paleovegetation simulations of lowland amazonia and implications for neotropical allopatry and speciation paleovegetation modeling simulations of the lowland amazon basin were made to assess the relative importance of glacial climate and atmospheric co2 for altering vegetation type and structure as well as to explore the potential physiological mechanisms underlying these ecosystem level responses modeling results support the view that widespread invasion of grasslands into the amazon lowlands during the last glaciation was not likely glacial cooling was probably responsible for maintaining glacial forest cover via its effects in reducing photorespiration and decreasing evapotranspiration which collectively improve plant carbon and water relations modeling results confirm that leaf area index lai a common proxy for canopy density is highly sensitive to independent and interactive changes in climate and low concentration of atmospheric co2 and the results show considerable region to region variation during the last glaciation heterogeneous variations in glacial vegetation lai may have promoted allopatric speciation by geographically isolating species called vicariance in the forest sub canopy the proposed vicariance hypothesis incorporating spatial variations in canopy density conforms to many of the essential tenets addressed by previous neotropical speciation models but also helps to overcome some of their inconsistencies c 2001 university of washington

paleo seawater ree compositions and microbial signatures preserved in laminae of lower triassic ooids abstract signals indicative of paleo seawater rare earth element ree composition and microbial activity were identified in marine ooids from the lower triassic of south china using in situ laser ablation inductively coupled plasma mass spectroscopy la icp ms together with petrographic and isotope geochemical techniques quantitative trace element profiles were generated across successive growth laminae in the cortices of selected ooids the shale normalized ree and yttrium y data of these layers show 1 light rare earth element depletion mean la sn yb sn 0 36 0 14 2 positive la anomalies mean la la sn 2 02 1 25 and 3 high ratios of y ho mean 53 12 which are similar to modern seawater compositions and bahamian ooids these findings imply that ooids in the study samples faithfully record early triassic paleo seawater chemical signals such as ree y distributions petrographic observations revealed dark colored layers with intense fluorescence containing structures that resemble microbial filaments or extracellular polymeric substances these layers also possess more enriched ree compositions and higher concentrations of nutrient like elements e g zn and ba than adjacent recrystallized light colored laminae most ooid laminae contain negative ce anomalies indicative of a well oxygenated environment of formation but some laminae have minimal negative anomalies suggesting the influence of suboxic porewater conditions the present study provides a new perspective on the role of microbes in ooid genesis and on the utility of ooids as proxies for paleo seawater chemistry

organomineralization in mesoproterozoic giant ooids abstract ooids are common carbonate particles that are traditionally considered as abiogenically formed by physical and chemical processes in highly agitated environments recent studies point to the importance of microbial activities in ooid formation but more case studies are required to confirm and clarify the roles of microbes and their organomineralization processes here we report an integrated petrographic element geochemical and isotopic study of mesoproterozoic giant ooids from the wumishan formation ca 1 50 1 45 ga of north china the wumishan giant ooids 2 0 14 4 mm are composed of small micritic nuclei and thick radial fibrous cortices abundant organic relics including putative bacterial filaments and mucus like extracellular polymeric substances eps are present in ooid cortices organominerals e g nanoparticles and polyhedrons are concentrated and lined with the axes of radial fibers suggesting in situ mineralization of bacterial filaments the abundance of organic relics and fiber aligned organominerals confirms the constructive roles of microbes in the formation of the wumishan giant ooids the preservation of bacterial filaments filament bundles in their growth orientation requires fast mineralization in caco 3 supersaturated environments which may have been controlled by the shallow chemocline in redox stratified mesoproterozoic basins

holocene oolitic marine sand complexes of the bahamas abstract although the general factors influencing the occurrence and distribution of oolitic systems are well known details of their landscape scale patterns and formative processes are less systematically explored by reviewing published studies and presenting new data and insights this review systematically examines a suite of holocene systems from the bahamas in which patterns and processes are characterized and explicitly linked with the goal of providing more realistic and accurate models for variability heterogeneity and predictability in these systems and their ancient analogs sedimentological geomorphic and hydrodynamical data document that each ooid shoal is unique in detail yet shoals share common elements within bar forms systematic trends in grain size type and sorting are related to spatial and temporal variability in wave tide and current energy these trends are driven by connections among sedimentology hydrodynamics and geomorphic forms as they shape and concomitantly are shaped by each other similarly due to feedbacks a limited number of bar forms occur among shoals including tidal sand ridges parabolic bars transverse shoulder bars tidal deltas and sand flats the dominant bar form broadly corresponds with flow velocities within and among shoals among bahamian tidal shoals the mean grain size of ooids maximum bar heights and the width of the oolitic facies belts are all positively correlated collectively these results illustrate the mode and magnitude of variability in shapes orientations and sedimentology of holocene oolitic bodies interpreted to be driven by self organization and autogenic processes these perspectives provide testable qualitative and quantitative insights that can be used to understand and predict the character of ancient analogs

observations on late pleistocene cooling and precipitation in the lowland neotropics although accurate reconstructions of amazonian palaeoclimates are central to under standing the distribution and history of neotropical biodiversity current reconstructions based on proxy data are discordant and subject to intense debate we review some current thinking in amazonian climatology and incorporate some new ideas in an attempt to explain the apparently con tradictory records of palaeoprecipitation from across the amazon basin we suggest that palaeoecol ogists need to recognise that organised convective radiation the process that induces most wet season rainfall in amazonia should be treated as a phenomenon related to but separate from the passage of the inter tropical convergence zone itcz decoupling itcz migration from larger con vective activity provides a mechanism to account for observed palaeoclimatic heterogeneity patterns of observed precipitation change are consistent with the long term persistence of closed forest across much of amazonia indicating that the greatest changes in precipitation during the last glacial max imum came during the wet season which would have little negative impact on forest extent neo tropical cooling at the last glacial maximum lgm is widely accepted although the estimates of that cooling range between 1 c and 5 c in answering the basic question what is meant by cooling we observe that interhemispheric ice mass asymmetry may have caused cooling to be manifested differently according to location a terrestrial cooling of ca 5 c as well as radiative cooling and event based cooling combined to induce vegetation change probably both absolute temperature and mean monthly minima were reduced by polar air incursions in the northern neotropics how ever in the southern neotropics mean monthly minima were reduced by more frequent incursions of patagonian air masses but absolute minima may have been largely unchanged copyright 2004 john wiley sons ltd

