrites have 26 mg dsm 3 0 0015 0 0020 which is identical to terrestrial olivine model ages from these deficits can be calculated by assuming that 26al was homogeneously distributed in the planetesimal forming regions of the proto planetary disc at the same level as calcium aluminium rich inclusions cais the absence of 26mg deficits in aubrites means these can only be constrained to have formed relatively late 2 9 myr after cai formation model ages calculated from pallasite olivine deficits would suggest that pallasite olivine crystallised and was diffusively isolated on its parent body 1 24 0 28 0 40 myr after formation of cais similarly ureilites would have experienced silicate partial melting and lowering of their bulk al mg ratios 1 9 0 7 2 2 myr after cai formation the model ages for silicate differentiation on the main group pallasite parent body are intermediate between those for metal silicate fractionation for core formation obtained from magmatic iron meteorites and those for asteroidal silicate magmatism obtained from basaltic meteorites

a new paradigm for the predominance of standing central pacific warming after the late 1990s canonical el nino has a warming center in the eastern pacific ep but in recent decades el nino warming center tends to occur more frequently in the central pacific cp the definitions and names of this new type of el nino however have been notoriously diverse which makes it difficult to understand why the warming center shifts here we show that the new type of el nino events is characterized by 1 the maximum warming standing and persisting in the cp and 2 the warming extending to the ep only briefly during its peak phase for this reason we refer to it as standing cp warming cpw global warming has been blamed for the westward shift of maximum warming as well as more frequent occurrence of cpw however we find that since the late 1990s the standing cpw becomes a dominant mode in the pacific meanwhile the epochal mean trade winds have strengthened and the equatorial thermocline slope has increased contrary to the global warming induced weakening trades and flattening thermocline we propose that the recent predominance of standing cpw arises from a dramatic decadal change characterized by a grand la nina like background pattern and strong divergence in the cp atmospheric boundary layer after the late 1990s the anomalous mean cp wind divergence tends to weaken the anomalous convection and shift it westward from the underlying sst warming due to the suppressed low level convergence feedback this leads to a westward shift of anomalous westerly response and thus a zonally in phase sst tendency preventing eastward propagation of the sst anomaly we anticipate more cpw events will occur in the coming decade provided the grand la nina like background state persists

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

investigation of magnesium isotope fractionation during basalt differentiation implications for a chondritic composition of the terrestrial mantle to investigate whether magnesium isotopes are fractionated during basalt differentiation we have performed high precision mg isotopic analyses by multi collector inductively coupled plasma mass spectrometry mc icp ms on a set of well characterized samples from kilauea iki lava lake hawaii usa samples from the kilauea iki lava lake produced by closed system crystal melt fractionation range from olivine rich cumulates to highly differentiated basalts with mgo content ranging from 2 37 to 26 87 wt our results demonstrate that although these basalts have diverse chemical compositions mineralogies crystallization temperatures and degrees of differentiation their mg isotopic compositions display no measurable variation within the limits of our external precision average 26 mg 0 36 0 10 and 25 mg 0 20 0 07 uncertainties are 2sd this indicates that mg isotopic fractionation during crystal melt fractionation at temperatures of 1055 c is undetectable at the level of precision of the current investigation calculations based on our data suggest that at near magmatic temperatures the maximum fractionation in the 26 mg 24 mg ratio between olivine and melt is 0 07 two additional oceanic basalts two continental basalts bcr 1 and bcr 2 and two primitive carbonaceous chondrites allende and murchison analyzed in this study have mg isotopic compositions similar to the kilauea iki lava lake samples in contrast to a recent report u wiechert a n halliday non chondritic magnesium and the origins of the inner terrestrial planets earth and planetary science letters 256 2007 360 371 the results presented here suggest that the bulk silicate earth has a chondritic mg isotopic composition 2007 published by elsevier b v

the mg isotope composition of presolar silicate grains from red giant stars abstract we report o and mg isotope compositions of presolar silicate grains which likely formed around asymptotic giant branch stars our grains represent the most abundant mg rich presolar grain group and their mg isotope composition provides thus far missing information about the contribution of isotopically anomalous presolar dust to the mg isotope inventory of the early solar system presolar silicate grains were identified in situ using the nanosims in the matrix of the ungrouped carbonaceous chondrite acfer 094 o isotope compositions suggest that the presolar grains of the present study formed in the stellar winds of low mass m 2 2 msolar red giant or asymptotic giant branch stars of close to solar metallicity and thus belong to the most abundant presolar silicate grain group in order to minimise matrix contributions during spatially poorly resolved mg isotope analyses spatial resolution comparable to average grain size meteorite matrix in the presolar grains vicinity was removed using a focussed ga ion beam to monitor accuracy we prepared and analysed o isotopically regular solar system matrix grains the same way as the presolar grains the 25mg 24mg ratios of all seven successfully analysed presolar silicate grains are identical to that of the solar system at the precision of our measurements the 26mg 24mg ratios of five grains are also solar but two grains have significant positive anomalies in 26mg 24mg on average however 25mg 24mg and 26mg 24mg ratios are higher than solar by a few all grain compositions are consistent with galactic chemical evolution and possibly isotope fractionation caused by interstellar or solar system processing sputtering and or recondensation the grain with the strongest enrichment in 26mg relative to 25mg 25mg 34 25 26mg 127 25 where xmg 1000 xmg 24mg grain xmg 24mg meteorite matrix 1 with x 25 or 26 the reported uncertainty corresponds to 1 probably incorporated 26al during grain condensation our and previously reported mg isotope data on presolar oxide and silicate grains indicate that the isotopically anomalous o rich dust component of the solar system s parent molecular cloud was heterogeneous with respect to mg isotope compositions and probably had a higher 26mg 24mg ratio on average than that of the present day solar system

