the new hominid skeleton from sterkfontein south africa age and preliminary assessment a new hominid skeleton from sterkfontein member 2 attaches to foot bones recovered from loose blocks during the 1980s and first described in 1995 several flowstone horizons are present above and below the skeleton and have given clear palaeomagnetic signatures five changes in magnetic polarity have been identified when constrained by the available biostratigraphy this sequence can be placed confidently between 3 22 and 3 58 ma interpolation of sedimentation rates over the small intervals between reversals allows this range to be reduced to 3 30 3 33 ma the skeleton is thus the oldest yet discovered and is considered to belong to a species of australopithecus other than africanus copyright 1999 john wiley sons ltd

what drives the north atlantic oscillation s temperature anomaly pattern part ii a decomposition of the surface downward longwave radiation anomalies abstractradiative transfer calculations are conducted to determine the contribution of temperature and water vapor anomalies toward the surface clear sky downward longwave radiation dlr anomalies

relation of substorm onset to harang discontinuity 1 in this study we investigate the relation of auroral substorm onset to the harang discontinuity hd various studies have reported that the substorm onset occurs poleward equatorward or within the hd the motivation for the present study is to further investigate this relation with a much larger database using a database of over 3700 onsets determined from auroral images taken on the image spacecraft we statistically examine the magnetic latitude location of the onset with respect to the location of the hd the location of the discontinuity is determined with data from the image ground magnetometer network we define the location of the hd as the transition from relatively strong eastward to relatively strong westward equivalent ionospheric currents at the latitude of the main nightside auroral electrojet flow our results show that the location of 75 onsets that occurred above the image ground array about 31 occurred within 6 of latitude of the hd observed during the growth phase of the substorm and 37 occur within 5 of latitude of the hd observed during the expansion phase we also find that 23 of the onsets occur in association with vortices of ionospheric currents observed during the growth phase the remaining 31 of the onsets do not appear to be associated with a hd or a vortex during the growth phase ten of the initial 75 onsets were identified as likely pseudo breakups and not fully developed substorms seven of the initial 75 onsets were probably poleward boundary intensifications pbi this study demonstrates that approximately 2 3 of the auroral substorm onsets do not occur within or near the hd identified in the growth phase these results do not support the prediction made by lyons et al 2003 that substorm auroral onset should occur within the upward field aligned current in the harang discontinuity

timing of the nihewan formation and faunas abstract magnetostratigraphic dating of the fluvio lacustrine sequence in the nihewan basin north china has permitted the precise timing of the basin infilling and associated nihewan mammalian faunas the combined evidence of new paleomagnetic findings from the hongya and huabaogou sections of the eastern nihewan basin and previously published magnetochronological data suggests that the nihewan formation records the tectono sedimentary processes of the plio pleistocene nihewan basin and that the nihewan faunas can be placed between the matuyama brunhes geomagnetic reversal and the onset of the olduvai subchron 0 78 1 95 ma the onset and termination of the basin deposition occurred just prior to the gauss matuyama geomagnetic reversal and during the period from the last interglaciation to the late last glaciation respectively suggesting that the nihewan formation is of late pliocene to late pleistocene age the nihewan faunas comprising a series of mammalian faunas such as maliang donggutuo xiaochangliang banshan majuangou huabaogou xiashagou danangou and dongyaozitou are suggested to span a time range of about 0 8 2 0 ma the combination of our new and previously published magnetostratigraphy has significantly refined the chronology of the terrestrial nihewan formation and faunas

mid pleistocene acheulean like stone technology of the bose basin south china stone artifacts from the bose basin south china are associated with tektites dated to 803 000 3000 years ago and represent the oldest known large cutting tools lcts in east asia bose toolmaking is compatible with mode 2 acheulean technologies in africa in its targeted manufacture and biased spatial distribution of lcts large scale flaking and high flake scar counts acheulean like tools in the mid pleistocene of south china imply that mode 2 technical advances were manifested in east asia contemporaneously with handaxe technology in africa and western eurasia bose lithic technology is associated with a tektite airfall and forest burning

two component auroral electrojet importance for substorm studies this paper attempts to synthesize the diverse number of observations of electric fields and currents in the high latitude ionosphere during substorms by demonstrating that there are often spatial shifts among regions of high ionospheric conductivity large electric fields and intense currents in the auroral electrojet it is shown that substorm time variations of the current patterns over the entire polar region consist of two basic components the first is related to the two cell convection pattern and the second to the westward electrojet in the dark sector which is in turn related to the three dimensional wedge current system these two components result from the relative strength of electric fields and conductivities in the intensification of the auroral electrojet and are identified as the signatures for directly driven and the unloading components in solar wind magnetosphere interactions we contend that disturbed intervals do not necessitate the presence of substorm expansion phase activity and that the vast number of earlier complex results concerning the auroral electrojet can be ascertained from the high degree of variability of the two components depending on substorm events substorm phases and their own spatial temporal scale sizes it is demonstrated that several major issues that have remained controversial are now accounted for reasonably well in terms of this two component electrojet model we also predict specific features of the substorm auroral electrojet that have not yet been observed

u pb isotopic age of the stw 573 hominid from sterkfontein south africa sterkfontein cave south africa has yielded an australopith skeleton stw 573 whose completeness has excited great interest in paleoanthropology stw 573 or little foot was found 25 meters below the surface in the silberberg grotto 238u 206pb measurements on speleothems immediately above and below the fossil remains corrected for initial 234u disequilibrium yield ages of 2 17 0 17 million years ago ma and 2 24 0 07 0 09 ma respectively indicating an age for stw 573 of close to 2 2 ma this age is in contrast to an age of approximately 3 3 ma suggested by magnetochronology and ages of approximately 4 ma based on 10be and 26al but it is compatible with a faunal age range of 4 to 2 ma

