persistent millennial scale climatic variability over the past 25 000 years in southern africa abstract data from stalagmites in the makapansgat valley south africa document regional climatic change in southern africa in the late pleistocene and holocene a new tims u series dated stalagmite indicates speleothem growth from 24 4 to 12 7 ka and from 10 2 to 0 ka interrupted by a 2 5 ka hiatus high resolution oxygen and carbon stable isotope data suggest that postglacial warming was first initiated 17 ka was interrupted by cooling probably associated with the antarctic cold reversal and was followed by strong warming after 13 5 ka the early holocene experienced warm evaporative conditions with fewer c4 grasses cooling is evident from 6 to 2 5 ka followed by warming between 1 5 and 2 5 ka and briefly at ad 1200 maximum holocene cooling occurred at ad 1700 the new stalagmite largely confirms results from shorter holocene stalagmites reported earlier the strongest variability superimposed on more general trends has a quasi periodicity between 2 5 and 4 0 ka also present are weaker 1 0 ka and 100 year oscillations the latter probably solar induced given similarities to the antarctic records the proximate driving force producing millennial and centennial scale changes in the makapansgat record is postulated to be atmospheric circulation changes associated with change in the southern hemisphere circumpolar westerly wind vortex

the geochemistry of vanadiferous magnetite in the bushveld complex implications for crystallization mechanisms in layered complexes detailed trace element analyses of pure magnetite from four continuous borehole intersections through the main magnetitite layer from the upper zone of the rustenburg layered suite of the bushveld complex are presented one section has been analysed at one centimetre intervals rapid depletion of cr occurs over short vertical sequences near the base of the layer which is due to bottom crystallization and the resulting chemical depletion of a thin layer of liquid sudden increases in cr content of magnetite are attributed to convection cells which bring undepleted magma into the zone or crystallization we suggest that these cells individually have lateral extents no greater than hundreds of metres but collectively may be traced at a specific stratigraphic horizon for several tens of km this lateral traceability of the effect of convection cells at approximately uniform stratigraphic height demonstrates the long held implicit assumption that time planes are in general parallel to the layering and does not support the hypothesis that layers in the bushveld complex grew laterally the activity of these cells is highly variable with long periods of quiescence interspersed with periods of rapid small scale overturn most convection cells do not impinge upon the floor and the abruptness of the resulting chemical reversal is largely a function of the thickness of the layer of depleted liquid trapped between the cumulates and the sole of the convection cell occasionally these cells do touch the cumulate pile and may even cause erosion this material may be redeposited elsewhere in the magnetitite layer either as mineralogically distinct fragments if erosion penetrated below the layer or in the present instance as a chemically chaotic pile of magnetite the abruptness of the chemical reversals severely restricts the extent to which post cumulus redistribution of elements or re equilibration with percolating trapped liquid infiltration metasomatism may have occurred the appearance of disseminated plagioclase in magnetite layers in variable proportions and in a non systematic manner in the four profiles is attributed to fluctuations in pressure

on the interpretation of caribbean paleo temperature reconstructions during the younger dryas 1 a conundrum exists regarding whether the sea surface temperatures decreased or increased over the southern caribbean and the western tropical atlantic region during the younger dryas when the north atlantic cooled substantially and the atlantic thermohaline circulation was weakened significantly despite the proximity of core locations some proxy reconstructions record a surface cooling while others indicate a warming we suggest that this seemingly paradoxical finding may at least partially be attributed to the competing physical processes that result in opposing signs of temperature change in the region in response to weakened north atlantic meridional overturning circulation our coupled ocean atmosphere model experiments indicate that the temperature response over the southern caribbean and western tropical atlantic regions is complex and can vary considerably in small spatial scales depending on the nature of physical processes that dominate

characterization of the last deglacial transition in tropical east africa insights from lake albert abstract new biomarker analyses from lake albert east africa spanning 15 9 ka show the most extreme abrupt multi stage climate and environmental shifts during the last deglacial transition of anywhere in africa records of hydroclimate expressed in compound specific d values from terrestrial leaf waxes and a tex86 paleotemperature record support multiple stages of pronounced drying and cooling from 13 8 to 11 5 ka and demonstrate the dynamic behavior of the low latitude tropics during the deglaciation the vegetation response illustrated by compound specific 13c values and fossil pollen records was an expansion of c4 grassland when the region was cool and arid these results advance our understanding of a spatially and temporally complex regional response to global climate forcing suggesting weakening of the indian ocean monsoon at the end of the pleistocene that coincides with a minor decrease in the rate of the atlantic meridional overturning circulation amoc and during a time of stepwise cooling in the northern high latitudes

reconstruction of a paleotemperature record from 0 3 3 7ka for subtropical south china using lacustrine branched gdgts from huguangyan maar abstract the concentrations of glycerol dialkyl glycerol tetraethers gdgts in catchment soils suspended particulate matter spm lake bottom sediments and sediment cores from huguangyan maar subtropical south china were investigated the distribution of isoprenoid gdgts has gdgt 0 crenachaol 2 and therefore the widely used tex 86 is precluded from being used for the calculation of lake water temperature in this lake the total concentration of branched gdgts br gdgts in the soils spm and lake bottom sediments ranged from 91 3 223 7 ng g 17 8 41 4 ng l and 864 2 2008 6 ng g respectively the molecular composition of br gdgts mbt values methylation of br gdgts and cbt values the cyclization ratio of br gdgts in the catchment soils differ from those in lake materials this difference indicates that br gdgts in the lake are largely produced in situ based on the global lake specific mbt cbt mat mean air temperature calibration the air temperature was reconstructed for lacustrine material in huguangyan maar the estimates fall in the range 23 2 23 8 c similar to the average value of local mat for the preceding 45 years the paleotemperature history of huguangyan maar was reconstructed using br gdgts extracted from a sediment core spanning the period 0 3 3 7 ka and ranged from 24 6 to 26 3 c the temperature pattern of huguangyan maar based on the global lake specific mbt cbt mat resembles those recorded in east china using numerous indicators the pattern consists of five cool and four warm periods including two distinct phases within the medieval warm period 900 1300 ad the coldest temperature in the little ice age 1550 1850 ad and reveals even finer temperature variations than other indicators this new method based on br gdgts produced in situ in the subtropical lacustrine environment provides a new sensitive and precise paleotemperature proxy for lacustrine sediments for which other gdgt based proxies are not applicable

insights into continental temperatures in the northwestern black sea area during the last glacial period using branched tetraether lipids abstract in the continental realm continuous quantitative temperature reconstructions spanning the last glacial are rare especially in central and eastern europe here we provide a reconstruction from the northwestern black sea catchment spanning 40 to 9 ka bp from a study of the relative distribution of branched glycerol dialkyl glycerol tetraethers brgdgts in black sea lacustrine sediments first the origins of brgdgts are discussed the comparison of geochemical proxies from the same core supports a dominant terrestrial origin for brgdgts during the last glacial and a strong decrease in the soil derived brgdgt proportion toward the holocene since the lowering of soil vs lacustrine derived brgdgts is prone to bias the temperature signal that is reconstructed using a soil calibration a correction for in situ production is applied the corrected signal is compared to independent discrete temperature records from the study area the brgdgt temperature relative evolution reconstructed in this work provides additional insight regarding millennial scale climate variability in central and eastern europe notably the imprints of heinrich event cold spells and lateglacial climatic oscillations are consistent with other regional paleorecords from the northern hemisphere

climate variability over the last 2000 years inferred from glycerol dialkyl glycerol tetraethers gdgts in alkaline nalin lake of inner mongolia china nalin lake from western inner mongolia of china is a shallow oxbow lake with a laminated sedimentary record the distributions of glycerol dialkyl glycerol tetraethers in lacustrine sediment core collected in nalin lake in june 2011 were examined in combination with other paleoclimate proxies the cyclization index of branched tetraethers cbts inferred ph values changed primarily between 7 67 and 8 63 these changes were synchronous with those from the actual measurement and previous studies the newly proposed cbt methylation index of branched tetraethers mbts palaeothermometer was also applied to produce a mean annual air temperature record for nalin lake spanning circa the last 2000 years over much of the record temperature fluctuated from 2 76 to 7 61 c with a mean value of 4 76 c the proposed cbt mbt based temperatures revealed a strong similarity to the local records both documenting the moderate medieval warm period from 600 to 1200 a d 1400 800 cal year bp and a cooling anomaly little ice age around 16th century the cbt mbt temperature patterns seemed to follow variations in the historical and northern hemisphere records of the mean annual air temperature these suggested that the signals were produced during this period identification of high alkalinity in association with the decreased fluvial input by multiple indices was consistent with the previous observations due to the cutoff of yellow river channel therefore cbt mbt temperature records of lake sediment core can potentially be a useful tool in reconstructing past variations of alkaline lacustrine climate

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

timing of the antarctic cold reversal and the atmospheric co2increase with respect to the younger dryas event the transition from the last glacial to the holocene is a key period for understanding the mechanisms of global climate change ice cores from the large polar ice sheets provide a wealth of information with good time resolution for this period however interactions between the two hemispheres can only be investigated if ice core records from greenland and antarctica can be synchronised accurately and reliably the atmospheric methane concentration shows large and very fast changes during this period these variations are well suited for a synchronisation of the age scales of ice cores from greenland and antarctica here we confirm the proposed lead of the antarctic cold reversal on the younger dryas cold event the antarctic cooling precedes the younger dryas by at least 1 8 kyr this suggests that northern and southern hemispheres were in anti phase during the younger dryas cold event a further result of the synchronisation is that the long term glacial interglacial increase of atmospheric co 2 was not interrupted during the younger dryas event and that atmospheric co 2 changes are not necessarily dominated by changes in the north atlantic circulation

gisp2 oxygen isotope ratios the gisp2 oxygen isotope record with its high resolution detail yields crucial information on past climate change the glacial 18o oscillations of the gisp2 core with their very fast onsets are templates of a prototype oscillation of variable duration with an amplitude of 3 9 the halfway mark of the cold warm transition is reached in 2 years the top is reached in 50 years the 18o time gradient of the leading front is about 7 8 per 100 yr after reaching the top 18o slowly declines by 0 14 per 100 yr the duration of 18o decline varies from a couple of centuries for fast oscillations to about 4000 yr for slower ones the subsequent 18o downturn during the warm cold transition has a 18o time gradient of 3 2 per 100 yr and lasts about 80 yr

