organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

pollen and lignin records of late quaternary vegetation lake washington analyses of lignin oxidation products and pollen for an 11 meter core from lake washington provide independent but similar reconstructions of the late quaternary vegetation in the puget lowland an exception is in sediments of the late pleistocene where pollen percentages and influx values suggest conifer forest whereas lignin compositions suggest a treeless source region this dissimilarity appears to result from different major provenances eolian transport of pollen to the lake from adjacent or downstream drainage basins as opposed to fluvial transport of lignified plant debris only from the lake washington drainage basin

biogenic silica record of the lake baikal response to climatic forcing during the brunhes abstract this work presents a detailed orbitally tuned biogenic silica record of continental paleoclimate change during the brunhes chron the brunhes matuyama boundary lies within the warm isotopic stage 19 in baikal and the boundaries between eight lithological cycles correspond to terminations in the marine oxygen isotope record the high amplitude and resolution of climatically driven changes in biosi content in lake baikal sediments permits tuning of almost every precessional cycle during the brunhes and reveals the structure of interglacial stages for example the last three interglacial stages mis 5 7 and 9 clearly consist of five substages a b c d e corresponding to precessional insolation peaks abrupt and intense regional glaciations in siberia during substages 5d and 7d were driven by extreme insolation minima during substage 9d cooling was more gradual in response to more moderate forcing the impact of strong glaciation is also observed in the middle of stage 15 where full glacial conditions appear to have lasted for over 30 000 yr during substages 15d 15c and 15b marine oxygen isotopic stage 11 appears to be the warmest period during the brunhes in the lake baikal record with at least three substages a new hypothesis is presented regarding the response of the lake baikal biosi record to insolation forcing based on the mechanism controlling modern diatom blooms biogenic silica production is hypothesized to be dependent on changes in the heat balance of the lake and consequently on changes in the thermal structure of the water column this mechanism is also sensitive to short term sub milankovich cooling events such as the mid eemian cooling the montaigu event during substage 5c and a cooling which appears to be analogous to the montaigu event during substage 9c the continuity of the lake baikal paleoclimate record its sensitivity to orbital forcing and its high resolution make it an excellent candidate for a new paleoclimatic stratotype section for continental asia

a model for slow motion of natural slopes a new model for describing the slow movement of natural slopes is proposed the geological material in the slope is modeled with a nonhomogeneous bingham constitutive equation this model describes the effect of gravitational consolidation on the material response and allows for a variation of density and yield stress with depth a criterion for shear flow initiation is formulated and the ensuing motion is described velocity profiles for several slip conditions at the interface with the bedrock are given the model is used to predict the observed field behavior of a natural slope villarbeney switzerland key words natural slope incipient shear flow nonhomogeneous bingham law creep flow gravitational consolidation

response of lake baikal ecosystem to climate forcing and pco2 change over the last glacial interglacial transition abstract the 13 c record of total organic carbon in the lake baikal core bdp 93 2 over the last glacial interglacial transition shows remarkable correlation with atmospheric co 2 fluctuations and the negative isotopic shift of 3 5 4 in response to the global increase in paleo p co 2 level with rapid evolution of the lake baikal carbon cycle from full glacial to full interglacial modes however the p co 2 signal in the baikal 13 c sedimentary organic matter is inundated by the basin wide productivity signal in the holocene the baikal diatom abundance record as a paleotemperature proxy lags behind the gisp2 ice core 18 o temperature proxy record by ca 1 ka possibly reflecting the response time of the baikal ecosystem to major climatic transitions there is no lag associated with the pronounced younger dryas cooling however suggesting a different forcing mechanism with a short response time for this abrupt climatic event in continental interior asia the phase difference observed between the diatom abundance and 13 c proxies in lake baikal core bdp 93 2 suggests their independent responses to different forcing mechanisms further justifying their importance for paleoclimate reconstructions from lake baikal records

lignin geochemistry of a late quaternary sediment core from lake washington long term lignin stability and paleovegetation patterns were investigated using cuo oxidation products of sediments from an 11 m core of late quaternary sediment collected from the mid basin of lake washington washington state relatively constant yields of lignin derived phenols normalized to organic carbon from the entire core indicate minimal in situ lignin degradation over the last 13 000 years compositional patterns within the phenolic suite and increased corresponding yields from baseextracted sediments indicate that sedimentary lignins are present predominantly as well preserved plant tissue fragments abundance patterns of vanillyl syringyl and cinnamyl phenols record four distinct sequences within the core characterized by 1 a high concentrations of gymnosperm wood in a basal horizon of glacial flour 11 10 m 2 b an essentially pure mixture of nonwoody angiosperm tissues in late pleistocene sediments 10 8 m 3 c relatively high concentrations of angiosperm woods in the bottom half of a limnic peat sequence deposited approximately 10 000 7 000 years b p 8 4 m and 4 d a progressive enrichment in gymnosperm woods at the expense of angiosperm woods over the last 7 000 years in the upper limnic peat 4 0 m vascular plant tissues account for less than half the total sedimentary organic carbon throughout the core

evidence from lake baikal for siberian glaciation during oxygen isotope substage 5d abstract the paleoclimatic record from bottom sediments of lake baikal eastern siberia reveals new evidence for an abrupt and intense glaciation during the initial part of the last interglacial period isotope substage 5d this glaciation lasted about 12 000 yr from 117 000 to 105 000 yr b p according to correlation with the specmap isotope chronology lithological and biogeochemical evidence of glaciation from lake baikal agrees with evidence for the advance of ice sheet in northwestern siberia during this time period and also with cryogenic features within the strata of kazantzevo soils in southern siberia the severe 5d glaciation in siberia was caused by dramatic cooling due to the decrease in solar insolation as predicted by the model of insolation changes for northern asia according to milankovich theory coupled with western atmospheric transport of moisture from the open areas of northern atlantic and arctic seas which became ice free due to the intense warming during preceeding isotope substage 5e other marine and continental records show evidence for cooling during 5d but not for intense glaciation late pleistocene glaciations in the northern hemisphere may have begun in northwestern siberia

fatty acid geochemistry of a 200 m sediment core from lake biwa japan early diagenesis and paleoenvironmental information abstract fatty acids fas and hydroxy acids dicarboxylic acids and n alkanes were studied in a 200 m sediment core taken from lake biwa japan fas showed bimodal distribution with peaks at c 16 and c 22 c 28 their distribution patterns clearly changed with depth from lower molecular weight c 12 c 19 predominance to higher molecular weight c 20 c 32 predominance in the upper 20 m interval analyses of related compounds and hydroxy acids and dicarboxylic acids suggest that and oxidative degradation of c 12 c 19 fas has occurred in the sediments the ratio of bound c 12 c 19 to unbound fas increases with depth in the upper 0 1 m sediments suggesting that unbound fas are more labile however the ratio varies significantly in deeper sections and may be associated with water temperature in the sediments deeper than 20 m in depth c 12 c 19 fas gradually decrease on the other hand higher molecular weight fas hfas c 20 c 32 which were probably derived from terrestrial plants increase in concentration from 20 m to 100 m suddenly decrease at 100 m and show progressively lower concentration in deeper sediments these fluctuations are interpreted in relation to paleolimnological changes of the lake and the drainage basin hydroxy c 20 c 30 acids and c 20 c 30 dicarboxylic acids show a distribution pattern similar to hfas branched chain fas hydroxy acids and c 9 c 19 dicarboxylic acids show a major peak around 3 15 m in depth this peak is probably caused by increased bacterial activity in the water column and surface sediments in the past which may be associated with an increase in primary production of the lake

ams radiocarbon analyses from lake baikal siberia challanges of dating sediments from a large oligotrophic lake abstract a suite of 146 new accelerator mass spectrometer ams radiocarbon ages provides the first reliable chronology for late quaternary sediments in lake baikal in this large highly oligotrophic lake biogenic and authigenic carbonate are absent and plant macrofossils are extremely rare total organic carbon is therefore the primary material available for dating several problems are associated with the toc ages one is the mixture of carbon sources in toc not all of which are syndepositional in age this problem manifests itself in apparent ages for the sediment surface that are greater than zero however because most of the organic carbon in lake baikal sediments is algal autochthonous in origin this effect is limited to about 1000 500 years which can be corrected at least for young deposits the other major problem with dating lake baikal sediments is the very low carbon contents of glacial age deposits which makes them extremely susceptible to contamination with modern carbon this problem can be minimized by careful sampling and handling procedures the ages show almost an order of magnitude difference in sediment accumulation rates among different sedimentary environments in lake baikal from about 0 04 mm year on isolated banks such as academician ridge to nearly 0 3 mm year in the turbidite depositional areas beneath the deep basin floors such as the central basin the new ams ages clearly indicate that the dramatic increase in diatom productivity in the lake as evidenced by increases in biogenic silica and organic carbon began about 13 ka in contrast to previous estimates of 7 ka for the age of this transition holocene net sedimentation rates may be less than equal to or greater than those in the late pleistocene depending on the site this variability reflects the balance between variable terrigenous sedimentation and increased biogenic sedimentation during interglaciations the ages reported here and the temporal and spatial variation in sedimentation rates that they imply provide opportunities for paleoenvironmental reconstructions at different time scales and resolutions

temporal changes in the phytoplankton community of the southern basin of lake baikal over the last 24 000 years recorded by photosynthetic pigments in a sediment core abstract photosynthetic pigments and other indicators of phytoplankton were analyzed in a dated undisturbed sediment core obtained from the southern basin of lake baikal to reveal temporal changes in the phytoplankton community in the lake through the last glacial post glacial transition the sedimentation age of the core spans the last 24 14c ka chlorophyll a its derivatives carotenoids and total organic carbon toc started to increase after 15 14c ka and the onset of biogenic silica occurred at 10 14c ka this indicated that the post glacial growth of diatoms was preceded by that of other phytoplankton groups in the record of the pigments and toc a temporary decrease was observed in the period 11 5 10 5 14c ka corresponding to the younger dryas cold period the similarity found between the depth profiles of pyropheophytin a and steryl chlorin esters formed through predation of phytoplankton by zooplankton and that of toc suggested the important contribution of fecal pellets to sedimentary organic matter in the lake

lignin phenols in sediments of lake baikal siberia application to paleoenvironmental studies abstract sediments from three cores obtained from distinct depositional environments in lake baikal siberia were analyzed for organic carbon total nitrogen and lignin phenol concentration and composition results were used to examine changes in paleoenvironmental conditions during climatic cycles of the late quaternary c n ratios and organic carbon accumulation rates were significantly higher in the holocene compared with the late pleistocene reflecting overall warmer temperatures and increased runoff during the holocene a holocene maximum in organic carbon was observed at about 6 ka and may represent the warmest wettest period of the holocene at one site academician ridge pronounced late pleistocene maxima in organic carbon and biogenic silica were observed at about 80 85 ka probably indicative of an interstadial period with enhanced aquatic productivity total sedimentary lignin phenol contents were generally lower in the late pleistocene compared to the holocene but with several peaks in concentration during the late pleistocene these late pleistocene peaks in total sedimentary lignin content dated at about 80 50 and 30 ka directly precede or occur during peaks in sedimentary biogenic silica contents these periods likely represent relatively warm interstadial times with increased precipitation producing the observed increase in terrestrial runoff and aquatic productivity lignin phenol ratios s v c v and p v were used to examine changes in terrestrial vegetation type resulting from changes in paleoenvironmental conditions during the late pleistocene a degree of caution must be used in the interpretation of these ratios with regard to vegetation sources and paleoenvironmental conditions because of potential compositional changes in lignin resulting from biodegradation nevertheless results show that long glacial periods were characterized by terrestrial vegetation composed of a mix of non woody angiosperm vegetation and minor gymnosperm forest shorter interstadial periods are defined by a change to dominant gymnosperm forest and were observed at about 80 75 63 50 and 30 ka ranging from about 2 6 kyr in duration these interstadial periods of the late pleistocene defined by lignin phenol ratios generally occur during longer periods of enhanced sedimentary biogenic silica content about 10 15 ka in duration providing corroborative evidence of these warm interstadial periods

permo triassic radiolaria from the semanggol formation northwest peninsular malaysia abstract a total of 32 species of radiolaria were identified from 20 chert samples at eight localities of the semanggol formation in north and south kedah three assemblages of radiolaria were recognised representing the early permian pseudoalbaillella scalprata m rhombothoracata late permian albaillella levis and middle triassic triassocampe deweveri assemblage zone the pseudoalbaillella scalprata m rhombothoracata assemblage zone is discovered from bukit kampung yoi and bukit larek north kedah the albaillella levis assemblage zone is recorded from bukit tok bertanduk north kedah and merbau palas south kedah the triassocampe deweveri assemblage zone is found from the lanjut malau area north kedah the radiolarian assemblages indicate that the age of the chert sequence in the semanggol formation ranges from early permian to middle triassic

lignin geochemistry of north american coastal and continental shelf sediments abstract the concentrations and composition of lignin in coastal and shelf sediments at five locations along the north american continent georges bank north atlantic shelf northwestern gulf of mexico southern california norton sound and nearshore beaufort sea have been characterized using alkaline cuo oxidation lignin concentrations are generally highest at close proximity to the mouth of major rivers indicating that deposition of river borne vascular plant debris is the principal source of lignin to the offshore sediments arctic sediments contain the highest concentrations presumably as a result of an abundant supply of terrestrial organic material and the prevalence of frigid temperatures and surface ice cover during much of the year concentrations are lowest in the georges bank north atlantic sediments where a dynamic physical environment persists over much of the year and the supply of terrestrial organic matter to the offshore in the form of major rivers is lacking stable carbon isotopic compositions show that sediments containing the highest lignin concentrations also contain isotopically lighter organic matter consistent with a terrestrial source input vanillyl syringyl and cinnamyl phenol distributions in these offshore sediments are consistent with primary contributions from gymnosperm predominant and angiosperm woods and secondary contributions from nonwoody tissues these estimates may be subject to some uncertainty due to diagenetic alteration of individual lignin phenols in contrast p hydroxyl phenol yields are not strongly correlated with those of the other lignin derived phenols suggesting generation from both lignin and non lignin sources elevated acid aldehyde ratios relative to undegraded plant tissues suggest that the lignin transported to these offshore sediments has undergone some biodegradative oxidation

biogenic silica accumulation and paleoproductivity in the northern basin of lake baikal during the holocene the effects of the holocene climatic amelioration productivity and preservation on biogenic silica accumulation in the northern basin of lake baikal are evaluated by analyzing biogenic silica organic carbon nitrogen and the stable carbon isotopic composition of organic matter in a 4 m piston core and a companion box core in the early holocene 11 000 8500 yr b p biogenic silica accumulation was low because of low productivity strong oligotrophy and the influx of nutrient limited alpine glacial meltwater in the middle holocene productivity increased significantly during 8500 7000 yr b p but little biogenic silica accumulated in sediments because the dominant primary producer was not diatom flora and because of the relatively higher productivity caused by enhanced terrestrial nutrient influx the highest accumulation rates of biogenic silica were those between 7000 and 4500 yr b p when aquatic productivity increased limnological stratification occurred a mature diatom flora developed in the late holocene the past 4500 yr biogenic silica accumulation decreased because of enhanced recycling and regeneration of silica and a low sedimentation rate

palaeoenvironmental history of lake baikal during the last 23000 years abstract a sediment core recovered from lake baikal was studied in an attempt to elucidate the palaeoenvironmental history of an intra continental lake under the control of last glacial to post glacial climatic fluctuations the lake conditions were characterised by subdued primary production and increased turbidity conditions during the last glacial maximum terrestrial vegetation and the development of soil layers were reduced in the drainage areas the deglaciation suggested by increased terrigenous sand influx and biological productivity took place at around 18 000 yr b p responding to the increased insolation in the northern hemisphere high latitude the onset of wet and warm conditions at ca 12 000 yr b p brought on a maximum of aquatic production and forestal expansion between 7 000 and 6 000 yr b p since 5 000 yr b p enhanced blooming of diatoms has occurred due to an increased nutrient supply and dissolved silica input into the lake

a high resolution palaeoclimatic record for the last 27 500 years in tropical west africa from the carbon and nitrogen isotopic composition of lacustrine organic matter variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of lake bosumtwi ghana reflect climatically induced changes to the lake and the catchment flora cores spanning the last 27 5 kyr of sedimentation in the lake show large oscillations in 13corg pdb and 15norg air the late pleistocene record is particularly detailed showing changes of ca 20 in carbon and ca 10 in nitrogen isotopic compositions these variations are of complex origin although different in magnitude major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the last glacial maximum the allerod younger dryas period also seems to have been marked by generally dry conditions in this part of tropical west africa nitrogen isotopic evidence suggests that during the period 9 2 3 2 kyr the lake had an extremely stable water column probably due to the absence of a windy or cool dry season or both regular circulation of the water column recommenced during the late holocene and has persisted until the present day

continental climate response to orbital forcing from biogenic silica records in lake baikal changes in insolation caused by periodic changes in the earth s orbital parameters provide the primary forcing for global ice ages1 6 but it is not clear to what extent the climates in continental interiors are controlled directly by regional variations in insolation and to what extent they are driven instead by the highly nonlinear response of the oceans and ice sheets here we investigate this question using the record of biogenic silica in lake baikal as a proxy for climate change in this high latitude mid continental region we find a good correlation between this record and that of marine oxygen isotopes4 over the past 250 kyr the baikal record exhibits both a strongly nonlinear component manifested in a 100 kyr periodicity and weaker direct insolation components manifested in the 41 kyr obliquity and 23 and 19 kyr precession orbital cycles these results show that even though extreme continental climates such as this are influenced directly by insolation variations they are dominated by the nonlinear rhythm of the oceans and ice sheets

diagenetic changes of lignin compounds in a more than 0 6 million year old lacustrine sediment lake biwa japan a vertical profile of lignin in the upper 700 m layer of a 1400 m sediment core of lake biwa an oligotrophic freshwater lake in japan was determined using a cuo oxidative degradation method the results indicated that lignin is found throughout the core demonstrating lignin to be very stable for over 0 6 million years moreover the upper 250 m approximately 0 6 million years old segment of the sediment core was investigated to determine the apparent long term degradation rate of lignin a downward lignin concentration decrease is observed over the upper 250 m of the core which corresponds to a calculated half life of at least approximately 40 104 years assuming that lignin decrease is due to its in situ degradation diagenesis

palaeoclimatic changes deduced from 13c 12c and c n ratios of karewa lake sediments india most long palaeoclimatic records based on isotope studies have come from deep sea cores however in order to obtain information on regional climatic variations it is essential to study continental deposits the chief limitation has been the lack of well preserved datable geological records with the exception of cave formations we report here values for the stable carbon isotope ratio 13c 12c and the elemental carbon to nitrogen c n ratio of the organic fraction of the palaeomagnetically and radiometrically dated pleistocene karewa lake sediments from kashmir india together the two ratios which are anticorrelated provide an excellent marker of the source of organic matter in the lake the karewa sediments indicate at least three major episodes of shallower than normal levels these episodes of shallow lake levels and hence a cold dry climatic regime are broadly correctable with deep sea records

lake baikal record of continental climate response to orbital insolation during the past 5 million years the sedimentary record of biogenic silica from lake baikal in south central siberia suggests that this region of central asia was impacted by two major cooling episodes at 2 8 to 2 6 and 1 8 to 1 6 million years ago the spectral evolution of this continental interior site parallels the evolutionary frequency spectra for various marine oxygen isotope records in the baikal record the 41 000 year obliquity cycle is particularly strong from 1 8 to 0 8 million years ago variance in the 100 000 year eccentricity band increases during the past 0 8 million years the expected precession frequency of 23 000 years is highest during the past 400 000 years the modulation of the predicted 23 000 and 41 000 year insolation forcing by the 100 000 and 400 000 year eccentricity bands indicates that the transfer of variance from the precession and obliquity frequencies to the eccentricity part of the spectrum occurred in the eurasian continental interior as well as in tropical and high latitude ocean sites

δ13c analyses of individual lignin phenols in quaternary lake sediments a novel proxy for deciphering past terrestrial vegetation changes this study of the sediments from sacred lake mount kenya demonstrates that 13 c analyses of individual lignin phenols can be used to assess past changes in the proportion of c 3 and c 4 plants within different plant groups in the lake catchment vegetation changes resulting from climatic and atmospheric changes since the last glacial maximum can be deduced from specific lignin phenols lignin a major biopolymer in vascular plants differs from n alkyl lipids in 1 its higher specificity and more quantitative representation of vascular plant input and 2 its major transport mechanism into the sediments by fluvial runoff as opposed to the greater importance of eolian transport for leaf waxes and pollen lignin 13 c data support the hypothesis that atmospheric co 2 concentration is an important factor controlling the vegetation in tropical mountain ecosystems and provide additional insights into past changes in vegetation structure specifically the 13 c values of p coumaric acid indicate the persistence of c 4 grasses during the late glacial when the lake level was lower than today suggesting that aridity also played a role in controlling the abundance of c 4 plants

a 15 000 year stable isotope record from sediments of lake steisslingen southwest germany abstract stable isotope records for carbon and oxygen in bulk carbonates carbon in bulk organic matter and for total and chromium reducible sulfur in a lacustrine sediment core from lake steisslingen southwest germany show several distinct and abrupt shifts during the last 15 000 years variations in the isotopic composition of authigenic carbonates indicate two major phases in the lake history in the pre holocene the hydrological budget of the lake was apparently stable variations of 18 o values of authigenic carbonates were therefore dominantly controlled by temperature changes a decrease in the 18 o carb values of about 2 at the allerod younger dryas transition is interpreted as a drop in mean annual air temperatures of approximately 5 c an abrupt temperature increase of a similar magnitude is inferred at the younger dryas preboreal boundary throughout most of the holocene the isotopic composition of authigenic carbonates was influenced by marked changes in the hydrological budget of the lake a major positive excursion in the 13 c carb and 18 o carb values at the beginning of the atlantic and a smaller one in the preboreal were related to evaporation effects which indicate that dry climatic conditions must have prevailed at that time a simultaneous increase in 13 c values of bulk organic matter at the beginning of the atlantic suggests a high level of productivity in the lake as a consequence aqueous sulfate became limited as indicated by variations in the 34 s values of total and chromium reducible sedimentary sulfur therefore we conclude that the beginning of the atlantic was characterized not only by dry but also by warm climatic conditions which triggered a higher productivity in the lake in the subatlantic sediments large variations in carbon oxygen and sulfur isotope ratios were observed as a result of human activities causing considerable perturbations in the biogeochemical element cycling of lake steisslingen results obtained by the study of the continuous 15 ka record of lake steisslingen document clearly that isotopic proxy data from lacustrine sediments can provide useful information on environmental and climatic changes of local regional and in the case of the younger dryas event of even hemispherical significance

lipid and lignin cutin compounds in lake baikal sediments over the last 37 kyr implications for glacial interglacial palaeoenvironmental change abstract a stratigraphic study of total organic carbon toc concentration carbon isotopic composition of total organic matter tom lipids n alkanes n alkanols n alkanoic acids and sterols and lignin cutin compounds has been conducted for a lake baikal core 323 pc1 over the last glacial interglacial toc concentrations mg g 1 dry sediment are low 2 4 in the glacial sections but high 10 29 in the interglacial ones the concentrations of land plant derived compounds such as n c14 to c28 hydroxyalkanoic acids lignin phenols p hydroxyl vanillyl and syringyl total cutin acids normalized to toc in the interglacial are 5 6 times higher than those in the glacial carbon isotopic compositions of tom are 24 0 9 in the glacial while they are 27 1 3 in the interglacial the heavy isotope composition of tom in the glacial might be due to a contribution from submerged plants and or grasses the light isotopic composition of tom for the interglacial may be due to a contribution from both land plant and phytoplankton mainly diatom derived om autochthonous organic carbon contents were estimated from the c n ratio corrected for the effect of inorganic nitrogen and based on the assumption of c n values of 8 for autochthonous and 25 for allochthonous om the estimation indicates that autochthonous oc comprises 74 6 of toc for the glacial and 72 9 for the interglacial respectively primary palaeoproductivity was estimated to be below 20 gc m 2 y 1 in the glacial before 18 ka but high 100 120 gc m 2 y 1 in the interglacial 11 8 ka which is 10 30 higher than the modern values

identification of unusual 17β h moret 22 29 ene in lake sediments an unusual 17 h moret 22 29 ene in lake sediments was identified for the first time based on the coincidence of its hydrogenation product with 17 h 21 h moretane in terms of mass spectrum and gas chromatographic retention time our survey revealed that 17 h moret 22 29 ene is present in sediments of 4 acid lakes 2 brackish lakes and 4 fresh lakes the abundance of 17 h moret 22 29 ene relative to diploptene is high in acid lakes whereas it is very low or almost absent in the latter two types of lakes this suggests that the formation of 17 h moret 22 29 ene is closely associated with the acidic conditions of these lake environments the dehydration of 17 h 21 h moretan 29 ol is proposed as a possible pathway of formation of 17 h moret 22 29 ene in lake sediments although the proposed precursor has yet to be identified