electrodynamic parameters in the nighttime sector during auroral substorms the characteristics of the large scale electrodynamic parameters field aligned currents facs electric fields and electron precipitation which are associated with auroral substorm events in the nighttime sector have been obtained through a unique analysis which places the ionospheric measurements of these parameters into the context of a generic substorm determined from global auroral images a generic bulge type auroral emission region has been deduced from auroral images taken by the dynamics explorer 1 de 1 satellite during a number of isolated substorms and the form has been divided into six sectors based on the peculiar emission characteristics in each sector west of bulge surge horn surge middle surge eastern bulge and east of bulge by comparing the location of passes of the dynamics explorer 2 de 2 satellite to the simultaneously obtained auroral images each pass is placed onto the generic aurora the organization of de 2 data in this way has systematically clarified peculiar characteristics in the electrodynamic parameters an upward net current mainly appears in the surge with little net current in the surge horn and the west of bulge the downward net current is distributed over wide longitudinal regions from the eastern bulge to the east of bulge near the poleward boundary of the expanding auroral bulge a pair of oppositely directed fac sheets is observed with the downward fac on the poleward side this downward fac and most of the upward fac in the surge and the middle surge are associated with narrow intense antisunward convection corresponding to an equatorward directed spikelike electric field this pair of currents decreases in amplitude and latitudinal width toward dusk in the surge and the west of bulge and the region 1 and 2 facs become embedded in the sunward convection region the upward fac region associated with the spikelike field on the poleward edge of the bulge coincides well with intense electron precipitation and aurora appearing in this western and poleward portion of the bulge the convection reversal is sharp in the west of bulge and surge horn sectors and near the high latitude boundary of the upward region 1 fac in the surge the convection reversal is near the low latitude boundary of the upward region 1 with a near stagnation region often extending over a large interval of latitude in the eastern bulge and east of bulge sectors the region 1 and 2 facs are located in the sunward convection region while a spikelike electric field occasionally appears poleward of the aurora but usually not associated with a pair of fac sheets in the eastern bulge magnetic field data show complicated fac distributions which correspond to current segments and filamentary currents

magnetostratigraphic dating of hominoid bearing sediments at zhupeng yuanmou basin southwestern china abstract the hominoid fossils found in the yuanmou basin southwestern china are among the key fossils for understanding the evolution of early hominoids in eastern asia and their relationship with coeval hominoids in europe and africa however their exact ages have not yet been well determined we provide a new high resolution magnetostratigraphy for the zhupeng profile which is one of the fossil bearing type sections in the region based on magnetostratigraphy of 227 remanent directions together with the age of micromammalian fauna indicate that the hominoid bearing layer is dated within polarity chron 3br 2r or 3br 1r i e within the interval 7 43 7 38 ma or 7 34 7 17 ma this unambiguously indicates that the yuanmou hominoid has a late miocene age which therefore makes it the youngest hominoid found in eurasia it is possible that the yuanmou basin provided a refuge for hominoids during a time of major environmental changes

magnetochronological sequence of the early pleistocene gigantopithecus faunas in chongzuo guangxi southern china abstract the gigantopithecus fauna the most important mammalian fauna during the early pleistocene in southern china was usually excavated from cave or fissure deposits without precise age constraints here we present new magnetostratigraphy results for four cave sedimentary sequences in chongzuo guangxi zhuang autonomous region of southern china from the highest and oldest to the lowest and youngest including baikong cave juyuan cave sanhe cave and queque cave magnetite was identified as the major carrier of characteristic remnant magnetizations in the cave deposits correlation to the geomagnetic polarity time scale was achieved by combining magnetostratigraphic and biochronologic data our correlation suggests that the cave sedimentary sequences span from the pre olduvai matuyama chron to the jaramillo subchron the combined magneto biochronology leads to the establishment of a chronological framework for the early pleistocene gigantopithecus faunas in chongzuo area the gigantopithecus faunal succession of early pleistocene were assigned to estimated ages of 2 0 ma baikong cave 1 8 ma juyuan cave 1 2 ma sanhe cave and 1 0 ma queque cave respectively the river incision rate in chongzuo area during this time span was estimated to be 14 mm ky

timing of the last glaciation and subsequent deglaciation in the ruby mountains great basin usa abstract the timing of the last pleistocene glaciation in western north america is becoming increasingly well understood largely due to improved methods of obtaining numerical ages of glacial deposits and landforms among these cosmogenic radionuclide surface exposure dating has been widely applied to moraines of mountain glaciers providing the framework for understanding terrestrial climate change during and since the last glaciation in western north america during the late pleistocene the great basin of the western united states hosted numerous mountain glaciers the deposits of which can provide valuable records of past climate changes if their ages can be precisely determined in this study twenty nine cosmogenic radionuclide 10be surface exposure ages from a suite of moraines in seitz canyon western ruby mountains limit the timing of the last glacial episode in the interior great basin known as the angel lake glaciation results indicate that deposition of a terminal moraine and two recessional moraines began just prior to 20 5 ka and continued until 20 0 ka retreat from the next younger recessional moraine began at 17 2 ka and final deglaciation began at 14 8 ka these ages are broadly consistent with cosmogenic surface exposure ages from the eastern sierra nevada and the western wasatch mountains in the western and eastern extremes of the great basin respectively furthermore these ages suggest that the valley glacier in seitz canyon was at or near its maximum extent before and during the hydrologic maxima of pleistocene lakes in the great basin supporting previous suggestions that a cool and wet climate persisted in this region during the early part of the last glacial interglacial transition

