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

proxy dependence of the temporal pattern of deglacial warming in the tropical south china sea toward resolving seasonality abstract sea surface temperatures ssts reconstructed from two globigerinoides ruber white morphotypes g ruber sensu stricto s s g ruber sensu lato s l mg ca and alkenones uk 37 from core md01 2390 from the tropical south china sea scs during the last deglaciation reveal a proxy dependent discrepancy in the temporal pattern of the deglacial warming alkenone data suggest that the deglacial warming is punctuated by a decrease in temperature between 17 and 15 ka bp corroborating previously published alkenone uk 37 sst records from the southern scs within dating uncertainties this cooling is coeval with the heinrich event 1 h1 time interval in the north atlantic region underscoring the imprints of northern hemisphere forcing on tropical scs ocean temperatures the deglacial uk 37 sst minimum is also paralleled by a maximum in g ruber morphotype specific 18o g ruber mg ca sst estimates suggest a morphotype specific record of ssts during the time interval of h1 whereas g ruber s s imply a continuous warming starting around 18 ka bp without any marked response to h1 g ruber s l based mg ca sst estimates reveal a cooling around 17 15 ka bp similar to the h1 interval cooling seen in the alkenone sst record similar proxy dependent differences in deglacial surface water warming have been recorded in the eastern equatorial pacific implying a common pattern on both sides of the tropical pacific ocean we submit that this discrepancy could be due to differences in seasonality of planktonic foraminifera g ruber morphotypes and alkenone producing algae

charcoal analysis for paleoenvironmental interpretation a chemical assay a nitric acid digestion and ignition technique developed to measure relative frequencies of charcoal in lake and bog sediments measures the weight of charcoal relative to the dry weight of the sample percentage charcoal and gives results comparable to counting of microscopic charcoal differences in the two techniques caused by changes in sediment type were found especially in postsettlement and late glacial parts of cores charcoal values from sediments less than 100 yr old cannot be compared to older charcoal values unless wood charcoal and charcoal from fossil fuel burning are separated microscopically tests of this chemical assay on mixtures of known weights of charcoal leaves and sand give correlations between observed and expected values of 0 99 to 1 00

elemental carbon record of paleofire history on the chinese loess plateau during the last 420 ka and its response to environmental and climate changes an elemental carbon ec record covering the last 420 ka was reconstructed using chemical oxidation method on a loess and paleosol sequence from the lingtai section on the chinese loess plateau the ec record reveals the paleofire history and its relationship with climate and vegetation changes on the chinese loess plateau our results show that the ec abundance is generally higher in the paleosols than in the loess layers showing a glacial interglacial pattern which is coincident with biomass changes this variation pattern indicates that paleofires were intensified when biomass accumulated and climate changed abruptly especially from wet to dry conditions the ec abundance increases sharply at similar to 130 kab p indicating a dramatic change in the vegetation and climate variation patterns the occurrence of a peak value with the highest average ec abundance in the holocene may reflect the occurrence of a major climate event at similar to 6 kab p and may also be partly due to more frequent anthropogenic fire usages c 2007 elsevier b v all rights reserved

remagnetization of the coast range ophiolite at stanley mountain california during accretion near 10 n paleolatitude paleomagnetic data are presented for a 50 m thick sequence of oxfordian to tithonian sedimentary rocks conformably overlying upper jurassic pillow basalt within the coast range ophiolite at stanley mountain california these new data are similar in direction and polarity to previously published paleomagnetic data for the pillow basalt the jurassic sedimentary rocks were deposited during a mixed polarity interval of the geomagnetic field and uniformity of the remanent magnetization within the entire section of pillow basalt and sedimentary rocks indicates later remagnetization remagnetization of the coast range ophiolite is interpreted to have occurred during accretion to the continental margin possibly by burial and low temperature alteration related to this event similar paleolatitudes calculated for the ophiolite 11 3 and for mid cretaceous sedimentary rocks of the stanley mountain terrane at figueroa mountain 6 5 are consistent with remagnetization of the ophiolite at low paleo latitudes uniform polarity directions for other remnants of ophiolite in southern california and elsewhere along the pacific coast imply that these rocks were also overprinted and their magnetic inclinations suggest remagnetization at low paleolatitudes as well the coast range ophiolite at stanley mountain is thus inferred to have been remagnetized along the north american margin near 10 n paleolatitude between earliest and mid cretaceous time and subsequently transported northward by strike slip faulting related to relative motions between the farallon kula pacific and north american plates

monsoon fluctuations over the past 350 kyr high resolution evidence from northeast asia northwest pacific climate proxies marine pollen and radiolarians abstract high resolution analyses of pollen and radiolarians from northwest pacific cores v28 304 and rc14 99 provide continuous directly linked evidence of oceanic atmospheric climate processes through the past three pleistocene glacial interglacial cycles systematic fluctuations in marine pollen assemblages which reflect changes in the forest communities of japan are compatible with fluctuations in faunal assemblages and inferred oceanographic properties offshore each interglacial has distinguishable characteristics which imply that the sequence timing and magnitude of climatic change were not identical during the three most recent interglacial intervals most interglacials contain at least one 10 15 kyr period of exceptionally high percentages 20 of cryptomeria which we interpret as reflecting increased levels of precipitation in response to intensification of the summer monsoon with the exception of oxygen isotope substage 5e in rc14 99 interglacial summer sea surface temperatures were similar to or slightly warmer than today glacial environments in central japan and in the northern subtropical gyre were similar to those which now support cold temperate and boreal forests on northernmost japan and a dominant subpolar fauna and associated low sea surface temperatures offshore climatic change was apparently not as severe in southern japan where temperate vegetation largely replaced warm temperate flora or in the southern subtropical gyre where only winter ssts were cooler than present we attribute these changes in vegetation and surface water conditions to shifts in the atmospheric polar and oceanographic subarctic fronts in response to the seasonal variations in the siberian high maxima in cryptomeria systematically lag maxima in solar insolation at 30 n this correlation between our summer monsoon indicator and summer insolation substantiates the view that the strength of the asian monsoon is linked to variations in northern hemisphere solar radiation

depositional model in subglacial cavities killiney bay ireland interactions between sedimentation deformation and glacial dynamics subglacial meltwater drainage and sedimentary processes play a major role in ice sheet dynamic but there is a lack of study of subglacial environment because modern ice sheet beds remain inaccessible previous authors already intended to provide diagnostic criterion and recent investigations suggest that fluid pressure variations are a key factor in subglacial environment this paper investigated the late devensian sedimentary record in order to describe subglacial sedimentological facies associations and deformation features related to fluid overpressures we used an integrated approach based on stratigraphy sedimentology and deformations styles to demonstrate a subglacial depositional model the studied interval is composed of stratified gravel and sand interbedded with diamicton and boulder pavement deposited in depressions formed by irregularity of the upper surface of diamicton deformation structures include convolutes dykes and normal micro faulting dykes show different dip directions from vertical oblique to subhorizontal from which both directions of shortening and extension can be determined vertical dykes are formed under pure shear strain related to ice weight only oblique dykes imply both ice bed coupling and simple shear strain between ice and substrate induced by flowing ice related to progressively increasing meltwater drainage intensity horizontal dykes are formed when minimum strain is vertical and therefore the overpressure exceeds the weight of overburden they are associated with high meltwater drainage intensity and ice bed uncoupling and refer to hydrofracturing overall depositional and deformation sequence also illustrates the increasing intensity of meltwater drainage in small cavity as high energy channelised deposits and in large cavities where subaqueous fan are deposited under hydraulic jump conditions moreover large cavities represent lee side cavities formed by fast flowing ice over an obstacle hydrofracturing is likely to occur when a dense fluid potentially associated with catastrophic drainage of an upstream cavity enters the low pressure confined environment of a downstream cavity and is injected under pressure in the soft substrate the studied glacial sequence represents a regional pattern probably related to an allocyclic control on sedimentation linked to long term glacial dynamics rather than local depositional conditions based on these results we provided a synthetic model linking depositional and deformation processes during ice sheet growth and decay but also valid at different timescales from annual to seasonal scale

problems of the quaternary on mountains of the sunda sahul region abstract two specific problems are identified in understanding the data on the quaternary of montane areas in the sunda sahul region these are 1 the upper montane rainforest according to palynological evidence appears to have been absent in the late pleistocene although it is well represented today 2 the estimates of temperature lowering in the late pleistocene are strikingly greater in the mountains than in the lowlands a single possible explanation for both problems is proposed it is argued that altitudinal zonation of vegetation is partly controlled by ultraviolet b light which is strikingly increased at high altitudes in the tropics this fact could account for both the above problems not only in the sunda sahul region but also in other tropical regions

contrast in surface water δ18o distributions between the last glacial maximum and the holocene in the southern south china sea abstract published core data of planktonic foraminiferal 18o and alkenone sea surface temperature sst are used to investigate seawater 18o w distributions in the south china sea scs during the last glacial maximum lgm and the holocene the holocene w distributions show a pattern correlated to modern salinity distributions displaying an increasing trend from the south to the north however the lgm w distributions show a different pattern displaying increasing values from the central to the southern scs and the lgm holocene differences in w w corrected by ice volume effect though negative in values display decreasing amplitude toward the south both of which could suggest increasing salinity toward the south by conventional approach this is somewhat counter intuitive because enhanced freshening could be expected for the southern scs due to extra discharge from the river systems on the emerged sunda land during the lgm here we propose an alternative explanation to reconcile the lgm w and w distributions with the above expectation in the proposal changes in w salinity relationship i e lowering the w salinity slope due to significant runoff contributions to freshwater input and less 18o depleted precipitation during the lgm are deeply discussed to reasonably explain the abnormity in lgm w distributions

no aridity in sunda land during the last glaciation evidence from molecular isotopic stratigraphy of long chain n alkanes molecular distribution and stable carbon isotopic composition n 13 c of n alkanes determined in a sediment core 17962 from the southern south china sea scs show that no obvious change has taken place in vegetation on sunda land from the last glacial period to the beginning of the holocene a shift in the accumulation rate of longchain n alkanes c27 to c33 was recorded at a depth of about 620 cm probably indicative of precipitation enhancement related to winter monsoon the n 13 c values are within the range of 333 7 to 327 1x for c29 n alkanes and 333 9 to 328 4 for c31 n alkanes in the whole core sequence such an isotopic composition is characteristic of n alkanes biosynthesized mainly by plants utilizing the c3 photosynthetic pathway continuous development of c3 plants on sunda land and its surroundings evidences that the climate during the last glacial period in the southern scs was not drier than what it is today 2003 elsevier b v all rights reserved

mechanisms of fast flow in jakobshavn isbrae west greenland part iii measurements of ice deformation temperature and cross borehole conductivity in boreholes to the bedrock at a site on the ice sheet adjacent to the jakobshavn ice stream in west greenland ice deformation rates and temperatures have been measured in boreholes to the bedrock at 830 m depth enhanced deformation rates were recorded just below the holocene wisconsin transition at 680 m depth a 31 m layer of temperate ice and the temperature minimum of 22 c at 520 m depth were detected the good agreement of these data with results of a two dimensional thermomechanically coupled flow model implies that the model input is adequate discrepancies between modelled and measured temperature profiles on a flowline at the ice stream centre have been attributed to effects not accounted for by the model we have suggested that the convergent three dimensional flow leads to a vertical extension of the basal ice entering the stream a thick basal layer of temperate and wisconsin ice would explain the fast flow of this ice stream as a test of this hypothesis the new core borehole conductivity cbc method has been used to compare conductivity sequences from the ice stream to those of the adjacent ice sheet the correlation thus inferred suggests that the lowest 270 m of the ice sheet correspond to the lowermost 1700 m of the stream and consequently that the lower part of the ice stream has experienced a very large vertical extension

paleomagnetic and 40ar 39ar evidence for remagnetization of mesozoic oceanic rocks on the vizcaino peninsula baja california sur mexico previously published paleomagnetic data for upper jurassic pillow lavas of the vizcaino peninsula indicate that they were deposited near a paleolatitude of 14 n or s whether or not this result implies northward transport with respect to the continental interior has been controversial due to the lack of reliable jurassic reference poles for the north american plate available paleomagnetic data for nearby upper triassic pillow basalts and overlying pelagic sediments at punta san hipolito however fail a fold test indicating that these rocks were remagnetized post folding indistinguishable in situ paleomagnetic directions and perturbed 40ar 39ar age spectra for the triassic and jurassic pillow lavas are consistent with resetting of their magnetic and isotopic systems in the middle cretaceous probably during burial by the overlap valle formation 10 km thick resetting apparently occurred post deformation so the paleolatitude of remagnetization is unknown high coercivity directions from a few samples of the triassic rocks might represent an older magnetization acquired during deposition at paleolatitudes near 6 n or s

ice volume forcing of east asian winter monsoon variations in the past 800 000 years particle size measurements of some typical loess soil samples taken in different localities of the chinese loess plateau demonstrate that the grain size ratio of 10 m can be used as an indicator of variations in intensity of the east asian winter monsoon winds grain size curves of the baoji and weinan sections show that this proxy indicator is very sensitive to loess soil alterations analytical results also suggest that during soil forming periods eolian dust accumulation was still substantial and hence loess deposition can be regarded as a nearly continuous process during the quaternary period in this study we compared the baoji grain size time series with the specmap marine isotope record with the objective of elucidating the dynamic linkage between changes in global ice volume and the winter monsoon circulation both records show good agreement at both time and frequency domains in particular the winter monsoon variations are also dominated by a 100 000 yr period over the past 800 000 yr it is thus inferred that direct local insolation forcing could be less important in driving the east asian winter monsoon variability and alternatively variations in glacial age boundary conditions may have played a key role in modulating and pacing its strength and timing

systematic biotic responses to palaeoenvironmental change in the late pleistocene southern south china sea a preliminary study oxygen and carbon isotopes from the planktonic foraminifer globigerinoides sacculifer trace element contents calcium carbonate biogenic silica grain size and abundances of diatoms radiolarians and foraminifera in a deep sea core from the southwestern south china sea were analysed to investigate the response of various marine ecological communities to environmental changes over the last 200 ka the synthesised results show that the quality of the palaeoecological environment for biological growth is primarily affected by nutrient supply and terrigenous disturbance ba and p are important nutrient elements for the growth of diatoms radiolarians and planktonic foraminifera together with dissolved silica and calcium carbonate in sea water these elements may control microbiotic development however variations in fe content appear to affect diatom and radiolarian abundance optimal biotic growth occurs when nutrients are abundant and when there is minimal terrigenous disturbance biotic growth decreases when sea water is highly oligotrophic and terrigenous input is high maximum biological growth occurred in the mid holocene but deteriorated soon afterwards owing to increased terrigenous input causing a decrease of biological abundance and productivity in the late holocene the results also indicate how the toba volcanic eruption ca 74 ka ago contributed to changing the ecological environment in the southern south china sea copyright c 2008 john wiley sons ltd

automated remote sensing of sediment plumes for identification of runoff from the greenland ice sheet the viability of employing sediment plumes emanating from outlets along the western margin of the greenland ice sheet as indicators of runoff is assessed an automated sediment plume quantification system based on daily 250 m moderate resolution imaging spectroradiometer modis band 1 reflectance imagery is developed coherent plumes are identified using spectral thresholds and polygon tracing validation employs imagery quality control procedures and manual verification of plume areas outlets at land terminating margins with wide and straight fjord geometries deliver the most accurate and consistent results plume area observations are also possible at marine terminating margins with relatively static fronts and low proximal sea ice concentrations variability in plume area is examined with reference to special satellite microwave imager ssm i derived daily melt extent at the hydrologic catchment scale at annual timescales plume areas tend to co vary with surface melt extent indicating that more mass is lost by runoff during years of extensive melting some synchronicity in plume areas from different catchments is apparent at seasonal and daily timescales plumes from individual outlets primarily relate to catchment specific melting

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

no analog planktonic foraminiferal faunas in the glacial southern south china sea implications for the magnitude of glacial cooling in the western pacific warm pool sea surface temperature sst estimates in the sediment core md01 2390 based on planktonic foraminiferal species abundances using five different transfer function techniques suggest nearly unchanged or unusually higher temperatures in the tropical southern south china sea scs during the last glacial maximum lgm relative to modern temperatures these results are in contrast to substantial cooling of 2 5 c inferred by geochemical uk 37 mg ca ratios and terrestrial proxies from the western tropical pacific region using multivariate statistics we show that the glacial southern scs harboured unique planktonic foraminiferal assemblages that have no modern analogs analyses of faunal variation through the core reveal that planktonic foraminiferal assemblages responded to temperature changes inferred from mg ca data but that this signal is subdued by superimposed variations in the relative abundance of pulleniatina obliquiloculata and neogloboquadrina pachyderma dextral these species occur in glacial samples at proportions that are not observed in the calibration data set the glacial high abundance of n pachyderma dextral are interpreted to reflect a seasonal winter inflow of cold surface water from the northeast via the bashi strait due to the combined effects of an intensified winter monsoon a southward shift of the polar front and the eastward migration of the kuroshio current in contrast processes controlling the high relative abundances of p obliquiloculata during the lgm may be unique to the southern scs we propose a scenario involving a stronger winter mixing or enhanced upwelling due to an intensified winter monsoon that prevented shallow dwelling warm indicators to establish larger populations during the lgm our results indicate that a no analog behaviour of planktonic foraminifera faunas is responsible for the warm glacial conditions in this part of the western pacific warm pool as implied by foraminiferal transfer functions and that a more significant surface cooling in the region as implied by terrestrial and geochemical mg ca ratios alkenone unsaturation index marine proxies is a more likely scenario

climatically forced organic carbon burial in equatorial atlantic and pacific oceans over the past ten years sedimentary geochemists have noted that climate changes associated with pleistocene glaciations have had a pronounced effect on the rate of organic carbon burial found in the tropical oceans1 4 in particular two to five times higher organic carbon accumulation rates have been observed for the 18 kyr bp glacial maximum than for the holocene in several short sediment cores from both oceans see fig 1 here i present 300 kyr time series for organic carbon mass accumulation rate from four sediment cores two each from the equatorial pacific and atlantic and show that orbital forcing of global climate has strongly affected the rate of organic carbon burial in the equatorial oceans

