japan sea oxygen isotope stratigraphy and global sea level changes for the last 50 000 years recorded in sediment cores from the oki ridge abstract we obtained twenty ams accelerator mass spectrometry radiocarbon dates 2 tephra layer chronologies and a planktonic foraminiferal 18 o stratigraphy for the last 50 000 years from japan sea cores from the oki ridge in this paper we report ams 14 c results that allow us to reconstruct a high resolution chronology of the cores and discuss millennial scale climate changes recorded in japan sea sediments the sedimentation rate for the site increased dramatically from the glacial stage to the holocene as a result of significant hydrological changes associated with deglaciation and global sea level rise a lighter 18 o anomaly for the planktonic foraminifers was found during the lgm last glacial maximum this shift corresponds to a freshening of the japan sea surface waters and is mainly due to a global sea level drop rather than anomalously warm ssts sea surface temperatures as previously reported our record combined with the global sea level data suggests that the lgm started about 30 kyr ago and that the salinity of the japan sea became fresher than at present the ssts during mis marine oxygen isotope stage 3 were relatively stable and global sea level was not lower than ca 80 m the surface water of the japan sea attained normal saline levels following the younger dryas cold event and reached the present day 18 o values 7 kyr ago

orbital and millennial scale paleoceanographic changes in the north eastern japan basin east sea japan sea during the late quaternary two gravity sediment cores gh99 1239 and gh99 1246 obtained from the north eastern japan basin in the east sea japan sea were analyzed for the orbital and millennial scale paleoceanographic changes chronostrati graphically core gh99 1239 represents a continuous sedimentary record since 32 ka based on correlation of distinct lithological markers i e dark layer or tl layer with those in core gh98 1232 collected nearby for core gh99 1246 the age model is constructed through correlation of lightness l values and tephra aso 4 and toya layers with those in the well dated oki ridge core md01 2407 indicating about 134 ka of sedimentation since the latest marine isotope stage mis 6 new geochemical data from both cores corroborate orbital scale paleoceanographic variation such that surface water productivity represented by biogenic opal and total organic carbon toc contents increased during mis 1 and mis 5 caco3 contents do not show such distinct glacial interglacial cycles but were influenced by dissolution and preservation rather than foraminiferal production during the glacial periods when sea ice was prevalent surface water productivity was low and bottom water conditions became anoxic as indicated by high total sulfur ts contents and high mo concentrations the geochemical data further document millennial scale paleoceanographic variability corresponding to a series of thin tl layers in response to dansgaard oeschger cycles but irrespective of the glacial or interglacial periods in particular thin tl layers formed during mis 3 are characterized by less toc about 1 and ts about 0 4 contents and lower mo about 5 p p m concentration whereas those during mis 4 and mis 5 exhibit more toc up to 4 and ts up to 5 contents and higher mo up to 120 p p m concentration such a discrepancy is attributed to different degree of surface water productivity and of bottom water oxygenation which is closely related to the sea level position and extent of ventilation flux of the east china sea coastal water controlled by millennial scale paleoclimatic events is the most critical factor in deciding the properties of tl layers in the north eastern japan basin our results strongly confirm that tl layers in the japan basin also validate the unique feature of basin wide paleoceano graphic signals in the east sea japan sea copyright 2011 john wiley sons ltd

effet de la vitesse de refroidissement sur l intensite de l aimantation thermoremanente etude experimentale consequences theoriques the experiments reported here compare intensity and thermal resistance of two thermal remanent magnetizations trm successively acquired by the same sample under a magnetic field but at two different cooling speeds the samples one with a base of cro2 powder and the others derived from oceanic basalts were representative of the different types of structure domains characteristic of magnetic grains the experimental procedure established aimed at limiting the various factors of uncertainty mineralogical and structural modifications related to heating inhomogeneity of the sample temperature at crucial stages of each experiment effects of undesirable magnetizations acquired concurrently with the trm the main conclusion of this study is that the trm intensity increases as a function of time of cooling independently of the types of structure domains carried by the magnetic grains the greatest effect is with the cro2 monodomain the trm obtained between 130 and 100 c during a cooling period of 120

late quaternary paleoceanographic changes in the southwestern okhotsk sea evidence from geochemical radiolarian and diatom records abstract high resolution analyses of geochemical parameters biogenic opal calcium carbonate organic carbon and nitrogen and microfossil assemblages diatoms and radiolarians on core md01 2412 clarified detailed paleoceanographic changes such as sea ice cover and biological production in the southwestern okhotsk sea during the last 115 kyr an age model of core md01 2412 was established based on 18o stratigraphy accelerator mass spectrometer ams 14c and tephrochronology sea ice history reconstructed by siliceous microplankton records indicated that the present sea ice condition was formed during the last 8 kyr only during marine isotope stage mis 2 was the duration of sea ice cover in this region much longer than that of today 4 5 months a year two diatom species thalassionema nitzschioides and fragilariopsis doliolus revealed that the soya warm current water swcw flowed into the okhotsk sea near the site of core md01 2412 during the last 12 14 kyr and during mis 5a and was associated with sea level rise biological productivity rapidly increased during mis 1 associated with sea ice retreat two major increases of organic carbon oc contents wt and corg n ratios were observed and the timings of these events were 15 8 16 7 ka event 1 and 13 1 13 6 ka event 2 corresponding to these events the abundance of cycladophora davisiana an intermediate water dwelling radiolarian species increased this high c davisiana abundance can be correlated to the input of terrestrial organic matter from the submerged shelf to the intermediate water apart from the radiolarians the production of diatoms in the surface waters was suppressed by the development of well stratified surface water along with sea ice melting during the early holocene diatom production increased gradually during the last 10 kyr with enhanced vertical mixing

last glacial holocene water structure in the southwestern okhotsk sea inferred from radiolarian assemblages abstract in order to reconstruct paleoceanographic conditions in the southwestern sw okhotsk sea radiolarian assemblages were analyzed from 10 surface sediments and 5 sediment cores obtained from various water depths ranging between 461 and 1348 m we also measured geochemical components such as biogenic opal calcium carbonate total organic carbon total sulfur and total nitrogen for one sediment core these data imply that the complicated water structure in the sw okhotsk sea changed with time from the last glacial to holocene the glacial surface water was characterized by low primary production in the summer and expanded sea ice coverage in the winter during this time the ventilation might have reached deeper than during the holocene during the major deglacial period including the melt water pulses 1a and 1b the deep sea oxygen content had declined with less ventilation and or more oxygen consumption with organic matter supply into the deeper depths the intermediate layer has been well ventilated and has supplied large amount of organic matter during the last 20 kyrs especially in the early mid holocene however such condition ceased during 3 to 2 ka the warm pacific deep water has been present since 9 ka the influence of warmer surface water such as the soya warm current swc increased in the coastal area during 7 to 4 ka and since 2 ka till present neritic derived productivity might be extended at 2 2 1 8 ka and since 1 2 ka till present

origin and evolution of cycladophora davisiana ehrenberg radiolaria in dsdp site 192 northwest pacific this paper documents the evolutionary history of cycladophora davisiana ehrenberg from an uppermost miocene to pleistocene sedimentary record in the high latitude northwest pacific it apparently evolved from c sakaii motoyama through a series of intermediates c sakaii has a relatively large shell with an external spongy layer the evolutionary transition is characterized by a relatively rapid decrease in thorax size with a reduction of the spongy appendage this change occurred during about 0 4 m y from 2 8 to 2 4 ma without cladogenesis following this interval a decrease in thorax size continued gradually up to the recent resulting in a very small morphology although the population of c davisiana first appeared at about 2 5 ma some morphotypic specimens may occur in earlier periods as indistinguishable very small endmembers in the c sakaii populations timing of the first appearance events both of morphotypic specimens and of a population of c davisiana in site 192 and previously reported cores does not disprove the idea that c davisiana evolved first in the northwest pacific region and later migrated into other regions of the world ocean biometrics clearly indicate no direct phylogenetic relationships between c davisiana and c cornutoides kling in the studied core thus the latter species which was originally described as a variation and later elevated to a subspecies of the former species is separated from the former species and raised to the species rank

palaeointensity results for historic lavas from mt etna using microwave demagnetization remagnetization in a modified thellier type experiment summary the bane of conventional thellier type palaeointensity experiments is the thermal alteration of the samples during experimentation however high frequency microwaves can be used to stimulate the magnetic minerals directly thus eliminating the need for the bulk sample to be heated walton et al 1993 the microwave technique has been successfully applied to ceramics shaw et al 1996 1999 and here we present results for historic lavas from mt etna sicily 20 samples were randomly selected from 10 diverent historic flows dating from 1843 to 1983 hysteresis parameters were monitored as a check for alteration during experimentation and minimal alteration was found rock magnetic analysis and af plus microwave demagnetizations were carried out on all samples and microwave intensity analysis was carried out on those samples that were stable to microwave demagnetization 16 in total with one exception all samples gave high quality intensity results two or three subsamples from each sample were investigated and a weighted average calculated to give a single estimate of the field when the intensity values were compared with the sv model based on direct observatory measurements bloxham gubbins 1985 it was found that those samples that contained a high multidomain md component gave intensity values around 20 per cent lower than expected this can be explained by the cooling rate evect dodson mcclelland brown 1980 and or the presence of an md component mcclelland et al 1996 those samples with the lowest numbers of md grains gave field values which within error were the same as those for the model or slightly too high this is compatible with the cooling rate evect

the production scheme of cycladophora davisiana radiolaria in the okhotsk sea and the northwestern north pacific implication for the paleoceanographic conditions during the glacials in the high latitude oceans 1 the sediment trap study clearly unraveled that the distinct peaks of c davisiana fluxes occurred during summer to autumn in both the okhotsk sea and the northwestern north pacific the production of c davisiana is closely related to the microbial production in the intermediate water in the okhotsk sea the distinct microbial biomass in the intermediate water which is associated with the seasonal sea ice rejected brine water during winter may support the high c davisiana abundance therefore the significantly high c davisiana abundance during the last glacial maximum lgm in the high latitude open oceans implies the distinct microbial biomass in the intermediate water caused by the seasonal sea ice coverage analogous to the present okhotsk sea

global warming may have slowed down the deep conveyor belt of a marginal sea of the northwestern pacific japan sea weakening of the abyssal circulation conveyor belt in the japan sea during the 20th century is deduced from the decreasing trend of bottom dissolved oxygen o2 this trend indicates a shortened o2 supply caused by too inactive conveyor belt to compensate for biological o2 consumption at the bottom of the sea recent climatic changes during the winter season in the northern japan sea may play a significant role in prohibiting the formation of surface seawater dense enough to sink to the bottom it is predicted that the japan sea bottom water will become anoxic within a few hundred years as it was in the last glacial maximum

orbital scale stratigraphy and high resolution analysis of biogenic components and deep water oxygenation conditions in the japan sea during the last 640 kyr abstract paleoceanographic conditions in the japan sea changed drastically during the late quaternary in association with orbital and suborbital cycles and glacio eustatic sea level changes however few studies have examined long term sediment records older than 160 ka because of the lack of long and continuous cores and the difficulty in constructing high resolution age models in this study we first constructed an orbital scale stratigraphy of the sediments covering the last 640 kyr by comparing the specmap 18o curve and the 18o curve of planktonic foraminifera 18opf in the japan sea together with the combination zones of dominant planktonic foraminifera species then we reconstructed temporal variations in biogenic silica biosil and biogenic carbonate biocarb contents calculated from high resolution major element analysis data determined by an xrf microscanner in order to evaluate the deep water oxygenation conditions we also defined excess s as the difference between the content of s in the sediments and that for normal marine sediments calculated from the organic carbon content corg estimated from lightness l by assuming a total sulfur content stotal corg ratio of 0 36 and examined its variability biosil shows orbital scale variation and is generally low except during interglacial maxima when global sea level was high enough to allow a strong influx of the tsushima warm current biocarb shows orbital and suborbital scale variations and tends to be higher in dark layers deposited during glacial stages whereas the relationship is reversed during interglacial stages the low biocarb in dark layers deposited during interglacial stages is probably due to dissolution of biogenic carbonate caused by the increase in surface productivity as a result of the strong influx of nutrient rich east china sea coastal water and consequent increase in surface productivity and decomposition rate of organic matter in the intermediate water excess s tends to be higher in thicker dark layers deposited during glacial maxima when the sea level dropped below 90 m compared to adjacent light layers suggesting development of euxinic deep water conditions during these periods the results demonstrated the presence of orbital and suborbital scale variations in biosil and biocarb and their association with dark and light layers in the japan sea that reflect variations in the nature and strength of inflow through the tsushima strait controlled by both climatic and sea level changes whereas higher excess s reflects the development of euxinic deep water condition during glacial maxima in association with glacio eustatic sea level drops below 90 m during the last 640 kyr

radiolarian responses of the central okhotsk sea to the global orbital and millennial scale climate oscillations over last 90 kyr abstract the study of total radiolarian content trc and species richness sr for radiolarian assemblage as well as absolute and relative abundance of cycladophora davisiana and abundance of other dominant taxa in the sediment core from the central okhotsk sea os over last 90 kyr with previously established age model position of millennial cycles of climatic changes and records of variations of various productivity proxies and activity of sea ices was carried out the trends of trc and sr in the radiolarian assemblage change synchronously on the orbital scale and are mainly determined by variations of paleoproductivity and input organic matter into the water column in turn the productivity of the os depends to a great extent on conditions of the sea ice formation and distribution and increases during the warmer mis 5a 3 and 1 with a shorter seasonal sea ice cover among various productivity proxies considered by us only ba bio reflects to the fullest extent the variations of trc and sr of radiolarians probably due to the fact that the accumulation of insoluble barite in sediment depends on degree of organic matter decomposition immediately within the water column and provision of more favorable for radiolarian food variations of trc of radiolarians and their sr on the millennial scale are also controlled by variations of productivity in the photic layer the millennial productivity minima associated with the cold greenland china stadials gs cs resulted in considerable sharp falls in trc and sr of radiolarians while subsequent increases in productivity during gi ci caused the smoother growth in trc and sr of radiolarians such a pattern of changes in the species richness and quantity of radiolarians in time is more similar to variations in 18o of stalagmite carbonates from the china caves than 18o of greenland ice core and probably is determined predominantly by variability of the winter monsoons in the east asia affecting the environment and ice cover of the os changes in absolute abundance aa of c davisiana on the orbital and millennial scales are closer related to changes in trc of radiolarians determined mainly by variations of the sea productivity changes in relative abundance ra of c davisiana in time are slightly different from variations in their absolute abundance as depend also on changes in percentage of other species in the assemblage

radiolarian faunal provinces in surface sediments of the greenland iceland and norwegian gin seas the overall abundance and species composition of the polycystine and phaeodarian radiolaria have been determined in 63 surface sediment samples from the gin seas these results are compared to chemical and physical properties of the overlying water masses there are three abundance maxima in the distribution of radiolarian skeletal debris preserved in these surface sediments centered on the iceland plateau southern norwegian basin and northern norwegian basin the most commonly encountered species were a spumellarida actinomma boreale a leptoderma larcospira minor and phorticium clevei b nassellarida amphimelissa setosa artobotrys boreale lithomelissa setosa lithocampe platycephala pseudodictyophimus gracilipes cycladophora davisiana a ndlithomitra lineata based on factor analysis of the core top assemblages the radiolarian species were grouped into three associations factor 1 a polar and arctic water association dominated by amphimelissa setosa varimax factor score 5 269 high factor component values are found in the iceland plateau area and in a wedge just north of the iceland faeroe ridge factor 2 an atlantic water association dominated by pseudodictyophimus gracilipes 3 247 lithomelissa setosa 2 731 and actinomma boreale 1 851 high factor component values are found in the eastern part of the norwegian sea particularly in the area under the influence of the norwegian current and factor 3 an atlantic and arctic water mixed association dominated by lithocampe platycephala 3 251 lithomelissa setosa 2 176 actinomma leptoderma 1 994 and artobotrys boreale 1 504 high factor component values are found immediately to the east of the iceland plateau in correspondence to the deepest part of the norwegian basin the correlation coefficients obtained between seasonal sea surface temperature and factors 1 r 2 d 0 835 a nd 2 r 2 d 0 891 show a good fit whilst for factor 3 there was a less marked r 2 d 0 497 but still significant at the 5 confidence level correlation for fifth degree polynomial regression functions the factors correlated better with the summer than the winter sea surface temperatures however at 20 50 100 and 200 m depth the correlation became increasingly better particularly so for the winter situation the highest species richness for polycystine radiolarians 28 species was found in the warm atlantic domain the lowest 24 species was found in the colder arctic and polar domains whilst an area approximating the position of the arctic front had between 24 and 28 species 1998 elsevier science b v all rights reserved

deep convection and brine rejection in the japan sea received 15 october 2002 accepted 13 january 2003 published 19 february 2003 1 direct water mass renewal through convection deeper than 1000 m and the independent process of dense water production through brine rejection during sea ice formation occur at only a limited number of sites globally our late winter observations in 2000 and 2001 show that the japan east sea is a part of both exclusive groups japan sea deep convection apparently occurs every winter but massive renewal of bottom waters through brine rejection had not occurred for many decades prior to the extremely cold winter of 2001 the sites for both renewal mechanisms are south of vladivostok in the path of cold continental air outbreaks index terms 4283 oceanography general water masses 4243 marginal and semienclosed seas 4223 4215 climate and interannual variability 3309 citation talley l d v lobanov v ponomarev a salyuk p tishchenko i zhabin and s riser deep convection and brine rejection in the japan sea geophys res lett 30 4 1159 doi 10 1029 2002gl016451 2003

high field intensity results from recent and historic lavas a total of 45 recent and historic lava flows of mount etna sicily were sampled to investigate changes in the strength and orientation of the geomagnetic field in the region of the flows sampled 11 yielded one or more samples which provided anomalously high field intensity results a rock magnetic study has shown that a high resistance to alternating field demagnetization and group 2 low temperature susceptibility behaviour are the two factors common to these samples

paleotemperature response to monsoon activity in the japan sea during the last 160 kyr abstract paleo sea surface temperatures in the northeastern and southeastern parts of the japan sea were reconstructed for the last 160 kyr using alkenone temperatures u k 37 temperatures u k 37 temperatures at two sites show distinct glacial interglacial changes during the last 160 kyr except for the interval corresponding to middle mis 3 to mis 2 on orbital timescales u k 37 temperature tends to be high during mis 5e mis 5c and mis 5a which coincides with the intervals of stronger east asian summer monsoon activity the amplitude of temperature fluctuations in the japan sea is significantly higher than those in the neighboring seas we suggest that the sst variation was amplified by the increasing source water kuroshio water temperature and the changes in the volume transport of the tsushima warm current twc and or the north south oscillation of the sub polar front position within the japan sea millennial scale temperature fluctuations in the japan sea show that the temperature at the northern site was higher than that at the southern site during warmer periods of mis 5 which is called temperature reversal by analogy with modern oceanography the temperature reversal could reflect the enhanced volume transport of the twc and the spatial relationship between the studied site and the branches of the twc which is an essential factor in north south temperature reversal around the eastern japan sea temperature drops were found at 114 ka 111 ka 93 ka 87 ka and 77 ka in mis 5 those events were associated with an increase in organic carbon and alkenone contents and can be correlated with the abundance peaks of ice rafted debris ird at site gh05 1208 in the northern japan sea suggesting that the surface water was cooled by enhanced mixing and consequent upwelling in a stronger winter monsoon regime

reconstruction of environmental changes using a multi proxy approach in the ulleung basin sea of japan over the last 48 ka based on elemental geochemical data we reconstructed the sediment provenance surface productivity and bottom water redox conditions for the last 48 ka in the ulleung basin sea of japan and inferred the factors controlling them al2o3 tio2 ratio and chemical index of alteration cia suggest that sediment provenance changed during the glacial period 48 18 ka compared to the deglacial ca 18 11 ka and holocene mass accumulation rates of total organic carbon toc caco3 phosphorus cadmium and excess barium reveal low paleoproductivity during low sea stand during 18 11 ka productivity increased due to increasing inflow of nutrient rich water masses the oyashio and the east china sea coastal water in tandem with the rising sea level maximum productivity occurred during younger dryas and pre boreal periods when sea level was at 60 m and then gradually decreased as the tsushima warm current inflow kicked off at ca 9 3 ka consistent with other paleoredox proxies which reveal the presence of anoxic bottom water during ca 12 9 ka with the changes in paleoredox proxies and their ratios toc mo u mn c s ratio and uauthigenic and mo contents we hypothesized that the redox changes were mainly ventilation driven and were superimposed on the influence of circulation induced productivity changes the global climate and sea level changes on a millennial timescale play a major role in enhancing paleoproductivity and restrict bottom water advection subsequently driving the oxygenation of bottom water in the ulleung basin copyright 2012 john wiley sons ltd

pleistocene and holocene distribution of the radiolarian amphimelissa setosa cleve in the north pacific and north atlantic evidence for water mass movement abstract the radiolarian amphimelissa setosa is one of the prominent species of the pleistocene radiolarian assemblages in the sea of okhotsk below the marine isotope stage mis boundary 5 4 and it represents one of the most abundant radiolarian species in holocene and modern environments of the nordic seas we studied the a setosa distribution in six cores from the sea of okhotsk and established morphometric measurements on a setosa specimens from two cores of the sea of okhotsk and one core from the labrador sea we further compared our data with other available studies from the subarctic pacific the labrador sea the north atlantic the norwegian sea and the iceland greenland seas in order to discuss the possible settling of the species from the north pacific via the arctic ocean into the iceland greenland seas a setosa exhibits a stable abundant population in the sea of okhotsk during most of the last ca 0 7 m y and might repeatedly extend its population into the north atlantic through the arctic ocean during the pleistocene interglacial optima the species declines from the sea of okhotsk and from the subarctic pacific at the end of mis 5 its final documented settling into the north atlantic is during mis 5 when a setosa appears in low numbers in sediments of the labrador sea however reaching significant percentages at the boundary of mis 5 4 based on the available information we propose that a setosa could migrate from the north pacific into the arctic ocean during the interglacial optimum mis 5e and then through the channels of the canadian arctic archipelago into the baffin bay and labrador sea a further migration step of a setosa occurs at the boundary of mis 5 4 when a setosa migrated from the labrador sea into the north atlantic probably related to a southward expansion of cold waters at the end of the mis 5 during the warming at termination i a setosa moved from the north atlantic into the nordic seas the abundant occurrence of a setosa in sediments south of iceland the norwegian and north seas within the younger dryas period points to a marked cooling and a southward movement of polar water masses restricted to this time interval

late pleistocene stratigraphy and palaeoceanographic implications in northern bering sea slope sediments evidence from the radiolarian speciescycladophora davisiana a high resolution abundance curve of the radiolarian species cycladophora davisiana was obtained from a late pleistocene sediment core pc 23a which was obtained from the northern slope of the bering sea the abundance pattern of this species was high during the glacial period and low during the holocene this general stratigraphic pattern was correlated with a previously reported pattern for the subarctic pacific ocean however planktonic foraminifera based accelerator mass spectrometry 14c dating revealed that a significant peak in the c davisiana curve during the glacial period correlates to 15 5 ka which is younger than that previously estimated as being the last glacial maximum the higher abundance of this species implies that there was well ventilated water with a large amount of organic matter in the intermediate water layer an unusually high propagation of c davisiana during the earliest holocene period bolling allerod b a and dansgaad oescheger interstadial event 12 was most likely related to a significant increase in the amount of organic matter released into the intermediate water depths by a brine pump system via ventilation in addition centennial scale variations in the abundance of c davisiana during the b a period suggest that the intermediate water ventilation was sensitively affected by brine rejection during sea ice formation as well as large scale atmospheric circulations such as the arctic oscillation copyright 2009 john wiley sons ltd

foraminiferal records of bottom water oxygenation and surface water productivity in the southern japan sea during 160 15ka associations with insolation changes abstract analyses of the benthic and planktonic foraminiferal record were conducted to understand temporal variations in sea floor oxygenation and surface productivity during periods of dark layer deposition between 160 and 15 ka based on data from sediment core images md01 2407 water depth 932 m from the southern japan sea the dark layers in the core were classified into six types on the basis of benthic foraminiferal assemblages which reflect the nature and amount of organic material on the sea floor as well as the degree of oxygenation of bottom waters three of the dark layer types were deposited in conditions strongly associated with increased surface productivity which correlates with positive or negative peaks of summer insolation in the northern hemisphere during periods of insolation maxima summertime surface productivity was enhanced because of the inflow of nutrient rich surface waters associated with high precipitation in eastern asia caused by intensification of the east asian summer monsoon in contrast relatively sustained organic matter fluxes to the sea floor occurred during insolation minima possibly affected by active vertical mixing when the east asian summer and winter monsoons were both intensified in a given period well oxygenated bottom water environments combined with high surface productivity may have resulted in dark layer deposition because of a combination of strong wintertime water convection and increased summertime surface productivity it is likely that the organic carbon content of sediments underestimates surface productivity during depositional conditions favoring the sedimentary decomposition of organic matter

radiolarian flux at an images site at the western margin of the subarctic pacific and its seasonal relationship to the oyashio cold and tsugaru warm currents seasonal changes of radiolarian flux in the far western area of the western subarctic gyre in the pacific ocean were examined based on samples from a sediment trap experiment deployed at a site off the northern honshu island of japan from june 2002 to may 2003 warm and neritic water species associated with the tsugaru warm current tgc originating from the japan sea were dominant while the cold water species associated with the oyashio cold current were relatively few in spite of the location of the site in the subarctic province r mode cluster analysis was used to divide species specific flux patterns into 5 groups of fauna associated with 1 the tgc forerunner in june 2002 2 the tgc main flow from september to november 2002 3 the neritic water in december 2002 4 the oyashio cold current in may 2003 and 5 surface productivity in the spring of 2002 2003 together with the tgc in summer 2002

radiolarian fauna in surface sediments of the northeastern east china sea radiolarian abundance and species composition have been determined in 72 surface sediment samples from the northeastern east china sea the results are compared with chemical and physical properties of the overlying water masses and with sediment conditions in the study area radiolarian abundance and species number increase markedly from northwest to southeast and their distributions can be divided into three provinces the low density zone corresponding to the shelf the middle density zone corresponding to the western slope of the okinawa trough and the high density zone corresponding to the central part of the okinawa trough the distribution of radiolarians correlates well with modem sea surface temperature and sea surface salinity but shows a negative relation with nutrients and primary productivity of the overlying water this distribution pattern is also strongly affected by the sediment type and terrigenous material input also the kuroshio current has an important effect on controlling the distribution and species composition of radiolarian fauna in this area based on three q mode factors accounting for 90 2 of the variance three radiolarian assemblages have been distinguished and their distributions are clearly correlated with oceanographic current patterns in the region the mixed water assemblage dominated by tetrapyle circularis tetrapyle quadriloba and ommatartus tetrathalamus tetrathalamus is restricted to the area of the mixed water but mainly influenced by the shelf water the kuroshio water assemblage which is dominated by lithelius minor dictyocoryne profunda stylodictya multispina acrosphaera spinosa dictyocoryne truncatum spongaster tetrars stylodictya arachnia and ommatartus tetrathalamus tetrathalamus is basically controlled by the kuroshio surface water and the transition assemblage dominated by tetrapyle quadriloba and monozonium pachystylum is associated with the tsushima warm current water the boundaries among these assemblages approximately coincide with the oceanographic front and the changes in the distribution of these assemblages could be regarded as not only modifications of the water masses but also indicators of the possible movements of the oceanic front c 2003 elsevier science b v all rights reserved

paleoenvironmental changes in the japan sea during the last 85 000 years five distinct changes in the paleoenvironment of the japan sea within the last 85 000 years are revealed from the sedimentary record of a piston core recovered from the oki ridge changes in both surface and deepwater conditions are registered by changes in lithology calcium carbonate content organic carbon content oxygen and carbon isotope ratios and microfossil assemblages including calcareous nannoplankton diatoms radiolaria and foraminifera between 85 and 27 ka the warm tsushima current did not flow into the japan sea and cold surface water conditions prevailed environments at the seafloor fluctuated between dysaerobic to weakly oxic conditions between 27 and 20 ka freshwater input to the japan sea probably from the huang ho river in china stratified the water column and the severe anoxic conditions eliminated most benthic fauna between 20 and 10 ka the cold oyashio current flowed into the japan sea through the tsugaru strait reestablishing deepwater ventilation shallow water benthic assemblages of the north pacific ocean subsequently colonized the japan sea and occupied the vacant niches of the deep basins between 10 and 8 ka the foraminifer compensation level fcl gradually rose to a depth shallower than 1000 m and bottom conditions changed from dysaerobic to oxic at 10 ka the warm tsushima current started to flow into the japan sea through the tsushima strait to establish the modern oceanographic regime which has existed since 8 ka the eustatic sea level during the last glacial maximum was above the sill depths 130 m of the tsushima and tsugaru straits assuming that tectonic movements at these straits were negligible for the last 20 ka

radiolaria as a reflection of environmental conditions in the eastern and southern sectors of the indian ocean a new statistical approach cluster analysis and species abundance plots of radiolarian abundance counts from core tops from the eastern indian ocean between 12 s and 31 s and the southern indian ocean between 31 s and 62 5 s demonstrate the existence of environmentallyrelated provinces supporting distinct taxa assemblages these provinces are closely associated with currents in the eastern sector of the indian ocean and with fronts in the southern sector the radiolarian assemblages correlate strongly with salinity normalised total alkalinity nta at the sea surface with temperature salinity and density from the sea surface to 300 m and with dissolved oxygen and nitrate and phosphate concentrations from the sea surface to 100 m palaeo reconstructions of these parameters at the sea surface have been made for six last glacial maximum lgm samples from five eastern indian ocean cores the lgm sea surface temperature estimates are comparable with those based on planktonic foraminiferal counts of the same samples obtained by other researchers the reconstructions show that since the lgm density increased markedly along the western australian coast south of 20 s but changed little further from the western australian coast by contrast phosphate concentrations were marginally lower than modern values along the western australian coast south of 20 s but more than twice modern values in the other lgm samples the utility of various regression and calibration techniques is discussed it is concluded that probably due to the effects of differences in radiolarian habitat ocean currents and or environmental gradients only one method weighted averaging partial least squares is reliable in a study area of this size and complexity if other methods are to be used the study area must be partitioned into at least two separate regions with the major split between the eastern and southern sectors of the indian ocean 2007 elsevier b v all rights reserved

sea level at the last glacial maximum constrained by oxygen isotopic curves of planktonic foraminifera in the japan sea the japan sea is connected with the okhotsk sea and northwest pacific through three straits viz mamiya tartarskiy soya and tsugaru and with the east china sea through tsushima strait all having sill depths of 3 recorded in the mis 3 4 sections of the studied cores this observation indicates nearly similar surface water conditions in the japan sea during both the previous glacial maxima and hence suggests negligible effect of strait tectonics on the sea level since the last 140 ka low d 18 opf values with small amplitude are also observed at the cold stage mis 6 4 but not observed at another cold stage mis 4 2 this observation suggests that the low salinity surface water in the japan sea started to develop at the sea level between mis 4 2 and 6 4 judging from the cross section of the tsushima strait and the sea floor topography of the east china sea the sea level between mis 4 2 and 6 4 must have been between 90 m and 100 m below the present from a proportional relationship between the standard d 18 o curve lr04 in deep sea cores and globally averaged sea level change the eustatic sea level obtained for the lgm is 120 7 m below the present thus the japan sea in a far field location from the continental ice sheets provides an important clue for estimation of the eustatic sea level at the lgm copyright 2012 john wiley sons ltd

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

a salinity related occurrence of a novel alkenone and alkenoate in late pleistocene sediments from the japan sea abstract the novel alkenoate ethyl tetratriacontadienoate c34 2ee has been found in late quaternary sediments of the japan sea by using gas chromatography mass spectrometry gc ms it accompanied hexatriacontadien 3 one c36 2ek previously found in black sea sediments a linear relationship between c36 2ek and c34 2ee concentrations points to both compounds being derived from the same source most likely a specific haptophyte the relative abundance of c34 2ee in total alkenones and alkenoates was significantly higher during the last glacial maximum when the 18o in planktonic foraminifera was anomalously light strongly suggesting that c34 2ee is associated with low salinity environments as samples with abundant c34 2ee also possessed anomalously high u 37 k values low salinity may have an ecological or physiological influence on both the unsaturation and carbon chain length of alkenones and alkenoates

the energetic surface circulation patterns of the japan east sea abstract in the period of 1988 2001 226 argos fixed drifters were deployed in the japan east sea jes from these and the historical file of temperature at a depth of 100 m 15 m depth circulation and its variances in relationship to the seasonal mean warm and cold water regions were constructed on 0 5 resolutions the strongest seasonal currents were the east korean warm current ekwc the tsushima current tc the north korean cold current nkcc and local eastwards intensifications along the sub polar frontal patterns the tc and nkcc were observed during summer and drifters passed through the soya strait only in summer the sub polar front occurred along 40 n in the northeastern jes a separate front occurred in winter that was associated with the flow of warm water restricted to the southern jes small eddy energy was found in the cold water regime and large eddy energy in the warm water regime satellite altimeter and drifter tracks were used to mark the wonsan eddy found in the east korean bay a yearly late summer occurrence mechanical energy flux from the mean circulation to mesoscale eddies occurred in ekwc tc and the sub polar front in the eastern jes with eddy kinetic energy doubling time of 15 60 days the yearly mean circulation east of the korean coast is organized into a broad eddy filled east sea current that contains weak anticyclonic gyres in the ulleung and yamato basins it accelerates toward the yamato rise and against the eastern coast of the jes the published numerical model solutions show several historical circulation features but fail to capture many of the new structures described by the drifter data

submarine landslide identified in md179 cores off joetsu area eastern margin of the sea of japan abstract gas hydrate is exposed on the sea floor and is buried in shallow sediments in the off joetsu area at the eastern margin of the sea of japan sediment cores recovered from topographic highs of the joetsu knoll and umitaka spur show pockmarks and mounds formed by gas hydrate dissociation but those from the un named ridge have no such topographic features all topographic highs and pockmarks mainly comprise bioturbated layers interbedded with thinly laminated tl layers which are common sea of japan sediments recovered sediments are however mostly disturbed by submarine landslides showing tilted horizons faults slump folds and breccia except that from the un named ridge the timing of events is well constrained by identification of the number of tl layers in some sediment cores landslides occurred both during the cold glacial period of the late mis3 to the last glacial maximum lgm and during the warm interglacial period of the post lgm all were caused by the explosive rise of gas hydrate formed at very shallow depths of the sea bottom by the supply of gas from the depth of the gas hydrate stability zone through gas chimney passages developed under the pockmarks seismic activity demands consideration as a factor because the off joetsu area is tectonically active

paleointensity determination on the late precambrian tudor gabbro ontario paleointensity determination by the coe modified thellier method was carried out on the 1100 ma tudor gabbro of southern ontario the tudor has a bivectorial natural remanent magnetization nrm the c nrm is a grenvillian uplift thermoviscous remagnetization which overprints the a nrm the surviving primary thermoremanent magnetization trm of the tudor intrusion a sharp junction at 530 c between the a and c vectors in laboratory thermal demagnetization matches the peak metamorphic reheating temperature of 480 500 c in nature when the difference in time scales is taken into account the unblocking temperature distributions of the a nrm and of laboratory trm also match a is carried by single domain or small pseudo single domain grains probably magnetite rods exsolved in plagioclase or pyroxene at temperatures above 580 c arai plots of nrm versus partial trm are linear from 520 c or 530 c to 580 c for 45 specimens of 19 samples from 9 sites the 45 reliable paleointensity values from these specimens give a virtual axial dipole moment vadm of 4 6 0 8 1022 a m2 around 1100 ma this is about one half of the modern field intensity but is similar to the mean cretaceous cenozoic intensity and to most archean and proterozoic vadms keweenawan rocks whose ages are within 20 myr of the tudor gabbro have a vadm of 11 4 1022 a m2 the difference between the tudor and keweenawan vadms is similar to differences recorded over similar time intervals in the cretaceous and seems to represent normal variation in geomagnetic field strength throughout earth s history

middle to late holocene changes of the okhotsk sea intermediate water and their relation to atmospheric circulation 1 high abundance of the radiolarian cycladophora davisiana in the sea of okhotsk has been observed at the okhotsk sea intermediate water osiw this water is formed by brine rejection in the polynya and is characterized by cold oxygenated conditions with high a microbial content the c davisiana abundance recorded in three sediment cores from the southwestern part of the sea implies ventilation changes of the osiw during the last 7 5 kyrs the ventilation had significantly increased during the interval from 7 5 to 3 5 ka corresponding to a warm period but declined during 3 to 2 ka and at 0 3 0 4 ka coincident with cold periods such as the neoglaciation and little ice age respectively the declined ventilation might be caused by reduction of the polynyas with the wind vector change from a northerly to an easterly direction relating to the southward shift of the aleutian low during the strong winter

pleistocene deep sea ostracods from the oki ridge sea of japan iodp site u1426 and condition of the intermediate water the sea of japan also termed the east sea has a circulation system isolated from the pacific ocean and east china sea the east asian winter monsoon drives the circulation system and cools the tsushima warm current twc to form the japan sea intermediate proper water jsipw the intermediate water conveys oxygen to deep sea floors which is available for benthic animals during the pliocene 3 5 2 8 ma temperate intermediate water tiw was formed under the weak winter monsoon and extinct ostracod tiw taxa were found little is known about early pleistocene intermediate water and the extinction mode of benthic ostracods we studied radiolarians and ostracods from deep sea sediments between 2 0 and 1 3 ma marine oxygen isotope stage mis 77 to mis 41 at integrated ocean drilling program site u1426 sea of japan the ostracod faunas contained tiw and jsipw taxa the radiolarian subtropical water taxa and the jsipw ostracods indicate a small influx of the twc and the jsipw the tiw occasionally expanded to the middle bathyal zone by analogy with the relationship between the modern jsipw and winter monsoon weak winter monsoon possibly caused gentle temperature gradients in the water column and the expansion of the tiw the jsipw taxa expanded their ranges into the deep sea during interglacial periods

paleoenvironmental changes in the east japan sea during the last 48 ka indications from high resolution x ray fluorescence core scanning paleoceanographic changes in the east japan sea during the late quaternary based on high resolution elemental variations particularly correlations between dark light laminations and millennial scale climatic changes have remained poorly understood because of the lack of the high resolution proxies the recent application of micro x ray fluorescence xrf core scanning provides the potential for high resolution study on the laminations deposited in the east japan sea in this study we present a geochemical study by using micro xrf core scanning on a 730 cm core recovered from the east japan sea elemental variations and factor analysis indicate that the sedimentary environment changed from anoxic to suboxic conditions from marine isotope stage mis 2 3 to mis 1 which is induced by increased contribution of high salinity sea water from the open ocean due to the rising sea level the dark and light laminations during mis 2 3 were correlated with dansgaard oeschger cycles and summer monsoon proxy with dark colored sediments related to higher terrigenous concentration corresponding to warm moist and enhanced summer monsoon period during the interstadial period more terrigenous sediments were transported to the east japan sea via the strengthened fluvial discharge from the surrounding continents caused by enhanced monsoon rainfall thus the development of the east asian summer monsoon and consequent variations in fluvial discharge would have significantly affected the paleoceanographic conditions in the east japan sea during the mis 2 3 sea level lowstand copyright 2012 john wiley sons ltd

last glacial holocene change in intermediate water ventilation in the northwestern pacific abstract the modern north pacific is the terminus for deep water circulation while no deep water mass is formed today the region is the source of north pacific intermediate water 300 800 m formed primarily in the sea of okhotsk however the source and strength of intermediate water in the glacial north pacific was likely different from the present intermediate water here we present microfossil evidence of late quaternary ventilation changes associated with changes in intermediate water intermediate water ventilation decreased drastically at the glacial termination when it switched to the modern circulation system the ventilation change appears to have been widespread and synchronous in the north pacific glacial microfossil assemblages indicate that there was relatively strong ventilation of intermediate water which seems to have been cold and well oxygenated as if produced by brine rejection during the formation of sea ice on the basis of the glacial distribution of microfossils in the north pacific we suggest that intermediate water was derived from the bering sea during the glacials rather than the sea of okhotsk

a new quality check for absolute palaeointensities of the earth magnetic field absolute palaeointensity determinations of recent lavas from mt etna have been carried out using the koenigsberger thellier thellier ktt method but with two different data presentations the first which is the standard method compares the natural remanent magnetization nrm demagnetized and the thermoremanent magnetization trm acquired in successive temperature intervals cumulatively the second compares the nrm and trm in the successive intervals in an incremental manner the latter method appears to distinguish aberrant behaviour better than the classical method such aberrant behaviour can be related to changes in hysteresis ratio parameters saturation remanent magnetization to saturation magnetization and remanent coercive force to coercive force which are reflected by displacements in the day et al 1977 plot these changes in hysteresis parameters are caused by irreversible changes in domain state or transformations of magnetic phases brought about by the thermal cycling the changes in hysteresis parameters serve as a useful quality factor for absolute palaeointensity determinations

sea level at the last glacial maximum evidence from northwestern australia to constrain ice volumes for oxygen isotope stage 2 new sea level information from the bonaparte gulf in northwestern australia is used to constrain the magnitude and rates of change of ice volumes during the last glacial maximum lgm the region is tectonically stable and far from the former ice covered regions the glacio hydro isostatic adjustment of the coast is therefore relatively small and the corrections for this evect are not sensitive to details of the rebound model microfossil analysis and ams radiocarbon dating of 11 gravity cores taken across the shelf and bonaparte gulf demonstrate that 1 the lgm sea levels were locally at 125 4 m 2 the lgm terminated abruptly at 19 000 cal yr bp with a rapid rise in sea level of about 15 m over the next 500 years and 3 the onset of the minimum sea levels occurred before 22 000 cal yr bp when corrected for the glacio hydro isostatic evects the increase of lgm ice volumes over the present day ice volume is 52 5 106 km3 the termination of the lgm is marked by a rapid ice discharge of 5 2 106 km3 2001 elsevier science b v all rights reserved

abrupt ventilation changes in the japan sea over the last 30 ky evidence from deep dwelling radiolarians abstract the japan sea has its own deep circulation system with its deeper parts occupied by cold and highly oxygenated water formed by winter convection in its northwestern reaches we elucidate the modern depth distribution of radiolarian species and their relation to water masses from the study of plankton tows and surface sediments cycladophora davisiana occurs in a depth interval between 1000 m and 2000 m deep layer of jspw japan sea proper water and actinomma boreale leptoderma group in depths below 2000 m bottom layer of jspw the study of seven sediment cores located in water depths ranging from 807 to 3613 m show that the radiolarian assemblages have varied since 30 cal ka bp indicating changes in water ventilation strength in this marginal sea during the interval from 30 to 17 cal ka bp ventilation was restricted to an intermediate layer beneath the low salinity surface water while the deeper zone was filled with static anoxic water deep ventilation began abruptly at 14 cal ka bp cold and oxygen rich water began to sink into the bottom layer as a result of cold oceanic inflow from the northwestern pacific through the tsugaru strait in the north deep convection activity increased from 13 to 12 cal ka bp which coincides with the younger dryas like cooling event and then stopped at 12 11 5 cal ka bp bottom water ventilation during the holocene has been dependent on high salinity inflow through the tsushima strait in the south and winter cooling in the northwestern part of the japan sea deep water was being actively formed in the early holocene in contrast to the static bottom water this bottom water formation has resulted in relatively constant water composition since 9 cal ka bp with the overall increase in high salinity oceanic water inflow although the latter decreased transiently from 7 to 5 cal ka bp in concert with climatic warming

early to middle pleistocene paleoceanographic history of southern japan based on radiolarian data from iodp exp 314 315 sites c0001 and c0002 abstract during the mid pleistocene transition mpt spanning from 0 8 to 1 2 ma the prevailing 41 kyr glacial cycles were replaced by longer cycles with a period of ca 100 kyr this event was also accompanied by important climate changes such as the expansion of the northern hemisphere ice sheet the impact of the mpt on the kuroshio current off southern japan remains unknown however in the absence of a long core covering the period of the mpt in this area preservation of calcareous microfossils is poor but polycystine radiolarians are abundant and well preserved therefore they are an excellent alternative proxy for reconstructing past climate change indeed because numerous studies have examined the geographic distribution of modern radiolarian species the relationships between several radiolarian assemblage groups e g equatorial to sub arctic assemblage groups and climatic conditions are well understood we examined the impact of the mpt on the kuroshio current off the kii peninsula southern japan by investigating radiolarian assemblages in deep sea cores collected during integrated ocean drilling program expedition 314 315 we studied the radiolarian assemblages in 293 samples from cores obtained at site c0001 holes e and f and site c0002 hole d the age models for these cores which are based on biostratigraphy and chemostratigraphy showed that sediments from the period between marine isotope stage mis 15 and mis 8 which includes the mid brunhes event are missing from these cores however continuous data are available between mis 63 1 82 ma and mis 15 0 5 ma therefore using the ecological properties of 11 key radiolarian species we reconstructed regional paleoceanographic changes between 1 82 and 0 5 ma radiolarian fauna revealed that the relative abundance of kuroshio and the central pacific water taxa e g didymocyrtis tetrathalamus and the polysolenia spinosa lappacea group respectively increased drastically during the mpt possibly indicating a northward shift of the kuroshio at that time the relative abundance of rhizosphaera mediana an oyashio kuroshio mixed water species also increased during this interval thus a southward shift of the oyashio current may have occurred synchronously with a northward shift of the kuroshio during the mpt

correlation between faunal transitions of benthic foraminifera and ballasting of particulate organic carbon by siliceous plankton during the holocene off san in district southwestern japan we investigated the biotic response of benthic foraminifera rhizaria to holocene paleoceanographic changes in a upper bathyal environment by examining fossil benthic foraminifera younger than 13

experiments on trm intensity dependence on cooling rate palaeointensity studies have an important role to play in understanding the origin and time variation of the geomagnetic field however theoretical considerations indicate that the intensity of magnetization recorded by a rock or archaeological sample will be dependent on the rate at which it cooled as well as field magnitude experiments on synthetic magnetite and titanomagnetites of varying grain sizes indicate that for acicular magnetite at low concentration slower cooled trm is stronger than faster cooled trm but for all other samples slower cooled trm is weaker this is the predicted behaviour however the magnitude of the effect is much greater than the predicted kinetic effects and indicates that the magnetization of sub microscopic magnetite rich inclusions in the titanomagnetites strongly controls the trm intensity of the matrix

drastic hydrographic changes inferred from radiolarian assemblages in the central japan sea since the last glacial maximum abstract assessing modern radiolarian distribution in the marginal seas is essential for understanding its relationship to hydrographic and environmental variables upon which subsequent interpretation of past radiolarian records can be made reliably here we combine published radiolarian assemblages in 69 surface sediments from the japan sea with those obtained from 15 new surface sediments in this study to determine the modern distribution of radiolarians the tsushima warm current twc taxa are only found in the south of the subpolar front the results of redundancy analysis confirm that the temperature at 10 m depth temperature10m is the main factor controlling the spatial variability of twc taxa the water depth plays a key role in affecting the abundances of japan sea proper water jspw assemblage including larcopyle buetschlii dreyer adult cycladophora davisiana ehrenberg and actinomma group the jspw assemblage can be used as a reliable indicator of ventilation changes in the japan sea based on the newly developed twc taxa and jspw assemblage we further reconstructed the water column structure in the central japan sea over the past 25 ka there was weak ventilation in the central japan sea even during the last glacial maximum lgm although a distinct decrease in the twc inflow resulted in surface water freshening and water column stratification after the lgm the twc taxa together with jspw assemblage resumed in the central japan sea at the 19 ka meltwater pulse mwp the mwp 1a was clearly marked by an enhanced intrusion of the twc synchronously jspw was ventilated deeply down after 14 6 ka attaining to the similar level of the holocene as a result of changing sea surface conditions along with the continuing sea level rise the matured twc entered the japan sea at 7 ka and since then the modern hydrographic condition has been established we suggest that the changes in the sea level and twc strength predominantly determined the surface hydrography and deep ventilation in the central japan sea since 25 ka and the twc might have notably affected the japan sea since the bolling allerod

early pleistocene evolution of the japan sea intermediate water the early pleistocene fossil record of the japan sea reveals that the planktonic foraminifer globorotalia inflata succeeded in expanding its range from the east china sea to the japan sea during interglacial stages of the early pleistocene however the species is only found in surface sediment samples from the southwestern most part of the sea based on the ecology of g inflata and the water mass structure of the japan sea it appears that its geographical distribution is mainly controlled by the low temperature of the intermediate water which is caused by the cool water mass of japan sea proper water the temporal and spatial patterns of g inflata occurrence indicate that the intermediate water at 200 m depth during interglacial stages between 1 46 and 1 3 ma was warmest during the quaternary this warm intermediate water probably resulted from the influence of the low salinity nature of the tsushima current due to the large inflow of east china sea coastal water after 1 3 ma the intermediate water at 200 m depth became cooler in a step wise manner this cooling can be explained by an intensification of thermohaline circulation in the japan sea associated with strengthening of the east asian winter monsoon and an increase in salinity due to enlargement of the southern strait copyright 2009 john wiley sons ltd

late quaternary climates of east asia deduced from the total organic carbon contents of cored sediments md179 3304 3312 off joetsu city japan sea abstract total organic carbon toc and total nitrogen tn concentrations are analyzed with high temporal resolution ca 100 years for cores md179 3304 and md179 3312 taken from the japan sea off joetsu city the temporal changes in toc and tn concentrations vary quasi regularly in similar patterns the age models are formed on the basis of the dates of 14c dating marker tephra beds tl layers and marine isotope events with depth toc concentration is high in mis 1 and 5 low in mis 2 and 4 and slightly elevated in mis 3 with frequent short fluctuations this general trend is very similar to lr04 curve except for the reduced dominance of toc around the mis 5 5 substage as shown typically in mis 3 there are many peaks of toc in a short interval the details of these toc peaks can be correlated with the warm interstadials of the greenland ice core we can identify a sawtooth like decreasing trend of toc in mis 3 in contrast the decreasing trend of 18o in the ice core corresponds to an increasing trend of toc in mis 5 the most plausible explanation for the correlation of climate changes between east asia and the north atlantic is oscillation of the arctic polar front through time the detailed correspondence of toc concentrations of the japan sea sediments to other common paleoclimate proxies means that the toc concentrations of these sediments is an excellent paleoclimate record in far east asia although the genetic relationship between air temperature and biological productivity in the japan sea is as yet unknown

millennial scale variations of late pleistocene radiolarian assemblages in the bering sea related to environments in shallow and deep waters abstract a high resolution record of the radiolarian assemblage from 60 to 10 ka was investigated using a piston core pc 23a obtained from the northern slope of the bering sea faunal changes based on the 29 major radiolarian taxa demonstrated that the surface and deep water conditions in the bering sea were related to the orbital and millennial scale climatic variations known as glacial interglacial and dansgaard oeschger d o cycles respectively during interstadial periods of the d o cycles the assemblage was characterized by increases in the high latitude coastal species rhizoplegma boreale and the upper intermediate water species cycladophora davisiana while the sea ice related species actinomma boreale and a leptodermum and many deep water species such as dictyophimus crisiae and d hirundo tended to be reduced this trend was more apparent in two laminated intervals at 15 13 5 and 11 5 11 ka which were correlated with well known ice sheet collapse events that occurred during the last deglaciation melt water pulse mwp 1a and mwp 1b respectively the radiolarian faunal composition in these periods suggests that oceanic conditions were different from today 1 surface water was affected by increased melt water discharge from continental ice sheet occurring at the same time as an abrupt increase in atmospheric temperature 2 upper intermediate water ca 200 500 m was well ventilated and organic rich and 3 lower intermediate water ca 500 1000 m was oxygen poor conversely the sea ice season might have been longer during stadial periods of the d o cycles and the last glacial maximum lgm compared to the interstadial periods and the earliest holocene in these colder periods deep water species were very abundant and this corresponded to increases in the oxygen isotope value of benthic foraminifera our findings suggest that the oxygen rich water was present in the lower intermediate layer resulting from intensified ventilation

full vector geomagnetic field records from the east eifel germany abstract to create meaningful models of the geomagnetic field high quality directional and intensity input data are needed however while it is fairly straightforward to obtain directional data intensity data are much scarcer especially for periods before the holocene here we present data from twelve flows age range 200 to 470 ka in the east eifel volcanic field germany these sites had been previously studied and are resampled to further test the recently proposed multi method palaeointensity approach samples are first subjected to classic palaeomagnetic and rock magnetic analyses to optimise the subsequent palaeointensity experiments four different palaeointensity methods izzi thellier the multispecimen method calibrated pseudo thellier and microwave thellier are being used in the present study the latter should be considered as supportive because only one or two specimens per site could be processed palaeointensities obtained for ten sites pass our selection criteria two sites are successful with a single approach four sites with two approaches three more sites work with three approaches and one site with all four approaches site averaged intensity values typically range between 30 and 35 t no typically low palaeointensity values are found in line with paleodirectional results which are compatible with regular palaeosecular variation of the earth s magnetic field results from different methods are remarkably consistent and generally agree well with the values previously reported they appear to be below the average for the brunhes chron there are no indications for relatively higher palaeointensities for units younger than 300 ka however our young sites could be close in age and therefore may not represent the average intensity of the paleofield three of our sites are even considered coeval encouragingly these do yield the same palaeointensity within uncertainty bounds

comparison of radiolarian vertical distributions in the okhotsk sea near the kuril islands and in the northwestern north pacific off hokkaido island abstract the vertical distribution of radiolarians was investigated by using a closing type net with 63 m mesh in the okhotsk sea station nu 2 near bussol strait down to 1000 m depth and in the northwestern north pacific oyashio region station x down to 500 m depth both stations were sampled in september 1995 radiolarian standing stocks were high between 50 and 200 m at both stations and generally decreased with depth the depth integrated living total radiolarian standing stock from 0 to 500 m at station nu 2 was more than three times higher than that at station x the maximum standing stocks of polycystine radiolarians occurred in the 50 100 m depth interval but there were also significant abundance peaks of phaeodarian radiolarians in the 100 200 m interval at both stations the radiolarian production is likely to be associated with not only phytoplankton production in upper waters but also with microbial production in intermediate waters a total of 79 taxa were encountered 25 spumellaria 41 nassellaria and 13 phaeodaria five radiolarian groups were obtained based on r mode cluster analysis group a lower intermediate water dwellers 300 1000 m group b taxa with different distributions in the okhotsk sea 300 1000 m and in the oyashio region 0 100 m group c upper intermediate water dwellers 200 500 m group d surface subsurface water dwellers 0 200 m and group e taxa with pronounced 200 m

radiolarians in the sea of okhotsk and their ecological implication for paleoenvironmental reconstructions to assess the relationship of radiolarian production species distribution in water and surface sediment to water mass characteristics biological productivity and export regimes in the sea of okhotsk sok we accomplished a quantitative analysis of radiolarian assemblages obtained from 35 surface sediment samples and 115 plankton samples recording the radiolarian depth distribution in the upper 1000 m of the water column at 23 locations this study augments the knowledge on the autecological demands of radiolarians dwelling in a specific hydrographic and biological environment and extracts new information on the significance of radiolarians for the assessment of past oceanographic and climatic development in high latitudes highest radiolarian accumulation rates and seasonal radiolarian standing stocks are encountered in the western part of the sok close to sakhalin marking the environmental conditions in this area as most favorable for radiolarian production maximum standing stocks occur during summer indicating that the radiolarian signal preserved in the sediment record is mainly produced during this season when the mesopelagic biomass is at highest activity we identified seven radiolarian species and groups related to specific water mass characteristics depth habitats and productivity regimes of those dictyophimus hirundo and cycladophora davisiana are most prominent in the sea of okhotsk intermediate water 200 1000 m the latter representing an indicator of the occurrence of cold and well ventilated intermediate deep water and enhanced export of organic matter from a highly productive ocean surface while antarctissa sp 1 is typically related to the cold water sea of okhotsk dicothermal layer sodl ranging between 50 and 150 m water depth the surface waters above the sodl affected by strong seasonal variability are inhabited predominantly by taxa belonging to the spongodiscidae having a broad environmental tolerance taxa only found in the sediment record show that the plankton study did not cover all assemblages occurring in the modern sok this accounts for an assemblage restricted to the western kurile basin and apparently related to environmental conditions influenced by north pacific and japan sea waters other important taxa include species of the plagoniidae group representing the most prominent contributors to the sok plankton and surface sediments these radiolarians show a more opportunistic occurrence and are indicative of high nutrient supply in a hydrographic environment characterized by pronounced stratification enhancing heterotrophic activity and phytodetritus export r 2005 elsevier ltd all rights reserved

sediment fabrics oxygenation history and circulation modes of japan sea during the late quaternary abstract the quaternary hemipelagic sediments of the japan sea are characterized by centimeter to decimeter scale alternations of heavily bioturbated organic poor light layers and finely laminated organic rich dark layers these dark and light layers which can be correlated throughout the deeper part of the basin are considered to reflect changes in bottom water oxygenation however depositional mechanisms responsible for individual dark layers and causes of oxygen depletion are not fully understood two possible settings for deposition of organic rich dark layers are recognized one is a stratified ocean like the black sea where limited vertical advection results in euxinic conditions in the deeper parts of the basin the other is an upwelling region like the arabian sea where the oxygen minimum zone is intensified by enhanced nutrient upwelling and surface productivity in this study fabrics of hemipelagic sediments deposited in the japan sea during the last 160 ka were studied in three cores collected from different latitudes and water depths fabrics were classified into 4 classes based on corresponding bottom water oxygenation level five dark layer types were defined based on the distribution patterns of sediment fabric classes within each dark layer comparison of dark layer types at shallower and deeper sites in a chronologic framework provided evidence for five different modes of deep water circulation these circulation modes which reflect relative intensities of upwelling and density stratification appear to be related to global sea level changes as well as climate impact on the nature of water influx through the tsushima strait

detailed japan sea paleoceanography during the last 25 kyr constraints from ams dating and δ18o of planktonic foraminifera abstract we have reconstructed paleoceanographic changes in the japan sea for the period from the last glacial maximum lgm to the present using expanded paleoclimate proxy records from two cores together with previously published results from three others a suite of new accelerated mass spectrometer ams 14 c dates provides chronologies that differ from earlier age models and suggest correlation between conditions in the japan sea changes in the north pacific and global sea level and climate changes we present evidence that reduced salinity of the japan sea surface water during the late pleistocene was due primarily to the increased importance of the precipitation evaporation balance at a time when lowered sea level had reduced water exchange with the pacific to a few percent of the present value

paleoceanographic changes of surface and deep water based on oxygen and carbon isotope records during the last 130 kyr identified in md179 cores off joetsu japan sea abstract we reconstructed the paleoenvironmental history of surface and deep water over the last 130 kyr from oxygen and carbon isotope ratios of planktonic and benthic foraminifera in two cores md179 3312 and md179 3304 from the joetsu basin eastern margin of the japan sea our data showed that paleoceanographic changes such as influx of surface currents and vertical circulation were associated with global glacial interglacial sea level change surface water conditions were influenced by the influx of tsushima current east china sea coastal or off shore waters through the tsushima strait during interglacial or interstadial stages and strongly affected by freshwater input during the glacial maximum during interglacial maximums such as marine isotope stages 1 and 5e development of well oxygenated bottom water was indicated a density stratified ocean with weak ventilation was inferred from the isotopic records of benthic foraminifera during the last glacial maximum local negative excursions in carbon isotopes during deglacial or interglacial periods may suggest the dissolution of gas hydrates or methane seep activities

paleointensity estimates from historic and modern hawaiian lava flows using glassy basalt as a primary source material abstract published paleointensity estimates derived from lavas extruded in known fields are highly variable and rarely recover the expected field strength within an accuracy of better than 10 inconsistent results on modern volcanic rocks lend even greater uncertainty to intensity experiments performed on lava flows emplaced during periods of unknown geomagnetic field strength the majority of published paleointensity data are collected from the slowly cooled massive centers of lava flows where the magnetic grains are more likely to be multi domain and produce non ideal experimental results glassy volcanic material found on subaerial lava flow tops and in sub aqueous and subglacial environments however is rapidly cooled and therefore most likely of all volcanic materials to behave as single domain particles demanded by neel theory we present a new paleointensity study of historic and modern hawaiian lavas and test the viability of subaerially emplaced glassy basaltic material as an accurate recorder of magnetic field intensity six of eight lava flows sampled on the big island of hawaii 1843 1859 1935 1950 1960 1990 c e produce well behaved arai plots and recover an average intensity to within 2 7 t of the expected field strength or better than 8 accuracy we apply very strict selection criteria including a minimum of three specimens per site to prevent extraneous field estimates from affecting the final results individual volcanic glass results from the 1960 c e lava flow have a much lower variance than published data from the same volcanic unit glassy materials should therefore be collected wherever possible as they allow recovery of geomagnetic field strength with unprecedented accuracy

distribution of polycystine radiolarians in the northern south china sea in september 2005 we studied the distribution of polycystine radiolarians in the northern south china sea scs in september 2005 in order to document the relation between radiolarian assemblages and environmental parameters vertical plankton tows were collected at depth intervals from 0 to 250 m at thirteen stations using a closing net 62 pm mesh the highest abundance of polycystine radiolarians generally occurred at depths of 0 75 m i e above the chlorophyll a maximum and thermocline in contrast the maximum polycystine abundance occurred below the chlorophyll a maximum at station e105 75 150 m possibly as a result of down welling of warm waters and the maximum fell within the chlorophyll a maximum at station e702 as a result of upwelling of intermediate cold waters during our sampling period the southwestern monsoon caused upwelling in the northern scs the taiwan bank region as shown by the high abundance of tetrapyle octacantha acanthodesimia vinculata cladococcus cervicoris octopyle octospinosa spongaster tetras streblacantha circumtexta and spongotrochus glacialis the patterns of distribution and the abundances of the species botryocyrtis scutum pterocorys hertwigii collosphaera tuberosa and didymocyrtis tetrathalamus tetrathalamus suggested that western equatorial pacific waters did not yet influence the region at the time of sampling the first two species were dominant in the northern scs during our sampling the species cornutella profunda and cyrtopera laguncula were rare at depths of 150 250 m in the tropical region of the scs and assemblages in northern and southern scs were very similar the relative abundance of b scutum and p hertwigii is an indicator for seasonal changes in monsoonal circulation c 2008 elsevier b v all rights reserved

late quaternary paleoceanographic changes in the bering sea and the western subarctic pacific based on radiolarian assemblages seven piston cores were obtained from the bering sea and the western subarctic pacific during cruise kh99 3 of r v hakuho maru in august 1999 cores bow 8a bow 9a bow 12a ab umk 3a gat 3a in the bering sea and core es in the western subarctic pacific the quantitative high resolution analyses of radiolarians in the cores revealed significant variations in both their faunal assemblages and accumulation rates ar a trend of conspicuous turn over of the surface dwellers and intermediate dwellers increase of one at expense of the other after the last glacial maximum lgm is clearly visible in the bering sea data set however this turn over is not present at site es in the western subarctic pacific core these changes in radiolarian assemblages around the lgm suggest that the surface waters had extremely low temperature and low salinity and that the subsurface dichothermal layer temperature minimum layer was thickened all the way across the entire east west span of the bering sea furthermore sea ice coverage extended to the central aleutian basin around the lgm this suggests that the water mass structure in the western subarctic pacific around the lgm was basically the same as that of the eastern bering sea based on the species composition of the surface dwellers however the detailed development of intermediate water masses differed from that of the eastern bering sea during marine isotope stage mis 5 to 3 such species turn over events did not occur and species abundance stayed relatively uniform in the studied cores therefore the present water mass structure is interpreted to have been formed after the lgm based on the relative abundances of cycladophora davisiana the most dominant species dwelling in the intermediate water and a useful tracer of cold and well oxygenated intermediate water in the north pacific the past north pacific intermediate water npiw had the following source regions during the last 100 kyr 1 both the okhotsk sea and the bering sea during mis 5 to 3 2 the bering sea around the lgm and 3 shifting from the bering sea to the okhotsk sea after the lgm relatively low radiolarian ar at site bow 8a which is the shallowest site studied here present water depth 884 m were observed during the glacial periods this is due to decrease of radiolarian production in the thinned upper water layer above the dicothermal layer caused by sea level drop cycladophora davisiana probably lived deeper during the glacials than today as it was absent in the shallow piston core r 2005 elsevier ltd all rights reserved

chronostratigraphy and paleoceanography of a piston core ebp 3 from the south korea plateau in the east sea japan sea abstract a piston core ebp 3 collected from the south korea plateau in the east sea japan sea preserved typical alternations of thick dark laminated mud layers and bioturbated hemipelagic mud layers but included several intercalated volcanic lapilli layers the age estimate of core ebp 3 was aided by correlation of biostratigraphic radiolarian data the abundance of microfossils warm water radiolarians and geochemical properties caco 3 with the proxies of the well dated core md01 2407 obtained from the oki ridge a part from the marine isotope stage mis 11 to mis 9 in the middle of core ebp 3 was missing presumably because of erosion following the abrupt deposition of a volcanic lapilli layer despite some uncertainty the age estimate of core ebp 3 revealed that the lower part of core ebp 3 represents mis 13 as was also evident from a comparison with the oxygen isotope stratigraphy downcore biogenic opal and caco 3 variations in core ebp 3 exhibited less distinct orbital scale cyclic changes than cores from other areas in the east sea japan sea however differences in features were discernible between mis 2 and mis 12 in terms of their lithology and caco 3 constituent although both periods were characterized by relatively high levels of caco 3 about 30 for mis 2 and about 50 for mis 12 mis 2 preserved a typical thick dark laminated mud layer whereas mis 12 preserved a distinctly light mud layer with thin parallel laminations this difference of the lithologic facies between mis 2 and mis 12 highlighted a discrepancy among the major constituents indicating that planktonic foraminifera were dominant in mis 2 whereas coccolithophores were dominant in mis 12 our results suggest that the thinly laminated light mud layer which is characterized by a high caco 3 content primarily composed of coccolithophores in mis 12 can be used as a reliable time marker for the establishment of chronostratigraphy in the east sea

a comparison of archaeointensity results from chinese ceramics using microwave and conventional thellier s and shaw s methods palaeo and archaeointensity determinations of the geomagnetic field are limited by mineralogical alteration that may occur when samples are heated in the laboratory to produce a trm thellier thellier 1959 shaw 1974 by using microwave excitation of the magnetic grains we have been able to create a trm without significantly heating the bulk samples thereby avoiding thermal alteration walton et al 1993 shaw et al 1996 when applied to peruvian ceramics in a manner analogous to the standard thellier method the microwave technique was found to reduce the scatter dramatically in the archaeointensity results shaw et al 1996 in the present study we apply this microwave technique to a collection of chinese ceramics covering the time interval 2700 7500 yr bp these ceramics have already been investigated using adaptations of both thellier s coe 1967 and shaw s rolph shaw 1985 palaeointensity methods yang et al 1993a although an acceptable agreement was found between those two methods the equivalent virtual axial dipole moments vadms were significantly lower than for the global model of mcelhinny senanayake 1982 the present study using the microwave technique with cooling rate correction has provided more consistent vadms and is much closer to the global model

depth related radiolarian assemblage in the water column and surface sediments of the japan sea plankton tows and surface sediments from the japan sea a marginal sea of the northwestern pacific were examined to study the depth distribution of modern radiolarians the depth distribution patterns between the living assemblage in the water column and the thanatocoenose in surface sediments are similar to each other indicating that the depth related assemblage in sediments is closely related to the living depths of major species four clear restrictions of many species to discrete depth zones are recognized in the water column from the surface down to 2000 m 1 upper subsurface water species which are abundant from 40 to 120 m larcopyle butschlii juvenile form spirocyrtis subscalaris spongodiscus resurgens and lipmanella virchowii 2 lower subsurface water species which are abundant from 40 to 300 m larcopyle butschlii adult form ceratocyrtis histricosa and spongotrochus glacialis 3 intermediate water species which have population maxima from 160 to 300 m ceratospyris borealis and 4 deep water species which have maxima between 1000 and 2000 m cycladophora davisiana and actinomma boreale only a few specimens of a boreale were found in the water column ranging from 1000 to 2000 m depth although this is a dominant species in surface sediments from depths below 2000 m of which the dominance increases with water depth a boreale may live mainly in the bottom water cycladophora davisiana and a boreale which characterize the japan sea deep assemblage are naturally shallow or intermediate dwellers in other oceans on the other hand the typical deep dwellers e g cornutella profunda cyrtopera languncula and peripyramis circumtexta of other oceans have not been found in the japan sea such a peculiar deep assemblage is a result of the deep circulation system in the japan sea and the shallow depths of the sills around it

oceanographic conditions associated with high abundances of the radiolarian cycladophora davisiana abstract the cosmopolitan radiolarian cycladophora davisiana usually comprises less than 5 of the radiolarian fauna in holocene sediments in recent sediments from the sea of okhotsk however this species frequently represents more than 20 of the radiolarian assemblage at times during the late pleistocene abundances of this species in excess of 40 are recorded in marine sediments from high latitude oceans 40 of both hemispheres the sea of okhotsk apparently represents a modern analogue of climatic and oceanographic conditions that existed throughout large portions of high latitude oceans at times during the late pleistocene the near surface water structure of the sea of okhotsk is characterized by a low salinity surface layer with a strong temperature minimum near its base the low surface salinities are responsible for maintaining near freezing subsurface temperatures as well as establishing relatively stable temperatures and salinities at depths below the temperature minimum this water structure is produced at least in part by intense freezing of sea ice in winter with subsequent summer melting the physical characteristics of the upper water column affect the abundance and activity of shallow dwelling flora and fauna while providing a stable subsurface environment for deeper dwelling fauna

orbital and millennial scale changes of radiolarian assemblages during the last 220 kyrs in the japan sea abstract significant abundance changes of seven radiolarian species during the last 220 kyrs in the japan sea are reported herein based on three sediment cores during the interglacial periods warm water species the tetrapyle octacantha group and warmer high nutrient water species lithomelissa setosa occurred commonly which may indicate inflows of the tsushima warm current on the other hand cold water species such as ceratospyris borealis and stylochlamydium venustum dominated the assemblage during the glacial periods when the japan sea was mostly isolated from the adjacent seas due to lower eustatic sea level however at glacial maxima the habitat of s venustum was strongly limited due to low salinity surface waters the abundance of the deep water species cycladophora davisiana seems to have changed significantly possibly related to the intrusion of oxygen and organic materials into deeper waters higher abundances of this species in mis marine isotope stage 1 mis 3 and mis 5c resulted from well ventilated deep water and high organic flux while its low abundance during the glacial maxima and mis 5e was probably caused by oxygen poor deep water millennial scale variations of c davisiana abundance show high abundance at the transition intervals from interstadial to stadial periods of the dansgaard oeschger cycles the disappearance events of lychnocanoma nipponica sakaii and amphimelissa setosa were recognized at 54 ka and 85 ka respectively both of these events in the japan sea can be correlated with those in the north pacific bering sea and sea of okhotsk

latest pleistocene and holocene palaeoenvironment of japan and its marginal sea abstract analyses of pollen and radiolarian abundance variations in a deep sea core from the sea of japan indicate that major vegetational changes on mainland japan during the last 80 000 years coincided with events of similar magnitude offshore in the marginal sea on land dry cold temperate conditions alternate with wet cold temperate periods throughout most of the last glacial period 80 000 10 000 yr b p offshore during glacial times of low winter precipitation the radiolarian fauna was dominated by assemblage similar to those present today along the subarctic front and throughout much of the subpolar gyre associated with cold winter and summer sea surface temperatures during most of the high precipitation stadials the dominant radiolarian assemblage was comparable with that existing in today s sea of okhotsk associated with cold winter and cool summer sea surface temperatures on the western coast of honshu warmer temperate conditions throughout the holocene were associated with a marine faunal assemblage similar to that living in waters overlying the core site today radiolarian abundance levels productivity were lower during most of the last glacial period compared to holocene values the presence of radiolaria throughout all but a portion of the early stage of the last glacial interval indicates that although restricted some degree of exchange between the southern sea of japan and north pacific waters took place throughout most of the last glacial period these data place major constraints on local reconstructions of sea level and of climate on the adjacent coast of honshu during this time

formation of pockmarks and submarine canyons associated with dissociation of gas hydrates on the joetsu knoll eastern margin of the sea of japan abstract this study based on 3 5 khz sbp 3d seismic data and long piston cores obtained during md179 cruise elucidated the timing and causes of pockmark and submarine canyon formation on the joetsu knoll in the eastern margin of the sea of japan gas hydrate mounds and pockmarks aligned parallel to the axis on the top of the joetsu knoll are associated with gas chimneys pull up structures faults and multiple bottom simulating reflectors bsrs suggesting that thermogenic gas migrated upward through gas chimneys and faults from deep hydrocarbon sources and reservoirs seismic and core data suggest that submarine canyons on the western slope of the joetsu knoll were formed by turbidity currents generated by sand and mud ejection from pockmarks on the knoll the pockmark and canyon formation probably commenced during the sea level fall lasting until transgression stages subsequently hydropressure release during the sea level lowering might have instigated dissociation of the gas hydrate around the base of the gas hydrate leading to generation and migration of large volumes of methane gas to the seafloor accumulation of hydrate caps below mounds eventually caused the collapse of the mounds and the formation of large depressions pockmarks along with ejection of sand and mud out of the pockmarks thereby generating turbidity currents prolonged pockmark and submarine canyon activities might have persisted until the transgression stage because of time lags from gas hydrate dissociation around the base of the gas hydrate until upward migration to the seafloor this study revealed the possibility that submarine canyons were formed by pockmark activities if that process occurred it would present important implications for reconstructing the long term history of shallow gas hydrate activity based on submarine canyon development

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

different nature of glacial caco3 constituents between mis 2 and mis 12 in the east sea japan sea and its paleoceanographic implication two piston cores pc 05 and pc 08 were collected on the yamato rise in the east sea japan sea during the kr07 12 cruise both cores showed typical alternations of light high l and dark low l layers which are characteristic in the hemi pelagic sediment deposited in the deep part of the east sea japan sea a composite core was achieved with the successful replacement of almost half of the upper part of core pc 05 by the entirety of core pc 08 based on the co equivalence of l values and the dark layers because an interval 170 cm 410 cm of core pc 05 was considerably disturbed due to fluidization during the core execution chronostratigraphy of the composite core was constructed by the direct comparison of l values to the well dated core md01 2407 that was obtained in the oki ridge the lower bottom of the composite core extended to marine isotope stage mis 14 based on the age estimate by lr04 stacks downcore opal variation of the composite core exhibited the distinct orbital scale cyclic changes high during the interglacial and low during the glacial periods however downcore caco3 variation showed no corresponding orbital scale cyclic change between glacial and interglacial periods some intervals of both periods were high in caco3 content frequent and large fluctuations in caco3 content seemed to be more related to the presence of dark layers containing thin lamination tl within the glacial and interglacial intervals it is worthy to note that mis 2 and mis 12 are characterized by distinctly high caco3 content showing up to 18 and 73 respectively among the glacial periods furthermore in terms of lithology mis 2 was characterized by a thick dark layer low l values with tl whereas mis 12 preserved the distinctly light layer high l values with parallel laminations another remarkable dissimilarity between mis 2 and mis 12 was the nature of their caco3 constituent the caco3 constituent of mis 2 consisted of mostly planktonic foraminifera whereas that of mis 12 was mostly dump of coccolithophorids regardless the presence of planktonic foraminifera the distinctness of the caco3 constituents between mis 2 and mis 12 indicates that the preservation of caco3 contents was different temporarily during the glacial periods in the east sea japan sea enhanced caco3 preservation in mis 2 is attributed primarily to less dissolution during the sinking through the water column or at the seafloor but increased caco3 preservation in mis 12 is mainly due to the high primary production in the surface water with respect to the different function of the biological pump which controls co2 cycles the east sea japan sea clearly experienced carbonate ocean like state during mis 12 despite normally silica ocean like state

radiolarians under the seasonally sea ice covered conditions in the okhotsk sea flux and their implications for paleoceanography abstract four time series sediment traps at two stations and three piston cores from the okhotsk sea were quantitatively examined for coarse sized radiolarian shells 63 m traps were deployed at 300 m and 1550 m at station m4 53 01 n 145 30 e and at 300 m and 700 m at station m6 49 30 n 146 28 e during august 1998 through may 2000 the chronologies of the piston cores were established applying 18 o and paleomagnetic intensity variations they provide records extending back to marine isotope stage mis 5 51 the modern and past changes in radiolarian assemblages are associated with environmental and productivity changes radiolarian fluxes in the sediment traps exhibited significant summer to autumn flux peaks with suppressed values during the winter when sea ice covered the sea surface at the trap sites total radiolarian accumulation rate rar variations in each core tended to correspond to glacial interglacial cycles and increased during the last deglaciation in particular the temporal rar variation in core xp98 pc1 off kamchatka showed a similar trend with the climatic changes expressed by 18 o values during the glacial interglacial cycles for the last 125 kyr regional differences were also apparent rars showed extremely low values during 12 40 kyr and 63 70 kyr in core xp98 pc2 central okhotsk sea indicating the enhanced sea ice impact the sea ice coverage might have continued for a significant part of the year during the intervals since radiolarians did not appear to increase even during the summer to autumn rar variations in core xp98 pc4 off sakhalin showed higher values than xp98 pc2 during mis 2 and 4 thus in eastern sakhalin around site xp98 pc4 sea ice coverage might have been seasonal but not perennial even during mis 2 and 4 among the radiolarian taxa cycladophora davisiana was the most abundant species at the lower traps and in all cores the fluxes of c davisiana at lower traps showed much higher values than those of upper traps and also showed similar temporal patterns with the fluxes of aluminum and terrigenous materials therefore c davisiana fluxes may be associated with terrigenous organic materials increased nutrient supply from the continental shelves presumably transported by seasonal sea ice and released by sea ice melting might be mainly responsible for the high production of c davisiana in the okhotsk sea especially during the last deglaciation

the secular variation of earth s magnetic field models of the magnetic field at the core mantle boundary at selected epochs from 1715 0 to 1980 0 reveal novel features in the field at the core these suggest that the flow of core fluid is coupled to the mantle and that magnetic diffusion is significant

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

microwave archaeointensities from peruvian ceramics summary accurate determination of the strength of the ancient geomagnetic field is limited by mineralogical alteration that may occur when samples are heated to produce a thermoremanent magnetization thellier thellier 1959 shaw 1974 by using direct microwave excitation of the magnetic grains we have been able to form a thermoremanent magnetization without significantly heating the bulk sample thus avoiding thermal alteration walton et al 1993 incorporation of this new microwave heating technique with the conventional thellier palaeointensity method has dramatically reduced the scatter of archaeointensity results from peruvian ceramics and clearly defined how the field strength has varied in peru over the past 2000 years the new microwave technique will therefore enhance the feasibility of archaeointensity dating and provide accurate field strength data for geomagnetic modelling

polycystine radiolarians in surface sediments in the arctic ocean basins and marginal seas abstract the polycystine radiolarian faunas in the arctic ocean including the adjacent arctic seas have been studied in more than 377 surface samples the deep basins in the arctic ocean have revealed 31 polycystine radiolarian species 11 spumellarians and 20 nassellarians the polycystine radiolarian fauna in the southern norwegian sea was introduced from the north atlantic ocean ca 13 400 yr bp the shallow low arctic marginal sea sediments iceland barents and chukchi seas have a strong dominance of cannobotryidae 79 77 and 74 respectively while the deep arctic ocean basins nansen amundsen and makarov basins have a dominance of actinommidae 90 70 and 75 respectively the arctic polycystine radiolarian faunas have a strong affinity with the norwegian sea fauna which supplies the arctic ocean with faunal elements that can live thrive and reproduce there in the chukchi sea the pacific faunal influence is obvious 41 species but none of the pacific species are found in any abundance in the amerasian basin no radiolarian species was found to be endemic to the arctic ocean except for a morphotype of actinomma l leptoderma with a round inner sphere this species is a possible endemic candidate for the arctic ocean eight species are to be found in all of the central arctic basins and can therefore be referred to as circumpolar species actinomma leptoderma leptoderma a l leptoderma with round middle sphere a l longispina a boreale spongotrochus glacialis pseudodictyophimus platycephalus cycladophora davisiana and tholospyris gephyristes while amphimelissa setosa probably is the only true arctic radiolarian species

variations in the radiolarian assemblages in the bering sea since pliocene and their implications for paleoceanography radiolarian assemblages were analyzed using samples from the iodp site u1340 to reconstruct the paleoceanographic conditions in the bering sea based on the characteristic faunal changes the radiolarian evolution at site u1340 was divided into four major intervals from stages i to iv with stage iv divided into substages iva and ivb the radiolarians in each stage recorded significant paleoenvironmental conditions in general the bering sea was governed by an ocean ecological environment with stable warm and saline surface water during stage i 4 15 myr to 3 91 myr the environment in the bering sea fluctuated strongly during stage 11 3 91 myr to 2 75 myr and was controlled by the cold water masses and sea ices during stage iii 2 75 myr to 1 07 myr with the gradual development of cold and well ventilated intermediate water stage iva 1 07 myr to 0 47 myr was a transitional period characterized by the enhanced formation of cold subsurface and intermediate water as well as of the oxygen rich deep water during stage ivb after 0 47 myr the bering sea was mainly characterized by enhanced warmth during interglacial episodes and well developed water layers that were generally comparable to those of the modern bering sea these conditions indicated that the vertical water mass structure of the modern bering sea began to form since 0 47 ma every stage boundary in the studied core was marked by notable changes in the radiolarian assemblages these changes corresponded to the climatic cooling event at similar to 3 91 ma the intensification of northern hemisphere glaciation at similar to 2 75 ma the beginning of the middle pleistocene transition at similar to 1 07 ma and the low latitude radiolarian ecology event at similar to 0 47 ma in addition the relative abundance pattern of cycladophora davisiana indicates that the bering sea was the main source of the past north pacific intermediate water at ca 0 85 ma mis22 ca 0 63 ma mis16 and ca 0 18 ma mis6 just as it was during the last glacial maximum c 2014 elsevier b v all rights reserved

fluctuations in the late quaternary east asian winter monsoon recorded in sediment records of surface water cooling in the northern japan sea the east asian monsoon climate system involves interactions between land and ocean and is composed of summer and winter monsoons cooling of surface water by the east asian winter monsoon eawm promotes the formation of sea ice and deep water in the northern japan sea modern observations suggest close relationships between intensification of the eawm and both sea ice formation and sea surface temperature sst decrease in the northeastern japan sea records of ice rafted debris ird and alkenone based sst in the northeastern japan sea are examined to clarify the temporal variability of the eawm and its controlling factors close relationships with oxygen isotope records of chinese stalagmites and northern hemisphere summer insolation are observed in the records of ird occurrence and sst during marine isotope stages mis 3 5 the co occurrence of maxima in the abundance of ird and minima in sst in the northeastern japan sea indicates that the intensity of the eawm was enhanced during periods of low summer insolation and high oxygen isotope ratios in chinese stalagmites decoupling between the ird and sst records during mis 2 and mis 6 might be the result of differences in surface water conditions caused by low sea levels and the resultant closure of the tsushima strait during mis 3 and 4 some small but clear maxima in ird and minima in sst occurred at relatively low summer insolation periods some of these peaks co occur with north atlantic heinrich events suggesting a possible climate linkage between the north atlantic and the asian monsoon the presence of finer fluctuations in the occurrence of ird than in summer insolation suggests finer millennial centurial timescale fluctuations in the intensity of the eawm furthermore some ird peaks occurred during periods of high insolation such as 39 86 103 128 145 and 153 ka some of these ird peaks correlate with minima in reconstructed sst and maxima in oxygen isotope ratios of chinese stalagmites this result suggests that extremely cold winters occur even during periods of enhanced east asian summer monsoon intensity and indicates that solar insolation is not the only factor that controls variations in the intensity of the eawm at millennial centurial timescales copyright 2012 john wiley sons ltd

magnetic field intensity study of the 1960 kilauea lava flow hawaii using the microwave palaeointensity technique summary it is extremely valuable to study historic lava flows where the geomagnetic field at their time of extrusion is well known in this study two vertical sections 16 m apart have been sampled from the approximately 1 m thick 1960 kilauea lava flow hawaii variations are seen in the rock magnetic and palaeomagnetic properties between and within the two sections indicating that there are small scale lateral and vertical variations in the lava flow the two sections showed dierent responses to microwave palaeointensity analysis section h6001 generally gave ideal linear behaviour on plots of natural remanent magnetization nrm lost against microwave induced thermoremanent magnetization t m rm gained whilst the majority of samples from h6002 showed anomalous two slope behaviour when all plots were interpreted by taking the best fitting line through all points the flow mean intensity for h6001 was 31 6 3 6 mt and that for h6002 was 37 1 6 4 mt compared with the expected intensity of 36 mt additional historic flows need to be studied in order to ascertain whether this behaviour is typical of all lava and whether it is best to always interpret nrm lost t m rm gained plots by taking the line of best fit regardless of shape

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

the effect of severe storms on the ice cover of the northern tatarskiy strait the tatarskiy strait is the northernmost region of the japan sea with an ice covered area in winter of about 4 104 km2 this study uses the daily passive microwave images of the region from the special sensor microwave imager ssm i which was launched in 1987 to estimate the production of ice and japan sea bottom water in winter the prevailing winds in the strait are northerly and cold these conditions create a region of reduced ice concentration in the northern strait which leads to an enhanced ice production throughout the season in addition to these prevailing winds each winter one or two severe storms generate very strong northerly winds and cold temperatures in the strait these storms create a large transient polynya in the strait at a time simultaneous with the greatest heat flux out of the open water calculation of the ice growth from open water in the northern strait yields about 25 km3 of ice per season of which severe storms provide about 25 the total ice production is sufficient to form about 5 12 102 km3 of the japan sea bottom water which is about 50 100 of the renewal rate required from 14c data because the oxygen bottom layer thickness decreased between 1969 and 1984 the study also investigates the frequency of the severe storms in the northern strait during 1966 1990 and finds that these storms are about 3 times as frequent at the beginning of this period than at the end this suggests the storms may play a role in the generation of the japan sea bottom water

vertical distribution of polycystine radiolarians in the northern east china sea abstract the east china sea ecs is a marginal sea influenced by the kuroshio current kc and by freshwater discharged by the changjiang river in this study the vertical distribution of polycystine radiolarians in the northern ecs was investigated we collected plankton tow samples from the water column at five stations in the northern ecs stations 11 and 11 were on the ecs continental shelf and stations 1 8 and 12 were in the northeastern ecs which is influenced by the kc we identified six distinct depth intervals by a q mode cluster analysis at stations 1 8 and 12 radiolarians were abundant and species diversity was high in the surface waters standing stocks of subtropical species such as didymocyrtis tetrathalamus phorticium pylonium pterocanium praetextum spongaster tetras tetras and the tetrapyle octacantha groups were high reflecting the influence of the warm kc in contrast at intermediate water depths standing stocks of subarctic radiolarians such as actinomma leptodermum cycladophora bicronis haliommetta miocenica pseudodyctiophimus gracilipes and lithelius minor were relatively high which may reflect the influence of a subarctic water mass that probably originated in the north pacific at stations 11 and 11 on the shelf the influence of freshwater from the changjiang river is high and radiolarians were absent in the upper 20 m of the water column and scarce at depths of 20 100 m where three species dominated archipera triclavigera pseudocubus obeliscus and cryptogyrus calvatus

sea level surface salinity of the japan sea and the younger dryas event in the northwestern pacific ocean abstract the japan sea was profoundly different during glacial times than today available 18 o evidence indicates that sea surface salinity was lower by several per mil this probably increased the stability of the water column and caused anoxic sedimentary conditions in the deep sea as shown by the absence of benthic microfossils and the presence of laminated sediment these changes are likely related to the effects of late quaternary sea level change on the shallow sills ca 130 m across which the japan sea exchanges with the open ocean the hwang he yellow river has previously been implicated as the source of fresh water to the japan sea during glaciation but the possible roles of the amur river and excess precipitation over evaporation must also be considered ambiguous radiocarbon chronologies for the latest quaternary of japan sea cores do not adequately constrain the timing of salinity lowering previous studies have suggested that lowest sea surface salinity was achieved 27 000 to 20 000 14 c yr b p however if global sea level fall restricted exchange with the open ocean circulation then lowest salinity in the japan sea may have occurred as recently as 15 000 to 20 000 yr ago when sea level was lowest if this alternative is correct then as sea level abruptly rose about 12 000 yr ago relatively fresh water must have been discharged to the open pacific this might have affected the dynamics of outflow local faunal and floral expression of the polar front and stable isotope ratios in foraminifera these environmental changes could be misinterpreted as evidence for the cooling of younger dryas age which has not been identified in nearby terrestrial records

are systematic differences between thermal and microwave thellier type palaeointensity estimates a consequence of multidomain bias in the thermal results a meta analysis which directly compares 13 datasets of microwave and thermal thellier palaeointensity measurements obtained from igneous rocks is reported the results clearly indicate systematic differences in the measurements made using the two approaches the thermal results tend to be higher often by several tens of percent and associated with slightly noisier arai plots additionally in nearly half of the cases considered higher thermal palaeointensity estimates were reported to be calculated from the lowtemperature portions of concave up arai plots while microwave measurements made on specimens from the same core sample or rock unit were derived from more linear arai plots the most plausible explanation for the bulk of these differences appears to be that non ideal behaviour caused by multidomain vortex state and or interacting ferrimagnetic grains is exaggerated in the results of the thermal experiments over their microwave counterparts a detailed investigation of the individual studies concludes that such effects may be adversely affecting some of the measurements thermal and or microwave in 10 of the 13 datasets considered it is probable that these non ideal effects are enhanced in the thermal results over their microwave counterparts at least in part because of the different thellier type protocols that are used in the two types of study the findings of this study suggest that biasing of absolute palaeointensity estimates by multidomain effects may be much more prevalent than previously thought and that this effect might be responsible for certain discrepancies that have been observed in the geomagia50 database they also clearly indicate that in addition to taking the steps they already do to avoid biasing from secondary overprints and thermally induced alteration future absolute palaeointensity studies of

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