palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

temporal variations of accumulation and temperature during the past two centuries from belukha ice core siberian altai 1 the temporal variation of accumulation and temperature in the siberian altai were investigated using a 86 m long ice core from belukha glacier 49 48 26 n 86 34 43 e 4062 m a s l covering the time period 1816 to 2001 as temperature sensitive parameters the melt percent profiles and the stable oxygen isotopes 18o were evaluated representing summer season and march to november temperatures respectively the accumulation record showed no long term trend and only minor deviations of limited duration from the accumulation average of 0 5 m water equivalent y weq y were observed in contrast the two temperature proxies indicate a strong warming trend in the order of 1 6 0 4 c and 1 7 1 1 c over the last century inferred from melt percentages and the 18o record respectively and 2 5 1 7 c since the mid 19th century inferred from the 18o record this reflects an amplified regional climate response following the little ice age lia as compared to the northern hemisphere average most probably caused by the strong continentality of the siberian altai region the sudden onset of large melt features since 1988 indicates that the upper reaches of belukha glacier are experiencing a change from the recrystallization to the cold infiltration zone that now allows for multiannual percolation of meltwater implying that the conservation of accumulation and geochemical properties including those providing temperature proxies is currently endangered

particulate organic matter in surface sediments of the laptev sea arctic ocean application of maceral analysis as organic carbon source indicator abstract surface sediments from the laptev sea and adjacent continental slope were studied for their composition of particulate organic matter om by means of maceral analysis the composition of macerals in sediments gives information about the environment terrigenous supply from the hinterland and marine om with reference to their biological sources we distinguish between terrigenous and marine macerals we found that the particulate om in the surface sediments of the laptev sea is predominantly of terrigenous origin o 78 however distinct variations exist when looking in detail in the shelf area sediments may contain up to 99 terrigenous om freshwater algae occur directly north of the river mouths reflecting the strong fluvial influence relatively high amounts of marine om 20 40 are restricted to the upper continental slope the vilkitsky strait and west of the new siberian islands explained by increased surface water productivity due to increased fluvial nutrient supply open water conditions and phytoplankton blooms at the ice edge

stable isotope time series and precipitation origin from firn core and snow samples altai glaciers siberia in the summers of 2001 and 2002 glacio climatological research was performed at 4110 4120ma s l on the belukha snow firn plateau siberian altai hundreds of samples from snow pits and a 21m snow firn core were collected to establish the annual seasonal monthly depth accumulation scale based on stable isotope records stratigraphic analyses and meteorological and synoptic data the fluctuations of water stable isotope records show well preserved seasonal variations the d 18 o and dd relationships in precipitation snow pits and the snow firn core have the same slope to the covariance as that of the global meteoric water line the origins of precipitation nourishing the belukha plateau were determined based on clustering analysis of d 18 o and d excess records and examination of synoptic atmospheric patterns calibration and validation of the developed clusters occurred at event and monthly timescales with about 15 uncertainty two distinct moisture sources were shown oceanic sources with d excess 12 two thirds of the annual accumulation was from oceanic precipitation of which more than half had isotopic ratios corresponding to moisture evaporated over the atlantic ocean precipitation from the arctic pacific ocean had the lowest deuterium excess contributing one tenth to annual accumulation

arctic palaeo river discharge and environmental change evidence from the holocene kara sea sedimentary record abstract in this paper we summarize data on terrigenous sediment supply in the kara sea and its accumulation and spatial and temporal variability during holocene times sedimentological organic geochemical and micropaleontological proxies determined in surface sediments allow to characterize the modern riverine terrigenous sediment input ams 14c dated sediment cores from the ob and yenisei estuaries and the adjacent inner kara sea were investigated to determine the terrigenous sediment fluxes and their relationship to paleoenvironmental changes the variability of sediment fluxes during holocene times is related to the post glacial sea level rise and changes in river discharge and coastal erosion input whereas during the late middle holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries huge amounts of sediments accumulated on the kara sea shelf farther north during the early holocene before about 9 cal kyr bp the maximum accumulation at that time is related to the lowered sea level increased coastal erosion and increased river discharge based on sediment thickness charts echograph profiles and sediment core data we estimate an average holocene 0 11 cal kyr bp annual accumulation of 194 106 t yr 1 of total sediment for the whole kara sea based on late holocene modern sediment accumulation in the estuaries probably 12 106 t yr 1 of riverine suspended matter i e about 30 of the input may escape the marginal filter on a geological time scale and is transported onto the open kara sea shelf the high resolution magnetic susceptibility record of a yenisei core suggests a short term variability in siberian climate and river discharge on a frequency of 300 700 yr this variability may reflect natural cyclic climate variations to be seen in context with the interannual and interdecadal environmental changes recorded in the high northern latitudes over the last decades such as the nao ao pattern a major decrease in ms values starting near 2 5 cal kyr bp being more pronounced during the last about 2 cal kyr bp correlates with a cooling trend over greenland as indicated in the gisp 2 ice core extended sea ice cover in the north atlantic and advances of glaciers in western norway our still preliminary interpretation of the ms variability has to be proven by further ms records from additional cores as well as other high resolution multi proxy arctic climate records

a geochemical investigation of carboxylic acids released via sequential treatments of two surficial sediments from the changjiang delta and east china sea two surface sediments from the delta of the changjiang river the fourth largest river in the world in terms of water discharge and the seventh in terms of sediment discharge and an adjacent area of the east china sea were subjected to sequential treatments in order to obtain complete quantitative and qualitative information on carboxylic acid moieties five successive treatments allowed for the release of all acid moieties occurring in each sample i the unbound acids isolated from extracts ii the oh labile acids released by classical saponification iii the oh ptc labile acids obtained via an additional saponification with a phase transfer catalyst iv the h labile acids released by a subsequent acid hydrolysis and v the tightly bound acids only released by thermolysis these five fractions correspond to distinct pools whose occurrence reflects diaerences in the mode of linkage of the acid moieties and or in the protection provided by the structures to which they are linked such analysis of acid moieties provided information on i the relative contributions from microalgae bacteria and higher plants in the delta and seaward stations ii the degree of early diagenetic alteration for the acids derived from these diaerent sources and iii the types of microalgal and bacterial species implicated these features were also compared with the results of the only previous study where the sequential treatments were applied on surficial sediments from a sharply diaerent environment the lena river delta arctic 2000 elsevier science ltd all rights reserved

depositional environment of sedimentary rocks inferred from normal fatty acid compositions normal saturated fatty acid n fatty acid in marine sediments from coastal and pelagic environments were analyzed the coastal sediments contain both short chained n fatty acids with carbon numbers from 12 to 18 and long chained acids from 22 to 32 whereas the pelagic sediments contain predominantly short chained acids the relative abundance of short chained to long chained n fatty acids expressed by the molar ratio c 16 c26 can be an indicator to assess the depositional environment of sedimentary rocks the ratio of long chained n fatty acids c22 c32 to the total n fatty acids also has the potential to discriminate sedimentary environments the indicators based on the n fatty acids were applied to the franciscan bedded cherts the result shows that the bedded cherts had deposited in continuous environments from the pelagic to the coastal this is in harmony with the same inference based on major trace and rare earth elements and normal paraffins 1999 elsevier science b v all rights reserved

abrupt and moderate climate changes in the mid latitudes of asia during the holocene a multiple parameter dating technique was used to establish a depth age scale for a 171 3 m 145 87 m w e surface to bedrock ice core bl2003 recovered from the cold recrystallization accumulation zone of the western belukha plateau 4115 m a s l in the siberian altai mountains the ice core record presented visible layering of annual accumulation and of delta o 18 delta d stable isotopes and a clear tritium reference horizon a steady state glacier flow model for layer thinning was calibrated and applied to establish a depth age scale four radiocarbon c 14 measurements of particulate organic carbon contained in ice core samples revealed dates for the bottom part of bl2003 from 9075 1221 cal a bc at 145 2 0 1 m w e 0 665 m w e from the bedrock to 790 93 ad at 121 1 m w e depth sulfate peaks coincident with volcanic eruptions the tunguska meteorite event and the 1842 dust storm were used to verify dating analysis of the bl2003 ice core reveals that the modern altai glaciers were formed during the younger dryas yd similar to 10 950 to similar to 7500 cal a bc and that they survived the holocene climate optimum hco similar to 6500 to similar to 3600 cal a bc and the medieval warm period mwp similar to 640 to similar to 1100 ad a decrease in air temperature at the beginning and an abrupt increase at the end of the yd were identified intensification of winds and dust loading related to asian desert expansion also characterized the yd during the yd major ion concentrations increased significantly up to 50 times for na background up to 45 times for ca2 and mg2 and up to 20 times for so42 relative to the recent warm period from 1993 to 2003 a warm period lasted for about three centuries following the yd signaling onset of the hco a significant and prolonged decrease in air temperature from similar to 2000 to similar to 600 cal a bc was associated with a severe centennial drought scd a sharp increase in air temperatures after the scd was coincident with the mwp after the mwp a cooling was followed gradually with further onset of the little ice age during the modern warm period 1973 2003 an increase in air temperature is noted which nearly reaches the average of hco and mwp air temperature values

biomarker proxy shows potential for studying the entire quaternary arctic sea ice history recently a novel and promising biomarker proxy for reconstruction of arctic sea ice conditions was developed and is based on the determination of a highly branched isoprenoid with 25 carbons ip25 so far ip25 records have been restricted to the last 150 kyr bp here we present a biomarker record from ocean drilling program odp site 912 going back to the pliocene pleistocene boundary and indicating that sea ice of variable extent occurred in the fram strait southern yermak plateau area at least since about 2 2 ma furthermore our data support the idea that a combination of ip25 and open water phytoplankton biomarker data pip25 index may give more reliable and quantitative estimates of past sea ice cover at least for the study area this study reveals that the novel ip25 pip25 biomarker approach has potential for semi quantitative paleo sea ice studies covering the entire quaternary and motivate to carry out further detailed high resolution research on odp iodp material using this proxy

coupling primary production and terrestrial runoff to ocean acidification and carbonate mineral suppression in the eastern bering sea water column ph and carbonate mineral saturation states were calculated from dissolved inorganic carbon dic and total alkalinity data collected over the eastern bering sea shelf in the spring and summer of 2008 the saturation states of the two most important carbonate minerals calcite calcite and aragonite aragonite were strongly coupled to terrestrial runoff from the yukon and kuskokwim rivers primary production in the surface waters and remineralization of organic matter at depth over the shelf in spring before ice melt occurred ph over the shelf was largely confined to a range of 7 9 8 1 and calcite and aragonite ranged from 1 5 to 3 0 and 0 8 to 2 0 respectively at the stations closest to river outflows aragonite was undersaturated in the water column from the surface to the bottom during the summer sea ice retreat high rates of primary production consumed dic in the mixed layer which increased ph and calcite and aragonite however calcite and aragonite decreased by 0 3 in the bottom waters over the middle and outer shelf over the northern shelf where export production is highest aragonite decreased by 0 35 and became highly undersaturated the observed suppression and undersaturation of calcite and aragonite in the eastern bering sea are correlated with anthropogenic carbon dioxide uptake into the ocean and will likely be exacerbated under business as usual emission scenarios therefore ocean acidification could threaten some benthic and pelagic calcifying organisms across the bering sea shelf in the coming decades

the disappearance of glaciers in the tien shan mountains in central asia at the end of pleistocene glaciers in central asia are among the largest ice masses in the eurasian continent and have supplied vital water to local inhabitants for thousands of years the glaciers in this region are generally believed to be remnants of the last deglaciation however glacier variability in the central asian mountains since the last glacial maximum lgm has not been well documented here we report an 86 87 m deep ice core record drilled on an ice cap in the tien shan mountains of central asia radiocarbon dating of organic soil from the bottom of the ice core borehole showed that the age of the soil was 12 656 e 12 434 cal years before present coincident with the beginning of the younger dryas cold period yd this result indicates that the ice cap did not exist in the bolling allerod period ba which was the warm period before the yd and that the ba climate was significantly warmer than at present it also indicates that the ice cap has never entirely disappeared in any warm periods throughout the holocene we estimated that during the ba its extent was 43 or less of the present glacier coverage in the mountains our results suggest that this region at the end of pleistocene was considerably warmer than at present and that most of the present glaciers in this region are not relics of the last glacial period but are composed of ice formed during the yd and holocene 2014 the authors published by elsevier ltd this is an open access article under the cc by nc nd license http creativecommons org licenses by nc nd 3 0

climatic dependence of the organic matter contributions in the north eastern norwegian sea over the last 15 000 years abstract lipids are used for the evaluation of the different organic matter contributions in the north eastern norwegian sea m23258 site 75 n 14 e over the last 15 000 years development of a mass balance model based on the down core quantification of the c 37 alkenones the odd carbon numbered n alkanes a odd and the unresolved complex mixture of hydrocarbons ucm has allowed three main organic matter inputs involving marine continental and ancient reworked organic matter to be recognized the model shows good agreement between measured and reconstructed toc values similarly a strong parallelism is observed between predicted components such as marine toc and carbonate content which was determined independently representation of the model results within a time scale based on 15 ams 14 c measurements shows that the main changes in organic matter constituents are coincident with the major climatic events of the last 15 000 years thus the predominance of reworked organic matter is characteristic of termination ia up to 70 continental organic matter was dominant during the bolling allerod b a and younger dryas yd periods about 85 and a strong increase of marine organic matter occurred in the holocene between 50 and 75 this agreement reflects the main hydrographic changes that determined the deposition of sedimentary materials between 0 and 15 cal ka ice rafted detritus from the barents continental platform ice melting waters from the arctic fluvial system discharging into the barents sea and dominance of north atlantic currents respectively in this respect the high resolution down core record resulting from the mass balance and lipid measurements allows for the identification of millennial scale events such as the increase of reworked organic matter at the final retreat of the barents ice sheet at the end of the deglaciation period termination ib

reconciling the westerlies and monsoon models a new hypothesis for the holocene moisture evolution of the xinjiang region nw china abstract the holocene evolution of moisture conditions in the arid xinjiang region in inland nw china is increasingly debated analysis of climatic reconstructions from lake sediments loess sand dunes and peats reveals a long term wetting trend westerlies model whereas other studies mainly of lake sediments and stalagmites have indicated a long term drying trend monsoon model two observations can be made about these conflicting interpretations i the monsoon model records are mainly from high altitude mountain areas with higher precipitation whereas the westerlies model records are mainly from low altitude piedmont areas and basins with lower precipitation ii an increasing number of studies of the xinjiang region and its surroundings demonstrate a long term warming trend during the holocene based on these observations we propose the following simple hypothesis which is a compromise between the westerlies and monsoon models against the background of long term holocene warming the increased meltwater supply from snow and ice in high altitude mountain areas fed the low altitude lakes which finally resulted in higher lake levels expanded oasis areas and enhanced local moisture recycling this potentially explains why the westerlies model evidenced in the moisture records from lakes and adjacent loess and peat deposits comprises a long term wetting trend this hypothesis is largely consistent with the parts of the region that are currently experiencing climatic warming more importantly with the likely acceleration of climatic warming in the near future the further ablation of ice and snow in the high altitude mountain regions will present a major and growing threat to the sustainable socioeconomic development of xinjiang consequently it is important that both the government and the public seriously consider the implications of an ice free environment in the region

transport of terrestrial organic carbon to the oceans by rivers re estimating flux and burial rates this study re estimates one important component in the global carbon cycle the modern global fluviatile organic carbon discharge and burial rates according to these results approximately 430 1012 g of terrestrial organic carbon are transported to the ocean in modern times this amount is higher than the latest estimates but takes into account new data from oceania not previously considered in global flux studies however only the minor amount of 10 or approximately 43 1012 gc year 1 is most likely buried in marine sediments this amount is similar to the burial of marine organic carbon in the coastal ocean 55 1012 gc year 1 adding both estimates gives approximately 100 1012 gc year 1 which is the value calculated by berner 1982 for terrestrial deltaic shelf sediments however the results in this study suggest that on a global scale the organic carbon content in coastal ocean sediments is not solely of terrestrial origin but a mixture of nearly equal amounts of marine and terrestrial organic carbon the major part of the terrestrial organic carbon that enters the ocean by rivers approximately 400 1012 gc year 1 seems to be either a remineralised in the ocean whereas the mechanism by which the terrestrial organic carbon is oxidised in the ocean are unknown or b is dispersed throughout the oceans and accumulates in pelagic sediments

