an early ecosystem of archean tidal microbial mats moodies group south africa ca 3 2 ga abundant microbial mats from the mesoarchean moodies group barberton greenstone belt south africa ca 3 2 ga are densely interbedded with coarse grained and gravelly sandstones in a nearly mud free setting they apparently grew in marginal marine and possibly subaerial coastal and tidal environments characteristic sedimentary structures include anastomosing bedding gas or fluid escape structures sand volcanoes biomat doming patchy silicified microstromatolites and microbial sand chip conglomerates they indicate rapid growth of mechanically tough microbial mats possibly aided by early seafloor silicification in a high energy high sedimentation rate environment the observations expand the knowledge of the habitat of archean microbial mats and life on early earth if tidal environments were more widespread in the archean than today biomats in extensive intertidal settings may have contributed to immobilize large volumes of sand

evidence for cavity dwelling microbial life in 3 22 ga tidal deposits cavities are considered plausible and favorable habitats for life on early earth in such microenvironments organisms may have found an adequate protection against the intense ultraviolet radiation that characterized the archean ozone free atmosphere however while there is clear evidence that benthic life existed in the paleoarchean the oldest traces of cavity dwelling microbes coelobionts have been found in neoarchean rocks here we present the results of a detailed investigation of early silicified cavities occurring in the oldest well preserved siliciclastic tidal deposits the 3 22 ga moodies group of the barberton greenstone belt south africa downward growing microstromatolitic columns composed of kerogenous laminae are commonly present in planar bedding parallel now silica filled cavities that formed in sediments of the peritidal zone in situ 13cpdb pdb peedee belemnite measurements of the kerogen range from 32 3 to 21 3 and are consistent with a biogenic origin scanning electron microscopy analysis of the silicified cavities shows well preserved chains of cell sized molds that are interpreted as fossil filamentous microorganisms the geological context the morphology of the microstromatolites the 13c composition of the kerogen and the presence of microfossils all suggest that a microbial community inhabited the cavities these results extend the geological record of coelobionts by 500 m y supporting the view that cavities were among the first ecological niches to have been occupied by early microorganisms

preservation and detection of microstructural and taxonomic correlations in the carbon isotopic compositions of individual precambrian microfossils abstract here we present techniques for and new data from in situ carbon isotope 13c analysis of precambrian permineralized microscopic fossils with a reproducibility of 1 2 using secondary ion mass spectrometry sims individual microfossils selected for their excellent preservation were analyzed in petrographic thin sections of stromatolitic cherts from the proterozoic gunflint 1880 ma bitter springs 830 ma min yar 740 ma and chichkan 775 ma formations the range of 13c values 34 6 to 22 1 vpdb among the 46 individuals analyzed falls within that expected for photoautotrophic carbon fixation by ribulose bisphosphate carboxylase rubisco consistent with morphology based taxonomic assignments for these specimens microfossils classified as cyanobacteria from the gunflint bitter springs and min yar formations for which published carbonate carbon isotope data can be used to estimate the 13c of the original dissolved inorganic carbon substrate exhibit a consistent 19 total fractionation 13c of dissolved inorganic carbon 13c of biomass similar to that observed in living cyanobacteria over a wide range of 13ccarb values 2 9 to 3 4 in stromatolitic chert of the min yar formation morphologically diverse microfossils preserved in a 1 mm2 part of a microbial mat exhibit systematic isotopic differences among and within taxa that correlate with their morphologically inferred biological affinities and suggest that isotopic signatures of their original biosynthetic processes e g lipid and peptidoglycan synthesis are preserved isotopic offsets consistent with the different rubisco based fractionations typical of cyanobacteria and photosynthetic eukaryotes are documented by the differing 13c values of a colonial cyanobacterium 22 6 0 5 and a phytoplanktonic protistan acritarch 28 9 1 0 situated

doppler profiler and radar observations of boundary layer variability during the landfall of tropical storm gabrielle abstract detailed observations of boundary layer structure were acquired on 14 september 2001 prior to and during the landfall of tropical storm gabrielle the mobile integrated profiling system mips and the shared mobile atmospheric research and teaching radar smart r were collocated at the western florida coastline near venice very close to the wind center at landfall prior to landfall the boundary layer was rendered weakly stable by a long period of evaporational cooling and mesoscale downdrafts within extensive stratiform precipitation that started 18 h before landfall the cool air mass was expansive with an area within the 23 c surface isotherm of about 50 000 km2 east northeasterly surface flow transported this cool air off the west coast of florida toward the convergent warm core of the gabrielle and promoted the development of shallow warm and cold fronts that were prominent during the landfall phase airflow properties of the boundary layer around the coastal zone are examined using

revised magnetostratigraphy of the plio pleistocene sedimentary sequence of the olduvai formation tanzania abstract the magnetic stratigraphy of the plio pleistocene sedimentary formation of the olduvai gorge tanzania which contains a well known series of prehistoric pebble cultures and hominid remains has been reinvestigated sixty one sites were sampled along 90 metres of stratigraphic section extending from the base of bed i into the masek beds palaeo and rock magnetic analyses reveal that magnetizations are stable carried by low coercivity magnetic minerals titano magnetites and are likely to be of depositional origin a revised magnetostratigraphic scale is proposed the base of the major normal magnetozone n1 interpreted as the olduvai sub chron lies ca 6 m below tuff ia i e significantly below the previously defined position this revision associated to 40ar 39ar ages recently determined on the tuffs of bed i supports the validity of the astronomical calibration of the geomagnetic polarity time scale for the olduvai sub chron the correlation of the normal magnetozone n2 with jaramillo or jaramillo cobb mountain is suggested by the discovery of a reverse magnetozone r3 in the uppermost part of the pleistocene sequence masek beds and implies that the fossiliferous sequence of the olduvai formation was entirely deposited before the brunhes matuyama boundary

an anaerobic 3400 ma shallow water microbial consortium presumptive evidence of earth s paleoarchean anoxic atmosphere abstract a microbial consortium preserved in shallow water carbonaceous chert of the paleoarchean 3400 ma strelley pool formation pilbara craton northwestern western australia is composed of copiously abundant globular cobweb like swirls of randomly oriented filaments intermingled with laterally extensive flat laminated masses of subparallel filaments the shallow water possibly mudflat like habitat of the biocoenose is established by its geological setting and intimately intermixed association with millimetric quartz radiating laths and rosettes interpreted to be pseudomorphs after evaporitic gypsum anhydrite the indigenousness and syngenicity of the permineralized fossils to the encompassing chert their uncompacted minimally altered life like spatial distribution and their biogenicity and bacterial affinity are shown by optical microscopic raman spectroscopic and confocal laser scanning microscopic analyses in situ that document the mineralogy of their embedding matrix and their cylindrical filamentous morphology cellularity and kerogenous composition by comparison with mid precambrian and modern sulfur cycling ecosystems and consistent with sulfur isotopic data and their intimate co existence with copious microgranular pyrite and pseudomorphs evidently after sulfate the swirled aggregates are interpreted to be anaerobic sulfuretums in contrast the intermixed flat laminated components like microbes of fossil and modern stromatolitic mat communities are interpreted to be co occurring light requiring phototrophs whether such phototrophs were anoxygenic photosynthesizers like extant photosynthetic bacteria e g chloroflexaleans or facultatively anaerobic cyanobacteria cf oscillatoria limnetica their anoxygenic metabolism seems plausibly established given its great age shallow water habitat and anaerobic microaerophilic physiology this evidently first reported occurrence from the fossil record of anoxygenic phototrophs and of a microbial sulfuretum phototroph consortium is consistent with the supposition that earth s paleoarchean environment was essentially anoxic and suggests that o2 producing photosynthesis may have been a later evolutionary innovation

downdrafts and the evolution of boundary layer thermodynamics in hurricane earl 2010 before and during rapid intensification abstractusing a combination of noaa p 3 aircraft tail doppler radar noaa and nasa dropsondes and buoy and drifter based sea surface temperature data different types of downdrafts and their infl

dating recent hawaiian lava flows using paleomagnetic secular variation hawaiian paleomagnetic secular variation sv is defined from samples at 67 sites on lava flows of known age paleomagnetic directions range through 40 of inclination and 30 of declination angular dispersion within sites is commonly dating precision is limited by dispersion of 4 5 among sites of apparently similar age the main dispersion sources are in 14 c dates 3 0 intra flow deformations 2 0 and local magnetic anomalies 1 5 results from 68 sites on undated flows show that 95 of kilauea9s surface is younger than 1 000 yr a hiatus in volcano growth 1 000 1 500 yr ago coincides with the filling of a large caldera averaging of available data yields an sv reference curve which is fairly reliable to 1 500 yr ago contains gaps and ambiguities 1 500 3 000 yr ago and remains highly uncertain 3 000 6 000 yr ago the sv dating method can be precise but is limited by the need for a calibrated sv history it can be a powerful correlation tool even if a history is unavailable

