diatom inferred salinity in palaeolakes an indirect tracer of climate change lakes in arid and semi arid regions respond to climatic change through shifts in lake water volume and ionic concentration because diatom distribution is highly correlated with lake hydrochemistry diatoms can be used to infer changes in salinity and brine composition and thus to infer past climates here we critically examine the use of diatom inferred salinity as a climate proxy with examples taken from both modern waterbodies and sedimentary profiles sediment records may contain assemblages mixed from periods or sites of differing hydrochemistries because of the high degree of spatial and temporal heterogeneity in saline systems dissolution and diagenesis in saline brines may further complicate interpretation of sedimentary assemblages furthermore threshold effects salinity regulation via groundwater seepage antecedent conditions and other aspects of local hydrology may modify the relationship between salinity change and climatic forcing these complexities necessitate critical examination of the ecology and taphonomy of sedimentary assemblages as well as evaluation of potential non linearities in the salinity climate relationship through comparison of diatom inferred salinity with other proxy records of hydrochemical change historical documents where they exist and with other regional lake systems

a 14 000 year sediment yield record from western germany based on annually laminated lake sediments the reconstruction of sediment yield data for the catchment of lake holzmaar 205 8 ha in the eifel mountains western germany is based on high resolution geochemical and physical analyses of an absolutely dated sediment record this technique provides flux rates of allochthonous minerogenic deposition for the last 13 840 years the pleistocene holocene transition is characterized by instable soils and vegetation caused by adjustment of the catchment to interglacial climatic conditions these instabilities are the reason for elevated mean sediment yields in the catchment of 16 t km 2 yr 1 until 9800 cal bp during most of the holocene erosive processes are insignificant and sediment yields are very low 1 5 t km 2 yr 1 since humans cleared the forests for agriculture and early industrial purposes the natural environment has been disturbed and sediment yields increased to mean values of 14 t km 2 yr 1 during the last 2750 years comparisons of reconstructions from the eifel area with similar data from southern sweden and with measured data from lakes reservoirs and monitoring sites suggest that quantitative reconstructions based on lake holzmaar sediments may be regarded as reliable despite uncertainties related to the methods of reconstruction applied

early holocene aeolian dust accumulation in northeast china recorded in varved sediments from lake sihailongwan abstract annually laminated sediments of lake sihailongwan shl in northeast china preserve a high resolution record of past climatic and environmental changes thin sections of varved early holocene sediments were analyzed using light optical and scanning electron microscopic methods sediment micro facies and geochemical analyses reveal two different seasonal clastic layer types spring snow melt and dust layers dust layers distinctly differ from snow melt layers through their finer grain size better sorting higher al and lower mg and ca contents in contrast to recent lake shl sediments during the early holocene silt sized dust has been deposited after spring snow melt and after pronounced spring diatom blooms for the time interval between 11 580 and 7060 varve years bp dust layers were quantified at annual resolution highest intensities and frequencies of dust accumulation are observed in the period from 11 100 to 8200 varve years bp in good agreement with dry conditions in this time interval documented by palaeoclimatic records derived from lake sediments and loess in central asia and northern china based on modern meteorological observation of dust storms in china the dust accumulation record mirrors mainly the variation in climatic conditions governing generation of cyclone and cold air surges in the arid and semi arid mid latitude regions of china and mongolia on multidecadal and centennial time scales solar activity might have been an additional forcing factor for dust accumulation frequency in the early holocene spectral analyses reveal 205 years and 88 years periodicities in variations of dust accumulation frequency that likely reflect the de vries suess and the gleissberg solar cycles

palaeolimnological approaches to climate change with special regard to the biological record abstract lakes systems respond physically chemically and biologically to changes in climate and these responses are registered in many various ways in lake sediment records this paper focuses principally on the biological record and describes recent research that aims to reconstruct i past variability in effective moisture and ii past variability in temperature changes in effective moisture are manifested especially by changes in lake water level in closed lake basins water level change can cause significant changes in water salinity that is registered in sediments by changes in the composition of fossil assemblages especially diatoms in open freshwater lake basins changes in water level are best reconstructed from the aquatic macrofossil record and potentially from the ratio of open water to littoral species of cladocera ostracods and diatoms the most promising biological method for reconstructing past temperature is chironomid analysis and a range of new chironomid temperature transfer functions are being developed however biological responses to changing temperature are usually indirect as a result of temperature effects on water column stratification nutrient cycling and alkalinity generation and in most cases a correct interpretation of the climatic significance of changes in the fossil record requires an understanding of the processes that are operating in the water column a multi proxy whole lake approach is advocated as the best way forward not only as a means of reconstructing past climate but also as a means of assessing the impact of climate change on lake systems

a quantitative holocene climatic record from diatoms in northern fennoscandia abstract a diatom based calibration model for predicting summer temperatures was developed using climatically sensitive subarctic lakes in northern fennoscandia the model was applied to a sediment core from a treeline lake to infer trends in holocene climate the record exhibits long term variations as well as a series of shorter term fluctuations on a time scale of centuries summers were warmest in the area about 6200 cal yr b p and featured distinct cooling episodes around 8300 7200 4200 3000 and 400 cal yr b p most of these coinciding with some known climate events e g the 8200 cal yr b p event and the little ice age the similarity of the observed shifts with the pacings of climate events from marine and ice core records represents evidence for coupled ocean atmosphere forcing of the regional climate

climatic change evidence and lacustrine varves from maar lakes germany annually laminated non glacial lake sediments from lake holzmaar eifel western germany were investigated using large merkt thin sections the absolute age of varve intervals with variations in thickness and composition were correlated to climatic changes recorded by glacier fluctuations in the alps back to 8800 years vt varve time varve years before 1950 glacier advances coincide with sedimentation rate minima prior to 8800 years vt they coincide with sedimentation rate maxima the early and middle holocene sediments suggest a periodicity of about 1000 years for cold warm cycles a sequence of 512 varve thickness measurements was subjected to spectral analysis these provide apparent evidence for a 11 year sun spot cycle

diatom response to the last glacial interglacial transition in the ioannina basin northwest greece implications for mediterranean palaeoclimate reconstruction uncertainty as to the pattern of lateglacial and early holocene climate change in the western balkans and greece has persisted despite extensive investigation of the ioannina i 284 lake sediment sequence northwest greece here we present a new diatom record from i 284 for this time period after dominance by eurytopic small fragilariales the lateglacial interstadial ca 14 9 12 7 cal kyr bp is marked clearly by a relative increase in planktonic cyclotella ocellata a return to small fragilariales from ca 12 7 to 11 6 cal kyr bp approximately coincides with the younger dryas chronozone it is followed by a major transition to dominance by cyclotella spp at the pleistocene holocene boundary we interpret these shifts as a response to both lake level and productivity change induced by shifts in effective moisture and temperature demonstrating that the diatom record provides the first strong evidence for a younger dryas event in northwest greece and for both warming and wetting during the lateglacial interstadial and early holocene we also present clear evidence for an abrupt phase of catchment instability during the early holocene in this case we must await the results of further research to test whether it was driven by climatic or tectonic forcing

diatom and geochemical evidence of mid to late holocene climatic changes at lake holzmaar west eifel germany abstract changes in diatom assemblages geochemistry and stable carbon isotope composition of bulk organic matter in a varved sediment section from lake holzmaar west eifel germany were used to infer mid to late holocene climatic changes and human impact from 6340 to 1470 cal yr bp shifts in total lacustrine primary production were derived from 13 c org values changes in non siliceous algae biomass productivity were deduced from accumulation rates of organic matter diatom valve accumulation rates and biogenic opal accumulation rates were used as proxies for diatom productivity and for siliceous phytoplankton abundance respectively based on weighted averaging of relative diatom abundance in subsamples qualitative changes in past trophic status were inferred accumulation rates of minerogenic material and the toc tn molar ratio permitted the deduction of past changes in allochthonous matter influx diatom assemblage composition showed statistically significant changes around 5130 3660 and 2900 cal yr bp whereas planktonic diatom productivity was subject to distinct shifts around 5900 5130 4500 3600 2660 and approximately 1630 cal yr bp and siliceous phytoplankton biomass changed ca 6100 4500 2660 1900 and 1700 cal yr bp causally determined changes in diatom assemblage composition and productivity for example due to shifts in nutrient ratios and or concentrations invoked by changes in lake circulation patterns precipitation rates and or erosion rates are discussed glacier fluctuations and lake level changes reported from other study sites in western europe support the finding that reconstructed lacustrine processes are at least indirectly linked to climate palynological and archaeological evidence however has shown a strong superimposition of lacustrine processes with local regional anthropogenic activity since the iron age

d h ratios of methoxyl groups of the sedimentary organic matter of lake holzmaar eifel germany a potential palaeoclimate hydrology proxy stable hydrogen isotope ratios dd values of methoxyl groups in lignin and pectin from a variety of plant types from different locations have been shown to mirror dd values of precipitation with a mean uniform isotopic fractionation since dd in precipitation is mainly influenced by climatic conditions including temperature evaporation and precipitation amount methoxyl groups of organic matter have been proposed as a potential palaeoclimate proxy here we measured the dd values of the methoxyl groups of sedimentary organic matter derived from sediment core segments of lake holzmaar eifel germany the sediment core covers the entire holocene and part of the late glacial until 13 650 years bp since the sedimentary organic matter was indicated by organic source proxies of predominantly phytoplanktonic origin we considered the dd values of the methoxyl groups as a proxy for the dd value of the lake water presently and probably during most of the holocene the dd value of precipitation was primarily controlled by temperature 2 4 5 c as well as in isotopic equilibrium with the dd value of the lake water we used these modern temperature sensitivities of the eifel region together with the measured dd values of the methoxyl groups of the sedimentary organic matter to evaluate temperature changes recorded for the holocene the resulting mean temperature variance was found to be consistently less than 1 8 4 c and is broadly in line with that reported from the ngrip ice core for the same period the transition from the holocene to the late glacial period was accompanied with more negative dd values of the methoxyl groups 13 for the younger dryas besides the association with temperature we assumed a higher susceptibility of the dd value of lake holzmaar to evaporative enrichment during the younger dryas which could serve as an explanation for discrepancies reported for existing palaeoclimate hydrology records of the eifel region our findings indicate that the dd values of methoxyl groups have great potential for assisting with palaeoclimate and palaeohydrology particularly when the organic matter is well characterized and of uniform origin 2014 elsevier ltd all rights reserved

sediments from lago di mezzano central italy a record of lateglacial holocene climatic variations and anthropogenic impact microscopic geochemical and pollen analysis of sediment samples of a lateglacial holocene profile from lago di mezzano a maar lake in central italy reveals evidence of significant climatic and human induced environmental changes time control is provided by a combination of varve chronology and radiocarbon dating the well known lateglacial climatic variations a warmer interstadial and the younger dryas cold phase are clearly represented in all the parameters during the interval between 9200 and 5600 cal bp of the holocene climatic optimum annually laminated organic rich diatom gyttja was deposited two periods of diminished total organic carbon are identified within this interval the first one p1 ranges from 8200 to 7800 cal bp while the second p2 is centred around 6500 cal bp during p1 a predominance of diatoms stephanodiscus parvus and s minutulus over other algae represented by the total organic carbon content is observed the timing of this period coincides with the early to mid holocene climatic transition reported from ice cores and lake sediments stager and mayewski 1997 p2 is characterized by a decrease in all biogenic parameters including biogenic opal organic carbon as well as arboreal pollen from 5000 cal bp to date the sediment pattern changes coincide with the mid holocene climatic deterioration in addition to these natural variations human impact has been recorded and recognized from sedimentological features such as turbidites and charcoal as well as from reduced arboreal pollen content two middle bronze age 3700 cal bp and 3300 cal bp etruscan early roman 2500 cal bp longobardic ad 900 and modern settlements since ad 1700 have been distinguished on the basis of these data

a 13 000 year paleolimnological record from the uinta mountains utah inferred from diatoms and loss on ignition analysis paleolimnological research in mountainous regions of the western united states provide baseline understanding of how these lake systems will respond to ongoing climate change fossil diatom assemblage and loss on ignition data were investigated from a 13 000 year lake sediment core from the uinta mountains northeastern utah usa results indicate the presence of three major zones of environmental change 1 from 12 9 10 9 cal ka modern lake formation began temperatures were cool and water was turbid 2 from 10 9 3 5 cal ka conditions were warmer than present and the lake stratified during the summer and 3 beginning approximately 3 5 cal ka temperatures decreased relative to the previous zone and the lake appears to have become increasingly alkaline shifts in diatom taxa relative abundances within the middle zone ca 8 2 6 5 and 5 0 3 5 cal ka are probably caused by precipitation driven decreases in alkalinity and increases in lake depth this record reflects evolution of the lake system and suggests that currently rising temperatures will reduce ice cover and enhance lake stratification and internal nutrient cycling any future changes in precipitation patterns may also impact lake ecology through shifts in alkalinity and or depth

diatom response to climatic warming over the last 200 years a record from gonghai lake north china abstract annual monitoring data and centennial and millennial scale paleolimnological records have revealed an increase in small celled planktonic diatom species relative to heavier tycho planktonic and small benthic diatoms in many high altitude lakes presumably in response to recent climatic warming in addition to changes in the composition and structure of lacustrine diatom assemblages there have also been changes in diatom biodiversity however these changes are not regionally consistent in this study we chose a temperate mid latitude lake to explore the response of changes in diatom assemblages and biodiversity to recent climatic warming the diatom record spans the past ca 200 years and reveals that since 1966 ce the small celled cyclotella ocellata stelligera has replaced the previously dominant large celled phytoplankton cyclotella schroeteri these changes are in accordance with the increasing trend in global mean surface temperature biodiversity increased remarkably from 1966 ce but began to decline after 1990 ce presumably in response to rapid climatic warming our findings indicate that the response of diatom biodiversity to climate change was a nonlinear process

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

late quaternary changes in ecosystems and carbon cycling on mt kenya east africa a landscape ecological perspective based on multi proxy lake sediment influxes abstract the degree to which different lakes within a landscape respond coherently in unison to external drivers such as climate change and soil development is uncertain presentation of multi proxy geochemical and palaeoecological data from individual lakes in the form of fluxes minimizes distortions resulting from variable sedimentation rates and changes in sediment composition we use the accumulation rates of magnetic minerals total organic c and n terrestrial and aquatic biomarkers graminoid epidermis pollen green algae diatoms and diatom c in four small lakes situated between 2350 and 4595 m a s l on the ne flank of mt kenya east africa to reconstruct changes in c cycling over the last 38 ka the results conflict with earlier models of landscape and lake development showing 1 that glacial interglacial changes in vegetation cannot be interpreted as simple altitudinal shifts in the modern vegetation belts and 2 that limnological changes were not coherent rapid variations in climate water level erosion and nutrient input overwhelmed long term successional trends in lake sedimentation and c accumulation since the last glacial maximum the results also reveal previously unrecognized features of the palaeoenvironmental record such as the rapid degradation of organic matter in diatoms and the occurrence of a productive fire prone montane grassland during the highly seasonal monsoonal climate of the lateglacial and early holocene

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

late quaternary environmental and climatic changes in central europe as inferred from the composition of organic matter in annually laminated maar lake sediments 1 geochemical elemental analysis bulk 13ctoc thermal degradation techniques molecular analysis of n alkanes and microscopic investigations maceral analysis vitrinite reflectance were performed 1 to characterize the organic matter om in sediments from two maar lakes in the westeifel volcanic field germany and 2 to discuss paleoenvironmental processes which have controlled the accumulation and preservation of om the annually laminated sediments show a wide range of organic carbon contents between 0 3 and 21 4 toc and hydrogen index values between 80 and 501 mg hc g toc well developed laminations mirror suboxic to anoxic bottom waters diagnostic compounds in the pyrolysates and microscopic analysis permit discrimination between the principal om sources and their variations over time provide important evidence for the reconstruction of the environmental histories of the lakes and their watershed the significance of terrigenous om is reflected by the occurrence of methoxyphenols in the insoluble as well as mid and long chain n alkanes in the soluble om which are indicative of land plant or macrophyte input to the lakes the relative abundance of certain homologues together with the amount of terrigenous macerals can be used to show differences in higher plant input and vegetation changes through time during the pleniglacial and younger dryas period high reflecting reworked om was introduced by soil erosion in an environment with relatively open vegetation the alkylphenols in the pyrolysates originate partly from the microbial reworking of proteinaceous tyrosine moieties and or reflect a direct contribution from cyanobacteria we assume that variations in the carbon isotopic composition of om are mainly due to changes in the lake s primary productivity with the exception of the pleniglacial various forms of land use are reflected by increasing amounts of terrigenous particles as well as chemical plant markers from 500 varve years b p until present the organic geochemical and microscopic data correlate well with other proxy information about climate dependent fluctuations in the ecosystem of the studied sites

tertiary oils from upper assam basin india a geochemical study using terrigenous biomarkers abstract the upper assam basin in northeast india is a tertiary sub basin of the assam arakan basin hydrocarbons are present in the langpar formation upper palaeocene lakadong member of the sylhet formation lower eocene and the barail oligocene tipam lower miocene and girujan middle miocene formations in the basin a detailed study to understand the nature and origin of the oils from different stratigraphic horizons using terrigenous and other biomarkers has been carried out further the variation in maturities of oils occurring in different stratigraphic horizons has also been studied the study shows that rearranged oleananes oleananes and bicadinanes are present in these oils implying land plant input to their source rocks the oils have been classified into different groups using ratios of rearranged oleananes oleananes bicadinanes and steranes indicating presence of multiple source rocks in the basin with subtle variation in characteristics maturity studies show that oils from younger horizons barail tipam and girujan are more mature than oils from older horizons langpar and lakadong there is an apparent mismatch in maturity of oils as measured by different biomarker maturity parameters this is due to the mixing of two different charges of oils having different maturities and generated from two different source rock kitchens in the same reservoir principal component analysis pca of biomarker data has also been able to classify the oils into various groups a new parameter has been developed using ratios of rearranged oleananes for determining maturity of these oils

biodiversity patterns of silurian radiolaria abstract data analysis of all published and well dated silurian radiolarian localities was conducted with the goal of revealing long term patterns in silurian radiolarian biological diversity the chronostratigraphic distribution of 161 species was compiled from 25 publications each selected because of their independent age control the pattern and dynamics of changes in biodiversity are described using indices that allow for the assessment of changes in taxonomic richness through time following the hirnantian end ordivician mass extinction the rhuddanian stage records very low levels of diversity which then increase gradually throughout the llandovery series and reach a maximum by the sheinwoodian stage before decreasing during the homerian and finally rebounding during the gorstian stage the early silurian llandovery appears to be an interval during which few species went extinct although the number of last occurrences increases progressively to reach a peak in the ludfordian at the same time first occurrences progressively decrease and are relatively low during the silurian only the gorstian is marked by a sudden increase in origination the early silurian is an interval of faunal recovery from the end ordovician mass extinction event similarly the gorstian stage is characterized by a recovery following the homerian low in radiolarian diversity that may be correlated with the c lundgreni extinction event which affected a number of other pelagic groups e g graptolites acritarchs conodonts and chitinozoans and with the mulde event which coincides with a 4 6 positive excursion of the 13 c curve

rapid climate change during the early holocene in western europe and greenland based on microfacies analyses of seasonally laminated varved sediments from lake holzmaar germany we report evidence of decadal to century scale climate variability during the early holocene the shifts in climate are documented in the thickness variations and changes in the composition of the varves in response to subtle shifts in limnological conditions the close similarity between the holzmaar varve record and the grip oxygen isotope record during 7 4 9 0 calendar cal ka suggests that the high frequency climatic variations in both regions were controlled by the same mechanism our more detailed studies covering the central 409 yr period 7 846 8 255 cal ka encompassing the 8 2 ka event document for the first time on a seasonal scale the changing precipitation regimes in western europe during these climate shifts we show i that winters were drier and summers shorter and cooler in western europe during colder periods in greenland ii in contrast to the present day climate in the holzmaar

the alps with little ice evidence for eight holocene phases of reduced glacier extent in the central swiss alps glacially deformed pieces of wood organic lake sediments and clasts of reworked peat have been collected in front of alpine glaciers since ad 1990 the palaeoglaciological interpretation of these organic materials is related to earlier phases of glacier recession surpassing that of today s shrunken glaciers and to tree growth and peat accumulation in the valleys now occupied by the glaciers glacial transport of the material is indicated by wood anatomy incorporated silt sand and gravel particles missing bark and deformed treerings a total of 65 samples have been radiocarbon dated so far and clusters of dates provide evidence of eight phases of glacier recession 9910 9550 9010 7980 7250 6500 6170 5950 5290 3870 3640 3360 2740 2620 and 1530 1170 calibrated years bp allowing for the timelag between climatic fluctuations glacier response and vegetation colonization these recession phases may lag behind climatic changes by 100 200 years

synchronous holocene climatic oscillations recorded on the swiss plateau and at timberline in the alps eight synchronous pre roman cold phases were found at 9600 9200 8600 8150 7550 6900 6600 6200 5350 4900 4600 4400 3500 3200 and 2600 2350 radiocarbon years bp by reconstructing past climate at two sites on the swiss plateau and at timberline in the alps the cooling events during the early and mid holocene represent temperature values similar to today and apparently the onset of cooling events represents a deviation from today s mean annual temperature of about 1 c and is triggered at a 1000 year periodicity at wallisellen langachermoos 440 m a former oligotrophic lake near zurich the correlation between sum mertime lake levels and the seed production of the amphi atlantic aquatic plantnajas flexilis was used to reconstruct lake levels over a 3000 year period during the first part of the holocene at lake seedorf on the western swiss plateau 609 m the sedimentological palynological and macrofossil record revealed fluctuations of lake levels for the complete holocene from lago basso in the

chrysophycean microfossils in paleolimnological studies abstract the chrysophyceae represent a diverse group of algae with approximately 1000 described species most of which are planktonic and found in oligotrophic lakes a characteristic feature of this class is the endogenous formation of a siliceous resting stage known as a statospore vegetative cells in the family mallomonadaceae are covered by overlapping siliceous scales that are often sculptured and ornamented both the statospores and scales are species specific and because they are siliceous they are usually well preserved in lake sediments this paper reviews the applicability of these microfossils in the interpretation of past lake conditions

ams radiocarbon dating of annually laminated sediments from lake holzmaar germany ams radiocarbon ages have been determined on terrestrial macrofossils selected from the annually laminated sediments of lake holzmaar germany the radiocarbon chronology of this lake covers the last 12 6 ka comparison of the radiocarbon dated varve chronology with tree ring data shows that an additional 878 years have to be added to the varve chronology the corrected c 14 varve chronology of holzmaar reaches back to ca 13 8 ka cal bp and compares favourably with the results from soppensee switzerland hajdas et al 1993 the corrected ages for the onset and the end of the younger dryas biozone are 11 940 cal bp and 11 490 cal bp respectively the ash layer of the laacher see volcanic eruption is dated at 12 201 224 cal bp and the ulmener tephra layer is dated at 10 904 cal bp

late quaternary vegetation and hydrological change at ljubljansko barje slovenia abstract this paper investigates changes in the vegetation and hydrology at ljubljansko barje slovenia using a multi proxy approach pollen diatoms geochemical and stable isotope analysis during the lateglacial ljubljansko barje was a deep oligotrophic lake surrounded by open woodland comprised predominantly of pinus and betula which in the early holocene when the lake became shallower and mesotrophic fragilaria pinnata 15 n 3 3 13 c 33 7 c n 7 9 was replaced by broadleaved tree taxa tilia ulmus quercus corylus and picea this was followed by the spread of fagus and after 9200 cal yr bp abies and planktonic and oligotrophic diatom taxa aulacoseira italica gomphonema angustum as well as an increased allochthonous influx silt sio 2 al 2 o 3 between ca 6750 and 6000 cal yr bp the diatom data suggest shallower and oligotrophic conditions whereas the stable isotope record increased 13 c and decreased 15 n indicates terrestrial input changes in forest composition increase of quercus alnus corylus and the spread of herb taxa were probably advanced by human impact on the environment the beginning of organic sedimentation dated to 6000 cal yr bp was followed by an increase of fagus and abies and by eutrophication and peat growth at 5200 cal yr bp

palaeoproductivity and environmental changes during the holocene in central italy as recorded in two crater lakes albano and nemi abstract three cores from two crater lakes in central italy albano and nemi spanning the last ca 11 kyr bp are discussed here they were analysed for organic matter dry density algal and photosynthetic bacteria pigments diatoms and cladocera these palaeolimnological records show great internal consistency in their response to distinct but inter related aspects of the lake catchment system and reflect major changes in these systems particularly in lake productivity the early holocene was characterised by very high productivity at both sites trends in productivity are similar for many proxies in the holocene records of lake albano and lake nemi trophic levels throughout much of the period of human activity ca 4000 yr bp onward are lower but have remained relatively high and stable at both lakes it is only in the last few decades that inferred productivity levels have exceeded those of the early holocene statistical analysis constrained incremental sum of square cluster analysis coniss showed five distinct periods during the holocene characterised by major variations in the abundance and community structure of biological remains and geochemistry a comparison of results from the different taxonomic groups has enabled the reconstruction of phases of increased productivity and the recognition of signals of anthropogenic impact on the lakes and their catchments from published pollen diagrams nine major deforestation events are recognised during the holocene these events in particular the one which occurred in both lakes at 1800 yr bp and identifies the roman period plus another at 3000 3500 yr bp related to agricultural activity during the bronze age produced profound changes in the pelagic community structure of diatoms and cladocera which in some cases were even more marked than the accelerated eutrophication seen in recent times the mid holocene climatic transition is also clearly evident and is characterised by a strong decrease in the concentrations of the biological proxies most of the observed lacustrine environmental changes are almost synchronous in the two lakes indicating the importance of regional rather than local changes

effect of lake evaporation on δd values of lacustrine n alkanes a comparison of nam co tibetan plateau and holzmaar germany compound specific hydrogen isotope ratio values of lacustrine n alkanes from two contrasting ecosystems the semiarid to arid nam co central tibet and the humid holzmaar germany were compared in order to assess whether or not these environmental conditions are recorded in the isotopic signatures of biomarkers increased evaporation of lake water at nam co is recorded by the n alkanes of aquatic origin hence isotopic enrichment results in a di erence between terrestrial and aquatic n alkanes in the opposite direction 68 from that known for humid climate conditions 30 predominating at holzmaar based on this isotopic di erence between terrestrial and aquatic n alkanes evaporation to inflow ratio e i values were estimated and suggest that the isotopic di erence is indicative of the general hydroclimatic characteristics of a lake system moreover the comparison with e i values calculated with actual stable water isotope data showed that the dd values of aquatic and terrestrial lacustrine n alkanes serve as a proxy for the relative isotopic di erences between lake and inflow waters and can be used to assess the proportion of water undergoing evaporation relative to the inflow and thus to reconstruct the lake water balance in the past 2008 published by elsevier ltd

successive oceanic and solar forcing indicated by younger dryas and early holocene climatic oscillations in the jura abstract the recent extension of 1 the residual 14 c curve back to 11 400 cal yr b p and 2 the lake level reconstruction in the jura back to ca 13 500 cal yr b p offers the opportunity of testing by proxy data the relationships between climate atmospheric 14 c the sun and the ocean recently suggested from the atmospheric 14 c record the climatic significance of the jura record is supported by correlations with climatic oscillations reconstructed in the alps from glaciers and timberline movements correspondence between the 14 c and paleoclimatic record from the jura suggests a working hypothesis two intervals within the holocene can be distinguished in the middle latitudes of western and central europe an early holocene period shows abrupt climatic oscillations linked to ocean forcing major colder climate phases developed between ca 9000 and 8800 and between ca 8000 and 7000 cal yr b c that coincide with higher 14 c values after 6000 cal yr b c a second period is characterized by smoother multicentury climatic oscillations linked to solar forcing

annually dated late weichselian continental paleoclimate record from the eifel germany a record extending back to 23 220 calendar yr b p was obtained from varved sediments from lake holzmaar germany by applying multiple dating methods and interlake comparison with meerfelder maar variations in the weichselian inorganic carbon content resulting from intensified eolian activities coincide with proxy parameters of dust accumulation in greenland the timing for the end of the last glacial maximum at holzmaar agrees with the greenland ice sheet project gisp2 data but suggests dating discrepancies with the greenland ice core project data grip assuming that periods of maximum dust deposition in the eifel and greenland coincide with ice advances in northeastern germany the holzmaar record provides a means of dating three late weichselian terminal moraines

holocene climate reconstructions from the fennoscandian tree line area based on pollen data from toskaljavri due to its location on the eastern north atlantic seaboard the fennoscandian tree line area is an ideal area to use biological proxies to assess the relative roles of the scandinavian ice sheet and of oceanic atmospheric and astronomic forcings on regional climate history here we report pollen based july mean temperature tjul and annual precipitation pann reconstructions from a sediment core from a high altitude tree line lake in northwestern finland the reconstructions suggest that at 9600 8300 cal yr b p tjul values were low but steadily rising while pann was high the period of warmest summers with tjul values ca 1 8 1 6 c higher than at present occurred at ca 8000 6500 cal yr b p since then climate has become gradually cooler tjul values during the medieval warm period ca 1400 1000 cal yr b p were ca 0 8 c higher that at present but decreased rapidly to the low little ice age levels at 800 cal yr b p we compare these results with an earlier pollen based climate reconstruction from the same region the reconstructions indicate a similar general holocene tjul pattern with lower values in the reconstruction from the high altitude lake however most of the small scale variations are not synchronous suggesting that they may represent noise rather than signal in our data c 2002 university of washington