calibration of cosmogenic 36cl production rates from ca and k spallation in lava flows from mt etna 38 n italy and payun matru 36 s argentina abstract published cosmogenic 36cl production rates from ca and k spallation differ by almost a factor of 2 in this paper we determine production rates of 36cl from ca and k in samples of known age containing little cl ca rich plagioclases and k feldspars were separated from a total of 13 samples collected on the surfaces of four basaltic lava flows at mt etna 38 n italy and from a trachyte lava flow at payun matru volcano 36 s argentina eruption ages determined by independent methods range between 0 4 and 32 ka sample site elevations range between 500 and 2500 m corresponding scaling factors were calculated using five different published scaling models four of which consider paleo geomagnetic field variations integrated over the exposure durations the resulting five data sets were then analyzed using a bayesian statistical model that incorporates the major inherent uncertainties in a consistent way spallation production rates from ca and k considering all major uncertainties are 42 2 4 8 atoms 36cl g ca 1 a 1 and 124 9 8 1 atoms 36cl g k 1 a 1 normalized to sea level and high latitude using the scaling method of stone 2000 scaling models that account for paleo geomagnetic intensity changes yield very similar mean values at most 4 if the uncertainties in the independent ages are neglected in the bayesian model the calculated element specific production rates would be about 12 higher our results are in agreement with previous production rate estimations both for ca and k if only low cl i e 20 ppm samples are considered

the winter midlatitude arctic interaction effects of north atlantic sst and high latitude blocking on arctic sea ice and eurasian cooling in this paper the effects of eurasian circulation patterns such as high latitude european blocking heb and ural blocking ub events on winter sea ice concentration sic in the barents kara seas bks and eurasian cooling is examined to differentiate the different roles of heb and ub in association with positive north atlantic oscillation nao events a particular focus is on the sic variability resulting from the effect of sea surface temperature sst near the gulf stream extension gse region through to the position change of eurasian blocking it is found that the sst shows a dipole pattern with a positive negative anomaly to the south north of the gse while the high sst in bks plays a major role in the bks sic decline the strengthening of north atlantic westerly winds associated with the sst dipole tends to promote long lived ub and heb events associated with nao to further reduce the bks sic while heb and ub depend on the prior bks warming and ub requires stronger north atlantic westerly winds than heb during ub warm moist air from the gse can reach the bks to enhance downward infrared radiation ir via increased northward transport produced by the nao ub relay the downward ir is weak during heb as the moisture is transported mainly into the western part of bks even though the nao heb relay still operates thus ub leads to more pronounced bks sea ice declines than under heb although the latter still significantly contributes to the sic loss it is also found that the central eastern asian cooling occurring during ub is related to an intense widespread sic decline in bks prior to the ub onset whereas the european cooling during heb is linked to a small sic decline in the western part of bks

analysis of the warmest arctic winter 2015 2016 december through february 2015 2016 defines the warmest winter season over the arctic in the observational record positive 2 m temperature anomalies were focused over regions of reduced sea ice cover in the kara and barents seas and southwestern alaska a third region is found over the ice covered central arctic ocean the period is marked by a strong synoptic pattern which produced melting temperatures in close proximity to the north pole in late december and anomalous high pressure near the taymyr peninsula atmospheric teleconnections from the atlantic contributed to warming over eurasian high latitude land surfaces and el nino related teleconnections explain warming over southwestern alaska and british columbia while warm anomalies over the central arctic are associated with physical processes including the presence of enhanced atmospheric water vapor and an increased downwelling longwave radiative flux preconditioning of sea ice conditions by warm temperatures affected the ensuing spring extent

thin ice and storms sea ice deformation from buoy arrays deployed during n ice2015 arctic sea ice has displayed significant thinning as well as an increase in drift speed in recent years taken together this suggests an associated rise in sea ice deformation rate a winter and spring expedition to the sea ice covered region north of svalbard the norwegian young sea ice2015 expedition n ice2015 gave an opportunity to deploy extensive buoy arrays and to monitor the deformation of the first year and second year ice now common in the majority of the arctic basin during the 5 month long expedition the ice cover underwent several strong deformation events including a powerful storm in early february that damaged the ice cover irreversibly the values of total deformation measured during n ice2015 exceed previously measured values in the arctic basin at similar scales at 100 km scale n ice2015 values averaged above 0 1 d 1 compared to rates of 0 08 d 1 or less for previous buoy arrays the exponent of the power law between the deformation length scale and total deformation developed over the season from 0 37 to 0 54 with an abrupt increase immediately after the early february storm indicating a weakened ice cover with more free drift of the sea ice floes our results point to a general increase in deformation associated with the younger and thinner arctic sea ice and to a potentially destructive role of winter storms

relation of substorm pre onset arc to large scale field aligned current distribution 1 substorm auroral onset often occurs along a pre existing arc that is associated with an enhanced upward field aligned current fac to determine the location of the upward fac of the pre onset arc relative to the large scale region 1 r1 and 2 r2 facs we present coordinated observations of the themis all sky imagers and champ satellite where champ passed over relatively stable pre onset arcs within the 30 min period before substorm auroral onset we found that the upward fac corresponding to the pre onset arc is latitudinally separated from the upward r1 fac within the onset mlt range in contrast the arc is located near the r1 r2 boundary to the west and east of the onset mlt range this mlt dependence suggests that an east west oriented upward fac sheet forms within the downward r2 fac as a precursor fac signature for substorm auroral onset

combining cosmogenic stratigraphic and paleomagnetic information using a bayesian approach general results and an application to sterkfontein abstract in geochronology it is increasingly common to apply several methods to a set of samples the task then arises of combining different types of data with perhaps qualitatively different types of uncertainty into a coherent age estimate which makes optimum use of the available information in this paper we discuss a method which uses bayesian reasoning to combine radiometric stratigraphic and paleomagnetic information when dating sediment layers after presenting a general formulation we derive an analytic formula for the probability distribution of the age of a sediment layer we then apply this methodology to refine previous cosmogenic nuclide burial dating results for the age of a sediment layer containing a hominin fossil at sterkfontein south africa

