the impact of rapid coastline changes and sea level rise on the tides in the bohai sea china 1 the tidal regime in the bohai sea china is investigated using observations and an established numerical tidal model the area has recently experienced rapid coastline changes due to natural developments of the yellow river delta and large scale anthropogenic land reclamation these morphological changes are not reflected in most global bathymetric databases and are thus rarely incorporated into investigations of the bohai sea it is shown that there have indeed been significant changes in the tidal regime in the bohai sea over the last 35 years with m2 amplitudes changing up to 20 cm in some parts the model captures some of these changes when the appropriate bathymetries are used furthermore the simulations show that the tides in the bohai sea have become more sensitive to future sea level rise and the way in which it is implemented in the model i e whether or not flood defenses are included these sensitivity changes are due to the recent coastal developments

on the factors behind large labrador sea tides during the last glacial cycle and the potential implications for heinrich events 1 labrador sea ls tidal elevations over the last glacial cycle are investigated in a near global numerical model that accurately captures the present day tides from 65 ka to 7 ka the modeled elevations at the debouchement point of the hudson strait ice stream in the ls are exceptionally large comparable to the largest elevations seen anywhere in the present day ocean new numerical simulations performed for this article demonstrate that both local changes in basin geometry e g ice cover over hudson bay and changes outside of the ls led to enhanced ls paleotides new simulations run at higher horizontal resolution and a considered examination of uncertainties including uncertainties in the adopted sea level models strengthen confidence in the robustness of the large ls paleotides the tide model is run with both spatially uniform sea level drops taken from curves of eustatic and red sea sea levels versus time and spatially variable sea level maps taken from two different gravitationally self consistent viscoelastic solid earth sea level models which both account for ice sheet geometry the tides are larger when the spatially variable sea level models are used observations in present day antarctica indicate that the mechanical action of tides significantly impacts the dynamics of both continental ice streams and their associated floating ice shelves it is postulated here that large ls paleotides played a key role in the formation of heinrich event icebergs that is massive discharges of ice from the ls into the glacial north atlantic ocean the paleotide calculations described here provide a potential explanation for why the ls region more than any other dominated the production of heinrich event icebergs most previous hypotheses of a tidal role in climate variability and ice sheet dynamics focus on tidal mixing in contrast here the role of tidal mechanical forcing of ice sheets is emphasized

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

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

can we model the effect of observed sea level rise on tides the link between secular changes in the lunar semidiurnal ocean tide m 2 and relative sea level rise is examined based on numerical tidal modeling and the analysis of long term sea level records from europe australia and the north american atlantic coasts the study sets itself apart from previous work by using a 1 12 global tide model that incorporates the effects of self attraction and loading through time step wise spherical harmonic transforms instead of iteration this novel self attraction and loading implementation incurs moderate computational overheads some 50 and facilitates the simulation of shelf sea tides with a global root mean square error of 14 6 cm in depths shallower than 1 000 m to reproduce measured tidal changes in recent decades the model is perturbed with realistic water depth changes compiled from maps of altimetric sea level trends and postglacial crustal rebound the m 2 response to the adopted sea level rise scenarios exhibits peak sensitivities in the north atlantic and many marginal seas with relative magnitudes of 1 5 per century comparisons with a collection of 45 tide gauge records reveals that the model reproduces the sign of the observed amplitude trends in 80 of the cases and captures considerable fractions of the absolute m 2 variability specifically for stations in the gulf of mexico and the chesapeake delaware bay system while measured to model disparities remain large in several key locations such as the european shelf the study is deemed a major step toward credible predictions of secular changes in the main components of the ocean tide

environmental changes since 8 4 ka reflected in the lacustrine core sediments from nam co central tibetan plateau china the tibetan plateau induces and enhances the asian monsoon that influences the plateau itself east china and even the whole of asia pursuing the changing monsoon history and its impact in this environment sensitive area is a key for understanding the climatic changes here we present the initial results from core sed iments in nam co central tibet to elucidate the holocene environment changes in this area the studied lake nam co is the second largest lake with an elevation of 4718 m water area of 2015 km 2 and catchment area of 10 610 km 2 by using echo seismic profiling and hydro echosounding we investigated the bathymetric dis tribution of the whole lake one 332 cm long piston core was successfully taken in the east part of the lake at 60 m water depth twelve ams 14 c dates from top to bottom of this core established a good time sequence toc tn n alkanes grain size clay minerals fe mn sr ba and caco3 content were analysed with sampling intervals from 1 cm to 10 cm results showed that since 8400 yr bp the environment changes in this region indicate three stages the early stage 8400 6900 yr bp was characterized by slight shifting from warm to cold with a cold dry interval at 8100 7800 yr bp the middle stage was from 6900 to 2900 yr bp during which cli mate changed from warm humid to cold dry however around 2900 yr bp the climate once was slightly cold but strongly dry the late stage from 2900 yr bp to present was characterized by a general tendency toward cold dry the first temperature decline was around 1700 1500 yr bp following which temperature increased once before decreasing again around 600 300 yr bp which might be the result of the little ice age

leaf wax lipids as paleovegetational and paleoenvironmental proxies for the chinese loess plateau over the last 170 kyr abstract high resolution records for long chain n alkane and n alkanol biomarkers have been obtained by extraction of sediments from the profiles of luochan 0 36 ka and xunyi 0 170 ka on the chinese loess plateau clp the two records are similar where they overlap over the last 36 ka at xunyi distributions of the n alkane and n alkanol homologues remain relatively constant over the full 170 kyr the n alkanes are characterized by high odd over even carbon number preference and predominance of the c31 n alkane whereas the n alkanols are dominated by even over odd carbon numbers and by the c28 n alkanol an alkane index a i c3l c29 c31 and an alkanol index alc i c30 c28 c30 are both positively related with magnetic susceptibility of the sediment with higher values during interglacials a lipid index l i averaging the normalized alkane and alkanol indices gives a measure of changing vegetation for palaeo environmental construction a further useful index is provided by the 13 c value of the most abundant n alkane c31 after adjustment for the calculated effect of the estimated atmospheric pco2 and precipitation the record of this index over the last 170 kyr which varies from 36 to 32 indicates that the vegetation on the clp has been mainly c3 plants and became even more so in the glacial periods especially mis 6 and 2 as the minor population of warm season grasses c4 favored in interglacial times declined when temperatures fell the lipid distributions and carbon isotope values are in general accord with the pollen and phytolith evidence recorded for the yuan areas of the clp in indicating steppe or meadow steppe vegetation with abundant cold season grasses c3 and some herbs bushes and trees especially in glacial times

