siderophile trace elements in alh84001 other snc meteorites and eucrites evidence of heterogeneity possibly time linked in the mantle of mars we report neutron activation analyses including radiochemical determination of trace siderophile elements au ge ir ni os and re for three snc martian meteorites and os and re results for numerous eucrites ratios such as ga al in the snc orthopyroxenite alh84001 confirm its martian affinity its many distinctive characteristics most notably its near primordial age notwithstanding to the list of alh84001 s idiosyncrasies can now be added extraordinarily low concentrations of au ni and especially re 17 pg g for a martian meteorite we consider several possible origins for the anomalously low re content in alh84001 including metasomatism or alteration the pyroxene cumulate nature of this rock probably does not account for its low re content other snc meteorites are also cumulates an examination of re nd variations among terrestrial basalts and komatiites suggests that re is compatible with mantle minerals in general and only incompatible with olivine however olivine dominates the mantle residuum especially during komatiite genesis our preferred model is that the alh84001 parent melt formed in a mantle source region that was far more re depleted and or at a substantially lower oxygen fugacity than the sources of the young snc meteorites such a contrast is consistent with models that replenish siderophile elements in planetary mantles by gradual admixture of late accreting matter and similarly derive most planetary water which serves as an oxidant very late in accretion according to this model alh84001 formed before the siderophile rich matter and water had been mixed well into the martian interior possibly the martian mantle never became generally as re rich and or oxidized as the source region s of the younger sncs

revised age of the late neogene terror bird titanis in north america during the great american interchange the giant flightless terror bird titanis walleri is known from florida and texas during the late neogene the age of t walleri is problematic because this taxon co occurs with temporally mixed i e time averaged faunas at two key sites thus prior to this study t walleri from the santa fe river florida type locality was either as old as late pliocene ca 2 2 ma or as young as latest pleistocene ca 15 ka likewise t walleri from the nueces river texas was either early pliocene ca 5 ma or latest pleistocene ca 15 ka in order to better resolve this age range the rare earth element ree patterns of t walleri from the santa fe river florida were compared to two biochronologically distinctive groups late pliocene versus late pleistocene of fossil mammals from the same locality similarly the ree patterns of t walleri from texas were compared to two groups early pliocene versus latest pleistocene of fossil mammals from the same locality the ree patterns of t walleri from florida are indistinguishable from those of the co occurring late pliocene mammals likewise the ree pattern of t walleri from texas is indistinguishable from those of the co occurring early pliocene mammals given these ree constraints the revised age of t walleri is early pliocene in texas ca 5 ma and late pliocene ca 2 2 1 8 ma in florida as such t walleri is interpreted as an early immigrant during the great american interchange prior to the formation of the isthmian land bridge no evidence currently exists for pleistocene t walleri in north america

quantifying noble gas contamination during terrestrial alteration in martian meteorites from antarctica we investigated exterior and interior subsamples from the martian shergottite meteorites allan hills alh a77005 and roberts massif rbt 04261 for secondary minerals oxygen isotopes ar ar and noble gas signatures electron microprobe investigations revealed that rbt 04261 does not contain any visible alteration even in its most exterior fractures whereas fracture fillings in alha77005 penetrate into the meteorite up to 300 m beyond which the fractures are devoid of secondary minerals light noble gases seem to be almost unaffected by terrestrially induced alteration in both meteorites thus a shock metamorphic overprint of 30 35 gpa can be deduced from the helium measurements in rbt 04261 oxygen isotopes also seem unaffected by terrestrially weathering and variations can easily be reconciled with the differences in modal mineralogy of the exterior and interior subsamples the measurements on irradiated samples ar ar showed a clear martian atmospheric contribution in alha77005 but this is less apparent in our sample of rbt 04261 exterior and interior subsamples show slight differences in apparent ages but the overall results are very similar between the two in contrast krypton and xenon are severely affected by terrestrial contamination demonstrating the ubiquitous presence of elementally fractionated air in rbt 04261 although seemingly contradictory our results indicate that rbt 04261 was more affected by contamination than alha77005 we conclude that irrespective of on which planet the alteration occurred exposure of martian rocks to atmosphere or brine introduces noble gases with signatures elementally fractionated relative to the respective atmospheric composition into the rock and relationships of that process with oxygen isotopes or mineralogical observations are not straightforward

formation and relative ages of maskelynite and carbonate in alh84001 the morphology and stoichiometry of feldspathic glass in the martian meteorite alh84001 indicates it is maskelynite a diaplectic glass rather than a flowed glass although this glass was heterogeneously affected by a tertiary set of processes an impact event with shock pressures in excess of 31 gpa was needed to convert the original plagioclase an36ab60or4 to maskelynite carbonate is intimately associated with the maskelynite and the carbonate s radiating crystalline fabric and globular forms suggest it was produced after plagioclase was converted to maskelynite textures also suggest carbonate was produced at the expense of maskelynite in a dissolution precipitation reaction that involved a carbonic fluid this fluid system is tentatively estimated to have been active for at least a few years at temperatures 300 c based on dissolution rates of plagioclase in mildly to strongly alkaline hydrothermal systems which is the only analogue currently available this reaction does not need to be mitigated by microbial life neither are bacteria needed to produce the radiating textures and globular forms of carbonate which may instead reflect kinetic phenomena associated with crystal nucleation and growth because the carbonate was produced at the expense of maskelynite it is younger than maskelynite which has previously been shown to have last degassed 3 92 0 04 ga turner et al 1997 however the specific age of the carbonate and the carbonic fluid system remains unknown

once again once again tidal friction topex poseidon t p altimetry has reopened the problem of how tidal dissipation is to be allocated there is now general agreement of a m2 dissipation by 2 5 terawatts 1 tw 1012 w based on four quite separate astronomic observational programs allowing for the bodily tide dissipation of 0 1 tw leaves 2 4 tw for ocean dissipation the traditional disposal sites since jeffreys 1920 have been in the turbulent bottom boundary layer bbl of marginal seas and the modern estimate of about 2 1 tw is in this tradition but the distribution among the shallow seas has changed radically from time to time independent estimates of energy flux into the marginal seas are not in good agreement with the bbl estimates t p altimetry has contributed to the tidal problem in two important ways the assimilation of global altimetry into laplace tidal solutions has led to accurate representations of the global tides as evidenced by the very close agreement between the astronomic measurements and the computed 2 4 tw working of the moon on the global ocean second the detection by ray and mitchum 1996 of small surface manifestation of internal tides radiating away from the hawaiian chain has led to global estimates of 0 2 to 0 4 tw of conversion of surface tides to internal tides measurements of ocean microstructure yields 0 2 tw of global dissipation by pelagic turbulence away from topography we propose that pelagic turbulence is maintained by topographic scattering of barotropic into baroclinic tidal energy via internal tides and internal waves previous estimates by baines 1974 baines 1982 of this conversion along 150 000 km of continental coastlines gave a negligible 0 02 tw evidently the important conversion takes place along mid ocean ridges the maintenance of the abyssal global stratification requires a much larger expenditure of power 2 tw versus 0 2 tw this is usually attributed to wind forcing if tidal power is to play a significant role here then the bbl estimates need to be reduced the challenge is to estimate dissipation from the energy flux divergence in the t p adjusted tidal models without prior assumptions concerning the dissipation processes