magnesium isotope analysis of olivine and pyroxene by sims evaluation of matrix effects abstract the performance of multi collector secondary ion mass spectrometry mc sims for mg isotope ratio analysis was evaluated using 17 olivine and 5 pyroxene reference materials rms the mg isotope composition of these rms was accurately and precisely determined by multi collector inductively coupled plasma mass spectrometry mc icp ms and these measured isotope ratios were used to evaluate sims instrumental mass bias as a function of the forsterite fo content of olivine the magnitude of the mg isotope matrix effects were 3 in 25mg and are a complex function of olivine fo content that ranged from fo59 3 to fo100 in addition to these mg isotope matrix effects si ion yields and mg si ion ratios varied as a complex function of the fo content of the olivine rms for example si ion yields varied by 33 based on the observations we propose instrumental bias correction procedures for sims mg isotope analysis of olivine using a combination of mg si ratios and fo content of olivine using this correction method the accuracy of 25mg analyses is 0 3 except for analysis of olivine with fo86 88 where instrumental biases and mg si ratios change dramatically with fo content making it more difficult to assess the accuracy of mg isotope ratio measurements by sims over this narrow range of fo content five pyroxene rms 3 orthopyroxenes and 2 clinopyroxenes show smaller ranges of instrumental bias 1 4 in 25mg as compared to the olivine rms the instrumental bias for the 3 orthopyroxene rms do not define a linear relationship with respect to enstatite en content that ranged from en85 5 96 3 the clinopyroxene rms have similar en and wollastonite wo contents but have 25mg values that differ by 0 5 relative to their 25mg values determined by mc icp ms these results indicate that additional factors e g minor element abundances likely contribute to sims instrumental mass fractionation in order to better correct for these sims matrix effects additional pyroxene rms with various chemical compositions and known mg isotope ratios are needed

carbonaceous achondrites northwest africa 6704 6693 milestones for early solar system chronology and genealogy abstract northwest africa nwa 6704 6693 are medium to coarse grained achondrites with unique petrologic and geochemical traits that are distinct from the currently established meteorite groups here we report on the extinct 26al 26mg and 53mn 53cr systems to establish fine scale chronology of its formation and cr and ti isotopic anomalies to constrain the composition of the source reservoir of nwa 6704 6693 excesses in the neutron rich 54cr and 50ti isotopes due to nucleosynthetic anomalies separate nwa 6704 6693 from the vast majority of established achondrites and instead resemble the excesses seen among the carbonaceous chondrites specifically the cr type chondrites the excesses in these isotopes indicate a common feeding zone during accretion in the protoplanetary disk between the source of nwa 6704 6693 and that of the carbonaceous chondrites the 26al 26mg data for pyroxene and plagioclase from nwa 6704 yield a 26al 27al 0 3 15 0 38 10 7 mswd 0 49 and an initial 26mg 0 004 0 005 at the time of isotopic closure this initial 26al 27al 0 translates to an absolute age of 4563 14 0 38 ma relative to the d orbigny angrite however given the potential heterogeneity of 26al the d orbigny angrite might not be a good age anchor for the purpose of calculating 26al 26mg ages the 26al 26mg age relative to another carbonaceous achondrite nwa 2976 is 4562 66 0 60 ma the 53mn 53cr systematics of nwa 6704 6693 indicate a 53mn 55mn 0 of 2 59 0 34 10 6 mswd 1 2 with an evolved initial e53cr of 0 14 0 03 the 53mn 55mn 0 yields an 53mn 53cr age of 4562 17 0 76 ma relative to the d orbigny angrite concordant ages determined using the short lived 26al 26mg and 53mn 53cr systems and extant 207pb 206pb system 4562 60 0 30 ma for nwa 6704 6693 amelin et al 2019 indicate rapid cooling and nearly contemporaneous closing of multiple isotope systems the ancient crystallization ages and positive 54cr and 50ti anomalies of nwa 6704 6693 indicate widespread melting and differentiation processes occurring in both non carbonaceous nc and carbonaceous chondrite cc regions of the protoplanetary disk additionally we report the cr and ti isotopic composition for a petrologic range of cr type materials cr2 cr6 and achondrites the additional cr and ti isotopic data for these cr type materials indicates a range in isotopic composition not previously observed based on cr2 chondrites alone

26 al 26 mg and 207 pb 206 pb systematics of allende cais canonical solar initial 26 al 27 al ratio reinstated abstract the precise knowledge of the initial 26 al 27 al ratio 26 al 27 al 0 is crucial if we are to use the very first solid objects formed in our solar system calcium aluminum rich inclusions cais as the time zero age anchor and guide future work with other short lived radio chronometers in the early solar system as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation new high precision multi collector inductively coupled plasma mass spectrometry mc icp ms measurements of 27 al 24 mg ratios and mg isotopic compositions of nine whole rock cais six mineralogically characterized fragments and three micro drilled inclusions from the cv carbonaceous chondrite allende yield a well defined 26 al 26 mg fossil isochron with an 26 al 27 al 0 of 5 23 0 13 10 5 internal mineral isochrons obtained for three of these cais a44a ajef and a43 are consistent with the whole rock cai isochron the mineral isochron of ajef with 26 al 27 al 0 4 96 0 25 10 5 anchored to our precisely determined absolute 207 pb 206 pb age of 4567 60 0 36 ma for the same mineral separates reinstate the canonical 26 al 27 al 0 of 5 10 5 for the early solar system the uncertainty in 26 al 27 al 0 corresponds to a maximum time span of 20 ka thousand years suggesting that the allende cai formation events were culminated within this time span although all allende cais studied experienced multistage formation history including melting and evaporation in the solar nebula and post crystallization alteration likely on the asteroidal parent body the 26 al 26 mg and u pb isotopic systematics of the mineral separates and bulk cais behaved largely as closed system since their formation our data do not support the supra canonical 26 al 27 al ratio of individual minerals or their mixtures in cv cais suggesting that the supra canonical 26 al 27 al ratio in the cv cais may have resulted from post crystallization inter mineral redistribution of mg isotopes within an individual inclusion this redistribution must be volumetrically minor in order to satisfy the mass balance of the precisely defined bulk cai and bulk mineral data obtained by mc icp ms the radiogenic 208 pb 206 pb ratio obtained as a by product from the pb pb age dating is used to estimate time integrated 232 th 238 u ratio value of cais limited variations among the minerals within a single cai contrasted by much larger variations among the bulk cais suggest th u fractionation occurred prior to crystallization of igneous cais if interpreted as primordial heterogeneity the value can be used to calculate the mean age of the interstellar dust from which the cais condensed

