the fate and accumulation of bromide during playa salt deposition an example from lake frome south australia an advectivn diffusion model describing the distribution of br in porewaters underlying an accumulating deposit of halite on a playa lake can be used to predict the evolving composition of the accumulating salt growing as a result of evaporation the br cl ratio of the accumulating halite is proportional to the concentration or br at the surface of the brine body from which it is growing the evolution of interstitial br and therefore the composition of the accumulating salt is a function of 1 the diffusion coefficient of br in the brine saturated sediment 2 the advective velocity of the interstitial water 3 the initial concentration of br and cl at the onset of evaporation and 4 the distribution coefficient of br into the accumulating salt all of which can be estimated for the sediments and brines of lake frome south australia at lake frome the model is used to estimate mean evaporation rates for the salt covered surfaces which are found to be between 0 5 and 3 0 cm y these rates are lower than the rates estimated for the salt free surfaces of the lake by allison and barnes 1985 but are consistent with the expectation that groundwater input and therefore evaporation rates will be focused at the salt free lake margins rather than at the salt covered central regions of the playa and that the surface albedo of the salt covered zones will reduce energy penetration to the sediment and thus evaporation

arid zone groundwater recharge and salinisation processes an example from the lake eyre basin australia in arid central australia the 1 14 m km2 endorheic lake eyre basin leb experiences sporadic floods and contains saline shallow groundwater in this basin where on ground physical and chemical data are very sparse new observations of major ion chemistry stable isotopes 2h 18o 13c radiogenic isotopes 3h 14c and remote sensing modis data were used to investigate groundwater recharge and salinisation processes in 2006 2007 in january 2007 there was a large and intense local rainfall event followed by flooding to the normally dry lake eyre resulting from heavy rainfall in the northern leb that took 2 months to arrive at lake eyre groundwater chemistry from this study show no evidence of recharge from the floodwaters or the local rainfall however this does not preclude the process low transit times and low infiltrating volumes may mean that the recharge event has not yet been detected over the longer term the stable isotope chemistry indicates that groundwater is predominantly diffusely recharged during heavy local rainfall events 100 150 mm month and radiogenic isotopes reflect an older shallow groundwater efficiently mixing with recent decadal recharge the high total dissolved solids tds of regional shallow groundwater up to 52 5 g l is intrinsically linked with these recharge processes where infiltrating diffuse rainfall is evaporated and heavy rainfall events transport saline pore water saline due to evaporation in the unsaturated zone to the groundwater system the high tds of shallow groundwater beneath the dry lake eyre bed up to 322 g l is also controlled by evaporation however although evaporite minerals are prolific in the lake area the non conservative behaviour of br in pore water limits analysis of the role of halite mineral dissolution and precipitation reactions controlling groundwater salinity evaporation driven salinisation of shallow groundwater in arid central australia is distinct from the transpiration driven salinisation of groundwater in the australian murray basin located in a semi arid climate and results in relatively high groundwater salinity values compared with many other large arid zone endorheic basins across the world

estimation of evaporation from the normally dry lake frome in south australia depth profiles of deuterium composition expressed as delta values have been used to make point estimates of evaporation from the floor of the normally dry lake frome a salt lake in northern south australia values from five sites varying between 90 and 230 mm yr 1 have been used to obtain a relatively crude approximation for mean evaporation rate from the lake of 170 mm yr 1 under the assumption that this represents discharge of water from the regional groundwater system the groundwater inflow into the lake is calculated as 5 108 m3 yr 1 two possible models which describe groundwater inflow into the lake are discussed

a lacustrine gdgt temperature calibration from the scandinavian arctic to antarctic renewed potential for the application of gdgt paleothermometry in lakes quantitative climate reconstructions are fundamental to understand long term trends in natural climate variability and to test climate models used to predict future climate change recent advances

evaporation rate from a salt pan estimates from chemical profiles in near surface groundwaters evaporation of water from saturated saline soils or sediments induces gradients of the solutes in the remaining interstitial solution these gradients lead to a systematic and predictable solute distribution in the soil solution which may be used in some cases to estimate the rate of evaporation simple one dimensional transport models for the distribution of cl and br indicate net evaporation rates from the salt covered surface of lake eyre south australia of between 0 9 and 2 8 cm yr 1 the former is a minimum estimate averaged over 20 yrs which includes the major 1974 filling event while the latter reflects the most recent summer evaporation period

timing and climate forcing of volcanic eruptions for the past 2 500 years volcanic eruptions contribute to climate variability but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual to decadal temperature variability in the northern hemisphere during the past 2 500 years our results are based on new records of atmospheric aerosol loading developed from high resolution multi parameter measurements from an array of greenland and antarctic ice cores as well as distinctive age markers to constrain chronologies overall cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth century pandemics famines and socioeconomic disruptions in eurasia and mesoamerica while allowing multi millennium quantification of climate response to volcanic forcing

identifying fluvial recharge and artesian upwards leakage contributions to arid zone shallow unconfined groundwater evaporation losses from unconfined groundwater can form an important part of the water balance of arid zone groundwater systems however in artesian groundwater systems the discrimination between artesian leakage and surface recharge contributions to the unconfined water table is required we use hydrochemical analysis techniques and isotopic data to investigate the provenance of unconfined groundwater in zones of artesian discharge along the margin of the great artesian basin gab of australia forward modelling of evapoconcentration and use of trilinear plots identified unconfined groundwater that was largely derived from fluvial recharge compared to upwards artesian leakage particularly in areas where the artesian groundwater had a na hco3 cl composition in contrast to the na cl so4 composition more typical of arid zone meteoric recharge mixing models combined with forward evapoconcentration models confirmed that the contribution of artesian groundwater was minimal in areas of na cl so4 unconfined groundwater underlain by na hco3 cl artesian groundwater however the evaporation modelling was still useful in identifying probable artesian versus meteoric contributions from na cl so4 composition artesian groundwater stable isotope data were consistent with the unconfined groundwater being evapoconcentrated from the artesian groundwater end member and were unable to discriminate between contributions from fluvial recharge and artesian discharge the hydrochemical analysis techniques can assist in water balance studies of aquifers with na hco3 cl composition groundwater discharging into semi arid and arid environments in addition to identifying areas of local fluvial recharge

development of a regional glycerol dialkyl glycerol tetraether gdgt temperature calibration for antarctic and sub antarctic lakes a b s t r a c t a regional network of quantitative reconstructions of past climate variability is required to test climate models in recent studies temperature calibration models based on the relative abundances of sedimentary glycerol dialkyl glycerol tetraethers gdgts have enabled past temperature reconstructions in both marine and terrestrial environments nevertheless to date these methods have not been widely applied in high latitude environments due to poor performance of the gdgt temperature calibrations at lower temperatures to address this we studied 32 lakes from antarctica the sub antarctic islands and southern chile to 1 quantify their gdgt composition and investigate the environmental controls on gdgt composition and 2 develop a gdgt temperature calibration model for inferring past temperatures from antarctic and sub antarctic lakes gdgts were found in all 32 lakes studied and in 31 lakes branched gdgts brgdgts were the dominant compounds statistical analyses of brgdgt composition in relation to temperature ph conductivity and water depth showed that the composition of brgdgts is strongly correlated with mean summer air temperature msat this enabled the development of the first regional brgdgt temperature calibration for use in antarctic and sub antarctic lakes using four brgdgt compounds gdgt ib gdgt ii gdgt iii and gdgt iiib a key discovery was that gdgt iiib is of particular importance in cold lacustrine environments the addition of this compound significantly improved the model s performance from r2 0 67 rmsep loo leave one out 2 23 c rmsep h h block 2 37 c when applying the re calibrated global gdgt

temperature fluctuations during the common era in subtropical southwestern china inferred from brgdgts in a remote alpine lake abstract documenting climate change over the past 2000 years or the common era is critical to understand how the climate system evolved from one controlled by natural forcings alone to one influenced by anthropogenic greenhouse gas forcing however global and regional temperature changes during this interval are still poorly understood largely due to the limited geographical coverage and scarcity of data here we report a well dated quantitative mean annual air temperature maat record with 10 yr resolution for the common era derived from a sediment core collected at a small alpine lake in remote subtropical southwestern china and based on a site specific temporal calibration between down core analyses of brgdgts and instrumental data for the interval 1959 2015 ad the record reveals distinct multicentennial scale temperature fluctuations including a relatively cold interval from 0 800 ad followed by warmer temperatures during the so called medieval climate anomaly mca 800 1400 ad cooling during the little ice age lia 1400 1900 ad and abrupt and rapid warming into the late 20th century after 1900 ad superimposed on these large scale features are three short term cold events centered on 250 310 ad 0 06 c 570 650 ad 0 87 c and 1800 1823 ad 0 83 c respectively the temperature variations captured in the record are supported by historical documents and existing regional and global paleoclimate records and correspond in time to a number of the major chinese dynastic transitions importantly the record captures large magnitude up to 4 c centennial scale temperature fluctuations documents cold conditions during the first millennium ad and demonstrates that the post 1989 ad warmth is greater than any other time during the past 2000 years the results suggest that high elevation areas have been more sensitive than low elevation regions to climate variations during the common era

environmental controls on branched tetraether lipid distributions in tropical east african lake sediments abstract quantifying past continental temperature changes is an important aspect of paleoclimate research as it allows us to constrain the amplitude of natural variability test predictive climate models and provide a proper context for changes that may arise in response to anthropogenically induced climate change the recently developed biomarker based methylation index of branched tetraethers cyclization ratio of branched tetraethers mbt cbt proxy shows potential as a new method for continental temperature reconstruction but thus far it has only been applied successfully in ocean margin sediments to assess whether this proxy is also applicable to the sedimentary record in tropical lacustrine systems we investigated the distribution of branched glycerol dialkyl glycerol tetraethers gdgts in recently deposited sediments from 46 lakes in tropical east africa these lakes span a substantial range in surface elevation 770 4500 m above sea level and thus also a wide gradient of mean annual temperature we find that saline lakes excepted branched gdgts are universally abundant in the lakes investigated and can be used to predict mean annual air temperature maat with a high degree of accuracy however the existing global mbt cbt calibration for maat based on soils predicts inaccurate temperatures when applied to our african lake dataset this observation together with the fact that surface water ph and to lesser extent lake depth appear to influence the distribution of branched gdgts among sites leads us to conclude that in situ production of branched gdgts in lakes is likely the robust relationship between branched gdgt distribution and the temperature and ph of african freshwater lakes makes these compounds suitable for paleoenvironmental reconstruction however we urge caution in using branched gdgts in lake sediments to infer past temperatures unless their exact origin can be determined

volcano induced regime shifts in millennial tree ring chronologies from northeastern north america the cooling effect on the earth s climate system of sulfate aerosols injected into the stratosphere by large volcanic eruptions remains a topic of debate while some simulation and field data show that these effects are short term less than about 10 years other evidence suggests that large and successive eruptions can lead to the onset of cooling episodes that can persist over several decades when sustained by consequent sea ice ocean feedbacks here we present a new network of millennial tree ring chronologies suitable for temperature reconstructions from northeastern north america where no similar records are available and we show that during the last millennium persistent shifts toward lower average temperatures in this region coincide with series of large eruptions

tree ring reconstructed summer temperature anomalies for temperate east asia since 800 c e we develop a summer temperature reconstruction for temperate east asia based on a network of annual tree ring chronologies covering the period 800 1989 c e the east asia reconstruction is the regional average of 585 individual grid point summer temperature reconstructions produced using an ensemble version of point by point regression statistical calibration and validation tests indicate that the regional average possesses sufficient overall skill to allow it to be used to study the causes of temperature variability and change over the region the reconstruction suggests a moderately warm early medieval epoch ca 850 1050 c e followed by generally cooler little ice age conditions ca 1350 1880 c e and 20th century warming up to the present time since 1990 average temperature has exceeded past warm epochs of comparable duration but it is not statistically unprecedented superposed epoch analysis reveals a volcanic forcing signal in the east asia summer temperature reconstruction resulting in pulses of cooler summer conditions that may persist for several years substantial uncertainties remain however particularly at lower frequencies thus requiring caution and scientific prudence in the interpretation of this record

fluxes and distribution of tetraether lipids in an equatorial african lake constraints on the application of the tex86 palaeothermometer and bit index in lacustrine settings abstract the distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether gdgt lipids was studied in material from various sources in and around lake challa a crater lake on the southeastern slope of mt kilimanjaro tanzania to examine the provenance of gdgts in lake sediments and their potential application as palaeoenvironmental and palaeoclimatic proxies the study material included samples collected at monthly intervals in a sediment trap over one complete annual cycle particles suspended in the stratified water column profundal surface sediments and soils surrounding the lake the sediment trap time series revealed that crenarchaeol and related isoprenoid gdgts were predominantly produced in january and february following the locally prominent short rain season november december the tex 86 inferred temperature derived from sedimenting particles corresponded well with lake surface water temperature at this time of largest crenarchaeol flux molecular ecological analysis showed that group 1 1a and 1 1b crenarchaeota are the most likely source organisms of these gdgts gdgt 0 in the lake sediments does not only originate from lake surface dwelling crenarchaeota but seems predominantly derived from archaea residing in the deeper anoxic part of the water column the main flux of branched gdgts to the sediment was during the short rain season and is most probably derived from eroded catchment soils in surface run off however a contribution from in situ production of branched gdgts in the lake sediment or water or in groundwater cannot be fully excluded we conclude that palaeoclimatic reconstruction based on branched gdgt distributions in lake sediments should only be performed when the origin of those branched gdgts is well constrained

a review of aridity and groundwater surface hydrological studies are seen as inadequate in hyperarid and arid areas to provide reliable estimates of recharge in most such areas surface discharges are not present so that assessments of groundwater resources are dependent upon ground interpretation and denied the flow control found in assessments elsewhere groundwater models show that gradients are sustained by long term dewatering and very small amounts of modern indirect recharge recharge indications are well within the error of a hydrological balance discharges appear equally small the development of groundwater in arid areas frequently faces problems of salination due to recycling of irrigation water and rising groundwater heads abstraction is often inadequately managed so that uncontrolled mining of groundwater occurs the advantage that groundwater has however is that it offers staged development and staged appraisal

salt crust development in paddy fields owing to soil evaporation and drainage contribution of chloride and deuterium profile analysis summary in northeast thailand lowlands with shallow saline watertable rainfed paddy fields often present high salt concentration in the dry season forming patches or spots of salt crusts on the soil surface in this context the mechanisms implied in salt concentration during dry season were studied by establishing salt budget with evaporation and drainage estimates inside and outside a saline patch drainage was estimated by hydrus 1d modelling constrained by an hydrodynamic characterization and the profile of water contents at the end of dry season evaporation rates at the end of the dry season were computed by interpreting natural detailed profiles of deuterium d and chloride cl contents because of the drastic diminution of hydraulic conductivity at saturation with depth and the decrease of groundwater level at the end of the cropping season simulated hydrological balance with hydrus 1d pointed out zero cumulated fluxes for depths of 39 5 cm outside the saline patch and 37 5 cm inside the saline patch therefore all the chloride accumulated in the very upper layers during dry season comes from the chloride that was present in the 0 39 5 cm layers before the beginning of the drying inside the saline patch the tentative cl budget is coherent with the hypothesis of saturation of the profile by aquifer saline water during the flooding evaporation rates computed from the diffusion of chloride and deuterium at the end of the drying season when the aquifer level was 1 4 m deep range between 0 121 and 0 378 mm d 1 this does not sustain the assumption of a considerable salinity contribution from the aquifer during the dry season moreover evaporation estimates based on cl and d diffusion equilibrium showed depleted rates 38 63 inside the saline patch due to salt accumulation in the first 12 cm of the soil in the vapour transfer layer estimated evaporation rate based on the vapour movement of d was in the same order of magnitude than computed rate assuming liquid cl diffusion this coincidence is attributed to the liquid fluxes that occurred during the expansion of the vapour transfer layer during the progression of the evaporation front

holocene history of landscape instability in iceland can we deconvolve the impacts of climate volcanism and human activity abstract biogeochemical proxy records from icelandic lake sediment track large scale shifts in north atlantic holocene climate and highlight the impact that north atlantic ocean and atmospheric circulation has on iceland s climate and environment following early holocene warmth centennial scale climate change is superimposed on millennial scale cooling culminating in the transition to the little ice age 1300 1900 ce although the long term cooling trend is presumably driven by variations in earth s orbit and the concomitant decline in northern hemisphere nh summer insolation the centennial scale variability has been linked to the strength of the atlantic meridional overturning circulation amoc volcanism coupled with sea ice ocean related feedbacks internal modes of atmospheric variability and plausibly variations in solar irradiance one manifestation of these regional climate changes on iceland is the intensification of soil erosion resulting in the degradation of ecosystems and landscape in recent millennia persistent and severe soil erosion has also been linked to human impact on the environment following the settlement 870 ce rapid population growth introduction of livestock and the poorly consolidated nature of tephra dominated soils lake proxy composite records suggest that although event dominated landscape instability and soil erosion from the early to middle holocene were likely triggered by large volcanic eruptions the landscape was capable of recovering however a threshold was reached 5 ka bp resulting in a state change whereby the icelandic landscape could no longer fully recover from cold events and or tephra fall landscape sensitivity to climate further intensified at 1 5 ka bp as identified by regime shift analysis hence widespread and irreversible soil erosion began several centuries before the acknowledged settlement of iceland with a second acceleration 1250 ce a 2 ka fully coupled climate transient simulation using cesm1 1 shows a 0 5 c reduction in summer temperature around iceland in the first millennium ce consistent with increased landscape instability and soil erosion in iceland a second phase of persistent summer cooling in the model occurs after 1150 ce with stronger cooling after 1450 ce reaching a maximum shortly after 1850 ce 1 c lower than at the start of the simulation our results suggest that natural variations in regional climate and volcanism are likely responsible for soil erosion prior to human impact with intensification of these processes following settlement particularly during the cooling associated with the little ice age given that the conclusions drawn in this review diverge from the standard paradigm of human induced soil erosion history in iceland research should continue to focus on this complex question from multiple disciplines in particular a combination of emerging biogeochemical techniques e g lipid biomarkers and ancient dna may be best poised to test and quantify the relative roles of natural environmental variables and human settlement in the history of soil erosion on iceland

evaporation and land surface energy budget at the salar de atacama northern chile playa systems are driven by evaporation processes yet the mechanisms by which evaporation occurs through playa salt crusts are still poorly understood in this study we examine playa evaporation as it relates to land surface energy fluxes salt crust characteristics groundwater and climate at the salar de atacama a 3000 km 2 playa in northern chile containing a uniquely broad range of salt crust types land surface energy budget measurements were taken at eight representative sites on this playa during winter august 2001 and summer january 2002 seasons measured values of net all wave radiation were highest at vegetated and rough halite crust sites and lowest over smooth highly reflective salt crusts over most of the salar de atacama net radiation was dissipated by means of soil and sensible heat fluxes dry salt crusts tended to heat and cool very quickly whereas soil heating and cooling occurred more gradually at wetter vegetated sites sensible heating was strongly linked to wind patterns with highest sensible heat fluxes occurring on summer days with strong afternoon winds very little energy available at the land surface was used to evaporate water eddy covariance measurements could only constrain evaporation rates to within 0 1 mm d k1 and some measured evaporation rates were less than this margin of uncertainty evaporation rates ranged from 0 1 to 1 1 mm d k1 in smooth salt crusts around the margin of the salar and from 0 4 to 2 8 mm d k1 in vegetated areas no evaporation was detected from the rugged halite salt crust that covers the interior of the salar though the depth to groundwater is less than 1 m in this area these crusts therefore represent a previously unrecorded end member condition in which the salt crusts form a practically impermeable barrier to evaporation q 2005 elsevier b v all rights reserved

distribution of bacterial and archaeal ether lipids in soils and surface sediments of tibetan lakes implications for gdgt based proxies in saline high mountain lakes bacterial and archaeal lipids such as glycerol dialkyl glycerol tetraethers gdgts and dialkyl glycerol diethers are increasingly used as proxies for specific environmental parameters such as air temperature and soil ph in lacustrine environments little is known however about the distribution and applicability of bacterial and archaeal lipids on the tibetan plateau we investigated nine different watersheds across the plateau by way of sediments from lakes and rivers as well as the surrounding soils our transect study included a salinity gradient and focused on saline lakes which are rarely examined we analyzed archaeal isoprenoid i and bacterial branched b gdgts as well as archaeol to trace their sources and environmental factors influencing their distributions we could show that igdgts were produced in situ and bgdgts were primarily soil derived although we could not exclude in situ production of bgdgts in the lakes the most important environmental variables correlating with gdgt distributions were temperature and salinity bacterial gdgt distributions correlated mainly with salinity while archaeal lipid distributions correlated with temperature based on the correlation of methylation mbt and cyclisation cbt indices of bgdgts with ph and mean annual air temperature maat we established local calibrations for the tibetan lakes tex86 could also be applied to reconstruct temperature which was strongly biased towards measured summer lake water temperature indicating enhanced production of igdgts in the summer months existing proxies show therefore potential for palaeoclimate reconstruction on the tibetan plateau if local calibrations are applied

distribution of glycerol dialkyl glycerol tetraether gdgt lipids in a hypersaline lake system isoprenoid glycerol dialkyl glycerol tetraethers isogdgts of archaeal origin and branched br gdgts of bacterial origin occur in a diverse range of lacustrine sedimentary environments they have attracted attention as potential temperature proxies providing high resolution palaeo environmental reconstruction from continental interiors for this study the distribution of gdgts in and application of gdgt based proxies to surface samples from chaka salt lake china as well as soils and in flow river sediments were investigated to assess whether gdgt based proxies were applicable to this hypersaline lake system we show that iso and brgdgts were present in all sediments and soils from the chaka salt lake system gdgt 0 and crenarchaeol were generally the two most abundant isogdgts suggesting thaumarchaeota as a major biological source of isogdgts the low ratio of crenarchaeol crenarchaeol regioisomer suggests that thaumarchaeota of the lake sediments is likely thaumarchaeota group i 1b derived from the surrounding alkaline soils arguing against the use of the tex86 proxy in this system because alkaline soils generally have high isogdgt concentrations it is likely that a large allochthonous input of isogdgts would be a pervasive challenge to palaeoclimate applications in such settings on the other hand the brgdgt distributions in the lake and river sediments differed markedly from those in the surrounding soils suggesting that instead of deriving from the surrounding soils at least part of the brgdgts is synthesized in situ or delivered from more distal upland soils taken together our results indicate that the mixed sources of gdgts in chaka salt lake complicate the application of gdgt based proxies and it will be challenging to use such proxies in this system

calibration and application of the branched gdgt temperature proxy on east african lake sediments branched glycerol dialkyl glycerol tetraethers brgdgts are a novel proxy for mean annual air temperature maat and have the potential to be broadly applicable to climate reconstruction using lacustrine sediments several calibrations have been put forth relating brgdgt distributions to maat using a variety of linear regressions including the methylation mbt and cyclization cbt indices of brgdgts the relative abundances of the major non cyclized brgdgts mbrgdgts and best subsets regression bsr of the fractional abundances of the nine most common brgdgts however these calibrations have rarely been applied to lake sediment cores to reconstruct temperatures and test the applicability of this proxy as a paleothermometer we present an expanded east african lakes surface sediment brgdgt dataset based upon 111 lakes and examine three methods of calibrating brgdgts to maat these methods include recalculations of the east african lake mbt cbt calibration and mbrgdgts calibrations as well as a new stepwise forward selection sfs calibration that uses the four combined brgdgts that explain the most variance in temperature in our calibration set we apply these new calibrations as well as five previously published lacustrine brgdgt calibrations to the brgdgt distributions of our surface sediment dataset and a 48 kyr sediment core from sacred lake mt kenya producing the first brgdgt temperature reconstruction available from a small tropical lake we compare the reconstructed temperatures to previously published paleotemperature records from east africa to help us assess the performance of the brgdgt calibrations we find that the sfs calibration has a consistently low root mean squared error of prediction rmsep over the entire range of maat while the mbt cbt and mbrgdgt calibrations have relatively large rmseps particularly between lakes with similar temperatures but variable ph this suggests that these techniques do not properly deconvolve the temperature and ph signals recorded in the distributions of the brgdgts we further find that only the sfs calibration produces a credible reconstructed temperature history from sacred lake when compared to other last glacial maximum paleotemperature estimates from east africa thus we advocate for the use of the sfs calibration when reconstructing paleotemperatures from brgdgts in east africa

distributions of branched gdgts in a tropical lake system implications for lacustrine application of the mbt cbt paleoproxy branched glycerol dialkyl glycerol tetraether gdgt lipids are abundant and ubiquitous in lake sediments potentially allowing for a paleolimnological application of the so called mbt cbt proxy methylation index of branched tetraethers cyclization ratio of branched tetraethers to investigate the origin and characteristics of these compounds in lacustrine environments we examined the distributions of gdgts in soils river sediments and lake sediments from lake towuti on the island of sulawesi indonesia we found significant differences in the degree of methylation and cyclization expressed by way of the mbt and cbt indices between the soil samples and the aquatic samples suggesting that there may be in situ production of gdgts in the aquatic environment based on these findings we urge caution in the application of the mbt cbt paleoproxy to lake sediments and encourage more rigorous study of these compounds in freshwater environments

salt lakes a discussion of processes influencing palaeoenvironmental interpretation and recommendations for future study abstract the observed state of a salt lake system reflects the interaction of groundwater runoff surface water porewater and sediments aeolian transport and chemical and biological reactions these processes in turn affect the lacustrine biota the sediment composition deposition diagenesis deflation and re deposition and the geomorphic features of the salt lake the interactive processes thereby control the deposition and preservation of the palaeoenvironmental record in salt lakes consequently considerable understanding of these processes is required to recover palaeoclimatic and palaeoenvironmental detail from the sedimentary record during the recent sleads workshop participants recognized several key discipline research needs and herein make recommendations for future salt lake research covering 1 hydrology and hydrochemistry 2 geomorphology and stratigraphy 3 mineralogy isotopes and trace metals and 4 biology

in situ produced branched glycerol dialkyl glycerol tetraethers in suspended particulate matter from the yenisei river eastern siberia abstract soil derived branched glycerol dialkyl glycerol tetraethers brgdgts in marine river fan sediments have a potential use for determining changes in the mean annual temperature mat and ph of the river watershed soils prior to their incorporation in marine sediments the compounds are transported to the marine system by rivers however emerging evidence suggests that the brgdgts in freshwater systems can be derived from both soil run off and in situ production the production of brgdgts in the river system can complicate the interpretation of the brgdgt signal delivered to the marine system therefore we studied the distribution of brgdgt lipids in suspended particulate matter spm of the yenisei river chromatographic improvements allowed quantification of the recently described hexamethylated brgdgt isomer characterized by having two methyl groups at the 6 6 instead of the 5 5 positions in an environmental dataset for the first time this novel compound was the most abundant brgdgt in spm from the yenisei its fractional abundance correlated well with that of the 6 methyl isomer of the hexamethylated brgdgt that contains one cyclopentane moiety the yenisei river watershed is characterized by large differences in mat 11 c as it spans a large latitudinal range 46 73 n which would be expected to be reflected in brgdgt distributions of its soils however the brgdgt distributions in its spm show little variation furthermore the reconstructed ph values are high compared to the watershed soil ph we therefore hypothesize that the brgdgts in the yenisei river spm are predominantly produced in situ and not primarily derived from erosion of soil this accounts for the absence of a change in the temperature signal as the river water temperature is more stable using a lake calibration the reconstructed temperature values agree with the mean summer temperatures mst recorded the brgdgts delivered to the sea by the yenisei river during this season are thus not soil derived possibly complicating the use of brgdgts in marine sediments for palaeoclimate reconstructions

the late quarternary salinity record of lake frome south australia evidence from na in stratigraphically preserved gypsum abstract traces of foreign ions are incorporated into the structure of gypsum during precipitation the amount of foreign material included in the crystal is dependent on its concentration in the precipitating solution and therefore the trace element composition of the gypsum can be related to the composition of brines from which it precipitated a late quaternary salinity record for lake frome south australia derived from the analysis of na in gypsum is consistent with much of the previously inferred climatic history of southeast australia the record indicates three periods of lake filling at 17 000 yr b p from 15 000 to 13 500 yr b p and from 13 000 to 11 000 yr b p lake frome was dry prior to 17 000 yr b p between 16 500 and 15 000 yr b p at 13 000 yr b p and between 6000 and 4000 yr b p

holocene high resolution quantitative summer temperature reconstruction based on subfossil chironomids from the southeast margin of the qinghai tibetan plateau this paper reports the first quantitative summer mean july temperature reconstruction based on subfossil chironomids from the southeast margin of the qinghai tibetan plateau qtp covering the end of the last deglaciation and the entire holocene spanning 11 800 cal yr bp to the present the record is based on 223 chironomid samples throughout a 927 cm sediment core providing a temporal resolution of 50 years per sample we validate the record by applying several statistical reconstruction diagnostics and comparing with pollen and diatom records from the same sediment core the record suggests the summer temperature varies by 2 5 c across the entire period a generally warmer period occurred between c 8500 and c 6000 cal yr bp and a cooling trend was initiated from c 5500 cal yr bp the overall pattern broadly matches the summer insolation at 30 n and the asian summer monsoon records from the surrounding regions suggesting that summer temperatures from the southeast margin of the qtp respond to insolation forcing and monsoon driven variability on a multi millennial time scale modifications of this overall trend are observed on the finer temporal resolution and we suggest that solar activity could be an important mechanism driving the centennial scale variability it may have a strengthened effect in the late holocene when the monsoon influence weakened further detailed investigation is needed to disentangle these effects on the climate change over the highlands of southwestern china

uncertainties around modelling of steady state phreatic evaporation with field soil profiles of δ18o and chloride summary the application of the general advection diffusion equation to model phreatic evaporation flux rates from solute concentration soil profiles has been applied to a variety of arid zone locations but the effects of heterogeneous and uncertain field data on modelling performance are rarely described we revisit and extend the model by accounting for the effects of variable water content and sediment type on the impedance factor and in turn effective diffusion coefficient we explore the local sensitivity of the extended model to its major assumptions and parameter values the mean diffusion coefficient of the soil profile data is most sensitive to the volumetric water content close to the evaporation front and so modelled evaporation results can be very sensitive to uncertainty around the position of the evaporation front the uncertainty in the position of the groundwater reservoir and its concentration has little effect where the lower part of the profile shows an asymptotic trend towards a representative value of groundwater concentration but can vary substantially with different values of groundwater depth and concentration if this is not the case field data from the southern margin of the great artesian basin are shown to exhibit considerable uncertainty around the boundary conditions of the advection diffusion model e g position of evaporation front depth and concentration of lower groundwater boundary condition resulting phreatic evaporation flux estimates show a wide range that needs to be considered when using these data in water balance studies of groundwater systems

synchronous change of temperature and moisture over the past 50 ka in subtropical southwest china as indicated by biomarker records in a crater lake abstract over the past few decades studies on the indian summer monsoon ism have been mainly based on paleo marine records whilst the sparsity of land records limits our understanding of the ism evolutionary process over continental landscapes here we provide paleoclimate reconstructions based on n alkanes and branched glycerol dialkyl glycerol tetraethers brgdgts from a 50 ka lacustrine sediment core collected from lake tengchong qinghai in southwestern subtropical china our results reveal that the botanical sources of sedimentary n alkanes in this lake are mainly from aquatic macrophytes and terrestrial plants the lake level evolution from the mis 3 to the holocene can be divided into four stages high in the mis 3 low in the lgm high in last deglacial and low in mid and late holocene our brgdgts based climate reconstructions indicate that the mean air temperature differences between the present day and the lgm were up to about 3 4 c from mis 3 to holocene there was a broadly and consistently synchronous trend between precipitation and air temperature in this ism region this is different from the asynchronous temperature and precipitation variations in the east asian summer monsoon easm regions in the period of last glacial termination our study shows that the climate in ism regions was primarily driven by changes in june summer solar insolation at 30 n and those glacial boundary conditions such as ice volume and sea surface temperature might also have affected the ism

century scale solar variability and alaskan temperature change over the past millennium 1 correlation of geologic histories from 130 alaskan glaciers with a record of solar variation suggests that multi decadal to century scale temperature variations in the north pacific and arctic sectors have been influenced by solar forcing over the past thousand years mountain glacier fluctuations are primarily a record of summer cooling and the composite glacial history from three climatic regions across alaska shows ice expansions approximately every 200 years compatible with a solar mode of variability the modulating effects of the cold phases of the pacific decadal oscillation and the arctic oscillation may when in phase with decreased solar activity serve to amplify cooling forcing glacier advance

paleoclimatic reconstruction and the response of carbonate minerals during the past 8000 years over the northeast tibetan plateau abstract the climatic significance of the carbonate content and composition of lake sediments remains unclear in this study we analyzed the glycerol dialkyl glycerol tetraethers and mineral contents of alake lake sediments to reconstruct temperature and moisture changes over the northeast tibetan plateau since 8000 cal yr bp we identified warm cold and wet dry conditions during the roman warm period and holocene climate optimum early neoglacial cooling period accompanied by a dominance of aragonite monohydrocalcite based on our results and previous laboratory experiments we suggest that monohydrocalcite is predominantly deposited in colder drier and higher mg ca conditions relative to that of aragonite the carbonate mineral composition should therefore be fully considered when sediment carbonate contents are used to reconstruct paleotemperature moisture changes

sandy contourites of the lower kazusa group in the boso peninsula japan kuroshio current influenced deep sea sedimentation in a plio pleistocene forearc basin abstract bottom current influenced sandy sediments sandy contourites were identified in outer fan and basin plain deposits of the kazusa group the infill of the plio pleistocene kazusa forearc basin in the boso peninsula of japan these are characterized by traction structures such as parallel lamination and ripple cross lamination together with minor inverse grading and wave ripple lamination in particular ripple cross lamination is commonly associated with mud drapes and flaser and lenticular bedding in general sedimentary structures of these sandy contourites do not display any regular vertical sequences such as the bouma sequence in turbidites these lithofacies indicate oscillating traction and suspension deposition in a deep sea environment and are interpreted to document long erm fluctuation in bottom currents additionally internal erosion surfaces in some of the sandy contourites similarly record fluctuations between periods of erosion versus deposition in general paleocurrent directions of sandy contourites are variable compared to those of associated turbidites the latter indicate northeastward to southeastward downslope transport in the kazusa forearc basin in contrast some paleocurrents of sandy contourites fall in a range of directions from north to northwest and other paleocurrents fall in a range of directions from south to southwest these indicate largely alongslope bottom currents although some upslope and downslope directed paleocurrents were also recognized within the sequence stratigraphic framework for the kazusa group no distinct relationship between paleocurrent directions of sandy contourites and associated systems tracts was evident variations in speed and direction of deep water currents under the modern kuroshio current and its associated deep sea environments have been documented off the japanese islands thus analogous processes appear to have been responsible for the deposition of sandy contourites in the kazusa forearc basin during the pliocene through pleistocene

identification and carbon isotope composition of a novel branched gdgt isomer in lake sediments evidence for lacustrine branched gdgt production branched glycerol dialkyl glycerol tetraethers brgdgts are bacterial membrane lipids that occur ubiquitously in soils and lacustrine sediments and have great potential as proxy indicators for paleotemperature and ph reconstructions initially brgdgts in lakes were thought to originate from soils of the watershed the composition of the lacustrine brgdgt pool however often differs substantially from that in catchment soils complicating the application of the brgdgt paleothermometer to lake sediments this suggests that terrigenous brgdgt signals in lacustrine sedimentary archives may be affected by aquatic in situ production in sediments of a swiss mountain lake we detected a novel hexamethylated brgdgt which elutes between the known 5 and 6 methyl brgdgt isomers during hplc ms analysis this novel isomer accounted for 8 5 of the total brgdgts most remarkably this brgdgt was not detected in soils collected from the catchment of the lake providing circumstantial evidence for an in situ brgdgt source in the lake s water column or sediments isolation of the compound by preparative hplc and subsequent gc ms analysis of the alkyl chains revealed that the novel brgdgt comprises two structural isomers one possesses a 5 13 16 and a 6 13 16 trimethyloctacosanyl moiety and constitutes 84 of the new brgdgt the second contains a 13 16 dimethyloctacosanyl and a 5 13 16 23 tetramethyloctacosanyl moiety the 13c values of both the alkyl chains derived from the novel brgdgt 46 and all other major brgdgts 43 to 44 were significantly lower than those of brgdgt derived alkanes in catchment soils 27 to 28 further attesting to in situ production of brgdgts in the studied lake

late holocene temperature fluctuations on the tibetan plateau abstract proxy data of palaeoclimate like ice cores tree rings and lake sediments document aspects of climate changes on the tibetan plateau during the last 2000 years the results show that the tibetan plateau experienced climatic episodes such as the warm intervals during ad 800 1100 and 1150 1400 the little ice age between ad 1400 and 1900 and an earlier cold period between the 4th and 6th centuries in addition temperatures varied from region to region across the plateau a warm period from ad 800 to 1100 in the northeastern tibetan plateau was contemporaneous with cooling in the southern tibetan plateau which experienced warming between ad 1150 and 1400 large scale trends in the temperature history from the northeastern tibetan plateau resemble those in eastern china more than the trends from the southern plateau the most notable similarities between the temperature variations of the tibetan plateau and eastern china are cold phases during ad 1100 1150 1500 1550 1650 1700 and 1800 1850

continental scale temperature variability during the past two millennia past global climate changes had strong regional expression to elucidate their spatio temporal pattern we reconstructed past temperatures for seven continental scale regions during the past one to two millennia the most coherent feature in nearly all of the regional temperature reconstructions is a long term cooling trend which ended late in the nineteenth century at multi decadal to centennial scales temperature variability shows distinctly different regional patterns with more similarity within each hemisphere than between them there were no globally synchronous multi decadal warm or cold intervals that define a worldwide medieval warm period or little ice age but all reconstructions show generally cold conditions between ad 1580 and 1880 punctuated in some regions by warm decades during the eighteenth century the transition to these colder conditions occurred earlier in the arctic europe and asia than in north america or the southern hemisphere regions recent warming reversed the long term cooling during the period ad 1971 2000 the area weighted average reconstructed temperature was higher than any other time in nearly 1 400 years

cl br ratios and environmental isotopes as indicators of recharge variability and groundwater flow an example from the southeast murray basin australia abstract systematic variations in cl br ratios together with r 36 cl values 14 c activities and 18 o values reflect differences in groundwater recharge and define groundwater flow paths in the riverine province of the southeast murray basin in groundwater from the shallowest shepparton formation homogenisation of cl br and 18 o values and a decline in 14 c activities with depth imply that vertical flow dominates the 14 c activities define variations in pre land clearing recharge in the palaeovalleys of present day rivers deep leads which contain sandier sediments higher recharge 0 5 to 1 4 mm year produced relatively fresh groundwater tds 36 cl values in groundwater from the goulburn subcatchment zones of groundwater with variable cl br ratios in the deeper calivil renmark aquifer also allow the detection of rapid leakage from the surface that has the potential to compromise groundwater resources

evidence for a mesoscale thermal circulation over dry salt lakes abstract because of albedo and thermal conductivity effects dry salt lakes in central australia exhibit a characteristics thermal signature within the overall landscape having much cooler daytime surface temperatures and warmer nocturnal temperatures than the surrounding environment various aspects of a possible mesoscale thermal circulation arising from such a thermal differentiation have been investigated for the salt lake a moderately sized 70 km 2 dry salt lake in northwestern new south wales 30 05 s 142 08 e surface temperatures across the salt lake and surrounding landscape determined by field and polar orbiting noaa 9 satellite observations show marked variation with the salt crust remaining up to 16 k cooler than the surrounding sand country during the day and up to 8 k warmer at night that this thermal forcing can provide a horizontal pressure gradient sufficiently strong to induce air motion is confirmed by analysis of hourly output from a network of anemographs which were established around the perimeter of the salt lake during a five month autumn and winter period an extremely regular pattern of nocturnal near surface convergence lake warm and daytime divergence lake cool is shown a pattern which is enhanced when data are stratified for anticyclonic conditions with a weak pressure gradient 24 of total observations wind roses produced for a number of sites around the lake show a distinct diurnal reversal in near surface airflow with generally onshore flow by day and offshore flow at night confirmation that a diurnally reversing thermal circulation does operate under certain conditions at the salt lake is provided by pilot balloon analysis of winds aloft and by preliminary mesoscale modelling of airflow this circulation which has not previously been described in the literature may have important environmental and climatic implications in the australian context

effects of temperature ph and nutrient concentration on branched gdgt distributions in east african lakes implications for paleoenvironmental reconstruction branched glycerol dialkyl glycerol tetraethers brgdgts are membrane lipids found in soils and sediments and their relative abundance correlates with temperature and ph enabling them to be used as proxies in reconstructing past climatic and environmental conditions however the potential for other environmental variables such as nutrient concentration to affect brgdgt distributions remains largely unexplored we have examined the influence of a suite of environmental factors including temperature lake water and sediment chemistry and lake morphometry on brgdgt concentration and distributions in the surface sediments of 111 lakes in east africa we found that temperature was the major control on the distributions while the influence of ph was relatively minor water depth also had a minor but statistically significant influence perhaps due to the relationship between lake depth and deep water anoxia water column nutrient concentration did not have a significant effect on the distributions or concentration we further explored the potential for these variables to affect brgdgt temperature reconstruction by examining the correlation between them and the residuals of our brgdgt temperature calibration we found that while the distribution of some cyclized brgdgts may be influenced by ph and other environmental variables they are necessary in brgdgt calibration equations in order to accurately reconstruct temperature likely due to covariation between temperature and other environmental variables while surface water ph correlated with the relative abundance of certain brgdgts caution should be exhibited when using brgdgts as a ph proxy because of systematic calibration errors

distributions and temperature dependence of branched glycerol dialkyl glycerol tetraethers in recent lacustrine sediments from china and nepal 1 glycerol dialkyl glycerol tetraether gdgt membrane lipids in surface sediments from 24 lakes in china and nepal were analyzed the result shows that branched gdgt lipids occur widely in the studied lake sediments the different distribution of branched gdgts between the chinese soils from weijers et al 2007b and the chinese lake sediments indicates that the branched gdgts in the lacustrine sediment are the mixture of allochthonous and autochthonous branched gdgts our result supports the suggestion that temperature is the principal factor affecting the distribution of gdgts seasonality sources and precipitation increase the uncertainty of the correlation between the methylation index of branched tetraethers mbt cyclization ratio of branched tetraethers cbt proxy and the temperature the correlations of the mbt cbt index with mean annual air temperature t for the global lakes are t 6 803 7 062 cbt 37 090 mbt n 139 p 0 0001 r2 0 62 and rmse 5 24 c for the global lakes with ph 8 5 t 3 949 5 593 cbt 38 213 mbt n 100 p 0 0001 r2 0 73 and rmse 4 27 c the significant correlation suggests that the mbt cbt proxy might be used as a potential paleotemperature proxy in the limnic environment the mbt cbt proxy provides an independent way to evaluate and verify the sensitivities of the different proxies for paleotemperature reconstruction from lacustrine sediments

temperature induced dry climate in basins in the northeastern tibetan plateau during the early to middle holocene abstract ongoing global warming will have a significant impact on terrestrial water resources especially in arid and semi arid regions assessing changes in the hydrology and water resources in inland basins under a warm climate in the recent geological past can provide a valuable context for assessing their current and possible future status here we present a record from a rapidly accumulating sediment core from lake dalianhai in the gonghe basin in the northeastern tibetan plateau the chronology of the uppermost 51 63 m of the core is based on ams 14c dates from 11 samples of terrestrial plant microfossils and 14 bulk samples hydroclimatic variations within the basin during the last 23 000 yr were reconstructed from sedimentological and geochemical parameters and paleoshoreline records the results indicate that the gonghe basin experienced relatively arid conditions during 23 000 14 700 cal yr bp lake dalianhai was refilled at 14 700 cal yr bp and a high lake level was sustained until the beginning of the holocene as indicated by changes in the concentration of oh gdgts however the lake level was low during the early to middle holocene 11 700 4700 cal yr bp and increased during the late holocene based on a comparison with lake level records and aeolian sand deposits from the region we conclude that the climate was extremely dry in basins in the northeastern tibetan plateau during the early to middle holocene we propose that strong evaporation combined with high summer temperatures during the early to middle holocene were responsible for the dry climate at that time rather than changes in mid latitude precipitation given the situation occurred during the early to middle holocene ongoing global warming may seriously threaten water resources in inland china even if precipitation increases substantially

latest pleistocene and holocene vegetation and climate history inferred from an alpine lacustrine record northwestern yunnan province southwestern china abstract reconstructing past changes of the summer monsoon in southwestern china is key to understanding the paleoclimatic dynamics of the indian summer monsoon southwest monsoon a major tropical system with impacts beyond the region high resolution pollen and conifer stoma data are presented from a sediment core tiancai lake located just below treeline in the hengduan mountains northwestern yunnan province of china these data record changes in vegetation and climate for the latest pleistocene and holocene c the last 12 230 cal yr bp and by comparing these results with the pollen records from the nearby erhai lake and lugu lake a regional climate history in yunnan province can be inferred during the period of 12 230 11 510 cal yr bp open alpine meadow around tiancai lake indicates a relatively cold and dry climate corresponding to the younger dryas cold event yd between 11 510 and 10 000 cal yr bp the vegetation types around tiancai lake changed into picea and abies forest and alpine rhododendron shrubland reflecting increases in the temperature and humidity from 10 000 to 6100 cal yr bp tsuga forest expanded persistently toward tiancai lake indicating further climate changed towards warmer and wetter conditions between 6100 and 3410 cal yr bp tsuga forest was the dominant vegetation type nearest to tiancai lake denoting warm and humid climatic conditions corresponding to the holocene climatic optimum in the northwestern yunnan province tsuga forest in mountains around lugu lake shrank quickly at 3410 cal yr bp reflecting significant decline of humidity since 2930 cal yr bp tsuga forest around tiancai lake shrank gradually indicating a fluctuating decrease of temperature these climatic changes reflect changes of the southwest monsoon namely warm and humid climate indicating strong southwest monsoon cold and dry climate denoting weak southwest monsoon