warm ocean is eroding west antarctic ice sheet 1 satellite radar measurements show that ice shelves in pine island bay have thinned by up to 5 5 m yr 1 over the past decade the pattern of shelf thinning mirrors that of their grounded tributaries the pine island thwaites and smith glaciers and ocean currents on average 0 5 c warmer than freezing appear to be the source the synchronised imbalance of the inland glaciers is the result of reduced lateral and basal tractions at their termini and the drawdown of grounded ice shows that antarctica is more sensitive to changing climates than was previously considered

holocene climatic and environmental change on the western tibetan plateau revealed by glycerol dialkyl glycerol tetraethers and leaf wax deuterium to hydrogen ratios at aweng co mean annual air temperature maat and precipitation isotope records for the holocene were obtained from the analysis of the relative distribution of branched glycerol dialkyl glycerol tetraethers and compound specific hydrogen isotope ratios of leaf waxes from a sediment core from aweng co on the western tibetan plateau wtp our results indicate that the indian monsoon mainly influenced aweng co during the holocene during the early holocene when summer insolation was at a maximum the monsoonal influence was strong and the climate was warm and wet both the summer and winter insolation were relatively weak and aweng co was cool and dry during the middle holocene 6 3 ka indicating a weakening of the indian monsoon the southward displacement of the intertropical convergence zone and relatively low atmospheric methane content may have contributed to the middle holocene cooling on the wtp during the late holocene with a further increase in winter insolation and decrease in summer insolation the summer monsoon weakened and the maat on the wtp gradually increased depleted leaf wax hydrogen isotope ratios during the late holocene can be attributed to accelerated glacier melting because of the elevated maat

holocene interdependences of changes in sea surface temperature productivity and fluvial inputs in the iberian continental shelf tagus mud patch 1 sea surface temperature sst marine productivity and fluvial input have been reconstructed for the last 11 5 calendar cal ka b p using a high resolution study of c37 alkenones coccolithophores iron content and higher plant n alkanes and n alkan 1 ols in sedimentary sequences from the inner shelf off the tagus river estuary in the portuguese margin the sst record is marked by a continuous decrease from 19 c at 10 5 and 7 ka to 15 c at present this trend is interrupted by a fall from 18 c during the roman and medieval warm periods to 16 c in the little ice age river input was very low in the early holocene but increased in the last 3 cal ka b p in association with an intensification of agriculture and deforestation and possibly the onset of the north atlantic oscillation atlantic multidecadal oscillation modes of variability river influence must have reinforced the marine cooling trend relative to the lower amplitude in similar latitude sites of the eastern atlantic the total concentration of alkenones reflects river induced productivity being low in the early holocene but increasing as river input became more important rapid cooling of 1 2 c occurring in 250 years is observed at 11 1 10 6 8 2 6 9 and 5 4 cal ka b p the estimated age of these events matches the ages of equivalent episodes common in the ne atlantic mediterranean region this synchronicity reveals a common widespread climate feature which considering the twentieth century analog between colder ssts and negative north atlantic oscillation nao is likely to reflect periods of strong negative nao

tropical climates at the last glacial maximum a new synthesis of terrestrial palaeoclimate data i vegetation lake levels and geochemistry palaeodata in synthesis form are needed as benchmarks for the palaeoclimate modelling intercomparison project pmip advances since the last synthesis of terrestrial palaeodata from the last glacial maximum lgm call for a new evaluation especially of data from the tropics here pollen plant macrofossil lake level noble gas from groundwater and delta 18 o from speleothems data are compiled for 18 2 ka c 14 32 degrees n 33 degrees s the reliability of the data was evaluated using explicit criteria and some types of data were re analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month mtco mean annual temperature mat plant available moisture pam and runoff p e cold month temperature mat anomalies from plant data range from 1 to 2 k near sea level in indonesia and the s pacific through 6 to 8 k at many high elevation sites to 8 to 15k in s china and the se usa mat anomalies from groundwater or speleothems seem more uniform 4 to 6 k but the data are as yet sparse a clear divergence between mat and cold month estimates from the same region is seen only in the se usa where cold air advection is expected to have enhanced cooling in winter regression of all cold month anomalies against site elevation yielded an estimated average cooling of 2 5 to 3 k at modern sea level increasing to approximate to 6 k by 3000m how ever neotropical sites showed larger than the average sea level cooling 5 to 6 k and a non significant elevation effect whereas w and s pacific sites showed much less sea level cooling 1 k and a stronger elevation effect these findings support the inference that tropical sea surface temperatures ssts were lower than the climap estimates but they limit the plausible average tropical sea surface cooling and they support the existence of climap like geographic patterns in sst anomalies trends of pam and lake levels indicate wet lgm conditions in the w usa and at the highest elevations with generally dry conditions elsewhere these results suggest a colder than present ocean surface producing a weaker hydrological cycle more arid continents and arguably steeper than present terrestrial lapse rates such linkages are supported by recent observations on freezing level height and tropical ssts moreover simulations of greenhouse and lgm climates point to several possible feedback processes by which low level temperature anomalies might be amplified aloft

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

a 15 ka ph record from an alpine lake in north china derived from the cyclization ratio index of aquatic brgdgts and its paleoclimatic significance abstract a well dated sediment core from an alpine lake in north china gonghai lake was used for analysis of branched glycerol dialkyl glycerol tetraether lipids brgdgts based on the cyclization ratio index cbt of the brgdgts and using different terrestrial and lacustrine cbt ph empirical relationships the reconstructed ph records over the past ca 15 ka exhibited similar trends of variation although the absolute ph values were different in order to better understand the reconstructed ph record samples of surface soils from the dust source area and the catchment of gonghai lake as well as surface sediments from the lake were collected for instrumental ph measurements and modern brgdgt analysis the instrumental ph results demonstrated that the surface soils from the dust source area were alkaline while those from the catchment of gonghai lake were acidic in addition the instrumental ph results for the surface sediments from the lake were slightly alkaline and the corresponding ph values were intermediate between those of the two surface soil source groups this may reflect the effect of the input of material from different sources on the sedimentary ph record however the results from modern brgdgts in some of the surface soils and surface sediment samples demonstrate that brgdgts in the core sediments from gonghai lake are predominantly of aquatic origin therefore the cbt derived ph record over the past ca 15 ka from the lake can be interpreted as a record of the lake water ph history which is consistent with the carbonate content record from a parallel core from the same lake in addition using the modern lacustrine calibration the cbt derived ph values for surface sediments of gonghai lake are consistent with instrumental modern lake water ph values for the lake further comparison indicates that the lake water ph is controlled mainly by the degree of humidity of the local climate which is closely related to the intensity of the east asian summer monsoon easm therefore the ph record can be used as an indicator of easm intensity our results demonstrate that on the basis of careful analysis of its origins the cbt index of aquatic brgdgts can be used for lake water ph reconstruction and subsequent paleoclimate reconstruction and that in north china the lake water ph is controlled mainly by the degree of humidity of the local climate

estimating the hydrogen isotopic composition of past precipitation using leaf waxes from western africa abstract the hydrogen isotopic composition of plant leaf wax n alkanes d wax is a novel proxy for estimating d of past precipitation d p however vegetation life form and relative humidity exert secondary effects on d wax preventing quantitative estimates of past d p here we present an approach for removing the effect of vegetation type and relative humidity from d wax and thus for directly estimating past d p we test this approach on modern day late holocene 0 3 ka sediments from a transect of 9 marine cores spanning 21 n 23 s off the western coast of africa we estimate vegetation type c 3 tree versus c 4 grass using 13 c of leaf wax n alkanes and correct d wax for vegetation type with previously derived apparent fractionation factors for each vegetation type late holocene vegetation corrected d wax d vc displays a good fit with modern day d p suggesting that the effects of vegetation type and relative humidity have both been removed and thus that d vc is a good estimate of d p we find that the magnitude of the effect of c 3 tree c 4 grass changes on d wax is small compared to d p changes we go on to estimate d vc for the mid holocene 6 8 ka the last glacial maximum lgm 19 23 ka and heinrich stadial 1 hs1 16 18 5 ka in terms of past hydrological changes our leaf wax based estimates of d p mostly reflect changes in wet season intensity which is complementary to estimates of wet season length based on leaf wax 13 c

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

tetraether lipids from the southern yellow sea of china implications for the variability of east asia winter monsoon in the holocene to better understand the origin and distribution of organic matter om in the yellow sea ys and to delineate potential interactions between the atmosphere and the marine system during the holocene we reconstructed terrestrial input and temperature variation for the last 8 8 ka bp using glycerol dialkyl glycerol tetraethers gdgts obtained from a 4 4 m sediment core ysc 1 from the southern ys the archaea derived isoprenoid gdgts igdgts were dominated by gdgt 0 and crenarchaeol the igdgts and bacteria derived branched gdgts bgdgts correlated well and varied in opposition to the bit branched vs isoprenoid tetraether index this may be due to varying river runoff and influence of the ys coastal current yscc and ys warm current yswc related to the east asia winter monsoon eawm which made the bit proxy less suitable for tracing soil om input to the ys tex86 tetraether index of tetraethers consisting of 86 carbons derived sea surface temperature values sst varied from 9t o 16c close to the sst in the ys cold season the mbt cbt methylation of branched tetraethers and cyclization of branched tetraethers derived continental temperature ranged from 10 to 19 c indicating an annual mean air temperature for the middle and low drainage basin of the ys these two temperature records were decoupled but both correlated with the variation in the eawm suggesting an intimate link between eawm and temperature variation in east asia

dissolved gas paleotemperatures and 18o variations derived from groundwater near uitenhage south africa abstract under the near ideal hydrologic conditions provided by the uitenhage artesian aquifer reliable estimates of paleotemperatures were obtained by measurement of the dissolved n2 and ar in groundwater confidently dated in the range 28 000 yr b p to the present using 14c the mean annual air temperature in this area during the last glaciation is calculated to have been on average 5 1 2 c lower than during the holocene the change in the 18 o 16 o ratio of the groundwater corrected for changes in ocean water amounted to 0 4 per c

distribution of glycerol dialkyl glycerol tetraethers in surface sediments of lake qinghai and surrounding soil abstract glycerol dialkyl glycerol tetraethers gdgts are increasingly used as proxies for paleoclimate studies of marine and lacustrine environments while gdgt based proxies have been applied to a number of lake environments globally little is known about the distribution of gdgts on the qinghai tibet plateau we have investigated the isoprenoid gdgts igdgts and branched gdgts bgdgts in lake qinghai sediments and the surrounding surface soil in order to examine their potential use as paleoclimate proxies on the qinghai tibet plateau the results show that i the values of the igdgt bgdgt ratio for surrounding soil were at the higher end among globally distributed soils and consequently bit values avg 0 71 at the lower end ii the tex86 values decreased while the mbt and cbt values increased along an onshore soil nearshore sediment offshore sediment transect iii the tex86 values for the offshore sediments were almost identical and their inferred temperatures were close to mean summer surface water temperature and iv the bgdgt inferred mean annual air temperature maat and ph for soil were consistent with measured maat and ph however the cbt inferred ph for offshore sediments seemed inconsistent with the ph of lake water or sediment our results suggest that i the higher ph may be an important factor leading to the higher igdgt bgdgt values and lower bit values in surrounding surface soil ii both igdgts and bgdgts may originate from terrestrial input and in situ production for this saline lake especially for nearshore sediments however for offshore sediments terrestrial igdgt input seems minor and tex86 may be useful for paleoclimate studies of lake qinghai

coupled thermal and hydrological evolution of tropical africa over the last deglaciation we analyzed the distribution of branched tetraether membrane lipids derived from soil bacteria in a marine sediment record that was recovered close to the congo river outflow and the results enabled us to reconstruct large scale continental temperature changes in tropical africa that span the past 25 000 years tropical african temperatures gradually increased from 21 to 25 c over the last deglaciation which is a larger warming than estimated for the tropical atlantic ocean a direct comparison with sea surface temperature estimates from the same core revealed that the land sea temperature difference was through the thermal pressure gradient an important control on central african precipitation patterns