the role of moist intrusions in winter arctic warming and sea ice decline abstractthis paper examines the trajectories followed by intense intrusions of moist air into the arctic polar region during autumn and winter and their impact on local temperature and sea ice concentration it is found that the vertical structure of the warming associated with moist intrusions is bottom amplified corresponding to a transition of local conditions from a cold clear state with a strong inversion to a warm opaque state with a weaker inversion in the marginal sea ice zone of the barents sea the passage of an intrusion also causes a retreat of the ice margin which persists for many days after the intrusion has passed the authors find that there is a positive trend in the number of intrusion events crossing 70 n during december and january that can explain roughly 45 of the surface air temperature and 30 of the sea ice concentration trends observed in the barents sea during the past two decades

recent changes in arctic sea ice melt onset freezeup and melt season length 1 in order to explore changes and trends in the timing of arctic sea ice melt onset and freezeup and therefore melt season length we developed a method that obtains this information directly from satellite passive microwave data creating a consistent data set from 1979 through present we furthermore distinguish between early melt the first day of the year when melt is detected and the first day of continuous melt a similar distinction is made for the freezeup using this method we analyze trends in melt onset and freezeup for 10 different arctic regions in all regions except for the sea of okhotsk which shows a very slight and statistically insignificant positive trend 0 4 d decade 1 trends in melt onset are negative i e toward earlier melt the trends range from 1 0 d decade 1 for the bering sea to 7 3 d decade 1 for the east greenland sea except for the sea of okhotsk all areas also show a trend toward later autumn freeze onset the chukchi beaufort seas and laptev east siberian seas observe the strongest trends with 7 d decade 1 for the entire arctic the melt season length has increased by about 20 days over the last 30 years largest trends of over 10 d decade 1 are seen for hudson bay the east greenland sea the laptev east siberian seas and the chukchi beaufort seas those trends are statistically significant at the 99 level

reconstructing the history of sediment deposition in caves a case study from wonderwerk cave south africa we applied cosmogenic isotope burial dating magnetostratigraphy and grain size distribution analysis to elucidate the history of the sedimentary sequence composed of fine quartz sands and silts of wonderwerk cave located on the southern edge of the kalahari desert south africa the source for the quartz sand is the kalahari sand dunes presently located 100 km to the north of the cave field observations and grain size analysis suggest a sediment transport scenario that includes eolian transport of kalahari sand abraded to a size of 70 100 m to the kuruman hills temporary storage on the hill slopes and valleys surrounding wonderwerk cave and later transport and deposition inside the cave our results suggest simple burial ages for sediments from both the front and back of the cave that range between 2 63 0 17 ma and 1 56 0 10 ma following initial exposure of 310 620 k y however 26 al 10 be ratios of 3 98 0 24 and 4 08 0 22 measured in a sand sample collected from the surface outside the cave may imply an initial burial signal equivalent to 0 78 0 15 ma thus reducing the possible age range of the buried samples to between 1 85 0 23 and 0 78 0 18 ma the paleomagnetic results for the front of the cave gave a polarity sequence of n r n n where n indicates normal polarity and r indicates reverse polarity this sequence can be correlated with both the older and younger cosmogenic burial age ranges the correlation suggests that in the cave front cosmogenic burial ages and the acquisition of stable remanent magnetization were not significantly affected by chemical and physical processes and that postburial production of cosmogenic isotopes was insignificant in contrast at the back of the cave the paleomagnetic polarity sequence of r n cannot be correlated with the cosmogenic burial ages since the temporal gap between the initial penetration of the sediment into the cave and the final acquisition of a stable remanent magnetization may have been long 10 5 yr and the single polarity transition can be correlated to any reverse normal transition that occurred during the quaternary this highlights the need for caution when cosmogenic burial ages and paleomagnetic sequences are compared the buried sediments in wonderwerk cave show similar grain size distributions to the fine sand sediment presently exposed at the surface in the vicinity of the cave furthermore calculated preburial 10 be concentrations for the buried sediment are similar to those measured in sediment outside the cave these similarities suggest that the environmental conditions and rates of geomorphic processes that persisted during sand deposition in wonderwerk cave during the late pliocene and early pleistocene may have been similar to those currently experienced in the southern kalahari the kuruman hills and the western ghaap plain these conditions favor the transport of fine grained quartz sand to the vicinity of the cave

interdecadal variability of the warm arctic and cold eurasia pattern and its north atlantic origin abstractthis study investigates the origin of the interdecadal variability in the warm arctic and cold eurasia wace pattern which is defined as the second empirical orthogonal function of surface air temperature sat variability over eurasian continent in northern winter by analyzing the twentieth century reanalysis dataset while previous studies highlight recent enhancement of the wace pattern ascribing it to anthropogenic warming we found that the wace pattern has experienced a seemingly periodic interdecadal variation over the twentieth century this long term variation in the eurasian sat is attributable to the altered coupling between the siberian high sh and intraseasonal rossby wave emanating from the north atlantic as the local wave branch interacts with the sh and consequentially enhances the continental temperature perturbation it is further identified that these atmospheric circulation changes in eurasia are largely controlled by the decadal amplitude modulation of the climatological

vertical thermodynamic structure of the troposphere during the norwegian young sea ice expedition n ice2015 the norwegian young sea ice n ice2015 expedition was designed to investigate the atmosphere snow ice ocean interactions in the young and thin sea ice regime north of svalbard radiosondes were launched twice daily during the expedition from january to june 2015 here we use these upper air measurements to study the multiple cyclonic events observed during n ice2015 with respect to changes in the vertical thermodynamic structure moisture content and boundary layer characteristics we provide statistics of temperature inversion characteristics static stability and boundary layer extent during winter when radiative cooling is most effective we find the strongest impact of synoptic cyclones changes to thermodynamic characteristics of the boundary layer are associated with transitions between the radiatively clear and opaque atmospheric states in spring radiative fluxes warm the surface leading to lifted temperature inversions and a statically unstable boundary layer further we compare the n ice2015 static stability distributions to corresponding profiles from era interim reanalysis from the closest land station in the arctic north atlantic sector ny alesund and to soundings from the sheba expedition 1997 1998 we find similar stability characteristics for n ice2015 and sheba throughout the troposphere despite differences in location sea ice thickness and snow cover for ny alesund we observe similar characteristics above 1000 m while the topography and ice free fjord surrounding ny alesund generate great differences below the long term radiosonde record 1993 2014 from ny alesund indicates that during the n ice2015 spring period temperatures were close to the climatological mean while the lowest 3000 m were 1 3 c warmer than the climatology during winter

