an 15 000 year record of el nino driven alluviation in southwestern ecuador debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the pacific ocean in ecuador these storm induced events were dated by radiocarbon and the age of laminae that are less than 200 years old matches the historic record of el nino events from about 15 000 to about 7000 calendar years before the present the periodicity of clastic deposition is greater than or equal to 15 years thereafter there is a progressive increase in frequency to periodicities of 2 to 8 5 years this is the modern el nino periodicity which was established about 5000 calendar years before the present this may reflect the onset of a steeper zonal sea surface temperature gradient which was driven by enhanced trade winds

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

the last glacial maximum and late glacial environmental and climate dynamics in the baikal region inferred from an oxygen isotope record of lacustrine diatom silica abstract the last glacial maximum and late glacial environmental and climatic variability in the baikal region southern siberia russia has been studied in a sediment sequence from lake kotokel located 2 km east of lake baikal using the oxygen isotope composition of diatom silica 18 o diatom the purification of diatom frustules involved the process of trimethylsilylation which has been shown to be suitable for preparation of diatoms for oxygen isotope analysis the lake kotokel 18 o diatom record presented here spans intervals from about 24 6 to 22 9 ka bp further referred to as last glacial maximum and 16 7 11 5 ka bp further referred to as late glacial displaying variations in the oxygen isotope composition between 26 7 and 31 2 overall high 18 o diatom values of about 29 to 31 during the two investigated intervals characterize a strongly evaporative lake system in a dry environment and suggest a lower than present lake level due to enhanced evaporation the lake kotokel diatom isotope record is roughly in line with the 60 n summer solar insolation pointing to a linkage to broader scale climate change but displays weaker reaction to short term climatic oscillations i e bolling allerod or younger dryas the climate warming at 14 3 ka bp is marked by negative spikes in the 18 o diatom record due to isotopically low melt water input from the mountainous hinterland

diatom stable isotopes sea ice presence and sea surface temperature records of the past 640 ka in the atlantic sector of the southern ocean 1 high resolution 13c and 15n records of diatom bound organic matter 13cd 15nd from odp site 1094 south of the polar front are combined with reconstructions of summer sea surface temperature and winter sea ice to establish changes in surface water characteristics associated with the main climatic events of the past 640 ka the six glacial interglacial 13cd cycles show excellent agreement with specmap 18o and vostok co2 content suggesting that global physical processes rather than local biological factors were the main influences on 13cd by contrast there is weak correspondence between the vostok dust record and the 13cd and 15nd records the data do not support the hypothesis that glacial iron fertilization of the southern ocean was the main factor lowering atmospheric co2 if dust accumulation represents iron input the records indicate that sea ice cover water column stratification and iron addition from deep water mixing are more likely to explain our observations

234u1b238u disequilibria as an aid to the hydrological study of the judea group aquifer in eastern judea and samaria israel abstract two distinct subaquifers can be defined within the judea group aquifer upon the basis of their uranium isotopic disequilibria the springs that issue from the phreatic upper aquifer clearly exhibit lower 234 u 238 u activity ratios than does the deeper confined water mass where faulting allows for interconnection of the aquifers intermediate values are found the isotopic values can be used to delineate regions where exploitation of the lower cenomanian subaquifer will not reduce the output of the overlying spring or conversely to delineate regions where reduction of the spring discharge may be expected

biological forcing of hemipelagic sedimentary laminae evidence from odp site 893 santa barbara basin california core observation x radiography and scanning electron microanalysis of distinctly laminated indistinctly laminated and nonlaminated sediments from odp site 893 show that laminated as well as nonlaminated i e massive hemipelagic sediments can form in the absence of bioturbation this view contrasts with conventional sedimentological interpretations equating laminated hemipelagic sediments with anoxic water masses i e absence of bioturbation and nonlaminated sedimentary intervals exclusively with oxygenation episodes that permitted infaunal colonization we conclude that heterogeneities in the texture and or composition of sediment supply are necessary for the production of laminated sediments the absence of hydraulic and biological reworking permits their preservation laminae at site 893 have two prominent components biosilica and terrigenous detritus compositional contrasts between adjacent laminae in x radiographs reflect short term seasonal and subseasonal heterogeneities in sediment flux core intervals with large contrasts in density and or composition between adjacent laminae are termed as having high bimodality hb hb couplets produce distinctly laminated sediments that intergrade vertically with indistinctly laminated and nonlaminated sediments adjacent laminae in indistinctly laminated sediments possess minimal contrasts in bulk density and composition nonlaminated sediments are compositionally and texturally homogeneous many biosiliceous laminae responsible for distinctly laminated hb couplets record mass flocculation and sedimentation of ungrazed diatom frustules formed during discrete bloom events ecological interpretation of diatomite laminae suggests that many were effectively self sedimenting i e the production of gelatinous exudates by phytoplankton facilitated their aggregation and rapid sedimentation the results indicate that lamination style preserves meaningful ocean climate data concerning episodicity heterogeneity and export efficiency of biologically mediated sedimentary flux in upwelling dominated coastal ecosystems

paleoenvironment of the central himalaya during late mis 3 using stable isotopic compositions of lacustrine organic matter occluded in diatoms and sediments abstract marine isotope stage mis 3 was an interstadial stage in the climate history of the earth where the last phase 40 30 ka showed relatively warmer climate over the northwest china tibetan plateau and northwestern india compared to other regions of the world however not many studies are reported for climate variability during this period from the himalayan region here an attempt has been made to understand the paleoenvironment of the central himalaya during 45 29 ka using stable isotopic compositions of carbon 13ctoc and nitrogen 15ntn along with their elemental ratios toc tn in bulk organic matter and occluded organic matter within diatom frustules 13cdiatom of a paleolake sequence the variabilities in 13cdiatom 13ctoc and toc tn ratios indicated intermittent changes in the lake carbon dynamics from bicarbonate dominated system to carbon dioxide dominated regime these changes in lacustrine carbon cycling provided evidence for existence of sporadic dry events in the central himalaya during 45 29 ka in agreement with the records from the northwest china tibetan plateau and northwestern india our results also confirm the existence of a relatively wet and humid period during 40 32 ka in the central himalaya therefore it appeared that compared to other parts of the world relatively wet and humid climate existed throughout this region however the mechanism behind this wet and humid phase remains to be explored and warrants a high resolution paleoclimate study in the himalaya

the relationship between δ13c of organic matter and co2 aq in ocean surface water data from a jgofs site in the northeast atlantic ocean and a model the 13c of suspended particulate organic matter spom in surface waters increased from 22 9 to 18 1 during april 25 may 31 1989 at the jgofs north atlantic bloom experiment site nabe site 47 n 20 w during the same period nearly parallel increases in sinking pom 13c were also found although these values were usually lower than those of the corresponding spom consistent with the hypothesis that plankton 13c and co2 aq are inversely related the increases in both sinking and suspended pom 13c were highly negatively correlated with mixed layer co2 aq that generally decreased from 10 1 13 2 moles kg during the five weeks the change in spom 13c per change in co2 aq however appears to be somewhat greater than that expected from previous though less direct ocean and laboratory evidence by adapting a model of plant 13c by farquhar et al 1982 it is shown that under a constant phytoplankton demand for co2 an inverse nonlinear spom 13c response to ambient co2 aq is expected such trends are unlike the negative linear relationships indicated by data from the nabe site and or from southern hemisphere waters such differences between predicted and observed spom 13c vs co2 aq trends and among observed relationships can be reconciled however if biological co2 demand is allowed to vary this has significant implications for the use of the 13c of plankton or their organic subfractions or sedimentary remains as a proxy for past or present ocean co2 concentrations and biological productivity

diatom bound 15n 14n new support for enhanced nutrient consumption in the ice age subantarctic 1 diatom bound 15n 14n was used to reconstruct the glacial nutrient status of the subantarctic zone in the southern ocean down core records from both the pacific and indian sectors show 15n of 5 to 6 during the last glacial maximum and a decrease coincident with the glacial termination to values as low as 2 the effect of either diatom assemblage or physiological change on the diatom bound 15n 14n is unknown and cannot yet be ruled out as a possible explanation for the observed change however the consistency between indian and pacific sector records and with other paleoceanographic data suggests that the glacial interglacial difference in diatom bound 15n 14n was driven by higher consumption of nitrate in the subantarctic surface during the last ice age such a change in nutrient consumption may have resulted from atmospheric iron fertilization and or decreased glacial mixed layer depths associated with sea ice melting enhanced nutrient consumption in the glacial subantarctic would have worked to lower the concentration of co2 in the ice age atmosphere it also would have reduced the preformed nutrient content of the low latitude thermocline leading to decreases in low latitude productivity suboxia and denitrification