the isotopic composition of magnesium in the inner solar system abstract we report high precision mc icpms measurements of 25 mg 24 mg and 26 mg 24 mg isotope ratios for 14 meteorites both primitive and differentiated 5 lunar basalts and breccia samples 5 terrestrial basalts 1 dunite and 3 peridotites we estimate the 26 mg value of the bulk silicate earth bse at 0 54 0 04 2se w r t dsm3 carbonaceous and ordinary chondrites show an average 26 mg of 0 52 0 04 2se martian meteorites show a narrow range in 26 mg with an average 26 mg of 0 57 0 02 2se average 26 mg of pallasite olivines is 0 54 0 04 2se whereas that of lunar samples including ilmenite basalts olivine basalt and one crystalline breccia is 0 51 0 03 2se our data demonstrate that the overall stable mg isotopic composition of the inner solar system average 25 mg 0 273 26 mg 0 535 is homogeneous to within 0 04 for 26 mg 24 mg this value is indistinguishable from that of the bse and lunar samples demonstrating that the mg isotopic composition of the earth moon system is chondritic accurate determination of the mg isotopic composition of the rocky planets is important for mg isotope studies of surface processes on earth as well as for using mg isotope data to understand evaporation and condensation effects in the solar nebula consistent with a recent report we find that clinopyroxenes have higher 26 mg than co existing olivines and orthopyroxenes in mantle peridotites although the magnitude of this difference varies 0 08 to 0 2 such small mineral fractionations along with differences between components in primitive meteorites cais chondrules and matrix preclude the resolution of mass dependent fractionation differences smaller than about 0 05 between solar system objects we demonstrate that our results do not support the recent claims that i the earth moon system has a unique mg isotope composition different from chondrites or ii the higher 26 mg values up to 0 0 reported for chondrites achondrites terrestrial basalts and peridotites to address the issue of inter laboratory discrepancies on the mg isotopic composition of silicate rocks we have prepared 3 pure mg standards with wide ranging 26 mg 3 75 to 0 69 with respect to dsm3 as well as a large volume of homogenized olivine from the san carlos peridotite which will be available to the scientific community for future comparative studies

the nature and origin of type b1 and b2 caal rich inclusions in the allende meteorite abstract the type b ca al rich inclusions in the allende carbonaceous chondrite form a continuous range from the mineralogically concentrically zoned b1 subtype to the unzoned b2 subtype these subtypes differ in i structure texture grain size and shape ii mineralogical proportions and compositions iii accessory mineralogy iv relative abundance of spinel framboids v rim layering vi major element chemistry and vii degree of secondary alteration these differences together with observations on the crystallization of synthetic melts suggest that the b1 inclusions crystallised relatively rapidly from molten parental material while b2 types crystallised relatively slowly close to the solidus from material that had not been completely melted the same data are used to construct an evaporative residue model for the origin of the parental type b materials in the model dust in the protosolar nebula was heated with removal of more volatile elements leaving completely melted type b1 residues at the highest temperatures and incompletely melted less highly evaporated type b2 residues at lower temperatures

high temperature silicon isotope geochemistry abstract silicon si is the defining element of silicate reservoirs yet despite its dominance in major earth processes there is still no clear understanding of how much is hosted in earth s core how the enriched continental crust forms or even if the crust is isotopically different from the mantle because of a long history of weathering erosion and subduction with the advent of multiple collector inductively coupled plasma mass spectrometry it has become relatively straightforward to explore small 100 ppm level mass dependent variations in si isotopic composition resulting from high temperature fractionation and to develop new isotopic fingerprints of magmatic processes and source regions this paper reviews the technique developments the new data and the veracity of current interpretations only a small si isotopic effect is associated with basalt formation via mantle melting however there now is compelling evidence based on a considerable number of samples 100 that the silicate earth is isotopically fractionated by 100 200 ppm per amu to a heavy composition relative to that of chondrites and also all differentiated stony meteorites this could reflect variability in the circumstellar disc but this is not well supported by data for enstatite chondrites which are isotopically light the most plausible current explanation is that si is a light element in earth s core and that differences in the bond stiffness between silicate and metal hosted si resulted in substantial fractionation interestingly the moon has the same si isotope composition as earth s mantle which is hard to explain unless the moon s atoms were mainly derived from earth differentiated magmatic sequences such as those of hekla iceland display a systematic relationship between isotopic composition and si content more complex magmatic suites such as i and s type granites reveal a range of isotopic compositions not well correlated with chemical composition similar effects are found in lower crustal granulite facies xenoliths nonetheless the overall composition of the continental crust is only slightly heavy relative to the mantle in fact the effect is barely resolvable therefore the amounts of surface dissolved heavy si removed to the mantle via weathering over time have been small or these losses have been balanced by subduction of isotopically light clay

