biogenic silica record of the lake baikal response to climatic forcing during the brunhes abstract this work presents a detailed orbitally tuned biogenic silica record of continental paleoclimate change during the brunhes chron the brunhes matuyama boundary lies within the warm isotopic stage 19 in baikal and the boundaries between eight lithological cycles correspond to terminations in the marine oxygen isotope record the high amplitude and resolution of climatically driven changes in biosi content in lake baikal sediments permits tuning of almost every precessional cycle during the brunhes and reveals the structure of interglacial stages for example the last three interglacial stages mis 5 7 and 9 clearly consist of five substages a b c d e corresponding to precessional insolation peaks abrupt and intense regional glaciations in siberia during substages 5d and 7d were driven by extreme insolation minima during substage 9d cooling was more gradual in response to more moderate forcing the impact of strong glaciation is also observed in the middle of stage 15 where full glacial conditions appear to have lasted for over 30 000 yr during substages 15d 15c and 15b marine oxygen isotopic stage 11 appears to be the warmest period during the brunhes in the lake baikal record with at least three substages a new hypothesis is presented regarding the response of the lake baikal biosi record to insolation forcing based on the mechanism controlling modern diatom blooms biogenic silica production is hypothesized to be dependent on changes in the heat balance of the lake and consequently on changes in the thermal structure of the water column this mechanism is also sensitive to short term sub milankovich cooling events such as the mid eemian cooling the montaigu event during substage 5c and a cooling which appears to be analogous to the montaigu event during substage 9c the continuity of the lake baikal paleoclimate record its sensitivity to orbital forcing and its high resolution make it an excellent candidate for a new paleoclimatic stratotype section for continental asia

hydrochemical characteristics and salinity of groundwater in the ejina basin northwestern china a hydrochemical investigation was conducted in the ejina basin to identify the hydrochemical characteristics and the salinity of groundwater the results indicate that groundwater in the area is brackish and are significantly zonation in salinity and water types from the recharge area to the discharge area the ionic ration plot and saturation index si calculation suggest that the silicate rock weathering and evaporation deposition are the dominant processes that determine the major ionic composition in the study area most of the stable isotope 18o and d compositions in the groundwater is a meteoric water feature indicating that the groundwater mainly sources from meteoric water and most groundwater undergoes a long history of evaporation based on radioactive isotope tritium 3h analysis the groundwater ages were approximately estimated in different aquifers the groundwater age ranges from less than 5 years between 5 years and 50 years and more than 50 years within 1 km of the river water influence zone the groundwater recharges from recent heihe river water and the groundwater age is about less than 5 years in shallow aquifer from 1 km to 10 km of the river water influence zone the groundwater sources from the mixture waters and the groundwater age is between 5 years and 50 years in shallow aquifer the groundwater age is more than 50 years in deep confined aquifer

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

major ion chemistry of groundwater in a river basin a study from india groundwater is the prime source in the area of varaha river basin andhra pradesh india groundwater samples collected during pre and post monsoon were analyzed for major ion chemistry to understand the operating mechanism of geochemical processes for variation of groundwater quality low ionic concentration is observed in the groundwater occurring at topographic highs and towards the river compared to the rest of the area this is caused by the influence of recharge water geochemistry of groundwater is observed to be mainly controlled by the rock weathering mineral dissolution leaching ion exchange and evaporation and is subsequently modified by the anthropogenic and marine activities contribution of residual soluble salts below the depth of 5 m from the ground surface is high while it is low beyond the depth of 5 m anthropogenic activities cause an accumulation of excess residual soluble salts in the former depth and the content of this soluble matter is reduced by the clay products beyond the latter depth seasonal ionic concentration of groundwater is greatly influenced by the recharge process with reference to topographical features lithological characteristics and anthropogenic activities groundwater quality is classified as mixed and non carbonate alkali groups due to a combined action of geogenic anthropogenic and marine sources respectively the groundwater quality is above the adequacy level for both drinking and irrigation and appropriate management measures are recommended for sustainable development

water level changes in lake baikal siberia tectonism versus climate relative changes in the level of lake baikal amounting to hundreds of meters in quaternary time are well documented data presented here show that tectonic displacements of the lake outlet or former shoreline features are entirely sufficient to explain these relative lake level changes in contrast the morphology and hydrology of the lake make its level hydrologically insensitive to climate change available evidence indicates that throughout the past several hundred thousand years lake baikal was a dilute through flowing lake controlled by the level of its outlet on the basis of geologic data alone climatic effects on lake level whatever their magnitude are difficult to separate from those caused by active rift tectonism however consideration of 1 the hydrologic budget of the lake and 2 the configuration of the outlet suggests that potential lake level fluctuations due solely to climate change were less than about 2 m

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

biological nitrate utilization in south siberian lakes baikal and hovsgol during the last glacial period the influence of climate change on primary productivity abstract stable nitrogen isotope ratios 15 n in sediment cores recovered from two siberian lakes baikal and hovsgol are determined in order to evaluate the biologically mediated nitrogen cycle from the last glacial period to the postglacial period the ranges of 15 n values from the two lakes are similar varying from 2 8 to 6 7 the high values of 15 n around 6 during the last glacial maximum lgm 26 5 19 cal ka bp indicate that a larger fraction of the available nitrate in both lakes was utilised by phytoplankton a cool and dry climate during the lgm may have limited the input of terrestrial nitrate resulting in the use of a large fraction of the nitrate and low productivity in both lakes the use of a smaller fraction of the nitrate by phytoplankton in both lakes after the lgm 19 12 cal ka bp is reflected in the lower 15 n values down to 3 0 the increase in summer insolation after the lgm caused increased vertical mixing of the lake water column which transported nitrate upwards from the deeper waters and into the photic zone the reduced rate of nitrogen consumption after the lgm indicates that nitrate was more readily available to phytoplankton at this time and did not limit their activities this change suggests that other factors limited phytoplankton activity during this period at the climatic transition between oxygen isotope stages 2 and 1 around 11 5 cal ka bp the rapid increase in 15 n from 3 0 to 6 0 reflected a rapid increase in nitrate utilization at this transition increases in precipitation and lake levels which were associated with the increased intensity of the east asian monsoon may have brought a large influx of nutrients required by the phytoplankton into the lakes from the watershed this hydrological change led to increased phytoplankton activity in both lakes resulting in increased nitrate consumption the 15 n data obtained here from the sediments of lakes baikal and hovsgol suggest that the nitrogen cycle in the siberian region is strongly linked to hydrological changes across the asian continent which are related to global climate change