geochemical and sedimentological control of the magnetic properties of hemipelagic sediments owing to their high sedimentation rates and wide areal extent hemipelagic sediments along continental borderlands are potentially important high resolution recorders of geomagnetic secular variation to assess this possibility we studied suboxic hemipelagic muds from the oregon continental slope and anoxic laminated diatomaceous oozes from the gulf of california these sediments were rapidly deposited with average sedimentation rates of 121 and 135 cm kyr respectively bulk sediment sedimentological and geochemical analyses indicate that the two areas represent contrasting depositional regimes the remanence in both environments resides in fine grained magnetite particles although minor amounts of hematite were observed in the topmost gulf of california sediments despite first order differences the sediments from both areas show similar downcore patterns of systematic increases in solid sulfur mainly as pyrite dramatic decreases in natural nrm anhysteretic and isothermal remanent magnetization intensities and accompanying shifts in the magnetic stabilities these changes are consistent with reduction and dissolution of the ferrimagnetic iron oxides with depth due to early diagenesis of organic matter the magnetic grain size distribution first appears to rapidly coarsen downcore as the smallest and most abundant grains are removed then slowly grows finer as the remaining particles dissolve no evidence was observed for authigenic formation of magnetite provided sufficient concentration and stability of the detrital magnetic particles paleomagnetic directions can survive this dissolution diagenesis however relative paleointensity determinations based on normalization of nrm by concentration in related parameters will give erroneous estimates of paleofield behavior in such diagenetically altered sediments

timing of deposition and deformation of the moodies group barberton greenstone belt south africa very high resolution of archaean surface processes abstract thin and largely discontinuous volcanic tuff beds in the alluvial fluvial and marginal marine siliciclastic strata of the middle archaean moodies group barberton greenstone belt bgb contain rare to abundant zircon dating of magmatic zircon grains from five tuff beds and one cross cutting dike yield ages which span the entire spectrum of bgb history from ca 3550 ma to 3215 ma and show variable degrees of post depositional alteration until ca 2500 ma the youngest pristine zircon grains in all tuff samples analyzed by ca id tims chemical abrasion ion dissolution thermal ion mass spectrometry yield upper intercept and concordia ages between 3227 6 0 3 and 3216 0 3 ma and those grains analyzed by la sf icp ms laser ablation sector field inductively coupled plasma mass spectrometry and shrimp sensitive high resolution ion microprobe yield ages between 3228 9 and 3214 9 ma most of these ages are either identical within error or significantly older than a ca id tims age of 3223 4 0 3 ma obtained from zircon grains of a tuff horizon of the schoongezicht formation at the top of the underlying fig tree group we interpret this age to mark the time of volcanic eruption whereas the significantly older and overlapping ages of the stratigraphically higher moodies tuff zircon grains point either to a high degree of magmatic inheritance and or a detrital contribution from surrounding sedimentary rocks during or after ash tuff deposition the minimum age for deposition of moodies group sediments and deformation is provided by a la icp ms zircon u pb age of 3219 9 ma obtained from an undeformed felsic dike which crosscuts folded moodies strata this age overlaps with a precise ca id tims u pb zircon age of 3216 0 0 3 ma obtained from a tuff horizon of the upper moodies group overall the new age data collectively imply that the up to 3 7 km thick sandstone dominated moodies group was deposited and deformed within

a late quaternary geomagnetic secular variation record from lake waiau hawaii and the question of the pacific nondipole low a continuous paleomagnetic record for the last 13 000 years was obtained from the sediments of lake waiau located near the summit of mauna kea volcano on the island of hawaii the secular variation sv of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector the hypothesis that there has been anomalously low geomagnetic sv in the central pacific was tested using angular dispersion analysis the inclination record has a mean value of 27 that is much lower than the 35 predicted by the geocentric axial dipole hypothesis the spectrum obtained from spectral analysis shows major inclination peaks at periodicities of approximately 3600 and 7900 years and major declination peaks at periodicities of approximately 1100 2000 3300 and 7800 years the approximately 8000 and 3500 year periodicities shown in both inclination and declination spectrums may represent the dipole and nondipole variation respectively the approximately 1100 and 2000 year periodicities are probably derived from either the sources that affect declination only or the offsets between the core sections in addition bauer plots of the magnetic vector are dominated by clockwise motion the angular dispersion calculated from lake sediments is 5 9 with respect to the mean virtual geomagnetic pole vgp and 9 1 with respect to the geographic pole both values are much lower than the 13 5 expected from paleosecular variation model g which separates the angular dispersion into components from the dipole and the quadruple families our results support the hypothesis that an anomalously low secular variation is a characteristic feature of the central pacific furthermore this geomagnetic behavior persists on time scales of 104 years regional anomalies in temperature topography or electrical conductivity at the core mantle boundary are inferred to cause the low sv

evidence for microbial life in synsedimentary cavities from 2 75 ga terrestrial environments fluviolacustrine sediments of the 2 75 ga hardey formation fortescue group australia preserve pendant columnar structures with stromatolitic lamination within synsedimentary cavities the millimeter sized finger like columns strongly resemble microbialites from modern basaltic caves and indicate the likely presence of microbial biofilms the ancient microbial columns are preserved by chert and locally occur as reworked clasts indicating a near depositional age for the structures sulfur isotopic analysis of pyrite in the columns and adjacent carbonaceous matrix yields 34scdt cdt canyon diablo troilite values between 8 5 and 19 showing significant fractionation characteristic of biological cycling of sulfur organic matter in cavity ceilings and shale matrix has 13cpdb pdb peedee belemnite values between 55 and 43 suggesting the presence of methanotrophs our results suggest that 2 75 ga terrestrial environments supported a microbial ecosystem including microbes that inhabited synsedimentary hollows extending the fossil record of coelobionts by 1 5 b y subsurface cavities represent a new habitable microenvironment for early life on earth and an analogue for ancient life on mars

global geomagnetic field models for the past 3000 years transient or permanent flux lobes psvmod1 0 is a compilation of globally distributed palaeodirectional data from archaeomagnetic artefacts lava flows and lake sediments at 24 sites evaluated at 100 year intervals from 1000 bc to ad 1800 we estimate uncertainty in these measures of declination and inclination by comparison with predictions from standard historical models in time intervals of overlap and use the 100 year samples and their associated uncertainties to construct a sequence of minimum structure global geomagnetic field models global predictions of radial magnetic field at the coremantle boundary cmb as well as inclination and declination anomalies at the earth9s surface provide an unprecedented view of geomagnetic secular variations over the past 3000 years and demonstrate a consistent evolution of the field with time resolution of the models is poorest in the southern hemisphere where only six of the 24 sites are located several with incomplete temporal coverage low flux regions seen in the historical field near the north pole are poorly resolved but the northern hemisphere flux lobes are clearly visible in the models these lobes are not fixed in position and intensity but they only rarely venture into the pacific hemisphere the pacific region is seen to have experienced significant secular variation a strong negative inclination anomaly in the region like that seen in 0 5 ma models persists from 1000 bc until ad 1000 and then gradually evolves into the smaller positive anomaly seen today on average between 1000 bc and ad 1800 the non axial dipole contribution to the radial magnetic field at the core mantle boundary is largest in the north central pacific and beneath central asia with clear non zonal contributions at the earth9s surface average inclination anomalies are large and negative in the central pacific and most positive slightly to the east of central africa inclination anomalies decrease with increasing latitude average declinations are smallest in equatorial regions again with strong longitudinal variations largest negative departures are centred over australia and eastern asia secular variation at the earth9s surface is quantified by standard deviation of inclination and declination about their average values and at the cmb by standard deviation in radial magnetic field all three show significant geographical variations but appear incompatible with the idea that secular variation in the pacific hemisphere is permanently attenuated by greatly enhanced conductivity in d 00 beneath the region

