hopanoid hydrocarbons and perylene in lake biwa japan sediments environmental control on their abundance and molecular composition abstract we examined the vertical distribution of hopanoid hydrocarbons and perylene in sedimentary sections from lake biwa japan and discuss the results with respect to paleoenvironmental information from around the lake region over the last 120 kyr moretene concentration was high above the sections where fall out events of tephra tephra at occurred ca 30 kyr before present bp this feature suggests that the tephra fall out events created o 2 deficient conditions resulting in high activity of methane producing bacteria and of methanotrophic moretene producing bacteria becoming active above the tephra layer five sections at 10 20 kyr ca 35 kyr ca 70 kyr ca 90 kyr and ca 110 kyr bp exhibited peaks in the ratio of 17 21 22r homohopane to 17 21 22r homohopane hopc 31 the n c 23 n c 31 alkane ratio in these sections was 0 6 0 1 n 49 very low if compared with typical characteristics of n alkanes for a sphagnum peat environment n c 23 n c 31 ca 3 6 bingham et al 2010 we conclude that sphagnum peat may not have been an important contributor of n alkanes over the past 120 kyr comparison with previous pollen records for the lake region suggests that high hopc 31 values may be caused by production of acidic soil from expansion of temperate conifer e g cryptomeria forest under cold and wet climate conditions the abundance of perylene relative to sediment or total organic carbon toc was high in the sections at ca 20 kyr ca 70 kyr and ca 90 kyr bp these sections were approximately in accord with those having a maximum in hopc 31 this concordance indicates that the climatic conditions suitable for the production of perylene quinone in soil surrounding the lake coincided with those for a high hopc 31 ratio thus hopc 31 and perylene toc might be useful as proxies of soil acidity temperature and humidity

reinterpretation of late quaternary sediment chronology of lake biwa japan from correlation with marine glacial interglacial cycles a review of published stratigraphic records of pollen sediment grain size diatoms and organic matter composition from lake biwa japan identifies four pre holocene episodes of milder climate increased surface runoff and enhanced aquatic productivity indicating intervals of warmer and wetter conditions which are interpreted as being interglacial correlation of these episodes to times of marine interglacial periods revises the age scale of the lake biwa sediment sequence which has been based on fission track dating the revised chronostratigraphic scale proposes an age of ca 430 000 yr b p for the base of the 250 m thick t bed instead of the former age of ca 700 000 yr b p

eolian deposition in the northeast pacific ocean cenozoic history of atmospheric circulation the mass accumulation rate and grain size distribution of the total eolian component of north pacific pelagic clays have been used to evaluate changes in eolian sedimentation and in the intensity of atmospheric circulation that have occurred during the past 70 m y eolian deposition was relatively low approximately 12 mg cm2 1 000 yr in the late cretaceous and paleocene reflecting an increasingly humid environment a peak in accumulation rates across the paleocene eocene boundary may be the result of episodic volcanism in mexico a sharp decrease in grain size across the paleocene eocene boundary is not readily interpreted fine eolian grain size and the low accumulation rates averaging 8 mg cm2 1 000 yr in the eocene and early oligocene are in agreement with low early tertiary thermal gradients and less vigorous atmospheric circulation large increases in grain size between 37 and 30 m y ago 20 and 10 m y ago and 5 m y ago to the present suggest that atmospheric circulation intensified by a factor of 1 5 1 8 and 1 4 respectively at these times eolian accumulation rates increased from 8 mg cm2 1 000 yr at the eocene oligocene boundary to approximately 25 mg cm2 1 000 yr at the end of the miocene with significant changes at 25 and 13 m y ago increased rates about 25 m y ago probably reflect movement of the core site into the influence of the westerlies and the increase 13 m y ago appears to be a response to steepening thermal gradients and intensifying atmospheric circulation resulting from major expansion of antarctic ice in the mid miocene along with a general increase in global aridity in the late cenozoic an order of magnitude increase in eolian accumulation rates 25 to 226 mg cm2 1 000 yr in pliocene pleistocene time coincides with the onset of northern hemisphere glaciation and consequent climatic deterioration the large increase in accumulation rates in pliocene pleistocene time coincides with a relatively smal increase in the intensity of atmospheric circulation compared to that in oligocene and miocene time suggesting that the increased deposition rates were the result of an increase in global aridity in glacial times rather than a further increase in the vigor of the global wind systems

atlas of pollen spores and further non pollen palynomorphs recorded in the glacial interglacial late quaternary sediments of lake suigetsu central japan abstract the record of well preserved palynomorphs from sediment samples of lake suigetsu mirrors temporal changes in the flora around the lake and spatial changes in the vegetation cover of central japan during the late quaternary this study presents photographic images of 169 identifiable types of moss lycophyte and fern spores and pollen of gymnospermous and angiospermous plants from the sg06 core sediment obtained at a standard magnification of ca 750 additionally non pollen palynomorphs npps which appeared in the pollen slides are documented including remains of fungi rhizopods arthropods rotifers flatworms as well as green algae and plant tissue fragments all documented taxa are presented in taxonomical order on 66 plates including 55 plates for pollen and spores of higher plants and 11 plates for npps this study renders an overview on quality of preservation and on the range of palynomorphs found in the last glacial interglacial sediments of lake suigetsu and furthermore may serve as a handy and thorough guide for palynological investigations aiming at the reconstruction of past vegetation environmental and climate dynamics

magnetic grain size and viscous remanent magnetization of pelagic clay unfossiliferous pelagic clay red clay cores from the pacific generally have unstable remanent magnetization except for tens of centimeters to several meters below the surface the origin of this instability has been considered to be viscous remanent magnetization vrm we conducted a rock magnetic study of a pelagic clay core from the south pacific which has the unstable to stable transition at about 1 5 m below the surface using the suspension method of yoshida and katsura 1985 we determined downcore variation of complete alignment magnetization cam and magnetic moment distribution geometric mean moment mg and log standard deviation log a assuming a lognormal distribution mean magnetic grain diameter was calculated from the mg using the saturation magnetization of magnetite 4 8 105 a m 1 on the assumption that all the magnetic grains are single domain magnetites of spherical shape this assumption is supported by thermomagnetic analyses isothermal remanent magnetization irm acquisition experiments and the ratio of cam to saturation irm the grain diameter ranges from about 0 02 to 0 15 m and decreases with depth below about 1 5 m the derived grain size holds even when the magnetites in the sediments suffered oxidation because the saturation magnetization of maghemite is close to that of magnetite the frequency dependence of magnetic susceptibility showed a downward increase in the amount of superparamagnetic grains on the other hand the magnetic viscosity acquisition coefficient normalized by the cam increases with depth we conclude that magnetic grain size can control the magnitude of the secondary magnetization vrm of pelagic clay it has been proposed that the major source of pelagic clay is atmospherically transported dust intensified global atmospheric circulation by the change of climate would raise the grain size of the magnetic minerals of the eolian component which can cause the unstable to stable transition of the remanent magnetization

the importance of double diffusion to the settling of suspended material the vertical fingering motions which can occur when warm salty water overlies colder fresher water are important to the vertical flux of salt in the ocean an analogous and not uncommon situation is that where turbid water overlies clearer and denser water for the case of an originally sharp horizontal interface between the two water layers associated as an example with an interflow due to a warm muddy river entering a stratified lake the resulting downward sediment flux is compared with that occurring by way of gravitational settling rules are proposed to ascertain when the fingering effect could be important to sedimentation for example it seems that fingering could be of consequence in the situation where the sediment has a diameter of 2 m and the upper layer is about 1 c warmer than the clear lower layer when the upper layer concentration is 1 ppm the effect of fingering on the residence time of a gravitationally stable turbid layer is calculated such layers may be more short lived than commonly thought

the characterization of viscous remanent magnetization in large and small magnetite particles previous work on the properties of viscous remanent magnetization vrm have shown that it can play an important role in some paleomagnetic investigations the results of this study on the properties of vrm of very fine single domain sd and coarse multidomain md magnetite particles ranging in size from 0 02 to 60 m indicate that the md samples are very sensitive to the previous magnetic history of the samples the af demagnetization causes a dramatic decrease in the ability of md samples to acquire vrm compared to the same sample with an undemagnetized thermal remanent magnetization trm thermal demagnetization of the same md samples causes an increase in the ability to acquire vrm components submicron sd samples show vrm acquisition and decay curves that are independent of previous magnetic treatment both md and sd samples are extremely sensitive to the length of time of zero and weak field storage that occurs prior to the application of the external vrm field a model using the total energy of the system is used to describe the above results

vegetation changes and associated climate variations during the past 38 000 years reconstructed from the shaamar eolian paleosol section northern mongolia abstract this study presents a pollen based reconstruction of the vegetation changes and associated climate variations at the shaamar eolian paleosol section in the northern mongolian plateau the semi quantitative reconstructions of paleovegetation types and temperature and moisture indices show that the vegetation in the shaamar area was a taiga forest dominated by picea abies and pinus sibirica type between 38 000 and 30 000 cal bp when the reconstructed moisture level was the highest of the past 38 000 years the vegetation during the ensuing period from 30 000 to 23 000 cal bp was mainly a steppe dominated by artemisia and poaceae under low temperature and relatively low moisture conditions the vegetation during the period from 23 000 to 10 000 cal bp varied from a taiga forest through steppe dominated by poaceae taiga forest and forest steppe to a taiga forest the climate was cold and relatively dry in the early phase 23 000 to 20 000 cal bp and warmer and somewhat drier in the later phase 19 000 to 11 000 cal bp the pollen assemblages and the vegetation zonal indices suggest that the vegetation was a forest steppe during the period from 10 000 to 3000 cal bp under rising temperature and low moisture conditions a taiga forest has dominated the landscape during the past 3000 years under cooling and wetting conditions comparison of our pollen record with other paleoclimatic records suggests that the climate changes in the northern mongolian plateau have been controlled or modulated by ocean atmospheric coupling dynamics in the north atlantic region

