multi proxy evidence of holocene climate variability in volhynia upland se poland recorded in spring fed fen deposits from the komarow site radiocarbon dated spring fed fen deposits from the komarow site volhynia upland se poland with its multi proxy data macrofossils molluscs geochemistry pollen stable isotopes of oxygen and c

chronology and directions of late glacial paleoenvironmental changes a multi proxy study on sediments of lake slone se poland the article presents the results of a multi proxy study on sediments of lake slone chelm hills located in the northern peripheral area of the lublin upland se poland the area remained in the periglacial zone with permafrost present in the geological substrate during the last glaciation this paper represents an attempt to determine the directions and intensity of changes in environmental conditions during the late glacial it also attempts to reconstruct lake development conditions within the area unaffected by the extent of the ice sheet the aim of the study was to investigate bottom sections of two sediment profiles representing the period of late glacial lake mire sedimentation occurring in varying thermal and humidity conditions conditions were indicated by lithological variations in the sediments and the content of micro and macrofossils the latter were identified based on palynological and malacological analyses as well as by subfossil ostracoda and cladocera analysis the chronology of the identified paleoenvironmental changes was determined based on the results of paleobotanical analysis in correlation with radiocarbon dating conventional and ams of the selected sediment layers the results were compared to other sites from north central europe and to the well dated laminated sediments sequences from the nearest late glacial site at perespilno it was estimated that the development of lake slone probably had its origin in the older dryas the development of the lake basin in turn is associated with specific processes of disappearance of permafrost in the upper cretaceous bedrock

temporally and spatially uniform rates of erosion in the southern appalachian great smoky mountains we measured 1 0 be in fluvial sediment samples n 27 from eight great smoky mountain drainages 1 330 km 2 results suggest spatially homogeneous sediment generation on the 10 4 10 5 yr time scale and 100 km 2 spatial scale at 73 11 t km 2 yr 1 equivalent to 27 4 m m y of bedrock erosion this rate is consistent with rates derived from fission track long term sediment budget and sediment yield data all of which indicate that the great smoky mountains and the southern appalachians eroded during the mesozoic and cenozoic at 30 m m y in contrast unroofing rates during the paleozoic orogenic events that formed the appalachian mountains were higher 10 2 m m y erosion rates decreased after termination of tectonically driven uplift enabling the survival of this ancient mountain belt with its deep crustal root as an isostatically maintained feature in the contemporary landscape

geomorphic constraints on surface uplift exhumation and plateau growth in the red river region yunnan province china field observations digital elevation model dem data and longitudinal profi le analysis reveal a perched low relief upland landscape in the red river region yunnan province china which correlates to an uplifted regional low relief landscape preserved over the eastern margin of the tibetan plateau as with other major rivers of the plateau margin the red river has deeply incised the lowrelief upland landscape which we interpret to be the remnants of a pre uplift or relict landscape we examine longitudinal river profi les for 97 tributaries of the red river most profi les consist of three segments separated by sharp knickpoints an upper lowgradient channel segment a steeper middle channel segment and a very steep lower channel segment upper channel segments correspond to the relict landscape and have not yet experienced river incision steeper middle and lower segments indicate onset of rapid two phase river incision on the basis of which changes in external forcings such as climate or uplift can be inferred in terms of two end member scenarios two phase incision could be the result of pulsed plateau growth in which relatively slow uplift during the fi rst phase is followed by rapid uplift during the second phase or it could refl ect adjustments of the main channel to changing climate conditions against the backdrop of steady plateau growth reconstruction of the paleo red river indicates 1400 m river incision 1400 1500 m surface uplift and a maximum of 750 m vertical displacement across the northern red river fault elevating the northern ailao shan range above the surrounding relict landscape on the basis of stratigraphic constraints incision along the red river likely began in pliocene time

environmental changes during the holocene climatic optimum in central europe human impact and natural causes abstract the priority programme changes of the geo biosphere aimed to reconstruct the environmental history of central europe with emphasis on the time interval from 9000 to 5500 cal bp time slice ii coinciding with the holocene climatic optimum during this period the onset of human activities such as settlement agriculture and animal husbandry caused environmental changes studies of different landscape units in germany were carried out to identify these anthropogenically induced changes and to distinguish them from natural effects on the environmental system the investigated archives included laminated lake sediments fluvial sediments colluvia and soils speleothems peat and coastal sediments the different archives were examined using refined research methods including a variety of sedimentary and geochemical analyses together with pollen analysis and dating methods for the establishment of a reliable chronology the results of the various research groups are summarised and critically discussed based on these results the climatic optimum can be subdivided into three periods 1 the early atlantic from 9000 to 7500 cal bp with negligible human impact and stable environmental conditions 2 the late atlantic during early and middle neolithic from 7500 to 6300 cal bp with pollen evidence for vegetation changes but only negligible changes detectable in other proxy records and 3 the late atlantic during the younger neolithic jungneolithikum after 6300 cal bp with human impact observed in many archives and proxy records especially in the pollen record but also in lacustrine and fluvial sediments during the whole climatic optimum natural causes such as minor shifts of temperature did not induce substantial environmental changes though some changes such as temporary droughts may have facilitated and amplified the observed human impact

the holocene palaeoenvironmental changes reflected in the multi proxy studies of lake slone sediments se poland abstract multi proxy data from the lake slone sediments se poland yielded information on the holocene changes of lake slone in a karst region changes of limnological conditions and vegetation reconstructions correspond to high resolution multi proxy records from north central europe ostracods showed several small oscillations most significant changes occurred at 12300 cal yr bp younger dryas preboreal transition and between 11800 and 11100 cal yr bp preboreal oscillation lowering of the water table at around 11100 10800 cal yr bp was probably connected with abrupt warming at ca 11000 cal bp temperature and water depth fell at about 8400 8100 cal yr bp 8200 cal yr bp the atlantic period was generally warm and is divided into two parts an older one with comparatively stable water level and a second one between 7000 and 6300 cal yr bp with two phases of higher water level separated by lowering at 6800 cal yr bp at the transition from the atlantic to the subboreal 6200 5950 cal yr bp the dry period is more pronounced than changes in the second half of the atlantic since the beginning of the subboreal an increase in human activity in central europe was the main factor shaping the landscape and changing the limnic regimes

