toward hydro social modeling merging human variables and the social sciences with climate glacier runoff models santa river peru summary glacier shrinkage caused by climate change is likely to trigger diminished and less consistent stream flow in glacier fed watersheds worldwide to understand model and adapt to these climate glacier water changes it is vital to integrate the analysis of both water availability the domain of hydrologists and water use the focus for social scientists drawn from a case study of the santa river watershed below peru s glaciated cordillera blanca mountain range this paper provides a holistic hydro social framework that identifies five major human variables critical to hydrological modeling because these forces have profoundly influenced water use over the last 60 years 1 political agendas and economic development 2 governance laws and institutions 3 technology and engineering 4 land and resource use and 5 societal responses notable shifts in santa river water use including major expansions in hydroelectricity generation large scale irrigation projects and other land and resource use practices did not necessarily stem from changing glacier runoff or hydrologic shifts but rather from these human variables ultimately then water usage is not predictable based on water availability alone glacier runoff conforms to certain expected trends predicted by models of progressively reduced glacier storage however societal forces establish the legal economic political cultural and social drivers that actually shape water usage patterns via human modification of watershed dynamics this hydro social framework has widespread implications for hydrological modeling in glaciated watersheds from the andes and alps to the himalaya and tien shan as well as for the development of climate change adaptation plans

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

modern and last local glacial maximum snowlines in the central andes of peru bolivia and northern chile late pleistocene snowlines in the central andes were 500 1200 m lower than at present radiocarbon dates imply that the late pleistocene glacial maximum in the region occurred prior to 20 14c ka but lack of maximum limiting ages adds considerable uncertainty to the exact timing snowline modeling demonstrates that snowlines in the eastern and western cordilleras of the central andes respond differently to temperature and precipitation changes in the eastern cordillera the snowline is near the level of the annual 0 c isotherm and melting occurs throughout the year here snowlines are sensitive to temperature changes but relatively insensitive to accumulation changes in the western cordillera the snowline rises 1000 higher owing to increasing aridity and the snowline exhibits a much stronger sensitivity to accumulation changes the consistent 1200 m snowline depression along the eastern cordilleras of the central andes can be modeled by a mean annual cooling of 5 9 c this is inconsistent with the 2 c cooling in tropical sea surface temperatures suggested by climap reconstructions the 800 1000 m snowline depression in the western cordillera cannot be accounted for solely by cooling but also requires an increase in precipitation

pronounced occurrence of long chain alkenones and dinosterol in a 25 000 year lipid molecular fossil record from lake titicaca south america abstract our analysis of lipid molecular fossils from a lake titicaca 16 s 69 w sediment core reveals distinct changes in the ecology of the lake over an 25 000 yr period spanning latest pleistocene to late holocene time previous investigations have shown that over this time period lake titicaca was subject to large changes in lake level in response to regional climatic variability our results indicate that lake algal populations were greatly affected by the changing physical and chemical conditions in lake titicaca hydrocarbons are characterized by a combination of odd numbered mid to long chain c 21 c 31 normal alkanes and alkenes during periods when lake level was higher latest pleistocene early holocene and late holocene the c 21 n alkane and the c 25 and c 27 alkenes dominate hydrocarbon distributions and indicate contribution from an algal source potentially the freshwater alga botryococcus braunii the c 30 4 methyl sterol dinosterol increases sharply during the mid holocene suggesting a greatly increased dinoflagellate presence at that time long chain alkenones lcas become significant during the early holocene and are highly abundant in mid holocene samples there are relatively few published records of lca detection in lake sediments but their occurrence is geographically widespread antarctica asia europe north america lake titicaca represents the first south american lake and the first low latitude lake in which lcas have been reported lca abundance and distribution may be related to the temperature dependent response of an unidentified algal precursor although the lca unsaturation indices cannot be used to determine absolute lake titicaca temperatures we suspect that the published lca u 37 k unsaturation calibrations can be applied to infer relative temperatures for early to mid holocene time when lca concentrations are high using these criteria the u 37 k unsaturation indices suggest relatively warmer temperatures in the mid holocene in contrast to previous speculation lipid analysis provides little evidence of a greatly increased presence of aquatic plants during the mid holocene instead it appears that a few algal species were dominant in the lake based on the dramatic rise in abundances of lcas and dinosterol during the early to mid holocene we suspect that the algal producers of these compounds rose in response to a combination of physical and chemical changes in the lake these include temperature salinity and alkalinity changes that occurred as lake level dropped sharply during a multi millennial drought affecting the central andean altiplano

lipid geochemistry of sediments from upton broad a small productive lake major lipid classes isolated from 3 sections of the sediment profile of upton broad a shallow lake formed about 500 yr ago were correlated with input and with changes attributable to early diagenesis surficial sediment contains lipids characteristics of the known recent algal and microbial input preservation of chlorophyll pigments and absence of appropriate markers suggest that diagenesis is minimal older deposits from the eutrophic phase of the lake s history contain higher levels of bacterial lipids and diagenetic products the earliest sediment contains lipids characteristic of terrigenous input subjected to more extensive diagenesis than the younger sediment recognition of early diagenesis in anoxic sediment suggests that distributions of the shorter chain homologous free n alkanes alkanols and alkanoic acids result from microbial synthesis using material initially deposited at the sediment surface rather than partial preservation of the lipids of primary source organisms

