applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

assessing δ13c and c n ratios from organic material in archived cores as holocene sea level and palaeoenvironmental indicators in the humber estuary uk organic 13c and c n analyses of estuarine deposits provide proxies for changes in the source of organic matter which can be driven by fluctuations in relative sea level river discharge and catchment disturbance here we present the results of a comprehensive vegetation and sediment 13c and c n survey of welwich marsh outer humber estuary uk together with high resolution 13c and c n analyses of holocene cores collected nine years previously from the humber estuary and the lincolnshire marshes eastern england uk the contemporary intertidal 13c and c n dataset shows a gradual increase in surface sediment 13c with decreasing marsh height and suggests that 13c is controlled by the degree of tidal inundation and thus reflects organic matter source however sediment c n ratios are less sensitive to tidal changes and the recent introduction of c4 salt marsh species complicates the contemporary analogue the holocene 13c and c n records are in general agreement with existing microfossil data and provide additional palaeoenvironmental information this includes support for an estuary wide expansion of marine conditions from c 3 3 ka cal yr bp followed by a contraction of marine conditions after c 2 7 ka cal yr bp and evidence for an increase in delivery of terrigenous organic matter to the inner estuary in the late holocene bulk organic 13c and c n analysis is shown to be a reliable and independent indicator of coastal environmental change and is therefore a complementary technique to the more commonly used microfossil approach however this study also shows that in some circumstances the technique may be compromised when applied to sediments from cores that have been stored for a period of time

bomb 14c time history recorded in two modern stalagmites importance for soil organic matter dynamics and bomb 14c distribution over continents carbon 14 activity measurements made by accelerator mass spectrometry on two modern stalagmites from the han sur lesse cave belgium and from the postojna cave slovenia permit the construction of 14c activity a14c time series over the last 50 years a high precision chronology is given by annual laminae in the first stalagmite and by a specific mark explosion in the postojna cave in 1944 in the second one in both stalagmites 14c activity increase due to nuclear tests in the atmosphere is remarkable however instead of a sharp peak like the one observed in the atmosphere around 1963 1964 the 14c activities of the stalagmite caco3 show an abrupt increase with an offset of 1 10 years followed by a high activity plateau for the han sur lesse sample and a slight decrease for the postojna sample for both stalagmites the variation of the a14c amplitude between pre and post bomb period is much lower than the atmospheric record which demonstrates the damping effect of the soil carbon reservoir we have modeled the caco3 activities using fractionation processes between atmosphere co2 soil co2 and organic matter om dissolved inorganic carbon and stalagmite caco3 in both cases studied the model and former soil studies suggest that co2 from soil organic matter som decomposition which has a slow turnover i e 1 y is of major importance in winter when the development of speleothem is the most important combined with the fact that 80 90 of the stalagmite carbon comes from soil co2 this produces a damping effect on the speleothem a14c consequently the geochemical time resolution at least for speleothem carbon is much lower than the structural resolution given by annual laminae alternations and is mainly controlled by soil carbon dynamics a14c and 13c are smoothed over several years differences between the 14c time series of the han sur lesse and postojna stalagmites are likely to be due to the double amount of precipitation in postojna which produces a faster soil om turnover and thus a system which is more sensitive to atmospheric changes

a modern isotope record of changes in water and carbon budgets in a groundwater fed lake blue lake south australia groundwater is often a major component of lake water and chemical balances alteration in catchment subsurface water balances through land use change and pumping can affect lake biogeochemical cycles through changes in groundwater flow rates we present a modern 200 yr sediment isotope record d 18 ocarb d 13 ccarb and d 13 corg o f changes to the water and carbon budget of blue lake which is situated in karstic limestone in south australia and is mostly fed by groundwater the 3 5 decrease in d 18 ocarb and d 13 ccarb deposited in lake sediments since 1850 reflects higher rates of groundwater through flow due to rainfall variability land use change and increased rates of pumping over the past 40 yr calculated water residence times based on the isotopic data were 23 6 2 yr before 1850 and decreased by the late twentieth century to 8 6 2 yr concomitant dissolved inorganic carbon dic residence times were 3 8 and 2 2 yr respectively although burial rates of caco3 have increased by about threefold over the past 40 yr there is no evidence that substantial changes in organic carbon deposition has occurred the shorter dic residence time is largely due to increased input and higher co2 evasion rates about 88 of ccarb and 96 of corg generated within the water column is remineralized but the isotopic composition is essentially unaltered in the sediments the measured variations in d 13 ccarb and d 13 corg of sediments are thought to reflect changes to dic residence time and increased co2 aq concentrations rather than changes in lake productivity

increased aridity during the early holocene in west greenland inferred from stable isotopes in laminated lake sediments abstract palaeoclimatic inferences from the greenland ice cores suggest that holocene climate was relatively uniform the ice core records primarily reflect hemispheric temperature related climate processes whereas lakes tend to reflect regional scale climatic variability stable isotopes in closed basin lakes are sensitive to changes in effective precipitation here we report stable isotope evidence 18 o and 13 c records from authigenic calcite in laminated lake sediments from two oligosaline closed basin lakes in southern west greenland sondre stromfjord the stable isotope profiles indicate a dynamic early to mid holocene climate as a strongly negative precipitation evaporation balance from 7000 to 5600 cal yr bp lowered lake levels throughout the region this interpretation of the stable isotope data is supported by a survey of modern lake water isotopic composition and fossil shorelines around many closed basin saline lakes which indicate higher lake levels in the past the increased aridity during the early holocene resulted from a shift in regional circulation patterns in the davis straits baffin bay area enhanced stability of the west greenland depression and the situation of a regional trough over the sondre stromfjord area caused weakened westerly airflow and strengthened outflow i e winds blowing off the ice sheet resulting in reduced precipitation in the region decreased precipitation coupled with higher insolation probably caused the negative precipitation evaporation balance

multiproxy record for the last 4500 years from lake shkodra albania montenegro a multi proxy record is presented for approximately the last 4500 cal a bp from lake shkodra albania montenegro lithological analyses c n ratio and d 13 c of the organic and inorganic carbon component suggest that organic matter and bulk carbonate are predominantly authigenic the d 18 o record of bulk carbonate indicates the presence of two prominent wet periods one at ca 4300 cal a bp and one at ca 2500 2000 cal a bp the latter phase is also found in southern spain and central italy and represents a prominent event in the western and central mediterranean in the last 2000 years four relatively wet intervals occurred between ca 1800 and 1500 cal a bp 150 450 ad 1350 1250 600 700 ad 1100 800 850 1150 ad and at ca 90 cal a bp 1860 ad between ca 4100 and 2500 cal a bp d 18 o values are relatively high with three prominent peaks indicating drier conditions at ca 4100 4000 cal a bp ca 3500 and at ca 3300 cal a bp four additional drier events are identified at 1850 ca 100 ad 1400 ca 550 ad 1150 800 ad and ca 750 cal a bp 1200 ad the pollen record does not show changes in accordance with these episodes owing to the poor sensitivity of vegetation in this area which is dominated by an orographic rainfall effect and where changes in altitudinal vegetation belts do not affect the pollen rain in the lake catchment however since ca 900 cal a bp a significant decrease in the percentage arboreal pollen and in pollen concentrations suggest major deforestation produced by human activities copyright 2012 john wiley sons ltd

differences in the 14c age δ13c and δ18o of holocene tufa and speleothem in the dinaric karst we studied holocene speleothems and tufa samples collected in numerous caves and rivers in the dinaric karst of croatia slovenia bosnia and herzegovina as well as serbia and montenegro differences in the formation process of tufa and speleothems are discussed in the context of their isotopic composition 14 c 13 c and 18 o as well as the chemistry of surface water rivers lakes and drip water in caves the physical and chemical parameters monitored in the surface water tufa precipitation and drip water speleothem precipitation show that more stable conditions accompany speleothem rather than tufa formation this is particularly obvious in the water temperature variations 2 22 c in surface water and 7 12 c in drip water and in saturation index variation 3 11 in surface water and 1 6 in drip water the range of 14 c ages recorded by holocene speleothems v12 000 yr is wider by several thousands years than that of holocene tufa samples v6000 yr n 13 c values for tufa samples range from 312x to 36x and for speleothem samples from 312x to 3x reflecting higher soil carbon and or vegetation impact on the process of tufa than on speleothem formation the differences in n 18 o values of tufa and speleothem samples from different areas reflect different temperature conditions and differing isotopic composition in the water the study shows that speleothems from the dinaric karst can be used as global palaeoclimatic records whereas tufa records changes in the local palaeoenvironment 2003 elsevier science b v all rights reserved

a 120 year record of changes in nitrogen and carbon cycling in lake alexandrina south australia c n δ15n and δ13c in sediments variations in 15n and 13c and c n ratios of organic matter in sediment cores in lake alexandrina south australia show that there have been modifications of n and c sources due to land use changes water diversions and irrigation since european settlement of the surrounding basin in the middle 1800s 15norg and 13corg concentrations from three short sediment cores range from 1 8 to 3 9 and 26 7 to 21 1 respectively all cores showed a 2 increase in 15n over the top 100 mm with little variation below about 150 mm 13c values increased by about 3 from the base of the sediment cores to a maximum of 21 at 150 mm depth before decreasing by 5 to 27 over the top 100 mm c n mass ratios 11 suggest that organic matter preserved in the sediment is composed primarily of aquatic plant material with terrestrial plants contributing 10 excess 210pb and 137cs dating indicate a sediment accumulation rate of 3 1 mm a 1 suggesting the enrichment in 15n began in the 1950s and the 13c maxima corresponds to approximately 1940 the increase in 15n concentration over the past 30 50 a is attributed to the increasing agricultural expansion and development in the lower catchment particularly intensive grazing of cattle for dairying the authors suggest that there has been an increased flux of 15n enriched inorganic n derived from mineralized animal waste and sewage to the river and lake over the past 30 40 a which in turn is incorporated into the aquatic plants the variation in 13c reflects a change from terrestrial dominated input of inorganic c to increasingly marine dominated sources after water diversions commenced in the late 1800s once barrages were completed at the outlet of the lake in 1939 to prevent seawater intrusion the aquatic plants in the lake reverted to assimilation of dissolved inorganic c derived from oxidation of terrestrial organic matter

elemental c n ratios and isotopic δ15norg δ13corg compositions of sedimentary organic matter from a high altitude mountain lake meidsee 2661 m a s l switzerland implications for lateglacial and holocene alpine landscape evolution the deposition of late pleistocene and holocene sediments in the high altitude lake meidsee located at an altitude of 2661 m a s l in the southwestern alps strikingly coincided with global ice sheet and mountain glacier decay in the alpine forelands and the formation of perialpine lakes radiocarbon ages of bottom core sediments point out pre holocene ice retreat below 2700 m a s l at about 16 13 10 and 9 cal kyr bp the meidsee sedimentary record therefore provides information about the high altitude alpine landscape evolution since the late pleistocene holocene deglaciation in the swiss southwestern alps prior to 5 cal kyr bp the c n ratio and the isotopic composition of sedimentary organic matter 15norg 13corg indicate the deposition of algal derived organic matter with limited input of terrestrial organic matter the early holocene and the holocene climatic optimum between 7 0 and 5 5 cal kyr bp were characterized by low erosion decreasing magnetic susceptibility and high c

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

climate change vegetation development and lake level fluctuations in lake purwin ne poland during the last 8600 cal bp based on a high resolution plant macrofossil record and stable isotope data δ13c and δ18o abstract this paper presents a history of the vegetation in lake purwin ne poland and its catchment along with water level changes for the last 8600 cal bp the reconstructions are based on a high resolution plant macroremains analysis and the stable isotope record in authigenic carbonates a fine fraction that is precipitated within the epilimnion of the lake the stable isotope records suggest that the lake had throughflow during the holocene and that isotope data can therefore be used in palaeoclimatic reconstructions the 18o values record the thermal maximum of the holocene and the subsequent cooling of the upper holocene water level changes and the history of the lake s productivity are both recorded in the 13c values a chronology is established using radiocarbon dating of terrestrial plant macrofossils the vegetation and water levels in lake purwin reflect regional climate changes the combination of the lithology along the sedimentary sequence the results of the plant macroremains analysis and the isotope data allowed several alternating periods of high 8600 7300 6500 5200 4400 3500 and 3000 950 cal bp and low 7300 6500 5200 4400 3500 3000 and 950 to 59 cal bp water stands to be distinguished in lake purwin low water levels are indicated by sediments that are enriched in coarse plant detritus seeds of rubus ideaus fruits of uritca dioica and more macroremains of alnus glutinosa and rushes

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

climatic changes vs catastrophic events in lacustrine systems a geochemical approach abstract a geochemical study of oligotrophic lake sanabria nw iberian peninsula allows us to distinguish the geochemical response of a lacustrine system to catastrophic events and climatic events the main major elements analysed were k na mg ca ti al fe mn p and s the organic matter content in the sediment of lake sanabria is determined by the rainfall regime of the region periods when sediments were enriched in ti mg k and al are indicative of relatively wet paleoenvironmental conditions whereas intervals when sediments were enriched in s and p associated with organic matter are indicative of dry conditions a factor analysis of the geochemical data shows a progressive temporal displacements from organic rich conditions relatively high values of s and p to inorganic rich conditions relatively high values of ti mg k al and na maximal inorganic content occurred at the beginning of two discrete sedimentary levels the lol2 cal 1160 1230 yr ad and the lol1 cal 1510 1680 yr ad horizons the lol2 and lol1 horizons constitute two discrete events related to climatic changes during the beginning and end of the little ice age respectively in contrast the geochemical analysis provides evidence that the samples associated with the 1959 catastrophic event that occurred in the catchment area of lake sanabria do not follow the long term geochemical evolution paths of the climate driven system

variability of the 14c reservoir effects in lake tangra yumco central tibet china determined from recent sedimentation rates and dating of plant fossils abstract sediments from lakes provide one of the most important archives for past environmental changes on the tibetan plateau the recent sedimentation rate of modern lakes is widely used as an independent method to calibrate 14 c derived chronologies because 14 c values are often affected by a reservoir effect terrestrial plant residues in lake sediments are believed to be the ideal material for 14 c dating because they normally provide the true ages of the sediments in this study we present the spatial and temporal variations in modern sedimentation rates over the past 150 years and evaluate the reservoir effects of 14 c ages determined from bulk sediments and plant residues from lake tangra yumco on the central tibetan plateau the results show that ages determined from plant residues are systematically younger than those of the bulk sediments however the reservoir effects associated with the bulk sediments are much more constant than those of the plant residues highlighting the complicated composition of these macro remains and the fact that they might not be the best dating materials in tangra yumco especially in southern part a similar reservoir effect of 2200 years is observed in the southern and northern parts of tangra yumco based on the dating of modern surface sediments and aquatic plants this study demonstrates the complexity of the reservoir effect in a closed lake on the tibetan plateau and careful consideration must be paid to the use of different approaches to date different materials in order to establish a reliable chronology

intracontinental miocene reconstruction of hydrology and paleoclimate change in the forez basin france part ii sedimentary successions of palustrine deposits from the forez graben recorded changes in depositional and hydrological conditions throughout the middle to late miocene of france paleontological mineralogical and geochemical data combined with mass balance calculation allowed the identification of modern diagenetic and eogenetic stages of authigenic precipitation within the sedimentary pile stratigraphic log contains six clay and sand rich sequences some associated with freshwater ostracods delta c 13 delta o 18 values and sr isotopic ratios of whole rock samples and ostracods indicate that the montrond les bains upper sequence 8 to 175 mbs is a continental lake system that recorded continental weather condition 15 to 25 degrees c during the upper miocene time geochemical changes permit the estimation of variations of evaporation inflow changes e i 8 to 75 and delta o 18 rainfall 6 to 8 parts per thousand associated with two sequences delta o 18 and e i progressive changes were related to runoff to colder climate conditions large e i values in below 100 mbs are associated with the appearance of authigenic calcite and dolomite precipitation euhedral dolomite seems to be related to desiccation period that induced capillary pumping of water undersaturated with respect to calcite but saturated for dolomite the lower part of the middle miocene sedimentary series 175 to 300 mbs hosts continental deposits with scarce fossil a larger proportion of dolomite and massive pyrite levels related to mixed eogenetic and diagenetic precipitation scarce preserved eogenetic levels with unrealistic e i ratios suggest either delta o 18 values similar to the upper section but with temperature lower than 15 c or a similar temperature but very low delta o 18 rainfall calculated delta o 18 h2o values have to be as low as 15 parts per thousand delta o 18 h2o values are similar to present day melted snow this stable isotope suggests episodes of regional warming melting surrounding snow and able to mobilize as well as deposit thick sand levels eogenetic to diagenetic calcite dolomite and pyrite precipitation involves sand mg fluid influxes associated with methanogenic process eogenesis mixed with recrystallized pyrite and dolomite with diagenetic fluid circulation

when did the anthropocene begin a mid twentieth century boundary level is stratigraphically optimal abstract we evaluate the boundary of the anthropocene geological time interval as an epoch since it is useful to have a consistent temporal definition for this increasingly used unit whether the presently informal term is eventually formalized or not of the three main levels suggested an early anthropocene level some thousands of years ago the beginning of the industrial revolution at 1800 ce common era and the great acceleration of the mid twentieth century current evidence suggests that the last of these has the most pronounced and globally synchronous signal a boundary at this time need not have a global boundary stratotype section and point gssp or golden spike but can be defined by a global standard stratigraphic age gssa i e a point in time of the human calendar we propose an appropriate boundary level here to be the time of the world s first nuclear bomb explosion on july 16th 1945 at alamogordo new mexico additional bombs were detonated at the average rate of one every 9 6 days until 1988 with attendant worldwide fallout easily identifiable in the chemostratigraphic record hence anthropocene deposits would be those that may include the globally distributed primary artificial radionuclide signal while also being recognized using a wide range of other stratigraphic criteria this suggestion for the holocene anthropocene boundary may ultimately be superseded as the anthropocene is only in its early phases but it should remain practical and effective for use by at least the current generation of scientists

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

authigenic calcium carbonate flux in groundwater controlled lakes implications for lacustrine paleoclimate records groundwater dominated lakes are an important feature of many landscapes their sediments are a particularly valuable source of paleoenvironmental information in semiarid regions where perennial lakes may otherwise be scarce where groundwater and lake composition are favorable carbonate mineral precipitation evaporative concentration of lake water and microbial processes can combine to strongly deplete dissolved ca relative to influent groundwaters the authigenic carbonate flux acf can then become limited by water column cation availability and thereby be coupled to groundwater inflow rates and aquifer recharge here we analyze sedimentary records from two marl producing groundwater controlled lakes and demonstrate a link between one dimensional acf and the palmer drought severity index pdsi a measure of land surface wetness in a restricted outflow lake with high carbonate alkalinity acf is enhanced during historically wet climatic periods in response to increased aquifer recharge rates acf in this lake declines during droughts a neighboring dilute lake with a high rate of groundwater outflow shows comparatively weak coupling between acf and pdsi history ionic chemistry carbonate mineral equilibria and 13 c patterns of dissolved inorganic carbon show that the sensitivity of the acf signal depends on the degree of evaporative evolution of lake water and the mineral saturation state of the water column under conditions of stratification and ice cover copyright 2005 elsevier ltd

a 700 year macrophyte productivity record inferred from isotopes of macrophyte remains and bulk carbonates in lake koucha northeast qinghai tibetan plateau abstract the isotopic composition of total organic carbon toc in lakes has been widely used to interpret paleoclimatic changes and the depositional environments of lake sediments however the main factors that affect the carbon isotopes of toc may vary in different lake sediment records limiting the ability of organic carbon isotopes to explain biogeochemical and environmental changes especially in lakes with a large number of aquatic plants in this study the 13c values of macrophyte remains and bulk carbonate in a sedimentary core from lake koucha were investigated to evaluate their paleoenvironmental implications we found that the bulk carbonate was dominated by authigenic carbonates formed in the lake and that their 18o and 13c values can be used to reconstruct environmental changes in the lake koucha area the macrophyte productivity derived from the carbon isotopic offset between the macrophyte remains and the bulk carbonate eremains bc in the lake koucha area agree well with total solar irradiance tsi records inferred from 10be and temperature records based on tree rings from the qinghai tibetan plateau although the distribution of macrophytes is related to water depth according past studies and our observations in the field our findings suggest that changes in macrophyte productivity may be primarily driven by temperature changes in the lake koucha area

mid holocene climate change in lake bosumtwi ghana lake bosumtwi is one of the most widely studied palaeoclimate archives in west africa results from numerous ams 14c dates of samples from four piston cores from lake bosumtwi show that an abrupt sedimentary transition from a mid holocene sapropel to calcareous laminated muds occurred at about 3200 cal yr b p high resolution analyses of the nitrogen isotopic composition of organic matter across this transition confirm its abrupt nature and suggest that the change may signal a step toward increased aridity and intensified surface winds that affected western equatorial africa from ghana to the congo basin northern and eastern africa experienced a similar abrupt shift toward aridity during the late holocene but at about 5000 cal yr b p a difference in timing that illustrates the regional nature of climate changes during the holocene and the importance of feedback mechanisms in regulating holocene climate variability furthermore an abrupt change at about 3000 cal yr b p occurs at several sites adjacent to the tropical and subtropical atlantic which may hint at major changes in the surface temperatures of the tropical atlantic and or pacific at this time

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

c and o stable isotope variability in recent freshwater carbonates river krka croatia three types of recent carbonate precipitates from the river krka croatia were analysed 1 bulk tufa from four main cascades in a 34 km long section of the river flow through the krka national park 2 a laminar stromatolite like incrustation formed in the tunnel of a hydroelectric power plant close to the lowest cascade and 3 recent precipitates collected on artificial substrates during winter spring and summer periods stable isotope compositions of carbon d 13 c and oxygen d 18 o in the carbonate and organic carbon d 13 corg were determined and compared with d 18 o of water and d 13 c of dissolved inorganic carbon dic the source of dic which provides c for tufa precipitation was determined from the slope of the line dic dic0 1 vs d 13 c dic dic dic0 sayles curry 1988 the d 13 c value of added dic was 13ae6 corresponding to the dissolution of co2 with d 13 c between 19ae5 and 23ae0 vienna pee dee belemnite vpdb the observed difference between the measured and calculated equilibrium temperature of precipitation of bulk tufa barriers indicates that the higher the water temperature the larger the error in the estimated temperature of precipitation this implies that the climatic signals may be valid only in tufas precipitated at lower and relatively stable temperatures the laminar crust comprising a continuous record of the last 40 years of precipitation shows a consistent trend of increasing d 13 c and decreasing d 18 o the lack of covariation between d 13 c and d 18 o indicates that precipitation of calcite was not kinetically controlled for either of the elements d 13 c and d 18 o of precipitates collected on different artificial substrates show that surface characteristics both of substrates and colonizing biota play an important role in c and o isotope fractionation during carbonate precipitation

carbon transfer dynamics from bomb 14c and δ13c time series of a laminated stalagmite from sw france modelling and comparison with other stalagmite records twenty two ams 14c measurements have been made on a modern stalagmite from sw france in order to reconstruct the 14c activity history of the calcite deposit annual growth laminae provides a chronology up to 1919 a d results show that the stalagmite 14c activity time series is sensitive to modern atmosphere 14c activity changes such as those produced by the nuclear weapon tests the comparison between the two 14c time series shows that the stalagmite time series is damped its amplitude variation between pre bomb and post bomb values is 75 less and the time delay between the two time series peaks is 16 years 3 a model is developed using atmosphere 14c and 13c data fractionation processes and three soil organic matter components whose mean turnover rates are different the linear correlation coefficient between modeled and measured activities is 0 99 these results combined with two other stalagmite 14c time series already published and compared with local vegetation and climate demonstrate that most of the carbon transfer dynamics are controlled in the soil by soil organic matter degradation rates where vegetation produces debris whose degradation is slow the fraction of old carbon injected in the system increases the observed 14c time series is much more damped and lag time longer than that observed under grassland sites the same mixing model applied on the 13c shows a good agreement r2 0 78 between modeled and measured stalagmite 13c and demonstrates that the suess effect due to fossil fuel combustion in the atmosphere is recorded in the stalagmite but with a damped effect due to som degradation rate the different sources of dead carbon in the seepage water are calculated and discussed

archaeology a major tool in the reconstruction of the coastal evolution of westergo northern netherlands abstract westergo is the name of the coastal area in the northern netherlands between the former tidal systems of marne and middelzee the area silted up and changed into a salt marsh area during the subatlantic 1000 bc 500 ad the history of seaward migration of the salt marshes in the area has been reconstructed with the help of the archaeologically dated settlements on dwelling mounds terps terps were constructed on the salt marshes when the process of silting had reached the stage of the middle marsh this zone is flooded less frequently than ca 50 days per year the construction of terps during the middle stage of marsh development is indicated by the thickness of the salt marsh deposits on which terps were built and by the diatoms found in these marsh deposits the oldest phase of terp settlement on the marshes of westergo is dated between the late bronze age and early iron age ca 600 bc and is found in the southern part of westergo the old land during the next period 500 bc 500 ad the funnel shaped tidal basin in the northern part silted up to the supratidal level the middle marsh zone in the funnel shaped basin expanded during this period 1000 years by ca 5 km at the western and eastern sides of the basin and by ca 10 km in the central part this implies a mean marsh extension in this former tidal basin of ca 5 10 m per year in this paper a reappraisal of the nature and genesis of the salt marsh ridges of the northern netherlands is presented

production sedimentation and isotopic composition of organic matter in lake ontario organic matter and its carbon and nitrogen isotopic composition were measured in sequential sediment trap and core samples from the rochester basin of lake ontario to evaluate their usefulness in reconstructing historic changes in lake productivity the greatest flux of organic matter from the epilimnion occurred during late summer and coincided with whiting events indicating that calcite precipitation is an effective mechanism for sedimenting organic matter carbon isotopes of organic matter were low prior to the onset of stratification increased to maximum values in late summer and then decreased following fall overturn this pattern is controlled mainly by the timing of stratification and primary productivity which preferentially removes 12co2 from the epilimnion the physiological effect of decreased carbon isotopic fractionation with decreasing supplies of co2 aq may have also contributed to increased 13corgc nitrogen isotopes showed a seasonal pattern opposite to that of carbon whereby 15n values were low during the summer stratified period and high for the remainder of the year seasonal variability in 15norgn probably reflects changes in the source of sedimented organic particles which is dominated by isotopically depleted phytodetritus during the stratified period and isotopically enriched organic matter from heterotrophic or detrital sources during the mixed period a comparison of organic carbon accumulation rates and 13corgc between sediment cores collected in 1987 and 1993 1994 confirms earlier predictions that diagenetic processes reduce the mass accumulation of organic carbon in the zone of oxic pore waters but will not change the 13corgc values all cores analyzed for 13corgc display the reproducible pattern of a progressive increase in the 19oos peaking in the early to mid 1970s and then decreasing to the present this pattern matches the historical trends of phosphorus loading to the basin suggesting that 13c of organic carbon is a reliable proxy for paleoproductivity and responds to spring phosphorus supplies in the water column the 15n of sedimentary organic matter increased linearly from 1840 to 1960 at a rate of 0 3ppt per decade and remained relatively constant thereafter except for an increase in the upper few centimeters of sediment the increase in 15norgn reflects a combination of factors including early forest clearance by europeans increased sewering by municipalities after 1940 and increased nitrate utilization as productivity increased in the lower great lakes increased rates of denitrification in the central basin of upstream lake erie from the 1930s to the early 1970s may have also contributed to the rise in 15norgn values

decadal diagenetic effects on δ13c and δ15n studied in varved lake sediment to assess the long term 27 yr effects of sediment aging on stable carbon and nitrogen isotope values 13c and 15n we used a collection of eight freeze cores of annually laminated varved lak

fracture energies at the rupture nucleation points of large strike slip earthquakes on the xianshuihe fault southwestern china abstract earthquake cycles along a pure strike slip fault were numerically simulated using a rate and state dependent friction law to obtain the fracture energies at the rupture nucleation points in the model deep aseismic slip is imposed on the fault which generates recurrent earthquakes in the shallower velocity weakening friction region the fracture energy at the rupture nucleation point for each simulated earthquake was calculated using the relation between shear stress and slip which indicates slip weakening behavior the simulation results show that the relation between the fracture energy at the nucleation point and other source parameters is consistent with a theoretical approach based on fracture mechanics in that an earthquake occurs when the energy release rate at the tip of the aseismic slip zone first exceeds the fracture energy because the energy release rate is proportional to the square of the amount of deep aseismic slip during the interseismic period which can be estimated from the recurrence interval of earthquakes and the deep aseismic slip rate the fracture energies for strike slip earthquakes can be calculated using this result we estimated the fracture energies at the nucleation points of large earthquakes on selected segments of the xianshuihe fault southwestern china we find that the estimated fracture energies at the rupture nucleation points are generally smaller than the values of average fracture energy for developed ruptures as estimated in previous studies suggesting that the fracture energy tends to increase with the rupture propagation distance

carbon cycling at the sediment water interface in a eutrophic mountain lake jezero na planini pri jezeru slovenia abstract the biogeochemical processes that dominantly influence carbon cycling at the sediment water interface in a eutrophic mountain lake jezero na planini pri jezeru slovenia were studied for 2 years using measurements of the stable isotopic composition of carbon as well as chemical analyses of the pore waters and sediment according to the isotopic mass balance the major contribution of the most important aquatic carbonate species dissolved inorganic carbon dic is derived from methanogenesis 67 92 and much less from decomposition of sedimentary organic carbon with other electron acceptors 8 23 the contribution of calcite dissolution was observed only in 1999 when it varied throughout the year from 3 16 and did not influence dic production appreciably the lake sediment is an important sink of organic carbon that accumulates at the bottom of the lake

mineralogical organic and isotopic composition as palaeoenvironmental records in the lake sediments of two lakes the plitvice lakes croatia abstract six sediment cores the top 30 40 cm from two lakes of different sizes lake prosce and lake kalu erovac situated in the karst region of the plitvice lakes system croatia were studied by mineralogical and structural c n and total organic carbon toc and isotopic analyses a14c and 13c of carbonate and organic fractions the study of the two karst lakes where sediment composition is mainly calcite showed that organic matter om also plays an important role and that both fractions analysed simultaneously give a good overview of the processes in the lakes the morphological and structural properties of the calcite particles at micron and submicron levels indicate that the calcite mineral phase is formed by active authigenic precipitation in the studied lake systems in the small lake kalu erovac the measured distributions of carbonate and om fractions c n toc and a14c and 13c values of both fractions along the sediment depth showed similar values for all three cores with small variations in each core indicating very homogenous precipitation of autochthonous calcite inside the lake without allochthonous fraction in the bigger lake prosce the large difference in sediment composition of the three cores indicated different conditions of sediment precipitation inside the lake significant fractions of land derived carbonate and om were recognized by mineralogical c n a14c and 13c values in the shallow coastal area indicating that the sediment was a mixture of allochthonous and autochthonous fractions in contrast the composition of the deep water sediment in the same lake indicated in situ calcite precipitation and aquatic om produced in the lake sedimentation rates of 0 7 cm yr and from 0 3 to 0 7 cm yr for lake prosce and lake kalu erovac respectively were determined based on the a14c of macrofossils extreme hydrological events in 1981 and 2010 were identified by disturbances in carbon isotopes distributions in sediment profiles no evidence of anthropogenic influence in either lake on the local level was found but the response to the global 14c contamination was observed by a14c peaks in both carbonate and organic fractions increased bioproductivity in the recent decades was observed in lake prosce which can be correlated with a slight increase in lake water temperature in the last three decades this process can be associated with enhanced eutrophication in lake prosce

inverse modelling of the 14c bomb pulse in stalagmites to constrain the dynamics of soil carbon cycling at selected european cave sites the decomposition of soil organic matter som is temperature dependent but its response to a future warmer climate remains equivocal enhanced rates of decomposition of som under increased global temperatures might cause higher co2 emissions to the atmosphere and could therefore constitute a strong positive feedback the magnitude of this feedback however remains poorly understood primarily because of the difficulty in quantifying the temperature sensitivity of stored recalcitrant carbon that comprises the bulk 90 of som in most soils in this study we investigated the effects of climatic conditions on soil carbon dynamics using the attenuation of the 14c bomb pulse as recorded in selected modern european speleothems these new data were combined with published results to further examine soil carbon dynamics and to explore the sensitivity of labile and recalcitrant organic matter decomposition to different climatic conditions temporal changes in 14c activity inferred from each speleothem was modelled using a three pool soil carbon inverse model applying a monte carlo method to constrain soil carbon turnover rates at each site speleothems from sites that are characterised by semi arid conditions sparse vegetation thin soil cover and high mean annual air temperatures maats exhibit weak attenuation of atmospheric 14c bomb peak a low damping effect d in the range 55 77 and low modelled mean respired carbon ages mrca indicating that decomposition is dominated by young recently fixed soil carbon by contrast humid and high maat sites that are characterised by a thick soil cover and dense well developed vegetation display the highest damping effect d c 90 and the highest mrca values in the range from 350 126 years to 571 128 years this suggests that carbon incorporated into these stalagmites originates predominantly from decomposition of old recalcitrant organic matter som turnover rates cannot be ascribed to a single climate variable e g maat but instead reflect a complex interplay of climate e g maat and moisture budget and vegetation development

a high resolution late glacial to holocene record of environmental change in the mediterranean from lake ohrid macedonia albania lake ohrid macedonia albania is the oldest extant lake in europe and exhibits an outstanding degree of endemic biodiversity here we provide new high resolution stable isotope and geochemical data from a 10 m core co1262 through the late glacial to holocene and discuss past climate and lake hydrology tic 13ccalcite 18ocalcite as well as the terrestrial and aquatic vegetation response to climate toc toc n 13corganic rock eval pyrolysis the data identifies 3 main zones 1 the late glacial holocene transition represented by low tic and toc contents 2 the early to mid holocene characterised by high toc and increasing toc n and 3 the late holocene present which shows a marked decrease in tic and toc in general an overall trend of increasing 18ocalcite from 9 ka to present suggests progressive aridification through the holocene consistent with previous records from lake ohrid and the wider mediterranean region several proxies show commensurate excursions that imply the impact of short term climate oscillations such as the 8 2 ka event and the little ice age this is the best dated and highest resolution archive of past late glacial and holocene climate from lake ohrid and confirms the overriding influence of the north atlantic in the north eastern mediterranean the data presented set the context for the international continental scientific drilling program scientific collaboration on past speciation conditions in lake ohrid project cores recovered in spring summer 2013 potentially dating back into the lower pleistocene and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history

limnological controls on stable isotope records of late holocene palaeoenvironment change in sw greenland a paired lake study stable isotope records are increasingly being used in palaeoenvironmental studies of arctic lakes here we compare stable isotope and elemental records 13c 15n c n with high resolution xrf derived geochemical and colour data from low arctic lakes ss1220 and ss85 in southwest greenland lake ss1220 sediments are laminated gyttja whereas ss85 consist of homogeneous gyttja both records cover the last c 5000 years 13c and carbon content suggest that organic matter in both lakes is predominantly autochthonous the c n variability ranging between 11 and 15 is interpreted to be a function of nitrogen deficiency which is further supported by 15n values at ss1220 falling close to atmospheric 15natmosphere although some changes in the geochemical stratigraphies presented here can be related to regional environmental change i e hydrology effective precipitation aeolian activity these effects are filtered through the lake catchments these changes alter the nutrient supply and hence lake productivity which appear to be the primary controls on the stable isotope data we suggest that information of past environmental change can only be gained from the stable isotope composition of lake sediments when there is a reasonable understanding of limnological processes and records may be lake specific