carbon isotopes and light element abundances in carbonaceous chondrites stepped combustions of whole rock samples of orgueil ci murchison cold bokkeveld and murray cm renazzo cr allende and mokoia c3v carbonaceous chondrites were carried out between 200 and 1200 c at each step co2 was collected for carbon isotope measurement and so2 and h2o yields were measured nitrogen was combined for several steps all samples released most of their carbon between 200 and 400 c due to combustion of the organic matter bulk carbon concentration and isotopic composition of each meteorite are therefore closely similar to those of this predominant reservoir between 400 and 700 c carbonates decomposed in all meteorites but the c3vs carbon isotopes in these carbonates matched previously published values in renazzo the carbonates have a 13c close to 42 pdb similar to those of cm meteorites above 700 c all meteorites but the c3vs show one or two occurrences of very13c rich carbon carbon concentration decreases from 350 to 30 ppb c as temperature increases between 700 and 885 c 13c reaches 240 4 in orgueil 73 9 in murchison 130 9 in cold bokkeveld and 125 5 in murray and then decreases between 950 and 1060 c 13c reaches 177 8 in renazzo 335 1 in cold bokkeveld and 384 6 in murchison finally murray yielded 3 ppm of carbon with a 13c of 1164 in the 1125 1210 c combustion step a qualitative inverse correlation among the c2 meteorites between the carbon concentration and 13c above 700 c suggests that these distinct heavy carbon releases could be actually due to a single heavy carbon component

the oxygen isotope record in murchison and other carbonaceous chondrites the ranges of 18o and 17o in components of the murchison c2 chondrite exceed those in all other meteorites analyzed previous authors have proposed that c2 chondrites are the products of aqueous alteration of anhydrous silicates a model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes the minimum number two of initial isotopic reservoirs is assumed two major stages of reservoir interaction are required one at high temperature to produce the16o mixing line observed for the anhydrous minerals and another at low temperature to produce the matrix minerals the isotopic compositions severely constrain the conditions of the low temperature process requiring temperatures 44 extension of the model to the data on c1 chondrites requires aqueous alteration in a warmer wetter environment

an la icp ms trace element classification of ochres in the weld range environ mid west region western australia laser ablation inductively coupled mass spectrometry la icp ms is successfully used to distinguish ochre from two nationally heritage listed aboriginal ochre mines in the mid west region of western australia wilgie mia and little wilgie the same technique is then used to test whether either ochre mine is the likely source of ochre used at archaeological sites in the local landscape the archaeological samples were retrieved from rock art and the surface of artefacts in excavated and surface contexts la icp ms offers advantages over other techniques for the geochemical characterisation of ochre including direct analysis of solid sample reduced laboratory preparation and breadth of trace element isotopes analysed this work highlights the potential for trace elemental analyses and profiling to develop an understanding of the past cultural significance of ochre from sources which are also important mythological sites

a late middle stone age artifact assemblage from sibudu kwazulu natal comparisons with the european middle paleolithic abstract it has been suggested that many behavioral innovations said to appear during the late middle stone age in sub saharan africa facilitated the expansion of anatomically modern humans from africa and the near east into europe at about 50 kyr the process eventually led to the replacement of neanderthals by modern humans and the emergence of the upper paleolithic however assemblages in this time range are little known in south africa in fact the transition from middle to the later stone age in southern africa is controversial the early appearance in south africa of many innovations such as sophisticated knapping techniques e g the use of soft hammer or indirect percussion in blade production of composite tools of microlithic and bladelet technologies remains to be established through technological analysis we present here the first results of a project designed to carry out detailed technological studies of several lithic assemblages in south africa and france dated to the transition period at this time we have completed the study of a post howiesons poort assemblage from the rock shelter site of sibudu the 2 m deep stratigraphic sequence of sibudu extends from howiesons poort at its base to final middle stone age directly under iron age layers we have analyzed in detail layer rsp ca 53 kyr 1 m above the howiesons poort levels which has provided a large assemblage of several thousand stone artifacts compared to published msa assemblages this industry is unusual for the very high proportions of retouched pieces 15 the technology is not very elaborate and there is no strong standardization of the end products there are no flakes of predetermined shapes retouch is used to modify irregular flakes to obtain desired edges knapping of flakes and blades is done by hard hammer soft hammer is used only for retouching tools interestingly the older howiesons poort blades were produced on the same raw materials by soft hammer raw material hornfels and dolerite was procured from distances of less than 20 km unifacial points are the dominant type and there is strong evidence of hafting and use as spear armatures detailed comparisons with middle paleolithic assemblages of western europe show that the late middle stone age technology in south africa is very similar to that of the middle paleolithic in fact we see no fundamental differences between the two entities as far as lithic technology is concerned implications for the out of africa hypothesis are discussed

