a new martian meteorite from oman mineralogy petrology and shock metamorphism of olivine phyric basaltic shergottite sayh al uhaymir 150 the sayh al uhaymir sau 150 meteorite was found on a gravel plateau 43 3 km south of ghaba oman on october 8 2002 oxygen isotope 17o 2 78 18o 4 74 cre age 1 3 ma and noble gas studies confirm its martian origin sau 150 is classified as an olivine phyric basalt having a porphyritic texture with olivine macrocrysts set in a finer grained matrix of pigeonite and interstitial maskelynite with minor augite spinel ilmenite merrillite pyrrhotite pentlandite and secondary terrestrial calcite and iron oxides the bulk rock composition in particular mg 68 molar mg mg fe 100 fe mn 37 9 and na al 0 22 are characteristic of martian meteorites based on mineral compositions cooling rates determined from crystal morphology and crystal size distribution it is deduced that the parent magma formed in a steady state growth regime magma chamber that cooled at 70 365 c sau 150 is essentially identical to sau 005 094 all representing samples of the same fall that are similar to but distinct from the dag shergottites

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

late quaternary pollen records from two ugandan mires evidence for environmental changes in the rukiga highlands of southwest uganda abstract high resolution pollen data from two mires in the rukiga highlands southwest uganda ahakagyezi swamp and muchoya swamp provide detailed evidence of the environmetal history of the region since ca 42 000 yr b p according to these data there a was period pre ca 42 000 yr b p when climatic conditions were similar to the present conditions considerably colder and drier than the present occurred during two periods in the past pre ca 42 000 yr b p to ca 32 000 yr b p and ca 21 000 yr b p to ca 12 000 yr b p the most recent period of climatic improvement began ca 14 000 yr b p moist lower montane forest colonised the muchoya catchment by ca 11 100 yr b p and the ahakagyezi catchment by ca 10 600 yr b p indicating the establishment there of climatic conditions broadly similar to the present pollen data from both mires reveal forest disturbances beginning ca 2200 yr b p this disturbances is likely to have been human induced

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

charcoal analysis for paleoenvironmental interpretation a chemical assay a nitric acid digestion and ignition technique developed to measure relative frequencies of charcoal in lake and bog sediments measures the weight of charcoal relative to the dry weight of the sample percentage charcoal and gives results comparable to counting of microscopic charcoal differences in the two techniques caused by changes in sediment type were found especially in postsettlement and late glacial parts of cores charcoal values from sediments less than 100 yr old cannot be compared to older charcoal values unless wood charcoal and charcoal from fossil fuel burning are separated microscopically tests of this chemical assay on mixtures of known weights of charcoal leaves and sand give correlations between observed and expected values of 0 99 to 1 00

density porosity and magnetic susceptibility of carbonaceous chondrites abstract we report physical properties bulk and grain density magnetic susceptibility and porosity measured using nondestructive and noncontaminating methods for 195 stones from 63 carbonaceous chondrites grain densities over the whole population average 3 44 g cm 3 ranging from 2 42 g cm 3 ci1 orgueil to 5 66 g cm 3 cb bencubbin magnetic susceptibilities in log units of 10 9 m3 kg 1 averaged log 4 22 ranging from 3 23 cv3 axtell to 5 79 cb bencubbin porosities averaged 17 ranging from 0 for a number of meteorites to 41 for one stone of the co ornans notably we found significant differences in porosity between the oxidized and reduced cv subgroups with the porosities of cvo averaging approximately 20 and cvr porosities approximately 4 overall porosities of carbonaceous chondrite falls trend with petrographic type from type 1 ci near 35 type 2 cm cr averaging 23 type 3 cv co 21 to type 4 ck and some co averaging 15 there is also a significant decrease in porosity between meteorites of shock stage s1 and those of s2 indicative of shock compression

pre aged plant waxes in tropical lake sediments and their influence on the chronology of molecular paleoclimate proxy records sedimentary records of plant wax hydrogen ddwax and carbon d 13 cwax stable isotopes are increasingly applied to infer past climate change compound specific radiocarbon analyses however indicate that long time lags can occur between the synthesis of plant waxes and their subsequent deposition in marginal marine sediments the influence of these time lags on interpretations of plant wax stable isotope records is presently unconstrained and it is unclear whether such time lags also affect lacustrine sediments we present compound specific radiocarbon 14 cwax data for n alkanoic acid plant waxes n c26 to n c32 from 1 a sediment core from lake chichancanab yucatan peninsula mexico 2 soils in the lake chichancanab catchment and 3 surface sediments from three other lakes in southeastern mexico and northern guatemala 14 cwax ages in the surface sediments are consistently older than modern and may be negatively correlated with mean annual precipitation and positively correlated with lake catchment area 14 cwax ages in soils surrounding lake chichancanab increase with soil depth consistent with deep subsoil horizons being the primary source of lacustrine aged plant waxes which are likely delivered to lake sediments through subsurface transport plant waxes in the lake chichancanab core are 350 1200 years older than corresponding ages of bulk sediment deposition determined by 14 c dates on terrestrial plant macrofossils in the core a ddwax time series is in closer agreement with other regional proxy hydroclimate records when a plant wax 14 c age model is applied as opposed to the macrofossil based core chronology inverse modeling of plant wax age distribution parameters suggests that plant waxes in the lake chichancanab sediment core derive predominantly from millennial age soil carbon pools that exhibit relatively little age variance 200 years our findings demonstrate that high temporal resolution climate records inferred from stable isotope measures on plant waxes in lacustrine sediments may suffer from possible chronologic distortions as a consequence of long residence times of plant waxes in soils they also underscore the importance of direct radiocarbon dating of these organic molecules

mapping of c4 plant input from north west africa into north east atlantic sediments abstract mapping the abundance of 13c in leaf wax components in surface sediments recovered from the seafloor off northwest africa 0 35 n reveals a clear pattern of 13c distribution indicating systematic changes in the proportions of terrestrial c3 and c4 plant input at 20 n latitude we find that isotopically enriched products characteristic of c4 plants account for more than 50 of the terrigenous inputs this signal extends westward beneath the path of the dust laden sahara air layer sal high c4 contributions apparently carried by january trade winds also extend far into the gulf of guinea similar distributions are obtained if summed pollen counts for the chenopodiaceae amaranthaceae and the poaceae are used as an independent c4 proxy we conclude that the specificity of the latitudinal distribution of vegetation in north west africa and the pathways of the wind systems trade winds and sal are responsible for the observed isotopic patterns observed in the surface sediments molecular isotopic maps on the marine sedimentary time horizons e g during the last glacial maximum are thus a robust tool for assessing the phytogeographic changes on the tropical and sub tropical continents which have important implications for the changes in climatic and atmospheric conditions

compositions and taxonomy of 15 unusual carbonaceous chondrites abstract we used instrumental neutron activation analysis and petrography to determine bulk and phase compositions and textural characteristics of 15 carbonaceous chondrites of uncertain classification acfer 094 type 3 0 ungrouped cm related belgica 7904 mildly metamorphosed anomalous cm like chondrite possibly a member of a new grouplet that includes wisconsin range wis 91600 dhofar 225 and yamato 86720 dar al gani dag 055 and its paired specimen dag 056 anomalous reduced cv3 like dag 978 type 3 ungrouped dominion range 03238 anomalous magnetite rich co3 1 elephant moraine 90043 anomalous magnetite bearing co3 graves nunataks 98025 type 2 or type 3 ungrouped grosvenor mountains gro 95566 anomalous cm2 with a low degree of aqueous alteration hammadah al hamra hah 073 type 4 ungrouped possibly related to the coolidge loongana c l 001 grouplet lewis cliff lew 85311 anomalous cm2 with a low degree of aqueous alteration northwest africa 1152 anomalous cv3 pecora escarpment pca 91008 anomalous metamorphosed cm queen alexandra range 99038 type 2 ungrouped sahara 00182 type 3 ungrouped possibly related to hah 073 and or to c l 001 and wis 91600 mildly metamorphosed anomalous cm like chondrite possibly a member of a new grouplet that includes belgica 7904 dhofar 225 and y 86720 many of these meteorites show fractionated abundance patterns especially among the volatile elements impact volatilization and dehydration as well as elemental transport caused by terrestrial weathering are probably responsible for most of these compositional anomalies the metamorphosed cm chondrites comprise two distinct clusters on the basis of their 17o values approximately 4 for pca 91008 gro 95566 dag 978 and lew 85311 and approximately 0 for belgica 7904 and wis 91600 these six meteorites must have been derived from different asteroidal regions

large scale atmospheric forcing by southeast pacific boundary layer clouds a regional model study abstract a regional model is used to study the radiative effect of boundary layer clouds over the southeast pacific on large scale atmosphere circulation during august october 1999 with the standard settings the model simulates reasonably well the large scale circulation over the eastern pacific precipitation in the intertropical convergence zone itcz north of the equator and marine boundary layer stratocumulus clouds to the south in a sensitivity experiment with the radiative effect of liquid clouds south of the equator over the eastern pacific artificially removed boundary layer clouds south of the equator almost disappear and precipitation in the itcz is reduced by 15 20 indicating that the stratocumulus clouds over the southeast pacific have both local and cross equatorial effects examination of the differences between the control and sensitivity experiments indicates that clouds exert a net diabatic cooling in the inversion layer in response to this cloud induced cooling an in situ anom

shisr 043 iiiab medium octahedrite the first iron meteorite from the oman desert the iron meteorite shisr 043 is a single mass of 8267 g found in the south oman desert 42 km ne of the shisr village it is the first iron identified among the 1400 individual meteorites reported from oman the meteorite is a slightly elongated mass showing only minor rusting a partially smooth and partially rough surface with octahedral cleavage and a partially preserved metallic fusion crust typically 0 75 mm thick the undeformed widmanstatten pattern with a mean kamacite bandwidth of 1 0 0 1 mm n 97 indicates structural classification as a medium octahedrite from the bulk composition ni 8 06 wt ga 18 8 ppm ge 37 25 ppm and ir 3 92 ppm the meteorite is classified as iiiab the most common group of iron meteorites the cosmic ray exposure cre age based on 3he 21ne 38ar concentrations and 10be 21ne 26al 21ne and 36cl 36ar ratios is 290 20 ma this age falls within the range observed for type iiiab iron meteorites but does not coincide with the main cluster the cosmogenic noble gas and radionuclide data indicate that shisr 043 had a relatively small preatmospheric mass the low degree of weathering is consistent with a young terrestrial age of 10 000 years based on the saturated 41ca concentration shisr 043 is not paired with any of the other eight known iron meteorites from the arabian peninsula