26al 26mg dating of asteroidal magmatism in the young solar system abstract we present high precision mg isotope data for most classes of basaltic meteorites including eucrites mesosiderite silicate clasts angrites and the ungrouped northwest africa nwa 2976 measured by pseudo high resolution multiple collector inductively coupled plasma mass spectrometry and utilising improved techniques for chemical purification of mg with the exception of the angrites angra dos reis lewis cliff lew 86010 nwa 1296 and nwa 2999 and the diogenite bilanga which have either been shown to have young ages by other dating techniques or have low al mg ratios all bulk samples of basaltic meteorites have 26mg excesses 26 mg 0 0135 to 0 0392 the 26mg excesses cannot be explained by analytical artefacts cosmogenic effects or heterogeneity of initial 26al 27al al mg ratios or mg isotopes in asteroidal parent bodies as compared to earth or chondrites the 26mg excesses record asteroidal melting and formation of basaltic magmas with super chondritic al mg and confirm that radioactive decay of short lived 26al was the primary heat source that melted planetesimals model 26al 26mg ages for magmatism on the eucrite mesosiderite angrite and nwa 2976 parent bodies are 2 6 3 2 3 9 4 1 and 3 5 myr respectively after formation of calcium aluminium rich inclusions cais however the validity of these model ages depends on whether the elevated al mg ratios of basaltic meteorites result from magma ocean evolution on asteroids through fractional crystallisation or directly during partial melting mineral isochrons for the angrites sahara sah 99555 and d orbigny and nwa 2976 yield ages of 5 06 0 05 0 06 myr and 4 86 0 09 0 10 myr respectively after cai formation both isochrons have elevated initial 26 mg values given the brecciated and equilibrated texture of nwa 2976 it is probable that its isochron age and elevated initial 26 mg 0 0175 0 0034 reflects thermal resetting during an impact event and slow cooling on its parent body however in the case of the angrites the marginally elevated initial 26 mg 0 0068 0 0058 may reflect either 26 mg ingrowth in a magma ocean prior to eruption and crystallisation or in an older igneous protolith with super chondritic al mg prior to impact melting and crystallisation of these angrites or partial internal re equilibration of mg isotopes after crystallisation 26al 26mg model ages and an olivine pyroxene whole rock isochron for the angrites sah 99555 and d orbigny are in good agreement with age constraints from 53mn 53cr and 182hf 182w short lived chronometers suggesting that the 26al 26mg feldspar controlled isochron ages for these angrites may be compromised by the partial resetting of feldspar mg isotope systematics even when age constraints from the 26al 26mg angrite model ages or the mafic mineral whole rock isochron are considered the relative time difference between sah 99555 d orbigny crystallisation and cai formation cannot be reconciled with pb pb ages for sah 99555 d orbigny and cais which are ca 1 0 myr too old angrites or too young cais for reasons that are not clear this discrepancy might indicate that 26al was markedly lower ca 40 in the planetesimal and planet forming regions of the proto planetary disc as compared to cais or that cai pb pb ages may not accurately date cai formation which might be better dated by the 182hf 182w and 26al 26mg chronometers as 4568 3 0 7 burkhardt et al 2008 and 4568 5 0 3 ma herein respectively when mapped onto an absolute timescale using pb pb ages for angrites

26al 26mg isotope systematics of the first solids in the early solar system high precision bulk aluminum magnesium isotope measurements of calcium aluminum rich inclusions cais from cv carbonaceous chondrites in several laboratories define a bulk 26al 26mg isochron with an inferred initial 26al 27al ratio of approximately 5 25 10 5 named the canonical ratio nonigneous cv cais yield well defined internal 26al 26mg isochrons consistent with the canonical value these observations indicate that the canonical 26al 27al ratio records initial al mg fractionation by evaporation and condensation in the cv cai forming region the internal isochrons of igneous cv cais show a range of inferred initial 26al 27al ratios 4 2 5 2 10 5 indicating that cai melting continued for at least 0 2 ma after formation of their precursors a similar range of initial 26al 27al ratios is also obtained from the internal isochrons of many cais igneous and nonigneous in other groups of carbonaceous chondrites some cais and refractory grains corundum and hibonite from unmetamorphosed or weakly metamorphosed chondrites including cvs are significantly depleted in 26al at least some of these refractory objects may have formed prior to injection of 26al into the protosolar molecular cloud and its subsequent homogenization in the protoplanetary disk bulk aluminum and magnesium isotope measurements of various types of chondrites plot along the bulk cv cai isochron suggesting homogeneous distribution of 26al and magnesium isotopes in the protoplanetary disk after an epoch of cai formation the inferred initial 26al 27al ratios of chondrules indicate that most chondrules formed 1 3 ma after cais with the canonical 26al 27al ratio

high precision mg isotopic systematics of bulk chondrites abstract variations of the mass independent abundance of 26 mg 26 mg and stable mg 25 mg isotope composition of chondrites are important because they constrain the homogeneity of 26 al and mg isotopes in the proto planetary disc and the validity of the short lived 26 al to 26 mg chronometer applied to meteorites we present high precision mg isotope data and al mg ratios of chondrites representing nearly all major chondrite classes including a step leaching experiment on the cm2 chondrite murchison 26 mg variations in leachates of murchison representing acid soluble material are 30 times smaller than reported for neutron rich isotopes of ti and cr and do not reveal resolvable deficits in 26 mg 0 002 to 0 118 very small variations in 26 mg anomalies in bulk chondrites 0 006 to 0 019 correlate with increasing 27 al 24 mg ratios and 50 ti reflecting the variable presence of calcium aluminium rich inclusions cais in some types of carbonaceous chondrites similarly release of radiogenic 26 mg produced by 26 al decay from cai material in the step leaching of murchison best explains the high 26 mg observed in the last aggressive leaching steps of this experiment overall the observed variations in 26 mg are small and potential differences beyond that which result from the presence of cai like material cannot be detected within the analytical uncertainties of this study 0 004 the results do not allow radical heterogeneity of 26 al 30 or measurable mg nucleosynthetic heterogeneity 0 005 to have existed on a planetesimal scale in the proto planetary disc combined with published 26 mg data for cais the bulk chondrite data yield a precise initial 26 al 27 al 0 5 21 0 06 10 5 and 26 mg 0 0340 0 0016 for the solar system however it is not possible with the currently available data to determine with certainty whether cais and the material from which planetesimals accreted including chondrite parent bodies had precisely the same initial levels of 26 al although planetesimals and planets appear to have accreted from material with a mean initial 26 al 27 al 0 in the range of 2 1 to 6 7 10 5 the average stable mg isotope composition of all analysed chondrites with the exception of a chondrule from the cba chondrite gujba 25 mg dsm 3 0 032 0 035 is 25 mg dsm 3 0 152 0 079 2 sd and is indistinguishable from that of the earth s mantle