moisture dynamics in central asia for the last 15 kyr new evidence from yili valley xinjiang nw china based on high resolution palynological investigations and ams 14 c dating the continuous lacustrine sediments contained in yili valley xinjiang provide an opportunity to reconstruct the effective moisture changes for the last 15 kyr in central asia the relatively warm and humid climate of the bolling allerod 15 12 9 cal kyr bp is a generalization but it seems to show some fluctuations the time of the younger dryas yd interrupted the increasing trend of effective moisture in the study region the climate was cold and relatively dry in the early yd period 12 9 12 0 cal kyr bp whereas the desert vegetation community appeared around 11 8 cal kyr bp almost the driest time since the 15 cal kyr br a sharp increase in effective moisture marked the beginning of the holocene in the yili valley the early holocene 10 6 7 6 cal kyr bp was the wettest time with a developed temperate steppe a dry climate with desert vegetation arose in the early mid holocene 7 6 6 5 cal kyr bp spanning 1100 years a second humid phase emerged between 6 5 and 5 2 cal kyr bp whose vegetation community was represented by temperate steppe moisture was reduced again and the climate became drier between 5 2 and 3 3 cal kyr bp when vegetation was dominated by desert steppe in the yili valley regional comparisons indicate that the moisture changes in yili valley were mainly influenced by the north atlantic ocean ssts through the westerlies the mean position of the siberian high pressure cell probably made a great contribution to the drought between 7 6 and 6 5 cal kyr bp the climate changes were generally consistent between the westerly dominant central asia and asian monsoon regions since the last deglaciation possibly forced by summer insolation conditions in the northern hemisphere c 2011 elsevier ltd all rights reserved

holocene climate and vegetation changes inferred from pollen records of lake aibi northern xinjiang china a potential contribution to understanding of holocene climate pattern in east central asia abstract this research focuses on the reconstructions of the lake hydrologic variations and the basin wide vegetation changes over past 13 870 years based on pollen data of 195 samples and the lithologic variations obtained from lake aibi in the western part of xinjiang area our results showed that lake or swamp environment did not come into existence until 13 870 cal bp and swamp or wetland environment dominated the depression of the basin between 13 870 and 7430 cal bp under ameliorated basin wide moisture conditions the following period between 7430 and 3620 cal bp witnessed lake transgression in the depression and vegetation amelioration within the basin the moisture conditions were continuously ameliorated from 3620 cal bp onward leading to further lake transgression and further basin wide vegetation amelioration a dry interval from 1400 to 1150 cal bp interrupted the late holocene wet epoch of the past 3600 years our synthesized regionally averaged moisture index of xinjiang area indicates that a gradual wetting climate dominated the mid to late holocene in xinjiang area this wetting trend in xinjiang area is hypothesized to have been associated with the winter warming and winter wetting trends in northern europe the gradual increase of winter insolation in mid to late holocene might have enhanced evaporation in the north atlantic ocean and injected more moisture to the westerlies system therefore bringing more precipitation to the downwind area including xinjiang

modern organic carbon deposition in the laptev sea and the adjacent continental slope surface water productivity vs terrigenous input sediment samples from the laptev sea taken during the 1993 rv polarstern expedition ark ix 4 and the rv ivan kireyev expedition transdrift i were investigated for the amount and composition of their organic carbon fractions of major interest was the identification of different processes controlling organic carbon deposition i e terrigenous supply vs surface water productivity long chain unsaturated alkenones derived from prymnesiophytes and fatty acids derived from diatoms and dinoflagellates were analysed by means of gas chromatography and mass spectrometry first results on the distribution of these biomarkers in surface sediments indicate that the surface water productivity signal is well preserved in the sediment data this is shown by the distribution of the 16 1 n 7 and 20 5 n 3 fatty acids indicative for diatoms and the excellent correlation with the chlorophyll a concentrations in the surface water masses and the biogenic opal content and increased hydrogen indices of the sediments the high concentration of these unsaturated fatty acids in shallow water sediments shows the recent deposition of the organic material in deep sea sediments on the other hand the concentrations are low this decreased content is typical for phytoplankton material which has been degraded by microorganisms or autoxidation in general the alkenone concentrations are very low suggesting low production rates by prymnesiophytes only at one station from the lower continental margin influenced by the inflow of atlantic water masses were some higher amounts of alkenones determined long chain n alkanes as well as high c n ratios and low hydrogen indices indicate the importance of fluvial supply of terrigenous organic matter

biomarker distributions in surface sediments from the kara and laptev seas arctic ocean indicators for organic carbon sources and sea ice coverage studies of spatial and temporal changes in modern and past sea ice occurrence may help to understand the processes controlling the recent decrease in arctic sea ice cover here we determined concentrations of ip25 a novel biomarker proxy for sea ice developed in recent years phytoplankton derived biomarkers brassicasterol and dinosterol and terrigenous biomarkers campesterol and sitosterol in the surface sediments from the kara and laptev seas to estimate modern spatial seasonal sea ice variability and organic matter sources c25 hbi dienes and trienes were determined as additional palaeoenvironmental proxies in the study area furthermore a combined phytoplankton ip25 biomarker approach pip25 index is used to reconstruct the modern sea ice distribution more quantitatively the terrigenous biomarkers reach maximum concentrations in the coastal zones and estuaries reflecting the huge discharge by the major rivers ob yenisei and lena maxima in phytoplankton biomarkers indicating increased primary productivity were found in the seasonally ice free central part of the kara and laptev seas neither ip25 nor pip25 however shows a clear and simple correlation with satellite sea ice distribution in our study area due to the complex environmental conditions in our study area and the transportation process of sea ice diatom in the water column differences in the diene ip25 and triene ip25 ratios point to different sources of these hbis and different environmental conditions the diene ip25 ratio seems to correlate positively with sea surface temperature while negatively with salinity distributions

alkane and pah biomarkers as tracers of terrigenous organic carbon in arctic ocean sediments abstract we present the first sedimentary biomarker study encompassing the entire arctic ocean a large data set of organic markers for terrigenous petroleum and combustion inputs alkanes hopanes and steranes parent and alkyl polycyclic aromatic hydrocarbons pahs is examined for patterns in space and time using principal components analysis pca and partial least squares pls biomarker patterns reveal the central arctic ocean basin sediments to be compositionally distinct from those of the mackenzie river beaufort sea and barents sea but similar to those of the laptev sea pah distributions reflected in pah ratios and pca projections demonstrate that arctic ocean sediment is dominated by natural inputs to the extent that anthropogenic combustion pahs are not significant we find only modest changes between the glacial and post glacial sediments for atmospherically transported hydrocarbon biomarkers while particle associated biomarkers were captured strongly at basin edges during the glacial period and much more evenly transported across basins during the post glacial period the orders of magnitude decreases in particle associated petrogenic alkanes and pahs in central basins during glacial times coupled with the uniformity of most petrogenic biomarker parameters for most basin and shelf locations reflect a massive reduction in ice transport that makes the margins the most likely source of petrogenic material for the pleistocene holocene central arctic basins the proximity of large coal deposits of various maturity levels along the lena river the overlap in pah and biomarker composition of the laptev sea and surficial sediments from the central arctic ocean and the location of the laptev sea at the origin of the main transpolar drift all point to eroded coals from the lena river laptev sea as the likely source of petrogenic hydrocarbons to the central arctic ocean the ubiquitous presence of allochthonous coal in arctic ocean surface sediments provides a major constraint on the use of petrogenic biomarkers to infer the presence of subsurface petroleum reserves

paleogene biomarker records from the central arctic ocean integrated ocean drilling program expedition 302 organic carbon sources anoxia and sea surface temperature 1 during integrated ocean drilling program expedition 302 arctic coring expedition acex a more than 200 m thick sequence of paleogene organic carbon oc rich black shale type sediments was drilled here we present new biomarker data determined in acex sediment samples to decipher processes controlling oc accumulation and their paleoenvironmental significance during periods of paleogene global warmth and proposed increased freshwater discharge in the early cenozoic specific source related biomarkers including n alkanes fatty acids isoprenoids carotenoids hopanes hopenes hopanoic acids aromatic terpenoids and long chain alkenones show a high variability of components derived from marine and terrestrial origin the distribution of hopanoic acid isomers is dominated by compounds with the biological 17 h 21 h configuration indicating a low level of maturity on the basis of the biomarker data the terrestrial oc supply was significantly enriched during the late paleocene and part of the earliest eocene whereas increased aquatic contributions and euxinic conditions of variable intensity were determined for the paleocene eocene thermal maximum and eocene thermal maximum 2 events as well as the middle eocene time interval furthermore samples from the middle eocene are characterized by the occurrence of long chain alkenones high proportions of lycopane and high ratios 0 6 of n c35 lycopane n c31 the occurrence of c37 alkenenones which were first determined toward the end of the azolla freshwater event indicates that the oc becomes more marine in origin during the middle eocene preliminary u37k based sea surface temperature sst values display a long term temperature decrease of about 15 c during the time interval 49 44 5 ma 25 to 10 c coinciding with the global benthic 18o cooling trend after the early eocene climatic optimum at about 46 ma parallel with onset of ice rafted debris sst interpreted as summer temperatures decreased to values 15 c for the late early miocene a sst of 11 15 c was determined most of the middle eocene acex sediments are characterized by a smooth short chain n alkane distribution which may point to natural oil type hydrocarbons from leakage of petroleum reservoirs or erosion of related source rocks and redeposition

lipid distribution in surface sediments from the eastern central arctic ocean abstract during the arctic 91 expedition with rv polarstern numerous short multicorer and long cores kastenlot cores including surface sediments were recovered along a transect crossing the eastern part of the arctic ocean in this paper we present data on the concentration and distribution of short c17 c19 and long chain c27 c29 c31 n alkanes as well as fatty acids 16 0 16 1 18 0 18 1 in the surface sediments from this transect these compounds among others have been used to distinguish between autochthonous marine organic matter and allochthonous terrigenous organic matter supply changes in short chain n alkane as well as fatty acid contents of the sediments allow us to distinguish between regions characterized by higher or lower marine productivity organic carbon contents of the surface sediments are generally high and vary between 0 3 and 2 in general the high organic carbon content of the sediments is derived from a high input of terrigenous organic matter marine productivity in the arctic ocean is mainly controlled by reduced sea ice cover which allows a higher production rate of phytoplankton regions with a higher marine organic matter content are the area nw of svalbard the yermak plateau a part of the lomonosov ridge and makarov basin and the morris yesup rise the pattern of distribution of long chain n alkanes in arctic ocean surface sediments is mainly controlled by sea ice and or direct transport from the adjacent shelf areas although dilution by turbidites influences the deep basins

a persistent holocene wetting trend in arid central asia with wettest conditions in the late holocene revealed by multi proxy analyses of loess paleosol sequences in xinjiang china abstract there are significant differences in the interpretation of the moisture precipitation history of arid central asia aca during the holocene as inferred on one hand from speleothem oxygen isotope records and on the other from lake sediments here we present the results of measurements of climatically sensitive magnetic properties and soil color from four well dated loess paleosol sequences from the northern slopes of the tienshan mountains and the yili river valley xinjiang china in the core area of aca our results demonstrate that the characteristic holocene paleosol indicating relatively moist conditions generally formed after 6 ka 1 ka 1000 cal yr bp in the study region and that the accumulation of unweathered loess prevailed during the early holocene indicating a dry climate at that time the magnetic proxies further reveal a trend of generally increasing moisture since the last glacial maximum with the wettest climate occurring during the late holocene this trend of increasing moisture during the holocene is representative of the xinjiang region and possibly of the whole of the core area of aca and is in marked contrast both to the mid holocene moisture maximum observed in the east asian summer monsoon region and to the general decrease in the strength of the indian summer monsoon since the early holocene our findings are supported by the results of a climate simulation which indicate a trend of increasing summer and winter precipitation during the holocene in the core area of aca caused mainly by an increase in the strength of the westerlies effected by an increasing latitudinal insolation gradient and by a negative trend of the arctic oscillation ao or north atlantic oscillation nao

assessing the importance of terrestrial organic carbon in the chukchi and beaufort seas abstract the western arctic ocean is a unique part of the world s oceans and is an area undergoing significant climate changes the effects and possible climate feedbacks of these changes are not yet fully understood decreased sea ice cover could lead to increased productivity in the water column or a reduction in total productivity through the loss of sea ice algal contributions climate change could also alter the patterns of terrestrial inputs from rivers and coastal erosion in order to better understand the balance of organic material inputs in the western arctic ocean this report presents carbon and nitrogen elemental and isotopic compositions from 19 surface sediment samples and 7 cores from 4 shelf to basin transects as evidence of the sources of organic matter buried in the sediments of the chukchi and alaskan beaufort seas the c n ratios for surface sediments were between 5 3 and 11 5 mean 9 0 1 3 the mean toc was 1 2 0 3 and mean tn was 0 16 0 02 the highest toc contents were observed in the barrow canyon transect likely reflecting heightened overlying productivity the 13 c of this preserved material varied from 22 1 to 16 7 mean 19 4 1 3 a trend to depletion in 13 c and higher c n in eastern sites was observed among the surface samples 15 n varied from 4 1 to 7 6 mean 5 7 1 1 an evaluation of the inputs of organic matter to the western arctic sediment was accomplished using 13 c and 15 n values with the novel technique of a bayesian analysis multi source mixing model this model was used to estimate proportional contributions of sea ice algae water column phytoplankton and terrestrial organic matter we conclude that water column productivity is the source of between 50 and 70 of the organic carbon buried in this portion of the western arctic the remaining 25 35 of carbon is mainly supplied by sea ice algal productivity with at most 15 of sedimentary carbon derived from terrestrial inputs

post glacial variability of sea ice cover river run off and biological production in the western laptev sea arctic ocean a high resolution biomarker study abstract multi proxy biomarker measurements were applied on two sediment cores ps51 154 ps51 159 to reconstruct sea ice cover ip25 biological production brassicasterol dinosterol and river run off campesterol sitosterol in the western laptev sea over the last 17 ka with unprecedented temporal resolution the absence of ip25 from 17 2 to 15 5 ka in combination with minimum concentration of phytoplankton biomarkers suggests that the western laptev sea shelf was mostly covered with permanent sea ice very minor river run off and restricted biological production occurred during this cold interval from 16 ka until 7 5 ka a long term decrease of terrigenous riverine organic matter and a coeval increase of marine organic matter reflect the gradual establishment of fully marine conditions in the western laptev sea caused by the onset of the post glacial transgression intensified river run off and reduced sea ice cover characterized the time interval between 15 2 and 12 9 ka including the bolling allerod warm period 14 7 12 9 ka prominent peaks of the dip25 index coinciding with maximum abundances of subpolar foraminifers are interpreted as pulses of atlantic water inflow on the western laptev sea shelf after the warm period a sudden return to severe sea ice conditions with strongest ice coverage between 11 9 and 11 ka coincided with the younger dryas 12 9 11 6 ka at the onset of the younger dryas a distinct alteration of the ecosystem reflected in a distinct drop in terrigenous and phytoplankton biomarkers was detected during the last 7 ka the sea ice proxies reflect a cooling of the laptev sea spring summer season this cooling trend was superimposed by a short term variability in sea ice coverage probably representing bond cycles 1500 500 ka that are related to solar activity changes hence atmospheric circulation changes were apparently able to affect the sea ice conditions on the laptev sea shelf under modern sea level conditions

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

late pleistocene changes in terrestrial biomarkers in sediments from the central arctic ocean abstract biomarkers in late pleistocene sediments collected from the integrated ocean drilling program iodp arctic coring expedition acex hole m0004c central arctic ocean were investigated the major biomarkers are long chain n alkanes n fatty acids and n alkan 1 ols indicating fresh organic matter om derived predominantly from higher plants the dominance of terrestrial biomarkers is attributed to severe om degradation caused by slow sedimentation in oxygen rich benthic water and or low primary production due to permanent sea ice coverage hopanes representing thermally altered om tend to be abundant in samples with abundant ice rafted debris ird an om rich dark grey layer deposited during marine isotope stage mis 6 contains a significant amount of branched glycerol dialkyl glycerol tetraethers branched gdgts suggesting ice erosion of organic rich continental soil followed by transportation to the central arctic by drifting ice the labile refractory index i e the abundance ratio of long chain n alkan 1 ols to the sum of long chain n alkanes and long chain n alkan 1 ols decreases above the dark grey layer indicating that the om became more refractory this change suggests that coverage of the source region by om rich soil decreased because of extensive glacial erosion during mis 6

vegetation and climate history reconstructed from an alpine lake in central tienshan mountains since 8 5 ka bp abstract high mountains are humid islands in arid central asia and alpine vegetation is sensitive to climate change especially to temperature variations here we present a palynological sequence and discuss the past vegetation and climate changes based on core by10a from the swan lake an alpine lake situated at an inter montane basin in the central tienshan mountains xinjiang northwestern china we collected 52 modern pollen surface samples at different elevations to aid in the interpretation of fossil pollen data which provide a reconstruction of vegetation and climate history for the last 8 5 ka 1 ka 1000 cal yr bp artemisia and amaranthaceae chenopodiaceae are the main pollen types in desert steppe zone below 1800 m elevation while poaceae and picea dominate the mid elevation forest steppe zone 1800 2800 m cyperaceae is the main indicator of high alpine meadows 2800 m from 8 5 to 6 9 ka the vegetation was steppe meadow suggesting relatively warm climate from 6 9 to 2 6 ka generally high values of cyperaceae and peaty sediments indicate a fen environment and cooler more humid conditions interrupting this mid holocene period is a 5 5 4 5 ka millennium of lacustrine sediments with lower cyperaceae higher poaceae and artemisia and high values of myriophyllum and pediastrum indicating higher water levels and warmer temperatures after 2 6 ka pollen data indicate alpine steppe and warmer climate the mid holocene pattern of cooler climate interrupted by a warmer period is consistent from other regional records from xinjiang including the guliya ice core and kesang cave speleothem record during the cooler periods the regional record indicates that a weakened summer asian monsoon is countered to some extent by a stronger winter monsoon

oceanic and atmospheric variations during the last deglaciation in the fram strait arctic ocean a coupled high resolution organic geochemical and sedimentological study abstract from a high sedimentation rate core obtained from the yermak slope arctic ocean we deduced short term climatic fluctuations of the last deglaciation lasting from 17 000 to 9000 years bp by using a coupled organic geochemical and sedimentological approach we reconstructed near bottom current conditions and assessed their significance in relation with comparable global thermohaline circulation patterns and surface water conditions highest concentrations and fluctuations of specific marine phytoplankton biomarkers were obtained in the bolling allerod when the major deglaciation of the svalbard barents sea ice sheet sbis occurred the marine biomarker record and the sedimentological record are consistent with climate reconstructions obtained from greenland ice cores and thermohaline circulation variations however beginning with the younger dryas yd episode bottom currents decreased during this time period but surface waters remained very productive the atmospheric conditions of the western fram strait reconstructed from biomarker data and thermohaline circulation signals reconstructed from sedimentological data were decoupled in the yd maximum insolation values of solar radiation and fohn like winds enabled open water conditions and increased productivity values in the northern fram strait at least in summer

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

climate forcing of fine grained deep marine systems in an active tectonic setting middle eocene ainsa basin spanish pyrenees abstract a multi proxy approach to understand environmental change in deep time was undertaken on about 150 m of core from a 230 m long middle eocene core from the ainsa basin spanish pyrenees representing deep marine siliciclastic sediments using detailed sedimentary logging high resolution multi element xrf geochemistry total organic carbon and stable carbon isotopes the well a6 was drilled as part of an industry university consortium through siltstones fine very fine grained sandstone turbidites and hemipelagic structureless mudstones that were deposited as overbank and off axis deposits from a sandy submarine fan and interfan deposits for comparative mineralogy between the sandstone turbidites and siltstones scanning electron microscopy sem and x ray diffraction xrd were undertaken on selected samples the sandstone turbidites show enrichment of detrital elements such as si zr and ti that can be linked to greater quartz and heavy mineral content compared with adjacent siltstones structureless hemipelagic mudstones comprise mainly clay minerals and carbonate we interpret the sandstone turbidites as from hyperpycnal flows during high river sediment discharge whilst hemipelagic mudstones resulted from the suspension fall out of hypopycnal flows cyclostratigraphic analysis of the core reveals milankovitch cyclicity at frequencies of 0 03 cycles m short eccentricity 0 09 cycles m obliquity 0 15 cycles m precession couplet and 0 19 cycles m precession couplet orbital parameters appear to have controlled the cyclic delivery of coarser grained sediment by turbidity currents two equally plausible depositional models both as milankovitch driven can explain the cyclical changes in the deep marine sediments 1 climatic cycles with humid periods of enhanced chemical weathering increased storminess and greater riverine run off leading to high sediment flux to the deep basin as sandstone turbidites 2 climatic cycles with cooler conditions linked to high frequency small scale eustatic sea level fluctuations with lowstand shelf edge delta progradation resulting in greater volumes of coarse detrital sediment to the seafloor by hyperpycnal flows this study provides an insight into the likely depositional effects of orbitally induced climate change on the nature and delivery of terrigenous sediment into deep marine environments

diploptene in varved sediments of saanich inlet indicator of increasing bacterial activity under anaerobic conditions during the holocene saanich inlet has been a highly productive fjord since the last glaciation during odp leg 169s nearly 70 m of holocene sediments were recovered from hole 1034 at the center of the inlet the younger sediments are laminated anaerobic and rich in organic material 1 2 5 wt corg whereas the older sediments below 70 mbsf are non laminated aerobic with glacio marine characteristics and have a significantly lower organic matter content this difference is also reflected in the changes of interstitial fluids and in biomarker compositions and their carbon isotope signals the bacterially derived hopanoid 17 h 21 h hop 22 29 ene diploptene occurs in saanich inlet sediments throughout the holocene but is not present in pleistocene glacio marine sediments its concentration increases after 6000 years bp up to present time to about 70 g g corg whereas terrigenous biomarkers such as the n alkane c31 are low throughout the holocene 51 g g corg and even slightly decrease to 36 g g corg at the most recent time the increasing concentrations of diploptene in sediments younger than 6000 years bp separate a recent period of higher primary productivity stronger anoxic bottom waters and higher bacterial activity from an older period with lesser activity heretofore undifferentiated carbon isotopic compositions of diploptene in the holocene are between 31 5 and 39 6 pdb after 6000 years bp these differences in the carbon isotopic record of diploptene probably reflect changes in microbial community structure of bacteria living at the oxic anoxic interface of the overlying water column the heavier isotope values are consistent with the activity of nitrifying bacteria and the lighter isotope values with that of aerobic methanotrophic bacteria therefore intermediate 13c values probably represent mixtures between the populations in contrast carbon isotopic compositions of n c31 are roughly constant at 31 4 1 1 pdb throughout the holocene indicating a uniform input from cuticular waxes of higher plants prior to 6000 years bp diploptene enriched in 13c of up to 26 3 pdb is indicative of cyanobacteria living in the photic zone and suggests a period of lower primary productivity more oxygenated bottom waters and hence lower bacterial activity during the earliest holocene

different sources and degradation state of dissolved particulate and sedimentary organic matter along the eurasian arctic coastal margin the amount of organic carbon oc present in siberian arctic permafrost soils is estimated at twice the amount of carbon currently in the atmosphere the shelf seas of the arctic ocean receive large amounts of this terrestrial oc from eurasian arctic rivers and from coastal erosion degradation of this land derived material in the sea would result in the production of dissolved carbon dioxide and may then add to the atmospheric carbon dioxide reservoir observations from the siberian arctic suggest that transfer of carbon from land to the marine environment is accelerating however it is not clear how much of the transported oc is degraded and oxidized nor how much is removed from the active carbon cycle by burial in marine sediment using bulk geochemical parameters total oc d13c and d14c isotope composition and specific molecular markers of plant wax lipids and lignin phenols the abundance and composition of oc was determined in both dissolved and particulate carrier phases the colloidal oc coc part of the dissolved oc particulate oc poc and sedimentary oc soc statistical modelling was used to quantify the relative contribution of oc sources to these phases terrestrial oc is derived from the seasonally thawing top layer of permafrost soil topsoil oc and frozen oc derived from beneath the active layer eroded at the coast commonly identified as yedoma ice complex deposit oc yedoma icd oc these carbon pools are transported differently in the aquatic conduits topsoil oc was found in young doc and poc in the river water and the shelf water column suggesting long distance transport of this fraction the yedoma icd oc was found as old particulate oc that settles out rapidly to the underlying sediment and is laterally transported across the shelf likely dispersed by bottom nepheloid layer transport or via ice rafting these two modes of oc transport resulted in different degradation states of topsoil oc and yedoma icd oc terrestrial cuo oxidation derived biomarkers indicated a highly degraded component in the coc in contrast the terrestrial component of the soc was much less degraded in line with earlier suggestions the mineral component in yedoma icd functions as weight and surface protection of the associated oc which led to burial in the sediment and limited oc degradation the degradability of the terrestrial oc in shelf sediment was also addressed in direct incubation studies molecular markers indicate marine oc from primary production was more readily degraded than terrestrial oc degradation was also faster in sediment from the east siberian sea where the marine contribution was higher compared to the laptev sea although terrestrial carbon in the sediment was degraded slower the terrestrial component also contributed to carbon dioxide formation in the incubations of marine sediment these results contribute to our understanding of the marine fate of land derived oc from the siberian arctic the mobilization of topsoil oc is expected to grow in magnitude with climate warming and associated active layer deepening this translocated topsoil oc component was found to be highly degraded which suggests degradation during transport and a possible contribution to atmospheric carbon dioxide similarly the yedoma icd oc and or old mineral soil carbon may become a stronger source with accelerated warming but slow degradation may limit its impact on active carbon cycling in the siberian shelf seas

contrasts in arctic shelf sea ice regimes and some implications beaufort sea versus laptev sea the winter ice regime of the 500 km from the mainland than in the beaufort sea as a result the annual freeze up does not incorporate old deep draft ice and with a lack of compression such deep draft ice is not generated in situ as on the beaufort sea shelf the laptev sea has as much as 1000 km of fetch at the end of summer when freezing storms move in and large 6 m waves can form also for the first three winter months the polynya lies inshore at a water depth of only 10 m turbulence and freezing are excellent conditions for sediment entrainment by frazil and anchor ice when compared to conditions in the short fetched beaufort sea we expect entrainment to occur yearly different from the intensely ice gouged beaufort sea shelf hydraulic bedforms probably dominate in the laptev sea corresponding with the large volume of ice produced more dense water is generated in the laptev sea possibly accompanied by downslope sediment transport thermohaline convection at the midshelf polynya together with the reduced rate of bottom disruption by ice keels may enhance benthic productivity and permit establishment of open shelf benthic communities which in the beaufort sea can thrive only in the protection of barrier islands indirect evidence for high benthic productivity is found in the presence of walrus who also require year round open water by contrast lack of a suitable environment restricts walrus from the beaufort sea although over 700 km farther to the south we could speculate on other consequences of the different ice regimes in the beaufort and laptev seas but these few examples serve to point out the dangers of exptrapolating from knowledge gained in the north american arctic to other shallow arctic shelf settings

a multiproxy approach to reconstruct the environmental changes along the eurasian continental margin over the last 150 000 years abstract sediment cores located along the eurasian continental margin arctic ocean have been studied to reconstruct the environmental changes in terms of waxing and waning of the barents kara sea ice sheets atlantic water inflow and sea ice distribution over the last 150 kyr the stratigraphy of the cores is based on stable oxygen isotopes ams 14 c and paleomagnetic data we studied variations in marine and terrigenous input by a multiproxy approach involving direct comparison of sedimentological and organo geochemical data extensive episodes of northern barents sea ice sheet growth during marine isotope stages mis 6 and 2 have been supported by at least subsurface atlantic water inflow moisture bearing storms low summer insolation and minimal calving of ice ice advance during mis 4 was probably restricted to the shallow shelf between mis 4 and mis 2 large ice sheet fluctuations correspond to contemporary laurentide surging events and indicate short term climatic changes in the arctic ocean as has been recorded in lower latitudes in contrast in low precipitation areas in eastern eurasia glacial activity was rather limited only distinct ice rafted debris ird input during termination ii and early mis 3 reflects severe glaciations on the northern severnaya semlya margin during mis 6 and mis 4 we conclude that 1 oscillations of ice sheets are less frequent along the eastern eurasian margin than in areas with continuous moisture supply like the western eurasian margins and that 2 major fluctuations of the kara sea ice sheet during the last 150 kyr apparently followed the major interglacial glacial mis 5 4 and mis 7 6 transitions rather than the precession 23 kyr and the tilt 41 kyr cyclicity of the earth s orbit as observed for the scandinavian sis and the svalbard ice sheets respectively mangerud j jansen e landvik j y 1996 late cenozoic history of the scandinavian and barents sea ice sheets in solheim a riis f elverhoi a faleide j j jensen l n cloetingh s eds impact of glaciations on basin evolution data and models from the norwegian margins and adjacent basins global and planetary chance special issue 12 pp 11 26 surface and or subsurface atlantic water masses coupled with seasonally ice free conditions penetrated continuously to at least the franz victoria trough during the last 150 kyr however sustained periods of open water were largely restricted to substages 5 5 5 1 and the holocene as indicated by distinct carbonate dissolution and higher accumulation of marine organic matter mom signals of periodic open water conditions along the northern margin of severnaya semlya are of less importance higher production of foraminifera probably due to atlantic water inflow occurred between 38 and 12 14 c kyr and corresponds to periodic atlantic water advection penetrating into the arctic ocean however marine organic proxies indicate a continuous decrease of surface water productivity from the western to the eastern eurasian continental margin due to a more extensive sea ice cover over the last 150 kyr

high resolution paleoproductivity fluctuations during the past 24 kyr as indicated by benthic foraminifera in the marginal arctic ocean abstract analyses of benthic foraminifera in sediment cores taken at about 1000 m water depth at the yermak plateau and the barents sea slope adjacent to the position of the ice sheet edge during the last glacial maximum show that paleoproductivity was reduced to about a third of its present level during peak glacial stadials these reduced values are still higher than values for modern permanently ice covered regions suggesting that the core locations were at least partially ice free even during stadials paleoproductivity at the core locations was higher than or equal to that of today during initial deglaciations and warm substages peak paleoproductivity occurred in samples with low salinity surface waters as indicated by oxygen isotope values of planktonic foraminifera and slightly after increased abundance of atlantic species suggesting that enhanced advection of warmer waters from the atlantic supported the initial ice sheet retreat during the holocene climatic optimum productivity was much less than at present on the yermak plateau high at the barents sea site perhaps because of increased advection of atlantic water to the latter site and heavier ice coverage at the former after this optimum paleoproductivity at both sites was similar with slightly lower values during cold periods such as the little ice age

new aspects of organic carbon deposition and its paleoceanographic implications along the northern barents sea margin during the last 30 000 years we studied variations in terrigenous tom and marine organic matter mom input in a sediment core on the northern barents sea margin over the last 30 ka using a multiproxy approach we reconstructed processes controlling organic carbon deposition and investigated their paleoceanographic significance in the north atlantic arctic gateways variations in paleo surface water productivity are not documented in amount and composition of organic carbon the highest level of mom was deposited during 25 23 ka as a result of scavenging on fine grained reworked and tom rich material released by the retreating svalbard barents sea ice sheet during the late weichselian a second peak of mom is preserved because of sorptive protection by detrital and terrigenous organic matter higher surface water productivity due to permanent intrusion of atlantic water and high suspension load release by melting sea ice during 15 9 11 2 ka

contrasting lipid biomarker composition of terrestrial organic matter exported from across the eurasian arctic by the five great russian arctic rivers contrasting lipid biomarker composition of terrestrial organic matter exported from across the eurasian arctic by the five great russian arctic rivers

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

stable isotope and trace element time series from fedchenko glacier pamirs snow firn cores in summer 2005 two pilot snow firn cores were obtained at 5365 and 5206 m a s l on fedchenko glacier pamirs tajikistan the world s longest and deepest alpine glacier the well defined seasonal layering appearing in stable isotope and trace element distribution identified the physical links controlling the climate and aerosol concentration signals air temperature and humidity precipitation were the primary determinants of stable isotope ratios most precipitation over the pamirs originated in the atlantic in summer water vapor was re evaporated from semi arid regions in central eurasia the semi arid regions contribute to non soluble aerosol loading in snow accumulated on fedchenko glacier in the pamir core concentrations of rare earth elements major and other elements were less than those in the tien shan but greater than those in antarctica greenland the alps and the altai the content of heavy metals in the fedchenko cores is 2 14 times lower than in the altai glaciers loess from afghan tajik deposits is the predominant lithogenic material transported to the pamirs trace elements generally showed that aerosol concentration tended to increase on the windward slopes during dust storms but tended to decrease with altitude under clear conditions the trace element profile documented one of the most severe droughts in the 20th century

tracking nutrient and productivity variations over the last deglaciation in the arctic ocean we have reconstructed the surface water environment of the arctic ocean over the last 50 000 years using measurements of the organic nitrogen and carbon isotope ratios carbonate and total organic carbon concentrations toc and terrestrial biomarkers lignin and long chain n alkanes in four multicores variations in nitrogen isotope ratios that are concordant with toc and carbonate concentrations representing foraminifera and excluding ice rafted debris reflect differences in relative nutrient utilization of phytoplankton in the surface waters however 15n variations also appear to be dependent on the stratification of the water column and therefore potentially track the exchange of nutrients between deep and surface waters low last glacial maximum lgm 15n values and higher holocene values are opposite to those recorded in the southern ocean the arctic ocean with higher nutrient utilization today compared to the lgm therefore acts as a counterpart to the southern ocean although the global impact on carbon dioxide variations compared to the southern ocean is probably low

organic matter sources and early diagenetic alterations in arctic surface sediments lena river delta and laptev sea eastern siberia ii molecular and isotopic studies of hydrocarbons abstract the hydrocarbons extracted from three surface sediment samples from the delta of the lena river and adjacent areas of the laptev sea were examined to derive information on their source s natural vs anthropogenic terrestrial vs marine the abundance nature distribution and individual stable carbon isotope ratios of these hydrocarbons were determined it thus appeared that the laptev samples are characterized by i a negligible level of oil pollution due to anthropogenic and or natural petrogenic inputs ii an almost exclusive occurrence of long chain predominantly odd carbon numbered n alkanes and iii some differences in the level of bacterial alteration with a relatively higher degradation of the n alkanes in the seaward sediment a non terrestrial origin is proposed for these n alkanes based on the present results and on previous observations on carboxylic acid moieties and the pyrolysis products of the three surface sediments such hydrocarbons are probably not derived from the epicuticular waxes of higher plants but chiefly correspond to autochthonous products likely of algal origin these observations added to recent results on samples from other types of marine environments stress that an abundance of long chain predominantly odd n alkanes in extracts should not be systematically considered alone as evidence for a major contribution of higher plant waxes the relatively low contribution of terrestrial n alkanes in the laptev sediments should result from the combination of i a major dilution of the terrestrial input due to high primary productivity in summer promoted both by a large influx of nutrients provided by the lena river and by the specific conditions in such an arctic environment and ii the high level of degradation of the organic material transported by the lena river thus the latter probably provided a low input of lipids from terrestrial sources to the laptev samples

alkane distributions in arctic ocean sediments reply to alkane and pah biomarkers as tracers of terrigenous organic carbon in arctic ocean sediments by mark b yunker robie w macdonald lloyd r snowdon brian r fowler comment by vera petrova and co authors

bacterial hopanoids as tracers of organic carbon sources and processing across the western arctic continental shelf tracing the inputs of bacterial organic carbon to marine systems has been constrained by the lack of distinguishing geochemical tracers and limited contribution in sediments compared to other sources of organic matter bacteriohopanepolyols bhps provide a direct means to identify bacterial inputs which also reflect potential bacterial groups and their activities in aquatic systems we applied recent analytical approaches to identify and quantify bacterial derived carbon contributions to surface sediments from the western arctic ocean using bhps the abundance and distribution of bhps resemble trends of water column primary production and suggest active heterotrophic recycling of in situ production with some component of long term preservation bhps proposed as terrestrial derived signatures i e adenosylhopanes were also abundant in western arctic sediments and reflect offshore trends of other terrigenous lipid signatures with a fraction representing their degradative products analysis of bhps in organic rich peat and surface sediments from two arctic rivers showed the highest inputs of adenosylhopanes implying active bacterial recycling of recalcitrant terrigenous material bhps observed in western arctic surface sediments reveal significant contributions of bacteria associated with organic carbon from multiple sources

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

organic matter deposition along the kara and laptev seas continental margin eastern arctic ocean during last deglaciation and holocene evidence from organic geochemical and petrographical data abstract organic petrologic maceral analysis and bulk organic geochemical studies were performed on five sediment cores from the eurasian continental margin to reconstruct the environmental changes during the last 13 000 yr the core stratigraphy is based on ams 14c dating and correlation by magnetic susceptibility and lithostratigraphic characteristics variations in terrigenous freshwater and marine organic matter deposition document paleoceanographic and paleoclimatic changes during the transition from the last deglaciation to the holocene glacigenic diamictons deposited in the st anna trough northern kara sea during the last glacial maximum lgm are characterized by reworked terrigenous organic matter in contrast the laptev sea shelf was not covered by an ice sheet but was exposed by the lowered sea level increased deposition of marine organic matter mom during deglaciation indicates enhanced surface water productivity possibly related to influence of atlantic waters the occurrence of freshwater alginite gives evidence for river discharge to the kara and laptev seas after the lgm at the eastern laptev sea slope the first influence of atlantic water masses is indicated by an increase in the contents of mom and dinoflagellate cysts with operculodinium centrocarpum prior to 10 000 yr bp high sedimentation rates in the kara and the laptev seas with the adjacent slope at the beginning of the holocene are presumably related to increased freshwater and sediment discharge from the siberian rivers evidence for elevated holocene freshwater discharge to the laptev sea has been found between 9 8 and 9 kyr bp at 5 kyr bp and at 2 5 kyr bp in the kara sea an increased freshwater signal is obvious at 8 5 kyr bp and at 5 kyr bp higher portions of mom were accumulated in the st anna trough and at the eurasian continental margin at several intervals during the holocene increased primary productivity during these intervals is explained by seasonally ice free conditions possibly associated with increased inflow of atlantic waters

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

holocene moisture evolution across the mongolian plateau and its surrounding areas a synthesis of climatic records abstract based on the review of 26 high standard holocene climatic reconstructions mainly pollen based from the mongolian plateau and its surrounding areas temporal and spatial patterns of the holocene moisture evolution are synthesized the regionally averaged moisture history from the summer monsoon influenced semiarid belt in china i e region a demonstrates that the moisture index curve is broadly in agreement with the synthesized east asian monsoon strength curve both following the general trend of the west tropical pacific sst that is in turn the delayed response to the northern hemispheric summer solar insolation the regionally averaged moisture indices from the winter monsoon dominated southern siberia including lake baikal area and the altai mountains i e region b exhibit a general declining trends since 10 6 9 6 cal kyr bp being largely consistent with the trends of the annual precipitation and the warm season temperature in the russian plain the consistency might be attributable to the holocene declining trend of the warm season temperature in north atlantic region the predominant feature of the regionally averaged moisture index from the westerlies affected northern xinjiang i e region c is a persistent increasing trend since 8 cal kyr bp the wetting trend of northern xinjiang during the past 8000 years might be attributable to the increasing trend of winter insolation and to the associated increasing trend of cold season temperature in northwestern europe the chronological correspondences between dry phases and warm intervals in the arid areas of the mongolian plateau i e northern mongolian plateau within mongolia and southern mongolian plateau within china region d lend a support to the proposal that the mid holocene dry phase was most likely the result of mid holocene high warm season temperature

a new approach for reconstruction of the holocene climate in the mongolian altai the high resolution δ13c records of toc and pollen complexes in hoton nur lake sediments abstract 13 c of total organic carbon toc and pollen grain toc c n ratio and 15 n of total organic nitrogen ton in a 2 57 m long core from hoton nur lake in mongolian altai have been measured for reconstruction of the holocene climates the 13 c values of toc and pollen carbon have similar average values but different ranges pollen 13 c has negative correlation with ap arboreal taxa pollen and positive correlation with nap herbaceous pollen and spores that are connected with conditions of humidity in the area taiga biome has lighter 13 c than steppe biome hence pollen 13 c composition is more sensitive to changes of humidity in the analogous spectra than palynotaxonomical structure and 13 c of toc based on our results the holocene climates in mongolian altai are 1 dry conditions prior to 11 5 kyr bp 2 wet conditions between 11 5 and 6 0 kyr bp 3 a relatively dry cool episode during 6 4 kyr bp 4 stable cool and semiarid conditions with moderately effective moisture during the past 4000 years two abrupt climatic changes occurred at 7 45 kyr bp and 11 5 kyr bp might be related to glacial activities the holocene climatic trend in mongolian altai which is controlled by the westerlies is similar to the trend of monsoonal climate shown by the chinese speleothem records as well as the lake sand dune evidence in the deserts of nw china the contact of the two climatic systems and shift of the monsoonal boundary during the past need to be further studied

dry early holocene revealed by sand dune accumulation chronology in bayanbulak basin xinjiang nw china understanding the holocene climate changes especially moisture variation and their mechanisms in the semiarid arid central asia sca is very important as water availability is crucial for sustainable developments in this area this study presents chronostratigraphy of an aeolian sedimentary sequence from bayanbulak basin xinjiang nw china aiming to infer the holocene moisture history in the sca luminescence dating technique was selected to construct the age framework of the study section since the luminescence signal intensity of quartz from the samples was too low to be detected feldspar was used as an alternative dosimeter a newly developed post infrared ir ir stimulated luminescence irsl pirir dating protocol on k feldspar was applied to determine the ages of samples a set of tests on luminescence characteristics was performed and demonstrate that this method is suitable and the resultant ages are reliable combined with the stratigraphic investigation on the sand dune palaeosol section the results imply a very dry climatic condition characterized by sand dune accumulation at similar to 9 8 kyr and a wet interval of 5 1 6 kyr when a soil layer was formed this moisture variation pattern is consistent with that inferred from many lacustrine records in the sca suggesting a widespread dry period at 11 8 kyr the present results appear to challenge a new stalagmite delta o 18 sequence located nearby to bayanbulak basin which instead suggested a humid early holocene

holocene paleoenvironmental implications of diatom and organic carbon records from the southeastern kara sea siberian margin diatom assemblages and organic carbon records from two sediment cores located within an estuarian bay of the inner kara sea trace changes in yenisei river runoff and postglacial depositional environments paleosalinity and sea ice reconstructions are based on modern relationships of local diatom assemblages and summer surface water salinity approximately 15 500 cal yr b p rivers and bogs characterized the study area when sea level reached the 38 to 40 m paleo isobath approximately 9300 cal yr b p the coring site was flooded from 9300 9100 cal yr b p estuarine conditions occurred proximal to the depocenter of fluvially derived material and salinity was 7 8 paleosalinity increased to 11 13 by 7500 cal yr b p following postglacial sea level rise and the southward shift of the siberian coast sharp decreases in diatom accumulation rates total sediment and organic carbon also occurred suggesting the presence of brackish conditions and greater distance between the coast and study site maximum paleosalinity up to 13 was recorded between 7500 and 6000 cal yr b p which was likely caused by the enhanced penetration of atlantic waters to the kara sea stepwise decreases to modern salinity levels happened over the last 6000 cal yr

molecular characterization of suspended and sedimentary organic matter in an arctic delta curie point pyrolysis gas chromatography cupy gc and curie point pyrolysis gas chromatography mass spectrometry cupy gc ms were used to characterize the macromolecular organic content of suspended particles in surface waters at intermediate water depths and in the surface sediments of the lena delta and the adjacent laptev sea eastern siberia the chromatograms of the pyrolysates of the lena river particles revealed several compound classes of biogenic significance polysaccharides phenolic substances and lipid constituents of higher plants the pyrolysates of the surface suspended particles of the laptev sea suggested mixed inputs some fatty acids phytadienes and n alkylnitriles were assigned to planktonic organisms pyrolysis products from terrigenous material encountered in the river were also present at intermediate water depths major differences with respect to the surface particles were evident in all cases we observed a substantial decrease of the precursors of phytadienes and the fatty acids that undergo biotransformation processes a peculiar pattern of three series of c14 c16 and cl8 alkanes and alkenes normal alkane the alki ene the e alk 2 ene and the z alk 2 ene was the prominent feature of these pyrolysates further investigations of the particle solvent extract and the corresponding residue suggested that these alkenes as well as the fatty acids derived from wax esters the composition of the sedimentary material in the laptev sea indicated preservation of the refractory terrigenous constituents however the presence of some algal constituents suggested that a fraction of marine derived macromolecules9 is resistant to degradation the arctic ocean is unique because of its ice cover and limited water exchange with surrounding oceans the marginal seas occupy 70 of this area and their physiography is such that broad shallow continental shelves coincide with the outflow of major rivers arctic environments have been poorly investigated in this respect the role of the arctic ocean and adjacent marginal seas in the global carbon budget has been neglected among other high latitude ecosystems the siberian aquatorium is of interest because of considerable discharge of major world rivers such as the lena yana ob and yenisei the lena river ranked the eighth largest world river discharging to the ocean has an annual water discharge entering the laptev sea of 525 km3 and a sediment discharge of 17 6 x 1 o6 t yr l which corresponds to an

appraisal of tex86 and tex86l thermometries in subpolar and polar regions tex86 tetraether index of tetraethers consisting of 86 carbon atoms is a sea surface temperature sst proxy based on the distribution of archaeal isoprenoid glycerol dialkyl glycerol tetraethers gdgts in this study we appraise the applicability of tex86 and view the mathml sourcetex86l in subpolar and polar regions using surface sediments we present tex86 and view the mathml sourcetex86l data from 160 surface sediment samples collected in the arctic the southern ocean and the north pacific most of the sst estimates derived from both tex86 and view the mathml sourcetex86l are anomalously high in the arctic especially in the vicinity of siberian river mouths and the sea ice margin plausibly due to additional archaeal contributions linked to terrigenous input we found unusual gdgt distributions at five sites in the north pacific high gdgt 0 crenarchaeol and gdgt 2 crenarchaeol ratios at these sites suggest a substantial contribution of methanogenic and or methanotrophic archaea to the sedimentary gdgt pool here apart from these anomalous findings tex86 and view the mathml sourcetex86l values in the surface sediments from the southern ocean and the north pacific do usually vary with overlaying ssts in these regions the sedimentary tex86 sst relationship is similar to the global calibration and the derived temperature estimates agree well with overlaying annual mean ssts at the sites however there is a systematic offset between the regional view the mathml sourcetex86l sst relationships and the global calibration at these sites temperature estimates based on the global view the mathml sourcetex86l calibration are closer to summer ssts than annual mean ssts this finding suggests that in these subpolar settings a regional view the mathml sourcetex86l calibration may be a more suitable equation for temperature reconstruction than the global calibration

constraining lithospheric flow the motion of earth s tectonic plates the lithosphere is driven by the subduction of relatively cold and dense oceanic plates into the mantle the resulting forces drive the motions of continental plates but the manner in which this happens depends on the effective viscosities of the lithosphere and mantle on page 1515 of this issue liu and hasterok 1 discuss a novel method of constraining viscosities of the lithosphere from geophysical data

variability in modern sea surface temperature sea ice and terrigenous input in the sub polar north pacific and bering sea reconstruction from biomarker data in order to study the modern sea surface characteristics of the sub polar north pacific and the bering sea i e sea surface temperature sst and sea ice cover surface sediments recovered during the rv sonne expedition 202 in 2009 were analysed to distinguish between marine and terrestrial organic carbon hydrogen index values long chain n alkanes and specific sterols have been determined the results show that in the bering sea especially on the sea slope the organic carbon source is mainly caused by high primary production in the north pacific on the other hand the organic material originates predominantly from terrestrial higher plants probably related to dust input from asia sst has been reconstructed using the modified alkenone unsaturation index calibration from muller et al 1998 offers the most reliable estimate of mean annual temperature in the central north pacific but does not correlate with mean annual temperature throughout the study area in the eastern north pacific and the bering sea the sikes et al 1997 calibration seems to be more accurate and matches summer sst the distribution of the novel sea ice proxy ip25 highly branched c25 isoprenoid alkene in surface sediments is in accord with the modern spring sea ice edge and shows the potential of this proxy to track past variation in sea ice cover in the study area