lunar meteorites from oman abstract sixty named lunar meteorite stones representing about 24 falls have been found in oman in an area of 10 7 103 km2 in southern oman lunar meteorite areal densities average 1 g km 2 all lunar meteorites from oman are breccias although two are dominated by large igneous clasts a mare basalt and a crystalline impact melt breccia among the meteorites the range of compositions is large 9 32 al2o3 2 5 21 1 feo 0 3 38 g g 1 sm and 1 to 22 5 ng g 1 ir the proportion of nonmare lunar meteorites is higher among those from oman than those from antarctica or africa omani lunar meteorites extend the compositional range of lunar rocks as known from the apollo collection and from lunar meteorites from other continents some of the feldspathic meteorites are highly magnesian high mgo mgo feo compared with most similarly feldspathic apollo rocks two have greater concentrations of incompatible trace elements than all but a few apollo samples a few have moderately high abundances of siderophile elements from impacts of iron meteorites on the moon all lunar meteorites from oman are contaminated to various degrees with terrestrial na k p zn as se br sr sb ba u carbonates or sulfates the contamination is not so great however that it seriously compromises the scientific usefulness of the meteorites as samples from randomly distributed locations on the moon

the kashiru pollen sequence burundi palaeoclimatic implications for the last 40 000 yr b p in tropical africa abstract a continuous pollen record from a central african highland site 3 28 s 29 34 e with 15 radio carbon dates spans at least the last 40 000 yr both modern and fossil pollen have been investigated a clear pattern of changes in vegetation and climate is suggested prior to 30 000 yr b p the occurrence of the montane conifer forest including the upper forest limit indicates climatic conditions colder and drier than now but more humid than in late glacial time between 30 000 and 15 000 yr b p grassland with afroalpine indicators expanded down to 2500 2000 m altitude as a result of dry and most probably cool climate the montane forest persisted in refuges although much reduced forest vegetation with the same floristic composition as today appeared after 13 250 200 yr b p suggesting more humid conditions the occurrence of a possible short term humid episode about 21 500 yr b p is correlated with some high lake level stages in east africa and with organic deposits in deep sea cores from the mediterranean and the atlantic ocean

feldspathic lunar meteorites pecora escarpment 02007 and dhofar 489 contamination of the surface of the lunar highlands by post basin impacts abstract pca pecora escarpment 02007 and dhofar 489 are both meteorites from the feldspathic highlands of the moon pca 02007 is a feldspathic breccia consisting of lithified regolith from the lunar surface it has concentrations of both incompatible and siderophile elements that are at the high end of the ranges for feldspathic lunar meteorites dhofar 489 is a feldspathic breccia composed mainly of impact melted material from an unknown depth beneath the regolith concentrations of incompatible and siderophile elements are the lowest among brecciated lunar meteorites among 19 known feldspathic lunar meteorites all of which presumably originate from random locations in the highlands concentrations of incompatible elements like sm and th tend to increase with those of siderophile elements like ir feldspathic meteorites with high concentrations of both suites of elements are usually regolith breccias iridium derives mainly from micrometeorites that accumulate in the regolith with duration of surface exposure micrometeorites have low concentrations of incompatible elements however so the correlation must reflect a three component system we postulate that the correlation between sm and ir occurs because the surface of the feldspathic highlands terrane has become increasingly contaminated with time in sm rich material from the procellarum kreep terrane that has been redistributed across the lunar surface by impacts of moderate sized post basin impacts the most sm rich regolith breccias among feldspathic lunar meteorites are about 3 enriched compared to the most sm poor breccias but this level of enrichment requires only a few percent sm rich material typical of the procellarum kreep terrane the meteorite data suggest that nowhere in the feldspathic highlands are the concentrations of k rare earths and th measured by the lunar prospector mission at the surface representative of the underlying bedrock all surfaces covered by old regolith as opposed to fresh ejecta are at least slightly contaminated dhofar 489 is one of 15 paired lunar meteorite stones from oman total mass of meteorite 1037 g on the basis of its unusually high mg fe ratio the meteorite is likely to have originated from northern feldspathic highlands

weathering of meteorites from oman correlation of chemical and mineralogical weathering proxies with 14c terrestrial ages and the influence of soil chemistry fifty four fragments of ordinary chondrites from 50 finds representing all searched areas in central oman and all weathering stages were selected to compare the physical chemical and mineralogical effect of terrestrial weathering with 14c terrestrial ages 14c ages range from 2 0 to 49 kyr with a median value of 17 9 kyr the peak of the age range which is between 10 20 kyr falls in an arid climate period a comparison of the chemical composition of omani chondrites with literature data for unweathered h and l chondrites demonstrates a strong enrichment in sr and ba and depletion in s during weathering water contents in h chondrites increase with terrestrial age whereas l chondrites show a rapid initial increase followed by nearly constant water content correlating sr ba and h2o with age indicates two absorption trends i an initial alteration within the first 20 kyr dominated by h2o uptake mainly reflecting fe ni metal alteration and ii a second baand sr dominated stage correlated with slower and less systematic weathering of troilite that starts after h2o reaches 2 wt sulfur released from troilite partly combines with ba and sr to form sulfate minerals other parameters correlated with 14c age are degree of weathering color of powdered meteorites and the ni fe ratio chemical analyses of 145 soils show a high degree of homogeneity over the entire interior oman desert indicating large scale mixing by wind soil samples collected from beneath meteorite finds typically are enriched in ni and co confirming mobilization from the meteorites high cr and ni concentrations in reference soil samples which decrease from ne to sw are due to detrital material from ultramafic rocks of the oman mountains

high resolution 14c dating of a 25 000 year lake sediment record from equatorial east africa abstract we dated a continuous 22 m long sediment sequence from lake challa mt kilimanjaro area kenya tanzania to produce a solid chronological framework for multi proxy reconstructions of climate and environmental change in equatorial east africa over the past 25 000 years the age model is based on a total of 168 ams 14 c dates on bulk organic matter combined with a 210 pb chronology for recent sediments and corrected for a variable old carbon age offset this offset was estimated by i pairing bulk organic 14 c dates with either 210 pb derived time markers or 14 c dates on grass charcoal and ii wiggle matching high density series of bulk organic 14 c dates variation in the old carbon age offset through time is relatively modest ranging from 450 yr during glacial and late glacial time to 200 yr during the early and mid holocene and increasing again to 250 yr today the screened and corrected 14 c dates were calibrated sequentially statistically constrained by their stratigraphical order as a result their constrained calendar age distributions are much narrower and the calibrated dates more precise than if each 14 c date had been calibrated on its own the smooth spline age depth model has 95 age uncertainty ranges of 50 230 yr during the holocene and 250 550 yr in the glacial section of the record the 13 c values of paired bulk organic and grass charcoal samples and additional 14 c dating on selected turbidite horizons indicates that the old carbon age offset in lake challa is caused by a variable contribution of old terrestrial organic matter eroded from soils and controlled mainly by changes in vegetation cover within the crater basin

palaeoecological evidence for holocene environmental change from the virunga volcanoes in the albertine rift central africa abstract this study presents two new well dated sedimentary pollen and charcoal records from high altitude crater sites in the virunga volcanoes located in the albertine rift central africa currently part of one of the world s most biodiverse areas here we argue that holocene vegetation changes in a ca 8000 year palaeoenvironmental record from a crater swamp at an altitude of 3474 m and a ca 2800 year record from a crater lake at an altitude of 4127 m are linked to variations in both climate and human activity climatic changes during the mid to late holocene are reflected in the high altitude sites and more widely in adjacent parts of the albertine rift vegetation changes comprising a decline in ericaceous vegetation at ca 5000 cal yrs bp and subsequent expansion of afroalpine vegetation together with a later increase in taxa associated with lower montane forest particularly podocarpus reflect increasing aridity during the mid to late holocene human induced environmental change in the virunga volcanoes is apparent only within the last millennium despite the long history of human occupation of the area both study sites record significant forest clearance at ca 900 cal yrs bp involving a reduction in lower montane forest taxa and increases in disturbance indicators changes in the composition of upper montane forest and particularly the expansion of hagenia are possibly linked to anthropogenic induced changes in the fire regime and are apparent from ca 900 cal yrs bp human induced environmental modification from the early part of the last millennium likely associated with onset of the late iron age appears to have extended to high altitudes the importance of natural long term climate change as a major cause of environmental change in the albertine rift has been eclipsed within the last millennium by human induced environmental effects

cosmic ray exposure ages of four acapulcoites and two differentiated achondrites and evidence for a two layer structure of the acapulcoite lodranite parent asteroid abstract we determined the he ne and ar isotopic abundances in the four acapulcoites dhofar dho 125 dho 290 dho 312 and graves nunataks 98028 the metal rich diogenite northwest africa nwa 1982 and a unique achondrite nwa 1058 that resembles the acapulcoites in its chemical composition the noble gases in these meteorites consist of three components trapped gases cosmic ray produced nuclides and nuclides produced by k th and u decay the four acapulcoites yield cosmic ray exposure cre ages in the range of 5 0 5 7 ma and confirm earlier conclusions concerning break up of all acapulcoites from a common s type parent asteroid possibly in three events 4 9 5 9 and 14 8 ma ago we also discuss the other characteristics mineralogy chemistry formation ages and oxygen and trapped noble gas isotopes of all other acapulcoites and their relatives the lodranites we propose that the acapulcoite lodranite parent asteroid had a shell structure similar to that of the h chondrites the less metamorphosed acapulcoites correspond to the h3 and h4 chondrites and originate from the exterior layers whereas the more severely metamorphosed lodranites similar to the h5 and h6 chondrites represent the inner regions of their parent body ungrouped achondrite nwa 1982 probably a diogenite shows a cre age of 18 9 2 0 ma that falls on the major exposure age cluster of the diogenites the unique achondrite nwa 1058 differs in cosmic ray exposure age 38 9 4 0 ma and in oxygen isotopic composition from the acapulcoites and lodranites and is probably a winonaite

a high resolution geochemical record from lake edward uganda congo and the timing and causes of tropical african drought during the late holocene abstract high resolution analyses of the elemental composition of calcite and biogenic silica bsi content in piston cores from lake edward equatorial africa document complex interactions between climate variability and lacustrine geochemistry over the past 5400 years correlation of these records from lake edward to other climatically forced geochemical and lake level records from lakes naivasha tanganyika and turkana allows us to develop a chronology of drought events in equatorial east africa during the late holocene major drought events of at least century scale duration are recorded in lacustrine records at about 850 1500 2000 and 4100 cal year bp of these the most severe event occurred between about 2050 and 1850 cal year bp during which time lake edward stood about 15 m below its present level numerous additional droughts of less intensity and or duration are present in the lake edward record some of which may be correlated to other lacustrine climate records from equatorial east africa these events are superimposed on a long term trend of increasingly arid conditions from 5400 to about 2000 cal year bp followed by a shift toward wetter climates that may have resulted from an intensification of the winter indian monsoon although the causes of decade to century scale climate variability in the east african tropics remain obscure time series spectral analysis suggests no direct linkage between solar output and regional rainfall rather significant periods of 725 125 63 72 31 25 and 19 16 years suggest a tight linkage between the indian ocean and african rainfall and could result from coupled ocean atmosphere variability inherent to the tropical monsoon system

