early diagenesis of terrigenous triterpenoids and its implications for petroleum geochemistry abstract the distribution of triterpanes in sediments and crude oils is commonly used for oil oil and oil source rock correlation in petroleum geochemistry while isomer ratios of such compounds are applied as maturity parameters the triterpane pattern in terrestrially influenced geological samples is however remarkably less diverse than the triterpenoid skeletons occurring in the extant higher plant biosphere natural observations laboratory experiments and molecular mechanics calculations have revealed that acid catalysed double bond isomerization and skeletal rearrangement reactions of terrigenous triterpenoids during early diagenesis are the key to understanding the triterpane patterns in more matured geological materials examples studied in detail are the double bond isomerization of oleanenes and the subsequent hydrogenation of the products into oleanane and 18 oleanane and the transformation of taraxer 14 ene and lup 20 29 ene into oleanenes although the reactions are likely to be kinetically controlled the main products formed and ultimately preserved are the thermodynamically most stable ones the experimental results and natural observations have significant implications for the use of terrigenous triterpenoid compounds in petroleum geochemistry

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

branched aliphatic alkanes with quaternary substituted carbon atoms in modern and ancient geologic samples a pseudohomologous series of branched aliphatic alkanes with a quaternary substituted carbon atom baqcs specifically 2 2 dimethylalkanes and 3 3 and 5 5 diethylalkanes were identified in warm 65 c deep sea hydrothermal waters and late cretaceous black shales 5 5 diethylalkanes were also observed in modern and holocene marine shelf sediments and in shales spanning the last 800 million years of the geological record the carbon number distribution of baqcs indicates a biological origin these compounds were observed but not identified in previous studies of 2 0 billion to 2 2 billion year old metasediments and were commonly misidentified in other sediment samples indicating that baqcs are widespread in the geological record the source organisms of baqcs are unknown but their paleobiogeographic distribution suggests that they have an affinity for sulfides and might be nonphotosynthetic sulfide oxidizers

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

large subglacial lake beneath the laurentide ice sheet inferred from sedimentary sequences subglacial lakes identifi ed beneath the antarctic ice sheet belong to a rare category of unexplored environments on earth s surface the key to understanding the origin and longevity of subglacial lakes is likely contained in their sedimentary sequences here we explore the nature of a sedimentary succession in a deep tectonic trough identifi ed as a prime candidate for a large subglacial paleolake the trough is the 100 km long 620 m deep christie bay located in the east arm of the great slave lake canada high resolution seismic refl ection data and short sediment cores collected in the deep trough show a 150 m thick sequence of fi sedimentary lake fi ll separating glacial ice contact deposits from draped holocene lake sediments we interpret this sequence to consist of sediments that accumulated in a subglacial lake that covered an area larger than 130 km 2 the inferred presence of a subglacial paleolake is supported by results from hydrologic modeling of drainage pathways beneath the laurentide ice sheet during the last glacial maximum our data point toward the existence of a dynamic subglacial lake environment where sediments were delivered by discharge of meltwater from a subglacial water system a core sample of the sedimentary lake fi ll in christie bay may elucidate whether living organisms exist in subglacial lakes

a case of post depositional aerobic degradation of terrestrial organic matter in turbidite deposits from the madeira abyssal plain abstract a set of oxidized and unoxidized sediment intervals from the f turbidite identified in two piston cores from the madeira abyssal plain map was analyzed for calcium carbonate total organic carbon toc total nitrogen tn stable carbon composition of toc 13c toc total hydrolyzable amino acids thaa total neutral sugars tsug lignin phenols lig two different lipid biomarkers of marine phytoplankton origin and vascular plantwax n alkanes and n acids comparison shows changes for all properties depicting the effect of post depositional aerobic oxidation the oxidation process re mineralized approximately 80 of the toc and approximately 60 of the tn in the original deposit and left the residual organic matter depleted in 13c by 1 7 2 9 thaa and tsug account for 10 or less of the toc in all samples leaving approximately 90 of the toc chemically unidentified thaa tsug lig marine phytoplankton biomarkers and plantwax n acids were lost from the oxidized deposit to an extent as great as that for toc two non protein amino acids alanine and aminobutyric acid and plant wax n alkanes displayed much less degradation 9 37 and concentrated 3 3 4 8 times relative to toc by the oxidation process these observations show that both marine and terrestrial components contribute to the re mineralized toc fraction a binary mixing approach was used to model quantitatively the change in 13c toc and plantwax n alkane concentration results suggest that terrestrial organic carbon contributes approximately 15 to the toc content of the original turbidite its abundance increases approximately 2 4 times as a consequence of the oxidation process and approximately 40 and 90 of the terrestrial and marine component of toc in the original turbidite respectively was destroyed by the oxidation process although selective preservation of terrestrial relative to marine organic carbon is a well documented phenomenon in sedimentary processes this study represents the first attempt to assess the sensitivity of terrestrial organic matter to oxidative degradation in a sedimentary environment

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

constraints on the pleistocene chronology of sediments from the lomonosov ridge 1 despite its importance in the global climate system age calibrated marine geologic records reflecting the evolution of glacial cycles through the pleistocene are largely absent from the central arctic ocean this is especially true for sediments older than 200 ka three sites cored during the integrated ocean drilling program s expedition 302 the arctic coring expedition acex provide a 27 m continuous sedimentary section from the lomonosov ridge in the central arctic ocean two key biostratigraphic datums and constraints from the magnetic inclination data are used to anchor the chronology of these sediments back to the base of the cobb mountain subchron 1215 ka beyond 1215 ka two best fitting geomagnetic models are used to investigate the nature of cyclostratigraphic change within this chronology we show that bulk and mineral magnetic properties of the sediments vary on predicted milankovitch frequencies these cyclic variations record glacial and interglacial modes of sediment deposition on the lomonosov ridge as evident in studies of ice rafted debris and stable isotopic and faunal assemblages for the last two glacial cycles and were used to tune the age model potential errors which largely arise from uncertainties in the nature of downhole paleomagnetic variability and the choice of a tuning target are handled by defining an error envelope that is based on the best fitting cyclostratigraphic and geomagnetic solutions

organic carbon carbonate and clay mineral distributions in eastern central arctic ocean surface sediments abstract results from a detailed sedimentological investigation of surface sediments from the eastern arctic ocean indicate that the distribution of different types of sediment facies is controlled by different environmental processes such as sea ice distribution terrigenous sediment supply oceanic currents and surface water productivity in comparison to other open ocean environments total organic carbon contents are high with maximum values in some deep basin areas as well as west and north of svalbard in general the organic carbon fraction is dominated by terrigenous material as indicated by low hydrogen index values and high c n ratios probably transported by currents and or sea ice from the eurasian shelf areas the amount of marine organic carbon is of secondary importance reflecting the low productivity environment described for the modern ice covered arctic ocean in the area north of svalbard some higher amounts of marine organic matter may indicate increased surface water productivity controlled by the inflow of the warm westspitsbergen current wsc into the arctic ocean and reduced sea ice cover this influence of the wsc is also supported by the high content of biogenic carbonate recorded in the yermak plateau area the clay mineral distribution gives information about different source areas and transport mechanisms illite the dominant clay mineral in the eastern central arctic ocean sediments reaches maximum values in the morris jesup rise area and around svalbard indicating north greenland and svalbard to be most probable source areas kaolinite reaches maximum values in the nansen basin east of svalbard and in the barents sea possible source areas are mesozoic sediments in the barents sea and franz josef land in contrast to the high smectite values determined in sea ice samples smectite contents are generally very low in the underlying surface sediments suggesting that the supply by sea ice is not the dominant mechanism for clay accumulation in the studied area of the modern central arctic ocean

sea ice motion as a drunkard s walk observations of sea ice displacement over short periods of time are used to deduce some statistics of the ice motion over long periods of time the objective is to follow the trajectory of a piece of ice starting at a randomly selected time and location and ending when the ice either melts or leaves the arctic basin trajectories are also followed backward in time to the time and location where the piece of ice was formed statistical properties considered are the age and remaining lifetime of ice in various locations and the probability that ice presently occupying a particular location was originally created or will ultimately melt in certain regions possible applications are to the distribution of pollutants by sea ice and to the design of experiments involving drifting measurement platforms