long chain alkenones preserved in miocene lake sediments abstract over the last few decades the occurrence of long chain alkenones lcas in quaternary lacustrine settings has been reported the distributions being remarkably different from those of open ocean settings we report here the occurrence of lcas with modern lake type composition from middle miocene sedimentary strata in the dahonggou section qaidam basin northern tibetan plateau this is the first report of lcas with preserved lake compositions in pre quaternary lacustrine sediments the discovery implies that the producers of modern lacustrine lcas could originate from similar lake species living at least as far back as the miocene epoch it also sheds new light on the potential of alkenones as palaeotemperature indicators in lacustrine systems back to at least 10 5 ma

a new global earth s gravity field model from satellite orbit perturbations grim5 s1 a new model of the earth s gravity field called grim5 s1 was prepared in a joint german french effort the solution is based on satellite orbit perturbation analysis and exploits tracking data from 21 satellites to solve simultaneously for the gravitational and ocean tide potential and tracking station positions the satellite only solution results in a homogeneous representation of the geoid with an approximation error of about 45 cm in terms of 5 5 degree block mean values and performs globally better in satellite orbit restitution than any previous gravity field model the grim5 normals which were generated taking into account the latest computational standards shall be the reference for use during the coming geopotential satellite mission champ and should provide new standards in computing orbits of next altimetric missions like jason and envisat the grim5 s1 normals also give the basis for the tracking surface data combined solution grim5 c1

temperature dependency of long chain alkenone distributions in recent to fossil limnic sediments and in lake waters distribution patterns of c37 and c38 polyunsaturated long chain alkenones lcas serve as proxies for the determination of paleotemperatures for marine surface waters we studied recent subrecent and late glacial holocene sediments from germany austria russia and the u s to test for a correspondence between lca distribution and surface water temperature in limnic systems previously reports of lca occurrence were restricted to sediments of 6 wide distributed freshwater and alkaline lakes in this study 13 of 27 investigated lakes contained lcas in surface sediments with concentrations varying between 12 to 205 g g toc late glacial to holocene sediment sequences from lake steisslingen and lake wummsee germany lake pichozero russia and brush lake u s a contained abundant lcas with averaged concentrations of 33 to 7536 g g toc for the first time we observed the occurrence of lcas within in the water column of oligotrophic lake stechlin ne germany alkenones were restricted to the zone of maximum chlorophyll concentration within the water column indicating that lcas have a biosynthetic origin and can be attributed to phototrophic micro algae attempts to identify the producing organism however were not successful culture experiments allow various phytoplankton to be excluded as producers alkenone producing algae are evidently of small size hindering microscopical identification lcas commonly occur in high concentrations in late glacial sediments mainly during the cold period of the younger dryas whereas the holocene usually is devoid of polyunsaturated alkenones the episodic occurrence of lcas restricts their utility as proxies for continuous geological records furthermore lack of microscopical verification and the episodic distribution allow for different producers of unsaturated alkenones in recent and late glacial sediments an empirical relationship between lca distribution and temperature was observed in fossil sediments from lake steisslingen there is a good correspondence between uk37 and the temperature controlled 18o isotope ratio of lake chalk comparison of lca patterns obtained from the uppermost centimetres of lake sediments with averaged summer surface water temperatures of the lakes studied demonstrates a trend of covariance r2 uk 37 0 90 uk37 0 67 n 9 hence the same mechanism that causes temperature dependence of lca patterns in marine systems might be effective in limnic settings identification of alkenone producers and their culture under controlled temperature are still mandatory before lcas can be routinely applied as paleotemperature proxy in limnic systems

does a monsoon climate exist over south america the climatology and the basic state of the summertime circulation and rainfall over south america are studied using assimilation products from the data assimilation system of goddard earth observing system 1 geos1 and satellite derived rainfall results indicate the existence of a regional summer monsoon circulation regime induced by strong diabatic heating over the subtropical south american highland centered at the altiplano plateau sensitivity of the results to the assimilation scheme is tested by comparing that with the national centers for environmental prediction ncep reanalysis and with satellite rainfall estimates results show general agreement between the model produced rainfall anomaly and the satellite estimates as well as consistency between the basic circulation features in the geos 1 and the ncep reanalyses a case study of 1989 90 south american summer monsoon sasm reveals the following characteristics 1 in late spring the onset of sasm is signaled by an abrupt merging of the upper tropospheric double westerly jets one in the subtropics and the other in the subpolar region into a single jet in the midlatitudes this is followed by the establishment of a vortex to the southeast of altiplano and occurrence of heavy precipitation over subtropical eastern brazil 2 during the mature phase of sasm the heavy rainfall zone moves over the altiplano plateau and the southernmost brazilian highland the fully established sasm features are the following a an enhancement of equatorial north atlantic trade wind which emanates from the sahara high and crosses the equator over the south american continent b a buildup of strong northwesterlies along the eastern side of the tropical andes and c development of the south atlantic convergence zone in the southernmost position with strong convective activity meanwhile the upper tropospheric return flow emerges from an anticyclone formed over the altiplano plateau crosses the equator and sinks over northwestern africa 3 the withdrawal of sasm in late summer is signaled by the resplitting of the midlatitude westerly jet at the same time the low level northwest monsoon flow diminishes reducing the moisture supply and leading to the termination of heavy precipitation over the subtropical highland results also show that the above mentioned characteristics of sasm are clearly linked to the tropospheric temperature changes over the central south american highland sensible versus latent heating over the highland are bound to play an important role in the evolution of sasm to provide further support of presence of a monsoon climate over south america sasm is compared and contrasted to the classic east asian summer monsoon easm many similar features including evolution characteristics between the two systems have been identified contrasting aspects of the sasm from the easm are also discussed it is pointed out that a number of monsoonal characteristics of the climate of south america such as the seasonal reversal of the low level wind become apparent only when the strong annual mean wind is removed based on the characteristic features and their evolution the authors conclude that a monsoon climate does exist over south america

long chain alkenones in qinghai lake sediments abstract long chain methyl and ethyl alkenones c 37 c 40 containing two to four double bonds have been detected in sediments from qinghai lake china this is the first report of the alkenones in lake sediments deposited under a variety of salinity conditions where the lake has not encountered any marine incursions the presence of the alkenones suggests the presence of prymnesiophyceae in the lake which may have reached the lake via eolian transportation or seabirds sediment samples from the more saline areas of the lake contained higher concentrations of the more highly unsaturated compounds widespread use of these compounds as paleotemperature indicators in marine sediments introduces the possibility of extrapolating this approach to lacustrine environments if appropriate calibrations can be undertaken

environmental controls on long chain alkenone occurrence and compositional patterns in lacustrine sediments northwestern china abstract long chain alkenones occur widely in lacustrine settings and their compositions are potential proxies for reconstructing terrestrial paleoclimatological and paleoenvironmental changes however factors influencing their occurrence abundance compositional pattern and unsaturation indices are not well understood here we investigated the alkenones in surface sediments from 19 lakes in northwestern china as well as potential environmental factors of the lakes 12 contain long chain alkenones 3 have the isomeric c 37 3 alkenone and 3 have very low abundance of alkenones our results show that salinity has a substantial influence on the occurrence concentration and compositional pattern most of the compositions are dominated by tri unsaturated compounds with c 38 methyl ketones absent the predominance of c 37 4 and the occurrence of a c 37 3 isomer are suggested to be responses to low salinity as both are only found in the three alkenone containing freshwater lakes the proportion of c 37 4 varies by up to 50 and shows a negative relationship with salinity within the surveyed region an arched relationship of alkenone content and salinity is apparent with no or very low contents of alkenones in freshwater salinity 100 g l environments the u 37 k index is suggested to be a better terrestrial temperature proxy than u 37 k as u 37 k values from lakes containing elevated alkenone content are all within the ranges of published u 37 k temperature calibrations and u 37 k values show a weak positive relationship with salinity

molecular isotopic stratigraphy of long chain n alkanes in lake baikal holocene and glacial age sediments the molecular distribution and the carbon isotopic composition d 13 c of n alkanes extracted from a lake baikal core spanning the last 20 kyr of sediment accumulation have been investigated a terrestrial origin has been inferred for the odd carbon numbered long chain c27 n alkanes on the basis of the observed high cpi27 33 values range 8 7 10 8 typical of n alkanes derived from leaf waxes of higher plants a shift in the abundance of n c27 alkane relative to n c31 homologue is observed across the late pleistocene glacial holocene interglacial climate change perhaps indicative of the climate induced vegetational change previously deduced from palynological analyses compound specific isotope analyses indicate remarkably uniform d 13 c values in the range of 31 0 to 33 5 for the leaf wax c27 c33 nalkanes in the entire cored sequence such an isotopic compositional range is characteristic for n alkanes biosynthesized by plants utilizing the c3 photosynthetic pathway our data suggest that the observed 13 c enrichment in the bulk organic matter in the glacial age sediments relative to d 13 c values of total organic carbon in the holocene section is therefore unlikely to be attributed to an expansion of c4 type vegetation in the baikal watershed during the late pleistocene glacial interval 2000 elsevier science ltd all rights reserved

origin and tentative identification of tri to pentaunsaturated ketones in sediments from lake fryxell east antarctica abstract chromatographic and mass spectrometric analysis of surface sediments from perennially ice covered lake fryxell mcmurdo dry valleys east antarctica enabled tentative identification from mass spectral data of previously unreported pentaunsaturated ketones octatriacontapentaen 2 one c38 5me nonatriacontapentaen 3 one c39 5et and tetradecapentaen 2 one c40 5me in addition the c37 c38 and c40 alkenones occur as di tri and tetraunsaturated compounds whereas the c39 alkenones only include the tetraunsaturated components analysis of environmental dna extracted from the water column of lake fryxell produced two 18s rdna sequences closely related to isochrysis spp chrysotila lamellosa and haptophyte sequences previously recognized in sediment samples collected from a greenland lake and from ace lake antarctica based on the alkenone distribution coupled with phylogenetic data we propose that haptophytes related to isochrysis and or c lamellosa are the source organisms of alkenones in lake fryxell the occurrence of pentaunsatured alkenones may represent a response to the year round cold water temperature ca 1 c average likely combined with oxygen supersaturation and growth under light and nutrient limited conditions in the upper water column