late quaternary lake level changes of lake el gygytgyn ne siberia abstract lake el gygytgyn is situated in a 3 6 ma old impact crater in northeastern siberia presented here is a reconstruction of the quaternary lake level history as derived from sediment cores from the southern lake shelf there a cliff like bench 10 m below the modern water level has been investigated deep water sediments on the shelf indicate high lake levels during a warm mid pleistocene period one period with low lake level prior to marine oxygen isotope stage mis 3 has been identified followed by a period of high lake level 10 m above present in the course of mis 2 the lake level dropped to 10 m at the end of mis 2 the bench was formed and coarse beach sedimentation occurred subsequently the lake level rose rapidly to the holocene level changes in water level are likely linked to climate variability during relatively temperate periods the lake becomes free of ice in summer strong wave actions transport sediment parallel to the coast and towards the outlet where the material tends to accumulate resulting in lake level rise during cold periods the perennial lake ice cover hampers any wave activity and pebble transport keeping the outlet open and causing the lake level to drop

uranium isotopes as proxies of the environmental history of the lake baikal watershed east siberia during the past 150 ka abstract a new experimental method for the determination of the isotopic composition of authigenic uranium in lake baikal siberia sediments has supplied a record of 234u 238u aut ratios during the past 150 ka with a resolution of ca 200 years reconstruction of the 234u 238u aut activity ratio as a proxy for lake water composition shows that the uranium isotope disequilibrium has not stayed constant throughout this period it varied greatly in response to regional climate the 234u 238u activity ratio in lake baikal paleowaters was inferred to be high during interglacial time 1 85 2 during mis 5 5 and the holocene 1 4 1 7 during mis 5 1 and 5 3 and dropped to 1 16 0 01 during glacial time the variability in the deduced 234u 238u ratios of lake baikal waters of the past may have been caused by the climatically modulated redistribution of contributions of riverine discharges from different provinces of the very large catchment of the lake aridity during ice ages was more pronounced in the south of eastern siberia and in northern mongolia relative to that in the northern regions of the lake baikal watershed the southern contribution of riverine input into the lake was essentially absent during glacial periods records of some elements ca k sr rb si al la th u th ciw from the bottom sediments of lake baikal during the last 0 5 myr with a resolution of 2 kyr have also been obtained coupling these data with records of weathering indices shows that not only riverine waters but also terrigenous material delivered into lake baikal from different regions of the very large watershed during interglacial and glacial times glacial erosion delivered fine siliciclastic material glacial milk mainly from the nearest mountain glaciers situated in the northwestern region of lake baikal while during warmer periods terrigenous material was sourced from the surrounding river valleys a conceptual model for the simulation of the fluvial discharge gradient between the northern and southern provinces of the lake baikal watershed is proposed and a first order simulation of past changes in the contribution of the selenga river to the lake water budget is given

oceanographic boundaries constrain microbial diversity gradients in the south pacific ocean marine microbes along with microeukaryotes are key regulators of oceanic biogeochemical pathways here we present a high resolution every 0 5 of latitude dataset describing microbial pro and eukaryotic richness in the surface and just below the thermocline along a 7 000 km transect from 66 s at the antarctic ice edge to the equator in the south pacific ocean the transect conducted in austral winter covered key oceanographic features including crossing of the polar front pf the subtropical front stf and the equatorial upwelling region our data indicate that temperature does not determine patterns of marine microbial richness complementing the global model data from ladau et al ladau j et al 2013 isme j 7 1669 1677 rather nh4 nanophytoplankton and primary productivity were the main drivers for archaeal and bacterial richness eukaryote richness was highest in the least productive ocean region the tropical oligotrophic province we also observed a unique diversity pattern in the south pacific ocean a regional increase in archaeal and bacterial diversity between 10 s and the equator rapoport s rule describes the tendency for the latitudinal ranges of species to increase with latitude our data showed that the mean latitudinal ranges of archaea and bacteria decreased with latitude we show that permanent oceanographic features such as the stf and the equatorial upwelling can have a significant influence on both alpha diversity and beta diversity of pro and eukaryotes

nitrate reduction in an unconfined sandy aquifer water chemistry reduction processes and geochemical modeling nitrate distribution and reduction processes were investigated in an unconfined sandy aquifer of quaternary age ground water chemistry was studied in a series of eight multilevel samplers along a flow line deriving water from both arable and forested land results show that plumes of nitrate contaminated groundwater emanate from the agricultural areas and spread through the aquifer the aquifer can be subdivided into an upper 10 to 15 m thick oxic zone that contains o2 and no3 and a lower anoxic zone characterized by fe2 rich waters the redox boundary is very sharp which suggests that reduction processes of o2 and no3 occur at rates that are fast compared to the rate of downward water transport nitrate contaminated groundwater contains total contents of dissolved ions that are two to four times higher than in groundwater derived from the forested area the persistence of the high content of total dissolved ions in the no3 free anoxic zone indicates the downward migration of contaminants and that active nitrate reduction is taking place nitrate is apparently reduced to n2 because both nitrite and ammonia are absent or found at very low concentrations possible electron donors in the reduced zone of the aquifer are organic matter present as reworked brown coal fragments from the underlying miocene and small amounts of pyrite at an average concentration of 3 6 mmol kg electron balances across the redoxcline based on concentrations of o2 no3 so42 and total inorganic carbon tic indicate that pyrite is by far the dominant electron donor even though organic matter is much more abundant groundwater transport and chemical reactions were modeled using the code phreeqm which combines a chemical equilibrium model with a one dimensional mixing cell transport model only the vertical component of the water transport was modeled since in contrast to rates along flow lines the vertical rates are close to constant as required by the one dimensional model average vertical transport rates of water in the saturated zone were obtained by tritium dating the modeling process is a two step procedure first the sediment column is initialized with natural water containing only oxygen as electron acceptor and subsequently agricultural waters containing both oxygen and nitrate are fed into the column the nitrate concentration of agricultural waters entering the saturated zone varies with time and an input function was therefore constructed by linear mixing of natural waters and agricultural waters this input function was fed into the column initialized with natural water and the model run forward in time to the year 1988 where field data are available comparison with field data shows that the variation in groundwater chemistry is well described by the model when reduction of oxygen and reduction of nitrate by pyrite oxidation are the only redox reactions occurring finally predictions are made for the distribution of water chemistry in the year 2003 downward progression of the redoxcline is accelerated by a factor of five due to nitrate pollution of the aquifer but absolute rates remain small of the order of a few centimeters per year the controlling factor for nitrate migration through the aquifer once it has reached the anoxic zone is the concentration and distribution of pyrite in the sediments