implications of increased greenland surface melt under global warming scenarios ice sheet simulations abstract the greenland ice sheet is likely to make a faster contribution to sea level rise in a warming world than previously believed based on numerical modelling using a parameterization of recent results showing surface meltwater lubrication of ice flow zwally et al science 297 557 2002 218 documented correlation between increased ice velocity and increased surface melt as parameterized by positive degree days they argued that surface water is piped directly to the bed with little delay causing increased basal water pressures and basal sliding velocities an effect not included in recent greenland ice sheet models known to the authors using the pennsylvania state university university of chicago thermomechanical flowline model numerous simulations were conducted to test a wide range of parameter space linking surface melt with a new sliding law based on the zwally et al data under three different global warming scenarios 2 co2 4 co2 and 8 co2 comparisons to reconstructions generated with a traditional sliding parameterization illustrate an enhanced sensitivity of the ice sheet to surface warming resulting in higher ablation rates additional thinning and retreat of the margin and a reduction in ice volume leading to an increased contribution to global sea level rise

new evidence from the south china sea for an abrupt termination of the last glacial period abrupt changes in climatic conditions have been seen at high latitudes in the north atlantic1 and the antarctic2 3 at 13 kyr bp it is important to determine whether this abrupt change was confined to high latitude regions or whether it was global here we present results demonstrating an abrupt change in the rate and character of sedimentation in the south china sea at the close of the last glacial period radiocarbon dating and its position in the oxygen isotope shift suggest that this change may be coincident with the changes found at high latitudes

stress balances of ice streams in a vertically integrated higher order formulation one challenge in improving our understanding of ice stream dynamics is to develop models of the spatial and temporal transition from ice sheet to ice stream flow we address this with a new vertically integrated higher order formulation for ice sheet dynamics that captures the leading order physics of low aspect ratio viscous fluid flow regardless of the amount of slip at the bed the theory introduces a parameter which approximates the ratio of the basal stress to the shear stress scale providing a measure of the relative importance of sliding and internal deformation our model is able to simultaneously describe the dynamics of both a slow moving sheet and rapidly flowing ice streams to test the formulation we apply a triple valued sliding law as the basal boundary condition and obtain numerical solutions that can be compared with previous work we investigate the sensitivity of flow regimes and shear margin width to parameter variation deriving a scaling for the latter we also consider a double valued sliding law which enforces a constant low basal stress beneath the ice stream comparisons of the resultant stress fields illustrate the different stress balances that can maintain

paleomagnetism paleogeographic origins and uplift history of the coast range ophiolite at mount diablo california divergent paleogeographic origins have been proposed for the coast range ophiolite of western california which are testable using paleomagnetic methods paleomagnetic data for middle jurassic pillow lavas and diabase sills of the coast range ophiolite at mount diablo northern california indicate that they contain two components of remanent magnetization the characteristic directions have normal and reversed polarities and apparently are carried by ti poor magnetite this magnetization is inferred to have been acquired during emplacement and seafloor alteration at an ancient spreading ridge the paleolatitude calculated from its structurally corrected mean direction is 20 n 9 and agrees with the expected direction for stable north america this result is also consistent with the concordant paleolatitude 32 n 8 recently determined for upper jurassic coast range ophiolite at stanley mountain in southern california in addition clockwise vertical axis rotation of mount diablo 143 11 is indicated by the characteristic magnetization direction an overprint component is inferred to have been acquired during uplift of mount diablo since the miocene

a record of fire vegetation and climate through the last three glacial cycles from lombok ridge core g6 4 eastern indian ocean indonesia abstract charcoal elemental carbon and clastic particle analyses have been undertaken on tropical marine core g6 4 collected from the eastern indian ocean between the lesser sunda islands of indonesia and northwestern australia to help interpret an existing pollen record in addition a new oxygen isotope record has been constructed and several radiocarbon dates produced to allow a refinement of the chronology of the core the record covers the last 300 000 years with three clear glacial interglacial cycles however the new oxygen isotope record and radiocarbon dates suggest a hiatus and it appears that most isotope stage 3 is missing interglacials are characterised by higher values of mangrove fern and rainforest pollen indicating wetter conditions than intervening glacials which have higher cyperaceae and chenopodiaceae values gramineae percentages are also generally higher during glacials but there is a sustained increase in grasses relative to eucalyptus about 185 000 years ago originally interpreted as a change to drier conditions an increase in burning from about 200 000 years ago from charcoal evidence suggests that fire may have been an important contributing factor this and subsequent increases in charcoal may reflect anthropogenic burning and are considered in relation to archaeological evidence for possible times of arrival of people within australia the elemental carbon record shows major differences to that from charcoal and further research is needed to interpret its meaning little consistent evidence for changes in climate or vegetation disturbance is provided by clastic particle influx which may well reveal a record of volcanicity within the region

new paleomagnetic rock magnetic and petrographic results from the valle group baja california mexico exploring the causes of anomalously shallow paleomagnetic inclinations 1 a detailed paleomagnetic rock magnetic and sedimentologic study was conducted on cenomanian age strata of the valle group at el campito baja california to examine the burial compaction effects on the paleomagnetic inclination of marine sedimentary rocks alternating field and thermal demagnetization isolated a characteristic remanence at 16 of 18 sites with a mean of dec 342 6 inc 19 1 and 95 3 4 the inclination is 38 7 shallower than that predicted by the reference paleopole for north america laboratory experiments indicate that compaction could account for only 7 5 of the inclination shallowing fold tests at different scales yield both positive and negative results making a tight constraint on the remanence s age impossible a primary postdepositional remanence is supported by bedding parallel foliations in the anisotropy of anhysteretic remanence fabric although primary anomalously shallow inclinations could indicate significant southerly then northerly paleolatitudinal offset a more likely scenario is a late cenozoic low temperature remagnetization which is suggested by alteration along the edges of some detrital silicate grains and a bimodal magnetic grain size distribution revealed by isothermal remanence data the synthesis of the data indicates that the vizcaino terrane was contiguous with the cordillera margin during remagnetization and underwent a subsequent 13 5 5 4 clockwise rotation we tentatively interpret that the remagnetization resulted from burial and or miocene volcanism which caused an acquisition of thermochemical remanent magnetization tcrm this study reveals a complicated remanence that resists easy interpretation and suggests caution in studies of similar rocks

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

refined estimation of marine and terrigenous contributions to sedimentary organic carbon molecular carbon isotopic 13c 12c ratios of a selected marine organic biomarker compound a c37 alkadienone from the pigmy basin deep sea drilling program hole 619 in the northern gulf of mexico varied by 5 3 in sychrony with the last 100 ka glacial interglacial cycle this carbon isotopic 13c variation is likely due to the effect of climatically linked variations in concentrations of co2 aq on photosynthetic fractionation of carbon isotopes by phytoplankton measurement of the 13c of the alkadienone 37 2 to reconstruct the carbon isotopic composition of total marine organic carbon permits improved estimates of the time varying 13c of preserved marine organic carbon end members with the time series record of marine end members the concentrations and net accumulation rates of terrigenous corg and marine corg are calculated and their paleoceanographic significance is considered although this method may be improved by consideration of additional biomarkers representative of diverse marine and terrigenous inputs it is the first application of molecular isotopic analysis to quantifying marine and terrigenous corg concentrations further application of such techniques will be become valuable in reconstructing regional and global budgets of marine and terrigenous corg accumulation

burial of different types of organic carbon in core 17962 from south china sea since the last glacial period abstract total organic carbon toc black carbon bc and land derived organic carbon loc extracted from marine sediment core 17962 from the southern south china sea and analyzed by pyrolysis gas chromatography elemental analyzers and mass spectroscopy can be interpreted in terms of regional land biomass burning climatic conditions vegetation cover and ocean paleoproductivity carbon from terrestrial sources including bc and loc appears to be a significant component of toc 3 1 39 3 range 16 5 average for bc 4 4 56 6 range 14 6 average for loc the production of bc and loc was only slightly higher during the last maximum glaciation lgm than during the holocene therefore dramatic changes in climate and vegetation cover do not seem to have occurred at the pleistocene holocene boundary paleoproductivity data calculated from marine organic carbon proved to be more accurate than those calculated from toc and exhibit the same pattern of temporal variation however the glacial interglacial contrast in the refined palaeoproductivity is less evident than that calculated from toc

human used upper montane ecosystem in the horton plains central sri lanka a link to lateglacial and early holocene climate and environmental changes abstract this study utilizes radiocarbon dated pollen spores sphagnum spp macrofossils and total organic carbon proxies to examine variability of past climate environment and human activity in montane rainforest grassland and wetland of the horton plains hp central sri lanka since the last glacial maximum lgm the lgm is largely characterized by grasslands and xerophytic herbs dominated open habitats arid lgm punctuated climatic ameliorations which took place in short episodes humans appear to have reached the hp ecosystem after 18 000 cal yrs bp occasionally the first intertropical convergence zone itcz induced changes in south west monsoon swm rains occurred at low latitudes between 16 200 and 15 900 cal yrs bp suggesting an onset of monsoon rains after this event monsoon rains weakened for several millennia except the period 13 700 13 000 cal yrs bp but human activity seems to have continued with biomass burning and clearances by slash and burn very large size grass pollen grains which are morphologically similar to pollen from closer forms of oryza nivara were found after 13 800 cal yrs bp early holocene extreme and abrupt climate changes seem to have promoted the forms of o nivara populations in association with humans new data from the hp would therefore be most interesting to investigate the dispersal and use of domesticated rice in south asia

evidence for the younger dryas climatic event in southeast asia abstract this article reviews evidence for the younger dryas climatic event from the limited data available from mainland and island southeast asia and from deep sea cores from the region data from highland indonesia and regional deep sea cores suggest a climatic reversal at the time of the younger dryas may be more widely detectable with finer resolution pollen analysis and additional radiocarbon dating but it should be remembered that dates of this age cannot be calibrated locations are suggested in the region where more sites and finer resolution analysis is needed before definite statements on the younger dryas can be made at present the best evidence for its occurrence comes from one sumatran pollen diagram but even that is very tentative

a 400 000 year record of vegetational and climatic changes from a volcanic basin leizhou peninsula southern china abstract the tianyang lake in leizhou peninsula is an enclosed crater formed during the early to middle pleistocene over 200 m of diatomaceous mud and clay were deposited in the last 400 000 years providing a continuous middle and late quaternary lacustrine sequence for paleoenvironmental studies the pollen record spans the last four glacial interglacial cycles equivalent to oxygen isotope stages ois 10 to 1 during most of the glacial phases fagaceous monsoon forest was replaced by altitudinal vegetation indicating a regional landscape transformation on the peninsula the montane forest reached down to the lowland by at least 600 m during the ois 6 and 8 in a cool and relatively wet condition with temperature estimated to be more than 4 c lower than present a further lowering of the montane forest belts by about 800 1000 m occurred in the ois 4 2 as implied by the appearance of many temperate elements during the last glacial maximum this mixed forest subsequently gave way to the poaceae grassland a savanna vegetation type favored by drier and cooler climatic conditions this drastic change implies a more significant drop in temperature and precipitation than the previous three glacial periods ois 10 8 and 6 it is thus inferred that the weakening of summer monsoon was more significant towards the end of the late pleistocene particularly during the last glacial maximum lgm

an integrated view of inorganic and organic biogeochemical indicators of palaeoproductivity changes in a coastal upwelling area in order to evaluate the role of the continental margin areas in the changes of atmospheric co2 during past climatic cycles it is crucial to reconstruct reliably export palaeoproductivity changes in such areas this paper examines and discusses the specific relationships between various productivity dependent geochemical signals recorded in a single sediment core from the northwestern africa continental slope including both major and trace parameters of inorganic and organic origin this paper clearly shows that the export productivity flux as well as its composition e g the relative contribution of calcareous siliceous and mineral free producers have changed these changes have subsequently modified benthic conditions which can have had in turn a retroaction on major biogenic element contents this effect seems however to be only minor compared to that one directly induced by changes in biogenic fluxes these results indicate that direct palaeoproductivity transfer functions which are based on present day statistical calibrations of one single parameter and which are valid to some extent for sediments from abyssal open ocean cannot be properly applied in marginal areas which are much more complex and in particular highly affected by sea level changes in such areas quantitative palaeoproductivity reconstructions should be only considered at a regional scale including off shoreward on shoreward and latitudinal migration or extension of the productive areas as well as the palaeoproductivity intensity and composition

late pleistocene charcoal in tropical atlantic deep sea sediments climatic and geochemical significance charcoal in late pleistocene marine sediments of the tropical atlantic was measured to examine the regional history of charcoal deposition as it relates to biomass burning on adjacent continents and carbon sequestration in the ocean detailed analysis 1 0 k y resolution of a deep sea core from the eastern tropical atlantic ocean reveals that charcoal from africa is a significant component of total organic carbon sedimentation during glacial intervals of the past 200000 yr these findings alter previous assumptions as to the character of carbon deposition in this region and reduce previous estimates of marine organic carbon burial fluxes by 50 furthermore the tempo of charcoal deposition is mainly linked to the growth and decay of high latitude ice sheets and appears to be caused by changes in wind strength or direction during glacial time

mechanisms of fast flow in jakobshavns isbrae west greenland part i measurements of temperature and water level in deep boreholes several holes were drilled to depths of 1500 1630 m along a profile across jakobshavns isbrae 50 km upstream from the calving front drilling was by hot water and required approximately 20 h the holes were rapidly closed by refreezing but it was possible to instrument them with thermistors and tilt sensors before this occurred near the margins of the ice stream the holes reached the bed and connected with the subglacial drainage system water level changes recorded in these holes are discussed in terms of the basal hydraulic system the temperature measurements show that the glacier is temperate based moreover extrapolation of a measured temperature profile and its curvature suggests that a temperate layer of substantial thickness may exist at the bed near the center of the ice stream there is a striking difference in the shapes of temperature profiles measured at different locations beneath the center line the temperature minimum is at a considerably smaller relative depth than near the margins but it is nearly the same in magnitude 22 1 c this may indicate a disproportionately large vertical stretching of the basal ice in the center of the ice stream since the basal ice is warmer and much less viscous than the ice above a thickening of that layer would cause a corresponding increase of surface velocity we presume that this mechanism contributes to the fast flow of jakobshavns isbrae

cenozoic remagnetization of the paleozoic rocks in the kitakami massif of northeast japan and its tectonic implications abstract secondary remanent magnetization is identified in the paleozoic igneous and sedimentary rocks of the kitakami massif the secondary nature is shown by a negative fold test for the permo carboniferous sedimentary rocks the northwesterly paleomagnetic declination with moderate inclination d 321 2 i 56 5 95 5 2 n 18 of this secondary remanent magnetization is almost parallel to the primary magnetization reported for the cenozoic welded tuffs of northeast japan indicating that the paleozoic rocks were subjected to remagnetization at any period between 62 and 16 ma the secondary magnetization of the serpentinized ultramafic rocks is carried by magnetite which grew in veins and mesh rims of serpentine whereas the carrier of the magnetization in limestones is fine grained pyrrhotite combining this with the previously reported remagnetization of the kitakami granitic rocks it is suggested that rocks in the kitakami massif were subjected to crystallization remanent magnetization at low temperature conditions since serpentinization requires fluid migration one of the most likely events is the eastward lateral migration of water into the kitakami massif we postulate a cenozoic suturing of the kitakami massif with the asian continent as a plausible tectonic event for this fluid migration

a 135 000 year record of vegetational and climatic change from the bandung area west java indonesia sedimentological and palynological analyses of sediment cores from the intramontane bandung basin west java indonesia provide a first palaeoclimatic record for the indonesian region covering continuously the last 135 000 years our data on palaeosol development indicate anomalously dry conditions for the final part of the penultimate glacial period around 135 000 yr b p and very warm and humid interglacial conditions from 126 000 to 81 000 yr b p during the transition to the last glacial period around 81 000 yr b p freshwater swamp forest of the bandung plain was replaced by an open swamp vegetation dominated by grasses and sedges indicating a change to considerably drier conditions possibly related to reduced moisture uptake by the nw monsoon as a consequence of lower sea levels at the onset of glacial conditions a strong reduction in asplenium ferns from 81 000 to 74 000 yr b p suggests that drier conditions may also have occurred in the mountains of the bandung area while increased numbers indicate that from 74 000 to 47 000 yr b p it was slightly wetter again inferred depression of montane vegetation zones and reduced fern percentages suggests distinctly cooler and possibly drier climatic conditions prevailed in the bandung area from 47 000 to approximately 20 000 yr b p for the last glacial maximum 4 7 c lower temperatures are recorded

glaciology greenland s glacial basics sliding of the greenland ice sheet is affected by the production of surface meltwater a new theory shows that whether the result is a long term speed up or slow down of ice motion depends on the variability in melt input see letter p 803 recent observations in greenland have led to the notion that surface meltwater supply to the ice sheet bed lubricates ice flow suggesting that climate warming could lead to runaway glacial acceleration christian schoof uses a physically based model that captures drainage channelization under the ice to challenge this view the model shows that increased melt supply leads to channelization and a drop in water pressure this causes ice flow to slow down rather than speed up however this effect can be overcome if melt supply is variable over short timescales when temporary pressure spikes can lead to accelerated flow the positive melt dynamic thinning feedback is therefore still viable but is heavily dependent on daily temperature variations and rain events that are largely ignored in current ice sheet models

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

the flooding of sundaland during the last deglaciation imprints in hemipelagic sediments from the southern south china sea abstract during the last 30 ka the south china sea scs experienced pronounced palaeogeographic changes associated with the postglacial sea level rise which significantly modified the hydrography of this marginal sea the most crucial effects in the southern part of the basin were the submergence of sundaland and the opening of the southern channels connecting the scs to the tropical indo pacific isotopic sedimentological and organic geochemical parameters determined in two sediment cores from the southern scs one in the open sea and the other close to the continental shelf sites 17961 and 17964 respectively show that the main hydrographical changes during this period were related to critical thresholds in sea level rise the main changes occurred at about 15 13 5 ky bp coincident with meltwater pulse mwp ia when sea surface temperatures ssts at both sites experienced a rapid 1 5 c rise and the clay content and n nonacosane concentrations dropped significantly both trends reflect a rapid retreat of the coastline and an initial flooding of sundaland at that time a second important change starting with the beginning of mwp ib at about 11 5 ky bp and culminating at 10 ky bp involved the establishment of modern hydrographic conditions this is evident from the rapid convergence of the foraminiferal oxygen isotope records and the establishment of holocene sst values these results highlight the need to include the flooding emergence of sundaland as an important boundary condition in future modelling studies of asian palaeomonsoons

a biomarker approach to the organic matter deposited in the north atlantic during the last climatic cycle abstract the study of the composition of total organic carbon toc c37 alkenones and c23 c33 n alkanes in the north atlantic ocean cores su90 08 and su90 39 has allowed the development of a model for the differentiation of marine and terrigenous toc this model gives rise to results in good agreement with inorganic markers such as magnetic susceptibility ms and non carbonate content according to this model the terrigenous toc accounts for most of the organic matter in the glacial sediments thus the higher toc of the glacial periods 0 1 0 45 vs 0 05 0 15 in the interglacials is due to the increase in terrigenous toc the changes in marine toc those associated to sea surface productivity are independent of the glacial interglacial evolution the terrigenous toc is more important at higher latitudes probably due to higher terrigenous detrital inputs associated with iceberg transport in this respect the correlation between n alkanes and ms strongly suggests that the main source of these hydrocarbons are ice rafted materials and that aeolian inputs only represent minor contributions the four peaks of reworked n alkanes in the su90 08 core that are coincident with the heinrich layers h1 h2 h4 and 115 are in agreement with this hypothesis on the other hand the abrupt marine toc peaks of su90 08 show a 23 ka periodicity indicating that the marine productivity at 43 n in the north atlantic ocean was precessionally driven the productivity maxima in this core correlate with low latitude oceanographic processes such as periods of enhanced trade wind intensity and equatorial upwelling which are also tuned to precession and independent of the global glacial interglacial evolution

paleomagnetic reconnaissance of early mesozoic carbonates from williston lake northeastern british columbia canada evidence for late mesozoic remagnetization three classic sections of middle and late triassic fossiliferous limestones cropping out around williston lake in british columbia canada were sampled for paleomagnetic study the objective was to test the suitability of these units for detailed magnetobiostratigraphic study with the aim of improving the reference triassic geomagnetic polarity time scale the williston lake characteristic magnetizations differ however from any triassic north america cratonic reference directions a satisfactory agreement is found instead with cretaceous early cenozoic north america cratonic reference directions the exclusive occurrence of normal polarity suggests that remagnetization likely occurred during the cretaceous long normal superchron remagnetizations may have been triggered by connate brines which moved along aquifers of porous sandstones and carbonates in the early stages of laramide folding resume trois sections fossiliferes classiques de calcaires trias moyen et tardif affleurant autour du lac williston en colombie britannique ont ete echantillonnees pour une etude paleomagnetique l objectif etait de s assurer de la pertinence de ces unites pour une etude magneto bio stratigraphique detaillee visant a ameliorer l echelle referentielle de temps de la polarite geomagnetique au trias les magnetisations caracteristiques du lac williston different toutefois de toute direction cratonique referentielle au trias en amerique du nord toutefois une correlation satisfaisante est etablie avec les directions cratoniques referentielles du cretace cenozoique precoce en amerique du nord l occurrence exclusive d une polarite normale suggere qu il y eut probablement une remagnetisation au cours du long superchron normal du cretace les remagnetisations peuvent avoir ete declenchees par des saumures connees qui se sont deplacees le long d aquiferes de gres et de carbonates poreux dans les premieres phases du plissement laramide

planktonic foraminiferal records of east asia monsoon changes in the southern south china sea during the last 40 000 years planktonic foraminiferal assemblages and benthic foraminiferal oxygen isotopes were obtained in a gravity core n507 25 6 degrees 39 945 n 113 degrees 32 9361 e water depth 2006 m collected from the southern south china sea scs to investigate east asia monsoon changes during the last 40 000 years four cold events identified from four peaks of the relative abundance of neogloboquadrina pachyderma dex and globigerina quinqueloba correlate well with those in the hulu monsoon record within age uncertainty and can be linked to heinrich events in the northern atlantic high latitudes we suggest that the relative abundance of n pachyderma dex and g quinqueloba in the southern scs can be used as a direct proxy for east asia winter monsoon eawm changes during glacial periods in contrast to its low abundance in the northern scs and okinawa trough the relative abundance of pulleniatina obliquiloculata shows high values during the last glacial in the southern scs caused likely by the combined impact of optimum winter sea surface temperature sst and stronger mixing enhanced upwelling at that time a p obliquiloculata minimum event pme found in the okinawa trough and the northern and southern scs during the h1 period was possibly related to a large drop in winter sst due to the intensified eawm we propose that this pme can be also used as a reliable regional stratigraphic marker as the holocene one a 9 cm sandy silt layer deposit in core ns07 25 during the hi period probably related to the enhanced current that was caused by the especially strengthened eawm at that time the last deglacial warming recorded in the relative abundance of warm and cold species of planktonic foraminifer reveals that changes between the easm and eawm were not in phase but alternating between a winter monsoon dominated northern hemisphere influence and a summer monsoon dominated influence of the tropical dynamics and or southern hemisphere climate changes c 2009 elsevier b v all rights reserved

terrigenous fluxes at the celtic margin during the last glacial cycle the sedimentary sections of three cores from the celtic margin provide high resolution records of the terrigenous fluxes during the last glacial cycle a total of 21 14 c ams dates allow us to define age models with a resolution better than 100 yr during critical periods such as heinrich events 1 and 2 maximum sedimentary fluxes occurred at the meriadzek terrace site during the last glacial maximum lgm detailed x ray imagery of core md95 2002 from the meriadzek terrace shows no sedimentary structures suggestive of either deposition from high density turbidity currents or significant erosion two paroxysmal terrigenous flux episodes have been identified the first occurred after the deposition of heinrich event 2 canadian ice rafted debris ird and includes ird from european sources we suggest that the second represents an episode of deposition from turbid plumes which precedes ird deposition associated with heinrich event 1 at the end of marine isotopic stage 2 mis 2 and the beginning of mis 1 the highest fluxes are recorded on the whittard ridge where they correspond to deposition from turbidity current overflows canadian icebergs have rafted debris at the celtic margin during heinrich events 1 2 4 and 5 the highresolution records of heinrich events 1 and 2 show that in both cases the arrival of the canadian icebergs was preceded by a european ice rafting precursor event which took place about 1 1 5 kyr before two rafting episodes of european ird also occurred immediately after heinrich event 2 and just before heinrich event 1 the terrigenous fluxes recorded in core md95 2002 during the lgm are the highest reported at hemipelagic sites from the northwestern european margin the magnitude of the canadian ird fluxes at meriadzek terrace is similar to those from oceanic sites 2002 elsevier science b v all rights reserved

equatorial origin for lower jurassic radiolarian chert in the franciscan complex san rafael mountains southern california lower jurassic radiolarian chert sampled at two localities in the san rafael mountains of southern california 20 km north of santa barbara contains four components of remanent magnetization components a b and b are inferred to represent uplift miocene volcanism and subduction accretion overprint magnetizations respectively the fourth component c isolated between 580 and 680 c shows a magnetic polarity stratigraphy and is interpreted as a primary magnetization acquired by the chert during or soon after deposition both sequences are late pliensbachian to middle toarcian in age and an average paleolatitude calculated from all tilt corrected c components is 1 3 north or south this result is consistent with deposition of the cherts beneath the equatorial zone of high biologic productivity and is similar to initial paleolatitudes determined for chert blocks in northern california and mexico this result supports our model in which deep water franciscan type cherts were deposited on the farallon plate as it moved eastward beneath the equatorial productivity high were accreted to the continental margin at low paleolatitudes and were subsequently distributed northward by strike slip faulting associated with movements of the kula farallon and pacific plates upper cretaceous turbidites of the cachuma formation were sampled at agua caliente canyon to determine a constraining paleolatitude for accretion of the jurassic chert sequences these apparently unaltered rocks however were found to be completely overprinted by the a component of magnetization similar in situ directions and demagnetization behaviors observed in samples of other upper cretaceous turbidite sequences in southern and baja california imply that these rocks might also give unreliable results

determination of black carbon by chemical oxidation and thermal treatment in recent marine and lake sediments and cretaceous tertiary clays abstract several sample treatments and analytical methods for the measurement of black carbon in a wide variety of sediments were considered in which the removal of organic carbon is a critical step in the procedure a comparison between chemical oxidation and thermal treatment was conducted and the latter was shown to be inappropriate due to the polymerisation of organic matter using acid dichromate oxidation reactive kerogen was separated from black carbon in a variety of lake and marine and recent and ancient sediments with relatively small and quantifiable losses 1 6 of black carbon under carefully controlled reaction conditions

climate in sundaland and asian monsoon variability during the last deglaciation abstract the lack of semi quantitative paleo data from mainland southeast asia especially from the emergent sundaland creates a marked difficulty in following the past asian monsoon variability the published pollen records from the adjacent sites to the sundaland were selected in this study and evaluated for the relationship between taxa and plant functional types pfts and subsequently between pfts and biome to eventually reconstruct the semi quantitative temporal temperature and precipitation profile in order to comprehend the asian monsoon modification between 18 5 and 11 ka bp the derived pollen based temperature and precipitation records were further analyzed together with other selected speleothem records from the asian monsoon region with reference to the greenland and antarctic ice cores the warmer temperature in the southern hemisphere caused a southward shift of the mean position of the intertropical convergent zone itcz and weakened the summer monsoon in the asian monsoon region between 18 5 and 15 ka bp the northern hemisphere temperature played an important role in the asian monsoon modification between 15 and 13 5 ka bp where the warmer northern hemisphere conditions strengthened the summer monsoon intensity in the asian monsoon region and moved the mean position of the itcz to the north however the opposing precipitation pattern between the east and the west indian ocean suggested the potential influence of the walker circulation on the sundaland climate from 13 5 to 11 ka bp

organic carbon accumulation in baffin bay and paleoenvironment in high northern latitudes during the past 20 m y the results of the investigation of organic carbon deposition in baffin bay provide important information about paleoenvironmental evolution in high northern latitudes during cenozoic time during miocene to quaternary time organic carbon enrichment of up to 3 insediments sampled at ocean drilling program site 645 was controlled mainly by increased supply of terrigenous organic matter two distinct maxima were identified 1 a middle miocene maximum possibly reflecting a dense vegetation cover and fluvial sediment supply from adjacent islands which decreased during late miocene and early pliocene time because of expansion of tundra vegetation due to global climatic deterioration 2 a late pliocene pleistocene maximum probably caused by glacial erosion and meltwater outwash significant amounts of marine organic carbon were deposited in baffin bay during middle miocene time suggesting higher surface water productivity triggered by the inflow of cold and nutrient rich arctic water masses the decrease in average surface water productivity to values similar to those of modern baffin bay occurred during the late miocene and were probably caused by development of a seasonal sea ice cover reaching maximum expansion during the past 3 4 m y

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

the vegetation and climate at the last glaciation on the emerged continental shelf of the south china sea studies on the dispersal mechanism and source areas of pollen from hemipelagic sediments recovered from the continental slopes of the south china sea scs reveal that vegetation existed on the exposed shelves at the last glacial maximum lgm and the latter part of the marine isotope stage 3 at the low sea level stand artemisiadominated grassland covered the northern continental shelf and tropical lowland rainforest and mangroves grew on the southern shelf sunda land consequently the climate in the northern scs must have been much colder and drier during the last glacial period compared to the present sunda land experienced only a marginally lower temperature but was not drier than today the enhanced contrast between the northern and southern parts of the scs in vegetation and climate during the lgm may be ascribed at least partly to the strengthening of winter monsoon during the last glacial period 2000 elsevier science b v all rights reserved

global fire at the cretaceous tertiary boundary cretaceous tertiary k t boundary clays from five sites in europe and new zealand are 102 104 fold enriched in elemental c mainly soot which is isotopically uniform and apparently comes from a single global fire the soot layer coincides with the ir layer suggesting that the fire was triggered by meteorite impact and began before the ejecta had settled