reconstruction of paleohydrology and paleohumidity from oxygen isotope records in the bolivian andes cellulose inferred lake water n 18 o n 18 olw records from lago potosi lp a seasonally closed lake in a watershed that is not currently glaciated and lago taypi chaka kkota ltck previously reported in abbott et al 2000 quat sci rev 19 1801 1820 an overflowing lake in a glaciated watershed provide the basis for late pleistocene and holocene paleoclimatic reconstruction in the bolivian andes deconvolution of the histories of changing evaporative isotopic enrichment from source water n 18 o in the lake sediment records is constrained by comparison to the sajama ice core oxygen isotope profile whereas local hydrological influence is distinguished from the regional moisture balance history by the response of the different catchments to climate change overall variations in the lp n 18 olw record appear to be dominantly controlled by evaporative 18 o enrichment reflecting shifts in local effective moisture this record is used to generate a preliminary quantitative reconstruction of summer relative humidity spanning the past 11 500 cal yr on the basis of an isotope mass balance model results indicate that the late pleistocene was moist with summer relative humidity values estimated at 10 20 greater than present increasing aridity developed in the early holocene with maximum prolonged dryness spanning 7500 6000 cal yr bp at lp an interval characterized by summer relative humidity values that may have been 20 lower than present highly variable but dominantly arid conditions persist in the mid to late holocene with average summer relative humidity values estimated at 15 below present which then increase to about 10 20 greater than present by 2000 cal yr bp slightly more arid conditions characterize the last millennium with summer relative humidity values ranging from 5 10 lower than present similar long term variations are evident in the ltck n 18 olw profile except during the early holocene when lake water evaporative 18 o enrichment in response to low relative humidity appears to have been offset by enhanced inflow from 18 o depleted snowmelt or groundwater from the large catchment although some temporal offset is evident significant correspondence occurs between the isotope inferred paleohumidity reconstruction and other paleohydrological proxies from the region these

lipid biomarkers in lacustrine sediments of subtropical northeastern mexico and inferred ecosystem changes during the late pleistocene and holocene abstract evolution of ecosystems in the northeastern mexico since the last glacial maximum lgm and through the holocene are yet to be fully characterised creating a gap in our understanding of the ecological response to climate change in this water scarce region here we explore the response of lacustrine and surrounding terrestrial habitats of this region to hydrological changes of the late pleistocene and especially the holocene biomarker based proxy data from the el potosi basin indicates dynamic and variable input of organic matter om into the basin with sources being the surrounding vegetation bacterial biomass and aquatic microfauna changes in these inputs reveal distinct stages of ecosystem development over the last 20 000 years overall low lipid abundances as a proportion of toc from 20 to 19 cal kyr bp mainly from aquatic in situ microbial biomass and degraded terrestrial om are attributed to relatively low runoff increasing lipid proportions during the deglaciation from 19 to 15 cal kyr bp were mostly derived from terrestrial sources like woodland vegetation soil and wetland vegetation and we attribute them to more rainfall and runoff subsequently the wetland biomarkers disappeared and woodland input began to dominate the om assemblage from 15 to 11 7 cal kyr bp during the early and mid holocene after about 11 7 cal kyr bp putative woodland and grass inputs decreased and the dominant vegetation appeared to shift to subtropical desert shrub which could have been due to increasing regional aridity the onset of the dry late holocene was characterised by gradual environmental transition and ecosystem adaption especially from 4 2 to 2 8 cal kyr bp the terrestrial vegetation comprised increasing proportions of c4 grasses documented by changes in leaf wax carbon isotopic compositions and potentially more open vegetation while the in lake bacterial production increased with increasing desertification from 2 8 cal kyr bp the terrestrial productivity decreased substantially the lake became shallower ephemeral and the surrounding soils became more alkaline changes of the limnic habitat from algal towards microbial communities occurred 300 years after the onset of terrestrial habitat changes during the last millennium the c3 components of the vegetation again dominated this implies an enhanced moisture supply possibly from agricultural activities overall this work reveals the marked sensitivity of northeastern mexico ecosystems to the climatic shifts that occurred since the lgm and this perhaps indicates their vulnerability to future global warming

late pleistocene climate and water budget of the south american altiplano abstract geomorphic evidence from the peruvian bolivian altiplano indicates that during episodes prior to 28 000 and around 12 500 11 000 yr b p lakes covered an area about six and four times as large as at present respectively within the constraints of the heat and water budget model calculations are used to estimate the precipitation rate that would allow hydrologic equilibrium on this basis it is suggested that rainfall on the altiplano during the episodes of enlarged lakes was respectively some 300 and 200 mm annum 1 larger than at present representing increases of about 75 and 50 respectively field evidence suggests that the episodes of enlarged lakes on the altiplano may have preceded or coincided with periods of maximum glaciation in the neigh boring andes in this region with high elevation of the ice equilibrium line increased precipitation is particularly conducive to glaciation

high resolution seismic reflection profiles from lake titicaca peru bolivia evidence for holocene aridity in the tropical andes high resolution seismic reflection profiles of the sediments of lake titicaca peru bolivia suggest that lake levels in the recent past were considerably lower than today incised channels on the major deltas extend to depths of 85 m below modern lake level erosional truncation of onlapping seismic reflectors is found at similar depths this interpretation of the seismic data is supported by analyses of sediment cores from the lake which indicate that there was a significant drop in lake level during the early to mid holocene

long chain unsaturated ketones and esters in living algae and marine sediments abstract series of c37 c39 di and triunsaturated ketones and methyl and ethyl esters of hexatriacontadienoic acid c36 2 have been previously identified in marine sediments and the coccolithophorid emiliania huxleyi these compounds have now been found in four further species of the isochrysidales prymnesiophyta which are not known to bear coccoliths suggesting that they are more widely distributed in living algae than previously thought in addition the ketones have been recognised in sediments of eocene age ca 45 ma which greatly extends their known geological time range and increases their potential as molecular markers for algal input heptatriacontatetraen 2 one c37 4 octatriacontatetraen 3 one c38 4 methyl and ethyl esters of hexatriacontatrienoic acid c36 3 and the ethyl ester of hexatriacontatetraenoic acid c36 4 have also been identified in varying amounts in these algae by gas chromatography and computerised gas chromatography mass spectrometry

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

the history of south american tropical precipitation for the past 25 000 years long sediment cores recovered from the deep portions of lake titicaca are used to reconstruct the precipitation history of tropical south america for the past 25 000 years lake titicaca was a deep fresh and continuously overflowing lake during the last glacial stage from before 25 000 to 15 000 calibrated years before the present cal yr b p signifying that during the last glacial maximum lgm the altiplano of bolivia and peru and much of the amazon basin were wetter than today the lgm in this part of the andes is dated at 21 000 cal yr b p approximately coincident with the global lgm maximum aridity and lowest lake level occurred in the early and middle holocene 8000 to 5500 cal yr b p during a time of low summer insolation today rising levels of lake titicaca and wet conditions in amazonia are correlated with anomalously cold sea surface temperatures in the northern equatorial atlantic likewise during the deglacial and holocene periods there were several millennial scale wet phases on the altiplano and in amazonia that coincided with anomalously cold periods in the equatorial and high latitude north atlantic such as the younger dryas

unusual distributions of long chain alkenones and tetrahymanol from the highly alkaline lake van turkey long chain c37 to c40 alkenones with di tri and tetra unsaturation are very abundant in sediment trap material and holocene to late pleistocene core samples from the earth s largest soda lake lake van turkey thus the known distribution range of these typical biomarkers for haptophyte microalgae is extended to highly alkaline environments the observed unsaturation patterns differ strikingly from those found in open marine haptophytes and sediments by an enhanced relative abundance of the tetra unsaturated compounds especially the c37 4 methyl ketone their preponderance is suggested to be a facies marker pattern for lacustrine and marginal marine areas of sedimentation using published u37k calibrations no reliable absolute temperatures were obtained for the lake van samples accordingly marine sea surface temperature determinations based on long chain alkenones should be applied with caution when a contribution of these compounds from coastal or nonmarine sources can not be excluded the presence of tetrahymanol and gammacer 3 one in the lake van materials is attributed to organic matter contributions of ciliates the relative abundance of long chain alkenones and of tetrahymanol gammacer 3 one is considered to reflect changes in the environmental conditions in particular in the hydrological setting we suggest that times of pronounced stagnation are recognised by very high tetrahymanol gammacer 3 one concentrations together with drastically increased stanol stenol ratios and intervals of enhanced convection or of high freshwater input are characterised by high alkenone contributions

compositional variations in sedimentary lacustrine organic matter and their implications for high alpine holocene environmental changes lake st moritz switzerland abstract organic matter accumulation and preservation in lakes with different geomorphological and climatic regimes is directly influenced not only by local but also by regional and more global climatic conditions thus compositional variations in lacustrine organic matter can be used as good indicators of paleoenvironmental conditions of deposition relatively high average toc 1 0 6 5 wt and good lamination characterize most of the holocene sequence of lake st moritz an alphine lake located in se switzerland however variations in the type and quality of the organic matter at discrete intervals have been distinguished using bulk parameters and biomarker distributions the most prominent change occurs at the late glacial holocene boundary where 13 c om hydrogen index and lipid concentrations indicate a substantial increase in primary productivity organic matter production and preservation appear to dominate from the early holocene until approximately 3 8 ka bp although variations in sterol contents and fatty acid distributions indicate superimposed fluctuations such as between 8 3 and 8 1 ka bp and 5 1 to 4 8 ka bp these variations in the lake trophic state can be correlated with other proglacial lakes in the region as well as with similar lacustrine records on both sides of the alps the result of this comparison indicates a synchronous character of major to medium amplitude climatic shifts on a european scale

distribution and significance of long chain alkenones as salinity and temperature indicators in spanish saline lake sediments abstract we investigated relationships between sedimentary solvent extractable long chain alkenone lca concentration and composition and environmental factors in a suite of endorheic lakes from inland spain lcas were found in 14 of the 54 lakes examined with concentrations comparable with those from previously published lacustrine settings the composition of lcas in our sites however contrast from the majority of those previously reported from lake environments in our study the tri unsaturated component is the most abundant component at most sites where lcas are detected and c38 3 is the most abundant lca in the majority of sites lca occurrence appears to be restricted to brackish hypersaline sites and c37 lcas are absent above a salinity of 40 g l 1 suggesting a salinity control on lca producing organisms in these sites low concentrations of c37 lca components means u 37 k and u 37 k temperature indices are generally not applicable instead we find good relationships between c38 components and in particular mean autumn temperature and the strongest lca temperature relationships are found when using a combination of all c37 and c38 compounds we propose a new alkenone temperature index for lakes with elevated salinity and where the c38 components dominate the lca distributions this is expressed as u 3738 k 0 0464 mautat 0 867 r2 0 80 n 13 in this paper we provide the first account of sedimentary lca distributions from lakes in inland spain extending the range of environments within which these compounds have been found and highlighting their significance as indicators of both salinity and temperature in saline endorheic lake environments this has important implications for extending the potential role of lcas as palaeoclimatic indicators in lacustrine environments

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

a 25 000 year tropical climate history from bolivian ice cores ice cores that were recovered from the summit of sajama mountain in bolivia provide carbon 14 dated tropical records and extend to the late glacial stage lgs oxygen isotopic ratios of the ice decreased 5 4 per mil between the early holocene and the last glacial maximum which is consistent with values from other ice cores the abrupt onset and termination of a younger dryas type event suggest atmospheric processes as the probable drivers regional accumulation increased during the lgs during deglaciation and over the past 3000 years which is concurrent with higher water levels in regional paleolakes unlike polar cores sajama glacial ice contains eight times less dust than the holocene ice which reflects wetter conditions and extensive snow cover

record of redox status in laminated sediments from lake titicaca a sulfur k edge x ray absorption near edge structure xanes study abstract laminated sediments are commonly used to examine limnological and ecological processes on short time scales here we examine changes in sulfur speciation of lamination couplets from lake titicaca south america using x ray absorption near edge structure xanes spectroscopy the dark colored layer of each lamination couplet contains a significant fraction of reduced organic sulfides with smaller fractions of iron sulfides and sulfate in contrast the light colored layer of each couplet is primarily composed of sulfate in all laminae the sulfate is present as inorganic sulfate substituted in calcite the differences in speciation likely reflect changes in productivity during sediment deposition during the warm productive summer months micritic calcite precipitation was induced in oxidized surface waters due to ph changes induced by consumption of dissolved co 2 this calcite incorporates dissolved sulfate and forms the light colored layers this pulse of productivity creates organic matter that partially decomposes during the austral winter months consuming oxygen and delivering organic rich sediment to the lake bottom this decomposition and the possible presence of a halocline kept bottom waters low in oxygen and lead to the production of organic matter rich in reduced sulfur these data suggest that these laminations are deposited annually and illustrate the utility of s k edge xanes for the analysis of laminated sediments

sedimentary biomarker and isotopic indicators of the paleoclimatic history of the walker lake basin western nevada walker lake a terminal saline lake in western nevada has experienced major fluctuations in its water level due to changes in the regional climate during quaternary times as part of a paleo climatological study of western nevada we have investigated organic matter 6 3c and c n values and lipid biomarker contents of sediments deposited at various periods over the past 150 thousand years of lake history surficial sediments from two cross lake transects contain mostly lake derived organic matter diagenetic losses of organic matter are evident in deeper sediments and the proportion of aquatic and terrigenous organic materials changes in response to variations in preservational factors source identification of organic matter is complicated by the probability that walker lake has experienced desiccation at various times in its history which impacts the degree of preservation of organic substances

distribution of the c37 tetra unsaturated alkenone in lake qinghai china a potential lake salinity indicator abstract the alkenone unsaturation index u k 37 has been applied to reconstruct past temperature changes in both marine and lacustrine systems however few studies have addressed whether the relative abundance of the c 37 4 alkenone to the total c 37 production c 37 4 can reflect surface salinity changes in lacustrine systems here we present long chain c 37 alkenone distribution patterns in surface sediments from lake qinghai china surface sediments were sampled over a large range of surface salinity changes 1 7 25 g l within lake qinghai and its surrounding lakes while temperature differences at these sampling locations should be relatively small we have found that c 37 4 varies from 15 to 49 as surface salinity decreases we tentatively describe this c 37 4 salinity link with a general linear regression c 37 4 53 4 7 8 1 73 0 45 s n 28 r 2 0 62 although step wise c 37 4 changes in response to salinity variation may exist u k 37 values vary between 0 10 and 0 16 at these sites and the inferred range of lake water temperature changes is 2 3 c suggesting that u k 37 largely reflects temperature signal across a large salinity range consistent with previous findings that u k 37 can indicate temperature changes over a large diversity of environmental settings we have also found that u k 37 values are correlated with salinity changes r 2 0 4 and thus cannot exclude potential temperature effect on c 37 4 and salinity effect on u k 37 in this study however even extreme estimates of temperature differences within the lake are still unable to explain the observed c 37 4 changes we therefore suggest that c 37 4 could be used to infer past lake salinity changes at a regional scale

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

glacial interglacial environmental changes inferred from molecular and compound specific δ13c analyses of sediments from sacred lake mt kenya abstract molecular stratigraphic analyses including lipid distributions and compound specific 13c measurements have been performed at 15 levels in a sediment core from sacred lake mt kenya a high altitude 2350 m a s l freshwater lake with a record extending from the last glacial 40 000 cal yr bp through the present interglacial terrestrial and aquatic organic matter sources were independently assessed using source specific biomarkers 13c values of long chain n alkyl lipids from terrestrial higher plants exhibit large glacial to interglacial shifts those from the last glacial maximum lgm 20 to 18 indicate a terrestrial vegetation dominated by c4 grasses or sedges whereas those from the early holocene 34 to 27 reflect recolonization of the catchment area by c3 plants consistent with a rapid rise in the upper treeline specific algal biomarkers including five unsaturated hydrocarbons of novel structure ascribed to the microalga botryococcus braunii were abundant as confirmed by scanning electronic microscopy sem an extreme 13c shift of over 25 is displayed by the algal biomarkers an elevated value of 5 1 at the last glacial maximum lgm contrasting with a minimum value of 30 3 at the beginning of the holocene a major change in the molecular distributions of the algal biomarkers parallels this large 13c shift with acyclic isoprenoid hydrocarbons dominating the last glacial and cyclic isoprenoid hydrocarbons the holocene the low atmospheric partial pressure of co2 pco2 at the lgm would favour photosynthetic organisms possessing co2 concentrating mechanisms including terrestrial c4 grasses and freshwater green algae hence glacial interglacial changes in pco2 and in the co2 o2 ratio in particular had a significant impact on both terrestrial and aquatic ecosystems on mt kenya in addition to the effects of climate and local environmental factors

huascaran δ18o as an indicator of tropical climate during the last glacial maximum the interpretation of the isotopic composition of andes tropical mountain glaciers is reconsidered using a simple rayleigh distillation model it is shown that andes snowline depression and huascaran ice core 18o are consistent with a 3 c drop in sea surface temperature during the last glacial maximum accompanied by an increase from 40 at present to 60 during the lgm in the annual mean proportion of atmospheric water lost to continental runoff broecker s interpretation of huascaran 18o as a paleo hygrometer is discussed

lipids of aquatic organisms as potential contributors to lacustrine sediments ii abstract the relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments previously examined for n alkanols and steroids is now reported for hydrocarbons ketones and carboxylic acids the n c7 alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment bacterial biomarkers including hopenes and i ai branched fatty acids were detected in the photosynthetic bacterial layer occurring just above the sediment water interface within the sediment the apparent conversion of free n alkanes alkan 2 ones and hydroxy acids to the corresponding bound form is noted microbiological oxidation of n alkanes to alkan 2 ones is supported by the detection of the intermediate alkan 2 ols with a distribution similar to that of the ketones the geochemistry of sediment deposited c 1900 prior to biological study of the site was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition a qualitative difference in algal input to the older sediment is inferred from the low 7 sterol content and presence of 2 6 10 trimethyl 7 3 methylbutyl dodecane however there was still significant dinoflagellate input as indicated by the presence of 4 methylsterols a difference in higher plant input to the older sediment indicated from the n alkane alkene and triterpenoid ketone distributions is consistent with the recent development of tree cover

a new estimate of the holocene lowstand level of lake titicaca central andes and implications for tropical palaeohydrology new evidence from piston cores and high resolution seismic reflection data shows that water levels in lake titicaca were as much as 100 m below the present level during the early to mid holocene between 6 and 3 8 14c kyr bp climatological and modelling studies indicate that lake titicaca rainfall depends on convective activity in upwind amazonia the lake level data therefore suggest a drier amazon basin during this time this view is bolstered by an excellent match between the titicaca lake level curve and decreased methane concentrations in greenland ice previously ascribed to drying of low latitude wetlands blunier et al 1995 the postglacial history of lake titicaca fits a global pattern of lake level change in the tropics characterized by opposite phasing between the southern and northern hemispheres this pattern is most likely the result of orbital controls over the intensity of summer insolation

origin and palaeoenvironmental significance of c25 and c27 n alk 1 enes in a 25 000 year lake sedimentary record from equatorial east africa we studied the distribution of long chain alkenes n c23 to n c31 in well dated sediments from lake challa a deep crater lake near mt kilimanjaro in equatorial east africa to reveal signatures of palaeo environmental and palaeo climatic changes affecting the production of these compounds during the last 25 kyr the apolar fractions of organic sediment extracts dated to the last 16 kyr showed an unusual dominance of d13c depleted n c25 1 and n c27 1 alk 1 enes these alkenes were not detected in soil and litter from near the shoreline and from the inner rim of the crater pointing to an autochthonous aquatic source analysis of suspended particulate matter indicated that the n alk 1 enes are produced in the well oxygenated upper 30 m of the water column indicating a phytoplanktonic origin sedimenting particles collected monthly from december 2006 to november 2007 showed increased fluxes of n alk 1 enes following the locally prominent short rain season in november december green algae and or cyanobacteria were identified as candidate sources of these alkenes production of the n c25 1 and n c27 1 alkenes in lake challa was much reduced during the last glacial maximum and early late glacial period suggesting a temperature or co2 effect on habitat suitability we explored the potential of n alk 1 ene accumulation rates and of a derived alkene index n c27 1 n c25 1 n c27 1 to record longer term climatic changes the alkene index record of lake challa over the past 25 kyr shows clear periodicity with a dominant frequency of 2 3 kyr potentially indicative of monsoon variability directly or indirectly forced by variation in solar radiation

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

long chain alkenone inferred temperatures from the last deglaciation to the early holocene recorded by annually laminated sediments of the maar lake sihailongwan northeastern china abrupt temperature changes during the last deglaciation are well recognized in greenland ice cores and in deep sea sediment records on the continent of monsoonal asia however only a few terrestr

alkenone based temperature and climate reconstruction during the last deglaciation at lake dangxiong co southwestern tibetan plateau the climate of the tibetan plateau is influenced by the monsoons and the westerlies due to land sea thermal contrasts however few quantitative temperature reconstructions have been made for the region and this hinders our ability to validate climate models and to understand the coupling process between monsoon ocean and ice sheets through time here we report a quantitative temperature reconstruction for the last deglaciation from a terrace of lake dangxiong co in the southwestern tibetan plateau based on the unsaturation index of long chain alkenones the reconstructed mean annual air temperature during the late last glacial maximum was about 0 2 c while the bolling allerod b a period was characterized by a rapid increase in temperature from 0 8 c to 2 4 c 2 9 followed by an abrupt decrease in temperature to 0 9 c in the early younger dryas yd the alkenones and n alkanes record indicates that dangxiong co experienced a cold and wet climate in the early part of the last deglaciation after the last glacial maximum a warm dry b a and a cold and dry yd our temperature reconstruction confirms that the thermal and dynamical effects of the tibetan plateau are one of the main elements contributing to abrupt changes in the indian summer monsoon

late quaternary lowstands of lake titicaca evidence from high resolution seismic data abstract approximately 600 km of high resolution seismic reflection data were collected to investigate the late quaternary stratigraphic development of lake titicaca the focus of this report is on two seismic sequence boundaries which are interpreted as erosional surfaces formed at times of low lake level the younger erosional surface occurs as much as 90 m below the present lake level and up to 8 m below the present sediment water interface this erosional surface is interpreted to be coeval with a well documented early to mid holocene lowstand dated between 8000 and 3600 cal yr bp an earlier and previously unknown erosional surface occurs at a sub bottom depth of approximately 30 m and as much as 240 m below the present lake level which implies a major late pleistocene lowstand of lake titicaca by extrapolation of sedimentation rates from the upper 14 m of sediment we estimate the age of this older lowstand at 90 000 cal yr bp both lowstands of lake titicaca indicated by the seismic data are likely to have been a response to climatic change in the region

salinity control on long chain alkenone distributions in lake surface waters and sediments of the northern qinghai tibetan plateau china abstract long chain alkenones in lacustrine settings are potentially excellent biomarkers for the reconstruction of past terrestrial environmental conditions and have been found in many different types of lakes around the globe a wider range of factors influence the occurrence and distribution of alkenones in lake sediments and waters when compared to marine systems lake environmental conditions such as temperature in particular and salinity are among the key factors controlling alkenone distributions in lacustrine settings here we investigated alkenone distribution patterns in lakes of the northern qinghai tibetan plateau china and their possible relationship with environmental conditions by analyzing paired samples of suspended particulate matter in surface waters and surface sediments salinity of investigated lake waters ranges from almost 0 to 100 g l while temperature variation among the lakes is minimal effectively eliminating temperature effects on the alkenone distribution patterns observed here we show that 1 alkenone concentrations vary substantially between the lakes yet controlling mechanisms remain elusive 2 c37 c38 ratios are substantially lower in the lakes of the qaidam basin than in the lake qinghai region probably indicating different alkenone producers in the two regions and 3 large variations in c37 4 the percentage of the c37 4 alkenone determined from both surface waters and sediments are negatively correlated with salinity we suggest that the c37 4 index could be used as a salinity indicator at least on a regional scale with careful considerations of other potentially complicating factors however potential reasons for why salinity could significantly affect c37 4 values need further investigation