nuclear tracks and light noble gases in allan hills 84001 preatmospheric size fall characteristics cosmic ray exposure duration and formation age cosmic ray produced nuclear tracks and noble gases have been studied in the martian orthopyroxenite allan hills 84001 to delineate its cosmic ray exposure history preatmospheric size and fall characteristics a k ar age of 3 9 ga cosmic ray exposure duration of 16 7 ma and a preatmospheric radius of 10 cm have been deduced from the noble gas and track data the track data suggest alh 84001 to be a single fall that has suffered atmospheric mass ablation in excess of 85 higher than the value deduced for the shergottites alha 77005 eeta 79001 and shergotty the formation age as well as the cosmic ray exposure duration determined in this work are in good agreement with values reported earlier and are distinctly different from other shergottite nakhlite and chassignite snc meteorites analysed so far the high cosmogenic 22ne 21ne ratio of 1 22 most probably reflects an effect due to non chondritic composition of alh 84001 as the track data suggest high shielding 5cm for the analysed samples there are signatures in the noble gas data that indicate the possible presence of trapped ar and ne of martian atmospheric origin in alh 84001

provenancing of hominid and mammalian fossils from kanjera kenya using edxrf abstract we describe a rapid non destructive energy dispersive x ray fluorescence edxrf technique for provenancing fossil bone and apply it to surface collected fossils from kanjera kenya the locality is best known for its controversial anatomically modern human fossils potentially among the earliest from africa excavations of the 1987 1988 smithsonian expedition provided the in situ fossil sample necessary to provenance the previous finds relative sr y zr u rb rn and th concentrations were used to characterize 301 fossils from six stratigraphic units the sources of the surface fossils important fossils from past kanjera expeditions including the hominid and theropithecus oswaldi samples were analysed and their relative elemental values used to assign them to a reference sample the hominids post date kanjera formation deposition the t oswaldi fossils are largely attributable to the early pleistocene kanjera bed kn 2a secondary deposition of kanjera formation fossils into later strata was noted

oldowan behavior and raw material transport perspectives from the kanjera formation the archaeological record of oldowan hominins represents a diverse behavioral system it has been suggested that exploitation of lithic resources by oldowan hominins was simplistic and represented mostly use of local sources of stone here we investigate the raw material selection and transport behaviors of oldowan hominins reflected in the stone artifact assemblages from the kanjera south formation south rachuonyo district kenya using geochemical methods ed xrf artifacts are linked to primary and secondary source outcrops throughout southwestern kenya these data show that hominins selected raw materials for transport at frequencies that are significantly different from their availability on ancient landscapes furthermore a substantial proportion of the assemblage represents transport over relatively long distances 10 km our study further suggests that in the early stages of stone tool use hominins used a wide variety of raw materials and selected these materials at some distance from their eventual discard locations early hominin behavior may have incorporated an understanding of raw material source distributions across a more extensive landscape than has been previously documented this supports the growing perspective that oldowan technology represents a more complex behavioral pattern than is usually associated with the beginnings of hominin tool use

chronology and petrogenesis of young achondrites shergotty zagami and alha77005 late magmatism on a geologically active planet a study was undertaken to determine the chronology petrogenesis and relationships among the shergottites shergotty and zagami and the unique achondrite alha77005 these meteorites are the product of a variety of complex processes petrogenesis chondrite normalized abundance patterns of shergotty and zagami are very similar and show pronounced depletions of both the light ree la nd and heavy ree dy lu relative to sm gd these characteristic depletions are even more pronounced for alha77005 the light ree depletion is qualitatively consistent with the presence of cumulus pyroxene and or olivine in these meteorites but trace element models show that the parental magmas of all three meteorites were probably also light ree depleted both trace element model calculations and combined rb sr and sm nd isotopic systematics show that the meteorites could not have been co magmatic nor can alha77005 be representative of the source material of the shergottites light ree depletion of the parental magmas also implies light ree depletion of the source material the sm nd systematics of the shergottites require a time averaged sub chondritic light ree enriched sm nd ratio since 4 6 ae ago the sm nd systematics of alha77005 permit a time averaged super chondritic light ree depleted sm nd ratio if its crystallization age is less than tice 0 72 ae chronology rb sr internal isochrons for all three meteorites and a sm nd internal isochron for zagami are concordant at 180 myr 39ar 40ar plateau ages of shergotty and zagami maskelynite are 250 260 myr these ages apparently reflect resetting of these isotopic systems by shock metamorphism which converted the feldspar to maskelynite the concordance of these ages suggests a single shock event during which the meteorites were in close physical proximity the time of this event is most precisely given by the rb sr age of 180 4 myr for zagami the crystallization ages of the meteorites were not precisely determined extreme upper limits are determined by sm nd model ages relative to an eucrite initial 143nd144nd 0 505835 at 4 6 ae ago these model ages for shergotty zagami and alha77005 are 3600 3500 and 2850 myr respectively the sm nd whole rock age of 1340 60 myr for the three meteorites gives the crystallization age if the sm nd ratios of the precursor materials were always the same we consider this 1340 myr age as a best estimate upper limit best estimate lower limits for shergotty and zagami are taken from the average 39ar 40ar ages of 1200 and 900 myr of pyroxene separates the average 39ar 40ar age of a whole rock sample of alha77005 was 1600 myr and can be partitioned between a low temperature feldspar phase and a high temperature olivine pyroxene inclusions phase the average apparent 39ar 40ar age of the low temperature phase is 1050 myr which is chosen as the best estimate lower limit to the age the crystallization ages of shergotty zagami and alha77005 probably lie within the ranges of 1200 1300 900 1300 and 1000 1300 myr respectively the rb sr whole rock age of 4400 400 myr and single stage babi model ages of 4800 5100 myr are interpreted as reflecting differentiation of the parent body at 4600 myr ago the complex geochemical and isotopic evolution recorded by these meteorites suggests a geologically active parent body capable of sustaining melting at two or more epochs in its history