a general cooling trend on the central tibetan plateau throughout the holocene recorded by the lake zigetang pollen spectra abstract a 741 cm long laminated sediment core covering the last 10 800 years was collected from lake zigetang central tibetan plateau 90 9 e 32 0 n 4560 m a s l and analysed palynologically at 69 horizons biome reconstruction suggests a dominance of temperate steppe vegetation mainly artemisia and poaceae on the central tibetan plateau during the first half of the holocene 10 8 4 4 cal ka bp while alpine steppes with desert elements mainly cyperaceae poaceae chenopodiaceae and characteristic high alpine herb families tend to dominate the second half 4 4 0 cal ka bp the artemisia cyperaceae ratio a semi quantitative measure for summer temperature indicates a general cooling trend throughout the holocene dense temperate steppe vegetation and maximum desert plant withdrawal however indicate that a suitable balance of wet and warm conditions for optimum vegetation growth likely occurred during the middle holocene 7 3 4 4 cal ka bp severe early holocene cold events have been reconstructed for 8 7 8 3 and 7 4 cal ka bp

millennial scale stratigraphy of a tide dominated incised valley during the last 14 kyr spatial and quantitative reconstruction in the tokyo lowland central japan spatial and quantitative analysis of infilling processes of the tide dominated incised valleys beneath the tokyo lowland during the last 14 kyr was undertaken by using data from 18 sediment cores 467 radiocarbon dates and 6100 borehole logs the post last glacial maximum valley fills consist of braided river meandering river estuary spit and delta systems in ascending order the boundary between the estuary and delta systems is regarded as the maximum flooding surface the maximum flooding surface beneath the tokyo lowland is dated at 8 ka in the arakawa valley and 7 ka in the nakagawa valley this age difference is due to the migration of the tone river from the arakawa valley to the nakagawa valley at 5 ka and suggests that the widely held view that the global initiation of deltas coincided with the abrupt rise of sea level at 9 to 8 ka is true only where there has been steady sediment supply from major rivers the meandering river system is dominated by sheet like sands that were deposited during lateral migration of channels during the younger dryas and isolated vertical sands within muds that reflect vertical aggradation of channels before and after the younger dryas the transition between these channel geometries is controlled by a threshold sea level rise of 4 to 7 mm yr 1 before migration of the tone river at 5 ka the tide dominated bay in the nakagawa valley was filled by upward fining laterally accreting muds the muds accreted from the margin to the axis of the bay such lateral accretion of suspended particles derived from outside the bay has been documented in other tide dominated coastal environments and is probably common in other similar settings after the migration of the tone river the bay was filled by upward coarsening deltaic sediments

a pollen record of holocene climatic changes from the dunde ice cap qinghai tibetan plateau pollen preserved in ice cores from the dunde ice cap provides a sensitive record of holocene climatic changes and vegetational response in the northern qinghai tibetan plateau at time scales ranging from millennia to centuries and decades pollen analysis of the annually resolvable ice layers for a 30 yr period 1957 1986 suggests that total pollen concentration is correlated positively with summer precipitation and negatively with summer temperature thus it is a sensitive indicator of moisture availability and vegetation density in the steppe and desert regions around dunde high pollen concentrations between 10 000 and 4800 yr b p suggest that the summer monsoon probably extended beyond its present limit to reach dunde and westernmost tibet in response to orbital forcing the summer monsoon retreated time transgressively across the qinghai tibetan plateau during the middle holocene relatively humid periods occurred at 2700 2200 1500 800 and 600 80 yr b p probably as a result of neoglacial cooling prominent pollen changes during the medieval warm period 790 620 yr b p and the little ice age 330 80 yr b p suggest that the vegetation in the qinghai tibetan plateau region is sensitive to abrupt century scale climatic changes such as those anticipated in scenarios of greenhouse warming

extent and spatial distribution of pleistocene glaciations in eastern tibet as a contribution to the controversial discussion regarding the nature and extent of the pleistocene glaciation on the tibetan plateau additional observations and results were obtained during several chinese german joint expeditions in the investigation area of the eastern and central tibetan plateau it will be shown that the maximum extent of the last glaciation was limited to the glaciation of isolated mountain groups or smaller plateau glaciations these glaciations are characterized by glacial erosional features such as u shaped valleys in the inner mountain massifs and cirques in the higher summit areas accumulation forms such as terminal and lateral moraines less common than basal moraines are marked by granitic and basaltic erratics using two examples from the eastern margin of the tibetan plateau nianbaoyeze shan and northern chola shan the extent of pleistocene glaciations can be mapped by the distribution of terminal and lateral moraines and erratic granite boulders on the slopes of the surrounding schists two to three main pleistocene glaciations can be separated using weathering criteria paleosols and the overlying stratum on the moraines and associated terrace sequences overlying stratum consist of aeolian sandy silt or solifluction debris the younger moraines are found to be characterized by large erratics were therefore named big boulder moraine and can be found over the investigated area the ice free areas are characterized by pleistocene terraces along the main rivers loess deposits with sand and ice wedges at higher elevations e g the basin of zoige and paleosols in the basins below 3500 m a s l e g aba basin or garze basin the hypothesis of an extensive plateau glaciation could not be verified for this region a rising snowline equilibrium line altitudes elas is revealed in two cross sections during the last glacial maximum lgm at the eastern and northern margin of the tibetan plateau snowlines migrated from about 4000 m in the east minshan to 4300 m in the nianbaoyeze and to about 4700 m in the west bayan har shan a rise was also recorded from about 3800 m in the north central qilian shan up to a range of 4300 4950 m different exposures in the kunlun shan to approximately 5200 m in the tanggula shan in the center of the tibetan plateau the general increase of modern and lgm snowlines or elas towards the plateau corresponds with a decrease of precipitation from east to west and from north to south respectively precipitation was more pronounced at the eastern margin during glacial times than compared to present

numerical modeling of the global semidiurnal tide in the present day and in the last glacial maximum 1 a hydrodynamic model incorporating a self consistent treatment of ocean self attraction and loading sal and a physically based parameterization of internal tide it drag is used to assess how accurately barotropic tides can be modeled without benefit of data and to explore tidal energetics in the last glacial maximum lgm m2 solutions computed at high resolution with present day bathymetry agree with estimates of elevations from satellite altimetry within 5 cm rms in the open ocean this accuracy and agreement with atlimetric estimates of energy dissipation are achieved only when sal and it drag are included in the model solutions are sensitive to perturbations to bathymetry and inaccuracies in available global databases probably account for much of the remaining error in modeled elevations the 100 m drop in sea level during the lgm results in significant changes in modeled m2 tides with some amplitudes in the north atlantic increasing by factors of 2 or more dissipation is also significantly changed by the drop in sea level if it drag estimated for the modern ocean is assumed dissipation increases by about 50 globally and almost triples in the deep ocean however it drag depends on ocean stratification which is poorly known for the lgm tests with modified it drag suggest that the tendency to a global increase in dissipation is a robust result but details are sensitive to stratification significant uncertainties about paleotides thus remain even in this comparatively simple case where bathymetry is well constrained