portales valley petrology of a metallic melt meteorite breccia portales valley pv is an unusual metal veined meteorite that has been classified as an h6 chondrite it has been regarded either as an annealed impact melt breccia as a primitive achondrite or as a meteorite with affinities to silicated iron meteorites we studied the petrology of pv using a variety of geochemical mineralogical techniques our results suggest that pv is the first well documented metallic melt meteorite breccia mineral chemical and other data suggest that the protolith to pv was an h chondrite the composition of feni metal in pv is somewhat fractionated compared to h chondrites and varies between coarse vein and silicate rich portions it is best modeled as having formed by partial melting at temperatures of 940 1150 c with incomplete separation of solid from liquid metal solid metal concentrated in the coarse vein areas and s bearing liquid metal concentrated in the silicate rich areas possibly as a result of a surface energy effect both carbon and phosphorus must have been scavenged from large volumes and concentrated in metallic liquid graphite nodules formed by crystallization from this liquid whereas phosphate formed by reaction between p bearing metal and clinopyroxene components depleting clinopyroxene throughout much of the meteorite and growing coarse phosphate at metal silicate interfaces some phosphate probably crystallized from p bearing liquids but most probably formed by solid state reaction at 975 725 c phosphate forming and feo reduction reactions were widespread in pv and entailed a change in the mineralogy of the stony portion on a large scale portales valley experienced protracted annealing from supersolidus to subsolidus temperatures probably by cooling at depth within its parent body but the main differences between pv and h chondrites arose because maximum temperatures were higher in pv a combination of a relatively weak shock event and elevated pre shock temperatures probably produced the vein and breccia texture with endogenic heating being the main heat source for melting and with stress waves from an impact event being an essential trigger for mobilizing metal portales valley is best classified as an h7 metallic melt breccia of shock stage s1 the meteorite is transitional between more primitive chondritic and evolved achondrite iron meteorite types and offers clues as to how differentiation could have occurred in some asteroidal bodies

on the relationship between tropical and north pacific sea surface temperature variations abstract empirical orthogonal function analysis of winter sea surface temperature sst anomalies over the pacific domain 60 n 20 s reveals an el nino southern oscillation enso mode that is linked to the eastern north pacific and a north pacific mode that is linearly independent of enso the north pacific mode exhibits maximum amplitude and variance explained along 40 n west of 170 w ssts in this region have decreased by 1 5 c from 1950 to 1987 the cooling in winter has been associated with a strengthening of the overlying westerly winds

trace element disequilibria and magnesium isotope heterogeneity in 3655a evidence for a complex multi stage evolution of a typical allende type b1 cai we used the panurge ion microprobe to measure concentrations of the rare earth elements rees ba hf and sr in melilite clinopyroxene plagioclase and perovskite and mg isotopes in plagioclase spinel melilite fassaite hibonite grossular and monticellite from the allende type b1 calcium aluminum rich inclusion cai usnm 3655a the distribution and concentration of ba and the ree in melilite from the melilite rich mantle of 3655a are unlike those predicted from melilite melt ree partitioning experiments for closed system crystal fractionation ree concentrations are lower than expected in the first crystallized gehlenitic melilite increase rapidly to higher than expected concentrations in melilite with intermediate akermanite contents ak30 ak40 and decrease as expected only during the late stage of mantle crystallization barium concentrations in melilite are 10 50 times those expected and the lree hree ratio increases continuously rather than remaining constant the unexpected distribution of trace elements in melilite reflects a progressive enrichment of trace elements in the melt during the early stages of crystallization a partial explanation for this observation is the dissolution of precursor perovskite that contained half or more of the total ree budget of the inclusion in addition there are large trace element enrichments adjacent to included spinel in melilite and similar but smaller enrichments adjacent to spinet in clinopyroxene these enrichments are consistent with the existence of trace element enriched boundary layers at the mineral melt interfaces the fact that kinetic processes partially control trace element abundances and distributions suggests rapid cooling during crystallization of the melilite rich mantle similar trace element signatures are ubiquitous in type b1 cai suggesting that each experienced a similar thermal history the mg isotope record of 3655a is distinguished by four salient features 1 large 26 mg excesses correlated with the respective ai mg ratios in plagioclase melilite and hibonite 2 f mg the mass dependent fractionation of mg is positive with enrichment of the heavier mg isotopes in all primary phases 3 a heterogeneous distribution of f mg values with f mg in melilite systematically greater than in either spinel or fassaite and 4 isotopically normal mg in the secondary alteration phases grossular and monticellite the occurrence of 26 mg the decay product of 26 al in anorthite implies early formation of 3655a while 26 al was extant at nearly the canonical solar system value of 5 10 5 the trace element and mg isotope heterogeneities suggest a formation scenario for 3655a which includes 1 flash heating to partially melt a solid precursor 2 rapid cooling to allow survival of relict phases 3 diffusive exchange of mg between melilite and a nebular reservoir and 4 alteration at low temperature although this model explains most of the trace element and isotopic characteristics of 3655a and other type bi cais it does not provide an explanation for the rapid change of lree hree ratios of melilite during crystallization

