landscape evolution and origin of lake fuquene colombia tectonics erosion and sedimentation processes during the pleistocene abstract the basin of ubate chichinquira 5 28 n 73 45 w c 2580 m altitude includes the fuquene valley and is located in the central part of the eastern cordillera of colombia rocks and sediments were folded and faulted during the miocene uplifted during the late pliocene and affected by glaciers during the pleistocene successive glacial and interglacial periods left significant marks in the landscape which were used to reconstruct six stages in the development of the landscape along a relative chronology during early pleistocene episode 1 glaciers formed u shape valleys evidence of the impact of ice sheets has been found as far downslope as ca 2900 m elevation during episode 2 moraines developed which were cut by the present san jose river during episode 3 abundant sediment was produced by glacial erosion it accentuated the sculpturing of hard rock and deepening of the drainage basin the ancestral ubate suarez river constituted a dynamic erosive system that gave rise to deep v shaped valleys and progressively formed a set of intricate valleys with a high sediment production finally intense glacial and fluvio glacial erosion led to a geomorphological system with high energy levels and intensive sediment transport leading to wide valleys during episode 4 the ubate suarez river eroded and deepened its valley until it captured the old el hato san jose valley it caused intense erosion of the moraine and the fluvio glacial gravels deep v shaped valleys stabilized in the high areas of the main drainage system and these valleys form the present day fluvial sub basins during episode 5 the deep valley in the northern part of the basin of ubate chichinquira developed during middle pleistocene episode 6 colluvial sediments formed the saboya dam and a lake was formed in the river valley of which the present lake fuquene is only a small remnant lithological changes indicate fluctuating water levels and lake fuquene must have expanded periodically up to an area 5 to 10 times the present day surface

timing of abrupt climate change a precise clock 1 many paleoclimatic data reveal a 1 500 year cyclicity of unknown origin a crucial question is how stable and regular this cycle is an analysis of the gisp2 ice core record from greenland reveals that abrupt climate events appear to be paced by a 1 470 year cycle with a period that is probably stable to within a few percent with 95 confidence the period is maintained to better than 12 over at least 23 cycles this highly precise clock points to an origin outside the earth system oscillatory modes within the earth system can be expected to be far more irregular in period

spectral analysis of unevenly spaced climatic time series using clean signal recovery and derivation of significance levels using a monte carlo simulation abstract we present a monte carlo based method for the determination of errors associated with frequency spectra produced by the clean transformation of roberts et al 1987 the monte carlo procedure utilises three different types of simulation involving a data stripping operation and the addition of white and red noise to the analysed time series the simulations are tested on both synthetic and real data sets demonstrating the ability of the procedures to extract coherent information from time series characterised by the low signal to noise ratio that is typical of many palaeoclimatic records significance levels derived for the monte carlo spectra of four time series from the vostok ice core are utilised in the study of eccentricity components contained within the palaeoclimatic archive since 420 ka inversion of the vostok frequency spectra into the time domain reveals the differing influence of orbital parameters in the palaeoclimatic proxy records as well as the relative magnitudes of the eccentricity components contained in the time series of greenhouse gas concentration ice volume and local temperature

the selection of sites for paleovegetational studies the judicious selection of sites for paleovegetational and paleoclimatic studies permits paleoecologists to answer specific research questions that go beyond primary descriptions of past vegetation we present a model that describes the relationship between basin size and pollen source area and predicts the proportions of local extralocal and regional pollen sampled by lake basins of different size the distinctive sampling properties of lakes peats and small hollows can be exploited to provide details of pattern in paleovegetation so long as attention is given to the limitations and problems of these types of sites combinations of site types in a single study most fully exploit the information contained in sediments

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

climate and vegetation changes 180 000 to 345 000 years ago recorded in a deep sea core off portugal a new high resolution combined marine proxy pollen sequence from the portuguese margin md01 2443 enables direct comparison of ocean and ice volume changes with vegetation development in south west iberia during marine isotope stages mis 7 8 and 9 changes in sea surface conditions on both orbital and millennial time scales are closely mirrored by forest extent indicating a coherence of climate variability between the north atlantic and south west iberia deglacial warming at the start of mis 7 and 9 was interrupted by incursions of subpolar water masses at the site accompanied by reversals in tree population expansion during mis 7e and 9e the close relationship in timing and amplitude between vegetation and offshore conditions broke down early forest collapse points to pronounced cooling and aridification on land which although not accompanied by a change in water masses at the portuguese margin appears to have coincided with abrupt decreases in atmospheric methane concentration recorded in antarctic ice cores the most extreme glacial conditions of mis 8 occurred during the early part followed by an interval of warmer conditions and tree population expansion similar to 263 ka this has sometimes been considered as indicating an early deglaciation but the data presented here show that it was distinct from termination iii which occurred later in line with milankovitch forcing a sub orbital oscillation in both isotopic and pollen records is observed at the end of mis 7 ca 184 ka which appears to be coeval with a recently identified sea level high stand c 2006 elsevier b v all rights reserved

