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

bacterial magnetite produced in water column dominates lake sediment mineral magnetism lake ely usa summary environmental magnetic studies of annually laminated sediments from lake ely northeastern pennsylvania usa indicate that bacterial magnetite is the dominant magnetic mineral in the lake sediment in previous studies of lake ely sediment the dark organic rich layers in the annual laminae were interpreted to have high intensity saturation isothermal remanent magnetizations sirms while the light coloured silt rich layers have low intensity sirms to test the hypothesis that the magnetic grains in the sediments were an authigenic product of magnetotactic bacteria rather than detrital magnetic grains eroded from the watershed we analysed samples from the water column the lake sediment and a sediment trap installed near the lake bottom direct microscopic observation of the water column samples showed the presence of magnetotactic bacteria in and below the oxic anoxic transition zone oatz to characterize the magnetic minerals rock magnetic parameters were measured for material from the water column the sediment trap and the dark and light coloured lake sediments low temperature magnetic measurements tested for the presence of magnetosomes in separated dark and light coloured layer samples numeric unmixing of the low temperature results showed that biogenic magnetites were present in the lake sediment and contributed more significantly to the sirm in the dark organic rich layers than in the light coloured inorganic silt rich layers observations under the transmission electron microscope tem of magnetic extracts also show the abundance of magnetosomes in the lake sediment the presence of live magnetotactic bacteria in the water column and the predominance of bacterial magnetites in filtered particulate matter sediment traps and recent lake sediment all suggest that bacterial magnetites are the main magnetic minerals in lake ely sediment this finding suggests that changes in environmental factors that control the productivity of magnetic bacteria in the lake likely contribute to the variability of magnetic mineral concentrations observed in the lake sediments

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

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

characterizing changes in the sedimentary environment of a varved lake sediment record in southern central finland around 8000 cal yr bp the varved lake sediment record of lake nautajarvi in southern central finland indicates fluctuations in the annual sedimentation pattern and lake environment around 8000 cal yr bp annual accumulation of catchment derived mineral matter peaks a number of times and there are changes in the deposition rate of organic matter based on evidence from the lake nautajarvi sediment record the climate was characterised by a millennial scale colder period that terminated at one or several cooling events around 8000 cal yr bp during one of these events diatom composition undergoes a change from planktonic species dominance to more littoral species dominance at 8160 cal yr bp and a recovery around 8010 cal yr bp the timing of this 150 year long diatom anomaly is convergent with increased catchment erosion and decreased organic matter accumulation we interpret that during such a period the environment was characterised by colder winter temperatures prolonged duration of ice cover higher than normal spring discharge and rapid development of thermal stratification in the spring coupled with reduced water circulation and shorter growing seasons copyright 2008 john wiley sons ltd

atmospheric radiocarbon calibration to 45 000 yr b p late glacial fluctuations and cosmogenic isotope production more than 250 carbon 14 accelerator mass spectrometry dates of terrestrial macrofossils from annually laminated sediments from lake suigetsu japan provide a first atmospheric calibration for almost the total range of the radiocarbon method 45 000 years before the present the results confirm the recently revised floating german pine chronology and are consistent with data from european and marine varved sediments and combined uranium thorium and carbon 14 dating of corals up to the last glacial maximum the data during the glacial show large fluctuations in the atmospheric carbon 14 content related to changes in global environment and in cosmogenic isotope production

assessing the reliability of holocene relative palaeointensity estimates a case study from swedish varved lake sediments we present palaeomagnetic secular variation and relative palaeointensity estimates from multiple sediment cores recovered from a varved lake sediment sequence in kalksjon a lake in central west sweden alternating field demagnetization of discrete samples reveals natural remanent magnetizations dominated by a stable single component magnetic grain size indicators which include day plots and first order reversal curves indicate that the main carrier of the natural remanence is single domain magnetite throughout the varved sequence which extends to similar to 9200 cal yr bp the millennial scale features of the kalksjon relative palaeointensity inclination and declination data are well matched against the fennoscandian master curves fennorpis and fennostack and a global dipole moment reconstruction curve there is evidence however of environmental bias in the relative palaeointensity estimates during specific time intervals we find that bias is particularly pronounced during the early holocene specifically between similar to 9000 and 7800 cal yr bp during this period the bias is apparent as a series of relative palaeointensity cycles with a wavelength of similar to 300 years some bias is also evident between 7800 and 3200 cal yr bp by comparing kalksjon s smoothed relative palaeointensity data with the reconstructed geomagnetic field intensity from c 14 on timescales longer than 500 years thereby removing the effect of relatively high frequency environmental bias in the early holocene we suggest that a distinct peak in intensity at centred on similar to 8700 cal yr bp is a true feature of the geomagnetic field a minimum at similar to 7400 cal yr bp and a maximum at similar to 2500 cal yr bp are also robust features our main conclusion is that sedimentary based relative palaeointensity reconstructions must be carefully assessed if short term centennial variations are to be examined less

fennostack and fennorpis varve dated holocene palaeomagnetic secular variation and relative palaeointensity stacks for fennoscandia a holocene palaeomagnetic secular variation master curve fennostack and a relative palaeointensity curve fennorpis for fennoscandia are presented these curves were produced by stacking palaeomagnetic data obtained from six annually laminated varved lake sediment sequences and one non laminated sediment sequence the six independent varve chronologies were combined to form a timescale which extends between the present year and 10 200 cal yr bp smoothed inclination and declination curves show trends that are similar to a palaeomagnetic secular variation curve for the united kingdom except that the ages of most of the statistically significant features are a few hundred years younger in the fennoscandian data set these differences are most likely due to excessively old ages of the united kingdom features produced by the radiocarbon dating of bulk sediments the standardized relative palaeointensity stack shows that the intensity of the geomagnetic field in fennoscandia was highest at 2300 cal yr bp and lowest at 7000 cal yr bp three palaeointensity peaks pips and three palaeointensity lows pils are identified in fennorpis and indicate that the intensity of geomagnetic field varied significantly on millennial scales in this region during the holocene but there is much scatter in the reconstruction prior to 8000 cal yr bp higher frequency palaeointensity features present in individual records are not significant in the stacked data set which implies that these are a result of local environmental bias significant discrepancies exist between the data and the output of the cals7k 2 geomagnetic field model for the last 7000 yr in particular the largest declination swing observed in the data at 2670 cal yr bp feature f is not produced by the model which is most likely due to the influence of an inaccurately dated icelandic secular variation curve on the model result short term trends in standardized relative palaeointensity do differ from the model output but it is difficult to make a comparison because of the relative nature of the sediment record better absolute palaeointensity data are needed to reduce uncertainties in reconstructions of past geomagnetic field strength

scandinavian glacial and climatic fluctuations during the holocene abstract historical documents and lichenometric studies give a detailed picture of the little ice age in scandinavia there was a large advance in norway which has been dated at a few places to 1750 small readvances during the retreat occurred around a d 1780 1810 1840 1850 1850 1870 1890 1910 and 1930 in sweden most of these advances have been recognized and in addition extensive advances are dated by lichenometry to around a d 1600 1650 and 1700 1720 soils buried beneath moraines often yield radiocarbon dates that are much too old methods dependent on these must therefore be used with care evidence for pre little ice age advances are often considered equivocal the most reliable information is probably provided by studies of lacustrine sediments combining information from all sources the most significant pre little ice age glacier advances most likely occurred in 7 5 5 1 4 5 3 2 2 8 2 2 1 9 and 1 5 1 1 radiocarbon ka bp advances that were less extensive or for which there is less evidence occurred around 6300 5600 2500 940 600 560 and 380 bp

late glacial to holocene volcanism of jom bolok valley east sayan mountains siberia recorded by microtephra layers of the lake kaskadnoe 1 sediments abstract this article presents first tephrochronological data on the volcanic activity in the valley of the jom bolok river east sayan mountains siberia which is the largest manifestation of the holocene eruptions in central asia the data results from our study of the proglacial kaskadnoe 1 lake situated near the jom bolok basalt field the lake sediments include a series of tephra rich layers radiocarbon dating of the lake sediments provided a robust age model which allowed us to build timing of eruptions formed the jom bolok volcanic field we recognize two large phases of volcanism separated by almost 5 thousand years dormant phase the first phase is traced back to ca 14 3 cal ka bp and lasted until 6 3 cal ka bp ten clusters of microtephra layers in the sediments of the first phase show 300 800 years recurrence of the volcanic events weakening upward the event of 14 3 13 3 cal ka bp probably represents the strongest eruptions of the jom bolok the second phase started ca 1 6 cal ka bp and highly likely continues in our days its strongest eruptions occurred between 1 6 and 0 8 cal ka bp with periodicity of 200 years this tephrostratigraphy shows a multiplicity of the jom bolok volcanic events and amplifies the earlier built scheme resulted from investigations of the stratified basalts pyroclasts and lake damming events additionally we indicate a possible influence of the jom bolok volcanic activity on the regional and global climatic changes

ams radiocarbon dating and varve chronology of lake soppensee 6000 to 12000 14c years bp for the extension of the radiocarbon calibration curve beyond 10000 14c y bp laminated sediment from lake soppensee central switzerland was dated the radiocarbon time scale was obtained using accelerator mass spectrometry ams dating of terrestrial macrofossils selected from the soppensee sediment because of an unlaminated sediment section during the younger dryas 10000 11000 14c y bp the absolute time scale based on counting annual layers varves had to be corrected for missing varves the soppensee radiocarbon verve chronology covers the time period from 6000 to 12000 14c y bp on the radiocarbon time scale and 7000 to 13000 calendar y bp on the absolute time scale the good agreement with the tree ring curve in the interval from 7000 to 11450 cal y bp cal y indicates calendar year proves the annual character of the laminations the ash layer of the vasset killian tephra massif central france is dated at 8230 140 14c y bp and 9407 44 cal y bp the boundaries of the younger dryas biozone are placed at 10986 69 cal y bp younger dryas preboreal and 1212 86 cal y bp allerod younger dryas on the absolute time scale the absolute age of the laacher see tephra layer dated with the radiocarbon method at 10 800 to 11200 14c y bp is estimated at 12350 135 cal y bp the oldest radiocarbon age of 14190 120 14c y bp was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile for the late glacial the offset between the radiocarbon 10000 12000 14c y bp and the absolute time scale 11400 13000 cal y bp in the soppensee chronology is not greater than 1000 years which differs from the trend of the u th radiocarbon curve derived from corals

holocene climatic change in swedish lapland inferred from an oxygen isotope record of lacustrine biogenic silica holocene climatic variability was studied in a 9500 year lake sediment sequence from the abisko region in swedish lapland using the oxygen isotope ratio in diatom biogenic silica d 18 osi oxygen and hydrogen isotope ratios of waters from the abisko area suggest that in this region the evaporative flux is small and the isotopic composition of most lakes reflects that of the local precipitation the hydrological setting of the region and sensitivity analysis of isotopic response to changing climatic parameters such as humidity inflow and evaporation show that the downcore diatom d18osi record is primarily controlled by changes in the summer isotopic composition of the lake water the overall 3 5 depletion in d 18 osi since the early holocene is interpreted as an increase in the influence of the arctic polar continental air mass that carries depleted precipitation we estimate that this change is associated with a 2 5 4 c cooling that has occurred since the early holocene in general the diatom d 18 osi record resembles the average annual air temperature reconstructed for the greenland ice core gisp2 especially during the past 4000 years with a pronounced cooling starting at 2000 years bp

palaeosecular variation of the earth s magnetic field during the last 10000 years based on the annually laminated sediment of lake nautajarvi central finland a palaeomagnetic study of the lake nautajarvi sediment sequence in central finland demonstrates that varved lake sediments can provideregionally applicable secular variations curves for holocene stratigraphic correlation and age control based on x ray radiography and digital image analysis techniques we constructed an inherent and continuous varve chronology for the lake nautajarvi varve sequence which covers nearly 10000 years with an estimated counting error of less than 1 and a mean sedimentation rate of 0 66 mm yr 1 we reconstructed a record of the palaeomagnetic secular variation psv of the earth s magnetic field in this nearly 7 m long section of clastic organic varves mineral magnetic measurements indicated that pseudosingle domain magnetite is the major carrier of the remanence psv shows many of the familiar features of declination and inclination that have previously been recorded in northern europe in addition the lake nautajarvi record contains a continuous record of relative palaeoi

the mineral magnetic properties of an annually laminated holocene lake sediment sequence in northern sweden detailed mineral magnetic measurements were conducted on a 9000 year varved lake sediment sequence in northern sweden lake sarsjon the results demonstrate that the paramagnetic susceptibility reflects the concentration of detrital minerogenic material in the lake sediments which is controlled to a large extent by the intensity of the spring snow melt in contrast the concentration of ferrimagnetic magnetite reflected by initial magnetic susceptibility and magnetic hysteresis parameters is positively correlated to the concentration of organic carbon which is most likely of an autochthonous origin this magnetite has magnetic properties that are characteristic of stable single domain magnetite grains produced by magnetotactic bacteria the paramagnetic susceptibility record clearly points to a climatic excursion in the early holocene between 6100 174 bc and 5700 167 bc which can be correlated to an d18o excursion a cold event in the greenland ice cores and lake sediments in southern germany an

lake sediment studies of holocene glacial activity in the karsa valley northern sweden contrasts in interpretation a multidisciplinary study of lake sediments deposited in lake basins in the karsa valley northern sweden suggests the complete disappearance of the karsa glacier during the early and mid holocene glacier reformation indicated by the deposition of sediment with a fine particle size distribution and low organic content in the three lakes took place at c 3000 14 c years bp this interpretation contrasts with a study based on the weight loss on ignition of the same sediments which suggests several glacier advances throughout the entire holocene the contrasting interpretation is due to different methodological approaches single core site studies should be avoided in the future and only features that are consistently reproducible and can be dated in spatially distributed cores should be interpreted in terms of variations in glacial activity environmental conditions and ultimately climate

absolute dating of the late glacial period in switzerland using annually laminated sediments abstract results of a high resolution late glacial ams 14 c chronology from rotsee central switzerland have given evidence that the atmospheric radiocarbon concentration was not constant between 13 000 and 9500 yr b p this resulted in three marked phases of constant radiocarbon age at 12 700 at 10 000 and at 9500 yr b p new results of a late glacial varve chronology from soppensee central switzerland suggest that the younger two phases of constant 14 c age each had a duration of ca 400 calendar years the length of the late glacial chronozones has been calculated on the basis of these replicate varve counts and a comparison with their estimated duration in radiocarbon years shows that the estimated duration of the chronozones bolling ca 800 calendar yr vs 1000 14 c yr and younger dryas ca 900 calendar yr vs 1000 14 c yr agree with the expected time span whereas the estimated duration of the allerod chronozone ca 400 calendar yr vs 1000 14 c yr is substantially shorter than expected furthermore a tentative comparison of varve ages and 14 c ages suggests that the varve chronology is more than 1000 yr offset toward older ages from the radiocarbon chronology during the late glacial period

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

lake catchment based studies of erosion and denudation in the merevale catchment warwickshire u k sediment yields estimated from contemporary stream monitoring of suspended sediment in the merevale forested catchment north warwickshire were compared with the sediment yield record obtained from analysis of lake sediment in the downstream reservoir total sediment volume and mass for nine periods since 1861 were calculated by extrapolation of synchronous levels in 54 cores identified from magnetic susceptibility and other magnetic measurements and by using 210pb and 137cs analysis to provide an absolute sediment chronology sediment yield estimated from the two methods show comparable but low 50 200 kg ha 1 yr 1 levels of sediment loss while suggesting that lake sediments can be a useful means for extending the period over which contemporary monitoring exists the study stresses the need for detailed historical records of land use and climate against which long term sediment yield records can be evaluated

documentation of the physical properties of annually laminated varved sediments at a sub annual to decadal resolution for environmental interpretation this paper describes a method to digitize high resolution physical properties of annually laminated lake sediments we modified a water acetone epoxy exchange method in order to preserve all the fine structural details that varved sequences provide by applying sediment microstratigraphical investigations x ray radiography sem and semi automatic image analysis we were able to establish detailed information about varve composition and structure mineral magnetic measurements were also applied for comparison by comparing all available physical data at high resolution it will be possible to identify environmental changes that has occurred in the lake drainage basin

holocene millennial scale summer temperature variability inferred from sediment parameters in a non glacial mountain lake danntjorn jotunheimen central southern norway holocene changes in summer temperature in the jotunheimen area have been inferred from variations in several sediment parameters from a composite combined from two overlapping sediment cores lake core record mean time resolution of 15 years from lake danntjorn a small mountain lake located close to the modern pine tree limit in jotunheimen central southern norway loss on ignition analysis at contiguous 0 5 cm intervals throughout the cores revealed that the variations in residue after ignition of the sediments at 5501c in the upper 260 cm 8500 calendar years were not associated with variations in magnetic susceptibility in the basal deglacial and early holocene sequence of the lake sediments however the two sediment parameters fluctuated mainly in phase in addition the biogenic silica bsi concentration is relatively high thus in the early part of the holocene the variations in the residue were probably primarily driven by input of minerogenic detrital material inwash and or windblown and biological productivity including bsi from diatoms in the lake itself and in the lake surroundings from approximately 8500 calendar years bp variations in the residue probably primarily reflect variations in low minerogenic low magnetic susceptibility with little variations and diatom bsi productivity as demonstrated with analysis of bsi concentration between 260 and 233 cm 8500 7760 calendar years bp the highest residue values probably mainly reflecting high diatom productivity occurred at 7800 7200 7000 6700 6200 5400 5050 4300 2500 1800 1550 900 700 and o100 calendar years bp the most significant o8000 calendar years bp residue minima mainly low diatom productivity were recorded at 7100 6800 6600 6000 5700 5000 4400 4200 3800 3600 3200 3000 2750 2300 1900 1700 1070 740 600 380 and 80 calendar years bp bp ad 2000 the lake record from jotunheimen is discussed in the context of holocene terrestrial and marine records from the north atlantic region and possible natural climate forcing factors r 2004 elsevier ltd all rights reserved

calendar year ages of three mid holocene tephra layers identified in varved lake sediments in west central sweden three intermediate to rhyolitic icelandic holocene tephra horizons hekla 3 kebister and hekla 4 have been identified in annually laminated varved lake sediments in the province of varmland west central sweden calendar year ages were obtained from varve counts and are supported by additional c 14 dating based on terrestrial plant macrofossils the varve ages of the three tephras are 3295 95 cal bp hekla 3 4030 103 cal bp kebister and 4390 107 cal bp hekla 4 the varve age of hekla 3 refines the former calibrated 14 c age based on studies in the british isles and germany considering the age error estimates associated with the varve chronology and calibrated c 14 ages the ages of kebister and hekla 4 are in agreement with former studies thus the age difference between kebister and hekla 4 is estimated to be ca 400 40 varve years formally estimated to ca 200 c 14 years between hekla 3 and hekla 4 to ca 1135 55 varve years formally estimated to ca 1100 calibrated c 14 years and between hekla 3 and kebister 708 20 varve years less

magnetic hysteresis properties of greigite fe3s4 and a new occurrence in holocene sediments from swedish lappland a new occurrence of ferrimagnetic greigite fe3s4 is reported in freshwater holocene sediments from gaskkamus gorsajavri in swedish lappland the presence of greigite was inferred from the mineral magnetic analysis of sediment cores the greigite bearing sediments possess a high saturation isothermal remanent magnetisation to susceptibility sirm ratio a characteristic shared by other natural sediments known to contain greigite the hysteresis properties measured using a vibrating sample magnetometer of natural greigite extracted from lake sediments show much higher saturation coercivity b0 c and mrsms ratio values approximately 50 mt and 0 5 respectively than synthetic samples of greigite approximately 12 mt and 0 2 the results suggest that synthetic greigite samples contain crystals ranging from small non remanence carrying superparamagnetic grains to large multi domain grains in contrast the natural samples probably consist predominantly of pseudo single domain and single domain crystals capable of carrying a chemical remanent magnetisation however the unstable nature of greigite under laboratory conditions creates difficulty in characterising its physical attributes

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

between the north atlantic oscillation and the siberian high a 4000 year snow accumulation history inferred from varved lake sediments in finland clastic organic varved sediments from the boreal lake kalliojarvi central finland record changes in snow accumulation for more than 4000 years the varve record was reconstructed using digital image analysis from 4132 varve yr bp to present with 2 2 counting error and is supported by paleomagnetic data two laminae are identified in a typical varve structure 1 the minerogenic lamina which accumulates during spring as a result of catchment erosion triggered by spring floods and 2 the organic lamina which is composed of allochthonous and autochthonous organic matter that accumulates during summer autumn and winter the minerogenic influx is related to variations in snow accumulation and follows the different phases of the north atlantic oscillation nao decreased snow accumulation is related to a weakened nao phase thus the minerogenic influx record provides additional information about nao variation the fe mn ratio is related to changes in redox conditions at the lake floor the oxygen ava

soil parent material relationship in a mountainous arid area of kopet dagh basin north east iran abstract the effects of parent rock types on soil evolution in arid areas were studied in a sequence of soils derived from different lithologies in the kopet dagh basin northeastern iran using micromorphology clay mineralogy magnetic susceptibility and physico chemical properties the selected parent rocks and associated soils were shale haplocalcids claystone haplotorrerts gypsiferous marl haplogypsids limestones haplocalcids and torriorthents siltstone and sandstones torriorthents the results showed that the properties and development of soils were mainly affected by grain size and mineralogy of parent materials soil magnetic susceptibility lf variations were attributed to the types of parent material and pedogenic processes redistribution of calcite and gypsum in soil profiles and natural and pedogenic formation of ferrimagnetic minerals were responsible for lf variations the soils clay mineral origins were found to be mainly of inheritance from parent materials smectite was the dominant clay mineral of the most soils based on the micromorphological index of soil evolution miseca the soils studied were categorized into weakly developed orthents weakly to moderately developed aridisols gypsids and calcids and moderately developed soils including calcids and torrerts the degree of microstructure development alteration of weatherable minerals and calcitic features were the most important criteria influencing assessment of soil development degree by miseca index the vertic features were only observed in soils of claystone in which there were considerable amounts of clay and smectite high amounts of gypsum and low smectite content were mainly responsible for the lack of vertic behavior in other fine grained soils derived from shale and marl

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

bacterial magnetite and the magnetic properties of sediments in a swedish lake a comparison of the magnetic properties of lake sediments and catchment materials from pajep njakajaure north sweden demonstrates that high concentrations of single domain sd magnetite in the upper 70 cm of gyttja in the deepest part of the basin are not of detrital origin tem and light microscope examination revealed the existence of bacterial cells and magnetosomes in the upper sediments which are responsible for the presence of the sd magnetite most of the fossil magnetosomes appear to have been dissolved through reductive processes at lower depths although some are preserved in the lower sediments and carry a post depositional remanent magnetization pdrm the results highlight the complex effects of post depositional processes on mineral magnetic assemblages and natural remanent magnetization aquisition and demonstrate how mineral magnetic measurements may be used to identify magnetic grain size changes brought about by sediment diagenesis

secondary ferrimagnetic minerals in welsh soils a comparison of mineral magnetic detection methods and implications for mineral formation summary a range of low temperature and isothermal magnetic measurements are used to identify the secondary ferrimagnetic mineral sfm grain sizes in 10 representative soil samples from wales a comparison of percentage frequency dependent susceptibility fd percentage and low temperature remanence measurements shows that they are sensitive to different ranges of superparamagnetic sp grains the relative distributions of sp grains and stable single domain ssd grains are similar in nine of the samples typical distributions for soils dominated by sfms are 20 30 per cent ssd and 70 80 per cent sp multidomain md grains were not detected in the samples studied there is evidence that some soils contain significant numbers of ultrafine sp grains 0 010 m that are not detected by low temperature remanence measurements at 20 k and which will have the effect of depressing values of low field susceptibility lf and fd percentage a mixing model suggests that fd percentage may be used semi quantitatively to estimate the proportion of sp grains in a sample the positively skewed grain size distributions strongly suggest a mechanism of sfm formation that is driven by processes at the 10 8 m scale thus supporting weathering and fermentation as controlling processes rather than the degradation of ssd bacterial magnetosomes and primary minerals

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

holocene environmental reconstruction of sediment source linkages at crummock water english lake district based on magnetic measurements to reconstruct lateglacial and holocene environmental changes in the british uplands two c 5 8 m long sediment cores from crummock water nw england together with several hundred soil samples from the crummock water catchment were studied using magnetic techniques optically stimulated luminescence osl dating using fine silt quartz and 14c dating of terrestrial plant macrofossils were used to establish a chronology for the lake sediments a good agreement between optical and 14c ages indicates first that the osl dating method can be used to date lake sediments in the british isles second that macrofossil based 14c dating can be used to avoid the problem of old carbon error associated with bulk sample 14c dating of lake sediments and third that the established chronology is robust the lake sediment magnetic properties indicate a series of changes in sediment composition during the holocene which correlate well with sediment lithology water content and weight loss on ignition the first change corresponds to the lateglacial postglacial climatic shift at around 11400 years ago the subsequent suite of changes corresponds to a probable regional onset of human activity at 2000 bc and particularly to the intensification of human activity at around ad 900 a comparison of the lake sediment magnetic properties and those of the catchment soils shows a clear linkage for the lateglacial period and for the period after ad 900 in contrast detailed magnetic measurements of the early through mid holocene sediments suggest that their magnetic properties are dominated by bacterial magnetosomes

on solar forcing of holocene climate evidence from scandinavia the focus of this study is the possible correlation between changes in the climate of scandinavian and changes in solar irradiation reliable information about holocene climatic change in sweden and norway is currently available from two main sources the 14c dating of pine wood retrieved from above the present pine tree limit and studies of glacier variations based on proglacial lacustrine sediments and on moraines the reconstructed alpine tree limit reveals that summer temperature in general was warmer during the early holo cene than it was during the late holocene superimposed on this general trend are several fluctuations of a few hundred years duration relatively cold periods with a duration of the order of 300 600 years occurred frequently during the holocene in this paper dates of the major climatic events are compared with an index of solar activity the so called 14c anomalies for most of the last 9000 years a good correspondence is demonstrated between the timing of cold events in scandi

gyroremanent magnetization and the magnetic properties of greigite bearing clays in southern sweden summary the acquisition of a gyroremanent magnetization grm by single domain sd greigite particles during alternating field af demagnetization is demonstrated previous palaeomagnetic studies failed to identify the presence of authigenic greigite in the glacio marine clays studied these clays formed the subject of an earlier debate about the validity of a late weichselian geomagnetic excursion the gothenburg flip in southern sweden the greigite carries a stable chemical remanent magnetization crm which coexists with a detrital remanent magnetization drm carried by magnetite af demagnetization could not isolate the primary remanence in the sediments where magnetite and greigite coexist due to the overlapping coercivity spectra of the two minerals and the inability to determine the time lag between sediment deposition and crm formation thermal demagnetization removed the crm at temperatures below 400 dc but this method was hindered by the unconsolidated nature of the sediments and the formation of secondary magnetic minerals at higher temperatures the results suggest that the low coercivity drm carried by magnetite was mistaken for a viscous component in the earlier studies hence the former debate about the record of the gothenburg flip may have been based on erroneous palaeomagnetic interpretations or non reproducible results af demagnetization procedures applied to samples suspected of bearing sd magnetic particles such as greigite should be carefully selected to recognize and account for grm acquisition

bacterial magnetite in swedish varved lake sediments a potential bio marker of environmental change abstract detailed mineral magnetic measurements were carried out on three varved lake sediment sequences in sweden which extend to ca 7000 bc the comparison of the magnetic properties of the organic rich varved lake sediments with their respective catchment materials indicates that the magnetic properties of the sediments are dominated by relatively high concentrations of single domain magnetite magnetosomes produced by magnetotactic bacteria the dimictic nature of the lakes which help form and preserve the varves due to the weakly oxic or suboxic environment also appear to be suitable for a high degree of magnetosome preservation the concentration of the magnetosomes in two of the sequences as determined by mass specific magnetic measurements exhibits a positive linear relationship with the total organic carbon content and suggests that magnetic remanence measurements reflect lake productivity via processes of organic matter accumulation and decomposition further research should focus on the potential to use the fossil magnetosomes as proxy climate environmental change indicators and as recorders of geomagnetic field variations and behaviour

testing a cellular modelling approach to simulating late holocene sediment and water transfer from catchment to lake in the french alps since 1826 this paper describes the application of a hydrogeomorphological numerical model caesar to simulate at hourly time steps changes in the hydrological and sediment regime of the petit lac d annecy catch ment the outputs of the model were validated in three ways in the short term 5 years water discharge out puts were compared against observed instrumental data over the longer term modelled sediment discharge ad 1825 2005 was compared with proxies for detrital sediment influx environmental magnetism and accumu lation rates discerned from a 210 pb chronology for the lake sediments finally spatial validation of the modelled erosion and deposition of sediment was undertaken by comparison with a field and remotely sensed survey of catchment geomorphology the results suggest that while minor perturbations in forest cover during the last 180 years have partially conditioned the response of the sediment system the bulk of modelled sediment discharge and particularly the peaks in sediment discharge were controlled by flood duration and magnitude which in turn is driven by precipitation storms floods and snowmelt basin geometry and geomorphology of each sub catchment ire and tamie were also important in producing differences in the modelled sediment discharge in essence these differences were a function of sediment accommodation space and the ability of each system to store and release sediments modelled sediment discharge and para lake sediments display similar histories and thus are both interpreted as reflecting variations in detrital sediment supply intriguingly the style of mod elled sediment discharge from the ire a confined mountain torrent displays a greater similarity to and perhaps dominates the lake sediment record these results provide partial validation of the caesar model and indi cate that perhaps in the future it may be used as an exploratory and predictive tool in determining the impact of changes in climate meteorology and land use on lake catchment systems

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

reconstruction of mid to late holocene winter temperatures in the skagerrak region using benthic foraminiferal mg ca and δ18o reconstruction of skagerrak deep water renewal is used to assess regional changes in winter thermal conditions over the past 6800 years changes in winter climate conditions from the skagerrak region are in turn linked to shifts in holocene large scale atmospheric circulation patterns prevailing over northern europe we use melonis barleeanus mg ca from two sediment cores in the central skagerrak to reconstruct temperature of skagerrak intermediate water representing the warm season temperature variability and deep water for monitoring skagerrak deep water renewal reflecting the winter temperature variability in addition m barleeanus 18o is used from the deeper core to reconstruct salinity also monitoring the deep water renewal our results show that the skagerrak deep water experienced phases of particularly enhanced renewal during the mid holocene reflecting severe winter conditions followed by a general shift to reduced renewal as a consequence of milder winter conditions over the north sea a

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

enso and sunspot cycles in varved eocene oil shales from image analysis abstract on the premise that sequential changes in varve thickness offer a proxy for climatic variations we investigated varve thickness in three core segments from the distal lacustrine oil shales tipton and laney members of the green river formation by means of an image analysis program of two strong bimodal periodicities one at 4 8 5 6 years is interpreted as an el nino type enso phenomenon of atmospheric dynamics while the other at 10 4 14 7 years is interpreted as the sunspot cycle originally recognized in this formation by bradley 1929 1931 weaker periodicities may exist at ca 8 and 33 years the latter also recognized by bradley taken in conjunction with the work of bradley 1929 1931 and of crowley et al 1986 this suggests that some but not all of the oil shale of the green river formation is truly varved and can be used to infer climatic time series automated instrumental scans have greatly extended the possibilities of varve studies as approaches to climatic variations in time but careful selection of facies in their geological framework is necessary

holocene history of drift ice in the northern north atlantic evidence for different spatial and temporal modes 1 we present new high resolution proxy data for the holocene history of drift ice off iceland based on the mineralogy of the 2 mm sediment fraction using quantitative x ray diffraction these new data bolstered by a comparison with published proxy records point to a long term increasing trend in drift ice input into the north atlantic from 6 to 5 ka toward the present day at sites influenced by the cold east greenland current this feature reflects the late holocene neoglacial or cooling period recorded in ice cores and further terrestrial archives on greenland in contrast a decrease in drift ice during the same period is recorded at sites underlying the north atlantic drift which may reflect a warming of this region the results document that holocene changes in iceberg rafting and sea ice advection did not occur uniformly across the north atlantic centennial scale climate variability in the north atlantic region over the last 4 kyr is linked to the observed changes in drift ice input increased drift ice may have played a role in the increase of cold intervals during the late holocene e g the little ice age cooling

sources of fine grained magnetic minerals in sediments a problem revisited progress in the discrimination of fine grained magnetic minerals in sediments and sediment sources using measurements of magnetic susceptibility at two frequencies and of magnetic remanence generated by a combination of direct and alternating currents is summarized the former measurements yield values for low field and frequency dependent susceptibility lf and fd respectively the latter generate an anhysteretic remanent magnetisation arm that when normalized to the dc bias field can be represented as the susceptibility of arm arm using quotients derived from lf fd and arm to generate bi logarithmic plots it is possible to discriminate between assemblages dominated by magnetic minerals formed through pedogenesis and those arising from the presence of magnetotactic bacteria that use chains of magnetic particles to seek optimum environments in surface sediments sediments to which both types of magnetic mineral contribute occupy positions between the envelopes of values typical of soil d

combined gps and insar models of postseismic deformation from the northridge earthquake models of combined global positioning system gps and interferometric synthetic aperture radar insar data collected in the region of the northridge earthquake indicate that significant afterslip on the main fault occurred following the earthquake additional shallow deformation occurred to the west of the main rupture plane both data sets are consistent with logarithmic time dependent behavior following the earthquake indicative of afterslip rather than postseismic relaxation aftershocks account for only about 10 of the postseismic motion the two data sets are complimentary in determining the postseismic processes fault afterslip and shallow deformation dominate the deformation field in the two years following the earthquake lower crustal deformation may play an important role later in the earthquake cycle

record of redox status in laminated sediments from lake titicaca a sulfur k edge x ray absorption near edge structure xanes study abstract laminated sediments are commonly used to examine limnological and ecological processes on short time scales here we examine changes in sulfur speciation of lamination couplets from lake titicaca south america using x ray absorption near edge structure xanes spectroscopy the dark colored layer of each lamination couplet contains a significant fraction of reduced organic sulfides with smaller fractions of iron sulfides and sulfate in contrast the light colored layer of each couplet is primarily composed of sulfate in all laminae the sulfate is present as inorganic sulfate substituted in calcite the differences in speciation likely reflect changes in productivity during sediment deposition during the warm productive summer months micritic calcite precipitation was induced in oxidized surface waters due to ph changes induced by consumption of dissolved co 2 this calcite incorporates dissolved sulfate and forms the light colored layers this pulse of productivity creates organic matter that partially decomposes during the austral winter months consuming oxygen and delivering organic rich sediment to the lake bottom this decomposition and the possible presence of a halocline kept bottom waters low in oxygen and lead to the production of organic matter rich in reduced sulfur these data suggest that these laminations are deposited annually and illustrate the utility of s k edge xanes for the analysis of laminated sediments

the occurrence of greigite in sediments from loch lomond greigite has been identified in the sediments of loch lomond using x ray diffraction greigite is the dominant magnetic mineral in the oldest sediments recovered while magnetite predominates in the younger sediments which had previously been used for palaeomagnetic secular variation studies a layer of sediment in between these two magnetic mineral regimes has very low magnetic concentrations probably as a consequence of magnetite dissolution associated with sulphide rich pore waters produced at the time of a marine incursion the greigite largely oxidises once the sediment is exposed to air but if freeze dried the greigite becomes surprisingly stable following freeze drying the greigite can be heated to 280 c in air before it alters and loses its strong ferrimagnetic properties

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

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

late holocene effective precipitation variations in the maritime regions of south west scandinavia at present the climate in south west scandinavia is predominantly controlled by westerlies carrying moist atlantic air which forms a main source of precipitation in all seasons past variations in the ratio between precipitation and evaporation effective precipitation from terrestrial sites however may indicate changes in the degree of maritime influence palaeoclimatic archives in this region are thus ideally situated to study past changes in atmospheric circulation patterns in this study multi proxy comparisons of records from three peat bogs and two lakes are used to reconstruct regional scale variations of effective precipitation in south west sweden during the late holocene the total aeolian sediment influx into two peat bogs is used as a proxy for storm activity the frequency of storm phases increases strongly after ca 2500 cal yrs bp dry conditions occur on a regional scale around 4800 4400 2000 1700 1300 1000 700 500 and 300 100 cal yrs bp in addition a comparison to winter precipitation reconstructed from four norwegian glaciers shows similar variations during the past ca 2000 years this indicates that the climate in both regions was controlled by large scale atmospheric circulation dynamics of the north atlantic region the strong variability of effective precipitation and storm activity after ca 2500 cal yrs bp indicates a highly variable climate

annually laminated lake sediments and the study of quaternary environmental changes a review abstract annually laminated lake sediments non glacial varves have in recent years been discovered in increasing abundance especially since the development of in situ freezer samplers so far the majority of examples have been found in three main areas eastern north america northern and central europe and east and central africa a much more widespread distribution seems highly probable however the formation of annual laminations in freshwater lakes is governed by a number of factors the most important of which appears to be morphometry seasonality of sediment supply which may be controlled by physical biological or even cultural processes in the lake or in its catchment is also clearly significant four main types of laminations here termed ferrogenic calcareous biogenic and clastic have so far been recorded although it is quite clear that others exist special field and laboratory techniques are needed in order that the particular properties of varved sediments may be fully exploited annually laminated sediments have so far been applied to the investigation of a number of aspects of the quaternary these include the study of a geochronology b climatic change c vegetation history especially the role of fire in forest ecosystems d the calculation of rates of sediment influx to lakes and of rates of erosion from their catchments and e the monitoring of processes in the modern environment such as heavy metal pollution eutrophication and acid rain annually laminated lake sediments combine an internal independent chronology with the preservation of discrete visible increments of seasonal and annual sedimentation given this unique property and the likelihood that many more examples will be discovered the prospects for further applications of studies of these sediments to the investigation of the quaternary seem very good indeed

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

10000 years of interannual sedimentation recorded in the lake nautajarvi finland clastic organic varves abstract physical properties of varves formed over the last ca 10 000 years from lake nautajarvi central southern finland provide a potential proxy record of winter precipitation and temperature via catchment runoff and erosion the seasonal scale varved data indicate that the winter severity and duration of summer growing season has changed considerably during the holocene in southern central finland periods of increased catchment erosion occurred at 7590 7530 bc 7450 7400 bc 7220 7110 bc 7000 6000 bc 5400 5200 bc 4400 4000 bc 2700 2400 bc ca 1500 bc to ad 500 and 1400 ad onwards the observed changes are likely related to severe winters conditions with high net accumulation of snow between ca 7500 bc and ad 300 whereas ad 300 onwards an increasing agricultural input is seen in the varve and pollen data periods that can be interpreted as indicating attenuated spring floods caused by milder and wetter winters appeared around 7000 bc and ad 1000 ad 1200 the latter corresponding with the last historically recorded warm interval in europe known as the medieval climate anomaly

testing the fidelity of sediment chronology comparison of varve and paleomagnetic results from holocene lake sediments from central finland abstract a careful construction of independent varve and paleomagnetic chronologies from three varved lake sediment records from central finland resulted in detailed and continuous age depth profiles cumulative varve calculation errors were estimated to be 3 for lake alimmainen savijarvi 10 295 340 varve years and 1 for lakes nautajarvi 9898 97 varve years and korttajarvi 9590 103 varve years paleomagnetic secular variation psv curves demonstrate good consistency between these sites and within a margin of varve chronology error they show similar declination and inclination features commonly described in the uk and sweden the timing of psv patterns from finnish varved sites agree well with uk curves between the present and 2000 bc and in pre 6000 bc deposits and with swedish data between the present and 5000 bc combined inclination records from three independently dated finnish varved sites possess an opportunity for accurate paleomagnetic comparisons within the margin of varve chronology errors and throughout the last 10 000 years

changes in lake stratification and oxygen distribution inferred from two contrasting records of magnetotactic bacteria and diatoms 1 magnetotactic bacteria mtb and diatoms produce hard parts on seasonal timescales that continuously becomes embedded in various soft sediment archives consequently they can and are frequently used to reconstruct past environmental conditions in oceans fjords and freshwater basins in this study we observe how these two cosmopolitan creatures can be used to track vertical shifts in the distribution of oxygen in a small mountain lake situated in western norway several short and long sediment cores have been retrieved from the lake allowing for a detailed reconstruction that spans the last 2500 years during periods of enhanced runoff from the catchment the oxic anoxic transition zone oatz is lowered down to the lake sediment interface due to increased convection we posit that this condition reduces the concentration of microaerophilic magnetite producing mtb an interpretation partly supported by rock magnetic analyzes preservation of diatom frustules is however improved whenever this oxygen rich scenario prevails similarly when runoff is low and the oatz is lifted above the lake sediment interface mtb concentration seems to increase whereas dissolution of diatoms is more common this consistent antiphase relationship between mtb concentration and diatom preservation occurring on a multidecadal timescale during lowest reconstructed lake water ph in the lake s history suggest a coupled response to subtle changes in external environmental variables that affect catchment and lake hydrology

geophysical surveys of earthquake induced liquefaction deposits in the new madrid seismic zone we explore the effectiveness and limitations of electrical and electromagnetic methods in imaging buried earthquake induced liquefaction deposits geophysical surveys conducted at liquefaction sites in the new madrid seismic zone nmsz in the central united states demonstrate that these subsurface imaging techniques can be useful tools in paleoseismology paleoseismological studies of liquefaction features provide one of the few means for estimating recurrence intervals of large earthquakes in the nmsz a region with widespread evidence of strong ground shaking but short instrumental record noninvasive geophysical methods minimize ground disturbance during these studies an attribute of particular importance when the studies are conducted at federally protected archaeological sites surveys such as those described here can be used to locate buried liquefaction deposits and to site trenches for detailed geologic studies

magnetic enhancement of baltic sea sapropels by greigite magnetofossils magnetotactic bacteria mtb are known to biosynthesise single domain magnetite fe3o4 for geomagnetic navigation and their relict magnetosomes called magnetofossils can control the magnetic properties of lake and marine sediments magnetotactic bacteria also produce greigite fe3s4 magnetosomes but compared to those made of magnetite relatively little is known about the sedimentary environments where they are produced and the magnetic properties of the preserved particles we studied the magnetic properties of sediment cores from two basins the north central baltic proper and eastern gotland basin that currently experience hypoxia and we discovered the magnetic enhancement of older laminated sapropels which are a signal of past occurrences of anoxia and hypoxia in the baltic sea magnetic concentrates extracted from the laminated sapropels were characterised by transmission electron microscopy and energy dispersive x ray spectrometry and we identified only single domain greigite fe3s4 particles with a mean size of 55 75 nm which we interpret as magnetofossils due to diagnostic chains of individual particles separated by an intact dividing membrane the degree of magnetic enhancement in the laminated sapropels has a positive relationship with loss on ignition data which indicates a link between the production of greigite magnetosomes organic matter supply and preservation and redox conditions the coercive force of collections of non interacting greigite magnetofossils is 13 mt which is considerably lower than the magnetite counterparts 30 mt and strictly non bacterial and larger greigite single domain grains 60 mt the values of the interparametric ratios of sirm w warm sirm and warm w that we obtain for our greigite magnetofossils overlap with those previously considered to be diagnostic of magnetosomal magnetite the presence of bacterial greigite which is easily detected by magnetic measurements forms a proxy for hypoxia and anoxia thus aiding the palaeoenvironmental interpretation of how oxygen conditions in the baltic sea have changed over time

reconstruction of holocene glacier history from distal sources glaciofluvial stream bank mires and a glaciolacustrine sediment core near sota saeter breheimen southern norway this study attempts to reconstruct the holocene glacier history of breheimen southern norway from four stream bank mire sites and a downstream lake sediment core near sota saeter based on lithostr

bacterial magnetite in lake sediments late glacial to holocene climate and sedimentary changes in northern norway magnetic properties of sediments retrieved from a small lake in northern norway spanning the last f14500 cal years have been analyzed in detail the high resolution core with its ability to detect sub centurial variability records the rapid retreat of the fennoscandian ice sheet fis in northern lyngen and subsequently the establishment of a stable allerod to younger dryas watershed from early holocene and to the present magnetotactic bacteria mb producing stable single domain ssb magnetite become the dominating magnetic carrier the small low relief catchment area with its quartzite bedrock scattered till and vegetated surface generates a negligible contribution of detrital magnetic minerals this allows for the opportunity to follow the presence and changes of the magnetosomes during the last 10000 years a strong positive statistical relationship r 2 0 83 between the anhysteretic remanent magnetisation susceptibility varm and loss on ignition loi suggests an environmental control over the bacteria magnitude quart int 88 2002 13 that most likely is related to summer climate a comparison between the magnetic mineralogy as evident from the s ratio jirm100mt jsirm3t and the reconstructed summer temperatures from a nearby lake shows a close covariation between cooler summers and harder s ratios for a series of climatic events intervariability of loi data and other proxies such as august sea surface temperatures sst from the nordic sea suggests land ocean connections during converging phases of cooler climate where the most prominent in phase periods are approximately 1 6500 5000 2 3500 2400 and 3 1700 1000 cal years bp the most significant change in the holocene magnetic signal is initiated at f3700 cal years bp which we refer to here as the holocene turnover d 2004 elsevier b v all rights reserved

flocculation a key process in the sediment flux of a large glacier fed lake this study investigates the consequences of flocculation for sediment flux in glacier fed lillooet lake british columbia based on density fractal dimension in situ profiles of sediment concentration and size distribution and settling velocity equations presented in the literature sediment flux attributed to macroflocs during the late spring and summer accounts for a significant portion of sediment flux in the lake equivalent to at least one quarter of the average annual sediment flux fine sediment is reaching the lake floor faster in flocs than occurs if settling as individual grains this flux varies both spatially and temporally over the observation period suggesting a link between deposition via flocculation and the properties of bottom sediments macrofloc flux increased through june reached a peak during july and then declined into august macrofloc flux was greatest in the distal end of the first basin approximately 10 km from the point of inflow relatively high excess densities 0 1 g cm 3 at 500 m for flocs in situ are consistent with a composition dominated by inorganic primary particles microlaminations within lillooet lake varves have been linked by earlier workers to discharge events and the action of turbidity currents emanating from the lillooet river while turbidity currents undoubtedly occur in lillooet lake these results demonstrate flocculation as an adjunct process linking discharge lake level macrofloc flux bulk density and microlaminations in situ measurements of sediment settling velocity in glacier fed lakes are required to better constrain flux rates and permit comparison between flocculation in lacustrine environments with existing studies of estuarine marine and fluvial flocculation copyright 2009 john wiley sons ltd

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