regionalized primary paleoproduction variability in the sea of okhotsk during late pleistocene and holocene abstract in order to reconstruct the history of primary paleoproductivity changes during the last 160 kyr in the okhotsk sea os the high resolution down core analyses of chlorin content were performed on 11 sediment cores obtained from various part of the studied area with wide ranged depths spatial and temporal distributions of the marine phytoplankton paleoproductivity depend on sea ice condition and nutrient supply the observed discrepancies among the reconstructed records allow us to separate out three main regions with specific environmental conditions during glacial stages the paleoproductivity was depressed and vice versa productivity in the central region is low comparing to other regions due to nutrient limitation increased paleoproductivity in the southeastern area was affected by influence of nutrient rich pacific waters

orbital scale changes of sea ice conditions of sea of okhotsk during the last glaciation and the holocene mis 4 mis 1 abstract in this paper 5 schemes for reconstructing the sea ice conditions in the sea of okhotsk the so during the last 74 kyr are presented these schemes were constructed based on calculations of the ice rafted debris ird fluxes in 16 sediment cores and the available published mineralogical data derkachev et al 2004 we obtained new data on the orbital scale changes of the ird fluxes in the studied area for the last four marine isotopic stages mis as a result the key areas of sea ice formation and general direction of sea ice drift and in turn dominate direction of geostrophic wind in the so were established for each of the investigated miss it allows us to suppose the positions of siberian high and aleutian low during the individual miss at that the sea ice was of predominantly seasonal for studied period except for the northwestern and western parts of sea where perennial sea ice fields were preserved over a period of several years during mis 2 the variations of sea ice conditions attest to a particular type of atmospheric pressure field prevailing over the so during individual miss the secondary sea ice drift directions points out that the predominant atmospheric pressure field during individual miss were inconstant except the mis 2

primary production in the glacial north atlantic and north pacific oceans the conditions controlling primary production are very different in the modern north atlantic and north pacific oceans1 a difference that is reflected in the composition of diatom fossils in surface sediments by contrast i report here evidence that during the last glacial interval the diatom assemblage and by extrapolation the primary production was very similar in the two regions the modern analogues of these assemblages occur in sediments of baffin bay and the sea of okhotsk both highly productive seas where ice is present i infer that during the last glacial interval plankton biomass was at least as high as it is today in the north atlantic and was as much as an order of magnitude higher in the north pacific the glacial assemblage occurs in lithologies dominated by ice rafted detritus which is generally believed to indicate the presence of icebergs2 6 i hypothesize that the presence of numerous icebergs possibly associated with sea ice supported high production by physical mechanisms such as turbulent mixing and enhanced density stratification and or biogeochemical ones such as supply of major or trace nutrients

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

responses of the okhotsk sea environment and sedimentology to global climate changes at the orbital and millennial scale during the last 350 kyr abstract we measured productivity proxies chlorin carbonate and organic carbon opal and biogenic ba content and lithophysical proxies magnetic susceptibility water content density and coarse sediment fraction in sediment of central okhotsk sea core pc 7r the age model covering the last 350 kyr of this core was constructed by correlating the dated series of relative paleointensity lows recognized in geomagnetic intensity records marine isotope stage mis boundaries determined in broad variations of the lithophysical and productivity proxies and tephrochronology the orbital changes of the lithophysical and productivity proxy stacks lag behind northern hemisphere summer radiation by approximately 6 3 and 5 9 kyr respectively this lag is consistent with a milankovich model of climate control by solar radiation through the northern ice sheet volume and sea surface and surrounding land responses which are fast compared with sedimentological evidence productivity proxies of the okhotsk sea also demonstrate 52 abrupt pronounced productivity minima associated with regional climate coolings during the last 350 kyr which present useful indicators of millennial scale climate changes in this marginal sea based on the postulated synchronicity of dansgaard oeschger cycles in the northern hemisphere and the established simultaneity of 11 okhotsk sea coolings in the last 77 kyr with abrupt severe cold events in the greenland ice core and north atlantic heinrich events all of these may be regarded as heinrich equivalent event anomalies the okhotsk sea events have their counterparts in the records of north atlantic sediments the greenland ice sheet east asia summer monsoon and the antarctic ice sheet probably the arctic oscillation was the main factor determining orbital and millennial climate oscillations in the high latitude northern hemisphere including the okhotsk sea region

processes controlling the advance and retreat of sea ice in the sea of okhotsk using defense meteorological satellite program dmsp special sensor microwave imager ssm i sea ice data and meteorological data we investigate processes controlling the advance and retreat of sea ice in the sea of okhotsk for this investigation we apply a new algorithm to the ssm i data which is capable of calculating ice concentration and distinguishing sea ice types this algorithm is confirmed by comparison with national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr imagery our investigations show that there exists a locality for the areas of new ice formation and the ice formation near the ice edge always occurs as a recovery after sea ice has retreated suddenly we also reveal that the speed of ice edge advance fairly coincides with that predicted by 2 of the geostrophic wind furthermore there exists a good correspondence between the times when the overall advance and retreat of ice cover begin and the decrease and increase of air temperature begin we conclude that the advance of the ice cover in the sea of okhotsk occurs primarily through ice advection by wind and that the interannual variation in the maximum sea ice extent can be interpreted by that in wind and air temperature conditions

woce line p1w in the sea of okhotsk 2 cfcs and the formation rate of intermediate water from august 30 to september 21 1993 temperature salinity nutrient and cfc data were collected along a section starting in the pacific ocean near bussol strait in the kuril islands crossing the basin and shelf region of the sea of okhotsk and ending near the coastal town of okhotsk at the northwest corner of the sea of okhotsk world ocean circulation experiment woce line p1w water on the continental shelf had potential density as great as 27 0 with high cfc concentrations and low temperature and salinity the sea of okhotsk intermediate water soiw ranging from 26 8 to 27 4 had uniform water properties along isopycnal surfaces that were distinctly different from either the north pacific intermediate water npiw or the shelf water found at the same density since the soiw was colder and fresher than the npiw we postulate that soiw is formed by sinking plumes and diapycnal mixing shelf derived water sdw as dense as 27 0 is formed on the shelf during the winter by cooling and brine rejection during ice formation prevailing winds move the sdw off the shelf where it sinks to an equilibrium depth and subsequently mixes isopycnally with north pacific water npw flowing into the sea of okhotsk through the kuril islands the observations on the shelf suggest that sdw directly modifies soiw to 27 0 using potential temperature salinity s and cfc data we calibrated a simple box model to determine the input of sdw into the soiw model results required a minimum of 0 9 sv 1 sv 10 6 m 3 s 1 of sdw in the formation of soiw and produced a minimum export of 2 7 sv of soiw from the sea of okhotsk our minimum calculated export of soiw into the north pacific ocean makes the sea of okhotsk a significant source of the salinity minimum present in the npiw below 27 2 the box model failed because the cfc concentrations of the sdw were too high this suggests that sdw directly ventilates the soiw to a maximum of 27 2 the unique properties of the soiw below 27 2 must be the result of diapycnal mixing in the sea of okhotsk and isopycnal mixing with inflowing npw

a novel method for the rapid determination of chlorin concentrations at high stratigraphic resolution in marine sediments a sensitive semi automated method has been developed for the rapid estimation of the total concentration of chlorophyll a transformation products chlorins in solvent extracts of aquatic sediments the methodology utilizes a laboratory robot for sample extraction and work up and a high pressure liquid chromatography hplc system operated under off column conditions use of an on line tuneable fluorescence detector allows measurement of total chlorin concentration at greater sensitivity than conventional u v vis spectrophotometric detection and allows reproducible results to be obtained from smaller sediment samples this is relevant to palaeoceanographic studies at high stratigraphic resolution or where sample demand is high for other stratigraphic studies

early diagenetic pyrite morphology in a mudstone dominated succession the lower jurassic cleveland ironstone formation eastern england abstract diagenetic pyrite in the mudstones and ironstones of the lower jurassic cleveland ironstone formation of eastern england exhibits two distinct morphologies framboidal pyrite commonly associated with organic matter and euhedral pyrite associated with detrital clay pellets these two morphologies are mutually exclusive in occurrence framboidal pyrite is present in clay rich mudstones ooidal ironstones apatite rich units and some silt rich mudstones euhedral pyrite is present in silt rich and sand rich mudstones 34s isotopic analysis of six samples of pyrite suggests that both types of pyrite morphology precipitated during early diagenesis from porewaters with open access to overlying sea water although both probably acted as sites for continued pyrite precipitation during burial it is proposed that framboidal pyrite precipitated from iron dominated porewaters at sites of sulfide supply i e in the region of organic matter as a result of bacterial sulfate reduction where locally sulfide production rates were high enough for porewaters to reach supersaturation with respect to fes euhedral pyrite also precipitated from iron dominated porewaters but sulfide production rates from organic matter was such that fes saturation was not reached at the sites of sulfide production instead euhedral pyrite was precipitated directly from porewater when fes2 saturation was reached the control over pyrite morphology was probably the amount and reactivity of the organic matter within the deposited sediments the sand rich mudstones contained less reactive organic matter due to clastic dilution and deposition in shallower environments with o2 rich bottom waters the ironstones and apatite rich units were deposited under very low sedimentation rates and as a result organic matter contents were very low and iron reduction dominated early diagenesis which inhibited sulfate reduction the presence of minor framboidal pyrite within these units however suggests that sulfide reduction took place in micro environments during early diagenesis

glacial holocene environment of the southeastern okhotsk sea evidence from geochemical and palaeontological data abstract environmental conditions and productivity changes in the southeastern okhotsk sea have been reconstructed for the last 20 ka using planktonic and benthic foraminiferal oxygen isotope records and calcium carbonate organic carbon and opal content data from two sediment cores species variability in benthic foraminiferal and diatom assemblages provides additional palaeoceanographic evidence ams radiocarbon dating of the sediments and oxygen isotope stratigraphy serve as the basis for the age models of the cores for the last 20 14 c kyr and for correlation between environmental variations in the okhotsk sea and regional and global climate changes benthic foraminiferal assemblages in the two cores depth 1590 and 1175 m varied with time so that we could recognise seven zones with different species composition changes in the benthic foraminiferal assemblages parallel major environmental and productivity variations during the last glaciation fluxes of organic matter to the sea floor showed strong seasonal variations indicated by the presence of abundant a weddellensis and infaunal uvigerina spp benthic foraminiferal assemblages changed with warming at 12 5 11 and 10 8 14 c kyr bp when productivity blooms and high organic fluxes were coeval with global meltwater pulses 1a and 1b younger dryas cooling caused a decline in productivity 11 10 kyr bp affecting the benthic faunal community subsequent warming triggered intensive diatom production opal accumulation and a strong oxygen deficiency causing significant changes in benthic fauna assemblages from 5 26 4 4 kyr bp to present time

reconstruction of paleoproductivity in the sea of okhotsk over the last 30 kyr 1 marine and terrestrial derived biomarkers alkenones brassicasterol dinosterol and long chain n alkanes as well as carbonate biogenic opal and ice rafted debris ird were measured in two sediment cores in the sea of okhotsk which is located in the northwestern pacific rim and characterized by high primary productivity down core profiles of phytoplankton markers suggest that primary productivity abruptly increased during the global meltwater pulse events 1a about 14 ka and 1b about 11 ka and stayed high in the holocene spatial and temporal distributions of the phytoplankton productivity were found to be consistent with changes in the reconstructed sea ice distribution on the basis of the ird this demonstrates that the progress and retreat of sea ice regulated primary productivity in the sea of okhotsk with minimum productivity during the glacial period the mass accumulation rates of alkenones caco3 and biogenic opal indicate that the dominant phytoplankton species during deglaciation was the coccolithophorid emiliania huxleyi which was replaced by diatoms in the late holocene such a phytoplankton succession was probably caused by an increase in silicate supply to the euphotic layer possibly associated with a change in surface hydrography and or linked to enhanced upwelling of north pacific deep water index terms 1050 geochemistry marine geochemistry 4835 4850 1055 geochemistry organic geochemistry 4267 oceanography general paleoceanography keywords okhotsk sea paleoproductivity sediment citation seki o m ikehara k kawamura t nakatsuka k ohnishi m wakatsuchi h narita and t sakamoto 2004 reconstruction of paleoproductivity in the sea of okhotsk over the last 30 kyr paleoceanography 19 pa1016

on the relationship between atmospheric circulation and the fluctuations in the sea ice extents of the bering and okhotsk seas monthly and 3 day averaged nimbus 5 electrically scanning microwave radiometer sea ice data have been analyzed to document the fluctuations of the bering sea and sea of okhotsk ice covers for the four winters 1972 1973 through 1975 1976 on the short term seasonal and interannual time scales and to define those periods for which there is an out of phase relationship between the fluctuations of the two sea ice covers the sea ice fluctuations are shown to be related to changes in the position and intensity of quasi stationary high and low pressure systems associated with large scale standing wave patterns in the atmosphere through a comparison of the areal changes in ice cover with changes in the amplitude and phase of zonal harmonics 1 2 and 3 of the sea level pressure field on the seasonal time scale the sea level pressure for december the month of most rapid seasonal sea ice growth for both the bering and okhotsk seas is dominated by harmonic 2 which explains almost 60 of the total sea level pressure variance on average over the four winters the phase of harmonic 2 which is associated with the position of the aleutian low shifts from 156 e in 1972 1973 to 190 e in 1975 1976 thus providing a connection between the increasingly heavy bering sea ice cover over these four winters and the general circulation of the atmosphere on the short term episodes of midwinter bering sea ice retreat are generally preceded by or coincident with the breakdown of harmonic 1 and the intensification of harmonics 2 and 3 these episodes are also related to the coincidence of the phases of harmonics 2 and 3 with a mean position of 165 e this result is in excellent agreement with a study of the north pacific oscillation showing that the two modes of the oscillation are associated with the longitudinal position of the aleutian low it is suggested here that these two modes result from changes in the amplitudes and phases of atmospheric long waves 1 2 and 3 evidence is also presented indicating that the interaction of standing and transient components of wave 1 may play an important role in these fluctuations finally these results establish an observational connection relating climate dynamics to changes in ice covers in seasonal sea ice zones

high resolution record of the upper olduvai transition from po valley italy sediments support for dipolar transition geometry abstract a detailed record of the upper olduvai polarity transition composed of 100 transitional directions has been obtained from the crostolo section in northern italy a careful examination of the rock magnetic properties of the sediments using standard paleomagnetic techniques thermomagnetic scanning electron microscopy microprobe x ray diffraction and mossbauer analysis shows that greigite is the main magnetic carrier of the remanence the correlation of a shift in the magnetic record to a small scale sedimentary feature observed in the section indicates that the magnetization was acquired at deposition or very shortly after the virtual geomagnetic pole vgp path is largely confined along a great circle over north and south america 90 west of the site and consists of three stages first the vgp moves to southern mid latitudes then after a period of standstill it comes back to almost true north and finally the south pole is reached in a third step although different from a record from the southern indian ocean this path is virtually identical to those obtained for the same transition from north pacific deep sea cores and partly coincides with a north atlantic record which suggests that a dipolar component may be present in the transitional field during the upper olduvai reversal a review of the recently obtained records of various transitions shows that in more than two thirds of the cases the vgp paths are similarly confined along a meridian over the americas or antipodal to them irrespective of the sampling site and of the sense of the transition although not deterministic this tendency suggests that a similar dipolar component might be present in the transitional fields of other reversals of different ages

glacial age hydrography of the far northwest pacific ocean stable isotope data on benthic foraminifera from more than 30 cores on the northern emperor seamounts and in the okhotsk sea are synthesized in paleohydrographic profiles spanning the depth range 1000 4000 m holocene core top benthic foraminiferal 18o and 13c data are calibrated to modern hydrographic properties through measurements of 13c of co2 and 18o of seawater cibicidoides stable isotope ratios are close to the 13c and equilibrium 18o of seawater whereas uvigerina 18o and 13c are variably offset from cibicidoides glacial maximum 13c of cibicidoides displays a different vertical profile than that of the holocene when results are adjusted by 0 32 to account for the secular change in 13c during the last glacial maximum the data coincide with the modern seawater and foraminiferal curves deeper than 2 km however at shallower depths 13c gradually increases by as much as 1 above the modern value furthermore above 2 km the benthic 18o decreases by 0 5 these results are consistent with a benthic front at 2 km in the north pacific see herguera et al 1992 but they differ from interpretations based on trace metal data which indicate a source of nutrient depleted deep water during glaciation the isotopic data suggest that during glaciation there was a better ventilated watermass at intermediate depths in the far northwestern pacific it was relatively fresher than deep waters there and deep waters were as nutrient rich as today

large changes in seasonal sea ice distribution and productivity in the sea of okhotsk during the deglaciations changes in the surface environment of the central sea of okhotsk were reconstructed using tex86 paleothermometry facilitated by the bit index in order to investigate paleoenvironmental changes during the glacial interglacial cycles the core top tex86 derived temperature is the same as the present day summer sea surface temperature sst suggesting that tex86 records seasonal rather than annually averaged ssts in this region the tex86 record reveals 3 c lower summer sst during glacial maxima than during interglacial periods and significant warming during the deglaciations 15 10 ka and 136 130 ka this is consistent with previous inferences of more expanded and persistent seasonal sea ice during the glacial periods than the present day and its substantial retreat during the deglaciation timing of the deglacial warming also coincided with a distinct increase in coccolithophorid productivity suggesting a causal relationship between sea surface warming and coccolithophorid blooms during the deglaciations the relationship could reflect an increase in the supply of fresh and warm water from the amur river during deglaciation which significantly impacted hydrology by facilitating sea surface stratification which in turn promoted production of coccolithophids

environmental change in the sea of okhotsk during the last 1 1 million years on the basis of two sedimentary records from the central sea of okhotsk we reconstruct the closely coupled glacial interglacial changes in terrigenous flux marine productivity and sea ice coverage over the past 1 1 myr the correspondance of our sedimentary records to the china loess grain size record china loess particle timescale chiloparts suggests that environmental changes in both the sea of okhotsk area and in se asia were closely related via the siberian atmospheric high pressure cell during full glacial times our records point to a strong siberian high causing northerly wind directions the extension of the sea ice cover and a reduced amur river discharge deglacial maxima of terrigenous flux were succeeded by or synchronous to high productivity events marine productivity was strengthened during glacial terminations because of an effective nutrient utilization at times of enhanced water column stratification and high nutrient supply from fluvial runoff and sea ice thawing during interglacials se monsoonal winds prevailed analogous to today s summer situation of a pronounced mongolian heat low and a strong hawaiian high strong freshwater discharge induced by high precipitation rates in the amur drainage area and a seasonally reduced and mobile sea ice cover favored marine productivity although being considerably lower than during the terminations and a lowered flux of ice rafted detritus

characteristics and ages of tephra layers in the central okhotsk sea over the last 350 kyr abstract a sequence of 9 ash layers tephra found in the middle late pleistocene and holocene sediments of the central okhotsk sea was established on the basis of glass chemical composition and refractive indices grain size distributions and heavy mineral assemblages five tephras were also characterized by rare earth element distributions volcanic sources and ages of the identified tephra were estimated based on pre existing marine sediment core chronostratigraphy and correlation between these marine tephra deposits with geochemically similar terrestrial deposits on the kamchatka peninsula and adjacent kurile islands areal distributions and approximate eruptive volumes of pyroclastic material were also estimated for some of these tephras

sea surface temperature changes in the okhotsk sea and adjacent north pacific during the last glacial maximum and deglaciation abstract we estimated sea surface temperatures ssts in the western okhotsk sea during the last glacial maximum lgm and the last glacial termination from measurements of the alkenone unsaturation index u k 37 the t etra e ther inde x of tetraethers consisting of 86 carbon atoms tex 86 and tex 86 l in piston core sediments which reveal the climate response of this region to different types of forcings tex 86 l is a modification of tex 86 proposed for high latitude ocean regions the tex 86 l derived temperatures were not different from the alkenone derived temperatures from the same and nearby sediment samples during the lgm alkenone derived temperatures in the okhotsk sea were relatively warm these and similarly warm alkenone derived temperatures found at many other sites in the western north pacific may reflect a shift in the season of biomarker production from early summer and autumn to mid summer during the lgm as a result of the expansion of the season of sea ice cover empirical orthogonal function eof analysis of alkenone derived temperatures at 14 sites from the north pacific suggested substantial cooling between 20 and 14 cal kyr bp during the deglaciation at 11 of the sites including 4 sites in the okhotsk sea this dominant eof mode suggests either an overall seasonal bias in alkenone derived temperatures or potential shifts in the haptophyseae production season the second eof mode of variability indicated a deglacial warming trend punctuated by millennial scale cold events associated with reorganizations of the atlantic meridional overturning circulation the sst pattern corresponding to this eof mode is indicative of millennial scale meridional shifts of the axis of the westerly jet which may have affected heat transport across the kuroshio reconstructed temperature changes in particular in the okhotsk sea provide insight into the conditions that modulated the ventilation history of intermediate waters in the north pacific

a multiproxy study of past environmental changes in the sea of okhotsk during the last 1 5 ma abstract long chain diols have been detected in a wide range of environments and have been used to reconstruct past environmental changes however only a few long term records exist to date here we reconstructed past environmental changes in the central sea of okhotsk over the last 1 5 million years covering the mid pleistocene transition mpt sea surface temperatures sst reconstructed using the long chain diol index ldi reflects glacial interglacial changes however when compared with other organic paleothermometers uk 37 and texl86 the ldi sst is lower during interglacials and similar or higher during glacials possibly suggesting a shift of diol production season during interglacials the ldi sst does not change in periodicity around the mpt as observed for the texl86 likely due to this seasonal shift diatom productivity as recorded by 1 14 diols and biogenic opal content increased during the main deglaciations with a succession from proboscia diatoms to diatoms with a more heavily silicified shell confirming that primary productivity in the central sea of okhotsk is driven by sea ice progress and retreat in contrast to the ldi sst the 1 14 diols record shows a change in periodicity around the mpt from 41 to 100 kyr cycle suggesting an influence of orbital parameters on diatom productivity in the central sea of okhotsk the relative amount of c32 1 15 diol fc32 1 15 a proxy for riverine input correlates with sea level change with more riverine derived material reaching the core site when the amur river mouth is closer at lower sea levels in agreement fc32 1 15 shows a change in periodicity during the mpt with the appearance of a 100 kyr cycle our results show that the long chain diols can provide important paleoceanographic information in subpolar environments over long time scales but that temperature reconstructions can be severely impacted by changes in seasonality

hydrodynamic evolution from quartz microtextures of a beach ridge in qinghai lake china abstract beach ridges are landforms that exist on beach shorelines and can supply abundant information regarding palaeoenvironments to better understand the hydrodynamic processes of beach ridges a quartz microtexture analysis was carried out in this study the microtextural features of a total of 1063 quartz grains from seven beach ridge samples and eight reference samples from rivers a dune and a nearby beach were observed and analysed by scanning electron microscopy the qualitative and quantitative results suggest that the quartz microtextures of the beach ridge samples present more fresh surfaces and percussion marks than the river samples but less angularity the upper sequence samples from the beach ridge present higher values of fresh surfaces and percussion marks and lower dissolution than the lower sequence samples a cluster analysis shows that the hydrodynamic conditions of qinghai lake underwent pronounced changes from weak to strong and then to weak at the present time furthermore quantitative analyses indicate that the beach ridge and river sedimentary environments can be distinguished through the microtextural features of the 250 125 m size fraction however more grain size fractions should be observed and analysed to interpret the hydrodynamic conditions the quartz microtextural analysis of beach ridges may be an effective method reflecting the palaeohydrodynamic conditions

contradictory magnetic polarities in sediments and variable timing of neoformation of authigenic greigite abstract in several recent published studies paleomagnetic results from greigite bearing sediments reveal characteristic remanences that are anti parallel to those carried by coexisting detrital magnetic minerals and polarities that are opposite to those expected for the age of the rock unit these observations have important implications for the reliability of paleomagnetic data from greigite bearing sediments we have investigated the origin of such contradictory magnetic polarities by studying the formation mechanisms of greigite in mudstones from the lower gutingkeng formation southwestern taiwan scanning electron microscope observations indicate that the gutingkeng greigite has three modes of occurrence including nodular framboidal and matrix greigite microtextural observations including transection of bedding by iron sulfide nodules with no deviation of sediment textures the presence of partially dissolved edges around detrital and early diagenetic phases and neoformation of greigite and fe rich clays around detrital phyllosilicates indicate that all three types of greigite have a diagenetic origin that post dates early diagenetic pyrite in addition paleomagnetic data yield contradictory polarities even for greigite bearing sister samples from the same stratigraphic horizon the data are collectively interpreted to indicate that neoformation of the gutingkeng greigite occurred after partial dissolution of syngenetic or early diagenetic pyrite the timing of greigite formation can apparently vary enough to give contradictory polarities for different greigite components even within a single stratigraphic horizon direct petrographic observation of authigenic magnetic iron sulfide phases as carried out in this study can provide important constraints on formation mechanisms and timing of remanence acquisition for these minerals and suggests that care should be taken when interpreting magnetostratigraphic data from greigite bearing sediments

sea level reversal during termination ii the termination of the penultimate glacial period tii shows both similarities and differences to the last termination ti both terminations show significant cold reversals in the postglacial warming trend ti consists of a continuously increasing sea level trend whereas tii may demonstrate a sea level reduction midway through the termination we present a new continuous sea level record for tii derived from red sea 18 o records that supports the existence of the tii sea level reversal the record gives an unprecedented look at the structure of the tii sea level reversal which consists of an early highstand lasting several millennia in duration followed by a 30 12 m to 40 12 m reduction in sea level and a stillstand of several millennia before the final sea level rise to the marine oxygen isotope stage mis 5e interglacial we suggest that there is a link between the sea level reversal and internal millennial scale variability in the climate system

diagenetic formation of ferrimagnetic iron sulphide minerals in rapidly deposited marine sediments south island new zealand abstract detailed magnetostratigraphic studies of late neogene siliciclastic sediments of the awatere group south island new zealand 41 45 s 174 05 e have revealed a wide range of palaeomagnetic behaviour examination of rock magnetic properties was undertaken using conventional palaeomagnetic techniques and thermomagnetic x ray diffraction and electron microprobe analyses these analyses indicate that the ferrimagnetic iron sulphide minerals greigite and pyrrhotite are responsible for a stable and intense magnetic remanence in fine grained sediments whereas titanomagnetite is the only remanence bearing mineral identified in coarser grained sediments which are less strongly and less stably magnetised than the fine grained sediments detrital titanomagnetite grains are likely to have undergone dissolution during early diagenesis as a result of iron sulphide formation which occurs commonly in rapidly deposited anoxic sediments that support active sulphate reduction and h 2 s formation preservation of greigite and pyrrhotite is inferred to result from the arrest of the pyritisation process probably due to the low permeability of the fine grained sediments and consumption of available h 2 s before full reaction to pyrite occurred relative palaeomagnetic instability and weak remanence intensities in coarser grained sediments is likely to be due to low titanomagnetite concentrations resulting from titanomagnetite dissolution

millennial mode of variability of sea ice conditions in the okhotsk sea during the last glaciation mis 4 mis 2 abstract coarse fraction cf content grain size distribution roundness of cf gravels and pebbles and examination of surface of pebbles were studied in core lv28 44 4 recovered from the eastern okhotsk sea os the age model of the studied core was based on the ams 14c data tephrochronology 18o benthic foraminifera record and correlation of peaks of productivity proxies with long lasted dansgaard oeschger do interstadials the results show that sea ice was the main transport agent for cf ice rafted debris ird in the eastern os published mineralogical studies of clastic material of the os indicated that the coast of western kamchatka was the main source of ird in the eastern os we found 19 peaks of ird which mostly coincided with do stadials the distribution of cf indicates a different pattern of ird supply during mis 4 3 and 2 comparison of ird records in the eastern and central parts of the os allow us to reconstruct millennial changes in ice and wind modes for mis 4 mis 2 significant strengthening of northeastern and eastern winds during doss of mis 3 and of northern and north western winds during mis 2 were observed

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

magnetostratigraphy and tephrochronology of the upper quaternary sediments in the okhotsk sea implication of terrigenous volcanogenic and biogenic matter supply seven lithological units alternating between horizons enriched in biogenic opal diatoms and carbonate foraminifera and units composed largely of terrigenous sediment with very low biogenic admixture were distinguished in a series of late quaternary sediment cores from the sea of okhotsk sediments were characterised using on board visual description smear slides analyses grain size composition and magnetic susceptibility ms records five tephra marker layers identified as ko tr k2 k3 and k4 were distinguished using petrological mineralogical and geochemical analyses age models were developed by comparing lithological units tephra stratigraphy and ms records with oxygen isotope curves and with records of biogenic caco3 opal content and sediment grain size composition in three ams radiocarbon dated okhotsk cores this chronological framework allowed us to investigate climate control over the sedimentation regime and productivity and to clarify the formation times of the lithological and tephra units the data show that sediment ms variations in the south eastern area of the glacial okhotsk sea arose primarily from volcanic material input the sedimentation in all other parts of the sea was mainly controlled by the supply of terrigenous material the cores show a tight correlation between ms sediment grain size and climate change in the okhotsk sea coarse sediments with a high ms were accumulated during the cold period oxygen isotope stages mis 2 4 6 fine sediments with a low ice rafted debris ird content and ms were formed in the warm isotope stages according to the oxygen isotope stratigraphy and radiocarbon data the ko tr k2 k3 and k4 tephra were deposited at 7 7 8 0 26 0 kyr bp in mis 4 about 60 70 kyr ago and near mis 5 4 respectively comparison of tephra mineralogy petrology spatial distributions and ages with the history of kurile kamchatka volcanism allows us to identify likely candidates for the tephra source eruptions the combined use of ms records tephrochronology and lithological unit sequences provides a detailed basis for okhotsk sea sediment stratigraphy

dissolution and pyritization of magnetite in anoxie marine sediments concentrations of magnetite were determined with depth in sediments of varying h2s content taken from long island sound foam nwc and sachem sites and from a site in the rapidly depositing subaqueous portion of the mississippi delta for the three long island sound sites dissolution of magnetite during burial is clearly demonstrated and for all four sites the rate of magnetite dissolution is proportional to the concentration of dissolved pore water sulfide by combining magnetite depth distributions with sedimentation rate data and measurements of dissolved sulfide we find that magnetite dissolution is well described by the following rate law dcmagdt 1 1 10 5c0 5bcmagamag where cmag is the concentration of magnetite grams per gram of sediment cs is the concentration of dissolved sulfide mm and amag is the specific surface area of magnetite in the sediment cm2 per gram of magnetite this equation means that for a typical range of magnetite surface areas and dissolved sulfide concentrations the half life of magnetite in anoxic marine sediments ranges from about 50 to 1000 years sem observations of magnetite grains from the different sediment sites reveal that magnetite dissolution may be accompanied by extensive replacement by pyrite this only occurs if magnetite is in contact with high concentrations of h2s 1 mm for relatively long periods of time several hundred years with low concentrations of h2s 1 mm magnetite dissolution occurs without identifiable pyrite replacement we suggest that this feature of magnetite diagenesis may prove to be a useful paleosulfide indicator

distribution and formation of okhotsk sea intermediate water an analysis of isopycnal climatological data 1 in order to clarify the distribution and formation of okhotsk sea intermediate water osiw an isopycnal climatological data set based on all of the available historical observations is developed and examined the isopycnal maps clearly show that there are two direct ventilation sources for osiw dense shelf water dsw with cold and fresh properties influenced by sea ice formation in the northwest shelf region and forerunner of soya warm current water fscw which has warm and saline properties originating in the japan sea the cold and fresh water extends southward from the northwest shelf to the shelf slope off sakhalin island it suggests that dsw is transported southward by the east sakhalin current the dsw enters the kuril basin and mixes with fscw and western subarctic water wsaw originating from the north pacific to form osiw the annual mean production rate of dsw estimated from the total volume of dsw over the shelf in spring and summer is 0 67 sv 1 sv 106 m3 s the annual mean volume transport of fscw is estimated to be 0 08 sv on the basis of its cross section area and the current speed assumption of isopycnal mixing yields a mixing ratio of 1 1 0 1 among dsw wsaw and fscw to form osiw we estimate the annual production rate of osiw to be 1 4 sv the corresponding osiw s renewal time is 7 years continued assumption of isopycnal mixing yields a mixing ratio of 0 6 0 4 between wsaw and osiw to form oyashio intermediate water oyiw

stable isotope and lithologic evidence of late glacial and holocene oceanography of the northwestern pacific and its marginal seas abstract stable isotopes geochemical lithological and micropaleontological results from cores from the far northwest fnw pacific and the okhotsk and bering seas are used to reconstruct the regional environment for the last glaciation the deglacial transition and the holocene 18 o records of planktonic foraminifera of the region show two light shifts during deglacial time provoked by the freshening of the surface water and climate warming these north pacific terminal events t1anp and t1bnp with ages of 12 500 and 9300 yr b p respectively occur almost simultaneously with two episodes of accelerated glacier melting around the north atlantic along with the isotopic shifts the caco 3 content in regional sediments increased abruptly 1a and 1b carbonate peaks probably due to changes of productivity and pore water chemistry of surface sediments organic matter and opal concentration increased during the transition between t1anp and t1bnp events in the sediments of the fnw pacific and the southern part of the bering sea and opal content increased in the holocene in the bering and okhotsk seas 13 c records of cores from the okhotsk and bering seas and the fnw pacific do not contradict the hypothesis of increased intermediate water formation in the region during glaciation during deglaciation accumulation of the coarse terrigenous component decreased in sediments of the bering sea and the fnw pacific before the t1anp event probably as a result of rising sea level and opening of the bering strait

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