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

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

lake lewis basin central australia environmental evolution and osl chronology abstract lake lewis is the furthest from the coast of australia s salt lakes and lies at the southern edge of influence of the australian monsoon regime the macdonnell ranges south of the lake intercept moist air masses crossing the region and efficiently deliver water and sediment to the lake and its surrounding alluvial plain we describe lacustrine fluvial and aeolian environments of the basin and report optically stimulated luminescence osl dates from representative sediments a long period of generally wetter conditions during most of the pleistocene is represented by thick uniform lacustrine clay beneath and near lake lewis this is overlain by more heterogeneous lacustrine sediments deposited since hydrologic closure of the basin which indicate fluctuating climatic conditions osl results show that dune building in the basin commenced before 95 ka when salinity at the depocentre was high dune building peaked around 23 21 ka osl ages of fluvial deposits show that floods occurred during the last 20 ka following the last phase of maximum aridity in the region

mid pleistocene acheulean like stone technology of the bose basin south china stone artifacts from the bose basin south china are associated with tektites dated to 803 000 3000 years ago and represent the oldest known large cutting tools lcts in east asia bose toolmaking is compatible with mode 2 acheulean technologies in africa in its targeted manufacture and biased spatial distribution of lcts large scale flaking and high flake scar counts acheulean like tools in the mid pleistocene of south china imply that mode 2 technical advances were manifested in east asia contemporaneously with handaxe technology in africa and western eurasia bose lithic technology is associated with a tektite airfall and forest burning

mis 21 and the mid pleistocene climate transition climate and sea level variation from a sediment core in osaka bay japan abstract we report climate and sea level variation for the marine oxygen isotope stage mis 21 encompassing the end of the mid pleistocene climate transition mpt based on pollen diatom and sulfur records from a 50 m thick sequence in a core from osaka bay an extremely warm climate coincided with the sea level highstand of substage 21 5 when the warm temperate element quercus cyclobalanopsis exceeds 40 of total arboreal pollen this was followed by a warm temperate to temperate and humid climate that continued until the end of mis 21 a linear age model shows that climate was dominated by precessional cyclicity with an inverse correlation between temperature and precipitation the postglacial sea level rise reached its highest peak in substage 21 5 when paleo osaka bay reached its maximum extent including kyoto and nara basins at this time pelagic diatoms were dominant in the central part of the bay sea level dropped below the osaka bay sill about 60 m at present during substage 21 4 followed by a rise above the sill in substage 21 3 and a drop at 21 2 sea level remained below the sill during substage 21 1 the thermal maximum and sea level peak occurred just after the rapid postglacial sea level rise after which there was a gradual decline in temperature and sea level accompanied by precession related oscillations these features are typical of the post mpt interglacials dominated by 100 ka cyclicity these features may be a sign of termination of the mpt

timing of the matuyama brunhes geomagnetic reversal decoupled thermal maximum and sea level highstand during marine isotope stage 19 recent high resolution magnetic and microfossil data from a long core penetrating the osaka group japan are astronomically tuned and reassessed to reveal detailed stratigraphic features across the matuyama brunhes mb polarity transition during marine isotope stage mis 19 the sediments have a uniform and high average accumulation rate of 63 cm ky astronomical tuning based on six calibration points including a clear mis 19 2 sea level lowstand dates the main mb boundary mbb to 777 6 ka the sea level peak of the mis 19 3 highstand to 780 7 ka and the climatic thermal maximum tm to 776 4 ka the mb transition began with a short lived normal polarity episode that occurred before the highstand at mis 19 3 and terminated with multiple rapid reversals that occurred between highstand mis 19 3 and lowstand 19 2 the tm just postdates the termination of the mb transition and occurs about 4000 years after the sea level peak the delayed tm is also observed at gesher benot ya aqov israel and on the mediterranean coast and possibly at lake baikal in high resolution records from chinese loess paleosols and deep sea sediments the rapid reversal zone of the mbb has a very similar climatostratigraphic character these magneto climatostratigraphic features in mis 19 are useful for correlating between terrestrial and marine sediments the delay in warming relative to the sea level highstand seems to have been due to a cloud albedo effect induced by an increase in galactic cosmic ray flux during an extremely low magnetic field intensity interval

multiple rapid polarity swings during the matuyama brunhes transition from two high resolution loess paleosol records 1 two high resolution magnetic records of the matuyama brunhes m b transition have been obtained from xifeng and baoji loess paleosol sequences in the chinese loess plateau the results of stepwise thermal and alternating field af demagnetizations confirm that both treatments are effective in isolating characteristic remanent magnetization chrm from specimens of loess paleosol sediments which suffer from weak pedogenesis and that af demagnetization clearly fails to isolate chrm from specimens of paleosol sediments which have undergone strong pedogenesis on the basis of virtual geomagnetic pole latitudes crossing the virtual geomagnetic equator the m b transition involves at least 15 rapid polarity swings rock magnetic experiments and anisotropy of low field magnetic susceptibility show that high frequency polarity swings during the m b transition cannot be attributed to rock magnetic and or sedimentary causes extrapolating a constant accumulation rate between the jaramillo matuyama and m b boundary ages the m b transition interval of both the xifeng and baoji sections is estimated to have a duration of more than 10 kyr durations of each short polarity interval are estimated to range from about 0 3 to 5 6 kyr our new results combined with previous paleomagnetic observations from lavas and marine sediments suggest that multiple rapid polarity swings occurred during the m b transition