quaternary sedimentation and subsidence history of lake baikal siberia based on seismic stratigraphy and coring the long continuous high latitude stratigraphic record of lake baikal was deposited in three broad sedimentary environ ments defined by high resolution seismic reflection and coring meth ods 1 turbidite depositional systems by far the most widespread characterizing most of the margins and floors of the main basins of the lake 2 large deltas of major drainages and 3 tectonically or topographically isolated ridges and banks holocene sedimentation rates based on radiocarbon ages vary by more than an order of mag nitude among these environments from less than about 0 03 mm yr on ridges and banks to more than about 0 3 mm yr on basin floors ex trapolating these rates with a correction for compaction yields ten tative estimates of about 25 and 11 ma for the inception of rifting in the central and north basins respectively and less than 6 ma for the 200 m sediment depth on academician ridge the selenga delta has the distinctive form of a classic prograding gilbert type delta but its history appears to represent a complex com bination of tectonism and sedimentation the central part of the delta is underlain by prograding shallow water sequences now several hun dred meters below the lake surface these deposits and much of the delta slope are mantled by fine grained deep water hemipelagic de posits whose base is estimated to be about 650 000 years old modern coarse grained sediment bypasses the delta slope through fault con trolled canyons that feed large subaqueous fans at the ends of the south and central basins these relations along with abundant other evidence of recent faulting and the great depths of the central and south basins suggest that these two rift basins have experienced a period of unusually rapid subsidence over the last 650 000 years dur ing at least part of which sedimentation has failed to keep pace

hydrogeology and geochemistry of the ogallala aquifer southern high plains the ogallala aquifer which underlies the southern high plains consists of saturated sediments of the ogallala formation neogene that are deposited mainly as a set of humid type alluvial fans derived from the rocky mountains the ogallala aquifer the main source of water for the high plains of texas and new mexico has been severely depleted by extensive pumpage the hydrology and geochemistry of the aquifer are controlled by the surface topography of the underlying formations and by the thickness and permeability of the alluvial fan deposits axes of three major alluvial fans trend from northwest to southeast the fans have increased thickness and permeability compared with interfan areas flow lines follow the orientation of the alluvial fans along these major axes the saturated section is thick and the chemical composition is relatively constant ca hco3 to mixed cation hco3 water depleted in 18o d and tritium external effects on the chemical composition are less pronounced the aquifer is thinner and less permeable in areas between major fan axes and along the caprock escarpment in these areas groundwater can discharge from aquifers in the cretaceous triassic and permian formations into the ogallala formation cross formational movement of water and low permeabilities in the ogallala formation result in varying hydrochemical facies and in isotopic compositions that differ from those of the major depositional areas areas where upward cross formational flow occurs are evident by the presence of permeable contacts between the ogallala and the underlying formations water level head differences and chemical and isotopic similarities secondary factors that locally affect the chemical composition of ogallala formation groundwater include contamination from evaporating saline lakes agricultural chemicals and fertilizers and oil field brines impact of chemicals and brines may increase in the future because much of these contaminants may still be moving through the unsaturated zone toward the water table

ams radiocarbon analyses from lake baikal siberia challanges of dating sediments from a large oligotrophic lake abstract a suite of 146 new accelerator mass spectrometer ams radiocarbon ages provides the first reliable chronology for late quaternary sediments in lake baikal in this large highly oligotrophic lake biogenic and authigenic carbonate are absent and plant macrofossils are extremely rare total organic carbon is therefore the primary material available for dating several problems are associated with the toc ages one is the mixture of carbon sources in toc not all of which are syndepositional in age this problem manifests itself in apparent ages for the sediment surface that are greater than zero however because most of the organic carbon in lake baikal sediments is algal autochthonous in origin this effect is limited to about 1000 500 years which can be corrected at least for young deposits the other major problem with dating lake baikal sediments is the very low carbon contents of glacial age deposits which makes them extremely susceptible to contamination with modern carbon this problem can be minimized by careful sampling and handling procedures the ages show almost an order of magnitude difference in sediment accumulation rates among different sedimentary environments in lake baikal from about 0 04 mm year on isolated banks such as academician ridge to nearly 0 3 mm year in the turbidite depositional areas beneath the deep basin floors such as the central basin the new ams ages clearly indicate that the dramatic increase in diatom productivity in the lake as evidenced by increases in biogenic silica and organic carbon began about 13 ka in contrast to previous estimates of 7 ka for the age of this transition holocene net sedimentation rates may be less than equal to or greater than those in the late pleistocene depending on the site this variability reflects the balance between variable terrigenous sedimentation and increased biogenic sedimentation during interglaciations the ages reported here and the temporal and spatial variation in sedimentation rates that they imply provide opportunities for paleoenvironmental reconstructions at different time scales and resolutions

a high resolution diatom record of the palaeoclimates of east siberia for the last 2 5 my from lake baikal abstract two parallel drilling cores bdp96 1 200 m and bdp96 2 100 m have been taken from top of the underwater akademichesky ridge in lake baikal and dated by paleomagnetic techniques these cores are part of the baikal drilling project kuzmin et al 1997a b diatom analysis of the first 100 m of these sediments reveals that they store a 2 5 myr high resolution continuous record of the palaeoclimates of east siberia sediments belonging to warmer climates have a high content of diatom algae frustules whereas those belonging to global glaciations are diatom barren the record of upper pleistocene 500 kyr bp strongly correlates with the oceanic specmap curve and contains distinct 100 41 23 and 19 kyr periods as revealed by fourier analysis diversity of diatom species was small in pliocene abrupt and frequent changes of the climate in pleistocene resulted in frequent dramatic changes in the diatom communities the extant dominating endemics cyclotella minuta and aulacoseira baicalensis became important in lake baikal 760 kyr and less than 120 kyr bp respectively

internal structure and evolution of the late quaternary sequence in a shallow embayment the amvrakikos gulf nw greece abstract the late quaternary stratigraphic pattern of the amvrakikos gulf in the eastern mediterranean has been studied on the basis of the analysis of high resolution seismic profiles and short sediment cores lowstand transgressive and highstand systems tracts have been identified that are configured in a major depositional sequence of a fifth order sea level cycle during the last glaciation when the sea level was lowered by 55 m relative to its present position ca 50 ka bp the amvrakikos gulf was probably emerged giving rise to a subaerial erosion and fluvial incision in the western shallow part of the gulf and b development of a paleo lake in the eastern deepest domain until the early phase of the post glacial transgression ca 11 50 ka bp a paleo river characterized by a dense network of v shaped valleys was draining the western part of the gulf and flowing into the ionian sea in the isolated eastern part lowstand lacustrine deposits deltaic and prodeltaic units accumulated within the paleo lake at the latter stage of the last post glacial transgression ca 11 ka bp seawater entered the gulf and the transgressive systems tract was deposited consisting of incised channel fills beach shoreface deposits and delta prodelta wedges buried terraces have been identified also within this transgressive tract that reveal a step like sea level rise since ca 6 ka bp when the sea level reached its present day position a distal prodeltaic unit has been deposited and overlain by prograding deltaic wedges the spatial distribution of these wedges provides evidence of a continuous shifting of the river mouths during holocene the recent sedimentation patterns are related to the terrigenous inputs primarily from the arachthos river located in the northeastern part of the gulf and secondarily from the louros river located in the northwestern part

18o studies on recharge of phreatic aquifers and groundwater flow paths of mixing in the delhi area widespread decline in the groundwater level and growth of salinization are the critical factors controlling future groundwater quality and availability in the delhi area s180 and salinity data have been integrated for studying recharge conditions of phreatic aquifers and tracing the flowpaths of groundwater mixing wide range 2 8 0 to 8 6 and spatial inhomogeneity of 6180 in groundwater indicate that the aquifer is characterized by a slow process of natural mixing of groundwater in its lateral extent there is infiltration of river water to the groundwater in addition to the recharge from rainfall groundwater recharge in the area also occurs through stagnant water pools in low elevation areas where water surface run off collects chloride concentration in groundwater has a wide range from 15 ppm to 5070 ppm with a log normal frequency distribution indicating that the salt deposits in the area are not homogeneously distributed the s180 c1 relationship clearly suggests mixing of multiple sources of high salinity groundwater with low salinity groundwater or river water along specific pathways the data also indicates leaching of salts present in the soil during vertical recharge from rainfall and irrigation large lateral variation in chloride concentration indicates changes in evapotranspiration rate during recharge detailed investigations on identifying the potential recharging zones flow paths of mixing and recharge conditions will be useful to protect the groundwater resources from depletion and salinization

glaciers and meltwater flux to lake baikal during the last glacial maximum abstract maximal 3d ice extent during mis 2 around lake baikal has been reconstructed using glacial landforms in the field aerial photos satellite images and gis analysis this regional glacial maximum is correlated 18 kyr bp with the global lgm based on available 14 c dates cosmogenic 10 be exposure ages correlation of lakeshore moraines with two raised shorelines and the ird record in lake sediments total ice area was 13 000 km 2 and ice volume 2000 km 3 1800 km 3 in water equivalent ice distribution was controlled by topography and ice fields with valley glaciers spreading to adjacent depressions locally ice caps with outlet glaciers existed averaged regional ela is estimated to be 1290 240 m with the ela depression at approximately 1340 m more acceptable regional scenario of the lgm precipitation reduction by 25 50 implies that summer temperature decreased by 6 12 c along with an increased solid fraction in precipitation up to 85 there were primary climatic controls for glaciation meltwater supply as a strong controller of lgm water budget 60 of total water input to the lake is estimated to have been from 6 4 to 9 0 km 3 yr 1 7 9 times less than present day river input preliminary balance estimation shows that during full glacial stage lake baikal was overflowing with the angara river output as 4 9 km 3 yr 1 and with lake level close to that today lake level drop down to the depth of 40 m is recorded by geological and geophysical evidence perhaps explaining the abrupt increase in effective evaporation in the lake watershed at the start of mis 2 24 18 ky bp

reconstruction of late quaternary sea and lake level changes in a tectonically active marginal basin using seismic stratigraphy the gulf of cariaco ne venezuela abstract the gulf of cariaco is a marginal basin located between the cariaco basin and the paria gulf offshore ne venezuela along a system of active right lateral strike slip faults it is connected to the caribbean sea via a shallow 58 m deep sill implying that the gulf was disconnected from the global ocean during eustatic lowstands a dense grid of high resolution reflection seismic profiles has been used to determine the overall tectonic structure of the gulf and to establish the seismic stratigraphy of its sedimentary infill six unconformity bounded seismic stratigraphic units were identified in the upper 200 m of the sedimentary infill detailed seismic stratigraphic and seismic facies analysis allowed defining a series of sedimentary features that can be used as indicators of past sea or lake level in the gulf of cariaco i delta offlap breaks ii evaporites and iii erosional unconformities using accurate measurements of these various indicators at several locations in the gulf and a simple total subsidence model a relative sea lake level history encompassing the last 130 kyr could be reconstructed in periods of connection with the open ocean reconstructed relative sea level correlates well with eustatic sea level in times of disconnection distinct lake level fluctuations occurred which sometimes resulted in total dessication of the gulf lake level fluctuations appear to correlate with major heinrich events stadials and interstadials mis 4 the lgm and the younger dryas were thus identified in the gulf of cariaco sedimentary record the last reconnection to the caribbean sea occurred during mwp1b around 11 5 kyr the very good fit of the cariaco sea lake level curve with the eustatic sea level curves both in terms of amplitude and of timing underscores potential for future paleoclimate research of the sedimentary record contained in this marginal basin despite its active tectonic setting

the ocean as a net heterotrophic system implications from the carbon biogeochemical cycle the global ocean apparently consumes more organic carbon than it produces the excess heterotrophy probably occurs in the nearshore zone this nearshore heterotrophy has significant implications with respect to processes such as organic matter transport from the nearshore zone to the adjacent open ocean nutrient limitation of primary production and the role of the coastal zone as a short term sink for anthropogenic co2

the impact of freshwater and wastewater irrigation on the chemistry of shallow groundwater a case study from the israeli coastal aquifer differences in the impact of irrigation with freshwater versus wastewater on the underlying shallow groundwater quality were investigated in the coastal aquifer of israel seven research boreholes were drilled to the top most 3 5 m of the saturated zone the water table region wtr in the agricultural fields the unsaturated zone and the wtr below the irrigated fields consist mainly of clayey sands while the main aquifer comprises mainly of calcareous sandstones and sands we show that the salinity and composition of the groundwater at the wtr are highly variable over a distance of less than 1 km and are controlled by the irrigating water and the processes in the overlying unsaturated zone tritium data in this groundwater 4 6 tritium units tu support that these water are modern recharge the water at the wtr is more saline and has a different chemical composition relative to the overlying irrigation water high sar values sodium adsorption ratio in wastewater irrigation lead to absorption of na c onto the clay and release of ca 2c into the recharging water resulting in low na cl 0 4 compared to 1 2 in the wastewater and high ca cl ratios in contrast in the freshwater irrigated field the irrigation water pumped from the aquifer na clz0 9 sarz0 6 is modified into na rich groundwater na clz2 0 due to reverse base exchange reactions the high no3 concentration 100 mg l in the wtr below both fields is derived from the agricultural activities in the freshwater field the source of no3 is fertilizer leachates whereas in the wastewater field where less fertilizers are applied nitrate is probably derived from nitrification of the nh4 in the wastewater some of the original inorganic nitrogen in the wastewater is consumed by the agricultural plants resulting in a lower inorganic n cl ratio in the wtr as compared to that in the wastewater this study demonstrates the important role of the composition of irrigation water combined with lithology and land use in determining the quality of the water that recharge the aquifer below agricultural fields q 2004 elsevier b v all rights reserved

