applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

the source and paleoclimatic implication of hydrogen isotopic composition of n alkanes in sediments from the yixian formation western liaoning province ne china abstract hydrogen isotopic composition of n alkanes was measured in sediments from an excavated profile of the early cretaceous yixian formation in liaoning province ne china aiming to assess the significance of the d value of n alkanes in ancient lacustrine sediments as the indicator for determining the source inputs of organic matters and paleoclimatic conditions the d values of n alkanes are in the range of 250 to 85 and display an obvious three stage variation pattern through the profile which is consistent with the distribution of the dominated n alkanes and the profile of their 13 c values the d and 13 c values of n alkanes suggest that short chain n alkanes are primarily derived from photosynthetic bacteria and algae n c 29 and n c 31 are mainly originated from terrestrial higher plants n c 28 and n c 30 may be derived from the same precursor but via the different biological mechanism of hydrogen isotopic fractionation while the source inputs of medium chain n alkanes are more complicated with n c 23 being derived from some specific algae or biosynthesized by various aquatic organisms the paleoclimatic conditions are reconstructed via two approaches the reconstructed hydrogen isotopic values of lake water and meteoric water expressed as d lw and d mw respectively were at the intervals of 51 8 to 17 0 and 118 1 to 43 5 respectively indicating a general climate transition from semi arid to arid the calculated d lw mw values vary from 37 0 to 89 1 and display a similar but a significant large scale variation trend with the d c 23 long 28 8 to 85 0 long represents long chain n alkanes and d mid long 15 4 to 43 4 mid represents medium chain n alkanes values the discrepancy may be attributed to the source input overlap for n alkanes and the uncertainties of e water lipid values the coupling of d c 23 long d mid long and d lw mw values with the paleoclimatic evidence indicates that the d values of n alkanes could be more sensitive to the change of paleoclimatic conditions

identification of cyclone track regimes in the north atlantic a langrangian type climatology of north atlantic cyclones is established based on the high resolution european centre for medium range weather forecasts data set of the 1000 hpa height field first an algorithm is introduced to identify mid latitude cyclones and cyclone paths with as few constraints as possible cluster analysis of relative cyclone displacements yields three types of cyclone tracks characterizing stationary north eastward and zonally travelling storms the internal lagrangian statistics of these cyclone track types reveal representative life cycles for central pressure and geopotential height gradients and a power law scaling behaviour of cyclone displacements finally a basic climatology of north atlantic cyclone track regimes is deduced in terms of a time series and circulation statistics

the summer cyclone maximum over the central arctic ocean abstract a fascinating feature of the northern high latitude circulation is a prominent summer maximum in cyclone activity over the arctic ocean centered near the north pole in the long term mean this pattern is associated with the influx of lows generated over the eurasian continent and cyclogenesis over the arctic ocean itself its seasonal onset is linked to the following an eastward shift in the urals trough migration of the 500 hpa vortex core to near the pole and development of a separate region of high latitude baroclinicity the latter two features are consistent with differential atmospheric heating between the arctic ocean and snow free land variability in the strength of the cyclone pattern can be broadly linked to the phase of the summer northern annular mode when the cyclone pattern is well developed the 500 hpa vortex is especially strong and symmetric about the pole with negative sea level pressure slp anomalies over the pole and positive anomalies over middle latitudes net prec

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

molecular isotopic characterisation of hydrocarbon biomarkers in palaeocene eocene evaporitic lacustrine source rocks from the jianghan basin china immature organic matter in lacustrine source rocks from the jianghan basin eastern china was studied for distributions and stable carbon isotopic compositions 13 c of hydrocarbon biomarkers all of the bitumens contain isorenieratane 13 c ca 17 indicating the presence of chlorobiaceae and thus periods of euxinic conditions extended into the photic zone aliphatic hydrocarbon fractions are dominated by pristane and phytane and contain relatively low amounts of 4a and 4 methylsteranes c 30 13 c ca 16 believed to originate from 4 methylsterols in dinoflagellates 13 c values of gammacerane ca 24 and c 30 17 21 h hopane ca 23 are consistent with an origin from bacterivorous ciliates that fed on chlorobiaceae the bitumens contain low relative amounts of organo sulphur compounds one rock contains c 37 and c 38 n alkanes 13 c ca 36 derived from alkadienes and alkenones of prymnesiophytes the distributions of hydrocarbon biomarkers suggest that they were initially sulphurised during early diagenesis and later released during early thermal maturation

atmospheric forcing on the barents sea winter ice extent abstract the atmospheric forcing on the barents sea ice extent during winter december february djf has been investigated for the period 1967 2002 the time series for the sea ice extent is updated and includes the winter of 2005 which marks a new record low in the wintertime barents sea ice extent and a linear trend of 3 5 decade 1 in the ice extent was found covariability between the barents sea ice extent and the atmospheric mean seasonal flow and the synoptic cyclones has been discussed separately for the mean flow linear correlations and regression analysis reveal that anomalous northerly southerly winds prevail in the nordic seas during winters with extensive sparse barents sea ice extent some of the variability in the mean flow is captured by the north atlantic oscillation nao however the wintertime link between the barents sea ice extent and the nao is moderate by studying the cyclone activity in the high latitude northern hemisphere using a dataset of individual cyclones two

impact of the messinian salinity crisis on black sea hydrology insights from hydrogen isotopes analysis on biomarkers the messinian salinity crisis 5 96 5 33 ma ago was a dramatic oceanographic event when evaporites kilometers thick precipitated in a desiccating mediterranean basin trapping more than 5 of the world s oceanic salt hydrological changes in the adjacent black sea and water exchange with the mediterranean region are crucial but poorly understood factors influencing messinian evaporite formation here we present compound specific hydrogen isotope d data from messinian black sea sedimentary rocks that show a rapid change to heavy waters at 5 8 ma when major glaciations occurred at the same time highly depleted d values of long chain n alkanes derived from plant waxes indicate that fresh river transported water originated from colder northern latitudes the d values of alkenones biosynthesized by haptophyte algae show an unprecedented increase of 60 within 100 kyr the corresponding rapid change to 110 for d of the black sea waters seem unrealistic being heavier than anywhere in the present day oceans regardless of the applied relation between the d values of the alkenones and d of the waters where they were produced the 60 enrichment in the d values of alkenones indicates strongly enhanced evaporitic conditions still the relative distribution of the alkenones implies in situ growth and reproduction of haptophyte algae requiring sustained marine conditions in the black sea up to 5 6 ma this indicates that mediterranean black sea connectivity persisted during the first msc phase when gypsum precipitated in the mediterranean basin when the black sea became isolated at the peak of the msc 5 6 ma it had a strongly negative hydrological budget and rapidly desiccated due to excess evaporation

