geochemistry of the holocene sediments of lake chenghai sw china and its implications for paleoenvironmental reconstruction abstract analysis of lake sediment geochemistry is valuable for understanding past hydroclimatic changes via the reconstruction of changes in catchment erosion chemical weathering redox processes and the intensity of evaporation in this study we analyzed the geochemical composition magnetic susceptibility and carbonate content of the holocene sediments of lake chenghai in the jinsha river valley southwest china our aims were to determine the influence of holocene hydroclimate evolution and geo hazards on lacustrine sedimentation the results show that the hydroclimate was generally humid during 7 57 4 65 cal ka bp and that subsequently it became relatively dry during 4 65 1 37 cal ka bp our results also reveal that the centennial scale variability of the lake level during the holocene is forced by changes in solar activity and oceanic atmospheric feedback in addition the interval of 3 31 1 95 cal ka bp was the driest due to highly variable and intense el nino events and the southward migration of the intertropical convergence zone furthermore three large landslide events occurred at 7 30 6 36 and 0 76 cal ka bp around lake chenghai which are correlated with unusually large floods during the period of weakened monsoon activity and or with earthquake events

weak monsoon event at 4 2 ka recorded in sediment from lake rara himalayas abstract the strength of the indian summer monsoon varied significantly on centennial to millennial timescales during the holocene among these variations a weak summer monsoon event occurred approximately at 4 ka the so called 4 2 ka event this event is considered to have been a relatively sustained and widespread phenomenon at regional scales across southern asia to eastern africa however little is known about the impact of such variations in the himalayas a key location for understanding the monsoon system here we present a record of changes in summer monsoon strength during the holocene from lake rara western nepal using redox sensitive elements mn ti and mn fe measured by x ray fluorescence xrf core scanner in addition organic matter properties toc 13c and c n and changes in the 14c age offset between bulk organic matter and leaf matter namely the old carbon offset are used to augment the environmental reconstruction collectively the data indicate a period of prolonged weak monsoon interval at around 4 ka the timing of onset and recovery from the event observed at lake rara exhibits particular similarity with changes in the indus river discharge this is the first record of the 4 2 ka event from the himalayas based on a relatively well constructed age model using 14c dates that are not influenced by reservoir effects these findings provide an important step towards better understanding the spatial and temporal variability in the holocene indian monsoon

timing of deglaciation and postglacial environmental dynamics in nw iberia the sanabria lake record abstract the multiproxy study sedimentology geochemistry and diatoms of sediment cores from sanabria lake 42 07 30 n 06 43 00 w 1000 m a s l together with a robust 14c chronology provides the first high resolution and continuous sedimentary record in the region extending back the last 26 ka the development of a proglacial lake before 26 cal ka bp demonstrates the onset of deglaciation before the global last glacial maximum similarly to other alpine glaciers in southern european mountains rapid deglaciation occurred at the beginning of the greenland interstadial gi 1e bolling 14 6 cal ka bp following a short lived episode of glacier re advance 14 4 14 2 cal ka bp gi 1d a climatic improvement at 13 9 cal ka bp suggests the glaciers retreated from the lake basin during the gi 1c another glacier reactivation phase occurred between ca 13 0 12 4 ka starting earlier than the onset of gs 1 younger dryas rapid deglaciation during the early holocene 11 7 10 1 cal ka bp was followed by a period of higher river discharge 10 1 8 2 cal ka bp after 8 2 ka the holocene is characterized by a general decreasing trend in humidity punctuated by the driest phase during the mid holocene ca 6 8 4 8 a wetter interval between 4 8 and 3 3 cal ka bp and a relatively decline of rainfall since then till present with a minor increase in humidity during some phases ca 1670 1760 of the little ice age discrete silt layers intercalated in the organic rich holocene deposits reflect large flooding events of the tera river ca 10 1 8 4 7 5 6 2 5 7 5 6 4 6 4 2 3 7 3 3 3 1 2 7 2 5 and 2 0 cal ka bp their synchronicity with a number of cold and humid events described in the atlantic demonstrates a strong control of nw iberian climate by north atlantic dynamics at centennial millennial scale comparison with western mediterranean records points to similar regional dynamics during the holocene although modulated in the nw iberian peninsula by the stronger atlantic influence