vegetation history in western uganda during the last 1200 years a sedimentbased reconstruction from two crater lakes pollen plant macrofossil and charcoal records from two neighbouring crater lakes lake wandakara and lake kasenda in lower montane altitude 1200m western uganda 0 5dn 30 reveal major changes in local and regional vegetation over the last 1200 years which can be related to regional variations in climate especially effective precipitation and human impact the biological signals are supplemented by evidence from physical sedimentary analyses magnetic susceptibility loss on ignition dry mass accumulation rate for major catchment changes in a wider regional context from ad 750 to 900 medium altitude moist forest existed around lake kasenda which was largely replaced by grassland by ad 1000 coincident e with evidence for increased catchment erosion and fire events linked to human impact during a brief arid phase despite wetter conditions from ad 1000 to 1200 and in the 1400s grassland prevailed around both sites until c ad 1700 1750 with increased catchment disturbance from ad 1600 t

northwest africa 482 a crystalline impact melt breccia from the lunar highlands northwest africa 482 nwa 482 is a crystalline impact melt breccia from the moon with highlands affinities the recrystallized matrix and the clast population are both highly anorthositic clasts are all related to the ferroan anorthosite suite and include isolated plagioclase crystals and lithic anorthosites troctolites and spinel troctolites potassium rare earth element and phosphorus bearing kreep and mare lithologies are both absent constraining the source area ofthis meteorite to a highland terrain with little to no kreep component most likely on the far side of the moon glass is present in shock veins cutting through the sample and in several large melt pockets indicating a second impact event there are two separate events recorded in the 40ar 39ar system one at 3750 ma which completely reset the k ar system and one at 2400 ma which caused onlypartial degassing these events could represent respectively crystallization ofthe impact melt breccia and later formation of the glass or the formation of the glass and a later thermal event the terrestrial age of the meteorite is 8 6 1 3 ka this age corresponds well with the modest amount ofweathering in the rock in the form ofsecondaryphyllosilicates and carbonates based on terrestrial age and location lithology and chemistry nwa 482 is unique among known lunar meteorites

dhofar 225 and dhofar 735 relationship to cm2 chondrites and metamorphosed carbonaceous chondrites belgica 7904 and yamato 86720 dhofar dho 225 and dho 735 are carbonaceous chondrites found in a hot desert and having affinities to belgica like antarctic chondrites belgica b 7904 and yamato y 86720 texturally they resemble cm2 chondrites but differ in mineralogy bulk chemistry and oxygen isotopic compositions the texture and main mineralogy of dho 225 and dho 735 are similar to the cm2 chondrites but unlike cm2 chondrites they do not contain any p cr sulfides nor tochilinite 6fe0 9s 5 fe mg oh 2 h2o contents of dho 225 and dho 735 1 76 and 1 06 wt are lower than those of cm2 chondrites 2 18 wt but similar to those in the metamorphosed carbonaceous chondrites of the belgica like group bulk compositions of dho 225 and dho 735 as well as their matrices have low fe and s and low fe si ratios relative to cm2 chondrites x ray powder diffraction patterns of the dho 225 and dho 735 matrices showed similarities to laboratory heated murchison cm2 chondrite and the transformation of serpentine to olivine dho 225 and 735 s oxygen isotopic compositions are in the high 18o range on the oxygen diagram close to the belgica like meteorites this differs from the oxygen isotopic compositions of typical cm2 chondrites experimental results showed that the oxygen isotopic compositions of dho 225 and dhofar 725 could not be derived from those of typical cm2 chondrites via dehydration caused by thermal metamorphism dho 225 and dho 735 may represent a group of chondrites whose primary material was different from typical cm2 chondrites and the belgica like meteorites but they formed in an oxygen reservoir similar to that of the belgica like meteorites

the constitution and structure of the lunar interior the current state of understanding of the lunar interior is the sum of nearly four decades of work and a range of exploration programs spanning that same time period missions of the 1960s including the rangers surveyors and lunar orbiters as well as earth based telescopic studies laid the groundwork for the apollo program and provided a basic understanding of the surface its stratigraphy and chronology through a combination of remote sensing surface exploration and sample return the apollo missions provided a general picture of the lunar interior and spawned the concept of the lunar magma ocean in particular the discovery of anorthite clasts in the returned samples led to the view that a large portion of the moon was initially molten and that crystallization of this magma ocean gave rise to mafic cumulates that make up the mantle and plagioclase flotation cumulates that make up the crust smith et al 1970 wood et al 1970 this model is now generally accepted and is the framework that unifies our knowledge of the structure and composition of the moon the intention of this chapter is to review the major advances that have been made over the past decade regarding the constitution of the moon s interior much of this new knowledge is a direct result of data acquired from the successful clementine and lunar prospector missions as well as the analysis of new lunar meteorites as will be seen results from these studies have led to many fundamental amendments to the magma ocean model much of what we know from sample analyses has been previously summarized elsewhere and only their most important aspects will be discussed in this chapter the reader is referred to the relevant chapters in the books basaltic volcanism on the terrestrial planets basaltic volcanism study project 1981 the

prehistorical record of cultural eutrophication from crawford lake canada cultural eutrophication the process by which human activities increase nutrient input rates to aquatic ecosystems and thereby cause undesirable changes in surface water quality is generally thought to have begun with the start of the industrial era the prehistoric dimension of human impacts on aquatic ecosystems remains relatively undescribed particularly in north america here we present fossil plankton data diatoms and rotifers organic and inorganic carbon accumulations and carbon isotope ratios from a 1000 yr sediment core record from crawford lake ontario canada the data document increased nutrient input to crawford lake caused by iroquoian horticultural activity from a d 1268 to 1486 and show how this increased nutrient input elevated lake productivity caused bottom water anoxia and irreversibly altered diatom community structure within just a few years iroquoian settlement in the region declined in the fifteenth century yet diatom communities and lake circulation never recovered to the predisturbance state a second phase of cultural eutrophication starting in a d 1867 initiated by canadian agricultural disturbance increased lake productivity but had comparatively less impact on diatom assemblages and carbon storage pathways than the initial iroquoian disturbance this study deepens our understanding of the impact of cultural eutrophication on lake systems highlights the lasting influence of initial environmental perturbation and contributes to the debate on the ecological impacts of density and agricultural practices of native north american inhabitants

paleoclimate changes of the last 1000 yr on the eastern qinghai tibetan plateau recorded by elemental isotopic and molecular organic matter proxies in sediment from glacial lake ximencuo abstract total organic carbon corg and nitrogen ntot concentrations and isotope compositions and n alkane and n alkan ol molecular biomarker compositions were measured in two parallel sediment cores from lake ximencuo a typical glacial lake on the eastern qinghai tibetan plateau qtp to reconstruct local climatic variations during the past 1000 yr concentrations of corg and ntot vary similarly with changes in precipitation recorded by tree rings in dulan northeastern qtp indicating their close relation to precipitation carbon preference index cpi values of c22 c33 n alkanes and c22 c28 n alkan 1 ols and average chain length acl values of c27 c33 n alkanes generally negatively correlate with 13corg and 15ntot and also vary comparably with the oxygen isotope temperature record from the dunde ice core northeastern qtp these patterns indicate that high cpi values and negative shifts of the 13corg and 15ntot correspond to warmer conditions that favor the growth of vascular land plants and that lower values and positive shifts correspond to cooler conditions in the lake ximencuo locality this observation contradicts previous interpretations from peat and modern soil studies that conclude that the cpi indices were controlled by microbial degradation under different climate conditions here we propose that the changes of organic matter sources under different climate regimes combined with physiological adjustments of vascular plants to different air temperatures might yield different cpi responses to climate changes in glacial plateau lakes air temperature and precipitation increases and decreases reconstructed in this 1000 yr study were generally independent of each other but they both occurred at centennial or multi centennial scales the interaction between subtropical asian monsoon and mid latitude westerly atmospheric circulation systems probably dominated the local precipitation variations in the lake ximencuo catchment whereas solar insolation volcanism and greenhouse gas variations were likely responsible for the air temperature changes that are recorded in the lake sediments and that are consistent with regional temperature variations in the eastern qtp

early solar system processes recorded in the matrices of two highly pristine cr3 carbonaceous chondrites met 00426 and que 99177 the mineralogy and bulk compositions of the matrices of the cr chondrites met 00426 and que 99177 have been studied using a combination of sem epma and tem techniques the matrices of these two chondrites are texturally chemically and mineralogically similar and are characterized by significant feo enrichments with respect to other cr chondrite matrices nearly flat refractory lithophile patterns variable volatile element patterns and a simple mineral assemblage dominated by amorphous silicate material and fe ni sulfides fine grained crystalline silicate phases such as olivine and pyroxene appear to be extremely rare in the matrices of both meteorites instead the mineralogy of matrices and fine grained rims of both meteorites consists of abundant amorphous feo rich silicate material containing nanoparticles of fe ni sulfides troilite pyrrhotite and pentlandite secondary alteration minerals that are characteristic of other cr chondrites e g renazzo and al rais such as phyllosilicates magnetite and calcite are also rare the texture and mineralogy of the matrices of met 00426 and que 99177 share many features with matrices in the primitive carbonaceous chondrites alh a77307 co3 0 and acfer 094 unique these observations show that met 00426 and que 99177 are very low petrologic type 3 chondrites that have escaped the effects of aqueous alteration unlike other cr chondrites which are typically classified as petrologic type 2 we suggest that these meteorites represent additional samples of highly primitive but extremely rare carbonaceous chondrites of petrologic type 3 00 according to the classification scheme of grossman and brearley 2005 the highly pristine nature of met 00426 and que 99177 provides important additional insights into the origins of fine grained materials in carbonaceous chondrites based on our new observations we infer that the amorphous silicate material and nanosulfide particles that dominate the matrices of these meteorites formed in the solar nebula by rapid condensation of material following high temperature events such as those that formed chondrules

vegetation response to rainfall variation and human impact in central kenya during the past 1100 years pollen data from a 625 cm sediment core from crescent island crater a subbasin of lake naivasha kenya provide an 1100 year record of vegetation change at a mean time resolution of 15 years earlier data from the same core show a record of lake depth and thus inferred rainfall variation in the form of changing sedimentary facies supported by salinity inferences based on diatom and chironomid assemblages stratigraphic variation in the abundances of aquatic and semi aquatic plants and chlorophyte algae generally supports the reconstructed lake depths woody afromontane and woodland plant taxa decreased relative to poaceae grasses during low rainfall periods and increased during high rainfall periods a decrease in the extent of lower montane forest coincident with favourable climatic conditions after about ad 1700 was probably caused by kikuyu immigration and population expansion around that time as indicated by simultaneous appearance of the food crop zea mays maize increases in ruderal herbaceous and exotic tree pollen during the twentieth century indicate increased local landscape disturbance during the colonial period there is little direct pollen evidence for accelerating clearance of the montane forest during recent decades