u pb and al mg systematics of the ungrouped achondrite northwest africa 7325 abstract northwest africa nwa 7325 is a unique ungrouped gabbroic achondrite which has characteristics consistent with a possible link to the planet mercury in order to understand the origin of this meteorite and the nature of its parent body we have determined its crystallisation age using the long lived u pb and short lived al mg chronometers an internal pb pb isochron defined by six acid leached pyroxene fractions yields an age of 4563 4 2 6 ma assuming that the 238u 235u ratio for nwa 7325 is identical to the bulk earth and solar system value of 137 794 the al mg isotope analyses of seven fractions four plagioclase one pyroxene one olivine and one whole rock define a regression line corresponding to 26al 27al0 3 03 0 14 10 7 and an initial 26mg of 0 093 0 004 when anchored to the d orbigny angrite this initial 26al 27al yields an age of 4563 09 0 26 ma the pb pb age of 4563 4 2 6 ma and al mg age of 4563 09 0 26 ma are in complete agreement but the low u concentrations of nwa 7325 resulted in a relatively low precision pb pb age the observed excess in initial 26mg can be explained by 27al 24mg fractionation and subsequent mg isotopic evolution after planetary differentiation furthermore the parental magma of nwa 7325 most likely formed within 1 72 ma after calcium aluminium rich inclusion cai formation nwa 7325 formed near simultaneously with quenched angrites and a number of ungrouped achondrites at 4563 ma suggesting that a multitude of planetary bodies had formed and differentiated by 4 5 myr after cai formation this ancient age may be interpreted as an argument against nwa 7325 originating from mercury however it does not completely rule it out

pb isotopic age of the allende chondrules we have studied pb isotope systematics of chondrules from the oxidized cv3 carbonaceous chondrite allende the chondrules contain variably radiogenic pb with a 206pb 204pb ratio between 19 5 268 pb pb isochron regression for eight most radiogenic analyses yielded the date of 4566 2 2 5 ma internal residue leachate isochrons for eight chondrule fractions yielded consistent dates with a weighted average of 4566 6 1 0 ma our best estimate for an average age of allende chondrule formation this pb pb age is consistent with the range of model 26al 26mg ages of bulk allende chondrules reported by bizzarro et al 2004 and is indistinguishable from pb pb ages of ca al rich inclusions cais from cv chondrites 4567 2 0 6 ma amelin et al 2002 and the oldest basaltic meteorites we infer that chondrule formation started contemporaneously with or shortly after formation of cv cais and overlapped in time with formation of the basaltic crust and iron cores of differentiated asteroids the entire period of chondrule formation lasted from 4566 6 1 0 ma allende to 4564 7 0 6 ma cr chondrite acfer 059 to 4562 7 0 5 ma cb chondrite gujba and was either continuous or consisted of at least three discrete episodes since chondrules in cb chondrites appear to have formed from a vapor melt plume produced by a giant impact between planetary embryos after dust in the protoplanetary disk had largely dissipated krot et al 2005 there were possibly a variety of processes in the early solar system occurring over at least 4 5 myr that we now combine under the umbrella name of chondrule formation

interannual variability in northeast pacific circulation 1 interannual variability of the circulation in the northeast pacific ocean is explored through a joint analysis of expendable bathythermograph xbt and expendable conductivity temperature depth xctd data satellite altimetry and output from a model that was constrained by ocean data xbt temperature profiles with high spatial resolution are available in the eastern north pacific along two repeated transects these ship tracks along with the coast of north america define a closed box which is used to study the time mean circulation and its variability on interannual timescales geostrophic velocities from xbt data are compared with geostrophic velocities from model output as well as the full model velocity fields correlations in variability on interannual timescales between transport in the subpolar gyre and in the subtropical gyre are present in both model output and data the nature of the variability and its relation to the changes of the strength of the north pacific current npc which supplies the water for both gyres are explored interannual variability in gyre transport is found to be related to both the bifurcation of the npc resulting in an anticorrelation in transport between the two gyres and to variations in npc strength resulting in simultaneous changes in the two gyres the dominant signal is found to be a long term increase in the npc which results in a strengthening of the subtropical gyre possible connections with local scale wind stress changes and with the el nino southern oscillation phenomenon are also explored

the north pacific oscillation west pacific teleconnection pattern mature phase structure and winter impacts abstract the north pacific oscillation npo in sea level pressure and its upper air geopotential height signature the west pacific wp teleconnection pattern constitute a prominent mode of winter midlatitude variability the npo wp its mature phase expression is identified from principal component analysis of monthly sea level pressure variability as the second leading mode just behind the pacific north american variability pattern npo wp variability primarily on subseasonal time scales is characterized by a large scale meridional dipole in slp and geopotential height over the pacific and is linked to meridional movements of the asian pacific jet and pacific storm track modulation the hemispheric height anomalies at upper levels resemble the climatological stationary wave pattern attributed to transient eddy forcing the npo wp divergent circulation is thermal wind restoring pointing to independent forcing of jet fluctuations intercomparison of sea level pressure geopotential height and zonal

