tracking holocene glacial and high altitude alpine environments fluctuations from minerogenic and organic markers in proglacial lake sediments lake blanc huez western french alps holocene palaeoenvironmental evolution and glacial fluctuations at high altitude in the western french alps are reconstructed based on a multiproxy approach within lake blanc huez 2550 m a s l drainage basin the combination of seismic profiling 3 5 khz piston coring and radiocarbon dating in proglacial lacustrine sediments together with a detailed organic analysis of autochthonous and allochthonous supply allows documenting the evolution of glacier activity during the holocene over the last 9700 years the holocene lake record has a bimodal pattern whose transition is progressive and occurring between 5400 and 4700 cal bp during the early holocene the organic lacustrine facies reflects reduced glacial activity in the catchment this major glacial retreat seems to result from solar forcing and high summer insolation after 5400 cal bp lacustrine sedimentation is marked by the gradual increase both of minerogenic supply and soil erosion suggesting a progressive transition to wetter climatic conditions this climate change is synchronous both from the gradual decrease of summer insolation and the gradual reorganization of oceanic and atmospheric circulations characterizing the beginning of the neoglacial period both colder temperature and humid climate induced significant glacier advance since 4700 cal bp over this global trend three periods are particularly associated with higher runoff processes and higher soil erosion interpreted as wetter time intervals resulting from enhanced northern westerlies regimes across the north atlantic and western europe they are dated from 8700 to 7000 4700 to 2500 and 1200 to 200 cal bp these wetter phases drastically contrast with periods of reduced glacial activities dated from the early bronze age ca 3870 3770 cal bp the iron age ca 2220 2150 cal bp the roman period ca ad115 330 and the medieval warm period ca ad760 1160 in addition these dryer periods are associated with mining activities at high altitude

a field study of the chemical weathering of ancient sedimentary organic matter weathering profiles developed on organic carbon rich black shales were studied to examine the loss and degradation of organic matter om during weathering and its role in the geochemical carbon cycle analysis of weathered shales reveals between 60 and nearly 100 total organic carbon toc loss in highly weathered samples relative to initial unweathered toc content pyrite loss coincides with or precedes organic carbon loss elemental analysis and flash pyrolysis gas chromatography py gc of kerogen concentrates indicate that there is little or no selective enrichment or depletion of norg containing sorg containing alkylaromatic branched alkyl or long chain n alkyl moieties in most profiles during weathering kerogen o c ratios consistently increase with toc and pyrite loss infrared spectroscopy ir reveals an increase in the relative abundance of c c and c o bonds relative to alkyl c h bonds in progressively weathered samples these results suggest a two component model for kerogen weathering largely non selective oxidation and hydration followed by cleavage dissolution of oxidized kerogen fragments the extent of weathering in a given outcrop is likely limited by a combination of the rate of physical erosion and exposure of the rock to oxidizing surface waters with om type composition playing a lesser role

detection of natural weathering of upper mcalester coal and woodford shale oklahoma u s a abstract natural weathering refers to the natural oxidation of organic and inorganic matter in rocks at the surface and in the shallow subsurface the objective of this study is to apply routine geochemical analyses including organic petrography to coal and shale samples extending from the weathered to unaltered zones to illustrate the effects of weathering on organic matter in coal and shale some significant observations from the upper mcalester coal and the woodford shale are 1 a sulfate index si using sulfur form analysis data that reveals the transformation of pyrite to sulfate minerals is a very sensitive weathering indicator it increased in weathered samples 2 rock eval pyrolysis data such as hydrogen index hi and oxygen index oi are very sensitive to weathering oi hi increased in weathered samples 3 vitrinite reflectance decreased in weathered samples and 4 petrographic signs of weathering include microfractures pitted surface dark reaction rims and high relief sulfate index and petrographic signs of weathering should be used on surface and shallow subsurface rock samples as an indication of the extent of weathering the validity of other analyses can then be evaluated accordingly

comparative mineralogy organic geochemistry and microbial diversity of the autun black shale and graissessac coal france there is growing evidence that microbial populations associated with rocks may be involved in weathering processes in particular they may play a role in the degradation of fossil organic carbon widely present in sedimentary rocks in this study we investigate the microbial diversity associated with two organic rich rocks exhibiting contrasted organic chemical structure a typical type i aliphatic carbon rich kerogen autun shale and a coal rich in aromatic carbon graissessac coal in both rocks the mineralogy and the geochemistry of the organic matter were investigated moreover the microbial diversity associated with these rocks was characterized using bacterial 165 rrna gene analysis in the autun shale one dominant species is observed ralstonia whereas a larger microbial diversity is retrieved from the graissessac coal altogether we conclude that potential hydrocarbonoclastic microorganisms detected by the presence of nag like genes potentially encoding dioxygenase may be associated with a possible biodegradation of fossil organic carbon in the two samples we conclude that under favorable conditions aerobic biodegradation could occur and oxidize a minor fraction of these two different kerogens using a similar enzymatic process c 2014 elsevier b v all rights reserved

using rock eval 6 pyrolysis for tracking fossil organic carbon in modern environments implications for the roles of erosion and weathering this work relates to the debate on the fossil organic carbon foc input in modern environments and its possible implication for the carbon cycle and suggests the use of rock eval 6 pyrolysis as a relevant tool for tracking foc in such environments considering that such a delivery is mainly due to supergene processes affecting the continental surface we studied organic matter in different reservoirs such as bedrocks alterites soils and rivers in two experimental catchments at draix alpes de haute provence france samples were subjected to geochemical rock eval 6 pyrolysis investigations and artificial bacterial degradations after comparing the geochemical fingerprint of samples geochemical markers of foc were defined and tracked in the different reservoirs our results confirm the contribution of foc in modern soils and rivers and display the various influences of weathering and erosional processes on the fate of foc during its exchange between these pools in addition the contrasting behaviour of these markers upon the supergene processes has also highlighted the refractory or labile characters of the fossil organic matter fom bedrock to river fluxes controlled by gully erosion are characterized by a qualitative and quantitative preservation of fom bedrock to alterite fluxes governed by chemical weathering are characterized by foc mineralization without qualitative changes in deeper alterites alterite to soils fluxes controlled by bio chemical weathering are characterized by strong foc mineralization and qualitative changes of fom thus weathering and erosional processes induce different fom evolution and affect the fate of foc towards the global carbon cycle in this study gully erosion would involve maintenance of an ancient sink for the global carbon cycle while bio chemical processes provide a source of co2 finally this study suggests that rock eval 6 pyrolysis can be considered as a relevant tool for tracking foc in modern environments copyright 2006 john wiley sons ltd

tracing sediment sources during floods using diffuse reflectance infrared fourier transform spectrometry drifts a case study in a highly erosive mountainous catchment southern french alps summary in mountainous catchments large quantities of sediment are exported within very short periods leading to numerous environmental problems e g reservoir siltation the origin of suspended sediment during two distinct floods was determined by conducting an original fingerprinting method coupling diffuse reflectance infrared fourier transform spectroscopy drifts and a chemometric technique i e partial least squares pls analysis samples of the potential sediment sources were collected in badland areas developed on various substrates i e molasse marly limestones black marls and gypsum in the galabre 20 km 2 catchment located in the french southern alps drifts spectra provided a way to discriminate between the different potential sediment sources furthermore the use of mid infrared spectra allowed the direct quantification of the gypsum proportion in sediment this contribution was systematically null at the catchment outlet because of the rapid dissolution of gypsum in the river a pls model was then constructed to estimate the contribution of the three other potential sources to the sediment flux during the floods this model was developed and validated using a set of 45 experimental samples that were prepared in the laboratory in order to contain various proportions of the three remaining sources by introducing drifts spectra into the pls model we could predict the proportions of those sources in the mixed experimental samples with a confidence interval of ca 10 the model was then applied to the sediment collected during the two selected floods in order to outline their origin black marls provided the highest contribution of sediment during both events but the analysis also revealed a significant contribution of molasse results also showed the remobilisation of sediment originated from molassic substrates that deposited on the riverbed during a preceding event opportunities for improvement and further use of this method as an alternative or rapid complementary sediment fingerprinting technique are finally discussed

storage and release of fossil organic carbon related to weathering of sedimentary rocks abstract the biogeochemical carbon cycle which plays an undeniable role in global climate change is defined both by the size of carbon reservoirs such as the atmosphere biomass soil and bedrock and the exchange between them of various mineral and organic carbon forms among these carbon forms fossil organic carbon foc i e the ancient organic matter stored in sedimentary rocks is widely observed in modern environments but is not included in the supergene carbon budget using a digitized map of the world and an existing model of co 2 consumption associated with rock weathering we establish the global distribution of foc stored in the first meter of sedimentary rocks and a first estimation of annual foc delivery to the modern environment resulting from chemical weathering of these rocks results are given for the world s 40 major river basins and extended to the entire continental surface with a mean value of 1100 10 9 t mainly controlled by shale distribution the global foc stock is significant and comparable to that of soil organic carbon 1500 10 9 t the annual chemical delivery of foc estimated at 43 10 6 t yr 1 and controlled by the areal distribution of shales and runoff is of the same order of magnitude as the foc output flux to oceans chemical weathering of bedrock within the amazon basin produces one quarter of the total global flux of foc derived from chemical weathering and thus is expected to govern foc release on a global scale these results raise important questions concerning the role of foc in the modern carbon cycle as well as the origin and the budget of carbon in soils and rivers

correction for the siderite effect on rock eval parameters application to the sediments of lake barombi southwest cameroon abstract originally developed for use in the petroleum industry rock eval pyrolysis is a technique commonly applied to lake sediments to infer paleoenvironmental reconstructions the standard rock eval parameters provide information on the amount of total organic and inorganic carbon toc and minc respectively and are usually interpreted as proxies for the source aquatic or terrestrial of the primary production of organic matter hydrogen index vs oxygen index although this method usually provides valuable evidence the common presence of siderite in tropical lake sediments can alter the primary signal of the sedimentary organic matter som indeed the co2 and co released by the pyrolysis of siderite are integral to the calculation of the som related standard rock eval parameters in this study we analyze sediments from a core collected in the lake barombi southwest cameroon and describe the impact of siderite on standard rock eval parameters we propose a workflow that allows standard rock eval parameters to be corrected based on the analysis of thermograms the proposed corrections provide siderite effect free parameters accurately reflecting the changes in sedimentary organic matter composition

the persistence of memory the fate of ancient sedimentary organic carbon in a modern sedimentary system the cycle of organic carbon burial and exhumation moderates atmospheric chemistry and global climate over geologic timescales the burial of organic carbon occurs predominantly at sea in association with clay sized particles derived from the erosion of uplifted continental rocks it follows that the history of the fine grained particles on land may bear on the nature of the organic carbon buried in this study the evolution of clay associated organic matter was followed from bedrock source to the seabed in the eel river sedimentary system of northern california using natural abundance 13c and 14c tracers approximately half of the fine grained organic carbon delivered to the shelf is derived from ancient sedimentary organic carbon found in the uplifted mesozoic tertiary franciscan complex of the watershed the short residence time of friable soils on steep hill slopes coupled with rapid sediment accumulation rates on the shelf slope act to preserve the ancient organic carbon a comparable quantity of modern organic carbon is added to particles in the watershed and on the shelf and slope the bimodal mixture of ancient and modern c in soils and sediments may be characteristic of many short mountainous rivers if the eel river chemistry is typical of such rivers more than 40 tg of ancient organic c may be delivered to the world s oceans each year a flux of that magnitude would have a significant influence on marine and global c cycles

guidelines for rock eval analysis of recent marine sediments rock eval pyrolysis a widely used petroleum screening technique developed primarily for ancient sedimentary rocks and kerogens has now been increasingly applied to the characterization of recent lacustrine or marine sediments however as illustrated by previous results from various authors and by the analysis of recent sediments from various areas the thermally labile character of recent organic matter om the presence of poorly crystallized mineral e g carbonate and the eventual presence of salts nacl sulfate might perturb the detection of the pyrolysis effluent the aim here was to outline the problems generated by such perturbation and to demonstrate that specific operating conditions needed for proper analysis o frecent marine sediments a modified rock eval pyrolysis program starting at lower temperature 180 c with a heating rate of 30 c min is proposed as a standard mode for the analysis of recent om in order to avoid misleading interpretation of rock eval data and make possible the inter comparison of results whatever the rock eval device used

source to sink sedimentary systems and global carbon burial a river runs through it abstract source to sink sedimentary systems are important settings of carbon cycling serving as sites of carbon transfer between terrestrial and marine reservoirs and as the primary locations for organic carbon burial on earth the age and character of the carbon that is buried at the terminal ends of these systems reflects the sources and transformations of the organic carbon oc throughout their linked terrestrial and marine segments profound differences are observed between large passive and small active margin systems large passive margin systems are characterized by large floodplains and relatively broad shelves where oc has protracted exposure to oxidants rapid burial in prograding subaqueous deltaic clinoforms or bypass to submarine fans however leads to high burial efficiency of terrestrial biospheric oc in some passive margin settings the oc in small active margin systems in contrast follows relatively short pathways from headwaters to seabed this rapid transit facilitated by the important role of storm driven transport in such settings can lead to high oc burial efficiencies the study of oc sources and transformations in contemporaneous source to sink sedimentary systems informs interpretations about the systems in which oc was buried in the geologic past their stratigraphic records of environmental change and their potential to produce petroleum resources

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

sensitivity of a greenland ice sheet model to ice flow and ablation parameters consequences for the evolution through the last climatic cycle sensitivity experiments are conducted to test the influence of poorly known model parameters on the simulation of the greenland ice sheet by means of a three dimensional numerical model including the mechanical and thermal processes within the ice two types of experiments are performed steady state climatic conditions and simulations over the last climatic cycle with a climatic forcing derived from the grip record the experiments show that the maximum altitude of the ice sheet depends on the ice flow parameters deformation and sliding law coefficients geothermal flux and that it is low when the ice flow is fast on the other hand the maximum altitude is not sensitive to the ablation strength and consequently during the climatic cycle it is driven by changes in accumulation rate the ice sheet extension shows the opposite sensitivity it is barely affected by ice flow velocity and the ice covered area is smaller for large ablation coefficients for colder climates when there is no ablation the ice sheet extension depends on the sea level an interesting result is that the variations with time of the altitude at the ice divide summit do not depend on the parameters we tested the present modelled ice sheets resulting from the climatic cycle experiments are compared with the present measured ice sheet in order to find the set of parameters that gives the best fit between modelled and measured geometry it seems that compared to the parameter set most commonly used higher ablation rate coefficents must be used

variations in sediment yield from the upper doubs river carbonate watershed jura france since the late glacial period abstract the upper doubs river valley is a 910 km2watershed feeding into lake chaillexon the lake was formed by a natural rockfall at the end of the bolling chronozone around 14 250 cal yr b p and since then has trapped material eroded from the watershed the filling process and variations in sediment yield have been investigated by mechanical coring seismic surveys and electric soundings the detrital sediment yield of the upstream watershed can be calculated by quantifying the sedimentary stocks for each climatic stage of the late glacial period and holocene epoch and estimating the lake s entrapment capacity this enables us to determine the intensity of the erosion processes in relation to climate and environmental factors the bolling allerod interstade produced the greatest yields with mean values of 19 500 metric tons per calendar year t yr the younger dryas chronozone saw a sharp fall 8900 t yr that continued into the preboreal 2100 t yr clastic supply increased during the boreal 4500 t yr before declining again in the early atlantic 2400 t yr since then yields have risen from 4500 t yr in the late atlantic to 6800 t yr in the subboreal and 11 100 t yr in the subatlantic comparison of quantitative data with the qualitative analysis of the deposits and with the paleohydrologic curve of the watershed based on level fluctuations in lakes around chaillexon shows that climate was the controlling factor of sediment yield until the late atlantic from the late atlantic subboreal around 5400 cal yr b p 470014c yr b p and especially from the end of the subboreal chronozone and during the subatlantic chronozone 2770 cal yr b p 270014c yr b p present climatic constraints have been compounded by human activity related to forest clearing and land use

quantification of loss of calcite pyrite and organic matter due to weathering of toarcian black shales and effects on kerogen and bitumen characteristics abstract comparison of geochemical data on posidonia shale early toarcian from a shallow unweathered core and from adjacent weathered exposures of the same fades was performed results revealed that quantitatively the most affected petrographic constituent is pyrite and that organic matter and carbonate were also altered by weathering due to this process of weathering the bulk composition of organic matter especially the molecular composition of soluble organic matter and the fluorescence colour of organic particles are changed estimates of weathering rates reveal that the annual release of sulphur and organic carbon from black shales may significantly add to anthropogenic pollution

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

quantitative palynofacies analysis as a new tool to study transfers of fossil organic matter in recent terrestrial environments classical palynofacies method which consists in an organic concentrate microscopic qualitative observation after mineral phase dissolution is commonly used in order to study sedimentary organic matter in the present study we develop a new quantitative palynofacies method that allows organic particles mass concentrations to be determined in studied samples this method was developed to help quantify the input of fossil organic matter fom into modern environments as a result of sedimentary rocks weathering studied samples were collected from different pools like bedrocks weathering profiles soils and riverine particles in an experimental watershed le laval this watershed overlying callovo oxfordian marls 1 km in area is located near digne alpes de haute provence in france in addition to palynofacies techniques rock eval 6 pyrolysis and al2o3 content measurements inductively coupled plasma emission spectrometry were carried out on the samples obtained results show that this quantitative palynofacies method is suitable for fom studies in modern environments and fom particles are quantified in the different pools results also give evidence that fom alteration depends on the type of weathering but also on the kind of organic particles soil formation under vegetation resulting from the bio chemical weathering lead to fossil organic particles concentration losses that do not exceed 30 elsewhere mechanical weathering appears extremely fast and has no qualitative or quantitative influence on the observed fom particles which feeds directly into riverine stocks fom appears to be very resistant to weathering processes this highlights its occurrence into supergene pools and then into carbon cycle quantitative palynofacies analysis is a new method adapted to a such study but can also be applied to other palynological paleoenvironmental or archeological studies

annual fossil organic carbon delivery due to mechanical and chemical weathering of marly badlands areas a key issue in the study of the carbon cycle is constraining the stocks and fluxes in and between c reservoirs among these the role and importance of fossil organic carbon foc release by weathering of outcropping sedimentary rocks on continental surfaces is still debated and remains poorly constrained our work focuses on foc fluxes due to chemical and mechanical weathering of marls in two experimental watersheds with typical badlands geomorphology draix watersheds laval and moulin alpes de haute provence france organic matter from bedrock soil litter and riverine particles are characterized by rock eval 6 pyrolysis foc fluxes due to mechanical weathering are then estimated by monitoring the annual particulate solid exports at the outlets of the watersheds 1985 2005 period foc fluxes from chemical weathering were calculated using ca2 concentrations in dissolved loads year 2002 to assess the amount of foc released by the dissolution of the carbonate matrix results show that foc delivery is mainly driven by mechanical weathering with a yield ranging from 30 to 59 t km 2 yr 1 in the moulin 0 08 km2 and laval 0 86 km2 catchments respectively 1985 2005 average the release of foc attributed to chemical weathering was 2 2 to 4 2 t km 2 for the year 2002 these high foc fluxes from badlands are similar to those observed in tectonically active mountain catchments at a regional scale badland outcropping within the durance watershed does not exceed 0 25 in area of the rhone catchment but could annually deliver 12 000 t yr 1 of foc this flux could correspond to 27 of the total particulate organic carbon poc load exported by the rhone river to the mediterranean sea at a global scale our findings suggest that erosion of badlands may contribute significantly to the transfer of foc from continental surfaces to depositional environments copyright 2012 john wiley sons ltd

coupled rock eval pyrolysis and spectrophotometry for lacustrine sedimentary dynamics application for west central african rainforests kamalete and nguene lakes gabon in recent years nguene lake and kamalete lake gabon west central africa have been studied repeatedly providing comprehensive reconstructions of environmental changes over the last millennia both lakes are in different geomorphological and environmental settings they are therefore excellent sites to test new methodological approaches indeed the sedimentary cores provide various facies and the previous studies provide references for calibrating the results of new methods in this methodological issue the present study aims to evaluate the potential of spectrophotometric and rock eval coupled analysis to describe the holocene lake and marsh deposits from tropical moist forests this assessment is carried out on samples taken from two well documented reference cores the spectrophotometric analysis provides reproducible colour measurements which inform about the nature of the main colour bearing constituents coupled with rock eval pyrolysis this technique can be used to describe lithological changes and identify the probable source of sedimentary organic matter in the studied cases this approach identified the facies dominated by detrital terrigenous inputs iron bearing signature and high oi values and those associated with a more abundant primary production chlorophyll signature low oi and high hi providing a distinction between palustrine and lacustrine dynamics however although the facies are comparable sedimentary dynamics and sediment sources may vary depending on geomorphological and climatic contexts

occurrence of fossil organic matter in modern environments optical geochemical and isotopic evidence abstract this study relates to the input and fate of fossil organic matter fom in the modern environment and focuses on two experimental watersheds overlying jurassic marls le laval and le brusquet 1 km2 in area located near digne alpes de haute provence france considering that fom delivery is mainly a result of different processes affecting sedimentary rocks bio chemical and mechanical weathering samples from different pools were collected bedrocks weathering profiles soils and riverine particles the samples were examined using complementary techniques optical palynofacies methods geochemical rock eval 6 pyrolysis c n ratio molecular gas chromatography mass spectrometry and isotopic stable c isotopic composition as a result fom markers were identified and tracked through the different pools the results highlight the contribution of fom which can be found in all the studied pools transfer of fom between bedrocks weathering profiles governed mainly by chemical weathering and bedrocks riverine particles governed mainly by mechanical weathering reveals any qualitative change weathering profiles soils transition governed by bio chemical weathering is characterized by alteration of the fom which is difficult to describe because fossil material is mixed with recent organic matter rom despite this latter point the study provides evidence for a relative resistance of fom to weathering processes and points to its contribution to the modern geosystem and the c cycle

gcm simulations of the last glacial maximum surface climate of greenland and antarctica the lmdz variable grid gcm was used to simulate the last glacial maximum lgm 21 ky bp climate of greenland and antarctica at a spatial resolution of about 100 km the high spatial resolution allows to investigate the spatial variability of surface climate change signals and thus to address the question whether the sparse ice core data can be viewed as representative for the regional scale climate change this study addresses primarily surface climate parameters because these can be checked against the limited ice core record the changes are generally stronger for greenland than for antarctica as the imposed changes of the forcing boundary conditions e g sea surface temperatures are more important in the vicinity of greenland over greenland and to a limited extent also in antarctica the climate shows stronger changes in winter than in summer the model suggests that the linear relationship between the surface temperature and inversion strength is modified during the lgm the temperature dependency of the moisture holding capacity of the atmosphere alone cannot explain the strong reduction in snowfall over central greenland atmospheric circulation changes also play a crucial role changes in the high frequency variability of snowfall atmospheric pressure and temperature are investigated and possible consequences for the interpretation of ice core records are discussed using an objective cyclone tracking scheme the importance of changes of the atmospheric dynamics off the coasts of the ice sheets especially for the high frequency variability of surface climate parameters is illustrated the importance of the choice of the lgm ice sheet topography is illustrated for greenland where two different topographies have been used yielding results that differ quite strongly in certain nontrivial respects this means that the paleo topography is a significant source of uncertainty for the modelled paleoclimate the sensitivity of the greenland lgm climate to the prescribed sea surface conditions is examined by using two different lgm north atlantic data sets

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

iron species determination to investigate early diagenetic reactivity in marine sediments iron speciation was determined in hemiplegic sediments from a high productivity area to investigate systematically the early diagenetic reactivity of fe a combination of various leaching agents 1 m hci dithionite buffered in citrate acetic acid hf h2so4 acetic cr ii was applied to sediment and extracted more than 80 of total fe subsequent fe species determination defined specific mineral fractions that are available for fe reduction and fractions formed as products of fe diagenesis to determine the fe speciation of sheet silicates we explored an extraction procedure hf h2so4 and verified the procedure by application to standard rocks variations of fe speciation of sheet silicates reflect the possible formation of fe bearing silicates in near surface sediments the same fraction indicates a change in the primary input at greater depth which is supported by other parameters the fe ii fe iii ratio of total sediment determined by extractions was compared with mossbauer spectroscopy at room temperature and showed agreement within 10 m6ssbauer spectroscopy indicates the occurrence of siderite in the presence of free sulfide and pyrite supporting the importance of microenvironments during mineral formation the occurrence of other fe ii bearing minerals such as ankerite ca fe mg carbonate can be presumed but remains speculative

long term holocene groundwater fluctuations in a chalk catchment evidence from rock eval pyrolysis of riparian peats he depositional history of peat dominated wetlands can be used to understand palaeoclimate and palaeohydrology and also constrain the impacts of future climate change however in chalkland valleys seasonal water table fluctuations and a high alkalinity have diminished key environment indicators such as pollen and there is a need for alternative investigative techniques the method of rock eval pyrolysis can track changes in organic matter source and degradation potentially relating to historic changes in vegetation cover this is the first rock eval on cores from a groundwater dependent riparian chalk valley wetland combined with radiocarbon dating the dating showed that the cores represented approximately 4000 years of depositional history changes in hydrocarbon chemistry including normal alkane composition of the peat indicated shifts of around 500 to 1000 years between terrestrial and more aquatic species relating to periods of climate wetness these climatic shifts are broadly consistent with other evidence from ombrotrophic peatland and lacustrine sediments across northwest europe however the connection between climate wetness and groundwater dependent chalkland wetlands is complicated by external anthropogenically driven factors relating to land use and vegetation cover changes in the catchment nonetheless this study suggests that rock eval pyrolysis is a useful and cost effective tool that can provide evidence for long term holocene groundwater fluctuations

comment on u pb baddeleyite ages and geochemistry of dolerite dykes in the bas drâa inlier of the anti atlas of morocco newly identified 1380 ma event in the west african craton by el bahat et al two important papers have been recently published in lithos by the same group of authors both dealing with the pre palaeozoic basic dykes that cut across the basement of the anti atlas mountain belt kouyate et al 2013 consider the precambrian inliers of the central part of the belt namely the zenaga iguerda and ait melloul inliers whereas el bahat et al 2013 consider the bas draa inlier in the south westernmost part fig 1 these papers report u pb baddeleyite and scarce zircon dating on samples from the numerous basic dykes crosscutting the palaeoproterozoic basement of the central and western anti atlas our comment concerns more particularly el bahat et al s 2013 paper surprisingly the ages obtained from the bas draa samples are markedly distinct from those of the zenaga iguerda and ait melloul inliers in the latter group kouyate et al 2013 obtain one date at 2040 2 three other dates around 1655 ma 1656 9 ca 1655 and 1654 16 ma and finally two dates at ca 885 ma in contrast el bahat et al 2013 obtain two dates of 1380 9 and 1384 6 ma in the bas draa inlier although using the same u pb tims method on structurally and geochemically equivalent material we will discuss the possible origin of this puzzling contrast a discussion which is overlooked in el bahat et al 2013 study it is possible that the ca 1380 ma old dykes did not intrude the central anti atlas inliers or were not sampled by kouyate et al 2013 or conversely that none of the 2040 1655 and 885 ma old

a new present day temperature parameterization for greenland near surface air temperature 2 m over the greenland ice sheet gris is parameterized using data from automatic weather stations located on land and on the ice sheet the parameterization is expressed in terms of mean annual temperatures and mean july temperatures both depending linearly on altitude latitude and longitude the temperature parameterization is compared to a previous study and is shown to be in better agreement with observations the temperature parameterization is tested in a positive degree day model to simulate the present 1996 2006 mean melt area extent of the gris the model accounts for firn warming rainfall and refreezing of meltwater with different degree day factors for ice and snow under warm and cold climate conditions the simulated melt area extent is found to have reasonable agreement with satellite derived observations

weathering rinds archives of paleoenvironments on mount kenya east africa abstractweathering rind thicknesses on pebble and cobble size sediment have been used for the past half century at least as an age indicator of postdepositional time following a geologic event in mountainous terrain rind thickness is taken as a measurement of weathering over time frames of 0 5 m yr variable thicknesses are used to discriminate relative ages of glacial deposits the effects of chemical and physical weathering that together produce rinds are only rarely considered and most research objectives have centered on lichen alteration of clast surfaces recent microscopic analyses of weathering rinds on volcanic clasts of 70 0 ka to 2 0 m yr age produced new data on weathering products as well as unexpected incorporated biotic materials undergoing diagenesis the question as to how much physical mineral chemical biotic paleoenvironmental data might be archived in rinds is discussed the character and classification of organic materials undergoing diagenesis are also discussed

influence of inherited paleotopography and water level rise on the sedimentary infill of lake ossa s cameroon inferred by continuous color and bulk organic matter analyses lacustrine records hold considerable archives providing access to valuable information however to decode this information it is necessary to know how the lake in question and its catchment area function in this study we propose to highlight the different factors that govern sedimentation by studying different core samples covering the holocene taken from lake ossa cameroon to do this we chose to use organic matter as a tracer of changes in sedimentation by coupling two complementary methods spectrophotometry for color measurement and rock eval pyrolysis for bulk geochemical analysis spectrophotometry is used classically to quantify color and obtain data very rapidly at very high resolution and non destructively rock eval data give geochemical indication on organic matter composition thus it was possible to highlight different types of organic matter at different stages of transformation including different sources that can be responsible of this transformation distal proximal autochtonous the synthesis of this information led to the formulation of a scenario of how lake ossa was filled although this lake had already been used for paleoclimatic environmental purposes we show here that most of the forcing responsible for the sedimentation in the lake was due to the paleotopography and the rise in the lake level during the holocene

worldwide distribution of continental rock lithology implications for the atmospheric soil co2 uptake by continental weathering and alkalinity river transport to the oceans 1 the silicate rock weathering followed by the formation of carbonate rocks in the ocean transfers co2 from the atmosphere to the lithosphere this co2 uptake plays a major role in the regulation of atmospheric co2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks this leads us to develop the first world lithological map with a grid resolution of 1 1 this paper analyzes the spatial distribution of the six main rock types by latitude continents and ocean drainage basins and for 49 large river basins coupling our digital map with the gem co2 model we have also calculated the amount of atmospheric soil co2 consumed by rock weathering and alkalinity river transport to the ocean among all silicate rocks shales and basalts appear to have a significant influence on the amount of co2 uptake by chemical weathering