hydroacoustic detection of volcanic activity on the gorda ridge february march 1996 abstract beginning at 0700 gmt on 28 february 1996 intense seismicity was detected in the northeast pacific ocean using the t phase monitoring system developed by noaa pmel to access the u s navy s sound surveillance system sosus in the north pacific the event was preliminarily located on the northernmost segment of the gorda ridge near 42 67 n and 126 8 w in the vicinity of the ridge segment high narrowgate the nature of the seismicity was similar to that observed in june 1993 at the coaxial segment of the juan de fuca ridge which was later documented to be a lateral magma injection with subsequent eruption due to several gaps in the data the detection information was not as comprehensive as during the coaxial event but an initial migration of epicenters from the narrowgate area down rift is inferred based on arrival bearings from a single array there is evidence for an additional diking event on the second and third day of activity there is also indication of a concentration of epicenters located near 42 6 n as occurred during the coaxial episode at what was later determined to be an eruption site examination of t wave rise times generally supports this interpretation based on the nature and duration of the activity a response effort was initiated which later confirmed hot water plumes and fresh lava flows at the site based on both hydroacoustic information and field observations it is proposed that the episode began with a lateral dike injection possibly with eruptive activity in the summit region followed by multiple magma pulses and eventual focusing of the seismic activity and extrusion near 42 6 n

a 4 gyr shock age for a martian meteorite and implications for the cratering history of mars analyses of meteorites that originated on mars provide important insights into the geological and atmospheric evolution of the planet such analyses have hitherto been restricted to relatively young martian rocks1 the oldest martian meteorites have an age of approximately 1 3 billion years but the recently recognized2 martian meteorite allan hills 84001 which is distinct from the other martian meteorites2 4 shows evidence for a much older age5 6 here we report an analysis of the shock alteration history of this meteorite based on argon isotope dating from which we derive a shock age of 4 0 0 1 billion years the age and geological history of this meteorite suggest that it came from the heavily cratered noachian age terrains of mars s southern hemisphere and it may thus provide an absolute chronology for this region of the planet independent of that inferred from the cratering record the shock age of the meteorite also coincides with that of the so called lunar cataclysm a relatively short period during which many of the craters on the moon are believed to have formed supporting the idea7 that intense bombardment was widespread throughout the inner solar system between 3 9 and 4 1 billion years ago

petrography and bulk chemistry of martian orthopyroxenite alh84001 implications for the origin of secondary carbonates abstract new petrologic and bulk geochemical data for the snc related martian meteorite alh84001 suggest a relatively simple igneous history overprinted by complex shock and hydrothermal processes alh84001 is an igneous orthopyroxene cumulate containing penetrative shock deformation textures and a few percent secondary extraterrestrial carbonates rare earth element ree patterns for several splits of the meteorite reveal substantial heterogeneity in ree abundances and significant fractionation of the rees between crushed and uncrushed domains within the meteorite complex zoning in carbonates indicates nonequilibrium processes were involved in their formation suggesting that co2 rich fluids of variable composition infiltrated the rock while on mars we interpret petrographic textures to be consistent with an inorganic origin for the carbonate involving dissolution replacement reactions between co2 charged fluids and feldspathic glass in the meteorite carbonate formation clearly postdated processes that last redistributed the ree in the meteorite

evidence of harmonic tremor from a submarine volcano detected across the pacific ocean basin 1 since the 1950s seismic activity associated with submarine volcanic eruptions has been detected throughout the pacific ocean basin using hydroacoustic methods however narrowband harmonic tremor with multiple overtones typically associated with subaerial volcanic eruptions has not commonly been observed this paper presents a series of recently recorded hydroacoustic signals that originated in the volcano islands arc south of japan a region that frequently experiences submarine eruptions the signals are characterized by a narrowband long duration high amplitude fundamental centered at 10 hz with three harmonics at 20 30 and 40 hz and are consistent with harmonic tremor signals observed using traditional seismic methods at active subaerial volcanoes throughout the world these hydroacoustic signals were detected 21 different times over the period from april 1998 through december 1999 typically lasting from several days to several weeks after a 6 month hiatus the signals were detected 26 more times from june 2000 through august 2001 the signals are qualitatively interpreted as a result of resonance of a magma gas mixture within a large chamber conduit near the surface of a shallow 1 km submarine volcanic edifice allowing for efficient release of acoustic energy into the ocean sound channel during periods of peak energy radiation the tremor could be clearly detected on hydrophones in the western aleutians hawaii west coast of the united states and eastern equatorial pacific and was detected by the french polynesian seismic network covering a maximum distance of 14 000 km

lunar and martian meteorite delivery services launch mechanisms for lunar and martian meteorites have been investigated by integrating physical modeling constraints geochemical cosmic ray exposure cre constraints and petrologic constraints the potential source region for lunar meteorites is remarkably small compared to the final crater volume cre constraints indicate that most launches start at depths of 3 2 m and cratering theory implies derivation of suitably accelerated objects from a subvolume with diameter only about 0 3 the final crater diameter the shallow depth provenance is probably related to shock wave interference enhanced by the lunar regolith s extremely low compressional wave velocity cre constraints alone imply that four to five separate launch events are represented among the eight well studied lunar meteorites most of the lunar meteorites are regolith breccias which tend to show only limited compositional diversity within any kilometer scale region of the moon several others are polymict breccias which also show relatively subdued compositional diversity compared to igneous rocks the observed diversity among these samples in terms of abundances of mare basalt and kreep and in mg mg fe ratio implies that among eight well studied lunar meteorites only two potential source crater pairings are plausible between asuka 881757 y 793169 most probable and between y 793274 eet875721 altogether these eight lunar meteorites apparently represent at least six separate source craters including three in the past 105 years and five in the past 106 years cre constraints imply that snc meteorites are launched from systematically greater depths than lunar meteorites sncs are also systematically bigger and all nine well studied sncs are uncommonly young by martian standards mafic igneous rocks comparison between viking and apollo results reveals that rocks the size of common meteorites are remarkably scarce in the martian regolith probably due to pervasive weathering a plausible explanation for these trends is that most old small and shallow rocks on mars have been weakened by a two stage process of brecciation followed by pervasive weathering to the point where they seldom survive the stresses of spallation off the planet the scarcity of source crater pairing among the lunar meteorites implies that these objects can be launched from craters much smaller than previously estimated and tends to support the suggestion of rabinowitz 1993 astrophys j 407 412 427 that present day cratering rates for the earth moon region may be higher than previously estimated

quaternary fossil fauna from the luangwa valley zambia this paper describes a large collection of quaternary fossil fauna from the luangwa rift valley zambia stone age artefacts have been recovered from stratified fluvial contexts but no in situ fossil faunas have yet been recovered we report on 500 fossil specimens collected from the surface of point bars exposed seasonally along the banks of the main luangwa river channel we used non destructive x ray fluorescence analysis of the fossils chemical signatures to determine whether they derive from one or many primary contexts and the relationship between chemical signature and state of preservation specimens are identified to taxon genus to reconstruct palaeoenvironments and biochronology a relatively wide range of taxa is identified including a fossil hominin talus described here none of the fossils is positively attributable to extinct species except a femur of an extinct theropithecus reported in 2003 although no additional extinct taxa were identified some of the remains were attributable to genera that are not currently found in this region the results suggest that most of the assemblage derives from sediments which are middle pleistocene or later and that past environments in the luangwa valley may have differed from the habitat availability found today

high resolution records of location and stratigraphic provenance from the rare earth element composition of fossil bones abstract bone apatite acts as a natural timed sampling device scavenging trace elements from local pore waters over timescales of ca 1 50 ka the rare earth element ree and u th composition of fossil bones reflects associated pore water compositions during the period of recrystallisation the ree composition of fossil bones is controlled by partitioning of ree between pore waters and particle surfaces and the ree composition of fossil bones reflects the ree composition of pore waters which vary spatially and temporally light ree are preferentially sorped onto particle surfaces thus the high la yb values seen in many bones from coastal marine and aeolian environments are best explained by release of ree from light ree enriched particles to local pore waters and subsequent immobilisation in recrystallising bones the ree compositions of bones recovered from pedogenically altered diatomite sediments of the olorgesailie formation of southern kenya vary over spatial scales of less than 10 m location accounts for 48 of the observed variation in bone chemistry and bones recovered from eight discrete excavations within the same time equivalent stratigraphic layer can be assigned to their excavation location with 70 accuracy based on a discriminant analysis of ree u and th composition despite this within layer variation bones recovered from different stratigraphic horizons within the olorgesailie formation can also be distinguished on the basis of their trace element composition bones recovered from four stratigraphic horizons spanning ca 0 5 million years were assigned to their correct stratigraphic layer with 90 accuracy where sedimentological conditions are favourable the trace element composition of fossil bone may be used to test stratigraphic provenance and burial location in excavated bone with a temporal resolution of

barotropic and baroclinic tides in the central north pacific ocean determined from long range reciprocal acoustic transmissions abstract travel times of reciprocal 1000 km range acoustic transmissions determined from the 1987 reciprocal tomography experiment are used to study barotropic tidal currents and a large scale coherent baroclinic tide in the central north pacific ocean the difference in reciprocal travel times determines the tidal currents while the sum of reciprocal travel times determines the baroclinic tide displacement of isotachs or equivalently isotherms the barotropic tidal current accounts for 90 of the observed differential travel time variance the measured harmonic constants of the eight major tidal constituents of the barotropic tide and the constants determined from current meter measurements agree well with the empirical numerical tidal models of schwiderski and cartwright et al the amplitudes and phases of the first mode baroclinic tide determined from sum travel times agree with those determined from moored thermistors and current meters the baroclinic tidal signals are consistent with a large

signatures of the martian atmosphere in glass of the zagami meteorite isotopic signatures of nitrogen argon and xenon have been determined in separated millimeter sized pockets of shock melted glass in a recently identified lithology of the meteorite zagami a shergottite the ratio of nitrogen 15 to nitrogen 14 which is at least 282 per mil larger than the terrestrial value the ratio of xenon 129 to xenon 132 2 40 and the argon isotopic abundances match the signatures previously observed in the glassy lithology of the antarctic shergottite eeta 79001 these results show that the signatures in eeta 79001 are not unique but characterize the trapped gas component in shock melted glass of shergottites the isotopic and elemental ratios of nitrogen argon and xenon closely resemble the viking spacecraft data for the martian atmosphere and provide compelling evidence for a martian origin of the two shergottites and by extension of the meteorites in the shergottites nakhlites chassignites snc group

the case for a martian origin of the shergottites nitrogen and noble gases in eeta 79001 abstract nitrogen and noble gases were measured in samples of a glass inclusion and the surrounding basaltic matrix from the antarctic shergottite eeta 79001 a nitrogen component trapped in the glass but not present in the matrix has a 15n value at least as high as 190 ratios of40ar 14n and15n 14n in the glass are consistent with dilution of a martian atmospheric component 15n 620 160 40ar 14n 0 33 0 03 by either terrestrial atmosphere adsorbed on the samples or by indigenous nitrogen from the minerals of the rock trapped noble gases in the glass reproduce within error the elemental and isotopic compositions measured in mars atmosphere by viking and are in general agreement with previous measurements except for much lower abundances of neutron generated krypton and xenon isotopes the most reasonable explanation at the present time for the noble gas pattern and the isotopically heavy nitrogen is that a sample of martian atmosphere has been trapped in the eeta 79001 glass and that this meteorite and thus the shergottites and probably the nakhlites and chassignites as well originated on mars nitrogen in the non glassy matrix of eeta 79001 amounts to less than 0 5 ppm and has a spallation corrected 15n value in the range 0 to 20 it may reflect indigenous nitrogen in the basalt or a mixture of indigenous and adsorbed terrestrial nitrogen spallogenic noble gases yield single stage exposure ages between 400 000 and 900 000 years depending on irradiation geometry trapped argon may have an unusually low36ar 38ar ratio trapped krypton except for a small excess at80kr is smoothly mass fractionated with respect to either terrestrial or chondritic kr the trapped xenon composition is consistent with addition of neutron capture radiogenic and fissiogenic isotopes to a base composition resembling terrestrial atmospheric xe the elemental84kr 132xe ratio of 25 is close to the terrestrial value and very different from the chondritic ratio

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

passive probing of the sound fixing and ranging channel with hydro acoustic observations from ridge earthquakes the international monitoring system includes a hydro acoustic part to verify the comprehensive nuclear test ban treaty besides explosive signals monitoring stations also detect acoustic waves from earthquakes that travel through the sound fixing and ranging sofar channel the travel times of such detections are listed in the reviewed event bulletin which is statistically evaluated for the stations located in the pacific indian and atlantic oceans the celerities of ridge earthquakes are calculated to build up a homogeneous data set based on similar source mechanisms the celerity is defined as the epicentral distance divided by the travel time the global characteristics of these celerities can be well understood in terms of temperature variations in the sofar channel a detailed velocity profile has been retrieved for the atlantic ocean where large differences 14 m s are found between the southern and northern parts of the basin propagation modeling with normal modes supports these findings which shows that the celerity gives an estimate of the sound speed in the sofar channel these results compare remarkably well with those from active experiments showing the ability of passively probing the sofar channel with hydro acoustic waves from earthquake sources

