kaikoura canyon new zealand active conduit from near shore sediment zones to trench axis channel kaikoura canyon is one of a few major active conduits between a near shore sediment transport system and a deep ocean channel it is the sink for mobile zones of gravel sand and mud that migrate northwards off northeastern south island new zealand it is presently the primary source for the 1500 km long hikurangi channel which supplies overbank turbidites to a filled trench an ocean plateau basin and a distal fan drift swath data seismic profiles side scan sonographs aerial photographs cores grab samples and current meter data are used to define the shape and texture of the canyon and adjacent shelf in order to better understand how coastal processes and canyon interact to supply sediment to the deep ocean kaikoura canyon is 60 km long up to 1200 m deep and generally u shaped in profile its head is within 500 m of the shore and within 200 m of rocky projections from the shore platform in a mountain backed bay without large rivers the canyon head incises the 18 m depth contour and boulders pebble gravel and megarippled coarse sand reach the canyon rim fine sand migrating northward along the shelf under the influence of waves and currents is trapped in a southward projecting canyon head gully which incises the thickest part of the holocene sediment prism it is estimated that about 1 5 106 m3 of sediment falls into the canyon head each year tensional fractures around the canyon rim suggest that sediments in the canyon head gully are unstable gravel turbidites with post last glacial age shells are at or near the seabed in the lower canyon but are blanketed by many thin silt and sand possibly storm generated turbidites in the upper canyon the top gravel contains a twig that is about 170 years old suggesting that the last major collapse in the canyon head coincides with many onshore rockfalls triggered by rupture of a major strike slip plate boundary fault in about 1833 an underlying gravel is about 300 years old and may again coincide with fault rupture most of the large earthquake triggered failures may ignite to form self perpetuating autosuspension flows that feed a 1500 km long deep sea turbidite channel

channel axis overbank and drift sediment waves in the southern hikurangi trough new zealand abstract in the southern apex of the hikurangi trough east of new zealand swath bathymetry and backscatter seismic profiles and cores from the proximal part of the 2000 km long hikurangi channel show different types of sediment waves in the channel axis and on the levee backslopes these represent different responses to large turbidity currents locally backslope sediment waves merge into sediment waves formed by a deep geostrophic flow in the channel axis and on channel walls sediment waves that have wavelengths of 1 4 km and heights of less than 6 m occur where cores show gravelly and coarse sandy turbidites they are not apparent in layering below the channel axis they are inferred to be thin transitory surface sand bodies migrating across coarser substrates and may have formed in a recent perhaps the last turbidity current their geometry suggests that they probably formed as antidunes in high velocity flows that were much thicker than the channel depth overbank sediment waves also have similar wavelengths of 1 4 km but heights of up to 45 m they have conspicuous sub seabed layering to a depth of at least 400 m beneath the seabed seismic stratigraphy indicates that they have developed for most of the last 2 ma during near vertical aggradation of the channel its levees and overbank slopes at average rates of 0 4 0 7 m ka the sediment waves migrate up levee backslopes towards the levee crest at rates of 3 20 m ka and are inferred to be formed beneath lee waves initiated in overbank flows by the linear perturbation of the levee they are best developed on the outsides of bends where centrifugal outflow of upper overspill parts of large turbidity currents might be concentrated they are particularly well developed at right hand bends on the left bank where centrifugal and southern hemisphere coriolis effects combine poorly developed sediment waves on the inside of some left hand bends may be the result of coriolis effects only overbank sediment waves decrease in height and wavelength away from the channel and continue into a depression along the slope toe deformation front at the landward edge of the turbidite plain where the channel intersects the slope toe depression the absence of a left bank levee suggests that overbank flows re enter the channel along the toe of the chatham rise sediment waves up to 5 m high and 2 5 km in wavelength migrate away from the channel and towards a slope toe moat they are inferred to be part of a drift deposit perhaps associated with a branch of the pacific deep western boundary current

sedimentological regimes for turbidity currents depth averaged theory turbidity currents are one of the most significant means by which sediment is moved from the continents into the deep ocean their properties are interesting both as elements of the global sediment cycle and due to their role in contributing to the formation of deep water oil and gas reservoirs one of the simplest models of the dynamics of turbidity current flow was introduced three decades ago and is based on depth averaging of the fluid mechanical equations governing the turbulent gravity driven flow of relatively dilute turbidity currents we examine the sedimentological regimes of a simplified version of this model focusing on the role of the richardson number ri dimensionless inertia and rouse number ro dimensionless sedimentation velocity in determining whether a current is net depositional or net erosional we find that for large rouse numbers the currents are strongly net depositional due to the disappearance of local equilibria between erosion and deposition at lower rouse numbers the richardson number also plays a role in determining the degree of erosion vs deposition the currents become more erosive at lower values of the product ro ri due to the effect of clear water entrainment at higher values of this product the turbulence becomes insufficient to maintain the sediment in suspension as first pointed out by knapp and bagnold we speculate on the potential for two layer solutions in this insufficiently turbulent regime which would comprise substantial bedload flow with an overlying turbidity current

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

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

chironomid inferred holocene temperature changes in the south carpathians romania we present a holocene summer air temperature reconstruction based on fossil chironomids from lake brazi 1740 m a s l a shallow mountain lake in the south carpathians summer air temperature rec

reconstructing thermal properties of firn at summit greenland from a temperature profile time series we have constrained the value for thermal diffusivity of near surface snow and firn at summit station greenland using a fourier type analysis applied to hourly temperature measurements collected from eight thermistors in a closed off air filled borehole between may 2004 and july 2008 an implicit finite difference method suggests that a bulk diffusivity of 25 3m2 a 1 is the most reasonable for representing macroscale heat transport in the top 30 m of firn and snow this value represents an average diffusivity and in a conduction only model generates temperature series whose phase shifts with depth most closely match those of the summit borehole data rms difference between measurements and model output is 6 days this bulk value derived numerically and corroborated analytically is useful over large tracts of the greenland ice sheet where density and microstructure are unknown

a 13 600 year diatom oxygen isotope record from the south carpathians romania reflection of winter conditions and possible links with north atlantic circulation changes this study provides a continuous lateglacial and holocene record of diatom silica oxygen isotope changes 18odiat in a subalpine lake sediment sequence obtained from the retezat mts taul dintre brazi 1740 m a s l this through flow shallow high altitude lake with a surface area of only 0 4 ha has short water residence time and is predominantly fed by snowmelt and rainwater its 18odiat record principally reflects the oxygen isotope composition of the winter and spring precipitation as diatom blooms occur mainly in the spring and early summer hence changes in 18odiat are interpreted as seasonal scale changes in the amount of winter precipitation low oxygen isotope values 27 28 5 occurred during the lateglacial until 12 300 cal bp followed by a sharp increase thereafter in the holocene 18odiat values ranged from 29 to 31 until 3200 cal bp followed by generally lower values during the late holocene 27 30 short term decreases in the isotopic values were found between 10 140 9570 9000 8500 7800 7300 6300 5800 5500 5000 and at 8015 4400 4000 cal bp after 3200 cal bp a decreasing trend was visible with the lowest values between 3100 2500 and after 2100 cal bp the general trend in the record suggests that contribution of winter precipitation was generally lower between 11 680 and 3200 cal bp followed by increased contribution during the last millennia the late holocene decrease in 18odiat shows good agreement with the speleothem 18o lake level and testate amoebae records from the carpathian mountains that also display gradual 18o decrease and lake level mire water table level rise after 3200 cal bp strong positive correlation with north atlantic circulation and solar activity proxies such as the austrian and hungarian speleothem records furthermore suggested that short term increases in the isotopic ratios in the early and mid holocene are likely connectable to high solar activity phases and high frequency of positive north atlantic oscillation indexes that may have resulted in decreased winter precipitation in this region

a laser fluorination method for oxygen isotope analysis of biogenic silica and a new oxygen isotope calibration of modern diatoms in freshwater environments abstract an empirical calibration for the oxygen isotope fractionation between biogenic silica and water was determined for diatom frustules sampled from living diatom communities in the jemez mountains of northern new mexico usa over a temperature range from 5 1 to 37 8 c the silica water fractionation is defined by the equation 1000 ln silica water 2 39 0 13 106t 2 4 23 1 49 this relationship is in close agreement with other published silica water fractionation factors for laboratory cultured diatom samples however it is as much as 8 lower than equilibrium quartz water fractionations and 3 4 lower than observed silica water fractionations in diatomaceous silica collected from sediment traps and sediment cores there are three possible explanations for the disparate silica water fractionation factors observed in diatom silica 1 silica does not precipitate in equilibrium with ambient water 2 silica does precipitate in equilibrium with ambient water but the silica water fractionation factor for diatom silica is considerably less than the equilibrium fractionation factor for quartz water or 3 silica precipitation is influenced by a vital effect where the 18o value of the water inside the diatom cell walls is lower than the 18o values of ambient water post mortem loss of organic material results in an alteration or maturation of diatom silica in which silica reequilibrates with a silica water fractionation closer to the equilibrium quartz water fractionation alteration is likely to occur rapidly after the diatom frustule loses its organic coating either as it settles through the water column or at the sediment water interface 18o values recorded by paleo diatom silica therefore do not record growing conditions but more likely record conditions at the sediment water interface in the case of lacustrine environments where the bottom water remains at a nearly constant 4 c the reequilibration of diatom silica with bottom conditions could reduce or remove the conflating effects of temperature on 18o values recorded by paleo diatom silica and provide direct information on the 18o value of the lake water

holocene environmental changes as recorded in the geochemistry of glacial lake sediments from retezat mountains south carpathians abstract sediment cores obtained from two deep 15 m glacial lakes were analyzed in context of terrestrial vegetation development and in lake processes from the retezat mountains southern carpathians romania only the holocene parts were chosen for study for testing what is the connection between geochemical changes and biotas around and in the lakes the lakes are situated at slightly different altitudes on the northern lake gales 1990 m a s l and southern slope lake bucura 2040 m a s l respectively changes in geochemical composition were relatively low amplitude during the studied period 10 300 1790 and 10 300 695 cal yr bp in both lakes but the applicability of enrichment factor ef for geochemical elements and diatom ecological traits guilds in paleoecological reconstruction were demonstrated in this paper the main changes have been observed at ca 10 670 9000 6500 and 3100 cal yr bp in geochemistry vegetation and siliceous algal assemblages catchment soil stabilization was apparent from 9000 cal yr bp onwards in lake and terrestrial productivity was the highest between 9000 and 6500 cal yr bp and human impact became the dominant driver in both terrestrial vegetation and sediment geochemical changes and in lake processes over the last 3400 years in both lakes the geochemical record displayed frequent erosional events within the holocene the strongest soil erosions clustered around 6500 7400 and 3200 900 cal yr bp

holocene and late pleistocene climate in the sub mediterranean continental environment a speleothem record from poleva cave southern carpathians romania the pp10 stalagmite from poleva cave provides a late pleistocene and holocene isotopic record characteristic for the sw of romania a sub mediterranean climatic region the speleothem was dated by eight tims and one alpha u series dates which showed that it was precipitated between 75 ka and 2 ka with at least two hiatuses the basal sector of the stalagmite showed a slow growing regime of 0 26 cm ka while the upper one grew relatively fast with about 5 cm ka the temporal resolution for the isotopic sampling is thus 2 ka sample for the lower sector and 150 years sample for the upper one the relationship between 18 o and temperature was found positive the isotopic record of the lower sector shows two marked cold intervals during 67 and 58 ka and 40 35 ka respectively which correlate well with the villars and soreq records the upper sector record is so far the most detailed holocene isotopic record in romania and the only one available for the regions located at the exterior of the carpathians range the signal shows a gradual warming after the gs1 event punctuated by several cold events at 8 7 2 and 4 2 ka and also by warm oscillations centered at about 5 2 and 3 3 ka the results seem to indicate that if the north atlantic firstorder signals may extend well to the south eastern europe their amplitude and general trend may be diminished by the interferences with the mediterranean circulation

was a change in thermohaline circulation responsible for the little ice age long term 800 year and short term 20 year estimates of the rate of deep water formation in the southern ocean are in serious disagreement this disagreement suggests to me that the rate of deep water formation may have been larger during the little ice age lia than it is now

detrital events and hydroclimate variability in the romanian carpathians during the mid to late holocene the romanian carpathians are located at the confluence of three major atmospheric pressure fields the north atlantic the mediterranean and the siberian despite its importance for understanding past human impact and climate change high resolution palaeoenvironmental reconstructions of holocene hydroclimate variability and in particular records of extreme precipitation events in the area are rare here we present a 7500 year long high resolution record of past climatic change and human impact recorded in a peatbog from the southern carpathians integrating palynological geochemical and sedimentological proxies natural climate fluctuations appear to be dominant until 4500 years before present yr bp followed by increasing importance of human impact sedimentological and geochemical analyses document regular minerogenic deposition within the bog linked to periods of high precipitation such minerogenic depositional events began 4000 yr bp with increased depositional rates during the medieval warm period mwp the little ice age lia and during periods of societal upheaval e g the roman conquest of dacia the timing of minerogenic events appears to indicate a teleconnection between major shifts in north atlantic oscillation nao and hydroclimate variability in southeastern europe with increased minerogenic deposition correlating to low nao index values by linking the minerogenic deposition to precipitation variability we state that this link persists throughout the mid to late holocene

orbital ice sheet and possible solar controls on holocene moisture trends in the north atlantic drainage basin holocene patterns of hydroclimatic change in the north atlantic region are poorly understood despite the importance to climate of the region9s freshwater flux to the ocean here we reconstruct the history of moisture balance in the north atlantic drainage by compiling lake level records from 95 lakes in europe and north america we show that recent millennia were significantly wetter than much of the holocene in both regions only 15 of lakes studied in the north atlantic basin were low in the past millennium in contrast 50 of lakes were low at 10 cal kyr b p low moisture levels in the early holocene likely resulted from high summer and fall insolation and the influence of the continental ice sheets water levels rose in many areas as these influences diminished a principal components analysis of the lake level data however also indicates that holocene atmospheric circulation changes possibly driven by solar activity generated additional moisture variation including low water levels at 5 2 cal kyr b p in eastern north america and scandinavia

on the ignition of geostrophically rotating turbidity currents two models of a geostrophically rotating turbidity current are examined to compare predictions for ignition with the catastrophic state both models describe the current as a tube of sediment laden water traversing along and down a uniform slope the first four equation model neglects the energy required to lift the sediment from the seabed into suspension the second five equation model rectifies this shortcoming by introducing a turbulent kinetic energy equation and coupling the bottom stress to turbulence in the plume these models can be used to predict the ignition path and sediment deposition of a geostrophically rotating turbidity current the criteria for ignition in the four equation model can be described by a surface in three dimensional phase space for a non entraining current this surface lies near the geostrophic equilibrium state for a turbidity current occurring in the greenland sea velocities above 0 053 m s 1 or volumetric concentrations of sediment above 2 7 10 5 lead to ignition in general if the tube is started pointing downslope then ignition is more likely than if it is initially directed alongslope however there exists a set of initial conditions in which the current ignites if started along or downslope but deposits if started at an intermediate angle the five equation model requires a larger initial velocity greater than 1 6 m s 1 to ignite than does the four equation model ignition is determined qualitatively by the geostrophic state and the initial normal froude number solutions show a tendency to travel further alongslope during ignition reflecting the restriction that the energy budget places on the sediment load a qualitative difference to phase space in the five equation model is the existence of a region in which the tube has insufficient energy to support the sediment turbulence dies rapidly in this region and so the sediment is deposited almost immediately

unravelling contamination signals in biogenic silica oxygen isotope composition the role of major and trace element geochemistry the oxygen isotope composition of diatom silica 18odiatom provides valuable information for palaeoclimate studies where carbonate proxies are either rare or absent in many lakes and ocean sediments unfortunately mineral and rock fragments found alongside diatoms in most sediments can be problematic as the method used will liberate oxygen from all components within the sediment producing both high frequency noise and low frequency excursions that can resemble climate signals removal of mineral contamination to date has largely relied upon the combination of chemical leaching and physical separation techniques e g sieving density this combination can be inefficient and often significant proportions of contaminants are present in the purified diatom sample using electron optical imaging and whole rock geochemistry on previously purified diatom samples a mass balance approach has been developed whereby the types and proportions of residual contaminants are identified by integrating this information with measured oxygen isotope ratios of the contaminants it is then possible to remove contamination effects from the 18odiatom record contamination effects relating to carbonates tephra and silt are modelled for cores from lake tilo ethiopia and lake baikal siberia in both lakes the new modelled 18odiatom curves show less high frequency noise thus enabling better resolution of low frequency climate signals

diatom oxygen isotopes in pro glacial lake sediments from northern sweden a 5000 year record of atmospheric circulation we use a pro glacial oxygen isotope record of diatom silica 18odiatom and a sedimentary proxy for glacier flutuations to determine centennial millennial scale climate change during the last 5000

reconciling diverse diatom based lake responses to climate change in four mountain lakes in the south carpathian mountains during the last 17 kyrs abstract climatic changes were studied using siliceous algae diatoms and chrysophyta stomatocysts analyses in four mountain lakes in the retezat mountains in the south carpathian mountains with the aim to search for synchrony in aquatic ecosystem responses according to the basal radiocarbon dating of the lake sediment cores these lakes were formed around 17 000 15 000 cal yr bp high resolution diatom analyses were carried out together with loss on ignition loi and biogenic silica bisi measurements on the lakes comparison of the proxy results suggests that despite the different slope aspect water depth and basin parameters diatom assemblage changes show clear synchrony the most remarkable changes in the aquatic ecosystems were observed around 6500 cal yr bp on the northern slope and around 6100 cal yr bp on the southern slope during the holocene evidences for sharp concomitant shifts were found between 9200 9000 and 3200 3000 cal yr bp in the siliceous algal communities on both slopes the late glacial holocene boundary was not pronounced in the shallow lakes but was significant in a deep lake the signs of a dry and bipartite younger dryas gs 1 were evident but floristic changes differed in the lakes principal component analyses explained very similar variances along the first and second axes for three lakes while the fourth lake lake bucura proved less sensitive to climate change due to the dominance of moss inhabiting diatom assemblages lake level changes have only been reconstructed on the basis of diatom life forms in one of the deep lakes lake gales high lake levels were inferred between 9300 9000 and 3000 1700 cal yr bp in addition to loi biogenic silica content bisi was measured on the sediments of the northern slope and pointed to different seasonal biological productivities increasing loi was often coupled with low bisi values

diatom inferred lateglacial and holocene climatic variability in the south carpathian mountains romania climatic and environmental changes were studied using siliceous algae diatoms and chrysophycean cysts analyses in a mountain lake in the south carpathian mountains for the lateglacial and holocene lake brazi 1740 a s l is a small shallow lake in the retezat mountains according to the basal radiocarbon dating of the core the lake was formed around 15 750 cal bp and sediment accumulation has been continuous ever since high resolution diatom analyses were carried out together with loss on ignition and biogenic silica measurements total epilimnetic phosphorus tp concentrations and ph were reconstructed quantitatively ten statistically significant zones were distinguished six of which appeared in the lateglacial and early holocene suggesting the instability of diatom assemblages after deglaciation the uppermost zone covered six thousand years which suggests that diatom assemblages remained quite stable during the second half of the holocene high lake level occurred between 9500 and 9000 cal bp after 6300 cal bp the lake level gradually increased again until 5800 cal bp a further increase was detected at 3000 cal bp while after 1500 cal bp water level decreased although there is limited knowledge regarding the environmental constraints of several diatom taxa present in the sequence e g aulacoseira laevissima which makes the precise environmental interpretation of the diatom record more difficult the available data provide an important new insight into the environmental history of lake brazi and the carpathian mountains the most remarkable changes in the aquatic ecosystem were observed at 6000 cal bp in the holocene and 12 800 cal bp at the onset of the younger dryas marked changes were also detected at 10 500 10 300 9800 9500 9000 8900 8800 8300 6300 5800 and 3100 3000 cal bp

limnological changes in south carpathian glacier formed lakes retezat mountains romania during the late glacial and the holocene a synthesis abstract remains of aquatic biota preserved in mountain lake sediments provide an excellent tool to study lake ecosystem responses to past climate change in the prolong project a multi proxy study was performed on sediments of glacier formed lakes from the retezat mountains southern carpathians romania the studied lakes lake brazi and gales are situated on the northern slope of the mountain at different altitudes 1740 m and 1990 m a s l our main objectives were 1 to describe the main limnological changes in these lakes during the last ca 15 000 years and 2 to summarize the environmental history of the studied lakes based on taxonomical and functional patterns of the biological proxies for this synthesis we used the results of diatom and chironomid analyses and indirect biotic and abiotic parameters including sediment organic matter loi content geochemical element concentrations al ca s sr and biogenic silica content using multivariate numerical approaches we analysed changes in the assemblage structure of siliceous algae and chironomids compared temporal patterns among proxies examined the relationship between potential driving factors chironomid and diatom assemblage changes and identified paleolimnological phases of the lake successions changes in assemblage composition and aquatic ecosystem state apparently followed summer insolation local climatic conditions and local productivity changes driven by these diatom and chironomid assemblages generally changed in a similar direction and at a similar time within a lake but differed to some extent between lake brazi and gales at both lakes the strongest variations were observed in the late glacial and the first half of the holocene the strongest holocene assemblage changes took place in the earliest holocene in lake brazi but extended into the mid holocene in lake gales following long term insolation changes and climatic changes in addition three common zone boundaries were identified at ca 14 200 and at ca 6500 cal yr bp for every records and at ca 3100 cal yr bp for diatom records in both of the lakes and for the chironomid record of lake brazi this multi proxy synthesis provides comprehensive data that increase our understanding of the past variability of lake ecosystem functioning and biodiversity in east central europe

timing and climatic impact of greenland interstadials recorded in stalagmites from northern turkey a 50 kyr long exceptionally well dated and highly resolved stalagmite oxygen 18o and carbon 13c isotope record from sofular cave in northwestern turkey helps to further improve the dating of greenland interstadials gi 1 and 3 12 timing of most gi in the sofular record is consistent within 10 to 300 years with the iconic hulu cave record larger divergences 500 years between sofular and hulu are only observed for gi 4 and 7 the sofular record differs from the most recent ngrip chronology by up to several centuries whereas age offsets do not increase systematically with depth the sofular record also reveals a rapid and sensitive climate and ecosystem response in the eastern mediterranean to gi whereas a phase lag of 100 years between climate and full ecosystem response is evident finally results of spectral analyses of the sofular isotope records do not support a 1 470 year pacing of gi

climatic and human impact on the environment a question of scale abstract the environmental context of cultural transformation frames the central issue of this paper how were neolithic and chalcolithic landscapes in the aegean balkan and carpathian abc zones shaped and transformed by climatic and anthropogenic impacts the difficulties in interpreting proxy records for the middle transitional stage of the holocene aridification sequence falling between the early wet stage and the late arid stage have been created by the conjoint influence of two kinds of impact climatic and anthropogenic an unhelpful influence in this debate stems from willis and bennett s 1994 hypothesis of minimal human impact on the pre bronze age landscapes of south east europe in this paper two questions are posed 1 what were the effects of the claimed global changes in holocene climate at the regional and local scale in the abc zones and 2 can we recognise human impact in these proxy records prior to the bronze age of our study regions following a discussion of general long term climatic trends and rccs episodes of rapid climatic change i base a discussion of the so called 8200bp event and pre bronze age human impacts on a suite of 24 well dated proxy records mostly pollen sequences the principal findings are that there is little evidence for impact from the 8200bp event in these records while there is substantial evidence for pre bronze age human impacts on the landscapes of the aegean balkan and carpathian regions

terminal settling velocity of commonly occurring sand grains published measurements of terminal settling velocity for commonly occurring sands are used to develop three equations which join into a single segmented curve of dimensionless form results are noticeably different from those for spheres of similar diameter and permit calculation of the settling velocity for usual sand grains without specification of exact grain shape for quartz in water the three equations of different settling regimes correspond approximately to very fine sand fine to coarse sand and very coarse sand

turbidity current flow over an erodible obstacle and phases of sediment wave generation 1 we study the flow of particle laden turbidity currents down a slope and over an obstacle a high resolution 2 d computer simulation model is used based on the navier stokes equations it includes poly disperse particle grain sizes in the current and substrate particular attention is paid to the erosion and deposition of the substrate particles including application of an active layer model multiple flows are modeled from a lock release that can show the development of sediment waves sw these are stream wise waves that are triggered by the increasing slope on the downstream side of the obstacle the initial obstacle is completely erased by the resuspension after a few flows leading to self consistent and self generated sw that are weakly dependant on the initial obstacle the growth of these waves is directly related to the turbidity current being self sustaining that is the net erosion is more than the net deposition four system parameters are found to influence the sw growth 1 slope 2 current lock height 3 grain lock concentration and 4 particle diameters three phases are discovered for the system 1 no sw 2 sw buildup and 3 sw growth the second phase consists of a soliton like sw structure with a preserved shape the phase diagram of the system is defined by isolating regions divided by critical slope angles as functions of current lock height grain lock concentration and particle diameters

a comparison of the palaeoclimate signals from diatom oxygen isotope ratios and carbonate oxygen isotope ratios from a low latitude crater lake the analysis of oxygen isotope ratios 18o from authigenic lake carbonates has become a well established palaeoclimate technique less common is the use of 18o in biogenic silica e g diatoms sponge spicules phytoliths but the technique is being increasingly utilised for non carbonate lakes this paper aims to compare 18odiatom with 18ocarbonate in a low latitude closed basin lake due to the influence of ph rarely are both carbonate and diatoms preserved in lake sediments in concentrations high enough to measure oxygen isotopes the 18o composition of both carbonate and silica should reflect the isotope composition and temperature of the lake water at the time of precipitation and hence theoretically they should be equivalent only one comparative study of 18odiatom and 18ocarbonate currently exists and that found differences between their 18o compositions probably because they precipitated in different seasons unless there is evidence to suggest that silica and carbonate precipitate at the same time their 18o records are likely to be different but complementary in this study we show that 18odiatom and 18ocalcite from lake tilo ethiopia show some similar broad climate trends however the 18odiatom curve is generally more variable and does not record two regional arid events picked up by the 18ocalcite data several possible reasons for this are discussed the precision of the 18odiatom extraction technique contamination of the diatom samples from tephra volcanic glass vital effects in the diatom samples differences in their respective equilibrium isotope fractionation rates and the possibility that the dominant diatom aulacoseira granulata and calcite precipitated in different seasons during this time currently the problems associated with the cleaning and extraction of 18odiatom suggests that details found in 18ocalcite records may be lost in 18odiatom records where contaminants such as tephra and clay minerals are difficult to remove

high resolution numerical simulations of resuspending gravity currents conditions for self sustainment received 21 february 2005 revised 30 june 2005 accepted 29 august 2005 published 22 december 2005 1 we introduce a computational model for high resolution simulations of particle laden gravity currents the features of the computational model are described in detail and validation data are discussed physical results are presented that focus on the influence of particle entrainment from the underlying bed as turbulent motions detach particles from the bottom surface resuspended particles entrained over the entire length of the current are transferred to the current s head causing it to become denser and potentially accelerating the front of the current the conditions under which turbidity currents may become self sustaining through particle entrainment are investigated as a function of slope angle current and particle size and particle concentration the effect of computational domain size and initial aspect ratio of the current on the evolution of the current are also considered applications to flows traveling over a surface of varying slope angle such as turbidity currents spreading down the continental slope are modeled via a spatially varying gravity vector particular attention is given to the resulting particle deposits and erosion patterns

a first chironomid based summer temperature reconstruction 13 5 ka bp around 49 n in inland europe compared with local lake development temperature reconstructions for the end of the pleistocene and the first half of the holocene based on biotic proxies are rare for inland europe around 49 n we analysed a 7 m long sequence of lake deposits in the vihorlat mts in eastern slovakia 820 m a s l chironomid head capsules were used to reconstruct mean july temperature tjuly other proxies diatoms green algae pollen geochemistry were used to reconstruct local environmental changes that might have affected the climate reconstruction such as epilimnetic total phosphorus concentrations tp lake level changes and development of surrounding vegetation during the younger dryas yd temperature fluctuated between 7 and 11 c with distinct decadal to centennial scale variations that agree with other palaeoclimate records in europe such as 18o content in stalagmites or greenland ice cores the results indicate that the site was somewhat colder than expected from the general south to north yd temperature gradient within europe possibly because of north facing exposition the warmer phases of the yd were characterised by low water level or even complete desiccation of the lake 12 200 12 400 cal yr bp at the late glacial holocene transition tjuly steeply increased from from 11 to 15 5 c 11 700 11 400 cal yr bp the highest tjuly for entire sequence this rapid climate change was reflected by all proxies as a compositional change and increasing species diversity the open woodlands of pinus betula larix and picea were replaced by broad leaved temperate forests dominated by betula later by ulmus and finally by corylus ca 9700 cal yr bp at the same time input of eroded coarse grained material into the lake decreased and organic matter loi and biogenic silica increased the early holocene climate was rather stable till 8700 cal yr bp with temporary decrease in tjuly around 11 200 cal yr bp the lake was productive with a well developed littoral as indicated by both diatoms and chironomids a distinct decline of tjuly to 10 c between 8700 and 8000 cal yr bp was associated with decreasing chironomid diversity and increasing climate moistening indicated by pollen tychoplanktonic and phosphorus demanding diatoms increased which might be explained by hydrological and land cover changes later a gradual warming started after 7000 cal yr bp and representation of macrophytes periphytic diatoms and littoral chironomids increased our results suggest that the holocene thermal maximum was taking place unusually early in the holocene at our study site but its timing might be affected by topography and mesoclimate we further demonstrated that temperature changes had coincided with variations in local hydrology

numerical simulation of powder snow avalanches la simulation numerique d une avalanche de neige poudreuse maseguichi japon est proposee la profondeur de neige frai che apparai t comme un parametre determinant au declenchement de ce type d avalanche

mid holocene climate conditions and moisture source variations based on stable h c and o isotope compositions of speleothems in hungary abstract this paper presents stable c and o isotope data as well as water contents and stable hydrogen isotope compositions of inclusion hosted water of 230 th dated stalagmites collected from the leany and pal volgyi caves of central hungary within and about 50 km nw from budapest respectively a good replication of contemporaneous stalagmite oxygen isotope records and their agreement with the comnispa record from the eastern alps suggest that the stalagmite oxygen isotope variation reflects past climate change h 2 o contents in the leany stalagmite indicate a relationship with the oxygen isotope compositions and hence with climate conditions raising the possibility of its use as a climate proxy in future studies the stalagmites show strong negative 18 o excursions for two cold periods at about 5 4 6 and 8 9 ka whereas the oxygen isotope data are relatively high in the period of 6 7 ka indicating warmer conditions the stalagmite hydrogen and d excess series positively correlate with the comnispa record interpreted as a sign of moisture source variations high d excess values in the periods of low 18 o data for the leany cave at about 5 4 6 and 8 9 ka suggest a shift to mediterranean moisture source domination when the comnispa record indicate weaker north atlantic oscillation nao activity lower d excess values in the period of 6 7 ka are associated with low 18 o values in the comnispa record corresponding to nao phase the inferred moisture source changes are in accordance with published instrumental data covering the last hundred years and atmospheric circulation model results and demonstrate that nao activity influenced the climate conditions of the carpathian basin during most of the holocene

a complete holocene climate and environment record for the western carpathians slovakia derived from a tufa deposit calcareous tufas are great archives of geochemical information for the reconstruction of past climate their importance increases in the regions where other proxies are rare such as western carpathians here we present the first whole holocene palaeoclimatic reconstruction for this region based on geochemical proxies we analysed o 18 c 13 and mg ca ratio on tufa calcite of the mituchovci site white carpathian mountains w slovakia and compared these with pollen plant macrofossil and mollusc data according to o 18 two distinct thermal maxima occurred in the region around 11 4 ka and between 7 3 and 6 9 ka bp according to c 13 and mg ca ratio a steep increase in moisture and rainfall took place around 8 5 ka cal bp preceded by a cold and dry event these events are well reflected in the biotic proxies and are suggested also by other palaeoenvironmental studies from the carpathians we found some later fluctuations with dry and warm bronze age ca 3 6 ka cal bp cold and wet urnfield period ca 2 8 ka cal bp warm roman period ca 2 ka cal bp and cold but humid migration period ca 1 5 ka cal bp we observed extreme abruptness and amplitude of the variation in all geochemical proxies in the last 500 years when biotic proxies imply a very intense human deforestation land use changes may have altered both the temperature regime in the studied fen and the carbon cycle in the recharge area

a review of the oxygen isotope composition of lacustrine diatom silica for palaeoclimate reconstruction diatom silica frustules are a form of biogenic opal and contain oxygen isotopes that are being increasingly used in palaeoclimate studies frustules are comprised of an inner tetrahedrally bonded silica skeleton si o si with an outer hydrous layer the hydrous layer is freely exchangeable and must be removed prior to oxygen isotope measurement using oxidising reagents and or high temperatures analysis of the oxygen isotope composition of diatom silica requires samples that are almost pure diatomite since extraction techniques will liberate oxygen from all the components in the sediment there is a generally acceptable protocol involving chemistry sieving and settling techniques and more recently laminar flow separation recent studies of lacustrine diatoms have shown that even a small proportion of contaminant can have a significant influence on the oxygen isotope value all lake sediments require their own specific procedure and every sample must be scrutinised by microscopy to check for the level of contamination prior to analysis where sediment cannot be purified sufficiently a semi quantitative assessment of the diatom content can facilitate mass balance techniques when robust preparation methods are used diatom silica offers an important palaeoclimate proxy providing an additional complementary rather than an alternative host of oxygen isotopes in carbonates in lacustrine isotope studies it is often assumed but rarely proven that diatom silica form in isotope equilibrium and hence empirically derived palaeotemperature equations usually made in vitro can be used most studies lack the detailed investigation of contemporaneous materials from natural waters of the region under study to test these equations further investigations need to be conducted in order to understand the systematic relationship between temperature water isotope composition and diatom isotope composition to enable quantitative interpretation of the sediment record experiments to test for vital effects and inter specific differences have so far revealed little variation it is useful to know when and where the diatom silica is formed in the modern environment so details of diatom ecology are important in the interpretation of isotope data here we show that valuable palaeoclimate data can be gained from the oxygen isotope composition of diatom silica 18odiatom especially since diatoms are abundant in many lakes sensitive to climate variation where other hosts e g carbonates are absent to date the most successful studies have been conducted in areas where the 18odiatom registers changes in the oxygen isotope composition of the lake water rather than temperature which is then related to other aspects of climate in these studies the range of values obtained is often greater than the error introduced by contaminating materials

archaeological evidence for holocene landslide activity in the eastern carpathian lowland abstract landslides are widespread phenomena that contribute to shape the landscape assessing the time sequence of landslide activity during the holocene can help i better frame the present day landslide distribution in the wider context of climate change and ii better define landslide hazard to take adequate mitigation measures to preserve the elements at risk such as archaeological heritage and currently used structures and infrastructures rigorous image interpretation criteria applied to the interpretation of remote sensing images can be a valuable tool to derive information on landslide spatial and temporal distribution however it only allows to broadly estimate the relative age of landslides based on their morphologic signature in this work we investigate the topological relations between landslides and archaeological sites for nine selected settlements in the moldavian plateau situated on ridges and hillslopes landslides and sites were mapped using high resolution lidar dems and extensive field validation activities landslides were classified as very old relict old and recent according to their morphologic appearance we argue the possibility of i assigning a relative age to the three main classes of landslides as they appear on the present day topography and ii assessing the landslide activity during the holocene using this information we set up a model of landslide evolution during the holocene for the lowland of eastern carpathians based on collected data we cannot exclude the pleistocene age for some very old landslides whereas the old and recent landslides appeared during the holocene we think this approach can be extended to other archaeological sites of the study area and to other areas furthermore similar studies can prove useful for landslide hazard analyses helping to adopt adequate protection and mitigation measures framed in a climate change scenario

persistent influence of the north atlantic hydrography on central european winter temperature during the last 9000 years 1 a prominent feature of the n atlantic s holocene climate is a series of centennial and millennial shifts in ocean surface hydrography bond et al 2001 oppo et al 2003 here we compare a climate reconstruction from the central alps for the last 9 000 years derived from the oxygen isotope record in stalagmites with the percentage of hematite stained grains in n atlantic sediments an indicator for the proportion of ice bearing surface water from north of iceland the excellent match between the two curves proves that meteorological conditions in the alpine region responded synchronously to changes in the hydrography of the n atlantic during winter in addition the speleothem record suggests significant multi centennial and millennial variability of n european winters throughout the past 9 000 years that might have been incompletely recorded in tree ring archives

prediction of ignitive turbidity currents in scripps submarine canyon swift highly erosive continuous turbidity currents are known to be triggered in scripps submarine canyon during storms a relatively modest agitation due to edge waves can generate currents at least as swift as 1 9 m s 1 pantin 1979 and parker 1982 have described a mechanism by which a turbidity current can self accelerate by entraining sediment from the bed parker termed the mechanism ignition herein two models of steady spatially developing turbidity currents are developed and applied to scripps submarine canyon fairly specific predictions are obtained for the onset of ignitive acceleration and for the downstream development of the turbidity currents the results are in general agreement with available measurements in the same canyon it is speculated that ignitive turbidity currents constitute a major mechanism by which sand submarine canyons are eroded and by which sand is delivered to the abyssal plain

thermal effects due to air flow and vapor transport in dry snow the thermal effects of air flow forced through a snow sample are investigated numerically a new method for calculating vapor transport in snow is presented which allows for the determination of the effects of sublimation in this method the snow is not assumed to be saturated with water vapor results of the model show very good agreement with analytical and experimental results

age depth relationship and accumulation rates in four sediment sequences from the retezat mts south carpathians romania abstract this study summarizes the results of radiocarbon dating and age depth modelling in four mountain lakes brazi gales bucura and lia in the retezat mountains altogether 69 ams 14 c measurements were performed on these deposits mostly on terrestrial plant macrofossils in several cases plant macrofossils aquatic animal remains cladoceran eggs and bulk sediment were measured from the same depth allowing for the comparison of various sediment components in terms of their dating potential age depth models were developed using both bayesian modelling with the bacon and smooth spline curve fitting with the clam software in this study bayesian models are applied to identify outlier 14 c dates while smooth spline models are used to model sediment accumulation age depth relations as these are more likely to follow natural deposition time changes of lake sediments changes in sediment deposition times dt in relation to catchment size and climate are also studied dt varied considerably in the late glacial lg part of the records the sediment sequence characterised by high deposition rates during the late glacial dt maximum around 100 110 years cm 1 was defined by small catchment size lake brazi 6 ha surface area 0 5 ha in contrast much slower lg sediment deposition in the southern slope lake characterised by large catchment area lake lia 171 ha 20 years cm 1 principally reflecting strong erosion in these catchment areas at times when vegetation cover was scarce holocene was characterised again by variable dt values but only lake gales showed extreme values 62 110 years between 10 900 and 6050 cal yr bp followed by much slower sediment deposition in the last 6000 years av 29 years cm 1 generally sediment deposition times were largely dependent on the stability and vegetation cover of the slope in the case of high altitude deep lakes while lower altitude shallow lakes showed slower sediment deposition time in the early and mid holocene when summer insolation was higher than today this reflects that in these shallow lakes in lake organic production probably increased with summer insolation which was a significant driver in the rate of deposition

late glacial to middle holocene climatic record of lacustrine biogenic silica oxygen isotopes from a southern ocean island late glacial to middle holocene climatic record of lacustrine biogenic silica oxygen isotopes from a southern ocean island

a precisely dated climate record for the last 9 kyr from three high alpine stalagmites spannagel cave austria 1 here we use the 18o time series of three stalagmites from the high alpine spannagel cave austria which grew in small distance from each other to construct a precisely dated continuous 18o curve for the last 9 kyr comnispa this speleothem record is not influenced by effects of kinetic isotope fractionation due to the low temperatures in the cave thus the variations in 18o can be interpreted in terms of past climate change comnispa exhibits several oscillations within the holocene and their timing and duration is in agreement with that documented by other alpine archives

transfer and early diagenesis of biogenic silica oxygen isotope signals during settling and sedimentation of diatoms in a temperate freshwater lake lake holzmaar germany abstract we have investigated the transfer of oxygen isotope signals of diatomaceous silica 18odiatom from the epilimnion 0 7 m through the hypolimnion to the lake bottom 20 m in freshwater lake holzmaar germany sediment traps were deployed in 2001 at depths of 7 and 16 m to harvest fresh diatoms every 28 days the 7 m trap collected diatoms from the epilimnion being the main zone of primary production while the 16 m trap collected material already settled through the hypolimnion also a bottom sediment sample was taken containing diatom frustules from approximately the last 25 years the 18odiatom values of the 7 m trap varied from 29 4 in spring autumn to 26 2 in summer according to the temperature dependence of oxygen isotope fractionation and represent the initial isotope signal in this study remarkably despite the short settling distance 18odiatom values of the 7 and the 16 m trap were identical only during spring and autumn seasons while from april to september 18odiatom values of the 16 m trap were roughly 1 5 enriched in 18o compared to those of the 7 m trap isotopic exchange with the isotopically lighter water of the hypolimnion would shift the 18odiatom value to lower values during settling from 7 to 16 m excluding this process as a cause for the deviation dissolution of opal during settling with intact organic coatings of the diatom cells and near neutral ph of the water should only cause a minor enrichment of the 16 m values nevertheless opal from the bottom sediment was found to be 2 5 enriched in 18o compared to the weighted average of the opal from the 7 m trap thus resuspension of bottom material must have contributed to the intermediate 18odiatom signal of the 16 m trap during summer dissolution experiments allowed further investigation of the cause for the remarkably enriched 18odiatom value of the bottom sediment experiments with different fresh diatomaceous materials show an increase of opaline 18o at high ph values which is remarkably reduced when organic coatings of the cells still exist or at near neutral ph in contrast high ph conditions do not affect the 18odiatom values of sub fossil and even fossil opal ir analyses show that the 18o enrichment of the sedimentary silica is associated with a decrease in si oh groups and the formation of si o si linkages this indicates a silica dehydroxylation process as cause for the isotopic enrichment of the bottom sediment silica dissolution and dehydroxylation clearly induce a maturation process of the diatom oxygen isotope signal presumably following an exponential behaviour with a rapid initial phase of signal alteration the dynamics of this process is of particular importance for the quantitative interpretation of sedimentary 18odiatom values in terms of palaeothermometry

long term summer temperature reconstruction inferred from tree ring records from the eastern carpathians the first 1 000 year long carpathian tree ring width chronology was established based on living and subfossil stone pine pinus cembra l samples from an upper timberline forest located in calimani mts romania tree ring data were standardized using the regional curve standardization method in order to preserve the low and medium frequency climate signals the de trended index strongly correlates with summer mean temperature both at annual and decadal scales the calimani summer mean temperature anomalies were reconstructed for the period ad 1163 2005 applying the rescaling method this new climate proxy from the carpathians shows similar fluctuations to other north hemispheric temperature reconstructions but with periods of distinct differences the fingerprint of little ice age in the calimani area is visible between ad 1370 and 1630 followed by lagged cold decades in ad 1820 and 1840 the recent warming is evident only after the 1980s in our reconstruction

small scale moisture availability increase during the 8 2 ka climatic event inferred from biotic proxy records in the south carpathians se romania in this paper we present high resolution early holocene pollen plant macrofossil charcoal diatom biogenic silica and loss on ignition records from a mountain lake in the south carpathians in order to reveal ecosystem response to the 8 2 ka climatic oscillation we found significant changes both in terrestrial vegetation and lake diatom assemblages in the northern slope of the retezat mts between c 8300 and 8000 cal yr bp rapid changes in relative frequencies and pollen accumulation rates of the major deciduous pollen types associated with peaks in microcharcoal accumulation rates suggested that vegetation disturbance mainly took place in the mixed deciduous forest zone where woodland fires partially destroyed the populations of fraxinus excelsior quercus and corylus avellana and facilitated the establishment of carpinus betulus in the forest openings the diatom record furthermore showed the spread of a planktonic diatom species aulacoseira valida at 8150 cal yr bp coincidently with a shor

oxygen isotopes of marine diatoms and relations to opal a maturation in order to develop the potential tool of diatom oxygen isotopes for paleoenvironmental studies we compared oxygen isotopes of natural marine diatoms sampled from ocean surface water sediment traps and surface sediments with oxygen isotopic fractionations determined for laboratory diatom cultures freshly grown natural diatoms phytoplankton samples and sediment trap material and cultured diatoms reveal similar oxygen isotope fractionation factors the fresh diatoms have 3 to 10 parts per thousand lower isotope fractionation factors than fossil sedimentary diatoms a temperature related oxygen isotope fractionation could not be established for the laboratory cultures and the natural phytoplankton samples and there is evidence that diatom growth rate until reaching the stationary growth state also controls the measured silica water oxygen isotope fractionation factor it is possible however that slow diatom growth in sea surface water may well lead to a temperature dependent silica water oxygen isotope fractionation which is the prerequisite for a use of diatom oxygen isotopes in palco surface water studies ftir spectroscopic analyses of various diatomaceous materials revealed that the ratio of integrated peak intensities for si o si si oh correlates with the 3 to 10 parts per thousand delta o 18 silica increase from fresh to fossil diatoms open system flow through silica dissolution experiments suggest that the diatom frustules are isotopically homogenous and that the increase in o 18 is therefore not due to dissolution of isotopically light surficial si oh groups it is concluded that slow internal condensation reactions during silica maturation in surface sediments cause both an increase in the intensity ratio of si o si si oh and the o 18 content of framework oxygen these findings also indicate that the oxygen isotope compositions of marine sediment diatoms do not indicate sea surface water temperature but rather reflect variable o 18 contents of surface sediments copyright c 2001 elsevier science ltd

predicting autosuspension in steady turbidity flow ignition points and their relation to richardson numbers abstract this paper describes a semi analytical model of spatially developing turbidity flows and concentrates on two particular aspects i the possible conditions for ignitive autosuspension in a particular submarine channel the kaikoura canyon hikurangi channel system east of new zealand and ii the relationship between the internal richardson number of the flow and the possibility of ignitive autosuspension the results confirm that autosuspension is promoted by a steep channel gradient a large flow thickness and fine grain size the model as applied to the kaikoura canyon hikurangi channel system in new zealand indicates that ignition is possible in the kaikoura canyon and the proximal reaches of the hikurangi channel from analysis of the turbulent energy balance within the flow it emerges that ignition is impossible in subcritical flows ri 1 our work implies that turbidity currents that are depositing significant volumes of sediment are subcritical rather than supercritical this may have significant implications for architectural development in natural systems

treeline and timberline dynamics on the northern and southern slopes of the retezat mountains romania during the late glacial and the holocene abstract to investigate treeline and timberline dynamics in the retezat mountains romanian carpathians late glacial and holocene sediment sequences from four lakes were studied the south and north slopes of the mountain range were compared using two lakes from the north flank lake brazi 1740 m a s l and lake gales 1990 m a s l and two from the south flank lake lia 1910 m a s l and lake bucura 2040 m a s l macrofossil and stomata analyses were performed to assess changes in the local vegetation supplemented by pollen charcoal and loss on ignition analyses our results show that treeline reached lake brazi on the northern side during the late glacial ca 14 000 cal yr bp and then lake gales between 11 000 and 10 800 cal yr bp during the early holocene the upper limit of closed forest the timberline reached and passed lake brazi and has stayed above it since but it has never reached lake gales at 1990 m a s l the expansion of larix decidua in the late glacialand early holocene around lake brazi is unique stomata and macrofossils of abies alba are also more abundant in the northern records on the southern flank treeline reached lake lia at around 12 000 cal yr bp and was either very close to or at the elevation of lake bucura between ca 8600 and 3000 cal yr bp timberline reached lake lia at ca 8000 cal yr bp some 3000 years after lake brazi only 170 m lower on the north slope local fire events delayed the advance of timberline around lake lia in the early holocene in a dry continental climate the surrounding forest was dominated by picea abies with individuals of pinus cembra and stands of p mugo until about 3000 cal yr bp when timberline retreated below the lake maximum elevation of timberline was attained between ca 8000 and 3000 cal yr bp after which it descended in response to climate cooling regional climate change appears to be the main driver of treeline dynamics but it was modified by local climatic differences due to slope aspect the first signs of human disturbance appeared ca 4200 cal yr bp when naturally open areas were used as alpine pastures human impact in the treeline ecotone mainly burning and grazing was intensified after ca 2600 cal yr bp contributing to the widening of the ecotone and the lowering of the timberline