paleomagnetism of late quaternary marine sediments from santa catalina basin california continental borderland paleomagnetic secular variation psv records have been recovered from three marine sediment cores from santa catalina basin california continental borderland in order to more accurately date these late quaternary sediments the psv records are not high in resolution due to low sedimentation rates coupled with a 3 cm sampling interval and some inherent smoothing of the psv signal during remanence lock in however the psv waveforms are sufficiently clear to permit their correlation among the three separate cores these psv records can also be correlated with four independent psv calibration curves from western north america that have detailed radiocarbon age control the four calibration curves are developed in this paper to improve the dating and regional comparison of psv records from western north america the psv correlations establish time depth curves for the three cores which indicate that the sediments are all younger than about 11 000 years b p the relative accuracy of the time depth curves is approximately 200 years which represents an order of magnitude improvement in the chronology of these sediments sedimentation rates derived from the three time depth curves indicate a constant rate of 20 25 cm kyr for the last 6700 years throughout santa catalina basin and more variable rates but constant within each core of 13 86 cm kyr prior to 6700 years b p in all three cores the change in sedimentation rate corresponds to a subtle but distinct change in lithology these changes probably indicate a major shift in paleoceanographic processes within santa catalina basin 6700 years b p

a 10 000 year high resolution diatom record from pilkington bay lake victoria east africa a new diatom record from lake victoria s pilkington bay subsampled at 21 to 25 year intervals and supported by 20 ams dates reveals a 10 000 calendar year environmental history that is supported by published diatom and pollen data from two nearby sites with their chronologies adjusted here to account for newly documented ancient carbon effects in the lake these three records provide a coherent finely resolved reconstruction of holocene climate change in equatorial east africa after an insolation induced rainfall maximum ca 8800 8300 cal yr b p precipitation became more seasonal and decreased abruptly ca 8200 and 5700 yr b p in apparent association with northern deglaciation events century scale rainfall increases occurred ca 8500 7000 5800 and 4000 yr b p conditions after 2700 yr b p were generally similar to those of today but major droughts occurred ca 1200 600 yr b p during europe s medieval warm period

the boundary layer dynamics of tropical cyclone rainbands abstractspiral bands are ubiquitous features in tropical cyclones and significantly affect boundary layer thermodynamics yet knowledge of their boundary layer dynamics is lacking prompted by rece

the time averaged geomagnetic field as recorded by lava flows over the past 5 myr summary a recently compiled lava flow data base spanning the last 5 million years is used to investigate properties of the time averaged geomagnetic field more than 90 per cent of the power in the palaeofield can be accounted for by a geocentric axial dipole however there are significant second order structures in the field declination and inclination anomalies for the new data base indicate that the main second order signal is the far sided effect and there is also evidence for non zonal structure vgp virtual geomagnetic pole latitude distributions indicate that over the last 5 million years normal and reverse polarity morphologies are different and that any changes in the normal polarity field morphology are undetectable given the present data distribution regularized non linear inversions of the palaeomagnetic directions support all these observations we test the hypothesis that zonal models for the time averaged field are adequate to describe the data and find that they are not non zonal models are needed to fit the data to within the required tolerance level normal and reverse polarity field models obtained are significantly different field models obtained for the brunhes epoch data alone are much smoother than those obtained from combining all the normal polarity data simulations indicate that these differences can be explained by the less extensive data distribution for the brunhes epoch the field model for all of the normal polarity data ln1 contains features observed in the historical field maps although the details differ ln1 suggests that although the two northern hemisphere flux lobes observed in the historical field are stationary to a first order approximation they do show changes in position and amplitude a third less pronounced flux lobe is observed in ln1 over central europe the lack of structure in the southern hemisphere is due in part to the paucity of data jackknife estimates of the field models for different subsets of the data suggest that a few sites contribute significant structure to the final field models more conservative estimates of the time averaged field morphology are obtained by removing these sites

detection of silica mediated dissolution of magnetic grains in sediments using forc diagrams 1 recently silica mediated dissolution has been recognized as a potentially important factor influencing magnetic studies of marine and lacustrine sediments although direct evidence for the dissolution of magnetic particles in silica rich environments is lacking the process is expected to produce changes in the magnetic grain size distribution a hypothesis that is tested in this study on sediments from lake tanganyika east africa using first order reversal curves forcs results from different magnetic intensity zones within the studied samples clearly show changes in the grain size distribution of magnetic minerals in particular zones with high biogenic silica content bsi correlated with depletion in fine grained magnetic material whereas zones with lower bsi showed no depletion these results are consistent with the idea that silica mediated dissolution results in the preferential removal of fine grained magnetic material and indicate that forc diagrams are effective in characterizing silica mediated dissolution in sediments

concentric eyewall asymmetries in hurricane gonzalo 2014 observed by airborne radar abstracttwo eyewall replacement cycles were observed in hurricane gonzalo by the noaa p3 tail ta radar and the recently developed nasa high altitude imaging wind and rain airborne profiler hiwrap radar these observations captured detailed precipitation and kinematic features of gonzalo s concentric eyewalls both before and after the outer eyewall s winds became the vortex maximum winds the data were analyzed relative to the deep layer environmental wind shear vector during the beginning eyewall replacement cycle stages the inner and outer eyewalls exhibited different asymmetries the inner eyewall asymmetry exhibited significant low level inflow updrafts and positive tangential acceleration in the downshear quadrants consistent with observational and theoretical studies the outer eyewall asymmetry exhibited these features in the left of shear quadrants further downwind from those of the inner eyewall it is suggested that the low level inflow occurring at the outer but not at the inner eyewal

uranium irradiation history of carbonado diamond implications for paleoarchean oxidation in the sao francisco craton carbonado is a porous polycrystalline diamond rock found in central african and brazilian placer deposits it contains unsupported radiogenic isotopes of he ne kr xe and pb here we show that these and the radiation related defects introduced to the diamond structure are a result of uranium precipitation with no isotopic or spectroscopic evidence of th enrichment the daughter products are unsupported due to proterozoic u remobilization combining existing carbonado pb isotope data with recent studies of the geochronology of the tectonic evolution of the sao francisco craton eastern south america reveals that the most likely scenario is paleoarchean uranium enrichment of carbonado followed by mesoproterozoic uranium dissolution under all possible scenarios the carbonado radiation damage history requires u mobilization in the mesoarchean or late paleoarchean this is consistent with recent studies of south africa and india mesoarchean paleosols which also show evidence for local oxygen activity greater than that of the archean atmosphere and ocean while those studies rely on whole rock trace element and transition metal stable isotope measurements this combination of crystallographic defects sedimentary geochronology and radiogenic isotopes supports the same conclusions of nonmarine near surface archean oxygen enhancement

morphological adaptations of 3 22 ga old tufted microbial mats to archean coastal habitats moodies group barberton greenstone belt south africa microbial life was well established and widespread by the paleoarchean however the degree of evolutionary advancement such as microbial motility intra and inter species interactions phototropism or oxygenic photosynthesis by that time remains highly debated the 3 22 ga moodies group in the barberton greenstone belt bgb south africa are earth s oldest well preserved siliciclastic tidal deposits they exhibit a unique assemblage of microbial mats providing an excellent opportunity to decipher the morphological adaptations of microbial communities to different paleoenvironmental settings the fossil mats are preserved as kerogenous laminations 0 5 1 mm thick that can be traced laterally for 15 km in a 1000 m thick succession of fine to coarse grained tidal sandstones and conglomerates we here present a detailed stratigraphic and depositional facies analysis documenting the association of the three principal mat morphotypes with specific environmental settings 1 planar type in coastal floodplain 2 wavy type in intertidal and 3 tufted type in upper inter to supratidal facies all mat types indicate a flourishing phototrophic biota moreover the tufted morphology suggests an intricate level of coordinated growth commonly known from cyanobacterial mats in modern environments

full vector paleomagnetic secular variation records from latest quaternary sediments of lake malawi 10 0 s 34 3 e abstract we have conducted a paleomagnetic study of late quaternary sediments from lake malawi east africa in order to develop a high resolution record of paleomagnetic secular variation psv this study has recovered psv records from two cores 3p 6p in northern lake malawi 10 0 s 34 3 e the psv appears to be recorded in fine grained detrital magnetite titanomagnetite grains detailed af demagnetization of the natural remanence nrm shows that a distinctive characteristic remanence chrm is demagnetized from 20 to 80 mt which decreases simply toward the origin the resulting directional psv records for 3p and 6p are easily correlatable with 29 distinct inclination features and 29 declination features the statistical character of the psv in both cores is consistent with holocene psv noted at other holocene equatorial sites radiocarbon dating of the cores is based on 18 independent radiocarbon dates and four dated stratigraphic horizons that can be correlated into each core the final directional psv time series cover the last 24 000 years with an average sediment accumulation rate of 30 cm kyr we have also developed a relative paleointensity estimate for these psv records based on normalizing the nrm after 20 mt af demagnetization by the sirm after 20 mt af demagnetization changing sedimentation patterns complicate any attempt to develop a single paleointensity record for the entire core lengths we have developed a relative paleointensity record for the last 6000 years that has 14 correlatable features including 5 notable peaks in intensity three of these peaks are synchronous with paleointensity highs farther north in se europe sw asia egypt but two of the peaks are at times of low paleointensity farther north we interpret this to indicate that lake malawi 10 s is at least partly under the influence of a different flux regeneration region of the outer core dynamo a relative paleointensity record was also developed for 11 000 24 000 ybp the general pattern appears to be consistent with other published records but our confidence in the correlations is more limited

low level kinematic thermodynamic and reflectivity fields associated with hurricane bonnie 1998 at landfall during 11 h on 26 august 1998 two noaa wp 3d aircraft deployed 85 global positioning system gps dropwindsondes within 2 of latitude of the circulation center of hurricane bonnie as it made landfall in north carolina about 75 of the sondes successfully collected data which were used to create a series of storm relative horizontal maps of kinematic and thermodynamic variables from 10 m to 2 km reflectivity fields were analyzed from the weather surveillance radar 1988 dopplers wsr 88ds located at wilmington and morehead city north carolina and the tail and lower fuselage radars aboard the wp 3ds gps sonde performance and deployment spacing is adequate to identify several aspects of the vortex these include 1 warm dry stable air in the offshore flow that results in reduced equivalent potential temperatures entering the southern portion of the eyewall 2 cooler air collocated with the upwelled water in the right rear quadrant and under the eyewall and 3 an atypical radial wind pattern with strong inflow southwest of the circulation center and outflow northeast of the center the strongly asymmetric structure found at 10 m becomes much more homogeneous by 2 km altitude no intense rainbands developed over land in the onshore flow nor did the bands in the onshore flow undergo any significant changes once they made landfall beyond the eyewall the offshore flow contained much less precipitation than the onshore portion of the storm characteristics beyond the eyewall appear to have been modulated by the proximity to land but hurricane intensity did not vary the authors infer that the lower energy content of the inflow was offset by the contraction of the eyewall

paleohydrology of lake victoria east africa inferred from 18o 16o ratios in sediment cellulose delta 18 o values of aquatic cellulose preserved in a 7 6 m sediment core from near the center of lake victoria east africa record a 13 000 yr hydrological history of the basin relative to the present value 3 4 highly elevated lake water 18 o values of 8 2 from 13 200 to 7250 14 c yr b p indicate closed basin conditions and precipitation evaporation ratios much smaller than at present an abrupt drop in the lake water 18 o to 0 1 marks the rapid transition to an open basin between 7250 and 7150 14 c yr b p from 7140 to 5400 14 c yr b p increasing lake water 18 o values from 0 1 to 5 1 5 are proposed to reflect outlet downcutting and a likely decrease in relative humidity these data have unexpectedly shifted our view of the timing of changes in the lake victoria water balance and imply a period of at least 10 000 years 17 000 to 7000 14 c yr b p when the lake victoria basin did not contribute waters to the main nile river

the dynamics of boundary layer jets within the tropical cyclone core part i linear theory abstract observations of wind profiles within the tropical cyclone boundary layer have until recently been quite rare the recent massive increase in observations due to the operational implementation of the global positioning system dropwindsonde has emphasised that a low level wind speed maximum is a common feature of the tropical cyclone boundary layer here is proposed a mechanism for producing such a maximum whereby strong inward advection of angular momentum generates the supergradient flow the processes that maintain the necessary inflow against the outward acceleration resulting from gradient wind imbalance are identified as being i vertical diffusion ii vertical advection and iii horizontal advection two complementary tools are used to diagnose the properties and dynamics of the jet the first presented here is a linear analytical model of the boundary layer flow in a translating tropical cyclone it is an extension of the classical ekman boundary layer model as well as of earlier w

eastern australian geomagnetic field intensity over the past 14000 yr summary two north eastern australian volcanic crater lake cores have been used to obtain relative intensity estimates for the geomagnetic field arm imparted in a low dc bias field has been used as a normalizing parameter the intensity fluctuations in the two lakes are in excellent agreement with each other and with south eastern australian archaeointensity data over their coeval time spans this strongly suggests that the same sources are influencing the geomagnetic secular variation throughout eastern australia at this time the relative intensity records go back to about 14000yr bp thereby extending currently available recent australian intensity records by some 7000 yr

late pleistocene desiccation of lake victoria and rapid evolution of cichlid fishes lake victoria is the largest lake in africa and harbors more than 300 endemic species of haplochromine cichlid fish seismic reflection profiles and piston cores show that the lake not only was at a low stand but dried up completely during the late pleistocene before 12 400 carbon 14 years before the present these results imply that the rate of speciation of cichlid fish in this tropical lake has been extremely rapid

genesis of large siliceous stromatolites at frying pan lake waimangu geothermal field north island new zealand lilypad stromatolites up to 3 m long and 1ae5 m wide were found to be actively growing in the shallow marginal waters of frying pan lake and its outflow channel these stromatolites composed of phormidium 90 fischerella and a variety of other microbes develop through a series of distinct growth stages dark green microbial mats cover the floor of the outflow channel and give rise to columns of various sizes and shapes in the shallower marginal waters once the columns reach the water level the mats spread laterally to form a lilypad stromatolite the lilypads are characterized by a raised dark green rim 4 5 mm high that encircles a flat interior covered with a distinctive orange red mat the microbes forming the columns and lilypad plate are being actively silicified the stromatolites are formed of i flat lying phormidium filaments p laminae ii upright filaments of phormidium that are commonly associated with fischerella u laminae and iii mucus diatoms and pyrite framboids m laminae p laminae dominate most of the columns with tripartite cycles of p u to m laminae being found mostly in the upper parts of the stromatolites the transition from the p to u laminae is marked by a change in the growth pattern of the phormidium and branching of fischerella which was probably triggered by a change in environmental conditions in the frying pan lake outflow channel this change may be related to fluctuations in water level and flow rates that are caused by periods of heavy rain seasonal changes long term variations in rainfall and or the unique 40 day hydrological cycle that exists between frying pan lake and inferno crater which is a nearby hydrothermal crater lake

the kinematic structure of a hurricane with sea level pressure less than 900 mb abstract a national oceanic and atmospheric administration aircraft recorded the first doppler radar data in a tropical cyclone with a minimum sea level pressure mslp 50 m s 1 extended to 12 km higher than has been reported in previous hurricanes the inner eyewall contained weak

reassessment of lake victoria upper nile river paleohydrology from oxygen isotope records of lake sediment cellulose reconstruction of lake water 1 8 o from analysis of cellulose 1 8 o in two sediment cores from lake victoria east africa shows a large shift to lower values during the terminal pleistocene this shift records the transition from closed to open basin conditions following desiccation at the last glacial maximum although oxygen isotope analysis of cellulose from one core had placed this overflow at 8 ka 7200 1 4 c yr b p reevaluation of the age model for this core in addition to new stratigraphic and chronological evidence from a second core suggests that basin overflow was established much earlier ca 13 ka our refined view of the timing of lake victoria overflow inferred from the oxygen isotope records is consistent with other paleolimnological studies indicating that lake sediment cellulose is an effective and sensitive isotopic archive of major hydrologic events in this region

intensity and structure changes during hurricane eyewall replacement cycles abstracta flight level aircraft dataset consisting of 79 atlantic basin hurricanes from 1977 to 2007 was used to develop an unprecedented climatology of inner core intensity and structure changes associated with eyewall replacement cycles ercs during an erc the inner core structure was found to undergo dramatic changes that result in an intensity oscillation and rapid broadening of the wind field concentrated temporal sampling by reconnaissance aircraft in 14 of the 79 hurricanes captured virtually the entire evolution of 24 erc events the analysis of this large dataset extends the phenomenological paradigm of ercs described in previous observational case studies by identifying and exploring three distinct phases of ercs intensification weakening and reintensification in general hurricanes intensify sometimes rapidly when outer wind maxima are first encountered by aircraft the mean locations of the inner and outer wind maximum at the start of an erc are 35 and 106 km from storm center respe

why is the tropical cyclone boundary layer not well mixed abstractplausible diagnostics for the top of the tropical cyclone boundary layer include i the top of the layer of strong frictional inflow and ii the top of the well mixed layer that is the layer over which potential temperature is approximately constant observations show that these two candidate definitions give markedly different results in practice with the inflow layer being roughly twice the depth of the layer of nearly constant here the authors will present an analysis of the thermodynamics of the tropical cyclone boundary layer derived from an axisymmetric model the authors show that the marked dry static stability in the upper part of the inflow layer is due largely to diabatic effects the radial wind varies strongly with height and therefore so does radial advection of this process also stabilizes the boundary layer but to a lesser degree than diabatic effects the authors also show that this differential radial advection contributes to the observed superadiabatic layer ad

palaeomagnetic study of the holocene and upper pleistocene sediments from lake barombi mbo cameroun first results abstract the analyses of the stable deposition and post depositional remanent magnetization carried by the lacustrine sediments contained in a 24 m sequence collected from the bottom of the maar lake barombi mbo cameroun yield well defined declination and inclination oscillations which can be attributed to palaeosecular variations of the local geomagnetic field the transformation to a time scale based on the interpolation and extrapolation of 14 c ages allows comparison of this record with contemporaneous records obtained in other parts of the world the successive inclination peaks can be individually identified with those found in western europe in spite of small chronological discrepancies which are in the range of the standard deviation of the ages normalization of the nrms by anhysteretic magnetization provides a profile of relative palaeointensities which shows similarities with that reconstructed from the same time interval in a sequence from western europe although an important phase shift appears

hells bells unique speleothems from the yucatan peninsula mexico generated under highly specific subaquatic conditions abstract we here report on a type of meter sized pendant speleothem growing under water in the submerged el zapote sinkhole cenote west of puerto morelos on the mexican yucatan peninsula these conical mantle shaped downward expanding and diverging calcareous structures here termed as hells bells are yet unreported in the scientific literature they are characterized by bell or trumpet shaped longitudinal and circular elliptical or horse shoe like horizontal cross sections hells bells grow downward based on the downward divergence of the structures and the horizontally laminated internal texture of both blade shaped spar calcite and microspar laminae age dating confirms that hells bells are young

sm nd rb sr pb pb dating of carbonates from the early archaean barberton greenstone belt south africa evidence for post depositional isotopic resetting at low temperature abstract two silicic carbonate sequences occurring in the onverwacht group og and the overlying fig tree group ftg of the early archaean barberton greenstone belt south africa contain silicified dolomites with primary structures and textures they occur with volcanic rocks dated by single zircons the associated onverwacht felsic volcanics have an age of 3440 3416 ma whereas the fig tree volcanics are 3225 ma old therefore the depositional age of both sequences is between 3440 and 3225 ma pb isotopic data for different parts of a single og whole rock sample form a linear array corresponding to a pb pb age of 2632 99 ma sm nd and rb sr isotopes were analysed in four whole rock samples of the ftg silicified carbonates and form an sm nd array corresponding to an age of 2612 84 ma with initial end 8 1 0 5 and an rb sr array of 2743 36 ma with initial 87 sr 86 sr 0 7013 0 0003 these whole rock samples have rb sr ratios of 1 and unusually high rb concentrations for carbonates 100 ppm which derive from processes accompanying silicification all three isotopic systems of whole rocks indicate ages of 2 7 ga much younger than the depositional age of the successions the agreement provides strong evidence that an alteration event reset all of the isotopic systems sm nd as well as rb sr and u pb we suggest that the ages represent the timing of silicification and sericitization of the carbonates by large scale fluid movement at an apparent temperature of 200 c

the time averaged paleomagnetic field 0 5 ma persistent departures from the geocentric axial dipole field model of the time averaged paleomagnetic field over the past 5 myr have been analyzed using oceanic data from deep sea cores and continental data from igneous rocks and sediments the data set comprises the equivalent of 9490 spot readings of the field 5831 normal and 3659 reverse from 930 groups of data variations in declination anomalies between groups of data strongly suggest the existence of second order tectonic effects small rotations that make it difficult if not impossible to identify any nonzonal terms that might exist inclination anomalies have therefore been modeled in terms of low degree zonal harmonics the calculated inclination anomalies within 10 latitude bands are widely scattered for both oceanic and continental data and do not appear to have been drawn from distributions with common means we attribute this large scatter to previously undetected or uncorrected second order tectonic effects in the continental data or in the oceanic data to small departures from the vertical in deep sea cores if it is assumed that these effects are random between groups of data and without a systematic bias they can be averaged out to a large extent if there are sufficient numbers of groups within each latitude band this method also has the major advantage that it maximizes time averaging of the field when this is done an acceptable fit to the inclination anomaly data is found using a zonal harmonic model although the point estimates for the reverse polarity zonal quadrupole term are consistently larger than those for the normal polarity zonal quadrupole term the difference is not significant and is likely due to contamination effects this finding is true for a combination of all the data or for separate combinations of continental igneous rocks and ocean sediments this conclusion differs from all previous analyses the major differences occur in model estimates of the zonal octupole term the estimates varying widely depending on the particular data combination we show that false octupole terms can be introduced by several factors including inclination errors in sediments and lavas the use of unit vectors in the analyses and incomplete magnetic cleaning particularly of reversely magnetized rocks thus we cannot impute a geomagnetic significance to the estimates of a zonal octupole term we suggest that the best estimates for the zonal quadrupole g2 g20 g10 are obtained from the combined brunhes age igneous rocks and oceanic normal data 0 033 0 019 and for the combined matuyama age igneous rocks and oceanic reverse data 0 042 0 022 when these two sets are combined the overall best estimate of g2 is 0 038 0 012

spiral rainbands in a numerical simulation of hurricane bill 2009 part i structures and comparisons to observations abstractthis study examines spiral rainbands in a numerical simulation of hurricane bill 2009 this paper the first part of the study evaluates the structures of spiral rainbands and compares them to previous observations four types of spiral rainbands are identified principal secondary distant and inner rainbands principal rainbands tend to be stationary relative to the storm center while secondary rainbands are more transient and move around the storm center both principal and secondary rainbands are tilted radially outward with height and have many of the commonly observed kinematic features such as overturning secondary circulation and enhanced tangential velocity on their radially outward sides principal rainbands are bounded by very dry air on their radially outward sides distant rainbands are radially inward tilting convective features that have dense cold pools near the surface inner rainbands are made of shallow convection that appears to have originated from near the eyewall dif

cryptic coral crinoid hanging gardens from the middle devonian of southern morocco an unusual and exceptionally well preserved cryptic community of cnidarians crinoids sponges and microbes developed in a submarine cavity of middle devonian age in the hamar laghdad area morocco the biota encrusted the cavity roof and grew predominantly in an upside down position forming spectacular hanging gardens the investigated assemblage differs strikingly from both its paleozoic and modern analogues it constitutes one of a very few known examples of fossil cryptic assemblages developed in relatively deep water settings and is the first report of a cryptic paleoecosystem dominated by rugose corals the results support the view that during the middle paleozoic there was no distinct polarization between open surface and cryptic faunas in deep water environments but keen competition for space already existed in devonian cryptic assemblages the regional species pool seems to have been the main determinant of the ecological succession and structure of this cryptic community

carbon isotopic composition of individual precambrian microfossils ion microprobe measurements of carbon isotope ratios were made in 30 specimens representing six fossil genera of microorganisms petrified in stromatolitic chert from the approximately 850 ma bitter springs formation australia and the approximately 2100 ma gunflint formation canada the delta 13c pdb values from individual microfossils of the bitter springs formation ranged from 21 3 1 7 to 31 9 1 2 and the delta 13c pdb values from microfossils of the gunflint formation ranged from 32 4 0 7 to 45 4 1 2 with the exception of two highly 13c depleted gunflint microfossils the results generally yield values consistent with carbon fixation via either the calvin cycle or the acetyl coa pathway however the isotopic results are not consistent with the degree of fractionation expected from either the 3 hydroxypropionate cycle or the reductive tricarboxylic acid cycle suggesting that the microfossils studied did not use either of these pathways for carbon fixation the morphologies of the microfossils suggest an affinity to the cyanobacteria and our carbon isotopic data are consistent with this assignment

atypical thermodynamic profiles in hurricanes the global positioning system dropwindsondes deployed in hurricane bonnie on 26 august 1998 with supporting deployments in hurricanes mitch 1998 and humberto 2001 are used to identify three unusual thermodynamic structures in the lower cloud and subcloud layers two of these structures impact the energy content of the inflow and therefore the intensity of the hurricane first positive lapse rates of equivalent potential temperature are found near the top of the inflow these layers insulate the inflow from the negative impacts of entrainment mixing and promote rapid energy increases especially near the eyewall the second structure is a rapid decrease of equivalent potential temperature adjacent to the sea surface this is essentially a prominent surface layer that owes its existence to both higher moisture content and a superadiabatic lapse rate the steep lapse rate most often occurs under and near the eyewall where wind speeds at the surface exceed hurricane force the author speculates that water loading from spray increases the residence time of air parcels in the surface layer contributing to the creation of this structure the third feature is a moist absolutely unstable layer previously identified by bryan and fritsch for the midlatitudes these layers are found adjacent to the eyewall in rainbands and in the hub cloud within the eye and are evidence of mesoscale or vortex scale convergence and the very modest instabilities often found in the core of a hurricane

palaeomagnetic and 210pb estimates of sedimentation in lake turkana east africa abstract sediment cores from lake turkana preserve a record of the historical geomagnetic secular variation in this part of east africa and therefore can be used to estimate sedimentation rates within the lake the results are supported by estimates based on 210pb measurements in several cores and annual lamination counts in one core and indicate a very high sedimentation rate about 1 cm yr 1 0 2 g cm 2 yr 1 during the last few hundred years a single radiocarbon age from near the base of a 12 m core from the south basin gives an average sedimentation rate of 0 19 cm yr 1 over the last 5600 years we conclude that the present lake and drainage pattern are very young the present day flow of the omo river into the lake is not a permanent feature of the basin and that a high lake level postulated at around 3500 years ago is unlikely though not ruled out the very rapid accumulation rate of sediment and burial of interstitial water in lake turkana provides an excellent opportunity to study the geochemistry of closed basin lake evolution

chronological potential of palaeomagnetic oscillations recorded in late quaternary sediments from lake tanganyika abstract the measurements of depositional and post depositional remanent magnetizations drm and pdrm in two piston cores collected at water depths of 140 m core mpu3 and 422 m core mpu12 in the southern lake tanganvika mpulungu sub basin zambia provide a palaeomagnetic record for south east central africa which spans over the last 25 5 ka ages on a conventional 14c time scale for the most characteristic inclination peaks were estimated by correlating the palaeomagnetic record with the lake barombi mbo cameroon and the western europe secular variation type curves ams 14c ages on total organic matter tom measured in mpu12 core appear to be 2 to 4 ka older in the lower part of the record from ca 25 to 15 ka bp i e during the last arid episode of the late pleistocene these apparent 14c ages exceed pdrm acquisition lagtimes evaluated to be about 800 years at most and also account for residence time of carbon in tom prior to its sedimentation therefore magnetostratigraphic correlations are believed to provide a better overall chronology for the late pleistocene and early holocene changes in lake tanganyika level major drops shown by breaks of deposition in core mpu3 at 1000 cm and 825 cm sub bottom are respectively dated at ca 21 5 ka bp and between 17 and 15 ka bp

depositional and tectonic setting of the archean moodies group barberton greenstone belt south africa the 3 22 3 10 ga old moodies group uppermost unit of the swaziland supergroup in the barberton greenstone belt bgb is the oldest exposed well preserved quartz rich sedimentary sequence on earth it is preserved in structurally separate blocks in a heavily deformed fold and thrust belt north of the inyoka fault moodies strata reach up to 3700 m in thickness detailed mapping correlation of measured sections and systematic analysis of paleocurrents show that the lower moodies group north of the inyoka fault forms a deepening and fining upward sequence from a basal alluvial conglomerate through braided fluvial tidal and deltaic sandstones to offshore sandy shelf deposits the basal conglomerate and overlying fluvial facies were derived from the north and include abundant detritus eroded from underlying fig tree group dacitic volcanic rocks shoreline parallel transport and extensive reworking dominate overlying deltaic tidal and marine facies the lithologies and arrangement of moodies group facies sandstone petrology the unconformable relationship between moodies strata and older deformed rocks presence of at least one syndepositional normal fault and presence of basaltic flow rocks and airfall fall tuffs interbedded with the terrestrial strata collectively suggest that the lower moodies group was deposited in one or more intramontane basins in an extensional setting thinner moodies sections south of the inyoka fault generally less than 1000 m thick may be correlative with the basal moodies group north of the inyoka fault and were probably deposited in separate basins a northerly derived southward thinning fan delta conglomerate in the upper part of the moodies group in the central bgb overlies lower strata with an angular unconformity this and associated upper moodies conglomerates mark the beginning of basin shortening by south to southeast directed thrust faulting along the northern margin of the bgb and suggest that the upper moodies group was deposited in a foreland basin timing orientation and style of shortening suggest that this deformation eventually incorporated most of the bgb into a major fold and thrust belt

a multiscale numerical study of hurricane andrew 1992 part vi small scale inner core structures and wind streaks abstract the objectives of part vi of this series of papers are to a simulate the finescale features of hurricane andrew 1992 using a cloud resolving grid length of 2 km b diagnose the formation of small scale wind streaks and c perform sensitivity experiments of varying surface fluxes on changes in storm inner core structures and intensity as compared to observations and a previous 6 km model run the results show that a higher resolution explicit simulation could produce significant improvements in the structures and evolution of the inner core eyewall and spiral rainbands and in the organization of convection the eyewall becomes much more compact and symmetric with its width decreased by half and the radius of maximum wind is reduced by 10 to 20 km a zone of deep and intense potential vorticity pv is formed at the edge of the eye a ring of maximum pv is collocated in regions of maximum upward motion in the eyewall and interacts strongly with the eyewall convection the convective cor

spectral characteristics of turbulence in the hurricane boundary layer over the ocean between the outer rain bands spectra and cospectra of wind velocity potential temperature and humidity have been analysed using data collected in the atmospheric boundary layer in hurricanes fabian 2003 and isabel 2003 during the coupled boundary layer air sea transfer cblast hurricane experiment the spectra and cospectra are normalized following the surface layer scaling methods according to similarity theory it is found that the cblast data gathered in the mixed layer between the outer rain bands below 400 m can be grouped into well defined curves for spectra of wind velocity potential temperature and humidity and for cospectra of momentum and humidity flux however the cospectra of sensible heat flux do not exhibit well defined universal shape the cblast universal shape spectra and cospectra generally resemble the shapes of those from previous studies but shift to higher frequencies that correspond to smaller wavelengths of turbulent eddies that contain most of the energy this work highlights the structural difference between the hurricane boundary layer and the standard atmospheric boundary layer over land and ocean copyright 2010 royal meteorological society

the dynamic response of the hurricane wind field to spiral rainband heating abstract the response of the hurricane wind field to spiral rainband heating is examined by using a three dimensional nonhydrostatic linear model of the vortex anelastic equations diabatic heat sources which are designed in accordance with previous observations of spiral rainbands are made to rotate with the flow around the hurricane like wind field of a balanced axisymmetric vortex common kinematic features are recovered such as the overturning secondary circulation descending midlevel radial inflow and cyclonically accelerated tangential flow on the radially outward side of spiral rainbands comparison of the responses to the purely convective and stratiform rainbands indicates that the overturning secondary circulation is mostly due to the convective part of the rainband and is stronger in the upwind region while midlevel radial inflow descending to the surface is due to the stratiform characteristics of the rainband and is stronger in the downwind region the secondary horizontal wind maxim

the dynamics of boundary layer jets within the tropical cyclone core part ii nonlinear enhancement abstract observations of wind profiles within the tropical cyclone boundary layer until recently have been quite rare however the recent spate of observations from the gps dropsonde have confirmed that a low level wind speed maximum is a common feature of the tropical cyclone boundary layer in part i a mechanism for producing such a maximum was proposed whereby strong inward advection of angular momentum generates the supergradient flow the processes that maintain the necessary inflow against the outward acceleration due to gradient wind imbalance were identified as being i vertical diffusion ii vertical advection and iii horizontal advection and a linear analytical model of the boundary layer flow in a translating tropical cyclone was presented and used to diagnose the properties of the jet and the near surface flow a significant shortcoming was that the jet was too weak which was argued to be due to the neglect of vertical advection here a high resolution dry hydrostatic numerical

paleomagnetic secular variation records from holocene sediments of lake victoria 0 5 s 33 3 e we have conducted a paleomagnetic study of holocene sediments from lake victoria in order to develop a high resolution record of paleomagnetic secular variation psv this study has recovered psv

microbial life and biogeochemical cycling on land 3 220 million years ago the colonization of emergent continental landmass by microbial life was an evolutionary step of paramount importance in earth history here we report direct fossil evidence for life on land 3 220 million years ago ma in the form of terrestrial microbial mats draping fluvial conglomerates and gravelly sandstones of the moodies group south africa combined field petrographic carbon isotope and raman spectroscopic analyses confirm the synsedimentary origin and biogenicity of these unique fossil mats as well as their fluvial habitat the carbon isotope compositions of organic matter 13corg from these mats define a narrow range centred on 21 in contrast to fossil mats of marine origin from nearby tidal deposits that show 13corg values as low as 34 bulk nitrogen isotope compositions 2 15n 5 are also significantly different from their marine counterparts 0 15n 3 which we interpret as reflecting denitrification in the terrestrial habitat possibly of an atmospheric source of nitrate our results support the antiquity of a thriving terrestrial biosphere during the palaeoarchaean and suggest that a complex and microbially driven redox landscape existed during the deposition of the moodies group with distinct biogeochemical cycling occurring on land by 3 220 ma microbial life colonized the land surface by 3 2 billion years ago forming complex communities distinct from those in nearby marine environments according to analyses of fossilized microbial mats in the moodies group south africa

microfossil assemblage from the 3400ma strelley pool formation in the pilbara craton western australia results form a new locality abstract a new microfossil locality for the ca 3400 ma strelley pool formation spf in the pilbara craton western australia was discovered in the panorama greenstone belt large and morphologically diverse microfossils 20 m up to 100 m along the major dimension are abundant in a carbonaceous laminated black chert of shallow water origin that was originally collected in 2010 and relocated in 2011 just south of the trendall reserve state geoheritage reserve r50149 over 300 small spherical and lenticular flanged and non flanged lenses carbonaceous cellular microfossils are present in each replicated thin section measuring 2 5 cm 3 4 cm in addition film like structures and tubular filaments were discovered narrow carbonaceous filaments of several types are also present in and around the secondary cavity fill cherts although their biogenicity is uncertain colonies of spherical and lenticular structures are often observed colonies composed of small spheroids can be classified into at least two groups based on the sizes of the individuals their mode of clustering is variable ranging from tight to loose and from spherical to random colonies of lenticular structures are often composed of a mixture of flanged and non flanged lenses in addition to those solely composed of either flanged or non flanged lenses the size ranges of these three types are not statistically distinguishable therefore it is currently unknown whether flanged and non flanged lenses represent different species or different life stages of the same species although more research will be needed to establish the taxonomic framework for these ancient microfossils they provide evidence that the coastal region of the 3 4 ga strelley pool sea was inhabited by various microbial communities reflecting the early stage diversification of life on earth

rock magnetic evidence for the dissolution and authigenic growth of magnetic minerals within anoxic marine sediments of the california continental borderland the rock magnetic properties of marine sediments from the california continental borderland san pedro santa catalina and san nicolas basins have been studied in order to quantitatively assess the effects of sediment diagenesis on magnetic minerals previous studies have noted that the natural remanent magnetization in these sediments primarily carried by detrital magnetite decays to 10 or less of its surface value soon after deposition this decrease is caused by magnetite dissolution related to sediment diagenesis and is unrelated to paleoclimatic variations or changes in the regional influx of detrital magnetic material detailed rock magnetic measurements show that shifts to softer remanent coercivity and differences in the rate and degree of magnetic intensity loss with depth can be related to the dissolution process the shift to softer remanent coercivity is related to a coarsening of the magnetic mineral grain sizes with depth due to preferential dissolution of the finest grained magnetic material the intensity decreases which are linearly proportional to magnetite concentration decreases indicate that dissolution occurs with rate constants ranging from 0 3 to 1 6 kyr 1 the rate constants sulfide concentrations and magnetite grain size estimates from the borderland are consistant with previous studies of magnetite dissolution our results demonstrate the importance of both sulfide and magnetite surface area in the dissolution process anomalous peaks in viscous remanence within the sediments suggest the authigenic growth of greigite and its subsequent transformation to pyrite

earliest life on earth evidence from the barberton greenstone belt south africa abstract studies investigating the structure and diversity of earth s record of life older than 3 2 ga are restricted to two locations worldwide in which sedimentary rocks have escaped regional high grade metamorphism and penetrative deformation the pilbara craton of western australia and the barberton greenstone belt in the kaapvaal craton of south africa this paper provides a south african perspective on the evidence of paleoarchean life a record that is often overlooked in the literature it aims to summarize and critically review previously reported claims of early life in the bgb gives an overview of the latest findings and provides an outlook on potential future discoveries the 15 km thick volcanic sedimentary succession making up the barberton supergroup was deposited between 3 55 to ca 3 20 ga and can be subdivided in three stratigraphic units that provide a unique window into a diverse and widespread paleoarchean microbial ecosystem landscape putative biosignatures occur almost throughout the entire bgb stratigraphy and range from carbonaceous cherts containing filamentous spheroidal and lenticular microstructures traces of hydrothermal biofilms photosynthetic microbial mats remnants of pseudocolumnar stromatolites and large organic walled spheroidal microfossils of currently unknown affinity the bgb also contains one of the world s oldest known record of tufted microbial mats which extensively colonized tidally influenced siliciclastic shorelines and were most likely formed by filamentous photosynthesizers other mat associated biosignatures include silicified gas bubbles domes and lenses that likely formed due to metabolic activity or the decay of buried organic matter some of these subsurface voids beneath the cohesive mats were inhabited by the earliest known forms of cavity dwelling microbial communities that were probably dominated by chemotrophic or photosynthetic microbes recently discovered terrestrial microbial mats once thriving in a fluvial dominated setting represent the oldest macroscopically visible fossil traces of life on land which is also supported by the occurrence of nearby paleosols that carry signals of biogenic sulfur fractionation the wealth of preserved microbial biosignatures from marine fluvial hydrothermal and possibly planktonic settings combined with the high spatial and temporal resolution of the barberton greenstone belt deposits is truly exceptional consequently the bgb deserves an equal level of attention and protection for future generations like its australian counterpart

paleosecular variation of brunhes age lava flows from british columbia canada 1 brunhes age lava flows have been sampled for paleosecular variation studies from several volcanic fields of southern british columbia silverthrone garibaldi lake mt meager clearwater wells gray park and kelowna area a total of 52 lava flows were sampled and 7 to 10 samples were drilled at each site previous radiometric studies indicate that the ages of these lava flows range from 2 3 to 760 ka stepwise thermal demagnetization 14 to 21 steps was carried out for all the samples in each site and af demagnetization was performed on one sample per site forty five sites were selected based on rigorous criteria 95 5 to calculate a mean direction d 356 9 i 70 2 95 2 8 that is statistically indistinguishable from the direction of the dipole field at the area i 68 3 virtual geomagnetic poles vgps do not show the far sided effect and the angular standard deviation is 17 5 a value in agreement with the paleomagnetic field dispersion for that latitude these high quality results are expected to improve the time averaged field taf and secular variation models

surface cold pools in the outer rainbands of tropical storm hanna 2008 near landfall surface mesonet observations were used to document the structure of prominent cold pools associated with twoconvectiveouterrainbandsoftropicalstormhannaon5september2008 thedevelopingrainbandswere located 400 kmnorth ofthestormcenterastheycrossedthecarolinacoastlineandpassedover themesonet the combination of moderate cape moderate low level cross band vertical shear and dry midlevel air provided an environment supportive of surface cold pool formation and long lived quasi linear convection both rainbands exhibited multiple outward tilting convective cells and discrete line segments centered within a narrow zone of nearly continuous stratiform precipitation the mesonet observations provided a unique along and cross band perspective of discrete cold pools situated beneath andbehind the convection portions of each rainband prominentcold pools extended 40 80 km behind the rainband s leading edge and exhibited maximum potential temperature mixing ratio and equivalentpotentialtemperaturedeficitsof2 4 k 1 2 g kg 21 and4 10 k respectively inthecross banddirection convergence of storm relative inflow along the cold pool leading edge was coincident with a modest high pressure anomaly while inflow divergence prevailed through the cold pool and rainfall maxima several cold pools expanded along band while being advected downband by the prevailing cyclonic flow cold pool wakes were observed more than 50 km behind the rainband leading edge and up to 20 km downband from intense convection variations in cold pool intensitywerenotwell correlated with convectiveintensity rainfallrate or the degree of midlevel dryness implications of prominent cold pools on tropical cyclone convection size and intensity are discussed

role of biomineralization as an ultraviolet shield implications for archean life cyanobacteria isolated from the krisuvik hot spring iceland were mineralized in an iron silica solution and irradiated with high levels of ultraviolet light analysis of the rates of photosynthesis chlorophyll a content and phycocyanin autofluorescence revealed that these mineralized bacteria have a marked resistance to uv compared to nonmineralized bacteria naturally occurring sinters composed of iron silica biominerals collected from

a new window into early archean life microbial mats in earth s oldest siliciclastic tidal deposits 3 2 ga moodies group south africa newly discovered sedimentary structures produced by ancient microbial mats in early archean sandstones of the 3 2 ga moodies group south africa differ fundamentally in appearance and genesis from early archean stromatolites and bacterial cell fossils preserved in chert wrinkle structures desiccation cracks and roll up structures record the previous existence of microbial mats that effectively stabilized sediment on the earliest known siliciclastic tidal flats in thin section the sedimentary structures reveal carpet like laminated fabrics characteristic of microbial mats negative d 13 c isotope ratios of 220 1 to 221 5 6 0 2 are consistent with a biological origin for the carbon preserved in laminae the biogenicity of the sedimentary structures in the moodies group is substantiated by comparative studies on identical mat related features from similar tidal habitats throughout earth history including the present day this study suggests that siliciclastic tidal flat settings have been the habitat of thriving microbial ecosystems for at least 3 2 billion years independently of controversial silicified microfossils and stromatolites the newly detected microbially induced sedimentary structures in sandstone support the presence of bacterial life in the early archean

geomicrobiology of carbonate silicate microbialites from hawaiian basaltic sea caves abstract modern microbial mats and microbialites are described from basaltic sea caves on the island of kauai hi the mats grow on the ceilings and walls in the photic zone of several open caves where fresh water seeps out of the rock scanning sem and transmission electron microscopy tem showed that the active mats are dominated by filamentous and nonfilamentous cyanobacteria in the surface layers and heterotrophic bacteria in deeper layers energy dispersive x ray analysis revealed that copious amounts of extracellular polymeric substances eps are rich in mg si o and ca likely concentrated from solution petrographic microscopy and electron microprobe analysis of the mineralized microbialites showed textures reminiscent of stromatolitic laminations consisting mainly of alternating calcium carbonate calcite and aragonite and magnesium rich silicate kerolite thin coatings rich in magnesite hydromagnesite and monohydrocalcite surround the microbialites on the rock surfaces and are likely inorganic in origin within the mats minerals tend to form and concentrate within or around dense matrices of eps microenvironments with geochemical conditions favorable for mineral crystallization likely develop in the mats as a result of the mucilaginous extracellular material and the development of bacterial microcolonies in addition copious amounts of extracellular polymers bind ions from solution and provide nucleation sites for mineral crystallization and growth this combination of biological and inorganic processes can explain the occurrence of the secondary minerals in these caves as well as the stromatolitic textures of the microbialites

carbon isotopes as biogeochemical recorders of life over 3 8 ga of earth history evolution of a concept ever since pioneering studies in the late 1930s had shown that the conversion of inorganic carbon into biogenic substances entails sizeable redistributions of the stable carbon isotopes biologically mediated 13c 12c fractionations have come to be recognized as a common corollary of biochemical reactions meanwhile it is firmly established that the universal bias in favour of 12c characterizing biological materials primarily derives from a kinetic isotope effect that is imposed on the first carbon fixing enzymatic carboxylation reaction in the primary metabolism of co2 fixing autotrophic organisms this preference for 12c has turned out to be one of the most enduring relics of the ordered state of the biological precursor substances that may be preserved in fossil organics over billions of years with the currently known sedimentary record at hand it can be stated with confidence that biological carbon isotope fractionations have persisted throughout 3 8 ga of recorded earth history indicating that microbial prokaryotic and archaeoprokaryotic ecosystems had been prolific already on the archean earth while for the time span 3 5 ga the isotopic evidence is unequivocal the information encoded in the preceding record is commonly blurred by a metamorphic overprint this holds particularly for the metasediments of the 3 8 ga old isua supracrustal belt of west greenland which apart from widespread metasomatism have suffered amphibolite grade metamorphism it is known that 13c 12c exchange occurs in organic kerogenous rock constituents during both amphibolite and granulite facies metamorphism if a second carbon partner is available as either fluids or carbonate with isotopic re equilibration often only partially achieved due to the sluggish kinetics of the exchange reaction thermodynamic equilibria predict however that 13c 12c ratios in kerogen and graphite increase during this process hence high t exchange equilibria are always bound to drive 13c values in positive direction the lowermost values encountered being consequently the least exchanged and most pristine with the lowest values of reduced graphitic carbon obtained in early isua studies falling into the range 22 to 28 pdb we had straightforward evidence since the late 1970s that carbon constituents with the isotopic composition of biogenic matter were indeed present in the pre metamorphic isua suite it was therefore by no means surprising that the results of recent isotope work performed on apatite hosted carbonaceous microdomains in isua banded iron formation utilizing advanced techniques of instrumental microanalysis had prompted similar conclusions hence the mainstream of the sedimentary carbon isotope record can be best interpreted as the geochemical manifestation of the isotope discriminating properties of the principal co2 fixing reactions s in biological carbon assimilation suggesting an extreme degree of evolutionary conservatism in the biochemistry of autotrophic carbon fixation as a consequence biological modulation of the geochemical carbon cycle had been established at least 3 8 ga ago having been fully operative by the time of formation of the earth s oldest sediments

life on land in the precambrian microfossils have been discovered in cavity fill and replacement silica that occurs between chert breccia clasts in 1200 million year old paleokarst at the top of the mescal limestone central arizona and in 800 million year old paleokarst at the top of the beck spring dolomite southeastern california microbial communities on precambrian g550 million years ago land may have been extensive enough to affect weathering erosion sedimentation and geochemical processes

multiscale analysis of tropical cyclone kinematic structure from airborne doppler radar composites abstractthe multiscale inner core structure of mature tropical cyclones is presented via the use of composites of airborne doppler radar analyses the structure of the axisymmetric vortex and the convective and turbulent scale properties within this axisymmetric framework are shown to be consistent with many previous studies focusing on individual cases or using different airborne data sources on the vortex scale these structures include the primary and secondary circulations eyewall slope decay of the tangential wind with height low level inflow layer and region of enhanced outflow radial variation of convective and stratiform reflectivity eyewall vorticity and divergence fields and rainband signatures in the radial wind vertical velocity vorticity and divergence composite mean and variance fields statistics of convective scale fields and how they vary as a function of proximity to the radius of maximum wind show that the inner eyewall edge is associated with stronger updrafts and higher refl

evolution of the inflow boundary layer of hurricane gilbert 1988 abstract on 12 september 1988 the two noaa wp 3d aircraft conducted an experiment in and around an intense outer rainband located 175 km southeast of the center of hurricane gilbert radial height cross sections along a constant azimuth reveal a rapid and an exceptionally large increase of the equivalent potential temperature e of the inflow but in a region radially outward from the rainband kinematic analyses that incorporate both in situ and pseudo dual doppler data illustrate that the inflow is only 2 km deep and strongly divergent prior to reaching the convective core of the band the doppler derived wind fields which compare favorably with the in situ wind fields demonstrate that there is a radially outward or return flow directly above the inflow soundings show that this return flow is unusually moist despite being dominated by mesoscale descent which contrasts the dry conditions found under the anvil of virtually all tropical mesoscale convective systems a one dimensional general structure

convective scale variations in the inner core rainbands of a tropical cyclone airborne doppler radar documented a variety of convective scale structures within the inner core rainbands of hurricane rita 2005 as predicted by past studies wind shear determined azimuthal variations in the convection all convective scale circulations had radial inflow at low levels upward motion and outflow in the midtroposphere convective cells at smaller radii contained a low level tangential jet determined largely by tangential acceleration due to angular momentum conservation uy r term while cells at larger radii contained a low level and or midlevel jet determined jointly by the uy r and vertical advection terms the outflow was at a higher lower altitude for the outer inner cells radial variations in the convective cells are attributable to differencesin buoyancy and vertical shear of the radial wind u z more buoyant updrafts at larger radii enhance vertical advection of y creating local tangential jets at midlevels at smaller radii the stronger low level radial inflow contributes to a greater u z confining convectively generated jets to low levels the low level tangential jet and convectively generated pressure gradients produce outward pointing supergradient acceleration that decelerates the boundary layer inflow consequently this supergradient flow will enhance convergence and convection at the radius of inner rainbandcells increasing the likelihoodof secondary eyewall formation it is hypothesized that a critical zone for secondary eyewall formation exists where sufficiently high u z consistently constrains the altitudes of convectively generated supergradient flow so that convection in this radial zone leads to a newly developed eyewall once an incipient secondary eyewall forms at a certain radius subsidence occurring along its inner edge separates it from the primary eyewall