meteorological conditions in a thinner arctic sea ice regime from winter to summer during the norwegian young sea ice expedition n ice2015 atmospheric measurements were made over arctic sea ice north of svalbard from winter to early summer january june 2015 during the norwegian young sea ice n ice2015 expedition these measurements which are available publicly represent a comprehensive meteorological data set covering the seasonal transition in the arctic basin over the new thinner sea ice regime winter was characterized by a succession of storms that produced short lived less than 48 h temperature increases of 20 to 30 k at the surface these storms were driven by the hemispheric scale circulation pattern with a large meridional component of the polar jet stream steering north atlantic storms into the high arctic nonstorm periods during winter were characterized by strong surface temperature inversions due to strong radiative cooling radiatively clear state the strength and depth of these inversions were similar to those during the surface heat budget of the arctic ocean sheba campaign in contrast atmospheric profiles during the opaquely cloudy state were different to those from sheba due to differences in the synoptic conditions and location within the ice pack storm events observed during spring summer were the result of synoptic systems located in the barents sea and the arctic basin rather than passing directly over n ice2015 these synoptic systems were driven by a large scale circulation pattern typical of recent years with an arctic dipole pattern developing during june surface temperatures became near constant 0 c on 1 june marking the beginning of summer atmospheric profiles during the spring and early summer show persistent lifted temperature and moisture inversions that are indicative of clouds and cloud processes

a multi disciplinary seriation of early homo and paranthropus bearing palaeocaves in southern africa abstract fossils of early homo and paranthropus have been recovered from several sites in southern africa unfortunately their precise age has historically been difficult to assess hampering the reconstruction of their relationships to each other and to fossils from eastern africa multi dating strategies combining biochronological archaeological palaeomagnetic electron spin resonance esr and uranium series techniques are now clarifying their age the following sequencing of sites is suggested swartkrans member 1 2 0 ma gondolin 1 8 ma kromdraai 1 8 1 7 ma sterkfontein m5a 1 8 1 4 ma swartkrans m2 1 7 1 1 ma sterkfontein m5b 1 4 1 1 ma sterkfontein m5c 1 3 0 8 ma swartkrans m3 1 0 0 6 ma the position of coopers d and drimolen is difficult to access because they only have faunal age ranges 1 9 1 6 ma esr suggests mixing is a potential major problem in multi generational sites the oldest southern african representatives of early homo and paranthropus occur around 2 1 1 9 ma in swartkrans member 1 and are recorded almost continuously in the palaeocave deposits until around 1 0 0 6 ma in swartkrans member 3 currently these data suggest that paranthropus and homo first occur significantly later in the southern african record than the eastern african record moreover paranthropus persists much later in southern africa than in eastern africa

rossby wave propagation from the arctic into the midlatitudes does it arise from in situ latent heating or a trans arctic wave train abstractthe relationship between latent heating over the greenland barents and kara seas gbks hereafter and rossby wave propagation between the arctic and midlatitudes is investigated using glo

lower pliocene hominid remains from sterkfontein cosmogenic aluminum 26 and beryllium 10 burial dates of low lying fossiliferous breccia in the caves at sterkfontein south africa show that associated hominid fossils accumulated in the lower pliocene these dates indicate that the skeleton stw 573 and newly discovered specimens from jacovec cavern have much the same age approximately 4 million years these specimens are thus of an age similar to australopithecus anamensis from east africa

contemporary flowstone development links early hominin bearing cave deposits in south africa abstract the cradle of humankind cave sites in south africa preserve fossil evidence of four early hominin taxa australopithecus africanus australopithecus sediba paranthropus robustus and early homo in order to integrate this record into a pan african scenario of human evolutionary history it is critical to have reliable dates and temporal ranges for the southern african hominins in the past a lack of precise and accurate chronological data has prevented the evaluation of the temporal relationships between the various sites here we report new uranium lead u pb radiometric ages obtained from sheets of calcium carbonate flowstone inter bedded between clastic cave sediments at the site of swartkrans providing bracketing ages for the fossiliferous deposits the fossil bearing units of swartkrans specifically the hanging remnant and lower bank of member 1 are underlain by flowstone layers dated to 2 25 0 05 ma and 2 25 0 08 ma and capped by layers of 1 8 0 01 ma and 1 7 0 07 ma the age bracket of the member 1 deposits is therefore between 2 31 and 1 64 ma however by combining the u pb with biostratigraphic data we suggest that this can be narrowed down to between 1 9 and 1 8 ma these data can be compared with other recently dated sites and a radiometrically dated u pb age sequence formed sterkfontein member 4 swartkrans member 1 malapa and cooper s d from this new u pb dataset a pattern of contemporary flowstone development emerges with different caves recording the same flowstone forming event specifically overlapping flowstone formation takes place at swartkrans and sterkfontein at 2 29 ma and 1 77 ma and at sterkfontein and malapa at 2 02 ma this suggests a regional control over the nature and timing of speleothem development in cave deposits and these flowstone layers could assist in future correlation both internal to specific deposits and regionally between sites