pollen based quantitative reconstructions of holocene climate variability in nw romania abstract a modern analogue technique is applied to two high resolution pollen sequences from nw romania to provide the first quantitative evidence for winter summer and annual temperatures and for precipitation across the holocene in this region the pollen based climate reconstructions allow the identification of four main intervals i an early less stable period between 11 700 and 11 200 cal yr bp ii generally stable conditions between 11 200 and 8300 cal yr bp with winter and annual temperatures and precipitation higher than at present and summer temperatures about the same iii lower winter and annual temperatures and higher summer temperatures and precipitation between 8000 and 2400 cal yr bp iv warmer winter and annual temperatures and lower precipitation for the last 2400 years whereas summer temperatures became cooler at steregoiu and remained stable at preluca tiganului the pollen based climate reconstructions at the two sites show similar patterns in annual and winter temperatures and precipitation changes during the holocene but the trends appear to be less consistent for summer temperatures our pollen based reconstructions revealed several short term climatic oscillations during the holocene the strongest of which occur between 10 300 10 100 8300 8000 6800 6400 5100 4900 4000 3600 and 3200 3000 cal yr bp

a mid european decadal isotope climate record from 15 500 to 5000 years b p oxygen isotope ratios of precipitation delta18op inferred from deep lake ostracods from the ammersee southern germany provide a climate record with decadal resolution the record in detail shows many of the rapid climate shifts seen in central greenland ice cores between 15 000 and 5000 years before the present b p negative excursions in the estimated delta18op from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the north atlantic deviating millennial scale trends however indicate that climate gradients between europe and greenland changed systematically reflecting a gradual rearrangement of north atlantic circulation during deglaciation

contrasting patterns of hydrological changes in europe in response to holocene climate cooling phases the quantitative reconstruction of climatic parameters from pollen and lake level data obtained at saint jorioz lake annecy eastern france gives evidence for cooler and wetter conditions during the 8 2 ka cold event a comparison of these regional data with other hydrological records reconstructed in europe for the same period suggests as a working hypothesis that mid latitudes between ca 50 and 43 underwent wetter conditions in response to the cooling whereas northern and southern europe were marked by drier climate in the latter case leading to an interruption of the sapropel 1 formation in the mediterranean a similar hydrological tri partition of europe can be observed during other holocene cooling phases associated with north atlantic ird events data indicate that the middle zone characterised by wetter climate conditions could have had a more extended latitudinal amplitude during phases of climate cooling weaker than the 8 2 ka event the differences in expansion of the wet mid european zone depending on holocene climate cooling phases could reflect variations in the strength of the atlantic westerly jet in relation with the thermal gradient between high and low latitudes

the preboreal climate reversal and a subsequent solar forced climate shift accurate chronologies are essential for linking palaeoclimate archives carbon 14 wiggle match dating was used to produce an accurate chronology for part of an early holocene peat sequence from the borchert the netherlands following the younger dryas preboreal transition two climatic shifts could be inferred around 11 400 cal yr bp the expansion of birch betula forest was interrupted by a dry continental phase with dominantly open grassland vegetation coeval with the pbo preboreal oscillation as observed in the grip ice core at 11 250 cal yr bp a sudden shift to a humid climate occurred this second change appears to be contemporaneous with i a sharp increase of atmospheric c 14 ii a temporary decline of atmospheric co2 and iii an increase in the grip be 10 flux the close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity which may have forced the changes in climate and vegetation at around 11 250 cal yr bp copyright c 2004 john wiley sons ltd

rich fen development in ce europe resilience to climate change and human impact over the last ca 3500 years here for the first time in se poland we document the long term development of a rich fen and assess its sensitivity to climate change and human impacts over the last ca 3500 years our results are based on a high resolution continuous plant macrofossil remains mollusc and pollen record complemented by geochemical mineral magnetic and physical characterisation and radiocarbon dating from bagno serebryskie rich fen located in se poland based on the palaeoecological data we distinguished five stages of wet habitat conditions 5000 3300 2800 2150 1600 1100 750 230 150 10 cal yr bp and five dry periods at ca 3300 2800 2150 1600 1100 750 230 150 10 to 64 cal yr bp the pollen and geochemistry records particularly pb show that the first human activity in the study area occurred ca 3200 cal yr bp and increased markedly from 500 cal yr bp affecting local plant development including the population size of cladium mariscus our study has shown that despite human impact drainage fire bagno serebryskie peatland has hosted rare presently protected species such as cladium mariscus for hundreds of years we conclude that in common with ombrotrophic bogs rich fen ecosystems can provide a reliable source of palaeoclimatic and palaeohydrological data our study also shows that a large peatland 376 ha can be as sensitive a palaeohydrological archive as smaller mires

changes to the environment of intramontane basins in the light of malacological research of calcareous tufa podhale basin carpathians southern poland the profiles of calcareous tufa occurring in the podhale basin carpathians southern poland were subject to a detailed malacological analysis studies were carried out in 15 sites five of them represent the period of the late glacial and holocene and the remainder is tufa deposited during historical times on the basis of malacological analysis 10 faunistic assemblages were defined each developed under specific environmental and climatic conditions the observed sequences of molluscan assemblages in vertical profiles were the basis for paleoenvironmental reconstruction determining the main phases of climatic changes and the human impact on the natural environment the faunal sequence observed indicates a cold climate and the predominance of open habitats in the late glacial with progressing warming and the increasing significance of shaded habitats in the early and middle holocene as well as anthropogenic pressure in modern times the results of malacological analysis were complemented with determination of the age of deposits by radiocarbon dating and the results of palynological analyses conducted in the sites of peatbogs occurring in podhale the reconstruction indicates similarities and differences in the paleogeographic development of mountain and upland areas of central europe

holocene climatic events linked to environmental changes at lake komořany basin czech republic former lake komo any located in northwest bohemia in central europe provides multiple proxies pollen plant macrofossils diatoms chironomids and sediment chemistry that allowed reconstruction of the development of its aquatic environment and catchment throughout the holocene in order to reconstruct the climatic forcing of this development we performed a pollen based reconstruction of climate changes using the best modern analogue method the climate reconstruction was successful for the interval of 10 0 3 2 ka bp we demonstrate that shifts in climate were coupled with biotic changes within the lacustrine environment both processes were interconnected mainly through changes in the water level status of the lake the most significant climatic and environmental changes were recorded at 9 1 6 3 4 8 4 7 3 8 and 3 5 ka bp

