characteristic straight chain lipid ratios as a quick method to assess past forest paramo transitions in the ecuadorian andes to assist sustainable reforestation efforts in the andes in northern ecuador the position of the natural upper forest line ufl has to be assessed to this end new vegetation reconstruction techniques to complement traditional reconstruction methods such as pollen analysis are being developed one such technique is the biomarker ratio approach that uses changes in characteristic ratios of extractable lipids such as n alkanes and n alcohols for a quick assessment at high spatial resolution of abrupt past vegetation changes in the present study we assessed the applicability of this approach as indicator of past vegetation shifts from forest to paramo or vice versa in northern ecuador we looked at the n alkane and n alcohol signals of two soil monoliths one taken in a forest patch located 100 m above the current ufl and the other at the same altitude in the surrounding paramo the monoliths were sampled to a depth corresponding to at least 1500 cal yr bc links were sought between biomarker ratio signals in soil organic matter som and those found in plants from the vicinity during previous research based on the outcome an attempt was made at determining whether the forest patch had been part of the continuous forest further down slope during the last 3500 cal years results show that specific ratios of extractable straight chain lipids can be used to get a quick indication of whether an area was forested or not in the past in som the n alkane relationship c29 c31 1 combined with the n alcohol relationship c22 c24 1 was found to be characteristic for dominant forest vegetation while the opposite relationships were indicative for past paramo vegetation the n alkane relationship could be explained very well by the lipid ratios of the current forest and paramo vegetation in the area while agreeing well with the n alkane signal the n alcohol signal was less robust probably partially due to degradation of wax esters in the soil contrary to expectations we conclude that the investigated forest patch was never part of the continuous forest in the vicinity in the past 3500 cal years instead our biomarker ratio approach suggests that the forest patch soil was once covered by paramo vegetation overall this study shows that the biomarker ratio approach in volcanic ash soils can serve as a quick method for an assessment of abrupt vegetation changes such as associated with past ufl shifts at a high spatial resolution and at the location where the shift occurred as such it is highly complementary to traditional proxies such as pollen analysis

climate information imprinted in oxygen isotopic composition of precipitation in europe abstract in this study we analyze the interannual variability of the oxygen isotopic composition of winter precipitation 18 o prec over europe and investigate its related climate information for this purpose we compare winter temperature precipitation and 18 o prec modeled by the atmospheric general circulation model echam5 wiso with different observational datasets over europe in general the model and data results are very similar for the present day climate and the modeled 18 o prec is matching the global network of isotopes in precipitation station data echam5 wiso only slightly underestimates the temperatures over europe mean difference 0 4 c the mean european precipitation amount is very similar 85 mm month however in central western europe the modeled precipitation is overestimated by up to 30 mm month we also evaluate the large scale circulation associated with the regional 18 o prec values by correlating the north atlantic oscillation nao index to modeled 18 o prec fields we show that the nao pattern is most pronouncedly imprinted in 18 o prec over central western europe consistent with observations we demonstrate for an example location near a stalagmite site in central germany how local isotope related climate variables are related to large scale european climate variability we find that in both the model results and the data present day winter variability of local 18 o prec is strongly related to atmospheric circulation remote sea level pressure fields and much less to the local and remote temperature or precipitation fields the simulated correlation pattern resembles the nao pattern but is tilted to the east due to the combined effect of temperature and precipitation

late holocene changes in vegetation and atmospheric circulation at lake uddelermeer the netherlands reconstructed using lipid biomarkers and compound specific δd analysis we reconstructed middle to late holocene changes in atmospheric circulation patterns and vegetation in northwest europe by applying novel geochemical techniques to the sediment record of lake uddelermeer the netherlands a comparison of higher plant derived leaf wax n alkane distributions archived in the lake sediments with those in living plant material combined with palynological analysis indicates that the vegetation immediately surrounding the lake became more open at 3150 cal a bp while the regional vegetation responded more gradually and 650 years later our record of the hydrogen isotopic composition of plant leaf waxes dwax shows a deuterium enrichment starting from 3500 cal a bp which we interpret as a change in atmospheric circulation a similar dwax record from nearby meerfelder maar germany shows an opposite trend around this time which could be explained by a change in sea level pressure resembling a negative north atlantic oscillation phase this could account for depleted d values of precipitation at meerfelder maar while confounding factors related to the more maritime position of uddelermeer cause the opposite shift there

development and refinement of proxy climate indicators from peats peat especially from acidic mires bogs is a natural archive of past environmental change reconstructions of past climate from bogs commenced in the 19th century through examination of visible peat stratigraphy and later formed the basis for a postglacial climatic scheme widely used in northwest europe nevertheless misconceptions as to how bogs grow led to a 50 year lacuna in peat climate study before the concept of cyclic regeneration in bogs was refuted in recent decades research using proxy climate indicators from bogs has burgeoned a range of proxies for past hydrological change has been developed as well as use of pollen bog oaks and pines and other data to reconstruct past temperatures most of this proxy climate research has been carried out in northern europe but peat based research in parts of asia and north america has increased particularly during the last decade while research has also been conducted in australia new zealand and south america this paper reviews developments in proxy climate reconstructions from peatlands chronicles use of a range of palaeo proxies such as visible peat stratigraphy plant macrofossils peat humification testate amoebae and non pollen palynomorphs and explains the use of wiggle match radiocarbon dating and relationship to climate shifts it details other techniques being used increasingly such as biomarkers stable isotopes inorganic geochemistry and estimation of dust flux and points to new proxies under development although explicit protocols have been developed recently for research on ombrotrophic mires it must be recognised that not all proxies and techniques have universal applicability owing to differences in species assemblages mire formation topographic controls and geochemical characteristics

compilation of non annually resolved holocene proxy climate records stacked holocene peatland palaeo water table reconstructions from northern britain abstract the number and range of holocene palaeoclimate reconstructions from various regions of the world have increased dramatically over the last decade the data density for many regions and proxies now offers the potential of robust regional scale reconstructions that avoid the problems of records from individual sites and improve communication between palaeoclimate subdisciplines and climate modellers however there are problems with chronological uncertainties and quantification of proxies which make compilation of multiple records difficult here we explore a stacking and tuning approach to the derivation of regional records from peatland climate proxies to test its applicability to non annually resolved terrestrial records twelve individual records from northern britain based on water table reconstructions from testate amoebae analysis were divided into four regions records were detrended normalised and compared within regions to identify clear correlative events the original chronologies of the records were tuned using both these events and independent age markers the stacked record for northern britain indicates pronounced changes to wet conditions at 3600 2760 and 1600 cal yr bp with more minor changes at 3060 2050 1260 860 550 and 260 cal yr bp the main wet phases are highly correlated with mid european lake highstands wider north atlantic climate change inferred from ocean and ice core records and solar variability tuning and stacking of non annual terrestrial palaeoclimate records is a new approach to the compilation and reconciliation of individual records within coherent climatic regions and provides a tool for upscaling of palaeoclimate records for climate model data comparisons

aeolian sediment reconstructions from the scottish outer hebrides late holocene storminess and the role of the north atlantic oscillation northern europe can be strongly influenced by winter storms driven by the north atlantic oscillation nao with a positive nao index associated with greater storminess in northern europe however palaeoclimate reconstructions have suggested that the nao storminess relationship observed during the instrumental period is not consistent with the relationship over the last millennium especially during the little ice age lia when it has been suggested that enhanced storminess occurred during a phase of persistent negative nao to assess this relationship over a longer time period a storminess reconstruction from an nao sensitive area the outer hebrides is compared with late holocene nao reconstructions the patterns of storminess are inferred from aeolian sand deposits within two ombrotrophic peat bogs with multiple cores and two locations used to distinguish the storminess signal from intra site variability and local factors the results suggest storminess increased after 1000 cal yrs bp with higher storminess during the medieval climate anomaly mca than the lia supporting the hypothesis that the nao storminess relationship was consistent with the instrumental period however the shift from a predominantly negative to positive nao at c 2000 cal yrs bp preceded the increased storminess by 1000 years we suggest that the long term trends in storminess were caused by insolation changes while oceanic forcing may have influenced millennial variability

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

multiproxy evidence of little ice age palaeoenvironmental changes in a peat bog from northern poland little ice age lia climatic deteriorations have been abundantly documented in various archives such as ice lake sediments and peat bog deposits palaeoecological analyses of peat samples have identified these climatic deteriorations using a range of techniques for example palynology plant macrofossils testate amoebae or carbon isotopic analyses the use of inorganic geochemistry and the reconstruction of dust fluxes has remained a challenge in tracing the nature of lia climatic changes although the idea of enhanced erosion conditions and storminess is commonly discussed the conditions for dust deposition in peatlands over europe during the lia are rarely favourable because the natural forest cover over europe was much more important than nowadays preventing dust deposition this intense forest canopy masks the deposition of dust in peatlands in northern poland near the baltic shore the slowin skie blota area was deforested around ad 1100 ie just before the lia and therefore constitutes a key area for the reconstruction of lia climatic change with the support of a well constrained chronology climatic fluctuations are recorded in an ombrotrophic bog using inorganic geochemistry plant macrofossils and carbon isotopic analyses the reconstruction of lia climatic changes is in good agreement with other records from poland and ne europe however a c 50 year discrepancy can be observed between various records this discrepancy is possibly due to progressive time dependent cooling gradient from north to south europe

evaluation of low latitude pi2 pulsations as indicators of substorm onset using polar ultraviolet imagery impulsive pi2 pulsations have long been recognized as one of the key signatures of magnetic activity during substorm periods due to their wide observable range both in latitudes and longitudes it is well documented that there is usually more than one pi2 wave burst associated with a substorm and only one of them corresponds to the onset of the substorm this observational fact poses obstacles to determining substorm onsets with pi2 signals although the pi2 have become one of the most popular indicators for substorm onsets the reliability of using the pi2 in this fashion has not been seriously investigated in this paper we address this question with a statistical approach by using 650 auroral substorm onsets identified with polar ultraviolet images for a time interval from april 1996 to may 1997 a comparison of the low latitude pi2 pulsation onsets from kakioka l 1 07 with the auroral breakups indicates that identifying substorm onset with the pi2 alone is often ambiguous of a total of 119 isolated defined as 10 min of quiet time preceding the onset pi2 bursts seen within 10 min from a magnetic positive bay there were 65 events 55 taking place within 3 min from breakups and 34 events 29 indicating no sign of an auroral breakup within 10 min of the pi2 burst this result suggests that pi2 may not be as a good indicator of the substorm onset as it was thought to be interestingly it is always possible to associate pi2 pulsations with some forms of auroral intensification when compared to auroral breakups pi2 onsets are subject to a small delay of 1 3 min with a peak around l min delays of pi2 onsets are revealed to be a function of location relative to auroral breakup this dependence is found to be consistent with the time of flight for a fast mode wave in a plasmapause cavity mode model propagating in the magnetosphere

on relative timing in substorm onset signatures we investigate the timing of popular substorm onset signatures to understand their temporal relationship proxies for substorm onsets include auroral breakups high latitude magnetic bays low latitude pi2 bursts dispersionless injections at geostationary orbits and auroral kilometric radiation we use the auroral breakup identified with polar uvi images as a common reference time frame to calibrate the others results illustrated by two well defined auroral substorms unambiguously indicate that none of the four frequently used substorm onset proxies can provide a consistent timing of substorm onset this inconsistency in substorm onset timing is attributed as a consequence of temporal and spatial limitations on each observational technique a delay between the proxy identifiers and the auroral breakup is found to be typical it is therefore strongly suggested from this study result that a common reference time frame for substorm onset is necessary and we propose it should be auroral breakups we argue that there is a need for an intercalibration of magnetospheric substorm phenomenology by using a unified definition of the substorm onset

holocene climate variability as reflected by mid european lake level fluctuations and its probable impact on prehistoric human settlements abstract a data set of 180 radiocarbon tree ring and archaeological dates obtained from sediment sequences of 26 lakes in the jura mountains the northern french pre alps and the swiss plateau was used to construct a holocene mid european lake level record the dates do not indicate a random distribution over the holocene but form clusters suggesting an alternation of lower and higher climatically driven lake level phases they provide evidence of a rather unstable holocene climate punctuated by 15 phases of higher lake level 11 250 11 050 10 300 10 000 9550 9150 8300 8050 7550 7250 6350 5900 5650 5200 4850 4800 4150 3950 3500 3100 2750 2350 1800 1700 1300 1100 750 650 cal bp and after 1394 ad a comparison of this mid european lake level record with the gisp2 polar circulation index pci record the north atlantic ice rafting debris ird events and the 14 c record suggests teleconnections in a complex cryosphere ocean atmosphere system correlations between the gisp2 pci the mid european lake level the north atlantic ird and the residual 14 c records suggest that changes in the solar activity played a major role in holocene climate oscillations over the north atlantic area

age geochemistry and distribution of the mid holocene hekla s kebister tephra the middle holocene hekla s kebister tephra originates in the hekla volcanic system on sw iceland the distal distribution of the tephra includes the faroe islands shetland and central sweden indicating a main dispersal towards the east the chemical composition of the tephra follows the pattern of other major eruptions of hekla and ratios between selected oxides may in some cases allow separation from other major holocene tephras from hekla tephra from the plinian phase dominates in eastern sites while tephra also from later phases is found in the faroe sites wiggle matching of radiocarbon dates around the tephra in a swedish peat bog suggests an age around 3720 cal yr bp 3750 3700 cal yr bp which is in accordance with previous attempts to date this tephra this is within a period with significant climate changes in nw europe and opens possibilities for exact comparisons of peat and lake sediment records from different geographical areas

environmental controls on branched tetraether lipid distributions in tropical east african lake sediments abstract quantifying past continental temperature changes is an important aspect of paleoclimate research as it allows us to constrain the amplitude of natural variability test predictive climate models and provide a proper context for changes that may arise in response to anthropogenically induced climate change the recently developed biomarker based methylation index of branched tetraethers cyclization ratio of branched tetraethers mbt cbt proxy shows potential as a new method for continental temperature reconstruction but thus far it has only been applied successfully in ocean margin sediments to assess whether this proxy is also applicable to the sedimentary record in tropical lacustrine systems we investigated the distribution of branched glycerol dialkyl glycerol tetraethers gdgts in recently deposited sediments from 46 lakes in tropical east africa these lakes span a substantial range in surface elevation 770 4500 m above sea level and thus also a wide gradient of mean annual temperature we find that saline lakes excepted branched gdgts are universally abundant in the lakes investigated and can be used to predict mean annual air temperature maat with a high degree of accuracy however the existing global mbt cbt calibration for maat based on soils predicts inaccurate temperatures when applied to our african lake dataset this observation together with the fact that surface water ph and to lesser extent lake depth appear to influence the distribution of branched gdgts among sites leads us to conclude that in situ production of branched gdgts in lakes is likely the robust relationship between branched gdgt distribution and the temperature and ph of african freshwater lakes makes these compounds suitable for paleoenvironmental reconstruction however we urge caution in using branched gdgts in lake sediments to infer past temperatures unless their exact origin can be determined

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

a 2000 year record of solar forcing on varved lake sediment in eastern finland abstract a high resolution study was performed on varved sediments from lake lehmilampi in eastern finland varve data was collected by digital image analysis using standard 1 8 mm thick samples impregnated in epoxy and x rayed climatic variability is imprinted on varve properties varve thickness and accumulation of mineral and organic matter during the last 2000 years the cumulative counting error of the varve record is estimated as 2 3 qualitative comparison of varve parameters and residual 14c constructed from tree rings revealed close correspondence between the two records suggesting solar forcing on lake sedimentation classical climatic periods of the last millennia medieval climate anomaly 1060 1280 in the varve record and little ice age cooler phases culminating in 1340 1465 1545 1680 1850 and also in 1930 in the varve record are clearly evident in the varve record at present the physical link between solar activity levels and lake sedimentation has not been established

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

centennial climate variability in the british isles during the mid late holocene abstract multi millennial climate changes were relatively minor over the mid late holocene in the british isles because orbitally forced insolation changes were smaller than those at higher latitudes centennial climate variability is thus likely to have exerted a greater influence on the environment and human society of the region proxy climate records from the british isles covering the last 4500 years are assembled and re evaluated with the aim of identifying centennial climate variability reflected by multi proxy indicators the proxies include bog oak populations peatland surface wetness flooding episodes from fluvial deposits speleothem annual band width and oxygen isotopes chironomids from lake sediments and sand and dune deposition most proxies reflect water balance rather than temperature alone and records predominantly reflect warm season climate a series of 12 key periods of enhanced precipitation evaporation p e are identified by their presence in two or more proxy records variability in p e is much greater than that shown by temperature proxies and there is no necessary association between warm cool and dry wet periods although the data for temperature are less robust than those for p e a series of key temperature changes are proposed based on speleothem 18o and chironomid inferred july temperature records relatively cool before c 3100 years bp warmer 3100 2000 years bp cool 2000 1250 cal years bp warm 1250 650 cal years bp and cool 650 cal years bp onwards some key increases in p e 2750 1650 550 cal years bp show a strong correspondence with bond cycles in ocean proxy records for increased ice rafted debris decreased summer sea surface temperatures and sometimes decreased north atlantic deep water circulation other higher frequency changes in p e are also strongly related to sst variability whilst some of the main changes to cooler ssts and increased p e are approximately coincident with reduced solar output most are not and thus must be the result of the internal dynamics of the ocean and atmosphere future work should concentrate on firmly establishing the pattern of temperature change improving chronological accuracy and precision in existing records and improving process based understanding of proxies

polar observations and model predictions during may 4 1998 magnetopause magnetosheath and bow shock crossings during the rise to the maximum phase of solar cycle 23 several periods of extreme solar wind conditions have occurred during such an example on may 4 1998 the solar wind monitors observed a period of strong southward interplanetary magnetic field imf accompanied by a solar wind dynamic pressure that was 30 times higher than average during this period the polar spacecraft crossed the magnetopause and bow shock and experienced its first solar wind encounter this case provides a rare opportunity to study the magnetopause low latitude boundary layer magnetosheath and bow shock and to test our ability to model the dynamic behavior of these boundary regions under extreme and highly variable solar wind conditions in this study we use the gas dynamic convected field model to predict the time dependent magnetic field and plasma properties upstream from the magnetopause and the location of the polar spacecraft relative to the magnetopause and bow shock during the event to test the accuracy of the prediction model magnetic field characteristics are compared to the fields observed along the satellite track by the magnetometer on polar the predicted model plasma characteristics density velocity and temperature are compared to moments derived from tide observations extrapolated to account for the higher energy portion of the magnetosheath distributions where ambiguities occur in identifying the satellite location plasma distribution functions from two additional ion detectors timas and hydra are used to resolve the observed location of polar relative to the boundaries with this procedure carried out separately for ace and wind and for two different magnetopause models observed features at polar can be traced back to drivers in the solar wind providing a unique opportunity to assess the evolution of the solar wind and its predictability from the solar wind monitors to the magnetopause when the polar apogee drifts to low latitudes in the future it will provide more and more observations in this region therefore what we learn from this case can be indicative of what we will see in the future in polar operations the high level correlation between the predictions and in situ measurements indicates that the solar wind monitors often provide adequate and useful solar wind conditions near the earth the tests indicate that in this event the vacuum dipole field magnetosphere model predicts a significantly larger magnetosphere than observed while the empirical magnetopause model predictions are more consistent with the observations they overpredict the response of the magnetosphere to transient southward turnings of the imf indicating that the magnetosphere does not respond to the southward imf turnings on small timescales sometimes there are significant differences at relatively small time scales between the measurements from the two solar wind monitors it is possible for the solar wind conditions near the earth to be different from the measurements made by at least one of the solar wind monitors cautions should be taken when interpreting near earth observations if the observations are inconsistent at small timescales with the predictions based on one solar wind monitor

solar forcing of climatic change during the mid holocene indications from raised bogs in the netherlands two cores of mid holocene raised bog deposits from the netherlands were 14 c wiggle match dated 14 c as a proxy for changes in solar activity is validated this paper adds to the increasing body of evidence that solar variability forced climatic changes during the holocene 14 c wiggle match dating mid holocene wet shifts

centennial scale climate change in ireland during the holocene we examine mid to late holocene centennial scale climate variability in ireland using proxy data from peatlands lakes and a speleothem a high degree of between record variability is apparent in the proxy data and significant chronological uncertainties are present however tephra layers provide a robust tool for correlation and improve the chronological precision of the records although we can find no statistically significant coherence in the dataset as a whole a selection of high quality peatland water table reconstructions co vary more than would be expected by chance alone a locally weighted regression model with bootstrapping can be used to construct a best estimate palaeoclimatic reconstruction from these datasets visual comparison and cross wavelet analysis of peatland water table compilations from ireland and northern britain show that there are some periods of coherence between these records some terrestrial palaeoclimatic changes in ireland appear to coincide with changes in the north atlantic thermohaline circulation and solar activity however these relationships are inconsistent and may be obscured by chronological uncertainties we conclude by suggesting an agenda for future holocene climate research in ireland

reconstruction of the late quaternary paleoenvironments of the nussloch loess paleosol sequence germany using n alkane biomarkers abstract this study contributes to the paleoenvironmental reconstruction of the loess paleosol sequence of nussloch germany by using n alkanes as plant leaf wax derived lipid biomarkers we found that n alkane patterns and concentrations in the saalian loess and the last interglacial eemian paleosol of nussloch point to very strong degradation and prevailing deciduous vegetation degradation effects in the overlying paleosols and loess layers are less pronounced and allow for the application of an end member mixing model to estimate vegetation changes semi quantitatively our findings highlight the potential for the interpretation of degradation corrected n alkane ratios n alkane modelling results for loess layers paleosols and an in filled paleochannel dated to 60 32 ka suggest that up to 50 of the n alkanes were derived from deciduous trees or shrubs this finding is in agreement with the abundant occurrence of wood fragments and indicates a highly variable and dynamic landscape dominated by tundra shrubland on the other hand deciduous trees or shrubs did not contribute significantly to the soil organic matter in the late weichselian loess layers and the intercalated gelic gleysols 32 18 ka

generating multi proxy holocene palaeoenvironmental records from blanket peatlands abstract ombrotrophic peatlands have provided important archives for understanding holocene palaeoenvironmental change however records are predominantly from raised bogs due to potential issues regarding preservation of proxy indicators record length and low temporal resolution in other peat types including blanket bogs by carrying out peat depth and stratigraphy surveys we demonstrate how blanket peatlands can provide archives capable of providing records that are not reliant on single proxies as has been often the case in the past and can provide good resolution records a record containing humification testate amoebae and plant macrofossils was derived for the last 3000 years with accumulation rates as high as 8 yrs cm 1 providing favourable temporal resolution particularly over the last 1500 years major changes in proxy indicators reflecting potential changes in water table depth were often coherent with changes in climate human activity also had a major impact on the peatland throughout the record especially in the last 100 years where the influence of wildfire and managed burning together with an effect of atmospheric pollution fundamentally changed the state of the peatland

distributions of branched gdgts in soils and lake sediments from western uganda implications for a lacustrine paleothermometer bacterially produced branched glycerol dialkyl glycerol tetraethers gdgts are ubiquitous in soils and lake sediments and can potentially be used to reconstruct past temperatures in lakes however it is still unclear if these compounds are derived from eroded soils or if they are produced in situ to better understand environmental controls on the distributions of these compounds and the sources of branched gdgts to lake sediments we compare branched gdgt distributions and concentrations in lake sediments and catchment soils within a 3600 m altitudinal transect in western uganda reconstructed mean annual air temperature maat determined from the degree of methylation mbt and cyclisation cbt of branched gdgts in soils decreases with increasing altitude as is expected from the air temperature gradient in our transect however we observe significant offsets between observed and reconstructed temperatures in soils from wet high elevation soils but not in most dry low elevation soils branched gdgt distributions differ significantly between lake sediments and soils at all elevations with greater differences at low elevations than at high elevations these data support previous hypotheses that branched gdgts are produced in situ in lakes and suggest that the abundance of water in soil environments may play a role in controlling the distribution of branched gdgts while branched gdgts in lacustrine sediments can be used to reconstruct temporal temperature variations in lakes we urge caution in utilizing this proxy in lacustrine systems with high soil loadings especially if there is evidence of changing clastic fluxes through time

dating raised bogs new aspects of ams 14c wiggle matching a reservoir effect and climatic change abstract high resolution ams dating of holocene raised bog deposits engbertsdijksvenen the netherlands shows natural 14c variations wiggles which can be matched with the dendrochronological calibration curve comparison of our results with other conventionally dated peat cores and the 14c record shows an unexpected and as yet unreported reservoir effect and a marked and sudden wetting of the bog surfaces coinciding with the advent of a sporer type solar minimum the homeric minimum the potential of ams dating to vastly improve the accuracy of holocene chronologies is demonstrated

climatic solar oceanic and geomagnetic influences on late glacial and holocene atmospheric 14c 12c change late glacial and holocene 14c12c ratios of atmospheric co2 vary in magnitude from a few per mil for annual decadal pertubations to more than 10 for events lasting millennia a data set illuminating 10 to 104 yr variability refines our understanding of oceanic climatic versus geomagnetic or solar forcing of atmospheric 14c12c ratios most of the variance in the holocene atmospheric 14c12c record can be attributed to the geomagnetic millennia time scale and solar century time scale influence on the flux of primary cosmic rays entering the atmosphere attributing the observed atmospheric 14c12c changes to climate alone leads to ocean circulation and or global wind speed changes incompatible with proxy records climate ocean related 14c redistribution between carbon reservoirs while evidently playing a minor role during the holocene may have perturbed atmospheric 14c12c ratios measurably during the late glacial younger dryas event first order corrections to the radiocarbon time scale 12 000 30 000 14c yr b p are calculated from adjusted lake sediment and tree ring records and from geomagnetically defined model 14c histories paleosunspot numbers 100 9700 cal yr b p are derived from the relationship of model 14c production rates to sunspot observations the spectral interpretation of the 14c12c atmospheric record favors higher than average solar activity levels for the next century minimal evidence was found for a sun weather relationship

relationship of spatial heterogeneity for vegetation and aeolian sand soil properties on longitudinal dunes in gurbantunggut desert china on longitudinal dunes in the southern gurbantunggut desert the vegetation was investigated and the texture water content organic matter total nitrogen salt content and ph of aeolian sand soil were measured by means of geostatistical methods the spatial heterogeneity for vegetation and aeolian sand soil properties was analyzed the vegetation pattern and aeolian sand soil properties were moderately to strongly spatially heterogeneous as a whole with a spatially dependent range of 8 8 74 8 m because both of them had a nest structure of grading system their spatial heterogeneity needed to be described by the fractal dimensions at different sampling scales the autocorrelated spatial range a 0 and fractal dimensions of the cover of vegetation and the diversity of herberious synusium were similar to these of soil water contents sm the coarse grain size 1 and sorting of soil the diversity of herbaceous synusium and the cover of vegetation had a closer dependent range a0 being 37 8 57 8 m the trends of spatial variation for organic matter and total nitrogen contents were very similar to that of vegetation cover the spatial heterogeneities of soil ph and salt content were mainly restricted by terrain and basically not related to vegetation

spatial heterogeneity of sources of branched tetraethers in shelf systems the geochemistry of tetraethers in the berau river delta kalimantan indonesia abstract the bulk organic matter composition total organic carbon toc content and 13ctoc and composition of isoprenoid and branched glycerol dialkyl glycerol tetraethers gdgt in surface sediments from 43 stations in the berau river delta east kalimantan indonesia including two coast shelf transects and stations within the river mouth were examined to reveal the spatial heterogeneity in these parameters in order to assess the impact of a tropical river loaded with suspended matter on the sedimentary organic matter in the shelf system the high resolution study showed that despite the extensive transport of eroded soil material by the river to the sea terrestrial organic matter and brgdgts are only deposited on a relatively small part of the shelf the concentrations of brgdgts are highest up to 120 g g 1 toc in sediments deposited in and close to the mouth of the berau river and their distribution indicates that they represent a mixture of soil derived and river in situ produced brgdgts crenarchaeol concentrations reach 700 g g 1 toc in sediments deposited on the outer shelf due to thaumarchaeotal production in shelf waters this results in a strong gradient 0 93 0 03 in the bit index with high values in the river mouth and low values on the shelf the decline in the bit index is caused by both decreasing concentrations of the brgdgts and increasing concentrations of crenarchaeol the bit index shows a highly significant but non linear relationship with 13ctoc on the shelf in the area not under the direct influence of the berau river cyclic brgdgts become relatively dominant most probably due to in situ production in the alkaline pore waters of the surface sediments the spatial heterogeneity of sources of brgdgts on the berau shelf complicates the use of brgdgts as temperature proxies application of the global soil calibration to sedimentary mixtures of brgdgts in the river influenced area of the shelf results in a severe underestimation of mean annual air temperature mat by 6 c this is due to the mixed origin of the brgdgts which are not only derived from soil erosion but likely also from riverine production as has been observed for other river systems comparison of the berau shelf other shelf systems indicates that in situ production of brgdgts in shelf sediments is a widespread phenomenon that is especially pronounced at water depths of ca 50 300 m it is hypothesized that this is so because benthic in situ production of heterotrophic brgdgt producing bacteria is fueled by the higher delivery of fresh organic matter to these sediments as the consequence of higher primary productivity in shelf waters and a decreased mineralization due to the relatively short settling times of particles on the shelf for palaeoclimatic studies of marine shelf sediments the application of brgdgts as proxies is severely complicated by the heterogeneity of sources of brgdgts comparison of the brgdgt composition of soils with those of shelf sediments may assist in deciding if sedimentary brgdgts are predominantly derived from soil erosion several methods to do so are discussed

evidence from northwest european bogs shows little ice age climatic changes driven by variations in solar activity fluctuations in holocene atmospheric radiocarbon concentrations have been shown to be due to variations in solar activity analyses of both 10 be and 14 c nuclides cone rm that production ratechanges during

changes in solar activity and holocene climatic shifts derived from 14c wiggle match dated peat deposits closely spaced sequences of accelerator mass spectrometer ams 14 c dates of peat deposits display century scale wiggles which can be e tted to the radiocarbon calibration curve by wiggle matching such sequences high precision calendar age chronologiescan be generated which show that changes in mire surface wetness during the bronze age iron age transition c 850 cal bc and the little ice age wolf sporer maunder and dalton minima occurred during periods of suddenly increasing atmospheric concentration of 14 c replicate evidence from peat based proxy climate indicators in northwest europe suggest these changes in climate may have been driven by temporary declines of solar activity carbon accumulation rates of two raised peat bogs in the uk and denmark record low values during the little ice age which ree ects reduced primary productivity of the peat forming vegetation during these periods of climatic deterioration

seasonal temperature variability of the neoglacial 3300 2500 bp and roman warm period 2500 1600 bp reconstructed from oxygen isotope ratios of limpet shells patella vulgata northwest scotland abstract seasonal sea surface temperature variability for the neoglacial 3300 2500 bp and roman warm period rwp 2500 1600 bp which correspond to the bronze and iron ages respectively was estimated using oxygen isotope ratios obtained from high resolution samples micromilled from radiocarbon dated archaeological limpet patella vulgata shells the coldest winter months recorded in neoglacial shells averaged 6 6 0 3 c and the warmest summer months averaged 14 7 0 4 c one neoglacial shell captured a year without a summer which may have resulted from a dust veil from a volcanic eruption in the katla volcanic system in iceland rwp shells record average winter and summer monthly temperatures of 6 3 0 1 c and 13 3 0 3 c respectively these results capture a cooling transition from the neoglacial to rwp which is further supported by earlier studies of pine history in scotland pollen type analyses in northeast scotland and european glacial events the cooling transition observed at the boundary between the neoglacial and rwp in our study also agrees with the abrupt climate deterioration at 2800 2700 bp also referred to as the subboreal subatlantic transition and therefore may have been driven by decreased solar radiation and weakened north atlantic oscillation conditions

a comparison of magnetic signatures and dmsp auroral images at substorm onset three case studies the authors explore the relationship between mid latitude and synchronous orbit magnetic signatures and the location of the auroral surge at the onset of three isolated magnetospheric substorms mid latitude data come from the air force geophysics laboratory magnetometer network synchronous orbit data form the satellites goes 2 and 3 and auroral data from defense meteorological satellite program auroral images and auroral magnetograms they find that the surge forms with its western edge approximately 1 hour west of the longitude where the major axis of the mid latitude pi 2 polarization ellipse is along magnetic north and where the d component perturbation of the magnetic bay is near zero these observations are in qualitative agreement with a current wedge consisting of a localized upward current in the west and a longitudinally distributed current in the east at synchronous orbit the longitude of the surge head appears to separate a region to the west where the magnetic field becomes more taillike from one to the east where the magnetic field becomes more dipolar

δd values of n alkanes in tibetan lake sediments and aquatic macrophytes a surface sediment study and application to a 16 ka record from lake koucha abstract a set of lake surface sediment samples and aquatic macrophytes from the eastern and central tibetan plateau and a sediment core from koucha lake northeastern tibetan plateau were analysed for hydrogen isotope signals of aliphatic lipid biomarkers the d values of n alkanes were correlated with those of meteoric water in the summer months and showed increasing pearson correlation coefficients with increasing n alkane chain length r 0 80 for n c 31 while in samples from the most humid regions southeastern tibetan plateau the apparent enrichment factors between meteoric water and lipids are close to those reported for other humid sites e 135 for mid chain and 125 for long chain n alkanes they become smaller e 118 to 41 mean value 86 at sites with a negative moisture balance northeastern and central tibetan plateau and qaidam basin this might be caused by enrichment in deuterium of the source water used for lipid synthesis as a result of lake water evaporation and soil and leaf water evapotranspiration in the core from lake koucha decreasing d values of all n alkanes between 15 and 10 cal ka bp give evidence for an intensification of the asian summer monsoon at ca 9 cal ka bp a ca 15 shift towards higher d values of mid chain n alkanes suggests enhanced evaporation of the lake water which outweighs higher precipitation amounts because of a temperature increase during the early holocene monsoonal maximum only a few surface sediment samples show a significant offset between d values of mid chain n alkanes and n c 31 d mid n c31 and no systematic dependence between this offset and environmental parameters such as mean annual precipitation was found in the core available data for most samples also do not show a significant offset only a slight increase 15 of d mid n c31 at ca 10 0 cal ka bp and a decrease 17 at ca 6 8 cal ka bp might indicate wetter and drier conditions respectively however interpretation of d mid n c31 throughout the record is difficult because of a lack of reliable data for n c 31 in key sections of the core so more records are necessary to further test the potential applicability of d mid n c31 as a proxy for palaeo hydrological conditions

millennial scale paleoclimate cycles recorded in widespread palaeozoic deeper water rhythmites of north america rhythmically interbedded limestone and shale or limestone and chert rhythmites are a common feature of many deep water phanerozoic carbonate marine deposits seventeen different palaeozoic rhythmite successions from across north america 8 studied in detail 9 studied in reconnaissance are described and summarized individual rhythmite couplets 4 20 cm thick are composed of fine grained laminated to massive detrital limestone alternating with shale or marl or laminated spiculitic chert stratigraphic and primary depositional features within rhythmites and associated facies indicates that the carbonate rich and carbonate poor interbedding is the result of repetitive changes in sediment input primary rather than due to diagenetic redistribution of calcareous material secondary the average duration of individual rhythmite couplets is calculated using spectral analysis to determine couplet thickness combined with biostratigraphically calibrated undecompacted average sediment accumulation rates the duration of rhythmite couplets from the eight well studied successions ranges between 150 and 4900 yrs with the majority lying between 1000 and 3000 yrs i e millennial scale the paucity and low diversity of skeletal and trace fossils preserved suspension laminae lack of sediment reworking and facies associations indicate rhythmite accumulation was favored by 1 deposition below storm wave base which limited reworking by currents 2 dysaerobic bottom waters which restricted bioturbation and intermixing of interbedded lithologies and 3 proximity to nearshore carbonates supplying abundant fine grained detrital carbonate these combined conditions were best met along flooded subtropical continental shelves or epeiric seas during my scale 3rd order sealevel rises the rhythmic alternation between carbonate rich and carbonate poor layers is interpreted to represent millennial scale paleoclimatic changes related to 1 wet dry climate cycles which influenced the amount of continent derived eolian and or fluvial sediment input 2 variations in offshore transport via storm generated or density currents of nearshore derived terrigenous or carbonate sediments and or 3 changes in wind driven upwelling and availability of recycled biogenic silica the various rhythmite successions accumulated under dramatically different paleoenvironment and paleogeographic conditions including active to passive tectonic settings equatorial to subtropical latitudes long term icehouse through greenhouse climatic conditions calcite versus aragonitic seas variable atmospheric co2 concentrations before and after land plant and animal evolution and across widely varying ocean basin configurations if our short term paleoclimatic interpretations for the rhythmites are correct then it is apparent that millennial scale climate changes occurred over a very wide spectrum of paleoceanographic paleogeographic paleoclimatic tectonic and biologic conditions and over time periods from the cambrian to the quaternary given this it is difficult to invoke models of internally driven thermohaline oceanic oscillations or continental ice sheet instabilities to explain their origin instead we suggest that

variability of the north atlantic oscillation over the past 5 200 years the north atlantic oscillation influences climate in the arctic region and northern europe reconstructions of circulation patterns associated with the north atlantic oscillation from a 5 200 year long lake sediment record suggest that the atmospheric circulation responded to significant transitions in northern hemisphere climate

magnetic dipolarization with substorm expansion onset 1 we compare the timing and spatial extent of dipolarization with auroral breakup by using magnetic field data 1 min time resolution from goes 8 and goes 9 and global auroral images 37 s frame rate from the polar ultraviolet imager we survey the entire year of 1997 data and obtain 32 unambiguous dipolarization events that had ionospheric footprints within 2 hours in magnetic local time mlt from their associated auroral breakups it is found that the auroral breakup preceded the arrival of dipolarization at goes by an average of 1 7 2 7 min 1 0 2 1 min for events 1 hour from the auroral breakup the delay of geosynchronous dipolarization represents a propagation time as the substorms rarely initiated at the goes location propagation velocities derived from the propagation time are 60 km s 1 eastward 75 km s 1 westward and 270 km s 1 earthward at geosynchronous orbit we also show for the first time that auroral bulge and dipolarization region closely map the bulge is the region of currents out of the ionosphere the eastern edge of the dipolarization region where field aligned currents are flowing into the ionosphere is based on the t89 magnetic field model located at 0 5 hour in mlt eastward of the eastern edge of the auroral bulge within the initiation site meridian the dipolarization onset was observed 1 min prior to the auroral breakup at the goes altitude this time is associated with alfven transit time and therefore depends on the radial location of the onset the azimuthal scale of the initiation site is found to be 0 5 hour in mlt in the ionosphere or less than 1 earth s radius at 6 6 re these results support current diversion into the ionosphere as a critical part of substorms finally a simple timing analysis of specific substorm onset time features suggests that near earth reconnection cannot occur before current disruption and therefore cannot be the cause of substorm

application of bacterial glycerol dialkyl glycerol tetraethers gdgts to develop modern and past temperature estimates from new zealand lakes abstract branched isoalkyl glycerol dialkyl glycerol tetraethers gdgts of bacterial origin have been found in high abundance in both modern and glacial sediments of new zealand south island freshwater lakes covering a wide range of altitude 101 2000 m like isoprenoid gdgts of archaeal origin they provide excellent potential for temperature assessment for this study their distribution patterns mbt methylation ratio and cbt cyclisation ratio of branched gdgts have been successfully used to develop an initial temperature calibration for the study area and to provide preliminary palaeo environmental interpretations mbt data from modern lake sediments correlate well with measured annual air temperature r2 0 74 enabling a regional calibration for reconstructing palaeotemperatures for fossil samples mbt derived palaeotemperatures for alpine lake calibrated against mean annual temperature were determined for the last glacial during an early cold phase between 29 000 and 26 000 years bp and for later less cold phases between 23 000 and 18 000 years bp compared with the modern temperature regime the mbt data indicate a decrease of ca 5 6 and 2 8 c respectively during this time modern and past mbt derived temperatures correlate with chironomid based temperature reconstructions in the area archaeal gdgts commonly used for the tex86 index are abundant in fossil sediments alpine lake but scarce in modern sediments hindering a new local calibration for this palaeotemperature proxy

holocene humidity changes in northern finnish lapland inferred from lake sediments and submerged scots pines dated by tree rings conclusive evidence for a rise in water levels has been found in connection with lake sediment studies undertaken partly in collaboration with the pine megafossil sampling and dendrochronological work in northern finnish lapland the change in lake level stands is shown by slow sedimentation rate in the early to mid holocene and an increase thereafter these data indicate a regional rise in water levels during the latter part of the holocene following a relatively dry period between 8000 and 4000 bp synchronous changes also indicating rising water levels have been observed in the diatom and cladoceran assemblages of the sediment cores subfossil scots pines pinus sylvestris l have been preserved in large quantities in small lakes in lapland because in many cases the rising water level has inundated the trunks after death the position of the subfossil trunks and stumps often indicates that the pines have been growing on dry land at the sides of the lakes in which they are now submerged traces of

distinction between auroral substorm onset and traditional ground magnetic onset signatures 1 to evaluate whether ground magnetic responses traditionally viewed as signatures of substorm onset may be related to postonset auroral streamers rather than to substorm onset seen in aurora we have analyzed ground magnetic and all sky image responses for 14 substorm onsets selected solely on imager coverage we find evidence supporting this possibility the response being approximately coincident for midlatitude positive bay and pi2 pulsation enhancements and for abrupt auroral zone h decreases at stations near a streamer these are all signatures of current wedge formation indicating that substorm current wedge formation may be more of a response to plasma sheet flow channels associated with postonset streamers than to the process leading to auroral onset and that the current wedge may develop via a series of distinctly narrower wedge like structures we also find evidence that periods of streamers can occur more than once during a substorm expansion phase and can give magnetic signatures of multiple onsets even if there are no additional auroral onsets furthermore the peak auroral zone h decreases are seen in association with streamers and at times varying from just a few minutes to well over a half hour after substorm auroral onset if there is a prolonged period of streamers this indicates that peak substorm ae and al values are likely related to features of postonset streamers and their locations relative to observing stations and are not a measure of the strength of the substorm auroral onset processes we discuss possible additional implications on substorm expansion phase development

observed feedback between winter sea ice and the north atlantic oscillation abstract feedback between the north atlantic oscillation nao and winter sea ice variability is detected and quantified using approximately 30 years of observations a vector autoregressive model var and testable definitions of granger causality and feedback sea ice variability is quantified based on the leading empirical orthogonal function of sea ice concentration over the north atlantic the greenland sea ice dipole gsd which in its positive polarity has anomalously high sea ice concentrations in the labrador sea region to the southwest of greenland and low sea ice concentrations in the barents sea region to the northeast of greenland in weekly data for december through april the var indicates that nao index n anomalies cause like signed anomalies of the standardized gsd index g and that g anomalies in turn cause oppositely signed anomalies of n this negative feedback process operates explicitly on lags of up to four weeks in the var but can generate more persistent effects because o

distributions of branched gdgts in a tropical lake system implications for lacustrine application of the mbt cbt paleoproxy branched glycerol dialkyl glycerol tetraether gdgt lipids are abundant and ubiquitous in lake sediments potentially allowing for a paleolimnological application of the so called mbt cbt proxy methylation index of branched tetraethers cyclization ratio of branched tetraethers to investigate the origin and characteristics of these compounds in lacustrine environments we examined the distributions of gdgts in soils river sediments and lake sediments from lake towuti on the island of sulawesi indonesia we found significant differences in the degree of methylation and cyclization expressed by way of the mbt and cbt indices between the soil samples and the aquatic samples suggesting that there may be in situ production of gdgts in the aquatic environment based on these findings we urge caution in the application of the mbt cbt paleoproxy to lake sediments and encourage more rigorous study of these compounds in freshwater environments

an information theory approach to the storm substorm relationship 1 one of the most interesting aspects of the global magnetospheric response to solar wind changes is the relationship between storms and substorms here we present new results on the relationship between these two different classes of magnetospheric phenomena by approaching the problem on the side of information theory using the auroral electrojet al and sym h indices as representative proxies of magnetic substorms and storms we investigate the transfer of information by means of transfer entropy analysis schreiber 2000 the obtained results seem on average to indicate the presence of a net transfer of information from al to sym h on time scales shorter than 10 h on the basis of this result geomagnetic substorms may act as a driver for the occurrence of geomagnetic storms however carrying out a more careful analysis which takes into account the global geomagnetic daily activity we suggest that the direction of information flow between substorms and storms depends on the global activity level indeed if it is true that a sequence of magnetospheric substorms may drive a moderate storm it is also true that very large storms may dominate and drive the occurrence of magnetospheric substorms

in situ produced branched glycerol dialkyl glycerol tetraethers in suspended particulate matter from the yenisei river eastern siberia abstract soil derived branched glycerol dialkyl glycerol tetraethers brgdgts in marine river fan sediments have a potential use for determining changes in the mean annual temperature mat and ph of the river watershed soils prior to their incorporation in marine sediments the compounds are transported to the marine system by rivers however emerging evidence suggests that the brgdgts in freshwater systems can be derived from both soil run off and in situ production the production of brgdgts in the river system can complicate the interpretation of the brgdgt signal delivered to the marine system therefore we studied the distribution of brgdgt lipids in suspended particulate matter spm of the yenisei river chromatographic improvements allowed quantification of the recently described hexamethylated brgdgt isomer characterized by having two methyl groups at the 6 6 instead of the 5 5 positions in an environmental dataset for the first time this novel compound was the most abundant brgdgt in spm from the yenisei its fractional abundance correlated well with that of the 6 methyl isomer of the hexamethylated brgdgt that contains one cyclopentane moiety the yenisei river watershed is characterized by large differences in mat 11 c as it spans a large latitudinal range 46 73 n which would be expected to be reflected in brgdgt distributions of its soils however the brgdgt distributions in its spm show little variation furthermore the reconstructed ph values are high compared to the watershed soil ph we therefore hypothesize that the brgdgts in the yenisei river spm are predominantly produced in situ and not primarily derived from erosion of soil this accounts for the absence of a change in the temperature signal as the river water temperature is more stable using a lake calibration the reconstructed temperature values agree with the mean summer temperatures mst recorded the brgdgts delivered to the sea by the yenisei river during this season are thus not soil derived possibly complicating the use of brgdgts in marine sediments for palaeoclimate reconstructions

a multiproxy climate record from a raised bog in county fermanagh northern ireland a critical examination of the link between bog surface wetness and solar variability a proxy climate record from a raised bog in county fermanagh northern ireland is presented the record spans the interval between 2850 cal yr bc and cal yr ad 1000 and chronological control is achieved through the use of tephrochronology and 14c dating including a wiggle match on one section of the record palaeoclimatic inferences are based on a combination of a testate amoebae derived water table reconstruction peat humification and plant macrofossil analyses this multiproxy approach enables proxy specific effects to be identified major wet shifts are registered in the proxies at ca 1510 cal yr bc 750 cal yr bc and cal yr ad 470 smaller magnitude shifts to wetter conditions are also recorded at ca 380 cal yr bc 150 cal yr bc cal yr ad 180 and cal yr ad 690 it is hypothesised that the wet shifts are not merely local events as they appear to be linked to wider climate deteriorations in northwest europe harmonic analysis of the proxies illustrates statistically significant periodicities of 580 423 373 307 and 265 years that may be related to wider holocene climate cycles this paper illustrates how the timing of climate changes registered in peat profiles records can be precisely constrained using tephrochronology to examine possible climatic responses to solar forcing relying on interpolated chronologies with considerable dating uncertainty must be avoided if the climatic responses to forcing mechanisms are to be fully understood copyright 2007 john wiley sons ltd

formal subdivision of the holocene series epoch a discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommission on quaternary stratigraphy international commission on stratigraphy this discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommision on quaternary stratigraphy sqs of the international commission on stratigraphy ics considers the prospects for a formal subdivision of the holocene series epoch although previous attempts to subdivide the holocene have proved inconclusive recent developments in quaternary stratigraphy notably the definition of the pleistocene holocene boundary and the emergence of formal subdivisions of the pleistocene series epoch mean that it may be timely to revisit this matter the quaternary literature reveals a widespread but variable informal usage of a tripartite division of the holocene early middle or mid and late and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology we propose an early middle holocene boundary at 8200 a bp and a middle late holocene boundary at 4200 a bp each of which is linked to a global stratotype section and point gssp should the proposal find a broad measure of support from the quaternary community a submission will be made to the international union of geological sciences iugs via the sqs and the ics for formal ratification of this subdivision of the holocene series epoch copyright 2012 john wiley sons ltd

determining the sun s influence on lateglacial and holocene climates a focus on climate response to centennial scale solar forcing at 2800 cal bp abstract the influence of solar variability on the climate of the lateglacial and holocene periods has been the subject of increasing discussion during the last decade in the mid holocene several studies have identified cold wet events that occur at ca 2800 cal bp and a link with a reduction in solar activity inferred from the 14c record has been postulated we present results from a multi proxy study of peat humification plant macrofossils and testate amoebae from a raised bog at glen west northwest ireland that indicate that dry bog surface conditions were experienced in the north of ireland at the time of the solar anomaly starting at 2800 cal bp with the aid of 14c wiggle matching and tephrochronology an abrupt shift to wetter conditions is dated to ca 2700 cal bp coinciding with a 14c maximum but clearly post dating the 2800 cal bp event identified elsewhere in europe we explore the significance of this apparent lag in the irish record considering the possible role of the ocean in generating spatial and temporal complexities in the climate patterns of the north atlantic region we conclude that these complexities are likely to give rise to time transgressive climate responses around the north atlantic that will only be recognised by more critical chronological approaches

14c ams wiggle matching of raised bog deposits and models of peat accumulation abstract high resolution accelerator mass spectrometer ams 14 c dates of selected plant macrofossils from the raised bog engbertsdijksvenen eastern netherlands show century scale wiggles analogous to the radiocarbon calibration curve we used three relative time scales viz based on depth mass and pollen concentration respectively to match the peat ams dates to the calibration curve this procedure is repeated for one conventionally dated core for each relative time scale realistic confidence intervals are calculated depth appears to be the best time scale for certain stratigraphical units of a core this justifies using depth for wiggle matching conventionally dated mire cores published by others even when 14 c errors are larger our evidence shows four major sources of 14 c variation for mire deposits compared to treerings 1 dating error due to sample composition this includes a reservoir effect demonstrated for many bulk peat samples 2 hiatuses causing a sudden leap of peat 14 c age 3 changing accumulation rates apparent from a break in the slope of the peat 14 c ages 4 sampling error these results shed doubt on the assumed continuities in theoretical peat accumulation models both mire stratigraphy and changing accumulation rates can be explained in qualitative hydrological terms more evidence for a previously discovered reservoir effect in bog deposits is presented though the physical biological mechanisms remain uncertain

bog burst in the eastern netherlands triggered by the 2 8 kyr bp climate event the nature and cause of the so called 2 8 kyr bp event have been a subject of much debate peat sequences have provided much of the evidence for this event but the process link between climate and peatland response is not well understood multiproxy high resolution analysis of a core from bargerveen in the eastern netherlands based on pollen non pollen palynomorphs testate amoebae and geochemistry identified an abrupt shift from relatively dry to extremely wet conditions radiocarbon based wiggle match dating wmd and biostratigraphy based on the pollen record show that this shift in local hydrology occurred around 2800 cal yr bp we interpret an erosional hiatus lasting up to 950 years immediately prior to this as the effect of a bog burst after excessive rainfall this phenomenon was not limited to our sampling location but occurred over a large part of the former bargerveen peat at the hiatus contains microfossils that reflect temporary eutrophication as a consequence of local fires and secondary decomposition because of increased drainage after the erosion event our data show how detailed multiproxy analyses can elucidate the past response of peatlands to changing climate and suggest that the climatic change in northwest europe at this time caused major non linear disruption to these ecosystems

detailed analysis of a substorm event on 6 and 7 june 1989 2 stepwise auroral bulge evolution during expansion phase 1 we have analyzed in detail the auroral bulge evolution during the expansion phase of an isolated substorm which was observed by the uv imager aboard the akebono satellite it was found that there were three distinct stages in the evolution stage 1 was characterized by rapid poleward and azimuthal predominantly westward expansions in a short time about 2 min stage 2 was characterized by a very slow poleward and slower and continuous azimuthal expansions there was a certain period for transition between stage 1 and stage 2 and it was characterized by a very slow poleward and rapid eastward expansions stage 3 started about 11 min after the onset and was characterized by a sudden reactivation of the rapid poleward and azimuthal expansions the reactivation started around the initial onset meridian and then spread both eastward and westward at the azimuthal front the expansion first occurred at the lowest latitudes spread poleward to around the highest latitudes of stage 1 and then spread further poleward after a brief interval hence the local expansion also had three distinct stages similar to the global one the ground based observations showed that the highest latitude of the local first stage was very close to the latitude of auroral activity that appeared near the ionospheric plasma sheet boundary layer psbl region a few minutes before the onset the further poleward expansion during the local third stage started with a significant intensification of the poleward most auroral activity during the local third stage the bright electron auroral region was bifurcated into a poleward expanding part and an equatorward moving part the proton auroral emission coexisted in the bulge during the local first and second stages and almost disappeared soon after the bifurcation during the local third stage based on these observations we discuss the evolution in the magnetosphere during the expansion phase

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

detailed analysis of a substorm event on 6 and 7 june 1989 1 growth phase evolution of nightside auroral activities and ionospheric convection toward expansion phase onset 1 we have analyzed in detail the evolution of nightside auroral activities and ionospheric convection during the growth phase of an isolated substorm the following three characteristic auroral activities were identified by meridian scanning photometers msp at ground stations 1 proton main oval 2 fast equatorward moving fem arc and 3 near plasma sheet boundary layer npsbl aurora the proton main oval corresponds to the main part of the proton auroral region and was located at the equatorward most region of the electron auroral emissions and gradually moved equatorward during the growth phase the fem arc was a discrete auroral arc having a clear longitudinally elongated form it appeared about 20 min before the onset on the high latitude side of the auroral region and moved equatorward toward the proton main oval its equatorward motion gradually slowed as it approached the proton main oval as the fem arc moved equatorward the location of the peak velocity in the nightside return flow of the two cell convection also moved equatorward the auroral breakup occurred in a localized area around the demarcation region between the two return flows close to the latitude of the fem arc this was observed by the uv imager aboard the akebono satellite the npsbl aurora appeared a few minutes before the onset around the poleward most region of the aurora and continued even after the onset our detailed analysis of these phenomena can give us important clues as to how the growth phase proceeds toward the expansion phase onset

polar ultraviolet imager observation of auroral breakup 1 the nasa s polar satellite completed its mission in march 2008 during its 12 year operation the ultraviolet imager uvi on board polar acquired a large number of auroral images in fuv bands with unprecedented spatial and temporal resolutions the purpose of this brief report is to provide a list of auroral substorm onset identified with uvi to the community for full use a total of 2003 auroral substorm onsets are identified in the northern hemisphere between 1996 and 2000 and 536 onsets in southern hemisphere in 2007 distributions of the onset locations are near gaussian with a population mean of 65 9 standard deviation 2 2 in magnetic latitude mlat and 22 6 1 1 in magnetic local time mlt for the northern hemispheric events and 68 0 2 3 in mlat and 22 6 1 1 in mlt for the southern hemispheric events a comparison with previously published image onset results suggests that substorms occur more frequently and intensely in the descending than in the ascending phase of solar cycle the list of onset events includes the onset times and locations and is provided as a supplement

short term dynamics of a low centred ice wedge polygon near chokurdakh ne yakutia ne siberia and climate change during the last ca 1250 years abstract palaeoecological studies including analysis of pollen macrofossils geochemistry and ams radiocarbon dates of four peat sections from one low centred ice wedge polygon in ne yakutia ne siberia allow the three dimensional reconstruction of polygon development during the last ca 1250 years after drainage of a lake peat forming vegetation invaded rapidly comparison with palaeotemperature data shows that the initial formation of mature ridges coincided with a period of high summer temperatures around ad 1400 the ridges persisted and expanded during the subsequent colder ca 200 years partial collapse of various ridges at the end of the 18th century corresponded to a phase with low summer temperatures during the warm 20th century one collapsed ridge regenerated whereas another persisted in its collapsed state ice wedge polygons are thus complex and highly dynamic ecosystems in which changes in temperature and precipitation may induce rapid ecological changes by the complex interplay of water ice and vegetation our study indicates that global warming associated with a decrease in summer precipitation may initially result in enhanced polygon ridge formation the combination of longer summers and increased winter precipitation as predicted for high latitudes will however eventually result in larger meltwater input in the polygon mires which may cause the partial collapse of polygon ridges and underlying ice wedges

a millennial record of environmental change in peat deposits from the misten bog east belgium in this study palaeoenvironmental changes recorded in the top metre of a peat profile misten bog east belgium were investigated using a multiproxy approach proxies include bulk density ti and si content pollen macrofossils d13c on specific sphagnum stems and d13ced18o on sphagnum leaves a highresolution chronology was generated using 210pb measurements and 22 14c ams dates on carefully selected sphagnum macrofossils d13c only records large change in mire surface wetness this is partly due to the fact that the core was taken from the edge of a hummock which may make it difficult to track small isotopic changes the d13c signal seems to be dependent upon the sphagnum species composition for example a change between sphagnum section cuspidata towards sphagnum imbricatum causes a significant drop in the d13c values on the whole the c and o isotopes record two shallow pool phases during the 8the9th and the 13th centuries pollen and atmospheric soil dust asd fluxes records increased human occupation in the area there may be some climatic signals in the asd flux but they are difficult to decipher from the increasing human impact land clearance agriculture during the last millennium the variations in the proxies are not always synchronous suggesting different triggering factors temperature wetness windiness for each proxy this study also emphasizes that compared to studies dealing with pollution using geochemical proxies palaeoclimatic inferences from peat bogs need as many proxies as possible together with highly accurate and precise age models in order to better understand climate variability and their consequences during the holocene

snapshots in time precise correlations of peat based proxy climate records in scotland using mid holocene tephras mid holocene tephra layers have been located and geochemically analysed from seven ombrotrophic bogs in scotland the tephras found in these scottish peats occur as stratigraphically discrete horizons not visible to the naked eye and originate from volcanic activity in iceland identifying and geochemically typing the tephra layers can enable precise correlations between sites on regional scales depending on the spatial extent of the airfall events dispersal of both the glen garry and hekla 4 tephras is excellent over scotland enabling snapshot views of the past at the time of these tephra depositions palaeoecological analyses have also been undertaken on these bogs providing detailed reconstructions of past changes in bog vegetation and surface wetness a proxy for past climates correlations between the ombrotrophic bogs at the time of the glen garry tephra revealed significant differences between the proxy climate records in the north and the south of scotland suggesting asynchronous changes between northern scotland and the rest of great britain

solar influences on holocene climatic changes illustrated by correlations between past lake level fluctuations and the atmospheric 14c record chronological correlations established at different time scales among the lake level fluctuations in the jura and french subalpine ranges glacier movements in the swiss and austrian alps and the atmospheric 14c record during the last 7 millennia show coincidences between lake level rises glacier advances and high 14c production and vice versa these correspondences suggest that the short term 14c variations may be an empirical indicator of holocene palaeoclimates and argue for possible origins of holocene climatic oscillations 1 the varying solar activity refers to secular climatic oscillations and to major climatic deteriorations showing a ca 2300 yr periodicity 2 a question is raised about a relationship between the earth s magnetic field and climate first the weak strength periods of the earth s dipole magnetic field between 3800 and ca 2500 b c coincide with higher climate variability and vice versa second the ca 2300 yr periods revealed by the 14c record and also by the major climatic deteriorations re corded in jurassian lakes ca 1500 a d ca 800 b c and ca 3500 b c coincide with the ca 2300 yr periods revealed by the earth s nondipole geomagnetic field the present warming induced by anthropogenic factors should be intensified during the next few centuries by natural factors of climate evolution

late holocene climatic changes in tierra del fuego based on multiproxy analyses of peat deposits a ca 1400 yr record from a raised bog in isla grande tierra del fuego argentina registers climate fluctuations including a medieval warm period although evidence for the little ice age is less clear changes in temperature and or precipitation were inferred from plant macrofossils pollen fungal spores testate amebae and peat humification the chronology was established using a 14c wiggle matching technique that provides improved age control for at least part of the record compared to other sites these new data are presented and compared with other lines of evidence from the southern and northern hemispheres a period of low local water tables occurred in the bog between a d 960 1020 which may correspond to the medieval warm period date range of a d 950 1045 generated from northern hemisphere tree ring data a period of cooler and or wetter conditions was detected between ca a d 1030 and 1100 and a later period of cooler wetter conditions estimated at ca cal a d 1800 1930 which may correspond to a cooling episode inferred from law dome antarctica

branched glycerol dialkyl glycerol tetraethers in lake sediments can they be used as temperature and ph proxies a series of surface sediments from 82 lakes of variable water depth and size was analyzed for glycerol dialkyl glycerol tetraethers gdgts in order to investigate the potential of the mbt cbt methylation ratio cyclization ratio of branched tetraethers as a continental palaeothermometer in lacustrine environments branched gdgts dominated in most sediments as indicated by the high branched vs isoprenoid tetraether bit values we observed that cbt and mbt varied substantially mean annual air temperature maat reconstructed and ph values were calculated using the cbt and mbt values and the calibration from the global soil data set the mbt cbt inferred temperatures were considerably lower than measured values nevertheless there was a significant correlation between maat reconstructed and maat observed on site although there was still considerable scatter r2 0 47 lacustrine sediments integrate organic remains of organisms in a lake and its drainage basin thereby offering a unique opportunity for calibrating mbt and cbt as small scale variability is averaged out since the source of the branched gdgts in the lake sediments is ambiguous it is not clear whether only temperature and ph in the catchment area are the driving factors therefore even in lake sediments with high concentrations of branched gdgts the straightforward application of mbt cbt as palaeoproxies may be difficult given the uncertainties regarding their source and origin

a synthesis of hydrogen isotope variability and its hydrological significance at the qinghai tibetan plateau abstract hydrogen isotope ratios of sedimentary biomarkers are known to record the climatic variability in terrestrial and marine environments however there is still a lack of calibration studies that can quantitatively retrace the driving forces especially at the tibetan plateau here we elaborate the actual influence of environmental parameters such as temperature evapotranspiration salinity and biosynthetic fractionation on d values of n alkanes we measured hydrogen isotope values d of n alkanes in recent sediment and plant samples as well as d values of different water sources lake and inflow water precipitation as well as leaf root and soil water from six tibetan lakes along a 10 spanning longitudinal transect covering an aridity gradient as expected the deuterium record can be used to distinguish two water pools at the plateau i precipitation water which supplies water for the lake inflow and terrestrial plants and ii enriched lake water having a clear evaporative signal based on significant correlations of the source water and d values of n alkanes d of alkane n c 23 record the lake water isotope composition and track the evaporative enrichment of the lake system in contrast d of alkane n c 29 can be used to retrace the isotope composition of the inflow displaying the integrated rainfall signal in the vegetation period modified by soil and leaf water evaporation while temperature changes are less pronounced across the tibetan transect the isotopic difference between c 23 and c 29 could potentially be used as a proxy to reconstruct effective moisture precipitation minus evaporation areas with lower precipitation amounts and higher evaporation rates are characterized by higher d c 23 c 29 values this relationship is more pronounced in regions with mean annual precipitation below 350 mm even in contrasting environments the application of the d proxies is very promising combining other tibetan studies it is possible to present a comprehensive picture of the usage of compound specific hydrogen isotopes of n alkanes on the tibetan plateau

grain size variation on dunes in the southwest kalahari southern africa abstract grain size parameters mean standard deviation skewness and kurtosis were determined for 83 sediment samples from six dune cross profiles and one 28 km long profile on dunes in the southwest kalahari desert in southern africa although some studies elsewhere and previous studies in the kalahari have reported significant grain size variation over dune cross profiles data presented here show no systematic variation of grain size parameters except that sediments from the crest of a dune are almost invariably better sorted indicated by the standard deviation of the sample than samples from the base or plinth of the dune the proportion of fines 63 m in plinth sediments is also greater than in crest samples there is no significant trend in grain size parameters along the length of a linear dune this lack of significant pattern corresponds with similar findings for central australian dunes

substorm onset timing via traveltime magnetoseismology 1 this letter introduces a traveltime magnetoseismic technique that can estimate the substorm onset time in the magnetotail from multi point observations of pi 2 pulsations the arrival time of pi 2 which is defined as the first peak in pi 2 amplitude observed by ground magnetometers presents a strong function of latitude using the tamao traveltime as the forward model the magnetoseismic inversion from the observed pi 2 arrival time infers that the onset of the 22 july 1998 substorm in the magnetotail started at x 20 re at 6 53 10 ut or 1 3 minutes earlier than the pi 2 onset time conventionally identified in ground records the magnetoseismic result is further compared with the observations of auroral brightening revealing a clear sequence of events during this substorm

centennial scale lake level lowstand at lake uddelermeer the netherlands indicates changes in moisture source region prior to the 2 8 kyr event the uddelermeer is a unique lake for the netherlands containing a sediment record that continuously registered environmental and climatic change from the late pleistocene on to the present a 15 6 m long sediment record was retrieved from the deepest part of the sedimentary basin and an age depth model was developed using radiocarbon dating 210pb dating and bayesian modeling lake level change was reconstructed using a novel combination of high resolution palaeoecological proxies e g pollen non pollen palynomorphs chironomids quantitative determinations of lake level change ground penetrating radar and estimates of changes in precipitation lipid biomarker stable isotopes we conclude that lake levels were at least as high as present day water levels from the late glacial to 3150 cal yr bp with the exception of at least one lake level lowstand during the preboreal period lake levels were ca 2 5 m lower than at present between 3150 and 2800 cal yr bp which might have been the result of a change in moisture source region prior to the so called 2 8 kyr event increasing precipitation amounts around 2800 cal yr bp resulted in a lake level rise of about 3 5 4 m to levels that were 1 1 5 m higher than at present in line with increased precipitation levels as inferred for the 2 8 kyr event from nearby raised bog areas as well as with reconstructions of higher lake levels in the french alps all of which have been previously attributed to a phase of decreased solar activity lake levels decreased to their present level only during recent times although the exact timing of the drop in lake levels is unclear the author s 2016

reconstruction of late holocene forest dynamics in northern ecuador from biomarkers and pollen in soil cores centuries of human interference have led to large scale reduction of montane forests in the northern ecuadorian andes as a result the natural position of the upper forest line ufl in the area is now subject of scientific debate which is hindering sustainable reforestation efforts uncertainty is fuelled by insufficient precision of fossil pollen spectra to reconstruct the natural ufl position here we tried to resolve this issue by using biomarkers i e plant species specific patterns of n alkanes and n alcohols preserved in soils in the northern ecuadorian andes as additional proxy to reconstruct the natural ufl position to unravel preserved biomarker patterns we used the recently developed verhib model and for the first time assessed its applicability in soil archives changes in holocene biomarker based vegetation composition were directly compared to changes in pollen based vegetation composition from the same soil profiles both proxies proved to be complementary and a combined application allowed for a more accurate reconstruction of past vegetation than with pollen analysis alone we found that the present day ufl in the study area has not been significantly depressed by human interference and was at 3650 m maximally during late holocene times for the moment of post glacial forest development we found a migration lag between pollen earlier and biomarkers later this reflects the difference between the non transported biomarker signal showing spot dating thus in paleoecological studies functionally equalling the information from plant macro remains in peat bogs and the upslope wind blown pollen signal showing an upslope forest expansion up to over a millennium ahead the combined pollen biomarker approach in soil cores shows great potential for vegetation reconstruction however more research of biomarker consistency and preservation is needed before application in other environments

effects of solar forcing and north atlantic oscillation on the climate of continental scandinavia during the holocene abstract 10 000 year long varved sediment records from lakes nautajarvi and korttajarvi finland provide evidence of climate and environment oscillations at multi decadal to millennial timescales we used two independent methods to extract periodic features from these time series of clastic laminae and assess their statistical reliability analyses revealed that seasonal sediment fluxes correspond to environmental changes with statistically significant periodicities of 1500 1800 1000 600 800 nearly 300 nearly 200 150 170 nearly 90 and 47 years showing variable coherency with different climate forcing factors and other palaeoproxy records in the northern hemisphere results indicate that the holocene winter climate in continental scandinavia was forced by a combination of several factors at least by solar variability and the north atlantic ocean atmosphere circulation patterns with varying influences through time

molecular proxies for paleoclimatology we summarize the applications of molecular proxies in paleoclimatology marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments loess deposits and ice cores the fundamentals of this approach are the molecular parameters the compound abundances and carbon hydrogen nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts these afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation we discuss two types of proxy those of terrigenous and those of aquatic origin and exemplify their application in the study of marine sediments through the medium of ten case studies based in the atlantic mediterranean and pacific oceans and in antarctica the studies are mainly for periods in the present the holocene and particularly the last glacial interglacial but they also include one study from the cretaceous the terrigenous proxies which are measures of continental vegetation are based on higher plant leaf wax compounds i e long chain circa c30 hydrocarbons alcohols and acids they register the relative contributions of c3 vs c4 type plants to the vegetation in the source areas the two marine proxies are measures of sea surface temperatures sst the longer established one u37k is based on the relative abundances of c37 alkenones photosynthesized by unicellular algae members of the haptophyta the newest proxy tex86 is based on c86 glycerol tetraethers gdgts synthesized in the water column by some of the archaeal microbiota the crenarchaeota

lipid and lignin cutin compounds in lake baikal sediments over the last 37 kyr implications for glacial interglacial palaeoenvironmental change abstract a stratigraphic study of total organic carbon toc concentration carbon isotopic composition of total organic matter tom lipids n alkanes n alkanols n alkanoic acids and sterols and lignin cutin compounds has been conducted for a lake baikal core 323 pc1 over the last glacial interglacial toc concentrations mg g 1 dry sediment are low 2 4 in the glacial sections but high 10 29 in the interglacial ones the concentrations of land plant derived compounds such as n c14 to c28 hydroxyalkanoic acids lignin phenols p hydroxyl vanillyl and syringyl total cutin acids normalized to toc in the interglacial are 5 6 times higher than those in the glacial carbon isotopic compositions of tom are 24 0 9 in the glacial while they are 27 1 3 in the interglacial the heavy isotope composition of tom in the glacial might be due to a contribution from submerged plants and or grasses the light isotopic composition of tom for the interglacial may be due to a contribution from both land plant and phytoplankton mainly diatom derived om autochthonous organic carbon contents were estimated from the c n ratio corrected for the effect of inorganic nitrogen and based on the assumption of c n values of 8 for autochthonous and 25 for allochthonous om the estimation indicates that autochthonous oc comprises 74 6 of toc for the glacial and 72 9 for the interglacial respectively primary palaeoproductivity was estimated to be below 20 gc m 2 y 1 in the glacial before 18 ka but high 100 120 gc m 2 y 1 in the interglacial 11 8 ka which is 10 30 higher than the modern values

paleoflooding reconstruction from holocene levee deposits in the lower meuse valley the netherlands this study investigates the holocene levee deposits and paleoflooding history of the lower meuse in the netherlands based on archeological investigations and sedimentary analyses grain size end member modelling magnetic susceptibility and thermogravimetric analyses the levee on the left bank in the study area near ooijen contains a continuous sedimentary record in the nw downstream part the archeological evidence and sedimentary results including a grain size based flood energy index lfei indicate that the lower meuse experienced a quiescent flooding period and low sedimentation rates during the mid late mesolithic when the levee was low and human influence was minor deposition during the mesolithic shows a fining upward trend and a highly developed soil containing abundant artefacts during the neolithic and bronze age the flooding intensity was low but gradually increased to a moderate level probably because of deforestation and increased runoff limited bronze age findings may reflect decreased human activity because of the increased flooding starting from the iron age the meuse experienced a generally enhanced flooding regime which is reflected by erosion and coarsened sedimentation in the iron age and roman period the high peak discharges during the iron age may have re opened a low lying paleochannel near to the levee during the intensified floods this general increasing trend is interrupted by the lower flooding phase in the early middle ages dark ages from the middle to the late middle ages the floods intensified again the coarsening deposition and higher sedimentation rates since the iron age resulted from increased floods and higher sediment supply by deforestation and soil erosion the findings of this study agree with a recent paleoflood reconstruction for the lower meuse by using a floodplain archive implying that levee sediment records have potential in paleohydrological studies if the completeness of the record and chronological information is guaranteed 2019 elsevier b v

an 8000 year multi proxy peat based palaeoclimate record from newfoundland evidence of coherent changes in bog surface wetness and ocean circulation energy carried by warm tropical water transported via the atlantic meridional overturning circulation amoc plays a vital role in regulating the climate of regions bordering the north atlantic o

grain size characteristics of namib desert linear dunes the results of a systematic sampling of linear dunes in the northern namib sand sea show that they are composed of two distinct groups of sands a fine well sorted near symmetrical crest and slip face population and a coarse moderately sorted positively skewed plinth population these may be explained in terms of the aeolian sorting processes operative on the dunes which involve differential rates of movement of creep and saltation load on windward flanks and avalanching on leeward slopes leading to the concentration of coarse sands towards the dune base