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

comments on on entrainment rates in nocturnal marine stratocumulus by bjorn stevens donald h lenschow ian faloona c h moeng d k lilly b blomquist g vali a bandy t campos h gerber s haimov b morley and d thornton october b 2003 129 3469 3493 stability against entrainment of the nocturnal stratocumulus case dycoms ii is discussed using a comparison between two ctei criteria copyright 2005 royal meteorological society

a new boundary layer mixing scheme part i scheme description and single column model tests a new boundary layer turbulent mixing scheme has been developed for use in the ukmo weather forecasting and climate prediction models this includes a representation of nonlocal mixing driven by both surface fluxes and cloud top processes in unstable layers either coupled to or decoupled from the surface and an explicit entrainment parameterization the scheme is formulated in moist conserved variables so that it can treat both dry and cloudy layers details of the scheme and examples of its performance in single column model tests are presented

hydrogen isotope ratios of palmitic acid in lacustrine sediments record late quaternary climate variations the rich paleoclimate information preserved in lacustrine sedimentary organic matter can be difficult to extract because of the mixed terrestrial and aquatic inputs herein we demonstrate that compound specific hydrogen isotope analysis of palmitic acid pa a ubiquitous compound in lacustrine sediments captures the d signals of lake water samples collected across a diverse range of 33 north american lakes show a strong correlation between water and dpa values at crooked pond massachusetts the dpa changes in a 14 k y sediment record parallel temperature trends inferred from fossil pollen downcore changes reveal differences between climatic trends in new england and in greenland that are consistent with important regional differences in climate controls

northeast african temperature variability since the late pleistocene abstract the development and application of lacustrine paleotemperature proxies based on microbial membrane lipid structures including the tex86 and branched glycerol dialkyl glycerol tetraether brgdgt paleothermometers have greatly advanced our understanding of the late glacial and postglacial temperature history of africa however the currently available records are from equatorial and southern hemisphere sites limiting our understanding of the spatial patterns of temperature change here we use the brgdgt paleotemperature proxy to reconstruct late pleistocene and holocene temperatures from lake tana ethiopia 12 n 37 e following the termination of heinrich stadial 1 at 15 ka lake tana experienced a 3 7 c oscillation over 1 2 ky temperatures then increased abruptly by nearly 7 c between 13 8 and 13 0 ka followed by a slow warming trend that peaked during the mid holocene temperatures subsequently cooled from 6 ka to 0 4 ka these data indicate that temperature at lake tana was sensitive to climate changes caused by variations in the atlantic meridional overturning circulation during the late pleistocene as well as to regional hydroclimatic changes and reorganizations of the monsoons our record suggests that late glacial temperature changes in northeast africa were linked to high latitude northern hemispheric climate processes but that subsequent post glacial temperature variations were strongly influenced by tropical hydrology

39ar 40ar ages and origin of excess 40ar in martian shergottites we report new 39ar 40ar measurements on 15 plagioclase pyroxene and or whole rock samples of 8 martian shergottites all age spectra suggest ages older than the meteorite formation ages as defined by sm nd and rb sr isochrons employing isochron plots only los angeles plagioclase and possibly northwest africa nwa 3171 plagioclase give ages in agreement with their formation ages isochrons for all shergottite samples reveal the presence of trapped martian 40ar 40arxs which exists in variable amounts in different lattice locations some 40arxs is uniformly distributed throughout the lattice resulting in a positive isochron intercept and other 40arxs occurs in association with k bearing minerals and increases the isochron slope these samples demonstrate situations where linear ar isochrons give false ages that are too old after subtracting 40ar that would accumulate by 40k decay since meteorite formation and small amounts of terrestrial 40ar all young age samples give similar 40arxs concentrations of 1 2 x 10 6 cm 3 g but a variation in k content by a factor of 80 previously reported nasa johnson space center data for zagami shergotty yamato y 000097 y 793605 and queen alexandra range que 94201 shergottites show similar concentrations of 40arxs to the new meteorite data reported here similar 40arxs in different minerals and meteorites cannot be explained as arising from martian atmosphere carried in strongly shocked phases such as melt veins we invoke the explanation given by bogard and park 2008 for zagami that this 40arxs in shergottites was acquired from the magma similarity in 40arxs among shergottites may reveal common magma sources and or similar magma generation and emplacement processes

lake level history of lake tanganyika east africa for the past 2500 years based on ostracode inferred water depth reconstruction assemblages of ostracodes from sediment cores illuminate lake level history at decadal to centennial timescales during the late holocene at lake tanganyika east africa the ostracode based lake level curves for several cores resemble both each other and the only previously published lake level record of comparable resolution for lake tanganyika during this interval successfully reconstructing known highstands improving the chronology of known lowstands and contributing new information on late holocene lake level variability at this important tropical african location in agreement with other late holocene records from east africa the surface level at lake tanganyika reflects predominantly arid conditions throughout this interval interrupted by relatively brief episodes of higher precipitation and lake level the most pronounced lowstand in the record occurs at v200 0 bc with other significant lowstands dating to the intervals v200 500 ad v700 850 ad the medieval warmperiod mwp v1050 1250 ad at lake tanganyika and the latter part of the little ice age lia v1550 1850 ad the most important wet intervals in the lake level record are centered on v500 ad v1500 ad and v1870 ad the highstands and lowstands reported here for lake tanganyika appear to be fairly coherent with other records of rainfall throughout east africa during the mwp and the lia prior to the mwp paleoclimate records are apparently less coherent although this may be a reflection of the resolution and abundance of recent paleoclimatic data available for this climatically complex region

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

can sedimentary leaf waxes record d h ratios of continental precipitation field model and experimental assessments abstract d h ratios of leaf waxes d wax derived from terrestrial plants and preserved in lake sediments can provide important information on past continental hydrology ideally d wax can be used to reconstruct precipitation d h ratios d p which is a well established paleoclimate proxy however many other factors such as vegetation and relative humidity rh also affect d wax variation how the combination of these factors affects sedimentary d wax is unclear here we use a transect of 32 lake surface sediments across large gradients of precipitation relative humidity and vegetation composition in the southwestern united states to study the natural factors affecting sedimentary d wax d values of c 28 n alkanoic acids show significant correlation with d p values r 2 0 76 with an apparent isotopic enrichment of 99 8 indicating that sedimentary d wax values track overall d p variation along the entire transect leaf waxes produced by plants grown under controlled conditions rh 80 60 40 show a small increase in d h ratios as rh decreases consistent with prediction from the craig gordon model however the isotopic effect of rh on d wax along the natural transect is partially countered by the opposing influence of vegetation changes the correlation between d wax and d p values is significantly higher r 2 0 84 in the drier portions of the transect than in the wetter regions r 2 0 64 this study suggests that d h ratios of sedimentary leaf waxes can be used as a proxy for precipitation d variations with particularly high fidelity in dry regions although more studies in other regions will be important to further test this proxy

organic geochemical investigations of the dali lake sediments in northern china implications for environment and climate changes of the last deglaciation in the east asian summer monsoon margin abstract millennial scale environment and climate changes in the east asian summer monsoon margin during the last deglaciation are reconstructed by systematic studies on the characteristic of sedimentary organic matter from dali lake in northern china concurrent increases in the toc and tn concentrations indicate increases in terrestrial organic matter and nutrient inputs to the lake and a development of terrestrial vegetation and phytoplankton productivity related to increases in regional temperature and precipitation c n ratios reflect changes in the proportions of terrestrial and aquatic organic matter decreases in both 13corg and 15n values indicate increases in the isotopically lighter terrestrial carbon and nitrogen inputs to the lake due to increases in surface runoffs while a sharp decrease in the 15n value implies a significant weakening in the biological activities of nitrifying and amonifying bacteria due to abrupt decrease in the water temperature the geochemical data indicate that regional temperature and precipitation exhibited increasing trends from 15 000 to 12 350 cal yr bp temperature decreased abruptly at 12 350 cal yr bp and then maintained a low level from 12 350 to 11 400 cal yr bp precipitation decreased to a relatively low level from 12 350 to 11 400 cal yr bp and both temperature and precipitation returned to increase after 11 400 cal yr bp the climate change in the dali lake region during the last deglaciation corresponds within age uncertainties to the bolling allerod ba warm phase and younger dryas yd cold reversal occurring over northern high latitudes however the gradual and mild increasing trends of regional temperature and precipitation during the ba warm period contrasts with the general cooling trend in northern high latitude temperature implying a dominant influence from increases in the northern hemisphere summer insolation while the slight decreases in regional precipitation relative to the rapid and significant decreases in northern high latitude temperature during the yd cold period may have resulted from local moisture recycling or from an insensitive response of hydrology and ecology to the regional precipitation change

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

a unique omphacite amphibole and graphite bearing clast in queen alexandra range que 99177 a metamorphosed xenolith in a pristine cr3 chondrite abstract a metamorphosed unshocked chondritic clast containing approximately equal volumes of matrix and chondrules has been identified in the primitive cr3 chondrite que 99177 the most striking features of this clast are the presence of ferroan omphacitic pyroxenes amphiboles pargasite and pargasitic hornblende and coarse grained up to 70 m graphite laths the clast also contains relatively equilibrated feo rich olivine low ca pyroxene and sulfides pentlandite and troilite the clast s matrix contains coarse interlocking crystals the chondrules are extensively recrystallized contain no mesostasis or metal and present poorly defined boundaries based on its compositional and crystallographic features omphacite appears to have formed at high pressures 6 gpa amphibole formation probably postdated graphite formation and occurred by reaction of olivine clinopyroxene and omphacite in the presence of an oxidizing na rich fluid at high temperatures 700 c the absence of metal suggests that this fluid was also rich in s

new noble gas data of primitive and differentiated achondrites including northwest africa 011 and tafassasset this work reports on the noble gas inventory of 3 new acapulcoites 3 brachinites 2 new eucrites from the dar al gani region in libya the unique achondrite dar al gani dag 896 from the same locality the new eucrite like achondrite northwest africa nwa 011 and the controversial sample tafassasset we determined cosmic ray exposure and gas retention ages evaluated shielding conditions and discuss the trapped noble gas component of the specimens all exposure ages are within the known range of stony meteorites and partly confirm previously established age clusters shielding conditions vary suggesting substantial shielding for all 3 brachinites and tafassasset we cannot exclude however that the mg rich composition of brachinites simply simulates heavy shielding regarding the trapped component we found q like compositions only for the acapulcoite thiel mountains til 99002 the brachinite elephant moraine eet 99402 yields a high subsolar 36ar 132xe ratio of 400 along with a slightly elevated 84kr 132xe ratio indicating minor atmospheric contamination all the other samples particularly the eucrite dag 983 are characterized by clearly elevated ar kr xe ratios due to significant terrestrial alteration tafassasset exhibits noble gas parameters that are different from those of cr chondrites including a relatively high cosmic ray exposure age the absence of a solar component low 132xe concentrations a low trapped 36ar 132xe ratio of 30 and a noticeable amount of radiogenic 129xe similar attributes have been observed for some primitive achondrites these attributes are also consistent with the metamorphic character of the sample we therefore consider tafassassets noble gas record to be inconclusive as to its classification primitive achondrite versus metamorphosed cr chondrite