bayesian methods applied to the interpretation of multiple osl dates high precision sediment ages from old scatness broch excavations shetland isles in this paper we illustrate the ways in which bayesian statistical techniques may be used to enhance chronological resolution when applied to a series of osl sediment dates such application can achieve an optimal chronological model by incorporating stratigraphic and age information the application to luminescence data is not straightforward owing to the sources of uncertainty in each date and here we present one solution to overcoming these difficulties and introduce the concept of unshared systematic errors using osl sediment dates from the site of old scatness broch shetland isles uk many measured with a high degree of precision we illustrate some of the ways in which bayesian techniques may be applied as a tool for assessing systematic errors when combined with independent chronological information and to determine the optimum chronological information for specific events and contexts we provide a detailed procedure for the application of bayesian methods to osl dates using the widely available radiocarbon calibration programme oxcal

an isochron method for cosmogenic nuclide dating of buried soils and sediments we describe an improved method for dating buried paleosols using measurements of the cosmic ray produced radionuclides 10be and 26al in quartz grains and apply it to a sequence of intercalated tills and paleosols in central missouri usa that record plio pleistocene advances of the laurentide ice sheet a buried paleosol implies a period of surface exposure and nuclide accumulation followed by burial and a halt to nuclide production if the paleosol is formed in a sedimentary unit such as till this unit may also have been emplaced with unknown 26al and 10be concentrations inherited from past surface exposure if the inherited nuclide concentrations are the same at all depths in the soil as is true for well mixed sediments such as till then the 26al and 10be concentrations at different depths in the paleosol will show a linear relationship the slope of this line depends on the duration of burial of the paleosol but not on the inherited nuclide concentrations or on the sample depths thus one can date strata overlying buried paleosols by measuring 26al and 10be at multiple depths in the paleosol and calculating the burial age of the paleosol from the resulting isochron we focus on applying this approach to till paleosol sequences but the basic idea of forming an 26al 10be burial isochron with a set of samples that share the same burial age but differ in other aspects of their exposure history applies to other stratigraphic settings as well the method yields ages for four tills in missouri that are stratigraphically consistent agree with paleomagnetic age constraints and show that ice advanced into missouri near 1 25 ma near 0 8 ma and twice between ca 0 4 and 0 2 ma

modulation of atmospheric rivers near alaska and the u s west coast by northeast pacific height anomalies atmospheric rivers ars can cause wide ranging impacts upon landfall at high northern latitudes but comparatively little is known about the dynamics supporting these ars in contrast to their mid latitude counterparts here ars near the u s west coast and the gulf of alaska during 1979 2015 are compared ars are found to occur in both regions with similar frequency but with different seasonality composited atmospheric conditions from the nasa modern era retrospective analysis for research and applications merra dataset reveal that a broad height anomaly over the northeast pacific is influential to ar activity in both regions when a positive height anomaly exists over the northeast pacific ar activity is often deflected poleward toward alaska while the u s west coast experiences a decrease in ar activity the opposing relationship also applies that is ar activity is decreased near alaska and increased along the u s west coast in the presence of a negative height anomaly quantitatively nearly 79 of gulf of alaska ars are associated with a positive northeast pacific height anomaly and 86 of u s west coast ars are associated with a negative anomaly results suggest that this relationship applies across a range of time scales to include subseasonal and interannual not just with respect to individual transient waves both ars and height anomalies are found to be associated with rossby wave breaking thereby dynamically linking ar activity with broader north pacific dynamics

critical role of snow on sea ice growth in the atlantic sector of the arctic ocean during the norwegian young sea ice n ice2015 campaign in early 2015 a deep snow pack was observed almost double the climatology for the region north of svalbard there were significant amounts of snow ice in second year ice syi while much less in first year ice fyi here we use a 1 d snow ice thermodynamic model forced with reanalyses to show that snow ice contributes to thickness growth of syi in absence of any bottom growth due to the thick snow growth of fyi is tightly controlled by the timing of growth onset relative to precipitation events a later growth onset can be favorable for fyi growth due to less snow accumulation which limits snow ice formation we surmise these findings are related to a phenomenon in the atlantic sector of the arctic where frequent storm events bring heavy precipitation during autumn and winter in a region with a thinning ice cover

the convection electric field in auroral substorms dynamics explorer 2 de 2 electric field and ion drift data are used in a statistical study of the ionospheric convection electric field in bulge type auroral substorms thirty one individual de 2 substorm crossings were carefully selected and organized by the use of global auroral images obtained by de 1 the selected passes which occurred during substorm expansion phase maximum or early recovery phase cover the entire nighttime substorm the organization of the data used the method developed by fujii et al 1994 which divided the data into six local time sectors covering the nighttime substorm region following the procedures employed in the paper by gjerloev and hoffman 2000b the latitudinal width and location of each auroral oval crossing was then adjusted to fit the sector average in addition to the detailed study of the characteristics of the field within each sector this database enabled us to compile a model of the ionospheric convection electric field the characteristics of the premidnight convection reversal show a pronounced local time dependency far west of the surge it is a fairly well defined point reversal or convection shear approaching the surge and within the surge it is a region of weak electric fields increasing in width toward midnight that separates regions of equatorward and poleward electric fields therefore we adopt the term harang region rather than the harang discontinuity for the premidnight convection reversal a relatively narrow convection channel is coincident with the highest conductances located just poleward of the harang region this channel drives the substorm current wedge component of the westward electrojet in the surge and middle surge sectors it is present in all premidnight passes and consequently is an integral part of the three dimensional substorm current wedge system

magnetostratigraphy of cave sediments wyandotte ridge crawford county indiana towards a regional correlation abstract the polarity of 42 sediment samples obtained from 21 sites in wyandotte cave and five smaller satellite caves in wyandotte ridge southern indiana is used as a basis for a magnetostratigraphic correlation with sediments in mammoth cave kentucky sediments in caves at elevations between 137 and 162 m have a normal polarity but the fill between 168 and 171 m exhibits a polarity reversal the reversal is interpreted to represent the most recent polarity change suggesting that the upper level of wyandotte cave was last active at about the same time not less than 0 78 ma as the c level in mammoth cave which lies at approximately the same elevation the local base level control in both cave systems is provided by tributaries of the ohio river thus the correlation is most likely a consequence of the contemporaneous abandonment of upper level passages in wyandotte and mammoth caves during the early pleistocene reconstruction of the ohio river drainage sediments in caves between 236 and 241 m have a normal polarity the fill in these little wildcat and galley door caves is probably at least 2 6 ma old it appears to correlate with the residuum that delimits the upper mitchell plain surface the pennyroyal plateau in kentucky and on the basis of our interpretation of the magnetostratigraphy is older than the fill in the highest a and b levels in mammoth cave

auroral arc and oval electrodynamics in the harang region 1 auroral arcs are typically described in terms of an upward field aligned current fac sheet above the arc connected by ionospheric pedersen current to a downward fac sheet near the arc on the basis of data measured by the fast spacecraft conjugate with ground optical observations we present first a wide and stable winter evening arc where this standard model does not apply the arc is observed in the harang region during the growth phase of a modest substorm poleward of the convection reversal cr boundary although the magnetic field data suggest the typical configuration the two fac sheets appear to be decoupled near the satellite footprint the upward fac is fed by the westward electrojet wej while the downward fac feeds the eastward electrojet eej the examination of the arc by the newly developed aladyn technique confirms this peculiar current topology for comparison we apply aladyn also to a second evening arc located within the harang region equatorward from the cr the arc is confirmed to have the standard configuration consistent with a former study but substantial fac ej coupling is inferred in the auroral oval both poleward and equatorward of the arc a key element for the topology of the current closure is the westward component of the electric field which influences the relative location of the cr with respect to the large scale fac reversal fr boundary as proved by tests on synthetic data a westward component of the electric field pushes the cr toward the fr preventing thus the standard fac closure while the conductance and fac pattern shape the cr profile since a westward electric field is often measured in the harang region the fac ej coupling is expected to be an essential ingredient there this has important implications for the current closure in the equatorial magnetosphere and for the auroral current circuit in the wej region closely related to the substorm process

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

magnetostratigraphy of sediments in mammoth cave kentucky clastic sediment deposits found within the caves of mammoth cave national park have yielded a magnetostratigraphic pattern of magnetic polarity reversals which indicates that they were deposited over a range of at least 1 million and most likely 2 million years

arctic lower tropospheric warm and cold extremes horizontal and vertical transport diabatic processes and linkage to synoptic circulation features abstractthe thermodynamic processes and synoptic circulation features driving lower tropospheric temperature extremes in the high arctic 80 n are investigated based on 10 day kinematic backward

sea ice loss and arctic cyclone activity from 1979 to 2014 abstractextensive summer sea ice loss has occurred within the beaufort chukchi east siberian and laptev seas over the last decade associated anomalies in sensible and latent heat fluxes in autumn have increased arctic atmospheric precipitable water and air temperatures with the potential to impact autumn and winter cyclone activity to examine if a connection exists between recent arctic sea ice loss and cyclone activity several cyclone metrics from 60 to 90 n are analyzed results show that following years with less september sea ice there is a subsequent increase in moisture availability regional baroclinicity and changes in vertical stability that favor cyclogenesis however tracking of individual cyclones indicates no coherent increase in cyclone frequency or intensity associated with sea ice loss furthermore no robust northward progression of extreme cyclones is observed

new cosmogenic burial ages for sterkfontein member 2 australopithecus and member 5 oldowan the cave infills at sterkfontein contain one of the richest assemblages of australopithecus fossils in the world including the nearly complete skeleton stw 573 little foot in its lower section as well as early stone tools in higher sections however the chronology of the site remains controversial owing to the complex history of cave infilling much of the existing chronology based on uranium lead dating and palaeomagnetic stratigraphy has recently been called into question by the recognition that dated flowstones fill cavities formed within previously cemented breccias and therefore do not form a stratigraphic sequence earlier dating with cosmogenic nuclides suffered a high degree of uncertainty and has been questioned on grounds of sediment reworking here we use isochron burial dating with cosmogenic aluminium 26 and beryllium 10 to show that the breccia containing stw 573 did not undergo significant reworking and that it was deposited 3 67 0 16 million years ago far earlier than the 2 2 million year flowstones found within it the skeleton is thus coeval with early australopithecus afarensis in eastern africa we also date the earliest stone tools at sterkfontein to 2 18 0 21 million years ago placing them in the oldowan at a time similar to that found elsewhere in south africa at swartkans and wonderwerk

comparison of freeboard retrieval and ice thickness calculation from als asiras and cryosat 2 in the norwegian arctic to field measurements made during the n ice2015 expedition we present freeboard measurements from airborne laser scanner als the airborne synthetic aperture and interferometric radar altimeter system asiras and cryosat 2 siral radar altimeter ice thickness measurements from both helicopter borne and ground based electromagnetic sounding and point measurements of ice properties this case study was carried out in april 2015 during the n ice2015 expedition in the area of the arctic ocean north of svalbard the region is represented by deep snow up to 1 12 m and a widespread presence of negative freeboards the main scattering surfaces from both cryosat 2 and asiras are shown to be closer to the snow freeboard obtained by als than to the ice freeboard measured in situ this case study documents the complexity of freeboard retrievals from radar altimetry we show that even under cold below 15 c conditions the radar freeboard can be close to the snow freeboard on a regional scale of tens of kilometers we derived a modal sea ice thickness for the study region from cryosat 2 of 3 9 m compared to measured total thickness 1 7 m resulting in an overestimation of sea ice thickness on the order of a factor 2 our results also highlight the importance of year to year regional scale information about the depth and density of the snowpack as this influences the sea ice freeboard the radar penetration and is a key component of the hydrostatic balance equations used to convert radar freeboard to sea ice thickness

dating sediment burial with in situ produced cosmogenic nuclides theory techniques and limitations abstract dating sediment burial over million year time scales is crucial in many areas of the earth sciences and archeology but is often difficult using traditional techniques sediment burial can be dated by the radioactive decay of cosmogenic nuclides provided that the sediment was exposed to cosmic rays prior to burial dating calculations are straightforward if sediment is buried deeply and rapidly enough to prevent cosmogenic nuclide production after burial however the analysis can be complicated by postburial production if sediment is insufficiently shielded from secondary cosmic ray nucleons and muons this paper discusses how buried sediments can be dated over timescales up to 5 myr using 26 al and 10 be in quartz

superposed epoch analysis of the ionospheric convection evolution during substorms imf by dependence we present superposed epoch analyses of the average ionospheric convection response in the northern and southern hemispheres to magnetospheric substorms occurring under different orientations of the interplanetary magnetic field imf observations of the ionospheric convection were provided by the super dual auroral radar network superdarn and substorms were identified using the far ultraviolet fuv instrument on board the imager for magnetopause to aurora global exploration image spacecraft we find that during the substorm growth phase the expected imf by dependent dawn dusk asymmetry is observed over the entire convection pattern but that during the expansion phase this asymmetry is retained only in the polar cap and dayside auroral zone in the nightside auroral zone the convection is reordered according to the local substorm electrodynamics with any remaining dusk dawn asymmetry being more closely related to the magnetic local time of substorm onset itself only weakly governed by imf by owing to the preponderance of substorms occurring just prior to magnetic midnight the substorm asymmetry tends to be an azimuthal extension of the dusk convection cell across the midnight sector a manifestation of the so called harang discontinuity this results in the northern southern hemisphere nightside auroral convection during substorms generally resembling the expected pattern for negative positive imf by when the preexisting convection pattern in the northern southern hemisphere is driven by positive negative imf by the nightside auroral convection changes markedly over the course of the substorm to establish this same harang configuration

u pb dating of fossil enamel from the swartkrans pleistocene hominid site south africa abstract we demonstrate that young fossil enamel older than the range of the u series 300 ka can be dated by the u pb methods using new models of u and pb loss and uptake contrary to the current hypothesis of u uptake that only considers the adsorption diffusion mechanism we here develop a complete time dependent model which takes gains and losses of the most critical nuclides 238u 234u and 230th into account both during chemical dissolved u and physical th and u recoil processes lead is assumed to be a mixture between two components of common pb and a radiogenic component the proportions of these components are calculated from the pb isotope abundances and u pb ratios we apply this new u pb method to bovid enamel from the swartkrans cave gauteng province south africa this cave has yielded abundant early pleistocene hominid remains attributed to paranthropus and homo as well as various associated archaeological vestiges biochronological comparisons with east africa have provided age estimates ranging between 1 8 and 1 0 ma which however remain poorly constrained after correction for initial 234u disequilibrium and further 238u loss the u and pb isotope data yield ages of 1 83 1 38 1 36 0 29 and 0 83 0 21 ma for the three stratigraphic units members 1 2 and 3 respectively we discuss the consequences of these radiometric results for hominid evolution in south africa

thin sea ice thick snow and widespread negative freeboard observed during n ice2015 north of svalbard in recent years sea ice conditions in the arctic ocean changed substantially toward a younger and thinner sea ice cover to capture the scope of these changes and identify the differences between individual regions in situ observations from expeditions are a valuable data source we present a continuous time series of in situ measurements from the n ice2015 expedition from january to june 2015 in the arctic basin north of svalbard comprising snow buoy and ice mass balance buoy data and local and regional data gained from electromagnetic induction em surveys and snow probe measurements from four distinct drifts the observed mean snow depth of 0 53 m for april to early june is 73 above the average value of 0 30 m from historical and recent observations in this region covering the years 1955 2017 the modal total ice and snow thicknesses of 1 6 and 1 7 m measured with ground based em and airborne em measurements in april may and june 2015 respectively lie below the values ranging from 1 8 to 2 7 m reported in historical observations from the same region and time of year the thick snow cover slows thermodynamic growth of the underlying sea ice in combination with a thin sea ice cover this leads to an imbalance between snow and ice thickness which causes widespread negative freeboard with subsequent flooding and a potential for snow ice formation with certainty 29 of randomly located drill holes on level ice had negative freeboard

effects of an explosive polar cyclone crossing the antarctic marginal ice zone antarctic sea ice shows a large degree of regional variability which is partly driven by severe weather events here we bring a new perspective on synoptic sea ice changes by presenting the first

comparison of u th paleomagnetism and cosmogenic burial methods for dating caves implications for landscape evolution studies caves are useful in landscape evolution studies because they often mark the level of previous water tables and when dated yield incision rates dating caves is problematic however because their ages are only constrained by the oldest deposits contained within which may be far younger than the cave itself we dated cave deposits in the sierra nevada using u th dating of speleothems paleomagnetic dating of fine sediment and cosmogenic 26 al 10 be burial dating of coarse sediment the sampled caves formed sequentially as the water table lowered providing an important stratigraphic test for the dating methods large discrepancies between deposit ages from similar cave levels demonstrate that even when accurately determined deposit ages can seriously underestimate the timing of cave development drip type speleothems are most prone to this minimum age bias because they can accumulate long after caves form and because the u th method is limited to 400 ka paleomagnetic dating requires correlation with the global reversal chronology and is hindered by a lack of continuous stratigraphy the fine sediment analyzed for paleomagnetism is also highly susceptible to remobilization and deposition in cave passages well above base level cosmogenic 26 al 10 be dates bedload material deposited when caves were at or very near river level and can date material as old as 5 ma in the sierra nevada speleothem u th ages and sediment burial ages from the same cave levels differ by as much as an order of magnitude these results suggest speleothem ages alone may significantly underestimate cave ages