ash deposits in hayonim and kebara caves israel macroscopic microscopic and mineralogical observations and their archaeological implications abstract a study of the hearths and ash layers preserved in hayonim and kebara caves israel showed that they are composed of one or several different minerals these include the polymorph of caco3 calcite a variety of phosphate minerals and a suite of siliceous minerals the major component of the latter are siliceous aggregates that are present in wood detailed studies of the mineral associations in these fossil ash layers as well as in fresh wood ash using optical and scanning electron microscopy in the back scattered electron mode together with elemental analyses showed that ash in these caves undergoes a series of diagenetic changes the best preserved ash layers resemble fresh ash and are composed mainly of calcite with minor amounts of siliceous minerals the calcite reacts with phosphate rich solutions to form carbonated apatite and with time the latter dissolves and a variety of other phosphate containing minerals form with each diagenetic change some of the more soluble minerals are lost and ultimately only the ash derived siliceous minerals remain in both caves there are local accumulations of such siliceous minerals that are metres thick in fact ash derived minerals in general are major components of the sediments in both kebara and hayonim caves their diagenesis involves a hugh reduction in volume which in turn may have important effects on the geological structures and stratigraphy of the sediments the changing mineralogy of the sediments due to diagenesis complicates the use of present day estimates of radiation content of the sediments for correcting age estimates by thermoluminescence and electron spin resonance finally the presence of the relatively stable ash derived siliceous minerals in a sedimentary layer in other caves could be a useful means of identifying the presence of ash in other archaeological sites where macroscopic hearth features are absent

modern thermokarst lake dynamics in the continuous permafrost zone northern seward peninsula alaska 1 quantifying changes in thermokarst lake extent is of importance for understanding the permafrost related carbon budget including the potential release of carbon via lake expansion or sequestration as peat in drained lake basins we used high spatial resolution remotely sensed imagery from 1950 51 1978 and 2006 07 to quantify changes in thermokarst lakes for a 700 km2 area on the northern seward peninsula alaska the number of water bodies larger than 0 1 ha increased over the entire observation period 666 to 737 or 10 7 however total surface area decreased 5 066 ha to 4 312 ha or 14 9 this pattern can largely be explained by the formation of remnant ponds following partial drainage of larger water bodies thus analysis of large lakes 40 ha shows a decrease of 24 and 26 in number and area respectively differing from lake changes reported from other continuous permafrost regions thermokarst lake expansion rates did not change substantially between 1950 51 and 1978 0 35 m yr and 1978 and 2006 07 0 39 m yr however most lakes that drained did expand as a result of surface permafrost degradation before lateral drainage drainage rates over the observation period were stable 2 2 to 2 3 per year thus analysis of decadal scale high spatial resolution imagery has shown that lake drainage in this region is triggered by lateral breaching and not subterranean infiltration future research should be directed toward better understanding thermokarst lake dynamics at high spatial and temporal resolution as these systems have implications for landscape scale hydrology and carbon budgets in thermokarst lake rich regions in the circum arctic

going underground experimental carbonization of fruiting structures under hearths we show that carbonized fruits and seeds recovered from middle stone age deposits in rock shelters are likely to have been carbonized as part of post depositional processes we buried indigenous south african fruits nuts and seeds at pre determined depths and distances from the centers of experimental fires the cold ashes of the hearths and the sand surrounding them were subsequently excavated using standard archaeological techniques and dry screening the fruiting structures from the oxidizing part of the fire were burnt to ashes whereas those buried in sand under anoxic conditions survived in varying forms those buried 5 cm below the center of the fire were carbonized those buried 10 cm below the center of the fire were dehydrated and those 5 cm and 10 cm below the surface at the outer edge of the fire were unaffected size moisture or oil content of the original fruit or seed did not appear to influence whether or not carbonization took place temperatures recorded 5 cm below the experimental fires suggest that the carbonization occurred at or before a maximum temperature of 328 c and also at lower maximum temperatures 152 c that were maintained for long periods even when the quantities of a particular wood are controlled open fires may produce variable underground temperatures and the temperatures below ancient hearths would have been equally variable we suggest that cyperaceae sedge nutlets the most numerous fruiting structures in the sibudu middle stone age archaeobotanical assemblage occur in the shelter as a result of human activity subsequent burial and accidental carbonization when hearths were built directly above the buried nutlets