hydrogen isotope ratios of lacustrine sedimentary n alkanes as proxies of tropical african hydrology insights from a calibration transect across cameroon abstract hydrogen isotope values d of sedimentary aquatic and terrestrial lipid biomarkers originating from algae bacteria and leaf wax have been used to record isotopic properties of ancient source water i e precipitation and or lake water in several mid and high latitude lacustrine environments in the tropics however where both processes associated with isotope fractionation in the hydrologic system and vegetation strongly differ from those at higher latitudes calibration studies for this proxy are not yet available to close this gap of knowledge we sampled surface sediments from 11 lakes in cameroon to identify those hydro climatological processes and physiological factors that determine the hydrogen isotopic composition of aquatic and terrestrial lipid biomarkers here we present a robust framework for the application of compound specific hydrogen isotopes in tropical africa our results show that the d values of the aquatic lipid biomarker n c17 alkane were not correlated with the d values of lake water carbon isotope measurements indicate that the n c17 alkane was derived from multiple source organisms that used different hydrogen pools for biosynthesis we demonstrate that the d values of the n c29 alkane were correlated with the d values of surface water i e river water and groundwater which on large spatial scales reflect the isotopic composition of mean annual precipitation such a relationship has been observed at higher latitudes supporting the robustness of the leaf wax lipid d proxy on a hemispheric spatial scale in contrast the d values of the n c31 alkane did not show such a relationship but instead were correlated with the evaporative lake water d values this result suggests distinct water sources for both leaf wax lipids most likely originating from two different groups of plants these new findings have important implications for the interpretation of long chain n alkane d records from ancient lake sediments in particular a robust interpretation of palaeohydrological data requires knowledge of the vegetation in the catchment area as different plants may utilise different water sources our results also suggest that the combination of carbon and hydrogen isotopes does help to differentiate between the metabolic pathway and or growth form of organisms and therefore the source of hydrogen used during lipid biosynthesis

simulated climate and biomes of africa during the late quaternary comparison with pollen and lake status data new compilations of african pollen and lake data are compared with climate ccm1 ncar boulder and vegetation biome 1 2 gsg lund simulations for the last glacial maximum lgm and early to mid holocene emh the simulated lgm climate was ca 4 c colder and drier than present with maximum reduction in precipitation in semi arid regions biome simulations show lowering of montane vegetation belts and expansion of southern xerophytic associations but no change in the distribution of deserts and tropical rain forests the lakes show lgm conditions similar or drier than present throughout northern and tropical africa pollen data indicate lowering of montane vegetation belts the stability of the sahara and a reduction of rain forest the paleoenvironmental data are consistent with the simulated changes in temperature and moisture budgets although they suggest the climate model underestimates equatorial aridity emh simulations show temperatures slightly less than present and increased monsoonal precipitation in the eastern sahara and east africa biome simulations show an upward shift of montane vegetation belts fragmentation of xerophytic vegetation in southern africa and a major northward shift of the southern margin of the eastern sahara the lakes indicate conditions wetter than present across northern africa pollen data show an upward shift of the montane forests the northward shift of the southern margin of the sahara and a major extension of tropical rain forest the lake and pollen data confirm monsoon expansion in eastern africa but the climate model fails to simulate the wet conditions in western africa

environmental change over the last millennium recorded in two contrasting crater lakes in western uganda eastern africa lakes kasenda and wandakara the last millennium is a key period for understanding environmental change in eastern africa as there is clear evidence of marked fluctuations in climate effective moisture that place modern concern with future climate change in a proper context both in terms of environmental and societal impacts and responses here we compare sediment records from two small nearby closed crater lakes in western uganda lake kasenda and lake wandakara spanning the last 700 wandakara and 1200 years kasenda respectively multiproxy analyses of chemical sedimentary parameters including c n ratios 13c of bulk organic matter and 13c and 18o of authigenic carbonates and biotic remains diatoms aquatic macrofossils chironomids suggest that kasenda has been sensitive to climate over much of this period and has shown substantial fluctuations in conductivity while wandakara has a more muted response likely due to the increasing dominance of human activity as a driver of change within the lake and catchment over the length of our record evidence from both records however supports the idea that lake levels were low from ad 700 1000 ad with increasing aridity from ad 1100 1600 and brief wet phases around ad 1000 and 1400 wetter conditions are recorded in the 1700s but drought returned by the end of the century and into the early 1800s becoming wetter again from the mid 1800s comparison with other records across eastern africa suggests that while some events are widespread e g aridity beginning ad 1100 at other times there is a more complex spatial signature e g in the 1200s to 1300s and from the 1400s to 1600s this study highlights the important role of catchment specific factors e g lakemorphometry catchment size and human impact in modulating the sensitivity of proxies and lake records as indicators of environmental change and potential hazards when regional inference is based on a single site or proxy

numerical simulations and a conceptual model of the stratocumulus to trade cumulus transition abstract a two dimensional eddy resolving model is used to study the transition from the stratocumulus topped boundary layer to the trade cumulus boundary layer the 10 day simulations use an idealized lagrangian trajectory representative of summertime climatological conditions in the subtropical northeastern pacific the sea surface temperature is increased steadily at 1 5 k day 1 reflecting the southwestward advection of the subtropical marine boundary layer by the trade winds while the free tropospheric temperature remains unchanged results from simulations with both a fixed diurnally averaged shortwave radiative forcing and a diurnally varying shortwave forcing are presented a two stage model for the boundary layer evolution consistent with these simulations is proposed in the first stage decoupling is induced by increased latent heat fluxes in the deepening boundary layer after decoupling cloud cover remains high but the cloudiness regime changes from a single stratocumulus layer to sporadic

spatial complexity of little ice age climate in east africa sedimentary records from two crater lake basins in western uganda lithostratigraphic analyses of the sedimentary record from two contrasting crater lake basins in western uganda africa provide evidence for three major century scale arid intervals during the last 2000 years variations in sedimentation and salt mineralogy of hypersaline lake kitagata and a succession of fine grained lake sediments and peat in the freshwater lake kibengo suggest century scale droughts centred on ad 0 1100 1550 and 1750 these results broadly support data from nearby lake edward on the timing of drought in western uganda but contrast with lake sediment records from eastern equatorial africa in particular our results suggest regional variability of east african climate during the main phase of the little ice age ad 1500 to 1800 with westernmost east africa experiencing drought while areas farther east were wet this spatial pattern highlights the strongly regional nature of century scale climate changes over the african continent and holds implications for the mechanisms governing african rainfall during the little ice age

the northwest africa 1500 meteorite not a ureilite maybe a brachinite the northwest africa nwa 1500 meteorite is an olivine rich achondrite containing approximately 2 3 vol augite 1 2 vol plagioclase 1 vol chromite and minor orthopyroxene cl apatite metal and sulfide it was originally classified as a ureilite but is currently ungrouped we re examined the oxygen three isotope composition of nwa 1500 results of ultra high precision 0 03 for d 17 o laser fluorination analyses of two bulk chips and high precision 0 3 secondary ion mass spectrometry sims analyses of olivine and plagioclase in a thin section show that the oxygen isotope composition of nwa 1500 d 17 o 0 22 from bulk samples and 0 18 0 06 from 16 mineral analyses is within the range of brachinites we compare petrologic and geochemical characteristics of nwa 1500 with those of brachinites and other olivine rich primitive achondrites including new petrographic mineral compositional and bulk compositional data for brachinites hughes 026 reid 013 nwa 5191 nwa 595 and brachina modal mineral abundances texture olivine and pyroxene major and minor element compositions plagioclase major element compositions rare earth element abundances and siderophile element abundances of nwa 1500 are within the range of those in brachinites and in most cases well distinguished from those of winonaites iab silicates acapulcoites lodranites ureilites and divnoe nwa 1500 shows evidence of internal reduction in the form of reversely zoned olivine fo 65 73 core to rim and fine grained intergrowths of orthopyroxene metal along olivine grain margins the latter also occur in reid 013 hughes 026 nwa 5191 and nwa 595 we argue that reduction olivine fi enstatite fe 0 o 2 is the best hypothesis for their origin in these samples as well we suggest that nwa 1500 should be classified as a brachinite which has implications for the petrogenesis of brachinites fe mn mg compositions of brachinite olivine provide evidence of redox processes among bulk samples nwa 1500 provides evidence for redox processes on a smaller scale as well which supports the interpretation that these processes occurred in a parent body setting sims data for 26 al 26 mg isotopes in plagioclase in nwa 1500 show no 26 mg excesses beyond analytical uncertainties 1 2 the calculated upper limit for the initial 26 al 27 al ratio of the plagioclase corresponds to an age younger than 7 ma after cai compared to 53 mn 53 cr data for brachina wadhwa et al 1998b this implies either a much younger formation age or a more protracted cooling history however brachina is atypical and this comparison may not extend to other brachinites

auger nanoprobe analysis of presolar ferromagnesian silicate grains from primitive cr chondrites que 99177 and met 00426 abstract we have investigated the presolar grain inventories of two cr chondrites que 99177 and met 00426 which are less altered than most members of this meteorite group both meteorites contain high abundances of o anomalous presolar grains with concentrations of 220 40 and 160 30 ppm for que 99177 and met 00426 respectively the presolar grain inventories are dominated by ferromagnesian silicates with group 1 oxygen isotopic compositions indicative of origins in low mass red giant or asymptotic giant branch stars grains with pyroxene like compositions are somewhat more common than those with olivine like compositions but most grains are non stoichiometric with compositions intermediate between these two phases consistent with recent work suggesting that amorphous interstellar silicates have stoichiometries between olivine and pyroxene type silicates although structural data are not available one grain contains only si and o and has a stoichiometry consistent with sio 2 our presolar grains are much more fe rich than predicted by astronomical observations although secondary alteration may play a role in enhancing the fe contents of presolar grains it seems unlikely that the large and ubiquitous fe enrichments observed in the grains from this study can be due only to secondary processing particularly given the highly primitive nature of these two meteorites grain condensation in the stellar outflows where these grains formed likely proceeded under rapidly changing kinetic conditions that may have enhanced the incorporation of fe into the grains over that expected based on equilibrium condensation theory both que 99177 and met 00426 appear to contain unusually low abundances of oxide grains and have higher silicate oxide ratios than other primitive meteorites analyzed to date we explore various possibilities for this discrepancy but note that most scenarios are not likely to result in the preferential destruction of oxides relative to silicates thus the highest silicate oxide ratios such as those observed in the cr chondrites should reflect the true initial proportions of presolar silicate and oxide grains in the parent molecular cloud from which the solar nebula evolved

brachinites igneous rocks from a differentiated asteroid we have done petrologic studies of brachinites allan hills alh 84025 elephant moraine eet 99402 and eet 99407 bulk geochemical studies of eet 99402 and eet 99407 ar ar studies of brachina and eet 99402 and a xe isotopic study of brachina textural mineral compositional and bulk compositional evidence show that eet 99402 and eet 99407 are paired alh 84025 eet 99402 and eet 99407 have igneous textures petrofabric analyses of alh 84025 and eet 99407 demonstrate the presence of lineations and probable foliations of olivine grains that support formation as igneous cumulates mineral minor element chemistry and bulk rock incompatible lithophile element contents of the brachinites are distinct from those of acapulcoite lodranite clan meteorites a suite of high grade metamorphic rocks and anatectic residues the differences demonstrate a higher blocking temperature of equilibration for the brachinites and that cumulus plagioclase is present in eet 99402 eet 99407 and probably alh 84025 thus indicating an igneous origin brachinites are differentiated ultramafic achondrites and are not part of a suite of primitive achondrites we infer that their parent asteroid is a differentiated body brachina has an excess of 129xe correlated with reactor produced 128xe demonstrating that short lived 129i was present at the time of formation this plus literature data attests to early formation of the brachinites within a few ma of the formation of chondrites ar ar age data show that brachina and eet 99407 were degassed about 4 13 ga ago possibly by a common impact event eet 99402 and eet 99407 show petrographic evidence for shock including possible conversion of plagioclase to maskelynite followed by devitrification brachina is unshocked making a direct association between the ar ar age and textures ambiguous

a 35 myr north american leaf wax compound specific carbon and hydrogen isotope record implications for c4 grasslands and hydrologic cycle dynamics article i nfo hydrology source region and timing of precipitation are important controls on the climate of the great plains of north america and the composition of terrestrial ecosystems moisture delivered to the great plains varies seasonally and predominately derives from the gulf of mexico atlantic ocean with minor contributions from the pacific ocean and arctic region for this work we evaluate long term relationships for the past 35 million years between north american hydrology climate and floral change using isotopic records and average carbon chain lengths of higher plant n alkanes from gulf of mexico sediments dsdp site 94 we find that carbon isotope values 13 c of n alkanes corrected for variations in the 13 c value of atmospheric co2 provide minor evidence for contributions of c4 plants prior to the middle miocene a sharp spike in c4 input is identified during the middle miocene climatic optimum and the influence of c4 plants steadily increased during the late miocene into the pleistocene consistent with other north american records chain length distributions of n alkanes indicative of the composition of higher plant communities remained remarkably constant from 33 to 4 ma however a trend toward longer chain lengths occurred during the past 4 million years concurrent with an increase in 13 c values indicating increased c4 plant influence and potentially aridity the hydrogen isotope values d of n alkanes are relatively invariant between 33 and 9 ma and then become substantially more negative 75 from 9 to 2 ma changes in the plant community and temperature of precipitation can solely account for the observed variations in d from 33 to 5 ma but cannot account for plio pleistocene d variations and imply substantial changes in the source region of precipitation and seasonality of moisture delivery we posit that hydrological changes were linked to tectonic and oceanographic processes including the shoaling and closure of the panamanian seaway amplification of north atlantic deep water production and an associated increase of meridional winds the southerly movement of the intertropical convergence zone near 4 ma allowed for the development of a near modern pressure storm track system driving increased aridity and changes in seasonality within the north american interior

rumuruti chondrites noble gases exposure ages pairing and parent body history in this paper we present concentration and isotopic composition of the light noble gases he ne and ar as well as of 84kr 132xe and 129xe in bulk samples of 33 rumuruti r chondrites together with previously published data of six r chondrites exposure ages are calculated and compared with those of ordinary chondrites a number of pairings especially between those from northwest africa nwa are suggested so that only 23 individual falls are represented by the 39 r chondrites discussed here eleven of these meteorites or almost 50 contain solar gases and are thus regolithic breccias this percentage is higher than that of ordinary chondrites howardites or aubrites this may imply that the parent body of r chondrites has a relatively thick regolith concentrations of heavy noble gases especially of kr are affected by the terrestrial atmospheric component which resides in weathering products compared to ordinary chondrites 129xe 132xe ratios of r chondrites are high

summer monsoon intensity controls c4 c3 plant abundance during the last 35 ka in the chinese loess plateau carbon isotope evidence from bulk organic matter and individual leaf waxes the natural abundance of c3 and c4 plants is affected by multiple environmental factors including temperature moisture balance and atmospheric pco2 the relative importance of these factors is a subject of considerable debate and may vary in different natural ecosystems previous studies generally focus on single loess sequences in the chinese loess plateau and conflicting conclusions on c4 c3 have been reached when studying carbon isotope ratios in carbonate and organic matter in this paper we report a comprehensive carbon isotopic characterization of total organic carbon toc and individual higher plant leaf waxes from five loess sequences spanning the last 35 ka from the chinese loess plateau clp the five coring sites encompass large gradients of annual mean temperature 9 2 13 9 c and precipitation 402 673 mm allowing us to assess the controlling mechanisms on c4 c3 plant ratios glacial interglacial sequences provide carbon isotope data for comparison with other climatic and environmental proxies such as lithology and magnetic susceptibility our results demonstrate that increased c4 c3 ratios are positively correlated with higher temperature and increased summer rainfall which characterize stronger summer monsoon in all five sites we conclude c4 abundance increases from the last glacial to the holocene in response to greater monsoon activity and that the c4 expression is suppressed in the cold and drier intervals

the tafassasset primitive achondrite insights into initial stages of planetary differentiation abstract tafassasset is an exceptional meteorite that has been linked to both the cr chondrites and the primitive achondrites because previous evidence suggests it might be a primitive achondrite from a known chondrite type we have undertaken a study of the petrology geochemistry and formation history of the meteorite tafassasset is predominantly feo rich olivine 58 yet contains abundant fe ni metal 10 vol and sulfide 3 vol other phases include high and low ca pyroxene plagioclase chromite and phosphate it has a recrystallized texture containing equigranular grains that often meet at 120 triple junctions there are no relict chondrules in the thin sections examined although they have been reported previously electron microprobe analyses reveal homogeneous olivine fa 28 6 both low and high ca pyroxene fs 23 6 wo 3 7 and fs 12 2 wo 39 3 1 a range of plagioclase composition an 23 47 fe ni metal with 5 3 36 6 wt ni and 0 1 0 8 wt co troilite chromite and ca phosphate bulk composition analyses reveal two chips depleted in refractory lithophile and some siderophile elements compared to ci chondrites exceptions are enrichments in fe ni and co a third chip is essentially chondritic in bulk composition different stones of the meteorite have slightly different oxygen isotope composition yet all lie in the cr chondrite trend with one in the acapulcoite lodranite field thermodynamic calculations show that tafassasset equilibrated at a temperature above the fe ni fes eutectic and at an oxygen fugacity of iw 1 the texture heterogeneous distribution of mineral phases plagioclase composition two mineral closure temperatures and bulk composition all provide evidence that tafassasset partially melted on its parent body a comparison with the cr chondrites the brachinites and two anomalous achondrites indicates that tafassasset is most similar to ungrouped primitive achondrites lewis cliff lew 88763 and divnoe and to the brachinites in overall petrography modal mineralogy mineral compositions oxidation state and bulk composition the comparison also excludes the possibility that tafassasset formed by partial melting of a cr chondrite tafassasset is a primitive achondrite and likely evolved on a parent body that experienced incomplete melting never reached isotopic homogeneity and was from the same oxygen isotopic reservoir as the cr chondrite parent body

sulfide rich metallic impact melts from chondritic parent bodies sacramento wash 005 saw 005 meteorite hills 00428 met 00428 and mount howe 88403 how 88403 are s rich fe ni rich metal meteorites with fine metal structures and homogeneous troilite we compare them with the h metal meteorite lewis cliff 88432 phase diagram analyses suggest that saw 005 met 00428 and how 88403 were liquids at temperatures above 1350 c tridymite in how 88403 constrains formation to a high temperature and low pressure environment the morphology of their metal troilite structures may suggest that met 00428 cooled the slowest saw 005 cooled faster and how 88403 cooled the quickest saw 005 and met 00428 contain h chondrite like silicates and saw 005 contains a chondrule bearing inclusion that is texturally and compositionally similar to h4 chondrites the compositional and morphological similarities of saw 005 and met 00428 suggest that they are likely the result of impact processing on the h chondrite parent body saw 005 and met 00428 are the first recognized iron and sulfide rich meteorites which formed by impact on the h chondrite parent body which are distinct from the iie iron meteorite group the morphological and chemical differences of how 88403 suggest that it is not from the h chondrite body although it likely formed during an impact on a chondritic parent body

a high resolution palaeoclimatic record for the last 27 500 years in tropical west africa from the carbon and nitrogen isotopic composition of lacustrine organic matter variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of lake bosumtwi ghana reflect climatically induced changes to the lake and the catchment flora cores spanning the last 27 5 kyr of sedimentation in the lake show large oscillations in 13corg pdb and 15norg air the late pleistocene record is particularly detailed showing changes of ca 20 in carbon and ca 10 in nitrogen isotopic compositions these variations are of complex origin although different in magnitude major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the last glacial maximum the allerod younger dryas period also seems to have been marked by generally dry conditions in this part of tropical west africa nitrogen isotopic evidence suggests that during the period 9 2 3 2 kyr the lake had an extremely stable water column probably due to the absence of a windy or cool dry season or both regular circulation of the water column recommenced during the late holocene and has persisted until the present day

little ice age drought in equatorial africa intertropical convergence zone migrations and el nino southern oscillation variability high resolution analyses of the mg concentration in authigenic calcite in five cores from lake edward provide a water balance history of central equatorial africa spanning the past 1400 yr a high ratio of mg to ca mg indicates strong droughts in central africa during the little ice age a d 1400 1750 in contrast to records from lake naivasha kenya which suggest a wet little ice age this spatial pattern in africa likely arose due to coupled changes in the high latitudes the position of the intertropical convergence zone and the el nino southern oscillation enso system our results further suggest that the patterns and variability of twentieth century rainfall in central africa have been unusually conducive to human welfare in the context of the past 1400 yr

paleoenvironmental change in tropical africa during the holocene based on a record from lake kifuruka western uganda a 10 000 year palynological record of vegetation and environmental changes in tropical africa is presented based on sediment data from a 230 cm long core recovered from lake kifuruka in western uganda the lake kifuruka record provides new sedimentary and paleoecological data for human environment interactions and anthropogenic disturbance in the tropical african region during the holocene the record shows evidence for prolonged dry conditions in the region at the terminus of the last glaciation period and the onset of the holocene period the early holocene and mid holocene periods were characterized by largely warm and wet climatic conditions the pollen record shows evidence of forest disturbance that is probably associated with agricultural activities near lake kifuruka shortly after ca 4300bp cal a bp coinciding with a time of increased desiccation in the region the forest disturbance in the record appears to have intensified and continued into the modern period but with no significant change in the overall vegetation diversity suggesting quick environmental recovery the lake kifuruka record is largely devoid of the abrupt climatic changes that have been observed from a couple of sites in the east african region which implies that the changes may be site specific rather than regional scale

human impacts climate change and aquatic ecosystem response during the past 2000 yr at lake wandakara uganda analyses of carbon and hydrogen isotope ratios of terrestrial leaf waxes and the carbon and nitrogen abundance ratio and isotopic composition of bulk sediments from lake wandakara a crater lake in western uganda east africa document human and climatic controls on the aquatic system and on the surrounding terrestrial vegetation during the past two millennia our data indicate that wandakara was a relatively stable productive lake surrounded by c3 vegetation from ad 70 to 1000 abrupt changes in the 13c of terrestrial leaf waxes indicate a series of abrupt shifts in the relative abundance of c3 and c4 vegetation caused by a combination of climate change and human activities around wandakara beginning at ad 1000 abrupt shifts in bulk sediment organic geochemistry particularly c n ratios and 15n indicate that human activities at this time caused permanent changes in the limnology of lake wandakara including eutrophication our results suggest that the biogeochemistry of lake wandakara was more sensitive to shifting human impacts than to climate variations during the past millennium highlighting the importance of understanding the intensity of pre colonial human impacts on africa s aquatic ecosystems

evolution and classification of acapulcoites and lodranites from a chemical point of view we examined 15 bulk samples of the acapulcoite lodranite clan for their major minor and trace element concentrations using inaa techniques among the analyzed meteorites are 2 new acapulcoites dhofar dho 290 thiel mountains til 99002 as well as an additional acapulcoite that has been described previously only in very brief form graves nunataks gra 98028 the petrographic attributes of these 3 samples are addressed thoroughly we also include petrographic information on 2 acapulcoites from africa northwest africa nwa 725 and nwa 1058 in general our study strongly supports the widely accepted idea that acapulcoites and lodranites evolved through partial melting and melt migration of metal sulfide phases and plagioclase furthermore we concur with previous researchers that the original bimodal classification scheme for acapulcoites and lodranites proves to be too simple based on our data set we introduce an alternative extended scheme with respect to their elemental distribution patterns we distinguish 5 subtypes comprising primitive typical transitional and enriched acapulcoites on one hand and lodranites on the other the chemical distinction between the primitive typical and transitional acapulcoites is rather subtle and gradual it stands in contrast to the clear modifications observed for the signatures of the enriched acapulcoites and the lodranites the definition of subcategories basically reflects the concentrations of 2 key elements k and se we note however that the assignment of subgroups may not be exclusively inferred from elemental abundances but should also consider additional petrographic information

palaeolimnological evidence for widespread late 18th century drought across equatorial east africa abstract the sediment records of three shallow climate sensitive lakes in equatorial east africa chibwera and kanyamukali in western uganda and baringo in central kenya contain clear lithological evidence of an episode of complete desiccation in the relatively recent past quantitative stratigraphic analyses of bulk sediment composition texture sand and coarse organic detritus the c n ratio of bulk organic matter and magnetic susceptibility allowed us to define a common succession of sedimentary units in all three lakes this common stratigraphy includes a basal unit of dry and stiff low organic clays capped by a horizon of peaty mud or peat overlain by organic lake sediment we interpret this stratigraphy to represent an episode of nearly complete desiccation of these lake basins this was followed first by an early phase of modest lake refilling during which time extensive littoral and submerged vegetation developed producing peaty lake deposits mostly higher lake levels later on resulted in deposition of fine grained lake muds using 210 pb and 137 cs activity profiles combined with four ams 14 c dates on single terrestrial plant macrofossils or multiple charred grass particles indicate that in all three lakes the episode of most recent complete desiccation occurred in the late 18th and early 19th century these results add to an accumulating body of palaeoenvironmental data revealing a prolonged period of extreme drought in equatorial east africa about 200 years ago also documented in the cultural history of the african great lakes region given the geographical spread of the study lakes across the east african plateau these results indicate that the climatic anomaly of reduced rainfall responsible for this drought was at least sub continental in scale

evaluation of a numerical weather forecast model using boundary layer cloud top temperature retrieved from avhrr abstract this study concerns the evaluation of the boundary layer bl subgrid parameterization of a numerical weather forecast model on the synoptic scale the method presented aims at separating the two possible origins of model defficiencies in representing a cloud topped boundary layer i large scale data assimilation issues and ii bl parameterization the method combines two sources of data model analyzed fields from the semaphore field experiment and the advanced very high resolution radiometer avhrr dataset from the noaa 11 and 12 satellite the application focuses on an anticyclonic period during field experiment 10 17 november 1993 for which a special version of arpege the meteo france numerical weather prediction model is used to analyze the data from the field experiment in the proposed method the boundary layer is globally characterized by its height which is converted to an inversion layer temperature in the model low level cloud top temperatures of optically thick clouds are

environmental change in montane southwest uganda a pollen record for the holocene from ahakagyezi swamp the environmental history of montane southwest uganda over the last c 12 300 years is described using data from a 22 84 m long core of sediment from ahakagyezi swamp rukiga highlands these data include plant microfossils and macrofossils charcoal and nine radiocarbon dates according to evidence from plant fossils and radiocarbon dates vegetation in the ahakagyezi catchment was very different to the expected climax today until c 10500 bp the surface of the swamp was dominated by sedges whilst the adjacent hillsides were largely devoid of trees changes in pollen suggest that a form of dry montane scrub was replaced by moist lower montane forest from c 11000bp subsequent fluctuations in pollen indicate that once established the composition of moist lower montane forest varied during the holocene and that unreversed forest reduction commenced in the ahakagyezi catchment at c 800 bp on the surface of the swamp itself syzygium dominated swamp forest increased in extent from c 5800 bp and mor

climate of east africa 6000 14c yr b p as inferred from pollen data this paper presents a spatial reconstruction of climate in east africa at 6000 14c yr b p two different approaches using pollen data have been used the standard best modern analogues method and the new plant functional type method based on groups of pollen taxa both methods have been applied to 32 fossil pollen spectra dated at 6000 14c yr b p for each site we have estimated two climatic parameters annual precipitation and mean annual temperature three bioclimatic parameters ratio of actual to potential evapotranspiration and the mean temperature of the coldest and warmest months results show that the temperature lapse rate was less steep at 6000 14c yr b p than it is today the climate was wetter north of 3 s precipitation anomalies 50 mm yr and slightly drier farther south precipitation anomalies 50 mm yr the ratio of actual to potential evapotranspiration also indicates conditions similar to or wetter than today north of 3 s anomalies 10 the climate was warmer than today by 2 c north of the equator and was cooler southward 1 c although both methods indicate similar climatic patterns the plant functional type method provides more consistent results

the meteoritical bulletin no 79 1996 july recently classified specimens in the united states antarctic meteorite collection 1994 1996 the meteoritical bulletin no 79 contains a list of all meteorites classified between 1994 march and 1996 february by the united states antarctic meteorite program the compilation includes available information on classification mass weathering olivine and pyroxene composition 26al activities natural thermoluminescence levels pairing collection location and references to published descriptions for 1761 meteorite specimens a list of the most significant meteorites in the entire ansmet collection of 7298 classified specimens is also included

dhofar 378 martian shergottite evidence of early shock melting 1 shock heating of the dhofar 378 dho 378 martian shergottite produced melting vesiculation and flow of the plagioclase which upon cooling recrystallized into complex textures heating experiments on the similar zagami shergottite indicate that dho 378 was shock heated to 1000 1100 c and was cooled at 2 5 c h an 39ar 40ar analysis of dho 378 plagioclase indicates different ar diffusion domains and k ca ratios the lower temperature phase defines an ar ar isochron age of 141 32 ma the higher temperature phase released more 40ar but does not define an age the meteorite s thermal history was examined by constructing a generic model to compare cooling rates for objects of different sizes against fractional diffusion loss of ar for different cooling times using gas diffusion parameter values measured for dho 378 this model indicates that it is improbable that the major shock heating event occurred at the time that dho 378 was ejected from mars 3 ma ago rather we suggest that the time of shock heating is probably given by its ar ar age for dho 378 to cool sufficiently fast not to lose most of its 40ar 3 ma ago would require it to have been ejected into space as an impossibly small object larger and more reasonable mars ejection sizes indicate that dho 378 should have lost most of its 40ar on the basis of plagioclase texture and ar data we suggest that a major impact event 141 ma ago melted dho 378 plagioclase degassed most of its 40ar and deposited it in crater ejecta to cool a smaller and later impact ejected it into space 3 ma ago

the meteoritical bulletin no 86 2002 july abstract meteoritical bulletin no 86 lists information for 1154 newly classified meteorites comprising 661 from antarctica 218 from africa 207 from asia 203 of which are from oman 62 from north america 3 from south america and 3 from europe information is provided for 5 falls el idrissia undulung dashoguz el tigre and yafa noteworthy specimens include 7 martian meteorites dhofar 378 grove mountains 99027 northwest africa 856 1068 and 1110 and sayh al uhaymir 060 and 090 4 lunar meteorites dhofar 301 302 303 and 489 9 new iron meteorites a mesosiderite northwest africa 1242 an ungrouped stony iron meteorite dar al gani 962 and a wide variety of other interesting stony meteorites including ch ck cm cr cv r enstatite unequilibrated ordinary and ungrouped chondrites primitive achondrites howardite eucrite diogenite hed achondrites and ureilites

spatial and temporal variability in sedimentological and geochemical properties of sediments from an anoxic crater lake in west africa implications for paleoenvironmental reconstructions abstract the physical inorganic and organic geochemical and stable isotopic characteristics of lacustrine sediments can provide valuable insights into past environmental changes provided that the environmental controls on these characteristics are well understood in the present study a set of 155 modern vegetation catchment soil river sediments and lake surface sediment samples are used to characterize the spatial patterns of toc tn c n ratios stable isotope major element and particle size distributions within lake bosumtwi a meromictic crater lake in west africa spatial variations in sediment characteristics are strongly correlated with depth and distance from shore reflecting the dominant influence of lake level on the relative proportions of littoral and pelagic depositional systems and their impact on the physical and geochemical properties of lacustrine sediments this is supported by a principal component analysis which indicates that 65 of the variance in the dataset is explained by depth related variability in the sedimentary components variations in sedimentary organic matter reflect the combined influences of productivity preservation and the relative proportions of aquatic and terrestrial organic matter sources grain size and si content are dominantly influenced by the delivery of clastic materials from the watershed to the lake whereas fe and ca appear to be most strongly influenced by the delivery of reduced metals and nutrients from the anoxic hypolimnion to the surface with the exception of grain size all of the sediment parameters record synchronous century scale variability over the past 2 5 ka consistent with independent evidence for changes in lake level however the magnitude of changes in sediment characteristics differs reflecting different sensitivities to water depth particularly in the deepest part of the lake basin where the sediment cores were collected however even the parameters with the most linear and strongly significant relationships with depth e g toc tn significantly overestimate the magnitude of lake level changes suggesting that these parameters may be best suited to qualitative paleolake level reconstructions over the last 2 centuries changes in c n and 13c became decoupled from the other geochemical proxies and the inferred rise in lake level we hypothesize that this reflects the influence of anthropogenic land use change on the composition of terrestrial organic matter sources contributing to the lake this result highlights the potential difficulties in reconstructing past environmental changes from indirect proxy measurements when those proxies may be subject to multiple varying controls