normalizing xrf scanner data a cautionary note on the interpretation of high resolution records from organic rich lakes x ray fluorescence xrf scanning of unlithified untreated sediment cores is becoming an increasingly common method used to obtain paleoproxy data from lake records xrf scanning is fast and delivers high resolution records of relative variations in the elemental composition of the sediment however lake sediments display extreme variations in their organic matter content which can vary from just a few percent to well over 50 as xrf scanners are largely insensitive to organic material in the sediment increasing levels of organic material effectively dilute those components that can be measured such as the lithogenic material the closed sum effect consequently in sediments with large variations in organic material the measured variations in an element will to a large extent mirror the changes in organic material it is therefore necessary to normalize the elements in the lithogenic component of the sediment against a conservative element to allow changes in the input of the elements to be addressed in this study we show that al which is the lightest element that can be measured using the itrax xrf scanner can be used to effectively normalize the elements of the lithogenic fraction of the sediment against variations in organic content we also show that care must be taken when choosing resolution and exposure time to ensure optimal output from the measurements

compound specific carbon and nitrogen isotopic compositions of chlorophyll a and its derivatives reveal the eutrophication history of lake zurich switzerland to reconstruct the impact of eutrophication on phototrophic communities and the biogeochemical cycling of carbon and nitrogen in the surface water we investigated the distributions and carbon and nitrogen isotopic compositions 13c and 15n values of chlorins in the sediments of lake zurich the chlorin distributions were dominated by chlorophyll a chl a and its derivatives which reflect rapid degradation to the pheopigments in the water column and sediments of the lake the 13c values of these sedimentary chlorins followed the historical trends of eutrophication and reoligotrophication except in the surface sediments which were characterised by higher relative contributions of aged redeposited organic matter om the 13c values of the sedimentary chlorins together with bulk sediment 13c values and c n ratios indicate that the phototrophic communities in the lake used a 13c depleted carbon source which is mainly of aquatic origin the 15n values of chlorins reflect the predominance of nitrate assimilating phototrophs especially the non n2 fixing cyanobacterium planktothrix rubescens prevalent during sediment deposition shifts in 15n values of chl a followed mostly the trends in eutrophication and reoligotrophication but were also affected by community assemblage shifts to diatoms and or other cyanobacteria at the end of the 19th century and during the eutrophication maximum in the 1970s the lower 15nchl a values in the surface sediments coincide with increasing nitrogen to phosphorus ratios and reduced water column mixing that characterise the recent reoligotrophication period and may explain the predominance of p rubescens in lake zurich in contrast the higher contributions of laterally transported om explains the large offset of 15n values of the pheopigments relative to chl a which is supported by the high radiocarbon age of the surface sediments

holocene lake level fluctuations and environmental changes at taro co southwestern tibet based on ostracod inferred water depth reconstruction lake level change is an important indicator of changes in the hydrological status of lakes triggered by the influence of atmospheric circulation systems previous studies show that the interaction

late pleistocene earthquake triggered moraine dam failure and outburst of lake zurich switzerland 1 lakes impounded by moraines may be considered hazardous in glaciated areas throughout the world because dams can fail suddenly producing destructive floods with peak discharges far in excess of normal flows here we present a comprehensive case study in the zurich switzerland area that reveals several independent lines of evidences for the occurrence of a late pleistocene 13 760 calibrated years b p moraine breach and subsequent lake zurich outburst discharge volume 2 5 km3 we use seismic and core data in order to track and date the geological fingerprint of this event data from areas downstream of the lake show coarse grained massive 25 m thick reworked morainic deposits behind four breached zones in lake zurich sedimentary structures recorded in a paleowater depth of 36 m indicate strong outburst induced currents hydrodynamic calculations reconstructing the sediment transport capacity explaining the observed bed forms allow estimating averaged outburst discharge to exceed minimum values of 2400 m3s 1 the potential maximal magnitude of the outburst is inferred from calculations considering critical flow conditions through the breaches revealing estimated peak discharge of 20 600 m3s 1 we also discuss long term causes and short term trigger mechanisms of the dam failure that occurred several thousand years after moraine formation and show that it coincides with a reconstructed strong northern alpine earthquake magnitude 6 5 our data thus suggest that catastrophic drainage of lake zurich was initiated as a consequence of the moraine dam failure that either was triggered by primary earthquake shaking or by secondary effects such as overtopping by landslide generated waves

a continuous record of vegetation fire regime and climatic changes in northwestern patagonia spanning the last 25 000 years abstract we present a high resolution precisely dated terrestrial paleovegetation paleoclimate record from lago pichilaguna northwestern patagonia 40 44 s which spans continuously from the last glacial maximum lgm to the present we find abundant and continuous presence of arboreal pollen chiefly nothofagus during the lgm accompanied by other trees shrubs and alpine herbs these results suggest subantarctic parkland and or scattered woodlands under a cold and hyperhumid climate during the lgm 25 000 17 800 cal yr bp with expansion of nothofagus under relatively warm interstadial conditions between 25 000 and 19 200 cal yr bp this was followed by cooling and a precipitation increase between 19 200 and 17 800 cal yr bp which was contemporaneous with the youngest lgm advance of andean glaciers in the region and maximum influence of the southern westerly wind sww the last glacial termination t1 started at 17 800 cal yr bp and featured the spread of thermophilous trees and ferns characteristic of north patagonian rainforests along with lake level lowering these results suggest a warm pulse and southward shift of the sww concurrent with a rapid collapse of andean glacier lobes subsequent changes led to the establishment of closed canopy rainforests under peak interstadial warmth between 16 000 and 15 000 cal yr bp we detect a shift to cold wet conditions during the antarctic cold reversal 14 800 12 700 cal yr bp and a precipitation decline during younger dryas time followed by maximum temperature relatively lower lake level and minimum sww influence between 11 300 and 7700 cal yr bp precipitation then rose punctuated by centennial scale variations since 6200 cal yr bp chilean european deforestation and spread of invasive exotic species started at 350 cal yr bp aided by fire we conclude that temperate rainforests have persisted with little interruption since t1 with major changes in floristic composition driven by climate change and fires rainforest composition and heterogeneity declined in response to chilean european disturbance during the 1600s and intensified since the 1800s these events constitute the fastest largest magnitude vegetation changes of the last 25 000 years

origin and dynamics of fe and mn sedimentary layers in lake baikal remobilization and accumulation of iron and manganese were measured by porewater and sediment core analyses at six contrasting sedimentary environments of lake baikal with bulk sedimentation rates varying between 0 8 and 0 02 mm year 1 the results allow for the distinction between two types of fe and mn diagenesis in areas of relatively high sedimentation and in regions of low sedimentation rates in the first case only small fe mn enrichments near the sediment water interface were observed in the central and southern basins at the high sediment flux area near the selenga delta and in maloe more strait massive sedimentary layers enriched in fe and mn were found within the upper 15 25 cm of the sediments exclusively in northern baikal and in the underwater academician ridge which are characterized by low sedimentation rates and deep sulfate penetration depths in the porewaters the mn content in the enriched layers ranged from 10 5 mol cm 2 at the sites near the selenga delta up to 10 2 mol cm 2 at academician ridge the accumulation times for the enriched fe mn layers calculated from the size of the fe and mn oxide pools and the diffusive fluxes into the enriched zones also varied by a factor of 1000 they ranged from a few years near the selenga delta to several thousand years for the sites at academician ridge and northern baikal these values were generally congruent with the sediment age of the accumulation zones calculated from sedimentation rates these findings have significant implications for paleolimnological studies iron and manganese dynamics at sites with high sedimentation rates is dominated by allochthonous input which is only partially dissolved close to the sediment surface in contrast the massive fe mn sedimentary layers at sites of slow sedimentation are of autochthonous origin slow dissolution and reprecipitation maintain their constant position with respect to the sediment surface and prevent burial as long as the sedimentation regime remains constant buried fe mn sedimentary layers widespread in lake baikal may therefore serve as general indicators for low sedimentation rates and as specific proxies for sudden changes in the sediment regime d 2004 elsevier b v all rights reserved