late quaternary palaeoecology and palaeoclimatology from pollen records of the savannas of the llanos orientales in colombia abstract pollen analysis of sediment cores from laguna angel 4 28 n 70 34 w 200 m elevation and laguna sardinas 4 58 n 69 28 w 80 m a s l in the savannas of the llanos orientales of colombia are presented the pollen record of laguna angel includes 7 radiocarbon dates and shows the holocene vegetation and climatic history since 10 030 yr b p the record of laguna sardinas includes 7 radiocarbon dates and shows the late glacial and holocene history since 11 570 yr b p both pollen records show that the present day savanna vegetation dominated by grassland poaceae with only few woody savanna taxa e g curatella bryrsonima was present since the late glacial indicating dry climatic conditions with a marked dry season shrubs and trees of forest and or gallery forest e g mauritia mauritiella moraceae urticaceae melastomataceae alchornea and myrtaceae are well represented during the recorded period the proportions between forest and savanna were subject to change in the past but also the composition of the forest and savanna ecosystems changed laguna sardinas shows a greater abundance during the late glacial holocene transition than today for alchornea especially from 10 680 to 10 070 yr b p for this interval synchronous to the el abra stadial younger dryas equivalent in colombia more humid climatic conditions have been inferred which are primarily the result of higher moisture levels under colder conditions during the early and middle holocene from 9730 to 5260 yr b p in laguna angel and from 9390 to 6390 yr b p in laguna sardinas the maximum expansion of grassland occurred indicating very dry climatic conditions the following period from 5260 to 3890 yr b p in laguna angel and from 6390 to 3680 yr b p in laguna sardinas shows a decrease of savanna herbs and an increase of forest and gallery forests reflecting a wetter period probably with a shorter annual dry season in both lake records the period after ca 3500 yr b p is incomplete but is characterized by a high representation of the palm genera mauritiella in laguna angel and mauritia in laguna sardinas this marked change has been interpreted as evidence of strong a anthropogenic influence on the vegetation but also wetter climatic conditions than during the late glacial and early and middle holocene periods

global seasonal and local time variations of ion density structure at the low latitude ionosphere and their relationship to the postsunset equatorial irregularity occurrences 1 seasonal and longitudinal s l variations of ion density structure near 600 km altitude in the low latitude ionosphere observed by rocsat 1 for two similar high solar activity years of 2000 and 2002 are examined in five different local time lt sectors the gross features in the s l variations of density structure during the daytime are very similar to each other in these 2 years a reproducibility of the daytime density structure can thus be assumed including the shape of equatorial ionization anomaly eia for similar solar flux input the nighttime structure during the solstice shows a shape preserving decay in the latitudinal variation and maintains similar density level for these 2 years in contrast the nighttime structure in the equinox indicates noticeable differences in the 2 years a strong global transport effect that exists in the solstice can be identified as the cause of such difference in density structure between the solstice and the equinox the model results from both the 2006 international reference ionosphere model and the thermosphere ionosphere electrodynamics general circulation model cannot reproduce the global seasonal and local time lt variations of the low latitude ionospheric structure observed by rocsat the observed longitudinal variation of the crest to trough ratio of the average background eia structure in the 1800 1900 lt sector fails to correlate with the longitudinal variation of the postsunset equatorial irregularity occurrences in a season there is also no correlation found between the seasonal variations of the crest to trough ratio and the irregularity occurrence at almost all longitudes except at the longitudes of south america atlantic sector where some correlation seems to exist

pollen based continental climate reconstructions at 6 and 21 ka a global synthesis subfossil pollen and plant macrofossil data derived from 14c dated sediment profiles can provide quantitative information on glacial and interglacial climates the data allow climate variables related to growing season warmth winter cold and plant available moisture to be reconstructed continental scale reconstructions have been made for the mid holocene mh around 6 ka and last glacial maximum lgm around 21 ka allowing comparison with palaeoclimate simulations currently being carried out as part of the fifth assessment report ar5 of the intergovernmental panel on climate change the synthesis of the available mh and lgm climate reconstructions and their uncertainties obtained using modern analogue regression and model inversion techniques is presented for four temperature variables and two moisture variables reconstructions of the same variables based on surface pollen assemblages are shown to be accurate and unbiased reconstructed lgm and mh climate anomaly patterns are coherent consistent between variables and robust with respect to the choice of technique they support a conceptual model of the controls of late quaternary climate change whereby the first order effects of orbital variations and greenhouse forcing on the seasonal cycle of temperature are predictably modified by responses of the atmospheric circulation and surface energy balance

intraglacial volcanism in the western volcanic zone iceland the western volcanic zone in iceland 64 19 to 65 22 n has the morphological characteristics of a distinct mid atlantic ridge segment this volcanic zone was mapped at a scale of 1 36 000 and 258 intraglacial monogenetic volcanoes from the late pleistocene 0 01 0 78 ma were identified and investigated the zone is characterized by infrequent comparatively large volcanic eruptions and the overall volcanic activity appears to have been low throughout the late pleistocene tholeiitic basaltic rocks dominate in the western volcanic zone with about 0 5 vol of intermediate and silicic rocks the basalts divide into picrites olivine tholeiites and tholeiites three main eruptive phases can be distinguished in the intraglacial volcanoes an effusive deep water lava phase producing basal pillow lavas an explosive shallow water phase producing hyaloclastites and an effusive subaerial capping lava phase three evolutionary stages therefore charcterize these volcanoes late dykes and irregular minor intrusions could be added as the fourth main stage these intrusions are potential heat sources for short lived hydrothermal systems and may play an important role in the final shaping of the volcanoes substantial parts of the hyaloclastites of each unit are proximal sedimentary deposits the intraglacial volcanoes divide into two main morphological groups ridge shaped volcanoes i e tindars including pillow lava ridges and subrectangular volcanoes i e tuyas and hyaloclastite or pillow lava mounds the volume of the tuyas is generally much larger than that of the tindars the largest tuya eiriksjokull is about 48 km3 and therefore the largest known monogenetic volcano in iceland many of the large volcanoes both tuyas and tindars show a similar systematic range in geochemistry the most primitive compositions were erupted first and the magmas then changed to more differentiated compositions the ridge shaped tindars clearly erupted from volcanic fissures and the more equi dimensional tuyas mainly from a single crater it is suggested that the morphology and structure of the intraglacial volcanos mainly depends on two factors a tectonic control and b availability of magma at the time of eruption

correlated millennial scale changes in surface hydrography and terrigenous sediment yield inferred from last glacial marine deposits off northeastern brazil abstract the stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern brazil stable oxygen isotope records of the planktonic foraminiferal speciesglobigerinoides sacculiferandglobigerinoides ruber pink reveal sub milankovitch changes in sea surface hydrography during the last 85 000 yr warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high xrf intensities of ti and fe and which suggest humid conditions in northeast brazil these tropical signals correlate with climatic oscillations recorded in greenland ice cores dansgaard oeschger cycles and in sediment cores from the north atlantic heinrich events trade winds may have caused changes in the north brazil current that altered heat and salt flux into the north atlantic thus affecting the growth and decay of the large glacial ice sheets

measurement of the latitudinal distributions of total electron content during equatorial spread f events we have constructed latitudinal profiles of the total electron content tec using measurements from six gps receivers conducted during 1998 the tec profiles have been divided into two groups one corresponds to days when plumes or equatorial spread f esf develops and the second group portrays days of no esf condition the presence absence of esf is based on the signature of the coherent echoes measured by the jicamarca unattended long term investigation julia radar and records of scintillations from two sites spaced in latitude one scintillation station is located near the magnetic equator ancon and the other 12 southward antofagasta the tec profiles display the typical day to day and seasonal variability seen at low latitudes during the equinoxes we observed quite often the crests of the anomaly located between 12 and 20 away from the magnetic equator and a trough in between the monthly distribution of the appearance of the anomaly and the local time of their appearance are in very good agreement with the reported variability of the upward vertical drifts and the current theory of the equatorial fountain effect during the equinoxes and the december solstice the tec anomaly is observed almost every day sometimes when there is no esf activity nevertheless fine inspection of the tec latitudinal profiles suggests the existence of a close relationship between the temporal evolution of the tec profiles near sunset and the onset of esf we have examined the tec latitudinal distributions in two different ways first we calculated time difference profiles using the distributions corresponding to 1800 and 2000 lt second we used a parameterization of the tec distributions obtained at 2000 lt the first method indicates quite drastic increases of the crest values and sharp decreases near the trough during esf days in contrast during days of no esf there exist almost uniform tec decreases at all latitudes the second method displays a preferred high crest trough ratio 2 small tec values at the trough and large latitudinal integrated values during esf events

fifty thousand year vegetation and climate history of noel kempff mercado national park bolivian amazon abstract pollen and charcoal records from two large shallow lakes reveal that throughout most of the past 50 000 yr noel kempff mercado national park in northeastern lowland bolivia southwestern amazon basin was predominantly covered by savannas and seasonally dry semideciduous forests lowered atmospheric co 2 concentrations in combination with a longer dry season caused expansion of dry forests and savannas during the last glacial period especially at the last glacial maximum these ecosystems persisted until the mid holocene although they underwent significant species reassortment forest communities containing a mixture of evergreen and semideciduous species began to expand between 6000 and 3000 14 c yr b p humid evergreen rain forests expanded to cover most of the area within the past 2000 14 c yr b p coincident with a reduction in fire frequencies comparisons between modern pollen spectra and vegetation reveal that the moraceae dominated rain forest pollen spectra likely have a regional source area at least 2 3 km beyond the lake shore whereas the grass and sedge dominated savanna pollen spectra likely have a predominantly local source area the holocene vegetation changes are consistent with independent paleoprecipitation records from the bolivian altiplano and paleovegetation records from other parts of southwestern amazonia the progressive expansion in rain forests through the holocene can be largely attributed to enhanced convective activity over amazonia due to greater seasonality of insolation in the southern hemisphere tropics driven by the precession cycle according to the milankovitch astronomical theory

microbes and ooids abstract the bahamian archipelago is one of the few locations in the world where ooid formation is actively occurring ooid cortices from six locations in the region were incrementally dissolved and analyzed for 14c 18o 13c mg ca and sr ca ratios ooids were examined under sem after each step in the incremental analyses to characterize the nature of dissolution radiocarbon dating indicates that ooids presently at the sediment water interface began forming across the archipelago between 1000 and 2800 yr bp and continue to form today the ooids have the same pattern of microboring alteration across the region the surface and outer cortex of the ooids are punctuated with unfilled microborings whereas the inner cortex contains two morphologies of aragonite cement filling the microborings the two morphologies of cement form in association with two different species of cyanobacteria one is solentia sp the other is interpreted to be hyella sp the chemistry of ooids from across the region is remarkably similar 18o and 13c values for all samples vary directly having a slope of approximately 1 the outer cortex has low 18o and 13c values of 3 4 and 0 2 respectively whereas the 18o and 13c values of the inner cortex are high with values of 1 9 and 6 8 respectively the presence of aragonite cement in microborings in the inner cortex increases the overall isotopic composition of both oxygen and carbon in the ooid causing it to appear close to equilibrium with seawater the isotopic variation in 18o and 13c within the cortex can be characterized as a mixing line between the low values in the unaltered ooid laminae and the aragonite cement in the microborings the most exterior portion of the ooid has very high mg ca values and is interpreted as an amorphous calcium carbonate acc coating there are two other phases in the cortex both being aragonite the outer cortex has a higher mg ca ratio and lower sr ca ratio than the inner cortex this difference in chemistry is a result of the presence of aragonite cement in the inner cortex stable isotopic and trace element results coupled with sem investigations indicate that microbes do not play a role in ooid formation but instead alter the texture and chemistry of ooids after they have formed a new model of ooid formation is proposed whereby a veneer of acc precipitates on an ooid while it is at the sediment water interface the active phase this veneer of acc later recrystallizes to aragonite needles and a new cortex layer is formed the stationary phase observations from this study lead to a deeper understanding of the chemical processes involved in ooid genesis which allow a better understanding of paleoenvironments hosting ooid formation

geochemical evidence of microbial activity within ooids ooid formation remains elusive despite their importance as palaeoclimatic indicators and important contributors to global carbonate budget based on stable isotopes nutrient and elemental analyses on solid components and ooidal leachates this study supports the notion of microbial involvement in the development of ooids from great bahama bank carbon and nitrogen isotopic analyses on organic fractions identified geochemical signatures of microbial activity the 13c values for organic carbon in the bulk 11 9 to 16 9 intercrystalline intracrystalline 11 9 to 16 7 and intracrystalline phases 12 4 to 17 7 were similar and except for the more enriched values of ooids from butterfly beach were within the range of photosynthesisers the 15n values for the bulk 0 5 to 0 2 intercrystalline intracrystalline 0 3 to 0 7 and intracrystalline organic matter 0 3 to 1 7 showed a narrow range consistent with nitrogen fixation while positive 15n and 18o values of the leached from the ooids provided evidence of denitrification the carbonate associated sulphate 34scas of the bulk sediments 19 2 to 19 6 and 34s of the leachates 16 6 to 18 3 provided weak indication of sulphate reduction suggesting either that high concentrations of isotopically enriched s are overriding bio signatures of sulphate reduction or that microbes are preferentially using as an electron acceptor in contrast the elevated sulphate concentrations of the leachates suggest the occurrence of microbial sulphide oxidation within ooids the high mg ca of the leachates and scanning electron microscope analyses provide putative evidence of amorphous calcium carbonate and a formative role in caco3 precipitation together these findings indicate that a redox dependent microbial consortium may influence caco3 precipitation in the form of ooid accretion cementation and micritization it is also inferred that ooid deposits are not suitable indicators of palaeoclimate because ooids are affected throughout their life by a complex chain of abiotic and biological processes which can lead to large geochemical offsets

amazonian paleoecological histories one hill three watersheds abstract data from the hill of six lakes in the northwestern brazilian amazon region provide three records of paleoclimatic and vegetation change in lowland amazonia that span the last 170 000 years three lakes verde pata and dragao which occupy separate watersheds on the hill provide the most detailed image yet obtained of ice age conditions in lowland amazonia well dated sedimentary records for fossil palynological charcoal cation and pigment data are presented the data indicate the continuous presence of mesic forest throughout the last ice age oscillations of lake level are recorded and the lowstands are attributed to reduced precipitation inputs to systems delicately balanced between water loss leakage through the floor of the basin and gain precipitation gross stratigraphy algal remains and paleochemistry suggest that the stands of high and low lake level were cyclic apparently correlating precessional orbital variation times of lake lowstand coincide with wet season december january february djf insolation minima the strongest of eight lowstand cycles occurred ca 35 000 to 27 000 cal bp even during lowstand episodes pollen is well preserved and provides a clear signal of uninterrupted forest cover the principal lowland elements are continuously present in the record suggesting the long term quaternary availability of the lowland forest biome in this region however during the late pleistocene the forest changed in composition with the expansion or invasion of montane floral elements creating communities of the mesic forest biome without modern analogs while precipitation cycles were causing lake levels to rise and fall the principal influence on vegetation appears to have been cooling in the late pleistocene the population expansion of montane elements at lower elevations is consistent with a cooling of 4 5 c

quantitative estimates of glacial and holocene temperature and precipitation change in lowland amazonian bolivia quantitative estimates of temperature and precipitation change during the late pleistocene and holocene have been difficult to obtain for much of the lowland neotropics using two published lacustrine pollen records and a climate vegetation model based on the modern abundance distributions of 154 neotropical plant families we demonstrate how family level counts of fossil pollen can be used to quantitatively reconstruct tropical paleoclimate and provide needed information on historic patterns of climatic change with this family level analysis we show that one area of the lowland tropics northeastern bolivia experienced cooling 1 3 c and drying 400 mm yr relative to present during the late pleistocene 50 000 12 000 calendar years before present cal yr b p immediately prior to the last glacial maximum lgm ca 21 000 cal yr b p we observe a distinct transition from cooler temperatures and variable precipitation to a period of warmer temperatures and relative dryness that extends to the middle holocene 5000 3000 cal yr b p this prolonged reduction in precipitation occurs against the backdrop of increasing atmospheric co2 concentrations indicating that the presence of mixed savanna and dry forest communities in northeastern bolivia durng the lgm was not solely the result of low co2 levels as suggested previously but also lower precipitation the results of our analysis demonstrate the potential for using the distribution and abundance structure of modern neotropical plant families to infer paleoclimate from the fossil pollen record

paleo environmental change in amazonian and african rainforest during the lgm abstract the paper provides new and comparative insight into the ecological history of the two largest continental tropical forest areas during the last glacial maximum lgm the tropical forest regions are of particular interest because they present a large source of heat and have been shown to have significant impact on the extra tropical atmospheric circulation they are also the most intense land based convective centers thus especially from the tropics paleoecological information is needed as benchmarks for climate modeling the african data for lgm climates were published earlier including the reconstructed paleoprecipitation patterns deduced from ssts the tropical south american lgm data were interpreted from pollen geochemical and 18o stable oxygen isotope data from brazil and selected surrounding areas the available terrestrial data are consistent with the sst derived precipitation data for the tropical forests in brazil and for africa however the impact of lgm climate extremes was less severe in the amazon than in the congo basin the lgm humid forest area including evergreen and semi deciduous forest types in africa was probably reduced by 84 in contrast the amazon humid forest area probably shrank to 54 of their present day extension still there are different interpretations with respect to the amount of reduction of the amazon forest area during the lgm although direct information about lgm climates in amazonia is still limited the more detailed map obtained in the present work however allows a more reliable characterization of the last glacial tropical environment than previously published for the amazon region

absence of last glacial maximum records in lowland tropical forests abstract environmental conditions of the lowland tropical forests during the last glacial maximum lgm between ca 20 000 and 18 00014c yr b p are reevaluated in terms of dating control and lithology analyzed in seven pollen records from south america the reevaluation shows that probably in none of the published records are lgm sediments present or abundant this conclusion is based on the occurrence of abrupt lithologic changes coupled with changes in sedimentation rate interpolated from radiocarbon dates these findings suggest that the lgm was represented probably by a hiatus of several thousand years indicative of drier climates than before or after

evidence of dry and cold climatic conditions at glacial times in tropical southeastern brazil last glacial paleoenvironments have been reconstructed from a pollen and charcoal record analyzed in organic sediments and dated between ca 18 000 and 48 00014c yr b p the site is located near the village catas altas in the lower highland region of southeastern brazil the last glacial landscape was covered by extensive areas of subtropical grasslands and small areas of gallery forests along the rivers where tropical semideciduous forests and cerrado ecosystems exist today the subtropical gallery forests were composed ofaraucariaforest trees such asaraucaria angustifolia podocarpus drimys ilex andsymplocos paleofires were frequent the record indicates that subtropical grassland vegetation which today is found in patches on the highlands in southern brazil especially in the state of santa catarina expanded from southern brazil to southeastern brazil over a distance of more than 750 km from latitudes of about 28 s to at least 20 s the completely different last glacial environment in comparison to the present day environment reflects a dry and cold climate with strong frosts during the winter months temperatures of 5 7 c below those of the present are inferred for the last glaciation

decoding the mechanism of formation in marine ooids a review abstract ooid shoals sedimentary structures consisting of carbonate grains are often used as proxies to explore changes in seawater chemistry over earth history despite their importance as contributors to the global carbonate budget and as paleo environmental indicators for water depth ph temperature and water energy the mechanism of formation of these concentric sub spherical concretions of tangentially or radially arranged aragonite or calcite crystals is still the subject of intense debate unlike oncoids whose microbial origins are well acknowledged ooids are traditionally viewed as abiotic grains mainly produced in suspension by agitated warm waters that are supersaturated with respect to caco3 yet there is considerable evidence including geochemical bio signatures and detection of viable microbes capable of mineralization and biofilm production and degradation to suggest otherwise the emergence of new and sophisticated technologies reveals that the level of microbial diversity of these sedimentary grains exceeds that of some microbialite systems these findings have refined our understanding of ooid genesis and ooid accretion processes and argue toward microbial mediation both as a direct result of metabolic activities inducing changes in the environment conducive to precipitation and by a passive mechanism in which mucilaginous extracellular polymeric substances eps act as a template for mineral nucleation furthermore new developments in the field indicate that carbonate mineralization in marine ooids occurs through sequential precipitations that involve an amorphous calcium carbonate phase acc which some argue are of biotic origins herein we discuss the most relevant theories of ooid formation including some of the early pioneering studies that laid the groundwork for new theories attempting to decode the origins of these controversial grains

late quaternary vegetational and climate dynamics in northeastern brazil inferences from marine core geob 3104 1 abstract late quaternary paleoenvironments from northeastern ne brazil have been studied by pollen analysis of marine sediment the studied core geob 3104 1 3 40 s 37 43 w 767 m b s l from the upper continental slope off ne brazil is 517 cm long and 42 000 14 c yr bp old chronological control was obtained by 12 radiocarbon ams dates from individuals of the foraminiferal species globigerinoides sacculifer modern pollen analogs were received from 15 river lake and forest soil surface samples from ne brazil marine pollen dates indicate the predominance of semi arid caatinga vegetation in ne brazil during the recorded period between 42 000 and 8500 14 c yr bp the increased fluvial input of terrigenous material with high concentrations of pollen and specially fern spores into the marine deposits about 40 000 33 000 and 24 000 14 c yr bp and between 15 500 and 11 800 14 c yr bp indicate short term periods of strong rainfall on the ne brazilian continent the expansion of mountain floodplain and gallery forests characterize the interval between 15 500 and 11 800 14 c yr bp as the wettest recorded period in ne brazil which allowed floristic exchanges between atlantic rain forest and amazonian rain forest and vice versa the paleodata from core geob 3104 1 confirm the in general dry pre last glacial maximum lgm and lgm conditions and the change to wet lateglacial environments in tropical south america the annual movement of the intertropical convergence zone over ne brazil the strong influence of the antarctic cold fronts and changes of the high pressure cell over the southern atlantic may explain the very wet lateglacial period in ne brazil the documented ne brazilian short term signals correlate with the documented dansgaard oeschger cycles and heinrich events from the northern hemisphere and suggest strong teleconnections

a 45 kyr palaeoclimate record from the lowland interior of tropical south america we present a well dated high resolution 45 kyr lake sediment record reflecting regional temperature and precipitation change in the continental interior of the southern hemisphere sh tropics of south america the study site is laguna la gaiba llg a large lake 95 km2 hydrologically linked to the pantanal an immense seasonally flooded basin and the world s largest tropical wetland 135 000 km2 lake level changes at llg are therefore reflective of regional precipitation we infer past fluctuations in precipitation at this site through changes in i pollen inferred extent of flood tolerant forest ii relative abundance of terra firme humid tropical forest versus seasonally dry tropical forest pollen types and iii proportions of deep versus shallow water diatoms a probabilistic model based on plant family and genus climatic optima was used to generate quantitative estimates of past temperature from the fossil pollen data our temperature reconstruction demonstrates rising temperature by 4 c at 19 5 kyr bp synchronous with the onset of deglacial warming in the central andes strengthening the evidence that climatic warming in the sh tropics preceded deglacial warming in the northern hemisphere nh by at least 5 kyr we provide unequivocal evidence that the climate at llg was markedly drier during the last glacial period 45 0 12 2 kyr bp than during the holocene contrasting with sh tropical andean and atlantic records that demonstrate a strengthening of the south american summer monsoon during the global last glacial maximum 21 kyr bp in tune with the 20 kyr precession orbital cycle holocene climate conditions occurred as early as 12 8 12 2 kyr bp when increased precipitation in the pantanal catchment caused heightened flooding and rising lake levels in llg in contrast to this strong geographic variation in lgm precipitation across the continent expansion of tropical dry forest between 10 and 3 kyr bp at llg strengthens the body of evidence for widespread early mid holocene drought across tropical south america

astronomical forcing of contrasting rainfall changes in tropical south america between 12 400 and 8800 cal yr b p abstract today precipitation over tropical south america is largely controlled by the seasonal movements of the inter tropical convergence zone itcz during the summer the itcz is shifted southward due to the warming of the continent paleoclimate data from southeastern amazonia and the central andes indicate that these two areas evolved similarly during the last 30 000 yr however between 12 400 and 8800 cal yr b p eastern amazonia received substantial moisture whereas the bolivian altiplano was arid this suggests that the itcz during summer was then farther north than it is today

modern pollen rain characteristics of tall terra firme moist evergreen forest southern amazonia the paucity of modern pollen rain data from amazonia constitutes a significant barrier to understanding the late quaternary vegetation history of this globally important tropical forest region here we present the first modern pollen rain data for tall terra firme moist evergreen amazon forest collected between 1999 and 2001 from artificial pollen traps within a 500 x 20 m permanent study plot 14 degrees 34 50 s 60 degrees 49 48 w in noel kempff mercado national park ne bolivia spearman s rank correlations were performed to assess the extent of spatial and inter annual variability in the pollen rain whilst statistically distinctive taxa were identified using principal components analysis pca comparisons with the floristic and basal area data of the plot stems 10 cm d b h enabled the degree to which taxa are over under represented in the pollen rain to be assessed using r rel values moraceae urticaceae dominates the pollen rain 64 median abundance and is also an important constituent of the vegetation accounting for 16 of stems 10 cm d b h and ca 11 of the total basal area other important pollen taxa are arecaceae cf euterpe melastomataceae combretaceae cecropia didymopanax celtis and alchornea however 75 of stems and 67 of the total basal area of the plot 10 em d b h belong to species which are unidentified in the pollen rain the most important of which are phenakospermum guianensis a banana like herb and the key canopy emergent trees erisma uncinatum and qualea paraensis

the history of south american tropical precipitation for the past 25 000 years long sediment cores recovered from the deep portions of lake titicaca are used to reconstruct the precipitation history of tropical south america for the past 25 000 years lake titicaca was a deep fresh and continuously overflowing lake during the last glacial stage from before 25 000 to 15 000 calibrated years before the present cal yr b p signifying that during the last glacial maximum lgm the altiplano of bolivia and peru and much of the amazon basin were wetter than today the lgm in this part of the andes is dated at 21 000 cal yr b p approximately coincident with the global lgm maximum aridity and lowest lake level occurred in the early and middle holocene 8000 to 5500 cal yr b p during a time of low summer insolation today rising levels of lake titicaca and wet conditions in amazonia are correlated with anomalously cold sea surface temperatures in the northern equatorial atlantic likewise during the deglacial and holocene periods there were several millennial scale wet phases on the altiplano and in amazonia that coincided with anomalously cold periods in the equatorial and high latitude north atlantic such as the younger dryas

probabilistic correlation of single stratigraphic samples a generalized approach for biostratigraphic data existing quantitative methods for biostratigraphic dating and correlation commonly ignore one of the key strengths of the microfossil record relative abundance data in this study we present a maximum likelihood based biostratigraphic method that demonstrates how microfossil abundance can be used in the stratigraphic placement of isolated samples precise correlation and dating of isolated paleontological samples is not possible with current methods which are primarily intended for the alignment of longer stratigraphic sequences in contrast the probabilistic approach provided by likelihood analysis results in sample age estimates with defined confidence intervals therefore all the uncertainties inherent in our age assessment resulting from small sample sizes incomplete sampling imperfect knowledge of stratigraphic distributions lack of taxonomic resolution of biostratigraphic data and underlying environmental paleogeographic and sedimentologic processes are explicit in our results we conclude with a field test of the method from data collected from an oil well from the catatumbo basin colombia illustrating the use of our approach in a real world case study and highlighting how our method could be generalized to a wide range of stratigraphic problems

preservation of cyanobacterial uvr shielding pigment scytonemin in carbonate ooids formed in pleistocene salt lakes in the qaidam basin tibetan plateau

a 25 000 year tropical climate history from bolivian ice cores ice cores that were recovered from the summit of sajama mountain in bolivia provide carbon 14 dated tropical records and extend to the late glacial stage lgs oxygen isotopic ratios of the ice decreased 5 4 per mil between the early holocene and the last glacial maximum which is consistent with values from other ice cores the abrupt onset and termination of a younger dryas type event suggest atmospheric processes as the probable drivers regional accumulation increased during the lgs during deglaciation and over the past 3000 years which is concurrent with higher water levels in regional paleolakes unlike polar cores sajama glacial ice contains eight times less dust than the holocene ice which reflects wetter conditions and extensive snow cover

late quaternary environmental change in the interior south american tropics new insight from leaf wax stable isotopes stable isotope analysis of leaf waxes in a sediment core from laguna la gaiba a shallow lake located at the bolivian margin of the pantanal wetlands provides new perspective on vegetation and climate change in the lowland interior tropics of south america over the past 40 000 years the carbon isotopic compositions 13c of long chain n alkanes reveal large shifts between c3 and c4 dominated vegetation communities since the last glacial period consistent with landscape reconstructions generated with pollen data from the same sediment core leaf wax 13c values during the last glacial period reflect an open landscape composed of c4 grasses and c3 herbs from 41 20 ka a peak in c4 abundance during the last glacial maximum lgm 21 ka suggests drier or more seasonal conditions relative to the earlier glacial period while the development of a c3 dominated forest community after 20 ka points to increased humidity during the last deglaciation within the holocene large changes in the abundance of c4 vegetation indicate a transition from drier or more seasonal conditions during the early mid holocene to wetter conditions in the late holocene coincident with increasing austral summer insolation strong negative correlations between leaf wax 13c and d d values over the entire record indicate that the majority of variability in leaf wax d d at this site can be explained by variability in the magnitude of biosynthetic fractionation by different vegetation types rather than changes in meteoric water d d signatures however positive d d deviations from the observed 13c d d trends are consistent with more enriched source water and drier or more seasonal conditions during the early mid holocene and lgm overall our record adds to evidence of varying influence of glacial boundary conditions and orbital forcing on south american summer monsoon precipitation in different regions of the south american tropics moreover the relationships between leaf wax stable isotopes and pollen data observed at this site underscore the complementary nature of pollen and leaf wax 13c data for reconstructing past vegetation changes and the potentially large effects of such changes on leaf wax d d signatures

amorphous calcium carbonate associated with biofilms in hot spring deposits abstract calcium carbonate nanoparticles are intimately associated with crystalline calcite and aragonite in the eryuan gongxiaoshe and zhuyuan hot springs water temperature 75 c which are located in yunnan province china the nanoparticles

numerical modeling of ooid size and the problem of neoproterozoic giant ooids temporal variation in ooid size reflects important changes in physical and chemical characteristics of depositional environments two numerical models are used to evaluate the effects of several processes influencing ooid size the first demonstrates that low supply of new ooid nuclei and high cortex growth rate each promote growth of large ooids the second model demonstrates that high average water velocity and velocity gradient also enhance ooid growth several neoproterozoic oolites contain unusually large ooids some reaching diameters of up to 16 mm while lower nuclei supply and higher ooid growth rate may have prevailed prior to the evolution of carbonate secreting organisms neither difference can explain the presence of giant ooids in neoproterozoic deposits because archean through mesoproterozoic ooids rarely exceed 5 mm in diameter in the presence of lower nuclei supply and higher growth rate high average water velocity may have allowed growth of such large ooids higher average water velocity could have been due to a prevalence of carbonate ramps over rimmed shelves during neoproterozoic time

late quaternary vegetation climate and fire history from the tropical mountain region of morro de itapeva se brazil late quaternary paleoenvironments have been interpreted from a 35 000 yr b p pollen and charcoal record from morro de itapeva 22 47 s 45 32 w 1850 m a s l in the se brazilian highlands changes in taxa composition and elevational shifts in high elevation grassland campos de altitude araucaria forest cloud forest and atlantic rain forest all of which can be found in the study area today indicate climatic changes in the past expanded high elevation grasslands absence of araucaria forest cloud forest and atlantic rain forest during the recorded last glacial period ca 35 000 17 000 yr b p suggest a climate markedly cooler and drier than today development of a sphagnum peat bog rare presence of araucaria forest taxa and existence of a narrow cloud forest and rain forest belt at lower elevations during the late glacial period 17 000 ca 10 000 yr b p indicate a change to a cool and somewhat moister climates during the early holocene cloud forest developed close to the study site reflecting a warm and moist climate on the east facing slopes but a drier climate on the highland plateau evidenced by the rare presence of araucaria and podocarpus only during the late holocene moisture increases in the highlands suggested by the higher frequency of araucaria and podocarpus fires were more frequent during the last glacial than during the holocene

late quaternary vegetation and climate change in the amazon basin based on a 50 000 year pollen record from the amazon fan odp site 932 hemipelagic sediments from the amazon deep sea fan odp site 932 5 12 7 n 47 1 8 w and continental shelf provide a 50 000 yr long pollen record of amazon basin vegetation the age model for hole 932a is constrained by eight magnetic remanence intensity features one paleomagnetic excursion and three ams14c dates alchornea melastomataceae myrtaceae and moraceae urticaceae are dominant taxa in the pollen record between 40 200 and 19 800 cal yr b p andean taxa such aspodocarpusandhedyosmum increase in abundance between 19 800 and 11 000 cal yr b p and prior to 40 200 cal yr b p the holocene pollen assemblage derived from amazon river and continental shelf sediments is dominated by secondary growth taxa such ascecropia climatic factors influencing the development of glacial and interglacial tropical vegetation are considered by comparing marine with terrestrial records of vegetation change this comparison shows that the amazon basin forests were not extensively replaced by savanna vegetation during the glacial period contradicting the refugia hypothesis

longitudinal variability of annual changes in activity of equatorial spread f and plasma bubbles global distribution maps of equatorial spread f esf activity for various annual periods were derived from the topside soundings by the ionosphere sounding satellite b iss b in 1978 1980 the esf activity during the northern winter period reveals maximum enhancement at the atlantic longitudes of large westward geomagnetic declination and during the northern summer at the pacific longitudes of large eastward declination on several orbits passing over the region of the esf activity enhancement abrupt depletions of the electron density or equatorial plasma bubbles were observed at the satellite altitude of about 1100 km it has also been found that the background electron density distributions tend to be symmetric with respect to the magnetic equator in the region of the enhanced esf activity and asymmetric in the region of the suppressed esf activity these observations are taken account of by the influence of a transequatorial thermospheric wind upon the suppression of the rayleigh taylor type plasma instability

vegetation and environmental changes in tropical south america from the last glacial to the holocene documented by multiple cave sediment proxies abstract 18 o values in speleothems have been utilized to document past changes in south american monsoon intensity however changes in regional vegetation and ecosystems have not been part of this discussion and other cave proxies such as speleothem 13 c values a useful proxy for vegetation reconstruction have been neglected due to interpretive complexities here we report 13 c values and 87sr 86sr ratios in stalagmites together with xrf derived elemental chemistry 13 corg values and carbon content from a sedimentary profile from the same cave where the stalagmites were collected in combination with a previously published 18 o record this enables us to clarify climate and environmental shifts that occurred between the last glacial maximum and the holocene in central south america we show that vegetation was sparse during the last glacial period in spite of a previously inferred strong monsoon and that changes in atmospheric pco2 combined with local hydrological and temperature feedbacks may have determined vegetation development during this time

on monthly seasonal longitudinal variations of equatorial irregularity occurrences and their relationship with the postsunset vertical drift velocities 1 monthly variation of global equatorial density irregularity distribution has been obtained with the data taken by rocsat 1 at the 600 km topside ionosphere from march 1999 to june 2004 during high to moderate solar activity years this global distribution of monthly irregularity occurrence rate not only provides the best spatial temporal distribution in existence so far but also serves to fill the gap of irregularity distribution missing over some eastern pacific region where no ground observation is available the 5 1 2 year result of the monthly occurrence pattern indicates a smooth variation across the longitudes contrary to some beliefs that a drastic change in irregularity occurrence pattern has occurred across the eastern pacific longitudes excellent agreement is noted for the current results with aarons 1993 conjectured sketch of the global scintillation distribution furthermore the seasonal longitudinal s l variations of quiet time postsunset vertical drift velocities are found to track closely with the s l variations of irregularity occurrences linear regression analysis between the vertical drift velocity and the irregularity occurrence rate indicates that the vertical drift velocities at three different longitude zones of magnetic declination have good correlations with the irregularity occurrences for all seasons this implies that the averaged postsunset vertical drift velocity is a good indicator for the occurrences of equatorial density irregularities in a longitude region of similar magnetic declination the smooth variation of monthly seasonal longitudinal distributions of the vertical drift velocities that results in the smooth variation of topside density irregularity occurrences implies that the global occurrence pattern of either distribution is controlled by the smooth global variation of the postsunset ionospheric condition related to the magnetic declination effect and the seasonal variation of the ionospheric density level at the dip equator located with respect to the geographic equator there seems little need to include the global distribution of instability perturbation seeds from atmospheric disturbances to complete the global distribution of topside irregularity occurrences

microboring versus recrystallization further insight into the micritization process sem observations of lightly etched thin sections of bahamian sediments reveal an unusual process of micritization that involves carbonate precipitation in microborings concurrent with endolithic activity a coccoid cyanobacterium tentatively identified as solentia sp bores tunnels which initially penetrate just beneath grain surfaces and eventually extend throughout the entire grain these tunnels are filled by radial fibrous aragonite which is precipitated as the microorganism advances extensive multicyclic repetitions of this process result in obliteration of original grain textures with almost complete preservation of grain margins and rare empty bore holes the rapidly filled tunnels cannot be detected by resin cast embedding techniques that are commonly used to study microboring this type of multicyclic boring and concurrent filling of bore holes forms micritized grains that can be difficult or impossible to distinguish from micritized grains formed by recrystallization

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

early local last glacial maximum in the tropical andes the local last glacial maximum in the tropical andes was earlier and less extensive than previously thought based on 106 cosmogenic ages from beryllium 10 dating from moraines in peru and bolivia glaciers reached their greatest extent in the last glacial cycle 34 000 years before the present and were retreating by 21 000 years before the present implying that tropical controls on ice volumes were asynchronous with those in the northern hemisphere our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle

an equatorial bubble its evolution observed in relation to bottomside spread f and to the appleton anomaly this is a case study that undertakes the first comprehensive description of the concurrent evolutions of an isolated equatorial bubble bottomside spread f bssf and the enhanced appleton anomaly a principal focus is the dynamics of the intersection of the bubble with the anomaly crest which is the source of maximum scintillation on transionospheric rf propagation conditions are equinox at solar maximum measurements were by an array of eight ionospheric sounders in the western hemisphere with a collective field of view extending along the dip equator for about 1600 km and to 40 north dip latitude that resolved rapid changes in the phenomena yet encompassed their extent and duration viewed locally the bubble was triggered by an upwelling of the bottomside f layer during e b upward drift that accelerated upward for 15 20 min before the onset of irregularities seen as range spread f rsf viewed macroscopically this onset was part of continuous front of rsf onset that coincided with e b reversal and moved westward at the velocity of the terminator so as to remain at 1920 lt to the east of the bubble as bssf within the bubble during the upwelling of the bottomside crest at the west wall of the bubble at the onset of its eastward drift and west of the bubble as bssf the bubble drifted eastward at 185 m s and rose upward at 190 m s intersecting the maximum of the anomaly crest at 2100 lt 95 min after bubble onset during this entire period the bubble was in continuous contact with the anomaly profile which was simultaneously increasing but as a function of lt thus the intersection was a function of the upward and eastward velocities of the bubble and the westward motion of the anomaly at the velocity of the terminator the time and place of the intersection is thus dependent on the entire sequence of events and on the differing dependences on ut and lt and since each can vary the time and place of maximum scintillation is highly variable in light of this variability observations at least as comprehensive as those reported here appear to be necessary to describe the region adequately and therefore to study it further

active ooid growth driven by sediment transport in a high energy shoal little ambergris cay turks and caicos islands ooids are a common component of carbonate successions of all ages and present significant potential as paleoenvironmental proxies if the mechanisms that control their formation and growth can be understood quantitatively there are a number of hypotheses about the controls on ooid growth each offering different ideas on where and how ooids accrete and what role if any sediment transport and abrasion might play these hypotheses have not been well tested in the field largely due to the inherent challenges of tracking individual grains over long timescales this study presents a detailed field test of ooid growth hypotheses on little ambergris cay in the turks and caicos islands british overseas territories this field site is characterized by westward net sediment transport from waves driven by persistent easterly trade winds this configuration makes it possible to track changes in ooid properties along their transport path as a proxy for changes in time ooid size shape and radiocarbon age were compared along this path to determine in which environments ooids are growing or abrading ooid surface textures petrographic fabrics stable isotope compositions 13 c 18 o and 34 s lipid geochemistry and genetic data were compared to characterize mechanisms of precipitation and degradation and to determine the relative contributions of abiotic e g abiotic precipitation physical abrasion and biologically influenced processes e g biologically mediated precipitation fabric destruction through microbial microboring and micritization to grain size and character a convergence of evidence shows that active ooid growth occurs along the transport path in a high energy shoal environment characterized by frequent suspended load transport median ooid size increases by more than 100 m and bulk radiocarbon ages decrease by 360 yr westward along the 20 km length of the shoal crest lipid and 16s rrna data highlight a spatial disconnect between the environments with the most extensive biofilm colonization and environments with active ooid growth stable isotope compositions are indistinguishable among samples and are consistent with abiotic precipitation of aragonite from seawater westward increases in ooid sphericity and the abundance of well polished ooids illustrate that ooids experience subequal amounts of growth and abrasion in favor of net growth as they are transported along the shoal crest overall these results demonstrate that in the ambergris system the mechanism of ooid growth is dominantly abiotic and the loci of ooid growth is determined by both carbonate saturation and sediment transport mode microbes play a largely destructive rather than constructive role in ooid size and fabric

deriving the effective scale height in the topside ionosphere based on ionosonde and satellite in situ observations chapman scale height is a valuable key parameter measuring the shape of the profile of plasma density in the f2 layer ionosphere currently the data of chapman scale height are routinely derived from ionogram observations at many ionosonde stations in terms of the sao explorer software in this report we collected the in situ observations of plasma density at altitudes around 600 km from the rocsat 1 satellite and of simultaneous f peak parameters from an ionosonde operated at wuhan 30 6 n 114 4 e a low latitude station in central china to estimate the topside plasma density profiles by using the chapman function and further retrieve chapman scale height evident solar cycle seasonal variation and local time variation are presented in the retrieved chapman scale height over wuhan the climatological features of the derived chapman scale height are significantly different from those from the ground based ionograms such significant discrepancy suggests that further improvements are required in the present extrapolating topside electron density profiles from ionosonde observations furthermore the attempt to constructing plasma density profiles through combining ionosonde and satellite in situ observations provides a new way to reanalyze observations from different sources and normalize plasma density recorded at varying altitudes to specified altitudes which is critical and more convenient for ionospheric climatology studies