global baroclinic tides an approximate estimate of the energy in the first mode m2 baroclinic tide has been made from satellite observations results based on topex poseidon t p precision altimetry indicate that the internal tide patterns are similar to those expected from mid ocean topographic features in the global oceans both the orthotide and harmonic analyses indicate that the total energy in global m2 baroclinic tide is approximately 50 pj for a variety of reasons m2 is the only component that can be obtained reliably from altimetric measurements even then the energy value may be an underestimate and the energy flux the dissipation rate cannot be deduced from altimetry since it is the tidal currents flowing over mid ocean topographic features that are responsible for generating internal tides a model calibrated by m2 observations is a plausible alternative currents from a high resolution 15 barotropic tidal model have therefore been used to obtain an estimate of both the energy and the dissipation rate in m2 s2 and k1 baroclinic tides a simple model of baroclinic tide generation has been used and the unknown constant in this model has been selected to yield a total energy of 50 pj in the first mode m2 baroclinic tide based on this calibration the total energy is 8 pj in s2 first mode baroclinic tide and 15 pj in k1 the total in all first mode baroclinic tides is 90 pj about 16 of the total energy 580 pj in barotropic tides the model results also suggest that about 360 gw of tidal energy are dissipated in m2 baroclinic tides alone and 520 gw are dissipated in all first mode baroclinic tides the latter value is approximately 15 of the power input into barotropic ocean tides 3490 gw by the lunisolar tidal forces we have preferred to be conservative and hence these are likely to be underestimates especially since the altimetric tracks do not often intersect mid ocean topographic features at optimum angles while these values are very much within the range of earlier estimates in literature they should be regarded as still uncertain to perhaps a factor of two the dissipation rate could be anywhere from 400 gw to 800 gw the most likely value being about 600 gw the small signal to noise ratio involved in altimetric measurements of the surface manifestation of internal tides and potential contamination by mesoscale signals are serious problems in situ measurements at least a few locations underneath altimetric tracks are essential for confirmation and or refinement of these preliminary estimates hopefully these very first estimates of the energy and dissipation rate in global baroclinic tides though rather crude will serve as a catalyst for a better estimation in the future since internal tides are likely to be a prominent source of mixing in the deep oceans and important to thermocline maintenance

precursors of mars constraints from nitrogen and oxygen isotopic compositions of martian meteorites we present an approach to assess the nature of materials involved in the accretion of mars by the planets nitrogen 15n and oxygen 17o isotopic compositions as derived from data on martian meteorites 15n for mars has been derived from nitrogen and xenon systematics while 17o has been taken from the literature data these signatures indicate that mars has most probably accreted from enstatite and ordinary chondritic materials in a ratio of 74 26 and may not have a significant contribution from the carbonaceous ci cm or cv chondrites this is consistent with the chromium isotopic e53cr signatures of martian meteorites and the bulk planet fe si ratio for mars as suggested by the moment of inertia factor i mr2 obtained from the mars pathfinder data further a simple homogeneous accretion from the above two types of materials is found to be consistent with the planets moment of inertia factor and the bulk composition of the mantle but it requires a core with 6 7 wt si which is consistent with the new results from the high pressure and temperature melting experiments and chemical data on the opaque minerals in enstatite chondrites

isotopic composition of trapped and cosmogenic noble gases in several martian meteorites isotopic abundances of the noble gases were measured in the following martian meteorites two shock glass inclusions from elephant moraine eet 79001 shock vein glass from shergotty and yamato y 793605 and whole rock samples of allan hills alh 84001 and queen alexandra range que 94201 these glass samples when combined with literature data on a separate single glass inclusion from eet 79001 and a glass vein from zagami permit examination in greater detail of the isotopic composition of ne ar kr and xe trapped from the martian atmosphere the isotopic composition of martian ne if actually present in these glasses remains poorly defined the 40ar 36ar ratio of trapped martian atmospheric ar is probably considerably lower than the nominal ratio of 3000 measured by viking and data on impact glasses suggest a value of 1900 the atmospheric 36ar 38ar ratio is 4 0 martian atmospheric kr may be enriched in lighter isotopes by 0 5 amu compared to both solar wind kr and to the martian composition previously reported the isotopic composition of xe in these glasses agrees with that previously reported in the literature the martian atmospheric 36ar 132xe and 84kr 132xe elemental ratios are higher than those reported by viking by factors of 2 5 1 6 depending on the 40ar 36ar ratio adopted and 1 8 respectively and are discussed in a separate paper cosmogenic gases indicate space exposure ages of 2 7 0 6 ma for que 94201 and shergotty and 14 1 ma for alh 84001 small amounts of 21ne produced by energetic solar protons may be present in que 94201 but are not present in alh 84001 or y 793605 the space exposure age for y 793605 is 4 9 0 6 ma and appears to be distinctly older than the ages for basaltic shergottites however uncertainties in cosmogenic production rates still makes somewhat uncertain the number of martian impact events required to produce the exposure ages of martian meteorites

submarine volcanic activity ocean acoustic waves and internal ocean tides 1 submarine volcanic event often generates acoustic waves t waves traveling over long distances through the low velocity channel sofar of the ocean by a method of coherent stacking of t waves from a submarine volcanic activity in northern mariana we found a significant semidiurnal variation of t wave travel times the amplitude of variation is an order of larger than those reported in the previous ocean sound transmission experiments ray theoretical consideration for the numerically simulated ocean tides indicates that such large t phase travel time variation is a consequence of large up and down movement of seawater around the axis of the sofar channel due to the m2 internal tide effectively converted from external tidal forcing t phases a ubiquitous feature of the ocean acoustic noise field can be used to infer internal tidal motion and the associated ocean mixing

petrological evidence for shock melting of carbonates in the martian meteorite alh84001 the meteorite alh84001 a shocked igneous rock of probable martian origin contains chemically and isotopically heterogeneous carbonate globules associated with which are organic and inorganic structures that have been interpreted as possible fossil remains of ancient martian biota a critical assumption underlying this suggestion is that the carbonates formed from low temperature fluids penetrating the cracks and voids of the host rock here we report petrological studies of alh84001 which investigate the effects of shock on the various mineralogical components of the rock we find that carbonate plagioclase and silica were melted and partly redistributed by the same shock event responsible for the intense local crushing of pyroxene in the meteorite texture and compositional data show that during the period of shock decompression monomineralic melts were injected into pyroxene fractures that were subsequently cooled and resealed within seconds our results therefore suggest that the carbonates in alh84001 could not have formed at low temperatures but instead crystallized from shock melted material this conclusion weakens significantly the arguments that these carbonates could host the fossilized remnants of biogenic activity