sensitivity of palaeotidal models of the northwest european shelf seas to glacial isostatic adjustment since the last glacial maximum abstract the spatial and temporal distribution of relative sea level change over the northwest european shelf seas has varied considerably since the last glacial maximum due to eustatic sea level rise and a complex isostatic response to deglaciation of both near and far field ice sheets because of the complex pattern of relative sea level changes the region is an ideal focus for modelling the impact of significant sea level change on shelf sea tidal dynamics changes in tidal dynamics influence tidal range the location of tidal mixing fronts dissipation of tidal energy shelf sea biogeochemistry and sediment transport pathways significant advancements in glacial isostatic adjustment gia modelling of the region have been made in recent years and earlier palaeotidal models of the northwest european shelf seas were developed using output from less well constrained gia models as input to generate palaeobathymetric grids we use the most up to date and well constrained gia model for the region as palaeotopographic input for a new high resolution three dimensional tidal model roms of the northwest european shelf seas with focus on model output for 1 ka time slices from the last glacial maximum taken as being 21 ka bp to present day we demonstrate that spatial and temporal changes in simulated tidal dynamics are very sensitive to relative sea level distribution the new high resolution palaeotidal model is considered a significant improvement on previous depth averaged palaeotidal models in particular where the outputs are to be used in sediment transport studies where consideration of the near bed stress is critical and for constraining sea level index points

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

vertical tectonic crustal movements along the japanese coastlines inferred from late quaternary and recent relative sea level changes abstract observed relative sea level rsl changes during the past 130 kyr make it possible to evaluate the vertical crustal movement due to several tectonic processes such as the subduction of oceanic plates here we infer average rates of tectonic crustal movement along the japanese coastlines on three typical timescales of 50 yr 6 kyr and 125 kyr based on tide gauge and holocene rsl observations and the altitudes of marine terraces formed at the last interglacial lig phase at 125 ka the rates on a timescale of 50 yr are derived from tide gauge data thermosteric sea level changes due to thermal expansion of the oceans and predictions due to the glacio hydro isostatic adjustment gia for the last deglaciation and also recent melting of the mountain glaciers and greenland and antarctic ice sheets those for 6 kyr and 125 kyr are based on the rsl observations and the predictions by gia modelling considering uncertainties for temporal changes in eustatic sea level for the mid to late holocene and lig phase the inferred rates for 50 yr are significantly different from those for 125 kyr in most sites particularly for sites along the coastline from eastern hokkaido to northeastern japan shikoku and south kyushu facing the pacific ocean in these regions the rates for 125 kyr and 50 yr are positive uplift and negative subsidence respectively also the observed rsl changes at 6 ka are consistent with the inferred rsl changes using the rates for 125 kyr and gia predictions in many sites but inconsistent with those for 50 yr in most sites except for a few sites these results suggest that the rates on a timescale of 50 yr are not representative of the tectonic crustal movements for timescales longer than 6 kyr in most sites along the japanese coastlines however the inferred rates on these timescales may be useful in discussing the recurrence of megathrust earthquake with its interval of 1 kyr such as the 2011 earthquake off the pacific coast of tohoku

paleoclimate changes of the last 1000 yr on the eastern qinghai tibetan plateau recorded by elemental isotopic and molecular organic matter proxies in sediment from glacial lake ximencuo abstract total organic carbon corg and nitrogen ntot concentrations and isotope compositions and n alkane and n alkan ol molecular biomarker compositions were measured in two parallel sediment cores from lake ximencuo a typical glacial lake on the eastern qinghai tibetan plateau qtp to reconstruct local climatic variations during the past 1000 yr concentrations of corg and ntot vary similarly with changes in precipitation recorded by tree rings in dulan northeastern qtp indicating their close relation to precipitation carbon preference index cpi values of c22 c33 n alkanes and c22 c28 n alkan 1 ols and average chain length acl values of c27 c33 n alkanes generally negatively correlate with 13corg and 15ntot and also vary comparably with the oxygen isotope temperature record from the dunde ice core northeastern qtp these patterns indicate that high cpi values and negative shifts of the 13corg and 15ntot correspond to warmer conditions that favor the growth of vascular land plants and that lower values and positive shifts correspond to cooler conditions in the lake ximencuo locality this observation contradicts previous interpretations from peat and modern soil studies that conclude that the cpi indices were controlled by microbial degradation under different climate conditions here we propose that the changes of organic matter sources under different climate regimes combined with physiological adjustments of vascular plants to different air temperatures might yield different cpi responses to climate changes in glacial plateau lakes air temperature and precipitation increases and decreases reconstructed in this 1000 yr study were generally independent of each other but they both occurred at centennial or multi centennial scales the interaction between subtropical asian monsoon and mid latitude westerly atmospheric circulation systems probably dominated the local precipitation variations in the lake ximencuo catchment whereas solar insolation volcanism and greenhouse gas variations were likely responsible for the air temperature changes that are recorded in the lake sediments and that are consistent with regional temperature variations in the eastern qtp

tidal evolution of the northwest european shelf seas from the last glacial maximum to the present 1 two dimensional paleotidal simulations have been undertaken to investigate tidal and tide dependent changes tidal amplitudes tidal current velocities seasonal stratification peak bed stress vectors that have occurred in the nw european shelf seas during the last 20 ka the simulations test the effect of shelf wide isostatic changes of sea level by incorporating results from two different crustal rebound models and the effect of the ocean tide variability by setting open boundary values either fixed to the present state or variable according to the results of a global paleotidal model the use of the different crustal rebound models does not affect the overall changes in tidal patterns but the timing of the changes is sensitive to the local isostatic effects that differ between the models the incorporation of ocean tide changes greatly augments the amplitude of tides and tidal currents in the celtic and malin seas before 10 ka bp and has a large impact on the distribution of seasonally stratified conditions magnitude of peak bed stress vectors and tidal dissipation in the shelf seas the predictions on seasonal stratification are supported by well dated evidence on tidal mixing front migration in the celtic sea additional experiments using the global model suggest that the variability of offshore tides has been caused mainly by changes of eustatic sea level and ice sheet extent in particular a large decrease observed at 10 8 ka bp is attributed to the opening of hudson strait accompanied by the retreat of the laurentide ice sheet

organic geochemical records from lake malawi east africa of the last 700years part ii biomarker evidence for recent changes in primary productivity abstract relatively few well dated and high resolution paleoclimate records of the past few centuries presently exist from tropical east africa here we examine the bulk and molecular geochemical records of two varved sediment cores from lake malawi which together provide a continuous record of environmental variability in east africa of the last 730 years we observe a number of changes in the aquatic ecosystem of lake malawi which are likely attributed to both natural climatic forcing and anthropogenic activities biomarkers of dinoflagellates dinosterol and bacterivorous ciliates tetrahymanol display increased accumulation rates from 1900 ad to the present while a simultaneous decrease in accumulation rates of diatom biomarkers isololiolide loliolide is observed increased accumulation rates of retene a compound derived from conifers are also noted since 1930 ad and likely reflect increased soil erosion due to deforestation of the lake malawi watershed spectral analysis of the high resolution toc record indicates a periodicity of 204 years similar to the 206 year cycle noted in 14c and 10be records suggesting a link between east african climate and solar forcing

tidal mixing and the meridional overturning circulation from the last glacial maximum 1 using a global tidal model it is shown that the supply of tidal energy to the deep ocean was larger during the last glacial maximum lgm 18 000 22 000 years bp the results were used to modify the rate of vertical mixing in a coupled ocean atmosphere model set up for the present and lgm oceans the increased levels of mechanical energy during the lgm were countered by a fresher upper north atlantic which led to a reduced circulation and deep water formation in spite of a trebling of the implicit mixing energy this identifies the significance of accurately representing vertical mixing in climate models to estimate the recovery time scales and timings of rapid catastrophic paleoceanographic events from the estimated levels of implicit energy in the vertical mixing scheme an amendment to diffusivity based mixing schemes is suggested

high resolution numerical modeling of tides in the western atlantic gulf of mexico and caribbean sea during the holocene 1 tidal constituents and datums are computed on a high resolution grid of the northwestern atlantic ocean including the gulf of mexico and the caribbean sea a global model is used to determine tidal parameters on a grid with a nominal resolution of 800 800 the global model includes self attraction and loading drag in shallow marginal seas and internal tide drag in the deep ocean simulations are performed at 1000 year intervals during the holocene 10 000 calibrated years before present 10 ka in combination with changes in bathymetry and coastline location derived from a glacial isostatic adjustment model the global model results are then used to force a regional barotropic tidal model the regional model uses an unstructured finite element grid with very high resolution at the coastline the model results reveal significant variations in tidal constituent amplitudes throughout the holocene in the northwestern atlantic semi diurnal components show a strong amplification at around 9 ka while in the gulf of mexico the response is much more muted variations in diurnal tidal parameters are found to be less significant than semi diurnal parameters throughout the model domain changes in tidal range of great relevance to changes in relative sea level rsl are also investigated throughout the holocene the overall structure is similar to the patterns observed in the m2 tide with peak increases of 200 300 relative to present day being observed along the east coast of the united states from 9 to 8 ka finally the high spatial resolution of the regional model allows for the investigation of tidal changes at spatial scales e g individual bays much smaller than in previous studies

tides and tidal torques of the world ocean since the last glacial maximum peltier s 1994 paleobathymetries are used to investigate tides and corresponding balances of torques of the world ocean since the last glacial maximum 21 000 years before present simulations with a numerical tidal model point out that variable ice loads at the earth s surface and rearrangements in the interior led to considerable modifications of the resonance behavior of the oceans associated evident changes of the tidal range were not confined to the vicinity of formerly ice covered areas in contrast to the tidal oscillation system that was subject to almost uniform changes since the beginning of ice retreat the dissipation rate of the m2 tide increased distinctly during the principal melting time from 15 to 8 kyr b p and reached a local extreme eight thousand years ago though surface and volume of the world ocean were already very similar to present conditions postglacial deformations during the following two thousand years caused the decrease of tidal dissipation from the maximum value to the present day level indicating the sensibility of tidal torques and dissipation rates to comparatively small variations of ocean s geometry since the vicinity of the tidal oscillation system to a resonance situation is more decisive with respect to total dissipation than the extension of shelves where most of the tidal dissipation is expected to take place states of extreme dissipation rates do not necessarily coincide with extreme bathymetric conditions

difference in timing of maximum flooding in two adjacent lowlands in the tokyo area caused by the difference in sediment supply rate abstract the arakawa incised valley fill beneath the tokyo area japan has formed by delta progradation during holocene transgression and highstand this paper presents the integrated stratigraphy of this valley fill as deduced from three continuous sediment cores with rich radiocarbon age control and abundant data from the surrounding and compares the filling history with the adjacent nakagawa valley six depositional units make up the valley fill distinguished based on sedimentary facies in a sequence stratigraphic framework these units span from lowstand fluvial deposits latest pleistocene through retrogradational to transgressive marine deposits early and middle holocene to highstand fluvio deltaic deposits middle and late holocene the isochron and stacking pattern of sedimentary facies indicate that around 8 cal ka bp the shoreline trajectory flipped from landwards to seawards and maximum flooding occurred in the arakawa valley this is considerably earlier than in the neighboring nakagawa valley where this happened between 7 and 6 cal ka bp differences in the sediment supply at the time of transgression explain the diachronicity the findings identify the tone river which was at that time feeding the arakawa valley as a system of very large sediment supply compared to average rivers worldwide

late holocene climatic and environmental changes in arid central asia abstract late holocene climate and environmental changes in arid central asia were analyzed using various paleoclimate archives such as ice cores tree rings lake sediments historical documents glacial fluctuations and archeological data over the last 2000 years arid central asia witnessed three humid periods from ad 0 410 650 890 and 1500 1820s dry periods occurred in 420 660 and in 900 1510s concerning temperature the most striking features are the existence of the medieval warm period mwp and the little ice age lia the mwp was recorded in the 9 12th centuries and was accompanied by an anomalously dry climate whereas the lia extended from the 15 18th centuries and was accompanied by pluvial conditions temperature and precipitation show significantly negative correlations on annual decadal and centennial timescales temperature was generally above average when dry climate conditions predominated on decadal to centennial timescales during the last 1000 years the coldest decades of the last millennium the period 1630 1650s matched with an anomalously wet episode the combination of paleoclimatic evidence clearly suggests that the combination of cold and wet climate condition during the lia was responsible for the strong glacial advances in several mountain systems of central asia

a lateglacial and holocene lake record from the nianbaoyeze mountains and inferences of lake glacier and climate evolution on the eastern tibetan plateau abstract our 12 81 m long record from lake ximencuo provides insight into the lateglacial and holocene evolution of the lake and the nianbaoyeze glacier in its catchment and the regional climate history since 19 kyr lake ximencuo was a permanent deep lake throughout its history in contrast to numerous lakes on the tibetan plateau which experienced shallow lake levels or even desiccation during the lateglacial lake ximencuo was fed by large quantities of meltwater in the lateglacial the existence of glaciated upper catchment areas is apparently a prerequisite for lakes on the tibetan plateau which maintained relatively high water levels during the generally cold and dry periods following the global lgm 21 kyr a minor re advance of the nianbaoyeze glacier was recorded coeval with the greenland stadial 2a 16 4 and 14 5 kyr followed by rapid warming apparently synchronous with the greenland interstadial 1 warmest conditions were recorded at lake ximencuo during the early holocene which was punctured by a remarkable pulse of climate deterioration around 8 3 kyr this spell represents probably the 8 2 kyr event of the north atlantic region suggesting that it had a significant impact on the tibetan plateau colder conditions of longer duration occurred from 4 7 to 3 7 kyr apparently in phase with numerous records signalling colder and drier conditions on the tibetan plateau two minor spells of colder conditions and probably catchment erosion were recorded in the late holocene between 2 0 and 1 4 kyr and between 0 5 and 0 1 kyr with the latter representing the little ice age it is unclear whether human activities may have accelerated or even solely triggered the late holocene erosion events