mineralogical and geochemical analyses of antarctic lake sediments a study of reflectance and mossbauer spectroscopy and c n and s isotopes with applications for remote sensing on mars abstract we analyzed lake bottom sediments from the dry valleys region of antarctica to study the influence of water chemistry on the mineralogy and geochemistry of these sediments as well as to evaluate techniques for remote spectral identification of potential biomarker minerals on mars lakes from the dry valleys region of antarctica have been investigated as possible analogs for extinct lake environments on early mars sediment cores were collected in the present study from perennially ice covered lake hoare in the taylor valley these sediments were taken from a core in an oxic region of the lake and another core in an anoxic zone differences between the two cores were observed in the sediment color fe ii fe iii ratio the presence of pyrite the abundance of fe s and some trace elements and the c n and s isotope fractionation patterns the results of visible infrared reflectance spectroscopy 0 3 25 m mossbauer spectroscopy 77 and 4 k and x ray diffraction are combined to determine the mineralogy and composition of these samples the sediments are dominated by plagioclase k feldspar quartz and pyroxene algal mats grow on the bottom of the lake and organic material has been found throughout the cores calcite is abundant in some layers of the sediment core from the shallow oxic region and pyrite is abundant in the upper sediment layers of the core from the deep anoxic region of lake hoare analysis of the spectroscopic features due to organics and carbonates with respect to the abundance of organic c and carbonate contents was performed in order to select optimal spectral bands for remote identification of these components in planetary regoliths carbonate bands near 4 and 6 8 m 2500 and 1500 cm 1 were detected for carbonate abundances as low as 0 1 wt co2 organic features at 3 38 3 42 and 3 51 m 2960 2925 and 2850 cm 1 were detected for organic c abundances as low as 0 06 wt c the 13c and 15n trends show a more complex organic history for the anoxic region sediments than for the oxic region sediments the biogenic pyrite found in the core from the anoxic zone is associated with depleted 34s values and high organic c levels and could be used as a potential biomarker mineral for paleolakes on mars

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

four climate cycles of recurring deep and surface water destabilizations on the iberian margin centennial climate variability over the last ice age exhibits clear bipolar behavior high resolution analyses of marine sediment cores from the iberian margin trace a number of associated changes simultaneously proxies of sea surface temperature and water mass distribution as well as relative biomarker content demonstrate that this typical north south coupling was pervasive for the cold phases of climate during the past 420 000 years cold episodes after relatively warm and largely ice free periods occurred when the predominance of deep water formation changed from northern to southern sources these results reinforce the connection between rapid climate changes at mediterranean latitudes and century to millennial variability in northern and southern polar regions

structure of the penultimate deglaciation along the california margin and implications for milankovitch theory the detailed structure and timing of the penultimate deglaciation are insufficiently defined yet critical for understanding mechanisms responsible for abrupt climate change here we present oxygen isotope records from planktonic and benthic foraminifera at unprecedented resolution encompassing late marine oxygen isotope stage mis 6 and termination ii ca 150 120 ka from the santa barbara basin supported by additional southern california margin records a region highly sensitive to millennial scale climate oscillations during the last deglaciation these records reveal millennial and centennial scale climate variability throughout the interval including an interstadial immediately preceding the deglaciation a brief warm event near the beginning of termination ii and a bolling allerod younger dryas like climate oscillation midway through the deglaciation recognition of these events in an oxygen isotope record from a 230th dated stalagmite allows the adoption of this radiometric chronology for the california margin records this chronology supports the milankovitch theory of deglaciation the suborbital history of climate variability during termination ii may account for records of early deglaciation

an environmental reconstruction of the sediment infill of the bogota basin colombia during the last 3 million years from abiotic and biotic proxies abstract the lacustrine sediments of the intramontane basin of bogota 4 n 2550 m altitude were collected in a 586 m deep core funza 2 absolute datings show sediment infill started c 3 2 ma and continued almost without interruptions as a result of the balance between tectonic subsidence and sediment infill analysis of downcore changes in lithology grain size facies loss on ignition loi and hydrosere vegetation at 20 cm intervals along the core produced a 2200 sample record of basin dynamics and lake level changes with a temporal resolution from c 800 years during the last 1 5 ma to c 2000 years from 1 5 to 3 2 ma we recognized 11 discrete sedimentary facies that reflect 4 different depositional environments facies 1 and 2 correspond to lacustrine environment where the loi is 20 a fluvio lacustrine environment is represented by the facies 3 4 5 7 and 9 a fluvial environment is reflected by facies 6 8 and 10 basin infill started with accumulation in a fluvio lacustrine environment between 586 and 530 m below the present day sediment surface of the basin in the 530 to 325 m interval c 3 1 5 ma the basin contained mainly shallow water and swamps in combination with some fluvial activity the 325 5 m interval 1 5 0 028 ma shows almost uninterrupted lacustrine paleoenvironmental conditions the uppermost 5 m reflect a fluvial paleoenvironment deposited by the bogota river and its tributaries the downcore changing ratio between shallow water aquatics myriophyllum ludwigia polygonum cyperaceae and aquatics of deeper water isoetes is indicative of lake level changes isoetes as an indicator of high water levels is not consistent with fluvial and fluvio lacustrine depositional regimes several lithological discontinuities evidenced by the sharp transition from swamp deposits to fluvio lacustrine and fluvial deposits are present in the core in the interval from 530 to 325 m in particular it is plausible that swamp deposits have been eroded during episodes during which the water table quickly raised or during events of sudden coarse fluvial input into the basin