insolation regime in siberia as a major factor controlling diatom production in lake baikal during the past 800 000 years abstract a unique diatom biostratigraphy of the brunhes chron in lake baikal revealed by detailed studies of pelagic diatom paleo assemblages indicates that dramatic changes in insolation during the past 800 ka bp produced surprisingly rapid diatom speciation and extinctions the orbitally tuned age model allows the diatom assemblages to be compared with individual marine isotopic stages and substages during the brunhes most of the interglacial periods are characterized by explosive speciation and appearances of new pelagic planktonic diatom species in contrast most of the glacial periods are characterized by spectacular extinctions three broad periods characterized by different degrees of stability in the pelagic diatom assemblages are distinguished during the brunhes chron in the lake baikal sedimentary record mis 19 15e mis 15a 11 and mis 9 5 these periods are apparently associated with the long term changes in the amplitude of precessional insolation variations examination of individual interglacial periods further reveals the sensitivity of the baikal ecosystem to the regional energy balance virtually every precessional insolation peak during the early brunhes is characterized by a unique and peculiar paleo assemblage for the first time the siliceous microfossil record has demonstrated such a high degree of sensitivity to insolation forcing of regional climate despite the dramatic changes in the pelagic plankton driven by extreme climatic changes diatoms never went fully extinct during any glacial period although greatly or completely renewed during each subsequent interglacial the pelagic diatom assemblage still managed to return dominated by the new baikal endemic species the diatom assemblage observed in modern lake baikal despite being mostly endemic has formed during the past 50 100 ka and is therefore rather young these results demonstrate the remarkable capacity of this large freshwater system to sustain the dynamic stability on the large time scales

reconstruction of deglaciation of northern mongolia for the last 330 ka bp inferred from ostracod stable isotope records from lake khubsugul we have compared 18o and 13c compositions of ostracod valves with elemental and grain size records of bottom sediments from the drill core kdp 01 northern mongolia nm formed for the last 330 ka bp the increase in the 18o values a high content of br and a low percentage of clay particles were found to positively correspond with high lake bio productivity and warm marine isotope stages mis 3 5 7 and 9 and visa versa during cold mis stages positive 13c values have been linked with high inflowing dissolved inorganic carbonates and forest steppe vegetation seems to be evidenced during cold mis stages mis 2 4 6 and 8 sharp depletions in the 18o values on 1 5 2 5 occurring during the ends of mis 6 and mis 4 could be induced by glacier meltwater discharge into lake khubsugul however shifts in the 18o values were not significant in mis 2 and mis 8 based on our assumption that the inflow rates of glacier meltwater were low due to the relatively small sizes of glaciers in the nm during these stages during mis 2 northern mongolian glaciers were the smallest in sizes due to high regional aridity the climate condition in mis 3 was not typically favorable for a warm mis stage while glaciers or snow patches formed in mis 4 most likely were still in the nm as a result isotopically depleted 18o meltwater was supplied into lake khubsugul at the period

changes in dissolved oxygen in the southern ocean with climate change 1 climate models predict that increasing greenhouse gases in the atmosphere will change our climate however the range of observations available to assess these model predictions is limited we have utilized an ocean biogeochemical model to project the impact of climate change on the oxygen cycle in the ocean and the air sea exchange of oxygen with climate change our model predicts an outgassing of oxygen from the ocean in the model the southern ocean is the region that displays the largest change in the air sea exchange of oxygen with climate change the reduced oxygen uptake in the southern ocean is dominated by a reduction in convective mixing and in the subduction rate of bottom water which decreases the amount of dissolved oxygen in the southern ocean our model results suggest that dissolved oxygen is sensitive to changes in southern ocean circulation revealing the potential to use dissolved oxygen to test model predictions of climate change from southern ocean observations collected 28 years a part we observed a decrease in dissolved oxygen that was consistent with model climate change simulation this provides credibility to the climate model predictions additional analysis and observations of dissolved oxygen are needed to substantiate our climate model simulations

processes affecting groundwater chemistry in a zone of saline intrusion into an urban sandstone aquifer abstract samples have been collected from inflows into railway tunnels in the triassic sandstone aquifer beneath liverpool and the mersey estuary england u k these provide a profile through a saline freshwater mixing zone analyses were made of major anions and cations 34s and 18o in so4 13c in dissolved inorganic c and 87sr 86sr the data demonstrate that the presence of a low permeability fault exerts a strong control on the local groundwater chemistry on the estuary side of the fault groundwater chemistry is dominated by mixing of intruding estuary water which is modified by so4 reduction and calcite dissolution with fresh groundwater the environment of so4 reduction in the tidal estuary is one of repeated reduction and re oxidation of s in an open system and has resulted in virtually no change in s isotopic composition but an enrichment in residual so4 18o of 1 5 groundwater chemistry on the landward side of the fault is primarily the result of recharge in an urban environment there is also evidence that saline water has been present in this region of the aquifer in the past and that this has now been flushed by fresh groundwaters this saline water was either transported along the landward side of the fault from nearer the estuary or more probably transmitted across the fault both mechanisms would have been driven by large landward head gradients caused by heavy industrial abstraction earlier this century this has produced a zone of groundwaters depleted in ca and radiogenic sr and enriched in na as a result of ion exchange between the fresh groundwaters and the aquifer previously occupied by more saline water sulphur isotopic composition however shows no variation since so4 does not undergo significant ion exchange a tracer test from a borehole to the tunnels showed multiple breakthroughs to some locations indicating a number of different flow paths through the aquifer the maximum flow velocity recorded in this test was 140 m d suggesting flow along fractures

the structure and development of the baikal rift depression abstract the baikal rift depression located in southeastern siberia is one of the best investigated intra continental rift structures in the world in addition to being the site of comprehensive studies by russian geo scientists for decades the baikal depression is now the subject of new international investigations using advanced technical means and technologies the present paper summarizes the principal results concerning the morphostructure of the baikal rift the stratigraphy of the cenozoic deposits and the stages of the baikal depression development based on cross sections which exhibit the impact of both tectonic and climatic processes the development of the baikal depression occurred through two stages i the pre crypto rift stage of the late cretaceous eocene and ii active rifting of the oligocene recent the second stage is divided into several steps and substeps separated by tectonic phases formation of the baikal rift zone appears to be related to the indo eurasian plate collision related to a model of passive rifting the uplifted shoulders of the depression have a complex morphostructure overlain by cenozoic deposits which are thin and restricted in area the near marginal zones of the rift are largely defined by the system of longitudinal blocks of different width surfaces of the blocks are inclined either to the uplifted shoulder of the rift bound by listric faults typical for western edges of the depression or to the axis of the depression cenozoic deposits on the blocks consist of accumulative plains composed primarily of thick lacustrine sequences