an early holocene sea level jump and delta initiation 1 early holocene sea level change controlled the evolution of clastic coastal depositional systems radiocarbon dated borehole cores obtained from three incised valley fill systems in asia changjiang song hong and kiso river record very similar depositional histories especially between about 9000 and 8500 cal bp sedimentary facies changes from estuarine sand and mud to shelf or prodelta mud suggest that the marine influence in the incised valleys increased during this period in addition large decreases in sediment accumulation rates occurred a sea level jump causes an estuarine system and its depocenter to move rapidly landward it is possible that the final collapse of the laurentide ice sheet accompanied by catastrophic drainage of glacial lakes at approximately 8500 cal bp caused such a jump the jump was followed immediately by a period of decelerated sea level rise that promoted delta initiation

space geodesy constrains ice age terminal deglaciation the global ice 6g_c vm5a model a new model of the last deglaciation event of the late quaternary ice age is here described and denoted as ice 6g c vm5a it differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available global positioning system gps measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal additional space geodetic constraints have also been applied to specify the reference frame within which the gps data are described the focus of the paper is upon the three main regions of last glacial maximum ice cover namely north america northwestern europe eurasia and antarctica although greenland and the british isles will also be included if peripherally in the discussion in each of the three major regions the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the gravity recovery and climate experiment satellites as an independent means of verifying the improvement of the model achieved by applying the gps constraints several aspects of the global characteristics of this new model are also discussed including the nature of relative sea level history predictions at far field locations in particular the caribbean island of barbados from which especially high quality records of postglacial sea level change are available but which records were not employed in the development of the model although ice 6g c vm5a is a significant improvement insofar as the most recently available gps observations are concerned comparison of model predictions with such far field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

lipid biomarker δ13c and plant macrofossil stratigraphy of a scottish montane peat bog over the last two millennia abstract seven horizons of a peat core covering the last 2000 years from moine mhor a blanket bog in the cairngorm mountains scotland have been examined for the carbon number distributions of the long chain hydrocarbon alcohol and acid components using gas chromatography gc and gas chromatography mass spectrometry gc ms compound specific 13 c values for individual n alkanes were obtained using gas chromatography isotope ratio mass spectrometry gc irms the lipid biomarker distributions and the 13 c values have been compared with those of eleven species of living plant dominant at the contemporary surface of the bog the observed lipid stratigraphy shows only partial agreement with that calculated using macrofossil abundance data and the lipid distributions for the living taxa a result which reflects the inherent uncertainties in both the lipid biomarker and the macrofossil approaches to palaeoenvironmental stratigraphy the carbon isotope values for the individual n alkanes of the plants 27 6 to 36 6 and of the peat layers 29 to 31 7 are as expected for the c 3 photosynthetic pathway however the n alkanes from the surface samples were more depleted by 2 in 13 c than those from the rest of the core a negative shift which may in part reflect the shift 1 2 in 13 c estimated for co 2 in a pre industrialised to an industrialised atmosphere

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

tropicana translated a foreland thrust system imbricate fan setting for c 2520 ma orogenic gold mineralization at the northern margin of the albany fraser orogen western australia

numerical simulation of mid holocene tidal regime and storm tide inundation in the south yangtze coastal plain east china abstract coastal flooding is reported as one of the major causes for the interruptions of neolithic cultures inhabiting the south yangtze coastal plain china during the middle holocene the archaeologically sterile transgressive sedimentary layers could be the results of extreme events or relative sea level rise induced by the enlargement of the local tidal range or global regional sea level rise to clarify the mechanism of the transgressive deposits at typical neolithic sites and the termination of neolithic liangzhu culture in the south yangtze coastal plain this study reconstructed the paleo topography at 7 6 6 4 and 4 5 cal ka bp on the basis of a database including 107 sediment cores and 644 radiocarbon ages and simulated the paleo tidal regimes and the inundation areas induced by typhoon events under the paleo topography and sea levels using a hydrodynamic model of high resolution changjiang estuary finite volume community ocean model ce fvcom the simulation results of tidal regimes showed that the tidal amplitude increased from 1 6 m to 2 2 m in the head of hangzhou bay induced by the paleo topographic change during the period 7 6 4 5 cal ka bp by contrast it reduced from 1 6 m to 1 0 1 2 m in the ningbo plain southeast of the bay which was unable to explain the long lasting marine inundation there and supported our previous assumption of an event of abrupt sea level rise at 4 5 4 4 cal ka bp simulation of the storm induced inundation further suggested that coastal flooding mainly occurred along the coastline of the taihu plain under the combined effect of tidal amplification and typhoon events at 4 5 cal ka bp while the inundation almost covered half of the taihu plain if all factors including tidal amplification extreme event and the abrupt sea level rise were considered we therefore suggest that the obvious increase in flood risk under the backdrop of sea level rise was a major cause for the abandonment of the liangzhu culture in the south yangtze coastal plain at around 4 4 cal ka bp

high resolution record of paleoclimate since the little ice age from the tibetan ice cores climate changes during the little ice age were studied based on oxygen isotope values 18o measured from ice cores recovered on and nearby the qinghai tibetan plateau three cold periods have been identified and are supported by three widely existing moraine ridges formed during the little ice age importantly the amplitude of the three cold periods differ in the cores studied in the dunde ice core the coldest period occurred in the 17th century while it occurred in the 19th century in the guliya ice core all the ice cores recovered from the tibetan plateau and nearby regions show strong climatic warming in the 20th century

n alkan 2 one distributions in a northeastern china peat core spanning the last 16 kyr abstract most research on long chain methyl ketones has focused on their origins and distributions their application in paleoclimate studies is less common than that of other n alkyl lipids the goal of this research was to explore this potential by studying n alkan 2 ones from the hani peat sequence in northeastern china they were identified using gas chromatography mass spectrometry gc ms and showed a distribution ranging from c 19 to c 31 with a strong odd even predominance this type of distribution is considered to derive from sphagum and microbial oxidation of n alkanes comparison with climate sensitive indicators and macrofossil analysis shows that microbial oxidation of n alkanes derived from higher plants was enhanced during the warm early holocene period this led us to develop three n alkan 2 one proxies c 27 c 23 31 c 27 hmw ket carbon preference index cpi h ket and average chain length acl 27 31 ket as possible indicators of paleoclimate in the peat forming environment these proxies in combination with c 27 n alkane d values and peat cellulose 18 o records might allow examination of paleo ecosystem behavior during climatic evolution in northeastern china over the past 16 000 yr