an experimental study of magnetic viscosity in synthetic monodomain titanomaghemites implications for the magnetization of the ocean crust a study of magnetic viscosity in well characterized synthetic monodomain titanomaghemites of composition fe2 4ti0 6o4 is described it is found that the samples are capable of acquiring a viscous remanent magnetization vrm only when they are highly oxidized the same assembly does not show significant magnetic viscosity for 0 1 z 0 6 where z is the oxidation degree this is a result of their being in the thermally stable monodomain state with high anisotropies the observed increase in vrm for the highly oxidized material may be entirely due to the decrease in magnetic anisotropy a decrease in the total number of fe2 as a functin of oxidation results in a decrease in coercive force i e magnetic anisotropy of the initial monodomain titanomaghemites it is thought that the dramatic decrease in magnetic anisotropy at room temperature may be the main cause of the observed increase in vrm for the highly oxidized material finally we conclude that the ability of the magnetic layer of the ocean crust to acquire a vrm increases as the maghemitization degree increases

magnetic properties of light and dark sediment layers from the japan sea diagenetic and paleoclimatic implications abstract rock magnetic paleoclimatic diagenetic relationships of sediments spanning the last 0 78 ma have been investigated using samples collected from light and dark layers recovered at odp sites 794 yamato basin and 795 japan basin rock magnetic parameters k k fd arm sirm s ratio are shown to reflect diagenetic processes and climate related variations in the concentration mineralogy and grain size of the magnetic minerals contained within the sediments the magnetic mineralogy is dominated by ferrimagnetic magnetite type minerals with a small contribution made by hematite and iron sulphides such as pyrrhotite and or greigite magnetic mineral concentration and grain size vary between light and dark layers with the former characterized by a higher magnetic content and a finer magnetic grain size magnetite dissolution related to sulfate reduction due to bacterial degradation of organic matter is the process responsible for the magnetic characteristics observed in the dark layers testifying to the reducing conditions in the basin variations in the rock magnetic properties of the sediments are strongly correlated with global oxygen isotope fluctuations with glacial stages characterized by a lower magnetic mineral content and a coarser magnetic grain size relative to interglacial stages major downcore changes in the magnetic properties observed at site 794 can be related to changes in the oceanographic conditions of the basin associated with the flow of the warm tsushima current into the japan sea at about 0 35 0 40 ma ago

orbital and millennial scale climate and vegetation changes between 32 5 and 6 9k cal a bp from hanon maar paleolake on jeju island south korea orbital and millennial scale climate and vegetation changes between 32 5 and 6 9k cal a bp from hanon maar paleolake on jeju island korea were demonstrated by high resolution multi proxy data pollen magnetic susceptibility total organic carbon carbon nitrogen ratios and sediment grain size high resolution pollen records provided detailed information on the vegetation response to climate change the thalictrum pollen percentage which corresponded to the magnetic susceptibility data and the first principal component of principal component analysis of pollen data were good indicators of the orbital and millennial scale dry wet cycle in the study area hanon pollen and magnetic susceptibility records suggested that colder and drier conditions were prevalent between 25 2 and 17 6k cal a bp in the study area due to a precession induced decrease in summer insolation hanon multi proxy data were correlated with oxygen isotope records from greenland and hulu cave suggesting the possible teleconnection of millennial scale climate oscillations between north atlantic and east asian regions according to our results heinrich like cold events probably occurred around 31 1 25 2 and 16 7k cal a bp and the warm intervals observed around 30 7 and 29 9k cal a bp may have corresponded to dansgaard oeschger warm events 4 and 3 respectively

the influence of diffusive convection on sedimentation from buoyant plumes abstract diffusive convection driven by the differential diffusion of density altering fluid properties may enhance the scavenging of particles from natural buoyant plumes for single phase fluid solute heat systems this phenomenon has been extensively studied because salt fingering generated at the oceanic thermocline is a major mechanism of salt transport in the oceans however the influence of this process on particle laden plumes for example fluvial plumes in lakes and estuaries volcanic clouds and seafloor hydrothermal plumes is largely unknown in this paper we present direct experimental measurements of the interfacial particle flux at the plume base which can be applied to predict particle scavenging from natural buoyant plumes particle flux is measured using a light attenuation technique employing a chain of photodiodes which average concentration over a large number of fingers the results are in good general agreement with earlier studies based on finger velocity flux measurements cover a wide range of conditions from those where diffusive convection dominates to those where settling and diffusive convection are of a similar magnitude for very small particles double diffusive salt finger theory is applicable to two component particulate systems as suggested by earlier studies green t 1987 the importance of double diffusion to the settling of suspended material sedimentology 34 319 331 two component diffusive convection theory is extended to three components in order to predict particle scavenging from marine fluvial plumes which involve the diffusion of sediment salt and heat for larger particles which settle significantly the flux can be approximated by adding the double diffusive and settling fluxes a theory to predict particle transport through the lower layer and sedimentation at the bed is developed based on the observation of strong convection below the plume application of our theory and experimental results indicates that while double diffusion may significantly influence the longitudinal distribution and vertical sorting of deposits from lacustrine plumes the diffusive convection process is generally insignificant in marine plumes observational evidence for lacustrine double diffusion based on water column measurements is presented

an alternative to exotic spore or pollen addition in quantitative microfossil studies uncertainties in availability and formulation of exotic microfossils e g lycopodium spp eucalyptus spp to be added to microfossil preparations may be resolved by the use of plastic microspheres 25 0 1 0 m which are unaffected by standard pollen preparative treatments koh hcl hf acetolysis and organic solvents the microspheres are sensitive to strongly oxidizing treatments e g schulze s reagent h2o2 h2so4 reflux for diatom preparation but can be added following digestion of organic material preparation of microsphere suspensions in a suitable electrolyte e g nacl formic acid water permits calibration by coulter counter of suitable dilutions e g 5000 100 ml 1 for delivery by tipet volumetric flasks the uniformity and distinctive appearance of the microspheres not only facilitate recognition but also provide a constant reference for both size 25 m and volume 8180 m3 as well as a reference standard for computerized microfossil scanning the microspheres are inert

response of vegetation in central japan to precession during the last 147 000 years a lignin record from lake biwa core biw08 b abstract to understand the responses of terrestrial vegetation in central japan to global climate changes we generated a record of lignin composition from core biw08 b in lake biwa central japan during the last 147 000 years by tmah pyrolysis gc ms lignin abundance was intermittently elevated and associated with a high ratio of cinnamyl c to vanillyl v phenols c v ratio of lignin suggesting episodic inflows of herbaceous plant derived organic matter into lake biwa the largest inflow occurred during the last deglaciation variation in the ratio of syringyl s to vanillyl v phenols s v ratio which is a contribution index of angiosperms against gymnosperms showed a precession like cycle was consistent with a pollen record from lake biwa and showed a pattern similar to the s v record from an offshore marine site in the northwestern pacific the variation reflected the regional replacement of cool temperate deciduous broadleaf forests subalpine conifer forests and japanese cedar forests in central japan caused by the repetition of warmer dry and cooler wet climates on a precession cycle

settling driven convection a mechanism of sedimentation from stratified fluids convection driven by sediment particles may play an important role in sedimentation from the base of buoyant hypopycnal plumes for example fluvial plumes in stratified estuaries and lakes black smokers on the ocean floor volcanic clouds and coastal currents in addition to the well known double diffusive convection mechanism another mode of convective instability development is by settling across the density interface we performed laboratory experiments to investigate this fingering convective instability mechanism and its effect on particle distribution in the water column and deposition at the bed a simple theoretical model of finger formation at a fluid density interface is developed based on an analogy with thermal plume formation at a flat heated plate this model which involves a thickening interface layer that becomes gravitationally unstable relative to the ambient fluid is in good agreement with measurements of finger size and instability wavelength from visualization experiments since fingering at the density interface drives larger scale convection in the fluid below a mass balance model of the lower layer assuming strong mixing i e uniform sediment concentration is successfully applied to predict sediment concentration in the water column and deposition at the bed strong mixing can be assumed since convective velocities are usually much greater than the particle fall velocities as convection proceeds the sediment concentrations in the two layers approach each other and convection will die out using the model equations we develop analytical expressions for the time when convection ceases and the portion of sediment remaining in the water column

neogene history of the south pacific tradewinds evidence for hemispherical asymmetry of atmospheric circulation rea d k and bloomstme m k 1986 neogene history of the south pacific tradewmds evidence for hemlsphermal asymmetry of atmospherm circulation palaeogeogr palaeochmatol palaeoecol 55 55 64 eohan dust grains extracted from southeast pacific pelagic sediments provide a neogene record of southern hemisphere atmospherm processes the mass accumulation rate of dust has been low and generally constant at 1 4 mg cm 2 103 y since the late ohgocene eohan grains ze data show an increase from 8 20 3 40 t m older sediments to 7 20 6 80 t m younger materml this shift occurred about 10 5 m y ago and reflects a s gmfmant increase in the intensity of atmospheric circulation then there s no obwous response to the onset of northern hemisphere glacmtmn 2 5 m y ago m these eohan records from the south pacific compamson with existing lnformatmn from the northern hemisphere suggests that the southern hemisphere has had more intense atmospheric circulation throughout the neogene and that this asymmetry reached its greatest extent between 10 5 and 2 5 ma

