what is diatomite different types of biogenic remains ranging from siliceous algae to carbonate precipitates accumulate in the sediments of lakes and other aquatic ecosystems unicellular algae called diatoms which form a siliceous test or frustule are an ecologically and biogeochemically important group of organisms in aquatic environments and are often preserved in lake or marine sediments when diatoms accumulate in large numbers in sediments the fossilized remains can form diatomite in sedimentological literature diatomite is defined as a friable light coloured sedimentary rock with a diatom content of at least 50 however in the quaternary science literature diatomite is commonly used as a description of a sediment type that contains a large quantity of diatom frustules without a precise description of diatom abundance here we pose the question what is diatomite what quantity of diatoms define a sediment as diatomite is it an uncompacted sediment or a compacted sediment we provide a short overview of prior practices and suggest that sediment with more than 50 of sediment weight comprised of diatom sio2 and having high 70 porosity is diatomaceous ooze if unconsolidated and diatomite if consolidated greater burial depth and higher temperatures result in porosity loss and recrystallization into porcelanite chert and pure quartz less

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

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

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

a 25 000 year record of climate induced changes in lowland vegetation of eastern equatorial africa revealed by the stable carbon isotopic composition of fossil plant leaf waxes the debate of climate versus co2 in controlling the long term dynamics of tropical african vegetation has focused on events at the upper tree line since the relevant paleodata tend to be from mid elevation sites 2000 3000 m less well known is the relative importance of co2 in regulating the dynamics of tropical lowland 1500 m vegetation particularly that of the dry open woodlands bush and grasslands covering much of eastern equatorial africa here we examine the stable carbon isotopic composition of n alkanes in the sediment record of lake challa a lowland crater lake near mt kilimanjaro covering the last 25 000 years the distributions of the n alkanes with dominance of the long chain odd carbon numbered components and their isotopic composition reveal a mixed origin the c23 and c25 n alkanes are depleted in 13c with 13c values between 30 and 50 in shallow lakes these n alkanes are thought to derive from non emergent aquatic plants but this is unlikely in this steep sided crater lake as it lacks a significant littoral habitat the c27 n alkanes are predominantly derived from leaf wax lipids of terrestrial plants brought into the lake predominantly by local soil run off their 13c values in particular that of the n c31 alkane reveal a marked transition in local lowland vegetation from being dominated 70 100 by c4 plants during the glacial period until 16 5 cal kyr bp to a more mixed c3 c4 composition 30 60 c4 during the holocene the start of the late glacial trend towards a greater proportion of c3 plants coincided with the start of increasing monsoon rainfall 1500 years after the onset of the rise in atmospheric co2 and 3500 years after the onset of post glacial warming the transition was interrupted during the dry younger dryas period 13 0 11 7 cal kyr bp when c4 plants again became much more prevalent almost reaching their glacial period abundance notably the principal trend in leaf wax 13c values infers c4 dominance during both wet and dry phases of the glacial period and a mixed c3 c4 vegetation during both wet and dry phases of the holocene our results indicate that long term variation in pco2 exerted important control on the composition of drought adapted savanna vegetation in this currently semi arid lowland region of equatorial east africa

high resolution 14c dating of a 25 000 year lake sediment record from equatorial east africa abstract we dated a continuous 22 m long sediment sequence from lake challa mt kilimanjaro area kenya tanzania to produce a solid chronological framework for multi proxy reconstructions of climate and environmental change in equatorial east africa over the past 25 000 years the age model is based on a total of 168 ams 14 c dates on bulk organic matter combined with a 210 pb chronology for recent sediments and corrected for a variable old carbon age offset this offset was estimated by i pairing bulk organic 14 c dates with either 210 pb derived time markers or 14 c dates on grass charcoal and ii wiggle matching high density series of bulk organic 14 c dates variation in the old carbon age offset through time is relatively modest ranging from 450 yr during glacial and late glacial time to 200 yr during the early and mid holocene and increasing again to 250 yr today the screened and corrected 14 c dates were calibrated sequentially statistically constrained by their stratigraphical order as a result their constrained calendar age distributions are much narrower and the calibrated dates more precise than if each 14 c date had been calibrated on its own the smooth spline age depth model has 95 age uncertainty ranges of 50 230 yr during the holocene and 250 550 yr in the glacial section of the record the 13 c values of paired bulk organic and grass charcoal samples and additional 14 c dating on selected turbidite horizons indicates that the old carbon age offset in lake challa is caused by a variable contribution of old terrestrial organic matter eroded from soils and controlled mainly by changes in vegetation cover within the crater basin