water in snc meteorites evidence for a martian hydrosphere the shergotty nakhla chassigny snc meteorites purportedly of martian origin contain 0 04 to 0 4 percent water by weight oxygen isotopic analysis can be used to determine whether this water is extraterrestrial or terrestrial such analysis reveals that a portion of the water is extraterrestrial and furthermore was not in oxygen isotopic equilibrium with the host rock lack of equilibrium between water and host rock implies that the lithosphere and hydrosphere of the snc parent body formed two distinct oxygen isotopic reservoirs if mars was the parent body the maintenance of two distinct reservoirs may result from the absence of plate tectonics on the planet

nitrogen isotopes in bulk ordinary chondrites nitrogen isotopic compositions of twenty one ordinary chondrites were measured using a stepwise combustion technique we observed a good correlation between the abundances of cosmogenic15n and cosmogenic 38ar we obtained a relationship between the abundances of these two cosmogenic nuclides as follows 15nc atoms g 16 0 3 7 38arc atoms g using this relationship the cosmogenic nitrogen production rate in l chondrites is calculated to be 5 0 1 2 10 12 g 15n g myr assuming the cosmogenic38ar production rate given by eugster 1988 this value is consistent with the production rate on the lunar surface estimated by becker et al 1976 isotopic ratios of trapped nitrogen in ordinary chondrites seem to be heterogeneous among both unequilibrated and equilibrated meteorites heterogeneity among the latter are well observed in this study the isotopic ratios of the trapped components seem to differ by more than 110 ranging from 18 observed in guaren a h6 to 95 observed in jilin h5 a lack of correlation between nitrogen abundances and isotopic ratios indicates that differences in nitrogen isotopic ratios are not produced by mass dependent isotopic fractionation an inverse correlation between nitrogen abundances and the degree of thermal metamorphism is observed among most of the unequilibrated chondrites nitrogen abundances decrease from 8 25 p p m to 1 p p m with increasing petrographic subtype from 3 4 3 9 the nitrogen abundance in equilibrated chondrites is generally higher than the amount expected by extending the trend observed among unequilibrated ones this is probably because contaminating nitrogen masked the trend at small amounts of trapped nitrogen

chassigny and the nakhlites carbon bearing components and their relationship to martian environmental conditions abstract the carbon and nitrogen inventories of chassigny and the nakhlites have been investigated by low resolution 100 c temperature increment stepped combustion in addition the contents and isotopic compositions of carbonate minerals have been assessed by the use of an acid dissolution technique low temperature carbon i e that which combusts below 500 c appears to be from two different sources one component is present in variable quantities 300 700 ppm and has 13 c 26 consistent with identification as terrestrial organic contamination the other is isotopically light with 13 c ca 36 which is unusual for normal sources of terrestrial contamination curiously the latter material is present in each sample in similar concentrations 45 15 ppm since this level of carbon is too high to be ascribed to a system blank it is considered that this component is probably indigenous to the meteorites the low temperature of release of the isotopically light carbonaceous material is testimony to its highly labile nature it is evidently organic material of some description the accompanying low temperature nitrogen also appears to be distributed between two components one with 15 n of ca 6 5 to 2 4 the other with 15 n 4 but it is not yet possible to establish relationships between the nitrogen and carbon components released below 500 c the meteorites investigated were found to contain 2 5 30 ppm carbon as carbonate with 13 c between 5 and 11 and 18 o between 23 and 29 variation in 13 c and 18 o of the carbonates indicates either a change in conditions during formation of the carbonate minerals or that there may be two distinct carbon sources magmatic species which are released on combustion at temperatures above 700 c apparently have an isotopically light carbon isotopic composition between 30 and 20 and are associated with light nitrogen 15 n superimposed on the magmatic species is a release of spallogenically produced isotopically heavy nitrogen seen most clearly in chassigny there is no evidence in any of the samples analysed for trapped martian atmospheric gases

martian atmosphere like nitrogen in the orthopyroxenite alh84001 abstract isotopic and elemental compositions of nitrogen neon and argon in the martian meteorite alh84001 were studied two whole rock samples of alh84001 57 were analyzed with detailed stepped combustion experiments from 200 to 1200 c with every 100 c and 200 c respectively with laser ablation experiments for melting the samples nitrogen with 15 n 418 44 and 366 15 after correction for cosmogenic nitrogen were obtained at 800 c which are the highest 15 n values ever found among shergottites nakhlites chassignite meteorites the heavy nitrogen in alh84001 may have the same origin as that in the glass portions of two shergottites eeta79001 and zagami and is likely to have been derived from the martian atmosphere however when and in which phase martian atmosphere like nitrogen was trapped in alh84001 is still unknown one possibility inferred from the released temperatures is that nitrogen is sited in maskelynite on the plot of 15 n versus ar n diagrams of 15 n vs 40 ar 14 n and 36ar 14 n the data points for alh84001 in this study form a linear trend which apparently differs from that defined by glass portions of the shergottites eeta79001 and zagami the present trend also differs from the trend seen by grady et al for alh84001 the 40 ar 14 n and 36 ar 14 n ratios obtained in this work are relatively smaller than those of the shergottites on such plots indicating the following possibilities 1 martian atmospheric ar n ratio changed throughout geologic time e g 4 ga without a large change in 15 n that is alh84001 trapped ancient martian atmospheric nitrogen and ar n ratio was initially lower or 2 different trapping sites or mechanisms between alh84001 and the shergottite glasses made an apparent difference in the ar n ratio and elementally fractionated gases were trapped in alh84001 in the case 1 either increase in ar concentration in the martian atmosphere due to preferential ar degassing from the martian interior or preferential escape of atmospheric nitrogen must have occurred nitrogen with 15 n from 13 to 5 and with 15 n 200 were released at low and high temperatures respectively the former may have been derived from the martian lithosphere or terrestrial atmosphere and the latter must be of cosmogenic nitrogen the largest amount of 40 ar was released at temperatures similar to the largest release of heavy nitrogen of 800 c according to reported k abundance in alh84001 the majority of 40 ar in our samples is considered to be of radiogenic origin

the history of allan hills 84001 revised multiple shock events the geologic history of martian meteorite allan hills alh 84001 is more complex than previously recognized with evidence for four or five crater forming impacts onto mars this history of repeated deformation and shock metamorphism appears to weaken some arguments that have been offered for and against the hypothesis of ancient martian life in alh 84001 allan hills 84001 formed originally from basaltic magma its first impact event i1 is inferred from the deformation d1 that produced the granular textured bands crush zones that transect the original igneous fabric deformation d1 is characterized by intense shear and may represent excavation or rebound flow of rock beneath a large impact crater an intense thermal metamorphism followed d1 and may be related to it the next impact i2 produced fractures fr2 in which carbonate pancakes were deposited and produced feldspathic glass from some of the igneous feldspars and silica after i2 carbonate pancakes and globules were deposited in fr2 fractures and replaced feldspathic glass and possibly crystalline silicates next feldspars feldspathic glass and possibly some carbonates were mobilized and melted in the third impact i3 microfaulting intense fracturing and shear are also associated with i3 in the fourth impact i4 the rock was fractured and deformed without significant heating which permitted remnant magnetization directions to vary across fracture surfaces finally alh 84001 was ejected from mars in event i5 which could be identical to i4 this history of multiple impacts is consistent with the photogeology of the martian highlands and may help resolve some apparent contradictions among recent results on alh 84001 for example the submicron rounded magnetite grains in the carbonate globules could be contemporaneous with carbonate deposition whereas the elongate magnetite grains epitaxial on carbonates could be ascribed to vapor phase deposition during i3