interannual variability of western north pacific sst anomalies and its impact on north pacific and north america in this study the interannual variability of sea surface temperature sst and its atmospheric teleconnection over the western north pacific wnp toward the north pacific north america during boreal winter are investigated first we defined the wnp mode as the first empirical orthogonal function eof mode of sst anomalies over the wnp region 100 165 e 0 35 n of which the principle component time series are significantly correlated with several well known climate modes such as the warm pool mode which is the second eof mode of the tropical to north pacific sst anomalies north pacific oscillation npo north pacific gyre oscillation npgo and central pacific cp el nino at 95 confidence level but not correlated with the eastern pacific ep el nino the warm phase of the wnp mode sea surface warming is initiated by anomalous southerly winds through reduction of wind speed with the background of northerly mean winds over the wnp during boreal winter i e reduced evaporative cooling meanwhile the atmospheric response to the sst warming pattern and its diabatic heating further enhance the southerly wind anomaly referred to the wind evaporation sst wes feedback thus the wnp mode is developed and maintained through winter until spring when the northerly mean wind disappears furthermore it is also known that anomalous upper level divergence associated with wnp mode leads to the npo like structure over the north pacific and the east west pressure contrast pattern over the north america through rossby wave propagation impacting the climate over the north pacific and north america

nickel isotope heterogeneity in the early solar system article i nfo ni of bulk iron and chondritic meteorites carbonaceous chondrites have variable positive e 62 ni 0 05 to 0 25 whereas ordinary chondrites have negative e 62 ni 0 04 to 0 09 the ni isotope compositions of iron meteorites overlap with those of chondrites and define an array with negative slope in the e 60 ni versus e 62 ni diagram the ni isotope compositions of the volatile depleted group ivb irons are similar to those of the refractory co cv carbonaceous chondrites whereas the other common magmatic iron groups have ni isotope compositions similar to ordinary chondrites only enstatite chondrites have identical ni isotope compositions to earth and so appear to represent the most appropriate terrestrial building material differences in e 62 ni reflect distinct nucleosynthetic components in precursor solids that have been variably mixed but some of the e 60 ni variability could reflect a radiogenic component from the decay of 60 fe comparison of the e 60 ni of iron and chondritic meteorites with the same e 62 ni allows us to place upper limits on the 60 fe 56 fe of planetesimals during core segregation we estimate that carbonaceous

differentiation and magmatic activity in vesta evidenced by 26al 26mg dating in eucrites and diogenites abstract the 26 al 26 mg short lived chronometer has been widely used for dating ancient objects in studying the early solar system here we use this chronometer to investigate and refine the geological history of the asteroid 4 vesta ten meteorites widely believed to come from vesta 4 basaltic eucrites 3 cumulate eucrites and 3 diogenites and the unique achondrite asuka 881394 were selected for this study all samples were analyzed for their 26 mg and 27 al 24 mg ratios in order to construct both whole rock and model whole rock isochrons mineral separation was performed on 8 of the hed s in order to obtain internal isochrons while whole rock al mg analyses of hed s plot on a regression that could be interpreted as a vestan planetary isochron internal mineral isochrons indicate a more complex history crystallization ages obtained from internal 26 al 26 mg systematic in basaltic eucrites show that vesta s upper crust was formed during a short period of magmatic activity at 2 66 0 58 1 39 million years ma after calcium aluminum inclusions after cai we also suggest that impact metamorphism and subsequent age resetting could have taken place at the surface of vesta while 26 al was still extant cumulate eucrites crystallized progressively from 5 48 0 60 1 56 to 7 25 ma after cai model ages obtained for both basaltic and cumulate eucrites are similar and suggest that the timing of differentiation of a common eucrite source from a chondritic body can be modeled at 2 88 0 12 0 14 ma after cai i e contemporaneously from the onset of the basaltic eucritic crust based on their cumulate texture we suggest cumulate eucrites were likely formed deeper in the crust of vesta diogenites have a more complicated history and their 26 al 26 mg systematics show that they likely formed after the complete decay of 26 al and thus are younger than eucrites this refined chronology for eucrites and diogenites is consistent with a short magma ocean stage on 4 vesta from which the basaltic eucrites rapidly crystallized in order to explain the younger age and the complex history of diogenites we postulate that a second episode of magmatism was possibly triggered by a mantle overturn we bring a refined chronology of the geological history of vesta that shows that the asteroid has known a more complex differentiation than previously thought

a modeling study of the relative roles of tropical and extratropical sst anomalies in the variability of the global atmosphere ocean system abstract in three parallel experiments an atmospheric general circulation model has been subjected to observed monthly varying sea surface temperature ssi conditions in each of the following domains near global ocean goga run tropical pacific toga run and midlatitude north pacific moga run four independent realizations were obtained for the model response to the sequence of sst anomalies during the 1946 88 period in each of the above regions the principal modes of coupling between the imposed sst forcing and the simulated northern hemisphere wintertime 5 1 5 mb height field in various experiments have been identified using a singular value decomposition svd procedure the leading svd mode for the goga experiment is qualitatively similar to that based on observational data although the amplitudes of the simulated height anomalies are notably lower than the observed value the sst pattern of this mode resembles that associated with el nino events the accompanying 5 1 5 mb height anomaly i

the impact of tropical western pacific convection on the north pacific atmospheric circulation during the boreal winter in this study we investigate the impact of atmospheric convection over the western tropical pacific 100 145 e 0 20 n on the boreal winter north pacific atmosphere flow by analyzing national center for environmental prediction reanalysis 1 extended reconstructed sea surface temperature and global precipitation climatology project data the western tropical pacific convection is not only the main energy source driving the local hadley and walker circulations but it also significantly influences north pacific circulation by modifying a mid latitude jet stream through the connection with the local hadley circulation on the one hand this strong convection leads to a northward expansion of local hadley cells simultaneous with a northward movement of the western north pacific jet because of the close correlation between the jet and hadley circulation boundaries on the other hand this strong convection also intensifies tropical pacific walker circulation which reduces the eastern pacific sea surface temperature resembling a la nina state through the enhanced equatorial upwelling the cooling of the eastern tropical pacific has an inter tropical convergence zone located further north thus the local hadley circulation moves northward as a result the jet axis over the eastern north pacific which also corresponds to the boundary of the local hadley circulation moves to higher latitude consequently this northward movement of the jet axis over the north pacific is reflected as a northwest southeast dipole sea level pressure slp pattern the composite analysis of slp over the north pacific against the omega pa s at 500 hpa over the western tropical pacific actually reveals that this northwest southeast dipole structure is attributed to the intensified tropical western pacific convection which pushes the pacific jet to the north finally we also analyzed south pacific for the austral winter as did previously to north pacific and found that the results were consistent

ferruginous vernadite in an indian ocean ferromanganese nodule select area electron diffraction and microanalysis of the optically dark component of a ferromanganese nodule from the south east indian ocean manganese field indicate that this is composed of a random stratification of crystallites of vernadite mno 2 r 2 o ro r 2 o 3 x y h 2 o where r represents elements such as k ba na ca mg and a disordered hydrated iron oxide possibly ferrihydrite 5fe 2 o 3 9h 2 o or feroxyhyte feooh whether the dark component is an irregular mixed layer hybrid mineral or a layered accumulation resulting from epitaxy of the above phases is uncertain

non chondritic magnesium and the origins of the inner terrestrial planets abstract high precision magnesium mg isotope data obtained using a large geometry high resolution mc icpms are reported for 9 carbonaceous and ordinary chondrites 9 eucrites and diogenites generally considered to originate from asteroid 4 vesta together with 4 martian meteorites and a variety of terrestrial and lunar materials the variation in mg isotopic composition found for mafic and ultramafic rocks mafic minerals and chondrites is smaller than reported previously the range of 26mg and 25mg of 0 6 and 0 3 defines a single mass dependent fractionation line consistent with a homogeneous mix of nucleosynthetic components data for the earth mars and vesta display no systematic mg isotopic differences despite large variations in the level of depletion in moderately volatile elements lunar mare basalts exhibit a significant range in 26mg 0 53 to 0 05 and 25mg 0 27 to 0 02 attributable to magmatic differentiation in the lunar magma ocean lmo lunar basalts derived from early segregated cumulates and thought to be the most primitive are on average slightly 0 17 26mg heavy relative to basalts from the earth mars and vesta however the difference is not well resolved more strikingly all differentiated planets and planetesimals as sampled have mg that is on average isotopically heavy compared with most chondrites analyzed thus far chondrules and cais also are generally heavy in terms of mg so this might reflect sorting of material in the proto planetary disk such an explanation would be similar to one previously proposed hewins r h and herzberg c t 1996 earth planet sci lett 144 1 7 to explain the non chondritic si mg of the earth in this model chondrule like objects separate from volatile rich planetary dust by accumulation in stagnant regions between eddies in the solar nebula small 1 km planetesimals formed by accumulation of such molten material then develop into planetary embryos and thence to larger terrestrial planets by combinations of runaway growth and collisions as such accumulation of molten chondrule like droplets provides an explanation that obviates some of the dynamic difficulties associated with the onset of planetary accretion the non chondritic mg isotopic composition of the earth is consistent with data for li and has important implications for earth s bulk composition and putative hidden reservoirs

magnesium isotope systematics in martian meteorites abstract magnesium isotope compositions are reported for a suite of martian meteorites that span the range of petrological and geochemical types recognized to date for mars including crustal breccia northwest africa nwa 7034 the 26mg values per mil units relative to dsm 3 reference material range from 0 32 to 0 11 basaltic shergottites and nakhlites lie to the heavier end of the mg isotope range whereas olivine phyric olivine orthopyroxene phyric and lherzolitic shergottites and chassignites have slightly lighter mg isotope compositions attesting to modest correlation of mg isotopes and petrology of the samples slightly heavier mg isotope compositions found for surface related materials nwa 7034 black glass fraction of the tissint shergottite fall 26mg 0 17 indicate measurable mg isotope difference between the martian mantle and crust but the true extent of mg isotope fractionation for martian surface materials remains unconstrained the range of 26mg values from 0 19 to 0 11 in nakhlites is most likely due to accumulation of clinopyroxene during petrogenesis rather than garnet fractionation in the source or assimilation of surface material modified at low temperatures the rather restricted range in mg isotope compositions between spatially and temporally distinct mantle derived samples supports the idea of inefficient absent major tectonic cycles on mars which would include plate tectonics and large scale recycling of isotopically fractionated surface materials back into the martian mantle the cumulative 26mg value of martian samples which are not influenced by late stage alteration processes and or crust mantle interactions is 0 271 0 040 2sd and is considered to reflect 26mg value of the bulk silicate mars this value is robust taking into account the range of lithologies involved in this estimate it also attests to the lack of the mg isotope variability reported for the inner solar system bodies at current analytical precision also noted for several other major elements

north pacific gyre oscillation synchronizes climate fluctuations in the eastern and western boundary systems abstract recent studies have identified the north pacific gyre oscillation npgo as a mode of climate variability that is linked to previously unexplained fluctuations of salinity nutrient and chlorophyll in the northeast pacific the npgo reflects changes in strength of the central and eastern branches of the subtropical gyre and is driven by the atmosphere through the north pacific oscillation npo the second dominant mode of sea level pressure variability in the north pacific it is shown that rossby wave dynamics excited by the npo propagate the npgo signature in the sea surface height ssh field from the central north pacific into the kuroshio oyashio extension koe and trigger changes in the strength of the koe with a lag of 2 3 yr this suggests that the npgo index can be used to track changes in the entire northern branch of the north pacific subtropical gyre these results also provide a physical mechanism to explain coherent decadal climate variations and ecosystem changes between the no