reconstruction of a subalpine grass dominated ecosystem lake rutundu mount kenya a novel multi proxy approach palaeoecological reconstructions based on a single proxy are limited but by combining pollen biogeochemistry and grass cuticle analysis ecosystem structure and function can be better understood lake rutundu is a small subalpine lake on the northeast flank of mt kenya during the last glacial pollen evidence suggests a shrub grassland dominated by afroalpine taxa and poaceae representing a dry cold open environment the 13c values of terrestrial biomarkers imply a high proportion of c4 plants grass cuticle analysis allows resolution of the different c4 subtypes and shows that the vegetation was dominated by tall c4 panicoid grasses prone to frequent fires during the holocene poaceae pollen declined while subalpine shrubs increased the 13c values of terrestrial biomarkers imply a c3 dominated vegetation together with an expansion of rainforest at lower altitudes this suggests wetter conditions more favourable to c3 plants increased percentages of c3 pooid grass cuticles confirm a reduction in moisture stress

anthropogenic organic matter in the great marsh of the indiana dunes national lakeshore and its implications abstract cores from the great marsh area of the indiana dunes national lakeshore were examined in order to document variations in concentration type and size of anthropogenic organic matter anom coal coke etc and discuss their relationship to the concentration of such trace elements as pb zn and mn in the near surface sediment section the results indicate that the first appearance of anom corresponds to the onset of industrialization in the area there is also a general relationship between the occurrence of anom and zn pb and mn trace metals were likely transported from the industrial sites to the area of their deposition as sulfur bearing coatings on small anthropogenic particles after deposition these sulfur bearing compounds reacted with organic matter within the marsh as a result of bacterial reduction the pyrite was produced as suggested by a close relationship between the pyrite and anom distance from the industrial complex upwind as well as local hydrologic conditions are among the major factors controlling distribution of anom and trace elements at the same distance from the source types and sizes of anom are influenced by the duration and frequency of flooding

late quaternary changes in carbon cycling on mt kenya east africa an overview of the δ13c record in lacustrine organic matter abstract the 13 c signature of sedimentary organic matter acts as a tracer for past changes in the terrestrial and aquatic carbon cycles compound specific 13 c analysis enables these two signals to be disentangled we compare the molecular isotopic records from a transect of five lakes between 1820 and 4595 m a s l on mt kenya east africa spanning the last 100 000 years with multiproxy palaeoenvironmental data in order to determine the mechanisms underlying late quaternary variations in carbon cycling at different altitudes the amplitude of down core variations in the 13 c values of total organic carbon varied from 4 8 to 17 4 the 13 c signals in compounds of terrestrial aquatic macrophyte and algal origin were tightly coupled reflecting strong atmospheric control during the early glacial and the last glacial maximum the effects of sub ambient co 2 and enhanced moisture stress reinforced each other resulting in carbon starvation and very high 13 c values in contrast smaller millennial scale shifts in 13 c during the late glacial and holocene were driven primarily by fluctuations in monsoon precipitation however the impact of late quaternary atmospheric changes were complex involving variations in biomass burning vegetation cover soil erosion lake levels and water chemistry in addition to direct physiological responses by higher plants and algae

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

late quaternary changes in ecosystems and carbon cycling on mt kenya east africa a landscape ecological perspective based on multi proxy lake sediment influxes abstract the degree to which different lakes within a landscape respond coherently in unison to external drivers such as climate change and soil development is uncertain presentation of multi proxy geochemical and palaeoecological data from individual lakes in the form of fluxes minimizes distortions resulting from variable sedimentation rates and changes in sediment composition we use the accumulation rates of magnetic minerals total organic c and n terrestrial and aquatic biomarkers graminoid epidermis pollen green algae diatoms and diatom c in four small lakes situated between 2350 and 4595 m a s l on the ne flank of mt kenya east africa to reconstruct changes in c cycling over the last 38 ka the results conflict with earlier models of landscape and lake development showing 1 that glacial interglacial changes in vegetation cannot be interpreted as simple altitudinal shifts in the modern vegetation belts and 2 that limnological changes were not coherent rapid variations in climate water level erosion and nutrient input overwhelmed long term successional trends in lake sedimentation and c accumulation since the last glacial maximum the results also reveal previously unrecognized features of the palaeoenvironmental record such as the rapid degradation of organic matter in diatoms and the occurrence of a productive fire prone montane grassland during the highly seasonal monsoonal climate of the lateglacial and early holocene

seasonality in equatorial climate over the past 25 k y revealed by oxygen isotope records from mount kilimanjaro multiproxy analysis of a well dated 25 ka lake sediment sequence from lake challa on the eastern flank of mount kilimanjaro east africa reveals the climatic controls that govern both the lake s paleohydrology and the climate proxy record contained in the mountain s receding ice cap the oxygen isotope record extracted from diatom silica 18odiatom in lake challa sediments captured dry conditions during the last glacial period and a wet late glacial transition to the holocene interrupted by younger dryas drought further it faithfully traced gradual weakening of the southeastern monsoon during the holocene overall 18odiatom matches the branched isoprenoid tetraether bit index of rainfall induced soil runoff except during 25 22 ka and the past 5 k y when insolation forcing due to orbital precession enhanced the northeastern monsoon this pattern arises because during these two periods a weakened southeastern monsoon reduced the amount of rainfall during the long rainy season and enhanced the opposing effect of evaporation intensity and or length of the austral winter dry season importantly our lake based reconstruction of moisture balance seasonality in equatorial east africa also helps us understand the oxygen isotope record contained in mount kilimanjaro ice negative correlation between ice core 18o and lake challa 18odiatom implies that moisture balance is not the primary climate control on the long term trend in ice core 18o

half precessional dynamics of monsoon rainfall near the east african equator extensive records exist with which to assess the relationship between external climate forcings such as changes in insolation and climate variability for middle and high latitudes but records from equatorial regions are relatively few especially from regions experiencing the passage of the intertropical convergence zone a continuous and well resolved climate proxy record of hydrological variability during the past 25 000 years from equatorial east africa is now presented and analysed

organic geochemical records of environmental variability in lake malawi during the last 700 years part i the tex86 temperature record abstract we have applied the tex86 paleothermometer to produce a surface water temperature record for lake malawi spanning the past 700 years over much of the record temperature fluctuates from 24 27 c with a mean of 25 c however there has been a substantial increase in temperature of 2 0 c during the past 100 years the tex86 temperature record reveals a strong similarity to the instrumental record both records demonstrate warming 0 7 1 4 c over the past 50 years as well as a cooling anomaly around 1959 comparison of the tex86 temperature record with the proxy records of primary productivity suggests that wind induced upwelling and or precipitation have a strong influence on the surface temperature of lake malawi

the seismic stratigraphic record of lake level fluctuations in lake challa hydrological stability and change in equatorial east africa over the last 140 kyr abstract seismic reflection data from crater lake challa mt kilimanjaro equatorial east africa reveal a 210 m thick sedimentary infill containing distinct seismic stratigraphic signatures of late quaternary lake level fluctuations extrapolation of a well constrained age model on the cored upper part of the sequence suggests that these lake level fluctuations represent a detailed and continuous record of moisture balance variation in equatorial east africa over the last 140 kyr this record indicates that the most severe aridity occurred during peak penultimate glaciation immediately before 128 kyr bp coeval with heinrich event 11 and during a last interglacial megadrought period between 114 and 97 kyr bp in comparison last glacial maximum lgm aridity was modest it was preceded by 75 000 years of relatively stable and moist climate conditions interrupted by eleven short lived dry spells five of which match the timing of heinrich events 2 to 6 climate history near the east african equator reflects variation in the precessional forcing of monsoon rainfall modulated by orbital eccentricity but precession driven moisture fluctuations were less extreme than those observed in northern and southern tropical africa the near continuous moist climate from 97 to 20 5 kyr bp recorded in the lake challa record contrasts with the trend towards greater aridity after 70 kyr bp documented in equatorial west africa this long period of moist glacial climate and a short relatively modest lgm drought can be attributed to greater independence of western indian ocean monsoon dynamics from northern high latitude glaciation than those in the tropical atlantic ocean this rather persistent moist glacial climate regime may have helped maintain high biodiversity in the tropical forest ecosystems of the eastern arc mountains in tanzania

distribution of tetraether lipids in the 25 ka sedimentary record of lake challa extracting reliable tex86 and mbt cbt palaeotemperatures from an equatorial african lake the distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether gdgt lipids was studied in the sedimentary record of lake challa a permanently stratified partly anoxic crater lake on the southeastern slope of mt kilimanjaro kenya tanzania to examine if the gdgts could be used to reconstruct past variation in regional temperature the study material comprised 230 samples from a continuous sediment sequence spanning the last 25 ka with excellent age control based on high resolution ams c 14 dating the distribution of gdgts showed large variation through time in some time intervals i e from 20 4 to 15 9 ka bp and during the younger dryas 12 9 11 7 ka bp crenarchaeol was the most abundant gdgt whereas at other times i e during the early holocene branched gdgts and gdgt 0 were the major gdgt constituents in some intervals of the sequence the relative abundance of gdgt 0 and gdgt 2 was too high to be derived exclusively from lacustrine thaumarchaeota suggesting a sizable contribution from methanogens and other archaea this severely complicated application of tex86 palaeothermometry in this lake and limited reliable reconstruction of lake water temperature to the time interval 25 13 ka bp i e the last glacial maximum and the period of post glacial warming the tex86 inferred timing of this warming is similar to that recorded previously in two of the large african rift lakes while its magnitude is slightly or much higher than that recorded at these other sites depending on which lake based tex86 calibration is used application of calibration models based on distributions of branched gdgts developed for lakes inferred temperatures of 15 18 degrees c for the last glacial maximum and 19 22 degrees c for the holocene however the mbt cbt palaeothermometer reconstructs temperatures as low as 12 degrees c for a lateglacial period centred on 15 ka bp variation in down core values of the bit index are mainly determined by the varying production rate of crenarchaeol relative to in situ produced branched gdgts the apparent relationship of the bit index with climatic moisture balance can be explained either by the direct influence of lake level and wind strength on nutrient recycling or by influx of soil nutrients promoting aquatic productivity and nitrification this study shows that gdgts can aid in obtaining climatic information from lake records but that the obtained data should be interpreted with care

late pleistocene oxygen isotope records of biogenic silica from the atlantic sector of the southern ocean we determined the isotopic composition of oxygen in marine diatoms in eight deep sea cores recovered from the atlantic sector of the southern ocean the analytical reproducibility and core to core consistency of the isotopic signal suggests that diatom 18o can be used as a new paleocenographic tool to reconstruct past variations in surface water characteristics and to generate 18o isotope based stratigraphy for the southern ocean the data indicate that diatom 18o reflects sea surface temperature and seawater isotopic composition and that diatoms retain their isotopic signal on timescales of a least 430 ka the 18o analyses of different diatom assemblages reveal that the isotopic signal is free of species effects and that the common antarctic species have the same water opal fractionation the transition from the last glacial maximum lgm to the holocene is fully recorded in high sedimentation rate cores an 18o enrichment during the lgm a post lgm meltwater spike and an input of meltwater during the late holocene are the main isotopic features observed in down core records the origin of this meltwater was very likely melting icebergs and or continental ice or by melting sea ice that had accumulated snow the most pronounced meltwater effects are recorded in cores that are associated with the weddel gyre our results provide the basis for extending isotope studies to oceanic regions devoid of carbonate further isotopic stratigraphies may be constructed for records and regions where they were previously not possible

late pleistocene temperature history of southeast africa a tex86 temperature record from lake malawi we present a tex86 derived surface water temperature record for lake malawi that provides the first continuous continental record of temperature variability in the continental tropics spanning the past similar to 74 kyr with millennial scale resolution average temperature during marine isotope stage mis 5a was 26 5 degrees c with a range from 25 7 to 27 3 degrees c comparable to holocene temperatures mis 4 was a relatively cold period with temperatures generally decreasing from 25 5 degrees c at 68 ka to a minimum of 20 degrees cat similar to 60 ka 1 5 2 degrees c colder than the last glacial maximum lgm termination of mis 4 is characterized by a rapid increase of 3 4 degrees c in only similar to 0 5 kyr temperatures were relatively stable throughout mis 3 at the resolution of this study with an average of 23 8 degrees c and a range from 25 1 to 22 9 degrees c the lack of millennial scale temperature variability during mis 3 suggests that lake malawi s documented response to the bipolar seesaw brown et al 2007 is not reflected in its thermal history our temperature estimates for the lgm and holocene are consistent with a previously published tex86 record from lake malawi with a temperature of similar to 22 6 degrees c for the lgm similar to 25 26 degrees c in the mid holocene and similar to 25 28 for the late holocene in general the present extended tex86 record indicates that temperature variability in tropical east africa during late mis 5 and mis 4 was as great as that associated with the deglaciation and holocene a decrease in southern hemisphere insolation between 70 and 60 ka may have played an important role in forcing temperatures during mis 4 but after 60 ka other factors such as the extent of the polar ice sheets or atmospheric co2 may have forced temperature in tropical africa to a greater extent than local summer insolation

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

physical and biogeochemical limits to internal nutrient loading of meromictic lake kivu lake kivu is one of the large african rift lakes situated between the democratic republic of the congo and rwanda in its permanently stratified hypolimnion unusually high methane concentrations have increased further in recent decades because methanogenesis is in part dependent on supply of organic material from the photic zone it is necessary to quantify upward nutrient fluxes from the saline nutrient rich deep waters these upward fluxes are mainly driven by advection caused by subaquatic springs biogenic calcite precipitation drives surface water depletion and deep water enrichment of ca2 s r 2 and ba2 methane is mainly oxidized aerobically at the redox interface at 60 m with a small contribution of anaerobic methane oxidation a subaquatic spring that sustains the major chemocline at 250 m depth was depleted of n p and ch4 and concentrations of major ions were slightly lower than in the lake water of the same depth enrichment of the deep waters with nutrients and ch4 are driven by mineralization of settling organic material whereas sio2 is influenced by uptake and mineralization of diatoms and inputs through subaquatic springs dissolved inorganic phosphorus and si fluxes supplied by internal loading through upwelling were found to be lower than the estimations for lakes malawi and tanganyika in contrast n flux was within the lower range for lake malawi whereas it was assumed to be totally lost by denitrification in lake tanganyika in lake kivu nutrient uptake by primary production is three times higher than nutrient upward fluxes

northern hemisphere controls on tropical southeast african climate during the past 60 000 years the processes that control climate in the tropics are poorly understood we applied compound specific hydrogen isotopes d and the tex86 tetraether index of 86 carbon atoms temperature proxy to sediment cores from lake tanganyika to independently reconstruct precipitation and temperature variations during the past 60 000 years tanganyika temperatures follow northern hemisphere insolation and indicate that warming in tropical southeast africa during the last glacial termination began to increase 3000 years before atmospheric carbon dioxide concentrations d data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial scale events recorded in northern hemisphere monsoonal climate records this implies that precipitation in tropical southeast africa is more strongly controlled by changes in indian ocean sea surface temperatures and the winter indian monsoon than by migration of the intertropical convergence zone

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

deterministic approach for susceptibility assessment of shallow debris slide in the darjeeling himalayas india abstract high magnitude rainfall triggers numerous shallow debris slides in the darjeeling himalayas causing widespread damage to the environment loss of life and property thin soil cover and steep topography make the region vulnerable to debris slides the objective of the present study is to assess the susceptibility of the eastern part of darjeeling himalayas covering about 330 km2 to shallow debris slides through the functional relationship of hillslope hydrology and mechanical properties of slope materials deterministic approach based shallow landsliding stability shalstab model following mohr coulomb failure law was adopted to assess landslide susceptibility topographical parameters were derived from 8 m resolution cartosat 1 digital elevation model dem and mechanical properties of soil were obtained from an analysis of 15 soil samples for slope stability assessment the topographical and soil parameters were put into three different scenarios i assuming the surface entirely free from vegetation model 1 ii involving the role of vegetation root cohesion model 2 and iii surcharge of vegetation buildings and other structures along with root cohesion model 3 these predictive models were used to classify the area into various susceptibility classes with specific amounts of critical rainfall qc the result shows that 28 9 and 10 of the study area come under unconditionally unstable class in the three models respectively about 22 land in model 1 and 42 in each model 2 and model 3 come under unconditionally stable class protective capacity of roots against debris slide played a significant role in model 2 and model 3 performance of models was validated by comparison of observed predicted landslide areas and the area under the receiver operating characteristic roc curve it is found that the overall success rate of all the three models is relatively low 56 60 to 64 50 thus it may be concluded that the shalstab model in assessing landslide should either not be used at all at a regional level in the himalayas or be used only with great caution along with additional field and lab data

new evidence for a reduced water balance in east africa during the last glacial maximum implication for model data comparison some syntheses of lake level data for the last glacial maximum lgm in east africa 10 n and 30 s east of 25 e show apparently wetter conditions than present for some basins whereas palaeovegetation reconstruction indicates a generally dry climate pmip gcm simulations for the lgm support both scenarios for this region when run under different boundary conditions here we compare three new records from lakes in the data poor southern part of east africa lake malawi lake massoko and lake rukwa we also re assess previously published lake level data and apply a salinity transfer function to the diatom record from lake manyara our results show that in contrast to previous interpretations these lakes were at least as low as today at the lgm and are thus in agreement with the palaeovegetation data relative drought across east africa is best simulated by gcms that use computed ssts rather than the higher climap values lower ssts and the presence of the northern hemisphere ice sheets must have been dominant over any monsoon precipitation rise caused by astronomically induced summer insolation enhancement in the southern african tropics

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