beware intercepts interpreting compositional ratios in multi component sediments and sedimentary rocks the corganic ntotal ratio and the hydrogen index hi are commonly used to describe the bulk composition the sources and the post depositional alteration of sedimentary organic matter data from modern sediments and sedimentary rocks frequently show significant intercepts and strong linear relationships in plots of corganic vs ntotal and of s2 vs corganic for many different data sets demonstrating that the ratios are not constant across the range of organic matter contents the presence of such intercepts whose causes are well understood means that changes in corganic ntotal and hi as corganic changes cannot be used to infer different organic matter sources and or post depositional alteration or degrees of organic matter preservation of different sediment fractions moreover the strong linear regressions in such x y plots imply that the organic fraction of sediments and sedimentary rocks in any given setting or stratigraphic section generally has a uniform composition

stepwise accelerations in the rate of sea level rise in the area north of tokyo bay during the early holocene abstract tokyo bay is situated near the triple junction of the north america pacific and philippine sea plates where relative sea level changes since the last glacial maximum lgm have been strongly affected by subduction tectonics in this study 55 sea level index points were extracted from the post lgm incised valley fills beneath the lowlands north of tokyo bay and used to construct a detailed relative sea level curve for the early holocene sea level jumps were detected at 10 1 10 0 9 2 9 1 and 8 9 8 7 ka each of 2 7 m and each followed by an acceleration in the rate of sea level rise these paired phenomena are attributed to coseismic subsidence and an interseismic decrease in the rate of uplift respectively the early holocene sea level changes in tokyo bay are characterized by remarkably short sea level jumps of

holocene environmental and climatic changes inferred from wulungu lake in northern xinjiang china abstract sedimentological geochemical and palynological data from wulungu lake in northern xinjiang china are used to reconstruct environmental and climate changes since 9550 cal yr bp high abundance of sparganium and poaceae low md median diameter and 13 c organic values indicate aridity between 9550 and 6730 cal yr bp high md and 13 c organic values and the prevalence of desert steppe and steppe vegetation between 4200 and 560 cal yr bp indicate that effective moisture increased after 6730 cal yr bp peaking at 4200 and 560 cal yr bp low md values a negative excursion of 13 c org and the transition from steppe to desert vegetation since 560 cal yr bp reflect a decrease in effective moisture during the latest holocene late holocene human activities were indicated by sharp increase in the abundance of pediastrum then variations in carbonate contents indicate that temperature was generally high between 9550 and 7740 cal yr bp low between 7740 and 6730 cal yr bp intermediate between 6730 and 560 cal yr bp and low during the last 560 yr regional comparison indicates that the asian monsoon did not extend to wulungu lake and westerlies were the main factor in determining the moisture availability during the holocene

late pleistocene changes of tidal amplitude and phase in osaka bay japan reconstructed from fossil records and numerical model calculations abstract calculations with a numerical model of the seto inland sea tides show that sea level changes cause strong changes in the tidal range and pattern of diurnal inequality in osaka bay a higher sea level produces a stronger diurnal inequality and a smaller tidal range a lower sea level produces a weaker diurnal inequality and a larger tidal range the best fit between the calculated tidal patterns and the tidal pattern that is reconstructed from the growth structures of fossils from the last interglacial is achieved with a sea level approximately 15 20 m lower than present for a such sea level and tidal pattern the numerical calculation gives a tidal range of about 2 65 2 8 m in osaka bay

glacial interglacial environmental changes inferred from molecular and compound specific δ13c analyses of sediments from sacred lake mt kenya abstract molecular stratigraphic analyses including lipid distributions and compound specific 13c measurements have been performed at 15 levels in a sediment core from sacred lake mt kenya a high altitude 2350 m a s l freshwater lake with a record extending from the last glacial 40 000 cal yr bp through the present interglacial terrestrial and aquatic organic matter sources were independently assessed using source specific biomarkers 13c values of long chain n alkyl lipids from terrestrial higher plants exhibit large glacial to interglacial shifts those from the last glacial maximum lgm 20 to 18 indicate a terrestrial vegetation dominated by c4 grasses or sedges whereas those from the early holocene 34 to 27 reflect recolonization of the catchment area by c3 plants consistent with a rapid rise in the upper treeline specific algal biomarkers including five unsaturated hydrocarbons of novel structure ascribed to the microalga botryococcus braunii were abundant as confirmed by scanning electronic microscopy sem an extreme 13c shift of over 25 is displayed by the algal biomarkers an elevated value of 5 1 at the last glacial maximum lgm contrasting with a minimum value of 30 3 at the beginning of the holocene a major change in the molecular distributions of the algal biomarkers parallels this large 13c shift with acyclic isoprenoid hydrocarbons dominating the last glacial and cyclic isoprenoid hydrocarbons the holocene the low atmospheric partial pressure of co2 pco2 at the lgm would favour photosynthetic organisms possessing co2 concentrating mechanisms including terrestrial c4 grasses and freshwater green algae hence glacial interglacial changes in pco2 and in the co2 o2 ratio in particular had a significant impact on both terrestrial and aquatic ecosystems on mt kenya in addition to the effects of climate and local environmental factors

lipids of aquatic organisms as potential contributors to lacustrine sediments ii abstract the relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments previously examined for n alkanols and steroids is now reported for hydrocarbons ketones and carboxylic acids the n c7 alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment bacterial biomarkers including hopenes and i ai branched fatty acids were detected in the photosynthetic bacterial layer occurring just above the sediment water interface within the sediment the apparent conversion of free n alkanes alkan 2 ones and hydroxy acids to the corresponding bound form is noted microbiological oxidation of n alkanes to alkan 2 ones is supported by the detection of the intermediate alkan 2 ols with a distribution similar to that of the ketones the geochemistry of sediment deposited c 1900 prior to biological study of the site was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition a qualitative difference in algal input to the older sediment is inferred from the low 7 sterol content and presence of 2 6 10 trimethyl 7 3 methylbutyl dodecane however there was still significant dinoflagellate input as indicated by the presence of 4 methylsterols a difference in higher plant input to the older sediment indicated from the n alkane alkene and triterpenoid ketone distributions is consistent with the recent development of tree cover

human impacts climate change and aquatic ecosystem response during the past 2000 yr at lake wandakara uganda analyses of carbon and hydrogen isotope ratios of terrestrial leaf waxes and the carbon and nitrogen abundance ratio and isotopic composition of bulk sediments from lake wandakara a crater lake in western uganda east africa document human and climatic controls on the aquatic system and on the surrounding terrestrial vegetation during the past two millennia our data indicate that wandakara was a relatively stable productive lake surrounded by c3 vegetation from ad 70 to 1000 abrupt changes in the 13c of terrestrial leaf waxes indicate a series of abrupt shifts in the relative abundance of c3 and c4 vegetation caused by a combination of climate change and human activities around wandakara beginning at ad 1000 abrupt shifts in bulk sediment organic geochemistry particularly c n ratios and 15n indicate that human activities at this time caused permanent changes in the limnology of lake wandakara including eutrophication our results suggest that the biogeochemistry of lake wandakara was more sensitive to shifting human impacts than to climate variations during the past millennium highlighting the importance of understanding the intensity of pre colonial human impacts on africa s aquatic ecosystems

δ15n values in lake erie sediments as indicators of nitrogen biogeochemical dynamics during cultural eutrophication abstract we have measured the stable nitrogen isotope values 15 n in two sediment cores sampled 15 years apart 1988 and 2003 from the eastern basin of lake erie and compared them to the total phosphorus tp and biogenic silica bsi concentrations in the 2003 core changes in the tp bsi and total nitrogen tn accumulations in the 2003 core correspond to three stages in the trophic history of the lake that include the onset 1910 to 1950 peak 1950 to 1970 and amelioration 1970 to 2003 of eutrophication owing to accelerated nutrient loading decreasing bsi tp atomic ratios bsi tp at from 1910 to 1970 suggest a gradual si drawdown in the lake during its progressive eutrophication which led to si limitation and reduced diatom settling rates 15 n values show pronounced variability in 1950 to 1970 which corresponds with rapid increases in n from runoffs from the lake catchment a trend of gradually increasing 15 n values from 1910 to 1970 is likely the result of denitrification associated with the development of anoxic bottom waters in the central basin of the lake this study illustrates the complexity of extracting environmental information from 15 n values in sediments and confirms the need for further studies of the multiple processes and their interactions that contribute to lacustrine 15 n records

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

late quaternary vegetation history of southeast africa the molecular isotopic record from lake malawi abstract accurate reconstructions of past hydrological variability are essential for understanding the climate history of the tropics in tropical africa the relative proportion of vegetation utilizing the c3 vs c4 photosynthetic pathway is mainly controlled by precipitation and thus past hydrological changes can be inferred from the vegetation record in this study biomarkers of terrestrial plants lignin phenols and plant leaf wax carbon isotopes are examined from a well dated sedimentary record from lake malawi to provide a vegetation aridity record of the past 23 cal ka from southeast africa we suggest that the ratio of cinammyl to vanillyl c v lignin phenols in lake malawi sediments mainly reflects inputs of c3 trees woody tissue vs c4 grasses non woody tissue and find that changes in the c v ratio generally support variability noted in the n alkane carbon isotope record together these records provide evidence for increased c4 vegetation grasses surrounding lake malawi during last glacial maximum lgm the younger dryas in the early holocene and from 2 cal ka to the present suggesting drier conditions at these times elevated inputs of c3 vegetation are noted in the intervals from 17 13 6 cal ka and 7 7 2 cal ka indicating wet conditions in southeast africa a relationship is noted between the n alkane average chain length acl and temperature with longer acls associated with higher temperatures higher n alkane carbon preference index cpi values correlate with higher mass accumulation rates of biogenic silica and may result from periodic increased northerly winds over lake malawi which enhance upwelling and diatom productivity while simultaneously increasing erosion and transport of plant leaf waxes to the lake the molecular data produced in this study suggest that the carbon isotopic signature of bulk sediment 13ctoc in lake malawi is primarily a reflection of terrestrial inputs c3 vs c4 vegetation and may not mainly reflect changes in algal productivity as previously thought

tidal amplitude decreases in response to estuarine shrinkage tokyo bay during the holocene abstract tidal changes in tokyo bay during the last 10 000 years were investigated by combining a numerical model with newly compiled model bathymetries for the present day the early 20th century and every 1000 years from 4000 to 10 000 years ago over this time period sea level has changed by more than 30 m and the coastline has shifted 50 60 km tides during the early 20th century and 4000 9000 years ago were larger than those at present from 9000 to 4000 years ago the bay setting was mesotidal in contrast to the modern microtidal setting the maximum tidal level at the head of the bay was 72 higher 7000 years ago than at present and m2 tidal currents at the bay mouth from 10 000 to 9000 years ago were three times stronger than those at present when tides were compared at a fixed location the greatest tidal enhancement was found to have occurred 9000 years ago the weakening of tides over the last 9000 years can be explained by introducing the concept of estuarine shrinkage together with quarter wavelength resonance theory tidal weakening occurred in two phases during the first phase 9000 7000 years ago it was due to the rise in sea level type 2 shrinkage and during the second phase a decrease in the length of the bay was responsible type 1 shrinkage these findings can be applied to the assessment of both past tidal changes and potential future tidal changes in other elongated estuaries with lengths of several tens of kilometers

holocene vegetation and climate histories in the eastern tibetan plateau controls by insolation driven temperature or monsoon derived precipitation changes abstract the climates on the eastern tibetan plateau are strongly influenced by direct insolation heating as well as monsoon derived precipitation change however the moisture and temperature influences on regional vegetation and climate have not been well documented in paleoclimate studies here we present a well dated and high resolution loss on ignition peat property and fossil pollen record over the last 10 000 years from a sedge dominated fen peatland in the central zoige basin on the eastern tibetan plateau and discuss its ecological and climatic interpretations lithology results indicate that organic matter content is high at 60 80 between 10 and 3 ka 1 ka 1000 cal yr bp and shows large magnitude fluctuations in the last 3000 years ash free bulk density as a proxy of peat decomposition and peatland surface moisture conditions oscillates around a mean value of 0 1 g cm 3 with low values at 6 5 4 7 ka reflecting a wet interval and an increasing trend from 4 7 to 2 ka suggesting a drying trend the time averaged mean carbon accumulation rates are 30 6 gc m 2 yr for the last 10 000 years higher than that from many northern peatlands tree pollen mainly from picea mostly reflecting temperature change in this alpine meadow forest ecotonal region has variable values from 3 to 34 during the early holocene reaches the peak value during the mid holocene at 6 5 ka and then decreases until 2 ka the combined peat property and pollen data indicate that a warm and wet climate prevailed in the mid holocene 6 5 4 7 ka representing a monsoon maximum or optimum climate for the region the timing is consistent with recent paleo monsoon records from southern china and with the idea that the interplays of summer insolation and other extratropical large scale boundary conditions including sea surface temperature and sea level change control regional climate the cooling and drying trend since the mid holocene likely reflects the decrease in insolation heating and weakening of summer monsoons regional synthesis of five pollen records along a south north transect indicates that this climate pattern can be recognized all across the eastern tibetan plateau the peatland and vegetation changes in the late holocene suggest complex and dramatic responses of these lowland and upland ecosystems to changes in temperature and moisture conditions and human activities

molecular proxies for paleoclimatology we summarize the applications of molecular proxies in paleoclimatology marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments loess deposits and ice cores the fundamentals of this approach are the molecular parameters the compound abundances and carbon hydrogen nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts these afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation we discuss two types of proxy those of terrigenous and those of aquatic origin and exemplify their application in the study of marine sediments through the medium of ten case studies based in the atlantic mediterranean and pacific oceans and in antarctica the studies are mainly for periods in the present the holocene and particularly the last glacial interglacial but they also include one study from the cretaceous the terrigenous proxies which are measures of continental vegetation are based on higher plant leaf wax compounds i e long chain circa c30 hydrocarbons alcohols and acids they register the relative contributions of c3 vs c4 type plants to the vegetation in the source areas the two marine proxies are measures of sea surface temperatures sst the longer established one u37k is based on the relative abundances of c37 alkenones photosynthesized by unicellular algae members of the haptophyta the newest proxy tex86 is based on c86 glycerol tetraethers gdgts synthesized in the water column by some of the archaeal microbiota the crenarchaeota

molecular and isotopic stratigraphy in an ombrotrophic mire for paleoclimate reconstruction a 40 cm deep sphagnum dominated peat monolith from bolton fell moss in northern england was systematically investigated by lipid molecular stratigraphy and compound specific 13c and d analysis using gas chromatography gc gc mass spectrometry gc ms gc combustion isotope ratio ms gc c irms and gc thermal conversion irms gc tc irms techniques 210pb dating showed the monolith accumulated during the last ca 220 yr a period encompassing the second part of little ice age while the distributions of lipids including n alkan 1 ols n alkan 2 ones wax esters sterols n alkanoic acids alkandioic acids and hydroxy acids display relatively minor changes with depth the cooler climate event was recorded in the concentrations of n alkanes and organic carbon cpi values of n alkanes and n alkanoic acids and the ratio of 5 n alkylresorcinols sterols superimposed on the fossil fuel effect the relatively cooler climate event was also recorded by 13c values of individual hydrocarbons especially the c23n alkane a major compound in certain sphagnum spp the d values of the c29 and c33n alkanes correlated mainly with plant composition and were relatively insensitive to climatic change in contrast the c23n alkane displayed variation that correlated strongly with recorded temperature for the period represented by the monolith agreeing with previously reported deuterium records in tree ring cellulose spanning the same period in scotland germany and the usa with more negative values occurring during the second part of little ice age these biomarker characteristics including the compound specific 13c and d records provide a new set of proxies of climatic change potentially independent of preserved macrofossils which will be of value in deeper sections of the bog where the documentary records of climate are unavailable and humification is well advanced

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

stable isotopes in bulk carbonates and organic matter in recent sediments of lake qinghai and their climatic implications abstract multi proxy indices on annual decadal scales during the past 600 years were developed from the surface sediments of lake qinghai based on 210pb and 137cs geochronology the 13ccarb 18ocarb and total carbonate content are consistent with one another in trends and their variations have been mainly ascribed to regional temperature it is suggested that the strong evaporation contributes in modifying 18o of lake water and 13c of the dissolved inorganic carbon of the surface water and appears to be responsible for the covariance between 13ccarb and 18ocarb photosynthesis of the aquatic plants appears to have played a significant role in determining 15n of organic matter the discrimination of 14n and 15n during photosynthesis may have triggered a positive linkage between temperatures and 15norg after removal of the stratigraphic trend variations of total organic carbon toc c n ratio and 13corg have been ascribed to local precipitation toc after removal of the stratigraphic trend is positively correlated with the c n ratio r 0 45

proxy value of n alkan 2 ones in the hongyuan peat sequence to reconstruct holocene climate changes on the eastern margin of the tibetan plateau abstract n alkan 2 ones in the hongyuan peat core from the eastern margin of the tibetan plateau were investigated to assess the paleoclimate proxy value of variations in their compositions over the last 13 500 cal years a homologous series of these compounds that ranged from c 19 to c 31 was identified throughout the peat sequence maximizing at c 23 and showing a strong odd over even carbon chain length predominance to help evaluate the possible paleoclimatic value of the n alkan 2 ones in the hongyuan peat core we compared our molecular results with the pollen records from the same sequence results show that past changes in monsoon precipitation amounts as revealed by the ratio of abies cyperaceae firs sedges are also recorded in the n alkan 2 one c 23 c 25 c 27 c 29 c 31 ket ratio and cpi ket carbon preference index value stratigraphic variations of n alkane and n alkanoic acid ratios suggest that changes in the moisture sensitive microbial oxidation of odd chain n alkanes and decarboxylation of even chain length n alkanoic acids is recorded in the abundance of n alkan 2 ones changes in the monsoon rain intensity on millennial scales are also evident in the n alkan 2 one proxies indicating that their variations in the peat sequence are correlative with changes in microbial activity controlled by the asian monsoon

holocene climatic change and the nomadic anthropocene in eastern tibet palynological and geomorphological results from the nianbaoyeze mountains abstract our study provides detailed information on the lateglacial landscape and vegetation development of tibet based on a suite of geomorphological and palynological proxy data from the nianbaoyeze shan on the eastern margin of the tibetan plateau 33 n 101 e 3300 4500 m asl we reconstruct the current state as a function of climate history and the longevity of human influence study results constrain several major phases of aeolian sedimentation between 50 15 ka and various glacier advances during the late pleistocene the holocene and the little ice age increased aeolian deposition was primarily associated with periods of more extensive glacial ice extent fluvial and alluvial sediment pulses document an increase of erosion starting at 3926 79 cal yr b p coinciding with cooling neoglacial and a growing anthropo zoogenic influence evidence for periglacial mass movements indicate that the late holocene cooling started at around 2000 cal yr b p demonstrating increased surface activity under the combined effects of human influence and climate deterioration the onset of peat growth generally depended on local conditions that include relief meso climate and in more recent times also on soil compaction due to animal trampling we distinguish three initiation periods of peat growth 12 700 10 400 cal yr b p for flat basins inside last glacial terminal moraines 7000 5000 cal yr b p for the main valley floors and 3000 1000 cal yr b p for the higher terrace surfaces the holocene vegetation history started with an open landscape dominated by pioneer shrubs along braided rivers picea juniperus abies and betula trees accompanied by a successive closing of the vegetation cover by poaceae cyperaceae and herbs 9800 8300 cal yr b p first signs of nomadic presence appear as early as 7200 cal yr b p when temperatures were up to 2 c warmer than today forest remained very patchy with strong local contrasts during the following cooling phase 5900 2750 cal yr b p the natural vegetation was transformed by nomadic grazing to bistorta rich kobresia pygmaea pastures modern nomadic migration routes were established at least 2200 years ago overgrazing and trampling led to the shrinking of bistorta and the spreading of annual weeds short lived cold events 8000 6200 3500 cal yr b p impacted on the vegetation only temporarily as the transformation of the natural poaceae rich vegetation into kobresia pastures modified the influence of the tibetan plateau hot plate on the monsoon system our data even point to an early start of a nomadic anthropocene nearly 6000 years ago against the background of a very long grazing history modern tibet must be seen as a cultural landscape