behavioural asymmetry in devonian trilobites abstract the cephalon of the trilobite phacopidae was usually separated from the thorax during moulting and abandoned near the trunk we statistically evaluated the distribution pattern of the cephala of omegops cornelius and found that near 70 of the total cephala were displaced on the right side from the upper devonian deposits of the western junggar in northwest china omegops cornelius might have actively pushed the cephalon to the right of its body during moulting indicating their preference to move counterclockwise this preferred movement direction manifested the behavioural asymmetry in trilobites a different type of asymmetry has been observed in phacopidae plagiolaria nandanensis from the lower devonian of guangxi in south china where about 67 of the cephala were found on the left side of the trilobite trunks so the behavioural asymmetry may be diverse or opposite in different species of trilobites and the reasons for the asymmetric moulting and movement patterns of the above two trilobites are likely related to their body structures or their living environments these new materials provide evidence for studying the origin and evolution of behavioural asymmetry

were abrupt lateglacial and early holocene climatic changes in northwest europe linked to freshwater outbursts to the north atlantic and arctic oceans during the lateglacial and early holocene abrupt millennial scale climatic variations are recorded in a wide range of high resolution proxy records from marine and terrestrial archives in nw europe our review of the evidence for these rapid climate events do not show an apparent link to possible forcing factors such as long term orbitally induced variations in solar radiation short term variations in solar activity as inferred from 14 c atmospheric carbon dioxide concentration or volcanic sulphate as recorded in the gisp2 ice core record there is however a remarkable degree of similarity with the number duration and timing of episodes of increased e ux of fresh water to the north atlantic and arctic oceans from the laurentide ice sheet and from the baltic ice lake in sw sweden these freshwater outburst events occurred when continental runoff from the laurentide ice sheet was rerouted from the mississippi river to the hudson river st lawrence river hudson strait and along the mackenzie river to the atlantic and arctic oceans and when the baltic ice lake in sw sweden drained to skagerrak periods of increased freshwater e ow to the north atlantic and arctic oceans may thus provide a mechanism to explain the abrupt and signie cant lateglacial and early holocene climate events in nw europe the idea that freshwater outbursts might drive abrupt climate events is not new but previous work may have underestimated the extent of support from proxy data and overestimated the ine uence of the laurentide ice sheet

mire development pathways and palaeoclimatic records from a full holocene peat archive at walton moss cumbria england plant macrofossil data have been used to identify the successive mire communities occupying both central and marginal locations in the walton moss peatland complex during the last 10 500 years the reconstructed pathways of mire development indicate that early holocene fen and fen carr communities were succeeded by species indicative of deep mire water tables and oligotrophic conditions the character of the fen bog transition fbt is compared with similar records of peatland development from britain and scandinavia and with independent climate data for the early holocene the pseudohochmoor of central europe is suggested as an approximate modern analogue for the dry pioneer oligotrophic mire type and alternative explanations for its presence are explored the first major increase in ombrotrophic sphagna occurred at c 7800 cal bp overlying sphagnum peats provide a continuous record of climate change inferred from fluctuations in raised mire surface wetness the proxy palaeoclimate record reconstr

4 1 5 c abrupt warming 11 270 yr ago identified from trapped air in greenland ice nitrogen and argon isotopes in air trapped in a greenland ice core gisp2 show two prominent peaks in the interval 11 800 10 800 b p which indicate two large abrupt warming events the first abrupt warming 10 4 c is the widely documented event at the end of the younger dryas here we report on the second abrupt warming 4 1 5 c which occurred at the end of a short lived cooler interval known as the preboreal oscillation 11 270 30 b p a rapid snow accumulation increase suggests that the climatic transition may have occurred within a few years the character of the preboreal oscillation and the subsequent abrupt warming is similar to the dansgaard oeschger d o events in the last glacial period suggestive of a common mechanism but different from another large climate change at 8 200 b p in which cooling was abrupt but subsequent warming was gradual the large abrupt warming at 11 270 b p may be considered to be the final d o event prior to the arrival of the present stable and warm epoch

correlation and synchronisation of lateglacial continental sequences in northern central europe based on annually laminated lacustrine sediments abstract the present study focusses on correlation and synchronisation of weichselian lateglacial varved lake sediments from western germany meerfelder maar eifel region northern germany hamelsee lower saxony central poland lake go ci a z and eastern poland lake perespilno by using varve chronology tephrochronology palynostratigraphy and stable isotopes comparison of the several independent time scales shows that biotic and abiotic parameters respond abruptly and quasi synchronously within the errors of the different chronologies during the younger dryas preboreal transition moreover there is a consensus about the length of the younger dryas cold stage of 1100 1150 varve years in the allerod the prominent laacher see tephra 12 880 varve years bp can be used to fix floating varve chronologies the relative duration of this biozone has been determined in meerfelder maar and hamelsee at between 625 and 670 varve years in the meerfelder maar a combination of continuous varve counting and biostratigraphy has been possible for the almost entire lateglacial the comparison between continental limnic sequences and greenland ice core records should be made on the basis of independent chronologies in both archives it is more practicable to develop regional stratotypes on the continental regions instead of simply using ice cores as stratotypes for the lateglacial for terrestrial european records in this respect annually laminated lacustrine sequences have a great potential

holocene environmental changes in northern poland recorded in alkaline spring fed fen deposits a multi proxy approach abstract spring fed fen deposits peat tufa sequences from northern poland were investigated for holocene environmental reconstruction climate and hydrology using multi proxy analysis lithofacies molluscs pollen plant macrofossils geochemistry and stable oxygen and carbon isotopes the main aims of these studies were 1 comparison of several similar sites with the same type of groundwater supply and sedimentation on a widespread space scale 2 detailed reconstruction of their long term development assessing their sensitivity to climate change 3 verification of the synchronicity of the record of different proxies in distant sites in the context of holocene climate changes in relation to specific well known global and or regional climate events so called bond events and 4 discussion on permafrost degradation as a driver of spring fed fens development based on our palaeogeographical data we have distinguished an asynchronicity of the beginning of the development of spring fed fens in the eastern and western parts of the studied region that is associated with different times of ascending groundwater supply unblocking after complete permafrost degradation therein asynchronicity of permafrost degradation was brought about by multiple climatic geological and structural conditions our results also indicate significant differences in the trends of succession ecological and lithological caused by the geographical location of the studied sites asynchronicity of the occurrence of wet and dry phases as well as significant differences in their duration were noted this depended upon the influence of oceanic western part or continental climates eastern part warm and humid oceanic climate promoted the domination and longer duration of wet phases especially in the eo and early mesoholocene while the harsh continental climate promoted the more frequent occurrence of dry phases with short episodes of increased humidity from the middle mesoholocene this marked regional diversification becomes less pronounced results also allowed for the recognition of several palaeoclimatic events on a regional scale four main cold episodes bond events 8 5 during lg h transition 11 5 ky cal bp eo 10 25 ky cal bp 9 4 ky cal bp and at the beginning of the mesoholocene 8 2 ky cal bp are well documented by multiple proxies at all study sites other cold episodes bond events 4 0 are slightly less documented and are not clear for interpretation the results of our study demonstrate the importance of spring fed fen deposits for detailed palaeoenvironmental reconstruction on a regional scale

early holocene climatic oscillations recorded by lake level fluctuations in west central europe and in central italy abstract on the basis of lake level data the period of the preboreal oscillation pbo at 11 300 11 150 cal yr bp as defined by the grip oxygen isotope record appears to correspond to wetter climatic conditions in west central europe and to a marked drying in north central italy additional short lived phases of higher lake level have been identified before the pbo at ca 11 450 11 400 and 11 350 cal yr bp in west central europe and at ca 11 500 cal yr bp in italy such multiple climatic oscillations around the pbo have been observed in various records in northwestern europe on the basis of various proxies a map of changes in moisture over western europe during the pbo indicates a mid latitude zone between 58 and 43 n characterised by wetter conditions while a drier climate developed in southern and northern europe this wet middle zone shows a larger extension and suggests a more meandering weaker atlantic westerly jet during the pbo than during the 8 2 kyr event a comparison of lake level records in west central europe with 1 outbursts from north american and north european proglacial lakes and 2 variations in solar activity as reflected by 14 c and the 10 be records supports the hypothesis that the pbo was a response to successive meltwater pulses at 11 300 11 250 11 200 and 11 170 cal yr bp and to a sudden decrease in solar activity at 11 250 cal yr bp this study points to the necessity of developing integrated multi proxy approaches to construct more robust regional event stratigraphies and of better documenting palaeohydrological changes in the mediterranean area

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

regional and local changes inferred from lacustrine organic matter deposited between the late glacial and mid holocene in the skaliska basin north eastern poland abstract the article presents the results of a combination of isotopic 15 n and 13 c geochemical toc tn c n and palaeobotanical investigations they were carried out on organic matter om that had been deposited from the younger dryas to the subboreal chronozone in palaolake sediments north eastern poland om from the late younger dryas consists only a small amount of toc and tn which together with the lack of aquatic macrophyte macrofossils confirm low primary production in the then reservoir the higher values of c n ratio 18 27 and 13 c ca 26 suggest that om was mainly terrestrial in origin during the preboreal chronozone 11 450 10 150 cal bp there was a probable deepening of the reservoir through the melting of dead ice this might have been intensified by an increase in precipitation and a fall in evapotranspiration during the preboreal oscillation from the early preboreal chronozone ca 11 345 cal bp a mixed source of om is indicated by c n ratio from 8 to 13 at the same time significant increase in toc and tn probably registered a rise in primary production in the palaeolake from the older part of the boreal chronozone ca 9865 cal bp algae productivity increased the c n ratio dropped to ca 8 and was then constant at the beginning of the atlantic chronozone ca 8650 cal bp a probable increase in the water level caused the partial relocation of om from the reed swamp belt and or the adjacent alder carr into deeper sections of the palaeolake an increase in toc and tn in the late atlantic chronozone ca 6965 6650 cal bp toc and tn decreased while 13 c had high values which probably reflected a more distinct stratification of the water column with anoxic bottom waters next in the late atlantic and early subboreal chronozone ca 6650 5205 cal bp the amount of om in palaeolake sediments was still rising the 13 c values dropped suggesting an intensification of processes of water mixing these processes were simultaneous with the constant shallowing of the palaeolake and the disappearance of habitats suitable for submerged macrophytes the topmost part of the profile is characteristic of a strong decomposition of peat causing a release of carbon dioxide and therefore the depletion of the carbon pool in the peat a drop in the c n ratio the concurrent upward trend of the 15 n curve is probably the effect of a greater anthropogenic impact on the palaeolake mire and its catchment and or more recent human interference in the topmost peat layers

distribution patterns of upper devonian phacopid trilobites paleobiogeographical and paleoenvironmental significance phacopid trilobites are relatively widespread in devonian deposits after a maximum diversity in the middle devonian most phacopids were severely affected by repeated sea level eustatic changes especially in the frasnian and it was during that time that the main groups of reduced eye or blind phacopids arose the aim of this investigation was to evaluate the distribution patterns of upper devonian phacopids at a global level through a clustering analysis in a paleogeographical and paleoenvironmental framework in order to understand their fluctuations in time and space the phacopid biodiversity is represented in this study by 22 taxa from the frasnian to the late famennian additionally four main time intervals frasnian i famennian post i famennian ii iii and famennian iv vi have been explored to complete the clustering analysis two ordering methods i e a seriation routine and a detrended correspondence analysis have been performed respectively to reveal chronological sequences and to identify indirect paleoenvironmental gradients analyses enabled us to establish 1 bathymetrical gradients showing some taxa such as omegops restricted to shallower environments and other taxa such as ductina or dianops to deeper environments and 2 paleobiogeographical affinities showing exchanges along the margins of north gondwana and avalonia baltica and probable connections along the margin of north east gondwana after the major mid givetian taghanic transgression

july mean temperature and annual precipitation trends during the holocene in the fennoscandian tree line area pollen based climate reconstructions july mean temperature and annual precipipation during the last 9900 cal yr bp were recon structed from pollen assemblages preserved in a sediment core from northern finland quantitative recon structions were performed using a modern pollen climate calibration model based on weighted averaging partial least squares regression the predictive ability of the model was evaluated against modern meteoro logical data using leave one out cross validation the prediction error for july mean temperature is c 1 0 c and for annual precipitation 340 mm the july mean temperatures during the earliest holocene were low c 1 1 0 c and annual precipitation was high c 600 800 mm between 8200 and 6700 cal yr bp july mean temperatures reached their maxima 12 5 13 0 c which are c 1 4 1 7 c higher than at present at the same time precipitation decreased during the late holocene july mean temperatures declined and the last 2000 years have been the coolest since the early holocene precipitation has slightly increased the spatial coherence between our results and of several other climate reconstructions from northern europe indicates that the holocene climate was strongly influenced by north atlantic oceanic and atmospheric circulation patterns we propose that the distinctly oceanic climate of the early holocene was due to enhanced westerly latitudinal airflow which was replaced at c 8200 cal yr bp by a more meridional flow pattern and by the development of predominantly anticyclonic summer conditions

vegetation responses to the 8200 cal bp cold event and to long term climatic changes in the eastern alps possible influence of solar activity and north atlantic freshwater pulses subfossil pollen from two bogs in temperature sensitive high altitude regions were analysed in order to reconstruct early to mid holocene summer temperature fluctuations in the eastern alps the p