sedimentary organic matter record of early cretaceous environmental changes in western liaoning province ne china abstract the abundance and composition of organic matter and the 13 c compositions of some specific individual compounds were analysed in sediments collected from an excavated profile of the early cretaceous yi xian formation in liaoning province ne china in order to provide organic geochemical information on palaeoclimate and environmental changes the distribution of n alkanes varies steadily through the profile with long chain n alkanes dominating in the lower and upper sections and medium chain length n alkanes dominating in the middle section of the profile the 13 c values of n alkanes hopanes and steranes show similar upward positive trends through the profile suggesting that these compounds originated from the same source material and also reflect consistent changes in the environment of the sedimentary basin the c 24 17 21 seco hopane was only detected in the lower and middle sections of the profile and has a more positive carbon isotopic composition by about 3 7 6 7 than that of associated n alkanes hopanes steranes and c 30 8 14 seco hopane this implies that the c 24 17 21 seco hopane had a different origin possibly connected with the volcanic ash deposits and massive vertebrate remains reconstruction of the 13 c composition of atmospheric co 2 based on plant derived c 29 and c 31 n alkanes shows a change from 10 to 3 from the bottom to the middle of the profile this upward positive excursion through the profile is consistent with the worldwide variation of atmospheric co 2 during the early cretaceous and indicates an upward warming trend likely related to globally intensified volcanic activity

an objective cyclone climatology for the southern hemisphere abstract an objective method is developed and used to derive a climatology of centers of cyclonic vorticity for the southern hemisphere based on twice daily european centre for medium range weather forecasts ecmwf 1000 hpa analyses during 1980 86 these centers were computed as local minima of geostrophic relative vorticity g extending previous studies based on pressure minima this use of g avoids a bias favoring slower and or deeper cyclones that occurs when pressure is used and includes a large number of additional mobile vorticity centers in the 45 55 s band that are missed where a local pressure minimum cannot be found an automated tracking algorithm similar to that of murray and simmonds is used to match predicted location pressure and g from previous track history with available centers large numbers of g centers were found south of 60 s and near the midlatitude continents as in previous studies these were a mixture of migratory centers and other fixed topographic features the maxi

reconstruction of palaeohydrological conditions in a lagoon during the 2nd zechstein cycle through simultaneous use of δd values of individual n alkanes and δ 18 o and δ 13 c values of carbonates for the first time 18o and 13c values from carbonates and d values of individual n alkanes were used to reconstruct palaeohydrological conditions in a lagoon at the southern margin of the central european zechstein basin cezb a 12 m core covering the complete ca2 interval and adjacent anhydrites a1 and a2 was analyzed for 18o and 13c values of dolomitized carbonates and d values of individual n alkanes 18ocarb values 2 to 5 vs vpdb were strongly influenced by evaporation and temporal freshwater input into the lagoon the 13ccarb values 1 to 4 vs vpdb were controlled mainly by changes in primary production both isotopic ratios show an inverse relationship throughout most of the core contradicting diagenetic alteration since 13ccarb values are not altered significantly during dolomitization assuming a temperature range of 35 40 c in the lagoon 18ocarb values of 2 5 to 8 vs vsmow for the lagoonal water can be reconstructed the lagoon may have desiccated twice during the ca2 interval as indicated by very high 18ocarb and low 13ccarb values coinciding with increasing amount of anhydrite in the analyzed sample these events seem to reflect not just local but a regional intra ca2 cyclicity measured d values of the short chain n alkanes namely n c16 and n c18 which are widely used as indicators for photosynthetic bacterial and algal input reflect the isotopic composition of the lagoonal water assuming constant fractionation during incorporation of hydrogen into lipids of 160 an average d value of 70 vs vsmow can be reconstructed for the lagoonal water accounting for very arid conditions the long chain n alkanes n c27 n c28 n c29 and n c30 thought to be derived from the leaf waxes of terrestrial higher plants were shown to be depleted in d relative to the short chain alkanes therefore indicating a different hydrogen source terrestrial plants in arid areas mainly use water supplied by precipitation by using a smaller fractionation of 120 due to evaporation processes in the leaves reconstructed values vary between 74 and 9 vs vsmow these values are not indicating extremely arid conditions implying that the long chain n alkanes were transported trough wind and or rivers into the lagoon at the zechstein sea coast dwater values reconstructed using the n c16 alkane and 18o water values independently reconstructed on the same sample using the temperature dependant fractionation for dolomites are good agreement and suggest high amounts of evaporation affecting the coastal lagoon altogether our results indicate that hydrogen isotopic ratios of n alkanes give information on their origin and are a useful proxy for palaeoclimatic reconstruction

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

surface cyclones in the era 40 dataset 1958 2001 part i novel identification method and global climatology abstract a novel method is introduced to generate climatological frequency distributions of meteorological features from gridded datasets the method is used here to derive a climatology of extratropical cyclones from sea level pressure slp fields a simple and classical conception of cyclones is adopted where a cyclone is identified as the finite area that surrounds a local slp minimum and is enclosed by the outermost closed slp contour this cyclone identification procedure can be applied to individual time instants and climatologies of cyclone frequency fc are obtained by simple time averaging therefore unlike most other climatologies the method is not based on the application of a tracking algorithm and considers the size of cyclones in combination with a conventional cyclone center tracking algorithm that allows the determination of cyclone life times and the location of cyclogenesis and cyclolysis additional frequency fields can be obtained for special categories of cyclones that are gener