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

high resolution climate stratigraphy across the matuyama brunhes transition from palynological data of osaka bay sediments in southwestern japan abstract this study presents a high resolution palynological analysis of a sedimentary core from osaka bay japan straddling marine oxygen isotope stage mis 19 i e across the matuyama brunhes magnetic polarity boundary mbb comparison with the standard marine oxygen isotope curve bassinot f c labeyrie l d vincent e quidelleur x shackleton n j lancelot y 1994 the astronomical theory of climate and the age of the brunhes matuyama magnetic reversal earth and planetary science letters 126 91 108 demonstrates that variations in vegetation and the basinal environment coincided with global ice volume changes the late mis 20 is characterized by boreal climate with coniferous forest in mis 19 the forest was generally dominated by fagus and quercus lepidobalanus suggesting onset of humid climatic conditions slightly cooler than the present excluding coastal vegetation components climate during mis 19 can be subdivided into three stages the early stage including substage 19 3 is characterized by high seasonality in precipitation this contrasts with the very abundant year round precipitation that is inferred for the late stage from substage 19 2 to substage 19 0 which is characterized by cool temperate coniferous taxa including cryptomeria the very high precipitation rates of the latter persisted at least up to substage 18 4 there was no apparent vegetational response to the sea level highstand of 19 3 in contrast a short lived thermal maximum event took place ca 6 7 kyr later i e in middle mis 19 this event is characterized by increases in the warm temperate element quercus cyclobalanopsis the mbb the recommended criterion for defining the lower middle pleistocene boundary took place in middle mis 19 these lines of evidence indicate that the occurrence of the mbb corresponded with a shift towards warmer and wetter climatic conditions similar warming and wetting events across the mbb are also observed in pollen records from southern italy and central japan this possibly provides long distance correlation and may suggest a connection between the earth s magnetic field and climate

travel times from buried and surface infiltration point sources solutions in closed form are found for the travel times of marked particles from buried and surface infiltration point sources the study is based on the quasi linear analysis of steady three dimensional unsaturated flow the results are presented graphically the mathematical analysis applies to all linear convection diffusion processes from continuous point sources in the appropriate infinite and seminfinite regions in the soil water context a limitation is that travel velocities are based on a mean volumetric moisture content

magnetostratigraphy of plio pleistocene sediments in a 1700 m core from osaka bay southwestern japan and short geomagnetic events in the middle matuyama and early brunhes chrons abstract a magnetic polarity stratigraphy spanning more than the past 3 2 myr was determined for a long 1545 m continuous sedimentary sequence of marine fluvial and lacustrine deposits from the osaka basin southwestern japan additionally two short geomagnetic reversal events were identified a short event at about 0 69 ma lasting for about 7 kyr in the early brunhes chron around the lower boundary of a marine clay deposited during a period of eustatic high sea level during the marine oxygen isotope stage 17 and another short matuyama event 1 60 1 58 ma correlated with stage 54 event and the early stage of the sangiran excursion accumulation rate was 0 3 0 4 mm yr from 3 to 2 ma and then increased by about 50 with a rate of 0 51 mm yr during the olduvai subchron high values of 0 59 mm yr were maintained from the upper olduvai boundary to the brunhes matuyama boundary from 1 77 to 0 78 ma with a peak at 0 74 mm yr during the jaramillo subchron these changes in accumulation rate probably reflect the history of tectonic subsidence of the drilling site the magnetic polarity stratigraphy provides a chronological framework for sedimentological paleoenvironmental tephrochronological and tectonic studies of the osaka basin

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

the middle pleistocene transition characteristics mechanisms and implications for long term changes in atmospheric pco2 abstract the emergence of low frequency high amplitude quasi periodic 100 kyr glacial variability during the middle pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system this middle pleistocene transition mpt began 1250 ka and was complete by 700 ka its onset was accompanied by decreases in sea surface temperatures ssts in the north atlantic and tropical ocean upwelling regions and by an increase in african and asian aridity and monsoonal intensity during the mpt long term average ice volume gradually increased by 50 m sea level equivalent whereas low frequency ice volume variability experienced a 100 kyr lull centered on 1000 ka followed by its reappearance 900 ka although as a broad band of power rather than a narrow persistent 100 kyr cycle additional changes at 900 ka indicate this to be an important time during the mpt beginning with an 80 kyr event of extreme sst cooling followed by the partial recovery and subsequent stabilization of long term north atlantic and tropical ocean ssts increasing southern ocean sst variability primarily associated with warmer interglacials the loss of permanent subpolar sea ice cover and the emergence of low frequency variability in pacific ssts and global deep ocean circulation since 900 ka ice sheets have been the only component of the climate system to exhibit consistent low frequency variability with the exception of a near universal organization of low frequency power associated with marine isotope stages 11 and 12 all other components show an inconsistent distribution of power in frequency time space suggesting a highly nonlinear system response to orbital and ice sheet forcing most hypotheses for the origin of the mpt invoke a response to a long term cooling possibly induced by decreasing atmospheric pco2 none of these hypotheses however accounts for the geological constraint that the earliest northern hemisphere ice sheets covered a similar or larger area than those that followed the mpt given that the mpt was associated with an increase in ice volume this constraint requires that post mpt ice sheets were substantially thicker than pre mpt ice sheets indicating a change in subglacial conditions that influence ice dynamics we review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline precambrian shield bedrock became exposed by glacial erosion of a thick mantle of regolith this exposure of a high friction substrate caused thicker ice sheets with an attendant change in their response to the orbital forcing marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the mpt if this carbon came from terrigenous sources an increase in atmospheric pco2 would be likely which is inconsistent with evidence for widespread cooling apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith a more likely source of organic carbon and nutrients which would mitigate pco2 rise is from shelf and upper slope marine sediments which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the mpt modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long term silicate weathering rates in good agreement with marine sr and os isotopic records we use a carbon cycle model to show that a post mpt increase in silicate weathering rates would lower atmospheric pco2 by 7 12 ppm suggesting that the attendant cooling may have been an important feedback in causing the mpt

minimal advective travel time along arbitrary streamlines of porous media flows the fermat leibnitz bernoulli problem revisited summary travel time of marked fluid particles along arbitrary streamlines in arbitrary porous streamtubes is estimated from below based on the cauchy bunyakovskii schwartz and jensen inequalities in homogeneous media the estimate is strict and expressed through the length of the streamline hydraulic conductivity porosity and the head fall the minimum is attained at streamlines of unidirectional flow the bounds for heterogeneous soils non darcian flows and unsaturated media are also written if such bounds are attained the corresponding trajectories become brachistochrones for example in a two layered aquifer and seepage perpendicular to the layers there is a unique conductivity porosity ratio which makes a broken streamline brachistocronic similarly if conductivities of two layers are fixed there is a unique incident angle between flow in one medium and the interface which makes a refracted streamline brachistocronic

a magnetostratigraphic reassessment of correlation between chinese loess and marine oxygen isotope records over the last 1 1 ma abstract we present a magnetic polarity based paleoclimatic correlation between chinese loess and marine oxygen isotope stage mis records over the last 1 1 ma this revised land ocean comparison indicates that inconsistent occurrence of the matuyama brunhes boundary which lies in mis 19 in marine sediments and occurs either at the base lower part of loess l8 or the uppermost part of soil s8 in chinese loess is due to regional and or local climate variability across the chinese loess plateau and does not need to be attributed to lock in effects of loess remanence acquisition associated with pedogenesis this result implies that the geomagnetic polarity boundaries in chinese loess in general are reliable chronostratigraphic time markers therefore astronomically tuned timescales for chinese loess that presume a downward shift of polarity boundaries due to a time lag in remanence acquisition may have overestimated ages of certain loess paleosol units

tension saturated and unsaturated flows from line sources in subsurface irrigation riesenkampf s and philip s solutions revisited riesenkampf s 1938 r 38 referred to here as r 38 analytical solution for steady 2 d flow from a buried line source in a homogeneous green ampt soil with a wetting plume bounded by a free surface capillary fringe is compared with philip s 1969 p 69 one for genuinely unsaturated wetting of gardner s infinite extension soil conformal mappings are used in r 38 from which we derived the flow net pore water isobars isochrones fields of darcian velocity and resultant force acting on saturated porous skeleton fine geometry shape and size of the constant head contour encompassing a mole emitter or leaky pipe as well as the dependence of the total discharge per unit pipe length on uniform pressure in the pipe capillarity of the soil radius of the pipe and saturated hydraulic conductivity an ovalic water table isobar encompassing p 69 source is compared with one of r 38 for a fixed discharge and saturated conductivity but adjusted sorptive numbers the whisler and bouwer 1970 relation between the static height of capillary rise and sorptive number is shown to give a good match between r 38 and p 69 isobars this allows to use r 38 in the source vicinity and p 69 in the far field zone computer algebra mathematica routines are used for visualization of the known and extended r 38 and p 69 solutions

santa barbara basin diatom and silicoflagellate response to global climate anomalies during the past 2200 years santa barbara basin sbb diatom and silicoflagellate assemblages are quantified from a box core record spanning ad 1940 2001 and an ocean drilling program hole 893a record from 220 bc to ad 1880 the combined relative abundance of the diatoms fragilariopsis doliolus and nitzschia interrupteseriata from continuous two year sampling intervals in the box core varies with sea surface temperature sst suggesting its utility in sst reconstruction the assemblage data from the odp 893a record indicate a broad interval of generally cooler ssts between ad 800 and 1350 which corresponds to the medieval climate anomaly mca a period of generally warmer temperatures across other regions of the northern hemisphere the assemblages also indicate an interval of generally warmer ssts between ad 1400 and 1800 a period of otherwise global cooling referred to as the little ice age lia the changes in assemblages of diatoms and silicoflagellates support the hypothesis that the widespread droughts of the medieval climate anomaly in the western us were associated with cooler eastern north pacific sst the box core assemblages have higher percentages of tropical and subtropical compared to temperate and subpolar species than the odp samples reflecting a response of phytoplankton communities to an unusual 20th century warming pseudonitzschia australis a diatom linked with domoic acid production begins to become more common 3 of the diatom assemblage in the box core only after ad 1985 suggesting a link to anthropogenic activity

a 900 year stable isotope record of interdecadal and centennial change from the california current this paper describes the development of a high resolution record of interdecadal and centennial variability of ocean climate of the california current from continuous 5 year sampling intervals based on varve counts from santa barbara basin sediments we show the importance of the choice of species and size fraction as well as the practice of making multiple measurements per interval to obtain a clear environmental signal capable of resolving interdecadal change changes in temperature and salinity from oceanographic surveys of the past 50 years indicate that thermal variability dominates the 18o signal a 18o record from neogloboquadrina dutertrei spanning 1030 1905 a d contains interdecadal thermal fluctuations within the upper thermocline that are centered around periods of roughly 55 70 and 90 years the interdecadal changes comprise the major share of total variability compared to a low amplitude mode of underlying multicentennial variability corresponding to the medieval warm period and the little ice age

paleoclimatic and paleoceanographic records through marine isotope stage 19 at the chiba composite section central japan a key reference for the early middle pleistocene subseries boundary abstract marine isotope stage mis 19 is an important analogue for the present interglacial because of its similar orbital configuration especially the phasing of the obliquity maximum to precession minimum however sedimentary records suitable for capturing both terrestrial and marine environmental changes are limited and thus the climatic forcing mechanisms for mis 19 are still largely unknown the chiba composite section east central japanese archipelago is a continuous and expanded marine sedimentary succession well suited to capture terrestrial and marine environmental changes through mis 19 in this study a detailed oxygen isotope chronology is established from late mis 20 to early mis 18 supported by a u pb zircon age and the presence of the matuyama brunhes boundary new pollen marine microfossil and planktonic foraminiferal 18o and mg ca paleotemperature records reveal the complex interplay of climatic influences our pollen data suggest that the duration of full interglacial conditions during mis 19 extends from 785 0 to 775 1 ka 9 9 kyr which offers an important natural baseline in predicting the duration of the present interglacial a younger dryas type cooling event is present during termination ix suggesting that such events are linked to this orbital configuration millennial to multi millennial scale variations in our 18o and mg ca records imply that the subarctic front fluctuated in the northwestern pacific ocean during late mis 19 probably in response to east asian winter monsoon variability the climatic setting at this time appears to be related to less severe summer insolation minima at 65 n and or high winter insolation at 50 n our records do not support a recently hypothesized direct coupling between variations in the geomagnetic field intensity and global regional climate change our highly resolved paleoclimatic and paleoceanographic records coupled with a well defined matuyama brunhes boundary 772 9 ka duration 1 9 kyr establish the chiba composite section as an exceptional climatic and chronological reference section for the early middle pleistocene boundary

vegetation and climate across the early middle pleistocene transition at montalbano jonico southern italy abstract pollen analysis of the montalbano jonico marine succession mjs southern italy provides a continuous vegetational record between 858 ka and 745 13 ka which includes marine isotope stage mis 19 now considered the closest orbital analogue to the holocene a comparison between paleoclimate proxies and global signals of past climate change allows the pollen record to be interpreted in terms of major environmental and climate modifications through mis 21 18 at the orbital and sub orbital scale this is also central to understanding migration patterns of the genus homo interglacials are expressed by the dominance of a mesophilic vegetation typical of a warm temperate and relatively humid climate deciduous quercus dominated fully temperate arboreal forest already devoid of subtropical taxa wooded steppes to steppes expanded during glacials when cold and dry conditions prevailed at mjs the main expansion of temperate forest dominated by broad leaved trees correlates to mis 19 3 whereas the expansion of steppe vegetation during drier conditions marks mis 19 2 directly above the volcaniclastic layer v4 dated at 773 9 1 3 ka more intensively arid conditions developed during mis 20 and mis 18 the pollen temperature index reaches its minimum in uppermost mis 20 in agreement with a significant cold and arid climate phase of wide significance in the north hemisphere as documented by prominent peaks in north atlantic ice rafted debris ird and mediterranean aeolian dust records on the other hand artemisia a significant component of steppes shows its maximum expansion during earlier phases of mis 18 millennial to sub millenial scale climate variability is evidenced by two abrupt short term pollen events within mis 19 3 which show a dominant increase of the cosmopolitan herbaceous component at around 783 54 ka and 774 84 ka respectively the vegetational and inferred climate changes for mis 19 offer two possibilities 1 to investigate the interglacial climate variability and discuss the linkage between climate and changes in geomagnetic field intensity close to the matuyama brunhes paleomagnetic boundary mbb and 2 to help evaluate the role of the mbb in defining the middle pleistocene global boundary stratotype section and point gssp with respect to point 2 a comparison of data at mjs with the pollen record at the nearby and coeval valle di manche section is relevant and evidences the complex response of vegetation to climate events possibly under the effects of both astronomical and local factors

sedimentological study of the stratigraphy at the site of homo erectus yunxianensis in the upper hanjiang river valley china abstract geomorphological and sedimentological investigations were carried out in the upper hanjiang river valley the sediments in the profile at the site of homo erectus yunxianensis were sampled systematically magnetic susceptibility loss on ignition particle size distribution and geochemical elements were analyzed in the laboratory the results show that the medium sand and gravel beds in the lower part of the profile are fluvial deposits of the third terrace land of the hanjiang river the upper part is a blanket of aeolian loess and palaeosol deposited from dust storms and dust falls according to stratigraphical correlation and palaeomagnetic dating the carbonate nodules encasing the fossils of h erectus yunxianensis and other mammalian faunas were formed during 800 785 ka the palaeosol overlying on the fossil layer is defined as the s8 that was developed during the mis 19 and the aeolian loess below the fossil layer is defined as l9 that was deposited during mis 20 these loess and palaeosol are similar to those over the chinese loess plateau and correlatable with those in the luochuan loess profile they are very different from the fluvial deposits in the hanjiang river valley these indicate that h erectus yunxianensis lived at a climatic transition from glacial to interglacial these results are very important in understanding the environment of h erectus yunxianensis in the upper hanjiang river valley

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

optimization and analysis of advective travel times beneath hydraulic structures steady 2d darcian seepage in a homogeneous isotropic porous medium under an impervious structure is studied by the methods of complex analysis the geometry of the structure is studied focusing on the travel time of a marked neutral tracer particle from the upper pool to the tailwater in the verigin problem the angle of inclination of a sheetpile resulting in minimal time along the bounding streamline is 2 if the maximum of the minimum of the travel time is searched between all streamlines originated in the upper pool then the optimal angles are found to be 0 404 and 0 596 the minimization of the total volume of fluid that arrives from the upper pool to the tailwater during a prescribed time span is also considered for arbitrary geometry structure optimization with respect to travel time is carried out explicitly for the bounding streamline with a constraint on the wetted perimeter of a depressed structure the minimal time shape is found to be the voshinin semicircular structure which is

planktonic foraminiferal response to the 1997 1998 el nino a sediment trap record from the santa barbara basin here we report results on a sediment trap study from the santa barbara basin in which we examine the response of planktonic foraminifera to el nino conditions planktonic foraminifera census counts were performed on biweekly sediment trap samples collected over the interval spanning late summer 1995 through early spring 1998 a period that captured the transition from normal conditions in 1996 to full el nino conditions during early 1997 through early 1998 intra annual variations in the foraminifera assemblage reflect changes in seasonal climate variability significant differences occurring in both foraminiferal relative abundance and flux values between non el nino and el nino years warmer waters in the basin during late 1997 were reflected by a significantly increased presence of warmer water species generally absent under normal conditions surprisingly despite greatly reduced upwelling conditions foraminiferal flux values during the spring 1997 upwelling season were more than four times greater than the year before the contrast between normal and el nino foraminifer populations has important implications for reconstructing the past history of both el nino events and more general climate histories from the santa barbara basin varved sediment record

paired δ18o signals of neogloboquadrina pachyderma s and turborotalita quinqueloba show thermal stratification structure in nordic seas abstract the vertical density gradients in the nordic seas are crucial for the preconditioning of the surface water to thermohaline sinking in winter these gradients can be reconstructed from paired oxygen isotope data in tests of different species of planktonic foraminifera the isotopic signatures of which represent different calcification depths in the water column comparison of 18 o values from foraminiferal tests in plankton hauls sediment traps and nearby core top samples with the calculated 18 o calcite profile of the water column revealed species specific 18 o vital effects and the role of bioturbational admixture of subfossil specimens into the surface sediment on the basis of core top samples obtained along a west east transect across various hydrographic regions of the nordic seas 18 o values of turborotalita quinqueloba document apparent calcification depths within the pycnocline at 25 75 m water depth the isotopic signatures of neogloboquadrina pachyderma s reflect water masses near and well below the pycnocline between 70 and 250 m off norway where the atlantic inflow leads to thermal stratification here temperatures in the calcification depth of n pachyderma s differ from sea surface temperature by approximately 2 5 c in contrast n pachyderma s calcifies very close to the sea surface 20 50 m in the arctic domain of the western nordic seas however further west n pachyderma s prefers somewhat deeper more saline water at 70 130 m well below the halocline that confines the low saline east greenland current this implies that the 18 o values of n pachyderma s do not fully reflect the freshwater proportion in surface water and that any reconstruction of past meltwater plumes based on 18 o is too conservative because it overestimates sea surface salinity minimum 18 o differences n pachyderma s and t quinqueloba may serve as proxy for sea regions with dominant haline and absent thermal stratification whereas thermal stratification leads to 18 o differences of 0 4 to 1 5

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

variability in vertical distributions of planktonic foraminifera in the california current relationships to vertical ocean structure 1 geochemical records from planktonic foraminifera are among the few means available to infer past changes in the upper ocean although interpretations can be confounded by variability in foraminifera habitat depths the principal environmental factors affecting foraminiferal vertical distributions were examined through 28 vertically stratified plankton tows taken off southern california in winter spring and summer each species has a dynamic range of preferred habitat depth from the mixed layer to the thermocline characterized by a unique relationship with environmental properties globigerina bulloides neogloboquadrina pachyderma dextral and neogloboquadrina dutertrei can live near the surface but frequently live deeper as stratification increases and a particular isotherm deepens globigerinoides ruber and orbulina universa vary more closely with the depth of the thermocline than the depth of a given isotherm the shifts in habitat depth are of sufficient magnitude to affect 18o records the effects of such shifts are observed for g bulloides and n pachyderma in santa barbara basin sediments geochemical signatures from multiple species of foraminifera each with a different predicted response to environmental change can permit the detection of changes in habitat depth of a given species and thus more accurately indicate past changes in hydrographic structure

calcareous phytoplankton response to the half century of interannual climatic variability in santa barbara basin california 1 a high resolution study of calcareous phytoplankton in a box core from the santa barbara basin sbb reveals floral assemblage fluctuations which can be related to climatic and paleoceanographic changes during the last half century 1940 1996 in particular gephyrocapsa oceanica production increased during el nino periods in response to high temperatures silica depletion and increased iron availability conversely helicosphaera carteri flux increases in conjunction with lower surface temperatures associated with la nina episodes increasing abundances of florisphaera profunda and umbilicosphaera sibogae after 1970 reflect a warming trend and increased stratification within the basin associated with the warm phase of the pacific decadal oscillation pdo conversely increased abundances of coccolithus pelagicus and calcidiscus leptoporus before 1970 mark the cold phase of pdo these coccolithophore production rate data are consistent with instrumental records of surface and thermocline temperatures monitored since 1950 this is the first study to document the response of calcareous phytoplankton to surface water warming occurring in sbb since 1970

a 2000 year record of caribbean and tropical north atlantic hydrographic variability 1 here we present near annually resolved oxygen isotope records from two species of planktic foraminifera from the cariaco basin that reflect sea surface temperature sst and intertropical convergence zone itcz precipitation related salinity variations over the caribbean and tropical north atlantic spanning the last 2000 years a strong broad spatial pattern of correlation exists between foraminiferal 18o and ssts over the period of instrumental overlap but the correlations weaken as they are extended back in time and instrumental sst records become discontinuous a long term trend in the globigerinoides ruber 18o record can be explained by two different but equally plausible scenarios first the increase in 18o may indicate that tropical summer fall ssts have cooled by as much as 2 c over the last 2000 years possibly as a result of a long term increase in upwelling intensity alternately comparisons to other studies of itcz and regional evaporation precipitation variability suggest that much of the 18o record is influenced by decadal to centennial scale variations in the mean annual position of the itcz and associated rainfall patterns similarities between the g bulloides 18o record and the 11 year sunspot cycle support prior studies that suggest solar variability plays a role in influencing the hydrologic balance of the circum caribbean

recent increase in surface water stability during warming off california as recorded in marine sediments warming of surface waters in the california current since the 1950s has coincided with a significant decline in zooplankton volume this has been attributed to reduced upwelling of nutrient rich waters caused by increased thermal stratification across the thermocline proxy microfossil evidence preserved in the santa barbara basin suggests that stability increased early in the 1900s intensified after the early 1940s and became well established by 1960 accumulation of upwelled radiolarians in the basin has steadily declined since 1900 while oxygen isotopes in surface dwelling planktonic foraminifera reflect increasing surface temperatures comparison of the delta sup 18 o records between surface and thermocline dwelling planktonic foraminifera reveals that the temperature difference between surface and thermocline water has increased during the twentieth century instrumental records of surface and thermocline temperatures monitored since 1950 support these results this evidence suggests that relaxation of north pacific anticyclonic gyre circulation deepened isopycnics causing onshore movement of warmer less saline waters and reduced upwelling of cool nutrient rich waters

dansgaard oeschger cycles and the california current system planktonic foraminiferal response to rapid climate change in santa barbara basin ocean drilling program hole 893a high resolution planktonic foraminiferal census data from santa barbara basin ocean drilling program hole 893a demonstrate major assemblage switches between 25 and 60 ka that were associated with dansgaard oeschger cycles stadials dominated by neogloboquadrina pachyderma sinistral and globigerinoides glutinata suggest a strong subpolar california current influence while interstadials marked by abundant n pachyderma dextral and g bulloides indicate a relative increase in subtropical countercurrent influence modern analog technique and transfer function f 20rsc temperature reconstructions support 18o evidence of large rapid 70 years or less sea surface temperature shifts 3 to 5 c between stadials and interstadials changes in the vertical temperature gradient and water column structure thermocline depth are recorded by planktonic faunal oscillations suggest bimodal stability in the organization of north pacific surface ocean circulation santa barbara basin surface water demonstrates the rapid response of the california current system to reorganization of north pacific atmospheric circulation during rapid climate change supporting assemblage data are available on diskette or via anonymous ftp from kosmos agu org directory apend username anonymous password guest diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 or by phone at 800 966 2481 5 00 payment must accompany order