a chironomid based holocene summer air temperature reconstruction from the swiss alps we developed a quantitative chironomid july air temperature inference model based on surface sediments from 81 swiss lakes and applied it to the holocene subfossil chironomid record of hinterburgsee a small subalpine lake in the northern swiss alps present day mean july air temperature of 11 3 c after smoothing to reduce the high between sample variability of inferred temperatures the reconstruction indicates july air temperatures of 10 4 10 9 c at the end of the younger dryas of 11 9 12 8 c during the early and mid holocene 11500 4000 cal bp and slightly lower temperatures of 11 5 12 0 c during the late holocene 3500 1000 cal bp a warming trend inferred for the past millennium is most likely an artifact of human impact on hinterburgsee s chironomid fauna rather than a genuine temperature signal the most prominent climatological events during the holocene were two periods of lower temperatures at c 10700 10500 cal bp and 8200 7700 cal bp and an abrupt shift to a cooler late holocene cl

mountain erosion over 10 yr 10 k y and 10 m y time scales we used cosmogenic 10 be to measure erosion rates over 10 k y time scales at 32 idaho mountain catchments ranging from small experimental watersheds 0 2 km 2 t o large river basins 35 000 km 2 these long term sediment yields are on average 17 times higher than stream sediment fluxes measured over 10 84 yr but are consistent with 10 m y erosion rates measured by apatite fission tracks our results imply that conventional sediment yield measurements even those made over decades can greatly underestimate long term average rates of sediment delivery and thus overestimate the life spans of engineered reservoirs our observations also suggest that sediment delivery from mountainous terrain is extremely episodic sporadically subjecting mountain stream ecosystems to extensive disturbance

weathering of granites in a temperate climate nw portugal granitic saprolites and arenization abstract saprolites or in situ weathering products from granitoid rocks of northwest portugal were studied by means of x ray diffraction xrd of their clay fraction and observations of polished thin sections combined with transmission electron microscopy tem scanning electron microscopy with energy dispersive spectrometer sem eds microanalyses their principal features are 1 depths of more than 10 m 2 mean material loss of 40 as calculated by an isovolumetric method 3 low clay content mean value of 7 and a high degree of mineralogical evolution the clay fraction is characterized by a predominance of kaolinite and gibbsite with subordinate 2 1 minerals illite chlorite vermiculitic mixed layers vermiculite the significance of the secondary minerals in granitic saprolites from northwest portugal is compared to published data from atlantic europe this allows the definition of a climatic zonality for weathering products and identifies arenization as an important weathering process

geomorphic inferences from regolith thickness chemical denudation and crn erosion rates near the glacial limit boulder creek catchment and vicinity colorado granitic regolith developed in the boulder creek catchment and adjacent areas records a history of deep weathering some of which may predate quaternary time field and well log measurements of weathering chemical denudation and rates of erosion derived from 10be cosmogenic radionuclide crn data help to quantify rates of landscape change in the post orogenic rocky mountains the density of oxidized fractured bedrock ranges from 2 7 to about 2 2 g cm 3 saprolite and grus have densities between 2 0 and 1 8 g cm 3 and 30 soil samples averaged 1 6 0 2 g cm 3 highly weathered regolith in 540 wells averages 3 3 m thick mean depth to bedrock in 1661 wells is 7 m and the weathered thickness exceeds 10 m in relatively large local areas east of the late pleistocene glacial limit thickness of regolith shows no simple relationship to rock type or structure local slope or distance from channels catchments in the vicinity of the boulder creek have an average crn erosion rate of 2 2 0 7 cm kyr 1 for the past 10 000 to 40 000 yr annual losses of cations and sio2 vary from about 2 to 5 g m 2 over a runoff range of 10 to nearly 160 cm using measured rates in simple box models shows that if a substantial fraction of void space is created by volume expansion in the weathering rock materials 7 m of weathered rock materials could form in as little as 230 kyr if density loss results mainly from chemical denudation and some volume expansion however the same weathering profile would take 1340 kyr to form rates of erosion measured by crn could be balanced by the rate of soil formation from saprolite if the annual solute loss from soil is 2 0 g m 2 and 70 of the density decrease from saprolite to grus and soil results from strain saprolite however forms from oxidized bedrock at a far slower rate and rates of saprolite formation cannot balance soil and grus losses to erosion the zone of thick weathered regolith is likely an eroding relict landscape the undulating surface marked by relatively low relief and tors is not literally a topographic surface of eocene oligocene or miocene age unless it was covered with deposits that were removed in pliocene or quaternary time

tunneling trilobites habitual infaunalism in an ordovician carbonate seafloor asaphus trilobites preserved in tunnel systems of the trace fossil thalassinoides from the mid ordovician ca 465 ma holen limestone sweden are interpreted as the trace makers enabled by shallow carbonate firm grounds to construct open tunnel networks and develop habitual infaunal behavior their in situ preservation confirms an infaunal ethology inferred for some trilobite taxa from functional morphology we suggest that predation pressure from large omnivorous nautiloid cephalopods orthoceras limestone facies may have triggered ecologic opportunism in trilobites well adapted for predatory scavenging behavior as well as excavation the tunnel networks functioned primarily for protection possibly assisting in feeding breathing and breeding strategies previously trilobite burrows have referred to seafloor traces of locomotion feeding and resting cruziana rusophycus infaunal tunneling trilobites provide new evidence of mid ordovician partitioning of the skeletal benthos adding to an ecologic and trophic tier hitherto interpreted as occupied by soft bodied organisms such trilobites also provide an identity for thalassinoides tracemakers prior to devonian evolution of decapod crustaceans

ichnological and sedimentological features of the hongguleleng formation devonian carboniferous transition from the western junggar nw china abstract two sections of the late devonian to early carboniferous hongguleleng formation in the sha erbuerti and xiemisitai mountains of western junggar nw china were logged in detail and studied with particular reference to their trace fossil content and sedimentary features the hongguleleng formation is composed essentially of shallow marine deposits formed in a volcanic arc related setting it contains trace fossils including indeterminate ellipsoid structures indeterminate shallow pit structures chondrites intricatus chondrites targionii chondrites isp dolopichnus gulosus multina isp nereites missouriensis nereites isp palaeophycus tubularis phycosiphon isp phymatoderma isp rhizocorallium commune rosselia cf socialis teichichnus rectus teichichnus ispp thalassinoides isp and zoophycos ispp these ichnofossils and related bioturbation structures constitute five distinct groups of ichnofabrics chondrites phymatoderma rhizocorallium commune anemone dwelling burrowing teichichnus and zoophycos ichnofabrics conforming to an upward trend from the cruziana to zoophycos ichnofacies the volcanic arc setting provides a natural laboratory to investigate the colonisation styles of benthic faunas during the devonian especially for environments with widespread and relatively frequent depositional events disturbing background deposition the distal event beds are especially suitable for the distinction of the relationship between background and post event ichnofaunas simple and composite ichnofabrics have been distinguished the simple ichnofabrics are typified by the indeterminate ellipsoid ichnofabric made by sea anemones representing short colonisation event and in situ death and burial resulted from relatively high sedimentation rates even during the periods between volcanic explosions the composite ichnofabrics are characterised by the chondrites phymatoderma multina zoophycos and multi tier zoophycos ichnofabrics representing vertical migration of benthic faunas in pace with either distal event deposition or steadily accreted sea floor the colonisation window in the arc related setting is closely related to sedimentation rates and frequency of depositional events determining the completeness of burrow system structure and maturity of benthic communities

reaction of the lake environment to the holocene warming depending on the distance to the maximum extent of the vistulian ice sheet abstract this study presents 1 the results of a stable isotope and subfossil cladocera analyses of lacustrine sediments from maliszewskie lake e poland and next 2 different reaction of the lake environments depending on the lake s localization maliszewskie lake is located in north podlasie lowland ca 30 km to the south of the vistulian ice sheet limit the approximately 4 80 m thick sediments maliszewo i profile are mainly comprised of calcareous gyttja covered by peat and organic detritus gyttja pollen analysis documents that the sediments accumulated from the late glacial allerod period to recent times based on the results of stable isotope and subfossil cladocera analyses of sediments the lake environmental changes were reconstructed a positive trend in 18o and 13c values documents a gradual climatic warming the fluctuations of the oxygen isotopic values suggest the multiple oscillation of water level due to a change in the evaporation precipitation ratio the subfossil cladoceran fauna in the maliszewo i profile is represented by 21 species belonging to five families three zones of cladocera development were distinguished the cladocera species indicate the initial oligotrophic status of the lake and its subsequent increase of trophic status currently maliszewskie lake is a very shallow declining reservoir the initial period of its existence probably saw its maximal depth in presented studies we compared our results with data from three other sites documenting the reaction of the lake environment during the late glacial and holocene transformation at that time we observed different reactions to the climate amelioration in the northern postglacial lakes the holocene warming at first provoked an input cold melting water characterized by more negative oxygen isotope values and then a rise in water temperature in the lakes further away from the glaciation border periglacial lakes the increase in water temperature documented by e g more positive oxygen isotopic immediately occurred the climate warming is commonly manifested by a significant increase of number of species and individuals of cladocera

preboreal climate oscillations in europe wiggle match dating and synthesis of dutch high resolution multi proxy records abstract in order to compare environmental and inferred climatic change during the preboreal in the netherlands five terrestrial records were analysed detailed multi proxy analyses including microfossils e g pollen spores algae and fungal spores macroremains e g seeds fruits wood mosses etc and loss on ignition measurements were carried out with high temporal resolution to link the five preboreal records accurate chronologies were produced by ams 14c wiggle match dating the dutch records show that following the lateglacial holocene climate warming birch woodlands expanded between 11 530 and 11 500 cal bp during the friesland phase of the preboreal after the friesland phase two distinct climatic shifts could be inferred 1 around 11 430 11 350 cal bp the expansion of birch forests was interrupted by a dry continental phase with open grassland vegetation the rammelbeek phase this phase was coeval with the coldest part of the preboreal oscillation pbo as observed in the 18o record of the greenland ice core records and has been attributed to a large meltwater flux that resulted in a temporary decrease of the thermohaline circulation in the north atlantic 2 at the start of the late preboreal between 11 270 and 11 210 cal bp a sudden shift to a more humid climate occurred and birch forests expanded again a simultaneous increase in the cosmogenic nuclides 14c and 10be suggests that these changes in climate and vegetation were forced by a sudden decline in solar activity expansion of pine occurred during the later part of the late preboreal at the onset of the boreal between 10 770 and 10 700 cal bp dense woodlands with hazel oak elm and pine started to develop in the netherlands

strontium 87 strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine subalpine watershed loch vale colorado sr isotopic ratios of atmospheric deposition surface and subsurface water and geologic materials were measured in an alpine subalpine watershed to characterize weathering reactions and identify sources of dissolved ca in stream water previous studies have noted an excess of ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals mixing calculations based on 87 sr 86 sr indicate that on an annual basis 26 67 of ca export in streams is atmospherically derived 23 61 is from weathering of plagioclase and the remainder is from weathering of calcite present in trace amounts in the bedrock a potential source of error when applying sr isotopes in catchment studies is determination of the 87 sr 86 sr of sr released by mineral weathering which is complicated by the wide range of mineral isotopic compositions particularly in older rocks and the variable rates at which the minerals weather in this study base flow stream chemistry was used to represent the 87 sr 86 sr of sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of sr released by weathering in the alpine environment

lateglacial and early holocene environmental changes in northeastern lithuania abstract multiproxy data pollen diatoms plant macrofossils 14c and loss on ignition measurements obtained from two cores petrasi nai and juodonys were used to reconstruct the pattern of lateglacial and early holocene environmental changes in ne lithuania the flourishing of open pinus forest and presence of light demanding taxa on poor unstable soils surrounding shallow water basins have been recorded from about 13 100 13 000 cal bp to 12 600 cal bp in the study area after 13 000 cal bp expansion of betula dominated vegetation and increased abundance of cold tolerant plants together with a simultaneous drop of water temperature indicates a short climate deterioration tentatively correlated with the gerzensee oscillation a sudden reduction of the forest cover and extensive development of grass herb dominated landscape is suggestive of a regional expression of the younger dryas cooling dated to 12 600 11 500 cal bp climate aridification resulted in a progressive lowering of the water level and subsequent overgrowth of the basins early holocene vegetation changes show a pattern of forest development with dominance of spruce shortly after 11 500 cal bp based on palynological evidence and the presence of plant macrofossils seeds and needles early holocene immigration of picea sp to juodonys 9410 310 bp vs 1433 and petrasi nai 9420 65 bp tua 6177 df2471 is indicated further development of the vegetation cover indicates multiple flourishing of predominant open birch vegetation subsequently followed by pine spruce forest development caused by preboreal climate instability the most prominent climate shift e g drop of the temperature and humidity recorded shortly before 11 100 cal bp has been correlated with the preboreal oscillation bjorck s rundgren m ingolfsson o funder s 1997 the preboreal oscillation around the nordic seas terrestrial and lacustrine responces journal of quaternary science 12 455 465 expansion of birch predominant forest around shallow water basins has been identified during the late preboreal after 11 100 cal bp

early oligocene paleovalleys in southern and central wyoming evidence of high local relief on the late eocene unconformity local relief in the mountains of southern and central wyoming at the end of the eocene was as great as if not greater than it is today this is indicated by large valleys containing the lower oligocene white river formation that extend into the precambrian cores of the medicine bow and laramie mountains there has been little deformation of white river rocks in the valleys or on the margins of the mountain ranges precluding post eocene block uplift as a source of modern topographic relief the regionally widespread low relief subsummit surface was developed during the miocene and is not part of the late eocene unconformity other oligocene valley fils in the rocky mountains indicate that high local relief was widespread during the late eocene

early holocene hydrology and environments of the ner river poland abstract the ner river valley central poland underwent substantial transformation during the weichselian holocene transition as a result of fluvial processes and climate changes resulting in the establishment of its present shape in the holocene a multiproxy study based on organic deposits from a palaeochannel fill lutomiersk koziowki shows that after the channel was cut off during the late glacial termination it became a shallow oxbow fed by local springs in the boreal period the oxbow lake was also fed by precipitation and became a telmatic environment overgrown by rush and swamp vegetation finally it was covered by overbank deposits the first flooding phase 9900 9600 cal bp was followed by the accumulation of overbank sediments after 9500 cal bp and flooding increased after ca 9300 9000 cal bp pollen data provide information on the regional vegetation context for local and regional changes in the atlantic period an increase in both summer and winter temperatures is inferred from the pollen data corresponding to an expansion of thermophilous deciduous forests while in general flooding phases of the early holocene are poorly recognised in eastern europe the lutomiersk koziowki site may be considered as one of the reference points for this phenomenon in the region

the temperature of europe during the holocene reconstructed from pollen data we present the first area average time series reconstructions of warmest month coldest month and mean annual surface air temperatures across europe during the last 12 000 years these series are based on quantitative pollen climate reconstructions from over 500 pollen sites assimilated using an innovative four dimensional gridding procedure this approach combines three dimensional spatial gridding with a fourth dimension represented by time allowing data from irregular time series to be focussed onto a regular time step we provide six regional reconstructed temperature time series as well as summary time series for the whole of europe the results suggest major spatial and seasonal differences in holocene temperature trends within a remarkably balanced regional and annual energy budget the traditional mid holocene thermal maximum is observed only over northern europe and principally during the summer this warming was balanced by a mid holocene cooling over southern europe whilst central europe occupied an intermediary position changes in annual mean temperatures for europe as a whole suggest an almost linear increase in thermal budget up to 7800 bp followed by stable conditions for the remainder of the holocene this early holocene warming and later equilibrium has been mainly modulated by increasing winter temperatures in the west which have continued to rise at a progressively decreasing rate up to the present day

strong tectonic and weak climatic control of long term chemical weathering rates the relationships among climate physical erosion and chemical weathering have remained uncertain because long term chemical weathering rates have been difficult to measure here we show that long term chemical weathering rates can be measured by combining physical erosion rates inferred from cosmogenic nuclides with dissolution losses inferred from the rock to soil enrichment of insoluble elements we used this method to measure chemical weathering rates across 22 mountainous granitic catchments that span a wide range of erosion rates and climates chemical weathering rates correlate strongly with physical erosion rates but only weakly with climate implying that by regulating erosion rates tectonic uplift may significantly accelerate chemical weathering rates in granitic landscapes

purujosa trilobite assemblage and the evolution of trilobite enrollment localities bearing abundant enrolled cambrian trilobites are extremely rare but here we report a new and exceptional such assemblage with a high diversity of enrolled specimens from the middle cambrian of spain this novel find demonstrates that encapsulated enrollment was a behavioral response available to many of the early benthic trilobite morpho types this result provides a new perspective for reviewing the evolution of trilobite enrollment through the paleozoic we find a significant and consistent increase in the proportion of enrolled trilobites within assemblages bearing abundant articulated trilobites similarly the mean number of coaptative devices also increased progressively during the paleozoic such devices likely provided later enrolled trilobites with greater structural integrity and may support an escalatory model of trilobite defense evolution likewise environmental circumstances favoring the preservation of enrolled trilobites may have become more common during post cambrian time

high resolution stable isotope records from southwest sweden the drainage of the baltic ice lake and younger dryas ice margin oscillations benthic foraminifera in two shallow marine sediment cores from southwest sweden were analyzed for oxygen isotopes several deglaciation events previously recognized in terrestrial and lake sediments throughout the baltic region are identified and radiocarbon dated an initial baltic ice lake bil drainage at the mount billingen threshold is inferred from a distinct 2 4 18o oscillation in one of the investigated cores the estimated radiocarbon age for this event is approximately 10 900 14c years the final drainage which ended bil history occurred in two steps during the younger part of the radiocarbon plateau at 10 000 14c years biostratigraphy suggests that the final drainage took place in the climatically warm early preboreal at approximately 11 150 14c years the deglacial trend toward lighter isotopic composition was interrupted and slightly reversed and is interpreted to represent the onset of the cold younger dryas period for a few hundred years prior to the younger dryas melting of the fennoscandian ice sheet appears to have been rapid besides the dramatic drainage events and reduced melting during the younger dryas the records display several other salinity variations these variations may reflect ice margin oscillations during the younger dryas previously identified throughout scandinavia as ice marginal deposits the isotopic records suggest approximately 10 climatically induced ice margin recession readvances of the southeastern fennoscandian ice sheet during the younger dryas

environmental changes related to the 8 2 ka event and other climate fluctuations during the middle holocene evidence from two dystrophic lakes in ne poland multi proxy palaeoecological data pollen diatom cladocera about the environment during the middle holocene from suchar ii and suchar wielki dystrophic lakes in ne poland are presented fluctuations in the pollen concentration indicative of changes in pollen productivity and shifts in woodland composition document the considerable instability of the climate in ne poland between 9200 and 5750 cal yr bp the recognised colder events were dated to ca 9050 8950 8700 7800 7600 7250 7100 6600 and 6050 5900 cal yr bp all these coolings are expressed as decreases in the pollen concentration of thermophilous taxa such as corylus avellana ulmus quercus tilia cordata t and fraxinus exelsior the most pronounced was the second of these cold climatic anomalies which lasted about nine centuries and can be equated with the 8 2 ka event significant cooling at that time is confirmed by the appearance of cold water species of cladocerans and diatoms

integrating soils and geomorphology in mountains an example from the front range of colorado soil distribution in high mountains reflects the impact of several soil forming factors soil geomorphologists use key pedological properties to estimate ages of quaternary deposits of various depositional environments estimate long term stability and instability of landscapes and make inferences on past climatic change once the influence of the soil forming factors is known soils can be used to help interpret some aspects of landscape evolution that otherwise might go undetected the front range of colorado rises from the plains of the colorado piedmont at about 1700 m past a widespread dissected tertiary erosion surface between 2300 and 2800 m up to an alpine continental divide at 3600 to over 4000 m pleistocene valley glaciers reached the western edge of the erosion surface parent rocks are broadly uniform granitic and gneissic climate varies from 46 cm mean annual precipitation map and 11 jc mean annual temperature mat in the plains to 102 cm and 4 jc respectively near the range crest vegetation follows climate with grassland in the plains forest in the mountains and tundra above 3450 m soils reflect the bioclimatic transect from plains to divide a bw or bt bk or k grassland to a e bw or bt c forest to a bw c tundra corresponding soil ph values decrease from 8 to less than 5 with increasing elevation the pedogenic clay minerals dominant in each major vegetation zone are smectite grassland vermiculite forest and 1 0 1 8 nm mixed layer clays tundra within the lower forested zone the topographic factor aspect results in more leached colder soils with relatively thin o horizons well expressed e horizons and bt horizons alfisols on n facing slopes whereas soils with thicker a horizons less developed or no e horizons and bw or bt horizons mollisols are more common on s facing slopes the topographic factor in the tundra results in soil patterns as a consequence of wind redistributed snow and the amount of time it lingers on the landscape an important parent material factor is airborne dust which results in fine grained surface horizons and if infiltrated contributes to clay accumulation in some bt horizons the time factor is evaluated by soil chronosequence studies of quaternary deposits in tundra upper forest and plains grassland few soils in the study area are 10 000 years old in the tundra 100 000 years old in the forest and 2 million years old in the grassland stages of granite weathering vary with distance from the continental divide and the best developed is grus near the sedimentary granitic rock contact just west of the mountain front grus takes a minimum of 100 000 years to form

quantitative reconstruction of younger dryas to mid holocene paleoclimates at le locle swiss jura using pollen and lake level data abstract pollen and lake level data from le locle in the swiss jura were used to quantitatively reconstruct climatic parameters for the younger dryas event and the first half of the holocene period the younger dryas cold event at le locle was characterized by i a general trend toward a slight increase in summer temperature and a decrease in annual precipitation and ii a marked drying phase at ca 11 900 cal yr b p that occurred between two wetter ones further phases of major deficit in moisture occured at ca 11 500 cal yr b p younger dryas holocene transition 10 800 cal yr b p 8700 cal yr b p and 6500 cal yr b p climatic parameters reconstructed here suggest that phases of higher lake level developing at ca 12 500 12 000 11 750 11 600 11 200 10 900 synchronous with the preboreal oscillation 10 400 8900 8400 8300 possibly related to the 8200 yr event and 7800 7000 cal yr b p coincided with an increase in annual precipitation a decrease in summer temperature and a shorter growing season conversely periods of low lake level corresponded to a decrease in annual precipitation an increase in summer temperature and a longer growing season this general pattern could have resulted from alternate southward northward displacements of the atlantic westerly jet

26al and10be dating of late pleistocene and holocene fill terraces a record of fluvial deposition and incision colorado front range cosmogenic 26al 10be and 14c dating of fluvial fill terraces in steep canyons of the colorado front range provides a temporal framework for analysing episodic aggradation and incision results from boulder canyon show that terrace heights above the modern channel grade can be divided into 1 bull lake 100 ka 20 15 m above grade 2 pinedale 32 10 ka 15 4 m above grade and 3 holocene age 15 m above grade record bull lake deposition well preserved terraces of pinedale age suggest that the range of terrace height above grade reflects short term fluctuations in the river profile during periods of rapidly changing stream load and power net river incision apparently occurred during transitions to interglacial periods soil development and stratigraphic position along with limited cosmogenic and 14c dating suggest that 130 ka terraces in boulder canyon correlate with the louviers alluvium and that 32 to 10 ka fills in the canyon correlate with the broadway alluvium on the adjacent high plains late pleistocene incision rates 0 15 m ka 1 along boulder canyon exceed pre late pleistocene incision rates and are higher than middle to late pleistocene incision rates 0 04 m ka 1 on the high plains this study provides an example of how modern geochronologic techniques allow us to understand better rivers that drain glaciated catchments copyright 2002 john wiley sons ltd

past hydrological events reflected in holocene history of polish rivers abstract a database of 335 radiocarbon dates from holocene fluvial sediments in poland has been compiled each sample is characterized by 25 parameters all samples were grouped into one of 7 regions characterized by hydrological regime and one of 8 depositional environments statistical analysis was used to enhance the palaeoenvironmental data and 17 phases may be distinguished 10 of which have a distinct sharp peak abandoned paleochannels 149 dates clearly reflect the major wetter phases of the holocene an opposite picture is presented by overbank aggradation 86 dates connected mainly with expansion of agriculture preliminary correlations are made on peat bog records changes in vegetation lake water level rates calcareous tufa and speleothems growth landslides phases and debris flow phases these show many convergences explained by climatic fluctuations during the holocene

possible courtship behaviour of devonian fish evidence from large radial trace fossils in northwestern china abstract one kind of mysterious underwater circle observed on the seafloor near southern amami oshima island in subtropical japan has attracted widespread attention but its origin has long been unknown in recent years based on successive underwater photography they were shown to represent the patterned structures constructed by male pufferfishes here we present a large radial trace fossil from the upper devonian hongguleleng formation in western junggar xinjiang northwestern china they are circular or near circular patterned structures consisting of numerous radial grooves and ridges based on morphological analysis of these specimens and comparison with the modern patterned structures made by pufferfish for courtship we suggest that this trace fossil may be patterned structure made by male fish in the devonian to attract females if true these structures would be the first reported example of courtship behaviour in the trace fossils of fish and suggest that animal courtship behaviour has existed for at least 360 million years these trace fossils provide new material for research on the breeding strategies and sexual selection of devonian animals and new insight on the origin and evolution of courtship behaviour