new ages for the post howiesons poort late and final middle stone age at sibudu south africa abstract optically stimulated luminescence osl measurements are reported for single grains of quartz from deposits within sibudu rock shelter such measurements enable rejection of unrepresentative grains and application of the finite mixture and central age models to obtain the most reliable age estimates three types of single grain equivalent dose de distributions were observed one sample represented a single dose population three samples indicated mixing between iron age ia and middle stone age msa deposits and 10 samples in addition to the three mixed samples showed scattered distributions the latter type resulted from differences in the beta dose received by individual grains for these samples the beta doses were modelled and adjusted accordingly ages for the 14 samples collected from msa deposits post dating the howiesons poort hp resulted in three age clusters which are stratigraphically consistent with the three informally named cultural phases at sibudu namely the post hp late msa and final msa weighted mean ages of 58 5 1 4 ka 47 7 1 4 ka and 38 6 1 9 ka were calculated for these phases respectively the three phases were separated by two occupational hiatuses with durations of 10 8 1 3 ka and 9 1 3 6 ka we hypothesise that the punctuated presence of humans at sibudu was determined by large scale fluctuations in climate during oxygen isotope stage ois 3 which resulted in alternating wet and dry periods phases of occupation correspond to wet periods when fresh water was available in the tongati river whereas intervals of site abandonment correspond to dry periods when people were forced to migrate in search of a reliable source of fresh water where people migrated to remains unresolved

huge variations in the isotopic ratio 196hg 202hg in some acid insoluble residues of sikhote alin and other iron meteorites the insoluble materials obtained on dissolution of iron meteorites in 2 m h2so4 have been analysed by radiochemical neutron activation to measure the isotopic ratio 196hg 202hg of hg released at different temperatures in many cases this ratio is found to be anomalous its extreme values relative to the reagent hg being 0 003 2 limit and 1 26 0 05 often in the same residue both positive and negative deviations are found at different temperatures the anomalous normal and isotopically diluted hg distillates have been re irradiated to eliminate the influence of neutron self shielding and interfering reactions from matrix elements the isotopic anomaly persists in the distillates proving that any artifacts during irradiation are essentially absent the presence of isotopically anomalous hg in iron meteorites puts some severe constraints on the formation history of these objects either iron meteorites have been formed in a non magmatic process entrapping presolar grains or some foreign matter has been injected into their solidified parent bodies by collisions with objects of different isotopic composition

heavy carbon in individual oxide grains from the murchison meteorite the carbon isotopic composition of individual oxide grains from murchison hf hcl acid residue cfoc has been measured in the ion microprobe many grains mg spinel cr spinel and fe oxide contain carbon with large 13 c excesses ranging to 7000 corresponding to 12 c 13 c 11 in most cases the carbon is present as micron sized subgrains the association of silicon with the anomalous carbon points towards sic as carrier if this tentative identification is correct then the sic grains most likely originated in the circumstellar atmospheres of red giants oxide grains in which the 18 o 16 o ratio has also been measured show variable 16 o excesses which are not correlated with the 13 c excesses this indicates that the sources of the anomalous carbon and oxygen isotopic compositions of the oxide grains are unrelated

quartz backed tools as arrowheads and hand cast spearheads hunting experiments and macro fracture analysis the invention of the bow and arrow was a milestone in late pleistocene technological evolution preservation biases and methodological problems imped our ability to detect its presence in the archaeological record currently south africa has the earliest suggested evidence for arrowheads amongst others small quartz backed tools dating 65 60 ka these artefacts inferred function is based on their small size micro and macro wear traces and micro residues recorded on quartz segments from sibudu cave experimental support for these inferences or to show that similar artefacts are associated with bow hunting are however lacking here we describe breakage patterns on 150 quartz backed tools hafted as transverse arrowheads and hand cast spearheads in simulated hunting experiments these experiments controlled for hafting variability to test the effects of propulsion velocity on the types patterns and area of diagnostic impact fractures difs our results show step terminating bending fracture spin off fracture and impactburination frequencies dif locations and ventrally situated dif frequencies to be robust means of distinguishing arrowheads from spearheads our experiments verify previous observations that overall dif frequencies differentiate between these weapon types importantly we confirm that dif size is linked to weapon propulsion velocity but that fracture area is affected by tool area these findings provide methods for future testing of the hypothesis that bow and arrow technology was in use at least 65 ka in southern africa and in other regions where quartz was used to tip weapons

role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization ground ice is abundant in the upper permafrost throughout the arctic and fundamentally affects terrain responses to climate warming ice wedges which form near the surface and are the dominant type of massive ice in the arctic are particularly vulnerable to warming yet processes controlling ice wedge degradation and stabilization are poorly understood here we quantified ice wedge volume and degradation rates compared ground ice characteristics and thermal regimes across a sequence of five degradation and stabilization stages and evaluated biophysical feedbacks controlling permafrost stability near prudhoe bay alaska mean ice wedge volume in the top 3 m of permafrost was 21 imagery from 1949 to 2012 showed thermokarst extent area of water filled troughs was relatively small from 1949 0 9 to 1988 1 5 abruptly increased by 2004 6 3 and increased slightly by 2012 7 5 mean annual surface temperatures varied by 4 9 c among degradation and stabilization stages and by 9 9 c from polygon center to deep lake bottom mean thicknesses of the active layer ice poor transient layer ice rich intermediate layer thermokarst cave ice and wedge ice varied substantially among stages in early stages thaw settlement caused water to impound in thermokarst troughs creating positive feedbacks that increased net radiation soil heat flux and soil temperatures plant growth and organic matter accumulation in the degraded troughs provided negative feedbacks that allowed ground ice to aggrade and heave the surface thus reducing surface water depth and soil temperatures in later stages the ground ice dynamics and ecological feedbacks greatly complicate efforts to assess permafrost responses to climate change

petrography composition and origin of large chromian spinels from the murchison meteorite abstract most spinel grains in murchison acid residues are mg al rich 16o rich 18o 50 small 10 30 m and probably from refractory inclusions they are quite unlike spinels we have recovered from murchison by freeze thaw disaggregation density separation and handpicking as reported here the latter spinels contain up to 37 wt cr2o3 and up to 17 wt feo are not 16o enriched 18o 1 9 2 4 are coarse 60 325 m and are not from refractory inclusions from backscattered electron images of fifty seven such grains we recognize five zoning types defined by variations in cr2o3 contents patchy 56 homogeneous 21 chevron 10 5 gradational 9 and core rim 3 5 many grains have silicate inclusions the most common being small anhedral grains of diopside with 12 24 wt al2o3 and up to 3 7 wt tio2 eleven spinel samples occur with forsteritic fo95 99 olivine in most cases the spinel partially encloses the olivine cr bearing spinel was found in situ in two al rich chondrules one with homogeneous spinel the other with homogeneous gradational and core rim spinel and both with forsterite and aluminous diopside in two irregularly shaped olivine bearing inclusions one with homogeneous spinel the other patchy and attached to an isolated olivine grain patchy observation of homogeneous gradational and core rim type spinels in chondrules and basalts shows that grains with these zoning patterns can crystallize from liquids although in murchison chondrules with the appropriate compositions and sufficiently coarse textures to yield the separated spinels are exceedingly rare chevronzoned grains also could have formed in chondrules alternatively they may have acquired their oscillatory zoning patterns by cycling through different p t o 2 regimes in the solar nebula during their formation the patchy spinel grains were probably never molten and they most likely formed by sintering of aggregates of smaller spinel grains which were enriched in cr and fe to varying degrees in spite of their various crystallization and thermal histories the spinels all have normal oxygen and chromium isotopic compositions consistent with formation from a single well mixed nebular reservoir based on the known slow rates of diffusion of oxygen in mgo al2o3 and mgal2o4 it is unlikely that the spinels of this study formed from an isotopically anomalous reservoir and later re equilibrated with a normal one it is more likely that they have retained their original isotopic compositions we see no evidence for anomalous cr which had been reported by others

a segment is not a monolith evidence from the howiesons poort of sibudu south africa segments from the howiesons poort of sibudu south africa can be separated into at least three populations based on quartz hornfels and dolerite rocks used for their production length breadth thickness and tip cross sectional areas are significantly different between segments made on the three rock types segments are not monoliths and they were not intended as a single tool type they were flexible enough to be mounted to shafts in a variety of ways several hafting strategies are evident including the use of different adhesive recipes most segments were probably parts of hunting weapons based on use trace analysis but weapon types varied quartz segments have standardized shapes short and deep perhaps because they were hafted as transverse arrowheads while hornfels and dolerite segments may on occasion also have been parts of projectiles the large dolerite segments could sometimes have served as parts of spearheads with two segments hafted back to back howiesons poort segment technology is sophisticated its makers appreciated distinct properties of rocks their flaking wear and impact possibilities further they recognized the best sizes and shapes for use with each kind of weapon they understood the qualities and applications of various adhesive recipes and they knew how to make a variety of hafts from materials that included bone and wood

a robust vegetation based elevation transfer method for reconstructing arctic polygon mire palaeo microtopography abstract the reconstruction of past environments by means of macrofossil and pollen analysis is commonly based on the modern ecological preferences of the taxa that may have produced these fossils here we present a modelling approach in which we use modern vegetation surface height relationships to quantify past surface heights in an arctic ice wedge polygon mire vegetation composition and ground surface height gsh were assessed in a polygon mire near kytalyk northeastern siberia cluster analysis revealed five plant communities which are clearly separated with respect to ground surface height frost surface height and coverages of open water and vegetation based on the composition of modern vegetation we constructed two sets of potential fossil types plant macrofossils and pollen an extensive one and a more restricted one to reflect different conditions of preservation and recognisability we applied canonical correspondence analysis to model the relationships between potential fossil types and measured gsh both models show a strong relationship between modelled and measured gsh values and a high accuracy in prediction finally we used the models to predict gsh values for holocene peat samples and found a fair correspondence with expert based multi proxy reconstruction of wetness conditions even though only a minor part of the encountered fossils were represented in the gsh models illustrating the robustness of the approach our approach can be used to reconstruct palaeoenvironmental conditions in a more objective way and can serve as a template for further palaeoecological studies