vegetation change in the baringo basin east africa across the onset of northern hemisphere glaciation 3 3 2 6 ma abstract vegetation in east africa is generally thought to have shifted from forests to more open grasslands and savannas as global climate cooled and high latitude ice sheets expanded during the plio pleistocene such a shift would have greatly influenced landscape resources and potentially hominin evolution as well existing records of african vegetation spanning these time scales are generally derived from offshore marine records that record continental scale changes or paleosol carbonate records that record very local vegetation changes during the short time intervals of soil carbonate formation here we present a new record of basin scale vegetation change from the late pliocene 3 3 2 6 ma derived from a drill core from the chemeron formation located in the baringo basin tugen hills region of the kenya rift valley specifically we present a new record of the relative abundance of c4 grasses and c3 vegetation based on the carbon isotopic composition of leaf wax biomarkers 13cwax which captures a signal of regional vegetation change these data demonstrate that vegetation in the baringo basin varied greatly between c3 forests and c4 grasslands and that vegetation exhibits both long term secular trends and orbital scale variations the contribution of c3 plants was lower than estimates based on low resolution carbon isotope data from paleosol carbonates and organic matter in the basin c3 plants averaged 53 of the vegetation during the late pliocene from 3 3 to 3 04 ma after which time 13cwax indicates more open vegetation and 41 c3 plants this transition may have been driven by changes in basin geomorphology but also possibly occurred as part of larger scale drying and expansion of c4 vegetation in east africa in addition to this secular change we observe high amplitude variability in the 13cwax record including oscillations between 80 and 0 c3 plants these vegetation changes are correlated with changes in precipitation inferred from 2hwax and lake level oscillations inferred from sedimentary facies implying that high amplitude orbital scale variations in precipitation drove significant changes in vegetation resources during the late pliocene in the baringo basin these variations have important implications for changes in terrestrial resources in light of the evolutionary innovations in the hominin fossil record related to changes in foraging strategies

influence of terrestrial vegetation on leaf wax δd of holocene lake sediments abstract the hydrogen isotope composition of terrestrial plant leaf wax in sediments is increasingly used as a paleoclimatic indicator modern calibration studies suggest that paleoclimatic interpretation of leaf wax d values requires consideration of the differences in the apparent fractionation of hydrogen isotopes among different groups of plants however it is not common that paleoecological data are used to help interpret leaf wax d profiles here we assess the relative importance of factors influencing millennial scale shifts in d values of n alkanoic acids at steel lake minnesota usa an extensively studied site with independent records of vegetation composition d of input water to the lake and evaporation the d values of the n c 28 alkanoic acid d c28 vary between 190 and 168 and do not correlate with d of input water or the extent of evaporation however d c28 is negatively correlated with the 13 c values of the n c 28 alkanoic acid 13 c c28 the correlation along with pollen assemblage and carbonate 13 c records suggests that holocene shifts between forest and grassland and or in the water use efficiency of c 3 plants influenced the stratigraphic variation in leaf wax d thus paleoecological information such as that inferred from pollen assemblages and carbon isotopes of plant derived compounds may aid paleoclimatic interpretation of leaf wax d profiles from lake sediments

tafassasset evidence of early incipient differentiation on a metal rich chondritic parent body abstract tafassasset is a primitive meteorite the origin of which is still debated its possible relationship to either the cr chondrites considered among the most primitive meteorites or the brachinites complex primitive achondrites makes it an interesting sample for studying the initial stages of planetary accretion and differentiation in the early solar system here we report tungsten w isotope data for bulk rock samples as well as for mineral fractions from tafassasset along with micro computed tomography of a piece of the meteorite silicates show mass independent w isotope anomalies while the metal phase does not these nucleosynthetic anomalies are interpreted as reflecting the presence of sic presolar grains in the matrix of the meteorite carrying s process 184w after correction of the nucleosynthetic anomalies a correlation is observed between the 182w 184w isotope compositions and the hf w ratios of the different fractions a 182hf 182w age of ca 2 9 ma after cais is inferred from the 182hf 182w chronometer slightly older than other estimates based on the 53mn 53cr 26al 26mg and pb pb chronometers but consistent with the difference in closure temperatures of the different isotopic systems numerical modeling of the thermal evolution of tafassasset indicates accretion of a parent body less than 50 km in diameter 1 ma after the formation of cais at a time when short lived radio nuclides induced metal silicate separation and partial melting of the silicates with extraction of a basaltic component according to our new data tafassasset may represent an inner part of a cr like parent body with a differentiation history similar to but less severe than that of brachinites

geochemical methods to infer landscape response to quaternary climate change and land use in depositional archives a review abstract understanding and quantifying the processes and geochemical cycles associated with catchment erosion the development of soils and weathering horizons and terrestrial habitat change beyond the scales of modern observations remain challenging such research however has become increasingly important to help predict future landscape change in light of increasing land use and rapid global warming we herein review organic and inorganic geochemical tools applied to depositional archives to better understand various aspects of landscape evolution on geological time scales we highlight the potentials and limitations of inorganic geochemical analytical methods such as major element geochemistry metal and radiogenic isotopes and in situ cosmogenic nuclides as qualitative semi quantitative and quantitative proxies for the transformation of bedrock material via regolith and soils to sediments we also show how stable isotope geochemistry applied to lacustrine endogenic carbonates can be used to infer rock water interactions vegetation change and soil development in limestone rich catchments proxies focusing on the silicilastic element of sediment formation transport and deposition are ideally combined with organic geochemical proxies for vegetation change and soil organic matter evolution in a catchment to gain a comprehensive picture of the critical zone s evolution over time multi proxy and multidisciplinary research combining organic and inorganic geochemical techniques from several sedimentary archives in the same catchment have high potential to provide comprehensive information on quaternary landscape evolution and thus improve the robustness of associated forecasting models

feldspathic lunar meteorites and their implications for compositional remote sensing of the lunar surface and the composition of the lunar crust we present new compositional data for six feldspathic lunar meteorites two from cold deserts yamato 791197 and 82192 and four from hot deserts dhofar 025 northwest africa 482 and dar al gani 262 and 400 the concentrations of feo or al2o3 and th or any other incompatible element together provide first order compositional information about lunar polymict samples breccias and regoliths and regions of the lunar surface observed from orbit concentrations of both elements on the lunar surface have been determined from data acquired by orbiting spacecraft although the derived concentrations have large uncertainties and some systematic errors compared to sample data within the uncertainties and errors in the concentrations derived from orbital data the distribution of feo and th concentrations among lunar meteorites which represent 18 source regions on the lunar surface is consistent with that of 18 random samples from the surface approximately 11 of the lunar meteorites are low feo and low th breccias consistent with large regions of the lunar surface particularly the northern farside highlands almost all regoliths from apollo sites on the other hand have larger concentrations of both elements because they contain fe rich volcanic lithologies from the nearside maria and th rich lithologies from the high th anomaly in the northwestern nearside the feldspathic lunar meteorites thus offer our best estimate of the composition of the surface of the feldspathic highlands and we provide such an estimate based on the eight most well characterized feldspathic lunar meteorites the variable but high on average mg fe ratio of the feldspathic lunar meteorites compared to ferroan anorthosites confirms a hypothesis that much of the plagioclase at the surface of the feldspathic highlands is associated with high mg fe feldspathic rocks such as magnesian granulitic breccia not ferroan anorthosite geochemically the high mg fe breccias appear to be unrelated to the mafic magnesian suite rocks of the apollo collection models for the formation of the upper lunar crust as a simple flotation cumulate composed mainly of ferroan anorthosite do not account for the complexity of the crust as inferred from the feldspathic lunar meteorites

quantitative estimates of full glacial temperatures in equatorial africa from palynological data this paper presents a new reconstruction of the mean annual temperature obtained from a high altitude pollen sequence in equatorial africa 3 28 s 29 34 e 2240 m it has been achieved with an extended modern african reference data set by adding spectra from 228 new sites and using another selection for pollen taxa the purpose of this paper is to test how the obtained temperature value depends upon the availability of modern analogues the results are in good agreement with those previously published reinforcing the validity of the method the mean standard error is reduced by 0 3 c the mean temperature for the holocene appears 1 4 c warmer than the present and the last glacial maximum 25 18 kyrs bp cooling is better specified at 3 1 9 c a conservative value more consistent with reconstructed sea surface temperature in the equatorial ocean

fe mn systematics of type iia chondrules in unequilibrated co cr and ordinary chondrites we have examined fe mn systematics of 34 type iia chondrules in eight highly unequilibrated co cr and ordinary chondrites using new data from this study and prior studies from our laboratory olivine grains from type iia chondrules in co chondrites and unequilibrated ordinary chondrites uoc have significantly different fe mn ratios with mean molar fe mn 99 and 44 respectively olivine analyses from both these chondrite groups show well defined trends in mn versus fe afu and molar fe mn versus fe mg diagrams in general type iia chondrules in cr chondrites have properties intermediate between those in uoc and co chondrites in most uoc and cr type iia chondrules the fe mn ratio of olivine decreases during crystallization whereas in co chondrites the fe mn ratio does not appear to change it is difficult to interpret the observed fe mn trends in terms of differing moderately volatile element depletions inherited from precursor materials instead we suggest that significant differences in the abundances of silicates and sulfides metals in the precursor material as well as open system behavior during chondrule formation were responsible for establishing the different fe mn trends using fe mn mg systematics we are able to identify relict grains in type iia chondrules which could be derived from previous generations of chondrules including chondrules from other chondrite groups and possibly chondritic reservoirs that have not been sampled previously

mesoscale shallow convection in the atmosphere this paper is a review of the observational experimental theoretical and numerical studies of mesoscale shallow convection msc in the atmosphere typically msc is 1 to 2 km deep has a horizontal length scale of a few to a few tens of kilometers and takes distinctive planforms linear and hexagonal the former is called a cloud street roll or band while the latter is called mesoscale cellular convection mcc comprising three dimensional cells msc is characterized by its shape horizontal extent convective depth and aspect ratio the latter is the ratio of the horizontal extent to that in the vertical for cells the horizontal extent is their diameter whereas for rolls it is their spacing rolls usually align along or at angles of up to 10 from the mean horizontal wind of the convective layer with lengths from 20 to 200 km widths from 2 to 10 km and convective depths from 2 to 3 km the typical value of aspect ratio ranges from 2 to 20 rolls may occur over both water surface and land surfaces mesoscale convective cells may be divided into two types open and closed open cell circulation has downward motion and clear sky in the cell center surrounded by cloud associated with upward motion closed cells have the opposite circulation both types of cell have diameters ranging from 10 to 40 km and aspect ratios of 5 to 50 and both occur in a convective layer with a depth of about 1 to 3 km both the magnitude and direction of horizontal wind in the convective layer change little with height msc results from a complex and incompletely understood mix of processes these processes are outlined and their interplay is examined through a review of theoretical and laboratory analyses and numerical modeling of msc