late quaternary variations of elemental ratios c si and n si in diatom bound organic matter from the southern ocean le cycle du carbone de l ocean austral est certainement un des facteurs majeurs controlant les concentrations atmospheriques passees en co 2 cependant les taux d accumulation de l opale biogene ne sont pas lineairement lies aux taux d accumulation du carbone organique et ne peuvent donc pas etre directement utilises en tant que traceur de la paleoproductivite nous montrons ici qu il est possible de mesurer les teneurs en carbone et azote dans la matiere organique intrinseque des diatomees c diat and n diat respectivement et que les signaux fossiles ne sont pas le resultat d artefacts analytiques l analyse de deux carottes provenant des secteurs atlantique et indien de l ocean austral indique que les c diat and n diat ont respectivement varie de 30 40 et de 120 175 au cours des cycles glaciaires interglaciaires les rapports c n ont en consequence varie de 3 a 7 au cours des cycles glaciaires interglaciaires si les variations enregistrees dans la matiere organique intrinseque sont representatives des changements du bulk des diatomees nous aurons un nouvel outil pour documenter le cycle oceanique du carbone et pour determiner son role dans les variations passees de pco 2 atmospheriques des experiences en laboratoire sur des cultures de diatomees sont cependant necessaires afin de valider l outil c diat and n diat comme traceur des conditions physiologiques des diatomees et des flux de carbone exportes depuis la couche euphotique

spatial delineation of groundwater salinity using deep time domain electromagnetic geophysical measurements a feasibility study 1 the objective of this study was to delineate the spatial distribution of fresh brackish and saline groundwater bodies as well as brine beneath the judea desert israel we used the deep time domain electromagnetic tdem geophysical system cycle 5m which provides the maximum exploration capability to depths 1 5 2 km below land surface the study was conducted at 21 locations at the desert plateau where fresh groundwater flows through the upper aquifers from the replenishment area at the judea mountains toward the dead sea springs in deeper aquifers brackish and saline groundwater bodies exist which originated from lakes and lagoons that existed at the dead sea rift valley during the pleistocene and pliocene respectively it was found that within carbonate formations fresh groundwater c 103 ppm total dissolved solids tds is characterized by a resistivity of more than 15 m brackish groundwater 103 c 104 ppm tds is characterized by 5 15 m saline groundwater 104 c 105 ppm tds is characterized by 0 5 5 m and brine 105 c ppm tds is characterized by less than 0 5 m

characterisation and modelling of conduit restricted karst aquifers example of the auja spring jordan valley summary the conduit system of mature karstified carbonate aquifers is typically characterised by a high hydraulic conductivity and does not impose a major flow constriction on catchment discharge as a result discharge at karst springs is usually flashy and displays pronounced peaks following recharge events in contrast some karst springs reported in literature display a discharge maximum attributed to reaching the finite discharge capacity of the conduit system flow threshold this phenomenon also often leads to a non standard recession behaviour a so called convex recession i e an increase in the recession coefficient during flow recession which in turn might be used as an indicator for conduit restricted aquifers the main objective of the study is the characterisation and modelling of those hydrogeologically challenging aquifers the applied approach consists of a combination of hydrometric monitoring a spring hydrograph recession and event analysis as well as the setup and calibration of a non linear reservoir model it is demonstrated for the auja spring the largest freshwater spring in the lower jordan valley the semi arid environment with its short but intensive precipitation events and an extended dry season leads to sharp input signals and undisturbed recession periods the spring displays complex recession behaviour exhibiting exponential coefficient and linear coefficient recession periods numerous different recession coefficients were observed 0 2 to 0 8 d 1 presumably main conduit system 0 004 d 1 fractured matrix 0 0009 d 1 plateau caused by flow threshold being exceeded plus many intermediate values the reasons for this observed behaviour are the outflow threshold at 0 47 m 3 s 1 and a variable conduit matrix cross flow in the aquifer despite system complexity and hence the necessity of incorporating features such as a flow threshold conduit matrix cross flow and a spatially variable soil epikarst field capacity the developed reservoir model is regarded as relatively simplistic as a number of required parameters were calculated from the hydrogeological analysis of the system it requires only six calibration parameters and performs well for the highly variable flow conditions observed calculated groundwater recharge in this semi arid environment displays high interannual variability for example during the 45 year simulation period only five wet winter seasons account for 33 of the total cumulative groundwater recharge

nutrient cycling in the indian sector of the southern ocean over the last 50 000 years most high southern latitude records of carbon and nitrogen isotopic ratios and elemental ratios are from the antarctic and polar front zones thus hindering a comprehensive view of nutrient cycling in the southern ocean we present for the first time two records from the subantarctic zone and the southern subtropical zone of the indian ocean these records provide a latitudinal transect covering the main oceanographic systems of the southern ocean carbon and nitrogen content of the diatom bound organic matter increases during the last glacial in the antarctic and subantarctic zones but does not show a clear climate related signal in the subtropical zone comparison of these records with sea surface temperatures reconstructed at the core locations and record of dust deposition over antarctica suggests that eolian iron input possibly switched diatom physiology toward higher carbon to silica and nitrogen to silica uptake and storage south of the subantarctic front due to the dependency of photosynthesis on iron concentration levels conversely the northernmost core was too remote from any iron source over the last 50 000 years antarctic diatoms therefore have the sole potential to change the nutrient content of the waters escaping from the southern ocean hence providing partial support to the silicic leakage hypothesis as a potential cause of lower glacial atmospheric co 2

climatically linked carbon isotope variation during the past 430 000 years in southern ocean sediments we use the isotopic composition of carbon from organic matter enclosed within diatom frustules as a proxy for paleoproductivity and paleo dissolved carbon dioxide concentrations in ocean surface waters a southern ocean record from south of the antarctic polar front and spanning 430 000 years of carbon isotopic variation in diatomaceous organic matter is presented for the first time the most refractory diatomaceous organic matter fraction was extracted and analyzed to avoid problems associated with diagenesis the results clearly indicate cyclic changes in organic carbon isotopic ratios with 13c depleted values associated with all of the last five glacial periods reflecting changes in surface water properties and primary productivity changes in dissolved carbon dioxide concentrations are the most probable cause of these cycles but the possible effect of seawater ph changes cannot be excluded

in search of a characteristic signature for groundwater aquifers a case study from israel the uranium isotopic and hydrogeochemical data of groundwaters in the galilee betshean samaria and beersheva regions of israel obtained from the published literature have been re interpreted according to new ideas gained from a study of uranium concentrations in groundwaters in australia it appears to be a general rule that the uranium concentration of natural waters is proportional to the hco 3 concentration in a way that is characteristic of individual aquifers in the israeli context the major limestone and basaltic aquifers can be clearly distinguished even to the extent of the mixing of waters from these two sources the limitations of tracing groundwater bodies by the 234u238u activity ratios vs u concentration plot are discussed and the need for interpreting uranium isotopic data in conjunction with hydrogeochemical data is demonstrated which suggests that some of the earlier inferences made in the papers discussed especially in regard to the beersheva region could be reconsidered the hco 3 vs u correlation technique appears to be a good technique for tracing and delineating groundwater bodies in an oxidizing environment irrespective of their size residence time and conditions at the time of recharge