soil n alkane δd vs altitude gradients along mount gongga china the altitude effect on the isotopic composition of precipitation and its application to paleoelevation reconstruction using authigenic or pedogenic minerals have been intensively studied however there are still no studies on variations in biomarker d along altitude transects to investigate its potential as a paleoelevation indicator although it has been observed that d of higher plant lipid may record changes in precipitation d dp here we present d values of higher plant derived c27 c29 and c31n alkanes from surface soil along the eastern slope of mount gongga china with great changes in physical variables and vegetation over a range from 1000 to 4000 m above sea level the weighted mean d values of these n alkanes dwax show significant linear correlations with predicted dp values r2 0 76 with an apparent isotopic enrichment ewax p of 137 9 indicating that soil dwax values track overall dp variation along the entire altitudinal transect leaf dwax is also highly correlated with mountain altitude by a significant quadratic relationship r2 0 80 evapotranspiration is found declining with altitude potentially lowering dwax values at higher elevations however this evapotranspiration effect is believed to be largely compensated by the opposing effect of vegetation changes resulting in less varied ewax p values over the slope transect this study therefore confirms the potential of using leaf dwax to infer paleoelevations and more generally to infer the d of precipitation

stable hydrogen isotopic composition of hydrocarbons in torbanites late carboniferous to late permian deposited under various climatic conditions we measured the stable hydrogen isotopic composition d of selected aliphatic compounds in torbanites from scotland and australia covering the late carboniferous to the late permian the torbanites contain organic matter predominantly from a single algal source botryococcus braunii and are of similar thermal maturity the d values of n alkanes in the extracts appear to reflect the depositional palaeoclimate of each torbanite in response to the typical d values of meteoric waters the d values of n alkanes in torbanites deposited at high latitude under glacial conditions are depleted in deuterium by up to 70 relative to n alkanes in a torbanite deposited at low latitude under a tropical climate regime torbanites deposited in mid latitude regions under cool temperature conditions contain n alkanes with d values between those of n alkanes in tropical and glacial sediments a saw toothed profile of d values obtained for the n alkanes in the australian torbanites is attributed to a dual source system perhaps a predominant b braunii input with a second minor contribution from land plants pristane and phytane from two australian torbanites are significantly depleted in deuterium relative to n alkanes in the same samples and a significant difference between the d values of pristane and phytane is suggested to be caused by different sources for the two isoprenoids or isotope effects associated with their derivation from a common phytol precursor the offset between the d of values of n alkanes and isoprenoids is similar to that found in modern biological samples indicating that their indigenous d signatures may have been preserved for at least 260 280 million years

diurnal and semidiurnal tides in global surface pressure fields global surface pressure data from 1976 to 1997 from over 7500 land stations and the comprehensive ocean atmosphere data set have been analyzed using harmonic and zonal harmonic methods it is found that the diurnal pressure oscillation s1 is comparable to the semidiurnal pressure oscillation s2 in magnitude over much of the globe except for the low latitude open oceans where s2 is about twice as strong as s1 over many land areas such as the western united states the tibetan plateau and eastern africa s1 is even stronger than s2 this is in contrast to the conventional notion that s2 predominates over much of the globe the highest amplitudes 1 3 mb of s1 are found over northern south america and eastern africa close to the equator here s1 is also strong 1 1 mb over high terrain such as the rockies and the tibetan plateau the largest amplitudes of s2 1 0 1 3 mb are in the tropics over south america the eastern and western pacific and the indian ocean here s1 peaks around 0600 0800 lst at low latitudes and around 1000 1200 lst over most of midlatitudes while s2 peaks around 1000 and 2200 lst over low and midlatitudes here s1 is much stronger over the land than over the ocean and its amplitude distribution is strongly influenced by landmasses while the land sea differences of s2 are small the spatial variations of s1 correlate significantly with spatial variations in the diurnal temperature range at the surface suggesting that sensible heating from the ground is a major forcing for s1 although s2 is much more homogeneous zonally than s1 there are considerable zonal variations in the amplitude of s2 which cannot be explained by zonal variations in ozone and water vapor other forcings such as those through clouds reflection and absorption of solar radiation and latent heating in convective precipitation are needed to explain the observed regional and zonal variations in s2 the migrating tides and 1 s 1 predominate over other zonal wave components however the nonmigrating tides are substantially stronger 2 s 2 than previously reported the amplitudes of both the migrating and nonmigrating tides decrease rapidly poleward with a slower pace at middle and high latitudes

a new hybrid framework for simulating hypervelocity asteroid impacts and gravitational reaccumulation abstract we present a hybrid approach for simulating hypervelocity impacts onto asteroids the overall system response is separated into two stages based on their different characteristic timescales first the short timescale fragmentation phase is simulated using a modified version of the tonge ramesh material model implemented in a material point method framework then a consistent hand off to an n body gravity code is formulated to execute the long timescale gravitational reaccumulation calculation we demonstrate this hybrid approach by considering the 5 km s head on impact of a 1 21 km diameter basalt impactor on a 25 km diameter target asteroid the impact event resulted in the fragmentation but not complete disruption of the entire target a granular core is observed at the end of the fragmentation simulations which acts as a gravity well over which reaccumulation occurs in the n body simulations our results suggest that disruption thresholds for rocky asteroids are higher when energy dissipating mechanisms such as granular flow and pore collapse are included

