holocene climatic and environmental changes inferred from midge records diptera chironomidae chaoboridae ceratopogonidae at lake berkut southern kola peninsula russia a radiocarbon dated sediment sequence from lake berkut in the southern part of the kola peninsula northwest russia was investigated by means of midge analysis in order to reconstruct the holocene climatic and environmental history of the region past mean july air temperatures at the study site and hypolimnetic oxygen contents of the lake water were inferred from chironomid based transfer functions the early holocene c 10 100 8400 cal yr bp is characterized by summer temperatures and hypolimnetic oxygen concentrations broadly similar to present day conditions the midge records give evidence of a lake level fall at c 7000 cal yr bp resulting in weakened thermal stratification of the lake water and improvement of the hypolimnetic oxygen conditions after c 4000 cal yr bp midge assemblages suggest a lake level rise related to increased effective moisture a secondary mid holocene climatic optimum with inferred mean july air temperatures of c 12 1 degrees c was recorded between 6000 and 4400 cal yr bp followed by minimum values c 11 3 degrees c between 3500 and 1500 cal yr bp accompanied by the onset of natural acidification of the lake the late holocene midge assemblages suggest weakly acidic conditions low hypolimnetic oxygen contents and a general warming trend during the last c 1500 years although paludification and natural acidification may have influenced the temperature reconstruction at this stage however the modern chironomid inferred mean july air temperature 12 5 degrees c is consistent with meteorological data from a nearby station in general the midge records reflect relatively warm and moist conditions at lake berkut before c 7000 cal yr bp a relatively warm and dry climate at c 7000 4000 cal yr bp and a shift to cooler and wetter climatic conditions in the region after c 4000 cal yr bp less

the effect of geomorphological setting on holocene lake sediment variability northern swedish lapland the effect of geomorphological setting on holocene lake sediment variability northern swedish lapland

holocene climate variability on the kola peninsula russian subarctic based on aquatic invertebrate records from lake sediments sedimentary records of invertebrate assemblages were obtained from a small lake in the khibiny mountains kola peninsula together with a quantitative chironomid based reconstruction of mean july air temperature these data provide evidence of holocene climate variability in the western sector of the russian subarctic the results suggest that the amplitude of climate change was more pronounced in the interior mountain area than near the white sea coast a chironomid based temperature reconstruction reflects a warming trend in the early holocene interrupted by a transient cooling at ca 8500 8000 cal yr bp with a maximum drop in temperature ca 1 c around 8200 cal yr bp the regional holocene thermal maximum characterized by maximum warmth and dryness occurred at ca 7900 5400 cal yr bp during this period july temperatures were at least 1 c higher than at present the relatively warm and dry climate persisted until ca 4000 cal yr bp when a pronounced neoglacial cooling was initiated minimum temperatures ca 1 2 c lower than at present were inferred at ca 3200 3000 cal yr bp faunal shifts in the stratigraphic profile imply also that the late holocene cooling was followed by a general increase in effective moisture

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

an expanded calibration model for inferring lakewater and air temperatures from fossil chironomid assemblages in northern fennoscandia chironomid temperature inference models based on an expanded data set of surface sediment and limnological data from 53 subarctic lakes in northern fennoscandia have been developed using eight different numerical techniques each based on slightly different underlying statistical models or ecological assumptions the study sites are mostly small shallow bathymetrically simple oligotrophic lakes with a ph range from 5 0 to 7 8 a total organic carbon range from 2 5 to 12 6 mg l 1 a mean july lakewater temperature ranging from 6 1 to 15 4 c and a mean july air temperature ranging from 8 5 to 14 9 c a series of redundancy analyses rda identified sediment organic content maximum lake depth and lakewater temperature as being the most important explanatory variables variance partitioning by partial rdas further suggested that each of these variables accounted for a significant fraction of variance independent from each other different cali bration models were assessed on the basis of their statisti

mid to late holocene climate transition and moisture dynamics inferred from south swedish tree ring data a 1561 year tree ring width trw chronology covering the period 2668 1108 bc 4617 3057 bp has been developed from 159 moisture sensitive peatland pines pinus sylvestris l sampled at abuamossen southern sweden tree population dynamics and annual growth responses of the trees were shown to reflect and give absolute age to regional hydro climatological changes the main wet shifts recorded in the trw data were precisely dated to 2150 2100 1550 and 1230 1150 bc 4100 4050 3500 and 3180 3000 bp and are likely to be related to the stepwise mid to late holocene climate transition during which the condition changed from relatively warm and dry towards cold and moist in the northern hemisphere the tree colonization phase was ended by several long lasting periods showing depressed annual tree growth and an abrupt dying off phase possibly caused by increasing water level in the peatland as well as the adjacent river helge a this study demonstrates that trw data obtained from subfossil peatland trees can provide detailed information and exact age control on moisture variability in peatlands associated with regional hydroclimatic changes moreover the combined information from the stratigraphical and the trw analyses enabled a detailed temporal and spatial site development reconstruction

holocene tree line dynamics and inferred climatic changes in the abisko area northern sweden based on macrofossil and pollen records lake sediment records of pollen and macroscopic plant remains of terrestrial origin provide evidence of long term changes in forest composition close to the altitudinal tree line in the abisko area northernmost sweden a dominance of mountain birch betula pubescens ehrh ssp tortuosa ledeb nyman with a field layer of ferns grasses and sedges suggests that an oceanic climate with relatively high precipitation existed during the early holocene macrofossils of mountain birch were found 300 400 m above the present tree line which corresponds to a 1 5 2 c higher summer temperature than at present scots pine pinus sylvestris was present to some extent at altitudes above its present limit during the early holocene a pronounced expansion of pine took place above its present limit around 6300 cal bp 5500 bp this is interpreted as a result of successively drier and more continental climatic conditions a decreased abundance of pine from c 5200 cal bp 4700 bp followed by a gradual retraction of

new evidence of warm early holocene summers in subarctic finland based on an enhanced regional chironomid based temperature calibration model abstract paleoclimate reconstructions based on biological proxies present methodological challenges especially during non analog conditions such as the early holocene here two chironomid based training sets from finland were amalgamated to create a more accurate transfer function of summer air temperature the aim was to reconstruct holocene paleoclimate in northernmost lapland in an area that has been either too warm or too cold for reliable reconstructions using the original calibration models the results showed that the combined calibration model had improved performance statistics the temperature trends inferred from the downcore chironomid record using the original and combined models were very similar however there were major changes in their absolute values with the combined model showing greatly improved accuracy the chironomid based temperature reconstruction showed significant correlation with the previous pollen based reconstructions from northwestern finnish lapland however differences were observed in the temperature trends of the early holocene when the chironomid inferred temperatures rapidly increased but the pollen based reconstructions lagged behind suggesting that a cool climate continued for much longer however similar to the chironomid record new plant macrofossil evidence from northwestern finland also showed warmer than present early holocene temperatures therefore we conclude that the early holocene was probably warm in northern lapland

model data comparison for the 8 2 ka bp event confirmation of a forcing mechanism by catastrophic drainage of laurentide lakes abstract to improve our understanding of the mechanism behind the 8 2 ka bp cooling event we compare proxy evidence with climate model simulations in which the thermohaline ocean circulation is perturbed by a freshwater pulse into the labrador sea both the proxy data and model results show a cooling that is mainly concentrated in the north atlantic region ranging from more than 5 c cooling in the nordic seas to about 0 5 1 c over europe and less than 0 5 c over the subtropical north atlantic data and model also indicate a weakening of the summer monsoon and generally a drier circum north atlantic over the south atlantic ocean the model simulates a slight warming mostly less than 0 5 c which falls within the uncertainty of proxy data and thus could not be confirmed to examine in detail the structure of the 8 2 ka bp event we also compare the modeled climatological evolution at two locations with high quality records revealing a generally consistent picture the good model data agreement confirms the hypothesis that the 8 2 ka bp event was forced by a freshwater induced weakening of the thermohaline circulation other forcings are unlikely since they would result in an alternative geographical distribution and expression of the climate response

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

holocene palaeoecology along the blekinge coast se sweden and implications for climate and sea level changes to investigate the holocene vegetation history and shoreline displacement along the southeastern swedish coast two radiocarbon dated pollen macrofossil and mineral magnetic sequences were studied in the western blekinge coast hunnemara lake and smygen bay both pollen records show mosaic vegetation with grasslands heaths and woodlands prior to 11 300 cal bp pinus dominated mixed forest was initially established by 11 000 cal bp by 10 000 cal bp mixed forest with higher species diversity was fully established expansion of broad leaved trees began at about 8600 cal bp indicating the onset of the mid holocene thermal maximum in scandinavia following the ulmus decline similar to 5800 cal bp the regional forest became much more open due to increased human disturbance both basins were isolated during the period of 11 300 11 000 cal bp and subsequently in contact with the ancylus lake between 10 700 and 9800 cal bp low abundance of brackish water diatoms at smygen suggests that this basin was connected with the baltic sea between 9800 and 8600 cal bp corresponding to the early littorina sea phase hunnemara was isolated during this period the two basins were in turn flooded at 8600 and 8300 cal bp as a result of global sea level rise a sedimentary hiatus 8300 7500 cal bp was present at hunnemara probably caused by a rapid sea level rise related to global meltwater pulse 3 aquatic macrofossil and mineral magnetic proxies reveal several minor transgressions at both sites probably regulated by centennial scale variations in regional storminess hunnemara was isolated from the baltic basin by 3100 cal bp concurrent with a lowering of the sea level at smygen less

quantitative palaeotemperature records inferred from fossil pollen and chironomid assemblages from lake gilltjarnen northern central sweden palaeotemperature reconstructions based on radiocarbon dated fossil pollen and chironomid stratigraphies obtained from lake gilltjarnen provide evidence of climate changes during the last 11 000 years in the boreal zone of northern central sweden the records show consistent trends during the early and mid holocene indicating low temperatures at 11 000 10 000 cal yr bp followed by a rising trend and a period of maximum values from about 7000 to 4000 cal yr bp at 3000 cal yr bp the chironomid inferred temperature values rise abruptly deviating from the late holocene cooling trend indicated by the pollen based reconstruction and most of the other palaeotemperature records from central scandinavia probably as a result of local limnological changes in lake gilltjarnen and its catchment comparison of the present results with a lake level reconstruction from lake ljustjarnen ca 100 km southwest of lake gilltjarnen shows that the low early holocene temperatures were associated with high lake levels at 10 500 8500 cal yr bp whereas low lake levels and dry conditions prevailed during the period of high temperatures at between 7500 and 5000 cal yr bp probably due to high summer evapotranspiration and lower precipitation copyright 2006 john wiley sons ltd

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

human response to the holocene environmental changes in the biržulis lake region nw lithuania abstract palaeoenvironmental studies combining 14c dating palaeobotanical and archaeological data provide information about the human reaction to holocene environmental changes registered in the surroundings of bir ulis lake in northwest lithuania responding to water regression early mesolithic communities were established on the lower lake terraces which were overgrown by predominantly birch and pine forest the formation of a mixed forest with ulmus immigrated at 8100 7500 cal yr bc corylus 7600 7200 cal yr bc and alnus 7300 6900 cal yr bc provided plenty of natural resources which led to the increase in population during the late mesolithic the expansion of tilia 6400 5900 cal yr bc and quercus 5900 5700 cal yr bc as well as the subsequent flourishing of broad leaved forest provided inhabitants with suitable living conditions the reduction of broad leaved woodland and the expansion of picea 4400 3700 cal yr bc which suggest changing temperature and moisture conditions as well as increasing erosion activity could have negatively influenced the early middle neolithic population as evidenced by the partial abandoning of the land the lowering of the water level and thinning of the forest structure possibly related to some dry episode positively influenced late neolithic groups as intensive exploitation of the area including the earliest attempts at agriculture has been registered since 1770 1490 cal yr bc when intensive bogging began evidence of periodic inhabitation around the lake has been registered

a continuous marine record 8000 1600 cal yr bp from the malangenfjord north norway foraminiferal and isotopic evidence holocene oceanography and climate were studied in the continuous marine sediment sequence in a piston core from the high latitude malangenfjord north norway using benthic foraminifera and stable isotopes radiocarbon dates indicate that the investigated sequence covers the period from c 8000 to 1600 cal bp and has a sedimentation rate of 0 3 12 7 m 1000 years bottom water temperatures reconstructed from benthic foraminiferal stable isotopes in the malangenfjord show a cooling of c 3 c ranging from 10 c and reaching c 7 c at 1600 cal yr bp which is similar to present bottom water temperature at the core location a planktic foraminiferal 18o record was established from c 6400 to 1600 cal yr bp generally following the same pattem as the benthic record this long term cooling correlates to the decreasing insolation at 70 n following the orbital forcing the long term cooling also corresponds well with atmospheric proxy records implying a close ocean atmosphere coupling it is also indicated both b

tilt observations in the normal mode frequency band at the geodynamic observatory cueva de los verdes lanzarote we have conducted observations with the aid of a seismo tiltmeter station which is based on the ostrovsky pendulum and installed at the geodynamic observatory cueva de los verdes at lanzarote island since 1995 in this station the signal is separated into two frequency bands tidal tilts from 0 to 5 mhz and ground oscillations in the frequency range of free earth s normal modes from 0 2 to 5 mhz the later band called accelerometer channel has additional amplification we analyzed the background records in the frequency range of earth s free oscillations from august 2000 to september 2001 as well as earth s normal modes after strong earthquakes we found several distinctive persistent peaks in the spectra of background oscillations both amplitudes of distinguished peaks and noises have seasonal variations we found that spectra of background oscillations are different in the frequency interval between 1 4 and 2 5 mhz for north south and east west components

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

near infrared spectrometry nirs a new tool for inferring past climatic changes from lake sediments this study tests the hypothesis that lake sediments contain climate related information that can be detected by near infrared spectrometry nirs and that nirs can be used to infer past climatic c

stable isotope variations in stalagmites from northwestern sweden document changes in temperature and vegetation during the early holocene a reply to hammarlund and edwards in a comment on the paper by sundqvist et al 2007a hammarlund and edwards suggest that the oxygen isotope signal of the speleothem records k1 and l4 from northwestern sweden as well as for the earlier published stalagmite sg93 from northern norway should mainly reflect variation in the 18o of mean annual precipitation the main argument used by the authors is that the sg93 18o record should show remarkable similarities with the lacustrine carbonate 18o record from lake tibetanus the similarities between sg93 and lake tibetanus are mainly seen for the period between 10 and 9 ka bp which is a period where both records have higher 18o values compared with later in the holocene if true this would indicate that temperatures in northern scandinavia would have reached their holocene maximum between 10 and 9 ka bp which is contrary to what has been reported from other archives in the region which place the holocene climatic optimum somewhere between 8 and 5 ka bp several factors affect the 18o of

radiocarbon evidence for rates of lateral expansion in raised mires in southern finland radiocarbon ages from the bottom peat deposits and detailed morphometric measurements at five peatlands in the boreal region of southern finland were used to reconstruct the holocene patterns of raised mire development the results suggest that the areal expansion of the mires has been extremely rapid at times up to several hundreds hectares per millennium but the periods of more rapid expansion were not coincident among the mires the rate of lateral extension was shown to depend mainly on the topography of the mineral substrate horizontal expansion did not always correlate with vertical growth mires expanded slowly between ca 6000 and 4000 yr b p probably as a consequence of drier climatic conditions at that time the mires also expanded slowly during the two to three recent millennia the reason for this most probably lying in steepening of the bottom gradient toward the marginal areas of the present mires the results point to a substantial measure of local environmental control over the lateral extension in raised mire ecosystems

diatom response to mid holocene climate in three small arctic lakes in northernmost finnmark palaeoclimatic reconstructions from lake sediment biological records can be challenging due to variation in non climatic factors which alter ecosystem responses to consider this it is important to replicate a study regionally so as to gain information on spatial variability of ecosystem response and the influence of site specific conditions previous pollen based palaeoclimatic records from three well dated arctic lake sites highlight the response of regional scots pine pinus sylvestris and mountain birch betula pubescens ssp czerepanovii forest tundra transition to holocene climatic variability and suggest the northernmost peninsulas of finnmark to be climatically sensitive this study analysed dated sediment sequences between c 3970 and c 6200 cal yr bp from these three previously published shallow lakes liten cap pesjav ri lcj over gunnarsfjorden ogf and over kobbkrokvatnet okv for freshwater diatoms diatom assemblages showed an increase in the planktonic diatoms relative to benthic diatoms with an onset towards higher abundances of small centric planktonic diatoms at ogf between c 5270 and 5350 cal yr bp and okv between c 5280 and 5350 cal yr bp additionally a diatom compositional shift was detected at lcj between c 5180 and 5300 cal yr bp trend analysis found the main diatom compositional change at all three sites to occur at 5300 cal yr bp however this synchronous diatom shift during the mid holocene varies in magnitude within the three finnmark lakes the abrupt planktonic benthic diatom ratio changes are independent of the pinus betula ratios and are likely to be a result of lake ice cover changes allowing longer growing seasons greater water column stability and higher nutrient concentrations from surrounding catchments this study highlights the significant differences in aquatic ecosystem and terrestrial vegetation response to climatic changes with diatom assemblages at these sites either responding before the regional tree line shift or to a separate climatic event within the mid holocene

chironomids as a tool for inferring holocene climate an assessment based on six sites in southern scandinavia abstract chironomid subfossil assemblages from six low alpine and sub alpine holocene stratigraphies are presented and compared they are from five lakes in mid southern and western norway and one in central sweden when comparing the chironomid inferred july air temperatures there are many time segments with a poor among lake fit in inferred temperatures possible environmental variables influencing the fossil chironomid assemblages are discussed using a modern norwegian calibration data set to indicate taxon environment relationships these analyses indicate that local changes in ph water chemistry and productivity at times may have overridden the regional temperature signal in addition other causes of poor among site temperature fit are discussed in particular those related to chronological uncertainties holocene temperature inferences from single cores based on chironomids may not always be able to provide a reliable regional temperature signal but can act as a guide from which hypotheses about past environmental conditions can be tested with the aid of chironomid inferred temperatures from several sites and from other environmental proxies we have obtained a regional picture of holocene summer temperature change by developing a consensus reconstruction based on the overall temperature signal from all six sites this consensus is developed by fitting a smoother through all 330 site specific temperature deviations from the holocene mean the consensus temperature deviations vary from 0 8 c at 8800 cal years bp to 0 8 c at 6500 cal years bp

diatom community responses to late holocene climatic variability baffin island canada a comparison of numerical approaches a high resolution diatom stratigraphy from the late holocene sediments of a small arctic lake on bafe n island nunavut canada has been analysed by several numerical methods and considered in relation to independent palaeoclimatic proxies to enable an objective assessment of the response of freshwater diatom communities to climatic change diatom relative frequencies and absolute abundances were subjected to several manipulations including application of a weighted averaging transfer function for summer water temperature conversion of valve concentrations to cell biovolumes biostratigraphic rate of change and taxonomic richness estimated by rarefaction analysis the major directions of variability within the derived diatom data were explored using principal components analysis diatom inferred lakewater temperatures and indices of diatom palaeoproductivity declined during late holocene cooling and they faithfully record post little ice age warm ing between 2000 cal bp and the little ice age which includes the coldest intervals of the neoglacial diatom assemblages diversie ed and destabilized ree ecting a state of intermediate disturbance together these results examine different methods of interpreting freshwater diatom stratigraphic data with the objective of gaining palaeoclimatic insights from fossil assemblages

holocene climatic variations in southern finland reconstructed from peat initiation data radiocarbon and pollen analytical dates of 71 basal peat samples from 23 sites in the boreal region of southern finland were used to reconstruct patterns of peat initiation and the subsequent sprea

tornetrask tree ring width and density ad 500 2004 a test of climatic sensitivity and a new 1500 year reconstruction of north fennoscandian summers this paper presents updated tree ring width trw and maximum density mxd from tornetrask in northern sweden now covering the period ad 500 2004 by including data from relatively young trees for the most recent period a previously noted decline in recent mxd is eliminated non climatological growth trends in the data are removed using regional curve standardization rcs thus producing trw and mxd chronologies with preserved low frequency variability the chronologies are calibrated using local and regional instrumental climate records a bootstrapped response function analysis using regional climate data shows that tree growth is forced by april august temperatures and that the regression weights for mxd are much stronger than for trw the robustness of the reconstruction equation is verified by independent temperature data and shows that 63 64 of the instrumental inter annual variation is captured by the tree ring data this is a significant improvement compared to previously published reconstructions based on tree ring data from tornetrask a divergence phenomenon around ad 1800 expressed as an increase in trw that is not paralleled by temperature and mxd is most likely an effect of major changes in the density of the pine population at this northern tree line site the bias introduced by this trw phenomenon is assessed by producing a summer temperature reconstruction based on mxd exclusively the new data show generally higher temperature estimates than previous reconstructions based on tornetrask tree ring data the late twentieth century however is not exceptionally warm in the new record on decadal to centennial timescales periods around ad 750 1000 1400 and 1750 were equally warm or warmer the 200 year long warm period centered on ad 1000 was significantly warmer than the late twentieth century p 0 05 and is supported by other local and regional paleoclimate data the new tree ring evidence from tornetrask suggests that this medieval warm period in northern fennoscandia was much warmer than previously recognized

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

diatoms as quantitative indicators of july temperature a validation attempt at century scale with meteorological data from northern sweden diatoms as quantitative indicators of july temperature a century scale validation with meteorological data from northern sweden

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

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

a high resolution 11 400 yr diatom record from lake victoria east africa abstract fine interval 30 45 yr sampling of a core from lake victoria s damba channel shows that numerous abrupt changes in the lake s diatom assemblages have occurred in response to climatic fluctuations over the past 11 400 14 c yr four distinct climatic phases bounded by sudden transitions are inferred 1 variably dry 11 400 10 000 yr b p 2 humid 10 000 7200 yr b p 3 more seasonal 7200 2200 yr b p and 4 more arid 2200 0 yr b p with a dry little ice age event 600 200 yr b p the diatom inferred paleoclimatic history for northern lake victoria closely resembles that inferred from a well dated pollen record from pilkington bay spectral analysis of the diatom record reveals strong periodicities including globally distributed 2360 2550 1400 1030 1130 and 500 cal yr cycles repeated rapid shifts between aulacoseira and nitzschia dominated diatom assemblages suggest that post 1960 changes in the lake s phytoplankton communities have had earlier climate driven analogs

the development of a pulsating supraglacial stream supraglacial streams are a significant part of the glacial hydrological system and important for understanding the connection between glacial hydrology and glacier dynamics here we determine the factors that influence the development of step pool formation and pulsating flow in a supraglacial stream on bylot island nunavut results show that during the second week of a 2 week study multiple successive rainfall events occurred stream temperature increased and ablation decreased which also caused stream discharge to decrease in addition the stream which flowed over a 13 m high waterfall off the front of fountain glacier rapidly formed 21 step pools and began to pulsate the pulsating phenomenon involved the complete stoppage of flow over the waterfall and the subsequent restart between 8 and 20 s later pulsating flow resulted from rapid changes in the streambed morphology in particular the formation of the step pool sequence was caused by helical flow around meander bends and hydrologically induced slippage along transverse shear planes evidenced by observations of high pressure artesian flow from transverse fractures contrary to previous literature this study shows that high discharge is not necessarily the cause of step pool formation and pulsating flow within supraglacial streams

abrupt changes in north american climate during early holocene times recent studies of the greenland ice cores have offered many insights into holocene climatic dynamics at decadal to century timescales1 2 3 despite the abundance of continental records of holocene climate few have sufficient chronological control and sampling resolution to compare with the greenland findings4 butannually laminated sediments varves from lakes can provide high resolution continental palaeoclimate data with secure chronologies here we present analyses of varved sediments from deep lake in minnesota usa trends in the stable oxygen isotope composition of the sedimentary carbonate indicate a pronounced climate cooling from 8 9 to 8 3 kyr before present probably characterized by increased outbreaks of polar air decreased precipitation temperatures and a higher fraction of the annual precipitation falling as snow the abrupt onset of this climate reversal over several decades was probably caused by a reorganization of atmospheric circulation and cooling of the arctic airmass in summer that resulted from the final collapse of the laurentide ice near hudson bay and the discharge of icebergs from the quebec and keewatin centres into the tyrell sea the timing and duration of this climate reversal suggest that it is distinct from the prominent widespread cold snap that occurred 8 200 years ago in greenland and other regions1 5 6 no shifts in the oxygen isotope composition of sediment carbonate occurred at 8 2 kyr before present at deep lake but varve thickness increased dramatically probably as a result of increased deposition of aeolian dust taken together our data suggest that two separate regional scale climate reversals occurred between 9 000 and 8 000 years ago and that they were driven by different mechanisms

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

holocene temperature changes in northern fennoscandia reconstructed from chironomids using bayesian modelling the recently developed bayesian multinomial calibration model bummer was applied to the fossil chironomid assemblages of a lake situated at the present tree line in northern fennoscandia to reconstruct patterns in holocene climates the results are compared with inferences derived using non bayesian weighted averaging partial least squares regression the reconstruction exhibits both long term trends as well as a series of shorter term oscillations abrupt climatic excursions were particularly characteristic for the early holocene period with cooling episodes around 9200 8600 and 8200 cal yr bp the interval from ca 8000 to 5800 cal yr bp appeared to be warm and stable but was followed by a pronounced climatic cooling around 5800 cal yr bp leading to a relatively long lasting mid holocene temperature minimum between ca 5800 and 4000 cal yr bp the reconstruction during the latter part of the holocene is relatively featureless which may partly be due to gradual shallowing of the lake by sedimentation that may have affected chironomid compositions thereby masking the climate signal the major climatic patterns in our reconstruction agree well with inferences from greenland ice and marine sediments and are also in line with the previous reconstructions based on diatoms and pollen from the same core although the finer scale variations reflected by the three proxies do not always match the overall results provide evidence for climatic complexity during the holocene epoch and demonstrate that bayesian modelling is highly suitable for reconstruction purposes

the cold event 8200 years ago documented in oxygen isotope records of precipitation in europe and greenland stable oxygen isotope ratios of ostracod valves in late glacial and holocene sediments of core as 92 5 from deep lake ammersee southern germany reflect variations of mean oxygen isotope ratios in past atmospheric precipitation the record reconfirms the strong similarity of climate evolution in europe and greenland during the last deglaciation for the first time in europe we find a 200 year long negative 18o excursion which is contemporaneous with the strongest negative 18o excursion in the greenland ice around 8 2 ky before present the 8 2 ky isotopic event on both sides of the north atlantic ocean is interpreted as a cold period most probably induced by a perturbation of the north atlantic thermohaline circulation we discuss two possible triggering mechanisms 1 weak forcing as proposed by alley et al and 2 forcing by a strong and sudden freshwater pulse from the collapse of the hudson ice dome

susceptibility of small boreal lakes to environmental changes as inferred from organic sediments of lake talvilampi finland during the holocene multiple thermal changes commonly occurred in the northern hemisphere they are well recorded in lakes with minimum human impact from the arctic circle area the development of

a chronostratigraphy of mid and late holocene slope evolution creagan a chaorainn northern highlands scotland unusual exposure of the drift stratigraphy of a typical vegetated hillslope in the northern highlands of scotland has allowed reconstruction of its holocene history graphic logging of palaeogully fill sediment analysis radiocarbon dating and microscopic investigation of horizon boundaries link periodic slope instability to changes in hydrology and vegetation cover the oldest preserved organic matter dates from about 7 5 cal ka bp several millennia of subsequent stability were followed at about 4 3 cal ka bp by destabilization whose magnitude and frequency markedly increased after about 2 7 cal ka bp precipitation driven weathering and erosion offer the best explanation for late holocene slope rejuvenation at this site with change effected through long lasting shifts in system equilibria as well as high magnitude inputs anthropogenic impacts on slope stability are apparently restricted to the last few hundred years the timing and episodicity of slope evolution suggests climate forcing resu

a regional 8200 cal yr bp cooling event in northwest europe induced by final stages of the laurentide ice sheet deglaciation the most notable change in 18o in greenland ice cores during the holocene occurs at 8200 cal yr bp here we present a new high resolution marine record from the northern north sea along with tree ring data from germany which contain evidence of a pronounced temperature drop 2 c contemporaneous with that of the greenland ice core records the synchronous timing of the cooling event in the greenland ice cores marine record and tree ring data from northwest europe reflects a regional influence on the north atlantic ocean atmospheric system suggesting a prominent role of the north atlantic thermohaline circulation the operation of the north atlantic ocean circulation is sensitive to variation in the freshwater budget implying that any change in freshwater flux is capable of altering the north atlantic circulation system we hypothesise minor but long term freshwater fluxes in the final stages of the deglaciation of the laurentide ice sheet as a forcing mechanism 1998 john wiley sons ltd

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

structure of the 8200 year cold event revealed by a speleothem trace element record abrupt first order shifts in strontium and phosphorus concentrations in stalagmite calcite deposited in western ireland during the 8200 year event the major cooling episode 8200 years before the present are interpreted as responses to a drier climate lasting about 37 years both shifts are centered on 8330 80 years before the present coinciding with a large oxygen isotope anomaly and a change in the calcite petrography in this very high resolution monthly record antipathetic second order oscillations in phosphorus and strontium reveal decreased growth rates and increased rainfall seasonality growth rate variations within the event reveal a two pronged structure consistent with recent model simulations

temperature patterns over the past eight centuries in northern fennoscandia inferred from sedimentary diatoms establishing natural climate variability becomes particularly important in remote polar regions especially when considering questions regarding higher than average warming we present a high resolution record of temperature variability for the past 800 yr based on sedimentary diatoms from a treeline lake in finnish lapland the bsizer multiscale smoothing technique is applied to the data to identify significant features in the record at different temporal levels the overall reconstruction shows relatively large multi centennial temperature variability with a total range of about 0 6 0 8 c at millennial scales the temperatures exhibit a statistically significant long term cooling trend prior to industrialization t 0 03 c century at the centennial timescale three warm time intervals were identified around ad 1200 1300 terminal phase of the medieval warm period mwp 1380 1550 and from 1920 until the present pronounced coolness occurred between ad 1600 and 1920 indicative of the little ice age lia at the decadal level certain shorter term climate excursions were revealed the warmest 10 30 yr nonoverlapping periods occurred in ad 1220 1250 1470 1500 and 1970 2000 respectively the classic events of mwp and lia are evident in our record as is also the 20th century warming

north atlantic fennoscandian holocene climate trends and mechanisms abstract to investigate the mechanisms behind holocene regional climate trends from north of 58 n in the north atlantic fennoscandian region principal component analysis pca was performed and a temperature anomaly stack produced from 81 proxy derived summer temperature time series from 74 sites the pc results show distinctly different trends for near surface versus surface temperatures demonstrating the importance of handling these separately the first pc of weighted sea surface summer temperature time series and continental time series explains 45 8 of the variance where the uncertainty is the standard deviation of the distribution of variance explained across the 1000 age uncertain ensemble members pc1 has a relatively uniform expression over the whole region closely following the summer insolation at 65 n the second pc explains 22 4 of the variance and shows a non uniform expression with loadings in opposite directions in the northern and southeastern parts of the region comparing the pc time series with model runs and with the timing of the demise of the laurentide ice sheet lis suggest that this pattern reflects both topographic and albedo effects of the lis as well as release of meltwater into the north atlantic and arctic oceans comparing the stack of gridded records with published global stacks reveals an unusual holocene temperature development in the north atlantic fennoscandian region most likely resulting from the location relative to the decaying lis

the significance of modern diatoms as paleoenvironmental indicators along an altitudinal gradient in the andean piedmont of central argentina abstract the objectives of this study were to a analyze the distribution pattern of diatom assemblages in freshwater systems from central western argentina b investigate the key climatic and limnological factors affecting the species distributions and c evaluate the extent and limitations of diatoms as quaternary paleoenvironmental indicators in the area diatoms were sampled and physical and chemical variables were quantified in a total of 45 lotic and lentic sites altitude annual precipitation and summer january temperature data were obtained from a world climate database previously published data from an adjacent region was incorporated into the modern dataset environmental variables significantly influencing diatom assemblage composition were identified through partial canonical correspondence analyses ccas in order to assess the degree of analogy between modern and fossil assemblages the modern analog technique mat was applied diatom taxa showed distinct abundance patterns in relation to altitude with a shift from communities dominated by periphitic and benthic taxa in lower sites to communities dominated by small benthic tychoplanktonic taxa in high elevated waterbodies the ph was the strongest variable explaining the variance within the diatom dataset followed by log conductivity and summer air temperature the comparison of modern diatom assemblages with fossil sequences allowed reconstruction of the evolution of shallow lentic and vegetated habitats a good analogy between modern and pleistocene diatom assemblages was found the strong relationship between diatoms and climate driven environmental variables such as ph conductivity and summer temperature enhances the importance of the diatom floras as paleoclimatic indicators in the area and encourages future development of quantitative inference models for the region

holocene climatic change reconstructed from diatoms chironomids pollen and near infrared spectroscopy at an alpine lake sjuodjijaure in northern sweden the results of a multiproxy study reconstructing the climate history of the last 9300 years in northern sweden are presented it is based on diatom chironomid and pollen analyses as well as near

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

comparison of quantitative holocene temperature reconstructions using multiple proxies from a northern boreal lake four biotic proxies plant macrofossils pollen chironomids and diatoms are employed to quantitatively reconstruct variations in mean july air temperatures tjul at lake loitsana northern finland during the holocene the aim is to evaluate the robustness and biases in these temperature reconstructions and to compare the timing of highest tjul in the individual reconstructions the reconstructed tjul values are evaluated in relation to local scale site specific processes associated with the holocene lake development at loitsana as these factors have been shown to significantly influence the fossil assemblages found in the lake loitsana sediments while pollen based temperatures follow the classical trend of gradually increasing early holocene tjul with a mid holocene maximum the aquatic wetland assemblages reconstruct higher than present tjul already during the early holocene that is at the peak of summer insolation the relatively low early holocene july temperatures recorded by the pollen are the

diatom based inference of variations in the strength of asian winter monsoon winds between 17 500 and 6000 calendar years b p 1 we present a continuous record of fossil diatoms from huguang maar lake hml in southeastern china spanning the time interval 17 500 to 6000 calendar years cal years b p the seasonal change in relative abundance of the dominant diatom taxa aulacoseira and cyclotella species can be used as a proxy of the strength of winter monsoon winds wmw which is supported by the results of a sediment trap experiment in hml and by an extensive review of the literature on the autoecologies of these species in the sediment high c stelligera abundance and high diatom concentration which indicate warm conditions and low wind driven turbulence of the water column characterize an interval equivalent to the greenland interstadial 1 this is followed by an interval with low diatom concentration and with assemblages dominated by aulacoseira species which suggests high wind driven turbulence and therefore strong wmw this interval corresponds with the greenland stadial 1 during the early and middle holocene another two episodes with strong wmw are evident from the data between 10 000 and 8500 and between 7000 and 6000 cal years b p the diatom record implies that strong winter monsoon episodes not only occurred during the last glacial holocene transition but also during the holocene thermal maximum

stable isotope variations in stalagmites from northwestern sweden document climate and environmental changes during the early holocene this paper presents two early holocene 9 6 5 9 ka bp high resolution stable isotope records of stalagmites from two caves in northwestern sweden korallgrottan and labyrintgrottan close similarities between the swedish records and a previously presented norwegian stalagmite oxygen isotope record emphasize the potential of scandinavian stalagmites to provide high resolution regional palaeoclimatic information the stable oxygen isotope records are interpreted to reflect the temperature evolution during the early holocene with a gradual warming from c 9 6 ka bp interrupted by cooler conditions at 8 5 8 0 ka bp the results indicate that the cooler conditions were driven by two to three abrupt cold events rather than one 8 2 event only except for these cold events the stalagmite oxygen isotope records show that temperatures in northwestern sweden were warmer than today between 9 6 and 5 9 ka bp and that during this period the interval between 7 8 and 5 9 ka bp seems to have been the warmest the hig

holocene solifluction climate variation and fire in a subarctic landscape at pippokangas finnish lapland based on radiocarbon dated buried charcoal a large number of radiocarbon dates from charcoal layers buried beneath stacked solifluction lobes at pippokangas in the northern boreal zone of finnish lapland are used to reconstruct a holocene history of solifluction although the site is surrounded by scots pine forest the solifluction lobes occur on the lower slopes of a kettle hole the microclimate of which prevents the growth of trees samples from the upslope end of charcoal layers have enabled the recognition of four synchronous phases of solifluction lobe initiation 7400 6700 4200 3400 2600 2100 and 1500 500 cal yr bp rates of lobe advance are shown to be lobe dependent and age dependent initially average rates were commonly 0 14 0 19 cm yr 1 later falling to 0 02 0 07 cm yr 1 or less as the lobes approached the bottom of the slope the absence of charcoal prior to 8000 cal yr bp together with single irsl and tl dates indicate a relatively stable early holocene landscape the onset of solifluction around 7400 cal yr bp appears to have followed the immigration of pine around the site which increased the frequency of forest fires phases of solifluction activity seem to have been triggered by millennial scale variations in effective moisture the climatic hypothesis rather than episodic burning of the surface vegetation cover the geoecological hypothesis although climate may also have affected fire frequency and severity copyright 2005 john wiley sons ltd

quantitative multiproxy assessment of long term patterns of holocene environmental change from a small lake near abisko northern sweden quantitative reconstructions are made of holocene changes in climatic and environmental conditions from analyses of pollen chironomids and diatoms in identical stratigraphic levels of a sediment c

chironomids temperature and numerical models a reply to seppala we reply to comments by seppala 2001 concerning the suitability of the surface water temperature measurements and mean july air temperature estimates used by olanderet al 1999 to derive quantitative chironomid temperature transfer functions we use new data for water temperatures based on two hourly recordings from thermistors installed in 32 lakes and air temperature data from an automatic weather station at one lake to refute seppala s accusations that our field data are unsatisfactory we also respond to seppala s suggestions about factors influencing chironomid distribution and abundance and suggest that there is a serious confusion of temporal and spatial scales between seppala s ideas and the olanderet al study we attempt to explain the underlying logic behind empirical transfer functions that form a major part of holocene quantitative environmental reconstructions and the major assumptions behind such transfer functions as seppala appears not to understand the basis or the assumptions of suc

centennial scale holocene climate variability revealed by a high resolution speleothem δ18o record from sw ireland evaluating the significance of holocene submillennial 18 o variability in the greenland ice cores is crucial for understanding how natural climate oscillations may modulate future anthropogenic warming a high resolution oxygen isotope record from a speleothem in southwestern ireland provides evidence for centennial scale 18 o variations that correlate with subtle 18 o changes in the greenland ice cores indicating regionally coherent variability in the early holocene evidence for previously undetected early holocene cooling events is presented but mid to late holocene ice rafting in the north atlantic appears to have had little impact on 18 o at this ocean margin site

development of an eemian mis 5e interglacial palaeolake at sokli n finland inferred using multiple proxies a 12 m long lacustrine record from sokli n finland was analyzed for diatoms non pollen palynomorphs macrofossils pollen and geochemistry in order to reconstruct the development of a high latit

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

similarities and discrepancies between chironomid and diatom inferred temperature reconstructions through the holocene at lake 850 northern sweden similarities and discrepancies between chironomid and diatom inferred temperature reconstructions through the holocene at lake 850 northern sweden

pairwise comparisons to reconstruct mean temperature in the arctic atlantic region over the last 2 000 years existing multi proxy climate reconstruction methods assume the suitably transformed proxy time series are linearly related to the target climate variable which is likely a simplifying assumption for many proxy records furthermore with a single exception these methods face problems with varying temporal resolutions of the proxy data here we introduce a new reconstruction method that uses the ordering of all pairs of proxy observations within each record to arrive at a consensus time series that best agrees with all proxy records the resulting unitless composite time series is subsequently calibrated to the instrumental record to provide an estimate of past climate by considering only pairwise comparisons this method which we call paico facilitates the inclusion of records with differing temporal resolutions and relaxes the assumption of linearity to the more general assumption of a monotonically increasing relationship between each proxy series and the target climate variable we apply paico to a newly assembled collection of high quality proxy data to reconstruct the mean temperature of the northernmost atlantic region which we call arctic atlantic over the last 2 000 years the arctic atlantic is a dynamically important region known to feature substantial temperature variability over recent millennia and paico allows for a more thorough investigation of the arctic atlantic regional climate as we include a diverse array of terrestrial and marine proxies with annual to multidecadal temporal resolutions comparisons of the paico reconstruction to recent reconstructions covering larger areas indicate greater climatic variability in the arctic atlantic than for the arctic as a whole the arctic atlantic reconstruction features temperatures during the roman warm period and medieval climate anomaly that are comparable or even warmer than those of the twentieth century and coldest temperatures in the middle of the nineteenth century just prior to the onset of the recent warming trend

a multiproxy palaeolimnological investigation of holocene environmental change between c 10 700 and 7200 years bp at holebudalen southern norway geochemical analyses x ray fluorescence 13c and c n ratios were used to reconstruct early holocene environments between 10685 and 7260 cal yr bp at a small lake near holebudalen southern norway results show a period of increasing stability with reduced catchment inwash shown by titanium and potassium minerals vegetation stabilization and increasing aquatic productivity c n ratios however periods of instability loss on ignition loi decrease are also seen most notably at c 9060 cal yr bp chironomid inferred july temperature ci t reconstructions show a cooling of c 2 c rmsep 1 0 c between c 8400 and 8000 cal yr bp and so high resolution 5 mm c 20 yr diatom analyses were conducted between 8675 and 7830 cal yr bp in order to further investigate this change between c 8270 and 8000 cal yr bp there were large reductions 50 in the abundance of tychoplanktonic diatoms eg aulacoseira species and absolute increases in periphytic diatom communities eg navicula pupula pinnularia mesolepta the multiproxy analyses suggest a period of increased lake ice cover with associated reductions in turbulence during this time diatom flora changes are concomitant with a fall in percent loi and increased catchment erosion at the site and other evidence of regional climatic perturbations in the early holocene therefore superimposed upon an early holocene warming trend at holebudalen there are climatic perturbations for example reflected between c 8200 and 8000 cal yr bp by diatom communities

evidence of increased rainfall prior to 3500 years bp as revealed by river borne terrigenous flux a study from west coast of india abstract the study has been conducted for insoluble residue and calcium carbonate content in a 4 80 m long shallow water at 22 m water depth sediment core at 22 m water depth off central west coast of india to reconstruct palaeo monsoonal precipitation linked with river discharge the down core profile of carbonate content shows that it is generally less than 28 below ca 3 00 m whereas above 3 00 m it is generally more than 28 and this showing an general upward trend on the contrary the average insoluble residue is marked by higher value 72 below ca 3 00 m while above 3 00 m it is low