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

sediments in arctic sea ice implications for entrainment transport and release despite the arctic sea ice cover s recognized sensitivity to environmental change the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood sea ice sediment inclusions were studied in the central arctic ocean during the arctic 91 expedition and in the laptev sea east siberian arctic region expedition 1992 results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central arctic ocean this study documents the regional distribution and composition of particle laden ice investigates and evaluates processes by which sediment is incorporated into the ice cover and identifies transport paths and probable depositional centers for the released sediment in april 1992 sea ice in the laptev sea was relatively clean the sediment occasionally observed was distributed diffusely over the entire ice column forming turbid ice observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment in the central arctic ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes the surface sediment accumulation in central arctic multi year sea ice exceeds by far the amounts observed in first year ice from the laptev sea in april 1992 sea ice sediments are generally fine grained although coarse sediments and stones up to 5 cm in diameter are observed component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles the biogenous components namely shells of pelecypods and benthic foraminiferal tests point to a shallow benthic marine source area apparently sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing clay mineralogy of ice rafted sediments provides information on potential source areas a smectite maximum in sea ice sediment samples repeatedly occurred between 81 n and 83 n along the arctic 91 transect indicating a rather stable and narrow smectite rich ice drift stream of the transpolar drift the smectite concentrations are comparable to those found in both laptev sea shelf sediments and anchor ice sediments pointing to this sea as a potential source area for sea ice sediments in the central arctic ocean sea ice clay mineralogy is significantly different from deep sea clay mineral distribution patterns the contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

arctic ice export events and their potential impact on global climate during the late pleistocene 1 ice sheets in the north american arctic and to a lesser extent those in northern eurasia calved large quantities of icebergs that drifted through fram strait into the greenland sea several times during the late pleistocene these icebergs deposited fe oxide grains 45 250 m and coarse lithic clasts 250 m matched to specific circum arctic sources four massive arctic iceberg export events are identified from the laurentide and the innuitian ice sheets between 14 and 34 ka calendar years in a sediment core from fram strait these relatively short duration 1 4 kyr events contain 3 5 times the background levels of fe oxide grains they began suddenly as indicated by a steep rise in the number of grains matched to an ice sheet source suggesting rapid purges of ice through fram strait due perhaps to collapse of ice sheets the larger events from the northwestern laurentide ice sheet are preceded by events from the innuitian ice sheet despite the chronological uncertainties the arctic export events appear to occur prior to heinrich events

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

the influence of oxic degradation on the sedimentary biomarker record ii evidence from arabian sea sediments abstract biomarker accumulation rates in nine different time slices in three cores on and at the foot of a submarine high in the northern arabian sea the murray ridge were measured to investigate the influence of oxygen exposure time on the preservation of biomarker signals in the sedimentary record all three sites experienced the same history of surface water productivity and sediment supply but had different bottom water redox conditions due to their different positions in just below well below relative to the present location of the intense oxygen minimum zone omz past variations in the intensity and position of the omz known from a wide variety of proxies toc content distribution and abundance of planktonic and benthic foraminifera and pteropods trace metals and 15 n enabled specific biomarker i e n alkanes steroids alkenones alkyldiols c 26 fatty acid loliolide biphytane diols and archaeal tetraether lipids accumulation rates at contrasting oxygen exposure times to be compared the results indicate that these accumulation rates can vary by more than an order of magnitude for marine biomarkers in addition there are significant differences in the degree of oxic degradation of different types of biomarkers terrestrial n alkanes are much more resistant than alkenones and n alkyl diols which are more refractory than steroids and biphytane diols these differences in degree of oxic degradation indicate that biomarker distributions will change on increasing exposure to oxygen these findings have a significant impact on the application of biomarkers to sedimentary settings in which oxygen exposure time is likely to change significantly

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

deposition of organic carbon in arctic ocean sediments terrigenous supply vs marine productivity during the arctic 91 expedition with rv polarstern several kastenlot cores were recovered along a profile crossing the eastern part of the arctic ocean in this paper we present results of detailed sedimentological and organic geochemical investigations on three of these cores which have yielded a wide range of data for the interpretation of the flux and type of organic matter in general the high organic carbon content of the sediments is derived from a high input of terrigenous organic matter the variation in content and composition of the organic carbon in the sediments of core ps2174 5 reflect glacial interglacial changes interglacial stages 7 and 5e reveal a low organic carbon content 0 5 and as indicated by high hydrogen indices low c n ratios higher content of n alkanes c 17 and c 19 and a high opal content reflect higher marine productivity during the glacial stages stages 6 upper 5 and 4 organic carbon values are significantly higher 0 7 1 3 low hydrogen indices high c n ratios low short chain n alkanes and low opal contents provide evidence for a higher input of terrigenous organic matter and reduced marine productivity changes in the content and composition of the organic carbon are believed to vary with the fluctuations in sea level and sea ice coverage

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

geomagnetic events and relative palaeointensity variations during the past 300 ka as recorded in kolbeinsey ridge sediments iceland sea indication for a strongly variable geomagnetic field magnetostratigraphic analyses of five sediment cores recovered from the kolbeinsey ridge area revealed consistent records of several geomagnetic events linked with low relative palaeointensities within the past 300 ka interpretation of various rock magnetic parameters clearly rule out the possibility that the recorded non normal polarity directions are linked to a deviating magnetomineralogical fraction or a distorted magnetic fabric therefore these directions are interpreted as true recordings of geomagnetic field variations hysteresis parameters and thermomagnetic measurements revealed pure pseudo single domain psd magnetite with curie temperatures of 580 c as the dominant remanence carrier mineral due to the homogeneity of the rock magnetic parameters the sediments are also suitable for relative palaeointensity determinations oxygen isotope stratigraphies for two of the cores provided a time frame to estimate the age ranges for the recorded geomagnetic field variations the obtained record of ten events of up to 12 ka duration during the past 300 ka and the related record of relative palaeointensity indicate a fairly dynamic character of the earth s magnetic field which is in clear contrast to published polarity time scales

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

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

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

a new paleogeographic configuration of the eurasian landmass resolves a paleomagnetic paradox of the tarim basin china 1 new paleomagnetic data from permian red beds and middle jurassic limestones from the tarim basin pose a paradox their declinations are similar to upper carboniferous to neogene rocks collected from the same sections and their inclinations parallel present values when assuming that lower than expected inclinations in continental sedimentary rocks arise from inclination shallowing effects then the paleolatitudes of all upper carboniferous to present rocks from tarim are indistinguishable local vertical axis block rotations occurring in the last 20 million years explain why declinations vary at different localities in the basin our middle jurassic data positions tarim 23 6 8 4 farther south than that predicted from the coeval reference pole for eurasia however no geologic argument exists to support the closure of a large ocean basin between tarim and siberia since the middle jurassic thus the paradox are the rocks from tarim totally overprinted or is the middle mesozoic part of the reference eurasian apparent polar wander path erroneous several lines of evidence suggest the tarim rocks are not remagnetized we conclude that tarim has experienced little or no apparent polar wander since the carboniferous moreover our middle mesozoic reconstruction of eurasia using the new middle jurassic pole from tarim results in a more geologically compatible solution for the eastern asian blocks over previous reconstructions

transport of terrestrial organic matter to the deep north atlantic ocean by ice rafting abstract total organic carbon toc 13c values of toc 13corg and glycerol dialkyl glycerol tetraethers gdgts were analysed for a sediment core from the north atlantic covering the last 30 kyr to investigate organic matter deposition due to ice rafting toc content was low in sediments representing glacial times 0 2 0 4 and even lower in holocene sediments