contrasting re os magmatic fractionation in planetary basalts abstract this work reports the first re os isotopic results for lunar basalts and eucrites both re and os concentrations are found to be very low and re os ratios are close to chondritic this contrasts with the much higher than chondritic re os ratio of terrestrial basalts osmium displays a rather uniform solid liquid fractionation in different planetary bodies moon earth eucrite parent body mars whereas rhenium is about three orders of magnitude more incompatible in terrestrial basalt genesis we argue that this is a function of oxygen fugacity in the source regions of basalts

fractionation of rare earth elements within bone mineral a natural cation exchange system the distribution of rare earth elements rees within fossil bones is controlled by their partition coefficients between apatite and pore waters and the rate of diffusion through the bone using simple theoretical models we show that rees are strongly fractionated from one another during diffusive transport and adsorption fractionation occurs due to the relative ease of substituting ree ions of differing ionic radius into the ca sites in the apatite lattice and the degree of fractionation is dependent on the rate of diffusion of ions within bone and therefore the rate of recrystallisation variations in bone thickness recrystallisation rate and potentially pore water composition may all influence the relative distribution of rees and thus ree ratios within bones increases in bone thickness and reductions in either diffusion coefficients or the duration of ree uptake lead to enhanced fractionation of rees in our model simulations interpretations of ree ratios in fossil bones either for palaeoenvironmental or taphonomic applications must consider how fractionation will influence ree ratios within bones particularly when interpreting spatially resolved analyses within single bones

a nitrogen and argon stable isotope study of allan hills 84001 implications for the evolution of the martian atmosphere the abundances and isotopic compositions of n and ar have been measured by stepped combustion of the allan hills 84001 alh 84001 martian orthopyroxenite material described as shocked is n poor n approximately 0 34 ppm delta 15n approximately 23 although during stepped combustion 15n enriched n delta 15n approximately 143 is released in a narrow temperature interval between 700 degrees c and 800 degrees c along with 13c enriched c delta 13c approximately 19 and 40ar cosmogenic species are found to be negligible at this temperature thus the isotopically heavy component is identified in part as martian atmospheric gas trapped relatively recently in the history of alh84001 the n and ar data show that alh84001 contains species from the martian lithosphere a component interpreted as ancient trapped atmosphere in addition to the modern atmospheric species and excess 40ar from k decay deconvolution of radiogenic 40ar from other ar components on the basis of end member 36ar 14n and 40ar 36ar ratios has enabled calculation of a k ar age for alh 84001 as 3 5 4 6 ga depending on assumed k abundance if the component believed to be martian palaeoatmosphere was introduced to alh 84001 at the time the k ar age was set then the composition of the atmosphere at this time is constrained to delta 15n or 200 40ar 36ar or 17 x 10 5 in terms of the petrogenetic history of the meteorite alh 84001 crystallised soon after differentiation of the planet may have been shocked and thermally metamorphosed in an early period of bombardment and then subjected to a second event this later process did not reset the k ar system but perhaps was responsible for introducing recent atmospheric gases into alh 84001 and it might mark the time at which alh 84001 suffered fluid alteration resulting in the formation of the plagioclase and carbonate mineral assemblages

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

detection of and response to a probable volcanogenic t wave event swarm on the western blanco transform fault zone the east blanco depression ebd a pull apart basin within the western blanco transform fault zone btfz was the site of an intense earthquake t wave swarm that began at 1317z on january 9 1994 although technically generated earthquakes occur frequently along the btfz this swarm was unusual in that it was preceded and accompanied by periodic low frequency long duration acoustic signals that originated from near the swarm epicenters these tremor like signals were very similar in character to acoustic energy produced by a shallow submarine eruption near socorro island a seamount several hundred km west of baja california the 69 earthquakes and 400 tremor like events at the ebd occurred sporadically with two periods of peak activity occurring between january 5 16 and 27 31 the swarm like character of the earthquakes and the similarity of the tremor activity to the socorro eruption indicated that the ebd was undergoing an intrusion or eruption episode on january 27 six ctd rosette casts were conducted at the site water samples from two of the stations yielded anomalous he concentrations with maxima at 2800 m depth over the main basin in june 1994 two camera tows within the basin yielded evidence of pillow lava volcanism and hydrothermal deposits but no conclusive evidence of a recent seafloor eruption in september 1994 deployments of the u s navy s advanced tethered vehicle resulted in the discovery of an active hydrothermal mound on the flanks of a pillow lava volcano the hydrothermal mound consists of fe rich hydrothermal precipitate and bacterial mats temperatures to 60 c were measured 30 cm below the surface this is the first discovery of active hydrothermal vents along an oceanic fracture zone although no conclusive evidence of volcanic activity associated with the t wave event swarm was found during these response efforts the ebd has been the site of recent seafloor eruptions

seismic detection of underwater volcanism the example of french polynesia we present a review of the principal methods used for the seismic detection and identification of active underwater volcanism based on our experience in french polynesia in particular we descrobe the 5 year activity in the tahiti mehetia area during which more than 32000 earthquakes were detected by the polynesian network we discuss the use of the following three types of seismic waves conventional mostly body waves seismic tremor andt waves propagated in the low velocity acoustic channel of the ocean for each of these waves we discuss the principal characteristics of the signals their spectral content the type of information they provide on the activity of the volcano and the various limitations faced by their use in detection or monitoring of underwater volcanic edifices we present a review of the principal swarms monitored by the polynesian network and discuss their characterization as either volcanic or tectonic

ar ar chronology of the martian meteorite alh84001 evidence for the timing of the early bombardment of mars abstract alh84001 a cataclastic cumulate orthopyroxenite meteorite from mars has been dated by ar ar stepped heating and laser probe methods both methods give ages close to 3 900 ma the age calculated is dependent on assumptions made about 39ar recoil effects and on whether significant quantities of 40ar from the martian atmosphere are trapped in the meteorite if as suggested by xenon and nitrogen isotope studies martian atmospheric argon is present then it must reside predominantly in the k rich phase maskelynite independently determined 129xe abundances in the maskelynite can be used to place limits on the concentration of the atmospheric 40ar these indicate a reduction of around 80 ma to ages calculated on the assumption that no martian atmosphere is present after this correction the nominal ages obtained are 3940 50 3870 80 and 3970 100 ma by stepped heating and 3900 90 ma by laser probe 1 statistical errors giving a weighted mean value of 3 920 ma ambiguities in the interpretation of 39ar recoil effects and in the contribution of martian atmospheric 40ar lead to uncertainties in the ar ar age which are difficult to quantify but we suggest that the true value lies somewhere between 4 050 and 3 800 ma this age probably dates a period of annealing of the meteorite subsequent to the shock event which gave it its cataclastic texture the experiments provide the first evidence of an event occurring on mars coincident with the time of the late heavy bombardment of the moon and may reflect a similar period of bombardment in the southern highlands of mars whether the age determined bears any relationship to the time of carbonate deposition in alh84001 is not known such a link depends on whether the temperature associated with the metasomatic activity was sufficient to cause argon loss from the maskelynite and or whether the metasomatism and metamorphism were linked in time through a common heat source

mineralogical and compositional changes in bones exposed on soil surfaces in amboseli national park kenya diagenetic mechanisms and the role of sediment pore fluids abstract bones exposed on tropical savannah grasslands of amboseli national park kenya undergo extensive post mortem alteration within 40 years a combined analytical approach involving tem microscopy trace metal analysis ftir spectroscopy and petrographic analysis has revealed a complex dynamic diagenetic environment operating within exposed bones driven by evaporative transport of soil water from the bone soil interface to the upper exposed surface of the bone this process results in extensive bone soil water interaction and is responsible for increases in the concentrations of trace elements such as ba and la of 100 1000 within 15 years the maximum and mean size of bone crystallites increases with continued exposure this change in mean crystallite length is correlated positively with increases in bone crystallinity which in turn is associated with degradation of the bone protein microbial decomposition is rarely observed in the amboseli bones but where present resulted in severe dissolution reprecipitation of bone mineral many bones showed extensive permineralization of the larger vascular spaces with calcite and barite and to a lesser extent crandallite permineralization of unburied bones may account for 95 reduction in macro micron millimeter scale porosity in the bone within 2 years of death we produce a model for pre burial diagenesis of bone in arid tropical environments that highlights extensive alteration of bone chemistry within 1 40 years post mortem

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

estimates of internal tide energy fluxes from topex poseidon altimetry central north pacific energy fluxes for first mode m2 internal tides are deduced throughout the central north pacific ocean from topex poseidon satellite altimeter data temporally coherent internal tide signals in the altimetry combined with climatological hydrographic data determine the tidal displacements pressures and currents at depth which yield power transmission rates for a variety of reasons the deduced rates should be considered lower bounds internal tides are found to emanate from several large bathymetric structures especially the hawaiian ridge where the integrated flux amounts to about 6 gigawatts internal tides are generated at the aleutian trench near 172 w and propagate southwards nearly 2000 km

underwater records of submarine volcanic activity el hierro canary islands 2011 2012 eruption abstract we present the monitoring of a submarine volcanic eruption that took place near the southernmost emerged land of el hierro island canary islands spain from october 2011 to february 2012 right after the onset of the eruption in mid october 2011 we deployed an offshore geophone array for the purpose of monitoring the submarine eruptive activity signals it acquired continuous data from october 2011 to may 2012 sometime after the end of the eruption the array consisted of 8 high frequency 3 component geophones assembled into a cable string with 6 m of separation the geophone string was installed in la restinga harbor at a distance of less than 2 km from the volcanic edifice the dataset acquired with the array is a unique continuous acoustic record of the activity associated with this eruption we analyzed the continuous signal of the eruptive activity with special interest in those events reflecting the eruption dynamics our results show that the geophone array was recording acoustic waves from a back azimuth source corresponding to the position of the submarine vent traveling at a speed of 1510 m s compatible with the speed of sound in water acoustic data shows a good correlation with the seismic data recorded on land for the case of earthquake occurrence in addition it provides relevant information towards the understanding of the eruptive surface activity therefore this methodology can be successfully used in cases of submarine eruptions

a topex poseidon global tidal model tpxo 2 and barotropic tidal currents determined from long range acoustic transmissions abstract tidal currents derived from the tpxo 2 global tidal model of egbert bennett and foreman are compared with those determined from long range reciprocal acoustic transmissions amplitudes and phases of tidal constituents in the western north atlantic are derived from acoustic data obtained in 1991 1992 using a pentagonal array of transceivers small spatially coherent differences between the measured and modeled tidal harmonic constants mostly result from smoothing assumptions made in the model and errors caused in the model currents by complicated topography to the southwest of the acoustical array acoustically measured harmonic constants amplitude phase of m2 tidal vorticity 3 8 10 9s 1 210 310 agree with those derived from the tpxo 2 model 2 5 10 9s 1 250 300 whereas harmonic constants of about 1 2 10 9s 1 350 360 are theoretically expected from the equations of motion harmonic constants in the north pacific ocean are determined using acoustic data from a triangular transceiver array deployed in 1987 these constants are consistent with those given by the tpxo 2 tidal model within the uncertainties tidal current harmonic constants determined from current meters do not generally provide a critical test of tidal models the tidal currents have been estimated to high accuracy using long range reciprocal acoustic transmissions these estimates will be useful constraints on future global tidal models

tidal effects on long range sound transmission time series of acoustic travel times over long distances have significant tidal components we discuss three experiments first for a 900 km westward transmission from a moored source southwest of bermuda the m2 constituent apart from mooring motion of 8 ms can be accounted for by a variable propagation with and against the 2 cm s barotropic tidal current the situation is different for the k1 and s2 constituents which have a significant solar component particularly for rays with shallow turning points suggesting an effect from a minute daily variation in the temperature of the upper 100 m second for a 500 km transmission from the bahamas northward and parallel to the continental margin the measured m2 constituent is not in phase with the computed effect of the barotropic tidal current unlike the westward transmission mentioned above here the mode conversion from barotropic to baroclinic tides plays a crucial role the principal cause of the travel time oscillations in quadrature with the tidal current is a vertical oscillation by several meters and attendant temperature and sound speed fluctuations associated with the baroclinic tide just seaward of the continental margin in the near zone of mode conversion third for 300 km transmissions from a moored source northwest of bermuda to both a moored receiver and a landbased receiver the tidal components in the travel time are dominated by tidally induced mooring motions the tidal amplitude varies in time as the tidal mooring motion is modulated by the variable current because of the nonlinear drag and the current can be so estimated an important part possibly a predominant part of the nontidal travel time variation of 0 7 s is evidently associated with the mean mooring motion the interpretation of the tidal fluctuations in travel time is varied and complex