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

exsolution features in titanomagnetites from massive magnetite layers and their host rocks of the upper zone eastern bushveld complex a systematic investigation of the exsolution textures in titanomagnetite grains of massive magnetite layers and their associated host rocks from the entire upper zone sequence has revealed noticeable differences that can be related to changes in the oxidation state of the magma during crystallization and cooling the observed oxidation exsolution intergrowths indicate a higher f sub o 2 during formation of the magnetite layers than during crystallization of the disseminated titanomagnetite as well as a decrease in the f sub o 2 required to precipitate successive titanomagnetite rich layers upward in the sequence peculiar composite lamellar intergrowths of magnetite and ilmenite in the uppermost magnetite layers and in some magnetite plugs are ascribed to a subsolvus oxidation of ulvoespinel in ulvoespinel rich magnetite the configuration of the magnetite ulvoespinel solvus dictates that ulvoespinel in ti rich magnetite ulvoespinel solid solution high in the succession exsolves at considerably higher temperature than in ti poor solid solution lower in the sequence subsolvus oxidation of ulvoespinel to ilmenite at higher temperatures near the top of the intrusion facilitated diffusion of ilmenite to produce the variety of different composite exsolution textures the textures are not developed where abundant oxidation exsolution of ilmenite has taken place at temperatures above the solvus

osmium isotopes and highly siderophile element fractionation in the massif type anorthosites of the mesoproterozoic kunene intrusive complex nw namibia abstract the behaviour of highly siderophile elements during differentiation of mafic melts and formation of cumulate rocks in the crust is little understood mostly because abundances of some of these elements are very low and reliable data is scarce data on massif type anorthosites and associated fe ti ore from the mesoproterozoic kunene intrusive complex nw namibia indicate the effects of fractional crystallisation crustal contamination cumulate formation and post cumulus re equilibration on the distribution of the highly siderophile elements and the osmium isotopic composition of the anorthositic cumulate rocks anorthosites and fe ti ore of the kunene intrusive complex are characterised by low concentrations and strongly fractionated chondrite normalised patterns of the highly siderophile elements the abundance of highly siderophile elements is dominated by fe ti oxides and traces of sulphides the osmium isotopic composition and highly siderophile element distribution of the anorthosites are consistent with their derivation from a mantle derived parental magma that was subject to fractionation of mafic minerals and variable extent of crustal contamination during its igneous evolution under conditions of the anorthosite formation re behaves as a compatible element in fractionating titanomagnetite the other highly siderophile elements are incorporated to a lesser extent into fe ti oxides during post cumulus re equilibration of fe ti oxides re is preferentially incorporated in magnetite whereas pt displays preference for ilmenite

bacterial tetraether membrane lipids in peat and coal testing the mbt cbt temperature proxy for climate reconstruction abstract peatlands are widespread and important natural archives of environmental change here we explore the potential of the recently introduced mbt cbt proxy methylation index and cyclisation ratio of branched tetraethers to estimate past annual mean air temperature mat based on the distribution of bacterially derived branched glycerol dialkyl glycerol tetraether gdgt membrane lipids in peat and coal to this end branched gdgts in an ombrotrophic peat bog from switzerland and three coal deposits of increasing maturity were analysed for the surface of the bog reconstructed annual mat is higher than both measured annual mat and measured in situ pore water temperature changes in the cbt ratio considered a proxy for ph with depth in the bog do not match with present day in situ pore water ph but coincide with a peat stratigraphic boundary this indicates that gdgts down the bog profile are predominantly fossil and not derived from extant biomass the mbt cbt derived annual mat record also shows a large drop at this stratigraphic boundary which likely relates to past change in trophic status of the bog branched gdgts are abundant in an immature lignite vitrinite reflectance r o 0 25 but occur in low amount in a slightly more mature coal r o 0 32 annual mat could be reconstructed for the lignite alone and is higher than other proxy based estimates from approximately the same time and location our results indicate potential for the application of the mbt cbt proxy in peat and immature coals but improved constraints on the effects of different types of peat on branched gdgt distributions as well as improved calibration of mat estimates are needed before the method can be confidently applied

branched glycerol dialkyl glycerol tetraethers in arctic lake sediments sources and implications for paleothermometry at high latitudes branched glycerol dialkyl glycerol tetraethers brgdgts are analyzed in different lakes of the mackenzie canadian arctic and kolyma siberian arctic river basins to evaluate their sources and the implications for brgdgt based paleothermometry in high latitude lakes the comparison of brgdgt distributions and concentrations in the lakes with those in river suspended particulate matter riverbank sediments and permafrost material indicates that brgdgts in arctic lake sediments have mixed sources in contrast to global observations distributional offsets between brgdgts in arctic lakes and elsewhere in the catchment are minor likely due to the extreme seasonality and short window of biological production at high latitudes consequently both soil and lake calibrated brgdgt based temperature proxies return sensible temperature estimates even though the mean air temperature mat in the arctic is below the calibration range the original soil calibrated mbt cbt methylation of branched tetraethers cyclisation of branched tetraethers proxy generates mats similar to those in the studied river basins whereas using the recently revised mbt cbt calibration overestimates mat the application of the two global lake calibrations generating summer air temperatures sat and mat respectively illustrates the influence of seasonality on the production of brgdgts in lakes as the latter overestimates actual mat whereas the sat based lake calibration accounts for this influence and consequently returns more accurate temperatures our results in principle support the application of brgdgt based temperature proxies in high latitude lakes in order to obtain long term paleotemperature records for the arctic although the calibration and associated transfer function have to be selected with care

millennial scale ice rafting events and hudson strait heinrich like events during the late pliocene and pleistocene a review abstract various types of abrupt millennial scale climate variability such as dansgaard oeschger and heinrich events characterized the last glacial period over the last decade a number of studies demonstrated that such millennial scale climate variability was not limited to the last glacial but inherent to quaternary climate here we review the occurrence and origin of millennial ice rafting events in the north atlantic during the late pliocene and pleistocene last 3 4 ma with a special focus on north atlantic hudson strait hs heinrich like events we show that heinrich layers 5 4 2 and 1 in marine sediment cores from across the north atlantic all bear the organic geochemical fingerprint of the hudson area using this framework and combining previously published results detailed investigations into the organic and inorganic chemistry of ice rafted debris ird found across the north atlantic demonstrate that prior to mis 16 650 ka ird in the north atlantic did not originate from the hudson area of northern canada the signature of this early ird is distinctly different compared to that of hs heinrich layers rather ice rafting events during the late pliocene and early pleistocene predominantly emanated from the calving of the greenland and fennoscandian ice sheets and possibly minor contributions from local ice streams from the north american and british ice sheets compared to north atlantic hs heinrich events these early pleistocene ird events had a limited impact on surface water characteristics in the north atlantic north atlantic hs heinrich like events first occurred during mis 16 at the same time the dominant frequency in silicate rich ird accumulation shifted from the obliquity 41 ka to a 100 ka frequency across the north atlantic iceberg survivability or a change in iceberg trajectory likely did not control this change in ird regime these results lend further support for the existing hypothesis that an increase in size thickness of the laurentide ice sheet controls the occurrence of north atlantic hs heinrich events favoring an internal dynamic mechanism for their occurrence

environmental fluctuation impacted the evolution of early pleistocene non human primates biomarker and geochemical evidence from mohui cave bubing guangxi southern china abstract quaternary climate variability profoundly impacting the evolution and distribution of plants and animals across the globe has been reconstructed by many sediment archives here we track past changes of temperature rainfall and plant type by using the n alkane and glycerol dialkyl glycerol tetraethers gdgts as well as weathering and pedogenesis by mineralogical and geochemical proxies from a 250 cm deep soil sediment profile from the early pleistocene deposits in mohui cave southern china indices for weathering intensity such as mineral composition quartz feldspar and calcite major element proxies ti na al na al mg ti mg ciw pia cpa cia trace element proxies ba sr and rb sr and biomarker proxies oep lsr and cpi show similar secular trends revealing a three stage historical accumulation the high long chain n alkane ratios c31 c29 and c31 c33 c27 c29 indicate that the vegetation in the region had increases in percentage of woody plants and decreases in herbs during periods of relatively lower temperature and less precipitation which evidenced from gdgts consistent with a weak weathering process influenced by summer monsoon strength further we compared the distribution of these plant types with the taxonomic variation in the vertebrate paleontological fossils excavated from the same profile in mohui cave the distribution of lufengpithecus appears in only one interval but gigantopithecus blacki appears throughout the profile despite an environment that experienced transitional stages from grassland to woodland in relatively cooler and drier conditions we infer that in face of these climatic changes lufengpithecus may have preferred to emigrate from the region while gigantopithecus blacki may have stayed given that it was limited to staying in its core area

distributions of branched gdgts in soils and lake sediments from western uganda implications for a lacustrine paleothermometer bacterially produced branched glycerol dialkyl glycerol tetraethers gdgts are ubiquitous in soils and lake sediments and can potentially be used to reconstruct past temperatures in lakes however it is still unclear if these compounds are derived from eroded soils or if they are produced in situ to better understand environmental controls on the distributions of these compounds and the sources of branched gdgts to lake sediments we compare branched gdgt distributions and concentrations in lake sediments and catchment soils within a 3600 m altitudinal transect in western uganda reconstructed mean annual air temperature maat determined from the degree of methylation mbt and cyclisation cbt of branched gdgts in soils decreases with increasing altitude as is expected from the air temperature gradient in our transect however we observe significant offsets between observed and reconstructed temperatures in soils from wet high elevation soils but not in most dry low elevation soils branched gdgt distributions differ significantly between lake sediments and soils at all elevations with greater differences at low elevations than at high elevations these data support previous hypotheses that branched gdgts are produced in situ in lakes and suggest that the abundance of water in soil environments may play a role in controlling the distribution of branched gdgts while branched gdgts in lacustrine sediments can be used to reconstruct temporal temperature variations in lakes we urge caution in utilizing this proxy in lacustrine systems with high soil loadings especially if there is evidence of changing clastic fluxes through time

comparison of soil derived tetraether membrane lipid distributions and plant wax δd compositions for reconstruction of canadian arctic temperatures abstract polar amplification of climate warming has received much attention as these rapidly rising temperatures have the potential to alter ecosystem function and biogeochemical cycles in particular carbon preserved in arctic tundra soil and permafrost may be especially vulnerable resulting in carbon cycle perturbations providing an additional positive feedback to climate change reliable methods for reconstructing past temperature changes in polar regions have been established from ice cores and marine sediments however techniques for the continental terrestrial environments are lacking but are imperative to examine polar amplification of climate warming here we compare two molecular methods for reconstructing continental annual mean air temperature mat for the canadian arctic based on the distribution of soil bacterial derived glycerol dialkyl glycerol tetraether gdgt membrane lipids mbt cbt proxy and the hydrogen isotopic composition d of plant wax derived n alkanes these two proxies were applied to both modern soil and paleosols collected from the yukon territory canada to evaluate both the accuracy of the reconstructed absolute temperatures as well as the relative change in temperature between the last glacial and the holocene branched gdgt based estimates using the recently revised mbt cbt calibration are overall higher by ca 6 c compared to the original calibration mat estimates for modern soils based on the original mbt cbt calibration are comparable with those based on the d of extracted c29 n alkanes and instrumental data however produced a 6 c higher temperature signal for the glacial paleosols therefore branched gdgt based temperature reconstructions for glacial soils in the high arctic may represent the higher temperatures at the time of soil formation when bacterial activity was optimal whereas d of c29 n alkane plant lipids appear to integrate an average annual signal when used in tandem these geochemical proxies may provide a more comprehensive method for reconstructing arctic paleoclimate

impact of riverine suspended particulate matter on the branched glycerol dialkyl glycerol tetraether composition of lakes the outflow of the selenga river in lake baikal russia branched glycerol dialkyl glycerol tetraethers brgdgts are bacterial membrane lipids found in several environments including soils rivers and lakes whose distribution varies with temperature and ph although this dependence is apparently not the same for the different environments mixing of brgdgt sources may thus complicate palaeoenvironmental reconstruction the extent to which brgdgts in a lake outflow reflect the distribution delivered by upstream rivers was studied for lake baikal russia one of the largest freshwater lakes worldwide fifteen brgdgts in suspended particulate matter spm of the selenga river and its outflow from the lake were quantified the river and lake spm had rather different distributions the riverine distribution was still apparent in the spm of the lake surface water 5 km from the river mouth but shifts in the distribution were already apparent in the spm of the surface water after 1 km based on the brgdgt distributions of the spm of the selenga outflow and that of the lake conservative mixing between the river and the lake brgdgt distributions could not fully explain the observed shifts in distributions both preferential degradation and in situ production of brgdgts in the surface and especially bottom water of the river outflow were potentially responsible this implies that a riverine lipid distribution delivered to a lake can be modified prior to being transported downstream the lacustrine brgdgt distribution that possibly could have reflected a mixture of mountainous and selenga river spm was not recognized in downstream yenisei river spm the watershed of lake baikal thus does not seem to contribute to the brgdgts transported to the marine system as many large rivers have major lakes in their watershed this has implications for palaeoclimate reconstruction from river fan sediments globally

glacial fluctuations in tropical africa during the last glacial termination and implications for tropical climate following the last glacial maximum abstract the tropics are a dynamic component of the global climate system and exert a profound influence on modern climate variability yet the role of the tropics in past climate changes for example during the last glacial termination is uncertain this uncertainty is due in part to the relative paucity of terrestrial temperature records from the tropics which hinders efforts to understand the mechanisms that influenced deglacial warming and abrupt climate events tropical glaciers are sensitive to changes in climate and mapping and dating past tropical glacial fluctuations provides a valuable record of terrestrial climate changes in the low latitudes we report a chronology of past glacial extents in the rwenzori mountains of uganda 0 3 n 29 9 e based on 51 beryllium 10 10be surface exposure ages from three separate glacial catchments results indicate that rwenzori glaciers retreated considerably during heinrich stadial 1 the rate of net glacial recession slowed between 15 and 11 ka although glaciers continued to retreat during this period rwenzori glaciers then retreated more rapidly during the early holocene the rwenzori glacial chronology is broadly similar to glacial chronologies reconstructed elsewhere in east africa and in tropical south america we suggest that this similarity may reflect coherent tropics wide temperature fluctuations during the last deglaciation the rwenzori glacial chronology provides crucial information on the global footprint of deglacial warming and abrupt climate events and thus the potential mechanisms that influenced tropical climate during the last glacial termination

correlations between microbial tetraether lipids and environmental variables in chinese soils optimizing the paleo reconstructions in semi arid and arid regions the bacterial membrane lipid based continental paleothermometer the mbt cbt or mbt cbt proxy methylation index of branched tetraethers cyclization of branched tetraethers results in a large temperature deviation when applied in semiarid and arid regions here we propose new calibration models based on the investigation of 100 surface soils across a large climatic gradient with a particular focus on semiarid and arid regions of china and apply them to a loess paleosol sequence as reported elsewhere mbt values exhibit a much higher correlation with maat than with summer temperature suggesting a minimal seasonality bias however mbt is apparently insensitive to temperature 20 degrees c additional complexities are apparent in alkaline and arid soils which are characterized by different relationships to climatic parameters than those in the complete chinese or global dataset for example mbt and cbt indices exhibit a negative correlation in alkaline and arid soils in contrast to their positive correlation in acid soils moreover the cyclization ratio of bgdgts cbt previously defined as a proxy for soil ph is apparently primarily controlled by maat in these alkaline soils thus we propose 1 a local chinese calibration of the mbt cbt proxy and 2 an alternative temperature proxy for use in semiarid and arid regions based on the fractional abundances of bgdgts the latter has a markedly higher determination factor and lower root mean square error in alkaline soils than the chinese local calibration and is suggested to be preferred for paleotemperature reconstruction in chinese loess paleosol sequences these new bgdgt proxies have been applied to the weinan holocene paleosol section of the chinese loess plateau clp the fractional abundance calibration when applied in the weinan holocene paleosol produces a total holocene temperature variation of 5 2 degrees c and a temperature for the topmost sample that is consistent with the modern temperature previously we showed that the ratio of archaeal isoprenoid gdgts to bgdgts r i b increases at map 0 5 in the clp suggest the presence of enhanced aridity in the late holocene in north china in combination the high r i b ratios 0 5 and the associated low mbt values 0 4 reveal the co occurrence of dry and cold events especially in the latest holocene in the loess paleosol sequences in clp and probably also in cold and arid regions outside of clp c 2013 elsevier ltd all rights reserved

last glacial maximum and holocene climate in ccsm3 abstract the climate sensitivity of the community climate system model version 3 ccsm3 is studied for two past climate forcings the last glacial maximum lgm and the mid holocene the lgm approximately 21 000 yr ago is a glacial period with large changes in the greenhouse gases sea level and ice sheets the mid holocene approximately 6000 yr ago occurred during the current interglacial with primary changes in the seasonal solar irradiance the lgm ccsm3 simulation has a global cooling of 4 5 c compared to preindustrial pi conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at lgm tropical sea surface temperature sst cools by 1 7 c and tropical land temperature cools by 2 6 c on average simulations with the ccsm3 slab ocean model suggest that about half of the global cooling is explained by the reduced lgm concentration of atmospheric co2 50 of present day concentrations there is an increase in the antarctic circumpolar current an

spatial heterogeneity of sources of branched tetraethers in shelf systems the geochemistry of tetraethers in the berau river delta kalimantan indonesia abstract the bulk organic matter composition total organic carbon toc content and 13ctoc and composition of isoprenoid and branched glycerol dialkyl glycerol tetraethers gdgt in surface sediments from 43 stations in the berau river delta east kalimantan indonesia including two coast shelf transects and stations within the river mouth were examined to reveal the spatial heterogeneity in these parameters in order to assess the impact of a tropical river loaded with suspended matter on the sedimentary organic matter in the shelf system the high resolution study showed that despite the extensive transport of eroded soil material by the river to the sea terrestrial organic matter and brgdgts are only deposited on a relatively small part of the shelf the concentrations of brgdgts are highest up to 120 g g 1 toc in sediments deposited in and close to the mouth of the berau river and their distribution indicates that they represent a mixture of soil derived and river in situ produced brgdgts crenarchaeol concentrations reach 700 g g 1 toc in sediments deposited on the outer shelf due to thaumarchaeotal production in shelf waters this results in a strong gradient 0 93 0 03 in the bit index with high values in the river mouth and low values on the shelf the decline in the bit index is caused by both decreasing concentrations of the brgdgts and increasing concentrations of crenarchaeol the bit index shows a highly significant but non linear relationship with 13ctoc on the shelf in the area not under the direct influence of the berau river cyclic brgdgts become relatively dominant most probably due to in situ production in the alkaline pore waters of the surface sediments the spatial heterogeneity of sources of brgdgts on the berau shelf complicates the use of brgdgts as temperature proxies application of the global soil calibration to sedimentary mixtures of brgdgts in the river influenced area of the shelf results in a severe underestimation of mean annual air temperature mat by 6 c this is due to the mixed origin of the brgdgts which are not only derived from soil erosion but likely also from riverine production as has been observed for other river systems comparison of the berau shelf other shelf systems indicates that in situ production of brgdgts in shelf sediments is a widespread phenomenon that is especially pronounced at water depths of ca 50 300 m it is hypothesized that this is so because benthic in situ production of heterotrophic brgdgt producing bacteria is fueled by the higher delivery of fresh organic matter to these sediments as the consequence of higher primary productivity in shelf waters and a decreased mineralization due to the relatively short settling times of particles on the shelf for palaeoclimatic studies of marine shelf sediments the application of brgdgts as proxies is severely complicated by the heterogeneity of sources of brgdgts comparison of the brgdgt composition of soils with those of shelf sediments may assist in deciding if sedimentary brgdgts are predominantly derived from soil erosion several methods to do so are discussed

seasonal variability of branched glycerol dialkyl glycerol tetraethers brgdgts in a temperate lake system quantitative climate reconstructions are crucial for understanding the magnitude of and mechanisms behind natural and anthropogenic climate change yet there are few proxies that can reliably reconstruct terrestrial temperature branched glycerol dialkyl glycerol tetraethers brgdgts are bacterial membrane lipids that are increasingly used to reconstruct paleotemperature from lake sediments but despite their potential we have a poor understanding of 1 autochthonous vs allochthonous sources of brgdgts in lakes and 2 the seasonality of and environmental controls on brgdgt production within lakes to investigate these factors we examined water column suspended particulate matter spm and settling particles from a sediment trap collected on a biweekly to monthly basis over a period of three years at lower king pond a small kettle lake in northern vermont usa we also compared the concentration and fractional abundances of brgdgts in spm and settling particles with those of catchment soils river sediments and lake surface sediments to constrain the relative importance of brgdgts derived from the landscape versus brgdgts produced within the lake itself we find significant differences in concentrations and fractional abundances of brgdgts between soil and river sediment samples from the catchment and lake sediments indicating a mostly autochthonous source for lacustrine brgdgts brgdgt concentrations fluxes and fractional abundances in spm vary over the annual cycle indicating that brgdgts are produced throughout the year and respond to changes within the water column the total annual flux of brgdgts settling through the water column is comparable to the brgdgt accumulation rates in surface sediments indicating that in this lake brgdgts are mostly produced within the water column not in the sediment itself while brgdgts are produced in all seasons within the water column the flux to the sediments is highest during periods of spring and fall isothermal mixing potentially biasing paleotemperature reconstructions towards mixing season temperature because the seasonal timing and frequency of lake mixing varies as a function of regional climate lacustrine brgdgt calibrations should be regional in nature and comprise lakes with similar mixing regimes

branched tetraether membrane lipids associated with rhizoliths in loess rhizomicrobial overprinting of initial biomarker record abstract loess palaeosol sequences are considered important terrestrial archives for studying quaternary climate recent studies have shown that calcified roots rhizoliths can be significantly younger than surrounding terrestrial sediment loess and that loess organic matter may be contaminated with root derived carbon from post sedimentary deep rooting plants branched glycerol dialkyl glycerol tetraethers gdgts are membrane lipids produced by unknown bacteria in soil and are increasingly being used as palaeoclimate proxies the aim of this work was to examine the impact of the temporal decoupling between rhizoliths and loess on the abundance and composition of branched gdgts and consequently on the application of branched gdgts as proxies in loess deposits branched gdgts in rhizoliths and the surrounding sediment from a loess palaeosol sequence in nussloch sw germany were examined their composition varied between the rhizolith and loess which may reflect the fact that branched gdgts were biosynthesized at different times late pleistocene for loess and holocene for rhizoliths and therefore under different environmental conditions a large difference ca 7 c in branched gdgt reconstructed palaeotemperature was observed between rhizoliths and loess in addition the reconstructed temperatures were the opposite from those expected from the assumed depositional ages of branched gdgts this might be explained by the post sedimentary input of root associated microorganism derived branched gdgts to loess which might have led to an overprint of the initial branched gdgt signal in the sediment our results suggest that post sedimentary penetration of deep rooting plants in loess might entail uncertainty regarding the application of branched gdgt palaeoproxies and that caution should be exercised in interpreting temperature estimates derived from branched gdgts in loess palaeosol sequences this is of special importance for loess where rhizoliths are abundant and where non calcified root remains of different age from that of the sediment are possible in addition the gdgt concentration in rhizoliths and surrounding loess supports the hypothesis of a heterotrophic lifestyle for branched gdgt producing bacteria

spatio temporal evolution of the west african monsoon during the last deglaciation on the basis of a multi proxy data set from the gulf of guinea eastern equatorial atlantic we reconstruct the spatio temporal evolution of the west african monsoon wam and present evidence for a decoupling between latitudinal shifts of the rain belt and wam intensification the onset of deglacial monsoon invigoration at 16 600 years before present lagged northward migration of a weak rainfall zone by 2800 years conversely during the younger dryas yd time interval wam precipitation was severely reduced but we find no evidence for a large scale retreat of the rainfall front this observation is not in agreement with the hypothesis of a large scale shift of the intertropical convergence zone south of the tropical wam region during the yd our results can be better reconciled with the newly emerging concept of a strong influence of tropical easterly and african easterly jets on modern wam

branched gdgt signals in fluvial sediments of the danube river basin method comparison and longitudinal evolution abundances and distributional changes of branched glycerol dialkyl glycerol tetraethers brgdgts in fluvially influenced sediments are used in various paleoclimate studies to reconstruct variations in soil export continental air temperature and soil ph in corresponding river basins for accurate interpretation of these records it is important to understand the provenance and the evolution of biomarker signals as they move through the river system here we investigate the brgdgt composition of modern river sediments of the danube river the second largest river in europe brgdgt based mean annual air temperature and soil ph parallel the actual values of air temperature and soil ph from the upper to the lower basin showing that signals predominantly reflect local as opposed to basin wide environmental conditions furthermore data generated using the recently developed method with improved chromatography separating the 6 methyl isomers from the 5 methyl isomers was compared with that resulting from the conventional method we show that the temperatures and ph values reconstructed using the data obtained by improved chromatography best resemble the local environmental conditions throughout the danube river basin our results highlight the importance of in depth studies within river systems to better understand the provenance of biomarker signals in fluvially derived sedimentary archives

near synchronous interhemispheric termination of the last glacial maximum in mid latitudes isotopic records from polar ice cores imply globally asynchronous warming at the end of the last glaciation however 10be exposure dates show that large scale retreat of mid latitude last glacial maximum glaciers commenced at about the same time in both hemispheres the timing of retreat is consistent with the onset of temperature and atmospheric co2 increases in antarctic ice cores we suggest that a global trend of rising summer temperatures at the end of the last glacial maximum was obscured in north atlantic regions by hypercold winters associated with unusually extensive winter sea ice

mechanisms of retrograde changes in oxide minerals from the proterozoic serrote da laje deposit northeastern brazil retrograde textural and chemical changes in oxide minerals from the proterozoic serrote da laje deposit northeastern brazil have been investigated the deposit is situated in a mafic ultramafic layered sill oxidation and cooling leading to successively decreasing diffusion rates resulted in disequilibrium on the microscale pleonaste in particular shows a rapid change in composition between a coarse grains in a granoblastic magnetite host indicating metamorphic peak conditions b coarse lamellae in magnetite indicating commencement of exsolution and c composite pleonaste ilmenite lamellae in magnetite which indicate oxidation exsolution barren rock layers cooled under more oxidized conditions compared with oxide rich layers formation of pleonaste and ilmenite lamellae in magnetite and ilmenite hematite relations are discussed

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

application of bacterial glycerol dialkyl glycerol tetraethers gdgts to develop modern and past temperature estimates from new zealand lakes abstract branched isoalkyl glycerol dialkyl glycerol tetraethers gdgts of bacterial origin have been found in high abundance in both modern and glacial sediments of new zealand south island freshwater lakes covering a wide range of altitude 101 2000 m like isoprenoid gdgts of archaeal origin they provide excellent potential for temperature assessment for this study their distribution patterns mbt methylation ratio and cbt cyclisation ratio of branched gdgts have been successfully used to develop an initial temperature calibration for the study area and to provide preliminary palaeo environmental interpretations mbt data from modern lake sediments correlate well with measured annual air temperature r2 0 74 enabling a regional calibration for reconstructing palaeotemperatures for fossil samples mbt derived palaeotemperatures for alpine lake calibrated against mean annual temperature were determined for the last glacial during an early cold phase between 29 000 and 26 000 years bp and for later less cold phases between 23 000 and 18 000 years bp compared with the modern temperature regime the mbt data indicate a decrease of ca 5 6 and 2 8 c respectively during this time modern and past mbt derived temperatures correlate with chironomid based temperature reconstructions in the area archaeal gdgts commonly used for the tex86 index are abundant in fossil sediments alpine lake but scarce in modern sediments hindering a new local calibration for this palaeotemperature proxy

millennial scale precipitation changes over central africa during the late quaternary and holocene evidence in sediments from the gulf of guinea we combine environmental magnetism geochemical measurements and colour reflectance to study two late quaternary sediment cores geob 4905 4 at 2 30 n off cameroon and geob 4906 3 at 0 44 n off gabon this area is suitable for investigating precipitation changes over central and west africa because of its potential to record input of aeolian and fluvial sediments three magnetozones representing low and high degree of alteration of the primary rock magnetic signals were identified the magnetic signature is dominated by fine grained magnetite while residual haematite prevails in the reduced intervals showing increase in concentration and fine grain size at wet intervals our records also show millennial scale changes in climate during the last glacial and interglacial cycles at the northern location the past 5 5 ka are marked by high frequency oscillations of ti and colour reflectance which suggests aeolian input and hence aridity the southern location remains under the influence of the intertropical convergence zone and thus did not register aeolian signals the millennial scale climatic signals indicate that drier and or colder conditions persisted during the late holocene and are synchronous with the 900 a climatic cycles observed in northern hemisphere ice core records copyright 2009 john wiley sons ltd

change in provenance of branched glycerol dialkyl glycerol tetraethers over the holocene in the baltic sea and its impact on continental climate reconstruction abstract the baltic sea is an enclosed basin that experienced a number of different salinity phases during the holocene corresponding to the establishment of a connection with the north sea branched glycerol dialkyl glycerol tetraethers brgdgts in surface sediments and holocene sedimentary successions from the gotland and arkona basins were analyzed to examine their potential applicability as indicators for soil organic matter input as well as their suitability for paleoclimate reconstructions our results show a marked change in brgdgt distributions and the branched and isoprenoid tetraether bit index the transition of the ancylus lake fresh to the littorina sea brackish phase is revealed by a large drop in the bit index and an increase in the mbt 5me which reveals a large shift in provenance of the sedimentary brgdgts during the lake phase brgdgts are presumed to be primarily produced by in situ production in the water column during the brackish phase in situ brgdgt production in the alkaline pore waters of the surface sediments as revealed by their high degree of cyclization was predominant although there was evidence of occasional input of soil derived brgdgts the predominant aquatic autochthonous production of brgdgts does not allow the use of brgdgts for continental air temperature reconstructions but they can be used for bottom water and lake temperature reconstructions during some intervals the results from this study demonstrate that geological changes and concomittant salinity variations can be revealed by the provenance of brgdgts

an automated purification method for archaeal and bacterial tetraethers in soils and sediments isoprenoid and branched glycerol dialkyl glycerol tetraethers gdgts are archaeal and bacterial polar lipids increasingly used as environmental biomarkers and are studied in a wide range of settings lacustrine and oceanic sediments water column particulate organic matter soils peats sedimentary rocks and extracts from archaeal and bacterial cultures in paleoclimatology for example typical work on a sediment core of several tens of m consists of several hundreds to more than a thousand hplc ms high performance liquid chromatography mass spectrometry analyses the measurements therefore require purification steps from total lipid extracts we propose an automated procedure for obtaining the gdgt core lipid fraction we first evaluate both the yield and efficiency of the separation using different cartridges we then compare the results from automated and classical manual procedures for a soil and a marine sediment as well as for a sedimentary paleosequence

the pace of east african monsoon evolution during the holocene african monsoon precipitation experienced a dramatic change in the course of the holocene the pace with which the african monsoon shifted from a strong early to middle to a weak late holocene is critical for our understanding of climate dynamics hydroclimate vegetation interaction and shifts of prehistoric human settlements yet it is controversially debated on the basis of planktonic foraminiferal ba ca time series from the eastern mediterranean sea here we present a proxy record of nile river runoff that provides a spatially integrated measure of changes in east african monsoon eam precipitation the runoff record indicates a markedly gradual middle to late holocene eam transition that lasted over 3500 years the timing and pace of runoff change parallels those of insolation and vegetation changes over the nile basin indicating orbitally forced variation of insolation as the main eam forcing and the absence of a nonlinear precipitation vegetation feedback a tight correspondence between a threshold level of nile river runoff and the timing of occupation abandonment of settlements suggests that along with climate changes in the eastern sahara the level of nile river and intensity of summer floods were likely critical for the habitability of the nile valley egypt

sources and distributions of branched and isoprenoid tetraether lipids on the amazon shelf and fan implications for the use of gdgt based proxies in marine sediments branched glycerol dialkyl glycerol tetraethers brgdgts in river fan sediments have been used successfully to reconstruct mean annual air temperature maat and soil ph of the congo river drainage basin however in a previous study of amazon deep sea fan sediments the reconstructed maats were ca 10 c colder than the actual maat of the amazon basin in this study we investigated this apparent offset by comparing the concentrations and distributions of brgdgts in amazon river suspended particulate matter spm and sediments to those in marine spm and surface sediments the riverine brgdgt input was evident from the elevated brgdgt concentrations in marine spm and surface sediments close to the river mouth the distributions of brgdgts in marine spm and sediments varied widely but generally showed a higher relative abundance of methylated and cyclic brgdgts than those in the river since this difference in brgdgt distribution was also found in intact polar lipid ipl derived brgdgts which were more recently produced the change in the marine brgdgt distribution was most likely due to marine in situ production consequently the maats calculated based on the methylation of branched tetraethers mbt and the cyclisation of branched tetraethers cbt were lower and the cbt derived ph values were higher than those of the amazon basin however spm and sediments from stations close to the river mouth still showed mbt cbt values that were similar to those of the river therefore we recommend caution when applying the mbt cbt proxy it should only be used in sediment cores that were under high river influence the influence of riverine derived isoprenoid gdgt isogdgt on the isogdgt based tex86 temperature proxy was also examined in marine spm and sediments an input of riverine isogdgts from the amazon river was apparent but its influence on the marine tex86 was minor since the tex86 of spm in the amazon river was similar to that in the marine spm and sediments

expanded glaciers during a dry and cold last glacial maximum in equatorial east africa glaciers on the world s highest tropical mountains are among the most sensitive components of the cryosphere yet the climatic controls that infl uence their fl uctuations are not fully under stood here we present the fi rst 10 be ages of glacial moraines in africa and use these to assess the climatic conditions that infl uenced past tropical glacial extents we applied 10 be surface exposure dating to determine the ages of quartz rich boulders atop moraines in the rwenzori mountains 1 n 30 e located on the border of uganda and the democratic republic of congo the 10 be ages document expanded glaciers ca 23 4 and 20 1 ka indicating that glaciers in equatorial east africa advanced during the global last glacial maximum ca 26 19 5 ka a comparison of these moraine ages with regional paleoclimate records indicates that rwen zori glaciers expanded contemporaneously with dry and cold conditions recession from the moraines occurred after ca 20 1 ka similar in timing to a rise in air temperature documented in east african lake records our results suggest that on millennial time scales past fl uctua tions of rwenzori glaciers were strongly infl uenced by air temperature

distribution of branched gdgts in surface sediments from the colville river alaska implications for the mbt cbt paleothermometer in arctic marine sediments significant climate fluctuations in the arctic over the recent past and additional predicted future temperature changes highlight the need for high resolution arctic paleoclimate records arctic coastal environments supplied with terrigenous sediment from arctic rivers have the potential to provide annual to subdecadal resolution records of climate variability over the last few millennia a potential tool for paleotemperature reconstructions in these marine sediments is the revised methylation index of branched tetraethers mbt cyclization ratio of branched tetraethers cbt proxy based on branched glycerol dialkyl glycerol tetraethers brgdgts in this study we examine the source of brgdgts in the colville river alaska and the adjacent simpson lagoon and reconstruct temperatures from simpson lagoon sediments to evaluate the applicability of this proxy in arctic estuarine environments the colville catchment soils fluvial sediments and estuarine sediments contain statistically similar brgdgt distributions indicating that the brgdgts throughout the system are soil derived with little alteration from in situ brgdgt production in the river or coastal waters temperatures reconstructed from the mbt cbt indices for surface samples show good agreement with regional summer june through september temperatures suggesting a seasonal bias in arctic temperature reconstructions from the colville system in addition we reconstruct paleotemperatures from an estuarine sediment core that spans the last 75 years revealing an overall warming trend in the twentieth century that is consistent with trends observed in regional instrumental records these results support the application of this brgdgt based paleotemperature proxy for subdecadal scale summer temperature reconstructions in arctic estuaries containing organic material derived from sediment laden episodic rivers

late quaternary behavior of the east african monsoon and the importance of the congo air boundary both atlantic and indian ocean climate dynamics exert influence over tropical african hydroclimate producing complex patterns of convergence and precipitation to isolate the indian ocean influence on african paleohydrology we analyzed the deuterium hydrogen ratio of higher plant leaf waxes delta d wax in a 25 000 year sediment record from lake challa 3 degrees s 38 degrees e in the easternmost area of the african tropics whereas both the seismic record of inferred lake level fluctuations and the branched and isoprenoidal tetraether bit index proxy record changes in hydrology within the challa basin delta d wax as a proxy for the isotopic composition of precipitation delta d p is interpreted as a tracer of large scale atmospheric circulation that integrates the history of the moisture transported to the lake challa area specifically based on modern day isotope rainfall relationships we argue that lake challa delta d wax reflects the intensity of east african monsoon circulation the three hydrological proxy records show generally similar trends for the last 25 000 years but there are important differences between them primarily during the middle holocene we interpret this deviation of delta d wax from local hydrological history as a decoupling of east african monsoon intensity which heavily influences the isotopes of precipitation in east africa today from rainfall amount in the challa basin in combination the hydrological proxy data from lake challa singularly highlight zonal gradients in tropical african climate that occur over a variety of timescales suggesting that the congo air boundary plays a fundamental role in controlling hydroclimate in the african tropics

early reactivation of european rivers during the last deglaciation during the last glacial maximum the sea level lowstand combined with the large extent of the fennoscandian and british ice sheets led to the funneling of european continental runoff resulting in the largest river system that ever drained the european continent here we show an abrupt and early reactivation of the european hydrological cycle at the onset of the last deglaciation leading to intense discharge of the channel river into the bay of biscay this freshwater influx probably combined with inputs from proglacial or ice dammed lakes dramatically affected the hydrology of the region both on land and in the ocean

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

cumulate origin and polybaric crystallization of fe ti oxide ores in the suwalki anorthosite northeastern poland fe ti oxide ores in the proterozoic suwalki massif type anorthosite northeastern poland have been recognized through geophysical exploration and extensive drilling down to 2 600 m depth the fe ti oxide rich rocks from suwalki consist of vanadium poor ti magnetite in lenses varying from the centimeter to the kilometer scale fe ti rich rocks are commonly layered and have gradational contacts with the host anorthosite they do not represent well defined intrusions such as the major tellnes and lac tio deposits based on petrography modal proportions whole rock analyses and liquidus phase compositions of fe ti oxide ores the sequence of crystallization is as follows plagioclase ti magnetite ilmenite followed by orthopyroxene then clinopyroxene and finally apatite the comparatively low v content 0 20 0 67 wt v in ti magnetite results from relatively oxidized crystallization conditions the diapiric emplacement of the anorthositic pluton influenced the crystallization of the fe ti ores and is responsible for the crystal sorting controlled by the density contrast of liquidus phases polybaric crystallization of fe ti oxide ores is evidenced by variable al2o3 ca 1 5 wt content of the associated orthopyroxene polybarism is responsible for the appearance of fe ti oxides before orthopyroxene due to the decreasing stability field of orthopyroxene with pressure

evaluating branched tetraether lipid based palaeotemperature proxies in an urban hyper eutrophic polluted lake in south africa we evaluate the application of the branched glycerol dialkyl glycerol tetraether br gdgt based palaeotemperature and palaeoenvironmental proxy to a hyper eutrophic polluted and shallow oxic lake lake zeekoevlei is the largest freshwater lake in south africa located close to cape town we use published lake based and soil based calibration equations and compare the reconstructed mean annual air temperature mat with regional south african and local cape town instrumental temperature records the distribution of br gdgts in the lake sediments is influenced by air temperature the lake based calibration equation which uses the methylation index of branched tetraethers cyclisation ratio of branched tetraethers mbt cbt formulated for african lakes tierney et al 2010 fits well with the instrumental temperature records moreover the cbt derived ph likely reflects historic socioeconomic changes in catchment our results suggest that a polluted hyper eutrophic status and shallow water urban setting do not preclude application of the mbt cbt mat proxy however further research is necessary to understand the behaviour of br gdgt producing bacteria in polluted and highly productive lakes

palaeo climate reconstruction from stable isotope variations in speleothems a review abstract speleothems are now regarded as valuable archives of climatic conditions on the continents offering a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores they are ideal materials for precise u series dating yielding ages in calendar years thereby circumventing the radiocarbon calibration problems associated with most other continental records stable isotope studies in speleothems have shifted away from attempting to provide palaeo temperature reconstructions to the attainable goal of providing precise estimates for the timing and duration of major o isotope defined climatic events characterised by high signal to noise ratios e g glacial interglacial transitions dansgaard oeschger oscillations the 8200 year event unlike the marine records speleothem data sets are not tuned and their independent chronology offers opportunities to critically assess leads and lags in the climate system that in turn can provide important insights into forcing and feedback mechanisms improved procedures for the extraction and measurement of stable isotope ratios in fluid inclusions trapped in speleothems are likely to provide in the near future a much enhanced basis for the quantitative interpretation of o isotope ratios in speleothem calcite the latter developments open up once again the tantalising prospect of palaeo temperature estimates but more importantly perhaps provide a direct test for a new generation of general circulation models whose hydrological cycles will incorporate the water isotopes the literature is reviewed briefly to provide for the reader a sense of the current state of the art and to provide some pointers for future research directions

oceanic link between abrupt changes in the north atlantic ocean and the african monsoon abrupt changes in the african monsoon which have been recorded throughout the late pleistocene and early holocene epochs tend to coincide with changes in north atlantic thermohaline circulation a numerical simulation shows that the interaction between thermohaline circulation in the north atlantic ocean and wind driven currents in the topical atlantic ocean contributes to the rapidity of african monsoon transitions during abrupt climate change events

a 1700 year n alkanes hydrogen isotope record of moisture changes in sediments from lake sugan in the qaidam basin northeastern tibetan plateau we present a hydrogen isotopic record of long chain n alkanes in lake sugan to reconstruct regional moisture changes in the last 1700 years at a sampling resolution of 25 years the d values decreased by over 30 from the medieval warm period mwp c ad 600 1500 to the little ice age lia c ad 1500 1850 and indicated that the moisture pattern included a relatively humid climate before the mwp becoming drier overall in the mwp wetter in the lia and then tending towards drought in the post industrial era in the study region chenopodiceae shrubs were more abundant in dry climates than in wet meanwhile d values of shrubs were more positive than those of grasses therefore we suggest that the vegetation type shrub or grass which depends on moisture changes is the controlling factor for d variations in lake sugan

coherent changes of southeastern equatorial and northern african rainfall during the last deglaciation during the last deglaciation wetter conditions developed abruptly 14 700 years ago in southeastern equatorial and northern africa and continued into the holocene explaining the abrupt onset and hemispheric coherence of this early african humid period is challenging due to opposing seasonal insolation patterns in this work we use a transient simulation with a climate model that provides a mechanistic understanding of deglacial tropical african precipitation changes our results show that meltwater induced reduction in the atlantic meridional overturning circulation amoc during the early deglaciation suppressed precipitation in both regions once the amoc reestablished wetter conditions developed north of the equator in response to high summer insolation and increasing greenhouse gas ghg concentrations whereas wetter conditions south of the equator were a response primarily to the ghg increase

three fe ti oxide ore bearing gabbro granitoid complexes in the panxi region of the permian emeishan large igneous province sw china the permian 260 ma emeishan large igneous province of sw china contains three nearly identical gabbro granitoid complexes that host giant fe ti oxide deposits the fe ti oxide deposits are within the lower portions of evolved layered gabbroic intrusions and are spatially and temporally associated with a type granitic plutons the 264 3 ma taihe layered gabbroic intrusion hosts a large magmatic fe ti oxide deposit and is coeval with the taihe peralkaline a type granitic pluton which is dated at 261 2 ma within the a type granitic pluton are microgranular enclaves which have compositions intermediate between the gabbro and host granite primitive mantle normalized incompatible element plots show corresponding reciprocal patterns between the mafic and felsic rocks the chondrite normalized ree patterns show eu anomalies changing from positive eu eu 1 5 to 5 9 in the gabbroic intrusion to negative in the enclaves eu eu 0 4 to 0 6 and granites eu eu 0 2 to 0 5 whole rock end t values of the gabbroic intrusion end t 2 5 to 3 3 are similar to those of the enclaves end t 1 0 to 2 0 and granite end t 1 5 to 1 9 whereas the zircon ehf t values of the gabbro ehf t 8 1 0 8 are indistinguishable from those of the granites ehf t 9 2 1 0 suggesting that the parent magmas for all rock types originated from the same mantle source geochemical modeling indicates that the gabbros and granites can be generated by fractional crystallization of a common parental magma similar to high ti emeishan flood basalt the compositional jump from the gabbro to the enclaves is attributed to the crystallization of fe ti oxide minerals the results of this study and other studies suggest that the magmatic conditions for example pressure composition fo2 which led to the formation of at least three fe ti oxide bearing gabbro granitoid complexes were relatively common during the development of the emeishan large igneous province

branched glycerol dialkyl glycerol tetraethers in lake sediments can they be used as temperature and ph proxies a series of surface sediments from 82 lakes of variable water depth and size was analyzed for glycerol dialkyl glycerol tetraethers gdgts in order to investigate the potential of the mbt cbt methylation ratio cyclization ratio of branched tetraethers as a continental palaeothermometer in lacustrine environments branched gdgts dominated in most sediments as indicated by the high branched vs isoprenoid tetraether bit values we observed that cbt and mbt varied substantially mean annual air temperature maat reconstructed and ph values were calculated using the cbt and mbt values and the calibration from the global soil data set the mbt cbt inferred temperatures were considerably lower than measured values nevertheless there was a significant correlation between maat reconstructed and maat observed on site although there was still considerable scatter r2 0 47 lacustrine sediments integrate organic remains of organisms in a lake and its drainage basin thereby offering a unique opportunity for calibrating mbt and cbt as small scale variability is averaged out since the source of the branched gdgts in the lake sediments is ambiguous it is not clear whether only temperature and ph in the catchment area are the driving factors therefore even in lake sediments with high concentrations of branched gdgts the straightforward application of mbt cbt as palaeoproxies may be difficult given the uncertainties regarding their source and origin

occurrence of tetraether lipids in stalagmites implications for sources and gdgt based proxies lipid biomarkers in stalagmites have potential in palaeoenvironmental reconstruction but glycerol dialkyl glycerol tetraethers gdgts in stalagmites have rarely been investigated we report the occurrence of archaeal isoprenoid gdgts and bacterial branched gdgts in heshang cave stalagmites in central china the archaeal component crenarchaeol dominated bacterial branched gdgts in the stalagmites and on the weathered parent rock surface collected inside the cave in contrast the distribution of gdgts in the overlying soil shows that branched gdgts dominated archaeal gdgts hence the majority of archaeal gdgts in stalagmites may be produced by crenarchaeota inhabiting the cave rather than being inherited from the overlying soil bacterial branched gdgt distributions expressed as mbt and cbt indices showed remarkable differences between stalagmite and soil samples implying that most branched gdgts may also be produced in situ in the cave the tex86 or tex86 values were found to increase with more depleted 18o values representing much stronger monsoon and therefore usually higher temperatures in the study region however the mbt cbt index in stalagmites may be influenced by a variety of factors besides palaeotemperature

minerals exsolution features and geochemistry of fe ti ores of the suwalki district north east poland the fe ti deposits of the suwalki district north east poland are magmatic in origin and were formed as a consequence of differentiation of magma melt that served as a parent for mineralization in the host and ore rocks ore mineralization in the host rocks is of accessory and segregational type and was formed in conditions characterized by low content of interprecipitable liquid relatively high oxygen fugacity and slow continuous cooling nearly all ti was removed from titanomagnetite above the solvus hence the true exsolution of ulvospinel was of minor importance in the host ore mineralization is characterized there by low content of impurities and low fe ti ratio high content of admixtures extreme mineralogical and compositional variations lack of geochemical cyclicity patterns in particular sections are typical of ore rocks both an increased amount of interprecipitable liquid and higher temperatures stimulated by intermediate fo2 controlled the formation of ore rocks the fo2 here remained credibly intermediate from early to late stages of mineral evolution the formation of magma and minerals enriched in fe ti settling in a bottom part of the magma chamber governed the formation of large ore bodies some other mechanisms such as filterpressing or immiscible segregation may be responsible for the formation of some discordant and concordant smaller ore bodies in the host the disclosed partitioning pattern of major and minor elements in ore minerals of host and ore rocks suggests that titanum free magnetite concentrate should be not practicable

the geochemistry of titanomagnetite in magnetite layers and their host rocks of the eastern bushveld complex more than 430 analyses of magnetite separates revealed pronounced differences in composition between magnetite from magnetite layers and disseminated magnetite from the host rocks magnetite from the massive layers is among others enriched in elements such as ti mg al and si which suggests that this magnetite crystallized under conditions of disequilibrium with the magma i e by spontaneous nucleation and rapid crystallization lower vanadium values in the magnetites from the massive layers suggest crystallization at higher f sub o 2 than from the rocks containing the disseminated magnetite variation diagrams reveal a cyclicity in compositional trends upward in the sequence which is related to nucleation of the magma in the roof zone of the intrusion the periodic collapse of this crystal laden magma and its incorporation in the zone of crystallization at the base of the magma chamber deviations of this normal trend are considered to reflect a stratification of the roof zone and a gradual incorporation of the stratified roof zone liquid into the convecting magma a pronounced upward increase in the cr content of magnetite is tentatively ascribed to a combination of olivine crystallization at the expense of pyroxene in the upper subzones and a possible increase in the partition coefficient of chromium between spinel and liquid with a decrease in the crystallization temperature

high relief topography of the nima basin in central tibetan plateau during the mid cenozoic time abstract there remains inconsistence of uplift history of the tibetan plateau here we estimated paleoelevation of mid cenozoic nima basin located in central tibet using multi proxies they included meteoric water and vegetation isotope proxies based on hydrogen and carbon isotopic compositions d and 13c respectively of terrestrial plant wax lipid of n alkanes and temperature proxy derived from microbial membrane lipid of branched glycerol dialkyl glycerol tetraethers brgdgts lipid analysis on sedimentary rocks in the nima basin yielded 222 12 and 30 0 0 7 for d and 13c of n c29 alkane respectively and brgdgt derived mean annual air temperature maat of 21 5 3 1 c for the paleo basin using the sea level meteoric water 18o and miocene siwalik paleovegetation 13c as low elevation references values of d and 13c of n c29 alkane in this study suggested paleoelevations of 4546 m and 2800 m respectively whereas by using a subtropical sea surface temperature as a reference brgdgt derived maats suggested a paleoelevation of 893 m we believed that the three estimates reflect a high relief topography in the study basin during the mid cenozoic representing elevations of orographic barrier of southerly oceanic moisture basin catchment and basin lake level respectively this scenario implies a low elevation of the basin relative to the lhasa terrane located to the south during the mid cenozoic hence challenging the classical crustal thickening models assuming a simple crustal thickening uplift relationship

distribution of glycerol dialkyl glycerol tetraethers in soils from two environmental transects in the usa abstract glycerol dialkyl glycerol tetraethers gdgts of both archaeal and bacterial origin form the basis of new temperature proxies applicable to soil and lake and marine sediments in soil branched gdgts are prevalent and their abundance of methyl or cyclic groups has been calibrated to mean annual temperature mat using mbt and cbt indices however soil ph is also known to be an important variable controlling the distribution of branched gdgts precipitation amount helps control soil moisture as well as ph and soil moisture is a leading variable affecting microbial diversity and activity in soil we have evaluated the distribution of gdgts from two soil transects in the usa a dry western transect covering six western states and a wet east coast transect from maine to georgia in order to assess the effect of precipitation on the distribution of soil gdgts our results show distinctly different gdgt distributions across climatic regions with dry western soils characterized predominantly by thaumarchaeotal isoprenoid iso gdgts and as a consequence low bit index values 0 2 0 6 and moist temperate east coast transect soils expressing mostly branched br gdgts and higher bit values 0 9 1 the predominance of iso gdgts in the western soils is related to the degree of aeration which in turn is related to precipitation amount and also to soil ph we also observed a substantial increase in the offset between measured mat and mbt cbt based mat below an annual precipitation of 700 800 mm yr 1 implying an impact of precipitation amount on mbt cbt based temperature reconstruction the data suggest that while soil tetraethers work well as a temperature proxy in moist temperate regimes they do not produce reliable measurements of temperature in sediments sourced from areas with 1 precipitation moreover erosion of soils with low bit values into lacustrine or marginal marine environments will not be detected via the bit index which can potentially affect paleotemperature reconstruction from sediments and so provide erroneous estimates of soil carbon delivery bit index values also show a correlation with precipitation amount the abundance of iso gdgts in western transect soils allowed calculation of tex 86 values but no correlation was found between tex 86 calculated temperature and mean annual temperature

branched glycerol dialkyl glycerol tetraethers in pleistocene loess paleosol sequences three case studies abstract branched glycerol dialkyl glycerol tetraethers branched gdgts are membrane lipids presumably derived from anaerobic heterotrophic soil bacteria empirical studies have shown that the composition of branched gdgts in topsoils varies in degree of cyclization and methylation expressed as cbt and mbt i e cyclization and methylation index of branched tetraethers depending on soil ph and mean annual air temperature mat here we present results from three case studies namely three well studied loess paleosol sequences lpss in which we measured the branched gdgts in order to test the applicability of these biomarkers for paleoclimate reconstruction the results show that major disagreements exist between expectations based on available stratigraphic pedological and geochemical data on the one hand and gdgt derived reconstructions on the other hand caution is therefore advised when interpreting the respective indices in lps studies we discuss several potential directions for future research i some of the target peaks in the hplc chromatograms consist of multiple unidentified compounds this needs to be addressed by way of improved component separation identification and new calibration studies ii factors other than mat and soil ph that could affect membrane composition should be further investigated e g nutrient availability and redox conditions as well as seasonality and changes in bacterial communities iii gdgts may be produced in non negligible amounts at depth and thus overprint the original in situ signal a concern that could be termed growth depth effect iv gdgts should also be analyzed in dust source regions and contemporaneous eolian sediments in order to address a potential redeposition effect

comparison of instrumental and gdgt based estimates of sea surface and air temperatures from the skagerrak sea surface temperatures ssts and annual mean air temperatures mats are estimated for the last 200 years from glycerol dialkyl glycerol tetraethers gdgts proxies in a marine sediment core from the skagerrak off southern norway the reconstructed values compare well with annual ssts and summer air temperatures obtained from composite regional instrumental records the results provide further confidence in the application of proxies based on gdgts to estimate past temperatures

using tetraether lipids archived in north sea basin sediments to extract north western european pliocene continental air temperatures the pliocene is often regarded as a suitable analogue for future climate due to an overall warmer climate 2 3 c coupled with atmospheric co2concentrations largely similar to present values 400 ppmv numerous pliocene sea surface temperature sst records are available however little is known about climate in the terrestrial realm here we generated a pliocene continental temperature record for northwestern europe based on branched glycerol dialkyl glycerol tetraether brgdgt membrane lipids stored in a marine sedimentary record from the western netherlands the total organic carbon toc content of the sediments and its stable carbon isotopic composition 13corg indicate a strong transition from primarily marine derived organic matter om during the pliocene to predominantly terrestrially derived om after the transition into the pleistocene this trend is supported by the ratio of branched and isoprenoid tetraethers bit index the marine terrestrial transition indicates a likely change in brgdgt sources in the core which may complicate the applicability of the brgdgt paleotemperature proxy in this setting currently the application of the brgdgt based paleothermometer on coastal marine sediments has been hampered by a marine overprint here we propose a method to disentangle terrestrial and marine sources based on the degree of cyclizationof tetramethylated brgdgts rings using a linear mixing model based on the global soil calibration set and a newly developed coastal marine temperature transfer function application of this method on our brgdgt record resulted in a corrected terrestrial temperature record matterr this latter record indicates that continental temperature were 12 14 c during the early pilocene and 10 5 12 c during the mid pilocene pollen based terrestrial temperatures estimate from nortern and central europe furthermore two colder 5 7 c periods in the pilocene maytterr record show that the influence of pilocene glacials reached well into nw europe

large temperature variability in the southern african tropics since the last glacial maximum 1 the role of the tropics in global climate change is actively debated particularly in regard to the timing and magnitude of thermal and hydrological response continuous high resolution temperature records through the last glacial maximum lgm from tropical oceans have provided much insight but surface temperature reconstructions do not exist from tropical continental environments here we used the tex86 paleotemperature proxy to reconstruct mean annual lake surface temperatures through the last glacial maximum lgm in lake malawi east africa 9 14 s we find a 3 5 c overall warming since the lgm with temperature reversals of 2 c during the younger dryas 12 5 ka bp and at 8 2 ka bp maximum holocene temperatures of 29 c were found at 5 ka bp a period preceding severe drought in africa these results suggest a substantial thermal response of southeastern tropical africa to deglaciation and to varying conditions during the holocene

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

micro textures and chemical compositions of metamorphic magnetite and ilmenite insights from the mianhuadi mafic complex in sw china abstract the compositions of titano magnetite in magmatic and hydrothermal ore deposits have shown the potential to discriminate mineral deposit types however primary fe ti oxides were sometimes overprinted by metamorphic event s over the long geologic history to what extent the fe ti oxide aggregates in mafic rocks can be modified either by re equilibration or interaction with the silicates during high grade metamorphism has not been systematically studied so far the mianhuadi mafic complex intruded at 260 ma as a layered intrusion in the emeishan large igneous province sw china has undergone granulite facies metamorphism in eocene during the development of the ailao shan red river shear zone the primary igneous titanomagnetite underwent oxyexsolution and reacted with the silicates to form magnetite ilmenite and pleonaste resulting in an increased volume proportion of ilmenite and pleonaste a retrograde chlorite carbonate assemblage was found to replace the magnetite whereas alo oh sometimes replaced pleonaste redistribution of elements associated with the oxyexsolution occurred that trace elements with larger partition coefficients in magnetite e g al ga v and cr than in ilmenite are more enriched in magnetite after metamorphism and vice versa iron ti oxide equilibrium calculations indicate that the increased oxygen fugacity is mainly responsible for the oxyexsolution of ilmenite and therefore the geochemical variation of magnetite metamorphic magnetite from the mianhuadi mafic complex can be clearly distinguished from its magmatic precursor by high ga zr and v ti ratios we further propose that v versus fe ti diagram can be used to discriminate between magmatic metamorphic and metasomatised titano magnetite

a simulation of the last glacial maximum climate using the ncar ccsm the national center for atmospheric research community climate system model ncar ccsm is used in a coupled atmosphere ocean sea ice simulation of the last glacial maximum lgm around 21 000 years ago climate in the tropics the simulation shows a moderate cooling of 3 c over land and 2 c in the ocean in zonal average this cooling is about 1 c cooler than the climap sea surface temperatures ssts but consistent with recent estimates of both land and sea surface temperature changes subtropical waters are cooled by 2 2 5 c also in agreement with recent estimates the simulated oceanic thermohaline circulation at the lgm is not only shallower but also weaker than the modern with a migration of deep water formation site in the north atlantic as suggested by the paleoceanographic evidences the simulated northward flow of antarctic bottom water aabw is enhanced these deep circulation changes are attributable to the increased surface density flux in the southern ocean caused by sea ice expansion at the lgm both the gulf stream and the kuroshio are intensified due to the overall increase of wind stress over the subtropical oceans the intensified zonal wind stress and southward shift of its maximum in the southern ocean effectively enhances the transport of the antarctic circumpolar current acc by more than 50 simulated ssts are lowered by up to 8 c in the midlatitudes simulated conditions in the north atlantic are warmer and with less sea ice than indicated by climap again in agreement with more recent estimates the increased meridional sst gradient at the lgm results in an enhanced hadley circulation and increased midlatitude storm track precipitation the increased baroclinic storm activity also intensifies the meridional atmospheric heat transport a sensitivity experiment shows that about half of the simulated tropical cooling at the lgm originates from reduced atmospheric concentrations of greenhouse gases

a review of the reconstructed palaeoenvironmental record of zimbabwe and call for multidisciplinary research abstract this paper is a review article focussing on the research on past environments of zimbabwe the paper synthesises the current knowledge on palaeo climates and other environmental parameters that inform debates and discussions on climate change and human adaptation the study of palaeoenvironments provides environmental knowledge that chronologically goes beyond the range of written climatic records that are available in the country the palaeoenvironmental data now available shows that our human ancestors in zimbabwe have survived numerous climatic upheavals since the beginning of the stone age however limited research in the stone age and the variety of proxy data available creates a less coherent record extrapolation of evidence from the region makes the data less reliable for archaeological interpretations the paper shows conflicting signals across the region at some specific periods there are numerous gaps in the record the paper concludes by calling for multidisciplinary research on the past environments of zimbabwe