climatic and lacustrine morphometric controls of diatom paleoproductivity in a tropical andean lake abstract the coupling of lake dynamics with catchment biogeochemistry is considered the key element controlling primary production in mountain lakes at time scales of a few decades to millennia yet little is known on the impacts of the morphometry of lakes throughout their ontogeny as lake chungara central andean altiplano northern chile experienced long term lake level fluctuations that strongly modified its area volume ratio it is an ideal system for exploring the relative roles that long term climatic shifts and lake morphometry play on biosiliceous lacustrine productivity in this paper we review previous data on the percent contents of total organic carbon total inorganic carbon total nitrogen total biogenic silica isotopic composition of organic matter carbonates and diatom frustules as well as data on the abundance of the chlorophycean botryococcus braunii in this lake for the period 12 400 1300 cal yr bp we also include new data on organic carbon and biogenic silica mass accumulation rates and the diatom assemblage composition of an offshore core dated using 14 c and u th biosiliceous productivity in lake chungara was influenced by shifts in allochthonous nutrient inputs related to variability in precipitation humid phases dated at approx 12 400 to 10 000 and 9600 to 7400 cal yr bp coincide with periods of elevated productivity whereas decreases in productivity were recorded during arid phases dated at approx 10 000 to 9600 and 7400 to 3550 cal yr bp andean mid holocene aridity period however morphometry related in lake controls led to a lack of a linear response of productivity to precipitation variability during the late glacial to early holocene lowstands facilitated complete water column mixing prompting episodic massive blooms of a large centric diatom cyclostephanos cf andinus thus moderate productivity could be maintained regardless of aridity by this phenomenon of morphometric eutrophy during the early history of the lake the subsequent net increase in lake level introduced modifications in the area of the epilimnion sediments versus the total volume of the epilimnion preventing complete overturn surpassing a certain depth threshold at approx 8300 cal yr bp caused cessation of the morphometric eutrophy conditions associated with cyclostephanos cf andinus superblooms after 7300 cal yr bp the lake experienced a decrease in biosiliceous productivity and a change of state that involved a stronger dependence on precipitation variability with a lesser contribution of diatoms to the total primary productivity our results show that the interpretation of lacustrine paleoproductivity records as paleoclimatic archives needs to take into account the effects of changes in the epilimnion sediment area to epilimnion volume ratio in association with lake ontogeny

long term fire and forest history of subalpine balsam fir abies balsamea and white spruce picea glauca stands in eastern canada inferred from soil charcoal analysis the northernmost balsam fir forest in eastern canada forms disjunct stands far beyond the extensive balsam fir forest zone of southern canada the northern balsam fir stands are distributed in the

the palaeohydrological evolution of lago chungara andean altiplano northern chile during the lateglacial and early holocene using oxygen isotopes in diatom silica oxygen isotopes of diatom silica and petrographical characterisation of diatomaceous laminated sediments of lago chungara northern chilean altiplano have allowed us to establish its palaeohydrological evolution during the lateglacial early holocene ca 12 000 9400 cal yr bp these laminated sediments are composed of light and dark pluriannual couplets of diatomaceous ooze formed by different processes light sediment laminae accumulated during short term diatom blooms whereas dark sediment laminae represent the baseline limnological conditions during several years of deposition oxygen isotope analysis of the dark diatom laminae show a general 18o enrichment trend during the studied period comparison of these 18odiatom values with the previously published lake level evolution suggests a correlation between 18odiatom and the precipitation evaporation ratio but also with the evolution of other local hydrological factors as changes in the groundwater outflow as well as shifts in the surface volume ratio of lago chungara the lake expanded probably increasing this ratio during the rising lake level trend due to changes in its morphology enhancing evaporation furthermore the lake s hydrology was probably modified as the groundwater outflow became sealed by sediments increasing lake water residence time and potential evaporation both factors could cause isotope enrichment natural environment research council nerc copyright 2008 reproduced with the permission of nerc published by john wiley sons ltd

the climate of the altiplano observed current conditions and mechanisms of past changes abstract the large scale controls on the climate of the south american altiplano are investigated using local observations reanalysis data and general circulation model experiments the objective is to gain understanding of causes of climate variability and climate change by relating mechanisms that operate on timescales ranging from the intraseasonal to the glacial interglacial our results suggest that on all timescales the climatic conditions on the altiplano are closely related to the upper air circulation with an easterly zonal flow aloft favoring wet conditions and westerly flow causing dry conditions different factors influence the upper air circulation on the different timescales intraseasonal variability is a reflection of the position and intensity of the bolivian high which is modulated by rossby waves emanating from the midlatitude south pacific the annual cycle of dry winter and wet summer conditions is caused by the seasonal expansion of the equatorial easterlies in the upper troposphere rather than direct insolation forcing over the altiplano or moisture changes in the source area interannual variability is primarily related to changes in the mean zonal flow over the altiplano reflecting changes in meridional baroclinicity between tropical and subtropical latitudes which in turn is a response to sea surface temperature changes in the tropical pacific orbitally forced changes in the land sea contrast drive continental scale circulation changes which significantly alter the zonal flow over the altiplano on glacial interglacial timescales the contrast in heating between northern and southern hemispheres during the glacial leads to upper air easterly anomalies throughout the tropics on modern timescales the marked submonthly seasonal and interannual changes of moisture over the altiplano cannot be accounted for by moisture changes in the humid tropical lowlands however the model experiments suggest that cooler conditions during a glacial reduce moisture availability from the tropical lowlands which counteracts the effect of the upper level circulation resulting in little overall change in precipitation this observational and modeling analysis provides a physical framework for relating the mechanisms of both internal and forced climate change on the altiplano on a wide range of timescales

southern ocean contributions to glacial interglacial changes of atmospheric pco2 an assessment of carbon isotope records in diatoms eleven new antarctic records of diatom bound 13corg show significantly lighter values during the last glacial maximum than during the holocene with a general trend of increasing depletions southward of the modern antarctic polar front mapf in contrast glacial diatoms from cores farther north of the mapf show 13corg values which are 1 heavier than during the holocene likely causes for the low glacial 13corg in antarctic diatoms are higher co2 aq lower growth rates and changes in diatom abundance or size taken at face value the glacial depletions of 13corg suggest that antarctic surface waters south of the mapf might have been a source of atmospheric pco2 during the glacial period alternatively the glacial depletions might have been caused by either a relatively small decrease in growth rates or changes in the abundance of the two dominant diatom species or their average cell size interpretations of the subantarctic records are complicated by similar uncertainties

a 14kyr record of the tropical andes the lago chungara sequence 18 s northern chilean altiplano abstract high resolution geochemical analyses obtained using an x ray fluorescence xrf core scanner as well as mineralogical data from the lago chungara sedimentary sequence in the northern andean chilean altiplano 18 s provided a detailed reconstruction of the lacustrine sedimentary evolution during the last 14 000 cal yr bp the high resolution analyses attained in this study allowed to distinguish abrupt periods identify the complex structures of the early and mid holocene arid intervals and to compare their timing with titicaca lake and sajama ice records three main components in the lake sediments have been identified a biogenic component mainly from diatoms b volcanics ash layers from the nearby parinacota volcano and c endogenic carbonates the correlation between volcanic input in lago chungara and the total particles deposited in the nevado sajama ice core suggests the parinacota volcano as the common source the geochemical record of lago chungara indicates an increase in siliceous productivity during the early holocene lagging behind the rise in temperatures inferred from the nevado sajama ice core the regional mid holocene aridity crisis can be characterized as a number of short events with calcite and aragonite precipitation in the offshore lake zones

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

the isotopic composition of diatom bound nitrogen in southern ocean sediments treatment of diatom microfossils from southern ocean sediments with hot perchloric acid leaves a diatom bound n fraction which is 0 4 lower in 15n than the bulk sediment typically 3 lower in recent antarctic diatom ooze results from southern ocean surface sediments indicate that early diagenetic changes in bulk sediment n content and 15n are not reflected in diatom bound n suggesting that diatom bound n is physically protected from early diagenesis by the microfossil matrix a meridional transect of multicores from the indian sector of the southern ocean shows a northward increase in the 15n of diatom bound n suggesting that diatom bound 15n like bulk sedimentary 15n varies with nitrate utilization in the overlying surface waters the 15n of diatom bound n is 3 4 higher in glacial age antarctic sediments than in holocene sediments supporting the hypothesis previously based on bulk sediment 15n that nitrate utilization in the surface antarctic was higher during the last ice age while there are important uncertainties the inferred range of utilization changes could potentially explain the entire 80 ppm amplitude of observed glacial interglacial variations in atmospheric co2

last glacial sea surface temperatures and sea ice extent in the southern ocean atlantic indian sector a multiproxy approach 1 on the basis of the quantitative study of diatom radiolarian and planktic foraminiferal assemblages we estimated summer sea surface temperature ssst and sea ice extent at 50 sediment core localities in the atlantic and western indian sector of the southern ocean to reconstruct the last glacial environment at the glamap 18 to 15 ka equal to 21 500 to 18 000 calendar cal years bp and epilog 19 5 to 16 0 ka equal to 23 000 to 19 000 cal years bp time slices stratigraphic identification of the time slices was accomplished by a combination of ams 14c measurements benthic isotope and siliceous microfossil abundance records while the ssst estimates reveal greater surface water cooling than reconstructed by climap 1981 reaching a maximum in the area of the present subantarctic zone the sea ice reconstruction indicates that climap overestimated the expansion of the antarctic sea ice field especially for austral summer during winter the sea ice field was expanded by 60 70 compared to the present last glacial summer sea surface isotherms indicate a northward shift of the zonal bands of the antarctic circumpolar current and a relative expansion of the cold water realm south of the subantarctic front by 5 in latitude this coincides with a northward displacement of the zone of enhanced biogenic silica deposition and iceberg occurrence as a result of northward expansion of antarctic cold waters and a relatively small displacement of the subtropical front thermal gradients were steepened during the last glacial in the area of the present subtropical front the northward displacement of antarctic cold waters and the related deflection of southern ocean waters along the eastern boundary of south america may have resulted in a weakened cold water route across the drake passage in contrast the transport of warm and salty surface water from the indian into the atlantic ocean via the warm water route was not blocked allowing continuous but reduced import of heat into the south atlantic

holocene oxygen isotope record of diatoms from lake kotokel southern siberia russia and its palaeoclimatic implications the oxygen isotope composition of diatom silica d 18 odiatom from marine and lake sediments is helpful for the interpretation of the past climate and environments especially when complemented by other proxy records this paper presents a holocene oxygen isotope record of diatoms from lake kotokel located 2 km east of lake baikal in southern siberia russia the isotope record displays variations in d 18 odiatom from 23 7 to 30 3 from about 11 5 ka bp until today comparing the isotope composition of recent lake kotokel water mean d 18 o 12 to that of the most recent diatom sample d 18 o 27 5 an isotope fractionation in the right order of magnitude was calculated the kotokel d 18 o diatom record is controlled by changes in the isotopic composition of the lake water rather than by

carbon cycling within an east african lake revealed by the carbon isotope composition of diatom silica a 25 ka record from lake challa mt kilimanjaro the carbon cycle of a lake is a balance between supply from the atmosphere and catchment and the net demand exerted by primary producers minus losses back to the atmosphere and to sediment storage evaluating the sum of these processes and reconstructing them from sediment records of lake history requires a range of methods and a multi proxy approach one promising technique is to explore the carbon isotope composition 13cdiatom of organic matter incorporated within the silica frustules of diatom algae here we present a 25 000 year record of 13cdiatom from the sediments of crater lake challa on the eastern flank of mt kilimanjaro and along with other proxy data we make inferences about the three major phases in the history of the lake s carbon cycle from 25 ka to 15 8 ka years bp 13cdiatom is positively correlated with the 13c of bulk sediment organic matter 13cbulk indicating that high diatom productivity as recorded by high biogenic silica at this time was preferentially removing 12c and enriching the 13c of lake water dissolved inorganic carbon from 15 8 to 5 5 ka the correlation between 13cdiatom and 13cbulk breaks down suggesting carbon supply to the lake satisfied or exceeded the demand from productivity from 5 5 ka bp the positive correlation resumes indicating an increase in the internal demand for carbon relative to external supply diatom frustule bound carbon isotopes offer an original tool in examining long term fluctuations in a lake s carbon budget and how the balance between supply and demand has changed through time

vegetation dynamics in relation to late holocene climate variability and disturbance outaouais quebec canada a pollen diagram from lac brule in southwestern quebec 45 43 09 n 75 26 32 w 270 m provides a late holocene history of the vegetation the presence of varved sediments permitted the development of a high resolution 10 year cross dated chronology with an estimated error of approximately 1 during the last 1400 years the forests were dominated by tsuga fagus betula acer and pinus a peak in microcharcoal and evidence of post fire succession suggest that the changes in the pollen assemblages around ad 1375 were a consequence of a fire in the region there was a decrease in pollen influx of several deciduous taxa and tsuga between ad 1600 and 1700 suggesting a rapid climate change that was significant enough to have affected pollen production of these taxa this change associated with the beginning of the little ice age in the region affected the forest composition for the subsequent centuries a detailed comparison of this pollen record with that from a nearby pollen diagram also prepared at high temporal resolution shows the ability of pollen records to record short period climate variations and disturbances

uranium isotopes as a natural tracer in the waters of the bet shean harod valleys israel abstract thirty four samples representative of each of the major aquifers and springs in the bet shean harod valleys were analyzed for their uranium isotopes whereas there is relatively small variation in the uranium content large differences are exhibited by the 234 u 238 u activity ratios three distinct water sources are delineated the higher degree of chemical weathering in the basalt aquifer yields low activity ratios it is proposed that the difference in activity ratio within the carbonate waters is due to isotopic changes related to the degree of water maturation which itself is related to the distance the average water travels from the recharge area to the outlets

a comparison of the palaeoclimate signals from diatom oxygen isotope ratios and carbonate oxygen isotope ratios from a low latitude crater lake the analysis of oxygen isotope ratios 18o from authigenic lake carbonates has become a well established palaeoclimate technique less common is the use of 18o in biogenic silica e g diatoms sponge spicules phytoliths but the technique is being increasingly utilised for non carbonate lakes this paper aims to compare 18odiatom with 18ocarbonate in a low latitude closed basin lake due to the influence of ph rarely are both carbonate and diatoms preserved in lake sediments in concentrations high enough to measure oxygen isotopes the 18o composition of both carbonate and silica should reflect the isotope composition and temperature of the lake water at the time of precipitation and hence theoretically they should be equivalent only one comparative study of 18odiatom and 18ocarbonate currently exists and that found differences between their 18o compositions probably because they precipitated in different seasons unless there is evidence to suggest that silica and carbonate precipitate at the same time their 18o records are likely to be different but complementary in this study we show that 18odiatom and 18ocalcite from lake tilo ethiopia show some similar broad climate trends however the 18odiatom curve is generally more variable and does not record two regional arid events picked up by the 18ocalcite data several possible reasons for this are discussed the precision of the 18odiatom extraction technique contamination of the diatom samples from tephra volcanic glass vital effects in the diatom samples differences in their respective equilibrium isotope fractionation rates and the possibility that the dominant diatom aulacoseira granulata and calcite precipitated in different seasons during this time currently the problems associated with the cleaning and extraction of 18odiatom suggests that details found in 18ocalcite records may be lost in 18odiatom records where contaminants such as tephra and clay minerals are difficult to remove

century to millennial scale climatic variability in lake malawi revealed by isotope records diatom based oxygen isotope data 18odiatom from lake malawi show multi centennial scale wet dry intervals spaced approximately every 2 3 ka throughout a 25 ka sequence the 18odiatom record is supported by a lower resolution deuterium dpa isotope curve derived from palmitic acid we interpret these isotope data in terms of major shifts in precipitation and evaporation moderated by seasonal controls on the host organisms dry periods marked by relatively positive isotope values represent the extension of abrupt holocene events noted from northern and equatorial africa to 10 15 s these events in lake malawi correspond to cool episodes in greenland thereby demonstrating teleconnections generated by meridional temperature gradients sea surface temperatures are likely to be the primary transmitter of deglacial climate changes although trade wind strength and direction is critical in controlling precipitation patterns in tropical regions conversely the global hydrological cycle driven by low latitude regions represents an important positive feedback amplifying deglacial processes

reconstruction of the long term fire history of an old growth deciduous forest in southern quebec canada from charred wood in mineral soils charcoal particles are widespread in terrestrial and lake environments of the northern temperate and boreal biomes where they are used to reconstruct past fire events and regimes in this study we used botanically identified and radiocarbon dated charcoal macrofossils in mineral soils as a paleoecological tool to reconstruct past fire activity at the stand scale charcoal macrofossils buried in podzolic soils by tree uprooting were analyzed to reconstruct the long term fire history of an old growth deciduous forest in southern quebec charcoal fragments were sampled from the uppermost mineral soil horizons and identified based on anatomical characters spruce picea spp fragments dominated the charcoal assemblage along with relatively abundant wood fragments of sugar maple acer saccharum and birch betula spp and rare fragments of pine pinus cf strobus and white cedar thuja canadensis ams radiocarbon dates from 16 charcoal fragments indicated that forest fires were widespread during the early holocene whereas no fires were recorded from the mid holocene to present the paucity of charcoal data during this period however does not preclude that a fire event of lower severity may have occurred at least eight forest fires occurred at the study site between 10 400 and 6300 cal yr b p with a dominance of burned conifer trees between 10 400 and 9000 cal yr b p and burned conifer and deciduous trees between 9000 and 6300 cal yr b p based on the charcoal record the climate at the study site was relatively dry during the early holocene and more humid from 6300 cal yr b p to present however it is also possible that the predominance of conifer trees in the charcoal record between 10 400 and 6300 cal yr b p created propitious conditions for fire spreading the charcoal record supports inferences based on pollen influx data labelle c richard p j h 1981 vegetation tardiglaciaire et postglaciaire au sud est du parc des laurentides quebec geographie physique et quaternaire 35 345 359 of the early arrival of spruce and sugar maple in the study area shortly after deglaciation we conclude that macroscopic charcoal analysis of mineral soils subjected to disturbance by tree uprooting may be a useful paleoecological tool to reconstruct long term forest fire history at the stand scale d 2005 university of washington all rights reserved

glacial to interglacial changes in surface nitrate utilization in the indian sector of the southern ocean as recorded by sediment δ15n we present a new approach for paleoceanographic reconstruction of surface nutrient utilization in the southern ocean it has been observed in the contemporary ocean that due to preferential uptake of 14no3 during photosynthesis the 15n of planktonic organic matter increases with increasing nitrate depletion in surface waters our results demonstrate that the 15n signal produced in surface waters is reflected in the underlying surface sediments core top 15n is inversely correlated with surface nitrate concentration along a transect across the subtropical convergence and the polar front in the southeast indian ocean these results are consistent with a four box model showing that the nitrogen isotopic composition of sinking organic matter depends on percent nitrate utilization in the euphotic zone by comparing the 15n of surface sediments with that measured in the glacial sections of several cores we infer changes in the intensity and latitudinal distribution of nitrate uptake in this region during the last glacial maximum these preliminary results argue against increased biological uptake of nutrients in southern polar waters as a major mechanism for glacial lowering of atmospheric co2 they also suggest that subantarctic waters in the se indian sector became more nutrient depleted as they migrated northward increased nitrate depletion might have also occurred slightly south of the glacial polar front we use a six box model to explore the possible impact of this observation on atmospheric co2

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

environmental processes of the ice age land oceans glaciers epilog knowledge of the state of the earth at the last glacial maximum lgm an interval around 21 000 years ago is an important benchmark for understanding the sensitivity of global environmental systems to change much progress in understanding climates of the lgm has occurred in the 20 years since the end of the climap project of the 1970s climate long range investigation mapping and prediction here we review this progress based on presentations and discussion at a rst open science meeting of the epilog project environmental processes of the ice age land oceans glaciers held in delmenhorst germany may 1999 we outline key controversies and document protocols for epilog contributions so that a new synthesis of the lgm earth can emerge as an open project of the world s community of scientists 2001 elsevier science ltd all rights reserved

sea ice diatom contributions to holocene nutrient utilization in east antarctica combined high resolution holocene 30sidiat and 13cdiat paleorecords are presented from theseasonal ice zone east antarctica both data sets re ect periods of increased nutrient utilization by diatomsduring the hypsithermal period circa 7800 to 3500 calendar years cal years b p coincident with a higherabundance of open water diatom species fragilariopsis kerguelensis increased biogenic silica productivity bsi and higher regional summer temperatures the neoglacial period after circa 3500 cal years b p isre ected by an increase in sea ice indicative species fragilariopsis curta and fragilariopsis cylindrus upto50 along with a decrease in bsi and 13cdiat 18 to 23 however over this period 30sidiatdata show an increasing trend to some of the highest values in the holocene record average of 0 43 competing hypotheses are discussed to account for the decoupling trend in utilization proxies including ironfertilization species dependent fractionation effects and diatom habitats based on mass balance calculations we highlight that diatom species derived from the semi enclosed sea ice environment may have a confoundingeffect upon 30sidowncorecompositions of the seasonal sea ice zone a diatom composition with approximately28 of biogenic silica derived from the sea ice environment diat si can account for the increased averagecompo sition of 30sidiatduring the neoglacial these data highlight the signi cant role sea ice diatoms can playwith relation to their export in sediment records which has implications on productivity reconstructions fromthe seasonal ice zone

a review of the oxygen isotope composition of lacustrine diatom silica for palaeoclimate reconstruction diatom silica frustules are a form of biogenic opal and contain oxygen isotopes that are being increasingly used in palaeoclimate studies frustules are comprised of an inner tetrahedrally bonded silica skeleton si o si with an outer hydrous layer the hydrous layer is freely exchangeable and must be removed prior to oxygen isotope measurement using oxidising reagents and or high temperatures analysis of the oxygen isotope composition of diatom silica requires samples that are almost pure diatomite since extraction techniques will liberate oxygen from all the components in the sediment there is a generally acceptable protocol involving chemistry sieving and settling techniques and more recently laminar flow separation recent studies of lacustrine diatoms have shown that even a small proportion of contaminant can have a significant influence on the oxygen isotope value all lake sediments require their own specific procedure and every sample must be scrutinised by microscopy to check for the level of contamination prior to analysis where sediment cannot be purified sufficiently a semi quantitative assessment of the diatom content can facilitate mass balance techniques when robust preparation methods are used diatom silica offers an important palaeoclimate proxy providing an additional complementary rather than an alternative host of oxygen isotopes in carbonates in lacustrine isotope studies it is often assumed but rarely proven that diatom silica form in isotope equilibrium and hence empirically derived palaeotemperature equations usually made in vitro can be used most studies lack the detailed investigation of contemporaneous materials from natural waters of the region under study to test these equations further investigations need to be conducted in order to understand the systematic relationship between temperature water isotope composition and diatom isotope composition to enable quantitative interpretation of the sediment record experiments to test for vital effects and inter specific differences have so far revealed little variation it is useful to know when and where the diatom silica is formed in the modern environment so details of diatom ecology are important in the interpretation of isotope data here we show that valuable palaeoclimate data can be gained from the oxygen isotope composition of diatom silica 18odiatom especially since diatoms are abundant in many lakes sensitive to climate variation where other hosts e g carbonates are absent to date the most successful studies have been conducted in areas where the 18odiatom registers changes in the oxygen isotope composition of the lake water rather than temperature which is then related to other aspects of climate in these studies the range of values obtained is often greater than the error introduced by contaminating materials

groundwater flow along and across structural folding an example from the judean desert israel abstract the considerable influence of the geological structure on groundwater flow regime is exhibited in the thick carbonate aquifer beneath the judean desert israel groundwater flow is diverted from the general steep hydraulic gradient creating a subsurface river like meandering flow pattern the structure of the extensive folded anticlinorium forces groundwater flow through synclinal axes in the upper aquifer and in places it overflows from one to an adjacent syncline groundwater outflows are at tsukim kane samar and en gedi springs near the dead sea shore and by sub surface flow across the graben faults towards the dead sea in this study all available data are integrated and processed first ever to form a complete representation of the three dimensional hydrostratigraphy and hydrogeology using numerical modeling modflow we analyzed quantitatively the flow regime leakage rates between upper and lower sub aquifers and between adjacent sub basins the groundwater mass balance and aquifer hydraulic properties this study has practical implications regarding recent groundwater management future possibilities of groundwater development for the benefit of both israelis and palestinians residing in the area and conservation of nature reserves located along the dead sea

orbital forcing of glacial interglacial variations in chemical weathering and silicon cycling within the upper white nile basin east africa stable isotope and biomarker evidence from lakes victoria and edward on quaternary time scales the global biogeochemical cycle of silicon is interlocked with the carbon cycle through biotic enhancement of silicate weathering and uptake of dissolved silica by vascular plants and aquatic microalgae notably diatoms for which si is an essential nutrient large tropical river systems dominate the export of si from the continents to the oceans here we investigate variations in si cycling in the upper white nile basin over the last 15 ka using sediment cores from lakes victoria and edward coupled measurements of stable o and si isotopes on diatom separates were used to reconstruct past changes in lake hydrology and si cycling while the abundances of lipid biomarkers characteristic of terrestrial emergent higher plants submerged floating aquatic macrophytes and freshwater algae document past ecosystem changes during the late glacial to mid holocene 15 5 5 ka bp orbital forcing greatly enhanced monsoon rainfall forest cover and chemical weathering riverine inputs of dissolved silica from the lake catchments exceeded aquatic demand and may also have had lower si isotope values since 5 5 ka bp increasingly dry climates and more open vegetation reinforced by the spread of agricultural cropland over the last 3 4 ka have reduced dissolved silica inputs into the lakes centennial to millennial scale dry episodes are also evident in the isotopic records and merit further investigation

last glacial holocene climate variability in the atlantic sector of the southern ocean abstract the southern ocean plays a major role in the glacial interglacial global carbon cycle however there is a substantial lack of information from its antarctic zone south of the polar front pf to understand key climate processes e g sea ice variability productivity changes co2 source region shifts of the southern westerly wind active in this region during the glacial interglacial transition due to the limited high resolution sediment records from this area to close this gap we investigated high resolution diatom records from a series of sediment cores from the atlantic and western indian sectors of the southern ocean between the modern pf and the winter sea ice wsi edge summer sea surface temperature ssst and sea ice information spanning the past 30 thousand years were derived from diatom transfer functions and indicators which augment comprehensive information on past surface ocean conditions and related ocean and atmospheric circulation as well as opal deposition these complementary lines of evidences also provide important environmental boundary conditions for climate simulations understanding the past climate development in the high latitudes southern ocean our reconstructions show that the last glacial lg sssts south of the modern pf are 1 3 c colder than modern conditions wsi expanded to the modern pf our data suggests effective carbon export in the antarctic zone during the lg deglacial two steps of warming support the bipolar seesaw mechanism antarctic zone is an important source region for the co2 deglacial increase the warming was more suppressed towards south due to continuous ice discharge from antarctica the sssts exceeded modern values during the early holocene optimum when wsi extent probably retreated south of its modern position the southern boundary of maximum opal deposition zone may have shifted to south of 55 s in the bouvet island area at this time the mid late holocene cooling with wsi re expanding to the bouvet island area probably related to enhanced cold water export by the weddell gyre from the developing cavity under the west antarctic ice shelf the cooling also suggests a northward shift of the southern westerly wind at least its southern boundary

characterization of the soil hydromorphic conditions in a paludified dunefield during the mid holocene hemlock decline near quebec city quebec abstract the mid holocene eastern hemlock tsuga canadensisl carr decline has been recently attributed to the activity of insect defoliators n bihiry and l filion quaternary research45 312 320 1996 in this study soil hydromorphic conditions were investigated for the period 6800 3200 yr b p using micromorphological data from a peat section from a swale in a paludified dunefield in southern quebec after a short period of plant colonization in shallow pools between 6800 and 6400 yr b p mesic conditions predominated in the interdune before the decline 6400 4900 yr b p as evidenced by strong bioturbation and abundance of excrements from the soil fauna during the decline a shift from mesic to wet conditions occurred 4900 4100 yr b p although xeric to mesic conditions persisted on dune ridges until at least 4200 yr b p wetness culminated when beaver occupied the site 4100 3750 yr b p hemlock needles with chewing damage typical of hemlock looper lambdina fiscellaria feeding were identified at levels dated 4900 4600 and 4200 yr b p respectively implying that the hemlock decline was associated with at least three defoliation events the ca 400 yr interval between these events likely represents the time required for this late sucessional tree species to recover

patterns of regional hydrological variability in central southern altiplano 18 26 s lakes during the last 500 years abstract paleohydrological reconstructions based on sedimentological geochemical and isotopic records from a lake transect in the central southern altiplano 18 26 s indicate abrupt moisture fluctuations during the last 500 years a change to modern conditions occurred in the late 19th century in all the records from northern chile lago chungara 18 15 s and the atacama laguna miscanti 23 45 s to the southern tip of the altiplano laguna el peinado nw argentina 26 30 s a previous drier period shows different patterns of timing duration and intensity in chungara the arid period was shorter and occurred during the late 19th and early 20th centuries while in miscanti it occurred earlier and ended at the beginning of the 20th century in el peinado conditions were wetter during the 17 19th centuries and the arid period occurred prior to the 17th century other records from the region show abrupt paleohydrological and paleoclimatic changes synchronous with the termination of the little ice age despite local differences and dating uncertainties the little ice age stands out as a significant though complex climatic event in the andean altiplano the discrepancies between the northern and southern altiplano records during the last few centuries may reflect contrasting responses to external forcing in two areas with different climatic regimes

the behavior of dissolved uranium in groundwaters of the morro do ferro thorium deposit brazil groundwater samples were collected for several months in boreholes drilled at morro do ferro a thorium and rare earth deposit located on the pocos de caldas plateau minas gerais state brazil an aquifer system has developed in the weathered mantle due to in situ intense alteration the weathered zone includes a thick argillaceous laterite greater than 100 m thick the u content and 324u 238u activity ratio were measured in the groundwater samples and in spoil samples of a borehole drilled in the ore body some possible mechanisms related to the mobilization of uranium are considered such as complexation with humic substances and adsorption by clays

climate catchment runoff and limnological drivers of carbon and oxygen isotope composition of diatom frustules from the central andean altiplano during the lateglacial and early holocene diatom based carbon and oxygen isotope analyses 13cdiatom and 18odiatom were performed on diatom rich laminated sediments of lake chungara andean altiplano northern chile deposited during the lateglacial and early holocene 12 400 8300 cal years bp to reconstruct climate change and environmental response across this major climate transition the 13cdiatom data show both centennial to millennial scale changes related to fluctuations in lake productivity and co2 concentration in the lake water and variations in carbon sources to the lake through time the 18odiatom data reflect changes in lake hydrology and climate the combination of 13cdiatom and 18odiatom data reveals interactions between the internal lake processes and its catchment runoff during wet periods low 18odiatom values 13cdiatom indicates an enhanced contribution of allochthonous carbon whereas during dry periods high 18odiatom 13cdiatom values suggest more autochthonous carbon production and recycling these decadal to centennial oscillations are not recognized after 10 000 cal years bp possibly as a result of enso like phenomenon weakening humid conditions during the lateglacial early holocene transition 12 400 10 100 cal years bp were possibly due to the establishment of la nina like conditions in the tropical south pacific whereas dry conditions in the early holocene 10 100 9100 cal years bp may be caused by the northward migration of the itcz due to both enso like weakening and an insolation minimum finally a return to humid conditions at the end of the early holocene 9100 8300 cal years bp is coincident with an increase in summer insolation

sequence of events during the last deglaciation in southern ocean sediments and antarctic ice cores variation depends on the age model as 14 c determinations cannot be obtained for the time interval of 29 5 14 5 ka assuming a constant sedimentation rate for this interval our data suggest that sea ice and nutrient changes at about 19 ka b p lead the increase in atmospheric pco2 by approximately 2000 years our diatom based sea ice record is in phase with the sodium record of the vostok ice core which is related to sea ice cover and similarly leads the increase in atmospheric co2 if gas exchange played a major role in determining glacial to interglacial co2 variations then a delay mechanism of a few thousand years is needed to explain the observed sequence of events otherwise the main cause of atmospheric pco2 change must be sought elsewhere rather than in the southern ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4267 oceanography general paleoceanography 4845 oceanography biological and chemical nutrients and nutrient cycling 4870 oceanography biological and chemical stable isotopes 9325 information related to geographic region atlantic ocean keywords biogenic opal stable isotopes diatoms ird last glacial southern ocean

lacustrine sedimentation in active volcanic settings the late quaternary depositional evolution of lake chungara northern chile lake chungara 18 15 s 69 09 w 4520 m above sea level is the largest 22ae5 km2 and deepest 40 m lacustrine ecosystem in the chilean altiplano and its location in an active volcanic setting provides an opportunity to evaluate environmental volcanic vs climatic controls on lacustrine sedimentation the late quaternary depositional history of the lake is reconstructed by means of a multiproxy study of 15 kullenberg cores and seismic data the chronological framework is supported by 10 14c ams dates and one 230th 234u dates lake chungara was formed prior to 12ae8 cal kyr bp as a result of the partial collapse of the parinacota volcano that impounded the lauca river the sedimentary architecture of the lacustrine succession has been controlled by i the strong inherited palaeo relief and ii changes in the accommodation space caused by lake level fluctuations and tectonic subsidence the first factor determined the location of the depocentre in the nw of the central plain the second factor caused the area of deposition to extend towards the eastern and southern basin margins with accumulation of high stand sediments on the elevated marginal platforms synsedimentary normal faulting also increased accommodation and increased the rate of sedimentation in the northern part of the basin six sedimentary units were identified and correlated in the basin mainly using tephra keybeds unit 1 late pleistocene early holocene is made up of laminated diatomite with some carbonate rich calcite and aragonite laminae unit 2 mid holocene recent is composed of massive to bedded diatomite with abundant tephra lapilli and ash layers some carbonate rich layers calcite and aragonite occur unit 3 consists of macrophyte rich diatomite deposited in nearshore environments unit 4 is composed of littoral sediments dominated by alternating charophyterich and other aquatic macrophyte rich facies littoral carbonate productivity peaked when suitable shallow platforms were available for charophyte colonization clastic deposits in the lake are restricted to lake margins units 5 and 6 diatom productivity peaked during a lowstand period unit 1 and subunit 2a and was probably favoured by photic conditions affecting larger areas of the lake bottom offshore carbonate precipitation reached its maximum during the early to mid holocene ca 7ae8 and 6ae4 cal kyr bp this may have been favoured by increases in lake solute concentrations resulting from evaporation and calcium input because of the compositional changes in pyroclastic supply diatom and pollen data from offshore cores suggest a number of lake level fluctuations a late pleistocene deepening episode ca 12ae6 cal kyr bp four shallowing episodes during the early to mid holocene ca 10ae5 9ae8 7ae8 and 6ae7 cal kyr bp and higher lake levels since the mid holocene ca 5ae7 cal kyr bp until the present explosive activity at parinacota volcano was very limited between c 12ae8 and 7ae8 cal kyr bp mafic rich explosive eruptions from the ajata satellite cones increased after ca 5ae7 cal kyr bp until the present

numerical analysis of the groundwater regime in the western dead sea escarpment israel west bank water is scarce in the semi arid to arid regions around the dead sea where water supply mostly relies on restricted groundwater resources due to increasing population in this region the regional aquifer system is exposed to additional stress this results in the continuous decrease in water level of the adjacent dead sea the interaction of an increasing demand for water due to population growth and the decrease of groundwater resources will intensify in the near future thus the water supply situation could worsen significantly unless sustainable water resource management is conducted in this study we develop a regional groundwater flow model of the eastern and southern judea group aquifer to investigate the groundwater regime in the western dead sea drainage basin of israel and the west bank an extensive geological database was developed and consequently a high resolution structural model was derived this structural model was the basis for various groundwater flow scenarios the objective was to capture the spatial heterogeneity of the aquifer system and to apply these results to the southern part of the study area which has not been studied in detail until now as a result we analyzed quantitatively the flow regime the groundwater mass balance and the hydraulic characteristics hydraulic conductivity and hydraulic head of the cretaceous aquifer system and calibrated them with pest the calibrated groundwater flow model can be used for integrated groundwater water management purposes in the dead sea area especially within the framework of the sumar project

characterization of trace elements and carbon isotopes across the ediacaran cambrian boundary in anhui province south china implications for stratigraphy and paleoenvironment reconstruction abstract characteristics of redox sensitive elements and organic carbon isotopes of a drilling section covering the ediacaran cambrian e c boundary at anhui province south china were studied total organic carbon toc organic carbon isotope values of organic compounds abundances of mo v u and ni and ratios of v v ni and th u co vary across the section suggesting that the redox condition is the main factor controlling carbon isotope values of organic matter and sequestration of trace elements the e c boundary is characterized by the lowest organic carbon isotope and the highest ratios of mo toc v toc and u toc in the section which are correlated with reported carbon isotope excursions in other regions this is the first time that signatures of mo v and u in the hetang formation at the lower yangtze platform are used for stratigraphic correlations the results highlight abnormally high ratios of mo toc v toc and u toc near the e c boundary petrological and geochemical characteristics in this section suggests that intense upwelling activities during the e c transition may be the main contributor to 13 c depleted co 2 and enrichment of trace metals the co existing pervasive transgression led to ocean anoxia and facilitated the preservation of 13 c depleted organic matter and trace metal sequestration furthermore oxidation of the bottom ocean water may have completed during the early cambrian a combination of these factors may be among the reasons for significant evolutionary changes during the e c transition

extensive phytoplankton blooms in the atlantic sector of the glacial southern ocean 1 the sources and sinks of atmospheric carbon dioxide over glacial interglacial cycles are under debate variation in productivity of the antarctic circumpolar current acc could potentially play a significant role but current interpretations of sedimentary geochemical proxies suggest that glacial productivity was not higher than today we present areal and down core distribution patterns of previously overlooked diatom resting spores that indicate the occurrence of extensive phytoplankton blooms across the entire atlantic sector of the acc particularly in the seasonal ice zone siz linked to higher iron input during the last glacial sea ice acts as an effective transporter of iron and enhances its bioavailability the dominance of the deep living radiolarian cyladophora davisiana in glacial siz sediments indicates that organic carbon export to mesopelagic depths was at least tenfold higher than today

revisiting nutrient utilization in the glacial antarctic evidence from a new method for diatom bound n isotopic analysis holocene in the indian sector is smaller than in previous measurements these data suggest no change in the degree of nitrate utilization in the atlantic sector and at most a 20 increase from 25 to 45 in the indian sector the new measurements suggest that during the last ice age in the atlantic sector of the antarctic the atmospheric source of biologically available iron was not so great as to become significant relative to the iron supply from below given the apparent spatial variability in the degree of nitrate drawdown more work is required to develop an adequate picture of the glacial antarctic nutrient field index terms 4806 oceanography biological and chemical carbon cycling 4845 oceanography biological and chemical nutrients and nutrient cycling 4894 oceanography biological and chemical instruments and techniques 9310 information related to geographic region antarctica

variation in holocene el nino frequencies climate records and cultural consequences in ancient peru analysis of mollusks from archaeological sites on the north and central coasts of peru indicates that between ca 5800 and 3200 2800 cal yr b p el nino events were less frequent than today with modern rapid recurrence intervals achieved only after that time for several millennia prior to 5 8 ka el nino events had been absent or very different from today the phenomena called el nino have had severe consequences for the modern and colonial historically recorded inhabitants of peru and el nino events also influenced prehistoric cultural development the onset of el nino events at 5 8 ka correlates temporally with the beginning of monumental temple construction on the peruvian coast and the increase in el nino frequency after 3 2 2 8 ka correlates with the abandonment of monumental temples in the same region

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

el nino like pattern in ice age tropical pacific sea surface temperature sea surface temperatures ssts in the cold tongue of the eastern equatorial pacific exert powerful controls on global atmospheric circulation patterns we examined climate variability in this region from the last glacial maximum lgm to the present using a sst record reconstructed from magnesium calcium ratios in foraminifera from sea floor sediments near the galapagos islands cold tongue sst varied coherently with precession induced changes in seasonality during the past 30 000 years observed lgm cooling of just 1 2 c implies a relaxation of tropical temperature gradients weakened hadley and walker circulation southward shift of the intertropical convergence zone and a persistent el nino like pattern in the tropical pacific this is contrasted with mid holocene cooling suggestive of a la nina like pattern with enhanced sst gradients and strengthened trade winds our results support a potent role for altered tropical pacific sst gradients in global climate variations

diatom δ13c δ15n and c n since the last glacial maximum in the southern ocean potential impact of species composition measurements of delta c 13 delta n 15 and c n on diatom bound organic matter were made over the holocene and last glacial maximum lgm from three sediment cores in the southern ocean one each from the atlantic indian and pacific sectors the site in the scotia sea atlantic sector differed considerably from the other two sites by having markedly lower delta c 13 more variable delta n 15 and c n ratios and a sedimentary diatom assemblage that was never dominated by fragilariopsis kerguelensis although environmental parameters certainly have a strong impact on the isotope ratios delta c 13 is also correlated to the proportion of f kerguelensis in the three cores investigated here r 2 0 8 extreme values of delta c 13 delta n 15 and c n at the last glacial maximum were also related to the abundance of winter stages of eucampia antarctica these results suggest that diatom specific isotope records should be interpreted in conjunction with information on the species composition of the samples

evolution of the lake titicaca basin and its diatom flora over the last 370 000 years abstract in recent years deep drilling undertaken as part of the international continental drilling program has generated multiple long lacustrine sedimentary records to reconstruct continental paleoclimate in many cases the tectonic and geomorphic history of these basins is under constrained and poorly known which affects the interpretation of climate history from geophysical geochemical and paleobiotic proxies in the sedimentary record in addition non analog biotic assemblages that reflect evolutionary processes may constrain the reconstruction of past environments in the drill core record of lake titicaca spanning the last 370 ka the diatom stratigraphy reflects both the influence of climate and the long term evolution of the lake basin and its biota in the upper part of the drill core sequence glacial intervals were deep and dominated by freshwater planktic taxa and peak interglacial intervals were shallow and dominated by benthic species some with saline affinities in the basal sections of the drill core record benthic diatoms are dominant in both glacial and interglacial units with freshwater taxa dominating the glacial strata this suggests that the ancient lake basin was shallower during intervals of both wet and dry climate and that the modern deep lake may result from a progressive subsidence and deepening of the basin over time in addition morphological evolution in one of the major lineages of planktic diatoms cyclostephanos indicates substantial change in the limnological environment that affected species morphology and may have driven speciation

reconciling down core anticorrelation of diatom carbon and nitrogen isotopic ratios from the southern ocean 1 oceanic nutrient cycling in the southern ocean is supposed to have an important impact on glacial interglacial atmospheric co2 changes and global climate in order to characterize such nutrient cycling over the last two climatic cycles we investigated carbon and nitrogen isotopic ratios of diatom bound organic matter 13cdiat and 15ndiat respectively in two cores retrieved form the atlantic and indian sectors of the antarctic ocean the two cores show the same isotopic patterns the 13cdiat values are depleted during glacial periods and enriched during interglacial periods indicating lower productivity during cold times the 15ndiat values are enriched during glacial periods and depleted during interglacial periods arguing for greater nitrate utilization during cold times taken at face value this apparent contradiction leads to opposite conclusions on the role of the southern ocean biological pump on the atmospheric co2 changes however the two sets of data can be reconciled by a sea ice plus mixing rate scenario that calls upon a balance between the effect of cutting off gas transfer at the ocean atmosphere boundary and the effect of reducing vertical transport of nutrients through the pycnocline

self sedimentation of phytoplankton blooms in the geologic record abstract understanding the formation of laminated organic rich sediments is an essential topic for researchers interested in fossil fuels biogeochemical cycles earth s environmental history and global change biologists have very recently demonstrated that some marine phytoplankton blooms actively govern their own sedimentation by the formation of sticky transparent gels that facilitate rapid aggregation accelerated sinking and efficient export flux here we present fossil evidence of unfragmented low diversity phytoplankton assemblages preserved as sedimentary laminae and irregular flocs that are attributable to a similar phytoplankton driven sedimentary mechanism we term self sedimentation the geological evidence suggests that self sedimentation precludes significant heterotrophic grazing propels the formation of some conspicuous hemipelagic sedimentary laminae and results in efficient carbon and opal flux to the sediments we suggest that the self sedimentation phenomenon may have broad implications for the geological history of biogeochemical cycling oceanic ecological dynamics and abrupt atmospheric environmental change broader recognition of the self sedimentation phenomenon as explicitly defined here is a prerequisite to testing these unconventional hypotheses

the reconstruction of late quaternary antarctic sea ice distribution the use of diatoms as a proxy for sea ice the study of annual diatom transfer from the southern ocean surface to the sea floor using time series sediment traps combined with the mapping of diatom assemblages from surface sediments results in the definition of a proxy for past variations of sea ice extent the application and robustness of the proposed proxy are demonstrated by the study of late pleistocene sediment cores recovered from different environmental regimes in the southern ocean relative amounts of the sea ice indicator diatoms fragilariopsis cylindrus and fragilariopsis curta of 3 in diatom assemblages preserved in sediments are representative of the presence of seasonal winter sea ice summer sea ice occurrence is signalled by a distinct drop in biogenic sedimentation rate as a result of strongly reduced biogenic export in the presence 3 of diatom assemblage of the deep temperature diatom fragilariopsis obliquecostata the spatial and temporal distribution pattern of the sea ice proxy indicates significant sea ice variations during marine isotope stages 1 and 5 in the present antarctic zone of the southern ocean during glacial maxima the antarctic winter sea ice was extended into the present polar front zone while the antarctic summer sea ice was most probably expanded into the area of the present winter sea ice edge during the short climatic optima at the onset of interglacial periods the winter sea ice extent was distinctly reduced

biogeochemical processes controlling oxygen and carbon isotopes of diatom silica in late glacial to holocene lacustrine rhythmites biogeochemical cycles and sedimentary records in lakes are related to climate controls on hydrology and catchment processes changes in the isotopic composition of the diatom frustules 18odiatom and 13cdiatom in lacustrine sediments can be used to reconstruct palaeoclimatic and palaeoenvironmental changes the lago chungara andean altiplano 18 15 s 69 10 w 4520 masl diatomaceous laminated sediments are made up of white and green multiannual rhythmites white laminae were formed during short term diatom super blooms and are composed almost exclusively of large sized cyclostephanos andinus these diatoms bloom during mixing events when recycled nutrients from the bottom waters are brought to the surface and or when nutrients are introduced from the catchment during periods of strong runoff conversely the green laminae are thought to have been deposited over several years and are composed of a mixture of diatoms mainly smaller valves of c andinus and discostella stelligera and organic matter these green laminae reflect the lake s hydrological recovery from a status favouring the diatom super blooms white laminae towards baseline conditions 18odiatom and 13cdiatom from 11 990 to 11 530 cal years bp allow us to reconstruct shifts in the precipitation evaporation ratio and changes in the lake water dissolved carbon concentration respectively 18odiatom values indicate that white laminae formation occurred mainly during low lake level stages whereas green laminae formation generally occurred during high lake level stages the isotope and chronostratigraphical data together suggest that white laminae deposition is caused by extraordinary environmental events el nino southern oscillation and changes in solar activity are the most likely climate forcing mechanisms that could trigger such events favouring hydrological changes at interannual to decadal scale this study demonstrates the potential for laminated lake sediments to document extreme pluriannual events

holocene dynamics of an eastern hemlock tsuga canadensis forest site at the northern range of the species limit eastern hemlock tsuga canadensis is a shade tolerant tree of the temperate conifer hardwood forests of northeastern north america whose northern limit of distribution coincides with the st lawrence river around quebec city canada we have analyzed the structure and dynamics of one of the very few old growth hemlock stands in this area to evaluate its successional status at the holocene scale to document the origin and long term development of the hemlock site we have used conventional forest surveys and macrofossil analysis of woody debris and charcoal pieces at the soil surface and buried in the mineral soil the riviere du moulin hemlock forest is an old growth forest at least 1000 years old whose structure has been rejuvenated by recurrent surface fires killing most plants of the shaded forest floor and facilitating hemlock regeneration according to the number of fires and the corresponding fire intervals the hemlock site experienced a sustained fire regime since the mid holocene first in

use of u isotopes in exploring groundwater flow and inter aquifer leakage in the south western margin of the great artesian basin and arckaringa basin central australia abstract the distribution of uranium isotopes 238u and 234u in groundwaters of the south western margin of the great artesian basin gab australia and underlying arckaringa basin were examined using groundwater samples and a sequential extraction of aquifer sediments rock weathering the geochemical environment and recoil of daughter products control the 238u and 234u isotope distributions giving rise to large spatial variations generally the shallowest aquifer j aquifer contains groundwater with higher 238u activity concentrations and 234u 238u activity ratios close to secular equilibrium however the source input of uranium is spatially variable as intermittent recharge from ephemeral rivers passes through rocks that have already undergone extensive weathering and contain low 238u activity concentrations other locations in the j aquifer that receive little or no recharge contain higher 238u activity concentrations because uranium from localised uranium rich rocks have been leached into solution and the geochemical environment allows the uranium to be kept in solution the geochemical conditions of the deeper aquifers generally result in lower 238u activity concentrations in the groundwater accompanied by higher 234u 238u activity ratios the sequential extraction of aquifer sediments showed that recoil of 234u from the solid mineral phases into the groundwater rather than dissolution of or exchange with the groundwater accessible minerals in the aquifer caused enrichment of groundwater 234u 238u activity ratios in the boorthanna formation decay of 238u in uranium rich coatings on j aquifer sediments caused resistant phase 234u 238u activity ratio enrichment the groundwater 234u 238u activity ratio is dependent on groundwater residence time or flow rate depending on the flow path trajectory thus uranium isotope variations confirmed earlier groundwater flow interpretations based on other tracers however spatial heterogeneity and the lack of clear regional correlations made it difficult to identify recharge and inter aquifer leakage