direct and indirect effects of holocene climate variations on catchment and lake processes of a treeline lake sw china sedimentary records of inorganic elements and pigments over the last 12 000 years are used to assess major changes in limnological conditions of tiancai lake a small treeline lake sw china in response to holocene climate variations algal communities shifted from the dominance of cyanobacteria and cryptophytes in the early holocene towards siliceous algae in the mid holocene and chlorophytes in the late holocene algae responded to a combination of climate mediated vegetation and soil development associated with allochthonous inputs of dissolved nutrients and organic matter and sediment infilling decreases in al pb cu and zn from the early holocene probably resulted from soil podsolization and the sequestration of these elements within soils changes in mn and fe were likely linked to redox condition in catchment soils and water column synchronous peaks in ti ba ca sr na k and mg median grain size and magnetic susceptibility coincided with the troughs in the chemical index of alteration indicating that episodic cold events enhanced upland bedrock erosion and transported unleached and coarse detritus into the lake these cold events broadly correlate with holocene ice rafting events in the north atlantic although the cold events altered the influx of minerogenic elements by regulating upland bedrock erosion climate mediated vegetation and soil development led to a muted impact on primary producers holocene algal community shifts were subtle reflecting the relative abundance of p derived from weathering and n derived from soils throughout the record with the most pronounced effects on the lake biota being benthic expansion which occurred in response to sediment infilling

the avaatech xrf core scanner technical description and applications to ne atlantic sediments abstract x ray fluorescence xrf core scanning provides rapid high resolution down to 1 mm records of chemical composition on split sediment cores the measurements are non destructive and require very limited sample preparation the new avaatech xrf core scanner operational since 2002 covers the atomic mass range from al to u instrument parameters especially tube voltage can be adjusted to provide optimum settings for selected elements or sets thereof owing to the nature of the surface of split sediment cores particularly effects resulting from sample inhomogeneity and surface roughness results are semiquantitative yet provide reliable records of the relative variability in elemental composition downcore selected case studies from diverse sedimentary settings in the ne atlantic ocean illustrate a range of applications of xrf logging data these include preliminary stratigraphic interpretations glacial interglacial cycles provenance studies of the terrigenous sediment fraction lithological characterization early diagenetic processes and distinction between carbonate phases aragonite v calcite

influence of the water content on x ray fluorescence core scanning measurements in soft marine sediments the x ray fluorescence xrf core scanner provides bulk sediment chemistry data measured nondestructively at the split core sediment surface although this method is widely accepted there is little known about the effects of physical properties such as density and water content on xrf core scanner data comparison of xrf scanner measurements from the sediment surface and dry powder samples of sediment core geob7920 indicates strongly reduced element intensities for the lighter elements al and si we relate the lower element intensities of the measurements taken at the sediment surface to the amount of water in the sample volume analyzed by the xrf core scanner the heavier elements k ca ti and fe remain relatively unaffected by the variation of any physical property within sediment core geob7920 additionally we successfully use the elemental intensity of cl as a proxy for the seawater content in the sample volume analyzed by the xrf core scanner this enables the establishment of a correction function for the elements al and si that corrects for the radiation absorption of the water content in sediment core geob7920 off cape blanc nw africa

calibration of xrf core scanners for quantitative geochemical logging of sediment cores theory and application abstract on line analysis of split sediment cores by xrf core scanners has become increasingly popular in the past decade because it allows nondestructive extraction of near continuous records of element intensities from sediment cores with a minimum of analytical effort a disadvantage of xrf core scanning relative to conventional geochemical analysis is the problematic conversion of core scanner output to element concentrations the main reason for this long standing problem is the poorly constrained measurement geometry attributable to inhomogeneity of the specimens e g variable water content and grain size distribution irregularities of the split core surface and in some setups spatial variations in thickness of an adhesive pore water film which forms directly below a protective foil covering the core surface we propose a log ratio calibration model for xrf core scanners derived from a combination of xrf spectrometry theory principles of compositional data analysis and empirical evidence the log ratio calibration model provides accurate and precise predictions of sediment composition element concentrations from xrf core scanner output with a limited number of parameters namely 2 d 1 where d equals the number of chemical elements whose concentrations are to be estimated the model can accommodate the inherent non linearity of the relation between relative intensities and concentrations which is apparent from the fact that it provides unbiased estimates an immediate corollary of our results is that log ratios of element intensities which are related to log ratios of element abundances by a simple linear transformation provide the most easily interpretable signals of relative changes in chemical composition consistent use of log ratios of element intensities or concentrations should minimise the risk of drawing erroneous conclusions from geochemical proxies the relative standard deviation precision of predicted element concentrations in core geob7920 is less than 2 stochastic simulations indicate that this level of precision can be attained with 40 randomly selected calibration specimens improved control over input errors and development of robust goodness of fit statistics allows xrf core scanning to be developed into a rigorous quantitative measurement technology the log ratio calibration equation derived in this study may be adapted to inter laboratory and inter instrument calibration as well

multiproxy analyses of lake allos reveal synchronicity and divergence in geosystem dynamics during the lateglacial holocene in the alps abstract palaeoenvironmental reconstructions of ecosystem responses to external forcing are generally limited by the difficulty of understanding the geosystem as a whole because of the complex interactions between ecological compartments therefore identifying which geosystem compartments or proxies co vary is a prerequisite in unravelling the propagation of disturbances e g climatic or anthropogenic from one compartment to another a multiproxy study of a continuous 13 500 year sedimentary profile cored in lake allos european alps 2200 m a s l was carried out on the basis of high resolution sedimentological geochemical and botanical analyses as well as determination of aquatic biotic proxies diatoms ostracods these multiproxy datasets are rare at these high altitudes major changes occurred in the course of the palaeoenvironmental history of this alpine watershed at 12 000 8600 7200 and 3000 cal bp during the holocene two main transitions were recorded in all the ecological compartments 8600 and 3000 cal bp but the period 4500 3000 cal bp stands out because of major changes that concerned only the lacustrine ecosystem the frequent switches in lake level might correspond to the 4 2 ka climatic event proximity of this alpine lake to climatically sensitive thresholds ice cover thermal stratification hydrological balance may have amplified climatic signals in the lake ecosystem this study illustrates the difficulties inherent to the use of common intra holocene stratigraphical limits given that ecological compartments are likely to have different responses to forcing factors depending on the characteristics of the watershed and its capacity to accommodate disturbances

holocene climate variability from the lake sediment core in schirmacher oasis region east antarctica multiproxy approach abstract a 1 62 m sediment core was retrieved from one of the landlocked freshwater lakes l 6 in the schirmacher oasis so east antarctica during the 24th indian antarctic expedition 2004 2006 the sediment core samples were analyzed for total organic carbon toc biogenic silica bsi grain size and elemental concentration ratios mg ca and mn fe the sediment core represents the time period of last 11 6 cal ka bp as ascertained by ams 14 c radiocarbon dates the sedimentation accumulation rate variation of 13 6 cm ka from 11 6 to 10 cal ka bp reveals a warm phase followed by a low sedimentation accumulation rate of 2 9 cm ka from 10 ka bp to 3 1 ka bp indicating a cold period in the region the sedimentation accumulation rate again increased from 3 1 cal ka bp to recent with a maximum of 88 cm ka which reveals the initiation of glacier retreat or ice free conditions in the study area the total organic carbon toc is

human climate interactions in the central mediterranean region during the last millennia the laminated record of lake butrint albania lake butrint 39 47 n 20 1 e is a ca 21 m deep coastal lagoon located in sw albania where finely laminated sediments have been continuously deposited during the last millennia the multi proxy analysis sedimentology high resolution elemental geochemistry and pollen of a 12 m long sediment core supported by seven ams radiocarbon dates and 137cs dating enable a precise reconstruction of the environmental change that occurred in the central mediterranean region during the last 4 5 cal kyrs bp sediments consist of triplets of authigenic carbonates organic matter and clayey laminae fluctuations in the thickness and or presence of these different types of seasonal laminae indicate variations in water salinity organic productivity and runoff in the lake s catchment as a result of the complex interplay of tectonics anthropogenic forcing and climate variability the progradation of the pavllo river delta favoured by variable human activity from the nearby ancient city of butrint led to the progressive isolation of this hydrological system from the ionian sea the system evolved from an open bay to a restricted lagoon which is consistent with archaeological data an abrupt increase in mass wasting activity between 1515 and 1450 bc likely caused by nearby seismic activity led to the accumulation of 24 homogenites up to 17 cm thick they have been deposited during the onset of finely laminated sedimentation which indicates restricted anoxic bottom water conditions and higher salinity periods of maximum water salinity biological productivity and carbonate precipitation coincide with warmer intervals such as the early roman warm period rwp 500 bc 0 ad the medieval climate anomaly mca 800 1400 ad and recent times after 1800 ad conversely lower salinity and more oxic conditions with higher clastic input were recorded during 1400 500 bc the late roman and the early medieval periods 0 800 ad and during the little ice age 1400 1800 ad hydrological fluctuations recorded in butrint are in phase with most central and western mediterranean records and correlate with nao variability in contrast opposite hydrological patterns have been recorded in the eastern balkans and the levant during the last millennium emphasizing a complex spatial variability in the region phases of maximum settlement intensity in butrint roman late antique coincide with warmer and or stable climate periods 0 800 ad and mca respectively indicating a long term influence of climatic conditions on human activities the late holocene sedimentary record of lake butrint demonstrates the complex interplay of climate variability tectonics and human impact in the recent evolution of coastal mediterranean regions

vegetation climate and lake changes over the last 7000 years at the boreal treeline in north central siberia abstract palaeoecological investigations in the larch forest tundra ecotone in northern siberia have the potential to reveal holocene environmental variations which likely have consequences for global climate change because of the strong high latitude feedback mechanisms a sediment core collected from a small lake radius 100 m was used to reconstruct the development of the lake and its catchment as well as vegetation and summer temperatures over the last 7100 calibrated years a multi proxy approach was taken including pollen and sedimentological analyses our data indicate a gradual replacement of open larch forests by tundra with scattered single trees as found today in the vicinity of the lake an overall trend of cooling summer temperature from a 2 c warmer than present mid holocene summer temperatures until the establishment of modern conditions around 3000 years ago is reconstructed based on a regional pollen climate transfer function the inference of regional vegetation changes was compared to local changes in the lake s catchment an initial small water depression occurred from 7100 to 6500 cal years bp afterwards a small lake formed and deepened probably due to thermokarst processes although the general trends of local and regional environmental change match the lake catchment changes show higher variability furthermore changes in the lake catchment slightly precede those in the regional vegetation both proxies highlight that marked environmental changes occurred in the siberian forest tundra ecotone over the course of the holocene

early diagenetic influences on iron transformations in a freshwater lake sediment abstract iron transformations in a calcium carbonate rich fresh water sediment were studied by analyzing the relevant constituents of both interstitial water and solid matter analysis of interstitial water shows that the observed redox sequence no 3 nh 4 mno 2 mn ii feooh fe ii so 2 4 s ii is roughly in agreement with that predicted by the gibbs free energy for the corresponding reactions in contrast to marine sediments these redox transitions occur in the uppermost sediments i e at depths of 0 4 cm deeper in the sedimentary sequence the depth profile for dissolved iron exhibits a steady non linear increase up to 400 mol dm 3 in this anoxic zone according to thermodynamic predictions iron ii minerals such as iron sulfide siderite and vivianite should precipitate while fe iii oxides should be completely dissolved however microscopic analysis showed that fe iii oxides were present throughout the studied sediment furthermore scanning electron microscope energy dispersive spectroscopy analysis suggests the presence of iron sulfide could be verified but not that of siderite or vivianite these observations indicate kinetic control of iron transformations we have investigated the importance of kinetic control of iron distribution in anoxic sediments using a diagenetic model for dissolved iron ii a rough estimate of time scales for dissolution and precipitation rates was made by imposing limiting boundary conditions using the calculated rate constant we established that more than 1000 years would be required for the complete dissolution of fe iii oxides which is agreement with our observations and experimental data from the literature calculated precipitation rates of fe ii for a given mineral phase such as siderite yield a maximum value of 3 g feco3 g 1 dry sediment yr 1 such low rates would explain the absence of siderite and vivianite finally it can be inferred from the mn t fe t ratio in the sediments that this ratio depends on the redox conditions of the sediment water interface at the time of deposition thus this ratio can be used as paleo redox indicator in lacustrine sediments

global temperature calibration of the alkenone unsaturation index uk 37 in surface waters and comparison with surface sediments in this paper we compile the current surface seawater c37 alkenone unsaturation uk 37 measurements n 629 1 to 30 c temperature range to derive a global field based calibration of uk 37 with alkenone production temperature a single nonlinear global surface water calibration of uk 37 accurately predicts alkenone production temperatures over the diversity of modern day oceanic environments and alkenone synthesizing populations t 0 957 54 293 uk 37 52 894 uk 37 2 28 321 uk 37 3 r2 0 97 n 567 the mean standard error of estimation is 1 2 c with insignificant bias in estimated production temperature among the different ocean regions sampled an exception to these trends is regions characterized by strong lateral advection and extreme productivity and temperature gradients e g the brazil malvinas confluence in contrast to the surface water data the calibration of uk 37 in surface sediments with overlying annual mean sea surface temperature anno is best fit by a linear model anno 29 876 uk 37 1 334 r2 0 97 n 592 the standard error of estimation 1 1 c is similar to that of the surface water production calibration but a higher degree of bias is observed among the regional data sets the sediment calibration differs significantly from the surface water calibration uk 37 in surface sediments is consistently higher than that predicted from anno and the surface water production temperature calibration and the magnitude of the offset increases as the surface water anno decreases we apply the global production temperature calibration to the coretop uk 37 data to estimate the coretop alkenone integrated production temperature coretop ipt and compare this with the overlying annual mean sea surface temperature anno we use simple models to explore the possible causes of the deviation observed between the coretop temperature signal as estimated by uk 37 and anno our results indicate that the deviation can best be explained if seasonality in production and or thermocline production as well as differential degradation of 37 3 and 37 2 alkenones both affect the sedimentary alkenone signal

new insights into the formation and burial of fe mn accumulations in lake baikal sediments abstract lake baikal is the deepest and oldest lake on earth extraordinary features of the lake are manganese and iron enriched layers and crusts occurring at different depths within the sediment they can be broadly subdivided into an upper accumulation at the o 2 mn ii redox boundary and one or more layers buried within the reducing part of the sediment the processes leading to their formation and peculiar distribution within the sediment have remained subject of debate in particular whether the burial of vast amounts of mn and fe oxides results from a steady state process or if it is the consequence of singular events such as changes in sedimentation rate bottom water oxygen concentrations or the mass accumulation rate mar of organic carbon c org mn or fe we retrieved short cores from the south basin the north basin and academician ridge determined sedimentation rates contents of c org mn and fe and estimated pore water fluxes from concentration profiles of o 2 no 3 mn ii fe ii so 4 2 and ch 4 a consistent picture emerged from the data showing that the upper fe mn layer formed at the lower end of the oxygen penetration depth as a dynamic pattern moving upward with the growing sediment thereby reductive dissolution of mn iv occurred at the lower margin upward diffusing mn ii was oxidized with o 2 forming the upper boundary of the fe mn accumulation the buried fe mn layers were immobilized within the sediment and underwent slow reductive dissolution mainly driven by the anaerobic oxidation of ch 4 the process leading to the detachment of the active fe mn layer from the top redox interface is not unambiguously clear however we suggest a cyclic pattern where the burial of a fe mn layer is accompanied by the generation of a new enrichment at the o 2 mn ii redox boundary which is subsequently nourished by the slowly dissolving old layer

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

late jurassic biogeochemical microenvironments associated with microbialite coated unionids bivalvia asturias n spain abstract the vega formation upper jurassic asturias spain contains two kimmeridgian outcrops the abeu and huerres sections with bivalves coated with carbonate microbialites oncoids the bivalve shells in the abeu section were replaced early by calcite while those of the huerres section were dissolved and the moulds filled by late diagenetic cements for the abeu shells there was a loss of sr and a gain of mg fe and mn during the replacement process but much of the original organic matter was retained part of the s present can be linked to this organic matter and part to the sulphate that replaced the carbonate groups in the calcite the thin microbialites inside the shells of some of the huerres bivalves have allowed us to estimate the influence of the growth rate on the incorporation of trace elements in calcite with an approximately six times lower growth rate the internal microbialite incorporates less mg and s and more fe and mn than the external one while maintaining the sr content the trace element content mg s sr fe and mn of the huerres and abeu microbialites are similar these coatings may therefore have been formed in the same type of freshwater but in different microenvironments given the substantial sulphate content of the microbialites from both sections this freshwater probably came from hot springs however the high fe mn ratio of the abeu microbialites suggests a reducing environment during their formation indeed 18o and 13c data confirm that the abeu and huerres microbialites were formed in different microenvironments the positive covariance for 18o and 13c of the abeu microbialites and replaced shells r2 0 83 and the wide range of variation for 18o 2 80 together suggest that the microbialite crusts grew in isolated ponds where evaporation was dominant in the huerres microbialites the positive covariance for 18o and 13c r2 0 59 and the narrow range of variation for 18o 0 74 indicate that the huerres section was formed in a more open environmental system where degassing predominated over evaporation

morphological functions with parallel sets for the pore space of x ray ct images of soil columns during the last few decades new imaging techniques like x ray computed tomography have made available rich and detailed information of the spatial arrangement of soil constituents usually referred to as soil structure mathematical morphology provides a plethora of mathematical techniques to analyze and parameterize the geometry of soil structure they provide a guide to design the process from image analysis to the generation of synthetic models of soil structure in order to investigate key features of flow and transport phenomena in soil in this work we explore the ability of morphological functions built over minkowski functionals with parallel sets of the pore space to characterize and quantify pore space geometry of columns of intact soil these morphological functions seem to discriminate the effects on soil pore space geometry of contrasting management practices in a mediterranean vineyard and they provide the first step toward identifying the statistical significance of the observed differences