a study of oxygen isotopic fractionation during bio induced calcite precipitation in eutrophic baldeggersee switzerland in order to better understand environmental factors controlling oxygen isotope shifts in autochthonous lacustrine carbonate sequences we undertook an extensive one year study march 1995 to february 1996 of water column chemistry and daily sediment trap material from a small lake in central switzerland comparisons between calculated equilibrium isotope values using the fractionation equation of friedman and o neil 1977 and measured oxygen isotope ratios of calcite in the sediment traps reveal that oxygen isotopic values of autochthonous calcite 18o are in isotopic equilibrium with ambient water during most of the spring and summer when the majority of the calcite precipitates in contrast small amounts of calcite precipitated in early spring and again in late autumn are isotopically depleted in 18o relative to the calculated equilibrium values by as much as 0 8 this seasonally occurring apparent isotopic nonequilibrium is associated with times of high phosphorous concentrations elevated ph 8 6 and increased co32 50 mol l in the surface waters the resulting weighted average 18o value for the studied period is 9 6 compared with a calculated equilibrium 18o value of 9 4 these data convincingly demonstrate that 18o of calcite are for the most part a very reliable proxy for temperature and 18o of the water

cycling of calcite in hard water lakes of different trophic states based on oxygen o2 ph calcium ca2 and carbonate co 22 3 sediment pore water concentration profiles we compare the benthic dissolution of autochthonous calcite in oligotrophic lake lucerne and eutrophic lake sempach despite their difference in trophic state the two lakes have similar benthic o2 regimes because l sempach is artificially oxygenated this peculiarity enabled the study of the direct effect of trophic state on benthic calcite dissolution although areal benthic o2 fluxes did not differ o2 penetrated deeper into the sediment of the oligotrophic l lucerne where most organic matter om 96 was degraded aerobically whereas in l sempach aerobic and anaerobic decomposition contributed about equal amounts to the biogenic carbon dioxide production release rates of bicarbonate from l sempach sediments exceeded those of l lucerne nearly twofold the hco 2 c a2 ratio of benthic fluxes was 3 7 in l lucerne compared to 10 3 in l sempach suggesting that in l sempach most of the released hco 2 did not originate from calcite dissolution furthermore benthic calcite dissolution in l lucerne exceeded that in l sempach by two fold despite lower ph values in the pore water of l sempach differences in benthic microbial decomposition of om and redissolution of calcite crystals are explained by the longer residence time of om and calcite in the oxic sediment layer of the oligotrophic lake and the larger weight specific surface area of its smaller autochthonous calcite crystals we suggest that trophic state and o2 supply to the sediment are key parameters controlling the cycling of calcite and organic carbon in lakes the cycling of calcium ca 2 and carbonate species hco 2 22 3 is a prominent seasonal process in hard water lakes it is driven by biogenic calcite precipitation and its redissolution related to aerobic decomposition of organic matter although the processes controlling calcite precipitation are relatively well understood the factors controlling redissolution of calcite are not the goal of this study was to help elucidate those factors and thus better understand the cycling of two biogeochemically important elements calcium ca and carbon c in freshwater systems most calcite formed in hard water lakes precipitates during the early algal bloom in spring and mid summer when nutrient enriched surface waters stimulate intense carbon dioxide co2 assimilation the consequent increase in ph shifts the hco 2 co 22

magnetic susceptibility of soil an evaluation of conflicting theories using a national data set magnetic susceptibility values for topsoils across england arc combined with data for soil type geochemistry and concentrations of magnetotactic bacteria in order to evaluate different theories for explaining soil magnetism strongly magnetic soils in unpolluted areas are found over weakly magnetic substrates and are dominated by ultrafine superparamagnetic grains magnetotactic bacteria are present in insufficient concentrations to account for strongly magnetic soils and crop burning is discounted as a major factor a small number of samples show high values associated with either airborne magnetic particulates from pollution or residual primary ferrimagnetic minerals from igneous substrates the results are used to construct a new mechanism for the formation of secondary ferrimagnetic minerals that links abiological weathering and biological fermentation processes the fundamental driving force in the mechanism is fe supply which may be linked to climate observed causative associations between climate and the magnetic susceptibility of loess palaeosol sequences are supported by the findings

heavy metal monitoring of beach sands through environmental magnetism technique a case study from vengurla and aravali beaches of sindhudurg district maharashtra india mineral magnetic geochemical and statistical analyses were carried on surface sediments collected from vengurla and aravali beach along west coast of india premonsoon prem monsoon m and postmonsoon pm magnetic concentration parameters lf arm sirm and hirm are strongly correlated within them prem during m and pm thermomagnetic analysis identifies titanomagnetite magnetite maghemite and hematite as the dominant magnetic mineralogy of the sediments strong correlation was deciphered between magnetic parameters and heavy metal cu cr zn and ni prem and pm which obliterated in m this shows influx of magnetic minerals and heavy metals is more in m than prem and pm the monsoonal influx is more haphazard and random in m because of enhanced weathering resulting in weak correlation between different mineralogical and geochemical entities this finding outlines the efficacy of simple rapid and non destructive magnetic measurement which can be used as an indicator for heavy metal contamination it can act as a proxy for measuring of heavy metal content in the coastal and beach environment

problems of core correlation sediment source ascription and yield estimation in ponsonby tarn west cumbria uk a suite of 27 short cores 10 of which have been used for magnetic measurements and four for radiometric dating provides a framework for reconstructing the processes patterns and rates of sedimentation in ponsonby tarn a small artificial impoundment created towards the end of the 19th century close to the sellafield nuclear reprocessing plant in nw england spatial and temporal changes in sedimentation are reconstructed and evidence presented for non synchroneity in magnetic property changes from core to core in the upper part of the sequence as a result of sorting and selective deposition at different distances from the inflow to the tarn magnetic measurements alone are therefore not a secure basis upon which to quantify sediment yield for defined time intervals at this site the chronology established mainly from 210pb and 134cs analyses allows estimates of mean sediment yield per annum for four periods prior to ad 1940 1940 1964 1964 1986 and 1986 1991 the rates of sediment accumulation have increased in recent times especially since 1964 with evidence for input from both magnetically enhanced soils and gleyed alluvial and or podsolized subsoil sources pre 1940 mean annual deposition within the present area of the lake is calculated as 19 5 t a 1 and for the period since 1986 the period of maximum sedimentation rates as 111 3 t a 1 these represent yields of 7 0 t km 2 a 1 and 39 8 t km 2 a 1 respectively for the catchment as a whole rock magnetic evidence based on measurements of both bulk samples and the finest particle size separates suggests that bacterial magnetite formed within the lake contributes to the magnetic properties of the sediments thus modifying the signatures relating to allochthonous sediment input copyright 1999 john wiley sons ltd