pan arctic ice wedge degradation in warming permafrost and its influence on tundra hydrology ice wedges are common features of the subsurface in permafrost regions they develop by repeated frost cracking and ice vein growth over hundreds to thousands of years ice wedge formation causes the archetypal polygonal patterns seen in tundra across the arctic landscape here we use field and remote sensing observations to document polygon succession due to ice wedge degradation and trough development in ten arctic localities over sub decadal timescales initial thaw drains polygon centres and forms disconnected troughs that hold isolated ponds continued ice wedge melting leads to increased trough connectivity and an overall draining of the landscape we find that melting at the tops of ice wedges over recent decades and subsequent decimetre scale ground subsidence is a widespread arctic phenomenon although permafrost temperatures have been increasing gradually we find that ice wedge degradation is occurring on sub decadal timescales our hydrological model simulations show that advanced ice wedge degradation can significantly alter the water balance of lowland tundra by reducing inundation and increasing runoff in particular due to changes in snow distribution as troughs form we predict that ice wedge degradation and the hydrological changes associated with the resulting differential ground subsidence will expand and amplify in rapidly warming permafrost regions the polygonal patterns in permafrost regions are caused by the formation of ice wedges observations of polygon evolution reveal that rapid ice wedge melting has occurred across the arctic since 1950 altering tundra hydrology

harding iceland spar a new δ18o δ13c carbonate standard for hydrothermal minerals abstract an isotopically homogeneous calcite harding iceland spar his having 6180 11 78 0 07 22 15 for co2 and 13c 4 80 0 02 has been prepared in quantities suitable for use as a working standard in mass spectrometric analysis the isotopic values are well suited for analysis of minerals of hydrothermal origin

the carbon and oxygen isotopic composition of meteoritic carbonates the 13c12c and 18o16o isotopic ratios of carbonates from carbonaceous and ordinary chondrites have been measured on co2 released by the action of h3po4 on whole rock samples carbonates from ci cm and cr carbonaceous chondrites exhibit a range in 18o of ca 15 20 5 to 35 1 relative to smow limited data from co2 water equilibration experiments suggest that meteoritic carbonates do not possess grossly anomalous 17o isotopic compositions therefore they are truly enriched in 13c with 13c between 23 7 and 80 7 relative to pdb large internal variations in 13c and 18o were found in individual meteorites and suggest that two or more isotopically distinct carbonates of different origin may be present the abundance 13c and 18o of carbonate in cm2 chondrites may be related to the extent of aqueous alteration of the meteorites carbonates in ci and cr chondrites have a median 13c ca 50 to 60 whereas 13c of cm meteorites lie in the range 40 to 50 although exceptions exist in both sets of samples cv3 and co3 carbonaceous chondrites and unequilibrated ordinary chondrites release small amounts of co2 on acid treatment which might be from carbonate dissolution but which is not enriched in 13c exhibiting 13c values ca 0 10 the exception to this is bishunpur with 13c ca 23 5 the difference in 13c of the ci cm and cr vs cv co and ordinary chondrite carbonates may be a result of the progressive enrichment in 13c of percolating fluids brought about by increasing solubilization of exotic 13c enriched grains

middle stone age bone tools from the howiesons poort layers sibudu cave south africa abstract recently discovered bone implements from middle stone age msa deposits at sibudu cave south africa confirm the existence of a bone tool industry for the howiesons poort hp technocomplex previously an isolated bone point from klasies river provided inconclusive evidence this paper describes three bone tools two points and the end of a polished spatula shaped piece from unequivocal hp layers at sibudu cave with ages greater than 61 ka comparative microscopic and morphometric analysis of the sibudu specimens together with bone tools from southern african middle and later stone age lsa deposits an iron age occupation nineteenth century bushman hunter gatherer toolkits and bone tools used experimentally in a variety of tasks reveals that the sibudu polished piece has use wear reminiscent of that on bones experimentally used to work animal hides a slender point is consistent with a pin or needle like implement while a larger point reminiscent of the single specimen from peers cave parallels large un poisoned bone arrow points from lsa iron age and historical bushman sites additional support for the sibudu point having served as an arrow tip comes from backed lithics in the hp compatible with this use and the recovery of older larger bone and lithic points from blombos cave interpreted as spear heads if the bone point from the hp layers at sibudu cave is substantiated by future discoveries this will push back the origin of bow and bone arrow technology by at least 20 000 years and corroborate arguments in favour of the hypothesis that crucial technological innovations took place during the msa in africa

the black layer of middle palaeolithic combustion structures interpretation and archaeostratigraphic implications certain aspects of the formation processes of simple flat archaeological combustion structures such as those present in the middle palaeolithic record remain unexplained such kind of combustion structures are commonly affected by postdepositional agents and often their only distinct well preserved component is a thin black lens on the ground hence understanding the nature of this black lens is essential towards archaeological interpretation from an interdisciplinary microstratigraphic approach we present a case study in which for an entire experimental series of flat combustion structures the black layer represents the fire altered topsoil on which the fire was made parallel analysis of archaeological middle palaeolithic combustion structures from the site of el salt alicante spain reveal similar patterns leading to significant implications for archaeological interpretation in the light of these results special attention must be paid to the formation processes of flat middle palaeolithic combustion features as black layers and the material contained in them are not necessarily linked with combustion but with preceding activities or events in such cases black layers represent intact remnants of occupation surfaces concealing significant behavioural and palaeoenvironmental information relevant to the reconstruction of middle palaeolithic societies

multi scale site evaluation of a relict active layer detachment in a high arctic landscape abstract investigations into the susceptibility of permafrost landscapes response to thermokarst can be performed using various approaches depending on the scale of investigation in many cases point based field measurements are extrapolated to larger scales and vice versa the integration of scales often requires some form of ground control in addition to remote sensing surveys which are at times exclusively conducted as upscaling from discrete field measurements can provide spatial coverage and landscape scale significance downscaling from remote sensing can offer insight into processes and serve as calibration or verification here we present a multiple scale evaluation of an area initially interpreted as a relict active layer detachment slide before 1950 on melville island in the high arctic where differential interferometric synthetic aperture radar dinsar showed subsidence between 2013 and 2015 ground based cryostratigraphy measurements were combined with ground penetrating radar gpr to investigate permafrost ice content the results indicate greater subsidence within the relict active layer detachment as detected by dinsar gpr surveys and permafrost coring indicated the presence of an ice rich or massive ice layer near the base of the active layer in this area in addition cryostratigraphic evidences of thaw unconformity and of massive ice depth helped validate the interpretations of the geomorphology in the active layer detachment this combination of methods indicated a localized and inherited landform subsidence association which brought further insight into the interpretation of dinsar subsidence data the framework presented in this study demonstrates the importance of site specific investigations of thermokarst signal in order to understand the processes behind the remote sensing results

correlated si isotope anomalies and large 13c enrichments in a family of exotic sic grains a suite of morphologically distinctive silicon carbide sic grains from the orgueil and murchison carbonaceous chondrite meteorites contains si and c of highly anomalous isotopic composition all of the sic grains in this suite are characterized by a distinctive platy morphology and roughly developed hexagonal crystal forms that allow them to be distinguished from other types of sic found in the host meteorites the 29 si and 30 si values of individual sic crystals deviate from those of normal solar material by more than 100 while the 13 c values range from 150 to 5200 isotopically normal c and si are not found in any of these sic crystals the sic grains belonging to this morphological suite are isotopically distinct from fine grained sic aggregates and other morphological types of sic in unequilibrated meteorites the 29 si 28 si and 30 si 28 si ratios of these platy grains are well correlated and define a linear array that does not pass through the composition of normal solar si this behavior contrasts sharply with the diverse and poorly correlated si isotopic compositions shown by the total sic population we suggest that the distinctive morphological characteristics and comparatively simple si isotope systematics identify the platy sic crystals as a genetically related family formed around a single isotopically heterogeneous presolar star or an association of related stars the enrichments in 13 c and the si isotope systematics of the platy sic are broadly consistent with theoretical models of nucleosynthesis in low mass carbon stars on the asymptotic giant branch the si isotope array most plausibly reflects mixing between 28 si rich material inherited from a previous generation of stars and material enriched in 29 si and 30 si produced in intershell regions by neutron capture during he burning 13 c is also produced in intershell regions by proton reactions on 12 c seed nuclei and is carried withs process nuclei to the stellar envelope by convection which penetrates down to the he shell the absence of a correlation between the si and c isotopic compositions of the sic suggests either episodic condensation of sic extending over several thermal pulses in the atmosphere of a single star or derivation of the sic from several stars characterized by different rates of 13 c production in the multiple star scenario the linear correlation of the 29 si 28 si and 30 si 28 si ratios among the platy sic indicates that these stars evolved from a common si seed composition under similar conditions of neutron capture nucleosynthesis the 29 si 30 si ratio of the sic inferred by us to be produced by neutron capture in the stellar interior is distinct from values calculated from models of nucleosynthesis in agb stars

recent acceleration of thaw slumping in permafrost terrain of qinghai tibet plateau an example from the beiluhe region abstract thaw slump activity has recently increased in permafrost areas of qinghai tibet plateau qtp thaw slumps may influence the stability of infrastructure and impact global biogeochemical cycles this study presents changes in retrogressive thaw slump in the beiluhe region based on interpretation of satellite imagery thaw slumping has become widespread in the region over the last ten years the total number of thaw slumps has increased by 253 and the total affected area increased by 617 the intensification of thaw slumping in the study region did not increase steadily over the study period but was rather concentrated during two years 2010 and 2016 this was mainly attributed to anomalously high air temperatures during the thawing season and abundant precipitation initiation of future thaw slumps on qtp will likely similarly be linked to changing trends in anomalous weather events and climate warming

isotropic thaw subsidence in undisturbed permafrost landscapes 1 observations in undisturbed terrain within some regions of the arctic reveal limited correlation between increasing air temperature and the thickness of the seasonally thawed layer above ice rich permafrost here we describe landscape scale thaw induced subsidence lacking the topographic contrasts associated with thermokarst terrain a high resolution 11 year record of temperature and vertical movement at the ground surface from contrasting physiographic regions of northern alaska obtained with differential global positioning systems technology indicates that thaw of an ice rich layer at the top of permafrost has produced decimeter scale subsidence extending over the entire landscapes without specialized observation techniques the subsidence is not apparent to observers at the surface this isotropic thaw subsidence explains the apparent stability of active layer thickness records from some landscapes of northern alaska despite warming near surface air temperatures integrated over extensive regions it may be responsible for thawing large volumes of carbon rich substrate and could have negative impacts on infrastructure

a chemical and isotopic study of hibonite rich refractory inclusions in primitive meteorites the ion microprobe has been used to determine the concentrations of a number of trace elements including all 14 stable rare earth elements and the isotopic compositions of ca and mg in seven hibonite rich refractory inclusions hibonite in every inclusion analyzed shows the effect of ree partitioning with other solid or liquid phases in which hibonite is enriched in light over heavy ree compared to other coexisting phases this partitioning causes cl chondritenormalized enrichments to drop by factors of 4 to 22 from lanthanum to lutetium fractionations due to gas solid partitioning of ree are sometimes superimposed on the pattern produced by partitioning between condensed phases two inclusions hal and dh h1 show evidence for formation in extremely oxidizing environments and their ca is mass fractionated in favor of the heavy isotopes by 7 and 12 amu respectively two corundum hibonite inclusions show evidence of extremely high temperature gas solid fractionation such that the more volatile light ree are depleted as a group relative to the more refractory heavy ree these inclusions both have ca that is mass fractionated in favor of the light isotopes hibonite preserves the largest nuclear isotope anomalies in ti found to date faheyet al 1985a hintonel al 1987b but there does not seem to be a simple relationship between chemical composition isotopic mass fractionation and the sign and magnitude of nuclear isotopic anomalies in hibonite rich inclusions one possibility for producing a variety of chemical compositions and degrees of mass fractionation while preserving nuclear isotope anomalies is by multiple cycles of condensation and evaporation in a turbulent protoplanetary accretion disk morfill 1983 morfill and r n clayton 1986a b these cycles could also occur in a presolar nebula with large non axisymmetric temperature and pressure distributions boss 1988 nuclear anomalies are most likely to be preserved in hibonite because hibonite is the most refractory major phase to occur commonly in meteorites

size matters preliminary results from an experimental approach to interpret middle stone age hearths abstract this paper reports on ten fire experiments and their significance for interpreting hearths from the middle stone age site sibudu kwazulu natal south africa the experiments were conducted on four different substrata and four wood taxa were used in the experiments four of the experiments consisted of a single fire while the other experiments consisted of multiple fires on top of each other the experimental fires produced hearth areas of 962 1 1661 9 cm and hearth depths of 3 12 cm hearth size and depth do not correlate hearth area seems to correlate with the fuel load used in a hearth and it is argued that this can be used in interpretations of fire use at an archaeological site nine hearths from the same layer at sibudu are used as examples and it is argued that variation in hearth area indicates variation in hearth use some hearths at sibudu were possibly only used once whereas others represent long term use and or repeated reloading of the same hearth

blombos cave southern cape south africa preliminary report on the 1992 1999 excavations of the middle stone age levels the later and middle stone age levels at blombos cave bbc were excavated over four field seasons between 1992 and 1999 here we report on the results from the middle stone age msa levels the taphonomy and depositional history of the msa levels is complex due to faulting folding and spalling careful observations during excavation have assisted in understanding some of these taphonomic and site formation processes microstratigraphic analysis currently in progress will add to this information the uppermost msa level the still bay phase contains high densities of bifacial points the fossile directeur of the still bay industry placing the still bay within the msa culture sequence has been problematic in the past because still bay assemblages are rarely found in situ and previous excavations were inadequately recorded however with the regional data discussed in the text the still bay can be securely placed before the howiesons poort dated at 65 70 ka flaked stone makes up the greatest proportion of all artefacts with the highest incidence of retouch and use of fine grained non local materials found in the still bay levels the ochre assemblage is remarkable for the mass of material compared to other msa sites finds uncommon in an msa context are two pieces of ochre from the still bay phase engraved with a geometric design a fragment of deliberately engraved bone also 28 shaped and polished bone tools recovered mainly from a phase just below the still bay blombos cave is the first site where well preserved faunal remains have been recovered in association with the still bay allowing for unique insights into human subsistence behaviour and palaeoenvironmental reconstruction large fish bones marine shells seals and dolphins attest to extensive exploitation of aquatic resources and a wide range of terrestrial animals were hunted and gathered the few human teeth recovered are heavily worn and damaged thus the issue of morphological modernity cannot be addressed the bbc findings are a useful adjunct to findings from other msa coastal sites in the southern cape especially klasies river kr and die kelders cave 1 dk1 uniquely bbc provides insights into human behaviour during a phase of the msa never before studied in detail

cemented ash as a receptacle or work surface for ochre powder production at sibudu south africa 58 000 years ago the white ash of sibudu hearths sometimes became cemented and when this was the case some of these crusts were used as work surfaces or receptacles particularly in occupations dating about 58 000 years ago substantial deposits of red and yellow ochre powder have been found on these crusts this suggests that the ochre was not associated with hearths for heat treatment because yellow ochre readily transforms to red even at low temperatures xrf readings suggest that the ochre used at the site derives from different geological sources micromorphological studies imply that phosphatization caused the cementation of the ashes in some hearths while gypsum growth hardened one of the hearths described here

depth resolved physicochemical characteristics of active layer and permafrost soils in an arctic polygonal tundra region author s wu y ulrich c kneafsey t lopez r chou c geller j mcknight k dafflon b soom f peterson j hubbard s abstract 2018 the authors permafrost physicochemical parameters play a key role in controlling the response of permafrost carbon to climate change we studied the physicochemical parameters of permafrost in an arctic tundra region to evaluate 1 how soil parameters vary with depth and whether and how they are interrelated 2 whether and how permafrost soil differs from its overlaying active layer and 3 whether soil property depth relationships are different across geomorphic features e g low flat and high centered polygons we also explored the possible biogeochemical processes that led to these soil characteristics and how they may affect biogeochemical reactions upon permafrost thaw we observed 1 consistent relationships between soil property and depth and between major parameters 2 large contrasts of key soil parameters between active layer and permafrost indicative of potentially different response of the permafrost carbon to warming when compared to the active layer and 3 a correlation between soil hydraulic conductivity and topographic features that impacts soil hydrologic processes our analysis suggests that the permafrost has a marine derived chemical signature that differs from the active layer and shapes the physicochemical fingerprints of the different geomorphic features specifically we revealed the unique signatures of the high center polygons indicative of possible microbial activity at depth g1 m our study suggested consistent key soil parameter depth correlations while demonstrating complex lateral and vertical variabilities these results are valuable for identifying approaches to upscale point based measurements and for improving model parameterization to predict permafrost carbon behavior and feedback under future climate

possible shell beads from the middle stone age layers of sibudu cave south africa recent excavations at sibudu cave kwazulu natal south africa uncovered an iron age horizon below which is a complex 3 m thick middle stone age sequence with post howiesons poort howiesons poort still bay and pre still bay layers available osl ages indicate that the howiesons poort occupation is older than 60 ky and the still bay older than 70 ky here we present the archaeological context and the taphonomic analysis of six afrolittorina africana three of which bear perforations from the still bay and howiesons poort layers of this site the single specimen from the latter cultural horizon comes from the lowermost layer attributed to this technocomplex this and the depositional context of this layer suggest that this shell derives as do the other five from the still bay occupation layers taphonomic analysis of the archaeological specimens based on present day afrolittorina africana biocoenoses microscopic examination morphometry experimental perforation of modern shells and a review of the natural agents that may accumulate marine shells at inland sites indicate probable human involvement in the collection transport modification and abandonment of afrolittorina africana in sibudu if confirmed by future discoveries these shells would corroborate the use of personal ornaments already attested at blombos cave western cape province by still bay populations the apparent absence of ornaments at howiesons poort sites raises the question of the mechanisms that have led to cultural modernity since it seems to contradict the scenario according to which cultural innovations recorded at middle stone age sites reflect a process of continuous accretion and elaboration interpreted as the behavioural corollary of the emergence of anatomically modern humans

isotopic composition of carbonaceous chondrite kerogen evidence for an interstellar origin of organic matter in meteorites abstract stepwise combustion has revealed systematic patterns of isotopic heterogeneity for c h and n in the insoluble organic fraction m kerogen from the orgueil and murray carbonaceous chondrites those patterns are essentially identical for both meteorites indicating a common source of m kerogen the data cannot be reconciled with a single mass fractionation process acting upon a single precursor composition this indicates either a multi path history of mass dependent processing or a significant nucleogenetic contribution or both if mass fractionation were the dominant process the magnitude of the observed isotopic variability strongly suggests that ion molecule reactions at very low temperatures probably in interstellar clouds were responsible in any case an interstellar rather than solar nebular origin for at least some of the meteoritic organic matter is indicated this has interesting implications for the origin of prebiotic molecules temperatures in the early solar system and the isotopic compositions of volatiles accreted by the terrestrial planets