lake level changes during the past 100 000 years at lake baikal southern siberia abstract lake level changes inferred from seismic surveying and core sampling of the floor of lake baikal near the selenga river delta can be used to constrain regional climatic history and appear to be correlated to global climate changes represented by marine oxygen isotope stages mis the reflection pattern and correlation to the isotope stages indicate that the topset and progradational foreset sediments of the deltas formed during periods of stable lake levels and warm climatic conditions during warm stages the lake level was high and during cold stages it was low the drop in the lake level due to cooling from mis 5 through mis 4 is estimated to be 33 38 m from mis 3 through mis 2 it fell an additional 11 15 m because the lake level is chiefly controlled by evaporation and river input we infer that more water was supplied to lake baikal during warm stages

recharge mechanisms and geochemical processes in a semi arid sedimentary basin eastern cape south africa abstract stable isotope 18 o and 2 h and geochemical signatures are used to gain some insight into recharge processes and groundwater salinization mechanisms in a semi arid rangeland catchment the 665 km 2 catchment is underlain by fractured lower beaufort sandstones and mudstones and is intruded by several dolerite dykes chloride and isotopic relationships suggest that chloride ions in ground water are of meteoric origin the hypothesized recharge and salinization mechanism is that large storm events periodically dissolve accumulated surficial meteoric salts and after a period of evaporative enrichment at or near the soil surface leach them into the ground water geochemical variations imply that spatial differences exist in recharge volumes in evaporative enrichment or in the extent of leaching of surficial salts meteoric sodium chloride contributes greater than 90 of the dissolved sodium except at low salinities where cation exchange processes yield additional sodium inputs in exchange for dissolved calcium and magnesium at high salinities this process reverses and sodium is adsorbed releasing calcium and magnesium this process accounts for up to 40 of the dissolved calcium and magnesium contributions from geochemical weathering are relatively uniform in spite of highly variable salinities which implies that residence times are also relatively uniform

evaluation of hydrogeochemical processes in the pleistocene aquifers of middle ganga plain uttar pradesh india evaluation of major ion chemistry and solute acquisition process controlling water chemical composition were studied by collecting a total of fifty one groundwater samples in shallow 25 m in the varanasi area hydrochemical facies mg hco3 dominated in the largest part of shallow groundwater followed by na hco3 and ca hco3 whereas ca hco3 is dominated in deep groundwater followed by mg hco3 and na hco3 high as concentration 50 g l is found in some of the villages situated in northeastern parts i e adjacent to the concave part of the meandering ganga river of the varanasi area arsenic contamination is confined mostly in tube wells hand pump within the holocene newer alluvium deposits whereas older alluvial aquifers are having arsenic free groundwater geochemical modeling using wateq4f enabled prediction of saturation state of minerals and indicated dissolution and precipitation reactions occurring in groundwater majority of shallow and deep groundwater samples of the study area are oversaturated with carbonate bearing minerals and under saturated with respect to sulfur and amorphous silica bearing minerals sluggish hydraulic conductivity in shallow aquifer results in higher mineralization of groundwater than in deep aquifer but the major processes in deep aquifer are leakage of shallow aquifer followed by dominant ion exchange and weathering of silicate minerals

late quaternary lake level changes and climates of australia abstract spatial and temporal patterns in lake level data from 38 sites in australia and papua new guinea provide a basis for reconstructing changes in water balance and atmospheric circulation during the past 30 000 years the reconstructions are consistent with hydrological changes inferred from pollen analysis and palaeowind directions inferred from dunes generally wetter conditions between 30 000 and 24 000 bp are consistent with a strong walker circulation with the sta near its present position general aridity at the glacial maximum until 12 000 bp with higher than present lake levels in the southeastern interior of australia implies that the southern margin of the subtropical anticyclone belt was expanded southward and the southern westerlies were correspondingly displaced this southward shift appears in all gcm simulations of the 18 000 bp climate and may be a result of the increased vigour of the northern hemisphere circulation a northward migration of the belt of high lake levels between 11 000 and 6000 bp suggests that the sta shifted back equatorward to north of its present position relaxation to modern conditions occurred after 6000 bp interrupted by an unexplained dry phase 6000 5000 bp in tasmania and queensland

catastrophic events in the quaternary outflow history of lake baikal abstract lake baikal is earth s deepest lake and an iconic site of scientific study this vast basin holds sedimentary archives of environmental change dating back to the miocene and its array of palaeoshorelines and surrounding relief record the past 1 3 ma of lake levels and outflows here we present an extensive review of previous work alongside a new set of observations concerning the quaternary development of lake baikal with special focus on lake level fluctuations and the formation and evolution of the lake s three known outlets the sequence of shoreline terraces indicates that lake levels were both higher and lower in the past lake baikal stood 200 m higher during the last interglacial i e marine isotope stage mis 5e and dropped to 40 m below present day during the last glacial maximum mis 2 the relative lake level variations reflect climate factors and gradual or sudden coseismic tectonic impacts on the elevation of the lake s outlet thresholds three successive outlets are known i the palaeo goloustnaya manzurka associated with the manzurka alluvium ii the palaeo irkut and iii the currently active angara river outlet we propose that the manzurka alluvium is the product of catastrophic events in lake baikal the sudden possibly coseismic collapse of the 15 3 km goloustnaya fault block into lake baikal triggered a mega tsunami that thrust overwash deposits across neighbouring drainage divides above lake baikal and the valleys of the goloustnaya manzurka river system the age of the manzurka alluvium remains poorly constrained but the mega tsunami is potentially traceable to an unconformity in drill core sediments at 0 8 1 0 ma although older late pliocene and younger 125 ka ages have also been proposed the irkut outlet existed between mis 6 and mis 5 when lake level was 200 m higher than present 640 650 masl and a large bay extended into the tunka rift at baikal s south west tip lake baikal retreated from the tunka rift when lake level fell by up to 100 m in early mis 5e we propose that the lake level fall is connected to a partial collapse of primorsky ridge at listvenichny bay which caused baikal to overspill into the angara river thereby forming a new outlet the release of a 4000 km3 megaflood down the angara river valley caused large scale modification and reworking of valley fills mis 5e at the end of mis 2 further collapse of primorsky ridge lowered the outlet threshold an additional 50 60 m and prompted a second megaflood down the angara river valley which left a widespread unconformity where horizontal bedded sands dated at 11 8 13 4 ka overlie cryoturbated deposits of the earlier megaflood the central role of catastrophic processes at lake baikal suggests that rather than being rare events coseismic landsliding and mega tsunami may be more frequent than hitherto recognised