cyclic fluvial sedimentation in a rapidly subsiding basin northwest washington abstract the eocene chuckanut formation of northwest washington comprises as much as 6000 m of alluvial strata and is one of the thickest nonmarine sequences in north america the bellingham bay member forms approximately the lower half of the chuckanut formation it is characterized by repetitive fining upward cycles consisting of a lower coarse grained and an upper fine grained member two types of cycle have similar vertical profiles but can be distinguished by the nature of their coarse member coarse members of the first type are thick 2 3 m are commonly multi storey have apparent sheet geometry and are interpreted as the deposits of meandering river channels and point bars coarse members of the second type are thinner down basin changes in the bellingham bay member include a major decrease in grain size and an increase in fine member thickness and cycle recurrence interval these changes reflect decreased flow competence and increased stability of channel banks similar trends might be found in other ancient alluvial sequences and could be useful in studies of both basin geometry and coal exploration sediment accumulation rates are a minimum of 50 cm 1000 yrs 1 implying rapid subsidence this subsidence probably had a major control on the sedimentation style of the bellingham bay member which resembles computer generated models of alluvial stratigraphy at high subsidence rates allen 1978

climatic variability of marine isotope stage 7 direct land sea ice correlation from a multiproxy analysis of a north western iberian margin deep sea core abstract the direct land sea ice correlation performed in the north western iberian margin core md01 2447 shows that marine isotope stage 7 mis 7 is marked by an alternation of five warm and cold periods this climatic variability is in general synchronously detected in marine and terrestrial realms by our record termination iii is marked by three cold episodes the last one interrupts the forest development in north western iberia related to the deglacial climatic amelioration it begins in the middle of termination iii but the maximal cold conditions occur at the beginning of low ice volume conditions mis 7 is characterised by three periods of very low ice volume associated with marine and continental high temperatures in and off north western iberia the correlation of our record with odp site 980 shows that the climatic variability detected in the north western iberian region has also an imprint in northern north atlantic it also highlights that most of the cold periods are associated with iceberg discharges in the north atlantic the comparison of the north western iberian margin sequence with the long european pollen records has allowed refining the correlation of the marine and continental stratigraphy for mis 7

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

orbital and millennial scale vegetation and climate changes of the past 225 ka from bear lake utah idaho usa continuous high resolution pollen data for the past 225 ka from sediments in bear lake utah idaho reflect changes in vegetation and climate that correlate well with variations in summer insolation and global ice volume during mis 1 through 7 spectral analysis of the pollen data identified peaks at 21 22 and 100 ka corresponding to periodicities in earth s precession and eccentricity orbital cycles suborbital climatic fluctuations recorded in the pollen data denoted by 6 and 5 ka cyclicities are similar to greenland atmospheric temperatures and north atlantic ice rafting heinrich events our results show that millennial scale climate variability is also evident during mis 5 6 and 7 including the occurrence of heinrich like events in mis 6 showing the long term feature of such climate variability this study provides clear evidence of a highly interconnected ocean atmosphere system during the last two glacial interglacial cycles that extended its influence as far as continental western north america our study also contributes to a greater understanding of the impact of long term climate change on vegetation of western north america such high resolution studies are particularly important in efforts of the scientific community to predict the consequences of future climate change r 2007 elsevier ltd all rights reserved

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

montane forest evolution during the last 650 000 yr in colombia a multivariate approach based on pollen record funza i the core interval of 0 140 m of the 357 m long pollen record from site funza i was analysed using multivariate analysis this long continental record is from the high plain of bogota located at 2550 m altitude in the eastern cordillera of colombia time control is based on a visual match with core funza ii from the same location which includes absolute fission track ages and a match with the 18o record of odp site 677 we reassessed the time frame of funza i compared with previous papers and conclude that the period of ca 650 25 kyr bp is represented in this study 73 fossil taxa present in 4 of the 409 pollen assemblages were analysed using the divisional classification program twinspan we recognised 10 cluster types that form three main cluster zones w warm cw cool and c cold pollen zones based on previous visual inspection were compared with new cluster types which were graphed as a bar code along the pollen diagram the use of two pollen sums standard pollen sum and a zonal pollen sum appeared useful for identifying local effects on the forest composition modern pollen rain data for the study area were summarised we used the concept of indicator taxa that behave as differential taxa to reconstruct climatic change during the period of 650 330 kyr bp alnus hedyosmum weinmannia melastomataceae myrica and podocarpus were the most important taxa of the andean forest the new time frame indicates that the first scattered presence of quercus started 478 kyr bp 102 m core depth the first continuous presence was from 423 kyr bp 92 m and the presence of zonal quercus forest occurred from 330 kyr bp 72 m during the period of 330 135 kyr bp zonal quercus and weinmannia forest developed replacing partly podocarpus dominated forest in the uppermost andean forest belt as a consequence during the last 135 kyr bp a high representation of quercus on the high plain of bogota no longer coincides with warm climatic conditions but now occurs during cool to cold conditions the pollen record was correlated with the 18o record temperature drop during marine oxygen isotope stage 4 and the very first part of marine oxygen oxygen stage 2 is calculated as a minimum of 6 6 to 7 8 c excluding a potential effect of low glacial pco2 the inferred maximum amplitude of the upper forest line during the last 650 kyr was from ca 1900 to 3400 m cf 3200 m at the present day corresponding to a range of ca 1 2 c to 7 8 c compared with today copyright 2000 john wiley sons ltd

glacier fluctuations in the eastern andes of colombia south america during the last 45 000 radiocarbon years abstract major glacial advances in the eastern cordillera of colombia preceded the global ice volume maximum at ca 20 ka bp two glacial events are recognized for isotope stage 3 dated between probably 43 and 38 ka bp and between 36 and 31 ka bp the events are recorded in glacial deposits and strongly subdued morainic ramparts three glacial advances during isotope stage 2 are dated between 23 5 and 19 5 ka bp 18 0 and 15 5 ka bp and 13 5 and 12 5 ka bp the glacial landforms associated with the period 18 0 to 15 5 ka bp are most distinct the arcuate multiple morainic ridge system of up to tens of meters of height can be traced throughout the region the moraines that formed during the earlier isotope stage 2 advance are more subdued the youngest isotope stage 2 morainic complex consists of low winding ridges isotope stage 1 glaciations affected only the highest areas of the eastern cordillera where morainic complexes associated with at least three glacial events occur but remain poorly dated the glacial record of the colombian eastern cordillera registers high climatic variability in the tropical andes during the late quaternary period

numerical zonation of log suites and logfacies recognition by multivariate clustering zonation of well logs and the correlation of zones between wells are routine fundamental tasks in subsurface geological analysis objective numerical multivariate clustering is an effective procedure to simultaneously comprehend a suite of well logs and partition it into geologically meaningful zones and for identifying zone specific logfacies discrimination of zones and logfacies from log suites was established by a hierarchical clustering algorithm that defines clusters so that their within cluster dispersion is minimal logfacies are defined by an unconstrained analysis of unzoned data whereas the special requirements of the stratigraphic context of the zonation are observed by an adjacency constraint which prohibits merging individual depth levels or lower order clu ters if their members are not vertically contiguous two test cases one involving a succession composed of several alternating lithologies and the other entailing a uniform carbonate sequence with only subtle changes demonstrate the applicability and efficacy of the method in both cases the numerical zonation matched the manual lithostratigraphic division extremely well the geological validity of the numerically defined zones was also borne out by density neutron crossplots the unconstrained analysis successfully identified logfacies which are zone specific indicating that logfacies can serve as important leads for the recognition of reverse faults in boreholes and for interwell correlations

palaeoclimate chronology and vegetation history of the weichselian lateglacial comparative analysis of data from three cores at lago grande di monticchio southern italy abstract palynological and chronological data are presented for the lateglacial from three cores taken at different locations in the basin of lago grande di monticchio plant macrofossil data from one core provide complementary evidence of the palaeovegetation quantitative palaeoclimate reconstructions are made from the pollen data using pollen climate response surfaces the chronological framework for late glacial events as well as the palaeoclimate are compared with other sources of evidence of lateglacial palaeoenvironments surface conditions in the north atlantic appear to be more directly linked to climatic conditions in italy than is the temperature in greenland nonetheless the palynological record exhibits high frequency variability that reflects high frequency climatic changes paralleling those seen in the ice core records from greenland

neotropical vegetation response to rapid climate changes during the last glacial period palynological evidence from the cariaco basin we present new palynological information from the anoxic cariaco basin off venezuela that provides insight into the response of northernmost south american vegetation to rapid climate changes between 68 and 28 ka specifically during north atlantic heinrich events hes and dansgaard oeschger cycles we defined three different vegetation modes 1 an interstadial mode characterized by the highest pollen concentration and the maximum extension of semi deciduous and evergreen forests 2 a stadial mode characterized by increases of salt marshes herbs and montane forests and 3 a heinrich event mode characterized by the lowest pollen concentrations abrupt increases of salt marshes and decreased forest abundance similarly indices of c4 c3 plants show increases during stadials with clear peaks during the onset of hes though grasslands did not become dominant during these periods we alternatively propose that these expansions of c4 plants are associated with the expansion of coastal salt marshes our vegetation record suggests the prevalence of humid conditions during interstadials dry and cold conditions during stadials and dry and cold conditions together with changes in sea level during hes this new palynological evidence supports previous interpretations that main environmental changes in northernmost south america were driven by latitudinal displacements of the intertropical convergence zone and sea level changes

mechanisms of abrupt climate change of the last glacial period 1 more than a decade ago ice core records from greenland revealed that the last glacial period was characterized by abrupt climate changes that recurred on millennial time scales since their discovery there has been a large effort to determine whether these climate events were a global phenomenon or were just confined to the north atlantic region and also to reveal the mechanisms that were responsible for them in this paper we review the available paleoclimate observations of abrupt change during the last glacial period in order to place constraints on possible mechanisms three different mechanisms are then reviewed ocean thermohaline circulation sea ice feedbacks and tropical processes each mechanism is tested for its ability to explain the key features of the observations particularly with regard to the abruptness millennial recurrence and geographical extent of the observed changes it is found that each of these mechanisms has explanatory strengths and weaknesses and key areas in which progress could be made in improving the understanding of their long term behavior both from observational and modeling approaches are suggested finally it is proposed that a complete understanding of the mechanisms of abrupt change requires inclusion of processes at both low and high latitudes as well as the potential for feedbacks between them some suggestions for experimental approaches to test for such feedbacks with coupled climate models are given

climatic pause during termination ii identified in shallow and intermediate waters off the iberian margin the sequence of termination ii from the end of marine isotopic stage 6 mis 6 to mis 5e is observed through an isotopic study 18o of planktic and benthic foraminifera in core md99 2331 42 09 n 09 41 w collected in the north atlantic on the iberian margin first to build an approximate time scale a record of the planktic 18o signal is achieved from the top of the core holocene to mis 6 the remarkable similarity of this planktic record to the greenland ice core project ice core 18o record allows a rough dating of our core a focus on termination ii reveals one standstill in the benthic record this pause can be linked either to a perturbation of north atlantic oceanic circulation pattern as a slowing down of the north atlantic deep water formation or to an interruption in polar ice sheet melting which could be a more global phenomenon

palaeoecology of three interstadial events during oxygen isotope stages 3 and 4 a lacustrine record from lago grande di monticchio southern italy abstract three interstadial events recorded in a pollen diagram from lago grande di monticchio southern italy 40 56 40 n 15 36 e can be correlated with dansgaard oeschger events 12 14 and 20 of the grip summit greenland ice core based on a chronology of varve counts the events are dated respectively to the intervals 37 600 40 000 43 600 50 000 and 72 000 74 600 calendar yr bp the interstadials are of unequal duration the longest occupying 6400 years they appear to begin and end abruptly each is characterised by a sequence of pollen changes in the mesic forest component similarities in these sequences of mesic forest trees imply similar patterns of climatic change within each interstadial the sequences resemble that of the late glacial interstadial at monticchio although tree pollen abundance values reach as much as 60 during the interstadials there is always a substantial proportion of herb pollen tree growth may have been constrained by low co2 levels during the glacial phase of the last glacial interglacial cycle this record illustrates the potential of long continental records to present opportunities for detailed ecological and chronological analyses of sub interglacial warming events during oxygen isotope stages 3 and 4

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

the penultimate deglaciation high resolution paleoceanographic evidence from a north south transect along the eastern nordic seas abstract the penultimate termination has been studied with focus on oceanographic changes in the eastern nordic seas and the influence of these changes on the surrounding ice sheets and vice versa repeatedly major changes in the strength of the atlantic meridional overturning circulation amoc occurred during the studied interval times of strong overturning and increased heat transport northwards were of importance in triggering one minor and two major disintegration events the two major disintegration events were separated by a deglacial pause characterized by a strong amoc the same variability is seen throughout the eastern nordic seas from the faeroe shetland channel in the south to the fram strait in the north some of the oceanographic changes occurring during the penultimate termination are comparable with changes seen through the last deglaciation reduced winter moisture flux and increased summer melting due to the present insolation forcing further amplified the rate of ice sheet disintegration calculated sea level change through tii shows a mean change of 121 4 m 41 16 m in the first step and 80 13 m in the last step

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

a high resolution paleoclimate record spanning the past 25 000 years in southern east africa high resolution profiles of the mass accumulation rate of biogenic silica and other geochemical proxies in two piston cores from northern lake malawi provide a climate signal for this part of tropical africa spanning the past 25 000 years the biogenic silica mass accumulation rate was low during the relatively dry late pleistocene when the river flux of silica to the lake was suppressed millennial scale fluctuations due to upwelling intensity in the late pleistocene climate of the lake malawi basin appear to have been closely linked to the northern hemisphere climate until 11 thousand years ago relatively cold conditions in the northern hemisphere coincided with more frequent north winds over the malawi basin perhaps resulting from a more southward migration of the intertropical convergence zone

spatial and temporal variation in cores from lake titicaca bolivia peru during the last 13 000yrs we compared the stratigraphy of sediment cores that span the last 13 000 yrs from three sites in the main basin of lake titicaca boliva peru as indicators of regional paleoclimate the cores show similar patterns of change after 6400 calendar yrs before present cal yr bp but differ before that time site ne98 pc2 which is near the rio illave and its delta shows differences in diatom species composition and in calcium carbonate concentrations relative to cores from the other two sites particularly during times of inferred high precipitation in contrast the carbon isotopic stratigraphy of the three sites is relatively similar the magnetic susceptibility data suggest that the proximity of site ne98 pc2 to the river and delta resulted in higher loads of detrital sediment prior to 6400 yr bp whereas pelagic sources contributed most of the sediment at the other sites these differences highlight the potential for spatial heterogeneity of sediment records in large lake systems and the importance of evaluating multiple cores for robust interpretation of paleoenvironmental history

climatic change during the younger dryas chron in northern south america a test of the evidence abstract new ams and palynological data are presented from the colombian andes to assess vegetational and climatic change during the lateglacial holocene transition with special emphasis on the younger dryas yd chronozone the new evidence is compared and discussed with other colombian cores and with data from other countries in the region the lateglacial climatic reversal in colombia known as the el abra stadial has an estimated lower boundary of 11 200 conventional and 10 900 interpolated 14 c yr bp respectively although the el abra stadial is assumed to be the equivalent of the european yd the present data suggest that the el abra stadial is a biostratigraphical signal representing both the yd chronozone and the earliest holocene 11 000 9000 14 c yr bp on the basis of new ams dates and a re evaluation of the pollen zones we divided the colombian el abra biozone into two phases from ca 11 000 to ca 10 500 14 c yr bp there is a sharp increase of subparamo and paramo pollen reflecting a relatively cool phase during the yd chronozone zone y1 after ca 10 500 14 c yr bp a slight increase of arboreal pollen and the presence of cactaceae zone z1 point toward a relatively milder but drier phase extending to ca 9000 14 c yr bp in the earliest holocene our conclusions add detail to the concept of astronomical forcing of contrasting rainfall changes in northern south america between 12 400 and 8800 14 c yr bp we propose an environmental drought during the el abra biozone with subsequent erosion of the sediments deposited during that period as a major factor explaining the poor presence of yd evidence in northern south america we conclude that at hydrologically sensitive sites without a clear lithological change around 11 000 9000 14 c yr bp a hiatus during the yd chronozone can only be detected if other cores are available with bracketed time control we state that the start of the temperature decline in central america and northern south america is related to the global yd cooling event however much work is still required to understand the duration and amplitude of the climatic reversal during the yd chronozone in this part of the globe

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

high resolution palynological record off the iberian margin direct land sea correlation for the last interglacial complex abstract we present high resolution pollen dinocyst and isotopic data for the last interglacial complex from marine core md952042 southwestern margin of the iberian peninsula 37 48 n 10 10 w 3148 m direct land sea correlation from this core indicates that during this period north atlantic sea surface temperatures were in phase with iberian climate our palynological analysis suggests a younger dryas like event at the marine isotope stage mis 6 5 transition the analysis also indicates that the eemian spans from the lightest isotopic values of mis 5e ca 126 ky bp to the heavier isotopic values towards the mis 5e 5d transition therefore the eemian is not entirely equivalent to mis 5e pollen analysis identifies four climatic phases of low amplitude during the eemian a mediterranean climate in southwestern europe is gradually replaced by oceanic conditions the middle of the eemian is characterized by an increase in precipitation on the land and ocean associated with a slight cooling this seems to be the result of a displacement of the polar front as far south as southern europe during this period after the eemian three relatively short climatic phases on land melisey i st germain ia and montaigu cold event occurred contemporaneously with three shifts of sea surface temperatures the montaigu event first identified in terrestrial pollen sequences is therefore also recorded in core md952042 on the basis of pollen dinocyst and planktonic isotopic data our results also show that the warm periods of mis 5 are not characterized by similar climatic conditions on land

palaeoenvironmental dynamics and underlying climatic changes in southeast amazonia serra sul dos carajas brazil during the late pleistocene and holocene abstract pollen fern spore micro charcoal sediment and mineral analyses have been carried out on a 466 cm long sediment core from the serra sul dos carajas swamp in southeastern amazonia ten ams radiocarbon dates suggest that the sediment covers at least the last 73 000 years shifts between tropical forests and savanna changes in species composition as well as changes in fire frequency indicate several wet and dry periods during this time interval during the assumed early pleniglacial 73 50 ka the dominance of savanna vegetation reflects drier conditions whereas vegetation changes in the mid pleniglacial 50 40 ka suggest alternating wet and dry phases under generally cool conditions the recorded next period before the last glacial maximum lgm shows a transition to wetter and cooler conditions followed by a cold and dry lgm and late glacial at the beginning of the holocene between 11 4 and 10 2 cal ka tropical forest expanded reflecting stable and very humid conditions during the early to mid holocene an increasingly seasonal generally warm and dry climate established dry seasons were longer than at present during mid holocene times with a pronounced dry phase from 9 to 3 4 cal ka only after 3 4 cal ka did modern tropical rainforests became established under present day climatic conditions comparison with other palaeoecological studies in the amazon basin and eastern andean regions suggests that environmental changes in serra sul were strongly coupled with large scale climatic changes and sea surface temperature variability in the tropical atlantic

a late quaternary diatom record of tropical climatic history from lake titicaca peru and bolivia abstract a composite high resolution diatom stratigraphy from three piston cores and one box core in the deep sub basin of lake titicaca reveals large moisture variations during the past 30 kyr in the altiplano region diatom sequences indicate orbital and millennial scale variability in water level and salinity the pelagic freshwater diatom species cyclotella andina and cyclotella stelligera dominate glacial age sediments suggesting that the lake was above its present outlet generally wet conditions continued until 11 000 cal yr bp as indicated by high percentages of freshwater planktonic diatoms large pulses of benthic diatom species between about 11 000 and 10 000 cal yr bp suggest brief intervals of large amplitude declines in lake level during the early holocene 10 000 8500 cal yr bp a freshwater diatom assemblage suggests overflowing conditions pelagic freshwater diatoms are replaced ca 8500 cal yr bp by the salinity indifferent species cyclotella meneghiniana and by benthic taxa indicating the beginning of lake regression during the mid holocene 6000 3500 cal yr bp the abundance of the saline taxon chaetoceros muelleri coupled with high abundances of epiphytic and epipelic diatoms indicates maximum salinity and lowest lake levels in the entire 30 000 year record lake transgression began ca 4000 cal yr bp and the lake achieved modern levels by about 1500 cal yr bp these water level changes imply changes in effective moisture most likely resulting from large precipitation changes precipitation was high throughout the last glacial maximum 21 000 18 000 cal yr bp likely due to an enhanced south american summer monsoon during peak summer insolation in the southern hemisphere in contrast the mid holocene transition was dryer than today in association with an austral summer insolation minimum and the subsequent weakening of the summer monsoon

holocene climatic variations in the western cordillera of colombia a multiproxy high resolution record unravels the dual influence of enso and itcz abstract the paramo de frontino 3460 m elevation in colombia is located approximately halfway between the pacific and atlantic oceans it contains a 17 kyr long stratigraphically continuous sedimentary sequence dated by 30 ams 14c ages our study covers the last 11 500 cal yr and focuses on the biotic pollen and abiotic microfluorescence x or xrf components of this high mountain ecosystem the pollen record provides a proxy for temperature and humidity with a resolution of 20 35 yr and xrf of ti and fe is a proxy for rainfall with a sub annual ca 6 month resolution temperature and humidity display rapid and significant changes over the holocene the rapid transition from a cold mean annual temperature mat 3 5 c lower than today and wet younger dryas to a warm and dry early holocene is dated at 11 410 cal yr bp during the holocene mat varied from ca 2 5 c below to 3 5 above present day temperature warm periods 11 410 10 700 9700 6900 4000 2400 cal yr bp were separated by colder intervals the last 2 4 kyr of the record is affected by human impact the holocene remained dry until 7500 cal yr bp then precipitations increased to reach a maximum between 5000 and 4500 cal yr bp a rapid decrease occurred until 3500 cal yr bp and the late holocene was dry spectral analysis of xrf data show rainfall cyclicity at millennial scale throughout the holocene and at centennial down to enso scale in more specific time intervals the highest rainfall intervals correlate with the highest activity of enso variability in solar output is possibly the main cause for this millennial to decadal cyclicity we interpret enso and itcz as the main climate change driving mechanisms in frontino comparison with high resolution xrf data from the caribbean cariaco basin a proxy for rainfall in the coastal venezuelian cordilleras demonstrates that climate in frontino was pacific driven enso dominated during the yd and early holocene whereas it was atlantic driven in cariaco itcz dominated from ca 8000 cal yr bp climate in both areas was under the dual influence of enso and itcz thereby showing existing teleconnections between the tropical pacific and atlantic oceans the frontino record is to date the highest resolution holocene study in nw colombia an implication of these results is that new records should be analyzed with multiproxy tools in particular those providing high resolution time series such as xrf

sea level reversal during termination ii the termination of the penultimate glacial period tii shows both similarities and differences to the last termination ti both terminations show significant cold reversals in the postglacial warming trend ti consists of a continuously increasing sea level trend whereas tii may demonstrate a sea level reduction midway through the termination we present a new continuous sea level record for tii derived from red sea 18 o records that supports the existence of the tii sea level reversal the record gives an unprecedented look at the structure of the tii sea level reversal which consists of an early highstand lasting several millennia in duration followed by a 30 12 m to 40 12 m reduction in sea level and a stillstand of several millennia before the final sea level rise to the marine oxygen isotope stage mis 5e interglacial we suggest that there is a link between the sea level reversal and internal millennial scale variability in the climate system

a new estimate of the holocene lowstand level of lake titicaca central andes and implications for tropical palaeohydrology new evidence from piston cores and high resolution seismic reflection data shows that water levels in lake titicaca were as much as 100 m below the present level during the early to mid holocene between 6 and 3 8 14c kyr bp climatological and modelling studies indicate that lake titicaca rainfall depends on convective activity in upwind amazonia the lake level data therefore suggest a drier amazon basin during this time this view is bolstered by an excellent match between the titicaca lake level curve and decreased methane concentrations in greenland ice previously ascribed to drying of low latitude wetlands blunier et al 1995 the postglacial history of lake titicaca fits a global pattern of lake level change in the tropics characterized by opposite phasing between the southern and northern hemispheres this pattern is most likely the result of orbital controls over the intensity of summer insolation

the el abra stadial a younger dryas equivalent in colombia abstract a survey of radiocarbon dated palynological stratigraphical and glacio morphological evidence from colombia is presented showing a cold climatic fluctuation most likely between 10 900 and 10 100 bp immediately preceding the initiation of the holocene this fluctuation called the el abra stadial is characterized by lower temperatures and less precipitation and occurs after the late glacial guantiva interstadial average annual temperature during the guantiva interstadial may have been 2 c lower than today and during the el abra stadial from 4 to 6 c lower than today the upper forest line during the el abra stadial was some 400 to 500 m lower than during the guantiva interstadial and some 600 to 800 m lower than today the guantiva interstadial el abra stadial early holocene sequence is radiocarbon dated by some 45 dates and evidence is shown from 14 areas mostly located at high elevations 2000 4000 m in the eastern and central cordillera and in the sierra nevada de santa marta but some from the tropical low lands although more precise dating of the boundaries is desirable we interpret the guantiva el abra climatic fluctuations as equivalents in time and climatic phenomena to the allerod younger dryas sequence in europe

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

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

rapid climate change from north andean lake fuquene pollen records driven by obliquity implications for a basin wide biostratigraphic zonation for the last 284 ka this paper compares a new super high resolution pollen record from a central location in lake fuquene 4 n with 3 pollen records from marginal sites from the same lake basin located at 2540 m elevation in the eastern cordillera of colombia we harmonized the pollen sum of all records and provided previously published records of climate change with an improved age model using a new approach for long continental pollen records we dissociated from subjective curve matching and applied a more objective procedure including radiocarbon ages cyclostratigraphy and orbital tuning using the new 284 ka long fuquene basin composite record fq bc as the backbone groot et al 2011 we showed that a common 9 m cycle in the arboreal pollen percentage ap records reflects obliquity forcing and drives vegetational and climatic change the ap records were tuned to the 41 kyr component filtered from standard benthic 18o lr04 record changes in sediment supply to the lake are reflected in concert by the four records making frequency analysis in the depth domain an adequate method to compare records from the same basin we calibrated the original 14c ages and used where necessary biostratigraphic correlation i e for records shorter than one obliquity cycle pollen records from the periphery of the lake showed changes in the abundance of alnus and weinmannia forests more clearly while centrally located record fq 9c shows a more integrated signal of regional vegetation change the revised age models show that core fq 2 reflects the last 44 ka and composite record fq 7c the last 85 5 ka marginally located core fq 3 has an age of 133 ka at 32 m core depth and the lowermost 11 m of sediments appear of older but unknown age the longest record fq bc shows 60 yr resolution over the period of 284 27 ka all pollen records are in support of a common regional vegetation development leading to a robust reconstruction of long series of submillennial climate oscillations reflecting dansgaard oeschger do cycles reconstructed climate variability in the tropical andes since marine isotope stage mis 8 compares well with ngrip 18o based epica dome c d based and the mediterranean sea surface temperature record md01 2443 44 uk 37 based underpinning the global significance of the climate record from this tropical andean lake a basin wide biostratigraphy is presented and we concluded although with varying robustness that each core is representative of regional vegetational and climatic change

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements