sedimentary rhythm of mn carbonate laminae induced by east asian summer monsoon variability and human activity in lake ohnuma southwest hokkaido northern japan abstract past and ongoing precipitations of mn carbonate rhodochrosite have occurred in the freshwater lake ohnuma which is situated about 8 km south of the hokkaido komagatake volcano southwest hokkaido northern japan lake sediments from a surface and a longer 4 m core contain the sedimentary rhythms of rhodochrosite laminae and volcanic deposits which were identified by nondestructive micro xrf fluorescence analyses the three tephra ash layers from the hokkaido komagatake volcano characterized by peaks of al si k ca and ti correspond to regionally recognized tephras 1640 1929 and 1996 ce based on ashfall isopachs and 137cs 210pb and 14c ages determined from the two cores the sedimentation rate showed a drastic change around 1929 ce 0 3 cm yr for 1640 1929 ce and 2 7 cm yr for 1929 2012 ce the mn content record of lake ohnuma sediments composed of rhodochrosite laminae showed a periodic variation with a decadal centennial scale over the interval 1640 2012 ce sediment petrography and hydrochemical measurements suggest that the metastable phase of rhodochrosite was deposited during summer after being precipitated followed by the crystal growth of rhodochrosite within the anoxic sediments on the basis of these results high mn content is interpreted as an indicator of strengthened summer stratification associated with reduced rainfall runoff the ti si ratios are representative of the relative abundance of detrital inputs from the watershed the combined signals of elevated mn content and ti si ratio for 1935 2012 ce indicate eutrophication and hypoxia in the lake and enhanced land erosion in the watershed associated with the post 1970s intensive land use such as livestock farming for 1640 1935 ce the lake ohnuma record shows an antiphase relationship between the mn content and ti si ratio which implies that the detrital inputs reflected the strength of the east asian summer monsoon easm and the reduced rainfall runoff resulted in weaker mixing followed by depleted o2 in the water column the antiphase variation in mn content and ti si ratio suggest weak easm during the little ice age 1850 ce followed by strong easm between 1860 and 1929 ce

origin of the lethal gas burst from lake monoun cameroun abstract on 15 august 1984 a lethal gas burst issued from a submerged 96 m deep crater in lake monoun in cameroun western africa killing 37 people the event was associated with a landslide from the eastern crater rim which slumped into deep water waters below 50 m are anoxic dominated by high fe 2 600 mg l and hco 3 1900 mg l anoxic and supersaturated with siderite which is a major component of the crater floor sediments the unusually high fe 2 levels are attributed to reduction of laterite derived ferric iron gradually brought into the lake as loess and in river input sulfur compounds are below detection limits in both water and gas gases effervescing from depressurized deep waters are dominantly co 2 with minor ch 4 having 13 c of 7 18 and 54 8 per mil respectively bacterial decomposition of organic matter may account for the methane but 14 c of lake water indicates that only 10 of the carbon is modern giving an apparent age of 18 000 years the dominant source of carbon is therefore attributed to long term emission of co 2 as volcanic exhalation from vents within the crater which led to gradual build up of hco 3 in the lake the density stratification of the lake may have been upset by an earthquake and underwater landslide on 15 august which triggered overturn of the lake and caused nucleation of co 2 in the deep water the resultant ebullition of co 2 from deep lake waters led to a gas burst at the surface and locally generated a water wave up to 5 m high people travelling through the gas cloud were asphyxiated presumably from co 2 and suffered skin discoloration from unidentified components

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

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

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

climate system transition from glacial to interglacial state around the beginning of the last termination evidence from a centennial to millennial scale climate rhythm a periodic variation on a centennial to millennial scale was observed in the manganese and iron contents of lake suigetsu sediments in japan dating from 19 0 to 5 7 cal kyr b p calibrated thousand years before present the increased manganese and iron contents which mainly indicate the relative abundance of siderite result from a greater vertical circulation in the lake during a cold period with a higher mass of manganese and iron oxide being precipitated the cold periods inferred from the increased manganese and iron contents coincide with the timing of ice rafting debris ird events in the north atlantic which span from the last termination to the holocene suggesting that the climate shift was hemispheric or probably global in nature the manganese variation resembles the residual atmospheric 14c production 14c data of the holocene that reflect variation in solar activity and its periodicities correspond with those of solar related climate changes from paleoproxy records in the north atlantic and east asia from the last cold stage to the holocene in particular the mn variation was larger in amplitude and shorter in timescale during the last cold stage when compared with those during the last termination and the holocene thereby possibly showing a significant difference in climate response to solar irradiance the transition of the climate system from a glacial to an interglacial state corresponds to the beginning of the last termination

hydroclimatic changes in china and surroundings during the medieval climate anomaly and little ice age spatial patterns and possible mechanisms abstract investigating hydroclimatic changes during key periods such as the medieval climate anomaly mca 1000 1300 ad and the little ice age lia 1400 1900 ad is of fundamental importance for quantifying the responses of precipitation to greenhouse gas induced warming on regional and global scales this study synthesizes the most up to date and comprehensive proxy moisture precipitation records during the past 1000 years in china and surroundings the proxy data collected include 34 records from arid central asia aca and 37 records from monsoonal asia our results demonstrate a pattern of generally coherent regional moisture variations during the mca and lia in mid latitude asia north of 30 n monsoonal northern china north china and northeast china was generally wetter while aca northwest china and central asia was generally drier during the mca than in the lia a west east mode the boundary between wetter northern china and drier aca was roughly consistent with the modern summer monsoon boundary in monsoonal china to the east of 105 e the northern part was generally wetter while the southern part was generally drier during the mca than in the lia a north south mode with a boundary roughly along the huai river at about 34 n these spatial patterns of moisture precipitation variations are also identified by instrumental data during the past 50 years in order to understand the possible mechanisms related to the moisture variations during the mca and lia we investigate the major sst and atmospheric modes e g the el nino southern oscillation enso the atlantic multidecadal oscillation amo and the north atlantic oscillation nao which affect the moisture precipitation variations in the study region using both the instrumental data and the reconstructed time series it is found that the enso may play an important role in determining hydroclimatic variability over china and surroundings on a multi centennial time scale and that the foregoing spatial patterns could be attributed to the la nina like el nino like condition during the mca lia in addition amo and nao may also have their own contributions

role of precursory less viscous mixed magma in the eruption of phenocryst rich magma evidence from the hokkaido komagatake 1929 eruption during the 1929 activity of hokkaido komagatake volcano the plinian eruption of a phenocryst rich andesite was preceded by a small eruption of more mafic magma formed by magma mixing a similar eruption sequence has been reported for some other eruptions pallister et al 1996 venezky and rutherford 1997 suggesting that eruption of a mixed magma is a precursor of phenocryst rich magmas for the purpose of understanding the tapping processes of the phenocryst rich magma chamber we investigated the temporal variation in the erupted magma and estimated the viscosity and density of the end member and mixed magmas with constraints drawn from petrography for the precursory mixed magma we estimate 33 4 vol phenocrysts andesitic dacitic melt composition 3 wt h2o content and temperature of 1040 c in comparison for the climactic silicic end member magma we estimate 48 3 vol phenocryst high silica rhyolitic melt 3 wt h2o and temperature of 950 c respectively the mafic end member magma which was not erupted is thought to be an almost aphyric basaltic andesitic magma based on mass balance calculation of the phenocryst content the proportion of the mafic end member magma component in the mixed magma was calculated to be 20 40 wt on the basis of these data we estimate magma viscosities of 103 9 106 9 and 102 0 pa s for the mixed silicic end member and mafic end member magmas respectively the calculated density differences among these magmas are inconsequential when possible errors are considered we calculate the minimum excess pressure required for dike propagation to be 31 mpa for the silicic end member magma and 8 mpa for the mixed magma using the estimated viscosity and dike propagation model of rubin 1995 if we assume that excess pressure is limited by the wall rock strength of the magma chamber excess pressure retainable in the magma chamber is less than ca 20 mpa this suggests that the mixed magma was able to ascend to the surface without freezing whereas the viscous silicic end member magma could not the formation and precursory eruption of the mixed magma are therefore effective and necessary initiation processes for the phenocryst rich viscous magma eruption

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

sedimentary geochemistry of manganese implications for the environment of formation of manganiferous black shales the sedimentary geochemistry of manganese is dominated by the redox control of its speciation higher oxidation states mn super 3 and super 4 occurring as insoluble oxyhydroxides in well oxygenated environments and the lower oxidation state mn super 2 being much more soluble in oxygen deficient settings its geochemical behavior is therefore quite different in oxic and anoxic environments and where oxic and anoxic conditions are juxtaposed mn is recycled between the two environments in modern marine sediments mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating pelagic sediments of the deep ocean and in surficial deposits of continental margin environments diagenetic recycling of mn in the latter causes surficial deposits to have larger mn enrichments than in many pelagic sediments bottom sediments of permanently anoxic basins show no enrichments and have mn concentrations that are controlled solely by the aluminosilicate fraction manganese carbonates kutnohorite and calcic rhodochrosite are found only in anoxic sediments accumulating beneath surface oxic horizons and therefore under oxygenated bottom waters in many nearshore environments such enrichments are due to delivery of mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved pore water mn levels can reach saturation with respect to a mixed mn ca carbonate phase in such sediments the diagenetic origin for these phases is shown by their carbon isotope compositions which typically indicate a carbon source from decomposing organic matter the presence of mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters on the basis of this information it is proposed that in contrast to several current explanations for the formation of mn carbonates kutnohorite and rhodochrosite in ancient organic rich shales limestone and marl sequences and in many mn ore deposits the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters by analogy with the present mn carbonates could not have formed in the bottom waters of anoxic basins these diagenetic phases however did form where mn was supplied at a high rate namely by the burial of oxyhydroxide enriched surface sediments to a subsurface anoxic environment this situation could only have occurred under oxygenated bottom waters the presence of mn carbonates in ancient black shales and in some carbonate rich rocks lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters probably in continental margin settings

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

an earthquake like magnitude frequency distribution of slow slip in northern cascadia 1 major episodic tremor and slip ets events with mw 6 4 to 6 7 repeat every 15 2 months within the cascadia subduction zone under the olympic peninsula although these major ets events are observed to release strain smaller tremor swarms without detectable geodetic deformation are more frequent an automatic search from 2006 2009 reveals 20 000 five minute windows containing tremor which cluster in space and time into 96 tremor swarms the 93 inter ets tremor swarms account for 45 of the total duration of tremor detection during the last three ets cycles the number of tremor swarms n exceeding duration follow a power law distribution n 0 66 if duration is proportional to moment release the slip inferred from these swarms follows a standard gutenberg richter logarithmic frequency magnitude relation with the major ets events and smaller inter ets swarms lying on the same trend this relationship implies that 1 inter ets slip is fundamentally similar to the major events just smaller and more frequent and 2 despite fundamental differences in moment duration scaling the slow slip magnitude frequency distribution is the same as normal earthquakes with a b value of 1

variation of transition zone high velocity anomalies and depression of 660 km discontinuity associated with subduction zones from the southern kuriles to izu bonin and ryukyu the seismic structure of the transition zone beneath the northwestern pacific ocean is studied by comparing regional distance seismic waveforms with synthetic seismograms by modeling waveforms we incorporate the travel times of secondary waves that are not included in traveltime data used in most p wave tomography experiments these secondary waves are highly sensitive to the velocity above the 660 km discontinuity and thus add information on the seismic structure of the transition zone independent of that used in many tomography experiments we used just two one dimensional models in the waveform comparison the iasp91 slightly modified in the shallower depths as aiasp is used as a global average structure and model m3 11 is used as representative of transition zone structure near a deep subducting slab model m3 11 is faster than iasp91 from 525 to 660 km depth but also has a 30 km deeper 660 km discontinuity our results show strong variations in the transition zone structure beneath the northwestern pacific data that sample beneath the northwestern japanese subduction zone and the southern kuriles are well fit by model m3 11 the deep structure beneath the bohai sea to the west of korea also appears to show slab related velocity anomalies in the transition zone in contrast the seismic data sampling beneath the yellow sea to the east china sea are better modeled using the global average model iasp91 data that sampled beneath the philippine sea showed evidence for anomalously high velocity in the transition zone but there is little apparent change in the depth of the 660 km discontinuity there the overall results are in agreement with past work indicating fairly broad regions where subducting plate is lying flat or piling up within the transition zone although we find that the region where this occurs and thus the total volume of slab within the upper mantle is considerably less than that seen in past studies the unusual structure beneath the philippine plate may be due to the relatively recent descent of slab beneath this region the slab itself is cold and thus anomalously fast but the deeper mantle may not have cooled enough for the 660 km discontinuity to have deepened

varves in lake sediments a review abstract downcore counting of laminations in varved sediments offers a direct and incremental dating technique for high resolution climatic and environmental archives with at least annual and sometimes even seasonal resolution the pioneering definition of varves by de geer 1912 had been restricted to rhythmically deposited proglacial clays one century later the meaning of varve has been expanded to include all annually deposited laminae in terrestrial and marine settings under favourable basin configurations and environmental conditions limnic varves are formed due to seasonality of depositional processes from the lake s water column and or transport from the catchment area subsequent to deposition of topmost laminae the physical preservation of the accumulating varved sequence requires the sustained absence of sediment mixing for example via wave action or macrobenthic bioturbation individual sub laminae in varved lake sediments typically express contrasting colours always differ in terms of their organic chemical and or mineralogical compositions and often also differ with regard to grain size various predominating climatic and depositional conditions may result in clastic biogenic or endogenic incl evaporitic varved sediments and their mixtures to reliably establish a varve chronology the annual character of laminations needs to be determined and verified in a multidisciplinary fashion sources and influences of possible errors in varve chronologies are best determined and constrained by repeated varve counts and by including radioisotopes and correlation with historically documented events a well established varve chronology greatly enhances the scientific value of laminated limnic archives by securely anchoring the wealth of multi proxy palaeoenvironmental information in the form of time series for multidisciplinary investigations applications of varved records are discussed with special reference to advances since the 1980s these span fields like calibrating radiometric dating methods reconstructing past changes of the earth s magnetic field or detecting fluctuations in solar forcing once a varve chronology is established it can be applied to precisely date events like volcanic ash layers earthquakes or human impact as well as short and long term climate temperature precipitation wind hydroclimatic conditions or flooding and environmental changes eutrophication pollution due to their exceptional high temporal resolution and in combination with their robust and accurate internal time scale in calendar years annually laminated sediments can be regarded as one of the most precious environmental archives on the continents these records are necessary to extend temporally limited instrumental records back in time as such they have societal relevance with regard to risk assessments related to natural hazards arising from e g flooding or volcanic eruptions

varved lacustrine sediments of lake tougou ike western japan with reference to holocene sea level changes in japan abstract eighteen metres of laminated sediments were recovered in a holocene sediment core taken from lake tougou ike in 1992 the lamination evident from the alternation of light and dark coloured laminae records cyclic deposition of biochemical sediments annual environmental changes in and around the lake caused seasonal variations in sediment flux to the lake floor explaining these cyclic variations in sedimentary facies ams 14 c dating of organic remains from 40 horizons in the succession supports the interpretation of each light to dark couplet as an annual increment each laminated couplet is identified as a non glacial varve formed mainly by seasonal changes in diatom productivity varve counting and 14 c dating provide a detailed holocene chronological framework with time resolution on the order of individual years within which to reconstruct paleoenvironmental changes recorded in the sediment core holocene relative sea level changes at lake tougou ike were estimated with 10 yr precision using the variable authigenic iron mineral content of the sediment as a proxy the results demonstrate that the relative sea level at lake tougou ike rose abruptly at about 8900 7700 5600 4000 3600 and 2700 cal yr bp and decreased gradually in the intervening intervals these relative rises in sea level are demonstrated to be coeval with ice sheet discharge events recorded in sediment cores from the north atlantic ocean abrupt coastal environmental changes caused by sea level changes likely took place throughout the japanese islands and will probably be identified in both the holocene and the last glacial interval the latter being a time when dansgaard oeschger cycles were clearly active in the north atlantic region

stable nitrogen isotope record of lacustrine sediments in lake onuma northern japan indicates regional hydrological variability during the past four centuries abstract discriminating natural and anthropogenic forcing on hydroclimatic changes is of fundamental importance for projecting future precipitation distribution under the warming climate a sediment core on12c obtained from lake onuma is used to study the evolution of precipitation in northern japan the age depth model for the core is based on three identified tephra layers combined with accelerator mass spectrometry 14 c measurements of plant remnants 137 cs dating and lithology multi proxy records including pollen concentration alnus pollen percentages and c n atomic ratios indicate that the 15 n record reflects nitrogen availability in the catchment where precipitation may exert a significant impact the 15 n record shows that the precipitation was gradually increasing from 1640 ad reaching peak strength in the middle of the 19th century followed by a dry interval during the 20th century the reconstructed variability in the precipitation from lake onuma is supported by other precipitation records from the asian monsoon region solar irradiance is likely responsible for the changes in the summer monsoon precipitation on the centennial timescales during the late little ice age and the winter monsoon may also have played an important role in snow precipitation however the 20th century anomaly indicates that the asian summer monsoon precipitation variability might be affected by anthropogenic forcing

a complete terrestrial radiocarbon record for 11 2 to 52 8 kyr b p radiocarbon 14c provides a way to date material that contains carbon with an age up to 50 000 years and is also an important tracer of the global carbon cycle however the lack of a comprehensive record reflecting atmospheric 14c prior to 12 5 thousand years before the present kyr b p has limited the application of radiocarbon dating of samples from the last glacial period here we report 14c results from lake suigetsu japan 35 35 n 135 53 e which provide a comprehensive record of terrestrial radiocarbon to the present limit of the 14c method the time scale we present in this work allows direct comparison of lake suigetsu paleoclimatic data with other terrestrial climatic records and gives information on the connection between global atmospheric and regional marine radiocarbon levels

chronology and sedimentation process of varved lacustrine sediment in lake fukami central japan abstract continuous varve sequences were taken from lake fukami a monomictic lake southern part of nagano prefecture central japan in 2000 total 196 varve units were recognized in the upper 2 m horizon of the sediment core sedimentation rates in the core have some high peaks indicating increments of clastic particles supplied to the lake owing to natural disasters including floods and earthquakes and the artificial construction around lake fukami the results of the correlation between the meteorological records in iida meteorological station and the total carbon flux change based on the varve chronology indicates that the total carbon flux shows an inverse relationship to february mean temperature and precipitation february mean temperature controlled the vertical mixing of lake water column that affects the productivity of phytoplankton in the epilimnion or decomposition of organic matter in the hypolimnion february precipitation probably has affected the activity of denitrifying bacteria in the stagnation period pyrite and siderite minerals are recognized in the core by observation of thin sections and x ray powder diffraction analysis the pyrite was deposited in summer and the siderite was deposited in summer and winter these iron minerals indicate the decomposition processes of organic matters in the water column in each season

tracing bottom water oxygenation with sedimentary mn fe ratios in lake zurich switzerland abstract redox dynamics of manganese mn were studied in the sediment of lake zurich using precise sediment core age models monthly long term oxygen o 2 monitoring data of the water column 1936 2010 and high resolution xrf core scanning the age models were based on bi annual lamination and calcite precipitation cycles if present mn exhibits distinct maxima which coincide with the annual maximum deep water o 2 concentrations in spring according to the monitoring data in contrast the iron fe signal is mainly the result of calcite dilution as indicated by a strong negative correlation between fe and calcium ca xrf data the mn fe ratio in the core from the maximum lake depth zh10 15 137 m revealed a moderate correlation with o 2 measurements in the lake bottom water confirming the successful application of the mn fe ratio to semi quantitatively reconstruct bottom water oxygenation in the lake mostly low ratios were observed between 1895 and the mid 1960s as a result of eutrophication however geochemical focusing and sedimentological factors can reduce the applicability of the mn fe ratio in reconstructing o 2 concentrations in the bottom water of lakes

quantitative pollen based climate reconstruction in central japan application to surface and late quaternary spectra abstract climate reconstruction in japan by the best modern analogues method was tested with 285 surface pollen spectra and then applied to the 47 000 years pollen profile from lake mikata central japan both pollen taxa percentages and plant functional type affinity scores were used in the reconstruction of six climate variables the reconstructed values were compared with the estimated modern climate at each surface pollen site in order to evaluate the accuracy of the pollen based reconstruction the reconstruction of thermal parameters is very reliable correlation coefficient r between 0 86 and 0 89 the reconstruction of annual precipitation is less accurate r 0 7 we also proposed a new technique to calibrate reconstructed values into both probability distribution and or confidence regions of observed values the specialized programs for this calibration polcalib and polhist are available at qsr website http www elsevier nl locate quascirev the reconstruction of the late quaternary climate changes around lake mikata shows that the summer and winter temperatures were 5 c lower than present around 40 uncal kyr bp reached a minimum around 20 uncal kyr bp 10 c lower than present and became similar to present day at 8 uncal kyr bp the estimates for annual precipitation show that it was driest around 20 uncal kyr bp