a 1600 year multiproxy record of paleoclimatic change from varved sediments in lake xiaolongwan northeastern china 1 a multiproxy record from lake xiaolongwan northeastern china reveals distinct stratigraphical patterns in organic carbon total nitrogen organic carbon isotope nitrogen isotope clastic content and dinocyst concentration over the past 1600 years high atomic c n ratios in the sediment suggest that a large amount of organic matter in the sediments is derived from vascular plants and soil in the catchment based on the good agreement between cyclical variations of 13corg in the sediments and the spring drought index from historical documents we interpret that the variation of 13corg in the sediments is an indicator of humidity or precipitation in the study area several notable drought periods with heavier 13corg occurred during ad 490 570 ad 780 990 ad 1360 1450 ad 1590 1670 and the last 150 years these century scale drought episodes correspond to solar activity it suggests that solar forcing plays an important role for the 13corg variation in the sediments through driving the changes in humidity vapor pressure deficit dinocyst concentration is high during most of the medieval warm period and low during the european dark age and the little ice age the increase in dinocyst concentration is generally synchronous with decrease of 15n value the 15n values in the studied lake are most likely influenced by the duration and intensification of lake overturn which regulates the amount of depleted 15n nutrients dissolved organic nitrogen and ammonium and dinoflagellate blooms

diagenetic cycling of arsenic in the sediments of eutrophic baldeggersee switzerland sedimentation and benthic release of as was determined in baldeggersee a eutrophic lake in central switzerland sediment traps recorded as sedimentation during 1994 including a flood event in spring diagenetic processes were studied using porewater profiles at the sediment water interface and in deeper sediment strata deposited in the mesotrophic lake before 1885 sediment cores were used to calculate the accumulation and to construct the balance of sedimentation and remobilisation the results showed that the lake sediment acts as an efficient sink for as only 22 of the particulate as flux reaching the sediment surface was remobilised at the sediment water interface the as accumulation in the recent varved section of the eutrophic lake was 40 mg as m 2 a 1 iron reduction in older sediment caused a remobilisation of 1 2 mg as m 2 a 1 this upward flux from the deeper sediment was quantitatively immobilised in the recent sulfidic sediments the flood event in spring contributed about 34 of the yearly sediment load and led to distinct peak profiles of dissolved as in the porewater this evidence for rapid remobilisation disappeared within months

the recent eutrophication of baldeggersee switzerland as assessed by fossil diatom assemblages diatom analyses with an annual resolution were carried out on varves of the hypertrophic baldeg gersee central swiss plateau for the timespan ad 1885 to 1993 they reveal seven major changes in the dominant planktonic diatoms as a result of progressive nutrient enrichment baldeggersee changed in the 1910s from a cyclotella to a tabellaria fenestrata dominated assemblage and eventually in the 1950s to a stephanodiscus parvusdominated diatom assemblage the timing and direction of diatom assemblage changes in the varved sediment compare well with sedimentological and limnological observations partitioning of the variance in the diatom data revealed that tp is a stronger explanatory variable than temperature for these changes a diatom inferred total phosphorus tp reconstruction indicates three major steps in eutrophication occurring at 1909 the mid 1950s and the mid 1970s comparison with tp measurements in the water column demonstrates that the diatom tp inference model used is able to hindcast past tp concentrations reliably the major steps in eutrophication led to decreases in diatom diversity and also resulted in a progressive increase of calcite grain size the lake restoration programme established since 1982 shows no direct impact on the composition of the diatom assemblages however the decrease in phosphorus loads since the mid 1970s is reflected in the diatom assemblages and in decreasing diatom inferred tp concentrations

factors controlling δ13c values of sedimentary carbon in hypertrophic baldeggersee switzerland and implications for interpreting isotope excursions in lake sedimentary records we use stable carbon isotope values d 13 c in sedimented organic matter and carbonate as proxy indicators of productivity changes in a highly eutrophic to hypertrophic lake stable isotope data from a seasonally sampled sediment core recovered from baldeggersee switzerland were compared with direct and inferred total phosphorus p concentrations carbon isotope values of sedimentary organic matter d 13 corg in both seasonal varves and over the past 100 yr are not linearly related to total p concentrations nor do they mirror observed trends in carbonate isotope values d 13 c baldeggersee d 13 corg values are influenced by both variations in the relative inputs of caco3 eukaryotic biomass which becomes enriched in 13 c with increasing primary productivity and the contribution of microbial biomass produced in the expanding anoxic bottom waters which is typically very depleted in 13 c we also examined the fractionation within the organic matter co2 caco3 system calculated as total organic carbon toc 5 10 3 d 13 c 1 1 000 d 13 corg 1 1 000 2 1 thresholds within the measured toc values represent baldeggersee caco3 trophic status more accurately than d 13 corg or d 13 c values alone in alkaline lakes with endogenic carbonate caco3 precipitates toc values can facilitate accurate interpretation of values and trends in organic carbon isotope data and can help to better assess trophic history and lake remediation efforts in lake systems that have been heavily affected by cultural eutrophication

terrestrial and aquatic ecosystem responses to late holocene climate change recorded in the sediments of lochan uaine cairngorms scotland abstract we summarise the results of a range of sediment based studies at lochan uaine a remote corrie lake in the heart of the cairngorm massif in scotland the site lies above the holocene forest limit and has been minimally affected by human activities the results presented are mainly based on magnetic measurements element analysis granulometry organic geochemical analysis and pollen analysis carried out over a period of some 15 years the magnetic properties and element concentrations record a coherent sequence of changes reflecting mainly stages in catchment erosion in terms of the chronology developed for the sedimentary record from the site increases in allochthonous minerogenic sediment delivery to the lake occurred around 1000 bc ad 330 480 and ad 1260 1410 the only notable change in the pollen diagram records a period of deforestation at lower altitude predating the last of the periods of increased erosion the organic geochemistry analyses record a series of higher frequency responses in the aquatic ecosystem already noted in previous papers e g battarbee et al 2001 these include fluctuations in organic carbon content and in the concentrations of biomarkers indicative of changing lake productivity both the terrestrial and aquatic ecosystem responses are superimposed on a longer term trend of declining aquatic productivity progressive catchment weathering and increasing erosion the sediments of lochan uaine thus appear to have recorded complex system responses on three timescales reflecting a the long term decline in northern hemisphere insolation during the holocene b the millennial scale forcing of the kind found in many other mid late holocene records and c much shorter term quasi cyclic but clearly a periodic sub millennial fluctuations

palaeoclimatic reconstruction by using the varvite sediments of bharatpur upper lahaul valley nw himalaya india a 6 m thick varvite profile exposed at bharatpur 77 27 e 32 48 n altitude 4692 m in the nw himalaya was investigated to understand the past climatic signatures during the late quaternary period the radiocarbon chronology brackets the varvite sedimentation between 24 3 and 7 2 ka bp and the sedimentary sequence is bounded by river born gravel at the top and glacial outwash at the bottom the proxies used were lithology chronology ams radiocarbon dating geochemical analysis loss on ignition loi and mineral magnetism other parameters e g chemical index of alteration cia chemical index of weathering ciw al2o3 sio2 fe2o3 cao mgo and al na ratio were also used based on the combined data set six phases of warm and cold climatic conditions are reconstructed the mean cia ciw and al na ratios reveal that the sediments were incorporated from sedimentary rocks by moderate silicate chemical weathering process based on the available chronology the basal most glacial outwash event can be estimated as ca 24 3 ka bp and the laminated section shows continuity of sedimentation from the late quaternary to holocene the period between ca 24 3 and 22 6 ka can be regarded as an arid phase from ca 22 6 20 5 ka bp a slight increase in monsoonal precipitation is observed followed by decreased precipitation from ca 20 5 to 18 ka bp the period from ca 18 to 15 7 reveals warm and humid climatic conditions we suggest that a cold event from ca 15 7 to 11 5 may correspond to the younger dryas yd which in turn is followed by a phase of maximum moisture of the holocene climate optimum hco ca 11 5 7 2 ka bp in the study area the increased cia during deglaciation and hco suggest high chemical weathering whereas the lgm last glacial maximum and yd are represented by the low cia the observed climatic phases events are in agreement with the records from other parts of the himalaya

magnetotactic bacteria and their magnetofossils in sediments abstract living magnetotactic bacteria from freshwater environments show under natural and laboratory conditions a great variety of morphological appearances their magnetosomes vary in number shape and size one species of bacteria yields up to 1000 magnetosomes per cell individual particles reach a size of up to 200 nm as a rule they form elongated chains in bacteria which are held under laboratory conditions loop shaped arrangements and nearly unordered clusters are also found during the laboratory experiments different species of bacteria periodically dominated freshwater samples always exhibited a great variety of different magnetosomes on the other hand samples from marine environment clearly showed the preponderance of one type of particle these observations may reflect specific properties of the physico chemical milieu in which the bacteria grew at the end of our experiments north and south seeking bacteria co existed in roughly equal quantities quaternary unconsolidated sediments from the ammersee bavaria and the antarctic quaternary to tertiary deep sea sediments from the atlantic and pacific and jurassic limestones from the sonnwendgebirge tyrol austria were analyzed for fossil magnetosomes we found that fossil magnetosomes were morphologically similar to those from living bacteria but seemed to be corroded in some cases the observed differences in quantity size and shape of magnetosomes from various sediments may be influenced by variations in bacterial viability and particle stability at different sites but are not determined by geographical latitude

a 200 year sedimentary record of progressive eutrophication in lake greifen switzerland implications for the origin of organic carbon rich sediments over the past 200 years lake greifen a small lake in northeastern switzerland has undergone dramatic changes in primary productivity and eutrophication due to increased nutrient supply from agricultural activity and industrialization a 40 year historical record of the water column chemistry indicates that productivity and eutrophication reached a maximum in 1974 after which stricter regulations on the input of nutrients resulted in a progressive decrease collected cores show the sedimentary expression of this anthropogenically induced eutrophication by a well developed annual sedimentation and by enhanced values of total organic carbon organic carbon accumulation rates and hydrogen indices hi of the kerogens analyses of the carbon isotopic composition of sedimentary carbonates and organic matter reveal that the fractionation between these two phases varies with the hi of kerogens this observation is explicable in terms of changing productivity and preservation of the organic matter and the co2 aq budget of the water body we propose that if high primary productivity were primarily responsible for the preservation and accumulation of organic matter then a negative correlation will occur between 13ccalcite organic matter 13ccal om and hi values in an environment with relatively low to moderate productivity but with bottom water anoxia a positive correlation will exist between 13ccal om and hi values this study of lake greifen has implications for understanding paleoenvironmental controls on ancient organic carbon rich sediments

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

sr and nd isotopes as tracers of clastic sources in lake le bourget sediment nw alps france during the little ice age palaeohydrology implications geochemical methods major elements and sr nd isotopes have been used to 1 characterize lake le bourget sediments in the french alps 2 identify the current sources of the clastic sediments and estimate the source variability over the last 600 years major element results indicate that lake le bourget sediments consist of 45 clastic component and 55 endogenic calcite in addition several individual flood levels have been identified during the little ice age lia on the basis of their higher clastic content 70 potential sources of lake le bourget clastic sediments have been investigated from sr and nd isotope compositions the sediments from the sierroz river and leysse river which are mainly derived from the mesozoic calcareous massifs are characterised by lower 87sr 86sr ratios and slightly lower nd 0 ratios than the arve river sediments which are derived from the palaeozoic mont blanc external crystalline massifs the rhone river appears to have been the main source of clastic sediments into the lake for the last 600 years as evidenced by a similar sr and nd isotopic compositions analyzed in core b16 sediments 87sr 86sr 0 719 nd 0 10 and in the sediments of the rhone river 87sr 86sr 0 719 nd 0 9 6 the isotopic signatures of flood events and background samples from core b16 in lake le bourget are also similar this indicates that prior to 1800 the inputs into the lake have remained relatively homogeneous with the proportion of clastic component mainly being a function of the palaeohydrology of the rhone river early human modification deforestation and agriculture of the lake catchment before the 1800s appears to have had little influence on the source of clastic sediments

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

oxygen isotope disequilibrium precipitation of calcite in lake arreso denmark lake carbonates are generally assumed to precipitate at or very close to oxygen isotopic equilibrium with the ambient water we present results from the eutrophic lake arreso northeastern sealand denmark that demonstrate disequilibrium precipitation of present day calcite according to the temperature equation of epstein et al these calcites are depleted in 18 o by 2 3 when compared to the expected equilibrium values core studies indicate that the development of disequilibrium conditions in lake arreso is correlated with the onset of an enhanced eutrophication a high precipitation rate is suggested as the mechanism responsible for the observed 18 o depletion of the calcite precipitates

biologically induced calcite and its isotopic composition in lake ontario we studied water sediment trap and core samples from eastern lake ontario to reconstruct the factors controlling the biologically induced production and sedimentation of calcite during so called whiting events calcite accumulation and its isotopic composition are controlled by a complex set of interrelated factors including temperature primary productivity and the abundance of pica cyanobacteria during the stratified period calcite precipitation is highly correlated to lake temperature because physical and biological factors interact to produce conditions favorable for whitings during warm years when the lake stratifies early in the seasonal cycle carbonate stratigraphies in multiple cores from eastern lake ontario revealed similar patterns of historical variation in percent carbonate an exponential rise in carbonate accumulation occurred in nine cores after 1930 culminating in peak values in the early 1980s this rise was related to historic increases in primary productivity resulting from increased phosphorus loading to lake ontario superimposed upon this rise were four peaks centered on 1940 1942 1957 1961 1971 1977 and 1983 that correlate with maxima in summer air temperature anomalies from the great lakes region and with strong el niiio events these peaks are also associated with maxima in s c values and minima in s180 values of carbonate lending support to our model that more calcite is precipitated with higher 6 c values during warm years when thermal stratitication occurs early in the seasonal cycle beginning in the mid 1980s calcite accumulation and its 6 c ratio began to decrease suggesting a reduction in primary productivity in surface waters probably related to lower phosphate concentrations in epilimnetic waters of lake ontario during the stratified period reduced summer p loading may be explained either by a lagged response to p abatement measures that began in the late 1970s or by decreased p loading from upstream lake erie beginning in the late 1980s as a result of the establishment of filter feeding zebra mussels

environmental change controls of lacustrine carbonate cayuga lake new york dated sediment cores from cayuga lake new york state document that biologically mediated precipitation of calcite has been controlled by environmental change both natural and anthropogenic over the past 10 000 yr during the holocene hypsithermal 9 4 ka 14 c milankovitch forcing of summer insolation in the northern hemisphere resulted in a broad increase to 55 then decrease to 5 of calcite content in bottom sediment warmer summers resulted in earlier onset of thermal stratification of the water column which increased the duration of primary production as well as the abundance of picoplankton which in turn increased the amount of calcite precipitated at the end of the hypsithermal ca 3500 yr ago global cooling greatly reduced the amount of calcite precipitated however since a d 1940 calcite contents in cayuga lake sediments have risen up to 20 one hypothesis is that this recent increase in calcite is the result of cultural eutrophication nutrient loading however this rise in calcite also closely tracks the anthr opogenic rise of atmospheric carbon dioxide suggesting a possible link to global environmental change further research on hard water lake basins will be needed to test which of these two hypotheses is corr ect

the late holocene history of gormire lake ne england and its catchment a multiproxy reconstruction of past human impact sedimentary evidence spanning the last 3500 years from cores taken from the centre of gormire lake cleveland northeast england points to two periods of deforestation and catchment erosion the first mainly late iron age romano british phase began c 200 bc and ended c ad 600 the second began c ad 1200 the time of early monastic activity and continued into the nineteenth century the chronology for the core rests on 137cs 210pb and 14c measurements and on the history of lead accumulation in the sediments the majority of the ams 14c dates are shown to be too old to varying degrees depending on the source of the organic matter in the sediments the record of vegetation change is derived from pollen analysis evidence for changes in sediment composition and source and for catchment erosion comes from magnetic measurements element analyses using xrf and organic biogeochemical analyses there is a high degree of coherence between all these lines of evidence interpretation of the magnetic record

calcification generates protons for nutrient and bicarbonate uptake abstract the biosphere s great carbonate deposits from caliche soils to deep sea carbonate oozes precipitate largely as by products of autotrophic nutrient acquisition physiologies protons constitute the critical link calcification generates protons which plants and photosynthetic symbioses use to assimilate bicarbonate and nutrients a calcium atpase based trans mechanism underlies most biological calcification this permits high calcium carbonate supersaturations and rapid carbonate precipitation the competitive advantages of calcification become especially apparent in light and nutrient deficient alkaline environments calcareous plants often dominate the lower euphotic zone in both the benthos and the plankton geographically and seasonally massive calcification concentrates in nutrient deficient environments including alkaline soils coral reefs cyanobacterial mats and coccolithophorid blooms structural and defensive uses for calcareous skeletons are sometimes overrated

understanding the transfer of contemporary temperature signals into lake sediments via paired oxygen isotope ratios in carbonates and diatom silica problems and potential abstract although the oxygen isotope composition 18o of calcite 18ocalcite and to a lesser extent diatom silica 18odiatom are widely used tracers of past hydroclimates especially temperature and surface water hydrology the degree to which these two hosts simultaneously acquire their isotope signals in modern lacustrine environments or how these are altered during initial sedimentation is poorly understood here we present a unique dataset from a natural limnological laboratory to explore these issues this study compares oxygen and hydrogen isotope data 18o 2h of contemporary lake water samples at 2 weekly intervals over a 2 year period 2010 12 with matching collections of diatoms 18odiatom and calcite 18ocalcite from sediment traps at 10 m and 25 m at rostherne mere maximum depth 30 m a well monitored eutrophic seasonally stratified monomictic lake in the uk the epilimnion shows a seasonal pattern of rising temperature and summer evaporative enrichment in 18o and while there is a temperature imprint in both 18odiatom and 18ocalcite there is significant inter annual variability in both of these signals the interpretation of 18odiatom and 18ocalcite values is complicated due to in lake processes e g non equilibrium calcite precipitation especially in spring leading to significant 18ocalcite depletion and for 18odiatom by post mortem depositional and possibly dissolution or diagenetic effects for 2010 and 2011 respectively there is a strong temperature dependence of 18ocalcite and 18odiatom in fresh trap material with the fractionation slope for 18odiatom of ca 0 2 c in agreement with several other studies the 18odiatom data indicate the initiation of rapid post mortem secondary alteration of fresh diatom silica within 6 months with some trap material undergoing partial maturation in situ diatom 18o of the trap material is also influenced by resuspension of diatom frustules from surface sediments notably in summer 2011 with the net effect seen as an enrichment of deep trap 18odiatom by about 0 7 relative to shallow trap values contact with anoxic water and anaerobic bacteria are potentially key to initiating this silica maturation process as deep trap samples that were removed prior to anoxia developing do not show enrichment dissolution perhaps enhanced by anaerobic bacterial communities may also be responsible for changes to 18odiatom that lead to increasing but potentially predictable error in inferred temperatures using this proxy high resolution multi year monitoring can shed light on the complex dynamics affecting 18odiatom and 18ocalcite and supports the careful use of sedimentary 18odiatom and 18ocalcite as containing valuable hydroclimatic signals especially at a multi annual resolution although there remain substantial challenges to developing a reliable geothermometer on paired 18odiatom and 18ocalcite in particular 18odiatom needs cautious interpretation where silica post mortem secondary alteration is incomplete and diatom preservation is not perfect and we recommend dissolution be routinely assessed on diatom samples used for isotopic analyses

frank oldfield and his contributions to environmental change research frank oldfield s immense contribution to palaeoenvironmental science is summarized in relation to pollen analysis vegetation history and peat stratigraphy palaeolimnology and 210pb dating environmental magnetism catchment lake relationships and soil erosional history multiproxy approaches pages and editing the holocene the tribute includes an introduction to the 14 other papers in this special issue which were inspired in diverse ways by this remarkable scientist

the influence of particle size variations on the magnetic properties of sediments from the north eastern irish sea this paper considers the magnetic properties of a range of recent and contemporary sediments from the north eastern part of the irish sea principal component ordinations of the results show a close link between magnetic property variations and particle size the magnetic properties of a subset of samples particles sized by a combination of sieving and pipette analysis confirm that variations in ferrimagnetic magnetite grain size parallel those in particle size despite the fact that the magnetic grains in the fine grades have diameters 1 2 orders of magnitude smaller than those of the particle size fraction in which they occur this is best explained by postulating that the fine magnetic grains occur in the clay fraction but are present in declining concentrations in the coarser grades up to 4o as an artefact of the pipette method most samples have a biomodal distribution of magnetic minerals with a coarse mode associated with heavy minerals in the sands or coarse silts and a fine mode in the clays magnetic susceptibility x and saturation isothermal remanent magnetization sirm largely pick out the coarse mode where present anhysteretic remanent magnetization arm largely picks out the fine mode the results open up the possibility of normalizing samples from these environments for particle size and more specifically clay content by means of arm or arm x values the most likely source for the uniform and almost exclusive stable single domain magnetite which dominates the magnetic properties of the clays is thought to be bacterial magnetosomes the measurements as a whole do not appear to hold much promise for discriminating sediment source types

abnormal positive δ13c values of carbonate in lake caohai southwest china and their possible relation to lower temperature abstract carbon source inputs co 2 exchange between atmosphere and lake water as well as lacustrine productivity are commonly served as the main controls on 13 c values of authigenic carbonates in lake sediments generally 13 c values of recent carbonates in most lakes are lower than 5 all values reported here with respect to the pdb standard and rather few reach up to 13 extreme positive 13 c values up to 23 10 are reported in authigenic carbonate in lake caohai southwest china and some 13 c values are the most positive values in the previously reported surface water carbonate 13 c values in lakes simultaneously there are two intervals of large carbonate 13 c enrichment during the past 500 years namely 1670 1714 ad and 1788 1881 ad on the basis of combination with the oxygen isotopic composition of carbonate and drought flood index proxies d f carbon source inputs co 2 exchange between atmosphere and lake water can not cause this extreme carbonate 13 c enrichment in addition the inconsistent between organic matter content and 13 c values of carbonate lower organic matter 13 c values as well as the weak negative correlation between 13 c values of organic matter and carbonate during these two intervals confirmed that lacustrine productivity is also not the dominant factor that controls abnormal positive carbonate 13 c values temperature variations in lake caohai during the past 500 years were reconstructed from co analysis of 18 o values of carbonate and organic matter cellulose and periods of abnormal positive 13 c values of carbonate correspond well with the lower temperature periods the 1670 1714 ad and 1788 1881 ad cold periods were synchronous with the coldest intervals of little ice age lia and also consistent with the maunder and dalton sunspot minimum respectively considering these geochemical data together although there is no direct effect between temperature and carbonate 13 c values the lower temperature restrains the degradation of organic matter and bacteria have the chance to participate the carbon isotopic fractionation of organic matter thus generating the methane ch 4 gas which has the extreme lower 13 c values up to 60 resulting in the extreme enrichment 13 c in carbonates due to the preferential synthesis of 12 ch 4 the important inputs of bacteria to sedimentary sequence during the periods of 1670 1714 ad and 1788 1881 ad have been further verified by the carbon isotopic fractionation between carbonate and organic matter therefore this mechanism may be responsible for abnormal positive 13 c values in lake caohai abnormal positive 13 c values of carbonate in lake caohai may be indirectly ascribed to the lower temperature and more attention should be paid to the carbon isotopic composition of carbonates in lake caohai in future research particular factors affecting carbonate carbon isotopic composition should be taken into account in order to avoid misinterpreting palaeoclimatic reconstructions

historic and contemporary sediment transfer in an upland pennine catchment uk a sediment budget for an upland catchment reservoir system at burnhope reservoir north pennines uk has been developed this provides a framework for quantifying historic and contemporary sediment yields and drainage basin response to disturbance from climate change and human activities in the recent past bathymetric survey core sampling 137cs dating and aerial photographs have been used to assess sediment accumulation in the reservoir the average reservoir sedimentation rate is 1 24 cm yr 1 annual sediment yield 33 3 t km 2 yr 1 10 trap efficiency 92 mean annual reservoir sedimentation over the 67 year period has been estimated at 592 t 10 inputs of suspended sediment from direct catchwater streams account for 54 of sediment supply to the budget best estimate yield of 318 t yr 1 129 while those from actively eroding reservoir shorelines contribute 328 t yr 1 92 sediment yield estimates from stream monitoring and reservoir sedimentation are an order of magnitude lower than those reported from south pennine reservoirs of comparable drainage basin area analysis of historical rainfall series for the catchment shows fluctuations in winter and summer rainfall patterns over the past 62 years from 1976 to 1998 there has been a diverging trend between winter and summer rainfall with a large increase in winter and a gradual decrease in summer totals periods of maximum variation occur during the summer drought events of the late 1970s early 1980s and mid 1990s analysis of the particle size of core sediments highlights abrupt increases in sand sized particles in the top 20 cm of the core based on the 137cs chronology these layers were deposited from the late 1970s onwards and relate to these diverging rainfall records and rapidly fluctuating reservoir levels this provides evidence of potential sediment reworking within the reservoir by rapid water level rise after drought copyright 2008 john wiley sons ltd

sedimentary characteristics and depositional models of two types of homogenites in an eocene continental lake basin shulu sag eastern china abstract homogenites are homogeneous and structureless fine grained rocks they have been studied extensively in marine settings and are typically interpreted as being related to catastrophic events such as earthquakes however studies on lacustrine homogenite like rocks are limited new core data from the shulu sag in china reveal that thick massive calcilutites exist in the lower shahejie 3 formation which formed during the middle eocene rifting stage based on petrographic geochemical and mineralogical data these massive calcilutites are interpreted as homogenites and grouped into two types type a homogenite is composed of intrabasinal materials characterized by high calcite total organic carbon toc content and 13c value type a homogenite has two facies successions the first of which is characterized by homogeneous appearance capped by an erosional interface and the second is characterized by repeated massive laminated calcilutite successions type b homogenite contains abundant allochthonous materials displaying relatively high dolomite content and low calcite toc and 13c content type b homogenite represents the topmost finer portion of a graded megabed which includes from base to top grain supported carbonate conglomerates slumped deformed portions and debrites the whole unit can be considered as a megaturbidite earthquakes are the most reasonable triggers of homogenite formation in the shulu sag type a homogenites are thought to be derived by fluidification resuspension and decantation of lacustrine fines due to shock waves generated by an earthquake type b homogenites might be deposits of distal turbidity currents and turbid clouds transformed from other gravity flows the results of this study provide a better understanding of the formation of homogenites caused by earthquakes in a confined lacustrine basin

catchment hydro geomorphological responses to environmental change in the southern uplands of scotland lake sediment and geomorphic evidence from the loch of the lowes st mary s loch basin in the central southern uplands of scotland provide a multiproxy reconstruction of changing sediment availability and transmission through the catchment interrogation of magnetic geochemical and grain size parameters for lake and catchment materials suggests it is possible to identify independent proxies that reflect both supply availability and discharge capacity controls on the sediment signal chronological control for the lake sediment record is proposed by linking a 210pb 137cs chronology for the last c 120 yr to an age depth profile based on proposed temporal correlations between cyclic hirm lf variability and the north atlantic oscillation geochronological studies on debris cones and alluvial fans yield evidence for episodic hillslope gullying 2000 0 bc with more extensive region wide slope instability ad 700 900 1100 1300 and after ad 1450 1550 and gully stabilization over the last 150 years the latter two episodes coincide with the lake sediment evidence for increased sediment supply from ad 1600 declining after ad 1870 the capacity related lake proxies appear to identify phases of increased flooding ad 1625 1650 1680 1700 1730 1760 1800 1815 1850 1880 1910 1930 1960 1970 and possibly the 1990s close correspondence between the sediment flood archive and historical records of flooding in scotland suggests that lake catchment systems of this type have the potential to yield valuable information on past hydrological response

quantitative sediment source ascription using magnetic measurements in a reservoir catchment system near nijar s e spain the magnetic properties of sediments from a dried out reservoir and its inflowing streams were measured to provide a basis for sediment source determination quantitative estimates of source component proportions in the reservoir sediments were made using linear programming procedures the study confirms that this type of research must be based on a detailed knowledge of the relationship between magnetic properties and particle size in both the sediments and the potential sources in the case of the site studied the isabel ii reservoir near nijar s e spain the sediments generated by contemporary surface processes within the reservoir catchment fail to reflect fully the 19th century material largely responsible for the rapid infill of the reservoir an additional source type namely unweathered schist derived material not represented in the fine sediments sampled within channels upstream from the reservoir has to be included in the model before calculations of source component contributions can be made it is inferred that one or more high magnitude low frequency event outside the amplitude of the most recently operating processes was largely responsible for the infilling of the reservoir

carbon isotope fractionation and changes in the flux and composition of particulate matter resulting from biological activity during a sediment trap experiment in lake greifen switzerland sediment traps were deployed in lake greifen a hard water eutrophic swiss lake for 2 weeks in may and june 1983 oxygen ph and suspended particle concentrations indicated a sharp increase in productivity during the experiment carbon isotope composition of the dissolved inorganic carbon recorded the balance between photosynthesis and respiration and showed possible evidence of difhtsion of atmospheric co across the water atmosphere interface most likely to replace co used during photosynthesis allochthonous mineral debris from resuspended sediments or river input was a major component of the sedimenting material due to removal of coz large newly formed calcite crystals precipitated when photosynthesis increased the carbon isotope ratio of trap calcite and the composition of trap amino acids showed the influence of the detrital input on the more dominant isotopic signal of authigenic calcite sediment calcite is enriched in 13c relative to authigenic calcite in the sediment traps this enrichment is likely due to fractionation during precipitation in the surface waters or during dissolution in the water and sediments due to caco undersaturation we found extensive loss of material from unpoisoned sediment traps in the euphotic zone most likely due to zooplankton feeding

stable isotopes in recent sediments of lake arendsee ne germany response to eutrophication and remediation measures abstract recent sediments of lake arendsee a small eutrophic lake in ne germany were examined in high temporal resolution in order to investigate the applicability of stable isotopes as proxies to trace paleoenvironmental conditions the age model of the sediment core is based on varve counting and 137cs 210pb dating and reveals that the sedimentary record covers the last 70 years during which the lake has undergone major changes in productivity and eutrophication in response to nutrient loading since 1965 toc tic tn and tp accumulation rates in general reflect the change from oligo mesotrophic to eutrophic level the isotopic compositions of autochthonous organic matter and authigenic calcite whitings demonstrate that carbon isotope fractionation takes place in a co2 limited pool in accordance with the historical limnological observations enhanced eutrophication is reflected by 13ctoc increases of over 3 from 1934 to 1985 as a result of less 12c 13c fractionation by photosynthesis during intense primary productivity decreasing 13ctic values indicate that biogenically induced calcite formation occurred during enhanced primary production accompanied by co2 limitation the gradual trend to more light nitrogen isotopic signatures towards the sediment surface reflects the dominance of air nitrogen fixation of cyanobacteria blooms during the last decades the 18otic distribution suggests that plankton blooms between 1934 and 1978 had shifted towards the early season with lower temperatures as a result of increasing nutrient level which subsequently favor plankton blooms even in colder waters since the mid 1980s decreasing 13ctoc and increasing 13ctic values since 1985 indicate a more efficient 12c 13c fractionation during photosynthesis with no co2 limitation this improvement in water quality is in accordance with several remediation measures carried out since the late 1970s linear isotopic trends are interrupted by high tic toc tn and tp accumulation rates in the early 1970s which can be clearly attributed to the artificial drainage of a nearby wetland carried out during that time this event can be considered an important external source for nutrient loaded water and particulate matter and is displayed by significantly heavier 13ctic and 18otic values in the sedimentary record

atmospheric warming at a high elevation tropical site revealed by englacial temperatures at illimani bolivia 6340 m above sea level 16 s 67 w in june 1999 a deep 138 7 m ice core was extracted from the summit glacier of illimani bolivia 6340 m above sea level 16 39 s 67 47 w and an englacial temperature profile was measured in the borehole using on site and regional meteorological data as well as ice core stratigraphy past surface temperatures were reconstructed with a heat flow model the englacial temperature measurements exhibit a profile that is far from a steady state reflecting an increasing atmospheric temperature over several years and nonstationary climatic conditions englacial temperature interpretation using air temperature data borehole temperature inversion and melting rate quantification based on ice core density shows two warming phases from 1900 to 1960 0 5 0 3 k starting approximately in 1920 1930 and from 1985 to 1999 0 6 0 2 k corresponding to a mean atmospheric temperature rise of 1 1 0 2 k over the 20th century according to various climate change scenarios the future evolution of englacial temperatures was simulated to estimate when and under what conditions this high elevation site on the illimani summit glacier could become temperate in the future results show that this glacier might remain cold for more than 90 years in the case of a 2 k rise over the 21st century but could become temperate in the first 20 m depth between 2050 and 2060 if warming reaches 5 k

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

the isotopic response of lake chenghai sw china to hydrologic modification from human activity the human modification of lake hydrology is widespread in the industrial era however anthropogenic impacts have occurred for thousands of years in regions of the world with long histories of human occupation here we use geochemical analyses of lake sediment to document the isotopic and geochemical response of cheng lake chenghai in southwestern china to catchment modification including the construction of a downstream dam the chenghai record indicates that land use changes affected the lake catchment by at least ad 1150 as evidenced by an increased flux of terrestrial organic matter sediment with high concentrations of sorbed metals and variations in stable isotopes of oxygen in precipitated aragonite decreases in magnetic susceptibility and metal concentrations after ad 1360 indicate a change in sediment basin dynamics the construction of a downstream dam between ad 1573 and 1620 caused positive shifts in the isotopic composition of aragonite indicative of increased evaporative loss and a lo

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

lacustrine carbonates of iberian karst lakes sources processes and depositional environments abstract carbonates are the main components of iberian quaternary lake sediments in this review we summarize the main processes controlling carbonate deposition in extant iberian lakes located in mesozoic and tertiary carbonate dominated regions and formed through karstic activity during the late quaternary the lakes relatively small 1 ha to 118 ha and relatively shallow zmax 11 to 40 m provide examples of the large variability of sedimentary facies depositional environments and carbonate sources hydrology is dominated by groundwater inflow except those directly connected to the fluvial drainage nine lakes have been selected for this review and the main facies in palustrine littoral and profundal environments described and interpreted clastic carbonates occur in all iberian lakes due to the carbonate composition of the bedrocks surface formations and soils of the watersheds low temperatures and dilute meteoric waters seem responsible for the low carbonate content of sediments in high elevation lakes in the glaciated terrains in the pyrenees and the cantabrian mountains clastic carbonates are dominant in small karst lakes with functional inlets where sediment infill is dominated by fining upward sequences deposited during flood events re working of littoral carbonates is common in shallow environments and during low lake level stages in most lakes endogenic carbonate production occurs in two settings i littoral platforms dominated by chara and charophyte meadows and ii epilimnetic zone as biologically mediated calcite precipitates continuous preservation of varves since the mid holocene only occurs in one of the deeper lakes montcortes lake up to 30 m where calcite laminae textures massive fining upward and coarsening upward reflect seasonal changes in limnological conditions however varves have been formed and preserved in most of the lakes during short periods associated with increased water depth and more frequent meromictic conditions most iberian lakes are in a mature stage and karstic processes are not very active an outstanding example of a lake with intense karstic activity is banyoles lake where increased spring discharge after long rainy periods causes large remobilization and re suspension of the sediments accumulated in the deepest areas leading to the deposition of thick homogeneous layers homogeinites the iberian karst lake sequences underline the large variability of facies carbonate sources and depositional environments in small lake systems they illustrate how lake types evolve through the existence of a lake basin at centennial or even smaller time scales hydrology is the paramount control on facies and depositional environment patterns distribution and lake evolution and consequently a lake classification is proposed based on hydrology and sediment input a correct interpretation of carbonate sources and depositional history is a key for using lake sequences as archives of past global changes

recent human induced trophic change in the large and deep perialpine lake lucerne switzerland compared to historical geochemical variations this study investigates the sedimentological and geochemical changes that occurred during the last 2200 years in the meromictic lake lucerne switzerland one of the largest freshwater lakes of central europe the stable isotope composition 13c and 18o values of bulk carbonates is compared to changes in grain size distribution clay and silt fraction natural trace element input titanium and thorium concentrations and organic material abundance corg nitrogen and phosphorus and composition c n ratios and hydrogen and oxygen indexes a drop in carbonate accumulation and in the 18o values of sediments between ca ad 500 and 700 followed a large and consistent rise in chemical weathering marked by increases in the silicate clay fraction and in crustal element concentrations during the following millennium there was a long term decreasing trend in the lithogenic trace element input and in the phosphorus loading suggesting decreasing terrigeneous input from runoff water the major sedimentological change over the studied period occurred after ca ad 1800 with a significant increase in the erosion driven silt fraction and in the sedimentation rate during the last century human induced increase in nutrient input to the lake highly enhanced the accumulation of organic matter in sediment changes in nutrients and oxygen conditions in the hypolimnion of lake lucerne during the eutrophication period i e the last 40 years highly modified the geochemical fluxes compared to the relatively stable oligotrophic conditions that prevailed during the previous 2000 years before the 19th century climate driven meromixis had a limited impact on the organic matter flux to the sediments but the accumulation of carbonate considerably decreased during periods of lower mechanical erosion rates and high chemical weathering rates

geochemical evidence for hydroclimatic variability over the last 2460 years from crevice lake in yellowstone national park usa abstract a 2460 year long hydroclimatic record for crevice lake yellowstone national park montana was constructed from the 18 o values of endogenic carbonates the 18 o record is compared to the palmer hydrologic drought index phdi and pacific decadal oscillation pdo indices as well as inferred discharge of the yellowstone river during the last century high 18 o values coincide with drought conditions and the warm phase of the pdo index low 18 o values coincide with wet years and a negative pdo index comparison of tree ring inferred discharge of the yellowstone river with the 18 o record over the last 300 years indicates that periods of high discharge i e wet winters with significant snow pack correspond with low 18 o values extrapolating this relationship we infer wet winters and high river discharge for the periods of 1090 1030 970 870 670 620 and 500 430 cal years bp the wet intervals at 670 and 500 cal bp are synchronous with similar events in banff canada and walker lake nevada the wet intervals at 970 and 670 cal bp overlap with wet intervals at walker lake and major drought events identified in the western great basin these results suggest that the northern border of yellowstone national park straddles the boundary between northern rocky mountains and great basin climate regimes

stable isotope response to lake eutrophication calibration of a high resolution lacustrine sequence from baldeggersee switzerland stable isotope analyses of discrete seasonal layers from a 108 yr annually laminated freeze core from baldeg gersee a small eutrophic lake in central switzerland provide information on the climatological and environmental factors including lake eutrophication that control oxygen and carbon isotopic composition of epilimnic biologically induced calcite precipitate during the last 100 yr baldeggersee has undergone major increases in productivity and eutrophication in response to nutrient loading from agriculture and industrialization in the lake s watershed calibration of the isotopic signal in baldeggersee to historical limnological data quantitatively links evidence of isotopic depletion in the sedimented calcite to trophic state of the lake 18o values from the spring summer light sediment layers steadily diverged to more depleted values in response to historical eutrophication measured 18o values were up to 21 5 more negative than calculated equilibrium 18o values evidence for 13c depletion in the calcite relative to equilibrium values is more difficult to ascertain because of an overall dominance of isotopic enrichment in the dissolved inorganic pool as productivity in baldeggersee increases a positive association exists between the degree of oxygen 18 depletion and the calcite crystal size thus large amorphous calcite grains can be used as a proxy for recognizing apparent isotopic nonequilibrium in sediment sequences from highly productive lacustrine environments from all geologic time scales in contrast to the light layers the oxygen isotopic composition of the calcite in the late summer fall dark sediment layers is unaffected by the apparent isotope nonequilibrium oxygen and carbon isotope values from the dark laminae in the baldeggersee sediment therefore provide environmental and climatological proxies that can be calibrated with known environmental and regional climate data for the last century

multidecadal to century scale arid episodes on the northern altiplano during the middle holocene abstract we present reconstructions of multidecadal to centennial scale shifts in the hydrologic balance of the northern altiplano during the middle holocene using stable isotopic geochemical and sedimentologic evidence from lake titicaca sediments large downcore changes in the 13corg of bulk organic matter previously shown to be a site specific lake level proxy indicate that extended periods of lake level regression occurred in response to sustained reductions in mean annual precipitation and or increases in air temperature supporting evidence from a floating interval of finely laminated sediments indicates that salinity and stratification were enhanced at lake titicaca during the middle holocene the age model used in this study is based on 7 ams 14c age dates estimated from bulk decalcified sediment from a 60 cm sequence spanning 7200 5600 14c cal yr bp simulations from a hydrological energy balance model of the titicaca basin indicate that the 38 m drop in lake level that preceded the maximum lowstand at 6200 yr bp would require a significant decrease in mean annual precipitation of up to 50 and or a significant increase in mean annual temperature of up to 8 c today the altiplano is often affected by drought during periods of enhanced summertime westerly wind flow which reduces the delivery of moisture from the east this investigation supports the idea of sustained periods of enhanced westerly air flow during the mid holocene and provides additional submillennial scale information about the timing and magnitude of regional drought results of our frequency domain analysis of the floating lamination interval indicate significant power at a decadal periodicity 10 12 yr associated with the schwabe cycle of solar activity frequency domain analysis also reveals power in a 75 year time series of modern lake level we suspect that solar influence on large scale atmospheric circulation features results in changes to the moisture balance in the titicaca basin over decadal and possibly century scale time periods

magnetofossils the magnetization of sediments and the evolution of magnetite biomineralization magnetite fe 3o 4 is one of the most stable carriers of natural remanent magnetization nrm in sedimentary rocks and paleomagnetic studies of magnetite bearing sediments such as deep sea cores and pelagic limestones have provided a detailed calibration between the biostratigraphic and magnetic polarity time scales despite this important role there is as yet a very poor understanding of how ultrafine grained 0 1 m magnetite is formed transported and preserved in marine environments a major conceptual advance in our understanding of these processes is the recent discovery that biogenic magnetite formed by magnetotactic bacteria and or other magnetite precipitating organisms is responsible for much of the stable magnetic remanence in many marine sediments and sedimentary rocks since these magnetite particles are of biogenic origin they are termed properly magnetofossils kirschvink chang 1984

isotopic and hydrologic responses of small closed lakes to climate variability hydroclimate reconstructions from lake sediment oxygen isotope records and mass balance models abstract hydroclimate sensitivity simulations were conducted with a lake catchment hydrologic and isotope mass balance model adapted to two small closed lakes castor and scanlon located in the pacific northwest model simulations were designed to investigate the combined influences of persistent disequilibrium reddening and equifinality on lake water and sediment i e biogenic and endogenic carbonate mineral oxygen isotope 18 o values and to provide a basis for quantitative probabilistic climate reconstructions using lake sediment 18 o records simulation results indicate that within closed basin lakes changes in long term i e multi decadal precipitation amounts produce inconsistent responses in lake water and sediment 18 o values that are strongly influenced by lake basin outseepage and morphometry simulations of variable initial conditions in which randomly generated monthly climate data i e precipitation temperature and relative humidity were used to force the model during the equilibration period which precedes the application of instrumental climate data demonstrate that castor lake and scanlon lake have a somewhat limited isotopic memory of 10 years additional tests conducted using a monte carlo ensemble in which random climate data were used to force the model combined with 18 o analyses of water samples collected from 2003 to 2011 ad indicate that within small closed lakes in the pacific northwest november february precipitation is the strongest seasonal climatic control on sediment oxygen isotope values further a monte carlo based reconstruction of 20 year average november february precipitation amounts strongly correlates r 2 0 66 to instrumental values from the 20th century with all observed values falling within modeled 95 prediction limits indicating that probabilistic quantitative paleoclimate interpretations of lake sediment 18 o records are attainable

the magnetic properties of particle sized samples from the luo chuan loess section evidence for pedogenesis abstract measurements of magnetic susceptibility and of laboratory remanences have been carried out on particle size fractions of loess and palaeosol samples from luo chuan china they show that the sub micron clay fraction of the palaeosol is greatly enriched in fine grained

13c 12c partitioning and kinetics of co2 absorption by hydroxide buffer solutions abstract absorption of co2 gas into a borate buffer solution is a linear function of time the measured absorption rate logr 10 33 mol cm 2 s 1 compares well to a value calculated from the diffusion constant of co2 aq and the rate constant for the reaction of co2 aq with oh the stable carbon isotope composition of the dissolved carbonate is constant as function of time and is depleted in13c by 19 5 with respect to the gas phase the kinetic fractionation due to diffusion is 13d 12d 0 5 1 103 0 7 while that caused by the chemical reaction is 13k 12k 0 5 1 103 18 8 these values have to be taken into account if a borate buffer is used for sample concentration techniques in order to deduce the carbon isotope composition of co2 g absorption of co2 into a ba oh 2 solution is a linear function of time too but the absorption rate varies with the experimental boundary conditions the precipitated baco3 is depleted in13c with respect to the gas phase however 13c values are not constant and decrease as a function of time

toward the discrimination of fine grained ferrimagnets by magnetic measurements in lake and near shore marine sediments the magnetic properties of low field susceptibility frequency dependent susceptibility fd and susceptibility of anhysteretic remanent magnetisation arm are used to define sets of natural soil and sediment samples within which by the criteria of king et al 1982 and maher 1988 the modal ferrimagnetic grain diameter is less than 0 07 0 1 m within this sample set two distinct groups with low and high values respectively for the quotients arm and arm fd are defined the first group includes sediment samples from sites where published studies propose a detrital origin for the fine grained ferrimagnetic content where catchment samples are available for comparison they fall within the same envelope as do clays from palaeosol samples within chinese loess this envelope of low quotient values also overlaps with the values for the fine grained synthetic magnetite samples within maher s 1988 new mt series the high quotient envelope of values includes sediments from the adriatic sea and clays from saltmarsh and shallow water marine sediments in nw britain in these cases no catchment source is postulated for the fine grained magnetite the size range of magnetite in this set appears to be almost exclusively stable single domain ssd and a bacterial origin seems likely sample sets from estuarine environments between river inflow sites and the open sea show intermediate values which in the case of the potomac are ordered by distance down river although at this stage magnetic measurements alone cannot discriminate between bacterial and fine grained detrital ferrimagnets in sediments they hold out some promise of doing so provided the distinctions proposed here can be substantiated by transmission electron microscopy

the iberian roman humid period 2600 1600 cal yr bp in the zonar lake varve record andalucia southern spain abstract the iberian roman humid period irhp 2600 1600 cal yr bp is the most humid phase of the last 4000 yr in southern spain as recorded in the sedimentary sequence of zonar lake 37 29 00 n 4 41 22 w 300 m a s l a varve chronology supported by several ams 14 c dates allows study of the lake evolution at annual scale in response to human impact and climate changes there are four climate phases within this period i gradual transition 2600 2500 yr ago 650 550 bc from a previous arid period ii the most humid interval during the iberian early roman epoch 2500 2140 yr ago 550 190 bc iii an arid interval during the roman empire epoch 2140 1800 yr ago 190 bc ad 150 and iv a humid period synchronous with the decline of the roman empire 1800 1600 yr ago ad 150 350 varve thickness and geochemical proxies show a multi decadal cyclicity similar to modern north atlantic oscillation nao 60 20 years and solar variability cycles 11 yr the timing and the structure of this humid period is similar to that described in eastern mediterranean and northern european sites and supports the same large scale climate control for northern latitudes and the mediterranean region

record of palaeoenvironmental changes in a lower permian organic rich lacustrine succession integrated sedimentological and geochemical study of the rudnik member krkonose piedmont basin czech republic abstract this study presents an integrated sedimentological and geochemical analysis of the lower permian rudnik member the most extensive lacustrine deposits in the krkonose piedmont basin grey to black and variegated lacustrine mudstones laminites and carbonates of the rudnik member have a lateral extent of more than 400 km 2 in the studied sections four facies associations were recognised a anoxic offshore b suboxic to oxic offshore c nearshore and mudflat and d slope deposits in the northern part of the e w elongated basin anoxic to suboxic organic rich offshore lacustrine facies dominate and form a succession up to 130 m thick fan delta and turbidite facies occur locally along the faulted northern basin margin the central part of the basin is occupied by anoxic to oxic offshore facies interfingering with nearshore carbonate and mudflat facies of the low gradient lacustrine margin in the central part of the basin the thickness of the lacustrine deposits of the rudnik member reaches up to 60 70 m in the southern part of the basin fluvial and alluvial plain facies dominate and alternate with minor lacustrine nearshore facies the lateral facies distribution indicates that subsidence along the northern basin fault was the main mechanism generating the asymmetric infill geometry in the basin s half graben setting the 1 8 o values of primary and early diagenetic calcite range between 11 0 and 1 3 v pdb and 1 3 c values between 5 1 and 3 7 most of the data fall within the range of freshwater limestones coarser grained pure microspar laminae show more positive 1 3 c values in comparison to clayey organic rich micrite laminae and are interpreted as a record of bioinduced precipitation during seasonal eutrophication the obtained 1 3 c toc values range from 29 0 to 24 0 the total organic carbon toc content from 0 26 to 23 maceral analysis and rock eval pyrolysis indicate that most of the samples contain a mixture of aquatic and terrestrial organic matter but two minor distinctive groups of samples with algally dominated and terrestrially dominated organic matter composition respectively were also found the study of vertical changes in boron content in the clay fraction of the lacustrine mudstones shows that high lake level stages were periods of lower salinity with the lowest boron contents from 73 to 268 ppm and periods of falling lake level were followed by significant increases in salinity with much higher boron values 293 603 ppm lake level fluctuations of the rudnik lacustrine system which are recorded by shallowing up units of sedimentary facies within most of the sections throughout the basin can also be traced within the monotonous black shale dominated sections where no sedimentological evidence of these lake level changes exists good indicators for such changes seem to be the 1 8 o and 1 3 c values of primary calcite 1 3 c toc and hi these lake level fluctuations are interpreted as driven by climatic oscillations in the order of tens of thousands years which could reflect climatic changes connected with the last glaciation event of gondwana