continental climate response to orbital forcing from biogenic silica records in lake baikal changes in insolation caused by periodic changes in the earth s orbital parameters provide the primary forcing for global ice ages1 6 but it is not clear to what extent the climates in continental interiors are controlled directly by regional variations in insolation and to what extent they are driven instead by the highly nonlinear response of the oceans and ice sheets here we investigate this question using the record of biogenic silica in lake baikal as a proxy for climate change in this high latitude mid continental region we find a good correlation between this record and that of marine oxygen isotopes4 over the past 250 kyr the baikal record exhibits both a strongly nonlinear component manifested in a 100 kyr periodicity and weaker direct insolation components manifested in the 41 kyr obliquity and 23 and 19 kyr precession orbital cycles these results show that even though extreme continental climates such as this are influenced directly by insolation variations they are dominated by the nonlinear rhythm of the oceans and ice sheets

late quaternary lake level record from northern eurasia lake records from northern eurasia show regionally coherent patterns of changes during the late quaternary lakes peripheral to the scandinavian ice sheet were lower than those today but lakes in the mediterranean zone were high at the glacial maximum reflecting the dominance of glacial anticyclonic conditions in northern europe and a southward shift of the westerlies the influence of the glacial anticyclonic circulation attenuated through the late glacial period and the westerlies gradually shifted northward such that drier conditions south of the ice sheet were confined to a progressively narrower zone and the mediterranean became drier the early holocene shows a gradual shift to conditions wetter than present in central asia associated with the expanded asian monsoon and in the mediterranean in response to local monsoon type circulation there is no evidence of mid continental aridity in northern eurasia during the mid holocene in contrast the circum baltic region was drier reflecting the increased incidence of blocking anticyclones centered on scandinavia in summer there is a gradual transition to modern conditions after ca 5000 yr b p although these broad scale patterns are interrupted by shorter term fluctuations the long term trends in lake behavior show a clear response to changes in insolation and glaciation

lake baikal record of continental climate response to orbital insolation during the past 5 million years the sedimentary record of biogenic silica from lake baikal in south central siberia suggests that this region of central asia was impacted by two major cooling episodes at 2 8 to 2 6 and 1 8 to 1 6 million years ago the spectral evolution of this continental interior site parallels the evolutionary frequency spectra for various marine oxygen isotope records in the baikal record the 41 000 year obliquity cycle is particularly strong from 1 8 to 0 8 million years ago variance in the 100 000 year eccentricity band increases during the past 0 8 million years the expected precession frequency of 23 000 years is highest during the past 400 000 years the modulation of the predicted 23 000 and 41 000 year insolation forcing by the 100 000 and 400 000 year eccentricity bands indicates that the transfer of variance from the precession and obliquity frequencies to the eccentricity part of the spectrum occurred in the eurasian continental interior as well as in tropical and high latitude ocean sites

sodium calcium ion exchange in the weathering of shales implications for global weathering budgets unpolluted rivers and streams that drain marine shales show an excess of sodium compared to chloride and a deficiency of calcium and magnesium compared to sulfate and alkalinity this is due in part to cation exchange of sodium for divalent cations on clay minerals consideration of the global weathering budget suggests that up to 34 of the sodium in the total dissolved stream load may be due to cation exchange rather than sodium production via silicate dissolution weathering reactions these results suggest that the weathering budgets for sodium and calcium are in need of revision because of the inclusion of cation exchange processes in the weathering cycle this implies that silicate dissolution is less important in determining the composition of global river water than was previously thought

fluoride dynamics in the granitic aquifer of the wailapally watershed nalgonda district india high concentrations of fluoride up to 7 6 mg l are a recognized feature of the wailapally granitic aquifer of nalgonda district andhra pradesh india the basement rocks provide abundant sources of f in the form of amphibole biotite fluorite and apatite the whole rock concentrations of f in the aquifer are in the range 240 990 mg kg calcretes from the shallow weathered horizons also contain comparably high concentrations of f 635 950 mg kg the concentrations of water soluble f in the granitic rocks and the calcretes are usually low 1 of the total or less but broadly correlate with the concentrations observed in groundwaters in the local vicinity the water soluble fraction of fluoride is relatively high in weathered calcretes compared to fresh calcretes groundwater major ion composition shows a well defined trend with flow downgradient in the wailapally aquifer from na ca hco3 dominated waters in the recharge area at the upper part of the catchment through to na mg hco3 and ultimately to na hco3 and na hco3 cl types in the discharge area in the lowest part the evolution occurs over a reach spanning some 17 km groundwater chemistry evolves by silicate weathering reactions although groundwaters rapidly reach equilibrium with carbonate minerals favouring precipitation of calcite and ultimately dolomite in the lower parts of the watershed this precipitation is also aided by evapotranspiration decreasing ca activity downgradient leads to a dominance of fluorite undersaturated conditions and consequently to mobilisation of f despite the clear downgradient evolution of major ion chemistry concentrations of f remain relatively uniform in the fluorite undersaturated groundwaters most being in the range 3 0 7 6 mg l the rather narrow range is attributed to a mechanism of co precipitation with and or adsorption to calcrete in the lower sections of the aquifer the model may find application in other high f groundwaters from granitic aquifers of semi arid regions

evolution of colpan barrier and lagoon complex lake van turkey sedimentological and hydrological approach abstract the northeastern coast of the lake van eastern anatolia turkey is exposed to energetic waves inducing large sediment transport rates intense wave activity on coastal environment shows the shaping impact on the shoreline either erosional or depositional processes sedimentation is characterized by gravelly beaches spit formation and barrier lagoon complex colpan barrier and lagoon complex forming the subject of this study occurred in these swashed environmental conditions this study aims to introduce formation and evolution of the colpan barrier and lagoon complex and to assess the future development of the coastal area around the lake van characteristics of barrier sediments as shape size provenance sedimentary structures and palaeocurrent directions are determined with field investigations smooth flattened and rounded polygenetic sediments compose the barrier drifted to the shoreline with coastal processes as wave and longshore currents colpan barrier was created a lagoon completely isolated from lake van this wetland constitutes a habitat for some animals and plants with relatively dilute water than sodic lake van s water level fluctuation is an important element for the constructive and destructive processes for the barrier and lagoon complex

reconstruction of the late glacial and holocene history of lake oron eastern siberia russia based on high resolution reflection seismic data high resolution seismic data have been used to study the sedimentary infill of lake oron we have tested the idea that glacial lake vitim could be formed when glaciers descending from the kodar mountains blocked the vitim river at lake oron the five seismic facies types shallow pelagic mudslide and turbidite rock sandslide and alluvial or glacial fan facies and five seismic units were identified in the sedimentary infill of lake oron however features that could represent moraines were not observed on the seismic profiles and along the shoreline of lake oron it is very likely that terminal moraines did not dam the vitim river up to 840 60 m a s l at the end of the last glacial maximum lgm we assume that the oron depression was mainly dry and glaciers lobes could be located close to the eastern edge of lake oron in valleys of the sygykta kultushnaya and kamennaya rivers during the lgm intensive inflow of meltwater and river input into lake oron began since ca 18 ka bp after ca 5 ka bp the supply of surface water into the lake sharply reduced

evaluation of hydrogeochemical characteristics of phreatic alluvial aquifers in southeastern coastal belt of prakasam district south india the assessment of hydrogeochemical processes that govern the water quality of inland freshwater aquifers in coastal environment especially in indian sub continent is occasionally attempted to bridge the gap a detail hydrochemical evaluation of groundwater occurring in coastal alluvium is attempted single set of high density water sampling is done from a limited area to gain an in depth knowledge of the processes that govern the water chemistry of the sandy aquifers the water is of weak alkaline nature and less mineralized ec being na ca2 hco3 so42 mg2 no3 na and cl are almost in similar proportions implying the influence of coastal climate on water quality the water shows modest variation in their ionic assemblage among different sample points as evident from schoeller scheme groundwater can be classified into three distinct facies viz cl ca2 mg2 na cl and ca2 mg2 hco3 types the ionic assemblages their indices ratios and cross plots substantiate that multiple processes were involved in the evolution of the water chemistry among them silicate weathering halite dissolution ion exchange and base exchange played prominent role in the ion enrichment of groundwater the aquatic chemistry is further influenced and modified by marine environment evapotranspiration and anthropogenic inputs which is authenticated by good correlation r2 1 among the na cl ec mg2 na and cl gibbs plots established that evaporation is more responsible for contribution of minerals to the groundwater than aquifer material nitrate contamination can be attributed for poor sewerage disposal mechanism which is aggravated by fertilizer inputs irrigation practices and agriculture activity a contrasting correlation r2 90 to 0 40 among select pairs of ions reassures dissimilar source of those ions involvement of multiple processes and limited interaction of formation water with aquifer material

european lakes as palaeohydrological and palaeoclimatic indicators abstract lakes in temperate regions have fluctuated in size on annual to millenial time scales changes in water level or depth can be reconstructed by applying geomorphic sedimentological and biostratigraphic methods to transects of sediment cores this systematic field based approach has been used at a number of sites in europe it is illustrated by reconstructions of water level changes in lakes from southern sweden these lakes have shown broadly synchronous changes during the holocene such synchronous changes in water levels at several sites in a region reflect climatic changes inferences about the mechanism of the climatic change depend on identifying both synchronous changes within a region and differences in the direction magnitude and timing of lake level changes between regions continental compilations of lake level data are therefore necessary detailed studies are not available from enough sites but the interpretation of already existing stratigraphic and biostratigraphic data in terms of lake level changes has greatly increased the number of sites available for a continental scale synthesis in europe this eclectic literature based approach is illustrated with examples from southern europe lakes in the mediterranean region were high around the glacial maximum and again somtime during the first half of the holocene in the western mediterranean the peak of late glacial aridity occurred at 15 000 16 000 bp and the lakes were already high again by 12 000 bp in the east maximum late glacial aridity occurred between 13 000 and 11 000 bp and there was a gradual return to wetter climates during the early holocene such that 9000 bp was more arid than 6000 bp most lakes in the mediterranean region were high at 6000 bp the transition to arid conditions after 5000 bp occurred abruptly in the west and more gradually in the east the lakes of southern sweden indicate drier climates in the early holocene ca 9000 bp more effective moisture between 8000 and 6000 bp increased aridity between 5500 and 3500 bp and increased effective moisture again during the last 3000 years the history of lake level changes in southern sweden and the mediterranean region can be partially explained in terms of changes in the direct effects of insolation and in the strength and position of the westerlies and of the subtropical high pressure cell during the late quaternary

reconstruction of glacier advance in northern baikal area east siberia russia in the pleistocene inferred from mitochondrial dna polymorphisms of baikal grayling salmonidae thymallus baicalensis the study of allopatric speciation or geographic speciation expressed by dna polymorphisms can be successfully used in paleogeography reconstructions in this study we have tested the idea that grayling from lake baikal could migrate following chersky glacier retreat to the baikalsky mountains and were isolated by this glacier in glacial lake gitara in the pleistocene in order to estimate the initial isolate time of this population we compared the control region mtdna polymorphism of lake gitara grayling with that known for the lake baikal region all fish from lake gitara have the same mtdna haplotype one of the most represented among lake baikal grayling indicating that the isolation of the population in lake gitara could happen not earlier than 335 90 ka this age estimations do not contradict the records from bottom sediments of lake baikal and glacial tills of the northern baikal area which suggest that glacial advance to lake baikal reached its maximum extent in mis 8 samarovskoe glaciation

the detailed record of climatic events during the past 75 000yrs bp from the lake baikal drill core bdp 93 2 abstract by correlating the pronounced interstadial type diatom peak with mis 3 the high resolution and well dated record bdp 93 2 from the selenga delta area of lake baikal complements the classical long paleoclimatic records from academician ridge which lack the pronounced mis 3 warm signal this correlation helps to resolve the age model controversies related to this interstadial interval the content and c n ratios of total organic carbon as well as its stable isotope composition and diatom abundance reveal high frequency oscillatory variations reflecting the more unstable conditions of mis 3 interstadial in the lake baikal region as compared with the holocene interglacial an important part of the regional climatic instability during the past 75 000 yrs bp revealed for the first time in the baikal record is the recurrence of the abrupt erosional events leading to the deposition of the detrital carbonate material at the hemipelagic bdp 93 site there were at least five such events at mis 5 4 transition in the middle of mis 4 and three during mis 3 stratigraphic and ams radiocarbon age models allow the baikal erosional carbonate events to be confidently correlated to the intervals of heinrich layers in the north atlantic this correlation suggests a surprisingly strong climatic teleconnection of the remote mid continent baikal location with the dansgaard oeschger events and the bond cycles in the north atlantic region

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr