the mera site revisited ice age amazon in the light of new evidence abstract the mera site is the only fossil pollen and forest bed radiocarbon dated 33 26 ka bp in tropical lowland amazonia here i conclude from the study of the geology geomorphology and paleopedology of the mera site area as well as from new 14c and u th age determination of the organic layers that the pollen sections are not of last glacial age but of middle pleistocene age at least no evidence of last glacial age has been found for the mera fossil forest beds the data from the mera sites therefore should neither be used for climate reconstructions of the last glacial maximum nor for disputing the refugial theories

trace element abundances in hibonites from the murchison carbonaceous chondrite constraints on high temperature processes in the solar nebula abundances of trace elements including 14 rare earth elements ree and 8 other refractory trace elements rte have been measured in 33 hibonite and 3 perovskite bearing grains from the murchison carbonaceous chondrite the normalized abundance patterns show a good correlation with three morphological and chemical groups of hibonites sixteen platy hibonite crystals placs typically have patterns which are depleted in the relatively volatile trace elements v nb ba eu and yb group iii three placs also show large depletions in ce one plac is enriched in the ultrarefractory ree while two other placs have fractionated patterns enriched in the light ree with positive tm anomalies the placs commonly have a roll off in the abundances of the hree which is consistent with solid liquid partitioning three blue aggregates bags have patterns with low overall abundances and depletions in the ultrarefractory ree except tm group ii spinel hibonite grains shibs show a variety of patterns mainly of group ii but 4 shibs have relatively smooth patterns with anomalies in the volatile ree ce eu and yb the perovskites have patterns similar to group ii but with excesses in eu and yb the hree roll off in the placs and the igneous morphologies of the shibs indicate that these grains formed by the crystallization of melts distillation may be important for the bags and two of the placs which have large isotopic mass fractionation effects placs have the simplest trace element patterns and the largest ti isotopic anomalies and probably were the first hibonites to form in the early solar system the shibs have trace element signatures that require multiple processing episodes they are somewhat complementary to the placs in that they are enriched in the volatile elements which are depleted in the placs on average the shibs contain isotopically less anomalous ti than the placs however shibs contain 26mg excesses that are consistent with the in situ decay of 26al whereas placs generally have only small or no excesses of 26mg despite high 27al24mg while an overall relationship exists between the morphology chemistry and ti and mg isotopic systematics of meteoritic hibonites they do not as yet fit into a simple scenario for the formation of the solar system

holocene mire development and climatic change from a high andean plantago rigida cushion mire a pollen diagram of a 225 cm long core from a small plantago rigida cushion mire turbera de calostros in the grassparamo belt at 3730m altitude in the paramo de chingaza eastern cordillera of colombia records the last 8500 years of holocene vegetational history three radiocarbon dates 8410 160 bp 7230 1340 bp and 5980 75 bp provide a time frame pollen of taxa of zonal grassparamo and subparamo vegetation are dominant and pollen of subandean lower montane forest elements are overrepresented due to upslope aeolian pollen supply to this high elevation site eight pollen zones were recognized and reflect on a regional scale a sequence of altitudinal shifts of the upper forest line oscillating between 3000 3100 and 3500m and synchronous changes in the composition of the andean upper montane forest based on the radiocarbon dates and using the pollen density record dates of changes in environmental conditions are estimated c 8700 8600 7800 7500 6650 5200 300 and 100bp correlation

late glacial and holocene vegetational history from two sites in the western cordillera of southwestern ecuador the deciphering of the late glacial and holocene vegetation glacial geological and climatic history of cajas national park in southwestern ecuador is undertaken focusing on close interval sampling of sediment cores from two high elevations lakes lagunas chorreras 3700 m and pallcacocha 4060 m this study involves extensive dating both accelerator mass spectrometry and tephra palynological and sediment analyses of lakes and bogs basal dates for the two cores analyzed for pollen range from about 17 000 to about 15 500 cal yr bp vegetation surveys and surface sample pollen and spore analyses were accomplished for two transects in the western cordillera one began east of the main divide near cuenca ecuador and the other began at the crest of the western cordillera descending towards the pacific ocean these vegetation surveys coupled with pollen analyses of surface samples were used to establish pollen analogues to help in the interpretation of the fossil pollen records the results of the pollen analyses from the two lake cores indicate two major climatic periods 1 the late glacial pollen record beginning about 17 000 yr bp and ending near 11 000 is characterized by an herb paramo dominated by pteridophytes primarily huperzia spp with asteraceae assumed to be woody species and puya spp the climate inferred from these pollen records was cooler and moister than today the sediments for this time period are characterized by low loss on ignition percentages and high magnetic susceptibility values with secondary peaks between 12 000 and 13 000 yr bp low concentrations of charcoal fragments indicate a low incidence of fire and several pronounced fluctuations in pollen assemblages could be interpreted as changes in the prevailing wind direction and or climate 2 the beginning of the holocene as represented in the pollen record is characterized by the disappearance of puya pollen vastly diminished huperzia representation high charcoal concentrations and the expansion of moist montane forest pollen asteraceae possibly gynoxys are replaced as dominant timberline taxa by polylepis dominated timberline forest the charcoal record suggests that fires were much more prevalent during the early to middle holocene than during the late glacial changes in isoe tes concentrations and trends in upland vegetation may be related to fluctuations in lake levels and precipitation

trace element abundances and magnesium calcium and titanium isotopic compositions of grossite containing inclusions from the carbonaceous chondrite acfer 182 the carbonaceous chondrite acfer 182 contains ca al rich inclusions cais that differ from most cais in other meteorites many of them contain grossite caal4o7 whose modal abundance exceeds 30 vol in most of these cais grossite rich inclusions similar inclusions have been found only in the ch chondrite alh85085 and the cr chondrite acfer 059 el djouf 001 ion microprobe analyses of trace elements were made on nineteen cais from acfer 182 and two cais from acfer 059 el djouf 001 of al mg isotopes on eighteen acfer 182 and the two acfer 059 el djouf 001 inclusions and of calcium isotopes on ten acfer 182 inclusions on six of them also of titanium isotopes and one acfer 059 el djouf 001 inclusion trace element and isotopic signatures of grossite containing inclusions from acfer 182 resemble those of some inclusions from alh85085 volatility fractionated trace element abundance patterns ranging from ultrarefractory depleted similar to group ii pattern to volatile enhanced are predominant 17 cais including both inclusions from acfer 059 el djouf 001 two inclusions have ultrarefractory patterns one has a group iii pattern and one inclusion has a group iii related pattern similar to patterns found in hal type inclusions only one cai from acfer 182 but both inclusions from acfer 059 el djouf 001 have nonlinear excesses of 26mg corresponding to the initial 26al27al ratio of 5 10 5 none of the twenty inclusions has a significant intrinsic isotopic mass fractionation of mg titanium is normal in all analyzed cais and only small 48ca excesses 4 3 and 3 8 are present in two inclusions isotopes of both ca and ti show no significant intrinsic mass fractionations grossite containing inclusions from acfer 182 occur in different petrographic contexts in many cases petrographic characteristics are correlated with trace element abundances almost all inclusions studied in this work have a condensation history but no evidence for extensive evaporation processes is present many of the cais must have formed by direct gas solid condensation while some inclusions with clearly identifiable igneous textures formed from a refractory melt grossite whose formation was the subject of controversy in the past probably condensed from a reservoir with a higher than chondritic ca al ratio and depleted in the highly refractory trace elements or crystallized from a ca al rich melt the two ultrarefractory inclusions from acfer 182 have extremely high refractory trace element abundances sometimes exceeding 105 ci the lack of isotopic fractionation indicates a formation at very high temperatures by condensation rather than evaporation the lack of 26mg excesses in almost all inclusions from acfer 182 is best explained by heterogeneous distribution of 26al in the primitive solar nebula grossite rich inclusions having volatility fractionated ultrarefractory depleted trace element abundance patterns and lacking 26mg excesses could be the complement of platy hibonites placs from murchison with group iii or ultrarefractory patterns and likewise no 26mg excesses

late quaternary vegetation fire and climate history reconstructed from two cores at cerro toledo podocarpus national park southeastern ecuadorian andes the last ca 20 000 yr of palaeoenvironmental conditions in podocarpus national park in the southeastern ecuadorian andes have been reconstructed from two pollen records from cerro toledo 04 22 28 6 s 79 06 41 5 w at 3150 m and 3110 m elevation paramo vegetation with high proportions of plantago rigida characterised the last glacial maximum lgm reflecting cold and wet conditions the upper forest line was at markedly lower elevations than present after ca 16 200 cal yr bp paramo vegetation decreased slightly while mountain rainforest developed suggesting rising temperatures the trend of increasing temperatures and mountain rainforest expansion continued until ca 8500 cal yr bp while highest temperatures probably occurred from 9300 to 8500 cal yr bp from ca 8500 cal yr bp paramo vegetation re expanded with dominance of poaceae suggesting a change to cooler conditions during the late holocene after ca 1800 cal yr bp a decrease in paramo indicates a change to warmer conditions anthropogenic impact near the study site is indicated for times after 2300 cal yr bp the regional environmental history indicates that through time the eastern andean cordillera in south ecuador was influenced by eastern amazonian climates rather than western pacific climates

ionospheric effects during the total solar eclipse over southeast asia pacific on 9 march 2016 part 1 vertical movement of plasma layer and reduction in electron plasma density

a late glacial holocene tephrochronology for glacial lakes in southern ecuador despite the presence of numerous active volcanoes in the northern half of ecuador few if any distal tephras have been previously recognized in the southern one third of the country in this article we document the presence of thin 0 1 1 0 cm thick distal tephras comprising glass and or phenocrysts of hornblende and feldspar in sediment cores from five glacial lakes and one bog in las cajas national park 2 40 3 00 s 79 00 79 25 w the lake cores contain from 5 to 7 tephras and each has a diagnostic major element geochemistry as determined from electron microprobe analysis of 710 glass shards and 440 phenocrysts of feldspar and hornblende the loss of sodium with exposure to the electron microbeam causes a 10 7 wt 1 reduction in na content which we empirically determined and corrected for before correlating tephras among the sediment cores we use a similarity coefficient to correlate among the sediment cores pair wise comparison of all tephras generally yields an unambiguous correlation among the cores six tephras can be traced among all or most of the cores and several tephras are present in only one or two of the cores twenty six accelerator mass spectrometry 14c dates on macrofossils preserved in the sediment cores provide the basis for establishing a regional tephrochronology the widespread tephras were deposited 9900 8800 7300 5300 2500 and 2200 cal yr b p the oldest tephras were deposited 15 500 and 15 100 cal yr b p but these are not found in all cores two of the tephras appear correlative with volcaniclastic strata on the flanks of volcan cotopaxi and one tephra may correlate with strata on the flanks of volcan ninahuilca both volcanoes are in central ecuador the absence of tephras in sediment cores correlative with the numerous eruptions of active volcanoes of the past two millennia implies that the earlier eruptions which did deposit tephras in the lakes must have been either especially voluminous or southerly winds must have prevailed at the time of the eruption or both

historical ecology in beringia the south land bridge coast at st paul island a 14 m core of lake sediments from st paul island yields a long environmental history of the south coast of the bering land bridge tritium assay demonstrates that sands in the bottom 8 m of deposit are injected with modern water suggesting that a radiocarbon anomaly is the result of modern carbon introduced in groundwater the remaining radiocarbon chronology coupled with a time stratigraphic pollen zone boundary suggests that the record penetrates to the mid wisconsin interstadial pollen percentage data picea pollen influx and pollen species lists allow reconstruction of the land bridge vegetation which was tundra without shrubs or trees with bare ground and comparable to bering land bridge tundras found further north there was no coastal mild or wet strip plant associations comparable to those of the modern aleutians or pribilofs probably did not exist along the land bridge coast and the region was probably not suitable for breeding by fur seals and other marine mammals a cold dry continental air mass system reached to the coast itself the south land bridge coast did not offer an environment to aboriginal human populations that was significantly milder than that of the land bridge plains to the north at about 11 000 yr b p the wisconsin dry climate was replaced by a regimen comparable to that at the modern tree line of the interior and this climate in turn was replaced with the modern system at about 9500 yr b p climatic change was independent of fluctuating sea level

quaternary glaciations in the northern andes venezuela colombia and ecuador abstract the nature and distribution of glacial drift in the high andes of venezuela colombia and ecuador suggest that deposits of only the last two quaternary glaciations isotope stages 6 and 4 2 are present the penultimate glaciation in ecuador may be represented by deeply weathered drift that is beyond the range of radiocarbon dating in colombia and venezuela subdued moraines covered with loess may be of equivalent age in places this drift extends 1000 m lower in altitude than the limits of the last glaciation which comonly reach 3400 3600 m radiocarbon dated organic deposits 33 43 ka bp lying between tills composing superposed terminal moraines suggest that andean glaciers may have been as extensive during isotope stage 4 as during isotope stage 2 a relatively long interstadial from 43 33 ka bp preceded the glacier advance that culminated during the interval ca 28 15 ka bp two late glacial stadials are marked by moraine complexes at 3900 4200 m altitude they are partly constrained by radiocarbon ages of 12 9 ka bp and 12 10 ka bp moraines apparently deposited during neoglacial advances of the last ca 5 ka lie in front of most of the glaciers remaining in the northern andes

a vegetation and fire history of lake titicaca since the last glacial maximum fine resolution fossil pollen and charcoal analyses reconstruct a vegetation and fire history in the area surrounding lake titicaca 3810 m peru bolivia since ca 27 500 cal yr bp hereafter bp time control was based on 26 accelerator mass spectrometer ams radiocarbon dates seventeen ams dates and 155 pollen and charcoal samples between ca 17 500 bp and ca 3100 bp allow a centennial scale reconstruction of deglacial and early to mid holocene events local and regional fire signals were based on the separation of two charcoal size fractions 180 m and 179 65 m charcoal abundance correlated closely with the proportion of woody taxa present in the pollen spectra little or no pollen was detected in the sedimentary record prior to ca 21 000 bp very cold climatic conditions prevailed with temperatures suggested to be at least 5 8 c cooler than present increases in pollen concentration suggest initial warming at ca 21 000 bp with a more significant transition toward deglaciation ca 17 700 bp between 17 700 bp and 13 700 bp puna brava is progressively replaced by puna and sub puna elements the most significant changes between the pleistocene and the holocene floras were largely complete by 13 700 bp providing an effective onset of near modern conditions markedly earlier than in other andean records fire first occurs in the catchment at ca 17 700 bp and becomes progressively more important as fuel loads increase no evidence is found of a rapid cooling and warming coincident with the younger dryas chron a dry event between ca 9000 bp and 3100 bp with a peak between 6000 and 4000 bp is inferred from changes in the composition of aquatics and the marsh community as pollen of cyperaceae is replaced by poaceae apiaceae plantago and the shrub polylepis human disturbance of the landscape is evident in the pollen spectra after ca 3100 bp with the appearance of weed species

reconstruction of the mid holocene paleoclimate of the ecuadorian andean paramo at tres lagunas ecuador previous paleoclimate studies have suggested a warm dry event during the mid holocene in paramo vegetation of the tropical andes of south america however the timing of the mid holocene warm dry event in tres lagunas ecuador remains uncertain since a previously reported bog core record characterized the warm dry event during a hiatus in sediment deposition in order to understand the timing of the warm dry event in tres lagunas in relation to regional records a lake sediment core was collected subsamples from the core were analyzed for radiocarbon dates pollen magnetic susceptibility and charcoal to reconstruct the depositional vegetational and fire history of the area a near constant sedimentation rate in the lake core indicated that the lake did not dry in contrast to the adjacent previously reported bog core increases in lower elevation pollen types suggest

hibonite hercynite inclusion hh 1 from the lance co3 meteorite the history of an ultrarefractory cai we studied the petrography major and trace element chemistry and magnesium calcium titanium and iron isotopic compositions of a hibonite rich refractory inclusion from the lance co3 meteorite the inclusion 290 230 m in size consists of a core of hibonite crystals containing small perovskite grains surrounded by a hercynite mantle and a thin diopside rim the hercynite contains many small perovskite ilmenite and sulfide grains trace element abundances show an ultrarefractory signature in all measured phases with an increasing depletion of the rees heavier than tb with increasing mass in hibonite perovskite and ilmenite but not hercynite calcium and titanium are isotopically anomalous with large deficits in 48ca and 50ti deficits are 60 in 50ti and 11 5 in 49ti in hibonite hercynite perovskite and ilmenite in addition the titanium isotopes show a mass dependent isotopic fractionation of 8 5 amu in favor of the heavy isotopes calcium isotope deficits in hibonite are 6 9 in 42ca 5 0 in 43ca and 32 5 in 48ca relative to 40ca 44ca the deficits are smaller in the rim diopside 48ca 21 and a neighboring pyroxene grain 48ca 8 magnesium shows excesses in 26mg but the lack of an isochron relationship between 26mg24mg and 27al24mg indicates redistribution of radiogenic 26mg magnesium in hibonite is isotopically light fmg 5 3 amu the iron isotopes in hercynite are normal the data show that inclusion hh 1 experienced a complex metasomatic history including fe metasomatism sulfurization and formation of nepheline and sodalite the isotopic data provide not only a record of nucleosynthetic processes and nebular inhomogeneity but also a tracer of the relative movement of elements which may have occurred during alteration

late quaternary glaciation in southern africa moraine ridges and glacial deposits at mount enterprise in the drakensberg of the eastern cape province south africa late quaternary moraines and diamictons containing striated clasts are described from near elliot in the drakensberg of south africa an equilibrium line altitude ela of 2109 m is suggested for the palaeoglacier associated with the innermost moraine this glacier was fed by a very extensive snowblow area and the ela may reflect the temperature precipitation wind ela rather than the temperature precipitation ela and be considerably below the regional ela mean annual air temperatures when glaciation occurred were probably at least 10 0 c below those of the present copyright 2001 john wiley sons ltd

rare earth element geochemistry and petrogenesis of miles iie silicate inclusions an ion probe study of rare earth element ree geochemistry of silicate inclusions in the miles he iron meteorite was carried out individual mineral phases among inclusions have distinct ree patterns and abundances most silicate grains have homogeneous ree abundances but show considerable intergrain variations between inclusions a few pyroxene grains display normal igneous ree zoning phosphates whitlockite and apatite are highly enriched in rees 50 to 2000 x ci with a relatively light rare earth element lree enriched ree pattern they usually occurred near the interfaces between inclusions and fe host in miles albitic glasses exhibit two distinctive ree patterns a highly fractionated lree enriched ci normalized la sm similar to 15 pattern with a large positive eu anomaly and a relatively heavy rare earth element hree enriched pattern ci normalized lu gd similar to4 with a positive eu anomaly and a negative yb anomaly the glass is generally depleted in rees relative to ci chondrites

late pleistocene and holocene environmental change inferred from the cocha caranga sediment and soil records in the southeastern ecuadorian andes abstract late pleistocene and holocene vegetation climate and fire dynamics of mountain forest and paramo ecosystems as well as human impact are presented from the cocha caranga area at 2710 m elevation in the podocarpus national park southeastern ecuadorian andes palaeoenvironmental changes inferred from two sediment cores and a soil core were investigated by pollen spore algae and charcoal analyses during the transition from late pleistocene to early holocene between ca 14 500 to 9700 cal yr bp upper mountain forest vegetation expanded suggesting increasing temperature and moisture this expansion abruptly stopped with increasing fires at ca 9700 cal yr bp and open grassy vegetation became established the period from ca 9700 to 1300 cal yr bp of strong fire intensity indicate that vegetation components mainly weinmannia and myrica react sensitively to past probably human caused fires during the last few centuries modern vegetation established characterised by open grassy areas with forest patches and small mires the green algae botryococcus braunii isoetes and cyperaceae were used to identify lake level fluctuation to reconstruct holocene wet dry phases drier climatic conditions occurred from ca 9700 to 6900 cal yr bp and from ca 4200 to 1300 cal yr bp from ca 6900 to 4200 cal yr bp and from ca 1300 cal yr bp to modern times wetter climatic conditions occurred

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

the midlatitude ionosphere during the total solar eclipse of march 9 1997 the total solar eclipse of march 9 1997 was visible from some regions of china mongolia and east siberia during 0045 0130 ut the eclipse coincided with a relatively long geomagnetically quiet period during the total solar eclipse the observations included oblique incidence ionograms recording also measurement the total electron content along specified directions to the visible global positioning system satellites and the doppler sounding on various hf ray paths over the region under consideration were carried out this paper presents results derived from studying the spatial pattern of midlatitude ionospheric response to this eclipse on the basis of a numerical simulations calculations have been executed using a model for ionosphere plasmasphere coupling comparison of model results with data of all measurements showed a good qualitative and quantitative agreement it is shown that by and large the behavior of the ionosphere during the eclipse manifests itself as a short lasting l hour rearrangement to nighttime conditions with the ion flow directed downward from the plasmasphere as a rise of the f2 layer maximum by about 20 km and as a twofold increase in electron density at the height of the maximum during the eclipse s totality phase the electron temperature decreases by 200 400 k while the ion temperature drops only slightly it is found that changes in the spatial distribution of electron density along the hf ray paths during the eclipse give rise to variations of doppler frequency shift with amplitudes of about 1 hz and a duration of about 120 min the findings reported in this paper do not validate the hypothesis that solar eclipses generate atmospheric gravity waves and associated traveling ionospheric disturbances

multiple generations of hibonite in spinel hibonite inclusions from murchison through freeze thaw disaggregation of the murchison meteorite we have recovered in addition to many spinel hibonite spherules several hibonite rich inclusion fragments in which the hibonite has wider ranges in tio2 contents e g 0 07 8 6 wt in one inclusion and 2 10 wt in another than previously observed within single inclusions in these inclusions there are sharp contacts between texturally early ti poor hibonite and relatively late ti rich hibonite and the two types occur in complex intergrowth textures that are not consistent with crystallization from a melt in a single stage cooling event one inclusion has in addition to relatively tio2 rich hibonite some that is virtually tio2 free but contains 1 wt mgo and 1 5 wt sio2 instead of the common substitution of mg ti for 2al mg coupled with si in this case probably reflecting crystallization from an unusual ti free silicate liquid ion microprobe analyses of ti rich and ti poor hibonite from this inclusion yield quite similar trace element patterns and mg isotopic compositions the results are most consistent with formation of ti rich hibonite from ti poor hibonite by addition of mg and ti to the latter by exchange with a hot ti rich liquid that this occurred without a resolvable change in the mg isotopic composition requires that the ti rich second generation of hibonite formed 2 5 times 105 yr later than the ti poor hibonite observations of spinel hibonite spherules and spherule fragments in our sample suite provide additional evidence that despite the claims by greenwood et al 1994 spinel hibonite spherules crystallized from individual molten droplets as earlier suggested by macdougall 1981 and macpherson et al 1983

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

vegetation and landscape dynamics under natural and anthropogenic forcing on the azores islands a 700 year pollen record from the sao miguel island abstract the azores archipelago has provided significant clues to the ecological biogeographic and evolutionary knowledge of oceanic islands palaeoecological records are comparatively scarce but they can provide relevant information on these subjects we report the palynological reconstruction of the vegetation and landscape dynamics of the sao miguel island before and after human settlement using the sediments of lake azul the landscape was dominated by dense laurisilvas of juniperus brevifolia and morella faya from ca 1280 ce to the official european establishment 1449 ce after this date the original forests were replaced by a complex of erica azorica myrsine africana forests shrublands and grassy meadows which remained until ca 1800 ce extractive forestry cereal cultivation rye maize wheat and animal husbandry progressed until another extensive deforestation ca 1774 ce followed by the large scale introduction 1845 ce of the exotic forest species cryptomeria japonica and pinus pinaster which shaped the present day landscape fire was a significant driver in these vegetation changes the lake levels experienced a progressive rise during the time interval studied reaching a maximum by ca 1778 1852 ce followed by a hydrological decline likely due to a combination of climatic and anthropogenic drivers our pollen record suggests that sao miguel were already settled by humans by ca 1287 ce approximately one century and a half prior to the official historically documented occupation of the archipelago the results of this study are compared with the few palynological records available from other azores islands pico and flores

petrographic studies of refractory inclusions from the murchison meteorite textural and mineral chemical data on freeze thaw disaggregated refractory inclusions from the murchison meteorite are reported the data were obtained with neutron activation analysis sem and spectroscopy the study revealed corundum bearing inclusions spinel hibonite aggregates and spherules and spinel pyroxene and elivine pyroxene inclusions one of the three spinel pyroxene forsterite rich inclusions had an amoeba shaped spinel pyroxene core implying vapor to solid condensation and therefore crystallization from a melt it is concluded that the meteorite formation encompassed diverse nebular materials and that further studies of the meteorite will enhance the data base on the planetary nebular processes

presolar isotopic and chemical signatures in hibonite bearing refractory inclusions from the murchison carbonaceous chondrite magnesium calcium and titanium isotopic compositions as well as trace element abundances have been determined by ion microprobe mass spectrometry for 37 hibonite bearing inclusions from the murchison carbonaceous chondrite these and previously analyzed hibonite bearing inclusions can be divided into three main groups based on morphological and mineralogical criteria platy crystal fragments placs generally have depletions in the relatively volatile refractory trace elements eu yb mb v ba little or no evidence of 26al i e little or no radiogenic 26mg 26mg and widely variable ca and ti isotopic compositions one plac 13 13 has excess 48ca of 104 and 50ti of 273 the largest effects yet measured in these elements four blue aggregates bags are distinctive in having low overall trace element abundances with large relative depletions in the ultrarefractory elements gd er lu zr hf y sc and mass fractionated mg isotopic compositions enriched in the heavy isotopes large 50ti deficits have been measured in three of the four bags the only bag analyzed for its ca isotopic composition also shows a deficit in 48ca spinel hibonite inclusions shibs show a wide variety of morphologies ranging from bladed hibonite crystals within spinel to spherules of hibonite and spinel to large uniform hibonite crystals within spinel shibs consisting of bladed hibonite in spinel or hibonite spinel spherules typically have ultrarefractory depleted trace element patterns although uncommon ultrarefractory enriched patterns were also found 26mg at a level consistent with 5 10 5 27al and generally small 10 ca and ti isotopic anomalies one of the shib spherules 7 170 has highly unusual systematics with a large 50ti deficit only a small 48ca deficit and no 26mg the large hibonite crystals within spinel have variable trace element patterns commonly with anomalies in the relatively volatile elements ce eu and yb 26mg is present in some of these inclusions but none of this type of shib has large ca or ti isotopic anomalies while at least four distinct components are required to model the ti isotopic compositions three components are sufficient to describe the variations in ca isotopic compositions measured thus far the systematics of plac 13 13 with large excesses of 48ca and 50ti match the predictions of the multiple zone mixing model for nucleosynthesis in supernova ejecta to a maximum neutron excess of 0 159 compositions depleted in 48ca and 50ti are unlikely to represent discrete nucleosynthetic components but represent material with a shortfall of neutron rich material relative to the solar system abundances additional components must be present but are not easily resolved within the morphological groups of hibonite bearing inclusions a few have exceptional chemical and isotopic characteristics such as shib spherule 7 170 however independent of the morphological groups there are correlations in hibonite isotopic systematics and chemistry that hold for all inclusions studied 1 no inclusion has both a large 50ti anomaly and 26mg and 2 inclusions depleted in the ultrarefractory elements have 26mg with the exception of those which have a large 50ti anomaly these features clearly establish a relationship between chemical and isotopic characteristics of the inclusions which must predate their formation several components were combined probably as mixtures of dust grains or crystals and were melted to form refractory inclusions the nucleosynthetic anomalies must be inherited from stellar environments it is possible that the depletions in ultrarefractory elements are also a memory of stellar condensation and are not necessarily related to a condensation event in the solar nebula as has generally been assumed

holocene lake level fluctuations of lake aricota southern peru lacustrine deposits exposed around lake aricota peru 17 22 s a 7 5 km2 lake dammed by debris flows provide a middle to late holocene record of lake level fluctuations chronological context for shoreline deposits was obtained from radiocarbon dating of vascular plant remains and other datable material with minimal 14c reservoir effects 350 yr diatomites associated with highstands several meters above the modern lake level indicate wet episodes maximum holocene lake level was attained before 6100 14c yr b p and ended 2700 14c yr b p moderately high lake levels occurred at 1700 and 1300 14c yr b p the highstand at lake aricota during the middle holocene is coeval with a major lowstand at lake titicaca 16 s which is only 130 km to the northeast and shares a similar climatology comparisons with other marine and terrestrial records highlight emerging contradictions over the nature of mid holocene climate in the central andes

a 21 000 cal years paleoclimatic record from caco lake northern brazil evidence from sedimentary and pollen analyses abstract sedimentological studies including seismic profiles mineralogy and organic geochemistry on two cores from the center and margin of caco lake maranhao state northern brazil revealed variable climatic and environmental conditions during the last 21 cal kyr bp between 21 and 17 cal kyr bp during the late glacial maximum regional climate was predominantly dry interrupted by short humid phases as reflected by a succession of very thin layers of sand and organic matter the late pleistocene climate was relatively wet as is suggested by rapid lake level rise and forest expansion the late pleistocene humid climate differed significantly from present conditions we suggest that late glacial humid conditions were the consequence of intensification of the inter tropical convergence zone or shifts of its position resulting in antarctic cold front occurrences the abrupt climatic changes during this period were marked by siderite deposition into caco lake which appears to be related to regional hydrologic changes linked to global northern hemisphere events the holocene was characterized by lower moisture availability and a distinct dry period until 7 cal kyr bp in response to south american insolation conditions

modern pollen vegetation relationships along a steep temperature gradient in the tropical andes of ecuador the characterization of modern pollen rain assemblages along environmental gradients is an essential prerequisite for reliable interpretations of fossil pollen records in this study we identify pollen vegetation relationships using modern pollen rain assemblages in moss polsters n 13 and lake sediment surface samples n 11 along a steep temperature gradient of 7 c 3100 4200 m above sea level on the western andean cordillera ecuador the pollen rain is correlated to vascular plant abundance data recorded in vegetation relevees n 13 results show that pollen spectra from both moss polsters and sediment surface samples reflect changes in species composition along the temperature gradient despite overrepresentation of upper montane forest taxa in the latter estimated pollen transport distance for a lake laguna llaviucu situated in a steep upper montane forest valley is 1 2 km while a lake laguna pallcacocha in the paramo captures pollen input from a distance of up to 10 40 km weinmannia spp podocarpus spp and hedyosmum sp are indicators of local upper montane forest vegetation while phlegmariurus spp and plantago spp are indicators for local paramo vegetation

complementary element relationships between chondrules and matrix in rumuruti chondrites abstract the complimentary chemical composition of chondrules and matrix has so far only been studied in carbonaceous chondrites we have extended these studies to the matrix rich rumurutis we have determined the chemical composition of 27 bulk chondrules and 100 matrix spots in unequilibrated fragments of three different rumuruti r chondrites nwa 2446 nwa 753 hughes 030 also the bulk chemical composition of nwa 753 was determined bulk r chondrites have about ci chondritic solar ratios of fe mg 1 89 al ti 18 62 and al ca 0 94 while chondrules and matrix are complementary to each other mean fe mg ratios in chondrules are 0 43 nwa 2446 0 36 nwa 753 and 0 34 hughes chondrules are depleted in fe while matrices are enriched in fe with respective values of 2 59 2 45 and 2 39 bulk fe mg ratio of nwa 753 the only sample which is unaffected by terrestrial weathering is reproduced by careful mass balance calculations using compositions and abundances of chondrules matrix and sulphides from the same thin section refractory element ratios are also complementary al ti and al ca are sub chondritic in chondrules al ti 10 43 in nwa 753 12 24 in nwa 2446 and 11 47 in hughes 030 al ca 0 66 in nwa 2446 0 53 in nwa 753 and 0 46 in hughes 030 while matrices generally have super chondritic al ca and al ti ratios al ti 28 00 in nwa 2446 23 20 in nwa 753 and 19 00 in hughes 030 al ca 2 30 in nwa 2446 1 90 in nwa 753 and 0 41 in hughes 030 calcium is enriched in the hughes 030 matrix due to terrestrial weathering these complementary element ratios and the ci chondritic bulk strongly suggest a common reservoir from which all r chondrite components formed similar to carbonaceous chondrites further super chondritic si mg and ci chondritic fe mg ratios in bulk r chondrites require addition of si to their reservoir most probably before chondrule formation

abrupt changes in early holocene tropical sea surface temperature derived from coral records for many high latitude regions of the globe it is now clear that the transition to modern climate following the last glacial maximum was punctuated by a number of rapid and substantial climate oscillations1 2 in contrast relatively little is known about how the tropics responded to the deglaciation because few high resolution records are available from lower latitudes corals have recently been shown to provide an important source of tropical climate records because they can be easily and accurately dated using either 14c or 230th and because past sea surface temperatures can be recovered from the sr ca ratios in coral skeletons here we use this technique to derive several early holocene sea surface temperature records from a coral drill core recovered from espiritu santo vanuatu in the tropical southwest pacific ocean these records indicate that sea surface temperatures in this region were depressed by as much as 6 5 c below modern values at 10 350 calendar years bp but rose very abruptly during the following 1 500 years this temperature increase lags the post younger dryas increase observed in a coral record from the tropical atlantic ocean3by about 3 000 years an unexpected phase shift that may ultimately shed light on the mechanisms of deglacial climate change

last glacial maximum in an andean cloud forest environment eastern cordillera bolivia climatically sensitive tropical ecosystems provide important information that may help us to fill the gaps in our knowledge concerning the evolution of rainforests during periods of full glaciation small changes in precipitation in the amazon basin have immediate consequences for the survival of the andean cloud forest because its dominant source of moisture today is the atlantic ocean a 40 k y lacustrine record from the eastern cordillera in bolivia in an endemic species rich and ecologically threatened region shows a dry last glacial maximum indicating a drastic decrease of the amazonian moisture source to explain this aridity we infer steep temperature gradients between the pole and equator in both hemispheres that would have reduced considerably the size and displacement of the intertropical convergence zone and the austral summer precipitation this major change in water supply induced a dramatic reduction in species diversity and suggests that the andean cloud forest did not provide refugia for tropical lowland taxa during full glacial times

correlated morphological chemical and isotopic characteristics of hibonites from the murchison carbonaceous chondrite twenty four hibonite dominated refractory grains from the murchison carbonaceous chondrite have been identified from polished grain mounts of density separates and have been morphologically and chemically divided into three groups 1 14 colourless platy crystal fragments placs with less than 2 7 tio2 2 3 pleochroic blue aggregates bags which are composed of crystal plates and fragments and have tio2 concentrations between 5 1 and 6 5 3 six spinel hibonite spherules and crystal aggregates shibs often with spinel fe silicate and clinopyroxene rims the maximum tio2 concentrations of hibonite in the shibs ranges from 3 5 to 7 6 but the tio2 concentration in one grain was heterogeneous and ranged from 0 5 to 5 0 hibonite in all types is stoichiometric with ti and mg predominantly in a coupled substitution of mg2 and ti4 for 2al3 one grain with a rounded hibonite core does not clearly fit into the three designated groups the hibonites have been analysed by ion microprobe mass spectrometry for their mg and ti isotopic compositions twelve of the placs have 26al27al 0 ratios less than 1 10 5 but the other two placs have 26al27al 0 of 5 5 10 5 and 7 7 10 5 the excess 26mg may reflect initial mg isotopic heterogeneities in the source region of the placs or be the result of in situ26al decay in which case the distribution of 26al was heterogeneous three bags show substantial positive mass fractionation of mg one grain has excess 26mg while the other two have 26mg depletions the 26mg depletions indicate the preservation of mg isotopic anomalies in the bags but the excess 26mg in one grain could be due to in situ26al decay the six shibs have excess 26mg that is correlated with 27al24mg the mg isotopic systematics of the shibs are consistent with the in situ decay of 26al with 26al27al 0 of ca 5 10 5 the unclassified hibonite has a clearly resolved deficit in 26mg titanium isotopic anomalies are common in the hibonites measured here the largest anomalies are in 50ti with variations in 50ti48ti ranging from 50 to 16 relative to terrestrial smaller anomalies are present in 49ti and 47ti the ti isotopic compositions are not directly correlated with morphological type but the placs show the largest variations in isotopic composition whereas the shibs are generally close to terrestrial the presence of hibonite populations with distinct morphological chemical and mg isotopic systematics suggests that there were several hibonite formation episodes within the early solar system the hibonites probably formed by the melting of refractory dust aggregates during local transient thermal events

forests of the tropical eastern andean flank during the middle pleistocene inter bedded volcanic and organic sediments from erazo ecuador indicate the presence of four different forest assemblages on the eastern andean flank during the middle pleistocene radiometric dates 40ar 39ar obtained from the volcanic ash indicate that deposition occurred between 620 000 and 192 000 years ago examination of the organic sediment composition and the fossil pollen wood and charcoal it contains provides insight into depositional environment vegetation assemblage and fire history the high organic content and abundance of macro fossils found throughout the sediment suggest that during the period of deposition the local environment was either a swamp or a shallow water body the correlation of fire activity peaks in charcoal abundance with volcanic ash deposits through most of the record suggests that volcanoes were the main source of ignition the low abundance of grass typically 10 throughout the sedimentary sequence along with the low abundance of other taxa indicative of open vegetation suggests the persistence of forest at erazo four types of forest assemblage were identified with the first taxa as the most dominant i alnus arecaceae ii miconia melastomataceae combretaceae moraceae urticaceae iii arecaceae alnus and iv podocarpus with oreopanax sp and melastomataceae combretaceae changes in the forest floristic composition indicate high vegetation turnover and reassortment of taxa between upper and lower montane forests during the middle pleistocene as well as the persistence of forest cover

abundance and morphometry changes across the high mountain lake size gradient in the tropical andes of southern ecuador the number size and shape of lakes are key determinants of the ecological functionality of a lake district the lake area scaling relationships with lake number and volume enable upscaling biogeochemical processes and spatially considering organisms metapopulation dynamics these relationships vary regionally depending on the geomorphological context particularly in the range of lake area 1 km2 and mountainous regions the cajas massif southern ecuador holds a tropical mountain lake district with 5955 water bodies the number of lakes deviates from a power law relationship with the lake area at both ends of the size range similarly to the distributions found in temperate mountain ranges the deviation of each distribution tail does not respond to the same cause the marked relief limits the size of the largest lakes at high altitudes whereas ponds are prompt to a complete infilling a bathymetry survey of 202 lakes selected across the full size range revealed a volume area scaling coefficient larger than those found for other lake areas of glacial origin but softer relief water renewal time is not consistently proportional to the lake area due to the volume area variation in midsize lakes the 85 of the water surface is in lakes 104 m2 and 50 of the water resources are held in a few ones 10 deeper than 18 m therefore midlakes and large lakes are by far more biogeochemically relevant than ponds and shallow lakes in this tropical mountain lake district

efremovka 101 1 a cai with ultrarefractory ree patterns and enormous enrichments of sc zr and y in fassaite and perovskite inclusion 101 1 from the cv3 carbonaceous chondrite efremovka is a compact type a ca al rich inclusion cai highly enriched in ultrarefractory ur oxides it is the first complete cai with a ur rare earth element ree pattern found in a cv3 chondrite the inclusion is petrographically complex and was formed in a multistage process it consists of several lithologically unrelated units the core contains abundant y and zr perovskite sc and zr rich fassaite and metallic feni enclosed in melilite all mineral species except spinel in all lithological units exhibit the same basic ur ree pattern four different populations of perovskites are distinguished by different y zr ratios a few of the perovskites have y zr ratios similar to those obtained from crystal liquid fractionation experiments perovskites from the other three populations have either chondritic lower than chondritic y zr ratios or extremely low zr contents ca isotopic ratios differ among three perovskites from different populations demonstrating a variety of sources and formational processes most fassaites crystallized in situ through reaction between the cai liquid and preexisting perovskites this process induced redistribution of zr y sc and v between perovskite and fassaite thus overprinting the original abundances in perovskite fassaite reaction rims around feni metals are also encountered they are enriched in v which was gained from the metal through oxidation of v in metal during fassaite crystallization the relative abundances of zr y and sc in perovskites are complementary to the abundances of these elements in sc and zr fassaite indicating subsolidus partitioning of these elements between the two phases perovskites are enriched in y and depleted in sc and zr in comparison to fassaites the core contains two complete captured cais several sinuous fragments and fine grained polygonal refractory fragments an assemblage of andradite wollastonite hedenbergite and pure metallic iron is encoun tered as enclaves in the interior of some sinuous fragments metallic fe and wollastonite formed by reduction of preexisting andradite and hedenbergite nebular alteration products upon inclusion in the highly reduced cai melt numerous spinel clusters and framboids with varying v2o3 and cr2o3 concentrations are enclosed in individual melilite crystals in the host cai and captured cais the rim sequence of the host consists of six layers from the inside outward a feo poor spinel b sc bearing fassaite c al diopside d al and ca bearing olivine e pure diopside and f ca poor olivine like the constituents of the cai core all mineral layers of the rim sequence except spinel have the same ur ree pattern however the total ree abundances decrease systematically by 1 order of magnitude from layer 2 to layer 6 this feature strongly suggests formation of the rim sequence by successive condensation from a unique reservoir enriched in ur elements and excludes formation by flash heating petrography mineral chemistry ree refractory lithophile element abundances and ca isotopic compositions demonstrate the complex multistage formation history of a cai that on the surface looks like a regular type a inclusion copyright 2002 elsevier science ltd

corundum bearing residues produced through the evaporation of natural and synthetic hibonite we have produced corundum bearing residues through the evaporation of natural and synthetic hibonite samples the sequence of major element losses as well as volatility related trace element fractionations in these residues are similar to those previously observed in residues from the evaporation of chondritic starting material which suggests that the processes by which these fractionations occur may be largely independent of the starting material used however the mineralogy of the residues does depend on the composition of the starting material and to some extent on the conditions under which evaporation took place similarly the degree of isotopic mass fractionation observed in the residues is composition dependent this observation means that it may be possible to use isotopic data for several elements to constrain the compositions of precursor materials of ca al rich inclusions which have an evaporation origin although corundum bearing inclusions are known their origins are complex and variable and the scarcity of such inclusions indicates that melting of hibonite with or without concomitant evaporation must have been a rare process in the solar nebula by evaporating mixtures of synthetic oxides of the rare earth elements we have reproduced the patterns of group iii inclusions and some of the characteristics of ultrarefractory patterns however the extreme conditions required to do so indicate that refractory inclusions with these patterns probably have a condensation rather than evaporation origin

late pleistocene glacial forest elements of brazilian amazonia abstract pollen data recovered from the sedimentary record of western amazonia is still inadequate to fully address climate changes over the last glaciation in this region the present work focuses vegetation dynamics from an area of southwestern amazonia during the past 42 000 cal yr b p based on the integration of previous and new pollen data sediment cores were sampled from two sites covered by tropical rainforest in fluvial terraces of the madeira river a major southern amazonian tributary the results indicated a significant proportion of cold adapted andean tree species represented by alnus 0 20 hedyosmum 1 15 podocarpus 0 5 illex 1 11 and weinmannia 0 1 at least between 43 163 42 018 cal yr b p and 10 394 10 240 cal yr b p during the holocene only pollen representative of herbs and modern amazonian vegetation persisted the new pollen record confirmed previous documented results that vegetation communities presently restricted to andean areas at altitudes higher than 2000 3000 m occupied this region of the amazonian lowlands close to the onset and probably also during the last glacial maximum

forest changes in the amazon basin during the last glacial maximum we report here the discovery of forest beds in the amazon basin radiocarbon dated to the wisconsin wurm glaciation these are the first dates from the last glaciation determined on amazonian samples the locality is in ecuador at 1 100 m elevation near the upper limit of the present amazonian rainforest both pollen spectra and podocarpus wood in the deposits suggest that vegetation comparable to the present andean forest grew at least 700 m lower than it does now suggesting a temperature depression of at least 4 5 c for the amazon lowlands

late quaternary vegetation climate and fire dynamics and evidence of early to mid holocene polylepis forests in the jimbura region of the southernmost ecuadorian andes abstract the vegetation climate and fire history of high mountain ecosystems in the southern ecuadorian andes are documented in a continuous pollen and charcoal record from lagunas natosas forest bog at 3495 m a s l spanning the late pleistocene and holocene periods since 15 930 cal yr bp the chronology of this record is based on four radiocarbon dates paramo vegetation with abundant poaceae and plantago rigida characterized the late glacial lg period implying cold and wet conditions slight expansions of mountain forests suggest warming during the lg the upper forest line was lower than today and fire events were rare during the pleistocene during the early and mid holocene until 4300 cal yr bp the area of paramo was markedly smaller and the subparamo with woody vegetation melastomataceae was larger the upper mountain forest dominated and the upper forest line shifted to higher elevations the pollen record provides the first evidence of the development of polylepis forests in the southern part of the so called andean depression reflecting warmer and drier climatic conditions during early and mid holocene the late holocene after about 4300 cal yr bp is characterized by larger areas of paramo and subparamo promoted by moister conditions these moister conditions and frequent fires may have been the cause of the very rare occurrence or even extinction of polylepis populations in the jimbura region since ca 1000 cal yr bp human occupation has altered the landscape by frequent burning wood cutting grazing and cultivation

late quaternary vegetational change in the central peruvian andes abstract new fossil pollen records from the central peruvian andes at elevations above 4000 m including pollen concentration data and additional radiocarbon dates provide information on late quaternary vegetation change for the region a pollen assemblage typical of superpuna plus low pollen concentrations and organics in the late glacial section of laguna tuctua indicate a cold dry climate but strong evidence for a late glacial climate reversal i e the younger dryas is not presently confirmed an abrupt increase in urticales pollen as compositae and polylepis acaena type pollen decline signals the beginning of the holocene subsequent increases in urticales and plantago rigida type pollen point to increased moisture as well as higher temperatures from about 11 000 to 7000 yr b p a possible correlation exists between the rapid expansion of puna and closed continuous forest and the rise in importance of camelids in the early holocene in the mid holocene plantago rigida cushion bogs and continuous montane forest elements decline suggesting a drier climate grasses and cheno ams then increase reaching maxima about 4000 yr b p pastoralism and agriculture are thought to have developed at this time according to ethnobotanical studies from this area and pollen evidence seems to support these findings between 3000 and 2000 yr b p pollen percentages of poaceae plantago rigida type and other local taxa decline as glacial activity was renewed in the higher mountains zea mays is present by 2000 yr b p and pollen of weeds and secondary successional plants associated with increasing agricultural disturbance are evident

hibonite bearing microspherules a new type of refractory inclusions with large isotopic anomalies reported are petrographic descriptions major and trace element chemistry and mg ca and ti isotopic compositions of a new class of refractory inclusions that consist of spherules composed of hibonite and a silicate glass the distinctive features of these inclusions are excesses in 48ca and 50ti in both glass and hibonite and 26mg depletions relative to terrestrial isotopic compositions three spherules have been examined and analyzed one from the lance co3 meteorite and two from the murchison cm2 meteorite lance 3413 1 31 la3413 1 31 and murchison 7 228 mur7 228 have euhedral to subhedral hibonite crystals enclosed within glass murchison 7 753 mur7 753 has a rounded hibonite core with several small inclusions of perovskite a small fragment of glass is attached to the hibonite and an fe silicate rim is imperfectly preserved around the grain la3413 1 31 has a group ii ree pattern mur7 228 a refractory pattern with depletions in the relatively volatile elements sr ba nb v and eu and mur7 753 a pattern characterized by the prior removal of an ultrarefractory component and overall fractionation of all rees the partitioning of the lrees between hibonite and glass in mur7 228 is consistent with equilibrium hibonite liquid partition coefficients previously determined la3413 1 31 shows much less partitioning while mur7 753 shows no evidence for partitioning and preserves an unequilibrated refractory component highly enriched in gd all spherules have initial magnesium depleted in 26mg by around 3 relative to terrestrial mg but only mur7 228 shows evidence for in situ decay of 26al with an initial 26al27al of 1 7 0 7 10 5 both hibonite and glass in all three spherules show excesses of 48ca and 50ti ranging up to 40 and 20 respectively relative to terrestrial ca and ti spherules such as these are rare and the only other occurrence is in the unique chondrite alh85085 the hibonite in the spherules shows similarities to isotopically anomalous hibonite crystal fragments placs but it is unlikely that the spherules formed by remelting of placs the precursors include isotopically anomalous ca ti carriers but also isotopically normal refractory components that probably formed as condensates the spherules formed by melting of these precursors under disequilibrium conditions and rapid cooling after hibonite crystallization these inclusions must have formed early prior to the dilution of isotopic anomalies by mixing processes and in an area characterized by excesses of 48ca and 50ti depletions of 26mg and lack of 26al

equatorial plasma fountain and its effects over three locations evidence for an additional layer the f 3 layer the equatorial plasma fountain and equatorial anomaly in the ionospheres over jicamarca 77 w trivandrum 77 e and fortaleza 38 w are presented using the sheffield university plasmasphere ionosphere model under magnetically quiet equinoctial conditions at high solar activity the daytime plasma fountain and its effects in the regions outside the fountain lead to the formation of an additional layer the f3 layer at latitudes within about plus or minus 10 of the magnetic equator in each ionosphere the maximum plasma concentration of the f3 layer which occurs at about 550 km altitude becomes greater than that of the f2 layer for a short period of time before noon when the vertical e b drift is large within the f3 layer the plasma temperature decreases by as much as 100 k the ionograms recorded at fortaleza on january 15 1995 provide observational evidence for the development and decay of an f3 layer before noon the neutral wind which causes large north south asymmetries in the plasma fountain in each ionosphere during both daytime and nighttime becomes least effective during the prereversal strengthening of the upward drift during this time the plasma fountain is symmetrical with respect to the magnetic equator and rises to over 1200 km altitude at the equator with accompanying plasma density depletions in the bottomside of the underlying f region the north south asymmetries of the equatorial plasma fountain and equatorial anomaly are more strongly dependent upon the displacement of the geomagnetic and geographic equators jicamarca and trivandrum than on the magnetic declination angle fortaleza

effects of syn pandemic fire reduction and reforestation in the tropical americas on atmospheric co2 during european conquest abstract a new reconstruction of late holocene biomass burning in the tropical americas is consistent with the expansion of fire use by mesoamerican and amazonian agriculturalists and a subsequent period of fire reduction beginning 500 years bp the marked reduction of biomass burning after 500 years bp a unique feature of the fire history of the tropical americas relative to other regions of the globe is synchronous with the collapse of the american indigenous population during pandemics accompanying european conquest we predict that fire reduction contemporaneous with pandemics in the tropical americas was associated with massive forest regeneration on 5 105 km2 of land and sequestration of 5 10 gt c into the terrestrial biosphere which contributed to the 2 global reduction in atmospheric co2 levels and the 0 1 increase in 13c of atmospheric co2 from 1500 to 1750 a d this study 1 builds upon prior fire history reconstructions by synthesizing a substantially greater number of stratigraphic charcoal accumulation records and soil charcoal 14c dates to resolve features of the late holocene biomass burning record in the tropical americas and 2 corroborates the hypothesis advanced by ruddiman ruddiman w f 2003 the anthropogenic era began thousands of years ago climatic change 61 261 293 ruddiman w f 2005 plows plagues and petroleum princeton university press princeton new jersey that biospheric carbon sequestration via reforestation of cropland abandoned during pandemics contributed to changes in atmospheric co2 concentration during the past millennium

an isotopic and petrologic study of calcium aluminum rich inclusions from co3 meteorites we have studied the mineralogy and petrology of 229 calcium aluminum rich inclusions cais from ten co3 meteorites of petrologic types 3 0 3 7 subsets of these inclusions were measured by ion probe for magnesium calcium and titanium isotopes and ree abundances most cais from co3 meteorites fall into three major types 1 melilite rich inclusions which also contain spinel hercynite perovskite and occasionally hibonite 2 spinel pyroxene inclusions and 3 hibonite hercynite inclusions in addition several isolated hibonite grains two grossite caal 4o 7 bearing cais two hibonite fassaite microspherules and one anorthite spinel pyroxene inclusion were found cais from co3 meteorites exhibit all of the ree patterns commonly seen in inclusions from cv3 and cm2 chondrites most exhibit evidence of 26 ai and many have inferred 26 ai 27 ai o 5 10 5 the relative abundances of different types of cais in co3 chondrites differ from those in cv3 and cm2 chondrites cais in co3 chondrites have experienced considerable secondary alteration both before and after accretion signatures of nebular alteration include wark lovering rims and the high fe contents in spinels from all hibonite hercynite inclusions occasionally melilite and anorthite show evidence of nebular alteration to feldspathoids and pyroxene the magnesium aluminum systematics of some melilite rich inclusions were apparently disturbed prior to final accretion of the parent body parent body alteration is indicated by correlations between cai characteristics and the petrologic type of the host meteorite spinel in melilite rich and coarse grained spinel pyroxene inclusions becomes more fe rich with the development of relatively homogeneous hercynitic spinel 50 60 mol in cais from metamorphic grades 3 4 perovskite has been converted to ilmenite in types 3 4 melilite rich inclusions are abundant in co3 0 3 3 meteorites rare in 3 4 meteorites and absent meteorites of types 3 5 3 7 melilite rich cais are probably replaced by inclusions rich in feldspathoids pyroxene and fe rich spinel isotopic disturbance of the magnesium aluminum systematics may be more severe in higher petrologic types hibonite seems to be unaffected by this level of metamorphism three isotopically unusual inclusions were found one single crystal hibonite isna sp16 has a ree pattern strongly depleted in ce and y 26 ai 27 ai o 2 4 0 3 10 5 and mass fractionated calcium f ca 12 2 amu but no resolvable nuclear anomalies in neutron rich calcium isotopes the ree pattern which is thought to reflect nebular conditions and mass fractionated calcium indicative of evaporation are similar to those of the fun inclusion hal and related hibonites indicating similar formation conditions the absence in isna sp16 of the nuclear anomalies observed in hal and the difference in 26 ai 27 ai o between hal and isna sp16 indicate that the processes that produced hal type hibonites operated on diverse materials two hibonite bearing microspherules colony sp1 and alh82101 sp15 exhibit nearly flat ree patterns with negative europium anomalies and slightly negative 26 mg alh82101 sp15 has resolved excesses of 48 ca and 50 ti these characteristics are similar to those of previously described microspherules from murchison and lance implying that the microspherules formed via a single process from related but not identical source materials

holocene climate variability and vegetation dynamics inferred from the 11700 cal yr bp laguna rabadilla de vaca sediment record southeastern ecuadorian andes palaeoenvironmental changes inferred from a 492 cm long lake sediment core from laguna rabadilla de vaca 3312 m in podocarpus national park southeastern ecuadorian andes were investigated usin

a hibonite corundum inclusion from murchison a first generation condensate from the solar nebula through freeze thaw disaggregation of the murchison cm carbonaceous chondrite we have recovered a 90 x 75 m refractory inclusion that consists of corundum and hibonite with minor perovskite corundum occurs as small 10 m rounded grains enclosed in hibonite laths 10 m wide and 30 40 m long throughout the inclusion perovskite predominantly occurs near the edge of the inclusion the crystallization sequence inferred petrographically corundum followed by hibonite followed by perovskite is that predicted for the first phases to form by equilibrium condensation from a solar gas for ptot 5 x 10 3 atm in addition the texture of the inclusion with angular voids between subhedral hibonite laths and plates is also consistent with formation of the inclusion by condensation hibonite has heavy rare earth element ree abundances of 40 x ci chondrites light ree abundances 20 x ci chondrites and negative eu anomalies the chondrite normalized abundance patterns especially one for a hibonite perovskite spot are quite similar to the patterns of calculated solid gas partition coefficients for hibonite and perovskite at 10 3 atm and are not consistent with formation of the inclusion by closed system fractional crystallization in contrast with the features that are consistent with a condensation origin there are problems with any model for the formation of this inclusion that includes a molten stage relic grains or volatilization if thermodynamic models of equilibrium condensation are correct then this inclusion formed at pressures 5 x 10 3 atm possibly with enrichments 1000x in ci dust relative to gas at low pressures below 10 4 atm both hibonite and corundum have 17o 18o 50 indicating formation from an 16o rich source the inclusion does not contain radiogenic 26mg and apparently did not contain live 26al when it formed if the short lived radionuclides were formed in a supernova and injected into the early solar nebula models of this process suggest that 26al free refractory inclusions such as this one formed within the first 6 x 10 5 years of nebular collapse

holocene palaeofires in neotropics high mountains the contribution of soil charcoal analysis abstract the holocene palaeofires in southern america has been generally attributed to climate until the middle holocene and to human activities for later periods soil charcoal analysis and extensive ams dating were carried out on six soil profiles between 3400 and 3900 m a s l in the guandera biological reserve western cordillera real north ecuador ams results showed an ordered stratification of charcoals allowing a fire history reconstruction over the last 11 700 cal bp the reported fire occurrences fit well with holocene global scale arid periods the association between fires and climate signals suggested a marginal role of humans in the environmental history of the studied area here the human inference started at ca 2500 cal bp but became considerable only in the last millennium

human environment interactions during the early mid holocene in coastal ecuador as revealed by mangrove coring in santa elena province coastal environments of the early mid holocene provided challenges and opportunities for agriculturalists living in the santa elena peninsula ecuador santa elena province formerly southwestern guayas province cores extracted from swamps in three river outflows namely the rio verde rio zapotal drainage chanduy estuary the rio grande punta carnero locality and the rio valdivia provided pollen phytolith sedimentary and elemental sequences relevant to documenting vegetation and agriculture the chanduy record documented maize and other cultigens from 3200 to 500 cal bc providing evidence for intensive cultivation of alluvial lands the punta carnero core provided the first evidence for occupation of the peninsula during the hiatus between the vegas and valdivia periods as maize was present in a stratum dating to 4857 cal bc records documented mid holocene sea level stabilization development of low energy depositional environments and variation in rainfall attributable to el nino sout

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

d region ionosphere response to the total solar eclipse of 22 july 2009 deduced from elf vlf tweek observations in the indian sector 1 observations of tweeks with higher harmonics n 1 at low latitude stations allahabad and nainital in the indian sector during the total solar eclipse on 22 july 2009 are presented allahabad and nainital stations were in 100 and 85 of the totality paths observations suggest that about 30 40 obscuration of solar disc can lead to the tweeks occurrence which otherwise occur only in nighttime a total of 148 tweeks at allahabad and 20 tweeks at nainital were recorded with some of them up to 3rd harmonics the world wide lightning location network data indicated that tweeks observed were generated by lightning s located in the partial eclipse area of asia oceania region the changes in d region ionospheric vlf reflection height and electron density 22 23 cm 3 during eclipse have been estimated from the first cut off frequency of the tweeks the reflection height increased from 89 km from the first occurrence of tweek to about 91 92 km at the totality and then decreased to 87 km at the end of the eclipse suggesting a change of about 5 km in the reflection height during eclipse the reflection heights are lower by 2 3 km as compared to normal nighttime tweek reflection heights the above increase in the reflection height indicate that the partial nighttime condition is created during eclipse as the main d region ionizing radiation lyman is blocked but solar soft x ray and euv radiations originating from the limb solar corona are not totally blocked which produce some of ionization in the d region

origin of spinel rich chondrules and inclusions in carbonaceous and ordinary chondrites our evaluation of three models of the origin of spinel rich chondrules and inclusions includes new calculations of the major element refractory mineral condensation sequence from a gas of solar composition over a wide pressure interval our condensation calculations show that spinel rich chondrules did not crystallize from metastable liquid condensates and that spinel rich inclusions are not aggregates of refractory nebular condensates we propose that spinel rich objects are fractionated distillation residues of small aggregates of primitive dust that lost ca si rich partial melts by evaporation ablation or splashing during collisions this model also explains why spinel rich chondrules and inclusions 1 are usually smaller than melilite rich chondrules and inclusions 2 often have highly fractionated trace element compositions and 3 usually do not contain pt metal nuggets even when they are more enriched in the pt group metals than nugget bearing melilite rich objects

glacial and postglacial pollen records from the ecuadorian andes and amazon abstract a long pollen record is derived from sediments of a lake dammed behind a low moraine of the last glaciation at 3 s latitude in the ecuadorian andes and is compared with a glacial age pollen record from the amazon rainforest immediately below lake surucucho llaviucu lies at 3180 m on the amazonian flank of the andes and above the glacial age pollen record from san juan bosco at 970 m the surucucho pollen record is interpreted as showing treeless vegetation in glacial times advance of treeline in late glacial time and holocene development of modern andean forests combining the surucucho and san juan bosco records shows that andean vegetation was affected by glacial cooling at all elevations vegetation did not move up and down slope as belts rather plant associations were reformed as temperature sensitive species found different centers of distribution with changing temperature

a unique ultrarefractory inclusion from the murchison meteorite through freeze thaw disaggregation of the murchison meteorite we have recovered a refractory inclusion hib 11 that is unique in terms of its texture mineral compositions and bulk composition it consists of anhedral y rich 1 6 wt y2o3 perovskite and lathlike spinel grains enclosed in a matrix of fine grained sc rich 10 5 wt sc2o3 avg ti rich 12 6 wt tio2 avg reporting all ti as tio2 clinopyroxene the chondrite normalized rare earth element ree pattern is complex with light ree lree at 10 c1 abundances increasing from gd through ho the latter at 104 c1 decreasing through yb at 200 c1 and lu at 400 c1 the pattern reflects several stages of high temperature volatility fractionation removal of lu and er from the source gas in the first condensation event was followed by partial to complete removal of the somewhat less refractory heavy ree gd through ho in the hib 11 precursors by condensation from the fractionated residual gas in a second event both of these events probably reflect condensation of ree into zro2 or a mixed zr sc ti y oxide at temperatures too high for hibonite stability a second lower temperature component which was subsequently added had fractionated nd poor ce rich lree abundances that resulted from condensation from a gas that had undergone prior removal of the more refractory lree resulting in enrichment in ce and the most volatile ree eu and yb the aggregate was then melted and quickly cooled forming a fine grained spherule this is the first reported inclusion in which the two most refractory ree lu and er are strongly fractionated from the other ree an absence of mass fractionation among the ti isotopes indicates that hib 11 is not an evaporative residue implying that volatility fractionation of trace elements took place during condensation the fact that the two most refractory heavy ree could be separated from the other only slightly less refractory heavy ree suggests that a wide variety of ree patterns is possible and that ultrarefractory inclusions with other unusual ree patterns important recorders of nebular condensation may yet be discovered

amazon diversity in light of the paleoecological record abstract disjunct distributions of amazonian species have been explained previously by a refugial theory which postulates that amazonian rain forest was preserved in large highland regions throughout the pleistocene no direct radiocarbon dated evidence exists for the last glacial maximum with which to test this theory the only radiocarbon dates of pleistocene age from the amazon basin are of fossiliferous deposits in the proposed napo refugium of the west where both pollen assemblages and wood samples indicate that forest with cool andean elements existed there at two intervals in the last cycle of northern hemisphere glaciation implying a temperature depression of at least 4 c in the amazon lowlands under modern climatic conditions lateral erosion by river meander together with surface erosion serves as a rejuvenating mechanism for the rain forests of peru and ecuador the instability of late holocene amazonian climates is demonstrated by documenting a precipitation event in the eastern andean cordillera that caused widespread flooding of western amazonian forests 800 1300 bp late holocene pollen histories from widely dispersed parts of central amazonia distinguish between vegetation histories in the drainage of northern south western and western watersheds but all show histories of fluctuating intensities of dry seasons radiocarbon dating of charcoal layers in soils of venezuelan amazonia demonstrates the apparently random incidence of wild fires at wide intervals over at least the last 6 ka the high species richness of amazonia is a result of numerous opportunities for vicariance because of a very large total area wide variety of habitats and intermediate levels of disturbance particularly by hydrological processes that has varied on timescales from years to millennia amazonian disjunct distributions probably reflect regional environmental discontinuities in both interglacial and glacial times

late pleistocene temperature depression and vegetation change in ecuadorian amazonia abstract paleoecological pollen phytolith and wood analyses of sediments radiocarbon dated 33 000 to 26 000 yr b p from two sites in ecuadorian amazonia provide data that suggest a cooling of ca 7 5 c below present in equatorial lowlands from 33 000 to 30 000 yr b p a period of warning followed in which novel species assemblages a blend of montane and lowland floral components persisted for at least 4000 years these data of forest community change from sites lying within the postulated glacial rain forest napo refugium provide the strongest paleoecological refutation of the refugial hypothesis yet obtained the large temperature depression at ca 30 000 yr b p allows the possibility that if maximum cooling at the equator was synchronous with the last glacial maximum lgm of the northern hemisphere freezing temperatures would have been experienced in parts of lowland amazonia between 25 000 and 18 000 b p

three dimensional and trans hemispheric changes in ionospheric electron density caused by the great solar eclipse in north america on 21 august 2017

microstructural evidence for a disequilibrium condensation origin for hibonite spinel inclusions in the alha77307 co3 0 chondrite two hibonite spinel inclusions cais 03 and 08 in the alha77307 co3 0 chondrite have been characterized in detail using the focused ion beam sample preparation technique combined with transmission electron microscopy these hibonite spinel inclusions are irregularly shaped and porous objects and consist of randomly oriented hibonite laths enclosed by aggregates of spinel with fine grained perovskite inclusions finally surrounded by a partial rim of diopside melilite is an extremely rare phase in this type of cai and occurs only in one inclusion cai 03 as interstitial grains between hibonite laths and on the exterior of the inclusion the overall petrologic and mineralogical observations suggest that the hibonite spinel inclusions represent high temperature condensates from a cooling nebular gas the textural relationships indicate that hibonite is the first phase to condense followed by perovskite spinel and diopside texturally melilite condensation appears to have occurred after spinel suggesting that the condensation conditions were far from equilibrium the crystallographic orientation relationships between hibonite and spinel provide evidence of epitaxial nucleation and growth of spinel on hibonite surfaces which may have lowered the activation energy for spinel nucleation compared with that of melilite and consequently inhibited melilite condensation hibonite contains abundant stacking defects along the 001 plane consisting of different ratios of the spinel and ca containing blocks within the ideal hexagonal hibonite structure this modification of the stacking sequence is likely the result of accommodation of excess al in the gas into hibonite due to incomplete condensation of corundum from a cooling gas under disequilibrium conditions we therefore conclude that these two hibonite spinel inclusions in alha77307 formed by high temperature condensation under disequilibrium conditions

pollen studies in the junin area central peruvian andes laguna junin is a large lake 675 km long but only 4 m deep located in the grass covered altiplano at an altitude of 4 100 m northeast of lima pollen analysis of a 30 m core indicates that from about 12 000 yr ago until some time after 3 000 yr ago about 30 of the pollen was carried in by easterly winds from the east andean forests which today are at least 600 m lower in elevation contemporaneous pollen deposition in lakes on moraines of the last glaciation west of the junin plain was dominated by local grassland types and had little contribution from this easterly source at some time after 3 000 yr ago perhaps about 1 200 yr ago the pollen influx to laguna junin from this distant forest source greatly diminished perhaps because of deforestation by increased human populations between about 12 000 and 24 000 yr ago in the junin core the sparse pollen concentration was dominated by grassland types supplemented by polylepis acaena alnus and compositae blown in from the sub puna shrublands that may have occupied much of the east andean slopes in place of the humid forest that occurs there today the silty sediment in this section of the core is interpreted as outwash from piedmont glaciers that invaded the plain especially from the cordillera to the west these glaciers left a distinctive pattern of moraines and outwash fans which served to dam tine lake basin an unconformity in the sediment covers the time from about 24 000 to 39 000 yr ago when the lake was probably dry before this time the silty sediment and the dominance of grassland and shrubland pollen types indicates an earlier interval of glaciation recorded on the landscape by an older set of moraines and outwash fans which initially dammed the lake basin

corundum hibonite inclusions and the environments of high temperature processing in the early solar system abstract corundum bearing ca al rich inclusions cais are a rare class of high temperature condensates from the inner regions of the protoplanetary disk their mineralogy is intermediate between isolated corundum grains and cais where corundum has been replaced by lower temperature phases these inclusions sample a critical transitional period of the inner nebula where both the sun and protoplanetary disk were rapidly evolving we conducted o isotopic al mg chronological petrographic and crystallographic studies of four corundum bearing inclusions in the murchison cm2 and alha 77307 co3 0 carbonaceous chondrites within each inclusion corundum hibonite and spinel have indistinguishable 16 o rich compositions the o isotopic compositions from all inclusions fall within a narrow range of 17 o 22 8 3 6 that matches values of most previously studied micrometer sized corundum grains and mineralogically pristine cais these data indicate that with few exceptions the most refractory inclusions in carbonaceous chondrites formed from the same o isotopic reservoir one cai from alha 77307 alh 61 exhibits a continuous corundum mantle overlying a hibonite core opposite the equilibrium condensation sequence at typical nebular pressures and dust gas ratios transmission electron microscopy examination of the hibonite corundum interface suggests that the corundum condensed on the hibonite and was itself then partially overlain with spinel additionally high dust gas ratios are interpreted from the w and mo depleted composition of a refractory metal nugget within a second corundum bearing cai alh 160 together these observations show that the primary formation conditions of some corundum bearing cais involved non equilibrium condensation in environments with elevated dust gas ratios the corundum bearing cais studied here have inferred initial 26 al 27 al ratios that fall within the roughly bimodal distribution of values observed in most cais alh 160 retains no resolvable excess 26 mg while alh 61 has a well resolved initial 26 al 27 al ratio of 4 2 0 4 10 5 the presence or absence of live 26 al at the time of cai formation may record distinct chronology if 26 al was initially homogeneously distributed in the early solar system alternatively variations in 26 al 27 al ratios may reflect late injection and or heterogeneous distribution of 26 al regardless of which model for 26 al distribution is correct the data presented here indicate that formation of corundum bearing cais was repeated during multiple heating and non equilibrium condensation events throughout early solar system history and within a single oxygen isotopic reservoir

chemical composition of hal an isotopically unusual allende inclusion thirty seven major minor and trace elements were determined by inaa and rnaa in samples of hibonite black rim and portions of friable rim from an unusual allende inclusion hal the peculiar isotopic mineralogical and textural properties of hal are accompanied by very unusual trace element abundances the most striking feature of the chemistry is the virtual absence of ce from an inclusion otherwise highly enriched in ree compared to cl chondrites hal is also depleted in sr ba u v ru os and ir relative to other refractory elements of the lithophile elements determined which are normally considered to be refractory in a gas of solar composition sr ba ce u and v are the most volatile in oxidizing gases the distribution of ree between hibonite and rims seems to have been established when hibonite and other refractory minerals were removed at slightly different temperatures from a hot oxidizing gas in which they previously coexisted as separate grains on the basis of hal s chemical and isotopic composition possible locations for the chemical and mass dependent isotopic fractionation are in ejecta from the low temperature helium burning zone of a supernova and in the locally oxidizing environment generated by evaporation of interstellar grains of near chondritic chemical composition

late holocene human impact and environmental change inferred from a multi proxy lake sediment record in the loja region southeastern ecuador abstract late holocene human impact and environmental changes were reconstructed from a sediment core of the laguna daniel alvarez 2200 m asl located on the outskirts of the city of loja southeastern ecuador palaeoenvironmental changes were investigated by pollen spore algae and charcoal analysis in combination with x ray fluorescence xrf scanning and element analysis of 13c total organic carbon toc total nitrogen tn and radiocarbon dating this multi proxy study provides in detail the settlement history in the inner andean dry valley in southern ecuador over the last ca 1400 years between 630 and 1470 ad zea mays was intensively cultivated around the studied lake by the native palta culture in the loja region after ca 1470 ad z mays cultivation collapsed accompanied by an increase in fallow vegetation such as mimosa and poaceae probably as a result of the inca invasion and occupation from 1463 to 1531 ad in southern ecuador after ca 1570 ad amaranthaceae chenopodiaceae markedly increased reflecting the beginning of the spanish conquest in 1531 ad loja became spanish and during the first ca 100 years of the spanish regime loja developed into the fortified capital of the province in the 17th century crop growing strongly declined due to the diminished indigenous population that probably suffered from new diseases introduced by the spanish invaders pinus and eucalyptus as well as plantago lanceolata were introduced in the loja region about 220 years ago

particle motion and the theory of charcoal analysis source area transport deposition and sampling principles from particle motion physics were applied to recurring problems of the interpretation of stratigraphic charcoal data 1 fires within catchments of lakes often produce no record in fossil charcoal curves and 2 periods characterized by no local fire e g 20th century fire suppression often display as much charcoal as times when local fire was frequent quantitative theory on source area transport deposition and sampling of charcoal shows the relationship between particle sizes counted by alternative methods of charcoal analysis pollen slides for particles 5 80 m in diameter petrographic thin sections for particles 50 10 000 m diameter and charcoal diagrams the relationship between diameter and critical and deposition velocities results in fundamental aerodynamic differences between the sizes of particles quantified by the two methods charcoal recorded on pollen slides is of a size that is difficult to lift but once entrained it remains in suspension thin section charcoal is lifted at relatively low wind velocities but it is not suspended at normal surface wind speeds thermal buoyancy during fire lofts charcoal above the forest canopy depending on particle size and wind speed pollen slide charcoal sizes are underrepresented near the fire because they remain in suspension and are preferentially exported from the burn area thin section charcoal is convected to lower heights on average and is deposited nearby following fire thin section charcoal is redistributed locally by wind and thus may enter lakes because of cohesive forces and aerodynamics more pollen slide charcoal remains on the ground and less enters lakes source areas for pollen slide charcoal are subcontinental to global and diagrams of pollen slide charcoal are biased toward nonlocal charcoal they can be used to interpret importance of fire for broad spatial and temporal scales thin section charcoal represents the catchment fire regime simulation models that generate charcoal during fire mix sediments and then sample at specified intervals indicate that 1 in the absence of sediment mixing the pollen slide method should consistently resolve individual fires that occur with an expectation of 30 50 yr 2 unless samples are continuous neither method will produce useful estimates of fire frequency and 3 even a modest amount of sediment mixing will obscure the signal

a 24 700 yr paleolimnological history from the peruvian andes abstract a new paleolimnological dataset from lake pacucha 13 s 3095 m elevation in the peruvian andes provides evidence of changes in lake level over the past 24 700 yr a late glacial highstand in lake level gave way to an early holocene lowstand this transition appears to have paralleled precessional changes that would have reduced insolation during the wet season the occurrence of benthic salt tolerant diatoms and caco3 deposition suggest that the lake had lost much of its volume by c 10 000 cal yr bp pronounced holocene oscillations in lake level included a second phase of low lake level and heightened volatility lasting from c 8300 to 5000 cal yr bp while a polymictic lake formed at c 5000 cal yr bp these relatively wet conditions were interrupted by a series of drier events the most pronounced of which occurred at c 750 cal yr bp paleolimnological changes in the holocene were more rapid than those of either the last glacial maximum or the deglacial period

the holocene treeline in the northern andes ecuador first evidence from soil charcoal abstract indications for the speed and timing of past altitudinal treeline shifts are often contradictory partly this may be due to interpretation difficulties of pollen records which are generally regional rather than local proxies we used pedoanthracology the identification and dating of macroscopic soil charcoal to study vegetation history around the treeline in the northern ecuadorian andes pedoanthracology offers a complementary method to pollen based vegetation reconstructions by providing records with high spatial detail on a local scale the modern vegetation is tussock grass paramo tropical alpine vegetation and upper montane cloud forest and the treeline is located at ca 3600 m charcoal was collected from soils in the paramo at 3890 and 3810 m and in the forest at 3540 m and represents a sequence for the entire holocene the presence of paramo taxa throughout all three soil profiles especially in combination with the absence of forest taxa shows that the treeline in the study area has moved up to its present position only late in the holocene after ca 5850 cal years bp the treeline may have been situated between 3600 m and 3800 m at some time after ca 4900 cal years bp or it may never have been higher than it is today the presence of charcoal throughout the profiles also shows that fires have occurred in this area at least since the beginning of the holocene these results contradict interpretations of palaeological data from colombia which suggest a rapid treeline rise at the pleistocene holocene transition they also contradict the hypothesis that man made fires have destroyed large extents of forest above the modern treeline instead paramo fires have probably contributed to the slowness of treeline rise during the holocene

environmental changes in southeastern amazonia during the last 25 000 yr revealed from a paleoecological record abstract new pollen micro charcoal sediment and mineral analyses of a radiocarbon dated sediment core from the serra sul dos carajas southeast amazonia indicate changes between drier and wetter climatic conditions during the past 25 000 yr reflected by fire events expansion of savanna vegetation and no analog amazonian forest communities a cool and dry last glacial maximum lgm and late glacial were followed by a wet phase in the early holocene lasting for ca 1200 yr when tropical forest occurred under stable humid conditions subsequently an increasingly warm seasonal climate established the onset of seasonality falls within the early holocene warm period with possibly longer dry seasons from 10 200 to 3400 cal yr bp and an explicitly drier phase from 9000 to 3700 cal yr bp modern conditions with shorter dry seasons became established after 3400 cal yr bp taken together with paleoenvironmental evidence from elsewhere in the amazon basin the observed changes in late pleistocene and holocene vegetation in the serra sul dos carajas likely reflect large scale shifts in precipitation patterns driven by the latitudinal displacement of the inter tropical convergence zone and changes in sea surface temperatures in the tropical atlantic