palynofacies as useful tool to study origins and transfers of particulate organic matter in recent terrestrial environments synopsis and prospects palynofacies analysis is based on transmitted light microscope study of organic constituents isolated and concentrated by acid and basic digestions published results of studies of present day terrestrial environments show that two complementary approaches successfully characterize particulate organic matter om from palynofacies analyses the first method is based on the identification and the quantification of some typical particles optical markers according to their origin i e aquatic or terrestrial their nature i e biogenic anthropogenic fossil and or their formation i e biodegradation combustion oxidation the second approach is based on the use of binary or ternary diagrams in order to define petrographical signatures from the relative proportions of significant organic constituents this approach can be used for tracking i changes in om composition during humification in soil profiles ii transport of reworked terrestrial particles iii diagenesis of peaty deposits or iv weathering of geological substratum the more advanced approach is based on the use of some predefined optical markers and their optical signatures to establish the relation between the om compositions palynofacies and their depositional environments in addition this kind of study aims to define a modern frame of reference that can be applied in paleoenvironmental reconstructions this paper combines a bibliographic review with previously unpublished data from palynofacies analyses the aim is to present some applied examples illustrating 1 the main approaches developed for characterization of the particulate om in surficial deposits and 2 the study of om transfers in terrestrial geosystems

carbon sinks in small sahelian lakes as an unexpected effect of land use changes since the 1960s saga gorou and dallol bosso sw niger for several decades global change has resulted in an increase in runoff in the sahelian belt provoking major changes in the quality and quantity of sediments transported by drainage networks one of the astonishing consequences is the establishment of numerous permanent lakes the origins of particulate organic matter om preserved within lacustrine sediments of three lakes were investigated by coupling optical observations palynofacies and bulk geochemistry rock eval 6 pyrolysis an initial estimate of particulate organic carbon oc stored in these lacustrine sediments was assessed soil organic matter som was sampled from the surface 0 10 cm of various land use and land cover areas and was characterized and compared with sedimentary organic matter our results reveal that lake tankalawal is subjected to high autochthonous organic sedimentation toc ranges between 3 0 and 10 0 wt while lakes bangou kirey and bi are characterized by weak sedimentation of non indigenous om originating from the soil erosion and shore vegetation toc 3 0 wt in sediments the effects of early diagenesis on the om induce not only a loss of labile and aquatic om but also a significant loss of terrestrial om which is supposed to be more resistant than its aquatic counterpart both the preservation of om in top sediments and the relative preservation of terrestrial om impact the oc storage in lakes indeed oc storage in lacustrine sediments lake bangou kirey was two to seven times higher than the oc storage in sahelian soils where greater contributions of terrestrial om to sedimentary om are associated with lower oc storage in lacustrine sediments for lakes bangou kirey and bi oc accumulation rates were also assessed due to the identification of a sedimentary limit corresponding to the establishment of permanent lakes dated earlier 1960s high oc fluxes were estimated and ranged between 104 and 213 g oc m 2 yr 1 compared with other oc accumulation rates for various african lakes these high values are similar to those calculated for reservoirs and are related to anthropogenic pressure soil textures favoring erosion and proper physical and chemical conditions for om preservation in sediments accordingly in these sahelian environments that are generally viewed as non efficient in storing oc we claim that global change could promote a new oc sink if other similar studies reinforce our assertion then regional c budgets should be revisited

postglacial paleoceanography of hudson bay stratigraphic microfaunal and palynological evidence cores containing representative sequences of postglacial sediments in northern and southern hudson bay were analyzed for their microfaunal foraminifers and ostracods and palynological dinocysts

assessment of current methods of positive degree day calculation using in situ observations from glaciated regions the continued use of the positive degree day pdd method to predict ice sheet melt is generally favoured over surface energy balance methods partly due to the computational efficiency of the algorithm and the requirement of only one input variable temperature in this paper we revisit some of the assumptions governing the application of the pdd method using hourly temperature data from the gc net network we test the assumption that monthly pdd total pddm can be represented by a gaussian distribution with fixed standard deviation of monthly temperature m the results presented here show that the common assumption of fixed m does not hold and that m may be represented more accurately as a quadratic function of average monthly temperature for greenland the mean absolute error in predicting pddm using our methodology is 3 9 c day representing a significant improvement on current methods 7 8 c day when m 4 5 c over a range of glaciated settings our method reproduces pddm on average to within 1 5 8 5 c day compared to 4 4 15 7 c day when m 4 5 the improvement arises because we capture the systematic reduction in temperature variance that is observed over melting snow and ice when surface temperatures cannot warm above o c