phase lagged warming and the disruption of climatic rhythms during the matuyama brunhes magnetic polarity transition abstract the influence of the geomagnetic field on climate a long hotly disputed issue was examined for the matuyama brunhes mb magnetic polarity transition using palynological and paleomagnetic data sets from a high accumulation rate ca 50 cm kyr sediment core from osaka bay during the period from marine oxygen isotope stages mis 20 to 18 climate change is well correlated with global ice volume variation in the precession cycle with the exception of the early half of mis 19 the postglacial warming after substage 20 2 was interrupted by cooling that began just before the sea level highstand correlated with substage 19 3 and persisted until about a mid point between 19 3 and 19 2 followed by a rapid warming the thermal maximum clearly postdates the highest sea level highstand by 6 7 kyr and the connection between orbital forcing and climate was disrupted the cooling event coincided with the center of the paleointensity low during the mb transition this unusual climate cooling across a sea level peak is very likely related to the field intensity decrease the data from osaka bay may suggest an instance where the geomagnetic field has influenced climate in the past

a study of the tex86 paleothermometer in the water column and sediments of the santa barbara basin california 1 particulate organic matter collected during a 2 year period as part of an ongoing sediment trap study and a high resolution sediment record from 1850 to 1987 a d from the santa barbara basin were analyzed for tex86 a temperature proxy based on marine crenarchaeotal membrane lipids highest fluxes of crenarchaeotal lipids in the water column were found in may june 1996 and from october 1996 to january 1997 and in general showed a good correlation with mass fluxes tex86 reconstructed temperatures from the sediment trap series ranged from 8 to 11 c and were usually substantially lower than sea surface temperatures sst indicating that unlike in previous studies the tex86 corresponds to subsurface temperatures likely between 100 and 150 m tex86 temperature variations observed in trap samples were not coupled to changes in sst or deep water temperatures and only to some degree with crenarchaeotal lipid fluxes this suggests that a complex combination of different depth origins and seasonal growth periods of crenarchaeota contributed to the variations in tex86 signal during the annual cycle tex86 temperatures in the two sediment cores studied 8 13 c were also substantially lower than those of instrumental sst records 14 17 5 c confirming that tex86 records a subsurface temperature signal in the santa barbara basin this result highlights the importance of performing calibration studies using sediment traps and core tops before applying the tex86 temperature proxy in a given study area

magnetostratigraphic lithostratigraphic and tephrostratigraphic constraints on lower and middle pleistocene sea level changes wanganui basin new zealand wanganui basin north island new zealand contains a complex sedimentary record of lower and middle pleistocene sea level changes palaeomagnetic results allow identification of the matuyama brunhes transition the jaramillo subchron and the cobb mountain subchron correlations of rhyolitic tuff horizons across the basin are consistent with magnetostratigraphic correlations between sections isothermal plateau fission track itpft ages of 1 05 0 05 ma and 1 63 0 15 ma on two tuffs potaka pumice and pakihikura pumice respectively are consistent with the interpreted magnetostratigraphy and also with the astronomically tuned timescale of odp site 677 magnetostratigraphy and itpft ages allow correlation of sedimentary cycles at wanganui with odd numbered oxygen isotope stages 17 31 in deep sea cores the stratotype section for the new zealand castlecliffian stage is shown to be incomplete relative to other studied sections in the basin below stage 31 the character of the cyclothems changes at wanganui from marine dominated to a greater representation of non marine and estuarine strata this change may be partly related to a change in amplitude and frequency of climatic cycles identified in oxygen isotope records but the primary cause is likely to be increased basinal uplift

climatic patterns revealed by pollen and oxygen isotope records across the matuyama brunhes boundary in the central mediterranean southern italy a c 50 m thick section located in the crotone basin southern italy was investigated using oxygen isotopes pollen and planktonic foraminifera the section records two complete trans gressive regressive cycles mainly driven by glacio eustasy biostratigraphy and oxygen isotope chronology indicate that the section spans from marine isotope stage mis 22 c 0 87 ma to mis 18 3 c 0 73 ma thus straddling the matuyama brunhes m b boundary which occurs in the middle of mis 19 the rich pollen assemblages provide a unique record of the vegetation in the central mediterranean during the early middle pleistocene climatic transition interglacials are characterized by a mesothermic vegetation similar to the present day whereas a rain demanding conifer forest dominates the glacials of mis 20 and mis 18 this is unexpected because it is gener ally considered that during the pleistocene glacials in central mediterranean were characterized by steppe arid conditions by contrast arid conditions occur during the deglaciations these results are inconsistent with the widespread practice of linking glacials with arid conditions in the central mediterranean during pliocene and early pleistocene times this study emphasizes the need to establish more accurate land sea correlation

sea level variation during mis 11 constrained by stepwise osaka bay extensions and its relation with climatic evolution abstract marine oxygen isotope stage mis 11 has been described as a super interglacial because of its long duration more than 30 ka but this view is often refuted by the observation that the peak sea level and maximum temperature did not surpass other interglacials including the last interglacial we address this problem using data from coastal sediments we conducted diatom and sulfur analyses on two cores of high accumulation rate 0 52 m ka sediments from osaka bay japan a linear age model applied to the diatom data shows that sea level variations with precession cycles are correlated with oxygen isotopic events 11 3 11 24 11 23 11 22 and 11 1 diatom abundances reveal sea level increases and falls because of environmental changes caused by stepwise extension of the bay this extension can be verified and mapped using data from 15 other drill cores sea level was above the sill for osaka bay during the marine interval in osaka bay spanning 60 ka it was above the sill for kawachi bay during the marine interval in kawachi plain for a duration of 44 ka including events 11 3 and 11 23 the highest sea level was above the sill for kyoto bay during an interval of 16 ka centered at event 11 3 estimates of sill elevations together with geological data suggest that the sea level of mis 11 changed within a range from 60 m to 20 m palynological data from the same core show that the mis 11 climate around osaka bay was divided into early warm temperate and late cool temperate times with a boundary between events 11 3 and 11 24 during the marine interval in kyoto the climate was an extremely warm hypsithermal almost coincided with the warmest interval in antarctica where temperatures are 0 c

a geomagnetic excursion during the late matuyama chron the osaka group southwest japan abstract duplicate records of a geomagnetic excursion during the late matuyama chron were obtained from sediments gathered at the takatsuki and izumi sites in southwest japan the excursion is dominated by westerly declinations with shallow inclinations and was found just above the volcanic ash known as the azuki tuff in a marine clay layer of the osaka group the excursion occurred at about 0 85 ma a recently revised age for the azuki tuff by extrapolating constant sedimentation rates for the holocene marine clay dated by the radiocarbon method the duration of the excursion is estimated at about 240 yr with a range of 200 500 yr if we consider possible fluctuations in sedimentation rates the kamikatsura excursion previously reported around this time from the osaka group data is estimated to be a few tens of thousands of years older than the excursion reported in this study based on correlations of changes in sea level recorded in the sediments of the osaka group and the oxygen isotope record of deep sea cores these two excursions in japan together with short normal events reported in the southern ocean north america and china suggest that during the period from 0 87 0 84 ma the geomagnetic field may have been unstable and excursions or short reversals may have occurred regionally and sporadically over the earth

comment on the paper biogenic silica record of the lake baikal response to climatic forcing during the brunhes by a a prokopenko e b karabanov d f williams m i kuzmin n j shakleton s j crowhurst j a peck a n gvozdkov and j w king

paleoenvironmental and climatostratigraphic insights for marine isotope stage 19 pleistocene at the montalbano jonico succession south italy abstract quantitative analyses on pollen and ostracods were performed on the montalbano jonico succession mjs through marine isotope stages mis 18 21 in order to acquire details of paleoenvironmental changes and climate pattern during mis 19 which includes the matuyama brunhes paleomagnetic boundary mbb while the mjs does not record the mbb which is the main criterion for defining the early middle pleistocene boundary it is a candidate global boundary stratotype section and point gssp for the ionian stage and middle pleistocene subseries because of its excellent exposure continuous deposition and astronomically tuned record between mis 37 and mis 16 the new 40ar 39ar age of 773 9 1 3 ka for volcaniclastic layer v4 allows the age model for the succession to be refined ostracod assemblages show significant paleodepth fluctuations at the glacial interglacial scale in agreement with the pollen distality index pinus vs caryophyllaceae amaranthaceae and ephedra which also suggests higher values during mis 19 pollen analysis provides supplementary paleoclimate data that are valuable to reconstruct temperature variation during the identified phases a major expansion of steppic vegetation at 790 ka in the uppermost mis 20 correlates with a significant cold and arid northern hemisphere climate phase as documented by a concurrent peak both in north atlantic ice rafted debris and mediterranean dust records climate conditions recorded in mis 19 3 were similar to those of the present interglacial whereas a dry climate phase marks mis 19 2 at 771 84 ka slightly above the v4 layer millennial scale climate variability occurred during mis 19 as evidenced by two abrupt short term moderately dry pollen events at 783 5 ka and 774 8 ka that could be related to a period of reduced geomagnetic field intensity through the mbb transition additional environmental chronological events accompanied this stratigraphic interval i the volcaniclastic layers v3 and v4 radiometrically dated at 801 2 19 5 ka and 773 9 1 3 ka respectively ii the co occurrence of maximum flooding and thermal maximum in agreement with the previously recorded co occurrence of the neopycnodonte community and tropical subtropical mesopelagic teleostean bonapartia pedaliota close to the increase of quercus and iii the maximum depth md between 777 3 and 773 25 ka as recorded by outer shelf upper slope macroinvertebrate fauna close to the highest value of pollen distality index in mis 19 results enhance the understanding of orbital suborbital paleoenvironmental change during the mid pleistocene and particularly of the climate pattern during mis 19 and across the mbb

muted climate variations in continental siberia during the mid pleistocene epoch the large difference in carbon and oxygen isotope data from the marine record between marine oxygen isotope stage 12 mis 12 and mis 11 spanning the interval between about 480 and 380 kyr ago has been interpreted as a transition between an extremely cold glacial period and an unusually warm interglacial period with consequences for global ice volume sea level and the global carbon cycle1 2 3 4 the extent of the change is intriguing because orbital forcing is predicted to have been relatively weak at that time5 here we analyse a continuous sediment record from lake baikal siberia which reveals a virtually continuous interglacial diatom assemblage a stable littoral benthic diatom assemblage and lithogenic sediments with interglacial characteristics for the period from mis 15a to mis 11 from about 580 to 380 kyr ago from these data we infer significantly weaker climate contrasts between mis 12 and 11 than during more recent glacial interglacial transitions in the late pleistocene epoch about 130 to 10 kyr ago for the period from mis 15a to mis 11 we also infer an apparent lack of extensive mountain glaciation

subdividing the pleistocene using the matuyama brunhes boundary mbb an australasian perspective abstract the last major reversal of the earth s magnetic field the matuyama brunhes boundary mbb dated at 0 78 ma is widely identified in australian and new zealand pleistocene deposits in new zealand the mbb is precisely located in shallow marine sediments of wanganui basin where it corresponds with the base of the new zealand putikian substage a combination of marine biostratigraphy sequence stratigraphy and tephrostratigraphy permit correlation from wanganui basin to other on land sections and deep sea cores in australia the mbb is identified in many continental sequences particularly saline lake basins however chemical weathering has resulted in variable brunhes age normal overprints that are sometimes difficult to remove australasian tektites are a potential lithostratigraphic marker just prior to the mbb but have yet to be identified in the same on land section as the mbb in australia identification of reverse polarity magnetisation in weathered deposits including soils provides a minimum age of 0 78 ma for these materials a widespread arid shift in paleoclimate succeeded the mbb in australia placement of the lower middle pleistocene boundary at the mbb would constitute the most recognisable chronostratigraphic marker in weathered continental deposits

geomagnetic palaeointensities and astrochronological ages for the matuyama brunhes boundary and the boundaries of the jaramillo subchron palaeomagnetic and oxygen isotope records from odp site 983 we have measured relative geomagnetic palaeointensity proxies palaeomagnetic directions and 18 o for the 700 1100 ka interval from odp site 983 gardar drift north atlantic where mean sedimentation rates are ca 13 cm kyr 1 the age model was generated by matching the benthic 18 o data to the ice volume model and confirmed by tuning the precessional components of both signals for the matuyama brunhes boundary mbb and the boundaries of the jaramillo subchronozone the duration of the polarity reversal process defined by virtual geomagnetic polar latitudes of less than 45 is ca 5 kyr whereas the generally accepted astrochronological estimates for the boundaries of the jaramillo subchronozone lie within the polarity transitions as recorded at site 983 the astrochronological age for the matuyama brunhes polarity transition 780 ka is ca 5 kyr older than the onset of this transition at site 983 775 ka the polarity reversals lie within palaeointensity lows with abrupt recovery of palaeointensity post reversal there is no progressive sawtooth decrease in palaeointensity within the jaramillo subchronozone or between the top of the jaramillo and the mbb but rather within polarity chrons several short intervals of low palaeointensity which sometimes coincide with high amplitude secular variation orbital 100 and 41 kyr periods are present in the palaeointensity record as they are not obviously attributable to climate lithology in these records they may be a feature of the geomagnetic field itself

identification of a pair of co ignimbrite ash and underlying distal plinian ash in the early pleistocene widespread tephra in japan abstract the early pleistocene azuki and the ku6c tephras in japan have been correlated with a compositionally zoned ignimbrite the imaichi pyroclastic flow deposit using ratios of accurately determined refractive indices of volcanic glass shards and phenocrysts and paleomagnetic directions thin fine grained white ash layers at the base of the azuki and the ku6c tephras have been correlated with the imaichi plinian fall deposit which underlies the imaichi pyroclastic flow deposit near the source shishimuta caldera on central kyushu this indicates that the azuki and the ku6c tephras comprise a pair of compositionally zoned co ignimbrite ash and underlying distal plinian ash thus the initial sequence of physical and chemical changes at the source of the pyroclastic eruption has been retained in the distal widespread tephras even though the ashes were blown downwind by westerlies as much as 900 km identification of a distal plinian ash at the base of a co ignimbrite ash ensures the stratigraphic correlation of the distal tephra with the source ignimbrite

a palynological study of an early pleistocene marine clay bed of the osaka group in southwest japan abstract pollen analytical data from the ma 3 marine clay bed of the gs k1 core from kobe city southwest japan provide a detailed record of paleoclimatic changes during the early pleistocene the pollen assemblage was mainly dominated by cool temperate deciduous broad leaved and coniferous tree taxa accompanied by taxa of warm temperate evergreen broad leaved trees the ma 3 bed is subdivided into five palynological zonules the paleoclimate during the age of the lowermost zonule was the warmest with high precipitation afterward the paleotemperature tended to decrease from the lower to the uppermost zonules although with some fluctuations moreover fluctuations in the percentage of fagus pollen and associated pollen of other taxa suggest that in addition to the decreasing tendency of the paleotemperature the amount of paleoprecipitation fluctuated repeatedly the results of the present study differ those of previous studies in that the ma 3 marine clay bed of the early pleistocene is interpreted as not having been deposited under continuous warm climatic conditions

sea level variations during marine isotope stage 7 and coastal tectonics in the eastern seto inland sea area western japan relative sea level rsl observations for marine isotope stage mis 7 were obtained from three sites higashinada kakogawa and mitsu of the eastern seto inland sea area western japan we evaluated the magnitude of sea level highstands during mis 7 and the local tectonics based on rsl records of this coastal area for this purpose we analyzed diatom assemblages and sedimentary sulfur and carried out tephra analysis we also constructed a linear age model to determine the depositional ages of the sediments using altitudes of astronomical age control points obtained mainly from the present diatom data at the mitsu site rsls were estimated to be 22 87 0 50 m at the mis 7 5 highstand peak 234 6 ka below 20 17 m at 211 2 ka and below 20 00 m at 209 9 ka with a tectonic subsidence rate of 0 11 0 02 m ka since the last interglacial maximum at the mitsu site the elevation of the tectonically corrected mis 7 5 highstand peak may have been 2 94 5 19 m the tectonically corrected sea level elevations during mis 7 3 are inferred to have been below 3 06 4 72 m at 211 2 ka and below 3 09 4 70 m at 209 9 ka comparisons between the diatom inferred rsls and the isotopically derived sea level curve indicate that the mis 7 3 highstand peak was above 18 m and may have been lower than the mis 7 5 and 7 1 highstands based on the isotopically derived sea level curve and the rsl data from higashinada and kakogawa a tectonic subsidence rate of 0 26 0 32 m ka was derived for higashinada and a tectonic uplift rate of 0 17 m ka and 0 43 m ka and 0 26 m ka and 0 42 m ka these values indicate the intensity of crustal movements associated with active faulting of the rokko awaji fault system along this tectonically active coast

millennial to submillennial scale features of the matuyama brunhes geomagnetic polarity transition from osaka bay southwestern japan 1 a high resolution magnetic record of the matuyama brunhes mb reversal transition was obtained from homogeneous marine clay in a 1700 m core from osaka bay the transition stretches over a core length of 6 4 m and yields four short reversal episodes two predate the main mb boundary mbb and two postdate it we made diatom analyses of sediments to estimate relative sea level changes and constructed an age model by correlation with the astronomically calibrated marine oxygen isotope curve the age model shows the short reversal episodes with durations of 1 kyr occurred at 4 5 kyr intervals within stage 19 and the mbb occurred about 5 kyr after the sea level highstand corresponding to isotopic event 19 3 it also shows the paleointensity minimum of 15 20 of the postreversal mean occurred at about 6 kyr before the mbb and another minimum at about 1 kyr after four virtual reverse to normal polarity boundaries found in this study suggest different ages for the mbb could be observed in lava flow studies some millennial to submillennial scale transition features found in this study are compatible with the previous numerical simulations of geomagnetic field reversal

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr