neogene and quaternary history of vegetation climate and plant diversity in amazonia the neotropical amazonian and andean plant diversity developed mainly during the tertiary in amazonia miocene oral diversity seems considerably higher than today during the neogene tropical taxa entered newly created montane area and montane taxa entered the tropical lowlands the general decrease of temperature during the upper neogene and especially during the quaternary glacial periods may have caused considerable extinctions in the lowlands representation of pollen of apparently principally montane taxa podocarpus hedyosmum in miocene pliocene and quaternary sediments of amazonia and surroundings is still di cult to interpret in terms of temperature decrease at low elevation changes in precipitation may have profound impact on the composition of vegetation communities ilex and melastomataceae increase signi cantly in many glacial pollen records increase of weinmannia in amazonian pollen records seems the best indicator of downward migration of montane vegetation belts a temperature lowering at sea level of 4 5 13c during the last glacial maximum lgm seems reasonable it may have caused a downslope migration of some 700 m of the lower montane vegetation belt lower montane arboreal species may have been able to grow in higher elevation areas 500 m of amazonia increasing background pollen values of montane taxa in the area di erence between a cool and wet middle pleniglacial 60 28 ka bp and a cold and dry upper pleniglacial 28 14 ka bp thus including the lgm is evident in andean and amazonian records statements about environmental conditions of the ice age amazon should be speci ed chronologically the middle pleniglacial is a time of accumulation of uvial sediments the upper pleniglacial is a time of incision of the rivers in their sediments sedimentation started again in the lateglacial since ca 13 ka bp and the holocene when lake levels rose again based on simpli ed considerations of precipitation changes and evaporation we estimate that lgm rainfall may have been reduced by values of ca 45 10 amazonian and cordilleran lakes dried up dry rain forest was locally replaced by savanna savanna forest or cerrado type vegetation dry rain forest savanna forest and pure savanna was locally replaced by extensive semi desert dune formations lower rio branco area in present day central amazonia the present day centers of higher rainfall 2500 mm surrounded by areas of lower rainfall are refuge areas of the very wet rain forest and of the very high plant diversity 300 plant species per 0 1 ha and they should have been that equally or more during the dry climate intervals plant diversity of drier forests is in the order of 100 150 species per 0 1 ha both extinction and speciation in isolation under precipitation and temperature stress may have taken place in these refugia 2000 elsevier science ltd all rights reserved

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

effect of degassing on sulfur contents and δ 34 s values in somma vesuvius magmas sulfur contents and 34s values of somma vesuvius magmas are consistent with syneruptive open system degassing at temperatures of 800 850 c for plinian pumices and 1100 1200 c for lavas the extent of degassing appears to be greater in lavas than in pumices the key parameter controlling the 34s 32s ratio of somma vesuvius volcanics is the average magma oxidation state which generally varies from 0 85 to 1 20 nno units for lavas and from 1 20 to 1 40 nno units for pumices consequently s contents and 34s values of magmas constitute a potentially valuable tool in estimating their average redox conditions the results of this study may help in risk mitigation when the vesuvius magmatic system evolves toward eruptive conditions

active and break phases in the south american monsoon system the south american monsoon system sams refers to the austral summer season features of deep convective activity and large scale circulation this study examines intraseasonal variations in the low level wind circulation in the amazon and their modulating effects on active and break phases in sams daily averages of outgoing longwave radiation olr ncep ncar reanalysis and gridded rainfall station data in brazil are used from 1 november to 28 february 1980 99 the direction of wind anomalies 10 70 days in the rondonia state brazil is used to classify periods of westerly w and easterly e low level wind regimes composites of w regime show low level wind anomalies crossing the equator southward and closing in a cyclonic anomalous circulation off the coast of argentina and uruguay broad areas of enhanced convection and rainfall are observed in central and southeast brazil suppressed convection is observed over the bolivian altiplano and in northern south america in contrast in the e regime opposite patterns are observed in the low level circulation con vection and rainfall anomalies the duration of active w regimes and break e regimes periods are quite similar with median values of 4 and 5 days respectively further investigation showed that the region of convection and rainfall anomalies over venezuela and northwest brazil is observed only in the 10 30 day band comparison of the results shown here with previous studies indicates the importance of intraseasonal variations in the activity of sams

hydrogen index and carbon isotopes of lacustrine organic matter as lake level indicators abstract optical and geochemical techniques were applied to organic matter of late quaternary sediments from lakes victoria and rukwa east africa variations in total organic carbon toc and hydrogen content expressed as hydrogen index hi can be related to known changes in lake level and used to identify periods of very low water or subaerial exposure in basinal sequences toc and hi both decline as an exposure surface is approached mainly due to the selective removal of unstable components by bacterial respiration and inorganic oxidation inert organic material of very low hi is typically concentrated at the overlying transgression surface the carbon isotopic composition of the particulate organic matter tends to be less negative in sediments associated with exposure surfaces although weathering may be partially responsible isotopic variations are mainly due to changes in the relative importance of material from plants using c4 photosynthesis such as grasses and sedges growing around the shore and on the exposed lake muds and of material from planktonic algae and terrestrial c3 plants

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

late glacial cooling in amazonia inferred from pollen at lagoa do caco northern brazil new pollen data from a core at lagoa do caco maranhao state brazil 2 58 s 43 25 w 120 m elevation show higher frequencies of podocarpus at the end of the pleistocene than today the increase in podocarpus which follows the successive increase of various pioneer species such as didymopanax melastomataceae combretaceae and cecropia implies a progressive late glacial increase of moist and cool climatic conditions a comparable increase in podocarpus is found in other lowland records in amazonia a review of published pollen data from amazonia suggests that the moisture source was from the southeast by contrast present day moisture comes from the tropical atlantic and from the amazon basin with its convective precipitation the likely cause for the southeastern moisture source between ca 15 000 and 14 500 cal yr b p was enhanced polar antarctic advection that reached low latitudes and maintained year round the meteorological equator in its austral winter position at northern latitudes or reduced drastically its southward summer displacement this hypothesis is consistent with marine and ice core records

elemental carbon record of paleofire history on the chinese loess plateau during the last 420 ka and its response to environmental and climate changes an elemental carbon ec record covering the last 420 ka was reconstructed using chemical oxidation method on a loess and paleosol sequence from the lingtai section on the chinese loess plateau the ec record reveals the paleofire history and its relationship with climate and vegetation changes on the chinese loess plateau our results show that the ec abundance is generally higher in the paleosols than in the loess layers showing a glacial interglacial pattern which is coincident with biomass changes this variation pattern indicates that paleofires were intensified when biomass accumulated and climate changed abruptly especially from wet to dry conditions the ec abundance increases sharply at similar to 130 kab p indicating a dramatic change in the vegetation and climate variation patterns the occurrence of a peak value with the highest average ec abundance in the holocene may reflect the occurrence of a major climate event at similar to 6 kab p and may also be partly due to more frequent anthropogenic fire usages c 2007 elsevier b v all rights reserved

amazonia during the last glacial abstract new data on the vegetational history and quaternary geology of amazonia permit an improved reconstruction of past environments in amazonia during the last glacial period although limited data from rondonia carajas and guyana show that in certain areas savanna type vegetation and savanna forest had replaced the rain forest during the late pleniglacial ca 22 000 13 000 yr b p the amazonian forest may have been split up into one major west amazonian and several other medium size forest areas this suggests a decline in rainfall of 500 to 1000 mm a reduction of 25 to 40 temperatures may also have been 2 to 6 c 4 2 c lower than today possibly substancially influencing amazonian vegetation during the humid middle pleniglacial 55 000 26 000 yr b p rivers carried a lot of water and sediment resulting in the deposition of lower terrace sediments with one dry interruption around 40 000 yr b p carajas and katira in carajas there is evidence of dry periods ocurring at about 40 000 yr b p and during the early pleniglacial ca 60 000 yr b p rivers carried little water and incised into the low terrace sediments during the dry late pleniglacial water levels rose during the late glacial 13 000 10 000 yr b p or at the beginning of the holocene 10 000 yr b p sedimentation in and of the present inundation valleys commenced after that

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

late quaternary pollen records from the middle caqueta river basin in central colombian amazon abstract three pollen records are presented from the pantano de monica region 0 42 s 72 04 w 160 m elevation on the lower terrace of rio caqueta of the central colombian amazonas ten radiocarbon dates from three cores indicate that the deposits are of holocene age but the pollen data suggest that the record may also contain the late glacial the core pantano de monica 1 covers the time interval from 11 150 bp extrapolated to 4730 bp during the late glacial and early holocene this swamp was smaller in size and waters were more shallow than today with abundant mauritia palm trees this indicates that the lower terrace of the caqueta river was better drained than today which might be related to changes in the drainage system and or drier conditions during that time late glacial and early holocene vegetational changes in the rain forests surrounding the swamp pantano de monica indicate successional stages probably related to changes in the drainage system and or climate changes presence of podocarpus pollen grains up to 2 6 of the total sum and influx of 78 grains cm 2 yr 1 point to the regional presence of podocarpus at the beginning of the holocene evidence of podocarpus during glacial times in other pollen records from the amazon basin has been taken as indicative of cooling core pantano de monica 2 was taken in a small swamp 1000 m distance to pantano de monica 1 and starts at 4000 bp when this location was well drained several changes in the composition of the rain forest are documented such as increase in disturbance increase of cecropia followed by a quick recovery increase of psychotria protium and caryocar tree taxa were frequent suggesting that the lower terrace area was well drained until 3080 bp after which small swamps developed core pantano de monica 3 is from the wet forest in between the two swamps and represents the period since 3260 bp pollen data show a continuously increasing presence of palms probably euterpe suggesting either a transition from well drained to less drained conditions in the lower terrace during the late holocene and or a more intensive human impact of the rain forest on the lower terraces of rio caqueta the three records from the lower terrace of rio caqueta show different forest compositions in the past and indicate that the rain forest environments were not stable during late glacial and holocene times comparison with other data from lowland records of northwestern south america suggest that climate change is a major factor for environmental change in central colombian amazon

north atlantic forcing of amazonian precipitation during the last ice age the last glacial period was marked by rapid reorganizations of oceanic and atmospheric circulation speleothem records from the amazon basin suggest that precipitation variability was linked to these events the last glacial period was marked by multiple abrupt reorganizations of ocean and atmosphere circulation1 on thousand year timescales slowing of the atlantic meridional overturning circulation was associated with cooling in the high northern latitudes whereas strengthened circulation was linked to northern warming1 2 in the tropics these millennial scale events were primarily reflected in altered patterns of precipitation3 these hydrologic fluctuations induced ecological changes in the atlantic seaboard and the high andes2 but less is known about the amazon basin here we reconstruct precipitation over amazonian ecuador over the past 94 000 years using a 18o record from speleothems collected in santiago cave in western amazonia we interpret the variability of the 18o record as changes in the source and amount of precipitation with the exception of the period between 40 000 and 17 000 years ago abrupt high frequency changes coincide with shifts in north atlantic circulation indicating a high latitude influence on amazonian precipitation over millennial timescales on longer timescales the record shows a relationship to precessional changes in the earth s orbit in light of the lack of extreme aridity in our records we conclude that ecosystems in western amazonia have not experienced prolonged drying over the past 94 000 years

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

holocene environmental changes in the central amazon basin inferred from lago calado brazil abstract holocene environments have been reconstructed by sedimentological mineralogical geochemical and high resolution pollen analysis of a 1190 cm long core from lago calado near manaus in central amazonia the sediment core dated by eight ams radiocarbon dates has a basal age of 8330 50 14 c yr bp and documents the landscape development from a river valley before 8280 14c yr bp to a lake environment this change is related to the rise of the central amazonian water level controlled by the postglacial sea level rise pollen analytical results show the formation of a local mauritia palm swamp along the river margin between 8280 and 7700 14c yr bp at that time highly diverse terra firme unflooded upland amazon rainforest and poorly developed varzea igapo inundated forests along the river characterized the vegetation the expansion of varzea igapo forests and a strong presence of aquatic plants started at 7700 14c yr bp reflecting the rise of the amazonian water level and the formation of the lago calado the occurrence of abundant poaceae and cyperaceae pollen in the lake sediments since 7770 14c yr bp suggest both the local colonization of unflooded mud banks around the lake margin and the formation of flooding meadows open exposed unflooded mud areas periodically colonized by herbs are related to seasonal amazonian high and low water stands in respect to the abundance of poaceae pollen during the early and mid holocene these open areas must have been large suggesting brief annual high and extensive annual low amazonian water stands after 4070 14c yr bp the proportion of varzea igapo forest areas was larger than before herbs were less abundant probably due to the smaller area of unflooded mud banks the amazonian water levels must have been higher and the period of the annual high water stands was probably longer than before since 2080 14c yr bp the largest proportion of varzea igapo forests is recorded reflecting the highest amazonian water level herbs were rare suggesting that open unflooded mud areas around the lake were relatively small this may perhaps also indicate that the seasonal period of the amazonian high water level was the longest since 2080 14c yr bp the increase of cecropia poaceae and alternanthera during the last 150 yr suggests stronger human impact on the local vegetation changes to higher amazonian water levels are related to the rise of the atlantic sea level relatively short annual high water levels during the early holocene and relatively long annual high water levels since 4070 and especially since 2080 14c yr bp can be interpreted as a climate change from a drier early holocene with lower annual rainfall rates and longer dry periods until 4070 14c yr bp to a wetter late holocene

comparison of quantification methods to measure fire derived black elemental carbon in soils and sediments using reference materials from soil water sediment and the atmosphere black carbon bc the product of incomplete combustion of fossil fuels and biomass called elemental carbon ec in atmospheric sciences was quantified in 12 different materials by 17 laboratories from different disciplines using seven different methods the materials were divided into three classes 1 potentially interfering materials 2 laboratory produced bc rich materials and 3 bc containing environmental matrices from soil water sediment and atmosphere this is the first comprehensive intercomparison of this type multimethod multilab and multisample focusing mainly on methods used for soil and sediment bc studies results for the potentially interfering materials which by definition contained no fire derived organic carbon highlighted situations where individual methods may overestimate bc concentrations results for the bc rich materials one soot and two chars showed that some of the methods identified most of the carbon in all three materials as bc whereas other methods identified only soot carbon as bc the different methods also gave widely different bc contents for the environmental matrices however these variations could be understood in the light of the findings for the other two groups of materials i e that some methods incorrectly identify non bc carbon as bc and that the detection efficiency of each technique varies across the bc continuum we found that atmospheric bc quantification methods are not ideal for soil and sediment studies as in their methodology these incorporate the definition of bc as light absorbing material irrespective of its origin leading to biases when applied to terrestrial and sedimentary materials this study shows that any attempt to merge data generated via different methods must consider the different operationally defined analytical windows of the bc continuum detected by each technique as well as the limitations and potential biases of each technique a major goal of this ring trial was to provide a basis on which to choose between the different bc quantification methods in soil and sediment studies in this paper we summarize the advantages and disadvantages of each method in future studies we strongly recommend the evaluation of all methods analyzing for bc in soils and sediments against the set of bc reference materials analyzed here

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

late quaternary vegetational and climatic changes in cerrado and palm swamp from central brazil abstract geochemical and palynological analyses of core cr1 from crominia goias provided information on the paleoenvironmental history of central brazil the records show that prior to 32 400 yr b p the vegetation of the crominia region was similar to the present one characterized locally by a complex of cerrado gallery forest and palm swamp indicating a semi humid tropical climate a palm swamp occupied the coring site from 32 400 to about 20 000 yr b p a treeless grassland replaced the arboreal cerrado and the gallery forest suggesting that humidity increased but temperature probably decreased the site was a shallow lake between ca 27 000 and 20 000 yr b p humidity started to decrease at ca 18 500 yr b p and the period from ca 18 500 to ca 11 500 yr b p was very dry a sparse vegetation was growing in the region during that time the dry climate continued until 6500 yr b p and the core site probably dried out several times at ca 5000 yr b p humidity increased again the palm swamp vegetation returned to the site and cerrado vegetation and gallery forest started to grow in the region the abundant charcoal particles prior to 20 000 yr b p and from 10 500 to ca 3500 yr b p document a long history of fires in the region results are compared with those from other sites in central brazil and with the climate sequence of the last glacial maximum and postglacial time in the tropical andes

late pleistocene glacial forest of humaita western amazonia abstract glacial aged vegetation dynamics of the humaita western brazilian amazonia were studied by pollen sedimentary facies 14 c dating 13 c org and c n molar two sediment cores were taken to a depth of 10 and 8 m from areas covered by grassland and dense open forest respectively the deposits represent a succession of sediment accumulation in active channel 42 600 cal yr b p abandoned channel floodplain 42 600 to 39 000 cal yr b p and oxbow lake sedimentary environments 39 000 cal yr b p to modern the predominance of mud sediments depletion of 13 c org and decrease in c n molar values identify the lake establishment in these settings low energy subaqueous conditions were developed locally favoring preservation of a pollen assemblage representing herbaceous vegetation some modern taxa from amazonia and cold adapted plants from the andes represented by alnus 2 11 hedyosmum 2 17 weinmannia 0 18 podocarpus 0 4 ilex 0 4 and drymis 0 1 at least between 42 600 and alnus with other cold adapted plants from the andes during the late pleistocene indicates that alnus probably penetrated the western amazonia lowland or was growing closer to the study site due to cooler temperatures during glacial times the present study presents the first report of a glacial age forest containing alnus in areas of the brazilian amazonian lowlands in addition to its palaeogeographical importance this work demonstrates the effectiveness of using a combination of proxies for reconstructing sedimentary environments associated with vegetation

a multiproxy palaeoecological record of holocene lake sediments from the rio tapajos eastern amazonia abstract two sediment cores up to 42 m in length were raised from the wide deep section of the lower tapajos river amazonia referred to as lago tapajos these cores reveal a history of subtle environmental change that began with the formation of lago tapajos as sea level rose about 11 000 years ago the sediments of the lake were deposited fairly quickly at a rate of ca 4 m per millennium and are uniformly fine grained with low organic content the fossil pollen record derived from these sediments reveals that forest surrounded this site throughout the holocene the largest change in the core took place between ca 5500 and 4200 cal years bp and reflects a transition from coarser to finer sediments coincident with the change in sediment is a slight transition in the pollen spectra with an increase in poaceae abundance at the expense of the pioneer tree cecropia cecropia a tentative explanation is offered in which increased human activity possibly spurred by climatic change resulted in the formation of some local grasslands however despite the apparent actions of humans there is no indication of basin wide transformation of landscapes in this record the holocene persistence of forest as the dominant landscape matrix around lago tapajos is supported by low 13 c values and by the constant geochemistry and mineralogy of the lake sediments

innovative tidal notch detection using tls and fuzzy logic implications for palaeo shorelines from compressional crete and extensional gulf of corinth tectonic settings abstract tidal notches are a generally accepted sea level marker and maintain particular interest for palaeoseismic studies since coastal seismic activity potentially displaces them from their genetic position the result of subsequent seismic events is a notch sequence reflecting the cumulative coastal uplift in order to evaluate preserved notch sequences an innovative and interdisciplinary workflow is presented that accurately highlights evidence for palaeo sea level markers the workflow uses data from terrestrial laser scanning and iteratively combines high resolution curvature analysis high performance edge detection and feature extraction based on the assumptions that remnants such as the roof of tidal notches form convex patterns edge detection is performed on principal curvature images in addition a standard algorithm is compared to edge detection results from a custom fuzzy logic approach the results pass through a hough transform in order to extract continuous line features of an almost horizontal orientation the workflow was initially developed on a single distinct and sheltered exposure in southern crete and afterwards successfully tested on laser scans of different coastal cliffs from the perachora peninsula this approach allows a detailed examination of otherwise inaccessible locations and the evaluation of lateral and 3d geometries thus evidence for previously unrecognised sea level markers can be identified even when poorly developed high resolution laser scans of entire cliff exposures allow local variations to be quantified edge detection aims to reduce information on the surface curvature and hough transform limits the results towards orientation and continuity thus the presented objective methodology enhances the recognition of tidal notches and supports palaeoseismic studies by contributing spatial information and accurate measurements of horizontal movements beyond that recognised during traditional surveys this is especially useful for the identification of palaeo shorelines in extensional tectonic environments where coseismic footwall uplift only 1 2 to 1 4 of net slip per event is unlikely to raise an entire notch above the tidal range

hydroclimate changes across the amazon lowlands over the past 45 000 years reconstructing the history of tropical hydroclimates has been difficult particularly for the amazon basin one of earth s major centres of deep atmospheric convection for example whether the amazon basin was substantially drier or remained wet during glacial times has been controversial largely because most study sites have been located on the periphery of the basin and because interpretations can be complicated by sediment preservation uncertainties in chronology and topographical setting here we show that rainfall in the basin responds closely to changes in glacial boundary conditions in terms of temperature and atmospheric concentrations of carbon dioxide our results are based on a decadally resolved uranium thorium dated oxygen isotopic record for much of the past 45 000 years obtained using speleothems from paraiso cave in eastern amazonia we interpret the record as being broadly related to precipitation relative to modern levels precipitation in the region was about 58 during the last glacial maximum around 21 000 years ago and 142 during the mid holocene epoch about 6 000 years ago we find that as compared with cave records from the western edge of the lowlands the amazon was widely drier during the last glacial period with much less recycling of water and probably reduced plant transpiration although the rainforest persisted throughout this time

the last glacial maximum stability and change in a western amazonian cloud forest the climatic and vegetation history of a western amazonian cloud forest is documen ted in a continuous pollen record spanning the full last glacial period between 43 5 and 22k cal yr bp the chronology for this record is based on eight radiocarbon dates yielding a low resolu tion pollen analysis for the region a bioclimatic envelope model was generated on the basis of mod ern altitudinal distributions and the pollen data which produced a glacial palaeotemperature estimate of ca 5 c relative to present palaeoecological evidence of continuous moist cloud forest cover in the basin indicates that western amazonian forests were not fragmented during the lgm this evidence supports wet conditions in western amazonia at the lgm and further refutes hypotheses of amazonian aridity during the last ca 44k cal yr bp copyright 2005 john wiley sons ltd

late quaternary of the middle caqueta river area colombian amazonia the late quaternary history of the middle caqueta river area in colombia northwestern amazonia is described based on observations of river bank sections radiocarbon dates and palynological analyses of organic layers in floodplain and low terrace sediments of the caqueta river it is shown that the late pleistocene and holocene climatic changes that took place in the andean cordilleras were related to the depositional and erosional history of the caqueta river in the colombian amazonian lowlands the low terrace sediments consist of sandy and gravelly deposits covered by clays that sometimes contain lenses of peaty material from these organic low terrace sediments seven finite radiocarbon dates were obtained of middle pleniglacial age between 56 000 and 30 000 yr bp the coarse textured basal deposits of the low terrace apparently stem from the early part of the middle pleniglaciai period during which the effective rainfall in the andes was relatively high and the andean glaciers had a considerable extension palynological data from silty sediments with organic remains at one site show an interval when drier and more open types of vegetation on poor soils must have covered a larger area than today but amazonian forest was still the dominating type of vegetation this interval might correspond to one of the middle pleniglacial savanna intervals from eastern amazonia carajas no organic sediments from the upper pleniglacial period were found and hence radiocarbon dates were not obtained in the andes this period had a very cold climate with low effective rainfall and in the east amazonian carajas area it is characterised by the relative extension of open savanna vegetation the river run off and sediment transport must have been much lower than in the middle pleniglacial and the caqueta river cut itself down in its own sediments two late glacial radiocarbon datings obtained at one site ca 12 500 yr bp indicate the existence of a late glacial sedimentation phase separated from the holocene sequence by a minor erosional phase organic layers in the holocene floodplain sediments yielded 28 radiocarbon dates between 10 000 and 355 yr bp holocene sedimentation started with the rapid deposition of sandy clay possibly in a partly permanently inundated caqueta valley during the major part of the holocene silty clays were deposited with a dominant seasonal inundation cycle

nature and causes of quaternary climate variation of tropical south america abstract this selective review of the quaternary paleoclimate of the south american summer monsoon sasm domain presents viewpoints regarding a range of key issues in the field many of which are unresolved and some of which are controversial 1 el nino southern oscillation variability while the most important global scale mode of interannual climate variation is insufficient to explain most of the variation of tropical south american climate observed in both the instrumental and the paleoclimate records 2 significant climate variation in tropical south america occurs on seasonal to orbital i e multi millennial time scales as a result of sea surface temperature sst variation and ocean atmosphere interactions of the tropical atlantic 3 decadal scale climate variability linked with this tropical atlantic variability has been a persistent characteristic of climate in tropical south america for at least the past half millennium and likely far beyond 4 centennial to millennial climate events in tropical south america were of longer duration and perhaps larger amplitude than any observed in the instrumental period which is little more than a century long in tropical south america these were superimposed upon both precession paced insolation changes that caused significant variation in sasm precipitation and eccentricity paced global glacial boundary conditions that caused significant changes in the tropical south american moisture balance as a result river sediment and water discharge increased and decreased across tropical south america lake levels rose and fell paleolakes arose and disappeared on the altiplano glaciers waxed and waned in the tropical andes and the tropical rainforest underwent significant changes in composition and extent to further evaluate climate forcing over the last glacial cycle 125 ka we developed a climate forcing model that combines summer insolation forcing and a proxy for north atlantic sst forcing to reconstruct long term precipitation variation in the sasm domain the success of this model reinforces our confidence in assigning causation to observed reconstructions of precipitation in addition we propose a critical correction for speleothem stable oxygen isotopic ratios which are among the most significant of paleoclimate proxies in tropical south america for reconstruction of variation of paleo precipitation or sasm intensity however it is already well known that any particular 18o value observed in speleothem carbonate is affected by two processes that have nothing to do with changes in precipitation amount the influence of temperature on carbonate water isotopic fractionation in the cave and the influence of changing 18o of seawater quantitatively accounting for both artifacts can significantly alter the interpretations of speleothem records in tropical south america both adjustments act in the same direction and have the tendency to increase the true amplitude of the paleo hydrologic signal but by different amounts in glacial and inter glacial stages these corrections have even graver implications for the interpretation of tropical northern hemisphere speleothem records e g chinese speleothems where the combined adjustments tend to decrease or even eliminate the true signal amplitude

palaeofires in amazon interplay between land use change and palaeoclimatic events interpreting the geological record of amazon biomass combustion requires comparing charcoal accumulation rates in various biomes at different time scales charcoal accumulation rates a proxy for palaeofire records were obtained in sediment cores from amazon lakes surrounded by several vegetation types and from a reservoirs in an intense land use change region the records presented in this study were obtained in the following areas i a reservoirs in alta floresta region northern mato grosso state ii lago do saci southern para state a lake close to alta floresta and located at the southern border of para state iii a bog in an ecotone area in the humaita region southern amazonas state iv lakes in lateritic iron crust of the carajas hills southeastern para state v lago comprido a floodplain lake close to the amazon river and surrounded by tropical rain forest monte alegre para state vi lagoa da pata in the morro dos seis lagos alkaline complex sao gabriel da cachoeira amazonas state and vii lago caracarana a secluded lake in the northern amazon cerrado roraima state the highest charcoal accumulation rates were observed for modern records related to an intense change in land use at alta floresta which had no precedent during the holocene history of the amazon high charcoal accumulation rates that were observed in the carajas region during low lake level phases in the amazon in the mid holocene were comparable to those at the onset of the human settlement in alta floresta region an increase in charcoal accumulation rate was observed in the late holocene when the lake level was high suggesting an interaction between climates and human presence low charcoal accumulation rates are typical of modern high rainfall environments as observed in lagoa da pata where the environment is not susceptible to occurrences of wildfires even during relatively drier climatic phases low charcoal accumulation rates also exist in the relatively dry cerrado savanna type biome even during relatively dry phases in the caracarana region where the savanna type vegetation biomass is lower and thus generates less charcoal particles than forest ecosystems

late quaternary vegetation dynamics in the southern amazon basin inferred from carbon isotopes in soil organic matter abstract carbon isotopes of soil organic matter som were used to evaluate and establish the chronology of the vegetation dynamics of an ecosystem presently composed of savannas surrounded by forests the study was carried out on a 200 km transect along highway br 319 on the border of amazonas and rondonia states in southern amazon brazil large ranges in 13 c values were observed in som collected from profiles in the savanna 27 to 14 and forest regions 26 to 19 reflecting changing distribution of 13 c depleted c 3 forest and 13 c enriched c 4 savanna vegetation in response to climate change these results indicate that from about 17 000 to 9000 14 c yr b p the study area was covered by forest vegetation between approximately 9000 and 3000 14 c yr b p savanna vegetation expanded at the expense of the forest although the expansion of savanna did not occur with the same intensity along the study transect this process was very clearly registered by 13 c enrichment in the som since 3000 14 c yr b p the carbon isotope data suggest that forested regions have expanded this study adds to the mounting evidence that extensive forested areas existed in the amazon during the last glaciation and that savanna vegetation expanded in response to warm and dry conditions during the early to middle holocene

holocene environmental changes from the rio curua record in the caxiuana region eastern amazon basin abstract holocene environments have been reconstructed by multiproxy studies of an 850 cm long core from rio curua dating to 8000 14 c yr b p the low energy river lies in the eastern amazon rain forest in the caxiuana national forest reserve 350 km west of belem in northern brazil sedimentological mineralogical and geochemical dates demonstrate that the deposits correspond to two different environments sediments of an active river before 8000 14 c yr b p and later a passive river system the pollen analytical results indicate four different local and regional holocene paleoenvironmental periods 1 a transition to a passive fluvial system and a well drained terra firme unflooded upland amazon rain forest with very limited development of inundated forests varzea and igapo 7990 7030 14 c yr b p 2 a sluggish river with a local mauritia palm swamp and similar regional vegetation as before 7030 5970 14 c yr b p 3 a passive river forming shallow lake conditions and with still abundant terra firme forest in the study region 5970 2470 14 c yr b p and 4 a blocked river with high water levels and marked increase of inundated forests during the last 2470 14 c yr b p increased charcoal during this last period suggests the first strong presence of humans in this region the atlantic sea level rise was probably the major factor in paleoenvironmental changes but high water stands might also be due to greater annual rainfall during the late holocene

variations of the amazonian rainforest environment a sedimentological record covering 30 000 years abstract two cores css 2 and css 10 were collected from two lakes situated in the carajas area 6 35 s 49 30 w that show different stages of silting up the results of geochemical and petrographic organic analyses backed up by 14 c radiometric dating lead to a reconstruction of the variations in the hydrological regime of these lakes over the last 30 000 years evidence is revealed for a period of drying up characterized by a sedimentary hiatus between 22 000 and 13 000 14 c years bp followed by a period of refilling between 13 000 and 11 000 14 c years bp 15 400 12 900 cal years bp the latter interval is primarily characterized by a mainly clastic sedimentary input rich in quartz kaolinite and iron hydroxides leading on to the authigenic formation of siderite this type of sedimentation implies the erosion of the small catchment basin during periods of transition between arid and humid climatic regimes from 8000 to 4000 14 c years bp 8900 4500 cal years bp as well as from 2700 to 1500 14 c years bp 2780 1360 cal years bp special hydrological conditions prevailed they are characterized in the sedimentary record by the presence of micro laminae containing wood charcoal interlayered with sponge spicule material this interlamination reflects the rapid alternation of dry and humid periods a comparison with the results obtained by pollen analysis shows that sedimentological indicators once filtered for strictly local effects can provide a full record of the regional scale variations in the environment

climatology of the low level jet east of the andes as derived from the ncep ncar reanalyses characteristics and temporal variability abstract a climatology of the south american low level jet east of the andes sallj is developed using the 1950 2000 circulation and moisture fields from the ncep ncar reanalyses and available upper air observations made in bolivia and paraguay since 1998 upper and low level circulation fields were derived for seasonal means and sallj composites during the warm and cold seasons the bonner criterion 1 was applied for sites in central bolivia and downstream near northern paraguay to determine the spatial and temporal characteristics of the sallj on the circulation characteristics sallj composites during the warm season show the enhanced low level meridional moisture transport coming from equatorial south america as well as an upper level wave train emanating from the west pacific propagating toward south america the intensification of the warm season sallj follows the establishment of an upper level ridge over southern brazil and a trough over most of argentina the circulation anomalies at upper a

holocene reef growth in the tropical southwestern atlantic evidence for sea level and climate instability the holocene epoch offers a potential analogue for understanding future sea level variability as both sst s and global mean sea levels gmsl were at times higher than observed today however gmsl can differ significantly from relative sea level rsl even at far field sites remote from margins of former ice sheets much of this spatial variability has been shown to be consistent with the predictions of glacial isostatic adjustment gia models whilst it is generally accepted that rsl at far field sites reached its maximum during the mid holocene there have been many interpretations of sea level fall following the highstand from 6 ka here we present a rsl history from several tectonically stable far field sites in eastern brazil derived from 17 microatoll and 45 fossil reef flat ages our results show evidence for two periods of rsl instability during the holocene which differ from gia predictions including a hiatus in reef growth 3 7 2 5 ka these results are broadly synchronous with several other locations in the southern hemisphere suggesting global rather than regional climatic forcing mechanisms are responsible variations in sst and southern hemisphere ice sheet dynamics are proposed as possible controlling mechanisms for the observed rsl oscillations beginning at 3 7 ka and 2 ka respectively we suggest that these global processes combined with increased precipitation and higher sediment flux from several regional climatic forces created inhospitable conditions for reef growth contributing to the observed hiatus and reduced reef flat accretion during the late holocene 2 ka to present

variations of sea surface temperature wind stress and rainfall over the tropical atlantic and south america abstract empirical orthogonal functions e0fs and composite analyses are used to investigate the development of sea surface temperature sst anomaly patterns over the tropical atlantic the evolution of large scale rainfall anomaly patterns over the equatorial atlantic and south america are also investigated the eof analyses revealed that a pattern of anomalous sst and wind stress asymmetric relative to the equator is the dominant mode of interannual and longer variability over the tropical atlantic the most important findings of this study are as follows atmospheric circulation anomalies precede the development of basinwide anomalous sst patterns over the tropical atlantic anomalous sst originate off the african coast simultaneously with atmospheric circulation anomalies and expand westward afterward the time lag between wind stress relaxation strengthening and maximum sst warming cooling is about two months anomalous atmospheric circulation patterns over northern tropical atlantic are phase

palaeohydrological controls on sedimentary organic matter in an amazon floodplain lake lake maraca brazil during the late holocene in order to understand the impact of hydrological changes of the amazon river on sedimentary organic matter om composition in amazonian floodplain lakes three sediment cores were collected from lake maraca eastern amazonia along a transect from the amazon river main channel to inland the cores were dated with 14c accelerator mass spectrometry ams and studied by x ray mineralogical composition total organic carbon toc and total nitrogen tn contents stable isotopic composition of toc and tn 13coc and 15n and glycerol dialkyl glycerol tetraether gdgt distributions two distinctive sedimentary depositional phases were identified based on the mineralogical composition and the geochemical characteristics of sedimentary om during the early mid holocene 13 000 3200 cal yr bp low values of toc followed by a break in sedimentation suggest a complete drying of the lake caused by drier climatic conditions between 3600 and 3200 cal yr bp this lake received a reduced influence of the amazo

late quaternary vegetational and climate dynamics in southeastern brazil inferences from marine cores geob 3229 2 and geob 3202 1 abstract late quaternary palaeoenvironments from southeastern se brazil have been reconstructed by pollen analysis of two marine sediment cores the core geob 3229 2 19 38 5 s 38 43 0 w 780 mbsl from the central depression south of the abrolhos bank is 505 cm long and 80 kyr bp old the core geob 3202 1 21 37 0 s 39 58 7 w 1090 mbsl from the upper continental slope off rio paraiba do sul is 495 cm long and 52 kyr bp old chronological control for core geob 3202 1 is based on seven ams radiocarbon dates from individuals of the foraminiferal species globigerinoides sacculifer the age scale for core geob 3229 2 was obtained by the detailed correlation of the oxygen isotope and x ray fluorescence records of both cores the two marine pollen records document vegetational changes in the drainage areas of two major se brazilian rivers the rio doce and the rio paraiba do sul which probably transported most of the pollen and spores deposited in the marine sediments during glacial times grassland vegetation dominated the landscape and atlantic rainforest and semideciduous forest were markedly reduced small areas of subtropical araucaria forest occurred in southeastern se brazil while cerrado vegetation was rare maximal grassland expansion and atlantic rainforest reduction were found during the last glacial maximum reflecting cold and relatively dry climatic conditions during the late glacial period grassland decreased and lowland forest taxa increased indicating wetter and warmer conditions comparison between the two marine pollen records with terrestrial records from the two river drainage areas confirms that grassland dominated the glacial age landscape reconstructed from terrestrial records

interactions between sea surface temperature over the south atlantic ocean and the south atlantic convergence zone 1 interactions between the sea surface temperature sst over the south atlantic ocean 40 s equador and the south atlantic convergence zone sacz were studied through numerical experiments with an atmospheric general circulation model agcm and an ocean general circulation model ogcm the agcm experiments showed that warm sst anomalies over the south atlantic tend to intensify the sacz and shift it northward while cool sst anomalies over the south atlantic tend to weaken the sacz the ogcm experiments on the other hand showed that the intensification of the sacz contributes to cool the underlying ocean through the reduction of incident shortwave solar radiation causing the appearance of cold sst anomalies or the weakening of pre existing warm sst anomalies the most important finding in this work was the predominance of the cloud shortwave sst negative thermodynamic feedback between the atmosphere and the ocean over the southwest tropical atlantic this is one order of magnitude larger than the dynamic feedback associated with ekman pumping the latter was verified only during strong sacz events the results suggest that negative sst anomalies often observed underlying the sacz represent an ocean response to atmospheric forcing

mechanisms of activity and unrest at large calderas large caldera collapses represent catastrophic natural events second only to large meteoritic impacts in addition some calderas are densely populated making the risk extreme even for moderate eruptions understanding caldera mechanisms unrest and the danger of eruption is therefore a crucial challenge for earth sciences several key features of caldera behaviour have yet to be fully understood through a combination of case studies and theoretical modelling the following topics are addressed in this volume the conditions required to produce and to release large volumes of magma erupted during caldera formation how magmatic feeding systems evolve before and after a caldera has formed the processes that limit the behaviour of precursors to eruptions how pre emptive precursors can be distinguished from those that drive unrest without an eruption and given that post collapse eruptions may occur across a wide area the optimum procedures for designing hazard maps and mitigation strategies

a long history of cloud and forest migration from lake consuelo peru abstract the complete paleoecological history from lake consuelo forest yields a record of ground level cloud formation and changes in its lower altitudinal limit over the last 46 300 cal yr bp the timing of early lake level fluctuations prior to 37 000 cal yr bp appears sensitive to north atlantic temperature oscillations corresponding to dansgaard oeschger interstadials 11 10 and 8 recorded in gisp2 after the lgm the first hint of warming is recorded in lake consuelo at 22 000 cal yr bp and agrees with other estimates for the region the mid holocene 7400 5000 cal yr bp was the period of highest rates of change and most significant reorganizations in the consuelo forest these community changes resulted from a regionally widespread dry period results from lake consuelo indicate that moisture availability mediated through cloud cover played the most significant role in ecological change in this system rates of past climate fluctuations never exceeded the forest capacity to accommodate change unfortunately this might not be the case under predicted scenarios for the end of the current century

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

changes in fire regimes since the last glacial maximum an assessment based on a global synthesis and analysis of charcoal data fire activity has varied globally and continuously since the last glacial maximum lgm in response to long term changes in global climate and shorter term regional changes in climate vegetation and human land use we have synthesized sedimentary charcoal records of biomass burning since the lgm and present global maps showing changes in fire activity for time slices during the past 21 000 years as differences in charcoal accumulation values compared to pre industrial there is strong broad scale coherence in fire activity after the lgm but spatial heterogeneity in the signals increases thereafter in north america europe and southern south america charcoal records indicate less than present fire activity during the deglacial period from 21 000 to 11 000 cal yr bp in contrast the tropical latitudes of south america and africa show greater than present fire activity from 19 000 to 17 000 cal yr bp and most sites from indochina and australia show greater than present fire activity from 16 000 to 13 000 cal yr bp many sites indicate greater than present or near present activity during the holocene with the exception of eastern north america and eastern asia from 8 000 to 3 000 cal yr bp indonesia and australia from 11 000 to 4 000 cal yr bp and southern south america from 6 000 to 3 000 cal yr bp where fire activity was less than present regional coherence in the patterns of change in fire activity was evident throughout the post glacial period these complex patterns can largely be explained in terms of large scale climate controls modulated by local changes in vegetation and fuel load

the hill of six lakes revisited new data and re evaluation of a key pleistocene amazon site the new analyses of a sedimentary record of lake pata in the hill of six lakes in nw amazon and its correlation with other quaternary proxy records in the region provide new insights regarding the vegetation and climate of the lowland forest during the last glacial despite what has been reported previously in the literature the sedimentary and pollen records are not continuous the hill remained forested however clear signals of structural change are seen in the record which indicate that the area experienced a significantly drier climate during the last glacial maximum lgm the herbs and taxa that are known to be more dominant in seasonally dry forests were all more abundant during the glacial part of the record and the cool adapted elements were mixed with warm lowland elements which indicates a temperature depression a comparison of the palaeoecological data with other regional geoenvironmental records of the upper negro river basin and other areas of the amazon provides additional support for a cooler and more seasonal environment during the middle pleniglacial which then became drier during the lgm a wet lgm is strongly refuted therefore the palaeoclimatic and ecological models that used the previous proxy data from six lakes to sustain wet conditions and a continuous forest record during the lgm to reconstruct the palaeoenvironmental conditions in the amazon should be reviewed

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

amazon plant diversity and climate through the cenozoic abstract the modern amazon lowlands date from the mid cenozoic when the andean orogeny defined an eastward or northward draining basin of immense size as the andean orogeny continued throughout the neogene and quaternary periods this system approached a steady state with andean flanks eroding to fill subsiding basins along the andean foreland followed by secondary erosion of sediments and transport in rivers across 3000 km to the atlantic ocean pollen data suggest that tropical forests were established on these lowlands at least by the end of the miocene with many modern amazon genera already present such antiquity is consistent with hypotheses that explain high diversity of modern amazon forests as the result of prolonged existence and minimal disturbance or extinction these museum models for amazon diversity came to be challenged by the paradigm of ice age aridity with its claim that the forests of the amazon lowlands were fragmented with each glacial advance into more or less tiny isolates called refugia separated by grass dominated communities like savanna for the latest pleistocene the arid amazon with forest refugia model can be tested by pollen analysis of lake sediments interpretation of amazon pollen data requires recognition both of the vast diversity of pollen types and an understanding of the dispersal of zoophilous pollen in the amazon amazon pollen analysis has been codified into a pollen atlas and this work used to review the available pollen data within the huge expanse of the amazon basin only three lacustrine records long enough and continuous enough to test this model have been published those from lake pata the carajas plateau and the amazon fan the review suggests community stability from all three data sets with no evidence for forest fragmentation in the amazon lowlands the principal response of amazon forest communities to climatic change is in the relative abundance of the more sensitive taxa particularly in response to interglacial warming a summary of geomorphological phenomena finds no evidence for glacial age aridity other than marginal reductions in precipitation within forest cover the amazon historical record is incomplete in time as well as in space there being essentially no paleobotanical data for much of the cenozoic particularly for the early pleistocene the data so far available however suggest stability and continuity of the forest cover over the vast amazon lowlands throughout the cenozoic as the circumstance in which the high amazon plant diversity evolved

paleolimnological record of the pampean plains argentina as a natural archive of south american hydroclimatic variability since the lgm to the current warm period abstract laguna mar chiquita lmc 30 54 s 62 51 w is a highly variable and shallow saline lake located in the pampean plains of argentina the paleolimnological record of lmc contains information on the environmental variability that occurred in a large area of southern south america since the last glacial maximum lgm until the present as inferred from the diatom assemblages sedimentary features and geochemical proxies prolonged intervals of high and lowstands have caused variations in water salinity trophic state and sedimentary processes this is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25 000 cal yr bp in the argentinean pampean region results are in accordance with well known global climatic phases the late pleistocene record is characterized by a scenario dominated by lowstands hypersaline and oligotrophic lake conditions radiocarbon ages 25 000 19 000 cal yr bp indicate that the onset of the record is coeval with the lgm later a progressive lake water level increase was registered at 17 000 cal yr bp which can be assigned to the heinrich stadial 1 a shift toward comparatively drier conditions identified in the record between 14 700 and 13 000 cal yr bp can be chronologically related to the antarctic cold reversal the transition from the late pleistocene to the holocene 13 500 10 500 cal yr bp is recorded by highstand phases while the early holocene record is characterized by high to intermediate water levels the hydrological reconstruction corresponding to the mid holocene is characterized by alternating phases of high lowstands the onset of the late holocene record is marked by the development of dry conditions and thus lowstand phases while around 1300 cal yr bp a distinct water lake level increase is recognized this humid phase ascribed to the medieval climatic anomaly is followed by the record of lowstands between 500 and 1000 cal yr bp being coeval with the little ice age the uppermost part of the record of lmc encompasses the current warm period showing a marked shift towards high lake water level conditions the hydrological variability registered in the paleolimnological record highlights the importance of laguna mar chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of south eastern south america

native sulfur sulfates and sulfides from the active campi flegrei volcano southern italy genetic environments and degassing dynamics revealed by mineralogy and isotope geochemistry abstract we investigated sulfur bearing minerals from the campi flegrei caldera southern italy in relation to the increase of hydrothermal activity phenomena since 2006 aimed at providing insights into the volcanic system dynamics mineral encrustations and muds were sampled between 2013 and 2015 at the long standing degassing crater of the solfatara tuff cone and its recently restless north eastern pisciarelli slope deep seated sulfides were further separated from two drill cores agip s mofete boreholes 1500 m and 2695 m depth the mineral assemblage and texture of sampled encrustations were determined by x ray diffraction optical and scanning electron microscopy and x ray microanalysis by energy dispersive spectrometry native sulfur and alunite dominate among the newly formed mineral phases other minerals are mostly alunogen and locally pickeringite potassium alum hematite and pyrite mereiterite and amarillite sporadically occur the mud pools are rich in gypsum potassium alum and pyrite quartz and argillic phases locally with analcime are dispersed in the outcropping rocks 34 s values were determined for shallow subsurface native sulfur 5 5 to 0 0 and alunite 1 7 to 0 2 as well as for the deep seated pyrite 3 3 to 7 4 in the depth range 1500 2695 m 18 o values were measured for shallow native alunite 4 2 to 7 0 pisciarelli alunite was finally analyzed for its 87 sr 86 sr ratio and 143 nd 144 nd ratios 0 707517 6 and 0 512459 6 respectively textural and isotopic data constrain the genesis of alunite at the expense of k feldspars through rock alteration by hydrothermal fluids we suggest that the caldera is a low sulfidation system hosting acid sulfate deposits in its active degassing area the acid sulfate environment developed on an argillitic facies that thins outwards and is characteristic for steam heated and magmatic steam environments these environments developed in relation to the fractured settings that facilitates the gas emissions from deeper levels and the meteoric infiltration from surface to depth newly determined 34 s data are lower than previously published values suggesting a progressive decrease in the sulfur isotopic composition through time at least since 1956 the isotopic variation is associated with a lowering of the so 2 h 2 s ratio and the widening of the surface of co 2 degassing in the absence of significant changes in the average co 2 flux values and in the carbon and helium isotope compositions native sulfur and sulfates move from sulfur isotope equilibrium to disequilibrium we ascribe this transition to enhanced so 2 scrubbing due to a high rock permeability that facilitates a faster gas ascent rate in the shallow crust

vegetation development in an amazonian peatland recent investigations of wetlands in western amazonia have revealed the presence of extensive peat deposits up to 7 5 m thick developing under a variety of vegetation types we report the first attempt to establish the long term centennial to millennial scale vegetation history of one of these peatland sites quistococha a palm swamp close to iquitos in northern peru pollen and sedimentological analyses show that peat formation began at the core site under sedge fen or floating mat vegetation c 2200 calendar years before present cal yr bp a seasonally flooded woodland developed c 1880 cal yr bp the permanently waterlogged palm swamp which persists today began to form c 1000 cal yr bp with the present vegetation community established by c 400 years ago the vegetation at this site has undergone continuous change throughout the period of peat formation with several abrupt transitions and reversals and repetitions in the apparent trajectory of change the pollen data combined with sedimentary evidence suggest that the dominant control on ecosystem functioning and development is the flooding regime there appears to have been a decrease in fluvial influence over time there is no clear evidence of direct climatic or anthropogenic influence although we cannot rule out the possibility of climatically driven hydrological changes our results caution against adopting a simple model of peatland vegetation succession in this region

two histories of environmental change and human disturbance in eastern lowland amazonia two long palaeoecological records pollen diatoms 14c chemistry and charcoal provide a detailed record of holocene environmental conditions in the lowlands of the lower amazon changes in the composition of the terra firme forest are evident but a forest cover is maintained throughout fluctuations in lake level and changes in seasonality are tracked in both sedimentary sequences rising early holocene sea levels and the consequent rise of local water tables probably caused the flooding of one of the sites a stepped increase in precipitation is suggested with increases evident at 8800 yr bp 7400 bp and between 6100 and 5800 yr bp increased storminess is suggested between 7400 yr bp and 6100 yr bp human disturbance is manifested in the palaeoecological records at one study site as early as 5500 yr bp c 6500 years ago and an intensifi cation or onset of agriculture is evident at c 3350 yr bp the terminating phase of the long record of disturbance is a period of forest regrowth that may correlate to the depopulation of amazonia following euro pean contact

holocene carbon cycle dynamics based on co2 trapped in ice at taylor dome antarctica a high resolution ice core record of atmospheric co2 concentration over the holocene epoch shows that the global carbon cycle has not been in steady state during the past 11 000 years analysis of the co2 concentration and carbon stable isotope records using a one dimensional carbon cycle model uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial scale changes of atmospheric co2 concentrations

black carbon in soils and sediments analysis distribution implications and current challenges this review highlights the ubiquity of black carbon bc produced by incomplete combustion of plant material and fossil fuels in peats soils and lacustrine and marine sediments we examine various definitions and analytical approaches and seek to provide a common language bc represents a continuum from partly charred material to graphite and soot particles with no general agreement on clear cut boundaries formation of bc can occur in two fundamentally different ways volatiles recondense to highly graphitized soot bc whereas the solid residues form char bc both forms of bc are relatively inert and are distributed globally by water and wind via fluvial and atmospheric transport we summarize chronologically the ubiquity of bc in soils and sediments since devonian times differentiating between bc from vegetation fires and from fossil fuel combustion bc has important implications for various biological geochemical and environmental processes as examples bc may represent a significant sink in the global carbon cycle affect the earth s radiative heat balance be a useful tracer for earth s fire history build up a significant fraction of carbon buried in soils and sediments and carry organic pollutants on land bc seems to be abundant in dark colored soils affected by frequent vegetation burning and fossil fuel combustion thus probably contributing to the highly stable aromatic components of soil organic matter we discuss challenges for future research despite the great importance of bc only limited progress has been made in calibrating analytical techniques progress in the quantification of bc is likely to come from systematic intercomparison using bcs from different sources and in different natural matrices bc identification could benefit from isotopic and spectroscopic techniques applied at the bulk and molecular levels the key to estimating bc stocks in soils and sediments is an understanding of the processes involved in bc degradation on a molecular level a promising approach would be the combination of short term laboratory experiments and long term field trials

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

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

a mineralogical and organic geochemical overview of the effects of holocene changes in amazon river flow on three floodplain lakes abstract a synthesis of the impacts of the amazon river hydrological changes on the sedimentation process of organic matter om in three different floodplain lakes santa ninha maraca and comprido lakes is presented in this study today the santa ninha and maraca lakes are directly and permanently connected with the main channel of the amazon river in contrast to comprido lake which is indirectly and periodically influenced by the amazon river due to its greater distance from the main channel all three lake sediment records showed a reduced river inflow due to dry climatic conditions during the early and middle holocene followed by an increased fluvial input during the wetter late holocene in santa ninha and maraca lakes the reduced river inflow period was recorded by sediments with a low abundance of smectite on average 20 wt a clay mineral mainly transported by the fluvial system high total organic carbon toc contents on average 8 2 wt and a predominantly acidic soil om input evidenced by high concentrations on average 180 g gtoc 1 of branched glycerol dialkyl glycerol tetraethers gdgt during the late holocene a higher smectite abundance on average 43 wt and a lower toc content on average 1 4 wt pointed to greater dilution by riverine lithogenic matter this change was accompanied by a proportional increase in the aquatically produced crenarchaeol suggesting a higher lake water level in comprido lake a sedimentation gap occurred during the early and middle holocene the wetter late holocene since 3000 cal years bp was characterized by high toc values on average 9 wt and a sharp increase in soil om input as recorded by an increase in branched gdgt concentrations on average 81 g gtoc 1 but the smectite content was low on average 14 this combination suggests that the soil om input to comprido lake from the local catchment area became dominant during the wet climate late holocene due to the large distance of the lake from the amazon river main channel consequently our study shows that the sedimentation processes of om in amazonian floodplain lakes were strongly influenced by variations in the hydrodynamic regime of the amazon river during the holocene however the impacts of the variations on the three floodplain lakes were different depending on the distance of each lake from the main channel of the amazon river

environmental and vegetation changes in southeastern amazonia during the late pleistocene and holocene abstract new insights about climate conditions and their effect on vegetation and lakes of southeastern amazonia were achieved over the last 50 cal ka using recent data obtained from a filled lake located in the serra sul de carajas our analysis was done in a sediment core r2 comprising of faciological palynological isotopic and radio carbon measurement supported by bayesian age depth modeling as well species distribution modeling wet and cool climate conditions are proposed for the mid pleniglacial which is favorable to intense weathering of the lake s catchment area and the expansion of high altitude taxa cool adapted into forest formations during this period from the late pleniglacial to the last glacial maximum a change from relatively wet to dry climate possibly converted the studied lake from oxidizing to reducing conditions which leads to the formation of diagenetic siderites at the end of this time interval warming during the pleistocene to holocene transition caused the disappearance of cool adapted taxa in the study site concomitantly increasing precipitation allowed the expansion of forest and high lake levels a drier early mid holocene produced extensive open vegetation and desiccated lakes current climate and environmental conditions were likely attained in the region from the mid to late holocene

neogene and quaternary development of the neotropical rain forest the forest refugia hypothesis and a literature overview abstract the upheaval of the northern andes in miocene and pliocene time changed the drainage system in northern south america significantly and caused the present day rain forest areas of choco and the lower magdalena valley became separated from amazonas plant diversity may have reached the highest level in the miocene or pliocene and excessive present day phytodiversity may be regarded as a legacy of the tertiary rather than an evolutionary product of the quaternary in the quaternary strong temperature oscillations related to the series of ice ages were superposed on the late tertiary forest dynamics which included river displacement and latitudinal migrations of the equatorial rain belt caloric equator with the rhythm of the precession cycle of orbital climate forcing the hypothesis that claims a permanent rain forest cover all over the amazon basin during the last glacial is in contrast with the forest refugia hypothesis which accepts replacement of rain forest by savanna or savanna forest during dry climatic intervals both scenarios have been evidenced by pollen records in this paper it is suggested that both hypotheses are not necessarily conflicting and apparently did occur in different parts of the amazon basin and in different periods depending on the climatological constraints a compilation of the most important literature concerning the vegetational climatic and environmental history of the rain forest areas of amazonas and choco and surrounding dry ecosystems has been included

submillennium scale migrations of the rainforest savanna boundary in colombia 14c wiggle matching and pollen analysis of core las margaritas abstract we present the 11 150 cal yr long pollen record laguna las margaritas 3 23 n 73 26 w 290 m altitude located at a site sensitive to climatic change near the transition from the amazonian rainforest to the savanna of the llanos orientales in colombia in the 10 m long core nine ams 14 c bulk samples show ages from 9760 60 to 854 36 bp and provide initial time control thirty one additional ams 14 c samples of selected macrofossils provide time control from 6250 to 4050 cal bp for this interval precise time control was obtained by 14 c wiggle match dating from 11 150 to 9100 cal bp grass savanna dominated the landscape while gallery forest along the drainage system was poorly developed water availability was lower than today and the length of the dry season longer from 9100 to 7330 cal bp gallery forest expanded pointing to wetter conditions from 7330 to 5430 cal bp savanna was increasingly replaced by forest but with alternating abundance of both vegetation types from 5430 to 2500 cal bp forest and wooded savanna dominated the western llanos orientales suggesting high precipitation rates expansion of mauritia palm forest at 2500 cal bp reflects increasing water availability and stagnant water environments increasing savanna between 2500 and 1000 cal bp may represent a combined natural and anthropogenic signal development from open savanna to forest during the middle holocene is synchronous with a decreasing caloric seasonality and a southward migration of the intertropical convergence zone suggesting that the large scale climatic and vegetational change in the colombian savannas is precession forced high frequent migration of the savanna rainforest boundary started around 6000 cal bp and continued at least to 3000 cal bp precipitation regimes in northwest and northeast south america seem opposite dry conditions in the colombian savanna area seem to reflect a la nina setting of the climate system wet conditions reflect an el nino setting 14 c fluctuations reflect changes of solar activity and we tested the hypothesis that 14 c fluctuations correspond to climatic and vegetational change for the interval 6250 to 4050 cal bp we applied 14 c wiggle match dating wmd i e matching a series of radiocarbon ages in 14 c bp from the sediment with the dendrochronology based calibration curve and we also wiggle matched the pollen record vs the 14 c record in this first attempt in a neotropical ecosystem we could not find unambiguous support that changes in solar activity did trigger climatic and vegetational change in the savannas of the llanos orientales

mid holocene pmip3 cmip5 model results intercomparison for the south american monsoon system the mean precipitation fields for eastern south america from eight mid holocene 6 ka simulations part of the third phase of palaeoclimate modeling intercomparison project pmip3 and the fifth p

modern pollen signatures of amazonian rivers and new insights for environmental reconstructions abstract paleoenvironmental reconstructions based on amazonian fluvial and marine pollen data are often hindered due to the scarcity of modern calibration data in amazonia rivers are the main pathways for pollen from upland and flooded forests to continental and marine sediment sinks linking pollen assemblages transported by rivers to watershed vegetation is crucial to interpret palynological archives in order to constrain the interpretation of palynological archives we analysed the pollen content of 36 riverbed sediment samples distributed from the mouth of the ica river ca 68ow to the amazon estuary ca 49ow with support of grain size and major element analyses of the inorganic sedimentary content the palynological analysis shows a strong imprint of the lowland floodplain vegetation as the main source of the riverborne pollen the upper reaches of the amazon river present abundant cecropia reflecting early successional stages induced by intense floodplain disturbance the middle and lower reaches of the amazon river exhibit a progressive increase in herbs mainly represented by poaceae and cyperaceae related to wider floodplains covered by seasonally inundated vegetation floodplain forests of whitewater rivers varzeas are palynologically characterized by iriartea mauritia ilex pseudobombax acalypha and luehea laetia with high frequency of cecropia or herbs and montane taxa at the black and clearwater rivers the igapo floodplain forests provide high percentages of symmeria myrtaceae and alchornea and can be distinguished by sapium sebastiana piranhea amanoa pouteria ferdinandusa genipa attalea astrocaryum and eschweilera which suggest conditions of higher stability and mature forests contribution from the non flooded uplands andean mountains and savannas cerrado occur but their signals are blurred by the high pollen production of the lowland floodplains our data provide a calibration set for environmental reconstructions of river influenced deposits across the amazon including offshore areas of the most iconic riverine dominated landscape in the world

biogeochemical indicators of environmental changes from 50 ka to 10 ka in a humid region of the brazilian amazon abstract we present a geochemical record of a 113 6 cm sediment core lpt v from lagoa da pata which is located in the forested upper rio negro basin the record reveals significant changes in the environmental history of amazonia during the late quaternary the results of biogeochemical analyses revealed three hydrological and climatic regimes from 50 000 to 10 000 cal yr bp the first phase between 50 000 and 26 300 cal yr bp was characterized by a relatively wet climate as suggested by relatively high total organic carbon toc and chlorophyll derivate concentrations indicating high productivity linked to a high lake level a decrease of the toc and chlorophyll derivate accumulation rates between 43 100 cal yr bp and 26 300 cal yr bp marks a decrease in the productivity linked to a reduced lake level indicating a decrease in moisture at the end of this phase the second phase between 26 300 and 15 300 cal yr bp was characterized by a decrease in productivity reaching a minimum at 21 950 cal yr bp as indicated by a minima in sedimentary chlorophyll and toc accumulation rates values of 13 c increased by 5 in relation to the preceding phase indicating an influence of the c 4 organic matter high iron concentrations and accumulation rates related to intense erosion of the lateritic crust in the watershed were observed all of the observations indicate a dry phase during this period a third phase from approximately 15 300 to 10 000 cal yr bp was characterized by an increase in lacustrine productivity as shown by an increased in toc and chlorophyll derivate concentrations and accumulation rates these increases likely correspond to a lake level rise due to a wetter climate

paleoenvironmental dynamics in south amazonia brazil during the last 35 000 years inferred from pollen and geochemical records of lago do saci abstract paleoenvironmental changes for the last 35 000 years were reconstructed from palynological sedimentological and organic geochemical evidence from a well dated sediment core from lago do saci south amazonia dry climatic conditions occurred between 35 000 and 18 200 cal yr bp as recorded by high frequencies of open savanna taxa and low lake level indicated by sagittaria and low total organic carbon content cold temperatures are indicated by the presence of podocarpus and ilex a sedimentation hiatus observed between 18 200 and 9200 cal yr bp was likely related to dry conditions the beginning of the holocene was marked by rainforest expansion and an increase in carbon content that represented high lake levels and warmer and wetter climate conditions between 7500 and 5000 cal yr bp the expansion of open savanna seasonal forest elements and abundant black carbon suggests a dry phase after 5000 cal yr bp rainforest expansion and higher lake levels indicate a return to wetter conditions a reduction of flooding taxa celtis and mauritia between 1800 and 1300 cal yr bp high lake level conditions and maintenance of a forest physiognomy suggests a decrease of regional precipitation and subsequent reduction of the flooded areas in a still humid climate regime

mineralogical geochemical and isotopic features of tuffs from the cfddp drill hole hydrothermal activity in the eastern side of the campi flegrei volcano southern italy abstract a 506 m drill hole has been recently drilled in the framework of the campi flegrei deep drilling project cfddp and the international continental scientific drilling program icdp with the intention of coring the subsurface in the eastern sector of the campi flegrei caldera the borehole located in the western district of the neapolitan city bagnoli plain 3 km to the east of the most active volcanic area and about 5 m above sea level is now targeted for monitoring purposes this paper reports the results obtained from the analysis of two short cores collected at depths of 443 and 506 m below the ground level the cores sampled two pre caldera tuffs observations performed by optical and scanning electron microscopy energy dispersive spectroscopy and powder x ray diffraction were used to achieve data on the primary lithology both primary and secondary mineralogical assemblages and the relationship between texture and secondary mineralization sr isotope ratios were determined on selected primary feldspars whereas 13c and 18o analyses were performed on carbonates from veins and filled voids in tuffs our results provide information on the hydrothermal system in the eastern sector of the caldera that was not among the goals in the previous drilling programs secondary mineralization suggests a saline hydrothermal environment characterized by fluids that progressively evolved from boiling toward more alkaline and cooler conditions a paleo temperature of ca 160 c has been inferred from authigenic mineral occurrences and calculated on the basis of equilibria between cored calcites and fluids presently emitted at the surface by using carbon and oxygen isotope data the temperature measured at the bottom of the drilling is about 80 c

accumulation of organic carbon in five brazilian lakes during the holocene abstract a comparative study was made of organic carbon accumulation in five lacustrine environments in brazil large open water lake ponds with floating meadows and marshes the most representative cores were used to calculate the accumulation of total organic carbon toc in the sediment over the past 12 000 cal years bp carbon accumulation rates were determined using the toc concentration sediment in situ density 14 c calibrated ages and the interpolated sedimentation rate cm year 1 or sediment accumulation rate g m 2 year 1 the c n ratio and microscopic observations were used to characterise the sedimentary organic matter recent toc accumulation in the lakes was estimated at 7 41 g m 2 year 1 by averaging the last 500 years this variation roughly correlated with the present day ratio of watershed area vs lake area indicating that nutrient input is important for the modern accumulation of organic matter the accumulation rates were greatest in lakes with floating macrophytes the largest lake dom helvecio with a strong thermal stratification low primary production and low carbon accumulation had relatively well preserved organic matter when its low watershed area lake area ratio was considered the general increase in carbon accumulation during the holocene followed the expansion of lakes and the development of a wetter climate due to a growing penetration of the atlantic and amazonian wet air mass over brazil driven by insolation changes this change in carbon accumulation was not controlled by the higher water and nutrient inputs alone more organic matter was decomposed when lake levels were low at the beginning of the holocene some lakes were also influenced by higher inputs of allochthonous organic matter during the early and middle holocene these inputs included high concentrations of charcoal fragments lake morphology and its changes as the lake level rose as well as the nature of primary producers strongly influenced the carbon accumulation rates our understanding of how climate changes are linked to changes in the lacustrine environment should not be based on measuring organic matter alone but requires a good description of the organic matter and other limnological parameters

black carbon records in chinese loess plateau over the last two glacial cycles and implications for paleofires abstract to study the temporal and spatial changes in paleofires over the chinese loess plateau black carbon concentrations were analyzed on the loess paleosol samples from three sections along a north south transect using the orbitally tuned time scales of the sections the black carbon mass sedimentation rates bcmsr were calculated results show that in the last two glacial cycles the bcmsr values in glacial periods are 2 3 times higher than in interglacial periods and the bcmsr variability has a relatively strong precession associated 23 ky period suggesting that the glacial cold dry climate conditions were apt to induce natural fires over the loess plateau comparison of the bcmsr records among the three loess sections demonstrates that natural fire occurrence was much more intensive and frequent in the northern loess plateau than in the southern part coinciding with the previous conclusion that the northern plateau has experienced a drier climate regime in both glacial and interglacial periods the substantial increase in bcmsr of the upper s0 relative to the lower s0 at lingtai and weinan indicates that human activities have exerted a significant influence on fire regimes in the middle and southern loess plateau during late holocene due to the relatively intensive agricultural usage of land

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