δd values of n alkanes in tibetan lake sediments and aquatic macrophytes a surface sediment study and application to a 16 ka record from lake koucha abstract a set of lake surface sediment samples and aquatic macrophytes from the eastern and central tibetan plateau and a sediment core from koucha lake northeastern tibetan plateau were analysed for hydrogen isotope signals of aliphatic lipid biomarkers the d values of n alkanes were correlated with those of meteoric water in the summer months and showed increasing pearson correlation coefficients with increasing n alkane chain length r 0 80 for n c 31 while in samples from the most humid regions southeastern tibetan plateau the apparent enrichment factors between meteoric water and lipids are close to those reported for other humid sites e 135 for mid chain and 125 for long chain n alkanes they become smaller e 118 to 41 mean value 86 at sites with a negative moisture balance northeastern and central tibetan plateau and qaidam basin this might be caused by enrichment in deuterium of the source water used for lipid synthesis as a result of lake water evaporation and soil and leaf water evapotranspiration in the core from lake koucha decreasing d values of all n alkanes between 15 and 10 cal ka bp give evidence for an intensification of the asian summer monsoon at ca 9 cal ka bp a ca 15 shift towards higher d values of mid chain n alkanes suggests enhanced evaporation of the lake water which outweighs higher precipitation amounts because of a temperature increase during the early holocene monsoonal maximum only a few surface sediment samples show a significant offset between d values of mid chain n alkanes and n c 31 d mid n c31 and no systematic dependence between this offset and environmental parameters such as mean annual precipitation was found in the core available data for most samples also do not show a significant offset only a slight increase 15 of d mid n c31 at ca 10 0 cal ka bp and a decrease 17 at ca 6 8 cal ka bp might indicate wetter and drier conditions respectively however interpretation of d mid n c31 throughout the record is difficult because of a lack of reliable data for n c 31 in key sections of the core so more records are necessary to further test the potential applicability of d mid n c31 as a proxy for palaeo hydrological conditions

the summertime annular mode in the northern hemisphere and its linkage to the winter mode 1 the seasonal variations of the northern hemisphere annular mode nam are investigated through empirical orthogonal function analysis of the zonally averaged geopotential height fields for each individual calendar month patterns of the winter and summer nams differ not only in the geopotential height fields but also in the mean meridional circulation and eddy structure the summer nam has a smaller meridional scale and is displaced poleward as compared to the winter nam the antinode on the lower latitude side in the summer nam is at the nodal latitude of the winter nam the summer nam is more strongly related to surface air temperatures over eurasia than the original arctic oscillation the summer nam is a wave driven internal atmospheric mode that is maintained by both stationary and transient waves the summer nam is associated with the arctic front polar jet and storm track around the arctic ocean the winter to summer linkage described by m ogi et al can be interpreted as a preferred transition from one polarity of the winter annular mode to the same polarity of the summer annular mode the spring cryosphere i e snow in eurasia and sea ice in the barents sea plays a supporting role in this transition index terms 1620 global change climate dynamics 3309 3309 meteorology and atmospheric dynamics climatology 1620 3319 meteorology and atmospheric dynamics general circulation 3349 meteorology and atmospheric dynamics polar meteorology keywords northern hemisphere s annular mode arctic oscillation winter to summer link

hydrogen isotope ratios of lacustrine sedimentary n alkanes as proxies of tropical african hydrology insights from a calibration transect across cameroon abstract hydrogen isotope values d of sedimentary aquatic and terrestrial lipid biomarkers originating from algae bacteria and leaf wax have been used to record isotopic properties of ancient source water i e precipitation and or lake water in several mid and high latitude lacustrine environments in the tropics however where both processes associated with isotope fractionation in the hydrologic system and vegetation strongly differ from those at higher latitudes calibration studies for this proxy are not yet available to close this gap of knowledge we sampled surface sediments from 11 lakes in cameroon to identify those hydro climatological processes and physiological factors that determine the hydrogen isotopic composition of aquatic and terrestrial lipid biomarkers here we present a robust framework for the application of compound specific hydrogen isotopes in tropical africa our results show that the d values of the aquatic lipid biomarker n c17 alkane were not correlated with the d values of lake water carbon isotope measurements indicate that the n c17 alkane was derived from multiple source organisms that used different hydrogen pools for biosynthesis we demonstrate that the d values of the n c29 alkane were correlated with the d values of surface water i e river water and groundwater which on large spatial scales reflect the isotopic composition of mean annual precipitation such a relationship has been observed at higher latitudes supporting the robustness of the leaf wax lipid d proxy on a hemispheric spatial scale in contrast the d values of the n c31 alkane did not show such a relationship but instead were correlated with the evaporative lake water d values this result suggests distinct water sources for both leaf wax lipids most likely originating from two different groups of plants these new findings have important implications for the interpretation of long chain n alkane d records from ancient lake sediments in particular a robust interpretation of palaeohydrological data requires knowledge of the vegetation in the catchment area as different plants may utilise different water sources our results also suggest that the combination of carbon and hydrogen isotopes does help to differentiate between the metabolic pathway and or growth form of organisms and therefore the source of hydrogen used during lipid biosynthesis

recurrent phases of drought in the upper miocene of the black sea region abstract since the miocene the black sea proved to be highly sensitive to fluctuations in the hydrological cycle because of its recurrent restricted connections with the open ocean and the location between the dry mediterranean and more humid higher northern latitudes although the black sea formed one of the foci of the 1975 deep sea drilling project leg 42b robust tools to reconstruct past changes in its hydrological cycle were lacking at that time here we revisit the sedimentary succession hole 380a and determined compound specific carbon 13c hydrogen isotope ratios d of terrestrial and aquatic biomarkers to investigate changes in the hydrological budget of the black sea during the late miocene the 13c and d isotopic composition of n alkanes as well as alkenones and palynology indicate large environmental changes in the black sea and or in the sources of the water entering the black sea during the late miocene the d of alkenones showing an enrichment of more than 80 at the end of the miocene implies a major shift in basin hydrology possibly resulting in severely increased salinity these changes in d composition of the alkenones coincide with both with sharp shifts in reconstructed sea surface temperature and palynological assemblages two intervals with negative water budget were identified most likely caused by enhanced evaporation the older and longer dry evaporative phase predates the maeotian pontian boundary regional stages at 6 1 ma the younger drying phase corresponds to the messinian salinity crisis this shift to highly evaporative conditions is related to a similar shift previously observed in a messinian pontian sedimentary succession from the taman peninsula russia these recurrent dry phases likely reflect regional climatic shifts over a significantly larger area around the black sea area during the upper miocene

circulation and surface controls on the lower tropospheric air temperature field of the arctic 1 characteristics of the 925 hpa arctic air temperature field are evaluated with respect to controls by horizontal temperature advection vertical motion and characteristics of the underlying land and ocean surface the highest winter mean temperatures in the arctic found in the norwegian and barents seas are maintained primarily by cold horizontal advection countered by diabatic heating the latter linked to open ocean waters by comparison temperatures over the central arctic ocean are primarily maintained by warm advection and diabatic cooling depending on the region vertical motion opposes notably off the east coast of greenland or reinforces forcing by advection for summer cold advection over snow free land is countered by diabatic warming this contrasts sharply with the arctic ocean where warm advection and locally downward vertical motion combine to oppose pronounced diabatic cooling the latter linked to surface melt and heat uptake in the ocean mixed layer prominent temperature anomalies in all seasons accompany onshore and offshore flow for example summer northerlies blowing off the arctic ocean yield cold anomalies over northern eurasia extending far inland from the coast while onshore winter westerlies yield above average temperatures over northwestern eurasia and the barents and kara seas easterlies yield cold anomalies in the same regions the most recent decade 2000 2009 has seen positive temperature anomalies over most of the arctic for northerlies easterlies southerlies and westerlies and for all seasons influences of recent shifts in atmospheric circulation reduced sea ice extent and rising sea surface temperature are prominent especially for winter and autumn

molecular indicators of palaeosalinity and depositional environment of small scale basins within carbonate platforms the late triassic hauptdolomite wiestalstausee section near hallein northern calcareous alps austria abstract microfacies and biomarker analyses are used to determine the environmental conditions during deposition of marly dolomicrites from the hauptdolomite wiestalstausee section near hallein salzburg austria part of the late triassic hauptdolomite dachstein carbonate platform of the northern calcareous alps phytoplankton and photosynthetic bacteria are considered to be the major primary producers of the organic matter in these immature 0 5 equivalent vitrinite reflectance carbonate rich rocks contributions from vascular plants are suggested from the n alkane distribution pattern and high content of c 29 steranes enhanced microbial activity in the depositional environment is proposed on the basis of the hopanoid content the occurrence of aryl isoprenoids probably derived from carotenoids of the photosynthetic green sulfur bacteria chlorobiaceae indicates the presence of free h 2 s in the bottom water mesohaline conditions in the upper part of the water column are deduced from the presence of dimethylated and trimethylated 2 methyl 2 tridecylchromans mttcs co variation in the distribution of mttcs and pristane phytane ratio and the concentration of a c 16 aryl isoprenoid argue for photic zone anoxia due to salinity stratification the biomarker composition points to a high productivity marine environment with limited water exchange and a stratified water column confirmed by microfacies analysis a small scale basin formed within the restricted inner lagoonal area of the hauptdolomite dachstein carbonate platform through erosion by currents followed by a sea level rise is considered the most appropriate depositional environment of the dolomicrites of the wiestalstausee section

high resolution palaeoecological and taphonomic analysis of early cretaceous lake biota western liaoning ne china abstract the faunal content of eighteen bedding planes within the jianshangou unit of the lower cretaceous yixian formation of western liaoning has been analysed in detail in order to understand the environmental and taphonomic framework of this famous lacustrine fossillagerstatte the bedding planes were excavated within a 3 m thick section which is composed of laminated mudstones graded sandstones and mudstones and horizontally stratified structureless sandstones and tuffs all investigated bedding planes occur within the laminated mudstone facies and contain elements of the so called jehol biota in particular the conchostracan eosestheria ovata the ephemerid nymph hexagenites trisetalis and the crustacean liaoningogriphus quadripartitus these three faunal elements occur in high abundance originally possessed chitinous skeletons and are preserved as compressed faintly mineralized coats or in the case of eosestheria still possess organic material the specimens do no represent exuviae but body fossils the fossils can be grouped into three low diversity associations each characterized by one of the three taxa the plan view orientation of the taxa is invariably random and size frequency histograms are bimodal or polymodal this indicates that the fauna is autochthonous and that the histograms reflect several recruitment phases apparently the faunal elements suffered seasonal mass mortality caused by anoxic conditions which became established in the lake during the summer months increased humidity during the winter led to mixing of the lake waters re establishment of oxic conditions and to deposition of a thin film of sediment such environmental conditions were episodically interrupted by flash floods and volcanic ash falls which may have been responsible for the preservation of the more spectacular elements of the jehol biota such as birds and feathered dinosaurs

a molecular and carbon isotope biogeochemical study of biomarkers and kerogen pyrolysates of the kimmeridge clay facies palaeoenvironmental implications abstract structures and carbon isotopic compositions of biomarkers and kerogen pyrolysis products of a dolomite a bituminous shale and an oil shale of the kimmeridge clay formation kcf in dorset were studied in order to gain insight into i the type and extent of water column anoxia and ii changes in the concentration and isotopic composition of dissolved inorganic carbon dic in the palaeowater column the samples studied fit into the curve of increasing 13 c of the kerogen 13 c toc with increasing toc reported by huc et al 1992 their hypothesis that the positive correlation between toc and 13 c toc is the result of differing degrees of organic matter om mineralisation in the water column was tested by measuring the 13 c values of primary production markers these 13 c values were found to differ on average by only 1 among the samples implying that differences in the extent of om mineralisation cannot fully account for the 3 difference in 13 c toc the extractable om in the oil shale differs from that in the other sediments due to both differences in maturity and differences in the planktonic community these differences however are not likely to have significantly influenced 13 c toc either all three sediments contain abundant derivatives of isorenieratene indicating that periodically euxinia was extending into the photic zone the sediments are rich in organic sulfur as revealed by the abundant sulfur compounds in the pyrolysates the prominence of c 1 c 3 alkylated thiophenes over n alkanes and n alkenes is most pronounced in the pyrolysate of the sediment richest in toc this suggests that sulfurisation of om may have played an important role in determining the toc 13 c toc relationship reported by huc et al 1992

low level temperature inversions of the eurasian arctic and comparisons with soviet drifting station data abstract seasonal and regional variations in characteristics of the arctic low level temperature inversion are examined using up to 12 years of twice daily rawinsonde data from 31 inland and coastal sites of the eurasian arctic and a total of nearly six station years of data from three soviet drifting stations near the north pole the frequency of inversions the median inversion depth and the temperature difference across the inversion layer increase from the norwegian sea eastward toward the laptev and east siberian seas this effect is most pronounced in winter and autumn and reflects proximity to oceanic influences and synoptic activity possibly enhanced by a gradient in cloud cover east of novaya zemlya during winter inversions are found in over 95 of all soundings and tend to be surface based for all locations however inversions tend to he most intense during winter due to the large deficit in surface net radiation the strongest inversions are found over eastern siberia and reflect the ef

change in hydrogen isotope composition of n alkanes pristane phytane and aromatic hydrocarbons in miocene siliceous mudstones with increasing maturity abstract the variation in the hydrogen isotope composition d h ratio values of n alkanes pristane phytane and aromatic hydrocarbons with increasing maturity was investigated using a set of immature to mature miocene siliceous mudstones the d h values of aromatic hydrocarbons change at the earliest stage vitrinite reflectance r o 0 4 0 5 by way of higher values in immature rocks a dramatic increase in values is observed for pristane and phytane during the mature stage r o 0 6 0 7 attributable to hydrogen exchange with sediment porewater the decrease in the values of short chain n alkanes and the disappearance of carbon number predominance in n alkane d h values with increasing maturity is a result of the thermal cracking of aliphatic structures in bitumen and kerogen the long chain n alkanes derived from higher plant wax can maintain their initial values even in the zone of extensive oil generation r o

assessment of the difference between mid and long chain compound specific δdn alkanes values in lacustrine sediments as a paleoclimatic indicator abstract previous studies have proposed that the difference between compound specific hydrogen isotopic composition of n alkanes d n alkanes of possible terrestrial origin and aquatic origin in lacustrine sediments is an indicator of hydroclimatic conditions for a lake environment e g terrestrial evapotranspiration of the lake drainage area or evaporation inflow ratio for the lake sachse d radke j gleixner g 2004 hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability geochimica et cosmochimca acta 68 4877 4889 sachse d radke j gleixner g 2006 d values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record organic geochemistry 37 469 483 mugler i sachse d werner m xu b q wu g j yao t d gleixner g 2008 effect of lake evaporation on d values of lacustrine n alkanes a comparison of nam co tibetan plateau and holzmaar germany organic geochemistry 39 711 729 and this proposed indicator has been applied to a paleoclimatic study of koucha lake kcl on the northeastern tibetan plateau netp however the application was not very successful due to an apparent discrepancy between the reconstructed possible hydroclimatic variation based on the proposed indicator and precipitation amount variation based on pollen in the same lake aichner b herzschuh u wilkes h vieth a bohner j 2010a d values of n alkanes in tibetan lake sediments and aquatic macrophytes a surface sediment study and application to a 16 ka record from lake koucha organic geochemistry 41 779 790 we report new compound specific d n alkanes data for sediments since the last glacial from hurleg lake klk and genggahai lake ggh both also on the netp ca 300 km apart together d n alkanes data from the three lakes were analyzed to assess the difference between mid chain and long chain compound specific d n alkanes values in the sediments as a paleoclimatic indicator our results indicate that mid chain n c 23 and n c 25 and long chain n c 27 n c 29 and n c 31 n alkanes as compounds representative of aquatic and terrestrial origins respectively were valid only for klk correspondingly the use of differences between mid chain and long chain compound specific d n alkanes as a possible paleoclimatic indicator was feasible only for this lake hence our results emphasize the complex relationship between the chain length of lacustrine n alkanes and their actual origins and suggest that the correlation analysis of d n alkanes data for different chain length could be part of the possible evaluation method for the application of lacustrine compound specific d n alkanes data in paleoclimatic studies

geochemical characterization of malm zeta laminated carbonates from the franconian alb sw germany ii abstract during jurassic times especially within the malm stage local depressions formed on the eastern bavarian carbonate platform that were surrounded by wall reefs this created a unique depositional environment where in an open marine setting stagnant and anoxic bottom waters developed in an intra reef depression anoxic conditions were stabilized below wave base by enhanced salinity in the bottom waters and establishment of a density stratification biomarker analysis was applied to characterize palaeosalinity and redox conditions utilizing organic sulfur compound methylated chroman hopanoid and saturated isoprenoid distributions prevention of terrigenous influx by protecting reef walls lead to iron deficiency in intra reefal sediments causing early diagenetic sulfurization of functionalized lipids absence of clay mineral catalysts and early sulfurization favored an unusual steroid distribution lacking rearranged analogues but providing coexistence of saturated steranes with and configuration 13 17 spirosterenes unknown sterenes and steradienes as well as mono di and triaromatic steroids desulfurization of the polar fraction was carried out for two samples to verify that palaeoenvironment reconstruction based on free hydrocarbon and heterocompound distribution was not invalidated by sulfur quenching of selected compounds gammacerane was found to be the only component to occur exclusively in the sulfur bound fraction only minor amounts of hydrocarbons were released upon desulfurization implying that free bitumen analysis was applicable for organofacies characterization organic petrological investigation of organic mats revealed the presence of two different types of such structures comparison of organoclast fluorescence spectra with those of extracted porphyrin fractions indicate an origin of porphyrins exclusively from cyanobacterial mats whereas algal dominated mats yield no porphyrins this aims towards a better localization of specific biomarker origin in geological samples

δd values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record abstract the compound specific hydrogen isotope composition d of sedimentary n alkanes is increasingly used as a palaeoclimate proxy to explore the origin of the hydrogen isotope signal of n alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n alkane composition and d values of 31 plant biomass samples birch betula beech fagus oak quercus alder alnus hornbeam carpinus and myrtle myrtus as well as non stomata containing sphagnum cladonia and moss from 14 sites along a climatic gradient from northern finland to southern italy eleven of the sites were previously investigated for the n alkane d values in adjacent lake sediments and are compared to the leaf wax n alkane d values the distribution of terrestrial n alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake evidently n alkane distributions within the same species at different sites were found to be variable these findings complicate the use of certain n alkane distributions in sediments as a palaeoenvironmental indicator d values of plant biomass n alkanes show a significant positive correlation with the precipitation d values biomass n alkane d values are in general less negative than the associated sedimentary n alkanes of terrestrial origin possibly due to the stronger evapotranspiration during the summer when sampling took place this suggests that n alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn when most leaves are incorporated into the sediment the variability of the d values from non stomata containing plants is much higher than for broadleaf trees since stomata can regulate water loss through evapotranspiration the average chain length acl of n alkanes from deciduous tree leaves increases from north to south with increasing acl the hydrogen isotopic fractionation e between source water and n alkanes also increases our results prove that terrestrial n alkane d values record the d value of precipitation modified by the amount of isotope enrichment in the leaf water due to plant anatomy stomata vs no stomata and site specific meteorological conditions such as evapotranspiration relative humidity and soil moisture therefore terrestrial n alkanes in lake sediments can deliver information on changes in these parameters over geological timescales in lake sediments where aquatic n alkanes such as n c 17 record the lake water d value the isotopic difference between terrestrial and aquatic n alkanes could therefore be used to reconstruct changes in evapotranspiration

depositional evolution of the early cretaceous sihetun lake and implications for regional climatic and volcanic history in western liaoning ne china numerous well known fossils of the jehol biota including early birds feathered theropods primitive mammals and putative early angiosperms have been discovered in lacustrine deposits lake sihetun of the lower cretaceous yixian formation of western liaoning province ne china based on extensive field investigations and four high resolution excavations we document in detail the spatio temporal changes of sedimentary facies facies associations and limnic community relicts reconstruct the depositional history and discuss the significance of these deposits regarding the regional climatic and volcanic history four phases are recognized in the history of lake sihetun they are 1 a phase of fluctuating but gradually rising water level indicated by subaerial and shallow water lacustrine deposits 2 a lake with beach nearshore facies along the marginal areas and suspension dominated lake floor facies in central areas 3 a lake phase with a lake floor dominated by hyperpycnal flows and 4 progradation of a fan delta two distinct depositional conditions are observed stratified and unstratified lake intervals the former occurred mainly during the second phase and produced clay poor and clay rich laminae whereas the latter developed during the other three phases and were dominated by deposition of subaqueous sedimentary density flows these alternations of depositional conditions in offshore lacustrine deposits suggest that the yixian formation may have formed under a transitional climate regime fluctuating gradually from warm and dry to warm and humid conditions resurgent volcanism is inferred to have become stronger during the late phase of lake development based on distribution of deposits characterizing the unstratified lake interval and volcanic rocks of the overlying upper lava unit a higher content of primary pyroclastic fragments and evidence of strong syndepositional disturbance

large and rapid climate variability during the messinian salinity crisis evidence from deuterium concentrations of individual biomarkers during the messinian 6 m y ago massive sea level fall and widespread deposition of evaporites occurred in the mediterranean sea when it became isolated from the world oceans here we present the first hydrogen isotope data from individual sedimentary biomarkers n alkanes and isoprenoids that tracked climatically driven hydrographic changes in response to extreme evaporation during the messinian salinity crisis the stable hydrogen and carbon isotope compositions of these biomarkers show a range of 160 in d values and 14 in 13 c values and roughly covary this indicates that the source waters of the biomarkers were therefore in some cases extremely enriched in deuterium having average d as great as 66 vsmow vienna standard mean ocean water such values are only known from desert climates today because the offset between the d values of n alkanes and isoprenoids preserved in the miocene sedimentary rocks is similar to the offset found in modern biological samples we conclude that diagenesis did not significantly affect the primary deuterium concentrations

hydrogen isotopic compositions of individual alkanes as a new approach to petroleum correlation case studies from the western canada sedimentary basin isotopic compositions of carbon bound hydrogen in individual n alkanes and acyclic isoprenoid alkanes from a number of crude oil samples were measured using gas chromatography thermal conversion isotope ratio mass spectrometry the precision of this technique is better than 3 for most alkanes compared to the large range of d variation among the samples up to 160 the oils were selected from major genetic oil families in the western canada sedimentary basin with source rocks ranging in age from ordovician and possibly cambrian to cretaceous the hydrogen isotopic composition of alkanes in crude oils is controlled by three factors isotopic compositions of biosynthetic precursors source water d values and postdepositional processes the inherited difference in the lipid s biosynthetic origins and or pathways is reflected by a small hydrogen isotopic variability within n alkanes but much larger differences in the d values between n alkanes and pristane phytane the shift toward lighter hydrogen isotopic compositions from paleozoic to upper cretaceous oils in the wcsb reflects a special depositional setting and or a minor contribution of terrestrial organic matter the strong influence of source water d values is demonstrated by the distinctively lower d values of lacustrine oils than marine oils and also by the high values for oils with source rocks deposited in evaporative environments thermal maturation may alter the d values of the alkanes in the oil to some extent but secondary oil migration does not appear to have had any significant impact the fact that oils derived from source rocks that could be of cambrian age still retain a strong signature of the hydrogen isotopic compositions of source organic matter and source water indicates that d values are very useful for oil source correlation and for paleoenvironmental reconstructions

effect of lake evaporation on δd values of lacustrine n alkanes a comparison of nam co tibetan plateau and holzmaar germany compound specific hydrogen isotope ratio values of lacustrine n alkanes from two contrasting ecosystems the semiarid to arid nam co central tibet and the humid holzmaar germany were compared in order to assess whether or not these environmental conditions are recorded in the isotopic signatures of biomarkers increased evaporation of lake water at nam co is recorded by the n alkanes of aquatic origin hence isotopic enrichment results in a di erence between terrestrial and aquatic n alkanes in the opposite direction 68 from that known for humid climate conditions 30 predominating at holzmaar based on this isotopic di erence between terrestrial and aquatic n alkanes evaporation to inflow ratio e i values were estimated and suggest that the isotopic di erence is indicative of the general hydroclimatic characteristics of a lake system moreover the comparison with e i values calculated with actual stable water isotope data showed that the dd values of aquatic and terrestrial lacustrine n alkanes serve as a proxy for the relative isotopic di erences between lake and inflow waters and can be used to assess the proportion of water undergoing evaporation relative to the inflow and thus to reconstruct the lake water balance in the past 2008 published by elsevier ltd

the arctic frontal zone as seen in the ncep ncar reanalysis abstract calculations of a thermal front parameter using ncep ncar reanalysis data over the period 1979 98 reveal a relative maximum in frontal frequencies during summer along northern eurasia from about 60 to 70 n best expressed over the eastern half of the continent a similar relative maximum is found over alaska which is present year round although best expressed in summer these high latitude features can be clearly distinguished from the polar frontal zone in the midlatitudes of the pacific basin and collectively resemble the summertime arctic frontal zone discussed in several early studies while some separation between high and midlatitude frontal activity is observed in all seasons the summer season is distinguished by the development of an attendant mean baroclinic zone aligned roughly along the arctic ocean coastline and associated wind maxima in the upper troposphere the regions of maximum summer frontal frequency correspond to preferred areas of cyclogenesis and to where the summertime

a 15 ka lake water δd record from genggahai lake northeastern tibetan plateau and its paleoclimatic significance abstract the mid chain and long chain n alkanes in sediments of genggahai lake on the northeastern tibetan plateau have been assigned as being predominantly from aquatic plants thus at the lake compound specific hydrogen isotopic data for mid and long chain n alkanes d n alkanes are indicators of the variation in lake water d d lw genggahai d lw is determined by the local meteoric water d d mw and by lake surface evaporation as evidenced by modern observational data and the broad correlation between genggahai d lw and average lake water depth during the past 15 ka with more negative d lw values corresponding to greater average water depth as demonstrated by the mid and long chain d n alkanes data the most negative interval of genggahai d lw was during the early holocene an overall trend towards more positive values from the early to the late holocene clearly indicates the long term evolutionary history of local d mw which could be related to the intensity of the indian summer monsoon ism via the rainfall amount effect therefore the record of d lw at genggahai during the past 15 ka which resembles that of stalagmite 18 o records from the core ism region apparently reflects the long term evolution of ism intensity furthermore several short term positive excursions in genggahai d lw values during the late holocene reflect enhanced lake surface evaporation via an isotopic enrichment mechanism that apparently resulted from periods of weakened ism intensity our results highlight the fact that unambiguous source determination of n alkanes is vital for determining the paleoclimatic significance of lacustrine d n alkanes data

compound specific δd values of long chain n alkanes derived from terrestrial higher plants are indicative of the δd of meteoric waters evidence from surface soils in eastern china the stable carbon and hydrogen isotope composition of higher plant derived long chain n alkanes 13cn alkanes and dn alkanes from 45 surface soil samples within well characterized vegetation zones from eastern china 18 n 50 n are reported the weighted average dn alkanes value for n c27 n c29 and n c31 in the samples and the annual average d of meteoric water recorded at 12 weather stations proximal to the sampling sites show similar spatial variations the d of n alkanes shows a gradual depletion in value with increasing latitude the results demonstrate that on a large spatial scale the d values of long chain n alkanes derived from higher plants have the potential to record the d of meteoric water although many other factors can also influence the isotope values there appears to be no apparent relationship between the d of the n alkanes extracted from the surface soil and the overlying vegetation type i e forest grassland or c3 c4 composition therefore palaeoenvironmental studies utilizing dn alkanes from higher plant derived material in geological samples have the potential to provide additional information with regard to the past hydrological cycle

distributions and stable carbon isotopic compositions of biomarkers in torbanites from different palaeogeographical locations abstract the relative distributions and stable carbon isotopic compositions of certain aliphatic and aromatic biomarkers from 11 botryococcus braunii rich torbanites from scotland south africa and australia covering the late carboniferous to late permian were investigated the data was scrutinised for any evidence of molecular features which may be characteristic of palaeogeography the torbanites studied were selected to cover a range of age and palaeoclimatic conditions e g permian and late carboniferous when gondwana was covered by an extensive ice sheet the late permian when the climate warmed from glacial to cool to temperate and the carboniferous when laurasia was located within the equatorial zone all torbanites are composed of abundant n alkanes and novel macrocyclic alkanes which based on similar 13c values are ascribed a common origin all samples are also characterised by a high cyanobacterial input as indicated by abundant hopanoids other biomarker distributions and stable carbon isotopic compositional differences separated the torbanites into three groups which also correlate to three different palaeogeographical palaeoclimatic precincts i group a southern africa and eastern australia temi torbanites which are characterised by a high relative abundance of cyanobacterial and methylotrophic hopanoids abundant branched hydrocarbons and 13c enriched homologous series of monomethylakanes ii group b eastern australia newnes and glen davis torbanites contain relatively high amounts of drimanes and abundant 13c enriched homologous series of monomethylakanes and iii group c scottish torbanites torbane hill and westfield contain high relative amounts of cyanobacterial hopanoids methylotrophic hopanoids and abundant branched aliphatics but no 13c enriched homologous series of monomethylakanes

does the summer arctic frontal zone influence arctic ocean cyclone activity abstractextratropical cyclone activity over the central arctic ocean reaches its peak in summer previous research has argued for the existence of two external source regions for cyclones contributing to this summer maximum the eurasian continent interior and a narrow band of strong horizontal temperature gradients along the arctic coastline known as the arctic frontal zone afz this study incorporates data from an atmospheric reanalysis and an advanced cyclone detection and tracking algorithm to critically evaluate the relationship between the summer afz and cyclone activity in the central arctic ocean analysis of both individual cyclone tracks and seasonal fields of cyclone characteristics shows that the arctic coast and therefore the afz is not a region of cyclogenesis rather the afz acts as an intensification area for systems forming over eurasia as these systems migrate toward the arctic ocean they experience greater deepening in situations when the afz is strong at midtropospheric levels

explosive cyclone development in the southern hemisphere and a comparison with northern hemisphere events abstract a compilation of southern hemisphere sh explosively developing cyclones or bombs has been assembled based on the national centers for environmental prediction department of energy reanalysis 2 data over the 21 yr period from 1979 to 1999 the identification of these features was undertaken with an objective automated cyclone finding and tracking scheme the procedure allows for the confounding influence of spatial variations of climatological mean pressure on the pressure deepening of explosive cyclones a perspective of particular importance in the sh on average 26 explosive cyclones occur per year in the sh they are more prevalent in winter although their seasonality is more modest than that seen in the northern hemisphere nh the distribution of sh explosive cyclones has a close association with that of strong baroclinicity although the relationship is not one to one it is found that many of these cyclones occurring south of 50 s show equatorward movement in contrast with the pol