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

origin of stable remanent magnetization of siliceous sediments in the central equatorial pacific abstract siliceous sediments distributed in the central equatorial pacific have a stable remanent magnetization regardless of age or depth this is in contrast with the unstable remanence of unfossiliferous red clay defined as pelagic clay here which accumulates in the middle latitudes of the pacific we have conducted a rock magnetic study of the siliceous sediments to clarify the magnetic carriers of the stable remanence for this purpose we combined magnetic granulometry by the suspension method and observation of magnetic grains with a transmission electron microprobe tem the advantage of the former is that the magnetic extraction procedure is not required for obtaining size distribution of the magnetic grains in sediments the tem observations revealed that most of the magnetic extracts are identical in size and shape to bacterial magnetosomes the suspension method proved that the magnetic assemblages of the siliceous sediments of both quaternary and early miocene age have mean diameters of about 0 05 m which is within the single domain range of magnetite and have narrow size distributions compared with pelagic clay these characteristics can be explained if the magnetofossils observed by tem are the major constituent of the magnetic grains in the sediments and have been preserved for a long period of time the difference in the stability of the remanent magnetization between the siliceous sediments and the pelagic clay can be explained by the difference in the size distribution of magnetic grains which would reflect differences in their sources i e biogenic vs detrital eolian

climate and environmental changes for the past 44 ka clarified by pollen and algae composition in the ulleung basin east sea japan sea abstract the pollen and algae records derived from core kces 1 in the east sea japan sea reveal vegetation and climate changes during the past 44 ka from 44 to 36 cal ka bp forest vegetation in the coastal regions of ulleung basin was composed predominantly of subalpine conifer forest open grassland covered the exposed continental shelves indicating a cool and dry climate during the period of 36 28 3 cal ka bp a warmer and wetter climate caused the contraction of subalpine conifer forest in the coastal regions of ulleung basin and the expansion of marsh in the exposed continental shelves from 28 3 to 17 6 cal ka bp the sea level decline restricted the herbs pollen originates in the exposed shelf of east china sea and yellow sea inflow into the east sea japan sea and caused the reduction of herbs pollen in the site location during the time interval of 17 6 15 1 cal ka bp a great expansion of subalpine conifer forest can be regarded as the consequence of enhanced east asian winter monsoon eawm the obvious increase in temperate deciduous broadleaved trees spores and algae can be attributable to the rising of sea level and the warming of climate from 15 1 to 12 1 cal ka bp during the period of 12 1 to 5 3 cal ka bp broadleaved taxa increased especially during the time period of 9 5 5 3 cal ka bp evergreen broadleaved trees pollen reach the highest values throughout the core as a result of the holocene climate optimum condition vegetation changes controlled by humid impacts occurred at the late holocene as indicated by an increase in pinus pollen

long term fire activity under the east asian monsoon responding to spring insolation vegetation type global climate and human impact inferred from charcoal records in lake biwa sediments in central japan abstract records of sedimentary charcoal provide fire histories for assessing the relationship between fires and climate conditions vegetation human impact and other factors we analyzed charcoal particles in sediments from lake biwa in central japan dating back to 150 000 years ago the sediments are well dated homogenous and had a constant sedimentation rate making them ideal for assessing the long term fire history through charcoal concentration analysis low charcoal concentrations in the glacial periods of marine isotope stage mis 2 and 6 indicate that few fires occurred in the periods under the cold climatic conditions variations in the microcharcoal concentration between 40 000 and 130 000 years ago with a periodicity of 21 000 23 000 years correspond to variations in the spring insolation in central japan vegetation type and global climate suggesting that the long term fire activity in central japan was determined mainly by spring insolation and vegetation type under the influence of global climate change this finding suggests that insolation changes induced by precession cycles could influence a long term phenomenon in an area as a direct local effect between 16 000 and 3000 years ago sediments were characterized by an extraordinarily high concentration of large charcoal particles 50 m and the predominance of elongated charcoal particles suggesting that grassland fires presumably anthropogenic occurred frequently in the lakeside area the frequent fire occurrence presumably contributed to the inflow of a large amount of organic materials resulting in changes in the aquatic environment of lake biwa and or its adjacent area

rock magnetic records of the sediments of the eastern arabian sea evidence for late quaternary climatic change abstract rock magnetic measurements along with grain size acid insoluble residue air organic carbon oc caco3 and 18o of the planktonic foraminifers of the sediments were determined for 15 gravity cores recovered from the western continental margin of india magnetic susceptibility ms values in the surficial sediments reflect the land derived input and in general are the highest in terrigenous sediment dominated sections of the cores off saurashtra ratnagiri followed by the sediments off indus gulf of kachchh and then mangalore cape comorin the down core variations in mineral magnetic parameters reveal that the glacial sediments off the indus are characterized by low ms values s ratios associated with high air content low oc caco3 contents and relatively high 18o values while those off sw india are characterized by low ms values high s ratio associated with low air content and relatively high oc caco3 and 18o values conversely the early holocene sediments of all cores are characterized by high ms values s ratio associated with high air content low oc caco3 contents and gradually decreased 18o values these results imply that during the last glacial maximum lgm the cores off northwestern india received abundant continental supply leading to the predominance of eolian fluvial sedimentation in the sw region the influence of hinterland flux is less evident during this period but convective mixing associated with the ne monsoon resulted in increased productivity during the early holocene intense sw monsoon conditions resulted in high precipitation on land which in turn contributed increased air content ms values in the continental margin sediments a shallow water core off kochi further suggests that the intense sw monsoon conditions prevailed until about 5 ka the late holocene organic rich sediments of the sw margin of india were however subjected to early diagenesis at different intervals in the cores therefore caution is needed when interpreting regional climatic change from down core changes in sediment magnetic properties

convective instability in sedimentation linear stability analysis 1 convective sedimentation in a stably stratified saltwater is studied using the linear stability analysis convective sedimentation is known to occur due to the double diffusive mechanism and the settling driven mechanism in this study a semi empirical closure of sediment diffusivity based on the long range hydrodynamics effect is adopted the sediment phase can act as either the slow or fast diffusing agent in the double diffusive system for the given salt diffusivity moreover the settling driven effect is proportional to the square of the sediment diameter via stoke settling law we consider sediment concentration grain size in the upper freshwater layer to be in the range of 0 1 to 39 4 g l 2 to 60 m which is on top of a saltwater layer with salinity 35 ppt linear stability analysis allows us to identify the dominant mechanism that triggers the instability the growth rate and the resulting characteristic finger width model results suggest that for fine sediment with grain diameter smaller than 10 m settling velocity 0 09 mm s double diffusive mechanism controls the instability and the resulting sediment finger size is of millimeter scale for the given threshold of growth rate of o 0 01 s 1 the minimum sediment concentration is about 8 15 g l for grain size greater than or around 10 m the settling driven mechanism dominates and instabilities occur at sediment concentration as low as o 0 1 g l with centimeter scale fingers our findings may contribute to a better understanding on the observed rapid sediment removal in the plume of small mountainous rivers

mixing by shear instability at high reynolds number 1 shear instability is the dominant mechanism for converting fluid motion to mixing in the stratified ocean and atmosphere the transition to turbulence has been well characterized in laboratory settings and numerical simulations at moderate reynolds number it involves rolling up i e overturning of the density structure within the cores of the instabilities in contrast measurements in an energetic estuarine shear zone reveal that the mixing induced by shear instability at high reynolds number does not primarily occur by overturning in the cores rather it results from secondary shear instabilities within the zones of intensified shear separating the cores this regime is not likely to be observed in the relatively low reynolds number flows of the laboratory or in direct numerical simulations but it is likely a common occurrence in the ocean and atmosphere

fossil bacterial magnetite in deep sea sediments from the south atlantic ocean the magnetostratigraphy of deep sea sediment cores has proven to be a powerful and high resolution method of dating and comparing sedimentary records in contrast to this widespread application relatively few attempts have been made to analyse and identify the mineralogy grain size and origin of the carrier of the remanent magnetization1 2 it is widely assumed that dominant ferrimagnetic minerals in deep sea sediments are of lithogenic origin that is that they derive from oceanic or continental detritus volcanic ashfalls micrometeorites hydrothermal precipitation or chemical mineralization processes a very different view was taken by kirschvink and lowenstam3 who suggested that fossil remnants of magnetite mineralizing organisms in particular magnetotactic bacteria might play an important part in the magnetization of sediments deposited in certain detritus poor aquatic systems we have used rock magnetic diagnostic methods to characterize the magnetic phases in deep sea sediments from the south atlantic these phases were then extracted and studied with the electron microscope our results indicate that fossil bacterial magnetite is the main carrier of the natural remanent magnetization in sediments ranging in age from quarternary to eocene different types of bacterial magnetosomes were detected most of them occurring in chains of identical particles and nearly all of them falling into the theoretically determined4 size range of single domain magnetitite

short term changes in seafloor character due to flood derived hyperpycnal discharge typhoon mindulle taiwan july 2004 during typhoon mindulle in early july 2004 the choshui river central western taiwan discharged similar to 72 mt of sediment to the eastern taiwan strait peak concentrations were g 200 g l similar to 35 40 of which was sand box core samples and chirp compressed high intensity radar pulse sonar records taken just before and after the typhoon indicate that the hyper pycnal sediment was first deposited adjacent to the mouth of the choshui subsequently resuspended and transported northward via the taiwan warm current and redeposited as a patchy coastal band of mud dominated sediment that reached thicknesses of 1 2 m within megaripples within a month most of the mud was gone probably continuing its northward transit but more mud appeared in late august in response to typhoon aere following autumn and winter storms the entire nearshore area was again sand dominated by early spring

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

modelling magnetization data using simplex two new approaches to modelling magnetization data are described the first approach models the magnetic properties of natural materials in terms of mixtures of possible source materials the second approach models the magnetic properties of natural materials in terms of mixtures of magnetite and haematite crystals of varying concentrations and grain sizes in the second approach the magnetic characteristics of magnetite and haematite and their variation with grain size are described by bicubic spline functions the methods are applied to remanence and susceptibility measurements on a suite of lake sediment particle size fractions and on a set of samples from a soil profile

temperature and seawater isotopic controls on two stalagmite records since 83 ka from maritime japan abstract millennial scale interstadial dansgaard oeschger d o cycles and heinrich h stadial events are pronounced paleoclimatic features during the last glacial period which were first demonstrated in the north atlantic region these stadial and interstadial events are expressed in marine and terrestrial high resolution records elsewhere in the world but the magnitude and mode of the regional climate changes are still poorly quantified here we present new replicated stalagmite 18o profiles from two caves in central japan which extend back to 83 4 ka the records clearly display the h7 to h3 events but not d o cycles an important feature of the two japanese stalagmites is the small difference 2 9 in 18o values between the mid holocene and the last glacial maximum lgm long term trends of the stalagmite 18o values at the more maritime site generally follow that of the 18o record of seawater which is responsible for 1 1 of the 2 9 difference between mid holocene and lgm the remaining 1 8 in the difference can be accounted for by 9 c of warming between the lgm and mid holocene and 3 c cooling at h events which are comparable with the previous estimates of land paleo temperature in the japanese islands the attenuated isotopic signal associated with d o interstadials indicates that the warming in the atlantic did not significantly transfer to the maritime japan these unique features of the isotopic records of the japanese stalagmites are due to the geographic position at the vicinity of the moisture source kuroshio warm current

characterization of viscous remanent magnetization in single and multi domain magnetite grains viscous remanent magnetization acquisition and decay coefficients are shown to be strongly affected by the previous magnetic history of the samples demagnetization of coarse grain multi domain magnetite samples using alternating magnetic fields causes a sharp reduction in the ability to acquire viscous magnetization vrm acquisition in single domain particles is not affected by af demagnetization but is sensitive to the amount of time the sample is kept in zero magnetic field storage prior to applying the vrm field vrm acquisition coefficients are strongly dependent on magnetic grain size with high values at both very small and very large grain diameters

14c activity and global carbon cycle changes over the past 50 000 years a series of 14c measurements in ocean drilling program cores from the tropical cariaco basin which have been correlated to the annual layer counted chronology for the greenland ice sheet project 2 gisp2 ice core provides a high resolution calibration of the radiocarbon time scale back to 50 000 years before the present independent radiometric dating of events correlated to gisp2 suggests that the calibration is accurate reconstructed 14c activities varied substantially during the last glacial period including sharp peaks synchronous with the laschamp and mono lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14c production rate together with plausible changes in deep ocean ventilation and the global carbon cycle during glaciation

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

magnetic mineral diagenesis abstract reduction oxidation redox reactions occur during burial because sediments contain reactive mixtures of oxidised and reduced components diagenetic chemical reactions represent the approach of all sedimentary components toward equilibrium and control the long term stability of sedimentary iron bearing minerals magnetic minerals are sensitive indicators of sedimentary redox conditions and of changes in these conditions through time with diagenetic effects ranging from subtle to pervasive despite the importance of magnetic mineral diagenesis in paleomagnetism rock magnetism and environmental magnetism and the usefulness of these subjects in the earth and environmental sciences there is no systematic single published treatment of magnetic mineral diagenesis this paper is an attempt to provide such a treatment for the full range of diagenetic environments magnetic mineral diagenesis during early burial is driven largely by chemical changes associated with organic matter degradation in a succession of environments that range from oxic to nitrogenous to manganiferous to ferruginous to sulphidic to methanic where the free energy yielded by different oxidants decreases progressively in each environment in oxic environments the most important diagenetic processes involve surface oxidation of detrital minerals and precipitation of fe3 bearing minerals from solution in ferruginous environments the most reactive detrital and authigenic iron oxides undergo dissolution often mediated by dissimilatory iron reducing bacteria which releases fe2 that becomes available for other reactions the fe2 in solution can diffuse upward where it is oxidised to form new authigenic iron oxyhydr oxide minerals or it can become bioavailable to enable magnetotactic bacteria to biomineralise magnetite generally at the base of the overlying nitrogenous zone alternatively dissimilatory iron reducing bacteria can produce extracellular magnetite within ferruginous environments in sulphidic environments iron bearing detrital mineral assemblages undergo more radical alteration hydrogen sulphide which is a byproduct of bacterial sulphate reduction or of anaerobic oxidation of methane reacts with the fe2 released from iron mineral dissolution or directly with solid iron oxyhydr oxide minerals to form iron sulphide minerals mackinawite greigite and pyrite authigenic growth of ferrimagnetic greigite has important implications for paleomagnetic recording secondary iron sulphide formation can also occur as a result of anaerobic oxidation of methane methane migration through sediments in association with biogenic or thermogenic methane production or in association with gas hydrate dissociation can disrupt the diagenetic steady state and give rise to greigite and monoclinic pyrrhotite formation that remagnetises sediments most of the above described diagenetic processes occur below 50 c with continuing burial above 50 c but at sub metamorphic temperatures magnetic minerals can undergo further thermally induced chemical changes that give rise to a wide range of mineralogical transformations that affect the magnetic record of the host sediment these changes include remagnetisations magnetic analysis can provide much valuable information concerning diagenesis in environmental processes the range of processes discussed in this paper should assist researchers in analysing sediment magnetic properties for which the assessment of diagenetic effects has become a necessary component

environmental rock magnetism of pelagic clay implications for asian eolian input to the north pacific since the pliocene we conducted a rock magnetic study of pelagic sediments in order to document variations of asian eolian input to the north pacific since the pliocene the materials studied consist of five pelagic clay red clay cores of several meters long taken from the central north pacific and surface sediments of box cores obtained at 40 sites along two lines a n s line along 175 e and an e w line along 20 n the magnetic susceptibility concentration of magnetic minerals and s ratio relative abundance of low coercivity magnetic minerals of the five pelagic clay cores have decreased synchronously since about 2 5 ma this age coincides with the onset of the northern hemisphere glaciation and chinese loess deposition geographical distribution of s ratios measured on the surface sediments revealed that they are remarkably low in the central north pacific these facts suggest that s ratio can be used as a proxy for asian eolian dust mossbauer spectroscopy showed that hematite dominates the high coercivity minerals observation with a transmission electron microscope suggests two sources of magnetic minerals in the pelagic clay biogenic magnetite produced in situ and detrital magnetite and hematite the variations of s ratio and magnetic susceptibility with time and region can be explained by a model that asian eolian dust has higher lower hematite magnetite concentration than other sources of magnetic minerals and that its input to the central north pacific has increased since 2 5 ma we recognized subtle s ratio fluctuations of about 400 kyr in recurring intervals superimposed on the decreasing trend since 2 5 ma rock magnetic parameters diagnostic of magnetic grain size on the other hand showed small or no variations with age although eolian grain size is generally thought to have increased significantly since the pliocene based on sedimentological studies

response of a coarse grained fluvial to coastal depositional system to glacio eustatic sea level fluctuation since the last glacial maximum an example from the tenryu river japan modern coarse grained deltas are common in tectonically active coastal zones however the stratigraphic architecture and evolution of these deltas in relation to allogenic forcing are poorly understood compared with fine grained deltas mainly because of short vertical exposure in outcrop and lack of detailed ages this paper investigates the coarse grained delta in the lower reaches of the tenryu river developed at an island arc collision coast through analyses of radiocarbon dated core sediments and borehole data the vertical successions of the proximal and distal part of the delta constitute basal coarse grained braided river deposits overlain by fine grained sand and mud accumulated under temporary marine influence the fine grained deposits in turn are covered mainly with coarse grained braided river deposits in the proximal part and upper shoreface to beach sand and gravel in the distal part at the apex of the delta in contrast the fine grained deposits are almost absent and thick gravels dominate allogenic forcing especially the rate of glacioeustatic sea level change has influenced the accumulation rates and stacking pattern of the delta most of the sediment may have been transported to the deep sea via a canyon and deposition has been minimal under the present subaerial delta before 14 ka although aggradation almost equivalent to rapid sea level rise 15 mm yr is found at the proximal part between ca 11 5 and 8 ka even with significant basin sediment yield and supply transgression occurred and gravel supply to the coast waned notably only 30 of the sediment yield from the upstream catchment might have been trapped under the present delta plain during that period this means that large amounts of sediment were transported farther offshore or alongshore in contrast slow aggradation in the proximal part and apex of the delta accompanied by progradation in the distal part might become dominant during the past 8 ka when the rate of sea level rise decreased to 10 mm yr a similar response was also observed at other holocene fluvio deltaic systems although they are very different in their geological setting such as sediment supply water discharge tectonic movement and gradient of river and shelf the results imply that the rate of sea level rise and its change have a greater significance on coastal depositional systems than other factors such as fluvial sediment supply this study contributes to an improved understanding of evolution of modern and ancient coarse grained deltas and reconstruction of sea level change from geological data

secondary remanent magnetization of pelagic clay in the south pacific application of thermal demagnetization previous paleomagnetic studies have revealed that pre quaternary pelagic clay with neither siliceous nor calcareous fossils has unstable remanent magnetization and that alternating field af demagnetization is not effective to remove the secondary magnetization this study applied thermal demagnetization on pelagic clay from the south pacific and recovered characteristic directions the observed paleolatitudes agree with those from plate tectonic analysis which proves that the thermal demagnetization worked well the magnetic overprint is estimated to be viscous remanent magnetization vrm from vrm acquisition experiment a hypothesis is proposed that the magnitude of the vrm of pelagic clay has been controlled by the grain size of magnetic minerals of eolian origin which has been subjected to the intensity of the global atmospheric circulation this can explain the late pliocene unstable to stable transition of the remanence which has been observed widely in the pacific

last 40ka climate changes as deduced from the lacustrine sediments of lake biwa central japan abstract sequential changes of aeolian dust and lake primary productivity since the last 40 ka observed in lacustrine sediment core from lake biwa central japan and provide high resolution climate changes in relation to the asian monsoon activities and the westerlies in east asia quartz content is very useful as a proxy record for reconstructing aeolian dust changes influenced by paleointensity of the asian winter monsoon and the westerlies since the last glacial on the other hand total organic carbon toc and opal a contents are useful as a proxy record for reconstructing primary biological production by paleo precipitation influenced by paleointensity of the asian summer monsoon activities aeolian dust and toc records in biw95 4 core indicated the millennial scale variation of the asian winter and summer monsoon activities and the westerlies during the last 40 ka suggesting good correlations with global cooling events in the last glacial period found in the north atlantic region the asian summer monsoon activities during the holocene are frequent and increased at 9 6 after 2 ka and decreased at 4 ka

enhanced sediment scavenging due to double diffusive convection abstract river water intruding into a lake or ocean typically results in a surface layer of warm sediment laden water overriding relatively dense cold fluid though this system is stable with respect to density instability may arise as a result of the different diffusivities of sediment and heat a series of experiments were conducted which indicated that double diffusive convection ddc was responsible for rapid sedimentation of slowly settling particles a simple theory based upon relevant physical processes is developed that describes this behavior it also incorporates the previously neglected effects of ambient stratification on the strength of the ddc application of the theory and our results to field data taken from oceanic river plumes demonstrates that the flux due to double diffusive sedimentation dds can be at least as strong as flocculation enhanced gravitational settling

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

a numerical investigation of convective sedimentation 1 understanding the fate of riverine sediment in the coastal environment is critical to the health of the coastal ecosystem and the changing morphology one of the least understood mechanisms of initial deposition is the convective sedimentation of hypopycnal plumes this study aims at investigating convective sedimentation by means of a numerical model for fine sediment transport solving the non hydrostatic reynolds averaged navier stokes equations for stratified turbulent flow model validation is sought by comparison to laboratory results for turbidity and saline currents over a changing slope the model is shown to be capable of predicting both the upstream supercritical and the downstream subcritical flows the numerical model is then utilized to study convective sedimentation and its depositional and mixing characteristics by analyzing model results of more than 40 runs for different inlet sediment concentration density ratio settling velocity particle reynolds number rep and inlet velocity height inlet reynolds number re four distinct flow regimes are revealed for large we observe divergent plumes with significant deposits near the inlet for intermediate and large rep intense convective fingers are predicted which are only marginally affected by ambient shear flow further reducing the density ratio or rep gives weak convective fingers that are significantly affected by the ambient shear flow eventually no convective fingers are observed during the computation for very small or rep sediment deposits in the divergent plume and intense convective finger regimes are relatively insensitive to re deposit increases with re in the weak convective finger regime

pollen event stratigraphy of the varved sediment of lake suigetsu central japan from 15 701 to 10 217 sg vyr bp suigetsu varve years before present description interpretation and correlation with other regions high resolution pollen data average interval between samples 15 years are reported on part of a varved sediment core from lake suigetsu japan spanning the interval 15 701 to 10 217 sg vyr bp suigetsu varve years before present this new record is compared with a previously proposed event stratigraphy based on pollen based reconstructed changes of mean annual temperature the deglacial climate history reconstructed at lake suigetsu resembles that observed in the north atlantic although the major boundaries of pollen zones are asynchronous with those in the north atlantic event stratigraphy by several centuries the onset of the late glacial interstadial occurred earlier in japan than in the north atlantic this demonstrates that the climate in japan was closely linked to the low latitude pacific sea surface temperatures that first reacted to orbital forcing conversely the onset of the subsequent cold reversal phase in japan lagged that of the north atlantic younger dryas by several centuries the duration of this cold phase was about the same as the younger dryas event but the amplitude was much reduced 4 2 c in mean annual temperature these findings support the hypothesis that this pan hemispheric cooling event was triggered by north atlantic forcing most probably by a meltwater pulse and an associated change in the north atlantic thermohaline circulation however the mechanism which transmitted the change in the north atlantic to the far east is unknown

acquisition of viscous remanent magnetization abstract viscous remanent magnetization vrm has been frequently suggested as a possible source of magnetic anomalies in ocean crust and as an important contributor of natural remanent magnetization in some volcanic and sedimentary rocks most references to vrm assume a linear dependence with log t yet long term experimental data on vrm while scarce often disagree with this simple notion here we investigate the angular dependence grain size dependence initial state dependence and time t dependence of vrm acquisition we observe a non linear log t dependence of vrm acquisition over all time intervals 104 s for all the samples regardless of various experimental conditions echoing earlier studies we also find that vrm acquisition is strongly dependent on the initial magnetic state of the samples samples in a thermally demagnetized initial state were most susceptible to vrm acquisition when vrm is produced parallel to the initial thermal remanence vrm acquisition is negligible vrm acquisition is more prevalent for magnetites in single domain and multidomain md grains than in the pseudo single domain range in md magnetites frequent removal and restoration of samples for the purpose of zero field remanence measurement apparently increases the efficiency of vrm acquisition

pollen records of orbitally modulated variation in east asian winter monsoon intensity and freshwater inflow to the ulleung basin of east sea south korea during the last glacial period abstract most pollen analysis in korea has focused on the holocene epoch because pre last glacial maximum terrestrial archives suitable for palynological study in the korean peninsula are limited thus to verify the responses of vegetation to climate changes over the orbital timescales analysis of pollen in marine sediments is needed here we present the pollen record of hemipelagic sediments of core dd09 st21 obtained from the northern ulleung basin in the east sea the palynofloral assemblages were dominated by warm temperate broadleaved trees and boreal conifers during interglacial and glacial periods respectively we also demonstrated that bisaccate pollen and herbaceous pollen in the palynological sequence can be used as indicators of the variation in the east asian winter monsoon eawm intensity during the last glacial period and freshwater inflow into the east sea respectively during glacial periods the eawm intensified in response to weakening of the summer insolation at 60 n while freshwater influx into the east sea decreased due to a decrease in precipitation

seasonally specific responses of the east asian monsoon to deglacial climate changes the deglacial meltwater pulse in the north atlantic that induced the younger dryas event also prompted climate cooling in east asian monsoon regions such as japan and coastal mid latitude china however very little is understood about the mechanism that can transmit changes in the north atlantic to the far east here we show that the shutdown of the north atlantic thermohaline circulation brought about significantly lower temperatures and higher precipitation in the japanese winter whereas the change in the japanese summer climate was considerably smaller the cooling of the siberian air mass seems to have caused an increased pressure gradient between siberia and the west pacific in winter intensifying the winter monsoon the mongolian high pressure system and the westerly jet stream played an important role in the teleconnection in contrast the warming at the onset of the late glacial interstadial gi 1 bolling allerod in the west pacific did not have season specific features implying that the principal driving mechanism of this warming event may lie in a pan hemispheric or global factor such as insolation changes

assessment of hydrogen isotopic compositions of n fatty acids as paleoclimate proxies in lake biwa sediments compound specific hydrogen isotopic compositions dd of free and bound forms of n fatty acids fa were measured throughout a 200m sediment core taken from lake biwa to assess application of biomarker dd values to paleoclimate study in this central japan lake the results of our study suggest that the sources of the c16 n fa in the two forms are different whereas both free and bound c28 n fa originate from terrestrial plants the dd of combined free plus bound c28 n fa in the 200m sediment core shows a large variability with relatively low and high values during the glacial and interglacial periods respectively based on comparison of our record with other marine and lacustrine paleoclimate data we found that the sedimentary record of c28 n fa dd likely reflects the temperature induced change in dd of summer precipitation this finding suggests that dd values of c28 n fa could be used as a proxy for summer paleotemperatures in the sediments of lake biwa and other lakes copyright 2012 john wiley sons ltd

influence of convective sedimentation on the formation of widespread tephra fall layers in the deep sea the formation of widespread volcanic ash fall layers in deep sea sediments was investigated experimentally to examine the settling behavior of tephra 20 180 m diameter as it travels from the atmosphere into water using a fallout mass flux rate that was constrained by measurements of distal fallout from the 1980 eruption of mount st helens 0 2 g cm 2 hr the experiments show that particle settling in the water column is dramatically accelerated by the formation of diffuse vertical gravity currents the currents form as a result of convective instabilities that develop in a surface boundary layer when the local particle concentration becomes large at the air water interface the settling velocity of particles drops abruptly and the concentration of particles increases because of the differential in mass flux above and below the fluid surface the implication of the experiments is that deposition of distal tephra fall layers in deep sea sediments may be dominantly controlled by diffuse vertical gravity currents as opposed to passive settling of individual particles through the water column this process greatly reduces the residence time of fine ash in the ocean and diminishes the role of ocean currents in influencing the distribution patterns of individual tephra layers support for this mechanism comes from observations of greatly accelerated tephra settling rates in the south china sea following the 1991 eruption of mount pinatubo in the philippines

chronology and processes of fluvial terrace formation in northeastern kinki district southwest japan based on cryptotephra analysis abstract kinki district is a tectonically active area in southwest japan this area is located far from active volcanoes and eolian deposits covering fluvial terrace deposits are not as thick as those in kanto district thus terrace chronology and processes of terrace formation previously were poorly established in kinki district cryptotephra analysis identified invisible tephra horizons in eolian deposits covering fluvial terrace deposits in takashima sekigahara and inabe regions including the kikai akahoya tephra k ah 7 3 ka aira tn tephra at 26 29 ka and kikai tozurahara tephra k tz 95 ka horizons taisanjino 1 terrace in takashima and md1 terrace in inabe were formed during marine isotope stage mis 5e and nakano terrace in takashima l2 terrace in sekigahara and l2 terrace in inabe were formed during mis 2 based on their ages and geomorphic features aggradational terraces formed during mis 2 exhibit similar geomorphic features among the three regions although these regions have different base levels of erosion and active fault movements this means that the terrace formation during mis 2 was mainly affected by climate changes not by base level changes and active fault movements the main factor of terrace formation during glacial periods was the decrease in precipitation and water discharge due to climate changes because the study area was not affected by glacial and periglacial processes during mis 2 this indicates that aggradational terraces formed during glacial periods not only in glacial and periglacial areas but also in non glacial and non periglacial areas from processes of terrace formation during mis 5e the tectonic base level descent was important for terrace formation during interglacial periods because terraces were formed during mis 5e by active fault movements in the takashima region despite small lake level changes uplift rates of the kamidera and kuwana faults were 1 08 mm y and 0 5 mm y respectively based on the height of terrace surfaces formed during mis 5e

sediment laden gravity currents with reversing buoyancy there are many natural occurrences of sediment laden gravity currents in which the density of the interstitial fluid is less than that of the ambient fluid although the bulk density of the current is greater such currents are driven by the excess density of suspended particles however after sufficient particles have sedimented the current will become buoyant cease its lateral motion and ascend to form a plume examples of such currents include brackish underflows in deltas turbidity currents and pyroclastic flows experimental studies are described which show that due to sedimentation sediment laden gravity currents decelerate more rapidly than saline currents of the same density there is little difference in the experiments between a sediment laden current with neutrally buoyant interstitial fluid and one with buoyant interstial fluid until sufficient sediment has been lost to cause the latter kind of current to lift off a marked deceleration is then observed and a plume is generated with lift off occurring along the length of the current the resulting buoyant plume then generates a gravity current below the upper surface of the fluid in the tank the deposit from a current with buoyant fluid shows a fairly abrupt decrease in thickness beyond the lift off distance and has a flatter profile than that from a simple sediment current a theoretical model is presented which is based on the two layer shallow water equations and incorporates a model of the sedimentation in which particles are assumed to be uniformly suspended by the turbulence of the current the model shows good agreement with the observed lengths of the experimental currents as a function of time and predicts the lift off distance reasonably well these processes have implications for the behaviour of turbidity currents the interpretation of turbidites mixing processes in the oceans and the lift off of pyroclastic flows

millennial scale vegetation changes during the last 40 000 yr based on a pollen record from lake biwa japan abstract a high resolution pollen record covering the last 40 000 yr biw95 4 from lake biwa western japan shows regional vegetation responses to millennial scale climate changes from 40 to 30 ka cryptomeria japonica was dominant around the lake among pinaceous conifers and deciduous broad leaved trees during this period fluctuations of c japonica are correlated with dansgaard oeschger d o cycles recognized from the anhysteretic remanent magnetization arm record increases in the abundance of this taxon may have been caused by wetter summer conditions influenced by the east asian monsoon or increased snowfall on the sea of japan side of the japanese archipelago between 29 and 14 ka pinaceous conifer forests mainly composed of pinus subgenus haploxylon tsuga and picea trees developed at approximately 23 ka picea trees increased in abundance as arm values decreased this expansion of picea trees has been correlated with heinrich event he 2 in the north atlantic at about 14 ka the distribution of broad leaved forest mainly composed of deciduous oaks began to expand after d o 1 evidence of significant vegetation change related to the abrupt younger dryas cooling event has not been found

sedimentary indicators of atmospheric activity in the northern hemisphere during the cenozoic abstract the concentrations and accumulation rates of eolian phases and the mineralogy of sediments from a north pacific core ll44 gpc3 have been used to evaluate changes in eolian sedimentation and atmospheric activity during the cenozoic the quartz content and clay mineralogy of the sediments reflect changing source areas for eolian material whereas the accumulation rates of eolian phases reflect climatic variation and wind intensity eolian sedimentation decreased from 70 to 50 m y ago at the site as it moved north out of the equatorial pacific where it was supplied with eolian debris from north america and africa low rates of eolian sediment accumulation 50 to 25 m y ago reflect the temperate humid environment of the early tertiary and the lack of vigorous atmospheric circulation at that time from 25 to 7 m y ago eolian accumulation increased as the site moved into the influence of the westerlies from 7 to 3 m y ago there was a more rapid increase in accumulation of eolian material at the site which was not accompanied by changes in mineralogy or quartz content and was therefore related to climatic change and more vigorous atmospheric circulation about 2 5 m y ago a dramatic increase in eolian sedimentation accompanied the onset of dry northern hemisphere glaciation

enhanced sedimentation beneath particle laden flows in lakes and the ocean due to double diffusive convection the transport rate of particles beneath sediment laden overflows and interflows in lakes and in the ocean can be enhanced by double diffusive and settling driven convection in previous experiments with sediment laden fluid overlaying a saline layer visual measurements could only be made in the optically clear lower layer hence there was difficulty distinguishing the two processes hindering predictions of when enhanced sedimentation occurs we used an acoustic doppler velocimeter adv to measure velocities and turbulence above and below the initial sediment salt interface the velocity of the sediment fingers in the lower layer were always larger than the stokes settling velocity of the particles leading to an asymmetry in the flow field of the two convective layers sediment fingers only dominated when there were marginal density differences between the two layers we conclude that double diffusive sediment fingers control sedimentation beneath interflows in most lakes whereas settling driven convection is dominant in most oceanic overflows

a rapid method for magnetic granulometry with applications to environmental studies we have developed a rapid method of characterizing the fine scale variation sub micron to hundreds of microns m in the grain size of magnetite in long sediment cores this method is a new rock magnetic tool and can be readily applied to the following disciplines 1 environmental studies 2 hydrology 3 petrology and 4 geomagnetism the method consists of a comparative plot of the depth variation of two magnetic parameters the first parameter low field less than 0 1 millitesla mt or 1 oe susceptibility in a steady field is plotted on the abscissa the second parameter anhysteretic remanent magnetization arm imparted by a smoothly decreasing af of peak value 100 mt 1 000 oe in the presence of a weak steady field 0 01 0 1 mt or 0 1 1 oe is plotted on the ordinate for a sediment column in which the magnetic mineral is magnetite a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points arm

climate changes for the past 52 ka clarified by total organic carbon concentrations and pollen composition in lake biwa japan total organic carbon toc and total nitrogen tn analyses have been performed for three core samples obtained recently from lake biwa which include biw07 5 biw07 6 and biw08 b cores the toc and tn data from these cores show similar stratigraphic changes and can be regarded as reliable records of biological productivity occurring in the lake during the past 52 ka pollen analysis data are also used to determine climate change during the past 40 ka by reconstructing meteorological parameters such as annual temperature and precipitation temporal changes in toc concentration show detailed climate changes in tens year intervals climate change of orbital scale are well recognized demonstrating the change from mis 3 to 1 associated with severe cold periods known as heinrich events 1 to 5 and warm periods known as greenland interstadials gis 1 13 these climate events in millennial time scale are also well supported by pollen characteristics and by modern analogue analysis the good concordance of climate change between north atlantic region and japan is explained by a hypothesis that the intensity of the arctic air mass controls the climate in both the north atlantic and east asia regions through the migration of the arctic polar front although the average annual mean temperature in mis 3 was 8 2 0 8 2 c it varied largely and frequently among its substages for example 9 4 2 0 c was detected in a warm interstadial gis 8 and 6 3 1 5 c indicated in a cold stadial heinrich event 4 the average annual temperature was 4 5 0 3 c in mis 2 when the average temperature of the coldest month was 7 3 0 2 c and that of the warmest month was 16 8 0 2 c through termination 1 the annual mean temperature suddenly increased more than 5 c and the annual mean temperature became 11 2 0 8 c in early mis 1 which is much lower than that of the present temperature this low temperature estimation is attributed to the delay in expansion of evergreen broadleaf trees the annual mean temperature in the late mis 1 was as same as that of present meteorological observation

late holocene human impact on the vegetation around mizorogaike pond in northern kyoto basin japan a comparison of pollen and charcoal records with archaeological and historical data abstract pollen and macroscopic charcoal analyses of ams radiocarbon dated sediment from mizorogaike pond located near japan s ancient capital established in ad 794 were used along with archaeological and historical data to reconstruct vegetation change in the northern kyoto basin since 7300 cal yr b p between ca 7300 and 3400 cal yr b p early to late jomon period the site was surrounded by warm temperate forest composed of quercus subgenus lepidobalanus and q subgenus cyclobalanopsis with celtis aphananthe trees with the occurrence of fire disturbance q subgenus lepidobalanus increased from ca 3400 to 1400 cal yr b p late jomon to kofun periods in the early seventh century asuka period pinus started to increase coinciding with a significant charcoal peak probably related to the operation of roof tile kilns near the site pinus continued to increase and q subgenus cyclobalanopsis decreased through the seventh to tenth centuries asuka to heian periods further increase of pinus occurred in the eleventh century possibly reflecting the establishment of the manor of kamigamo shrine from the eleventh to seventeenth centuries heian to medieval periods no significant vegetational change or fire disturbance took place in the eighteenth century the landscape became totally open with poor vegetation and sparse pinus woodland the medieval and early modern landscapes reconstructed from the palaeoecological record are rather similar to those described from studies of ancient artwork and historical documents this study demonstrates that late holocene vegetation change in the northern kyoto basin was closely tied to anthropogenic activities such as the pottery industry and fuel wood collection

event layers in the japanese lake suigetsu sg06 sediment core description interpretation and climatic implications event layers in lake sediments are indicators of past extreme events mostly the results of floods or earthquakes detailed characterisation of the layers allows the discrimination of the sedimentation processes involved such as surface runoff landslides or subaqueous slope failures these processes can then be interpreted in terms of their triggering mechanisms here we present a 40 ka event layer chronology from lake suigetsu japan the event layers were characterised using a multi proxy approach employing light microscopy and xrf for microfacies analysis the vast majority of event layers in lake suigetsu was produced by flood events 362 out of 369 allowing the construction of the first long term quantitative with respect to recurrence and well dated flood chronology from the region the flood layer frequency shows a high variability over the last 40 ka and it appears that extreme precipitation events were decoupled from the average long term precipitation for instance the flood layer frequency is highest in the glacial at around 25 ka bp at which time japan was experiencing a generally cold and dry climate other cold episodes such as heinrich event 1 or the late glacial stadial show a low flood layer frequency both observations together exclude a simple straightforward relationship with average precipitation and temperature we argue that especially during glacial times changes in typhoon genesis typhoon tracks are the most likely control on the flood layer frequency rather than changes in the monsoon front or snow melts spectral analysis of the flood chronology revealed periodic variations on centennial and millennial time scales with 220 yr 450 yr and a 2000 yr cyclicity most pronounced however the flood layer frequency appears to have not only been influenced by climate changes but also by changes in erosion rates due to for instance earthquakes

the reconstruction of boreal forest fire history from lake sediments a comparison of charcoal pollen sedimentological and geochemical indices abstract fossil charcoal fossil pollen sedimentological and geochemical analyses of lake sediments have been used previously to reconstruct a history of local fires and resulting vegetation change the rationale behind these approaches is described and the usefulness of each technique for reconstructing fire history in the boreal forest is assessed empirically historical and dendrochronological records provide regional and local fire histories for a site in wood buffalo national park alberta canada the local and regional history of fires is compared with the microscopic charcoal content macroscopic charcoal content elemental carbon content fossil pollen content sedimentology and geochemistry of annually laminated sediments from a small lake there is no significant correlation between the abundance of microscopic charcoal macroscopic charcoal and total elemental carbon content of the sediments automated measures of microscopic charcoal abundance made with an image analysis system are correlated significantly with optical counts of microscopic charcoal none of the charcoal measures provide unequivocal records of local fire activity and the abundance of microscopic charcoal appears to be influenced by variations in regional fire activity however the highest depositional rate of macrofossil charcoal occurred during the time of a fire that burned within the drainage basin variations in sedimentological measures and geochemistry do not correlate with local fire activity fossil pollen percentages and accumulation rates display a pattern of variation that is consistent with observed vegetation responses to fire in the boreal forest what is likely apparent in the pollen record are the results of a series of burns of sufficient extent and intensity to kill most of the above ground biomass of the vegetation in an area at least as great as the drainage basin the inability of evidence from lake sediments to provide detailed histories of past fire activity is not surprising given the wide range of variation in the spatial extent proximity intensity and impact of individual fires

orbital and millennial scale variations in asian dust transport path to the japan sea abstract orbital and millennial scale variations in the asian monsoon and its probable association with the dansgaard oeschger d o cycles have been demonstrated by previous studies however the origin and nature of such variations are poorly understood the japan sea is located down wind of the arid areas of the eurasian continent and thus receives significant amounts of aeolian dust consequently the hemipelagic sediments of the japan sea are expected to record a continuous aeolian dust accumulation which may provide information about the past variations in asian monsoon grain size flux and provenance of aeolian dust in the sediments were examined using two sediment cores obtained from the northern and southern parts of the japan sea in order to understand the spatial variability of asian monsoon since the silt fraction of the detrital materials in hemipelagic sediments of the japan sea is composed predominantly of aeolian dust the grain size flux and provenance of the silt fraction were examined the taklimakan desert loess plateau and siberia northeast china areas were identified as possible source areas of aeolian dust in the sediments of the japan sea based on the electron spin resonance esr signal intensity and crystallinity of quartz moreover the relative contribution of aeolian dust from each source area was estimated based on the esr signal intensity and crystallinity of quartz aeolian dust fluxes from the two source areas at the southern site were then estimated grain size and flux of eolian dust at the northern site and fluxes of aeolian dust from two source areas at the southern site show orbital scale variations in harmony with the insolation change at 30 n in june these results indicate orbital scale changes in the extent of the arid area and or frequency of dust storms in the taklimakan desert loess plateau and siberia northeast china areas and suggest that southward northward shifts of the westerly jet axis occurred together with either intensified weakened winter monsoon decreased increased winter precipitation in the siberia northeast china area or southeastward northwestward shifts of summer monsoon limit during periods of smaller larger insolation at 30 n in june in addition to these orbital scale variations millennial scale variations possibly associated with the d o cycles are observed in the grain size record of aeolian dust at the two sites based on analogy with orbital scale variations these millennial scale variations are considered to reflect millennial scale changes in the position of the westerly jet axis together with the changes either in winter monsoon intensity winter precipitation or position of summer monsoon limit our results suggest n s oscillations in the westerly jet and summer monsoon limit and changes in the intensity of the winter monsoon on orbital and millennial timescales

vegetation responses to the last glacial and early holocene environmental changes in the northern leizhou peninsula south china abstract a well dated palynological record spanning the interval 40 500 7060 cal yr bp retrieved from a peatland on the leizhou peninsula in south china clearly shows regional vegetation and climate changes during the last glacial period pollen data showed that the study region was mainly covered by subtropical evergreen trees during marine isotope stage 3 mis 3 indicating a subtropical climate with relatively high temperature and precipitation during mis 2 subtropical evergreen deciduous forest with large areas of grassland occurred implying cooler and drier conditions some tropical forest elements increased during the early holocene indicating a warm and wet trend several millennial scale oscillations of the pollen records appeared to correlate with the cold anomalies in the north atlantic region our records agree well with many records from other regions but they are a bit different than that inferred from the neighboring huguang maar lake furthermore our results suggest that the vegetation surrounding xialu peatland was strongly influenced by the migration of the intertropical convergence zone itcz and variability in the east asian summer monsoon easm changes of atmospheric co2 concentration pco2 levels may have also affected the long term vegetation changes in the study region

a rock magnetic study of giant piston core ll44 gpc3 from the central north pacific and its paleoceanographic implications previous magnetostratigraphic studies of nonfossiliferous pre pliocene age pelagic clay cores from the central north pacific have proven unsuccessful because of the unstable behavior of the natural remanent magnetization the inability to obtain a reliable magnetostratigraphy has severely limited the temporal resolution that can be achieved in paleoceanographic studies of these nonfossiliferous pelagic clays we carried out a rock magnetic study of core ll44 gpc3 which spans the interval 0 70 m y ago to determine whether rock magnetic parameters can be used to construct a high resolution stratigraphic framework for paleoceanographic studies of central north pacific pelagic clays despite the instability of the natural remanence in addition we tested the ability of rock magnetic methods to detect and characterize the paleoceanographic changes that are recorded in the sediments of ll44 gpc3 stratigraphic variations in rapid and nondestructive rock magnetic parameters and related ratios reflect changes in the concentration mineralogy and grain size of the magnetic minerals within the sediments rock magnetic parameters exhibit coherent fluctuations within both the stable and unstable sections of ll44 gpc3 this result suggests the potential use of these parameters for regional correlation and relative dating of the nonfossil bearing pelagic clays of the central north pacific gyre major fluctuations in rock magnetic parameters plotted as accumulation rates correspond to intervals of paleoenvironmental change that have been previously detected by other paleoceanographic methods in addition variations in a parameter proportional to the concentration of goethite hematite correlate remarkably well with the mass accumulation rate of the total eolian component suggesting that in some situations it can be used as a proxy indicator for eolian activity

contrasting impacts of dansgaard oeschger events over a western european latitudinal transect modulated by orbital parameters abstract terrestrial and marine proxies pollen planktic and benthic foraminiferal oxygen isotopes alkenone and foraminifer derived sea surface temperatures ssts ice rafted debris from images deep sea cores md95 2042 and su81 18 37 n 10 w md99 2331 and md03 2697 42 n 9 w and md04 2845 45 n 5 w show that western european and offshore environments were strongly affected by dansgaard oeschger d o and heinrich h events we concentrate here on latitudinal variability in the forest cover extent and composition of western europe during the succession of d o events showing new pollen records for core md04 2845 and for marine isotopic stages mis 3 and 4 of core md99 2331 in general cold ssts characteristic of greenland stadials were contemporaneous with the expansion of semi desert or steppic vegetation while greenland interstadials were synchronous with the expansion of forest our data reveal that the amplitude of atlantic and mediterranean forest expansions differs for any given d o warming during the glacial period 74 18 ka in the western mediterranean d o 16 17 and d o 8 and 7 corresponding to minima in precession were associated with strong expansion of forest cover contrasting with weak expansion of forest cover during d o 14 and 12 the opposite pattern is revealed at the atlantic sites further north the strongest greenland warmings are recorded for d o 19 11 and 8 this contrasting latitudinal climatic scenario is compared with other northern hemisphere records revealing similarities between the mediterranean climate and the asian monsoon regime which may relate to a summer atmospheric teleconnection between the two regions comparable to the present day situation parallels between mediterranean climate enhancement and peaks in global methane ch 4 during the last glacial period suggest a significant role of monsoon activity in determining ch 4 emission from wetlands

late pleistocene vegetation change in korea and its possible link to east asian monsoon and dansgaard oeschger d o cycles abstract late pleistocene carbon isotope 13c records from a paleolithic sedimentary sequence collected from baeki hongcheon central korea show long term changes with superimposed short term isotopic excursions the 13c value of the sedimentary organic matter a proxy for past vegetation change varied from 26 to 23 for the period between 30 and 90 ka with a long term variation similar to insolation changes high amplitude 1 to approximately 1 5 fluctuations superimposed on the long term changes in the 13c values decreased during stronger summer monsoon intervals but increased during the weakened summer monsoon this millennial scale pattern is generally similar to greenland dansgaard oeschger d o cycles the possible connection between the hongcheon area korea and high latitudes may be explained by atmospheric circulation changing in response to the d o oscillations in the northern hemisphere

a lateglacial climatic reversion in hokkaido northeast asia inferred from the larix pollen record abstract at present larix gmelini is a main component of taiga developed in north sakhalin northeast china and east siberia during the interval from 11 8 to 12 4 ka bp pollen assemblages from north hokkaido japan are dominated by larix pollen assemblages of this lateglacial climatic reversal known as the kenbuchi stadial are similar to pollen assemblages from the last glacial maximum in north hokkaido vegetation of hokkaido inferred from these pollen assemblages open taiga composed of larix gmelini pinus pumila and picea jezoensis and or picea glehnii may have been like that of north sakhalin today comparison of these fossil pollen assemblages from hokkaido with pollen assemblages from modern surface samples in sakhalin suggests that 11 8 to 12 4 ka bp temperatures relative to today were at least 9 c lower in january and 7 c lower in august and that annual precipitation was at least 735 mm lower than present

a preliminary magnetic study of soil samples from west central minnesota abstract various rock magnetic techniques were applied to characterize magnetically the samples of a soil profile taken from west central minnesota there is a marked change in magnetic properties as a function of depth in the core x ray analysis and curie temperature measurements carried out on the magnetic fractions indicate that magnetite is the dominant iron oxide in both the top soil and the subsoil the intensity of anhysteretic remanent magnetization arm decreases sharply as the depth increases in contrast the stability of arm was found to be higher for the subsoil the surface soil sample was capable of acquiring a significant amount of viscous remanent magnetization vrm the vrm acquisition coefficient s a of the subsoil s a 3 18 10 6 emu g 1 3 18 10 6 a m 2 kg 1 was about ten times weaker than that of the top soil sample s a 3 868 10 7emu g 1 3 868 10 7 a m 2 kg 1 the magnetic domain state indicator the ratio of coercivity of remanence to coercive force h cr h c was 1 5 and 3 85 for the top soil and subsoil respectively it appears that the observed variations in magnetic properties down the present soil core is due only to a difference in grain size we conclude that the magnetic grains in surface soil samples were more single domain sd like whereas the magnetite grains in the subsoil samples were more likely in pseudo single domain psd or small multidomain md range the observed lower stability for the surface soil samples is attributed to the presence of superparamagnetic grains whose presence was confirmed by transmission electron micrographs

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

vegetation and climate history since the last interglacial in kurota lowland western japan abstract the pollen record of a long core from the kurota lowland of central honshu in western japan provides a continuous vegetation and climate history from beyond 120 000 to 25 000 yr bp the chronology is based on widely dispersed tephra and six conventional 14c dates prior to 120 000 yr bp forests were composed predominantly of abies tsuga picea and pinus haploxylon which indicate a cold climate probably corresponding to oxygen isotope stage 6 during the last interglacial around 120 000 yr bp cryptomeria japonica was dominant in forests with a small amount of evergreen oaks the early stage of the last glacial period is characterised by dominance of c japonica with two increases at 105 000 and 90 000 80 000 yr bp of pinaceous conifers and cool temperate deciduous broad leaved trees between 70 000 and 60 000 yr bp pinaceous conifer vegetation developed indicating a dry and cold climate and this was succeeded by a cool temperate deciduous broad leaved forest composed mainly of fagus crenata and deciduous oaks indicating a wet and cool cold climate from 55 000 to 40 000 yr bp temperate coniferous forests composed of c japonica and cupressaceae associated mainly with tsuga and deciduous oaks occurred after 40 000 yr bp mixed forests of c japonica tsuga and cool temperate deciduous broad leaved trees such as fagus crenata and deciduous oaks prevailed in a wet and cool climate at 28 000 yr bp an abrupt decrease of c japonica and development of forests composed of tsuga pinus haploxylon and betula with some deciduous broad leaved trees imply climatic deterioration to the lgm the vegetation history since the lgm has been revealed previously at iwaya site in kurota lowland time series of these pollen records can be correlated with the marine oxygen isotope stages 1 through 6

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

land ocean linkages over orbital and millennial timescales recorded in late quaternary sediments of the japan sea late quaternary sediments of the japan sea are characterized by centimeter to meter scale alternations of dark and light layers which are synchronous basinwide high resolution analyses of the sediments from ocean drilling program site 797 reveal that deposition of the meter scale alternations reflect variations in paleoceanographic conditions which were closely associated with glacio eustatic sea level changes through the modulation of the volume and character of the influx to the sea through the tsushima strait the centimeter to decimeter scale alternations reflect millennial scale variations which are possibly associated with dansgaard oeschger d o cycles with each dark layer appearing to correspond to an interstadial this variability is attributed to the development of a humid climate in central to eastern asia and the consequent increase in discharge from the huanghe and changjiang rivers during interstadials this caused expansion of the east china sea coastal water ecscw which penetrated more strongly into the japan sea the increased influence of the lower salinity nutrient enriched ecscw reduced deep water ventilation and enhanced the surface productivity leading to the development of anoxic bottom waters and deposition of the dark layers thus the centimeter to decimeter scale alternations of the dark and light layers record wet and dry cycles in central to eastern asia possibly associated with d o cycles

magnetic properties of marine limestones numerous paleomagnetic investigations have been carried out on limestones but their rock magnetic properties have often been neglected in this review geological and rock magnetic factors which determine whether marine limestones are suitable for paleomagnetic study are summarized and laboratory techniques for the identification of the magnetic mineralogy are evaluated the conditions under which pelagic limestones form are especially favorable for the acquisition of a stable primary natural remanence nrm probably by a postdepositional alignment process the effectiveness and timing of acquisition of this remanence are influenced by the thoroughness of bioturbation other remanence components can be acquired during diagenesis in the soft sediment right after deposition or much later even in the indurated limestone the magnetic mineralogy of a limestone is difficult to describe optically because of the small grain size and low concentration magnetic techniques are more convenient direct analysis of extracted magnetic minerals is handicapped by the difficulty of obtaining a representative extract a particularly useful technique involves combined observations of isothermal remanent magnetization irm acquisition in strong fields up to at least 4 t and the subsequent destruction of this irm during stepwise or continuous thermal demagnetization the magnetic minerals most commonly identified by these techniques are magnetite goethite hematite and maghemite these magnetic minerals occur in different combinations in the marine limestones of central europe and the mediterranean realm pyrite is common in certain limestones where it can be the precursor of an unwelcome late goethite pyrrhotite may be responsible for unstable magnetization in the swiss helvetic limestones but otherwise is rare thermal demagnetization of some limestones causes changes of susceptibility and coercivity at quite low temperatures 300 400 c due to the breakdown of a metastable mineral such as maghemite goethite or pyrrhotite at high temperatures above 500 c pronounced changes of magnetic mineralogy occur in all limestones because of the growth of new magnetite this necessitates great care in interpretation of thermal demagnetization of high blocking temperature components and often results in observational difficulties due to viscous remanent vrm behavior of the newly formed magnetite vrm is a widespread component of nrm in many limestones but it can usually be removed effectively by standard magnetic cleaning techniques the susceptibility serves as a simple control of mineralogical change during heating and can serve as an indicator of lithologic variation of magnetic mineral concentration and type in magnetostratigraphic profiles the susceptibility is anisotropic and shows a classical depositional pattern of the distribution of principal axes however the probable postdepositional mechanism of nrm acquisition especially in bioturbated sediments implies that the anisotropy pattern results from postdepositional compaction of the sediment

sakurajima satsuma sz s and noike yumugi n ym tephras new tephrochronological marker beds for the last deglaciation southern kyushu japan abstract two prominent tephras sakurajima satsuma sz s erupted from sakurajima volcano and noike yumugi n ym erupted from kuchierabujima island provide new key marker beds for dating and synchronizing palaeoenvironmental and archaeological records in the last deglaciation in southern japan these tephras were identified on the basis of glass major element compositions in two distal areas a marine core images md982195 in the northern part of the east china sea and on the central part of tanegashima island and we related their stratigraphic positions to the marine oxygen isotope based chronology in md982195 sz s 0 8 cm in thickness at 9 12 m depth and n ym 3 cm in thickness at 9 30 m depth are both white vitric ash grade tephras on tanegashima island sz s 10 cm in thickness and n ym 3 cm in thickness are stratigraphically constrained by well characterised marker tephras kikai akahoya 7300 cal bp and aira tn 29 000 cal bp sz s is rhyolitic and homogeneous on the basis of glass major element compositions assayed by electron microprobe pumiceous glass shards predominant in distal sz s tephra indicate that it derived from pumice fall units that correspond to pumiceous and phreatomagmatic fine ash units constituting proximal sz s tephra n ym is rhyolitic and glass major element analyses reveal compositional diversity between units suggesting that the lower and middle tephra units dispersed to the east whereas the upper unit was dispersed north to northwest from the vent stratigraphically sz s occurs at around the start of the late glacial reversal cooling in oxygen isotope records of md982195 corresponding to the end of gi 1 and the start of gs 1 in the ice core events of ngrip gicc05 consistent with a terrestrial age of 12 800 cal bp based on the oxygen isotope stratigraphy the tephra identified in the core as n ym at 9 30 m depth is close to the end of greenland gi 1 and hence has an age of 13 000 cal bp but on kuchierabujima island it has an age based on 14 c assay of charcoal of c 14 900 cal bp although this age discrepancy 14 9 vs 13 0 cal ka needs resolution the occurrence in core md982195 of n ym shows that it is more widespread than hitherto demonstrated the widespread distributions and key stratigraphic positions for the two marker tephras indicate that they are thus critical isochrons for precise correlation of palaeoenvironmental changes and prehistoric cultural events during the last deglaciation in southern kyushu and for relating such changes and events to the ice core chronology via the marine oxygen isotope chronostratigraphy

millennial scale east asian monsoon variability of the last glacial deduced from annually laminated sediments from lake sihailongwan n e china abstract lake sihailongwan in jilin province ne china provides the first continuous and almost entirely seasonally laminated sediment record on the east asian mainland comprising the complete holocene the late glacial period and large parts of the last glacial sediment and palynological proxy data provide a finely resolved regional environmental history of the east asian monsoon a varve based chronology shl vc2 has been established for the last 65 000 years and allows a detailed comparison with other long regional and global palaeoclimate records vegetation density of the study area depends on the long run on precessionally forced insolation changes with superimposed millennial scale variability during the last glacial periodic increase of organic carbon content and thermophilous tree species like ulmus and fraxinus and contemporary decrease of shrub alnus precisely mirror millennial scale climatic variations primarily known from greenland ice cores as dansgaard oeschger cycles as well as late glacial period climate changes percentages of trees shrubs pollen and in particular lake productivity related data reveal substantial differences between interstadial intensities with those between 50 and 60 ka bp being more pronounced than the following ones

convection and particle entrainment driven by differential sedimentation when a suspension of small particles is overlain by a clear fluid whose density is greater than that of the interstitial fluid but less than that of the bulk suspension the settling of the dense suspended particles can lead to vigorous convection in the overlying fluid this novel situation is investigated experimentally and theoretically a sharp interface is observed between the convecting upper region and a stagnant lower region in which there is unimpeded sedimentation at low reynolds number there is no transport of fluid from the upper region into the lower though there is mixing of both buoyant fluid and entrained particles from the lower region into the upper the interface between the two regions is found to descend at a constant velocity systematic laboratory measurements have determined how this velocity depends on the densities of the layers and the distributions of settling velocities of the particles a theoretical description is developed which calculates the evolution of the density of the lower region due to differential sedimentation of polydisperse particles buoyancy arguments based on the calculated density profile are used to placc upper and lower bounds on the amount of particle entrainment into the upper layer and on the rate of fall of the interface between the convecting and sedimenting regions the theoretical predictions are in good agreement with the experimental observations the analysis of the interaction between convection and sedimentation in the system considered here may be particularly relevant to the description of evolving crystal rich layers in magma chambers and of silt laden outflow from rivers and has a wide range of other industrial environmental and geological applications